MEEDICAL 
OIBT& 

--  - 

.SCHOOL 
AJSY 

GIFT  OF  THE 

SAN  FRANCISCO  COUNTY 

MEDICAL  SOCIETY 


HUMAN  ANATOMY 


The  skeleton  in  relation  to  the  contour  of  the  body. 


HUMAN   ANATOMY 

INCLUDING  STRUCTURE  AND  DEVELOPMENT 

AND 

PRACTICAL  CONSIDERATIONS 


BY 

THOMAS  DWIGHT,  M.D.,   LL.D. 

PARKMAN     PROFESSOR      OF      ANATOMY      IN      HARVARD 
UNIVERSITY 

CARL  A.  HAMANN,  M.D. 

PROFESSOR     OF      ANATOMY      IN      WESTERN       RESERVE  PROFESSOR     OF     ANATOMY     IN     THE     UNIVERSITY     OF 

UNIVERSITY  PENNSYLVANIA 


J.  PLAYFAIR  McMURRICH,  PH.D. 

PROFESSOR     OF     ANATOMY     IN     THE     UNIVERSITY      OF 
MICHIGAN 

GEORGE  A.  PIERSOL,  M.D.,  SC.D. 


J.  WILLIAM  WHITE,  M.D.,  PH.D.,  LL.D. 

JOHN   RHEA    BARTON   PROFESSOR  OF    SURGERY    IN   THE    UNIVERSITY   OF    PENNSYLVANIA 


WITH    SEVENTEEN    HUNDRED    AND    THIRTY-FOUR    ILLUSTRATIONS, 

OF    WHICH    FIFTEEN    HUNDRED    AND    TWENTY-TWO  ARE  ORIGINAL 

AND  LARGELY  FROM   DISSECTIONS  BY 

JOHN  C.  HEISLER,  M.D. 

PROFESSOR   OF   ANATOMY    IN   THE   MEDICO-CHIRURGICAL   COLLEGE 


EDITED    BY 

GEORGE  A.  PIERSOL 


PHILADELPHIA  &  LONDON 

J.  B.  LIPPINCOTT  COMPANY 


Copyright,  1906,  by  J.  B.  Lippincott  Company. 


Copyright,  1907,  by  J.  B.  Lippincott  Company. 


Entered  at  Stationers'  Hall,  London,  England. 


All  Rights  Reserved. 


ELECTROTYPEO  AND  PRINTf  D  0V  J.  B.  LIPPINCOTT  COMPANY,  PHILADELPHIA,  U.S.A. 


6jwy~: 


PREFACE. 


THE  preparation  of  this  work  was  undertaken  with  three  chief  considerations  in 
mind.  i.  The  presentation  of  the  essential  facts  of  human  anatomy,  regarded  in  its 
broadest  sense,  by  a  descriptive  text  which,  while  concise,  should  be  sufficiently  com- 
prehensive to  include  all  that  is  necessary  for  a  thorough  understanding  not  only  of 
the  gross  appearances  and  relations  of  the  various  parts  of  the  human  body,  but  also 
of  their  structure  and  development.  2.  Adequate  emphasis  and  explanation  of  the 
many  and  varied  relations  of  anatomical  details  to  the  conditions  claiming  the  atten- 
tion of  the  physician  and  surgeon.  3.  The  elucidation  of  such  text  by  illustrations 
that  should  portray  actual  dissections  and  preparations  with  fidelity  and  realism. 

To  the  first  of  these  ends  the  co-operation  of  several  American  teachers  of 
anatomy  was  enlisted,  whose  contributions  have  been  welded  into  a  homogeneous 
whole. 

Dr.  Thomas  Dwight  has  written  the  description  of  the  skeleton,  including  the 
joints,  and  that  of  the  gastro-pulmonary  system  and  of  the  accessory  organs  of 
nutrition. 

Dr.  Carl  A.  Hamann  has  contributed  the  account  of  the  cerebro-spinal  and 
sympathetic  nerves. 

Dr.  J.  Playfair  McMurrich  has  supplied  the  systematic  description  of  the  mus- 
cular and  of  the  blood-  and  lymph- vascular  system. 

Dr.  George  A.  Piersol  has  written  the  introductory,  histological  and  embryolog- 
ical  paragraphs  throughout  the  work  and  contributed  the  description  of  the  central 
nervous  system,  including  the  deep  relations  of  the  cranial  nerves,  of  the  organs  of 
special  sense,  of  the  carotid,  coccygeal  and  aortic  bodies,  and  of  the  uro-genital  system. 

The  second  desideratum — adequate  consideration  of  the  practical  applications 
of  anatomy — has  been  ensured  by  the  co-operation  of  Dr.  J.  William  White, 
whose  ripe  experience,  both  as  a  surgeon  and  as  a  teacher  of  surgery,  has  enabled 
him  to  point  out  with  unusual  force  the  relations  of  anatomy  to  the  requirements  of 
the  practitioner,  and  to  associate  for  the  benefit  of  the  student  anatomical  facts  with 
those  conditions,  resulting  from  injury  or  disease,  that  these  facts  elucidate. 

While  no  attempt  has  been  made  to  cover  the  field  of  operative  surgery,  brief 
descriptions  of  operative  methods  have  been  given  when  they  have  seemed  necessary 
to  complete  the  study  of  an  anatomical  region  or  of  an  important  organ.  Occasion- 
ally a  relatively  rare  operation  has  been  included  because  of  the  exceptional  practical 
importance  of  the  subject  from  an  anatomical  standpoint. 

The  writer  of  the  Practical  Considerations  has  aimed  at  presenting,  in  connection 
with  each  organ  or  system,  enough  facts  illustrative  of  the  dependence  of  the  diag- 
nostician and  practitioner  upon  anatomical  knowledge  to  awaken  interest  and  to  com- 
bat the  tendency  to  regard  anatomy  as  something  to  be  memorized  during  student 
days  and  forgotten  when  examinations  are  over.  Even  when  such  facts  do  not  seem 
at  a  first  glance  to  come  within  the  scope  of  a  text-book  of  anatomy,  it  will  be  found 
that  a  careful  comparison  of  this  text  with  the  descriptive  portion  of  the  book  will 
show  a  real  and  practical  relation  between  them — a  relation  which,  once  established 

v 


VI 


PREFACE. 


in  the  minds  of  the  student  and  the  physician,  will  make  it  easier  for  the  former  to 
learn  his  anatomy  and  for  the  latter  to  remember  and  apply  it. 

Dr.  White  desires  to  acknowledge  fully  his  obligations  to  the  existing  treatises 
on  applied  anatomy  and  to  the  various  text-books  and  encyclopedias  on  surgery  and 
medicine  from  which  many  valuable  suggestions  were  gathered.  To  Drs.  Gwilym 
G.  Davis  and  T.  Turner  Thomas,  his  thanks  are  due  for  a  careful  search  for  possible 
errors,  for  friendly  criticism,  and  for  help  in  the  selection  of  illustrations. 

The  illustrations  for  the  anatomy — a  matter  of  fundamental  importance  in  a  work 
of  this  character — have  received  most  conscientious  attention.  The  determination  to 
produce  a  series  of  original  drawings  that  should  faithfully  record  the  dissections  and 
preparations  as  they  actually  appear,  and  not  as  diagrammatic  figures,  has  involved 
an  expenditure  of  time  and  painstaking  effort  that  only  those  having  experience  with 
similar  tasks  can  appreciate.  When  it  is  stated  that  considerably  more  than  two 
thousand  original  drawings  have  been  made  in  the  preparation  of  the  figures  illus- 
trating the  work,  some  conception  will  be  had  of  the  magnitude  of  this  feature. 

In  the  completion  of  this  labor  the  editor  has  been  most  fortunate  in  having 
the  assistance  of  Dr.  John  C.  Heisler,  to  whose  skill  and  tireless  enthusiasm  he  is 
indebted  for  the  admirable  dissections  from  which  most  of  the  illustrations  of  the 
muscles,  blood-vessels,  nerves,  perineum  and  inguinal  region  were  drawn,  as  well  as 
for  many  suggestions  for  and  revision  of  the  drawings  themselves.  Professor  Gwilym 
G.  Davis  has  also  rendered  valuable  assistance  in  supplying  the  dissections  for  the 
drawings  relating  to  the  Practical  Considerations,  as  well  as  in  supervising  that 
portion  of  the  artist's  work. 

In  addition  to  the  numerous  dissections  and  preparations  made  especially  for  the 
illustrations,  advantage  has  been  taken  of  the  rich  collections  in  the  museums  of  the 
Medical  Department  of  the  University  of  Pennsylvania,  of  the  Harvard  Medical 
School  and  of  the  Wistar  Institute  of  Anatomy,  which  were  kindly  placed  at  the 
editor's  service. 

Records  of  the  dissections,  in  many  cases  life  size,  were  made  in  water  colors 
chiefly  by  Mr.  Hermann  Faber,  whose  renditions  combine  faithful  drawing  with 
artistic  feeling  to  a  degree  unusual  in  such  subjects.  The  records  not  made  by  the 
last-named  artist  are  from  the  brush  of  Mr.  Ludwig  E.  Faber.  The  translations 
of  the  colored  records  into  black  and  white,  from  which  the  final  blocks  have  been 
made,  as  well  as  the  original  drawings  of  the  bones  and  of  the  organs,  have  been 
made  by  Mr.  Erwin  F.  Faber.  To  the  conscientious  and  tireless  efforts  of  this  artist 
are  due  the  technical  beauty  that  distinguish  these  illustrations.  Mr.  J.  H.  Emerton 
drew  the  joints,  as  well  as  some  figures  relating  to  the  gastro-pulmonary  system,  from 
dissections  and  sections  supplied  by  Professor  Dwight. 

The  numerous  illustrations  representing  the  histological  and  embryological  de- 
tails throughout  the  work,  and  in  addition  the  sections  of  the  brain-stem  under  low 
magnification,  are  by  Mr.  Louis  Schmidt.  In  all  cases  sketches  with  the  camera 
lucida  or  projection  lantern  or  photographs  have  been  the  basis  of  these  drawings, 
the  details  being  faithfully  reproduced  by  close  attention  to  the  original  specimens 
under  the  microscope. 

Notwithstanding  the  unusually  generous  allotment  of  drawings  from  original 
dissections  and  preparations,  advantage  has  also  been  taken  of  a  number  of  illus- 
trations which  have  appeared  in  special  monographs  or  in  foreign  journals  or  works. 
With  very  few  exceptions  such  borrowed  illustrations  have  been  redrawn  and  modi- 
fied to  meet  the  present  requirements,  due  acknowledgment  in  all  cases  being  given. 


PREFACE.  vii 

The  editor  gratefully  acknowledges  the  many  kindnesses  shown  by  a  number  of 
his  associates.  Dr.  William  G.  Spiller  generously  placed  at  his  disposal  a  large 
collection  of  microscopical  preparations  of  the  central  nervous  system,  from  which 
drawings  of  selected  sections  were  made.  To  Dr.  George  Fetterolf  the  editor  is 
indebted  for  valuable  assistance  in  preparing  for  and  seeing  through  the  press  the 
section  on  the  peripheral  nervous  system.  The  collaboration  of  Dr.  Edward  A. 
Shumway  very  materially  facilitated  the  preparation  of  the  description  of  the  eye, 
which  received  only  the  editor's  revision.  Likewise,  Dr.  Ralph  Butler,  by  placing 
in  the  editor's  hands  a  painstaking  review  of  the  more  recent  literature  on  the  ear 
and  preliminary  account  of  that  organ,  greatly  lightened  the  labor  of  writing  the  text. 
Further,  Dr.  Butler  supplied  the  microscopical  preparations  from  which  several  of 
the  drawings  were  made.  In  addition  to  assuming  the  preparation  of  the  index — a  no 
insignificant  undertaking  in  a  work  of  this  character — Dr.  Ewing  Taylor  gave  valu- 
able assistance  in  the  final  revision  of  the  first  hundred  pages  of  the  book.  The 
editor  is  indebted  to  Dr.  W.  H.  F.  Addison  for  repeated  favors  in  preparing  special 
microscopical  specimens.  Dr.  T.  Turner  Thomas  kindly  assisted  in  locating  cross- 
references.  This  opportunity  is  taken  to  express  full  appreciation  and  thanks  to  the 
various  authors  and  publishers,  who  so  kindly  have  given  permission  to  use  illus- 
trations which  have  appeared  elsewhere. 

Very  earnest  consideration  of  the  question  of  nomenclature  led  to  the  conclusion, 
that  the  retention,  for  the  most  part,  of  the  terms  in  use  by  English-speaking 
anatomists  and  surgeons  would  best  contribute  to  the  usefulness  of  the  book.  While 
these  names,  therefore,  have  been  retained  as  the  primary  terminology,  those 
adopted  by  the  Basle  Congress  have  been  included,  trie  BNA  synonyms  appear- 
ing in  the  special  type  reserved  for  that  purpose.  The  constant  aim  of  the  editor 
has  been  to  use  the  simplest  anatomical  terminology  and  preference  has  always 
been  given  to  the  anglicized  names,  rather  than  to  the  more  formal  designations. 
Although  in  many  cases  the  modifications  suggested  by  the  new  terminology  have 
been  followed  with  advantage,  consistent  use  of  the  Basle  nomenclature  seems  less  in 
accord  with  the  conceded  directness  of  English  scientific  literature  than  the  enthusi- 
astic advocates  of  such  adoption  have  demonstrated. 

The  editor  desires  to  express  his  appreciation  of  the  generous  support  given  him 
by  the  publishers  and  of  the  unstinted  facilities  placed  by  them  at  his  disposal 
throughout  the  preparation  of  the  work. 

UNIVERSITY  OF  PENNSYLVANIA, 
SEPTEMBER,   1907. 


CONTENTS. 


INTRODUCTION. 


Relation  of  Anatomy  to  Biology  .  . 
Subdivisions  of  Anatomical  Study 


General  Plan  of  Vertebrate  Construction 
Descriptive  Terms 


THE  ELEMENTS  Of  STRUCTURE. 


The  Elementary  Tissues 

The    Cells    and    Intercellular    Sub- 
stances   

The  Embryonal  Cell 

Vital  Manifestations 

Metabolism  

Growth 

Reproduction   


Irritability  

The  Animal  Cell  , 

Structure  of  the  Cytoplasm  . , 
Structure  of  the  Nucleus 

The  Centrosome 

Division  of  Cells  

Mitotic  Division  . . 


PAGE 
I 


6 

6 

7 
8 

9 
10 
ii 


Amitotic  Division 14 


EARLY  DEVELOPMENT. 


The  Ovum 15 

The    Spermatozoon 16 

Maturation  of  the  Ovum 16 

Fertilization  of  the  Ovum 18 

Segmentation  of  the  Ovum 21 

The  Blastoderm  and  the  Blastodermic 

Layers 22 

Derivatives  of  the  Blastodermic  Layers.  .  24 
The  Primitive  Streak  and  the  Gastrula.  .  24 
The  Significance  of  the  Primitive  Streak.  .  25 
The    Fundamental    Embryological    Pro- 
cesses   26 

The  Neural  Canal 26 

The  Notochord 27 

The  Coelom 28 

The    Somites 29 

The  Fcttal   Membranes 30 

The  Amnion 30 

The  Serosa 31 

The  Vitelline  Sac 32 

The  Allantois  and  the  Chorion 32 


The  Human  Fcetal  Membranes 35 

The  Amnion  and  Allantois 35 

The  Chorion 41 

The  Amniotic  Fluid 41 

The  Umbilical  Vesicle 42 

The  Deciduse 44 

The  Trophoblast 46 

The  Decidua  Vera 46 

The  Decidua  Placentalis 48 

The  Placenta 49 

The  Umbilical  Cord 53 

The  After-Birth 55 

Development  of  Body-Form 56 

The  Stage  of  the  Blastodermic  Ves- 
icle    56 

The  Stage  of  the  Embryo 56 

The  Visceral  Arches  and  Fur- 
rows   59 

The  Development  of  the  Face  .  .  62 

The  Stage  of  the  Foetus 63 


THE  ELEMENTARY  TISSUES. 


The  Epithelial  Tissues 67 

Squamous  Epithelium 68 

Columnar  Epithelium 69 

Modified  Epithelium 70 

Specialized  Epithelium 70 

Endothelium ;..'..  71 

The  Connective  Tissues 73 

The  Cells  of  Connective  Tissue 73 

The  Intercellular  Constituents 74 

Fibrous  Tissue 74 

Reticular  Tissue 75 

Elastic  Tissue 76 

Development  of  Connective  Tissue..  77 

Tendon 77 

Adipose  Tissue 79 

Cartilage So 


Hyaline  Cartilage 80 

Elastic  Cartilage Si 

Fibrous  Cartilage 82 

Development  of  Cartilage 82 

Bone 84 

Chemical  Composition 84 

Physical  Properties 85 

Structure  of  Bone 85 

Bone  Marrow 90 

Red  Marrow 91 

Yellow  Marrow 93 

Development  of  Bone 94 

Endochondral  Bone 94 

Membranous  Bone 98 

Subperiosteal  Bone 98 


THE  SKELETON,   INCLUDING  THE  JOINTS. 


The  Axial  Skeleton 103 

The  Appendicular  Skeleton 104 

General  Considerations  of  the  Bones.  . .  .     104 


General  Considerations  of  the  Joints  ....     107 

The  Spinal  Column 114 

The  Thoracic  Vertebrae 115 


CONTENTS. 


The  Thoracic  Vertebrae — Continued 

The  Cervical  Vertebra;  

The  Lumbar  Vertebra? 

Peculiar  Vertebrae 

Dimensions  of  Vertebrae 

Gradual  Regional  Changes 

The  Sacrum 

The  Coccyx 

Development  of  the  Vertebra 

Variations  of  the  Vertebrae 

Articulations  of  the  Vertebral  Column  .  . 

Ligaments  Connecting  the  Bodies  .  . 

Ligaments  Connecting  the  Laminae, 

and  the  Processes 

Articulations  of  the  Occipital  Bone,  the 

Atlas  and  the  Axis 

The  Spine  as  a  Whole 

Dimensions  and  Proportions 

Movements  of  the  Head 

Movements  of  the  Spine 

Practical  Considerations  :  The  Spine .... 

Curvature  of  the  Spine 

Sprains,  Dislocations  and  Fractures  . 

Landmarks 

The  Thorax 

The  Ribs 

The  Costal  Cartilages 

The  Sternum 

Articulations  of  the  Thorax 

The  Anterior  Thoracic  Articulations . 

The  Intersternal  Joints 

The  Costo-Sternal  Joints 

The  Interchondral  Joints 

The  Costo- Vertebral  Articulations.  . 

The  Thorax  as  a  Whole 

The  Movements  of  the  Thorax 

Practical  Considerations  :  The  Thorax  .  . 

Deformities 

Fractures  and  Disease  of  the  Ribs  .  . 

Landmarks .  .  , 

The  Skull  

The  Cranium 

The  Occipital  Bone 

The  Temporal  Bone 

The  Tympanic  Cavity 

The  Sphenoid  Bone 

The  Ethmoid  Bone 

The  Frontal  Bone 

The  Parietal  Bone 

The  Bones  of  the  Face    

The  Superior  Maxilla 

The  Palate  Bone 

The  Vomer 

The  Lachrymal  Bone 

The  Inferior  Turbinate  Bone 

The  Nasal  Bone 

The  Malar  Bone 

The  Inferior  Maxilla 

The  Temporo-Maxillary  Articulation .... 

The  Hyoid  Bone 

The  Skull  as  a  Whole 

The  Exterior  of  the  Cranium 

The  Interior  of  the  Cranium 

The  Architecture  of  the  Cranium  .... 

The  Face 

The  Orbit 

The  Nasal  Cavity 

The  Accessory  Pneumatic  Cav- 
ities   

The  Architecture  of  the  Face  . .  . 

The  Anthropo|ogy  of  the  Skull 

Practical  Considerations  :  The  Skull  .... 

The  Cranium.  . 


116 
117 
119 

122 
122 
124 
I27 
128 

131 
132 

132 
133 

135 
138 
141 
142 
142 

*43 
144 

144 
146 
149 
149 
153 
155 

'57 
158 

159 
160 
160 
160 
162 
165 
167 
167 
169 
170 
172 
172 
172 
176 

183 
1 86 
191 
194 
197 
199 
199 
204 
205 
207 
208 
209 
209 

211 
214 
216 
216 
218 
220 
220 
222 
222 
223 

226 

228 
228 
235 
235 


Malformations 

The  Wormian  Bones  

Diseases  of  the  Cranial  Bones 

Fractures  

Landmarks 

The  Face 

Deformities  and  Fractures 

Dislocation  of  the  Jaw 

Landmarks 

The  Bones  of  the  Upper  Extremity 

The   Shoulder-Girdle 

The  Scapula 

Practical  Considerations 

Malformations 

Fractures  and  Disease 

Landmarks 

Ligaments  of  the  Scapula 

The  Clavicle 

Practical  Considerations 

Malformations 

Fractures  and  Disease 

Landmarks 

The  Sterno-Clavicular  Articulation  . 
The  Coraco-Clavicular  Ligament. . .  . 
Movements  of  the  Clavicle  and  Scap- 
ula  

Surface  Anatomy  of  the  Shoulder- 
Girdle.. 

Practical  Considerations 

The  Sterno-Clavicular  Articula- 
tion   

The  Acromio-Clavicular  Articu- 
lation   

The  Humerus 

Practical  Considerations 

Malformations 

Separation  of  the  Epiphyses  .... 

Fractures  and  Disease 

The  Shoulder-Joint 

Practical  Considerations 

Dislocations  and  Diseases 

Landmarks 

The  Ulna 

Practical  Considerations 

Malformations 

Fractures 

Landmarks 

The  Radius 

Practical  Considerations 

Malformations 

Fractures  and  Disease 

Landmarks 

The  Radio-Ulnar  Articulations 

The  Forearm  as  a  Whole 

The  Elbow-Joint 

Practical  Considerations 

Dislocations  and  Disease 

Landmarks 

The  Bones  of  the  Hand 

The  Carpal  Bones 

The  Metacarpal  Bones 

The  Phalanges 

Practical  Considerations 

The  Carpus 

The  Metacarpus 

The  Phalanges 

Landmarks 

Ligaments  of  Wrist  and  Metacarpus 

Movements  and  Mechanics  of   Wrist 

and     Carpo-Metacarpal    Articu- 
lations   

Surface    Anatomy    of     the     Wrist     and 

Hand  . 


235 
236 
237 
238 
240 
242 

243 
246 
246 
248 
248 
248 
253 
253 
254 
255 
256 
257 
258 
259 
259 
260 
261 
262 

262 

263 
263 

263 

264 
265 
270 
270 
271 
273 
274 
278 
278 
280 
281 
285 
285 
286 
287 
287 
293 
293 
294 
296 

297 
299 
301 
305 
305 
308 

309 
309 
3U 
317 
319 
319 
319 
320 
320 
320 


326 
328 


CONTENTS. 


XI 


Practical     Considerations:   The     Wrist- 
Joint 329 

Landmarks 33° 

The  Joints  of  the  Carpus,  Metacarpus 

and  Phalanges 630 

The  Bones  of  the  Lower  Extremity 332 

The  Pelvic  Girdle 332 

The  Innominate  Bone 332 

Joints  and  Ligaments  of  the  Pelvis.  .  337 

The  Sacro-Iliac  Articulation.  . .  .  338 

The  Symphysis  Pubis 339 

The  Sacro-Sciatic  Ligaments. .  .  339 

The  Pelvis  as  a  Whole 341 

Mechanics  of  the  Pelvis 342 

Surface  Anatomy 345 

Practical  Considerations:  The   Pelvis...  345 

Malformations 345 

Fractures  and  Disease 346 

Landmarks 349 

Joints  of  the  Pelvis 350 

The  Femur 352 

Surface  Anatomy 360 

Practical  Considerations: 361 

The  Epiphyses 361 

Fractures  and  Disease 363 

Landmarks 366 

The  Hip-Joint 367 

Practical  Considerations 374 

Outward  or  Posterior  Luxations ....  375 

Inward  or  Anterior  Luxations 377 

Congenital  Luxation 380 

Disease  of  the   Hip- Joint 380 

The  Framework  of  the  Leg 382 

The  Tibia 382 

Practical  Considerations 387 

Separation  of  the  Epiphyses 387 

Fractures  and  Disease 389 

Landmarks 390 


The  Fibula 391 

Practical  Considerations 393 

Separation  of  Upper  Epiphysis ....  393 

Fractures   and   Disease 394 

Landmarks 396 

Connections  of  the  Tibia  and  Fibula.  . .  .  396 

The  Bones  of  the  Leg  as  one  Apparatus  397 

The  Patella 398 

The  Ligamentum  Patellae 400 

The  Knee-joint 400 

Practical     Considerations :    The    Knee- 
joint 409 

Dislocations 409 

Subluxation  of  Semilunar  Cartilages  411 

Disease  of  Knee-joint 412 

The  Patella 416 

The  Bones  of  the   Foot 419 

The  Tarsal   Bones 419 

The  Metatarsal  Bones 428 

The   Phalanges 432 

Practical     Considerations :     The     Foot- 
Bones  436 

Fracture,  Dislocation  and  Disease .  .  437 

Landmarks 437 

The  Ankle-joint 438 

The  Articulations  of  the  Foot 440 

Intertarsal   Joints 445 

Tarso-Metatarsal  Joints 446 

Metatarso-Phalangeal  Joints 447 

Synovial  Cavities 447 

The  Foot  as  a  Whole 447 

Surface  Anatomy 449 

Practical     Considerations:     The   Ankle- 
joint  450 

Dislocations  and  Disease 450 

Tarsal,    Metatarsal    and  Phalangeal 

Joints 45i 

Landmarks 453 


THE   MUSCULAR   SYSTEM. 


Muscular  Tissue   in  general 454 

Nonstriated  or  Involuntary  Muscle.  .  454 

Structure 455 

Development 457 

Striated  or  Voluntary  Muscle 457 

General  Structure 458 

Structure  of  the  Muscle-Fibre.  .  459 

Cardiac  Muscle 462 

Development  of  Striated  Muscle.  465 
Myomeres    and   their   Modifica- 
tions    467 

General  Consideration  of  the  Muscles ....  468 

Attachments 468 

Form 469 

Fasciae 470 

Tendon  -  Sheaths 470 

Bursae 471 

Classification 471 

Nerve-Supply 473 

The  Branchiomeric  Muscles 474 

The  Trigeminal  Muscles 474 

Muscles  of  Mastication 474 

Submental  Muscles 477 

Trigeminal  Palatal  Muscle 479 

Trigeminal  Tympanic  Muscle 479 

The  Facial  Muscles 479 

Hyoidean  Muscles  480 

Platysma  Muscles 480 

Superficial  Layer 481 

Deep  Layer  486 


Practical   Considerations:    Muscles    and 

Fasciae  of  Cranium 489 

The  Scalp  489 

The  Face 492 

Landmarks  494 

The  Vago- Accessory  Muscles 495 

Muscles  of  Palate  and  Pharynx 495 

Muscles  of  Larynx 1824 

Trapezius  Muscles 499 

The  Metameric  Muscles 502 

The  Axial  Muscles 502 

Orbital  Muscles  502 

Fasciae  of  Orbit  ....... 504 

Movements  of  Eyeball 505 

Hypoglossal  Muscles 506 

The  Trunk  Muscles : 50? 

The  Dorsal  Muscles 507 

Transverso-Costal  Tract 508 

Transverso-Spinal  Tract 511 

The  Ventral  Muscles 515 

Abdominal  Muscles 515 

Rectus  Muscles   516 

Obliquus  Muscles    517 

Ventral  Aponeurosis 521 

Inguinal  Canal 523 

Anterior  Abdominal  Wall.  .  525 

Hyposkeletel  Muscles 526 

Practical   Considerations :     The     Abdo- 
men    526 

The  Loin  ...                   53° 


XII 


CONTENTS. 


Practical  Considerations — Continued 

Landmarks    and    Topography     o  f 

Abdomen    

Anatomy  of  Abdominal  Incisions  .  . 

Examination  of  Abdomen. 

The  Thoracic  Muscles 

kectus  .Muscles 

Obliquus  Muscles 

Hyposkeletal  Muscles, 

The  Cervical  Muscles 

The  Deep  Cervical  Fascia 

Rectus  Muscles 

Obliquus  Muscles 

Triangles  of  the  Xeck 

1 1  y pi  >skeletal  Muscles 

Practical  Considerations  :  The  Neck.  . .  . 

Cervical  Fascia  and  its  Spaces 

Landmarks 

The  Diaphragm 

The  Pelvic  and  Perineal  Muscles 

Pelvic  Fascia 

Obturator  Fascia 

Pelvic  Muscles 

Perineal  Muscles 

The  Appendicular  Muscles  

The  Muscles  of  the  Upper  Limb 

Muscles  extending  between  Axial  Skele- 
ton and  Pectoral  Girdle 

Pectoral  Fascia 

Preaxial  Muscles 

Postaxial  Muscles 

The  Axilla 

Muscles  passing   from  Pelvic  Girdle  to 

Brachium 

Preaxial  Muscles 

Postaxial  Muscles 

Practical   Considerations :    Muscles   and 
Fascia  of  Axilla  and  Shoulder.  . 

Fracture  of  Clavicle 

Dislocation  of  Shoulder- Joint 

The  Brachial  Muscles 

Preaxial  Muscles.     

Postaxial  Muscles 

Practical   Considerations :    Muscles  and 

Fascia  of  the  Arm 

Fractures  of  Humerus 

The  Antibrachial  Muscles 

Preaxial  Muscles 

Postaxial  Muscles 

Practical  Considerations  :   The  Forearm. 

The  Muscles  of  the  Hand 

Deep   Fascia 


531 
535 

537 
538 
538 
538 

542 
542 
543 
546 
547 
548 
55° 
55i 
554 
556 
558 
558 
559 
559 
562 
566 
568 

568 
568 

568 
571 
574 

575 
575 
575 

579 
579 
582 

585 
585 
588 

589 
590 
591 
592 
598 
603 
606 
606 


Preaxial    Muscles 607 

Muscles  of  First  Layer    607 

Muscles  of  Second  Layer  610 

Muscle  of  Third  Layer ;  610 

Muscles  of  IV  and  V  Layers.  ...  611 
Postaxial  Muscle 
Practical  Considerations  :  The  Wrist  and 

Hand    613 

Palmar  Abscesses 616 

Dislocation  of  Thumb 617 

Surface  Landmarks  of  Upper  Extremity  .  618 

The  Muscles  of  the  Lower  Limb 623 

Muscles  extending  from  Pelvic  Girdle  to 

Femur 623 

Preaxial  Muscles 623 

Postaxial  Muscles 630 

The  Femoral  Muscles 633 

P'ascia  Lata 633 

Preaxial  Muscles 636 

Postaxial  Muscles 639 

Practical    Considerations :    Muscles   and 

Fascia; 641 

The  Buttocks 641 

The  Hip  and  Thigh 642 

Fractures  of  the  Femur 644 

The  Knee   645 

Bursae  of  Popliteal  Region 646 

The  Crural  Muscles 647 

The  Crural  Fascia 647 

Preaxial  Muscles 648 

Superficial  Layer 649 

Middle  Layer 651 

Deep  Layer 654 

Postaxial  Muscles 655 

The  Muscles  of  the  Foot 659 

The  Plantar  Fascia 659 

Preaxial  Muscles 659 

First  Layer 660 

Second  Layer 662 

Third  Layer 662 

•       Fourth  and  Fifth  Layers 663 

Postaxial  Muscles 665 

Practical   Considerations  :    Muscles    and 

Fascia; 665 

The  Leg 665 

The  Ankle  and  Foot 666 

Club- Foot 667 

Surface  Landmarks  of  Lower  Extremity  669 

The  Buttocks  and  Hip '.  669 

The  Thigh 670 

Tin-  Kurt- 671 

The  Leg 671 

The  Ankle  and  Foot   672 


THE   VASCULAR   SYSTEM. 


Tin    MM  ><  >n-Y.\soi.AK    SYSTEM. 

The  Structure  of  Blood- Vessels 673 

The  Arteries 675 

The  Veins 677 

The  Capillaries 678 

The  Blood 680 

General  Characteristics 680 

Blood-Crystals 680 

The  Colored  MU.d-eYlls 681 

The  Colorless  l',lood-( /ells 684 

The  Blond-Plaques 685 

Development      of      Blood-Vessels      and 

Cells..  686 


The  Heart 

General  Description    689 

Position  and   Relations 692 

Chambers  of  the  I  leart 693 

Architecture  of  the  Heart-Muscle  . .  .  700 

Structure 702 

Blood* Vessels  and  Lymphatics 71.3 

Nerves ;»i 

1  ).-\eli  (pinellt ;. -5 

Practical  Considerations:  The  Heart.  ..  .  710 

Valvular  Disease 711 

Rupture  and  \Vounds 713 

The  Pericardium 71.} 


CONTENTS. 


Xlll 


Practical   Considerations:    The   Pericar- 
dium    717 

The  General  Plan  of  the  Circulation  ....  719 

THE  ARTERIES 719 

General  Plan  of  Arterial  System.  ..  .  720 

The  Pulmonary  Aorta 722 

The  Systemic  Aorta 723 

The  Aortic  Arch  723 

Practical    Considerations:    Aortic    Arch 

and  Thoracic  Aorta 726 

Surface  Relations 726 

Aneurisms 727 

The  Coronary  Arteries 728 

The  Innominate  Artery 729 

Practical  Considerations 729 

The  Common  Carotid  Arteries 730 

Practical  Considerations 731 

The  External  Carotid  Artery 733 

Practical    Considerations 733 

Branches  of    External    Carotid   Ar- 
tery   734 

The  Internal  Carotid  Artery 746 

Practical  Considerations.. 747 

Branches  of  Internal  Carotid  Artery,  748 

Anastomoses  of  Carotid  System.  ..  .  753 

The  Subclavian  Artery 753 

Practical  Considerations 756 

Branches  of  Subclavian  Artery 758 

The  Axillary  Artery 767 

Practical  Considerations 769 

Branches  of  Axillary  Artery 771 

The  Brachial  Artery 773 

Practical  Considerations 775 

Branches  of  Brachial  Artery 777 

The  Ulnar  Artery 778 

Practical  Considerations 780 

Branches  of  Ulnar  Artery 781 

The  Radial  Artery 785 

Practical  Considerations 786 

Branches  of  Radial  Artery 787 

The  Thoracic  Aorta 791 

Branches  of  Thoracic  Aorta 792 

The  Abdominal  Aorta 794 

Practical  Considerations 796 

The  Visceral  Branches. 797 

The  Parietal  Branches 805 

The  Common  Iliac  Arteries 807 

Practical  Considerations 807 

The  Internal  Iliac  Artery 808 

Practical  Considerations 810 

Branches  of  Internal  Iliac  Artery.  ..  .  810 

The  External  Iliac  Artery 818 

Practical  Considerations 819 

Branches  of  External  Iliac  Artery  . .  .  820 

The  Femoral  Artery 821 

Practical  Considerations 824 

Branches  of  Femoral  Artery 826 

Anastomoses  of  Femoral  Artery. ...  831 

The  Popliteal  Artery 831 

Practical  Considerations 832 

Branches  of  Popliteal  Artery 833 

The  Posterior  Tibial  Artery 835 

Practical  Considerations 836 

Branches  of  Posterior  Tibial  Artery,  838 

The  Anterior  Tibial  Artery 842 

Practical  Considerations 842 

Branches  of  Anterior  Tibial  Artery,  844 

The  Dorsal  Artery  of  the  Foot 845 

Development  of  the  Arteries 846 

THE  VEINS 850 

General  Characteristics 850 

Classification 852 

The  Pulmonary  System 852 


The  Pulmonary  Veins 852 

The  Cardinal  System 854 

The  Cardiac  Veins 854 

The  Superior  Caval  System 857 

Vena  Cava  Superior 857 

Practical  Considerations 858 

The  Innominate  Veins 858 

Practical  Considerations 859 

Tributaries  of  Innominate  Veins 859 

The  Internal  Jugular  Vein 861 

Practical  Considerations 863 

Tributaries  of  Internal  Jugular  Vein.  863 

The  Sinuses  of  the  Dura  Mater 867 

Practical  Considerations 869 

The  Diploic  Veins 874 

Practical  Considerations 875 

The  Emissary  Veins 875 

Practical  Considerations 876 

The  Cerebral  Veins 877 

Practical  Considerations 878 

The  Ophthalmic  Veins 879 

Practical  Considerations 880 

The  External  Jugular  Vein. 880 

Practical  Considerations 881 

Tributaries  of  External  Jugular  Vein  882 

The  Subclavian  Vein 884 

Practical  Considerations 885 

Veins  of  the  Upper  Limb 886 

The  Deep  Veins 886 

The  Superficial  Veins ' 889 

Practical  Considerations 891 

The  Azygos  System 893 

The  Azygos  Vein 893 

Tributaries 893 

Practical  Considerations 895 

The   Hemiazygos  Vein 895 

The  Accessory  Hemiazygos  Vein.  .  895 

The  Intercostal  Veins 896 

The  Spinal  Veins 897 

Practical  Considerations 898 

The  Veins  of  the  Spinal  Cord 898 

The  Inferior  Caval  System 898 

Vena  Cava  Inferior 899 

Practical  Considerations   900 

Tributaries  of  Inferior  Cava.  ...  901 

Practical  Considerations . .  .  904 

The  Common  Iliac  Veins 905 

The  Internal  Iliac  Veins 905 

Tributaries  of  Internal  Iliac  ....  905 

The  External  Iliac  Vein 909 

Tributaries  of  External  Iliac.  . .  .  909 

The  Veins  of  the  Lower  Limb 910 

The  Deep  Veins 910 

The  Superficial  Veins 914 

Practical   Considerations  of   Iliac  Veins 

and  Veins  of  Lower  Limb  ....  917 

The  Portal  System 919 

The  Portal  Vein 919 

Tributaries  of  Portal  Vein 920 

Practical  Considerations 925 

Development  of  the  Veins 926 

The  Foetal  Circulation 929 

THE  LYMPHATIC  SYSTEM. 

General  Consideration 931 

Lymph-Spaces 931 

Lymph-Capillaries   933 

Lymph-Vessels  934 

Lymph-Nodes 935 

Structure  of  Lymphoid  Tissue 936 

Development  of  Lymphatic  Vessels  and 

Tissues 939 

The  Thoracic  Duct 94* 


XIV 


CONTENTS. 


The  Thoracic  Duct — Continued 

Practical  Considerations 944 

The  Right  Lymphatic  Duct 945 

The  Lymphatics  of  the  Head 945 

The  Lymph-Nodes 945 

The  Lymph- Vessels 949 

Practical  Considerations 955 

The  Lymphatics  of  the  Neck 957 

The  Lymph-Nodes 957 

The  Lymph-Vessels 958 

Practical  Considerations 959 

The  Lymphatics  of  the  Upper  Limb  ....  961 

The  Lymph-Nodes 961    i 

The  Lymph- Vessels 963  ^ 

Practical  Considerations 965  * 


The  Lymphatics  of  the  Thorax 966 

The  Lymph-Nodes 966 

The  Lymph-Vessels 968 

Practical  Considerations 971 

The  Lymphatics  of  the  Abdomen 972 

The  Lymph-Nodes 972 

The  Lymph- Vessels 976 

The  Lymphatics  of  the  Pelvis 983 

The  Lymph-Nodes 983 

The  Lymph -Vessels 984 

Practical  Considerations 990 

The  Lymphatics  of  the  Lower  Limb  ....  991 

The  Lymph-Nodes 991 

The  Lymph-Vessels 993 

Practical  Considerations 994 


THE    NERVOUS   SYSTKM. 


General  Considerations 996 

The  Nervous  Tissues 997 

The  Nerve-Cells 997 

The  Nerve-Fibres 1000 

Neuroglia 1003 

The  Nerve-Trunks 1006 

The  Ganglia 1007 

Development  of  the  Nervous  Tissues  . .  .  1009 

Nerve-Terminations 1014 

Motor  Endings 1014 

Sensory  Endings 1015 

THE  CENTRAL  NERVOUS  SYSTEM. 

THE  SPINAL  CORD 1021 

Membranes 1022 

Cord-Segments 1024 

Form  of  the  Spinal  Cord 1026 

Columns  of  the  Cord 1027 

Gray  Matter 1028 

Central  Canal 1030 

Microscopical  Structure 1030 

White  Matter 1036 

Fibre  Tracts 1039 

Blood- Vessels  of  Spinal  Cord 1047 

Development  of  Spinal  Cord 1049 

Practical  Considerations  :  Spinal  Cord. .  1051 

Malformations  1051 

Injuries 1052 

Localization  of  Lesions 1053 

THE  BRAIN 1055 

General  Description 1056 

General  Development 1058 

Derivatives  from  the  Rhombencephalon  1063 

The  Medulla  Oblongata 1063 

Internal  Structure 1068 

The  Pons  Varolii 1077 

Internal  Structure 1078 

The  Cerebellum 1082 

Lobes  and  Fissures 1084 

Architecture 1088 

Internal  Nuclei 1088 

Cerebellar  Cortex 1090 

Cerebellar  Peduncles 1093 

The  Fourth  Ventricle 1096 

Development  of  the  Hind- Brain  Deri- 
vatives    1 100 

The  Medulla 1 101 

The  Pons 1 103 

The  Cerebellum 1 103 

The  Mesencephalon 1 105 

The  Corpora  Quadrigemina 1106 

The  Cerebral  Peduncles 1 107 

The  Sylvian  Aqueduct 1 108 


Internal  Structure  of  the  Mid-Brain  1112 

The  Tegmentum 1112 

The  Crusta 1115 

The  Median  Fillet 1115 

The  Posterior  Longitudinal  Fas- 
ciculus     1116 

Development  of  Mid-Brain 1117 

The  Fore-Brain 1 1 19 

The  Diencephalon 1119 

The  Thalamus 1119 

Structure 1120 

Connections 1121 

The  Epithalamus 1 123 

The  Trigonum  Habenulae 1123 

The  Pineal  Body 1 124 

The  Posterior  Commissure 1125 

The  Metathalamus 1 1 26 

The  Hypothalamus 1127 

The  Subthalamic  Region 1127 

The  Corpora  Mammillaria  ...  . .  .   1128 

The  Pituitary  Body 1129 

The  Third  Ventricle 1131 

The  Telencephalon 1 132 

The  Cerebral  Hemispheres 1 133 

Cerebral   Lobes  and  Interlobar 

Fissures 1135 

Lobes  of  the  Hemispheres 1139 

Frontal  Lobe 1 139 

Parietal  Lobe 1 143 

Occipital  Lobe 1 145 

•Temporal  Lobe 1147 

Insula 1149 

Limbic  Lobe 1 150 

The  Rhinencephalon 1151 

The  Olfactory  Lobe 1151 

Architecture  of  the  Hemispheres 1 155 

The  Corpus  Callosum 1155 

The  Fornix 1158 

The  Septum  Lucidum • 1159 

The  Lateral  Ventricles 1160 

Internal  Nuclei  of  the  Hemisphere 1169 

The  Caudate  Nucleus 1 169 

The  Lenticular  Nucleus 1169 

The  Claustrum 1172 

The  Amygdaloid  Nucleus 1172 

The  Internal  Capsule 1 173 

Structure  of  the  Cerebral  Cortex. 1175 

The  Nerve-Cells  of  Cortex 1 176 

The  Nerve-Fibres  of  Cortex 1179 

Variations  in  Cerebral  Cortex 1180 

White  Centre  of  the  Hemisphere 1 1  s^ 

The  Association   Fibres 1182 

The  Commissnral  Fibres 1184 


CONTENTS. 


White  Centre  of  the  Hemisphere — Continued 

The  Projection  Fibres 1187 

Development  of  the  Derivatives  of  Fore- 
Brain  1189 

The  Pallium 1189 

The  Sulci  and  Gyri 1 190 

Histogenesis  of  Cerebral  Cortex.  ..  .   1192 

The  Rhinencephalon 1 193 

The  Corpus  Striatum 1 193 

The  Diencephalon 1193 

The  Cerebral  Commissures 1194 

Measurements  of  the  Brain 1195 

The  Membranes  of  the  Brain 1197 

The  Dura  Mater 1 198 

The  Pia  Mater  1202 

The  Arachnoid 1203 

The  Pacchionian  Bodies 1205 

The  Blood -Vessels  of  the  Brain 1206 

Practical  Considerations  :  The  Brain  and 

Its  Membranes 1207 

Congenital  Errors  of  Development.  .   1207 

The  Meninges ' 1208 

Cerebral  Hemorrhage 1209 

Cerebral  Localization 1210 

Cranio-Cerebral  Typography 1214 

THE  PERIPHERAL  NERVOUS  SYSTEM. 

THE  CRANIAL  NERVES 

The  Olfactory  Nerve 

The  Optic  Nerve 

The  Oculomotor  Nerve 

The  Trochlear  Nerve 

The  Trigeminal  Nerve 

The  Gasserian  Ganglion 

The     Ophthalmic     Nerve     and 

Branches 

The  Ciliary  Ganglion 

The  Maxillary  Nerve  and 

Branches 

The  Spheno-Palatine  Gang- 
lion   

The     Mandibular     Nerve     and 

Branches 

The  Otic  Ganglion 

The  Submaxillary  Ganglion 
Practical  Considerations:    The  Tri- 
geminal Nerve 

The  Abducent  Nerve 

The  Facial  Nerve 

Practical  Considerations 

The  Auditory  Nerve 

The  Glosso-Pharyngeal  Nerve 

The  Vagus  or  Pneumogastric  Nerve 

Practical  Considerations 

The  Spinal  Accessory  Nerve 

Practical  Considerations 

The  Hypoglossal  Nerve 

Practical  Considerations 

THE  SPINAL  NERVES 

The  Posterior  Primary  Divisions 

The  Cervical  Nerves 

The  Thoracic  Nerves 

The  Lumbar  Nerves 

The  Cpccygeal  Nerve 

The  Anterior  Primary  Divisions 

The  Cervical  Nerves 

The  Cervical  Plexus  and  Branches 


1 220 

1220 

1223 
1225 
1228 
1230 
1232 

1233 
1236 

1237 

1240 

1242 
1246 

1247 

1248 
1249 
1250 

1254 
1256 

1260 

1265 
1272 

1274 
1275 
1275 
1277 
1278 
1279 
1281 
1282 
1282 
1284 
1284 
1285 
1286 


The  Phrenic  Nerve 1290 

Practical  Considerations 1 292 

The  Brachial  Plexus  and  Branches 1292 

The     External     Anterior    Thoracic 

Nerve 1 297 

The  Musculo-Cutaneous  Nerve 1298 

The  Median  Nerve 1298 

Practical  Considerations 1301 

The     Internal     Anterior     Thoracic 

Nerve 1303 

The      Lesser      Internal     Cutaneous 

Nerve 1303 

The  Internal  Cutaneous  Nerve 1303 

The  Ulnar  Nerve 1303 

Practical  Considerations 1306 

The  Subscapular  Nerves 1306 

The  Circumflex  Nerves 1307 

Practical  Considerations 1308 

The  Musculo-Spiral  Nerve 1308 

Practical  Considerations 1314 

The  Thoracic  Nerves 1314 

Practical  Considerations 1318 

The  Lumbar  Plexus  and  Branches 1319 

The  Ilio-Hypogastric  Nerve 1320 

The  Ilio-Inguinal  Nerve 1321 

The  Genito-Crural  Nerve 1322 

The  External  Cutaneous  Nerve ..'...   1324 

The  Obturator  Nerve 1324 

The  Accessory  Obturator  Nerve.  . .  .   1324 
The  Anterior  Crural  Nerve 1327 

Practical  Considerations  :  Lumbar  Plexus  1330 

The  Sacral  Plexus  and  Branches 1331 

The  Great  Sciatic  Nerve 1335 

The  External  -Popliteal  Nerve 1336 

The  Anterior  Tibial  Nerve 1336 

The  Musculo-Cutaneous 1338 

The  Internal  Popliteal  Nerve 1339 

The  Posterior  Tibial  Nerve 1342 

The  Pudendal  Plexus  and  Branches 1345 

The  Small  Sciatic  Nerve 1348 

The  Pudic  Nerve 1349 

The  Coccygeal  Plexus 1352 

Practical  Considerations  :   Sacral  Plexus  1352 

THE  SYMPATHETIC  NERVES 1353 

General   Constitution  and  Arrange- 
ment     1355 

The  Gangliated  Cord 1356 

Rami  Communicantes 1356 

Cervico-Cephalic  Portion  of  Gangliated 

Cord 1358 

The  Superior  Cervical  Ganglion 1359 

The  Middle  Cervical  Ganglion 1362 

The  Inferior  Cervical  Ganglion 1362 

Thoracic  Portion  of  Gangliated  Cord .  . .  .   1364 

The  Splanchnic  Nerves 1364 

Lumbar  Portion  of  Gangliated  Cord.  ..  .  1366 

Sacral  Portion  of  Gangliated  Cord 1367 

The  Plexuses  of  the  Sympathetic  Nerves  1367 

The  Cardiac  Plexus 1367 

The  Solar  Plexus 1368 

Subsidiary  Plexuses 1369 

The  Hypogastric  Plexus 1374 

Subsidiary  Plexuses 1374 

Practical   Considerations :    The    Sympa- 
thetic Nerves 1375 

Development  of  the  Peripheral  Nerves.  .   1375 


THE    ORGANS    OF   SENSE. 


THE  SKIN. 
General  Description 1381 


Structure 1382 

The  Hairs 1389 


XVI 


CONTENTS. 


The  Hairs  —  Continued 

Structure  ............. 

The  Nails  .............................   1394 

The  Cutaneous  Glands  .................   J397 

The  Sebaceous  Glands  .............   :397 

The  Sweat  Glands  .................   1398 

Development  of  the  Skin  and  its  Append- 
ages ........................ 

THE  NOSE. 


The  Outer  Nose 

Cartilages  of  the  Nose  .............   i4°4 

Practical   Considerations  :    The   External 

Nose  .......................  1407 

The  Nasal  Fossa?  ......................  1409 

The  Vestibule  .....................  1409 

The  Septum  ......................  1410 

The  Lateral  Wall  ..................   1410 

The  Nasal  Mucous  Membrane  ......   1413 

The  Olfactory  Region  ..........  1413 

The  Respiratory  Region  .......   1415 

Jacobson's  Organ  .................   I4J7 

Practical    Considerations  :     The    Nasal 

Cavities  ....................   1417 

The  Accessory  Air-Spaces  .............   1421 

The  Maxillary  Sinus  ...............   I422 

The  Frontal  Sinus  .................   i423 

The  Ethmoidal  Air-Cells  ...........   1424 

The  Sphenoidal  Sinus  .............   1425 

Practical  Considerations  :  The  Accessory 

Air-Spaces  ..................  1426 

Development  of  the  Nose  ..............   1429 

THE  ORGAN  OF  TASTE 
The  Taste-Buds  .......................  1433 

Structure  .........................  1434 

Development  .....................   1436 

THE  EVE'. 

The  Orbit  and  its  Fascke  ..............  1436 

Practical  Considerations  ...........  1438 

The  Eyelids  and  Conjunctiva  ..........  1441 

Practical  Considerations  ...........  1446 

The  Eyeball  ..........................  1447 

Practical  Considerations  ...........  1448 

The  Fibrous  Tunic  ....................  1449 

The  Sclera  ........................  1449 

The  Cornea  .......................  1450 

Practical  Considerations  ...........  1453 

The  Vascular  Tunic  ...................  1454 

The  Choroid  ....................  :  .  1455 

The  Ciliary  Body  ..................  1457 


Practical  Considerations 1459 

The  Iris  1459 

Practical  Considerations 1461 

The  Nervous  Tunic 1462 

The  Retina 1462 

Practical  Considerations  , 1468 

The  Optic  Nerve 1469 

Practical  Considerations 1470 

The  Crystalline  Lens 1471 

Practical  Considerations 14/3 

The  Vitreous  Body 1473 

Practical  Considerations 1474 

The  Suspensory  Apparatus  of  the  Lens..  1475 
The  Aqueous  Humor  and  its  Chamber.  .  1476 

Practical  Considerations 1476 

The  Lachrymal  Apparatus 1477 

The  Lachrymal  Gland 1477 

The  Lachrymal  Passages  1478 

Practical  Considerations 1479 

Development  of  the  Eye i4So 

THE  EAR. 

The  External  Ear 1484 

The  Auricle 1484 

The  External  Auditory  Canal 1487 

Practical  Considerations 1490 

The  Middle  Ear I492 

The  Tympanic  Cavity I492 

The  Membrana  Tympani   1494 

The  Auditory  Ossicles I496 

The  Mucous  Membrane 1500 

The  Eustachian  Tube 1501 

The  Mastoid  Cells 1504 

Practical    Considerations :    The    Middle 

Ear 1504 

The  Tympanic  Cavity I5°4 

The  Tympanic  Membrane 1505 

The  Eustachian  Tube 1507 

The  Mastoid  Process  and  Cells 1508 

The  Internal  Ear i510 

The  Osseous  Labyrinth 1511 

The  Vestibule   15" 

The  Semicircular  Canals 1512 

The  Cochlea 1513 

The  Membranous  Labyrinth 1514 

The  Utricle I5U 

The  Saccule  15*5 

The  Semicircular  Canals    1515 

The  Cochlear  Duct 151? 

The  Nerves  of  the  Cochlea   1521 

Development  of  the  Ear    1523 


THE   GASTRO-PULMONARY    SYSTEM. 


General  Considerations 1527 

Mucous  Membranes 1528 

Structure 1528 

Glands 1531 

Types  of  ('.lands 1331 

Simple  Tubular  Glands 1532 

Compound  Tubular  (".lands 1532 

Tubo- Alveolar  Glands 1532 

>< TOUS  ('.lands 1534 

Mucous  ( '.lauds 1534 

Simple  Alveolar 1535 

Compound  Alveolar  <  .lands.  ..  .  1535 

Development  of  <  '.lands 1537 

THK  AIIMI  NTARV  CANAL. 
Th<-  Mouth.  .  1538 


The  Lips,  Cheeks  and  Vestibule 1538 

The  Teeth '.  '542 

Description  of  Individual  Forms.  . .  .  1543 

Structure  of  the  Teeth 1548 

The  Enamel i.S4s 

The  Dentine 155° 

The  Cementum 1552 

The  Alveolar  Periosteum 1553 

Implantation   and    Relations   of    the 

Teeth 1554 

Development  of  the  Teeth 1556 

First  and  Second  I  Jentition 1564 

The  Gums 1567 

The  Palate 1567 

The  Hard  Palate 1567 

The  Soft  Palate 1568 


CONTENTS. 


XV11 


The  Tongue 1573 

General  Description 1573 

The  Glands  of  the  Tongue '1575 

The  Muscles  of  the  Tongue 1577 

The  Sublingual  Space 1581 

The  Salivary  Glands 1582 

The  Parotid  Gland 1582 

The  Submaxillary  Gland '.  1583 

The  Sublingual  Gland 1585 

Structure  of  the  Salivary  Glands.  ...  1585 

Development  of  the  Oral  Glands.  . .  .  1589 

Practical  Considerations:  The  Mouth.  ...  1589 
Malformations :    Harelip    and    Cleft 

Palate 1589 

The  Lips 159° 

The  Gums 159° 

The  Teeth I591 

The  Roof  of  the  Mouth 1592 

The  Floor  of  the  Mouth 1593 

The  Cheeks 1594 

The  Tongue 1594 

The  Pharynx 1596 

The  Naso-Pharynx 1598 

The  Oro-Pharynx 1598 

The  Laryngo-Pharynx 1598 

The  Lymphoid  Structures 1599 

The  Faucial  Tonsils 1600 

The  Pharyngeal  Tonsil 1601 

Relations  of  the  Pharynx 1601 

Development  and  Growth  of  Pharynx  1603 

Muscles  of  the  Pharynx 1604 

Practical  Considerations  :  The  Pharynx..  1606 

The  (Esophagus 1609 

General  Description 1609 

Course  and  Relations 1609 

Structure 161 1 

Practical  Considerations  :  (Esophagus.  ..  1613 

Congenital  Malformations 1613 

Foreign  Bodies 1613 

Strictures 1614 

Carcinoma 1614 

Extrinsic  Disease 1614 

Diverticula : 1614 

The  Abdominal  Cavity 1615 

The  Stomach 1617 

General  Description 1617 

Peritoneal  Relations 1619 

Position  and  Relations 1619 

Structure 1621 

Growth 1629 

Variations 1629 

Practical  Considerations  :  The  Stomach  1629 

Congenital  Malformations 1629 

Injuries  of  the  Stomach 1630 

Ulcers  and  Cancer 1631 

Dilatation  and  Displacement 1631 

Operations  on  the  Stomach 1632 

The  Small  Intestine 1633 

General  Description 1633 

Structure 1634 

The  Duodenum 1644 

Duodeno-Jejunal  Fossae 1647 

Interior  of  the  Duodenum 1648 

The  Jejuno-Ileum 1649 

The  Mesentery  and  Topography  ....  1650 

MeckePs  Diverticulum 1652 

Practical  Considerations:  The  Small  In- 
testine   1652 

The  Peritoneal  Coat 1652 

The  Muscular  Coat 1653 

The  Mucous  and  Submucous  Coats  1653 

Ulcers  of  the  Duodenum 1653 

Infection 1654 


Typhoid  Ulcers 1654 

Contusion  and  Rupture 1654 

Obstruction 1655 

Operations 1656 

The  Large  Intestine 1657 

General  Description 1657 

Structure 1657 

The  Caecum 1660 

The  Vermiform  Appendix 1664 

Peritoneal  Relations 1665 

Pericaecal  Fossae 1666 

Retro-Colic  Fossae 1667 

The  Colon 1668 

General  Description 1668 

Peritoneal  Relations 1670 

The  Sigmoid  Flexure 1671 

Development  and  Growth 1671 

The  Rectum 1672 

The  Anal  Canal 1673 

The  Anus 1673 

Muscles  and  Fasciae  of  Rectum  and 

Anus 1675 

The  Ischio-Rectal  Fossa 1678 

Practical  Considerations:    The  Large  In- 
testine    1680 

The  Caecum j  680 

The  Vermiform  Appendix 1681 

Etiology  of  Appendicitis 1681 

Anatomical  Points  relating  to  the 
Symptoms  and  to  the  Treat- 
ment of  Appendicitis 1683 

Operations  for  Appendicitis  ....   1685 
The  Colon  and  Sigmoid  Flexure.  . .  .   1685 

Distention  and  Rupture 1686 

Displacements 1686 

Obstruction  and  Stricture 1687 

Wounds 1688 

Operations 1688 

The  Rectum  and  Anal  Canal 1689 

Development  of  the  Alimentary  Canal  .  .   1694 

Formation  of  the  Mouth 1694 

Formation  of  the  Anus 1695 

Differentiation  of  the  Body-Cavity. .  .   1700 
Development  of  the  Peritoneum.  ...   1702 

The  Liver 1705 

General  Description 1705 

Borders  and  Surfaces 1707 

Blood-Vessels 1709 

Structure 1712 

The  Hepatic  Duct 1718 

The  Gall-Bladder 1719 

The  Common  Bile-Duct 1720 

Peritoneal  Relations  of  the  Liver.  ...    1721 

Position  of  the  Liver 1722 

Development  and  Growth 1723 

Practical    Considerations :     The    Biliary 

Apparatus 1726 

Anomalies  in  Form  and  Position  of 

the  Liver 1726 

Hepatoptosis  and  Hepatopexy 1726 

Obstruction  of  Hepatic  Circulation.  .  1727 

Wounds  and  Hepatic  Abscess 1727 

Malformations  of  Gall-Bladder 1729 

Wounds  and  Rupture 1729 

Distention  and  Cholecystitis 1729 

The  Cystic  and  Common  Bile-Ducts.    1731 
Operations  on  Gall-Bladder  and  Bili- 
ary Ducts 1732 

The  Pancreas 1732 

General  Description 1732 

Structure 1734 

Pancreatic  Ducts 1736 

Development 1737 


XV111 


CONTENTS. 


Practical  Considerations  :  The  Pancreas.   1738 

Malformations 1738 

Injuries 1738 

Pancreatitis 1739 

The  Peritoneum 1740 

General  Considerations 1740 

The  Anterior  Parietal  Peritoneum..  .  1742 

The  Anterior  Mesentery 1744 

The  Posterior  Mesentery  :  Part  I.  .  .    1746 
The  Posterior  Mesentery  :  Part  II..  .  1751 
The  Posterior  Mesentery  :  Part  III.  .   1753 
Practical    Considerations :    The    Perito- 
neum    1754 

Anatomical  Routes  for  Infections. .  .   1754 
Peritonitis  anatomically  considered. .  1756 

Abdominal  Hernia 1759 

General  Considerations 1759 

Predisposing  anatomical  conditions.   1759 

Inguinal  Hernia 1763 

Anatomy  of  Inguinal  Canal 1763 

Anatomy    of    Indirect    Inguinal 

Hernia 1766 

Varieties  of  Inguinal  Hernia.  .. .  1767 
Anatomy  of  Direct  Inguinal  Her- 
nia   1770 

Anatomical    Considerations    of 

Treatment 1770 

Femoral  Hernia 1773 

Anatomy  of  Femoral  Canal.  . .  .   1773 
Anatomical     Considerations    of 

Treatment 1774 

Umbilical  Hernia 1775 

Ventral  Hernia 1776 

Lumbar  Hernia 1777 

Obturator  Hernia 1777 

Sciatic  Herniae 1778 

Perineal  Herniae 1778 

Diaphragmatic  Hernise 1778 

Intraabdominal  Herniae 1779 

ACCESSORY  ORGANS  OF  NUTRITION. 

The  Spleen 1781 

General  Description 1781 

Structure 1 783 

Peritoneal  Relations 1785 

Development  and  Growth 1787 

Accessory  Spleens 1787 

Practical  Considerations  :  The  Spleen.  . .  .1787 

The  Thyroid  Body 1789 

General  Description 1789 

Structure 1791 

Development 1793 

Accessory  Thyroids 1793 

Practical  Considerations :    The  Thyroid 

Body 1794 


m\jr. 

The  Parathyroid  Bodies 1795 

General  Description 1795 

Structure 1795 

The  Thymus 1796 

General  Description 1796 

Structure 1798 

Development  and   Changes 1800 

The  Suprarenal  Bodies 1801 

General  Description 1801 

Structure 1802 

Development  and  Growth 1804 

Accessory  Suprarenals 1805 

Practical  Considerations:  The  Suprarenal 

Bodies 1806 

The  Anterior  Lobe  of  the  Pituitary  Body,   1807 
Development 1808 

The  Carotid  Body 1809 

The   Coccygeal  Body 1811 

The  Aortic   Bodies 1812 

THE  ORGANS  OF  RESPIRATION. 

The   Larynx 1813 

Cartilages,  Joints  and  Ligaments.  ..  .   1813 
Form  of  Larynx  and  Mucous  Mem- 
brane        : 1818 

Muscles  of  the  Larynx 1825 

Changes  with  Age  and  Sex 1828 

Practical  Considerations  :  The  Larynx..  1828 

The   Mediastinal  Space 1832 

Practical  Considerations 1833 

The  Trachea 1834 

General  Description   1835 

Structure 1835 

Relations 1836 

Growth  and  Subsequent  Changes  1837 
Bifurcation  of    Trachea    and    Roots 

of  Lungs 1837 

The  Bronchi 1838 

Practical  Considerations  :    The  Air-Pas- 
sages    1840 

The  Lungs 1843 

General  Description    1843 

Lobes  and  -Fissures 1845 

Physical   Characteristics 1846 

The  Bronchial  Tree 1847 

The  Lung  Lobule 1849 

Structure 1851 

Blood- Vessels 1853 

Relations  to  Thoracic  Walls.  . . .   1855 

The  Pleurae 1858 

General  Description 1858 

Relations  to  the  Surface 1859 

Structure 1860 

Development  of  the   Respiratory  Tract  1861 
Practical  Considerations  :  The  Lungs  and 

Pleurae 1864 


THE  URO-GENITAL   SYSTEM. 


THE  URINARY  ORGANS. 

The  Kidneys 1869 

General  Description 1869 

Position  and  Fixation 1870 

Relations 1873 

Architecture 1875 

Structure  1877 

Practical  Considerations:  The  Kidneys  .   1887 
Anomalies  of  Form,  Size  or  Num- 
ber     1887 

Anomalies  of  Position 1887 


Renal  Calculus 1890 

Injuries  and  Tumors 1893 

Operations 1893 

The  Renal  Ducts 1894 

Pelvis  of  the  Kidney 1894 

The  Ureter 1895 

Structure, 1896 

Practical  Considerations:  The  Ureters. ..  1898 

Congenital  Anomalies 1898 

Ureteral  Calculus 1899 

Wounds 1900 

Operations 1901 


CONTENTS. 


xix 


The  Bladder I901 

General  Description 1901 

Peritoneal  Relations 1904 

Fixation  and  Relations 1905 

Structure  , i9°8 

Practical  Considerations:  The  Bladder.  .   1910 

Congenital  Anomalies 1910 

Effects  of  Distention 1911 

Retention  of  Urine 1912 

Rupture  and  Wounds 1913 

Cystitis  and  Vesical  Calculus 1914 

The  Male  Perineum 1915 

The  Triangles 1916 

The  Perineal  Interspaces 1916 

Landmarks i9l8 

Lateral  Lithotomy 1919 

Median  Lithotomy 1921 

Suprapubic  Lithotomy 1921 

The  Female  Bladder 1922 

The  Urethra I922 

The  Prostatic  Portion 1922 

The  Membranous  Portion 1923 

The  Spongy  Portion 1923 

The  Female  Urethra 1924 

Structure  1924 

Practical  Considerations:  Male  Urethra.  .   1927 

Congenital  Abnormalities 1927 

Clinical  Division  of  Urethra 1928 

Rupture  of  Urethra 1930 

Anatomical    Consideration    of   Ure- 

thritis 1930 

Stricture  of  Urethra 1931    l 

Urethral  Instrumentation 1933 

Development  of  the  Urinary  Organs.  ..  .  1934 

The  Pronephros 1934 

The Mesonephros  (Wolffian  Body).  .   1935 

The  Metanephros  (Kidney) 1937 

The  Bladder  and  Urethra 1938 

THE  MALE  REPRODUCTIVE  ORGANS. 

The  Testes 1941 

General  Description 1941 

Architecture 1942 

Structure 1942 

Spermatogenesis 1944 

The  Spermatozoa 1946 

The  Epididymis 1947 

General  Description 1947 

Structure 1947 

The  Appendages  of  the  Testicle 1949 

The  Appendix  Testis 1949 

The  Appendix  Epididymidis J949 

The  Paradidymis 1950 

The  Vasa  Aberrantia 1950 

Practical  Considerations:     The  Testicles  1950 

Congenital  Anomalies 1950 

Orchitis   1951 

Epididymo-Orchitis 1952 

Castration 1952 

Hydrocele 1953 

The  Spermatic  Ducts 1953 

The  Vas  Deferens 1954 

The  Ejaculatory  Duct 1955 

Structure  of  Spermatic  Duct 1956 

The  Seminal  Vesicles 1956 

General  Description 1956 

Structure 1958 

Practical  Considerations:    The    Seminal 

Vesicles 1959 

The  Spermatic  Cord 1960 

Practical  Considerations:  The  Spermatic 

Cord 1961 

The  Scrotum 1961 


General  Description 

Coverings  of  the  Testicle 

Practical  Considerations:   The  Scrotum  . 
The  Penis  

General  Description 

The  Corpora  Cavernosa 

The  Corpus  Spongiosum 

The  Glans  Penis 

Structure  

Practical  Considerations:   The  Penis.  ..  . 

Congenital  Abnormalities 

Circumcision 

Contusions  and  Wounds 

Amputation 

The  Prostate  Gland 

General  Description 

Position  and  Relations 

Structure 

Development 

Practical  Considerations :    The  Prostate 
Gland 

Relations  to  Generative  System 

Injuries 

Hypertrophy 

Operations 

The  Glands  of  Cowper 

General  Description 

Structure 

Development 


1961 
1963 
1964 
1965 
1965 
1966 
1967 
1968 
1968 
1972 
1972 
1973 
1974 
1975 
1975 
1975 
1976 
1977 
1979 

1979 
1979 
1979 
1980 
1982 
1984 
1984 
1984 
1984 


THE  FEMALE  REPRODUCTIVE  ORGANS. 


The  Ovaries 

General  Description 

Position  and  Fixation 

Structure 

Follicles  and  Ova 

The  Human  Ovum 

Corpus  Luteum 

Development 

Variations 

Practical  Considerations  :  The  Ovaries.  . 
The  Fallopian  Tubes 

General  Description 

Course  and  Relations 

Structure 

Development  and  Changes 

Variations 

Practical  Considerations  :   The  Fallopian 

Tubes 

Rudimentary  Organs 

The  Epoophoron 

Gartner's  Duct 

The  Paroophoron 

Vesicular  Appendages 

The  Uterus 

General  Description 

Attachments    and   Peritoneal    Rela- 
tions   

The  Broad  Ligament 

The  Round  Ligament 

Position  and  Relations 

Structure 

Development  and  Changes 

Menstruation  and  Pregnancy 

Practical    Considerations :     Uterus    and 
Attachments 

Compartments  of  Pelvis 

Displacements  of  Uterus 

The  Broad  Ligament 

The  Round  Ligaments 

The  Vagina 

General  Description 

Relations.  . . 


1985 
1985 
1986 
1987 
1988 
1990 
1990 
1993 
1995 
1995 
1996 
1996 
1997 
1997 
1999 
1999 

1999 

2OOO 
2OOO 
2OOI 
2OO2 
2OO2 
2003 
2003 

2004 
2OO4 
2005 
2007 
2007 
2010 
2012 

2012 
2013 
2014 
2014 
2015 
20l6 
20l6 
20l6 


XX 


CONTENTS. 


The  Vagina — Continued 

Structure 2017 

Development 2019 

Variations 2019 

Practical   Considerations:    The  Vagina.  2019 

Relations  to  Uterine  Cervix 2019 

Fistulae 2020 

The  Labia  and  the  Vestibule    2021 

The  Labia  Majpra 2021 

The  Mons  Pubis 2021 

The  Labia  Minora 2022 

The  Vestibule    2022 

The  Clitoris 2024 

The  Bulbus  Vestibuli 2025 

The  Glands  of  Bartholin 2026 

Practical  Considerations :  The   External 

Genitals  2027 

The  Mammary  Glands 2027 

General  Description  2027 

Structure 2029 


Milk  and  Colostrum  

Development 

Variations  

Practical  Considerations  :  The  Mammary 

Glands 

The  Nipple    

Paths  of  Infection 

Carcinoma 

Removal  of  the  Breast 

Development  of  Reproductive  Organs  .  . 

General  Considerations 

The  Indifferent  Stage 

Differentiation  of  the  Male  Type.  . . . 

Descent  of  the  Testis 

Differentiation  of  the  Female  Type .  . 

Descent  of  the  Ovary  .* 

The  External  Organs 

In  the  Female   

In  the  Male  

Summary  of  Development 

The  Female  Perineum  . . 


PAGE 
2030 
2032 


2033 
2033 
2034 

2035 
2036 
2037 
2037 
2038 
2038 
2040 
2042 
2043 
2043 
2044 
2044 
2045 
2046 


HUMAN  ANATOMY. 


ANATOMY  is  that  subdivision  of  morphology — the  science  of  form  as  contrasted 
with  that  of  function  or  physiology — which  pertains  to  the  form  and  the  structure  of 
organized  beings,  vegetal  or  animal.  Phytotomy  and  Zootomy,  the  technical  names 
for  vegetal  and  animal  anatomy  respectively,  both  imply  etymologically  the  dissocia- 
tion, or  the  cutting  apart,  necessary  for  the  investigation  of  plants  and  animals. 

The  study  of  organized  bodies  may  be  approached,  evidently,  from  several  stand- 
points. When  the  details  of  the  -structure  of  their  various  tissues  and  organs  par- 
ticularly is  investigated,  such  study  constitutes  General  Anatomy  or  Histology,  fre- 
quently also  called  Microscopical  Anatomy,  from  the  fact  that  the  magnifying  lens  is 
used  to  assist  in  these  examinations.  The  advantages  of  comparing  the  organization 
of  various  animals,  representing  widely  different  types  as  well  as  those  closely  related, 
are  so  manifest  in  arriving  at  a  true  estimate  of  the  importance  and  significance  of 
structural  details,  that  Comparative  Anatomy  constitutes  a  department  of  biological 
science  of  far-reaching  interest,  not  merely  for  the  morphologist,  but  likewise  for 
the  student  of  human  anatomy,  since  we  are  indebted  to  comparative  anatomy  for 
an  intelligent  conception  of  many  details  encountered  in  the  human  body.  Devel- 
opmental Anatomy,  or  Embryology,  also  has  been  of  great  service  in  advancing  our 
understanding  of  numerous  problems  connected  with  the  adult  organism  by  tracing 
the  connection  between  the  complex  relations  of  the  completed  structures  and  their 
primitive  condition,  as  shown  by  the  sequence  of  the  phases  of  development.  These 
three  departments  of  anatomical  study — general,  comparative,  and  developmental 
anatomy — represent  the  broader  aspects  of  anatomical  study  in  which  the  features 
of  the  human  body  are  only  incidents  in  the  more  extended  contemplation  of 
organized  beings. 

The  exceptional  importance  of  an  accurate  knowledge  of  the  body  of  man  has 
directed  to  human  anatomy,  or  anthropotomy ,  so  much  attention  from  various  points 
of  view  that  certain  subdivisions  of  the  subject  are  conveniently  recognized  ;  thus, 
the  systematic  account  of  the  human  body  is  termed  Descriptive  Anatomy,  while 
when  the  mutual  relations  and  peculiarities  of  situation  of  the  organs  located  in  par- 
ticular parts  of  the  body  especially  claim  attention,  such  study  is  spoken  of  as  Topo- 
graphical or  Regional  Anatomy.  Consideration  of  the  important  group  of  anatomi- 
cal facts  directly  applicable  to  the  diagnosis  and  the  treatment  of  disease  constitutes 
Applied  Anatomy. 

General  Plan  of  Construction. — Vertebrate  animals,  of  which  man  rep- 
resents the  most  conspicuous  development  of  the  highest  class,  — fishes,  amphibians, 
reptiles,  birds,  and  mammals  being  the  recognized  subdivisions  of  the  vertebrata, — 
possess  certain  characteristics  in  common  which  suffice  to  distinguish  the  numerous 
and  varied  members  of  the  extended  group. 

The  fundamental  anatomical  feature  of  these  animals  is  the  possession  of  an 
axial  column,  or  spine,  which  extends  from  the  anterior  or  cephalic  to  the  poste- 
rior or  caudal  pole  and  establishes  an  axis  around  which  the  various  parts  of  the 
elongated  body  are  grouped  with  more  or  less  symmetry.  While  this  body-axis  is 
usually  marked  by  a  series  of  well-defined  osseous  segments  constituting  the  ver- 
tebral column  of  the  higher  animals,  among  certain  of  the  lower  fishes,  as  the  sharks 
or  sturgeons,  the  axial  rod  is  represented  by  cartilaginous  pieces  alone  ;  in  fact,  the 
tendency  towards  the  production  of  a  body-axis  is  so  pronounced  that  the  formation 


HUMAN  ANATOMY. 


of  a  primitive  axis,  the  notochord,  takes  place  among  the  early  formative  processes  of 
the  embryo. 

In  addition  to  the  fundamental  longitudinal  axis,  vertebrate  animals  exhibit  a 
transverse  cleavage  into  somatic  or  body-segments.  While  such  segmentation  is  rep- 
resented in  the  maturer  conditions  by  the  series  of  vertebrae  and  the  associated  ribs, 
the  tendency  to  this  division  of  the  body  is  most  marked  in  the  early  embryo,  in 
which  the  formation  of  body-segments,  the  somites,  takes  place  as  one  of  the  primary 
developmental  processes.  Although  these  primary  segments  do  not  directly  corre- 
spond to  the  permanent  vertebrae,  they  are  actively  concerned  in  the  formation  of 
the  latter  as  well  as  the  segmental  masses  of  the  earliest  muscular  tissue.  In  man 
not  only  the  skeleton,  but  likewise  the  muscular,  vascular,  and  nervous  systems  are 
affected  by  this  segmentation,  the  effects  of  which,  however  are  most  evident  in  the 
structure  of  the  walls  of  the  thoracic  portion  of  the  body-cavity. 

Disregarding  the  many  variations  in  the  details  of  arrangement  brought  about 
by  specialization  and  adaptation,  the  body  of  every  vertebrate  animal  exhibits  a 
fundamental  plan  of  construction  in  which  bilateral  symmetry  is  a  conspicuous  fea- 
ture. Viewed  in  a  transverse  section  passing  through  the  trunk,  the  animal  body 

FIG.   i. 


Neural  arch 
Neural  tube 
Spinal  cord 


Vertebral  axis 

Epidermi 
Coriutn 
Parietal  mesoblast 


Costal  segment 
Parietal  mesoblast 

Aorta 

==3^'  Parietal  mesothelium 
'  TTf    Visceral  mesothelium 
Entoblastic  epithelium 

Subepithelial  mesoblast 
Visceral  mesoblast 


Diagrammatic  plan  of  vertebrate  body  in  transverse  section.     (Modified from  Wiedersheim.} 

may  be  regarded  as  composed  primarily  of  the  axis,  formed  by  the  bodies  of  the 
vertebrae,  and  two  tubular  cavities  of  very  unequal  size  enclosed  by  the  tissues  con- 
stituting the  body-walls  and  invested  externally  by  the  integument  (Fig.  i). 

The  smaller  of  these,  the  neural  tube,  is  situated  dorsally,  and  is  formed  by  the 
series  of  the  vertebral  arches  and  associated  ligaments  ;  it  surrounds  and  protects 
the  great  cerebro-spinal  axis  composed  of  the  spinal  cord  and  the  specialized  cephalic 
extremity,  the  brain.  The  larger  space,  the  visceral  tube  corresponding  to  the  body- 
cavity,  or  ccelom,  lies  on  the  ventral  side  of  the  axis  and  contains  the  thoracic  and 
abdominal  viscera,  including  the  more  or  less  convoluted  digestive-tube  with  its 
accessory  glandular  organs,  the  liver  and  the  pancreas,  and  the  appended  respiratory 
tract,  together  with  the  genito-urinary  organs  and  the  vascular  and  lymphatic  appa- 
ratus. 

The  digestive-tube,  which  begins  anteriorly  at  the  oral  orifice  and  opens 
posteriorly  by  the  anus,  is  extended  by  two  ventral  evaginations  giving  rise  to  the 
respiratory  tract  and  the  liver,  a  dorsal  glandular  outgrowth  representing  the  pan- 
creas. The  sexual  and  urinary  glands  and  their  ducts  primarily  occupy  the  dorsal 
wall  of  the  body  cavity.  The  vascular  system  consists  essentially  of  the  ventrally 
placed  contracting  dilatation,  the  heart,  divided  into  a  venous  and  an  arterial  com- 


DESCRIPTIVE   TERMS.  3 

partment,  and  the  great  arterial  trunk,  the  aorta,  the  major  part  of  which  occupies 
the  dorsal  wall  of  the  space. 

The  elongated  typical  vertebrate  body  terminates  anteriorly  in  the  cephalic 
segment,  posteriorly  in  the  caudal  appendage  ;  between  these  two  poles  extends  the 
trunk,  from  which  project  the  ventrally  directed  limbs,  when  these  appendages  exist. 
Just  as  the  axial  segments,  represented  by  the  bodies  of  the  vertebrae,  take  part, 
in  conjunction  with  the  neural  arches,  in  the  formation  of  the  neural  canal,  so  do  these 
segments  also  aid  in  forming  the  supporting  framework  of  the  ventral  body-cavity 
in  connection  with  the  series  of  ribs  and  the  sternum. 

Descriptive  Terms. — The  three  chief  planes  of  the  vertebrate  body  are  the 
sagittal,  the  transverse,  and  the  frontal.  The  sagittal  plane,  when  central,  passes 
through  the  long  axis  of  the  body  vertically  and  bisects  the  ventral  or  anterior  and 
the  dorsal  or  posterior  surfaces.  The  transverse  plane  passes  through  the  body 
at  right  angles  to  its  long  axis  and  to  the  sagittal  plane.  The  frontal  plane  passes 
vertically  but  parallel  to  the  anterior  or  ventral  surface,  being  at  right  angles  to  both 
the  sagittal  and  transverse  planes  (Fig.  2.  ) 

The  vertical  position  of  the  long  axis  in  the  human  body  is  unique,  since  man, 


FIG.  2. 


FIG.  3. 


Three  principal  planes  of  human  body.      T,  T, 
transverse;  S,  S,  sagittal ;  F,  F,  frontal. 


Human  embryo  showing  primary  relations  of 
limbs,  a,  a,  preaxial  surfaces ;  6,  6,  postaxial ; 
s,  s,  somitic.  segments  of  trunk. 


of  all  animals,  is  capable  of  habitually  maintaining  the  erect  posture  with  full  exten- 
sion of  the  supporting  extremities.  The  lack  of  correspondence  between  the  actual 
position  of  the  chief  axis  of  man  and  the  horizontal  fore-and-aft  axis  of  vertebrates 
in  general  results  in  discrepancies  when  the  three  principal  planes  of  the  human 
body  are  compared  with  those  of  other  animals.  Thus,  the  sagittal  plane  alone 
retains  the  relation,  as  being  at  right  angles  to  the  plane  of  the  support,  in  all  verte- 
brates, although  in  man  its  greatest  expansion  is  vertical.  The  transverse  plane  in 
man  is  parallel  with  the  suppprting  surface,  while  it  is,  obviously,  at  right  angles 
to  the  corresponding  plane  in  the  four-footed  vertebrate  ;  likewise,  the  frontal  plane 
in  man  is  vertical,  while  it  is  horizontal  in  other  animals. 

The  various  terms  employed  in  describing  the  actual  position  of  the  numerous 
parts  of  the  human  body  and  their  relations  to  surrounding  structures  have  been 
adopted  with  regard  to  the  erect  attitude  of  man  and  the  convenience  of  the  student 
of  human  anatomy  ;  hence,  in  many  cases,  they  must  be  recognized  as  having  a 
limited  specific  and  technical  application  and  often  not  directly  applicable  to  other 


4  HUMAN   ANATOMY. 

vertebrates.  Superior  and  inferior,  upper  and  lower,  as  indicating  relations  towards 
or  away  from  the  head-end  of  the  body,  are,  probably,  too  convenient  and  useful  as 
expressing  the  peculiar  relations  in  man  to  readily  be  relinquished,  although  when 
directly  applied  to  animals  possessing  a  horizontal  body-axis  they  refer  entirely  to 
relations  with  the  plane  of  support,  the  additional  terms  cephalic  and  caudal  being 
necessary  to  indicate  relations  with  the  head- and  tail-pole.  Likewise,  "anterior" 
and  "posterior,"  as  referring  respectively  to  the  front  and  back  surfaces  of  the 
human  body,  are  more  logically  described  as  ventral  and  dorsal,  with  the  advantage 
that  these  terms  are  directly  applicable  to  all  vertebrates.  ' '  Outer' '  and  ' '  inner, ' '  as 
expressing  relations  with  the  sagittal  plane,  are  now  largely  replaced  by  the  more 
desirable  terms  lateral  and  mesial  respectively,  external  and  internal  being  reserved 
to  indicate  relations  of  depth.  Cephalic  and  caudal,  central  and  peripheral,  prox- 
imal and  distal,  are  all  terms  which  have  found  extensive  use  in  human  anatomy. 

Preaxial  and  postaxial,  in  addition  to  their  general  and  obvious  significance 
with  reference  to  axes  in  common,  have  acquired  a  specific  meaning  with  regard  to 
the  limbs,  the  appreciation  of  which  requires  consideration  of  the  primary  relations 
observed  in  the  embryo.  In  the  earliest  stage  the  limbs  appear  as  flattened  buds 
which  project  from  the  side  of  the  trunk  and  present  a  dorsal  and  ventral  surface  ; 
subsequently  the  limbs  become  folded  against  the  body,  the  free  ends  being  directed 
ventrally,  while  one  border  looks  headward,  the  other  tailward.  If  an  axis  corre- 
sponding to  the  transverse  plane  of  the  body  be  drawn  through  the  length  of  the 
extremities,  each  limb  will  be  divided  into  two  regions,  one  of  which  lies  in  front  of 
the  axis,  and  is,  therefore,  preaxial,  the  other  behind,  or  postaxial.  On  reference  to 
Fig.  3  it  is  obvious  that  the  preaxial  border  or  surface  of  each  limb  is  primarily 
directed  towards  the  cephalic  or  head-end  of  the  animal,  and,  conversely,  that  the 
postaxial  faces  the  caudal  or  tail-end.  These  fundamental  relations  are  of  great  im- 
portance in  comparing  the  skeleton  of  the  upper  and  lower  extremities  with  a  view 
of  determining  the  morphological  correspondence  of  the  several  component  bones, 
since  the  primary  relations  become  masked  in  consequence  of  the  secondary  dis- 
placements which  the  limbs  undergo  during  their  development. 

The  terms  homologue  and  analogue  call  for  a  passing  notice,  since  an  exact 
understanding  of  their  significance  is  important.  Structures  or  parts  are  homologous 
when  they  possess  identical  morphological  values  founded  on  a  common  origin  ;  thus, 
the  arm  of  a  man,  the  front  leg  of  a  dog,  and  the  wing  of  a  bat  are  homologues,  because 
each  represents  the  fore-limb  of  a  vertebrate,  although  they  differ  in  individual  func- 
tion. On  the  other  hand,  the  wing  of  a  bat  and  that  of  a  butterfly  are  analogous, 
since  they  are  structures  of  functional  similarity,  although  of  wide  morphological 
diversity.  Homologue,  therefore,  'implies  structural  identity,  analogue  implies 
functional  similarity.  Parts  are  said  to  be  homotypes  when  they  are  serial  homo- 
logues ;  thus,  the  humerus  and  the  femur  are  homotypes,  being  corresponding 
structures  repeated  in  the  same  animal.  Where  parts  possess  both  morphological 
and  functional  identity,  as  the  wing  of  a  bird  and  of  a  bat,  they  are  analogous  as  we'll 
as  homologous. 


THE  ELEMENTS  OF  STRUCTURE. 


WHEN  critically  examined,  the  various  organs  and  parts  going  to  make  up  the 
complex  economy  of  the  most  highly  specialized  vertebrate — and,  indeed,  the  same 
is  true  of  all  animals  whose  organization  does  not  approach  the  extremely  simple  uni- 
cellular type — are  found  to  be  constituted  by  the  various  combinations  of  a  very 
small  number  of  elementary  tissues ;  these  latter  may  be  divided  into  four  funda- 
mental groups  : 

Epithelial  tissues  ; 

Connective  tissues  ; 

Muscular  tissues  ; 

Nervous  tissues. 

Of  these  the  nervous  tissues  are  most  specialized  in  their  distribution,  while  the 
connective  tissues  are  universally  present,  in  one  or  another  form  contributing  to  the 
composition  of  every  organ  and  part  of  the  body.  The  tissues  of  the  circulatory 
system,  including  the  walls  of  the  blood-vessels  and  lymph-channels  and  the  corpus- 
cular elements  of  their  contained  fluids,  the  blood  and  the  lymph,  represent  special- 
izations of  the  connective  tissues  of  such  importance  that  they  are  often  conceded 
the  dignity  of  being  classed  as  independent  tissues  ;  consideration  of  the  develop- 
ment of  the  vascular  tissues,  however,  shows  their  genetic  relations  to  be  so  nearly 
identical  with  those  of  the  great  connective- tissue  group  that  a  separation  from  the 
latter  seems  undesirable. 

Each  of  the  elementary  tissues  may  be  resolved  into  its  component  morphologi- 
cal constituents,  the  cells  and  the  intercellular  substances.  The  first  of  these  are  the 


FIG.  4. 


Pseudopod 


Vegetal  food- 
inclusions 


Entoplasm 


Exoplasm 


A,  unicellular  animal  (amceba);  B,  embryonal  cell, — leucocyte. 


descendants  of  the  embryonal  elements  derived  from  the  division  or  segmentation  of 
the  parent  cell,  the  ovum,  and  are  highly  endowed  with  vital  activity  ;  the  intercellu- 
lar substances,  on  the  other  hand,  represent  secondary  productions,  comparatively 
inert,  since  they  are  formed  through  the  more  or  less  direct  agency  of  the  cells.  The 
animal  cell  may  exist  in  either  the  embryonal,  matured,  or  metamorphosed  condition. 
The  embryonal  cell,  as  represented  by  the  early  generations  of  the  direct  off- 
spring of  the  ovum,  or  by  the  lymphoid  cells  or  colorless  blood-corpuscles  of  the 
adult,  consists  of  a  small,  irregularly  round  or  oval  mass  of  finely  granular  gelati- 
nous substance — the  protopla sm — in  which  a  smaller  and  often  indistinct  spherical 
body — the  nucleus — lies  embedded.  In  the  embryonal  condition,  when  the  cell  is 
without  a  limiting  membrane,  and  composed  almost  entirely  of  active  living  matter, 
the  outlines  are  frequently  undergoing  change,  these  variations  in  shape  being  known 
as  amoeboid  movements,  from  their  similarity  to  the  changes  observed  in  the  outline 
of  an  active  amoeba,  the  representative  of  the  simplest  form  of  animal  life,  in  which 


6  HUMAN  ANATOMY. 

the  single  cell  constitutes  the  entire  organism,  and  as  such  is  capable  of  performing 
the  functions  essential  for  the  life-cycle  of  the  animal. 

As  the  embryonal  cell  advances  in  its  life-history,  the  conditions  to  which  it  is 
subjected  induce,  with  few  exceptions,  further  specializations,  since  in  all  but  the 
lowest  forms  division  of  labor  is  associated  with  a  corresponding  differentiation  and 
adaptation  to  specific  function. 

Vital  manifestations  of  the  cell  include  those  complex  physico-chemical 
phenomena  which  are  exhibited  during  the  life  of  the  cellular  constituents  of  the 
body  in  the  performance  of  the  functions  necessary  for  fulfilment  of  their  appointed 
life-work.  These  embrace  metabolism,  growth,  reproduction,  and  irritability. 

Metabolism,  the  most  distinctive  characteristic  of  living  matter,  is  that  process 
by  which  protoplasm  selects  from  the  heterogeneous  materials  of  food  those  partic- 
ular substances  suitable  for  its  nutrition  and  converts  them  into  part  of  its  own  sub- 
stance. Metabolism  is  of  two  forms, — constructive  and  destructive.  Constructive 
metabolism,  or  anabolism,  is  the  process  by  which  the  cell  converts  the  simpler  com- 
pounds into  organic  substances  of  great  chemical  complexity;  destructive  metabolism, 
or  katabolism,  on  the  contrary,  is  the  process  by  which  protoplasm  breaks  up  the 
complex  substances  resulting  from  constructive  metabolism  into  simpler  compounds. 
Vegetal  cells  possess  the  power  of  constructive  metabolism  in  a  conspicuous  degree, 
and  from  the  simpler  substances,  such  as  water,  carbon  dioxide,  and  inorganic  salts, 
prepare  food-material  for  the  nutritive  and  katabolic  processes  which  especially  dis- 
tinguish the  animal  cell,  since  the  latter  is  dependent,  directly  or  indirectly,  upon 
the  vegetal  cell  for  the  materials  for  its  nutrition. 

Growth,  the  natural  sequel  of  the  nutritive  changes  effected  by  metabolism, 
may  be  unrestricted  and  equal  in  all  directions,  resulting  in  the  uniform  expansion 
of  the  cell,  as  illustrated  in  the  growth  of  the  ovum  in  attaining  its  mature  condition. 
Such  unrestricted  increase,  however,  is  exceptional,  since  cells  are  usually  more  or 
less  intimately  related  to  other  structural  elements  by  which  their  increase  is  modi- 
fied so  as  to  be  limited  to  certain  directions ;  such  limitation  and  influence  result  in 
unequal  growth,  a  force  of  great  potency  in  bringing  about  the  differentiation  and 
specialization  of  cells,  and,  secondarily,  of  entire  parts  and  organs  of  the  body. 
Familiar  examples  of  the  result  of  unequal  growth  are  observed  in  the  columnar 
elements  of  epithelium,  the  fibres  of  muscular  tissue,  and  the  neurones  of  the  ner- 
vous system. 

Reproduction  may  be  regarded  as  the  culminating  vital  manifestation  in  the 
vegetative  life-cycle  of  the  cell,  since  by  this  process  the  parent  element  surrenders 
its  individuality  and  continues  its  life  in  the  existence  of  its  offspring.  While  the 
details  of  the  process  by  which  new  cells  arise  from  pre-existing  cells  are  reserved  for 
consideration  in  connection  with  the  more  extended  discussion  of  the  cell  to  follow 
(see  page  9),  it  may  here  be  stated  that  reproduction  occurs  by  two  methods, — 
the  indirect  or  mitotic  and  the  direct  or  amitotic.  The  first  of  these,  involving  the 
complicated  cycle  of  nuclear  changes  collectively  known  as  mitosis  or  karyokinesis, 
is  the  usual  method ;  the  second  and  simpler  process  of  direct  division,  or  amitosis, 
is  now  recognized  as  exceptional  and  frequently  associated  with  conditions  of  im- 
paired vital  vigor. 

Irritability  is  that  property  of  living  matter  by  virtue  of  which  the  cell  ex- 
hibits changes  in  its  form  and  intimate  constitution  in  response  to  external  impres- 
sions. These  latter  may  originate  in  mechanical,  thermal,  electrical,  or  chemical 
stimuli  to  which  the  protoplasm  of  even  the  lowest  organisms  responds,  or  they  may 
be  produced  in  consequence  of  the  obscure  and  subtle  changes  occurring  within  the 
protoplasm  of  neighboring  elements,  as  illustrated  by  the  reaction  of  the  neurones  in 
response  to  the  stimuli  transmitted  from  other  nervous  elements. 

THE  ANIMAL  CELL. 

Ever  since  the  establishment  of  the  Cell  Doctrine,  in  1838,  by  the  announcement 
of  the  results  of  the  epoch-making  investigations  of  Schleiden  and  Schwann  on  "The 
Accordance  of  Structure  and  Growth  of  Animals  and  Plants,"  the  critical  examination 
of  the  cell  has  been  a  subject  of  continuous  study.  Notwithstanding  the  tireless  cnthu- 


STRUCTURE   OF  THE   CELL. 


siasm  with  which  these  researches  have  been  pursued  by  the  most  competent  investi- 
gators and  the  great  advance  in  our  accurate  knowledge  concerning  the  intricate 
problems  relating  to  the  morphology  and  the  physiology  of  the  cell,  much  pertaining 
to  the  details  of  the  structure  and  the  life  of  the  cell  still  remains  uncertain,  and  must 
be  left  to  the  future  achievements  in  cytology.  The  account  here  given  of  the  mor- 
phology of  the  cell  presents  only  those  fundamental  facts  which  at  the  present  time 
may  be  accepted  as  established  upon  the  evidence  adduced  by  the  most  trustworthy 
observers.  The  more  speculative  and  still  unsettled  and  disputed  problems  of  cy- 
tology, interesting  as  such  theoretical  considerations  may  be,  lie  beyond  the  purpose 
of  these  pages  ;  for  such  discussions  the  student  is  referred  to  the  special  works  and 
monographs  devoted  to  these  subjects.  An  appreciation,  however,  of  the  salient 
facts  of  cytology  as  established  by  the  histologists  of  the  present  generation  is  essen- 
tial not  only  for  an  intelligent  conception  of  the  structure  of  the  morphological  ele- 
ments, but  likewise  for  the  comprehension  of  the  highly  suggestive  modern  theories 
concerning  inheritance,  since,  as  will  appear  in  a  later  section,  the  present  views 
regarding  these  highly  interesting  problems  are  based  upon  definite  anatomical 
details. 


FIG.  5. 


Cytoplasm 


Spongioplastn 
Hyaloplasm  — 


Metaplastic  inclusions 


Exoplasm 

Endoplasm 

Nuclear  membrane 
Nucleolus 


Centrosome  surrounded  by 
centrosphere 


Cytoplasm 
Cell-wall 


Diagram  of  cell-structure.     In  the  upper  part  of  the  figure  the  granular  condition  of  the  cytoplasm  is  represented ; 

in  the  lower  and  left,  the  reticular  condition. 

Notwithstanding  the  great  variations  in  the  details  of  form  and  structure,  cells 
possess  a  common  type  of  organization  in  which  the  presence  of  the  cell-body  or  cyto- 
plasm and  the  nucleus  is  essential  in  fulfilling  the  modern  conception  of  a  cell.  The 
latter  may  be  defined,  therefore,  as  a  nucleated  mass  of  protoplasm. 

The  term  protoplasm,  as  now  generally  employed  by  histologists,  signifies  the 
organized  substance  composing  the  entire  cell,  and  with  this  application  includes 
both  the  cytoplasm  and  the  nucleus. 

Structure  of  the  Cytoplasm.— The  cytoplasm,  or  the  substance  of  the  cell- 
body,  by  no  means  invariably  presents  the  same  appearance,  since  it  may  be  regarded 
as  established  that  the  constituents  of  this  portion  of  the  cell  are  subject  to  changes  in 
their  condition  and  arrangement  which  produce  corresponding  morphological  varia- 
tions ;  thus,  the  cytoplasm  may  be  devoid  of  definite  structure  and  appear  homoge- 
neous ;  at  other  times  it  may  be  composed  of  aggregations  of  minute  spherical  masses 
and  then  be  described  as  granular,  or,  where  the  minute  spheres  are  larger  and  con- 
sist of  fluid  substances  embedded  within  the  surrounding  denser  material  of  the  cell, 
as  alveolar ;  or,  again,  and  most  frequently,  the  cytoplasm  contains  a  mesh- work  of 
fibrils,  more  or  less  conspicuous,  which  arrangement  gives  rise  to  the  reticidar  con- 
dition. The  recognition  of  the  fact  established  by  recent  advances  in  cytology,  that 
the  structure  of  cytoplasm  is  not  to  be  regarded  as  immutable,  but,  on  the  contrary, 
as  capable  of  undergoing  changes  which  render  it  probable  that  a  cell  may  appear 


8 


HUMAN   ANATOMY. 


during  one  stage  of  its  existence  as  granular  and  at  a  later  period  as  reticular,  has 
done  much  to  bring  into  accord  the  conflicting  and  seemingly  irreconcilable  views 
regarding  the  structure  of  the  cell  championed  by  competent  authorities. 

Whatever  be  the  particular  phase  of  structural  arrangement  exhibited  by  the 
cell,  histologists  are  agreed  that  the  cytoplasm  consists  of  two  substances, — an  act  ire 
and  a  passive  ;  while  both  must  be  regarded  as  living,  the  vital  manifestations  of  con- 
tractility are  produced  by  the  former. 

Since  a  more  or  less  pronounced  reticular  arrangement  of  the  active  and  passive 
constituents  of  cytoplasm  is  of  wide  occurrence  in  mature  cells,  this  condition  may 
serve  as  the  basis  for  the  description  of  the  morphology  of  the  typical  cell. 

Critical  examination  of  many  cells,  especially  the  more  highly  differentiated 
forms  of  glandular  epithelium,  shows  the  cytoplasm  to  contain  a  mesh-work  com- 
posed of  delicate  fibrils  and  septa  of  the  more  active  substance,  the  spongioplasm  ; 
although  conspicuous  after  appropriate  staining,  the  spongioplastic  net-work  may  be 
seen  in  the  unstained  and  living  cell,  thereby  proving  that  such  structural  details  are 
not  artefacts  due  to  the  action  of  reagents  upon  the  albuminous  substances  com- 
posing the  protoplasm. 

The  interstices  of  the  mesh-work  are  filled  with  a  clear  homogeneous  semifluid 
material  to  which  the  name  of  hyaloplasm  has  been  applied.  Embedded  within  the 
hyaloplasm,  a  variable  amount  of  foreign  substances  are  frequently  present ;  these 


FIG.  6. 
B 


C 


Spermatogenic  cells,  showing  variations  in  the  condition  and  the  arrangement  of  the  constituents  of  the  cyto- 
plasm and  the  nucleus;  the  centrosomes  are  seen  within  the  cytoplasm  close  to  the  nucleus.  A,  from  the  guinea-pig 
X  1685  (Afeves) ;  £,  from  the  salamander  X  500  (Meves) ;  C,  from  the  cat  X  750  (von  Lenhossek). 

include  particles  of  oil,  pigment,  secretory  products,  and  other  extraneous  materials, 
which,  while  possibly  of  importance  in  fulfilling  the  purposes  of  the  cell,  are  not  among 
its  true  morphological  constituents.  These  substances,  which  are  inert  and  take  no 
part  in  the  vital  activity  of  the  cell,  are  termed  collectively  metaplasm. 

Cytoplasm  consists,  therefore,  morphologically,  of  the  spongioplasm  and  the 
hyaloplasm  ;  chemically,  cytoplasm  consists  of  certain  organic  compounds,  salts  and 
water.  The  organic  compounds  are  grouped  under  the  term  proteins,  which  are 
complex  combinations  of  carbon,  hydrogen,  nitrogen,  and  oxygen,  with  often  a  small 
percentage  of  sulphur.  The  proteins  of  the  cytoplasm  contain  little  or  no  phosphorus. 

Structure  of  the  Nucleus. — The  nucleus,  during  the  vegetative  condition  of 
the  cell,  or  the  "resting  stage,"  as  often  less  accurately  called,  appears  as  a  more 
or  less  spherical  body  whose  outline  is  sharply  defined  from  the  surrounding  cyto- 
plasm by  a  definite  envelope,  the  nuclear  membrane.  Since  the  nucleus  is  the 
nutritive,  as  well  as  reproductive,  organ  of  the  cell,  the  fact  that  this  part  of  the  cell 
is  relatively  large  in  young  and  actively  growing  elements  is  readily  explained. 

The  nucleus  consists  of  two  parts,  an  irregular  reticulum  of  nuclear  fibres  and 
an  intervening  semifluid  nuclear  matri.\\  therein  resembling  the  cytoplasm.      Exam 
ined  under  high  magnification,  after  appropriate  treatment  with  particular  stains,  such 
as  hsematoxylin,  safranin,  and  other  basic  dyes,  the  nuclear  fibres  are  shown  to  be 
composed  of  minute  irregular  masses  of  a  deeply  colored  substance,  appropriately 


STRUCTURE   OF   THE   CELL. 


called  chromatin  in  recognition  of  its  great  affinity  for  certain  stains  ;  the  chromatin 
particles  are  supported  upon  or  within  delicate  inconspicuous  and  almost  colorless 
threads  of  linin.  The  latter,  therefore,  forms  the  supporting  net-work  of  the  nuclear 
fibrils  in  which  the  chromatin  is  so  prominent  by  virtue  of  its  capacity  for  staining. 
The  forms  of  the  individual  masses  of  chromatin  vary  greatly,  often  being  irregular, 
at  other  times  thread-like  or  beaded  in  appearance.  Not  infrequently  the  chromatin 
presents  spherical  aggregations  which  appear  as  deeply  stained  nodules  attached  to 
the  nuclear  fibres  ;  these  constitute  the  false  nucleoli,  or  karyosomes,  as  distinguished 
from  the  true  nucleolus  which  is  frequently  present  within  the  karyoplasm.  Chemi- 
cally, chromatin,  the  most  essential  part  of  the  nucleus,  contains  nuclein,  a  com- 
pound rich  in  phosphorus. 

The  matrix,  or  nuclear  juice,  which  occupies  the  interstices  of  the  net-work, 
possesses  an  exceedingly  weak  affinity  for  the  staining  reagents  employed  to  color 
the  chromatin,  and  usually  appears  clear  and  untinted,  and  is  probably  closely 
related  to  the  achromatin.  It  contains  a  substance  described  as  paralinin. 

The  micleolus,  or  plasmosome,  ordinarily  appears  as  a  small  spherical  body — 
sometimes  multiple — lying  among,  but  unattached  to,  the  nuclear  fibres  ;  its  color  in 
stained  tissues  varies,  sometimes  resembling  that  of  the  chromatin,  although  less 
deeply  stained,  but  usually  presenting  a  distinct  difference  of  tint,  since  it  responds 
readily  to  dyes  which,  like  eosin  or  acid  fuchsin,  particularly  affect  the  linin  and 
cytoplasm.  Concerning  the  exact  nature,  purpose,  and  function  of  the  nucleolus 
much  uncertainty  still  exists  ;  according  to  certain  authorities,  these  bodies  are  to  be 
regarded  as  storehouses  of  substances  which  are  used  in  the  formation  of  the  chro- 
matin segments  during  division,  while  other  cytologists  attribute  to  the  nucleolus  a 
passive  role,  even  regarding  it  as  by-product  which,  at  least  in  some  cases,  is  cast  out 
from  the  nucleus  into  the  cytoplasm,  where  it  degenerates  and  disappears.  Since 
trustworthy  observations  may  be  cited  in  support  of  both  of  these  conflicting 
views,  definite  conclusions  regarding  the  exact  nature  of  this  constituent  of  the 
nucleus  must  be  deferred.  The  nucleolus  is  credited  with  containing  a  peculiar 
substance  known  as  pyrenin.  The  term  amphipyrenin,  as  applied  to  the  substance 
of  the  nuclear  membrane,  is  of  doubtful  value. 

The  Centrosome. — In  addition  to  the  parts  already  described,  which  are  con- 
spicuous and  readily  seen,  the  more  recent  investigations  into  the  structure  of  cells 
show  the  presence  of  a  minute  body,  the  cen- 
trosome, which  plays  an  important  role  in 
elements  engaged  in  active  change,  as  con- 
spicuously during  division  and,  in  a  lesser 
degree,  during  other  phases  of  cellular  activity. 
Ordinarily  the  centrosome  escapes  attention 
because,  on  account  of  its  minute  size  and  varia- 
ble staining  affinity,  it  is  with  difficulty  distin- 
guished from  the  surrounding  particles.  Its 
usual  position  is  within  the  cytoplasm,  but  the 
exact  location  of  the  centrosome  seems  to  de- 
pend upon  the  focus  of  greatest  motor  activity, 
since,  as  shown  by  Zimmermann,  this  little 
body,  or  bodies,  being  often  double,  is  always 
found  in  that  part  of  the  cell  which  is  the  seat 
of  greatest  change  ;  thus,  in  a  dividing  ele- 
ment, the  centrosome  lies  immediately  related 
to  the  actively  changing  nucleus,  while  within 
ciliated  epithelium  it  is  removed  from  the  nu- 
cleus and  is  found  closely  associated  with  the 
contractile  filaments  which  probably  produce  the  movements  of  the  hair-like  ap- 
pendages. In  recognition  of  the  intimate  relations  between  this  minute  body  and  the 
active  motor  changes  affecting  the  morphological  constituents  of  the  cell,  the  cen- 
trosome may  be  regarded  physiologically  as  its  dynamic  centre  ;  the  name  kino- 
centrum  has  been  suggested  by  Zimmerman  as  best  expressing  this  probable 
function  of  the  centrosome.  This  little  body  is  frequently  surrounded  by  a  clear 


FIG. 


Centrosomes  (c,  c)  in  human  epithelium; 
A,  B,  cells  from  gastric  glands;  C,  from  duo- 
denal glands ;  D,  from  tongue ;  /,  leucocyte  with 
centrosome  X  625:  (K.  W.  Zimmermann.) 


10 


HUMAN    ANATOMY. 


area  or  halo,  the  centrosphere  or  the  attraction  sphere,  within  which  it  appears  as  a 
minute  speck,  frequently  being  double  instead  of  single. 

In  recapitulation,  the  chief  constituents  of  the  animal  cell  may  be  tabulated  as 
follows  : 

(  Meshwork — Spongioplasm. 

Cytoplasm     \  Ground-substance— Hyaloplasm,  containing  inclusions,  l\fela- 
(.     plasm. 

f  Linin  fibrils. 

PROTOPLASM    •{  f  Nuclear  reticulum  consisting  of    I  Chromatin   (containing  Nu- 

|  Centrosome  (     clein}. 

I  Nuclear  matrix  (containing  Para/in  in}. 

I  Nucleus  \ucleolus  (containing  Pyrenin. 

I  Nuclear  membrane. 

DIVISION   OF   CELLS. 

Disregarding  for  the  present,  at  least,  the  occurrence  of    direct  fission  as  a 
means  of  producing  new  elements  observed  among  the  simplest  forms  of  animal  life, 


Diagram  of  mitosis.  A,  resting:  stage,  chromatin  irregularly  distributed  in  nuclear  reticulum;  a,  centrosphere 
containing  double  centrosome;  n,  nucleolus.  B,  chromatin  arranged  as  close  spirem  ;  c,  r,  centrosomes  surrounded 
by  achromatic  radial  striations.  C,  stage  of  loose  spirem,  achromatir  figure  forming  amphiaster  (am/>).  D,  chra 


segments  towards  new  nude!,  as  established  by  centrosomes  (c,  c)  ;  <•  p,  <.  i|iiatoi  ial  plate  formed  by  intonningliiig 
segments.  (,.  separating  groups  of  daughter  chromosomes  (rf,  rf)  united  bv  connecting  threads  (c  t).  //,  daughter 
chrOMOSOmei  ('/,  •/)  becoming  arranged  around  daughter  c-rntr.>s<iim>s  whirh  have  already  divided;  C,  C,  beginning 
cleavage  of  cytoplasm  across  plane  of  equatorial  spinale.  /,  completed  daughter  nuclei  (D,  D) ;  cytoplasm  almost 
divided  into  two  new  cells.  (Modi/ltd from  H'ilson), 


or  as  an  exceptional  method  among  effete  and  diseased  cells  of  the  higher  types,  the 
production   of   IH-U    generations  of  cells   may  be  assumed  as  accomplished   for  all 


DIVISION   OF   CELLS. 


varieties  of  elements  by  a  complicated  series  of  changes,  collectively  known  as  kar- 
yokinesis,  or  mitosis,  especially  affecting  the  nucleus.  As  already  pointed  out,  in 
addition  to  presiding  over  the  nutritive  and  chemical  changes,  the  nucleus  is  par- 
ticularly concerned  in  the  process  of  reproduction  ;  further,  of  the  several  morpho- 
logical constituents  of  the  nucleus,  the  chromatin  displays  the  most  active  change, 
since  this  substance  is  the  vehicle  by  which  the  characteristics  of  the  parent  cell  are 
transmitted  to  the  new  elements.  So  essential  is  this  substance  for  the  perpetuation 
of  the  characteristics  of  each  specific  kind  of  cell  that  the  entire  complex  mitotic 
cycle  has  for  its  primary  purpose  the  insurance  of  the  equal  division  of  the  chroma- 
tin  of  the  mother  cell  between  the  two  new  nuclei,  such  impartial  distribution  of  the 
chromatin  taking  place  irrespective  of  any,  or  even  very  great,  dissimilarity  in  the 
size  of  the  daughter  cells,  the  smaller  receiving  exactly  one-half  of  the  maternal 
chromatin. 

Mitotic  Division. — The  details  of  karyokinesis,  or  mitosis,  sometimes  also 
spoken  of  as  indirect  division,  include  a  series  of  changes  involving  the  centrosome, 

FIG.  9. 
ADC 


\x 


-•  - 


^i,  .?ti 


D 


H 


Chromatic  figures  in  dividing  cells  from  epidermis  of  salamander  embryo.  X  960.  A,  resting  stage;  B,  close 
spireme  ;  C,  loose  spireme;  D,  chromosomes  (*'  wreath  " ),  seen  from  surface;  E,  similar  stage,  seen  in  profile;  F, 
longitudinal  cleavage  of  chromosomes  ;  G,  beginning  migration  of  segments  towards  centrosomes  ;  ff,  separating 
groups  of  daughter  segments  ;  /,  daughter  groups  attracted  towards  poles  of  new  nuclei,  cytoplasm  exhibits  begin- 
ning cleavage. 

the  nucleus,  and  the  cytoplasm,  which  are  conveniently  grouped  into  four  stages  ; 
(i)  the  Prophases,  or  preparatory  changes;  (2)  the  Metaphase,  during  which  the 
chromatin  is  equally  divided  ;  (3)  the  Anaphases,  in  which  redistribution  of  the 
chromatin  is  accomplished  ;  (4)  the  Tclophases,  during  which  the  cytoplasm  under- 
goes division  and  the  daughter  cells  are  completed. 


12  HUMAN   ANATOMY. 

In  anticipation  of  the  consideration  of  the  details  of  mitosis,  it  should  be  pointed 
out  that  the  process  includes  two  distinct,  but  intimately  associated  and  coinci- 
dent series  of  phenomena,  the  one  involving  the  chromatin,  the  other  the  centro- 
somes  and  the  linin.  While  as  a  matter  of  convenience  these  two  sets  of  changes  are 
described  separately,  it  must  be  understood  that  they  take  place  simultaneously  and 
in  coordination.  The  purpose  of  the  changes  affecting  the  chromatin  is  the  accu- 
rate and  equal  division  of  this  substance  by  the  longitudinal  cleavage  of  the  chroma- 
tin  segments  ;  the  object  of  the  activity  of  the  centrosomes  and  the  linin  is  to  supply 
the  requisite  energy  and  to  produce  the  guiding  lines  by  which  the  chromatin 
segments  are  directed  to  the  new  nuclei,  each  daughter  cell  being  insured  in  this 
manner  one-half  of  the  maternal  chromatin. 

The  Prophases,  or  preparatory  stages,  include  a  series  of  changes  which 
involve  the  nuclear  substances  and  the  centrosomes  and  result  in  the  formation  of  the 
karyokinetic figure ;  the  latter  consists  of  two  parts,  ( i )  the  deeply  staining  chro- 
matin filaments,  and  (2)  the  achromatic  figure,  which  colors  but  slightly  if  at  all. 
The  chromatin  loses  its  reticular  arrangement  and,  increasing  in  its  staining  affinities, 
becomes  transformed  into  a  closely  convoluted  thread  or  threads,  constituting  the 
"  close  skein  ;"  the  filaments  composing  the  latter  soon  shorten  and  thicken  to  form 
the  "  loose  skein."  The  skein,  or  spireme,  may  consist  of  a  single  continuous  fila- 
ment, or  it  may  be  formed  of  a  number  of  separate  threads.  Sooner  or  later  the 
skein  breaks  up  transversely  into  a  number  of  segments  or  chromosomes,  which  ap- 
pear as  deeply  staining  curved  or  straight  rods.  A  very  important,  as  well  as  remark- 
able, fact  regarding  the  chromosomes  is  their  numerical  constancy,  since  it  may  be 
regarded  as  established  that  every  species  of  animal  and  plant  possesses  a  fixed  and 
definite  number  of  chromosomes  which  appear  in  its  cells  ;  further,  that  in  all  the 
higher  forms  the  number  is  even,  in  man  being  probably  twenty-four.  During  these 
changes  affecting  the  chromatin  the  nucleolus,  or  plasmosome,  disappears,  and,  prob- 
ably, takes  no  active  part  in  the  karyokinesis  ;  the  nuclear  membrane  likewise  fades 
away  during  the  prophases,  the  nuclear  segments  now  lying  unenclosed  within  the 
cell,  in  which  the  cytoplasm  and  the  nuclear  matrix  become  continuous. 

Coincident  with  the  foregoing  changes,  the  centrosome,  which  by  this  time  has 
already  divided  into  two,  is  closely  associated  with  phenomena  which  include  the  ap- 
pearance of  a  delicate  radial  striation  within  the  cytoplasm  around  each  centrosome, 
thereby  producing  an  arrangement  which  results  in  the  formation  of  two  stars  or 
asters.  The  centrosomes  early  show  a  disposition  to  separate  towards  opposite  poles 
of  the  cell,  this  migration  resulting  in  a  corresponding  migration  of  the  asters.  In 
consequence  of  these  changes,  the  retreating  centrosomes  become  the  foci  of  t\vo 
systems  of  radial  striation  which  meet  and  together  form  an  achromatic  figure  known 
as  the  amphiaster,  which  consists  of  the  two  asters  and  the  intervening  spindle. 
Notwithstanding  the  observations  which  tend  to  question  the  universal  importance 
of  the  centrosome  as  the  initiator  of  dynamic  change  within  the  cell,  as  held  by  Van 
Beneden  and  Boveri,  there  seems  to  be  little  doubt  that  the  centrosome  plays  an 
important  role  in  establishing  foci  towards  which  the  chromosomes  of  the  new  nuclei 
become  attracted. 

The  nuclear  spindle,  which  originates  as  part  of,  or  secondarily  from  the 
amphiaster,  often  occupies  the  periphery  of  the  nucleus,  whose  limiting  membrane  by 
this  time  has  probably  disappeared.  The  delicate  threads  of  linin  composing  the 
nuclear  spindle  lie  within  an  area,  the  polar  field,  around  which  the  chromosomes 
become  grouped.  The  chromosomes,  which  meanwhile  have  arisen'  by  transverse 
division  of  the  chromatin  threads  composing  the  loose  skein,  appear  often  as 
V-shaped  segments,  the  closed  ends  of  the  loops  being  directed  towards  the  polar 
field  which  they  encircle.  Owing  to  this  disposition,  when  seen  from  the  broader 
surface,  the  chromosomes  constitute  a  ring-like  group,  sometimes  described  as  the 
mother  r.vvv////  ;  the  same  segments,  when  viewed  in  profile,  appear  as  a  radiating 
group  of  fibrils  known  as  the  mother  star  \  the  apparent  differences,  therefore,  be- 
tween these  figures  depend  upon  the  point  of  view  and  not  upon  variations  in  the 
arrangement  of  the  111  ires. 

The  Metaphase  includes  the  most  important  detail  of  karyokinesis, — namely, 
the  longitudinal  cleavage  of  the  chromosomes,  whereby  the  number' of  the  latter  is 


MITOTIC    DIVISION.  13 

doubled  and  the  chromatin  is  equally  divided.  This  division  is  the  first  step  towards 
the  actual  apportionment  of  the  chromatin  between  the  new  nuclei,  each  of  which 
receives  exactly  one-half  of  the  chromatin,  irrespective  of  even  marked  inequality 
in  the  size  of  the  daughter  cells. 

Meanwhile  the  centrosomes  have  continued  to  separate  towards  the  opposite 
poles  of  the  cell,  where,  surrounded  by  their  attraction  spheres,  each  forms  the 
centre  of  the  astral  striation  that  marks  either  pole  of  the  amphiaster,  the  nuclear 
spindle  being  formed  by  the  junction  of  the  prolonged  and  opposing  striae.  The 
purpose  of  the  achromatic  figure  is  to  guide  the  longitudinally  divided  chromosomes 
towards  the  new  nuclei  during  the  succeeding  changes. 

The  Anaphases  accomplish  the  migration  of  the  chromosomes,  each  pair  of 
sister  segments  contributing  a  unit  to  each  of  the  two  groups  of  chromosomes  that 
are  passing  towards  the  poles  of  the  achromatic  spindle  ;  in  this  manner  each  new 
nucleus  receives  not  only  one-half  of  the  chromatin  of  the  mother  nucleus,  but  also 
the  same  number  of  chromosomes  that  originally  existed  within  the  mother  cell,  the 
numerical  constancy  of  the  particular  species  being  thus  maintained. 

Anticipating  their  passage  towards  the  poles  of  the  achromatic  figure,  the  mi- 
grating chromatic  segments,  attracted  by  the  linin  threads,  for  a  time  form  a  com- 
pact group  about  the  equator  of  the  spindle  known  as  the  equatorial  plate.  As  the 
receding  segments  pass  towards  their  respective  poles,  the  opposed  ends  of  the  sep- 
arating chromosomes  are  united  by  intervening  achromatic  threads,  the  connecting 
fibres.  Sometimes  the  latter  exhibit  a  linear  series  of  thickenings  known  as  the 
cell-plate  or  mid-body.  The  migration  of  the  chromosomes  establishes  the  essential 
features  of  the  division  of  the  nucleus,  since  the  subsequent  changes  are  only  repe- 
titions, in  inverse  order,  of  the  changes  already  noted. 

The  Telophases,  in  addition  to  the  final  stages  in  the  rearrangement  of  the 
chromatic  segments  of  the  new  nuclei,  including  the  appearance  of  the  daughter 
wreath,  the  daughter  skeins,  the  new  nuclear  membrane,  and  the  nucleolus,  witness 
the  participation  of  the  cytoplasm  in  the  formation  of  the  new  cells.  In  these  final 
stages  of  mitosis  the  cell-body  becomes  constricted  and  then  divides  into  two,  the 
plane  of  division  passing  through  the  equator  of  the  nuclear  spindle.  Each  of  the 
resulting  masses  of  cytoplasm  invests  a  new  nucleus  and  receives  one-half  of  the 
achromatic  figure  consisting  of  a  half-spindle  and  one  of  the  asters  with  a  centro- 
some.  The  new  cell,  now  possessing  all  the  constituents  of  the  parent  element, 
usually  acquires  the  morphological  characteristics  of  its  ancestor  and  passes  into  a 
condition  of  comparative  rest  until  called  upon,  in  its  turn,  to  enter  upon  the  com- 
plicated cycle  of  mitosis. 

MITOTIC   DIVISION. 

I.  Prophases. 

A.  Changes  within  the  nucleus  :    Chromatic  figure. 

Chromatin  loses  reticular  arrangement, 

Close  skein, 

Loose  skein, 

Disappearance  of  nucleolus, 

Division  of  skein  into  chromosomes, 

Arrangement  around  polar  field — mother  wreath, 

Disappearance  of  nuclear  membrane. 

B.  Changes  within  the  cytoplasm  :  Achromatic  figure. 

Division  of  centrosome. 
Appearance  of  asters. 
Migration  of  centrosomes, 
Appearance  of  spindle, 
.     Formation  of  amphiaster, 

Appearance  of  nuclear  spindle  and  polar  field. 

II.  Metaphase. 

Longitudinal  cleavage  of  chromosomes, 


HUMAN   ANATOMY. 


III.  Anaphases. 

Rearrangement  of  chromosomes  into  two  groups, 
Migration  of  groups  towards  poles  of  amphiaster. 
Appearance  of  connecting  fibres  between  receding  groups, 
Construction  of  daughter  nuclei. 

IV.  Telophases. 

Constriction  of  cell-body  appears  at  right  angles  to  spindle, 

Chromosomes  rearranged  in  daughter  nuclei  to  form  skeins, 

Reappearance  of  nuclear  membrane, 

Reappearance  of  nucleoli, 

Complete  division  of  cell-body, 

Daughter  nuclei  assume  vegetative  condition, 

Achromatic  striation  usually  disappears, 

Centrosomes,  single  or  divided,  lie  beside  new  nuclei. 

AMITOTIC   DIVISION. 

The  occurrence  of  cell  reproduction  without  the  foregoing  complex  cycle  of 
karyokinetic  changes  is  known  as  amitotic  or  direct  division.  That  this  process  does 
take  place  as  an  exceptional  method  in  the  reproduction  of  the  simplest  forms  of  ani- 
mal life,  or  in  the  multiplication  of  cells  within  pathological  growths  or  tissues  of  a 

transient  nature,  as  the  fcetal  envelopes,  may 
FIG.  10.  be  regarded  as  established  beyond  dispute. 

The  essential  difference  between  amitotic 
and  the  usual  method  of  division  lies  in  the 
fact  that,  while  in  the  latter  the  chromatin  of 
the  nucleus  is  equally  divided  and  the  number 
of  chromosomes  carefully  maintained,  in  direct 
division  the  nucleus  remains  passive  and  suffers 
cleavage  of  its  total  mass,  but  not  of  its  indi- 
vidual components.  Since  the  nucleus  re- 
mains in  the  vegetative'  condition,  neither 
the  chromatic  nor  achromatic  figure  is  pro- 
duced, the  activity  of  the  centrosome,  when 
exhibited,  being  possibly  directly  expended  in 
effecting  a  division  of  the  cytoplasm,  and  inci- 
dentally that  of  the  nucleus.  In  many  cases 
the  amitotic  division  of  the  nucleus  is  not  ac- 
companied by  cleavage  of  the  cytoplasm,  such 
processes  resulting  in  the  production  of  multi- 
In  general,  it  may  be  assumed  that  cells  which 
undergo  direct  division  are  elements  destined  to  surfer  premature  degeneration, 
since  such  cells  subserve  special  purposes  and  are  not  capable  of  perpetuating  their 
kind  by  normal  reproduction.  Flemming  has  pointed  out  the  fact  that  those  leuco- 
cytes which  arise  by  amitotic  division,  and  therefore  deviate  from  the  usual  mode  of 
origin  of  these  elements,  are  cells  which  are  doomed  to  early  death;  this  form  of 
cell-division  among  the  higher  forms  must  be  regarded,  probably,  as  a  secondary 
process. 


Decidual  cells  showing  amitotic  division  of 
nucleus  (A-D) ;  in  E  an  attempt  at  mitosis  has 
occurred.  X  410. 


nuclear  and  aberrant  nuclear  forms. 


EARLY   DEVELOPMENT. 


THE  human  body  with  all  its  complex  organism  is  the  product  of  the  differentia- 
tion and  specialization  of  the  cells  resulting  from  the  union  of  the  parental  sexual 
elements, — the  ovum  and  the  spermatozoon. 

The  Ovum. — The  maternal  germ-cell  is  formed  within  the  female  sexual  gland, 
the  ovary,  in  which  organ  it  passes  through  all  stages  of  its  development,  from  the 
immature  differentiation  of  its  early  condition  to  the  partially  completed  matura- 
tion of  the  egg  as  it  is  liberated  from  the  ovary. 

The  human  ovum,  in  common  with  the  ova  of  other  mammals,  is  of  minute 
size,  being,  as  it  is  discharged  from  the  ovary,  about  .  2  millimetre  in  diameter.  Ex- 
amined microscopically  and  after  sectioning,  the  human  ovum  is  seen  to  be  enclosed 
within  a  distinct  envelope,  the  zona  pellucida,  .014  millimetre  in  thickness,  which 
in  favorable  preparations  exhibits  a  radial  striation,  and  hence  is  also  named  the 
zona  radiata.  This  envelope  at  first  was  confounded  with  the  proper  limiting  mem- 
brane of  the  cell,  and  for  a  time  was  erroneously  regarded  as  corresponding  to  the 

FIG.  n. 


Corona  radiata 


Zona  pellucida 


Germinal  vesicle  (nu- 
cleus) containing  germ- 
inal spot  (nucleolus) 

Zone  rich  in  deutoplasm 


Zone  poor  in  deutoplasm 
fading  into  homogene- 
ous peripheral  zone 


*    »>  .^' 
Human  ovum  from  ripe  Graafian  follicle.    X  170.    (Nagel.} 

cell-wall.  The  nature  of  the  zona  pellucida  is  now  generally  conceded  to  be  that  of 
a  protecting  membrane,  produced  through  the  agency  of  cells  surrounding  the 
ovum. 

The  substance  of  the  ovum,  the  yolk,  or  vitellus,  consists  of  soft,  semifluid  pro- 
toplasm modified  by  the  presence  of  innumerable  yolk-granules,  the  representatives 
of  the  important  stores  of  nutritive  materials  present  in  the  bird's  egg.  Critically 
examined,  the  vitellus  is  resolvable  into  a  reticulum  of  active  protoplasm,  or  obplasm, 
and  the  nutritive  substance,  or  deutoplasm.  At  times  the  yolk  is  limited  externally 
by  a  very  delicate  envelope,  the  vitelline  membrane,  which  usually  lies  closely  placed, 
or  adherent,  to  the  protecting  zona  radiata  ;  sometimes,  however,  it  is  separated 
from  the  latter  by  a  perivitelline  space.  The  vitelline  membrane  is  probably  absent 
in  the  unfertilized  human  ovum. 

A  large  spherical  nucleus,  the  germinal  vesicle,  approximately  .037  millimetre  in 
diameter,  usually  lies  eccentrically  within  the  yolk,  surrounded  by  the  distinct  nuclear 
membrane.  Within  the  germinal  vesicle  the  constituents  common  to  nuclei  in 


i6 


HUMAN   ANATOMY. 


FIG.  12. 


•Head 

•  End-knob 

•Middle-piece 


•Axial  filament 


Tail 


general  are  found,  including  the  all-important  chromatin  fibrils,  nuclear  matrix,  and 
nucleolus  ;  the  latter,  in  the  original  terminology  of  the  ovum,  is  designated  as 
the  germinal  spot,  and  measures  about  .05  millimetre  in  diameter.  In  addition  to 
these  more  easily  distinguished  components  of  the  maternal  cell,  the  centrosome 
must  be  accepted  as  a  constant  constituent  of  the  fully  formed,  but  unmatured, 
ovum,  although  its  presence  may  escape  detection. 

The  Spermatozoon. — The  male  germ-cell,  the  spermatic  filament,  is  produced 
by  the  specialization  of  epithelial  elements  lining  the  seminiferous  tubules  within  the 
testicle.  The  human  spermatozoon  consists  of  three  parts, 
— the  ovoid  head,  the  cylindrical  middle-piece,  and  the  attenu- 
ated, greatly  extended  tail ;  of  these  the  head  and  middle- 
piece  are  the  most  important,  since  these  parts  contain  re- 
spectively the  chromatin  and  the  centrosome  of  the  cells  from 
which  the  spermatic  filaments  are  derived.  The  centrosome 
is  represented  by  a  minute  spherical  body,  the  end-knob,  which 
lies  in  the  middle-piece  immediately  beneath  the  head  at  the 
extremity  of  the  axial  fibre  ;  the  latter  extends  throughout  the 
spermatozoon  from  the  head  to  the  termination  of  the  tail, 
ending  as  an  extremely  attenuated  thread,  the  terminal  fila- 
ment. The  tail  corresponds  to  a  flagellum  and  serves  the 
purposes  of  propulsion  alone,  taking  no  part  in  the  important 
changes  produced  in  the  ovum  by  the  entrance  of  the  male 
element.  It  is  of  interest  to  note  that  both  the  ovum  and 
the  spermatozoon  are  the  direct  specializations  of  epithelial 
tissue,  the  active  elements  of  the  primary  indifferent  sexual 
glands  being  derived  from  the  mesodennic  lining  of  the 
body-cavity. 

Maturation  of  the  Ovum. — Maturation,  or  ripening 
of  the  ovum,  is  that  process  by  which  the  female  element  is 
prepared  for  the  reception  of  the  spermatozoon.  It  takes  place, 
however,  entirely  independently  of  the  influence  of  the  male 
or  of  the  probability  of  fertilization,  every  healthy  ovum  un- 
dergoing these  changes  before  it  becomes  sexually  ripe. 
About  the  time  that  the  ovum  is  liberated  from  the  ovary  by 
the  bursting  of  the  Graafian  follicle,  as  the  sac  which  encloses 
the  egg  within  the  ovarian  stroma  is  called,  its  nucleus  en- 
gages in  the  complicated  cycle  already  described  as  mitotic 
division.  The  nucleus  migrates  to  the  periphery  of  the  ovum, 
loses  its  limiting  membrane,  and  undergoes  division,  one  pole 
of  the  nuclear  spindle  being  located  within  the  protrusion  of 
protoplasm  which  has  coincidently  taken  place.  With  the 
division  of  the  nuclear  chromatin,  the  protruded  protoplasm 

becomes  constricted  and  finally  separated  from  the  ovum  ;  the  minute  isolated  mass 
thus  formed,  containing  one-half  of  the  maternal  chromatin,  is  the  first  polar  body. 
Almost  immediately  the  mitotic  cycle  is  repeated,  and  again  results  in  the  constric- 
tion and  final  separation  of  a  minute  cell,  the  second  polar  body.  These  two  isolated 
portions  of  the  ovum  remain  visible  for  a  long  time  as  small,  deeply  stained  cells 
lying  within  the  perivitelline  space  beneath  the  zona  pellucida. 

The  chromatin  remaining  within  the  ovum  after  the  repeated  division  becomes 
collected  within  a  new  nucleus,  which  now  takes  a  non-central  position  within  the 
egg,  and  is  henceforth  known  as  the  female  pronnclcus  or  egg-nucleus.  After  matu- 
ration the  ovum  is  prepared  for  union  with  the  spermatozoon,  although  in  many 
cases  the  male  sexual  element  has  actually  entered  the  ovum  before  the  completion 
of  the  maturation  cycle  :  should,  however,  impregnation  not  occur,  the  ovum  passes 
nliuig  the  oviduct  into  the  uterus  and  is  firtally  lost.  The  passage  of  the  human 
egg  from  the  ovary 'to  the  uterus  occupies,  probably,  about  eight  days,  a  period 
corresponding  closely  to  the  length  of  time  that  the  ovum  retains  its  capability  of 
fertilization. 

The  significance  of  the  extrusion  of  the  polar  bodies — a  process  which  occurs 


-Terminal  filament 


Human  spermatozoon,  semi 
diagrammatic.    X  1650. 


EARLY    DEVELOPMENT.  17 

with  great  constancy  in  almost  all  animals,  and,  indeed,  is  probably  represented  in 
the  development  of  vegetal  organisms  as  well — has  been  the  subject  of  much  dis- 
cussion and  speculation.  The  most  satisfactory  explanation  of  the  significance  of 
maturation  has  been  proposed  by  Van  Beneden,  Boveri,  and  others,  based  upon  the 
comparison  of  the  changes  which  take  place  in  the  development  of  the  germ-cells 
of  the  two  sexes. 

In  order  to  appreciate  the  necessity  and  the  meaning  of  maturation  of  the  ovum, 
it  will  be  of  advantage  to  take  a  brief  survey  of  the  phenomena  attending  the  devel- 
opment of  the  male  sexual  elements.  The  seminiferous  tubules  of  the  testicle  are 
lined  with  epithelial  cells,  certain  of  which,  known  as  the  primary  spermatocytes, 

FIG.  13. 


-•"* 


Semi-diagrammatic  representation  of  the  formation  of  the  polar  bodies,  based  upon  observations  of  invertebrate 
ova  (Ascaris  and  Physa).  n,  nucleus;  c,  c,  centrosomes ;  J,  nuclear  spindle;  p',  />",  first  and  second  polar  bodies; 
<?,  egg-nucleus.  (After  Kostanecki  and  IVierzejski.) 

increase  in  size  and  undergo  division,  the  daughter  cells  constituting  the  secondary 
spermatocytes.  Each  of  the  latter,  in  turn,  gives  rise  to  a  new  generation,  the  sper- 
matids,  from  which  the  spermatozoa  are  directly  formed,  the  chromatin  of  the  sper- 
matid  being  stored  within  the  head,  and  the  centrosome  forming  the  end-knob  within 
the  middle-piece.  The  spermatozoon,  therefore,  represents  the  third  generation 
and  corresponds  to  the  mature  ovum. 

Turning  to  the  phenomena  of  maturation,  a  parallel  process  is  presented,  since 
the  ovarian  egg,  or  primary  oocyte,  divides  into  two  cells,  the  secondary  oocytes, 
represented  by  the  ovum  and  the  first  polar  body,  each  of  which  receives  one-half  of 
the  chromatin,  notwithstanding  that  one  of  the  daughter  cells,  the  first  polar  body, 
is  disproportionately  small  ;  the  repetition  of  division  effects  a  second  distribution  of 


18 


HUMAN    ANATOMY. 


the  chromatin,  so  that  the  mature  egg,  after  the  completion  of  maturation,  represents 
the  third  generation,  and  is,  therefore,  morphologically  equivalent  to  a  spermatozoon. 
Attention  has  already  been  directed  to  the  important  fact  that  the  cells  of  a 
given  species  contain  a  fixed,  definite,  and  even  number  of  chromosomes  (page 
12);  hence,  in  their  primary  condition,  each  germ-cell  contains  the  full  complement 
of  chromatin  segments.  Since,  however,  the  new  being  arises  from  the  elements 
derived  from  the  segmentation  of  a  cell  to  the  nucleus  of  which  both  parents  con- 
tribute an  equal  number  of  chromosomes,  it  follows  that,  unless  some  provision  be 
made  whereby  the  number  of  chromosomes  in  each  germ-cell  be  reduced  to  one- 


Primordial  germ-cell 


MALE 


Spermatogonia 


Primary  sperma- 
tocyte 

Secondary   sper- 
matocytes 

Spermatids 
Spermatozoa 


FlG.   14. 


Division-period 


Growth-period 


Maturation-period 


Primordial  germ-cell 


FKMALK 


Oogonia 


Primary  oocyte 
(ovarian  egg) 

Secondary  oocytes 

(egg  and  first 

polar  body) 

Mature  egg  and 
polar  bodies 


Diagram  illustrating  the  genesis  of  the  male  and  female  germ-cells.    (After  Boveri.) 

half  the  full  number,  the  elements  of  the  new  being  would  be  provided  with  double 
the  number  required  to  satisfy  the  normal  complement  for  the  particular  species. 
In  fact,  such  reduction  of  the  chromosomes  of  the  germ-cells  does  take  place  during 
the  development  of  these  elements,  in  consequence  of  which  the  ovum  and  the 
spermatozoon  each  contribute  only  one-half  the  number  of  chromosomes,  the  nor- 
mal quota  being  restored  to  the  segmentation  nucleus,  and  subsequently  to  the  cells 
of  the  new  being,  by  the  sum  of  the  contributions  of  both  parents. 

Interpreted  in  the  light  of  these  considerations,  maturation  may  be  regarded  as 
the  means  by  which  correspondence  between  the  sexual  cells  is  secured,  and,  further, 
the  polar  bodies  may  be  considered  as  abortive  ova. 

Fertilization  of  the  Ovum. — Impregnation,  or  fertilization  of  the  ovum, 
includes  the  meeting  of  the  male  and  female  elements,  the  penetration  into  the  sub- 
stance of  the  latter  by  the  former,  and  the  changes  immediately  induced  by  the 
presence  of  the  spermatozoon  within  the  egg. 

Coincidently  with  the  rupture  of  the  distended  Graafian  follicle,  the  surface  of 
the  ovary  is  embraced  by  the  expanded  fimbriated  extremity  of  the  oviduct,  along  the 
plications  of  which  the  liberated  matured  ovum  is  guided  into  the  tube.  It  is  highly 
probable  that  not  an  inconsiderable  number  of  the  ova  discharged  from  the  ovary  fail 
to  reach  the  oviduct  and  are  lost  in  the  abdominal  cavity. 

Fertilization  usually  takes  place  in  the  upper  third  of  the  oviduct,  shortly  after 
the  ovum  has  escaped  from  the  Graafian  follicle,  although  any  part  of  the  tract  from 
the  ovary  to  the  uterus  may  be  the  seat  of  impregnation. 

The  spermatozoa  overcome  the  obstacles  offered  within  the  narrow  channels 
by  the  mucus  and  the  opposed  ciliary  currents  of  the  uterine  and  tubal  mucous 
membranes  by  virtue  of  their  long  actively  vibrating  tails,  and  advance  at  a  rate 
estimated  at  from  1.5  to  2.5  millimetres  per  minute  ;  it  is  therefore  probable  that 
the  seminal  cells  accomplish  the  journey  from  the  mouth  of  the  uterus  to  the  ovum 
in  from  eight  to  ten  hours.  Spermatozoa  retain  their  vitality  and  fertilizing  pow- 
ers for  many  days  within  the  normal  female  genital  tract  ;  repeated  observation  on 
the  human  subject  has  shown  that  this  period  may  extend  throughout  an  entire 


FERTILIZATION    OF   THE   OVUM. 


menstrual  cycle  of  twenty-eight  clays, — a  possibility  to  be  remembered  when  calcu- 
lating the  probable  termination  of  pregnancy. 

Of  the  many  millions  of  spermatic  elements  deposited  within  the  vagina,  only 


FIG.  15. 
B 


C 


D 


'E 


Fertilization  of  the  ovum  as  illustrated  by  sections  of  the  eggs  of  the  mouse.  (Sobotta.)  All  the  figures  ait- 
magnified  500  diameters  except  D-G,  in  which  the  amplification  is  1500  diameters.  A-C,  prophases  of  formation  of 
fust  polar  body  (p)  ;  z,  zona  pellucida  ;  n,  nuclear  figure;  »/,  head  of  spermatozoon.  D-G,  entrance  of  spermato- 
zoon (.0  into  ovum  and  subsequent  changes.  H-M,  sequence  of  changes  during  the  formation,  approach,  and  blend- 
ing of  the  male  (m)  and  female  (/)  pronuclei ;  p,p,  polar  bodies. 

an  insignificant  number  ever  reach  the  vicinity  of  the  ovum.  Notwithstanding 
that  probably  a  number  of  spermatozoa  penetrate  the  zona  pellucida,  normal  fertili- 
zation in  man  and  the  higher  animals  is  effected  by  a  single  seminal  element.  After 


20 


HUMAN   ANATOMY. 


the  entrance  of  the  favored  spermatozoon  into  the  substance  of  the  ovum,  an  effec- 
tual barrier  to  the  penetration  of  additional  seminal  cells  is  presented  by  the  thick 
vitelline  membrane  which  immediately  forms.  The  point  at  which  the  spermatozoon 
is  about  to  enter  the  egg  is  indicated  by  a  conical  elevation,  the  receptire  eminence, 
into  which  the  male  germ-cell  sinks, — the  tail  only  partly  entering  the  protoplasm 
of  the  egg  and  very  soon  disappearing. 

The  position  of  the  remains  of  the  spermatozoon  within  the  substance  of  the 
ovum  is  indicated  by  an  ovoid  body,  the  male  pronucleus,  which  contains  the  chro- 
matin  and  centrosome  of  the  paternal  germ-cell.  The  sperm-nucleus  zx\&  the  egg- 
nucleus,  as  the  male  and  female  pronuclei  are  now  often  designated,  usually  break 
up  into  their  respective  chromosomes  without  fusing  into  a  single  segmentation 

FIG.  16. 

B  C 


H 


Early  stapes  of  segmentation  as  seen  in  ova  of  mouse,  surface  view.  X  5°o.  (Sobotta.)  The  external  double 
contour  represents  the  zona  pellucida ;  the  cell  marked  with  X,  the  polar  body.  A,  fertilized  ovum  at  stage  of  the 
pronuclei;  /?,  two  segmentation  spheres  of  equal  size;  C,  segmentation  spheres  of  unequal  size;  D,  three-cell  stage 
resulting  from  division  of  larger  sphere  ;  E,  stage  of  four  spheres;  F,  six;  Cr,  eight ;  //.sixteen;  /.twenty-five. 

nucleus.      In  this  case  the  two  groups    of  chromosomes  unite  in  the  first  mitotic 
figure,  the  segmentation  spindle  (Fig.  17). 

After  the  fusion  of  the  pronuclei,  and  just  as  segmentation  is  beginning,  tin- 
fertilized  ovum  presents  a  clear  oval  area  which  contains  the  two  groups  of  chromo- 
somes  contributed  by  the  germ-cells  of  both  parents  ;  on  opposite  sides  of  the  chro- 
matin  figure  are  the  centrospheres,  each  containing  a  centrosome  and  surrounded 
by  a  marked  polar  striation  within  the  substance  of  the  egg.  The  centrosomes  now 
present  within  the  ovum  are  usually  both  derived  from  the  substance  of  the  cen- 
trosome of  the  spermatic!,  \\hirh  entered  the  ovum  as  the  end-knob  within  the  mid- 
dle-piece of  the  fertilizing  spermatozoon.  The  role  of  the  latter,  therefore,  is  two- 
fold,— to  contribute  the  chromatin  necessary  to  restore  to  the  parent  cell  the  normal 


SEGMENTATION    OF   THE   OVUM. 


21 


complement  of  chromosomes,  and  to  furnish  the  stimulus  required  to  inaugurate  the 
karyokinetic  cycle  of  segmentation. 

Segmentation  of  the  Ovum. — The  union  of  the  male  and  female  pronuclei 
and  the  resulting  formation  of  the  segmentation  nucleus  is  followed  immediately 
by  the  division  of  the  ovum  into  two  new  elements  ;  each  of  these  gives  rise  to  two 
additional  cells,  which,  in  turn,  produce  following  generations  of  segmentation  cells, 
or  blastomeres.  This  process  of  repeated  division  of  the  fertilized  ovum  and  its 

FIG.  17. 
ABC 


cp 


descendants  constitutes  segmentation, — a  process  common  to  the  development  of 
all  animals  and  plants  above  the  very  simplest. 

Study  of  the  details  of  segmentation  in  the  various  classes  of  animals  shows 
that  a  close  relation  exists  between  the  character  of  the  cleavage  and  that  of  the 
ovum  with  regard  to  the  amount  and  distribution  of  the  nutritive  yolk,  or  cleuto- 
plasm,  present. 

In  the  human  and  mammalian  egg  the  nutritive  yolk  particles  are  compara- 
tively meagre  and  are  uniformly  distributed  throughout  the  vitellus  ;  in  such  eggs 
there  is  no  aggregation  of  the  food  particles,  hence  such  ova  are  termed  komolecflkal 
or  with  a  homogeneous  yolk.  In  the  eggs  of  birds,  reptiles,  and  fishes,  on  the  con- 


22  HUMAN   ANATOMY. 

trary,  the  deutoplasm,  or  nutritive  material,  is  collected  towards  one  pole  of  the  egg, 
while  the  protoplasm,  or  formative  material,  is  limited  to  the  other  ;  eggs  in  which 
these  conditions  obtain  possess  a  distinctly  polar  yolk,  and  hence  are  known  as 
telolecithal  ova.  These  aggregations  of  the  protoplasm  and  the  deutoplasm  con- 
stitute respectively  the  formative  and  the  nutritive  yolk,  and  correspond  in  position 
to  the  animal  and  the  vegetative  poles  of  the  egg.  In  an  additional  class  of  eggs, 
the  centrolecithal,  the  yolk  occupies  the  centre  of  the  ovum,  being  covered  by  a 
peripheral  zone  of  formative  material  ;  since  such  ova  belong  alone  to  certain  in- 
sects and  are  not  found  among  vertebrates,  they  possess  limited  interest  to  students 
of  mammalian  forms. 

Comparison  of  the  behavior  of  these  various  groups  of  ova  .during  segmen- 
tation shows  that  only  eggs  poor  in  deutoplasm,  as  the  alecithal  mammalian  and 
amphibian  ova,  undergo  complete  cleavage  during  segmentation,  those  of  the  bird, 
reptile,  and  fish  undergoing  cleavage  only  within  the  formative  yolk.  Ova,  there- 
fore, are  classified  according  to  the  completeness  of  their  division  into  those  exhibit- 
ing complete  segmentation  and  those  undergoing  partial  segmentation;  the  former 
are  known  as  holoblastic,  the  latter  as  meroblastic.  The  embryologist  further  recog- 
nizes an  equal  and  an  iinequal  complete  segmentation  according  to  the  equality  or 
inequality  of  the  cells,  or  blastomeres,  resulting  from  the  division  of  the  ovum. 
Since  the  segmentation  spheres  derived  from  the  mammalian  egg  may  be  regarded 
as  practically  of  equal  size,  the  egg  of  this  class  of  animals,  including  the  human 
ovum,  is  described  as  an  homolecitkal  holoblastic  ovum,  undergoing  equal  segmenta- 
tion. It  must  be  understood,  however,  that  even  in  the  segmentation  of  such  ova 

FIG.  19. 

,---      ^~~~. 

FIG.    18.  X^^liii^i^r—  Ectoblast 

-Entoblast 

/  A"  TM»>».  \ 

.    , ^     .  ^    Inner  cells 

Outer  cells 


Zonapellucida— -V^y-V^v^^7^-Trophc  X^x  _  ^/^- 

-Zona  pellucida 

Diagram  of  early  mammalian  blastodermic  vesicle,  Diagram  of  mammalian  blastodermic  vesicle;  inun 

consisting  of  trophoblast  and  inner  cell-mass.  cells  differentiating  into  ectoblast  and  entoblast.    (After 

(After  Van  Reneden.)  Van  Reneden.} 

the  blastomeres  very  early  exhibit  inequality  in  size  and  in  rapidity  of  division  (Fig. 
1 6),  the  effect  of  this  differentiation  being,  that  the  more  rapidly  multiplying  blas- 
tomeres are  smaller  than  the  rnore  slowly  dividing  elements.  It  is  of  interest,  in  this 
connection,  to  note  that  the  purest  type  of  total  equal  segmentation  is  observed  in 
the  ovum  of  the  lowest  vertebrate,  the  amphioxus, — an  animal  whose  development 
has  shed  much  light  on  many  obscure  problems  in  the  embryology  of  the  higher 
forms,  including  mammals  and  even  man. 

The  meroblastic  bird's  egg,  on  the  contrary,  undergoes  cleavage  only  within  a 
limited  circular  field  at  its  animal  pole  ;  it  is  said,  therefore,  to  undergo  partial  dis- 
coidal  segmentation.  In  contrast  to  this,  the  centrolecithal  ova  exhibit  partial  super- 
ficial segmentation,  the  peripheral  zone  of  formative  material  alone  undergoing 
cleavage. 

The  Blastoderm  and  the  Blastodermic  Layers. — The  completion  of 
segmentation  in  holoblastic  ova  results  in  the  production  of  a  mass  of  blastomeres, 
which  is  a  solid  sphere  composed  of  mutually  compressed  segmentation  cells  ;  to  this 
sphere  the  older  anatomists  gave  the  name  of  the  montla.  or  the  mulberry  ma>s. 
The  solidity  of  the  morula  is  temporary,'  since  a  cavity  is  soon  developed  within  it. 
This  cavitv,  often  called  the  segmentation  cavity,  increases  to  such  an  extent  that  a 


THE   BLASTODERMIC   VESICLE. 


hollow  sac  is  formed,  walled  by  a  single  layer  of  cells,  at  one  point  on  the  inner  sur- 
face of  which  is  attached  a  small  mass  of  cells.  The  outer,  covering  layer  of  cells  is 
known  as  the  trophoblast ;  the  small  group  of  cells  attached  to  the  inner  surface  of 
the  trophoblast  is  known  as  the  inner  cell-mass  (Fig.  18).  Examined  from  the  sur- 
face, this  aggregation  of  inner  cells  appears  as  an  opaque  circular  field,  the  embryonic 
area,  due  to  the  increased  thickness  and  consequent  diminished  transparency  of  the 
wall  of  the  blastodermic  vesicle  at  the  place  of  attachment  of  the  included  cells.  In 
the  purest  type  of  the  blastodermic  vesicle,  that  seen  in  the  amphioxus  (Fig.  26, 
A),  the  sac  consists  of  a  single  layer  of  blastomeres  of  almost  uniform  size  ;  the 
mammalian  blastodermic  vesicle,  however,  presents  greater  complexity,  due  to  the 
unequal  rate  at  which  some  of  the  segmentation  cells  divide  and  to  the  rapid  increase 
in  the  size  of  the  vesicle. 

The  inner  mass  of  germinal  cells  soon  undergoes  differentiation  (Fig.  19)  into 
two  strata, — an  outer  layer,  closely  applied  to  the  trophoblast,  and  an  inner  layer. 
These  layers  are  respectively  the  ectoblast  and  the  entoblast, — two  of  the  three  great 
primary  blastodermic  layers  from  which  the  embryo  is  differentiated. 

Coincidently  with  the  formation  of  these  germinal  layers,  the  mammalian  blas- 
todermic vesicle  grows  with  great  rapidity,  increasing  from  a  sphere  of  microscopic 
size  to  a  vesicle  of  one  or  more  millimetres  in  diameter.  In  consequence  of  this 
precocious  growth  the  trophoblast  undergoes  great  expansion,  with  the  result 
that  its  cells,  in  some  cases  at  least,  become  temporarily  reduced  to  flattened 
plate-like  elements.  For  a  time  these  flattened  trophoblast  cells  may  extend  over 
the  embryonic  ectoblast,  as  in  the  rabbit,  and  have  been  called  the  cells  of  Raiiber. 
In  such  cases,  therefore,  the  ectoblast  is  overlaid  within  the  embryonic  area  by  the 
cells  of  Rauber,  but  at  the  margin  of  the  area,  the  embryonic  ectoblast  is  continuous 
with  the  trophoblast  forming  the  outer  layer  of  the  wall  of  the  blastodermic  vesicle. 
With  the  subsequent  expansion  of  the  blastodermic  vesicle,  the  cells  of  Rauber  dis- 
appear from  the  surface  of  the  embryonic  ectoblast,  which  then  lies  upon  the  surface 
of  the  vesicle. 


FIG.  21. 


Fro.  20. 


Entoblast 


Trophoblast 


Embryonic 
ectoblast 


Mesoblast 


Diagram  of  mammalian  blastodermic  vesicle; 
the  entoblast  forms  an  almost  complete  inner  layer. 


Entoblast 
Trophoblast 


Diagram  of  mammalian  blastodermic  vesicle  ;  the 
mesoblast  is  just  appearing  as  the  third  blastodermic 
layer. 


The  early  blastodermic  vesicle  at  first  consists  of  only  two  primary  layers,  the 
ectoblast  and  the  entoblast  ;  this  stage  of  development  is  appropriately  termed  that 
of  the  bilaminar  blastoderm  (Fig.  20);  a  little  later,  a  third  layer,  the  mesoblast, 
makes  its  appearance  between  the  outer  and  inner  blastodermic  sheets  ;  this  stage  is 
designated  as  that  of  the  tri laminar  blastoderm  (Fig.  21). 

The  early  embryo,  shortly  after  the  formation  of  the  blastodermic  vesicle,  con- 
sists of  three  layers  of  cells, — the  ectoblast,  the  mesoblast,  and  the  entoblast.  The 
histological  characters  of  the  outer  and  inner  of  these  primary  layers  differ,  almost 


24  HUMAN   ANATOMY. 

from  the  first,  from  those  of  the  mesoblast,  their  component  elements  being  more 
compact  in  arrangement  and  early  manifesting  a  tendency  to  acquire  the  character- 
istics of  covering  cells  or  epithelium. 

The  mesoblastic  elements,  on  the  contrary,  soon  assume  irregular  forms  and 
are  loosely  held  together  by  intercellular  substance,  thus  early  foreshadowing  the 
special  features  which  distinguish  the  subsequently  differentiated  connective  tissues. 
This  early  distinction  becomes  more  marked  as  differentiation  proceeds,  the  epithelial 
tissues  possessing  elements  of  comparatively  regular  form,  separated  by  minute 
amounts  of  intercellular  substance  ;  the  latter  in  the  connective  tissues,  on  the  con- 
trary, becomes  conspicuous  on  account  of  its  excessive  quantity  and  the  resulting 
profound  modifications  in  the  physical  character  of  the  tissue;  the  cells  of  the  con- 
nective tissues  rapidly  assume  the  irregularly  stellate  or  triangular  form  so  charac- 
teristic in  young  tissues  of  this  class.  Since  the  three  primary  layers  give  rise  to  all 
the  tissues  of  the  organism,  a  brief  synopsis  presenting  these  genetic  relations  here 
finds  an  appropriate  place. 

DERIVATIVES  OF  THE  BLASTODERMIC  LAYERS. 

From  the  ectoderm  are  derived — 

The  epithelium  of  the  outer  surface  of  the  body,  including  that  of  the  conjunc- 
tiva and  anterior  surface  of  the  cornea,  the  external  auditory  canal,  to- 
gether with  the  epithelial  appendages  of  the  skin,  as  hair,  nails,  sebaceous 
and  sweat-glands  (including  the  involuntary  muscle  of  the  latter). 

The  epithelium  of  the  nasal  tract,  with  its  glands,  as  well  as  of  the  cavities 
communicating  therewith. 

The  epithelium  of  the  mouth  and  of  the  salivary  and  other  glands  opening  into 
the  oral  cavity. 

The  enamel  of  the  teeth. 

The  tissues  of  the  nervous  system. 

The  retina  ;  the  crystalline  lens,  and  perhaps  part  of  the  vitreous  humor. 

The  epithelium  of  the  membranous  labyrinth. 

The  epithelium  of  the  pituitary  and  pineal  bodies. 

From  the  mesoderm  are  derived — 

The  connective  tissues,  including  areolar  tissue,  tendon,  cartilage,  bone,  den- 
tine of  the  teeth. 

The  muscular  tissues,  except  that  of  the  sweat-glands  and  dilator  pupillae. 

The  tissues  of  the  vascular  and  lymphatic  systems,  including  their  endothelium 
and  circulating  cells. 

The  sexual  glands  and  their  excretory  passages,  as  far  as  the  termination  of  the 
ejaculatory  ducts  and  vagina. 

The  kidney  and  ureter. 

From  the  entoderm  are  derived — 

The  epithelium  of  the  digestive  tract,  with  that  of  all  glandular  appendages 
except  those  portions  derived  from  ectodermic  origin  at  the  beginning 
(oral  cavity)  and  termination  of  the  tube. 

The  epithelium  of  the  respiratory  tract. 

The  epithelium  of  the  urinary  bladder  and  urethra. 

The  epithelium  of  the  thyroid  and  thymus  bodies,  the  atrophic  primary  epithe- 
lium of  the  latter  being  represented  by  Hassall's  corpuscles. 

The  Primitive  Streak  and  the  Gastrula. — Examined  from  the  surface 
during  the  formation  of  the  primary  layers,  the  mammalian  blastodermic  vesicle,  as 
represented  by  that  of  the  rabbit,  presents  a  circular  light -colored  field,  the  embryonic 
area,  which  corresponds  to  the  expansion  of  the  original  embryonic  spot,  the  latter 
becoming  larger  with  the  extension  of  the  ectoblast  and  the  entoblast  differentiated 
from  the  inner  cell  mass.  At  first  circular,  the  embryonic  area  later  becomes  oval 
or  pyriform  in  outline  (  Figs,  jj,  j^),  the  larger  end  corresponding  with  the  cephalic 


THE    EMBRYONIC   AREA. 


pole  of  the  future  embryo.  In  consequence  of  the  proliferation  of  the  ectoblastic 
cells,  the  embryonic  area  becomes  differentiated  into  a  central  field,  the  embryonic 
shield,  and  a  peripheral  zone,  the  area  pellucida,  which  by  transmitted  light  appear 
respectively  dark  and  light,  owing  to  the  varying  transparency  of  the  thicker  cen- 
tral and  thinner  peripheral  portions  of  the  germinal  field. 


FIG.  22. 


FIG. 


23- 


•Area  pellucida 


-Embryonic  shield 
-Area  pellucida 

-Wall  of  blastoder- 
mic  vesicle 


Embryonic  area  of  rabbit  of  about  six  and  one- 
half  days,  seen  from  the  surface  by  transmitted  light. 
X  26.  (Kollmann.} 


-Embryonic  shield 


-Wall  of  blastodermic 
vesicle. 


Embryonic  area  of  rabbit  of  about  seven  days,  seen  from 
the  surface.    X  26.     (Kollmann.) 


FIG.  24. 


Coincidently  with  the  assumption  of  the  oval  or  pyriform  outline,  the  caudal 
border  of  the  embryonic  area  exhibits  a  luniform  thickening,  the  embryonic  crescent ; 
from  the  latter  proceeds  the  formation  of  a  conspicuous,  although  transient,  structure, 
known  as  the  primitive  streak  (Fig.  24).  The  latter  appears  as  a  lineal  thicken- 
ing which  extends  forward  well  towards  the 
centre  of  the  embryonic  area.  The  pro- 
liferation of  the  outer  blastodermic  layer 
along  the  primitive  streak  is  accompanied 
by  the  appearance  or  a  narrow  longitudinal 
furrow,  the  primitive  groove,  throughout  its 
extent  with  the  exception  of  its  anterior  end, 
at  which  point  the  primitive  streak  termi- 
nates in  a  thickened  extremity,  the  node  of 
Hensen.  Although  indicating  the  direction 
of  the  axis  of  the  future  embryo,  the  primi- 
tive streak  takes  no  part  in  the  formation 
of  the  new  organism,  being  entirely  tran- 
sient in  its  career.  Transverse  section  of  the 
anterior  end  of  the  primitive  streak  (Fig. 
25)  shows  that  in  that  place  all  three  of  the 
blastodermic  layers — ectoblast,  mesoblast, 
and  entoblast — are  completely  fused,  the 

mesoblast  in  this  situation — and  here  alone — forming  a  continuous  sheet  interposed 
between,  as  well  as  blended  with,  the  ectoblast  and  entoblast. 

The  Significance  of  the  Primitive  Streak  and  the  mode  of  formation  of 
the  mesoblast  are  vexed  problems  in  embryology.  A  brief  note  on  this  topic  will 
suffice  here.  In  amphioxus,  the  lowest  vertebrate,  the  immediate  result  of  segmen- 
tation is  a  hollow  sphere,  the  blastula,  filled  with  fluid,  lined  by  a  single  layer  of  cells. 
Invagination  at  one  point  of  the  wall  of  the  blastula  occurs,  forming  eventually  a 
two-layered  cup,  the  gastrula,  the  outer  layer  of  which  is  the  ectoblast,  and  the 
inner  one  the  entoblast.  The  cavity  within  the  entoblast  is  the  archcnteron  or  primi- 
tive gut.  The  opening  into  the  archenteron  is  the  blastoporc.  Cells  given  off  from 
the  entoblast,  near  the  blastopore,  form  a  third  layer,  the  mesoblast.  Typical  gas- 
trulation  does  not  occur  in  the  higher  mammals,  although  in  the  early  human 
embryo  a  canal  appears,  known  as  the  neurenteric  canal,  the  opening  of  which  is 
often  regarded  as  homologous  with  the  blastopore.  The  primitive  streak  is  regarded 
by  some  authorities,  notably  Hertwig,  as  an  elongated  blastopore  with  lips  fused. 
The  mesoblast  is  commonly  thought  to  arise  from  the  entoblast,  although  the  ecto- 
blast, in  the  region  of  the  primitive  streak,  seems  to  have  a  share  in  the  production 
of  the  middle  germ-layer. 


-Head  process 


Hensen's  node 


-Primitive  streak 


Embryonic  area 


Extra-embryonic 
part  of  blasto- 
dermic vesicle 


Embryonic  area  of  rabbit  of  about  eight  days,  seen 
from  the  surface.    X  20.    (After  Van  Beneden.) 


26 


HUMAN    ANATOMY. 


THE    FUNDAMENTAL    EMBRYOLOGICAL    PROCESSES. 

Shortly  after  the  appearance  of  the  primitive  streak — a  structure,  it  will  be 
remembered,  which  is  only  transient  and  takes  no  part  in  the  formation  of  the 
embryo  proper — a  series  of  phenomena  mark  the  earliest  stages  of  the  future  new 
being.  These  changes  are  known  as  the  fundamental  embryological  processes,  and 
result  in  the  formation  of  the  neural  canal,  the  notochord,  and  the  somites.  While 
described  for  convenience  as  separate  processes,  they  progress  to  a  great  extent 
simultaneously. 


Ectoblast 


Mesoblast 


Transverse  section  through  cephalic  end  of  primitive  streak  of  very  young  rabbit  embryo.     X  100. 

The  Neural  Canal.  —  The  earliest  indication  of  the  embryo  consists  in  the 
appearance  of  two  slightly  diverging  folds  (Fig.  27),  enclosing  the  anterior  end  of 
the  primitive  streak,  which  are  produced  by  a  local  proliferation  and  thickening 
of  the  ectoblast.  These  are  the  medullary  folds  and  mark  the  beginning  of  the 
formation  of  the  neural  canal,  from  which  the  great  cerebro-spinal  nervous  axis, 
together  with  its  outgrowths,  the  peripheral  nerves,  is  derived.  The  medullary  folds 
at  first  border  a  shallow  and  widely  open  furrow  (Fig.  28),  the  •  medullary  groove  ; 


FIG.  26. 


Blastula  and  gnstrtila  stages  in  the  development  of  amphioxus,  drawn  from  the  model*  <>t  Hatsclifk.  X  ago. 
A,  blastula  composed  of  single  layer  of  cells  surrounding  segmentation  cavity;  re,  <•>:,  respectively  ectoblastic  and 
i-nt'iMastic  areas.  />',  beginning  imagination  of  entpblastic  area  (en).  C,  completed  gastrula  ;  ec,  en,  ectoblast  and 
entoblast ;  nt,  mcsoblast  cell ;  b,  blastopore,  leading  into  archenteron. 

the  latter  becomes  rapidly  deeper  and  narrower  as  the  medullary  folds  increase 
in  height  and  gradually  approach  each  other.  The  approximation  of  the  folds 
(  Fig.  29)  and  subsequent  fusion  take  place  earliest  at  some  distance  behind  the 
ivphalic  end  of  the  groove,  at  a  point  which  later  corresponds  to  the  upper  cervical 
region  of  the  spinal  cord. 

After  the  closure  of  the  groove  and  its  conversion  into  the  medullary  canal 
(Fig.  32),  the  thickened  and  invaginated  ectoblast  forming  tin-  lining  of  the  neural 
tube  becomes  separated  from  the  outer  layer  of  the  embryo  by  the  ingrowth  of  the 


THE   NOTOCHORD. 


27 


FIG.  27. 


mesoblast.  The  subsequent  differentiation  of  the  walls  of  the  neural  tube  will  be 
more  fully  considered  in  connection  with  the  nervous  system  ;  suffice  it  here  to 
state  that  the  cephalic  portion  expands  into  the  brain  vesicles,  and  subsequently 
becomes  the  brain  with  the  contained 
ventricles,  while  the  remainder  of 
the  tube  becomes  the  spinal  cord, 
enclosing-  the  minute  central  canal. 

The  Notochord. — Coinci- 
de.ntly  with  the  formation  of  the  med- 
ullary groove  the  entoblast  opposite 
the  bottom  of  that  furrow  exhibits  —Medullary  groove 

proliferation     and     thickening  ;     the 

group  of  cells  thus  differentiated  be-  ~ ~ Wmic°vfeSjf der" 

comes    separated    from    the    general  -  Primitive  streak 

mass    of   the   inner   layer  and    takes 

up  a  position  immediately  below  the  "~~  Embryonic  area 

neural  tube  (Figs.  30,  31).  This 
isolated  column  of  entoblastic  cells 
constitute  the  notochord,  or  chorda 
dorsalis.  the  earliest  suggestion  of  c-  , 

'  &&  Embryonic  area  of  rabbit  of  about  eight  and  one-half  days 

the     cardinal    Vertebrate    axis     around  seen  from  the  surface.     X  24.     (Kollmann.) 

which  the  parts  of  the  early  embryo 

are  symmetrically  arranged.      While  for  a  time  constituting  the  sole  longitudinal  axis 

of  the  embryo,  extending  from  a  point  near  the  cephalic  pole,  which  corresponds  later 


Medullary  fold 


FIG.  28. 

Groove 


Medullary  fold 


Transverse  section  of  rabbit  embryo  of  about  eight  and  one-half  days.    X  80.    Future  neural  canal  is  represented  by 

widely  open  groove. 


Amniotic  sac 


FIG.  29. 

Closing  neural  canal 


•Somatopleura 
Body-cavity 


/  /  /          / 

Visceral  mesoblast    Entoblast    Chorda    Open  gut-tube 


V  isceral  mesoblast     Entoblast    Chorda    Open  gut-tube  Splanchnopleura 

Transverse  section  of  rabbit  embryo  of  about  nine  and  one-quarter  days.     X  80.     Neural  canal  is  just  closing. 


to  the  base  of  the  skull,  to  the  caudal  extremity,  the  notochord  is  but  a  temporary 
structure,    and    subsequently   is    supplanted    by   the   true  vertebral    column.      It  is 


28 


HUMAN    ANATOMY. 


interesting  to  note,  that  in  the  connecting  link  between  the  vertebrates  and 
invertebrates,  the  amphioxus,  the  notochord  remains  as  the  permanent  and  sole 
spinal  axis. 

The  history  of  the  notochord  in  man  and  mammals  presents  three  stages  :  (a) 
it  exists  as  an  unbroken  cord  which  extends  uninterruptedly  through  the  series 
of  cartilaginous  vertebrae  ;  (6)  the  notochord  suffers  segmentation  in  such  manner 
that  the  breaks  in  its  continuity  correspond  to  the  vertebral  bodies,  conspicuous 
proliferation  and  local  increase  in  its  substance,  on  the  contrary,  marking  the 


FIG.  30. 


FIG.  31. 


Transverse  sections  through  axis  of  early  human  embryo  of  about  fifteen  days,  showing  formation  of  notochord 
from  entoblast.  High  magnification.  (After  Kollmann.)  n,  neural  canal;  ch,  cells  forming  notochord  differenti- 
ating from  entoblast  (e ) ;  tn,  mesoblast ;  s,  early  somite  ;  6,  sections  of  primitive  aortse. 

position  of  the  intervertebral  disks  in  which  the  chordal  tissue  during  the  first 
months  after  birth  is  represented  by  a  considerable  mass  of  central  spongy 
substance  ;  (>)  atrophy  of  the  remains  of  the  notochord,  resulting  in  the  entire 
disappearance  of  the  chordal  tissue  within  the  vertebrae  and  the  reduction  of  the 
proliferated  intervertebral  cell-mass  to  the  pulpy  substance  existing  within  the 
intervertebral  disks. 

The  cephalic  end  of  the  notochord  in  man  corresponds  in  position  to  the  dorsum 
sellae,  and  marks  the  division  of  the  skull  into  two  parts,  that  lying  in  front  of 


FIG.  32. 

Paraxial  mesoblast 


Ectoblast 


Amniotic  cavity 
Somatopleura 


£W 

'•.*&4&!g&  \ 

\  ,-^-^1- 

*£$3&&* 

*3*T* 

Body-cavity     Splanchno-      Open    Ento-   Chorda    Neural    Visceral     Body-cavity 
pleura  gut       blast  tube        mesoblast 

Transverse  section  of  rabbit  embryo  of  about  nine  and  one-quarter  days.     X  80.     Neural  canal  is  now  closed. 

the  termination  of  the  notochord,  the  prechordal  portion,  and  that  containing  the 
notochord,  the  chordal  portion  ;  the  latter  is  sometimes  described  as  the  vertebral 
segment  of  the  skull. 

The  Coelom. — The  downward  growth  of  the  neural  ertoblast  and  the  upward 
extension  of  the  chordal  entoblast  effect  a  division  of  the  mesoblast  along  the 
embryonic  axis  into  two  sheets  (  Fig.  28).  These  latter  undergo  further  division 
in  consequence  of  the  formation  of  a  cleft  within  their  substance,  as  the  result  of 
which  the  mesoblast  becomes  split  into  two  layers  enclosing  a  space,  the  ccclom,  or 
primary  body-cavity  (Fig.  29). 


THE    SOMITES. 


29 


The  cleavage  of  the  mesoblast,  however,  does  not  extend  as  far  as  the  mid-line 
of  the  embryo,  but  ceases  at  some  distance  on  either  hand,  thus  leaving  a  tract  of 
uncleft  mesoblast  on  either  side  of  the  medullary  groove  and  the  chorda.  The 
uncleft  area  constitutes  the  paraxial  mesoblast  (Fig.  32),  which  extends  from  the 
head  towards  the  caudal  pole  and  appears  upon  the  dorsal  surface  of  the  embryo  as 
two  distinct  ribbon-like  tracts  bordering  the  neural  canal.  Beyond  the  paraxial 
mesoblast,  the  cleft  portions  of  the  middle  layer  extend  on  either  side  as  the  lateral 
plates  ;  each  lateral  plate  consists  of  two  laminae,  the  one  forming  the  dorsal  and  the 


FIG.  33. 


FIG.  34. 


•Neural  canal 


Intermediate  cell- 
mass 

Primary  gut-tube 
Parietal  mesoblast 


' Visceral  mesoblast 


Transverse  section  of  human  embryo  of  about 
fifteen  days,  showing  early  differentiation  of  somite. 
X  210.  (Kollmann.) 


-.   x:.v<vy*-         «?"' 

§^eSi £»r/ —  Gut-tui 

i  -ill        5?r.  f 

— *lfr*  > Coelom 


Transverse  section  of  human  embryo  of  about 
twenty-one  days,  showing  differentiation  of  somite. 
X  90.  (Kollmann.} 


FIG.  35. 

Dorsal  border  of 
yotome 


;-plate 


other  the  ventral  boundary  of  the  enclosed  primary  body-cavity  ;  in  view  of  their 
subsequent  relations  to  the  formation  of  the  body-walls  and  the  digestive  tube 
respectively,  the  dorsal  mesoblastic  lamina  is  appropriately  named  the  parietal  layer 
and  the  ventral  lamina  the  visceral  layer  (Fig.  32).  In  the  separation  of  these 
layers,  which  soon  takes  place  in  consequence  of  the  dorsal  and  ventral  folding 
occurring  during  the  formation  of  the  amnion  and  the  gut-tube,  the  parietal  mesoderm 
adheres  to  the  ectoblast,  in  conjunction  with  which 
it  constitutes  the  somatopleura  (Fig.  29),  the 
ecto-mesoblastic  sheet  of  great  importance  in  the 
production  of  the  lateral  and  ventral  body- walls. 
Similarly,  the  visceral  mesoblast  unites  with  the 
entoblast*to  form  the  splanchnopleura  (Fig.  29),' 
the  ento-mesoblastic  layer  from  which  the  walls  of 
the  primary  digestive  canal  are  formed. 

The  Somites. — The  paraxial  mesoblast  at  an 
early  stage — about  the  twentieth  in  man — exhibits 
indications  of  transverse  division,  in  consequence 
of  which  this  band-like  area  becomes  differentiated 
into  a  series  of  small  quadrilateral  masses,  the 
somites,  or  protovertebrte.  This  segmentation  of 
the  embryonic  mass  appears  earliest  at  some 
distance  behind  the  cephalic  end  of  the  embryo, 
at  a  point  which  later  corresponds  to  the  beginning 

of  the   cervical    region.      The  somites  are   seen  to   best  advantage  in   the   human 
embryo  at  about  the  twenty-eighth  day   (Fig.  71). 

The  early  somites,  on  transverse  section,  appear  as  irregular  quadrilateral  bodies, 
composed  of  mesoblast  and  covered  externally  by  ectoblast,  lying  on  either  side  of 
the  neural  canal  and  the  notochord  (Fig.  33).  Each  somite  consists  of  a  dorsomesial 
principal  cell-mass,  which  is  connected  with  the  lateral  plate  by  means  of  an 
intervening  cell-aggregation,  the  intermediate  cell-mass  (Fig.  33).  Subsequently, 


Differentiation  of  myotome  of  human 
embryo  of  about  twenty-one  days.  X  525- 
(Kollmann.) 


30  HUMAN   ANATOMY. 

the  latter  becomes  separated  from  the  remaining  portion  of  the  somite  and  is  probably 
identified  with  the  formation  of  the  segmented  excretory  apparatus  of  the  embryo, 
the  Wolffian  body,  and  hence  is  known  as  the  ncphrotome. 

The  principal  mass,  including  the  greater  part  of  the  somite  proper,  consists  of 
an  outer  or  peripheral  zone  of  condensed  mesoblast  enclosing  a  core  of  looser  struc- 
ture. The  less  dense  mesoblastic  tissue  later  breaks  through  the  surrounding  zone 
on  the  side  directed  towards  the  notochord  and  forms  a  fan-shaped  mass  of  embryonic 
connective  tissue  which  envelops  the  chorda  and  grows  around  the  neural  canal. 
The  cell-mass  derived  from  the  core  of  the  myotome  constitutes  the  sclerotomc,  and 
directly  contributes  the  tissue  from  which  the  permanent  vertebrae  and  the  associated 
ligamentous  and  cartilaginous  structures  arise.  The  remaining  denser  part,  the 
myotome,  which  collectively  forms  a  compressed  C-like  mass,  becomes  differentiated 
into  a  lateral  and  a  mesial  stratum  (Fig.  35).  The  lateral  stratum,  sometimes  called 
the  cutis-plate,  consists  of  several  layers  of  closely  packed  elements.  By  some  these 
cells  are  regarded  as  concerned  in  producing  the  connective  tissue  portion  of  the 
skin  ;  according  to  others  they  are  in  large  part  converted  into  myoblasts,  which,  with 
those  of  the  mesial  stratum,  or  muscle-plate,  give  rise  to  the  voluntary  muscles  of  the 
trunk.  The  genetic  relations  of'  the  somite,  therefore,  may  be  expressed  as  follows  : 

I    Myolome — muscle  segment. 

SOMITE -j   Sclerotome — axial  segment. 

(.  Nephrotome — excretory  gland  segment. 

The  number  of  somites  of  the  human  embryo  is  about  thirty-seven,  comprising  eight 
cervical,  twelve  thoracic,  five  lumbar,  five  sacral,  and  from  five  to  seven  caudal 
segments. 

THE   FCETAL    MEMBRANES. 

The  Amnion. — With  the  exception  of  fishes  and  amphibians, — animals  whose 
development  takes  place  in  water, — the  young  vertebrate  embryo  is  early  enveloped 
in  a  protecting  membrane,  the  amnion.  Animals  possessing  this  structure,  including 
reptiles,  birds,  and  mammals,  are  classed,  therefore,  as  amniota,  in  contrast  to  the 
anamnia,  in  which  no  such  envelope  is  formed.  An  additional  foetal  appendage,  the 

allantois,  is  always  developed 
as  a  structure   complemental 

-Embryonic  ectobiast  to  the  amnion  ;  hence  the  am- 

,Mesobiast  niota  possess  both  amnion  and 

cEntoblast  allailtois. 

Since  the  development  of 
the  fcetal  membranes  in   man 
presents     certain     deviations 
from  the  process  as  seen   in 
other  mammals,  due  to  pecu- 
liarities   affecting     the     early 
human  embryo,  it  is  desirable 
cavitv  of  biastodermic        l?  examine  briefly  the  forma- 
vesicie      tion  of  these  structures  as  ob- 
'rrophobiast  served  in  animals  less  highly 

specialized. 
^_^^^  Referring    to    the    early 

niajjram  of  mammalian  biastodermic  vesicle.  mammalian   embryo,   ill  which 

the    biastodermic    layers    are 

arranged  as  somatopleura  and  splanchnopleura  on  either  side  of  the  embryonic  axis 
and  the  surrounding  uncleft  mesoderm,  and  extend  as  parallel  sheets  over  the  en- 
larging biastodermic  vesicle,  the  first  trace  of  the  amnion  appears  as  a  duplicature 
of  the  somatopleura.  The  earliest  indication  of  the  process  is  seen  slightly  in  front 
of  the  cephalic  end  of  the  embryo,  the  resulting  head-fold  being,  however,  soon  fol- 
lowed by  the  appearance  of  the  lateral  and  tail-folds.  The  rapid  growth  of  these 


THE    AMNION. 


duplicatures  of  somatopleura  from  all  sides  results  in  the  encircling  of  the  embryo 
within  a  wall  which  increases  in  height  until  the  prominent  edges  of  the  folds  meet 
and  coalesce  over  the  dorsal  aspect  of  the  enclosed  embryo.  The  folds  of  the 
ainnion  first  meet  over  the  head-end,  from  which  point  the  union  extends  tailward, 
where,  however,  fusion  may  be  delayed  for  some  time.  The  line  along  which  the 
junction  of  the  folds  takes  place  is  known  as  the  amniotic  suture. 
The  amnion  thus  forms 

FIG.  37- 

^Serosa 

'Ectoblast  1 

f  Amnion 
rMesoblast) 

-Exocoelom 


pen  gut-t'ube 
Splanchnopleura 


a  closed  sac  completely  in- 
vesting the  embryo  and  con- 
taining a  fluid,  the  liquor 
atnnii ;  at  first  closely  sur- 
rounding the  embryo,  the 
amniotic  sac  rapidly  expands 
until  its  dimensions  allow  the 
enclosed  foetus  to  turn  freely, 
practically  supported  by  the 
amniotic  fluid,  which  pos- 
sesses a  specific  gravity  of 
1003.  It  has  long  been 
known  that  in  certain  forms, 
conspicuously  in  the  chick, 
the  amnion  executes  rhythmi- 
cal contractions,  at  the  rate 
of  ten  per  minute,  whereby 
the  embryo  is  swayed  from 
end  to  end  of  the  sac.  From 
the  manner  of  its  formation, 
as  folds  of  the  somatopleura 
(Figs.  37  and  38),  it  is  evident  that  the  amnion  consists  of  an  inner  ectoblastic  and 
an  outer  mesoblastic  layer. 

The  Serosa,  cr  False  Amnion. — Coincident  with  the  fusion  of  the  inner 
layers  of  the  somatopleuric  folds  to  form  the  closed  sac  of  the  amnion,  the  outer 

layers  of  the  same  folds  unite  to 
FIG.  38. 

Serosa 

Amnion 


Trophoblast 


Vitelline  sac 


Entoblast 


Diagram  showing  formation  of  amniotic  folds  and  of  gut-tube  ;  trans- 
verse section  of  axis  of  embryo. 


\mniotic  sac 

Gut-tube 


produce  a  second  external  en- 
velope, the  serosa,  or  false  am- 
nion. The  serosa  soon  becomes 
separated  from  the  amnion  by 
an  intervening  space  to  form  the 
primitive  chorion ;  the  latter, 
therefore,  consists  of  ectoblastex- 
ternallyand  mesoblast  internally, 
the  reverse  of  the  disposition  of 
these  layers  in  the  amnion. 

The  outer  surface  of  the 
mammalian  primitive  chorion — 
the  outer  envelope  formed  of 
the  serosa  and  the  trophoblast 
— is  distinguished  by  prolifera- 
tion of  the  epithelial  elements, 
which  process  results  in  the 
production  of  more  or  less  con- 
spicuous projections  or  villi 
(Fig.  40),  this  villous  condition 
being  particularly  well  marked 
in  man. 

The  ectoblast  of  the  primitive  chorion  takes  no  part  in  the  formation  of 
the  body  of  the  embryo,  but,  on  the  other  hand,  assumes  an  important  r61e  in 
establishing  the  earliest  connection  between  the  embryo  and  the  maternal  tissues 
and,  later,  participates  in  the  formation  of  the  placenta.  The  ectoblast  of  the 


Diagram  showing  formation  of  amniotic  folds  and  vitelline  sac  ; 
longitudinal  section  of  embryo. 


HUMAN   ANATOMY. 


primitive  chorion  is  the  direct  derivative  of  the  original  ectodermal  layer  of  the 
blastodermic  vesicle  beyond  the  embryonic  region  proper,  a  layer  which,  on 
account  of  this  important  nutritive  function,  has  been  called  by  Hubrecht  the 
trophoblast. 

As  already  noted  (Fig.  32),  the  cleft  between  the  parietal  and  visceral  layers 
of  the  mesoblast  is  the  primary  body-cavity  or  ccelom  ;  with  the  separation  of  these 
layers  following  the  dorsal  and  the  ventral  folding  associated  respectively  with  the 
formation  of  the  amniotic  sac  and  the  gut-tube,  the  intramesoblastic  space  becomes 
greatly  expanded  and  extends  between  the  amnion  and  primitive  chorion.  This 
large  space  is  appropriated  only  to  a  limited  extent  by  the  future  definite  body- 
cavity,  and  hence  is  divisible  into  an  embryonic  and  an  extra-embryonic  portion,  or 
exocce/om  (Fig.  38),  which  are  temporarily  continuous. 

The  Vitelline  Sac. — While  the  somatopleura  is  engaged  in  producing  the 
protecting  amniotic  sac,  the  splanchnopleura,  composed  of  the  entoblast  and  the 
adherent  visceral  layer  of  mesoblast,  becomes  approximated  along  the  ventral  sur- 
face of  the  embryo  to  define  the  primitive  gut-tube  by  enclosing  a  part  of  the 
blastodermic  vesicle  ;  the  remaining,  and  jar  larger,  portion  of  the  latter  cavity 
constitutes  the  vitelline  sac,  and  corresponds  to  the  yolk-sac  of  the  lower  forms. 

The  constriction  and  separation  of  the  gut-tube  from  the  vitelline  sac  is  accom- 
plished    earliest     at     the 

FIG-  39-  cephalic   and  caudal  ends 

of  the  future  alimentary 
canal,  the  intervening  por- 
tion remaining  for  a  time 
in  widely  open  communi- 
cation with  the  yolk-sac. 
During  the  rapid  diminu- 
tion of  the  latter  the  com- 
munication becomes  re- 
duced to  a  narrow  channel, 
the  vitelline  duct,  which 
persists  as  a  slender  stalk 
terminating  at  its  distal  end 
in  the  remains  of  the  yolk- 
sac. 

In  animals  other  than 
mammals  in  which  a  pla- 
centa is  developed,  the 
yolk-sac  is  the  chief  nutri- 
tive organ  of  the  embryo  ; 
the  mesoblastic  tissue  of 
the  vesicle  becomes  vascu- 
larized  by  the  development 
of  the  blood-vessels  consti- 
tuting the  vitelline  circulation,  of  which  the  •vitelline  or  omphalomesenteric  arteries 
and  veins  form  the  main  trunks.  The  contents  of  the  yolk-sac  as  such  do  not 
directly  minister  to  the  nutrition  of  the  embryo,  but  only  as  materials  absorbed  by 
the  vitelline  blood-vessels.  In  man  and  other  high  mammals  the  nutritive  function  of 
the  yolk  is  at  best  insignificant,  the  vitelline  sac  of  these  animals  representing  the 
more  important  organ  of  their  humbler  ancestors.  In  the  lowest  members  of  the 
mammalian  group,  the  monotremata,  in  which  the  large  ova  are  comparatively  rich 
in  deutoplasm,  the  vitelline  circulation  is  of  great  importance  for  respiration  and  nu- 
trition, since  it  constitutes  the  means  for  the  performance  of  these  functions  until  the 
immature  animals  are  transferred  to  the  marsupial  pouch  to  complete  their  develop- 
ment. In  the  kangaroo  and  opossum  the  yolk-sac  at  one  point  forms  a  disk-like 
organ,  which,  from  the  fact  that  it  becomes  provided  with  vascular  villi  that  lie  in 
contact  with  the  uterine  mucous  membrane,  is  termed  tin-  vitelline  placenta. 

The  Allantois  and  the  Chorion. — Coincidently  with  the  formation  of  the 
amnion,  another  foetal  appendage,  the  allantois,  makes  its  appearance  as  an  out- 


Primitive  chorion 


Amnion 


Amniotic  sac 


Gut-tube 


Ccelom 


Allantois 


Yitelline  duct 


Diagram  showing  completed  amnion  and  serosa,  beginning  allantois  and 
vitelline  duct. 


THE   VITELLINE    SAC.  33 

growth  from  the  caudal  segment  of  the  primary  gut-tract.  Although  modified  in 
man  and  certain  mammals  to  such  an  extent  that  its  typical  form  and  relations  are 
obscured,  the  allantois,  when  developed  in  a  characteristic  manner,  as  in  the  chick, 
assumes  the  appearance  of  a  free  vesicle  connected  with  the  embryo  near  its  caudal 
pole  by  means  of  a  narrow  pedicle,  the  allantoic  stalk.  Since  the  allantois  is  an 
evagination  from  the  primitive  gut,  its  walls  are  formed  by  direct  continuations  of 
the  primary  layers  enclosing  the  digestive  canal, — namely,  a  lining  of  entoblastic 
cells,  reinforced  externally  by  a  layer  of  visceral  mesoblast. 

Beginning  as  a  wide  bay  on  the  ventral  wall  of  the  hind-gut,  the  allantois  elon- 
gates and  appears  as  a  pyriform  sac  projecting  from  the  embryo  behind  the  attach- 
ment of  the  still  large  vitelline  stalk  (Fig.  39).  It  rapidly  grows  into  the  exoccelom, 
and  in  mammals  expands  in  all  directions  until  it  comes  into  contact  with  the  inner 
surface  of  the  primitive  chorion,  with  which  it  fuses  to  constitute  the  true  chorion. 
The  latter,  sometimes  spoken  of  as  the  allantoic  chorion  in  contrast  to  the  amniotic 
or  primitive  chorion,  now  becomes  the  most  important  envelope  of  the  mammalian 
embryo  on  account  of  the  role  that  it  is  destined  to  play  in  establishing  the  respira- 

FIG.  40. 

A 

'Primitive  chorion 
-Amnion 

-Amniotic  sac 


Allantois 


^Vitelline  sac 
Diagram  showing  villous  condition  of  serosa,  expanding  allantois,  and  diminishing  vitelline  sac. 

tory  and  nutritive  organ  of  the  foetus,  the  placenta.  After  the  fusion  of  the  allantois 
with  the  primitive  chorion  to  form  the  chorion,  the  villous  projections  upon  the 
external  surface  of  the  latter  become  more  highly  developed,  consisting  of  a  core  of 
mesoblastic  tissue  covered  externally  by  the  ectoblast. 

The  primary  purpose  of  the  allantois,  as  a  receptacle  for  the  effete  materials  ex- 
creted by  the  Wolffian  body  of  the  early  foetus,  is  soon  overshadowed  by  its  function 
as  a  respiratory  organ  ;  this  occurs  with  the  appearance  of  the  rich  vascular  supply 
within  the  chorion  following  the  invasion  of  its  mesoblastic  tissue  by  the  blood-vessels 
constituting  the  allantoic  circulation.  The  latter  includes  the  two  allantoic  arteries, 
which  are  extensions  from  the  aortic  stem  of  the  embryo  and  convey  venous  blood, 
and  the  two  allantoic  veins,  which  return  the  oxygenated  blood  to  the  embryo  and 
become  tributary  to  the  great  venous  segment  of  the  primitive  heart.  The  vascu- 
larization  of  the  chorion  extends  to  the  highly  developed  villi  occupying  its  outer 
surface  in  many  mammalian  forms,  especially  man. 

The  vascular  villi  of  the  chorion,  bearing  the  terminal  loops  of  the  blood-vessels 
conveying  the  foetal  blood,  are  important  structures  on  account  of  their  intimate 
relations  with  the  uterine  mucous  membrane  (Fig.  41),  in  conjunction  with  which 

3 


34 


HUMAN    ANATOMY. 


they  form  a  respirative  and  nutritive  apparatus.  The  intimacy  between  the  uterine 
mucous  membrane  and  the  chorionic  tufts  presents  all  degrees  of  association,  from 
simple  apposition,  as  seen  in  the  sow,  where  the  feebly  developed  and  almost  uni- 
formly distributed  vascular  projections  are  received  within  corresponding  depressions 
in  the  richly  vascular  uterine  tissue,  to  the  firm  and  complex  attachment  found  in  the 
highly  developed  human  placenta. 

FIG.  41. 


Villi  of  extraplacental  chorion 
Gut-tube 


Ectoblast— 


Amniotic  meso 
blast 


Space  between  am- 
nion  and  chorion 


Allantois 

Allantoic  blood- 
vessels 
Allantoic  sac 


Mesoblast 

Entoblast 


"Maternal  blood-spaces 
"Decidua  placentalis 
Diagram  showing  villous  chorion,  differentiation  of  placenta!  area,  and  vascularization  of  chorion. 

In  contrast  with  the  chorion  of  those  animals  in  which  the  nutritive  relations 
between  the  maternal  tissues  and  the  embryo  are  uniformly  distributed  are  the  local 
specializations  seen  in  the  chorion  of  those  types  in  which  a  placental  area  is  de- 
veloped. The  animals  in  which  the  latter  condition  obtains  are  known  as  placentalia, 
of  which  three  subgroups  are  recognized  depending  upon  the  multiple  (cotyledons), 


FIG.  42. 


Diagrams  illustrating  the  various  types  of   development  of   the  chorion.     A,  uniformly  developed  villi  (hog, 
horse)  ;"/?,  multiple  placentae  or  cotyledons  (cow,  sheep);  C,  zonular  placenta  (cat,  dog);    />,  discoidal  placenta    • 
(monkey,  man).    A-B  comprise  non-deciduate ;  C-D,  deciduate  mammals. 

zonular,  or  discoidal  form  of  the  placenta,  man  and  the  apes  representing  the  highest 
specialization  of  the  last  division.  In  its  general  plan  of  development,  therefore,  the 
placenta  is  formed  of  a  fatal  and  a  maternal  portion,  the  former  consisting  of  the 
vascular  villi  which  are  unusually  well  developed  within  a  particular  portion  of  the 
chorion,  and  the  latter  of  the  opposed  uterine  lining  which  becomes  highly  special- 
ized throughout  a  corresponding  area  and  more  or  less  intimately  united  with  the 


THE    HUMAN    FCETAL    iMEMBRANES.  35 

foetal  structures.  The  mucous  membrane  of  the  entire  uterine  cavity,  in  many  of  the 
higher  mammals,  suffers  profound  change,  and  before  the  end  of  gestation  becomes 
inseparably  attached  to  the  chorion  even  in  its  extent  beyond  the  placental  area  ;  in 
such  animals  the  fused  uterine  and  chorionic  tissue  constitute  the  deciduce  which, 
lined  internally  by  the  closely  applied  amnion,  form  the  membranous  envelope  en- 
closing the  foetus.  After  rupture  consequent  upon  the  expulsion  of  the  foetus  at  the 
termination  of  pregnancy,  the  deciduae,  including  the  specialized  placental  portion, 
are  separated  from  the  uterine  wall  and  expelled  as  the  membranes  and  the  placenta 
which  are  known  collectively  as  the  after-birth. 

The  foregoing  sketch  of  the  general  development  of  the  foetal  membranes  in 
the  higher  mammals  must  be  now  supplemented  by  consideration  of  the  peculiarities 
encountered  in  the  development  of  these  structures  in  man. 

THE    HUMAN    FCETAL    MEMBRANES. 

The  young  human  embryo  is  distinguished  by  the  very  early  formation  of  the 
amniotic  cavity,  by  the  precocious  development  of  the  mesoblast  and  extra- 
embryonic  ccelom,  by  the  presence  of  the  body-stalk  and-  by  the  great  thickening  of 
the  trophoblast.  It  must  be  remembered,  in  considering  the  formation  of  the  human 
fcetal  membranes,  that  the  earliest  stages  of  development,  to  wit,  fertilization, 
segmentation,  the  formation  of  the  blastodermic  vesicle,  the  earliest  differentiation  of 
the  embryonic  area  and  the  formation  of  the  amniotic  cavity  have  not  yet  been 
observed  on  human  specimens.  Our  knowledge  of  these  processes  is  derived  from  a 
study  of  some  of  the  lower  types  ;  beyond  these  very  early  stages,  however,  the 
conditions  in  the  human  embryo  have  been  subject  to  direct  study. 

The  Human  Amnion,  Amniotic  Cavity  and  Allantois. — The  accompany- 
ing diagrams  (Fig.  43)  will  serve  to  illustrate  the  process  of  formation  of  the  fcetal 
membranes  in  man.  Of  these  five  diagrams,  A  alone  is  purely  hypothetical  with 
reference  to  the  human  embryo.  In  diagram  A  the  amniotic  cavity  is  already 
indicated  as  a  small  cleft  between  the  embryonic  area  below  and  a  covering  layer  of 
cells  above  continuous  with  the  trophoblast.  This  layer,  the  trophoblast,  forms  the 
outer  covering  of  the  entire  vesicle.  It  is  presumably  already  thickened  at  as  early 
a  stage  as  this  diagram  represents.  Presumably  also  the  surface  of  the  trophoblast 
shows  irregularities,  for  this  tissue  it  is  which  comes  into  direct  contact  with  the 
uterine  mucous  membrane  and  which,  by  its  activities,  forces  its  way  into  the 
maternal  decidua.  This  latter  process  is  known  as  implantation,  a  process  which 
supposedly  is  taking  place,  if  not  completed,  at  about  the  stage  of  this  diagram. 
Whether  the  trophoblastic  layer  in  man  is  originally  a  thin  single  sheet  of  cells,  as 
for  instance  is  the  case  in  the  rabbit,  or  whether  it  is  from  the  beginning  thickened, 
we  do  not  know.  Certainly  the  thickened  condition  appears  at  a  very  early  stage. 
The  embryonic  area  shows  the  embryonic  ectoblast  proper,  which  is  of  small  extent ; 
this  ectoblast  being  so  distinguished  from  the  trophoblastic  ectoblast.  The  ento- 
blast  beneath  is  represented  as  already  arranged  in  the  form  of  a  sac.  Between  the 
entoblast  and  ectoblast  the  mesoblast  has  made  its  appearance.  It  will  be  noted 
that  in  the  diagram  the  entoblastic  sac  is  much  smaller  than  the  outer  trophoblastic 
vesicle.  We  do  not  know  that  this  is  really  the  condition  when  the  entoblastic  sac 
is  first  formed  or  only  appears  in  conjunction  with  the  great  development  of  the  extra 
embryonic  ccelom  in  the  mesoblast.  It  is  certainly  not  unreasonable  to  suppose  that 
the  former  case  is  the  true  one. 

The  early  appearance  of  the  amniotic  cavity  is  to  be  explained  in  this  way. 
After  the  blastodermic  vesicle  has  reached  the  stage  when  the  inner  cell  mass  is 
attached  to  one  point  on  the  inner  surface  of  the  trophoblast,  the  formation  of  a 
cavity  occurs  in  the  region  of  the  inner  mass.  This  cavity,  at  first  very  small,  has 
below  it  the  cells  of  the  inner  mass,  which  soon  become  arranged  into  the  two 
primary  germ  layers  of  the  embryonic  area,  ectoblast  and  entoblast,  while  above 
the  cavity  is  a  layer  of  cells  continuous  with  the  trophoblast.  Such  a  method 
of  formation  of  the  amniotic  cavity  has  been  observed  in  some  of  the  lower 
forms,  for  instance,  by  Hubrecht,  in  the  hedge  hog,  and  since  the  earliest  human 
embryo  accurately  studied  shows  a  completely  closed  amniotic  cavity,  while  in 


36  HUMAN   ANATOMY. 

a  very  early  stage  of  development,   it  is  a  reasonable  inference  that  in  man  such 
a  process  actually  occurs. 

In  diagram  B  the  mesoblast  has  not  only  surrounded  the  entoblastic  sac  and 
the  inner  surface  of  the  trophoblast,  so  enclosing  the  large  extra-embryonic  ccelom, 
but  has  invaded  the  layer  of  cells  above  the  amniotic  cavity,  dividing  this  layer  into 
two  parts,  the  inner  part  going  to  form  the  ectoblast  of  the  amnion,  the  outer  part 
being  a  continuation  of  the  trophoblast  of  the  chorion.  There  is  here  evidently  a 
very  great  development  of  the  extra-embryonic  ccelom.  In  explanation  of  this 
condition,  it  may  be  assumed  that  the  entoblastic  sac  is  at  first  much  smaller  than  the 
trophoblastic  covering  of  the  vesicle  ;  that  the  mesoblast,  shortly  after  its  appearance, 

FIG.  43 


•am 


Diagrams  illustrating  development  of  human  fu-tal  membranes.  Staged  is  hypothetical ;  others  are  basr<l  <>n 
stages  which  have  been  actually  observed.  Red  represents  trophoblast;  purple,  embryonic  ectoblast;  Kr;l>  •  »"^" 
blast;  blue,  entoblast.  ac,  amniotic  cavity;  «/,  allantois  ;  am,  amnion;  f>,  body-stalk;  r/i,  chorion;  ee,  embryonic 
ectoblast;  en,  entoblast;  ?,  gut-tube;  m,  mesoblast ;  p,  placental  area;  /.trophoblast;  v,  yolk-sac  ;  vs,  yolk-stalk. 

around  the  vesicle  ;  the  splanchnic  layer  around  the  entoblast,  the  somatic  layer 
around  the  trophoblast,  so  enclosing  between  them  as  they  grow,  the  considerable 
space  which  becomes,  by  this  process,  extra-embryonic  body  cavity.  This  diagram 
corresponds  roughly  to  the  condition  of  Peters'  embryo  (  Fig.  44).  The  trophoblast 
is  greatly  thickened  ;  its  outer  surface  very  irregular,  showing  lacuna-  or  spaci-s 
filled  with  maternal  blood.  This  early  intimate  contact  of  the  fulal  tissue  with  the 
maternal  blood  permits  nutrition  of  the  young  embryo  from  the  maternal  blood  to  be 
carried  on  through  the  trophoblast  cells  some  time  before  the  allantoic  circulation 
and  definite  placenta  are  established.  Hence  the  significance  of  this  term  trophoblast. 


THE    HUMAN    FCETAL   MEMBRANES.  37 

In  the  next  diagram,  (Fig.  43),  C,  the  extra-embryonic  coelom  has  invaded  the 
sheet  of  mesoblast  above  the  amniotic  cavity  to  such  an  extent  that  the  chorion  is 
completely  separated  from  the  amnion  and  the  body  of  the  embryo  except  at  one 
point,  the  posterior  end  of  the  body,  where  a  solid  stalk  of  mesoblast  connects 
the  chorion  and  embryo.  This  solid  band  of  mesoblast  is  called  the  body -stalk. 
It  represents,  therefore,  a  primary  and  permanent  connection  between  the  chorion 
and  the  body  of  the  embryo.  A  small  diverticulum  from  the  entoblastic  sac  growing 
into  the  mesoblast  of  the  body-stalk  marks  the  beginning  of  the  allantois.  As  the 
diagram  shows,  the  amnion  is  at  first  a  comparatively  small  membrane  overlying  the 
embryonic  area.  The  ectoblast  of  the  amnion  is  on  the  inner  side  facing  the  embryo, 
the  mesoblast  on  the  outer  side.  In  the  chorion  these  layers  are  placed  inversely, 
the  mesoblast  on  the  inner  side,  the  ectoblast  (trophoblast)  outside.  The  space 
between  amnion  and  chorion  is  seen  to  be  a  continuation  of  the  extra-embryonic 
ccelom. 

In  diagram  D,  the  amnion  has  become  considerably  expanded  in  association 
with  the  growth  of  the  body  of  the  embryo  and  the  accumulation  of  amniotic  fluid. 
A  constriction  in  the  entoblastic  sac  has  made  its  appearance,  a  constriction  which 
separates  the  gut  of  the  embryonic  body  from  its  appendage,  the  yolk-sac,  the 
narrower  connecting  piece  being  known  as  the  yolk-stalk,  or  sometimes  as  the 
vitello-intestinal  duct.  This  constricted  area  is  brought  about  by  the  rapid  growth  of 
the  body  of  the  embryo.  In  the  early  condition  the  entoblastic  sac  is  attached  to 
the  embryonic  body  practically  along  its  entire  ventral  surface.  The  body  region 
grows  very  rapidly,  particularly  the  head  end,  which  comes  to  project  from  the 
entoblastic  sac  to  a  marked  extent ;  the  tail  end  also  projects  somewhat.  There  is  a 
corresponding  growth  of  the  gut  within  the  body  of  the  embryo.  As  a  consequence 
of  this  process  of  expansion  of  the  body,  the  area  of  attachment  of  the  entoblast 
external  to  the  body  becomes  relatively  much  reduced  in  size,  occupying  only  a 
small  portion  of  the  ventral  surface  of  the  body,  and  a  progressively  smaller  portion 
as  the  body  increases  in  bulk.  In  other  words,  the  narrow  area  of  the  yolk-stalk 
makes  its  appearance. 

In  the  diagram  (/?,  al ')  the  allantois  projects  from  the  posterior  end  of  the 
embryonic  gut  into  the  body-stalk.  It  will  be  noticed  that  the  human  allantois  is 
never  a  free  structure  as  it  is  in  many  of  the  'lower  types,  where  it  grows  from  the 
body  freely  into  the  extra-embryonic  ccelom  and  only  later  becomes  connected  with 
the  chorion  to  form  the  placenta,  but  that  in  man  it  grows  directly  into  the  body- 
stalk,  where,  outside  of  the  body  of  the  embryo,  it  is  an  insignificant  structure. 
Inside  the  body,  part  of  the  allantois  persists  as  the  bladder.  The  urachus,  a  fibrous 
cord  which  in  the  adult  passes  from  the  top  of  the  bladder  to  the  umbilicus,  is  also  a 
remnant  of  the  allantois.  The  thick  irregular  projections  of  the  trophoblast  have 
received  a  core  of  mesoblast  tissue,  so  forming  the  early  chorionic  villi.  These  villi, 
at  the  point  of  attachment  of  the  body-stalk,  the  area  where  the  placenta  is 
developing,  are  increasing  in  size,  while  the  villi  over  the  remainder  of  the  chorion 
are  diminishing  in  size. 

In  diagram  /?,  the  amnion  has  become  greatly  expanded.  It  lies  closer  to  the 
inner  surface  of  the  chorion.  In  close  association  with  this  expansion  of  the  amnion, 
and  the  accompanying  growth  of  the  body  of  the  embryo,  the  structures  which  form 
the  umbilical  cord  are  so  closely  approximated  that  the  area  of  the  cord  is  clearly 
defined.  These  structures  are  the  body-stalk  containing  the  allantois  and  allantoic 
vessels,  the  yolk-stalk,  and,  bounding  the  other  side  of  this  area,  the  fold  of  the 
amnion  from  beneath  the  head.  At  first  the  body-stalk  projects  from  beneath 
the  extreme  posterior  end  of  the  body  of  the  embryo,  but  as  growth  in  this  part  of 
the  body  advances  and  the  tail  projects  more  and  more,  the  body-stalk  is  brought  to 
the  ventral  surface  of  the  abdominal  region  in  close  proximity  to  the  yolk-stalk. 
The  allantoic  blood-vessels  grow  from  the  embryo  through  the  body-stalk  to  the 
chorion,  where  they  ramify  in  the  chorionic  villi.  At  first  there  is  an  extension  of 
the  coelom  about  the  yolk-stalk  in  the  umbilical  cord,  but  the  mesoblast  tissues  of  the 
structures  of  the  cord  soon  fuse  together,  obliterating  this  cavity.  The  area  of  attach- 
ment to  the  abdomen  of  the  umbilical  cord  becomes  relatively  very  much  reduced  in 
size  and  is  known  in  the  adult,  after  the  separation  of  the  cord,  as  the  umbilicus 
or  navel. 


HUMAN    ANATOMY. 


The  chorionic  villi  at  the  point  of  attachment  to  the  chorion  of  the  body-stalk 
are  enlarged.  These  villi  constitute  the  foetal  portion  of  the  placenta,  the  so-called 
chorion  frondosuui.  They  are  imbedded  in  the  maternal  decidua,  more  specifically, 
the  decidua  basalis  or  placentalis.  It  must  be  remembered  that  the  villi  contain  a 
core  of  mesoblast  tissue  in  the  stage  represented  by  diagram  E,  although  this  meso- 
blastic  core  is  not  shown  in  the  figure,  and  that  the  allantoic  bipod -vessels  run  in 


FIG.  44. 

Comf>.     Ca      £.  Z.        Tr.   g. 


Caf>. 


K. 


U.  E. 


B.L. 


Sy. 


tissue  of  uterine  mucosa  ;  E.,  embryo;  g.,  gland  of  uterus  :  Af.,  mesoblast ;  Sv.,  syncytium  ;  T.  M.,  covering  tissue- 
over  break  in  uterine  surface;  Tr.,  trophoblast.  X  50  (Pfters}. 

this  mesoblast  :  also  that  the  villi  are  in  reality  considerably  branched,  not  straight 
as  in  the  diagram.  The  remainder  of  the  chorion  is  acquiring  a  smooth  surface  and 
is  commonly  known  as  the  clnnion  l<m\  as  a  means  of  distinguishing  the  extra- 
placental  portion  of  this  membrane.  The  yolk-sac,  sometimes  called  the  umbilical 
vesicle,  at  the  extremity  of  the  yolk-s'talk,  is  retained  usually  in  the  placental  area 
just  beneath  the  amnion.  It  is  possible  to  find  the  yolk-sac  in  nearly  every  placenta 


THE   HUMAN    FCETAL   MEMBRANES. 


39 


by  slightly    stretching  the    umbilical   cord  at  its    insertion,   when    a   fold    appears 
containing  no  large   vessels.      This  fold  points   to   the    position  of    the    yolk-sac. 

To   sum  up,  the  chief  peculi- 
arities of    the   human   fcetal  mem-  FIG.  45. 
branes  are  the  following  : 

1.  The     amniotic     cavity     is 
developed   at  a  very  early  period 
apparently  by  a  process  of  hollowing 
out  in  the  region  of  the  cells  of  the 
inner  mass,  and  not  by  any  folding- 
process.     The  cells  above  this  primi- 
tive amniotic  cavity  are  later  split 
into  two  portions  by  the  entrance  of 
the  mesoblast  and  extra-embryonic 
ccelom  ;  the  inner  portion  becomes 
the    ectoblast    of    the    amnion,  the 
outer  portion  is  merely  a  part  of  the 
the  trophoblast  of  the  chorion. 

2.  The  mesoblast    and   extra- 
embryonic  ccelom  are  precociously 
developed  at  a  very  early  period. 

3.  The   body-stalk  constitutes 
a  primary  and  permanent  connection 
between  the  embryo  and  the  chorion. 

4.  The    allantois,    which,    ex- 
ternal to  the  body  of  the  embryo,  is 

an      insignificant     Structure,      grOWS  Dorsal  surface  of  early  human  embryo,  two  millimetres  in 

into  the  body-stalk  and  therefore  is     SSX'rn^d  ^de!4^  *"')    The  amni°n  haS  been  divided 
never  a  free  vesicle. 

.     5.   The  trophoblast  is  very  early  greatly  proliferated  and  very  early  in  intimate 
contact  with  the  maternal  blood. 

FIG.  46. 

Ectoblast 
Vitelline  sac        Mesoblast 


Vitelline  sac 

Reflected  amnion 

Medullary  folds— ^ — 
Medullary  groove — 

Neurenteric  canal. — 


Primitive  streak- 


Belly-stalk 


Chorion. 
Chorionic  villi- 


Wall  of  vitelline 
sac 


Belly-stalk 


Neurenteric 
canal 


Primitive 
streak 


Chorion 


Longitudinal  section  of  human  embryo  represented  in  preceding  figure.     X  23.     (After  Spee.) 


Fig.  44,  page  38,  is  a  reproduction  of  the  drawing  of  Peter's  embryo  and 
deserves  special  attention.  The  figure  shows  a  small  portion  of  the  mucous  mem- 
brane of  the  uterus  in  which  is  imbedded  the  embryonic  or  chorionic  vesicle. 


4o 


HUMAN   ANATOMY. 


Between  the  points  a,  b  in  the  figure  lies  the  area  through  which  the  embryonic 
growth  has  made  its  way  into  the  mucous  membrane  of  the  uterus,  and,  in  consequence, 
the  uterine  epithelium  in  this  area  has  disappeared.  Above  this  small  area  there 
lies  a  covering  mass  of  tissue  (  7\  M. )  mainly  composed  of  blood,  the  result  evidently 
of  hemorrhage  following  the  breaking  of  the  mucosa  of  the  uterus  in  this  region. 
The  chorionic  vesicle  as  a  whole  is  quite  large,  especially  in  proportion  to  the 
embryonic  area  E,  the  surface  of  which  is  covered  with  a  distinct  columnar  epithelium. 
Surrounding  the  chorionic  vesicle  there  are  two  kinds  of  tissue,  which  make  a  very 
striking  feature  of  the  picture.  P'irst,  there  is  the  thickened  and  very  irregular 
trophoblast,  the  cells  of  which  appear  dark,  and  which  forms  the  outer  covering  of  the 
wall  of  the  embryonic  vesicle  itself.  Then  there  are  numerous  large  blood-spaces  or 

FIG.  47. 


Amnion- 


Umbilical  or  yolk-sac 


Bod  y-stalk 


Chorion 


Human  embryo  of  about  twenty  days,  enclosed  within  the  amnion.     X  30. 

blood-lacunae  lying  among  the  irregular  projections  of  the  trophoblast.  The  maternal 
blood,  therefore,  in  this  very  early  condition  bathes  the  trophoblast  cells  of  the 
embryo,  a  relation  very  significant  with  reference  to  the  nutrition  of  the  embryo 
before  the  allantoic-placental  circulation  is  established.  The  mesoderm  (Af)  extends 
around  the  vesicle  on  the  inner  side  of  the  trophoblast.  In  several  places  there  are 
outgrowths  of  the  mesoderm  into  the  trophoblast,  so  indicating  the  beginnings  of  the 
villi  of  the  chorion.  It  will  be  remembered  that  the  cells  of  the  trophoblast  form  the 
epithelial  covering  of  the  chorion.  At  several  places  in  the  figure  the  syncytial 
layer  of  the  trophoblast  Sy  can  be  distinguished.  The  proportionally  large  cavity 
within  the  vesicle  is  extra-embryonic  ccelom,  a  fact  which  can  readily  be  verified  by 
observing  the  relations  of  the  mesoderm.  The  latter  layer  of  tissue  is  seen  to  extend 
around  the  small  yolk  sac  as  the  visceral  layer  of  the  mesoderm,  while  the  layer  of  the 
mesoderiji  on  the  inner  side  of  the  trophoblast  is  of  course  the  parietal  layer,  hence 
the  cavity  within  these  respective  layers  is  the  extra-embryonic  ccelom,  precociously 
developed  for  this  early  stage.  There  is  a  small  amniotic  cavity  above  the  embryo. 
Between  this  cavity  and  the  trophoblast  the  mesoderm  extends  as  a  solid  sheet. 
There  are  one  or  two  more  points  to  be  noted  in  the  figure.  In  the  areas 


THE    HUMAN    CHORION. 


FIG. 


marked  B.  Z.  ,  which  are  merely  portions  of  the  uterine  mucosa  lying'  against  the 
trophoblast,  the  tissue  is  oedematous  in  character.  This  tissue  is  described  by  Peters 
as  the  bordering  zone.  In  other  portions  of  the  mucous  membrane  there  are  seen 
parts  of  some  of  the  uterine  glands  (,§").  In  the  region  marked  Cap.  ,  is  seen  the 
beginning  of  the  deciclua  capsularis,  growing  in  over  the  area  through  which  the 
embryonic  vesicle  broke  into  the  surface  of  the  uterus.  This  layer,  decidua  capsu- 
laris, is  at  this  stage  scarcely  developed,  only  the  beginning  of  it  is  apparent. 

This  embryo,  described  by  Peters,  is  the  youngest  human  embryo  which  has 
been  accurately  studied.  The  inner  dimensions  of  the  vesicle,  as  given  by  Peters, 
are  as  follows  :  1.6  by  0.8  by  0.9  mm.  The  growth  was  found  on  the  dorsal  wall 
of  the  body  of  the  uterus.  The  mucous  membrane,  decidua,  of  the  fundus  and 
dorsal  wall  was  about  8  mm.  thick,  that  of  the  ventral  wall  about  5  mm. 

The  Human  Chorion.  —  The  vascular  chorionic  villi,  although  becoming 
more  complex  by  the  addition  of  secondary  branches,  are  for  a  time  equally  well 
developed  over  the  external  surface  of  the  entire  embryonic  vesicle  ;  subsequently, 
from  the  end  of  the  second  month,  a  noticeable  differentiation  takes  place,  the  villi 

included  within  the  field  that  later  corre- 
sponds to  the  placental  area  undergoing 
unusual  growth  and  far  outstripping  those 
covering  the  remaining  parts  of  the  chorion. 
This  inequality  in  the  development  of  the 
villi  led  to  the  recognition  of  the  chorion 
frondosum  and  the  chorion  l<zve,  as  the 
placental  and  non-placental  portions  of  the 
chorion  respectively  are  termed  (Fig.  48). 
The  vascular  supply  of  the  villi  also  shares 
in  this  differentiation,  the  vessels  to  those 
of  the  placental  area  becoming  progres- 
sively more  numerous,  while,  on  the  con- 
trary, those  distributed  to  the  remaining 
villi  gradually  atrophy  as  the  chorion 
comes  into  intimate  apposition  with  the 
uterine  tissue.  When  well  developed,  the 
chorionic  villi  possess  a  distinctive  appear- 
ance, the  terminal  twigs  of  the  richly 
branched  projections  being  clubbed  and 
slightly  flattened  in  form.  Their  recogni- 
tion in  discharges  from  the  vagina  often 
affords  valuable  information  as  to  the  ex- 

/~>f    t-vt-c.o-r>on/-ir 
reglldliey. 

The  Amniotic  Fluid.  - 


Extraplacental  area 
(Choi ion  Iteve) 


u  TV  us' U-   -^ 

Placental  a  i 
(Chorion frondosum)  •^•Bi 


External  surface  of  part  of  the  human  chorion  of 
the  third  month  ;  the  lower  portion  is  covered  with  the 
highly  developed  villi  of  the  placental  area. 

at  first  lies  closely  applied  to  the  embryo, 

but  soon  becomes  separated  by  the  space  which  rapidly  widens  to  accommodate  the 
increasing  volume  of  the  contained  liquor  amnii.  The  accumulation  of  fluid  within 
the  amniotic  sac,  which  in  man  takes  place  with  greater  rapidity  than  in  other  mam- 
mals, results  in  'the  obliteration  of  the  cleft  between  the  chorion  and  amnion  until 
the  latter  envelope  lies  tightly  pressed  against  the  inner  surface  of  the  chorion. 
The  union  between  the  two  envelopes,  however,  is  never  very  intimate,  as  even  after 
the  expulsion  of  the  membranes  at  birth  the  attenuated  amnion  may  be  stripped  off 
from  the  chorion,  although  the  latter  is  then  inseparably  fused  with  the  remaining 
portions  cf  the  deciduae. 

The  amniotic  fluid,  slightly  alkaline  in  reaction,  is  composed  almost  entirely 
of  water  ;  of  the  one  per  cent,  of  solids  found,  albumin,  urea,  and  grape-sugar  are 
constituents.  The  quantity  of  liquor  amnii  is  greatest  during  the  sixth  month  of 
gestation,  at  which  time  it  often  reaches  two  litres.  With  the  rapid  increase  in  the 
general  bulk  of  the  foetus  during  the  later  months  of  pregnancy,  the  available  space 
for  the  amniotic  fluid  lessens,  resulting  in  a  necessary  and  marked  decrease  in  the 
quantity  of  the  liquid  ;  at  birth,  less  than  one  litre  of  amniotic  fluid  is  usually 
present.  Sometimes,  however,  the  amount  of  the  liquor  amnii  may  reach  ten 


HUMAN   ANATOMY. 


litres,  due  to  pathological  conditions  of  the  foetal  envelopes  ;  such  excessive  secre- 
tion constitutes  hydramnion.  During  the  later  months  of  pregnancy  the  foetus  swal- 
lows the  amniotic  fluid,  as  shown  by  the  presence  of  hairs,  epithelial  cells,  etc., 
within  the  stomach.  In  view  of  the  composition  of  the  fluid,  consisting  almost  en- 
tirely of  water,  it  seems  certain  that  the  introduction  of  the  liquor  amnii  does  not 
serve  the  purposes  of  nutrition  ;  on  the  other  hand,  it  is  probable,  as  held  by  Preyer, 
that  the  unusual  demands  of  the  fcetal  tissues  for  water  may  be  met  largely  in  this 
manner. 

The  source  of  the  amniotic  fluid  in  man  has  been  the  subject  of  much  discus- 
sion. While  it  has  been  impossible  to  determine  accurately  the  extent  to  which  the 
mother  participates  in  the  formation  of  this  fluid,  it  may  be  accepted  as  established 
that  the  maternal  tissues  are  the  principal  contributors  ;  it  is  also  probable  that  the 
foetus  likewise  aids  in  the  production  of  the  liquor  amnii  ;  the  latter,  therefore,  orig- 
inates from  a  double  source, — maternal  and  fcetal.  The  early  amniotic  fluid  resembles 

FIG.  49. 


Umbilical  vesicle 


Umbilical  stalk- 


Inner  surface 
of  chorion 


Umbilical  cord  - 


Cut  edge  of 
amnion- 


Masses  of 
chorionic  villi- 


Human  embryo  of  about  thirty-three  days.    X  4.     Amnion  and  chorion  have  been  cut  and  turned  asid 

in  appearance  and  chemical  composition  a  serous  exudate  ;  later,  after  the  formation 
of  the  urogenital  openings,  the  liquor  amnii  becomes  contaminated,  as  well  as  aug- 
mented, by  the  addition  of  the  fluid  derived  from  the  excretory  organs  of  the  foetus. 
During  the  later  weeks  of  gestation  the  contents  of  the  digestive  tube  are  discharg 
into  the  amniotic  sac  as  meconium. 

The  Umbilical  Vesicle. — The  umbilical  vesicle,  as  the  yolk-sac  in  man  is 
termed,  presents  a  reversed  growth-ratio  to  the  amnion  and  body-stalk  since  it  pro- 
gressively decreases  as  these  latter  appendages  become  more  voluminous.  The  early 
human  embryo  is  very  imperfectly  differentiated  from  the  large  and  conspicuous 
yolk-sac,  with  which  its  ventral  surface  widely  communicates.  With  the  advances 
made  during  the  third  week  in  the  formation  of  the  primitive  gut,  the  connection 
between  the  latter  and  the  vitelline  sac  becomes  more  definitely  outlined  in  conse- 
quence of  the  Inrlnning  constriction  which  indicates  the  first  suggestion  of  the  later 
vitelline  or  umbilical  duet  (  Fig.  47).  By  the  end  of  the  fourth  neek  the  connection 


- 


THE    UMBILICAL    VESICLE. 


43 


between  the  umbilical  sac  and  the  embryo  has  become  reduced  to  a  contracted  channel 
extending  from  the  now  rapidly  closing  ventral  body-wall  to  the  yolk-sac,  which  is 
still,  however,  of  considerable  size.  The  succeeding  fifth  (Fig.  50)  and  sixth  weeks 
effect  marked  changes  in  the  umbilical  duct,  now  reduced  to  a  narrow  tube,  which 
extends  from  the  embryo  to  the  chorion,  where  it  ends  in  the  greatly  diminished 
vitelline  sac.  The  lumen  of  the  umbilical  duct  is  conspicuous  during  the  earliest 
months  of  gestation,  but  later  disappears,  the  entoblastic  epithelial  lining  remaining 
for  a  considerable  time  within  the  umbilical  cord  to  mark  the  position  of  the  former 
canal. 

The  chief  factor  in  producing  the  elongation  of  the  umbilical  duct  is  the  rapid 
expansion  of  the  amnion  ;  with  the  increase  in  the  amniotic  sac  the  distance  between 
this  envelope  and  the  embryo  increases,  until  the  amnion  fills  the  entire  space  within 

FIG.  50. 


Amnion  _ 


Umbilical 

vesicle, 
(yolk-sac) 


Inner  surface 

of  chorion,- 


Chorionic  villi 

of  outer  surface  . 


Chorionic  sac  of  thirty-five  day  embryo  laid  open,  showing  embryo  enclosed  by  amnion.     X  2. 


the  chorion,  against  which  it  finally  lies.  In  consequence  of  this  expansion,  the 
attachment  between  the  embryo  and  the  amnion  around  the  ventral  opening,  which 
later  corresponds  to  the  umbilicus,  becomes  greatly  elongated  and  narrowed.  At 
this  point  the  tissues  of  the  embryonic  body-wall  and  the  amniotic  layers  are  directly 
continuous.  The  tubular  sheath  of  amnion  thus  formed  encloses  the  tissue  and 
structures  which  extend  between  the  embryo  and  the  chorion,  as  the  constituents  of 
the  belly-stalk,  together  with  the  umbilical  duct  and  the  remains  of  the  vitelline 
blood-vessels  ;  the  delicate  mesoblastic  layer  of  the  amnion  fuses  with  the  similar 
tissue  of  the  allantois,  the  whole  elongated  pedicle  constituting  the  umbilical  cord  or 
funiculus.  The  latter  originates,  therefore,  from  the  fusion  of  three  chief  com- 
ponents, the  amniotic  sheath,  the  belly-stalk,  and  the  vitelline  duct  ;  the  belly-stalk. 


44  HUMAN    ANATOMY. 

as  already  noted,  includes  the  allantois,  with  its  blood-vessels,  and  diverticulum, 
while  traces  of  the  vitelline  circulation  are  for  a  time  visible  within  the  atrophied 
walls  of  the  umbilical  duct.  As  gestation  advances,  the  amnion  and  the  chorion 
become  closely  related,  but  not  inseparably  united  ;  between  these  attenuated  mem- 
branes lie  the  remains  of  the  once  voluminous  yolk-sac,  which  at  birth  appears  as 
an  inconspicuous  vesicle,  from  three  to  ten  millimetres  in  diameter,  situated  usually 
several  centimetres  beyond  the  insertion  of  the  umbilical  cord. 

In  cases  in  which  the  closure  and  the  obliteration  of  the  vitelline  duct  before  birth 
are  imperfectly  effected,  a  portion,  or  even  the  whole,  of  the  intra-embryonic  segment 
of  the  canal  may  persist  as  a  pervious  tube.  Although  in  extreme  cases  of  faulty 
closure  a  passage  may  lead  from  the  digestive  tube  to  the  umbilicus,  and  later  open 
upon  the  exterior  of  the  body  as  a  congenital  umbilical  anus,  the  retention  of  the 
lumen  of  the  vitelline  duct  is  usually  much  less  extensive,  being  limited  to  the  prox- 
imal end  of  the  canal,  where  it  is  known  as  Mecke? s  diverticulum.  The  latter  is  con- 
nected with  the  ileum  at  a  point  most  frequently  about  82  centimetres  (thirty-two 
inches)  from  the  ileo-caecal  valve.  Such  diverticula  usually  measure  from  five  to 
7.5  centimetres  in  length,  and  possess  a  lumen  similar  to  that  of  the  intestine  with 
which  they  communicate. 

The  foregoing  envelopes,  the  amnion  and  the  chorion,  are  the  product  of  the 
embryo  itself ;  their  especial  purpose,  in  addition  to  affording  protection  for  the  deli- 
cate organism,  is  to  aid  in  establishing  close  nutritive  relations  between  the  embryo 
and  the  maternal  tissues,  which,  coincidently  with  the  development  of  the  foetal 
envelopes,  undergo  profound  modifications  ;  these  changes  must  next  be  considered. 

The  Deciduse. — The  birth  of  the  child  is  followed  by  the  expulsion  of  the 
after-birth,  consisting  of  the  membranes  and  the  placenta,  which  are  separated  from 
the  uterine  wall  by  the  contractions  of  this  powerful  muscular  organ.  Close  inspection 
of  the  inner  surface  of  the  uterus  and  of  the  opposed  outer  surface  of  the  extruded 
after-birth  shows  that  these  surfaces  are  not  smooth,  but  roughened,  presenting  evi- 
dences of  forcible  separation.  The  fact  that  the  external  layer  of  the  expelled  after- 
birth consists  of  the  greater  portion  of  the  modified  mucous  membrane  which  is 
stripped  off  at  the  close  of  parturition  suggested  the  name  deciduce  for  the  mater- 
nal portion  of  the  foetal  envelopes  shed  at  birth. 

Since  the  deciduae  are  directly  derived  from  the  uterine  mucous  membrane,  a 
brief  sketch  of  the  normal  character  of  the  last-named  structure  appropriately  pre- 
cedes a  description  of  the  changes  induced  by  pregnancy.  The  normal  mucous 
membrane  lining  the  body  of  the  human  uterus  (Fig.  51)  presents  a  smooth,  soft, 
velvety  surface,  of  a  dull  reddish  color,  and  measures  about  one  millimetre  in  thick- 
ness. The  free  inner  surface  is  covered  with  columnar  epithelium  (said  to  be  cili- 
ated) which  is  continued  directly  into  the  uterine  glands.  The  latter,  somewhat 
sparingly  distributed,  are  cylindrical,  slightly  spiral  depressions,  the  simple  or  bifur- 
cated blind  extremities  of  which  extend  into  the  deeper  parts  of  the  mucosa  in  close 
relation  to  the  inner  bundles  of  involuntary  muscle  ;  all  parts  of  the  tubular  uterine 
glands  are  lined  by  the  columnar  epithelium.  The  muscular  bundles  representing 
the  muscularis  mucosae  are  enormously  hypertrophied  and  constitute  the  greater 
part  of  the  inner  more  or  less  regularly  disposed  circular  layer  of  the  uterine  muscle. 
The  unusual  development  of  the  muscular  tissue  of  the  mucous  membrane  reduces 
the  submucous  tissue  to  such  an  insignificant  structure  that  the  submucosa  is  gener- 
ally regarded  as  wanting,  the  extremities  of  the  uterine  glands  being  described  as 
reaching  the  muscular  tunic.  The  glands  lie  embedded  in  the  connective-tissue 
complex,  rich  in  connective-tissue  elements  and  lymphatic  spaces,  that  forms  the 
tunica  propria  of  the  mucosa. 

With  the  beginning  of  pregnancy  the  uterine  mucous  membrane  undergoes 
marked  hypertrophy,  becoming  much  thicker,  more  vascular,  and  beset  with  nu- 
merous irregularities  of  its  free  surface  caused  by  the  elevations  of  the  soft  spongy 
component  tissue.  These  changes  take  place  during  the  descent  of  the  fertilized 
ovum  along  the  oviduct  and  indicate  the  active  preparation  of  the  uterus  for  the 
reception  of  the  ovum. 

According  to  the  classical  description  of  the  encapsulation  of  the  ovum  (Fig.  52) 
by  the  uterine  mucous  membrane,  the  embryonic  vesicle  becomes  arrested  within 


THE    DECIDtLE. 


45 


one  of  the  depressions  of  the  uterine  lining,  usually  near  the  entrance  of  the  ovi- 
duct, whereupon  the  adjacent  mucosa  undergoes  rapid  further  hypertrophy,  which 
results  in  the  formation  of  an  annular  fold  surrounding  the  product  of  concep- 
tion. This  encircling  wall  of  uterine  tissue  continues  its  rapid  growth  until  the 
embryonic  vesicle  is  entirely  enclosed  within  a  capsule  of  modified  mucous  mem- 
brane, known  as  the  decidua  rcflexa,  as  distinguished  from  the  decidua  vera,  the 
name  applied  to  the  general  lining  of  the  pregnant  uterus.  That  portion  of  the 
uterine  mucosa,  however,  which  lies  in  close  apposition  to  the  embryonic  vesicle, 
constituting  the  outer  wall  of  the  decidual  sac,  is  termed  the  decidua  serotina  ;  later 
it  becomes  the  maternal  part  of  the  placenta. 

FIG.  51. 


Duct  of  gland 


Spiral  portion  of 
gland 


Process  of  muscular 
tissue  extending  be- 
tween the  glands 


Muscular  tissue 


-Uterine  blood- 
vessel 


Ut.erine  mucous  membrane  with  part  of  muscular  tissue.    X  45. 

Our  knowledge  of  the  details  regarding  the  encapsulation  of  the  ovum  has 
been  materially  advanced  by  the  recent  observations  of  Peters,  who  had  the  rare 
good  fortune  of  carefully  studying  the  details  of  the  process  at  an  earlier  stage  than 
any  hitherto  accurately  investigated.  The  results  of  Peters' s  observations  lead  to  a 
somewhat  modified  conception  of  the  early  phases  of  the  encapsulation  of  the  ovum, 
as  well  as  shed  additional  light  on  some  of  the  vexed  problems  concerning  the  details 
of  the  formation  of  the  placenta. 

According  to  these  investigations,  the  embryonic  vesicle,  on  reaching  the  uterine 


46 


IH'MAN    ANATOMY. 


FIG.  52. 


cavity  and  becoming  arrested  at  some  favorable  point,  usually  in  the  vicinity  of 
the  oviduct,  brings  about  a  degeneration  of  the  uterine  epithelium  over  the  area  of 
contact.  The  disappearance  of  the  epithelial  lining  is  followed  by  sinking  and  em- 
bedding of  the  embryonic  vesicle  within  the  softened  mucous  membrane,  the  process 
being  accompanied  by  erosion  of  some  of  the  uterine  capillaries  and  consequent 
hemorrhage  into  the  opening  representing  the  path  of  the  ovum.  The  extravasated 
blood  escapes  at  the  point  of  entrance  on  the  uterine  surface  and,  later,  forms  a 

mushroom-shaped  plug  marking  the 
position  of  the  embedded  ovum. 
The  latter  thus  comes  into  closer 
relations  with  the  maternal  tissues  at 
an  earlier  period  than  was  formerly 
recognized. 

The  Trophoblast.—  The  ear- 
liest human  embryonic  vesicle  that 
has  been  accurately  studied,— that 
of  Peters, — while  measuring  only 
1.6  millimetres  in  its  greatest  di- 

Diagrams  representing  relations  of  the  uterine  mucous  mem-  ameter,  Was  already  enclosed  CXter- 
brane  to  the  embryonic  vesicle,  or  ovum,  during  the  embedding  nallv  bv  a  COnsoicUOUS  CCtoblastic 
of  the  latter,  s,  v,  c,  decidua  serotina,  vera,  and  reflexa,  re-  '  J 

spectively ;  o,  ovum.  envelope,    m    places  .5    millimetre 

or  more  in  thickness.      This  thick 

ectoblastic  layer  is  evidently  the  proliferated  trophoblast  (page  31),  a  membrane  so 
designated  to  indicate  the  important  nutritive  functions  which  it  early  assumes. 

Very  early  the  trophoblast  becomes  honeycombed  by  the  extension  of  the 
maternal  vascular  channels  into  the  ectoblastic  tissue  (Fig.  53),  which  consequently 
is  broken  up  into  irregular  epithelial  trabeculae  separating  the  maternal  blood-spaces. 
The  inner  surface  of  the  trophoblastic  capsule  presents  numerous  irregular  depres- 
sions into  which  corresponding  processes  of  the  adjacent  young  mesoblast  project  ; 
this  arrangement  foreshadows  the  formation  of  the  chorionic  villi  which  soon  become 
so  conspicuous  in  the  human  embryonic  vesicle.  Coincidently  with  the  invasion  of 
the  trophoblast  by  the  vascular  lacuna 

externally  and  the  penetration  of  the  F-JG.  53. 

mesoblastic  tissue  internally,  the  pe- 
ripheral portions  of  the  ectoblastic 
capsule  undergo  proliferation  and 
extend  more  deeply  into  the  sur- 
rounding maternal  tissues.  In  con- 
sequence of  the  rapid  growth  of  the 
embryonic  vesicle,  that  part  of  the 
hypertrophied  uterine  mucosa  which 
overlies  the  embedded  embryonic 
vesicle  soon-  becomes  elevated  and 
projects  into  the  uterine  cavity,  thus 
giving  rise  to  the  structure  described 
as  the  decidua  reflexa,  or,  preferably, 
the  decidua  capsularis. 

The  Decidua  Vera.  —  The 
changes  which  affect  the  uterine  mu- 
cous membrane,  the  decidua  vera, 

result  in  great  thickening,  so  that  the  mucosa  often  measures  nearly  a  centimetre  ; 
this  thickening,  however,  is  most  marked  in  the  immediate  vicinity  of  the  embedded 
ovum,  throughout  the  greater  part  of  the  uterus  the  decidua  attaining  a  much  less 
conspicuous  hypertrophy.  Towards  the  cervix  the  mucosa  is  least  affected,  and  at 
the  internal  orifice  of  the  cervical  canal  presents  its  normal  appearance.  Examina- 
tion of  the  decidua  shows  that  the  normal  constituents  of  the  uterine  mucosa  undergo 
hypertrophy  which  results  in  enlargement  of  the  uterine  glands  (  Fig.  54),  as  well 
as  in  increase  of  the  intervening  connective-tissue  stroma.  The  enlargement  of  the 
glands  is  not  uniform,  but  is  limited  to  the  middle  and  terminal  or  deeper  parts  of 


Mesoblast 
Trophohlast 

Intervillous 
blood-space 

Sviu-ytium 


Diagram  showing  early  stage  oi  attachment  between  f<ctal 
and  maternal  tissues;  invasion  of  trophoblast  by  maternal 
blood-vessels.  ( Peters. ) 


THE   DECIDUA    VERA. 


47 


the  tubular  depressions  ;  the  inner  portions  of  the  glands,  directed  towards  the  sur- 
face of  the  uterus,  become  elongated  and  lie  embedded  within  a  comparatively 
dense  matrix.  In  consequence  of  these  changes,  the  decidua  in  the  vicinity  of  the 
ovum,  where  the  hypertrophy  is  most  marked,  presents  in  section  two  strata,  an 
inner  compact  and  an  outer  spongy  layer.  The  ciliated  columnar  epithelium  that 
normally  clothes  the  free  surface  of  the  uterus,  and  perhaps  also  the  uterine  glands, 
gradually  disappears,  the  degeneration  beginning  before  the  end  of  the  first  month. 
The  integrity  of  the  cells  lining  the  uterine  glands  is  maintained  for  a  longer  period, 
but  the  glandular  epithelium  likewise,  after  a  time,  suffers,  losing  its  columnar 
character  and  changing  to  small  cubical  or  flattened  elements,  which,  after  appear- 
ing as  shrunken  columns  during  the  fourth  and  fifth  months,  finally  disappear 
during  the  latter  half  of  gestation.  An  important  exception,  however,  is  to  be  noted 
in  the  behavior  of  the  epithelium  lining  the  deeper  portion,  or  the  fundus,  of  the 
glands  next  the  muscular  tissue  ;  the  epithelium  situated  in  this  position  does  not 
participate  in  the  atrophic  changes  above  described,  but  retains  more  or  less  per- 

FIG.  54. 


Enlarged  gland    £ 


Enlarged  glane 


Uterine  muscle 


Section  of  mucous  membrane  lining  body  of  uterus  (decidua  vera)  ;  fourth  month  of  pregnancy.     {After  Leopold.) 


fectly  its  normal  condition  to  the  close  of  pregnancy.  After  the  expulsion  of  the 
decidual  portion  of  the  uterine  mucous  membrane,  the  epithelium  remaining  in  the 
fundus  of  the  glands  becomes  the  centre  of  regeneration  for  the  new  lining  of  the 
uterus. 

The  connective-tissue  elements  of  the  matrix  surrounding  the  glands,  especially 
in  the  compact  layer  in  the  vicinity  of  the  ovum,  undergo  active  proliferation,  in 
consequence  of  which  large  spherical  elements,  the  decidual  cells,  are  produced.  The 
latter,  from  .030  to  .040  millimetre  in  diameter,  in  places  are  so  densely  packed 
that  they  assume  the  appearance  of  epithelium  ;  although  most  typical  and  nu- 
merous in  the  compact  layer,  they  are,  nevertheless,  present  in  the  spongy  stratum, 
in  this  situation  being  more  elongated  and  lanceolate  in  form. 

The  decidua  vera  retains  this  general  character  during  the  first  half  of  preg- 
nancy ;  from  this  time  on,  however,  the  increasing  volume  of  the  uterine  contents 
subjects  the  decidua  to  undue  pressure,  in  consequence  of  which  the  hypertrophied 
mucosa  undergoes  the  atrophic  changes  characteristic  of  the  so-called  second  stage. 
These  include  a  gradual  reduction  in  the  thickness  of  the  decidua  vera  from  nearly 


48 


HUMAN   ANATOMY. 


one  centimetre  to  about  two  millimetres,  the  disappearance  of  the  ducts  and  open- 
ings of  the  uterine  glands,  and  the  conversion  of  the  compact  layer  into  a  dense 
homogeneous  stratum,  in  which  the  tightly  compressed  glands  later  entirely  disap- 
pear. The  spongy  layer,  on  the  contrary,  retains  the  dilated  gland-lumina,  which, 
however,  in  consequence  of  pressure,  are  converted  into  irregular  spaces  arranged 
with  their  longest  dimensions  parallel  to  the  uterine  surface.  The  clefts  next  the 

FIG.  55. 


Amnion 
Chorion 
Decidua  reflexa 


Blood-space  of 
compact  layer 


Spongy  layer 


Muscle 


Enlarged  lumen 
of  glands 


Degenerating 
glandular  epi- 
thelium 


FIG.  56. 


A  -  v  *v ' 

Section  through  fcetal  membranes  and  uterus  at  margin  of  the  placenta ;  sixth  month  of  pregnancy.  (After  Leopold.) 

muscular  tissue  are  clothed  with  well-preserved  epithelium  ;   the  lining  cells  of  those 
towards  the  compact  layer,  on  the  contrary,  early  atrophy  and  disappear. 

The  Decidua  Placentalis. — The  decidua  placentalis,  vrdeciduaserotina,  being 
destined  to  contribute  the  maternal  portion  of  the  placenta,  undergoes  profound 
changes  which  particularly  affect  the  blood-vessels  of  the  mucosa.  In  addition  to 
the  initial  general  hypertrophy  of  the  mucous  membrane,  which  the  placental  decidua 
shares  in  common  with  other  parts  of  the  uterine  lining,  peculiar  polynucleated  ele- 
ments, the  giant  cells,  make 
their  appearance  during  the  fifth 
month  ;  by  the  end  of  preg- 
nancy they  are  found  in  large 
numbers  within  the  basal  plate 
and  the  septa  of  the  placenta, 
although  they  are  not  wanting 
within  the  remains  of  the  spongy 
layer.  The  giant  cells  are  par- 
ticularly numerous  in  the  im- 
mediate vicinity  of  the  large 
blood-vessels.  The  relations 
between  the  ingrowing  fcetal 
trophoblastic  tissue  and  the  ma- 
ternal structures  early  become 
so  intimate  within  the  placental 
area  that  especial  modifications 
are  instituted  destined  for  the  production  of  the  vascular  arrangement  by  which  the 
maternal  and  fcetal  blood-streams  are  brought  into  close  relations. 

The  proliferating  trophoblastic  tissue  invades  the  stroma  of  the  mucous  mem- 
brane and  encroaches  upon  the  capillaries  until  the  latter  in  places  bra  urn-  ruptured, 
allowing  the  escape  of  the  maternal  blood,  which  thus  is  brought  into  direct  contact 
with  the  trophoblast.  The  erosion  effected  by  the  blood,  on  the  one  hand,  and  the 
encroachment  of  the  fcetal  mesoblast,  on  the  other,  gradually  reduces  the  tropho- 
blastic stratum,  which  is  broken  up  into  narrow  epithelial  trabeculae  separating  the 
rapidly  enlarging  vascular  lacunae,  the  primary  representatives  of  the  intervillous 


Sections  of  chorionic  villi  from  placenta.  X  170.  a,  b,  small 
branches  of  umbilical  artery  and  vein;  v,  capillary  vessels;  c,  cell- 
aggregations  of  syncytium  (d) ;  m,  mesoblastic  stroma  of  villi. 


THE   PLACENTA. 


49 


FIG.  57. 


Main  stalk 


maternal  blood-spaces  of  the  placenta.  The  active  outgrowth  of  the  mesoblastic 
tissue  of  the  chorion  into  the  trophoblastic  envelope  results  in  the  production  of  the 
characteristic  villous  condition  distinguishing  the  early  human  embryonic  vesicle. 

When  sectioned,  the  well-developed  chorionic  villi  are  seen  to  be  composed  of 
two  portions,  (a)  the  central  core  of  gelatinous  connective  tissue,  containing  nu- 
merous stellate  cells  and  blood-vessels,  repre- 
senting the  fcetal  mesoblast,  and  (<5)  the  epi- 
thelial covering  derived  from  the  trophoblast. 
The  investment  of  the  villi  consists  of  two 
layers, — an  inner  stratum,  next  the  connective- 
tissue  core,  composed  of  low,  distinctly  out- 
lined polyhedral  cells,  the  chorionic  epithe- 
lium, and  an  outer  stratum,  the  syncytium, 
composed  of  an  apparently  continuous  proto- 
plasmic layer,  in  which  nuclei  are  visible,  but 
definite  cell  boundaries  are  wanting.  Irregu- 
larly distributed  aggregations  of  nuclei,  or 
cell-patches  (Fig.  56),  form  slight  elevations 
on  the  surface  of  the  villi.  The  derivation 
of  the  outer  layer,  or  syncytium,  has  been 
the  subject  of  much  discussion  ;  its  close  rela- 
tion to  the  maternal  blood-spaces  suggested  a 
maternal  origin  to  some  investigators,  while 
others  regard  it  as  a  fcetal  production.  The 
observations  of  Peters  on  the  very  early  human 
ovum,  already  mentioned,  conclusively  show 
the  correctness  of  the  latter  view,  and  lhat 

the  syncytium  is  formed  by  the  transformation  of  the  trophoblast  next  the  vascular 
lacunae  (Fig.  58)  ;  the  syncytium,  as  well  as  the  remaining  parts  of  the  villi  of  the 
chorion,  therefore,  is  of  fcetal  origin.  The  epithelium  covering  the  villi  of  the  pla- 
cental  area  early  evinces -a  tendency  towards  regression,  and  by  the  fourth  month 
exists  only  as  isolated  patches  ;  during  the  later  stages,  and  particularly  on  the 
larger  villi,  the  layer  of  chorionic  epithelium  disappears,  the  syncytium  remaining 
as  the  sole  attenuated  covering  of  the  connective-tissue  core  of  the  villi.  In  certain 
parts  of  its  extent,  especially  where  it  covers  the  chorion  and  the  decidua  serotina, 


Isolated  tuft  of  chorionic  villi  from  placenta. 


FIG.  58.. 


Chorionic  mesoblast 


Mesoblastic  core  of  fcetal 

villus 

Trophoblast 
Syncytium 
Maternal  blood-space 

Muscle 


Endothelium 
Maternal  blood-vessel 

Diagram  showing  formation  of  placenta.     (Peters.} 

as  well  as  upon  some  of  the  villi,  the  syncytium  undergoes  degeneration  and  is 
replaced  by  a  peculiar  layer  of  hyaline  refracting  material  known  as  canalized 
fibrin. 

The  Placenta. — The  placenta  constitutes,  from  the  third  month  of  intra- 
uterine  life,  the  nutritive  and  respiratory  organ  of  the  foetus.  As  seen  at  birth,  it  is 
of  irregular  discoidal  form,  concavo-convex  in  section,  and  measures  from  fourteen 
to  eighteen  centimetres  in  diameter  and  from  three  to  four  centimetres  in  thickness. 

4 


HUMAN   ANATOMY. 


Its  convex  external  or  uterine  surface  is  rough,  owing  to  the  separation  from  the 
deeper  part  of  the  lining  of  the  uterus  which  has  taken  place  at  the  termination  of 
labor.  This  surface,  moreover,  presents  a  number  of  divisions,  the  cotyledons,  de- 
fined by  deep  fissures.  The  inner  or  fcetal  surface  is  smooth,  being  covered  by  the 
amnion,  and  slightly  concave.  The  weight  of  the  fully  developed  placenta  averages 
about  500  grammes. 

The  position  of  the  placenta  is  determined,  evidently,  by  the  point  at  which  the 
ovum  forms  its  attachment  with  the  maternal  tissues  ;  in  the  majority  of  cases  this 
location  is  at  the  fundus  of  the  uterus  in  the  vicinity  of  the  oviduct,  right  or  left, 
the  orifice  of  which  becomes  occluded  by  the  expansion  of  the  placental  structures. 
Less  frequently  the  placenta  occupies  the  more  dependent  portions  of  the  uterine 
wall  and,  in  exceptional  cases,  its  position  is  in  the  immediate  vicinity  of  the  internal 
mouth  of  the  uterus  ;  in  these  latter  cases  the  placenta  may  partially,  or  even  com- 
pletely, grow  over  the  latter  opening,  thus  constituting  the  grave  condition  known  as 
placenta  prsevia.  The  general  constitution  of  the  placenta  (Fig.  59),  as  consisting 


Uterine  blood-vessels 


FIG.  59. 

Maternal  blood-spaces 


Foetal  villi 


Umbilical  vesicle 


Decidua  placentalis 


Allantois 


Decidua  capsularis 


Amnion 


Chorion 


Decidua  vera 


Intcrdecidual  space 


Amniotic  sac 


Diagram  illustrating  the  relations  of  the  fcetus,  the  membranes,  and  the  uterus  during  the  early  months  of 

pregnancy. 

of  the  fcetal  and  the  maternal  portions,  has  already  been  sketched  ;  it  now  remains 
consider  briefly  the  arrangement  of  these  structures. 

The  foetal  portion  of  the  placenta,  the  contribution  of  the  chorion  frondosum, 
soon  becomes  a  mass  of  richly  branching  villi,  the  more  robust  main  stalks  of  which 
are  attached  to  the  maternal  tissue,  while  the  smaller  secondary  ramifications  are 
free,  completely  surrounded  by  the  contents  of  the  maternal  blood-sinuses  in  which 
they  float.  In  all  cases  the  villous  processes  support  the  terminal  loops  of  the  fcetal 
blood-vessels,  the  blood  being  conveyed  to  and  from  the  placenta,  along  the  umbil- 
ical cord,  by  the  umbilical  arteries  and  vein.  Although  coming  into  close  relation, 
the  syncytium  and  the  meagre  connective  tissue  surrounding  the  fcetal  capillaries 
alone  intervening,  the  blood-streams  of  the  mother  and  of  the  child  never  actually 
mingle  ;  the  delicate  septum,  however,  allows  the  free  interchange  of  gases  necessary 
for  the  respiratory  function  as  well  as  the  passage  of  nutritive  substances  into  the 
fcetal  circulation. 


THE   PLACENTA. 


The  maternal  portion  of  the  placenta  is  contributed  by  that  portion  of  the  uterine 
mucous  membrane  known  as  the  decidua  serotina  ;  its  especial  peculiarities  consist 
in  the  intervillous  blood-spaces,  which  may  be  regarded  as  derivations  from  the 
eroded  maternal  blood-vessels.  As  already  described,  the  trophoblast  and  maternal 
tissues  early  come  into  close  relation,  and  the  capillary  blood-vessels  are  opened  by 
the  invasion  of  the  foetal  tissue,  which  latter,  in  turn,  is  eroded  and  channelled  out 
by  the  maternal  blood  which  escapes  upon  the  rupture  of  the  blood-vessels  of  the 
mucosa.  The  extension  of  the  blood-spaces  thus  originating  constitutes  the  elaborate 
system  of  vascular  lacunae,  or  intervillous  spaces,  forming  so  conspicuous  a  part  of 
the  fully  developed  placenta. 

In  its  earlier  changes  the  decidua  serotina  closely  resembles  the  decidua  vera, 
presenting  an  inner  compact  and  an  outer  spongy  layer  ;  by  the  middle  of  preg- 
nancy, however,  the  previously  enlarged  glands  have  entirely  disappeared  in  conse- 
quence of  the  atrophy  induced  by  the  increasing  pressure  caused  by  the  augmenting 
volume  of  the  uterine  contents.  When  the  placenta  is  detached  from  the  uterus  the 

FIG.  60. 

Stump  of  umbilical  cord 


Chorion 


Villus 


Placenta 


Placental  septum 

Decidua  serotina 
IkS^'''  ^Line  of  separation 


Spiral  branches  of  uterine  artery  Inner  limit          Arteries 

of  muscle 

Section  of  placenta  and  uterus  at  the  seventh  month.     (Ecker.) 

line  of  separation  passes  through  the  junction  of  the  former  spongy  and  compact 
layers  ;  according  to  Webster,  however,  the  separation  occurs  in  the  compact  layer. 
The  condensed  decidual  tissue  closing  in  the  vascular  lacuna,  on  the  one  hand,  and 
covering  the  surface  of  separation,  on  the  other,  constitutes  the  basal  plate.  The 
latter  is  continued  deeply  within  the  placenta  by  connective-tissue  portions,  the  septa 
placenta,  which  extend  between  the  groups  of  chorionic  villi,  forming  the  cotyledons 
visible  on  the  outer  surface  of  the  placenta  as  irregular  lobules  separated  by  deep 
furrows.  These  septa  do  not  reach  as  far  as  the  chorion  except  at  the  margin  of  the 
placenta,  where  they  form  a  thin  membranous  sheet  beneath  the, chorion,  the  subcho- 
rionic  occluding  plate  of  Waldeyer.  Large,  round,  multinucleated  elements,  the 
giant  cells,  measuring  from  .04  to  .08  millimetre  in  diameter,  are  present  within  the 
tissue  of  the  maternal  placenta,  especially  within  the  basal  plate  and  the  septa.  At 
the  margin  the  placental  tissue  becomes  directly  continuous  with  the  foetal  mem- 
branes, the  chorion  and  the  decidua  being  closely  united. 

The  numerous  branches  of  the  arteries  supplying  the  uterus  pierce  the  muscular 
tunic  and  gain  the  basal  plate  ;  here  the  arterial  vessels  lose  their  muscular  coat  and 


HI -MAX    ANATOMY. 


penetrate  the  placental  septa  as  spirally  directed  channels  of  enlarged  calibre  bounded 
by  endothelial  walls.      After  a  shorter  or  longer  course  within  the  septa,  the  arterial 


FIG.  61. 


Ainnion 


^f\ — Maternal  bloml 
fr- — Basal  plate 

~-~       Torn  surface  at  line  of 

Reparation 

1 


Si-ctimi  of  liuinan  placenta  at  end  of  pregnancy.     X  it.     The  foetal  blood-vessels  have  Keen  injected  ;  the  materna 
mood  span  s  appear  as  clear  areas  surrounding  the  sections  of  the  fcetal  villi. 


trunks  open  directly  into  the  intervillous  or  intraplaccntal  blood-spaces  which  are 
limited  by  the  chorion  and  the  villi  on  the  one  side  and  by  the  septa  and  basal  plate 


THE    UMBILICAL   CORD. 


53 


on  the  other.  Maternal  capillaries  are  wanting  within  the  placenta,  since  they  have 
become  early  replaced  by  the  intervillous  lacunae.  The  maternal  blood  is  carried 
away  from  these  spaces  by  wide  venous  channels  which  pass  directly  from  the  lacunae 
through  the  placental  septa  into  the  basal  plate,  where  they  form  net-works  from  which 
proceed  the  larger  venous  trunks.  At  the  edge  of  the  placenta  the  anastomosing  cav- 
ernous spaces  form  an  annular  series  of  intercommunicating  venous  channels  known 
collectively  as  the  marginal  sinus ,  into  which  empty  numerous  placental  veins,  on  the 
one  hand,  and  from  which,  on  the  other,  pass  tributaries  to  the  larger  veins  of  the 
uterus. 

FIG.  62. 


Umbilical  vein 


Umbilical  arteries ~—  ~ 


Corrosion  preparation  of  human  placenta,  showing  general  grouping  of  foetal  vessels  into  lobules. 

The  Umbilical  Cord. — The  umbilical  cord,  or  funiculus  umbilicalis,  which 
connects  the  body  of  the  fcetus  with  the  placenta,  thereby  conveying  the  foetal  blood 
to  and  from  the  respiratory  and  nutritive  apparatus,  is  formed  in  consequence 
of  the  fusion  of  three  originally  distinct  structures, — the  belly-stalk,  the  vitelline 
stalk,  and  the  amnion.  The  first  of  these,  in  addition  to  forming  the  early  attach- 
ment of  the  fcetus  to  the  chorion,  supports  the  rudimentary  allantoic  canal  and  the 
allantoic,  later  umbilical,  blood-vessels.  The  vitelline  stalk  encloses  the  diminish- 
ing vitelline  duct  and  the  remains  of  the  vitelline  blood-vessels,  while  surrounding 
these  stalks  the  amniotic  sheath  gradually  becomes  more  closely  applied.  These 


54 


HUMAN   ANATOMY. 


FIG.  63. 


Umbilical  vein 


three  constituents  of  the  cord  lie  embedded  within  the  delicate  stroma  formed  by 
the  gelatinous  connective  tissue,  \hz  jelly  of  Wharton,  surrounded  externally  by  the 
common  amniotic  investment. 

The  details  of  the  cord  must  necessarily  vary  with  the  period  of  gestation, 
since  the  component  structures  undergo  marked  changes.  On  section  of  the  funic- 
ulus  at  the  end  of  pregnancy,  the  following  features  may  usually  be  distinguished  : 

(1)  The  amniotic  sheath,  which  is  closely  united  with  the  underlying  connective 
tissue,  except  for  a  short  distance  beyond  the  umbilical  opening,  at  which  point  the 
amnion  may  be  separated  as  a  distinct  layer. 

(2)  The  jelly  of  Wharton  forms  the  common  ground-substance  in  which  the 
remaining  constituents  of  the  cord  lie  embedded.      This  tissue  corresponds  to  the 
mucoid  type,  and  contains  a  generous  distribution  of  stellate  connective-tissue  cells 
which  form  a  reticulum  by  their  anastomosing  processes. 

(3)  The  umbilical  blood-vessels — two  arteries  and  one  vein — are  the  most  con- 
spicuous components  of  the  cord,  since  their  size  increases  with  the  demands  made  by 
the  growing  foetus.    The  markedly  tortuous  umbilical  arteries  usually  entwine  the  single 
umbilical  vein  and  slightly  increase  in  lumen  in  their  progress  towards  the  placenta, 
in  the  immediate  vicinity  of  which   an  anastomosis  very  constantly  is  to  be  found. 
Seldom  in  man,  but  always  in  certain  mammals,  as  the  mouse,  the  umbilical  artery  is 
single.     According  to  His,  even  the  youngest  human  cords  possess  only  a  single 

umbilical  vein,  except  in  the  immediate  vi- 
cinity of  the  placenta  ;  again,  on  entering 
the  body  of  the  foetus  the  single  vessel  is 
represented  by  two  umbilical  veins  which, 
for  a  time,  course  within  the  abdominal 
wall.  The  right  vein,  however,  soon  un- 
dergoes atrophy,  while  the  left  takes  part 
in  the  formation  of  the  hepatic  circulation. 
Valves  have  been  described  within  the  um- 
bilical vein.  The  latter  shares  with  the 
pulmonary  vein  the  distinction  of  conveying 
blood  which  has  been  oxygenated  by  respi- 
ratory function. 

(4)  The  allantoic  duct,   as 
canal,   is  usually  obliterated   by 
month   of    foetal    life  ;    at    birth, 
atrophic   remains,   consisting  of 
column  of  epithelial  cells  situated  between  the  umbilical  blood-vessels,  are  seen  in 
sections  of  the  cord  taken  from  the  vicinity  of  the  navel. 

The  stalk  of  the  vitelline  sac,  or  umbilical  vesicle,  enclosing  the  vitelline  duct 
and  supporting  the  vitelline,  or  omphalomesenteric,  blood-vessels,  is  still  present 
during  the  second  month  ;  at  this  period  it  lies  within  the  extension  of  the  ccelom, 
which  is  continued  into  the  young  cord.  With  the  early  disappearance  of  this  spare 
the  vitelline  stalk  and  the  associated  structures  disappear,  and  by  the  end  of  IM -sta- 
tion usually  all  traces  of  these  structures  have  vanished  from  the  cord.  The  most 
conspicuous  details  of  the  umbilical  cord  at  birth,  therefore,  are  the  three  umbilical 
vessels,  embedded  within  the  gelatinous  connective  tissue  and  invested  by  the  shea 
of  amnion. 

The  human  umbilical  cord  is  conspicuous  on  account  of  its  exceptional  lengt 
which  averages  from  fifty  to  sixty  centimetres,  while  measuring  only  about  twelve 
millimetres  in  thickness.  The  extremes  of  length  include  a  wide  range,  varying  from 
twelve  to  160  centimetres  (four  and  three-quarters  to  sixty-three  inch' 

The  cord  almost  constantly  exhibits  a  torsion,  the  spirals  passing  from  left  to 
right  when  traced  towards  the  placenta.  In  addition  to  the  general  twisting  of  the 
cord,  which  begins  towards  the  close  of  the  second  month,  the  umbilical  arteries 
display  even  more  marked  spiral  windings,  usually  enclosing  the  somewhat  less 
twisted  umbilical  vein.  The  cause  of  this  conspicuous  torsion  is  probably  to  be 
sought  in  the  spiral  growth  of  the  umbilical  blood-vessels,  the  twisting  of  the  con 
as  well  as  the  revolutions  of  the  foetus,  being  secondary. 


Remains  of  vitelline 

duct  and  vessels 
Umbilical  artery 

Transverse  section  of  umbilical  cord  of  third  month. 
X  12. 


a  distinct 
the  third 
however, 
a  narrow 


a  i 

: 


THE   AFTER-BIRTH. 


55 


While  the  attachment  of  the  cord  usually  is  situated  near  the  middle  of  the 
placenta,  it  is  seldom  exactly  central  ;  the  insertion  is  subject  to  great  variation, 
however,  the  eccentricity  sometimes  being  so  great  that  the  cord  is  fixed  to  the 
periphery  of  the  placenta,  such  disposition  constituting  insertio  marginalis.  Among 
the  more  exceptional  variations  in  the  arrangement  of  the  cord  are  the  cleft  and  the 
extraplacental  attachment  known  respectively  as  insertio  furcata  and  insertio  vela- 
mentosa.  In  the  former  condition,  where  the  cord  divides  before  reaching  the  pla- 
centa, each  limb  conveys  one  of  the  umbilical  arteries  and  a  branch  of  the  umbilical 
When  the  insertion  of  the 


FIG.  64. 


Artery 


Artery 


Vein 


Transverse  section  ot  umbilical  cord  at  end  of  pregnancy, 
taken  from  placental  end;  the  umbilical  blood-vessels  are  em- 
bedded within  the  embryonal  connective  tissue.  X  10. 


vein. 

cord  is  into  the  chorion  entirely 
outside  the  placental  area,  in  ex- 
ceptional cases  being  as  far  re- 
moved as  the  opposite  pole  of  the 
membranous  capsule,  the  umbilical 
vessels  course  within  the  non-vil- 
lous  portions  of  the  chorion  until 
they  reach  the  fcetal  placenta.  In 
addition  to  the  true  knots,  which 
often  occur  and  are  due  to  the 
excursions  of  the  foetus,  the  um- 
bilical cord  sometimes  presents 
nodular  thickenings  and  irregular 
constrictions,  as  well  as  projections 
formed  by  loops  and  varicosities  of 
the  blood-vessels. 

The  After-Birth.— The  ex- 
pulsion of  the  child  through  the 
rupture  in  the  enveloping  mem- 
branes, which  is  produced  by  the 
powerful  contractions  of  the  uterine 

muscle  at  the  close  of  pregnancy,  is  followed,  after  a  short  interval,  by  the  separa- 
tion and  expulsion  of  the  "after-birth  ;"  under  this  term  are  included  the  placenta 
and  the  enveloping  membranes.  The  latter,  as  will  be  understood  from  the  fore- 
going consideration  of  the  encapsulation  of  the  foetus,  consist  of  three  chief  constit- 
uents,— the  remains  of  the  decidua  vera,  the  chorion,  and  the  amnion  ;  the  reflexa 
undergoes  complete  absorption.  Since  the  decidua  represents  the  shed  portion  of 
the  modified  uterine  mucosa,  the  outer  surface  of  the  after-birth  appears  rough  and 
studded  with  shreds  of  uterine  tissue  ;  the  inner  surface  of  the  decidua  is  so  closely 

fused  with  the  adjacent  cho- 

FIG.  65.  rion  by  means   of   delicate 

connective  tissue  that  only 
a  limited  and  uncertain 
separation  is  possible.  The 
amnion,  on  the  other  hand, 
although  attached  to  the 
chorion  by  bands  of  connec- 
tive tissue,  may  be  peeled 
off  the  chorion  with  relative 
ease,  since  the  union  be- 
tween the  tw^o  membranes  is  never  firm.  The  inner  ectoblastic  surface  of  the 
amnion  in  contact  with  the  foetus  is  smooth  and  bathed  in  the  liquor  amnii.  The 
external  and  unshed  portion  of  the  modified  uterine  mucosa  contains  the  incon- 
spicuous remains  of  the  epithelium  lining  the  fundus  of  the  glands  :  these  elements 
are  of  the  utmost  importance  for  the  regeneration  of  the  glandular  and  epithelial 
tissues  of  the  new  uterine  mucous  membrane,  since  the  'reparation  of  these  struc- 
tures, which  is  effected  within  a  few  weeks  after  labor,  begins  in  the  proliferation  of 
the  deeper  glandular  epithelium,  which  remains  throughout  pregnancy  as  the  latent 
source  of  subsequent  repair. 


Amnion 
Chorion 

Decidua 
Remains  of 
uterine  glands 

Uterine  muscle 


Section  through  foetal  membranes  and  uterus  at  end  of  pregnancy. 
(After  Leopold.) 


HUMAN   ANATOMY. 


DEVELOPMENT   OF   THE   GENERAL    BODY-FORM. 

In  considering  the  evolution  of  the  external  form  of  the  human  product  of  con- 
ception, it  is  convenient  to  recognize  the  three  developmental  epochs  suggested  by 
His, — the  stage  of  the  ovum,  the  stage  of  the  embryo,  and  the  stage  of  the  foetus. 

The  Stage  of  the  Blastodermic  Vesicle. — This  stage,  or  the  stage  of  the 
ovum,  embraces  the  first  two  weeks  of  intra-uterine  life,  during  which  the  initial  phases 
of  development,  including  fertilization,  segmentation,  and  the  formation  of  the  blasto- 

FIG.  66. 


Villous  chorion 


Embryo 
with  amnion 


— :J — Umbilical  vesi- 
cle; blood- 
islands  appear- 
ing 


Early  human  embryonic  vesicle  of  about  thirteen  days  laid  open,  showing  the  young  embryo  (.37  millimetre 
long)  attached  to  the  wall  of  the  serosa  by  means  of  the  belly-stalk.     X  25.     (After  Spee.) 

dermic  vesicle,  are  completed,  and  the  fundamental  processes  resulting  in  the  differ- 
entiation of  the  medullary  tube,  the  notochord,  the  somites,  and  the  mesoblastic  plates 
are  begun.  The  early  details  of  many  of  these  processes  have  never  been  observed 
in  man,  but  there  is  little  reason  to  doubt  that  in  its  essential  features  the  early  human 
embryo  closely  follows  the  changes  directly  observed  in  other  mammals. 

The  Stage  of  the  Embryo.  —  The  stage  of  the  embryo,  from  the  second  to 

the   fifth   week,    is   distin- 

FIG.  67.  guished  by  the  formation  of 

organs  essentially  embry- 
onic and  transient  in  char- 
acter, as  the  somites,  the 
notochord,  the  Wolffi 
body,  and  the  visce 
arches. 

The  earliest  phase 
the  differentiation  of  th 
vertebrate  body-form  con- 
sists in  the  establishment  of 
a  dorsal  tube  by  the  appo- 
sition and  fusion  of  the  ectoblastic  medullary  folds,  and  a  ventral  tube  by  the  approxi- 
mation and  final  union  of  the  folds  directly  derived  from  the  somatopleura.  The 
dorsal,  or  animal,  tube  represents  the  early  neural  canal,  and  becomes  the  great 
cerebro-spinal  nervous  axis  ;  the  ventral,  or  rcgctntirc,  tube,  formed  by  the  ventral 
extension  and  approximation  of  the  somatopleura,  constitutes  the  body-cavity,  and 
encloses  the  primary  gut  and  the  associated  thoracic  and  abdominal  viscera,  and  the 
vascular  system.  The  primitive  gut-tube  originates  by  the  delimitation  of  a  part  of 


Mesoblast 


Belly-stalk 


antoic  duct 


•iilnlif.il  sac 
Section  of  preceding  embryonic  vesicle  and  embryo.     X  25.     (After  Spef.) 


THE   EARLY    HUMAN    EMBRYO. 


57 


the  vitelline  sac  accomplished  by  the  ventral  approximation  of  the  splanchnopleura, 

and  for  a  time  maintains  a  wide  communication  with  the  remains  of  the  yolk-cavity. 

The  early  embryo,  lying  flatly  expanded  upon  the  blastodermic  vesicle,  becomes 

differentiated  in  form  by  the  appearance  of  head-  and  tail-grooves,  in  consequence  of 


is 

v  >, 

II 


which  constriction  the  cephalic  and  the  caudal  poles  of  the  body  become  denned  and 
partially  separated  from  the  embryonal  area  ;  the  middle  segment,  however,  em- 
bracing the  widely  open  gut-tract,  for  a  time  remains  closely  blended  with  the  vitel- 
line sac,  of  which,  at  first,  the  embryo  appears  as  an  appendage  (Fig.  68,  i  and  2). 


HUMAN   ANATOMY. 


The  more  complete  differentiation  of  the  digestive  tube  and  the  ventral  folding  in  of 
the  body-walls  change  this  relation,  the  rapidly  decreasing  umbilical  vesicle  soon 
becoming  secondary  to  the  embryo. 

At  the  close  of  the  stage  of  the  vesicle — about  the  fifteenth  day — the  human 
embryo  possesses  a  general  cylindrical  body-form,  the  dilated  cephalic  pole  being 
free,  while  the  belly-stalk  attaches  the  caudal  segment  to  the  chorion  ;  the  amniotic 
sac  invests  the  dorsal  aspect,  the  large  umbilical  vesicle  occupying  the  greater  part 

of  the  ventral  surface.      Human 
FIG.  69. 

Otic  vesicle  Second  visceral  arch 

X 


Cephalic  flexure 

Optic 
Maxillary  process 


•4 


-Third  visceral 
arch 

Fourth  visceral 
arch 

Heart 


Upper  limb-bud 


Mandibular  process  —  ' 
of  first  visceral  arch 

Caudal  end  ot  — 

embryo 

Umbilical  cord  in 
section 

Lower  limb-bud 


Human  embryo  of  about  twenty-three  days,  drawn  from  the  model 
of  His.    X  10. 


FIG.  70. 

Otic  vesicle 


embryos  of  the  fourteenth  and 
fifteenth  days  (Fig.  68,  3  and  4) 
are  distinguished  by  a  conspicu- 
ous flexure  opposite  the  attach- 
ment of  the  umbilical  vesicle,  the 
convexity  being  directed  ven- 
trally,  the  deep  corresponding 
concavity  producing  a  marked 
change  of  profile  in  the  dorsal 
outline.  During  these  changes 
the  expansion  of  the  cerebral 
segments  outlines  the  three  pri- 
mary divisions  of  the  cephalic 
portion  of  the  neural  tube,  the 
anterior,  the  middle,  and  the 
posterior  brain-vesicles. 
A  little  later  a  series  of  conspicuous  bars,  the  visceral  arches,  appears  as  ob- 
liquely directed  parallel  ridges  on  either  side  of  the  head,  immediately  above  the 
prominent  heart-tube,  which  is  now  undergoing  marked  torsion.  By  the  nineteenth 
day  the  dorsal  concavity,  which  is  peculiar  to  the  human  embryo,  has  entirely  disap- 
peared, the  profile  of  this  part  of  the  embryo  presenting  a  gentle  convexity  ;  the 
cephalic  axis,  however,  exhibits  a  marked  bend,  the  cephalic  flexure,  in  the  vicinity 
of  the  middle  cerebral  vesi- 
cle, in  consequence  of  which 
the  axis  of  the  anterior  cere- 
bral segment  lies  almost  at 
right  angles  to  that  of  the 
middle  vesicle.  The  com- 

...  r     .v        ii  •    j  i  Cephalic  flexure 

pletion  of  the  third  week 
finds  the  characteristic  de- 
tails of  the  cephalic  end  of 
the  embryo,  the  cerebral, 
the  optic,  and  the  otic  vesi- 
cles, and  the  visceral  arches 
and  intervening  furrows  well 
advanced,  with  correspond- 
ing definition  of  the  primitive 
heart  and  the  umbilical  stalk 
and  vesicle.  The  limb-buds 
usually  appear  about  this 
time,  those  of  the  upper  ex- 
tremity slightly  preceding 
those  of  the  lower. 

The  period  between  the 

twenty-first  and  the  twenty-third  days  witnesses  remarkable  changes  in  the  gener 
appearance  of  the  embryo  ;  in  addition  to  greater  prominence  of  the  visceral  arches, 
the  cerebral  segments,  and  the  limb-buds,  the  embryonic-  axis,  which,  with  the 
exceptions  already  noted,  up  to  this  time  is  only  slightly  curved,  now  undergoes 
flexion  to  such  extent  that  by  the  twenty-third  day  the  overlapping  cephalic  and 
caudal  ends  of  the  embryo  are  in  close  apposition,  the  body-axis  describing  ratu 
more  than  a  complete  circle  (Fig.  69). 


Optic  vesicle 

Mandibular  process 

of  first  visceral  arch 

Olfactory  pit 


Umbilical  cord- 


Lower  limb-bud' 


Cervical  flexure 

Second  visceral  arch 

Third  visceral  arch 
•Fourth  visceral  arch 


—  Heart 


'pper  limb-bud 


:• 


Human  embryo  of  about  twenty-live  days,  drawn  from  the  model  of 
X  10. 


THE   VISCERAL   ARCHES   AND    FURROWS. 


59 


From  the  twenty-third  to  the  twenty- eighth  day  the  excessive  flexion  gradually 
disappears,  owing  to  the  increased  volume  of  the  heart  and  the  growth  of  the  head, 
and  by  the  end  of  the  fourth  week  the  embryo  has  acquired  the  most  characteristic 
development  of  the  embryonic  stage  (Fig.  71).  The  reduction  in  the  curvature 
of  the  body-axis  and  the  consequent  separation  of  its  poles  and  the  raising  of  the  head 
are  accompanied  by  the  appearance  of  four  well-marked  axial  flexions,  the  cephalic, 
the  cervical,  the  dorsal,  and  the  sacral  flexures  (Fig.  71).  The  first  of  these,  the 
cephalic,  is  an  accentuation  of  the  primary  flexure,  which  is  seen  as  early  as  the 
eighteenth  day,  and  is  indicated  by  the  projection  of  the  midbrain  ;  it  corresponds 
in  position  to  the  future  sella  turcica.  The  second  and  very  conspicuous  bend,  the 
cervical  flexure,  marks  the  caudal  limit  of  the  cephalic  portion  of  the  neural  axis, 
and  agrees  in  position  with  the  subsequent  upper  cervical  region.  The  dorsal  and 
sacral  flexures  are  less  well  defined,  the  former  being  situated  opposite  the  upper 
limb-bud,  where  the  cervical  and  dorsal  series  of  somites  join,  the  latter,  near  the 
lower  limb-bud,  corresponding  with  the  junction  of  the  lumbar  and  sacral  somites. 
The  cephalic  segment  at  this  stage  presents  numerous  prominent  details,  the 


FIG.  71. 


Cervical  flexure 


Otic  vesicl 


Maxillary  process  of  first-- 
visceral arch 


Cephalic  flexure-l|. 
Eye--5 
Olfactory  pit 
Umbilical  cord 

Lower  limb 


Third  visceral  arch 

First  external  visceral  furrow 


Second  visceral  arch 

Mandibular  process  of  first 
visceral  arch 

"Dorsal  flexure 
"Upper  limb 

Heart 


Sacral  flexure 
Human  embryo  of  about  twenty-eight  days,  drawn  from  the  model  of  His.     X  10. 

secondary  cerebral  vesicles,  the  forebrain,  the  interbrain,  the  midbrain,  the  hind- 
brain,  and  the  after-brain,  the  visceral  arches  and  furrows,  the  optic  and  otic  vesicles, 
the  olfactory  pits,  and  the  primitive  oral  cavity  all  being  conspicuous.  The  heart  ap- 
pears as  a  large  protrusion,  occupying  the  upper  half  of  the  ventral  body-wall,  on 
which  the  primary  auricular  and  ventricular  divisions  are  distinguishable.  The  somites 
form  a  conspicuous  longitudinal  series  of  paraxial  quadrate  areas,  about  thirty-seven 
in  number  ;  they  correspond  to  the  intervertebral  muscles,  and  may  be  grouped  to 
accord  with  the  primary  spinal  nerves,  being,  therefore,  distinguished  as  eight  cer- 
vical, twelve  dorsal,  five  lumbar,  five  sacral,  and  five  or  more  coccygeal  somites. 

THE   VISCERAL   ARCHES   AND    FURROWS. 

Since  the  visceral  arches  are  best  developed  in  the  human  embryo  during  the 
last  half  of  the  third  week,  a  brief  consideration  of  these  structures  in  this  place  is 
appropriate.  The  visceral  arches  in  mammalian  embryos  constitute  a  series  of  five 
parallel  bars  separated  by  intervening  furrows,  obliquely  placed  on  the  ventro-lateral 
aspect  of  the  cephalic  segment,  occupying  the  region  which  later  becomes  the 
neck.  They  represent,  in  rudimentary  development,  the  important  branchial  or  gill- 


6o  HUMAN    ANATOMY. 

apparatus  of  water-breathing  vertebrates,  in  which  the  respiratory  function  is  per- 
formed by  means  of  the  rich  vascular  fringes  lining  the  clefts  through  which 
the  water  passes,  thus  permitting  the  exchange  between  the  oxygen  of  the  water 
and  the  carbon  dioxide  of  the  blood.  Each  arch  is  supplied  by  a  blood-vessel,  or 
aortic  bow,  which  passes  from  the  main  ventral  stem,  the  truncus  arteriosus,  through 
the  substance  of  the  visceral  arch  backward  to  unite  with  the  similar  bows  to  form 
the  dorsal  aortce.  In  aquatic  vertebrates  the  aortic  bows  supply  an  elaborate  system 
of  secondary  branchial  twigs,  which  form  rich  capillary  plexuses  within  the  gills  ;  in 
air-breathing  vertebrates,  however,  in  which  these  structures  are  only  rudimen- 
tary, the  main  stems,  the  aortic  bows,  are  alone  represented.  With  the  loss  of  func- 
tion which  follows  the  acquisition  of  aerial  respiration  in  the  higher  vertebrates,  the 
number  of  visceral  arches  is  reduced  from  six,  or  even  seven,  as  seen  in  fishes,  to 
five,  the  fifth  arch  in  man,  however,  being  so  blended  with  the  surrounding  struc- 
tures that  it  is  not  visible  externally  as  a  distinct  bar.  In  their  condition  of  great- 
est perfection,  as  in  fishes,  each  visceral  arch  contributes  an  osseous  bar,  whicli 
forms  part  of  the  branchial  skeleton  ;  these  bony  bars  are  represented  in  man  and 
mammals  by  cartilaginous  rods,  which  temporarily  occupy  the  upper  arches,  for  the 
most  part  entirely  disappearing.  When  viewed  in  frontal  section  (Fig.  73),  the 
mammalian  visceral  arches  are  seen  as  mesodermic  cylinders  imperfectly  separated 
by  external  and  internal  grooves,  the  visceral  furrows  and  the  pharyngeal  pouches 
respectively  ;  this  arrangement  emphasizes  another  modification  following  loss  of 
function, — namely,  the  conversion  of  the  true  visceral  clefts  of  the  lower  forms  into 

furrows, — since  in  man  and  mammals  the 

FIG.  72.  fissures  are  closed  by  the  occluding  mem- 

brane formed  by  the  apposition  of  the 
ectoblast  and  the  entoblast  at  the  bottom 
of  the  outer  and  inner  furrows. 

The  First  or  Mandibular  Arch 
c       ,  early  becomes  differentiated  into  a  short 

Second  arch  '  , 

Third  arch       upper  or  maxillary  process  and  a  longer 

lower  or  mandibular  process.  The  maxil- 
lary process,  in  conjunction  with  its  fellow 
of  the  opposite  side  and  the  fronto-nasal 

Head  of  human  embryo  of  about  twenty-one  days,        />»vwcf    whirri  rlp^rprulu  a<s  a  mprliin  nro- 
seen  from  the  side,  showing  visceral  arches  and  external       process    Will 

visceral  furrows,    x  20.    (After  His.)  jection  from  the  head  (rig.  75),  contnb- 

utes  the  tissue  from  which  the  superior 

and  lateral  boundaries  of  the  oral  cavity  and  the  nasal  region  are  derived.  The 
mandibular  process  joins  with  its  mate  in  the  mid-line  and  gives  rise  to  the  lower 
jaw  and  other  tissues  forming  the  inferior  boundary  of  the  primary  oral  cavity.  The 
latter  in  its  original  condition  appears  as  a  widely  open  space  leading  into  the  primi- 
tive pharyngeal  cavity  ;  later  the  septum  is  formed  which  divides  the  oral  from  the 
nasal  cavity.  The  mandibular  process  contains  a  cartilaginous  rod,  which  for  a 
time  represents  the  corresponding  bony  arch  of  the  visceral  skeleton  of  lower  types. 
The  ventral  and  larger  part  of  this  rod,  known  as  Meckel s  cartilage,  entirely  disap- 
pears, the  lower  jaw  being  developed  independently  around  this  bar  of  cartilage  : 
the  upper  end  of  the  cartilaginous  bar,  however,  persists  and  forms  two  of  the  ear- 
ossicles,  the  malleus  and  the  incus. 

The  Second  or  Hyoid  Arch  also  contains  a  cartilaginous  bar,  from  the  ven- 
tral segment  of  which  (known  as  the  cartilage  of  Rcichcrt )  is  derived  the  smaller 
cornu  of  the  hyoid  bone  ;  the  dorsal  end  of  the  bar,  which  is  fused  with  the  tem- 
poral bone,  gives  rise  to  the  styloid  process,  the  intervening  portion  of  the  cartilage 
persisting  as  the  stylo-hyoid  ligament.  The  cartilage  of  the  second  arch  is  also  con- 
cerned in  the  formation  of  the  stapes.  The  origin  of  this  car-ossicle  is  double,  since 
the  crura  of  the  stapes  are  derived  from  the  cartilage  of  the  hyoid  arch,  while-  the 
base  is  contributed  by  the  general  cartilaginous  capsule  of  the  labyrinth.  The  char- 
acteristic form  of  the  stapes  is  secondary  and  due  to  the  perforation  of  the  triangu- 
lar plate,  the  early  representative  of  this  bom-,  which  thus  acquires  its  characteristic 
stirrup-shape  in  consequence  of  the  penetration  of  a  minute  blood-vessel,  the  perfo- 
rating stapcdial  artery,  a  branch  of  the  internal  carotid,  which  later  disappears. 


THE    VISCERAL    ARCHES.  61 

The  Third  or  First  Branchial  Arch  contains  a  rudimentary  cartilaginous 
bar  from  which  the  body  and  the  greater  cornu  of  the  hyoid  bone  are  derived.  The 
fourth  and  fifth  arches,  or  second  and  third  branchial,  in  man  are  devoid  of 
skeletal  bars  and  rapidly  become  blended  with  the  surrounding  parts,  soon  losing 
their  identity  as  distinct  arches. 

The  External  Visceral  Furrows  (Fig.  73),  the  representatives  of  the  true 
clefts  of  the  lower  types,  appear  with  decreasing  distinctness  from  the  first  towards  the 
fourth  ;  the  third  and  fourth  early  suffer  modification,  so  that  by  the  twenty-eighth 
day  the  first  and  second  furrows  alone  are  clearly  defined. 

The  First  Visceral  Furrow,  the  hyomandibular  cleft,  undergoes  obliteration 
except  at  its  dorsal  part,  which  becomes  converted  into  the  external  auditory  meatus. 
the  surrounding  tissue  giving  rise  to  the  walls  of  the  canal  and  the  external  ear.  The 
remaining  clefts  gradually  disappear,  becoming  closed  and  covered  in  by  the  over- 
hanging corresponding  arches  ;  this  relation  is  particularly  marked  towards  the 


FIG.  73. 


Optic  vesicle 


Maxillary  process 


Dorsal  wall  of  primitive 
oropharynx 


Primitive  oesophagus 
Upper  end  of  body-cavity 


Right  umbilical  vein ^      lfc\W\  &     f)Ti>     ^  J M      Primitive  aortse 

"Neural  tube 

Upper  half  of  human  embryo  of  about  eighteen  days,  drawn  from  His's  models.  X  45.  A,  dorsal  wall  of  primitive 
oropharynx  bounded  by  visceral  arches,  external  and  internal  furrows.  B,  anterior  wall  of  primitive  oropharynx, 
seen  from  behind.  1-5,  sections  of  aortic  arches;  I-IV,  external  visceral  furrows. 

caudal  end  of  the  series,  where  the  sinking  in  of  the  arches  and  the  included  furrows 
produces  a  depression  or  fossa — the  sinus  pracervicalis  of  His — in  the  lower  and  lateral 
part  of  the  future  neck  region.  This  recess  subsequently  entirely  disappears  on 
coalescence  of  the  bordering  parts  ;  sometimes,  however,  such  union  is  defective, 
the  imperfect  closure  resulting  in  a  permanent  fissure  situated  at  the  side  of  the  neck, 
known  as  cervical  fistula,  by  means  of  which  communication  is  often  established 
between  the  pharynx  and  the  exterior  of  the  body.  Such  communication  must, 
however,  be  regarded  as  secondary,  as  originally  the  external  furrows  were  sepa- 
rated from  the  primitive  pharyngeal  cavity  by  the  delicate  epithelial  septum  already 
mentioned  as  the  occluding  plate.  Where  entrance  into  the  pharynx  through  the 
fistula  is  possible,  it  is  probable  that  the  septum  has  been  destroyed  as  the  result 
of  absorption  or  of  mechanical  disturbance  following  the  use  of  the  probe. 

The  Inner  Visceral  Furrows,  or  pharyngeal  pouches,  repeat  the  general 
arrangement  of  the  external  furrows.  The  first  pharyngeal  pouch  becomes 
narrowed  and  elongated,  and  eventually  forms  the  Eustachian  tube  ;  a  secondary 


62 


HUMAN   ANATOMY. 


FIG.  74. 


Fronto-nasal 
process 


Primitive 
oral  cavity 


lesial  nasal  process 
Maxillary  process 
Mandibular  process 


Head  of  human  embryo  of  about  twenty-seven  days, 
showing  boundaries  ot  primitive  oral  cavity.  X  7. 
(After  His.) 


dorsal  expansion  gives  rise  to  the  middle  ear,  while  the  occluding  plate  separating 
the  outer  and  inner  furrows  supplies  the  tissue  from  which  the  tympanic  membrane  is 
formed.  The  second  furrow  partially  disappears  without  giving  origin  to  perma- 
nent structures  ;  its  upper  part,  however,  is  probably  represented  by  the  fossa  of 
Rosenmiiller,  which  lies,  on  each  side,  as  a  lateral  recess  in  the  pharynx.  The  third 
and  fourth  pouches  give  rise  to  ventral  entoblastic  outgrowths  from  which  the 
epithelial  portions  of  the  thymus  and  of  the  thyroid  body  are  developed  respectively. 
The  last-named  organ  has  an  additional  unpaired  origin  from  the  entoblast  forming 
the  ventral  wall  of  the  pharynx  in  the  vicinity  of  the  second  visceral  arch. 

The  Development  of  the  Face 
and  the  Oral  Cavity. — The  earliest 
suggestion  of  the  primitive  oral  cavity  is 
the  depression,  or  stomodccum,  which  ap- 
Laterai  nasal  process  pears  about  the  thirteenth  day  on  the 
ventral  surface  of  the  cephalic  end  of  the 
embryo  immediately  beneath  the  ex- 
panded anterior  cerebral  vesicle.  Tire 
oral  pit  at  first  is  separated  from  the  ad- 
jacent expanded  upper  end  of  the  head- 
gut  by  the  delicate  septum,  the  pharyn- 
geal  membrane,  composed  of  the  opposed 
ectoblast  and  the  entoblast,  which  in  this 
location  are  in  contact  without  the  inter- 
vention of  mesoblastic  tissue.  With  the  rupture  of  the  pharyngeal  membrane,  the 
deepened  oral  pit  opens  into  the  cephalic  extremity  of  the  head-gut,  now  known  as 
the  primitive  pharynx. 

The  formation  of  the  face  is  closely  associated  with  the  growth  and  fusion  of 
the  upper  visceral  arches  in  conjunction  with  the  surrounding  parts  of  the  ventral 
surface  of  the  head.  The  first  visceral  arch,  as  already  described,  presents  two 
divisions,  the  maxillary  and  the  mandibular process.  The  latter  grows  ventrally  and 
joins  in  the  mid-line  its  fellow  of  the  opposite  side,  to  form,  with  the  aid  of  the 
second  visceral  arches,  the  tissues  from  which  the  lower  boundary  and  the  floor  of 
the  mouth  are  derived.  The  upper  and 
lateral  boundaries  of  the  primitive  oral 
cavity  and  the  differentiation  of  the  nasal 
region  proceed  from  the  modification  and 
fusion  of  three  masses,  the  two  lateral 
paired  maxillary  processes  of  the  first 
visceral  arches  and  the  mesial  unpaired 
fronto-nasal process,  which  descends  as  a 
conspicuous  projection  from  the  ventral 
surface  of  the  anterior  part  of  the  head. 
The  maxillary  processes  grow  towards 
the  mid-line  and,  in  conjunction  with  the 
descending  fronto-nasal  projection,  form 
the  lateral  and  superior  boundary  of  the 
primitive  oral  cavity  (Fig.  74).  Very 
soon  the  development  of  the  future 
nares  is  suggested  by  the  appearance  of 

slight  depressions,  the  olfactory  pits,  one  on  each  side  of  the  fronto-nasal  process  : 
these  areas  constitute  part  of  the  wall  of  the  forebrain,  a  relation  which  foreshadows 
the  future  close  association  between  the  olfactory  mucous  membrane  and  the  cortex 
of  the  olfactory  lobe. 

During  the  fifth  week  the  thickened  margins  of  the  fronto-nasal  process  undergo 
differentiation  into  the  mesial  nasal  processes,  while  coincidently  the  lateral  portions 
of  the  fronto-nasal  projection  grow  downward  as  the  lateral  nasal  processes,  these 
newly  developed  projections  constituting  the  inner  and  outer  boundaries  of  the 
rapidly  deepening  nasal  pits.  The  line  of  contact  between  the  lateral  nasal  process 
and  the  maxillary  process  is  marked  by  a  superficial  furrow,  the  uaso-optic groove , 


FIG.  75. 


Lateral  nasal  process 

Maxillary  process 

First  external  vis- 

ci-ral  furrow 

Second  visceral  arch 

Third  visceral  arch 


Head  of  human  embryo  of  about  thirty-four  days. 
(After  Hit.) 


X5- 


THE   STAGE   OF   THE    FCETUS. 


which  leads  from  the  nasal  pit  to  the  angle  of  the  eye  ;  this  furrow,  however,  merely 
indicates  the  position  of  the  naso-lachrymal  duct  which  develops  independently  at  the 
bottom  of  the  primary  groove.  Reference  to  Figs.  74  and  75  emphasizes  the  fact 
that  the  nasal  pits  and  the  primitive  oral  cavity  are  for  a  time  in  widely  open  com- 
munication ;  towards  the  close  of  the  sixth  week,  however,  the  maxillary  processes 
of  the  first  arch  have  approached  the  mid-line  to  such  an  extent  that  they  unite  with 
the  lateral  margins  of  the  fronto-nasal  process  as  well  as  fuse  with  the  lateral  nasal 
processes  above.  Owing  to  this  union  of  the  three  processes,  the  nasal  pits  become 
separated  from  the  oral  cavity, 

and  with  the  appearance  and  FIG.  76. 

completion  of  the  palatal  sep- 
tum the  isolation  of  the  nasal 
fossae  from  the  mouth  is  ac- 
complished. The  lateral  nasal 

processes  contribute  the  nasal 

Naso-optic  groove 


Anlage  producing 
nasal  tip 

Nasal  groove- 


Oral  surface  of 
maxillary  process 


Dorsum  of  nose 


^-Lateral  nasal  pro- 
cess 

—Mesial  nasal  pro- 


Maxillary  process 
of  first  arch 


Roof  of  oropharynx 


Portion  of  head  of  human  embryo  of  about  thirty-four  days,  showing 
roof  ot  primitive  oral  cavity.     X  10.     {After  His.} 


FIG.  77. 


alae,  while  from  the  conjoined 
.mesial  nasal  process  are  devel- 
oped  the  nasal  septum  and  the 
bridge  of  the  nose  in  addition 
to  the  middle  portion  of  the 
upper  lip  and  the  intermaxil- 
lary segment  of  the  upper  jaw, 
the  superior  maxillary  part  of 
the  latter  being  a  derivative  of 
the  maxillary  process  of  the  first  arch.  Arrested  development  and  imperfect  union 
between  the  maxillary  processes  and  the  fronto-nasal  process  result  in  the  congenital 
defects  known  as  harelip  and  cleft  palate,  the  degree  of  the  malformation  depending 
upon  the  extent  of  the  faulty  union. 

The  Stage  of  the  Fcetus.  —  The  fifth  week  marks  the  completion  of  the 
period  of  development  during  which  the  product  of  conception  has  acquired  the 
characteristic  features  of  its  embryonal  stage  ;  beginning  with  the  second  month  and 
continuing  until  the  close  of  gestation,  the  succeeding  stage  of  the  foetus  is  distin- 
guished by  the  gradual  assumption  of  the  external  features 
which  are  peculiar  to  the  young  human  form.  In  addition  to 
the  already  mentioned  changes  affecting  the  visceral  arches 
and  frontal  process  in  the  development  of  the  face,  the  fifth 
week  witnesses  the  differentiation  of  the  limbs  into  segments, 
the  distal  division  of  the  upper  extremity  exhibiting  indica- 
tions of  the  future  fingers,  which  thus  anticipate  the  appear- 
ance of  the  toes.  The  Hver  is  already  conspicuous  as  a 
marked  protuberance  occupying  the  ventral  aspect  of  the 
trunk  immediately  below  the  heart.  The  head  by  this  time 
has  acquired  a  relatively  large  size,  the  prominent  cephalic 
flexure  which  marks  the  position  of  the  midbrain  being  par- 
ticularly conspicuous.  At  the  end  of  the  fifth  week,  or  the 
thirty-fifth  day,  the  foetus  measures  about  fourteen  millimetres 
in  its  longest  dimension. 

The  sixth  week  finds  the  foetus  elongated  with  greater 
distinctness  of  the  human  form,  the  large  size  of  the  head, 
on  which  the  cervical  flexure  is  very  evident,  being  highly 
characteristic  when  compared  with  corresponding  stages  of  the 

lower  mammals.  The  several  constituents  of  the  face  become  more  perfectly  formed, 
including  the  completion  of  the  superior  boundary  of  the  oral  cavity  and  its  separation 
from  the  nasal  pits  by  the  septum  resulting  from  the  union  of  the  fronto-nasal  process 
with  the  maxillary  processes  ;  the  fusion  of  the  latter  with  the  lateral  frontal  processes 
now  defines  the  external  boundary  of  the  nostrils  of  the  still,  however,  broad  and 
flattened  nose,  which  lies  immediately  above  the  transverse  cleft-like  oral  opening. 
The  visceral  arches  are  no  longer  visible  as  individual  bars,  having  undergone  com- 
plete fusion.  The  differentiation  of  the  digits  on  both  hands  and  feet  has  so  far 


Head  of  human  embryo 
of  about  seven  weeks.     X  5- 

(After  Ecker.) 


64  HUMAN   ANATOMY. 

progressed  that  fingers  and  toes  are  distinctly  indicated,  although  the  fingers  only 
are  imperfectly  separated.  The  first  suggestion  of  the  external  genitals  appears 
about  the  end  of  the  sixth  week.  At  this  time  the  foetus  measures  about  nineteen 
millimetres. 

During  the  seventh  and  eighth  weeks  the  fcetal  form  of  the  body  and  the 
limbs  attain  greater  perfection,  the  large  head  becoming  raised  from  the  trunk  and  the 
toes,  as  well  as  fingers,  being  now  well  formed,  although  the  rudiments  of  the  nails 
do  not  appear  until  some  time  during  the  third  month.  At  the  close  of  the  second 
month  the  extra-embryonic  protrusion  of  the  intestine  through  the  umbilicus  into 
the  umbilical  cord  reaches  its  greatest  extent.  The  genito-urinary  system  is  repre- 
sented by  the  fully  developed  Wolffian  body,  the  vesical  dilatation  of  the  allantoic 
duct,  the  separation  of  the  cloaca  into  rectum  and  genito-urinary  passage,  the  indif- 

FIG.  78. 


Umbilical  vesicle, 


Umbilical  stalk. 


Inner  surface  of- 
amnion 


Umbilical  cord. 


Human  embryo  of  about  thirty-five  days.     X  4-    Amnion  and  chorion  cut  and  turned  aside. 

ferent  sexual  gland,  and  the  undifferentiated  external  genitals,  consisting  of  the 
tal  eminence  and  the  associated  genital  folds  and  genital  ridges.  The  external  ear 
has  assumed  its  characteristic  form,  and  the  eyelids  appear  as  low  folds  encircling  the 
conspicuous  eye,  in  which  the  pigmentation  of  the  ciliary  region  is  visible.  Although 
the  face  is  well  formed,  the  nose  is  still  flat,  the  lips  but  slightly  prominent,  and  the 
palate  not  completely  closed.  The  rapid  growth  of  the  brain  results  in  the  dispro- 
portionate size  of  the  head,  which  at  this  stage  almost  equals  the  trunk  in  bulk.  It 
is  to  be  noted  that  by  the  close  of  the  second  month  the  permanent  organs  are  so 
far  advanced  that  the  subsequent  growth  of  the  foetus  is  effected  by  the  further  de- 
velopment of  parts  already  formed  and  not  by  the  accession  of  new  organs.  The 
beginning  of  the  second  month  marks  the  period  of  greatest  re/atirc  growth ;  at 
the  end  of  this  month  the  foetus  measures  about  thirty  millimetres  in  its  longest 
dimension. 


STAGE   OF   THE   FCETUS.  65 

The  third  month  is  characterized  by  greater  perfection  of  the  external  form, 
the  rounded  head  is  raised  from  the  trunk  so  that  a  distinct  neck  appears,  while  the 
thorax  and  abdomen  are  less  prominent  ;  the  limbs,  which  are  well  developed  with 
completed  differentiation  of  the  fingers  and  toes,  provided  with  imperfect  nails,  now 
assume  the  characteristic  foetal  attitude.  The  eyelids  become  united  by  the  tenth 
week,  remaining  closed  until  the  end  of  the  seventh  month.  The  cloacal  opening 
becomes  differentiated  during  the  ninth  and  tenth  weeks  into  the  genito-urinary  and 

FIG.  79. 


Umbilical  cord 


Umbilical 
stalk 


Allantoic 

vessels 


Umbilical  vesicle 


Human  foetus  of  about  eight  weeks.    X  31A-    Amnion  has  been  cut  and  reflected,  but  still  covers  the  umbilical  vesicle 

and  its  stalk. 

the  anal  orifice,  while  during  the  eleventh  and  twelfth  weeks  the  external  genital 
organs  acquire  the  distinguishing  peculiarities  of  a  definite  sex.  The  greatest  length 
of  the  foetus,  measured  in  its  natural  position  and  excluding  the  limbs,  at  the 
end  of  the  third  month,  is  about  eighty  millimetres  ;  its  weight  approximates  twenty 
grammes. 

The  fourth   month  witnesses  augmented  growth  in  the  foetus,  which,    how- 
ever, resembles  in  its  general  appearance  the  foetus  of  the  preceding  month.     The 

5 


66  HUMAN    ANATOMY. 

extra-foetal  portion  of  the  intestinal  canal,  which  at  an  earlier  period  passes  into 
the  umbilical  cord,  during  the  fourth  month  recedes  within  the  abdomen.  The 
differentiation  of  sex  is  still  more  sharply  exhibited  by  the  external  organs  :  in  the 
male  the  penis  is  acquiring  a  prepuce,  and  in  the  female  the  labia  majora  and  the 
clitoris  are  becoming  well  developed.  At  the  close  of  this  period  the  foetus  measures 
approximately  150  millimetres  and  weighs  about  120  grammes. 

During  the  fifth  month  the  first  foetal  movements  are  usually  observed.  .  The 
heart  and  the  liver  are  relatively  of  large  size.  The  decidua  capsularis  fuses  with 
the  decidua  vera,  thereby  obliterating  the  remains  of  the  uterine  cavity.  The  meco- 
nium  within  the  intestinal  canal  shows  traces  of  bile.  The  advent  of  the  fine  hair, 
the  lanugo,  first  upon  the  forehead  and  the  eyebrows,  and  somewhat  later  upon 
the  scalp  and  some  other  parts  of  the  body,  represents  a  conspicuous  advance. 
Likewise  adipose  tissue  appears  in  places  within  the  subcutaneous  layer.  The 
approximate  length,  at  the  end  of  the  fifth  month,  is  twenty-three  centimetres 
and  the  average  weight  about  320  grammes. 

The  sixth  month  is  characterized  by  complete  investment  of  the  body  by 
lanugo  and  by  the  appearance  of  the  vernix  caseosa,  the  protecting  sebaceous  secre- 
tion which  coats  the  body  of  the  foetus  to  prevent  as  far  as  possible  maceration  of 
the  epidermis  in  the  amniotic  fluid.  The  latter  now  reaches  the  maximum  quantity, 
being  contained  within  the  large  sac  of  the  amnion.  The  sixth  month  is  distin- 
guished by  the  conspicuous  increase  both  in  the  size  and  weight  of  the  foetus,  and 
is  known,  therefore,  as  the  period  of  greatest  absolute  growth.  At  the  close  of  the 
sixth  month  the  foetus  measures  approximately  thirty-four  centimetres  in  its  longest 
dimension  and  weighs  about  980  grammes. 

The  seventh  month  is  marked  by  progressive  changes  in  the  various  parts 
of  the  foetus,  whereby  the  more  advanced  details  become  pronounced  in  the  central 
nervous  system  and  digestive  tract.  The  length  of  the  foetus  at  the  close  of  the 
seventh  month  approximates  forty  centimetres  and  its  weight  about  170x3  grammes. 

The  eighth  month  is  occupied  by  the  continued  growth  and  general  develop- 
ment, as  part  of  which  the  foetus  acquires  greater  plumpness  than  before  and  a 
brighter  hue  of  the  integument,  now  entirely  covered  with  vernix  caseosa.  The 
lanugo  begins  to  disappear,  while  the  scalp  is  plentifully  supplied  with  hair  ;  the  nails 
have  reached,  or  project  beyond,  the  tips  of  the  fingers.  By  the  close  of  the  eighth 
month  the  foetus  has  attained  a  length  of  about  forty-six  centimetres  and  a  weight 
of  about  2400  grammes. 

The  ninth  month  witnesses  the  gradual  assumption  of  the  characteristics  of 
the  child  at  birth,  among  which  are  the  rounder  contours,  the  extensive,  although 
not  complete,  disappearance  of  the  lanugo,  except  from  the  face,  where  it  largely 
persists  throughout  life,  the  completed  descent  of  the  testicles  within  the  scrotum, 
the  approximation  of  the  labia  majora,  the  permanent  separation  of  the  eyelids,  with 
well-developed  lashes,  and  the  presence  of  dark  greenish  meconium  within  the  in- 
testinal canal.  The  umbilicus  has  reached  a  position  almost  exactly  in  the  middle 
of  the  body.  The  average  length  of  the  foetus  at  birth  is  about  fifty  centimetres, 
or  twenty  inches  ;  its  average  weight,  while  included  between  widely  varying 
extremes,  may  be  assumed  as  approximately  3100  grammes,  or  6.8  pounds.  The 
weight  of  the  foetus  at  term  is  materially  influenced  by  the  age  of  the  mother, 
women  of  about  thirty-five  years  giving  birth  to  the  heaviest  children.  The  weight 
and  stature  of  the  mother  probably  also  affect  the  weight  of  the  child.  Repeated 
pregnancies  exert  a  pronounced  effect  upon  the  foetus,  since  the  weight  of  the  child 
reaches  the  maximum  with  the  fifth  gestation. 


The  purpose  of  the  preceding  pages  is  to  present  an  outline  of  the  general 
developmental  processes  leading  to  the  differentiation  and  establishment  of  the  defi- 
nite body-form  of  the  human  embryo  ;  .a  more  detailed  account  of  the  development 

of  the  various  parts  of  the  body  is  given  in  connection  with  the  descriptions  of  the 
systems  and  the  individual  organs,  to  which  the  reader  is  referred. 


THE    ELEMENTARY    TISSUES. 

THE  various  parts  and  organs  of  the  complex  body  may  be  resolved,  in  their 
morphological  constitution,  into  a  few  component  or  elementary  tissues,  of  which 
there  are  four  principal  groups, — the  epithelial,  the  connective,  the  muscular,  and 
the  nervous  tissues.  The  first  two  of  these  may  be  discussed  at  this  place  ;  the  re- 
maining groups,  the  muscular  and  the  nervous  tissues,  are  considered  most  advan- 
tageously in  connection  with  the  muscular  and  nervous  systems  to  which  they  are 
directly  related  and  under  which  sections  they  will  be  found. 

THE   EPITHELIAL   TISSUES. 

The  epithelial  tissues  include,  primarily,  the  integumentary  sheet  of  protecting 
cells  covering  the  exterior  of  the  body  and  the  epithelium  lining  the  digestive  tube. 
Secondarily,  they  embrace  the  epithelial  derivatives  of  the  epidermis,  such  as  the 
nails,  hairs,  and  glands  of  the  skin  and  its  extensions,  and  the  epithelial  lining  of 
the  ducts  and  compartments  of  the  glands  formed  as  outgrowths  from  the  primi- 
tive gut-tube,  as  well  as  the  epithelium  clothing  the  respiratory  tract  which  originates 
as  an  evagination  from  the  digestive  canal. 

An  apparent  exception  to  the  usual  origin  of  the  epithelial  tissues  from  either 
the  ectoblast  or  the  entoblast  is  presented  by  the  lining  of  the  genito-urinary  tract, 
since  all  the  epithelium  occurring  in  connection  with  these  organs,  as  far  as  the 
bladder,  is  of  mesoblastic  origin,  and  hence  genetically  related  closely  with  the 
extensive  mesoblastic  group  of  tissues.  It  is  to  be  noted  in  this  connection  that  the 
epithelium  of  the  bladder  and  of  a  part  of  the  urethra  is  derived  from  outgrowths  of 
the  primary  gut,  and  therefore  is  entoblastic  in  origin. 

The  primary  purpose  of  epithelium  being  protection  of  the  more  delicate 
vascular  and  nervous  structures  lying  within  the  subjacent  connective  tissue  of  the 
integument  or  of  the  mucous  membrane,  the  protecting  cells  are  arranged  as  a  con- 
tinuous sheet,  the  individual  elements  being  united  by  a  small  amount  of  inter- 
cellular substance. 

Epithelium  contains  no  blood-vessels,  the  necessary  nutrition  of  the  tissue  being 
maintained  by  the  absorption  of  the  nutritive  juices  which  pass  to  the  cells  by  way 
of  the  minute  clefts  within  the  intercellular  substance.  Likewise,  the  supply  of 
nerve-fibres  within  epithelium  ordinarily  is  scanty,  although  in  certain  localities 
possessing  a  high  degree  of  sensibility,  as  the  cornea  or  tactile  surfaces,  the  termi- 
nations of  the  nerves  may  lie  between  the  epithelial  elements. 

The  epithelial  tissues  are  frequently  separated  from  the  subjacent  connective 
tissue  by  a  delicate  basement  membrane,  or  membrana  propria  ;  the  latter,  which  may 
be  regarded  as  a  derivative  or  modification  of  the  connective  tissue,  usually  appears 
as  a  delicate  subepithelial  boundary,  being  particularly  well  marked  beneath  the 
epithelium  of  glands. 

According  to  the  predominating  form  of  the  component  cells,  the  epithelial 
tissues  are  best  divided  into  two  chief  groups, — squamous  and  columnar, — with  sub- 
divisions as  shown  in  the  following  table  : 

VARIETIES   OF   EPITHELIUM. 

I.-  SQUAMOUS  : 

a.  Simple, — consisting;  of  a  single  layer. 

b.  Stratified, — consisting  of  several  layers. 
II.— COLUMNAR  : 

a.  Simple, — consisting  of  a  single  layer. 

b.  Stratified, — consisting  of  several  layers. 
III. — MODIFIED  : 

a.  Ciliated,     b.  Goblet.,   c.  Pigmented. 
IV.— SPECIALIZED  : 

a.  Glandular  epithelium,     b.  Neuro-epithelium. 

67 


68 


HUMAN   ANATOMY. 


Squamous  epithelium,  when  occurring  as  a  single  layer,  is  composed  of 
flattened  polyhedral  nucleated  plates  which,  when  viewed  from  the  surface,  present 
a  regular  mosaic,  sometimes  described  by  the  terms  ' '  pavement' '  or  "  tessellated. ' ' 
Such  arrangement  of  the  squamous  type  is  unusual  in  the  human  body,  the  lining 
of  the  alveoli  of  the  lungs,  the  posterior  surface  of  the  anterior  capsule  of  the 
crystalline  lens,  the  membranous  labyrinth,  and  a  few  other  localities  being  the 
chief  places  where  a  single  layer  of  squamous  cells  occurs. 

The  far  more  usual  arrangement  of  such  cells  is  several  superimposed  layers, 
this  constituting  the  important  group  of  stratified  squamous  epithelia.  When 


FIG.  81. 


FIG.  80. 


€ 

,    v  *v  * 


•  -V©, 


Simple  squamous  epithelium  from 
anterior  capsule  of  crystalline  lens. 
X400. 


Section  of  stratified  squamous  epithelium  from  anterior  surface  of 
cornea.     X  500. 


seen  in 'section,  the  deepest  cells  are  not  scaly,  but  irregularly  columnar,  resting 
upon  the  basement  membrane  by  slightly  expanded  bases.  The  surface  of  the  un- 
derlying connective  tissue  supporting  this  variety  of  epithelium  is  beset  with  minute 
elevations  or  papillae,  which  serve  as  advantageous  positions  for  the  terminations  of 
the  blood-vessels,  as  well  as  specialized  nerve-endings.  Owing  to  the  more  favored 
nutrition  of  the  deepest  stratum,  the  cells  next  the  connective  tissue  exhibit  the 
greatest  vitality,  and  often  are  the  exclusive  source  of  the  new  elements  necessary 


FIG.  82. 


FIG.  83. 


, 


Isolated  surface  cells  from   epithe- 
lium lining  the  mouth.     X  350. 


Epithelial  cells  from  epider- 
mis, showing  intercellular  bridges. 
X675. 


to  replace  the  old  and  effete  cells  which  are  continually  being  removed  at  the  free 
surface  ;  this  Joss  is  due  not  only  to  mechanical  abrasion,  but  also  to  the  displace- 
ment of  the  superficial  elements  by  the  new  cells  formed  within  the  deeper  layers. 

Passing  from  the  basement  membrane  towards  the  free  surface,  the  form  of  the 
cells  undergoes  a  radical  change.  The  columnar  type-  belongs  to  the  deepest  layer 
alone  ;  the  superimposed  cells  assume  irregularly  polyhedral  forms  and  then  gradu- 
ally expand  in  the  direction  parallel  to'the  free  surface  to  become,  finally,  converted 
into  the  large,  thin  scales  so  characteristic  of  the  superficial  layers  of  stratified 
epithelium.  The  position  of  the  nucleus  also  varies  with  the  situation  of  the  cells, 


EPITHELIUM. 


69 


since  within  those  next  the  basement  membrane  the  relatively  large  nucleus — the 
nutritive  organ  of  the  cell — occupies  the  end  nearest  the  subjacent  connective  tissue  ; 
in  the  middle  and  superficial  strata,  the  nucleus,  comparatively  small  in  size,  is 
placed  about  the  centre  of  the  cell. 

The  irregularly  polyhedral  cells  of  the  deep  or  middle  strata  frequently  are 
connected  by  delicate  processes  which  bridge  the  intervening  intercellular  clefts  ; 
when  such  elements  are  isolated,  the  delicate  connecting  threads  are  broken  and  the 
disassociated  elements  appear  beset  with  minute  spines,  then  constituting  the  prickle- 
cells. 

In  certain  localities,  as  in  the  urinary  bladder,  the  columnar  cells  of  the  deepest 
layer  rapidly  assume  the  scaly  character  of  the  superficial  strata  ;  such  epithelium 


FIG.  85. 


Ml 


FIG.  86. 


Transitional  epithelium  from  bladder  of  child. 
X  300. 


Simple  columnar  epi- 
thelium from  intestinal 
mucosa.  X  750. 


Stratified  columnar  epithelium 
from  vas  deferens.     X  500. 


possesses  relatively  few  layers,  and  from  the  readiness  with  which  the  type  of  the 
cells  changes,  is  often  described  as  transitional  epithelium ;  the  latter  cannot  be 
regarded  as  a  distinct  variety,  but  only  as  a  modification  of  the  stratified  scaly  group. 
Columnar  epithelium,  when  occurring  as  a  single  layer  of  cells,  constitutes 
the  simple  columnar  variety,  which  enjoys  a  much  wider  distribution  than  the  cor- 
responding squamous  group,  the  lining  of  the  stomach  and  of  the  intestinal  tube 
being  important  examples.  When  the  single  layer  of  such  epithelial  tissues  is  re- 
placed by  several,  as  in  the  stratified  columnar  variety,  the  superficial  cells  alone 


FIG.  87. 


Stratified  ciliated  columnar  epithelium  from  trachea  of 
child.     X  550. 


Ciliated  epithelial  cells.  A,  from  intes- 
tine of  a  mollusk  (cyclas) ;  JS,  from  nasal 
cavity  of  frog.  X  750.  (Engclniaini.) 


are  typically  columnar.  The  free  ends  of  the  columnar  elements  not  infrequently 
present  specializations  in  the  form  of  a  cuticular  border  or  of  cilia,  while  their  ends 
which  rest  upon  the  basement  membrane  are  pointed,  forked,  or  club-shaped.  The 
intervals  thus  formed  by  irregularities  of  contour  are  occupied  by  the  cells  of  the 
deeper  stratum  next  the  basement  membrane.  Each  cell  is  provided  with  a  nucleus, 
which  is  situated  about  midway  between  the  ends  of  the  superficial  elements  and 
nearer  the  base  within  the  deeper  ones.  The  surface  cells  often  contain  collections 
of  mucous  secretion  which  distend  their  bodies  into  conspicuous  chalice  forms  known 
as  goblet-cells,  which  occur  in  great  profusion  in  the  lining  of  the  large  intestine  and 
the  respiratory  mucous  membrane. 


yo 


HUMAN   ANATOMY. 


FIG. 


Goblet-cells  from  epithelium  lining  large 
intestine.    X  500. 


Modified  Epithelium. — The  free  surface  of  the  epithelium  in  many  localities, 
as  in  the  trachea,  the  inferior  and  middle  nasal  meatuses,  and  the  uterus,  is  pro- 
vided with  minute,  hair-like  vibratile  processes,  or  cilia,  which  are  produced  by  the 
specialization  of  the  cytoplasm  of  the  free  end  of  the  cell.  The  exact  relations  of 
the  cilia  to  the  cytoplasm  are  still  matters  of  uncertainty,  although  the  investigations 
of  Engelmann  and  others  on  the  ciliated  epithelium  of  invertebrates  render  it  prob- 
able that  the  hair-like  processes  attached  to  the  cells  of  higher  animals  are  also 
connected  with  intracellular  fibrillse,  which  appear  as  delicate  striations  within  the 
superficial  and  more  highly  specialized  parts  of  the  cells.  In  man  and  the  higher 
mammals  ciliated  epithelium  is  limited  to  the  columnar  variety.  The  exact  number 
of  individual  cilia  attached  to  the  free  surface  of  each  cell  varies,  but  there  are  usually 

between  one  and  two  dozen  such  appendages.  Their 
length,  likewise,  differs  with  locality,  those  lining 
the  epididymis  being  about  ten  times  longer  than 
those  attached  to  the  tracheal  mucous  membrane. 
When  favorable  conditions  obtain,  including  a  suffi- 
cient supply  of  moisture,  oxygen,  and  heat,  ciliary 
motion  may  continue  for  many  hours  and  even  days. 
On  surfaces  clothed  with  columnar  epithelium 
certain  cells  are  distinguished  by  unusually  clear 
cytoplasm  and  exceptional  form  and  size  ;  these  are 
the  goblet-cells,  the  peculiar  elliptical  or  chalice 
form  of  which  results  from  the  accumulation  of  the 
mucoid  secretion  elaborated  within  their  protoplasm.  When  the  distention  becomes 
too  great  the  cell  ruptures  in  the  direction  of  least  resistance,  and  the  secretion  is 
poured  out  upon  the  surface  of  the  mucous  membrane  as  the  lubricating  mucus. 
The  goblet-cells,  therefore,  may  be  regarded  as  unicellular  glands,  and  represent  the 
simplest  phase  in  the  specialization  of  glandular  tissues. 

The  protoplasm  of  epithelial  cells  often  becomes  invaded  by  particles  of  foreign 
substances  ;  thus,  granules  of  fatty  and  proteid  matters  are  very  commonly  encoun- 
tered, while  the  presence  of  granules  of  eleidin  in  certain  cells  of  the  epidermis  char- 
acterizes the  stratum  granulosum.  When  the  invading  particles  are  colored,  as  when 
composed  of  melanin,  the  affected  cells  acquire  a  dark  brown  tint,  and  are  then  known 
as  pigmented  epithelium.  Examples  of  such  cells  are  seen  in  the 
retina  and  in  the  deeper  cells  of  the  epidermis  in  certain  races. 
Specialized  Epithelium. — Reference  has  already  been 
made  to  goblet-cells  as  representing  unicellular  glands  ;  these 
may  be  regarded,  therefore,  as  instances  of  a  temporary 
specialization  of  epithelium  into  glandular  tissue.  When  the 
epithelial  elements  become  permanently  modified  to  engage  in 
the  elaboration  of  secretory  substances,  they  are  recognized 
as  glandular  epithelium.  The  cells  lining  the  ducts  and  the 
ultimate  compartments  of  glands  are  modified  extensions  of 
the  epithelial  investment  of  the  adjacent  mucous  membrane. 
Their  form  and  condition  depend  upon  the  degree  of  speciali- 
zation, varying  from  columnar  to  spherical  and  polyhedral,  on 
the  one  hand,  and  upon  the  nature  and  number  of  the  secre- 
tion particles  on  the  other.  The  cells  lining  parts  of  certain  glands,  as  those  clothing 
the  ducts  of  the  salivary  glands,  or  the  irregular  portion  of  the  uriniferous  tubules, 
exhibit  a  more  or  less  pronounced  striation  ;  cells  presenting  this  peculiarity  are 
termed  rod-epithelium. 

The  highest,  and  often  exceedingly  complex,  specializations  affecting  epithelial 
tissues  are  encountered  in  connection  with  the  neurones  supplying  the  organs  of 
special  sense.  The  epithelium  in  these  localities  is  differentiated  into  two  groups  of 
elements, — the  sustentacular  and  the  perceptive;  to  the  latter  the  name  of  ncuro- 
epithelium  is  applied.  Conspicuous  examples  of  such  specialization  are  the  rod-  and 
cone-cells  of  the  retina  and  the  hair-cells  of  Corti's  organ  in  the  internal  ear. 

A  more  detailed  description  of  the  glandular  tissues  is  given  with  the  digestive 
tract  ;  that  of  the  neuro-epithelia  with  the  organs  of  special  sense. 


FIG.  90. 


PigmenU-cl  epithelium  from 
human  retina.     X  435- 


ENDOTHELIAL   TISSUES. 


Mesothelial  cells  from  omentum  of  dog.    X  300.    Intercellular 
cement-substance  stained  by  argentic  nitrate. 


ENDOTHELIUM. 

The  modified  mesoblastic,  later  connective-tissue,  cells  that  line  serous  surfaces, 
including  ihose  of  the  pericardial,  the  pleural,  and  the  peritoneal  divisions  of  the 
body- cavity,  together  with  those  of  the  blood-  and  lymph-vessels  and  the  lymphatic 
spaces  throughout  the  body,  constitute  endothelium.  These  spaces,  in  principle,  are 
intramesoblastic  clefts  and  the  elements  forming  their  lining  are  derivatives  of  the 
great  connective-tissue  layer.  The  endothelia,  therefore,  belong  to  the  connective 
tissues  and  are  properly  regarded  as 

modified  elements  of  that  class  ;  as  FIG.  91. 

a  matter  of  convenience,  however, 
they  may  be  considered  at  this  place 
in  connection  with  the  epithelial  tis- 
sues. 

The  most  striking  difference  in 
situation  between  the  endothelia  and 
the  epithelia  is  found  in  the  fact  that 
the  former  cover  surfaces  not  com- 
municating with  the  atmosphere, 
while  the  epithelial  tissues  clothe 
mucous  membranes  all  of  which  are 
directly  or  indirectly  continuous 
with  the  integumentary  surface.  A 
further  contrast  between  these  tis- 
sues is  presented  in  their  genetic  re- 
lations with  the  primary  blastodermic 
layers,  since  the  epithelia,  with  the 
exception  of  those  lining  certain 
parts  of  the  genito-urinary  tracts  which  are  derived  from  the  mesoblast,  are  the  trans- 
formations and  outgrowths  from  the  ectoblast  and  the  entoblast,  while  the  endo- 
thelia are  direct  modifications  of  the  mesoblastic  cells. 

The  young  mesoblastic  cells  bordering  the  early  body-cavity  become  differenti- 
ated into  a  delicate  lining,  the  mesothelium,  and  later  give  rise  to  the  characteristic 

plate-like  elements  which  constitute  the 
lining  of  the  permanent  serous  sacs.  The 
name  mesothelium  is  sometimes  retained  to 
designate  the  permanent  investment  of  the 
great  serous  cavities,  as  distinguished  from 
the  endothelium  which  clothes  the  vascular 
and  other  serous  spaces. 

Seen  in  typical  preparations,  as  ob- 
tained from  the  peritoneum  after  treatment 
with  argentic  nitrate  and  subsequent  stain- 
ing with  haematoxylin,  the  endothelial  cells 
on  surface  view  appear  as  irregularly  polyg- 
onal areas  mapped  out  by  deeply  tinted 
lines.  The  latter  represent  the  silver- 
stained  albuminous  intercellular  cement- 
substance  which  unites  the  flattened  cells 
in  a  manner  similar  to  that  observed  in 

simple  squamous  epithelium  ;  this  superficial  likeness  is  so  marked  that  it  has  led  to 
much  confusion  as  to  the  proper  classification  of  endothelium  under  the  connective 
tissues.  The  lines  of  apposition  are  sinuous  and  less  regular  than  between  epithelial 
elements,  in  many  cases  appearing  distinctly  dentated.  The  exact  form  of  the  cells 
and  the  character  of  their  contours,  however,  are  not  constant,  since  they  probably 
depend  largely  upon  the  degree  of  tension  to  which  the  tissue  has  been  subjected. 

Not  infrequently  the  intercellular  substance,  at  points  where  several  endothelial 
cells  are  in  apposition,  shows  irregular,  deeply  colored  areas  after  silver  staining  ; 


FIG.  92. 


Endothelial  cells  lining  artery  of  dog,  after  silver 
staining.    X  500. 


72  HUMAN   ANATOMY. 

these  figures  are  described  as  stigmata  or  pscudostomata,  and  by  some  are  interpreted 
as  indications  of  the  existence  of  openings  leading  from  the  serous  cavity  into  the 
subjacent  lymphatics.  Critical  examination  of  these  areas,  however,  leads  to  the 
conclusion  that  they  are  largely  accidental,  and  due  to  dense  local  accumulations  of 
the  stained  intercellular  materials ;  they  are  not,  therefore,  to  be  regarded  as  intercellu- 
lar passages.  True  orifices  or  stomata,  however,  undoubtedly  exist  in  certain  serous 
membranes,  as  in  the  septum  between  the  peritoneal  cavity  and  the  abdominal 
lymph-sac  of  the  frog,  and,  possibly,  the  peritoneal  surface  of  the  diaphragm  of 
mammals.  The  positions  of  these  stomata  are  marked  by  a  conspicuous  modification 
in  the  form  and  arrangement  of  the  surrounding  endothelial  plates,  which  exhibit  a 
radial  disposition  about  the  centres  occupied  by  the  stomata.  The  immediate  walls 
of  the  orifices  are  formed  by  smaller  and  more  granular  elements,  the  guard  or  ger- 
minating cells,  the  contraction  and  expansion  of  which  probably  modify  the  size  of 
the  openings. 

Although  the  ectoblast  and  the  entoblast  are  the  germ  layers  which  furnish  great 
tracts  of  epithelium  in  the  adult  body,  yet  the  mesoblast,  the  middle  germ  layer, 
also  supplies  distinct  epithelial  tissues.  As  it  has  been  already  pointed  out,  the 
epidermis,  the  epithelial  portion  of  the  skin,  with  its  derivatives,  is  a  product  of  the 
ectoblast.  The  epithelial  lining  of  the  mouth  cavity  as  far  back  as  the  region  of  the 
palatine  arches,  and  the  epithelium  of  the  anus  are  also  of  ectoblastic  origin,  since 
they  are  formed  as  in-pocketings  of  the  outer  germ  layer  during  early  embryonic 
life.  With  the  exception  of  these  areas,  the  epithelium  lining  the  entire  digestive 
tube,  and  that  of  its  accessory  glands,  notably  the  liver  and  the  pancreas,  is  of 
entoblastic  origin.  The  same  thing  is  true  of  the  epithelium  of  the  respiratory  tract, 
since  this  entire  tract  is  an  outgrowth  from  the  primitive  intestine.  But  in  the  case  of 
the  uro-genital  system,  the  epithelium  there  found,  or  most  of  it,  is  derived  directly 
from  the  mesoblast.  To  be  more  specific,  the  Fallopian  tubes  (uterine  tubes), 
uterus  and  vagina  of  the  female,  which  have,  of  course,  a  distinct  layer  of  epithelium 
on  their  inner  surface,  are  formed  from  certain  embryonic  tubes  known  as  the 
Miillerian  ducts,  which  are  derived  from  the  mesoblast.  The  vas  (ductus)  deferens 
of  the  male  is  first  represented  in  the  embryo  by  a  tube  known  as  the  Wolffian  duct, 
which,  with  its  epithelium,  is  also  derived  from  the  mesoblast.  The  sex-cells  found  in 
the  sex -glands,  which  in  the  case  of  the  male  retain  a  distinct  epithelial  character, 
are  apparently  of  mesoblastic  origin.  The  ureter  and  part  of  the  kidney  are  out- 
growths from  the  Wolffian  duct  and  therefore  mesoblastic,  while  the  rest  of  the 
kidney  not  formed  in  this  way  is  also  of  mesoblastic  origin.  Hence,  it  is  evident 
that  distinct  layers  of  epithelium  are  formed  from  all  three  germ  layers,  and  that 
in  this  respect  no  peculiarity  is  attributable  to  any  one  of  them. 


THE   CONNECTIVE   TISSUES. 


THE  important  group  of  connective  substances  the  most  widely  distributed  of 
all  tissues,  is  the  direct  product  of  the  great  mesoblastic  tract  ;  the  several  members 
of  this  extended  family  are  formed  by  the  differentiation  and  specialization  of  the 
intercellular  substance  wrought  through  the  more  or  less  direct  agency  of  the  meso- 
blastic cells.  The  variation  in  the  physical  characteristics  of  the  connective  tissues 
is  due  to  the  condition  of  their  intercellular  constituents.  During  the  period  of  em- 
bryonal growth  these  latter  are  represented  by  gelatinous,  plastic  substances  ;  a 
little  later  by  the  still  soft,  although  more  definitely  formed,  growing  connective 
tissue,  which,  in  turn,  soon  gives  place  to  the  yielding,  although  strong,  adult 
areolar  tissue. 

Grouped  as  masses  in  which  white  fibrous  tissue  predominates,  the  intercellular 
substance  presents  the  marked  toughness  and  inextensibility  of  tendon  ;  where,  on 
the  contrary,   large  quantities  of  yellow  elastic  tissue  are  present,   extensibility  is 
conspicuous.      Further  conden- 
sation of   the  intercellular  sub-  FIG.  93. 
stance  produces   the   resistance 
encountered    in    hyaline    carti- 
lage,    intermediate    degrees    of- 
condensation     being     presented 
by  the  fibrous  and  elastic  varie- 
ties.     In  those  cases  in  which 
the   ground-substance   becomes 
additionally    impregnated    with 
calcareous  salts,  the  well-known 
hardness  of  bone  or  dentine  is 
attained.    Notwithstanding  these 
variations  in  the  density  of  the 
intercellular  substance,   the  cel- 
lular elements  have  undergone 
but  little  change,  the  connective- 
tissue  corpuscle,  the  tendon-cell, 
the  cartilage- cell,  and  the  bone- 
corpuscle  being  morphologically 
identical. 

The  principal  forms  in  which  the  connective  substances  occur  may  be  grouped  as 
follows  : 

1.  Immature  connective  tissue,  as  the  jelly  of  Wharton  in  the  umbilical  cord 
and  the  tissues  of  embryos  and  of  young  animals. 

2.  Areolar  tissue,  forming    the   subcutaneous   layer  and   filling    intermuscular 
spaces,  and  holding  in  place  the  various  organs. 

3.  Dense  fibro-elastic  tissue,  found  in  the  fasciae,  the  sclera,  the  ligaments,  etc. 
Where  white  fibrous   tissue   predominates   and   yellow   elastic   tissue  is  practically 
wanting,  structures  of  the  character  of  tendon  or  of  the  cornea  are  produced  ;  where, 
on   the   other  hand,  elastic   tissue   is   in  excess  of   fibrous  tissue,  highly  extensible 
structures,  as  the  ligamentum  nuchae  or  the  ligamenta  subflava,  result. 

4.  Cartilage,  fibrous,  elastic,  and  hyaline  varieties. 

5.  Bone  and  dentine,  in  which  impregnation  of  lime  salts  contributes  character- 
istic hardness. 

6.  Reticulated  connective  tissue,  occurring  as  the  supporting  framework  in  the 
lymphatic  tissues,  and  as  the  interstitial  reticulum  of  many  organs. 

7.  Adipose  tissue. 

The  Cells  of  Connective  Tissue.— The  cellular  elements  of  the  connective 

73 


Embryonal  connective-tissue  cells  from  the  umbilical  cord.    X  500. 


74 


HUMAN    ANATOMY. 


tissues  are  usually  described  as  of  two  kinds,  — the  fixed  or  connective-tissue  cells 
proper,  and  the  migratory  or  wandering  cells.  The  latter,  while  frequently  included 
among  the  elements  of  these  tissues,  are  usually  only  migratory  leucocytes  which 
temporarily  occupy  the  lymphatic  clefts  within  the  connective  substance. 


FIG.  94. 


FIG.  95. 


Young  connective-tissue  cells 
from  subcutaneous  tissue  of  cat  em- 
bryo. X  680. 


Granule-cells  (mast-cells)  from  suhmucous  tissue  of  mouth.     X  1000. 
v,  v,  sections  of  blood-vessels. 


The  typical  connective-tissue  cell,  in  its  younger  condition,  possesses  a  flattened, 
plate-like  body  from  which  branched  processes  extend.     With  the  completed  growth 

of  the  tissue,  the  expanded, 

FIG.  96.  often      irregularly     stellate, 

element  contracts  to  the 
inconspicuous  spindle  cell 
commonly  observed  in  adult 
areolar  tissue. 

Granule-cells  are  addi- 
tional elements  occasionally 
encountered  in  connective 
tissues.  They  are  irregularly 
spherical  in  form  and  are  dis- 
tinguished by  conspicuous 
granules  within  their  proto- 
plasm possessing  a  strong 
affinity  for  dahlia  and  other 
basic  aniline  stains.  They 
include  the  plasma-cells  of 
Waldeyer  and  the  mast-cells 
of  Ehrlich. 

Pigment-Cells.— The 
fixed  cells  sometimes  contain 
accumulations  of  dark  parti- 
cles within  their  cytoplasm, 
the  elements  then  appearing 
as  large,  irregularly  branched 
pigment-cells;  these  are  con- 
spicuous in  man  within  the  choroid,  the  iris,  and  certain  parts  of  the  pia  mater. 
The  nucleus  usually  remains  uninvaded,  and  hence  appears  as  a  lighter  area  within 
the  •dark  brown,  or  almost  black,  cell-body. 

The  Intercellular  Constituents  of  the  connective  substances  occur  in  three 
forms, — -fibrous  tissue,  reticular  tissue,  and  clastic  tissue. 

Fibrous  tissue  consists  morphologically  of  varying  bundles  of  silky  fibrils  of 


Migratory 
leucocytes 
(Wandering 
cells) 


Fibrous 
tissue 


Section  of  subcutaneous  tissue,  showing  the  usual  constituents  of  areolar 
tissue.     X  300. 


FIBROUS   TISSUE. 


75 


such  fineness  that  they  possess  no  appreciable  width.  The  fibrils  are  united  by  and 
embedded  within  a  semifluid  ground- sub  stance,  which  may  be  present  in  such  meagre 
amount  that  it  suffices  only  to  hold  together  the  fibrillae,  or,  on  the  other  hand,  it 
may  constitute  a  large  part  of  the  entire  intercellular  tissue,  as  in  the  matrix  of  hya- 


FIG.  97- 


FIG.  98. 


•  «."» 
:^^l 


Surface  view  of  portion  of  omentum.  X  130.  Fi- 
brous and  elastic  tissue  are  arranged  as  a  fenestrated 
membrane;  the  nuclei  belong  to  the  connective-tissue 
and  the  endothelial  cells. 


Pigrnented  connective-tissue  cells  from  choroid. 
X  400. 


line  cartilage.  Depending  upon  the  dis- 
position of  the  bundles,  fibrous  tissue 
occurs  in  two  principal  varieties, — areolar 
and  dense  connective  tissue. 

The  fibrous  tissue  of  the  areolar 
group  is  arranged  in  delicate  wavy  bun- 
dles which  are  loosely  and  irregularly  in- 
terwoven, as  seen  in  the  subcutaneous 
layer,  the  intervening  clefts  being  largely 
occupied  by  the  ground-substance.  In 
the  denser  connective  tissues  the  fibrous 
tissue  is  disposed  with  greater  regularity, 
either  as  closely  packed,  parallel  bundles, 
as  in  tendon  and  aponeuroses,  or  as  intimately  felted,  less  regularly  arranged,  bands 
forming  extended  sheets,  as  in  fasciae,  the  cornea,  and  the  dura  mater.  The  ground- 
substance  uniting  the  fibrillae  of  dense  connective  tissues  often  contains  a  system  of 

definite   interfascicular  lymph-spaces, 

f* IG-  99-  which,    in  suitably  stained   prepara- 

tions,   appear  as    irregularly  stellate 

^fC^J'"--'--^  clefts   that  form,    by  union   of    their 

JH  ,       „  -      ramifications,  a  continuous  net-work 

of  channels  for  the  conveyance  of  the 
tissue-juices  throughout  the  dense 
connective  substances  ;  in  non-vascu- 
lar structures,  as  the  cornea  and  the 
denser  parts  of  bone,  these  systems 
of  intercommunicating  lymph-spaces 
serve  to  convey  the  nutritive  sub- 
stances to  the  connective-tissue  cells 
which  lie  within  these  clefts.  Fibrous 
tissue  yields  gelatin  on  boiling  in 
water,  and  is  not  digested  by  pan- 
creatin  ;  on  the  addition  of  acetic  acid 
this  tissue  becomes  swollen  and  trans- 
parent, the  individual  fibrillae  being 
no  longer  visible. 

Reticular  Tissue. — The  in- 
vestigations of  Mall  have  emphasized 
the  presence  of  a  modified  form  of  fibrous  tissue  in  many  localities,  especially  in 
organs  rich  in  lymphoid  cells.  This  variety  of  intercellular  substance,  known  as 
reticular  tissue  or  reticulum,  consists  of  very  fine  fibrillae,  either  isolated  or  associated 


Cell-spaces  of  dense  connective  tissue  from  cornea  of  calf ; 
the  surrounding  ground-substance  has  been  stained  with  argen- 
tic nitrate.  X  525. 


76 


HUMAN   ANATOMY. 


FIG.  100. 


FIG.  101. 


as  small  bundles,  which  unite  in  all  planes  to  form  delicate  net-works  of  great  intri- 
cacy. In  lymphatic  tissues,  where  the  reticulum  reaches  a  typical  development,  the 
mesh-work  contains  the  characteristic  lymphoid  elements  and,  in  addition,  supports 
the  superimposed  stellate  connective-tissue  cells  which  formerly  were  erroneously 

regarded  as  integral  parts  of  the  fibrillar 
net-work.  Reticular  tissue,  associated 
with  fibrous  and  elastic  tissue,  is  also 
present  in  many  other  organs,  as  the 
liver,  kidney,  and  lung.  This  modifica- 
tion of  fibrous  tissue  differs  from  the  more 
robustly  developed  form  in  the  absence 
of  the  ground-substance  and  not  yield- 
ing gelatin  upon  boiling  in  water  (Mall); 
like  fibrous  tissue,  the  reticulum  resists 
pancreatic  digestion. 

The  development  of  fibrous  tissue 
has  been  a  subject  of  much  discussion  re- 
garding which  authorities  are  still  far  from 
accord.  Two  distinct  views  are  held  at 
the  present  time  ;  according  to  the  one, 

Connective-tissue  cells   from   cornea  of  calf  which       the     fibres    appear    within     the     Originally 
occupy  cell-spaces  similar  to  those  shown  in  preceding  rr  t>  j 

figure,   x  525.  homogeneous  intercellular  matrix  of   the 

early  embryonal  connective  tissue  without 

the  direct  participation  of  the  cells,  the  fibres  being  formed  as  the  result  of  a  process 
somewhat  resembling  coagulation.  This  conception  of  the  formation  of  the  fibres  of 
connective  tissue,  known  as  the  indirect  mode,  is  held  to  account  for  the  earliest 
production  of  the  fibrils  in  embry- 
onic tissue. 

The  other  view,  held  by  Hem- 
ming, Reinke,  and  others,  attributes 
an  active  participation  of  the  young 
connective  tissue  cell,  the  peripheral 
zone  of  its  protoplasm,  known  as  ex- 
oplasm,  being  directly  transformed 
into  fibrillae.  In  consideration  of 
the  careful  observations  of  Flem- 
ming,  it  is  now  generally  believed 
that  the  method  of  formation  of  the 
fibres  of  connective  tissue  directly 
from  the  exoplasm  of  young  con- 
nective tissue  cells  is  the  usual  one. 

It  is  highly  probable  that  the 
connective  tissue  cells  are  concerned 
in  the  production  of  the  fibrous 
tissue,  since  these  elements  become 
much  smaller  as  the  formation  of 
the  fibrous  tissue  advances. 

Elastic  tissue  usually  occurs 
as  a  net-work  of  highly  refracting, 
homogeneous  fibres  lying  among  the 
bundles  of  fibrous  tissue.  The  indi- 
vidual fibres  are  much  thicker  than 
the  fibrillae  of  fibrous  tissue  and, 

although  differing  in  width,  maintain  a  constant  diameter  until  augmented  by  fusion 
with  others.  When  disassociated,  as  in  teased  preparations,  the  elastic  fibres  assume 
a  highly  characteristic  form,  being  wavy,  bowed,  or  coiled.  The  proportion  of  elastic 
tissue  in  connective  substances  is,  ordinarily,  small  ;  in  certain  localities,  however,  as 
the  ligamenta  subflava  of  man,  or  especially  the  ligamentum  nuchre  of  the  lower 
mammals,  almost  the  entire  structure  consists  of  bundles  of  robust  fibres  of  elastic 


Fibrous  and  reticular  connective  tissue  from  human  liver  after 
pancreatic  digestion.     X  23°- 


ELASTIC   TISSUE. 


77 


tissue  held  together  by  a  small  amount  of  intervening  fibrous  tissue.  In  transverse 
section  of  such  ligaments  (Fig.  104),  the  individual  elastic  fibres  appear  as  minute 
polygonal  areas  separated  by  the  fibrous  fibrillae  and  the  associated  connective-tissue 
cells.  Within  the  walls  of  the  large  blood-vessels  the  elastic  tissue  is  arranged  as 

membranous    expansions    containing    numerous 

p,G   I02  openings  of  vary  ing  size  :  these  f ene sir  ate  d  mem- 

branes, as  they  are  called,  are  probably  formed 
by  the  junction  and  fusion  of  broad  ribbon-like 
V"  /  /  j'  elastic  fibres.  Elastic  tissue  yields  elastin  upon 

•*•  -^^4^    y 

=jj/   ,H«:iL / 

FIG.  103. 


FIG.  104. 


Reticular    connective  tissue    from    lymph-  Portions  of  isolated  elastic  fibres  from  ligamen- 

node.     X  35°-    The  cells  lie  upon  the  fibrous  tum  nucha  of  ox.    X  375. 

tissue  at  the  points  of  intersection. 

boiling  in  water,  and  disappears  upon  being  subjected  to  pancreatic  digestion,  thus 
differing  from  fibrous  and  reticular  tissue ;  by  taking  advantage  of  the  especial  affinity 
that  elastic  tissue  possesses  for  certain  stains,  as  orcei'n,  a  much  wider  and  more 
generous  distribution  of  elastic  tissue  has  been  established  than  was  formerly  appre- 
ciated. 

The  development  of  elastic  tissue  has  shared  the  uncertainty  surrounding 
the  mode  of  production  of  fibrous  tissue,  since  here,  as  there,  two  opposed  views 
have  been  held, — one  of  a  cellular  and 
one  of  an  independent  origin.  Accord- 
ing to  the  view  of  an  independent  origin, 
the  older  one,  the  elastic  fibres  first 
appear  as  rows  of  minute  beads  in  the 
intercellular  matrix.  These  linearly  dis- 
posed beads  gradually  fuse,  thus  produc- 
ing the  primary  elastic  fibres.  According 
to  the  view  of  an  intracelhdar  origin, 
the  one  now  generally  accepted,  the 
elastic  fibres  are  derived  directly  from 
the  exoplasm  of  the  young  connective 
tissue  cells,  as  in  the  case  of  the  white 
fibrils. 

The  density  of  connective  substances 
depends  upon  the  amount  and  arrange- 
ment of  the  fibrous  tissue  ;  the  extensibility 
is  determined  by  the  proportion  of  elastic 
tissue  present.  When  the  former  occurs 
in  well-defined  bundles,  felted  together 

into  interlacing  lamellae,  dense  and  resistant  structures  result,  as  fasciae,  the  cornea, 
etc. ;  in  such  structures  the  cement-  or  ground-substance  within  the  interfascic- 
ular  clefts  usually  contains  the  lymph-spaces  occupied  by  the  connective-tissue 

cells. 

Tendon. — Tendon  consists  of  dense  connective  tissue  composed  almost  en- 
tirely of  white  fibrous  tissue  arranged  in  parallel  bundles.      The  individual  fibrillae 


Elastic  fibres — - 
in  section 


Interfibrillar 
connective  tissue 

Nucleus  of  con- 
nective-tissue 
cell 


Transverse  section  of  ligamentum  nuchse  of  ox.    X  45°- 


HUMAN   ANATOMY. 


of  the  fibrous  tissue,  held  together  by  cement-substance,  are  associated  as  compara- 
tively large  primary  bundles,  which  in  turn  are  united  by  interfascicular  ground- 


G.  iu6. 


Blood-vessel  within  septa 
enclosing  tertiary  bundles 


Tendon-bundle- 


Profile  view 


Oblique  view 


Surface  view 


Longitudinal  section  of  tendon  from   young  subject;         Tendon-bundles  from  tail  of  mouse,  showing  different 
the  tendon-cells  are  seen  in  profile  between  the  bundles  views  of  the  cells.     X  300. 

of  fibrous  tissue.     X  300. 

substance  and  grouped  into  secondary  bundles.     The  latter,  invested  by  a  delicate 
areolar  sheath  and  partially  covered  by  endothelial  cells,  are  held  together  by  the 

septal    extensions    of    the 

FIG.  107.  general     connective-tissue 

envelope  which  surrounds 
the  entire  tendon  ;  the 
larger  septa  support  the 
interfascicular  blood-ves- 
sels and  the  lymphatics. 

The  flattened  connec- 
tive-tissue elements,  here 
known  as  the  tendon-cells, 
occur  in  rows  within  the 
clefts  between  the  primary 
bundles,  upon  and  between 
which  the  thin,  plate-like 
bodies  and  rings  of  the 
tendon-cells  expand.  Seen 
from  the  surface,  these 
cells  appear  as  nucleated 
quadrate  bodies  (Fig- 
106)  ;  viewed  in  longitudi- 
nal profile,  the  tendon-cells 
present  narrow  rectangular 
areas,,  while,  when  seen  in 
transverse  section,  the 
same  elements  appear  as 

stellate  bodies,   the  extended  limbs  of  which,   often  stretching  in  several  planes, 
represent  sections  of  the  wing-plates. 

Examined  in  cross-section  (Fig.  107),  the  cut  ends  of  the  primary  tendon-bun- 
dles appear  as  light  irregular  polygonal  areas,  which,  under  high  amplification,  at 


Primary 
bundle 


Transverse  section  of  a  tendon,  showing  grouping  of  primary,  secondary 

.-Hid  tertiary  bundles  of  tendon-tissue.     X  85. 


ADIPOSE   TISSUE. 


79 


times  exhibit  a  delicate  stippling  due  to  the  transversely  sectioned  fibrillae.  The 
interfascicular  clefts  frequently  are  represented,  in  such  preparations,  by  stellate 
figures  in  which  the  sections  of  the  tendon-cells,  lying  upon  the  primary  bundles,  can 
be  distinguished  ;  the  remaining  portion  of  the  stellate  cleft  is  occupied  by  the 


FIG.  108. 


-  ! 


' 


YX/X 
P*H       :'Sa 


•  .fiS^  " 

^/  :  -  •  ,  ^,-r 

Adipose  tissue  from  omentum.     X  160.    The  fat-cells  are  arranged  as  groups  betwee 

connective  tissue. 


:n  the  bundles  of 


FIG.  109. 


coagulated  and  stained  interfascicular  cement-substance.  The  larger  divisions  of 
the  tendon,  composed  of  the  groups  of  secondary  bundles,  are  separated  by  the 
septa  prolonged  inward  from  the  general  sheath  investing  the  entire  tendon.  Ten- 
don is  composed  almost  exclu- 
sively of  fibrous  tissue,  elastic 
fibres  being  practically  absent. 

Adipose  Tissue.  —  The 
fatty  material  contained  within 
the  body  is  to  a  large  extent  en- 
closed within  connective-tissue 
cells  in  various  localities  ;  these 
modified  elements  are  known  as 
fat-cells,  which,  together  with 
the  areolar  tissue  connecting  the 
cells  and  supporting  the  rich 
supply  of  blood-vessels,  consti- 
tute the  adipose  tissue. 

The  distribution  of  adipose 
tissue  includes  almost  all  parts  of 
the  body,  although  accumulations 

of    fat    are   especially  Conspicuous  Young  fat-cells  from  subcutaneous  tissue.     X  550. 

in  certain  localities.      Among  the 

latter  are  the  subcutaneous  areolar  tissue,  the  marrow  of  bones,  the  mesentery  and 
the  omentum,  the  areolar  tissue  surrounding  the  kidney,  the  vicinity  of  the  joints,  and 
the  subpericardial  tissue  of  the  heart.  On  the  other  hand,  in  a  few  situations,  in- 
cluding the  subcutaneous  areolar  tissue  of  the  eyelids,  the  penis  and  the  labia 
minora,  the  lungs,  except  near  their  roots,  and  the  interior  of  the  cranium,  adipose 


Peripheral  zone~ 
of  protoplasm 
enclosing  oil- 
drop 


Young  fat-cell— 


Connective-tissue' 
cells 


8o  HUMAN   ANATOMY. 

tissue  does  not  occur  even  when  developed  to  excess  in  other  parts.  As  ordinarily 
seen,  adipose  tissue  is  of  a  light  straw  color  and  often  presents  a  granular  texture 
due  to  the  groups  of  fat-cells  within  the  supporting  areolar  tissue. 

Examined  microscopically  in  localities  where  the  fat-cells  are  not  crowded,  but 
occur  in  a  single  stratum  and  hence  retain  their  individual  form,  adipose  tissue  is 
seen  to  be  made  up  of  relatively  large,  clear,  spherical  sacs  held  together  by  deli- 
cate areolar  tissue.  Unless  treated  with  some  stain,  as  osmic  acid,  Sudan  III.  or 
quinoline-blue,  possessing  an  especial  affinity  for  fat,  the  oily  contents  of  the  cells 
appear  transparent  and  uncolored,  and  apparently  occupy  the  entire  cell-body. 
Critical  study  of  the  fat-cell,  however,  demonstrates  the  presence  of  an  extremely 
thin  enveloping  layer  of  protoplasm,  a  local  thickening  on  one  side  of  the  sac  mark- 
ing the  position  of  the  displaced  and  compressed  nucleus  (Fig.  109). 

Fat-cells  occur  usually  in  groups,  supported  and  held  together  by  highly  vas- 
cular connective  tissue.  In  localities  possessing  considerable  masses  of  fat,  as  be- 
neath the  scalp  and  the  skin,  the  cells  are  grouped  into  lobules  which  appear  as 
yellow  granules  to  the  unaided  eye  ;  in  such  localities  the  typical  spherical  shape  of 
the  individual  fat-cells  is  modified  to  a  polyhedral  form  as  the  result  of  the  mutual 
pressure  of  the  closely  packed  vesicles. 

In  connective-tissue  elements  about  to  become  fat-cells,  isolated  minute  oil- 
drops  first  appear  within  the  protoplasm  ;  these  increase  in  size,  coalesce,  and  grad- 
ually encroach  upon  the  cytoplasm  until  the  latter  is  reduced  to  a  thin,  almost 
inappreciable,  envelope,  which  invests  the  huge  distending  oil-drop.  The  nucleus, 
likewise,  is  displaced  towards  the  periphery,  where  it  appears  in  profile  as  an  incon- 
spicuous crescent  embedded  within  the  protoplasmic  zone.  After  the  disappearance 
of  the  fatty  matters,  as  during  starvation,  the  majority  of  fat-cells  are  capable  of 
resuming  the  usual  appearance  and  properties  of  connective-tissue  corpuscles  ;  cer- 
tain groups  of  cells,  the  fat-organs  of  Toldt,  however,  exhibit  an  especial  tendency 
to  form  adipose  tissue,  and  hence  only  under  exceptional  conditions  part  with  their 
oily  contents. 

CARTILAGE. 

Cartilage  includes  a  class  of  connective  tissue  in  which  the  intercellular  substance 
undergoes  increasing  condensation  until,  as  in  the  hyaline  variety,  the  intercellular 
matrix  appears  homogeneous,  the  constituent  fibres  being  so  closely  blended  that 
the  fibrous  structure  is  ordinarily  no  longer  appreciable. 

Depending  upon  the  differences  presented  by  the  intercellular  matrix,  three 
varieties  of  cartilage  are  recognized, — hyaline,  elastic,  andji&roits.  Considered  in 
relation  to  the  denser  connective  tissues,  the  description  of  fibrous  cartilage,  which 
differs  but  little  from  white  fibrous  tissue,  should  next  follow  ;  since,  however,  the 
term  ' '  cartilage' '  is  usually  applied  to  the  hyaline  variety,  the  latter  will  first  claim 
attention. 

Hyaline  cartilage,  or  gristle  (Fig.  no), enjoys  a  wide  distribution,  forming 
the  articular  surfaces  of  the  bones,  the  costal  cartilages,  the  larger  cartilages  of  the 
larynx  and  the  cartilaginous  plates  of  the  trachea  and  bronchi,  the  cartilages  of  the 
nose  and  of  the  Eustachian  tube.  In  the  embryo  the  entire  skeleton,  with  the  ex- 
ception of  part  of  the  skull,  is  mapped  out  by  primary  hyaline  cartilage. 

The  apparently  homogeneous  matrix  of  hyaline  cartilage,  after  appropriate 
treatment,  is  resolvable  into  bundles  of  fibrous  tissue  ;  ordinarily,  however,  these  are 
so  closely  united  and  blended  by  the  cementing  ground-substance  that  the  presence 
of  the  component  fibrils  is  not  evident. 

The  cartilage-cells,  as  the  connective-tissue  elements  which  lie  embedded  within 
the  hyaline  matrix  are  called,  are  irregularly  oval  or  spherical,  nucleated  bodies. 
They  occupy  more  or  less  completely  the  interfascicular  clefts,  or  lacuna:,  within 
which  they  are  lodged.  In  adult  tissue  usually  two  or  more  cells  share  the  same 
compartment,  the  group  representing  the  descendants  from  the  original  occupant  of 
the  space.  The  matrix  immediately  surrounding  the  lacunse  is  specialized  as  a  laver 
of  different  density,  and  is  often  described  as  a  capsule  ;  a  further  differentiation 
of  the  ground-substance  is  presented  by  the  more  recently  formed  matrix,  which 


CARTILAGE. 


81 


Perichondrium 


Young  cartilage- 
cells 


Group 
cell; 


of  older 


often  stains  with  greater  intensity,  thereby  producing  the  appearances  known  as 
the  cell-areas.  The  lacunae  of  hyaline  cartilage  are  homologous  with  the  lymph- 
spaces  of  other  dense  forms  of  connective  tissue  ;  although  canals  establishing  com- 
munication between  the  adjacent  lacunas  are  not  demonstrable  in  the  tissues  of 
the  higher  vertebrates,  it  is  not  improbable  that  minute  interfascicular  passages 
exist  which  facilitate  the  access  of  nutritive  fluids  to  the  cells  enclosed  within  the 
lacunae. 

The  free  surface  of  cartilage  is  covered  by  an  envelope  of  dense  connective 
tissue,  the  perichondrium  ;  the  latter  consists  of  an  external  fibrous  layer  of  dense 
fibro-elastic  tissue  and  an  inner  looser  stratum  or  chondrogenetic  layer,  containing 
numerous  connective-tissue  cells.  These  are  arranged  in  rows  parallel  to  the  sur- 
face of  the  cartilage  and,  during  the  growth  of  the  tissue,  gradually  assume  the 
characteristics  of  the  cartilage-cells,  being  at  first  spindle-shaped  and  later  ovoid 
and  spherical.  The  young  cartilage-cells  thus  formed  become  gradually  separated 
by  more  extensive  tracts  of  the  newly  deposited  intercellular  matrix  ;  as  the  groups  of 
cells  originating  from  the  division  of  the  original  occupant  of  the  lacuna  recede  from 
the  perichondrial  surface,  they 

lose  their  primary  parallel  dis-  FIG.  no. 

position  and  become  irregu- 
larly arranged  and  still  further 
separated.  Those  portions  of 
the  ground-substance  most  re- 
mote from  the  perichondrium 
at  times  appear  granular,  this 
feature  being  intensified  when, 
as  in  aged  subjects,  a  deposition 
of  calcareous  matter  takes  place 
in  these  situations. 

In  articular  cartilage  the  su- 
perficial zone  contains  sparsely 
distributed  groups  of  small  cells 
arranged  parallel  to  the  free 
surface  ;  in  the  deeper  strata 
these  groups  are  replaced  by 
elongated  rows  of  larger  ele- 
ments lying  perpendicular  to 
the  articular  surface.  This 
columnar  disposition  of  the  car- 
tilage-cells is  particularly  evi- 
dent towards  the  underlying 
zone  of  calcified  matrix. 

The  blood-vessels  of  normal 
cartilage  are  usually  limited  to 
the  periphery,  within  the  perichondrium  or  the  associated  synovial  membranes  ;  the 
nutrition  of  the  cartilage  is  maintained  by  imbibition  of  the  fluids  through  the  matrix 
into  lacunae,  the  existence  of  minute  interfascicular  canals  being  highly  probable. 
In  the  thicker  masses  of  the  tissue,  as  in  the  cartilages  of  the  ribs,  nutrient  canals 
exist  in  those  portions  most  remote  from  the  perichondrium  ;  these  spaces  contain  a 
small  amount  of  areolar  tissue  supporting  the  blood-vessels,  which  are,  however, 
limited  to  the  channels,  the  nutrition  of  the  cartilage  tissue  being  effected  here,  as  at 
the  periphery,  by  absorption  through  the  matrix. 

Nerves  have  never  been  demonstrated  within  the  cartilages,  which  fact  explains 
the  conspicuous  insensibility  of  these  tissues  so  well  adapted  to  the  friction,  concus- 
sion, and  compression  incident  to  their  function. 

Elastic  cartilage,  called  also  yellow  elastic  or  reticular  cartilage  (Fig.  in), 
has  a  limited  distribution,  occurring  principally  in  the  cartilages  of  the  external  ear, 
part  of  the  Eustachian  tube,  the  epiglottis,  the  cartilages  of  Wrisberg  and  of  San- 
torini,  and  part  of  the  arytenoid  cartilages  of  the  larynx.  In  its  physical  properties 
this  variety  differs  markedly  from  hyaline  cartilage,  as  it  is  dull  yellowish  in  color 

6 


Cartilage-cells 


Lacuna  contain- 
ing nest  of 
cells 


-Empty  lacuna 
surrounded  by 
hvaline  matrix 


Transverse  section  of  peripheral  portion  of  costal  cartilage,    X  250. 


82 


HUMAN    ANATOMY. 


and  pliable  and  tough  in  consistence,  in  contrast  to  the  bluish  opalescent  tint  and 
comparative  brittleness  of  the  hyaline  variety. 

The  characteristic  feature  of  the  structure  of  the  elastic  cartilage  is  the  presence 
of  elastic  fibres  within  the  intercellular  matrix.  The  cell-nests  are  immediately  sur- 
rounded by  limited  areas  of  hyaline  intercellular  substance  corresponding  to  the 
matrix  of  hyaline  cartilage.  The  matrix  intervening  between  these  homogeneous 
fields,  however,  is  penetrated  by  delicate,  often  intricate,  net-works  of  elastic  fibres 
extending  in  all  directions.  The  connective-tissue  cells  lie  within  the  lacunae,  in  the 
hyaline  areas,  and  closely  resemble  the  elements  of  hyaline  cartilage.  Elastic  carti- 
lage possesses  a  perichondrium  of  the  usual  description. 

Fibrous  cartilage,  or  fibro-cartilage  (Fig.  112),  as  the  fibrous  variety  is  usu- 
ally designated,  is  found  in  comparatively  few  localities,  the  marginal  plates  and  the 
interarticular  disks  of  certain  joints,  the  symphyses,  the  intervertebral  disks,  sesamoid 
cartilages,  and  the  lining  of  bony  grooves  for  tendons  being  its  chief  representatives. 

FIG.  IT i. 


\y"         i     ' 

'l-G>   '• 


"-A, 

•&    ;:    .-£     : 

...    —         ~.;;    M          .  - 

WftA 

.-<      "fc     • 


Cartilage-cells — |r 


Hyaline  areas 


;^ 


" 

Mf 


ilw^i 


Elastic  net-work ;  >•'>/•.'   -T^^ 

of  intertx-llular 
tissue 


| 

Lacuna  contain-      V;VS'.':,^   — — : 
ing  cell 


Section  of  elastic  cartilage  from  the  epiglottis.     X  450. 


In  its  physical  properties  this  tissue  resembles  both  fibrous  tissue  and  cartilage,  pos- 
sessing the  flexibility  and  toughness  of  the  former  combined  with  the  firmness  and 
elasticity  of  the  latter.  A  proper  perichondrium  is  wanting. 

In  structure  fibro-cartilage  closely  resembles  dense  fibrous  tissue,  since  its  prin- 
cipal constituent  is  the  generally  parallel  wavy  bundles  of  fibrous  connective  tissm-  : 
among  the  latter  lie  small,  irregularly  disposed  oval  or  circular  areas  of  hyaline 
matrix  which  surround  the  cartilage-cells,  singly  or  in  groups.  The  number  of  cells 
and  the  proportion  of  fibrous  matrix  differ  in  various  localities. 

The  development  of  cartilage  proceeds  from  the  mesoblast,  the  cells  of  which 
undergo  proliferation  and,  forming  compact  groups,  become  ^he  embryonal  cartilage- 
cells  ;  at  first  the  latter  lie  in  close  apposition,  since  the  matrix  is  wanting.  During 
the  later  stages,  when  the  masses  of  embryonal  cartilage  map  out  the  subsequent 
skeletal  segments,  the  cells  are  separated  by  a  small  amount  of  homogeneous  matrix 
formed  through  the  influence  of  these  elements. 


DEVELOPMENT   OF   CARTILAGE.  83 

Cartilage  grows  in  two  ways  :  («)  by  the  expansion  produced  by  the  inter- 
stitial growth  effected  by  the  formation  of  new  cells  and  the  associated  matrix  and 
(b)  by  the  addition  of  the  new 

tissue   developed    by  pcrichon-  p,G   II2 

drial growth  at  the  periphery  of 
the  cartilage  from  the  chondro- 
genetic  layer.  The  latter  mode  \;.\" 

continues  throughout  the  period 
of  growth,  and  includes  the  di- 
rect Conversion  of  the  COnneC-  —Hyaline  area 

live-tissue  cells  of  the  perichon-  cartHage-cefis 

drium  intothecartilage  elements, 
and  the  accompanying  formation 
of  new  matrix. 

The  development  of  the 
elastic  fibres  within  the  elastic 
cartilage  is  secondary,  the  matrix 
during  the  early  stages  of  growth  ;  —Fibrous  inter- 

Being  hyaline.      The  elastic  tis-  cellular  sub- 

/-  •          i        r  _  '*••"•  X-,     A         stuncc 

sue  first  appears  in  the  form  of 

minute    granules,     which    later  \ 

fuse    and    become    the    elastic 

fibres;  this  change  first  appears  ,  ^" — •    ;     -Cartilage-ceils 

in  the  vicinity  of  the  cartilage- 
cells,  the  elastic  reticulum  sub- 
sequently invading  the  more  re-  -'•-' 

mote  portions  Of  the  matrix.      In  Section  of  fibrous  cartilage  from  intervertebral  disk.     X  225. 

the   development  of   the   fibro- 

cartilage,  the  fibres  appear  coincidently  with  the  limited  pericellular  areas  of  hyaline 

substance. 

CHEMICAL  COMPOSITION  OF  THE  CONNECTIVE  SUBSTANCES. 

Connective  Tissue. — The  fibrils  of  white  fibrous  connective  tissue  consist  of  a 
substance  known  as  collagen.  The  interfibrillar  ground-substance  contains  mainly 
mucoid  and  the  albuminous  materials  serum  globuli  and  serum  albumin.  Gelatin  is 
the  hydrate  of  collagen,  and  is  obtained  by  boiling  fibrous  tissue  with  water,  when 
the  gelatin  separates  like  a  jelly  on  cooling.  In  the  case  of  the  yellow  elastic 
fibres,  elastin  is  found  in  place  of  collagen.  In  reticular  tissue  rcticulin  is 
found.  The  latter  substance  contains  phosphorus.  These  substances,  namely, 
collagen  with  its  hydrate  gelatin,  elastin  and  perhaps  reticulin,  are  among  those 
known  as  albuminoids,  which  are  closely  related  to  the  true  albumins,  yet  differ  in 
some  important  respects.  The  albuminoids,  for  the  most  part,  contain  less  carbon 
and  more  oxygen  than  the  albumins  proper. 

Cartilage. — The  fibres  which  are  found  in  the  matrix  of  fibro-cartilage  and 
elastic  cartilage  are  respectively  composed  of  collagen  and  of  elastin,  just  as  they  are 
in  the  corresponding  connective  tissues. 

According  to  His,  the  chemical  composition  of  human  cartilage  is  as  follows  : 

Costal  cartilage.  Articular  cartilage. 

Water 67.67  73.59 

Solids  .  32.33  26.41 

Organic  matter 30.13  24.87 

Mineral  salts 2.20  1.54 

In  the  mineral  salts  there  is  about  45  per  cent,  of  sodium  sulphate.  A  somewhat 
smaller  percentage  of  potassium  sulphate,  and  smaller  amounts  of  the  phosphates  of 
sodium,  calcium  and  magnesium,  as  well  as  of  sodium  chloride,  are  present. 

Adipose  Tissue. — The  fats  in  the  animal  body  are  mainly  the  triglycerides  of 
stearic,  palmitic  and  oleic  acid.  There  is  found  in  man  a  comparatively  large  amount 
of  olein.  Small  quantities  of  lecithin,  cholesterin  and  free  fatty  acids  are  also  found 
in  fat  tissue. 


8j  HUMAN   ANATOMY. 

BONE   OR   OSSEOUS   TISSUE. 

In  the  higher  vertebrates,  osseous  tissue  forms  the  bony  framework,  or  skeleton, 
which  gives  attachment  and  support  to  the  soft  parts,  affords  protection  to  the  more 
or  less  completely  surrounded  delicate  organs,  supplies  the  passive  levers  for  the 
exercise  of  muscular  action,  insures  stability,  and  maintains  the  definite  form  of  the 
animal. 

In  addition  to  contributing  the  individual  bones  composing  the  principal,  and 
in  man  the  only,  framework,  or  entoskeleton,  osseous  tissue  occurs  in  the  lower  ver- 
tebrates associated  with  the  integument  as  an  exoskeleton.  Representatives  of  the 
latter  are  seen  in  the  bony  plates  present  in  the  skin  of  certain  ganoid  fishes, 
the  dermal  plates  of  crocodiles,  the  dorsal  and  ventral  shields  of  turtles,  or  the 
dermal  armor  of  the  armadillo.  Osseous  tissue  also  exists  within  various  organs  in 
certain  animals  and  then  constitutes  the  splanchnoskeleton.  Examples  of  the  latter 
are  furnished  by  the  bony  plates  encountered  in  the  sclerotic  coat  of  the  eyes  of 
birds,  in  the  diaphragmatic  muscle  of  the  camel,  in  the  tongue  of  certain  birds,  in 
the  heart  of  ruminants,  in  the  nose,  as  the  snout-bones  of  the  hog,  in  the  respiratory 
organs,  as  the  laryngeal,  tracheal,  and  bronchial  bones  of  birds,  and  in  the  genital 
organs,  as  the  penile  bone  of  carnivorous  and  certain  other  mammals. 

True  osseous  tissue  does  not  occur  outside  the  vertebrates.  Many  invertebrate 
animals  possess  a  skeletal  framework,  usually  external  but  in  some  cases  internal. 
Such  a  framework,  however,  consists  of  calcareous  incrustations,  hardened  excre- 
tions or  concretions  composed  principally  of  calcium  carbonate  and  of  silicious 
structures.  These  earthy  or  mineral  hard  parts  of  invertebrates  are  structureless 
deposits,  so  differing  materially  from  the  bone  tissue  of  the  higher  vertebrates  as 
well  in  structure  as  in  chemical  composition.  Sometimes  a  deposit  of  calcareous 
material  occurs  in  adult  cartilage,  a  process  entirely  distinct  from  the  formation  of 
bone  tissue.  Familiar  examples  of  such  calcification  are  seen  in  the  costal  and  some 
of  the  laryngeal  cartilages. 

Chemical  Composition. — Bone  is  a  dense  form  of  connective  tissue,  the 
matrix  of  which  is  impregnated  with  lime  salts  ;  it  consists,  therefore,  of  two  parts, 
an  animal  and  an  earthy  portion,  the  former  giving  toughness  and  the  latter  hardness 
to  the  osseous  tissue. 

The  animal  or  organic  part  of  bone  may  be  removed  by  calcination,  leaving  the 
inorganic  constituents  undisturbed.  If  a  bone  be  heated  in  a  flame  with  free  access 
of  air,  the  animal  matter  at  first  becomes  charred  and  the  bone  black  ;  continued 
combustion  entirely  removes  the  organic  materials,  the  earthy  portion  alone  remain- 
ing. After  such  treatment,  while  retaining  its  general  form,  the  bone  is  fragile  and 
easily  crushed,  and  has  suffered  a  loss  of  one-third  of  its  weight,  due  to  the  destruc- 
tion and  elimination  of  the  animal  constituents.  The  latter,  evidently,  constitute 
one-third  and  the  mineral  matters  two-thirds  of  the  bone.  The  inorganic  constitu- 
ents include  a  large  amount  of  calcium  phosphate,  much  less  calcium  carbonate,  with 
small  proportions  of  calcium  fluoride  and  chloride,  and  of  the  salts  of  magnesium  and 
sodium. 

The  animal  portion  of  the  bone,  on  the  other  hand,  may  be  separated  from  the 
inorganic  salts  by  the  action  of  dilute  hydrocnloric  acid,  which  desolves  out  the 
earthly  constituents  ;  after  such  treatment  the  bone,  although  retaining  perfectly 
its  form  and  details,  is  tough  and  flexible,  a  decalcified  rib  or  fibula  being  readily 
tied  into  a  knot.  The  animal  constituents  of  bone  yield  gelatin  upon  prolonged 
boiling  in  water,  therein  resembling  fibrous  connective  tissue. 

The  composition  of  bone,  according  to  Berzelius,  is  as  follows  : 

ORGANIC  MATTER Gelatin  and  blood-vessels,  33-3° 

f  Calcium  phosphate,  51-04 

I   Calcium  carbonate,  1 1  ;v  > 

INORGANIC  MATTER \  Calcium  fluoride,  2.00 

Magnesium  phosphate,  1.16 

Sodium  oxide  and  sodium  chloride,  1. 20 

100.00 


PHYSICAL    PROPERTIES   OF    BONE. 


FIG.  113. 


Physical  Properties. — Rauber  has  shown  that  a  five-millimetre  cube  of  com- 
pact bone  of  an  ox  when  calcined  will  resist  pressure  up  to  298  pounds ;  when  decal- 
cified up  to  136  pounds  ;  under  normal  conditions  up  to  852  pounds,  the  pressure 
being  applied  in  the  line  of  the  lamellae. 

It  results  from  its  composition  that  while  bone  is  very  hard  and  resistant  to  press- 
ure, it  is  also  somewhat  flexible,  elastic,  and  capable  of  withstanding  a  tearing  strain. 
It  is  remarkable  that  in  many  substances  the  power  to  resist  a  crushing  strain  is  very 
different  from  that  of  resisting  a  tearing  one.  Thus,  cast  iron  is  more  than  five  times 
as  resistant  to  the  former  strain  as  to  the  latter,  and  wrought  iron  is  nearly  twice  as 
resistant  to  the  latter  as  to  the  former.  Neither  of  these  materials,  therefore,  is  well 
fitted  to  resist  both  strains,  since  a  much  greater  quantity  must  be  used  than  would 
be  needed  were  either  material  to  be  exposed  only  to  the  strain  it  is  best  able  to  with- 
stand. Bone,  however,  has  the  property 
of  resisting  both  strains  with  approximately 
equal  facility,  its  tearing  limit  being  to  its 
crushing  limit  about  as  3  is  to  4.  This  has 
the  advantage  that  strength  need  not  be 
obtained  by  great  increase  of  weight,  con- 
sequently the  plan  of  bone  structure  com- 
bines lightness  and  strength. 

Structure  of  Bone.  —  On  sawing 
through  a  bone  from  which  the  marrow  and 
other  soft  parts  have  been  removed  by  ma- 
ceration and  boiling,  the  osseous  tissue  is 
seen  (Fig.  113)  to  be  arranged  as  a  pe- 
ripheral zone  of  compact  bone  enclosing  a 
variable  amount  of  spongy  or  cancellated 
bone.  In  the  typical  long  bones,  as  the 
humerus  or  femur,  the  compact  tissue  al- 
most exclusively  forms  the  tubular  shaft 
enclosing  the  large  marrow-cavity,  the  can- 
cellated tissue  occupying  the  expanded 
extremities,  where,  with  the  exception  of 
a  narrow  superficial  stratum  of  compact 
bone,  it  constitutes  the  entire  framework  ; 
the  clefts  between  the  lamellae  of  the  spongy 
bone  are  direct  extensions  of  the  general 
medullary  cavity  and  are  filled  with  mar- 
row-tissue. In  the  flat  bones  (Fig.  116), 
as  those  of  the  skull,  the  compact  substance 
consists  of  an  outer  and  inner  plate,  or 
tables,  enclosing  between  them  the  cancel- 
lated tissue,  or  diploe,  as  this  spongy  bone 
is  often  termed.  Short  and  irregular  bones 
are  made  up  of  an  inner  mass  of  spongy 

bone  covered  by  an  external  shell  of  compact  substance  which  often  presents  local 
thickenings  in  order  to  insure  additional  strength  where  most  needed. 

The  cancellated  bone  consists  of  delicate  bars  and  lamellae  which  unite  to 
form  an  intricate  reticulum  of  osseous  tissue  well  calculated  to  insure  considerable 
strength  without  undue  weight  ;  in  many  positions,  conspicuously  in  the  neck  of  the 
femur  (Fig.  374),  the  more  robust  lamellae  are  disposed  in  a  definite  manner  with 
a  view  of  meeting  the  greatest  strains  of  pressure  and  of  tension. 

Although  composed  of  the  same  structural  elements,  compact  and  spongy  bone 
differ  in  their  histological  details  in  consequence  of  the  secondary  modifications 
which  take  place  during  the  conversion  of  the  spongy  bone,  the  original  form,  into 
the  compact  substance.  To  obtain  the  classic  picture  of  osseous  tissue,  in  order  to 
study  its  general  arrangement  in  the  most  typical  form,  it  is  desirable  to  examine 
thin  ground  sections  of  the  compact  substance  cut  at  right  angles  to  the  axis  of  a 
long  bone  which  has  been  macerated  and  dried,  and  in  which  the  spaces  contain  air. 


Section  of  upper  end  of  humerus,  showing  the 
external  layer  of  compact  bone  surrounding  the  med- 
ullary cavity  below  and  the  spongy  bone  above. 


86 


HUMAN    ANATOMY. 


The  compact  bone  in  such  preparations,  when  examined  under  low  ampli- 
fication (Pig.  114),  is  seen  to  be  composed  of  osseous  layers  arranged  as  three 
chief  groups  :  (a)  the  circumferential  lamellcc,  which  extend  parallel  to  the  external 
and  internal  surfaces  of  the  compact  bone  ;  (b)  the  Haversian  lamellcc,  which  are 
disposed  concentrically  and  form  conspicuous  annular  groups,  the  Haversian  systems. 
enclosing  the  Haversian  canals  ;  and  (c~)  the  interstitial  or  ground  lamellcc,  which 
constitute  the  intervening  more  or  less  irregularly  arranged  bony  layers  filling  up 
the  spaces  between  the  Haversian  systems  and  the  peripheral  strata. 

FIG.  114. 


-External   circumferen- 
tial lamella; 


.      i         *      'A~  ->-i\)j'. 


-Haversian  canal  sur- 
rounded by  Havci- 
sian  lamella: 


r-s 


— Interstitial  latnclhe 


^-v^^V^.- "  -  *$^l**K'- 

^ »  •  r  O  •;*  *  *-***•**  x-  -  <  ~  „  -  -   <-  --. .  Jv .  S* 

m^^!§!^^; 

-  ~  -i-  .^^vc~>  ^  Wc^+  %2H : 

^  --  ^^^v  ^>*V.*r^^*SSs  ^  Jf 

-^-  —     -    S.    "-      —  «ir   x.  -  v  — -  / '*"-'/ •-*>  —  ~^>. 

,«^^=x  — .•__  ^^-  ^~7J2'_""t-  -~~  *-— '-1—  .^  ^t  :-^^v  CTi^ 


— *-   -ifc- 

' 


Tra 


•Internal  i  ii<  unilrioti- 
tial  lar 

insvcrse  section  of  compact  bone  (metatarsal) ;  the  section  has  been  ground  and  dik-d,  IK-IKO  tin.-  lacuna-  are 

filled  with  air.     X  85. 

Each  Haversian  system  consists  of  the  concentrically  disposed  lamellae  and 
the  centrally  situated  channel,  or  Haversian  canal,  enclosing  the  ramifications  of  the 
medullary  blood-vessels  and  associated  marrow-tissue.  Between  the  annularly 
arranged  lamellae  are  seen  small  spindle-shaped  or  oval  spaces,  the  hicnn<s,  about 
.02  millimetre  long,  .or  millimetre  wide,  and  .006  millimetre  thick,  from  which  ex- 
tend minute  radiating  channels,  the  canalicnli,  establishing  Communication  between 
the  adjacent  lacume  of  the  same  Haversian  system.  The  lacuna-  and  the  canaliculi 
constitute  an  intercommunicating  net-work  of  lymph-spaces  similar  to  those  encoun- 


STRUCTURE   OF   BONE. 


tered  in  other  forms  of  dense  connective  tissue.  Since  the  lacunae  are  compressed 
oval  cavities  lying  between  the  lamellae  of  the  osseous  matrix,  when  viewed  in  sec- 
tions which  pass  through  the  layers  at  right  angles  (Fig.  117),  the  lacunae  present 
their  narrower  dimensions,  appearing  thus  in  profile  as  small  lentiform  spaces  ;  seen 
in  sections,  on  the  contrary,  which  pass  parallel  to  the  lamellae  (Fig.  118),  the 
lacunae  are  broader  and  more  circular,  the  spaces  with  the  canaliculi  forming  the 
spider-like  figures  so  conspicuous  in  longitudinal  sections  of  dried  bone. 

The  characteristic  arrangement  of  the  lamellae  of  the  Haversian  systems  is  due 
to  the  secondary  formation  of  the  osseous  tissue  during  the  conversion  of  the  older 
spongy  bone  into  compact  tissue,  the  circumference  of  the  system  corresponding  to 
the  Haversian  space  in  which  the  subsequent  development  of  the  concentric  lamellae 

FIG.  115. 


Circumferential 

lamellae 


Interstitial  lamellae 


Haversian  canal 


Obliquely  cut  Haver- 
sian canal 


Longitudinal  section  of  compact  bone,  ground  and  dried. 


took  place.  It  follows,  from  this  relation,  that  Haversian  systems  exist  only  in  com- 
pact bone,  since  the  necessary  secondary  deposit  does  not  occur  during  the  growth 
of  the  spongy  or  cancellous  tissue. 

The  lamellae  of  osseous  tissue,  when  deprived  of  the  mineral  matters  and  exam- 
ined in  thin  fragments,  often  display  the  ultimate  fibrous  structure  which  they  pos- 
sess, since  they  consist  of  delicate  fibrils  of  fibrous  tissue  embedded  within  a  ground- 
substance  and  associated  into  bundles  which  are  arranged  as  crossing  and  interwoven 
layers.  Within  the  Haversian  lamellae  the  fibrous  bundles  cross  generally  at  right 
angles,  but  in  other  locations  they  are  less  regularly  and  more  acutely  disposed. 

The  perforating  fibres  of  Sharpey  (Fig.  119)  consist  of  bundles  of  fibrous 
tissue  which  penetrate  the  lamellae  in  a  direction  perpendicular  or  oblique  to  their 


88 


HUMAN    ANATOMY. 


surface,  and  thus  pin  or  bolt  the  layers  together.  These  fibres  are  especially  numer- 
ous in  the  superficial  lamellae  beneath  the  periosteum,  to  which  membrane  they  owe 
their  formation,  and  with  which  many  seem  to  be  directly  continuous.  They  are 


FIG. 


Section  of  frontal  bone,  showing  the  absence  of  Haversian  systems.     X  20 

readily  found  on  the  surfaces  of  the  lamellae  of  decalcified  bone  which  have  been 
forcibly  separated.  Although  usually  consisting  of  bundles  of  fibrous  tissue,  it  is 
probable  that  in  some  cases  the  perforating  fibres  are  elastic  in  nature.  They  are 
sometimes  imperfectly  calcified  and  leave,  therefore,  on  drying,  tubular  canals, 

which  pierce  the  lamella  from  the  ex- 
terior of  the  bone.  Since  the  perfo- 
rating fibres  are  associated  genetically 
with  the  periosteum,  they  are  never 
found  in  the  secondary  lamellae  consti- 
tuting the  Haversian  systems. 

The  Haversian  canals  are  co 
tinuations  of  the  medullary  cavity  and 
serve  the  important  purpose  of  con- 
veying the  blood-vessels  within  the 
compact  substance  ;  from  these  vessels 
the  nutritive  fluids  pass  into  the  peri- 
vascular  lymph-spaces  between  the 
walls  of  the  canal  and  the  blood-ves- 
sels and  thence,  by  way  of  the  cana- 
liculi,  which  open  into  these  Ivmph- 

Portion  of  adjacent  Haversian  systems  rut  transversely.  .  1*1  i 

x  250.  spaces,  into  the  adjacent  lacuna  .  and 

so  on  into  the  surrounding  portions  of 

the  compact  substance,  the  nutrition  of  which  is  thus  maintained.  Although  the 
average  size  of  the  canals  is  about  .05  millimetre,  those  next  the  medullary  cavity 
are  larger,  some  measuring  .  i  millimetre  or  more  in  diameter,  and  contain,  in  addi- 


ti- 

„. 


Haversian 
canal 

Lacuna  in 
profile 


THE   BONE-CELLS. 


89 


FIG.  118. 


Lacunae  and  canaliculi  from  dried  bone  cut  parallel  with 
the  lamellae.     X  300. 


tion  to  the  blood-vessels,  an  extension  of  the  marrow-tissue.  The  individual  chan- 
nels are  short,  and  communicate  by  oblique  branches  with  adjacent  canals  (Fig. 
115).  The  Haversian  canals  indirectly  communicate  with  the  external  surface  of 
the  bone  by  means  of  the  channels,  or  Volkmanri s  canals,  within  the  circumfer- 
ential lamellae,  which  open  by  minute  orifices  and  receive  vascular  twigs  from  the 
periosteal  blood-vessels  (Fig.  122);  the  latter  are  thus  brought  into  free  anasto- 
mosis with  the  branches  derived  from  the  medullary  vessels,  the  two  constituting  a 
freely  communicating  vascular  net-work  throughout  the  compact  substance. 

The  Bone-Cells.— The  details  of 
osseous  tissue  thus  far  considered  per- 
tain to  the  structure  of  the  passive  in- 
tercellular constituents  of  a  dense  con- 
nective tissue  ;  in  addition  to  these,  as 
in  other  forms  of  connective  substances, 
the  more  active  elements  are  the  con- 
nective-tissue cells,  here  known  as  the 
bone-cells.  As  already  pointed  out,  the 
lacunae  and  the  canaliculi  represent  in- 
tercommunicating lymph-spaces,  similar 
to  those  encountered  in  the  cornea  or 
other  dense  connective  tissue  ;  as  in  the 
latter  so  also  in  the  osseous  tissue,  the 
cellular  elements  occupy  the  lymph- 
spaces,  the  bone-cells  lying  within  the  lacunae.  Since  the  classic  pictures  of  bone 
are  derived  from  ground  sections  of  dried  tissue,  in  such  preparations  the  deli- 
cate bone-cells  have  shrunken  and  disappeared,  and  the  lacunae  contain,  at  best, 
only  the  indistinguishable  remains  of  the  cells  mingled  with  debris  produced  during 
the  preparation  of  the  section  ;  the  lacunae  and  the  canaliculi  in  dried  sections 
are  filled  with  air,  by  reason  of  which  condition  they  appear  as  the  familiar  dark, 

sharply  defined,  conspicuous  spider- 
like  figures. 

In  order  to  study  the  bone- 
cells,  the  tissue  after  fixation  is  de- 
calcified and  stained,  and  mounted 
in  an  approved  preserving  medium  ; 
in  consequence  of  such  treatment 
the  air  is  displaced  from  the  spaces 
within  the  bone,  which  now  appear 
faintly  outlined,  the  delicate  ramifi- 
cations of  the  canaliculi  in  places 
being  almost  invisible.  The  bone- 
cells,  after  being  stained  in  such 
decalcified  preparations,  appear  as 
small  lenticular  or  stellate  bodies 
within  the  lacunae  (Fig.  121),  -which 
they  almost  entirely  fill.  Each  cell- 
body  consists  of  granular  cytoplasm 
from  which  delicate  processes  ex- 
tend for  a  variable  distance  into  the 
canaliculi,  in  favorable  localities  the 

protoplasmic  processes  sent  out  by  adjacent  bone-cells  sometimes  meeting.  The 
deeply  staining  nucleus  appears  as  a  brilliant  point  within  the  stellate  cell. 

The  Periosteum. — The  external  surface  of  bones  is  closely  invested,  except 
where  covered  with  cartilage,  with  a  fibrous  membrane,  the  periosteum,  a  structure 
of  great  importance  during  development  and  growth,  and  later  for  the  nutrition 
and  protection  of  the  osseous  tissue.  During  childhood  an  end  of  the  immature 
bone  may  be  broken  off  and  yet  held  in  place  by  the  periosteum.  The  adult  peri- 
osteum consists  of  two  layers,  an  outer  fibrous  and  an  inner  fibro-elastic ;  when 
covering  young  bones,  however,  in  which  growth  is  actively  progressing,  the  peri- 


FIG.  119. 


Semi-diagrammatic  view  of  perforating  fibres  of  Sharpey;  the 
lamellae  of  decalcified  bone  have  been  partially  separated. 


90  HUMAN   ANATOMY. 

osteum  contains  an  additional  stratum,  the  osteogenetic  layer,  which  lies  closely  asso- 
ciated with  the  exterior  of  the  bone.  After  growth  has  ceased,  the  osteogenetic 
layer  becomes  reduced  to  an  inconspicuous  stratum  included  as  part  of  the  fibro- 
elastic  constituent  of  the  periosteum. 

The  fibrous  layer  is  composed  of  closely  placed  bundles  of  fibrous  connective 
tissue,  and  serves  to  support  larger  blood-vessels  which  break  up  within  the  deeper 
parts  of  the  periosteum  into  the  minute  twigs  entering  the  canals  opening  onto  the 
surface  of  the  bone. 

FIG.  120. 


Sharpev's 
fibres 


'*     ! 

Lacuna 


Oblique  section  of  decalcified  tibia,  showing  fibrous  character  of  lamellae  and  groups  of  Sharpey's  fibres.     X  42°. 

The  fibro-elastic  layer  consists  of  a  rich  felt-work  of  elastic  fibres,  often  arranged 
as  several  distinct  strata  ;  the  elastic  tissue  is  separated  from  the  surface  of  the  bone 
by  a  layer  of  fibrous  tissue  comparatively  rich  in  flat,  plate-like  connective-tissue 
cells,  the  remains  of  the  elements  of  the  osteogenetic  layer.  The  inner  surface  of 
the  periosteum  is  intimately  attached  to  the  osseous  tissue  by  means  of  delicate 
processes  of  connective  tissue  which  accompany  the  blood-vessels  into  the  nutrient 
canals  ;  this  relation  persists  from  the  continuity  of  the  formative  tissue  of  the  young 

periosteum  with   the    early  marrow-tissue. 

FIG.  121.  Between  the  fibrous  bundles  next  the  bone 

numerous  cleft-like  lymph-spaces  exist  ; 
these  are  imperfectly  lined  by  the  endothe- 
lioid  connective-tissue  cells  and  communi- 
cate with  the  lymph-channels  within  the 
bone. 

MBh^  The    osteogenetic    layer,     conspicuous 

during  the  development  and  growth  of  the 
osseous  tissue,  consists  of  delicate  bundles 
of  fibrous  tissue  and  large  numbers  of 
connective-tissue  cells  of  an  embryonal 
type.  Those  next  the  growing  bone  as- 
sume a  low,  irregular  columnar  form,  and 
are  disposed  in  rows  upon  the  surface  of 

Bone-ceils  lying  within  tin-  ia>  „„.,        700.  the  developing  osseous  tissue;  sinre  these 

cells  are  concerned  in  the  production  of  the 

latter,  they  are  appropriately  termed  osteoblasts.  Later  some  of  them  become  sur- 
rounded by  the  bony  matrix,  and  are  thus  transformed  into  bone-cells.  The  osteo- 
genetic layer  is  rich  in  blood-vessels  which,  as  the  bone  is  formed,  are  continued  into 
the  primary  marrow-cavities. 

The  Marrow. — The  spaces  in  the  interior  of  bones,  whether  the  large 
medullary  cavities  surrounded  by  the  compact  substance  forming  the  shaft  of  the 
long  bones  or  the  irregular  interstices  between  the  trabeculae  composing  the  cancel- 


THE    RED    BONE-MARROW.  91 

lated  tissue,  are  filled  with  bone-marrow.  The  latter  also  extends  within  the  larger 
Haversian  canals. 

Although  originally  only  of  one  variety  within  the  bones  of  the  early  skeleton, 
the  marrow  in  the  adult  consists  of  two  kinds,  the  yellow  and  the  red.  Thus,  within 
the  shaft  of  the  long  bones  it  consists  of  a  light  yellowish  tissue,  presenting  the  char- 
acteristics of  ordinary  adipose  tissue,  while  within  the  spaces  of  the  cancellated  tissue 
at  the  ends  of  the  same  bones  the  marrow  appears  of  a  dull  red  color.  In  addition 
to  the  ends  of  the  long  bones,  the  localities  in  which  red  marrow  especially  occurs 
are  the  bodies  of  the  vertebrae,  the  ribs,  the  sternum,  the  diploe  of  the  cranium,  and 
the  short  bones. 

Red  Marrow. — The  ingrowth  of  the  periosteal  tissue  and  blood-vessels  con- 
stitutes the  primary  marrow  within  the  embryonal  skeleton  ;  from  this  tissue  the  red 
marrow  filling  the  young  bones  is  directly  derived.  The  red  marrow  is,  therefore, 


FIG.  122. 


u 

f    «. 


\        ''it  \  I  Y      i  !  /  i  •    v  ' 

Vs.%      <    '   I.v'M 

^''iulfS^ 

t\h  A™  A&        /     .  M  "  -,        .       ;:  •  '      ,  vU;   v  '-'  j  .IV-     •  '  /       /  ,i. 


Dense  fibrous  layer 


Last  formed  lamella 
of  bone 


Periosteal  blood- 
vessel  passing  into 
the  bone 


Bone-cell  within 
lacuna 


•  ••-•• 
tt •ife'xfljs  \v       ous  with  periosteum 


'TOffi-V'"i   Remains  of  osteogenetic 

Y         Invpr 


n 


Section  of  young  periosteum  and  subjacent  bone.     X  275. 

the  typical  and  first  formed  variety  within  the  foetus  and  the  young  animal  ;  subse- 
quently, that  situated  within  the  shaft  of  the  long  bones  becomes  converted  into 
yellow  marrow  by  the  replacement  of  the  majority  of  the  marrow  elements  by  fat- 
cells. 

The  red  marrow  (Fig.  123),  when  examined  in  section  after  fixation  and  staining, 
presents  a  delicate  reticulum  of  connective  tissue  which  supports  the  numerous 
medullary  blood-vessels  and  the  cellular  elements.  Next  the  bone  the  fibrous  tissue 
forms  a  thin  membrane,  the  endosteum,  lining  the  medullary  cavity  and  the  larger 
Haversian  canals  into  which  the  marrow  extends.  This  membrane  is  highly  vascu- 
lar, its  vessels  joining  those  within  the  osseous  canals  on  the  one  side  and  those  of 
the  marrow  on  the  other. 

The  delicate  fibrous  reticulum,  in  addition  to  the  thin-\valled  blood-channels 
which  it  supports,  contains  within  its  meshes  the  several  varieties  of  elements  char- 


HUMAN   ANATOMY. 


acteristic  of  the  red  marrow  ;  these  are  :  (i)  the  marroiv-cells,  (2)  the  eosinophiie 
cells,  (3)  the  giant  cells,  and  (4)  the  nucleated  red  blood-cells. 

The  marrow-cells,  or  mychcytes,  resemble  the  large  lymphocytes  of  the 
blood,  but  may  differ  from  the  latter  in  their  slightly  larger  size  and  in  the  possession 
of  a  relatively  large  round  or  oval  nucleus  which  contains  comparatively  little 
chromatin;  the  presence  of  neutrophile  granules  within  the  cytoplasm  of  the  marrow- 
cells  affords  an  additional  differential  characteristic  when  compared  with  the  large 
lymphocytes  in  which  these  granules  are  absent. 

The  eosinophiie  cells  occur  in  considerable  numbers  within  the  red  marrow, 
and  appear  in  varying  stages  of  growth,  as  evidenced  by  their  round  vwnonudear, 
the  indented  transitional  and  segmented  polymorphonuclear  condition  ;  the  cells  con- 
taining the  latter  form  of  nucleus  are  most  abundant  and  represent,  probably,  the 
mature  elements. 

The  giant  cells,  or  myeloplaxes,  are  huge  elements  of  irregular  oval  form,  and 
contain  simple  or  polymorphous  nuclei.  They  represent  specialized  myelocytes, 

FIG.  123. 


Marrow-cells— 


Young  red  blood-cells—-*-^ 


Giant  cell 


Blood-Vessel 


'mmr^^ 


Blood-vessel 


Connective-tissue  reticulum 


Section  of  red  marrow  from  epiphysis  ot  young  femur.    X  300. 

and  during  the  processes  resulting  in  the  removal  of  osseous  tissue  they  are  the. 
osteoclasts  which  are  actively  engaged  in  effecting  the  absorption  of  the  bony 
matrix.  Ordinarily  the  giant  cells  occupy  the  central  portions  of  the  marrow  : 
when,  however,  they  enter  upon  the  role  of  bone- destroyers,  they  lie  on  the  sur- 
face of  the  osseous  trabeculae  within  the  depressions  known  as  Howship" s  lacionr 
(Fig.  128). 

The  nucleated  red  blood-cells  within  the  red  marrow  are  concerned  in  the 
important  function  of  renewing  the  colored  cells  of  the  blood,  the  red  marrow  being 
the  chief  seat  in  which  this  process  takes  place  after  birth  ;  hence  the  red  marrow  is 
classed  as  a  blood-forming  organ.  The  nucleated  red  blood-cells  exist  within  the 
marrow  in  two  forms,  an  older  and  a  younger.  The  genetically  older  cells,  the 
erythroblasts,  are  the  descendants  of  the  embryonal  nucleated  blood-cells  on  the  one 
hand  and  the  immediate  parents  of  the  younger  blood-elements  on  the  other.  The 
erythroblasts  possess  relatively  large  nuclei,  with  chromatin  reticulum  and  cytoplasm 
tinged  with  haemoglobin  ;  they  are  frequently  observed  during  mitosis,  since  they  give 
rise  to  the  second  generation  of  nucleated  red  blood-cells.  The  latter,  the  normo- 


THE   YELLOW    BONE-MARROW.  93 

blasts,  are  directly  converted  into  the  mature,  non-nucleated  red  blood-disks  on  the 
disappearance  of  their  nucleus.  In  addition  to  a  larger  amount  of  haemoglobin  in  their 
cytoplasm,  the  normoblasts  differ  from  the  erythroblasts  in  the  possession  of  a  deeply 
staining  nucleus,  in  which  the  chromatin  no  longer  appears  as  a  reticul.um. 

It  is  usual  to  find  isolated  groups  of  fat-cells  distributed  within  the  red  marrow, 
although  the  amount  of  adipose  tissue  is  very  meagre  in  localities  farthest  removed 
from  the  medulla  of  the  long  bones.  The  varieties  of  leucocytes  usually  seen  in  the 
blood  are  also  encountered  within  the  red  marrow  in  consequence  of  the  intimate 
relations  between  the  latter  tissue  and  the  blood-stream  conveyed  by  the  medullary 
capillaries. 

Yellow  Marrow. — Since  the  appearance  of  the  yellow  marrow  is  due  to  the 
preponderating  accumulation  of  fat-cells  which  have  replaced  the  typical  elements 
of  the  marrow  contained  within  the  shaft  of  certain  bones,  the  formation  of  this 
variety  is  secondary  and  must  be  regarded  as  a  regression. 

Examined  in  section,  yellow  marrow  resembles  ordinary  adipose  tissue,  since 
it  consists  chiefly  of  the  large  oval  fat-cells  supported  by  a  delicate  reticulum  of 
connective  tissue.  In  localities  in  which  the  latter  exists  in  considerable  quantity, 
numerous  lymphoid  cells  represent  the  remaining  elements  of  the  originally  typical 
marrow-tissue.  After  prolonged  fasting  the  yellow  marrow  loses  much  of  its  oily 
material  and  becomes  converted  into  a  gelatinous  substance  containing  compara- 
tively few  fat-cells  ;  upon  the  re-establishment  of  normal  nutrition  this  tissue  may 
again  assume  the  usual  appearance  of  yellow  marrow. 

Blood-Vessels. — The  generous  blood-supply  of  bones  is  arranged  as  two  sets 
of  vessels,  the  periosteal  and  the  medullary.  The  former  constitutes  an  external 
net-work  within  the  periosteum,  from  which,  on  the  one  hand,  minute  twigs  enter 
the  subjacent  compact  substance  through  channels  (  Volkmanri  s  canals}  communi- 
cating with  the  Haversian  canals,  within  which  they  anastomose  with  the  branches 
derived  from  the  medullary  system  ;  additional  vessels,  on  the  other  hand,  pass  to 
the  cancellated  tissue  occupying  the  ends  of  the  long  bones. 

The  medullary  artery  is  often,  as  in  the  case  of  the  long  bones,  a  vessel  of  con- 
siderable size,  which,  accompanied  by  companion  veins,  traverses  the  compact  sub- 
stance through  the  obliquely  directed  medullary  canal  to  gain  the  central  part  of  the 
marrow.  On  reaching  this  position  the  medullary  artery  usually  divides  into  ascend- 
ing and  descending  branches,  from  which  radiating  twigs  pass  towards  the  periphery. 
The  latter  terminate  in  relatively  narrow  arterial  capillaries,  which,  in  turn,  expand 
somewhat  abruptly  into  the  larger  venous  capillaries.  Such  arrangement  results  in 
diminished  rapidity  of  the  blood-stream,  the  blood  slowly  passing  through  the  net- 
work formed  by  the  venous  capillaries.  The  latter  vessels,  within  the  red  marrow, 
possess  thin  walls  and  an  imperfect  endothelial  lining  in  consequence  of  which  the 
blood  comes  into  close  relation  with  the  elements  of  the  medullary  tissue.  During 
its  sluggish  course  within  the  blood-spaces  of  the  red  marrow,  the  blood  takes  up  the 
newly  formed  red  cells,  which  thus  gain  entrance  into  the  circulation  to  replace  the 
effete  corpuscles  which  are  continually  undergoing  destruction  within  the  spleen.  It 
is  probable  that  leucocytes  also  originate  in  the  bone-marrow. 

After  thus  coming  into  intimate  relations  with  the  marrow-tissue,  the  blood  is 
collected  by  capillaries  which  form  small  veins.  In  addition  to  the  companion  veins 
accompanying  the  nutrient  artery  along  the  medullary  canal,  in  many  instances  the 
larger  veins  pursue  a  course  independent  of  the  arteries  and  emerge  from  the  can- 
cellous  tissue  by  means  of  the  canals  piercing  the  compact  substance  at  the  ends  of 
the  bones.  Although  destitute  of  valves  within  the  medulla,  the  veins  possess  an 
unusual  number  of  such  folds  immediately  after  escaping  from  the  bone. 

Lymphatics. — The  definite  lymphatic  channels  of  the  bones  are  principally 
associated  with  the  blood-vessels  of  the  periosteum  and  the  marrow  as  perivascular 
channels,  although  it  is  probable  that  lymphatic  spaces  exist  within  the  deeper  layers 
of  the  periosteum,  in  close  relation  to  the  osseous  tissue.  The  perivascular  lym- 
phatics follow  the  blood-vessels  into  the  Haversian  canals,  where,  as  well  as  on  other 
surfaces  upon  which  the  canaliculi  open,  the  system  of  intercommunicating  juice- 
channels  represented  by  the  lacunae  and  the  canaliculi  is  directly  related  with  the 
lymphatic  trunks. 


94 


HUMAN    ANATOMY. 


Nerves. — The  periosteum  contains  a  considerable  number  of  nerves,  the  ma- 
jority of  which,  however,  are  destined  for  the  supply  of  the  underlying  osseous 
tissue,  since  those  distributed  to  the  fibrous  envelope  of  the  bone  are  few.  The 
periosteal  nerves  follow  the  larger  blood-vessels,  in  the  walls  of  which  they  chiefly 
terminate.  Medullary  nerves  accompany  the  corresponding  blood-vessels  through 
the  medullary  canal,  and  within  the  marrow  break  up  into  fibrillae  to  be,  probably, 
distributed  to  the  walls  of  the  vascular  branches  along  which  they  lie.  Regarding 
the  ultimate  endings  and  arrangement  of  the  sensory  fibres  little  is  known  ;  in  view 
of  the  low  degree  of  sensibility  possessed  by  healthy  bones  and  their  periosteum, 
the  number  of  such  nerves  present  in  osseous  structures  must  be  very  small. 


FIG.  124. 


.... 


DEVELOPMENT   OF   BONE. 

The  bones  composing  the  human  skeleton,  with  few  exceptions,  are  preceded 
by  masses  of  embryonal  cartilage,  which  indicate,  in  a  general  way,  the  forms  and 
relations  of  the  subsequent  osseous  segments,  although  many  details  of  the  model- 
ling seen  in  the  mature  bones  appear  only  after  completed  development  and  the  pro- 
longed exercise  of  the  powerful  modifying  influences  exerted  by  the  action  of  the 
attached  muscles.  Since  the  primary  formation  of  such  bones  takes  place  within 
the  cartilage,  the  process  is  appropriately  termed  endochondral  development. 

Certain  other  bones,  notably  those  forming  the  vault  of  the  skull  and  almost  all 
those  of  the  face,  are  not  preceded  by  cartilage,  but,  on 
the  contrary,  are  produced  within  sheets  of  connective  tis- 
sue ;  such  bones  are  said,  therefore,  to  arise  by  intra- 
membranous  development.  It  will  be  seen,  however,  that 
the  greater  part  of  the  bone  formed  by  endochondral  de- 
velopment undergoes  absorption,  the  spongy  substance 
within  the  ends  of  the  long  and  the  bodies  of  the  irregu- 
lar bones  representing  the  persistent  contribution  of  this 
process  of  bone-production.  Even  in  those  cases  in  which 
the  intracartilaginous  mode  is  conspicuous,  as  in  the  de- 
velopment of  the  humerus,  femur,  and  other  long  bones, 
the  important  parts  consisting  of  compact  substance  are  the 
product  of  the  periosteal  connective  tissue,  and  hence  ge- 
netically resemble  the  intramembranous  group.  Although 
both  methods  of  bone-formation  in  many  instances  proceed 
coincidently  and  are  closely  related,  as  a  matter  of  con- 
venience they  may  be  described  as  independent  processes. 
Endochondral  Bone  Development. — The  pri- 
mary cartilage,  formed  by  the  proliferation  and  condensa- 
tion of  the  elements  of  the  young  mesoblastic  tissue,  grad- 
ually assumes  the  characteristics  of  embryonal  cartilage, 
which  by  the  end  of  the  second  month  of  intra-uterine  life 
maps  out  the  principal  segments  of  the  fct-tal  cartilaginous 
skeleton.  These  segments  are  invested  by  an  immature 
form  of  perichondrium,  or  primary  periosteum ,  from  which 
proceed  the  elements  actively  engaged  in  the  production 
of  the  osseous  tissue.  The  primary  periosteum  consists  of  a 
compact  outer  fibrous  and  a  looser  inner  osteogcnctic  layer; 
the  latter  is  rich  in  cells  and  delicate  intercellular  fibres. 
The  initial  changes  appear  within  the  cartilage  at  points  known  as  centres  of 
ossification,  which  in  the  long  bones  are  situated  about  the  middle  of  the  future  shaft. 
These  early  changes  (Fig.  125)  involve  both  cells  and  matrix,  which  exhibit  con- 
spicuous increase  in  si/c  and  amount  respectively.  As  a  further  consequence  of  this 
activity,  the  cartilage-cells  become  larger  and  more  vesicular,  and  encroach  upon  the 
intervening  matrix,  in  which  deposition  of  lime  salts  now  takes  place,  as  evidenced 
by  the  gritty  resistance  offered  to  the  knife  when  carried  through  such  ossific  centres. 
On  acquiring  their  maximum  growth  the  cartilage-cells  soon  exhibit  indications  of 
impaired  vitality,  as  suggested  by  their  shrinking  protoplasm  and  degenerating 


Clarified  human  foetus  of  about 
three  and  one-half  months,  show- 
ing the  partially  ossified  skeleton. 
Two-thirds  natural  size. 


DEVELOPMENT   OF   BONE. 


95 


Embryonal  cartilage 


nuclei.      The  enlarged  spaces  enclosing  these  cells  are  sometimes  designated  as  the 
primarv  arcohe. 

Coincidently  with  these  intracartilaginous  changes,  a  thin  peripheral  layer  of 
bone  has  been  formed  beneath  the  young  periosteum  ;  from  the  latter  bud-like 
processes  of  the  osteogenetic  layer  grow  inward  from  the  periphery  and  invade 
the  embryonal  cartilage,  by  absorption  of  the  cartilage-matrix  gaining  the  centre 
of  ossification  and  there  effecting  a  destruction  of  the  less  resistant  cells  and  inter- 
vening matrix.  In  consequence  of  the  penetration  of  the  periosteal  processes  and 
the  accompanying  absorption  of  the  cartilage,  a  space,  the  primary  marrow-cavity, 
now  occupies  the  centre  of  ossification  and  contains  the  direct  continuation  of  the 
osteogenetic  laver.  This  tissue,  t\\e  primary  marrow,  which  has  thus  gained  access 
to  the  interior  of  the  cartilage,  contributes  the  cellular  elements  upon  which  a  double 
role  devolves, — to  produce  osseous  tissue  and  to  remove  the  embryonal  cartilage. 

The  cartilage-matrix  closing  the 

enlarged    cell-spaces    next    the   pri-  FIG.  125. 

mary  marrow-cavity  suffers  absorp- 
tion, whereby  the  cartilage-cells  are 
liberated  and  the  opened  spaces  are 
converted  into  the  secondary  arcolcz, 
and  directly  communicate  with  the 
growing  medullary  cavity.  After 
the  establishment  of  this  communi- 
cation, the  cartilage- cells  escape  from 
their  former  homes  and  undergo  dis- 
integration, taking  no  part  in  the 
direct  production  of  the  osseous  tissue. 

Beyond  the  immediate  limits  of 
the  primary  marrow- cavity  the  car- 
tilage-cells, in  turn,  repeat  the  pre- 
paratory stages  of  increased  size  and 
impaired  vitality  already  described, 
but  in  addition  they  often  exhibit  a 
conspicuous  rearrangement,  where- 
by they  form  columnar  groups  sepa- 
rated by  intervening  tracts  of  calci- 
fied matrix  (Figs.  126,  129).  This 
characteristic  belt,  or  zone  of  calci- 
fication, surrounds  the  medullary 
cavity  and  marks  the  area  in  which 
the  destruction  of  the  cartilage  ele- 
ments is  progressing  with  greatest 
energy.  In  consequence  of  the 
columnar  grouping  of  the  enlarged 
cartilage-cells  and  the  intervening 
septa  of  calcified  matrix,  an  arrange- 
ment particularly  well  marked  in  the  ends  of  the  diaphysis  of  the  long  bones,  a  less 
and  a  more  resistant  portion  of  the  cartilage  are  offered  to  the  attacks  of  the  marrow- 
tissue  by  the  cell-  and  matrix-columns  respectively  ;  as  a  result  of  this  difference, 
the  cells  and  the  immediately  surrounding  partitions  are  first  absorbed,  while  the 
intervening  trabeculee  of  calcified  cartilage-matrix  remain  for  a  time  as  irregular  and 
indented  processes,  often  deeply  tinted  in  sections  stained  with  hsematoxylin,  which 
extend  beyond  the  last  cartilage-cells  into  the  medullary  cavity.  These  trabeculffi 
of  calcified  cartilage-matrix  serve  as  supports  for  the  marrow-cells  assigned  to  pro- 
duce the  true  bone,  since  these  elements,  the  ostcoblasts,  become  arranged  along 
these  trabeculce,  upon  which,  through  the  influence  of  the  cells,  the  osseous  tissue  is 
formed. 

Simultaneously  with  the  destructive  phase  attending  the  absorption  of  the  car- 
tilage, the  constructive  process  is  instituted  by  the  osteoblasts  by  which  the  bone- 
tissue  is  formed.  These  specialized  connective-tissue  elements,  resting  upon  the 


Cartilage-cells  be- 
coming enlarged 
and  regrouped 


Enlarged  cartilage- 
cells  at  centre  of 
ossification 


Periosteum 


Section  of  tarsal  bone  of  foetal  sheep,  showing  centre  of  ossifi- 
cation.    X  50. 


96 


HUMAN    ANATOMY. 


irregular  trabeculae  of  the  calcified  cartilage,  bring  about,  through  the  influence  of 
their  protoplasm,  the  deposition  of  a  layer  of  bone-matrix  upon  the  surface  of  the 


FIG.  126. 


Embryonal 
cartilage 


Cartilage-cells  becoming  en- 
larged and  grouped 


Zone  of  calcification 


Osteogenetic  layer  of  perios- 
teum 


Central  spongy  bone  en- 
closing remains  of  carti- 
lage 


;#;  •'• 

.•H'  .  •    •          '•    &'«'.?.'i 


•  4    >• 

•:    •'     ?/  I 

: '.-''    ••''  '"•        *  ! 


Longitudinal  section  of  tnetatarsal  bone  of  foetal  sheep,  showing  stages  of  endochoodral  boae-developtneat.    X  40. 

trabeculse,  which  thus  becomes  enclosed  within  the  new  bone.  After  the  latter  has 
attained  a  thickness  of  at  least  the  diameter  of  the  osteoblasts,  some  of  the  cells  in 
closest  apposition  are  gradually  surrounded  by  the  osseous  matrix  (Fig.  127),  until, 


ENDOCHONDRAL    BONE. 


97 


FIG.  127. 


Bone-cell 


Section  of  a  portion  of  osseous  tra- 
becula  and  foetal  marrow.    X  375- 


finally,  they  lie  isolated  within  the  newly  formed  bone  as  its  cells  ;  the  bone-cells  are 
therefore  imprisoned  osteoblasts,  which,  in  turn,  are  specialized  connective-tissue 
elements.  The  bone-cells  occupy  minute  lenticular  spaces,  the  primary  lacuna,  at 
this  immature  stage  the  canaliculi  being  still  unformed.  The  early  bone-matrix  is  at 
first  soft,  since  the  deposition  of  the  calcareous  materials  takes  place  subsequently. 

The  increase  in  the  thickness  of  the  new  bone  is  attended  by  the  gradual  disap- 
pearance of  the  enclosed  remains  of  the  calcined  cartilage,  the  last  traces  of  which, 
however,  can  be  seen  for  some  considerable  time  as 
irregular  patches  within  the  osseous  trabeculae  (Fig. 
131),  somewhat  removed  from  the  zone  of  calcification. 
The  cartilage  and  the  bone  of  the  trabeculae  stand, 
therefore,  in  inverse  relations,  since  the  stratum  of  bone 
is  thinnest  where  the  cartilage  is  thickest,  and,  con- 
versely, the  calcified  matrix  disappears  within  the  robust 
bony  trabeculae.  A  number  of  the  latter,  together  with 
the  enclosed  remains  of  the  calcified  cartilage,  soon 
undergo  absorption,  with  a  corresponding  enlargement 
of  -the  intervening  marrow-spaces.  The  remaining  tra- 
beculae increase  by  the  addition  of  new  lamellae  on  the 
surface  covered  by  the  osteoblasts,  and  at  some  distance 
from  the  zone  of  calcification  form  a  trabecular  reticulum, 
the  primary  central  spongy  bone.  In  the  case  of  the 
irregular  bones,  the  central  spongy  bone  is  represented 
by  the  cancellated  substance  forming  the  internal  frame- 
work ;  in  the  long  bones,  on  the  contrary,  the  primary 

cancellated  tissue  undergoes  further  absorption  within  the  middle  of  the  shaft  simul- 
taneously with  its  continued  development  at  the  ends  of  the  diaphysis  from  the  car- 
tilage. As  the  result  of  this  absorption,  a  large  space — the  central  marrow- cavity — is 
formed  (Fig.  129),  the  growth  of  which  keeps  pace  with  the  general  expansion  of 
the  bone. 

The  absorption  of  the  young  osseous  tissue  to  which  reference  has  been  made 
is  effected  through  the  agency  of  large  polymorphonucleated  elements,   the  osteo- 

clasts.      These  are  specialized  marrow- 

FIG.  128.  cells  whose  particular  role  is  the  break- 

_rj^.  ing  up  and  absorption  of  bone-matrix. 

They   are   relatively   very  larg-e,   their 

'.*)-    ,;,  -  irregularly  oval  bodies  measuring  from 

.050  to  .100  millimetre  in  length  and 
from  .030  to  .040  millimetre  in  breadth. 
The  osteoclasts  (Fig.  128),  singly  or 
in  groups,  lie  in  close  relation  to  the 
surface  of  the  bone  which  they  are  at- 
tacking within  depressions,  or  How- 
ship''  s  lacuna,  produced  in  consequence 
of  the  erosion  and  absorption  of  the 
osseous  matrix  which  they  effect. 
When  not  engaged  in  the  destruction  of 
bone,  these  cells  occupy  the  more  central 
portions  of  the  marrow-tissue,  where, 
in  the  later  stages,  they  are  probably 
identical  with  the  myeloplaxes  or  giant 
cells  encountered  in  the  red  marrow. 
The  only  part  of  the  central  spongy  bone  which  persists  after  the  completed 
development  and  growth  of  the  long  bones  is  that  constituting  the  cancellated  tissue 
occupying  their  ends.  It  will  be  seen,  therefore,  in  many  cases,  that  the  product  of 
the  endochondral  bone-formation,  the  primary  central  osseous  tissue,  is  to  a  large 
extent  absorbed,  and  constitutes  only  a  small  part  of  the  mature  skeleton.  The 
early  marrow-cavity,  as  well  as  all  its  ramifications  between  the  trabeculae,  is  filled 
with  the  young  marrow-tissue  ;  the  latter  gives  rise  to  the  permanent  red  marrow 

7 


'Osteoclast 


Bone-cell 
within 
lacuna 


Howship's- 
lacuna 


Osteoblasts 


Portion  of  trabecula  of  spongy  bone   undergoing  absorp- 
tion by  osteoclast.     X  500. 


98 


HUMAN    ANATOMY. 


FIG.  129. 


Embryonal 
cartilage 


Zone  of  calci 
fication 


in  the  limited  situations  where  the  central  spongy  bone  persists,  as  in  the  vertebrae, 
the  ribs,  the  sternum,  and  the  ends  of  the  long  bones. 

The  important  fact  may  be  here  emphasized  that  the  process  sometimes  spoken 
of  as  the  ' '  ossification  of  cartilage' '  is  really  a  substitution  of  osseous  tissue  for  car- 
tilage, and  that  even  in  the  endochondral  mode  of  formation  cartilage  is  never 
directly  converted  into  bone. 

.The  ossification  of  the  epiphyses  (Fig.  130),  which  in  the  majority  of  cases 
does  not  begin  until  some  time  after  birth,  the  cartilage  capping  the  diaphysis  mean- 
while retaining  its  embryonal  character,  repeats  in  the  essential  features  the  details 
already  described  in  connection  with  endochondral  bone-formation  of  the  shaft. 
After  the  establishment  of  the  primary  marrow-cavity  and  the  surrounding  spongy 
bone,  ossification  extends  in  two  directions, — towards  the  periphery  and  towards  the 
adjacent  end  of  the  diaphysis.  As  this  process  continues,  the  layer  of  cartilage  in- 
terposed between  the  central  spongy  bone  and  the  free  surface  on  the  one  hand, 

and  between  the  central  bone  of  the  epiphysis 
and  the  diaphysis  on  the  other,  is  gradually 
reduced  until  in  places  it  entirely  disappears. 
Over  the  areas  which  correspond  to  the  later 
joint-surfaces  the  cartilage  persists  and  be- 
comes the  articular  cartilage  covering  the 
free  ends  of  the  bone.  With  the  final  ab- 
sorption of  the  plates  separating  the  epiphyses 
from  the  shaft  the  osseous  tissue  of  the  seg- 
ments becomes  continuous,  "bony  union" 
being  thus  accomplished. 

Intramembranous  Bone-Develop- 
ment.— The  foregoing  consideration  of  the 
formation  of  bone  within  cartilage  renders  it 
evident  that  the  true  osteogenetic  elements 
are  contributed  by  the  periosteum  when  the 
latter  membrane  sends  its  processes  into  the 
ossific  centre  ;  the  distinction,  therefore,  be- 
tween endochondral  and  membranous  bone 
is  one  of  situation  rather  than  of  inherent 
difference,  since  in  both  the  active  agents  in 
the  production  of  the  osseous  tissue  are  the 
osteoblasts,  and  in  essential  features  the  pro- 
cesses are  identical.  Since  in  the  produc- 
tion of  membrane-bone  the  changes  within 
pre-existing  cartilage  do  not  come  into  ac- 
count, the  development  is  less  complicated 
and  concerns  primarily  only  a  formative  pro- 
cess. 

Although  the  development  of  all  osseous 
tissue  outside  of  cartilage  may  be  grouped 
under  the  general  heading  of  intramembranous,  two  phases  of  this  mode  of  bone- 
formation  must  be  recognized  ;  the  one,  the  intramembranous,  in  the  more  literal 
sense,  applying  to  the  development  of  such  bones  as  those  of  the  vault  of  the  skull 
and  of  the  face,  in  which  the  osseous  tissue  is  formed  within  the  mesoblastic  shtvts, 
and  the  other,  the  subpcriosteal>  contributing  with  few  exceptions  to  the  production 
of  every  skeletal  segment,  in  which  the  bone  is  deposited  beneath  rather  than  within 
the  connective-tissue  matrix.  In  consideration  of  its  almost  universal  participation, 
the  periosteal  mode  of  development  will  be  regarded  as  the  representative  of  the 
intramembranous  formation. 

Subperiosteal  Bone. — The  young  periosteum,  it  will  be  recalled,  consists  of 
an  outer  and  more  compact  fibrous  and  an  inner  looser  osteogenetic  layer.  The 
latter,  in  addition  to  numerous  blood-vessels,  contains  young  connective-tissue  ele- 
ments and  delicate  bundles  of  fibrous  tissue.  These  cells,  or  osteoblasts,  become 
more  regularly  and  closely  arranged  along  the  fibrillae,  about  which  is  deposited  the 


Zone  of  calci- 
fication 


Embryonal 
cartilage 


Longitudinal  section  of  phalanx  of  fretus  of  five 
months.     X  23. 


SUBPERIOSTEAL    BONE. 


99 


new  bone-tissue,  the  osteoblasts  becoming-  enclosed  within  the  homogeneous  matrix 
to  constitute  the  bone-cells.     The  osseous  trabecula  thus  begins  to  increase  not  only 

FIG.  130. 


Columns  of  carti- 
lage-cells 


Spongy  bone  of 
epiphysis 


Epiphyseal  bone 


Remains  of  carti- 
lage separating 
bone  of  epiphysis 
and  diaphysis 


aphyseal  bone 


Marrow-tissue 


Longitudinal  section  including  epiphysis  and  upper  end  of  diaphysis  of  long  bone  of  cat,  just  before  osseous  union 

of  the  head  and  shaft  takes  place.     X  50. 

in  length,  by  the  addition  of  the  last-formed  matrix  upon  the  supporting  fibres,  but 
also  in  width,  by  the  deposition  of  new  layers  of  osseous  material  by  the  osteoblasts. 


IOO 


HUMAN   ANATOMY. 


These  cells  cover  the  exterior  of  the  trabeculae  as  they  lie  surrounded  by  the  young 
marrow-tissue  which  extends  from  the  osteogenetic  layer  of  the  periosteum  into  the 
intertrabecular  spaces.  The  union  of  the  young  trabeculae  results  in  the  production 
of  a  subperiosteal  net-work  of  osseous  tissue,  the  peripheral  spongy  bone.  The  latter 
forms  a  shell  surrounding  the  central  endochondral  bone,  or,  where  the  latter  has 
already  disappeared,  the  central  marrow-cavity  of  the  shaft.  The  two  processes, 
central  and  peripheral  bone-formation,  progress  simultaneously,  so  that  the  produc- 
tions of  both  lie  side  by  side,  often  in  the  same  microscopical  field  (Fig.  131). 


-Fibrous  layer  of 
periosteum 

Osteojjenetic 


.    •»    »V»H  ..        '    '-L*-    _  WSICU^UIKIU 

-        '.'.  V,\.     %  *  layer  of  peri- 

v-vp ** .'.;"* -*  ""**'.        ^ "•  >  osteum 


-  /^ 


/    ~  ~~Wa™^  -  *y  t 

-;-'.'jy^  ,fe'»U't-i    :"       "    - 

,  .  Ss?r  «,, ',       ,  *          .1  . 

"  •-  '"'•"•  <-;* 


i, 

ffjjfl  • 

•*:-'';  v> 

hone  trabecula 

AV    ^%'     '/     J^| 

<»        «^    ^     .     «"         'V^A    •'"  "•'•-•.-  ",'..->  '"     ^  •          "; 

:>^^- — i"-'  :  sS  Vv.^'    ri'-— *  »v-X^^^. 


Portion  of  developing  humerus  of  foetal  sheep,  showing  periostea!  and  central  spongy  bone.     X  i 


The  development  of  compact  bone  involves  the  partial  absorption  of  the 
subperiosteal  net-work  of  osseous  trabeculae  and  the  secondary  deposition  of  new 
bone-tissue.  The  initial  phase  in  the  conversion  of  the  peripheral  spongy  bone  into 
compact  substance  is  the  partial  absorption  of  the  trabeculae  by  the  osteoclasts  of  the 
primary  marrow-tissue  ;  in  consequence  of  this  process  the  close  reticulum  of  pcrios- 
teal  bone  is  reduced  to  a  delicate  framework,  in  which  the  comparatively  thin  remains 
of  the  trabeculae  separate  the  greatly  enlarged  primary  marrow-cavities,  which,  now 
known  as  the  Haversian  spaces,  are  of  round  or  oval  form. 

After  the  destructive  work  of  the  osteoclasts  has  progressed  to  the  required 
extent,  the  osteoblastic  elements  of  the  young  marrow  contained  within  the  Havrr- 


INTRAMEMBRANOUS    BONE. 


101 


sian  spaces  institute  a  secondary  formative  process,  by  which  new  bone  is  deposited 
on  the  walls  of  the  Haversian  spaces.  This  process  is  continued  until,  layer  after 
layer,  almost  the  entire  Haversian  space  is  rilled  with  the  resulting  concentrically 
disposed  osseous  lamellae  ;  the  cavity  remaining  at  the  centre  of  the  new  bone  per- 
sists as  the  Haversian  canal,  while  the  concentrically  arranged  layers  are  the  lamellae 
of  the  Haversian  system,  the  extent  of  the  latter  corresponding  to  the  form  and  size 
of  the  Haversian  space  in  which  the  secondary  deposit  of  bone  occurs.  It  is  evident 
from  the  development  of  the  compact  substance  that  the  interstitial  or  ground- 
lamellae  of  the  adult  tissue  correspond  to  the  remains  of  the  trabeculae  of  the  primary 
spongy  bone  ;  these  lamellae  are,  therefore,  genetically  older  than  those  constituting 
the  Haversian  systems.  The  details  of  the  formation  of  the  Haversian  lamellae,  in- 
cluding the  deposition  of  the  matrix  and  the  inclusion  of  the  osteoblasts  to  form  the 
bone-cells,  are  identical  with  those  of  the  production  of  the  trabeculae  of  the  earlier 
bone. 

Intramembranous  Bone. — The  development  of  certain  bones,  as  those  con- 
stituting the  vault  of  the  skull  and   the  greater  part  of  the  skeleton  of  the  face, 
differs  in  its  earliest  details  from  that  of  the  subperiosteal  bone,  although  the  essen- 
tial features  of  the  processes  are  identi- 
cal.     The  mode  by  which  these  mem-  FIG.  132. 
brane-bones    are    formed    may    claim, 
therefore,  a  brief  consideration. 

The  early  roof  of  the  skull  consists, 
except  where  developing  muscle  occurs, 
only  of  the  integument,  the  dura  mater, 
and  an  intervening  connective-tissue 
layer  in  which  the  membranous  bones 
are  formed.  The  earliest  evidences  of 
ossification  usually  appear  about  the 
middle  of  the  area  corresponding  to  the 
later  bone,  delicate  spicules  of  the  new 
bone  radiating  from  the  ossific  centre 
towards  the  periphery.  As  the  tra- 
beculae increase  in  size  and  number  they 
join  to  form  a  bony  net-work  (Fig. 
132),  close  and  robust  at  the  centre  and 
wide-meshed  and  delicate  towards  the 
margin  where  the  reticulum  fades  into 
the  connective  tissue.  With  the  con- 
tinued growth  of  the  bony  tissue  the 

net-work  becomes  more  and  more  compact  until  it  forms  an  osseous  plate,  which 
gradually  expands  towards  the  limits  of  the  area  devoted  to  the  future  bone.  For  a 
time,  however,  until  the  completion  of  the  earliest  growth,  the  young  bones  are 
separated  from  their  neighbors  by  an  intervening  tract  of  unossified  connective  tissue. 
Subsequent  to  the  earlier  stages  of  the  formation  of  the  tabular  bones,  the  continued 
growth  takes  place  beneath  the  periosteum  in  the  manner  already  described  for 
other  bones. 

On  examining  microscopically  the  connective  tissue  in  which  the  formation  of 
membrane-bone  has  begun,  this  layer  is  seen  to  contain  numerous  osteogenetic fibres 
around  and  upon  which  are  grouped  many  irregularly  oval  or  stellate  cells  ;  the  latter 
correspond  to  the  osteoblasts  in  other  locations,  since  through  the  agency  of  these 
elements  the  osseous  matrix  is  deposited  upon  the  fibres.  As  the  stratum  of  bony 
material  increases  some  of  the  cells  are  enclosed  to  form  the  future  bone-cor- 
puscles. Although  the  osteogenetic  fibres  correspond  to  delicate  bundles  of  fibrous 
tissue,  they  are  stiffer,  straighter,  and  present  less  indication  of  fibrillar  structure. 
Since  the  fibres  forming  the  ends  of  the  bony  spicules  generally  spread  out,  they  fre- 
quently unite  and  interlace  with  the  fibres  of  adjacent  spicules,  thus  early  suggesting 
the  production  of  the  bony  net-work  which  later  appears. 

Growth  of  Bone. — It  is  evident,  since  the  new  bone  is  deposited  beneath  the 
periosteum,  that  the  growth  of  the  subperiosteal  bone  results  in  an  increased  diame- 


Parietal  bone  of  human  foetus  of  three  months,  showing 
trabecular  net-work  of  intramembranous  bone.     X  5. 


102  HUMAN   ANATOMY. 

ter  of  the  shaft  as  well  as  in  thickening  of  the  osseous  wall  separating  the  medullary 
cavity  from  the  surface.  In  order,  therefore,  to  maintain  the  balance  between  the 
longitudinal  growth  of  the  medullary  cavity,  effected  by  the  absorption  of  the  endo- 
chondral  bone,  and  its  lateral  expansion,  the  removal  of  the  innermost  portions  of 
the  subperiosteal  bone  soon  becomes  necessary.  Absorption  of  the  older  internal 
trabeculae  thus  accompanies  the  deposition  of  new  osseous  tissue  at  the  periphery  ; 
by  this  combination  of  destructive  and  formative  processes  the  thickness  of  the 
cylindrical  wall  of  the  compact  substance  of  the  diaphysis  is  kept  within  the  proper 
limits  and  the  increased  diameter  of  the  medullary  cavity  insured. 

Throughout  the  period  of  early  growth  the  increase  in  length  of  the  bone  is 
due  to  the  addition  of  new  cartilage  at  the  ends  ;  later,  the  cartilaginous  increments, 
contributed  by  the  chondrogenetic  layer  of  the  perichondrium,  are  supplemented  by 
interstitial  expansion  following  the  multiplication  of  the  existing  cartilage-cells.  On 
attaining  the  maximum  growth  and  the  completion  of  epiphyseal  ossification,  a  por- 
tion of  the  cartilage  may  persist  to  form  the  articular  surfaces.  After  the  cessation 
of  peripheral  growth  and  the  completion  of  the  investing  layer  of  compact  substance, 
the  osteogenetic  layer  of  the  periosteum  becomes  more  condensed  and  less  rich  in 
cellular  elements,  retaining,  however,  an  intimate  connection  with  the  last-formed 
subjacent  bone  by  means  of  the  vascular  processes  of  its  tissue,  which  are  in  con- 
tinuity with  the  marrow-tissue  within  the  intraosseous  canals.  In  addition  to  being 
the  most  important  structure  for  the  nutrition  of  the  bone,  on  account  of  the  blood- 
vessels which  it  supports,  the  periosteum  responds  to  demands  for  the  production  of 
new  osseous  tissue,  whether  for  renewed  growth  or  repair,  and  again  becomes  active 
as  a  bone-forming  tissue,  its  elements  assuming  the  r61e  of  osteoblasts  in  imitation 
of  their  predecessors. 


THE   SKELETON: 


INCLUDING 


THE   BONES   AND   THE  JOINTS. 


FIG.  133. 


THE  skeleton  forms  the  framework  of  the  body.  In  the  widest  sense  it  includes, 
besides  the  bones,  certain  cartilages  and  the  joints  by  which  the  different  parts  are 
held  together.  The  skeleton  of  vertebrates 
is  divided  into  the  axial  and  the  appendic- 
ular ;  the  former  constitutes  the  support- 
ing framework  of  the  trunk  and  head  ;  the 
latter,  that  of  the  extremities. 

The  Axial  Skeleton.— The  general 
plan  of  the  axial  skeleton  of  the  trunk  is 
as  follows  :  a  rod  composed  of  many  bony 
disks  (the  vertebral  bodies)  connected  by 
fibro-cartilage  separates  two  canals,  a  dorsal 
and  a  ventral.  In  most  vertebrates  the  rod 
is  in  the  main  horizontal,  with  the  dorsal 
canal  above  and  the  ventral  below  ;  but  in 
man  the  rod  is  practically  vertical,  with  the 
dorsal  canal  behind  and  the  ventral  in  front. 
The  former  is  called  the  neural,  because  it 
encloses  the  central  nervous  system  ;  the 
latter,  the  visceral.  The  vertebral  column 
has  developed  about  the  primary  axis,  the 
notochord.  The  neural  canal  is  enclosed 
by  a  series  of  separate  arches  springing  one 
from  each  vertebra.  The  skeletal  parts  of 
the  anterior,  or  ventral,  canal  are  less  nu- 
merous ;  they  are  the  ribs,  the  costal  carti- 
lages, and  the  breast  bone.  Above  is  the 
bony  framework  of  the  head,  or  the  skull. 
This  also  is  divided  into  a  dorsal  and  a  ven- 
tral portion  by  a  bony  element  which  is 
apparently  a  continuation  of  the  bodies  of 
the  vertebrae,  and,  indeed,  is  actually  de- 
veloped, in  part,  around  the  front  of  the 
notochord.  The  cephalic  axis,  however,  is 
bent  at  an  angle  with  the  vertebral  bodies, 
so  that  the  neural  arches,  which  here  en- 
close the  brain,  are  chiefly  no  longer  be- 
hind but  above.  Below  and  in  front  of 
the  brain-case  is  the  face,  which  contains 
the  beginning  of  the  digestive  tube,  of 
which  the  jaws  and  teeth  are  special  organs. 
In  the  head  we  do  not  find  the  separation 
of  the  parts  enclosing  the  brain  into  a 
series  of  vertebrae,  but  they  are  clearly  a 
continuation  of  the  vertebral  arches,  the 
posterior,  or  occipital,  division  strongly  suggesting  a  vertebra.  The  face  is  far  more 
complicated,  the  vertebral  plan  being  lost.  In  short,  the  axial  skeleton  consists  of  a 

103 


The  tinted  portions  constitute  the  axial  skeleton ;   the 
untinted,  the  appendicular  skeleton. 


104  HUMAN   ANATOMY. 

central,  many-jointed  rod  bent  forward  near  the  top,  with  very  perfect  bony  walls 
behind  and  above  it,  enclosing  the  central  nervous  system,  and  very  imperfect  bony 
and  cartilaginous  walls  before  and  below  it,  enclosing  the  digestive  apparatus  and  its 
associates,  the  circulatory,  respiratory,  urinary,  and  reproductive  organs. 

The  Appendicular  Skeleton  has  an  entirely  distinct  origin  ;  it  is  the  frame- 
work of  the  limbs.  It  consists  of  two  girdles,  a  thoracic  and  a  pelvic,  to  each  of 
which  is  attached  a  series  of  segments,  the  terminal  one  of  which  expands  into  five 
rays, — -fingers  and  toes.  According  to  some  anatomists,  the  true  vertebrate  plan  is 
of  seven  terminal  rays,  but,  the  question  being  still  undecided,  the  more  usual  sys- 
tem is  followed.  Each  of  these  rays  consists  of  three  or  four  bones.  Proximal  to  this 
comes  a  series  of  short  bones, — wrist  and  ankle  ;  still  nearer,  a  pair  of  bones,  —fore- 
arm and  leg ;  then  a  single  bone, — aim  and  thigh ;  and  lastly  a  bony  arch, — the 
girdle. 

In  man,  the  thoracic  girdle,  made  up  of  collar-bone  and  shoulder-blade,  lies 
external  to  the  chest,  while  the  pelvic  girdle  fuses  on  each  side  into  one  bone,  meets 
its  fellow  in  front,  and  unites  with  the  bodies  of  certain  vertebrae.  Thus,  besides 
bearing  a  limb,  the  pelvic  girdle  forms  a  part  of  the  wall  of  the  abdominal  and  the 
pelvic  cavities  and  would  seem  to  belong  to  the  axial  skeleton,  but  embryology  and 
comparative  anatomy  show  that  it  does  not. 

GENERAL  CONSIDERATION  OF  THE  BONES. 

The  bones  have  the  physiological  function  of  bearing  weight,  of  affording  pro- 
tection, and  especially,  by  the  systems  of  levers  composing  the  limbs,  of  effecting 
movements  through  the  action  of  the  muscles.  They  must,  therefore,  be  capable  of 
resisting  pressure,  accidental  violence,  and  the  strain  caused  by  the  pull  of  the 
muscles.  The  size  of  the  bones  must  be  such  that  besides  serving  the  obvious  needs 
of  support  and  protection  they  may  be  sufficiently  large  to  offer  adequate  surface  for 
the  origin  and  insertion  of  muscles,  and  the  shape  must  be  such  as  to  allow  this 
without  undue  weight. 

Shapes  of  Bones. — Bones  are  divided,  according  to  their  form,  into  long, 
flat,  and  irregular ;  such  classification,  however,  is  of  little  value,  since  many  bones 
might  be  variously  placed. 

Long  bones  form  the  best-defined  group.  They  consist  of  a  shaft  and  two 
extremities,  each  of  which  takes  part  in  the  formation  of  a  joint,  or,  as  in  the  case  of 
the  last  phalanges,  is  terminal. 

Flat  bones,  where  very  thin,  consist  of  a  single  plate  ;  where  thicker,  they  con- 
sist of  two  plates  separated  by  spongy  substance  called  diploe. 

Irregular  bones  may  be  regarded  as  embracing  all  others.  The  group  of  the 
so-called  short  bones  has  no  significance. 

Sesamoid  Bones,  with  the  exception  of  the  patella,  are  not  usually  included 
in  the  description  of  the  skeleton.  With  the  above  exception,  they  are  small  rounded 
bones  developed,  for  the  most  part,  in  the  capsules  of  joints,  but  sometimes  in  ten- 
dons. Usually  one  surface  is  cartilage-covered,  and  either  enters  into  the  formation 
of  a  joint  or,  separated  by  a  bursa,  plays  on  another  bone,  or  on  cartilage  or  liga- 
ment. Their  function  is  to  obviate  friction,  and,  in  some  cases,  to  change  the  direc- 
tion of  the  pull  of  a  muscle.  The  number  of  sesamoid  bones  is  very  variable  ;  but 
the  usual  idea  that  they  are,  so  to  speak,  accidental,  depending  on  the  mechanics  of 
a  certain  joint  or  tendon,  must  probably  be  abandoned.  They  are  rather  to  be  con- 
sidered as  real  parts  of  the  skeleton,1  all  of  which  have  their  places  in  certain 
animals,  but  all  of  which  either  are  not  developed,  or,  if  they  do  appear,  are  again 
lost  in  others.  Thus,  certain  sesamoid  bones  of  the  fingers  are  very  frequent  in  the 
foetus  and  very  rare  in  the  adult. 

Growth  of  Bones. — The  microscopical  details  of  bone-growth  are  given  else- 
where (page  94).  Suffice  it  to  say  here  that  each  bone  has  certain  so-called  centres 
of  ossification  from  which  the  formation  of  the  new  bone  spreads.  In  the  long  bones 
there  is  one  main  centre  in  the  shaft,  or  diaphysis,  which  appears  in  the  first  half  of 
foetal  life.  Other  centres  appear,  usually  some  time  after  birth,  in  the  ends  of  the 

1  Thilenius  :  Morpholog.  Arbeiten,  Ikl.  \i.,  1896. 


MECHANICS   OF    BONE.  105 

bones.  There  may  be  one  or  several  in  each  end.  The  part  formed  around  each 
of  these  secondary  centres  is  called  an  epiphysis.  Growth  takes  place  chiefly  in  the 
cartilage  between  the  epiphyses  and  the  shaft.  When,  therefore,  a  joint  is  resected 
in  childhood  the  surgeon  tries  to  leave  a  part  of  the  epiphysis  in  place.  A  curious 
relation  exists  between  the  course  of  the  chief  medullary  artery  of  the  shaft  of  a  long 
bone  and  the  behavior  of  the  epiphyses.  The  epiphysis  towards  which  the  vessel  is  di- 
rected is  the  last  to  appear  and  the  first  to  unite.  (The  fibula  furnishes  an  exception.  ) 
As  a  rule,  also,  the  largest  epiphyses  appear  first  and  unite  last.  In  long  bones  with 
an  epiphysis  at  one  end  only,  the  nutrient  canal  leads  towards  the  opposite  extremity. 

Mechanics  of  Bone. — A  long  bone  has  a  hollow  shaft  containing  marrow, 
the  wall  being. of  compact  bone.  The  hollowness  of  the  shaft  takes  from  the  weight, 
and,  moreover,  conforms  to  the  well-known  law  that  a  given  quantity  of  matter  is 
much  stronger,  both  lengthwise  and  crosswise,  when  disposed  as  a  hollow  cylinder 
than  as  a  solid  one  of  equal  length.  The  proportion  of  the  central  or  medullary 
cavity  is  not  the  same  in  all  bones.  Perhaps,  as  an  average,  its  diameter  may  be 
said  to  equal  one-third  of  that  of  the  bone.  In  the  shaft  this  cavity  is  crossed  by  a 
few  bony  trabeculae,  almost  all  of  which  are  destroyed  in  maceration.  Towards  the 
ends,  as  the  outer  wall  becomes  thinner,  large  numbers  of  thin  plates  spring  from  its 
inner  surface  and  incline  towards  one  another  in  graceful  curves,  until  at  last  the 
expanded  end  of  the  bone  consists  of  spongy  or  cancellated  tissue  enclosed  within  a 
delicate  wall  of  compact  substance.  The  arrangement  of  these  plates  is  distinctly  pur- 
poseful, since  it  has  been  shown  that  they  are  so  disposed  as  to  correspond  with  the 
stress-lines  an  engineer  would  construct  for  the  special  purpose  served  by  the  end  of 
the  bone.  None  the  less,  it  would  be  unwarranted  to  maintain  that  mathematical 
correctness  is  always  to  be  found,  or  that  there  are  not  other  modifying  influences. 
The  internal  structure  of  all  bones,  excepting,  perhaps,  those  of  the  skull,  is  of  this 
nature,  so  that  the  following  remarks  apply  to  spongy  bone  in  general. 

The  delicate  cancellated  structure  is  for  the  most  part  in  thin  plates.  The  sim- 
plest arrangement  occurs  in  a  short  bone  exposed  to  pressure  only  at  two  opposite 
surfaces  ;  in  such  cases  the  plates  run  between  these  surfaces  with  few  and  insignifi- 
cant cross-pieces.  Where  severe  pressure  may  come  in  almost  any  direction,  as  in 
the  case  of  the  globular  heads  of  the  humerus  and  femur,  the  round-meshed  pattern 
predominates,  producing  a  very  dense  spongy  structure  which  may  be  represented 
diagrammatically  by  drawing  lines  crossing  at  right  angles  and  by  enlarging  every 
point  of  intersection.  In  the  midst  of  this  round-meshed  type  there  is  very  fre- 
quently a  central  core  with  stronger  plates  and  larger  spaces.  The  vaulted  system 
is  found  at  the  projecting  ends  of  bones,  and  between  the  round-meshed  cancellated 
substance  and  the  shaft.  Several  special  arrangements  will  be  described  in  connec- 
tion with  the  bones  in  which  they  occur.  An  epiphysis,  until  it  has  fused,  shows  the 
mechanical  structure  of  a  separate  bone.  A  process  for  the  attachment  of  muscles 
or  ligaments  generally  contains  a  very  light  internal  structure,  the  surface  of  the  shaft 
of  the  bone  being  rarely  continued  under  it.  The  continuation  of  the  fibres  of 
attached  tendons  is  not  represented  by  internal  plates  of  bone,  although  the  oppo- 
site opinion  has  supporters. 

Certain  of  the  bones  of  the  cranium  and  the  face  are  in  parts  hollowed  out  into 
mere  shells  bounding  a  cavity  lined  with  mucous  membrane  continuous  with  that  of 
the  nose  or  the  pharynx. 

The  elasticity  of  bones  is  enhanced  by  curves.  The  long  bones  very  usually 
present  a  double  curve.  It  has  been  maintained  that  these  curves  form  a  spiral 
structure.  There  are  striking  instances  of  it,  but  the  universality  of  the  law  is  not 
proved  ;  although  shocks  are  thus  lessened,  the  passage  of  one  curve  to  another  is 
a  weak  point  in  the  bone. 

The  ends  of  the  long  bones  are  enlarged  for  articulation  with  their  neighbors. 
The  greater  part  of  this  enlargement  forms  the  joint,  the  various  shapes  of  which 
will  be  discussed  later.  Besides  this,  there  are  usually  at  the  ends  prominences  for 
muscles.  The  shaft  generally  bears  ridges,  which  in  some  cases  are  made  of  dense 
bone  and  materially  add  to  the  strength  of  the  bone.  A  ridge  or  prominence 
usually  implies  the  insertion  of  a  fibrous  aponeurosis  or  a  tendon.  Muscular  fibres, 
however,  may  spring  from  the  periosteum  over  a  flat  surface. 


106  HUMAN    ANATOMY. 

Parts  of  Bones. — The  following  are  some  of  the  names  applied  to  features 
of  bone  : 

A  process  is  a  general  term  for  a  projection. 

A  spine  or  spinous  process  is  a  sharp  projection. 

A  tuberosity  is  a  large  rounded  one,  a  tubercle  is  a  small  one,  either  rounded  or 
pointed. 

A  crest  is  a  prominent  ridge. 

A  head  is  an  enlargement  at  the  end  of  a  bone,  in  part  articular. 

A  neck  is  a  constriction  below  a  head. 

A  condyle  is  a  rounded  articular  eminence,  generally  a  modification  of  a  cylinder. 

A  fossa  is  a  pit. 

A  glenoid  cavity  is  a  shallow  articular  depression. 

A  cotyloid  cavity  is  a  deep  one. 

A  sulcus  is  a  furrow. 

A  foramen  is  a  hole,  in  the  sense  of  a  perforation. 

A  sinus  is  the  cavity  of  a  hollow  bone,  equivalent  to  antrum.  It  is  used  also 
to  designate  certain  grooves  for  veins  in  the  cavity  of  the  cranium. 

In  addition  to  the  cartilage-covered  articular  surfaces  proper,  the  fresh  bones 
show  in  some  places  a  plate  of  cartilage  quite  like  one  for  a  joint  ;  such  plates  serve 
to  lessen  the  friction  of  a  tendon  playing  over  the  bone.  In  other  places  a  look  of 
peculiar  smoothness  is  conferred  by  the  presence  of  a  bursa,  although  cartilage  is 
wanting. 

Sex  of  Bones. — The  general  characteristics  of  the  bones  of  the  female  sub- 
ject are,  first,  a  greater  slenderness  ;  second,  a  smaller  development  of  processes 
and  ridges  for  muscular  attachment ;  third,  and  most  important  of  all,  the  small 
size  of  the  articular  surfaces.  These  guides  usually  suffice  to  determine  the  sex  of 
the  chief  bones  ;  some,  especially  those  of  the  pelvis,  possess  characteristic  sexual 
differences  of  form. 

Age  of  Bones. — At  birth  the  long  bones  have  cartilaginous  ends  in  which, 
with  one  or  two  exceptions,  the  centres  of  ossification  have  not  yet  appeared.  Many- 
bones  at  this  period  still  consist  of  several  pieces  which  ultimately  fuse.  The  shape 
and  proportions  are  in  some  cases  different  from  those  of  the  adult.  Sexual  differ- 
ences cannot  in  most  cases  be  determined.  During  the  Jirst  years  new  centres  of 
ossification  appear,  distinct  pieces  unite,  and  the  proportions  change  from  the  type 
of  the  infant  to  that  of  the  child.  Towards  puberty  important  further  changes  in 
proportion  occur,  and  sexual  differences  develop. 

After  puberty  the  bones  present  three  stages, — adolescence,  maturity,  and  senility. 
In  the  first  the  union  of  the  epiphyses  is  going  on  ;  after  this  has  taken  place  the 
line  of  separation  is  visible  for  a  time,  but  gradually  disappears.  Our  knowledge  of 
the  time  at  which  these  changes  occur  enables  us  to  determine  the  age  of  the  skel- 
eton. The  long  period  of  maturity  presents  little  that  allows  of  a  precise  estimate 
of  age.  The  separate  bones  of  the  vault  of  the  cranium  gradually  fuse  into  one. 
The  senile  skeleton  in  its  extreme  stage  is  very  striking.  There  is  a  general  atrophy 
of  the  bones  both  within  and  without,  those  of  the  face  becoming  in  parts  of  papery 
thinness  ;  not  only  the  cavities  within  the  cranial  bones  become  larger,  but  also  the 
spaces  within  the  cancellous  tissue  inside  the  bones,  due  to  the  partial  absorption  of 
the  spongy  substance.  The  only  bones,  however,  which  show  a  distinct  change  of 
form  are  the  jaws,  and  this  is  a  secondary  result  of  the  loss  of  the  teeth.  In  many 
cases,  however,  senile  absorption  and  atrophy  do  not  occur,  except,  perhaps,  in  the 
head  ;  it  may  be,  therefore,  absolutely  impossible  to  distinguish  a  long  bone  of  an 
old  subject  from  one  of  an  individual  in  early  maturity.  The  periods  at  which  the 
age  of  bones  is  most  often  a  matter  of  medico-legal  inquiry  are  at  the  time  of  birth 
and  in  childhood  and  youth.  The  dates  of  the  first  appearance  of  ossification  in 
the  various  bones  are  the  criteria  for  the  first.  These  are  to  be  used,  however,  with 
great  caution,  since  variation  is  considerable.  The  information  to  be  derived  from 
consideration  of  the  general  development  of  the  body  is  perhaps  of  equal  value. 
The  same  holds  good  for  childhood  and  adolescence.  The  particular  point  on  which 
the  writer  holds  strong  views,  based  on  his  own  observations,  differing  from  those 
generally  accepted,  is  as  to  the  time  of  union  of  the  epiphyses  at  the  end  of  ado- 


GENERAL   CONSIDERATION    OF   THE  JOINTS.  107 

lescence.  He  is  convinced,  as  his  statements  will  show,  that  this  union  occurs  earlier 
than  is  generally  taught. 

Relation  of  the  Bones  to  the  Figure. — While  it  may  be  said  that  power- 
ful muscles  leave  their  imprint  on  the  bones  in  strong,  rough  ridges,  yet  it  is  impos- 
sible to  give  a  trustworthy  description  of  the  figure  from  the  size  and  shape  of  the 
bones,  since  these  are  determined  chiefly  by  prenatal  influences.  Very  delicate, 
even  puny,  bodies  may  have  large  and  strong  bones,  and  great  muscular  develop- 
ment may  coexist  with  a  light  framework. 

Variations. — Besides  the  great  range  of  individual  variation,  without  departure 
from  the  usual  type,  bones  occasionally  show  greater  peculiarities.  These  may  occur 
through  either  excess  or  defect  of  ossification.  Structures  which  are  normally  car- 
tilaginous or  fibrous  may  become  replaced  by  bone,  and  abnormal  foramina  may 
occur  in  consequence,  or  to  accommodate  the  aberrant  course  of  blood-vessels  or 
nerves.  The  most  interesting  of  these  variations  are  such  as  present  an  arrangement 
which  is  normal  in  some  of  the  lower  animals.  Many  variations  may  be  plausibly 
accounted  for  as  reversions,  but  others  cannot  be  explained  in  this  way  according 
to  any  conceivable  scheme  of  descent.  By  speaking  of  these  variations  as  animal 
analogies  we  avoid  theories  and  keep  to  scientific  truth. 

Number  of  Bones. — The  usual  enumeration  of  the  bones  composing  the 
human  skeleton  is  misleading,  for  while  it  is  customary  in  some  parts,  as  the  head, 
to  count  each  bone,  in  others,  like  the  sacrum  and  the  hyoid,  only  the  ultimate 
condition,  after  union  of  the  component  segments,  is  considered.  In  other  cases, 
like  the  sternum,  there  may  be  grave  doubt  which  course  is  the  proper  one  to 
follow  ;  and  finally,  as  in  the  coccyx,  the  number  is  variable.  Bearing  these  impor- 
tant facts  in  mind,  it  may  be  stated  that  the  human  skeleton  in  middle  life  usually 
comprises,  as  conventionally  reckoned,  two  hundred  separate  bones,  excluding  the 
sesamoids  within  the  tendons  of  the  short  flexor  of  the  thumb  and  of  the  great  toe 
and  the  ear-ossicles,  but  including  the  patella  and  the  hyoid  bone.  Of  this  number, 
seventy-four  bones  belong  to  the  axial  and  one  hundred  and  twenty-six  to  the  appen- 
dicular  skeleton. 

The  skeleton  is  advantageously  described  in  the  following  order  :  the  spine,  the 
thorax,  the  head,  the  shoulder-girdle  and  the  arm,  the  pelvic  girdle  and  the  leg. 
The  account  of  the  bones  of  each  region  is  succeeded  by  that  of  the  joints  and  the 
ligaments  holding  them  together,  followed  by  a  consideration  of  the  region  as  a 
whole  and  of  its  relation  to  the  surface.  The  applications  of  anatomical  details  of 
the  skeleton  to  the  requirements  of  medicine  and  surgery  are  pointed  out  in  appro- 
priate places. 

GENERAL   CONSIDERATION   OF  THE  JOINTS. 

A  JOINT  or  articulation  implies  the  union  of  two  or  more  bones.  Joints  may  be 
divided,  according  to  their  mobility,  into  three  great  classes  :  the  FIXED  JOINT  (Syn- 
arthrosis),  the  HALF-JOINT  (Amphiarthrosis} ,  and  the  TRUE  JOINT  (Diarthrosis}. 

Fixed  Joints. — These  allow  no  motion  in  the  mature  condition,  and  are  rep- 
resented by  two  subdivisions,  the  Suture  and  the  Synchondrosis. 

The  suture  is  the  direct  union  of  two  bones  which  at  first  may  be  separated  by 
membrane  or  by  fibrous  tissue,  but  which  eventually  become-firmly  united.  Several 
varieties  of  this  form  of  union  are  recognized  ;  thus  a  serrated  suture  is  one  in  which 
the  edges  are  interlocked,  as  the  teeth  of  two  saws  ;  conspicuous  examples  are  seen 
in  the  interparietal  and  the  parieto-occipital  junctures.  Frequently  one  bone  tends 
to  overlap  at  one  end  of  the  suture  and  to  be  overlapped  at  the  other.  A  squamous 
suture  is  one  in  which  a  scale-like  bone  very  much  overlaps  another,  as  in  the  relation 
between  the  temporal  and  the  parietal  bone.  An  harmonic  sutiire  is  one  in  which 
two  approximately  plane  surfaces  are  apposed,  as  in  the  case  of  the  vertical  plate  of 
the  palate  and  the  maxillary  bone.  The  term  grooved  suture  is  sometimes  employed 
to  designate  a  form  of  union  in  which  one  bone  is  received  within  the  grooved  sur- 
face of  another,  as  the  rostrum  of  the  sphenoid  and  the  vomer.  Wormian  bones  are 
small,  irregular  ossifications  which  appear  as  bony  islands  in  the  course  of  a  suture. 
Familiar  examples  of  these  are  seen  in  the  line  of  the  parieto-occipital  suture. 


io8 


HUMAN   ANATOMY. 


Synchondrosis  is  the  union  of  two  bones  by  an  intervening  strip  of  cartilage, 
which  usually  ultimately  becomes  replaced  by  bone.  Such  is  the  union  between 
the  pieces  of  the  body  of  the  sternum  and  between  certain  bones  of  the  base  of  the 
skull.  The  term  is  also  applied  to  the  union  of  the  shaft  and  the  epiphyses  of  long 
bones. 

Half-Joints,  including  Symphysis  and  Syndcsmosis.  From  the  stand-point  of 
development,  there  is  no  fundamental  difference  between  symphyses  and  the  true 
joints.  In  both  cases  a  small  cavity  appears  within  the  intervening  mesoblastic  tissue 
connecting  the  ends  of  the  embryonal  bones.  This  small  cavity,  in  the  case  of  the 
true  joints,  rapidly  increases,  and  later  is  lined  by  the  flattened  mesoblastic  cells 
investing  the  subsequently  differentiated  synovial  membrane.  When,  on  the  con- 
trary, the  bones  are  to  become  united  by  dense  fibrous  and  fibro-cartilaginous  tissue, 
as  in  the  case  of  a  symphysis,  the  interarticular  space  is  always  a  mere  cleft  sur- 
rounded by  the  interlacing  and  robust  bundles  of  the  dense  tissue  forming  the  union 
in  the  mature  joint. 

A  symphysis  implies  great  strength  and  very  limited  and  indefinite  motion, 
there  being  no  arrangement  of  surfaces  to  determine  its  nature.  The  chief  function 
of  this  form  of  union  seems  rather  to  be  to  break  shocks.  The  central  cavity  is  not 
always  found.  The  symphysis  pubis  (Fig.  361)  is  a  typical  half -joint.  Those  con- 
necting the  bodies  of  the  vertebrae  are  usually  so  classed,  but  it  is  not  certain  that 
they  quite  agree  either  in  structure  or  development  with  the  description.  A  transi- 

FIG.  134. 


Diagrams  of  various  forms  of  suture.    A,  serrated  ;  JS,  squamous  ;   C,  harmonic  ;  D,  grooved. 

tional  form  leading  from  the  symphysis  to  the  true  joint  is  one  in  which  the  limited 
synovial  cavity,  instead  of  being  in  the  centre  of  a  mass  of  fibro-cartilage,  lies  between 
two  cartilaginous  surfaces,  somewhat  like  that  of  a  true  joint,  but  so  interlocked  and 
surrounded  by  short,  tense  fibres  as  to  preclude  more  than  very  slight  motion.  This 
arrangement  is  often  seen  in  the  articulation  between  the  sacrum  and  ilium,  some- 
times improperly  called  the  sacro-iliac  synchondrosis. 

Syndesmosis  is  to  be  included  among  the  half-joints.  It  is  the  binding 
together  of  bones  by  fibres,  either  in  bundles  or  as  a  membrane,  without  any  inter- 
vening cartilage  ;  an  example  of  this  arrangement  is  seen  in  the  union  effected  by 
the  interosseous  ligament  in  the  lower  tibio-fibular  articulation. 

True  Joints. — These  articulations  develop  in  a  similar  manner  to  the  half- 
joints,  except  that  the  opposed  ends  of  the  developing  bones  are  of  hyaline  carti- 
lage, fibro-cartilage  being  present  only  at  the  sides,  except  in  the  case  of  a  compound 
joint,  where  it  forms  the  intervening  plate.  The  tissue  at  the  sides  of  the  articular 
cleft  differentiates  into  two  layers, — the  inner,  which  is  the  svnvrial  membrane,  consist- 
ing of  a  layer  of  cells  continuous  with  the  superficial  layer  of  the  cartilage-cells  and 
secreting  a  viscid  fluid,  the  synovia,  which  lubricates  the  joint  ;  and  the  outer  part, 
which  becomes  a  fibrous  bag  called  the  eapsiilar  ligament.  The  latter,  in  its  simplest 
form,  consists  of  only  enough  fibrous  tissue  to  support  the  synovial  membrane.  The 
capsular  ligament  is  strengthened  by  accessory  ligaments  developing  in  or  around  it, 
the  arrangement  of  which  depends  on  the  needs  of  the  joint.  During  development, 


STRUCTURE   OF  JOINTS. 


109 


independent  of  the  influence  of  motility  or  of  muscular  action,  the  articular  ends  of 
the  bones  assume  definite  shapes  such  as  will  allow  the  motion  peculiar  to  that  joint, 
and  (barring  the  frequent  want  of  perfect  coaptation)  no  other.  The  common  char- 
acteristics of  true  joints  are  articular  surfaces  covered  by  hyaline  cartilage,  so 
shaped  as  to  determine  the  nature  of  the  movement,  enclosed  by  a  capsule  lined  with 
a  synovial  membrane.  The  articular  surfaces  are  not  necessarily  formed  wholly  of 
bone,  since  very  often  increased  concavity  is  secured  by  the  addition  of  a  lip  of  fibro- 
cartilage  to  the  margin  of  the  bone  ;  in  other  cases  ligaments  coated  with  carti- 
lage complete  a  socket  ;  or  again,  disks  of  fibro-cartilage  loosely  attached  to  the 
periphery  may  project  into  a  joint  and  partially  subdivide  it,  following  one  bone  in 
certain  movements  and  the  other  in  others. 

Compound  joints  result  from  the  persistence  and  differentiation  of  a  portion  of 
the  tissue  uniting  the  ends  of  the  embryonal  bones  into  a  partition  which,  in  the 
complete  compound  joint,  separates  the  two  synovial  cavities  developed,  one  on 
either  side  of  the  septum.  The  tissue  between  the  bones  becomes  a  fibre-cartilagi- 
nous disk,1  which  partially  or  completely  subdivides  the  cavity.  In  such  a  joint, 
when  typical,  there  are  two  ends  of  bone  covered  with  articular  cartilage,  separated 


D 


Diagrams  illustrating  formation  of  joints.  A,  bones  are  united  by  young  connective  tissue;  B,  appearance  of 
joint-cavity;  C,  differentiation  of  joint-cavity  and  capsule;  D,  development  of  two  joint-cavities  separated  by 
fibrous  septum,  resulting  in  a  compound  joint. 

by  a  fibro-cartilaginous  disk  or  meniscus,  and  two  distinct  synovial  membranes.  The 
movements  are,  however,  still  determined  to  a  considerable  extent  by  the  shape  of 
the  bones,  so  that  these  articulations  may  be  classed  as  true  joints.  The  fibro- 
cartilaginous  meniscus  may  be  replaced  by  a  row  of  bones  as  in  the  wrist. 

Structure  of  True  Joints. — The  opposed  ends  of  the  bones,  and  sometimes 
other  tissues,  are  coated  with  hyaline  articular  cartilage,  which  gives  a  greater 
smoothness  to  the  articulating  surfaces  than  is  found  on  the  macerated  bones. 
Though  following  in  the  main  the  bony  contours,  the  cartilage  does  not  do  so  accu- 
rately ;  details  are  found  on  the  cartilage  that  are  obscure  on  the  bones.  It  dimin- 
ishes the  force  of  shocks.  Although,  as  already  stated,  the  shape  of  the  articular  ends 
determines  the  nature  of  the  motion,  it  is  important  to  recognize  that,  as  in  the  case 
of  saddle-joints,  the  opposed  surfaces  are  not  so  accurately  in  apposition  that  irreg- 
ular movements  cannot  and  do  not  occur.  Failure  to  appreciate  this  fact  has  given 
rise  to  much  difficulty  in  accounting  for  motions  that  undoubtedly  take  place,  but 
which,  according  to  the  mathematical  conception  of  the  joint,  are  impossible. 
Further,  the  range  of  individual  variation  is  great  ;  just  as  a  man  may  have  a  long 
or  a  short  head,  so  any  of  the  articular  ends  of  his  bones  may  depart  considerably 
from  the  average  proportions.  It  is  even  possible  in  some  of  the  smaller  joints  that 

1  Discus  articularis. 


no 


HUMAN   ANATOMY. 


FIG. 


the  articular  surface  of  a  certain  bone  may  be  plane,  convex,  or  concave  in  different 
persons. 

The  capsule. — Every  joint,  with  possibly  some  exceptions  in  the  carpus  and 
the  tarsus,  is  enclosed  by  a  capsule?  or  capsular  ligament,  which  arises  from  the  peri- 
osteum near  the  borders  of  the  articular  cartilage  and  surrounds  the  joint.  This 
envelope  consists  of  a  membrane,  often  containing  fat  within  its  meshes,  composed 
of  two  layers,  the  inner  delicate  synovial  membrane  and  the  external  fibrous  layer. 
The  latter,  while  in  some  places  very  thin,  is  usually  strengthened  by  the  incorpora- 
tion of  fibrous  bands  which,  from  their  position,  are  known  as  lateral,  anterior,  or 
posterior  ligaments.  These  bands  are  of  strong,  non-elastic  fibrous  tissue  which 
under  ordinary  circumstances  do  not  admit  of  stretching.  The  strength  and 
security  of  the  joint  are  often  materially  increased  through  thickenings  of  fasciae  and 
expansion  of  tendons  which  blend  with  the  underlying  capsule.  The  capsule  must 
be  large  enough  to  allow  the  characteristic  movements  of  the  joint  ;  consequently, 
when  the  bone  is  moved  in  any  particular  direction  that  side  of  the  capsule  is  relaxed 
and  thrown  into  folds.  These  folds  are  drawn  out  of  the  way  either  by  small  special 
muscles  situated  beneath  those  causing  the  chief  movement  or  by  fibres  from  the 

deeper  surfaces  of  these  latter  muscles.  In 
the  joints  of  the  arches  of  the  vertebrae,  there 
being  no  muscles  inside  the  spinal  canal,  a  dif- 
ferent arrangement  exists  for  the  inner  side  of 
the  capsule,  elastic  tissue  there  taking  the 
place  of  muscle.  The  relation  of  the  insertion 
of  the  capsule  to  the  line  of  the  epiphysis  is 
important.  Although  this  point  is  fully  con- 
sidered in  the  description  of  the  individual 
joints,  it  may  be  here  stated  that,  as  a  rule,  in 
the  long  bones,  the  capsule  arises  very  near 
the  line  of  the  epiphysis. 

The  synovial  membrane  which  lines 
the  interior  of  the  capsule  and  other  portions 
of  the  joint,  except  the  surfaces  of  the  articular 
cartilages,  consists  of  a  delicate  connective- 
tissue  sheet,  containing  many  branched  and 
flattened  connective-tissue  cells.  The  latter, 
where  numerous,  as  is  the  case  except  at  points 
subjected  to  considerable  pressure,  are  ar- 
ranged on  the  free  surface  of  the  synovial  mem- 
brane as  a  more  or  less  continuous  layer,  often 
spoken  of  as  the  endothelium  of  the  synovial 
Since  in  many  places  the  layer  of  connective-tissue  elements  is  imperfect  and 


Capsule 

Synovial  membrane 

Articular  cartilage 

Joint-cavity 


Reflection  of  syno- 
vial membrane 

Epiphyseal  bone. 


Diagram  showing  the  parts  of  a  typical  joint. 


sac. 


the  component  cells  retain  their  stellate  form,  the  cellular  investment  of  the  joint- 
cavity  is  at  best  endothelioid,  suggesting,  rather  than  constituting,  an  endothelium. 
The  synovial  membrane  is  in  certain  places  pushed  inward  by  accumulations  of  fat 
of  definite  shape  between  it  and  the  capsule.  It  is  also  prolonged,  as  the  synovial 
fringes, 2  into  any  space  that  might  otherwise  be  left  vacant  in  the  various  movements. 
They  are  alternately  drawn  in  or  thrust  out,  according  to  circumstances.  Some- 
times pieces  of  them,  or  of  fibro- cartilage,  become  detached  in  the  joint,  giving  rise 
to  much  trouble. 

The  cavity  which  is  found  when  a  joint  is  opened  on  the  cadaver,  with  the 
tissues  dead  and  relaxed,  easily  suggests  a  false  impression.  It  is  to  be  remembered 
that  the  synovial  fluid  normally  is  present  in  quantity  little  more  than  sufficient  to 
lubricate  the  joint,  and  that  in  life  all  the  parts  are  strongly  pressed  together  so  that 
no  true  cavity  exists.  This  is  well  shown  by  frozen  sections. 

Certain  so-called  intra-articidar  ligaments,  as  the  ligamentum  teres  of  the  hij>, 
or  the  crucial  ligaments  of  the  knee-joint,  are  found  in  the  adult,  roughly  speaking, 
inside  the  joint.  The  sketch  of  development  given  above  shows  that  they  Cannot 
be  truly  within  the  articular  cavity.  In  fact,  either  they  wander  in  from  the  capsule, 
carrying  with  them  a  reflection  of  synovial  membrane,  or  they  are  the  remnants  of 

1  Cnpiuln  nrtlcularis.     '-'  IMicav  synovliiles. 


Ill 


the  capsules  separating  two  distinct  joints  which  have  broken  down  so  as  to  make  a 
common  articular  cavity.  Such  ligaments  retain  their  synovial  covering  and  really 
lie  without  the  joint-cavity. 

Vessels  and  Nerves.  —  Important  arterial  anastomoses  surround  all  the  larger 
joints  ;  from  the  larger  vessels  small  branches  pass  inward  to  the  ends  of  the  bones, 
to  the  periphery  of  the  articular  cartilages,  and  to  the  capsule.  The  margins  of  the 
cartilages  are  surrounded  by  vascular  loops  ;  the  articulating  surfaces  are,  however, 
free  from  blood-vessels.  The  synovial  membrane  is  usually  well  supplied  with 
minute  branches,  a  rich  net-work  being  described  at  the  bases  of  the  synovial  fringes. 
The  veins  form  strong  plexuses. 

Lymphatics  are  found  well  developed  directly  beneath  the  inner  surface  of  the 
synovial  membrane  ;  while  it  is  certain  that  they  absorb  from  the  joint,  direct  open- 
ings into  the  articular  cavity  have  not  been  demonstrated. 

Nerves,  presumably  sensory  and  vasomotor,  end  in  the  tissues  around  the  syno- 
vial membrane.  In  addition  to  the  Pacinian  bodies,  which  are  sometimes  very 
numerous,  Krause  has  described  special  articular  end-bulbs  outside  the  synovial 
membrane  surrounding  the  finger-joints  in  man. 


FIG.  137. 


Blood-vessel 


Free  surface  of 
articular  car- 
tilage 


Bone 


Marrow-cavity 


Synovial  mem- 

brane 


Union  of  carti- 
lage and  syno- 
vial membrane 


Section  through  margin  of  joint,  showing  articular  cartilage  and  capsule.    X  135. 


Bursae '  are  sacs  rilled  with  fluid  found  in  various  places  where  friction  occurs 
between  different  layers  or  structures.  They  are  sometimes  divided  into  synovial 
and  mucous  bursae.  These  varieties  are  distinct  in  typical  instances,  but,  since  the 
one  passes  insensibly  into  the  other,  it  is  doubtful  whether  this  subdivision  is  war- 
ranted. Some  bursse,  especially  those  around  the  tendons  of  the  fingers,  have  a 
true  synovial  lining  reflected  over  the  tendons,  and  are  surrounded  by  strong  fibrous 
sheaths  known  as  the  theca  synoviales. 2  Other  bursae  are  placed  as  capsules  around 
a  cartilage-coated  facet  over  which  a  tendon  plays.  Both  the  vaginal  and  capsular 
varieties  may  be  classed  as  synovial  bursae.  Representatives  of  the  mucous  bursae 
are  those  within  the  subcutaneous  tissue  where  the  skin  is  exposed  to  friction,  as  at 
the  elbow  and  the  knee.  These  bursae  seem  little  more  than  exaggerations  of  the 
spaces  between  layers  of  areolar  tissue.  The  same  may  be  said  of  some  of  those 
among  the  muscles.  The  mucous  bursat  are  provided  with  more  or  less  of  a  cellu- 
lar lining,  but  the  latter  is  less  perfect  than  in  the  synovial  class.  A  bursa  may  be 
simple  or  composed  of  several  cavities  communicating  more  or  less  freely.  They 
often  communicate  with  joints.  Their  number  is  uncertain.  Many,  perhaps  most, 
are  present  at  birth,  but  new  ones  may  appear  in  situations  exposed  in  certain 

1  Bursae  synoviales.     -  Vaginae  raucosae  tendinura. 


ii2  HUMAN   ANATOMY. 

individuals  to  uncommon  pressure  or  friction,  and,  under  these  circumstances,  the 
ones  usually  present  may  be  enormously  enlarged. 

Modes  of  Fixation  in  Joints. — Ligaments,  muscles,  atmospheric  pressure, 
and  cohesion  are  the  agents  for  fixation. 

Ligaments. — A  capsular  ligament,  pure  and  simple,  has  little  retaining 
strength.  The  accessory  ligaments,  on  the  contrary,  have  great  influence.  Their 
arrangement  differs  with  the  nature  of  the  joint.  Thus,  a  ball-and-socket  joint  has 
thickenings  at  such  parts  of  the  capsule  as  the  particular  needs  of  that  joint  require. 
A  hinge-joint  implies  strong  lateral  ligaments  ;  a  rotary  joint,  some  kind  of  a  retain- 
ing-band  that  shall  not  arrest  motion.  Sometimes  certain  ligaments  are  tense,  or 
nearly  so,  in  every  position  of  the  joint,'  as  the  lateral  ligaments  of  a  hinge-joint. 
Often  a  ligament  is  tense  only  when  a  joint  is  in  a  particular  position,  as  the  ilio- 
femoral  ligament  of  the  hip  when  the  thigh  is  extended.  A  strong  ligament  like 
the  one  just  mentioned  is,  when  tense,  the  greatest  protection  against  displace- 
ment. 

Muscles. — The  action  of  the  muscles  is  of  great  importance  in  maintaining 
the  joints  in  position,  in  certain  instances  being  the  most  efficient  agency.  The  con- 
stant pull  of  the  muscles  keeps  the  more  movable  bone  closely  applied  to  the  more 
fixed  in  all  positions.  Muscles  which  are  nowhere  in  contact  with  the  joint  may 
exercise  this  function.  The  tendons  of  muscles  sometimes  act  as  ligaments,  which 
differ  from  the  ordinary  ligamentous  bands  in  that  they  may  be  made  tense  or 
relaxed  by  muscular  action.  Sometimes  they  are  intimately  connected  with  the 
capsule,  at  other  times  distinct  from  it.  Some  muscles,  whose  tendons  cross  several 
joints,  exercise,  by  their  tonicity,  an  influence  on  them  all.  Thus,  the  peroneus 
longus  is  essential  to  the  maintenance  of  the  transverse  arch  of  the  foot.  Certain 
muscles  passing  over  more  than  one  joint  exert  a  ligamentous  action  on  one  joint 
determined  by  the  position  of  the  other.  This,  however,  is  more  properly  dis- 
cussed in  connection  with  the  action  of  muscles. 

Atmospheric  Pressure.— Much  has  been  written  about  the  action  of  this 
agency  in  holding  joints  in  place.  The  atmosphere  exerts  a  certain  pressure  on  all 
bodies,  animate  or  inanimate,  and  thus  tends  to  compress  them.  The  joints,  as 
parts  of  the  body,  are  subject  to  this  general  influence.  It  is  by  no  means  very  effi- 
cacious. The  shoulder- joint  has  a  capsule  long  enough  to  allow  very  free  motion, 
and  consequently  too  long  to  hold  the  humerus  in  place.  This  is  done  chiefly  by 
the  muscles.  When  these  are  paralyzed  the  arm  falls  out  of  place,  atmospheric 
pressure  being  inadequate  to  resist  the  weight.  The  most  important  action  of 
atmospheric  pressure  is  to  keep  the  soft  parts  closely  applied  to  the  bones. 

Cohesion  is  the  action  of  the  viscid  synovial  fluid  which  tends  to  hold  the 
surfaces  together.  It  is  very  feeble,  but  probably  has  an  appreciable  influence  in 
the  smaller  joints. 

Limitation  of  Motion. — The  shape  of  the  joint  determines  the  nature  of  the 
movement ;  its  range  depends  in  part  on  other  factors,  such  as  the  tension  of  liga- 
ments or  of  the  tendons  of  muscles  and  the  resistance  of  the  soft  parts. 

Motion  in  True  Joints. — It  is  easy  to  conceive  that  an  upright  rod  on  the 

highest  point  of  rather  less  than  half  a  sphere  may 

FIG.  138.  slide  to  the  periphery  along  an  indefinite  number  of 

ROTATION^  At/o^  lines.     This  is  angular  motion.     The  rod  on  reach - 

-4^?  ing  the  periphery,  or  at  any  point  on  the  way,  may 

travel  round  in  a  circle  describing  the  surface  of  a 
cone.  This  is  circumduction.  Finally,  without  an}' 
change  of  position,  the  rod  may  revolve  on  its  own 
axis.  This  is  rotation. 

Changes  of  Position  of  Parts  of  the  Body. 
— Assuming  that  the  palms  are  looking  forward,  an- 

Uiagram  illustrating  different  kinds  of  .  ^        .        ,•      , 

motion.  gular  motion  ot  a  limb,  or  of  a  part  of  one,  towards 

the  median  plane  of  the  body  is  called  adduction  ;  tin- 
opposite  movement,  abduction.  A  motion  bringing  the  distal  end  of  a  limb  bone? 
nearer  to  the  head  is  called  Jlc. \~ion  ;  the  opposite  movement,  extension.  The  move- 
ments of  the  ankle  and  the  foot,  however,  present  a  difficulty,  although  the  above 


VARIETIES   OF   TRUE  JOINTS.  113 

nomenclature  is  generally  accepted,  since  the  digital  extensor  muscles  flex  and  the 
flexors  extend.  It  is  best  with  reference  to  the  ankle-joint  to  speak  of  plantar 
flexion  and  dorsal  flexion.  Pronation  in  the  arm  is  turning  the  front  of  a  limb 
downward  ;  supination,  the  converse.  Thus,  when  the  palm  rests  upon  a  table  the 
arm  is  pronated  ;  when  the  back  of  the  hand  rests  upon  the  same  support  the  arm 
is  supinated.  Reference  to  the  skeleton  during  these  movements  will  show  that  pro- 
nation  is  associated  with  crossing  of  the  bones  of  the  forearm,  while  during  supina- 
tion  they  are  parallel.  These  terms  should  not  be  applied  to  motions  of  the  leg. 
Rotation  is  inward  or  outward,  according  as  it  is  towards  or  away  from  the  median 
line  of  the  body. 

Varieties  of  True  Joints. — The  following  are  the  chief  kinds  of  true  joints, 
the  nature  of  the  motion  being  determined  by  the  articular  surfaces  : 

Arthrodia,1  a  gliding  joint  permitting  merely  a  sliding  between  two  nearly 
plane  surfaces,  as  between  the  articular  processes  of  the  vertebrae. 

Enarthrosis,2  a  ball-and-socket  joint  permitting  angular  motion  in  any  direc- 
tion, circumduction  and  rotation.  The  shoulder-  and  hip-joints  are  conspicuous 
examples, 

Condylarthrosis,'  an  egg-shaped  joint  permitting  angular  motions  more  freely 
on  the  long  axis  than  on  the  short  one,  circumduction  but  (theoretically,  at  least) 
no  rotation,  as  in  the  radio-carpal  articulations.  The  imaginary  axes  for  the  angular 
motions  lie  in  the  convex  bone. 

The  Saddle-Joint,4  is  a  modification  of  the  above,  the  end  of  one  bone  being 
convex  in  one  plane  and  concave  in  another,  at  right  angles  to  the  first,  while  the 
other  bone  is  the  converse  ;  thus  in  one  plane  one  bone  is  the  receiver  and  in  the 
other  the  received.  The  articulation  of  the  trapezium  with  the  first  metacarpel  bone 
is  an  example.  The  motions  in  such  joints  are  precisely  the  same  as  those  of 
the  preceding  form.  The  two  imaginary  axes  are,  however,  on  opposite  sides  of  the 
joint,  each  being  at  right  angles  to  the  convex  plane  of  its  own  bone.  It  is  clear 
that  if  the  reciprocal  curves  of  the  two  bones  of  a  saddle-joint  coincide,  and  that  if 
they  fit  closely,  rotation  is  out  of  the  question  ;  but,  in  point  of  fact,  that  is  not  the 
case,  for  there  is  no  very  accurate  agreement  of  the  surfaces,  and  the  contained 
curve  is  smaller  than  the  containing,  so  that  a  certain  amount  of  rotation  is  possible.5 

Ginglymus,6  a  hinge-joint  permitting  motion  only  on  a  single  axis  approxi- 
mately transverse  to  the  long  axis  of  the  bone,  consequently  the  moving  bone  keeps 
in  one  plane.  The  ankle-joint  is  an  example.  The  inclination  of  the  transverse 
axis  may  vary,  and  one  end  of  the  joint  be  larger  than  the  other.  If  the  course  of 
the  revolving  bone  is  that  of  a  spiral  around  the  transverse  cylinder  the  articulation 
constiutes  a  screw-joint,'1  as  the  humero-ulnar  articulation. 

Trochoides,8  a  pivot-joint  permitting  motion  only  on  one  axis  coincident  with 
at  least  a  part  of  the  long  axis  of  the  bone, — namely,  rotation,  as  in  the  atlanto-axial 
articulation.  Should  a  part  of  the  bone  be  so  bent  as  to  lie  outside  of  the  axis,  as 
in  the  radius,  this  part  undoubtedly  changes  position  ;  nevertheless,  there  is  merely 
rotation,  for  the  change  of  position  is  accidental,  depending  on  the  shape  of  the 
bone,  not  on  the  nature  of  the  motion. 

Certain  complicated  joints  may  combine  several  of  the  above  forms. 
5Reneclu  Rois-Reymond.     Archiv  fiir  Anat.  u.  Phys.,  Phys.  Abtheil.,  1895. 

1  Arthrodia.      -'Enarthrosis.      :l  Articulatio  cllipsoidea.      4  Articulatio  sellaris.      6  Ginglymus.      ~  Articulatio  cochlearis. 
"  Articulntio  trochoidea. 


THE  SPINAL. COLUMN. 


THE  spinal  column  is  the  central  part  of  the  skeleton.  It  supports  the  head, 
bears  the  ribs,  thus  indirectly  supporting  the  arms,  and  encloses  the  spinal  cord.  It 
gives  origin  to  many  muscles,  some  passing  between  different  parts  of  the  spine, 
others  connecting  it  with  the  body.  These  purposes  demand  great  strength  and 
flexibility.  The  spine  is  composed  of  many  pieces  united  by  tough  fibro-cartilagi- 
nous  disks,  by  which  the  force  of  shocks  is  broken  and  the  great  range  of  move- 
ment is  distributed  among  many  joints.  It  is  convex  behind  in  the  regions  of  the 
thorax  and  pelvis,  so  as  to  enlarge  those  cavities,  and  has  forward  convexities  in  the 
neck  and  loins.  The  numerous  prominences  which  it  presents  serve  for  the  support 
of  the  ribs,  the  attachment  of  muscles,  and  the  interlocking  of  the  various  pieces. 
The  spinal  column  is  firmly  fixed  near  the 'lower  end  between  the  bones  of  the  pelvis. 

The  bones  composing  this  column  are  called  vertebra,  of  which  in  the  adult 
there  are  thirty-three  or  thirty-four  in  all.  They  are  divided  into  five  groups.  The 


FIG.  139. 


ipinous  process 


Facet  for  tubercle 
of  rib 


Transverse  process 
Superior  articular  process 


Demi-facet  for  head  of  rib 


Body 


Sixth  thoracic  vertebra  from  above. 


first  seven  are  the  cervical ;  the  next  twelve,  which  bear  ribs,  are  the  thoracic ;  the 
next  five  are  the  lumbar,  making  twenty-four  above  the  pelvis.  These  are  known 
as  the  presacral  vertebrae.  The  remainder  are  in  the  adult  united  into  two  bones, 
the  first  five  forming  the  sacrum,  the  last  four  or  five  the  coccyx.  As  many  as 
thirty-eight  are  seen  in  the  young  embryo,  but  some  disappear  or  are  fused. 

With  the  exception  of  the  first  two,  the  atlas  and  the  axis,  which  require  a 
separate  description  (page  119),  the  vertebrae  above  the  sacrum  present  the  following 
features,  which  are  common  to  all,  but  which  are  modified  in  the  different  regions  : 
(i)  a  body1  or  centrum  ;  (  2)  n.  pedicle*  springing  from  the  back  of  the  body  on  either 
side,  supporting  (3)  the  lamina?  a  plate  which  meets  its  fellow  in  the  middle  line  to 
form  an  arch  bounding  the  spinal  or  vertebral  foramen*  for  the  spinal  cord.  Each 
vertebra  gives  origin  to  several  processes. — namely,  (4)  a  spinous process?  sprin^in^ 
from  the  point  of  union  of  the  laminae  ;  (5)  a  transverse  process  on  each  side,  pro- 
jecting outward  from  the  junction  of  the  pedicle  and  lamina  ;  (6)  two  articulating 

1  Corpus.     "  Radix  arcus  vertebrae.     •'  Arcus.     *  Foramen  vertebrale.     •'  1'rorrssus  spinoMis.''  I'rm  I'XMIS  transversus. 
114 


THORACIC   VERTEBRA. 


processes1  on  each  side,  one  above  and  one  below  the  lamina,  forming  true  joints 
with  the  opposed  processes  of  the  neighboring  vertebrae  ;  (7)  a  rib  or  costal  element, 
which  in  the  thoracic  region  is  a  separate  bone,  in  the  cervical  region  is  a  part  of  the 
vertebra,  and  in  the  lumbar 

FIG.  140. 

Pedicle 


Superior  articular  process-, 
and  facet 


Articular  facet 
on  transverse 
process 


Superior  demi-facet  for  rib 


Inferior  demi-facet  for  rib 
Inferior  articular  process 


Spinous  process 


Sixth  thoracic  vertebra  from  the  side. 


region  mingles  with  the  trans- 
verse process.  The  costal  ele- 
ment is  also  represented  in 
the  sacrum. 

Thoracic  Vertebrae. 
— A  vertebra  from  the  middle 
of  the  thoracic  region  is  de- 
scribed first  as  intermediate  in 
several  respects  to  the  others. 
The  body  is  but  a  little 
broader  transversely  than 
from  before  backward.  It  is 
a  little  deeper  behind  than  in 
front,  thereby  helping  to  form 
the  curve  of  the  spine.  The 
upper  and  lower  borders  pro- 
ject a  little  anteriorly.  The 
upper  and  lower  surfaces,  as 
in  all  the  vertebrae,  are  rough 
where  the  intervertebral  disks 
join  them.  The  posterior 
surface  is  concave  from  side 
to  side,  and  presents  in  the 
middle  one  or  two  foramina 

for  the  escape  of  the  veins.  At  the  back  of  the  side  of  the  body  there  is  half  an 
articular  facet  both  above  and  below,  which,  with  the  intervening  disk,  forms  an  oval, 
shallow  socket  for  the  head  of  the  rib  belonging  to  the  lower  vertebra. 

The  spinal  foramen,  en- 
closed by  the  arch,  is  circular. 

The  pedicles,  which  are  much 
deeper  than  thick,  arise  from  the 
upper  half  of  the  body.  The  supe- 
rior border  rises  gradually  to  the 
articular  process.  The  inferior  bor- 
der is  concave,  forming  the  top  of 
the  notch?  which,  when  the  succeed- 
ing vertebra  is  in  place,  forms  the 
top  of  the  intervertebral  foramen? 
which  is  wholly  behind  the  lower 
half  of  the  body. 

The  laminae  are  broad,  each 
reaching  to  the  level  of  those  of  the 
next  vertebra. 

The  spinous  process  is  long, 
and  points  strongly  downward,  over- 
lapping the  one  below.  It  has  a 
narrow  under  surface  which  is 
grooved,  and  two  lateral  ones  meet- 
ing above  in  a  ridge  continued  from 
the  laminae.  This  arrangement  of 
the  laminae  and  spines  completely 
closes  the  cavity  of  the  spinal  canal. 

The  spinous  processes  are  slightly  enlarged  at  the  end  for  the  supraspinous  liga- 
ment and  muscles. 

The  transverse  processes  are  strong,  having  to  support  the  ribs.     They  pro- 


Superior  articu- 
lar process 
and  facet 


Spinous  process 


Sixth  thoracic  vertebra  from  behind. 


1  Processus  articularis.     -  Incisura  vertebral! 


'  Fissura  IntervertebrnHs 


n6 


HUMAN   ANATOMY. 


ject  outward  and  backward,  and  enlarge  at  the  tip,  which  anteriorly  presents  a  con« 
cave  articular  surface  for  the  tubercle  of  the  rib,  and  is  rough  behind  for  muscles. 

The  articular  surfaces  are  in  two  pairs  above  and  below,  each. pair  facing  in 
opposite  directions,  so  that  the  lower  ones  of  one  vertebra  meet  the  upper  ones  of 


Inferior  articular  process 

Superior  articular  process 

Transverse  foramen 
Transverse  process 


FIG.  142. 


Spinous  process 


Posterior  limb  of  transverse 
process 


Posterior  tubercle 


'ostal  element 
Anterior  tubercle 

Body  Anterior  limb  of  transverse  process 

Fourth  cervical  vertebra  from  above. 


the  next.  Each  presents  a  smooth,  roughly  oval  articular  surface.  The  superior 
ones  face  backward,  a  little  outward,  and  a  very  little  upward  ;  the  inferior,  con- 
versely, look  forward,  inward,  and  slightly  downward. 


Groove  for  spinal  nerve 


FIG.  143. 


Superior  articular  process 


Anterior  tubercle 
Posterior  tubercle 


Fourth  cervical  vertebra  from  in  front. 


Cervical  Vertebrae.  —  A  typical  cervical  vertebra  is  much  smaller  than  the 
thoracic. 

The  body  is  decidedly  longer  from  side  to  side  than  from  before  backwan 

The  upper  surface  is  raised  at  the  sid 

FIG.  144.  so  as  to  embrace  the  body  next  above, 

superior  articular  process  and  facet  •  ancj  has  its  front  border  rounded  for  the 

latter  to  descend  over  it  ;  for  this  pur- 
Anterior      pose  the  lower  anterior  border  is  pro- 
t..i,e,vie     longed  downward.      The  height  of  the 
i'«";tenoi     body  is  about  the  same  before  and  be- 

tubercle       ,  . 

hind. 

The  spinal  foramen  is  triangular, 
v/ith  the  greatest  diameter  transverse. 

The  pedicles  are  short  and  light, 

"nerve  °r  and  extend  backward  and  outward  from 

the  body.      The  notches  above  and  be- 
low them  are  about  equal. 

The  intervertebral  foramen  is  opposite  the  intervertebral  disk,  and  a  part 
of  the  bodies  of  two  vertebrae. 


Inferior  articular  pro- 
cess and  facet 

Inlet  vertebral 
notcb 

Fourth  cerviral  vertebra  from  the  side. 


LUMBAR   VERTEBRA. 


117 


The  laminae  are  smooth  and  do  not  quite  meet  those  of  the  next  vertebra, 
unless  the  head  be  bent  backward. 

The  spinous  process  projects  backward  and  a  little  downward.  It  is  short 
and  forked  at  the  end,  very  often  unevenly. 

The  transverse  processes  are  often  described  as  double.  The  posterior  limb, 
which  is  the  true  transverse  process,  projects  outward  and  somewhat  forward  from 
the  junction  of  the  pedicle  and  lamina,  and  ends  in  a  flattened,  nearly  vertical  pro- 
jection, the  posterior  transverse  tubercle.  The  anterior  limb,  a  vertical  plate  spring- 
ing from  the  side  of  the  body  and  extending  outward,  ends  in  the  anterior  transverse 
tubercle.  This  limb  is  the  shorter  of  the  two  and  its  tubercle  the  larger.  The  limbs 
are  cdnnected  by  a  concave  plate  or  bone,  slanting  slightly  outward,  which  forms 
the  floor  of  a  gutter 1  in  which  the  spinal  nerve  lies,  and  which  represents  the  costal 
element.  A  round  hole,  the  transverse  foramen,  for  the  vertebral  artery  and  veins, 
lies  internal  to  this  plate  ;  the  artery  usually  does  not  pass  through  the  foramen  of 
the  seventh  vertebra.  Since  the  scalenus  anticus  muscle  springs  from  the  anterior 


FIG.  145. 


Spinous  process 


Superior  articular  facet 
Mammillary  process 


Third  lumbar  vertebra  from  above. 

tubercles  and  the  scalenus  medius  from  the  posterior  ones,  on  leaving  the  spine  the 
spinal  nerves  pass  between  these  muscles. 

The  articular  processes  are  placed  at  the  outer  ends  of  the  laminae ;  the 
upper  face  upward  and  backward,  the  lower  forward  and  downward. 

Lumbar  Vertebrae. — A  typical  lumbar  vertebra  is  very  much  larger  than  the 
others. 

The  body  is  broad  from  side  to  side,  the  upper  and  lower  borders  projecting 
especially  at  the  sides.  The  posterior  surface  is  slightly  concave  and  presents  two 
large  venous  openings. 

The  spinal  foramen  is  three-sided,  with  a  transverse  diameter  but  slightly 
exceeding  the  antero-posterior. 

The  pedicles  are  short  and  strong,  diverging  only  slightly.  They  are  very 
nearly  on  a  level  above  with  the  top  of  the  body,  so  that  there  is  a  small  notch  above 
and  a  large  one  below. 

The  laminae  are  broad  at  the  sides,  but  less  so  near  the  mid-line,  so  that  in  this 

1  Sulcus  n.  spinalis. 


u8 


HUMAN    ANATOMY. 


region  there  is  a  large  opening  into  the  spinal  canal.  A  considerable  part  of  the  arch 
is  lower  than  the  body. 

The  spinous  process  is  a  flat  projection  extending  nearly  straight  backward, 
with  two  lateral  surfaces  and  a  superior,  inferior,  and  posterior  border.  The  last  is 
rough  and  thickened  below,  with  occasionally  a  tendency  to  become  bifid. 

The  transverse  processes,  which  are  solely  for  muscular  attachments,  and 


FIG.  146. 


Superior  articular  proces 

Mammillary  process 
Transverse  process 


Accessory  process 
•Inferior  articular  process  and  facet 


Third  lumbar  vertebra  from  the  side. 


therefore  not  heavy,   project  outward   and  somewhat  backward.      They  are  thin, 
having  an  anterior  and  a  posterior  surface  and  a  blunt  end. 

The  articular  processes  are  large,  very  nearly  vertical,  and  curved.  The 
superior,  facing  somewhat  backward  but  chiefly  inward,  are  concave  and  embrace 
the  inferior  ones  of  the  vertebra  above,  which  are  convex,  and  face  in  the  opposite 
direction. 


Superior  articular  process  and  facet 


Mammillary  process 


Accessory  process 


Inferior  articular  process 


Spinous  process         Lamina 
Third  lumbar  vertebra  from  behind  and  the  side. 


The  mammillary  processes  form  on  either  side  a  rounded  lateral  projection 
on  the  posterior  border  of  the  superior  articular  process.  Additional  tiilu-rcli>s,  the 
accessory  processes,  appear  as  inconspicuous  elevations  at  the  junction  of  the 
posterior  border  of  the  transverse  with  the  superior  articular  processes.  The  details 
:m<l  the  morphological  significance  of  the  mammillary  and  the  accessory  processes 
are  discussed  later  (page  123). 


PECULIAR   VERTEBRA. 

The  chief  points  of  difference  between  typical  vertebrae  of 
groups  may  be  tabulated  as  follows  : 


BODY. 


CERVICAL. 

1.  Broad. 

2.  Upper    surface    with 
raised       sides       and 
rounded  anterior  bor- 
der. 

3.  No  facets. 


THORACIC. 
Diameters  nearly  equal; 

concave  behind. 
Plane. 


Costal  semifacets. 


119 
the  three  presacral 

LUMBAR. 


SPINAL  FORAMEN.      Triangular,  with   great-     Nearly  circular, 
est     diameter     trans- 
verse. 


PEDICLES. 
LAMINAE. 


Notches  above  and  be- 
low nearly  equal. 


Rising  from  top  of  body; 
great  notch  below. 


Narrow,  with  spaces  be-     Broad, ;    no  spaces   be- 
tween, tween. 


TRANSVERSE  PRO-     Double  foramen  at  root ;    Strong,    with     articular 
two  tubercles.  facet. 


CESSES. 


SUPERIOR  ARTICU-    Nearly  plane  ;   face  up-    Plane,  vertical ;    face 
LAR  SURFACES.          ward  and  backward.          nearly  backward. 


Broad. 
Plane. 

No  facets. 

Triangular,  with  diam- 
eters nearly  equal. 


Small  notch  above, 
great  one  below. 

Extending  downward; 
large  spaces  be- 
tween. 

Slender. 


Concave,  vertical  ; 
face  chiefly  inward. 


PECULIAR   VERTEBRA. 

Certain  vertebrae  differ  more  or  less  markedly  from  the  type  of  their  respective 
groups  ;  in  some  cases,  as  the  upper  two  cervical  vertebrae,  these  variations  result  in 
conspicuous  modifications  ;  in  others,  as  the  lower  thoracic,  the  peculiarities  are  less 
pronounced.  Although  the  most  noteworthy  differences  are  here  given,  the  reader 


FIG.  148. 

Posterior  tubercle 


Posterior  arch 


Lateral  mass 


roove  for  vertebral  artery 

Superior  articular  facet 


Transverse  pr< 
cess 


Transverse  foramen 


Facet  for  odontoid  process  of  axis 


Anterior  arch 


Anterior  tubercle 
The  atlas  from  above. 


is  referred  to  the  discussion  of  the  gradual  changes  which  occur  in  passing  from  one 
region  to  the  other  (page  122)  for  a  more  complete  account  of  the  modifications  to 
be  observed. 

The  first  and  second  cervical  vertebrae,  known  as  the  atlas  andaxzs,  consti- 
tute a  special  apparatus  for  the  security  and  movements  of  the  head.     The  key  to 


I20  HUMAN    ANATOMY. 

the  arrangement  is  that  the  part  which  in  the  ordinary  process  of  development 
should  become  the  body  of  the  atlas  is  instead  fused  with  the  body  of  the  axis. 

The  atlas,  having  no  body,  consists  of  two  lateral  masses,  connected  by  a  short 
anterior  arch  and  a  long  posterior  one.  The  lateral  masses  present  the  articular 
facets  on  their  lower  and  upper  surfaces.  The  inferior  look  downward  and  slightly 
inward,  and  are  very  slightly  concave  from  before  backward.  The  superior  facets 
are  oval  concavities  the  backs  of  which  are  strongly  raised  from  the  surface.  Their 
long  axis  runs  forward  and  inward,  the  outer  wall  being  decidedly  higher  than  the 
inner.  The  articular  facet  narrows  at  the  middle,  and  is  often  marked  by  a  trans- 
verse ridge  at  this  point ;  rarely  it  is  divided  into  two  parts.  The  articular  surfaces 
of  the  two  sides  sometimes  very  nearly  correspond  with  parts  of  the  surface  of  a 
single  imaginary  sphere. 

Their  variation  in  all  respects  is  great.  Thus,  Macahster  finds  in  one  hundred 
bones  that  the  distance  between  the  front  ends  of  the  two  facets  varies  from  ten  to 
twenty  millimetres,  being  usually  from  fifteen  to  twenty  millimetres,  and  that  the 
hind  ends  are  from  thirty-two  to  fifty  millimetres  apart,  the  greater  number  being 
separated  from  thirty-five  to  forty  millimetres.  The  angle  formed  by  the  intersec- 

FIG.  149. 

Posterior  tubercle 


Posterior  arch 


Transverse  foramen 


Anterior  arc 


Inferior  articular  facet 


Position  of  transverse  ligament  (dotted  lines) 


Facet  for  odontoid  process  Anterior  tubercle 

The  atlas  from  below. 

tion  of  the  prolonged  axes  of  the  articular  facets  ranges  from  thirty-two  to  sixty- 
three  degrees.  Each  lateral  mass  presents  a  rough  tubercle  on  the  inner  side  between 
which  passes  the  transverse  ligament  holding  the  odontoid  process  close  against  the 
anterior  arch.  The  anterior  arch  is  compressed  from  before  backward.  It  presents 
the  anterior  tubercle  in  front  in  the  median  line,  and  behind  has  a  slightly  concave 
articular  facet  for  the  odontoid  process.  The  posterior  arch  bounds  the  spinal  canal 
behind.  The  transverse  ligament,  confining  the  odontoid  process,  bounds  the  spinal 
canal  in  front,  and,  being  in  place,  the  transverse  diameter  of  the  canal  is  the  longer. 
The  place  of  the  spinous  process  is  taken  by  the  posterior  tubercle.  The  transverse 
processes  extend  farther  out  than  any  in  the  cervical  region.  Each  ends  in  a  single 
flattened  knob  with  a  surface  slanting  downward  and  forward.  Bifurcation  is  rare. 
The  transverse  foramen  is  at  its  base  ;  from  the  foramen  a  groove  for  the  vertebral 
artery  crosses  the  root  of  the  posterior  arch  and  winds  round  behind  the  raised 
border  of  the  articular  surface.  This  groove  is  occasionally  bridged  over  by  a  little 
arch  of  bone  extending  from  the  edge  of  the  articular  surface  either  to  the  trans- 
verse process  or  to  the  posterior  arch. 

Variations. — The  atlas  may  be  fused  with  the  occipital  bone  in  various  ways; 
this  may  occur  by  the  pathological   destruction   of  the  joint,  or  the  arch,   or  a 

1  Journal  of  Anatomy  and  Physiology,  vol.  xxvii.,  1893. 


THE   AXIS. 


121 


FIG.  150. 


Superior 
articular 
facet 


Articular  facet  on  front 
of  odontoid  process 


part  of  it,  may  be  fused  with  the  skull  around  the  foramen  magnum.  Such  union 
may  be  partial  or  complete,  and  is  usually  associated  with  an  imperfect  development 
of  the  atlas,  especially  on  one  side.  There  is  reason  to  regard  such  cases  as  con- 
genital. The  transverse  process  and  the  paroccipital  process  of  the  occipital  bone 
may  be  connected  by  bone. 

The  axis  :  differs  less  from  the  other  cervical  vertebrae  ;  seen  from  below  it  pre- 
sents no  essential  peculiarity.  The  body  is  very  long  even  without  the  odontoid 
process  (the  separated  body  of  the  atlas)  which  surmounts  it.  The  odontoid?  a 
cylindrical  process  lower  behind  than 
in  front,  ends  above  in  a  median  ridge, 
on  either  side  of  which  is  a  rough,  slant- 
ing surface  for  the  origin  of  the  check 
ligaments  connecting  it  with  the  skull. 
It  bears  an  oval  articular  facet  in  front, 
resting  against  one  on  the  atlas,  and  a 
smaller  facet  behind  at  a  lower  level 
which  forms  part  of  a  joint  with  the 
transverse  ligament.  The  la-mince^  in- 
stead of  being  plates,  are  heavy  and 
prismatic,  each  with  a  .  rather  sharp 
upper  edge,  which,  meeting  its  fellow, 
forms  a  ridge  on  the  spine.  The  spinous 

process  is  heavy,  projecting  considerably  Ni^^^jj'  inferior  articu- 

beyond  the  third.      It  varies  greatly  in  The  axis  from  in  front, 

length    and    in    degree   of    bifurcation. 

The  transverse  process  is  small  ;  the  anterior  tubercle  is  a  mere  point  or  altogether 
wanting.  The  transverse  foramen  is  replaced  by  a  short  canal,  so  curved  that  its 
upper  opening  looks  almost  outward.  The  superior  articular  siirfaces  are  approxi- 
mately circular  facets  on  the  upper  surface  of  the  body  instead  of  on  the  arch,  as 
are  all  below  ;  they  look  upward  and  a  little  outward.  Although  nearly  plane,  they 
present  a  very  slight  antero-posterior  convexity. 

The  seventh  cervical  vertebra,  called  vertebra  prominens  on  account  of  its 
long,  knobbed  spine,  rather  resembles  the  upper  thoracics.  The  transverse  foramen 

is  smaller  than  those  above  it, 

FIG.  151.  and  the  anterior  tubercle  of  the 

transverse  process  is  particu- 
larly small  and  near  the  body. 
The  first  thoracic  ver- 
tebra has  the  sides  of  the 
upper  surface  somewhat  raised 
at  the  roots  of  the  pedicles. 
It  has  a  complete  facet  for  the 
head  of  the  first  rib  and  a  half- 
facet  at  the  lower  border  of  the 
body.  Sometimes  the  former 
is  imperfect,  beyig  completed 
on  the  intervertebral  disk. 
The  facet  on  the  transverse 
process  is  smaller  and  less  con- 
cave than  the  ones  following  ; 
sometimes  it  is  even  convex. 
The  ninth  thoracic  vertebra  has  no  half-facet  below. 

The  tenth  thoracic  vertebra  has  a  nearly  complete  facet  above  and  none 
below. 

The  eleventh  thoracic  vertebra  has  a  complete  facet  on  the  body  and  none  on 
the  transverse  process,  which  is  small. 

The  twelfth  thoracic  vertebra  has  a  complete  facet  a  little  above  the  middle 
of  the  body.  The  transverse  process  is  broken  up  into  the  three  tubercles.  The 
lower  articular  facets  face  outward.  The  spine  is  of  the  lumbar  type. 

1  Epistropheus.     -  Dens. 


Odont 


Articula 


Spinous  process 


Inferior  articular 
process  and  facet 

The  axis  from  the  side. 


Body 


Transverse  foramen 


122 


HUMAN   ANATOMY. 


The  fifth  lumbar  vertebra  is  much  higher  in  front  than  behind.  The  trans- 
verse process  is  broad  at  the  base,  springing  in  part  from  the  body  ;  the  spine  'is 
relatively  small. 

DIMENSIONS   OF   VERTEBRA. 

(The  measurements  are  given  in  centimetres.) 


Vertebrae. 

Height       of 
Front     of 
Bodies. 
(Dwight.) 

Height       of 
Front      of 
Bodies. 
(Anderson.1) 

Height       of 
Back       of 
Bodies. 
(Anderson.) 

Transverse 
Diameter. 
(Anderson.) 

Antero- 
Posterior 
Diameter. 
(Anderson.) 

Spread       of 
Transverse 
Processes. 
(Dwight.) 

Twenty 

Thirty 

Thirty 

Fifty-three 

Twenty-eight 

Fourteen 

spines. 

spines. 

spines. 

spines. 

spines. 

spines. 

Cervical        .    .    . 

2 

i-9 

.    . 

1-9 

1-5 

5-5 

3 

1.2 

1.2 

1-9 

i-5 

5-4 

4 

1.2 

1.2 

.    . 

2.1 

i-5 

5-4 

5 

1.2 

1.2 

.    . 

2-3 

1.6 

5-7 

6 

I.I 

I.I 

2-5 

1.7 

5-9 

7. 

1-3 

1-3 

2-7 

1.8 

7-2 

Thoracic        .    .   . 

i 

1-5 

1.4 

i-5 

2.7 

1-7 

7.6 

2 

1.7 

1.6 

i-7 

2.8 

i-7 

7-i 

3 

1.7 

i-7 

1.8 

2.6 

i-9 

6-3 

4 

'  i-7 

1.7 

i-9 

2.6 

2.2 

6-3 

5 

1.7 

1.7 

2.0 

2.5 

2.4 

6.4 

6 

1.8 

1.8 

i-9 

2.7 

2-5 

6.4 

7 

1.8 

1.8 

2.O 

2.8 

2.6 

6-3 

8 

1.8 

1.8 

2.1 

3-o 

2.8 

6-3 

9 

i-9 

i-9 

2.1 

3-i 

2.9 

6.2 

10 

2.1 

2.1 

2.2 

3-4 

2.9 

5-8 

ii 

2.1 

2.1 

2.4 

3-6 

2.9 

5-2 

12 

2-3 

2-3 

2-5 

4.0 

3-0 

4.7 

Lumbar         .   . 

I 

2.4 

2.4 

2.6 

4.2 

2-9 

7-3 

2 

2-5 

2-5 

2.7 

4-4 

3-i 

8.0 

3 

2-5 

2.6 

2.7 

4-7 

3-6 

9.0 

4 

2-5 

2.6 

2.6 

4.8 

3-3 

8-5 

5 

2.6 

2.7 

2.2 

5-2 

3-6 

9-1 

GRADUAL  CHANGES  FROM  ONE  REGION  TO  ANOTHER. 

Bodies. — The  height  of  the  bodies  increases  as  we  descend  the  spine,  very 
gradually  in  each  region  but  rather  rapidly  at  the  junction  of  two  regions,  as  shown 
in  the  table.  The  first  two  lumbars,  like  those  above  them,  are  rather  deeper  behind 
than  in  front,  but  the  reverse  is  true  of  the  last  two,  and  especially  of  the  fifth,  in 
which  the  difference  is  considerable.  The  breadth  of  the  bodies  increases  to  the 
first  or  second  thoracic,  then  dwindles  to  the  fourth  or  fifth,  and  then  again  increases 
to  the  sacrum.  The  elevation  at  the  sides  of  the  upper  surfaces  of  the  bodies  of  the 
cervical  vertebrae  diminishes  in  the  lower  part  of  that  region  ;  in  the  seventh  it  is 
limited  to  near  the  root  of  the  pedicle.  The  same  condition  is  found  in  the  first 
thoracic  vertebra  and  to  a  slight  extent  in  the  next  two.  The  downward  prolonga- 
tion of  the  front  of  the  body  of  a  cervical  vertebra  is  slight  in  the  lower  part  of  the 
neck.  The  first  thoracic  has  an  entire  facet  for  the  head  of  the  first  rib  near  the  top 
of  the  body  and  a  part  of  one  at  the  lower  border  for  a  portion  of  the  head  of  the 
second.  As  a  rule,  in  the  thoracic  region  the  head  of  each  rib  rests  in  a  facet  on 
two  vertebrae  and  the  intervening  disk,  the  lower  vertebra  contributing  more  of  the 
joint  than  the  upper,  and  corresponding  with  the  rib  in  name.  Thus,  the  head 
of  the  fourth  rib  lies  between  the  third  and  fourth  thoracic  vertebrae,  and  its  tubercle 
rests  on  the  transverse  process  of  the  fourth.  Towards  the  lower  part  of  the  region 
the  heads  have  a  tendency  to  take  a  lower  relative  position  on  the  column  coinci- 
dently  with  the  increase  in  size  of  the  bodies.  The  head  of  the  tenth  rib  usually 
rests  wholly  on  the  body  of  the  tenth  vertebra  or  on  it  and  the  disk  above,  conse- 

1  Journal  of  Anatomy  and  Physiology,  vol.  xvii.,  1883.  Anderson  states  that  the  vertical 
diameters  of  the  front  and  back  of  the  cervir.il  vertebrae  are  generally  the  same  ;  hence,  prob- 
ably, he  thought  it  needless  to  give  the  posterior  measurements.  The  close  correspondence  of 
his  anterior  measurements  with  those  of  the  author  is  very  striking. 


REGIONAL   CHANGES.  123 

quently  the  ninth  vertebra  has  no  half-facet  below.  The  tenth  has  a  nearly  or  quite 
complete  facet  at  its  upper  border,  the  eleventh  has  a  complete  one  rather  below 
the  top  of  the  body,  and  the  twelfth  has  a  complete  facet  nearly  half-way  down. 
At  the  ninth  or  tenth  the  facet  begins  to  leave  the  body  and  to  travel  backward 
onto  the  root  of  the  pedicle. 

When  the  body  is  seen  from  above  or  below  in  certain  parts  of  the  thoracic 
region  the  front  curve  is  flattened  on  the  left  by  the  pressure  of  the  aorta.  This  com- 
pression usually  is  first  seen  at  the  top  of  the  fifth  thoracic,  and  is  traceable  down- 
ward for  a  few  vertebrae,  sometimes  as  far  as  the  lumbar  region.  The  depression 
gradually  passes  from  the  side  to  the  front  as  it  descends  the  spine. 

The  Transverse  Processes. — As  shown  by  the  table,  the  spread  of  the 
transverse  processes  increases  greatly  at  the  junction  of  the  cervical  and  the  thoracic 
regions,  falls  rapidly  to  the  third  thoracic,  remains  stationary  to  the  tenth,  falls  to  the 
last  thoracic,  the  narrowest  point,  and  then  gains  at  once,  reaching  the  maximum  at 
the  third  lumbar.  The  anterior  tubercles  of  the  transverse  processes  of  the  cervical 
region  increase  to  the  sixth,  which  is  the  tubercle  of  Chassaignac,  who  taught  that 
the  carotid  artery  can  be  compressed  against  it,  the  force  being  directed  backward 
and  a  little  inward.  The  anterior  limb  of  the  transverse  process  of  the  seventh  ver- 
tebra is  very  short,  and  its  tubercle  is  usually  rudimentary.  It  is  distinctly  in  series 
with  the  slight  elevation  of  the  socket  for  the  head  of  the 'first  rib  often  seen  on  the 
first  thoracic  vertebra.  The  piece  of  bone  between  the  tubercles,  forming  the  floor 
of  the  gutter  for  the  spinal  nerve,  is  much  longer  and  more  anteriorly  placed  in  the 
seventh  than  in  those  above  it.  It  is  this  piece  connecting  the  two  tubercles  that  is 
the  true  costal  element  in  the  neck.  The  so-called  anterior  limb  of  the  transverse 
process  with  the  tubercle  on  it  is  in  line,  not  with  the  ribs  but  with  the  anterior 
tubercle  called  the  processus  costarius.  The  articular  facet  on  the  transverse  process 
of  the  first  thoracic  is  shallow,  often  convex,  and  faces  a  little  downward.  That  of 
the  second,  at  which  point  the  processes  slant  more  backward,  is  concave  and  some- 
what overhung  above  ;  this  is  seen  in  the  two  or  three  following,  after  which  the 
facets  grow  smaller,  more  shallow,  and  look  upward  as  well  as  forward.  As  the 
eleventh  rib  has  but  a  rudimentary  tubercle  and  the  twelfth  none  at  all,  there  is  no 
facet  on  the  transverse  process  of  the  last  two  thoracic  vertebrae.  The  latter  process 
of  the  eleventh  is  small,  and  that  of  the  last  broken  up  into  three  tubercles,  ( i )  the 
superior  or  mammillary,  rising  from  the  posterior  surface  ;  (2)  the  accessory  or  infe- 
rior, pointing  downward  ;  (3)  the  external,  a  knob,  the  smallest  of  the  three.  The 
latter  two  represent  the  transverse  process  of  the  upper  thoracic  vertebrae.  All  three 
tubercles  are  usually  to  be  recognized  on  the  eleventh  thoracic,  although  the  acces- 
sory tubercle  is  usually  not  seen  higher  up.  The  knobs  for  muscular  attachment  on 
the  backs  of  the  thoracic  transverse  processes  are  evidently  in  line  with  the  mammil- 
lary tubercles,  rudiments  of  which  are  found  in  a  large  part  of  the  thoracic  region. 
In  the  lumbar  ^region  they  are  found  on  the  side  of  the  superior  articular  processes, 
growing  smaller  in  the  lower  vertebrae,  and  being  lost  in  the  fifth. 

The  lumbar  transverse  processes  increase  in  length  to  the  third,  which  is  the 
longest,  unless  it  be  equalled  by  the  fifth.  That  of  the  fourth  is  peculiar  in  being 
shorter  and  lighter  than  its  neighbors.  It  usually  has  a  rather  triangular  outline, 
owing  to  the  lower  Border  approaching  the  upper  near  the  tip,  and  also  arises  farther 
forward, — i.e. ,  nearer  the  side  of  the  pedicle  than  those  above  it.  The  fifth  is  much 
heavier  and  arises  from  the  side  of  the  body  as  well  as  from  the  pedicle,  so  that  its  ante- 
rior portion  is  evidently  in  series  with  the  costal  element  developed  in  the  sacrum, 
described  in  connection  with  that  bone.  The  process  which,  in  accordance  with  gen- 
eral usage,  has  been  called  the  lumbar  transverse  process,  is  clearly  in  direct  continua- 
tion with  the  line  of  the  ribs.  This  is  particularly  striking  in  certain  cases  in  which  it  is 
not  easy  to  determine  whether  there  is  a  thirteenth  rib,  or  whether  this  process  is  to 
be  considered  as  free  in  the  first  lumbar.  The  accessory  tubercle,  which  can  be 
made  out  in  the  lumbar  region,  and  is  particularly  large  in  the  lower  vertebrae,  is 
in  line  with  the  ends  of  the  transverse  processes  of  the  thorax.  Thus  the  so-called 
lumbar  transverse  process  represents  at  its  root  both  a  rib  and  the  accessory  and 
transverse  tubercles,  and  beyond  its  root  a  rib  only.  This  is  especially  marked 
in  the  broad  process  of  the  fifth  lumbar,  which  springs  from  the  side  of  the  body 


I24 


HUMAN   ANATOMY. 


as  well  as  from  the  pedicle.  The  homologies  of  the  costal  elements  are  shown  in 
Fig.  158. 

The  Spinous  Processes. — These  are  short  and  bifid  in  the  third,  fourth,  and 
fifth  cervical  vertebrae  ;  longer  and  usually  not  forked  in  the  sixth  ;  and  longer,  larger, 
and  knobbed  in  the  seventh.  The  type  is  that  of  the  last  mentioned  in  the  upper 
thoracic,  only  the  spine  is  a  little  longer,  stronger,  and  more  slanting.  At  about  the 
fourth  a  sudden  change  occurs  :  the  process  becomes  longer,  sharper,  and  more 
descending.  At  about  the  tenth  it  shortens  again,  points  more  backward,  and 
approaches  the  lumbar  type,  which  is  generally  reached  in  the  last  thoracic.  The 
spine  of  the  last  lumbar  is  usually  much  smaller  than  those  above  it. 

The  Articular  Processes. — The  change  from  the  cervical  type  to  the  thoracic 
is  gradual,  but  that  from  the  thoracic  to  the  lumbar  occurs  suddenly  at  the  junction 
of  those  regions.  The  inferior  processes  of  the  last  thoracic  face  outward.  Not  infre- 
quently the  change  occurs  a  space  higher,  but  rarely  one  lower.  Occasionally  the 
facets  between  the  regions  face  in  an  intermediate  direction.  Sometimes  the  change 
is  normal  on  one  side  and  not  on  the  other. 


Superior  articular  process 


FIG.  152. 

Promontory 


Transverse  process 


Lines  of  union 
between  fused 
sacral  vertebrae 


Iliacus 


Anterior  sacral 
foramina 


Pyriformis. 


Coccygeus 


Notch  for  fifth  sacral  nerve  Apex 

The  sacrum,  anterior  surface. 


THE   SACRUM. 

This  bone '  is  composed  of  five  fused  and  modified  vertebrae,  of  which  the  three 
upper  support  the  pelvis  laterally.  The  vertebrae  decrease  very  much  in  si/e  from 
above  downward,  the  lower  being  bent  strongly  forward.  The  first  vertebra  is  com- 
paratively but  little  changed  ;  the  last  consists  of  little  more  than  the  body.  The 


THE   SACRUM. 


125 


essential  modification,  besides  the  fusion,  is  the  occurrence  of  the  lateral  masses,1 
representing  transverse  processes  and  ribs,  which,  springing  from  the  bodies  and 
arches,  are  connected  with  the  innominate  bones  by  joints  and  ligaments.  The 
sacrum  has  an  upper  surface,  or  base,  a  lower,  or  apex,  and  a  front,  back,  and  two 
lateral  surfaces.  The  base  has  above  a  rough  space  representing  the  end  of  the 
body  of  a  vertebra  to  which  the  last  lumbar  disk  is  attached.  It  is  raised  a  little 
from  the  bone  and  forms  an  acute  projecting  angle  with  the  front  surface,  known  as 
the  promontory  of  the  sacrum,  an  important  landmark  in  midwifery.  Behind  the 
body  of  the  first  sacral  vertebra  is  the  triangular  orifice  of  the  sacral  canal,  the 


Articular  process 


FIG.  153. 

Lamina  Sacral  canal 


Transverse  process  of 
first  sacral  vertebra 


Spinous 
process 


Gluteus  maximus 


Sacral  cornu 


Sacral  canal 
The  sacrum,  posterior  surface. 

transverse  diameter  of  which  is  the  greater.  The  articular  process,  springing  from 
the  side  of  the  arch,  is  vertical,  the  concave  facet  facing  backward  and  inward.  The 
upper  surface  of  the  lateral  mass,  the  ala,  springs  from  the  side  of  the  body  and 
the  pedicle,  expanding  into  a  broad  area,  and  is  bounded  in  front  by  an  ill-marked, 
rounded  border  which  separates  it  from  the  anterior  surface  and  curves  forward  ; 
behind  by  a  shorter  border  curving  backward,  on  which  the  auricular  process  rests  ; 
and  outside  by  an  irregular  convex  border.  The  latter  may  often  be  subdivided 
into  two  parts  :  an  anterior,  running  pretty  nearly  forward  and  backward  and  cor- 
responding to  the  top  of  the  auricular  surface,  and  a  posterior,  running  backward 

1  Partcs  laterales. 


126 


HUMAN   ANATOMY. 


Articular  process 


and  inward.  Thus  the  sacrum  is  broader  before  than  behind.  The  apex  is  nothing 
but  the  under  side  of  the  body  of  the  very  small  fifth  sacral  vertebra. 

The  anterior  surface  is  a  triangular  concavity  formed  by  the  bodies  and  lat- 
eral masses  of  the  five  sacral  vertebrae.  It  has  a  double  row  of  four  openings,  the 
anterior  sacral  foramina,  one  on  each  side  of  the  ridges,  representing  the  ossified 
disks  connecting  the  bodies  of  the  fused  sacral  vertebrae.  The  sacral  nerves,  like 
the  other  spinal  nerves,  divide  into  an  anterior  and  a  posterior  division  on  leaving 
the  spinal  canal  ;  in  the  case  of  the  sacral  nerves,  however,  this  takes  place  inside 
the  bone,  the  anterior  divisions  escaping  by  these  foramina.  The  bodies  and  the 
foramina  grow  smaller  from  above  downward,  and  the  latter  are  nearer  together.  A» 
transverse  depression  across  the  body  of  the  third  vertebra  usually  marks  a  rather 

sudden    change    in    the 

FIG.  154.  curvature  of  the  anterior 

Transverse  process  surface.      The    irregular 

outline  of  the  lateral  bor- 
ders may  be  divided  into 
two  parts  :  the  upper, 
rather  concave,  ends  be- 
low in  a  little  point  on  a 
level  with  the  third  verte- 
bral body,  and  represents 
the  extent  of  the  articu- 
lar surface.  Below  this 
the  border  slants  down- 
ward and  inward  until 
opposite  the  lower  part 
of  the  fifth  sacral  seg- 
ment, when  it  suddenly 
turns  inward,  forming  a 
notch  over  the  anterior 
division  of  the  fifth  sacral 
nerve,  which  emerges  be- 
tween it  and  the  coccyx. 
The  posterior  sur- 
face is  composed  of  the 
fused  lamina  and  their 
modifications.  The  up- 
per borders  of  the  first 
laminae  slant  downward, 
and  below  their  junction 
is  a  well-marked  spine.1 
Below  this  the  laminae  of 
the  sacral  vertebrae  are 
fused  and  the  spines 
small.  The  laminae  of 
the  fifth  sacral  never  join, 
and  those  of  the  fourth 

frequently  do  not,  thus  leaving  the  lower  end  of  the  canal  uncovered.  The  laminae 
that  do  not  meet  end  in  tubercles  each  representing  one-half  of  a  spinous  process. 
The  lowest  two  project  downward  at  the  sides  of  the  open  canal,  and  are  called  the 
sacral  cornua.  Four  posterior  sacral  foramina  for  the  exit  of  the  posterior  divisions 
of  the  nerves  appear  on  each  side  of  the  laminae.  Outside  of  these  are  some  irregu- 
lar tubercles  representing  the  transverse  processes*  and  internal  to  the  first  tlmv 
foramina  are  tubercles  in  line  with  the  articular  processes.* 

The  lateral  surface  begins  just  outside  of  the  transverse  tubercles.  It  is 
broad  above,  but  below  the  third  vertebra  is  merely  a  line.  The  upper  part  is 
divided  into  two  portions  :  the  front  one  is  the  auricular  surface,  from  a  slight 
resemblance  to  an  ear,  which  joins,  by  fibro-cartilage,  the  corresponding  surface  on 
the  ilium.  It  is  broader  above  than  below,  convex  in  front,  indented  behind,  with 

1  Crlstn  media.     -  CrNtnc  liitcrnlcs.     ''Crlntnc  jirlii  ul.it  is. 


Auricular 
(articular) 
surface 


Fourth  posterior  sacral  foramen 


\otch 


Sacral  cornu 
The  sacrum,  lateral  view. 


THE   COCCYX.  127 

slightly  raised  edges  and  a  rough,  irregular  surface.  The  auricular  surface  is  formed 
chiefly  by  the  lateral  mass  of  the  first  sacral  (vertebra  fulcralis ,  as  having  the  most 
to  do  in  supporting  the  pelvis),  to  a  less  extent  by  that  of  the  second,  and  very  little 
by  that  of  the  third.  Behind  this  articular  portion  lies  the  rough  ligamentous  sur- 
face, which  slants  backward  and  inward,  and  affords  origin  for  the  posterior  sacro- 
iliac  ligaments. 

Differences  depending  upon  Sex. — The  female  sacrum  is  relatively  broader 
than  the  male.  The  sacral  index,  or  the  ratio  of  the  breadth  to  the  length  ( I0°  *J^dth )  > 
is  1 12  for  the  white  male  and  116  for  the  female.  Such  a  rule  is,  however,  not  abso- 
lute, there  being  many  doubtful  cases,  but  a  narrow  sacrum  is  almost  invariably 
male.  Another,  and  very  reliable,  guide,  especially  in  conjunction  with  the  first,  is 
the  curve.  There  are  contradictory  statements  among  authors,  but  the  truth  is,  as 
originally  shown  by  Ward,  that  the  male  sacrum  is  the  more  regularly  curved,  while 
the  anterior  surface  of  the  female  bone  runs  in  nearly  a  straight  line  from  the  prom- 
ontory to  the  middle  of  the  third  piece  and  then  suddenly  changes  its  direction. 

Variations. — The  sacrum  often  consists  of  six  vertebrae.  Such  a  one  may 
be  recognized  even  when  the  lower  part  is  wanting,  so  that  the  vertebrae  cannot  be 
counted.  If  a  line  across  the  front,  connecting  the  lowest  points  of  the  auricular 
surfaces,  passes  below  the  middle  of  the  third  sacral,  the  sacrum  is  of  six  pieces  ;  if 
above,  of  five.1  Sacra  consisting  of  only  four  vertebrae  are  rare. 

THE   COCCYX. 

This  bone  is  composed  of  four  or  five2  flattened  plates  representing  vertebral 
bodies.  It  is  an  elongated  triangle  with  the  apex  below.  The  base,  joined  by  fibro- 
cartilage  to  the  apex  of  the  sacrum,  is  oblique,  the  posterior  border  being  higher 
than  the  front,  so  that  the  coccyx  slants  forward  from  the  sacrum.  The  anterior 
surface  of  the  coccyx  is,  moreover,  very  slightly  concave.  ^^  first  vertebra  consists 
of  a  thin.foWy,  about  twice  as  broad  as  long,  from  the  back  of  which  on  each  side  the 
rudiment  of  an  arch  extends  upward  as  a  straight  process,  the  coccygeal  cornu,  which 

FIG.  155. 

//&  (Sa— Cornu 

/  iB?r     '          —  ~\  a  f  ..•  i  Yl»»«k 

Surface  for  sacrum^ 

Transverse  P-ess 


Coccygeus  < 

•  Gluteus  maximus 
III 


V 

Posterior 


IV 

•Sphincter  ani 


The  coccyx. 


overlaps  the  back  of  the  body  of  the  last  sacral  vertebra  and  joins  the  sacral  cornu. 
A  short  lateral  projection  from  the  side  of  the  body  represents  the  transverse  process; 
perhaps  the  costal  element  also.  On  the  upper  border  of  this  process,  at  its  origin,  is 
a  notch,  which  usually  forms  a  foramen  with  the  sacrum  for  the  anterior  division  of 
the  fifth  sacral  nerve.  Very  faint  rudiments  of  these  two  pairs  of  processes  are 
sometimes  to  be  made  out  on  the  second  vertebra,  which  is  much  smaller  than  the 
first,  but  also  broad  and  flat.  The  succeeding  ones  are  much  smaller  and  ill-defined. 
Constrictions  on  the  surfaces  and  notches  on  the  edges  mark  the  outlines  of  the 

1  Bacarisse  :  Le  sacrum  suivant  le  sexe  et  suivant  les  races.     These,  Paris,  1873. 

2  According  to  Steinbach,  there  are  five  in  man  and  four  or  five  in  woman.     Die  Zahl  der 
Caudalwirbel  beim  Menschen.    Inaugural  Dissertation,  Berlin,  1899. 


128 


HUMAN   ANATOMY. 


original  pieces,  which  become  less  and  less  flat  and  more  and  more  rounded.  It  is 
rare  to  see  more  than  four  distinct  segments,  but  very  often  the  last  is  somewhat 
elongated  and  shows  signs  of  subdivision.  It  is  not  uncommon  for  the  first  piece 
to  remain  separate,  neither  fusing  with  the  sacrum  nor  the  next  coccygeal  plate. 

STRUCTURE   OF   THE   VERTEBRAE. 

The  shell  of  compact  bone  forming  the  surface  is  everywhere  very  thin.  The 
general  plan  of  the  internal  spongy  bone  is  one  of  vertical  plates  which  in  a  frontal 
section  (Fig.  156,  A)  are  bowed  somewhat  outward  from  the  middle  of  the  bone,  and 
of  transverse  plates  connecting  them  near  together  at  the  ends  and  farther  apart  in  the 

FIG.  156. 


Frontal  (A)  and  sagittal  (£)  sections  of  body  of  lumbar  vertebra,  showing  the  arrangement  of  the  bony  lamellae. 

Natural  size. 

middle  third  where  larger  spaces  occur.  The  strongest  plates  spring  from  the  pedi- 
cles and  diverge  through  the  bone,  joining,  probably,  for  the  most  part  the  hori- 
zontal system.  In  the  sacrum  the  same  general  plan  prevails,  but  in  addition  there 
are  series  of  plates,  mainly  horizontal,  in  the  lateral  parts  ;  those  from  the  first  sacral 
are  the  most  important. 

DEVELOPMENT  OF  THE  VERTEBRA. 

Presacral  Vertebrae. — These  vertebrae  ossify  from  three  chief  centres  and 
at  least  five  accessory  ones.  The  median  one  of  the  three  chief  centres  forms  the 
greater  part  of  the  body  ;  while  the  other  two,  one  appearing  in  each  pedicle,  form 
the  postero-lateral  part  of  the  body,  the  arch,  and  the  greater  part  of  the  processes. 
The  oblique  neuro-central  sutures  separate  the  regions  of  these  centres.  The  lat- 
eral centres  of  the  upper  thoracic  and  the  cervical  vertebrae  appear  first.  It  is 
usually  taught  that  they  appear  in  the  sixth  or  seventh  week  of  fcetal  life,  but  Bade l 
with  the  Rontgen  rays  found  no  sign  of  them  at  eight  weeks.  The  point  is  unset- 
tled. The  first  median  centres  to  appear  are  those  of  the  lower  thoracic  and  the 
upper  lumbar  vertebrae.  In  this  region  and  below  it  the  median  centres  precede  the 
lateral  ones  ;  in  the  upper  part  of  the  spine  the  growth  is  much  more  vigorous  in 
the  lateral  centres.  The  median  centres  of  the  cervical  vertebrae  appear  in  order 
from  below  upward.  The  upper  ones  (judging  from  Rontgen-ray  work  and  from 
transparent  foetuses)  sometimes  have  not  appeared  as  late  as  the  sixth  month, 
although  we  have  seen  them  towards  the  close  of  the  third. 

.  //  />/;///  the  upper  and  lower  ends  of  the  bodies  are  still  cartilaginous,  but  the 
arches  are  well  advanced  in  ossification,  although  bone  does  not  cross  the  median 
lint-  until  some  months  later.  The  transverse  processes  of  the  thoracic  vertebrae  are 
farther  advanced  than  those  in  other  regions.  The  spines  are  still  cartilaginous. 
The  neuro-central  suture  is  lost  at  from  four  to  six  years,  disappearing  first  in  the 

'Arch,  fiir  Mikros.  An;it.,  Bel.  lv,,  1899. 


DEVELOPMENT  OF  THE  VERTEBRAE. 


129 


lumbar  region.      The  tips  of  the  spinous  and  transverse  processes  develop  from  cen- 
tres which  appear  about  puberty  and  fuse  about  the  eighteenth  year.      A  thin  epi- 
physeal  disk,  covering  the  upper  and  lower  surfaces  of  each  body,  grows  from  a  centre 
seen  about  the  seventeenth  year,  and  joins  by  the  twentieth,  the  line  of  union  per- 
sisting a  year  or  two  longer.     The  mammillary  processes  of  the  lumbar  region  arise 
from  separate  centres  ;  so  do  also  the  costal  elements  of  the  sixth  and  seventh  cer- 
vicals,  and  sometimes  that  of  the  first  lumbar.     In  cases  in  which  this  costal  element 
of  the  seventh  cervical  remains  free  there  is  a  cervical  rib  and  no  transverse  fora- 
men ;  exceptionally  in  these  cases  a  foramen  persists.     According  to  Leboucq,1  the 
development  of  the  anterior  limb  of  the  transverse  process  of  the  cervical  vertebrae 
is  more  complicated  than  is  usually  taught.     There  is  a  slight  outward  projection 
from  the  ventral  side  of  the  body  rep- 
resenting the  prominence  for  the  head  FIG.  157. 
of  the  rib  to  rest  upon  ;  this  grows  out- 
ward and   meets   a  growth  from   the 
transverse  process  that  grows  inward 
like  a  hook.     This  inward  growth  rep- 
resents what  we   commonly   call    the 
costal  element  of  a  cervical  vertebra, 
but  there  may  be  also  a  separate  ossi- 
fication representing  an  actual  rib, — 
namely,  a  small  piece  of  bone  on  the 
ventral  aspect  of  the  tip  of  the  trans- 
verse process  of  the  seventh  cervical 
vertebra.      When  a  separate  ossifica- 
tion occurs  in  this  region  in  the  fifth 
or  sixth  vertebra,   it    is  situated    still 
more  externally  than  in  the  seventh, 
and  forms  the  floor  of  the  gutter  be- 
tween the  anterior  and  the  posterior 
tubercles,  which  is  the  true  costal  ele- 
ment.     It  is  probable  that  in  certain 
cases  of  cervical  ribs  accompanied  by 
a  transverse  foramen,  the  latter  is  en- 
closed by  the  hook-like  process  from 
the   transverse    process    meeting   the 
growth  from  the  body  of  the  vertebra, 
and    that    the    rib    coming   from    the 
separate  ossification  lies  anteriorly  to 
it  and  distinct  from  it.      At  birth  the 

i         I  ,  •       i  ii  Ossification  of  the  vertebrae.      A,  cervical  vertebra  at 

lumbar  articular  processes  resemble 
the  thoracic.  The  type  changes  in 
early  childhood. 

The  Sacrum. — Each  sacral  ver- 
tebra has  the  three  primary  centres  of 
the  others,  the  median  ones  appearing  before  the  lateral  of  the  same  vertebra.  Proba- 
bly the  median  centres  of  the  first  three  appear  first  and  then  the  lateral  ones  of  the 
first  vertebra  ;  data,  however,  are  wanting  for  a  definite  statement.  The  time  of  the 
first  appearance  of  ossification  in  the  sacral  vertebrae  is  very  variable  ;  probably  the 
earliest  median  centres  appear  about  the  beginning  of  the  fourth  month  and  the 
lateral  ones  some  weeks  later.  In  a  skiagraph  of  a  foetus  estimated  to  be  about 
three  and  a  half  months  old  the  median  centres  of  the  upper  three  vertebrae  and 
the  lateral  ones  of  the  first  are  visible.  This  is,  perhaps,  earlier  than  the  rule.  Little 
progress  in  ossification  of  the  last  two  sacrals  takes  place  before  birth.  The  lateral 
centres  join  the  median,  in  the  lower  vertebrae,  during  the  second  year  ;  in  the  upper 
ones,  three  or  four  years  later.  In  the  upper  three  vertebrae  a  centre  appears  out- 
side the  anterior  sacral  foramen,  from  which  a  part  of  the  lateral  mass  is  developed. 


Ossification  of  the  vertebras, 
birth  ;  centres  for  body  (a),  neural  arches  (6),  and  costal  ele- 
ment (c).  B,  dorsal  vertebra  at  two  years;  cartilaginous 
tips  of  transverse  (a)  and  spinous  (b)  processes;  rf,  centre 
for  body.  C,  lumbar  vertebra  at  two  years ;  position  of  ad- 
ditional later  centres  for  various  processes  indicated  (a,  f>,  c) ; 
d,  centre  for  body. 


1  Me'moires  couronne's,  etc.,  Acad.  Royale  des  Sciences  de  Belgique,  tome  lv.,  1896. 

9 


130 


HUMAN    ANATOMY. 


This  represents  a  costal  clement  which  fuses  with  the  front  of  the  pedicle.  Those  of 
the  first  two  sacrals  appear  shortly  before  birth  (Bade).  The  line  of  union  can  still 
be  seen  at  seven  years  on  the  top  of  the  first  vertebra.  The  time  at  which  the  laminae 


FIG.  158. 


C.   f 

(rib) 


F 


Costal  element 


Illustrating  homology  of  costal  element  (c.  <?.).   A,  sixth  cervical  vertebra;  /?,  seventh  cervical;  C,  fifth  thoracic; 
D,  second  lumbar;  £,  fifth  lumbar;  f,  sacrum  in  transverse  section. 

meet  in  the  middle  is  uncertain  ;  the  arch  of  the  first  vertebra  is  sometimes  complete 
at  seven,  those  below  it  being  still  open.  The  five  distinct  sacral  vertebrae  which  are 
thus  formed  remain  separate  for  some  time,  the  bodies  being  separated  by  interver- 


FIG.  159. 


FIG.  160. 


Superior  anil  anti-tinr  sm  fares  of  young  sacrum 
of  about  live  yi-ats. 


Sacium  anil  coccyx  •  >!'  about  seventeen  years 


tebral  disks.  A  thin  plate  appears  in  the  upper  and  lower  parts  of  these  disks  which 
fuses  with  the  bodies  before  the  latter  unite.  The  union  of  the  vertebrae  begins  below 
and  proceeds  upward  in  a  very  irregular  manner. 

Probably  union  generally  occurs  first  in  the  lateral  masses,  between  the  laminae 


VARIATIONS   OF   THE   VERTEBRA.  131 

sooner  than  between  the  bodies.  By  the  fifteenth  year  the  lower  three  vertebrae  are 
generally  fused,  the  second  joining  them  from  eighteen  to  nineteen.  The  five  pieces 
are  united  by  the  twentieth  year.  In  some  cases  several  of  the  sutures  are  still  to  be 
seen,  but  all  may  have  disappeared.  The  union  of  the  bodies,  as  shown  by  sections, 
in  the  case  of  the  upper  ones,  may  not  be  complete  internally  till  a  much  later  period. 
Two  thin  epiphyses  appear  on  each  side  of  the  sacrum  about  the  eighteenth  year, 
one  for  the  aiiricular  surface  and  the  other  below  it.  The  lines  of  union  of  these 
plates  may  be  visible  after  twenty-one. 

The  Coccyx. — Our  data  concerning  the  ossification  of  the  coccyx  are  very  un- 
satisfactory. Each  segment  has  one  centre,  but  the  first  may  have  two,  one  on  each 
side,  and,  according  to  some,  secondary  centres  for  the  cornua.  Ossification  begins 
in  the  first  piece  at  about  birth,  and  successively  in  the  others,  from  above  down- 
ward, until  puberty.  The  lower  three  or  four  pieces  fuse  within  two  or  three  years 
after  birth,  and  join  the  first  at  perhaps  about  twenty ;  there  is,  however,  great 
diversity,  and  frequently  the  first  unites  with  the  sacrum  instead  of  with  the  others. 

The   Atlas. — The  atlas  is  almost 

wholly  formed  from  two  centres  which  FIG-  161. 

appear  in  the  seventh  week  of  foetal  life 
in  the  root  of  the  posterior  arches ;  from 
these  points  ossification  spreads  most 
rapidly  backward.  In  the  course  of  the 
first  year  a  centre  is  found  in  the  middle 
of  the  anterior  arch.  The  lateral  masses 
meet  behind  in  the  fourth  year  and  join 
the  median  anterior  nucleus  in  the  fifth. 
Sometimes  the  union  of  the  posterior  __ 

arches  does  not  OCCUr.     The  anterior  nu-        Unique  case  of  absence  of  the  anterior  arch  of  the  atlas. 

cleus  may  be  absent,  and  the  front  arch 

may  show  a  median  suture  or  be  represented  by  ligament  or  cartilage.  In  one  in- 
stance the  anterior  arch  was  wholly  wanting,  the  lateral  masses  being  fastened  to  the 
odontoid  by  ligament1  (Fig.  161). 

The  Axis. — The  ossification  of  the  axis  begins  by  two  lateral  points  appearing 
by  the  eleventh  week.  The  median  one,  which  does  not  com'e  till  the  fifth  month, 
is  at  first  double,  but  the  two  points  speedily  fuse.  At  about  the  same  time  two 
nuclei  appear  side  by  side  in  the  odontoid  process,  which  join  together  before  birth, 
leaving  a  space  between  them  at  the  tip.  This  may  be  closed  by  the  extension  of 
ossification,  or  a  centre  may  appear  in  it  at  the  second  year,  which  fuses  by  the 
twelfth.  The  piece  thus  formed  has  been  held  to  represent  the  epiphyseal  plate  for 
the  top  of  the  atlas.  The  odontoid  process  joins  the  body  at  the  periphery,  the  union 
beginning  in  the  third  year  and  being  complete  a  year  or  two  later ;  a  piece  of  car- 
tilage in  the  middle  of  the  juncture  is  said  to  persist  under  the  odontoid  until  old 
age.  Very  rarely  the  odontoid  remains  distinct.  The  arches  join  the  body  in  the 
third  year,  and  usually  meet  behind  at  the  same  time ;  the  latter  union,  however, 
may  be  delayed. 

Variations  of  the  Vertebrae.  —The  commonest  and  most  interesting  variations  are  those 
of  number.  These  are  very  frequent  in  the  coccyx,  since  there  are  originally  more  elements  than 
persist,  and  indeed  we  are  not  sure  even  of  the  normal  number  in  this  bone.  Numerical  varia- 
tions are  also  often  observed  in  the  sacrum,  less  so  in  the  lumbar,  still  less  so  in  the  thoracic, 
and  extremely  rare  in  the  cervical  region.  The  number  of  vertebrae  above  the  sacrum  (twenty- 
four)  is  usually  unchanged,  but,  owing  to  differences  in  development  of  the  costal  element,  one 
region  is  not  rarely  increased  or  diminished  at  the  expense  of  the  next  one.  Thus  the  very  com- 
mon condition  of  six  lumbar  vertebra,'  is  due  to  the  want  of  development  of  the  costal  element 
(the  rib)  of  the  last  thoracic,  and  implies  only  eleven  vertebrae  in  that  region.  Conversely,  thir- 
teen thoracics  imply  an  undue  development  of  the  costal  element  of  the  first  lumbar,  and  con- 
sequently only  four  lumbar  vertebrae.  Often  the  costal  element  of  the  last  cervical  is  free  and 
over-developed,  making  a  cervical  rib.  But  even  if  this  be  large  enough  to  reach  the  aternum, 
which  is  exceedingly  rare,  the  number  of  cervical  vertebrae  is  usually  considered  unchanged. 
Other  changes  are  due  to  variations  in  development  of  the  costal  element  in  the  last  lumbar 
and  the  first  sacral.  Transitional  forms  are  here  very  frequently  met  with.  The  last  lumbar 

1  Dwight :  Journal  of  Anatomy  and  Physiology,  vol.  xxi.,  1887. 


132  HUMAN   ANATOMY. 

may,  by  an  excessive  growth  of  these  elements,  become  sacralized,  articulating  more  or  less  per- 
fectly with  tlie  ilium,  and,  conversely,  the  first  sacral  may  have  almost  freed  itself  from  those 
below  it.  Thus  we  may  find  a  partially  sarrali/ed  vertebra,  which  may  be  either  the  twenty-fifth 
or  the  twenty-fourth.  It  often  happens,  particularly  in  the  latter  case,  that  a  vertebra  appears  to 
be  a  first  sacral  on  superficial  examination,  which  is  found  to  have  little  or  nothing  to  do  in  form- 
ing the  articular  surface,  in  which  case  it  is  not  a  true  sacral,  for  the  first  sacral  is  the  fnlc rails 
which  has  the  largest  surface  for  the  joint  with  the  ilium.  A  false  promontory  may  coexist  with 
the  normal  one.  This  is  probably  most  frequent  when  the  twenty-fourth  vertebra  is  partly 
sacralized.  Any  of  the  preceding  peculiarities  may  be  unilateral,  so  that  sometimes  a  vertebra 
may  seem  from  one  side  to  belong  surely  to  one  region,  and  equally  surely  to  the  other  region 
when  seen  from  the  opposite  side. 

There  is,  however,  another  set  of  variations  in  which  the  number  of  presacral  vertebrae  is 
increased  or  diminished.  There  may  be,  for  instance,  one  thoracic  or  one  lumbar  vertebra  too 
many  or  too  few,  without  any  compensatory  change  in  the  next  region.  In  these  cases,  more- 
over, the  terminal  vertebrae  of  the  region  may  be  very  nearly  typical  ones,  and  sometimes  even 
the  size  of  the  vertebrae  will  be  modified  so  as  to  give  the  region  its  approximate  relative  length. 
Similar  changes  may  be  found  in  the  neck,  but  they  are  exceedingly  rare. 

Variations  of  either  kind  are  likely  to  have  an  effect  on  the  column  as  a  whole  ;  thus,  if 
there  be  a  large  cervical  rib  the  last  thoracic  rib  is  likely  to  be  small,  or  if  the  first  rib  is  rudi- 
mentary the  last  is  apt  to  be  large.  It  follows  that  the  thorax  seems  to  be  in  certain  cases 
moved  upward  or  downward  ;  this  change  may  occur  on  one  side  only. 

Rosenberg's  theory,  formerly  much  in  vogue,  is  that  there  are  opposite  tendencies  at  the 
two  ends  of  the  spine.  At  the  upper  there  is  a  tendency  for  the  cervical  region  to  encroach  on 
the  thoracic,  and  at  the  lower  for  each  of  the  regions  to  encroach  on  the  one  above  it.  Such 
changes  he  considers  progressive.  On  the  other  hand,  the  opposite  movement  by  which  the 
thorax  encroaches  on  the  neck  or  loins  is  considered  reversive.  Rosenberg  has  described  a 
spine  which  he  considers  archaic,  in  which  there  are  two  extra  presacral  vertebrae  and  fifteen 
pairs  of  ribs,  the  first  being  cervical.  There  are  two  spines  in  the  Warren  Museum  with  a  simi- 
lar number  of  presacrals  in  which  the  last  is  sacralized  on  one  side.  As  to  the  way  in  which 
anomalies  of  the  lower  part  of  the  spine  come  about,  Rosenberg1  thinks  he  has  shown  that  in 
the  course  of  development  the  sacrum  is  composed  of  vertebrae  placed  farther  back  than  the 
permanent  ones,  and  that  the  ilium  enters  into  connection  with  vertebrae  more  and  more  ante- 
rior. As  new  ones  join  it  above  former  ones  become  detached  from  it  below.  If  it  does  not 
make  the  usual  progress  the  spine  is  archaic,  having  too  many  presacrals  ;  if  it  goes  too  far  the 
spine  is  of  the  future.  Rosenberg's  theory  has  been  overthrown  by  Bardeen,*  who  has  shown 
that  the  original  position  of  the  ilium  is  opposite  the  superior  part  of  the  lumbar  region  and 
that  it  travels  tailwards.  Having  joined  a  vertebra  at  the  fifth  week,  it  never  leaves  it.  At  this 
early  time  the  thoracic  vertebrae  are  differentiated.  The  author3  and  Fischel*  believe  that 
numerical  variation  is  the  result  of  an  error  in  segmentation. 

A  want  of  development  of  the  bodies,  which  may  be  only  half  the  normal  height,  is  found 
almost  exclusively  in  the  lumbar  region.  We  have  seen  (apparently  congenital)  fusion  of  the 
lumbar  bodies  while  all  the  arches  were  present,  but  three  of  them  crowded  together.  The 
separation  of  the  pedicles  of  the  fifth  lumbar  from  the  body  is  a  very  rare  anomaly  among 
whites,  but  not  among  American  aborigines. 

ARTICULATIONS   OF   THE   VERTEBRAL    COLUMN. 
The  ligaments  connecting  the  segments  of  the  spine  may  be  divided,  according 
to  the  parts  of  the  vertebrae  which  they  vinite,  into  two  groups  : 

1.  Those  connecting  the  Bodies  of  the  Vertebrae  ; 

2.  Those  connecting  the  Laminae  and  the  Processes. 

LIGAMENTS  CONNECTING  THE  BODIES. 
Intervertebral  Disks5  (Figs.  162,  163). — These  form  a  series  of  fibro-carti- 
lages  interposed  between  the  bodies  of  the  vertebrae,  forming  about  one-fourth  of  the 
movable  part  of  the  spine  and  adding  greatly  to  its  strength.  They  are  developed, 
like  the  bodies,  around  the  notochord,  persisting  parts  of  this  structure  forming  a 
central  core  to  each  disk.  The  outer  part  of  the  disks  consists  of  oblique  layers  of 
fibres,  slanting  alternately  in  opposite  directions,  some  almost  horizontal,  which  hold 
the  vertebral  bodies  firmly  together  ;  the  centre  of  the  disks  is  occupied  by  a  spare 
containing  iluid  in  the  meshes  of  a  yellowish  pulp.6  This  central  core  is  strongly 
compressed,  so  as  practically  to  be  a  resistant  ball  within  the  more  yielding  fibro- 
cartilaginous  socket.  The  proportion  of  the  disks  to  the  vertebral  bodies  varies  in 
the  different  parts  of  the  spine.  They  are  absolutely  largest  in  the  lumbar  region, 
but  relatively  in  the  cervical.  For  many  reasons  it  is  difficult  to  reckon  the  per- 

1  Morph.  Jahrbuch,  Bd.  i.  and  xxvii.  4  Anatomische  Hefte,  No.  95,  1906. 

*Anat.  Anzeiger,  Bd.  xxv.,  1904,  and  American  Journal  of  Anatomy,  vol.  iv.,  1905. 

'Ihvi-lit  :   Memoirs  Boston  Society  of  Nat.  Hist.,  vol.  v.,  1901. 

1  l  MM..,  .11  iM.iiiiiu^  Intervertcbralcs.     '''Nucleus  pulposus. 


LIGAMENTS    OF   THE   SPINE. 


133 


Posterior  at- 
lanto-axial 
ligament 


centage  very  accurately,  and  there  is  much  variation.  The  following  proportions 
are,  therefore,  only  approximate.  The  disks  form  in  the  cervical  region  forty  per 
cent. ,  in  the  thoracic,  twenty  per  cent. ,  and  in  the  lumbar,  thirty-three  per  cent,  of 
the  length  of  the  spine. 

Anterior  and  Posterior  FIG.  162. 

Common  Ligaments. The       Odontoid  process  of  axis      Transverse  ligament 

bodies  are  connected  by  short 
fibres  surrounding  the  disks, 
and  by  long  bands  which  are 
only  partially  separable  from 
the  general  envelope.  The  an- 
terior common  ligament1  (Figs. 
163,  165)  begins  at  the  axis 
and  extends  to  the  sacrum.  It 
consists  of  shorter  and  longer 
fibres  blending  with  the  peri- 
osteum and  springing  from  the 
edges  of  the  vertebrae  and  from 
the  disks,  to  end  at  similar 
points  on  the  next  vertebra,  or 
on  the  second,  third,  fourth,  or 
fifth.  The  borders  are  not 
sharply  defined.  The  posterior 
common  ligament'  (  Fig.  164) 
is  a  much  more  distinct  struc- 
ture. It  arises  from  the  back 
of  the  body  of  the  axis,  re- 
ceiving fibres  from  the  occipito- 
axial  ligament,  and  runs  to  the 
sacrum.  It  also  is  attached 
to  the  disks  and  the  edges  of 
the  bodies,  but  possesses  a  dis- 
tinct margin,  which,  except  in 
the  neck,  expands  laterally 
into  a  series  of  points  at  the 
intervertebral  disks.  It  stands 
well  out  from  the  middle  of 
the  bodies,  bridging  over  the 
veins  of  the  larger  ones. 


Interspinous 
ligament 

Seventh  cervi- 
cal spine 


Intervertebral 
foramen 


Lamina 


Ligamentum 
subflavum 


•Supraspinous 
ligament 


LIGAMENTS  CONNECT- 
ING THE  LAMINAE  AND 
THE  PROCESSES. 

The  articular  processes 

(Fig.  165)  are  coated  with 
hyaline  articular  cartilage  and 
surrounded  by  loose  capsules, 
with  which,  especially  in  the 
thorax,  the  ligamenta  subflava 
are  inseparably  connected,  pre- 
venting by  their  tension  the 
occurrence  of  folds. 

The  ligamenta  subflava3  (  Fig.  163)  are  elastic  membranes  of  considerable 
strength  connecting  the  laminae  from  the  axis  to  the  sacrum.  They  are  particularly 
developed  in  the  lumbar  region.  As  just  mentioned,  they  encroach  on  the  side  of 
the  capsules  towards  the  canal.  They  also  extend  a  short  distance  under  the  spinous 
processes. 

The  supraspinous  ligament  (Figs.  162,  163)  extends  as  a  well-marked  cord 

1  Lig.  longitudinalc  iinterius.      -  Liu    Inngitudinalc  postcrius.     '' Ligg    flava. 


Tenth  tho-- 
racic  ver- 
tebra 


Median  section  of  upper  half  of  spine. 


134 


HUMAN   ANATOMY. 


along  the  tips  of  the  spines  from  the  last  cervical  to  the  sacrum.  The  interspinous 
ligaments  are  membranes  connecting  the  spinous  processes  between  the  tips  and 
the  laminae,  extending  from  the  ligamenta  subflava  to  the  supraspinous  ligament. 


FIG.  163. 


Tenth  thoracic  vertebra 


Ligamentum  su.bflavum 


Intervertebral  foramen 


First  lumbar  vertebra 


Posterior  common  ligament 


Intervertebral  disk 


Anterior  common  ligament 


Fifth  lumbar  vertebra 


First  sacral  vertebra  - 


Supraspinous  ligament 


Fifth  lumbar  spine 


Median  section  of  lower  half  of  spim-. 


The  ligamentum  nuchae  (Fig.   166)  represents  in  the  neck  a  modification  of 
the  two  last-mentioned  ligaments.      It  is  a  vertical  curtain  reaching  from  the  exter- 


LIGAMENTS   OF    THE   SPINE. 


135 


FIG. 


nal  occipital  protuberance  to  the  spine  of  the 
muscles  of  the  two  sides.  The  free  border  is 
continuous  with  the  supraspinous  ligament,  but, 
instead  of  touching  the  cervical  spines,  it  lies 
in  the  superficial  layer  of  muscles,  and  is  rein- 
forced below  by  radiating  fibres  from  each,  of  the 
spinous  processes  of  the  cervical  region.  It  is 
inseparably  blended  with  the  origin  of  the  trapezii 
and  with  the  fasciae  between  the  muscular  layers, 
especially  with  that  covering  the  semispinalis  and 
the  short  suboccipital  muscles.  In  the  region  of 
the  axis  it  is  a  thick  median  membrane  ;  in  the 
lower  cervical  region  it  is  of  little  importance. 
In  man  it  contains  but  a  small  proportion'of  elas- 
tic fibres,  in  marked  contrast  to  what  is  found 
in  many  quadrupeds  in  which  the  structure  con- 
sists principally  of  elastic  tissue,  since  in  these 
animals  the  ligamentum  nuchae  forms  an  important 
organ  for  the  support  of  the  head  at  the  end  of 
the  horizontal  vertebral  axis. 

The    intertransverse    ligaments    (Fig. 
162)  are  trifling  collections  of  fibres  between  the 
transverse  processes,   although  occasionally  distinct  round  cords 
region. 

FIG.  165. 

Anterior  occipito-atlantal  ligament 


Mastoid  process 


Lateral  occipito-atlantal 
ligament 


Anterior  tubercle  of  atlas 


seventh   cervical,   separating  the 


Posterior 
common 
ligament 


Posterior  surface  of  bodies  of  vertebrae 
shown  after  removal  of  arches  by  cutting 
through  the  pedicles. 


in  the  thoracic 


Atlanto-axial  ligament  and  joint 


Anterior  common  ligament 


Anterior  ligaments  of  upper  end  of  spine. 


ARTICULATIONS    OF    THE    OCCIPITAL    BONE,    THE    ATLAS,    AND 

THE    AXIS. 

The  arrangement  here  differs  in  some  points  considerably  from  that  of  the  rest 
of  the  spine  in  order  to  provide  for  the  security  and  the  free  movement  of  the  head. 
The  ligaments  effecting  this  union  consist  of  three  groups  : 
i.   Those  connecting  the  Atlas  and  the  Axis,  including  the. 

Anterior  Atlanto- Axial  ;  Transverse  ; 

Posterior  Atlanto-Axial  ;  Two  Capsular. 


1 36 


HUMAN   ANATOMY. 


2.  Those  connecting  the  Occipital  Bone  and  the  Atlas,  including  the 

Anterior  Occipito-Atlantal  ;  Posterior  Occipito-Atlantal  ; 

Accessory  Occipito-Atlantal  ;  Two  Capsular. 

3.  Those  connecting  the  Occipital  Bone  and  the  Axis,  including  the 

Lateral  Odontoid  or  Check  ;  Middle  Odontoid  ; 

Occipito- Axial. 

The  important  peculiarities  are  the  odontoid  and  the  transverse  ligaments. 

The  odontoid,  or  check  ligaments1  (  Fig.  168),  are  two  strong,  symmetrical 

bundles  of  fibres  extending  from  the  slanting  surface  on  each  side  of  the  top  of  the 

odontoid  process  outward  and  a  little  upward  to  a  roughness  on  the  inner  side  of 

each  occipital  condyle.      Some  fibres  pass  directly  across  from  one  condyle  to  the 

FIG.  166. 


Ligamentutn  nuchse 


Trapezius  muscle 


Ligamentum  nuchae 


Posterior  occipitoatlantal 
ligament 


Posterior  atlanto-axial 
ligament 


Ligaments  of  back  of  neck. 

other.  These  are  occasionally  collected  into  a  distinct  round,  glistening  bundle. 
The  space  above  the  odontoid  process,  between  it  and  the  basilar  process,  is  oc- 
cupied by  a  mass  of  dense  fibrous  tissue  reaching  to  the  anterior  occipito-atloid 
ligament,  in  the  midst  of  which  is  a  more  or  less  distinct  median  band  connecting 
these  parts,  the  middle  odontoid  ligament.2  A  supra-odontoid  bursa  may  be 
developed  in  this  tissue. 

The  transverse  ligament4  (Figs.  167,  168)  of  the  atlas  is  a  strong  band 
passing  between  the  tubercles  on  the  inner  side  of  each  lateral  mass  of  the  atlas.  It 
does  not  run  straight,  but  curves  backward  around  the  odontoid,  from  which  it  is 
separated  by  a  bursa.  A  band  from  the  middle  of  the  transverse  ligament  ; 
upward  to  the  cerebral  side  of  the  basilar  process,  and  another  downward  to  the 
body  of  the  axis,  so*  that  the  whole  structure  is  called  the  cruciform  ligament. ' 
sTrolard:  Journ.  tie  1'Anat.  et  tk-  la  Physio!.,  1897. 

1  I.iKK.   aliiii.i.         I. in.  .i|>i<  is  di'iittv      4  l.ijj.    I  rarisvcrsum    iitliintis.       '  l.ij    triu  iiituni  .itl.mtis. 


OCCIPITO-SPINAL    LIGAMENTS. 


137 


Another  bursa  lies  between  the  odontoid  and  the  anterior  arch  of  the  atlas.  The 
transverse  ligament  and  the  two  check  ligaments  are  in  series  with  the  interarticular 
ligaments  of  the  heads  of  the  ribs. 

The  other  ligaments  of  this  region  are  in  the  main  simple  membranes  connect- 

FIG.  167. 


Upper  end  of  occipito-axial  ligament 


Lateral  odontoid  ligament 

Occipito-atlantal  joint 

Cruciform  ligameht 

Atlas 
Atlanto-axial  joint 

Axis 

; — Occipito-axial  ligament,  fused  with  dura, 

turned  down 
Dura 
Back  of  occiput  and  arches  removed ;  occipito-axial  ligament  cut  and  turned  down. 

ing  neighboring  parts.  The  anterior  occipito-atlantal  ligament l  (  Fig.  165  ) 
extends  between  the  front  of  the  foramen  magnum  and  the  anterior,  arch  of  the 
atlas  ;  the  anterior  atlanto-axial  (Fig.  165)  is  in  serial  continuation  with  it.  A 
distinct  rounded,  raised  band,  the  accessory  occipito-atlantal,  passes  in  the 
median  line  from  the  under  side  of  the 
occiput  to  the  front  tubercle  of  the  atlas 
(Fig.  165),  and  thence  to  the  body  of  the 
axis,  where  it  joins  the  anterior  common 
ligament  of  the  spine. 

The  occipito-axial  ligament 2  {appa- 
ratus ligamentosus)  (Fig.  167)  descends  in- 
side the  spinal  canal  from  the  basilar  process 
to  the  body  of  the  axis,  where  it  joins  the 
posterior  common  ligament  and  completely 
conceals  the  odontoid  process  and  its  special 
ligaments. 

The  posterior  occipito-atlantal3  and 
the  posterior  atlanto-axial  ligaments4 
lie  in  the  region  of  the  arches  (Fig.  166).  The 

former  extends  between  the  posterior  border     removaieof0mfddieCof0transve?se  fig 
of  the  foramen  magnum  and  the  arch  of  the     Pr°cess  is  thrown  strongly  upward, 
atlas  ;    the  latter   between   the  arch   of    the 

atlas  and  that  of  the  axis.  These  are  in  series  with  the  ligamenta  subflava,  but  differ 
from  them  in  being  non-elastic.  In  the  former  of  these  membranes  there  is  an 
opening  just  behind  the  facets  on  the  atlas  for  the  condyles,  bridged  over  by  a  band, 
for  the  entrance  of  the  vertebral  artery. 


FIG.  168. 


Front  of 
foramen 
magnum 


Lateral  odontoid 
ligament 


Bursa  on  back  of 
odontoid 


=-  Atlas 


Transverse   liga- 
ment, cut 

Articular  facet  of 
axis 


1  Mcmbrana    atlantooccipitalis  anterior.     "  Mcmbrana    tcctoria.     ;i  Mcmbrana  atlantooccipitalis  posterior.     4  Membrana 
atlantoepistrophk-a. 


133 


HUMAN    ANATOMY. 


Synovial  joints,  the  shapes  of  which  are  described  with  the  bones,  exist  be- 
tween the  occipital  bone  and  the  atlas  and  between  the  atlas  and  the  axis.  The 
capsule  of  the  upper  joint  is  very  thick,  especially  behind,  where  it  is  continuous 
with  the  posterior  occipito-atloid  ligament.  The  capsule  surrounding  the  articular 
surfaces  of  the  atlas  and  axis  is  strengthened  posteriorly  by  a  bundle  running  upward 
and  outward  from  the  axis. 

FIG.  169. 


rior  tubercle  of  atlas 


cord 


Posterior  bursa 


Trartsverse  process  of 
atlas 


tebral  artery  cut  obliquely 


Apparatus  ligamentosus 


Vertebral  artery  cut  in 
transverse  foramen 


r  bursa  Transverse  ligament 


Anterior  tubercle  of  atlas 
Transverse  section  of  spine  passing  through  atlas  and  odontoid  process. 

THE  SPINE  AS  A  WHOLE. 

Anterior  Aspect  (Fig.  170). — The  bodies  enlarge,  in  the  main,  regularly 
from  above  downward.  This  progression  is  interrupted  only  by  a  slight  decrease 
from  the  first  to  the  fourth  thoracic.  .  In  the  cervical  region  the  origin  of  the  costal 
elements  from  the  sides  of  the  bodies  gives  the  latter  a  false  appearance  of  breadth. 
The  middle  of  the  thoracic  region  is  particularly  prominent  in  front,  owing  in  part 
to  the  aortic  depression  on  the  left.  A  slight  curve  to  the  right  in  this  region  is 
generally  seen  ;  it  is  probably  attributable  to  this  cause. 

Posterior  Aspect  (Fig.  170). — A  deep  gutter  extends  on  each  side  of  the 
spinous  processes,  bounded  externally  in  the  neck  and  loins  by  the  articular  pro- 
cesses and  in  the  back  by  the  transverse.  In  the  latter  region  the  spines  which  are 
subcutaneous  are  often  deflected  from  the  median  line,  and  may  be  arranged  in  zig- 
zag. The  laminae  completely  close  the  spinal  canal  in  the  convex  thoracic  and 
sacral  regions,  while  it  is  left  open  in  the  neck  and  loins,  except  during  extension  of 
the  former. 

Lateral  Aspect  (Fig.  171). — The  profile  view  shows  best  of  all  the  increase  in 
the  importance  of  the  bodies  from  above  downward,  and  coincidently  with  this  the 
gradual  moving  backward  of  the  intervertebral  foramina.  These  increase  greatly  in 
size  from  the  lower  part  of  the  thoracic  region. 

The  Curves. — The  curve  of  the  spine  is  necessarily  an  arbitrary  one,  since  it 
varies  not  only  in  individuals  and  according  to  age,  sex,  and  occupation,  but  also 
with  position  and  the  time  of  day,  being  longer  when  lying  than  standing,  and  after 
a  night's  rest  than  after  a  day's  work.  The  difference  occasioned  by  position  occurs 
especially  in  youth,  when  it  may  amount  to  half  an  inch  or  more.  It  is  of  little 
consequence  after  middle  age.  Bearing  these  variations  in  mind,  the  following  guide 
to  the  curve,  suggested  by  Humphry,  may  be  accepted  :  a  line  dropped  from  the 
middle  of  the  odontoid  process  passes  through  the  middle  of  the  body  of  the  second 
thoracic,  that  of  the  twelfth  thoracic,  and  the  anterior  inferior  angle  of  the  fifth 
lumbar.  Henle  divides  the  spine  into  four  quarters  ;  and  although  this  method  has 
the  defect  of  using  the  unreliable  pelvic  section,  it  very  often  proves  remarkably 
correct.  Thus,  if  we  continue  Humphry's  line  to  the  level  of  the  tip  of  the  coccyx, 
the  middle  point  is  opposite  the  eleventh  thoracic,  the  end  of  the  first  quarter  oppo- 
site the  lower  border  of  the  third  thoracic,  and  that  of  the  third  quarter  opposite 
the  lower  edge  of  the  fourth  lumbar. 

The  development  of  the  curves  can  hardly  be  said  to  have  begun  at  birth.     At 


THE   SPINE   AS   A   WHOLE. 


Anterior 


FIG.   170. 


I.  Cervical 


Posterior 


139 


I.  Thoracic 


I.  Lumbar 


Sacrum 


r'<       -  -2 

o 


Coccyx 

Anterior  and  posterior  views  of  adult  spine. 


140 


HUMAN    ANATOMY. 


FIG.  171. 


-I.  Thoracic 


-I.  Lumbar 


Sacral 


I.  Coccygeal 


I.:iU  i.il  view  of  adult  spine. 


that  age  the  infant's  spine  presents  in  front 
one  general  concavity,  slightly  interrupted 
by  the  promontory  of  the  sacrum.  The  liga- 
mentous  spine,  containing  little  bone,  is  ex- 
ceedingly flexible  in  any  direction  :  the  atlas 
can  be  made  to  touch  the  sacrum.  It  is 
more  accurate  to  say  that  the  general  axis  of 
the  spine  is  a  curved  one  than  that  any  per- 
manent or  fixed  curve  exists.  The  cervical 
curve  appears  as  the  infant  grows  strong 
enough  to  hold  up  its  head  ;  it  is  never, 
properly  speaking,  consolidated  (Syming- 
ton), since  it  is  always  obliterated  by  a 
change  in  the  position  of  the  head.  The 
lumbar  curve  appears  at  from  one  to  two 
years  when  the  child  begins  to  walk.  The 
mechanism  of  its  production  is  explained  as 
follows.  When  an  infant  lies  on  its  back  the 
thighs  are  flexed  and  fall  apart.  If  these  be 
held  together  and  pressed  forcibly  down,  the 
lumbar  region  will  spring  upward,  owing  to 
the  shortness  of  the  ilio-femoral  ligaments, 
which  bend  the  pelvis  and,  indirectly,  the 
spine.  The  psoas  muscles,  moreover,  act 
directly  on  the  spine.  When  the  child  first 
stands,  the  body  is  inclined  forward  ;  when 
the  muscles  of  the  back  straighten  it,  the 
lumbar  curve  is  produced  by  the  same  mech- 
anism, since  it  is  immaterial  whether  the  legs 
are  extended  on  the  trunk  or  the  trunk  on 
the  legs.  How  or  when  these  curves  be- 
come consolidated  is  very  difficult  to  deter- 
mine. The  influence  of  differences  in  thick- 
ness of  the  front  and  back  of  the  various 
bodies  and  disks  is  inappreciable  in  the  neck  ; 
in  the  lower  part  of  the  back  and  in  the  first, 
and  perhaps  the  second,  lumbar  vertebrae  the 
height  is  greater  behind.  In  the  loins  the 
third  vertebra  is  much  thicker  in  front  and, 
likewise,  the  fourth  and  fifth  in  a  less  degree. 
The  intervertebral  disks  are  also  much  thicker 
in  front.  How  soon  actual  difference  in 
the  diameters  of  the  vertebrae  appears  is  un- 
certain. A  child  of  about  three  shows  little 
of  it,  except  in  the  last  lumbar,  and,  accord- 
ing to  Symington's  plates,  there  is  not  much 
more  difference  at  five  or  even  thirteen  years. 
It  is  certain  that  throughout  the  period  of 
growth  the  curves  can  be  nearly  or  quite 
effaced.  The  restraining  influences  are  the 
gradually  developing  differences  in  the  verte- 
brae and  the  disks,  the  effect  of  the.  sternum 
and  the  ribs  on  the  thoracic  region,  the  pull 
of  the  elastic  ligaments  of  the  arches,  and 
perhaps,  above  all,  muscular  tonieity.  In 
the  latter  part  of  middle  age  the  curves  of 
the  back  and  loins  become  consolidated; 
this  is,  however,  distinctly  a  degenerative 
process. 


LENGTH    OF    PRESACRAL   REGIONS. 


141 


Dimensions  and  Proportions. — The  length  and  the  proportions  of  the  dif- 
ferent presacral  regions  (including  the  intervertebral  disks),  measured  along  the  an- 
terior surface  of  the  spine,  have,  in  fifty  males  and  twenty-three  female  bodies,  been 
found  by  us  as  stated  below.  We  give  for  comparison  Ravenel' s1  and  Aeby's2  propor- 
tions combined.  The  former  measured  eleven  and  the  latter  eight  spines  of  each  sex. 
Cunningham's3  proportions,  from  six  male  and  five  female  spines,  are  also  added. 
In  the  proportions,  one  hundred  represents  the  total  presacral  length  along  the  curves. 

ACTUAL  LENGTH   OF   PRESACRAL  REGIONS   OF  SPINE. 


Male. 

Centimetres.  (Inches.) 

Neck 13.3  (  5.25) 

Back 28.7  (11-31) 

Loins 19.9  (  7.82) 

61.9  (24.38) 


Female. 
Centimetres.  (Inches.) 

I2.I  (    4-75) 

26.5  (10.44) 


57-3 


_ 
(22.57) 


PROPORTIONS   OF   PRESACRAL   REGIONS   OF  SPINE. 


Neck 
Back 
Loins 


(Dwight.) 

Male. 
(R.  &  A.) 

(Cunningham.) 

21-5 
46.3 

21.7 
46.7 

21.8 

46.5 

32.2 

31-4 

31-7 

IOO.O 

99-8 

IOO.O 

Female. 
(Dwight.)         (R.  &  A.)   (Cunningham.) 

21.2  21.7  21.6 

46.1  46.5  45.8 

32.7  _32.4  32.8 

IOO.O  IOO.6  IOO.2 


Thus,  while  it  is  true  that  the  lumbar  region  is  relatively  longer  in  woman,  the 
difference  is  trifling. 

ABSOLUTE    AND     RELATIVE     LENGTH    OF     PRESACRAL    REGIONS     DURING 

GROWTH. 


AGE. 

OBSERVER. 

ABSOLUTE  LENGTH. 
(In  Millimetres.) 

RELATIVE  LENGTH. 
(Total  =  loo.) 

Neck. 

Back. 

Loins. 

Total. 

Neck. 

Back. 

Loins. 

At  birth                      

Ravenel. 
Ravenel. 
Ravenel. 
Chipault.4 
Chipault. 
Ravenel. 
Aeby. 
Aeby. 
Dwight. 
Chipault. 
Chipault. 
Chipault. 
Chipault. 
Chipault. 
Ravenel.  • 
Aeby. 
Dwight. 
Aeby. 
Chipault. 
Symington.5 
Ravenel. 
Symington. 
Ravenel. 
Aeby. 
Symington. 
Dwight. 
Aeby. 
Aeby. 
Dwight. 

50 
40 
40 
40 
42 
50 
52.5 
53-5 
61 
60 
69 

67 
62 
68 
70 

79-5 
78 

79-9 
81 
80 
80 
80 
85 
9i 
95 
1  20 

IOO 

107.5 
113 

93 
IOO 

95 
80 
80 

IOO 

103 

107 

125 

121 
129 

08 
130 
132 
140 

153-5 
162 
162 

174 
170 
1  80 
175 
195 
218.7 

220 
265 

221.8 

229.5 
250 

50 
50 
50 
45 
44 
58 
60 
61 
77 
72 
83 
79 
69 

79 
9° 
98 

101 

103.3 

102.8 

104 

135 

106 
150 
153-5 
136 
183 
151 
152-5 
161 

193 
190 

185 
I65 
1  66 
208 

215-5 
221.5 
263 

253 
281 
264 
261 
279 
300 
331 
34i 
345-2 
357-8 
354 
395 
36i 
430 
463.2 

45i 
568 
472.8 
489-5 
524 

25-9 
21 
21.6 
24.2 
25-3 
24 
24-3 
24.1 
23.2 
23-7 
24-5 
25-2 

23-7 
24-3 
23-3 
24 
22-9 
23.1 
22.6 
22.5 
20.3 
22.2 
19.8 
19.7 

21-5 
21.  1 
21.  1 
21-9 
21-5 

48.2 
52.6 
51-3 

48.4 
48.1 
48.1 

47-5 
48.6 

47-5 
47-8 

45-9 
44-8 
49-7 
47-4 
46.7 
46.4 

47-5 
46.9 
48.9 
48 
45-6 
48-5 
45-4 
47.2 
48.7 
46.6 
46.9 
46.9 
47-7 

25-9 
26.3 

27 
27.4 
26.6 

27-9 
27.8 

27-5 
29.2 
28.5 
29.6 
30 
26.6 
28.3 
30 
29.6 
29.6 

29-9 
28.5 
29.4 

34-2 
29-3 
34-9 
33-i 
29.1 

32-2 
3i-9 
3i-i 

30-7 

.At  birth   ...       
At  birth  

One  month 

One  month     

Three  months            

Six  months     .            . 

Six  months            ... 

Ten  months    •        

One  year  boy 

One  year  boy    

One  year  and  one  month,  boy  . 
One  and  a  half  years,  girl  .    .    . 
One  and  a  half  years,  boy     .    . 
Two  years   boy    

Three  years    girl             .... 

Four  and  a  half  years,  boy    .    . 
Five  years   boy     .    .               .    . 

Five  years  boy    

Six  years   boy               

Nine  years   girl 

Eleven  years,  boy    
Thirteen  years,  girl     
Fifteen  years  boy    

Sixteen  years  girl    

Sixteen  years    girl       

Seventeen  years  girl  

1  Zeitschrift  fiir  Anat.  und  Entwicklng.,  1876. 
3  Cunningham  :  Memoirs,  1886. 
6  The  Anatomy  of  the  Child. 


2  Arch,  fiir  Anat.  und  Entwicklng.,  1879. 
4  Revue  d' Orthopedic,  1895. 


1 42  HUMAN   ANATOMY. 

It  appears  from  the  above  that  in  the  adult  the  neck  is  a  little  more  than  one- 
fifth  of  the  movable  part  of  the  spine  and  the  loins  a  little  less  than  one-third.  In 
the  young  embryo  these  proportions  are  reversed,  biit  by  the  time  of  birth  these  two 
parts  are  nearly  equal. 

Movements  of  the  Head. — Those  between  the  occiput  and  atlas  are  almost 
wholly  limited  to  flexion  and  extension,  of  which  the  latter  is  much  the  greater. 
This  is  in  part  due  to  the  reception  of  the  posterior  pointed  extremities  of  the  articu- 
lar processes  of  the  atlas  into  the  inner  parts  of  the  posterior  condyloid  fossae.  The 
anterior  occipito-atlantal  ligament  and  the  odontoid  ligaments  are  tense  in  extreme 
extension.  In  flexion  the  tip  of  the  odontoid  is  very  close  to,  if  it  does  not  touch, 
the  basilar  process.  The  range  of  both  these  motions  is  much  increased  by  the 
participation  of  the  cervical  region.  There  may  be  a  little  lateral  motion  between 
the  atlas  and  head,  and  there  is  some  slight  rotation.  The  great  variation  of  the 
shape  of  the  articular  facets  makes  it  clear  that  both  the  nature  and  extent  of  the 
motions  must  vary  considerably. 

The  joint  between  the  atlas  and  axis  is  devoted  almost  wholly  to  rotation.  The 
transverse  ligament  keeps  the  odontoid  in  place,  and  the  very  strong  odontoid  liga- 
ments check  rotation  alternately.  The  head  is  highest  when  directed  straight  forward, 
but  the  joints  are  in  more  perfect  adaptation  if  one  condyle  be  a  little  anterior  to  the 
other,  and  if  the  atlas  be  slightly  rotated  on  the  axis.  This  position,  though  entail- 
ing a  slight  loss  of  height,  is  the  one  naturally  chosen,  as  that  of  greatest  stability. 

Movements  of  the  Spine. — The  very  extensive  range  of  motion  of  the 
whole  spine  is  the  sum  of  many  small  movements  occurring  at  the  intervertebral 
disks.  The  whole  column  is  a  flexible  rod,  but  this  conception  is  modified  by  the 
following  peculiarities  :  ( i )  the  motion  is  not  equally  distributed,  owing  to  the  vary- 
ing distances  between  the  disks  and  the  differences  of  thickness  of  the  disks  them- 
selves ;  (2)  the  bodies,  which  form  the  essential  part  of  the  rod,  are  not  circular,  so 
that  motion  is  easier  in  one  direction  than  in  another  ;  (3)  the  rod  is  not  straight 
but  curved  ;  (4)  the  kind  of  motion  is  influenced  by  the  articular  processes,  and 
varies  in  the  different  regions.  Other  modifying  circumstances  exist,  but  these  suf- 
fice to  show  that,  while  certain  general  principles  may  be  laid  down,  an  accurate 
analysis  of  the  spinal  movements  is  absolutely  impossible. 

The  incompressible  semifluid  centre  of  each  disk  has  been  compared  to  a  ball 
on  which  the  rest  of  the.  disk  plays.  This  would,  therefore,  be  a  universal  joint 
were  there  no  restraining  apparatus.  The  motions  are  flexion  and  extension, — 
i.e.,  angular  movements  on  a  transverse  axis  ;  lateral  motion, — i.e. ,  the  same  on 
an  antero-posterior  axis,  and  rotation  on  a  vertical  axis.  It  is  unlikely  that  any 
single  one  of  these  motions  ever  occurs  without  some  mingling  of  another.  Flexion 
and  extension  are  greatest  in  the  neck  and  loins.  Extension  is  more  free  than 
flexion  in  the  neck,  where  it  is  limited  by  the  locking  of  the  laminae,  which,  when 
the  head  is  thrown  as  far  back  as  possible,  gives  great  rigidity  to  the  neck.  In  the 
loins  and  in  the  region  of  the  last  two  thoracic  vertebrae  flexion  is  the  more  exten- 
sive. Before  the  spine  is  consolidated,  slight  flexion  is  possible  throughout  the  back, 
but  extension  is  very  quickly  checked  by  the  locking  of  the  laminae  and  spines. 
Lateral  motion  is  greatest  in  the  neck,  but  it  is  considerable  also  in  the  back  and 
loins.  Such  motion  is  always  associated  with  rotation,  which  is  most  free  in  the 
neck,  considerable  in  the  back,  and  very  slight,  at  most,  in  the  loins.  It  is  to  be 
remembered  that  motions  both  in  the  antero-posterior  and  in  the  transverse  plane 
are  checked  by  the  tension  of  the  ligaments  on  the  side  of  the  body  of  the  vertebra 
opposite  to  the  direction  of  the  motion,  and  also  by  the  resistance  to  compression 
of  that  side  of  the  intervertebral  disk  towards  which  the  motion  occurs.  The  liga- 
menta  subflava,  being  elastic,  tend  continually  to  bring  the  bones  back  into  position 
from  the  innumerable  slight  displacements  to  which  they  are  subject.  That  this 
replacement  is  effected  by  a  purely  physical  p'roperty  of  the  tissue  instead  of  by 
muscular  action  implies  a  great  saving  of  energy.  The  amount  of  all  motions,  and 
of  rotation  in  particular,  decreases  throughout  life  and  varies  much  in  individuals. 
According  to  Keen,  the  rotary  motion  between  the  atlas  and  the  axis  amounts  to 
twenty-five  degrees,  that  in  the  rest  of  the  neck  to  forty-five  degrees,  and  that  of  the 
thoracic  and  lumbar  regions  to  about  thirty  degrees  on  each  side. 


PRACTICAL   CONSIDERATIONS:    THE   SPINE.  143 


PRACTICAL   CONSIDERATIONS. 

While  the  number  of  vertebrae  in  the  neck  is  almost  invariable  in  man  (and 
indeed  in  all  the  mammalia  except  the  sloth  and  the  sea-cow),  the  length  of  the 
cervical  region  varies  greatly  in  individuals.  As  it  is  apparently  shortened  during 
full  inspiration  and  lengthened  during  full  expiration,  so  an  actual  change  in  its 
length  is  associated  with  the  types  of  thorax  that  correspond  to  these  conditions. 
The  long  neck  is  therefore  found  in  persons  with  chests  that  are  flat  above  the 
mammae,  with  wide  upper  intercostal  spaces  and  narrow  lower  ones,  and  with  lack  of 
prominence  of  the  sternum.  These  conditions  are  often  associated  with  phthisical 
tendencies.  The  short  neck  is  found  in  persons  with  chests  of  the  reverse  type. 
Its  theoretical  association  with  apoplectic  tendencies  is  very  doubtful. 

The  remaining  variations  both  in  the  length  and  in  the  shape  of  the  vertebral 
column  are  closely  connected  with  corresponding  variations  in  its  curves. 

The  normal  curves  of  the  spine  are  four  :  the  cervical,  thoracic,  lumbar,  and 
pelvic  (or  sacro-coccygeal).  The  cervical  and  lumbar  are  concave  backward,  the 
thoracic  and  pelvic  convex  backward  (Fig.  171).  These  curves  are  produced  and 
kept  up  partly  by  the  twenty-three  intervertebral  disks.  They  are  altered  by  disease. 
An  additional  curve  not  uncommon  in  absolutely  healthy  persons  consists  in  a  slight 
deflection  of  the  thoracic  spine  to  the  right  ;  this  asymmetry  is  usually  ascribed  to  the 
greater  use  of  the  right  arm,  but  it  is  due  to  the  position  of  the  heart  and  the  aorta. 

All  the  vertebral  bodies  are  composed  of  cancellous  tissue,  which  is  more  spongy 
in  direct  proportion  to  the  size  of  the  vertebrae,  and  therefore  is  least  so  in  the  neck 
and  most  spongy  in  the  lumbar  region.  This  corresponds  with  the  greater  succu- 
lence and  elasticity  of  the  lower  intervertebral  disks  and  aids  in  minimizing  the  effect 
of  jars  and  shocks  such  as  are  received  in  alighting  from  a  height  upon  the  feet,  the 
lower  portion  of  the  column  of  course  receiving  the  greater  weight.  If  in  such  falls 
the  calcaneum  or  tibia  is  broken,  the  spine  usually  escapes  injury.  If  the  lower 
extremity  remains  intact,  the  safety  of  the  spine  depends  largely  upon  the  elasticity 
given  by  its  curves  and  by  the  disks. 

The  fact  that  the  bodies  have  to  bear  the  chief  strain  of  such  shocks  and  of 
extreme  flexion  and  extension,  the  most  usual  forms  of  spinal  injury,  serves,  together 
with  their  comparative  vascularity,  to  make  them  the  seat  of  tuberculous  infection 
when  it  invades  the  spine.  Their  spongy  texture,  once  they  are  softened  by  inflam- 
mation, leads  to  their  ready  disintegration  under  the  superincumbent  weight.  In 
the  neck  and  in  the  loins  the  process  may  at  first  merely  cause  a  straightening  of  the 
column,  the  normal  curves  being  concave  backward.  In  the  thoracic  region — the 
most  common  situation — it  soon  produces  kyphosis,  an  exaggerated  backward  curve, 
the  sharp  projection  of  the  spinous  processes  of  the  affected  vertebrae  causing  it  to 
be  known  as  ' '  angular  curvature. ' '  The  abscesses  which  result  from  caries  of  the 
vertebrae  are  governed  as  to  their  position  and  course  by  the  fasciae  and  muscles 
that  surround  them.  They  will,  therefore,  be  described  later  (page  643). 

The  suspension  of  the  whole  body  from  the  chin  and  occiput  separates  the  indi- 
vidual vertebrae  so  that  they  are  held  together  mainly  by  their  ligaments.  This 
obviously  relieves  or  removes  the  pressure  of  the  superincumbent  weight  on  the 
bodies  of  diseased  vertebrae.  The  relief  of  pressure  in  cases  of  thoracic  caries  is 
continued  by  the  use  of  appliances  which  transfer  the  weight  of  the  head. and 
shoulders  to  the  pelvis.  The  simplest  of  these  is  the  plaster  jacket.  For  cervical 
caries,  the  weight  of  the  head  is  transferred  to  the  trunk  beneath  the  level  of  disease 
by  means  of  an  apparatus  extending  from  above  the  head  to  a  band  (of  leather  or 
plaster)  encircling  the  chest. 

In  cases  of  kyphosis  corrected  by  the  method  of  "forcible  straightening"  it 
is  obvious  that  a  gap  proportionate  to  the  amount  of  bone  which  has  previously 
been  destroyed  must  be  left  between  the  bodies  of  the  diseased  vertebrae.  The 
ultimate  integrity  of  the  spinal  column  will  depend  upon  the  extent  and  character 
of  the  ankylosis  which  takes  place  between  the  separated  vertebrae.  It  is  asserted 
(Calot)  that  such  consolidation  does  occur  between  the  bodies  in  moderately  severe 
cases,  and  between  the  laminae,  transverse  processes,  and  spines  in  the  more  serious 


144  .  HUMAN   ANATOMY. 

ones.  It  has  been  shown  (Wullstein)  that  injury  to  the  dura  and  cord  and  even 
fracture  of  the  arches  and  processes  are  possible  concomitants  of  forcible  rectifica- 
tion of  kyphosis. 

If  the  curve  forward  of  the  lumbar  spine  is  exaggerated,  constituting  lordosis, 
it  is  usually  compensatory,  and  is  acquired  in  an  effort  to  maintain  the  erect 
position,  as  in  cases  of  high  caries,  great  obesity,  pregnancy,  ascites,  abdominal 
tumors,  etc. 

Scoliosis  or  lateral  curvature  commonly  results  from  faulty  positions  in  young, 
undeveloped  persons  with  weak  muscles,  as  school-girls,  who  sit  or  stand  in  such  atti- 
tudes that  the  muscles  are  relieved  and  the  strain  is  borne  by  insensitive  structures, 
like  ligaments  and  fasciae.  This  results  in  a  deflection  of  one  part  of  the  column — 
generally  the  thoracic — to  one  side,  usually  the  right,  and  the  formation  of  a  compen- 
satory curve  below,  and  occasionally  of  one  above  also.  The  bodies  of  the  affected 
vertebrae  are  at  the  same  time  rotated,  partly  by  the  action  of  the  slips  of  the  longis- 
simus  dorsi  which  are  attached  to  the  ribs  near  the  angles  and  to  the  tips  of  the  trans- 
verse processes  (Fig.  520),  so  that  in  advanced  cases  the  tips  of  the  spinous  pro- 
cesses of  the  affected  segments  turn  towards  the  concavity  of  the  curves,  while  the 
transverse  processes  of  the  vertebrae  involved  tend  to  lie  in  an  antero-posterior  plane 
and  can  often  be  felt  projecting  backward. 

A  further  explanation  of  the  causes  of  the  rotation  may  be  found  in  the  behavior 
of  a  straight  flexible  rod  under  similar  conditions.  Torsion  results  from  any  motion 
in  which  all  particles  of  a  straight  flexible  rod  do  not  move  in  parallel  columns. 
Therefore,  if  it  be  bent  in  two  planes  at  the  same  time  torsion  must  inevitably  occur. 
The  vertebral  column  being  bent  in  the  antero-posterior  plane  by  a  series  of  gentle 
curves,  lateral  bending  must,  therefore,  inevitably  lead  to  torsion,  since  it  means 
bending  in  two  planes. 

A  little  consideration  of  the  relations  of  the  spine  to  the  ribs,  scapula,  and  pelvis 
will  show  that  lateral  flexion  and  rotation  cannot  take  place  without  causing  (a)  sep- 
aration of  the  ribs  on  the  convex  side  ;  (£)  change  in  the  costal  angles,  making 
the  ribs  more  horizontal  on  the  convex  and  more  oblique  on  the  opposite  side  ;  (f) 
undue  prominence  of  their  angles  on  the  convex  side,  the  scapula  being  carried  upon 
them  so  that  it  also  is  more  prominent  ;  (a? )  diminution  of  the  ilio-costal  space  on 
the  concave  side  ;  (e)  elevation  of  the  shoulder  on  the  convex  side  ;  (/")  flatten- 
ing of  the  chest  in  front  on  the  convex  and  undue  prominence  of  the  chest  on  the 
opposite  side  ;  {g}  projection  of  the  ilium  on  the  concave  side.  Lateral  curvature 
with  these  secondary  deformities  may  also  be  produced  by  unequal  length  of  the 
lower  limbs,  one-sided  muscular  atrophy,  hypertrophy,  or  spasm,  sacro-iliac  disease, 
empyema,  and  asymmetry  of  either  the  pelvis  or  the  head. 

The  latter  factor  is  especially  interesting  from  an  anatomical  stand-point.  From 
what  has  been  said  (page  142)  of  the  position  of  greatest  stability  of  the  joints  be- 
tween the  head  and  the  atlas  and  the  latter  and  the  axis,  it-is  evident  that  the  position 
of  greatest  ease  is  with  the  head  slightly  turned  to  one  side,  the  condyles  of  the 
occiput  not  being  in  their  best  contact  with  the  superior  articular  surfaces  of  the 
atlas  when  the  head  is  held  straight,  but  rather  when  the  head  is  slightly  twisted 
(Dwight).  The  effects  of  this  are  far-reaching.  First,  there  is  an  instinctive  effort 
to  get  the  eyes  on  the  same  plane  in  looking  forward,  which  is  presumably  the 
primary  cause  of  the  asymmetry  of  the  face  that  is  usually  found.  It  is  also  easier 
to  sypport  the  weight  in  standing  chiefly  on  one  leg,  hence  the  other  side  of  the 
pelvis  is  allowed  to  fall  so  that  the  lumbar  region  slants  away  from  the  supporting  leg. 
This  must  be  corrected  by  a  lateral  motion  of  the  spine  above  it,  and  as  this  is  not 
pure  but  mixed  with  rotation,  there  occurs  a  twist  in  the  spine  ;  one  shoulder  is  higher 
than  the  other  as  well  as  farther  forward.  In  healthy  persons  such  positions,  if  not 
maintained  too  long,  do  little  harm  ;  but  there  is  likely  to  be  some  spinal  asymmetry 
in  all,  and  there  is  the  danger  that  it  may  become  pronounced  and  fixed  in  the  weak. 

Strains  of  the  spine  are  most  common  in  the  cervical  and  lumbar  regions  :  in 
the  former  because  of  the  greater  mobility  of  the  articulation  with  the  cranium,  and 
in  both  because  of  their  own  mobility,  the  greatest  degree  of  bending  in  an  antero- 
posterior  direction  being  possible  in  those  two  segments  of  the  spine.  The  thoracic 
and  pelvic  curves  are  primary,  form  part  of  the  walls  of  the  thorax  and  pelvis, 


PRACTICAL   CONSIDERATIONS:    THE   SPINE.  145 

appear  early,  and  are  chiefly  due  to  the  shape  of  the  vertebral  bodies.  The  cervical 
and  lumbar  curves  are  secondary,  develop  after  birth,  and  depend  mainly  on  the 
shape  of  the  disks.  Greater  mobility  would  naturally  be  expected  under  the  latter 
circumstances.  The  close  articulation  between  the  separate  vertebrae  throughout 
the  whole  column,  while  it  renders  a  slight  degree  of  sprain  not  uncommon,  tends 
at  the  same  time  to  diffuse  forces  applied  to  the  spine  and  to  concentrate  them  within 
certain  areas.  These  areas  are  the  points  at  which  fixed  and  movable  portions  of  the 
spine  join  each  other,  as  in  the  neighborhood  of  the  atlanto-axial,  the  cervico- 
thoracic,  and  the  dorso-lumbar  regions. 

If  the  force  is  sufficient  to  cause  an  injury  of  greater  severity  than  a  sprain 
it  is  apt  to  be  a  dislocation  or  a  fracture  with  dislocation  at  one  or  other  of  these 
localities.  The  latter  accident  is  usually  caused  by  extreme  flexion  of  the  spine,  and 
of  the  three  points  mentioned  is  most  often  found  in  the  segment  including  the 
lower  two  thoracic  and  the  upper  one  or  two  lumbar  vertebrae.  This  is  due  to  the 
fact  that  ( i )  this  segment  has  to  bear  almost  as  much  weight  as  the  lumbar  spine, 
and  yet  its  vertebrae  are  smaller  and  weaker.  (2)  The  transverse  processes  are 
short,  while  the  longer  ones  below,  together  with  the  crest  of  the  ilium  and  the  ribs 
above,  give  a  powerful  leverage  to  the  muscles  that  move  the  region  in  question. 
(3)  It  is  the  region  at  which  the  most  concave  part  of  the  thoracico-lumbar  curve  is 
found,  making  the  "  hollow  of  the  back"  and  corresponding  to  the  "  waist"  where 
the  circumference  of  the  trunk  is  smallest.  (4)  Its  nearness  to  the  middle  of  the 
column  enables  a  greater  length  of  leverage  to  be  brought  to  bear  against  it  than 
against  any  other  part.  (5)  The  different  segments  of  the  spine  above  it  are  com- 
paratively fixed  (Humphry).  These  anatomical  facts  account  for  the  frequency 
and  severity  of  the  injury  known  as  ' '  fracture-dislocation' '  in  this  region  as  a  result 
of  extreme  flexion. 

A  view  of  the  vertebral  column  from  behind  (Fig.  170)  serves  well  to  illustrate 
some  of  these  points. 

Pure  dislocations  are  rare,  but  are  more  frequent  in  the  upper  than  in  the  lower 
part  of  the  spine,  because  the  bodies  of  the  cervical  vertebrae  are  small,  and  the 
interlocking  of  the  articular  processes  is  less  firm  than  it  is  lower  in  the  column. 
The  vertebra  most  commonly  dislocated  is  the  fifth  cervical,  which  might  be  expected 
from  the  fact  that  in  the  neck  flexion  and  extension  are  freest  between  the  third  and 
sixth  vertebrae.  The  dislocation  is  usually  anterior, — that  is,  the  articular  process 
of  one  vertebra  slips  forward  and  falls  down  on  the  pedicle  of  the  vertebra  below, 
resting  in  the  intervertebral  notch, — this  accident  being  rendered  easy  by  the  com- 
paratively horizontal  position  of  the  articular  processes  in  the  cervical  region.  Such 
dislocation  is  practically  impossible  in  the  thoracic  or  lumbar  region  without  fracture, 
while  fracture  is  comparatively  rare  in  the  cervical  region.  The  lumen  of  the  spinal 
canal  may  be  but  little,  if  at  all,  invaded. 

As  to  reduction,  experiments  show  (Walton)  that  no  moderate  amount  of  exten- 
sion in  a  direct  line  would  raise  the  displaced  articular  processes  in  the  least  degree. 
It  was,  however,  found  easy  to  unlock  these  processes  by  retro-lateral  flexion,  bend- 
ing the  head  towards  the  side  to  which  the  face  was  already  turned,  an  inappreciable 
amount  of  force  being  necessary.  Rotation  into  place  completed  the  reduction. 

All  pure  dislocations  are  really  subluxations,  as  without  extensive  fracture  of 
the  processes  and  great  laceration  of  ligaments  a  complete  separation  of  the  articu- 
lar surfaces  of  two  adjoining  vertebrae  is  practically  impossible. 

Pure  fracture,  not  the  result  of  a  gunshot  wound,  is  rare.  If  from  flexion,  the 
fracture  involves  the  body  ;  if  from  direct  violence,  usually  the  laminae.  These  facts 
require  no  explanation. 

Dislocations  and  fractures  of  the  upper  two  cervical  vertebrae  are  especially 
serious  on  account  of  the  proximity  of  the  medulla  and  of  their  position  above  the  roots 
of  the  phrenic  nerve  and  of  the  nerves  supplying  the  external  muscles  of  respiration. 
If  the  accident  is  from  overflexion,  it  may  be  a  dislocation  between  the  occiput  and 
the  atlas,  as  it  is  there  that  the  movements  of  flexion  and  extension  of  the  head  take 
place.  If  it  arises  from  extreme  rotation,  and  especially  if  there  is  rupture  of  the 
check  ligaments,  it  may  be  a  dislocation  of  the  atlas  from  the  axis,  as  it  is  there  that 
the  rotary  movements  of  the  head  occur.  "  A  dumb  person  expresses  '  yes'  at  the 


146  HUMAN   ANATOMY. 

occipito-atloid  joint  and  'no'  at  the  atlo-axoid"  (Owen).  Painless  nodding  and 
rotation  of  the  head  aid,  therefore,  in  the  exclusion  of  the  occipito-atlantal  and 
atlanto-axial  regions  in  obscure  cases  of  high  caries. 

The  axis  is  more  spongy  than  the  atlas,  and  is  weakest  about  one  centimetre 
below  the  neck  of  the  odontoid  process,  and  this  is  one  of  the  most  frequent  seats 
of  fracture. 

In  fracture-dislocations,  which  constitute  from  seventy  to  eighty  per  cent,  of  se- 
vere spinal  injuries,  the  thoracico-lumbar  region  suffers  most  commonly  for  the  reasons 
above  stated.  The  almost  vertical  direction  of  the  articular  processes  of  the  thoracic 
vertebrae  causes  them,  when  flexion  is  extreme,  as  when  a  weight  has  fallen  on  the 
back,  to  be  frequently  fractured,  which,  together  with  the  accompanying  crushing 
of  the  vertebral  body  and  rupture  of  the  supra-  and  interspinous  ligaments  and 
the  ligamenta  subflava,  permits  the  immediate  sliding  forward  of  the  vertebrae  above 
the  crushed  one  and  the  compression  of  the  cord — often  its  practical  severance — 
between  the  anterior  edge  of  the  posterior  arch  of  the  upper  vertebra  and  the  poste- 
rior edge  of  the  body  of  the  lower  one. 

(For  the  resulting  symptoms,  see  section  on  Nervous  System,  page  1053.)  It 
may  be  mentioned  here  that  the  spinal  nerves  do  not  arise  from  the  cord  opposite 
the  vertebrae  after  which  they  are  named.  Their  regions  of  origin  may  briefly  be 
stated  as  follows  : 

1 i )  Occiput  to  sixth  cervical  spine,  — eight  cervical  nerves. 

(2)  Seventh  cervical  to  fourth  thoracic  spine, — upper  six  thoracic  nerves. 

(3)  Fifth  to  tenth  thoracic  spine, — lower  six  thoracic  nerves. 

(4)  Eleventh  and  twelfth  thoracic  spines, — five  lumbar  nerves. 

(5)  First  lumbar  spine, — five  sacral  nerves. 

Landmarks. — To  fix  the  limits  of  the  spine  in  the  living,  draw  a  horizontal 
line  from  the  anterior  nasal  spine  to  the  lower  edge  of  the  external  occipital  pro- 
tuberance and  another  backward  from  the  top  of  the  symphysis  pubis.  Seen  from 
the  side,  the  top  of  the  spine  is  in  a  line  connecting  the  front  of  the  lobe  of  each  ear, 
passing  behind  the  neck  of  the  lower  jaw.  Frozen  sections  show  that  the  front  of 
the  vertebral  bodies  is  much  nearer  the  centre  of  the  body  than  one  is  prepared  to 
expect.  A  vertical  transverse,  or  frontal,  plane  through  the  thorax  at  its  greatest 
breadth  strikes  the  angle  of  the  jaw,  the  front  of  the  cervical  convexity  of  the  spine, 
and  cuts  the  body  of  the  fourth  lumbar  (Langer). 

The  relations  of  the  spine  anteriorly  are  considered  with  the  parts  in  front  of  it. 
The  parts  felt  from  the  surface  are  the  spinous  processes  and  some  few  of  the  trans- 
verse ones.  The  line  of  the  spines  is  a  good  example  of  the  general  rule  that 
prominences  on  the  skeleton  lie  in  hollows  in  the  flesh  ;  a  deep  furrow  between  the 
muscular  masses  marks  their  position. 

Palpation  of  the  normal  spine  with  the  soft  parts  in  place  gives  the  following 
information.  The  spine  of  the  second  cervical  can  be  felt  by  deep  pressure  a  little 
below  the  occiput.  The  short  spines  of  the  succeeding  vertebrae  are  made  out  with 
great  difficulty.  The  fifth  is  longer  than  those  just  above  it.  The  sixth  is  much 
longer  and  nearly  as  long  as  that  of  the  seventh.  The  name  vertebra  prominent 
conferred  on  the  seventh  is  misleading,  for  the  spine  of  the  first  thoracic  is  the  most 
prominent  in  this  region.  The  third,  fourth,  and  fifth  cervical  spines  recede  from 
the  surface  by  reason  of  the  forward  curve  of  the  cervical  segment  and  on  account 
of  their  shortness.  This  permits  of  free  extension  of  the  head  and  neck.  The  liga- 
mentum  nuchae  also  prevents  them  from  being  felt  distinctly.  The  sixth  and  seventh 
cervical  and  first  thoracic  are  easily  felt.  The  remainder,  lying  in  the  groove  caused 
by  the  prominence  of  the  erector  spinae  muscles,  can  usually  be  palpated  without 
much  difficulty. 

The  relative  sizes  vary  so  much  that  it  is  not  safe  to  identify  any  spine  in  this 
way.  If  the  whole  series  from  the  second  cannot  be  counted,  it  is  best  to  start  from 
the  fourth  lumbar,  which  is  on  a  level  with  the  highest  points  of  the  ilia.  \\rt (bra- 
can  also  be  identified  from  the  lower  rrbs  by  the  relations  of  the  heads  to  the  bodies. 
The  relations  of  the  spinous  processes  to  the  body  vary.  Thus,  in  the  cervical 
region  the  first  five  spines  pass  nearly  straight  backward.  The  sixth  and  seventh, 
like  the  upper  two  or  three  thoracic  spines,  descend  a  little,  so  that  the  tip  is  opposite 


LANDMARKS   OF   THE   SPINE. 
FIG.  172. 


147 


Pons 

Anterior  boundary  of  foramen 
magnum 


Superior  laryngeal  opening 
Cricoid  cartilage 

Thyroid  gland 

Upper  border  of  manubrium 

Left  innominate  vein 

Innominate  artery 

Ascending  portion  of  aortic  arch 

Upper  border  of  body  of  sternum 

Section  of  right  lung 

Right  auricular  appendage 

Right  auricle 

Lower  border  of  body  of  sternum 
Diaphragm 

Lower  end  of  ensiforn,  cartilage 
Liver 


Stomach 
Pancreas 


Duodenum 
Transverse  colon 


Sigmoid  flexure 


Bladder 
Symphysis  pubis 


Medulla 

Posterior  boundary  of  foramen 
magnum 

Odontoid  process  of  axis 


(Esophagus 

Division  of  trachea 
Right  pulmonary  artery 
Left  auricle 


Aorta 


End  of  abdominal  aorta 
Left  common  iliac  vein 


Sacrum 


Rectum 

Coccyx 

Seminal  vesicles 
Prostate 


Median  section  of  the  body  of  a  man  aged  twenty-one  years.     (After  Braune.) 


I48  HUMAN   ANATOMY. 

to  the  body  next  below  it.  With  the  fourth  or  fifth  thoracic  they  point  much  more 
strongly  downward,  so  as  to  be  opposite  the  disk  below  the  succeeding  body.  This 
continues  to  the  tenth,  where  they  are  opposite  the  body  below.  In  the  loins  the 
spines  have  a  considerable  posterior  surface,  which  is  opposite  the  disk  and  the 
upper  part  of  the  body  below  it.  The  tips  of  the  spines  are  not  always  in  a  straight 
line,  but  sometimes  describe  a  zigzag.  The  transverse  process  of  the  atlas  can  be 
felt  below  the  tip  of  the  mastoid  process,  moving  with  the  head  when  the  latter  is 
turned.  The  transverse  processes  below  this  are  felt  with  great  difficulty  through 
the  muscles  of  the  side  of  t-he  neck.  Those  of  the  back  and  loins  are  too  thickly 
covered  to  be  felt.  The  laminae  are  also  thickly  covered  with  muscles,  so  that  the 
operation  of  laminectomy  necessarily  involves  a  deep  wound,  and  in  the  thoracic 
region  this  difficulty  is  increased  by  the  backward  projection  of  the  ribs. 

As  landmarks  the  spines  of  the  vertebrae,  on  account  of  their  accessibility,  have 
great  value.  These  spines  have  the  following  relations.  The  fourth  cervical  spine 
corresponds  to  (i)  the  opening  of  the  larynx;  (2)  the  bifurcation  of  the  carotid 
artery,  and  hence  the  point  of  origin  of  both  the  external  and  internal  carotid 
arteries.  The  sixth  cervical  indicates  the  level  of  the  carotid  tubercle  (transverse 
process  of  the  sixth  vertebra)  and  the  entrance  of  the  vertebral  artery  into  the  bony 
canal.  The  seventh  cervical  spine  is  a  guide  to  ( i )  the  lower  border  of  the  cricoid 
cartilage  ;  the  lower  opening  of  the  larynx  and  the  beginning  of  the  trachea  ;  (2) 
the  lower  end  of  the  pharynx  and  the  upper  opening  of  the  oesophagus  ;  (3)  the 
crossing  of  the  omo-hyoid  over  the  common  carotid  ;  (4)  the  level  of  the  apex  of 
the  lung  and  to  the  summit  of  the  arch'of  the  subclavian  artery.  The  fourth  thoracic 
spine  corresponds  to  the  level  at  which  the  aorta  reaches  the  spinal  column,  the 
trachea  bifurcates,  and  posteriorly  the  apex  of  the  lower  lobe  of  the  lung  is  found. 
It  is  on  the  same  level  as  the  root  of  the  spine  of  the  scapula.  The  seventh  thoracic 
lies  on  a  level  with  the  inferior  angle  of  the  scapula.  The  eighth  thoracic  indicates 
the  lower  level  of  the  heart  and  that  of  the  central  tendon  of  the  diaphragm  and  the 
level  at  which  the  inferior  vena  cava  passes  through  the  diaphragm.  The  ninth  tho- 
racic marks  the  level  at  which  the  upper  edge  of  the  spleen  is  found  in  health,  and  at 
which  also  the  oesophagus  pierces  the  diaphragm.  The  tenth  thoracic  corresponds 
to  the  lower  edge  of  the  lung,  the  spot  at  which  the  liver  comes  to  the  surface  poste- 
riorly. The  spines  of  the  third  to  the  ninth  thoracic  correspond  to  the  heads  of  the 
fourth  to  the  tenth  ribs  respectively.  The  eleventh  thoracic  is  a  guide  to  the  normal 
situation  of  the  lower  border  of  the  spleen  and  to  the  upper  part  of  the  kidney. 
The  tivelfth  thoracic  marks  the  lower  limit  of  the  pleura,  the  passage  of  the  aorta 
through  the  diaphragm,  and  the  situation  of  the  pyloric  end  of  the  stomach,  and 
is  on  a  level  with  the  head  of  the  last  rib.  The  first  lumbar  spine  is  on  the  line  of 
the  renal  arteries  and  the  pelvis  of  the  kidney.  The  second  lumbar  spine  corre- 
sponds to  (i)  the  termination  of  the  duodenum  and  the  commencement  of  the 
jejunum  ;  (2)  the  opening  of  the  ductus  communis  choledochus  into  the  intestine  ; 
(3)  the  lower  border  of  the  kidney  ;  (4)  the  lower  border  of  the  pancreas  ;  (5)  the 
upper  end  of  the  root  of  the  mesentery  ;  (6)  the  point  of  origin  of  the  superior 
mesenteric  artery  5(7)  the  commencement  of  the  thoracic  duct  ;  (8)  the  commence- 
ment of  the  vena  porta  ;  (9)  the  termination  of  the  spinal  cord  and  the  origin 
of  the  cauda  equina  ;  (10)  the  upper  end  of  the  receptaculum  chyli.  The  third 
lumbar  corresponds  to  the  level  of  the  umbilicus  and  the  origin  of  the  inferior 
mesenteric  artery  ;  the  fourth  lumbar  spine  marks  the  point  of  bifurcation  of  the 
abdominal  aorta  into  the  two  common  iliac  arteries,  and  lies  on  a  level  with  the 
highest  part  of  the  ilium  ;  and,  finally,  the  fifth  lumbar  spine  is  a  little  below  the 
beginning  of  the  inferior  vena  cava. 

Direct  cocainization  of  the  spinal  cord  has  recently  been  employed  in  surgery  in 
operations  on  the  lower  abdomen,  pelvis,  and  lower  extremities.  The  injection  into 
the  subarachnoid  space  surrounding  the  cord  is  made  through  the  space  between 
the  fourth  and  fifth  lumbar  vertebrae.  To  find  this  space,  draw  a  line  connecting 
the  highest  points  of  the  crest  of  the  ilium  posteriorly.  This  will  pass  through  the 
spine  of  the  fourth  lumbar  vertebra.  The  point  for  injection  is  one  centimetre  below 
and  one  centimetre  to  the  outer  side  of  the  point  at  which  the  transverse  line  crosses 
the  vertebral  spine  in  the  median  line. 


THE  THORAX. 

THE  thorax  is  that  part  of  the  body-cavity  separated  by  the  diaphragm  from 
the  abdomen  below,  but  without  complete  separation  from  the  neck  above.  Its 
bony  walls  are  formed  behind  by  the  thoracic  vertebrae,  at  the  sides  by  the  ribs,  and 
in  front  by  their  continuations,  the  costal  cartilages,  and  the  sternum. 

Kic;.    173. 


The  bony  thorax,  anterior  view. 

THE   RIBS. 

The  ribs,  arranged  as  twelve  pairs,  are  flat  bars  of  bone,  curved  and  twisted, 
which  are  attached  behind  to  the  spine  and  continued  in  front  by  the  costal  cartilages  ; 
they  form  the  greater  part  of  the  bony  walls  of  the  thorax.  The  first  seven  pairs, 

149 


150 


HUMAN   ANATOMY. 


exceptionally  eight,  reach  the  sternum  through  their  cartilages  ;  hence  they  are  called 
sternal  ribs,1  as  distinguished  from  the  remaining  five  pairs  of  asternal  ribs.2  Each 
cartilage  of  the  next  three  joins  that  of  the  rib  above  it.  The  last  two  pairs  have 
the  cartilages  ending  free,  and  are  termed  floating  ribs.  Their  complicated  curves 
are  best  understood  by  studying  them  in  place.  Each  rib  (with  certain  exceptions 
to  be  detailed  later)  has  an  articular  surface,  the  head,  at  the  posterior  end  ;  followed 
by  a  narrower  neck,  succeeded  by  an  articular  facet  on  the  tubercle  which  rests  on 
the  transverse  process  of  the  vertebra.  The  first  rib  has  an  .upper  and  a  lower 
surface,  an  outer  and  an  inner  border  ;  the  second  faces  in  a  direction  intermediate 
to  this  and  the  following,  which  have  an  outer  and  an  inner  surface,  an  upper  and  a 
lower  border.  They  are  placed  obliquely,  the  front  end  being  lower  than  the  hind 
one.  The  outline  of  the  ribs  is  irregular,  so  that  their  declination  is  not  due  wholly 
to  their  position,  but  in  part  also  to  their  shape.  Thus,  one  in  the  middle  of  the 
series  slants  a  little  downward  as  far  as  the  tubercle,  then  declines  more  sharply 
to  a  roughness  near  the  tubercle  known  as  the  angle,  and  thence  more  gradually 
to  the  end.  The  main  curve  of  such  a  rib  is  backward,  outward,  and  downward 
as  far  as  the  angle,  which  marks  a  rather  sudden  change  of  direction,  the  course 
changing  to  one  forward,  slightly  outward,  and  downward,  until,  as  it  reaches  the 
front  of  the  chest,  it  runs  forward,  downward,  and  inward.  The  external  surface 
is  vertical  at  the  back  and  side  and  slants  slightly  upward  in  front.  Bearing  the 
declination  of  the  rib  in  mind,  it  is  evident  that  to  accomplish  this  the  rib  must  be 
twisted  on  itself,  otherwise  the  upper  edge  would  project  in  front. 

FIG.  174. 

Articular  facets  for  bodies  of  vertebrae . 


Articular  facet  on  tubercle  for  transverse  process 

Right  fifth  rib  from  behind. 

The  head:i  is  an  enlargement  at  the  posterior  end  and  on  the  outer  surface, — i.e., 
the  one  farthest  from  the  cavity  of  the  chest.  It  has  an  articular  surface  at  the 
end  facing  inward  and  backward,  divided  into  an  upper  and  a  lower  facet,  each  for 
the  body  of  a  vertebra,  by  a  transverse  ridge,  whence  a  ligament  passes  to  the  inter- 
vertebral  disk.  The  lower  facet  is  the  larger,  and  is  generally  concave  ;  the  upper 
is  nearly  plane.  The  head  increases  in  size  to  the  ninth  rib  and  then  lessens. 

The  neck  *  is  compressed  from  before  backward,  smooth  in  front  and  rough  for 
ligaments  behind.  The  upper  aspect  has  a  sharp  border,  the  crest?  for  the  superior 
costo-transverse  ligament.  The  neck  grows  slightly  longer  in  descending  the  series 
to  the  same  level.  The  crest  on  the  top  of  the  neck  is  most  developed  in  the  sixth, 
seventh,  and  eighth  ribs. 

The  tubercle 6  is  an  elevation  beyond  the  neck  on  the  posterior  surface  of  the 
rib,  bearing  internally  a  round  articular  surface  facing  backward  and,  in  most  cases, 
downward,  to  rest  on  the  transverse  process  ;  beyond  the  articular  facet  is  a  rough 
knob  for  the  external  costo-transverse  ligament. 

The  shaft 7  is  smooth  inside,  the  surface  being  continuous  with  that  of  the  neck. 
The  subcostal  groove*  for  the  intercostal  vein  is  best  marked  in  the  middle  ribs,  begin- 
ning at  the  tubercle  and  running  forward,  growing  fainter,  along  three-quarters  of 
the  rib,  just  under  cover  of  the  lower  border.  The  outer  surface  is  rather  irregular. 

The  angle !(  at  which  the  shaft  changes  its  direction  is  marked  by  a  rough  line 
on  the  posterior  surface,  some  distance  beyond  the  tubercle,  receiving  muscles  from 
the  system  of  the  erector  spinae.  The  angle,  which  is  not  found  in  the  first  rib,  is 

1  Coatae    verne.      2  Coatae    spurine.      ^Capitulum.     *  Colin  in      ;'Crista    colli.     '"'  Tulicrculuin      "Corpus    costac.      *  Snlcns 
coatalia.     '•'  Angulu*   costae. 


THE    RIBS. 


very  near  (one  centimetre  beyond)  the  tubercle  in  the  second  ;  it  gradually  recedes 
from  the  tubercle,  being  in  the  ninth  and  tenth  about  five  centimetres  distant.  The 
angle  is  a  little  nearer  in  the  eleventh,  and  is  wanting  in  the  last.  The  twist  is 
greatest  from  the  sixth  to  the  ninth  rib.  Several  of  the  upper  ribs  present  near 


FIG.  175. 

Tuberosity 


Angle 


Head    __, 


Articular  facets  for 
bodies  of  vertebrae 


A 


Inferior  border  (external  intercostal) 


Right  fifth  rib:  A,  under  surface;  B,  postero-lateral  aspect. 

the  middle  a  rough  impression  for  a  point  of  the  serratus  magnus.  The  upper 
border  of  the  shaft  is  thick  and  rounded  behind,  but  thin  near  the  front.  The  lower 
border  is  sharp  where  it  overhangs  the  subcostal  groove ;  less  so  in  front.  The 
anterior  end  of  each  rib  is  cupped  to  receive  the  costal  cartilage. 


152 


HUMAN   ANATOMY. 


The  ribs  increase  in  length  from  the  first  to  the  seventh  or  eighth,  after  which 
they  decrease  to  the  last,  which  is  usually  the  shortest.  The  length  of  the  last  rib 
is,  however,  Very  uncertain,  varying  from  one  centimetre  to  perhaps  fifteen  centime- 
tres or  more.  It  often  is  longer  than  the  first.  The  curve  is  comparatively 
regular  in  the-  first  rib,  after  which  the  difference  between  the  two  ends  becomes 
more  marked,  the  curve  being  very  pronounced  behind  and  less  so  in  front.  The 
curve  is  much  less  throughout  in  the  lower  ribs  ;  in  fact,  it  decreases  continually. 
The  first  rib  is  the  broadest  of  all  at  the  anterior  end.  There  is  a  general,  but  not 
regular,  increase  from  the  second  to  the  seventh  rib,  and  a  subsequent  decrease. 
The  fourth  rib  is  relatively  broad,  the  fifth  narrow.1 

Exceptional  Ribs. — Certain  of  the  ribs — the  first,  second,  tenth,  eleventh, 
and  twelfth — present  peculiarities  which  claim  mention. 

FIG.  176. 


Cervicalis  ascendens 

Serratus  posticus  superior 


External 
intercostal 


Second  (limitation  of  sen  atus  »itiff>iu» 


Third  (limitation  of  serratus  magnus 


First  and  second  ribs  of  right  side,  upper  surface. 

The  first  rib  is  flat,  not  twisted,  with  an  outer  and  an  inner  border.  The 
head  is  small  and  has  but  one  facet,  resting  as  it  does  on  the  first  thoracic  vertebra. 
The  neck  is  small  and  flat  like  the  body.  The  tubercle  is  very  prominent.  The 
scalene  tubercle  is  a  very  small  but,  from  its  relations,  important  elevation  on  the 
inner  margin  of  the  upper  surface,  at  about  the  middle,  for  the  insertion  of  the 
scalenus  anticus.  It  separates  two  grooves  crossing  the  bone  for  the  subclavian 
artery  and  vein.  The  posterior  one  for  the  artery  is  the  more  marked.  There  is  a 
rough  impression  behind  the  latter  near  the  outer  border  for  the  scalenus  medius. 
There  is  no  subcostal  groove. 

The  second  rib  is  intermediate  in  shape  between  the  first  and  the  rest.     The 
roughness  for  the  serratus  magnus  is  very  marked  about  the  middle  of  the  shaft. 

1  Anderson  :  Journal  of  Anatomy  and  Physiology,  vol.  xviii.,  1884. 


EXCEPTIONAL    RIBS. 


153 


The  tenth  rib  has  usually  only  a  single  articular  facet  on  the  head  ;  it  may  or 
may  not  have  a  facet  on  the  tubercle. 

The  eleventh  rib  has  a  single  articular  facet  on  the  head  ;  the  tubercle  is  rudi- 
mentary and  non-articular  ;  the  angle  and  the  subcostal  groove  are  slightly  marked. 

The  twelfth  rib  has  also  a  single  articular  facet  on  the  head  ;  the  tubercle  is  at 
most  a  faint  roughness  ;  the  angle  and  the  subcostal  groove  are  wanting. 

Development. — The  first  centre  for  the  shaft  appears  in  the  ninth  week  of 
foetal  life,  and  spreads  so  rapidly  that  by  the  end  of  the  fourth  month  the  perma- 
nent proportion  of  bone  has  been  formed.  At  an  uncertain  period,  probably  before 
puberty,  a  centre  appears  for  the  head  and  another,  except  in  the  last  two  or  three 
ribs,  for  the  tubercle  ;  these  unite  presumably  by  the  twentieth  year. 

Variations. — The  num- 
ber of  ribs  is  often  increased  or  FIG. 
diminished  by  one,  generally  by 
a  change  at  the  end  of  a  re- 
gion, as  explained  in  varia- 
tions of  the  spine  (page  131). 
Cervical  ribs  occur  by  the  cos- 
tal element  of  the  seventh  cer- 
vical becoming  free.  In  the 
lowest  and  most  common  grade 
it  consists  of  a  head,  a  neck,  a 
tubercle,  and  a  rudimentary 
shaft  one  or  two  centimetres 
long,  ending  free.  In  the  next 
grade  it  is  longer,  and  its  end, 
perhaps  continued  in  cartilage, 
rests  on  the  first  rib.  Some- 
times it  fuses  with  the  first  rib, 
which  then  becomes  bicipital, 
as  is  normal  in  certain  whales. 
In  the  third  grade,  which  is 
very  uncommon,  it  resembles  a 
small  first  rib,  reaching  the  ster- 
num. A  cervical  rib  has  been 
seen  more  than  once  with  the 
transverse  foramen  persisting. 

The  explanation  of  this  condition  is  given  under  ossification  of  the  vertebrae.  When 
a  cervical  rib  reaches  the  sternum,  the  next  rib  is  usually  attached  to  the  side  of  the 
manubrium  by  a  broad  cartilage,  fusing  with  that  of  the  cervical  rib.  The  rib  of  the 
eighth  vertebra  has  been  seen  to  end  like  an  ordinary  second  rib.  It  is  also  very 
rare  to  have  only  twelve  pairs  of  ribs,  of  which  the  first  is  cervical.  There  may  be 
thirteen  ribs  by  the  addition  of  the  costal  element  of  the  first  lumbar.  This  may 
be  so  small  as  to  present  no  rib-like  feature,  or  it  may  resemble  an  ordinary  twelfth 
rib.  In  cases  of  an  extra  rib  from  this  source  the  twelfth  rib  is  usually  uncom- 
monly long.  Very  rarely  the  first  true  thoracic  rib  is  imperfect,  being  continued 
in  ligament  to  the  sternum,  joining  the  shaft  of  the  second  rib,  or  even  ending  free. 
A  bicipital  rib  may  occur  also  by  the  fusion  of  the  first  thoracic  with  the  second  be- 
yond the  tubercles.  The  resulting  plate  later  subdivides,  to  be  continued  by  two 
normal  costal  cartilages.  Ribs  sometimes  divide,  generally  near  the  front.  The 
parts  formed  by  such  cleavage  are  continued  by  costal  cartilages  which  usually  re- 
unite, so  that  a  foramen  is  formed  which  is  bounded  laterally  or  externally  by  bone, 
mesially  by  cartilage.  This  occurs  most  commonly  in  the  third  and  fourth  ribs,  espe- 
cially in  the  latter. 

THE   COSTAL   CARTILAGES. 

The  costal  cartilages '  continue  the  ribs,  the  first  seven  going  directly  to  the  ster- 
num, the  next  three  each  to  the  one  above  it,  and  the  last  two  ending  free.  They 
grow  longer  from  the  first  to  the  seventh,  sometimes  to  the  eighth.  The  last  two 

1  Cartilagines  costalcs. 


Vertebral  ends  of  tenth,  eleventh,  and  twelfth  ribs  of  right  side  from 
below. 


154 


HUMAN   ANATOMY. 


cartilages  are  short  and  pointed.  There  is  occasionally  a  projection  downward 
from  the  fifth,  at  its  most  dependent  point,  which  articulates  with  the  sixth.  Usually 
there  is  a  similar  projection  on  the  latter  for  the  seventh.  The  eighth,  ninth,  and 


FIG.  178. 


Interclavicular  notch 


Posterior  Anterior 

Surfaces  of  sternum  with  coossified  ensiform  cartilage. 


tenth  cartilages  have  usually  their  chief  connection  with  the  one  above,  not  through 
their  ends,  but  through  similar  facets.  As  to  direction  :  the  first  cartilage  descends, 
the  second  is  horizontal,  the  third  rises  very  slightly,  and  the  fourth  is  the  first  to  fall 
and  then  rise.  This  change  of  direction  occurs  in  each  to  the  ninth  or  tenth  carti- 


THE   STERNUM. 


155 


lage,  the  falling  portion  becoming  always  relatively  shorter  and  the  rising  longer. 
The  last  two  cartilages  continue  the  line  of  their  ribs,  having  no  rising  portion.  It 
is  not  uncommon  to  find  eight  cartilages  joining  the  sternum.  Tredgold  found  this 
condition  in  ten  per  cent,  of  white  men.  It  is  very 

much    more  frequent   in   negroes    and   in   other  dark  FIG.  179. 

It  is  said  to  occur  more  often  on  the  right  side. 

Clavicular 


races. 


THE   STERNUM. 


facet 


First  rib-- 
cartilage 


Third' 


BODY 


FourtJ 


The  adult  sternum  consists  of  three  flat  median 
plates,  the  two  former  being  bone,  the  last  largely  car- 
tilage,— namely,  the  presternum  or  manubrium,  the 
mesosternum,  gladiolus,  or  body,  and  the  metasternum 
or  ensiform  cartilage. 

The  manubrium 2  is  broad  in  mammals  having 

clavicles,  to  which  it  gives  support  at  the  upper  angles.  MANUBRIUM 

In  man  it  is  irregularly  quadrilateral,  with  the  angles 
cut  off,  broad  above,  narrower  below,  the  greatest 
breadth  equalling  or  exceeding  the  length.  It  is  con- 
cave behind,  but  in  front  it  is  convex  from  side  to  side  second 
and  slightly  concave  from  above  down.  The  upper 
border  is  concave  in  the  middle,  forming  the  bottom 
of  the  interclavicular  notch?  On  each  side  of  this,  in 
the  place  of  a  corner,  is  a  concavity  for  the  sternal  end 
of  the  clavicle.  This  depression 4  is  more  on  the  top 
than  on  the  side  of  the  sternum,  and  usually  encroaches 
more  on  the  back  of  the  bone.  It  is  concave  from 
within  outward  and  may,  or  may  not,  be  slightly  con- 
cave from  before  backward.  The  facet  is  coated  with 
articular  cartilage.  Just  below  the  joint,  the  side  of 
the  manubrium  projects  outward  to  meet  the  cartilage 
of  the  first  rib.  This  is  the  widest  part  of  the  first 
piece,  the  border  then  slanting  inward  to  the  lower 
angle,  which  also  is  cut  off  by  a  notch  for  the  second 
costal  cartilage,  which  is  received  between  it  and  the 
body.  The  lower  border,  separated  from  the  meso- 
sternum by  fibro-cartilage,  projects  a  little  forward  into 
a  transverse  ridge,  always  to  be  felt  in  life,  which  in- 
dicates the  level  of  the  second  costal  cartilage. 

The  oblong  body,  or  gladiolus,5  ossifying  origi- 
nally in  four  pieces,  one  above  another,  varies  con- 
siderably in  shape.  It  is  generally  slightly  concave 
behind  and  nearly  plane  in  front,  but  it  may  be  convex 
or  even  concave.  The  greatest  breadth  is  below  the 
middle,  whence  the  borders  slant  inward  to  the  lower 
end,  the  narrowest  part,  where  it  joins  the  ensiform 
cartilage.  The  sides  of  the  body  present  alternately 
smooth  concavities  opposite  the  spaces  between  the 
costal  cartilages  and  articular  facets  for  the  latter.  To 
understand  the  position  of  these  articular  facets,  we 
must  recall  the  composition  of  the  mesosternum  as 
consisting  of  four  pieces.  The  second  cartilage  reaches 
the  junction  of  the  manubrium  and  the  body  ;  the  third, 
that  of  the  first  and  second  pieces  of  the  body  ;  the 
fourth,  that  of  the  second  and  third  pieces  ;  the  fifth,  that  of  the  third  and  fourth 
pieces.  The  two  remaining  sternal  ribs  send  their  cartilages  to  this  fourth  piece  of 
the  body  ;  the  sixth  to  the  side,  and  the  seventh  to  the  lower  angle,  or  even  the 
1  Journal  of  Anatomy  and  Physiology,  vol.  xxxi,  1897.  Lamb  :  Nature,  1888. 

-Manubrium  sterni,     x  Incisura  jugularis.     4  Incisura  clavicularis.     •'  Corpus  stcrni. 


Fifth- 


Sixth- 


Seventh- 


Right  side  of  sternum. 


156 


HUMAN   ANATOMY. 


lower  edge.  The  first  and  second  pieces  of  the  body  are  about  equal  in  length  ;  the 
third  is  shorter,  and  the  fourth  still  more  so  ;  hence  the  fifth,  sixth,  and  seventh 
cartilages  end  very  close  togetluT,  especially  the  two  last. 

The  ensiform  cartilage,1  or  xiphoid  process,  more  or  less  bony  in  middle 
life,  is  a  flat  plate  with  a  rounded  end,  not  rarely  bifid.  It  is  fastened  to  the  lower 
end  of  the  body  in  such  a  way  that  their  posterior  surfaces  are  continuous,  but  that 
the  ensiform,  being  thinner,  is  overlapped  by  the  ends  of  the  seventh  cartilages  ;  its 
front  is  therefore  at  a  deeper  level  than  that  of  the  body.  The  size  and  shape  of 
the  ensiform  cartilage  are  very  uncertain  ;  usually  the  tip  projects  somewhat  forward. 

Differences  due  to  Sex. — The  body  of  the  male  sternum  is  both  absolutely 
and  relatively  longer  than  that  of  the  female.  This  is  in  accordance  with  the  greater 
development  of  the  male  thorax.  The  following  table  gives  the  actual  size,  accord- 
ing to  the  writer2  and  to  Strauch.3 


DWIGHT. 

Men. 
Centimetres. 

Manubrium 5.37 

Body 11.04 

Total 16.41 


STRAUCH. 


Women. 

Men. 

Women. 

Centimetres. 

Centimetres. 

Centimetres. 

4-94 

5-049 

5-056 

9.19 

11.014 

9-059 

14.13 


16.063 


14.115 


FIG.  i 80. 


.  Hyrtl  gave  a  rule  for  determining  the  sex,  that  the  manubrium  of  the  female 
exceeds  half  the  length  of  the  body,  while  the  latter  in  the  male  is  at  least  twice  as 

long  as  the  manubrium.  A  study  of  342  sterna,  of 
which  222  were  male  and  120  female,  confirmed  Hyrtl's 
law  for  the  mean  ;  since,  however,  approximately  forty 
per  cent,  of  the  cases  were  exceptions,  it  is  clearly 
worthless  to  determine  the  sex  in  any  given  case. 
Probably  the  law  would  be  correct  if  we  had  to  do 
only  with  well-formed  sterna,  but  the  body  varies 
greatly.  It  is  easy  to  recognize  a  typical  male  or 
female  sternum.  The  former  has  a  long,  regular  body, 
the  lower  pieces  of  which  are  well  developed,  sepa- 
rating the  lower  cartilages  of  the  true  ribs.  The  latter 
has  a  shorter  and  relatively  broader  body,  the  lower 
parts  of  which  are  poorly  developed,  so  that  the  carti- 
lages are  near  together,  and  the  seventh  ones  of  the  two 
sides  almost,  or  quite,  meet  below  the  body  in  front  of 
the  base  of  the  ensiform. 

Variations. — The  very  rare  cases  of  fissure  of 
the  sternum,  and  the  not  uncommon  ones  of  perfora- 
tion in  the  median  line,  represent  different  degrees  of 
arrest  of  development.  The  lower  half  of  the  sternum 
is  sometimes  imperfectly  developed.  We  have  de- 
scribed a  case  in  a  negress  in  which  there  was  but  little 
and  irregular  ossification  below  the  fourth  costal  carti- 
lage. A  very  rare  anomaly  is  that  of  the  manubrium 
being  prolonged  to  the  insertion  of  the  third  costal 
cartilages,  as  occurs  usually  in  the  gibbons  and  occa- 
sionally in  other  anthropoid  apes. 

The  suprasternal  bones,  very  rarely  seen  in  the 
adult,  are  a  pair  of  rounded  bones  compressed  later- 
ally, about  the  size  of  peas,  placed  on  the  top  of  the 
manubrium  at  the  posterior  border  just  internal  to  the  sterno-clavicular  joint.  They 
are  presumably  the  tops  of  the  lateral  cartilaginous  strips  forming  the  sternum,  in 
which  they  are  normally  lost.  They  are  regarded  as  representing  the  episternum 
of  lower  vertebrates. 

*  Journal  of  Anatomy  aixl  Physiology,  vol.  xxiv.,   1890.     "  Inau.y;.  Disscr.,  Porp.it,  1881. 

1  rrmc-Miv  xipliiiiilcii-. 


Foramen 


Sternum,  showing  foramen  due  to  im- 
perfect union  of  lateral  parts. 


DEVELOPMENT   OF   THE   STERNUM. 


157 


FIG.  181. 
B 


Development  and  Subsequent  Changes. — The  cartilaginous  bars  repre- 
senting the  ribs  in  the  early  embryo  end  in  front  in  a  strip  connecting  them  from  the 
first  to  the  ninth,  which  approaches  its  fellow  above  and  recedes  from  it  below. 
The  union  of  these  two  strips,  which  begins  above,  forms  the  future  sternum  as  far 
as  the  ensiform  cartilage.  Thus  at  this  early  stage  there  are  nine  sternal  ribs.  While 
the  mesosternum  is  forming  by  the  union  of  the  lower  part,  a  portion  of  the  ninth 
strip  separates  itself  from  the  rest  to  fuse  with  its  fellow  for  the  ensiform  cartilage, 
and  the  remainder  of  the  ninth  joins  the  eighth,  which,  as  a  rule,  itself  later  recedes 
from  the  sternum. 

The  original  cartilaginous  strips  having  fused,  points  of  ossification  first  appear 
in  the  manubrium  about  the  sixth  month  of  foetal  life.  There  is  one  chief  one  and 
a  varying  number  of  small  ones  variously  disposed.  Sometimes  it  ossifies  in  a  larger 
upper  and  a  smaller  lower  piece.  In  the  latter  months,  before  birth,  several  points 
appear  in  the  mesosternum.  The  first  piece  generally  has  a  single  centre,  those  below 
two  in  pairs.  At  birth  one  usually  finds  ossification  begun  in  the  first  three  pieces 
of  the  body.  The  centre  for  the  last  piece  of  the  body  begins  to  ossify  at  a  very 
variable  time.  We  have  seen  bone  in  it  at  thirteen  days  and  have  found  none  at 
seven  years.  Perhaps  three  years  is  not  far  from  the  average.  The  centre,  or  cen- 
tres, for  this  last  piece  of  the  body  are  placed  in  its  upper  part.  Its  cartilage  is 
directly  continuous  with  that  of  the 
ensiform,  the  line  of  demarcation 
being  determined  by  the  difference 
in  thickness,  the  ensiform  being 
thinner  and  continuing  the  plane  of 
the  posterior  surface.  Thus,  the 
lower  part  of  the  last  piece  may 
continue  cartilaginous  for  a  con- 
siderable time.  A  centre  in  the 
ensiform  is  sometimes  seen  at  three, 
but  may  not  come  for  several  years 
later.  The  four  pieces  of  the  meso- 
sternum join  one  another  from  be- 
low upward,  the  union  being  com- 
pleted on  the  posterior  surface  first. 
The  process  is  extremely  variable. 
The  only  points  regarding  which  we 
are  certain  are  that  it  is  more  rapid 
than  is  usually  stated  and  that  the 
body  is  almost  always  in  one  piece 
at  twenty.  The  fourth  piece  of  the  body  joins  the  third  at  about  eight,  the  third 
joins  the  second  at  about  fifteen,  and  the  second  unites  with  the  first  usually  at 
eighteen  or  nineteen.  We  once  saw  all  four  pieces  distinct  at  eighteen,  but  in 
one  or  two  instances  only  have  we  found  the  body  incomplete  after  twenty.  The 
amount  of  bone  in  the  ensiform  at  twenty  is  still  small.  The  adult  condition,  except 
that  the  ensiform  gradually  becomes  wholly  bone,  may  persist  to  extreme  old  age. 
The  ensiform  often  joins  the  body  after  middle  age,  rarely  before  thirty.  The 
union  of  the  manubrium  and  the  body  is  rare,  and  appears  to  be  the  result  of  a  con- 
stitutional tendency  rather  than  of  age,  as  in  our  observations  we  have  repeatedly 
found  it  under  fifty,  and  have  seen  all  three  pieces  united  at  twenty-five.  The 
different  pieces  are  more  apt  to  fuse  in  man  than  in  woman. 

ARTICULATIONS    OF   THE    THORAX. 

The  joints  uniting  the  bones  taking  part  in  the  formation  of  the  bony  thorax 
constitute  two  general  groups,  the  Anterior  and  the  Posterior  Thoracic  Articula- 
tions. The  former  include  the  joints  between  the  pieces  of  the  sternum,  those  be- 
tween the  sternum  and  the  costal  cartilages,  and  those  between  the  costal  cartilages  ; 
the  latter,  or  the  costo-vertebral  articulations,  include  those  between  the  vertebrae 
and  the  ribs. 


Ossification  of  the  sternum.  A,  at  sixth  foetal  month  ;  a,  centre 
for  manubrium.  B,  at  birth  ;  a,  for  manubrium  ;  b,  c,  d,  for  seg- 
ments of  body.  C,  at  about  ten  years  ;  a,  manubrium  ;  b,  c,  d,  seg- 
ments of  body  ;  e,  ensiform  cartilage. 


158 


HUMAN   ANATOMY. 


THE   ANTERIOR   THORACIC  ARTICULATIONS. 

These  include  three  sets  : 

i.  The  Intersternal  Joints,  or  those  uniting  the  segments  of  the  sternum  ; 


FIG.  182. 


Sterno-clavicular  joint 


Anterior  intersternal 

ligament 
Chondro-sternal  ligament 


Costo-xiphoid  ligament 


Interchondral  ligament 


The  sternum  and  costal  cartilages  from  before. 


2.  The  Costo-Sternal  Joints,  or  those  uniting  the  ribs  by  means  of  their 
cartilaginous  extensions  with  the  sternum  ; 

3.  The  Interchondral  Joints,  or  those  uniting  certain  of  the  costal  cartilages 
with  one  another. 


INTERSTITIAL   ARTICULATIONS. 


159 


THE    INTERSTERNAL   JOINTS. 

While  the  manubrium  and  the  four  pieces  of  the  body,  or  sternebrse,  are  still 
separate  ossifications  in  a  common  strip  of  cartilage,  the  structure  is  greatly  strength- 

FIG.  183. 


First  rib. 


MANUBRIUM 


Interarticular  ligament 


Chondro-sternal  joint 


BODY 


Interchondral  joint 
ENSIFORM  CARTILAGE 


Interchondral  ligament 


Longitudinal  section  through  sternum  and  costal  cartilages. 


ened  by  the  thick  periosteum,  reinforced  by  the  radiating  bands  from  the  costal 
joints  and  longitudinal  fibres  before  and  behind.  When  the  body  has  become  one 
piece  it  is  separated  from  the  manubrium  by  the  persisting  cartilaginous  strip.  The 


160  HUMAN   ANATOMY. 

strengthening  bands  require  no  further  description.  A  cavity  is  often  found  in  the 
cartilage,  making  a  typical  half-joint.  At  what  time  it  appears  is  unknown.  Some- 
times it  is  so  developed  that  the  joint  is  practically  a  true  one,  with  articular  carti- 
lage ;  this  exceptional  arrangement  is  more  common  in  women  than  in  men,  being 
especially  adapted  to  the  female  type  of  respiration.  The  cartilage  persisting 
between  body  and  ensiform  is  strengthened  in  a  similar  manner.  A  cavity  rarely 
occurs  in  the  cartilage,  which,  on  the  contrary,  often  undergoes  ossification. 

THE  COSTO-STERNAL   JOINTS. 

The  first  costal  cartilage  joins  directly,  without  interruption,  the  lateral  expan- 
sion of  the  sternum  ;  the  following  costal  cartilages  articulate  at  the  points  already 
mentioned  by  synovial  joints.  Those  that  come  between  different  sternebrae — that 
is,  from  the  second  to  the  fifth — often  have  the  joint  subdivided  by  a  band  into  an 
upper  and  a  lower  half.  This  is  usual  in  the  joint  of  the  second  cartilage  ;  progres- 
sively rare  as  we  descend.  The  sixth  and  seventh  cartilages  frequently  have  no 
true  joint.1  Each  of  these  joints  is  enclosed  by  a  capsule,  the  front  and  back  fibres 
of  which  radiate  over  the  sternum. 

THE   INTERCHONDRAL  JOINTS. 

The  seventh,  eighth,  ninth,  and  tenth  costal  cartilages  have  each  an  articulation 
by  a  true  joint  on  the  projections  above  described  with  the  one  above  it.  There  is 
a  connection  between  the  fifth  and  sixth  cartilages  ;  usually  on  the  right,  very 
frequently  on  the  left.2  This  is,  as  a  rule,  also  a  true  joint,  but  the  cartilages  may 
be  merely  bound  together  by  bands  of  fibres.  The  joint  on  the  right  side  is  almost 
always  a  true  one.  The  ends  of  the  eighth,  ninth,  and  tenth  cartilages  are  joined 
by  fibrous  tissue  to  the  cartilage  above. 

The  costo-xiphoid  ligament  is  a  band  extending  from  either  side  of  the  base 
of  the  ensiform  to  the  lower  border  and,  perhaps,  the  front  of  the  seventh  cartilage 
near  its  end. 

THE   COSTO-VERTEBRAL   ARTICULATIONS. 

The  joints  between  the  ribs  and  the  spine  are  in  two  series  :  an  inner,  or 
Costo- Central,  between  the  heads  of  the  ribs  and  the  bodies  of  the  vertebrae  ;  an 
outer,  or  Costo-  Transverse,  between  the  tubercles  and  the  transverse  processes. 

The  Costo-Central  Joints. — The  head  of  the  rib  is  received  in  a  hollow 
articular  fossa  formed  by  a  part  of  two  bodies  and  the  disk  between  them.  Although 
as  a  whole  concave,  it  may  in  a  typical  case  be  further  analyzed.  The  lower  half  of 
the  socket  is  convex  from  above  downward,  fitting  into  the  hollow  at  the  lower  part 
of  the  joint  of  the  rib  ;  the  upper  part  is  about  plane,  looking  downward  and  out- 
ward, with  the  upper  border  considerably  overhanging  the  joint.  These  two  facets 
have  each  a  synovial  capsule  and  are  separated  by  an  inten>ertebral  ligament?  a 
band  running  from  the  ridge  on  the  head  of  the  rib  to  the  posterior  part  of  the  inter- 
vertebral  disk.  In  the  foetus  before  term  it  extends  across  the  back  of  the  disk 
the  head  of  the  opposite  rib. 

The  front  of  the  capsules  is  strengthened  by  the  anterior  costo-rcrfcbral  ligament, ' 
which  is  a  series  of  radiating  fibres  from  the  head  to  both  vertebrae  and  the  interven- 
ing disk,  not  clearly  separable  into  three  bands.  These  stellate  ligaments  (Fig.  184) 
are  least  developed  in  the  upper  part  of  the  thorax.  The  strongest  collection  of 
fibres  is  to  the  lower  vertebra.  The  joint  of  the  first  and  last  two  ribs  is  not  sub- 
divided ;  that  of  the  tenth  is  uncertain.  Strong  fibres  pass  from  the  head  of  the 
first  rib  to  the  seventh  cervical  vertebra.  Few  or  no  fibres  from  the  last  rib  reach 
the  body  of  the  eleventh  thoracic.  The  lower  fibres  are  made  tense  when  the  rib  is 
raised  and  the  upper  when  it  is  depressed. 

The    Costo-Transverse   Joints.— The   articular  surfaces    <>f    the   tubercles, 

'Musgrove:  Journal   of  Anatomy  and   Physiology,  vol.    xxvii.,    1893.     2Fawcett:   Anat. 
Anzeiger,   Ikl.  xv.     Bardeleben  :  ibid. 

•'tig-  cnpltull  costne  intcrartirul.-irc.      '  I. in.  rapitnli  costnc  rndlatum. 


COSTO-TRANSVERSE   ARTICULATIONS. 


161 


convex  vertically,  are  received  into  the  hollows  on  the  facets  of  the  transverse  pro- 
cesses. The  cavities  are  deepest  in  the  upper  part  of  the  thoracic  region,  but  the 
facet  on  the  first  transverse  process  is  nearly  plane.  In  the  lower  part  of  the  region 


FIG.  184. 


VII  rib. 


Superior  costo-trans- 
verse  ligament 


VIII  ri 


Posterior  costo-trans- 
verse  ligament 


IX  rib 


Intervertebral 
foramen 

Upper  part  of  stellate 
ligament 


Lower  part  of  same 


Body  of  ninth  thoracic 
vertebra 


Ligaments  uniting  ribs  with  spine,  from  before. 


these  cavities  are  smaller  and  less  concave,  allowing  freer  motion.  There  is  none 
for  the  twelfth  rib,  and  but  a  poor  one,  if  any,  for  the  eleventh.  There  are  three 
costo-transverse  ligaments :  the  posterior,  the  middle,  and  the  siiperior.  The  pos- 


FIG.  185. 

Transverse  process 
Lamina  of  vertebra  above  of  vertebra  below- 


Middle  costo- 
transverse  liga- 
ment 


Posterior  costo- 
transverse  ligament 


Costo-transverse 
joint 


Middle  costo-trans- 
verse ligament 

Costo-vertebral 
joint 


Interarticular  liga- 
ment 


Intervertebral  disk 


Transverse  section  through  intervertebral  disk  and  ribs. 


terior1  are  strong  bands  running  outward  from  the  tips  of  the  transverse  processes 
to  the  rough  part  of  the  tubercle  beyond  the  joint.  The  middle *  are  strong  short 
fibres  connecting  the  front  of  the  transverse  process  and  the  back  of  the  neck  of  the 

1  Lig.  costotransvcrsarium  posterius.     -  Lig.  colli  costae. 


162 


HUMAN   ANATOMY. 


rib  between  the  head  and  the  tubercle.  Those  for  the  last  two  ribs  are  small,  that 
for  the  twelfth  springing  from  the  accessory  tubercle.  The  superior  costo-transverse 
ligaments '  are  thin  bands,  passing  downward  and  a  little  inward  from  the  under  side 
of  the  transverse  processes  to  the  crest  on  the  upper  edge  of  the  neck  of  the  rib 
below.  Those  of  the  first  and  last  two  ribs  are  of  little  account.  This  band  becomes 
tense  when  the  rib  is  depressed  and  carried  inward  ;  the  inner  fibres  are  tense  when 
the  rib  is  raised.  The  outer  fibres  fuse  with  the  front  surface  of  the  posterior  inter- 
costal aponeurosis.  Weaker  and  inconstant  bands  of  the  same  general  direction  are 
described  behind  these.  The  fibres  of  the  aponeurosis  are  particularly  strong 
between  the  last  two  ribs.  A  special  band  of  the  same  series  runs  from  the 
transverse  process  of  the  first  lumbar  upward  and  outward  to  the  last  rib.  The 
movements  of  the  ribs  are  described  with  those  of  the  thorax  (page  165). 

THE  THORAX   AS   A   WHOLE. 

The  thorax  is  a  cage  with  movable  walls  capable  of  expansion.  In  shape  it  is 
an  irregular  truncated  cone,  much  deeper  behind  than  in  front  and  broader  from  side 
to  side  than  from  before  backward.  The  thoracic  vertebrae  form  the  posterior 


Tubercle 


Lamina  of  VII  thoracic 
vertebra 


Middle  cost o-trans verse 
ligament 

Posterior  costo-transverse, 
ligament 


Superior  costo-transverse 
ligament 

Ligamentum  subflavum 


Intertransverse  ligament 


'' 


VII  thoracic  rib 


VIII  rib 


IX  rib 


Ligaments  uniting  ribs  with  spine,  from  behind. 


boundary  ;  the  sternum,  including  the  very  beginning  of  the  ensiform  cartilage,  th 
anterior.  The  inlet,  or  upper  boundary,  is  an  imaginary  plane  slanting  downward 
and  forward  from  the  top  of  the  first  thoracic  vertebra  to  that  of  the  sternum,  and 
bounded  laterally  by  the  inner  borders  of  the  first  rib.  The  inferior  boundary,  made 
by  the  diaphragm,  does  not  exist  in  the  skeleton.  Suffice  it  to  say  that  the  dome- 
like disposition  of  the  diaphragm  makes  the  abdomen  much  larger  and  the  thorax 
much  smaller  than  one  would  expect  from  the  skeleton  alone.  The  thorax  of  the 
living  presents  a  fairly  well-defined  posterior  surface,  while  the  lateral  ones  pass  in- 
sensibly into  the  anterior  ;  the  upper  part  is  hidden  by  the  shoulder-girdle  and  arm. 
The  line  of  the  angles  of  the  ribs  marks  the  limits  of  the  back  and  sides.  The  inside 
of  the  thorax  is  heart-shaped  in  horizontal  section.  The  spine  projects  into  it  behind, 
and  the  ribs  recede  from  this  on  either  side.  As  the  bodies  of  the  vertebra  are 
larger  in  the  lower  part,  the  projection  into  the  thorax  is  greater  :  but  as  the  area  of 
the  section  is  much  larger,  the  effect  is  less  striking.  The  distance  from  front  to 

1  Lig.  costotninsM-i-.ni  iiim  iintcrlus. 


THE   THORAX   AS   A   WHOLE. 


163 


back  in  the  median  line  is  least  at  the  top.  It  increases  at  once,  owing  to  the  back- 
ward bend  of  the  spine  and  the  forward  slant  of  the  sternum,  reaching  the  maxi- 
mum at  about  the  middle  of  the  thorax.  It  decreases  slightly  below,  owing  to  the 
forward  sweep  of  the  spine,  but  the  position  of  the  lower  end  of  the  sternum  is  so 
uncertain  that  this  is  very  variable.  The  breadth  of  the  thorax  increases  very 
rapidly,  reaching  nearly  the  maximum  where  the  third  rib  crosses  the  axillary  line. 
Below  this  it  increases  a  little,  being  greatest  where  the  fifth  rib  crosses  the  same 


The  bony  thorax,  lateral  view. 

line.  It  then  continues  very  nearly  the  same  with  some  slight  diminution  below. 
The  greatest  length  of  the  thoracic  framework  is  in  the  axillary  line,  the  lowest 
point  being  the  cartilage  of  the  tenth  or  eleventh  rib,  which  in  the  male  may  nearly 
reach  the  crest  of  the  ilium.  The  downward  slant  of  the  ribs  and  the  rise  of  most  of 
the  cartilages  make  the  study  of  horizontal  sections  at  first  very  confusing.  The 
relations  at  certain  levels  must  be  somewhat  conventional,  for  the  variations  are  very 
great,  depending  on  figure,  age,  health,  position,  and  the  stage  of  the  respiratory 
movements.  Two  levels  must  be  taken  as  standards,  subject  to  these  corrections. 


164 


HUMAN   ANATOMY. 


The  top  of  the  sternum  is  on  a  level  with  the  disk  between  the  second  and  third 
thoracic  vertebrae  ;  the  junction  of  manubrium  and  body  of  sternum  is  on  a  level 


FIG.  188. 


FIG.   189. 


Transverse  section  through  thorax  at  level  of 
third  thoracic  vertebra.     (Sraune.) 


Transverse  section  at  level  of  fourth  thoracic 
vertebra.     (Braune.) 


"0 
-0 


Transverse  section  at  level  of  eighth  thoracic  vertebra. 
(Braune.) 


with  the  top  of  the  fifth  thoracic  vertebra.      Less  accurate,  but  still  useful,  is  a  third 

level  :   the  lower  end  of   the  body  of  the  sternum  is  opposite  the  ninth  thoracic 

vertebra.     Accompanying  diagrams, 

FIG.  190.  taken  from  Braune,  show  the  varia- 

C~~_J3  tions  of  size,  form,  and  relations  at 

different  levels  (Figs.  188  to  191). 

The  breadth  of  the  intercostal 
spaces  is  very  different  in  diverse 
parts.  Between  the  tubercles  and 
angles  it  is  pretty  nearly  the  same 
Q  5  throughout, butthelasttwo  spaces  are 
a  little  broader.  The  first  two  spaces 
are  much  the  broader  at  the  sides 
and  in  front.  They  are  broad  near 
the  sternum  as  far  down  as  the  fifth 
cartilage.  At  the  sides  the  ribs  are 
very  close  together,  from  the  fourth 
to  the  ninth  often  almost  in  contact. 
The  lowest  spaces  are  again  broader. 
The  Thorax  in  Infancy  and  Childhood. — At  birth  the  thorax  is  relatively 

insignificant.     The  sternum  is  small  and  undeveloped  in  the  lower  part.     The  ribs 

are  more  horizontal.     The  top  of 

the  sternum  is  opposite  the  body  FIG.  191. 

of  the  first  thoracic  vertebra.      In  7 

the  course  of  the  first  year  it  lies 

opposite    the    upper   part   of    the 

second,    and    at   five   or    six    has 

reached  its  definite  level  opposite 

the  disk  between  the  second  and 

third  thoracic  vertebrae.     The  lower 

part  of  the  sternum  is  undeveloped, 

and  the  ribs  do  not  fall  so  low  at 

the  sides.     The  want  of  breadth  is 

very  striking,  while  in  the  adult, 

throughout    the    chest    below    the 

level  of  the  second  costal  cartilage, 

the  antero-posterior  diameter  is  to 

the  transverse  as   i   to  2*4,  or  as 

i  to  3  ;  at  birth  it  is  as   2   to   3. 

We    have    found    it    at    probably 

three  years  as  i  to  2  ;  at  five  or  six  the  thorax  has  nearly  reached  its  permanent 

shape. 

Differences  due  to  Sex. — The  whole  structure  is  lighter  in  women,  but  the 


'<? 
•0 


Transverse  section  at  level  of  elcvi-ntli  \vru-bra.     Shaded  areas 
(6,  7)  are  sections  of  costal  cartilages.     ( /•'*  aum\  i 


MOVEMENTS   OF   THE   THORAX.  165 

chief  differences  in  the  proportions  appear  below  the  third  rib.  The  manubrium  is 
as  large,  relatively  to  the  height,  in  one  sex  as  the  other,  although  the  mesosternum 
in  women,  especially  its  lower  part,  is  less  developed  ;  hence  the  ends  of  the  car- 
tilages of  the  lower  sternal  ribs  are  crowded  together,  and  those  of  the  seventh  often 
meet  below  the  sternum,  in  front  of  the  ensiform,  thus  practically  lengthening  the 
body.  The  effect  of  this  is  that  the  relations  of  the  viscera  to  the  walls  are  not  so 
different  in  the  sexes  as  one  would  expect.1  The  floating  ribs  are  small  in  women 
and  do  not  approach  the  pelvis  so  closely  as  in  the  male.  The  antero-posterior 
diameter  of  the  female  chest  is  to  the  transverse  as  i  to  2^  (subject  to  variation), 
thus  more  resembling  the  proportions  of  the  child. 

THE  MOVEMENTS  OF  THE  THORAX. 

The  motions  permitted  by  the  following  joints  are  to  be  considered  separately, 
although  their  interdependence  is  to  be  remembered.  First,  the  joints  of  the  verte- 
bral ends  of  the  ribs,  the  costo-central  and  the  costo-transverse  being  taken  together  ; 
second,  those  between  the  manubrium  and  gladiolus  ;  third,  the  costo-sternal  and 
interchondral  joints  ;  fourth,  as  modifying  these,  flexion  and  extension  of  the  spine  ; 
and  fifth,  the  elasticity  of  the  ribs  and  cartilages. 

Motions  in  the  Costo-Vertebral  Joints. — These  vary  greatly  in  different 
parts  of  the  column.  The  first  rib  moves  as  a  hinge  on  a  fixed  axis  running  out- 
ward, backward,  and  a  little  upward  through  the  joint  on  the  body  of  \he  verte- 
bra and  that  on  the  transverse  process.  If  this  axis  were  strictly  transverse,  the 
rising  of  the  front  of  the  rib  would  increase  only  the  antero-posterior  diameter  of  the 
thorax,  as  the  motion  occurs  in  a  plane  at  right  angles  to  the  axis.  Since,  however, 
the  axis  is  oblique,  a  plane  at  right  angles  to  it  extends  forward  and  outward,  and 
motion  in  it  thus  increases  also  the  transverse  diameter  of  the  chest.  The  shape  of 
the  first  rib  is  such  that  this  transverse  increase  amounts  to  little  or  nothing,  but  this 
principle  comes  into  play  with  the  longer  ribs.  The  joint  of  the  second  rib  is  prac- 
tically similar,  except  that  the  outer  end  of  the  axis  at  the  tubercle  is  farther  back, 
so  that  the  plane  of  motion  slants  more  outward  and  the  lateral  expansion  gained 
by  raising  the  second  rib  is  more  marked  independently  of  the  greater  length  of  that 
rib.  With  the  third  rib,  usually,  an  important  modification  begins  ;  the  outer  end 
of  the  axis  is  not  fixed,  for  the  tubercle  slides  on  the  transverse  process.  The 
changes  in  the  facets  on  the  transverse  processes  have  been  described  ;  it  appears 
that,  as  we  descend  the  spine,  they  are  so  placed  and  so  shaped  as  to  allow  this 
movement  more  and  more  freely.  Thus,  in  the  middle  of  the  thoracic  region  the 
outer  end  of  the  axis  of  rotation  is  so  movable  that  the  motion  is  to  be  decomposed 
into  two, — namely,  one  on  the  axis  already  described  through  the  head  and  the 
tubercle,  and  another  on  an  antero-posterior  axis  passing  through  the  head  of  the 
rib  and  the  joint  between  its  costal  cartilage  and  the  sternum.  At  the  eighth  rib  of 
the  dissected  spine  a  new  motion  appears,  which  becomes  much  more  extensive 
in  the  succeeding  ones.  The  ligaments  connecting  the  tubercle  and  neck  to  the 
transverse  process  are  less  tense,  and  it  is  possible  to  move  the  tubercle  a  little 
forward  from  its  socket  ;  in  the  lower  joints  the  rib  can  be  moved  upward,  down- 
ward, forward  and  backward,  and  circumducted.  These  motions  are  particu- 
larly free  at  the  last  two  thoracic  vertebrae.  Motion  backward  is  checked  by 
contact  with  the  transverse  process  ;  forward,  by  the  posterior  and  middle  costo- 
transverse  ligaments  ;  upward  motion  of  the  last  two  ribs  by  the  particularly  strong 
bands  of  fascial  origin  described  with  the  ligaments  ;  downward  motion  by  the  in- 
tercostal structures.  An  important  deduction  from  this  is  that  the  last  ribs  can 
be  pulled  downward  and  backward,  so  as  to  fix  the  posterior  costal  origin  of  the 
diaphragm. 

Motions  in  the  Intersternal  Joints. — The  joint  between  the  manubrium 
and  the  body  of  the  sternum  admits  of  motion  on  a  transverse  axis,  which  is  free  in 
the  young,  but  much  restricted  or  abolished  in  the  old.  At  rest,  the  two  parts  form 
a  slight  angle  open  behind.  This  is  effaced  by  the  forward  motion  of  the  body  on 

1  Henke  :  Arch,  fur  Anat.  u.  Phys.,  Anat.  Abtheil,  1883. 


1 66  HUMAN   ANATOMY. 

the  manubrium,  but  in  no  case  is  an  entering  angle  formed  in  front.  A  slight  twisting 
may  also  occur  in  this  joint  in  the  young.  In  these  motions  the  second  costal 
cartilages  follow  the  manubrium.  The  motions  at  the  inconstant  joint  between  the 
sternal  body  and  the  ensiform  process  are  necessarily  indefinite  ;  they  appear  to 
consist  chiefly  of  a  drawing  in  of  the  ensiform. 

Motions  in  the  Costo-Sternal  and  the  Interchondral  Joints. — On  the 
dissected  preparation  the  second  cartilage  can  be  moved  up  and  down,  forward  and 
backward,  and  circumducted  ;  these  motions,  however,  are  very  slight.  In  the 
succeeding  joints  the  same  motions  are  more  and  more  free  as  we  descend.  The 
lower  cartilages  of  the  true  ribs  from  the  fifth  to  the  seventh,  or  to  the  eighth,  inclu- 
sive, should  the  latter  meet  the  sternum,  move  in  a  somewhat  similar  manner,  but 
nearly  as  in  one  piece.  The  motion  on  an  antero-posterior  axis  is  most  free.  The 
joints  between  the  costal  cartilages  are  very  lax,  and  the  surfaces  are  so  placed  that 
the  lower  one  slides  forward  on  the  upper.  The  advantage  of  these  joints  is  that 
the  lower  ribs  and  the  thorax  give  and  receive  support,  while  greater  freedom  of 
motion  is  possible  than  would  be  the  case  were  they  of  one  piece.  Flexion  and 
extension  of  the  spine  modify  these  motions.  The  more  the  spine  is  flexed  the  more 
the  upper  ribs  in  particular  are  depressed,  and  the  more  it  is  extended  the  more  they 
are  raised,  independently  of  any  motion  in  the  joints.  Thus,  when  the  chest  is 
fully  inflated  the  spine  is  always  strongly  extended. 

The  elasticity  of  the  ribs  and  cartilages,  particularly  of  the  latter,  exercises  an 
important,  but  indefinite,  influence  on  all  motions  which  does  not  admit  of  accurate 
analysis.  Even  the  ribs  (except  in  the  old)  are  not  rigid  bars,  and,  especially  in 
forced  inspiration,  there  is  a  pull  upon  them  increasing  their  convexity.  Moreover, 
the  walls  of  the  chest  adapt  themselves  to  the  surface  of  the  lungs  and  to  abnormal 
contents  of  the  thorax,  so  that  certain  conditions  are  marked  by  particular  forms  of 
thorax. 

It  follows  from  the  above  that  the  nature  of  the  respiratory  movements  cannot 
be  deduced  solely  from  the  movements  of  each  set  of  joints  considered  separately. 
The  soft  parts  connecting  them  alone  modify  greatly  the  freedom  of  motion.  Braune 
has  shown  that  the  motion  of  the  ribs  is  much  limited  by  the  sternum,  and  that  if 
the  gladiolus  be  divided  into  its  original  pieces  and  the  cartilage  above  it  cut  through, 
the  thorax  can  be  more  fully  inflated.  Beyond  question  in  forced  inspiration  the 
sternum  is  raised,  thus  increasing  the  antero-posterior  diameter  ;  since  the  ribs  at 
the  same  time  swing  upward  and  outward,  the  transverse  diameter  is  likewise 
increased. 

Surface  Anatomy. — The  sternum  is  always  to  be  felt  in  the  middle  line. 
The  suprasternal  notch  is  filled  up  to  a  large  extent  by  the  interclavicular  ligament. 
The  angle  between  the  manubrium  and  the  body  varies  considerably,  but  it  is  always 
easily  recognized  by  a  cross-ridge.  The  ensiform  cartilage  is  at  a  deeper  level  and 
overhung  on  each  side  by  the  costal  arch.  The  front  of  the  chest  on  each  side  is 
covered  by  the  pectoralis  major,  making  it  hard  to  feel  the  ribs,  except  at  the  borders 
of  the  sternum.  At  the  side  they  are  easily  felt  to  near  the  top  of  the  axilla,  where 
the  third  can  be  recognized. 

The  upper  ribs  are  concealed  by  thick  muscles,  especially  between  the  spine 
and  the  angles.  The  scapula  covers  them  from  the  second  to  the  seventh,  with 
considerable  variations.  The  first  rib  cannot  be  felt  except  where  its  cartilage 
joins  the  sternum.  To  count  the  ribs,  begin  with  the  second  at  the  junction  of  the 
manubrium  and  body  of  the  sternum.  There  is  no  possibility  of  error,  for  the  rare 
cases  of  the  manubrium  reaching  to  the  third  cartilage  may  be  disregarded  ;  feel  the 
third  and  fourth  cartilages  below  it,  and  then  carry  the  finger  downward  and  out- 
ward across  the  chest.  The  twelfth  rib  may  be  too  small  to  be  made  out.  It  is  not 
safe  to  begin  counting  from  below,  for  the  error  of  mistaking  the  eleventh  rib  for 
the  twelfth  has  led  to  opening  the  pleural  cavity  in  an  operation  in  the  lumbar 
region.  The  nipple  is  said  to  be  usually  over  the  fourth  intercostal  space  some  two 
centimetres  external  to  the  cartilage,  but  it  is  very  variable,  especially  in  women, 
and  should  never  be  used  as  a  starting-point  for  counting  the  ribs.  The  width 
of  the  intercostal  spaces  at  different  parts  is  of  obvious  importance,  but  has  been 
described  elsewhere  (page  164). 


PRACTICAL   CONSIDERATIONS  :    THE   THORAX.  167 

PRACTICAL   CONSIDERATIONS. 

The  bony  and  cartilaginous  thorax  is  made  up  of  the  ribs,  sternum,  costal  car- 
tilages, and  thoracic  vertebrae,  and  varies  in  shape  as  a  result  of  several  influences. 
The  slightly  larger  circumference  of  the  right  side  of  the  chest  as  compared  with 
the  left  side  is  probably  due  to  the  greater  use  of  the  right  upper  limb,  and  may 
be  accepted  as  physiological.  Increased  circumference  of  the  left  side,  therefore  (in 
a  right-handed  person),  should  indicate  careful  examination  of  the  spine  (for  lateral 
curvature)  and  of  the  thoracic  viscera. 

In  pigeon-breast  the  sternum  protrudes  together  with  the  costal  cartilages,  while 
the  line  of  the  costo-chondral  junction  becomes  a  deep  groove.  The  sides  of  the 
chest  are  flattened,  and  a  transverse  section  would  be  almost  triangular  in  shape. 
There  are  three  modes  of  production  of  this  very  common  deformity  : 

1.  In  rickety  children  it  is  favored  by  the  softening  of  the  bones  and  cartilages, 
which  are  thus  of  diminished  resiliency,  the  actual  exciting  cause  being  often  some 
form   of    respiratory   obstruction, — e.g. ,    enlarged    pharyngeal  and   faucial    tonsils, 
bronchitis,  nasal  obstructions,  etc.      In  ordinary  breathing,  on  inspiration,  air  enters 
the  chest  freely  to  prevent  the  production  of  a  vacuum,  and  at  the  end  of  the  act 
the  external  atmospheric  pressure  is  balanced  by  the  pressure  within.      If  an  impedi- 
ment to  the  free  ingress  of  air  exists,  the  external  pressure  during  at  least  part  of 
the  act  is  in  excess,  and  in  young   children,   particularly  rickety  children,   this  is 
followed  by  the  bending  inward  along  the  weakest  part  of  the  thorax  (the  costo- 
chondral  line)  and  the  relative  projection  of  the  sternum. 

2.  The  lowest  five  costal  cartilages  form  an  especially  weak  portion  of  the  chest- 
wall.     They  are  the   most  distant  from  the  fulcrum  (the  spine)  on  which  the  ribs 
move  in  respiration,  and  hence  the  expansive  forces  act  with  the  greatest  disadvan- 
tage of  leverage  (Humphry).     At  the  same  time  the  diaphragm,  during  its  contrac- 
tion,  tends  to  draw   them  inward.       If,   however,   its  central  arch  cannot  descend 
during  inspiration  on  account  of  an  engorged  liver,  enlarged  abdominal  lymphatics, 
persistent  flatulence,  etc.  (as  in  a  poorly  nourished  child),  it  becomes  the  fixed  point, 
and  the  lateral  walls  are  pulled  in  and  the  sternum  correspondingly  protruded. 

3.  Some  cases  of  "  pigeon-breast"  are  seen  at  or  soon  after  birth  in  otherwise 
healthy  children.      It  is  probable  that  these  are  cases  of  arrest  of  development.     The 
so-called  "  keeled  chest  "-  (in  which  the  antero-posterior  diameter  is  increased  at  the 
expense  of  the  transverse   diameter)  is  characteristic  of  the  quadrupedal  class  of 
mammals,  and  is   necessitated  by,  and  correlated  with,  the  backward  and  forward 
swing  of  the  anterior  limbs  in  walking.1      In  the  foetus  the  antero-posterior  diameter 
is  relatively  greater  than  in  the  adult. 

Attention  has  already  been  called  (page  164)  to  the  varying  ratio  between  the 
antero-posterior  and  transverse  diameters  of  the  chest,  the  transverse  diameter  in 
the  adult  exceeding  the  anterior  in  the  proportion  of  2.5  to  i.  If  this  change  stops 
short  of  full  completion,  a  greater  or  less  degree  of  relative  prominence  of  the  ster- 
num results. 

The  ' '  bellows  chest " 2  is  found  among  mammals  almost  exclusively  in  the  bats, 
the  anthropoid  apes,  and  man,  that  have  in  common  simply  the  disuse  of  the  anterior 
limbs  as  a  means  of  support.  In  them  the  chief  movements  of  these  limbs  tend  to 
pull  the  sternum  towards  the  vertebral  column.  The  exaggeration  of  this  type  results 
in  the  so-called  "flat  chest,"  which  is,  however,  within  proper  limits,  the  type  of 
vigor,  as  it  results  from  the  full  contraction  of  normal  muscles. 

Emphysema  produces  a  rotund  configuration  of  the  chest-walls,  affecting  chiefly 
the  upper  portion,  throwing  out  the  ribs,  effacing  the  intercostal  spaces,  and  making 
the  thorax  "barrel-shaped." 

Old  age,  owing  to  an  increased  bowing  of  the  thoracic  spine  under  the  weight 
of  the  head  and  shoulders  and  to  a  slipping  forward  of  Jhe  shoulder-girdle  with  its 
mass  of  muscles,  often  causes  a  depression  of  the  sternum  and  its  approximation  to 
the  spine, — a  common  form  of  flat  chest. 

1  Woods  Hutchinson  :  Journal  of  the  American  Medical  Association,  vol.  xxix.,  1897. 
1  Ibid. 


1 68  HUMAN   ANATOMY. 

The  pulmonary  capacity  is  but  roughly  indicated  by  the  circumference  of  the 
chest,  as  the  vertical  diameter  is  also  obviously  an  important  determining  factor. 
Chest  measurements,  to  be  of  value,  should  therefore  be  supplemented  by  investiga- 
tion into  the  amount  of  air  which  can  be  inhaled  and  exhaled.  The  resulting 
information  is  often  of  great  value  as  a  basis  for  prognosis  and  for  advice  as  to  exer- 
cise and  hygiene,  especially  in  persons  with  a  predisposition  to  pulmonary  disease. 

In  the  infant  the  thorax  is  relatively  smaller  than  in  the  adult.  In  the  female 
the  upper  portion  of  the  thorax  is  less  compressed  from  before  backward  and  is 
more  capacious  than  in  the  male.  The  upper  aperture  is  larger  and  the  range  of 
movement  between  the  upper  ribs  and  the  sternum  and  vertebrae  is  greater.  These 
circumstances  account  both  for  the  fulness  of  the  upper  portion  of  the  chest  in  the 
female  and  for  the  character  of  the  respiratory  movement,  which  is  known  as 
thoracic ;  while  that  of  the  male,  in  which  the  lower  ribs  and  abdominal  walls  move 
more  freely,  is  known  as  the  abdominal  type  of  respiration. 

The  sternum  may  be  entirely  wanting,  or  may  be  divided  into  two  portions  by 
a  fissure  down  the  middle,  the  result  of  developmental  failure,  which,  when  it  exposes 
the  thoracic  cavity  and  the  heart,  is  known  as  cctopia  cordis. 

Its  subcutaneous  position  makes  it  the  subject  of  slight  but  frequent  traumatisms, 
which  often  serve  to  localize  the  bone  lesions  of  syphilis,  tuberculosis,  and  other 
infections  ;  and  this  fact,  in  conjunction  with  its  cancellous  structure,  accounts  for 
the  frequency  with  which  it  is  the  seat  of  gummatous  periostitis  and  tuberculous 
caries.  There  are  sometimes  little  circular  defects  in  the  body  of  the  sternum, 
through  which  an  abscess  may  pass  from  the  mediastinum  outward,  or  infections  from 
without  may  find  their  way  within  the  thorax.  They  are  congenital  defects  due  to 
a  failure  of  the  two  halves  of  the  body  of  the  sternum  to  unite. 

The  seven  depressions  on  each  side  of  the  sternum  for  the  reception  of  the 
cartilages  of  the  seven  true  ribs  are  so  shaped  that  the  upper  and  anterior  edges  of 
each  notch  are  more  prominent  and  larger  than  the  lower  and  posterior  edges. 
This  accounts  for  the  rarity  of  luxation  forward  of  these  cartilages  and  their  ribs  by 
the  forces  which  so  constantly  pull  the  ribs  upward  and  forward,  as  the  action  of  the 
scaleni  and  intercostals  in  violent  inspiratory  efforts,  that  of  the  pectorals  in  swinging 
by  the  hands  or  on  parallel  bars,  etc. 

Backward  dislocation  at  the  chondro-sternal  junction  is  even  rarer  ;  but  this  is 
because,  owing  to  the  elastic  curves  of  the  ribs,  the  sternum  and  the  anterior 
extremities  of  the  ribs  move  backward  together  on  the  application  of  direct  force  to 
the  front  of  the  chest. 

As  it  is  thus  movable,  and  is  supported  on  the  ends  of  elastic  levers  or  springs, 
the  sternum  is  rarely  fractured.  When  the  fracture  is  the  result  of  indirect  violence, 
it  is  often  associated  with  injuries  to  the  spine,  as  the  extreme  extension  or  extreme 
flexion,  which  is  the  common  cause  of  a  sternal  fracture,  must  necessarily  put  a 
severe  strain  on  the  thoracic  spine. 

In  extension  the  sternum  is  fixed  between  the  sterno-mastoids  and  sterno- 
hyoids  and  thyroids  above  and  the  recti  and  diaphragm  below.  In  flexion  the 
force  may  be  transmitted  through  the  chin.  In  either  case  the  most  common  seat 
of  fracture  is  at  or  about  on  a  line  with  the  second  costal  cartilage,  because  (a)  the 
bone  there  is  narrowest  (Fig.  173),  and  (£)  at  that  level  lies  the  junction  between 
the  manubriuin  and  body.  As  the  various  portions  of  the  bone  are  not  united 
until  about  twenty  years  of  age,  fracture  is  almost  unknown  before  that  time. 
Moreover,  during  that  period  the  symphysis  between  the  manubrium  and  the  body 
is  so  shaped  that,  together  with  the  natural  curve  forward  of  the  bone,  it  increases 
the  elasticity  of  the  sternum  and  enables  it  to  resist  both  direct  violence  and  tensile 
strain. 

The  projection1  at  the  union  between  the  manubrium  and  body  (a)igu/i(s 
Lndorici}  is  sometimes  exceptionally  prominent,  and  when  this  is  noticed  for  the 
first  time  after  an  accident  or  an  illness,  may  give  rise  to  the  erroneous  diagnosis  of 
fracture  or  of  bone  disease.  This  angle  is  increased  in  phthisis,  owing  to  the  reces- 
sion of  the  manubrium  ;  it  is  inn-rased  in  emphysema,  as  the  second  ribs  carry  for- 
ward the  lower  border  of  the  manubrium. 

The  greater  thickness  and  strength  of  the  layer  of   fibrous  tissue  that  cmns 

1  Angulu*  sterni. 


PRACTICAL   CONSIDERATIONS  :    THE   THORAX.  169 

the  posterior  surface  of  the  sternum,  as  compared  with  that  on  the  anterior  surface, 
account  for  the  rarity  with  which  effusions  of  blood  or  collections  of  purulent  fluid 
rind  their  way  to  the  anterior  mediastinum. 

The  ribs,  in  addition  to  the  already  described  classification  into  sternal, 
asternal,  and  floating,  are  sometimes  designated  as  upper  and  lower.  It  may  be 
well  to  mention  that  the  term  ' '  upper' '  includes  the  first  six  ribs,  which  have  convex 
lower  borders,  give  origin  to  the  pectoralis  major  (an  elevator  of  the  ribs),  and  move 
upward  in  inspiration  ;  while  the  term  "lower"  applies  to  the  last  six  ribs,  which 
have  concave  lower  borders,  give  origin  to  the  diaphragm  (a  depressor  of  the  ribs), 
and  move  downward  in  inspiration. 

The  obliquity  of  the  ribs  adds  greatly  to  their  range  of  movement  in  respiration. 
The  most  oblique  rib,  the  longest,  and  the  most,  movable — the  seventh — is  a  part 
of  the  wall  of  that  portion  of  the  thorax  that  contains  the  largest  amount  of  pulmo- 
nary tissue.  The  most  fixed  and  most  nearly  horizontal  of  the  ribs  (and  the  shortest 
of  the  sternal  ribs) — the  first — is  a  part  of  the  wall  where  the  least  lung  tissue  is  to 
be  found.  The  ribs  below  the  eighth  have  less  and  less  relation  to  the  lungs,  and 
become  both  shorter  and  more  horizontal.  They  have  increased  mobility  as  regards 
their  anterior  ends,  but  lessened  rotation  on  a  line  drawn  between  their  two  extrem- 
ities, the  movement  most  important  in  respiration. 

These  facts  have  relation  to  the  distribution  of  acute  and  chronic  disease  in 
the  lungs  :  the  acute  affecting  particularly  the  area  of  greatest  movement  and  vas- 
cularity,  the  bases  ;  the  chronic,  the  area  of  lessened  mobility  and  expansion,  the 
apices. 

The  involuntary  partial  immobilization  of  the  chest-wall  after  injury  and  in 
inflammatory  affections  of  the  pleura  is  of  some  diagnostic  value,  as  is  also  the 
permanent  restriction  of  its  movements  following  the  contraction  of  old  adhesions, 
as  after  a  pleurisy,  or  pleuro-pneumonia,  or  fibroid  phthisis. 

The  obliquity  of  the  ribs  serves  also  the  purpose  of  securing  the  necessary 
expansion  of  the  chest  with  the  least  possible  motion  in  the  joints  between  the  ribs 
and  the  spine  and  between  the  cartilages  and  the  sternum.  They  are  thus  but  little 
liable  to  strain,  and,  in  spite  of  their  unceasing  movement  during  life,  are  very  rarely 
the  seat  of  either  dislocation  or  disease. 

At  the  articulation  of  the  ribs  with  the  spine  the  provision  for  preventing  the 
ascent  of  the  ribs  during  the  action  of  the  inspiratory  muscles  (similar  to  that  at  the 
costo-sternal  junction)  is  seen  in  the  fact  that  the  articulating  surface  of  the  upper 
vertebra  entering  into  the  joint  stands  out  more  boldly  than  that  of  the  lower  one. 
The  participation  of  the  intervertebral  disks  in  the  costo-vertebral  articulation  gives 
greater  safety  to  those  joints  and  adds  to  the  elasticity  of  the  whole  thorax  by 
furnishing  a  resilient  buffer  which  takes  up  and  distributes  forces  directed  against 
the  chest-wall. 

Variation  in  the  development  of  the  costal  element  of  the  seventh  cervical 
vertebra  (page  129)  may  result  in  the  production  of  a  cervical  rib.  This,  growing 
beyond  its  ordinary  limits,  sometimes  reaches  half-way  to  the  sternum,  running 
parallel  to  the  first  rib,  with  which  its  anterior  end  is  sometimes  joined.  Occasion- 
ally a  process  grows  up  from  the  first  rib  to  meet  it.  This,  or  the  cervical  rib  itself, 
may  raise  the  subclavian  artery  and  give  rise  to  a  mistaken  diagnosis  of  aneurism, 
or  may  be  thought  to  indicate  chronic  (tuberculous  or  syphilitic)  infection  of  bone, 
and  lead  to  unnecessary  operation  or  treatment. 

As  a  result  of  rickets,  changes  often  take  place  at  the  chondro-costal  junctions, 
causing  beaded  ribs  when  a  few  bones  only  are  affected,  or  the  ' '  rickety  rosary' ' 
when  the  enlargements  are  bilateral  and  numerous. 

The  ribs  most  frequently  broken  are  the  sixth,  seventh,  and  eighth  ;  the  first 
and  second  are  protected  by  the  clavicle  ;  the  lower  two  by  their  small  size  and  great 
mobility.  The  most  common  form  of  muscular  action  causing  fracture  is  coughing  ; 
sneezing  and  lifting  heavy  weights  have  had  the  same  effect.  The  lower  ribs  are 
most  frequently  broken  in  this  way.  When  the  first  rib  is  broken,  a  character- 
istic symptom  is  said  to  be  pain  behind  the  upper  part  of  the  sternum  on  lifting 
with  the  hand  on  the  injured  side.  This  may  be  due  to  the  fact  that  the  first 
thoracic  nerve  lies  for  about  two  inches  in  contact  with  the  under  surface  of  the  first 


ijo  HUMAN   ANATOMY. 

rib,  and  ends  at  or  near  the  region  mentioned,  pain  being  often  referred  to  the 
peripheral  ends  of  sensory  nerves. 

In  fractures  by  indirect  violence  (when  the  sternum  and  spine  are  forced 
together),  the  theoretical  point  of  fracture  would  be  at  or  about  the  summit  of  the 
arch  ;  but  practically  it  is  often  found  very  near  the  point  at  which  the  force  is  apt 
to  be  received, — i.e.,  an  inch  or  two  outside  of  the  sternal  extremity. 

Unless  the  force  has  been  great,  there  is  but  little  displacement  in  fracture  of  a 
rib,  owing  to  the  splinting  of  the  bone  between  the  two  sets  of  intercostal  muscles 
above  and  below  it.  Shortening  is  absent,  unless  an  extensive  crush  of  the  whole 
side  of  the  chest  has  occurred,  because  the  two  ends  of  the  bone  are  fixed,  and 
because  of  the  unbroken  bones  above  and  below  the  fractured  one.  The  complica- 
tions are  those  obviously  due  to  the  proximity  of  the  pleura  and  lung  on  the  inner 
surface  of  the  fracture,  the  common  results  of  wounds  of  those  structures  being 
various  degrees  of  haemothorax,  or  pneumothorax,  or  sometimes  (by  valvular  action) 
emphysema  of  the  cellular  tissue  of  the  trunk  (page  1865). 

Broken  ribs  always  unite  with  a  considerable  amount  of  ensheathing  or  pro- 
visional callus,  due  to  the  motion  which  to  some  degree  must  be  present  between 
the  fragments  during  the  process  of  union. 

Rupture  of  an  intercostal  artery  (unless  associated  with  a  wound  of  the  pleura) 
is  not  usually  a  serious  complication  ;  but  occasionally  it  is  necessary  to  arrest 
hemorrhage  from  this  vessel.  It  lies  between  the  inner  and  outer  intercostal  muscles 
in  the  groove  running  along  the  lower  part  of  the  inner  surface  of  each  rib.  The 
collateral  branch  runs  near  the  upper  surface  of  the  ribs.  Midway  between  the  ribs 
is,  therefore,  the  safest  place  to  introduce  a  trocar  or  to  make  an  incision  in  opening 
the  chest.  The  intercostal  spaces  are  wider  in  the  antero-lateral  parts  of  the  chest 
than  they  are  more  posteriorly,  especially  in  the  neighborhood  of  the  seventh  rib  ; 
they  are  narrowest  in  close  proximity  to  the  sternum  and  spine.  They  can  be 
widened  by  bending  the  body  to  the  opposite  side. 

For  paracentesis  of  the  thorax  the  centre  of  the  sixth  or  seventh  space  should  be 
selected  in  the  mid-axillary  line.  The  lower  spaces  are  in  too  close  proximity  to  the 
diaphragm,  especially  on  the  right  side.  More  anteriorly  it  is  also  in  danger  ;  farther 
posteriorly  the  intercostal  artery  (which  runs  more  horizontally  than  the  ribs) 
crosses  the  space  obliquely,  and  behind  the  angles  the  ribs  are  covered  by  the  thick 
muscles  of  the  back. 

The  ribs  are  frequently  subject  to  infectious  disease.  Syphilis  and  tubercu- 
losis often  produce  periostitis  or  caries,  and  they  are  more  often  the  seat  of  post- 
typhoidal  osteitis  than  any  other  bones  of  the  skeleton.  This  is  due  to  their 
subcutaneous  position  exposing  them  to  frequent  traumatisms  and  to  the  similar 
effects  produced  by  the  numerous  strains  through  muscular  action  in  coughing  and 
sneezing  and  in  lifting  or  straining. 

Pus  is  very  apt  to  travel  along  the  loose  connective  tissue  between  the  two  planes 
of  intercostal  muscles,  and  it  is  therefore  unusual  to  find  suppurative  disease  confined 
to  one  rib,  or  even  to  the  immediate  vicinity  of  its  point  of  origin. 

No  instance  of  traumatic  separation  of  the  epiphysis  of  either  the  head  or  the 
tuberosity  of  a  rib  has  been  recorded. 

The  internal  mammary  artery  runs  from  above  downward  beneath  the  cartilages 
about  half  an  inch  from  the  sternum. 

Landmarks. — The  oblique  elevations  formed  by  the  ribs  can  usually  be  seen 
extending  downward  from  the  axillary  region.  The  upper  ribs  are  covered  by  the 
great  pectoral,  but  beneath  its  lower  border  the  ribs  from  the  sixth  to  the  tenth 
can  often  be  seen.  The  lower  border  of  the  great  pectoral  follows  the  direction  of 
the  fifth  costal  cartilage. 

The  curved  arch  of  the  costal  cartilages  is  frequently  plainly  visible,  and  is 
accentuated  during  forced  expiration  and  when  a  superincumbent  weight  is  held  up 
by  the  trunk  and  arms.  In  short  persons  the  arch  is  commonly  flatter  than  in  tall 
ones. 

In  counting  the  ribs  it  is  well  to  begin  with  the  second,  which  is  easily  identified 
by  its  relation  to  the  ridge  between  the  mamibrium  and  body  of  the  sternum. 

The  nipple  is  usually  over  the  fourth  intercostal  space,  somewhat  less  than  2.5 


PRACTICAL   CONSIDERATIONS:    THE   THORAX.  "171 

centimetres  (one  inch)  external  to  the  costo-chondral  junction,  or  about  ten  centi- 
metres (four  inches)  from  the  middle  line.  Its  position  is  variable,  and  is  much 
lower  in  fat  persons,  especially  females.  In  emphysema  the  nipple  may  remain 
stationary,  while  the  upper  ribs  ascend,  and  it  may  be  opposite  the  fifth,  sixth, 
seventh,  or  even  the  eighth  rib.  In  phthisis  with  a  shallow  depressed  chest  it  may 
be  opposite  the  fourth  rib.  A  line  drawn  horizontally  from  the  nipple  around  the 
chest  is  on  a  level  with  the  sixth  intercostal  space  at  the  mid-axillary  line. 

A  horizontal  line  around  the  trunk  on  the  level  of  the  angle  of  the  scapula  (the 
arms  hanging  down)  would  traverse  the  sternum  between  the  fourth  and  fifth  ribs, 
the  fifth  rib  at  the  nipple  line,  and  the  ninth  rib  at  the  vertebral  column  (Treves). 

The  sternum  is  subcutaneous  in  the  groove  between  the  pectoral  muscles. 
Near  the  upper  third  the  ridge  between  the  manubrium  and  body  may  be  seen  or 
felt.  It  is  on  a  level  with  the  second  costal  cartilage.  This  cartilage  projects  for- 
ward more  than  the  others.  As  the  origins  of  the  pectoral  muscles  diverge  the 
sternal  groove  becomes  broader.  It  ends  at  the  lower  portion  of  the  body  of  the 
sternum  in  a  slight  projection  usually  seen  and  easily  felt.  This  marks  the  upper 
limit  of  the  "  infrasternal  depression"  {epigastric  fossa,  scrobiculus  cordis},  the 
floor  of  which  is  over  the  ensiform  process,  and  which  is  bounded  laterally  by  the 
seventh  costal  cartilages  and  inferiorly  by  the  upper  ends  of  the  recti  muscles.  In 
many  abdominal  diseases,  and  sometimes  after  laparotomies,  the  obliteration  of  this 
depression  (by  the  occurrence  of  tympany)  is  an  important  clinical  symptom. 

When  the  arm  is  raised,  the  highest  visible  digitation  of  the  serratus  corre- 
sponds to  the  fifth  rib  ;  the  largest  is  that  attached  to  the  sixth  rib. 

During  expiration  the  upper  end  of  the  sternum  is  on  a  level  with  the  second 
dorsal  intervertebral  disk  ;  the  line  between  the  manubrium  and  body  is  on  a  level 
with  the  fifth  thoracic  vertebra  ;  the  junction  of  the  sternal  body  and  the  ensiform 
process  is  opposite  the  lower  part  of  the  ninth  thoracic  vertebra. 

The  eleventh  and  twelfth  ribs  can  be  felt  as  blunt  bony  projections  directed 
downward  and  outward  just  outside  the  erector  spinae  muscles. 

(The  relations  of  the  various  thoracic  viscera  to  the  chest-wall  will  be  con- 
sidered in  connection  with  the  anatomy  of  the  former. ) 


THE  SKULL 

THE  head  consists  of  the  cranium  and  the  face.  The  former  is  the  brain-case  ; 
the  latter  is  chiefly  concerned  in  forming  the  jaws.  The  head  also  contains  the 
terminal  organs  of  four  special  senses.  That  of  hearing  is  entirely  inside  one  of  the 
cranial  bones,  while  the  organs  of  sight  and  of  smell  lie  in  cavities  formed  partly  by 
cranial  and  partly  by  facial  bones.  The  special  organ  of  taste,  a  part  of  the  surface 
of  the  tongue,  is  in  the  mouth,  bounded  wholly  by  facial  bones.  Thus,  while  the 
cranial  bones  have  a  share  in  forming  the  face,  no  facial  bone  has  any  part  in  forming 
the  brain-case.  The  latter  is  an  egg-shaped  cavity  which  communicates  by  a  large 
opening — the  foramen  magnum — with  the  spinal  canal,  through  which  the  spinal  cord 
passes  down  from  the  brain.  The  brain-case  has  many  smaller  openings  in  the  base, 
through  which  nerves  escape  both  to  the  face  and  to  a  large  part  of  the  body  and 
blood-vessels  pass  for  the  nutrition  of  the  brain  and  its  membranes  and  the  walls  of 
the  skull. 

As  the  bones  of  the  head  can  be  separated  in  a  young  subject,  it  is  customary 
to  describe  every  bone  by  itself.  It  is  too  often  forgotten  that  this  knowledge  is 
merely  a  means  to  an  end, — namely,  the  understanding  of  the  skull  as  a  whole.  In 
the  following  account  this  end  is  kept  constantly  in  view. 

THE   CRANIUM. 

The  cranial  cavity  is  formed  by  eight  bones  :  the  occipital,  the  sphenoid,  the 
two  temporals,  the  ethmoid,  the  frontal,  and  the  two  parietals.  The  cranium  consists 
of  the  vault  and  the  base.  The  vault  is  formed  by  the  parietals,  the  greater  part  of 
the  frontal ',  and  a  part  of  the  sphenoid,  of  the  temporals,  and  of  the  occipital. 

The  base  of  the  cranium  is  divided  into  three  fossae  extending  across  the  skull. 
The  posterior  fossa  is  the  lowest  ;  it  opens  by  the  foramen  magnum  into  the  spinal 
canal,  and  contains  the  cerebellum,  the  medulla,  and  the  pons.  The  middle  one  is 
narrow  at  the  centre  and  expands  laterally  into  the  temporal  regions.  The  anterior 
is  the  highest,  lying  above  the  orbits  and  the  nose.  The  anterior  fossa  transmits  the 
olfactory  nerves,  the  middle  the  optic,  the  posterior  the  auditory  and  the  glosso- 
pharyngeal,  the  nerve  of  taste. 

THE   OCCIPITAL    BONE. 

The  occipital  bone1  is  divided  for  description  into  an  anterior  part,  the  basilar ; 
two  lateral  ones,  the  condylar ;  and  a  posterior  one,  the  tabular  or  squammis  portion. 
These  correspond  to  the  basi-occipital ,  the  exoccipital,  and  the  supra-occipital  of 
comparative  anatomy.  They  all  develop  from  separate  centres  and  bound  the 
foramen  magnum?  a  nearly  circular  opening,  transmitting  the  spinal  cord  with  its 
enveloping  membranes.  The  spinal  accessory  nerves  and  the  vertebral  arteries 
ascend  within  the  latter  from  the  cavity  of  the  spine  to  that  of  the  cranium. 

The  basilar  portion :i  bounding  the  foramen  magnum  in  front  is  originally  rough 
anteriorly,  but  shortly  after  puberty  it  coosifies  with  the  body  of  the  sphenoid.  Its 
superior  surface  is  smooth  and  concave  and  supports  the  medulla  oblongata.  Just 
internal  to  the  edges  is  a  very  shallow  groove  for  the  inferior  petrosal  sinus.  The 
inferior  surface  is  smooth  for  about  one  centimetre  in  front  of  the  foramen  magnum, 
and  rough  in  front  of  this  for  the  rectus  capitis  antirus  major  and  minor.  In  the  mid- 
dle line  at  the  junction  of  the  rough  and  smooth  surfaces  is  the  pluu -yugcal  tubercle^ 
Very  rarely  this  aspect  presents  a  depression,  the  pharyngcal  fossa.  Sometimes 
there  is  a  facet  near  the  edge  of  the  foramen  for  the  anterior  arch  of  the  atlas.  Also, 
there  may  be  a  tubercle  on  the  posterior  part  of  the  basilar  portion  against  which  the 
odontoid  process  may  rest,  called  tlu-  third  cotidylf.  I  .at<  i;illy,  the  basilar  portion 

1  Os  occlpltale.     -  Foramen  occipitalc  magnum.        1'nrs  Imsllnrl*.     ^Tuberculum  pharyngi'um. 

172 


THE   OCCIPITAL   BONE. 


173 


is  separated  by  a  suture,  the  petro-occipital,  containing  cartilage,  from  the  petrous 
portion  of  the  temporal. 

Each  condylar  portion  l  {exocdpitai)  presents  on  the  inferior  surface  an  oval 
articular  swelling,  the  condyle,  which  rests  in  the  hollow  on  the  atlas.  They  are 
placed  on. each  side  of  the  front  half  of  the  foramen  magnum.  The  hind  ends  reach 
almost  precisely  to  the  middle  of  the  aperture,  and  anteriorly  they  extend  to  the  line 
of  the  anterior  border,  their  long  axes  converging  in  front.  The  articular  surface, 
which  is  convex  in  the  line  of  the  long  axis,  faces  downward  and  outward.  The  curve 
it  presents  varies  greatly.  In  some  cases  it  is  nearly  regular,  in  others  the  front  and 
back  halves  almost  meet  at  an  angle.  There  is  usually  a  constriction  of  the  articular 
surface  at  the  middle,  where  it  may  be  crossed  by  a  groove  or  a  ridge.  On  the  thick 
inner  border  of  each  condyle  is  a  tubercle  for  the  odontoid  ligament.  Behind  the 
condyle  is  a.  fossa,  into  which  usually  opens  the  inconstant  posterior  condyloid  fora- 
men? transmitting  a  vein.  In  front  of  the  base  of  the  condyle  at  its  outer  border  is 
the  constant  anterior  condyloid  foramen?  the  termination  of  a  canal,  from  hve  to  ten 
millimetres  long,  which  pierces  the  bone  above  the  condyle  and  transmits  the  hypo- 


FIG.  192. 


Highest  curved  line 
Superior  curved  line 


Inferior  curved  line-^ 


Condyle 

Jugular  process 

Jugular  notch 
Pharyngeal  tubercle 


External  occipital  protuberance 
Trapezius 
Complexus 

Occipitahi 

Sterno-mastoideus 

fleet,  capit.  post. 

minor 
Splenius 
Rect.  capit.  post. 

major 

Obliquus  superior 


Posterior  condyloid  fora- 
men 
Rect.  capit.  lateralis 


nterior  condyloid  foramen,  probe  in  canal 
Rect.  capit.  antic,  minor 
Superior  constrictor 
Rect.  capit.  antic,  major 


Occipital  bone,  external  surface,  from  below. 

glossal  nerve  and,  usually,  a  branch  from  the  ascending  pharyngeal  artery  and  vein 
or  veins.  It  is  sometimes  divided  into  two.  The  bone  projects  outward  from  the 
condyle  as  the  jiigular  process*  which  is  enlarged  at  its  outer  end  where  it  coossifies 
with  the  petrous  portion  of  the  temporal.  This  enlargement,  moreover,  extends 
downward  as  \hzparoccipital  process,  which  shows  its  greatest  development  in  odd- 
toed  ungulates.  In  man  it  is  usually  very  small,  but  it  may  be  large  and,  very  rarely, 
join  the  atlas.  The  concave  front  of  the  jugular  process  and  the  bone  extending 
forward  on  its  inner  side  form  the  jugular  notch?  which  bounds  the  posterior  lacer- 
ated foramen 6  behind  and  internally.  This  is  completed  by  the  temporal  bone.  A 
very  small  point,  the  anterior  jugular  process,  marks  the  front  of  the  foramen.  A 
little  behind  this  a  larger  though  very  delicate  spine,  the  intrajugular  process, 
reaches  across,  marking  off  a  small  anterior  part  of  the  jugular  foramen  for  the 
passage  of  the  ninth,  tenth,  and  eleventh  nerves  from  the  larger  one  behind  for  the 
lateral  sinus.  Sometimes  the  front  of  the  jugular  process  is  a  smooth  surface 
bounded  below  by  a  ridge  to  which  is  attached  the  rectus  capitis  lateralis,  and  above 
by  a  short  border  marking  off  a  fossa  on  the  upper  surface  of  the  bone  ;  occasionally 

1  Pars  lateralis.     -  Canalis  condyloidens.     J  Canalis  bypoglossi.     4  Processus  jugularis.     6  Incisura  jugularis.     ll  Foramen 
ugulare. 


HUMAN    ANATOMY. 


the  latter  ridge  is  wanting,  the  groove  of  the  lateral  sinus  curving  over  the  jugular 
process.  The  upper  surface  of  the  lateral  portion  of  the  process  shows  on  its  inner 
side  the  entrance  of  the  anterior  condyloid  foramen,  which  is  really  a  short  canal. 
Above  and  anterior  to  this  is  a  slight  swelling,  the  jugular  tubercle.  The  upper 
surface  of  the  jugular  process  is  marked  by  the  termination  of  the  groove  of  the 
lateral  sinus,  which  curves  round  an  upward  projection  of  the  process.  In  some 
cases,  as  just  mentioned,  the  groove  is  depressed  into  a  deep  hollow.  The  inner 
opening  of  the  posterior  condyloid  foramen,  when  present,  is  connected  with  the 
lateral  sinus. 

The  squamous  portion  '  forms  the  lower  and  back  part  of  the  skull.  Below  it 
contributes  the  posterior  boundary  of  the  foramen  magnum  and  joins  the  exocciphals. 
The  lateral  borders  meet  above  at  a  sharp  angle.  These  borders  may  be  subdivided 
into  a  lower  part,  which  ascends  nearly  vertically  in  articulation  with  the  mastoid 
part  of  the  temporal,  and  into  a  higher  part,  very  serrated  and  joining  the  parietal. 
A  slight  angle  lies  on  either  side  at  the  junction  of  these  two  divisions. 

FIG.  193. 


Internal  occipital  protuber- 
ance 


Superior  occipital 
fossa 


Groove  for  right 
lateral  sinus 


Inferior  occipital 
fossa 


Groove  for  left 
ateral  sinus 


Jugular  process 

Jugular  notch 


Groove  for  lateral  sinus 
Jugular  tubercle 


Anterior  condyloid  foramen,  probe 
'n  canal 


Occipital  bone,  internal  surface,  from  before. 

The  posterior  surface  is  marked  by  a  prominence,  somewhat  below  t he- 
middle,  the  external  occipital  protuberance,'2-  to  which  is  attached  the  ligamentum 
nuchae.  This  tuberosity  varies  greatly  in  development.  From  it  the  svpfrior  cur-rd 
tine3  extends  laterally  to  the  above-mentioned  angle.  To  this  line  are  attached  a 
series  of  muscles  which  form  the  contour  of  the  back  of  the  neck,  chiefly  the  trupe/ius 
and  part  of  the  sterno-cleido-mastoid.  A  short  and  varying  distance  above  the  supe- 
rior ridge  is  often  seen  the  so-called  lii^/icst  cunrrf  line.''  It  is  usually  very  faint, 
and  may  curve  down  to  the  external  occipital  protuberance,  or  pass  above  it.  The 
epicranial  aponeurosis  and  part  of  the  occipitalis  spring  from  this  line.  The  surface 
of  the  bone  above  the  level  of  the  protuberance  is  smooth  ;  below  it  is  ratlu-r  rough 
and  irregular.  The  torus  occipitalis  tnuisirrsiis  is  an  occasional  prominence  in- 
volving the  protuberance  and  extending  laterally  along  the  superior  curved  line. 
It  sometimes  involves  the  space  between  that  line  and  the  highest  one.  The  upper 
border  of  the  swelling  may  have  a  median  concavity.  In  the  mid-line  a  slight  ridge, 

1  Sqtinrnoaa  occi|>i;;i!is.      -  I'rotuheriintin  occipital)*  extcrnn.     "Linen  rm.li.u-  superior.     *  Linen  nuchne  supremo. 


DEVELOPMENT   OF   THE   OCCIPITAL    BONE. 


175 


FIG.  194. 

Superior  median  fissure 


the  external  occipital  crest?  runs  from  the  protuberance  to  the  foramen  magnum. 
Above  the  middle  of  this  crest  the  inferior  curved  line'1  leaves  it  to  extend  outward  and 
downward  to  the  border  of  the  bone.  The  inner  part  of  this  line  is  rough,  the  outer 
indistinct.  Below  this  line  there  is  usually  a  depression  on  either  side  of  the  crest. 

The  internal  surface  of  the  squamous  portion  is  divided  into  four  depressions 
orfosst? ;  the  upper  two  lodge  the  occipital  lobes  of  the  cerebrum  and  the  lower  two 
the  lateral  lobes  of  the  cerebellum.  Below  the  middle  is  the  internal  occipital  pro- 
tuberance? approximately  opposite  to  the  outer.  A  ridge  runs  from  the  apex  of  the 
bone  to  the  protuberance,  and  is  continued  as  the  internal  occipital  crest*  to  the 
foramen  magnum.  Very  often  the  second  part  of  this  ridge  divides  shortly  after  its 
origin,  so  as  to  enclose  a  depression,  the  vermian  fossa,  so  called  because  it  is  below 
the  middle  lobe,  or  vermis,  of  the  cerebellum.  A  ridge  runs  transversely  from  the 
protuberance  to  the  lateral  angle  of  the  bone.  The  superior  vertical  ridge  may  be 
grooved  for  the  superior  longitudinal  sinus  and  the  transverse  ridge  for  the  lateral 
sinus.  More  frequently  the  longitudinal  sinus  lies  to  one  side  of  the  vertical  ridge 
and  is  continued  into  one  of  the  lateral  ones,  much  larger  than  its  fellow,  and  usually 
the  right,  which  lies  above  the 
transverse  ridge,  and  shows  in 
the  bone  no  communication  with 
the  smaller,  which  lies  in  or  above 
the  other  ridge.  There  are  many 
variations  in  this  arrangement,  of 
which  the  rarest  is  a  symmetrical 
course  and  division  of  the  supe- 
rior groove.  A  single  or  a  bifur- 
cated groove  is  sometimes  found 
on  the  internal  crest. 

Development. — Four  cen- 
tres appear  in  the  cartilage  around 
the  foramen  magnum  about  the 
eighth  week  of  fcetal  life :  one  for 
the  basilar,  one  for  each  exoccipi- 
tal,  and  one  (or  more  probably 
a  pair  that  speedily  fuse)  for  the 
lower  part  of  the  squamous  por- 
tion, the  siip r a- occipital.  A  week 
or  so  later  two  nuclei  appear  in 
the  membrane  above  the  latter, 
from  which  a  strip  of  bone  de- 
velops which  soon  joins  it.  From 
this  upper  ossification,  the  supe- 
rior occipital,  is  developed  all  the 
upper  part  of  the  squamous  por- 
tion, including  the  external  occipital  protuberance  and  the  superior  curved  line.0 
Occasionally  still  another  nucleus  appears  on  each  side,  anterior  and  external  to  the 
preceding,  which  probably  accounts  for  certain  separate  ossifications  often  found  in 
the  lambdoidal  suture.  The  squamous  part  shows  a  median  cleft  above,  which 
quickly  disappears,  two  lateral  ones  between  the  ossifications,  which  persist  till 
birth,  and  a  notch  at  the  posterior  border  of  the  foramen  magnum.  The  squa- 
mous portion  joins  the  exoccipitals  in  the  course  of  the  second  or  third  year.  The 
latter  begin  to  unite  with  the  basilar  a  year  or  so  later.  None  of  these  sutures,  es- 
pecially the  latter,  is  completely  closed  before  the  seventh  year,  or  even  later. 
The  front  parts  of  the  condyles  are  formed  from  the  basilar,  which  joins  the  ex- 
occipitals at  the  anterior  condyloid  foramina.  Separate  ossifications,  large  Woimian 
bones,6  are  found  in  the  suture  between  the  squamous  portion  and  the  parietals. 
Sometimes  there  is  a  large  median  triangular  one  which  is  interpreted  as  the  result 
of  a  want  of  union  of  the  usual  superior  centre  of  the  squamous  portion,  and  said  to 

5  Consult  Stieda  :  Anatomische  Hefte,  iv.,  1892,  and  Debi£rre  :  Journ.  de  1'Anat.  et  de  la 
Phys.,  1895. 

1  Linia  nuchae  raediana.     ~  L.  nuchae  inferior.     3Protub.  occip.  interna.    4  Crista  occipitalis   interna.     C0ssa  suturarum. 


superior  oc- 
cipital 


Squamous  por- 
tion 


Fissure  be- 
tween upper 
and  lower 
portions 

Supra-occipital 


Exoccipital 


Basi-occipital  Posterior  condyloid  foramen 

Occipital  bone  at  birth,  from  before. 


76 


HUMAN    ANATOMY. 


be  the  homologue  of  the  interparietal  bone.  This  interpretation  is  inconsistent  with 
the  history  of  ossification.  Kerkring  has  described  an  occasional  triangular  minute 
piece  of  bone  which  appears  during  the  fifth  month  in  the  notch  at  the  back  of  the 
foramen  magnum,  and  is  fused  before  birth.  We  have  specimens  which  imply  that 
it  is,  or  may  be,  originally  double.  Improved  methods  of  investigation  will  prob- 
ably' show  that  this  bone  is  not  uncommon.  The  cerebral  side  of  the  basilar  is 
fused  with  the  sphenoid  by  seventeen  ;  the  lower  side  unites  later,  probably  before 
twenty. 

THE   TEMPORAL    BONE. 

The  plan  of  the  organ  of  hearing  must  be  known  to  understand  the  temporal 
bone.1  The  external  ear,  besides  the  auricle,  consists  of  a  cartilaginous  and  bony 
tube,  the  external  auditory  meatus*  leading  to  the  membrane  of  the  tympanum  which 
closes  it.  The  middle  ear,  the  cavity  of  the  tympanum,  is  a  space  internal  to  the 

FIG.  195. 

SQUAMOUS  PORTION 


Supramastoid  crest 

Occipitahs 

Spina  suprameatum 


Splenins  capitii 

Squamo-mastoid  suture 

Sterno-mastoid 

Mastoid  foramen 


Auricularis  posterio 


Zygoma 


Masseter 

Anterior  root  of  zygoma 
Glenoid  fossa 

APEX  OF  PETROUS  PORTION 
Glaserian  fissure 


Trachelo-mastoid 
MASTOID  PORTION' 


Tympano-mastoid  fissure 

Mastoid  process        /       ; 
External  auditory  meatus       / 
TYMPANIC    PORTION 
Vaginal  process 


'Stylo-glossus 
'  Stylo-hyoid 


Styloid  process 
Right  temporal  hone,  external  aspect. 


membrane,  opening  through  the  Eustachian  tube  into  the  throat,  and  communicating 
behind  with  cavities  in  the  bone.  It  is  lined  with  mucous  membrane  and  is  crossed 
by  a  chain  of  small  bones,  the  car  ossicles,  the  embryological  importance  of  which  is 
explained  elsewhere.  The  internal  ear  is  a  complicated  system  of  cavities  in  the 
substance  of  the  bone  containing  the  organ  of  hearing  connected  with  the  brain  by 
the  auditory  nerve,  which  leaves  the  bone  through  a  canal,  the  internal  auditory 
meatus. 

Development  shows  that  the  bone  consists  of  the  following  three  parts.  ( i ")  The 
petro-mastoid,  the  petrous  part  of  which  is  first  found  surrounding  the  special 
apparatus  of  the  organ  of  hearing,  constituting  the  internal  ear,  while  the  mastoid 
process  is  a  much  later  outgrowth.  (2)  The  tympanic  portion,  which  at  birth  is  a 
ring,  incomplete  above,  encloses  the  membrane  of  the  tympanum  as  a  frame  holds 
a  glass.  This  ring  grows  out  later  into  a  cylinder,  still  open  above,  which  forms  the 
external  auditory  meatus.  Not  all  its  growth,  however,  is  outward,  since  a  part 

1  Os  lemporalc.     '-'  Meatus  acuaticus  externus 


THE   TEMPORAL    BONE. 


177 


expands  forward  and  deeper  than  the  original  ring,  making  the  front  part  of  the 
tympanic  plate,  bounding  the  cavity  of  the  tympanum  and  the  Eustachian  tube 
externally.  The  tympanic  cavity,  or  the  middle  ear,  lies  between  the  petro-mastoid 
and  the  tympanic  portion,  the  roof  and  floor  being  developed  from  the  former. 
(3)  The  squamou s portion  is  external  and  above.  It  forms  a  part  of  the  side  of  the 
skull,  the  roof  of  the  external  meatus  where  the  tympanic  portion  is  deficient,  the 
articulating  surface  for  the  jaw,  and  a  part  of  the  mastoid  process.  There  is  also  the 
long,  slender  styloid  process,  which  is  a  part  of  the  hyoid  bar  of  the  second  visceral 
arch  of  the  embryo.  It  begins  as  an  ossification  of  a  distinct  piece  of  cartilage,  but 
joins  the  petro-mastoid.  The  following  description  is  that  of  the  adult  bone. 

The  Squamous  Portion.1 — Most  of  this  is  a  thin  vertical  layer  forming  part 
of  the  wall  of  the  skull,  joined  below  by  a  horizontal  one  which  forms  a  small  part  of 
the  base  of  the  skull,  the  articulating  surface  for  the  jaw,  and  the  roof  of  the  external 

FIG.  196. 

Eminentia  articularis 


Zygoma 


Glenoid  fossa 

Postglenoid  tubercle 

Fissure  of  Glaser 

Tympanic  plate 


External  auditory  meatus 


Eustachian  tube 


Carotid  canal 


Cochlea 


Semicircular  canal 
Facial  canal 


Antrum 


Groove  for  lateral  sinus 
Horizontal  section  through  right  temporal  bone,  seen  from  below. 

auditory  meatus.  The  edge  of  the  vertical  part  is  convex  except  below.  The  upper 
and  posterior  borders  overlap  the  parietal  bone  by  a  broad  bevelled  surface.  The 
anterior  border  joins  the  great  wing  of  the  sphenoid,  overlapping  above  and  over- 
lapped below,  where  it  passes  into  the  horizontal  part.  The  posterior  angle  of  the 
vertical  portion  sends  downward  the  postauditory  process,  from  which  the  upper  part 
of  the  mastoid,  including  some  of  the  mastoid  cells,  is  developed.  The  squamo- 
mastoid  siiture,  separating  this  from  the  mastoid  portion,  is  usually  lost  in  the  second 
year.  When  it  persists,  it  shows  that  the  anterior  portion  of  the  mastoid  down  to 
the  lower  border  of  the  external  meatus,  or  even  lower,  is  formed  from  the  squamosal. 
Its  surface  is  smoother  than  that  of  the  mastoid  proper.  A  small,  particularly 
smooth,  but  inconstant  patch  situated  on  the  level  of  the  upper  part  of  the  meatus, 
one  centimetre  or  more  behind  it,  marks  the  position  of  the  antrum.  The  thick- 
ness of  the  bone  at  this  place,  which  is  that  of  note-paper  in  the  infant  reaches 

1  Pars  squamosa. 
12 


I78 


IK  MAN   ANATOMY. 


six  millimetres  in  the  adult.  A  small,  sharp  prominence,  the  spina  suprameatum ,  is 
found  just  behind  the  upper  part  of  the  meatus.  It  is  an  important  landmark  in  the 
surgery  of  the  region.  Just  posterior  to  it  is  usually  a  minute  venous  foramen. 
The  inner  side  of  the  squamous  portion,  besides  the  large  bevelled  articular  surface, 
presents  a  smooth  one,  forming  part  of  the  wall  and  floor  of  the  cranial  cavity.  This 
is  separated  from  the  petrous  portion  by  the  petro- squamous  suture,  which  is  closed 
early.  Two  grooves  for  branches  of  the  middle  meningeal  artery  diverge  from  its 
lower  border,  one  running  upward  and  the  other  backward.  The  front  of  the  hori- 
zontal part  forming  the  floor  is  rough  and  thick,  joining  the  great  wing  of  the 
sphenoid.  The  zygomatic  process J  projects  forward  from  the  outer  surface  of  the 
squamosal  to  complete  the  zygomatic  arch  with  the  malar,  which  it  joins  by  a 
serrated  end.  The  free  part  has  an  external  and  an  internal  surface,  a  rounded  bor- 
der below  and  a  sharp  edge  above.  The  latter,  which  receives  the  insertion  of  the 
temporal  fascia,  can  be  followed  back  to  the  origin  of  the  process.  The  zygoma 
has  two  roots.  The  posterior  root  passes  directly  backward  above  the  auditory 

FIG.  197. 
SQUAMOUS  PORTION 


Zygoma 
Groove  for  meningeal  artery 

Internal  auditory  meatus 
Carotid  canal 

PETROUS  PORTION 
,  Styloid  process 


Aquaeductus  ves- 
tibuli 


Groove  for  lateral  sinus 
MASTOID  PORTION 


Aquaeductus  cochleae 
Right  temporal  bone,  internal  aspect. 

meatus,  crosses  the  squamous  portion  above  the  postauditory  process,  and,  curving 
slightly  upward,  is  lost  at  the  notch  between  the  squamous  and  mastoid  portions. 
Its  hind  part  is  the  supramastoid  crest,  which  joins  the  inferior  temporal  ridge  on 
the  parietal.  The  anterior  root  bends  sharply  inward.  It  is  grooved  above  for  the 
passage  of  the  fibres  of  the  temporal  muscle.  Its  lower  surface  forms  a  semi-cylin- 
drical transverse  elevation,  the  cniinen/ia  articular  is?  the  front  part  of  the  articular 
cavity  of  the  lower  jaw.  Near  its  outer  end  is  a  tubercle  for  the  external  lak-ral 
ligament.  Just  in  front  of  the  auditory  meatus,  on  the  under  side  of  the  bone,  is 
the  smaller  postgUnoid  tubercle,  sometimes  described  as  a  third  root.  Tlu-  glcnoid 
fossa''  is  a  deep  hollow  on  the  under  side  of  the  squamous  portion,  with  its  greatest 
diameter  nearly  transverse,  but  passing  somewhat  forward  and  outward,  bounded 
externally  by  the  posterior  root  of  the  zygoma  ;  behind,  by  the  fissure  of  Closer* 
which  separates  it  from  the  tympanic  portion  ;  and  extends  forward  and  inward  to 
meet  the  inner  end  of  the  eminentia  articularis.  Both  gk-noid  fossa  and  articular 
eminence  are  covered  with  cartilage.  The  bone  separating  the  glenoid  fossa  from 

1  Procesau*  zygnmatlcos.     "Tuberculum  nrticulnre.     ''Fossa  innndilmlnris.     '  Flssurn  pctrntympnnlca. 


THE    TEMPORAL    BONE. 


179 


the  interior  of  the  cranium  is  very  thin.      Behind  the  glenoid  fossa  the  horizontal 
part  of  the  squamosal  forms  the  roof  of  the  external  auditory  meatus. 

The  Tympanic  Portion.1 — The  tympanic  portion  of  the  temporal  bone 
appears  as  a  trumpet-shaped  layer  of  bone,  forming  all  but  the  roof  of  the  external 
auditory  meatus.  Its  edge  is  thin  in  front,  thick  below,  and  very  thin  behind,  where 
it  curls  up  before  the  mastoid  to  meet  the  postauricular  process  of  the  squamosal. 
It  is  separated  from  the  mastoid  by  the  minute  tympano-mastoid  fissure.  The  ante- 
rior part  of  the  tympanic  portion,  called  the  tympanic  plate,  runs  obliquely  forward, 
concealing  the  petrosal.  It  is  separated  from  the  glenoid  fossa  and  from  the  thick 
anterior  edge  of  the  squamosal  by  the  fissure  of  Glaser,  which  opens  into  the  tym- 
panic cavity.  The  outer  end  of  the  fissure  is  closed  ;  the  inner  part  is  double,  since 
a  thin  piece  of  the  petrous,  the  tegmen  tympani,  bends  down  between  the  squamous 
and  tympanic  portions.  The  lower  edge  of  the  tympanic  plate  ends  free.  A  part 
covering  the  base  of  the  styloid  process  is  the  vaginal  process,"1  which  sometimes 

splits  to  enclose  it. 

FIG.  198. 

SQUAMOUS  PORTION 


Eustachiantube 


Carotid  canal 


Aquaeductus  cochleae 
PETRO-MASTOID  PORTION 
•Jugular  fossa 


Joining  occipital 


Zygoma 


Articular  eminence 

Glenoid  fossa 
Tegmen  tympani 
Glaserian  fissure 

TYMPANIC  PORTION 
Styloid  process 

Stylo-mastoid  foramen 
Mastoid  process1 

Digastric  groove 


Occipital  groove 
Right  temporal  bone  from  below. 

The  Petro-Mastoid  Portion.1'  —This  part  of  the  temporal  bone  may  for 
convenience  of  description  be  subdivided  into  the  mastoid  and  the  petrous.  The 
mastoid  subdivision  forms  a  part  of  the  wall  of  the  skull  behind  the  tympanic. 
It  is  prolonged  downward  into  a  nipple-shaped  process,  the  outside  of  which  is  rough 
and  slightly  prominent.  On  its  lower  surface,  under  cover  of  the  apex,  is  the 
digastric  groove^  for  the  origin  of  the  posterior  belly  of  the  digastric  muscle.  Just 
internal  to  this,  at  the  very  edge  of  the  bone,  is  the  much  smaller  occipital  groove 
for  the  occipital  artery.  The  ridge  between  the  two  may  be  developed  into  a  para- 
mastoid  process.  The  greater  part  of  the  internal  surface  is  occupied  by  a  broad  and 
deep  groove?  running  obliquely  downward,  forward,  and  inward  for  the  lateral  sinus 
on  its  way  to  the  jugular  foramen.  The  direction  of  this  groove  is  very  uncertain. 
Sometimes  it  descends  gradually  ;  at  others  it  turns  far  forward  and  descends  nearly 
vertically.  In  the  latter  case  it  approaches  closer  than  otherwise  to  the  outer  wall 
of  the  skull,  but  the  distance  in  all  cases  is  very  variable  (Figs.  199,  200).  It 
may  be  only  a  few  millimetres.  As  it  descends  it  reaches  the  inner  side  of  the 
antrum  and  the  mastoid  cells.  It  is  separated  from  the  antrum  by  a  plate  some  six 

1  Pars  tympanica.    -  Vagina  processus  stytoldeus.    ;1  Pars  petrosa  ct  mastoidea.    4  Incisura  mastoidea.    ;'Sulcus  sigmoideus. 


i8o 


HUMAN    ANATOMY. 


millimetres  thick  in  early  childhood,  and  from  the  antrum  or  upper  mastoid  cells  by 
a  very  thin  one  in  adult  life.1  Behind  the  groove  a  small,  smooth  surface  forms  a 
part  of  the  cerebellar  fossa. 

FIG.  199. 
A  B 


Carotid  canal 


Tympanic  cavity 
Jugular  fossa 

Facial  canal 


External  auditory 
meatus 


Groove  for  lateral  sinus 


Tympanic  cavity 


Facial  canal 


External  auditory 
meatus 


Groove  for  lateral 
sinus 


Mastoid  canal 

U^ 

Horizontal  sections  through  a  right  temporal  bone  with  slight  development  of  the  mastoid  cells.    A,  just  above  the 
floor  of  the  external  auditory  meatus  ;  B,  near  the  roof  of  the  same  canal. 

FIG.  200. 


Tympanic 
cavity 


Similar  sections  of  a  right  temporal  l>one  with  considerable  development  »t  tin-  mastoid  cells  and  oonsequ 
removal  of  the  lateral  sinus  from  the  surface. 


A  small  canal,  the  mastoid  foramen*  transmitting  a  vein,  runs  from  the  sinus  to 

the  outside  of  the  bone,  which  it  sometimes  reaches  as  far  back  as  the  suture  between 

'Clarke:  Journal  of  Anatomy  and  Physiology,  vol.  \\vii,  1893. 

"Foramen  mnstnidcnui. 


THE  TEMPORAL    BONE. 


181 


Facial  canal  — 


Crista  falci- 
form is 

Tractus  spi- 
ralis 


^-r-Area  cribrosa 
superior 

r| Cut  wall  of  in- 

f'"AiJ      •        ternal  meatus 
fe^ — -  — Area  cribrosa 
•y  media 


-Foramen  singu- 
lare 


Bottom  of  right  internal  auditory  meatus.     X  5. 


the  temporal  and  the  occipital.  The  interior  of  the  mastoid  process  contains  spaces, 
the  mastoid  cells,  to  be  described  later.  The  size  and  shape  of  the  mastoid  process 
are  very  variable.  The  rough  upper  border  of  the  mastoid  subdivision  forms  an 
entering  angle  with  the  squamosal,  into  which  fits  a  sharp  point  from  the  lower  bor- 
der of  the  parietal,  which  rests  on 

it   above.       Behind  and  below   the  FIG.  201. 

mastoid  joins  the  occipital  bone. 

The  petrous  subdivision  is 
an  elongated  pyramid  running  for- 
ward and  inward,  presenting  four 
surfaces  (besides  the  base  covered 
by  the  mastoid),  four  borders,  and 
an  apex.  The  surfaces  are  the  supe- 
rior, posterior,  inferior,  and  anterior. 
The  superior  surface  slants 
forward  and  downward  in  the  floor 
of  the  middle  cerebral  fossa.  It  has 
the  following  features.  Above  the 
apex  there  is  a  depression  *  for  the 
Gasserian  ganglion.  Just  external 
to  this  the  bone  is  excessively  thin 

and  often  deficient,  so  as  to  leave  the  end  of  the  carotid  canal  uncovered.  Behind 
the  middle  of  the  pyramid  is  an  elevation,  nearly  at  right  angles  to  its  long  axis, 
caused  by  the  superior  semicircular  canal.  External  to  this  the  surface  is  made  of  a 
very  thin  plate  of  bone,  the  tegmen  tympani,  which,  extending  outward  from  the 
petrous,  forms  the  roof  of  the  tympanum  and  of  its  continuation,  the  Eustachian 
tube.  Externally,  this  plate  bends  down  into  the  Glaserian  fissure,  so  that  its  edge 
may  appear  between  the  squamosal  and  tympanic  portions  (Fig.  198).  At  the  inner 

border  of  the  tegmen  tympani  near 

FIG.  202.  its  front  is  a  groove  leading  to  a  little 

rent  in  the  bone,  the  hiatus  Fa/lopii,2 
through  which  passes  the  great  su- 
perficial petrosal  nerve.  A  minute 
opening,  more  external,  transmits 
the  smaller  superficial  petrosal  nerve. 
In  youth  the  outer  side  of  the  teg- 
men is  bounded  by  the  petro-sqtia- 
mous  suture. 

The  posterior  surface  forms 
a  part  of  the  posterior  cranial  fossa. 
The  chief  feature  is  the  internal 
auditory  meatus?  a  nearly  round 
canal  with  a  slight  groove  leading 
to  it  from  the  front.  Its  shorter 
posterior  wall  is  about  five  milli- 
metres long.  The  canal  is  closed  by 
a  plate  of  bone,  the  lamina  cribrosa 
(Fig.  201),  which  is  divided  by  the 
falciform  crest  into  a  smaller  fossa 
above  and  a  larger  one  below.  The 
former  has  an  opening  by  which  the 
facial  nerve  enters  its  canal,  the 
aqueduct  of  Fallopius.  Branches  of 

the  auditory  nerve  pass  through  minute  openings  in  both  fossae.  About  one  centi- 
metre behind  the  meatus  is  a  little  cleft,  the  aqu&ductus  vcstibuli?  entering  the  bone 
obliquely  from  below.  Higher  and  nearer  to  the  meatus  is  a  minute  depression,  the 
remnant  of  tib&  floccul&r  fos&a?  which  is  large  in  some  animals  and  in  the  infant.  It 
receives  a  fold  of  the  dura. 

The  inferior  surface  of  the  petrous  presents  in  front  a  large  rough  surface  for 

1  Impressio  tegmenti.     -  Hiatus  canalis  facialis.     3  Meatus  acusticus  interims.     4  Apertura  cxterna  aquaeductus  vestibuli. 
6  Fossa  «ubarcuata. 


Petro-squamous  suture 


Squamous  por- 
tion 


Internal  audi- 
tory meatus 
Internal  ear 

Aquaeductus 
cochleae 
Tympani 


External  audi- 
tory canal 


Tympanic  ring 


Styloid  process 


Frontal  section  through  temporal  bone,  showing  the  cavities 
of  the  outer,  middle,  and  inner  ear  and  the  four  sides  of  the 
petrous. 


182 


HUMAN    ANATOMY. 


the  origin  of  the  levator  palati  and  tensor  tympani  muscU-s.  Kxtcrnal  to  the  hack 
of  this  is  the  round  orifice  of  the  carotid  canal1  ;  back  of  this,  and  more  internal,  is 
the  jugular  fossa.  This  presents  two  extreme  types,  entirely  different,  \vith  inter- 
mediate forms.  It  may  be  a  large  thimble-shaped  hollow,  the  edge  of  which  bounds 
the  venous  part  of  the  jugular  foramen  internally,  forming  a  large  reservoir  for  the 
blood  of  the  lateral  sinus  as  it  leaves  the  skull.  On  the  other  hand,  it  may  be  a 
small  flat  surface.  A  minute,  but  very  constant,  foramen  in  the  ridge  between  it  and 
the  carotid  canal  transmits  the  tympanic  branch  of  the  glosso-pharyngeal  nerve.  A 
minute  foramen,  usually  found  in  the  jugular  fossa,  transmits  the  auricular  branch  of 
the  vagus.  The  aquadudus  cochlece  ends  at  a  small  triangular  opening  -  in  front  of  the 
jugular  fossa,  close  to  the  inner  edge.  Behind  the  fossa  is  a  small  surface  where  the 
temporal  bone  is  united  to  the  occipital,  first  by  cartilage  and  then  by  bone.  The 
stylo-mastoid  foramen,  the  orifice  of  the  facial  canal  for  the  facial  nerve,  is  near 
the  outer  edge  of  this  surface.  The  stylo-mastoid  branch  of  the  posterior  auricular 
artery  enters  it. 

FIG.  203. 


SQUAMOUS  PORTION 


Groove  for  meningeal  artery 


Foramen  for  lesser  superficial  pe- 

trosal  nerve- 
Hiatus  Fallopji 

Depression  for  Gasserian  ganglion 
Eustachian  tube 

Carotid  canal 
APEX  OF  PETROUS 

Carotid  canal  (lower  end) 


Tympanic  plate- 
Vaginal  process 

Styloid  process 


Right  temporal  bone  from  before. 

The  anterior  surface  of  the  petrous  is  nearly  all  hidden  by  the  tympanic 
plate.  It  forms  the  inner  wall  of  the  cavity  of  the  tympanum  and  of  the  bony  part  of 
the  Eustachian  tube,  which  leaves  the  bone  in  the  entering  angle  between  this  surface 
of  the  petrous  and  the  tympanic.  The  features  of  this  surface  are  treated  in  the 
section  on  the  ear.  The  -processes  cochUariformis*  attached  like  a  shelf  to  this  outer 
wall,  divides  the  canal  for  the  tensor  tympani  muscle  from  the  Eustachian  tube 
below  it.  The  front  of  this  plate  can  be  seen  at  the  entering  angle,  where  the  bony 
tube  ends.  The  small  portion  of  the  outer  surface  of  the  petrous  which  is  visible 
is  in  front  of  this  point,  and  rests  against  the  inner  edge  of  the  great  wing  of  t' 
sphenoid. 

The  superior  internal  border  of  the  petrous  is  a  prominent  ridge  in  the  bas< 
of  the  skull,  separating  the  middle  and  the  posterior  fossae.  The  tentorium  is 
attached  to  it.  The  superior  petrosal  sinus  runs  along  it  in  a  shallow  gnwrc  within 
the  attached  border  of  the  tentorium.  Near  the  front  a  groove  by  which  the  fifth 
nerve  reaches  the  Gasserian  ganglion  crosses  this  border. 

The  inferior  internal  border  articulates  anteriorly  with  the  basilar  process  of 

1  CanalU  carotlcus.     -  Apertura  externa  atiuaeductus  cochleae.     ''Septum  canalls  musculotubarll. 


THE  TEMPORAL   BONE. 


183 


the  occipital  bone,  and  is  separated  posteriorly  from  the  occipital  by  the  jugular 
foramen.  A  little  spine  on  the  edge  of  the  thimble-shaped  fossa,  or  on  the  plane 
surface  that  may  take  its  place,  the  intrajugular  process,  joins  the  corresponding 
process  of  the  occipital  either  directly  or  by  ligament,  so  as  to  divide  the  foramen 
into  two  parts,  the  posterior  for  the  vein,  the  anterior  for  nerves.  In  front  of  the 
foramen  a  small  groove  on  the  cerebral  edge  of  this  border  marks  the  position  of  the 
inferior  petrosal  sinus. 

The  superior  and  the  inferior  external  borders  are  concealed  by  the  other 
elements  of  the  temporal,  except  near  the  front,  where  they  bound  the  surface  which 
touches  the  sphenoid. 

The  apex  of  the  petrous  is  mostly  occupied  by  the  opening  of  the  carotid  canal. 

The  styloid  process  is  a  part  of  the  hyoid  bar  (from  the  second  branchial 
arch),  which  joins  the  temporal  under  cover  of  the  vaginal  process.  It  is  thick  at  its 
origin,  but  presently  becomes  thinner  and  ends  in  a  sharp  point.  It  is  usually  about 
an  inch  long,  but  varies  greatly.  It  runs  downward,  forward,  and  inward,  and  is  con- 
tinued as  the  stylo-hyoid  ligament  to  the  lesser  horn  of  the  hyoid.  Three  muscles, 
the  stylo-glossus,  stylo-hyoid,  and  stylo-pharyngeus,  diverge  from  it  to  the  tongue, 
the  hyoid  bone,  and  the  pharynx.  An  ill-defined  process  of  the  cervical  fascia,  the 
stylo-maxillary  ligament,  passes  from  it  to  the  back  of  the  ramus  of  the  lower  jaw. 


Canal  for  tensor  tympani 


CAVITIES   AND    PASSAGES   WITHIN   THE   TEMPORAL   BONE. 

The  Cavity  of  the  Tympanum.1 — The  tympanic  cavity  is  a  narrow  cleft 
about  five  millimetres  broad  at  the  top,  narrowing  to  a  mere  line  below.  It  measures 
about  fifteen  millimetres 

vertically  and  from  be-  FIG.  204. 

fore  backward.  It  is 
bounded  internally  by 
the  petrous  ;  above  by 
a  projection  from  it,  the 
legmen  tympani ;  below 
by  the  jugular  fossa,  or, 
if  this  be  very  small,  by 
the  bone  external  to  it  ; 
externally  by  the  tym- 
panic portion  of  the 
bone  and  the  membrane, 
except  at  the  top,  where 
the  squamosal  is  ex- 
ternal to  it.  The  part 
above  the  level  of  the 
membrane  is  the  supra- 
tympanic  space,  the  attic, 
or  the  epitympanum. 
This  is  separated  from 
the  cranial  cavity  by  a 
very  thin  plate,  which 
is  sometimes  imperfect.  In  front,  the  cavity  of  the  tympanum  narrows  to  the  Eusta- 
chian  tube.  It  opens  behind  through  the  antrum,  which  serves  as  a  vestibule,  into 
the  mastoid  cells.  The  antrum  is  a  cavity  of  irregular  size  and  shape,  compressed 
somewhat  from  side  to  side,  with  an  antero-posterior  diameter  of  from  ten  to  fifteen 
millimetres,  situated  behind  the  epitympanum  in  the  backward  projection  of  the 
squamosal,  which  forms  the  superficial  part  of  what  appears  to  be  the  mastoid,  and 
contains  some  of  the  so-called  mastoid  cells.  The  communication  with  the  tympanum 
is  a  narrow  one,  and  a  certain  number  of  cells  open  into  the  latter  independently. 

The  antrum  and  the  cells  nearest  it  are  lined  with  mucous  membrane  continued 
from  the  middle  ear.  The  inside  of  the  mastoid  varies  greatly.  Sometimes  it  con- 

1  The  detailed  description  of  this  space  is  given  in  connection  with  the  ear. 


Carotid  canal  (inferior  end) 


Sagittal  section  through  right  temporal  bone,  seen  from  outer  side. 


184  HUMAN   ANATOMY. 

tains  large  pneumatic  cavities,  sometimes  diploe  instead  of  air-cells,  and,  again,  it 
may  be  almost  solid  ;  the  latter  condition  is,  however,  probably  always  pathological. 
According  to  Zuckerkandl's1  investigations  of  250  temporal  bones,  the  mastoid  is 
entirely  pneumatic  in  36.8  per  cent,  and  wholly  diploetic  in  20  per  cent.  The  re- 
maining 43.2  per  cent,  were  mixed,  the  diploe  being  at  the  point  of  the  mastoid  and 
the  cells  above.  Neither  size  nor  shape  indicates  its  internal  structure.  The  relation 
of  the  cells  to  the  lateral  sinus  has  been  already  mentioned. 

The  Facial  Canal. — The  course  of  the  canal 2  for  the  facial  nerve  is  important. 
It  runs  outward  from  the  superior  fossa  of  the  internal  auditory  meatus  for  some 
three  millimetres,  until  joined  by  the  canal  from  the  hiatus  Fallopii.  It  then  makes 
a  sharp  turn  (the  genu}  backward,  passing  internal  to  the  attic  of  the  tympanum  just 
below  the  external  semicircular  canal,  which  almost  always  projects  a  little  farther 
outward.  It  then  curves  backward  to  descend  to  the  stylo-mastoid  foramen,  passing 
just  above  the  fenestra  ovalis.  The  descending  portion  is  rarely  strictly  vertical. 
Below  the  genu  the  facial  canal  may  make  a  bend  either  outward  or  inward,  but  its 
general  line  of  descent  usually  inclines  outward,  sometimes  very  strongly.  Rarely 
the  descent  is  tortuous.  The  lower  part  may  incline  forward.  The  genu  is  opposite 
a  point  on  the  surface  above  the  external  meatus,  and  the  subsequent  course  of  the 
canal  can  be  indicated  in  general  by  a  line  following  the  posterior  border  of  the 
auditory  opening.  An  instrument  introduced  straight  into  the  front  of  the  mastoid 
will  pass  behind  the  facial  canal.3  The  diameter  of  the  latter  is  about  one  and  one- 
half  millimetres.  Just  before  its  lower  end  a  very  minute  canal,  transmitting  the 
chorda  tympani  nerve,  runs  upward  and  forward  from  it  to  the  cavity  of  the  tympa- 
num. From  the  front  of  the  cavity  this  nerve  escapes  by  the  minute  canal  of  Hug uter, 
which  opens  near  the  inner  end  of  the  fissure  of  Glaser,  passing  between  the  tym- 
panic plate  and  the  tegmen  tympani.  The  facial  canal  has  several  other  minute 
openings.  There  are  also  minute  canals  for  Jacob  so  ti1  s  nerve  from  the  glosso- 
pharyngeal,  leading  to  the  tympanum,  and  for  Arnold' 's  branch  of  the  vagus,  which 
enters  the  jugular  fossa  and  leaves  by  the  fissure  between  the  mastoid  and  tympanic 
portions. 

The  carotid  canal 4  is  close  to  the  front  of  the  tympanum  and  just  before  the 
cochlea  of  the  internal  ear.  The  internal  auditory  meatus  is  almost  behind  the  canal, 
and  the  Eustachian  tube  lies  to  the  outer  side  of  its  horizontal  portion. 

The  temporal  bone  is  porous  in  structure,  except  about  the  internal  ear,  where 
it  is  very  dense.  A  transverse  section,  either  vertical  or  horizontal,  through  the 
external  and  internal  meatus  (the  middle  and  internal  ears)  shows  how  nearly  the 
entire  bone  is  pierced  (Fig.  202).  The  carotid  canal  and  the  jugular  fossa,  when 
deep,  are  further  sources  of  weakness.  The  fossa  sometimes  opens  into  the  middle 
ear  by  a  small  rent. 

Articulations. — The  temporal  bone  joins  the  occipital  by  the  petro-mastoid 
portion.  These  two  bones  form  the  entire  posterior  fossa  of  the  skull,  except  at  the 
extreme  front,  in  the  middle,  where  it  extends  along  the  back  of  the  sphenoid, 
and  at  the  side,  where  a  small  portion  of  the  lateral  sinus  is  made  by  the  posterior 
inferior  angle  of  the  parietal.  This  latter  bone  articulates  with  the  squamous  and 
the  top  of  the  mastoid.  The  great  wing  of  the  sphenoid  fits  into  the  angle  between 
the  squamous  and  petrous  portions,  articulating  at  the  side  of  the  skull  with  the  front 
of  the  foramen.  These  two  bones — the  sphenoid  and  the  temporal — form  the  entire 
middle  fossa.  The  malar  bone  joins  the  zygoma,  completing  the  arch.  The  lower 
jaw  articulates  with  the  glenoid  fossa  by  a  true  joint. 

Development. — The  squamous  portion  is  ossified  in  membrane  from  one 
centre,  appearing  near  the  end  of  the  second  month  of  foetal  life.  In  the  course  of 
the  third  month  a  centre  appears  in  the  lower  part  of  the  future  tympanic  ring. 
The  ossification  of  the  petro-mastoid  portion  comes  from  several  nuclei,  the  number 
of  which  probably  varies.  The  process  begins  towards  the  end  of  the  fifth  month 
about  the  membranous  labyrinth.  The  opisthotic  nucleus  lies  at  the  inner  side  of 
the  tympanic  cavity  and  spreads  to  the  lower  part  of  the  bone.  The  prootic  is  near 
the  superior  semicircular  canal.  The  cpiotic,  arising  near  the  posterior  canal, 

1  Monatsschrift  fiir  Ohrenheilkunde,  Bd.  xiii,  1879. 

'Joyce  :  Journal  of  Anatomy  and  Physiology,  vol.  xxxiv.,  1900. 

2Canalls  fnclnlla.     4CnnnlK  i.-initunv 


DEVELOPMENT  OF  THE  TEMPORAL  BONE. 


185 


FIG. 


205. 

Squatnous  portion 


spreads  into  the  mastoid  portion.  This  one  is  sometimes  double.  There  is  also  a 
separate  nucleus  for  the  tegmen,  but  this  is  not  constant.  When  present,  it  seems 
to  be  the  last  to  fuse  with  the  others, 
which  become  one  by  the  end  of  the 
sixth  month.  The  carotid  artery  passes 
at  first  along  the  base  of  the  skull  in  a 
groove  which  is  made  into  a  canal  by 
the  opisthotic.  The  separated  petrous 
portion,  when  ossification  has  made 
some  progress,  shows  a  very  promi- 
nent superior  semicircular  canal,  and  a 
deep  cavity  under  it,  extending  back- 
ward from  the  inner  surface.  This  is 
the  floccular  fossa,  which,  however,  is 
completely  hidden  by  the  dura.  The 
mastoid  process  becomes  fairly  distinct 
in  the  course  of  the  second  year.  It 


Tegmen  tympani  in 
Inner  wall    Glaserian  fissure 


Tympanic  ring    Malleus 

of  tympanum 
Temporal  bone  at  about  birth,  outer  aspect. 


FlG.    206. 


Petro-squamous  suture 


Position  of  superior 
semicircular  canal 


develops    greatly   about   the   time    of 

puberty,  when  it  becomes  pneumatic. 

This  may  occur  much  earlier.      J.   J. 

Clarke  has  seen  it  wholly  pneumatic  several  times  before  the  tenth  year  ;  once  at 

three  and  a  half.1     The  squamosal  joins  the  petrous  in  the  course  of  the  first  year. 

At  birth  the  tympanic por- 
•  tion  consists  solely  of  the  im- 
perfect ring  open  above.  This 
enlarges  trumpet-like  from  the 
edges,  the  front  one  forming 
the  tympanic  plate.  The 
growth  is  of  unequal  rapidity, 
so  that  the  lower  part  is  left 
behind,  presenting  a  deep 
notch  the  outer  edges  of 
which  meet  by  the  end  of  the 
second  year,  leaving  a  foramen 
below,  which  usually  closes 

Carotid  canal- ^    •••'  \  two  or  three  years  later,  but 

exceptionally  persists.  The 
tympanic  plate  fuses  almost  at 
once  with  the  petrous,  but  the 

Glaserian  fissure  remains  ;  the  groove  showing  the  line  of  union  of  the  tympanic  and 

mastoid  processes  generally  disappears  in  the  second  year,  but  occasionally  persists 

through  life.    Kircher2  found  it  present  on 

both  sides  in  five  per  cent,  of  300  skulls. 

The  styloid  process  consists  of  two  parts. 

The  first  joins  the  petrous  at  about  birth. 

The  second,  which  represents  all  but  the 

base,  is  an  ossification  of  the  stylo-hyoid 

ligament,  and  does  not  join  till  puberty 

or  later.       In   very  early  foetal   life  the 

chief  vein  returning  the  blood  from  the 

brain  passes  through  the  membrane  that 

is  to  become  the  squamosal.     This  open- 
ing— the  foramen  jugulare   spurium — 

is  later  of  less  importance,  and  is  finally 


Posterior  semicir- 
cular canal 
Floccular  fossa 


Internal  auditory  canal 
Temporal  bone  at  about  birth,  from  above  and  within. 


FIG.  207. 

Malleus 


Tympanic  ring 


Tegmen  tympani  in 
Glaserian  fissure 


Tympanic  portion  of  temporal  bone  in  the  second  year. 


closed.     In  the  skull,  at  birth,  a  pin-hole 

representing  it  may  be  found  at  the  postglenoid  tubercle. 

later. 


It  is  sometimes  seen 


1  Journal  of  Anatomy  and  Physiology,  vol.  xxvii.,  1893. 

2  Archiv  fur  Ohrenheilkunde,  Bd.  xiv.,  1879. 


1 86 


HUMAN  ANATOMY. 


THE   SPHENOID    BONE. 

In  the  adult  this  bone '  consists  of  a  cubical  body,  from  the  sides  of  which  arise 
the  great  wings,  from  its  front  the  lesser  wings,  and  from  below  the  pterygoid  pro- 
cesses. Both  development  and  comparative  anatomy  show  that  these  parts  represent 
several  bones.  The  body  consists  of  two  parts,  a  posterior  and  an  anterior.  The 
posterior,  the  basisphenoid,  is  the  centre  of  the  middle  fossa  of  the  base  of  the  skull  ; 
from  its  sides  spread  the  great  wings,  or  alisphenoids.  These  with  the  temporal 
bones  complete  the  middle  fossa.  The  anterior  part,  the  prcsphenoid,  inseparably 
connected  with  the  basisphenoid,  is  in  both  the  middle  and  the  anterior  fossae.  The 
lesser  wings,  the  orbito-sphenoids,  spread  out  from  the  presphenoid  and  cover  the 
apices  of  the  orbits.  The  pterygoid  processes  consist  each  of  two  plates,  the  inner  of 
which  represents  a  separate  bone  of  the  face,  the  outer  being  an  expansion  from  the 
alisphenoid.  Two  bones  called  the  cornua  sphenoidalia,  or  sphcnoidal  turbinates,  of 
independent  origin,  ultimately  form  a  part  of  the  body  of  the  sphenoid. 


Optic  foramen 


FIG.    208. 

Sphenoidal  turbinate 

Sphenoidal  foramen 


Infratemporai 
crest 


External  ptery- 
goid plate 


Hamular  process 


Pterygoid  notch 


Internal  pterygoid  plate 
The  sphenoid  bone  from  before. 


The  Body. — It  is  necessary  to  describe  the  basisphenoid  and  the  presphenoid 
together,  since  they  form  the  roughly  cubical  body.  The  superior  surface  con- 
tains the  deep  pituitary  fossa?  or  sella  turcica,  in  which  hangs  the  pituitary  body 
from  the  brain.  Behind  it  is  the  dor  sum  sclla,  a  raised  plate  continuous  with  the 
surface  of  the  basilar  process  of  the  occipital  and  which  completes  the  posterior  fossa. 
Its  outer  angles  are  knobs  pointing  both  forward  and  backward,  the  posterior  dinoid 
processes,  to  which  the  tentorium  is  fastened.  Beneath  these,  on  either  side  of  the 
dorsum,  is  a  groove  for  the  sixth  nerve.  In  front  of  the  sella  is  the  olivary  eminence' 
(of  the  presphenoid),  which  is  usually  an  oval  swelling,  though  it  may  be  plane  or 
concave.  At  its  sides  grooves,  often  very  poorly  marked,  lead  to  the  optic  foramina. 
The  posterior  edge  of  this  eminence  is  sometimes  grooved  for  a  vein  and  sometimes 
sharp.  Its  lateral  ends  may  become  tubercles,  the  middle  dinoid  processes.  The 
olivary  eminence  is  in  most  cases  bounded  in  front  by  a  transverse  elevation  con- 
necting the  lesser  wings,  of  which,  indeed,  it  is  a  part,  forming,  when  present,  the 
separation  of  the  anterior  and  middle  fossae.  The  front  border  presents  in  the 
median  line  a  triangular  point,  the  cthmoidal  spine. 

At  each  lateral  surface  of  the  body  is  the  carotid  groove*  for  the  internal 
carotid  artery.  It  is  well  marked  only  at  the  posterior  edge,  where  the  artery  enters 

1  Os  sphcnuidalc.     "  Fossa  hypophyscos.     "Tubvrrulum  sellat.     4  Stilcus  cnroticus. 


THE   SPHENOID    BONE. 


187 


it  from  the  apex  of  the  petrosal.  It  is  here  bounded  internally  by  a  little  tubercle, 
the  petrosal  process,  at  the  base  of  the  dorsum,  and  externally  by  a  very  delicate 
plate,  the  lingula,  which  sometimes  projects  considerably  ;  these  .two  processes 
touch  either  side  of  the  end  of  the  carotid  canal  in  the  petrous.  The  rest  of  the 
side  of  the  body  is  hollowed  for  the  cavernous  sinus,  in  which  the  carotid  artery  runs. 
It  is  covered  below  by  the  origin  of  the  great  wing.  The  posterior  surface  of  the 
body  is  rough  up  to  puberty  for  the  cartilage  that  binds  it  to  the  basilar  process  of 
the  occipital  ;  later  these  parts  coossify,  and  thereafter  the  posterior  surface  is  made 
artificially  by  the  saw.  The  anterior  surface  presents  in  the  middle  a  sharp  ridge, 
the  sphenoidal  crest  ,^  to  join  the  vertical  plate  of  the  ethmoid.  Just  at  the  sides  of  this 
the  bone  is  smooth  and  aids  in  forming  the  wall  of  the  nasal  fossa.  In  each  lateral 
half  is  an  opening,  the  sphenoidal  foramen?  into  the  cavity  of  the  bone.  The 
inferior  surface  presents  in  the  middle  a  longitudinal  swelling,  thick  behind, 
narrow  and  sharp  in  front,  the  rostrum,  fitting  into  the  vomer  and  usually  joining 
the  lower  edge  of  the  crest  without  interruption.  It  may  stop  short  of  it.  On  either 
side  of  the  rostrum  there  is  a  smooth  triangular  surface  made  of  delicate  plate,  which 
extends  up  onto  the  front,  forming  the  smooth  surface  beside  the  crest,  and  bound- 

FIG.  209. 


Foramen  rotundum 


Carotid  groove 
Scaphoid  fossa 

Pterygoid  fossa 


External  pterygoid  plate 


Hamular  process 


The  sphenoid  bone  from  behind. 


ing  a  large  part  of  the  hole  into  the  antrum.  These  are  the  bones  of  Bertin,  or 
sphenoidal  spongy  bones,  of  which  more  is  to  be  said  under  Development  (page  191). 

The  body  of  the  sphenoid  is  hollow,  enclosing  two  cavities,  the  sphenoidal 
sinuses,  separated  by  a  septum,  which  runs  obliquely  backward  from  the  crest,  so 
that  one  sinus  is  usually  much  larger  than  the  other.  These  sinuses  have  irregular 
ridges  partially  subdividing  them.  They  are  lined  by  mucous  membrane  and  open 
into  the  nasal  cavity  by  the  sphenoidal  foramina.  The  opening  is  reduced  when  the 
ethmoid  is  in  place. 

The  great  wings  3  have  each  a  cerebral  or  superior  surface  forming  a  large  part 
of  the  middle  fossa,  an  external  surface  looking  outward  into  the  temporal  and 
downward  into  the  zygomatic  fossa,  and  an  orbital  surface  forming  most  of  the  outer 
wall  of  that  cavity.  The  superior  surface  is  smooth  and  concave  ;  springing  from 
the  side  of  the  basisphenoid,  it  spreads  upward  and  outward  and  also  backward  to 
fill  the  gap  between  the  petrous  and  squamosal  parts  of  the  temporal.  By  the  side 
of  the  body  there  is  a  short  canal  running  forward  to  open  on  the  front  of  the  bone 
into  the  spheno-maxillary  fossa  ;  this  is  the  foramen  rotundum  for  the  superior  max- 
illary division  of  the  fifth  nerve.  A  little  further  back  and  more  internal  is  a  pin- 

1  Crista  sphenoidalis.     -  Apertura  sinus  sphcnoidalis.     3  Alac  magnae. 


1 88 


HUMAN    ANATOMY. 


hole,  the  foramen  of  Vesalius,  for  a  minute  vein.  Farther  back  and  outward  near 
the  angle  is  the  foramen  ovale,  transmitting  the  mandibular  division  of  the  fifth 
cranial  nerve  to  the  base  of  the  skull,  and  admitting  the  small  meningeal  branch 
of  the  internal  maxillary  artery.  Just  beyond  this,  in  the  extreme  angle,  so  as  some- 
times to  be  completed  by  the  temporal,  is  the  foramen  spinosum,  admitting  the 
middle  meningeal  artery  to  supply  the  bone  and  the  dura.  The  external  surface 
is  divided  into  a  larger,  superior,  vertical  part,  looking  towards  the  temporal  fossa, 
and  one  looking  into  the  zygomatic  fossa.  These  are  separated  by  the  infratcm- 
poral  crest,  which  near  the  front  points  downward  as  a  strong  prominence,  the  infra- 
temporal  spine.  The  inferior  surface  contains  the  foramen  ovale  and  the  foramen 
spinosum.  Just  behind  the  latter,  at  the  posterior  angle,  is  the  spine  of  the  sphenoid, 
pointing  downward,  grooved  at  the  inner  side  by  the  chorda  tympani  nerve.  The 
external  surface  has  an  anterior  border  where  it  meets  the  orbital  surface,  which 
joins  the  malar.  The  superior  border  slants  upward,  overlapping  the  frontal  and 
parietal  bones.  The  posterior  border  is  about  vertical  as  far  down  as  the  infra- 
temporal  crest,  and  bevelled,  especially  above,  to  be  overlapped  by  the  squamous 
part  of  the  temporal.  The  lower  part  of  this  border  runs  backward  and  somewhat 
overlaps  the  squamosal.  The  posterior  border  of  this  surface,  from  the  spine  to  the 


Articulates  with  frontal 


FIG.  210. 

Ethmoidal  crest 


Sphenoidal 
fissure 


Foramen  rotun- 
diini 


Foramen  ovale 
Foramen  spinosum 


Post,  cli 
process 

The  sphenoid  bone  from  above. 

body,  is  slightly  rough  for  the  petrous,  making  with  it  a  groove  on  the  under  side 
for  the  cartilaginous  Eustachian  tube.  The  smooth  orbital  surface,  facing  inward 
and  forward,  is  quadrilateral,  broader  in  front  than  behind.  Almost  the  whole  of  it  is 
in  the  outer  wall  of  the  orbit,  of  which  it  forms  the  greater  part  ;  but  a  small  portion, 
narrow  behind  and  expanding  in  front,  looks  into  the  spheno-maxillary  fissure,  which 
bounds  this  surface  below.  It  joins  the  malar  in  front.  On  the  top  of  the  bone 
there  is  a  rough  triangular  region  in  the  angle  formed  by  the  meeting  of  the  external 
and  orbital  surfaces,  on  which  the  frontal  bone  rests.  This  is  above  the  front  half 
of  the  orbital  plate.  The  remainder  of  the  upper  and  the  whole  of  the  posterior 
border  of  the  latter  bound  the  sphcnoidal  fissure. '  This  cleft  is  an  elongated  aper- 
ture, directed  obliquely  outward  and  upward  between  the  great  and  lesser  wings  of 
the  sphenoid,  completed  externally  by  the  frontal.  It  opens  anteriorly  into  the 
orbit  and  transmits  the  third,  the  fourth,  the  ophthalmic  division  of  the  fifth  and 
sixth  cranial  nerves,  and  the  ophthalmic  veins.  There  is  a  small  projection  near  the 
middle  of  the  hind  border  for  a  ligament  crossing  the  fissure  and  for  the  outer  head 
of  the  external  rectus. 

The  lesser  wings,2  forming  the  back  part  of  the  anterior  fossa  and  of  the  roof 
of  the  orbit,  arise  by  two  roots.  The  superior  is  a  plate  covering  the  presphenoid  ; 
the  inferior  is  a  strong  process  from  the  side  of  the  body.  With  the  latter  they 

1  I'issur.i  orbltallH  superior.     '•'  Alne  parvae. 


THE  SPHENOID  BONE. 


189 


pIG    2II 


Sphenoid  bone,  showing  abnormal  development  of 
middle  clinoid  processes,  especially  on  the  left  side.  Re- 
duced one-half. 


enclose  a  canal,  commonly  called  the  optic  foramen,^  for  the  optic  nerve,  which  is 
accompanied  by  the  ophthalmic  artery.  The  length  of  the  canal  measured  along 
the  inferior  root  is  about  five  millimetres.  The  length  of  the  roof  is  greater,  per- 
haps nearly  twice  as  much,  but  it  is  variable  from  the  uncertain  development  of 
that  part  of  the  bone  ;  definite  dimensions  are,  therefore,  wanting.  The  vertical 
diameter,  some  five  millimetres,  of  the  opening  into  the  orbit  is  a  little  greater  than 
the  transverse.  The  small  wing  over- 
hangs the  front  of  the  middle  fossa 
bounding  the  sphenoidal  fissure  above, 
and  ends  laterally  in  a  sharp  point.  The 
anterior  clinoid  process  is  a  sharp  pro- 
jection backward  above  the  inferior 
root  and  towards  the  posterior  clinoid. 
Sometimes  it  reaches  the  latter  ;  some- 
times it  is  connected  by  a  spur  with  the 
middle  clinoid  process,  then  bridging  the 
carotid  groove  and  making  a  carotico- 
flinoid  foramen  (Fig.  211).  The  an- 
terior border  of  the  lesser  wings  is 
rough  at  its  inner  part  and  smooth  at 
the  outer,  where  it  joins  the  posterior 
edge  of  the  horizontal  plate  of  the  frontal.  The  posterior  border  is  smooth,  form- 
ing most  of  the  boundary  of  the  anterior  and  middle  cranial  fossae. 

The  pterygoid  processes 2  are  downward  projections  which,  articulating  with 
the  palate  bone,  form  the  back  of  the  framework  of  the  upper  jaw.  Each  consists  of 
two  plates,  an  inner  and  an  outer,  united  in  front,  diverging  behind  to  form  the 
pterygoid  fossa,  and  separating  below  on  either  side  of  the  pterygoid  notch.  The 
inner  springs  from  the  body,  the  outer  from  the  great  wing.  The  inner  pterygoid 
plate3  is  the  longer.  It  is  nearly  vertical,  ending  in  the  slender  hamular  process* 
which  points  outward,  bounding  a  deep  little  notch  through  which  the  tendon  of  the 
tensor  palati  plays.  At  the  inner  side  of  its  origin  the  internal  plate  presents  a 

scale-like  curved  projection,  the  vaginal 
process,  above  which  is  an  antero-poste- 
rior  groove  below  the  body  of  the  sphe- 
noid, in  which  the  lateral  expansion  of 
the  base  of  the  vomer  is  received.  Just 
external  to  the  vaginal  process  is  an- 
other small  groove,  the  ptery go-palatine, 
which  the  palate  bone  converts  into  a 
canal  leading  back  from  the  spheno- 
maxillary  fossa.  The  outer  pterygoid 
plate5  is  broader  and  flares  outward. 
The  anterior  surface  of  the  root  is  nearly 
smooth,  forming  the  back  wall  of  the 
spheno-maxillary  fossa.  It  has  the 
openings  of  two  canals  :  the  upper  and 
outer  is  that  of  the  foramen  rotundum  ; 

Portion  of  sphenoid  bone,  showing  the  foramen  pterygo-         -11  j    •  i  •    1     •  11  • 

spinosum.  the  lower  and  inner,  which  is  smaller,  is 

the  Vidian  canal,  transmitting  the  nerve 

and  vessels  of  that  name.  There  is  a  vertical  ridge  between  the  two,  and  a  slight 
groove  below  the  latter,  forming  with  the  palate  bone  the  beginning  of  the  poste- 
rior palatine  canal  which  runs  from  the  spheno-maxillary  fossa  through  the  hard 
palate,  transmitting  a  descending  palatine  nerve  and  vessels.  The  lower  anterior 
edges  of  both  plates  are  rough  to  articulate  with  that  bone.  The  outer  surface  of 
the  external  plate  is  irregular  for  the  origin  of  the  external  pterygoid  muscle.  The 
inner  wall  of  the  inner  plate  is  smooth.  It  bounds  laterally  the  back  of  the  nasal 
cavity.  The  posterior  borders  of  both  plates  are  sharp,  excepting  that  the  inner  is 
formed  by  the  union  of  two  lines  which  enclose  the  scaphoid  fossa  where  the  tensor 
palati  arises.  Rather  less  than  half  way  down  the  internal  plate  presents  a  promi- 

1  Foramen  opticum.    -  Processus  pterygoidei.    :i  Lamina  mcdialis  proc.  pteryg.     *  Hamulus  pterygoidei.    •"'  Lamina  lateral!.- 
proc.  pteryg. 


FlG.    212. 

Spheno-maxillary  fossa  Foramen  ovale 


External 
pterygoid 
plate 


190 


HI 'MAN    ANATOMY. 


Great  win. 
(alisphenoid) 


nence  bounding  a  groove  below,  which  supports  the  Eustachian  tube.  The  posterior 
border  of  the  outer  plate  is  irregularly  scalloped.  Near  the  top  a  transverse  ridge 
crosses  its  inner  surface  ;  if  well  marked,  this  forms  the  top  of  the  pterygoid  fossa. 
It  may  be  barely  discernible  (Waldeyer l).  Just  above  the  scaphoid  fossa  is  the 
hind  end  of  the  Vidian  canal  opening  into  the  middle  lacerated  foramen  opposite  the 
apex  of  the  petrous.  The  development  of  the  pterygoid  plates  varies  greatly.  The 
upper  part  of  the  outer  may  be  prolonged  to  the  spine  of  the  sphenoid,  just  outside 
of  the  foramen  ovale,  with  a  perforation  at  this  point,  so  that  some  of  the  branches 
of  the  third  division  of  the  fifth  cranial  nerve  may  pass  on  either  side  of  it.  This 
occurs  by  the  ossification  of  a  band  of  fibrous  tissue,  connecting  the  back  of  the 

plate  with  the  spine,  and  thus 

FIG.  213.  forming  the  foramen  ptcrygo- 

spinosum  of  Civinini  (Fig.  212). 
This  is  always  behind  the  fora- 
men ovale,  or  internal  to  it. 
Just  outside  of  the  foramen  is 
found,  very  rarely,  a  little  canal 
on  the  under  side  of  the  great 
wing,  transmitting  a  branch  of 
the  mandibular  division  of  the 
fifth  nerve,  the  porus  crotaphit- 
ico-buccinatorius  of  Hyrtl. 

Articulations. — Much 
has  been  already  said  incident- 
ally on  this  point  in  the  fore- 
going description.  The  sphenoid  bone  joins  the  occipital  behind.  The  great  wings 
send  the  spine  into  the  entering  angle  between  the  squamous  and  petrous  portions 
of  the  temporal.  These  two  bones — the  sphenoid  and  the  temporal — form  the 
entire  middle  fossa  of  the  skull.  The  middle  lacerated  foramen  is  just  behind  the 
carotid  groove  at  the  side  of  the  body  and  in  front  of  the  end  of  the  petrous.  At 
the  side  of  the  skull  the  great  wings  join  the  squamous  behind,  the  parietal  and  the 
frontal  above,  and  the  malar  in  front.  The  ethmoid  covers  the  front  of  the  body  of 
the  sphenoid,  its  vertical  plate  joining  the  crest.  The  vomer  covers  the  rostrum 
below.  The  palate  bone  fills 

FIG.  214. 

Presphenoid 


xt.  pterygoid  plate 
Int.  pterygoid  plate 

Sphenoid  bone  at  about  birth,  seen  from  before. 


Jugum  sphenoidale 
Si 


mall  wing-  (orbito-sphenoid) 
Foramen  rotundum 
Great  wing 
(alisphenoid) 


up  the  pterygoid  notch,  com- 
pleting the  fossa,  and  by  its 
sphenoidal  process  touches 
the  edge  of  the  body.  The 
frontal  bone  joins  the  lesser 
wings. 

Development. — The 
presphenoid  and  basisphenoid 
each  ossify  from  a  pair  of 
nuclei,  those  of  the  former 
appearing  at  the  end  of  the 
second  month  of  foetal  life  and 
the  latter  a  little  later.  At 
about  the  eighth  week  a  nu- 
cleus is  to  be  seen  in  each  of 
the  greater  wings  near  the  body  and  extends  outward,  involving  also  the  external 
pterygoid  plate.  The  internal  pterygoid  plate  has  a  nucleus  of  its  own,  which 
is  present  in  the  fourth  month  and  joins  the  outer  a  month  later.  Two  little  gran- 
ules appear  in  the  fourth  month  for  the  lingula  and  a  neighboring  piece  of  Un- 
bone. The  orbito-sphenoids  have  each  two  centres, — one  on  either  side  of  the  optic 
foramen.  It  would  seem  that  the  inner  may  in  some  cases  take  the  place  of  those  for 
the  presphenoid.  In  any  case  the  presphenoid  and  the  lesser  wings  unite  before  birth. 
In  the  seventh  or  eighth  month  the  presphenoid  and  basisphenoid  unite,  but  at  birth 
they  are  still  separated  by  cartilage  on  their  lower  surface.  At  birth  the  bone  con- 
1  Sitzungsber.  Acad.  Wissen.,  Berlin,  1893. 


Basisphenoid      Lingula    Foramen  ovale 
Sphenoid  bone  at  about  birth,  seen  from  behind. 


THE   ETHMOID    BONE. 


191 


Crista  galli 


sists  of  the  basisphenoid,  the  presphenoid,  and  the  lesser  wings  in  one  piece,  and  a 
lateral  one  on  each  side, — namely,  the  greater  wing  and  the  pterygoids.  The  dorsum 
sellae  has  a  separate  epiphysis  which  appears  after  birth.  In  the  first  year  the  lesser 
wings  spread  across  the  top  of  the  presphenoid,  joining  the  jugum  sphenoidale,  so 
that  it  does  not  show  in  the  anterior  fossa.  The  external  pterygoid  plate  is  an  out- 
growth of  the  great  wing. 

The  cornua  sphenoidalia,  bones  of  Berlin,  or  sphenoidal  turbinate  bones,  are  two 
thin  plates  which  appear  before  birth  at  the  front  of  the  presphenoid.  They  cover 
both  the  front  and  its  inferior  surface  at  the  sides  of  the  rostrum.  At  five  years  they 
are  still  free,  but  have  approached  their  permanent  shape  of  hollow  cones.  The 
hollowing  out  of  the  body  of  the  sphenoid  now  begins,  and  at  the  same  time  the 
upper  part  of  these  bones  is  absorbed,  so  that  the  foramina  become  notches.  These 
bones  are  ultimately  joined  to  the  sphenoid,  the  ethmoid,  and  the  palate.  Though 
usually  reckoned  as  parts  of  the  sphenoid,  there  is  reason  to  believe  that  they 
are  generally  fused  earlier  with  the  ethmoid.  The  basisphenoid  begins  to  coossify 
with  the  occipital  at  about  the  fifteenth  year.  The  process  is  first  completed  above. 

THE    ETHMOID    BONE. 

The  ethmoid J  consists  of  a  median  plate  forming  a  part  of  the  nasal  septum,  of 
the  cribiform  plate  joining  it  at  the  top  on  either  side  and  forming  the  roof  of  the 
nasal  cavity,  and  of  two  lateral  masses  attached  to  the  lateral  border  of  each  cribriform 
plate,  and  touching  the  vertical  plate  very  slightly  just  below  its  junction  with  the 
front  of  the  cribriform  plate.  These  lateral  masses  are  roughly  cubical,  interposed 
between  the  cavities  of  the  nose 

and  of  the  orbit.     They  consist  of  FIG.  215. 

a  series-  of  delicate  plates  forming 
the  walls  of  air-spaces  or  cells, 
which  are  mostly  completed  by 
neighboring  bones. 

The  vertical  or  median 
plate  2  projects  near  the  front  into 
cranial  cavity  as  the  crista 
galli,  thicker  in  front  than  behind, 
with  an  oblique  upper  border  run- 
ning sinuously  downward  and 
backward.  Its  greatest  elevation 
is  about  one  centimetre.  The 
front  part  is  occasionally  hollow, 
forming  a  part  of  the  frontal  sinus. 
It  gives  attachment  to  the  falx 
cerebri,  a  fold  of  dura  separating  Uncinate  process 

the  hemispheres  of  the  brain.       A  Trie  ethmoid  bone,  outer  aspect  from  the  right  side. 

little  plate,  a/a,3  facing  downward 

and  forward,  arises  from  the  front  on  either  side,  articulating  with  the  frontal.  Just 
before  the  crista  galli  is  a  pin-hole,  the  foramen  c&cum,  usually  formed  by  both 
ethmoid  and  frontal,  but  which  may  be  in  either.  It  is  said  to  transmit  a  vein  in 
early  life,  but  is  closed  later.  The  part  of  the  vertical  plate  below  the  horizontal  one 
is  five-sided.  The  upper  border  runs  along  the  base  of  the  skull  ;  one  in  front  of 
it  slants  downward  and  forward  under  the  nasal  spine  of  the  frontal,  sometimes 
reaching  the  nasal  bones  ;  another  descends  nearly  vertically  along  the  crest  of  the 
sphenoid.  Of  the  two  inferior  borders,  the  posterior  runs  downward  and  forward 
along  the  greater  part  of  the  vomer,  while  the  anterior,  running  downward  and 
backward  to  meet  it,  is  free  in  the  skeleton,  but  in  life  is  attached  to  the  triangular 
cartilage  which  forms  a  large  part  of  the  septum.  The  sides,  covered  with  mucous 
membrane,  are  smooth  except  at  the  upper  part,  where  there  are  vertical  grooves 
for  the  olfactory  nerves.  This  plate  usually  slants  to  one  side. 

The  horizontal  or  cribriform  plate  4  forms  the  floor  of  a  narrow  groove  on 
either  side  of  the  crista  galli  and,  farther  back,  in  the  middle  of  the  anterior  fossa  of 

1  Os  cthmoidale.     -  Lamina  pcrpendicularis.     3  Processus  alaris.     4  Lamina  cribrosa. 


Mid.  turbinate 


192 


HUMAN    ANATOMY. 


the  skull.  The  greatest  breadth  of  the  groove  is  about  five  millimetres.  It  nar- 
rows in  front  to  a  point,  and  thus  allows  the  lateral  masses  to  touch  the  median 
plate.  It  supports  the  olfactory  lobe  of  the  brain,  and  is  perforated  by  holes  for  the 
passage  of  the  olfactory  nerves.  These  are  arranged  rather  vaguely  in  three  rows. 
There  are  many  in  front  and  few  behind.  Many  of  the  larger  ones,  which  are  near 
the  septum  or  at  the  outer  side,  are  small  perforated  pits.  At  the  front  a  longi- 
tudinal fissure,  close  to  the  crista  galli,  transmits  the  nasal  branch  of  the  fifth  nerve. 
The  lateral  masses  1  are  two  collections  of  bony  plates  imperfectly  bounding 
cavities.  They  are  roughly  six-sided,  the  greatest  diameter  being  antero-posterior. 
The  outer  surface  presents  a  vaguely  quadrilateral  plate,  the  os planum?  forming 
a  large  part  of  the  inner  wall  of  the  orbit.  In  its  upper  border  are  two  notches, 
which  become  the  anterior  and  posterior  ethmoidal  foramina  when  the  frontal  bone 
is  in  place.  The  former  transmits  the  nasal  branch  of  the  fifth  nerve  from  the  orbit 
to  the  cranial  cavity.  The  os  planum  is  bounded 
behind  by  the  body  of  the  sphenoid  ;  below  by  the 
palate  bone  and  superior  maxilla,  the  former  of  which 
usually,  and  the  latter  always,  complete  some  eth- 
moidal cells  which  appear  along  the  lower  border. 
There  is  a  large  mass  of  open  cells  in  front  of  the  /  /  / 

os  planum.     Those  nearest  to  it  are  completed  by 
the  lachrymal  and  the  more  anterior  ones  by  the 


Median  or  perpendicular  plate  of  ethmoid  bone  in  place.     The  right  lateral  mass  of  the  ethmoid  has  been  removed. 

nasal  process  of  the  superior  maxilla.  Posteriorly,  the  lateral  mass  rests  against  the 
body  of  the  sphenoid,  the  posterior  cells  being  separated  from  those  of  the  sphenoid 
by  the  cornua  sphenoidalia.  The  open  cells  on  the  upper  surface  of  the  lateral  mass 
are  closed  by  the  imperfect  cells  on  the  under  side  of  the  horizontal  plate  of  the 
frontal  beside  the  sphenoidal  notch.  The  few  cells  that  open  anteriorly  are  contin- 
uous with  the  lateral  ones,  and  are  closed  by  the  nasal  process  of  the  upper  jaw. 
The  numerous  spaces  within  the  ethmoid  are,  for  the  most  part,  completed  by  the 
neighboring  bones,  after  which  they  are  named.  There  are  some  beneath  the  os 
planum,  however,  entirely  within  the  ethmoid.  Tin-  fthmoidal  ccUs*  are  divided  into 
anterior  and  posterior,  of  which  the  former  open  into  the  nose  below  the  middle 
turbinate  bone  and  the  latter  above  it.  The  si/e  and  shape  of  the  ethmodial  cells 
are  very  irregular  ;  sometimes  the  middle  turbinate  is  hollowed  into  one,  some- 

1  Labyrinthii!)  ethmoldalis.     "Lamina  pupyracea.     3Cellulae  cthmoldalcs. 


THE   ETHMOID    BONE. 


193 


Median  plate 


Crista  galli 


Infundibulum 


Orbital 
plate 


The  ethmoid  bone  from  above. 


times  they  swell  out  into  the  cavities  of  other  bones,  notably  into  the  frontal  sinus. 
The   internal   surface  of  the  lateral  mass,  forming  the  outer  wall  of   the  nasal 
cavity,    cannot  be  seen  on   the   entire  bone.       It   is  best  studied  on  the  bisected 
skull  ;  but  to  study  the  whole  bone,   further  cutting  is  necessary,   since  this  sur- 
face is  made  of  a  series  of  con- 
voluted  plates,    some  of   which  FIG.  217. 
conceal  others.      At  least  two  of 
these — the  superior  and  the  mid- 
dle turbinate  bones 1 — are  evident. 
They  are  curled  with  their  con- 
vexities    towards     the     median 
plane,    so   as    to   overhang  two 
antero-posterior    passages,     the 
superior  and  the  middle  meatus 
of   the  nasal  fossa.      According 
to  Zuckerkandl,  there  are  three 
ethmoidal    turbinate     bones     in 
.more  than  eighty  per  cent.,  and 
sometimes    four.       When    only 
two  are  seen,  it  is  owing  either 
to    the   absence    of    the    second 
or  to  its  slight  development,  so 
that  it  is  hidden  by  the  upper. 
It  is  certain   that  only  two  are 
evident  in   most  cases,   and  we 
shall  follow  the  usual  method  of 
so    describing   the   bone.2     The 
inferior  ethmoidal  (middle)  tur- 
binate is  much  the  larger,  very  prominent,  and  joins  the  ascending  process  of  the 
superior  maxilla  at  the  crista  ethmoidalis  or   superior  turbinate  crest.      Its  general 
course  is  backward  and  downward,  to  end  in  a  point  at  the  posterior  border  of  the 

bone.  The  free  edge  is  so  much 
curled  under  as  to  be  hidden. 
The  superior  turbinate  is  much 
smaller,  occupying  the  postero- 
superior  angle.  It  appears  to 
separate  from  the  turbinate  below 
it  at  about  the  middle  of  this  sur- 
face. The  siiperior  meatus,  which 
it  overhangs,  is  therefore  small. 
As  above  implied,  an  additional 
ethmoidal  turbinate  may  appear 
from  beneath  it,  and  still  another 
small  one  may  very  exceptionally 
be  found  above  it  at  the  extreme 
upper  posterior  angle.  At  the 
point  at  which  the  middle  turbi- 
nate bone  joins  the  nasal  process 
of  the  maxilla  there  is  often  a 
slight  elevation,  the  agger  nasi, 
which  is  supposed  to  be  the  an- 
terior end  of  another  turbinate  which  passes  under  the  preceding.  When  the 
middle  turbine  is  removed,  a  curved  projecting  plate,  the  uncinate  process?  is  seen 
on  the  lateral  mass,  curving  downward  and  backward.  It  is  some  two  or  three 
millimetres  broad  and,  extending  beneath  the  rest  of  the  bone,  joins  the  inferior 
turbinate.  The  uncinate  process,  together  with  the  agger,  is  held  to  represent  the 

2  There  are  practically  three  turbinate  bones,  the  upper  two  of  which  are  parts  of  the 
ethmoid  and  the  lowest  a  separate  bone.  These  are  called  superior,  middle,  and  inferior ; 
hence  we  speak  of  the  inferior  ethmoidal  turbinate  as  the  middle  one. 

1  Concha  nasalis  superior  ct  media.     3  Processus  uncinatus. 

13 


FIG.  218. 


Superior  surface 


Alar  process 
of  crista  galli 


Posterior  ethmoidal 
cells 


Posterior  ethmoidal 
cells 


Middle  turbinate 


Sup.  meatus 


Median  plate 


The  ethmoid  bone  from  behind,  showing  median  plate  and  lateral 
masses. 


194 


HUMAN   ANATOMY. 


FIG.  219. 

Probe  in  infundibulum 


Crista  gal!' 

Cribriform- 
plate 


Sup.  turbinate 


Bulla 


Uncinate  process 

The  ethmoid  bone,  inner  aspect  from  left  side,  part  of  the  middle  turbinate 
having  been  removed. 


naso-turbinal  bone  of  many  mammals.  Behind  this  is  a  globular  swelling,  the  bulla,1 
formed  by  a  plate  springing  from  the  os  plenum,  covering  cells,  which  also  is  held 
to  represent  a  turbinate.  Between  the  uncinate  process  and  the  bulla  is  a  deep 
groove,  the  infundibulum*  curving  downward  and  backward,  the  opening  into  which 
from  the  nasal  fossa  is  known  as  the  hiatus  semilunaris.  The  upper  end  of  the 

infundibulum  opens  into 
the  frontal  sinus  in  about 
half  the  cases,  3  ending 
blindly  in  the  others  ;  it 
is  bounded  externally  to 
a  varying  extent  by  the 
lachrymal.  A  number 
of  anterior  ethmoidal 
cells  generally  open  into 
this  portion.  The  lower 
end  of  the  infundibu- 
lum has  an  opening  on 
its  outer  side  into  the 
antrum. 

Articulations.— 
These  have  already  been 
described  incidentally. 
Briefly  recapitulated, 
however,  the  articula- 
tions of  the  ethmoid  are 
with  the  frontal,  the 

sphenoid,  the  palatals,  the  vomer,  the  inferior  turbinates,  the  lachrymals,  and  the 
nasals. 

Development. — The  ethmoid  is  very  small  at  first  and  backward  in  its 
development.  About  the  middle  of  foetal  life  ossification  appears  in  the  os  planum 
and  the  middle  turbinate  bone.  A  centre  (two,  according  to  Poirier)  for  the  vertical 
plate  occurs  in  the  first  year,  from  which  ossification  extends  into  the  crista  galli. 
The  cribriform  ossifies  chiefly  (perhaps  wholly)  from  the  lateral  masses.  The  date 
of  the  union  of  the  three  pieces  is  rather  uncertain  ;  it  takes  place,  probably,  at 
about  the  sixth  year.  The  cells  appear  first  as  depressions  during  foetal  life. 
According  to  the  more  generally  accepted  view,  their  growth  is  by  absorption  of 
bone.  It  is  hard  to  believe  that  this  is  not,  at  least,  a  factor  ;  Poirier,  however, 
holds  that  they  are  due  to  the  course  of  ossification. 

THE   FRONTAL   BONE. 

This  bone,4  which  forms  the  front  of  the  vault  of  the  skull,  most  of  the  floor  of 
its  anterior  fossa,  and  bounds  the  greater  part  of  the  orbits  and  the  ethmoidal  cells 
above,  is  developed  into  two  symmetrical  halves  which  unite  in  the  second  year.  It 
is  convenient  to  divide  the  bone  thus  formed  into  a  vertical  and  a  horizontal  portion, 
although  this  division  rests  on  no  scientific  basis. 

The  vertical  portion,5  convex  anteriorly,  presents  on  either  side,  below  its 
middle,  the  frontal  eminence?  which  represents  the  chief  centre  of  ossification  of 
either  half.  Very  prominent  in  infancy,  it  diminishes  during  growth,  and  is  hardly 
to  be  made  out  in  most  adult  skulls.  The  lower  border  of  the  vertical  portion  grows 
downward  in  front  between  the  orbits.  At  the  sides  of  this  projection  are  the 
internal  angular  processes  of  the  orbits.  In  the  middle-line  a  faint  zigzag  line  marks 
the  remnant  of  the  iutcrfroutal  suture.  Above  this  is  a  smooth,  rather  prominent 
surface,  called  the  glabclla,  external  to  which  are  the  superciliary  ridges'"  or  emi- 
nences, which  extend  outward,  somewhat  above  the  inner  ends  of  the  orbits.  The 
development  of  these  varies  greatly.  On  either  side  of  the  nasal  projection  is  the 
orbital  arch,  extending  outward  from  the  internal  angular  process.  At  about  the 
s  H.  A.  Lothrop  :  Annals  of  Surgery,  vol.  xxviii.,  1898. 

1  Knl  I. -i    cthmuiilnlis.      "Infundibulum    tthinuidalc.      *  0»    frontolc.      r'  Squama    frontalis.      'Iul.it     frnntnle.      "Arena 
MijiiTi-illares. 


THE   FRONTAL    BONE. 


195 


inner  third  of  the  arch  is  the  supraorbital  notch  *  for  the  nerve  and  the  artery  of  the 
same  name.  The  outer  edge  of  the  notch  is  more  prominent  than  the  inner.  Very 
often  this  is  replaced  by  a  foramen,  which  may  be  four  or  five  millimetres  above  the 
edge  of  the  bone.  The  arch  ends  externally  in  the  external  angular  process?  which 
joins  the  malar  and  is  very  prominent.  From  it  springs  the  temporal  crest?  which, 
curving  upward  and  backward,  separates  the  anterior  surface  of  the  bone  from 
the  lateral  one,  which  is  a  part  of  the  temporal  fossa.  This  crest  generally,  before 
leaving  the  bone,  divides  into  two  lines,  of  which  one  is  much  more  distinct  than  the 
other.  The  vertical  part  of  the  bone  has  a  slight  point  above  in  the  middle  and  a 
very  jagged  posterior  border  interlocking  with  the  parietal.  The  latter  is  slightly 
overlapped  above  and  overlaps  below.  The  bevelled,  though  jagged,  articular  sur- 
face broadens  below  to  meet  a  triangular  rough  space  on  the  inferior  surface.  At  the 
lower  lateral  edge  the  bone  is  covered  by  the  top  of  the  great  wing  of  the  sphenoid. 

FIG.  220. 


Temporalis 


External  angular 

""  /  *MBffi¥^  iyffii'ffiW  1IU- a"K- PIOL'ess          "vyp 

Supra-orbital  foramen 

Corrugator  supercilii 

Orbicularis  palpebrarum 

Nasal  spine 
The  frontal  bone  from  before. 

The  horizontal  portion  4  shows  in  the  middle  of  its  lower  aspect  a  rough  surface 
extending  onto  the  front,  called  the  nasal  process,  which  articulates  anteriorly  with 
the  nasal  bones  and  laterally  with  the  ascending  processes  of  the  upper  jaw.  In  the 
middle  projects  a  thin  plate,  the  nasal  spine,  behind  and  between  the  nasal  bones. 
On  either  side  of  this  there  is  often  found  a  small  smooth  surface  forming  a  small 
part  of  the  roof  of  the  nasal  cavity.  Behind  this  lies  the  median  ethmoidal  notch?  on 
either  side  of  which  is  an  irregular  space  reaching  to  the  inner  edge  of  the  orbit, 
made  of  imperfect  cells,  completing  the  ethmoidal  ones.  In  front  of  these  a  cavity 
extends  directly  up,  hollowing  out  the  bone  into  \hefrontal  sinus,  which  may  extend 
outward  and  backward  over  the  orbits.  A  partition  separates  the  sinuses  of  the  two 
sides,  which  are  rarely  symmetrical.  The  sinus  opens  into  the  middle  meatus  either 
directly,  under  the  front  of  the  middle  turbinate,  or  through  the  infundibulum. 
When  the  ethmoid  is  in  place,  the  cribriform  plate  and  the  crista  galli  fill  up  the 
ethmoidal  notch  ;  the  ethmoidal  cells  are  then  closed,  and  the  ethmoidal  foramina 

1  Incisura  supraorbitalis.     -  Processus  zygomaticus.     3  Linca  temporalis.     4  Pars  orbitalis.     "' Incisura  cthiuoidults. 


196 


HUMAN   ANATOMY. 


and  canals  are  formed.  External  to  this  lies  the  orbital  plate,  the  front  of  which  is 
overhung  by  the  supraorbital  arch.  It  is  slightly  concave  from  side  to  side.  Just 
under  cover  of  the  external  angle  is  an  ill-marked  depression 1  for  the  lachrymal  gland. 
Near  the  internal  angular  process  there  may  be  a  small  fossa  2  for  the  cartilaginous 
pulley  for  the  superior  oblique  muscle.  More  frequently  there  is  a  minute  tubercle. 
The  inner  border  of  the  orbital  surface  runs  nearly  straight  backward.  Its  sharp 
edge  articulates  from  before  backward  with  the  ascending  process  of  the  maxilla, 
the  lachrymal,  and  the  ethmoid.  The  outer  edge  runs  obliquely  inward.  External 
to  it,  behind  the  angular  process  which  joins  the  malar,  is  a  rough  triangular  surface 
articulating  with  the  great  wing  of  the  sphenoid.  The  posterior  border  of  the  orbital 
plate  is  short  and  serrated  to  join  the  small  wings  of  the  sphenoid. 

The  internal  surface  of  the  frontal  presents  the  frontal  crest  below  in  the 


Groove  for  longitudinal 
sinus 


Pacchionian 
depressions 


External  angular  process 


Supra-orbital  foramen 

Frontal  sinus 


Frontal  crest 
Foramen  caecum 


Nasal  spine 
Nasal  process 

The  frontal  bone  from  behind. 


median  line.  It  is  a  slight  ridge,  to  which  the  falx  is  attached.  A  narrow  groove 
runs  along  it,  starting  at  the  foramen  c^ci/iu,  a  hole  either  in  this  bone  or  between 
it  and  the  ethmoid.  This  groove  is  for  the  superior  longitudinal  sinus.  After  a 
short  distance  the  crest  disappears,  but  the  groove  broadens  and  extends  to  the  top 
of  the  bone.  There  are  a  few  grooves  for  branches  of  the  middle  meningeal  artery 
at  the  side  and  some  small  Pacchionian  depressions.3  Below,  on  either  side  of  the 
notch,  are  the  orbital  plates,  which  slant  strongly  downward  and  inward,  so  as  to 
leave  the  ethmoid  in  a  deep  gutter.  Their  upper  surfaces  are  very  irregular  with 
so  called  digital  impressions  for  the  opposed  cerebral  convolutions.  It  is  now  evident 
how  the  frontal,  the  ethmoid,  and  the  lesser  wings  of  the  sphenoid  form  the  anterior 

fossa  of  the  skull. 

8  See  Parietal  Rone  (pai^e  igS). 

1  Fossa  nl.ni.liil.il'  l.u  i  iin.iliv     2  Foven  trochlcnrl*. 


THE   PARIETAL    BONE. 


197 


Articulations. — The  frontal  articulates  with  the  nasal,  superior  maxillary, 
lachrymal,  malar,  ethmoid,  sphenoid,  and  parietal  bones. 

Development  and  Changes. — The  only  important  centres  are  the  two  sym- 
metrical ones  appearing  in  the  membrane  at  the  frontal  eminences  towards  the  end 
of  the  second  month  of  fcetal  life.  There  is  a  separate  point  for  the  nasal  spine 
and  one  near  each  angular  process  of  the  orbit.  These  smaller  ones  are  fused  in  the 
seventh  month  of  fcetal  life.  There  is  a  centre  for  the  posterior  angle  (Gegenbaurj, 
which  also. unites  before  birth.  The  median  (in'etopic)  suture  usually  closes  towards 
the  end  of  the  second  year,  and  a  year  or  two  later  is  hardly  to  be  recognized,  except 
by  the  rudiment  at  the  lower  end.  Occasionally  the  suture  persists  ;  in  that  case  it 
remains  in  extreme  old  age  after  the  others  have  vanished.  Not  very  rarely  in 
the  foetus  or  infant  a  dilatation  of  the  fissure,  metopic  fontanelle,  is  found  near  the 
upper  part  of  its  lower  third.  There  are  a  few  cases  of  traces  of  this  in  the  adult.1 
The  frontal  sinuses  appear  about  the  seventh  year  and  increase  up  to  adult  life. 
Later  they  are  said  to  grow  again,  since  in  the  latter  part  of  life  the  inner  table  of 
the  skull  follows  the  shrinking  brain.  As  their  size  is  dependent  chiefly  on  the 
behavior  of  the  inner  table,  we  can  infer  little  about  it  from  the  shape  of  the  fore- 
head, unless  the  superciliary  eminences  are  very  prominent. 

THE    PARIETAL   BONE. 

The  two  parietal  bones '  complete  the  vault  of  the  skull.  Each  is  a  thin  quadri- 
lateral bone  with  an  inner  and  an  outer  table  separated  by  diploe.  Near  the  middle 

FIG.  222. 


Parietal  foramen 


Post.  sup.  angle    .< 


Ant.  sup.  angle 


Anterior  inferior  angle 


Mastoid 


Right  parietal  bone,  outer  surface. 


Sphenoid 


on  the  convex  external  surface  is  \\\z  parietal  eminence?  where  ossification  begins. 

It  is  very  prominent  in  childhood,  but,  as  a  rule,  is  not  very  evident  in  the  adult. 

Crossing  this  surface  below  the  middle  are  two  curved  lines  *  continuous  with  those 

'Schwalbe  :  Zeitschrift  fur  Morph.  und  Anthrop.,  Bd.  iii.,  1901. 


"  Ossa  parietalia.     3  Tuber  parictale.     4  Linac  tcmporales 


198 


HUMAN   ANATOMY. 


into  which  the  temporal  crest  of  the  frontal  divides.  The  superior  crosses  the  bone, 
ending  at  its  posterior  border.  The  inferior  turns  down  towards  the  posterior 
part  so  as  to  reach  the  lower  border  to  become  continuous  with  the  supramastoid 
crest  of  the  temporal.  In  the  middle  of  their  course  the  lines  are  about  two  centi- 
metres apart.  The  space  between  them  is  a  little  smoother  than  the  surface  above 
and  below.  It  is  uncommon  to  be  able  to  trace  both  lines  throughout.  The  inferior 
is  usually  the  better  marked.  Sometimes  a  part  of  each  is  suppressed.  The  identity 
of  a  single  line  is  shown  by  its  termination.  Near  the  upper  posterior  angle  is  a 
minute  pin-hole,  the  parietal  foramen?  which  transmits  a  vein.  This  foramen  is  very 
often  wanting,  and,  when  visible,  may  be  closed.  In  very  rare  cases  it  is  a  large 
hole,  which  may  even  admit  a  finger.  It  is  occasionally  double.  The  internal 
surface  is  smooth  and  glistening,  as  is  the  case  throughout  the  inside  of  the  cranium. 
It  is  marked  by  tree-like  grooves  for  the  branches  of  the  middle  meningeal  artery. 

FIG.  223. 


Groove  for  longitudi- 
nal sinus 


Post.  sup.  angle 


Ant.  sup.  angle 


Grooves  for  middle 
meningeal  artery 


Anterior  inf.  angle 


sterior  inferior  angle 


Right  parietal  bone,  inner  surface. 


One  of  these  starts  close  to  the  anterior  lower  angle,  being  at  first  very  deep  and 
sometimes  a  canal  for  a  short  distance.  Its  situation  is  exceedingly  constant.  One 
or  two  other  branches  appear  in  the  posterior  half  of  the  lower  border.  The  superior 
longitudinal  sinus  rests  in  a  groove  *  completed  by  both  bones  along  the  upper  border. 
This  groove  is  rarely  symmetrical,  being  generally  largest  on  the  right.  At  the 
posterior  inferior  angle  there  is  a  small  surface  completing  the  groove 3  of  the  lateral 
sinus  at  the  point  at  which  it  turns  from  the  occipital  into  the  temporal  bone.  Pacchi- 
onian  depressions  are  small  pits  of  varying  size  and  number,  found  in  the  upper  part 
of  the  inner  surface,  and  most  commonly  near  the  groove  for  the  longitudinal  sinus, 
which  contain  the  Pacchionian  bodies  of  the  arachnoid.  The  largest  might  receive 
the  tip  of  the  little  finger. 

The  anterior,  superior,  and  posterior  borders  are  all  jagged.  The  anterior 
border  meets  the  frontal,  overlapping  it  below,  overlapped  above.  The  superior 
border  meets  that  of  its  fellow.  The  serrations  are  most  developed  in  the  middle, 

1  Foramen  parietalc.     '*  Sulcus  sagittal-*.       Sulcu*  trunsvcrsus. 


THE   SUPERIOR   MAXILLA.  199 

the  end  of  the  suture  behind  the  parietal  foramina  being  nearly  straight.  The  pos- 
terior border  interlocks  with  the  squamous  portion  of  the  occipital  by  a  very  irregular 
line  of  suture.  The  inferior  border,  concave  in  the  middle,  is  bevelled  on  its  outer 
surface,  except  behind.  It  is  covered  anteriorly  by  the  top  of  the  great  wing  of  the 
sphenoid,  and  along  the  concavity  by  the  squamous  part  of  the  temporal.  The  pos- 
terior portion  presents  a  point  at  the  back  of  the  concavity  which  fits  into  an  angle 
between  the  squamous  and  mastoid  parts  of  the  temporal.  Behind  this  it  is  thick 
and  jagged  for  the  top  of  the  mastoid  portion.  The  anterior  superior  corner  is  about 
a  right  angle.  The  inferior  one  is  somewhat  drawn  out.  The  superior  posterior 
corner  is  rounded.  The  inferior  is  cut  off. 

Parietal  impressions  is  the  term  applied  to  depressions  which  are  observed 
very  exceptionally  on  the  outer  surface  of  the  parietal  bones  above  the  parietal  emi- 
nences and  near  the  upper  border.  They  are  usually  large, — i.e. ,  some  seven  centi- 
metres long  by  five  or  six  centimetres  broad.  Some  sections  have  shown  that  they 
involve  only  the  outer  surface  of  the  bone.  A  thinning  above  the  sagittal  suture 
has  also  been  observed,  and  even  one  over  the  lambdoidal  suture.  These  latter  are 
generally  considered  atrophic  changes  occurring  in  old  age.  The  same  explanation 
is  offered  for  the  parietal  impressions  proper,  and  very  possibly  with  justice  ;  still,  the 
case  is  reported  by  Shepherd l  of  an  old  woman  who  remembered  having  them  all 
her  life,  and  who  declared  that  her  father  had  them  likewise.  This  would  point  to 
their  being  occasionally  both  congenital  and  hereditary.  The  late  Professor  Sir 
George  Humphry 2  observed  them  in  the  orang-outang. 

Articulations. — Each  parietal  articulates  with  its  mate,  the  occipital,  temporal, 
sphenoid,  and  frontal  bones. 

Development. — A  single  centre  appears  in  the  membrane  at  the  end  of  the 
second  fcetal  month.  According  to  Toldt  {Lotos,  1882),  this  is  double,  consisting 
of  an  upper  and  a  lower  part,  which  soon  fuse.  The  centre  becomes  very  prominent, 
and  bone-rays  extend  from  it,  making  the  bone  very  rough  till  after  birth.  The 
fontanelles  at  the  four  corners  of  the  bone  are  discussed  in  describing  the  skull  as 
a  whole  (page  231).  The  radiating  lines  of  bone  leave  an  interval  near  the  back  of 
the  upper  border  of  the  bone,  called  the  sagittal  fontanelle,  which  closes  during  the 
latter  part  of  foetal  life.  According  to  Broca,  this  can  be  seen  at  birth  once  in  four 
times.  The  parietal  foramen  is  left  as  this  fissure  closes.  Its  occasional  great  size 
is  accounted  for  by  irregularities  in  the  process.  Very  rarely  a  suture  divides  the 
parietal  into  an  upper  and  a  lower  portion. 


THE   FACE. 

The  face  consists  of  the  orbits,  the  nose,  and  the  jaws.  Portions  of  the  sphe- 
noid and  the  ethmoid  form  a  considerable  part  of  it,  as  has  been  described.  The 
facial  bones  are  two  superior  maxillce,  two  malar,  two  nasal,  two  lachrymal,  two 
palate,  two  inferior  turbinates,  the  vomer,  the  inferior  maxilla,  and  the  hyoid. 
The  future  nasal  septum,  extending  in  the  median  plane  from  the  base  of  the  skull 
to  the  upper  jaw,  is  very  early  developed  in  cartilage.  Ossification  progresses  from 
superficial  centres  on  either  side.  These  form  the  vertical  plate  of  the  ethmoid  and 
the  vomer  ;  but  a  considerable  part,  the  triangular  cartilage,  remains  cartilaginous. 

THE   SUPERIOR   MAXILLA. 

The  superior  maxilla :i  is  a  very  irregular  bone,  which  with  its  fellow  forms  the 
front  of  the  upper  part  of  the  face,  the  floor  of  the  orbit,  much  of  the  outer  wall  and 
floor  of  the  nasal  cavity,  much  of  the  hard  palate,  and  supports  all  the  upper  teeth. 
It  has  a  body,  and  malar,  nasal,  alveolar,  and  palatal  processes.  The  general  shape 
of  the  body'  is  that  of  a  four-sided  pyramid  ;  the  base  looking  towards  the  nasal 
cavity,  one  surface  forming  the  floor  of  the  orbit  and  the  other  two  the  front  and 
back  of  the  bone.  These  three  surfaces  meet  at  the  apex,  which  is  the  malar  process? 

'Journal  of  Anatomy  and  Physiology,  vol.  xxvii.,  1893. 

2  Ibid,  vol.  viii.,  1874. 

3  Maxilla.      4Corpus  maxillae.     5  Pfocessus  zygomaticus. 


2OO 


HTM  AN   ANATOMY. 


This  is  a  rough  triangular  surface  articulating  with  the  malar,  often  perforated,  and 
sending  downward  a  smooth  ridge  separating  the  anterior  and  posterior  surfaces  ; 
the  former  is  in  the  front  of  the  face,  the  latter  in  the  zygomatic  fossa.  The  lower 
border  of  both  is  the  alveolar  process,1  which  is  simply  a  curved  row  of  tooth 
sockets  made  of  very  light  plates  of  bone,  which  are  absorbed  after  the  loss  of  the 
teeth.  The  palatal  process 2  joins  the  inner  side  of  the  body  like  a  shelf  and  supports 
the  anterior  part  of  the  alveolar  process.  The  nasal  process 3  rises  from  the  anterior 
inner  part  to  meet  the  frontal  bone.  In  certain  parts  of  the  description  it  is  con- 
venient to  disregard  these  subdivisions.  The  anterior  surface  of  the  bone  forms 
the  lower  and  outer  boundary  of  the  nasal  opening,  which  is  finished  above  by  the 
nasal  bone.  On  the  entire  skull  this  aperture  resembles  an  ace  of  hearts  inverted. 
The  lower  boundary  of  the  opening  is  slightly  raised  and  smooth.  On  the  side  it  is 
sharp.  The  pointed  anterior  nasal  spine  projects  forward  where  the  two  bones  meet 
below  the  opening.4  There  is  a  slight  depression — the  incisor  or  my rtiform  fossa — 
over  the  lateral  incisor  tooth.  External  to  this  is  a  ridge  caused  by  the  socket  of  the 
canine  tooth.  Farther  outward  is  a  well-marked  hollow,  the  canine  fossa.  Above 


Lachrymal  groove 

Lachrymal  notch 
Orbital  surface 


Infra-orbital  groove 


Posterior  dental  canal 

Zygomatic  surface 
Masseter 

Malar  process 

Tuberosity 
Buccinator 


—Nasal  process 

Orbicularis  palpebrarum 


Lev.  lab.  sup.  alceq.  nasi 
Orbicularis  palpsbrarum 
Infra-orbital  foramen 


Lev.  labii  sup. 
Canine  fossa 

Incisor  crest 


Lev.  ang,  art's 
Compres.  naris 
Incisor  fossa 
•Depres.  alee  nasi 
Alveolar  process 


Right  superior  maxillary  bone,  outer  surface. 

this,  about  five  millimetres  below  the  edge  of  the  orbit,  is  the  infra-orbital  foramen, 
transmitting  the  nerve  and  artery  of  the  same  name.  This  surface  is  bounded  above 
and  externally  by  the  malar  process. 

The  zygomatic  surface  is  in  the  main  convex,  except  for  a  smooth  concavity 
behind  the  malar  process.  The  lower  posterior  portion,  the  tuber osity?  is  rough, 
and  presents  at  its  upper  part  two  or  three  minute  posterior  dental  foramina6  by 
which  those  nerves  enter  canals  in  the  bone.  The  smooth  superior  or  orbital 
surface,  slanting  a  little  downward  and  outward,  is  triangular.  The  posterior 
border  is  free,  forming  the  lower  limit  of  the  spheno-maxillary  fissure,  and  running 
obliquely  forward  to  the  malar  process.  The  anterior  border  passes  outward  and 
backward  to  the  same.  The  inner  border  is  in  the  main  antero-posterior.  The 
hind  end  slants  outward,  articulating  with  the  little  triangular  orbital  surface  of  the 
palatal.  Anterior  to  this,  the  border  joins  the  os  planum  of  the  ethmoid  ;  and  anterior 
to  the  latter,  at  the  base  of  the  nasal  process,  lies  a  semicircular  indentation,  the  lachry- 
mal notch?  the  posterior  border  of  which  touches  the  lachrymal  bone.  The  deep  infra- 
orbital  groove*  runs  more  than  half  across  the  orbital  surface  from  behind,  and  then 
4  For  a  more  detailed  account,  see  the  section  on  the  Nasal  Cavity. 

1  I'rnresMis    .-ilvrolarK.      '-'  I'rm'ussus    pulntinus.      :l  Proccssus    frontalis.      ''Tuber    maxillare.      ''Foramina    alveolarla. 
7  Im  iMir:i    l:ii  i  im.iliv        Snlrns  infraorhltalls. 


THE   SUPERIOR    MAXILLA.  201 

becomes  a  canal,  opening  at  the  corresponding  foramen  in  front.  Occasionally  a 
suture  marks  the  course  of  the  canal.  The  internal  wall  of  the  body  presents 
on  the  separate  bone  a  very  large  opening  into  the  antrum,  or  maxillary  sinus, 
which  is  much  reduced  when  the  other  bones  are  in  place.  In  front  of  this  opening 
the  wall  is  smooth  and  concave,  forming  a  part  of  the  lachrymal  groove.  Near  the 
level  of  the  top  of  the  body  there  is  the  rough  horizontal  inferior  turbinate  crest  for 
articulation  with  that  bone.  The  wall  at  the  back  of  this  surface  has  a  vertical 
groove,  which,  when  the  palate  bone  is  in  place,  forms  part  of  the  posterior  palatine 
canal,  opening  near  the  back  of  the  hard  palate  and  transmitting  the  descending 
palatine  artery  and  the  anterior  palatine  nerve. 

The  malar  and  the  alveolar  processes  have  been  incidentally  described.  The 
nasal  or  ascending  process  rises  at  the  inner  side  of  the  orbit.  It  is  thin  below,  with 
an  outer  surface  towards  the  face  and  an  inner  towards  the  nose.  The  top  is  thick 
and  rough,  joining  the  frontal.  The  lachrymal  groove^  for  the  tear-sac  and  the  nasal 
duct  begins  on  its  outer  surface  and  passes  down  behind  it,  making  a  deep  notch  at 
the  front  of  the  orbital  plate.  The  lower  part  of  the  process  extends  down  as  far  as 
the  inferior  turbinate  crest,  forming,  with  the  lachrymal,  the  inner  side  of  the  groove. 
The  point  of  junction  of  the  front  border  of  the  groove  with  the  orbital  plate  is 
usually  marked  by  the  lachrymal  tubercle.  The  inner  side  shows  above  at  the  pos- 
terior border  some  cellular  spaces  completing  the  anterior  ethmoidal  cells,  bounded 
below  by  a  ridge,  the  crista  ethmoidalis,  which  articulates  with  the  front  of  the  middle 
turbinate  bone.  Below  it  the  bone  is  concave,  forming  part  of  the  vestibule  of  the 
nose  ;  above  it  is  plane  and  marked  with  vascular  grooves. 

The  palatal  process  projects  inward  from  the  anterior  two-thirds  of  the  body 
and  joins  the  alveolar  process  in  front.  It  is  very  smooth  above,  the  mucous  mem- 
brane being  lightly  attached  to  it.  It  is  slightly  concave  from  side  to  side,  and  has 
a  raised  edge  in  front.  It  is  also  raised  along  the  median  line  to  form  the  nasal  crest"1 
with  its  fellow.  The  front  of  this  ridge,  called  the  incisor  crest,  suddenly  rises  to  a 
higher  level  and  juts  out  below  the  nose  as  the  anterior  nasal  spine.  The  vomer 
rests  on  the  ridge,  except  at  the  front,  where  its  place  is  taken  by  the  triangular 
cartilage.  The  under  surface  of  the  palatal  process,  horizontal  behind,  slants  down- 
ward in  front  to  the  incisor  teeth.  It  is  rough  for  the  firm  support  of  the  mucous 
membrane.  The  median  surface  of  the  palate  is  rough  to  join  with  its  fellow.  A 
little  behind  the  incisors  it  shows  a  groove  in  the  lower  part,  which  becomes  a  canal 
in  the  upper,  and  opens  into  the  floor  of  the  nasal  fossa  of  either  side.  Thus  there 
are  two  canals  above  and  one  below,  like  a  Y  placed  transversely.  These  are  the 
canals  of  Stenson,  which  transmit  an  artery  connecting  the  vessels  of  the  nose  and 
mouth.  Their  common  orifice  is  called  the  anterior  palatine  canal?  Into  this  open 
two  minute  canals,  the  left  anterior  to  the  right,  made  by  the  junction  of  the  -bones. 
These  are  the  canals  of  Scarpa,  and  transmit  the  naso-palatine  nerves.  They  are 
by  no  means  always  to  be  found.  The  canals  of  Stenson  represent  the  anterior 
palatine  canal  of  lower  animals,  which  in  them  is  generally  double  throughout.  In 
man  the  whole  opening  is  usually  closed  by  mucous  membrane.  The  back  of  the 
palate  process  joins  the  horizontal  plate  of  the  palate  bone,  which  completes  the 
palate  behind. 

The  antrum  or  maxillary  sinus4  is  a  large  cavity  within  the  body,  the  shape 
of  which  it  follows  in  the  main,  although  with  many  variations  of  size.  The  large 
opening  on  its  inner  wall  is  much  diminished  when  the  palate,  the  ethmoid,  and  the 
inferior  turbinate  are  in  place.  It  lies  near  the  anterior  end  of  the  lateral  wall  of  the 
middle  nasal  meatus,  covered  by  the  middle  turbinate.  A  small  part  of  the  roof  of 
the  antrum  is  often  formed  by  the  palate  bone,  and  sometimes  the  cavity  extends  into 
the  malar.  The  inner  and  most  of  the  posterior  and  outer  walls  are  generally  very 
thin,  as  is  also  the  roof,  except  around  the  infra-orbital  canal,  which  projects  into  the 
antrum.  The  development  outward  towards  the  malar  bone  varies  much,  as  does 
the  downward  and  forward  growth  towards  the  alveolar  process.  The  lower  border 
of  the  antrum  is  usually  a  trifle  below  the  level  of  the  floor  of  the  nares.  According 
to  C.  Reschreiter,5  this  is  a  male  characteristic.  Be  that  as  it  may,  it  certainly  is  in 
5Zur  Morphologic  des  Sinus  Maxillaris,  Stuttgart,  1878. 

1  Sulcus  lacrlraalis.     '- Crista  nasalis.     3  Foramen  incisivum.     *  Sinus  maxillaris. 


202 


HUMAN   ANATOMY. 


accord  with  the  larger  size  of  the  sinuses  in  man.  The  internal  surface  is  largely 
smooth.  Bony  ridges  springing  from  various  parts  tend  to  subdivide  the  cavity. 
They  sometimes  form  little  pockets  above  the  teeth.  According  to  Gruber,1  it 
may  in  rare  cases  be  completely  subdivided  into  a  smaller  posterior  chamber  and  a 
larger  front  one,  both  of  which  open  into  the  nasal  cavity.  The  lowest  part  of  the 
antrum  is  indented  by  the  roots  of  the  molars  and  of  the  second  bicuspid,  at  least 
very  frequently.  The  first  and  second  molars  always  indent  it,  but  the  bicuspid  and 
the  wisdom-tooth  may  not.  (For  further  details,  see  Teeth,  page  1556.) 

Articulations. — All  the  bones  of  the  face,  except  the  lower  jaw  and  the  hyoid, 
touch  the  superior  maxilla.  It  has  been  described  as  the  key  to  the  architecture 
of  the  face.  The  palate  bone  both  completes  the  palate  and  lies  between  this  bone 
and  the  pterygoids,  closing  the  posterior  part  of  the  opening  into  the  antrum.  The 
malar,  joining  the  process  of  that  name,  makes  the  prominence  of  the  cheek  and 
helps  to  bound  the  orbit.  The  nasals  complete  the  anterior  nasal  aperture.  The 
lachrymals  and  ethmoid  touch  the  inner  side  of  the  orbital  plate,  and  the  ethmoid 
the  inner  surface  of  the  nasal  process.  The  frontal  rests  on  the  nasal  process,  the 


FIG.  225. 


Nasal  process — -j 


Ethmoidal  crest 
Middle  tneatus 


Inferior  turbinate  crest 

Inferior  meatus 

Incisor  crest 


Anterior  nasal  spine— (     <JB>Wi,  /  ' 
\  At  Mi  no  '•    \ 


Anterior  palatine  canal — fa 
Alveolar  proc 


Completes  ethmoidal 
cells 


Antrum 

Posterior  palatine  canal 
Nasal  crest 
Palatal  process 

Tuberosity 


Right  superior  maxillary  bone,  inner  surface. 


crest 


inferior  turbinate  rests  on  the  inner  surface  of  the  maxilla,  and  the  vomer  on  the 
made  by  the  union  of  the  palate  processes. 

Development  and  Changes. — There  are  certainly  four  chief  centres,  all  of 
which  appear  at  about  the  end  of  the  sixth  week  of  foetal  life.  Three  of  them  fuse 
very  rapidly.  There  is  one  on  either  side  of  the  infra-orbital  groove,  a  malar  and 
an  orbito-facial,  and  below  and  internally  a  palatine.  The  fourth,  the  intermaxillary, 
stays  distinct  longer.  It  comprises  the  front  of  the  palate  as  far  back  as  the  anterior 
palatine  canal,  and  represents  a  very  constant  separate  ossification  in  vertebrates, 
the  premaxilla,  in  front  of  the  maxilla,  except  in  certain  mammals  in  which  it  is 
between  them.  It  bears  the  incisor  teeth,  and  at  the  third  foetal  month  fuses  with 
the  maxilla.  As  the  intermaxillary  grows,  the  suture  in  the  roof  of  the  mouth  per- 
sists for  a  time.  It  is  very  plain  at  birth  and  often  for  a  year  or  two  later.  Some- 
times it  is  seen  in  the  adult.  At  first  the  posterior  suture  is  very  close  to  the 
incisors,  but  as  it  grows  the  intermaxillary  forms  a  large  part  of  the  palate.  If 
detached,  it  is  seen  notched  behind,  so  as  to  form  the  inner  wall  of  the  upper  part  of 

1  Virchow's  Archiv,  Bd.  Ixiii. 


THE   SUPERIOR    MAXILLA. 


203 


Stenson's  canal.  The  suture  is  rarely  seen  above  and  never  in  front,  being  concealed 
by  the  plate  forming  the  front  of  the  bone.  Albrecht J  asserts  that  each  intermaxil- 
lary is  double.  In  support  of  this  is  the  fact  that  in  cleft  palate  the  fissure  does 
not  always  come  between  the  incisor  teeth  and  the  canine,  but  an  incisor  may  be 
found  on  its  outer  side.  In  reply  to  this  it  has  been  pointed  out  that  three  incisors 
on  each  side  occasionally  occur,  and  that,  as  anomalies  are  likely  to  be  found  in 
groups,  this  is  merely  an  irregular  arrangement.  Moreover,  in  cases  in  which  the 
cleft  has  but  one  incisor  on  each  side  of  it,  it  is  well  argued  that  the  original  position 
of  the  tooth-sacs  has  no  certain  relation  to  the  bones  (Th.  Kolliker2).  In  sup- 
port of  Albrecht  is  the  occasional  presence  of  a  line  subdividing  the  lower  surface 
of  the  premaxilla  ;  but,  on  the  other  hand,  it  is  not  certain  that  this  is  really  a 
suture,  and  there  seems  no  evidence  that  the  premaxilla  has  two  centres  of  ossifi- 
cation. While  there  is  much  that  is  plausible  in  Albrecht' s  views,  they  cannot  be 
considered  as  established. 

Sir  William  Turner3  thus  concludes  an  excellent  discussion  of  the  question  : 
"  What  is  yet  wanted,  however,  to  give  completeness  to  the  evidence  of  the  division 
of  the  intermaxillary  bone  into  an  inner  and  an  outer  part  is  the  discovery  that  the 
intermaxillary  bone  normally  rises  from  two  distinct  centres  of  ossification,  one  for 
the  inner,  the  other  for  the  outer  part.  Of  this  we  have  at  present  no  evidence. 


FIG.  226. 


Alveolar  process 


FIG.  227. 

Lachrymal  groove 


Inferior  surface  of  upper  jaw  at  about  birth. 


Antrutn 


Ant.  palatine  canal  Palatal  process 

Mesial  surface  of  upper  jaw  at  about  birth. 


But,  in  connection  with  this  matter,  we  ought  not  to  forget  that  it  is  quite  recently 
that  the  embryological  evidence  of  the  origin  of  the  intermaxillary  part  of  the  human 
upper  jaw  from  a  centre  distinct  from  that  of  the  superior  maxilla  has  been  completed. 
And  yet  for  nearly  a  century,  on  such  minor  evidence  as  was  advanced  by  Goethe, 
— viz.,  the  suture  on  the  hard  palate  extending  through  to  the  nasal  surface, — 
anatomists  have  believed  and  taught  that  the  human  upper  jaw  represented  both  the 
superior  and  intermaxillary  bones  in  any  other  mammal.  Where  a  question  in 
human  embryology  hinges  upon  an  examination  of  parts  in  a  very  early  stage  of 
development,  we  often  have  to  wait  for  many  years  before  an  appropriate  specimen 
falls  into  the  hands  of  a  competent  observer. 

The  upper  and  lower  sides  of  the  bone  are  at  first  very  near  together.  The 
tooth-sacs  are  directly  below  the  orbit.  In  the  latter  part  of  foetal  life  the  antrum 
appears  as  a  slight  pouch  growing  in  from  the  nasal  side.  As  the  bone  grows,  the 
antrum  remains  for  some  time  on  the  inner  side  of  the  infra-orbital  canal.  The  outer 
part  of  the  bone,  especially  towards  the  malar,  is  filled  with  diploe,  which  subse- 
quently is  absorbed  as  the  sinus  extends  outward.  By  the  end  of  the  second  year 
the  cavity  has  extended  above  the  first  permanent  molar  ;  by  the  twelfth  or  thirteenth 
year,  when  the  second  molar  has  appeared,  the  antrum  approaches,  though  it  has 
not  yet  reached,  its  definite  shape.  During  the  first  dentition  it  is  separated  by  the 
uncut  teeth  from  the  front  of  the  bone. 

1  Sur  les  quatres  os  intermaxillaires,  Soc.  d'Antropol.  de  Bruxelles,  1883.     Die  morpho- 
logische  Bedeutung  der  Kiefer-,  Lippen-,  und  Gesichtsspalten,  Langenbeck's  Archiv,  Bd.  xxi. 

2  Ueber  das  Os  intermaxillare  des  Menschen.     Nova  Acta  der  Leopold.  Carol.  Akad.  der 
Naturforschen,  Bd.  xliii.,  1882. 

3  Journal  of  Anatomy  and  Physiology,  vol.  xix.,  1895. 


204 


HUMAN   ANATOMY. 


Orbital  surface 


Spheno-maxillary  fossa 
Spheno-palatine  notch 


VERTICAL  PLATE 


For  ext.  pteryg. 

plate 
Pterygoid  fossa 


HORIZONTAL  PLATE  ^ 
For  int.  pterygoid  plate 

Right  palate  bone  from  behind. 


TUBEROSITY 


After  the  loss  of  the  teeth  from  old  age  or  otherwise  the  alveolar  process  is 
absorbed.     Senile  atrophy  is  particularly  marked  in  this  bone. 

THE   PALATE    BONE. 

This1  consists  of  a  horizontal  and  a  vertical  plate  and  three  processes,  the  py- 
ramidal, the  orbital,  and  the  sphenoidal.    The  horizontal  plate  *  is  quadrilateral.     It 

completes   with    its    fellow    the    hard 

FIG.  228.  palate,  filling  the  space  left  vacant  be- 

prbitai  process  tween  the  back  parts  of  the  superior 

maxillae.  Its  superior  surface  is 
smooth  like  the  rest  of  the  floor  of 
the  riares,  and  the  lower  rough,  but 
less  so  than  that  of  the  superior  max- 
illa. The  anterior  border  fits  the  back 
of  the  palatal  process  of  the  maxilla  ; 
the  inner  border  is  rough  to  meet  its 
fellow,  and  raised  into  a  nasal  crest 
meeting  the  back  of  the  lower  edge 
of  the  vomer.  This  is  prolonged 
behind  to  form  with  the  other  the 
posterior  nasal  spine.  The  posterior 
border  is  smooth  and  concave  from 
side  to  side.  The  outer  border  joins 
the  vertical  plate.3  This  is  very 
thin,  with  an  outer  and  an  inner  sur- 
face. It  is  surmounted  by  two  processes,  between  which  is  a  deep  notch  which 
forms  three-quarters  or  more  of  the  spheno-palatine  foramen 4  when  the  bone  is  in 
position,  so  that  both  processes  touch  the  body  of  the  sphenoid.  The  outer  surface 
presents  near  the  top  a  smooth  vertical  surface  forming  part  of  the  ptery go-maxillary 

FIG.  229. 

For  ethmoid  Orbital  process 


To  complete 
ethmoidal  cells 


Spheno-palatine 
foramen 


Sup.  turbinate  crest 

Sphenoidal  process 
Middle  nasal 
meatus 

•Inf.  turbinate  crest 


Inferior  meatus 
Tuberosity 


Posterior  nasal  spine 
Nasal  crest 
Inner  aspect  of  right  palate  bone  in  place.     Part  of  inferior  turbinate  removed. 

fissure.  This  narrows  below  into  a  groove  which  makes  the  posterior  palatine 
canal  when  applied  to  the  corresponding  groove  in  the  maxilla.  In  front  of  this 
the  surface  is  at  first  rough  where  it  rests  against  that  bom-,  and  more  anteriorly 
smooth  where  it  closes  the  lower  part  of  the  opening  of  the*  antrum  by  an  irregular 

1  IK  |.  ,1  ii  mum       -  I'.n  s  hot  i/iiiii.iliv         I'. II-.  iu-iiii-iulirnl.il  ix.      '  1'iit.iim-ii  Nphi>nnpal;i< iiiuiii. 


Ant.  part  of  inf. 
turbinate 


THE   PALATE  BONE. 


205 


prolongation.  The  inner  surface,  looking  towards  the  nasal  cavity,  is  free  and 
smooth.  It  is  crossed  below  the  middle  by  a  ridge,  the  inferior  turbinate  crest1  for 
the  posterior  attachment  of  the  inferior  turbinate  bone.  Nearly  on  a  level  with  the 
base  of  the  notch  is  another  ridge  faintly  marked  behind  it ;  this  is  the  superior 
turbinate  crest  *  for  the  middle  turbinate  bone  of  the  ethmoid.  A  small  part  of  the 
top  of  the  vertical  plate  looks  into  the  superior  meatus.  The  pyramidal  process, 
or  tuberosity,  is  the  only  solid  part  of  the  bone.  It  projects  backward  and  some- 
what outward  from  the  lower  part  of  the  vertical  plate.  A  smooth,  hollowed, 
triangular  surface  fits  into  the  space  left  between  the  pterygoid  plates,  completing 
the  floor  of  the  pterygoid  fossa  ;  on  one  side  of  this  is  a  groove  for  the  front  of  the 
internal  pterygoid  plate  and  on  the  other  a  rough  surface  for  that  of  the  outer. 
Thus,  through  the  palate  bone,  the  pterygoids  support  the  back  of  the  upper  jaw. 
The  outer  side  of  the  process  rests  against  the  tuberosity  of  the  maxilla  in  front  of 
the  tip  of  the  external  pterygoid  plate.  The  orbital  process,  is  the  anterior  of  the 
two  processes  above  the  vertical  plate,  the  larger  and  higher,  so  called  because  it 
forms  a  small  part  of  the  floor  of  the  orbit  near  its  apex  on  the  inner  side.  This 
little  surface,  on  the  outer  side  of  the  process,  is  triangular,  one  edge  articulating 
with  the  upper  jaw  and  one  with  the  os  planum,  the  hind  edge  being  free.  Another 
smooth  surface  looks  outward  and  backward  towards  the  spheno-maxillary  fossa. 
It  is  separated  from  the  preceding  surface 
by  an  angle.  Three  other  surfaces  rest 
against  other  bones.  An  antero-inferior 
one  joins  the  maxilla,  sometimes  helping 
.to  close  the  antrum  ;  an  anterior  one 
touches  the  ethmoid,  bounding  part  of  a 
cell  ;  and  a  small  one,  just  at  the  top  of 
the  notch,  touches  the  sphenoidal  spongy 
bone.  The  posterior  or  sphenoidal 
process  has  a  narrow  upper  surface, 
which,  joining  the  sphenoidal  spongy 
bone  near  the  base  of  the  internal  ptery- 
goid plate,  completes  the  ptery go -palatine 
canal.  This  surface  reaches  the  edge  of 
the  vomer.  The  internal  surface,  slant- 


FIG.  230. 


Spheno-maxillary 
foss; 


Sphenoida 
process 


Tuberosity 


Orbital  surface 


Orbital  process 


Maxillary 
surface 


Antrum 


Post,  pala- 
tine canal 

For  sup. 
maxillary 


Right  palate  bone,  outer  aspect. 


ing  a  little  downward,  is  free,  looking  into 
the  nasal  fossa.      The  outer  surface  is  di- 
vided by  a  vertical  ridge  into  an  anterior 
part,  free  and  smooth,  looking  into  the  spheno-maxillary  fossa,  and  a  scale-like  pos- 
terior portion  which  rests  against  the  external  pterygoid  plate. 

The  Spheno-Maxillary  Fossa. — When  the  palate  bone  is  applied  to  the 
sphenoid  and  the  maxilla,  the  spheno-palatine  foramen  forms  a  window  between  the 
nasal  chamber  and  a  little  hollow,  the  spheno-maxillary  fossa ,  just  below  and  behind 
the  apex  of  the  orbit.  The  posterior  wall  of  this  space,  formed  by  the  smooth  sur- 
face of  the  sphenoid  above  the  pterygoid  plates,  is  pierced  by  the  foramen  rotundum 
and  the  Vidi an  canal.  Below,  it  narrows  funnel-like  into  the  posterior  palatine  canal. 

Articulations. — The  palate  bone  articulates  with  its  fellow,  the  superior  max- 
illary, sphenoid,  ethmoid,  vomer,  and  inferior  turbinate  bones. 

Development. — Ossification  begins  from  a  single  centre  appearing  in  mem- 
brane near  the  end  of  the  second  fcetal  month  at  about  the  junction  of  the  vertical 
and  horizontal  plates.  It  is  very  delicate  throughout  fcetal  life,  but  the  posterior 
free  edge  of  the  palate  is  very  early  much  denser.  Originally  the  horizontal  plate  is 
larger  than  the  vertical  one  ;  at  birth  they  are  about  equal. 

THE  VOMER. 

The  vomer'  is  a  thin,  irregularly  quadrilateral  plate,  forming  the  back  and  lower 
part  of  the  nasal  septum.  The  superior  border  expands  laterally  into  two  wings,  or 
alee,  which  articulate  with  the  under  surface  of  the  body  of  the  sphenoid,  and  enclose 
a  medium  groove  for  the  rostrum.  Laterally,  the  wings  fit  under  the  vaginal  pro- 

1  Crista  turbinatis.     -  Crista  ethmoidalis.     3  Vomer. 


206 


HUMAN   ANATOMY. 


cesses  of  the  sphenoid.     The  posterior  border  is  free.     Thick  above,  just  under  the 
alse,   it  soon  narrows  and  runs  downward  and  forward.      The  inferior  border  fits 

FIG.  231. 


SUPERIOR    BORDER 

Ala 


Naso-palatine  groove 


Vomer  in  place,  from  left  side. 


FIG. 


Vomer,  superior  surface. 


between  the  nasal  crests  of  the  palatals  and  maxillae,  and  anteriorly  changes  its  direc- 
tion so  as  to  rise  over  the  higher  incisor  crests  as  far  as  the  anterior  palatine  canal. 
The  anterior  border  is  the  longest.      Its 
upper  part   articulates  with   the  back   of       FIG.  233. 
the   vertical    plate   of    the   ethmoid,    the  A\X 

lower  part  with  the  triangular  cartilage  of 
the  nasal  septum.  The  latter  is  received 
into  a  groove  which  may  extend  behind 
the  vertical  plate.  The  sides  of  the  vomer 
are  covered  with  mucous  membrane. 
They  present  a  few  irregularities,  the 
most  important  of  which  is  a  groove  on 
either  side,  nearer  the  front  than  the 
back,  for  the  naso-palatine  nerve  ;  and, 

just  anterior  to  this,  a  thickening  which  is  normally  insignificant, 
but  occasionally  is  developed  to  one  side  or  the  other,  forming  a 
spur  which  may  nearly  close  the  passage. 

Articulations. — The  vomer  articulates  with  the  sphenoid, 
ethmoid,  palate,  and  superior  maxillary  bones  and  the  median 
triangular  cartilage. 

Development. — It  is  to  be  remembered  that,  although  the 
vomer  becomes  through  ossification  one  of  the  separate  bones  of 
the  face,  at  an  early  period  it  is  but  a  portion  of  the  septal  car- 
tilage without  any  hint  of  demarcation.  A  single  centre  appears 
before  the  close  of  the  second  foetal  month  in  the  membrane  at  the  under  border 
of  the  cartilage,  which  then  forms  the  septum.  This  grows  upward  on  either  side 
of  the  cartilage  until  the  bone  is  complete.  The  young  bone  shows  very  clearly 
its  formation  in  two  plates  ;  but  in  the  adult  this  appears  only  in  the  groove  between 
the  wings  and  in  the  lower  part  of  the  front  border,  which  still  receives  the  triangular 
cartilage. 


Groove  for 

rostrum  of 
sphenoid 


Ant.  border 
for  ethmoid 


Grooved 
ant.  border 
for  septal 
cartilage 


Vomer  from  before 
and  above. 


THE    LACHRYMAL    BONE. 


207 


THE   LACHRYMAL    BONE. 

The  lachrymal  bone  l  is  an  exceedingly  thin  osseous  plate,  filling  the  vacancy  in 
the  inner  wall  of  the  orbit  between  the  orbital  plate  of  the  ethmoid  and  the  ascending 
process  of  the  superior  maxilla.  It  is  quadrilateral,  the  long  diameter  being  vertical, 
and  presents  an  outer  surface  directed  towards  the  orbit  and  an  inner  surface  towards 
the  nasal  fossa.  The  latter  rests,  in  part,  against  the  turbinate  process  of  the  eth- 
moid, which  more  or  less  overlaps  it.  It  closes  the  infundibulum  and  several  anterior 

FIG.  234. 


Lachrymal  crest 


Nasal  process  of  sup.  max. 
Lachrymal  groove 


Orbital  surface 


Hamular  process 


Right  lachrymal  bone  in  place,  outer  aspect. 


FIG.  235. 


ethmoidal  cells.  The  lower  and  anterior  portion  of  this  surface  forms  a  part  of  the 
wall  of  the  middle  nasal  meatus.  The  outer  surface  is  subdivided  by  a  vertical  ridge,2 
marking  off  a  smaller  anterior  part,  which  forms  the  lachrymal  groove  ;3  and,  joining 
the  corresponding  groove  of  the  superior  maxillary,  complete  the  lachrymal  canal. 
The  posterior  part  of  the  orbital  surface  is  plane.  The  hamular 
process 4  is  a  small  tongue  of  bone  curving  forward  from  the  lower 
part  of  the  dividing  ridge  to  form  the  posterior  border  of  the 
canal  at  the  floor  of  the  orbit.  The  descending  process  is  a 
downward  prolongation  of  the  grooved  portion,  forming  part  of 
the  wall  of  the  canal,  and  meeting  the  lachrymal  process  of  the 
inferior  turbinate.  The  bone  also  articulates  with  the  frontal  by 
its  upper  surface,  and  with  the  front  of  the  os  planum  by  its  pos- 
terior border. 

Articulations. — The  lachrymal  articulates  with  the  eth- 
moid, frontal,  superior  maxillary,  and  inferior  turbinate  bones. 

Development. — Ossification  is  from  a  single  centre  said 
to  appear  in  the  eighth  foetal  week,  although  the  variations  imply  meatus" 
extra  ones.  Macalister5  enumerates  six  separate  ossicles  which 
may  occur  about  the  bone.  It  varies  greatly  iii  size  ;  it  may  be  wanting,  though 
rarely,  and  sometimes  is  very  large.  A  considerable  development  of  the  hamular 
portion,  which  may  be  separate,  represents  the  condition  of  prosimians  and  platyrhine 
apes.6  It  may  be  subdivided  or  perforated.7 

5  Proc.  Royal  Society,  1884. 

fi  Gegenbaur :  Morph.  Jahrbuch,  Bd.  vii. 

7  Le  Double  :  Essai  sur  la  Morphogenie  et  les  Variations  du  Lacrymal,  1900  ;  and  Zabel  : 
Varietaten  und  Vollstandiges  Fehlen  des  Tranenbeins  beim  Menschen,  Anat.  Hefte.  Bd.  xv., 
Heft  i,  1900. 

1  Os  lacrimalc.     "  Crista  lacrimalis.     3  Sulcus  lacrimalis.     4  Hamulus  lacrimalis. 


Right  lachrymal  bone, 
inner  aspect.  Upper 
part  completes  anterior 
ethmoidal  cells,  lower 
looks  into  middle  nasal 


208 


HUMAN   ANATOMY. 


THE  INFERIOR  TURBINATE  BONE. 

This  is  an  elongated  curved  bone '  placed  in  the  lateral  wall  of  the  nasal  cavity 
below  the  superior  and  middle  turbinates,  which  are  parts  of  the  ethmoid.    The  inner 

convex  surface  is  pitted  and  grooved  by  the 
cavernous  tissue  beneath  the  mucous  membrane. 
This  condition  is  continued  round  the  free  lower 
border  a  little  way  up  the  outer  side.  The  rest 


Ethmoidal  process 


Right  inferior  turbinate  bone  in  place,  inner  aspect. 


FIG.  237. 


of  the  outer  surface,  overhanging  the  inferior  nasal  meatus,  is  nearly  smooth.     The 

ends  of  the  bone  are  pointed.     They  are  connected  below  by  the  regular  curve  of 

the  inferior  border.  The  upper  border  is 
thin  and  irregular.  It  articuiates  in  front 
with  the  inferior  turbinate  crest  of  the  max- 
illa. Behind  this  rises  the  lachrymal  process  * 
— the  highest — to  meet  the  lachrymal  bone. 
Posterior  to  this  the  maxillary  process 3  bends 
outward  and  downward.  It  does  not,  how- 
ever, usually  hook  over  the  upper  edge  of 
the  plate  bounding  the  entrance  of  the  an- 
trum,  but  meets  it  edge  to  edge,  consider- 
ably reducing  the  opening.  Still  farther 

back  is  the  ethmoidal process*  meeting  the  uncinate  process  ;  and,  finally,  the  border 

rests  on  the  inferior  turbinate  ridge  of  the  palate  bone. 

Articulations. — The  inferior  turbinate  articulates  with  the  superior  maxillary, 

ethmoid,  palate,  and  lachrymal  bones. 

Development. — Ossification   proceeds   from    a    single  center   which  appears 

about  the  middle  of  foetal  life. 

1  Concha  inferior.     -  1'roc.  lacrimalls.     3  Proc.  maxlilarl*.     4  Proc.  ethmoidalis. 


Right  inferior  turbinate  bone,  outer  aspect. 


THE  NASAL  AND  MALAR  BONE. 


209 


Crest 


Groove  10  r 
nasal  nerve 


Right  nasal  bone,  outer  and  inner  aspects. 


THE  NASAL  BONE. 

The  two  nasal  bones1  bound  the  anterior  nasal  opening  above.  Each  one  is  a 
four-sided  plate  with  an  outer  and  an  inner  surface.  The  upper  end  is  thick  and 
jagged,  articulating  with  the  frontal  above  and  also  behind.  The  anterior  border, 
which  articulates  with  its  fellow,  is  thick  above  and  thin  below.  When  the  two 
bones  are  in  place,  the  united  upper  portions  of  these  borders  form  posteriorly  the 
nasal  crest,  which  articulates 

with  the  nasal  spine  of  the  FIG.  238. 

frontal,  and  sometimes  with  F"/ATAL 

the  vertical  plate  of  the  eth- 
moid below  it.  The  pos- 
terior border  joins  the  as- 
cending process  of  the 
maxilla.  The  thin  lower 
border,  slanting  downward 
and  outward,  has  one  or 
two  indentations.  The  outer 
surface  is  broader  below 
than  above.  It  is  depressed 
in  the  upper  third,  and  has 
there  a  foramen  for  a  vein. 
The  extreme  upper  part  of 
the  inner  surface  is  rough 
to  join  the  frontal.  Below 
this  it  is  smooth  where  it 
forms  the  front  of  the  nasal 
chamber  ;  the  lower  part  of  the  Jnner  surface  sometimes  seems  hollowed  out.  A 
vertical  groove  for  the  nasal  nerve  ends  near  the  notch  in  the  lower  border. 

Articulations. — The  nasal  bone  articulates  with  the  frontal,  ethmoid,  superior 
maxilla,  and  the  opposite  nasal. 

Development. — Ossification  spreads  from  a  centre  appearing  about  the  eighth 
week  of  foetal  life.  At  first  the  bone  is  broad  and  short.  Occasionally  a  little 
Wormian  bone  is  found  in  the  median  line  between  the  nasals  and  the  frontal.  The 
two  bones  sometimes  coossify,  after  the  fashion  of  apes.  Either  a  vertical  or  a  trans- 
verse suture  may  be  found. 

THE  MALAR   BONE. 

This  bone2  forms  the  prominence  of  the  cheek,  the  outer  border  of  the  orbit, 
most  of  the  wall  separating  the  orbit  from  the  temporal  fossa,  and  completes  the 
zygomatic  arch.  For  simplicity  of  description  it  is  best  to  consider  it  a  diamond- 
shaped  bone,  with  an  outer  and  an  inner  surface,  four  angles,  four  borders,  and  one 
important  process,  the  orbital,  which  is  neither  an  angle  nor  a  border.  The  outer 
surface  presents  a  slight  prominence,  the  tuberosity?  a  little  below  the  middle.  The 
surface  is  nearly  smooth,  except  that  near  the  lower  border  there  is  often  a  certain 
roughness  extending  onto  the  zygomatic  process  for  the  origin  of  the  masseter  muscle. 
The  greater  part  of  the  inner  stirface  is  smooth,  looking  towards  the  temporal  and 
zygomatic  fossae  ;  but  a  rough  space  under  the  front  angle  joins  the  malar  process  or 
the  maxilla.  It  sometimes  helps  to  close  the  antrum,  in  which  case  a  part  of  it  is 
smooth,  being  lined  with  mucous  membrane.  The  superior  angle,  or  frontal  process* 
joins  by  a  rough  surface  the  external  angular  process  of  the  frontal.  The  posterior 
angle,  or  zygomatic  process?  more  prominent  below  than  above,  joins  the  zygomatic 
process  of  the  temporal,  passing  below  it.  The  anterior  and  the  inferior  angles 
have  no  special  names.  The  postero-superior,  or  temporal  border,  is  at  first  vertical, 
becoming  horizontal  towards  the  hind  end.  Near  the  beginning  there  is  a  posterior 
projection,  the  marginal  process,  which  varies  considerably.  The  postero-inferior, 
or  masseteric  border,  slightly  irregular,  is  free,  forming  the  lower  edge  of  the  front  of 
the  zygoma.  The  antero-inferior,  or  maxillary  border,  is  slightly  concave.  It  articu- 

1  Ossa  nasalia.     -  Os  zygomaticum.     3Tuberositas  malaris.     4  Processus  frontosphenoidalis.     D  Processus  tcmporalis. 

14 


210 


HUMAN    ANATOMY. 


lates  with  the  front  of  the  malar  process  of  the  maxilla,  bounding  externally  the 
rough  surface  of  the  inner  side  of  the  malar.  The  antero-superior,  or  orbital  border, 
is  smooth  and  concave,  forming  the  external  and  most  of  the  inferior  boundary  of 
the  orbit.  The  orbital  plate,  or  process,  which  forms  the  front  of  the  outer  wall  of 
the  orbit,  projects  inward  from  this  border,  joining  the  bone  at  nearly  a  right  angle. 

FIG.  239. 


Malar  canal 


Tuberosity 
Right  malar  bone,  outer  aspect. 

It  is  narrow  in  front  and  broad  behind,  where  its  anterior  surface  looks  .towards  the 
orbit  and  its  posterior  towards  the  temporal  fossa.  Its  projecting  edge  is  jagged 
throughout,  and  in  front  meets  the  superior  maxilla.  Behind  that  it  joins  the  outer 
border  of  the  great  wing  of  the  sphenoid,  and  above  articulates  with  the  frontal.  Be- 
tween the  part  meeting  the  maxilla  and  that  meeting  the  great  wing  there  is  usually  a 

short,  smooth  surface  bound- 

FIG.  240.  ing  the  end  of   the   spheno- 

Frontai  process  maxillary    fissure,    which   lies 

between  these  bones  in  the 
lower  outer  angle  of  the  orbit. 
Two  foramina  on  the  orbital 
surface  lead  to  minute  canals. 
The  lower,  the  malar,1  ope 
on  the  outer  surface  of  th 
bone ;  the  upper,  the  tem- 
poral? opens  on  the  back  of 
the  orbital  process.  They 
transmit  branches  from  the 
superior  maxillary  division  of 
the  fifth  nerve.  They  va 
greatly. 

In   all  mammals  the  pri- 
mary function  of  the  malar  is 
to  unite  the  maxilla  and  the 
temporal    bone.        Its    union 
Only  in  primates  does  it  join  the  sphe- 


Temporal  canal 


Malar  canal 


Maxillary  surface 


Orbital  process 

Temppro-zygo- 
matic  surface 


Right  malar  bone,  inner  aspect. 


with  the  frontal  is  a  further  development. 

noid  and  separate  the  orbit  from  the  temporal  fossa. 

Articulations.     Tin-  malar  bone  articulates  with  the  frontal,  superior  maxillary, 
temporal,  and  sphenoid  bones. 

Development  and  Variations. — There  are  three  centres  of  ossification- -an 

1  Foramen  zygumaticufacialc.     '-'  Foramen  zyuoinaticotemporale. 


THE   INFERIOR   MAXILLA. 


211 


anterior,  a  posterior,  and  an  inferior — appearing  towards  the  end  of  the  second  foetal 
month.  They  fuse  in  the  course  of  the  third.  Sometimes,  but  very  rarely  in  the 
white  races,  the  bone  is  divided  by  a  fissure — as  in  some  apes — into  an  upper  and  a 
lower  part.  This  is  said  to  be  relatively  common  (seven  per  cent.)  in  the  Japanese. 
A  division  into  three  has  been  seen.  The  roughness  for  the  masseter  sometimes 
gives  a  deceptive  appearance  of  a  separate  piece  to  this  portion.  On  the  other  hand, 
an  occasional  slight  horizontal  cleft  in  the  zygomatic  process  is  probably  a  remnant 
of  a  division. 

THE   INFERIOR   MAXILLA. 

The  inferior  maxilla,1  mandible,  or  lower  jaw  develops  in  two  symmetrical 
halves,  which  soon  fuse.  The  bone,  as  a  whole,  consists  of  a  central  part — the  body 
—forming  the  chin  and  supporting  the  teeth,  and  two  rami  projecting  upward  from 
the  back  on  either  side  and  articulating  with  the  glenoid  fossa  of  the  temporal. 

The  body  is  convex  in  front  and  concave  behind.  The  line  of  junction  of  the 
original  halves  is  the  sywp/iysis,  marked  by  a  slight  line.  There  is  a  forward  pro- 
jection of  the  lower  border  of  the  chin  which  is  a  human  characteristic.  A  short 

FIG.  241. 

Coronoid  process 


External  pterygoid 
CONDYLE 


Temporal 


Sigmoid  notch 
Neck 


Masseter. 


ANGLE 


BODY 
External  oblique  line 

Platysma 
Inferior  maxillary  bone,  outer  aspect. 


Mental  foramen 
Depressor  anguli  oris 


Incisor  fossa 
Levator  menti 

SYMPHYSIS 

Mental 

tubercle 
Depressor 

labii  inf. 


distance  from  the  median  line  at  the  lower  border  is  the  mental  tubercle*  bounding 
this  projection  laterally.  The  alveolar  process,  above  the  body,  is  of  the  same  nature 
as  that  of  the  upper  jaw.  A  slight  depression,  the  incisor  fossa,  is  found  below  the 
teeth  of  that  name  on  the  front  of  the  bone.  The  mental  foramen  for  the  terminal 
branches  of  the  inferior  dental  nerve  and  artery  is  rather  below  the  middle  of  the 
bone  under  the  second  bicuspid,  sometimes  just  before  it.  The  external  oblique 
line?  starting  from  the  mental  tubercle,  passes  below  the  mental  foramen  into  the 
front  edge  of  the  ramus.  Sometimes  it  seems  to  spring  from  the  lower  border  under 
the  molar  teeth,  and  sometimes  both  these  origins  may  be  present  at  once.  On  the 
lower  border  of  the  bone,  rather  to  its  inner  side,  there  is  a  rough  oval  behind  each 
mental  tubercle  for  the  anterior  belly  of  the  digastric  muscle.  The  inner  side  of  the 
body  is  in  the  main  smooth.  The  superior  and  inferior  genial  tubercles*  are  two 
pairs  of  small,  sharp  spines  near  the  lower  part  of  the  inner  side  of  the  symphysis  for 
the  genio-glossi  and  genio-hyoid  muscles  respectively.  The  internal  oblique  line 
begins  at  first  very  indistinctly  near  the  genial  tubercles,  and  is  lost  on  the  inner 
side  of  the  ramus.  It  is  particularly  prominent  under  the  molars,  and  gives  attach- 

1  Mandibula.     -Tubcrculum  mcntale.      ;  Linca  obliyua.     *Spinac  incntalcs.     •"  Linca  mylohyoidca. 


212 


HUMAN   ANATOMY. 


ment  to  the  mylo-hyoid,  which  forms  the  muscular  partition  separating  the  oral 
cavity  from  the  superficial -region  under  the  chin.  There  is  a  faint  hollow,  the  sub- 
lingual  fossa,  above  it,  below  the  incisors,  for  the  sublingual  gland  lying  beneath  the 
mucous  membrane,  and  a  deeper  one,  the  submaxillary  fossa,  for  the  submaxillary 
gland  below  the  line  near  the  junction  of  the  body  and  ramus. 

The  ramus,  which  joins  the  body  at  an  angle  of  from  110°  to  120°  in  the 
adult,  is  a  four-sided  plate  with  an  outer  and  an  inner  surface.  The  point  of  union 
of  the  posterior  and  inferior  borders  is  called  the  angle,  and  is  generally  turned  out- 
ward with  a  lip,  which  helps  to  form  the  under  part  of  the  massctcric  fossa,  on  its 
outer  side,  for  that  muscle.  When  well  marked,  it  represents  the  fossa  which  is  so 
striking  in  the  carnivora  and  some  other  orders.  The  fossa  is  not  always  present, 
the  muscle  being  then  inserted  into  a  roughness.  At  the  front  of  this  space  the 
lower  border  of  the  bone  is  often  grooved  by  the  facial  artery  crossing  it.  A  projec- 
tion, known  as  the  lemurine  proces-s,  may  extend  from  the  angle  either  backward  or 
downward,  but  is  not  often  large.  The  lower  border  of  the  ramus,  where  it  joins 
the  body,  often  presents  a  concavity,  which  is  sometimes  very  marked,  giving  a 
peculiar  outline  ;  it  is  named  the  antegonium  by  Harrison  Allen.  There  is  a  rough- 


FIG.  242. 


Coronoid  process 


Sigmoid  notch 


Fossa  for  sublin- 
gual gland 
Sup. genial  tuber. 
(genio-glossus) 
Inf.  genial  tuber. 
(genio-hyoid) 


Superior  constrictor 
Alveolar  border 


Int.  pterygoid 


Angle 


Digastric          Mylo-hyoid 


Submaxillary  gland 


Inferior  maxillary  bone,  inner  aspect. 

ness  on  the  inner  side  of  the  ramus  at  the  angle  for  the  internal  pterygoid.  About 
on  a  line  with  the  free  edge  of  the  alveolar  process  is  the  lowest  point  of  the  inferior 
dental  foramen,1  an  opening  into  the  inferior  dental  canal  for  the  nerve  and  artery  to 
the  teeth  ;  the  foramen  is  guarded  in  front  by  a  sharp  point,  the  lingula.  A  faint 
groove  is  continued  from  this  opening  below  the  internal  oblique  line  for  the  mylo- 
hyoid  vessels  and  nerve.  The  front  border  of  the  ramus  is  thick  below  and  narrow 
above,  where  it  becomes  the  coronoid  process, z  pointing  upward  and  outward,  into 
which  the  temporal  muscle  is  inserted.  The  outer  border  of  the  thick  part  is  made 
by  the  external  oblique  line,  which  is  continued  into  the  thin  edge  above ;  the  inner 
border  is  continued  from  the  inner  edge  of  the  alveolar  process,  or  sometimes  from 
the  internal  oblique  line.  It  ends  on  the  inner  surface  of  the  coronoid  process. 
The  posterior  border  of  the  ramus  slants  upward,  backward,  and  a  little  outward. 
It  is  rough  at  the  angle  and  smooth  above,  where  it  widens  to  form  the  back  of  the 
head  or  condyle. '  This  presents  an  articular  surface  convex  from  before  backward 
and  higher  at  the  middle  than  at  the  ends.  The  longest  diameter  is  not  quite  trans- 
verse, for  the  axes,  if  prolonged,  would  meet  near  the  front  of  the  foramen  magnum. 
There  is  a  pretty  distinct  tubercle  at  the  outer  and  inner  ends.  The  condyle  has 

1  Foramen  imimliliulnrc.     -  I'roccssus  coronoldcin.      'Ciipltulnm   mnndlbulac. 


THE  INFERIOR  MAXILLA. 


213 


the  appearance  of  being  set  rather  on  the  front  of  the  neck,*  which  is  merely  a 
constriction  below  the  head  ;  the  articular  surface,  however,  extends  at  least  as  far 
down  behind  as  in  frontv  There  is  a  depression  for  a  part  of  the  insertion  of  the 
external  pterygoid  on  the  front  of  the  neck  internal  to  the  sigmoid  notch?  which 
is  the  deep  depression  separating  the  coronoid  process  from  the  condyle.  The 
dental  canal'1"  sweeps  downward  and  forward  with  a  slight  curve,  and  then  runs 


FIG.  244. 

Alveolar  process         Coronoid  process 


Condyle 


Symphysis  Dental  canal 

Right  inferior  maxilla  at  about  birth,  inner  aspect. 


Dental  canal 


Section  through  body  of  lower 
jaw,  anterior  surface. 


FIG.  245. 


Condyle 


horizontally  nearer  the  lower  than  the  upper  border  of  the  body  of  the  jaw.4  It 
lies  at  first  against  the  inner  wall,  but  soon  is  nearer  the  outer.  This  relation 
then  varies,  but  towards  the  anterior  end  of  its  course  it  is  against  the  inner  wall. 
It  divides  under  the  second  bicuspid  into  the  mental  canal,  some  five  millimetres 
long,  running  to  the  mental  foramen,  and  into  the  incisive  canal,  much  smaller,  for 
the  vessels  and  nerves  of  the  front  teeth,  which, 
after  dividing,  is  lost  in  the  cancellated  tissue  under 
the  lateral  incisor. 

Structure. — The  jaw  is  of  very  tough  bone, 
especially  at  the  symphysis,  where  it  is  almost  solid. 
On  section  the  body  shows  very  thick  walls  below, 
before,  and  behind.  The  alveolar  processes,  on  the 
contrary,  are  made  of  very  light  plates  that  are  ab- 
sorbed rapidly  after  the  loss  of  the  teeth. 

Development  and  Growth. — The  two  halves 
of  the  inferior  maxilla  are  formed  separately,  each 
from  six  centres.  They  are  at  first  connected  by 
ligament.  Even  before  birth  the  union  seems  very 
close,  but  they  become  coossified  only  in  the  course 
of  the  first  year.  The  centres  appear  from  the  sixth 
to  the  eighth  week  of  foetal  life  in  the  membrane  of 
Meckel's  cartilage,  except  as  otherwise  mentioned. 
They  fuse  during  the  third  month.  The  centres 

are  :  ( i )  the  dentary,  which  is  a  line  of  ossific  deposit  forming  the  lower  border 
and  the  front  of  the  alveolar  process  ;  (2)  one  in  the  distal  end  of  Meckel's  carti- 
lage, for  the  region  of  the  symphysis  ;  (3)  one  for  the  coronoid  ;  (4)  one  appearing 
in  cartilage,  not  that  of  Meckel,  for  the  condyle  and  top  of  the  ramus  ;  (5)  one  for 
the  angle  ;  (6)  the  splenial,  for  the  inner  alveolar  plate,  extending  back  to  include 
the  lingula.  This  one  appears  some  three  weeks  later  than  the  others.  Still 
another  minute  one  is  said  to  help  to  form  the  mental  foramen  (Rambaud  et 
Renault).  All  these,  except  that  for  the  condyle,  which  unites  at  fifteen,  fuse 
shortly  after  their  appearance.  The  mandible,  being  at  first  nothing  but  a  hollow 
bar  to  hold  tooth-sacs,  is  very  shallow.  The  ramus  is  small,  the  head  bent  back- 
ward and  the  angle  very  large.  At  birth  it  is  about  140°.  With  the  loss  of  teeth, 
from  whatever  cause,  the  alveolar  process  atrophies.  In  old  age  the  bone  is  very 
small  and  of  light  structure,  and  the  angle  enlarges  considerably,  so  as  to  mimic 
the  infantile  form. 

*Fawcett  :  Journal  of  Anatomy  and  Physiology,  vol.  xxix.,  1895. 

1  Collum  mandibulac.     -  Incisura  mandiluilac.     :;  Canalis  maiidibulae. 


Alveolar 
process 


Right  half  of  lower  jaw  at  about  birth, 
from  above. 


HUMAN  ANATOMY. 


Intra-articular 
fibre-cartilage 


FIG.  246. 

Zygoma,  cut  surface 


External  pterygoid 


\ 


THE  TEMPORO-MANDIBULAR  ARTICULATION. 

This  is  a  compound  joint,  the  elements  of  which  are  the  socket,  the  condyle,  and 
the  meniscus,  an  intra-articular  disk  of  fibro-cartilage,  dividing  the  cavity  into  an 
upper  and  a  lower  part,  both  being  enclosed  by  one  capsular  membrane.  The  socket 

includes  the  glenoid  fossa  and  the  articular 
eminence  of  the  temporal  bone.  The  articu- 
lar coating  of  the  socket,  which  is  continued 
onto  the  front  of  the  articular  eminence,  is 
not  true  cartilage  (Langer),  though  resem- 
bling it  to  the  naked  eye.  The  socket  is 
bounded  behind  by  the  fissure  of  Glaser. 
The  tympanic  plate  behind  it  is  covered  by 
areolar  tissue  and  a  part  of  the  parotid  gland, 
which  extend  to  the  back  of  the  head  of  the 
jaw  and  make  the  socket  much  narrower  and 
deeper  than  it  seems  on  the  dry  bone.  The 
intra-articular fibro-cartilage^  is  oblong  trans- 
versely with  rounded  angles.  It  rests  more 
on  the  front  of  the  condyle  than  on  the  top. 
It  is  concave  both  above  and  below,  being 
moulded  on  the  eminentia  articularis  and  on 
the  condyle.  It  may  be  merely  one  millimetre 
thick  in  the  middle,  and  is  said  to  be  some- 
times perforated.  The  thick  posterior  border 
fits  into  the  highest  part  of  the  socket.  The 

capsule,  lax  and  weak,  is  attached  to  the  borders  of  the  articular  surfaces  and  to  the 
edges  of  the  intra-articular  fibro-cartilage.  The  external  lateral  ligament"1  is  a  com- 
paratively strong  collection  of  fibres,  strengthening  the  capsule  externally.  The 
fibres  run  downward  and  back- 

FIG.  247. 

External  lateral  ligament 


The  temporo-mandibular  articulation  ;  the  joint 
opened. 


ward  from  the  tubercle  on  the 
zygoma,  at  the  outer  end  of  the 
articular  eminence,  to  the  outer 
side  of  the  neck  as  far  as  the 
hind  border.  The  effect  of  this 
insertion  is  to  place  the  trans- 
verse axis  of  rotation  of  the  jaw, 
not  in  the  head  of  the  mandible, 
but  in  the  neck.  The  capsule 
receives  at  the  front  and  inner 
side  two  bands  of  fibrous  tissue 
continuous  with  the  dura  mater, 
which  passes  through  the  fora- 
men ovale  around  the  third  di- 
vision of  the  fifth  nerve.3  The 
spheno-mandibular  ligament, 4 
formerly  improperly  called  the 
internal  lateral,  is  a  weak  fibrous 
structure  originally  developed 
around  a  part  of  Meckel's  car- 
tilage. It  runs  from  the  spine 
of  the  sphenoid  to  the  lingula 
without  connection  with  the 
joint.  The  capsule  is  far  too 

loose  to  hold  the  jaw  firmly  in  place,  hence  it  is  supplemented  by  the  powerful 

muscles  of  mastic -.itum.      One  of  these,  the  external  pterygoid,  is  inserted  into  both 

the  head  of  the  lower  jaw  and  the  meniscus,  which  it  draws  forward,  bring  incorpo- 

"Fuwri-U  :  Journal  of  Anatomy  ami  Physiology,  vol.  x.xvii.,  1893. 

'•  hUrus  iirtiriilaris.     -  Llg.  tcmporomnnilil>ul:iro.     1  Llg.  sphenoinandlhulnre. 


Ext.  auditory 
meatus 


Styloid  process 


Stylo-  mandihu- 
lar  ligament 


Stylo-hyoid 

ligament 


Hyoid  bone 


The  tenipou)  maiuliluikir  artu-ululion,  ouu  ' 


THE   ARTICULATION    OF   THE   MANDIBLE. 


215 


FIG.  248. 


Carotid 
canal 


Spine  of 
sphenoid 


Spheno- 
mandibular 
ligament 


•Capsule 


The  temporo-mandibular  articulation  from 
behind. 


rated  with  the  front  of  the  capsule.  The  stylo-maxillary  ligament  is  a  bundle  of 
fibres  of  the  cervical  fascia  running  from  the  styloid  process  to  the  angle  of  the  jaw. 
Movements.— These  occur  on  both  sides  of  the  meniscus,  which  slides  for- 
ward and  backward  on  the  articular  eminence.  They  may  be  divided  into  those 
of  opening  and  closing  the  mouth  and  of  grinding  the  teeth.  In  the  former, 
as  the  mouth  begins  to  open,  the  meniscus  and 
the  head  of  the  jaw  move  forward,  the  condyle 
at  the  same  time  advancing  on  the  former  as 
the  lower  jaw  turns  on  a  transverse  axis  pass- 
ing through  the  neck  in  both  halves  of  the  jaw. 
This  continues  as  the  mouth  opens  wider,  the 
meniscus  descending  onto  the  articular  eminence, 
and  probably,  when  the  movement  is  extreme, 
rising  a  little  on  the  other  side.  This  has  been 
graphically  demonstrated  on  the  living  by  an 
apparatus  bearing  luminous  points  at  the  sym- 
physis,  the  condyle,  and  the  angle  of  the  jaw, 
which  were  photographed  as  the  mouth  opened 
to  various  widths.1  It  was  shown  that  the  for- 
ward movement  of  the  meniscus  occurs  even  in 
a  very  slight  opening  of  the  mouth.  The  angle 
of  the  jaw  moves  forward  at  the  very  beginning 
of  the  act,  but  soon  passes  backward.  The 
point  on  it  describes  some  very  complex  curves. 
Grinding  movements,  in  which  the  mouth  is  not 
opened,  must  occur  chiefly  between  the  skull  and 
the  meniscus  ;  just  what  occurs  below  the  latter 
is  uncertain.  The  lower  jaw  can  be  thrust  for- 
ward evenly,  as  the  meniscus  of  each  side  de- 
scends onto  the  articular  eminence  ;  but  in  ordinary  motions  it  seems  to  advance 
on  one  side  and  perhaps  to  recede  on  the  other.  Spec  *  has  shown  that  the  opposed 
crowns  of  the  molars  (and  apparently  of  the  premolars  also)  fall  on  the  arc  of  a  cir- 
cle that  touches  the  front  of  the  condyle,  drawn,  when  projected  on  a  plane,  from  a 
centre  on  the  crest  of  the  lachrymal  bone.  This  allows  the  teeth  of  the  lower  jaw  to 
slide  on  those  of  the  upper,  which  the  joint  would  not  allow  were  the  line  between 

the  teeth  a  straight  one.  To  this  may  be  added 
that  the  inferior  incisors  rest  against  the  lingual 
surfaces  of  the  superior,  and  that  the  tendency 
of  the  edges  of  the  former  to  make  a  transverse 
arch,  increased  by  the  wearing  away  of  the  outer 
corners  of  the  lower  lateral  incisors,  implies  an 
alternate  rising  and  falling  of  either  side  of  the 
jaw  in  grinding  movements  with  the  mouth  closed, 
though  the  axis,  in  the  main  antero-posterior,  can- 
not be  a  fixed  one.  It  must  be  remembered  in 
this  connection  and  in  the  mechanics  of  the  jaw 
throughout  that  the  range  of  variations  is  great, 
and  that  there  is  frequently  a  want  of  symmetry 
in  the  joints.  This  want  of  precise  working  is  in- 
creased by  the  laxity  of  the  ligaments  and  the  num- 
ber of  muscles  acting  on  various  parts  of  the  jaw. 
Development. — The  tympanic  portion  of 
the  temporal  being  at  birth  nothing  but  the  ring, 

it  is  evident  that  the  joint  belongs  solely  to  the  squamous  portion,  and  is  always 
bounded  by  the  fissure  of  Glaser.  At  this  age  the  glenoid  fossa  is  nearly  fiat  and 
the  eminentia  articularis  but  slightly  raised.  Even  after  birth  the  joint  below  the 
meniscus  is  very  slight,  so  that  but  little  motion  can  occur  in  it,  while  the  meniscus 

1  Luce  :  Boston  Medical  and  Surgical  Journal,  July  4,  1889. 
*  Arch,  fur  Anat.  und  Phys.,  Anat.  Abtheil.,  1890. 


FIG.  249. 


Transverse  section  of  right  tempqro-man- 
dibular  articulation  from  behind. 


216  HUMAN   ANATOMY. 

itself  can  play  freely  on  the  flat  glenoid.     The  socket  gradually  deepens,  and  as- 
sumes something  like  its  definite  shape  apparently  in  the  course  of  the  third  year. 

THE   HYOID    BONE. 

This  is  a  U-shaped  bone '  not  in  contact  with  any  other,  situated  below  the  jaw 
and  above  the  larynx,  with  which  its  physiological  relation  is  intimate.  It  gives 
origin  to  a  large  part  of  the  muscular  fibres  forming  the  tongue.  It  consists  of  a 
central  body,  elongated  transversely,  and  of  a  pair  of  greater  and  lesser  horns.  The 
convex  anterior  surface  of  the  body  looks  forward  and  upward  ;  the  posterior  surface, 
which  is  deeply  hollowed,  faces  in  the  opposite  direction.  The  front  surface  is  divided 
by  a  median  and  a  transverse  ridge  into  four  spaces,  of  which  the  upper  are  the 
larger.  The  greater  cornua  extend  with  a  curve  backward  and  a  little  upward. 

They  are  broadest  at  their  front,  and 

KIG.  250.  as  they  pass  backward  are  somewhat 

twisted,    so    that    the   upper   surface 
comes  to  look  outward.    Each  ends  in  a 
small  knob.    They  are  connected  with 
I— Great  cornu     the  body  sometimes  by  fibro-cartilage, 
occasionally  by  a  synovial  joint.     The 
lesser  cornua,  slender  processes  some 
five  millimetres  long,  are  the  bony  ter- 
minations of  the  stylo-hyoid  ligaments. 
There  is  usually  a  synovial  joint  be- 
5maii  comu     tween  them  and  the  body,  which  they 
join  at  the  ends  of  the  upper  border. 
They  may  be  connected  by  ligament, 
.Body  and  are  not  very  rarely  wanting,  which 

simply  means  that  ossification  has  not 

The  hyoid  bone  from  in  front.  Occurred     at     the     lower     ends     of     the 

stylo-hyoid   ligaments.      The  outline 

of  the  body  and  greater  horns  is  easily  felt  from  the  surface,  and  the  whole  bone 
can  be  grasped  and  moved  from  side  to  side. 

Development. — As  embryology  shows,  the  basihyoid,  or  body,  is  connected 
with  the  second  visceral  arch  through  the  stylo-hyoid  ligaments,  the  lower  ends  of 
which  become  the  lesser  horns,  or  cerato-hyoids,  and  with  the  third  arch  by  the 
greater  horns,  the  thyro-hyoids.  The  bone  ossifies  in  cartilage,  two  nuclei  appearing 
(according  to  Sutton)  in  the  fourth  fcetal  month,  one  on  each  side  of  the  median 
line,  and  speedily  fusing.  A  nucleus  appears  in  each  greater  horn  in  the  fifth  month. 
Statements  as  to  the  time  of  appearance  of  ossification  in  the  lesser  horns  vary  from 
a  few  months  after  birth  to  the  end  of  adolescence.  The  latter  is  probably  nearer 
the  truth.  The  greater  horns  rarely  coossify  with  the  body  before  forty-five,  but 
after  that  age  not  infrequently.  Indeed,  in  old  age  they  are  generally  joined.  The 
lesser  horns  are  rarely  consolidated  before  advanced  age. 

THE   SKULL  AS   A   WHOLE. 

In  connection  with  the  description  of  the  skull  as  a  whole,  which  is  not  intended 
to  recapitulate  the  points  already  mentioned,  but  to  discuss  the  general  features, 
especially  those  resulting  from  the  apposition  of  the  distinct  parts,  let  it  be  remem- 
bered that  the  skull  is  an  egg-shaped  structure,  and  that  the  face  is  placed  under  its 
anterior  and  middle  fossae. 

The  Cranial  Sutures. — There  are  three  antero-posterior  sutures,  ;i  median 
and  a  lateral  one  on  each  side,  and  two  transverse  ones.  The  median  antero- 
posterior  suture  is  the  sagittal;'1  it  lies  between  the  parietal  bones,  and  is  jagged, 
except  at  the  posterior  part,  which  is  usually  straight.  Occasionally  the  inctopic 
suture''  persists  between  the  original  halves  of  the  frontal  bone.  It  is  rarely  in  direct 
continuation  with  the  sagittal.  The  coronal  suture*  crosses  the  top  of  the  head,  sep- 
arating the  frontal  from  tin-  parietals.  It  ends  at  the  top  of  the  great  wing  of  the 

1  Os  hyoidcum.     -  Sutura  saglttalia.     ''  S.  frontalls.     4  S.  coronalls. 


THE   SKULL   AS   A   WHOLE. 


217 


sphenoid  below.  Its  termination  is  at  a  vague  region  where  several  sutures  approach 
one  another,  called  the  pterion.  In  the  lower  races  occasionally,  but  rarely  in  the 
higher,  the  lower  end  of  the  coronal  is  continuous  with  the  suture  between  the  squa- 
mosal  and  the  great  wing,  in  which  case  two  sutures  cross  each  other  at  right  angles, 
and  the  pterion  is  a  definite  point,  an  ape-like  feature.  If  the  lower  corner  of  the 
parietal  bone  is  carried  downward,  and  the  suture  between  the  great  wing  and  the 
lower  border  of  the  frontal  falls  considerably,  the  general  plan  is  that  of  an  H,  the 
cross-piece  being  the  suture  between  the  parietal  and  the  sphenoid  ;  but  the  H  is 
not  often  very  clear.  A  separate  bone,  the  epipteric,  is  occasionally  found  in  this 

FIG.  251. 


Supra-orbital  foramen 


Frontal 
Exter.  angular  process 

Lesser  wing  of  sphenoid 

Optic  foramen 

Great  wing  of  sphenoid 

Lachrymal  groove 

Ethmoid 

Malar 
Superior  maxillary 


Infra-orbital  foramen 

Middle  turbinate 

Nasal  septum 

Inferior  turbinate 

Anterior  nasal  spine 

Styloid  process 


Corrugator  superciHi 


rbicularis 
palpebrarum 


'endo  oculi 
rbicularis 
palpebrarum 
evator  labii  superiovis 
alceque  nasi 
•Levator  labii  superiorly 

Zygomaticus  major 
Zygomaticus  minor 
Masseter 

evator  anguli  arts 

Compressor  naris 
Depressor  alee  nasi 
Buccinator 


Mental  foramen 


Levator  nienti 

Depressor  labii  inferioris 
Depressor  anguli  oris 
Platysma 


The  skull  from  in  front. 


region.  (See  under  Growth  and  Age  of  the  Skull.)  The  lambdoidal  suture l  starts 
from  the  top  of  the  mastoid  on  each  side  to  run  upward  and  backward  to  a  point 
separating  the  occipital  from  the  parietals,  the  interlocking  teeth  being  very  long. 
What  is  practically  a  continuation  of  this  suture  runs  downward  between  the  oc- 
cipital and  the  mastoid.  Wormian  bones  are  often  found,  and  sometimes  in  great 
numbers,  in  the  lambdoidal  suture.  Sometimes  there  is  a  very  large  triangular  one 
occupying  the  place  of  the  upper  part  of  the  occipital.  Such  a  one  may  be  sub- 
divided. We  incline  to  consider  it  a  Wormian  bone  rather  than  a  representative  of 
the  interparietal. 

1  Sutura  lambdoidca. 


218 


HUMAN    ANATOMY. 


The  lateral  antero-posterior  suture  begins  at  the  root  of  the  nose  and  runs 
through  the  orbit  to  the  side  of  the  head,  ending  at  the  lambdoidal.  Its  various 
parts  are  named  from  the  adjacent  bones.  Thus,  it  begins  with  the  fronto-nasal,  to 
continue  between  the  frontal  and  the  following  bones  :  the  superior  maxilla,  the 
lachrymal,  the  os  planum  of  the  ethmoid,  the  body,  the  lesser  and  greater  wings  of 
the  sphenoid,  the  malar,  and  in  the  temporal  fossa  the  great  wing  of  the  sphenoid 
again.  Then  behind  the  coronal  it  runs  between  the  parietal  above  and  the  sphenoid 
and  temporal  below. 

FIG.  252. 


Inferior  temporal  line 


Coronal  suture 


Sup.  temporal  line 


Ext.  angu- 
lar process 
Great  \vin.u 
of  sphenoid 


.*•*        ^\  ' 

/'        ^  *&&' 


External 

occipital 

protuberance 


Mastoid  process 

External  auditory  meat  us 


Styloid  process 


The  skull  from  the  side. 

THE  EXTERIOR  OF  THE  CRANIUM. 

Superior  Aspect.1 — This  is  oval  and  broader  behind  than  in  front,  showing 
the  coronal,  sagittal,  and  the  top  of  the  lambdoidal  sature.  On  either  side  is  the 
parietal  eminence,  and  in  front  the  smaller  frontal  ones.  The  superior,  and  perhaps 
a  little  of  the  inferior,  curved  lines  appear  laterally.  It  is  rarely  quite  symmetrical. 

Posterior  Aspect.2 — This  is  circular  in  outline,  or  sometimes  five-sided,  having 
an  inferior,  two  lateral  (nearly  vertical),  and  two  oblique  superior  borders.  Below 
the  middle  is  the  external  occipital  protuberance,  which  is  beneath  the  most  posterior 
point  of  the  skull. 

Lateral  Aspect/' — This  shows  nothing  of  the  face  that  has  not  been  mentioned. 
The  zv^oniatic  arch  is  prominent,  bridging  over  a  deep  hollow.  The  part  of  the 
hollow  above  the  arch  is  tin-  temporal fossa^  deepest  in  front,  and  nearly  tilled  by  tilt- 
temporal  muscle.  The  inner  wall  is  formed  by  the  squamosal  and  tin-  ^ivat  wing  of 
the  sphenoid  ;  the  front  one  chiefly  by  the  orbital  plate  of  tin-  malar.  Tin-  inj'ni- 
tcniporal  crest  o\\  the  great  wing  separates  the  temporal  fossa  from  the  -ygomatu •  fosta 
below.  (The  latter  fossa  is  described  with  the  face,  page  227.)  The  two  temporal 

1  Virniii  vertical)*.     "  Xorinn  occipital!*.      "'  Virma  latiT.ili-. 


THE  EXTERIOR  OF  THE  CRANIUM. 


219 


lines  are  to  be  seen  in  whole  or  in  part.  The  inferior  always  ends  in  the  supra- 
mastoid  ridge.  The  mastoid  process  varies  much  in  development. 

Anterior  Aspect.1— The  cranial  portion  of  the  skull  is  seen  only  above  the 
orbits  and  the  root  of  the  nose.  Much  of  its  lower  part  is  occupied  by  the  frontal 
sinuses. 

Inferior  Aspect.2 — (The  lower  jaw  is  supposed  to  be  removed.)  This  aspect 
may  be  divided  into  three  regions  by  two  cross-lines,  one  being  at  the  roots  of 
the  pterygoid  plates  and  one  at  the  front  edge  of  the  foramen  magnum.  Passing 
from  behind  forward,  near  the  posterior  surface,  are  seen  the  external  occipital  pro- 


FIG.  253. 


Anterior  palatine  canal 


Posterior  nasal  spine 


Posterior  palatine  canal 


Hamular  process 


Great  wing  of 
sphenoid 


Carotid  canal 
Styloid  process 

Jugular  fossa 

Stylo-mastoid 

foramen 
Mastoid  proces 

Digastric  fossa 
Occipital  groov 


Parietal  bone 


Posterior  condyloid  foramen 


Posterior  nares 


Vomer 


Foramen  ovate 

Eminentia 

articularis 
Middle  lacerated 

foramen 
Foramen  spino- 

sum 
Glenoid  fossa 

Fissure  of  Glaser 


Condyle 


Inferior  curved  line 


External  occipital  protuberance  Superior  curved  line 

Base  of  skull  from  below,  the  lower  jaw  removed. 

tuberance  and  the  superior  and  inferior  curved  lines.  In  front  of  the  latter  the 
occipital  bone  is  convex  to  the  outer  side  of  the  foramen  magnum.  A  line  con- 
necting the  backs  of  the  condyles  halves  the  foramen  magnum.  The  mastoid  pro- 
cesses appear  laterally.  Internal  to  them  are  the  digastric  grooves,  and  just  internal 
to  these  the  occipital  grooves,  nearly  or  quite  in  the  suture.  Between  the  mastoid 
and  styloid  processes  is  the  stylo-mastoid  foramen.  The  region  between  the  two 
above-mentioned  lines  includes  the  guttural  fossa  in  the  middle  for  the  pharynx  ; 
on  each  side  of  this  are  openings  for  great  vessels  and  nerves,  and,  externally,  the 
joint  of  the  jaw.  The  basilar  process  in  front  of  the  foramen  magnum  forms  the 

1  Xorma  frontalis.     -  A'orina  basalb. 


220  HUMAN    ANATOMY. 

roof  of  the  pharynx.  On  either  side  of  it  is  a  rent  separating  it  from  the  temporal 
bone.  The  back  of  this  rent  is  \hzjugular  foramen  ;  then  comes  \.\i&  fissure  proper  ; 
and,  at  the  apex  of  the  petrous  portion,  the  middle  lacerated  foramen,  which  in  life  is 
filled  with  cartilage,  as  is  also  the  fissure.  Outside,  in  the  petrous  bone,  is  the 
carotid  opening,  internal  to  the  tympanic  plate,  which  is  separated  by  the  fissure  of 
Glaser  from  the  glenoid  fossa.  The  outer  border  of  the  petrous  forms  a  gutter 
with  the  great  wing  of  the  sphenoid  for  the  cartilaginous  part  of  the  Eustachian 
tube.  Just  outside  of  this  is  the  foramen  spinosum,  often  in  the  suture  between 
the  sphenoid  and  temporal,  and  before  it  the  foramen  ovale.  In  the  front  part  of  the 
base  outside  of  the  pterygoid  is  that  part  of  the  great  wing  which  looks  downward, 
overhanging  the  zygomatic  fossa. 

THE   INTERIOR    OF   THE   CRANIUM. 

The  vault1  of  the  cranium  has  the  groove  for  the  superior  longitudinal  sinus 
in  the  middle,  with  Pacchionian  depressions  on  each  side  of  it.  The  grooves  for  the 
middle  meningeal  artery  cover  the  parietal  region.  The  base  of  the  cranium  is 
divided  into  three  fossae, — the  anterior,  the  middle,  and  the  poster  io r. 

The  anterior  fossa 2  is  bounded  behind  by  the  line  in  front  of  the  olivary  emi- 
nence and  by  the  edge  of  the  lesser  wings  of  the  sphenoid.  It  has  a  deep  hollow 
over  the  nasal  cavity,  the  floor  of  the  depression  being  the  cribriform  plate  of  the 
ethmoid.  In  the  median  line  are  the  crista  galli  and  the  foramen  caecum.  The 
lateral  part  of  the  anterior  fossa  slants  downward,  inward,  and  backward,  and  is  quite 
smooth  in  the  middle  behind  the  hollow. 

The  middle  fossa3  is  limited  in  the  centre  to  the  sclla  turcica,  but  expands  at 
the  sides.  It  is  separated  from  the  posterior  fossa  by  the  dorsum  sell&  and  the 
superior  border  of  the  petrous.  The  middle  fossa  has  the  olivary  eminence  and  the 
optic  foramina  in  front  of  the  sella  turcica,  at  each  side  of  which  is  the  groove  for  the 
internal  carotid  artery  and  the  cavernous  sinus.  The  clinoid  processes  tend  to  meet 
above  its  sides,  and  sometimes  do  so,  especially  when  the  middle  clinoid  is  developed. 
On  the  anterior  border  of  the  fossa,  near  the  middle,  is  the  sphenoidal  fissure  opening 
into  the  orbit.  Just  behind  its  inner  end  is  the  foramen  rotundum  ;  farther  back  and 
outward  are  the  foramen  ovale  and  foramen  spinosum,  from  which  latter  start  the 
grooves  of  the  middle  meningeal  artery  ;  more  internal  lies  the  middle  lacerated 
foramen.  The  depression  for  the  Gasserian  ganglion  is  seen  at  the  apex  of  the 
anterior  surface  of  the  petrous  portion  of  the  temporal  bone  ;  the  ganglion  is  very 
conveniently  placed  for  its  ophthalmic,  superior  maxillary,  and  mandibular  branches 
to  reach  the  sphenoidal  fissure,  the  foramen  rotundum,  and  the  foramen  ovale  re- 
spectively. 

The  posterior  fossa4  is  much  the  larger.  In  the  middle  is  the  foramen  Mag- 
num, with  the  basilar  groove  before  it.  The  impression  for  the  superior  petrosal 
sinus  is  at  the  top  of  the  petrous.  The  inferior  petrosal  sinus  lies  on  the  suture 
between  the  petrous  bone  and  basilar  process.  The  internal  auditory  mcatits,  the 
jugular  foramen,  and  the  anterior  condyloid  foramen  are  very  nearly  in  a  vertical 
line.  The  impressions  for  the  lateral  sinuses  run  outward  from  the  internal  occipital 
protuberance  until  they  suddenly  turn  downward,  making  a  deep  groove  in  the  tem- 
poral bone.  The  course  of  the  second  portion  of  the  sinus  is  straight  downward 
and  inward,  the  highest  point  of  the  sinus  corresponding  with  the  supramastoid  crest 
above  the  middle  of  the  mastoid  process.  This  point  is  sometimes  so  near  to  the 
surface  that  the  bone  is  translucent.  In  its  descent  the  sinus  may  for  a  time  keep 
near  the  surface,  or  leave  it  at  once.  There  is  much  variation  in  many  respects  ; 
sometimes  the  downward  turn  of  the  sinus  is  less  sharp.  The  claim  that  anything 
can  be  predicated  of  this  from  the  shape  of  the  head  is  extremely  uncertain.  Just 
before  reaching  the  jugular  foramen  the  sinus  once  more  changes  its  direction, 
running  forward  and  upward. 

THE   ARCHITECTURE   OF   THE   CRANIUM. 

The  curved  vault  of  the  skull  is  well  adapted  to  break  shocks,  but  the  bast- 
is  much  weaker  ;  not  only  is  the  bone  thin  in  many  places,  but  it  is  interrupted  by 

1  C.-ilviiriii.        rn-.;i  i-iMiiii  :iiiti-riiir.        I  .  iTunii  nu-fli.-i.      4  K.  criinii  posterior. 


THE   ARCHITECTURE   OF   THE   CRANIUM. 


221 


many  openings.  The  whole  of  the  anterior  fossa  is  very  thin  ;  so  is  the  sella  turcica, 
being  just  over  the  sphenoidal  sinus.  A  chain  of  openings  crosses  the  middle  fossa 
on  either  side.  The  temporal  bone  is  practically  crossed  by  the  external  and  internal 
meatuses  and  the  middle  ear,  besides  containing  other  cavities.  Thus  the  petrous 
is  brittle,  although  the  bone  is  very  dense.  A  rim  of  comparatively  firm  bone 
extends  around  two-thirds  of  the  skull,  starting  on  each  side  from  the  occipital 
protuberance,  which  may  be  even  two  centimetres  in  thickness,  along  the  line  of  the 
lateral  sinus  to  the  supramastoid  ridge  ;  it  follows  the  line  of  origin  of  the  zygoma, 


FIG.  254. 


Ethmoidal  spine 


Crista  galli 


Foramen  caecum 

Frontal  sinus 


Cribriform  plate 


Optic  foramen 


Olivary  emi- 
nence 


Sella  turcica 


Sphenoidal 
fissure  (con- 
cealed) 


Lateral  sinus 


Torcular  Herophili 


Base  of  skull  from  above. 


and  ends  in  the  infratemporal  crest  on  the  great  wing  of  the  sphenoid.  A 
median  ridge  strengthens  the  skull  in  both  the  frontal  and  occipital  regions. 
The  average  thickness  of  the  vault  is  about  four  millimetres.  It  is  thick  through- 
out the  frontal  region  and  at  the  parietal  eminences,  a  thin  area  lying  behind  and 
below  the  latter.  The  Pacchionian  depressions  may  almost  perforate  the  skull.  It 
is  very  thin  in  the  squamous  part  of  the  temporal  ;  less  so  in  the  superior  occipital 
fossae. 

If  the  base  of  a  skull  be  held  to  the  light  and  examined  from  within,   the 


222  HUMAN    ANATOMY. 

translucency  of  'the  following  parts  will  be  very  evident  :  the  roofs  of  the  orbits,  one 
or  two  uncertain  points  in  the  great  wing  of  the  sphenoid,  one  in  the  lower  part  of 
the  squamous  portion  just  outside  of  the  petro-squamous  suture  corresponding  to 
the  glenoid  fossa,  the  beginning  of  the  basilar  process,  a  varying  portion  of  the 
descending  part  of  the  groove  for  the  lateral  sinus,  and  nearly  the  whole  of  the  floor 
of  the  cerebellar  fossa.  A  little  rim  of  firm  bone  surrounds  the  foramen  magnum 
except  in  front. 

THE   FACE. 

This  consists  essentially  of  the  framework  of  the  jaws  and  of  the  orbital  and 
nasal  cavities,  as  well  as  of  certain  accessory  regions,  the  zygomatic  and  spheno- 
maxillary  fossa.  Apart  from  features  in  the  bones  already  described,  the  front 
view  shows  the  outline  of  the  orbits,  of  the  nasal  opening,  of  the  prominence  of  the 
cheek,  and  of  a  vacant  space  left  between  the  upper  jaw  and  the  ramus  of  the  lower. 
The  foramina  for  the  escape  of  the  terminal  branches  of  the  three  divisions  of  the 
fifth  nerve  are  very  nearly  in  a  vertical  line,  only  the  mental  foramen  is  usually  a 
little  lateral.  The  side  view  shows  the  zygomatic  fossa  below  the  arch  and  within 
the  ramus. 

The  Orbit. — Although  the  base  is  quadrilateral,  the  orbital  cavity  is  conical 
rather  than  pyramidal,  since  its  section  a  little  behind  the  base  is  almost  circular. 
The  upper  margin  of  the  entrance  is  formed  by  the  frontal  bone,  which  slants  down- 
ward to  the  very  prominent  external  angular  process,  which  affords  great  protection 
to  the  eye.  The  suture  with  the  malar  can  easily  be  felt  in  life,  owing  to  the  greater 
projection  of  the  upper  bone.  The  outer  border  and  the  inner  half  of  the  lower  are 
made  by  the  malar,  which  has  a  sharp  orbital  edge  throughout.  This  is  continued 
by  an  ascending  sharp  edge  of  the  superior  maxillary  into  the  front  border  of  the 
lachrymal  canal,  at  the  top  of  which  it  becomes  indistinct.  This  is  to  be  considered 
the  inner  boundary ;  but  there  is  difficulty  in  accurately  determining  this  border,  for 
if  the  upper  border  be  followed  down  at  the  inner  side,  It  will  be  seen  to  run  to  the 
posterior  edge  of  the  lachrymal  groove  made  by  the  ridge  in  the  lachrymal  bone.  In 
some  skulls  this  is  much  the  more  evident  border.  The  upper  part  of  the  inner  border 
is  the  only  one  that  cannot  easily  be  felt  in  life.  The  roof  of  the  orbit  is  arched  from 
side  to  side  and  from  before  backward.  It  is  overhung  by  the  border,  especially  at 
the  outer  angle,  where  it  lodges  the  lachrymal  gland.  The  inner  wall,  composed  of 
part  of  the  ascending  process  of  the  maxilla,  the  lachrymal,  the  os  planum  of  the  eth- 
moid, and  part  of  the  body  of  the  sphenoid,  is  nearly  vertical  in  front,  but  farther 
back  slants  inward.  The  inner  wall  is  frequently  quite  convex  in  the  middle  ;  if  this 
condition  is  marked,  it  is  probably  pathological.  There  is  an  approach  to  an  angle 
between  this  surface  and  the  upper.  The  two  ethmoidal  foramina  are  found  above 
the  os  planum.  The  inner  wall  curves  gradually  into  the  inferior  surface,  formed 
by  the  maxilla,  and  presenting  the  infra-orbital  groove  and  canal.  The  outer  r.W/ 
slants  strongly  inward,  its  lower  border  being  internal  to  the  upper.  It  is  formed 
by  the  malar  bone  in  front  and  the  great  wing  of  the  sphenoid  behind.  The  back 
part  of  the  upper  angle  of  the  outer  wall  is  occupied  by  the  sphenoidal  fissure,  which 
opens  into  the  middle  fossa  of  the  skull,  and  the  lower  angle  by  the  spheno-maxillary 
fissure,  separating  the  wing  of  the  sphenoid  from  the  maxilla  ;  the  outer  end  of  this 
fissure,  closed  by  the  malar  bone,  opens  into  the  zygomatic  fossa.  The  optic  fora- 
men is  at  the  posterior  point  of  junction  of  the  roof  and  the  inner  wall.  The  apc.v 
of  the  orbit  is  at  the  inner  end  of  the  sphenoidal  fissure. 

The  axes  of  the  orbits,  if  prolonged,  cross  each  other  at  the  back  of  the  sella 
turcica  at  an  angle  of  from  42°  to  44°.  The  orbital  axis  is,  therefore,  very  differ- 
ent from  the  visual  axis,  which  is  antero-posterior.  The  former,  moreover,  runs 
downward  from  the  apex  to  the  base,  making  an  angle  of  from  15°  to  20°  with  tin- 
horizontal  plane. 

The  dimensions  of  the  adult  orbit  vary  with  different  observers  and,  no  doubt, 
in  different  localities.  The  depth  is  from  forty  to  forty-five  millimetres,  the  breadth 
at  the  base  is  about  forty  millimetres,  and  the  height  about  thirty-five  millimetres 
in  males.  In  females  the  dimensions  are  rather  less. 

The   roof  is  thin  and  separates  the  orbit  from  the   cranial  cavity,   except   in 


THE   NASAL   CAVITY. 


223 


front,  at  the  inner  side,  where  the  frontal  sinus  intervenes.  This  sinus  extends 
downward,  mesially,  almost  to  the  top  of  the  lachrymal  groove.  The  inner  and 
lower  walls,  separating  the  orbit  from  the  nasal  cavity  and  the  antrum  respectively, 
are  very  thin  and  offer  little  resistance  to  a  tumor  or  a  foreign  body.  The  great 
wing  of  the  sphenoid  in  the  outer  wall  is  thick,  except  just  at  the  edge  of  the 
sphenoidal  fissure  ;  it  separates  the  orbit  from  the  middle  cranial  fossa.  The  outer 
wall  just  behind  the  anterior  border  is  thin,  where  it  cuts  off  union  with  the 
temporal  fossa. 

The  Nasal  Cavity. — The  nasal  cavity  of  each  side  has  an  anterior  and  a  pos- 
terior opening,  a  roof,  a  floor,  an  outer  wall,  and  an  inner,  the  septum,  which,  when 

FIG.  255. 


Crista  galli 


Partition  sepa- 
rating frontal 
sinus  from  orbit 


Sup.  turbinate 

Lower  part  of 
infundibulum 


Nasal  septum 


Antrum 


Inferior 
turbinate 


Floor  of  nasal  fossae 


Inferior  meatus 


Front  section  of  skull  through  plane  of  outer  border  of  orbits.     Arrows  pass  through  communication  between 

antrum  and  middle  meatus. 

the  cartilage  is  present,  completely  separates  it  from  its  fellow.  The  anterior 
common  opening  of  the  two  cavities  is  shaped  like  an  inverted  ace  of  hearts, 
bounded  above  by  the  border  of  the  nasal  bones  and  elsewhere  by  the  superior 
maxillae.  In  the  middle  of  the  floor  of  the  opening  is  the  anterior  nasal  spine, 
resembling  closely  the  bow  of  a  boat.  The  anterior  edge  where  the  two  bones  meet 
is  the  cutwater,  and  above  is  a  triangular  surface,  the  deck,  bounded  by  a  sharp 
line,  which  runs  outward,  forming  the  lower  border  of 'the  opening.  In  the  adult 
this  line  is  usually  continuous  with  the  lateral  border  of  the  opening,  but  in  infants' 
skulls  the  line  passes  from  the  side  onto  the  anterior  surface  of  the  maxillary  bone. 
Another  line  a  little  behind  this,  starting  inside  the  nose  at  the  front  of  the  inferior 
turbinate  crest,  runs  close  to  the  line  from  the  spine.  Though  these  lines  are  usually 


224 


II  I'M  AX    ANATOMY. 


Probe  in  infundibulutn 
t 


fused  in  the  adult,  forming  a  rather  dull  inferior  border  continuous  with  the  lateral 
sharp  one,  they  may  remain  distinct  and  enclose  a  well-marked  fossa  on  the  face  just 
below  the  nasal  opening  ;  this  is  the  fossa  pratnasalis,  rarely  seen  in  other  than  low 
races.  Variations  in  the  arrangement  of  these  lines  may  occur,  and  according  to 
Zuckerkandl,1  the  line  from  the  border  of  the  nose  may  not  always  form  the  anterior 
border  of  the  fossa.  The  combined  nasal  openings,  though  in  the  main  triangular, 
may  be  roughly  quadrilateral.  More  or  less  asymmetry  is  the  rule.  The  nasal  bones 
and  the  nasal  spine  may  point  sideways,  but  not  necessarily  to  the  same  side.  The 
spine  points  to  the  side  on  which  the  opening  is  the  wider  ;  the  broader  aperture 
usually  does  not  descend  so  low  as  the  narrower  one.  The  tip  of  the  nose  is  more 
often  turned  to  the  right.  In  life  the  shape' of  the  nose  depends  quite  as  much  on 
the  soft  parts  as  on  the  bones. 

The  posterior  openings  of  the  nares,  the  choance,  are  remarkably  symmet- 
rical ;  bounded  above  by  the  wings  of  the  vomer,  which  conceal  the  body  of  the 
sphenoid,  on  the  sides  by  the  internal  pterygoid  plates,  internally  by  the  vomer, 
and  below  by  the  horizontal  plate  of  the  palate,  each  is  much  higher  than  broad. 
The  index  of  the  choanae,  showing  the  proportion  of  the  breadth  to  the  height 
(~fieTh7^)»  k  ^°  *or  men  anc^  ^4  ^or  women>  showing  relatively  lower  openings  in 
the  latter  (  Escat).  Measuring  the  combined  breadth  from  one  pterygoid  process 

to  the  other  at  the  hard  palate  on 

FIG.  256.  ten  adult  skulls  irrespective  of  sex, 

we  found  the  average  breadth  27.7 
centimetres  and  the  average  height 
28.4  centimetres.  The  extremes 
were  24  and  31  centimetres  for  the 
breadth  and  25  and  31  for  the 
height.2  The  inclination  of  the 
posterior  border  of  the  vomer  is  in 
a  general  direct  ratio  to  the  degree 
of  prognathism,3  or  the  forward 
projection  of  the  face. 

Each  nasal  chamber  (  Figs. 
255,  256)  is  very  narrow,  and 
much  higher  in  the  middle  than 
at  either  orifice.  The  front  part, 
the  vestibule,  extends  under  the 
bridge  of  the  nose.  The  roof  is 
extremely  narrow  except  at  the 
posterior  end.  It  is  composed  of 
the  nasal  bones,  thin  below,  thick 
above  ;  of  a  small  part  of  the  frontal,  a  thin  plate  separating  it  from  the  frontal 
sinus  ;  the  very  thin  cribriform  plate,  easily  broken  ;  the  vertical  anterior  surface 
of  the  sphenoid,  pierced  by  an  opening  into  the  sinus  ;  and,  finally,  the  wing  of  the 
vomer.  The  floor  is  a  smooth  gutter,  formed  by  the  palatal  processes  of  the  maxillae 
and  palate  bones.  The  lower  border  of  the  anterior  nasal  opening  is  higher  than 
the  floor,  so  that  an  instrument  has  to  be  tilted  over  it. 

The  anterior  palatine  canal  opens  through  the  floor  near  the  front  on  either 
side  of  the  septum.  The  floor,  except  at  the  posterior  part,  is  of  strong  bone,  and 
is  smooth  all  over.  The  median  wall  is  derived  from  a  plate  of  cartilage,  developed 
at  a  very  early  period,  from  which  the  vertical  plate  of  the  ethmoid  and  the  vomer 
are  also  formed.  A  large  quadrilateral  space  is  left  vacant  in  the  macerated  skeleton, 
which  in  life  is  filled  by  the  unossified  portion  of  the  original  plate,  known  as  the 
triangular  cartilage.  Apparently  the  process  of  ossification  is  excessive  along  the 
line  of  union  between  the  ethmoid  and  the  vomer,  since  the  adult  septum  is  usually 
bent  to  one  side  in  its  anterio'r  two-thirds,  thus  making  one  nasal  cavity  much  smaller 

1  Normale  und  pathologische  Anatomic  der  Nasenhohle,  2te  Auflage,  Vienna,  1893. 
1  The  development  of  tin-  nasal  cavity  is  described  with  that  of  the  head. 
•  Escat :  Cavite"  Naso-Pharyngiene,  Paris,  1894. 


Inferior 
turbinate 

Anirum 


Portion  of  anterior  section  of  preceding  skull,  seen  from  be- 
hind. The  arrows  occupy  the  opening  from  the  antrum  into  the 
hiatus  semilunaris. 


THE    NASAL   CAVITY. 


225 


than  the  other.  A  ridge  is  often  found  at  or  near  the  junction  of  these  two  bones 
on  the  prominent  side,  thereby  still  further  reducing  the  smaller  cavity.  This  ridge 
may  be  developed  into  a  shelf,  called  a  spur,  which  may  even  touch  the  opposite 
wall.  The  outer  wall  is  the  most  instructive,  as  giving  the  most  light  on  the  con- 
struction of  the  region.  In  front  is  the  smooth-walled  vestibule,  formed  by  the 
inner  side  of  the  nasal  and  the  ascending  process  of  the  maxilla,  extending  upward 
under  the  frontal  sinus.  The  swelling  known  as  the  agger  may  be  found  near  the 
top  of  its  outer  wall.  The  inferior  turbinate  is  much  the  larger,  reaching  forward 
almost  to  the  opening  in  the  bone.  The  large  inferior  meatus  which  it  overhangs 
is  higher  in  front  than  behind.  The  middle  turbinate,  over  the  middle  meattis,  does 
not  extend  nearly  so  far  forward.  The  little  superior  turbinate  with  the  limited 
superior  meatus  below  it  is  still  farther  back,  reaching  only  half-way  along  the 


FIG.  257. 

Spheno-ethmoidal  recess          Extension  of  sphenoidal  sinus 


Pituitary  fossa 


Crista  galli 
Frontal  sinus 

Sup.  turbinate 

Middle 

turbinate 

Middle  meatus 

Inf.  turbinate 

Inf.  meatus 

Anterior 
palatine  canal 


Spheno-palatine 

foramen 


Hamular  process 


Palatal  plate  of  sup.  maxilla 
Inner  aspect  of  outer  wall  of  right  nasal  fossa. 


middle  turbinate.  The  three  turbinates  end  behind  very  nearly  in  a  vertical  line, 
the  middle  sometimes  projecting  farthest.  The  lines  of  attachment  of  the  turbinates 
all  slant  downward  and  backward,  but  the  inclination  of  the  middle  one  is  greatest. 
The  variations  in  number  of  the  turbinates  and  the  structures  concealed  by  the 
middle  one  have  been  described  with  the  ethmoid.  The  spheno-ethmoidal  recess  is  a 
lateral  expansion  of  the  cavity  behind  the  superior  turbinate  and  the  front  of  the 
body  of  the  sphenoid.  The  posterior  portion  of  the  outer  wall  of  the  nasal  chamber, 
formed  by  the  palate  bone  and  the  internal  pterygoid  plate,  is  smooth.  The  outer 
wall  slants  inward,  so  that  the  roof  of  the  nasal  cavity  is  narrower  than  the 'floor 
and  has  the  following  openings:  in  the  superior  meatus  that  of  the  posterior  ethmoidal 
cells  ;  farther  back  is  the  spheno-palatine  foramen  communicating  with  the  spheno- 
maxillary  fossa.  The  middle  meatus  receives  the  opening  of  \\\e  frontal  sinus  either 
directly  under  the  front  of  the  middle  turbinate  or  through  the  infundibulum. 

15 


226 


HUMAN    ANATOMY. 


These  arrangements  are  about  equally  common.  It  receives  also  the  openings  of 
the  anterior  ethmoidal  cells,  the  aperture  of  the  antruni  into  the  infundibulum,  and 
a  larger  opening  from  the  antruni  behind  the  infundibulum.  The  lachrymal  canal 
opens  into  the  inferior  meatus  under  the  fore  part  of  the  turbinate.  External  to  the 
outer  wall  are  the  orbit,  the  antrum,  and  farther  back  the  spheno-maxillary  fossa 
with- the  posterior  palatine  canal  below  it. 

The  Accessory  Pneumatic  Cavities. — These  include  the  frontal  sinuses, 
the  maxillary  antra,  the  ethmoidal  cells,  and  the  sphenoidal  sinuses.  They  have 
already  been  described  with  the  separate  bones,  but  may  be  here  further  briefly  con- 
sidered in  their  mutual  relations  to  the  nasal  fossae  and  the  skull.  All  of  these  spaces 
open  into  the  nasal  chambers  above  the  inferior  meatus, — the  sphenoidal  cells  into 
the  roof,  the  posterior  ethmoidal  cells  into  the  superior  meatus,  the  anterior  eth- 
moidals,  the  antra,  and  the  frontal  sinuses  into  the  middle  meatus. 

FIG.  258. 


Infratemporal  crest      Spheno-maxillary  fissure 


Spheno-palatine  foramen 
Glenoid  fossa 


Mastoid  process 
External  auditory  meatus 

Styloid  process      Zygoma 
Inner  wall  of  zygomatic  fossa  (external  ptery- 
goid  plate) 

Spheno-maxillary  fossa  seen  through  pterygo- 
maxillary  fissure 


Posterior  dental  canal 
Hamular  process 


Lateral  view  of  skull  with  zygomatic  arch  removed. 

The  sphenoidal  sinuses  (Fig.  257)  are  almost  invariably  unequal,  the  sep- 
tum being  much  to  one  side.  The  large  openings  in  the  front  of  the  body  of  the 
sphenoid  are  much  reduced  when  the  cornua  sphenoidalia  are  in  place.  The  open- 
ings of  the  posterior  ethmoidal  cells  are  small  and  irregular.  The  anterior 
cells  make  a  part  of  the  floor  of  the  frontal  sinuses.  They  open  either  into  the 
infundibulum  or  under  the  middle  turbinate. 

The  frontal  sinuses  (Figs.  255,  257),  when  exposed  from  the  front,  have 
a  vaguely  triangular  outline.  One  side  is  against  the  septum,  separating  it  from 
its  fellow,  which  is  rarely  symmetrical.  The  upper  border  runs  from  the  top  of 
this  downward  and  outward.  The  lower  border  bends  downward  at  the  inner  end, 
where  the  cavity  runs  down  to  the  nose  at  the  inner  angle  of  the  orbit.  The  inner 
part  extends  back  for  a  varying  distance  over  the  orbit.  In  about  half  the  cases 
the  cavity  opens  directly  into  the  middle  meatus;  in  the  rest  it  opens  into  the  top  of 


THE   SPHENO-MAXILLARY    FOSSA. 


227 


the  canal  in  the  ethmoid,  known  as  the  infundibulum.  In  the  former  cases  one  of 
the  cells  of  the  ethmoid  is  particularly  liable  to  make  a  projection — the  frontal  bulla 
— into  the  floor  of  the  sinus. 

The  antrum  (Fig.  255)  is  a  four-sided  pyramid  with  an  irregular  base  towards 
the  nasal  cavity  (Merkel).  The  apex  is  at  the  malar.  In  addition  to  the  base, 
an  orbital,  an  anterior,  and  a  posterior  surface  are  recognized.  Owing  to  the 
irregularity  of  the  base  there  is  a  groove  instead  of  an  angle  below,  above  the 
alveolar  process.  (This  relation  is  described  with  the  upper  jaw. )  The  large  in- 
ternal aperture  in  the  superior  maxilla  is  divided  into  two  when  the  other  bones  are 
in  place.  Both  are  near  the  top  ;  the  anterior  opens  into  the  infundibulum,  the  pos- 
terior into  the  middle  meatus.  Partial  septa  project  into  the  antral  cavity.  An 
important  projection  is  that  of  the  infra-orbital  canal. 

The  zygomatic  fossa  (Fig.  258)  is  the  space  internal  to  the  lower  jaw,  sepa- 
rated from  the  temporal  fossa  by  an  imaginary  plane  at  the  level  of  the  upper 
border  of  the  zygoma.  It  is  open  below  and  behind.  The  front  wall  is  made  by 


FIG.  259. 


Orbital  surface  of  great 

wing  of  sphenoid 
Frontal  process  of  malar 


Cut  surface  of  zygoma 


Tympanic  plate  of 
temporal 

Mastoid  process 


Optic  foramen 
Sphenoidal  fissure 
Sphenoidal  sinus 
Foramen  rotundum 
Vidian  canal 

Probe  in  pterygo-palatine 

canal 

Posterior  wall  of  spheno- 
maxillary  fossa 

Palate  bone 


-Hamular  process  of  internal  pterygoid  plate 
Zygomatic  surface  of  external  pterygoid  plate 

Portion  of  right  half  of  skull,  showing  posterior  wall  of  spheno-maxillary  fossa.    The  superior  maxilla,  ethmoid, 

and  part  of  malar  have  been  removed. 

the  maxilla,  what  little  roof  there  is  by  that  part  of  the  great  wing  of  the  sphenoid 
internal  to  the  infratemporal  crest,  and  the  inner  wall  by  the  external  pterygoid 
plate.  It  "has  two  important  fissures, — the  spheno-^naxillary ',  horizontal,  admitting 
to  the  orbit,  between  the  sphenoid  and  maxilla  ;  the  other,  the  pterygo-maxil- 
lary,  vertical,  between  the  maxillary  bone  and  the  front  of  the  united  pterygoid 
plates. 

The  spheno-maxillary  fossa  (Fig.  259)  is  a  small  cavity  below  and  behind 
the  apex  of  the  orbit  at  the  point  of  junction  of  the  spheno-maxillary  and  the 
pterygo-maxillary  fissures.  The  posterior  wall  is  formed  by  the  sphenoid  above  the 
roots  of  the  pterygoid  plates.  The  transverse  and  antero-posterior  diameters  of  the 
fossa  are  about  fifteen  millimetres.  It  contains  the  spheno-palatine  or  Meckel's 
ganglion.  The  foramen  rotundum  opens  into  it  behind,  transmitting  the  superior 
maxillary  division  of  the  trifacial  nerve.  More  internal  and  lower  on  the  posterior 
wall  is  the  orifice  of  the  Vidian  canal,  transmitting  the  great  superficial  and  deep 
petrosal  nerves  and  accompanying  blood-vessels.  Still  nearer  the  median  line  is 


228  HUMAN   ANATOMY. 

the  minute  pterygo-palatine  canal,  formed  by  the  palate  and  sphenoid  bones.  The 
spheno-palatine  foramen  opens  through  the  inner  wall  into  the  nasal  cavity.  The 
fossa  opens  below  into  the  posterior  palatine  canal. 

The  Roof  of  the  Mouth. — This  comprises  the  hard  palate  and  the  inner 
aspect  of  the  alveolar  process.  The  proportions,  as  stated  elsewhere  (page  229), 
vary  ;  as  a  rule,  the  broad  palate  is  less  vaulted  than  the  narrow  one.  The  oral 
roof  presents  the  orifices  of  three  canals, — the  anterior^  and  the  two  posterior 
palatine.  The  first  is  situated  in  the  mid-line  in  front,  the  others  at  the  outer 
posterior  angles.  The  palatine  grooves  for  the  anterior  palatine  nerves  and  accom- 
panying blood-vessels  extend  forward  from  the  posterior  palatine  foramina.  Be- 
hind, but  close  to,  the  latter  are  the  orifices  of  the  accessory  palatine  canals. 
The  inner  side  of  the  alveolar  process  is  rough  except  opposite  the  second  and 
third  molai*  teeth,  and  the  same  is  true  of  that  part  of  the  palate  made  by  the  superior 
maxillae.  An  occasional  swelling,  the  torus  palatinus,  is  in  the  mid-line  at  the 
junction  of  the  superior  maxillae.  Internal  to  the  first  molar  is  a  ridge  with  the 
groove  outside  of  it  at  the  lateral  border  of  the  maxilla.  The  line  separating  the 
superior  maxillae  from  the  horizontal  plates  of  the  palate  bones  has  a  forward  curve 
in  the  middle  in  nearly  three-quarters  of  the  cases.  It  is  about  straight  in  some 
twenty  per  cent,  and  curved  backward  in  the  rest.  The  fissures  are  not  always 
symmetrical.2 

The  Architecture  of  the  Face. — With  the  exception  of  the  lowef  jaw,  the 
structure  of  the  face  is  extremely  light.  It  is  subject  to  no  strain  save  through  that 
bone,  and  to  some  extent  through  the  action  of  the  tongue  on  the  palate  ;  it  has, 
however,  to  be  protected  against  occasional  violence.  There  are  certain  strong  and 
strengthening  regions.  The  hard  palate  is  strong  throughout,  except  at  the  hind 
part,  and  especially  strong  back  of  the  incisors.  Some  strength  is  gained  by  a 
thickening  just  outside  of  the  nasal  opening  above  the  canine  teeth,  running  up 
into  the  ridge  in  front  of  the  lachrymal  groove.  The  root  of  the  nose  is  also  very 
thick.  The  face  is  considerably  strengthened  through  the  malar  bone  and  its  con- 
nections, especially  with  the  robust  external  angular  process.  A  little  support  is 
probably  given  to  the  back  of  the  jaw  through  the  pterygoids. 

ANTHROPOLOGY  OF  THE  SKULL. 

There  are  certain  terms  and  measurements  which  should  be  known,  especially  as  some  of 
them  come  into  practical  use  in  the  surgery  of  the  skull. 

Points  on  the  Surface  of  the  Skull. — (See  also  Fig.  265,  page  241.) 

Alveolar  point,  the  lowest  point  in  the  mid-line  of  the  upper  alveolar  process. 

Asterion,  the  lower  end  of  the  lambdoidal  suture  ;  three  sutures  diverge  from  it  like  rays. 

Auricular  point,  the  centre  of  the  external  auditory  nieatus. 

Basion,  the  anterior  point  of  the  margin  of  the  foramen  magnum. 

Bregma,  the  anterior  end  of  the  sagittal  suture. 

Dacryon,  the  point  of  contact  of  the  frontal,  maxillary,  and  lachrymal  bones. 

Glabella,  the  region  above  the  nose  between  the  superciliary  eminences. 

Glenoid point,  the  centre  of  the  glenoid  fossa. 

Gonion,  the  outer  side  of  the  angle  of  the  lower  jaw. 

Inion,  the  external  occipital  protuberance. 

Lambda,  the  posterior  end  of  the  sagittal  suture. 

Malar  point,  the  most  prominent  point  of  that  bone. 

Mental  point,  the  most  anterior  point  of  the  symphysis  of  the  lower  jaw. 

Nasion,  the  point  of  contact  of  the  frontal  bone  with  both  nasals. 

Obelion,  the  sagittal  suture  in  the  region  of  the  parietal  foramina. 

Occipital  point,  the  most  posterior  point  in  the  mid-line.     (It  is  above  the  protuberance.) 

Ophryon,  the  point  of  intersection  of  the  median  line  with  a  line  connecting  the  tops  of  the 
orbits. 

Opisthion,  the  posterior  point  of  the  margin  of  the  foramen  magnum. 

Pterion,  the  region  where  the  frontal,  the  great  \vingof  the  sphenoid,  the  parietal,  and 
the  temporal  bones  almost  meet.  (As,  in  fact,  they  very  rarely  do  meet,  the  term  is  a  \ague 
one. ) 

1  For  the  description  of  this  canal,  see  under  Superior  Maxilla  (page  201). 
1  Stieda  :  Arch,  fiir  Anthropol.,  1893. 


ANTHROPOLOGY    OF   THE   SKULL.  229 

Stephanion,  the  region  where  the  curved  lines  on  the  temporal  bone  cross  the  coronal 
suture. 

Subnasal point,  in  the  median  line  at  the  root  of  the  anterior  nasal  spine. 

Indices. — The   cephalic    index  is   the   ratio  of  the   breadth   to   the   length   of   the   skull 

(I00^nbrte^dthj.     The  length  is  taken  from  the  glabella  to  the  occipital  point,  and  the  breadth  is 

the  greatest  transverse  diameter  above  the  supramastoid  ridge.  A  high  index  means  a  short 
skull  ;  a  low  index,  a  long  one.  A  skull  with  an  index  above  80  is  brachycephalic  ;  from  75  to 
80,  mesaticephalic ;  below  75,  dolichocephalic. 

The  index  of  height  is  the  ratio  of  the  line  from  basion  to  bregma  to  the  length 
/TOO  x_eig_t\  ^  skull  with  an  index  above  75  is  hypsicephalic  ;  from  70  to  75,  orthocephalic  ; 
below  70,  platycephalic. 

The  facial  index  is  the  ratio  of  the  length  to  the  breadth  of  the  face  ( '"^^"h  *** )  •  The 
length  is  from  the  nasion  to  the  mental  point,  and  the  breadth  is  the  greatest  at  the  zygomatic 
arches.  A  high  index  means  a  long  face.  A  head  with  a  facial  index  above  90  is  leptoprosopic  ; 
one  with  a  lower  one,  chamo'prosopic.  In  the  absence  of  the  lower  jaw  the  index  of  the  upper 
face  may  be  taken,  which  is  almost  equally  valuable.  The  only  difference  is  that  the  length  is 
taken  from  the  nasion  to  the  alveolar  point,  and  that  an  index  above  50  is  leptoprosopic,  and  one 
below  it  chaincEprosopic. 

The  nasal  index  is  the  ratio  of  the  length  of  the  nose  to  the  breadth  ( I0°.  x  ^".f h ) .     The 

V      breadth      / 

length  is  measured  in  a  straight  line  from  the  fronto-nasal  suture  to  the  anterior  nasal  spine. 
A  skull  is  Icptorhine  when  the  index  is  below  48  ;  when  from  48  to  53,  mesorhine ;  and  when 
above  53,  platyrhine. 

The  orbital  index  is  the  ratio  of  the  height  of  the  base  to  the  breadth,  thus  /IooXhe'ght\ 

V      breadth      / 

The  breadth  is  a  horizontal  from  the  outer  border  to  the  point  of  contact  of  the  frontal  with  the 
maxilla  and  lachrymal.  A  large  index  means  a  high  orbit.  An  orbit  with  an  index  below  84  is 
tnicroseme  ;  with  one  from  84  to  89,  mesoseme  ;  with  one  above  89,  megaseme.  An  index  of  70 
is  low  for  a  Caucasian,  and  one  of  106  very  high.  The  average  for  English  skulls  is  said  to  be  88. 
The  index  depends  considerably  on  the  extent  to  which  the  upper  border  overhangs. 

The  palatal  index  is  the  ratio  of  the  breadth  to  the  length.  The  former  is  taken  from  the 
socket  of  the  second  molar  of  one  side  to  that  of  the  other ;  the  latter  is  from  the  alveolar 

process  in  the  middle  line  to  the  posterior  nasal  spine  ( I0°  ^en  rt^ —  ) . 

Prognathism  denotes  the  forward  projection  of  the  face.  This  was  formerly  expressed  by 
what  is  known  as  Camper's  facial  angle,  which  was  measured  on  the  arc  between  two  lines 
meeting  at  the  nasal  spine,  one  starting  from  the  auricular  point,  the  other  from  the  most  promi- 
nent part  of  the  forehead  in  the  middle  line  (avoiding  the  projecting  nose).  This  has  fallen  into 
disuse  owing  to  inherent  defects,  and  perhaps  in  part  to  the  discordant  directions  given  for 
drawing  the  lines.  Flower's  gnathic  index  is  the  ratio  of  the  line  from  the  basion  to  the 

11  •    A.  A.t-      \'        t  ^1.      u      •  iU  •         /  loo  X  basi-alveolar  line  \         .      in- 

alveolar  point  to   the  line  from  the  basion  to  the  nasion  -PP —         .     A  sku  1  is 

\          basi-nasal  line          / 

orthognathous  with  an  index  below  98  ;  mesognathous  with  one  from  98  to  103  ;  prognathous 
with  one  above  103. 

Shape  of  the  Skull. — Extreme  forms  occur  in  Caucasians.  The  long,  narrow  skull,  with 
often  a  slight  prominence  along  the  sagittal  suture,  the  scaphoid  form,  is  due  to  the  early  closure 
of  the  sagittal  suture,  and  the  short,  round  skull  to  that  of  the  transverse  ones.  In  support  of  this 
theory  is  the  fact  that  the  metopic  or  median  frontal  suture  is  never  found  in  narrow,  but  only  in 
broad  skulls.  The  high,  sugar-loaf,  acrocephalic  skull  shows  obliteration  of  all  three  sutures  on 
the  top  of  the  vault.  The  great  backward  occipital  projection  sometimes  seen  is  usually  asso- 
ciated with  many  Wormkin  bones  in  the  lambdpidal  suture. 

The  long  type  of  skull  is  naturally  associated  with  the  long,  narrow  face,  and  the  round 
head  with  the  broad  face  ;  but  the  connection  is  not  absolute.  The  two  types  of  face  deserve  a 
short  consideration.  The  narrow  face  has  the  high  orbit,  the  narrow  nose,  with  the  aperture 
pointed  above,  and  a  long,  narrow  palate.  The  outline  of  the  range  of  teeth  in  one  jaw  to  a  great 
extent  determines  that  of  the  other  ;  but,  in  addition  to  the  smaller  curve,  the  lower  jaw  in  this 
form  is  rather  delicate,  is  particularly  likely  to  show  the  constriction  in  front  of  the  masseter, 
and  has  a  more  obtuse  angle.  The  short  and  broad  face  has  wide,  low  orbits,  a  broad  and 
almost  quadrilateral  opening  of  the  nose,  and  a  wide  pair  of  jaws,  the  lower  with  an  approxi- 
mately square  angle.  If,  as  is  most  probably  the  case,  the  head  is  orthognathous,  the  edges  of 
the  teeth  tend  to  form  part  of  an  antero-posterior  curve,  which  is  particularly  marked  in  the 
region  of  the  molars.  It  is  to  be  noted,  however,  that  some,  or  any,  of  these  features  may  be 
found  in  a  face  of  the  opposite  type. 

Dimensions  of  the  Skull. — The  actual  length  of  the  various  diameters  is  of  much  less 
importance  than  their  relations  to  one  another  in  the  science  of  craniology ;  they  may,  however, 
be  important  in  medico-legal  questions.  With  the  exception  of  the  height,  they  vary  within 
wide  limits,  even  among  Caucasians.  In  the  following  table  the  means  of  both  sexes  are  from 
Broca : 

Males.  Females. 

Mean.  Millimetres.     Millimetres. 

Length 182  174 

Breadth 145  135 

Height 132  125 


23o  HUMAN   ANATOMY. 

Cranial  Capacity.  —  This  may  vary  in  all  races  from  1000  to  1800  cubic  centimetres. 
Welcker  gives  the  following  means  and  extremes  for  white  races  :  ' 


Mean.  Maximum.          Minimum. 

Cu.  cm.  Cu.  cm.  Cu.  cm. 


Males     .....................     i45>->  179° 

Females    ...........    ........ 


A  skull  with  a  capacity  exceeding  1450  cubic  centimetres  is  mc^accphalic  ;  one  with  a 
capacity  from  1350  to  1450,  mesocephalic  ;  one  below  1350,  microcephalic. 

Manouvrier  has  devised  a  formula  for  calculating  the  weight  of  the  brain  from  the  cranial 
capacity,  as  follows  :  weight  in  grammes  is  to  capacity  in  cubic  centimetres  as  i  to  0.87. 

Asymmetry.  —  The  whole  head  is  almost  always  asymmetrical.  The  left  side  of  the 
cranium,  as  shown  by  hatters'  models,  is  larger,  especially  in  the  frontal  region.  The  right 
side  of  the  head  is  usually  the  higher.  The  cause  of  this  is  probably  to  be  found  in  habitual 
position.  The  spine  is  not  held  symmetrically,  but  the  atlas  inclines  to  the  left  ;  the  head,  when 
held  most  firmly,  does  not  rest  evenly  on  both  condyles,  but  on  one,  usually  the  left.  The 
position  of  the  head,  thus  taken,  is  not  enough  to  compensate  for  the  obliquity  of  the  base  ;  but 
certain  changes  take  place  in  the  relations  of  the  component  parts.  Thus  a  face  which  seems 

FIG.  260. 


Anterior  fontanelle 


Anterior  lateral 
fontanelle 


The  skull  at  birth,  from  before.  , 

tolerably  symmetrical  when  resting  on  the  left  condyle  only  becomes  quite  uneven  if  placed 
upon  both.  The  right  orbit  is  usually  the  higher,  the  right  side  of  the  jaw  is  the  stronger,  and 
its  teeth  are  set  in  a  smaller  curve.  The  tip  of  the  nose  turns  to  the  right.  Moreover,  the  face 
lacks  symmetry  in  another  direction  :  the  right  upper  jaw  and  the  malar  bone  are  more  promi- 
nent than  the  left.  More  striking  differences,  depending  on  these,  are  seen  (luring  litV,  which 
are  ascribed  to  the  effect  of  gravity  on  soft  parts  habitually  held  unevenly,  the  right  side  being 
the  higher.  The  right  eye  is  the  higher  and,  apparently,  the  larger,  the  lids  being  farther  apart  ; 
while  the  cleft  is  narrow  on  the  left  and  the  eye  nearer  the  nose.  The  left  nostril  is  the  larger  ; 
the  left  fold  of  the  cheek  is  less  marked.  In  a  certain  proportion  of  persons  all  these  peculiarities 
are  reversed,  and  some  of  them  may  be  transposed  without  the  others. 

Growth  and  Age  of  the  Skull. — By  the  sixth  month  of  fcetal  life  the  skull,  though  smaller,  is 
in  much  the  same  condition  as  at  birth,  except  that  then  the  occipital  region  is  relatively  larger. 
The  most  striking  points  are  the  insignificance  of  the  face  and  the  flatness  of  the  inferior  surface. 
In  the  cranium  the  frontal  region  is  relatively  small.  The  vault,  which  is  developed  in  mem- 
Inane,  presents  marked  prominences  at  the  parietal  and  frontal  eminences,  and  a  smaller  one  at 

1  Kxtreme  cases  occasionally  pass  these  limits.  There  is  in  the  Warren  Museum  the  skull 
of  a  Highlander  with  a  capacity  of  1990  cubic  centimetres,  and  one  of  a  tall  man,  presumably  an 
American,  who  could  read  and  write,  though  his  intelligence  was  defective,  with  a  capacity  <>f 
1225  cubic  centimetres.  Turner  has  noted  the  skull  of  a  female  Australian  of  930  cubic  centi- 
metres' capacity. 


GROWTH    OF   THE   SKULL. 


231 


the  external  occipital  protuberance,  from  which  radiating  lines  in  the  bone  mark  the  process  of 
development.  The  bones  of  the  vault  are  exceedingly  thin.  Each  is  separate,  the  external 
periosteum  and  the  dura  uniting  at  the  edges,  thus  limiting  the  spread  of  an  effusion  under  the 
former  to  one  bone. 

Six  places  where  there  are  considerable  membranous  intervals  between  the  developing 
bones  are  called  fontanelles.  They  are  situated  at  the  four  angles  of  the  parietal  bones,  so  that 
two  are  median  and  two  are  on  either  side.  The  median  ones,  by  far  the  most  prominent,  are 
the  anterior  and  posterior  fontanelles.  The  anterior  fontane lie,  an  important  landmark  in  mid- 
wifery, is  a  diamond-shaped  space  between  the  rounded  angles  of  the  parietals  and  frontals,  some 
thirty-five  millimetres  long  by  twenty-five  millimetres  broad.  This  one  continues  to  grow  after 
birth,  and  is  not  closed  till  some  time  in  the  first  half  of  the  second  year,  or  even  later.  The 
posterior  fontanelle  is  situated  at  the  apex  of  the  squamous  portion  of  the  occipital,  extending 
between  the  parietals.  At  an  early  stage,  owing  to  the  median  fissure  in  the  occipital,  it  is 
diamond-shaped,  but  later  it  is  triangular.  The  space  is  more  or  less  filled  up  in  the  last  two 
months  before  birth,  but  it  may  not  be  truly  closed  for  a  month  or  two  after.  The  anterior 
lateral  fontanelle  is  a  small  unimportant  space  at  the  lower  anterior  angle  of  the  parietal,  above 
the  great  wing  of  the  sphenoid,  and  extending  around  it.  It  usually  closes  at  from  two  to  three 
months  after  birth.  The  part  between  the  sphenoid  and  squamosal  is  likely  to  persist  the 
longest.  According  to  Sutton,1  in  early  fcetal  life  the  orbito-sphenoid  bone  reaches  the  lateral 

FIG.  261. 


Anterior  lateral 
fontanelle 


Posterior  lateral  fontanelle 


The  skull  at  birth,  lateral  aspect. 


wall  of  the  skull  at  this  point,  and  a  piece  of  cartilage  belonging  to  it  is  found  in  this  fontanelle. 
It  becomes  bone  in  the  course  of  the  first  year,  and  may  unite  with  either  sphenoid,  temporal, 
frontal,  or  parietal,  or  persist  as  the  epipteric  bone.  It  most  often  joins  the  parietal.  The  pos- 
terior lateral  fontanelle,  under  the  corresponding  angle  of  the  parietal,  extends  down  between 
the  temporal  and  the  occipital.  It  is  larger  than  the  preceding,  and  may  be  very  distinct  for  a 
month  or  more  after  birth.  Its  complete  closure  is  said  never  to  occur  before  the  twelfth  month, 
and,  perhaps,  usually  not  till  the  second  year.2  The  sagittal  fontanelle  (see  Ossification  of 
Parietal)  may  be  present  at  the  seventh  month  of  fcetal  life,  or  later.  The  oblique  fissure  at  the 
line  of  junction  of  the  two  parts  of  the  squamous  portion  of  the  occipital  persists  till  after  birth, 
and  must  not  be  mistaken  for  an  effect  of  violence. 

The  mastoid  process  does  not  exist  at  birth.  The  tympanic  bone  is  a  mere  frame  for  the 
ear-drum.  The  base  of  the  cranium  is  very  flat.  The  condyles  are  barely  prominent,  and  the 
basilar  process  rises  but  slightly. 

In  the  first  year  the  outer  surface  of  the  bones  of  the  vault  becomes  smooth.  The  bones  gain 
in  thickness,  and  in  the  second  year  the  cliploe  appears.  At  the  same  time  the  jagged  points 
develop  in  the  sutures,  and  at  the  end  of  that  year  the  metopic  suture  between  the  frontals 
closes. 

1  Journal  of  Anatomy  and  Physiology,  vol.  xviij.,  1884. 

2  Adachi  :  Ueber  die  Seitenfontanellen,  Zeitschrift  fur  Morph.  und  Anthrop.,  Bd.  ii.,  Heft  2. 


232 


HUMAN    ANATOMY. 


The/ace,  while  helping  to  form  the  orbit  and  nasal  cavities,  is  essentially  for  the  jaws,  and 
the  jaws  for  the  teeth.  The  greatest  change  in  the  head  after  birth  is  the  downward  growth  of 
the  face.  According  to  Froriep,  in  the  infant  the  face  is  to  the  cranium  as  i  to  8  ;  at  two  years 
as  i  to  6  ;  at  five,  as  i  to  4  ;  at  ten,  as  i  to  3  ;  in  the  grown  woman  as  i  to  2.5  ;  in  the  man 
as  i  to  2.  On  contrasting  the  front  view  in  the  infant  and  adult,  counting  as  "face"  all  below 
a  line  at  the  top  of  the  orbits  and  as  "cranium"  all  above  it,  it  will  be  seen  that  in  the  infant 
the  cranium  forms  about  one-half  and  in  the  adult  much  less.  The  lower  border  of  the  nasal 
opening  is  at  birth  but  very  little  below  the  orbit.  A  line  connecting  the  lowest  points  of  the 
malar  bones  passes  at  this  age  midway  between  the  nasal  opening  and  the  border  of  the  alveolar 
process.  At  birth  the  nasal  aperture  is  relatively  broad  ;  its  lower  border  is  not  sharply  marked 
off  from  the  face  A  line  from  the  nasal  spine  runs  outward  to  end  inside  the  cavity,  and  the 
crest  from  the  outer  border  is  still  rudimentary,  ending  shortly  on  the  front  of  the  face,  so  that 
at  the  outer  angle  there  is  no  distinct  separation  between  face  and  nasal  cavity.1  The  nasal 
cavity  is  shallow,  the  posterior  nares  very  small.  The  vomer  slants  strongly  forward.  The 
lower  jaw  is  small  and  the  angle  of  the  ramus  very  obtuse.  The  alveolar  processes  are  rudi- 
mentary. The  breadth  of  the  skull  at  its  widest  equals  or  exceeds  the  combined  height  of  the 

Fir,.   262. 


Posterior  fontanelle 


Interparietal  suture-H 


Anterior  fontanell 


The  skull  at  birth,  from  above. 

cranium  and  face  in  the  infant ;  in  the  adult  it  is  but  three-quarters  of  it.     The  breadth  o 
face  is  to  its  height  as  10  to  4  at  birth,  and  about  as  9  to  8  in  the  adult. 

Merkel  divides  the  growth  of  the  head  into  two  periods,  with  an  intervening  one  of  rest. 
The  first  ends  with  the  seventh  year,  and  is  followed  by  inactivity  till  puberty,  when  tin.-  second 
period  begins.  Thejtrstperioamay  be  subdivided  into  three  stages.  In  the  first  stag?,  reach- 
ing to  the  end  of  the  first  year,  the  growth  is  general,  but  the  face  gains  on  the  cranium.  At  six 
months  the  basilar  process  rises  more  sharply,  which,  with  the  downward  growth  of  the  face-,  lias 
an  important  effect  on  the  shape  of  the  naso-pharynx.  The  lower  part  of  the  nasal  cavity  gains 
particularly.  The  posterior  opening  doubles  its  size  in  the  first  six  months,  to  re-main  stationary 
till  the  end  of  the  second  year.  In  the  second  stage,  to  the  end  of  the  fifth  year,  the  vault  grows 
more  than  the  base,  assuming  a  more  rounded  and  finished  appearance.  The  face  still  gains 
relatively,  but  grows  more  in  breadth  than  in  height.  In  the  third  stag?,  corresponding  roughly 
to  the  seventh  year,  the  base  grows  more  and  the  vault  less.  The  face  lengthens  considerably, 
the  growth  in  the  nasal  chambers  being  chiefly  in  the  lower  part.  The  head,  though  small,  has 
lost  the  infantile  aspect.  The  foramen  magnum  and  the  petrous  portion  of  the  temporal  have 
reached  their  full  size,  and  the  orbit  very  nearly.  The  parietal  and  frontal  eminences  are  still 
very  prominent.  The  mastoid  is  rudimentary.  This  condition  lasts  till  puberty,  when  the 

1  Macalister  :  Journal  of  Anatomy  and  Physiology',  vol.  xxxii.,  1898. 


GROWTH    OF   THE   SKULL.  233 

second  period  begins.  This  is  marked  by  growth  in  all  directions,  the  gradual  rounding  off  of 
the  eminences  of  the  vault,  the  progress  of  the  mastoid,  the  strengthening  of  ridges,  the  greater 
curving  of  the  zygomatic  arches,  and  the  increase  of  the  face.  This  last  is  due  chiefly  to  the 
advance  of  the  nose,  the  gain  of  the  superciliary  eminences,  and  the  increase  of  the  lower  jaw. 
The  rise  of  the  basilar  process  increases  and  the  occipital  condyles  stand  out  more  from  the  bases 
at  the  front  edges.  These  processes  are  nearly  finished  in  the  female  by  nineteen  and  in  the 
male  one  or  two  years  later,  though,  especially  in  the  latter,  they  require  several  years  more  for 
their  absolute  completion.  The  thickness  of  the  vault  is  very  nearly  reached  by  puberty.  At 
seven  the  frontal  sinus  is  only  as  large  as  a  pea.  Its  development  is  not  completed  before  the 
twentieth  year.  There  is  no  means  of  knowing  whether  or  not  it  then  entirely  ceases. 

The  orbit  bears  nearly  the  same  proportion  to  the  cranium  at  all  ages  ;  but  at  birth  it  equals 
about  one-half  of  the  height  of  the  face,  and  in  the  adult  rather  less  than  one-third.  At  birth  the 
axis  of  the  orbit  is  horizontal.  While  sometimes  the  transverse  diameter  of  the  base  of  the  orbit 
is  much  the  larger,  this  does  not  seem  to  be  always  so.  As  the  face  grows  the  vertical  diameter 
increases  rapidly,  so  that,  according  to  Merkel,  at  five  the  base  lacks  only  two  or  three  millimetres 
of  the  adult  height,  which  it  gains  in  the  next  two  years.  The  full  breadth  is  probably  not 
attained  before  puberty. 

The  changes  in  the  nasal  cavity  are  important  as  an  essential  element  in  the  growth  of  the 
face.  At  birth  the  line  of  the  hard  palate,  if  prolonged  back,  would  strike  near  the  junction  of 
the  basilar  process  and  sphenoid  ;  at  three  it  strikes  near  the  middle  of  the  basilar  ;  at  six,  the 
front  edge  of  the  foramen  magnum,  which  is  nearly  or  quite  the  condition  of  the  adult.  The 
measurements  of  the  vertical  diameter  of  the  choanae  are  important  from  their  significance  with 
regard  to  both  the  nose  and  the  pharynx.  At  birth  the  height  is  from  five  to  six  millimetres 
(seven  millimetres  is  exceptional)  and  the  breadth  of  each  opening  very  little  greater.  At  from 
six  months  to  a  year  both  diameters  have  doubled,  their  proportions  remaining  unchanged. 
There  is  little  change  before  the  end  of  the  second  year,  when  the  height  increases  more  rapidly. 
Thus  they  change  from  circular  to  oblong  openings.  It  is  not  till  after  puberty  that  the  height 
exceeds  the  distance  between  the  internal  pterygoid  plates. 

HEIGHT  OF  POSTERIOR  NARES. 

Authority.                                                                                                       Age.  Sex.             Millimetres. 

Disse     4  male                 16 

Disse     5  female               n 

Escat 5  15 

Escat     8  18 

Dwight 7  or  8  20 

Dwight .    .    .    .  7  or  8  21 

Dwight 10  female                22 

Dwight ii  22 

Dwight. 14  female                22 

Escat 14  20 

Dwight 15  male                 23 

Dwight 16^  female                23 

Dwight 17  female                19 

Dwight. 18  male                  29 

Dwight .     19  male                 24 

Escat I5toi8  (9  cases)  25 

The  Closure  of  the  Sutures. — The  occipital  bone  unites  with  the  basisphenoid  at  the 
cerebral  aspect  about  seventeen  and  on  the  outside  of  the  skull  some  three  years  later.  The 
lower  end  of  the  suture  between  the  occipital  and  the  mastoid  process  is  one  of  the  first  to  close. 
We  have  seen  it  lost  in  a  skull  of  fourteen,  of  which  the  other  bones  were  almost  falling  apart. 
No  doubt  this  was  exceptionally  early.  The  closure  of  the  great  sutures  of  the  vault 1  ( to  which 
the  term  is  usually  applied )  begins  on  the  inside  of  the  skull,  probably  before  thirty,  at  the  lower 
ends  of  the  coronal  and  at  the  back  of  the  sagittal,  and  spreads  irregularly.  The  process  is 
generally  far  advanced  before  it  appears  on  the  outside.  The  closure  of  the  sutures  on  one  side 
of  the  head  does  not  necessarily  follow  the  same  course  on  the  other.  It  has  usually  begun  on 
the  outside  by  forty,  although  the  sutures  are  still  distinct.  They  probably  are  nearly  or  quite 
obliterated  on  the  inside  by  fifty-five.  The  apex  of  the  lambdoidal  suture  is  one  of  the  last 
points  to  persist  internally.  It  is  impossible  to  state  with  accuracy  the  time  at  which  the 
sutures  disappear  on  the  outside,  as  this  may  never  occur,  and  the  process  throughout  is  utterly 
irregular.  All  may  be  gone  very  early  or  all  may  be  distinct  at  an  advanced  age.  When  the 
metopic  suture  fails  to  close  in  early  childhood  it  is  one  of  the  very  last  to  disappear.  It  is 
unsafe  from  the  sutures  alone  to  draw  any  conclusions  as  to  the  age  of  a  skull. 
The  weight  of  the  skull  in  both  sexes  is  greatest  from  twenty  to  forty-five.2 
The  changes  in  old  age  are  essentially  atrophic.  The  most  striking  is  the  absorption  of 
the  alveolar  processes  ;  this,  however,  may  occur  prematurely  from  the  loss  of  teeth.  The 
angle  of  the  lower  jaw  becomes  much  more  obtuse.  The  thin  parts  of  the  face  and  of  the  base 

1  Dwight  :  The  Closure  of  the  Cranial  Sutures  as  a  Sign  of  Age,  Boston  Medical  and  Sur- 
gical Journal,  1890.     Parsons  :  Anthrop.  Institute  G.  Brit,  and  Ireland,  vol.  xxx,  1905. 

2  Gurriere  and  Massetti :  Rivista  speriment.  di  Freniatria  e  de  Med.  legale,  1895. 


234  HUMAN   ANATOMY. 

of  the  skull  become  still  thinner  and  may  be  quite  absorbed.  The  thinning  of  the  vault  is  less 
marked.  Occasionally,  in  extreme  age,  symmetrical  depressions  appear  in  the  upper  parts  of 
the  parietals  behind  the  vertex.  In  the  latter  part  of  life  the  frontal  sinuses  enlarge,  as  the  inner 
table  follows  the  shrinking  brain.  In  some  rare  cases  the  skull  grows  heavier  in  old  age,  owing 
to  an  increase  in  thickness  of  the  inner  table. 

Differences  due  to  Sex. — There  is  no  marked  sexual  difference  in  skulls  up  to  puberty. 
These  characteristics  appear  during  the  last  stage  of  growth.  They  may  be  summed  up  by 
saying  that  the  female  skull  differs  less  than  the  male  from  that  of  childhood.  The  parietal  and 
frontal  eminences  are  more  prominent ;  the  superciliary  prominences  and  glabella  less  marked  ; 
the  zygomata,  mastoid,  occipital  protuberance,  and  muscular  ridges  less  developed.  The  whole 
structure  is  lighter.  The  face  is  smaller  in  proportion  to  the  cranium,  owing  to  the  lighter 
jaws.  The  lower  jaw  alone  is  also  relatively  lighter  to  the  cranium.1  The  frontal  and  occipital 
regions  are  less  developed  than  the  parietal.  Two  points  are  of  especial  value, — namely,  in  the 
female  skull  the  change  of  direction  from  the  forehead  to  the  top  of  the  head  is  more  sudden, 
suggesting  a  definite  angle,  while  in  man  the  passage  is  imperceptible  ;  and,  secondly,  in  man  a 
wedge-shaped  growth  above  the  front  of  the  condyle  is  more  developed,  so  as  to  throw  the  face 
higher  up.  There  is  no  trouble  in  recognizing  a  typical  skull  of  either  sex  ;  but  in  many  cases 
the  decision  is  difficult,  and  sometimes  impossible. 

Surface  Anatomy. — It  is  convenient  for  many  reasons  to  settle  on  what  shall 
be  called  the  normal  level  of  the  skull.  This  should  be  parallel  with  the  axis  of  the 
eye  when  looking  at  the  horizon.  It  is  expressed  by  a  plane  passing  through  the 
points  above  the  middle  of  each  external  auditory  meatus  and  the  lowest  points  of 
the  anterior  border  of  each  orbit.  A  simple  method  is  to  regard  the  upper  border 
of  the  zygoma  as  horizontal,  but  this  is  not  sufficiently  accurate  with  skulls  of  low 
races.  The  following  parts  are  easily  explored  by  the  finger  :  the  whole  of  the  vault 
as  far  as  the  superior  occipital  line,  the  occipital  protuberance  behind,  and  the  supe- 
rior temporal  ridges  at  the  sides.  Often  the  bregma  and  sometimes  the  chief  sutures 
can  be  made  out.  The  possibility  of  parietal  depressions  is  to  be  remembered  in  cases 
of  injury  ;  also  that  they  may  be  expected  to  be  symmetrical. 

The  superciliary  eminences  and  the  upper  borders  of  the  orbits  are  easily 
explored.  The  .prominence  of  the  former  is  likely  to  imply  a  large  frontal  sinus  ; 
but  the  converse  is  not  true,  for,  especially  in  the  latter  part  of  life,  there  may  be  a 
large  sinus  with  no  external  indication.  The  sinus  always  extends  downward  to  the 
inner  side  of  the  orbit,  but  its  expansion  outward  and  backward  is  very  uncertain. 
The  external  angular  process  protects  the  outer  side  of  the  eye,  and  one  or  both 
temporal  ridges  can  be  followed  from  it.  The  suture  between  the  process  and  the 
malar  is  easily  felt  through  the  skin.  A  line  connecting  the  most  prominent  points 
of  the  zygomatic  arches  indicates  the  depth  of  the  orbits. 

The  zygoma  is  easily  followed  backward  to  the  auricle.  By  pressing  the  latter 
forward,  the  supramastoid  crest  can  be  made  out.  Just  below  this  is  the  spina  supra- 
meatum,  close  to  the  cartilaginous  meatus.  The  outside  of  the  mastoid  is  easily 
explored.  The  course  of  the  lateral  sinus  is  in  a  curved  line  with  the  convexity 
upward  from  the  external  occipital  protuberance  to  the  upper  part  of  the  mastoid, 
only  the  lower  part  of  the  sinus  touching  a  straight  line  between  those  points. 
According  to  Birmingham,  the  descending  part  follows  roughly  the  line  of  the 
attachment  of  the  ear.  There  is,  however,  great  variation  in  its  course  as  to  the 
sharpness  of  its  descent  and  its  relation  to  the  surface  of  the  mastoid.  It  may 
be  exceedingly  close,  or  in  no  particular  relation  to  it  (Figs.  199,  200,  and  de- 
scription of  the  temporal  bone,  page  179).  The  antrum  leading  to  the  mastoi 
cells  is  just  back  of  the  upper  part  of  the  meatus,  often  under  a  small,  smoot 
surface. 

The  antrum  of  Highmore  in  the  superior  maxilla  extends  upward  to  the  floo 
of  the  orbit,  outward  into  the  malar  prominence,  downward  to  just  above  the  line  of 
reflection  of  the  mucous  membrane  from  the  lips  to  the  alveolar  process,  and  inward 
to  the  line  of  attachment  of  the  ala  of  the  nose,  which  is  above  the  canine  eminenc 
and  marks  the  separation  of  the  antrum  from  the  nasal  cavity. 

The  variations  of  the  upper  end  of  the  infundibulum  are  of  interest.  In  the 
cases  (about  one-half)  in  which  it  drains  the  frontal  sinus  it  is  easy  for  fluid  from  the 
latter  to  run  through  the  infundibulum  both  into  the  nasal  cavity  through  the  hiatus 
scmilunaris  and  into  the  antrum  through  the  opening  in  its  outer  side.  If  the 

1  Gurriere  and  Massrtii  :   Rivista  speriment.  di  I-'n-niatria  e  de  Mt-d.  K-gale,  1895. 


PRACTICAL   CONSIDERATIONS  :    THE   SKULL.  235 

infundibulum  ends  blindly,  there  is  less  likelihood  of  inflammation  spreading  from 
the  frontal  sinus  to  the  antrum.  The  nasal  bones  and  their  junction  with  the  nasal 
cartilages  are  easily  recognized.  The  ramus  and  body  of  the  lower  jaw  are  to  be 
examined  from  the  outside.  The  head  and  coronoid  process  are  felt  more  easily  if 
the  mouth  be  opened. 

PRACTICAL    CONSIDERATIONS. 

The  Cranium. — In  the  development  of  the  cranium,  provision  is  made  for  its 
continuous  enlargement,  so  that  it  may  accommodate  the  rapidly  growing  brain. 
Accordingly,  the  first  rudiment  is  a  membranous  capsule,  at  the  base  of  which  carti- 
lage is  soon  formed,  giving  support  to  the  overlying  portions.  Then  several  centres 
of  ossification  appear  in  various  portions  of  the  membrane  and  grow  quickly,  so  as 
to  protect  the  cerebral  mass,  the  membrane  remaining  between  these  centres  still 
permitting  the  growth  and  expansion  of  the  contents.  Finally,  the  separate  bones 
become  united,  first  at  their  edges,  then  at  their  angles,  to  make  the  complete 
unyielding  bony  cranium. 

Arrest  of  these  processes  at  various  stages  produces  the  equally  various  forms 
of  malformation,  only  a  few  of  which  need  be  mentioned  here.  It  is  to  be  observed 
that,  as  a  rule,  they  affect  that  part  of  the  cranium  that  is  of  membranous  origin,  the 
base  (developed  from  cartilage)  being  much  more  rarely  involved.  Turner  (quoted 
by  Allen)  states  that  this  is  because  the  areas  of  the  different  bones  are  less  precisely 
defined,  and  because  the  process  of  ossification  is  more  liable  to  disturbance  in  mem- 
brane than  in  cartilage. 

In  some  cases  the  whole  calvaria  may  be  lacking  and  represented  only  by  a 
membrane.  Fissures  extending  from  the  margins  of  the  bones  towards  the  centres 
may  exist,  especially  in  the  frontal  and  parietal  bones,  and  may  be  mistaken  for 
fractures.  Other  irregular  gaps  filled  with  membrane  may  be  found,  and  are  gen- 
erally situated  at  or  near  the  natural  foramina  for  vessels.  The  ossification  of  the 
bones  may  be  so  incomplete  as  to  constitute  what  is  called  aplasia  cranii  congenita, 
a  condition  in  infants  due,  usually,  to  maternal  cachexia,  and  characterized  by  the 
absence  of  bone  either  in  localized  patches  or  at  points  scattered  over  the  entire 
calvaria. 

The  non-closure  of  the  sutures,  or  defective  development,  may  be  followed  by 
protrusion  of  the  dura  mater,  either  with  or  without  part  of  the  brain,  constituting  a 
meningocele  if  the  protrusion  consists  only  of  the  membranes  and  cerebro-spinal 
fluid  ;  an  encephalocele  if  it  contains  brain  ;  or  a  hydrencephalocele  if  the  contained 
brain  is  distended  by  an  excess  of  ventricular  fluid. 

These  protrusions,  in  the  order  of  frequency,  occur  (a)  in  the  occipital  region  ; 
(£)  at  the  fronto-nasal  junction  ;  (f)  in  the  course  of  the  sagittal,  lambdoidal,  and 
other  sutures  ;  (d)  at  the  anterior  or  lateral  fontanelles,  and  at  the  base  of  the  cranium, 
entering  the  orbit,  nose,  or  mouth  through  normal  or  abnormal  openings. 

In  hydrocephalus  there  are  practically  always  atrophy  and  thinning  of  the 
cranium.  "The  deformities  of  hydrocephalus  are  largely  determined  by  the  con- 
dition of  the  sutures  at  the  time  of  the  occurrence  of  the  disease.  Fixation  at  the 
line  of  the  sagittal  suture  causes  bulging  at  the  forehead  and  the  occiput.  Fixation 
at  both  the  lambdoidal  and  the  sagittal  sutures  causes  vertical  bulging  at  the  line  of 
the  coronal  suture  and  enormous  increase  of  the  ascending  portion  of  the  frontal 
bone.  Should  the  intracranial  pressure  announce  itself  prior  to  the  closure  of  any 
of  the  sutures  of  the  vertex,  the  several  bones  composing  it  become  widely  separated 
and  the  fontanelles  enormously  increased  in  size"  (Allen). 

In  microcephalus  there  is  diminution  in  the  size  of  the  cranium  and  of  its  cavity, 
due  to  premature  ossification  of  the  sutures.  The  subjects  of  microcephalus  are 
usually  idiotic.  The  operation  of  "linear  craniotomy,"  by  which  a  strip  of  bone  is 
excised  on  either  side  of  the  median  line  of  the  cranium,  was  intended  to  permit  of 
the  expansion  of  the  brain  in  such  cases.  It  has  not  established  itself  in  surgical 
favor.  The  arrested  growth  of  the  skull  is  thought  to  be  due  to  the  arrested 
development  of  the  brain,  and  not  vice  versa.  The  skulls  of  idiots,  even  when  not 
markedly  microcephalic,  approximate  in  many  ways  to  those  of  the  lower  animals, 


236  HUMAN   ANATOMY. 

and  form  a  distinct  type  characterized  by  the  proportionate  largeness  of  the  facial 
bones,  the  contraction  of  the  brain-case,  especially  in  front  and  above,  the  upward 
slant  of  the  occipital  bone  between  the  foramen  magnum  and  the  occipital  crest,  the 
projection  backward  of  the  frontal  bone  between  the  parietals  at  the  situation  of  the 
anterior  fontanelle,  and  by  many  minor  peculiarities. 

In  spite  of  these,  however,  they  are  easily  referred  to  the  human  species  by  the 
descent  of  the  cranial  cavity  below  the  level  of  the  glenoid  fossa,  the  number  of  the 
nasal  bones,  the  shap'e  of  the  jaws,  the  number  and  direction  of  the  teeth,  etc. 

Cretinism  is  said  to  be  associated  with  initial  deformities  of  the  base  pertaining 
to  errors  of  development  and  trophic  changes  in  the  bones  arising  from  cartilage, 
especially  the  basilar  process  of  the  occipital  and  the  body  of  the  sphenoid. 
Accessory  to  these  deviations,  and  in  a  measure  dependent  upon  them,  are  the 
modified  facial  proportions  and  dental  irregularity  of  cretins. 

The  Wormian  bones,  "detached  centres  of  ossification  in  the  marginal  area  of 
growing  membrane  bones,  which  they  aid  in  occupying  intervening  spaces  among 
the  bones  themselves,"  have  been  depressed  in  injuries  of  the  skull,  and  have 
resembled  fragments  of  bone  pressing  against  the  meninges.  The  edge  of  such  a 
bone  has  been  mistaken  for  a  line  of  fracture.  The  most  frequent  cause  of  the 
formation  of  Wormian  bones  is  the  stretching  of  the  membranous  envelope  of  the 
cranial  cavity  which  occurs  in  hydrocephalus,  assistance  in  the  completion  of  the 
cranial  cavity  being  supplied  by  Wormian  bones,  which  may  form  in  numbers,  espe- 
cially along  the  sagittal,  lambdoidal,  and  squamous  sutures. 

The  fact  that  in  development  the  cranial  bones  touch  first  and  unite  first  at  the 
points  nearest  their  centres  of  ossification  explains  the  formation  and  situation  of  the 
fontanelles.  The  four  sides  of  each  parietal  bone,  for  example,  become  united  to  the 
four  surrounding  bones  earlier  in  the  middle  than  at  the  four  angles.  At  the  latter, 
therefore,  there  remain  spaces  covered  with  membrane. 

The  anterior  fontanelle,  at  the  junction  with  the  frontal  of  the  antero-superior 
angles  of  the  parietal,  is  the  largest,  and  is  not  closed  for  from  one  to  two  years  after 
birth.  In  rickets  its  closure  is  much  retarded.  Its  condition,  as  to  fulness  or  the 
reverse,  gives  a  valuable  indication  in  many  of  the  diseases  of  children.  In  a  state 
of  health,  the  opening,  while  still  membranous,  is  level  with  the  cranial  bones  or  is 
very  slightly  depressed.  Systemic  exhaustion,  malnutrition,  diseases  associated 
with  depletion  of  the  vascular  system,  gastric  catarrh,  chronic  diarrhoea,  and  maras- 
mus, or  simple  atrophy,  all  produce  a  marked  depression  of  the  fontanelle,  which  in 
the  great  majority  of  cases  indicates  feeding  and  stimulation. 

A  bruit  de  souffle  of  greater  or  less  intensity,  and  synchronous  with  the  pulse,  is 
often  heard  over  the  anterior  fontanelle,  and  was  at  one  time  thought  to  be  charac- 
teristic of  rickets  and  of  hydrocephalus,  but  has  little  diagnostic  significance. 

The  thickness  of  the  skull  varies  in  individuals,  in  the  various  portions  of  the 
skull,  and  often  even  in  the  two  halves  of  the  same  skull. 

Humphry  observes  that,  as  he  has  often  found  the  skull  to  be  thick  in  idiots, 
and  the  several  bones  to  be  thickest  when  the  skull  is  small, — i.e.,  when  the  brain  is 
small, — "the  term  '  thick-headed,'  as  a  synonym  for  '  stupid,'  derives  some  confirma- 
tion from  anatomy."  Anderson  says,  however,  that  the  weight  of  the  brain  does 
not  seem  to  have  any  relation  to  the  thickness  of  the  skull,  although  this  does  not 
affect  the  truth  of  the  statement  that  as  the  brain  diminishes  with  age  the  skull  is  apt 
to  thicken,  the  addition  of  bone  taking  place  on  the  interior  and  giving  rise  to  the 
irregular  surface  with  close  dural  adhesions  often  met  with  in  operations  upon  the 
cranium  in  old  persons. 

The  middle  cerebral  fossa,  the  centre  of  the  squamous  portion  of  the  temporal, 
and  the  middle  of  the  inferior  occipital  fossae  arc  the  thinnest  parts  of  the  skull, 
varying  from  1.75  millimetres  to  .85  of  a  millimetre,  and  in  exceptional  skulls  m» -as- 
tiring  only  .  2  millimetre  in  thickness.  This  has  an  important  bearing  on  the  location 
of  fractures  (page  239).  At  the  parietal  eminence,  the  posterior  superior  angle  of 
the  parietal,  the  superior  angle  of  the  occipital,  and  especially  at  the  frontal  eminences 
and  the  occipital  protuberance  areas  of  thickening  are  found  ;  at  the  latter  point  the 
skull  may  measure  fifteen  millimetres  in  thickness  (Anderson).  The  average  thick- 
ness of  the  remaining  parts  of  the  calvaria  is  from  five  to  7.5  millimetres. 


PRACTICAL   CONSIDERATIONS  :    THE   SKULL.  237 

In  trephining  these  general  facts  should  be  remembered,  as  should  the  occa- 
sional want  of  parallelism  between  the  inner  and  outer  tables. 

The  shape  of  the  skull  is  influenced  by  race  and  by  disease.  The  racial  pecu- 
liarities have  sometimes  a  medico-legal  significance,  but  cannot  be  described  here. 
(See  also  page  229.)  Pathological  asymmetry  is  caused  in  many  ways. 

In  rickets  the  head  is  enlarged,  and  this  enlargement  seems  greater  than  it 
really  is  on  account  of  the  retarded  growth  of  the  facial  bones.  All  the  fontanelles 
are  larger  than  usual  and  close  later.  The  anterior  fontanelle  is  sometimes  patent 
at  the  end  of  the  third  or  fourth  year. 

In  craniotabes  the  rhachitic  softening  of  the  bones  favors  absorption  under 
pressure.  Consequently  the  regions  most  affected  by  the  thinning  of  the  bones  are 
the  occipital  and  the  posterior  half  of  the  parietal,  which  are  between  two  forces,— 
the  expanding  and  growing  brain  within  and  the  supporting  surface,  as  the  pillow, 
without.  Various  peculiar  shapes  may  result. 

The  changes  in  hydrocephalic  and  microcephalic  skulls  have  already  been 
described. 

Syphilis  in  the  young  affects  especially  the  fronto-parietal  region,  producing 
thickening  or  nodes  of  those  bones  in  the  vicinity  of  the  anterior  fontanelle.  This 
site  is  probably  determined  by  the  vascularity  accompanying  growth,  as  this  is  the 
last  portion  of  the  cranium  to  become  bony.  Such  nodes  are,  therefore,  analogous 
to  the  rings  or  collars  that  form  in  the  long  bones  of  syphilitic  children  near  the 
epiphyses  ;  the  immobility  of  the  cranial  bones,  however,  causing  the  exudate  to 
harden  rather  than  to  take  on  inflammatory  action.  The  bulging  of  the  forehead  in 
some  hereditary  syphilitics  is  due  to  the  catarrh  of  the  frontal  sinuses  which  often 
accompanies  the  Schneiderian  catarrh,  that  produces  first  the  so-called  "snuffles" 
and  later  caries  of  the  nasal  bones,  with  the  characteristic  flattening  of  the  nose. 

In  adults  syphilis  of  the  cranium  usually  causes  necrosis,  spreading  from  the 
external  to  the  internal  table.  Necrosis  from  whatever  cause  is  more  apt  to  affect 
the  external  table,  which  is  more  exposed  to  injury  and  less  richly  supplied  with 
blood. 

The  calvaria  is  far  more  frequently  attacked  by  disease  than  the  base,  doubt- 
less from  its  greater  liability  to  traumatism. 

The  bones  of  the  cranium  are  supplied  with  blood  by  arteries  entering  from  the 
pericranium  on  one  side  and  from  the  dura  mater  on  the  other.  The  dural  supply 
is  the  larger  ;  hence  the  foramina  on  the  inside  of  the  cranium  are  larger  and  more 
numerous  than  those  on  the  exterior,  and  hence  also  traumatic  detachment  of  the 
pericranium  over  considerable  areas  may  not  result  _  in  necrosis.  When  detached 
from  disease,  the  latter  (as  in  syphilis),  even  when  originating  externally,  is  apt  to 
spread  along  the  vessels,  and  thus  cause  necrosis  by  finally  affecting  the  dural  supply. 

The  meningeal  blood-vessels  running  on  the  exterior  surface  of  the  dura — the 
remnant  of  the  primitive  membranous  cranium  (Humphry) — and  sending  branches 
to  the  cranium  are  not  very  strong,  and  consequently  do  not  offer  much  resistance 
to  the  separation  of  the  dura  from  the  skull  ;  neither  do  their  branches  furnish  a 
very  large  quantity  of  blood,  surgically  considered.  It  follows  that  a  traumatic 
separation  of  the  dura  is  not  in  itself  a  lesion  followed  by  serious  consequences, 
unless  the  separation  takes  place  at  or  about  the  situation  of  the  main  trunks. 
Hence,  when  an  extradural  clot  is  suspected  to  be  the  cause  of  grave  symptoms,  it 
is  usually  sought  for  first  over  the  anterior  inferior  angle  of  the  parietal  bone, — i.e. , 
about  three  centimetres  (approximately  one  inch  and  a  quarter)  behind  the  external 
angular  process  on  a  level  with  the  upper  border  of  the  orbit.  This  will  make 
accessible  the  region  of  the  main  trunk  and  the  anterior  branch  of  the  middle 
meningeal.  This  latter  branch  at  this  point  runs  through  a  bony  canal  on  the  inner- 
surface  of  the  cranium,  and  is  therefore  frequently  torn  when  fracture  occurs  in  this 
region.  An  opening  on  the  same  level,  but  just  below  the  parietal  eminence,  will 
permit  the  posterior  branch  to  be  reached. 

The  venous  channels  (emissary  veins)  connecting  the  sinuses  within  and  the 
superficial  veins  without  the  cranium  sometimes  convey  infective  disease,  such  as 
erysipelas  or  cellulitis  of  the  scalp,  and  thus  bring  about  a  septic  meningitis  or  sinus 
thrombosis. 


FIG. 


238  HUMAN   ANATOMY. 

The  time-honored  custom  of  blistering  or  leeching  behind  the  ear  in  intra- 
cranial  inflammations  rests  on  the  fact  that  the  largest  emissary  vein  is  the  mastoid, 
traversing  the  mastoid  foramen  and  connecting  the  lateral  sinus  with  an  occipital 
vein  or  with  the  posterior  auricular.  (For  further  discussion  of  these  channels  of 
communication,  see  the  section  on  the  Venous  System. ) 

While  the  spinal  dura  mater  has  no  intimate  connection  with  the  inner  surfaces 
of  the  vertebrae  (being  separated  from  the  arches  by  adipose  tissue  and  from  the 
bodies  by  the  posterior  ligament),  the  dura  mater  of  the  cranium  becomes  closely 
attached  to  the  bones,  especially  at  the  base,  where  it  adheres  tightly  to  the  many 
ridges  and  prominences  and  to  the  edges  of  the  foramina  which  transmit  the  nerves 
and  vessels.  To  the  sides  and  summit  of  the  skull  the  dura  is  less  closely  attached  ; 
hence  in  fractures  at  the  base  the  dura  is  generally  torn,  and  the  risk  both  of 
serious  hemorrhage  and  of  infection  is  thereby  increased,  while  in  fracture  of  the 
calvaria  it  much  oftener  escapes. 

Fractures  of  the  Cranium. — That  fractures  in  this  region  are  not  vastly 
more  frequent  is  due  to  various  factors  ;  among  them  are  the  rounded  shape  of  the 

calvaria,  causing  blows  to  glance  off  ;  the 
division  of  the  separate  bones  into  inner  and 
outer  tables,  with  the  comparatively  spongy 
diploe  intervening;  aud  the  curved  thicken- 
ings which,  like  buttresses,  strengthen  the 
skull  externally,  and  extend  on  each  side 
through  the  supra-orbital  ridge  and  the 
upper  border  of  the  temporal  fossa  to  the 
mastoid  process  and  thence  to  the  occipital 
tuberosity.  From  this  latter  point  on  the 
inner  surface  other  ridges,  like  the  groining 
of  a  roof,  run  forward  in  the  median  line  to  the  frontal  bone,  downward  to  the  foramen 
magnum,  and  laterally,  on  either  side  of  the  groove  for  the  lateral  sinus,  extend  to 
the  mastoid.  In  very  young  persons  the  dome  of  the  skull  is  made  up  of  three  dis- 
tinct arches  composed  of  the  occipital,  the  frontal,  and  the  parietal  bones.  In  child- 
hood the  centre  (the  most  prominent  portion)  of  each  of  these  bones  is,  on  account 
of  early  ossification,  thicker  than  the  rest,  while  the  edges  are  connected  by  mem- 
brane and  are  comparatively  movable.  These  mechanical  conditions,  together  with 
the  elasticity  of  the  individual  bones  in  young  persons,  make  fractures  of  the  skull  in 
them  comparatively  rare. 

In  the  adult  the  membranous  layer  between  the  sutures  becomes  thinner  or  disap- 
pears and  the  bones  denser  and  less  elastic  ;  they  are,  therefore,  more  easily  fractured. 
The  two  tables  may  be  broken  separately,  although  this  is  rare.  In  almost  all 
cases  in  which  fracture  is  complete  the  inner  table  suffers  more  than  the  outer. 
This  is  because  (a)  it  is  more  brittle  ;  (<$)  the  fibres  on  the  side  of  greatest  strain 
suffer  most  (as  in  "green-stick"  fracture)  ;  (c)  the  material  carried  inward  from 
without  is  greater  at  the  level  of  the  inner  table  than  at  the  point  of  application  of 
the  external  force. 

Agnew  explains  this  diagrammatically  as  follows  : 


Section  of  frontal  bone,  natural  size,  showing  rela- 
tion of  external  and  internal  tables  of  compact  bone  to 
intervening  diploe. 


AB  represents  a  section  of  the  arch  of  the  skull.  CD  and  EF  represent  the  lines 
of  a  vertical  force  applied  about  G.  The  effect  is  to  flatten  the  curve  so  that  it  is 
as  HI,  while  at  the  same  time  the  vertical  lines  diverge  (JK  and  LM)  and  the  particles 
of  bone  in  the  external  table  tend  to  be  forced  together  at  N  and  separated  or  burst 
apart  at  O. 


PRACTICAL   CONSIDERATIONS  :    THE   SKULL. 


239 


FIG.  264. 


Force  applied  to  the  vertex  would  tend  to  drive  apart  the  lower  borders  of  the 
parietal  bones,  but  the  bases  of  the  great  arch  formed  by  these  bones  are  overlapped 
by  the  squamous  portions  of  the  temporal,  and  thus  this  outward  thrust  is  prevented. 
If  the  force  be  applied  to  the  frontal  bone,  as  it  overlaps  the  parietals  at  the  middle 
of  the  coronal  suture,  it  is  transmitted  to  them  and  is  resisted  by  the  same  mechanism. 
The  occipital  bone  and  the  bones  at  the  sides  of  the  skull  (beneath  the  level  of  the 
ridges  that  have  been  described)  break  more  easily,  as  they  are  thinner,  the  diploe 
is  less  developed,  and  the  two  tables  are  more  closely  united  (Humphry);  but 
from  their  situation  they  are  less  exposed  to  injury,  and  are  protected  by  a  thicker 
covering  of  soft  parts. 

Fractures  of  the  base  are  usually  due  to  indirect  violence.  They  may  result 
from  foreign  bodies  thrust  through  the  nose,  orbit,  or  pharynx  ;  or  from  a  blow 
upon  the  nose  acting  through  the  bony  septum  to  produce  fracture  of  the  cribriform 
plate  of  the  ethmoid  ;  or  through  a  blow  or  fall  upon  the  point  of  the  chin,  driving 
the  condyles  of  the  inferior  maxilla  into 
the  cranium.  As  a  rule,  however,  the  force 
traverses  the  vault  or,  more  rarely,  the 
spinal  column  (as  in  falls  upon  the  feet  or 
buttocks). 

Fractures  of  the  base  are  very  frequent 
for  several  reasons.  The  large  expanse  of 
bone  forming  the  vault  is  contracted  at  the 
base  into  three  comparatively  narrow  por- 
tions, which  descend  in  successively  lower 
planes  from  before  backward,  but  which 
all  have  relatively  thin  floors,  on  which  the 
force  received  at  a  distant  portion  of  the  cra- 
nium is  ultimately  expended.  This  impact 
reaches  the  base  by  the  shortest  route,  so 
that  a  blow  of  sufficient  violence  upon  the 
frontal  bone  will  fracture  the  orbital  plates  in 
the  anterior  cerebral  fossa;  upon  the  vertex, 
the  petrous  portion  of  the  temporal  and 
the  floor  of  the  middle  fossa  ;  and  upon 
the  occiput,  the  floor  of  the  posterior  or 
cerebellar  fossa.  Furthermore,  the  base 
is  provided  with  a  series  of  well-marked 
ridges  which  aid  in  the  transmission  of 
force  and  which  fade  away  into  the  vault. 

The  anterior  ridges  are  gathered  into 
the  lesser  wing  of  the  sphenoid  and  end  at  the  sides  of  the  anterior  clinoid  process. 

The  middle  group,  collected  into  the  petrous  portion  of  the  temporal  bone, 
passes  to  the  centre  of  the  base  of  the  skull  and  terminates  at  the  foramen  lacerum 
medium. 

The  ridges  of  the  posterior  group,  meeting  at  the  torcular  Herophili,  continue 
to  the  foramen  magnum,  at  the  posterior  limit  of  which  they  divide  and  pass  for- 
ward to  meet  again  in  the  basilar  process,  and  end  in  the  posterior  clinoid  process. 
The  region  of  the  sella  turcica  is  therefore  the  centre  of  resistance  to  the  transmis- 
sion of  forces  from  the  vault  to  the  base.  This  is  well  surrounded  by  fluid,  and  the 
vibrations  which  are  concentrated  here  may  thus  become  lost  in  the  fluid  without 
injuring  the  brain-substance. 

The  region  of  the  middle  fossa  suffers,  however,  most  frequently  because  :  i.  It 
is  connected  (by  the  fronto-sphenoidal  and  petro-occipital  sutures)  with  both  the 
other  fossae,  and  hence  often  participates  in  their  injuries.  2.  It  is  intrinsically  one 
of  the  weakest  parts  of  the  skull,  on  account  of  the  presence  of  the  foramina  lacera, 
the  carotid  grooves,  the  hollows  for  the  pituitary  body,  the  depression  for  the  sphe- 
noidal  sinus,  the  petro-sphenoidal  suture,  and  the  thin  walls  of  the  tympanum,  of 
the  external  auditory  canal,  and  of  the  temporal  fossa.  Moreover,  just  in  front  of 
this  region  the  descending  pterygoid  processes  and  the  lower  jaw  reinforce  the 


Base  of  skull  from  above,  showing  lines  of  fractures. 


24o  HUMAN    ANATOMY. 

cranium  proper,  while  behind  it  are  the  thickening  of  the  basilar  process  and  the 
posterior  clinoid  plate  (Humphry)  (Fig.  254). 

The  differential  symptoms  of  fracture  through  the  floors  of  these  fossae  are 
determined  by  their  anatomical  relations.  They  are  as  follows  : 

1.  Anterior  Cerebral  Fossa. — (a)  Epistaxis  when  the  Schneiderian  membrane 
and  the  dura  and  arachnoid  are  torn.     It  should  not  be  forgotten  that  the  blood  may 
come  from  the  mucous  membrane  alone,      (b')   Loss  of  smell  from   injury  to  the 
olfactory  bulbs  resting  on  the  cribriform  plate,      (c)   Subconjunctival  ecchymosis. 

The  blood  is  usually  derived  from  the  meningeal  vessels  over  the  orbital  plates, 
but  in  bad  cases  may  come  from  the  ophthalmic  artery,  ophthalmic  vein,  or  cavern- 
ous sinus.  If  the  body  of  the  sphenoid  is  fractured,  the  blood  may  find  its  way 
through  the  sphenoidal  sinuses  into  the  pharynx  and  stomach,  and  then  be  vomited, 
giving  rise  to  a  mistaken  diagnosis  of  gastric  injury. 

2.  Middle   Cerebral  Fossa. — (a)    Hemorrhage  from  the  ear.     This  may   be 
merely  from  a  torn  tympanic  membrane.      (£)   Escape  of  cerebro-spinal  fluid  from 
the  ear.     This  indicates  that  the  petrous  portion  of  the  temporal  is  broken,  the  dura 
mater  and  the  arachnoid  torn,  and  the  membrana  tympani  ruptured.      If  the  latter 
escapes  injury,  the  fluid  may  trickle  into  the  throat  through  the  Eustachian  tube. 
(c)   In  rare  and  very  severe  cases  the  lateral  sinus  has  been  opened  or  the  internal 
carotid  torn,      (d)  There  may  be  deafness  or  facial  paralysis,  or  both. 

3.  Posterior  or  Cerebellar  Fossa. — (a)    Hemorrhage  into  the  pharynx  if   the 
basilar  process  is  involved  and  the  pharyngeal  mucous  membrane  torn.     (6)  Ecchy- 
mosis at  the  nape  of  the  neck  and  about  the  mastoid. 

Of  course  the  characteristic  symptoms  of  any  two  or  even  of  all  three  of  these 
injuries  may  be  commingled  if  the  fracture  is  extensive  enough. 

Just  as  fractures  would  be  more  frequent  were  it  not  for  the  mechanism  that  has 
been  described,  so  concussion  or  laceration  of  the  brain  would  occur  far  oftener  were 
it  not  for  certain  factors,  among  which  may  be  mentioned  the  different  strata  of 
tissue  of  varying  density  intervening  between  the  brain  and  the  scalp.  The  soft 
diploe  and  the  dense  inner  "vitreous"  table  both  tend  to  diminish  shock  to  the 
brain,  the  former  by  arresting  vibrations  and  the  latter  by  lateralizing  them.  The 
eminences  on  the  inner  surface  of  the  skull  project  into  the  spaces  between  the  great 
divisions  of  the  brain,  where,  in  places,  there  is  more  subarachnoid  fluid  than  else- 
where ;  such  elevations  are  intimately  connected  at  their  edges  and  terminal  points 
with  the  strong  expansions  of  the  dura  mater, — the  falx  and  the  tentorium, — which 
still  further  take  up  and  distribute  the  final  vibrations.  ' '  Thus  there  is  every  facility 
for  causing  jarring  impulses  to  deviate  from  the  direct  line  and  take  a  circumferential 
route,  in  which  they  are  gradually  weakened  and  rendered  harmless"  (Humphry). 

The  conditions  tending  to  minimize  the  effects  of  violence  inflicted  upon  the 
skull  are  thus  summarized  by  Jacobson  :  "(i)  The  density  and  mobility  of  the 
scalp.  (2)  The  dome-like  shape  of  the  skull.  This,  like  an  egg-shell,  is  calculated 
to  bear  hard  blows  and  also  to  allow  them  to  glide  off.  (3)  Before  middle  life  the 
number  of  bones  tends  to  break  up  the  force  of  a  blow.  (4)  The  sutures  interrupt 
the  transmission  of  violence.  (5)  The  internal  membrane  (remains  of  foetal  peri- 
osteum) acts  in  early  life  as  a  linear  buffer.  (6)  The  elasticity  of  the  outer  table. 
(7)  The  overlapping  of  some  bones, — e.g. ,  the  parietal  by  the  squamous  ;  and  the 
alternate  bevelling  of  adjacent  bones, — e.g. ,  at  the  coronal  suture.  (8)  The  pus 
ence  of  ribs  or  groins, — e.g. ,  (a)  from  the  crista  galli  to  the  internal  occipital  pro- 
tuberance ;  (b}  from  the  root  of  the  nose  to  the  zygoma  ;  (r)  the  temporal  ridge 
from  orbit  to  mastoid  ;  (</)  from  mastoid  to  mastoid  ;  (e}  from  the  external  occipital 
protuberance  to  the  foramen  magnum.  (9)  Buttresses, — e.g. ,  malar  and  /ygomatic 
processes,  and  the  greater  wing  of  the  sphenoid.  (10)  The  mobility  of  the  head 
upon  the  spine. ' ' 

Landmarks. — The  prominence  of  the  occiput,  of  the  parietal  region,  or  of  the 
frontal  eminence  indicates  in  a  ^eneral  way  the  development  of  the  corresponding 
portions  of  the  brain. 

The  terms  used  to  designate  particular  points  on  the  skull  have  already  been 
described  (page  228);  additional  attention  may  here  be  paid  to  those  of  especial 
importance  as  landmarks. 


PRACTICAL   CONSIDERATIONS:    THE   SKULL. 


241 


The  inion  or  external  occipital  protuberance,  which  approximately  corresponds 
to  the  point  of  convergence  of  five  sinuses  (the  superior  longitudinal,  the  two  lateral, 
the  straight,  and  the  occipital),  is  easily  felt  in  the  mid-line  behind.  The  superior 
curved  lines  which  run  outward  from  this  point  indicate  the  muscular  origin  of  the 
occipito-frontalis,  and  hence  are  often  the  lower  limit  of  effusions  beneath  the 
aponeurosis.  These  ridges  indicate  approximately  the  course  of  the  lateral  sinuses, 
which  are  on  a  line  drawn  from  the  inion  to  the  superior  border  of  the  mastoid 
apophysis, — i.e.,  to  a  point  about  2.5  centimetres,  or  one  inch,  behind  the  external 
auditory  meatus. 

The  astcrion  or  junction  of  the  squamous  and  lambdoid  sutures  is  12.5  milli- 
metres, or  half  an  inch,  above  and  18.5  millimetres,  or  three-quarters  of  an  inch, 
behind  the  upper  level  of  the  posterior  border  of  the  mastoid.  A  line  from  the 
asterion  to  the  inion  is  therefore  also  the  line  of  the  lateral  sinus. 

The  lambda,  the  junction  of  the  lambdoid  and  sagittal  sutures,  lies  in  the  median 
line  posteriorly  about  seventy  millimetres,  or  two  and  three-quarters  inches,  above 
the  inion.  In  early  life  the  posterior  fontanelle  is  found  at  that  point. 

FIG.  265. 

Bregma    Biauricular  line 


Stephanion 
Inferior  stephanion 


Obelion 


Malar  point — ;     ,/. 

,i  i  ,  / 

Alveolar  point 


Mental  point 

Gonion 
Lateral  aspect  of  the  skull,  showing  the  various  points.     (See  also  description  on  page  228.) 

The  bregma,  the  junction  of  the  coronal  and  sagittal  sutures  (and  in  childhood 
of  the  frontal  suture),  marks  the  position  of  the  anterior  fontanelle,  and  is  found  a 
little  anterior  to  the  centre  of  the  shortest  line  that  can  be  drawn  over  the  vertex 
between  the  two  external  auditory  meatuses. 

The  pterion  is  the  point  of  junction  of  the  temporal,  sphenoid,  frontal,  and 
parietal  bones.  It  is  from  thirty  to  thirty-eight  millimetres,  or  one  and  a  quarter 
to  one  and  a  half  inches,  above  the  zygoma,  and  the  same  distance  behind  the 
external  angular  process  of  the  frontal.  It  represents  the  position  of  the  trunk  and 
of  the  large  anterior  branch  of  the  middle  meningeal  artery. 

The  zygoma  can  easily  be  traced  from  its  anterior  to  its  posterior  extremity. 

The  temporal  ridges  can  often  be  felt  as  two  curved  lines,  the  upper  one  mark- 
ing the  attachment  of  the  temporal  fascia  and  the  lower  one  that  of  the  muscle. 
They  indicate  the  upper  boundary  of  the  temporal  fossa,  and  often  limit  the  spread 
of  effusions  or  the  growth  of  tumors. 

16 


242  HUMAN   ANATOMY. 

The  course  of  the  longitudinal  sinus  is  indicated  by  a  line  drawn  from  the 
nasion  (the  junction  of  the  nasal  and  frontal  bones)  to  the  inion. 

The  lateral  sinus  is  irregular  in  its  course  (page  234).  According  to  Macewen, 
it  may  be  fairly  indicated  by  the  two  following  lines  :  ' '  The  first  from  the  asterion  to 
the  superior  margin  of  the  external  osseous  meatus,  of  which  line  the  posterior  two- 
thirds  correspond  to  the  upper  part  of  the  sigmoid  groove,  which  is  also  the  more 
superficial.  The  second  line  from  the  parieto-squamo-mastoid  junction  to  the  tip  of 
the  mastoid  process  corresponds  in  its  upper  two-thirds  to  the  vertical  part  of  the 
sigmoid  groove.  The  knee  of  the  sigmoid — its  most  anterior  convexity — is  variable 
in  its  position,  but  is  generally  on  a  level  with  the  upper  part  of  the  external  osseous 
meatus.  The  sigmoid  groove  is  situated  at  a  variable  distance  from  the  external 
auditory  meatus,  the  tympanum,  and  the  exterior  of  the  skull.  The  distance 
between  the  external  osseous  meatus  and  the  sigmoid  groove  varies  from  one  or  t\vo 
to  thirteen  millimetres." 

The  frequency  with  which-infective  thrombosis  of  the  lateral  sinuses  occurs  as 
a  complication  of  middle  ear  disease  renders  the  topographical  anatomy  of  these 
sinuses  and  the  associated  region  of  the  skull  of  great  practical  importance. 

The  suprameatal  triangle  is  formed  by  the  posterior  root  of  the  zygoma  running 
somewhat  horizontally  above,  the  portion  of  the  descending  plate  of  the  squamous 
which  forms  the  arch  of  the  osseous  part  of  the  external  auditory  meatus  below,  and 
a  base  line  uniting  the  two,  dropped  from  the  former  on  a  level  with  the  posterior 
border  of  the  external  auditory  meatus.  At  this  point  there  is  usually  a  depression 
in  the  bone,  though  occasionally  there  is  a  slight  prominence  as  if  the  antrum  had 
bulged  at  that  point.  The  apex  of  this  triangular  depressed  area  points  forward 
(Macewen).  The  mastoid  antrum  may  be  reached  through  this  triangle. 

(The  relations  of  this  antrum,  the  facial  canal,  and  the  lateral  sinus  to  one 
another,  to  the  temporo-sphenoidal  lobe,  and  to  the  surface  of  the  skull  will  be 
considered  in  connection  with  the  general  subject  of  Cranio- Cerebral  Topography, 
page  1214.) 

The  size  and  extent  of  the  frontal  sinuses  vary,  as  described  on  page  234. 
The  communication  of  these  sinuses  with  the  nose  accounts  for  the  frontal  headache 
in  ozaena,  and  the  fact  that  a  patient  with  a  compound  fracture  opening  up  the 
sinuses  can  blow  out  a  flame  held  close  by.  The  frontal  sinuses  may  be  occu- 
pied by  bony  or  other  tumors  ;  emphysema  may  result  from  fracture  of  the  sinus 
wall  ;  insects  may  gain  access  to  these  cavities  and  give  rise  to  infection  or  to 
epistaxis  ;  infective  inflammations  of  the  nose  and  naso-pharynx  may  involve  the 
sinuses. 

The  sphenoidal  sinuses  are  less  important  surgically,  but  these  points  should  be 
remembered  :  (i)  fracture  through  them  may  lead  to  bleeding  from  the  nose,  which 
is  thus  brought  into  communication  with  the  middle  fossa  ;  (2)  the  communication 
of  their  mucous  membrane  with  that  of  the  nose  may  explain  the  inveteracy  of  cer- 
tain cases  of  ozaena  ;  (3)  here  and  in  the  frontal  sinuses  very  dense  exostoses  are 
sometimes  formed  (Jacobson). 

The  Face.— The  nasal  bones  are  so  joined  together  as  to  form  a  strong  arch 
resting  upon  the  nasal  processes  of  the  superior  maxillary  bones.  They  are  sel- 
dom dislocated,  because  this  line  of  union  is  one  in  which  there  is  an  alternation 
in  the  bevelling  of  the  sutures  (similar  to  that  between  the  frontal  and  parietal 
bones).  Thus  the  lower  portion  of  the  nasal  bones  overlaps  the  maxillary,  while 
nearer  the  root  of  the  nose  the  latter  is  external.  The  line  between  the  bones 
and  the  nasal  cartilages  can  easily  be  felt.  The  skin  is  very  tightly  attached  to 
the  cartilages. 

The  upper  or  frontal  portion  of  these  bones  is  very  strong,  and  will  resist  a 
great  degree  of  force  without  fracture.  The  lower  portion  is  most  frequently  broken, 
usually  within  a  half-inch  of  the  lower  margin. 

The  resulting  deformity  is  usually  lateral,  but  if  the  perpendicular  plate  of  the 
ethmoid  is  broken  the  nose  will  be  depressed.  The  thinness  and  close  application 
of  the  mucous  membrane  to  the  bones  render  these  fractures  almost  invariably  com- 
pound. Emphysema  of  the  cellular  tissue  of  the  face  and  forehead  may  follow  such 
an  injury.  The  vascularity  of  the  bones  leads  to  very  rapid  union,  and  it  is  therefore 


PRACTICAL   CONSIDERATIONS:    THE   FACE.  243 

important  to  secure  early  reposition  of  the  fragments.  The  relation  of  the  perpen- 
dicular plate  of  the  ethmoid  through  the  crista  galli  to  the  olfactory  bulbs  and  the 
base  of  the  brain  should  be  remembered  in  severe  injuries  to  the  bones  of  the  nose. 
By  reason  of  this  relation  suspension  or  destruction  of  the  sense  of  smell  has  re- 
sulted ;  and  even  septic  meningitis  and  death  have  followed  accidents  in  which  the 
prominent  early  symptom  was  fracture  of  the  nasal  bones. 

The  malar  bones,  binding  together  the  maxillae  and  the  cranium,  are  very  strong, 
and  seldom  broken  unless  by  severe  force  directly  applied. 

Fracture  of  the  body  is  apt  to  run  into  the  orbit,  producing  a  subconjunctival 
ecchymosis  near  the  outer  canthus,  and  there  may  also  be  a  loss  of  sensation  in  some 
of  the  teeth,  the  gums,  the  ala  of  the  nose,  and  a  part  of  the  cheek,  on  account  of 
injury  to,  or  pressure  upon,  the  infra-orbital  branch  of  the  fifth  nerve. 

The  zygomatic  process  is  most  subject  to  fracture  ;  that  part  of  the  arch  which 
is  on  the  temporal  side  of  the  suture  is  much  weaker  and  most  apt  to  give  way. 
The  deformity  may  usually  easily  be  recognized  by  touch.  The  fragments  are 
always  driven  inward,  and  sometimes  become  entangled  in  the  fibres  of  the  tem- 
poral muscles.  The  attachment  of  the  strong  temporal  fascia  to  the  upper  edge  of 
the  zygoma,  and  of  the  masseter  muscles  to  its  lower  edge,  prevents  displacement 
upward  or  downward. 

The  superior  maxilla,  on  account  of  its  very  various  and  complicated  relations 
(being  associated  with  nine  other  bones),  has  considerable  surgical  importance.  Its 
position  in  the  same  vertical  plane  as  the  forehead  (instead  of  in  advance  of  it,  as  in 
the  lower  animals)  indicates  the  limitation  of  its  function  to  mastication,  the  need  for 
its  use  in  prehension  having  disappeared.  Many  of  its  diseases  (infections,  tumors, 
etc.)  originate  in  the  teeth  or  teeth-sockets,  and  may  be  avoided  by  early  atten- 
tion to  these  structures.  Others  arise  by  reason  of  the  contiguity  of  the  maxillary 
antrum  to  the  inferior  turbinated  bone,  the  mucous  membrane  of  which  is  often  the 
subject  of  chronic  catarrh. 

Injuries  of  the  superior  maxilla  causing  fracture  must,  as  a  rule,  be  direct  and 
of  considerable  violence.  The  line  of  fracture  may  involve  the  antrum,  the  nose 
through  the  nasal  process,  the  orbit  through  the  orbital  process,  or  the  mouth 
through  the  alveolar  or  palatine  process.  It  may  also  run  into  the  zygomatic  or  the 
spheno-maxillary  fossa.  The  force  may  be  transmitted  from  the  malar  bone,  or  from 
the  lower  jaw  through  the  teeth. 

The  maxilla  is  very  vascular,  and  hence  recovery  from  even  serious  or  crushing 
injuries  is  apt  to  be  rapid  and  thorough.  Like  the  nasal  bones,  it  has  attached  to 
it  no  muscles  that  can  cause  or  perpetuate  deformity,  and  therefore,  unless  it  is 
comminuted,  its  fragments  will  retain  their  position  when  once  replaced. 

It  is  frequently  affected  by  "  phosphorus  necrosis,"  the  osteitis  causing  the  ne- 
crosis being  probably  due  to  the  direct  toxic  action  of  the  phosphorus  fumes  gaining 
access  through  carious  teeth.  This  theory  is  not  undisputed. 

Tumors  involving  the  alveolar  border  show  first  in  the  mouth.  Tumors  of  the 
body  usually  occupy  the  antrum  (maxillary  sinus).  They  are  apt  to  grow  in  every 
direction  except  towards  the  malar  bone,  where  they  meet  with  the  greatest  resist- 
ance. They  accordingly  produce  prominence  of  the  eye  from  pushing  upward  the 
floor  of  the  orbit,  bulging  of  the  cheek  from  pushing  outward  the  thin  anterior  wall, 
and  depression  of  the  roof  of  the  mouth  from  pressure  upon  the  palatal  plate.  After 
the  anterior  the  most  yielding  wall  of  the  antrum  is  the  orbital. 

Abscess  of  the  antrum  gives  rise  to  the  same  symptoms  when  it  attains  a  large 
size. 

The  relations  of  the  molar  teeth  to  the  floor  of  the  antrum  and  of  the  infra- 
orbital  nerve  to  its  roof  account  for  the  toothache  and  facial  neuralgia  that  so  often 
accompany  antral  disease.  It  is  said  to  be  a  fact  that  cystic  distention  does  not 
involve  the  lachrymal  duct,  while  solid  tumors  may  cause  overflowing  of  the  tears 
(Warren-Heath). 

The  chief  deformity  associated  with  the  superior  maxilla  is  cleft  palate,  which 
results  from  a  failure  of  the  palatal  plates  to  unite  in  the  median  line.  The  cjeft 
in  the  hard  palate  is  always  median,  but  when  it  reaches  the  alveolus  it  follows  the 
line  of  the  suture  between  the  premaxillary  bone  (os  incisivum)  and  the  superior 


244  HUMAN   ANATOMY. 

maxilla,  ending,  therefore,  opposite  the  space  between  the  lateral  incisor  and  the 
canine.  In  single  harelip,  which  is  often  associated  with  cleft  palate,  and  due  to 
faulty  union  of  the  fronto-nasal  and  maxillary  processes  (page  60),  the  gap  is  found 
at  the  same  point,  never  in  the  middle  line.  Sometimes  the  premaxillary  bone, 
which  carries  the  two  upper  central  incisors,  is  left  attached  to  the  nose.  This  con- 
dition is  usually  associated  with  double  harelip.  Cleft  palate  may  involve  only  the 
soft  palate  and  not  the  hard,  but  the  reverse  is  almost  never  true. 

Occasionally  the  identity  of  the  premaxilla  is  established  pathologically. 
Instances  of  exfoliation  of  this  bone  carrying  the  two  incisor  teeth  have  been 
recorded,  not  only  in  children  but  even  in  adults. 

Excision  of  the  superior  maxilla  involves  (the  bone  having  been  exposed  by  a 
suitable  incision  through  the  soft  parts)  the  disjunction  of  (a)  its  connection  with 
the  malar  bone  ;  ( b }  its  nasal  process  from  the  nasal,  lachrymal,  and  frontal  bones  ; 
(c)  its  orbital  plate  from  the  ethmoid,  malar,  lachrymal,  and  palate  bones  ;  (d)  its 
posterior  connection  with  the  pterygoid  processes  and  palate  bone  ;  and  (e )  its 
articulation  with  its  fellow  through  the  palatal  plates  and  its  connection  with  the  soft 
palate. 

These  indications  are  met,  as  a  rule,  by  sawing  through  the  malar  bone  just 
beyond  its  articulation  with  the  maxilla  (so  that  advantage  may  be  taken  of  the 
proximity  of  the  spheno-maxillary  fissure),  dividing  the  nasal  process  a  little  below 
the  junction  with  the  nasal  bones,  sawing  through  the  hard  palate  (from  the  nose 
downward)  at  or  beyond  the  median  line,  dividing  the  orbital  plate  with  a  fine 
chisel  (or  leaving  it  to  be  brought  away  at  the  last  step),  and,  finally,  wrenching 
the  bone  away  from  its  attachment  to  the  pterygoid  processes  (and  the  orbit)  by 
means  of  a  pair  of  lion-forceps.  The  hinder  wall,  in  contact  with  the  palate  bone, 
is  very  thin,  and  may  give  way  and  remain  behind  at  this  stage.  This  is  most  likely 
to  happen  when  it  is  most  undesirable, — i.e.,  when  the  operation  is  performed  for 
malignant  disease. 

The  inferior  maxilla,  the  only  bone  of  the  skull  which  is  movable  upon  the 
others,  is  especially  dense,  so  that  it  may  be  strong  enough  to  withstand  the  very 
considerable  force  which  its  muscles  exert  upon  it  in  mastication.  It  is,  therefore, 
not  easily  divided  in  operations.  The  alveolar  processes  are  thicker  and  stronger 
than  those  of  the  upper  jaw,  and  more  force  is,  therefore,  usually  required  to  extract 
a  tooth  ;  hence  damage  to  the  bone  through  rough  or  unskilful  effort  at  extraction 
is  more  frequent  in  the  lower  than  in  the  upper  jaw.  The  last  molar,  or  wisdom 
tooth,  is  often  a  cause  of  trouble,  owing  to  the  limited  space  it  occupies  near  the 
angle  between  the  ramus  and  the  body  of  the  jaw.  The  smaller  that  angle  the 
greater  the  difficulty  in  cutting  this  tooth,  which  may  be  compelled  to  carry  before 
it  a  portion  of  the  gum  closely  applied  to  the  base  of  the  coronoid  process,  causing 
inflammation  or  ulceration,  or,  through  irritation  of  the  sensory  branches  of  the  fifth 
nerve,  may  even  produce  trismus,  since  the  motor  supply  of  the  muscles  of  mastica- 
tion is  derived  from  the  same  nerve-trunk.  It  is  thus  much  oftener  the  source  of 
trouble  in  the  white  races  than  in  negroes,  in  whom  the  angle  between  the  ascending 
and  horizontal  portions  of  the  bone  is  more  obtuse. 

Congenital  deformities  of  the  lower  jaw  are  very  rare.  When  they  do  occur, 
as  in  a  case  reported  by  Humphry,  they  show  that  the  jaw  consists  essentially  of  two 
portions,  the  alveolus  and  the  remainder  of  the  jaw.  In  that  case  the  jaw  in  adult 
life  preserved  the  proportions  of  infancy  so  far  as  the  body  was  concerned,  but  the 
teeth  and  alveolus  had  attained  normal  dimensions.  The  division,  as  Allen  has 
emphasized,  is  an  important  one  to  remember  for  the  following  reasons  :  the  alveolus 
is  developed  with  the  teeth  ;  it  is  an  outgrowth  from  the  jaw  for  a  specific  temporary 
purpose.  John  Hunter  declared  that  the  "alveolar  processes  of  both  jaws  should 
rather  be  considered  as  belonging  to  the  teeth  than  as  parts  of  the  jaws. "  Hence 
all  diseases  of  the  alveolus  are  to  be  considered  as  dental  in  their  significance. 
Kpulis,  or  fibroma  of  the  gums,  is  essentially  an  alveolar  disease.  A  tooth  in  any 
portion  of  the  jaw  other  than  the  alveolus  is  a  foreign  body.  If  it  is  lodged  beneath 
the  alveolus,  it  may  give  rise  to  chronic  abscess,  or  may,  through  long-continued 
irritation,  cause  one  of  the  various  forms  of  odontomata.  Cystic  disease  about  the 
of  the  jaw  is  often  excited  1>\  a  misplaced  third  molar. 


PRACTICAL   CONSIDERATIONS  :    THE   FACE.  245 

The  inferior  maxilla  has  no  epiphysis,  and,  as  might  therefore  be  expected,  the 
ends  of  the  bone  at  and  near  the  articular  surfaces  are  usually  exempt  from  disease, 
in  marked  contrast  to  the  long  bones,  in  which  those  regions  especially  suffer. 

The  inferior  maxilla  is  not  a  very  vascular  bone  ;  the  mucous  membrane  of  the 
gum  is  in  close  contact  with  it  ;  it  occupies  a  peculiarly  exposed  position,  and  is 
subject  to  frequent  minor  traumatisms  ;  it  is  readily  infected  through  carious  teeth 
or  tooth-sockets.  Such  a  tooth  or  an  open  socket  communicates  directly  with  the 
cancellous  tissue  of  the  bone,  thus  probably  permitting  in  the  lower,  as  in  the  upper 
jaw  the  direct  contact  of  the  toxic  agent  in  phosphorus  necrosis.  Similar  conditions 
are  found  in  no  other  bones  of  the  skeleton. 

As  a  result  of  the  conditions  just  enumerated,  osteitis  and  necrosis  are  common, 
are  associated  with  much  pain,  and  are  often  very  slow  in  their  progress. 

The  excessive  pain,  dysphagia,  dribbling  of  saliva,  and  occasional  aphasia  and 
marked  nervous  symptoms  are  thought  to  be  due  to  reflex  irritation  associated 
with  compression  of  the  inferior  dental  nerve  in  the  dental  canal  by  the  products 
of  inflammation.  Such  irritation  of  a  cranial  nerve  confined  within  a  bony  canal  is 
rare,  and  associates  the  above  symptoms  with  those  occasioned  by  pressure  from 
similar  causes  on  the  other  branches  of  the  fifth  pair  and  on  the  seventh. 

Fracture  Q{  the  lower  jaw  may  occur  at  any  point.    The  whole  bone  is  to  a  great 
extent  protected  from  fracture  by  its  horse- 
shoe   shape,    which    gives    it   some    of   the  FlG-  266> 
properties  of  a  spring,  by  its  density  of  struc- 
ture, by  its  great  mobility,  and  by  the  buffer- 
like  interarticular  cartilages  that  protect  its 
attached  extremities  (Treves). 

The  neck  of  the  condyloid  process  and 
the  coronoid  process  are  so  deeply  situated 
and  so  sheltered  in  the  temporal  fossa  by 
the  zygomatic  arches  that  they  are  seldom 
broken. 

The    ramilS    is    protected    (though    tO    a  Mandible,  showing  lines  of  fractures. 

less  extent)  by  the  masseter  externally  and 

the  internal  pterygoid  internally,  and  is  not  often  fractured.      The  angle  and  the 

symphysis  are  thickened,  and  thus  resist  fracture. 

About  three  centimetres  (approximately  one  and  a  quarter  inches)  laterally  to 
the  symphysis  the  bone  is  weakened  by  the  presence  of  the  mental  foramen  and  the 
large  socket  for  the  canine  tooth.  It  is  most  often  broken  there  or  thereabouts 
either  by  direct  or  by  indirect  violence.  Most  fractures  of  the  body  of  the  bone 
are  compound  on  account  of  the  firm  adhesion  of  the  gum,  which  is  usually  torn  ; 
hence  necrosis  and  non-union  following  infection  from  the  mouth-fluids  are  not  un- 
common results.  (For  the  displacement  accompanying  this  fracture  see  section 
on  Muscles,  page  493.)  The  deformity,  in  so  far  as  it  is  produced  by  anatomical 
forces,  is  apt  to  consist  of  depression  of  the  anterior  and  larger  fragment  by  the 
digastric,  the  genio-hyo-glossus,  and  the  genio-hyoid,  and  elevation  of  the  posterior 
and  smaller  fragment  by  the  temporal,  the  masseter,  and  the  internal  pterygoid. 

The  dental  nerve,  while  escaping  injury  at  the  time  of  the  accident,  may  later 
be  compressed  by  callus,  and,  if  irritated,  may,  by  reason  of  its  anatomical  associa- 
tions with  the  regions  in  front  of  the  pinna  or  in  the  external  auditory  meatus,  give 
rise  to  "  faceache"  or  to  "earache."  If  paralyzed,  and  the  patient  puts  a  cup  to 
his  lips,  he  feels  with  his  lower  lip  only  half  of  it  ;  in  paralysis  of  the  fifth  nerve  itself 
it  seems  to  him  exactly  as  though  it  were  broken  (Owen). 

The  capsule  of  the  temporo-maxillary  joint  is  thinnest  anteriorly  and  strongest 
externally  ;  hence  suppuration  is  most  likely  to  extend  in  a  forward  direction. 
The  strong  external  lateral  ligament  arising  from  the  lower  edge  of  the  zygoma  and 
running  backward  and  downward  seems  to  prevent  the  condyle  being  pressed  back- 
ward against  the  bony  meatus  and  the  middle  ear  (Fig.  247).  As  Treves  observes, 
if  it  were  not  for  this  provision,  blows  upon  the  chin  would  be  far  more  dangerous 
than  they  are. 

In  spite  of  its  great  mobility  and  its  frequent  use,  the  joint  is  rarely  the  subject 


246  HUMAN   ANATOMY. 

of  acute  disease,  the  intra-articular  cartilage  being  so  arranged  (page  214)  that  it 
acts  as  an  elastic  buffer  presenting  one  surface  upon  which  the  hinge-like,  and 
another  upon  which  the  sliding,  movement  of  the  jaw  may  take  place.  Suppurative 
disease  of  the  middle  ear  may  extend  to  the  joint  (Barker). 

Rheumatoid  arthritis  is  perhaps  the  most  common  disease  of  the  joint,  and  may 
be  localized  there  in  subjects  otherwise  predisposed  by  the  frequent  exposure  of  the 
joint  to  cold  and  wet. 

The  so-called  "  subluxation,"  sometimes,  perhaps,  depending  upon  relaxation 
of  the  ligaments,  is  more  probably  in  the  majority  of  cases  due  to  rheumatic  or  gouty 
changes  in  the  joint. 

Dislocation  of  the  jaw  (discussed  in  connection  with  the  action  of  the  associ- 
ated muscles,  page  493)  occurs  only  when  the  mouth  is  widely  open,  as  in  yawning, 
so  that  the  condyle  passes  beyond  its  proper  limits,  over  the  summit  of  the  ridge, 
and  is  lodged  in  front.  "  When  the  mouth  is  widely  opened  the  condyles,  together 
with  the  interarticular  fibre-cartilage,  glide  forward.  The  fibre-cartilage  extends 
as  far  as  the  anterior  edge  of  the  eminentia  articularis,  which  is  coated  with  cartilage 
to  receive  it.  The  condyle  never  reaches  quite  so  far  as  the  summit  of  that  emi- 
nence. All  parts  of  the  capsule  save  the  anterior  are  rendered  tense.  The  coronoid 
process  is  much  depressed.  Now,  if  the  external  pterygoid  muscle  (the  muscle 
mainly  answerable  for  the  luxation)  contract  vigorously,  the  condyle  is  soon  drawn 
over  the  eminence  into  the  zygomatic  fossa,  the  interarticular  cartilage  remaining 
behind.  On  reaching  its  new  position  it  is  immediately  drawn  up  by  the  temporal, 
internal  pterygoid,  and  masseter  muscles,  and  is  thereby  more  or  less  fixed.  A 
specimen  in  the  Muse"e  Dupuytren  shows  that  the  fixity  of  the  luxated  jaw  may 
sometimes  depend  upon  the  catching  of  the  apex  of  the  coronoid  process  against 
the  malar  bone"  (Treves). 

Excision  of  the  inferior  maxilla,  since  it  is  concerned  chiefly  with  the  soft  parts, 
will  be  considered  in  connection  with  the  Muscles  (page  493). 

Landmarks. — The  supra-orbital  ridges  mark  the  boundary  between  the  face 
and  the  cranium.  The  supra-orbital  notch  can  be  felt  at  the  junction  of  the  inner 
and  middle  thirds  of  the  supra-orbital  margin.  A  line  from  that  point  to  the 
interval  between  the  two  bicuspid  teeth  in  both  jaws  crosses  the  infra-orbital  and 
the  mental  foramina  (Holden). 

The  attachment  of  the  nasal  cartilages  to  the  superior  maxillae  and  to  the  nasal 
bones  can  easily  be  felt.  The  connective  tissue  between  the  skin  and  the  cartilages 
is  very  scanty.  This  is  a  source  of  difficulty  in  some  of  the  plastic  operations  on  the 
nose,  and  is  also  a  cause  of  the  severe  pain  felt  in  cellulitis  and  in  furuncles  of  that 
region.  The  great  vascularity  of  the  part  and  the  fact  that  "  the  edge  of  the  nostril 
is  a  free  border  and  the  circulation  therefore  is  terminal"  (Treves)  favor  congestion 
and  engorgement,  while  the  close  connection  of  the  skin  and  cartilage  resists  the 
swelling  ;  hence  the  nerve-pressure  and  the  excessive  pain. 

The  malar  prominence,  the  concavity  of  the  superior  maxilla  representing  the 
anterior  wall  of  the  antrum,  its  malar  process,  corresponding  to  the  apex  of  that 
cavity,  the  incisor  fossa,  and  the  canine  fossa  can  easily  be  recognized  either  through 
the  cheek  or,  more  readily,  through  the  gums  with  a  finger  in  the  mouth. 

The  zygoma  can  be  both  seen  and  felt,  the  lower  border  more  distinctly  than 
the  upper  on  account  of  the  attachment  to  the  latter  of  the  dense  temporal  fascia. 
Wasting  diseases  cause  an  apparent  increase  in  the  prominence  of  the  zygoma. 

The  condyle  of  the  inferior  maxilla  can  be  outlined  and  its  motions  observed 
(Fig.  246)  just  in  advance  of  the  ear. 

A  line  drawn  from  the  angle  to  the  condyle  indicates  the  posterior  border  of 
the  ramus.  In  making  incisions  in  this  region  for  inflammatory  or  suppurative 
conditions  this  line  is  to  be  remembered.  Posterior  to  it  important  blood-vessels 
may  be  injured  ;  anterior  to  it  deep  punctures  may  be  mack'  with  safety,  the  only 
structure  of  consequence  endangered  being  branches  of  the  facial  nerve. 

From  the  angle  of  the  jaw  forward  the  outline  of  the  inferior  maxilla  can  be 
seen  and  felt  both  externally  and  within  the  mouth.  The  alignment  of  the  teeth  is 
usually  disturbed  in  fracture,  and  is  often  the  most  easily  recognized  symptom. 
With  a  finger  between  the  cheek  and  the  teeth,  the  anterior  border  of  the  coronoid 


PRACTICAL   CONSIDERATIONS  :    THE    FACE. 


247 


process  may  readily  be  defined.  In  dislocation  this  is  unnaturally  prominent.  Be- 
tween its  base  and  the  last  molar  tooth  there  is  often  a  space  through  which  liquid  food 
or  other  fluids  can  be  conveyed  by  a  tube  to  the  pharynx  in  cases  in  which  fracture- 
dressing,  or  trismus,  or  ankylosis  rend-ers  the  lower  jaw  immovable.  Along  the  lower 
border  externally,  just  in  advance  of  the  anterior  edge  of  the  masseter,  the  groove 
for  the  facial  artery  may  be  felt,  and  in  the  middle  line  the  ridge  which  indicates  the 
thickening  at  the  symphysis. 

On  the  inner  surface  of  the  jaw  may  be  recognized  the  genial  tubercles,  some- 
times in  two  distinct  pairs,  indicating 

the    attachments    of     the    genio-hyo-  FIG.  267. 

glossi  and  genio-hyoidei.  The  sub- 
lingual  fossae  may  be  located,  and  just 
external  to  them,  and  at  their  lower 
border,  the  faint  beginning  of  the 
mylo-hyoid  ridge,  which  runs  upward 
and  backward,  becoming  more  evident 
opposite  the  last  two  molars. 

Above  this  line  the  bone  is  cov- 
ered by  the  mucous  membrane  of  the 
mouth  ;  hence  diseases  of  this  portion 
find  their  expression  in  the  oral  cavity, 
while  those  of  the  lower  portion  of  the 

bone  are  more  apt  to  involve  the  soft  parts  and  glands  of  the  neck  (Fig.  267). 
The  fossae  for  the  submaxillary  glands  cannot  be  felt  through  the  mouth,  but,  as  they 
lie  below  the  ridge,  while  the  sublingual  fossae  lie  above  it,  the  well-known  clinical 
relations  of  the  former  glands  to  the  neck  and  of  the  latter  to  the  mouth  are  explained. 

The  familiar  change  in  the  shape  of  the  lower  jaw  in  edentulous  old  persons  is 
due  to  absorption  of  the  alveolar  process. 

(Most  of  the  landmarks  of  the  face  are  of  more  importance  in  relation  to  the 
soft  parts,  the  nerves,  and  the  contents  of  the  cavities  of  the  orbit,  nose,  and  mouth 
than  in  connection  with  the  bones  themselves.  They  will,  therefore,  be  further  con- 
sidered in  those  connections.) 


Inner  surface  of  lower  jaw,  showing  various  areas. 


THE  UPPER   EXTREMITY. 

The  Shoulder-Girdle. — This  consists  of  the  clavicle  and  scapula.  The  latter 
is  far  the  most  important  morphologically,  representing,  as  it  does,  both  the  scapula 
and  the  coracoid  of  the  lower  classes  of  vertebrates  ;  while  the  clavicle  is  inconstant 
in  mammals,  and  seems  to  be  no  part  of  the  primitive  shoulder-girdle.  The  scapula 
bears  the  socket  for  the  humerus.  It  has  no  bony  attachment  to  the  trunk  save 
through  the  clavicle,  which,  interposed  between  it  and  the  sternum,  is  connected 
with  both  by  joints. 

THE   SCAPULA. 

Physiologically,  the  essential  part  of  the  scapula  is  the  socket  for  the  shoulder  ; 
a  part  of  this  is  made  by  the  coracoid  element,  which  in  man  is  an  insignificant  pro- 
cess of  the  shoulder-blade.  The  secondary  functions  of  the  bone  are  to  give  origin 
to  some  muscles  and  to  afford  leverage  to  others  for  their  action  on  the  arm.  In 
most  mammals  the  scapula  may  be  considered  a  rod  running  upward  from  the  joint, 
from  which  three  plates  expand,  one  towards  the  head,  one  towards  the  tail,  and  one 
outward.  In  man  the  second  of  these  plates  points  downward  and  is  excessively 
developed.  It  is  more  convenient  in  man  to  speak  of  one  main  plate,  the  body  of  the 
scapula,  with  the  spine  springing  from  the  dorsal  surface. 

The  body  is  triangular,  with  two  surfaces, — a  ventral  one  towards  the  ribs  and 
a  free  dorsal  one, — three  borders,  and  three  angles. 

The  posterior  or  vertebral  border,1  sometimes  called  the  base,  is  the  longest. 
It  is  nearly  vertical  from  the  lower  angle  to  a  triangular  space  on  the  dorsum,  oppo- 
site the  origin  of  the  spine,  above  this  it,  as  a  rule,  slants  forward,  but  at  a  very 
varying  angle.  The  upper  border  2  slants  downward  and  forward  to  the  supra- 
scapular  notch*  at  the  base  of  the  coracoid  process.  This  notch,  transmitting  the 
suprascapular  nerve,  is  sometimes  imperceptible,  but  usually  is  well  marked  and 
sometimes  very  deep.  It  is  bridged  by  a  ligament,  which  may  be  replaced  by  bone, 
transforming  the  notch  into  a  foramen.  The  anterior  or  axillary  border4  is  the 
only  thick  one.  Just  below  the  glenoid  cavity  it  begins  as  a  triangular  roughness 
for  the  long  head  of  the  triceps.  This  is  continued  as  a  line  which  ends  on  the 
dorsal  surface  near  the  lower  angle,  a  little  above  an  unnamed  process  curving  for- 
ward and  inward  from  which  a  part  of  the  teres  major  arises.  This  is  the  analogue 
of  a  process  much  developed  in  some  small  monkeys.  It  is  sometimes  very  large, 
the  increase  of  size  being  in  no  relation  to  that  of  the  bone  nor  of  the  muscle. 
Above  this  on  the  anterior  border  there  is  a  deep  groove  for  a  part  of  the  sub- 
scapularis  muscle  just  internal  to  the  anterior  edge  proper.  Below  the  process  the 
border  runs  downward  and  backward  to  the  inferior  angle.5  This  angle  is  some- 
times very  sharp,  sometimes  quite  the  reverse.  The  same,  in  a  less  degree,  may 
be  said  of  the  upper  angle,6  usually  sharp,  sometimes  squarely  truncated.  The 
anterior  angle  7  is  the  glenoid  cavity.  This,  with  the  base  of  the  coracoid  process, 
is  called  the  head  of  the  scapula,  the  neck  being  a  constricted  region  behind  it, 
reaching  to  the  suprascapular  notch.  The  glenoid  cavity8  is  an  oval,  slightly 
hollowed,  cartilage-covered  surface  expanding  from  a  narrower  base.  The  long  a\in 
is  vertical  and  the  broad  end  below.  There  is  often  an  indentation  at  the  upper 
part  of  the  inner  margin.  The  edge  is  a  little  raised  where  it  bears  the  glenoid 
ligament,  which  deepens  the  cavity  for  the  reception  of  the  head  of  the  humerus. 
The  top  of  the  edge  forms  the  supraglenoid  tubercle,  whence  starts  the  long  head  of 
the  biceps. 

The  coracoid  process  springs  from  the  top  of  the  head  just  behind  the  glenoid 
cavity  and  a  little  to  the  inner  side.  The  first  part,  or  root,  which  is  compressed 
from  side  to  side,  rises  inclining  somewhat  inward.  The  second,  the  free  projecting 
portion,  irregularly  cylindrical,  runs  forward,  rather  outward  and  downward,  to  end 
in  a  knob  near  the  inner  side  of  the  shoulder-joint.  The  upper  and  inner  surface  is 

1  Marge  vcrtebrnlls.     •  M.  superior.    :!  IncUura  scapulae.    H  M.  nxillarls.    fl  Anifiilus  inferior.    "  A.  incdinlis.     ~  A.  latcrnlis. 
8  Cavltas  iilrii.iiil.ilis. 
248 


THE  SCAPULA. 


249 


rough  and  convex,  the  under  and  outer  smooth  and  concave.  A  rounded  promi- 
nence, the  conoid  tubercle,  for  the  conoid  ligament,  is  situated  on  the  top  of  the  first 
part  and  rather  to  the  inner  side,  just  above  the  angle  formed  by  the  two  parts.  A 
ridge  from  behind  this,  running  outward  and  forward,  separates  the  two  parts  dis- 
tinctly. The  trapezoid  ridge  for  the  trapezoid  ligament  runs  forward  from  the  conoid 
tubercle  along  the  inner  side.  The  outer  side  of  the  upper  aspect  has  a  ridge  for 

FIG.  268. 
ACROMION  PROCESS 


Root  of  spine 


Superior  border 

SUPERIOR  ANGLE 


Long  head  of  triceps 


Supraglenoid  tubercle 

Conoid  tubercle 


CORACOID  PROCESS 


Riceps  and  cot  aco- 
brachialis 


ANTERIOR  SURFACE 
(Siibscapulans) 


POSTERIOR  SURFACE 


Axillary  border 


INFERIOR  ANGLE 

Right  scapula  from  before. 

the  coraco-acromial  ligament.  The  short  head  of  the  biceps  and  the  coraco- 
brachialis  arise  from  a  roughness  at  the  tip  of  the  process,  and  the  pectoralis  minor 
from  one  at  its  inner  side. 

The  anterior  surface,  or  venter,1  is  concave,  forming  the  subscapular  fossa, 
the  deepest  hollow  being  along  the  origin  of  the  spine.  At  the  very  top  the  bone 
often  takes  a  turn  outward.  The  serratus  magnus  is  attached  to  rough  surfaces 
inside  the  upper  and  lower  angles  and  to  a  narrow  line  connecting  them  just  beside 

1  Facies  costalis. 


250 


HUMAN    ANATOMY. 


the  vertebral  border.  These  surfaces  are  separated  from  the  rest  of  the  fossa  by 
well-marked  lines,  which,  with  some  four  ridges  running  forward  and  upward  from  the 
spinal  border,  give  origin  to  tendinous  septa  from  which  the  subscapularis  springs. 
This  muscle  arises  also  from  the  deep  groove  inside  the  axillary  border. 

The  posterior  surface,1  or  dorsum,  is  divided  by  the  spine  into  a  supraspinous 
and  an  infraspinous  fossa.  The  former  gives  origin  to  the  supraspinatus  ;  near  the 
back  it  is  often  strengthened  by  a  vertical  swelling.  The  infraspinous  fossa  is  chiefly 
occupied  by  the  infraspinatus,  but  two  other  areas  are  marked  off  by  two  lines  :  one, 
running  forward  and  upward,  separates  the  dorsal  side  of  the  lower  angle  and  of  the 
unnamed  process  on  the  axillary  border  ;  from  this  space  springs  the  teres  major. 
The  second  line  leaves  the  axillary  border  near  the  glenoid  cavity  and,  diverging 
slightly,  strikes  the  former  line  near  the  front,  bounding  a  narrow  region  for  the 
teres  minor,  which  is  crossed  high  up  by  a  groove  for  the  dorsal  scapular  artery. 

FIG.  269. 

Anterior  tubercle        ACROMION 
Coraco-acromial  ligament^ 
~~^ 

'^l&iJwx'Metacrorntal  tubercle 

Short  head  of  biceps  -7^ 

CORACOID  PROCESS 

Long  head  of  biceps 


Suprascapular  notch 


SUPERIOR  ANGLE 


Upper  part  of  vertebral  border 


Right  scapula  from  above. 

The  spine 2  is  a  triangular  plate  arising  from  a  small  triangular  surface  at  the  pos- 
terior border,  running  outward  and  somewhat  upward.  Its  attached  border  stops  at 
the  neck  before  reaching  the  glenoid  cavity.  The  spine  forms  an  acute  angle  with 
the  floor  of  the  supraspinous  fossa,  and  an  obtuse  one  with  that  of  the  infraspinous. 
Its  front  border  is  rounded  and  curves  forward,  and  forms  the  posterior  boundary 
of  the  great  scapular  notch  connecting  the  supra-  and  infraspinous  fossre.  The  free 
border  is  narrow  beyond  the  triangular  area,  but  soon  broadens,  presenting  an  upper 
and  a  lower  lip.  The  descending  fibres  of  the  trape/ius  are  inserted  into  the  whole 
length  of  the  former,  and  of  its  continuation  into  the  acromion.  The  lower  lip  often 
begins  with  a  tubercle  for  the  ascending  and  horizontal  fibres,  a  little  beyond  which 
it  narrows  again.  It  gives  origin  to  the  deltoid  muscle,  which  also  is  continued 
along  the  acromion. 

The  acromion3  is  a  broad,  llat  expansion  overhanging  the  shoulder-joint  and 
articulating  with  the  clavicle  by  an  elongated  faret  slanting  slightly  upward.  A 

1  Fades  dursulls.     -  Splna  scapulae.      '  Acnnuion. 


THE   SCAPULA. 


251 


short  preclavicular  border  in  front  of  this,  receiving  the  outer  end  of  the  coraco- 
acromial  ligament,  runs  forward  and  outward  to  the  anterior  tubercle.  From  this 
the  outer  border  runs  backward  to  the  metacromial  tiibercle,  whence  the  posterior 
border  runs  into  the  hind  edge  of  the  spine.  The  outer  border  has  three  or  four 
irregularities  above  for  the  tendinous  septa  of  the  deltoid,  and  is  smooth  at  its  lower 
edge  for  the  same  muscle.  The  lower  lip  of  the  spine  runs  directly  into  the  hind 
border  of  the  acromion,  but  often  splits  so  as  to  enclose  a  narrow  space  continued  into 
the  back  of  the  process,  from  which  the  deltoid  springs.  The  acromion  varies  much 
in  shape  ;  according  to  this  description  it  is  quadrate  ;  often,  however,  the  pre- 

FIG.  270. 


SUPERIOR  ANGLE 


Levator  anguli  scapula; 

Supraspinatii 

Trapezius. 

Rhomboideus 
minor 


Coraco-acromial  ligament 

RACOID  PROCESS     Biceps  and  coraco- 

brachialis 
ACROMION 

Anterior 
tubercle 


eltoid 


acromial  tubercle 


iceps,  long  head 
Groove  for  dorsal  artery 


ANTERIOR  ANGLE 


Teres  major 


-Occasional  origin  of  latissinms  dor  si 
Right  scapula  from  behind. 


clavicular  edge  is  rudimentary,  so  that  it  is  three-sided  ;  or  the  metacromial  tubercle 
is  at  the  apex  of  a  very  obtuse  angle,  so  that  it  is  curved  and  narrow.  There  are 
also  intermediate  forms.1  The  inclination  of  the  acromion  to  the  horizon  is  on  an 
average  not  far  from  45°,  with  a  variation  of  probably  15°  either  way.  This  may  or 
may  not  depend  on  a  corresponding  variation  of  slant  in  the  spine. 


All  the  details  determining  the  outline  of  the  scapula  vary  greatly.  The  hind  border  may 
be  convex,  or  the  infraspinous  portion  concave.  The  bone  lying  with  the  dorsum  up  should 
rest  on  the  coracoid  and  the  upper  and  lower  angles,  with  the  vertebral  edge  rising  from  the 
table  ;  but  this  may  be  almost  straight,  or  even  bend  the  other  way  so  as  to  change  the  usual 
points  of  support.  The  length  from  the  upper  to  the  lower  angle  ranges  from  13.2  centimetres 

1  Macalister  :  Journal  of  Anatomy  and  Physiology,  vol.  xxvii.,  1893. 


252 


HUMAN    ANATOMY. 


or  less  up  to  20.  i  centimetres.  The  scapular  indi-.v  is  the  ratio  of  the  breadth,  measured  along 
the  base  of  the  spine,  to  the  length  (~y~"e3i~~  )•  It  ranges  from  55  to  82.  The  following 
means  have  been  given  for  Caucasians  :  Broca,  65.9  ;  Flower  and  Garson,  65.2  ;  Dwight,  63.5. 
A  high  index  means  a  broad  scapula,  which  is  one  of  a  low  type.  The  infraspinous  index  is 
the  ratio  of  the  breadth  to  the  length  of  the  infraspinous  fossa,  measured  from  the  lower  angle 

.    ,      e  .,  .  100  X  breadth       \       TU-  r  •«.!_ 

to  the  starting-point  of  the  spine  ( fiifaispinous  j^n ) •     Thls  ranges  from  72.3  to  100.2.  with  a 

mean  of  about  87.  High  indices  imply  a  broad  scapula,  but  this  method  is  of  small  value,  as 
very  diverse  shapes  may  have  similar  indices.  It  is  not  possible  to  predicate  anything  of  the 
figure  during  life  from  the  shape  of  this  bone.  The  most  that  can  be  said  is  that  a  long  arm 
requires  the  leverage  furnished  by  a  long  scapula. 

Differences  due  to  Sex.. — The  chief  point  is  the  size.  From  the  study  of 
eighty-four  male  and  thirty-nine  female  bones  it  appears  that  of  123  bones,  twenty- 
six  measure  less  than  fifteen  centimetres  in  length,  of  which  only  three  were  male  ; 
also  that  seventy-six  measure  sixteen  centimetres  or  more,  of  which  only  five  were 

FIG.  271. 


SUPERIOR  ANGLE 


— Serratus  niafnus 


Glenoid  cavity 


Triceps  (long 
head) 


\ Subscap  u  la  ris 


VERTEBRAL  BORDER 


Ridges  for  tendi- 
nous attach- 
ments 


Process  for  teres  major 


-    Serratus  magnus 


Right  scapula  from  before. 


INFERIOR  ANGLE 


female.  There  was  no  single  instance  of  a  bone  measuring  less  than  fourteen  centi- 
metres being  male,  nor  of  one  measuring  seventeen  centimetres  being  female.  In 
doubtful  cases  the  glenoid  cavity  is  very  valuable.  In  woman  it  is  not  only  smaller, 
but  relatively  narrower.  Very  few  male  sockets  are  less  than  3.6  centimetres  in 
length,  and  very  few  female  as  long.  The  typical  female  scapula  is  very  delicate  ; 


PRACTICAL   CONSIDERATIONS  :   THE   SCAPULA. 


253 


the  lower  angle  is  sharp,  the  process  on  the  front  border  small  ;  the  hind  border 
straight  up  to  the  spine,  then  slanting  forward  in  another  straight  line  ;  the  upper 
border  descends  sharply  ;  the  coracoid  is  slight,  with  the  end  compressed  instead  of 
knobbed  ;  the  acromion  is  curved  and  narrow.  An  expert  should  be  reasonably 
sure  of  the  sex  four  times  in  five.  Doubtful  bones  are  almost  always  male  ;  so  are 
those  of  peculiar  shape,  with  the  exception  of  concave  vertebral  borders.  The 
scapular  index  has  no  sexual  significance.1 

Structure. — The  strong  parts  are  seen  when  the  bone  is  held  to  the  light. 
The  head,  neck,  coracoid,  acromion,  and  most  of  the  spine  are  strong.  So  also 
are  the  front  border,  the  lower  angle,  and,  to  a  less  extent,  the  hind  border,  which 
is  strongest  above  the  spine.  Most  of  the  body  is  very  thin.  A  section  through 
the  socket,  along  the  origin  of  the  spine,  shows  the  bony  plates  so  disposed  as  to 
resist  pressure  in  that  line. 

Development. — There  is  one  chief  centre  for  the  scapula  proper  and  one  for 
the  coracoid,  besides  an  indefinite  number  of  accessory  ones.  The  first  appears 
about  the  eighth  week  (Rambaud  et  Renault)  at  the  neck,  and  forms  nearly  the 


FIG.  272. 


D 


Ossification  of  scapula.  A,  at  eighth  fcetal  month  ;  S,  towards  end  of  first  year ;  C,  from  fourteen  to  fifteen  years  ; 
£>,  from  seventeen  to  eighteen  years  ;  E,  about  twenty  years,  a,  chief  centre ;  b,  for  coracoid  process ;  c,  for  acro- 
mion ;  d,  for  inferior  angle ;  e,  additional  for  acromion  ;  /,  for  vertebral  border. 

whole  bone,  including  the  spine  and  the  root  of  the  acromion  and  the  dorsal  part  of 
the  root  of  the  coracoid.  The  coracoid  centre  appears  in  the  first  year  ;  it  forms 
also  the  top  of  the  glenoid  cavity,  and  fuses  with  the  first  at  fourteen  or  fifteen, 
beginning  to  unite  at  the  ventral  surface.  At  the  earlier  age  the  acromion  is  carti- 
lage beyond  a  line  drawn  from  the  back  of  the  clavicular  facet  to  the  front  of  the 
metacromion.  At  about  fifteen  many  little  nuclei  appear  in  the  acromion.  The 
anterior  tubercle  is  formed  from  a  single  nucleus  ;  the  others  coalesce  into  two 
groups, — one  in  the  centre,  the  other  at  the  outer  margin.  At  about  eighteen  the 
latter  joins  the  body  and  the  other  two  fuse.  A  year  later  the  mass  so  formed  also 
joins  the  body.  Sometimes  this  remains  connected  by  fibro-cartilage  ;  very  rarely 
several  pieces  persist.  A  scale-like  epiphysis  appears  at  the  conoid  tubercle  of  the 
coracoid  about  fifteen,  and  soon  fuses.  About  seventeen  or  eighteen  a  nucleus 
appears  in  the  strip  of  cartilage  along  the  posterior  border  and  one  at  the  lower 
angle.  Both  are  generally  fused  by  twenty,  but  the  lower  is  one  of  the  last  to  fuse 
in  the  skeleton,  and  the  line  of  union  may  remain  for  years. 

PRACTICAL    CONSIDERATIONS. 

The  scapula  is  rarely  absent  and  rarely  malformed.  The  outer  part  of  the 
acromion  may  exist  as  a  distinct  bone,  as  may,  but  less  frequently,  the  coracoid. 
Many  cases  of  so-called  fracture  of  the  acromion  and  others  of  supposed  traumatic 
separation  of  the  acromial  epiphysis  are  probably  cases  of  persistent  epiphysis.  The 
centre  for  the  inferior  angle  sometimes  remains  distinct,  being  united  to  the  body 

1  Dwight :  The  Range  and  Significance  of  Variation  in  the  Human  Skeleton,  Proc.  Mass. 
Mecl.  Soc.,  1894. 


HUMAN   ANATOMY. 


FIG.  273. 


Lines  ot  fracture  of  the  scapula. 


by  a  synchondrosis.  The  possibility  of  its  detachment  by  excessive  action  of  the 
latissimus  dorsi  has  been  mentioned,  but  no  case  of  traumatic  separation  has  been 
recorded. 

Fracture  is  rare,  in  spite  of  the  thinness  of  much  of  the  bone,  because  of  its 
mobility,  the  adaptation  of  its  curves  to  the  underlying  thoracic  surface,  the  elasticity 
and  compressibility  of  that  surface,  the  thickness  of  the  muscles  that  cover  the 
scapula  and  of  those  that  lie  beneath  it,  the  fragility  of  the  clavicle  (which  by  frac- 
turing often  saves  the  scapula),  and  the  great  range  of 
movement  and  corresponding  weakness  of  the  shoulder- 
joint,  which,  in  like  manner,  by  undergoing  luxation, 
prevents  the  force  of  the  traumatism  from  reaching  the 
scapula. 

Fracture  of  the  body  and  of  the  inferior  angle  from 
indirect  violence  has  been  reported  in  a  few  cases.  The 
arms  were  fixed,  and  strong  traction  was  being  exer- 
cised in  more  than  one  case.  It  seems  probable  that 
the  bone  breaks  between  the  opposing  forces  of  the 
rhomboids  and  trapezius  on  the  one  hand,  and  the 
teres  muscles,  the  subscapularis,  and  the  infraspinatus 
on  the  other. 

The  most  common  fracture  is  that  of  the  body, 
usually  running  transversely  or  obliquely  through  the 
subspinous  fossa.  The  attachments  of  the  subscapu- 
laris beneath  and  of  the  infraspinatus  above  usually 
prevent  any  marked  displacement.  There  is  pain  on 
lifting  the  arm  to  a  horizontal  position,  because,  in  order 
that  the  deltoid  may  be  able  to  do  this,  the  acromion 
must  become  a  fixed  point,  and  that  necessitates  the  contraction  of  the  rhomboids 
and  other  muscles  whose  function  it  is,  aided  by  the  leverage  afforded  by  the  pro- 
longation of  the  scapula  downward,  to  fix  the  blade  of  the  scapula  when  the  deltoid 
is  in  action. 

Superficial  ecchymosis  is  rare  on  account  of  the  dense  infraspinous  fascia  which 
prevents  the  effused  blood  from  reaching  the  surface. 

Fracture  of  the  acromion  is  attended  with  slight  flattening  of  the  tip  of  the 
shoulder,  the  weight  of  the  arm,  acting  through  the  deltoid,  dragging  the  frag- 
ment downward.  There  may  be  the  usual  symptoms  of  preternatural  mobility, 
crepitus,  etc. 

Fracture  of  the  coracoid  is  rare.  Before  the  age  of  seventeen  it  may  be  an 
epiphyseal  separation.  Displacement  is  not  common,  as  the  downward  pull  of  the 
pectoralis  Tninor,  short  head  of  the  biceps,  and  coraco-brachialis  (page  590)  is 
effectually  resisted  by  the  coraco-acromial  and  coraco-clavicular  ligaments.  Crepitus 
and  preternatural  mobility  may  possibly  be  recognized  by  sinking  the  fingers  into 
the  interval  between  the  deltoid  and  pectoral  muscles.  The  coracoid  will  be  found 
just  beneath  the  inner  deltoid  margin. 

Fractures  of  the  neck  of  the  scapula  include,  in  surgical  language,  those  which 
begin  at  the  suprascapular  notch  and  run  to  the  axillary  border  of  the  bone  detach- 
ing the  glenoid  cavity  and  the  coracoid  process.  There  is  no  instance  of  fracture  of 
the  anatomical  neck, — the  constricted  part  supporting  the  glenoid  cavity.  The 
fragment,  with  the  arm,  will  drop  downward,  away  from  the  acromion.  This  puts 
the  deltoid  on  the  stretch  and  causes  flattening  of  the  shoulder.  There  will  be  a 
depression  beneath  the  edge  of  the  acromion.  The  arm  will  be  increased  in  length. 
These  symptoms  (which  will  occur  only  if  the  coraco-acromial  and  coraco-clavicular 
ligaments  are  torn)  are  also  found  in  subglenoid  luxation  of  the  luinierus  (  page  583); 
but  in  the  fracture,  the  presence  of  crepitus,  the  downward  displacement  of  the 
coracoid,  the  ready  disappearance  of  the  deformity  on  pushing  the  head  of  the 
hunicnis  upward,  its  prompt  reappearance  when  the  arm  is  allowed  to  hang  by  the 
side,  and  the  ease  with  which  the  hand  may  be  placed  on  the  opposite  shoulder 
serve  clearly  to  denote  the  character  of  the  accident. 

Excision  of  the  scapula  itself  is  not  uncommonly  indicated  on  account  of  malig- 


PRACTICAL   CONSIDERATIONS  :     THE   SCAPULA.  255 

nant  neoplasm,  subperiosteal  and  central  sarcomata  especially.  The  main  danger 
of  the  operation  is  hemorrhage.  The  subclavian  should,  therefore,  be  controlled. 
The  dorsalis  scapulae,  crossing  the  axillary  border  of  the  scapula  at  a  point  on  a  level 
with  the  centre  of  the  vertical  axis  of  the  deltoid  (Treves),  and  the  subscapular  run- 
ning along  the  lower  border  of  the  subscapularis  muscle  to  reach  the  inferior  angle, 
are  the  largest  vessels  that  require  division,  but  the  suprascapular,  posterior 
scapular,  and  branches  of  the  acromio-thoracic  artery  will  also  be  cut. 

Infectious  diseases  giving  rise  to  caries  and  necrosis  and  to  suppuration  are 
rare.  When  they  affect  the  supraspinous  region  the  pus  is  directed  forward  by  the 
fascia  covering  the  supraspinatus,  which  encloses  that  muscle  in  an  osseo-fibrous 
compartment.  In  the  infraspinous  region  the  still  denser  infraspinous  fascia  con- 
ducts the  pus  in  the  same  direction  ;  hence  abscesses  originating  in  scapular  dis- 
ease are  likely  to  point  near  the  axilla  and  in  the  neighborhood  of  the  insertions  of 
the  scapular  muscles  into  the  humerus.  On  the  under  surface  of  the  scapula,  between 
the  ridges  which  give  origin  to  the  tendinous  fibres  that  intersect  the  subscapularis 
muscle,  the  periosteum  is  loose  and  easily  separated.  Suppuration  following  caries 
of  this  aspect  of  the  bone  may,  therefore,  cause  extensive  detachment  of  the  perios- 
teum, and  it  has  been  found  necessary  to  trephine  the  thin  portion  of  the  blade  of 
the  scapula  to  give  vent  to  such  a  purulent  collection. 

Landmarks. — The  greatest  breadth  of  the  scapula  is  in  a  line  from  the  glenoid 
margin  to  the  vertebral  border  ;  the  greatest  length  in  a  line  from  the  superior  to 
the  inferior  angle. 

The  general  outlines  of  the  scapula  can  easily  be  felt.  The  bony  points  most 
readily  recognized  by  touch  are  the  acromion,  the  coracoid,  the  spiae,  the  vertebral 
ejdge,  and  the  inferior  angle. 

The  edge  of  the  acromion  is  an  important  landmark.  Measurement  from  it  to 
the  suprasternal  notch  is  the  easiest  way  of  determining  shortening  in  fracture  of  the 
clavicle.  If  this  measurement  is  less  than  on  the  sound  side,  and  the  clavicle  itself 
is  unchanged  in  length,  it  indicates  a  dislocation  of  the  acromial  end  of  the  latter. 

Undue  prominence  of  the  edge  of  the  acromion  is  seen  in  luxation  of  the 
humerus  (page  582)  and  in  fracture  of  the  neck  of  the  scapula.  In  these  conditions 
the  fingers  may  be  pressed  beneath  the  acromion,  as  they  can  in  old  cases  of  deltoid 
paresis  or  paralysis  with  atrophy  of  that  muscle,  when  the  weight  of  the  arm  drags 
the  humerus  downward  and  increases  the  space  between  the  greater  tuberosity  and 
the  acromial  edge. 

The  coracoid  process  may  be  felt  through  the  inner  deltoid  fibres,  below  the 
inner  portion  of  the  outer  third  of  the  clavicle,  by  thrusting  the  fingers  into  the 
space  between  the  pectoral  and  deltoid.  In  fracture  it  may  be  depressed,  as  it  is  in 
fracture  of  the  scapular  neck.  The  axillary  artery  can  be  felt  just  to  the  inner  side 
of  the  coracoid  as  it  passes  over  the  second  rib. 

The  spine  is  least  prominent  in  muscular  and  most  conspicuous  in  feeble  and 
emaciated  persons.  This  is  also  true  of  the  inferior  angle,  which  in  weak,  and 
especially  in  phthisical,  subjects  is  not  held  tightly  to  the  chest,  but  projects  in  a 
wing-like  manner  (scapulae  alatae).  This  is  partly  due  to  general  muscular  weak- 
ness, in  which  the  latissimus  dorsi  and  serratus  magnus  participate,  and  partly  to 
the  shape  of  the  thorax  and  the  direction  of  the  clavicles.  The  flatter  and  shallower 
the  chest  the  more  oblique  in  direction  and  the  lower  are  the'  collar-bones,  carrying 
with  them  downward  and  forward  the  upper  and  anterior  portions  of  the  scapulae, 
and  by  that  much  tending  to  make  the  lower  and  posterior  portions  more  promi- 
nent. 

The  length  of  the  arm  is  usually  measured  from  the  junction  of  the  spine  of  the 
scapula  and  the  acromion — the  acromial  angle — to  the  external  condyle  of  the 
humerus. 

The  vertebral  edge  of  the  scapula  lies  just  at  the  side  of  the  spinal  gutter. 
When  the  arm  hangs  at  the  side  of  the  body,  this  edge  is  parallel  with  the  line 
of  the  spinous  processes.  It  can  be  made  prominent  (for  palpation)  by  carrying 
the  hand  of  the  patient  over  the  opposite  shoulder.  The  superior  angle  is  made 
accessible  by  the  same  position.  The  axillary  border  of  the  scapula  and  the  inferior 
angle  are  best  examined  with  the  elbow  flexed  and  the  forearm  carried  behind  the 


256 


HUMAN    ANATOMY. 


back.  With  the  arm  at  the  side,  the  superior  angle  is  about  on  the  level  of  the 
upper  edge  of  the  second  rib  ;  the  inferior  angle  is  opposite  the  seventh  intercostal 
space  (and  hence  is  a  guide  in  selecting  a  space  for  the  various  operations  for  em- 
pyema,  page  1867);  the  inner  end  of  the  spine  is  opposite  the  spinous  process  of  the 
third  dorsal  vertebra. 

With  the  shoulders  drawn  forcibly  backward,  the  vertebral  borders  of  the  scapula 
can  be  made  almost  to  touch  at  the  level  of  the  spines,  and  are  not  more  than  from 
two  to  three  inches  apart  at  the  angles.  With  the  hands  clasped  on  the  vertex,  the 
inferior  angles  are  from  sixteen  to  seventeen  inches  apart.  By  crossing  the  arms  on 
the  front  of  the  chest,  and  leaning  forward,  the  scapulae  are  also  widely  separated, 
and  this  position  is  therefore  selected  for  auscultation  and  percussion. 

The  mobility  of  the  scapula  lessens  the  functional  disability  in  ankylosis  of  the 
shoulder-joint. 

LIGAMENTS   OF   THE   SCAPULA. 

Two  ligaments — the  transverse  and  the  coraco-acromial — pass  from  one  part  of  the 
scapula  to  another. 

The  transverse  or  suprascapular  ligament l  (Fig.  289)  is  a  little  band  on  the 
upper  border,  'just  behind  the  root  of  the  coracoid,  making  a  bridge  over  the  supra- 
scapular  notch,  under  which  the  suprascapular  nerve  passes.  It  may  be  replaced  by 
bone. 

The  coraco-acromial  ligament2  (Fig.  274)  is  a  triangular  structure,  broad 
at  its  base,  along  the  outer  border  of  the  coracoid  process,  and  narrowing  to  its 
insertion  into  the  inner  side  of  the  end  of  the  acromion  just  in  front  of  the  acromio- 
clavicular  joint.  The  borders  are  strong,  converging  bands  with  a  weak  space 
between,  the  front  one  being  the  stronger  and  overlapping  the  other  when  they 


Capsule  of  shoulder-joint 
Humerus 

Tendon  of  biceps 
Coraco-acromial  ligament 

Coracoid  process 
Coraco-clavicular  ligament 


FIG.  274. 

Acromio-clavicular  joint 


I 'hivirle 


Ligaments  about  the  right  shoulder  from  above. 


meet.  The  course  of  the  fibres  in  the  weaker  part  is  variable  ;  sometimes  they 
diverge  from  near  the  front  of  the  coracoid  to  the  posterior  band,  sometimes  they 
are  in  the  main  parallel  with  the  latter,  sometimes  a  band  passes  from  this  membrane 
to  the  front  of  the  clavicle.  The  weak  portion  of  this  ligament  is  pierced  by  the 
pectoralis  minor,  when,  as  often  happens,  this  muscle  is  inserted  into  the  capsule  of 
the  shoulder  <>r  the  upper  end  of  the  humerus.  This  ligament  is  really  part  of  the 
apparatus  of  the  shoulder-joint,  forming  a  roof  over  the  capsule,  from  which  it  is 
separated  by  a  bursa.  Before  dissection  the  hind  border  of  the  ligament  is  not  very 

1  LIg.  transversum  scapulae  supcrlus.     "  Llg.  coracracromiale. 


THE   CLAVICLE. 


257 


distinct,  since  the  bursa  appears  to  connect  it  with  the  capsule  below  and  a  thin 
fascia  with  the  clavicle  above. 

The  spino-glenoid  ligament1  is  an  occasional  little  band  at  the  great  scapular 
notch,  running  from  the  anterior  border  of  the  spine  to  the  posterior  edge  of  the 
glenoid  cavity,  crossing  the  suprascapular  vessels  and  nerve. 

THE   CLAVICLE. 

The  function  of  the  clavicle,2  or  collar-bone,  which  extends  from  the  top  of  the 
sternum  to  the  acromion,  is  to  give  support  to  the  shoulder-joint  in  the  wide  and 
varied  movements  of  the  arm.  It  is  found  in  mammals  that  climb,  fly,  dig,  or  swim 
with  movements  requiring  an  outward  and  backward  sweep  of  the  arm.  It  is 
absent  in  those  that  use  the  fore-limb  simply  for  progression  with  movements  nearly 
restricted  to  one  plane.  It  is  present,  but  imperfectly  developed,  in  some  carnivora 


FIG.  275. 


T>  apezius 


ACROMIAL   END 


Right  clavicle,  superior  and  posterior  surfaces. 


STERNAL  END 
'ectoralis  major 


whose  arms  serve,  in  part,  for  prehension.      In  man  it  has  a  doubly  curved  shaft,  a 
thick  inner  end,  and  a  flattened  outer  one. 

The  shaft  is  convex  in  front  through  the  two  inner  thirds  and  concave  in  the 
outer  one.  The  former  portion  has  a  superior,  an  inferior,  an  anterior,  and  a  pos- 
terior surface  ;  but  in  the  outer  third  the  two  latter  surfaces  narrow  into  borders. 
The  superior  surface  is  smooth,  except  for  a  slight  unevenness  at  the  inner  end, 


FIG.  276. 


Acromial  facet 


Pectoralis  major 


Sternal  facet 


Sterno-hyoid 


Trapezoid  ridge 


Conoid  tubercle 

Right  clavicle,  anterior  and  inferior  surfaces. 


giving  origin  to  the  clavicular  head  of  the  sterno-cleido-mastoid.  The  inferior  sur- 
face has  near  the  inner  end  an  oval  roughness,  which  may  or  may  not  be  raised, 
for  the  rhomboid  ligament  from  the  cartilage  of  the  first  rib.  Beyond  this  is  a  longi- 
tudinal groove,  more  marked  near  the  outer  end,  for  the  insertion  of  the  subclavius 
muscle.  Outside  of  the  middle,  near  the  hind  border  (sometimes  on  the  hind  surface), 
is  the  nutrient  foramen,  directed  outward.  The  anterior  surface  narrows  continu- 
ally from  within  outward.  The  inner  two-thirds  are  rough  for  the  pectoralis  major  ; 

1  Lig.  transversum  scapulae  infcrius.     -  Clavicula. 


258  HUMAN    ANATOMY. 

external  to  this  the  rough  concave  edge  gives  origin  to  the  deltoid.  The  beginning 
of  this  is  often  marked  by  a  minute  tubercle,  which,  when  exceptionally  large,  is 
the  deltoid  tubercle.  The  posterior  surface  is  smooth,  and  narrows  gradually  till 
it  reaches  the  outer  end,  the  beginning  of  which  is  marked  by  a  tubercle  on  the 
under  surface. 

The  borders  are  very  ill  marked.  The  sharpest  is  that  separating  the  anterior 
from  the  inferior  surface.  That  between  the  anterior  and  superior  ones  is  fairly  well 
marked  near  the  inner  end  ;  but  it  soon  grows  indistinct,  so  that  often  at  the  middle 
of  the  bone  the  front  surface  seems  to  twist  into  the  upper,  and  the  anterior  inferior 
border  becomes  the  front  border  of  the  outer  end.  Of  the  posterior  borders,  the 
upper,  though  rounded,  is  distinct  along  the  middle  of  the  bone  ;  the  lower  is  very 
vague,  but  usually  is  well  defined  in  the  outer  part  ;  when  it  is  not,  the  posterior 
surface  seems  to  twist  into  the  lower. 

The  inner  or  sternal  extremity 1  is  club-shaped,  drawn  out  downward  and 
somewhat  backward.  Its  inner  surface,  coated  with  articular  cartilage,  is  of  very 
variable  shape.  It  is  approximately  oval,  with  the  long  axis  slanting  downward  and 
backward,  and  is  rough  and  generally  concave,  but  not  always  so.  The  front  edge 
of  the  inner  surface  forms  an  acute  angle  with  the  anterior  border  of  the  bone,  and 
the  hind  one  an  obtuse  angle. 

The  outer  or  acromial  extremity  -  is  flattened  above  and  below  and  curved 

forward.     At  the  very  front  of  this  end  is 

FIG.  277.  an  articular  surface  joining  the  scapula.     It 

A  is  oval,  with  the  long  axis  horizontal,  and 

usually  faces  downward  as  well  as  outward. 
There  is  generally  behind  this  a  rough  space 
for  ligament  at  the  end,  which  gradually 
slants  into  the  hind  border.  The  conoid 
tubercle9'  is  at  the  posterior  border  of  the 
lower  surface  of  the  outer  extremity  just  at 
its  junction  with  the  shaft.  The  trapezoid 
ridge  extends  from  it  forward  and  outward 

Ossification ,  of  clavicle.     A,  at  birth ;  a, ,  chief  cen-       across    the    bone.        Its     anterior    portion    is 
tre ;  b,  c,  cartilaginous  ends.     £,  at  about  eighteen  .  .      •  i 

years ;  d,  sternal  epiphysis.  often  broad.  I  his  tubercle  and  ridge  are 

for  the  insertion  of  ligaments  of  correspond- 
ing names,  passing  upward  from  the  base  of  the  coracoid.  Between  the  ridge  and 
the  end  of  the  bone  there  is  a  smooth  space,  sometimes  almost  a  groove,  which  lies 
above  the  supraspinatus  muscle  as  it  crosses  the  shoulder-joint.  The  clavicle  varies 
greatly  in  length,  thickness,  amount  of  curve,  and  in  the  outline  of  the  ends.  Some- 
times the  outer  end  is  but  little  broader  than  the  shaft.  A  very  rare  form  is  one  in 
which  the  inner  part  of  the  shaft  is  flat  and  but  slightly  thicker  than  the  outer. 

Differences  due  to  Sex. — The  male  bone  is  longer,  stronger,  more  curved, 
and  with  larger  articular  facets.  Apart  from  sex,  a  strong  bone  is  generally  more 
curved. 

Development. — The  centre  for  this  bone,  evident  in  the  sixth  week,  precedes 
all  others.  It  is  remarkable  as  developing  in  indifferent  tissue  before  any  hint  of  the 
bone  is  to  be  seen.  A  little  later  a  cartilaginous  outline  appears,  which  is  shortly 
involved  in  the  ossifying  process.  At  about  seventeen  a  centre  is  formed  in  the 
epiphysis  at  the  sternal  end,  and  joins  the  shaft  a  year  or  so  later. 

Surface  Anatomy. — In  life  the  anterior  surface  and  edge,  as  well  as  the 
superior  surface,  are  easily  felt  through  the  skin.  The  joint  with  the  acromion  is  dis- 
tinct, the  clavicle  being  higher  than  the  scapula.  The  position  of  the  bone  is  nearly 
horizontal,  but  in  strong  men  the  outer  end  is  often  the  higher.  The  bone  is  highly 
elastic,  owing  to  its  curves. 

PRACTICAL   CONSIDERATIONS. 

The  chief  function  of  the  clavicle  is  to  steady  the  shoulder  and  keep  the  upper 
arm  at  such  a  distance  from  the  trunk  that  the  muscles  running  from  tin.-  latter  to 
the  humiTiis  may  give  it  lateral  motion.  Therefore,  in  animals,  in  which  no  such 

1  Extrcmitas  stcmalls.     "  Extremitas  ucromialis.     'TutMTMitU  coracoidcn. 


PRACTICAL   CONSIDERATIONS:   THE   CLAVICLE.  259 

movement  exists,  and  the  fore-limbs  are  used  only  in  progression,  no  clavicle,  or  a 
mere  rudiment  of  it,  is  present. 

Congenital  absence  of  both  clavicles  is  rare.  In  several  reported  cases  the 
shoulders  could  be  brought  together  in  front  of  the  body.  The  congenital  absence 
of  both  acromial  ends  is  not  so  uncommon.  Theoretically,  one  would  expect,  as  a 
result  of  absence  of  the  clavicle,  a  weakened  upper  extremity,  some  lateral  curvature 
of  the  spine,  interference  with  the  upper  chest  (from  the  weight  of  the  arm  and 
scapula),  and  hence  diminished  lung  capacity  with  the  secondary  ill  effects  upon 
growth,  nutrition,  etc. 

Such  consequences  were  predicated  (Maunder)  as  a  result  of  arrest  of  growth 
from  epiphyseal  separation,  but  neither  in  those  cases,  in  non-union  after  fracture, 
nor  in  congenital  absence  have  they  been  noted.  On  the  contrary,  in  the  four 
cases  of  symmetrical  absence  of  the  acromial  end  recorded  by  Gegenbaur  the  func- 
tional disability  was  slight,  the  motions  of  the  scapula  being  unimpaired. 

The  whole  bone  becomes  ossified  very  early,  beginning  before  any  other  long 
bone  of  the  skeleton.  Its  one  epiphysis,  at  the  sternal  end,  is,  on  the  contrary,  the 
last  of  the  epiphyses  of  the  long  bones  to  ossify,  appearing  about  the  seventeenth  or 
eighteenth  year  and,  according  to  Poland,  joining  the  diaphysis  from  the  twenty- 
second  to  the  twenty-fifth  year.  D wight  places  the  time  of  union  somewhat  earlier. 

Separation  of  this  epiphysis  is  among  the  rarest  of  epiphyseal  detachments. 
But  five  cases  have  been  recorded.  Two  of  them  were  from  muscular  action,  the 
pectoralis  major  and  the  clavicular  fibres  of  the  deltoid  being  apparently  the  agencies 
that  carried  the  sternal  end  of  the  diaphysis  forward. 

The  age  of  the  patient  (from  seventeen  to  twenty-five),  the  shape  of  the  flattened 
diaphyseal  end  (unlike  the  pointed  end  of  a  fractured  bone),  and  the  integrity  of  the 
shape  of  the  suprasternal  notch  aid  in  distinguishing  this  accident  from  a  forward 
dislocation  or  a  fracture  on  the  inner  side  of  the  costo-clavicular  ligament. 

Fracture  of  the  clavicle  is  more  common  than  that  of  any  other  bone,  except  possi- 
bly the  radius  ;  it  is,  likewise,  the  most  frequent  seat  of  incomplete  ( ' '  greenstick' ' ) 
fracture.  About  one-half  of  all  clavicular  fractures  occur  during  early  childhood, 
This  frequency  is  due  ( i )  to  the  early  ossification  of  the  bone,  so  that  it  is  relatively 
more  brittle  than  are  the  other  bones  ;  (2)  to  the  lack  of  close  attachment  between 
the  periosteum  and  the  bone  ;  (3)  to  the  unusual  thickness  of  the  periosteum  (prob- 
ably associated  with  the  early  ossification),  which  tends  to  prevent  complete  fracture  ; 
and  (4)  to  the  common  occurrence  of  falls  and  minor  accidents  among  children. 

The  amount  of  disability  is  often  surprisingly  slight,  and  the  diagnosis,  unless 
confirmed  by  skiagraphic  testimony,  may  have  to  be  made  on  the  basis  of  very  trifling 
deformity  with  localized  tenderness  and  swelling. 

Muscular  action  may  produce  fracture  through  the  violent  contraction  of  the 
pectoralis  major  or  of  the  clavicular  portion  of  the  deltoid. 

Indirect  violence  (received  through  falls  on  the  hand,  elbow,  or  shoulder)  is 
the  common  cause.  The  frequency  with  which  such  falls  occur,  and  the  uniformity 
with  which  the  force  is  transmitted  to  a  slender  bone  containing  but  little  cancellous 
tissue,  and  held  firmly  at  either  end  by  strong  ligamentous  attachments,  sufficiently 
explain  the  common  occurrence  of  clavicular  fracture. 

The  break  usually  occurs  about  the  junction  of  the  middle  and  outer  thirds, 
because:  (i)  the  outer  end  (like  the  inner)  is  firmly  held  by  the  ligamentous  connec- 
tions, the  middle  of  the  bone  being  the  most  movable  ;  (2)  at  the  outer  end  of  the 
middle  third  the  bone  is  smaller,  and  therefore  weaker  ;  (3)  at  this  point  the  sternal 
curve  (convex  forward)  and  the  acromial  curve  (concave  forward)  meet,  and  force 
applied  to  the  extremity  of  the  bone  is  there  expended. 

Fracture  of  the  clavicle  is  rarely  compound,  because,  although  the  bone  is  sub- 
cutaneous, the  skin  is  very  freely  movable  over  it,  and  because  the  usual  displace- 
ment carries  the  sharp  end  of  the  outer  fragment  backward  and  the  sharp  end  of 
the  inner  fragment  upward  (Fig.  278). 

The  anatomical  causes  of  the  common  form  of  displacement  will  be  considered 
in  connection  with  the  muscles  concerned  (page  579). 

The  relations  of  the  clavicle  to  great  vessels  and  nerve-trunks  would  seem  to 
render  frequent  complications  probable,  but  as  a  matter  of  fact  the  latter  occur  with 


260  HUMAN   ANATOMY. 

comparative  rarity  :  ( i )  because  of  the  elastic  curves  of  the  bone,  which  enable 
it  to  escape  fracture  in  many  cases  of  direct  violence  ;  (2)  because  of  the  inter- 
position of  the  subclavius  muscle  between  the  bone  and  the  nervous  and  vascular 
trunks  ;  (3)  because  of  the  situation  of  the  common  fracture,  the  inner  end  of 
the  outer  fragment  (the  portion  most  likely  to  inflict  injury)  being  both  above  and 
external  to  the  region  of  danger.  Still,  cases  of  wound  of  the  subclavian  vessels, 

internal  jugular  vein,  and  of  pressure  pa- 

pIG   2_s  ralysis  of  the  upper  extremity  have  been 

reported  as   complications   of    fracture   of 
the  clavicle. 

The  supraclavicular  nerves  (  branches 
of  the  third  and  fourth  cervical)  pass  in 
front  of  the  bone,  and  may  be  involved  in 
the  callus,  giving  rise  to  severe  and  per- 
sistent pain. 

In  resection  or  excision  of  the  clavi- 
cle, either  for  disease  or  as  a  step  in  the 
performance  of  an  interscapulo-thoracic 

Lines  of  fracture  of  the  clavicle  and  acromion  process.       amputation,     the     protection     afforded    the 

vessels  by  the  subclavius   muscle  should 

be  remembered.  Superficially,  the  cephalic  vein  and  the  supraclavicular  nerves  may 
have  to  be  divided. 

Disease  of  the  clavicle  is  not  uncommon  as  a  result  of  the  various  infections, — 
syphilitic,  tuberculous,  typhoidal,  etc.  The  bone  is  also  the  subject  of  new  growths, 
especially  of  sarcomata.  The  anatomical  relations  already  alluded  to  are  those  chiefly 
involved  in  these  cases. 

Swelling  and  oedema  of  the  arm  may  result  from  pressure  on  the  subclavian 
vein  in  the  angle  between  the  clavicle  and  the  rib  ;  gangrene,  from  pressure  upon 
the  artery  ;  pain  or  paralysis,  from  pressure  upon  the  brachial  plexus  at  the  outer 
part  of  the  costo-clavicular  space.  It  is  probable  that,  in  view  of  the  subcutaneous 
position  of  the  clavicle  and  its  consequent  exposure  to  slight  traumatisms,  osteitis  of 
one  form  or  another  would  be  more  frequent  if  it  were  not  for  its  great  elasticity, 
which  probably  limits  the  effect  of  minor  blows  to  the  superficies  of  the  bone.  Ac- 
cordingly, syphilitic  subperiosteal  nodes  are  fairly  common,  while  tuberculosis  and 
septic  and  post-typhoidal  osteitis  are  relatively  rare. 

Landmarks. — The  clavicle  is  subcutaneous  through  its  entire  length.  When 
at  rest  the  bone  is  about  on  the  same  level  as  the  spine  of  the  scapula.  In  inspira- 
tion it  moves  forward  an  inch. 

The  inner  end  of  the  bone  is  its  largest  portion,  and  its  projection  in  front  of 
and  above  the  clavicular  notch  on  the  sternum  should  not  be  erroneously  regarded 
as  evidence  of  disease  or  injury.  The  deltoid  tubercle  at  its  outer  third  is  sometimes 
unusually  prominent,  and  should  not  then  be  mistaken  for  an  exostosis. 

The  curves  of  the  bone  may  easily  be  traced  from  end  to  end.  The  normal 
curves  may  be  increased  in  greenstick  fracture  without  any  positive  angularity  being 
produced  ;  but  in  this  case  careful  measurement  will  show  that  the  distance  between 
the  two  ends  of  the  bone  is  slightly  lessened  as  compared  with  the  uninjured  side. 
It  should  not  be  forgotten,  however,  that  the  curves  are  apt  to  be  increased  in  mus- 
cular persons,  and  that  for  the  same  reason  the  right  clavicle  is  sometimes  more 
curved,  thicker,  and  a  little  shorter  than  the  left. 

In  general  terms  it  may  be  said  that  the  inner  third  of  the  bone  is  in  relation 
below  to  the  first  rib,  which  it  crosses  obliquely  ;  the  middle  third  to  the  axillary 
vessels  and  the  brachial  plexus  (and  below  them  to  the  first  intercostal  space);  and 
the  outer  third  to  the  coracoid  process  and  the  acromio-clavicular  joint  (Fig.  274). 
In  the  male,  and  in  robust,  vigorous  persons  generally,  the  clavicles  are  on  a  high 
plane  and  pass  almost  horizontally  outward,  giving  the  "square-shouldered"  appear- 
ance usually  associated  with  ideas  of  muscular  strength  and  decreasing  the  apparent 
length  of  the  neck.  In  the  strong  male  the  outer  end  may  even  be  higher  than  tin- 
inner. 

In  narrow-chested  and  in  consumptive  persons  the  clavicles  are  depressed  and 


THE   STERNO-CLAVICULAR   ARTICULATION. 


261 


incline  downward,  and  hence  the  sloping  narrow  shoulders  and  long  necks  so  often 
seen  in  feeble  or  in  phthisical  individuals. 

In  very  fat  persons,  in  those  suffering  from  organic  heart  disease  attended  with 
dyspncea,  and  in  emphysematous  subjects  the  clavicles  are  raised  and  the  neck 
thereby  apparently  shortened. 

THE   STERNO-CLAVICULAR    ARTICULATION. 

This  is  the  only  joint  between  the  trunk  and  the  upper  extremity.  The  socket 
on  the  upper  angle  of  the  manubrium  is  coated  with  cartilage  which  often  extends 
a  little  onto  the  first  costal  cartilage.  This  very  shallow  socket  is  made  rather 
more  secure  by  the  forward  inclination  of  the  manubrium  and  also  by  being  rather 


FIG.  279. 


Clavicle        Sterno-clavicular  ligament 


Interclavicular  ligament 


Clavicle 


First  costal  cartilage 


Sternum 


First  costal  cartilage 


Sterno-clavicular  articulations  from  before  ;  clavicles  horizontal. 

more  on  the  back  than  on  the  front  of  that  bone,  so  that  to  some  extent  it  over- 
laps the  front  of  the  clavicle.  The  very  irregular  end  of  the  clavicle  is  coated  with 
cartilage,  which,  however,  gives  it  no  regular  nor  constant  shape.  As  a  rule,  it 
is  concave  from  before  backward,  but  there  is  often  a  swelling  at  the  posterior 
lower  angle. 

The  interarticular  fibre-cartilage  l  (Fig.  280),  a  disk  subdividing  the  joint 
into  two,  is  the  chief  factor  in  maintaining  the  great  security  of  the  joint.      It  is  a 

FIG.  280. 


Rhomboid 
ligament 


Right  sterno-clavicular  joint  opened.     Left  clavicle  raised  to  show  rhomboid  ligament.     Front  view. 

rounded  disk,  thinnest  in  the  middle  and  generally  thickest  at  the  upper  border, 
which  is  attached  to  the  upper  edge  of  the  inner  end  of  the  clavicle,  while  the  lower 
border  is  attached  to  the  first  costal  cartilage  at  the  outer  border  of  the  joint.  In 
the  main  it  faces  upward  and  outward,  so  that  the  clavicle  rests  upon  it.  It  is  said 
to  be  sometimes  perforated. 

1  Discus  articularis. 


262  HUMAN    ANATOMY. 

The  capsule  (Fig.  280)  surrounds  the  joint,  being  attached  to  the  borders  of 
the  articular  surfaces  and  also  to  the  borders  of  the  interarticular  disk.  It  is 
strengthened  before  and  behind  by  bands  running  upward  and  outward  from  the  ster- 
num, of  which  the  posterior  are  the  stronger,  and  sends  some  deep  fibres  to  the  disk. 
These  bands  strengthening  the  capsule  are  sometimes  described  as  the  anterior  and 
posterior  sterno- clavicular  ligaments.  There  are  two  distinct  synovia/  cavities. 

The  interclavicular  ligament  (Fig.  279)  is  a  fairly  well-defined  band  run- 
ning from  the  top  of  one  clavicle  across  to  the  other.  It  is  closely  connected  with  the 
top  of  the  joint  and  loosely  with  the  top  of  the  sternum,  towards  which  it  sinks  with 
a  slight  curve.  This  does  much  towards  filling  up  the  deep  interclavicular  notch. 

The  costo-clavicular  1  or  rhomboid  ligament  (Fig.  280)  arises  from  the 
costal  cartilage  just  outside  of  the  joint,  with  which  it  is  loosely  connected,  and  runs 
upward  and  outward  to  the  rough  rhomboid  impression  on  the  under  side  of  the 
clavicle.  It  is  a  layer  of  strong,  short  fibres. 

THE   SCAPULO-CLAVICULAR   A-RTICULATION. 

The  Acromio-Clavicular  Articulation. — This  joint  includes  a  capsular 
ligament  (Fig.  274)  and  occasionally  an  intra-articular  fibro-cartilage.  The  elongated 
facet  on  each  bone  is  covered  with  articular  cartilage,  that  of  the  clavicle  usually 
overlapping  the  other. 

The  capsule  is  weak,  except  above  and  behind,  where  there  are  strong  bands 
extending  outward  from  the  clavicle.  Of  these  the  posterior  are  the  longer. 

The  fibro-cartilage,  when  present,  is  wedge-shaped,  attached  by  the  base  to 
the  superior  part  of  the  capsule,  the  thin  edge  reaching,  perhaps,  half-way  through 
the  cavity  of  the  joint.  Sometimes  it  divides  the  joint  into  two.  There  may  be 
merely  a  thick  pad  of  fibrous  tissue  attached  to  the  outer  end  of  the  clavicle  with 
only  a  very  rudimentary  joint. 

The  coraco-clavicular  ligament  is  an  important  ligamentous  apparatus 
divided  into  an  outer  part,  the  trapezoid,  and  an  inner,  the  conoid  (Fig.  289).  These 
are  continuous  behind,  but  diverge  in  front.  The  trapezoid  ligament a  is  a  four- 
sided  layer  of  parallel  fibres,  springing  from  the  trapezoid  ridge  and  the  top  of  the 
first  part  of  the  coracoid,  to  run  outward  to  the  trapezoid  ridge  on  the  under  side  of 
the  clavicle.  The  line  of  attachment  to  the  clavicle  is  usually  the  longer,  and,  as  this 
runs  forward  and  outward,  the  anterior  fibres  are  almost  horizontal.  The  conoid 
ligament,3  or  inner  part,  is  less  strong.  It  arises  from  the  posterior  border  of  the 
conoid  tubercle  at  the  root  of  the  acromion,  and  runs  to  the  tubercle  of  the  same 
name  at  the  back  of  the  under  side  of  the  clavicle.  Both  these  tubercles  being 
prominences  of  some  size,  this  ligament  is  not  a  cord,  as  might  be  inferred,  but 
another  layer  continuous  with  the  trapezoid  behind.  The  inner  fibres  incline  inward 
as  they  ascend.  The  general  direction  is  upward  and  perhaps  a  little  backward,  but 
this  changes  with  the  position  of  the  bones.  There  may  be  a  synovial  bursa  in  the 
open  angle  seen  from  the  front  between  these  two  parts  of  the  ligament. 

Movements  of  the  Clavicle  and  Scapula. — The  compound  joint  at  the 
inner  end  of  the  clavicle  is  practically  a  universal  one.  The  clavicle  can  be  raised, 
depressed,  carried  forward  or  backward,  circumducted,  and  slightly  rotated.  The 
outer  and  lower  end  of  the  disk  being  attached  to  the  corresponding  border  of  the 
facet,  it  follows  that  the  clavicle  lies  upon  it.  When  the  shoulder  is  raised  or 
depressed  the  motion  is  almost  wholly  between  the  clavicle  and  the  disk,  though  the 
latter  slides  a  little,  and  in  marked  falling  of  the  shoulder  the  top  of  the  disk  starts 
to  come  out  of  the  socket,  but  is  restrained  by  the  top  of  the  capsule.  Forward  and 
backward  motions  occur  chiefly  between  the  disk  and  the  sternum,  but  there  is  some 
displacement  of  the  former.  Circumduction,  therefore,  involves  both  parts  of  the 
joint  ;  rotation  is  chiefly  in  the  inner  one. 

It  is  remarkable  that  a  joint  at  which  there  is  so  much  strain,  owing  to  lever.i^e, 
should  be  so  strong  with  such  apparently  imperfect  bony  arrangements  for  retention. 
Part  of  the  safety  is  due  to  the  subdivision  of  the  joint  and  a  great  deal  to  the  assist- 
ance of  muscles.  At  both  ends  of  the  clavicle,  as  Morris  has  pointed  out,  the  great 
muscles  are  so  placed  that  by  their  contraction  they  draw  the  bones  together. 

1  Lig.  costoclavlcularc.     "  Llg.  trnpezoitleutn.     ;1  Llg.  conoidcum. 


MOVEMENTS    OF   THE   CLAVICLE   AND    SCAPULA.  263 

The  obvious  advantage  of  a  joint  between  the  clavicle  and  the  acromion,  apart 
from  breaking  shocks  and  -making  the  shoulder-girdle  much  more  elastic,  is  that  it 
allows  the  angle  between  the  bones  to  change  with  the  position  of  the  arm,  and  thus 
the  direction  of  the  glenoid  cavity  may  be  modified  so  as  to  give  the  best  support  to 
the  arm  in  different  positions.  The  motion  at  the  outer  end  of  the  clavicle  is  con- 
siderable, but  indefinite.  The  overlapping  clavicle  can  advance  a  little  laterally 
onto  the  acromion,  except  in  the  cases  in  which  the  plane  of  the  joint  is  vertical. 
There  is  also  motion  on  an  approximately  vertical  axis  when  the  shoulder  is  thrown 
forward  and  the  outer  end  of  the  clavicle  advances,  the  angle  between  the  back  of 
the  clavicle  and  the  spine  of  the  scapula  being  diminished.  When  the  clavicle  can 
advance  no  farther,  the  tension  of  the  trapezoid  ligament  checks  the  progress  of  the 
coracoid.  In  the  withdrawal  of  the  shoulder  the  reverse  occurs,  the  movement 
being  finally  checked  by  the  conoid.  In  up-and-down  movements  of  the  shoulder 
the  motion  is  on  an  approximately  antero-posterior  axis.  When  it  rises  the  base  of 
the  coracoid  comes  into  direct  contact  with  the  clavicle  and  the  rhomboid  ligament 
is  strained  ;  when  it  falls  the  clavicle  rests  on  the  first  rib  and  the  conoid  is  put  on 
the  stretch,  as  are  also  the  interclavicular  ligament  and  the  top  of  the  capsule  of  the 
sternal  end.  Probably  the  freest  movement  is  when  the  arm  is  raised  vertically,  in 
which  case  the  lower  angle  of  the  scapula  swings  strongly  forward  so  as  to  direct  the 
glenoid  cavity  more  nearly  upward.  The  clavicle  rises  from  the  sternal  end,  and 
perhaps  slightly  rotates.  Possibly  the  lower  end  of  the  scapula  is  withdrawn  slightly 
from  the  chest.  Apart  from  the  movements  of  the  arm  the  scapula  may  change  its 
position  considerably.  It  may  rotate  on  either  the  end  of  the  acromion  (as  in  rais- 
ing the  arm)  or  on  the  superior  angle,  the  lower  angle  being  the  most  movable 
point.  When  it  is  carried  far  forward  a  larger  portion  of  the  posterior  surface  of 
the  lungs  can  be  examined.  The  scapulae  may  also  be  raised  or  brought  nearer 
together. 

Surface  Anatomy  of  the  Shoulder-Girdle. — The  general  shape  of  the 
clavicle  is  easily  made  out  by  pressing  on  its  front  and  superior  surfaces  with  the 
muscles  relaxed.  The  degree  of  backward  projection  of  the  inner  end  can  be  deter- 
mined. It  is  placed  horizontally  in  woman  ;  in  man  the  outer  end  is  slightly  raised. 
The  joint  with  the  acromion  is  easily  felt  from  above,  the  clavicle  being  the  higher. 
The  outline  of  the  acromion,  which  slopes  somewhat  downward,  is  easily  felt.  It 
forms  the  point  of  the  shoulder-girdle,  but  not  of  the  shoulder,  as  the  humerus 
always  projects  beyond  it  externally.  A  plane  vertical  surface  placed  against  the 
outside  of  the  shoulder  cannot  touch  the  acromion  if  the  head  of  the  humerus  is  in 
place.  The  possibility  that  the  outer  epiphysis  of  the  acromion  may  not  unite  by 
bone  is  to  be  remembered.  The  finger  can  be  carried  from  the  acromion  along  the 
spine  to  its  triangular  origin.  The  tip  of  the  coracoid  is  to  be  felt  by  manipulation 
in  the  infraclavicular  fossa  at  the  inner  side  of  the  humerus.  The  posterior  border 
of  the  scapula  is  always  to  be  felt ;  in  thin  persons  its  outline  can  be  traced  and  the 
shape  of  the  inferior  angle  approximately  recognized. 

PRACTICAL   CONSIDERATIONS. 

The  Sterno-Clavicular  Articulation. — The  interposition  of  an  elastic  buffer 
in  the  shape  of  the  interarticular  fibro-cartilage,  united  to  both  the  bones  by  very 
strong  ligamentous  fibres,  and  completely  bisecting  the  joint  (Fig.  280),  in  fact, 
converting  it  into  two  separate  joints,  prevents  the  clavicle  from  transmitting  to  the 
sternum  the  full  force  of  blows  and  falls  received  upon  the  hand  or  shoulder,  and 
allows  of  the  varied,  though  limited,  movements  of  the  articulation. 

Dislocation  is  rare.  The  ligaments  are  stronger  than  .the  clavicle,  which  is 
therefore  usually  broken  by  any  force  sufficient  to  threaten  the  integrity  of  the  joint. 
The  curves  of  the  clavicle,  the  mobility  of  the  scapula,  and  the  play  of  the  acromio- 
clavicular  joint  all  tend  to  diffuse  forces  that  might  otherwise  have  been  expended 
on  this  articulation,  which  is  furthermore  strengthened  by  the  tendinous  origins 
of  the  sterno-cleido-mastoid  and  of  the  pectoralis  major. 

The  most  common  form  of  dislocation  is  the  forward  one,  the  anterior  sterno- 
clavicular  ligament  being  the  weaker  and  thinner.  Backward  luxation  is  re- 


264  HUMAN    ANATOMY. 

sisted  by  the  more  powerful  posterior  ligament  and  by  the  rhomboid.  Upward 
displacement — the  least  frequent — is  resisted  by  the  interarticular  cartilage,  which  is 
strongly  inserted  below  into  the  cartilage  of  the  first  rib  and  the  sternum,  and  above 
into  the  clavicle  itself,  by  the  rhomboid  and  interclavicular  ligaments  and  by  both 
the  anterior  and  posterior  ligaments  ;  hence  the  rarity  of  this  luxation. 

In  many  displacements  of  the  sternal  end  of  the  clavicle  the  shoulder  is  carried 
downward  or  backward  until  the  clavicle  is  in  contact  with  the  strong  first  rib,  which 
then  acts  as  a  fulcrum,  the  sternal  end  of  the  bone  continuing  its  upward  or  forward 
motion  until  the  resisting  ligaments  are  torn  and  the  luxation  is  produced. 

In  backward  dislocation  by  indirect  violence  the  force  has  usually  pushed  the 
shoulder  forward  and  inward,  as  when  the  patient  has  been  caught  between  two  cars 
or  between  a  wall  and  a  wagon. 

In  this  dislocation  the  sternal  end  may  press  upon  the  trachea,  the  internal 
jugular,  or  the  beginning  of  the  innominate  vein,  and  may  therefore,  if  the  faulty 
position  has  become  permanent,  require  excision. 

Disease  of  the  sterno-rclavicular  joint  is  not  very  common,  considering  its  super- 
ficial position  and  its  constant  motion.  This  is  probably  due  to  the  fact  that  the 
motion  is  slight  and  that  strains  and  injury  to  the  synovia!  membranes  are  prevented 
by  the  strong  and  elastic  interarticular  cartilage  and  by  the  strength  of  the  ligaments. 
Suppuration  usually  shows  itself  in  front  (as  the  anterior  ligament  is  the  thinnest), 
but  may  perforate  by  ulceration  the  posterior  ligament  and  find  its  way  to  the  medi- 
astinum. With  the  arm  at  the  side  the  articulation  becomes  V-shaped,  the  clavicle 
touching  the  joint  surface  only  at  its  lowest  angle.  With  the  arm  elevated,  the  two 
joint  surfaces  are  brought  into  closer  relation,  and  the  shape  of  the  joint  viewed  from 
the  front  becomes  linear  ;  hence  raising  of  the  arm  is  uniformly  productive  of  pain 
in  disease  of  the  joint. 

Ankylosis  is  rare,  probably  owing  to  the  separation  of  the  diseased  joint  surfaces 
by  the  thick,  resistant  fibro-cartilage. 

The  Acromio-Clavicular  Articulation. — This  is  one  of  the  shallowest  of 
the  articulations,  the  clavicle  being  merely  superimposed,  as  it  were,  upon  the  upper 
edge  of  the  acromion.  The  powerful  ligaments  which  bind  the  clavicle  to  the  cora- 
coid  (the  conoid  and  trapezoid),  although  they  have  no  direct  relation  to  the  joint, 
are  the  most  important  factors  in  preserving  its  integrity  when  force  is  applied  to  the 
point  of  the  shoulder. 

The  movements  of  the  joint  are  around  two  axes,  an  antero-posterior  and  a 
vertical  one,  so  that  the  relations  of  the  glenoid  cavity  to  the  humerus  may  remain 
relatively  unchanged  when  the  arm  is  elevated  or  is  advanced.  The  scapula  must 
obviously  move  backward  or  forward  on  the  side  of  the  chest  in  a  curve  established 
by  the  curve  of  the  ribs.  It  does  this  on  a  radius  represented  by  the  clavicle,  the 
centre  of  the  rotation  being  at  the  sterno-clavicular  joint.  The  acromio-clavicular 
joint  enables  this  motion  to  take  place,  while  at  the  same  time  the  glenoid  cavity 
continues  to  point  obliquely  forward.  If  it  were  not  for  this,  the  act  of  pushing 
or  striking  with  the  arm  advanced,  or  of  falling  upon  the  hand  with  the  arm  in 
a  like  position,  would  bring  the  head  of  the  humerus  against  the  capsule  of  the  joint 
instead  of  against  the  glenoid  cavity,  and  would  thus  increase  the  frequency  of 
luxation.  Conversely,  "rigidity  of  this  little  joint  may  be  a  cause  of  insecurity  in 
the  articulation  of  the  shoulder  and  of  weakness  in  certain  movements  of  the  limb" 
(Treves). 

Dislocation  is  rare.  The  dislocation  of  the  acromial  end  of  the  clavicle  upward 
(described  by  some  surgical  writers,  for  the  sake  of  uniformity,  as  dislocation  of  the 
scapula  downward)  is  much  the  more  frequent.  The  capsular  ligament  is  torn  or 
stretched,  even  in  the  incomplete  forms.  In  the  complete  variety  the  coraco- 
clavicular  ligaments  must  be  torn  or  ruptured,  but  their  great  strength,  increased  in 
effectiveness  by  their  distance  from  the  joint,  renders  this  accident  uncommon. 

Dislocation  of  the  clavicle  beneath  the  acromion — between  it  and  the  coracoid 
process — and  dislocation  of  the  clavicle  beneath  the  coracoid  are  extremely  rare 
accidents.  It  is  not  certain  that  the  latter  has  ever  occurred.  Both  obviously 
require  for  their  production  extensive  laceration  of  all  of  the  ligaments  binding 
together  the  scapula  and  the  outer  portion  of  the  clavicle. 


THE  HUMERUS.  265 

THE  HUMERUS. 

The  bone  of  the  arm  consists  of  a  shaft  and  two  enlarged  extremities. 

The  upper  extremity  includes  a  globular  articular  head  and  two  tubcrosities 
for  muscular  insertions.  The  head1  looks  upward,  inward,  and  backward.  It  is 
not  truly  a  part  of  a  sphere,  for  the  curve  in  the  horizontal  plane  is  bolder  than  that 
in  the  vertical.  The  vertical  diameter  between  the  edges  of  the  articular  surface  is 
longer  than  the  transverse.  It  is  surrounded  by  a  slight  groove  for  the  attachment 
of  the  capsular  ligament  at  what  is  called  the  anatomical  neck?  The  siirgical  neck*  is 
just  below  the  whole  upper  extremity.  The  tuberosities  are  separated  in  front  by  a 
deep  furrow,  the  bicipital  groove, ,4  through  which  runs  the  tendon  of  the  long  head 
of  the  biceps.  The  greater  tuberosity 5  is  a  rough  enlargement  placed  externally. 
Its  highest  point  is  at  the  front,  just  by  the  groove.  A  superior  surface  of  this 
tuberosity  begins  here  and,  passing  downward  and  backward  beside  the  head, 
broadens  as  it  goes.  It  bears  three  smooth  facets  for  the  insertion  of  the  supra- 
spinatus,  the  infraspinatus,  and  the  teres  minor,  in  this  order  ;  the  first  being  highest 
and  most  in  front,  the  last  and  lowest  most  behind.  The  lesser  tuberosity,6  much 
smaller,  is  on  the  front  of  the  bone.  It  bears  a  prominent  angle,  sometimes  an 
actual  crest  running  downward  and  inward  for  the  subscapularis.  The  upper  aspect 
of  the  process,  which  looks  also  inward,  is  smooth  for  a  bursa  beneath  the  tendon. 

The  shaft  is  roughly  cylindrical  above  and  prismatic  below.  It  is  convenient 
to  divide  it  by  three  borders  into  three  surfaces.  The  anterior  border  starts  from 
the  greater  tuberosity  as  the  outer  lip  of  the  bicipital  groove,  which,  growing 
shallower,  can  be  traced  through  the  first  quarter  of  the  shaft.  This  •  outer  lip 
becomes  thicker  and  more  prominent  for  some  two  inches  below  the  surgical  neck 
to  receive  the  insertion  of  the  pectoralis  major.  Below  this  it  is  joined  by  the  lower 
end  of  the  deltoid  eminence,  after  which,  smooth  and  rounded,  it  grows  fainter,  but 
may  be  traced  downward  to  a  ridge  separating  the  capitellum  from  the  trochlea, 
where  it  ends.  The  internal  border  starts  at  the  inner  side  of  the  neck,  often  so 
near  the  inner  lip  of  the  bicipital  groove  as  to  be  confounded  with  it,  and  runs 
straight  down  to  the  very  tip  of  the  internal  condyle.  It  is  at  best  very  faint  in  the 
first  quarter,  and  often  barely  visible  ;  but  it  is  distinct  in  the  middle  and  prominent 
in  the  last  third,  where  it  is  known  as  the  internal  supracondylar  ridge.  The 
external  border  begins  at  the  back  of  the  greater  tuberosity  and  runs  to  the  outer 
condyle,  the  lower  part  being  the  external  supracondylar  ridge,  which  has  a  forward 
curve.  A  great  exaggeration  of  this  ridge  has  been  seen  in  the  negro.  The  internal 
surface  bears  the  inner  lip  of  the  bicipital  groove,  which,  starting  from  the  lesser 
tuberosity,  is  often  very  faint  ;  it  receives  the  tendon  of  the  teres  major.  The 
bicipital  groove  soon  becomes  shallow,  and  is  lost  after  two  or  three  inches.  The 
nutrient  foramen,  running  downward  into  the  bone,  is  rather  below  the  middle  of 
this  surface,  sometimes  being  almost  in  the  internal  border.  The  external  surface 
is  convex  in  the  upper  half  and  concave  in  the  lower.  Its  second  quarter  is  occupied 
by  a  long,  rough  elevation,  the  deltoid  eminence?  slanting  downward  and  forward 
against  the  interior  border  for  the  insertion  of  the  deltoid  muscle.  The  posterior 
surface  is  twisted,  facing  somewhat  inward  above  and  backward  below.  'The  upper 
plane  portion  gives  origin  to  the  outer  head  of  the  triceps,  and  the  lower,  convex 
except  below,  to  the  inner  head.  A  broad  spiral  groove  beginning  on  the  external 
surface  behind  the  deltoid  eminence,  in  front  of  the  outer  border,  twists  forward  and 
downward.  This  is  generally  improperly  called  the  musculo-spiral  groove*  The 
groove  truly  deserving  that  name,  containing  the  musculo-spiral  nerve  and  the  supe- 
rior profunda  artery,  occupies  the  lower  and  posterior  part  of  the  greater  groove, 
from  which  it  usually  is  not  to  be  distinguished  throughout,  though  both  grooves 
may  be  distinct.  The  musculo-spiral  groove  is  some  five  millimetres  broad,  and, 
when  well  developed,  begins  on  the  posterior  surface,  separating  the  areas  for  the 
outer  and  inner  heads  of  the  triceps  muscle,  and  interrupts  the  external  border, 
behind  which  the  broad  spiral  groove  never  passes.  A  second  nutrient  foramen, 
also  running  downward  and  sometimes  the  larger  of  the  two,  may  occur  in  the 
groove.  The  shaft  takes  a  forward  bend  just  at  its  termination,  so  that  most  of  the 
lower  end  lies  in  front  of  the  continuation  of  the  axis  of  the  shaft. 

1  Caput    humeri.     2Collum   anatomicum.      3  C.   chirurgicum.      4  Sulcus  intertubercularis.     5Tubcrculura   niajus.     GTub. 
minus.      '  Tuberositas  deltoidea.     *  Sulcus  radialis. 


266 


HUMAN      ANATOMY. 
FIG.  281. 


Greater  tu- 
berositv 


Head 


-Lesser  tuberosity 


L Bicipital  groove 


! 


Brachio-radialis 


-  Sup  ra  sp  Hiatus 
\Subscapularis 


.  Pecioralis  major 
•  Lalissimus  dor  si 
,  Teres  major 

^Deltoid 


Deltoid- 
•Coraco-brachiahs          eminence 


^Rrachialis  anticus 


External- 
border 


-  Internal  bicipital  ridge 


-External  bicipital  or  pecto- 
ral ridge 


•  Internal  border 


Extensor  carp  i  /I            i 

\ 

radialis  long,    y           ,A^ 

^^^Pronator  radii 

§^;  ^T      teres 

Tendon  common  i         W  ^i. 

^Jjjfl^  j—  Tendon  common 

to  exten.  carp.  ^A^^^Bjj 
rod.  brev.,  ex-     xaSP^*1 

k     JjP*^       \opronator  ra- 
S^p)               ilii  teres,  flex. 

ten.    communis 

carpi   radialis, 

digitorum,  ex- 

palmaris      lon- 

ten,  min.  digiti, 
exten.  carpi  ul- 

gns,  flex,  sub- 
lim.   dig.,  flex. 

naris 

carpi  ulnaris 

External 

supra- 

condylar 

ridge      y 

s  Anterior  border 


Internal  supracondylar  ridge 


Radial- 

fossa 


K\tn  iia 
condyle 


roronoid  fossa 


I  Internal  condyle 


Vommoti  u-iulon 
for  flexor  muscl 


CapiU-llum  Troclilcii 

Right  hutnerus  from  before.    The  outline  figure  shows  the-  areas  of  muscular  attachment. 


Heac 


Neck 


THE   HUMERUS. 

FIG.  282. 


Greater  tuber- 
ositv 


267 


Surgical  neck 


Spiral  groove 


Musculo-spiral 
groove 


Internal  condyle 


Groove  for  ulnar 
nerve 


Supraspinatus 


Inner  head  of — 
triceps 


External  head  of 
triceps 


Deltoid 
Brachialis  anticus 

Brachio-radialis 


Anconeus 


Olecranon  fossa 
External  condyle 


Trochlea 
Right  humerus  from  behind.    The  outline  figure  shows  the  areas  of  muscular  attachment. 


268 


HUMAN   ANATOMY. 


FIG.  28-1. 


The    lower    extremity    is    broad   from   side  to  side,  with   an   articular  surface 
below,  and   two   lateral   projections,  the  condyles.     The   inner  condylc,1   much   the 

larger,  is  sharp  and  prominent,  giving  rise  with  a  part 
of  the  supracondylar  ridge  to  the  flexor  pronator  mus- 
cles. It  is  faintly  grooved  behind  by  the  ulnar  nerve, 
and  the  lower  part  of  the  front  often  presents  a  smooth 
surface.  The  outer  condylc  ~  is  a  slightly  raised  knob. 
The  articular  surface,  most  of  which  is  at  a  lower  level 
than  the  condyles,  consists  of  two  parts, — an  inner 
pulley-like  surface,  the  trochlea,  for  the  ulna,  and  an 
outer  convexity,  the  capitellum,  for  the  radius. 

The  trochlea11  is  bounded  internally  by  a  sharp 
border,  forming  about  three-quarters  of  a  circle,  and 
projecting  below  the  rest  of  the  bone  as  well  as  before 
and  behind  it.  It  is  bounded  externally  by  a  ridge, 
which  is  prominent  behind  where  the  trochlea  forms 
the  whole  of  the  articular  surface,  but  is  faint  in  front 
where  it  separates  the  trochlea  from  the  capitellum. 
Above  the  joint  this  ridge  is  continuous  with  the  an- 
terior border  of  the  shaft. 

The  trochlea  is  convex  from  before  backward.  A 
section  through  the  middle  forms  almost  a  complete 
circle,  being  broken  only  above,  where  a  thin  plate  con- 
nects it  with  the  shaft.  It  is  concavo-convex  from  side 
to  side,  the  convexity  being  greatest  at  the  inner  bor- 
der. There  is  a  depression  above  the  trochlea  both 
before  and  behind  ;  the  former,  the  coronoid  fossa,  is 
small  and  receives  the  coronoid  process  of  the  ulna  in 
flexion  ;  the  posterior  depression,  triangular  and  much 
the  larger,  is  the  olecranon  fossa,  receiving  that  process 
in  extension.  The  bone  separating  these  fossae — the 
plate  just  alluded  to — is  so  thin  as  to  be  translucent. 
It  may  be  perforated  by  the  supratrochlear  foramen, 
most  frequently  found  in  savage  tribes.  The  joint  be- 
tween the  humerus  and  ulna  is  commonly  called  a 
hinge-joint,  but  there  are  serious  modifications.  First, 
the  axis  of  the  trochlea  is  not  at  right  angles  to  that  of 
the  shaft,  but  slants  downward  and  inward  ;  next,  the 
borders  of  the  trochlea  are  not  at  right  angles  to  its 
axis,  but  are  so  placed  as  to  transform  it  into  a  spiral 
or  screw-joint  ;  finally,  these  borders  are  not  parallel  to 
each  other,  but  the  inner  slants  downward  and  inward 
so  that  the  transverse  diameter  of  the  joint  is  greater 
below  than  at  the  top,  either  before  or  behind. 

The  capitellum,4  on  which  the  concave  head  of 
the  radius  plays,  is  situated  on  the  front  of  the  outer 
part  of  the  lower  end.  It  is  not  far  from  being  a  por- 
tion of  a  sphere,  since  it  is  convex  and  nearly  equally 
so  in  all  directions,  but  the  arc  from  above  downward 
is  the  longest.  A  groove  runs  between  it  and  the  outer 
ridge  of  the  trochlea  ;  the  outer  border  is  straight  :  the 
posterior  runs  from  it  obliquely  backward  and  inward. 
The  capitellum  is  placed  so  much  to  the  front  as  to  be 
nearly  or  quite  invisible  from  behind  ;  hence  the  articu- 
lar surface  is  much  more  extensive  on  the  front  than 
the  back.  The  radial  fossa,  a  small  depression  above  the  capitellum,  receives  tin- 
edge  of  the  head  of  the  radius  in  extreme  flexion. 

The  supracondylar  process  is  a  small   bony  spur   occurring    in    probably  two 
or  three  per  cent.,  which  arises  from  the  front  of  the  bone  a  little  anterior  to  the 

1  Eplcondylus  inedialis.     '•'  Epicondylus  latcralN.        Tin  lilc.i.     '  Ciipituluui. 


Longitudinal  section  of  humerus, 
showing  relation  of  compact  and 
spongy  none. 


THE   HUMERUS. 


269 


internal  supracondylar  ridge.  It  is  usually  connected  by  a  fibrous  band  to  the  tip 
of  the  inner  condyle,  thus  representing'  the  supracondylar  foramen  found  very 
generally  among  mammals.  The  median  nerve  and  generally  either  the  brachial  or 
the  ulnar  artery  pass  through  it.  The  process,  without  any  completing  ligament, 
has  been  seen  hooking  over  the  nerve  alone.  We  have  once  seen  a  bony  foramen. 

The  so-called  torsion  of  the  humerus  is  a  very  complicated  problem  arising  from  the 
theory  of  the  changes  necessary  to  account  for  the  adult  condition  of  the  humerus  and  femur, 
assuming  theni  to  have  been  originally  symmetrical.  The  practical  point  is  that  the  horizontal 
axis  subdividing  the  articular  surface  of  the  head  of  the  humerus,  imagined  on  the  same  plane 
as  the  transverse  axis  of  the  elbow,  forms  an  angle  with  the  latter.  This  angle  varies  consider- 
ably ;  according  to  Gegenbaur,  it  is  12°  for  the  adult  European.  In  the  lower  races  it  is  greater, 
and  still  greater  in  the  lower  animals.  (This  is  what  Continental  anatomists  call  the  supple- 
mental angle,  as  they  assume  that  the  twisting  has  approached  180°,  and  that  thus  the  true 
angle  is  168°.  We  give  this  as  the  simplest. )  The  angle  is  greater  in  the  foetus.  Gegenbaur 
gives  it  as  59°  at  from  three  to  four  months,  and  as  34°  at  from  three  to  nine  months,  after  birth. 
This  change  probably  occurs  in  the  epiphyses.  It  is  certain  that  the  shaft  of  the  developing 
humerus  does  not  actually  twist,  for  the  borders  are  straight,  as  are  all  the  long  nerves  with  the 
single  exception  of  the  musculo-spiral.  No  spiral  fibres  have  been  found  in  the  bone. 

Structure. — The  walls  of  the  shaft  are  of  compact  bone  enclosing  a  cavity.  At 
the  upper  end  the  head  is  made  of  round-meshed  tissue  of  considerable  density  ;  the 
greater  tuberosity  is  of  lighter  structure  ;  both  are  enclosed  by  thin  bone.  The  line 
of  union  of  the  upper  epiphysis  is  seen  on  section  after  it  has  disappeared  from  the 
surface.  Transverse  sections  at  the  lower  end  show  a  system  of  strong  plates  passing 
obliquely  from  the  front  to  the  back  above  the  inner  condyle. 

Differences  due  to  Sex. — The  chief  guides  are  the  greater  delicacy  of  the 
female  bone,  and  especially  the  smaller  size  of  the  head.  It  is  generally  thought 
that  the  female  humerus  presents  a  sharper  angle  between  the  axis  of  the  shaft  and 
the  transverse  axis  of  the  trochlea  than  does  the  male,  but  Berteaux's 1  measurements 
make  the  difference  too  slight  to  be  significant, — 79°  for  man  and  78°  for  woman. 

Development. — The  primary  centre  for  the  shaft  appears  towards  the  end  of 
the  second  fcetal  month,  and  before  birth  bone  has  reached  to  the  extremities,  which 
are  formed  by  the  union  of  several  centres.  There  are  two  or  three  for  the  upper, 
a  chief  one  for  the  head  coming  soon  after  birth  and  sometimes  earlier.  It  is 


Ossification  of  humerus.  A,  just  before  birth;  II.  in  the  first  year;  Cat  three  years;  C',  sections  of  ends  of 
preceding  ;  D,  at  five  years  ;  /•;,  at  about  thirteen  years  ;  F,1 ',  sections  of  ends  of  preceding ;  /•",  at  about  sixteen  ;  /•"', 
sections  of  ends  of  preceding,  a,  centre  for  shaft ;  f>,  for  head  ;  c ,  for  capitellum  and  part  of  trochlea  ;  d,  for  greater 
tuberosity ;  e,  for  head  and  tnberosities  in  transverse  section  ;  /",  for  internal  condyle  ;  g,  for  inner  part  of  trochlea. 

present  at  birth  in  22.5  per  cent,  of  foetuses  weighing  seven  pounds  and  over  (Spen- 
cer2). It  is  almost  always  present  by  the  end  of  the  third  month  after  birth.  In 
the  third  year  ossification  begins  in  the  greater  tuberosity,  and  another  point  may 
appear  somewhat  later  in  the  lesser  one.  At  five  all  the  centres  for  this  end  have 

1  l.e  Humerus  et  le  Femur,  Paris,  1891. 

2  Journal  of  Anatomy  and  Physiology,  vol.  x\\.,  1891. 


270 


HUMAN   ANATOMY. 


become  one,  making  a  cap  for  the  top  of  the  shaft,  which  latter  extends  into  the 
head.  The  largest  centre  for  the  lower  end  is  that  for  the  capitellum,  which  is  seen 
by  the  end  of  the  first  half-year.  It  forms  also  a  part  of  the  outer  side  of  the 
trochlea.  A  centre  for  the  tip  of  the  inner  condyle  is  evident  by  the  fifth  year.  One 
or  more  minute  points  of  ossification  for  the  trochlea  appear  in  the  tenth  year,  and 
one  for  the  tip  of  the  external  condyle  in  the  fourteenth.  Although  all  these 
epiphyses  are  originally  in  the  same  strip  of  cartilage,  they  do  not  unite  into  one- 
piece  of  bone.  The  capitellum  is  joined  by  the  ossification  for  the  trochlea,  and  joins 
the  shaft  at  from  fourteen  to  fifteen.  We  are  not  sure  whether  the  insignificant  centre 
for  the  outer  condyle,  which  fuses  at  about  the  same  time,  joins  the  epiphysis  or  the 
shaft.  Rambaud  and  Renault  seem  to  believe  the  latter.  The  centre  for  the  internal 
condyle  remains  separate  after  the  rest  are  fused  and  joins  the  shaft  at  about  eighteen. 
The  upper  end  joins  at  about  nineteen,  the  line  of  union  being  lost  at  twenty  or 
twenty-one.  It  is  usually  lost  earlier  in  the  female. 

Surface  Anatomy. — The  external  and  internal  condyles  are  the  only  points 
that  are  truly  subcutaneous.  The  outer  is  easily  recognized  under  normal  conditions, 
but  is  quickly  obscured  by  swelling.  The  internal  is  so  prominent  that  it  can  always 
be  recognized,  unless  the  joint  has  been  utterly  broken  to  pieces.  The  fact  that  the 
inner  condyle  joins  the  shaft  after  the  rest  of  the  lower  end  exposes  it  to  the  danger  of 
being  broken  off  before  the  union  has  occurred,  or  while  it  is  still  weak.  The  upper 
end  of  the  humerus  is  everywhere  covered  by  muscle,  but  much  of  its  outline  can  be 
explored.  The  amount  of  its  forward  projection  varies  much  ;  but  it  always  projects 
outward  beyond  the  acromion.  The  lesser  tuberosity  and  the  bicipital  groove  can 
be  recognized  on  rotating  the  bone,  but  indistinctly.  The  groove  is  filled  by  the 
tendon  and  still  further  obscured  by  the  capsule  and  muscles.  The  surgical  neck  is 
best  felt  in  the  axilla,  whence,  the  arm  being  extended,  the  head  can  be  examined, 
though  imperfectly. 

PRACTICAL   CONSIDERATIONS. 


FIG.  285. 


Head 


The  humerus  occasionally  fails  to  develop,  either  alone  or  together  with  the 
other  bones  of  the  extremity.     The  bone  of  one  arm  may  be  shorter  and  thicker 

than  the    normal   bone.       Lengthening   beyond    normal 
limits  is  much  rarer. 

The  shallowness  of  the  glenoid  cavity  obviates  the 
necessity  for  projecting  the  head  of  the  bone  from  the 
shaft,  as  in  the  femur  ;  the  "neck"  is,  therefore,  merely 
a  very  narrow  and  superficially  shallow  constriction  of  an 
inward  prolongation  of  the  shaft  between  the  tuberosities 
below  and  the  joint  surface  above.  Both  its  shortness 
and  its  shallowness  render  it  far  less  liable  to  fracture  than 
the  femoral  neck.  When,  in  old  age,  absorption  and 
fatty  degeneration  of  the  cancellous  tissue  have  occurred, 
fracture  does  take  place,  as  a  result  usually  of  falls  upon 
the  shoulder.  It  is  often  accompanied  by  impaction,  the 
head  being  driven  into  the  broad  surface  of  cancellated 
tissue  on  the  upper  end  of  the  lower  fragment  (Fig.  285  ). 
This  results  in  a  lessening  of  the  bulk  of  the  upper  end, 
or  subacromial  portion,  of  the  humerus,  and  thus  in  a 
little  flattening  of  the  deltoid  and  a  little  increased  promi- 
nence of  the  acromion.  If  impaction  does  not  occur, 
and  the  capsule  of  the  joint  is  completely  torn  through  its 
entire  circumference,  necrosis  of  the  upper  fragment 
must  follow.  Usually,  through  untorn  periosteum  and 
through  portions  of  capsule  reflected  from  the  inner  side 
of  the  shaft  below  the  anatomical  neck  to  the  edge  of 
the  articular  cartilage  on  the  head,  the  blood-supply  is 
maintained  so  that  necrosis  is  prevented  and  union  results. 
There  is  no  direct  blood-supply  to  the  head  of  the  humerus  corresponding  to  that 
received  by  the  femoral  head  through  the  ligamentum  teres.  The  displacement 


Shaft 


Fracture  of  anatomical  neck  of 
humerus,  slmwini;  mipartiori. 


PRACTICAL   CONSIDERATIONS:    THE   HUMERUS. 


271 


is  apt  to  be  slight,  the  muscles  inserted  into  the  bicipital  groove  and  acting  on 
the  lower  fragment  being  antagonized  by  those  inserted  into  the  greater  tuberosity. 
That  tuberosity  may  be  torn  off  as  a  rare  accident.  The  displacement — theoreti- 
cally— will  depend  upon  the  action  of  the  muscles  inserted  into  that  portion  of  the 
bone  (page  590). 

The  large  upper  epiphysis  of  the  humerus  (made  up  of  centres  for  the  head  and 
the  tuberosities  which  begin  to  coalesce  about  the' sixth  year)  is  fully  formed  by  the 
age  of  puberty.  It  includes  then  the  two  tuberosities,  the  upper  fourth  of  the  bicipi- 
tal groove,  all  of  the  head,  the  anatomical  neck,  and  a  little  of  the  shaft  just  below  it. 
A  line  nearly  horizontal  and  crossing  the  bone  beneath  the  great  tuberosity,  and 
therefore  considerably  below  the  anatomical  neck,  represents  the  epiphyseal  line  at 
the  twentieth  year,  when  the  epiphysis  and  shaft  become  united.  It  is  within  a  half 
inch  of  the  so-called  surgical  neck  (Fig.  286). 

The  lower  surface  of  the  epiphysis  is  concave  and  the  upper  surface  of  the 
diaphysis  convex  or  conical  (Fig..  287). 


FIG.  287. 


FIG.  286. 


Upper  end  of  humerus,  showing  epiphyseal  line.    A,  on  surface; 
£,  in  section. 


Upper  end  of  humerus,  showing  cupping 
01  epiphysis  to  receive  the  pointed  end  of 
diaphysis. 


The  traumatic  separation  of  this  epiphysis  is  a  not  infrequent  accident  of  child- 
hood and  adolescence.  It  is  commonly  caused  by  forcible  traction  of  the  arm 
upward  and  outward.  In  such  cases  three  anatomical  factors  probably  enter  into 
the  production  of  the  lesion.  ( i )  The  partial  fixation  of  the  epiphysis  by  the  sub- 
scapularis,  supra-  and  infraspinatus,  and  the  upper  fibres  of  the  teres  minor.  Even 
on  the  dead  subject,  rotation  outward  with  abduction  will  most  readily  produce  the 
disjunction.  (2)  The  ease  with  which  the  periosteum,  strongly  attached  to  the 
epiphysis  but  very  loosely  to  the  diaphysis,  may  be  separated  from  the  latter.  This 
is  illustrated  by  the  fact  that  in  cases  of  detachment  the  teres  minor,  though  inserted 
below  the  epiphyseal  line,  is  apt  to  retain  its  connection  with  the  periosteum  covering 
the  epiphysis.  (3)  The  powerful  muscles  resisting  abduction  and  inserted  into  the 
diaphysis  just  below  the  epiphyseal  line. 

There  may  be  only  separation  with  little  or  no  displacement  ;  but  if  displace- 
ment occurs,  the  muscles  just  alluded  to  (the  latissimus,  pectoral,  and  teres)  tend  to 


272  HUMAN   ANATOMY. 

draw  the  diaphyseal  fragment  strongly  towards  the  chest-wall,  so  that  its  upper  end 
may  be  found  beneath  the  coracoid  process.  The  shape  of  the  opposing  surfaces  of 
the  epiphysis  and  diaphysis  lessens  both  the  frequency  and  the  amount  of  the  dis- 
placement. The  two  surfaces  usually  remain  in  contact  at  some  point :  ( i )  on 
account  of  that  shape  ;  (2)  because  the  humerus  on  the  epiphyseal  line  is  broader 
than  at  any  other  part  of  its  upper  end. 

The  deformity  will  be  recurred  to  in  connection  with  that  of  the  conditions 
which  it  most  closely  resembles, — fracture  of  the  surgical  neck  and  dislocation  of 
the  humerus, — which  (on  account  of  the  importance  of  muscular  action  in  their 
production  and  in  their  treatment)  will  be  considered  after  the  muscles  have  been 
described. 

It  might  be  expected  that,  as  the  chief  growth  of  the  humerus  takes  place  from 
its  upper  epiphysis,  arrest  of  growth  and  development  should  be  a  usual  sequel. 
The  upper  epiphysis  from  the  tenth  year  to  adult  life  will,  according  to  Vogt,  add 
from  seven  to  ten  centimetres  to  the  length  of  the  humerus,  the  lower  epiphysis 
during  the  same  time  adding  but  one-fifth  as  much.  The  activity  of  the  upper 
epiphysis  is  shown  by  the  frequency  of  conical  stump  after  amputation  through  the 
upper  end  of  the  humerus.1  Despite  these  facts,  in  comparatively  few  cases  of 
disjunction  is  atrophy  or  arrest  of  growth  reported  as  a  result.  It  has  been  sup- 
posed, too,  that  necrosis  of  the  epiphysis  should  follow  this  injury  on  account  of 
deficient  blood-supply  to  the  head  ;  but,  through  the  tuberosities,  through  the 
connection  of  the  reflected  capsule  to  the  articular  cartilage,  and  through  portions 
of  untorn  periosteum,  the  blood-supply  is  ample.  Firm  bony  union  is  therefore 
the  usual  result  in  well-treated  cases.  This  is  favored  by  the  fact,  already  alluded 
to,  that  the  opposing  surfaces  are  nearly  always  in  contact  at  some  point. 

The  portion  of  the  shaft  just  beneath  the  head  and  tuberosities  is  known  as  the 
' '  surgical  neck' '  because  it  is  so  often  the  seat  of  fracture. 

It  contains,  as  will  be  seen  on  examining  a  longitudinal  section  of  the  humerus 
(Fig.  283),  a  considerable  quantity  of  cancellous  tissue,  the  absorption  of  which  in 
old  persons  leaves  the  bone  weak  at  that  point.  The  factors  already  described  as 
favoring  epiphyseal  separation  are  operative  in  this  case  (page  271). 

The  upper  curve  of  the  bone,  beginning  on  this  level,  ends  inferiorly  at  about 
the  lower  margin  of  the  deltoid  tubercle.  Its  convexity  is  forward  and  outward. 
The'  lower  curve  is  concave  forward.  Both  curves  may  be  markedly  increased 
in  rickets.  The  middle  of  the  bone  is  not  only  the  point  of  union  of  these  curves, 
but  is  also  the  smallest  and  hardest  and  least  elastic  portion  of  the  shaft  ;  hence 
it  is  most  frequently  broken,  though  fractures  of  the  shaft  at  various  levels  below 
and  above  this  point  are  not  uncommon.  The  deltoid  tubercle,  when  unusually 
developed,  should  not  be  taken  for  an  exostosis.  The  region  is,  however,  a  fre- 
quent seat  of  bony  outgrowths  on  account  of  the  insertion  and  origin,  respectively, 
of  the  coraco-brachialis  and  deltoid,  and  the  brachialis  anticus  and  internal  head  of 
the  triceps. 

The  close  attachment  of  the  periosteum  to  the  shaft  which  is  thus  necessi- 
tated favors  the  development  of  osteo-periostitis,  and  thus  of  osteophytes  as  a 
consequence  of  repeated  muscular  strains.  Other  favorite  seats  of  exostoses  are  near 
the  insertion  of  the  pectoralis  major,  the  latissimus  dorsi,  and  the  third  head  of 
the  triceps. 

Tumors  of  a  more  serious  variety,  especially  the  sarcomata,  attack  the  h 
merus.  The  central  sarcomata  are  found  in  the  upper  extremity  chiefly  at  th< 
upper  end  of  the  humerus  and  at  the  lower  ends  of  the  radius  and  ulna.  It  may 
be  interesting  to  note  that  those  are  the  extremities  towards  which  the  respective 
nutrient  arteries  are  not  directed,  and  therefore,  in  accordance  with  the  general 
rule,  the  extremities  at  which  bony  union  of  the  epiphyses  and  diaphyses  takes 
place  latest. 

The  close  attachment  of  the  periosteum  at  the  middle  of  the  shaft  has  been  said 
to  account  for  the  fact  that  non-union  after  fracture  occurs  in  this  region  more  fre- 
quently than  in  the  shaft  of  any  other  long  bone  of  the  skeleton.  This  has  also  been 
attributed  to  interference  with  the  nutrient  artery  (which  enters  the  bone  near  its 

1  Owen,  Lejars,  and  others,  quoted  by  Poland. 


PRACTICAL   CONSIDERATIONS  :    THE   HUMERUS. 


273 


FIG.  288. 


middle)  and  to  imperfect  immobilization  of  the  humerus,  the  elbow  being  fixed  by 
splints,  any  motion  of  the  hand  or  forearm  under  those  circumstances  being  trans- 
formed into  motion  of  the  upper  end  of  the  lower  fragment.  These  may  be  factors, 
but  the  chief  reason  for  non-union  is  the  entanglement  of  muscular  and  tendinous 
fibres  of  the  brachialis  anticus  and  of  the  triceps  between  the  bony  fragments  (page 
590). 

Descending  the  shaft  it  is  not  difficult  to  see  why  a  fracture  just  above  the  con- 
dyles  ("at  the  base  of  the  condyles,"  "  supracondylar"  )  should  often  be  met  with. 
The  olecranon  fossa,  the  coronoid  fossa,  the  shallower  fossa  for  the  radius  just  above 
the  external  condyle,  all  contribute  to  weaken  the  bone  at  this  point.  Moreover,  in 
falls  upon  the  elbow  (the  common  cause  of  this  fracture)  the  tip  of  the  olecranon  is 
frequently  driven  directly  into  its  fossa  and  against  the  very  thin  lamina  at  its  base, 
starting  a  fracture  which  extends  laterally  through  the  supracondylar  and  supra- 
trochlear  ridges  to  the  border  of  the  bone.  If  this  transverse 
line  of  fracture  is  associated  with  one  running  perpendicularly 
into  the  joint,  it  constitutes  the  so-called  "  T-fracture"  ("inter- 
condylar' ' )  ;  it  is  produced  in  the  same  manner,  but  usually 
by  a  greater  degree  of  force. 

In  the  so-called  "extension"  and  "flexion"  fractures  in 
this  region  the  same  mechanism  is  probably  present,  though  it 
is  easy  to  imagine  the  same  result  (if  the  capsule  and  ligaments 
of  the  elbow-joint  remain  intact)  without  the  agency  of  the 
olecranon. 

It  should  be  noted  that  the  external  supracondylar  ridge, 
the  strongest  and  most  prominent,  springs  from  the  external 
condyle,  ascends  in  the  line  of  the  shaft,  and  terminates  in  the 
head,  so  that  it  is  well  adapted  to  receive  and  distribute  force 
applied  through  the  radius,  as  in  falls  on  the  hand,  or  in  pushing 
or  striking  strongly.  The  external  is  smaller  than  the  internal 
condyle  because  the  extensors  and  supinators  arising  from  it  are 
less  powerful  muscles  than  the  flexors  and  pronators  connected 
with  the  former.  This  makes  it  less  prominent;  but  in  spite  of 
these  protective  conditions  it  is  at  least  as  frequently  broken,  es- 
pecially from  indirect  violence,  because  of  its  direct  connection 
with  the  hand  through  the  radius  and  capitellum.  On  account 
of  the  dense  triceps  fascia  covering  it,  and  its  connection  with  the 
ligaments  of  the  elbow-joint,  the  displacement  is  slight.  The 
line  of  fracture  usually  passes  through  the  radial  fossa  and  enters 
the  joint  through  the  depression  between  the  capitellum  and 
the  trochlear  ridge. 

The  internal  condyle  is  more  often  broken  by  direct  violence, 
or  by  the  wedge-like  action  of  the  olecranon  starting  a  fracture 
which  runs  through  the  thin  bone  of  the  olecranon  and  coronoid 
fossae,  and  through  the  trochlear  depression.  The  displacement 
is  usually  upward,  is  the  result  of  the  force  causing  the  break, 
and  is  but  little  influenced  by  anatomical  factors.  The  brachialis 

anticus  may  elevate  the  fragment,  but  the  ulna  remains  attached  and  prevents  much 
displacement. 

Either  epiconclyle  may  be  broken.  The  line  of  the  lower  epiphysis  runs 
obliquely  across  the  bone  from  just  above  the  external  epicondyle  to  a  point  just 
below  the  internal  epicondyle.  In  infancy  both  epicondyles  (as  well  as  the 
trochlea  and  capitellum)  enter  into  the  epiphysis  ;  but  at  the  thirteenth  year  the 
internal  epicondyle  is  quite  distinct,  and  the  trochlea,  capitellum,  and  external 
epicondyle  are  welded  into  the  lower  epiphysis  proper,  which  by  the  fourteenth 
to  the  fifteenth  year  (Dwight),  sixteenth  year  (Treves  and  Stimson),  seventeenth 
year  (Poland),  is  firmly  united  to  the  diaphysis.  After  the  thirteenth  year,  there- 
fore, separation  of  the  epiphysis  will  probably  leave  the  internal  epicondyle  attached 
to  the  diaphysis.  "The  point  of  junction  of  the  trochlear  and  capitellar  portions 
of  the  lower  epiphysis  at  the  middle  of  the  trochlear  groove  at  the  sixteenth  year 

18 


Lines  of  fractures  of 
the  humerus.  a,  through 
anatomical  neck ;  b, 
through  tuberosities ;  c, 
through  surgical  neck  ;  rf, 
through  shaft;  e,  T-frac- 
ture involving  condyles. 


274  HUMAN   ANATOMY. 

is  the  narrowest  portion  of  the  bone,  and  much  more  likely  to  be  broken  across, 
detaching  one  or  other  portion  of  bone  rather  than  the  whole  epiphysis  separating 
at  this  age"  (Poland). 

As  the  synovial  membrane  is  attached  on  the  inner  side  about  five  millimetres 
(three-sixteenths  of  an  inch)  below  the  internal  epicondyle,  fracture  of  the  latter 
does  not  necessarily  extend  into  the  joint-cavity.  On  the  outer  side  it  is  attached 
up  to  the  level  of  the  external  epicondyle,  so  that  the  joint  is  likely  to  be  involved 
in  traumatic  separation  of  that  process. 

As  the  capsule  of  the  joint  is  attached  at  a  higher  level  than  the  epiphysis  in 
front,  behind,  and  laterally,  the  displacement  in  epiphyseal  separations  is  within  the 
capsule,  and  therefore  likely  to  be  limited.  The  close  relationship  of  the  synovial 
membrane  gives  rise,  however,  to  extensive  effusion,  which  affects  both  diagnosis 
and  treatment. 

The  union  to  the  diaphysis  at  about  the  fifteenth  year  leaves  the  further  growth 
of  the  bone  dependent  upon  the  upper  epiphysis  (page  272 )  ;  hence  injuries  involving 
the  epiphysis,  or  excision  of  the  elbow  in  which  the  epiphyseal  limits  are  overstepped, 
will  not  be  followed  by  arrest  of  growth  if  the  patient  is  more  than  fifteen  years  of 
age. 

Epiphysitis,  on  account  of  the  synovial  and  capsular  relations  above  described, 
is  apt  to  involve  the  elbow-joint,  and  to  result  in  considerable  stiffness. 

The  anatomical  deformity  and  diagnosis  of  epiphyseal  separation  will  be  con- 
sidered in  connection  with  the  subjects  of  supracondylar  fracture  and  luxation  of  the 
elbow  (page  590). 

About  two  inches  above  the  inner  condyle  there  is  often  found  (one  per  cent, 
of  recent  skeletons,  Turner)  a  hook-like  process  projecting  downward  and  converted 
into  a  foramen  by  a  ligamentous  band.  When  it  is  present  the  median  nerve 
usually  passes  through  it,  which  demonstrates  that  "  it  is  the  homologue  and  rudi- 
ment of  the  supracondyloid  foramen  of  the  lower  animals"  (Darwin).  The  process 
can  sometimes  be  recognized  by  the  sense  of  touch.  The  intercondylar  foramen, 
which  is  occasionally  present  in  man,  occurs,  but  not  constantly,  in  various  anthro- 
poid apes,  and,  though  it  weakens  the  bone  somewhat,  is  chiefly  interesting  because 
it  is  found  in  much  greater  frequency  in  skeletons  of  ancient  times,  and  thus  illus- 
trates Darwin's  assertion  that  "ancient  races  more  frequently  present  structures 
which  resemble  those  of  the  lower  animals  than  do  modern." 

THE   SHOULDER-JOINT. 

The  ligaments  of  this  articulation  are  : 

Capsular ;  Glenoid 

Accessory  ligaments  : 

Coraco-Humeral  ;     Gleno-Humeral. 

This  is  a  very  simple1  instance  of  the  ball-and-socket  joint,  the  only  irregularity 
being  the  position  of  the  humeral  head  somewhat  on  one  side  instead  of  at  the  top 
of  the  bone,  so  that  the  axis  of  rotation  does  not  correspond  with  tin-  axis  of  the 
shaft. 

The  shallow  socket  of  the  glenoid  cavity,  lined  with  articular  cartilage,  is 
deepened  by  the  glenoid  ligament'  (Figs.  290,  292),  a  fibro-cartilaginous  band 
attached  by  its  base  to  the  border  of  the  cavity  and  ending  in  a  sharp  edge.  It  is 
thus  triangular  on  section  (Fig.  291),  the  breadth  of  the  base-  being  live-  millimetres 
and  the  height  at  its  greatest  about  one  centimetre.  This  ligament  is  composed 
chiefly  of  fibres  running  around  the  socket.  It  is  directly  continuous  with  the  fibres 
of  the  long  head  of  the  biceps  from  the  insertion  of  the  latter  into  the  top  of  the 
socket. 

The  capsular  ligament2  (Fig.  289)  is  so  lax  that  in  the  dissected  joint  the 
head  of  the  humerus  falls  away  from  the  socket.  In  life  it  is  kept  in  place  chiefly 
by  the  tonicity  of  the  surrounding  muscles.  The  course  of  the  tilnvs  is  in  the  main 
longitudinal,  but  they  are  indistinct.  Tin-  capsule  arises  above  from  tin-  edge  of  the 

1  Lalirum  ulcnoidalc.     "Capsulu  artirularis. 


THE   SHOULDER-JOINT. 


275 


glenoid  cavity  and  the  bone  just  around  it,  from  the  outer  surface  of  the  glenoid 
ligament  as  far  as  its  edge,  excepting  at  the  top,  where  it  does  not  encroach  on  the 
ligament,  and  at  the  inner  side,  where  its  origin  is  uncertain.  It  may  arise  there  as 


FIG.  289. 


Coracoacromial  ligament 
Bursa 


Trapezoid  ligament 
Clavicle 


Capsule 


Long  head  of 
biceps 


Humerus 


Conoid  ligament 


Suprascapular  ligament 


Right  shoulder-joint  from  before. 


described,  but  very  often  it  arises  at  some  distance  from  the  border  of  the  joint  from 
the  anterior  surface  of  the  scapula.  In  exceptional  cases  this  distance  may  be  half 
an  inch,  perhaps  more.  The  inferior  attachment  of  the  capsular  ligament  is  to  the 


FIG.  290. 

Acromio-clavicular  joint 


Acromion 


Tendon  of  biceps 


Head  of  humerus 


Glenoid  ligament 
Glenoid  cavity 

Spine  of  scapula 


<Mty  Superior  gleno-humeral  ligament 

-Anterior  border  of  scapula 

Right  shoulder-joint,  capsule  opened  and  humerus  everted. 

groove  round  the  head,  close  to  the  latter  above  and  externally,  but  a  little  way 
from  it  below  and  internally.      This  applies  to  the  attachment  as  seen  from  within 


276 


HUMAN   ANATOMY. 


the  opened  joint  ;  on  the  outside,  the  fibres  can  be  traced  for  a  considerable  distance 
from  the  joint  before  they  are  lost  in  the  periosteum.  Fibres  going  to  the  tuberosi- 
ties  blend  with  the  tendons  of  insertion  of  the  muscles  of  the  scapular  group,  the 
supra-  and  infraspinati,  the  teres  minor,  and  the  subscapularis,  which  materially 
strengthen  the  capsule.  The  latter  is  thinnest  behind. 

Certain  accessory  ligaments  strengthen  the  capsule.  The  most  important  is 
the  coraco-humeral  (Fig.  289),  which,  arising  from  the  outer  edge  of  the  horizontal 
portion  of  the  coracoid  where  a  bursa  separates  it  from  the  capsule,  soon  fuses  with 
the  latter  and  runs,  without  very  distinct  borders,  to  both  tuberosities,  crossing  the 
bicipital  groove.-  A  few  transverse  fibres  (the  transverse  humeral  ligament }  bridge- 
in  the  bicipital  groove  below  the  capsule  proper.  Three  gleno-humeral  bands  (  Fig. 
290)  are  described  on  the  inside  of  the  capsule,  of  which  the  most  important  is  the 


Tendon  of  subscapularis  and  capsule 


FIG.  291. 

Lesser  tuberosity 


Tendon  of  biceps  in  bicipital  groove 


Glenoid  ligament 


Glenoid  cavity 


Glenoid  ligament 


, —  Greater  tuberosity 


Subdeltoid  bura 


on  of  infraspinatus 
d  capsule 


Horizontal  frozen  section  through  the  right  shoulder-joint  from  above. 


superior.  This  band  springs  from  near  the  top  of  the  inner  border  of  the  glenoid 
cavity  and  is  inserted  into  the  lesser  tuberosity.  In  a  part  of  its  course  it  makes  a 
prominent  fold  of  the  synovial  membrane  along  the  inner  border  of  the  tendon  of 
the  long  head  of  the  biceps.  This  ligament  has  been  described  as  a  deep  part  of  the 
coraco-humeral.  The  middle  ligament  is  ill-defined.  The  inferior,  running  from 
the  lower  end  of  the  glenoid  socket  to  the  inner  side  of  the  neck  of  the  humerus, 
may  be  seen  both  from  without  and  within  the  capsule.  It  is  made  tense  when  the 
arm  is  abducted,  and  materially  strengthens  the  joint.  The  capsule  usually  presents 
an  opening  on  the  inner  side  in  the  upper  part,  by  which  the  bursa  below  tin-  tendon 
of  the  subscapularis  communicates  with  the  joint.  The  cases  in  which  the  capsule 


THE   SHOULDER-JOINT. 


277 


arises  internally  at  quite  a  distance  from  the  glenoid  cavity  are  probably  due  to  a 
very  free  opening  into  a  large  bursa.  The  tendon  of  the  long  head  of  the  biceps 
lies  within  the  capsule  from  its  origin  at  the  top  of  the  glenoid  till  it  leaves  the  cap- 
sule in  the  bicipital  groove.  The  tendon  does  not  lie  free  within  the  joint,  but  is 
covered  by  a  reflection  of  the  synovial  membrane  as  it  lies  curved  over  the  head  of 
the  humerus.  On  the  young  foetus  it  is  attached  to  the  inside  of  the  capsule  by  a 
synovial  fold.  The  synovial  membrane  of  this  joint  is  remarkably  free  from  synovial 
fringes. 

The  bursae  about  the  joint  are  numerous.  The  largest  is  the  subacromial  or 
subdeltoid  bursa  (Figs.  291,  292),  situated  between  the  top  of  the  capsule,  the 
coraco-acromial  ligament,  and  the  acromion,  and  extending  downward  under  the 
deltoid.  The  subcoracoid  bursa  separates  that  process  and  the  beginning  of  the 

FIG.  292. 


Clavicle 


Coraco-clavicular  ligament 


Coracoid 
process 


Capsule. 


Subdeltoid  bur: 


Deltoid  muscle 


Frontal  frozen  section  through  the  right  shoulder-joint. 


coraco-humeral  ligament  from  the  capsule.  Other  bursae  are  often  found  between 
the  capsule  and  the  muscles  inserted  into  the  tuberosities  ;  that  under  the  subscapii- 
laris  is  constant.  Of  the  others,  the  one  most  frequently  found  is  under  the  infra- 
spinatus  ;  it  also  may  open  into  the  joint. 

Movements. — When  the  arm  is  hanging  close  to  the  side  adduction  is  almost 
wanting,  since,  apart  from  the  interference  of  the  body,  the  humerus  is  arrested 
at  once  by  the  lower  border  of  the  glenoid  cavity.  Backzvard  movement  is  not 
free,  for  the  arm  soon  impinges  on  the  overhanging  acromion.  Abduction  has  a 
range  of  some  90°  before  the  tenseness  of  the  lower  part  of  the  capsule  stops  it. 


278  HUMAN   ANATOMY. 

(Unless  the  arm  is  raised  somewhat  forward,  it  is  stopped  still  sooner  by  the 
acromion. )  Forward  movement  is  about  equal  to  abduction,  and  is  checked 
in  the  same  way.  When  the  arm  is  at  a  right  angle  with  the  body,  the  range  of 
motion  in  a  horizontal  plane  is  about  90°.  The  degree  of  rotation  in  the  shoulder 
is  very  variable.  It  is  greatest  when  the  arm  is  partially  abducted,  when  in  a  dis- 
sected joint  it  may  approximate  135°.  When  raised  to  a  right  angle  it  is  about 
90°,  and  in  the  hanging  arm,  if  not  closely  adducted,  nearly  the  same.  Circum- 
duction  is  free. 

Probably  none  of  the  important  joints  is  so  dependent  on  others  as  that  of  the 
shoulder.  The  scapula  takes  part  in  practically  all  the  movements,  not  waiting  till 
the  range  of  movement  at  the  shoulder  is  exhausted,  but  sharing  in  it  from  the  start. 
The  acromion  and  coraco-acromial  ligament  make  an  extra  socket  under  certain  cir- 
cumstances, as  when  the  body  is  supported  by  the  arms,  the  subacromial  bursa  act- 
ing as  a  synovial  membrane.  The  long  head  of  the  biceps  is  a  great  assistance  to 
the  stability  of  the  joint,  the  muscle  pulling  the  bones  firmly  together  and  making 
them  rigid  under  circumstances  of  strain.  It  has  the  further  advantage  over  a  liga- 
ment that  its  tension  can  vary  without  change  of  position. 

PRACTICAL   CONSIDERATIONS. 

The  extremely  wide  range  of  motion  of  the  humerus  upon  the  scapula  in  the 
human  species  is  associated,  for  mechanical  reasons,  with  many  anatomical  conditions 
of  interest  to  the  surgeon.  The  most  important  of  these  conditions  in  relation  to 
displacement  are:  (i)  The  shallowness  of  the  glenoid  cavity.  (2)  The  relatively 
large  size  of  the  humeral  head,  only  one-third  of  which  is  in  contact  with  the  glenoid 
surface  when  the  arm  is  by  the  side  of  the  body.  (3)  The  thinness  and  the  great 
laxity  of  the  capsule,  which,  if  fully  distended,  would  accommodate  a  bulk  twice  as 
large  as  the  head  of  the  humerus.  This  laxity  (to  permit  of  free  elevation  of  the 
arm )  is  greater  at  the  inferior  portion  of  the  joint.  The  primary  office  of  the  cap- 
sular  ligament  in  this  joint  is  not  to  maintain  apposition,  but  to  limit  movement. 
(4)  The  maintenance  of  the  contact  between  the  articular  surfaces  by  muscular 
action,  aided  by  atmospheric  pressure,  and  not  by  the  ligamentous  or  capsular  at- 
tachments. (5)  The  length  of  the  humerus,  affording  a  very  long  leverage  ;  and 
the  exposed  position  of  the  shoulder. 

All  these  circumstances  favor  dislocation,  and  render  this  joint  more  frequently 
the  subject  of  that  accident  than  any  other  joint  in  the  body.  The  usual  position  in 
which  luxation  occurs  is  that  of  abduction  and  advancement  of  the  arm,  as  in  falls 
on  the  hand. 

It  is  to  be  noted  that  this  attitude  brings  the  most  prominent  part  of  the  lower 
edge  of  the  head  of  the  bone  against  the  thinnest  and  weakest  part  of  the  capsule. 
Moreover,  the  greatest  diameter  of  the  head  of  the  humerus  is  involved,  adding  to 
the  pressure  against  the  capsule  (Fig.  293).  As  such  accidents  happen  suddenly, 
the  muscles  are  usually  taken  off  their  guard,  and  hence  that  source  of  protection  to 
the  joint  is  lacking. 

As  opposed  to  these  factors,  and  as  tending  to  prevent  displacement,  should  be 
mentioned  :  (i)  The  exceptional  relation  of  the  biceps  tendon  to  the  joint,  strength- 
ening the  capsule  at  its  upper  portion,  preventing  the  humerus  from  being  too 
strongly  pressed  against  the  acromion  by  the  powerful  deltoid  and  the  other 
elevators  of  the  arm  ;  steadying  the  head  of  the  bone  through  its  connection  in  the 
bicipital  groove,  in  which  way  "  it  serves  the  purpose  of  a  ligament,  with  the  advan- 
tage of  being  available  in  all  positions  of  the  joint,  and  without  restricting  the  range 
of  movement  in  any  direction"  (Humphry).  (2)  The  arrangement  of  the  glenoid 
cup,  the  inner  and  lower  edges  of  which  are  more  prominent  than  the  outer  and 
upper,  resisting  somewhat  the  tendency  of  the  powerful  axillary  muscles,  and  of 
blows  on  the  shoulder,  to  displace  the  humerus  inward,  and  of  falls  with  the  arm  in 
abduction,  to  displace  it  downward.  (3)  The  glenoid  ligament  deepening  the 
articular  cavity,  and  aided  in  this  by  the  insertions  of  the  long  head  of  the  bice] is 
above  and  the  scapular  head  of  the  triceps  below.  (4)  The  resistance  offered  by 
the  strong  coraco-acromial  ligament  to  any  upward  displacement.  If  it  were  not  for 


PRACTICAL   CONSIDERATIONS  :    THE   SHOULDER-JOINT.      279 


these  provisions,  luxations  of  the  shoulder  would  be  even  more  frequent  than 
they  are. 

The  head  of  the  bone  may  leave  the  joint-cavity  at  other  points  than  the  in- 
ferior. If  the  force  is  so  applied  as  to  drive  the  head  of  the  bone  against  the  cap- 
sule at  the  anterior  portion,  a  direct  subcoracoid  luxation  may  result  ;  if  against  the 
posterior  portion,  a  subspinous.  The  latter  is  very  rare,  and  the  former  is  also  rare 
as  a  primary  luxation. 

The  further  mechanism  of  luxations,  their  deformities  and  anatomical  diagnosis, 
will  be  considered  after  the  muscles,  which  are  such  important  factors  in  producing 
and  modifying  them,  have  been  described  (page  582). 

Disease  of  the  shoulder-joint  may  be  of  any  variety.  In  spite  of  the  frequent 
strains  to  which  the  joint  is  subjected  and  its  wide  range  of  movement,  the  diseases 
produced  by  traumatism  are  not  exceptionally  frequent.  This  is  probably  because 
of  ( i)  its  ample  covering  of  muscles  protecting  it  from  the  effects  of  cold  and  damp. 
(2)  The  mobility  of  the  scapular  segment  of  the  shoulder-girdle  lessening  greatly 
the  effect  of  traumatisms.  (3)  The  laxity  of  its  capsular  and  synovial  elements, 
which,  though  it  favors  luxation,  permits  a  moderate  effusion  to  occur  without  harm- 
ful tension.  (4)  The  influence  of  the  weight  of  the  upper  extremity  in  the  usual 
position  of  the  body  in  resisting  by  gravity  the  destructive  pressure  of  joint  surfaces 
against  each  other,  caused  by  muscular  spasm  after  injury  or  during  disease.  (5)  The 


Spine  of  scapula 


FlG.    293. 


Supraspinatus 

Reflection  of  capsule 


Deltoid 


Reflection  of  capsule 


Infraspinatus        Head  of  scapula         Teres  minor 

Section  through  right  shoulder-joint  with  arm  in  abduction. 

ease  with  which  the  joint  may  be  immobilized  without  irksome  confinement  of  the 
patient. 

These  circumstances,  especially  the  latter,  account  also  for  the  facts  that  tuber- 
culous disease  of  the  joint  and  epiphysitis  involving  the  joint  are  not  so  common  as 
in  other  joints,  and  that  the  results  are  exceptionally  good,  operative  interference 
being  required  with  comparative  rarity. 

Synovial  distention  causes  a  uniform  rounded  swelling  of  the  shoulder,  but  it 
can  best  be  recognized  by  the  touch  in  the  bicipital  groove,  where  one  synovial 
diverticulum  runs,  and  in  the  axilla,  where  part  of  the  capsule  is  exposed  beyond 
the  margin  of  the  subscapular  muscle.  The  diverticula  beneath  the  tendons  of  that 
muscle  and  (more  rarely)  of  the  infraspinatus  are  usually  involved,  pain  when  the 
arm  is  rotated  being  a  resultant  symptom. 

The  subdeltoid  bursa  does  not  usually  communicate  with  the  joint.  It  may 
be  the  subject  of  independent  disease.  When  it  is  inflamed  the  position  of  ease 
will  be  one  which  relaxes  the  deltoid  (abduction  of  the  arm),  and  rotation  or 
pressure  upward  will  be  painless.  In  disease  of  the  subacromial  bursa,  abduc- 
tion and  upward  pressure  are  painful  because  the  sac  is  then  pinched  between 


280  HUMAN   ANATOMY. 

the  head  of  the  bone  and  the  under  surface  of  the  acromion  and  coraco-acromial 
ligament. 

When  suppuration  occurs,  pus  may  find  its  way  out  from  the  joint.  ( i )  By 
following  the  bicipital  tendon  and  opening  on  the  arm  below  the  anterior  border  of 
the  axilla.  (2)  By  following  the  subscapular  tendon,  getting  between  that  muscle 
and  the  body  of  the  scapula,  and  opening  beneath  and  behind  the  axilla.  (3)  By 
penetrating  the  capsule  beneath  the  deltoid,  when  the  dense  deltoid  and  infraspinous 
fascia  prevent  it  from  going  backward  and  direct  it  to  the  anterior  aspect  of  the 
arm.  Treves  mentions  a  case  in  which  it  followed  the  course  of  the  musculo-spiral 
nerve  and  appeared  on  the  outer  side  of  the  elbow. 

Landmarks. — The  edge  of  the  acromion  and  the  tip  of  the  coracoid  can 
readily  be  felt,  though  the  coraco-acromial  ligament  completing  the  important  arch 
above  the  joint  is  beneath  the  deltoid,  and  therefore  cannot  be  so  distinctly  pal- 
pated, but  can  usually  be  recognized  by  touch.  An  incision  through  the  centre 
of  this  ligament  would  open  the  shoulder-joint  where  the  bicipital  tendon  enters 
its  groove.  The  head  of  the  bone,  when  pressed  upward  against  this  arch,  com- 
municates motion  to  the  outer  fragment  in  cases  of  fractured  clavicle,  and  this  is 
often  the  easiest  way  in  that  lesion  of  eliciting  crepitus  and  preternatural  mobility. 
In  cases  of  paresis  or  paralysis  of  the  deltoid,  the  resultant  atrophy  may  leave  the 
whole  arch  palpable,  or  even  visible,  in  some  instances  the  bone  dropping  from  one 
to  several  inches. 

The  lower  margin  of  the  glenoid  cup  and  the  head  of  the  humerus  may  be  felt 
in  the  axilla  when  the  arm  is  abducted  (Fig.  293). 

The  greater  tuberosity  may  be  felt  through  the  deltoid,  directly  beneath  the 
acromion,  the  arm  hanging  at  the  side.  It  faces  in  the  direction  of  the  external 
condyle.  Together  with  the  lesser  tuberosity  it  produces  the  normal  roundness  of 
the  deltoid. 

The  head  of  the  bone  cannot  be  felt  externally.  It  faces  in  the  general  direction 
of  the  internal  condyle.  Two-thirds  of  it,  when  the  arm  is  by  the  side,  is  in  front 
of  a  vertical  line  drawn  from  the  anterior  border  of  the  acromion  process.  It  is  also 
altogether  external  to  the  coracoid  process. 

The  lesser  tuberosity  faces  forward.  Between  it  and  the  greater  tuberosity, 
when  the  arm  is  hanging  loosely  and  is  supine,  the  lower  part  of  the  bicipital  groove 
may  be  felt  in  thin  subjects.  This  also  faces  directly  forward,  and  is  on  a  line  drawn 
through  the  middle  of  the  biceps  and  its  lower  tendon. 

The  upper  part  of  the  humeral  shaft  cannot  be  felt.  The  circumflex  nerve  winds 
around  it  a  little  above  the  middle  of  the  deltoid.  The  deltoid  tubercle  may  be 
recognized  at  the  middle  of  the  arm.  From  there  downward  the  bone  is  more 
superficial  externally,  and  the  outer  supracondylar  ridge  may  be  traced  down  to  the 
condyle.  The  less  prominent  internal  ridge  can  be  felt  only  for  a  short  distance 
above  the  elbow. 

The  middle  of  the  humerus,  indicated  by  the  insertion  of  the  deltoid  on  the 
outer  side,  is  also  on  a  level  with  that  of  the  coraco-brachialis  on  the  inner  and  with 
the  upper  portion  of  the  brachialis  anticus  on  the  anterior  surface,  with  the  origin 
of  the  nutrient  and  inferior  profunda  arteries,  with  the  exit  through  the  deep  fascia 
of  the  nerve  of  Wrisberg  and  the  entrance  of  the  basilic  vein,  with  the  pa>sa^<-  <>f 
the  median  nerve  across  the  brachial  artery,  and  with  the  departure  of  the  tilnar 
nerve  from  its  proximity  to  the  vessel.  Posteriorly,  the  middle  of  the  bone  is  covered 
by  the  triceps. 

Just  below  the  middle  the  musculo-spiral  nerve  and  the  superior  profunda  wind 
around  in  the  groove  below  the  deltoid  insertion,  and  the  inner  head  of  the  triceps 
arises  from  the  bone. 

At  the  junction  of  the  middle  and  lower  thirds  the  brachial  artery  from  the 
inner  side  and  the  musculo-spiral  nerve  from  the  outer  side  tend  to  approach  the 
front  of  the  bone. 

The  landmarks  at  the  lower  extremity  will  be  considered  in  relation  to  the 
elbow-joint  and  the  bones  of  the  forearm. 

The  surface  anatomv  and  the  relations  of  the  soft  parts  to  the  humerus  will  be 
KM urrod  to  after  those  structures  have  been  described. 


THE   ULNA.  281 


THE   FOREARM. 

The  skeleton  of  the  forearm  consists  of  two  bones, — an  inner,  the  ulna,  and  an 
outer,  the  radius.  The  former  is  large  above  and  small  below  ;  the  latter,  the  con- 
verse. The  ulna  plays  around  the  trochlea  in  flexion  and  extension,  carrying  the 
radius  with  it.  The  radius  plays  on  the  ulna  in  pronation  and  supination,  carrying 
with  it  the  hand.  These  bones  are  connected  by  an  interosseous  membrane,  which 
gives  origin  to  muscles,  adds  to  the  security  of  the  framework,  and  yet  implies  a 
great  saving  in  weight. 

THE    ULNA. 

The  ulna  consists  of  a  shaft  and  two  extremities. 

The  upper  extremity  is  devoted  to  the  joint  with  the  humerus,  and  laterally 
to  that  with  the  head  of  the  radius.  The  former  articular  surface  is  the  greater  sig- 
moid cavity  hollowed  out  of  the  continuous  surfaces  of  the  olecranon  process  behind 
and  above  and  the  coronoid  process  in  front.  The  olecranon,1  a  cubical  piece  of 
bone  projecting  upward  in  continuation  with  the  shaft,  presents  this  articular  surface 
in  front  (to  be  described  later),  and  a  superior,  a  posterior,  and  two  lateral  surfaces. 
The  siiperior  surface  is  pointed  in  front,  with  the  ooint  or  beak  external  to  the 
middle.  A  slight  groove  just  back  of  the  edge  serves  for  the  attachment  of  the 
capsular  ligament.  Behind  this  are  two  parts  of  different  texture,  the  posterior  of 
which  is  for  the  insertion  of  the  triceps.  The  posterior  surface  is  triangular,  bounded 
above  by  the  irregular  edge  of  the  top,  and  laterally  by  two  lines  which  meet  below 
to  make  the  posterior  border  of  the  shaft.  It  is  subcutaneous,  and  is  covered  by  a 
bursa  (Fig.  294).  The  outer  stirface  is  bounded  in  front  by  the  sharp  edge  of  the 
sigmoid  cavity,  along  which  is  the  groove  for  the  capsule.  Behind  this  is  a  hollow 
for  the  anconeus.  The  inner  surface  has  in  front  the  inner  border  of  the  sigmoid, 
less  sharp  than  the  outer,  the  capsular  groove,  and  farther  back  a  rough  elevation. 
The  coronoid  process  z  rises  from  the  anterior  surface  of  the  front  of  the  shaft.  It 
has  an  upper,  articular  surface,  an  anterior,  and  two  lateral  ones.  The  front  surface 
rises  to  a  point  nearer  the  outer  side.  The  capsular  groove  runs  along  the  border  ; 
and  below  this,  bounded  by  two  lines  meeting  below,  is  a  rough  region  for  the 
brachialis  anticus.  Within  the  angle  formed  by  the  meeting  of  these  two  lines  is  a 
rough  rounded  space,  the  tuberosity  of  the  ulna,  from  the  edge  of  which  arises  the 
oblique  ligament.  The  brachialis  anticus  is  inserted  into  the  lower  part  of  this  sur- 
face and  the  tuberosity.  The  inner  surface  is  bounded  above  by  the  sharp  project- 
ing border  of  the  sigmoid  cavity,  at  the  edge  of  which  is  a  rough  prominence  from 
which  certain  fibres  of  the  flexor  sublimis  digitorum  take  origin.  The  outer  surface 
presents  the  lesser  sigmoid  cavity. 

The  greater  sigmoid  cavity 3  occupies  the  anterior  surface  of  the  olecranon  and 
the  superior  one  of  the  coronoid  process.  There  is  a  constriction  in  the  middle  of 
both  borders,  but  deeper  in  the  outer,  where  the  two  processes  meet,  and  the  articu- 
lar surface  on  the  dry  bone  seems  often  to  be  interrupted  in  a  line  between  them. 
The  sigmoid  cavity,  concave  from  above  downward,  is  broader  in  the  upper  half  than 
the  lower.  It  is  surrounded,  except  where  it  is  joined  by  the  lesser  sigmoid  cavity, 
by  an  ill-marked  groove  for  the  capsular  ligament.  The  articular  surface  is  subdivided 
by  a  rounded  ridge,  running  from  the  point  of  the  olecranon  to  that  of  the  coronoid, 
into  a  larger  inner  and  a  smaller  outer  portion.  The  course  of  this  ridge  is  generally 
somewhat  inward  as  well  as  downward.  This  and  the  cross-line  divide  the  articular 
surface  into  four  spaces.  Of  the  upper,  the  inner  is  concave  and  the  outer  convex 
from  side  to  side.  Of  the  lower,  the  inner  is  concave  in  the  same  direction  and  the 
curve  of  the  outer  is  uncertain  ;  probably,  as  a  rule,  slightly  concave,  it  may  be 
plane  or  a  little  convex. 

The  lesser  sigmoid  cavity,4  for  the  head  of  the  radius,  is  a  concavity  on  the 
outer  side  of  the  coronoid  process,  separated  from  the  greater  by  a  ridge,  which 
does  not  interrupt  the  cartilage  coating  both.  It  generally  is  an  oblong  quadrilateral 
area  forming  about  one-sixth  of  the  circumference  of  a  cylinder,  with  parallel  borders  ; 

'Olecranon.     -  Processus  coronoideus.     3Incisura  semilunaris.     4  Incisura  radialis. 


282 


HUMAN   ANATOMY. 


FIG.  294. 


FIG.  295. 


Triceps 


Subcutaneou 
surface 

Flex,  sublim 
digitorum 


Aponeurosis  of 
ext.  carpi  ulnaris, 
flex,  profundus 
digitorum  and 
flex,  carpi  ulnaris 


Lesser  sigmoid 
cavity 


Posterior  border 


Upper  end  of  right  ulna,  posterior  aspect. 


Tip  of  olecranon 


Greater  — 
sigmoid  cavity 


Tuberosity 


Nutrient  canal. 
Interosseous  border- 


-Anterior  border 


Brachialis  anticus 
Supinator  brevi* 


Flex,  profund \ 

digitorum 


Flex,  sublim.  dig. 
(coronoid  head) 
Pronat.  radii  teres 
(lesser  head) 
Flex.  long,  pollicis 
(accessory  head) 


J—  Pronator  qttadratus 


Styloid  process 


Right  ulna,  inner  aspri-t.     Tin-  nutliin-  li^un-  sln>\vs  tin.-  ;uvus  ot  inusi-tihir  ;iti:n. •littK-nt. 


THE    ULNA. 


283 


FIG.  296. 


(  Olecranon  tip 
Greater  sigmoid  cavity 


)  Coronoid 
process 


Lesser  sigmoid 
cavity 


-Supinator  ridge 


nterosseous  border 
— Vertical  ridge 


Triceps 


Anconeus 


Ext.  carpi  ulnaris— 


I 
{ 
Supinator  brevis 


—  Ext.  ossis  met.  pollicis 


—  Ext.  long,  pollicis 


—  Ext.  indicis 


Groove  for  ext.. 
carp,  ulnar. 

Styloid  process . 


Right  ulna,  outer  aspect.    The  outline  figure  shows  the  areas  of  muscular  attachment. 


284 


HUMAN    ANATOMY. 


...••••:• 

••'••if.'- 


but  sometimes  the  front  border  is  short  and  the  inferior  runs  obliquely  backward, 
making  it  almost  triangular. 

The  shaft,1  which  presents  three  borders  and  three  surfaces,  steadily  diminishes 
from  above  downward.  In  the-  upper  part  the  bone  curves  slightly  backward  and 
outward  (i.e. ,  towards  the  radius),  then  inward  through  the  greater  part  of  its 
extent,  till  at  the  lower  quarter  it  again  bends  outward  and,  at  the  same  time,  for- 
ward. The  posterior  border'  is  formed  by  the  union  of  the  two  lines  bounding  the 
subcutaneous  surface  at  the  back  of  the  olecranon.  Following 
FIG.  297.  the  curves  just  described,  it  runs  to  the  back  of  the  styloid 

process,  being  very  distinct  in  the  first  two-thirds,  where  it  gives 
origin  to  the  aponeurosis  of  the  flexor  carpi  ulnaris.  The  anterior 
border?  springing  from  the  junction  of  the  front  and  inner  sides 
of  the  coronoid,  runs  down  to  end  just  above  the  front  of  the 
styloid  process.  Its  last  quarter,  which  is  rough  to  give  origin  to 
the  pronator  quadratus,  has  a  backward  slant.  The  outer  or  in- 
terosseous  border*  is  very  sharp  in  the  middle  two-fourths  of  the 
shaft,  where  it  gives  origin  to  that  membrane.  It  begins  above 
by  the  union  of  two  lines,  which,  starting  from  the  front  and 
back  of  the  lesser  sigmoid  cavity,  bound  a  triangular  depression. 
The  posterior  of  these  lines,  sharp  and  raised,  is  the  supinator 
ridge.  The  depression  which  gives  origin  to  the  supinator  brevis 
receives  the  bicipital  tuberosity  of  the  radius  in  pronation.  The 
border  becomes  indistinct  below  and  is  lost  as  it  approaches  the 
head  of  the  ulna.  The  anterior  surface  is  usually  concave  through- 
out, though  the  upper  part  may  be  convex.  In  the  third  quarter 
a  line  often  appears  which  slants  downward  into  the  front  border, 
giving  origin  to  the  upper  fibres  of  the  pronator  quadratus. 
Below  this  line,  when  present,  there  is  a  depression  occupied  by 
that  muscle.  Above  this  arises  the  flexor  profundus  digitorum. 
The  nutrient  foramen  running  upward  is  a  little  above  the  mid- 
dle. The  inner  surface,  concave  at  the  side  of  the  upper  ex- 
tremity and  convex  below,  gives  further  origin  in  its  upper  two- 
thirds  to  the  last-named  muscle.  The  posterior  surface  has 
several  features  which  are  to  be  recognized  only  on  a  well-marked 
bone,  and  are  very  variable.  The  oblique  line  starts  from  the 
supinator  ridge,  or  from  the  hind  edge  of  the  lesser  sigmoid  cav- 
ity, and  runs  downward  to  the  posterior  border  at  the  end  of 
the  first  third.  It  gives  origin  to  a  part  of  the  supinator  brevis, 
and  helps  to  mark  off  a  three-sided  depression  running  onto 
the  olecranon  for  the  anconeus.  It  is  sometimes  the  apparent 
continuation  of  the  supinator  ridge,  as  in  Fig.  296.  The  region 
below  this  is  subdivided  by  a  vertical  ridge  of  uncertain  beginning 
and  end.  Sometimes  it  springs  from  the  interosseous  border, 
and  it  is  usually  lost  below  in  the  hind  one.  The  extensor  carpi 


ulnaris  springs  from  the  surface  internal   to   it,  which  is  some- 
times a  deep  gutter.       External  to  the  vertical  ridge  are  areas 


Longitudinal  section 
of  ulna. 


for  the  extensor  ossis  metacarpi  pollicis,  extensor  longus  pol- 
licis,  and  extensor  indicis  from  above  downward  in  the  order 
named. 

The  lower  extremity  of  the  ulna  consists  of  the  head  and 
the  styloid  process.  The  head'  is  a  rounded  enlargement  pro- 
jecting forward  and  outward,  presenting  an  articular  surface  on 
the  outer  side,  which  passes  onto  the  front  and  the  back,  making 
at  least  two-thirds  of  a  circle,  around  which  the  radius  swings.  A  ridge  marks 
the  upper  border  of  this  surface,  which  overhangs  the  lower.  The  latter  is  rounded, 
so  that  the  lateral  articular  surface  continues  without  real  interruption  into  the 
inferior,  which  is  separated  from  the  wrist-joint  by  the  triangular  tibro-cartilage. 
The  under  side  of  the  articular  surface  is  somewhat  kidney-shaped,  the  concavity 
looking  towards  the  styloid  process,  from  which  it  is  separated  by  a  groove  for  the 

1  Corpus  ulnnc.     -  Margo  ilnrxilis.        \largovotaris.     4Crlsta  intcrossea.     '' Ciipitiiluin. 


I 


PRACTICAL   CONSIDERATIONS  :    THE   ULNA. 


285 


attachment  of  the  fibre -cartilage.  The  styloid  process  is  a  short,  slender  process 
running  down  from  what  may  be  called  the  posterior  internal  angle  of  the  lower 
end.  There  is  a  distinct  groove  between  the  styloid  process  and  the  head  on  the 
posterior  aspect,  and  sometimes  a  faint  one  in  front,  transmitting  respectively  the 
tendons  of  the  extensor  and  the  flexor  carpi  ulnaris. 

Structure.— There  is  much  solid  bone  in  the  shaft,  and  altogether  the  ulna  is 
a  strong-walled  bone.  Many  plates  near  together  from  the  anterior  surface  pass 
upward  under  the  coronoid  process  to  the  middle  of  the  greater  sigmoid  notch. 
The  best-marked  system  of  plates  in  the  coronoid  is  in  the  main  parallel  to  these. 
The  greater  sigmoid  notch  is  bounded  by  compact  substance.  Sagittal  sections 
show  plates  radiating  from  it,  some  of  which  form  arches  near  the  top  of  the 
olecranon  with  others  from  the  posterior  surface.  The  head  is  composed  of  spongy 
tissue  within  thin  walls. 

Development.— The  centre  for  the  shaft  appears  in  the  eighth  week,  from 
which  practically  all  the  bone  except  the  lower  end  is  developed.  At  about  five, 


Ossification  of  ulna.    A,  at  birth  ;  B,  at  five  years ;  C,  at  ten  years  ;  D,  at  about  sixteen  years,    a,  centre  for 
shaft ;  b,  c,  cartilaginous  epiphyses  ;  d,  centre  for  lower  epiphysis  ;  e,  for  upper  epiphysis. 

one  appears  for  the  head  and  styloid  process  ;  and  at  about  ten,  one  for  the  top  of 
the  olecranon.    This  fuses  at  about  sixteen  ;  the  lower  end  joins  the  shaft  at  eighteen. 

PRACTICAL   CONSIDERATIONS. 

The  ulna  may  be  absent,  or  may  be  more  or  less  defective  in  size  or  shape. 
Such  deformities  are  not  common.  Fracture  of  the  olecranon  at  its  junction  with 
the  shaft,  where  it  is  narrowed,  is  frequent.  The  degree  of  displacement  is  largely 
determined,  as  in  the  parallel  case  of  the  patella,  by  the  amount  of  laceration  of 
the  enveloping  fibrous  structure.  If  this  is  great,  the  triceps  strongly  elevates 
the  fractured  process.  Occasionally  the  mere  tip  of  the  olecranon,  or  even  a  thin 
portion  of  the  superficies  only,  may  be  separated  either  by  muscular  action  or  by 
direct  violence. 

The  epiphyseal  line  is  above- the  constriction  that  marks  the  union  of  the  olec- 
ranon with  the  shaft.  The  epiphysis  is  small  and  includes  the  upper  part  of  the 
olecranon  with  the  insertion  of  the  triceps,  a  part  only  of  the  attachment  of  the  pos- 
terior ligament,  and  a  very  small  portion  of  the  posterior  triangular  subcutaneous 
surface.  The  epiphyseal  line  runs  from  the  upper  part  of  the  sigmoid  cavity  in 
front  downward  and  backward.  The  epiphysis  enters  but  little  into  the  elbow-joint  ; 
it  is  largely  within  the  limits  of  strong  periosteal  and  tendinous  and  ligamentous 
expansions,  is  of  small  size,  and  before  the  fourteenth  or  fifteenth  year  is  on  a 


286 


HUMAN    ANATOMY. 


FIG. 


plane  anterior  to  the  epicondyles.      For  these  anatomical  reasons,  neither  muscular 
action  (triceps)  nor  falls  on  the  elbow  are  so  productive  of  separation  of  this  epipb- 
ysis  in  children  as  of  fracture  of  the  olecranon  in  adults.      It  is,  in  fact,  one  of  the 
rarest  of  epiphyseal  disjunctions.      The  symptoms  are  very 
similar  to  those  of  fractured  olecranon. 

The  coronoid  process  is  rarely  broken  except  in  cases 
of  dislocation  of  the  forearm  backward  from  falls  upon  the 
hand.  The  mechanism  is  obvious.  The  force  is  applied 
through  the  medium  of  the  oblique  fibres  of  the  interosseous 
membrane.  The  line  of  fracture  is  nearer  the  tip  than  the 
base  of  the  process.  The  insertion  of  the  brachialis  anticus 
tendon  in  the  latter  region  prevents  much  displacement  of 
the  fragment,  and  the  attachment  of  the  capsule  of  the 
joint  to  its  edge  insures  a  sufficient  vascular  supply  for  pur- 
poses of  repair.  Great  proneness  to  recurrence  after  re- 
duction in  a  case  of  backward  dislocation  of  the  forearm 
should  lead  to  a  suspicion  of  the  existence  of  this  fracture. 

Fracture  of  the  shaft  of  the  ulna  alone  may  occur  at 
any  point,  and  is  usually  the  result  of  direct  violence,  as 
when  the  arm  is  raised  to  protect  the  head  from  a  blow, 
or  in  a  fall  upon  the  ulnar  side  of  the  forearm.  In  the  lat- 
ter case,  when  the  ulnar  fracture  is  in  the  upper  third,  it 
is  not  infrequently  associated  with  forward  dislocation  of 
the  head  of  the  radius  (Fig.  300).  ' 

The  subcutaneous  position  of  the  ulna  renders  fracture 
frequently  compound.  This  accounts  for  the  greater  fre- 
quency of  non-union  in  this  bone  as  compared  with  the 
radius.  In  fracture  at  the  lower  third  the  lower  fragment 
is  drawn  towards  the  radius  by  the  pronator  quadratus. 

Fractures  associated  with  those  of  the  radial  shaft  will 
be  considered  in  relation  to  the  effect  of  muscular  action 
upon  them  (page  604). 

The  lower  epiphysis  of  the  ulna  comprises  the  articular  surfaces  on  the  radial 
and  inferior  aspects  and  the  styloid  process.  It  is  concave  superiorly  to  fit  the 
rounded  lower  end  of  the  diaphysis.  The  level  of  the  epiphyseal  line  is  about  one- 
sixteenth  of  an  inch  above  the  level  of  that  of  the  radius.  This  epiphysis  is  strongly 


Lines  of  fracture  of  corp- 
noid,  olecranon,  and  styloid 
processes  of  ulna. 


FIG.  300. 


Fracture  of  upperthird  of  ulna,  with  dislocation  of  radius  forward. 

held  to  the  lower  epiphysis  of  the  radius  by  the  inferior  raclio-ulnar  ligaments  and 
also  by  the  triangular  fibro-cartilage  extending  from  the  root  of  the  styloid  pro<vss 
to  the  concave  margin  of  the  radius.  For  that  reason,  and  because  of  its  indirect 
relation  to  the  hand,  the  uncomplicated  separation  of  this  epiphysis  is  of  givat 


THE    RADIUS. 


287 


rarity.  Even  in  cases  of  separation  of  the  lower  epiphysis  of  the  radius,  or  of 
Colics' s  fracture,  the  strain  reaches  the  tip  of  the  ulnar  styloid  through  the  internal 
lateral  ligament  and  produces  fracture  of  that  process,  or  of  the  ulnar  diaphysis  at 
its  smallest  point  (about  three-quarters  of  an  inch  above  the  lower  end),  rather  than 
separation  of  the  epiphysis. 

As  the  growth  of  the  ulna  depends  almost  exclusively  upon  the  lower  epiphy- 
sis, injuries  stopping  short  of  recognizable  disjunction  have  been  followed  in  a 
number  of  cases  by  failure  of  development,  resulting  in  lateral  displacement  (adduc- 
tion) of  the  hand. 

Landmarks. — The  olecranon  can  always  easily  be  felt  at  the  back  of  the 
elbow.  It  is  somewhat  nearer  the  internal  than  the  external  condyle.  With  the 
forearm  at  right  angles  to  the  arm,  the  tip  of  the  olecranon  and  the  two  condyles 

FIG.  301. 


Posterior  view  of  elbow,  showing  relative  position  of  condyles  and  olecranon.    A,  in  extension  ;  S,  in  flexion. 

are  on  the  same  plane  as  the  back  of  the  upper  arm.  In  extreme  extension  it  is 
about  one-sixteenth  of  an  inch  or  less  above  a  straight  transverse  line  joining  the 
two  condyles  ;  in  full  flexion  it  is  anterior  to  them.  In  front  the  tip  of  the  coronoid 
process  can  be  felt  with  difficulty  in  non-muscular  subjects.  The  shaft  is  subcutaneous 
through  its  entire  length.  The  styloid  process  is  a  half-inch  nearer  the  forearm  than 
the  styloid  process  of  the  radius.  It  is  most  distinct  in  full  supination,  and  is  found 
at  the  inner  and  posterior  aspect  of  the  wrist.  In  full  pronation  the  head  of  the  ulna 
becomes  prominent  posteriorly. 

THE   RADIUS. 

The  radius  includes  a  shaft  and  two  extremities. 

The  upper  extremity  consists  of  a  head  and  neck.     The  head 1  is  a  circular 
enlargement  with  a  shallow  depression  on  top  to  articulate  with  the  capitellum,  and 

'Capitulum. 


288 


HUMAN    ANATOMY 


Head 

Neck- 

Bursal  surface- 
Bicipital  surface- 


FlG.    302. 


Biceps  tendon- 
Supinator  brevis- 


Flex.  sublimis. 
digitorum 


-Interosseous  border 


ator  brevis 


.  Ext.  ossis  met.  pollicis 


-  Ext.  bi  evis  pollicis 


^Ulnar  surface 


,  . ,       .  _„          vSemilunar  surface 

Styloid  process 

Scaphoid  surface 
Right  radius,  inner  aspect.    The  outline  figure  shows  the  areas  of  muscular  attachment. 


THE    RADIUS.  289 

a  smooth  margin  to  turn  in  the  socket  formed  by  the  lesser  sigmoid  cavity  and  the 
orbicular  ligament,  which  completes  it.  The  term  "circular"  is  not  used  with 
mathematical  precision,  for  slight  variations  from  it  are  the  rule.  The  most  common 
one  is  an  increase  of  the  antero-posterior  diameter.  The  depression  on  top  is  not 
symmetrical,  for  there  is  almost  invariably  a  greater  thickness  of  the  rim  in  front, 
extending  more  to  the  inner  than  to  the  outer  side.  The  smooth  margin  has  a 
downward  projection  internally.  The  plane  of  the  upper  surface  is  not  always  at 
right  angles  to  the  axis  of  the  neck,  but  often  looks  a  little  outward.  The  neck  is 
a  smooth  constricted  portion  some  two  centimetres  in  length  and  approximately 
cylindrical. 

The  shaft 1  immediately  bends  outward  below  the  neck,  and  has  a  slight  forward 
curve  at  the  lower  end,  where  it  broadens  considerably.  The  bicipital  tuberosity  '*  is 
a  large  prominence  at  the  inner  and  front  aspect  of  the  shaft,  just  below  the  neck. 
Its  posterior  border,  which  is  rough  and  projecting,  slants  forward  and  receives  the 
biceps  tendon.  In  front  of  this  the  tuberosity  is  smooth  for  a  bursa,  lying  beneath 
the  tendon,  which,  in  pronation,  is  rolled  around  it.  The  shaft  is  described  as  having 
three  surfaces  separated  by  three  borders  ;  there  is  convenience  in  retaining  the 
plan,  although  only  one  border  is  always  distinct  and  one  is  almost  imaginary. 
The  distinct  border  is  the  internal  or  interosseous?  which,  starting  from  the  bicipital 
tuberosity,  soon  becomes  sharp  for  the  interosseous  membrane,  and  runs  to  the 
lower  quarter  of  the  bone,  where  it  divides  into  two  descending  lines  to  the  front 
and  back  of  the  articular  facet  on  the  inner  side  of  the  lower  end.  The  anterior 
border*  which  is  generally  distinct  above,  starts  from  the  front  of  the  tuberosity  and 
runs  downward  and  outward  to  about  the  middle  of  the  bone.  This  part  is  known 
as  the  oblique  line  of  the  radius,  which  gives  origin  to  a  part  of  the  flexor  sublimis 
digitorum,  and  separates  the  insertion  of  the  supinator  brevis  from  the  origin  of  the 
flexor  longus  pollicis.  The  border  is  thence  poorly  marked  till,  slanting  forward  to 
the  beginning  of  the  lower  fourth,  it  becomes  a  distinct  ridge  running  to  the  front  of 
the  styloid  process  and  receives  the  insertion  of  the  pronator  quadratus.  It  broadens 
at  the  end  into  a  triangular  tubercle  for  the  insertion  of  the  brachio-radialis.  The 
posterior  border  is  important  only  as  helping  to  define  the  posterior  and  outer  sur- 
faces ;  it  is  usually  to  be  seen  in  the  middle  third  of  the  bone,  and  has  neither  a 
definite  beginning  nor  end.  The  anterior  surface,  limited  above  by  the  oblique  line, 
is  slightly  concave,  and  gives  origin  to  the  flexor  longus  pollicis  as  far  down  as  the 
last  quarter,  which  is  slightly  hollowed  for  the  pronator  quadratus  and  sometimes 
separated  from  the  upper  part  by  an  oblique  ridge.  The  nutrient  foramen  is  seen 
above  the  middle,  running  upward.  The  outer  siirface,  which  is  convex,  presents 
about  the  middle  a  roughness  for  the  insertion  of  the  pronator  radii  teres.  The 
posterior  surface  has  a  concavity  in  the  middle  third,  internal  to  the  posterior  border, 
and  is  convex  both  above  and  below. 

The  lower  extremity  bends  slightly  forward,  ending  in  front  in  a  prominent 
ridge  to  which  the  capsule  is  attached.  The  outer  side  is  prolonged  downward  as 
the  styloid  process,  ending  in  a  blunt  point.  It  usually  shows  grooves  for  the  tendons 
of  the  extensors  of  the  metacarpal  bone  and  first  phalanx  of  the  thumb,  which  pass 
over  it.  The  external  lateral  ligament  of  the  wrist  arises  from  it.  The  posterior 
surface  has  a  groove  at  its  edge  for  the  capsule,  and  above  this  is  furrowed  for  the 
passage  of  certain  tendons.  Next  to  the  styloid  process  is  a  broad  depression, 
sometimes  faintly  divided  into  two,  for  the  extensores  carpi  radialis  longior  et 
brevior  ;  internal  to  this  is  a  marked  ridge,  the  tubercle,  slanting  downward  and 
outward,  with  a  narrow,  deep  gutter  beyond  it  for  the  tendon  of  the  long  extensor 
of  the  thumb.  A  very  slight  border  separates  this  internally  from  a  broad,  shallow 
groove  for  the  tendons  of  the  extensor  communis  and  that  of  the  index-finger.  At 
the  extreme  limit  of  the  posterior  surface  is  sometimes  a  minute  furrow  for  a  part 
of  the  tendon  of  the  extensor  of  the  little  finger,  which  passes  over  the  radio-ulnar 
joint.  The  inner  side  of  the  lower  end  is  occupied  by  a  concave  articular  area,  the 
si<j moid  cavity  °  of  the  radius,  which  receives  the  head  of  the  ulna  and  much  resembles 
the  lesser  sigmoid  cavity  of  that  bone.  The  lower  surface  is  articular  for  the  scaph- 
oid and  semilunar  bones  of  the  wrist.  It  is  in  the  main  triangular,  the  base  being 
the  inner  side.  It  is  overhung  both  before  and  behind,  and  is  continued  onto  the 

'Corpus.     -  Tuherusitas  radii.     :1Crista  interossea.      4  M;irgo  volaris.     ''  Incisura  ulnaris. 

19 


290 


HUMAN   ANATOMY. 


FIG.  303. 


Supinator  brevis{ 


Pronator  radii  teres. 


Flex,  sublimis 
digitorum 


—Flex.  long,  pollicis 


-Pronator  quadratic 


Brachio-radialis—t  '  .^ 


Head 

Neck 

Bursal  surface 
Tuberosity 
Biceps  tendon 


Oblique  line 


Nutrient  foramen 


Interosseous  border 


Anterior  border 


Groove  for  ext.~ 

os.  met.  pol. 
Groove  for  fxt.<~ 

brevis  pol.         

Semilunar  surface 
Scaphoid  surhuv 
Styloid  process 
Right  radius  from  before.    The  outline  figure  shows  the  areas  of  muscular  attachment. 


Sigmoid 
avity  for 

ulna 


THE   RADIUS. 


291 


Head 


Tuberosity . 


FIG.  304. 


Posterior  border. 


Interosseous  border- 


Supinator 


Ext.  ossis  met.  pollicis— 


Ext.  brevis  pollicis 


—  Pronator  radii  teres 


Sigmoid  cavity 


,Tuberc1e 

J  Ext.  oss.  met.  poll. 
\  Ext.  brev.  poll. 
-Ext.  carp.  rad.  long,  et  brev. 


-  Styloid  process 


Ext.  com.  dig.  and 
ext.  hid  ids 

Ext.  long.  poll. 

Right  radius  from  behind.    The  outline  figure  shows  the  areas  of  muscular  attachment. 


HUMAN    ANATOMY. 


inner  side  of  the  styloid.  A  faint  ridge  from  before  backward,  beginning  at  a  slight 
notch,  marks  off  an  inner  square  surface  for  the  semilunar  and  an  outer  triangular 
one  for  the  scaphoid.  The  surface  looks  slightly  forward,  thus  causing  the  forward 
rising  of  the  hand  from  the  forearm. 

In  man  the  ulna  is  evidently  the  more  important  bone  at  the  elbow  and  the 
radius  at  the  wrist.  In  mammals  below  primates  they  are  often  more  or  less  fused 
and  the  upper  end  of  the  radius  relatively  larger  than  in  man.  It  often  occupies 
the  front  of  the  elbow-joint,  being  anterior  instead  of  external  to  the  upper  end  of 
the  ulna. 

Structure. — The  radius,  like  the  ulna,  is  thick-walled  through  the  greater 
part  of  the  shaft.  The  tuberosity  is  composed  internally  chiefly  of  longitudinal 

FIG.  305.  FIG.  306  A. 

Scaphoid  surface  Semilunar  surface 


Sigmoid  cavity 


Styloid  process 

Ext.  oss.  met.  poll.  ~l 
Ext.  brev.  poll.         j 


Ext.  carp.  rad.  Jong.     /    f^_y  \  A'lY.  communis  dig. 

Ext.  carp.  rad.  brev.       I          Ext.  long,  pollicis  and  ext.  indicts 
Tubercle 

Lower  end  of  right  radius. 


FlG.  306  B. 


Longitudinal  sections  of  radius;   B  in  frontal  plane,  showing  arrangement  of  trabecuhe  in  lower  end  of  bone. 

plates.  A  frontal  section  of  the  lower  end  of  tin-  radius  shows  the  walls  splitting 
up  into  longitudinal  plates,  which  run  to  the  lower  end,  connected  by  a  system  of 
lighter  transverse  ones. 


PRACTICAL   CONSIDERATIONS:   THE   RADIUS. 


293 


Development. — The  centre  for  the  shaft  appears  at  the  end  of  the  second 
month,  and  forms  the  whole  bone,  except  the  lower  end  and  the  head.  The  nucleus 
for  the  former  appears  at  the  end  of  the  second  year  and  that  for  the  head  at  the 


ft /> 


Ossification  of  radius.    A,  at  birth  ;  S,  at  two  years  ;  C,  at  five  years  ;  /?,  between  eighteen  and  nineteen  years. 
a,  centre  for  shaft  ;  6,  for  lower  epiphysis  ;  c,  for  upper  epiphysis. 


end  of  the  fifth.  The  latter  unites  at  about  fifteen,  the  lower  at  eighteen  or  nineteen. 
A  scale-like  epiphysis  for  the  bicipital  tuberosity  is  said  to  appear  towards  eighteen 
and  to  fuse  very  promptly. 


PRACTICAL   CONSIDERATIONS. 

The  radius  may  be  absent  or  more  or  less  defective,  and  in  either  case  there  is 
apt  to  be  corresponding  absence  or  deficiency  in  the  hand  (Humphry). 

As  might  be  expected,  injuries  of  the  upper  end  in  the  adult  are  extremely 
rare.  Except  at  one  point  (just  below  the  external  condyle  posteriorly),  the  head 
is  far  from  the  surface  and  deeply  buried  beneath  the  thick  supinators  and  the  long 
and  short  radial  extensors  of  the  carpus.  Even  at  that  point,  more  prominent  bony 
processes — the  external  condyle  and  the  olecranon — receive  the  brunt  of  the  injury 
in  cases  of  falls  or  blows. 

The  upper  epiphysis  does  not  become  fully  ossified  until  the  fifteenth  year,  and 
is  united  to  the  diaphysis  at  the  beginning  of  the  sixteenth  year.  It  is,  therefore, 
among  the  last  of  the  epiphyses  of  the  long  bones  to  ossify  and  the  first  to  join  its 
diaphysis.  The  violence  which  separates  it  from  the  shaft  is  often  direct.  In  cases 
of  indirect  violence  the  force  is  applied  usually  as  a  combined  pull  and  twist  on  the 
forearm  of  a  very  young  child.  As  the  epiphysis  is  altogether  intra-articular  (the 
synovial  membrane  lining  the  whole  inner  surface  of  the  orbicular  ligament),  swelling 
is  early  and  marked.  As  there  is  direct  communication  with  the  larger  synovial 
cavities  of  the  elbow,  the  whole  joint  will  participate  in  the  effusion. 

Although  no  ligaments  or  tendons  are  attached  to  the  epiphysis,  the  orbicular 
ligament  hugs  it  closely  and  holds  it  in  place.  If  any  displacement  occurs,  the 
upper  part  of  the  diaphysis  may  go  either  forward  or  backward.  On  movements  of 
pronation  and  supination,  the  epiphysis  can  be  felt  immovable  just  below  the  external 
condyle. 

An  injury  known  as  "elbow-sprain,"  or  "pulled  elbow,"  and  described  as  a 
' '  subluxation  of  the  orbicular  ligament' '  and  as  a  "  subluxation  of  the  head  of  the 
radius,"  should  be  mentioned  here  because,  although  it  has  been  known  for  more 
than  two  hundred  years,  has  well-defined  and  constant  symptoms,  occurs  in  one 


294 


HUMAN   ANATOMY. 


FIG.  308. 


per  cent,  of  all  surgical  cases  in  children  under  six  years  of  age,  and  is  believed  to 
depend  on  a  distinct  anatomical  lesion,  the  exact  nature  of  that  lesion  is  still  un- 
known. It  is  usually  caused  by  traction  on  the  forearm.  The  most  plausible  of 
many  theories  are  :  ( i )  that  it  is  due  to  the  head  of  the  radius  slipping  out  from 
beneath  the  orbicular  ligament,  which  is  pinched  between  it  and  the  capitellum  (Fig. 
311)  ;  and  (2)  that  it  is  a  partial  epiphyseal  separation.  The  differential  diagnosis  is 
said  to  depend  chiefly  on  the  facts  that  in  the  "  subluxation"  the  head  of  the  radius 
will  rotate  with  the  shaft,  and  that  all  the  symptoms  disappear  rapidly  after  forced 
supination  has  removed  the  functional  disability.  There  seems  nothing  absolutely 
inconsistent  with  these  symptoms  in  the  view  that  a  slight  epiphyseal  separation  has 
occurred,  the  upper  end  of  the  diaphysis  being  displaced  forward,  but  carrying  with 
it  the  radial  head.  This  theory  is  strongly  favored  by  the  fact  that  very  few  cases 
have  occurred  in  children  over  five  years  of  age.  Ossification  of  the  radial  head 
begins  towards  the  end  of  the  fifth  year.  It  should  be  remembered  that  the  epiphy- 
sis  includes  only  the  upper  part  of  the  head,  the  lower  portion  and  the  neck  being 
ossified  from  the  shaft.  The  upper  end  of  the  diaphysis  is  therefore  approximately 
of  the  same  size  and  shape  as  the  head,  and  may  easily  have  been  mistaken  for  it  in 

many  of  the  cases.  The  problem  pre- 
sented is  so  purely  an  anatomical  one 
that,  in  spite  of  the  prevalent  differences 
of  opinion,  it  seems  proper  to  make  this 
brief  presentation  of  it. 

Fractures  of  the  head  are  uncom- 
mon. Fractures  between  the  head  and 
the  lower  end  will  be  considered  in  refer- 
ence to  the  effect  of  muscular  action  upon 
them  (page  604). 

In  the  neighborhood  of  the  tubercle 
the  thickness  of  the  bone,  the  ridges  that 
run  up  towards  the  head  and  down 
towards  the  outer  edge,  and  the  ample 
covering  of  muscles  render  fracture  com- 
paratively uncommon.  A  little  lower  the 
union  of  the  two  secondary  curves  near 
the  point  of  greatest  curvature  in  the 
primary  curve  of  the  whole  shaft  renders 
the  bone  more  vulnerable.  Still  lower 
the  effects  of  indirect  violence  through 
falls  upon  the  hand,  the  union  near  the 
lower  end  of  the  compact  tissue  of  the 
shaft  with  the  cancellous  tissue  of  the 
expanded  lower  extremity,  the  compara- 
tively superficial  position  of  the  bone, 
and  the  projection  of  the  anterior  articular  lip,  into  which  the  anterior  carpo-radial 
ligament  is  inserted,  all  very  markedly  favor  fracture. 

Accordingly,  we  find  that,  on  account  of  these  anatomical  conditions,  of  one 
hundred  fractures  of  the  radius,  approximately-  three  will  be  in  the  upper  third, 
six  in  the  middle  third,  and  ninety-one  in  the  lower  third,  the  large  majority  of 
these  latter  being  within  from  2.5  to  5  centimetres  (one  to  two  inches)  of  the  wrist- 
joint. 

Fractures  of  the  lower  end  of  the  radius  are  almost  always  produced  by  a 
cross-breaking  strain  caused  by  falls  on  the  hand,  and  exerted  through  the  strong 
anterior  common  ligament.  The  broad  attachment  of  this  ligament  to  almost  the  whole 
anterior  lip  of  the  radius  brings  the  strain  equally  on  the  bone  through  its  entire  width. 
The  fracture  is,  therefore,  usually  irregularly  transverse.  In  addition  to  the  force 
transmitted  by  means  of  the  ligament,  there  is  an  approximately  vertical  force,  due 
to  the  weight  of  the  body,  which  thrusts  the  sharp  lower  end  of  tin-  shaft  into  the 
lower  fragment,  made  up  chiefly  of  spongy  tissue,  with  merely  a  thin  shell  of  com- 
pact tissue  holding  it  together.  This  vertical  force  transmitted  through  the  forearm 


Lines  of  fracture  of  neck  and  of  lower  end  of  radius 
(Colles's  fracture).     A,  dorsal;  R,  lateral  aspect. 


PRACTICAL   CONSIDERATIONS  :   THE    RADIUS. 


295 


FIG. 


and  hand  not  only  thus  impales  the  lower  fragment  on  the  upper,  but  necessarily 
carries  the  former  to  a  higher  level.  In  addition,  the  ulno-carpal  fasciculus  of  the 
common  ligament  drags  on  the  lower  end  of  the  ulna,  and  either  causes  fracture  of 
the  styloid  process,  into  the  side  and  base  of  which  it  is  attached,  or  causes  the  lower 
end  of  the  ulna  to  project  unduly  on  the  antero-internal  aspect  of  the  wrist.  The 
stripping  up  of  the  periosteum,  the  laceration  of  the  tendon  sheaths  that  are  so  closely 
applied  to  the  bone, — especially  the  flexor  tendons  by  the  jagged  edge  of  the  upper 
fragment, — and  the  consequent  effusion  are  the  chief 
remaining  anatomical  factors  in  producing  the  character- 
istic deformity  of  this  most  common  of  all  fractures.  The 
lower  fragment  is  found  on  the  dorsum  of  the  wrist. 
The  lower  end  of  the  upper  fragment  is  found  anteriorly 
beneath  the  pronator  quadratus  or  under  the  flexor  ten- 
dons. The  styloid  process  of  the  radius  is  on  a  higher 
level  than  that  of  the  ulna  ;  in  dislocation  of  the  wrist 
this  is  not  the  case.  The  hand  is  carried  towards  the 
radial  side  (Fig.  309). 

In  cases  with  but  very  trifling  displacement  it  is 
still  possible  to  recognize  the  absence  of  the  projection 
of  the  anterior  articular  lip  of  the  bone  on  the  front  of 
the  wrist,  and  some  slight  elevation  of  the  dorsum. 
The  angle  between  the  axis  of  the  forearm  and  the 
ground  is  said  (Chiene)  to  determine  whether  in  such 
a  fall  the  line  of  force  passes  upward  in  front  of  the  axis 
of  the  forearm  and  the  radius  is  broken,  or  extends  up 
the  forearm  itself,  resulting  in  a  sprain  of  the  wrist  or  a 
dislocation  of  the  bones  of  the  forearm  backward  at  the 
elbow.  The  forward  sloping  of  the  carpal  surface  of  the 
radius  causes  the  posterior  edge  of  the  bone  to  receive 
the  greater  part  of  the  force  ;  hence  the  lower  fragment 
is  rotated  backward  on  a  transverse  axis,  and  hence  the 
disappearance  of  the  prominence  of  the  anterior  articular 
lip.  The  carpal  surface  of  the  radius  also  slopes  down- 
ward and  outward  ;  hence  the  radial  edge  of  the  lower 
fragment  receives  (through  the  ball  of  the  thumb)  a 
greater  part  of  the  shock  than  the  ulnar  edge,  which  is, 
moreover,  firmly  attached  by  the  triangular  ligament. 
This  favors  the  upward  displacement  of  the  radial  styloid 
and  the  radial  displacement  of  the  hand.  There  are 
almost  always  some  crushing  and  distortion  of  the  lower 
spongy  fragment,  even  when  it  is  not  materially  displaced. 

Anterior  displacement  of  this  fragment  may  occur 
when  the  force  is  applied  in  the  reverse  direction, — i.e. , 
with  the  hand  in  forced  palmar  flexion.  The  infre- 
quency  of  falls  on  the  back  of  the  hand  explains  the 
rarity  of  this  accident,  but  the  greater  weakness  of  the 
posterior  ligament  and  the  absence  of  any  projecting 
articular  lip  to  increase  the  leverage  exerted  through 
the  ligament  also  contribute  to  make  the  accident 
uncommon. 

The  later  results  of  these  fractures  are  much  influ- 
enced by  the  close  proximity  of  the  flexor  and  extensor 

tendons  to  the  region  of  injury,  as,  even  when  the  sheaths  escape  laceration  origi- 
nally, they  are  liable  to  become  adherent  during  the  process  of  repair. 

The  lower  epiphysis  of  the  radius  is  osseous  about  the  end  of  the  tenth  year 
and  is  united  to  the  shaft  in  the  nineteenth  or  twentieth  year.  The  epiphyseal  line  is 
almost  transverse  (Fig.  310),  and  extends  from  about  nineteen  millimetres  (three- 
fourths  of  an  inch)  above  the  apex  of  the  styloid  process  to  six  millimetres  (one- 
fourth  of  an  inch)  above  the  lower  edge  of  the  sigmoid  cavity.  The  epiphysis  is 


Fracture  of  lower  end  of  radius, 
showing  hand  carried  towards  the 
radial  side. 


296 


HUMAN    ANATOMY. 


thinnest  in  the  centre  (five  millimetres),  the  line  at  that  point  crossing  the  bone 
about  three  millimetres  below  the  tip  of  the  prominent  middle  thecal  tubercle. 

The  need  for  an  accurate  conception  of  this  epiphysis  is  emphasized  by  the 
facts:  (i)  that  it  is  more  often  separated  than  any  other  in  the  body,  with  the 
possible  exception  of  the  lower  epiphysis  of  the  femur  ;  (2)  that  its  line  has  more 
than  once  been  figured  and  described  as  a  line  of  fracture  on  the  basis  of  skia- 
graphs. 

The  cause  of  separation  is  almost  always  a  fall  on  the  pronated  hand.  The 
carpal  bones  are  carried  against  the  posterior  border  of  the  radial  epiphysis,  the  pro- 
nator  quadratus  and  other  muscles  fix  the  lower  ends  of  the  diaphyses  of  the  radius 
and  ulna,  and  the  epiphysis  is  forced  backward.  The  anterior  carpal  ligament  and 
the  tendons  on  the  palmar  surface  of  the  wrist  are  put  on  the  stretch  and  aid  in  the 
displacement.  The  supinator  longus  is  directly  attached  to  the  epiphysis  and  aids  in 
maintaining  the  deformity. 

The  synovial  membrane  of  the  wrist- joint  does  not  reach  the  level  of  the  epi- 
physeal  line  of  either  the  radius  or  the  ulna.  That  joint  is,  therefore,  not  frequently 
involved. 

The  thinness  of  the  centre  of  the  epiphysis  would  lead,  to  the  expectation  that 
fracture  would  often  complicate  the  separation.  This  is  not  the  case,  however. 
Poland  says  that  the  epiphysis  is  more  solid  than  the  lower 
end  of  the  bone  of  the  adult  (which  has,  of  course,  become 
cancellous  in  structure),  and  that  it  thus  escapes  the  fracture, 
comminution,  and  impaction  which  are  so  frequent  in  later 
life. 

The  radius  is  often  the  subject  of  rickets,  and  of  both 
syphilitic  and  tuberculous  epiphysitis,  especially  at  its  lower 
end,  on  account  of  the  exceptional  'frequency  of  falls  upon 
the  hand  and  strains  of  the  epiphyseal  joint. 

Subperiosteal  sarcomata  are  rare.  Central  sarcomata 
almost  invariably  attack  the  lower  end  of  the  bone  (page 
366). 

Landmarks. — The  head  of  the  bone  may  be  felt  at  the 
bottom  of  the  dimple  or  depression  just  below  the  external 
condyle  and  to  the  outer  side  of  the  olecranon.  It  lies  be- 
tween the  outer  border  of  the  anconeus  and  the  muscular 
swell  of  the  supinator  longus  and  radial  extensors  of  the  car- 
pus. It  is  covered  by  the  external  lateral  and  orbicular  liga- 
ments. It  can  readily  be  felt  to  move  when  the  forearm  is 
pronated  and  supinated.  Its  presence  in  that  position  demon- 
strates that  dislocation  of  the  radius  or  of  both  bones  of  the 
forearm  backward — the  common  dislocation  at  the  elbow — 
Its  free  rotation  negatives  the  existence  of  a  non-impacted 


FIG.  310. 


Lower  end  of  left  radius, 
showing  epiphyseal  line, 
dorsal  aspect. 


has  not  occurred, 
fracture  of  the  radius. 

The  upper  edge  of  the  head  lies  immediately  below  the  elbow-joint.  In  full 
supination  the  tubercle  can  be  indistinctly  felt  a  little  below  the  lower  edge  of  the 
head.  The  upper  half  of  the  radial  shaft  cannot  be  felt,  as  it  lies  beneath  the  bellies 
of  the  extensors  and  the  supinator  brevis.  The  lower  half  is  almost  subcutaneous 
and  can  readily  be  palpated  through  or  between  the  tendons  and  muscles.  The 
expanded  lower  extremity  is  partly  subcutaneous  (at  the  base  of  the  styloid  exter- 
nally) and  is  readily  felt.  The  styloid  itself,  the  prominent  tubercle  at  the  radial 
side  of  the  groove  for  the  extensor  longus  pollicis  (middle  thecal  tubercle),  and 
the  sharp  tubercle  at  the  base  of  the  styloid  can  easily  be  recognized.  The  latter 
is  the  inferior  termination  of  the  pronator  crest  of  the  diaphysis,  marks  the  ex- 
ternal termination  of  the  epiphyseal  line,  and  is  on  a  level  with  the  lower  and  outer 
part  of  the  pronator  quadratus  muscle.  The  posterior  end  of  the-  middle  thecal 
tubercle  is  three  millimetres  above  the  epiphyseal  line  on  the  posterior  aspect  of  the 
bone. 

The  styloid  process  of  the  radius  is  lower — i.e.,  nearer  the  hand — than  the  sty.loid 
process  of  the  ulna. 


RADIO-ULNAR    ARTICULATIONS. 


297 


JOINTS   AND    LIGAMENTS    BETWEEN    RADIUS  AND    ULNA. 

These  include,— 

1.  Superior  Radio-Ulnar  Articulation  : 

Orbicular  Ligament  ;          Capsular  Ligament. 

2.  Inferior  Radio-Ulnar  Articulation  : 

Triangular  Cartilage  ;         Capsular  Ligament. 

3.  Ligaments  uniting  the  Shafts  : 

Interosseous  Membrane  ;  Oblique  Ligament. 

The  superior  radio-ulnar  joint1  (Figs.  311,  312)  is  between  the  circum- 
ference of  the  head  of  the  radius  and  the  lesser  sigmoid  cavity  of  the  ulna  extended 
into  a  circle  by  the  orbicular  ligament.  The  articular  ends  of  the  bones  are  coated 

FIG.  311. 


External  conclyle 


Orbicular  ligament  surrounding  head 
of  radius 


Tuberosity  of  radius 


\ — Internal  condyle 


i —  Coronoid  process 


Oblique  ligament 


Radius — 


Superior  radio-ulnar  articulation,  anterior  aspect.    The  capsule  of  the  elbow  has  been  removed. 


with  cartilage  requiring  no  particular  description.  The  orbicular  ligament2  (Fig. 
311)  surrounds  the  head  of  the  radius,  springing  from  the  two  ends  of  the  lesser  sig- 
moid cavity  and  from  the  lines  running  down  from  them.  This  band  embraces  the 
head  tightly,  but  is  separated  from  it  by  the  cavity  of  the  joint,  and  is  lined  with 

1  Artie,  radioulnaris  proximalis.     -  Lig.  annularc  radii. 


298 


HUMAN   ANATOMY. 


synovial  membrane.  It  narrows  below  so  as  to  fold  under  the  projecting  head,  and 
is  attached,  chiefly  through  fibres  from  the  lower  border  of  the  lesser  sigmoid  cavity, 
to  the  inner  side  of  the  neck.  It  is  connected  above  with  the  capsular  ligament 
of  the  elbow-joint.  That  the  fibres  to  the  neck  limit  rotation  is  easily  shown  by 
dividing  all  bands  connecting  the  bones,  excepting  the  orbicular  ligament  ;  for  were 
it  not  so,  the  radius  could  then  be  turned  continuously,  which  is  not  the  case.  It  is 
doubtful,  however,  whether  these  fibres  become  tense  by  any  movement  which  can 
occur  in  the  undissected  joint. 

The  inferior  radio-ulnar  joint1  is,  when  seen  from  the  front,  an  L-shaped 
cavity,  the  vertical  part  being  between  the  head  of  the  ulna  and  the  hollow  on 
the  radius,  and  the  horizontal  limb  between  the  ulna  and  the  triangular  cartilage, 
which  is  attached  by  its  base  to  the  border  between  the  inner  and  lower  ends  of 
the  radius  in  such  a  manner  that  its  distal  surface  is  in  the  same  plane  as  the 
lower  end  of  the  radius.  The  apex  of  the  cartilage  is  attached  by  a  ligament  some 
three  millimetres  long  to  the  groove  between  the  head  and  the  styloid  process  of  the 
ulna  and  to  the  inner  surface  and  anterior  edge  of  the  latter.  Strong  bands, 
inseparable  from,  the  ligaments  of  the  wrist,  run  along  its  border  to  the  front  and 
back  of  the  articular  surface  of  the  radius.  The  fibro-cartilage  2  is  very  flexible 


Front  of  capsule 


FIG.  312. 

Median  nerve 


Radial  nerve 


Coronoid  process 


Inner  side  of  greater 
sigmoid  cavity 


Ulnar  nerve 


Orbicular  ligament 


Horizontal  section  through  right  elbow-joint  from  above.    The  trochlea  of  humerus  has  been  removed. 


and  adapts  itself  to  the  surfaces  of  the  lower  end  of  the  ulna  and  of  the  first  row  of 
the  carpus.  Its  inner  end,  however,  is  not  as  broad  as  the  lower  end  of  the  ulna. 
It  is  in  some  cases  perforated.  The  membrana  sacciformis  is  the  synovial  mem- 
brane of  this  joint,  lining  the  capsule  between  the  ulna  and  the  triangular  cartilage, 
between  the  ulna  and  radius,  and  extending  a  little  above  the  level  of  the  top  of  the 
apposed  articular  surfaces  of  these  bones.  The  capsule  enveloping  it  is  delicate, 
but  strengthened  in  front  and  behind  by  ill-marked  bands  passing  between  the 
bones  ;  these  are  sometimes  described  as  distinct  anterior  and  posterior  ligaments. 
The  connection  between  the  lower  ends  of  the  bones  is  much  strengthened  by  the 
pronator  quadratus. 

The  ligaments  between  the  shafts  are  the  interfesseous  membrane  and  the 
oblique  ligament.  The  interosseous  membrane a  (Fig.  315),  composed  of  fibres 
running  downward  and  inward,  closes,  except  above,  the  opening  between  the  bones. 
Beginning  from  one  to  two  centimetres  below  the  tubercle  of  the  radius  on  tin- 
anterior  surface  of  the  interosseous  riclge,  and  lower  from  the  sharp  edge,  it  connects 
the  two  ridges  as  far  as  the  lower  joint,  following  the  posterior  division  of  the  inter- 
ossemis  ridge  <>f  the  radius.  The  upper  fibres  are  nearly  transverse.  Some  long 
til  ins,  particularly  on  the  posterior  surface,  run  from  ulna  to  radius.  There  are 

'Artie,  radloulnarls  distiilis.     '-'hi-nis  .11 1  i>  uliiris.      :  Mcmhnuiu  inU-ni-*si-;i  intcrlir;u  Iiii. 


THE   FOREARM    AS   A   WHOLE. 


299 


several  small  openings  for  the  passage  of  vessels  and  nerves.  Pressure  transmitted 
upward  from  the  hand  through  the  radius  would  tend  to  stretch  the  greater  number 
of  the  fibres,  and  thus  distribute  the  strain  through  both  bones.  While  the  radius 


FIG.  313. 


Capsule  of  wrist-joint 


Head  of  ulna 


Styloid  process  of  radius 


Capsule  of  inferior  radio-ulnar 
joint 


Ligament  of  triangular  cartilage 


Triangular  cartilage  Styloid  process  of  ulna 

Lower  end  of  right  radius  in  supination. 


can  hardly  be  enough  displaced  to  bring  this  about,  it  is  conceivable  that  the  bones 
might  bend  sufficiently  to  make  this  action  effective. 

The  oblique  ligament1  (Fig.  311),  an  inconstant  little  band,  runs  downward 
arid  outward,  partly  closing  the  space  above  the  membrane,  from  the  tubercle  of  the 


Head  of  ulna 

( 

Ligament  of  triangular  cartilage-^* 
Styloid  process  of  ulna 


FIG.  314. 

Capsule  of  inferior  radio-ulnar  joint 


tyloid  process  of  radius 


Triangular  cartilage'  Capsule  of  wrist-joint 

Lower  end  of  right  radius  in  pronation. 

ulna  to  the  beginning  of  the  oblique  line  of  the  radius.      It  has  been  plausibly  sug- 
gested that  it  represents  a  part  of  the  flexor  longus  pollicis  muscle. 


THE   FOREARM  AS  A  WHOLE,  AND  ITS   INTRINSIC   MOVEMENTS. 

The  two  bones  and  the  ligaments  form  an  apparatus  capable  of  being  moved  as 
a  whole  on  either  the  arm  or  the  hand,  and  of  greatly  changing  its  own  shape  by 
the  movements  of  the  radius  on  the  ulna.  As  these  latter  are  theoretically  inde- 
pendent of  the  position  of  the  forearm  with  regard  to  the  arm,  it  is  best  to  consider 
them  here. 

The  movement  of  the  radius  is  a  very  simple  one  of  rotation  on  an  axis  coincid- 
ing with  that  of  the  neck  of  the  bone,  and  then,  owing  to  the  outward  bend  of  the 
shaft,  passing  down  between  the  bones  and  finally  through  the  head  of  the  ulna. 
The  amount  of  rotation  probably  rarely  exceeds  160°.  Rotation  is  limited  chiefly  by 
the  anterior -and  posterior  radio-ulnar  ligaments,  the  former  being  very  tense  at  the 
end  of  supination  and  the  latter  at  the  end  of  pronation.  The  oblique  ligament 
limits  forced  supination.  As  above  stated,  it  is  unlikely  that  the  fibres  of  the 
oroicular  ligament  to  the  radius  become  tense  during  life.  The  fact  that  the  lower 
end  of  the  radius  swings  round  the  ulna  in  no  way  changes  the  character  of  the 
movement.  If  the  radius  were  throughout  in  continuation  of  the  axis  of  the  neck, 
and  the  ulna  enlarged  below  to  support  it,  rotation  on  the  axis  of  the  neck  would 
not  change  the  position  of  the  bone.  The  departure  of  the  greater  part  of  the  radius 
from  that  line  necessitates  the  swinging  round  of  the  lower  end,  but  does  not  affect 
the  nature  of  the  movement. 

The  changes  of  relative  position  of  the  bones  during  rotation  are  very  important. 
It  must  be  remembered  that  when  the  ulna  is  held  so  that  the  front  of  the  middle  of 
the  shaft  is  horizontal,  the  head  of  the  radius  is  in  a  plane  above  that  of  the  main 

1  Chorda  obliqua. 


300 


H  I'M  AN    ANATOMY. 


axis  of  the  ulna.  When  the  radius  is  brought  into  semipronation  (so  that  the 
thumb  will  point  upward)  the  bones  are  most  nearly  parallel  and  at  the  greatest 
possible  distance  from  each  other,  and  the  membrane  is  approximately  tense  (  Fig. 
315).  The  forearm  is  broadest  at  about  the  middle.  The  membrane  is  at  the 
bottom  of  a  moderate  hollow  seen  from  either  the  front  or  the  back.  In  extreme 
supination  the  anterior  hollow  is  effaced  and  the  posterior  deepened.  The  radius 
approaches  the  ulna,  especially  above  the  middle.  In  extreme  pronation  the  front 
hollow  is  much  deepened  and  the  hind  one  lost.  The  bones  are  much  nearer 
together  than  in  any  other  position.  The  radius  crosses  the  ulna,  and-  is  above  and 
internal  to  it  at  the  wrist. 

Should  the  capsule  be  opened  from  below  without  disturbing  the  triangular  car- 
tilage in  a  specimen  from  which  the  hand  has  been  disarticulated,  in  supination  the 
front  of  the  under  side  of  the  head  of  the  ulna  will  be  exposed  ;  in  forced  pronation 


FIG.  315. 


Supination. 


Interosseous  membrane.. 


Head  of  ulna. 


-Oblique  ligament 


-Interosseous  membrane 


Position  of  the  bones  of  the  forearm  in  pronation  and  supination. 

almost  the  whole  under  end  will  appear  (Figs.  313,  314).  As  the  radius  passes 
behind  the  head,  the  ligament  of  the  triangular  cartilage  is  relaxed  and  the  band 
at  the  back  of  the  joint  is  made  tense.  This  ligament  becomes  tense  before  com- 
plete supination  and  is  somewhat  relaxed  when  supination  is  extreme. 

The  motion  above  described  is  the  only  one  between  the  radius  and  ulna  ; 
nevertheless,  in  certain  movements  of  twisting  the  hand  and  arm  the  ulna  plays  a 
part  to  be  considered  later  (page  304). 

Surface  Anatomy  of  the  Radius  and  Ulna. — The  position  of  both  bones 
can  be  felt  in  a  body  that  is  not  very  muscular,  though  comparatively  little  of  them 
is  subcutaneous.  The  triangular  space  of  the  back  of  tin-  olecranon,  and  the  pos- 
terior border  of  the  ulna  starting  from  it  and  running  to  the  styloid  process,  can  all 
be  traced  with  the  finger.  When  tin-  arm  is  straight,  the  top  of  the  olecranon  is  a 
little  above  the  level  of  the  internal  condyle  and  behind  it  ;  when  the  arm  is  brut  at 
a  right  angle,  the  top  of  the  olecranon  is  in  the  same  vertical  plane  as  the  back  of 


THE    ELBOW-JOINT. 


301 


the  humerus  ;  and  when  it  is  strongly  flexed,  the  top  of  the  olecranon  corresponds 
to  the  vertical  plane  of  the  internal  condyle.  The  head  of  the  radius  and  the  furrow 
above  it  opening  into  the  joint  are  easily  felt  at  the  outside  and  behind.  In  the  lower 
third  of  the  forearm  the  bones  can  easily  be  felt.  The  ulna  here  is  posterior  and 
best  felt  at  the  back.  '  In  supination  the  styloid  process  is  distinct.  It  is  hidden  by 
the  soft  parts  in  pronation,  and  the  head  is  exposed.  The  forward  sweep  of  the 
lower  end  of  the  radius  is  evident.  The  inferior  expansion  can  be  felt  both  before 
and  behind  ;  the  styloid  process  is  examined  best  from  the  outer  side.  It  extends 
nearly  one  centimetre  lower  than  that  of  the  ulna.  The  inequalities  on  the  back  can 
be  felt  vaguely  ;  the  most  evident  is  the  ridge  bounding  the  groove  for  the  long 
extensor  of  the  thumb. 

THE   ELBOW   JOINT.1 

This  is  a  considerably  modified  hinge-joint,  the  axis  of  rotation  being  oblique  to 
the  long  axis  of  both  the  humerus  and  the  ulna,  and  the  course  of  the  latter  at  the 
joint  being  also  a  spiral  one.  It  is  to  be  understood  that  the  radius  follows  the  ulna, 
which  is  the  directing  bone  of  the  forearm  in  the  motions  of  the  elbow. 

The  Articular  Surfaces. — These  have  been  described  with  the  bones  ;  it 
remains  only  to  give  here  a  summary.  The  motions  between  the  forearm  and  the 
humerus  depend  essentially  on  the  trochlea  and  on  the  surfaces  of  the  greater  sigmoid 
cavity.  This  is  a  modified  hinge-joint.  As  has  been  shown,  the  transverse  axis  of 

FIG.  316. 


Triceps 


Trochlea  - 


Bursa 


Subcutaneous  bursa  — - 


Olecranon 


Coronoid  process 


Ulna 


Sagittal  section  of  right  elbow-joint  through  the  trochlea. 

the  trochlea  is  not  at  right  angles  to  the  shaft,  and  it  may  be  added  that  the  same  is 
true  of  the  sigmoid  cavity  and  the  axis  of  the  ulna.  The  effect  of  this  will  be  noticed 
later.  Again,  as  already  pointed  out,  the  trochlea  is  not  only  oblique,  but  is  so 
shaped  that  the  ulna  in  turning  on  it  describes  a  spiral  line.  It  has  also  been  shown 
that  the  trochlea  is  not  equally  broad  throughout,  and  that  there  are  curious  differ- 
ences of  curve  in  the  sigmoid  cavity.  Finally,  the  lateral  ligaments  are  not  quite 
tense,  "especially  when  the  joint  is  half  flexed.  It  follows  from  these  facts  that  the 
motion  is  a  very  complicated  one,  and  that  a  certain  lateral  motion  of  the  ulna  on 

1  Articulatio  cubiti. 


302 


HUMAN   ANATOMY. 


the  humerus  is  possible.      The  head  of  the  radius  plays  on  the  capitellum,  but  it 
follows  the  ulna. 

The  capsular  ligament '  surrounding  the  joint  is  very  weak  behind,  stronger 
in  front,  and  very  strong  at  the  sides,  which  last-named  parts  are  usually  called  the 
lateral  ligaments.  The  anterior  fibres  arise  from  the  humerus  above  the  coronoid 
and  radial  fossae,  and  from  the  front  of  the  bases  of  both  condyles.  Behind,  they 
arise  from  about  the  middle  of  the  olecranon  fossa,  which  is  only  partly  within  the 
capsule.  Transverse  fibres  bridge  it,  passing  between  the  highest  points  of  the 
borders  of  the  trochlea.  Below  this  the  posterior  fibres  arise  beyond  these  borders, 
so  that  the  trochlea  is  included  in  the  joint.  At  the  sides  the  fibres  forming  the 
so-called  lateral  ligaments  radiate  from  points  below  the  tips  of  the  condyles.  A 
little  of  the  external  and  a  large  part  of  the  internal  condyle  are  not  enclosed.  The 

FIG.  317. 


Band  strengthening  front  of 
capsule 


Fibres  of  orbicular  ligament 
Thin  part  of  capsule 


Bursa  for  tendon  of  biceps 


Radius 


nternal  condyle  of  humerus 


Cut  tendon  of  biceps 
Oblique  ligament 

Ulna 


Capsule  of  right  elbow-joint  from  before. 


capsule  is  inserted  below,  posteriorly,  into  the  little  groove  described  with  the  bone 
at  the  border  of  the  olecranon.  The  radiating  fibres  from  the  external  condyle  arc- 
inserted  into  the  surface  of  the  orbicular  ligament,  behind,  outside,  and  in  front. 
They  are  covered  by  tendinous  fibres  of  the  muscles  from  the  condyle,  which  arc- 
almost  inseparable  from  them,  and  which  greatly  strengthen  tin-  joint.  The  fibres 
radiating  from  the  tip  of  the  inner  condyle,  or  the  internal  lateral  Kgeunent*  are  in 
two  layers.  The  posterior,  the  deeper,  is  attached  to  the  side  of  the  olecranon  ; 
the  anterior  is  a  strong  band  passing  to  the  side  of  the  coronoid  process,  which  sends 
fibres  backward,  overlapping  the  deeper  layer.  The  anterior  fibres  go  to  tin- 
orbicular  ligament  and  to  the  coronoid  process  near  its  edge.  The  front  part  of  the 
capsule  is  strengthened  by  delicate  oblique  fibres  from  the  front  of  the  internal  ron- 
dyle,  passing  downward  and  outward.  Masses  of  fat,  incorporated  in  the  capsule 
both  before  and  behind,  project  into  the  joint,  carrying  the  synovial  membrane  before 

'Capsula  articular!*.     '-'  Lig.  collateralc  ulnare. 


THE    ELBOW-JOINT. 


303 


them.  There  is  a  thick  pad  of  fat,  which,  when  large,  may  bear  well-marked 
synovial  folds  at  the  notch  on  the  inner  side  of  the  ulna  where  the  olecranon  joins 
the  coronoid. 

Movements. — These  are  of  two  orders  :  that  of  flexion  and  extension,  and 
those  which  occur  in  twisting  the  forearm.  For  practical  purposes  the  former  may 
be  reduced  to  those  of  the  ulna,  which  the  radius  is  forced  to  follow.  The  move- 
ments of  the  ulna  are  not  far  from  turning  on  an  oblique  axis,  which  cuts  the  long 
axis  of  the  humerus  at  an  angle  of  approximately  80°  externally.  When  the  forearm 
is  fully  extended,  it  therefore  forms  externally  an  obtuse  angle  with  the  humerus. 
Were  the  long  axis  of  the  ulna  perpendicular  to  the  axis  of  the  joint,  the  forearm  in 
flexion  would  cross  the  humerus,  as  indeed  is  often  erroneously  stated  ;  in  fact, 
however,  the  long  axis  of  the  ulna  also  forms  an  angle  of  about  80°  with  the  axis  of 
the  joint,  and,  as  these  angles  equal  each  other,  in  flexion  the  forearm  is  parallel 
with  the  humerus.  A  simple  demonstration  of  this  is  gained  by  cutting  out  a  copy 
of  Fig.  320. '  On  folding  it  at  the  line  of  the  joint  (a  b}  the  two  parts  will  lie  one  on 

FIG.  318. 


Olecranon 


Internal  condyle 


Posterior  part  of  capsule 


Radius 


External  part  of  capsule  con- 
(        cealing  orbicular  ligament 
Ulna 


Right  elbow-joint,  posterior  and  outer  aspect. 

the  other.  If  then  another  model  be  made  with  the  axis  of  the  lower  piece  at  right 
angles  to  the  joint,  it  will  show  that  the  lower  piece  crosses  the  upper.  When 
extension  is  complete,  the  tip  of  the  olecranon  can  go  no  farther  into  the  fossa  on 
the  back  of  the  humerus,  and  the  front  of  the  capsule  is  tense.  In  complete  flexion 
of  the  dissected  arm,  the  tip  of  the  coronoid  is  in  contact  with  the  humerus  in  front  ; 
but  in  life  the  motion  may  be  checked  by  the  soft  parts  before  it  has  reached  its 
limit.  Morris  has  shown  that  there  is  much  variation  in  the  range  of  movement, 
depending  on  differences  in  the  upper  end  of  the  ulna.  The  lateral  ligaments  of  a 
theoretically  perfect  hinge-joint  should  always  be  tense  ;  in  the  elbow  they  are  not 
quite  tense  in  semiflexion.  Moreover,  the  imaginary  axis  does  not  remain  fixed 
throughout  the  motion. 

Motions  of  the  Forearm  on  the  Humerus  in  twisting  the  Hand.— 
The  articulation  between  the  concave  head  of  the  radius  and  the  convex  capitellum 
of  the  humerus  is  practically  a  ball-and-socket  joint  ;  the  radius  may  glide  on  the 
humerus,  following  the  ulna,  or  it  may  rotate  on  a  fixed  axis,  as  described  above. 
It  is  easily  shown,  however,  that  the  swinging  of  the  lower  end  of  the  radius  round 

1  Potter  :  Journal  of  Anatomy  and  Physiology,  vol.  xxix.,  1895. 


304 


HUMAN   ANATOMY. 


a  motionless  ulna  is  not  what  actually  occurs  in  life.  Let  the  reader  grasp  lightly 
his  right  wrist  with  his  left  thumb  and  forefinger,  so  that  they  nearly  meet  at  the 
styloid  process  of  the  radius,  and,  pressing  the  right  elbow  to  the  side  for  steadiness, 

FIG.  319. 


Radius  Oblique  ligament       /r 

I'i,    (//" 


Interosseous  membrane 


Ulna        Tendon  of  biceps 

Right  elbow-joint,  inner  aspect. 


Superficial  layer  of 
inter,  lat.  ligament 


Posterior  part 
of  capsule 


•Olecranon 


Deeper  layer  of  internal 
lateral  ligament 


FIG.  320. 


pronate  the  right  arm.  The  lower  end  of  the  radius  will  occupy  the  place  at  the 
base  of  the  left  thumb  previously  occupied  by  the  ulna,  which  will  have  travelled 
outward  along  the  left  forefinger.  It  is  very  doubtful  whether  in  this  experiment  all 
motion  at  the  shoulder  is  eliminated  ;  nevertheless,  the  ulna  undoubtedly  changes  its 
place,  and  with  equal  certainty  it  does  not  ' '  rotate. ' '  To  prove  this,  let  the  arm  of 
a  subject  be  held  in  a  vice  above  the  elbow,  which  should  be 
semiflexed,  and,  the  forearm  being  supine,  let  a  long  pin 
pointing  outward  be  fixed  into  the  outer  side  of  the  radius 
above  the  wrist,  and  another  pointing  inward  into  a  corre- 
sponding point  of  the  ulna.  On  pronating  the  hand,  the  pin 
in  the  radius  will  describe  a  large  curve  and  that  in  the  ulna 
will  make  no  evident  movement.  On  close  inspection,  aided 
by  placing  some  object  close  to  the  head  of  the  pin  in  the 
ulna,  it  will  appear  that,  though  the  bone  has  not  rotated, 
the  pin-head  has  changed  its  place  :  it  has  moved  down- 
ward and  outward.  If  the  hand  be  now  disarticulated,  and 
two  pins  bearing  brushes  dipped  in  paint  be  placed  in  the 
end  of  the  head  of  the  ulna  and  in  the  lower  surface  of  the 
radius,  pointing  downward  so  as  to  continue  the  line  of  the 
shafts  of  these  bones,  on  twisting  the  forearm,  each  of  these 
brushes  will  describe  a  curve  on  a  sheet  of  paper  held  against 
them  ;  that  in  the  radius  making  a  large  curve  upward  and 
inward,  and  the  ulnar  pin  a  small  one  downward  and  out- 
ward. The  relative  size  of  these  curves  mav  be  varied 
greatly  by  the  operator.  What  has  occurred  is  this  :  besides 

the  rotation  of  the  radius,  there  has  been  a  lateral  movement  between  the  ulna  and 
humerus  combined  with  a  slight  extension.  This  movement  is  less  when  the  arm  is 
nearly  straight  than  when  Hexed,  for  in  the  latter  position  the  lateral  parts  of  the 


Diagram    showing    tin- 

l:il     :umlfs     i  if     tin-     lung 

axes  of  tin-  Imiii-s  \\ith  iiu- 

;i\is  ill   lln-   joint. 


PRACTICAL   CONSIDERATIONS  :     THE   ELBOW-JOINT.          305 

capsule  are  least  tense.  It  is  probably  assisted  by  a  want  of  perfect  adaptation 
between  the  articular  surfaces.  These  experiments  on  the  dead  body  do  not  quite 
fulfil  the  conditions  of  the  living,  because  we  have  no  evidence  that  then  the  muscles 
can  produce  quite  the  same  movement  ;  moreover,  Cathcart  has  shown  that  in  anky- 
losis  of  the  shoulder-joint  this  motion  is  greatly  impaired,  thus  proving  that  in  life  a 
small  amount  of  motion  at  that  joint  is  an  essential  part  of  free  twisting  of  the  hand. 
Experiments  by  Hultkrantz  on  the  living  subject  tend  to  show  that  the  slight  motion 
of  the  ulna  is  in  the  opposite  direction  to  that  described.  There  is  probably  much 
individual  variation. l 

PRACTICAL   CONSIDERATIONS. 

The  Elbow-Joint. — This  joint  is  dependent  for  its  strength  more  upon  the 
shape  of  the  bones  that  enter  into  it  than  upon  the  ligaments  or  muscles.  As  the 
elbow  ceased  to  be  useful  for  support,  but  became  of  the  utmost  importance  for 
prehension,  the  radius  became  movable  instead  of  fixed,  and  the  strength  of  the  joint 
came  to  depend  in  much  larger  proportion  upon  the  ulna. 

Force  applied  in  the  line  of  the  long  axis  of  the  limb,  as  in  hanging  by  the 
hands  (the  weight  being  transferred  from  the  wrist  and  the  radius  to  the  ulna  and 
the  elbow,  largely  by  means  of  the  triangular  and  orbicular  ligaments,  with  very 
slight  help  from  the  oblique  ligament),  is  resisted  in  the  order  of  effectiveness  (a) 
by  the  hook  of  the  olecranon  over  the  trochlea  ;  (b')  by  the  lateral  ligaments  ;  (c) 
by  the  biceps,  triceps,  and  brachialis  anticus,  aided  by  the  flexors,  extensors,  prona- 
tors,  and  supinators.  The  lower  part  of  the  lesser  sigmoid  cavity  of  the  ulna  under- 
hangs  the  inner  edge  of  the  radial  head,  and  aids  in  preventing  the  radius  from  being 
drawn  away  from  the  ulna. 

Force  applied  in  the  same  line,  but  in  the  opposite  direction,  as  in  falls  upon 
the  hands  (the  thrust  being  transferred  from  the  radius  to  the  ulna  by  means  of 
the  oblique  fibres  of  the  interosseous  membrane),  is  resisted  almost  exclusively  by 
the  coronoid  process,  aided  perhaps  by  the  surface  of  contact  between  the  radial 
head  and  the  capitellum,  which  is  diminished  in  full  extension. 

As  the  dislocation  usually  occurs  with  the  forearm  hyperextended,  the  lateral 
ligaments,  particularly  the  inner  one,  are  often  stretched  and  torn  ;  the  brachialis 
anticus  is  drawn  tightly  over  the  humerus  and  is  sometimes  ruptured.  The  coronoid 
process  is  not  infrequently  broken. 

Antero-posterior  dislocations  are  the  most  frequent,  because  of  («)  the  lesser 
antero-posterior  diameter  of  the  joint  as  compared  with  the  lateral  diameter  ;  (£)  the 
varying  efficiency  of  the  hold  of  the  ulnar  processes — the  coronoid  and  olecranon — 
on  the  humerus  in  different  positions  of  the  elbow  ;  (c*)  the  weakness  of  the  anterior 
and  posterior  ligaments,  and  the  absence  of  effective  muscular  support. 

Backward  dislocation  of  both  bones  is  far  more  frequent  than  forward,  be- 
cause :  (i)  The  capsular  ligament  is  weakest  posteriorly.  (2)  The  coronoid,  which 
resists  backward  displacement,  is  smaller,  less  curved,  and  received  in  a  shallower 
fossa  than  the  olecranon,  which  prevents  luxation  forward.  (3)  It  is  in  its  relation  of 
least  effectiveness  when  the  joint  is  in  full  extension.  (4)  Falls  upon  the  hand  with 
the  forearm  extended  greatly  outnumber  all  other  causes  of  dislocation  of  the  elbow. 
(5)  In  full  extension  the  already  slight  surface  of  contact  between  the  radius  and 
humerus  is  diminished  and  the  posterior  articular  edge  of  the  radial  head  projects 
behind  the  capitellum.  (6)  The  ulna  and  radius  are  apt  to  be  dislocated  together 
rather  than  separately  because  of  the  strong  ligaments  which  hold  them  to  each 
other — the  triangular  ligaments  below,  the  interosseous  membrane,  and  the  orbicular 
and  oblique  ligaments  above — and  because  of  the  absence  of  any  such  intimate 
connection  of  either  bone  with  the  humerus. 

It  is  this  ligamentous  connection  with  the  ulna  which  enables  the  radius,  in  spite 
of  the  shallowness  of  the  articular  cup  upon  its  head,  to  resist  the  powerful  forward 
pull  of  the  biceps. 

1  Heiberg  :  Ueber  die  Drehung  der  Hand,  1884  ;  contains  an  exhaustive  bibliography. 
Heiberg  :  Journal  of  Anatomy  and  Physiology',  vol.  xix.,  1885.  Cathcart :  ibid.  Dwight :  ibid. 
Hultkrantz  :  Das  Ellenbogen  Gelenk  und  seine  Mechanik,  Jena,  1897  ;  contains  the  later 
bibliography. 


306  HUMAN   ANATOMY. 

Lateral  dislocations  of  the  separate  bones  are  infrequent  for  the  same  reason  ; 

.of  both  bones  because  of  the  great  relative  width  of  the  joint,  its  irregular  undulating 

transverse  outline,  the  prominences  of  the  border  of  the  trochlea  and  of  the  capi- 

tellum,  the  strength  of  the  lateral  ligaments,  and  the  presence  of  the  flexor  and 

extensor  muscular  masses  arising  from  the  condyles. 

Inward  dislocation  is  the  rarest  on  account  of  the  greater  projection  of  the  inner 
border  of  the  trochlea. 

When  either  bone  is  dislocated  separately,  it  is  most  apt  to  be  the  radius,  and 
in  the  forward  direction  on  account  of  the  slightness  of  its  humeral  connection,  its 
mobility,  its  direct  relation  with  the  hand  and  wrist,  and  the  effect  of  muscular  action 
(biceps)  upon  its  upper  extremity.  The  orbicular  ligament  offers  the  chief,  if  not 
the  only  resistance  to  this  forward  pull  of  the  biceps.  Therefore,  if  this  is  torn, 
recurrence  of  the  luxation  is  common,  unless  the  arm  is  kept  in  the  acutely  flexed 
position.  When  the  ulna  is  dislocated  alone,  it  is  almost  always  backward  for 
reasons  already  mentioned. 

In  the  common  backward  dislocation  of  both  bones,  the  tip  of  the  coronoid  may 
rest  upon  the  posterior  surface  of  the  trochlea,  or  may  ascend  to  the  level  of  the 
olecranon  fossa,  which,  however,  it  is  prevented  from  actually  entering  by  the  pres- 
ence of  the  soft  parts  and  by  the  tension  of  the  structures  on  the  front  of  the  joint. 
The  most  easily  recognized  symptom  of  this  displacement  is  the  change  in  the  rela- 
tion of  the  tips  of  the  condyles  and  the  olecranon,  the  latter  occupying  a  much  higher 
position  in  extension,  or  lying  much  more  posteriorly  in  flexion  (page  287,  Fig. 
301).  In  making  this  measurement  it  is  important  to  be  sure  that  the  line  uniting 
the  tips  of  the  condyles,  and  in  full  extension  in  the  normal  arm,  crossing  the  olec- 
ranon about  one-sixteenth  of  an  inch  below  its  tip,  is  a  straight  line  at  right  angles 
to  the  long  axis  of  the  humerus.  Any  upward  or  downward  curve  given  to  this  line 
destroys  its  diagnostic  significance. 

The  large  majority  of  cases  of  dislocation  of  the  elbow  occur  in  young  males, 
usually  below  the  age  of  twenty.  Kronlein  has  called  attention  to  the  fact  that  at 
this  age  fractures  of  the  clavicle  are  also  common  and  luxation  of  the  shoulder  is 
rarely  met  with,  while  after  twenty  both  clavicular  fracture  and  elbow  dislocation 
are  comparatively  rare  and  shoulder  dislocation  is  common.  He  concludes  that  in 
childhood  fracture  of  the  clavicle  is  the  equivalent  of  dislocation  of  the  shoulder  by 
direct  violence,  and  dislocation  of  the  elbow  is  the  equivalent  of  the  shoulder  dis- 
location from  indirect  violence. 

The  anatomical  explanation  may  be  that  the  disproportion  between  the  head  of 
the  humerus  and  the  glenoid  cavity  (page  278)  is  less  marked  in  childhood,  the 
articular  surfaces  are  therefore  not  so  easily  separated,  and  force  applied  to  the  point 
of  the  shoulder  is  more  apt  to  reach  and  be  expended  upon  the  clavicle. 

As  to  the  elbow,  the  shallowness  in  children  of  the  fossae  which  receive  the 
processes  and  a  corresponding  want  of  prominence  in  the  latter,  together  with  the 
ease  with  which  the  elbow-joint  in  childhood  may  be  hyperextended  (which  is  not 
the  case  in  adult  life),  are  possible  explanations  of  the  frequency  of  this  dislocation 
in  young  persons. 

Congenital  dislocations  occur.  In  some  instances  they  have  been  associated 
with  deficiency  of  the  capitellum,  and  have  then  been  accompanied  by  such  elonga- 
tion of  the  radial  neck  as  to  place  the  head  of  that  bone  on  a  level  with  the  tip  of  the 
olecranon. 

This  affords  an  illustration  of  the  general  law,  which  may  be  mentioned  here, 
that  the  rate  of  growth  of  epiphyses  is  inversely  as  the  pressure  upon  them.  Other 
examples  are  to  be  seen  in  the  overgrowth  of  the  cranial  bones  in  hydrocephalus, 
when  their  edges  are  separated  by  the  pressure  of  the  ventricular  fluid  ;  in  the  pro- 
jection of  the  vomer  and  intermaxillary  bones  beyond  the  level  of  the  alveolar  arch 
in  some  cases  of  cleft  palate  ;  in  the  bony  outgrowths  that  fill  up  the  glenoid  cavity 
or  the  acetabulum  in  unreduced  luxations  of  the  humerus  or  femur  ;  and  in  many 
other  similar  conditions. 

/V.vw.sr  <>f  the  elbow-joint  is  most  often  tuberculous,  but  may  be  of  any  variety. 
In  spite  of  the  constant  exposure  of  the  joint  to  traumatism,  it  is  not  attacked  by 
disease  with  exceptional  frequency.  This  is  probably  partly  due  to  the  firm  inter- 


PRACTICAL   CONSIDERATIONS  :   THE    ELBOW-JOINT.  307 

locking  of  its  bony  constituents,  preserving  its  ginglymoid  character  and  preventing 
the  injurious  effect  of  side  strains,  partly  to  the  similar  protective  effect  of  its  strong 
lateral  ligaments,  and  somewhat  to  the  laxity  of  its  capsule,  permitting  of  moderate 
distention  without  undue  tension.  It  is  easily  and  often  spontaneously  immobilized 
in  the  early  stages  of  disease  ;  it  then  bears  no  weight  and  is  but  little  exposed  to 
harmful  increase  of  intra-articular  pressure  from  muscular  spasm  ;  and  finally,  as  its 
fixation  does  not,  as  in  the  joints  of  the  lower  extremity,  interfere  greatly  with 
moderate  out-door  exercise,  the  general  resistant  power  is  not  so  easily  lowered. 
Swelling  first  shows  itself  posteriorly  on  either  side  of  the  olecranon  process,  and 
extends  to  the  fossa  over  the  head  of  the  radius.  In  these  directions  the  capsule  is 
thinnest  and  most  lax  and  the  synovial  cavity  is  nearest  the  skin.  As  distention 
continues  there  may  be  a  bulging  beneath  the  anconeus  to  the  outer  side  of  the 
olecranon,  or  on  the  front  of  the  elbow  beneath  the  brachialis  anticus  and  extending 
towards  the  outer  side,  as  it  is  limited  internally  by  the  thickening  of  the  capsule 
constituting  the  internal  lateral  ligament. 

Pus  is  apt  to  follow  the  same  lines  of  least  resistance,  and  discharge  upon  the 
back  of  the  arm  on  either  side  of  the  triceps,  but  especially  on  the  outer  side  on 
account  of  the  attachment  of  the  dense  intermuscular  fascia  above  the  internal  con- 
dyle  ;  over  the  head  of  the  radius  beneath  the  external  condyle  ;  or  in  front  to  the 
outer  side  of  the  tendon  of  the  biceps,  a  position  determined  by  the  resistance  of  the 
bicipital  aponeurosis  on  the  inner  side. 

The  radio-ulnar  joint,  which  is  part  of  the  articulation,  is  often  involved,  affecting 
the  motions  of  pronation  and  supination. 

The  upper  radial  epiphysis  and  most  of  the  lower  humeral  epiphysis  are  within 
the  limits  of  the  capsule,  and  may  either  be  the  starting-point  of  joint  disease  or 
become  secondarily  involve'd. 

The  position  of  semiflexion  which  gives  the  greatest  ease,  and  is  therefore 
voluntarily  assumed,  is  that  which  affords  most  room  for  synovial  distention  and 
relaxes  the  muscles  most  immediately  in  relation  with  the  joint.  Distention  of 
the  joint  is  easily  distinguished  from  disease  of  the  neighboring  bursae.  The 
bursa  over  the  olecranon,  when  enlarged,  constitutes  a  single  rounded  superficial 
prominence  ;  that  beneath  the  triceps  tendon,  while  it  causes  swelling  on  either 
side  of  that  structure,  does  not  extend  to  or  obliterate  the  fossa  over  the  head 
of  the  radius,  nor  does  it  cause  a  ' ;  puffiness  between  the  inner  condyle  and  the 
olecranon  process  when  the  arm  is  bent  at  a  right  angle"  (Harwell).  The  bursae 
beneath  the  brachialis  anticus  and  between  the  tubercle  of  the  radius  and  the  biceps 
tendon,  if  enlarged,  cause  a  vague  fulness  over  those  regions,  but  none  of  the  charac- 
teristic appearances  of  synovitis.  Chronic  enlargement  of  the  latter  bursa,  in  a  case 
of  Agnew,  caused  pressure  paralysis  of  the  muscles  supplied  by  the  median  and 
posterior  interosseous  nerves. 

The  obliquity  of  the  line  of  the  elbow-joint  (page  268)  should  be  remembered 
in  the  treatment  of  fractures  involving  the  articulation.  In  obscure  injuries  about 
the  joint  the  position  of  acute  flexion,  with  the  hand  upon  the  front  of  the  chest,  is 
the  one  least  likely  to  be  followed  by  serious  ankylosis,  as  in  that  position  the  full 
functional  value  of  this  obliquity  is  more  apt  to  be  preserved  than  when  the  forearm 
is  at  a  right  angle.  The  position  is  also  the  one  in  which  it  is  easiest  to  retain  in 
place  many  fractures  in  the  region  of  the  elbow.  Especially  in  fractures  of  the  lower 
end  of  the  humerus,  if  the  fragments  are  at  once  replaced,  the  coronoid.  process  in 
front  and  the  muscular  and  tendinous  structures  behind  hold  them  firmly  and  prevent 
recurrence  of  deformity.  If  the  fracture  is  intercondylar,  or  T-shaped,  the  acutely 
flexed  position  not  only  holds  the  condyles  in  position,  but  tends  to  prevent  by 
pressure  the  involvement  of  the  joint  line  by  callus,  which  later  would  prove 
obstructive.  If  either  the  coronoid  or  olecranon  fossa,  or  both,  be  involved,  it  is 
more  important  to  prevent  the  filling  up  of  the  former  than  of  the  latter,  as  full  flexion 
is  of  far  greater  functional  importance  than  full  extension.  If  the  condyles — espe- 
cially the  inner — be  split  off,  the  position  relaxes  the  muscles  that  cause  displacement. 
It  is  also,  of  course,  the  most  useful  position  of  the  limb  in  case  ankylosis  does  occur. 

In  excision  of  the  elbow-joint  the  following  anatomical  points  should  be  remem- 
bered :  (i)  The  lines  of  the  various  epiphyses.  (2)  The  position  of  the  ulnar  nerve 


3o8 


HUMAN    ANATOMY. 


in  the  groove  between  the  internal  condyle  and  olecranon.  (3)  The  close  relation 
of  the  posterior  interosseous  nerve  to  the  head  of  the  radius.  (4)  The  post-operative 
value  (in  extending  the  forearm)  of  the  outer  aponeurotic  expansion  of  the  triceps 
and  of  the  anconeus  muscle.  These  should  be  carefully  protected  from  injury. 

Landmarks. — The  following  points  may  be  mentioned  in  addition  to  those 
which  may  be  found  under  the  Humerus,  Radius,  and  Ulna  : 

A  line  from  one  condyle  to  the  other  will  be  at  right  angles  with  the  humeral 
axis,  but  will  be  oblique  in  relation  to  the  axis  of  the  forearm. 

The  line  of  the  radio-humeral  articulation  is  horizontal.  The  line  of  the  humero- 
ulnar  articulation  is  oblique  downward  and  inward  ;  the  tip  of  the  internal  condyle 
is  therefore  from  a  quarter  to  a  half  inch  farther  above  the  articular  line  than  is  the 
tip  of  the  external  condyle.  The  internal  condyle  points  backward  rather  than 
inward. 

The  length  of  the  articulation  line  is  about  two-thirds  of  the  length  of  a  line 
joining  the  tips  of  the  condyles.  In  semiflexion  the  external  condyle  is  easily  seen  ; 
in  acute  flexion  it  disappears,  and  the  rounded  capitellum  of  the  humerus,  with  the 
outer  edge  of  the  triceps  stretched  over  it,  can  be  seen  and  felt. 

The  Inferior  Radio-Ulnar  Joint. — This  articulation  has  been  dislocated  in 
a  few  instances,  in  most  of  which,  the  cause  having  been  extreme  pronation  of  the 
wrist,  the  lower  end  of  the  ulna  was  carried  backward,  projecting  on  the  back  of  the 
wrist  and  pointing  outward, — i.e. ,  towards  the  middle  finger.  The  backward  dis- 
placement probably  involves  the  tearing  of  the  triangular  fibre-cartilage  and  a  rup- 
ture of  the  posterior  radio-ulnar  ligament.  The  deviation  of  the  ulna  to  the  radial 
side  may  be  due  to  the  action  of  the  pronator  quadratus.  The  shallowness  of  the 
sigmoid  cavity  on  the  radius  favors  recurrence  after  reduction.  But  little  is  known 
of  this  injury. 


THE   CARPUS. 


309 


THE   HAND. 

THE  hand  is  composed  of  the  carpus  or  wrist,  consisting  of  eight  small  bones 
arranged  in  two  rows,  which  is  succeeded  by  five  rays  of  four  segments  each, — 
namely,  a  metacarpal  bone  and  three  phalanges,  excepting  the  thumb,  in  which  one 
phalanx  is  wanting. 

THE   CARPUS. 

There  are  eight  carpal  bones  arranged  in  two  rows  of  four  each.  The  first  row 
includes,  named  from  the  radial  towards  the  ulnar  side,  the  scaphoid,  the  semilunar, 
the  cuneiform,  and  the  pisiform  ;  the  second  row,  the  trapezium,  the  trapezoid,  the 
os  magnum,  and  the  unciform.  Exceptionally,  several  other  bones  may  occur,  due 
to  the  persistence  of  centres  laid  down  in  early  fcetal  life,  which  normally  fuse  with 
other  centres  or  disappear.  Thus  there  is  much  in  favor  of  the  view  that  the  plan 
of  the  carpus  is  more  complicated.  This  point  is  further  considered  in  the  dis- 
cussion of  variations  (page  313).  The  pisiform  of  the  first  row,  whatever  may  be 
its  morphological  significance,  is  in  man  practically  nothing  but  a  sesamoid  bone 
in  the  tendon  of  the  flexor  carpi  ulnaris,  resting  on  the  palmar  surface  of  the  cunei- 
form, and  having  no  share  in  the  mechanics  of  the  wrist  excepting  as  giving  attach- 
ment to  a  part  of  the  anterior  annular  ligament.  The  first  row,  therefore,  consists 
really  of  the  three  first-mentioned  bones,  which  are  joined  into  one  flexible  piece  by 
interosseous  ligaments.  The  upper  end  of  this  combination  bears  an  egg-shaped 
articular  surface  for  the  wrist-joint,  to  which  all  three  bones  contribute.  Its  lower 
side  has  a  concavo-convex  outline,  the  concavity  receiving  the  inner  two  bones  and 
the  convexity  bearing  the  outer  two  of  the  second  row.  The  latter  consists  of  four 
bones  connected  by  ligaments  :  the  trapezium,  for  the  thumb  ;  the  trapezoid  and 
os  magnum,  for  the  next  two  fingers  ;  and  the  unciform,  for  the  ring  and  little 
fingers.  The  dorsal  side  of  the  carpus  is  slightly  convex  and  the  palmar  deeply 
concave,  forming  by  its  middle  the  floor  of  a  deep  canal,  bridged  by  the  anterior 
annular  ligament,  which  runs  between  bony  elevations  on  each  side  of  the  carpous. 
To  shorten  the  description,  it  may  be  said  that  little  depressions  for  ligaments  can 
be  seen  on  well-marked  bones  near  their  edges  on  the  dorsal  and  palmar  aspects, 
especially  the  former. 

The  scaphoid  [os  naviculare],  or  boat-shaped  bone,  is  the  largest  and  most 
external  of  the  first  row.  It  is  a  flattened  elongated  disk  placed  with  the  long  axis 
running  outward  and  downward.  It  receives  its  name  from  being  convex  on  the 
upper  and  outer  side  for  the  radius  and  concave  on  the  opposite  side  for  the  head 
the  os  magnum.  Nearly  corresponding  with  the  long  axis  is  the  long  and  very 


FIG.  321. 

For  trapezium 


FIG.  322. 


For  trapezoid 


Tuberosity 


Tuberosity 


For  radius 
Right  scaphoid,  dorsal  aspect. 


Palmar  surface 
Right  scaphoid,  inner  aspect. 


narrow  dorsal  surface.  The  palmar  surface  is  broader,  runs  more  downward,  and 
the  outer  end  rises  into  the  tuberosity  of  the  scaphoid,  from  which  part  of  the  anterior 
annular  ligament  springs.  The  convex  proximal  surface  for  the  radius  is  wholly 
articular  ;  the  inner  edge  is  straight,  the  dorsal  and  palmar  converge  externally  ;  it 
tends  to  encroach  on  the  dorsal  surface.  Internally  there  are  two  surfaces,  both 


3io 


HUMAN  ANATOMY. 


articular  :  the  upper,  very  narrow,  articulates  at  its  lower  border  with  the  semilunar 
and  gives  attachment  above  to  the  fibre-cartilaginous  ligament  connecting  these 
bones  ;  the  lower  is  an  elongated  cavity  embracing  part  of  the  top  and  the  outer 
side  of  the  head  of  the  os  magnum.  The  outer  surface,  continuous  with  the  dorsum, 
is  a  small  groove  for  the  lateral  ligament  of  the  wrist.  The  distal  surface,  forming 
the  convexity  of  the  medio-carpal  joint,  articulates  with  the  trapezium  and  trapezoid. 
It  is  convex  in  all  directions.  The  scaphoid  articulates  withy?z(<?  bones, — the  radius, 
semilunar,  trapezium,  trapezoid,  and  os  magnum. 

The  semilunar  [os  lunatum]  receives  its  name  from  its  outline  when  seen  from 
the  side,  the  proximal  surface  being  convex  and  the  distal  deeply  concave.  The 
dorsal  surface  is  quadrilateral.  Its  proximal  and  inner  borders  are  longer  than  the 


FIG.  323. 


FIG.  324. 

For  cuneiform  For  unciform 

Dorsal 


For  radius 


For  magnum 


For  scaphoid 
Right  semilunar,  outer  aspect. 


Palmar 
Right  semilunar,  inner  aspect. 


others,  so  as  to  make  it  kite-shaped,  the  long  axis  running  distally  outward.  The 
two  shorter  surfaces  meet  at  an  overhanging  point.  The  palmar  surface  is  of  the 
same  general  shape.  Its  larger  distal  portion  is  smooth  as  for  a  bursa.  The/r0.rz- 
mal  surface  is  convex  and  articular,  chiefly  for  the  radius  ;  but,  extending  under  the 
triangular  cartilage,  broadest  at  the  scaphoid  edge,  it  narrows  internally.  The  con- 
cave distal  surface  is  divided  by  a  ridge  into  a  larger  part  for  the  os  magnum  and  an 
inner  for  the  edge  of  the  unciform.  An  outer  surface  articulates  with  the  scaphoid 
and  an  inner  with  the  cuneiform.  Both  are  semilunar,  but  the  outer  is  the  more 
slender.  Both  are  nearly  plane  and  practically  wholly  articular,  there  being  but  a 
slight  roughness  for  the  interosseous  ligaments  at  the  proximal  end  near  the  dorsum. 
The  semilunar  articulates  with  five  bones, — the  radius,  scaphoid,  cuneiform,  os 
magnum,  and  unciform. 

The  cuneiform  [os  triquetrum],  or  Pyramidal,  is  of  such  form  that  the  latter 
name  is  the  more  fitting.  The  base  is  the  articular  surface  for  the  semilunar  ;  the 
apex  is  at  the  inner  side  of  the  wrist.  The  base  is  plane  and  articular  except  where 
the  interosseous  ligament  joins  it.  The  dorsal  surface  is  narrow  and  not  clearly 


FIG.  325. 

For  unciform 


For  pisiform 


For  semilunar 


Lateral 
ligament 


Palmar  surface 


For  triangular  cartilage 
Right  cuneiform,  palmar  aspect. 


Dorsal  surface 
For  semilunar 


Non-articular 
Right  cuneiform,  distal  aspect. 


separated  from  the  proximal  on  the  macerated  bone.  The  proximal  surface  is  a 
triangle  with  the  base  inward,  and  has  near  the  base  a  smaller  triangle  of  articular 
surface  for  the  triangular  cartilage.  The  inner  half  of  the  palmar  surface  is  occupied 
by  a  round  facet  for  the  pisiform.  The  distal  surface  is  a  very  complexly  curved 
articular  facet  for  the  unciform.  It  suggests  a  saddle-joint  that  lias  been  spirally 
twisted.  A  transverse  section  of  this  surface  is  concavo-convex  from  without  inward. 


THE   CARPUS.  311 

A  vertical  section  near  the  outer  end  is  concave,  near  the  inner  convex.  It  is  prac- 
tically a  screw  surface.  A  small  part  of  the  inner  side  is  non-articular.  The  inner 
surface  is  the  apex  of  the  pyramid,  a  small  knob  for  the  lateral  ligament.  The 
cuneiform  articulates  with  three  bones, — the  semilunar,  pisiform,  and  unciform. 

The  pisiform  [os  pisiforme]  is  a  small  rounded  bone,  rough  everywhere  except 
where  the  greater  part  of  one  surface  is  occupied  by  a  round,  slightly  concave  articu- 
lar facet  which  joins  the  palmar  aspect  of  the  cuneiform.  The  facet  is  at  the  proxi- 


FIG.  327. 


FIG.  328. 


Rough  surface  for  an- 
terior annular  lig- 
ament and  flexor 
carpi  ulnaris 


— iiWH-For  cuneiform 


Right  pisiform,  dorsal  aspect. 


Right  pisiform,  palmar  aspect. 


mal  part  of  the  dorsal  surface,  the  bone  projecting  from  it  downward,  forward,  and 
inward,  lying  in  a  plane  anterior  to  that  of  the  outer  carpal  bones.  The  pisiform 
articulates  with  only  one  bone, — the  cuneiform. 

The  trapezium  [os  multangulum  majus]  is  distinguished  by  an  isolated  facet 
on  the  distal  surface  for  the  metacarpal  bone  of  the  thumb.  This  surface  is  that  of 
a  typical  saddle-joint,  concave  from  side  to  side  where  the  borders  are  most  raised  ; 
convex  from  before  backward  ;  broadest  transversely.  The  proximal  sicrface  is  a 
four-sided  concavity  for  the  scaphoid,  separated  by  a  ridge  from  the  inner  surface. 
The  inner  surface  is  subdivided  :  the  proximal  portion,  much  the  larger,  is  an 
articular  concavity  for  the  trapezoid  ;  the  distal  portion  is  rough  except  for.  a  facet 
at  the  dorsum  for  a  part  of  the  side  of  the  second  metacarpal.  The  outer  surface  is 
concave,  receiving  the  lateral  ligament.  The  dorsal  surface  is  elongated  from  side 
to  side,  slightly  hollowed  in  the  middle,  with  a  variously  developed  tubercle  on 


FIG.  329. 


FIG.  330. 


For  first  metacarpal 


For  second 
metacarpal 

For  trapezoid 


Ridge 


Groove  for 
exor  carpi  radialis 
For  scaphoid 


Ridge     For  scaphoid 


For  second 
metacarpal 


Right  trapezium,  palmar  aspect. 


For  trapezoid 
Right  trapezium,  proximal  and  inner  aspect. 


either  side.  On  the  palmar  surface  is  a  deep  groove  for  the  tendon  of  the  flexor 
carpi  radialis.  Just  beside  this  is  a  prominent  ridge  at  the  junction  with  the  external 
surface  for  a  part  of  the  outer  insertion  of  the  palmar  annular  ligament.  The  trape- 
zium articulates  with/^r  bones, — the  scaphoid,  trapezoid,  and  first  and  second  meta- 
carpals. 

The  trapezoid  [os  multangulum  minus]  is  best  recognized  by  the  dorsal  surface, 
which  is  pointed  distally  where  it  projects  into  the  second  metacarpal.  The  outer 
convex  border  against  the  trapezium  is  much  longer  than  the  inner  against  the  os 
magnum.  The  proximal  border  runs  obliquely  forward  and  inward.  The  small 
palmar  surface  is  irregularly  quadrilateral.  The  proximal  surface  is  a  quadrilateral, 
nearly  plane,  facet  for  the  scaphoid,  longer  from  dorsum  to  palm  than  transversely. 
The  distal  surface,  entering  the  base  of  the  second  metacarpal,  is  divided  by  a  ridge 
into  two  facets,  concave  from  dorsum  to  palm,  of  which  the  inner  is  the  longer. 
The  internal  surface,  in  the  main  concave,  articulates  with  the  body  of  the^os  mag- 
num, but  has  a  non-articular  surface  near  the  dorsum  for  an  interosseous  ligament. 
The  outer  surface  is  mostly  articular  and  slightly  convex,  joining  the  trapezium  ; 


312 


HUMAN    ANATOMY. 


distally  and  towards  the  palm  there  is  a  rough  surface  for  ligaments.      The  styloid 
process  of  the  third  metacarpal  often  reaches  the  dorsal  aspect  of  the  trapezoid 


FIG.  331. 

Dorsal  surface 


FIG.  332. 


For  trapezium 


For  magnum 
Right  trapezoid,  inner  aspect. 


Right  trapezoid,  outer  and  distal  aspect. 


between  the  os  magnum  and  the  second  metacarpal.     The  trapezoid  articulates  with 
foiir  bones, — the  scaphoid,  trapezium,  os  magnum,  and  second  metacarpal. 

The  os  magnum  [os  capitatum]  is  the  largest  bone  of  the  carpus,  and  possesses 
a  head,  neck,  and  body.  The  head  is  a  rounded  articular  eminence  at  the  proximal 
end,  playing  in  a  socket  formed  by  the  scaphoid,  semilunar,  and  unciform.  The  con- 
vex articular  surface  extends  much  farther  on  the  dorsal  side  than  on  the  palmar.  A 
faint  line  above  often  separates  the  part  resting  on  the  scaphoid  from  that  resting  on 
the  semilunar.  The  former  extends  down  the  outer  side  of  the  head.  The  inner 
side  of  the  head  is  a  sharply  cut  plane  surface  articulating  with  the  unciform.  The 
neck  is  a  constriction,  best  marked  on  the  dorsal  aspect,  generally  seen  on  all  sides 
except  the  inner.  The  distal  surface,  broader  on  the  dorsal  end,  faces  a  little  out- 
ward. It  is  wholly  articular,  bearing  the  third  metatarsal  bone.  A  groove  in  the 
place  of  the  outer  angle  receives  the  edge  of  the  second  metatarsal.  A  smaller 
surface  for  the  fourth  exists  at  the  inner  angle  just  below  the  dorsum.  The  dorsal 


FIG.  333. 

For  unciform 


FIG.  334. 

Dorsal  surface    Neck    For  scaphoid 


For  fourth 
metacarpal 


Head 


For  third 
metacarpal 

For  second 
metacarpal 

For  trapezoid 


Head 


For  semilunar 


Neck 
Right  os  magnum,  inner  aspect. 


Right  os  magnum,  outer  aspect. 


surface  shows  the  head,  and  distally  to  it  a  sharp,  slightly  concave  inner  border,  a 
shorter  outer  one,  and  a  distal  one  slanting  downward  and  inward,  so  that  the  outer 
angle  is  obtuse  and  the  inner  would  be  acute,  but  that  the  point  of  the  angle  is 
replaced  by  a  small  border  touching  the  fourth  metacarpal.  The  palmar  surface  is 
narrow  and  prominent  below  the  neck.  The  inner  surface  is  rough  for  a  ligament 
near  the  palmar  border  ;  above,  it  has  a  narrow  articular  surface  for  the  unciform, 
continuous  with  that  on  the  head.  The  outer  surface  has  a  small  articulation  with 
the  trapezoid,  which  exceptionally  is  continuous  with  the  facet  on  the  head.  The 
os  magnum  articulates  with  seven  bones, — the  scaphoid,  semilunar,  trapezoid,  unci- 
form, and  second,  third,  and  fourth  metacarpals. 

The  unciform  [os  hamatum]  is  distinguished  by  a  prominent  hook  projecting 
from  the  inner  side  of  the  palmar  surface  for  a  part  of  the  annular  ligament.  The* 
dorsal  surface  is  nearly  or  quite  triangular.  It  presents  an  oblique  proximal  border, 
a  nearly  straight,  but  often  convex,  outer  one,  and  a  distal  one  tending  to  meet  the 
inner  end  of  the  proximal  border.  Should  they  meet,  the  surface  is  triangular  ;  but 
more  often  there  is  a  very  short  inner  border  separating  them,  which  is  c-itlu-r  straight 


THE   CARPUS.  313 

or  concave.  The  palmar  surface,  of  about  the  same  shape  as  the  dorsal,  presents 
externally  a  deep  groove,  a  part  of  the  canal  for  the  flexor  tendons,  overhung  inter- 
nally by  the  unciform  process,  which  has  a  broad  outer  and  inner  surface,  the  former 
concave  and  smooth,  the  latter  convex.  The  free  border  of  the  hook  presents  a 
curved  outline  from  the  inner  side.  The  rounded  edge  between  the  proximal  and 
outer  surfaces  rests  against  the  semilunar.  The  proximal  surface  is  a  spirally 
twisted,  oblong  facet  corresponding  to  the  adjacent  side  of  the  cuneiform,  with  a 
prominent  convexity  at  the  proximal  end.  The  outer  surface,  rough  at  the  distal 
and  palmar  angles  for  an  interosseous  ligament,  is  elsewhere  articular  for  the  os 


FIG.  335. 


For  cuneiform 


Hook 


Right  unciform,  inner  and  proximal  aspect. 


FIG.  336. 


For  magnum 


Hook 
Right  unciform,  outer  and  distal  aspect. 


magnum.  The  distal  surface,  wholly  articular,  bears  the  fourth  and  fifth  metacarpals, 
a  ridge  marking  the  interspace  between  them.  The  surface  is,  in  the  main,  convex 
from  side  to  side  and  concave  from  dorsum  to  palm.  Often,  however,  the  part  for 
the  fourth  finger  is  concave  from  side  to  side  and  convex  in  the  other  direction. 
The  distal  surface  may  meet  the  proximal  at  a  sharp  border,  or  a  very  narrow  rough 
surface  may  intervene.  The  unciform  articulates  with  five  bones, — the  semilunar, 
cuneiform,  os  magnum,  and  fourth  and  fifth  metacarpals. 

Development  and  Variations. — In  early  fcetal  life  centres  appear  for  the 
above-described  carpal  bones,  and  also  for  many  others,  which  disappear,  or  are 
fused  with  the  usual  ones,  long  before  the  appearance  of  bone.  Additional  carpals 
depend  either  on  the  persistence  and  subsequent  ossification  of  centres  that  normally 
are  lost  or  on  the  separate  development  of  two  or  more  that  should  fuse.  The 
number  of  carpal  elements  is  put  by  Pfitzner1  at  thirty-three.  He  arranges  the 
constant  and  possible  bones  in  five  rows  :  ( I )  an  antibrachial  row,  consisting  of  an 
ossification  in  or  on  the  triangular  cartilage,  representing  the  os  intermedium,  and  a 
little  apparent  outgrowth  from  the  pisiform  ;  (2)  a  proximal  row,  consisting  of  the 
normal  bones  and  certain  subdivisions  of  the  scaphoid  and  cuneiform  ;  (3)  a  central 
row,  composed  entirely  of  occasional  bones  ;  (4)  a  distal  row,  composed  of  the  four 
normal  bones  plus  a  minute  metastyloid ;  (5)  a  carpo-metacarpal  row,  composed 
entirely  of  occasional  bones.  The  most  common  anomaly  is  the  appearance  of  a 
styloid  bone,  which  is  the  separated  styloid  process  of  the  third  metacarpal.  The 
metastyloid  of  the  fourth  row  is  a  minute  bone  representing  the  very  tip  of  the  styloid. 
Very  rarely  the  scaphoid  is  divided  into  a  radial  and  an  ulnar  part.  The  os  centrale 
is  the  persistence  of  still  another  piece,  which  normally  either  joins  the  scaphoid  in 
the  third  month  of  fcetal  life  or  disappears.  It  apparently  is  composed  of  a  dorsal 
and  a  palmar  element,  of  which'  the  latter  is  the  more  subject  to  degeneration.  The 
os  magnum  contains  two  elements  exceedingly  rarely  found  distinct,  the  subcapi- 
tatnni  on  the*  distal  end  of  the  palmar  surface  and  the  siibcapitatum  secund'arium 
forming  the  inner  distal  angle  of  the  dorsum.  The  hook  of  the  unciform  may  be 
separate.  Fusion  may  occur  between  bones  normally  distinct.  The  semilunar  may 
fuse  with  the  cuneiform,  especially  in  negroes. 

Ossification  occurs  from  one  centre  for  each  bone  ;  but  according  to  some 
authorities,  the  unciform  and  the  scaphoid  have  two  centres.  The  former  and  the  os 

1  Zeitschrift  fur  Morphologic  und  Anthropol.,  Bd.  ii.,  1900. 


HUMAN   ANATOMY. 

magnum  are  the  first  to  ossify,  the  process  beginning  in  the  latter  part  of  the  first 
year.  The  order  of  its  appearance  in  the  other  bones  is  very  uncertain.  Those  of 
the  first  row,  excepting  the  pisiform,  contain  bone  by  the  end  of  the  first  five  or  six 

FIG.  337. 


Ossification  of  bones  of  hand.  A,  at  birth;  R,  latter  half  of  first  year;  Cat  three  years;  D,  at  eight  years; 
E,  at  twelve  years,  a,  centres  for  shafts  of  metacarpals  and  phalanges ;  6,  magnum ;  c,  unciform  ;  rf,  cuneiform  ; 
f,  base  of  first  metacarpal ;  f,  heads  of  metacarpals ;  g,  bases  of  proximal  phalanges ;  h,  bases  of  distal  phalanges ; 
»',  scaphoid  ;  j,  trapezium  ;  k,  trapezoid  ;  /,  semilunar  ;  m,  bases  of  middle  phalanges  ;  n,  pisiform. 

years.  These  are  followed  by  the  trapezium  and  the  trapezoid,  so  that  by  the  eighth 
year  the  process  has  begun  in  all  the  carpals  save  the  pisiform,  in  which  it  begins 
about  the  twelfth  year. 

THE  METACARPAL  BONES. 
The  metacarpal  bone  of  the  thumb !  in  many  respects  resembles  a  phalanx  and 
calls  for  a  separate  description;  the  others  have  the  following  points  in  common. 
They  possess  a  shaft2  and  two  extremities,  of  which  the  proximal  is  the  base  and  tin- 
distal  the  head?  Each  base*  has  an  articular  surface  at  the  end  to  join  the  carpus  and 
one  on  the  side  or  sides  that  come  into  contact  with  the  other  metacarpal  bones,  with 
a  depression  for  an  interosseous  ligament  beyond  it.  The  bases  themselves  are 
cubical  and  rough  both  above  and  below.  The  shaft  narrows  in  front  of  the  base, 
and  has  a  median  dorsal  ridge,  which  soon  divides  into  two  lines  running  to  either 
side  of  the  head,  thus  bounding  a  long,  flat  dorsal  surface  occupying  more  than  half 
the  bone.  A  palmar  ridge  runs  nearly  the  whole  length  of  the  shaft,  dividing  very 
near  the  head  into  two  faint  lines  to  either  side  of  it.  Thus,  near  the  base  the 
shaft  may  be  called  cylindrical,  with  a  ridge  above  and  below,  while  farther  forward 
it  has  a  dorsal  and  two  lateral  sides.  This  description  applies  most  closely  to  the 
bone  of  the  index,  and  becomes  less  and  less  accurate  as  we  proceed  to  the  little 

1  Os  mctacarpale  1.     '-'Corpus.     ::  Citpituliiin.     *  Basis. 


THE   METACARPAL   BONES. 


finger.  The  distal  end  or  head  has  a  rounded  articular  surface  projecting  to  the 
palmar  side,  while  it  does  not  rise  above  the  level  of  the  dorsum.  Both  on  the  palmar 
and  dorsal  aspects,  but  especially  on  the  former,  its  angles  are  produced  backward, 
and  the  whole  surface  encroaches  a  little  more  on  the  palmar  side,  where  it  is  de- 
cidedly broader  than  on  the  back.  A  tubercle  exists  on  each  side  where  the  diverging 

FIG.  338. 


Ext.  carpi  ulnaris 
Styloid  process 


.Ext.  carpi  rad.  long. 
'Ext.  carpi  rad.  brev. 


Ext.  brev. 
poll. 


HIRD    PHALANX 


Bones  of  right  hand,  dorsal  aspect. 

lines  of  the  dorsum  end,  with  a  depression  below  it  on  the  side  of  the  head.  The  lat- 
eral ligaments  spring  from  both  tubercle  and  depression.  The  nutrient  foramina, 
excepting  that  of  the  first  metatarsal,  are  recurrent,  running  towards  the  proximal  end. 
Peculiarities  of  the  Different  Metacarpals. — The  first  metacarpal  is 
shortest,  the  second  longest,  from  which  the  remaining  ones  decrease  in  length 
from  without  inward.  The  chief  distinguishing  marks  are  on  the  bases. 


HUMAN   ANATOMY. 


The  first  metacarpal,  shorter  than  the  others,  has  a  nearly  flat  dorsal  surf  ace 
bounded  by  two  definite  borders,  of  which  the  outer  is  the  sharper.  The  palmar 
surface  of  the  shaft  is  overhung  by  the  ends.  It  is  thickest  and  most  convex  towards 
the  inner  side.  These  two  points  are  the  best  guides  to  determine  the  side  the  bone 
belongs  to.  The  difference  is  striking  in  a  transverse  section.  The  base  is  broad 


FIG.  339. 


For  radius 


Tuberosity 
Abductor  pollicis 

TRAPEZOID 

Adductor  obliquus 
Opponens  poll 

TRAPEZIUM 

Ext.  os.  met.  po 
Flex,  carpi  rod. 
Opponens  poll. 


',11. 


Abductor  and  flexor 
brevis  pollicis 

Adductores 
obliquus  ct 
transversus 


For  triangular  cartilage 


PISIFORM 

Abductor  minimi  digiti 


UNCIFORM 

I  'nciform  process, _/?<> x.  brevis 
and  oppvii.  mm.  dig. 
,  carpi  u/iuu  is 


Opponent  win.  dig. 


Palmar  interossei 


Abductor  and 
flex,  brevis 
mi>i.  digit  i 


Flex,  sublim.  digit. 


Flex,  profund.  digit 


Bones  of  right  hand,  palmar  aspect. 


and  runs  to  a  point  on  the  palmar  aspect  rather  nearer  the  inner  side.  A  groove 
for  the  capsule  surrounds  the  joint,  and  on  the  outer  side  is  a  tubercle  for  the  tendon 
of  the  extensor  of  the  bone.  The  articular  pro.\~hnal  end  is  convex  from  side  to  side 
and  concave  from  above  downward,  forming  a  typical  saddle-joint  with  the  trupe/.ium. 
The  head  is  also  broader  from  side  to  side.  The  articular  surface  is  carried  only  a 


THE   PHALANGES.  317 

little  way  onto  the  dorsum,  but  bends  strongly  forward,  ending  in  two  lateral  pro- 
longations with  a  notch  between  them,  on  each  of  which  a  sesamoid  bone  plays. 
The  outer  of  these  is  the  more  prominent.  The  nutrient  foramen  runs  towards  the 
distal  end. 

The  second  metacarpal  has  a  base  which  is  triangular  when  seen  from  the 
end.  and  forked  to  straddle  the  point  of  the  trapezoid.  On  the  outer  side  is  a  small 
square  facet  near  the  dorsum  for  the  trapezium  ;  on  the  inner  side  there  is  a  narrow 
oblique  surface  for  the  os  magnum,  and  in  front  of  it  one  showing  a  tendency  to 
subdivide,  articulating  with  the  next  bone. 

The  third  metacarpal  has  an  oblong  proximal  surface,  broadest  on  the  dor- 
sum,  where  a  tubercle,  the  stylo  id  process,  projects  towards  the  trapezoid.  We  have 
found  the  third  metacarpal  touching  this  bone  in  forty  per  cent,  of  100  specimens, 
and  sometimes  this  occurred  when  the  styloid  process  was  not  particularly  developed. 
Externally  there  is  a  facet  like  the  lower  part  of  the  inner  one  of  the  second,  and 
internally  a  double  one  to  meet  the  next. 

The  fourth  metacarpal  has  a  nearly  square  upper  surface  articulating  with 
the  unciform,  and  therefore  of  uncertain  nature, — sometimes  convex,  sometimes 
concave.  At  the  outer  dorsal  angle  of  this  surface  is  a  small  distinct  facet  for  a  joint 
with  the  os  magnum.  On  the  outer  side  are  two  facets  for  the  third,  and  on  the 
inner  a  long  one,  concave  from  dorsum  to  palm,  for  the  fifth. 

The  fifth  metacarpal  has  a  base  generally  broader  than  deep,  concave  from 
side  to  side  and  convex  from  above  downward.  A  single  facet  on  the  outer  side 
has  a  convexity  to  meet  the  concavity  on  the  fourth.  The  inner  side  has,  of  course, 
no  facet,  but  a  tubercle.  The  dorsal  ridge  on  this  bone  is  twisted,  starting  from  the 
inner  side. 

Development. — Each  bone  has  two  centres,  a  primary  one  for  the  shaft, 
appearing  early  in  the  third  month  of  foetal  life,  and  one  for  an  end,  appearing  in  the 
third  year.  The  secondary  centre  is  for  the  distal  end  in  the  four  inner  metacarpals 
and  in  the  proximal  of  the  first, — that  is,  at  the  end  towards  which  the  nutrient 
artery  does  not  run.  They  fuse  at  about  eighteen.  Rarely  smaller  epiphyses 
appear  at  the  other  ends  also,  as  in  mammals  generally.  A  centre  for  the  styloid 
process  of  the  third  is  sometimes  seen,  and  it  may  become  distinct,  suggesting  an 
extra  carpal  bone,  or  it  may  fuse  with  one  of  the  adjoining  ones. 

THE   PHALANGES. 

Features  of  Each  Bone. — The  phalanges 1  of  the  first  and  second  row  differ 
(except  in  size)  only  in  the  proximal  ends.  The  dorsum  of  the  shaft  is  rounded 
from  side  to  side  ;  the  palmar  surface  is  flat  with  raised  edges  for  the  sheaths  which 
bind  down  the  tendons  very  closely.  It  is  considerably  overhung  by  the  distal  and 
somewhat  by  the  proximal  end.  The  nutrient  foramen,  when  present,  runs  distally. 

The  proximal  end  of  they?™/  row  is  a  concave  articular  surface,  broadest  trans- 
versely. A  groove  runs  round  the  end,  except  on  the  palmar  surface,  for  the  cap- 
sule and  for  fibres  from  the  extensor  tendons  of  the  fingers  on  the  dorsum.  Two 
very  slight  inequalities  in  front  mark  the  attachment  of  the  glenoid  ligament.  There 
is  a  rough  tubercle  on  each  side,  just  below  the  groove  for  the  partial  insertion  of 
the  interosseous  muscles.  The  distal  end  in  both  the  first  and  second  rows  has  an 
articular  surface  which  curves  over  two  condylar  prominences,  separated  by  a  median 
furrow,  onto  the  palmar  aspect.  This  surface  is  seen  on  the  dorsum  only  as  a  small 
curved  median  facet  which  broadens  as  it  passes  over  the  end  and  continues  to 
expand  to  its  termination.  The  lateral  borders  of  the  joint  are  well  defined.  A 
depression  with  an  overhanging  tubercle  is  on  each  side  of  this  end  ;  both  depression 
and  tubercle  give  attachment  to  the  lateral  ligament. 

The  pro ximal  ends  of  the  second  and  third  rows  are  essentially  the  same.  They 
differ  from  that  of  the  first  row  because,  while  the  latter  fits  onto  the  single  rounded 
end  of  a  metacarpal,  those  of  the  two  distal  rows  fit  onto  double  condylar  ends. 
Thus  the  proximal  articular  surface  presents  a  median  elevation,  separating  two 
hollows,  continued  into  a  projecting  point  on  the  surface  front  and  back.  In  the 
phalanges  of  the  second  row  the  dorsal  point  is  the  larger  ;  in  the  last  row  the  points 

1  Phalanges  digitorum  manus. 


3i8  HUMAN   ANATOMY. 

are  about  equal.  In  the  last  row  the  palmar  point  is  at  a  lower  level  than  the  rough- 
ness that  succeeds  it.  There  is  a  transverse  ridge  in  both  on  the  dorsal  aspect  for 
extensor  tendons  ;  the  flexor  tendons  are  inserted  on  the  palmar  side  to  a  slight 
ridge  on  the  second  phalanx  and  to  a  roughness  spreading  considerably  on  the  shaft 
of  the  terminal  one. 

The  phalanges  of  the  third  row  are  much  smaller  and  flatter  than  the  preceding. 
The  dorsum  of  the  diminutive  shaft  is  convex  from  side  to  side  and  its  palmar  aspect 
plane  where  not  encroached  upon  by  roughnesses.  The  free  end  is  sharp  and 
rounded,  with  points  at  each  end  projecting  backward.  The  dorsal  distal  border 
bears  a  narrow  semilunar  roughness  ;  a  much  broader  one  on  the  palmar  side  sup- 
ports the  pulp  of  the  end  of  the  finger,  giving  firm  attachment  to  the  connective 
tissue. 

Peculiarities  of  Individual  Phalanges.  — Every  phalanx  of  the  first  row  is 
longer  than  any  of  the  second  row.  The  first  and  second  phalanges  of  the  middle 
finger  are  longer  than  the  corresponding  ones  of  the  ring  finger,  which  in  turn  sur- 
pass those  of  the  index.  Those  of  the  little  finger  are  the  smallest.  The  terminal 
phalanges  are  of  very  nearly  the  same  length. 

The  phalanges  of  the  first  row  have  the  following  peculiarities.  That  of  the 
index-finger  has  a  very  large  external  tubercle  at  the  dorsum  ;  the  hollow  at  the  base 
is  deeper  than  that  of  any  other  ;  the  base  is  relatively  strong  compared  with  the  shaft, 
which  is  flatter  than  any  other.  The  phalanx  of  the  middle  finger  is  strong  in  all  its 
parts ;  there  is  a  large  external  tubercle,  often  divided  into  a  dorsal  and  a  palmar  part ; 
at  the  distal  end  the  ulnar  condyle  is  more  prominent.  The  phalanx  of  the  ring 
finger  has  the  base  relatively  small  and  the  condyles  relatively  large,  so  that  the 
borders  are  nearly  parallel  ;  the  dorsum  is  more  convex  transversely  than  that  of  the 
third,  and  much  more  so  than  that  of  the  index  ;  it  is  also  narrower.  The  phalanx 
of  the  little  finger  is  weak,  narrowing  rapidly  so  as  to  appear  pointed  ;  there  is  a 
tubercle  at  the  inner  and  dorsal  side  of  the  base,  and  the  radial  condyle  is  the  more 
projecting.  One  cannot,  therefore,  determine  to  which  side  the  phalanx  of  the  ring 
finger  belongs. 

In  the  second  row  the  phalanx  of  the  middle  finger  is  always  stronger  than 
that  of  the  ring  finger,  and  the  latter  than  that  of  the  index.  According  to  Pfitzner,1 
the  distal  ends  are  the  more  characteristic.  In  the  second  finger  the  radial  condyle 
is  the  more  prominent  ;  this  is  also  true  in  the  third,  but  to  a  less  degree  ;  the  ulnar 
condyle  is  the  larger  in  the  fourth,  and  still  more  so  in  the  fifth. 

The  distal  or  terminal  phalanges  can  be  distinguished  more  surely  by 
strength  than  by  length  ;  the  third  is  the  strongest  ;  then  comes  the  fourth  ;  next 
the  second,  which  is  more  or  less  pointed  ;  and  last  the  fifth,  which  is  relatively 
weak.  These  characteristics  are  to  be  used  with  great  caution  in  drawing  differential 
deductions. 

Development. — The  phalanges  have  each  a  centre  for  the  shaft  and  one  for 
the  proximal  end.  The  former  appears  in  the  latter  half  of  the  third  month  of  foetal 
life  at  about  the  same  time  in  the  terminal  and  proximal  rows.  Probably  the  termi- 
nal row  shows  ossification  somewhat  earlier  than  the  other  (Bade).  The  centres 
for  the  second  phalanges  appear  after  a  distinct  interval  about  the  middle  of  the 
fourth  month.  In  both  the  first  and  second  rows  the  centre  appears  nearer  the 
proximal  end.  It  is  said  that  in  all  the  rows  ossification  begins  in  the  middle  finger, 
next  in  the  index,  and  later  in  the  ring  and  little  fingers  ;  there  is,  however,  con- 
siderable variation.  The  centre  for  the  second  phalanx  of  the  little  finger  is  dis- 
tinctly later  than  the  others.  Ossification  begins  in  the  epiphyses  in  the  third  year 
or  later.  They  are  fused  by  eighteen.  In  addition  to  the  proximal  epiphyses,  the 
terminal  phalanges  have  each  a  distal  cap-like  ossification  of  perichondrial  origin. 
which  quickly  joins  the  shaft. 

Sesamoid  bones'-  occur  in  the  metacarpo-phalangeal  joints.  In  the  f  cut  us  of 
the  fourth  month  they  are  very  numerous,  but  many  disappear  by  fusion  or  other- 
wise during  development.  A  pair  is  constant  in  the  joint  of  the  thumb.  They  are 
t\vo  bones  of  variable  si/e,  in  general  rather  larger  than  a  small  pea,  lying  on  the 
palmar  side  of  the  head  of  the  first  metacarpal.  The  tendon  of  the  long  flexor  passes. 
'Sclmalbi-'s  Morpholog.  Arbeiten,  lid.  i.  ami  ii.,  1893. 

20ssn  scsamoidca. 


PRACTICAL   CONSIDERATIONS  :   THE   HAND    BONES. 


319 


between  them.  They  each  have  one  cartilage-covered  surface  against  the  bone  and 
are  otherwise  surrounded  by  fibrous  tissue.  A  small  one  on  the  radial  side  of  the 
joint  of  the  index-finger  occurs  in  rather  less  than  half  the  cases,  and  one  on  the 
ulnar  side  of  the  little  finger  in  rather  more  than  four-fifths.  Pfitzner1  gives  the 
following  table  of  percentages  showing  the  frequency  of  the  various  sesamoid  bones, 
combining  his  work  and  that  of  Thilenius  : 


Number 
of  Hands. 

Thumb. 

Index. 

Middle. 

Ring. 

Little. 

Fourth-month  foetus  .    . 
Fourteen  to  ninety  years 

30 
1323 

Rad.  Uln. 

IOO            IOO 

99.9  100 

R.          L. 
46         23 

47.8       o.i 

R.         L. 

30          15 
1-5         0 

R.        L. 

23      30 
O         O.I 

Rad.      Uln. 

15         63 
2.3     82.4 

Variations  in  the  number  of  the  fingers  are  generally  regarded  as  malforma- 
tions. The  most  common  occurrence  is  an  extra  finger,  the  identification  of  which 
is  not  certain.  It  seems  often  as  if  we  should  content  ourselves  with  saying  that 
there  is  an  extra  finger,  but  that  no  particular  one  has  been  repeated.  Sometimes 
the  thumb  has  three  phalanges.  Occasionally  any  of  the  terminal  phalanges  is 
doubled.  A  very  uncommon  condition  is  that  of  seven  or  eight  fingers  and  no 
thumb.  The  dissection  of  such  a  case  revealed  the  absence  of  the  radius  and  of  the 
radial  side  of  the  wrist,  the  skeleton  of  the  forearm  consisting  of  two  ulnae  and  that 
of  the  hand  of  the  ulnar  sides  of  two  opposite  ones  fused  together. 

PRACTICAL    CONSIDERATIONS. 

The  Carpus. — Of  the  carpal  bones  the  scaphoid  and  semilunar  are  most  fre- 
quently broken,  on  account  of  their  more  direct  relation  to  the  line  of  transmission 
of  force  in  falls  upon  the  hand.  The  diagnosis  is  difficult,  and  has  been  made 
oftenest  by  the  help  of  a  skiagraph.  There  is  but  little  displacement.  The  other 
bones  of  the  carpus,  on  account  of  their  shortness,  irregular  and  rounded  shape, 
and  compact  union  by  strong  ligaments  which  yet  permit  slight  movements  be- 
tween the  bones,  usually  escape  injury  except  in  cases  of  crush  of  the  whole  hand. 
They  are,  however,  not  infrequently  the  seat  of  tuberculous  disease,  as  might  be 
expected  from  their  great  liability  to  traumatism  of  all  grades.  Their  synovial  re- 
lations (Fig.  342)  favor  the  spread  of  such  disease  from  one  bone  to  the  remainder, 
and  render  conservative  treatment  unsatisfactory.  The  result,  too,  is  affected  by  the 
close  proximity  of  the  flexor  and  extensor  tendons,  which  become  involved  in  the 
tuberculous  process  or  bound  down  by  adhesions. 

The  Metacarpus. — The  first  metacarpal  bone,  which  is  morphologically  a 
phalanx,  is,  like  all  the  phalanges,  developed  from  an  epiphysis  situated  at  its 
proximal  end.  But  one  case  of  disjunction  has  been  recognized  during  life.  It  re- 
sembled a  dislocation  at  the  carpo-metacarpal  joint,  but  the  seat  of  abnormal  move- 
ment was  below  the  level  of  the  lower  edge  of  the  trapezium.  In  the  remaining 
metacarpal  bones  the  epiphysis  is  situated  at  the  distal  extremity. 

Falls  upon  or  striking  with  the  closed  fist  tend  to  produce  forward  displace- 
ment. As  the  metacarpal  bones  of  the  index-,  middle,  and  ring  fingers  are  the 
longer,  their  epiphyses  are  more  likely  to  be  separated  in  this  manner.  A  fall  on 
the  extended  fingers  and  metacarpo-phalangeal  region  may  cause  backward  displace- 
ment, though  this  is  rarer. 

The  diagnosis  from  dislocation  of  the  proximal  phalanges  is  not  easy.  It  is 
aided  by  the  recognition  of  "  muffled  crepitus"  (Poland)  and  by  the  great  tendency 
of  the  deformity  to  recur,  due  partly  to  the  small  articular  areas  of  the  separated 
bones  and  partly  to  the  action  of  the  flexors  and  the  interossei.  Skiagraphy  will 
usually  establish  the  diagnosis. 

Fracture  of  the  metacarpal  bones  is  usually  the  result  of  a  blow  with  the 
clinched  fist.  The  metacarpals  of  the  thumb  and  little  finger  are  therefore  rarely 
broken.  On  account  of  the  mode  of  application  of  the  force,  the  seat  of  fracture  is 
1  Zeitschrift  fur  Morph.  und  Anthropol.,  Bd.  ii.,  1901. 


320  HUMAN   ANATOMY. 

apt  to  be  near  the  distal  end,  although  the  thinnest  and  weakest  parts  of  the  bones 
are  just  above  the  middle  and  they  sometimes  break  there.  The  proximal  fragment 
is  held  firmly  by  its  ligamentous  attachments  and  is  less  movable  than  the  phalangeal 
portion  ;  its  distal  end  may  project  on  the  dorsum.  The  knuckle  of  the  affected 
finger  sinks  and  partially  disappears.  The  lumbricales  and  the  interossei  aid  in 
producing  this  deformity,  and  may  cause  the  proximal  end  of  the  distal  fragment  to 
become  prominent  on  the  dorsum  of  the  hand.  In  examining  for  these  fractures  it 
should  be  remembered  that  the  metacarpal  bones  of  the  index-  and  middle  fingers  are 
bound  tightly  to  the  carpus  and  possess  but  little  power  of  independent  movement. 
The  others  are  more  movable.  In  the  treatment  of  these  fractures  the  normal  palmar 
concavity  of  the  metacarpal  bones  should  never  be  forgotten. 

The  Phalanges. — Epiphyseal  separation  of  the  phalanges  is  extremely  rare. 
The  epiphyses  are  all  at  the  upper  ends  of  the  bones.  The  diagnosis  from  severe 
sprain  or  from  fracture  will  usually  be  made  by  the  X-rays.  It  is  now  thought  that  not 
a  few  of  the  cases  of  necrosis  of  the  proximal  end  of  a  phalanx  following  acute  inflam- 
mation or  whitlow  are  the  result  of  epiphyseal  sprain  or  disjunction.  Of  course, 
necrosis  is  often  the  sequel  of  the  spread  of  infection  from  the  superficial  structures 
of  the  hand  to  the  closely  applied  fibro-cellular  tissue  over  the  terminal  phalanges. 

Fractures  occur  most  frequently  in  the  proximal  and  most  rarely  in  the  ter- 
minal phalanges.  The  relation  of  the  tendons  on  the  dorsal  and  palmar  surfaces 
usually  prevents  any  marked  displacement.  Occasionally  an  anterior  angular  de- 
formity of  the  proximal  phalanx  is  seen  after  fracture.  It  is  believed  to  be  favored 
by  the  action  of  the  interossei. 

The  frequency  with  which  both  tuberculous  and  syphilitic  inflammations  affect 
the  phalanges  is  probably  due  to  their  exposure  to  slight  injury.  They  are,  how- 
ever, not  often  the  subject  of  post-typhoidal  infection.  The  cause  of  whitlow  has 
already  been  mentioned,  and  will  be  recurred  to.  The  reason  for  the  over- 
growth of  the  bony  structures  of  the  hand  in  acromegaly  and  in  hypertrophic  pul- 
monary osteo-arthropathy  is  not  known.  In  the  latter  case  it  has  been  suggested 
that  the  enlargement  of  the  terminal  phalanges,  like  the  ' '  clubbing' '  of  the  fingers  in 
phthisical  patients,  may  be  due  to  an  osteogenetic  stimulus  derived  from  the  pres- 
ence in  the  circulation  of  the  secondary  products  of  the  pulmonary  infection.  This 
would  be  analogous  to  the  increased  rapidity  of  growth  observed  in  adolescents 
during  convalescence  from  typhoid. 

Landmarks. — On  the  inner  side  of  the  hand,  below  the  wrist,  the  pisiform 
bone  can  be  felt,  and  when  grasped  firmly  can  be  given  slight  lateral  movement. 
Lower  and  more  externally  the  hook  of  the  unciform  can  be  made  out.  On  the 
outer  side  the  tuberosity  of  the  scaphoid  just  below  and  internal  to  the  radial  sty- 
loid  and  still  lower  the  ridge  of  the  trapezium  may  both  be  felt.  With  the  hand 
in  full  flexion,  the  dorsal  prominence  of  the  scaphoid  and  semilunar  and  the  curved 
line  of  their  articulation  with  the  radius  may  be  felt  ;  the  anterior  and  posterior 
lips  of  the  articular  surface  of  the  latter  bone  can  be  palpated  and  the  groove  or 
depression  beneath  them  recognized.  The  projection  of  the  os  magnum  on  the 
back  of  the  hand,  and  occasionally  of  the  base  of  the  third  metacarpal  at  its  articu- 
lation with  the  os  magnum,  may  easily  be  felt.  When  an  unusual  prominence  of  these 
bones  exists,  and  is  first  noticed  after  a  fall  or  strain,  it  sometimes  leads  to  a  mis- 
taken diagnosis  of  exostosis  or  of  ganglion. 

The  metacarpal  bones,  their  concavity,  their  expanded  anterior  extremities  form- 
ing the  knuckles,  the  shape  and  size  of  the  shafts  and  ends  of  the  phalanges,  and  of 
their  articulations  with  the  metacarpus  and  with  each  other,  can  all  readily  be  made 
out  through  or  between  the  overlying  tendons. 

The  surface  markings  of  the  hand  and  of  its  joints  will  be  considered  later  (page 
621.) 

LIGAMENTS   OF  THE  WRIST  AND   METACARPUS. 

The  ligaments  and  joints  of  the  wrist  include  three  articulations,  the  radio- 
carpal,  the  intracarpal,  and  the  carpo-metacarpat ',  which  often  receive  detailed 
separate  description.  The  simpler  and  in  many  ways  more  desirable  conception  of 
these  joints  is  to  regard  them  as  parts  of  a  common  articulation  consisting  of  a 


LIGAMENTS   OF   THE   WRIST   AND    METACARPUS. 


321 


general  capsular  ligament  enclosing  synovial  cavities  separated  by  an  interarticular 
fibre-osseous  septum  composed  of  the  bones  of  the  first  row  and  their  interosseous 
ligaments.  Preparatory  to  the  common  description  which  follows,  it  is  necessary  to 
consider  the  ligaments  and  relations  of  the  groups  of  bones  which  take  part  in  the 
formation  of  the  subdivisions  of  the  general  articulation. 

The  pisiform  being  practically  a  sesamoid  bone,  the  upper  end  of  the  carpus  is 
an  egg-shaped  articular  surface  made  chiefly  by  the  convexities  of  the  scaphoid  and 
semilunar  and  to  a  small  extent  by  the  cuneiform  (Fig.  340).  These  three  bones 
are  united  into  one  apparatus  by  two  strong  interosseous  ligaments  situated  just 
below  the  proximal  ends  of  the  bones,  covered  by  synovial  membrane  and  com- 

FIG.  340. 


Ulna 


Triangular  cart 
Semil 


merit  of  first  row 


Interosseous 
carpo-metacarpal 
ligament 


Dorsal  ligament  of 
second  row 


Dorsal  intermetacarpal  ligaments 


Dorsal  aspect  of  right  wrist.  The  joint  of  ulna  is  opened  and  the  shaft  displaced  forward  and  inward  to  show 
under  side  of  head.  The  radio-carpal,  intracarpal,  and  carpo-metacarpal  joints  are  shown  by  removing  the  dorsal 
ligaments  and  flexing  the  hand. 

pleting  the  articular  surface.  They  completely  shut  off  the  radio-carpal  from  the  in- 
tracarpal joint.  The  latter  is  concavo-convex,  the  concave  part  being  formed  by  the 
cuneiform,  the  semilunar,  and  the  hollow  surface  of  the  scaphoid  ;  the  convexity  by 
the  lower  surface  of  the  latter  bone,  which  articulates  with  the  trapezium  and  trape- 
zoid.  The  concavity  amounts  to  a  socket,  of  which  the  side  formed  by  the  scaphoid 
is  nearly  at  right  angles  to  the  base,  while  the  inner,  formed  by  the  cuneiform,  is 
oblique.  The  scaphoid  is  attached  to  the  semilunar  much  less  tightly  than  is  the 
cuneiform,  so  that  considerable  motion  occurs  between  them.  The  scaphoid,  besides 
sliding  in  various  directions  on  the  semilunar,  can  turn  on  an  approximately  trans 
verse  axis  through  its  proximal  part,  which  permits  of  flexion  and  extension,  to 
some  degree  independent  of  the  rest  of  the  first  row.  Its  lower  end  may  also  move 


322 


HUMAN   ANATOMY. 


somewhat  outward  and  inward,  so  as  to  broaden  or  narrow  the  socket.  The  distal 
row  of  carpal  hones  presents  a  prominence  made  by  the  os  magnum  and  the  unci- 
form,  which  are  held  firmly  together  so  as  to  move  nearly  as  one,  fitting  into  the 
socket  presented  by  the  first  row.  The  outer  side  of  this  prominence  is  quite 
straight,  making  an  entering  angle  with  the  trapezoid,  receiving  the  ridge  between 
the  concavity  and  convexity  of  the  scaphoid.  At  this  point  near  the  palmar  surface 
the  os  magnum  receives  a  ligament  from  the  scaphoid,  which  may  occasionally 
deserve  to  be  called  interosseous.  The  pisiform  has  a  capsular  ligament  enclosing 
the  joint  between  it  and  the  cuneiform. 

The  four  bones  of  the  second  row  are  joined  by  three  interosseous  ligaments:  one 

FIG.  341. 

Ulna     Interosseous  membrane     Radius 


Inferior  dorsal  radio-ulnar, 
ligament  (relaxed) 


Dorsal 
carpo-metacarpal  ligaments 


Dorsal  transverse  ligament 


Accessory  bands 


Scapho-metacarpal 
band 


Dorsal  aspect  of  right  wrist. 

between  the  trapezium  and  trapezoid,  near  the  palm  ;  one  between  the  trapezoid  and 
os  magnum,  near  the  dorsum  ;  and  one  between  the  os  magnum  and  unciform,  much 
the  strongest,  connecting  the  palmar  halves  of  the  bones  at  the  distal  end.  None 
of  these  interrupt  the  communication  of  the  synovial  cavity  of  the  intracarpal  joint 
and  those  at  the  bases  of  the  metacarpals.  The  scaphoid,  semilunar,  and  cuneiform 
have  very  properly  been  compared  to  an  intra-articular  fibro-cartilage  or  meniscus, 
subdividing  a  joint.  No  muscle  of  the  forearm  is  inserted  into  them.  (The  flexor 
carpi  ulnaris,  which  has  the  pisiform  as  a  sesamoid  bone  in  its  tendon,  has  its  real 
termination  in  the  fifth  metacarpal. )  Hence  this  series  is  never  directly  moved,  but 
changes  position  under  the  pressure  of  the  distal  row,  which  is  pulled  against  it 
by  the  muscles  moving  it.  It  plays  an  important  part  in  the  movements  of  the 
joint 


LIGAMENTS    OF    THE   WRIST    AND    METACARPUS.  323 


The  bases  of  the  metacarpals,  except  the  thumb,  articulate  with  one  another  by 
the  lateral  facets,  and  just  below  these  joints  are  held  together  by  strong  interosseous 
ligaments  connecting  the  rough  depressions  below  the  bases.  The  fibres  of  the 


Radiu 


Radio-caipal  joint 


Intracar_ 
(between  scaphoid  and  os  m 


pal  j 


Joint  between  trapezium  a 
first  metacarpal 


agn 


nd 


Ulna 

Inferior  radio-ulnar  joint 

Triangular  fibro-cartilage 


v—Intracarpal  joint 

(between  cuneiform  and  unciform) 


Carpo-metacarpal  joint 


Carpal  synovial  sacs  seen  in  longitudinal  section. 

interosseous  ligament  from  the  trapezium  to  the  trapezoid  are  inseparable  from  some 
from  the  trapezium  to  the  second  metatarsal. 

A  common  description  will  best  serve  for  the  ligaments  connecting  the  forearm, 
the  first  row,  the  second  row,  and  the  bases  of  the  metacarpals  (Figs.  340,  341). 
The  simplest  conception  is  of  a  capsule  passing  from  the  forearm  to  the  metacarpus 
and  attached  to  the  intervening  bones.  It  is  much  strengthened  by  neighboring 


324 


HUMAN   ANATOMY. 


tendons  and  their  sheaths.  It  is  strong  at  the  sides  ;  weak  in  front  and  behind. 
The  stronger  bands  are  inextricably  blended  with  the  rest  ;  that  on  the  outside,  the 
external  lateral  ligament?  runs  from  the  radial  styloid  process  to  the  outer  side  of 
the  scaphoid,  thence  to  the  trapezium,  and  is  continuous  with  the  capsule  of  the 
carpo-metacarpal  joint  of  the  thumb.  The  internal  lateral  ligament'1'  runs  from  the 
styloid  process  of  the  ulna  to  the  side  of  the  cuneiform,  and  to  the  pisiform,  thence 
to  the  narrow  internal  edge  of  the  unciform,  and  finally  to  the  fifth  metacarpal.  The 
dorsal  part  of  the  capsule  is  the  weakest,  but  is  much  strengthened  by  the  extensor 
tendons.  A  continuous  layer  passes  from  the  radius  and  ulna  to  the  first  row,  thence 
to  the  second,  and  thence  to  the  metacarpals.  The  general  direction  of  the  fibres  of 

FIG.  343. 

Radius    Interosseous  membrane     I'lna 


Styloid  process 
Radio-carpal  ligament 

Tubercle  of  scaphoid 

Ridge  of  trapezium 
Anterior  carpal  ligament 


Ant.  inferior  radio-ulnar 
ligament 


Styloid  process 
Pisiform  ligament 


Pisiform 


Int.  lateral  ligament 


ciform 


Tendon  of  ext.  carpi 
ulnaris 


Outer  end  of  ant.  annular  ligament 


Inner  end  of  ant.  annular  ligament 


Anterior  aspect  of  right  wrist-joint.     A  portion  oi  the  anterior  annular  ligament  has  been  removed  and  the  canal  for 

the  flexor  carpi  radialis  opened. 

the  proximal  part  is  transverse,  inclining  inward  from  the  styloid  process  of  the  radius 
and  the  scaphoid  to  the  cuneiform.  This  constitutes  the  dorsal  transverse  ligament, 
which  serves  to  hold  the  head  of  the  os  magnum  and  the  adjoining  part  of  the  unci- 
form in  the  socket  made  by  the  concavity  of  the  first  row.  It  has  no  definite  borders. 
Tolerably  distinct  bands  pass  to  the  bases  of  the  four  inner  metacarpals  ;  those  to 
the  second  and  third  are  tense  and  the  others  lax.  Various  accessory  bands  are 
often  found.  The  anterior  part  of  the  capsule  in  the  hollow  of  the  wrist  is  stronger  : 
it  is  reinforced  by  oblique  bands  converging  downward.  Many  of  these  fibres  are 
attached  to  the  narrow  palmar  prominence  of  the  os  magnum.  Pretty  distinct 
bundles  go  to  the  bases  of  the  metacarpals.  Very  small  disks  project  into  both  the 
radio-carpal  and  tin-  intracarpal  joints  from  the  dorsum,  which  are  hardly  seen 

1  Llg.  t  "1l.-iiri.ili-  carpi  rudlulc.     •  Lltf.  oolluteralv  carpi  ulnare. 


LIGAMENTS   OF   THE   WRIST   AND    METACARPUS. 


325 


in  frozen  sections.      Their  broader  bases  are  attached  to  the  capsule,  and  the  free 
sharp  edges  end  in  the  joint  fitting  in  between  the  bones. 

The  pisiform  has  a  special  joint  on  the  palmar  side  of  the  cuneiform,  with  a  lax 
capsule.     This  is  strength- 
ened internally  by  a  bundle  FIG.  344. 


Palmar  fascia 
Muscles  of  little  finger          \ 


Pisiform 


Cuneiform 


Anterior  annular  ligament 

Palmar  carpal  ligaments 

Tendon  of  flex,  carpi  rad. 


Scaphoid 


Unciform 


Os  magnum 
Dorsal  carpal  ligaments 


Transverse  section  through   right   wrist  from  above.      The  flexor  tendons 
have  been  removed  from  the  canal  beneath  the  annular  ligament. 


Radius 


Intra-articular  disk 

Semilunar 

Intra-articular  disk 

Os  magnum 


from  the  cuneiform  run- 
ning from  the  dorsal  to  the 
palmar  side.  Two  well- 
marked  bands  pass  down- 
ward from  it  on  the  latter 
aspect  ;  the  one  to  the  base 
of  the  fifth  metacarpal  is 
really  the  end  tendon  of 
the  flexor  carpi  ulnaris, 
the  other  passes  obliquely 
to  the  proximal  edge  of 
the  unciform  process. 

The  Anterior  An- 
nular Ligament. — This 
is  an  extremely  strong  structure,  bridging  the  hollow  of  the  wrist,  and  enclosing  a 
canal  through  which  pass  the  tendons  of  the  long  flexors  of  the  thumb  and  fingers 
and  the  median  nerve.  It  springs  internally  from  the  process  of  the  unciform  and 

from  the  pisiform,  the  latter  part  being  fused  with 

FIG.  345.  the  band  from  it  to  the  unciform.      It  is  attached 

externally  to  the  ridge  on  the  trapezium,  and  by  a 
deeper  process  to  the  tuberosity  of  the  scaphoid 
and  to  the  inner  side  of  the  front  surface  of  the 
trapezium,  thus  splitting  to  allow  the  passage  of 
the  tendon  of  the  flexor  carpi  radialis  through  a 
special  canal  in  the  groove  of  the  trapezium. 
Frozen  sections  through  the  wrist,  passing  through 
the  pisiform  (Fig.  344)  (but  not  those  through  the 
unciform),  show  deep  fibres  from  the  annular  liga- 
ment passing  down  under  the  canal  and  blending 
with  the  front '  of  the  capsular  ligament  of  the 
wrist.  The  proximal  and  distal  borders  of  the 
ligament  are  somewhat  artificial,  as  it  is  connected 
with  the  fascia  of  the  forearm  and  with  the  palmar 
fascia,  besides  receiving  fibres  from  the  flexor  carpi 
ulnaris.  This  anterior  annular  ligament  holds  the 
sides  of  the  wrist  firmly  together  and  prevents  them 
from  spreading  when  pressure  is  applied  from 
above.  Its  fibres  mingle  with  the  origins  of  mus- 
cles of  the  thumb  and  of  the  little  finger. 

The  posterior  annular  ligament  is  but  a 
thickening  of  the  fascia  of  the  back  of  the  forearm, 
and  has  no  place  among  the  true  ligaments. 

The  Carpo-Metacarpal  Articulations.— 
Those  of  the  four  inner  fingers  have  been  partially 
described.  They  connect  with  the  general  articular 
cavity  of  the  wrist.  A  band  from  the  adjacent 
edges  of  the  os  magnum  and  unciform  to  those  of 
the  third  and  fourth  metacarpals  (Fig.  340)  does 
not  completely  interrupt  the  continuity  of  this 
cavity,  as  it  does  not  reach  the  dorsal  surface. 
The  carpus  and  metacarpus  are  connected  on  both 

front  and  back  by  bands  which  can  be  fairly  distinguished  from  the  capsule.  Trans- 
verse bands  run  also  on  both  surfaces  from  the  base  of  one  metacarpal  to  the 
next.  The  opposed  sides  of  the  bases  are  partly  covered  with  articular  cartilage, 


Third  metacarpa! 


Frozen  section  through  right  middle  finger, 
the  hand  being  straight. 


326 


HUMAN    ANATOMY. 


Radius 


Disk 
Semilunar 


Os  magnum  Third  metacarpal 

Same  as  Fig.  345,  the  hand  being  flexed. 


as  has  been  described.  Interosseons  metacarpal  ligaments  connect  their  sides  distally 
from  this.  These  complete  the  capsules,  which  are  imperfect  only  on  the  carpal 
side. 

The  articulation  of  the  thumb  (  Fig.  342)  differs  from  the  others  in  being 
complete  in  itself.      It  is  a  saddle-shaped  joint.     The  hand  lying  supine,  the  long 

axis  of  the  joint  slants  down- 

FIG.  346.  ward    and    inward.       In    this 

direction  the  trapezium  is  con- 
cave ;  at  right  angles  to  it  con- 
vex. The  joint  is  surrounded 
by  a  capsule,  which  is  strongest 
on  the  dorsal  and  palmar  sides, 
where  the  direction  of  the 
fibres  is  longitudinal  ;  it  is 
weak  at  the  outer  anterior  end, 
where  it  is  strengthened  by 
the  tendon  of  the  extensor  of 
the  metacarpal  bone. 

The  motions  are  flexion, 
extension,    adduction,    abduc- 
tion, and  circumduction.     Ro- 
tation   in   the  flexed    position 
may  be  possible  from  the    im- 
perfect  adaptation  of   the  ar- 
ticular surfaces,  but  can  hardly  be  of  practical  importance.      Flexion  is  limited  by 
the  locking  of  the  palmar  projection  of  the  metacarpal  against  the  trapezium  ;  the 
other  angular  motions  by  the  tension  of  the  ligaments. 

Movements  and  Mechanics  of  the  Wrist  and  Carpo-Metacarpal 
Articulations. — It  is  convenient  in  studying  these  movements  to  imagine  that  the 
metacarpus  follows  the  motions  of  the  second  row  of  carpal  bones.  This  is  true  of 
the  index-  and  middle  fingers,  but  not  of  the  others.  The  motions  of  the  wrist  in 
the  widest  sense  are  flexion,  extension,  adduction,  abduction,  and  circumduction. 
The  joint  is  a  compound  one,  egg-shaped  above,  the  scaphoid,  semilunar,  and 
cuneiform  acting  as  a  meniscus.  The  motions  are  best  studied  by  removing  the 
skin  and  tendons  on  the  dorsal  aspect  and  inserting  long  pins  into  the  radius,  semi- 
lunar,  and  os  magnum,  and,  for  some  purposes,  the  scaphoid.  The  Rontgen  rays 
have  been  useful  chiefly  as 
corroboratory  evidence.  In 
flexion  the  motion  begins  in 
the  upper  joint,  where  it  is 
most  extensive  ;  as  it  goes 
on  the  lower  takes  part.  In 
extension,  starting  with  the 
arm  straight,  more  than  half 
occurs  in  the  lower  joint. 
Adduction  (ulnar  flexion) 
(Fig.  348,  It),  owing  to  the 
lesser  prominence  of  the  ulna, 
is  more  free  than  abduction. 
The  meniscus  glides  towards 
the  radial  side,  and  in  so 


FIG.  347. 


Third  metacarpal 


( K  magnum 


Same  as  Fig.  345,  the  hand  being  overextended. 


doing  assumes  the  relation  to 
the  radius  that  it  has  in 
extension.  The  scaphoid 
touches  the  radius  only  by  one  end,  so  that  its  long  axis  approaches  the  direction  of 
that  of  the  forearm,  and  the  semilunar  leaves  the  triangular  cartilage.  The  curve  of 
the  meniscus  broadens,  increasing  the  distance  between  the  ends  of  the  cuneiform 
and  the  scaphoid.  A  small  part  of  the  motion  occurs  in  the  mid-carpal  joint.  The 
unciform,  moving  with  the  os  magnum,  comes  nearer  to  the  semilunar.  The  space 


LIGAMENTS   OF   THE   WRIST   AND    METACARPUS. 


327 


between  the  neck  of  the  os  magnum  and  the  scaphoid  enlarges.  In  abduction  (radial 
flexion)  (Fig.  348,  A)  the  second  row  of  the  carpus  has  a  larger  share  in  the  motion 
than  in  adduction.  The  meniscus  moves  to  the  ulnar  side  and  is  flexed,  while  its 
ends  approach  each  other,  narrowing  the  arch.  The  lower  end  of  the  scaphoid  is 
crowded  against  the  os  magnum  and  the  proximal  end  of  the  unciform  recedes  from 
the  semilunar.  Lateral  motions  do  not  occur  when  the  wrist  is  either  strongly  flexed 
or  extended.  The  screw  surfaces  of  the  cuneiform  and  unciform  are  important 
factors  in  the  combination  of  antero-posterior  and  lateral  motions  ;  but  the  os  mag- 
num and  unciform,  which  move  together,  do  not  twist  in  the  socket  formed  by  the 
first  row  if  the  latter  be  fixed.  Circumduction  is  a  combination  of  the  preceding 
motions.  Though  the  meniscus  moves  as  a  whole,  the  scaphoid  is  less  closely 
attached  to  the  semilunar  than  is  the  cuneiform. 


FIG.  348. 


Reduced  tracings  from  skiagraphs,  showing  the  position  of  the  carpal  bones.    A ,  in  radial  flexion  ;  S,  in  ulnar  flexion.1 


Flexion  is  limited  by  the  tension  of  the  dorsal  ligaments  ;  extension  in  the 
upper  joint  chiefly  by  the  lateral  ligaments,  in  the  lower  by  the  locking  of  the  bones 
of  the  meniscus  against  those  of  the  first  row.  The  anterior  fibres  of  the  capsule 
probably  assist.  Lateral  motion  is  checked  in  the  upper  joint  by  the  side  liga- 
ments ;  in  the  lower  joint  it  is  limited  chiefly  by  the  shape  of  the  bones.  The 
number  of  joints  between  the  carpal  bones  divide  the  force  of  shocks  transmitted 
through  the  hand. 

The  motions  of  the  carpo-metacarpal  joints  of  the  fingers  are  almost  wanting, 
except  for  the  ring  and  little  fingers.  In  both  these  the  motion  is  essentially  flexion, 
most  marked  in  the  latter,  and,  owing  to  the  dorsal  convexity  of  the  carpus,  tending 
to  oppose  the  little  finger  to  the  thumb. 

The  metacarpo-phalangeal  articulations  are  surrounded  by  a  rather  loose 
capszile,  which  is  inserted  into  both  bones  pretty  close  to  the  articular  cartilage. 
It  is  weakest  on  the  dorsum,  where  it  is  supported  by  the  extensor  tendons.  It 

1  In  tracings  from  X-ray  photographs  it  is  in  places  very  difficult  satisfactorily  to  outline  the 
separate  bones,  partly  because  the  contours  of  both  surfaces  as  well  as  of  thick  processes  are 
shown,  and  partly  because  some  bones  lie  in  front  of  others,  owing  to  the  palmar  concavity  of 
the  wrist.  The  greatest  difficulty  is  with  the  respective  outlines  of  the  trapezium  and  trapezoid. 
In  the  above  figures  the  outline  of  the  latter  is  indicated  in  dotted  lines.  This  confusion  is  of 
little  practical  importance,  since  the  drawings  are  to  illustrate  the  changes  of  position  between 
the  first  row  and  the  forearm  on  one  side  and  the  second  row  on  the  other. 


328 


HUMAN   ANATOMY. 


FIG.  349. 


Glenoid  cartilage 


Insertion  of 
ext.  commun. 
cligitorum 


Outer  side  of  right  forefinger.     The  metacarpo- 
phalangeal  joint  is  opened. 


springs  from  little  hollows  on  the  sides  of  the  heads  of  the  metacarpals.  Longi- 
tudinal fibres  are  distinct  at  the  sides,  if  sought  for  from  within  the  joint.  The  cap- 
sule is  strengthened  on  the  palmar  surface  by  fibrous  or  fibro-cartilaginous  plates, — 
the  glenoid  cartilages, — which  form  the  beginnings  of  the  floor  of  the  canals  for  the 

flexor  tendons  (Fig.  350).  These  plates  are 
firmly  fastened  to  the  bases  of  the  phalanges, 
whose  motions  they  follow,  and  loosely  to  the 
metacarpals.  In  the  thumb  the  glenoid  plate 
amounts  to  little  or  nothing,  as  the  palmar 
aspect  of  the  joint  is  chiefly  covered  by  the  two 
sesamoid  bones,  which  are  firmly  held  near 
together  by  transverse  fibres.  When  sesamoids 
are  present  in  the  other  joints,  they  are  lost  in 
the  fibrous  tissue  at  the  sides  of  these  plates. 
The  glenoid  cartilages  of  the  four  inner  fingers 
are  attached  to  one  another  by  a  series  of  bands 
of  little  strength, — the  transverse  metacarpal 
ligament  (Fig.  351). 

The  articular  surface  of  the  metacarpal  is 
in  the  main  convex  and  that  of  the  phalanx 
concave.  They  do  not  make  a  true  ball-and- 
socket  joint,  for  the  long  axis  of  the  latter  is 
transverse  and  at  right  angles  to  that  of  the 
former,  which,  moreover,  is  much  broader  at 
its  palmar  than  at  its  dorsal  end.  As  the 
glenoid  disks  are  parts  of  the  floors  of  the 
canals  for  the  tendons  diverging  from  the  mid- 
dle of  the  wrist,  those  of  the  second  and  fifth  fingers  are  not  squarely  placed,  but 
incline  to  the  middle  of  the  hand. 

Movements. — When  the  finger  is  straight,  it  can  be  moved  laterally,  a  little 
backward,  and  flexed,  as  well  as  circumducted.  It  can,  on  the  dead  hand,  be 
slightly  rotated  ;  but  this  motion  does  not  occur  in  life.  When  it  is  fully  flexed, 
lateral  motion  is  impossible  owing  to  the  tenseness  of  the  capsule,  which  has  occurred 
in  two  ways, — partly  from  the  fact  that  in  flexion  the  phalanx  rests  on  the  broadest, 
instead  of  the  narrowest,  part  of  the  head,  and  because,  the  depressions  for  the 
origins  of  the  strongest  lateral 
parts  being  near  the  dorsum, 
these  are  stretched  when  the 
phalanx  has  travelled  round  the 
palmar  prominence  of  the  head. 

The  interphalangeal  ar- 
ticulations differ  from  the  pre- 
ceding by  the  peculiarities  of  the 
articular  ends  and  the  greater 
relative  strength  of  the  lateral 
parts  of  the  capsules.  The  gle- 
noid cartilages  are  small.  There 
is  no  lateral  motion.  They  are 
the  purest  hinge-joints  in  the 
body. 

The  Surface  Anatomy 
of  the  Wrist  and  Hand.— 
The  joint  between  the  forearm 
and  the  carpus  can  be  approxi- 
mately indicated  by  a  line  either 
on  the  back  or  the  front,  but  more  accurately  on  the  former,  starting  from  the 
head  of  the  ulna,  running  nearly  transversely,  but  with  a  slight  upward  bend, 
to  near  the  radial  styloid,  and  then  sweeping  downward  to  its  tip.  The  first  row  of 
carpal  bones  can  be  made  prominent  on  the  back  by  flexing  the  wrist.  The  hollow 


FIG. 


ii. 


350. 

Transverse  metacarpal  ligament 
III.      A      IV.  V. 


Metacarpals 


Phalanges 


Palmar  aspect  of  right  metacarpo-plialangeal  joints 
flexor  tendons  opt'iu-d. 


Glenoid  cartilages 

Sheaths  for 


PRACTICAL   CONSIDERATIONS:    THE   WRIST-JOINT,  329 


Metacarpals 


on  the  dorsum  of  the  os  magnum  is  distinct,  and  some  indication  of  the  mid-carpal 
joint  may  be  felt  near  it.  ' '  Slightly  external  to  the  middle  of  the  hand  is  a  promi- 
nence, sometimes  indistinct,  but  often  very  well  marked,  formed  by  the  styloid 
process  on  the  base  of  the  third  metacarpal  bone  at  its  articulation  with  the  os 
magnum"  (Thane  and  Godlee).  On  the  palmar  side  the  pisiform  can  be  felt  just 
at  the  beginning  of  the  hypothenar  eminence.  When  the  hand  is  flexed  and  the 
muscles  relaxed,  it  is  easily  moved  from  side  to  side.  The  unciform  process  can 
be  indistinctly  felt  below  it. 

The  tubercle  of  the  scaphoid  FIG.  351. 

is  felt  with  difficulty  below 
and  internal  to  the  radial 
styloid,  and  at  the  beginning 
of  the  thenar  eminence  (the 
ridge  on  the  trapezium)  more 
clearly.  The  position  of  the 
annular  ligament  may  be  de- 
duced from  these  points,  and 
it  may  be  felt  by  pressure  on 
the  hand.  It  is  a  general  rule 
for  the  joints  between  the  meta- 
carpals  and  the  phalanges,  as 
well  as  for  those  between  the 
latter,  that  the  more  distal 
moves  on  the  proximal,  and 
that,  therefore,  the  promi- 
nence of  the  knuckle  in  flexion 
is  made  by  the  head  of  the 
metacarpal.  All  the  meta- 
carpo-phalangeal  joints  can  be 
made  out  from  the  dorsum. 
The  sesamoid  bones  of  the 
thumb  are  felt  with  difficulty. 

The  web  of  the  fingers  lies  about  thirteen  millimetres  distal  to  the  palmar  aspect  of 
the  metacarpo-phalangeal  joints.  That  of  the  index-finger  is  about  midway  between 
the  transverse  furrow  reaching  the  radial  side  of  the  hand  and  the  first  crease  on 
the  finger  ;  those  of  the  other  fingers  are  in  the  same  relation  to  the  second  furrow 
and  the  respective  creases.  The  interdigital  joints  are  slightly  distal  to  the  upper 
line  of  the  complicated  creases  of  the  first  joints  and  to  the  single  line  of  the  creases 
of  the  second  row. 


Sheath  for  flexor 
tendons  opened 


Transverse  metacarpal  ligament 


Palmar  aspect  of  right  metacarpo-phalangeal  joints.     Sheath  for  flexor 
tendons  on  one  finger  opened  ;  on  adjacent  finger  still  closed. 


PRACTICAL   CONSIDERATIONS. 

The  Wrist-Joint. — The  radio-carpal  has  the  greatest  amount  of  motion  of 
the  three  rows  of  joints  that  intervene  between  the  metacarpus  and  the  forearm.  Its 
strength  is  not  derived  from  the  shallow  concavity  on  the  lower  end  of  the  radius, 
or  from  the  ligaments  which,  taken  together,  compose  the  capsule,  but  rather  from 
the  tough  fibrous  tissues  forming  the  sheaths  of  the  large  number  of  tendons  that 
pass  over  the  anterior  and  posterior  aspects  of  the  joint  and  are  closely  united  to 
the  bones.  It  escapes  frequent  injury,  also,  because  of  the  numerous  bones  that 
enter  into  the  carpus,  which  by  their  gliding  motion  one  upon  the  other  diffuse  force 
received  through  falls  upon  the  hand  ;  because  of  the  same  effect  produced  by  the 
movement  of  the  mid-carpal  joint  (intracarpal  of  Dwight),  which  takes  up  part  of  the 
force  in  overextension  of  the  hand  before  it  reaches  the  wrist  ;  and  because  of  the 
absence  of  any  long  rigid  lever  on  the  distal  side  of  the  joint. 

Dislocation  backward  is  by  fai  the  most  common,  on  account  of  the  frequency 
of  falls  upon  the  hand.  The  diagnosis  from  Colics' s  fracture  is  made  by  observing 
that  in  dislocation  :  (i)  the  anterior  swelling  is  nearer  the  ball  of  the  thumb  ;  (2) 
the  posterior  swelling  is  more  sharply  defined  at  its  upper  edge  ;  (3)  the  styloid 
process  of  the  radius  is  nearer  the  hand  than  that  of  the  ulna  ;  (4)  the  distance  from 


330  HUMAN   ANATOMY. 

it  to  the  head  of  the  metacarpal  bone  of  the  index-finger  is  shortened  ;  (5)  the 
antero-posterior  diameter  of  the  wrist  is  increased  ;  (6)  the  flexion  and  immobility 
of  the  wrist  are  greater. 

In  dislocation  forward  the  posterior  swelling  (the  sharp  border  of  the  radius 
and  ulna)  approaches  the  hand  ;  the  rounded  prominence  of  the  carpus  is  on  the 
front  of  the  wrist ;  the  antero-posterior  diameter  is  increased  and  the  stylo-meta- 
carpal  measurement  is  lessened. 

Outward  (radial)  dislocation  of  the  wrist  is  resisted  by  the  contact  of  the 
scaphoid  with  the  styloid  process  of  the  radius  and  by  the  internal  lateral  ligament. 
Inward  dislocation  would  theoretically  be  easier,  as  there  is  no  bony  obstacle,  and 
as  adduction  may  be  effected  to  a  greater  extent  than  abduction,  and  with  greater 
power,  on  account  of  the  leverage  afforded  by  the  projection  of  the  cuneiform  and 
pisiform  bones  on  the  inner  side  of  the  wrist.  It  is  for  this  reason  that  the  hand 
commonly  assumes  the  position  of  adduction  and  the  little  finger  becomes  inclined 
towards  the  ulna  when,  from  disease  or  other  cause,  the  muscles  lose  the  influence 
of  volition  and  exercise  an  uncontrolled  sway  over  the  part  (Humphry).  Disloca- 
tion in  either  lateral  direction  is,  however,  very  rare. 

Spontaneous  subluxation  forward  is  a  condition  thought  to  be  associated  with 
hard  manual  labor  in  which  the  strong  anterior  ligament  becomes  stretched  and  the 
radial  side  of  the  carpus  is  displaced  forward  and  upward.  This  is  followed,  in 
accordance  with  a  general  law  of  growth  (page  104),  by  an  overgrowth  of  the 
posterior  portion  of  the  lower  end  of  the  radius,  from  which  the  normal  opposing 
pressure  of  the  carpus  has  been  removed.  The  lower  end  of  the  ulna  becomes 
unduly  prominent. 

Disease  of  the  wrist-joint  is  frequently  tuberculous,  but  may  be  septic  or  rheu- 
matic or  gonorrhceal  in  its  origin.  As  the  joint-cavity  does  not  include  the  epiphyseal 
lines  of  either  the  radius  or  ulna,  the  synovial  membrane  being  attached  to  the 
margins  of  the  epiphyses,  disease  and  injury  of  the  latter  do  not  of  necessity  involve  the 
joint.  The  circumstances  already  detailed  that  protect  the  joint  from  dislocation 
also  protect  it  from  sprains  and  lessen  the  frequency  of  traumatic  synovitis  and  of 
the  sequelae  of  traumatism. 

Disease  of  any  variety  once  established  is  apt  to  extend  to  the  various  synovial 
pouches  of  the  carpus  on  account  of  their  proximity,  to  involve  the  flexor  and  ex- 
tensor tendon  sheaths  for  the  same  reason,  and  to  result,  in  accordance  with  its 
character,  in  either  extensive  disorganization  or  much  limitation  of  motion.  The 
flexors  and  extensors  on  the  front  and  back  of  the  wrist  act  with  about  equal  force, 
and  therefore  but  little  displacement  occurs. 

The  swelling  usually  shows  itself  first  on  the  dorsum  through  the  thinner  pos- 
terior ligament,  the  joint  being  nearer  the  surface  on  that  aspect. 

Landmarks. — The  line  of  the  wrist-joint  is  convex  upward.  A  straight  line 
drawn  between  the  two  styloid  processes  is  oblique  downward  and  outward.  It 
unites  the  two  extremities  of  the  arc  which  represents  the  line  of  the  joint.  The 
highest  point  of  that  arc  is  a  half-inch  above  the  interstyloid  line. 

If  a  knife  were  introduced  horizontally  below  the  tip  of  the  styloid  process  of 
the  ulna,  it  would  open  the  wrist-joint  ;  below  the  styloid  of  the  radius,  it  would 
strike  the  scaphoid. 

The  remaining  landmarks  are  described  on  page  621. 

The  Joints  of  the  Carpus,  Metacarpus,  and  Phalanges. — As  the  inter- 
mediate ligaments  uniting  the  separate  bones  of  each  row  of  the  carpus  are  all  trans- 
verse, and  do  not  pass  from  one  row  to  another,  the  mid-carpal  (intracarpal )  joint 
permits  of  considerable  motion  in  both  flexion  and  extension.  It  undergoes  disloca- 
tion with  extreme  rarity,  and  usually  only  as  a  result  of  a  degree  of  force  sufficient 
to  stretch  or  tear  tendons  and  ligaments. 

Dislocation  of  the  second  row  of  the  carpus  forward  is  prevented  by  the 
manner  in  which  the  concave  surfaces  of  the  trapezium  and  trapeze  ml  rest  upon  the 
posterior  convex  facet  of  the  scaphoid,  as  well  as  by  the  undulating  manner  in 
which  the  side  of  the  unciform  is  disposed  with  regard  to  the  side  of  the  cuneiform. 
I  )is|)lacement  backward  is  prevented  by  the  manner  in  which  the  round  head  of  the 
os  magnum  and  the  convex  posterior  and  upper  surface  of  the  unciform  are  let  into 


PRACTICAL   CONSIDERATIONS  :   THE   CARPAL   JOINTS.        331 

the  hollow  formed  in  the  anterior  and  inferior  surfaces  of  the  bones  of  the  first  row 
(Humphry). 

The  joints  between  the  individual  bones  of  the  carpus  allow  of  but  little  motion, 
and  much  force  is  needed' to  produce  displacement  of  those  bones.  In  the  order  of 
frequency  the  os  magnum,  semilunar,  scaphoid,  pisiform,  trapezium,  trapezoid,  and 
unciform  have  been  reported  as  separately  dislocated.  It  is  interesting  to  note  in 
relation  to  the  order  of  frequency  that  the  middle  finger  is  the  longest,  and  is  the 
one  most  exposed  to  injury  and  to  force  applied  to  the  fingers  ;  its  metacarpal  bone 
is  the  longest  ;  it  articulates  directly  with  the  strongest  carpal  bone, — the  os 
magnum, — and  it,  in  its  turn,  with  the  semilunar,  which  unites  with  the  scaphoid  in 
connecting  the  hand  with  the  forearm.  In  reported  cases  the  pisiform  was  thought 
to  be  dislocated  secondarily  after  the  rupture  of  the  tendon  of  the  flexor  carpi 
ulnaris  below  the  bone. 

The  other  separate  carpal  luxations  have  but  little  anatomical  interest. 

Disease  of  the  mid-carpal  joint  is  usually  tuberculous,  and  is  apt  to  begin  in  or 
extend  to  the  os  magnum  because — i.  It  is  the  bone  most  exposed  to  traumatism 
(vide  supra),  receiving  the  effects  of  injury  to  three  metacarpal  bones.  2.  The  joint 
participates  in  the  movements  of  flexion  and  extension  of  the  wrist,  which  are  partly 
limited  by  the  portion  of  the  oblique  fibres  (both  radial  and  ulnar)  of  the  anterior 
annular  ligament  (page  325)  and  by  some  of  the  radial  fibres  of  the  weak  posterior 
ligament,  which  are  attached  to  the  os  magnum.  3.  The  slight  rotation  permitted  in 
the  mid-carpal  joint  is  around  a  vertical  axis  drawn  through  the  head  of  the  os  mag- 
num. A  very  slight  enlargement  of  the  bone  would  tend  to  pinch  and  bruise  the 
synovial  membrane  between  it  and  the  trapezoid,  those  two  being  more  closely  bound 
together  than  any  of  the  other  bones.  It  has  been  noticed  (Mundell)  that  the  point 
of  greatest  tenderness  in  these  cases  of  carpal  tuberculosis  was  in  a  line  between  the 
index-  and  middle  fingers,  corresponding  to  the  junction  of  the  os  magnum  and  the 
trapezoid.  Harwell  says  that  in  tuberculosis  of  the  wrist-joint  the  point  of  special 
tenderness  is  on  the  outer  side  of  the  extensor  indicis  tendon.  This  is  on  the  same 
line,  and,  in  cases  in  which  the  carpus  has  become  involved,  would  correspond  to 
the  same  point  of  junction. 

Dislocations  of  the  metacarpal  bones  from  the  carpus  usually  involve  single 
bones,  are  incomplete,  and  are  in  the  backward  direction.  The  wavy,  irregular  out- 
line of  the  distal  edge  of  the  carpus,  the  dovetailing  of  the  metacarpals  and  carpals 
by  means  of  the  alternating  convexities  and  concavities,  and  the  strength  of  the 
interosseous  and  transverse  metacarpal  ligaments  sufficiently  explain  the  infrequency 
of  dislocation  of  the  metacarpus  as  a  whole. 

Dislocations  of  the  metacarpo-phalangeal  and  interphalangeal  joints  amount  to 
"  nearly  thirty  per  cent,  of  all  dislocations"  (Stimson).  Backward  displacement  of 
the  proximal  phalanx  of  the  thumb  is  the  most  frequent  and  the  most  important. 
The  cause  is  usually  exaggerated  extension  of  the  phalanx,  which  carries  its  proximal 
end  up  onto  the  dorsum  of  the  metacarpal  bone  above  the  articular  surface.  The 
relation  to  the  muscles  of  the  thumb  is  so  important  that  the  luxation  will  be 
described  in  that  connection  (page  617). 

Dislocations  between  the  phalanges  usually  occur  at  the  first  phalangeal  joint, 
and  in  the  backward  direction,  as  the  cause  is  common! v  a  fall  upon  the  palmar 
surface  of  the  finger  in  extension. 


THE   LOWER  EXTREMITY. 

The  Pelvic  Girdle. — This  consists  of  the  two  innominate  bones,  which  join 
each  other  in  front,  and  the  sacrum  behind.  While  the  thoracic  girdle  is  adapted 
to  freedom  of  motion,  the  pelvic  is  fitted  for  strength  and  support. 

The  study  of  the  innominate  bone  should  be  preceded  by  a  general  idea  of  the 
pelvis.  A  plane  between  the  promontory  of  the  sacrum  and  the  top  of  the  pubes 
divides  the  pelvis  into  the  false  pelvis  above,  formed  chiefly  by  the  ilia,  and  the  true 
pelvis  below.  The  latter  presents  the  sacrum  and  coccyx  behind,  the  arch  of  the 
pubes  in  front  and  below,  and  the  tuberosity  of  the  ischium  at  the  side.  Behind  this 
is  the  sacro-sciatic  notch,  much  reduced  by  ligaments.  On  the  sides  are  the  hip- 
joints,  and  towards  the  front  the  obturator  or  thyroid  foramen. 

THE    INNOMINATE    BONE. 

This1  consists  originally  of  the  ilium,  pubis,  and  ischium,  each  of  which  forms  a 
part  of  the  hip-joint,  but  which  fuse  so  completely  that  the  lines  of  union  are  not 
usually  to  be  seen  in  the  adult.  The  ilium  forms  the  upper  and  posterior  part  of  the 
bone,  the  pubis  the  front,  and  the  ischium  the  inferior.  The  two  latter  enclose  the 
obturator  foramen. 

The  Ilium. — The  ilium,2  a  plate  of  bone  forming  the  side  of  the  false  pelvis 
and  a  part  of  the  true,  may  be  said  to  have  four  borders.  The  superior  border, 
or  crest,:!  very  much  the  longest,  is  convex  upward  and  outward.  It  connects  two 
tubercles,  the  anterior  and  posterior  superior  spines  of  the  ilium,  of  which  the  former 
is  a  knob  overhanging  the  concave  anterior  border  and  giving  attachment  to  Pou- 
part's  ligament  and  the  sartorius,  while  the  latter  is  less  prominent.  The  crest  has 
a  double  lateral  curve,  the  front  half  being  convex  externally  and  the  posterior  inter- 
nally. It  is  thicker  at  the  ends  than  in  the  middle,  and  presents  also  a  thickening 
near  the  middle  of  each  curve,  projecting  on  the  convex  side.  There  is  an  external 
lip,  from  the  whole  length  of  which  springs  the  fascia  lata  of  the  thigh,  an  internal 
lip,  and  ^n  intermediate  space.  The  anterior  border  i^  short,  rounded,  and  con- 
cave, descending  to  the  anterior  inferior  spine,  a  knob  a  little  above  the  border  of 
the  acetabulum  giving  origin  to  the  straight  head  of  the  rectus  femoris  and  a  part  of 
the  ilio-femoral  band  of  the  capsule  of  the  hip-joint.  The  posterior  border,  very 
short  and  also  concave,  ends  in  the  posterior  inferior  spine,  an  ill-marked  angle  at 
the  bottom  of  the  surface  that  joins  the  sacrum.  The  inferior  border  consists 
anteriorly  of  an  attached  part,  which  meets  the  other  bones  in  the  acetabulum,  and 
behind  this  of  a  free  concave  part,  which  bounds  the  upper  part  of  the  great  sacro- 
sciatic  notch.*  The  ilium  might  also  be  described  as  consisting  of  an  expanded  por- 
tion, narrowing  below  to  a  stem,  which  joins  the  other  bones  in  the  acetabulum.  Its 
upper  part  follows  the  curves  of  the  crest. 

The  lateral  or  outer  surface  is  crossed  by  the  three  curved  or  gluteal  lines, 
convex  above  and  behind,  all  ending  at  or  near  the  sciatic  notch.  The  superior, 
much  the  strongest,  arises  from  the  crest  at  the  middle  of  its  second  curve  and  ends 
a  little  in  front  of  the  posterior  inferior  spine,  marking  off  a  raised  rough  surface 
behind  its  upper  two-thirds.  The  middle  begins  at  the  crest,  one  or  two  inches 
from  the  anterior  superior  spine,  and  ends  near  the  top  of  the  notch.  The  inferior, 
the  faintest,  starts  a  little  above  the  anterior  inferior  spine  and  is  lost  near  the 
front  of  the  notch.  The  three  gluteal  muscles,  maximus,  medius,  and  minimus 
arise  respectively  behind  these-  three  lines  in  the  order  given.  A  slight  groov 
for  the  reflected  tendon  of  the  rectus  femoris,  starting  at  the  anterior  inferior  spine, 
runs  backward  above  the  acetabulum. 

The  ventral  or  inner  surface  is  divided  into  an  upper  posterior  and 
a  lower  anterior  part  by  the  ilio-pcctincal  Hue  '  in  front,  and  a  rough  border  con- 
tinuing it.  The  former  is  a  line  beginning  on  the  pubis  and  continued  across  the 

1  <N  coxae.     -Os  ilium.      '  Crista  iliaca.     *  Incisurn  ischiadlca  major.     •''  Linea  arcuata. 
332 


THE   INNOMINATE   BONE. 


333 


ilium  to  the  sacrum,  separating  the  true  pelvis  below  from,  the  false  above.  '  All  of 
the  ilium  above  this  line,  except  a  small  part  posteriorly,  is  a  smooth,  shallow  con- 
cavity, the  iliac  fossa,1  which  contains  the  iliac  muscle.  It  ends  in  front  in  a  groove 
between  the  anterior  inferior  spine  of  the  ilium  and  the  ilio-pedineal  eminence?  a 
swelling  above  the  inner  part  of  the  acetabulum  made  by  both  the  ilium  and  the 
pubis  at  their  point  of  meeting.  The  bone  is  very  thin  at  the  middle  of  the  fossa. 
The  lower  half  of  the  inner  surface  of  the  ilium  may  be  subdivided  into  two  very 
dissimilar  parts.  The  front  one,  forming  the  wall  of  the  true  pelvis,  opposite  a  part 


FIG.  352. 


Middle  gluteal  line 


External  lip 


I.atissimus  dors 


tern  us 

uus  internus 


Superior 
gluteal  line 


Gemellus  superior 
Spine  of  ischium 


LESSER  SACRO-SCIATIC  NOTCI 

Gemellus  inferiot 


Semitendinosus  and  biceps 

Semimembi  anosus 
Quadratusfemoris 


Adductor  loii 

FERIOR  RAMUS 

Gi  acilis 
Adductor  brevis 


Cotyloid  notch 
Obturator  extetnus 


Adductor  magnus ' 
Right  innominate  bone,  outer  aspect. 

of  the  socket  and  above  the  sciatic  notch,  is  smooth  ;  the  posterior  is  rough.  The 
latter  presents  anteriorly  the  rough  and  pitted  auricular  surf  ace""  corresponding  to 
that  of  the  sacrum.  A  narrow  depression,  t\\z  pre-articular  groove,  bounds  this  on  the 
smooth  surface,  receiving  the  fibres  of  the  anterior  sacro-iliac  ligament.  Behind  the 
auricular  surface  is  a  rough  area  of  a  different  character  with  an  elevation  at  or  below 
the  middle  of  the  preceding  surface.  This  area  serves  for  the  attachment  of  the 
strong  posterior  sacro-iliac  ligaments.  Still  farther  back  the  bone  has  a  smoother 
finish  where  it  gives  origin  to  the  erector  spinae.  The  ilium  has  several  large 

1  Fossa  iliaca      -  Eminentia  iliopectinea.     "  Facias  auricularis. 


334 


HUMAN   ANATOMY. 


nutrient  foramina  ;  one  on  the  inside  of  the  lower  hind  part  of  the  iliac  fossa  runs 
forward,  one  or  two  on  the  outside  near  the  anterior  inferior  spine  run  backward, 
and  one  near  the  middle  of  the  second  curved  line  runs  downward. 

The  Pubis.  —  The  pubis1  (ps  pectinis)  has  a  flat  squarish  body,  which,  meeting 
its  fellow  at  the  symphysis,  forms  the  front  wall  of  the  pelvis,  and  two  raitii,  the 
superior  joining  the  ilium  and  the  inferior  joining  the  ischium.  The  median  end  of 
the  body2  is  wholly  taken  up  by  a  rough  oval  area,  the  symphysis  pubis,  bearing  the 
fibre-cartilage  of  the  joint.  The  spine''  of  the  pubis  is  a  pointed  tubercle,  projecting 


353- 


CREST    OF    ILIUM 


Internal  lip 
Transversal's  — 


Ant.  sup. 
spine 


^ — Quadratus  lumborum 


Post.  sup. 
spine 

Post.  int.  spine 


SPINE  OF  PUBIS 


Levator  ani 


MUS  OF   ISCHIUM 


SYMPHYSIS 


TUBEROi  ITY  OF  ISCHIUM 

Obturator  into  tuts 


Compressor  urethrtr 
Attachment  of  crus  penis 

Ischio-cavernosus 

Transvrrsus  perinei 

Rij;ht  innominate  bone,  inner  aspect. 

forward  from  the  front  of  the  upper  border  of  the  bone  some  two  centimetres 
the  symphysis.  to  which  Poupart's  ligament  is  attached.  A  ridge  runs  from  this 
obliquely  backward  and  inward  to  the  posterior  end  of  the  top  of  the  symphysis, 
which,  together  with  the  rough  surface  internal  to  it,  constitutes  the  crest.  The 
term  angle  is  applied  to  the  line  of  junction  of  this  surface  with  the  symphysis.  The 
superior  ramus  *  is  prismatic,  having  an  antero-superior,  an  inferior,  and  a  posterior 
side.  It  enlarges  as  it  runs  outward  to  form  a  part  of  the  socket.  The  ilio-pcctincal 

1  (Is  pubis.     -  Corpus  ossis  pubis.     ^Tubcrculum  puhicum.     4  Ktiinus  superior. 


THE   INNOMINATE   BONE. 


335 


line  starts  from  the  spine  and  runs  obliquely  backward  and  outward  to  the  ilium. 
The  triangular  antero-superior  side  of  the  ramus,  narrow  at  the  inner  end,  broad  at 
the  outer,  concave  from  side  to  side,  convex  from  before  backward,  is  bounded 
behind  by  the  ilio-pectineal  line,  in  front  by  the  obturator  crest,1  which  runs  from  the 

FIG.  354. 


Conjoined  tendo: 
Gimbernat's  ligament 

Poupart's  ligament 

Conjoined  tendon     /       / 

Rectus  abdominis    Pyramidalis 

Region  of  symphysis  pubis  from  above. 


ilio-pectineal  eminence 


Obturator  crest 
Spine  of  pubis 


spine  to  the  inner  border  of  the  acetabular  notch,  and  externally  by  a  swelling  at  the 
upper  inner  part  of  the  socket, — the  ilio-pectineal  eminence.  The  posterior  side,  broad 
at  the  inner  end  and  narrow  at  the  outer,  is  quite  smooth.  The  inferior  border  is 
marked  by  the  broad  obturator  groove'1  above  the  foramen,  passing  from  behind  for- 

FIG.  355. 


Epiphyseal  lamina  on  ilium 


Os  acetabuli 


nodules 

Epiphyseal  lamina  on  ischium 


Innominate  bone  at  about  fifteen  years. 


ward  and  inward  for  the  obturator  vessels  and  nerve.  The  inferior  ramus, :i  flat 
and  thin,  rough  in  front,  smooth  behind,  extends  backward  and  outward  to  join  the 
ramus  of  the  ischium.  It  is  constricted  just  above  the  point  of  union.  The  inner 
edge,  forming  part  of  the  pubic  arch,  is  somewhat  everted. 

1  Crista  obturatoria.     '-  Snlcus  obturatorius.     3  Ramus  inferior. 


336 


HUMAN   ANATOMY. 


Iliac  crest 


The  Ischium. — The  ischium/  the  thickest  and  most  solid  part  of  the  bone, 
consists  of  a  body,  chiefly  concerned  with  the  acetabulum,  a  tuberosity,  and  a  ramus. 
The  body,  continuous  above  with  the  ilium,  forms  the  front  of  the  great  sciatic  notch? 
below  which  is  the  sharp  spine  of  the  ischium  pointing  backward  and  inward  for  the 
lesser  sacro-sciatic  ligament.  The  tuberosity  '•'  is  a  great  thickening  of  the  back  of 
the  lower  end  of  the  body  of  the  ischium  which  bears  the  weight  in  sitting.  It  is 
broad  above  and  behind,  narrowing  in  front  as  it  passes  into  the  ramus.  It  extends 
but  little  onto  the  inner  side  of  the  bone,  which  otherwise  is  smooth.  Its  inner  lip 
receives  the  great  sacro-sciatic  ligament  and  its  falciform  prolongation.  A  smooth 
surface  (in  life  coated  with  cartilage)  passes  from  the  inside  of  the  back  of  the 
bone  just  below  the  spine  and  above  the  tuberosity,  forming  the  lesser  sciatic  notch  ^ 

occupied  by  the  tendon  of 

FIG.  356.  the  obturator  internus.      In 

front  of  this,  under  the  ace- 
tabulum and  above  the  tu- 
berosity, is  a  groove  for  a 
part  of  the  obturator  ex- 
ternus.  The  upper  part  of 
the  tuberosity  is  divided  into 
an  upper  and  front  area  for 
the  origin  of  the  semimem- 
branosus,  and  one  behind 
and  below  it  for  the  semi- 
tendinosus  and  biceps.  Be- 
low these,  extending  onto 
the  ramus,  is  a  surface  for 
the  adductor  magnus.  The 
ramus 5  is  a  strip  of  bone 
running  forward  to  meet  the 
inferior  ramus  of  the  pubis. 
The  lower  edge,  forming 
the  margin  of  the  stibpubic 
arch,  is  twisted  outward  and 
rough.  The  border  towards 
the  foramen  is  relatively 
sharp.  The  line  of  junction 
of  the  rami  of  the  ischium 
and  pubes  can  be  distin- 
guished by  the  greater 
Pubes  (ttHHg£3Rft!  \3aBBHie&  breadth  of  the  former. 

The  acetabulum,  the 
socket  for  the  hip,  is  a  deep 
hemispherical  cavity  with  a 
raised  border,  imperfect  be- 
low. The  imaginary  axis 
of  the  cavity  runs  upward, 
inward,  and  backward.  It 
is  formed  by  all  three  bones,  the  ischium  contributing  the  most  and  the  pubes  the 
least.  The  lines  of  union  are  sometimes  seen  on  the  smooth  posterior  surface  in 
the  adult.  The  cavity  is  only  in  part  articular.  In  shape  this  portion  may  be  com- 
pared to  a  horseshoe  beaten  concave  and  fitted  into  the  cavity  with  the  two  ends 
pointing  downward,  enclosing  a  non-articular  cavity  at  a  somewhat  deeper  level, 
which  extends  mpre  than  half-way  up  the  back  of  the  socket.  The  bone  at  the 
bottom  of  the  cavity  is  very  thin.  The  articular  strip  is  broadest  above  and  behind 
the  middle  and  narrowest  in  front.  Of  the  t\vo  ends  of  this  articular  strip  the 
posterior  is  the  more  prominent,  overhanging  a  groove  leading  into  the  non- 
articular  hollow  from  below.  The  front  one  has  no  corresponding  projection.  The 
border  of  the  acetabulum  is  formed  by  the  convexity  of  this  horseshoe-shaped  strip, 
and  consequently  is  wanting  below.  The  interruption  is  the  cotyloid  notch*  The 

ii,  i-,,  lni.     '-'  Inclsura  Ischludicn  major.     :i  Tuber  ischii.     4  Incls.  isch.  minor.      '  Ramus  Inferior.     *  Incisurn  acetabuli. 


Ischium 


Oblique  sagittal  section  of  right  innominate  bone  passing  through  bottom 
of  acetabulum  ;  inner  surface. 


JOINTS    AND    LIGAMENTS  OF   THE   PELVIS. 


337 


border  rises  from  the  surface  of  the  bone  distinctly  below  and  to  a  less  degree  behind 
and  above. 

The  thyroid  or  obturator  foramen '  is  a  large  oval  opening,  with  the  larger 
end  above  and  the  long  axis  running  downward  and  outward,  bounded  by  the 
pubis  and  ischium.  A  little  tubercle,  seen  best  from  the  inner  side,  marks  the 
upper  limit  of  the  ischium.  Above  is  the  obtiirator  groove  under  the  ramus  of  the 
pubis.  It  is  closed  by  a  membrane,  except  under  the  groove. 

Structure. — The  innominate  bone  is,  as  a  whole,  very  strong.  The  two  thin 
places  are  in  the  middle  of  the  ilium  and  of  the  cotyloid  cavity.  It  is  very  thick 
round  the  joint  wherever  pressure  may  be  transmitted  through  the  head  of  the 
femur.  Sections  show  radiating  trabeculae  from  the  socket  connected  by  concentric 
lines.  The  bone  is  very  thick  in  a  line  from  the  socket  to  the  outer  expansion  of 
the  iliac  crest,  which  runs  nearly  vertically  in  the  upright  position.  It  is  very 
strong  also  at  and  behind  the  auricular  surface. 

Development. — A  centre  for  the  ilium  appears  early  in  the  third  foetal 
month  above  the  acetabulum  and  spreads  quickly  through  the  upper  part  of  the 
bone.  One  for  the  ischium  appears  below  the  socket,  usually  before  the  end  of  the 
same  month.  One  for  the  pubis  comes  decidedly  later  in  the  iliac  ramus.  It  is 
said  to  appear  from  the  fourth  to  the  fifth  month,  but  it  may  not  be  present  till  the 
sixth.  At  birth  there  is  still  much  cartilage  around  and  between  the  bony  expan- 
sions from  these  centres.  The  rami  of  the  pubis  and  ischium  unite  at  about  eight 
years  or  earlier,  but  the  suture  may  be  visible  on  the  inside  at  eighteen.  Ossifica- 
tion commences  by  several  centres  in  the  Y-shaped  cartilage  separating  the  bones  in 


FIG.  357- 


Ossification  of  innominate  bone.  A,  at  third  foetal  month  ;  £,  at  birth  ;  C,  during  first  year;  D,  at  six  years  ; 
E,  at  about  fifteen  years,  a,  chief  centre  for  ilium ;  b,  chief  centre  for  ischium  ;  c,  for  pubis ;  d,  for  tuberosity  of 
ischium  ;  e,  for  iliac  crest ;  /,  for  anterior  inferior  spine. 

the  socket  at  an  uncertain  date,  probably  before  ten  years.  One  of  these  centres, 
much  larger  than  the  rest,  the.  os  acetabuli,  persists  at  the  front  of  the  cavity  be- 
tween the  pubis  and  ilium  till  perhaps  fifteen,  when  union  has  made  much  progress 
between  the  various  parts  of  the  acetabulum.  The  lines  of  junction  may  be  seen  on 
the  inside  of  seventeen  or  eighteen,  that  between  the  pubis  and  ischium  persisting 
longest.  Secondary  centres  come  about  puberty  for  the  crest  of  the  ilium,  the  an- 
terior inferior  iliac  spine,  the  symphysis  pubis,  and  the  ischial  tuberosity.  They 
are  fused  at  twenty,  excepting,  perhaps,  that  for  the  crest  of  the  ilium,  the  union  of 
which  may  be  delayed  ;  the  suture  marking  its  presence  is  one  of  the  last  in  the 
body  to  disappear. 

JOINTS   AND   LIGAMENTS   OF   THE   PELVIS. 

These  may  be  divided  into  ( i )  those  connecting  the  ilium  with  the  sacrum  and 
last  lumbar  vertebra,  (2)  those  connecting  the  pubic  bones  at  the  symphysis,  and  (3) 
the  ligaments  forming  the  lateral  walls, — the  sacro-sciatic  ligaments  and  the  obtu- 
rator membrane. 


1  Foramen  obturatum. 
22 


338 


HUMAN   ANATOMY. 


THE   SACRO-ILIAC   ARTICULATION. 

The  sacro- iliac  articulation,  often  improperly  called  the  sac ro- iliac  synchondrosis , 
partakes  of  the  nature  of  both  a  true  and  a  half-joint.  The  opposed  surfaces  of 
the  sacrum  and  ilium  vary  greatly  in  shape.  The  sacrum  is  broader  in  front  than 
behind,  so  that  the  line  of  the  joint  slants  inward  as  well  as  backward  ;  but  occasion- 


FIG.  358. 


Ilium 


Posterior  sacro-iliac  ligament 


Sacro-iliac  joint 


Anterior  sacro-iliac  ligament 
Horizontal  section  through  right  sacro-iliac  joint. 

ally  in  some  part  it  is  a  little  broader  behind  than  in  front.  Often  there  is  an  out- 
ward swelling  between  the  borders,  so  that  a  part  of  the  sacrum  is  received  into  a 
hollow  in  the  ilium,  and  a  transverse  cut  of  the  joint  shows  a  sinuous  line.  Perhaps 
quite  as  often  the  ilium  projects  into  the  sacrum.  In  any  case,  as  a  rule,  there  is  a 
certain  amount  of  interlocking.  The  opposed  surfaces  are  covered  with  cartilage. 
The  layer  on  the  sacrum,  from  one  to  two  millimetres  thick,  is  at  least  twice  as  thick 
as  the  other,  and,  though  generally  reckoned  fibro-cartilage,  has  much  the  appear- 
ance of  hyaline.  The  two  are  sepa- 
FIG.  359- 

Ilio-lumbar  ligament 


rated  by  a  synovial  cavity,  which 
is  enclosed  by  the  sacro-iliac  liga- 
ments. The  size  of  this  cavity  is 
very  uncertain.  It  may  extend 
backw.ard  beyond  the  auricular 
surfaces,  occupying  on  the  ilium 
a  part  of  the  space  usually  serving 
for  the  origin  of  the  posterior 
sacro-iliac  ligaments,  or  it  may  be 
encroached  upon  by  fibres.  Some- 
times, before  old  age,  the  joint  is 
replaced  by  bone. 

The  fibres  around  the  joint 
are  severally  named  according  to 
position.  The  posterior  sacro- 
iliac  ligament  (  Fig.  358)  is  very 
important.  It  comprises  many 

layers  of  strong  fibres,  filling  up  the  depths  of  the  cleft  between  the  sacrum  and  the 
overhanging  ilium,  extending  from  the  rough  area  on  the  latter  behind  the  auricular 
surface  to  the  back  of  the  lateral  masses  of  the  sacrum,  nearly  or  quite  to  the  pos- 
terior sacral  foramina  below  the  three  upper  sacral  vertebrae.  Those  of  both  sides 


Promontory 
of  sacrum 


Sacrum 


Anterior  view  of  the  sacro-iliac  joint  and  of  the  last  lumbar  ver- 
tebra. 


THE   SYMPHYSIS   PUBIS. 


339 


resist  any  tendency  of  the  weight  of  the  body  to  force  the  sacrum  forward.  A  rather 
distinct  superficial  band,  the  oblique  sacro-iliac  ligament1  (Fig.  362),  passes 
from  the  posterior  superior  iliac  spine  to  the  second  and  third  sacral  vertebrae. 
Anterior  and  superior  fibres  are  spread  about  the  joint,  and  require  no  special 
description.  Some  of  them  go  to  the  pre-auricular  sulcus  of  the  ilium. 

The  ilio-lumbar  ligament2  (Fig.  359)  is  a  triangular  band  of  strong  fibres 
diverging  from  the  apex  and  the  front  surface  of  the  transverse  process  of  the  last 
lumbar  vertebra  to  the  top  of  the  crest  of  the  ilium  opposite  to  it  and  to  the  an- 
terior surface,  where  it  mingles  with  the  anterior  sacro-iliac  fibres.  A  more  or  less 
distinct  bundle  of  diverging  fibres  to  the  top  of  the  sacrum  near  the  joint  with  the 
ilium  is  the  sacro-lumbar  ligament  (Fig.  359). 

THE   SYMPHYSIS    PUBIS. 

The  symphysis  pubis  is  generally  a  typical  half-joint,  the  fibro-cartilage  coating 
the  opposed  pubic  surfaces  being  very  dense  and  the  central  cavity  small.  In 
section  it  appears  as  a  linear  cleft  nearer  the  back  than  the  front.  Sometimes, 
however,  especially  in  women,  a  part  of  the  surfaces  is  coated  with  hyaline  cartilage. 
The  total  breadth  of  the  soft  parts  (greater  in  woman  than  in  man)  rarely  exceeds 
five  millimetres.  The  cartilages  are  ensheathed  in  fibres,  the  deeper  parts  of  which 


FIG.  360. 


FIG.  361. 

Synovial 
cavity 


Fibro-cartilage 


The  symphysis  pubis,  anterior  surface. 


pubic  ligament 
Frontal  section  through  the  symphysis  pubis. 


are  inseparable  from  them  :  those  above  and  behind  are  of  little  consequence. 
The  anterior  ones  are  in  several  layers,  being  in  part  composed  of  fibres  from  the 
aponeurosis  of  the  external  oblique  and  of  fibres  of  origin  of  the  rectus.  They  are 
in  the  main  transverse,  but  those  from  the. obliques  run  downward  and  inward, 
sometimes  making  a  distinct  decussation.  The  inferior  or  subpubic  fibres  are  col- 
lected into  a  dense  transverse  band,  bounding  by  the  lower  side  the  pubic  arch  and 
being  joined  by  the  upper  to  the  fibro-cartilage. 

THE   SACRO-SCIATIC    LIGAMENTS. 

These  are  two  layers  of  fibres  passing  from  the  sides  of  the  sacrum  to  the 
ischium  and  forming  a  partial  wall  for  the  pelvis  at  the  sacro-sciatic  notch,  where  the 
bony  walls  are  wanting. 

The  great  or  posterior  sacro-sciatic  ligament"  (Fig.  362)  is  external  to 
the  lesser,  which  it  conceals  to  a  large  extent.  It  arises  from  the  outer  surface  of 
the  pelvis,  beginning  at  the  inferior  posterior  spine  of  the  ilium,  where  its  fibres 
mingle  with  those  of  the  posterior  sacro-iliacs,  then  from  the  posterior  edge  of  the 
border  of  the  three  lower  pieces  of  the  sacrum  and  from  one  or  two  of  the  coccyx. 
From  this  broad  origin  it  narrows  as  it  passes  forward,  and  at  the  same  time  twists 
so  that  the  outer  surface  becomes  the  inferior  as  it  is  inserted  into  the  under  side  of 
the  tuberosity  of  the  ischium.  As  it  reaches  the  tuberosity  the  fibres  at  its  inner 

1  Lig.  sacroiliacum  postcrius  longum.     "  Lig.  iliolumbale.     3  LIB.  sacrotuherosum. 


340 


HUMAN   ANATOMY. 
FIG.  362. 


Posterior  superior  spine  of  ilium 


Oblique  sacro-iliac 
ligament 


Supraspinous  ligament 


Sacro-coccygeal  ligament 


Tip  of  coccyx 

Great  sacro-sciatic  ligament 


Origin  of  biceps 


Lesser  sacro-sciatic 
foramen 


Tuberosity  of  ischium 


External  surface  of  the  sacro-sciatic  ligaments. 

FIG.  363. 


Fifth  lumbar  vertebra 


Obturator  canal  _ 


Symphysis  pubis 


Ohturalor  membrane 


Auricular  surface 


—  Non-articular  surface 


Lesser  sacro-sciatic 
ligament 


Falciform  process  of  great  sacro-sciatic 
ligament 

Internal  surface  of  the  sacro-sciatic  ligaments,  showing  the  falciform  continuation  of  the  great. 


THE   PELVIS   AS   A   WHOLE.  341 

border  become  raised  from  the  rest  and  are  inserted  into  the  inner  border  of  the 
ramus  of  the  ischium,  from  which  they  rise  in  a  fold,  the  falc iform  ligament,  within 
the  pelvis,  continuous  with  the  obturator  fascia.  The  ligament  at  its  insertion  into 
the  tuberosity  is  continuous  with  the  fibres  of  origin  of  the  biceps. 

The  lesser  or  anterior  sacro-sciatic  ligament '  (Fig.  363),  much  the  smaller, 
is  situated  internally  to  the  great,  springing  from  the  edge  of  the  sacrum  below 
the  junction  with  the  ilium  and  from  the  side  of  the  upper  part  of  the  coccyx,  being 
more  or  less  continuous  with  the  interior  surface  of  the  great.  It  narrows  to  its 
insertion  into  the  spine  of  the  ischium. 

The  great  sacro-sciatic  foramen  '  (Fig.  362)  is  bounded  above  by  the  ilium, 
in  front  by  the  ilium  and  the  ischium,  behind  by  the  great  ligament,  and  below  by 
the  lesser.  It  transmits  the  pyriformis  muscle,  the  gluteal,  sciatic,  and  internal  pudic 
vessels  and  nerves,  and  the  nerves  to  the  obturator  internus  and  quadratus  femoris. 

The  lesser  sacro-sciatic  foramen3  (Fig.  362)  is  bounded  in  front  by  the 
body  of  the  ischium,  above  by  the  lesser  ligament,  and  below  and  behind  by  the 
oblique  border  of  the  great.  Through  it  pass  the  obturator  internus  muscle,  the 
internal  pudic  vessels  and  nerve,  and  the  nerve  to  the  obturator  internus. 

The  obturator  membrane4  (Fig.  363)  is  attached  to  the  margin  of  the  fora- 
men of  that  name,  which  it  completely  closes,  except  for  a  small  space  at  the  top  of 
the  groove  under  the  ramus  of  the  pubis.  Sometimes  there  are  perforations.  The 
attachment  at  the  inner  side  is  directly  to  the  sharp  edge  of  the  rami  of  the  pubis 
and  ischium.  At  the  outer  border  it  passes  into  the  periosteum  lining  the  pelvis. 

THE  PELVIS  AS  A  WHOLE. 

The  promontory  of  the  sacrum  and  the  ilio-pectineal  line  separate  the  true  pelvis" 
below  from  the  false6  above.  The  latter  is  bounded  by  the  lower  lumbar  vertebrae 

FIG.  364. 


The  pelvis  from  behind. 

and  by  the  flaring  ilia.      The  true  pelvis  is  bounded  by  the  sacrum  and  coccyx  behind, 
by  the  bodies  and  symphysis  of  the  pubis  in  front,  and  by  the  sacro-sciatic  ligaments, 

1  Lig.  sacrospinosum.     -  Foram.  ischiadicum    majus.     "  Foram.   Isch.   minus.     4  Membrana   obturatoria.     •'  Pelvis    minor. 
0  Pelvis  major. 


342 


HUMAN   ANATOMY. 


the  ischia,  part  of  the  ilia,  and  the  pubic  rami  and  obturator  membrane  at  the  sides 
and  front.  The  plane  just  described  as  separating  the  true  and  false  pelvis  is  the 
plane  of  the  inlet1  of  the  latter.  Its  greatest  individual  variations  are  due  to  the 
greater  or  less  projection  forward  of  the  sacral  promontory.  The  outlet'1  is  bounded 
behind  by  the  coccyx,  from  the  sides  of  which  the  great  sacro-sciatic  ligaments 
pass  to  the  ischial  tuberosities,  thence  by  the  rami  of  the  ischia  and  pubes,  forming 
the  pubic  arch,  and  by  the  subpubic  ligament  below  the  symphysis.  It  is  evident 
that  these  planes  converge  in  front  and  that  the  axis  of  the  pelvis  (an  imaginary  line 
in  the  centre,  perpendicular  to  an  indefinite  number  of  intermediate  planes)  must  be 
a  curved  one. 

The  Position  of  the  Pelvis. — The  plane  of  the  inlet  of  the  pelvis  is  inclined 
to  the  horizon  about  60°  when  the  body  is  upright.  This  inclination  varies  accord- 
ing to  the  figure  and  to  the  individual  peculiarities  of  the  pelvis  itself.  Hermann 
von  Meyer's  conjugata  vera,  a  line  from  the  top  of  the  symphysis  to  the  line  usually 

FIG.  365. 


Male  pelvis  from  before. 

found  in  the  third  sacral  vertebra,  runs  at  about  30°  with  the  horizon.  This  is  a  more 
trustworthy  angle  than  that  of  the  plane  of  the  inlet  ;  but  even  this  is  not  constant. 
It  is  better  to  try  to  determine  the  proper  position  of  every  pelvis  for  itself  than  to 
attempt  to  make  all  conform  to  one  angle,  which  for  these  reasons  is  impossible. 
The  two  borders  of  the  cotyloid  notch  should  be  put  in  the  same  level,  which  will 
bring  the  anterior  superior  spines  of  the  ilia  into  the  same  vertical  plane  as  the  spines 
of  the  pubes.  The  tip  of  the  coccyx  should  be  at  about  the  level  of  the  top  of  the 
symphysis  ;  owing  to  the  many  variations  of  the  former,  however,  its  position  must 
be  uncertain.  The  height  of  the  promontory  above  the  symphysis  is  about  9.5 
centimetres  (3^  inches)  in  man  and  about  10.5  centimetres  (4^6  inches)  in 
woman. 

The  diameters  of  the  true  pelvis  of  woman  are  of  great  practical  importance  in 
midwifery.  The  standards  are  the  antcro-posterior,  the  transverse,  and  the  oblique 
(the  latter  from  the  sacro-iliac  joint  to  the  acetabulum  of  the  opposite  side)  measured 
at  the  inlet,  the  outlet,  and  at  an  intermediate  plane. 

1  Apertura  pelvis  superior.     '-'  Aperturn  pelvis  Inferior. 


THE    PELVIS   AS   A   WHOLE. 


343 


DIAMETERS   OF  THE  TRUE    PELVIS. 

MALE. 


Antero-posterior 
Transverse  .    .    . 
Oblique     .... 

Inlet. 
Cm.  (Inches). 

10.25  (4) 
12.75  (5) 

12.00  (4^) 

Cavity. 
Cm.  (Inches). 

12.0  (4%) 
ii.  5  (4/2) 

Outlet. 
Cm.  (Inches). 

8-25(3*) 
9°°  (3/4) 
10.25  (4) 

FEMALE. 

Outlet. 
Cm.  (Inches). 

Inlet. 
Cm.  (Inches). 

Cavity. 
Cm.  (Inches). 

Outlet. 

Cm.  (Inches) 

8.25(3*) 
9°°  (3/4) 
10.25  (4) 

10.25  (4) 
13.25(5*) 
12-75  (5) 

12-75  (5) 
12-75  (5) 
13.25(5*) 

II-5  (41A] 
12.0  (4%} 

The  index  of  the  pelvis,  of  interest  in  anthropology,  is  the  proportion  of  the 
antero-posterior  diameter  to  the  transverse  at  the  pelvic  inlet,  the  latter  being  100. 
This  index  is  80  for  European  males  and  78  for  females  (Verneau).  In  the  lower 
races  it  is  considerably  higher,  implying  a  narrower  pelvis.  Pelves  with  indices 
below  90  are  platypellic,  with  indices  from  90  to  95  mesatipellic,  and  above  95 
dolichopellic. 

Another  index  to  show  the  relative  depth  of  the  pelvis  is  the  proportion  of  the 
breadth  between  the  most  distant  points  of  the  iliac  crests  to  the  height  from  the 
top  of  the  crest  to  the  tuberosity  of  the  ischium,  the  latter  being  100.  According  to 

FIG.  366. 


Female  pelvis  from  before. 

Topinard,  this  index  is  126.6  for  male  and  136.9  for  female  Europeans.      It  is  lower 
in  the  lower  races,  showing  that  in  them  the  pelvis  is  relatively  deeper. 

Differences  due  to  Sex. — The  sexual  differences  of  the  pelvis  are  far  more 
marked  than  those  of  any  other  part  of  the  skeleton.  The  male  pelvis  is  deeper  and 
narrower,  the  female  shorter  and  broader.  It  is  to  be  noted  that  the  greater  breadth 
of  the  female  applies  essentially  to  the  true  pelvis.  At  the  inlet  this  is  both  relatively 
and  absolutely  broader  in  woman.  The  male  promontory  is  more  projecting.  The 
most  characteristic  feature  is  the  pubic  arch,  which  is  of  a  much  greater  angle  in 
woman.  According  to  Verneau,  it  is  from  38°  to  77°  in  the  male,  with  an  average 
of  60°  ;  and  from  56°  to  104°  in  the  female,  with  an  average  of  74°.  The  symphy- 
sis  is  shorter  in  woman,  and  the  borders  of  the  arch  probably  more  everted.  The 


344  HUMAN    ANATOMY. 

greater  lightness  of  the  female  skeleton  shows  particularly  in  this  part  of  the  pelvis. 
It  is  owing  to  the  greater  divergence  of  the  rami  that  the  front  of  the  obturator  fora- 
men is  straighter  in  the  female,  making  it  more  triangular  and  less  oval  than  in  the 
male.  The  spines  of  the  ischia  are  farther  apart  in  woman.  According  to  Verneau, 
those  in  man  are  rarely  more  than  10.7  centimetres  (4^  inches)  apart,  and  often 
less  than  9  centimetres  (3%  inches)  ;  while  in  woman  they  are  often  more  than  10.7 
centimetres  apart,  and  never  less  than  9  centimetres.  He  states  also  that  in  man 
the  spines  of  the  ischia  are  sometimes  internal  to  the  posterior  inferior  spines  of  the 
ilia,  but  that  they  are  always  external  to  them  in  woman.  The  sacro-sciatic  notch 
is  usually  wider  and  less  deep  in  the  female.  There  is  much  irregularity  in  regard 
to  the  false  pelvis.  The  anterior  superior  spines  of  the  ilia  are  farther  apart  in 
woman.  It  does  not  follow  that  the  same  is  true  of  the  most  lateral  points  of  the 
crests  of  the  ilia.  In  powerful  male  bodies  they  are  farther  apart  than  in  female 
ones.  The  vertical  depth  of  the  false  as  well  as  of  the  true  pelvis  is  greater  in 
the  male.  As  has  been  stated  elsewhere,  the  male  sacrum  is  the  more  regularly 
curved.1 

Development. — The  pelvis  of  the  foetus  and  infant  is  strikingly  small,  and 
continues  relatively  so  for  some  years.  The  peculiarity  of  its  shape  is  largely  due 
to  the  sacrum.  Even  at  birth  there  is  but  a  very  rudimentary  promontory,  and  the 
sacrum  is  straight  or  nearly  so.  Consequently  the  pelvis  is  funnel-shaped,  being 
largest  above.  The  height  is  greater  in  proportion  to  the  breadth  than  later.  It 
has  been  shown  by  Fehling 2  and  Thompson 3  that  the  sex  of  the  pelvis  may  be 
recognized  by  the  usual  signs  as  early  as  the  fourth  month  of  foetal  life.  In  the 
foetus  the  transverse  diameter  of  the  inlet  exceeds  the  conjugate,  especially  in  the 
female.  The  average  subpubic  angle  of  the  foetus  is  50°  in  males  and  about  68°  in 
females.  In  the  latter  the  ischial  spines  are  farther  apart  and  the  sacro-sciatic 
notches  wider.  Although  after  birth  the  promontory  becomes  stronger,  it  has  a 
tendency  to  be  double  partly  above  and  partly  below  the  first  sacral.  This  is  cor- 
rected at  a  very  indefinite  time  in  early  childhood.  Of  the  details  of  the  changes  by 
which  the  great  difference  between  the  sexes  is  brought  about  we  know  very  little. 
Waldeyer*  states  that  the  external  measurements  of  the  female  pelvis  surpass  those 
of  the  male  from  the  eleventh  to  the  fifteenth  year,  but  particularly  from  the  four- 
teenth to  the  sixteenth.  The  growth  of  the  male  pelvis  is  more  regular. 

Mechanics  of  the  Pelvis. — The  mechanical  function  of  the  human  pelvis, 
apart  from  protecting  the  viscera,  is  chiefly  to  support  the  spine,  whether  sitting  or 
standing.  The  interruptions  of  the  bony  girdle  at  the  symphysis  and  the  sacro-iliac 
joints  add  to  the  strength  of  the  structure  and  break  shocks.  There  is,  however,  a 
real  motion  at  the  sacro-iliac  joints  which,  slight  under  ordinary  circumstances,  is  of 
importance  in  childbirth.  The  weight  of  the  body  transmitted  through  the  spine 
may  theoretically  be  said  to  tend  to  force  the  sacrum  down  between  the  innominate 
bones  and  also  to  carry  the  promontory  downward  and  forward  into  the  pelvis;  the 
sacrum  rotating  on  a  transverse  axis  passing  through  the  second  piece  at  the  sacral 
canal.  Motion  in  the  former  direction  does  not  occur,  but  in  the  latter  it  may  to 
a  slight  degree.5  With  the  body  lying  on  the  back,  if  the  legs  are  strongly  flexed 
and  pressed  against  the  abdomen,  the  pelvis  rotates  on  the  sacrum,  the  symphysis 
rises,  and  the  antero-posterior  diameter  of  the  inlet  is  lessened  ;  if  the  legs  be  strongly 
extended  by  being  brought  down  over  the  edge  of  the  table,  this  diameter  is  in- 
creased, the  difference  between  the  extremes  being  one  centimetre.  At  the  end 
of  pregnancy  these  joints,  as  well  as  that  of  the  symphysis,  are  loosened  so  as  to 
admit  of  more  motion,  which  is  no  doubt  of  real  value.  Assuming,  as  at  first,  the 
pelvis  to^  be  the  fixed  part,  the  tendency  to  displacement  of  the  sacrum  in  either  of 
these  directions  is  resisted  by  the  posterior  sacro-iliac  ligaments.  The  sacrum  is  not 
really  a  keystone,  for  the  anterior  surface  is  broader  than  the  posterior,  except  in 
some  few  sections. 

1  Le  bassin  clans  les  sexes  et  dans  les  race,  Paris,  1870. 

1  . \rrh.  fiir  C.yniikol..  Bel.  \.,  iS-6. 

s  Journal  of  Anatomy  and  Physiology,  vol.  xxxiii.,  1899. 

4  I  )as   I'.crkrn,    lioilll,    1X99. 

5  G.  Klein  :  Zeitschrift  fiir  Geburtshiilfe  und  Gynakol.,  Hd.  xxi.,  1891. 


PRACTICAL   CONSIDERATIONS  :    THE    PELVIS.  345 

The  weight  in  standing  is  transmitted  to  the  thigh  bones,  in  sitting  to  the 
tuberosities  of  the  ischia  ;  in  both  cases  the  parts  of  the  pelvis  running  to  the  pubes 
act  as  "ties"  to  prevent  the  spreading  of  the  arch.  The  circumference  of  the 
acetabulum  is  of  strong  bone  to  resist  pressure  from  the  joint,  and  in  the  erect 
position  a  strong  part  runs  from  the  socket  directly  upward  to  the  crest  of  the 
ilium.  The  thinness  of  the  bottom  of  the  acetabulum  in  all  ages  and  the  meeting 
there  in  childhood  of  the  three  bones  make  it  a  weak  place. 

Surface  Anatomy. — The  anterior  superior  spine  of  the  ilium  is  easily  felt, 
but  care  must  be  taken  not  to  mistake  for  it  a  swelling  of  the  crest  an  inch  or  more 
behind  it.  To  make  sure  of  this  spine  as  a  point  for  measurements,  the  finger 
should  be  carried  over  it  from  the  crest  and  then  back  again  till  it  is  arrested  by 
the  overhanging  spine.  The  anterior  inferior  spine  cannot  be  felt.  The  outer 
lip  of  the  crest  of  the  ilium  can  easily  be  followed  to  the  posterior  superior  spine, 
which  is  marked  by  a  dimple,  and  is  on  a  level  with  the  middle  of  the  sacro-sciatic 
joint.  The  tuberosity  of  the  ischium  is  readily  felt,  but  it  is  too  thickly  covered  for 
details  to  be  recognized.  A  line  drawn  from  the  posterior  superior  spine  to  the  outer 
part  of  the  tuberosity  of  the  ischium  will  cross  the  inferior  spine  of  the  ilium  and  the 
spine  of  the  ischium.  A  line  from  the  same  point  to  the  top  of  the  greater  trochanter 
will  pass  very  close  to  the  highest  point  of  the  great  sacro-sciatic  notch.  The  sym- 
physis  of  the  pubes  and  most  of  the  borders  of  the  pubic  arch  can  be  felt.  The 
spine  of  the  pubes  can  be  recognized,  but  usually  not  without  some  difficulty.  It 
may  be  necessary  to  feel  for  it  beneath  the  skin  by  invaginating  the  scrotum  or 
labium.  In  woman  it  is  nearly  2.5  centimetres  from  the  median  line  ;  in  man  some- 
what less. 

PRACTICAL   CONSIDERATIONS. 

Failure  of  development  in  the  separate  bones  of  the  pelvis  produces  certain 
well-known  deformities.  In  the  sacrum,  the  arch  of  the  upper  sacral  vertebra, 
which  is  formed  later  than  the  others  and  varies  notably  in  thickness,  is  frequently 
incomplete,  which  results  in  the  very  common  occurrence  of  spina  bifida  at  this 
region  (page  1051). 

When  the  pelvic  girdle  is  incomplete  anteriorly,  there  is  an  interval  of  several 
inches  between  the  pubic  bones,  and  all  the  bones  of  the  pelvis  are  changed  some- 
what in  shape  and  direction.  The  defect  may  be  associated  with  exstrophy  of  the 
bladder,  epispadias  in  the  male,  split  clitoris  in  the  female,  double  inguinal  hernia, 
ectopia  of  the  testicles,  and  sometimes  ventral  hernia  from  separation  of  the  recti 
muscles. 

Deformities  of  the  pelvis  have  even  more  interest  to  the  obstetrician  than  to 
the  surgeon.  The  usual  differences  between  the  male  and  female  pelves  are  some- 
times absent,  constituting  an  abnormality,  though  perhaps  stopping  short  of  actual 
deformity.  The  so-called  masculine  pelvis,  for  example,  is  characterized  by  a 
diminution  in  the  breadth  of  the  pubic  arch  and  an  increase  in  the  pubic  angle. 

The  female  pelvis,  as  compared  with  that  of  the  male,  is  lighter,  less  compact, 
more  expanded,  shorter  in  vertical  depth,  broader  at  the  inlet,  with  a  greater  angle 
in  its  pubic  arch,  a  lesser  curve  in  the  sacrum,  and  a  greater  separation  between  the 
ischial  spines,  and  is  thus  more  perfectly  adapted  to  the  purposes  of  parturition. 

The  chief  deformities  due  to  faulty  development  may  be  at  least  enumerated 
here  on  account  of  their  importance  in  this  relation.  In  the  simple  flat  pelvis  the 
antero-posterior  diameter  is  contracted  by  the  advancement  of  the  sacrum  in  a  down- 
ward and  forward  direction  between  the  iliac  bones.  The  equally  contracted  pelvis 
resembles  a  miniature  normal  female  pelvis  with  other  peculiarities  that  approxi- 
mate it  to  the  infantile  type.  The  funnel-shaped  pelvis  is  contracted  transversely 
at  the  outlet  in  both  the  antero-posterior  and  transverse  diameters,  the  cavity  is 
deeper,  the  sacrum  is  narrow  and  less  curved.  These  peculiarities  are  found  in 
very  early  life,  and  hence  this  is  also  known  as  the  fcetai,  pelvis.  The  obliquely  con- 
tracted pelvis  is  due  to  imperfect  development  of  the  ala  on  one  side  of  the  sacrum, 
which  is  associated  with  many  secondary  deformities,  among  them  a  lack  of  curva- 
ture of  the  innominate  bone  on  the  affected  side.  The  transversely  contracted  pelvis 
in  which  both  sacral  alae  are  undeveloped  is  rarest  of  all  contracted  pelves.  The 


346  HUMAN   ANATOMY. 

functional  importance  of  these  pelvic  contractions  should  be  studied  in  connection 
with  the  mechanism  of  labor. 

The  pelvis  may  be  deformed  as  a  result  of  morbid  conditions  in  other  parts  of 
the  skeleton.  A  lateral  curvature  of  the  lumbar  spine  to  the  left  may  thus  be  ac- 
companied not  only  by  the  usual  compensatory  dorsal  curve  to  the  right,  but  by  a 
curve  in  the  latter  direction  in  the  sacrum,  the  upper  margin  of  which  will  be  higher 
on  the  right  side  than  on  the  left.  Even  the  corresponding  rotation  will  take  place, 
and  the  ala  on  the  concave  side  will  be  rotated  forward,  as  are  the  transverse  pro- 
cesses of  the  dorsal  vertebrae. 

Irregularity  in  the  lengths  of  the  lower  limbs  may  produce  a  similar  curve  in 
the  sacrum. 

In  both  cases  the  whole  pelvis  will  be  tilted  laterally,  the  iliac  crest  being 
higher  on  the  convex  side  of  the  sacrum.  It  has  been  suggested  that  this  continu- 
ation of  a  spinal  curvature  into  the  sacrum  is  sometimes  a  cause,  and  not  a  result,  of 
the  obliquely  contracted  pelvis  described  above,  with  which  it  is  often  associated, 
but  which  is  regarded  as  congenital  in  its  origin. 

Humphry,  after  describing  the  ring  of  the  pelvis  as  heart-shaped,  and  calling 
attention  to  the  wide  arch  with  a  flattened  or  depressed  centre  of  the  upper  or 
posterior  half,  and  the  greater  curve  with  flattening  at  the  ilio-pectineal  regions 
of  the  lower  or  anterior  half,  says,  ' '  It  results  from  this  configuration  of  the  pel- 
vic ring  that  it  is  weakest  at  five  points, — viz.,  at  or  a  little  external  to  both  sacro- 
iliac  synchondroses,  at  the  symphysis  pubis,  and  midway  between  the  latter  and 
the  acetabula.  Hence  fractures,  whether  from  falls,  blows,  or  foreign  bodies  pass- 
ing over  the  pelvis,  are  most  frequent  at  these  points." 

In  studying  the  clinical  effects  of  traumatism  applied  to  the  pelvis,  it  is  helpful, 
however,  to  consider  it  with  reference  to  its  various  functions, — i.e.,  (a)  as  inter- 
posed between  the  vertebral  column  and  the  lower  extremities  as  a  weight- carrier  ; 
(6)  as  a  means  of  providing  for  the  motions  of  the  trunk  upon  the  lower  limbs  and 
of  affording  advantageous  points  of  attachment  for  the  muscles  which  effect  that 
motion  ;  (c)  as  a  bony  protection  or  receptacle  for  the  abdominal  and  pelvic 
viscera. 

i.  If  it  is  viewed  as  a  bony  ring  between  the  spine  and  the  thigh  bones, 
intended  to  transmit  the  weight  of  the  head  and  trunk  from  the  former  to  the  latter, 
the  pelvis  may  be  regarded  as  made  up  of  two  main  arches, — one  which  is  in  use 
when  standing,  the  other  when  sitting.  The  sacrum  is  the  point  of  union  of  both 
these  arches, — one,  the  femoro-sacral  (Morris),  extending  from  the  acetabulum 
through  the  strong  thickened  mass  of  bone  indicated  on  the  inner  surface  by  the 
upper  third  of  the  ilio-pectineal  line  to  the  sacrum  through  the  sacro-iliac  joint  ;  the 
other,  the  ischio-sacral,  extending  from  the  tuber  ischii  through  the  strong  bony 
mass  at  the  posterior  edge  of  the  acetabulum  to  the  same  point.  These  are  the 
essential  weight-carrying  portions  of  the  pelvis. 

Although  Cunningham  says  that,  as  the  sacrum  narrows  towards  its  dorsal  sur- 
face, and  is  really  suspended  from  the  iliac  bones  by  the  posterior  sacro-iliac  liga- 
ments, it  cannot  be  considered  as  the  keystone  of  an  arch,  yet  the  union  between 
the  sacrum  and  the  ilia  is  so  close  by  virtue  of  these  powerful  ligaments,  of  those 
upon  the  anterior  aspect,  and  of  the  reciprocal  irregularities  of  the  sacro-iliac  articu- 
lar surfaces,  that  the  objection,  though  technically  correct,  is  clinically  a  theoretical 
one  only.  In  describing  the  mechanics  of  the  remaining  or  accessory  portions  of 
the  pelvis,  regarded  as  a  weight-carrier,  Morris  calls  attention  to  the  fact  that  when 
much  strength  is  essential  in  an  arch,  it  is  often  prolonged  into  a  ring  so  as  to  form 
a  counterarch, — i.e.,  the  ends  of  the  arch  are  tied  together  to  prevent  them  from 
starting  outward.  A  portion  of  any  weight  to  be  carried  by  the  arch  is  thus  con- 
veyed to  the  centre  of  the  counterarch,  and  borne  in  what  is  called  the  sine  of  the 
arch.  In  the  pelvis  "the  body  and  horizontal  rami  of  the  pubes  form  the  tie  or 
counterarch  of  the  femoro-sacral,  and  the  united  rami  of  the  pubes  and  ischium  the 
tie  of  the  ischio-sacral  arch. ' '  The  ties  of  both  arches  are  united  in  front  at  the 
symphysis  pubis,  which,  like  the  sacrum,  is  common  to  both  arches. 

It  can  now  be  understood  how  and  why  a  fall  upon  the  feet,  or  a  crush  either 
antero-posterior  or  lateral  in  direction,  though  such  dissimilar  accidents,  are  so  apt  to 


PRACTICAL   CONSIDERATIONS  :    THE   PELVIS. 


FIG. 


produce  fracture  of  the  horizontal  or  the  descending  ramus  of  the  pubes,  the  ramus 
of  the  ischium,  or  of  the  ilia  external  to  the  sacro-iliac  junction. 

If  the  accident  has  been  a  fall  upon  the  feet,  the  injury  will  probably  be  confined 
to  the  acetabulum  or  to  the  pubes.  In  young  subjects  the  acetabulum  may  be  sep- 
arated into  its  three  anatomical  components  (Fig.  355),  or  a  portion  of  the  rim  may 
be  broken  off,  or  in  rare  cases  the  head  of  the  femur  may  be  driven  through  into  the 
pelvic  cavity. 

If  the  traumatism  has  been  a  crush  in  the  antero-posterior  direction,  the  pubes 
will  probably  first  fracture  ;  if  the  force  is  continued,  the  protection  afforded  by  the 
"  tie  arch"  having  been  withdrawn,  the  pressure  comes  upon  the  main  arches,  which 
tend  to  open  out.  A  portion  of  one  of  these  arches  may  then  give  way,  and  a  sec- 
ond fracture  may  occur  through  the  ilium  into  the  sacro-sciatic  notch,  or  vertically 
through  the  sacrum  itself.  More  commonly,  however,  the  anterior  sacro-sciatic 
ligaments  give  way  and  a  certain  amount  of  disjunction  of  that  joint  occurs.  Even 
if  the  crushing  force  is  applied  laterally,  it  is  usual  to  find  the  pubes  again  fractured 
from  indirect  violence.  If  the  application  of  the  force  is  continued,  the  strain  comes 
upon  the  posterior  sacro-iliac 
ligaments,  which  may  rupture, 
but  are  more  likely  to  with- 
stand the  violence,  which  then 
may  result  in  the  tearing  away 
of  a  portion  of  the  bone  into 
which  the  ligament  is  inserted. 

The  pubic  fracture  is  dis- 
coverable by  the  usual  means. 
The  vertical  fracture  of  the 
ilium  or  the  disjunction  of  the 
sacro-iliac  synchondrosis  an- 
teriorly should  be  suspected 
if  there  is  pain  in  the  region 
supplied  by  the  superior  glu- 
teal,  the  lumbo-sacral,  the 
upper  sacral  nerves,  or  the 
obturator, — i.e. ,  in  the  sacral 
region,  the  buttock,  the  back  or  inner  part  of  the  thigh,  or  the  knee, — on  account 
of  the  relation  of  these  nerves  to  the  anterior  surface  of  the  joint. 

Marked  ecchymosis,  swelling,  and  tenderness  over  the  sacro-iliac  regions  pos- 
teriorly indicate  tearing  of  the  posterior  ligaments  or  the  fracture  by  arrachement 
that  has  been  described. 

In  all  these  cases  the  gravity  of  the  injury  depends  upon  the  presence  or  absence 
of  visceral  complications.  If  a  double  vertical  fracture  exists,  extending  through 
the  rami  of  the  pubes  and  ischium  in  front  and  through  the  ilium  near  the  sacro- 
iliac  junction  posteriorly,  it  is  obvious  that  there  will  be  one  large  fragment  of  the 
pelvis  more  or  less  movable,  to  which  the  femur  on  that  side  is  connected.  This 
condition  may  be  associated  with  upward  displacement  of  the  fragment,  carrying  the 
femur  with  it,  and  it  may  give  rise  to  a  mistaken  diagnosis  of  fracture  of  the  neck  of 
the  femur.  It  should  be  remembered,  as  Tillaux  has  pointed  out,  that  in  the  pelvic 
lesion  the  relation  of  the  greater  trochanter  to  the  anterior  superior  iliac  spine  is 
normal,  and  the  real  length  of  the  limb  on  the  affected  side  is  the  same  as  that  on 
the  sound  side. 

2.  Other  fractures,  as  those  through  the  lateral  expansions  of  the  ilia,  and 
epiphyseal  separations  involving  the  pelvis,  have  relation  more  especially  to  its 
function  as  affording  a  means  of  moving  the  trunk  upon  the  lower  limbs.  The 
epiphyses  chiefly  separated  are  those  of  (<z)  the  iliac  crest,  (£)  the  anterior  superior 
spine,  (V)  the  posterior  superior  spine,  and  (d)  the  anterior  inferior  spine. 

The  first  three  of  these  are  often  united  in  one  long  epiphysis,  but  portions  of 
this  may  be  detached  separately  by  muscular  action  or  by  direct  violence.  Cases  of 
separation  of  the  anterior  superior  spine  by  the  action  of  the  abdominal  muscles 
and  by  that  of  the  sartorius  have  been  reported. 


Lines  of  fractures  of  the  pelvis. 


348  HUMAN   ANATOMY. 

The  anterior  inferior  spine,  which  is  peculiar  to  the  human  pelvis,  and  affords 
a  slight  leverage  which  partly  enables  the  rectus  femoris  to  overcome  the  disadvan- 
tage of  the  erect  position,  has  been  torn  off  in  the  act  of  running. 

Although  the  ischial  tuberosities  are  subjected  to  enormous  pull  from  the  pow- 
erful hamstring  muscles,  as  in  the  act  of  suddenly  straightening  the  trunk  from  a 
bending  position  (when  these  bones  project  far  behind  the  axial  plane  and  thus  offer 
better  leverage),  their  epiphyseal  disjunction  or  their  fracture  from  muscular  action 
is  practically  unknown.  From  direct  violence  both  of  these  lesions  occur,  but  with 
great  rarity. 

3.  Considered  in  relation  to  the  abdominal  and  thoracic  viscera,  the  injuries 
and  diseases  of  the  bones  of  the  pelvis  are  of  great  importance.  FYactures  of  the 
false  pelvis  have  been  followed  by  fatal  wound  of  the  small  intestine.  Fractures 
running  through  the  brim  of  the  pelvis  have  been  associated  with  hemorrhage  from 
the  iliac  vessels  ;  fractures  of  the  pubis  and  ischium  have  constantly  been  compli- 
cated by  wounds  of  the  urethra  and  bladder,  and  even  of  the  rectum.  The  pos- 
sibility of  these  complications  should  never  be  forgotten.  The  obvious  ana- 
tomical reasons  for  their  occurrence  will  be  recurred  to  when  these  viscera  are 
described. 

Disease  of  the  pelvic  bones,  like  their  deformities,  is  of  chief  importance  in  its 
relation  to  parturition. 

In  rickets  the  shape  of  the  pelvis  is  modified  through  the  medium  of  the  super- 
imposed weight  of  the  trunk  and  through  the  pull  of  muscles  resisted  by  the  inter- 
osseous  ligaments. 

The  weight  of  the  body,  aided  by  the  psoas  muscles,  tends  to  press  the  sacrum 
downward  and  forward  between  the  iliac  bones  and  to  rotate  the  upper  end  forward 
on  a  transverse  axis.  The  sacro-sciatic  and  sacro-iliac  ligaments  resist  this  force, 
which  thus  results  in  thrusting  the  promontory  of  the  sacrum  towards  the  pubes  and . 
in  increasing  the  sacro-vertebral  angle,  or  making  a  sharp  bend  in  it,  often  at  the 
junction  of  the  fourth  and  fifth  sacral  vertebrae.  The  sacro-iliac  ligaments  convey 
this  movement  to  the  posterior  superior  spinous  processes,  which,  advancing  some- 
what forward  and  inward,  would  tend  to  throw  the  anterior  half  of  the  innominate 
bones  outward.  These  are  held,  however,  firmly  at  the  symphysis  and — mudh  less 
effectively — by  Poupart's  ligament.  The  ilia  are  thus  thrown  outward  and  back- 
ward, so  that  the  distance  between  their  spines  may  be  equal  to  or  greater  than 
that  between  the  summits  of  the  crests.  As  a  further  result  of  these  combined 
forces  pushing  the  innominate  bones  forward  from  behind  and  holding  them  in  place 
in  front,  they  are  abnormally  curved,  as  a  bow  is  bent  between  one's  hand  and  the 
ground  (Hirst).  This  bending  of  the  ilia,  together  with  the  pull  of  the  external 
rotators  of  the  thigh  (increased  by  the  usual  bowing  of  the  femurs),  carries  the 
tuberosities  of  the  ischium  outward,  so  that  they  diverge  like  a  monkey's,  flattening 
and  widening  the  pubic  arch  and  increasing  the  transverse  diameter.  The  weight  of 
the  trunk  on  the  summit  of  the  sacrum  is  so  much  the  most  effective  and  continuous 
force  applied  as  the  growing  child  walks  or  stands  that  the  whole  pelvis  is  tilted 
forward  on  its  transverse  axis,  the  inclination  of  the  superior  strait  being  increased 
and  the  external  genitals  displaced  backward. 

In  osteomalacia  the  bones  are  much  softer  than  in  rickets  and  the  mechanism 
of  the  pelvic  deformity  is  simpler.  The  sacrum  yields  under  the  pressure  of  the 
body  weight,  and  becomes  acutely  angulated  and  driven  forward  and  downward  into 
the  pelvis  ;  the  ischia  and  pubes  are  pushed  inward  and  backward  by  the  force 
transmitted  through  the  acetabula,  the  pubic  angle  is  greatly  increased,  and  the 
pelvis  assumes  an  irregularly  triangular  or  ' '  triradiate' '  shape. 

The  rhachitic  and  osteomalacic  pelves  may  approximate  each  other  in  shape,  b 
are  usually  distinct. 

Exostoses  of  the  pelvis  are  usually  found  over  one  of  the  joints,  or  at  points  of 
muscular  or  fascial  attachment,  as  along  the  pubic  crests  where  the  iliac  fascia  is 
inserted. 

Enchondroma  is  relatively  common  in  the  pelvis,  and  other  growths  occasion- 
ally originate  there. 

Congenital  tumors  are  often  found  in  the  sacro-coccygeal  region.     Their  sha 


PRACTICAL   CONSIDERATIONS  :    THE    PELVIS. 


349 


FIG.  368. 


sometimes  resembles  the  tail  of  lower  animals.  They  frequently  arise  from  the  an- 
terior part  of  the  coccyx  behind  the  rectum,  and  contain  muscular,  bony,  epithelial, 
or  cartilaginous  elements  in  an  imperfect  and  fragmentary  condition.  When  a  third 
lower  limb  is  found  connected  with  this  part  of  the  pelvis,  the  condition  is  known  as 
' '  tripodism. ' ' 

In  some  of  the  reported  cases  of  parasitic  foetuses  the  point  of  junction  has  been 
in  this  region. 

Sinuses  over  the  sacrum  and  coccyx  occasionally  persist  after  abscesses  following 
blows  or  falls.  If  the  pus  has  travelled  in  a  lateral  direction,  the  suppurating  track 
will  be  found  to  lead  to  the  region  of  origin  of  the  tendinous  sacral  and  coccygeal 
fibres  of  the  gluteus  maximus.  The  probe  may  catch  against  these  points  and  give 
a  kind  of  grating  sound,  like  that  due  to  bare  or  dead  bone.  The  continuance  of  the 
sinuses  is  not  the  result  of  necrosis,  but  is  due  to  the  unyielding  character  of  the 
tendinous  structures.  This  prevents  apposition  and  union  of  the  sinus  walls  until 
tension  has  been  removed. 

Landmarks. — Anteriorly,  the  anterior  superior  spinous  process  of  the  ilium  is 
most  easily  recognized  as  a  prominence  at  the  outer  end  of  the  fold  of  the  groin. 
In  very  fat  subjects  its  situation  is  indicated  by  an  oblique,  slightly  elongated  de- 
pression. It  is  a  little  above  the  level  of  the  promontory  of  the  sacrum.  Running 
upward  and  outward  and  curving  backward  in  an  irregularly  S-shaped  line  is  the 
iliac  crest.  In  muscular  subjects  the  fibres  of  the 
external  oblique  overhang  the  crest,  causing  a  crease 
in  the  soft  parts  which  lie  between  these  fibres  and 
those  of  the  gluteus  medius  a  little  below  the  level  of 
the  crest ;  it  is  known  as  the  "  iliac  furrow."  It  is  less 
marked  where  the  crest  passes  below  the  tendinous 
portion  of  the  erector  spinae. 

The  posterior  superior  spine  is  not  so  prominent 
as  the  anterior,  but  may  easily  be  found  by  following 
the  crest  to  its  posterior  termination.  Its  position  is 
indicated  by  a  slight  depression  on  the  surface  on  a 
level  with  the  second  sacral  spine  and  behind  the 
middle  of  the  sacro-iliac  joint.  The  third  sacral  spine 
lies  just  below  in  the  mid-line,  and  indicates  the  level 
to  which  the  membranes  of  the  cord  enclose  a  distinct 
space,  and,  therefore,  the  lowest  point  at  which  cerebro- 
spinal  fluid  can  be  found.  The  curve  of  the  sacrum 
and  coccyx  may  be  traced  to  the  tip  of  the  latter. 

The  ischial  tuberosities  are  easily  felt  when  the 
hip  is  flexed  and  the  fibres  of  the  gluteus  maximus  are 
thus  withdrawn.  A  bursa  is  interposed  between  them 
and  the  layer  of  subcutaneous  fat  which  covers  them. 
They  can  be  felt,  but  with  more  difficulty,  through 
the  gluteus  fibres  when  the  hip  is  in  extension.  Five 
centimetres  (two  inches)  below  the  posterior  superior 
spine,  on  a  line  drawn  from  it  to  the  outer  part  of  the  tuberosity,  lies  the  pos- 
terior inferior  spine,  and  five  centimetres  (two  inches)  lower  still  the  spine  of  the 
ischium.  The  sciatic  and  internal  pubic  arteries  emerge  at  the  junction  of  the 
lower  and  middle  thirds  of  this  line.  The  pudic  artery  crosses  the  spine  of  the 
ischium  on  its  way  between  the  great  and  small  sacro-sciatic  foramina.  A  line, 
called  Nelaton's,  drawn  from  the  anterior  superior  spine  to  the  prominence  of  the 
tuber  touches  the  top  of  the  greater  trochanter  and  crosses  the  centre  of  the  ace- 
tabulum  (Fig.  368). 

The  pubic  symphysis  may  be  felt  indistinctly  and  the  horizontal  rami  more 
easily. 

The  pubic  spine  is  readily  felt  in  thin  persons.  In  fat  males  it  may  be  most 
easily  found  by  invaginating  the  scrotum.  In  either  sex  the  tendon  of  the  adductor 
longus — made  tense  by  abducting  the  thigh — is  an  unfailing  guide  to  it.  It  lies  on 
the  level  of  the  upper  edge  of  the  greater  trochanter.  It  is  just  below  and  a  little 


Diagram  showing  Nelaton's  line. 


350  HUMAN    ANATOMY. 

internal  to  the  external  abdominal  ring,  and  is  on  the  outer  side  of  an  inguinal 
hernia  and  on  the  inner  side  of  a  femoral  hernia. 

With  the  finger  in  the  rectum,  the  tip  of  the  coccyx  and  a  little  of  the  anterior 
curve  can  be  felt,  as  well  as  the  small  sacro-sciatic  ligaments  leading  to  the  ischial 
spines.  Laterally,  the  tuberosities  of  the  ischium,  the  smooth  bone  forming  the 
wall  of  the  pelvis,  and  the  structures  back  of  the  acetabulum  (page  1693)  can  be 
palpated. 

Through  the  vagina  the  configuration  of  the  subpubic  arch  can  be  felt,  also 
the  pelvic  wall  to  either  side.  If  the  promontory  of  the  sacrum  can  be  touched, 
it  indicates  deformity  accompanied  by  diminution  of  the  antero-posterior  pelvic 
diameter. 

With  the  hand  in  the  rectum,  the  brim  of  the  pelvis,  the  arch  of  the  pubes,  the 
sacral  promontory,  the  curve  of  the  sacrum  and  coccyx,  the  spines  of  the  ischium, 
and  the  margins  of  the  sacro-ischiatic  foramina  can  be  palpated. 

The  Joints  of  the  Pelvis. — The  sacro -lumbar  joint  has  a  wider  range  of 
movement  than  any  of  the  joints  between  the  contiguous  dorsal  or  lumbar  verte- 
brae. This  is  due  to  the  greater  thickness  of  the  intervertebral  substance,  permit- 
ting flexion  and  extension,  and  to  the  fact  that  the  inferior  articulating  processes 
point  more  antero-posteriorly  than  those  of  the  other  lumbar  vertebrae,  thus  admit- 
ting of  more  rotation  on  a  vertical  axis. 

In  spite  of  this,  on  account  of  the  strength  of  the  ligaments  of  the  joint,  and 
more  particularly  for  the  reasons  that  tend  to  localize  the  effect  of  traumatism  some- 
what higher  in  the  spine  (page  145),  sprain  and  disease  of  the  sacro-lumbar  articu- 
lation are  both  uncommon. 

Overextension  of  the  joint  is  brought  about  if  with  the  body  prone  the  shoul- 
ders are  raised  while  the  hips  are  fixed.  Pain  thus  produced  suggests  lumbar  or 
sacro-lumbar  disease,  as  in  sacro-iliac  disease  this  movement  is  often  painless. 

The  sacro-coccygeal  joint  is  not  infrequently  strained  by  falls  upon  the  buttocks, 
and  occasionally  the  coccyx  is  displaced  forward.  The  joint  is  sometimes  the  subject 
of  disease.  The  symptoms  are  very  similar  in  all  these  conditions.  Tha  attachment 
of  the  gluteus  maximus  makes  a  change  from  a  sitting  to  a  standing  posture  or  the 
reverse  movement  painful  ;  it  also  causes  pain  if  long  steps  are  taken  or  if  running 
is  attempted,  and  this  is  aggravated  by  the  action  of  the  hamstring  muscles  through 
the  medium  of  the  great  sacro-sciatic  ligament.  As  the  fixed  point  of  the  external 
sphincter  is  at  the  tip  of  the  coccyx,  and  as  the  levator  ani  is  inserted  into  the  sides 
of  the  tip,  defecation  is  associated  with  movement  in  this  joint,  and  therefore  with 
pain.  The  latter  is  often  disproportionate  to  the  apparent  severity  of  the  injury  or 
disease,  and  there  may  be  also  great  tenderness  to  the  touch  posteriorly,  with  no  swell- 
ing or  local  heat.  As  these  cases  chiefly  occur  in  women,  Hilton  thinks  that  they 
are  truly  "hysterical,"  and  calls  attention  to  the  intimate  structural  communication 
between  the  many  sacral  nerves  spread  over  the  posterior  surface  of  the  sacrum  and 
coccyx  and  the  anterior  sacral  nerves,  which  join  with  the  hypogastric  plexus  of  the 
sympathetic  within  the  pelvis  and  thence  proceed  to  the  uterus  and  ovaries. 

The  motion  of  the  sacro-coccygeal  joint  is  of  great  importance  in  its  relation 
to  obstetrics.  Ankylosis  occurs,  as  a  rule,  between  the  thirtieth  and  fortieth  years, 
but  the  joint  between  the  first  and  second  sacral  vertebrae  usually  remains  unaffected, 
and  leaves  the  capacity  for  antero-posterior  expansion  during  labor  practically  un- 
impaired. 

The  Sacro- Iliac  Joint. — Injury  to  and  disjunction  of  this  joint  have  been  suffi- 
ciently described  under  Fractures  of  the  Pelvis  (  page  347). 

Disease  of  the  joint,  on  account  of  its  strength  and  immobility,  is  rare.  It  is 
usually  tuberculous  in  character,  and  is  often  secondary  to  suppuration  beneath  the 
ilio-psoas  from  disease  of  the  spine,  ilium,  or  hip.  Pain  is  felt  on  standing,  walking, 
or  sitting,  as  the  sacrum  in  all  these  positions  bears  the  weight  of  all  the  super- 
incumbent structures,  and  on  account  of  its  shape  (page  346)  transmits  it  to  the 
sacro-iliac  synchondrosis.  The  pain  is  increased  by  roughing,  straining,  or  twisting 
the  loins, — i.e.,  by  whatever  calls  into  action  the  muscles  attached  to  the  ilium. 
Through  the  relation  of  the  superior  .gluteal  nerve  to  the  front  of  this  joint,  pain  is 
often  felt  in  the  buttock,  and  there  is  wasting  of  the  deep  gluteal  muscles.  The 


PRACTICAL  CONSIDERATIONS  :   THE   PELVIC  JOINTS.         351 

relation  of  the  lumbo-sacral  cord,  the  upper  sacral  nerves,  and  the  obturator  has 
already  been  mentioned  (page  347). 

The  body  is  inclined  to  the  sound  side,  so  that  when  sitting  the  pressure  on  the 
diseased  structures  may  be  lessened,  and  when  standing  separation  of  the  joint  sur- 
faces may  be  secured  by  the  weight  of  the  lower  limb.  The  length  of  the  latter  is 
apparently  increased  on  account  of  a  downward  rotation  of  the  innominate  bone  on 
the  affected  side,  but  measurements  from  the  anterior  spines  to  the  malleoli  will  be 
the  same.  Tenderness  on  direct  pressure  may  be  elicited  just  below  the  posterior 
iliac  spine  ;  on  indirect  pressure  by  squeezing  the  ilia  together  or  by  separating 
thein  so  as  to  put  the  anterior  ligaments  on  the  stretch. 

Pus  may  find  its  way  backward  and  appear  at  or  near  the  joint  line.  It  more 
often  passes  forward  on  account  of  the  greater  thinness  of  the  anterior  ligament. 
It  may  then  enter  the  sheath  of  the  ilio-psoas  and  be  conducted  to  the  anterior  surface 
of  the  thigh  ;  it  may  follow  the  obturator  vessels  through  the  obturator  canal  and 
point  on  the  inner  aspect  of  the  thigh  ;  it  may  be  guided  by  the  sciatic  nerve  and 
the  lumbo-sacral  cord  to  the  region  behind  the  greater  trochanter  ;  it  may  descend 
between  the  obturator  fascia  and  the  anal  fascia  into  the  ischio-rectal  fossa  and  appear 
at  the  side  of  the  anus  ;  or,  finally,  it  may  ulcerate  into  the  rectum  and  be  dis- 
charged per  anum. 

The  symphysis pubis,  as  the  centre  of  the  counterarch  of  the  pelvis  (page  346), 
is  subject  to  manifold  strains  and  injuries  ;  but,  as  the  union  between  the  two  innomi- 
nate bones  at  that  point  is  really  by  a  strong,  solid,  fibro-cartilaginous  band,  and  is 
without  a  synovial  cavity,  and  as  it  is  greatly  strengthened  by  the  decussation  of 
the  fibres  of  the  anterior  and  inferior  ligaments,  its  separation  by  traumatism  is  very 
rare,  and  is  in  effect  a  fracture. 

.  The  anterior  ligament  is  much  stronger  than  the  posterior  to  resist  the  down- 
ward and  forward  pull  of  the  adductors  and  the  weight  of  the  abdominal  walls  and 
viscera.  Its  strength  accounts  for  the  fact  that  fracture  of  the  horizontal  rami  is 
more  common  than  disjunction  of  the  symphysis  in  cases  in  which  compressing  force 
has  been  applied  to  the  pelvis  laterally. 

In  cases  of  disease  when  the  bond  of  union  is  weakened,  the  function  of  the 
counterarch  readily  explains  the  weakness  and  powerlessness  in  standing  or  sitting. 

The  symphysis  is  of  great  importance  in  its  relation  to  obstetric  mechanics  and 
measurements.  The  plane  of  greatest  pelvic  expansion  extends  from  the  junction  of 
the  second  and  third  sacral  vertebrae  posteriorly  to  the  middle  of  the  symphysis  ; 
the  plane  of  least  pelvic  diameter  from  the  sacro-coccygeal  articulation  to  the  lower 
third  of  the  symphysis. 

There  is  thought  to  be  a  trifling  separation  of  the  symphysis  during  pregnancy 
and  labor,  but  this  is  counteracted  by  the  decussation  of  the  aponeurotic  fibres  of 
the  oblique  muscles  at  the  linea  alba.  On  account  of  this  decussation  these  muscles 
tend,  when  in  vigorous  action,  as  in  parturition,  to  draw  the  pubic  bones  together. 

The  symphysis,  however,  although  comparatively  unyielding,  is  in  almost  the 
same  horizontal  plane  with  the  coccyx,  the  most  movable  bone  that  enters  into  the 
formation  of  the  pelvis,  and  with  the  obturator  foramina  and  the  lower  part  of  the 
great  sacro-sciatic  foramina.  This  is  in  accord  with  the  fact  that  in  no  horizontal 
plane  does  the  pelvis  form  a  complete  bony  and  unyielding  ring,  but  everywhere  the 
resisting  bony  portion  has  opposite  to  it  one  or  more  soft  and  yielding  segments, 
as,  for  example,  the  hypogastric  region  of  the  abdomen  is  opposite  the  fixed  and 
immovable  sacrum  (Morris). 

In  obstructed  labor  in  which  the  delivery  of  a  living  child  may  be  made  possible 
by  a  moderate  increase  in  the  pelvic  outlet,  the  operation  of .  symphyswtomy  is  often 
performed.  The  aponeurosis  of  the  recti  is  incised,  the  retro-pubic  structures  sepa- 
rated by  a  finger,  and  a  probe-pointed  bistoury  passed  down  and  made  to  cut  for- 
ward and  upward.  The  incision  may  with  advantage  be  made  in  the  reverse  direc- 
tion, as  the  symphysis  is  wider  at  its  upper  than  at  its  lower  margin,  and  is  wider 
anteriorly  than  posteriorly.  The  subpubic  ligament  and  the  deep  perineal  fascia 
should  then  be  detached  from  the  pubic  arch  close  to  the  bone,  so  as  to  avoid  tear- 
ing the  structures  that  penetrate  the  fascia — the  vagina,  the  urethra,  the  dorsal  vein 
of  the  clitoris,  and  other  venous  channels — when  the  pubes  are  separated. 


352  HUMAN   ANATOMY. 

The  motion  which  permits  of  separation  takes  place  in  the  sacro-iliac  joints,  and 
the  pubic  bones  move  downward  as  well  as  outward,  adding  materially  to  the 
amount  of  pelvic  space  gained.  With  a  separation  of  seven  centimetres  (two  and 
three-fourths  inches),  which  is  possible  under  gentle  pressure  without  laceration  of 
the  sacro-iliac  ligaments,  the  gain  in  the  conjugate  diameter  is  1.5  centimetres 
(three-fifths  of  an  inch).  The  projection  of  the  anterior  parietal  boss  into  the  pubic 
interspace  as  the  bones  recede  from  each  other  adds  to  the  space  gained,  so  that  by 
opening  the  pubic  joint  to  the  extent  of  6.5  centimetres  (two  and  three-fifths  inches) 
the  increase  in  the  conjugate  diameter  amounts  in  effect  to  about  two  centimetres 
(three-fourths  of  an  inch)  (Cameron). 

THE   FEMUR. 

The  femur,  a  typical  long  bone,  has  a  shaft  and  two  extremities.  The  lower 
end  rests  on  the  tibia,  pretty  nearly  in  a  horizontal  plane  ;  from  this  the  shaft  slants 
outward,  forming  an  angle  of  about  10°  with  a  vertical  line. 

The  upper  extremity  consists  of  a  head,  a  neck,  and  two  trochanters.  These 
last  are  on  the  shaft  at  the  junction  with  the  neck,  which  runs  upward  and  inward, 
forming  with  it  an  angle  of  about  125°  on  the  average. 

The  head  is  a  rounded  swelling,  representing  rather  more  than  half  a  sphere, 
capping  the  end  of  the  neck.  It  is  not  put  on  symmetrically,  but  covers  more  of 
the  upper  side  of  the  neck  than  of  the  lower,  and  probably,  as  a  rule,  more  of  the 
front  than  of  the  back.  Occasionally  it  is  prolonged  onto  the  upper  anterior  aspect 
of  the  neck.  It  is  smooth  and  covered  with  articular  "cartilage  except  at  a  depression 
for  the  ligamentum  teres,  below  and  posterior  to  the  axis  of  the  head.  Brockway,1 
having  examined  300  femurs,  found  this  depression  oval  in  43  per  cent. ,  with  the 
long  axis  running  downward  and  somewhat  backward,  triangular  in  35  per  cent. , 
and  circular  in  22  per  cent.  In  84  per  cent,  he  found  vascular  foramina,  which  are 
larger  in  the  young  and  not  necessarily  pervious  in  the  old.  In  a  few  cases  he  found 
a  persistence  of  the  fcetal  condition, — namely,  a  groove  descending  nearly  to  the 
border  of  the  articular  surface. 

The  neck4  extends  upward  and  inward,  and  usually  forward.  Being  compressed 
from  before  backward,  it  has  a  front  and  a  back  surface  with  thick  upper  and  lower 
borders.  The  lower  rises  more  steeply  from  the  shaft  than  the  upper,  so  that  the 
neck  is  much  broader  at  the  base  than  where  it  joins  the  head.  The  lower  border  is 
the  longer,  and  the  posterior  surface  is  longer  than  the  anterior.  The  neck  is  smooth 
below  and  behind,  rather  rough  in  front  and  above.  The  upper  border  has  numer- 
ous nutrient  foramina.  The  lower  border,  springing  from  the  inner  aspect  of  the 
shaft,  often  presents  a  rounded  ridge  running  to  the  lesser  trochanter.  The  neck  is 
bounded  behind  by  an  elevation  connecting  the  trochanters,  the  posterior  inter- 
trochanteric  ridge?  The  spiral  line6  (formerly  the  anterior  intertrochantcric  ridge} 
bounds  the  greater  part  of  the  front.  It  starts  at  the  little  superior  cervical  tubercle, 
at  the  junction  of  the  top  of  the  neck  with  the  greater  trochanter,  runs  downward  and 
inward  to  the  level  of  the  lesser  trochanter,  where  it  sometimes  presents  a  smaller 
inferior  cervical  tubercle,  and  then,  descending  more  rapidly,  twists  round  the  shaft 
to  join  the  inner  lip  of  the  linea  aspera.  Thus  a  small  part  of  the  neck  between  fhis 
line  and  the  lesser  trochanter  has  no  boundary.  We  have  found  the  average  length 
of  the  neck  on  thirty-eight  male  bones  and  twenty-six  female  ones  respectively  4.3 
centimetres  and  4  centimetres.  Bertaux  gives  46.6  millimetres  and  43.  i  millimetres 
respectively. 

The  greater  trochanter7  is  a  large  process  projecting  upward  and  outward  from 
the  top  of  the  shaft  and  turning  inward  to  overhang  the  back  of  the  neck.  Seen 
from  the  outside  its  outline  is  roughly  square,  but  the  upper  border  generally  rises 
towards  the  back  so  as  to  form  a  point.  The  anterior  surface  presents  a  depressed 
area  for  the  insertion  of  the-  glutens  minimus.  The  outer  side  is  crossed  by  a  ridge 
running  downward  and  forward,  to  and  in  front  of  which  is  attached  the  glutens 
medius.  The  upper  border  receives  at  the  front  end  the  tendons  of  the  obturator 
internus  and  gemelli,  and  a  little  farther  back  that  of  the  pyriformis.  The  hollow 
3  Proceedings  of  the  Association  of  American  Anatomists,  1896. 

'Cuput  fcmorls.     -  Fovea   capltls  fcmorls.      'fnllnm    fenioris.     ''Cristn   Intcrtrochantcrlca.     "Linea   intertrochanterica. 
'  Trochanter  major. 


THE  FEMUR. 


353 


between  the  neck  and  the  overhanging  trochanter  is  the  trochanteric  or  digital  fossa. ' 
There  is  usually  a  round  recess  at  its  anterior  end  for  the  tendon  of  the  obturator 
externus. 

The  lesser  trochanter2  is  a  rounded  knob  at  the  inner  side  of  the  posterior 
aspect  of  the  shaft  at  its  junction  with  the  neck.  The  posterior  side  is  triangular. 
It  is  at  the  junction  of  three  lines  :  the  posterior  intertrochanteric  ridge,  a  line  run- 
ning down  to  the  linea  aspera,  and  an  inconstant  ridge  on  the  neck.  It  receives  on 
its  end  the  tendon  of  the  ilio-psoas,  and  below  some  of  the  iliac  fibres  of  that  muscle 

FIG.  369. 


Fossa  for  round 
ligament 


OREATER  TROCHANTER 


Tubercle  for 
quadratus  femoris 


Third  trochanter. 


Gluteal  ridge 


Upper  extremity  of  left  femur  from  behind. 


That  part  of  the  spiral  line  above  the  level  of  the  lesser  trochanter  (the  so- 
called  anterior  intertrochanteric  ridge)  is  generally  a  very  distinct  rough  line.  It 
may  be  so  faint  as  to  be  hardly  distinguishable,  and  extremely  rarely  a  hollow  may 
be  found  in  its  place.  The  posterior  intertrochanteric  ridge  is  a  thick  swell- 
ing, broader  above  than  below.  Near  its  junction  with  the  greater  trochanter  it  has 
a  slightly  rounded  prominence,  or  occasionally  a  vertical  line,  linea  quadrati,  for  the 
quadratus  femoris. 

The  shaft H  is  very  strong,  and  convex  in  front,  except  below  the  neck,  where  it 
is  slightly  concave.  In  the  middle  it  would  be  nearly  cylindrical  were  it  not  for  the 

1  Fossa  trochantcrica.     2  Trochanter  minor.     3  Corpus  femoris. 

23 


354 


HUMAN    ANATOMY. 
FIG.  370. 


Superior  cervical  tubercle      M         HEAO      «L_Fossa  {or  round  Hgament 


GREATER  TROCHANTER 


Spiral  line 


Psoas 
-  Vastus  interims 


Obturator  inttrnttl  and  gemelli 
Pyriformis 


Adductor  tubercle 


EXTERNAL  CONOYLE 

femur  from  before.     The  outline  figure 


INTERNAL  CONDVLE 


reas  of  muscular  attachment. 


THE    FEMUR. 
FIG.  371. 


355 


Fossa  for  round  ligament  — 


Psoas  and  iliacus 

Pectittfus 

Adductor  brevis 

Adductor  lotions 
I  ~<t<,tns  inter  >ms 


Adductor  magnns — 


Gastrdcttemius—ft. 

(inner  head) 


Inner  lip  oi 
linea  aspera 


Groove  for  femoral  vessels  _  .  W 


GREATER 

TROCHANTER 


Linea  Quadrat! 


Gluteal  ridge 


—  Outer  lip  of  linea  aspera 


Ext.  supracondylar  ridge 


Adductor  tubercle 
Depression  for  gastrocnemius 

INTERNAL  TUBEHOSITY 


Depression  for  gastrocnemius 

EXTERNAL  TUBERO8ITY 

Popliteal  groove 


Intercondylar  notch 
Right  femur  from  behind.     The  outline  figure  shows  the  areas  of  muscular  attachment. 


356  HUMAN   ANATOMY. 

prominence  of  the  linea  aspera  at  the  back.  The  surface  on  either  side  of  this  line 
may  be  plane,  concave,  or  convex,  perhaps  more  often  concave.  The  shaft  expands 
slightly  above,  where  it  is  roughly  four-sided  with  rounded  borders.  A  ridge,  which 
is  very  variously  developed,  often  runs  from  the  lower  side  of  the  neck,  separating 
the  anterior  and  internal  surfaces.  When  strong,  it  emphasizes  the  concavity  of  the 
former.  The  lower  third  of  the  shaft  broadens. 

The  linea  aspera1  is  a  prominent  longitudinal  ridge  along  the  back  of  the 
middle  third  of  the  bone,  strengthening  the  concavity  and  giving  attachment  to 
many  muscles.  It  has  two  more  or  less  well-defined  borders  or  lips.  It  is  formed 
from  above  by  the  union  of  three  lines  :  the  spiral,  a  faint  intermediate  line  coming 
down  from  the  lesser  trochanter,  and  a  third  external  one  coming  from  the  back  of 
the  greater  trochanter.  The  upper  part  of  the  last  is  called  the  ghdeal  ridge,  as  it 
receives  fibres  of  the  gluteus  maximus.  This  part  may  be  considerably  elevated, 
especially  in  muscular  subjects,  into  a  rough  knob,  the  spurious  third  trochanter. 
The  true  third  trochanter,  which  is  sometimes  seen  at  this  point,  is  a  smooth  rounded 
eminence,  the  analogue  of  the  third  trochanter  extensively  found  among  mammals 
and  particularly  developed  in  the  odd-toed  ungulata.  This  is  sometimes  best 
developed  on  delicate  female  femurs  with  no  rough  muscular  ridges.  Of  course  the 
two  forms  may  coexist.  A  rough  elongated  depression,  \he  fossa  hypotrochanterica, 
also  receiving  fibres  of  the  gluteus,  is  sometimes  found  outside  the  gluteal  ridge. 
The  linea  aspera  divides  somewhat  below  the  middle  of  the  bone  into  two  supra- 
condylar  ridges,  which  bound  a  triangular  space2  as  they  pass  down  to  the  tops 
of  the  condyles.  The  outer  ridge  is  at  first  much  the  sharper,  but  it  becomes  indis- 
tinct an  inch  or  more  above  the  condyle.  The  inner  is  but  slightly  raised  ;  it  is 
interrupted  above  its  middle  for  the  passage  of  the  femoral  vessels  into  the  popliteal 
space.  It  ends  in  the  sharp  adductor  tubercle  above  the  inner  border  of  the  condyle. 
At  its  termination  the  shaft  has  four  surfaces :  a  posterior  one  nearly  plane,  a  front 
one  slightly  convex,  a  distinct  outer  one,  and  an  oblique  inner  one,  passing  insensibly 
backward  and  inward  from  the  anterior  surface.  There  are  usually  two  nutrient 
foramina,  both  directed  upward,  the  larger  between  the  lines  converging  to  the 
linea  aspera,  the  other  near  the  middle  of  the  bone,  a  little  to  the  inside  of  that  line. 

The  lower  extremity,  articulating  with  the  tibia  below  and  the  patella  in 
front,  presents  two  backward  prolongations,  the  condyles,  along  which  the  tibia 
travels  in  flexion.  These  are  compressed  from  side  to  side,  and  separated  by  the 
intercondylar  fossa?  which  is  beneath  the  back  part  of  the  shaft.  The  inner  condyle'' 
is  the  lower  when  the  shaft  is  vertical,  but  in  life  both  are  in  the  same  plane.  The 
outer3  is  longer  from  before  backward  ;  it  lies  in  an  antero-posterior  plane,  while  the 
inner  extends  backward  and  inward.  The  lateral  outline  of  each  has  been  well  com- 
pared to  a  watch-spring  partly  uncoiled.  Each  bears  a  tuberosity  near  the  posterior 
end  of  the  lateral  side,  very  nearly  in  continuation  with  the  supracondylar  ridges 
for  the  so-called  lateral  ligaments  of  the  knee.  A  depression  on  each  side  for  the 
head  of  the  gastrocnemius  is  found  above  and  behind  the  tuberosities.  The  ex- 
ternal condyle  bears  a  deep  oblique  groove  for  the  tendon  of  the  popliteus  at  the 
back  of  the  outer  surface. 

The  articular \surj "ace  for  the  knee  not  only  covers  the  lower  and  posterior 
aspects  of  the  condyles,  but  is  prolonged  upward  on  the  front  for  the  support  of  the 
patella,  as  a  groove  which  is  shown  by  horizontal  sections  to  be  concave  in  the 
middle  and  convex  at  either  side.  The  upper  boundary  slants  upward  and  outward, 
the  shaft  just  above  it  presenting  a  slight  depression.  Its  outer  border  is  a  promi- 
nent ridge  resisting  outward  dislocation  of  the  knee-pan.  The  patellar  surface  is 
continuous  with  the  articular  facets  of  the  condyles,  being  marked  off  only  by  certain 
lines,  which,  though  distinct  on  the  fresh  cartilage,  are  often  obscure  on  the  dried 
bone,  representing  the  separation  of  these  joints.  In  some  animals  the  separation  is 
complete.  The  outer  lhn\  usually  concave  posteriorly,  runs  obliquely  inward  to 
just  in  front  of  the  intercondylar  notch.  The  inner,  less  clear  and  generally  straight, 
begins  much  farther  forward  and  runs  obliquely  backward  to  the  inner  side  of  the 
front  of  the  notch.  The  outer  in  particular  marks  n  distinct  change  of  level.  Be- 
hind these  lines  the  articular  surfaces  extend  along  the  lower  and  posterior  sides  of 
the  condyles  even  onto  the  upper  aspect,  so  as  to  allow  extreme  llexion  of  the  knee. 

'  Linea  aspcra.     '•' IMiiitiim  !><>|>lilcum.     3  Fossa  Intcrcondyloiden.     4Conilylus  medialis.     •'  Cundyliis  l.Ucralis. 


THE   FEMUR. 


357 


Frontal  sections  through  the  back  part  of  the  condyles  show  that  the  inner  is  nearly 
symmetrical  in  its  convexity  from  side  to  side,  while  the  inferior  surface  of  the  outer 


FIG.  372. 


Outer  head  of  gastrocnemius 


External  lateral  ligament 

External  tibial  face 
Popliteal  groove 


Patellar  facet 


Lower  end  of  right  femur,  outer  aspect. 


slants  upward  and  inward.  The  length  of  the  articular  surface  of  the  inner  condyle 
from  the  back  to  the  line  marking  off  the  patellar  facet  is  considerably  greater 
(perhaps  two  centimetres)  than  that  of  the  outer. 


FIG.  373. 

Patellar  surfa 


External  tuberositv 


Limit  of  patellar  surface 
Internal  tuberosity 


Lower  end  of  right  femur  from  below. 

Structure. — Transverse  sections  in  series  through  the  whole  length  of  the 
femur  are  very  instructive.  They  show  the  great  strength  of  the  shaft,  the  thick- 
ness of  its  walls,  the  smallness  of  the  central  canal,  and  the  addition  made  by  the 
linea  aspera  ;  likewise  that  the  shaft  becomes  four-sided  both  above  and  below, 
and  that  in  the  latter  region  the  greater  diameter  is  transverse.  Coincident  with 
these  changes  are  a  great  diminution  of  the  thickness  of  the  walls  and  a  great  increase 
of  the  spongy  tissue.  The  weakness  of  the  walls  just  above  the  knee  is  very  striking. 
The  architecture  of  the  condyles  is  well  exhibited,  consisting  of  vertical  plates  run- 


358 


HUMAN    ANATOMY. 


ning  in  the  main  forward  and  backward,  crossed  by  transverse  ones,  in  part  diverging 
from  the  solid  bone  at  the  bottom  of  the  intercondylar  notch.  Such  sections  show 
also  the  prominence  of  the  outer  border  of  the  patellar  surface  and  the  curve  of  that 
articulation.  At  the  upper  end  they  display  the  prominence  of  the  lesser  trochanter, 
the  series  of  strong  plates  crossing  it,  which  at  a  higher  level  are  seen  diverging  from 
a  single  plate,  Bigelow's  true  neck1  (Merkel's  calcarfemorale'},  to  which  we  shall 
return.  The  greater  trochanter,  quite  free  from  all  pressure,  is  very  light  and  the 
head  very  dense.  Frontal  sections  of  the  head  and  neck  (Fig.  374)  show  the  series 
of  plates  given  off  successively  from  both  the  inner  and  outer  walls  forming  Gothic 

FIG.  374. 


Lesser 
trochanter 


Oblique  section  of  right  femur  parallel  to  lower 
border  ot  neck,  through  upper  end  of  lesser  tro- 
chanter. 


Frontal  section  through  upper  end  ot  jciniu  ,  showing 
aiiangement  of  pressure  and  tension  lamella-. 

arches  at  the  top  of  the  bone.  The  under  side  of  the  neck  is  thick  and  gives  off  a 
series  of  plates,  near  together,  running  obliquely  up  into  the  "head  in  the  line  of  the 
greatest  pressure,  especially  when  the  shaft  is  oblique,  as  in  life.  A  less  distinct 
&  ri.-s  of  long  arches  springs  from  the  outer  side,  curving  across,  and  acting  as 
"ties."  The  head  is  of  the  round-meshed  pattern,  fitted  t<»  resist  pressure  in  any 
direction,  often  presenting  an  almost  solid  core  at  the  middle,  and  generally  showing 
the  curved  line  of  union  of  the  epiphysis  of  the  head.  The  true  neck  of  the  femur  is 
a  plate,  or  a  series  of  plates,  springing  from  a  thick  spur  of  bone,  which  leaves  the 
hind  wall  of  the  neck  to  run  outward  towards  the  greater  trochanter.  This  is  best 

1  The  Hip.  Philadelphia,  iS6<)  ;  also  Huston  Medical  and  Surgical  Journal,  1875. 
1  Virchow's  Archiv,  Ikl.  1.,  1870. 


THE   FEMUR.  359 

seen  in  sections  parallel  with  the  lower  wall  of  the  neck  (Fig.  375)  ;  it  appears  also 
in  transverse  ones.  When  strongly  developed  it  can  be  shown  as  a  real  septum  by 
gouging  away  the  spongy  tissue  of  the  posterior  intertrochanteric  ridge  beneath 
which  it  passes. 

Sexual  and  Individual  Variations. — Apart  from  general  lightness  of  struc- 
ture, the  female  femur  presents  distinctly  smaller  articulations  than  the  male.  The 
average  diameter  of  the  head  of  thirty-eight  male  bones  is  4.8  centimetres,  and  of 
twenty-six  female  ones  4.15  centimetres.  In  only  two  of  the  male  bones  is  the 
diameter  less  than  4. 5  centimetres,  and  in  only  two  of  the  female  is  it  greater.  Both 
of  the  latter  are  long  ones.  In  women  the  size  of  the  head  increases  with  the  length, 
but  in  men  a  short  femur  is  about  as  likely  to  have  a  large  head  as  a  long  one.  The 
breadth  of  the  articular  surface  of  the  knee  is  less  conclusive  ;  the  averages  are  8.3 
centimetres  and  7.4  centimetres,  but  there  is  much  overlapping.  The  peculiarity 
of  outline  in  the  typical  female  femur  is  very  characteristic  when  well  marked  :  the 
shaft  narrows  gradually  from  the  condyles  till  at  or  above  the  middle  the  nar- 
rowest part  is  reached,  above  which  there  is  a  much  less  evident  expansion.  The 
typical  male  bone  narrows  much  more  suddenly  above  the  condyles,  so  that  the 
stouter  shaft  soon  reaches  a  tolerably  uniform  thickness.  The  inclination  of  the 
shaft  is  somewhat  greater  in  woman.  The  angle  with  a  vertical  line  in  the  above 
series  is  9.3°  in  man  and  10. 6°  in  woman.  (According  to  Bertaux,  it  is  8.75° 
and  n°.)  It  is  naturally  greater  in  shorter  femurs,  and  consequently  is  of  very 
doubtful  value  as  a  sexual  characteristic,  especially  in  view  of  the  great  individual 
variation.  The  angle  of  the  neck  with  the  shaft  is  of  minor  significance.  In  the 
writer's  series  it  ranges  from  110°  to  144°,  the  average  for  men  being  125.1°  and 
that  for  women  125.6°.  In  the  male  bones  there  is  little  connection  between  the 
length  of  the  femur  and  the  size  of  the  angle  ;  in  women  long  bones  have  a  large 
angle  and  short  bones  a  small  one.  The  average  angle  of  the  longer  half  of  the 
male  bones  is  126.5°  and  that  of  the  shorter  123.6°,  while  the  longer  and  shorter 
halves  of  the  female  series  give  129.2°  and  121.9°  respectively.  A  long  neck  gen- 
erally has  a  high  angle  and  a  short  neck  a  low  one.1  Thus  it  appears  that  there  are 
great  variations  in  the  angle  of  the  shaft  and  that  of  the  neck.  The  same  is  true  of 
almost  every  detail.  The  forward  inclination  of  the  neck  is  in  two-thirds  of  the  cases 
from  5°  to  20°,  and  usually  from  12°  to  14°.  Its  extreme  is  37°.  Very  rarely  this 
angle  is  negative, — that  is,  the  neck  slants  backward.  An  extreme  negative  angle 
of  25°  has  been  observed,  but  this  is  extraordinary.2  The  curve  and  outline  of  the 
shaft  vary  much.  An  extreme  form  is  the  pilastered  femur,  very  convex,  with  a 
prominent  linea  aspera,  generally  stout,  implying  strength.  An  opposite  form  is 
nearly  straight,  has  a  low  linea  aspera,  and  is  flattened  before  and  behind  in  the 
upper  part  of  the  shaft.  In  extreme  forms  the  depression  in  the  front  of  the  top  of 
the  shaft  is  increased  and  bounded  internally  by  a  sharp  ridge  running  up  to  the 
under  side  of  the  neck,  which  usually  has  a  low  angle.  Though  apparently  weaker, 
this  form  is  sometimes  found  in  very  powerful  men. 

The  index  of  the  shaft  is  the  proportion  of  the  thickness  to  the  breadth,  the 
latter  being  100.  Thus  (— j^-^22).  This  is  taken  at  about  the  middle  of  the 
shaft  where  the  linea  aspera  is  most  prominent.  It  is  said  to  be  greater  on  the  right 
than  on  the  left  and  in  men  than  in  women.  Bertaux  found  the  average  in  adults 
104.4,  and  m  a  series  of  young  femurs  112.1. 

The  index  of  the  neck  is  the  proportion  of  the  thickness  to  the  height.  Thus 
(Ul'''^gh*  I0°).  The  average  is  133.05.  It  is  a  trifle  higher  in  women,  but  the 
difference  in  unimportant. 

A  strong  convexity  of  the  shaft  outward  as  well  as  forward  suggests  a  patho- 
logical condition. 

Development  and  Changes. — The  shaft  begins  to  ossify  not  later  than  the 
seventh  week  of  fcetal  life.  A  centre  appears  in  the  lower  end  during  the  last  month 
of  pregnancy.  It  is  rarely  wanting  at  birth,  but  the  precise  time  of  its  appearance 
as  well  as  its  size  are  too  variable  to  make  it  a  very  valuable  guide  to  the  age  of  the 

1  H.  H.  Hirsch  :  Anatomische  Hefte,  Bd.  xxxvii.,  1899. 
•  Mikulicz  :  Arch,  fiir  Anat.  uncl  Phys.,  1878. 


360 


HUMAN    ANATOMY. 


foetus  or  infant.  Its  growth  seems  to  be  slight  during  the  first  three  weeks  after 
birth.  The  neck  grows  as  a  part  of  the  shaft  and  receives  three  epiphyses, — one  for 
each  trochanter  and  one  for  the  head,  which  fits  over  it  like  a  cap.  The  latter 
appears  in  the  second  half  of  the  first  year,1  and  is  pretty  conclusive  evidence  that 
the  age  of  six  months  at  least  has  been  reached.  The  epiphysis  for  the  greater 
trochanter  comes  in  the  third  year  (sometimes  some  years  later),  and  that  for  the 
lesser  at  a  time  variously  stated  as  from  eight  to  fourteen  years.  It  is  probable  that 

FIG.  376. 


Ossification  of  femur.  A,zA  eighth  foetal  month;  ft,  at  birth;  C,  during  first  year;  D,  at  eight  years;  E,a\. 
about  fifteen  years,  a,  centre  for  shaft;  i>,  lower  epiphysis;  c,  for  head;  d,  for  greater  trochanter;  e,  for  lesser 
trochanter. 

the  former  is  much  nearer  the  mark.  The  head  unites  with  the  shaft  at  about 
eighteen,  the  trochanters  somewhat  later  ;  probably  there  are  great  variations  ;  but 
all  these  superior  epiphyses  should  be  joined  by  nineteen,  and  at  twenty  the  line  of 
union  is  indistinct  or  lost.  An  epiphysis  for  the  third  trochanter  has  been  seen. 
The  lower  epiphysis  is  joined  by  twenty,  and  often  sooner.  At  birth  the  angle  of 
the  neck  may  be  160°,  but  is  often  less  ;  it  diminishes  under  the  pressure  of  the 
weight  as  the  child  walks,  and  by  the  time  of  puberty  has  probably  assumed  about 
its  permanent  angle.  There  is  no  reason  to  believe  that  the  angle  diminishes  in 
old  age. 

Surface  Anatomy. — The  greater  trochanter  can  be  explored  when  the  muscles 
about  it  are  relaxed.  The  lesser  trochanter,  though  deep,  can  be  felt  from  behind. 
A  large  third  trochanter  can  be  recognized,  and  must  not  be  mistaken  for  a  tumor. 
Owing  to  the  individual  variations  of  the  neck  and  the  pelvis,  the  relations  of  the 
trochanter  must  vary.  According  to  Langer,  a  horizontal  line  at  the  top  of  the 
greater  trochanter  divides  the  head,  touches  the  top  of  the  symphysis,  and  about 
divides  the  nates.  This  is  particularly  true  of  broad  pelves,  and  therefore  of  women. 
We  have  found  from  measurements  of  118  males  and  37  females  that  the  trochanter 
is  i.i  centimetres,  on  the  average,  higher  than  the  symphysis  in  the  male  and  three 
millimetres  in  the  female.  Topinard  gives  as  provisional  distances  in  the  male  the 
following  :  the  anterior  superior  spine  of  the  ilium  is  six  centimetres  above  the  head 
of  the  femur,  the  latter  two  centimetres  above  the  greater  trochanter  (practically 
agreeing  with  Langer),  and  the  greater  trochanter  two  centimetres  above  the  pub.es. 
The  head  of  the  femur  lies  under  a  crease  beneath  the  proper  fold  of  the  groin,  and 
can  sometimes  be  distinguished  at  the  inner  side  of  the  sartorius.  Nelaton's  line  is 
drawn  from  the  anterior  superior  spine  of  the  ilium  to  the  most  prominent  point  of 
the  tuberosity  of  the  ischium.  It  should  just  touch  the  top  of  the  greater  trochanter. 
The  shaft  is  too  thickly  covered  to  be  examined  in  detail,  except  near  the  knee.  The 
sides  of  both  condyles  are  easily  examined  ;  the  lateral  tubercles  and  the  adductor 

1  Fagerlund  :  Wiener  Med.  Presse,  1890. 


PRACTICAL   CONSIDERATIONS:    THE   FEMUR. 


361 


tubercle  can  be  felt.  The  latter  marks  the  line  of  union  of  the  lower  epiphysis 
with  the  shaft.  When  the  knee  is  flexed,  the  patellar  surface,  its  borders,  and  part 
of  the  articular  surface  of  the  condyles  can  be  felt. 

PRACTICAL   CONSIDERATIONS. 

Before  the  age  of  four  the  upper  epiphysis  is  not  distinct,  and  traumatism  is  apt 
to  result  in  separation  of  the  upper  cartilaginous  end  of  the  bone, — i.e. ,  a  fracture 
through  some  part  of  the  cartilaginous  neck.  Later  three  epiphyses  may  be  affected 
by  injury, — viz.,  those  for  the  head  and  the  two  trochanters. 


FIG.  377. 


Section  through  hip-joint,  showing  epiphyses  of  head  and  greater  trochanter  of  femur. 

The  epiphysis  for  the  head  is  shaped  like  a  hollow  hemisphere  set  upon  the 
convex  upper  end  of  the  neck.  The  epiphyseal  line  slopes  downward  and  inward, 
and  is  entirely  within  the  synovial  membrane. 

Separation  by  indirect  violence  occurs  as  a  result  of  extreme  extension  of  the 
thigh,  as  in  falls  backward  with  the  limb  fixed,  or  as  when  a  child  carried  in  the 
arms  of  a  nurse  throws  itself  violently  backward.  The  force  is  thus  in  effect 
applied  at  the  lower  end  of  the  femur,  which  acts  as  the  long  arm  of  a  lever.  When 
it  is  carried  far  backward  the  ilio-femoral  ligament  is  put  upon  the  stretch,  and  its 
point  of  insertion  becomes  the  fulcrum.  The  resistance  (or  weight)  is  at  the  point 
where  the  forward  movement  of  the  short  arm  of  the  lever — the  neck  and  head — 


362 


HUMAN   ANATOMY. 


is  resisted,  perhaps  slightly,  by  the  ligamentum  teres,  but  chiefly  by  the  anterior 
margin  of  the  acetabulum. 

Separation  is  followed  by  shortening.  This  may  be  recognized  by  Nelaton's  line 
(Fig.  378),  by  the  base  line  of  the  "  ilio-femoral  triangle"  (Bryant's)  (Fig.  379), 
or  by  Robson's  line,  which  is  a  line  dropped  vertically  from  the  anterior  spine  to 
meet  a  transverse  line  drawn  forward  and  inward  from  the  tip  of  the  greater  tn>- 
chanter  across  the  front  of  the  thigh,  the  patient  being  in  dorsal  decubitus. 

Eversion,  from  the  weight  of  the  limb,  is  usually  present. 

The  toughness  of  the  periosteum  and  the  strength  of  the  cartilaginous  bond 
betweeji  the  neck  and  head  in  childhood  may  make  the  epiphyseal  line  stronger 
than  the  thin  neck  beneath  it,  and  fracture  of  the  neck  may  therefore  occur  even  in 
young  children  or  adolescents.  The  symptoms  are  very  similar  to  those  of  epi- 
physeal separation.  The  crepitus  may  be  rough  instead  of  ' '  muffled. ' '  The  X-rays 
will  sometimes  differentiate  the  two  conditions.  In  a  case  of  injury  to  the  hip  in  a 
young  person,  it  is,  however,  probable  that  epiphyseal'  disjunction  will  result  rather 
than  fracture  of  the  neck;  but  in  youth,  on  account  of  the  presence  of  the  epiphyseal 


FIG.  378. 


FIG.  379. 


Showing  Nelaton's  line. 


Showing  Bryant's  triangle. 


joint  and  the  weakness  of  the  neck,  both  of  these  lesions  are  more  frequent  than 
dislocation.  Either  of  them  will  convert  the  normal  obliquity  of  the  neck  to  a 
position  more  nearly  horizontal,  causing  prominence  and  ascent  of  the  trochanter, 
and  bringing  about  at  once  the  condition  known  as  coxa  vara,  which  will  probably 
increase  later,  as  whenever  the  angle  of  the  neck  with  the  shaft  is  diminished  the 
strain  upon  the  former  is  increased.  Thus,*  either  epiphyseal  separation,  fracture 
of  the  neck,  or  slight  rhachitis  in  early  childhood  may  result  in  coxa  vara  at  the 
period  of  adolescence,  when  the  softening  incident  to  rapid  growth  is  taking  place, 
the  body  weight  is  increasing, — often  disproportionately, — and  laborious  occupations 
are  frequently  begun. 

The  cpiphysis  for  the  greater  trochanter  unites  at  about  tin-  nineteenth  year.  It 
is  easily  dislocated,  almost  always  from  direct  violence,  and  usually  between  the 
thirteenth  and  eighteenth  years,  because  that  is  the  period  of  greatest  exposure  to 
traumatism,  and  because  at  the  latter  date  the  epiphysis  is  joined  to  the  shaft.  The 
line  of  junction  with  the  shaft  is  on  the  level  of  the  tubercle  for  the  quadratus  on  the 
posterior  edge  of  the  greater  trochanter  (  Fig.  3^3).  It  is  therefore  below  the  level  of 
the  capsule  of  the  hip-joint  and  of  the  insertions  of  the  ^lutei,  obturators,  pyrifonnis, 


PRACTICAL   CONSIDERATIONS  :   THE   FEMUR. 


363 


FIG.  380. 


and  gemelli.  Disjunction  from  indirect  violence — through  the  action  of  these 
muscles — is  rare,  on  account  of  :  (i)  The  prolongation  downward  and  outward  of 
the  fibres  of  the  capsular  ligament  which  extend  below  the  epiphyseal  line.  (2)  The 
attachment  above  that  line  of  some  of  the  aponeurotic  fibres  of  origin  of  the  vastus 
externus.  (3)  The  toughness  of  the  periosteum. 

For  these  same  reasons,  when  disjunction  does  occur,  there  is  usually  but  little 
displacement.  If  it  exists,  and  is  marked,  the  epiphysis  is  drawn  into  approxi- 
mately the  same  position  as  that  occupied  by  the  head  of  the  bone  in  a  dislocation 
onto  the  dorsum  of  the  ilium.  The  age  of  the  patient  (epiphyseal  separation  being 
impossible  after  nineteen  and  dislocation  rare  before  that  age)  and  the  failure  of  the 
displaced  epiphysis  to  move  with  rotation  of  the  femur  are  aids  to 
diagnosis.  The  absence  of  rotation  and  of  shortening  of  the  limb 
distinguishes  this  lesion  from  "  extracapsular"  fracture  of  the 
neck. 

About  fifty  per  cent,  of  the  recorded  cases  have  died  of  py- 
aemia. This  is  probably  because  :  ( i )  The  greater  trochanter  is 
an  apophysis  rather  than  an  epiphysis,  and  is  in  contact  at  its 
base  with  cancellous  tissue  of  a  lighter  and  more  spongy  character 
than  that  adjoining  the  true  terminal  epiphyses  of  the  long  bones. 
(2)  The  violence  causing  the  injury  is  direct  and  thus  associated 
with  much  bruising  and  crushing  of  that  tissue.  (3)  The  disjunction 
is  attended  by  extensive  detachment  of  the  periosteum  from  the 
vascular  upper  end  of  the  bone,  as  the  periosteum  over  the  tro- 
chanter is  very  thin  and  the  dense  tendinous  fibres  are  almost  di- 
rectly attached  to  the  osseous  tissue  itself  (Poland). 

The  epiphysis  for  the  lesser  trochanter  can  be  separated  usu- 
ally only  between  the  thirteenth  year  and  the  nineteenth,  when  it 
joins  the  shaft.  But  one  case  has  been  recorded.  It  was  then 
torn  off  in  a  boy  of  fourteen,  as  the  result  of  the  strain  on  the  ilio- 
psoas  in  a  fall  backward  on  the  feet.  Death  from  pyaemia  followed. 

Fracture  of  the  neck  of  the  femur  is  common  (especially  in 
old  age),  in  spite  of  its  depth  and  its  thick  covering  of  soft  parts, 
because  :  (i)  In  falls  upon  the  feet  or  hip  it  receives  and  transmits 
much  of  the  weight  of  the  body,  which,  in  the  former  case  at 
least,  reaches  it  in  a  direction  which  causes  a  cross-strain  favorable 
to  fracture.  (2)  It  is  a  comparatively  fixed  portion  of  a  very 
long  lever  into  the  upper  end  of  which  many  powerful  muscles  are 
inserted.  (3)  It  is  of  itself  lengthened  and  thus  made  more  vul- 
nerable,— as  compared,  for  example,  with  the  neck  of  the  hu- 
merus, — so  as  to  increase  the  leverage  of  these  muscles,  the  degree 
of  mobility  of  the  hip-joint,  and  the  basis  of  support  for  the  trunk. 
(4)  Its  mechanical  weakness  increases  in  old  age  (<z)  from  the 
absorption  of  cancellous  tissue  which  occurs  everywhere  in  the 
skeleton,  but  begins  and  proceeds  most  quickly  (according  to 
Humphry)  in  the  femoral  neck  ;  (b}  from  a  corresponding  thin- 
ning of  the  compact  tissue,  including  that  part  of  the  cortex  which  unites  the  lesser 
trochanter  and  the  under  and  anterior  part  of  the  head,  the  line  of  greatest  press- 
ure in  the  erect  position.  (5)  The  angle  between  the  neck  and  the  shaft  is 
believed  by  many  surgeons  gradually  to  decrease,  though  this  change  is  not  in- 
variable and  is  denied  by  some  excellent  authorities.  It  is  true,  however,  that  the 
angle  is  smaller  the  less  the  stature  ;  that  it  is  thus  smaller  in  women,  and  that 
in  them,  after  the  age  of  fifty,  these  fractures  are  two  and  a  half  times  more  common 
than  in  men. 

When  the  age  of  the  patient  is  advanced,  and  the  violence  is  slight  and  indirect, 
the  femoral  neck  breaks  more  frequently  near  its  junction  with  the  head,  because 
there  it  is  thinnest  and  weakest.  Such  fractures  are  entirely  intracapsular. 

In  younger  persons,  and  especially  if  the  violence  is  severe  and  is  received 
directly  upon  the  hip,  the  fracture  is  more  apt  to  involve  the  base  or  wider  portion 
of  the  neck,  and  is  likely  to  be  partly  intra-  and  partly  extracapsular.  If  it  is 


Lines  of  fracture  of 
femur. 


364 


HUMAN   ANATOMY. 


Showing;  elevation  of  tip  of  trochanter  and  shortening  of  base 
of  Bryant's  triangle  in  fracture  of  neck  of  femur. 


entirely  below  the  line  of  capsular  attachment  both  in  front  and  behind,  it  cannot  be 
a  fracture  of  the  neck,  as  it  would  then  be  below  the  anterior  intertrochanteric  line, 
and  would  involve  the  extreme  upper  end  of  the  shaft.  Posteriorly,  it  is  possible 

for  a  partial  fracture  of  the  neck  to 

FIG.  381.  be  extracapsular,   as  the  insertion  of 

the  capsule  is  from  twelve  to  seven- 
teen millimetres  (one-half  to  two- 
thirds  of  an  inch)  above  the  base 
of  the  neck.  Impaction  of  fracture 
at  the  narrow  part  of  the  neck  is  not 
very  common.  When  it  occurs, 
some  spicula  of  the  compact  cortex 
of  the  neck  are  driven  into  the  ex- 
panded cancellated  structure  of  the 
head. 

Impaction  of  fracture  at  the  base 
is  common,  because  the  spongy  tro- 
chanter is  easily  thrust  upon  and 
sometimes  split  by  the  small  and 
relatively  compact  cervix. 

In  most  fractures  of  the  neck 
there  will  be  found  : 

(i)  Eversion,  due  chiefly  to  (a) 

the  weight  of  the  limb,  which  tends  normally  to  roll  outward  ;  but  also  to  a  certain 
extent  to  (<£)  the  action  of  the  ilio-psoas  and  other  external  rotators  ;  (c)  the  greater 
comminution  or  crushing  of  the  posterior  wall  of  the  neck,  which  is  weaker  than  the 
anterior  wall. 

(2)  A  fulness  over  the  upper  portion  of  Scarpa's  triangle,  due  to  effusion  into 
the  hip-joint   or  to  forward  projection  of  the  fragments  against  the  front    of  the 
capsule.     This  is  likely  to  occur  because  the  neck  is  normally  convex  forward,  the 
lesser  trochanter,  marking  the  inner  and  lower  boundary  of  the  neck,  being  on  a 
plane  posterior  to  the  head  ;  and   because 

of  the  greater  destruction  of  the  posterior 
portion  of  the  neck. 

(3)  Relaxation  of   the  ilio-tibial  band 
of  the  fascia  lata  (page  367). 

(4)  Approximation  of   the   trochanter 
to  (a)  the  anterior  superior  spine,  as  shown 
by     shortening,    best    determined    by   the 
length  of  the  horizontal  side  or  base  of  the 
ilio-femoral  triangle  ;  and  to  (<$)  the  mid- 
line  of  the  body,  as  shown  by  Morris's  line. 
Nelaton's  line  shows  the   former,    but    in- 
volves more    disturbance   of    the    patient. 
Chiene  demonstrates  shortening  by  placing 
the  edge  of  a  straight  flexible  piece  of  metal 
on  the  two  anterior  spines  and  that  of  an- 
other  on  the   tips  of  the  two  trochanters. 
Parallelism   negatives    the  idea  of  fracture. 
Morris  measures  from  the  symphysis  pubis 
to  the  trochanteric  summits.     The  distance 
is  lessened  on  the  side  of  fracture. 

These  points  can  easily  be  understood 
by  reference  to  Fig.  382. 

Emphasis  is  placed  on  these  measurements  because  it  is  perhaps  more  important 
in  this  than  in  any  other  fracture  to  avoid  vigorous  efforts  to  elicit  crepitus. 

The  blood-supply  of  the  proximal  fragment — the  head — will  reach  it  only 
through  the  reflected  portions  of  the  capsule,  untorn  strips  of  periosteum,  and  the 
ligamentum  teres,  that  through  the  cervix  being  cut  off.  It  is,  therefore,  scanty  and 


FIG. 


Morris's  measurements  to  show  the  trochanter 
of  the  injured  side  nearer  the  median  line  in  fracture 
of  neck  of  femur. 


PRACTICAL   CONSIDERATIONS:    THE   FEMUR. 


365 


FIG.  383. 


may  be  insufficient  to  furnish  reparative  material.  Any  movement  that  might  tear 
the  remaining  connections  between  the  fragments  is,  therefore,  most  undesirable. 
The  great  length  of  the  lower  fragment,  and  the  leverage  thus  exerted  as  a  result  of 
any  motion  of  the  inferior  extremity,  together  with  the  action  of  the  powerful  muscles 
running  from  the  pelvis  to  the  thigh,  make  it  especially  difficult  to  keep  the  frac- 
tured surfaces  in  close  apposition,  particularly  if  the  small  part  of  the  neck  is  involved. 
Impaction,  even  if  very  slight,  may  thus  be  a  favorable  circumstance,  and  should  not 
be  broken  up  by  rough  handling. 

Intracapsular  fractures,  in  spite  of  the  scanty  blood-supply,  the  presence  of 
synovial  fluid,  which  is  perhaps  the  most  important  unfavorable  factor,  and  the  mo- 
bility of  the  lower  fragment,  do  unite,  but  rather  as  an  excep- 
tion. As  a  rule,  fractures  at  the  base  of  the  neck  unite. 

Fracture  of  the  shaft  is  most  common  at  the  middle,  at 
the  point  of  greatest  convexity  of  the  forward  curve,  in  spite 
of  the  fact  that  here  the  bone  is  denser  and  its  compact  outer 
wall  thicker.  At  the  upper  third  fracture  is  usually  due  to 
indirect  violence,  at  the  lower  third  to  direct  violence.  In  the 
former  case  it  is  apt  to  be  oblique,  in  the  latter  transverse. 
These  lesions,  as  well  as  those  of  the  lower  end,  just  above  the 
condyles,  will  be  considered  in  their  relation  to  the  muscles 
that  influence  them  (page  644). 

The  lower  cpiphysis  of  the  femur,  the  only  one  whose  ossi- 
fication begins  before  birth, — "with  the  exception  of  the  occa- 
sional early  appearance  of  the  osseous  nucleus  in  the  upper 
epiphysis  of  the  tibia' '  (Poland), — is  the  last  to  join  its  diaphy- 
sis,  union  occurring  about  the  twentieth  year.  It  has  a  cup- 
shaped  upper  surface,  which  is  higher  externally.  Its  internal 
level  is  just  beneath  the  adductor  tubercle.  The  epiphysis 
includes  all  the  articular  surfaces  of  the  lower  end  of  the 
femur. 

In  the  majority  of  the  cases  of  disjunction  of  this  epiphy- 
sis the  cause  has  been  hyperextension  of  the  tibia  on  the  femur, 
often  combined  with  some  twisting  and  traction  upon  the  leg, 
as  when  a  boy  hanging  behind  a  cab  has  his  foot  caught  be- 
tween the  spokes  of  a  wheel.  In  twenty-seven  out  of  sixty- 
eight  cases  the  lesion  was  caused  in  this  way. 

The  ligaments  of  the  knee-joint  are  so  powerful  (as  they 
must  be  for  security,  on  account  of  the  shape  of  the  bones  that 
enter  into  it)  that  when  the  leg  is  brought  into  overextension 
tremendous  leverage  is  exerted  on  this  epiphysis  through  the 
crucial  ligaments,  the  external  and  internal  lateral  ligaments, 
and  the  popliteus  muscle,  aided  by  the  gastrocnemius.  Al- 
though the  latter  is  attached  partly  above  the  epiphyseal  line, 
the  periosteum  is  torn  off  the  lower  end  of  the  diaphysis  down 
to  the  extremely  dense  layer  at  the  cartilaginous  junction. 
The  muscle  then  becomes  an  important  factor  in  carrying  the 
epiphysis  forward — the  usual  displacement — and,  aided  by  the 

popliteus,  in  rotating  its  posterior  upper  edge  downward.  The  mechanism  has  been 
compared  to  that  of  fractures  of  the  radius  in  falls  upon  the  hand,  the  posterior 
ligament  of  the  knee-joint  bringing  a  cross-strain  upon  the  epiphysis  similar  to  that 
conveyed  to  the  radius  by  the  anterior  ligament  of  the  wrist. 

The  diaphysis  projects  into  the  popliteal  space  or  through  the  skin,  and  has 
caused  grave  injuries  to  vessels  and  nerves.  Amputation  has  been  required  in  a 
large  proportion  of  these  cases,  on  account  of  these  injuries  or  because  of  the  de- 
tachment of  the  periosteum  and  the  suppuration  that  often  follows  it.  The  joint 
is  rarely  involved,  because  the  ligaments  uniting  the  bones  of  the  leg  to  the 
epiphysis  are  more  powerful  than  the  cartilaginous  connections  of  the  latter  with  the 
diaphysis. 

As  might  be  expected,  the  chief  growth  of  the  femur  taking  place  from  this 


Showing;  epiphyses  of 
femur. 


366  HUMAN   ANATOMY. 

epiphysis,  a  number  of  cases  of  arrest  of  growth  have  been  reported.  The  disjunc- 
tion has  been  mistaken  for  a  dislocation  of  the  knee  or  a  supracondylar  fracture 
of  the  femur,  but  the  undisturbed  relations  of  the  condyles  and  the  head  of  the 
tibia  and  the  freedom  of  motion  in  the  knee-joint  serve  to  distinguish  it  from  the 
luxation,  while  the  fracture  is  rare  in  children,  and  presents  differential  signs  that 
will  be  mentioned  later  (page  644). 

Fractures  between  the  condyles  (intercondylar),  when  T-shaped,  as  they  often 
are,  are  thought  to  be  secondary  to  the  main  or  supracondylar  fracture, — i.e. ,  the 
shaft  breaks  above  the  condyles  and  the  force  continuing  splits  them  apart.  The 
line  of  the  latter  fracture  is  nearly  vertical  and  follows  the  intercondylar  notch, 
already  weakened  by  numerous  foramina  for  vessels.  The  proximity  of  the  popliteal 
vessels  has  resulted  in  grave  complications  from  pressure  or  from  rupture.  Either 
condyle  may  be  split  off  separately.  The  joint  is  necessarily  involved  in  all  these 
fractures,  and  rapid  distention  may  make  the  diagnosis  difficult.  The  X-rays  should, 
of  course,  be  employed  in  such  cases,  and  indeed  in  all  doubtful  fractures  of  the 
femur. 

Osteotomy  for  genu  valgum  may  be  done  through  an  incision  on  the  outer 
side  of  the  thigh — the  region  of  safety — about  two  inches  above  the  external  condyle. 
The  ilio-tibial  band  of  fascia  is  cut  ;  the  incision  passes  in  front  of  the  biceps  ;  when 
about  two-thirds  of  the  shaft  has  been  divided  by  the  osteotome,  the  remainder  will 
fracture  easily,  as  the  outer  part  of  the  bone  is  here  thicker  than  the  inner.  The 
operation  has  the  advantages  of  remoteness  from  the  epiphyseal  line,  from  important 
blood-vessels,  and  from  the  synovial  membrane  of  the  knee.  The  bone  is  divided 
at  a  narrow  part. 

Disease. — Infective  disease  of  the  upper  end  of  the  femur  usually  involves  the 
hip-joint,  even  when  it  begins  in  the  diaphysis,  the  epiphyseal  line  being  intra- 
articular. 

In  spite  of  the  protective  covering  of  muscles  surrounding  the  shaft,  it  is  not 
infrequently  the  subject  of  inflammation,  probably  as  a  result  of  the  great  strains  and 
numerous  traumatisms  to  which  it  is  subjected,  and  of  the  physiological  activity 
necessitated  by  its  rapid  growth,  which  between  birth  and  maturity  is  proportionately 
nearly  twice  as  much  as  that  of  the  leg  and  more  than  twice  as  much  as  that  of  the 
whole  body.  Thus,  post-typhoidal  osteitis  attacks  the  femur  in  about  twenty-five 
per  cent,  of  the  cases  in  which  the  lower  extremity  is  involved,  and  more  frequently 
than  any  other  bone  except  the  tibia  and  ribs,  although  the  superficial  bones  of  the 
skeleton  are  involved  by  this  disease  three  and  a  half  times  more  frequently  than  the 
deep  bones. 

At  the  lower  end  of  the  femur,  disease  resulting  in  necrosis,  especially  of  the 
posterior  aspect,  often  requires  amputation,  as,  owing  to  the  thinness  of  the  perios- 
teum in  that  region,  there  is  scarcely  any  attempt  at  the  formation  of  an  involucrum 
(Rose). 

Exostoses  of  the  femur  are  not  uncommon,  especially  in  horsemen,  in  the  neigh- 
borhood of  the  tendon  of  the  adductor  longus — i.e. ,  at  the  upper  end  of  the  femur 
— and  occasionally  in  that  of  the  adductor  magnus  at  the  lower  end, — "rider's 
bones. ' ' 

The  great  comparative  frequency  with  which  sarcomata  attack  the  femur  is  in 
accord  with  the  general  rule  that  they  are  more  frequently  found  on  long  bones 
than  on  short  ones,  on  the  lower  limb  than  on  the  upper,  and  on  bones  near  the 
trunk  than  on  those  remote  from  it.  As  they  are  also  more  malignant  the  nearer 
they  approach  the  trunk,  these  tumors,  like  those  of  the  humerus,  are  clinically  more 
serious  than  those  of  the  distal  portions  of  the  extremity.  Both  central  and  sub- 
periosteal  sarcomata,  but  especially  the  former,  have  a  predilection  for  the  ends 
of  the  bones  ;  but  whereas  they  affect  chiefly  the  upper  end  of  the  humerus  and  the 
lower  ends  of  the  radius  and  ulna,  in  the  inferior  extremity  they  are  most  often 
found  at  the  lower  end  of  the  femur  and  the  upper  ends  of  the  tibia  and  fibula, — that 
is,  at  the  ends  towards  which  the  nutrient  arteries  are  not  directed,  and  at  which 
epiphyso-diaphyseal  union  takes  place  latest  (page  272). 

Landmarks. — In  very  thin  persons  the  head  of  the  femur  can  sometimes 
felt  immediately  below  Poupart's  ligament  and  just  external  to  its  middle. 


THE   HIP-JOINT.  367 

The  greater  trochanter  is  almost  subcutaneous,  being  covered  by  the  aponeu- 
rotic  insertion  of  the  upper  fibres  of  the  gluteus  maximus.  It  is  from  7.5  to  10  cen- 
timetres (three  to  four  inches)  below  the  crest  of  the  ilium.  In  the  erect  position 
it  is  slightly  anterior  to  and  farther  from  the  mid-line  than  the  mid-point  of  the 
crest.  It  is  visible  in  thin  persons,  and  assumes  abnormal  prominence  when  there 
has  been  wasting  of  the  gluteal  muscles,  as  the  gluteus  medius  and  minimus  nor- 
mally efface  the  hollows  between  it  and  the  ilium.  In  fat  or  muscular  persons 
the  fascial  attachments  to  the  trochanter  cause  a  visible  depression.  Its  upper 
border  is  on  a  level  with  the  centre  of  the  acetabulum  (so  that  N61aton's  line  passes 
over  those  two  points),  is  nineteen  millimetres  (three-quarters  of  an  inch)  lower 
than  the  top  of  the  femoral  head,  and  is  almost  on  a  level  with  the  pubes.  The 
depression  immediately  beneath  it  corresponds  to  the  tendinous  lower  portion  of 
the  gluteus  maximus  close  to  its  insertion.  The  gap  between  it  and  the  iliac  crest 
is  bridged  over  by  the  upper  portion  of  that  part  of  the  fascia  lata  known  as  the 
ilio-tibial  band.  Relaxation  of  this  band  in  fracture  of  the  femoral  neck  can  be  both 
felt  and  seen  (Allis). 

The  three  gluteal  bursae  interposed  between  the  trochanter  and  the  gluteal 
muscles  may  become  enlarged,  especially  that  beneath  the  gluteus  maximus,  and 
obscure  the  outlines  of  the  trochanter.  This  condition  is  sometimes  mistaken  for 
hip-joint  disease,  as  the  thigh  is  usually  adducted  and  flexed  on  the  pelvis,  because 
abduction  and  extension  bring  into  action  the  gluteal  muscles,  and  thus  cause  painful 
pressure  on  the  bursa.  Inflammation  of  that  bursa  is  almost  always  the  result  of 
a  blow  upon  the  trochanter  ;  the  joint  movements  are  free,  there  is  no  referred  pain 
in  the  knee,  and  forcing  the  head  of  the  femur  against  the  acetabulum  by  pressure 
upon  the  knee  is  painless,  as  is  pressure  over  the  capsule  of  the  joint  below  Pou- 
part's  ligament. 

In  subcutaneous  osteotomy  of  the  neck  of  the  femur  the  incision  for  admission 
of  the  saw  is  made  about  one  inch  in  front  and  one  inch  above  the  top  of  the 
trochanter.  The  saw  cut  runs  parallel  with  Poupart's  ligament  and  is  about  2.5 
centimetres  (one  inch)  below  it. 

The  lesser  trochanter  cannot  be  felt. 

The  shaft  of  the  femur  is  deeply  situated  and  cannot  be  closely  approached 
for  palpation,  except  at  the  outer  side  of  the  lower  third  in  the  space  between  the 
biceps  and  vastus  externus. 

The  most  prominent  part  of  the  inner  rounded  surface  of  the  knee  is  the 
tuberosity  on  the  inner  condyle  of  the  femur.  Above  it  is  the  adductor  tubercle 
marking  the  tendinous  insertion  of  the  great  adductor  and  just  above  the  inner  end 
of  the  epiphyseal  line. 

The  external  condyle  is  subcutaneous. 

The  remaining  landmarks  in  this  region  will  be  considered  in  relation  to  the 
knee-joint  and  the  soft  parts  (page  671). 

THE   HIP-JOINT. 

This  is  a  ball-and-socket  joint.  The  socket  is  formed  by  the  acetabulum  with 
the  assistance  of  the  transverse  and  cotyloid  ligaments.  The  articular  facet  which 
bears  the  articular  cartilage  has  been  described.  The  notch  at  the  lower  part  of  the 
periphery  of  the  acetabulum  is  bridged  over  by  the  transverse  ligament1  (Fig. 
384),  a  collection  of  interlacing  fibres,  which  thus  completes  the  margin  of  the  socket. 
An  opening  is  left  below  it  through  which  vessels  and  nerves  pass  ;  from  its  sides 
the  round  ligament2  arises.  Some  fibres  of  the  transverse  ligament  mingle  with 
those  of  the  latter.  The  cotyloid  ligament ''  (Fig.  384)  is  a  fibro-cartilaginous  rim, 
which  deepens  the  socket  overlapping  the  head  of  the  femur  until  the  cavity  embraces 
more  than  half  a  sphere.  It  is  attached  to  the  edge  of  the  acetabulum,  and,  where 
this  is  wanting,  to  the  transverse  ligament.  The  cotyloid  ligament  is  about  five 
millimetres  broad  at  the  attached  base,  and  narrows  to  a  sharp  border,  so  as  to  be 
triangular  on  section.  The  distance  from  the  base  to  the  free  edge  is  very  nearly 
one  centimetre  at  the  top^)f  the  joint,  where  it  is  greatest.  The  non-articular  space 
at  the  bottom  of  the  joint  is  filled  with  fat  and  by  the  round  ligament  nearly  up  to 

1  Lin.  transversum  acetabuli.     "  Lig.  teres  femoris.      ;L;il>rum  Klenoidale. 


368 


HUMAN  ANATOMY. 


the  level  of  the  articular  surface.  These  structures  are  covered  by  synovial  mem- 
brane. The  head  of  the  femur  is  covered  by  articular  cartilage,  except  at  the  de- 
pression for  the  insertion  of  the  round  ligament. 

The  bones  are  connected  by  the  capsule  and  the  round  ligament. 

The  capsule1  (Figs.  385,  386)  is  a  fibrous  envelope  enclosing  the  joint, 
strengthened  by  certain  bands,  which  are  inseparable  parts  of  its  substance,  though 
they  have  names  of  their  own.  The  capsule  is  attached  to  the  cotyloid  ligament  and 
to  the  periphery  of  the  acetabulum  just  outside  of  the  origin  of  the  latter.  In  this 
respect  there  is  much  uncertainty  ;  the  capsule  always  rises  from  the  free  edge  of  the 
transverse  ligament,  and,  as  a  rule,  elsewhere  outside  the  base  of  the  cotyloid  ;  but  it 
may  in  parts  arise  from  its  edge.  This  applies  to  the  capsule  examined  from  within  ; 
externally  the  fibres  extend  a  considerable  distance  from  the  border  of  the  joint. 
They  almost  conceal  the  opening  at  the  notch  below  ;  above,  they  partly  bridge 
over  the  reflected  tendon  of  the  rectus  and  partly  join  its  deeper  fibres.  The  cap- 

FIG.  384. 


Articular  surfac 


Fat  in  acetabular  fossa 


Tuberosity  of  ischium 


Anterior  inferior  spine  of 
ilium 


Cotyloid  ligament 
Stump  of  round  ligament 
Transverse  ligament 


Capsule  reflected 


Socket  of  right  hip-joint.     The  capsule  has  been  divided  near  its  origin  and  reflected. 

sule  extends  to  the  base  of  the  anterior  inferior  spine  of  the  ilium  and  some  distance 
on  the  obturator  crest.  The  attachment  to  the  femur,  seen  from  without,  runs  from 
the  top  of  the  greater  trochanter,  just  above  the  superior  cervical  tubercle,  down  the 
spiral  line  to  the  level  of  the  top  of  the  lesser  trochanter,  where  the  line  of  insertion 
turns  in  for  about  two  centimetres,  when  it  passes  upward  along  the  back  of  the 
neck,  less  than  half-way  from  the  head  to  the  posterior  intertrochanteric  line,  till, 
reaching  the  top  of  the  neck,  it  gradually  passes  outward  to  the  starting-point. 
Thus  the  capsule  stops  about  a  finger' s-breadth  short  of  the  lesser  trochanter,  in- 
cludes less  than  half  the  hind  side  of  the  neck,  and  stops  short  of  the  digital  fossa 
and  of  the  inner  side  of  the  top  of  the  greater  trochanter.  Posteriorly,  it  is  not 
truly  inserted  into  the  neck,  but  simply  crosses  it,  its  position  being  determined 
by  the  line  of  reflection  of  the  synovial  membrane.  The  general  direction  of  the 
fibres  is  longitudinal  ;  but  the  posterior  fibres,  when  the  femur  is  strongly  extended, 
assume  the  form  of  a  twisted  band  running  from  the  back  of  the  socket  outward 

1  Capsuln  nrticularls. 


I 
I 


THE   HIP-JOINT. 


369 


and  upward  across  the  back  of  the  neck  to  the  top  of  the  greater  trochanter  (Fig. 
387).  Moreover,  beneath  the  longitudinal  layer  there  is  a  sling  of  circular  fibres, 
the  zona  orbicularis,  starting  from  the  anterior  inferior  spine  of  the  ilium  and  pass- 
ing behind  the  neck  to  return  to  the  same  point.  It  lies  near  the  head  of  the 
femur,  completely  concealed  by  the  longitudinal  fibres.  It  is  isolated  only  by  a 
rather  artificial  dissection. 

The  capsule  varies  much  in  thickness  in  different  places  ;  thus,  it  is  very  weak 
behind  and  very  strong  in  front.     It  is  strengthened  by  three  collections  of  accessory 

FIG.  385. 


Ilio-femoral  ligament 


Right  hip-joint,  anterior  aspect. 

fibres.  Much  the  most  important  is  the  ilio-femoral  ligament '  (Fig.  385),  a  thick 
triangular  expansion,  intimately  fused  with  the  capsule,  arising  by  its  apex  from  the 
lower  part  of  the  anterior  inferior  spine  of  the  ilium  and  from  the  bone  below  and 
behind  it  above  the  lip  of  the  acetabulum,  and  extending  by  its  base  from  the 
superior  cervical  tubercle  to  the  level  of  the  lesser  trochanter.  The  borders  of  this 
are  often  particularly  strong,  and  are  spoken  of  as  the  outer  and  inner  limbs  of  the 
ligament.  A  weak  space  is  sometimes  seen  between  them  near  the  insertion,  whence 
it  has  been  called  by  Bigelow  the  Y-ligament  from  a  resemblance  to  an  inverted  Y. 

1  Lig  iliofcmorale. 
24 


370 


HUMAN  ANATOMY. 


Striking  examples  of  this  are  generally  artificial  productions.  The  beginning  of 
the  ilio-femoral  ligament  covers  the  outer  part  of  the  head.  The  capsule  is  much 
thinner  over  the  inner  part  of  the  head,  and  is  covered  by  the  bursa  under  the  ilio- 
psoas,  which  often  communicates  with  the  joint.  The  pubo-femoral  liga- 
ment1 (Fig.  385)  is  a  slender  band  of  fibres,  thickening  the  under  side  of  the 
capsule,  extending  from  the  lowest  point  of  the  capsular  insertion  on  the  spiral 
line  to  the  outer  end  of  the  obturator  crest.  It  is  rarely  very  evident.  The 
ischio-femoral  ligament2  (Fig.  387)  is  a  strong  but  ill-defined  bundle  at  the  back 
of  the  joint,  extending  from  the  ischial  origin  of  the  capsule  to  the  top  of  the  digital 
fossa.  The  capsule  is  further  supported  by  muscles  and  by  bands  of  fibrous  tissue, 
generally  expansions  from  tendons  or  fasciae.  Morris  describes  a  band  on  the  upper 

FIG.  ;VS6. 


Cotyloid  ligament 


Capsul 


Z.Fat  in  acetabular 
fossa 


Round  ligament 


Obturator  membrane 


Frontal  section  through  right  hip-joint.    The  femur  has  been  allowed  to  fall  from  the  socket. 


anterior  aspect,  passing  between  the  reflected  tendon  of  the  rectus  and  the  highest 
origin  of  the  vastus  externus,  which  is  sometimes  very  strong,  but,  in  our  opinion, 
inconstant.  The  relation  of  the  ilio-psoas  has  been  mentioned.  Fibres  are  received 
at  the  upper  outer  part  from  the  gluteus  minimus.  The  obturator  internus  and  the 
gemelli  are  close  against  it  behind,  and  the  obturator  externus  behind  and  below. 
We  have  seen  a  tendinous  band  beneath  the  tendon  of  the  obturator  internus  quite 
distinct  from  the  capsule  internally  and  fused  with  it  externally.  It  may  have  been 
n  reduplication  of  that  muscle  or  an  extra  ischio-fcmoral  ligament . :1 

The  round  ligament   (/io-anifntmn  fcrcs]    (Figs.    384,    389)   is  a  weak   band 

of  fibrous  tissue,  containing  vessels  and  nerves,  surrounded  by  synovial  membrane, 

lying  under  the  fat  in  the  deep  non-articular  hollow  of  the  socket,  connecting  the 

;!  Journal  of  Anatomy  and  Physiology,  vol.  viii., 

'Li||-  pubocnpstilarc      "  Lig.  ischiocapsulare. 


THE   HIP-JOINT. 


37i 


rim  of  the  acetabulum  with  the  head  of  the  femur.  The  origin  is  from  each  edge 
of  the  notch  and  from  the  deeper  fibres  of  the  transverse  ligament,  the  insertion 
into  the  deepest  part  and  upper  edge  of  the  depression  in  the  femoral  head.  A 
fresh  specimen,  especially  from  a  child,  shows  the  lower  half  of  the  depression 
becoming  gradually  shallower  and  forming  a  groove  in  which  the  upper  part  of 
the  band  rests,  which,  covered  with  the  synovial  membrane,  completes  the  spheri- 
cal shape  of  the  head.  Vessels  run  along  the  round  ligament,  which  in  infancy 


FIG. 


Reflected  tendon  of  rectus 


Back  of  capsule 


Tuberosity  of  ischium 


Ischio-femoral 
ligament 


Right  hip-joint,  posterior  aspect. 

and  early  childhood  nourish  the  head,  but  in  the  adult  they  often  do  not  enter  the 
bone. 

This  ligament  is  sometimes  wanting.  According  to  Moser,1  this  defect  is  only  in 
the  o1d,  and  is  to  be  looked  upon  as  a  degenerative  change.  Comparative  anatomy 
teaches  that  it  is  the  analogue  of  a  part  of  the  capsule.  It  is  remarkable  that  it  is 
wanting  in  certain  species  closely  allied  to  others  possessing  it.  Besides  the  two 
extremes  of  complete  freedom  within  the  joint  and  of  total  absence,  the  ligamentum 
teres  of  animals  is  also  found  in  an  imperfectly  developed  condition  as  a  fold  along 

1  Schwalbe's  Morpholog.  Arbeiten,  Bd.  ii.,  1893.     This  paper  gives  the  literature. 


372 


HUMAN   ANATOMY. 


the  side  of  the  cavity  between  the  notch  in  the  acetabulum  and  the  head  of  the  bone. 
Many  of  the  statements  of  its  absence  require  confirmation  by  more  observations. 
Thus,  among  the  anthropoid  apes  it  seems  to  be  generally  present  in  all  but  the 
ourang.  In  this  animal,  though  usually  wanting,  it  has  been  found  in  a  rudimentary 
condition.  Meckel  declared  that  it  was  absent  in  the  gibbon,  but  we  believe  no 
other  observer  has  had  a  similar  experience.  It  is  very  strongly  developed  in  the 
ostrich,  but  is  wanting  in  the  rhea  (the  American  ostrich)  and  probably  in  the  casso- 
wary. Sutton *  considers  it  as  the  tendon  of  the  pectineus  muscle  which  has  become 
separated  through  skeletal  modifications.  Sutton  relies  a  good  deal  on  the  condition 
in  the  horse  for  support  in  his  argument.  He  found  it  consisting  of  two  bands, — 
one  within  the  joint,  apparently  the  usual  ligament,  and  another  passing  out  of  the 
cavity  to  the  linea  alba  at  its  junction  with  the  pubes,  which  he  calls  the  pubo- 
femoral  portion.  The  pectineus  muscle  arises  in  part  from  this  latter  portion. 
Sutton  gives  a  table  telling  the  story  of  the  structure  according  to  his  theory.  In 
sphenodon  (a  lizard)  the  tendon  of  the  ambiens,  representing  the  pectineus,  passes 

FIG.  388. 

Bursa  beneath  ilio-psoas 
I 


Round  ligament 


•Front  of  capsule 


Spine  of  ischium 


Capsule  a  tached  to  neck 
of  femur 


Tendon  of  obturator  externus 


Cotyloid  ligament 
Horizontal  section  through  right  hip-joint. 


into  the  joint  to  the  head  of  the  femur  ;  in  the  ostrich  the  ligament  is  continuous 
with  the  tendon  by  means  of  connective  tissue  ;  in  the  horse  the  two  parts  are 
distinct  ;  and  in  man  the  external  part  is  wanting.  The  structure  is  evidently  a  very 
variable  one. 

The  synovial  membrane  (Figs.  386,  388)  lines  the  capsule,  covers  the  cotyloid 
and  transverse  ligaments,  surrounds  the  ligamentum  teres,  and  covers  the  fat  in  the 
fossa  of  the  acetabulum.  It  is  reflected  from  the  femoral  attachment  of  the  capsule 
onto  the  neck,  which  it  invests  to  the  border  of  the  articular  cartilage.  This  reflected 
part  presents  certain  folds  caused  by  fibres  from  the  capsule  running  up  along  the 
neck,  called  retinacula  (Fig.  390).  There  are  generally  three  chief  ones  :  a  superior, 
starting  from  the  superior  cervical  tubercle  and  running  along  the  upper  border,  or 
backward  across  the  neck  to  the  head  of  the  femur  ;  a  middle,  from  near  the  inferior 
cervical  tubercle  along  the  front  of  the  lower  border  of  the  neck  ;  and  an  inferior, 
from  near  the  lesser  trochanter  along  the  lower  side.  Any  of  these  may  be  more 
or  less  free  from  the  neck. 

1  Journal  of  Anatomy  and  Physiology,  vol.  xvii.,  1883. 


THE   HIP-JOINT. 


373 


The  retinacula l  probably  strengthen  the  union  of  the  head  and  neck  before  the 
union  of  the  epiphyses. 

Movements. — As  a  ball-and-socket  joint,  the  hip  permits  motion  on  an  indefi- 
nite number  of  axes.  If  the  ball  were  on  the  end  of  a  straight  rod,  we  could  assume 
that  flexion  and  extension  occur  on  a  transverse  axis  and  adduction  and  abduction 
on  an  antero-posterior  one,  but  the  inclination  of  the  shaft  of  the  femur  and  that  of 
the  neck  in  two  directions  complicates  the  problem,  so  that  accurate  analysis  of  the 


FIG.  389. 


Crest  of  ilium 


Head  of  femur 


Obturator  membrane 


Symphysis  pubis 


The  inner  wall  of  the  hip-joint  socket  has  been  cut  away,  exposing  the  head  and  round  ligament  without  disturbing 

the  capsule. 


movements  is  practically  impossible.  Rotation  is  motion  on  a  vertical  axis  which 
is  generally  assumed  to  pass  through  the  head  and  the  intercondylar  notch.  This 
must,  of  course,  vary  with  the  shape  of  the  bone.  Although  the  angular  motions  in 
the  four  conventional  planes  are  far  from  simple,  they  may  be  assumed  to  be  so 
for  practical  purposes.  Flexion  is  stopped  in  life  by  the  contact  of  the  thigh  and 
the  trunk  before  the  limits  of  the  motion  are  reached.  Extension  is  limited  by  the 

1  Fawcett :  Journal  of  Anatomy  and  Physiology,  vol.  xxx.,  1896. 


374 


HUMAN    ANATOMY. 


Retinaculum 


Posterior 

intertrochanteric 

ridge 


resistance  of  the  strong  ilio-femoral  ligament,  excepting  the  outer  band.      Abduction 
is  limited,  the  thigh  being  extended,  by  the  pubo-femoral  ligament  and  perhaps  by 

the    inner    limb  of    the    ilio-femoral. 

FIG.  390.  When  the  thigh  is  flexed,  the  latter  is 

Round  ligament  certainly  relaxed,  and  the  strain  comes 

on  the  pubo-femoral  and  a  part  of  the 
capsule  behind  it, — a  very  weak  re- 
gion. Adduction  with  a  straight  thigh 
is  limited  by  the  outer  limb  of  the 
ilio-femoral,  the  top  of  the  capsule, 
and  Morris's  band  from  the  rectus 
tendon  to  the  vastus  externus,  if  it 
be  present.  After  moderate  flexion 
is  passed,  the  ilio-femoral  is  relaxed. 
Outward  rotation,  the  thigh  being 
Capsule  straight,  is  checked  by  the  ilio-femoral, 
especially  by  its  inner  band.  As  the 
thigh  is  flexed  the  inner  band  is  re- 
laxed and  the  outer  is  at  first  tense, 
but  both  are  relaxed  as  flexion  reaches 
about  45°.  Morris's  band  now  be- 
comes tense,  and  -as  flexion  becomes 
extreme  the  round  ligament  is  tense 
also,  unless  the  thigh  be  abducted, 
when  it  is  completely  relaxed.  In- 
ward rotation  is  checked  by  the  ischio- 
femoral  ligament  in  any  position. 

The  most  important  part  of  the 
capsule  is  the  ilio-femoral  band,  which 
is  extremely  strong  and  prevents  over- 
extension.  It  is  an  essential  element 
in  maintaining  the  upright  position. 
The  round  ligament  has  probably  no 
mechanical  function,  though  it  can  be 
made  tense  by  flexing,  and  at  the  same 
time  either  adducting  the  femur  or 
rotating  it  outward.  It  is  too  weak  to  be  of  any  real  use  as  a  restraint.  Probably 
its  chief  usefulness  is  to  carry  vessels  to  the  head  of  the  femur  in  childhood. 

PRACTICAL   CONSIDERATIONS. 

The  greater  security  of  the  hip-joint,  as  compared  with  the  shoulder-joint,  is 
due  to  the  depth  of  the  acetabular  cavity  ;  to  its  reinforcement  by  the  cotyloid  fibro- 
cartilage  ;  to  the  attachments  of  the  ilio-psoas,  gluteus  minimus,  and  vastus  externus 
to  the  capsule  ;  but  chiefly  to  the  thickenings  of  the  capsule  itself,  which  are  described 
as  the  ilio-,  ischio-,  and  pubo-femoral  ligaments. 

The  greatest  pressure  upon  the  capsule  in  all  ordinary  positions  is  in  an  upward 
and  outward  direction,  or  upon  the  anterior  surface  of  the  capsule,  as  when,  under 
the  influence  of  the  powerful  extensors,  the  pelvis  and  trunk  tend  to  roll  backward 
upon  the  thighs  in  the  erect  posture.  The  tension  and  pressure  are,  of  course, 
greatest  near  the  pelvic  attachment  of  the  capsule  where  the  head  will  impinge  upon 
it  with  the  most  advantage  as  to  leverage.  The  capsule  is  especially  fitted  to  resist 
this  pressure. 

If  two  lines  be  drawn,  one  from  the  anterior  inferior  iliac  spine  to  the  inner 
border  of  the  femur  near  the  lesser  trochanter,  the  other  from  the  anterior  part  of 
the  groove  for  the  external  obturator  (/.<-'.,  the  upper  part  of  the  tuberosity  of  the 
ischium)  to  the  digital  fossa,  all  the  ligament  outside  and  above  these  lines  is  very 
thick  and  strong  ;  whereas,  all  to  the  inner  side  and  below,  except  along  the  narrow 
pubo-femoral  band,  is  very  thin  and  weak,  so  that  the  head  of  the  bone  can  be 


Right  femur  seen  from  inner  side,  showing  reflection  of 
synovial  membrane  onto  the  neck. 


PRACTICAL   CONSIDERATIONS:   THE   HIP-JOINT. 


375 


FIG.  391. 


Diagram  indicating  strong  and  weak  portions  of  capsule  of  hip- 
joint.     (At/is.) 


IS 


seen  through  it  (Morris).     Fig.  391  represents  this  diagrammatically.      In  addition, 

the  greater  elevation  and  thickness  of  the  upper  and  outer  rim  of  the  acetabulum, 

and  the  pressure  against  the  trochanter  exerted  by  the  ilio-tibial  band  of  the  fascia 

lata  (Allis)  in  adduction  of  the  thigh  (which  means  an  outward  movement  of  the 

upper  extremity  of  the  femur),  should 

be  mentioned  among  the  factors  that 

resist   displacement.      The    ligamen- 

tum    teres   is  of    little  value,    as    its 

bony  attachment  to  the  femoral  head 

is    easily    separated  by  a    force  less 

than    that   required    to  rupture    the 

ligament. 

A  line  drawn  from  the  anterior 
spine  to  the  tuber  ischii  will  approxi- 
mately bisect  the  acetabulum  and 
will  divide  each  half  of  the  pelvis 
into  two  planes,  the  pubo-ischiatic, 
inner  or  anterior,  and  the  ilio-ischi- 
atic,  outer  or  posterior  (Fig.  392). 
When  the  head  of  the  femur  escapes 
from  the  acetabulum  it  must  lie  on 
the  surface  of  one  or  other  of  these 
planes.  All  dislocations  are,  there- 
fore, either  (i)  outward — i.e. ,  pos- 
terior— or  (2)  inward — i.e.,  anterior. 

i.  Outward  or  Posterior  Luxations. — Traumatisms  in  which  the  force 
expended  upon  the  region  of 'the  hip  result,  as  a  rule,  in  children  in  epiphyseal  sep- 
aration (page  361),  in  old  persons  in  fracture  of  the  neck  of  the  femur  (page  363). 
In  173  cases  of  dislocation  of  the  hip,  138  were  between  fifteen  and  forty-five  years 
of  age. 

In  practically  all  positions  of  the  hip  in  which  luxation  is  probable  the  force 
acts  through  some  form  of  leverage  which  brings  the  short  arm  of  the  lever — always 

the  head  and  neck  of  the  femur — 
against  a  weak  portion  of  the  cap- 
sule. If  it  does  this  with  the  aid  of 
a  bony  fulcrum,  the  power  is  ex- 
erted to  the  greatest  possible  ad- 
vantage. Thus,  in  hyperextension 
of  the  thigh,  the  acetabular  rim  acts 
as  a  fulcrum,  but  the  head  of  the 
bone  is  brought  against  the  anterior 
part  of  the  capsule, — the  ilio-femoral 
ligament, — which  is  usually  stronger 
than  the  bone  itself.  Hyperflexion 
is  arrested  by  the  contact  of  the 
soft  parts  of  the  front  of  the  thigh 
with  the  abdomen  ;  hyperadduetion 
by  the  contact  of  the  shaft  with  the 
pubes.  Hyperabduction,  however, 
brings  the  greater  trochanter  against 
the  prominent  outer  lip  of  the  ace- 
tabulum, while  the  head  is  carried 
downward  against  the  thin  inner 
and  lower  part  of  the  capsule  ;  the 
ilio-femoral  and  ischio-femoral  liga- 
ments are  relaxed,  and  the  weak  pubo-femoral  ligament  offers  but  little  resistance  ; 
the  head,  being  opposite  the  shallowest  part  of  the  acetabulum,  projects  half  its 
bulk  out  of  that  cavity  ;  the  weight — i.e.,  the  resistance  of  the  capsule — is  very 
close  to  the  fulcrum,  greatly  increasing  the  power  of  the  leverage. 


FIG.  392. 


Superior  spine 


Diagram  showing  dividing  line  (A",   )")  between  outer  and  inner 
pelvic  planes.     (A/Us.) 


376 


HUMAN   ANATOMY. 


The  ilio-femoral  ligament  may,  in  cases  in  which  the  thigh  is  adducted  and 
rotated  inward  at  the  time  of  application  of  the  force,  take  the  place  of  the  acetabu- 
lar  rim  as  a  fulcrum.  In  that  position  it  is  wound  round  the  neck  of  the  femur,  and 

FIG.  393. 


Luxation  of  the  head  of  the  femur  onto  the  dorsum  of  the  ilium. 


when  the  flexed  leg  is  used  as  a  crank  the  head  may  be  made  to  burst  through  the 
lower  and  posterior  part  of  the  capsule. 

Allis '  has  shown  that  these  conditions,  easily  demonstrated  experimentally,  are 
reproduced  in  many  forms  of  accident.      It  is  obvious  that  they  are  all  favorable  to 
a  downward  dislocation,  and  this,  as  is  the  case  with  the  humeral  head,  is  the  direc- 
tion  primarily  taken    in    the 

FIG.  394.  vast  majorit;y  of   these  luxa- 

tions. If  the  thigh  has  been 
rotated  inward,  either  in  ad- 
duction or  abduction,  the 
head  of  the  bone  will  pass 
outward  and  backward  and 
rest  behind  the  acetabulum 
on  some  part  of  the  outer  or 
posterior  plane  of  the  pelvis. 
If  it  lies  upon  the  ilium,  a 
little  above  the  acetabulum, 
it  constitutes  the  ' '  iliac' '  dis- 
location,— "above  the  obtu- 
rator tendon  ;"  if  upon  the 
ischium,  on  a  level  with  or 
a  little  below  the  acetabulum, 
it  is  the  "  ischiatic"  or  "sci- 
atic" dislocation,  —  "  below 
the  obturator  tendon.' 
obturator  internus 
sometimes  interposes  an 
stacle  to  the  upward 
of  the  head,  but  its  impor- 
tance in  this  respect  has  been  exaggerated.  The  degree  of  flexion  of  the  limb  at 
the  time  of  the  accident  is  more  likely  to  determine  the  level  at  which  the  head  rests. 

1  Reduction  of  Dislocations  of  the  Hip,  Philadelphia,  1896. 


Relation  of  the  head  of  the  femur  to  the  innominate  bone  in  dorsal  luxa- 


This 
tendon 
ob- 


PRACTICAL   CONSIDERATIONS:    THE   HIP-JOINT.  377 

In  both  positions  the  ilio-femoral  ligament,  which  is  almost  invariably  intact, 
has  now  become  the  fulcrum.  As  the  short  arm  of  the  lever — the  head  and  neck — 
has  moved  outward,  the  long  arm — the  shaft  of  the  femur — must  move  inward  ;  hence 
adduction  is  present  in  all  cases  of  outward  luxation  in  which  the  Y-ligament  is  not 
lacerated,  and  is  persistent  because  the  head  lying  in  contact  with  the  outer  wall  of 
the  pelvis  cannot  be  moved  inward.  Rotation  inward,  which  is  also  present  and 
persistent,  is  due  to  the  same  tension  upon  the  Y-ligament.  This  explains  the 
usual  position  of  the  limb  with  the  line  of  the  femur  crossing  that  of  the  opposite 
thigh  a  little  above  the  knee  and  the 

great  toe  resting    upon   the  instep  of  FIG.  395. 

the  sound  foot.  Flexion  of  the  thigh 
is  maintained  partly  by  the  tension  on 
the  ilio-psoas. 

The  muscles  have  a  very  minor 
part  in  the  production  or  maintenance 
of  the  characteristic  deformity.  The 
external  rotators,  the  glutei  and  the 
pectineus,  are  often  lacerated.  There 
is  shortening,  and  the  trochanter  is 
above  the  level  of  Nelaton's  line. 

In  the  rare  cases  in  which  the  Y- 
ligament — or  its  outer  limb — is  torn, 
outward  luxation  with  neither  adduc- 
tion nor  inversion  becomes  possible. 

2 .  Inward  or  Anterior  L  uxations. 
—These  always  occur  with  the  thigh 
in  abduction,  and  are  favored  by  out- 
ward rotation,  which  carries  the  head 
towards  the  lower  anterior  part  of  the 
capsule.  If  it  passes  upward  and  rests 
on  the  body  of  the  pubis,  it  constitutes 
the  "pubic"  luxation  (Figs.  395, 
396)  ;  if  downward,  it  is  in  or  opposite 
the  thyroid  foramen,  and  is  often  called 
an  ' '  obturator' '  or  "  thyroid' '  luxa- 
tion (Figs.  397,  398).  The  ilio-femoral 
ligament  again  becomes  the  fulcrum  ; 
the  short  arm  of  the  lever  has  been 
carried  inward,  necessitating  a  corre- 
sponding outward  movement  of  the 
long  arm  ;  hence  abduction  is  present. 
The  exaggerated  rotation  outward  is 
maintained  by  the  tension  of  the  liga- 
ment ;  hence  the  eversion  of  the  limb. 
Neither  abduction  nor  eversion  can  be 
overcome,  because  the  head  is  held 
firmly  against  the  pubo-ischiatic  pelvic 
plane.  The  gracilis,  pectineus,  and  ad- 

dllCtOrS  are  apt  tO  be  torn  J  the  Stretch-  Luxation  of  the  head  of  the  femur  onto  the  pubis. 

ing  of  the  ilio-psoas,  the  glutei,  and  the 

muscles  inserted  into  the  greater  trochanter  aids  in  maintaining  both  the  flexion  and 
the  eversion.  The  ilio-tibial  band  of  fascia  will  be  found  relaxed  ;  the  trochanteric 
prominence  disappears  as  the  trochanter  approaches  the  mid-line  and  is  in  a  measure 
sunk  in  the  socket.  There  will  be  shortening  on  measurement  from  the  anterior 
superior  spine  to  the  condyle  ;  the  head  of  the  femur  will  be  unduly  prominent  in 
the  pubic  variety. 

With  the  patient  in  dorsal  decubitus,  it  will  be  evident  that  the  acetabula  are 
situated  on  a  horizontal  plane  about  midway  between  the  pubes  and  the  sacrum. 
From  this  level  the  pelvis  slopes  upward  to  the  symphysis  and  downward  to  the 


378 


HUMAN    ANATOMY. 


FIG. 


sacro-iliac  junction.      It  is  obvious  that  no  anterior  dislocation  can  be  below  the  bi- 
acetabular  line  and  no  posterior  dislocation  can  be  above  it. 

As  the  femur  is  about  equal  in  length  to  the  tibia  and  tarsus,  if  the  head  is  in 
the  socket  the  foot  will  be  on  the  acetabular  level  when  the  thigh  is  vertical  and  the 
knee  flexed.  If  the  head  is  dislocated  anteriorly,  the  foot  will  be  on  a  higher 
level  ;  if  posteriorly,  the  foot  will  be  lower,  and  may  even  touch  the  surface  on 
which  the  patient  lies.  There  will  be  corresponding  changes  in  the  level  of  the 
knees  (Allis). 

The  femoral  vessels  are  not  often  injured  in  hip  luxations,  because  they  lie 
above  the  joint  and  luxations  are  always  primarily  downward  ;  and  because,  as  the 
head  approaches  them  in  the  inward  variety  only,  and  as  for  the  production  of  that 
variety  abduction  is  necessary,  the  muscles  beneath  them — the  pectineus  and  ilio- 
psoas — are  put  upon  the  stretch  and  the  vessels  are  lifted  out  of  harm's  way. 

The  relations  of  the  sciatic  nerve  to  these  injuries  are  of  great  importance.  The 
nerve  is  in  close  relation  to  the  hamstring  muscles,  especially  to  the  biceps.  These 

structures  are  made  tense 
and  are  stretched  across 
the  neck  of  the  femur  pos- 
teriorly by  flexion  of  the 
thigh  on  the  pelvis,  espe- 
cially if  the  leg  is  also 
extended  on  the  thigh,  so 
that  the  origin  and  inser- 
tion of  the  hamstring  mus- 
cles are  separated.  If,  in 
a  dislocation,  the  head  of 
the  femur  originally  lies  on 
the  anterior  plane  of  the 
pelvis,  and  either  by  the 
force  producing  the  dis- 
placement (as  is  commonly 
the  case),  by  the  action  of 
muscles,  or  during  efforts 
at  reduction  is  made  to  pass 
to  the  posterior  plane,  it 
must  traverse  the  narrow 
space  between  the  sciatic 
nerve  and  hamstrings  and 
the  edge  of  the  acetabu- 
lum.  The  nerve  is  thus 
very  apt  to  be  bruised  and 
stretched  and  separated 
somewhat  from  the  biceps 
tendon.  Later,  if  replace- 
ment by  "  circumduction"  is  attempted,  the  head  may  pass  beneath  the  nerve, 
which  will  then  be  tightly  stretched  over  the  front  of  the  neck,  will  prevent  full 
extension  of  the  thigh,  and  will  cause  continued  pain  and  disability.  Other  com- 
plications associated  with  the  nerve  may  occur,  and  have  been  fully  demonstrated 
by  Allis,  whose  excellent  experimental  and  clinical  work  forms  the  basis  for  the  fore- 
going summary  of  the  anatomy  of  hip  luxations. 

In  reduction  of  posterior  dislocations  by  the  method  of  circumduction  the 
thigh,  which  is  already  flexed,  adducted,  and  inverted  by  the  agencies  above 
described,  is  still  furtheryfetrd' and  adducted  and  lifted  upward  to  relax  the  ilio-psoas 
and  to  bring  the  head  of  the  bone  near  the  margin  of  the  acetabulum  ;  it  is  then 
abducted,  tightening  the  inner  band  of  the  ligament,  and  crcrtcd,  tightening  the  outer 
band  and  converting  the  femoral  attachment  of  the  whole  ligament  (  but  chiefly  of 
its  outer  limb)  into  a  fulcrum  around  which,  as  a  centre, — the  abduction  and  eversion 
being  continued  into  circumduction, — the  head  of  the  bone  sweeps,  skirting  the 
lower  edge  of  the  acetalniliun,  and  finally,  by  extension  of  the  thigh,  re-entering 


Relation  of  the  head  of  the  femur  to  the  innominate  bone  in  pubic  luxation. 


PRACTICAL   CONSIDERATIONS:   THE   HIP-JOINT. 


379 


that  cavity  at  the  point  where  it  emerged.  The  whole  movement  is  made  up  of  the 
successive  steps  of  flexion,  adduction,  abduction,  eversion,  and  extension. 

In  reduction  of  anterior  dislocations  some  of  the  steps  of  the  procedure  are 
reversed, — i.e.,  the  movement  consists  of  flexion,  abduction,  adduction,  inversion, 
and  extension,  in  the  order  mentioned.  The  inner  limb  of  the  ligament  is  then  of 
chief  importance  as  a  fulcrum.  The  objection  to  this  method  in  both  cases  is  the 
danger  to  the  sciatic  nerve,  already  pointed  out,  and  also  to  the  femoral  vessels. 

Allis's  methods  of  reduction  are  intended  to  avoid  this  danger.  He  endeavors 
to  cause  the  head  to  retrace  accurately  the  path  by  which  it  left  the  socket.  In  a 
posterior  dislocation  the 

head  has  usually  left  the  FIG.  397. 

acetabulum  in  a  down- 
ward direction,  has  fallen 
below  the  socket,  and  has 
passed  outward  around 
the  edge  of  the  acetabu- 
lum to  its  new  position  ; 
the  limb  has  then  fallen 
into  partial  extension  by 
its  own  weight.  Thus 
there  are  three  steps, 
which,  naming  them  in 
their  reverse  order,  are  : 
3,  extension  ;  2,  motion 
outward  ;  i,  motion 
downward.  The  steps 
of  his  method  are  accord- 
ingly :  i,  flexion  ;  2,  ro- 
tation of  the  head  inward 
(by  carrying  the  leg 
out),  placing  it  where  it 
was  immediately  after 
leaving  the  acetabulum  ; 
3,  lifting — to  bring  the 
head  to  the  level  of  the 
socket  —  and  extension 
(using  the  ilio-femoral 
ligament,  which  then  be- 
comes tense,  as  a  ful- 
crum, and  aided  by  the 
upward  pressure  of  the 
thumbs  of  an  assistant), 
carrying  the  head  up- 
ward into  the  socket. 

In  the  reduction  of 
anterior  dislocations  the 
anatomical  and  mechani- 
cal principles  involved 
are  the  same.  In  those 
dislocations  the  head  has 
left  the  socket  by  tearing 

the  capsule  on  its  inner  margin,  and  has  passed  inward  to  the  pubo-ischiatic  plane  ; 
the  limb  representing  the  other  end  of  an  inflexible  lever  must  move  in  the  opposite 
direction,  or  outward  ;  and  as  it  falls  a  little  downward  by  its  own  weight,  the  head 
rises  slightly.  To  restore  it,  reversing  these  steps,  flex  to  a  perpendicular,  lowering 
the  head  somewhat  ;  make  traction  on  the  limb,  drawing  the  head  outward  ;  and 
then,  the  head  being  fixed  by  the  hands  of  an  assistant,  adduct  and  extend  the  thigh, 
causing  the  head  to  enter  the  socket. 

By  these  methods  reduction  of  dislocation  complicated  with  fracture   of    the 


Luxation  of  the  head  of  the  femur  into  the  obturator  foramen. 


380 


HUMAN    ANATOMY. 


FIG.  398. 


femur  becomes  possible  because  of  the  firm  connection  between  (a)  the  base  of  the 
neck  and  the  acetabulum  through  the  unruptured  portion  of  the  capsule,  and  (6) 
the  two  fragments  through  the  attachment  of  muscles  along  the  linea  aspera. 
These  connections  enable  the  limb  to  be  used  for  traction,  although  the  fracture 
quite  precludes  the  employment  of  circumduction  and  rotation. 

Allis  summarizes  the  principles  of  his  method  by  saying  that  the  cardinal  rule 
applicable  to  every  form  of  dislocation  of  the  hip  is  :  draw  the  head  in  the  direction  of 
the  socket ;  apply  a  fulcrum  at  the  upper  part  of  the  lever  ;  pry  the  head  into  the 
socket. 

The  old  view  that  the  opening  in  the  capsule  was  often  a  slit  which  required 
enlargement  before  the  head  could  be  replaced  has  been  shown  (Allis  and  Morris) 
to  be  fallacious.  The  inelastic  character  of  the  capsular  fibres,  the  globular  shape 
of  the  femoral  head,  and  the  suddenness  of  application  of  the  force  (preventing 

stretching)  make  the  rent  in  every 
case  as  large  as  the  head  ;  it  is  not 
infrequently  larger.  If,  however,  it  is 
situated  near  the  femoral  attachment 
of  the  capsule,  it  may  leave  a  cuff  of 
the  latter  hanging  from  its  pelvic  ori- 
gin over  the  acetabulum,  and  offering 
a  serious,  if  not  insuperable,  obstacle 
to  reduction. 

Congenital  dislocation  of  the  hip 
may  be  unilateral  or  bilateral,  and 
while  occasionally  the  result  of  intra- 
uterine  traumatism,  is  usually  due  to 
an  arrest  of  development  of  the  ace- 
tabulum. The  head  rests  on  the  dor- 
sum  ilii,  either  directly  upon  the  bone 
or  on  the  gluteus  minimus.  The  cap- 
sule is  stretched  and  thickened  to  bear 
the  weight  of  the  trunk.  The  tro- 
chanters  can  be  seen  through  the 
glutei  ;  they  are  above  N61aton's  line  ; 
there  is  usually  lumbar  lordosis  to 
compensate  for  the  displacement  pos- 
teriorly of  the  centre  of  gravity.  The 
perineum  is  widened. 

Disease  of  the  hip-joint  is  fre- 
quent and  grave.  It  may  begin  in 
the  epiphysis  for  the  head,  in  the 
synovial  membrane,  or,  much  more 
rarely,  in  the  articular  cartilage.  It 
may  be  of  any  variety,  but  tuberculous  disease  outnumbers  all  others. 

Both  the  frequency  and  the  gravity  of  disease  of  the  hip-joint  are  due  to  :  i, 
the  exceptional  exposure  of  the  joint  to  strains  or  traumatism  on  account  of  its  im- 
portance in  carrying  the  weight  of  the  trunk  and  in  progression  ;  2,  the  intra- 
capsular  situation  of  the  upper  femoral  epiphysis  ;  3,  the  relation  of  the  joint  to 
some  of  the  most  powerful  muscles  of  the  body,  so  that  great  intra-articular  pressure- 
is  easily  set  up  and  with  difficulty  overcome  ;  4,  its  enclosure  by  dense,  unyielding 
fibrous  structures  that  increase  tension  after  disease  has  begun  ;  5,  the  thinness  of 
the  non-articular  plate  of  bone  that  separates  it  from  the  pelvis,  and  the  presence 
up  to  puberty  of  the  Y-shaped  cartilage  which  divides  the  acetabulum  into  three 
bony  segments  (Fig.  353)  ;  6,  its  deep  situation,  rendering  the  early  symptoms  in 
many  cases  inconspicuous  ;  7,  the  deprivation  of  fresh  air  and  exercise,  and  often 
of  sunlight,  involved  in  the  immobilization  of  the  joint. 

The  disease  is  attended  by  certain  symptoms  having  a  definite  anatomical  basis  : 
i.  Swelling,  which  is  most  easily  demonstrated  (a)  at  the  lower  anterior  portion  of 
the  joint  just  internal  to  the  ilio-femoral  ligament,  where  the  capsule  is  thin  and  the 


Relation  of  the  head  of  the  femur  to  the  innominate  bone  in 
obturator  luxation. 


PRACTICAL   CONSIDERATIONS:   THE   HIP-JOINT.  381 

joint  is  nearest  the  surface  ;  and  (<£)  at  the  lower  posterior  part  of  the  capsule,  which 
is  also  thin.  2.  Tenderness  over  these  points, — i.e. ,  beneath  the  middle  of  Pou- 
part's  ligament  and  behind  the  trochanter.  3.  Alteration  in  position,  the  femur  being 
flexed,  abducted,  and  everted.  This  puts  the  joint  in  the  position  of  greatest 
comfort,  which  is  that  of  its  greatest  capacity.  In  extension  the  head  of  the  bone 
presses  against  the  upper  anterior  portion  of  the  capsule,  and  the  Y-ligament  is 
drawn  as  a  dense  band  across  the  front  of  the  joint.  Flexion  relaxes  the  superior 
or  main  portion  of  the  Y-ligament  and  the  ilio-psoas  muscle  ;  abduction,  the  outer 
limb  of  the  ligament  and  the  ilio-tibial  band  of  fascia  lata  ;  eversion,  the  inner 
limb.  Flexion  is,  in  its  effect  on  tension,  the  most  effective  of  these  motions  ; 
eversion  the  least.  The  joint  will  now  hold  a  larger  quantity  of  fluid  than  when  the 
limb  is  in  extension.  4.  At  this  stage,  to  bring  the  limb  parallel  with  its  fellow,  to 
overcome  the  shortening  caused  by  abduction,  and  to  relieve  strain,  as  the  thigh 
cannot  be  moved  on  the  pelvis,  the  lumbar  spine  is  curved  with  the  convexity 
towards  the  diseased  side  and  the  pelvis  is  tilted  downward  on  that  side.  This  is 
the  stage  of  apparent  lengthening.  The  real  position  of  the  limb  in  abduction  is 
shown  by  straightening  the  pelvis  so  that  a  line  drawn  between  the  two  anterior 
superior  spines  is  at  right  angles  to  the  longitudinal  mid-line  of  the  body.  5.  With 
the  same  object  of  securing  parallelism, — i.e.,  of  reducing  strain  upon  the  mus- 
cular and  fibrous  structures  which  are  holding  the  limb  in  its  abnormal  position, 
— the  deformity  caused  by  flexion  (maintained  by  the  ilio-psoas,  which  is  in 
such  close  relation  to  the  front  of  the  capsule)  is  met  by  an  arching  forward — 
lordosis — of  the  lumbar  spine.  The  real  position  of  the  limb  in  flexion  is  shown 
by  raising  the  thigh  of  the  affected  side  until  the  lumbar  curve  is  effaced  and  the 
lumbar  spines  touch  the  surface  on  which  the  patient  lies.  6.  Pain  in  the  knee  is 
often  marked.  It  is  due  to  the  association  of  the  nerve-supply  to  the  two  joints, 
both  being  innervated  from  the  same  spinal  segments,  as  they  both  receive  twigs 
from  the  anterior  crural,  obturator,  sciatic,  and  sacral  plexus.  7.  Rigidity  of  the 
joint  is  due  to  fixation  by  (a)  the  muscles  inserted  into  and  passing  over  the  cap- 
sule ;  (£)  all  the  muscles  moving  the  lower  limb  on  the  pelvis.  Rotation  is  the 
most  valuable  movement  for  diagnostic  purposes  because  it  is  least  likely  to  be 
interfered  with  by  extra-articular  disease.  For  example,  in  abscess  beneath  the 
gluteus,  or  in  enlargement  of  the  subgluteal  bursa,  flexion  of  the  thigh  is  interfered 
with  ;  in  psoas  or  iliac  abscess  extension  is  limited  ;  in  superficial  disease  of  the 
upper  end  of  the  shaft,  or  in  suppuration  of  the  bursa  over  the  trochanter,  adhe- 
sions of  the  soft  parts  may  limit  both  flexion  and  extension.  8.  Muscular  wasting 
is  often  a  very  early  symptom,  and  is  then  due  to  reflex  atrophy  from  the  associa- 
tion— emphasized  long  ago  by  Hilton — of  the  nerves  supplying  a  joint  with  those  of 
the  muscles  moving  that  joint  ;  in  this  instance  both  joint  and  muscles  are  supplied 
by  the  anterior  crural,  the  sciatic,  the  sacral  plexus,  the  obturator,  etc.  Later, 
atrophy  of  muscles  may  be  due  to  disuse.  The  glutei  and  the  thigh  muscles  are 
those  most  obviously  affected.  The  atrophy  of  the  former  aids  in  producing  the 
characteristic  obliteration  of  the  gluteo-femoral  crease.  9.  After  softening  of  the 
capsule  and  diminution  of  tension  have  occurred,  the  adductors  draw  the  limb 
inward.  The  lumbar  spine  is  now  curved  so  that  the  concavity  is  towards  the 
diseased  side,  thereby  drawing  up  the  pelvis  on  that  side  so  as  to  relieve  strain  and 
secure  parallelism  of  the  limb.  This  is  the  stage  of  apparent  shortening.  The 
real  position  of  the  limb  in  adduction  is  shown  by  bringing  the  interspinous  line  to 
a  right  angle  with  the  longitudinal  axis  of  the  body.  The  adductors  are  supplied 
almost  exclusively  by  the  obturator  nerve,  which  enters  largely  into  the  supply  of 
the  articulation,  and  act  to  great  advantage  when  the  capsular  and  ligamentous 
resistance  has  partly  disappeared.  As  the  shaft  and  lower  end  of  the  femur  move 
inward,  the  head  is  necessarily  brought  more  forcibly  against  the  outer  fibres  of  the 
capsule  near  its  pelvic  attachment,  and  when  they  soften  is  partially  projected  from 
the  acetabulum,  against  the  upper  and  outer  rim  of  which  it  rests.  10.  During 
this  stage  the  trochanter  on  the  diseased  side  is  often  found  to  be  nearer  the  middle 
line  of  the  body  than  the  other  trochanter.  The  cause  of  this  is  either  absorption 
of  the  head  and  neck  of  the  femur  or  deepening  of  the  acetabulum  with  sinking 
in  of  the  head,  and  the  diagnosis  between  these  may  be  made  by  rectal  examina- 


382  HUMAN    ANATOMY. 

tion,  which  sometimes  shows  thickening  over  the  inner  surface  of  the  acetabulum  in 
the  latter  case  and  not  in  the  former  (Cheyne).  In  dislocation  from  disease,  unless 
there  has  been  separation  of  the  head  or  great  absorption  of  the  neck,  the  tro- 
chanter  will  be  farther  away  from  the  middle  line  on  the  affected  side  than  on  the 
sound  one.  This  will  serve  to  distinguish  shortening  of  the  limb  due  to  this  cause 
from  shortening  due  to  acetabular  deepening.  Abscesses  developing  within  the 
joint  may  pass  outward  through  the  thin  posterior  part  of  the  capsule,  and  under 
the  gluteal  muscles,  to  a  point  beneath  the  greater  trochanter ;  they  may  make  their 
exit  through  the  cotyloid  notch  and  point  in  Scarpa's  triangle  ;  they  frequently 
pass  out  anteriorly,  and  are  found  beneath  the  tensor  vaginae  femoris  at  the  outer 
aspect  of  the  thigh  ;  they  may  perforate  the  acetabulum  and  point  within  the 
pelvis.  A  finger  in  the  rectum  may  then  detect  fluctuation  through  the  structures 
that  separate  the  abscess  from  the  rectal  wall, — viz. ,  the  anal  fascia,  the  levator  ani,  the 
obturator  fascia  and  obturator  internus,  and  the  periosteum  of  the  inner  surface  of 
the  innominate  bone.  After  perforation  of  the  acetabulum,  an  abscess  may  extend 
upward  and  point  above  Poupart's  ligament  on  the  inner  side  of  the  vessels. 

Excision  of  the  hip  may  be  done  either  by  means  of  an  anterior  incision 
passing  between  the  tensor  vaginae  and  sartorius  muscles  superficially  and  the 
glutei  and  rectus  more  deeply,  or  by  a  posterior  incision  in  the  line  of  the  limb 
and  just  back  of  the  greater  trochanter,  the  muscles  attached  to  which  being  divided 
as  close  to  the  bone  as  possible. 

THE   FRAMEWORK   OF   THE   LEG. 

This  is  formed  by  the  tibia  and  the  fibula  and  the  intero^seous  membrane  (Fig. 
411).  The  bones  are  so  closely  united  as  to  constitute  one  apparatus,  but  as  they 
are  separable  it  is  necessary  to  describe  them  apart.  The  tibia,  very  much  the  larger, 
is  the  only  one  concerned  in  forming  the  knee-joint,  and  bears  almost  the  whole 
weight.  It  forms  the  upper  and  inner  side  of  the  mortise  known  as  the  ankle-joint. 
The  fibula,  placed  externally  and  posteriorly,  is  a  slender  bone.  The  upper  end  has 
a  true  joint  with  the  tibia,  the  lower  is  more  closely  fastened  to  it.  The  interosseous 
membrane  is  at  the  bottom  of  a  hollow  between  the  bones.  The  arrangement  favors 
lightness,  as  it  gives  increased  size  for  the  origin  of  muscles.  The  joints  of  the 
fibula,  as  well  as  its  elasticity,  serve  to  break  shocks. 

THE   TIBIA. 

The  tibia  consists  of  a  shaft,  an  upper  and  a  lower  extremity. 

The  upper  extremity,  or  head,  composed  of  an  outer  and  an  inner  tubcrosity, 
is  very  large,  expanding  laterally  from  the  shaft.  The  outline  of  the  upper  surface 
is  transversely  oval,  the  inner  end  being  the  broader.  It  is  chiefly  occupied  l>y  two 
articular  surfaces  for  the  condyles  of  the  femur,  separated  at  the  middle  by  a  promi- 
nence, the  spine,1  with  a  triangular  non-articular  surface  before  and  behind  it.  The 
former  of  these  is  rough,  the  latter  smooth  and  grooved.  The  spine  itself  is  com- 
posed of  two  lateral  parts  connected  behind,  of  which  the  inner  is  the  longer  from 
before  backward,  rising  from  the  condylar  surfaces.  The  crucial  ligaments  of  the 
knee-joint  are  attached  to  the  non-articular  surfaces  before  and  behind  it.  The 
inner  condylar  facet  is  concave  ;  it  has  an  oval  outline  and  is  longer  from  before 
backward  than  transversely.  It  rises  as  a  ridge  on  the  side  of  the  spine.  The  outer 
facet  is  more  nearly  circular,  being  shorter  than  the  inner.  It  is  slightly  depressed 
in  the  middle.  The  posterior  half  is  usually  a  little  convex  from  before  backward, 
and  is  often  prolonged  onto  the  posterior  surface  of  the  bone.  The  convexity  is 
much  greater  when  the  semilunar  cartilage  is  intact.  The  front  half  may  be  plane, 
convex,  or  concave  in  the  same  direction.  This  facet  rises  to  a  point  on  the  outer 
side  of  the  spine.  The  tuberosities2  overhang  the  back  of  the  tibia.  They  are 
separated  behind  by  the  popliteal  notch*  continuous  with  the  groove  from  the  top. 
Under  the  back  of  the  outer  tuberosity  is  a  small  articular  facet  for  the  head  of  the 
fibula,  looking  downward  and  a  little  backward  and  outward.  Its  outline  is  uncer- 
tain, being  either  round  or  quadrilateral.  It  may  be  curved  in  any  direction,  and 

1  Eminentia  iutercondyloidcu.     -Comlylus   hitcialis  i-l    nu-ili.ilis.     "  Fnss;i   intvroiimlyloiilcii  imstrrior. 


THE  TIBIA.  383 

its  inclination  varies  much.  In  some  cases  it  nearly  or  quite  reaches  the  superior 
articular  surface.  Laterally,  this  tuberosity  is  rough  for  the  ligaments  of  the  knee- 
joint.  The  same  may  be  said  of  the  side  of  the  inner  tuberosity,  which  towards  the 
back  has  a  broad  horizontal  groove  running  along  it  for  the  tendon  of  the  semi- 
membranosus.  The  tubercle1  of  the  tibia  is  a  triangular  prominence  on  the  front  of 
the  upper  end.  Its  lower  part  is  rough  for  the  tendon  of  the  extensor  quadriceps, 
and  its  upper  smooth  for  a  bursa  between  this  tendon  and  the  bone.  The  top  of 
the  tubercle  is  about  an  inch  below  the  top  of  the  bone  ;  it  is  lost  below  in  the  ridge 
of  the  front  of  the  shaft. 

The  shaft 2  has  three  borders  and  three  surfaces.  The  anterior  border,  the  crest 3 
begins  at  the  outer  side  of  the  tubercle,  curves  as  it  descends,  at  first  a  little  inward, 
then  a  little  the  other  way  through  the  middle  of  the  shaft,  where  it  is  very  sharp, 
and,  finally,  at  the  lower  third,  becoming  much  less  prominent,  it  sweeps  to  the 
front  of  the  inner  malleohis.  The  inner  border,  the  least  marked  of  the  three,  begins 
under  the  inner  tuberosity  near  the  back  and  goes  to  the  back  of  the  inner  malleohis. 
It  is  most  distinct  in  the  middle.  The  older  border,  or  interosscous  ridge,*  begins  below 
the  facet  for  the  head  of  the  fibula,  runs  downward  and  somewhat  backward  past  the 
middle  of  the  shaft,  and  then,  inclining  forward,  divides  some  two  or  three  inches 
above  the  lower  end  into  two  lines  enclosing  a  space  on  the  outer  side  of  the  lower 
end,  to  which  the  fibula  is  bound  by  ligaments.  The  anterior  of  these  divisions  is 
the  more  evident  continuation  of  the  ridge.  The  internal  surface  is  subcutaneous  : 
generally  convex  above  and  concave  below  ;  the  outer,  bounded  behind  by  the  in- 
terosseous  ridge,  is  at  first  external,  but  in  the  lower  third  twists  to  the  front.  The 
Posterior,  in  its  upper  and  lower  parts,  faces  also  somewhat  outward.  It  is  crossed 
in  the  upper  third  by  the  oblique  linef  which,  running  downward  and  inward  from 
the  back  of  the  fibular  facet  to  the  inner  border,  marks  off  a  triangular  space  above 
it  which  is  occupied  by  the  popliteus  muscle.  A  vertical  line,  generally  very  faint, 
running  down  for  some  distance  from  the  oblique  line  partially  divides  this  sur- 
face into  an  inner  broader  and  an  outer  narrower  part :  the  former  for  the  flexor  of 
the  toes,  the  latter  for  the  tibialis  posticus.  The  nutrient  foramen,  the  largest 
in  the  body,  is  on  this  surface  at  the  junction  of  the  first  and  second  thirds  external 
to  the  oblique  line  ;  it  runs  down  into  the  bone.  The  shaft  is  triangular  on  section  in 
the  upper  and  middle  thirds,  being  narrower  and  sharper  in  front  in  the  middle  one. 
In  the  lower  third  the  section  becomes  quadrilateral  as  the  shaft  broadens  and  the 
anterior  border  sinks  and  turns  inward. 

The  lower  extremity  is  thickest  transversely.  The  internal  matteolus*  is  a 
thick  projection  downward  and  inward  from  the  whole  of  the  inner  side,  to  form 
one  boundary  of  the  ankle.  Its  lower  end  is  thick,  reaching  farthest  down  in  front, 
with  a  depression  at  the  back  for  the  lateral  ligament  of  the  ankle.  The  surface 
looking  towards  the  joint  is  articular  ;  it  slants  a  little  away  from  the  median  line  of 
the  bone.  The  outer  side  of  the  lower  end  of  the  shaft  is  slightly  concave,  with  a 
tubercle  both  before  and  behind.  The  articular  cartilage  of  the  lower  end  is  pro- 
longed some  two  or  three  millimetres  onto  this  outer  side.  Both  in  front  and  behind, 
but  especially  in  front,  the  bone  presents  a  swelling,  separated  by  a  depression  from 
the  lower  border,  above  which  the  capsule  is  inserted.  On  the  posterior  surface  a 
broad  groove  for  the  tendons  of  the  tibialis  posticus  and  the  flexor  longus  digitorum 
runs  obliquely  downward  and  inward  onto  and  along  the  hind  border  of  the  mal- 
leolus.  A  faint  groove  for  the  flexor  longus  hallucis  is  sometimes  seen  near  the 
outer  end  of  the  posterior  surface.  The  lower  side  forms  the  top  of  the  ankle- 
joint  and  is  wholly  articular.  It  is  broader  before  than  behind,  as  the  sides  converge 
towards  the  back.  It  is  concave  from  before  backward.  There  is  a  slight  antero- 
posterior  elevation  in  the  middle,  fitting  into  a  depression  on  the  top  of  the  as- 
tragalus. 

Variations. — The  transverse  axes  of  the  knee-  and  ankle-joints  are  rarely 
parallel.  The  shaft  of  the  tibia  is  so  twisted  as  to  make  the  foot  point  outward. 
The  angle  between  the  two  axes  varies  from  o  to  48°,  but  is  usually  between  5°  and 
20°.  The  backward  inclination  of  the  top  of  the  tibia  varies  considerably.  When 
excessive,  it  seems  to  imply  an  aptitude  for  the  squatting  position,  as  among  the 
natives  of  India,  but  no  inability  to  assume  the  upright  position.  A  continuation 

1  Tuberositas  tibiae.     "  Corpus  tibiae.     3Crista  anterior.     4  Crista  interossea.     •' Linea  poplitea.     '' Malleolus  medialis. 


HUMAN   ANATOMY. 


FIG.  399. 

Spine 
Ext.  condylar  surface    ,-»    ._    Int.  condylar  surface 


Tubercle- 


Bursal  surface 


For  ligamentum- 
patellas 


'„    1 


Biceps 

Ext.  long.- 
digitorum 


Tibialis  anticust 


)  Internal 
surface 
(subcuta- 
neous) 


Tendon  patella 
(extensor 

quadriceps) 
-Gracilis 


-Senritendinosus 


Anterior  border- 
or  crest 


-Internal  border 


External  or  inter-  - 
osseous  border 


For  MtncmhuInternaJ  malleolus 
Riglit  tibia  from  before.    Tlie  outline  figure  shows  the  areas  of  muscular  attachment. 


THE  TIBIA. 


385 


FIG.  400. 

Int.  condylar  surface 


Spine 


Internal  tuberosity 
Groove  for  seminiembranosus 


Semimembranosus- 


Popliteus 


Soleus  (tibial  head) — \ 
Flex. long,  digitorum 


Soleus 
(tibial  head) 


—  Tibialis  posttcus 


Popliteal  notch 

Ext.  condylar  surface 


External  tuberosity 

Articular  surface 
for  fibula 


Popliteus 


Oblique  line 


Groove  for  tibial.  post,  andyfc.r.  long,  digit 
Internal  malleolus 


1 — -    Nutrient  foramen 


Posterior  surface 


External  (interosseous) 
border 


Posterior  division  of 
interosseous  border 
Tibio-fibular  ligament 

Groove  ior  flex,  long.  hall. 


astragalus 
Right  tibia  from  behind.    The  outline  figure  shows  the  areas  of  muscular  attachment. 


386 


HUMAN   ANATOMY. 


of  the  lower  articular  cartilage  onto  the  front  of  the  tibia,  allowing  extreme  dorsal 
flexion  of  the  ankle,   is  often  associated  with  this.     The  thickness  of  the  tibia  is 

FIG.  401. 

Spine 

Ext.  fibro-cartilage      ,\     Post,  crucial  ligament 
Int.  fibro-cartilage 


Ext.  condylar  surface 


Ext.  fibro-cartilage 
Anterior  crucial  ligament 


Int.  condylar  surface 


— Int.  fibro-cartilage 


ft — Bursal  surface 

Attachment  of  tendon 
patella? 


Upper  end  of  right  tibia  from  above  and  before. 


very  variable.     The  very  thin,  platycnemic^  form  is  most  common  in  savage  races, 
and  is  therefore  associated  with  the  pilastered  femur.      It  is  found  not  rarely  among 

FIG.  402. 


FIG.  403. 


Frontal  section  of  upper  end  of  tibia.  Frontal  section  of  lower  end  of  tibia. 

whites,  but  the  shape  of  the  accompanying  femur  is  uncertain.      The  tibia/  iinic.i 

(transverse  diameter  X  ioo\    •       .1  .•         r    .«  .«  •         j- 

amero-posterio,  a,;,,,,,,,,  )  ls   tlu>  r;ltl°  of  tlu'  transverse  t«>  tlu-  antcM-o-postcrior  (liameter. 


PRACTICAL   CONSIDERATIONS  :   THE   TIBIA. 


387 


According  to  French  statistics,  this  in  whites  is  from  70  to  80  ;  in*  savage  races  it  is 
much  lower.  The  method  of  reckoning  it  at  the  level  of  the  nutrient  foramen  is 
likely  to  be  superseded  by  one  choosing  the  middle  of  the  bone. 

Structure. — The  shaft  has  strong  walls  in  the  middle,  being  especially  thick 
under  the  crest.  At  both  ends  the  walls  become  thin.  The  head  contains  a  large 
amount  of  cancellated  tissue  with  comparatively  thin  walls.  The  architectural  arrange- 
ment of  the  trabeculae  at  the  ends  is  very  clear.  A  frontal  section  of  the  upper  end 
shows  successive  vertical  plates  springing  from  the  sides  to  support  the  expanding 
tuberosities,  with  an  irregular  system  in  the  middle.  Sagittal  sections  show  plates 
from  the  walls  meeting  each  other  in  arches.  A  somewhat  similar  pattern  is  seen 
at  the  lower  end.  In  a  frontal  section  there  are  several  transverse  plates,  of  which 
the  strongest  marks  the  border  of  the  epiphysis.  Several  of  these  from  the  outer 
side  turn  down  to  join  the  lower  surface  at  the  origin  of  the  malleolus,  where  there 
is  a  distinct  thickening  of  the  crust.  There  is  sometimes  an  imperfect  bony  canal 
for  the  nutrient  artery  for  a  short  distance  after  its  entrance  into  the  cancellated 
tissue. 

Development. — There  are  only  three  centres  of  ossification  :  one  for  the 
shaft,  appearing  in  the  seventh  or  eighth  foetal  week  ;  one  for  the  upper  end,  appear- 
ing usually  in  the  last  month  of  foetal  life  ;  and  one  in  the  lower,  appearing  in  the 
second  half-year.1  These  epiphyses  correspond  to  what  has  been  described  as  the 

FIG.  404. 


Ossification  of  tibia  and  fibula.  A,  at  eighth  foetal  month ;  S,  at  birth  ;  C,  at  two  and  one-half  years  ;  £>,  at  four 
years  ;  E,  at  about  fifteen  years,  a,  centre  for  shafts  ;  &,  for  upper  epiphysis  of  tibia  ;  c,  for  lower  epiphysis  of  fibula  ; 
d,  for  lower  epiphysis  of  tibia  ;  e,  for  upper  epiphysis  of  fibula  ;  f,  for  tubercle  of  tibia. 

ends  of  the  bone.  The  upper  extends  farthest  down  on  the  front,  including  the 
tubercle,  which  may  have  a  separate  nucleus.  According  to  Rambaud  and  Renault, 
this  is  of  usual  occurrence,  appearing  at  from  eight  to  fourteen  years  and  quickly 
joining  the  epiphysis.  The  lower  end  joins  the  shaft  at  about  eighteen  and  the 
upper  at  nineteen  or  twenty. 

PRACTICAL   CONSIDERATIONS. 

The  upper  epiphysis  of  the  tibia  is  separated  only  by  traumatism  of  marked 
severity  because  of  :  (i)  its  great  width;  (2)  its  irregularly  cupped  surface;  (3) 
the  downward  projection  in  which  the  tibial  tubercle  is  developed,  or  to  which  the 
latter  becomes  united  when  it  arises  from  a  separate  centre  ;  (4)  the  protection 
afforded  it  (#)  on  the  outer  side  by  the  head  of  the  fibula  (which  is  connected 
exclusively  with  this  epiphysis),  the  anterior  and  posterior  upper  tibio-fibular  liga- 
ments, and  indirectly  by  the  external  lateral  ligament  ;  (£)  on  the  inner  side  by 
the  internal  lateral  ligament,  and  (e^>  on  both  sides  by  the  fibres  of  insertion  of  the 

1  Fagerlund  :  loc.  cit. 


388 


HUMAN   ANATOMY. 


FIG.  405. 


vasti  and  semimefnbranosus  and  of  their  fascial  expansions  ;  (5)  the  toughness  of 
the  periosteum  uniting  it  with  the  diaphysis  ;  and  (6)  the  fact  that  while  there  is 
no  possibility  of  its  displacement  by  muscular  action,  it  does  not  project  enough 
to  be  exposed  to  the  effects  of  direct  violence.  The  possibility  of  disjunction  of 
this  epiphysis  complicating  an  injury  to  the  knee  continues  up  to  the  twentieth 
year  at  least  ;  in  injuries  to  the  elbow  epiphyseal  separation  may  be  excluded 
after  the  eighteenth  year. 

Three-fourths  of  the  recorded  cases  have  occurred  in  males,  as  might  be 
expected  on  account  of  their  more  frequent  exposure  to  serious  injury.  The 
epiphysis  has  been  displaced  forward,  and  outward  and  forward.  It  has  never  been 
displaced  backward,  partly,  at  least,  on  account  of  the  tongue-like  process  con- 
necting it  with  the  tibial  tubercle.  Its  inward  displacement  would  necessitate  the 
separation  of  the  head  of  the  fibula  or  the  laceration  of  the 
superior  tibio-fibular  ligaments.  The  attachment  of  the  syno- 
vial  membrane  of  the  knee-joint  does  not  descend  to  the  level 
of  this  epiphysis  ;  hence  that  articulation  is  often  not  involved 
in  these  injuries.  They  should  not,  when  severe,  be  mistaken 
for  dislocation,  or,  when  slight,  for  sprains  of  the  knee.  They 
may  be  distinguished  from  the  former  by  the  age  of  the  patient 
and  the  unimpaired  mobility  of  the  knee,  and  from  the  latter 
by  the  situation  of  the  pain  or  tenderness.  Dislocation  of  the 
knee  is  very  rare  in  children. 

Good  union  has  taken  place  in  some  cases  ;  arrest  of  growth 
has  followed  in  others,  as  might  be  expected  from  the  fact  that 
the  chief  increase  in  length  of  the  tibia  takes  place  from  this 
epiphysis. 

The  tubercle  of  the  tibia  has  been  detached  in  ten  recorded 
instances,  all  males  :  nine  from  violent  action  of  the  quadriceps 
in  powerful  young  men,  eight  of  whom  were  between  sixteen 
and  eighteen  years  of  age,  the  age  of  the  remaining  two  not 
having  been  mentioned  (Poland). 

This  separation  should  be  carefully  distinguished  from  frac- 
ture of  the  patella.  In  disjunction  the  latter  bone  is  drawn 
upward,  the  patient  is  unable  to  extend  the  leg,  and  the  swell- 
ing following  laceration  of  the  subligamentous  bursa  may  simu- 
late swelling  of  the  knee-joint.  The  latter  may  be  involved 
directly — as  the  synovial  membrane  is  in  close  proximity  to  the 
tubercle — or  indirectly,  through  the  occasional,  though  rare, 
communication  with  the  subligamentous  bursa.  Fracture  of  the 
patella,  however,  does  not  occur  in  children  and  is  very  rare 
in  adolescence.  In  patella  fracture  the  fragments  of  bone  are 
brought  together,  so  that  crepitus  may  be  felt  only  by  pushing 
the  two  fragments  towards  each  other;  the  groove  between 
them  can  almost  always  be  recognized.  In  disjunction  of  the 
tubercle  crepitus  can  be  elicited  only  by  pulling  the  fragment 
downward  ;  the  outline  of  the  patella  is  normal,  and  can  usually 
be  made  out.  The  X-rays  would  be  conclusive.  Bony  union  should  be  expected. 

The  shaft  of  the  tibia  gradually  decreases  in  size  to  about  the  junction  of  the 
middle  and  lower  thirds,  and  then  expands  again  to  the  ankle.  At  its  smallest 
point — on  an  average  about  ten  centimetres  (four  inches)  above  its  lower  end — it 
has  to  bear  a  greater  weight  on  a  smaller  area  than  any  other  bone  (Humphry).  At 
this  level  meet  the  two  independent  vertical  columns  into  which,  according  to 
Fayel  and  Duret,  the  spongy  tissue  of  the  tibia  is  divided  (one  occupying  the 
upper  two-thirds,  the  other  the  lower  third  of  the  bone),  and  hence  these  authorities 
assert  that  this  spot  represents  the  minimum  of  resistance  (Treves).  In  some 
tibiae  it  is  at  or  near  the  junction  of  an  ill-defined  long  upper  curve,  in  which  the 
crest  terminates,  and  a  short  lower  curve.  On  transverse  section  the  tibia  is  seen 
to  be  cylindrical  in  its  lower  third  and  three-sided  above.  As  it  has  been  demon- 
strated that  if  two  homogeneous  solids  present  on  section  equal  areas,  the  one 


Epiphyseal  lines  of  tibia. 


PRACTICAL   CONSIDERATIONS:     THE   TIBIA. 


389 


FIG.  406. 


triangular  and  the  other  circular,  the  former  has  the  greater  power  of  resistance 
(Tillaux),  the  shape  of  the  tibia  in  this  region  is  thought  to  be  an  additional  source 
of  weakness. 

For  all  these  reasons  it  is  the  most  frequent  seat  of  fracture  from  indirect  vio- 
lence. As  in  such  cases  the  breaking  strain  is  usually  continued  for  a  moment 
after  the  tibia  gives  way,  the  weak  fibula  is  apt  to  be  broken  also.  The  line  of 
fracture  usually  runs  from  its  level  on  the  crest  upward  and  backward,  and  under 
the  action  of  the  calf  muscles  and  the  weight  tof  the  body  the  sharp  lower  end  of 
the  upper  fragment  frequently  protrudes,  making  the  fracture  compound. 

Fracture  at  about  the  same  level  from  direct  violence  is  also  very  common  on 
account  of  the  exposed  position  of  the  bone,  and  all  fractures  are  apt  to  be  com- 
pound as  a  result  of  the  large  proportionate  area  of  the  bone  which  is  subcutaneous. 

Fracture  of  the  shaft  at  the  upper  end  involving  the  knee-joint  is  rare,  and  is 
usually  from  either  direct  violence  or  a  fall  from  a  considerable  height, — "com- 
pression fracture."  Fracture  of  the  lower  end  of  the  shaft  involving 
the  ankle-joint  is  a  not  infrequent  complication  of  Pott's  fracture. 

Separation  of  the  lower  epiphysis  is  nearly  three  times  as  fre- 
quent as  that  of  the  upper.  It  is  caused  usually  by  a  considerable 
degree  of  violence,  and  in  fifty  per  cent,  of  recorded  cases  has  been 
associated  with  fracture  of  the  lower  end  of  the  fibula  or  separation 
of  the  fibular  epiphysis,  in  which  case  the  displacement  is  often 
outward  ;  usually  it  is  backward. 

It  may  be  mistaken  for  dislocation  of  the  ankle.  In  patients 
from  eleven  to  seventeen  years  of  age  disjunction  of  the  epiph- 
ysis is  more  frequent  than  dislocation  ;  as  the  malleolus  and  the  foot 
go  backward  with  the  epiphysis,  the  inner  malleolus  preserves  its 
normal  relation  to  the  foot,  but  not  to  the  leg  or  outer  ankle.  In 
dislocation  the  reverse  is  the  case. 

The  ankle-joint  usually  escapes,  as  both  anteriorly  and  pos- 
teriorly the  synovial  membrane  is  below  the  epiphyseal  line.  The 
synovial  pouch  of  the  lower  tibio-fibular  joint  that  extends  upward 
between  these  two  bones  is  in  close  relation  to  that  line,  but  is  sepa- 
rated by  the  periosteum  which  is  continuous  over  the  epiphysis,  and 
thus  also  escapes  injury. 

Arrest  of  growth  is  not  common,  but  has  occurred,  and  severe 
ankle  sprains  in  the  young  should  be  treated  with  especial  care  on 
account  of  the  possibility  of  involvement  of  the  epiphyseal  joint  and 
later  disease  or  deformity. 

Disease  of  the  tibia,  if  infectious,  is  most  common  in  the  neigh- 
borhood of  its  two  epiphyses  and  at  the  junction  of  the  middle  and 
lower  thirds.  The  region  is  a  favorable  one  for  ' '  juxta-epiphyseal 
sprain,"  in  which  the  violence  is  expended  on  the  spongy  tissue  of 
the  diaphysis  near  the  epiphyseal  line.  "  Many  of  the  pains  called 
'  growing  pains'  are  due  to  juxta-epiphyseal  sprain  or  injury.  Such 
a  sprain  is  often  nothing  but  the  first  degree  of  an  epiphyseal  separation,  in  the 
same  way  that  an  articular  sprain  is  nothing  but  the  first  degree  of  dislocation' ' 
(Poland). 

The  usual  causes — strain,  traumatism,  cold,  etc. — influence  the  localization  of 
tuberculous  disease  in  or  near  the  epiphyses.  If  recognized  early,  and  if  the 
infected  focus  is  removed  by  operation,  the  knee-  and  ankle-joints  will  usually  escape. 
In  the  later  stages  the  products  of  liquefaction  may  find  their  way  from  the  upper 
epiphyseal  line  to  the  knee-joint,  either  directly  through  the  intervening  half-inch  of 
bone  or  by  way  of  the  tibio-fibular  joint, — which  is  in  close  relation  to  the  epiphysis 
(Fig.  425), — and  then  to  the  subpopliteus  bursa,  which  always  communicates  with 
the  knee-joint  and  often  with  both  ;  or  they  may  gain  the  surface  of  the  tibia  and 
extend  upward  beneath  the  periosteum. 

If  the  lower  epiphysis  is  involved  a  similar  direct  or  indirect  infection  of  the 
ankle-joint  may  occur,  the  tibio-fibular  synovial  pouch  being  sometimes  first 
involved. 


Lines  of  fracture  of 
tibia  and  fibula. 


390  HUMAN   ANATOMY. 

Post-typhoidal  periostitis  and  osteitis  of  the  tibia  are  exceedingly  common,  an,d 
affect  particularly  the  subcutaneous  area  of  the  bone  near  the  lower  third,  where 
there  are  no  muscular  attachments.  They  are  probably  due,  therefore,  to  slight 
traumatisms.  This  same  area  is  peculiarly  subject  not  only  to  this  form  of  infection 
and,  as  has  been  said,  to  fracture,  but  also  to  tuberculosis  (when  the  epiphyses  are 
spared),  to  syphilitic  nodes  and  gummata,  to  softening  and  deformity  from  rickets, 
and  to  sepsis  spreading  inward  from  cutaneous  inflammations  and  ulcers.  It  is 
probably  so  vulnerable  by  reason  of  t  its  exposure  to  frequent  slight  injury  and  to 
strain  disproportionate  to  its  size  and  strength  (vide  supra),  and  because  of  its 
dependent  position  and  its  distance  from  the  main  source  of  the  blood-supply  of  the 
bone  (the  nutrient  artery  entering  it  at  its  upper  third),  both  of  which  circumstances 
favor  passive  hyperaemia  and  the  localization  of  infection. 

Sarcoma,  in  accordance  with  the  general  rule  already  mentioned  (page  366), 
affects  chiefly  the  upper  third  of  the  tibia. 

Landmarks. — On  the  inner  side  of  the  knee  the  internal  tuberosity  of  the 
tibia  is  in  close  relation  in  extension  with  the  internal  condyle  of  the  femur,  the  two 
making  a  uniform  rounded  prominence.  The  interval  between  them  can  be  felt 
but  not  seen.  If  the  leg  is  flexed  and  the  ankle  rested  upon  the  opposite  knee,  the 
tibial  tuberosity  becomes  visible  and  lies  in  advance  of  the  inner  condyle.  The 
prominence  of  the  outer  tuberosity  is  distinctly  to  be  seen  and  felt  on  the  antero- 
external  aspect  of  the  limb  about  2.5  centimetres  (one  inch)  below  the  joint-line. 
It  represents  the  lowest  level  of  the  synovial  membrane.  Into  it  is  inserted,  about 
half-way  between  the  tip  of  the  patella  and  the  head  of  the  fibula,  the  important 
ilio-tibial  band  of  fascia  to  which  illusion  has  been  made  in  reference  to  fracture  of 
the  neck  of  the  femur  and  dislocation  of  the  hip  (page  377). 

The  posterior  edge  of  the  head  of  the  tibia  is  not  accessible  to  direct  examina- 
tion, and  this  is  true  of  the  external  and  posterior  surfaces  throughout. 

The  internal  border  can  be  traced  from  the  tuberosity  to  the  malleolus.  The 
antero-internal  surface,  which  is  subcutaneous  throughout,  can  be  seen  and  felt. 
The  anterior  border  or  crest  constitutes  the  prominence  of  the  "shin."  It  is 
sharp  in  the  upper  two-thirds  and  fades  into  the  shaft  at  the  summit  of  the  lower 
third.  In  well-marked  tibiae  it  presents  a  distinct  double  curve,  the  upper  part  of 
which  has  its  concavity  outward.  The  tubercle  is  easily  felt  and  seen.  It  should 
be  in  line  with  the  ligamentum  patellae  and  a  point  on  the  front  of  the  ankle  mid- 
way between  the  malleoli.  It  is  about  on  a  level  with  the  head  of  the  fibula. 

The  inner  malleolus  is  twelve  millimetres  (half  an  inch)  above  and  in  front  of 
the  outer  malleolus,  but  on  the  same  plane  posteriorly.  Its  lower  border  is  rounded. 
The  notch  for  the  internal  lateral  ligament  can  be  felt.  Its  tip  is  twelve  millimetres 
below  the  joint-line.  Its  sharp  posterior  border  forms  the  inner  boundary  of  the 
groove  for  the  tibialis  posticus  tendon. 

THE   FIBULA. 

The  fibula  is  a  long,  slender  bone  with  a  knob-like  upper  end  and  a  pointed 
lower  one. 

The  upper  extremity,  called  the  head,1  has  a  rounded  or  vaguely  quadri- 
lateral articular  surface  above,  looking  upward,  a  little  inward  and  forward,  to 
meet  the  corresponding  one  on  the  tibia.  The  styloid  process, 2  a  short  prominence, 
juts  upward  from  its  outer  posterior  angle.  The  outer  part  of  the  head  is  rough. 
An  ill-marked  neck  below  it  is  indistinguishable  from  the  shaft. 

The  shaft  '  is  best  described  as  having  four  borders,  separating  four  sic  Us,  though 
one  of  the  borders  joins  another  near  the  lower  end.  The  borders,  proceeding  in 
regular  order  round  the  bone  from  the  front,  are  (i)  the  antero-external,  (2)  the 
postero-external,  (3)  the  postero-internal,  sometimes  called  the  oblique  ridge,  and  (4) 
the  antero-internal  or  interosseous.  The  antero-c.vlrnni/  border  begins  faintly  on  the 
front  of  the  shaft,  a  little  below  the  neck,  and  becomes  very  prominent  as  it  descends, 
twisting  slightly  outward.  In  the  last  quarter  it  splits  into  two  lines  which  run  to 
the  front  and  back  of  the  outer  malleolus,  enclosing  a  triangular  subcutaneous  space. 
The  postero-external  bonier  begins  on  the  outer  side  of  the  neck  below  the  styloid 

1  Cnpitulum  fibulae.     "Apex  capitull  tihuluc.     ''Corpus  fibulae. 


THE   FIBULA. 


39i 


FIG.  407. 

Styloid  process 


FIG.  408. 

Styloid  process 


Head 


Biceps 


Biceps 


Soleus 


Flex.  long, 
hallucis 


External  malleolus 


Groove  for  tendons 
External  malleolus 


Right  fibula  from  before.  Right  fibula  from  behind. 

The  outline  figures  show  the  areas  of  muscular  attachment. 


392 


HUMAN    ANATOMY. 


Tibial  facet 


FIG.  409. 

-Styloid  process 
Head 


Neck 


Anterior  surface  - 
Antero-internal  border 
Antero-external  border 

Internal  surface^ 


•  Posterior  surface 


'Soieus 


Tibialis! 
posticus 


.Postero-external  border 


-Postero-internal  border 


\     ]      }Flex.  long, 
hallucii 


Inferior  interosseous  ligament 


Facet  for  astragalus  j 

-Fossa 

^Ext.  lateral  ligament 
Right  fibula,  inner  aspect.    The  outline  figure  shows  the  areas  of  muscular  attachment. 


PRACTICAL   CONSIDERATIONS:   THE   FIBULA.  393 

process.  It  is  strongest  at  and  below  the  middle  of  the  bone.  It  twists  backward 
and  is  lost  at  the  back  of  the  malleolus.  The  postero-internal  border  begins  at  the 
inner  side  of  the  back  of  the  head.  It  is  very  strong  at  about  the  middle.  It  ends 
in  the  last  quarter  by  joining  the  interosseous  ridge.  The  latter,  or  antero-internal 
border,  begins  poorly  marked  at  the  inner  side  of  the  neck,  soon  becomes  sharp, 
and  descends  rather  straighter  than  the  others  to  some  three  inches  above  the  lower 
end,  where  it  divides  into  two  lines  which,  ending  at  the  borders  of  the  articular  facet 
for  the  astragalus,  enclose  a  rough  space  for  ligaments.  The  interosseous  membrane, 
being  attached  to  this  ridge,  separates  the  front  of  the  bone  from  the  back.  The 
anterior  surface,  between  this  and  the  antero-external  border,  is  very  narrow.  It 
forms  a  part  of  a  hollow,  of  which  the  membrane  is  the  floor,  from  which  certain 
extensor  muscles  arise.  The  external  surface,  between  the  antero-external  and  the 
postero-external  borders,  is  a  characteristic  one,  presenting  for  more  than  the  lower 
half  a  shallow  groove  for  the  peroneus  longus  and  brevis,  which  sweeps  down  to 
the  back  of  the  malleolus  behind  the  subcutaneous  space  enclosed  by  the  splitting 
of  the  antero-external  border.  The  posterior  siirface  is  bounded  by  the  postero- 
external  border  and  by  the  postero-internal  till  that  border  joins  the  interosseous 
ridge,  which  bounds  the  surface  in  its  lower  part.  It  faces  backward  above  and 
inward  below.  The  nutrient  foramen,  running  downward,  enters  it  rather  above  the 
middle,  usually  near  the  postero-internal  border.  A  roughness  on  the  outer  part 
of  this  surface  is  for  the  origin  of  the  soleus.  The  internal  surface,  relatively  broad 
in  the  greater  part  of  its  course,  looks  inward  to  the  hollow  between  the  two  bones. 
It  ends  in  the  last  quarter  where  the  oblique  ridge  joins  the  interosseous  one. 

The  lower  extremity  of  the  fibula  is  pointed,  forming  the  outer  malleolus,1 
which  projects  downward  and  a  little  outward.  Its  outer  surface  is  a  continuation  of 
the  subcutaneous  triangle,  and  the  greatest  prominence  near  its  back  is  in  line  with 
the  posterior  of  the  borders  of  the  space.  Most  of  the  internal  surface  is  occupied 
by  a  triangular  articular  facet  for  the  astragalus,  the  upper  part  of  which  is  nearly 
vertical,  while  the  lower  slants  outward.  Below  and  behind  this,  on  the  inner  side 
of  the  greatest  projection,  is  a  deep  hollow  for  part  of  the  external  lateral  ligament. 
The  malleolus  is  broader  behind  than  in  front,  presenting  a  groove  in  continuation 
of  the  external  surface  for  the  peroneal  tendons. 

Development. — The  centre  for  the  shaft  appears  in  the  eighth  fcetal  week  ; 
that  for  the  head  of  the  bone,  which,  according  to  the  usual  order  of  long  bones, 
should  develop  next,  does  not  come  till  after  that  of  the  malleolus.  The  latter  ap- 
pears in  the  second  year,  the  former  two  or  three  years  later.  The  lower  epiphysis 
is  probably  fused  with  the  shaft  by  eighteen  or  nineteen  and  the  upper  by  twenty. 

PRACTICAL   CONSIDERATIONS. 

The  upper  epiphysis  has  a  flat  lower  surface  and  is  about  on  a  level  with  the 
most  prominent  part  of  the  tibial  tubercle.  It  includes,  therefore,  all  that  portion 
of  the  head  of  the  fibula  into  which  the  biceps  tendon  and  external  lateral  ligament 
are  inserted.  Its  line  of  cartilage  at  and  after  the  thirteenth  year  is  in  close  relation 
with  the  synovial  membrane  of  the  tibio-fibular  joint.  Its  disjunction  is  favored 
by  its  situation  on  the  most  exposed  aspect  of  the  limb,  its  subcutaneous  position, 
and  the  insertion  into  it  of  the  biceps  muscle.  The  attachment  of  the  external 
lateral  ligament  also  enables  a  powerful  strain  to  be  brought  upon  it  in  over-adduction 
of  the  leg.  In  spite  of  these  favorable  circumstances,  the  protection  afforded  by 
the  slight  overhang  of  the  external  tubefbsity  of  the  tibia  and  the  fixation  given  by 
the  strong  anterior  and  posterior  upper  tibio-fibular  ligaments  make  separation  of 
this  epiphysis  a  very  rare  occurrence.  Boyd  says  that  several  cases  are  known  in 
which  it  has  been  pulled  off  by  violent  contraction  of  the  biceps  in  an  effort  to  prevent 
falling.  It  is  then  felt  as  an  easily  recognizable  fragment  the  space  between  which 
and  the  diaphysis  is  increased  upon  extension  of  the  leg. 

Fracture  of  the  shaft  of  the  fibula  in  its  upper  two-thirds  occurs  from  direct 
violence  and  as  a  secondary  result  of  fracture  of  the  tibia.  In  spite  of  the  slender- 
ness  of  the  bone  and  its  position  on  the  outer  aspect  of  the  leg,  fracture  is  not  very 
frequent  because  of  {a)  its  elasticity,  which  is  marked  ;  (£)  its  protective  covering 

1  Malleolus  lateralis. 


394  HUMAN    ANATOMY. 

of  muscles  and  fascia  ;  and  (V)  its  backward  curvature,  which  carries  it  to  a  plane 
posterior  to  that  of  the  tibia,  which  thus  protects  it  both  internally  and  anteriorly 
from  direct  violence. 

Fractures  about  the  middle  of  the  lower  third  of  the  shaft,  and  especially  those 
about  7.5  centimetres  (three  inches)  from  the  ankle,  are  so  commonly  produced  by 
leverage  that,  whatever  their  exact  level,  most  of  them  may  be  grouped  as  instances 
of  Pott's  fracture,  although  an  effort  has  been  made  to  draw  between  them  distinc- 
tions that  are  ordinarily  academic  rather  than  practical. 

These  fractures  usually  result  from  over-abduction  of  the  foot.  When  that 
occurs  suddenly,  the  weight  of  the  body  being  upon  the  limb,  the  tension  first  comes 
upon  the  deltoid  ligament.  This  may  stretch  slightly  or  some  of  its  fibres  may  be 
torn,  or  there  may  be  a  small  detachment  from  its  malleolar  origin.  As  a  rule,  such 
a  case  ends  in  a  more  or  less  severe  sprain.  If  the  ligament  ruptures,  or  the  tip  of 
the  malleolus  is  torn  off,  or  the  malleolus  itself  is  fractured,  the  abduction  of  the 
foot  continues,  and  the  astragalus  is  subluxated  and  carried  against  the  inner  surface 
of  the  external  malleolus.  The  fibula  is  thus  converted  into  a  lever  of  the  first  order. 
The  force  is  applied  at  its  lower  end  ;  the  fulcrum  consists  of  the  stout  tibio-fibular 
ligaments,  which  are  often  stronger  than  the  bone  itself  and  which  are  rarely  com- 
pletely ruptured,  though  often  stretched  and  lacerated  ;  the  weight  or  resistance  is 
in  the  body  of  the  bone,  which  is  prevented  from  moving  inward  by  the  articulation 
of  its  Opper  end  with  the  tibia.  As  soon,  therefore,  as  its  limit  of  elasticity  is  ex- 
ceeded, it  breaks  at  a  weak  (if  not  its  weakest)  point,  and  the  upper  end  of  the 
lever — i.e. ,  of  the  lower  fragment — is  forced  in  the  direction  opposite  to  that  of  the 
lower  end, — i.e.,  the  malleolus  (Fig.  410).  The  impact  of  the  astragalus  and  the 
pull  of  the  ligaments  may  cause,  in  addition  to  the  fracture  of  the  tip  of  the  malleolus, 
fracture  of  the  anterior  or  of  the  outer  articular  edge  of  the  tibia.  If  the  tibio- 
fibular  ligaments  rupture,  the  fibula  becomes  a  lever  of  the  second  order,  the 
fulcrum  shifting  to  its  upper  end.  The  dislocation  of  the  astragalus  outward  will  be 
more  marked.  The  bone  may  break  at  any  point,  but  the  fracture  is  still  likely  to 
be  within  the  limits  of  the  lower  third. 

Rose  and  Carless  have  adopted  the  following  useful  classification  based  on  the 
injury  to  the  inner  side  of  the  foot  or  to  the  tibia  itself.  It  divides  these  fractures 
into  four  groups,  the  term  Pott's  fracture  being  correctly  applied,  according  to  these 
authors,  to  the  first  two  only.  i.  The  internal  lateral  ligament  is  torn  through  ; 
the  intact  internal  malleolus  can  be  felt  projecting  beneath  the  skin  (Fig.  410,  A). 
2.  The  malleolus  is  torn  off  and  a  distinct  sulcus  can  be  felt  between  it  and  the  lower 
end  of  the  tibial  shaft  (Fig.  410,  B).  3.  The  interosseous  tibio-fibular  ligament  is 
ruptured  (or  the  flake  of  bone  at  the  tibial  attachment  is  torn  off)  ;  the  subluxation 
outward  is  very  marked  ;  either  the  inner  malleolus  or  the  deltoid  ligament  yields, — 
"  Dupuytren's  fracture"  (Fig.  410,  C).  4.  The  tibia  fractures  transversely  just 
above  the  base  of  the  malleolus  ;  the  lower  end  of  the  upper  fragment  may  be  mis- 
taken for  the  tip  of  the  malleolus  (Fig.  410,  Z>). 

The  less  frequent  accident  of  forcible  over-inversion  of  the  foot,  if  the  external 
lateral  ligament  holds,  produces  by  the  same  mechanism  a  similar  series  of  occur- 
rences. The  tip  of  the  external  malleolus  is  dragged  violently  inward,  the  tibio- 
fibular  ligaments  act  again  as  a  fulcrum,  and  the  bone  is  apt  to  break  at  about  the 
same  level, — i.e. ,  from  5  to  7.5  centimetres  (two  to  three  inches)  above  the  joint,— 
the  upper  end  of  the  lower  fragment  being  carried  outward  instead  of  inward.  In 
these  cases  there  is  a  subluxation  of  the  astragalus  inward  which  not  infrequently 
results  in  a  fracture  of  the  inner  malleolus.  In  all  these  forms  of  fracture  the  lacera- 
tion of  ligamentous  structures  loosening  the  connection  of  the  foot  to  the  leg,  the 
upward  pull  of  the  calf  muscles,  and  the  weight  of  the  foot  itself  combine  to  produce 
a  subluxation  of  the  foot  backward  which  is  often  overlooked. 

The  cardinal  symptoms  of  the  common  form  of  Pott's  fracture  are  eversion  of 
the  foot,  prominence  of  the  inner  malleolus,  shortening  of  the  distance  from  the  front 
of  the  ankle  to  the  web  of  the  great  toe,  increased  width  between  the  malleoli,  and 
tenderness  over  (a)  the  space  between  the  til>i;i  and  the  external  malleolus  anteriorly, 
— i.e.,  over  the  strained  or  torn  tibio-fibular  ligaments  ;  (6)  over  the  base  or  tij>  or 
anterior  border  of  the  internal  malleolus, — i.e.,  over  a  ruptured  internal  lateral 


PRACTICAL   CONSIDERATIONS:    THE   FIBULA. 


395 


ligament  or  a  fracture  of  the  malleolus  ;  and  (<r)  over  the  fibula  from  two  to  four 
inches  above  the  tip  of  the  malleolus, — i.e. ,  over  the  fibular  fracture. 

The  lower  epiphysis  of  the  fibula  is  an  exception  to  the  rule  that  the  epiphyses 
of  long  bones  appear  first  at  the  end  from  which  the  nutrient  artery  is  directed,  and 
to  the  more  important  rule  that  the  chief  growth  of  the  long  bones  takes  place  at 
the  end  where  the  epiphysis  is  last  united  to  the  shaft  ;  in  the  other  long  bones  this 
is  also  the  end/n?w  which  the  nutrient  artery  is  directed.  We  have  seen  that  in 
the  upper  extremity,  the  nutrient  canals  being  directed  towards  the  elbow,  the  epiph- 
yses at  the  upper  end  of  the  humerus  and  the  lower  ends  of  the  radius  and  ulna  appear 
earlier  and  join  the  shaft  later  than  those  at  the  elbow,  and  that  thus  it  is  from  the 
shoulder  and  wrist  that  the  chief  growth  of  the  upper  limb  takes  place.  In  the  lower 
extremity,  the  nutrient  canals  being  directed  towards  the  hip  and  the  ankle,  the  lower 
epiphysis  of  the  femur  and  the  upper  epiphysis  of  the  tibia  appear  first  and  are  joined 
on  last,  and  the  chief  growth  of  the  lower  limb  takes  place  at  the  knee. 


FIG.  410. 


Showing  four  types  of  Pott's  fracture  of  lower  end  of  fibula  according  to  classification  of  Rose  and  Carless. 

In  the  case  of  the  fibula — the  upper  part  of  which  is  in  man  in  a  comparatively 
rudimentary  condition  (Poland) — the  exception  is  noted  to  avoid  confusion  in  the 
mind  of  the  student.  The  nutrient  artery  runs  downward,  but  the  lower  epiphysis 
is  both  the  first  to  appear  and  the  first  to  consolidate,  and  is  the  chief  seat  of 
growth.  It  is  not  of  great  practical  importance,  although  it  is  probable  that  in  most 
so-called  fractures  of  the  extreme  lower  end  of  the  fibula  occurring  between  the 
twelfth  and  nineteenth  years  there  has  been  a  disjunction  of  this  epiphysis.  The  so- 
lution of  continuity  would  then  be  below  instead  of  above  the  tibio- fibular  ligaments. 

The  synovial  membrane  of  the  ankle-joint  is  attached  above  the  epiphyseal  line, 
and  that  articulation  is  therefore  likely  to  be  involved  more  frequently  than  in 
fractures  of  the  diaphysis.  This  fact,  together  with  the  importance  of  the  epiphysis 
in  its  relation  to  growth  of  the  bone,  should  cause  the  possibility  of  its  disjunction  to 
be  borne  in  mind.  If  arrest  of  growth  does  ensue,  a  condition  of  talipes  valgus  may 
result  from  the  relative  overgrowth  of  the  tibia.  For  the  relief  of  this  the  operation 
of  "  conjugal  chondrectomy" — removal  of  the  lower  epiphyseal  cartilage  of  the  tibia 
— has  been  suggested.  This  at  twelve  years  of  age  is  seventeen  millimetres  from  the 
tip  of  the  malleolus.  It  is  subcutaneous. 


396 


HUMAN   ANATOMY. 


FIG.  411. 


Ant.  super,  tibio- 
fibular  ligaments 


Sarcoma  of  the  fibula  attacks  the  upper  end  in  the  great  majority  of  cases. 
Osteophytes  are  not  infrequent  upon  the  median  margin  of  the  shaft  above  the  lower 
end.  ' 

Landmarks. — In  extension  of  the  leg  the  position  of  the  head  of  the  fibula  is 
indicated  by  a  depression  on  the  posterior  part  of  the  outer  surface  of  the  leg  a  little 
below  the  level  of  the  tibial  tubercle,  corresponding  to  the  interval  between  the 
tendon  of  the  biceps  above  and  the  peroneus  longus  below.  The  head  is  subcu- 
taneous and  may  be  distinctly  felt  there.  In  flexion  it  projects  above  the  surround- 
ing surfaces  and  may  be  seen.  The  insertion  of  the  biceps  may  show  as  a  rounded 
prominence  at  the  base  of  the  styloid  process.  The  synovial  membrane  of  the  knee 
descends  to  a  point  just  above  the  upper  level  of  the  head.  The  upper  half  of  the 
fibula  is  so  covered  by  muscles  that  its  outline  cannot  be  recognized  distinctly  by 
palpation.  In  the  lower  half  it  may  be  felt  through  the  muscles.  Its  lower  fifth  lies 

between  the  tendons  of  the  peroneus  tertius  and 
those  of  the  peroneus  longus  and  peroneus 
brevis,  and  is  subcutaneous,  as  is  the  malleolus. 
The  relation  of  the  plane  of  the  shaft  to  that  of 
the  tibia  should  be  remembered,  as  should  the 
plane  of  the  external  to  that  of  the  internal  mal- 
leolus (page  390).  The  tip  of  the  external 
malleolus  is  from  twelve  to  eighteen  millimetres 
(one-half  to  three-quarters  of  an  inch)  nearer  to 
the  heel  than  that  of  the  internal  malleolus.  The 
whole  malleolus,  viewed  from  without  inward, 
is  in  the  mid-line  (antero-posteriorly)  of  the 
ankle-joint.  It  becomes  abnormally  prominent 
in  cases  of  atrophy  of  the  peroneal  muscles, 
particularly  of  the  peroneus  longus. 

CONNECTIONS   OF   THE  TIBIA   AND 
FIBULA. 

These  are  the  superior  and  inferior  joints 
and  the  interosseous  membrane. 

The  Superior  Tibio-Fibular  Articu- 
lation '  (Fig.  411). — The  cartilage-covered  ar- 
ticular surfaces  already  described  vary  greatly 
both  in  direction  and  in  the  nature  of  their 
curves.  Perhaps  the  more  ordinary  arrange- 
ment is  fo/  the  tibial  facet  to  be  concave  in  a 
horizontal  and  convex  in  a  vertical  plane  ;  but 
the  converse  may  occur,  and  there  are  many 
intermediate  forms.  The  synovial  sac  extends 
upward  behind  and  may  communicate  with  the 
knee-joint.  The  capsule  is  very  strong,  except 
below,  and  especially  so  at  the  outer  side  where 
the  long  external  lateral  ligament  of  the  knee 
is  incorporated  with  it.  The  anterior  and  pos- 
terior superior  tibio-fibular  ligaments  '2  are  strong 
fibres,  strengthening  the  capsule  and  passing 
outward  and  slightly  downward  from  the  tibia 
to  the  fibula. 

The  interosseus  membrane11  (Fig.  411) 
extends  from  the  head  of  the  fibula  down  along 
the  interosseous  ridges  of  both  bones  till  these 
split.  Its  fibres  run  in  the  main  downward 

and  outward,  but  in  the  upper  part  many  run  downward  and  inward.      There  is  a 

large  opening  at  the  top  above  the  membrane  or  through  it. 

The  Inferior  Tibio-Fibular  Articulation4  (Fig.  411).— This  joint  is  essen- 

1  Artlculatlo  tibiolibulari*.      -  Lltfit.  capituli  fibulae  nnterius    et  posterlus       3  Memb.   Interossea  cruris.      '  Syndesmosls 
tibiofibularc. 


Antero-internal 
surface 


Anterior  border — 


Ant.  infer,  tibio-fibular 
ligament 


Tibio-fibular  ligaments  from  before. 


THE   BONES   OF   THE   LEG   AS   ONE   APPARATUS.  397 

tially  ligamentous,  though  the  articular  cartilage  of  the  ankle-joint  extends  for  a  few 
millimetres  onto  the  opposed  sides  of  each  bone. 

The  inferior  ligaments  are  the  interosseous,  the  anterior  and  posterior,  and  the 
transverse.  The  interosseous  ligament  is  a  thickened  continuation  of  the  mem- 
brane, consisting  of  short  fibres  connecting  the  rough  surfaces  bounded  by  the  split- 
ting of  the  interosseous  ridges. 

The  anterior  and  posterior  ligaments1  (Fig.  411,  412)  are  strong  bands  situ- 
ated respectively  on  the  front  and  the  back  of  the  tibia  and  running  downward  and 
outward  to  the  fibula.  The  anterior  deepens  the  socket  but  slightly,  while  the 
posterior,  reaching  nearly  half-way  down  to  the  malleolus,  makes  a  considerable 
addition  to  the  back  of  the  joint.  The  transverse  ligament  (Fig.  412)  containing 


FIG.  412. 


Ant.  tibio-fibular 


Capsule  reflected 


Ant.  lateral  ligame 


Middle  lateral  ligament 


Outer  malleolus 


Transverse  ligamen 


Deltoid  ligament 


Pad  of  fat 
Post,  external  lateral  ligament 


Capsule 
Post,  tibio-fibular  ligament 


Socket  of  right  ankle-joint  from  below. 

probably  elastic  fibres,  runs  obliquely  from  the  back  of  the  lower  border  of  the 
tibia  to  the  tip  of  the  inner  malleolus.  It  projects  into  the  joint,  the  capsule  form- 
ing a  pouch  between  it  and  the  posterior  tibio-fibular  ligament.  It  is  closely  con- 
nected at  the  fibula  with  the  posterior  fibulo-astragaloid  ligament.  The  two  have 
the  appearance  of  diverging  bundles  of  the  same  structure.  The  synovial  cavity  is 
prolonged  some  three  millimetres  upward  between  the  bones.  The  back  part  of  the 
crack  between  the  bones  is  concealed  by  a  pad  of  fat  (Fig.  412)  covered  by 
synovial  membrane  projecting  into  the  joint.  It  advances  or  recedes  between  the 
bones  according  to  changes  of  position. 

Movements. — The  motions  between  the  tibia  and  the  fibula  are  slight  and 
not  very  definite.  The  head  of  the  fibula  may  play  a  little  forward  and  backward, 
and  the  bone  may  rotate  on  its  long  axis.  These  motions  are  resisted  alternately 
by  the  anterior  and  posterior  ligaments  at  both  ends. 

THE  BONES  OF  THE  LEG  AS  ONE  APPARATUS. 
Surface  Anatomy. — The  upper  part  of  this  support  consists  of  the  head  of 
the  tibia  with  that  of  the  fibula  well  back  on  the  outer  side.  The  framework  nar- 
rows to  the  junction  of  the  middle  and  lower  thirds,  where  the  tibia  is  nearly  at  its 
smallest  and  seems  to  bend  towards  the  fibula.  Below  this  it  broadens  for  the 
socket  of  the  ankle.  The  fibula  in  the  lower  third  is  close  to  the  tibia  and  no  longer 
so  much  behind  it,  which  is  due  in  part  to  the  subsidence  of  the  crest  of  the  tibia. 
The  difference  of  relations  is  shown  by  sections  at  three  levels  (Fig.  413).  The 
whole  apparatus  is  described  as  having  three  borders  and  three  surfaces.  As  the 
details  have  been  given  with  the  bones,  the  chief  features  only  are  here  enumerated. 
The  anterior  border  is  the  crest  of  the  tibia  ;  the  posterior  and  internal  border  is  the 
posterior  border  of  the  same  bone ;  between  them  is  the  subcutaneous  internal  surface. 
The  posterior  and  external  border  is  the  postero-external  border  of  the  fibula.  Thus 
there  remain  an  antero-external  and  a  posterior  surface,  each  of  which  is  formed  in 

1  Liga.  malleoli  lateralis  anterius  et  posterius, 


398 


HUMAN    ANATOMY. 


part  by  the  interosseous  membrane.  The  antero-external  surface  presents  the  fol- 
lowing  features:  (i)  a  large  surface  of  the  tibia,  looking  outward  as  far  as  the 
lower' third  and  then  forward  ;  (2)  the  interosseous  membrane  ;  (3)  a  narrow1  sur- 
face of  the  fibula,  bounding  externally  the  fossa  of  the  front  of  the  leg,  shallow 
above,  deep  and  narrow  below  ;  (4)  the  antero-external  border  of  the  fibula,  split- 
ting below  to  enclose  the  subcutaneous  surface  above  the  outer  malleolus  ;  (5)  the 
grooved  surface  of  the  fibula  occupied  by  the  peronei. 

The  posterior  surface  presents,  continuing  in  the  same  course  :  (i)  the  posterior 
surface  of  the  fibula,  looking  backward  above,  inward  below  ;  (2)  the  postero-in- 
ternal  border,  ending  in  the  interosseous  ridge  ;  in  the  upper  two-thirds  this  over- 
hangs a  deep  hollow  ;  (3)  the  internal  surface,  which  ends  below  with  the  preceding 
border;  (4)  the  interosseous  membrane;  (5)  the  posterior  surface  of  the  tibia. 
The  interosseous  membrane  is  at  the  bottom  of  a  much  deeper  gutter  than  in  front, 
which  also  becomes  very  narrow  below. 

The  outward  twist  of  the  ankle  has  been  mentioned,  and  it  has  been  shown  that 
this  depends  on  the  twist  of  the  tibia.  It  is  to  be  noticed  that  while  the  antero- 
external,  the  postero-external,  and  the  postero-internal  borders  of  the  fibula  run  as  if 


Anterior  border 


Anterior  border 


Oblique  line 
Postero-int.  border' 


Anterior  border 


Antero-ext.  border 

Internal  border 

Postero-ext.  border 


Internal  borde 

*Antero-ext.  border 

Postero-int.  border, 

^Postero-ext.  border 

Postero-ext.  border 

Sections  across  the  bones  of  right  leg,  showing  their  relations  at  different  levels;  seen  from  above.    A,  near  head  of 
fibula  ;  B,  near  the  middle  ;  C,  a  little  above  the  ankle. 

the  lower  end  of  that  bone  had  been  twisted  outward,  the  same  is  not  true  of  the 
borders  and  surfaces  of  the  tibia.  On  the  contrary,  the  crest,  with  the  surface  on 
each  side  of  it,  slants  in  the  lower  half  of  the  leg  downward  and  inward.  It  is  as 
if  these  borders  of  both  bones  had  been  twisted  away  from  the  median  line  of  the 
leg,  one  to  each  side,  and  that  the  interosseous  ridge  had  stayed  straight.  There 
seems  to  be  no  relation  between  the  degree  of  forward  bend  of  the  neck  of  the 
femur  and  the  outward  twist  of  the  socket  of  the  ankle.  Probably  both  have  an 
influence  on  the  direction  of  the  foot,  but  it  depends  chiefly  on  the  latter.  It  is  un- 
warranted, therefore,  to  expect  all  children  to  turn  out  the  toes  alike.  The  whole 
of  the  front  and  sides  of  the  head  of  the  tibia  is  easily  felt,  but  it  is  thickly  covered 
behind.  The  top  of  the  tuberosities  is  clear  on  either  side,  and  in  front  the  whole 
of  the  tubercle  can  be  explored  when  the  tendon  is  relaxed.  The  head  of  the  fibula 
is  distinct  far  back  on  the  outer  side.  Descending  the  leg,  it  is  easy  to  follow  the 
sharp  crest  of  the  tibia  into  the  lower  third,  and  the  internal  subcutaneous  surface 
down  to  the  malleolus.  The  external  surface,  where  it  becomes  anterior  above  the 
ankle,  is  plain  in  spite  of  the  tendons  crossing  it.  The  shaft  of  the  fibula  is  so 
covered  with  muscles  that  little  more  than  its  general  position  is  to  be  made  out 
above  the  triangular  subcutaneous  surface  over  the  outer  malleolus,  which  latter  is 
also  easily  explored.  The  relations  of  the  malleoli  are  considered  with  the  foot 
(page  449). 

THE   PATELLA. 

The  knee-pan,  the  largest  sesamoid  bone,  is  triangular  or  shield-shaped.  The 
anterior  surface  is  covered  by  the  tendinous  fibres  of  the  quadriceps,  which  re- 
place the  periosteum  and  mark  the  surface  with  longitudinal  lines.  Jai^rd  spines 
(nun  the  ossification  of  the  tendon  are  often  found  at  the  top.  The  transverse 

1  In  the  transverse  sections  (Fig.  413)  this  surface  is  exceptionally  small. 


THE  PATELLA. 


399 


diameter  is  usually  rather  larger  than  the  vertical,  especially  in  strong,  and  conse- 
quently in  male,  bones. 

The  base1  is  above  with  a  slightly  curved  outline,  and  the  apex*  below,  usually 
somewhat  internal  to  the  middle.      The  outer  lower  border  is  more  oblique  than  the 


FIG.  414. 


Tendon  of  quadriceps  extensor 


Ligamentum  patellae  Ligamentum  patellae 

Right  patella,  anterior  and  posterior  surfaces. 

inner.     The  posterior  surface  is  divided  into  an  upper  articular  part  and  a  much 
smaller  non-articular  one  below,  in  which  the  bone  is  thinner  at  the  expense  of  the 


FIG.  415 


Prepatellar  bursa 


Alar  ligament 


Cavity  of  joint 

Lateral  part  of  capsule 


Cavity  of  joint 


Posterior  crucial  ligament 
Horizontal  frozen  section  through  right  knee-joint. 

posterior  surface  and   is  covered  by  the  fibres   of  the  ligamentum   patellae.      The 
upper  part,  covered  with  articular  cartilage  and  forming  a  part  of  the  knee-joint,  is 

1  Basis  patellae.     s  Apex  patellae.     3  Facies  articularis. 


400  HUMAN   ANATOMY. 

much  broader  transversely  than  vertically.  The  outer  three-fifths  or  so,  which 
plays  on  the  external  condyle,  is  concave  transversely  and  the  inner  two-fifths  con- 
vex. The  convexity  begins  with  a  vertical  prominence  which  marks  the  greatest 
thickness  of  the  bone  and  appears  to  divide  the  hind  surface  into  two  parts,  as  a 
horizontal  section  shows,  the  surface  receding  from  it  on  either  side.  Neverthe- 
less, the  whole  inner  part  is  convex,  as  described.  Vertically,  both  sides  are  slightly 
concave.  A  close  examination  of  a  fresh  specimen  shows,  what  rarely  is  to  be  seen 
on  the  dry  bone,  that  the  articular  surface  is  to  be  further  subdivided.  A  narrow 
vertical  facet  is  seen  along  the  inner  side,  constituting  a  surface  which  rests  on  the 
edge  of  the  inner  condyle  in  extreme  flexion.  The  rest  of  the  articular  surface  is 
divided  into  three  horizontal  zones,  one  above  another,  by  two  transverse  lines.  The 
top  of  the  bone  is  very  thick,  most  of  it  being  occupied  by  the  insertion  of  the 
rectus.  The  capsule  of  the  knee-joint  is  inserted  all  around  the  articular  surface 
some  two  or  three  millimetres  from  its  edge,  so  that  a  little  of  the  border  is  enclosed 
in  the  joint.  Several  nutrient  foramina  are  found  on  the  anterior  surface. 

Development. — The  patella  appears  as  a  cartilaginous  point  in  the  course  of 
the  third  fcetal  month.  Ossification  begins  by  the  deposit  of  several  granules  some 
time  between  two  and  five  years.  These  soon  unite  into  a  central  mass,  from  which 
ossification  spreads,  more  rapidly,  however,  in  the  deeper  parts.  The  bone  is  not 
fully  formed  till  after  puberty,  perhaps  not  before  eighteen. 

THE   LIGAMENTUM    PATELLA. 

This  name  is  applied  to  the  tendon  of  the  quadriceps  extensor  muscle,  in  which 
the  patella  is  a  sesamoid  bone  (Fig.  416).  It  is  a  strong,  flattened,  fibrous  band 
some  two  inches  long.  Just  below  the  knee-pan  it  is  at  least  one  and  one- quarter 
inches  broad,  but  at  its  insertion  into  the  front  of  the  upper  part  of  the  tuberosity 
of  the  tibia  its  breadth  is  not  over  one  inch.  The  line  of  insertion  is  oblique,  the 
outer  end  being  the  lower.  Just  above  the  insertion  a  synovial  bursa  lies  between 
the  tendon  and  the  bone.  A  mass  of  fat  above  the  bursa  separates  the  tendon  from 
the  capsule.  The  tendon  is  fused  at  the  sides  with  fibrous  expansions  from  the 
quadriceps. 

THE    KNEE-JOINT. 

This  is  a  compound  joint  between  the  femur  and  the  tibia,  the  patella  being  a 
sesamoid  bone  in  the  tendon  of  the  extensor  of  the  leg,  incorporated  in  the  front  of 
the  capsule.  The  patella  is  in  relation  to  the  femur  only,  and  sometimes  it  is  con- 
venient to  consider  the  knee-joint  as  the  sum  of  three  distinct  ones, — namely,  that 
betvyeen  femur  and  patella,  and  one  for  each  condyle  with  the  tibia.  The  joint  is 
enclosed  by  a  capsule  partially  subdivided  in  many  ways.  Fibro-cartilaginous  disks, 
the  semilunar  cartilages  on  the  top  of  the  tibia,  tend  to  subdivide  the  joint  below 
each  condyle  into  an  upper  and  a  lower  half.  The  crucial  ligaments  nearly  cut  off 
communication  between  the  parts  of  the  joint  under  each  condyle.  The  mucous 
ligament  assists  in  this,  and  with  the  alar  ligaments  tends  to  isolate  the  patella. 

Discussion  of  the  knee-joint  calls  for  the  description  of  the  following  component 
structures  : 

The  Capsule  and  its  Accessories. 

The  Semilunar  Cartilages  and  their  Accessories. 

The  Crucial  Ligaments. 

The  Subpatellar  Fat  with  the  Ligamentum  Mucosum  and  the  Ligamenta 
Alaria. 

The  Synovial  Membrane. 

Certain  Bursae. 

The  capsule  (Fig.  416)  arises  from  the  femur,  mingling  with  the  periosteum, 
a  little  above  the  anterior  articular  surface  ;  from  the  sides  of  the  condyles  as  high 
as  the  level  of  the  lateral  tuberosities  ;  from  the  back  one  centimetre  beyond  the 
highest  point  that  the  cartilage  reaches  on  the  top  of  the  condyles  ;  and  from  a 
slightly  lower  level  above  the  intercondyloid  notch.  It  is  attached  in  front  around 
the  articular  surface  of  the  knee-pan  and  inferiorly  to  the  tibia  all  around,  but  a 


" 


THE   KNEE-JOINT. 


401 


little  below  the  top  ;  for  the  articular  cartilage  is  continued  over  the  border  onto 
the  sides.  It  is  lower  at  the  back  of  the  outer  tuberosity,  where  the  joint  sometimes 
joins  that  of  the  head  of  the  fibula.  It  is  attached  to  the  periphery  of  the  semi- 
lunar  cartilages.  This,  which  is  the  capsule  proper,  is  very  much  strengthened  by 
surrounding  structures.  On  each  side  a  strong  fibrous  layer  passes  from  the  con- 
dyles  to  the  patella  {ailerons  de  la  rotule  of  French  authors)  (Fig.  418).  Super- 
ficial to  this,  and  not  adherent  to  it,  come  the  aponeurotic  fibres  of  the  vasti,  and 
still  more  superficially  the  fascia  lata.  They  fuse  with  the  capsule  at  the  sides  of 

FIG.  416. 

Tendon  of  quadriceps  extensor 


Capsule 

External  lateral  ligament- 
Tendon  of  biceps 


Internal  lateral  ligament 
Ligamentum  patellae 


Sartorius  turned  back 


Fibula        Interosseous        Tibia 
membrane 

Right  knee-joint  from  before. 

the  patella,  but  extend  over  the  latter  in  two  tolerably  distinct  layers.  Both  heads 
of  the  gastrocnemius  and  the  plantaris  are  to  a  great  extent  incorporated  with  the 
capsule  behind  (Fig.  417).  The  tendon  of  the  semimembranosus,  which  has  its 
chief  insertion  in  the  groove  in  the  inner  side  of  the  tibia  where  it  is  covered  by  the 
more  superficial  lateral  fibres  of  the  capsule,  sends  across  the  back  of  the  capsule 
strong  transverse  diverging  fibres,  known  as  the  ligament  of  ^Afinslow,  some  of 
which  are  directly  continuous  with  the  outer  head  of  the  gastrocnemius  (Fig.  417). 
Some  longitudinal  fibres  near  the  back  of  the  inner  side,  only  artificially  separable 

26 


402 


HUMAN   ANATOMY. 


from  the  rest,  have  been  called  the  internal  lateral  ligament1  (Fig.  416).  The 
long  external  lateral  ligament2  (Fig.  418;,  though  connected  with  the  capsule 
by  areolar  tissue  on  its  deep  surface,  is  truly  a  distinct  ligament.  It  arises  from  the 
external  tuberosity  of  the  femur  and  runs  as  a  flattened  cord  downward  and  some- 
what backward  to  the  outer  surface  of  the  head  of  the  fibula,  almost,  or  quite, 
splitting  the  tendon  of  the  biceps,  which  is  inserted  external  to  it,  overlapping  the 
ligament  in  front  and  behind.  A  shorter  band  placed  more  posteriorly  and  insepa- 
rable from  the  capsule  can  often  be  traced  to  the  styloid  process.  The  tendon  of  the 

FIG.  417. 

Femur 


Fibres  to  capsule  from 
tendon  of  adductor  magnus 


Int.  head  of  gastrocnemius 
Bursa  opening  into  joint 

{ 

Tendon  of  semitendinosus 


Posterior  ligament  of  Winslow 


External  head  of  gastrocnemius 


Head  of  plantaris 

External  condyle 

Bursa  opening  into  joint 

Popliteus  tendon 

External  lateral 
igament 

•__— - -4-Tendon  of  biceps 


uperior  tibio-fibular  ligament 


Tibia 


Interosseous 
membrane 


Fibula 


Right  knee-joint  from  behind. 

popliteus  entering  the  joint  from  behind  is  incorporated  with  the  capsule  beneath 
the  long  external  lateral  ligament,  as  described  with  the  bursse. 

The  semilunar  cartilages  (Figs.  419,  420)  are  two  crescentic  disks  of  fibro- 
cartilage  lying  each  on  top  of  one  of  the  tuberosities  of  the  tibia,  with  their  thick 
outer  borders  at  the  periphery  attached  to  the  capsule  and  their  thin  edges  tree,  so 
as  partially  to  divide  the  joint  into  an  upper  and  a  lower  part.  The  pointed  ends 
(conuta]  arc  fastened  near  the  middle  line  of  the  joint.  Those  of  the  external 
cartilage 3  are  attached  to  the  front  and  back  of  the  nbular  facet  of  the  spine  of  the 
tibia  and  to  the  inner  border  of  the  raised  articular  facet  before  and  behind  it.  The 

1  Lig.  cullnternlc  tiliialv.     "Liu.  collatcralc  tibulurc.         \Kni-i  u>  l;iUr;ilis. 


THE   KNEE-JOINT. 


403 


posterior  horn,  moreover,  joins  the  posterior  crucial  ligament.  There  is  not  more 
than  one  centimetre  between  the  two  horns,  so  that  this  cartilage  is  almost  circular. 
The  internal  cartilage  l  is  C-shaped.  The  anterior  horn,  thin  and  fibrous,  is  in- 
serted into  the  rough  surface  near  the  anterior  border  at  no  very  definite  point. 
Sometimes  it  runs  into  the  transverse  ligament  without  any  fixed  ending  ;  some- 
times the  extreme  point  is  free.  The  posterior  horn  is  attached  to  the  back  of  the 
tibial  facet  of  the  spine  and  to  the  edge  of  the  articular  facet  behind  it.  The 


FIG.  418. 


Femur 


Inner  head  of 
gastrocnemius 


Popliteus  tendon  and 
opening  into  joint 


Long  external  lateral 
ligament 


Tendon  of  biceps 

Head  of  fibula 


Extensor  tendon 


Subrectal  bursa 


Superficial  band  to  patella 


Ligamentum  patellae 


Anterior  tibio-fibular  ligament 


Right  knee-joint,  external  aspect.    The  extensor  tendon  is  drawn  forward  and  upward. 

distance  between  the  horns  is  about  three  centimetres.  The  anterior  horn  of  the 
internal  cartilage  may  not  come  into  contact  with  the  femur.  The  vertical  diameter 
of  the  cartilages  at  the  periphery  is  from  six  to  eight  millimetres.  The  breadth 
varies  in  different  joints,  ranging  from  one  to  nearly  two  centimetres.2  The  broadest 
part  is  near  the  back  of  the  internal  one,  but  the  external  is,  on  the  whole,  the 
broader.  It  is  said  sometimes  to  completely  divide  that  half  of  the  joint.  The 
free  border  is  very  thin  and  may  present  fine  prolongations  with  scalloped  edges. 

2  For  various  statistics,  consult  Higgins  :  Journal  of  Anatomy  and  Physiology,  vol.  xxix., 
1895- 

1  Meniscus  medialis 


404 


HUMAN    ANATOMY. 


The  lower  surfaces  of  the  disks  adapt  themselves  to  the  top  of  the  tibia,  the  outer 
cartilage  concealing  the  convexity  at  the  back  of  the  tuberosity.  The  upper  surfaces 
form  cups  to  receive  the  femoral  condyles.  At  the  sides  of  the  spine,  where  the 
cartilages  are  wanting,  the  cups  are  completed  by  the  upward  slope  of  the  tuber- 
osities. 

The  coronary  ligaments  (Fig.  420)  are  parts  of  the  capsule  connecting  the 
periphery  of  the  semilunar  cartilages  with  the  tibia.  They  are  of  little  strength  and 
allow  more  or  less  motion.  Those  of  the  external  cartilage  are  more  than  two  cen- 
timetres long  at  the  front  and  1.3  centimetres  at  the  back,  while  those  of  the  internal 
are  from  four  to  five  millimetres.  Thus  the  external  cartilage  can  move  very  freely 
on  the  tibia,  both  from  the  length  of  these  ligaments  and  from  the  approximation  of 
its  horns,  while  the  internal  can  move  but  little.  This  has  an  important  influence 


FIG.  419. 

Shaft  of  femur 


P$ —  Capsule 
I 


Alar  ligament 

Anterior  crucial  ligament 

External  semilunar  cartilage 
-Tendon  of  popliteus 

Capsule  reflected 


Bursa  of  tendon 
of  semimembranosus 


Anterior  wall  of  right  knee-joint  seen  from  behind,  the  lower  end  of  the  femur  having  been  removed. 

on  the  mechanics  of  the  joint.  The  popliteus  muscle  is  attached  to  the  outer, 
which  is  significant  in  the  same  connection. 

The  transverse  ligament '  (Fig.  420)  is  a  band,  usually  ill-defined  and  often 
quite  wanting,  which  connects  the  cartilages  at  the  front  of  the  knee,  running  from 
the  convexity  of  the  outer  to  near  the  anterior  cornu  of  the  inner  and  sometimes 
into  it.  It  is  closely  attached  to  the  capsule  in  front. 

The  crucial  ligaments  *  (Figs.  419,  420)  are  two  broad,  thick  bands, the  strong- 
est in  the  joint.  The  anterior  arises  from  the  depression  in  front  of  the  spine  of  the 
tibia,  close  to  the  external  semilunar  cartilage,  and  runs  upward,  backward,  and 
outward  to  the  back  of  the  inner  side  of  the  outer  condyle.  The  posterior,  the 
stronger,  arises  from  the  back  of  the  groove  at  the  posterior  aspect  of  the  top  of  the 
bone,  and  from  its  outer  border,  leaving  the  floor  of  the  groove  and  the  transverse 
piece  of  the  spine  of  the  tibia  free  and  covered  by  synovial  membrane.  It  is  also 
closely  connected  with  the  external  semilunar  cartilage.  It  runs  forward,  upward, 
and  a  little  inward  to  the  front  of  the  outer  side  of  the  inner  condyle  and  of  the 

1  l.i«    transvcrsum  uunu.     '-'  l.iu:mimt,-i  cruclata  gcnu. 


THE   KNEE-JOINT. 


405 


intercondylar  notch.  The  fibres  from  the  external  semilunar  cartilage  run  along  it 
in  a  varying  position,  but  usually  as  a  well-defined  bundle.  When  the  joint  is 
straight  the  surface  of  the  anterior  ligament  looks  approximately  forward  and  up- 
ward, its  line  of  insertion  being  about  vertical  ;  when  it  is  fully  flexed  the  outer 
edge  is  brought  forward  so  that  the  ligament  is  somewhat  twisted  on  itself  and  the 
upper  part  looks  inward,  the  line  of  insertion  slanting  slightly  downward  and  back- 
ward. In  the  former  position  the  posterior  crucial  has  the  anterior  surface  looking 
outward,  forward,  and  downward,  the  line  of  insertion  being  horizontal,  with  the 
front  external.  With  the  knee  flexed  the  ligament  is  closely  applied  to  the  internal 
condyle. 

The  Subpatellar  Fat,  the  Ligamentum  Mucosum,  and  the  Ligamenta 
Alaria  (Figs.  419,  423). — If  the  joint  be  opened  by  dividing  the  capsule  just  above 

FIG.  420. 


Patellar  surface 


Capsule  reflected 


External  condyle 


Ant.  crucial  ligament 
Ext.  semilunar  cartilage 

Transverse  ligament1 

Coronary  ligament 
Edge  of  superior  surface  of  tibia 


Capsule  reflected 


Post  crucial  ligament 
Internal  condyle 


Internal  semilunar 
cartilage 


Coronary  ligament 


Bursa  beneath  ligamentum  patellae 


Tuberosity  of  tibia 


Right  knee-joint,  opened  and  the  knee  flexed.    Seen  from  before. 

the  patella,  or,  better,  by  splitting  the  patella  and  turning  one-half  to  either  side,  a 
large  mass  of  fat  is  seen  inside  the  capsule,  below  the  patella  and  above  the  front 
and  top  of  the  tibia,  covered  by  the  synovial  membrane.  This  mass  has  a  definite 
shape,  though,  of  course,  subject  to  change  by  pressure.  It  is  perhaps  best  described 
as  pyramidal,  the  base  being  towards  the  surface  between  the  knee-pan  and  the  tibia. 
When  the  knee  is  straight  it  fills  the  patellar  surface  of  the  femur  and  laterally 
passes  'under  the  condyles,  filling  the  space  between  them  and  the  tibia.  It  reaches 
to  the  semilunar  cartilages.  Towards  the  joint  it  has  two  free  angles,  a  larger  one 
below  entering  between  the  bones  as  just  described  and  a  smaller  one  above.  The 
lateral  halves,  including  the  synovial  covering,  are  called  the  alar  ligaments  l  (Figs. 
419,  423).  From  the  middle  of  this  mass  below  the  patella  runs  a  collection  of  fat 
with  areolar  and  elastic  tissue,  invested  by  synovial  membrane,  to  the  top  of  the  inter- 
condylar notch.  This  is  the  ligamentum  mucosum,2  of  little  strength  and  not 
absolute  constancy,  which  acts  as  a  guy,  preventing  the  mass  of  fat  from  falling 
away  from  the  femur.  There  are  also  collections  of  fat  about  the  crucial  ligaments 
and  at  the  back  of  the  joint  between  the  posterior  crucial  and  the  capsule. 

The  synovial  membrane  lines  the  capsule  in  a  general  way,  but  is  separated 

1  Plicae  alares.     -  Plica  synovialis  patellae. 


406 


HUMAN    ANATOMY. 


from  it  by  the  masses  of  fat  just  described.  It  surrounds  the  lower  halves  of  the 
crucial  ligaments  with  the  fat  in  a  common  envelope,  so  that  there  is  in  nature  no 
interval  between  them.  There  is  but  a  small  chink  between  the  upper  halves, 
though  each  has  its  separate  sheath.  The  back  of  the  posterior  crucial  is  partly  un- 
covered by  synovial  membrane.  Synovial  fringes  formed  by  the  membrane  and 
more  or  less  underlying  tissue  project  from  the  folds  of  the  alar  ligaments,  from  the 
ligamentum  mucosum,  and  from  near  the  borders  of  the  patella. 

Bursae. — ( i )  The  most  important  is  a  large  one  under  the  extensor  tendons, 
just  above  the  capsule,  with  which  it  usually  communicates.  It  probably  in  most 
cases  develops  independently  of  the  capsule,  which  then  lies  in  front  of  its  lowest 

FIG.  421. 

Posterior  surface  of  femur 


Gastrocnemius-, 

Back  of  capsule 

Internal  condyle 

Post,  crucial  ligament 

Int.  semilunar  cartilage 
Tibia 


Gastrocnemius 


Insertion  of  anterior 
crucial  ligament 

External  condyle 


Ext.  semilunar  cartilage 
Tendon  of  popliteus 
Tendon  of  biceps 


Fibula 


Frontal  frozen  section  of  right  knee-joint  passing  through  condyles  and  behind  shaft  of  femur.    Seen  from  behind. 

The  superior  tibio-hbular  joint  is  opened. 

part,  a  communication  forming  subsequently.  Such  a  communication  almost 
always  exists  in  the  adult,  less  frequently  in  the  infant.  The  opening  may  be  small 
and  well  defined  or  so  large  that  the  cavities  of  the  joint  and  bursa  give  no  sign  of 
subdivision.  This  carries  the  cavity  of  the  joint  any  part  of  three  finger-breadths 
above  the  knee-pan.  It  is  possible  that  sometimes  there  is  a  communication  from 
the  beginning.  (2)  Prepatellar  bursce  are  found  on  the  front  of  the  patella 
at  different  depths.  Directly  below  the  skin  is  the  superficial  fascia,  often  lamel- 
lated  and  adherent  to  the  layer  beneath  it.  According  to  Bize,1  (#)  a  bursa  is 
present  in  this  superficial  layer,  usually  over  the  lower  half  of  the  patella,  in  eighty- 
eight  per  cent,  of  knees  examined.  The  next  layer  is  an  aponeurotic  one  continu- 
ous with  the  fascia  lata,  beneath  which  (<£)  a  bursa  is  found  in  ninety-five  per  cent., 
most  commonly  at  the  inner  inferior  part.  A  still  deeper  (c}  bursa  occurs  beneath 

1  Journal  de  1'Anat.  et  de  la  Phys.,  1896. 


THE   KNEE-JOINT. 


407 


the  fibrous  layers  from  the  tendon  of  the  quadriceps  over  the  lower  part  of  the  bone 
in  eighty  per  cent.  (3)  A  large  and  constant  bursa  lies  on  the  smooth  anterior 
surface  of  the  tubercle  of  the  tibia  beneath  the  ligamentum  patellae,  which  is  inserted 
into  the  lower  part.  It  extends  upward  to  about  the  level  of  the  top  of  the  tibia, 
from  which  it  is  separated  by  the  fat  below  the  knee.  It  practically  never  communi- 
cates with  the  knee-joint.  As  the  tendon  before  it  is  inserted  obliquely,  descend- 
ing lower  on  the  outer  side,  the  shape  of  the  bursa  is  roughly  triangular.  The 
greatest  diameter  is  the  transverse  one  at  the  top,  the  outer  border  is  not  quite  so 
long,  and  the  inner  about  half  the  length  of  the  outer.  The  breadth  is  from  3  to  4 
centimetres,  the  outer  border  from  2.5  to  4,  and  the  inner  from  1.5  to  2.5  centi- 
metres. (4)  A  subcutaneous  bursa  is  often  found  over  the  tuberosity  of  the  tibia 


Posterior  crucial  ligament 

Anterior  crucial  ligament 
Capsule 

Internal  semilunar 
cartilage 

Fascia  lata 


Fascia  lata 


External  semilunar 
cartilage 

Capsule 


\  wMLiiiiiMiiiii'M'ai/aiii^^^u.'Ui.'^ii'^y  ill'    I'll/     i-.fttn  ) 
Frontal  section  through  middle  of  right  knee-joint.    Seen  from  hehind. 


and  (5)  another  over  the  ligament  of  the  patella.  At  the  back  of  the  knee  there  are 
several  bursae.  (6)  The  largest  is  that  beneath  the  inner  head  of  the  gastrocne- 
mius  (Fig.  426),  which  later  in  life  often  connects  with  the  joint.  It  is  usually 
prolonged  between  the  gastrocnemius  and  the  tendon  of  the  semimembranosus. 
(7)  A  bursa  is  commonly  found  between  the  long  lateral  ligament  and  the  tendon 
of  the  popliteus  as  it  passes  beneath  it,  and  another  between  the  ligament  and  the 
tendon  of  the  biceps. 

The  relations  of  the  tendon  of  the  popliteus  muscle  are  so  important  as  to  re- 
quire a  separate  description.  The  muscular  belly  is  usually  separated  from  the  back 
of  the  tibia,  near  the  top,  by  a  prolongation  of  the  capsule  between  the  tibia  and  the 
back  of  the  external  semilunar  cartilage,  which  is  described  by  some  as  a  bursa  com- 
municating with  the  joint.  According  to  either  view,  there  is  a  deficiency  of  the 
coronary  ligament  at  this  point.  The  muscle  is  connected  beyond  this  with  the 
outer  side  of  the  external  semilunar  cartilage.  Passing  above  this,  it  becomes  a  part 


408 


HUMAN    ANATOMY. 


of  the  capsule^  and  on  reaching  its  insertion  it  makes  a  more  or  less  prominent  pro- 
jection into  the  joint.  There  may  or  may  not  be  a  projection  of  the  capsule  like  a 
bursa  at  the  point  where  the  two  are  .fused.  On  its  way  the  tendon  often  sends 
some  fibres  to  the  posterior  crucial. 

Movements. — The  motions  between  the  femur  and  the  patella  will  be  consid- 
ered after  those  between  the  thigh  and  the  leg.  The  knee  cannot  be  a  hinge-joint, 
for  in  such  the  moving  part  is  always  at  the  same  distance  from  the  axis  of  rotation, 
which  is  out  of  the  question  in  the  knee,  owing  to  the  shape  of  the  condyles.  The 
fact  that  these  are  neither  of  equal  length  nor  parallel  complicates  the  problem.  The 
joints  are  further  subdivided  by  the  semilunar  cartilages,  which  make  a  slight 
socket  for  each  condyle.  This  socket  is  more  or  less  movable  and  also  compressible 
and  elastic,  so  that  it  may  change  its  shape  to  accommodate  itself  to  the  form  of 

FIG.  423. 


Tendon  of  extensor  quadriceps 


Capsule 

Post,  crucial  ligament 

Internal  condyle 
Alar  ligament 


Capsule 
Ligamentum  mucosum 

External  condyle 
Alar  ligament 


Ligamentum  patellae 


Tubercle  of  tibia 


Patella  removed  from  right  knee,  which  is  strongly  flexed  to  show  alar  ligaments  and  ligamentum  mucosum.    A 

probe  is  passed  beneath  the  latter. 

different  parts  of  the  condyle.  The  external  semilunar  cartilage,  having  its  horns 
securely  attached  near  together  and  having  a  long  coronary  ligament,  can  swing 
backward  and  forward  pretty  freely  as  a  whole.  The  internal  cartilage  is  more 
closely  fastened  to  the  tibia,  excepting  the  anterior  horn,  which  has  no  constant 
arrangement.  Not  only  can  the  semilunar  cartilages  change  shape,  but,  as  Braune 
has  shown,  the  cartilage  of  the  joint  is  capable  of  compression.  For  all  these 
reasons  accurate  mathematical  statements  are  impossible. 

In  extension  of  the  .leg  on  the  thigh,  beginning  with  the  knee  flexed,  the  tibia 
travels  along  the  irregular  curve  of  the  condyles,  carrying  the  semilunar  cartilages 
with  it.  There  is  practically  no  movement  between  the  internal  cartilage  and  the 
tibia,  unless  at  the  end,  and  probably  little  beneath  the  external.  The  external 
tuberosity  of  the  tibia  reaches  the  front  of  the  shorter  condyle  before  the  internal 
tuberosity  has  completed  its  course.  The  last  part  of  the  advance  of  the  latter  is 
accompanied  by  an  outward  rotation  of  the  tibia  on  a  vertical  axis  passing  through 
about  the  middle  of  the  outer  condyle,  so  that  while  the  inner  tuberosity  still  swings 


PRACTICAL   CONSIDERATIONS:   THE   KNEE-JOINT.  409 

forward,  the  outer  part  of  the  external  swings  back.  This  motion  occurs  below  the 
external  semilunar  cartilage.  Flexion  begins  with  a  corresponding  inverse  rotation 
of  the  tibia.  While  the  knee  is  straight  the  tibia  is  firmly  fixed,  so  that  in  rotation 
of  the  limb  at  the  hip  the  bones  move  as  one.  The  long  lateral  ligament  and  that 
part  of  the  capsule  called  the  internal  ligament  are  placed  so  far  back  that  they  are 
relaxed  in  flexion  but  become  tense  in  extension.  Both  the  crucial  ligaments  are 
always  nearly  tense,  especially  the  posterior.  The  anterior  is  quite  tense  in  exten- 
sion, the  posterior  in  flexion.  The  latter  prevents  forward  displacement  of  the 
femur  on  the  tibia  when,  as  in  alighting  from  a  leap,  the  whole  weight  is  carried  for- 
ward by  the  impetus,  the  knee  being  flexed.  Another  rotation  on  a  vertical  axis 
through  the  middle  of  the  joint  may  occur  when  the  knee  is  flexed.  The  motion 
is  between  the  femur  and  the  internal  semilunar  cartilage,  and  both  above  and  below 
the  external  one.  This  motion  is  chiefly  passive, — i.e. ,  imparted  by  another  person 
twisting  the  leg  when  the  muscles  are  relaxed.  It  probably,  however,  can  be  exe- 
cuted actively  to  some  extent.  It  is  very  slight  in  less  than  semiflexion  of  the  knee, 
and  diminishes  as  flexion  becomes  more  extreme.  The  precise  angle  at  which  it  is 
greatest  seems  uncertain.  Rotation  of  the  tibia  outward,  tending  to  untwist  the 
crucial  ligaments,  is  resisted  by  neither,  but  by  the  internal  lateral  ligament.  Rota- 
tion inward  is  resisted  by  both  crucials,  especially  the  anterior,  and  by  the  external 
lateral.  The  posterior  ligament  is  made  tense  in  life  in  positions  in  which  it  would 
otherwise  be  lax  by  the  action  of  the  semimembranosus.  It  is  tense  in  extension.  The 
front  part  of  the  capsule  is  tense  in  flexion  and  relaxed  in  extension,  but  its  condi- 
tion in  the  latter  state  is  considerably  modified  by  the  degree  of  contraction  of  the 
quadriceps  extensor. 

Movements  of  the  Patella.— The  patella  in  the  upright  position,  when  the 
muscles  are  relaxed,  has  the  lower  part  of  the  articular  surface  resting  against  the 
top  of  that  of  the  femur.  When  the  muscle  is  contracted  the  former  is  drawn 
entirely  above  the  latter.  As  flexion  begins  the  lower  zone  of  the  articular  surface 
fits  into  the  groove  on  the  femur,  the  two  upper  and  the  internal  strip  not  being  in 
contact  with  it.  In  semiflexion  the  knee-pan  has  passed  below  the  patellar  surface 
of  the  femur,  and  the  middle  zone  rests  on  the  front  of  the  outer  condyle  and  on  a 
small  part  of  the  inner.  As  flexion  becomes  extreme  the  patella  follows  the  outer 
condyle,  resting  on  its  under  side  by  its  superior  zone,  the  convex  portion  is  in  the 
notch,  and  only  the  strip  along  the  inner  edge  is  in  contact  with  the  outer  side  of  the 
internal  condyle.  In  the  latter  part  of  the  movement  the  mucous  ligament  becomes 
tense,  and  through  it,  and  still  more  by  atmospheric  pressure,  the  alar  ligaments  are 
brought  close  in  to  fill  the  chink  between  the  femur  and  the  tibia. 

PRACTICAL   CONSIDERATIONS. 

The  Knee-joint. — The  anatomical  conditions  which  should  render  the  knee- 
joint  peculiarly  subject  to  dislocation  are  as  follows  :  i.  Its  situation  between  the 
longest  bones  of  the  skeleton  and  its  consequent  exposure  to  tremendous  leverage. 
2.  Its  similar  exposure  to  frequent  strain  and  traumatism.  3.  The  extensive  and 
varied  character  of  its  movements.  4.  The  absence  of  bony  prominences,  which 
could  effectively  strengthen  the  joint,  upon  either  the  articular  surface  of  the  lower 
end  of  the  femur  or  the  shallow  upper  surface  of  the  tibial  tuberosities. 

The  ability  of  the  joint  to  resist  dislocation,  which  is  of  very  rare  occurrence, 
lies  in  («)  the  strength  of  the  ligaments,  especially  the  crucial  ;  (£)  the  expansions 
of  the  quadriceps  tendon  on  the  front  of  the  joint  ;  (>)  the  reinforcement  of  the 
posterior  ligament  by  the  semimembranosus  tendon  ;  (d)  the  similar  relation  of  the 
internal  lateral  ligament  to  the  semimembranosus,  and  of  the  external  lateral  to  the 
tendons  of  the  biceps  and  popliteus  ;  (e)  the  power  thus  conferred  upon  strong 
muscles  to  meet  and  modify  or  resist  sudden  strains  by  varying  the  tension  of  the 
capsule  and  even  of  the  ligaments  ;  (/)  the  deepening  of  the  tibial  cup  by  the  semi- 
lunar  cartilages,  and  the  adaptation  of  the  latter  to  the  varying  positions  of  the  bones 
so  that  the  contact  between  and  pressure  upon  the  joint-surfaces  are  as  extensive  and 
as  uniform  as  the  shape  of  the  condyles  will  permit. 

Dislocations  of  the  knee  may  be  antero-posterior  or  lateral  in  direction.      The 


410  HUMAN   ANATOMY. 

former  usually  and  the  latter  invariably  are  incomplete,  owing  to  the  large  superficial 
areas  of  the  joint-surfaces.  In  the  great  majority  of  cases  dislocations  of  the  knee 
are  due  to  indirect  violence  acting  through  the  femur  as  a  lever, — as,  for  example,  in 
falls  forward,  the  foot  and  leg  being  fixed.  The  weight  of  the  trunk  carrying  the 
upper  end  of  the  thigh  forward,  brings  the  lower  end  with  great  power — the  fulcrum 
and  the  resistance,  or  weight,  being  so  close  to  each  other — against  the  posterior 
ligament,  a  rupture  of  which  permits  the  movement  to  continue  and  results  in  an 
anterior  dislocation  of  the  knee,  which  is,  regarded  from  an  etiological  stand-point, 
a  displacement  of  the  femur  backward. 

If  the  fall  is  in  the  opposite  direction,  the  femur  may  be  displaced  anteriorly, — 
i.e. ,  posterior  dislocation  of  the  knee  may  occur.  Occasionally  the  anterior  disloca- 
tion has  followed  the  fall  of  a  weight  upon  the  front  of  the  femur.  The  application 
of  force  to  the  front  of  the  leg  when  the  knee  was  flexed  has  produced  a  posterior 
dislocation,  the  effect  of  the  biceps,  popliteus,  and  semimembranosus  in  reinforcing 
the  posterior  ligament  being  minimized  in  that  position. 

Lateral  dislocations  are  caused  by  adduction  or  abduction  of  the  leg,  the  thigh 
being  fixed,  or  by  falls  sideways  when  the  foot  and  leg  are  fixed.  The  great  width 

FIG.  424. 

Vastus  internus 
Patella -_^  , 


Lateral 
expansion  of 
quadriceps 
tendon 


Tendon  of 
adductor  inagnus 


Tibia' 

v  Internal  condyle 


„ 


Tendon  of  sartorius 
Inner  aspect  of  right  knee-joint,  showing  expansion  of  quadriceps  tendon. 

of  the  joint  and  the  slight  resistance  offered  by  the  interposition  of  the  tibial  spine 
between  the  femoral  condyles  render  them  rarer  than  antero-posterior  luxations. 

Forward  dislocation  is  more  common,  possibly  because  of  the  greater  laxity 
of  the  capsule  in  front,  and  is  more  apt  to  be  complete  than  the  backward.  The 
knee  is  extended  ;  the  tibial  tubercle  prominent ;  the  antero-posterior  diameter 
increased  ;  the  anterior  margin  of  the  tibial  tuberosities  palpable  in  front  ;  the 
rounded  condyles  may  be  felt,  but  less  distinctly  posteriorly  ;  the  popliteal  concavity 
is  obliterated  ;  the  aponeurotic  expansion  of  the  quadriceps  is  loose  and  lies  in  folds 
about  the  upper  border  of  the  patella.  The  femoral  vessels  and  nerves  may  be 
bruised,  compressed,  or  lacerated. 

In  backward  dislocation  also  the  knee  is  in  extension  and  the  antero-posterior 
diameter  increased.  The  displaced  bony  prominences  may  be  recognized  by  palpa- 
tion. This  dislocation  is  even  less  apt  to  be  complete  than  the  forward  variety  :  but 
if  it  is,  the  vessels  and  nerves  are  oftener  injured,  as  shown  by  the  more  frequent 
occurrence  of  gangrene.  This  is  probably  due  to  the  sharpness  and  prominence  of 
the  backward  projection  of  the  upper  edge  of  the  tibial  tuberosities,  as  compared 
with  the  rounded  depressed  notch  between  the  femoral  condyles  which  receives  the 
vessels  in  forward  dislocation. 

In  lateral  dislocation,   in  accordance  with  the  direction  of  the  displacement, 


.PRACTICAL   CONSIDERATIONS:    THE   KNEE-JOINT.  411 

one  or  other  condyle  becomes  prominent,  as  does,  on  the  opposite  aspect  of  the 
limb,  the  head  of  the  fibula  or  the  inner  tuberosity  of  the  tibia.  The  patella,  owing 
to  the  shortness  and  strength  of  its  ligament,  is  carried  with  the  tibia.  The  lateral 
diameter  of  the  joint  is  increased.  The  foot  is  apt  to  be  rotated  in  the  direction  of 
the  luxation  owing  to  the  tension  of  the  biceps  in  the  outward  and  of  the  popliteus 
and  inner  hamstrings  in  the  inward  variety. 

Dislocations  by  rotation  have  also  occurred. 

FIG.  425. 

///  /  Femur 


Internal  semilunar 
cartilage 


Crucial  ligaments 


External  semilunar 
cartilage 


Cavity  of  knee-joint 


Superior  tibio-fibular 
articulation 


Tibia  .  Fibula 

Frontal  section  through  knee-joint,  showing  articulating  surfaces  and  epiphyseal  lines. 

In  the  various  forms  of  luxation  the  crucial,  the  lateral,  and  the  posterior  liga- 
ments and  the  biceps  and  gastrocnemius  muscles  suffer  most  severely  ;  the  popliteus 
and  semimembranosus  less  so.  They  are  often  compound,  and  may  for  that  reason 
necessitate  amputation.  The  injury  to  the  ligaments  leaves  the  joint  weak  and 
insecure  for  a  long  time. 

Subluxation  of  the  semilunar  cartilages  occurs  usually  when  the  leg  is  fixed, 
the  knee  slightly  flexed,  and  the  femur  rotated  upon  the  tibia,  because  the  move- 
ments of  flexion  and  extension  take  place  between  the  femur  and  these  cartilages, 
which,  therefore,  follow  the  motion  of  the  tibia  ;  whereas  in  rotation — the  move- 


4i2  HUMAN   ANATOMY. 

meats  then  occurring  between  the  tibia  and  the  cartilages — one  of  them  is  fixed 
between  the  corresponding  condyle  and  the  tibia  which  rotates  beneath  it  ;  the 
remaining  cartilage,  especially  if  the  rotation  is  marked,  may  be  dragged  or  squeezed 
so  that  it  is  nipped  between  the  tibia  and  femur.  Thus  the  contraction  of  the  biceps 
which  effects  outward  rotation  of  the  leg  brings  more  closely  together  the  external 
tuberosity  of  the  tibia  and  the  external  condyle,  and  the  outer  cartilage  is  held  firmly 
between  them.  This  increases  slightly  the  distance  between  the  internal  condyle  and 
the  head  of  the  tibia,  leaving  the  internal  cartilage  freer  to  move  into  an  abnormal 
position.  When  the  popliteus,  semitendinosus,  and  semimembranosus  contract  to 
rotate  the  leg  inward,  they,  in  like  manner,  fix  the  internal  cartilage  and  allow  of 
increased  mobility  of  the  external  cartilage. 

Subluxation  of  the  inner  cartilage  is  the  more  frequent  because  (i)  outward 
rotation  of  the  leg  is  far  more  common  than  inward  rotation  ;  (2)  the  muscle  chiefly 
concerned  in  effecting  inward  rotation, — the  popliteus, — when  it  contracts,  steadies 
and  supports  the  external  cartilage  by  pressure  against  its  outer  margin  (Morris)  ; 
no  corresponding  support  is  given  the  internal  cartilage  during  outward  rotation  ; 
(3)  the  anterior  crucial  ligament  is«attached  somewhat  in  front  of,  and  often  directly 
to  the  inner  cornu  of  the  external  cartilage,  tending  to  limit  its  forward  motion.  It 
is  altogether  behind  the  internal  cartilage  ;  (4)  the  external  cartilage  has  a  strong 
attachment  to  the  femur  through  the  ligament  of  Wrisberg  posteriorly. 

The  displacement  is  forward  in  the  majority  of  cases.  The  symptoms  are  pain, 
from  the  pressure  on  the  cartilage  itself,  increased  by  reflex  spasm  of  the  muscles 
moving  the  joint,  and  followed  by  a  synovitis.  The  edge  of  the  cartilage  may  often 
be  felt. 

Disease  of  the  knee-joint  is  of  great  frequency  on  account  of  its  exposure  to  (a) 
direct  violence  and  to  cold  and  wet,  by  reason  of  its  superficial  position,  and  (6*)  to 
strains  and  wrenches  through  the  leverage  of  the  femur  and  tibia.  The  factors 
competent  to  resist  luxation  are  not  able  to  protect  it  from  minor  injuries.  It  is  a 
favorite  seat,  therefore,  of  traumatic  synovitis,  and — on  account  also  of  its  complexity, 
its  large  size,  and  the  difficulty  in  keeping  it  at  absolute  rest — disease,  if  acute,  is 
apt  to  be  severe  and  threatening  ;  if  subacute,  tends  to  become  chronic  or  to  recur. 
All  the  above  reasons,  combined  with  its  inclusion  of  the  lower  femoral  epiphysis 
and  its  close  relation  to  the  upper  tibial  epiphysis, — the  seats  of  the  chief  growth  of 
the  lower  limb, — make  it  also  one  of  the  joints  most  commonly  subject  to  tuberculous 
disease,  while  gout,  rheumatism,  and  syphilitic  and  gonococcic  infection  are  often 
localized  in  it. 

Most  of  the  chronic  diseases  due  to  infection,  as  well  as  those  directly  following 
traumatism,  begin  in  the  synovial  membrane  because  of  the  large  superficial  expanse 
of  that  membrane.  The  intra-articular  effusion — whether  "simple,"  from  hyper- 
lemia,  or  inflammatory,  from  infection — causes  the  knee  to  assume  the  position  of 
moderate  flexion  because  ( i )  its  capacity  is  then  greater  than  in  full  extension  or 
full  flexion,  and  maximum  capacity  is  equivalent  to  minimum  pressure  ;  (2)  flexion, 
relaxes  the  densest  and  most  resistant  ligaments, — the  posterior  and  the  lateral  (as 
they  are  attached  behind  the  centre  of  the  bone)  and  (if  moderate)  the  posterior 
crucial.  It  is  resisted  only  by  the  ligamentum  patellae,  which  is  in  less  close  rela- 
tion to  the  joint  (being  separated  by  the  pad  of  fat  on  which  it  lies),  and  by  the 
thinner  and  more  extensible  anterior  portion  of  the  capsule  ;  (3)  the  joint  is  inner- 
vated in  accordance  with  the  general  law  that  the  same  nerves  which  supply  the 
interior  of  an  articulation  supply  also  both  the  muscles  moving  it  and  the  skin  over 
the  insertion  of  those  muscles  (Hilton).  The  knee-joint  is  acted  on  by  ten  muscles, 
four  of  which  are  extensors  and  six  flexors.  The  latter  are  not  only  numerically  in 
excess,  but  are  also  the  more  powerful  and  the  more  favorably  situated  for  acting 
upon  the  joint.  Therefore,  when  the  articular  twigs  of  the  obturator,  sciatic,  and 
anterior  crural  nerves  are  irritated  by  disease,  and  both  the  anterior  and  posterior 
groups  of  muscles  contract  reflexly,  the  flexors  predominate.  The  principle  is  of 
wide-spread  application,  and  should  be  considered  in  reference  to  the  position  of 
most  joints,  at  least  in  the  early  stages  of  disease. 

Later  in  knee-joint  disease  the  softening  and  elongation  of  the  ligaments  permit 
the  pull  of  the  flexors  to  produce  posterior  displacement  of  the  bones  of  the  leg 


PRACTICAL   CONSIDERATIONS:    THE   KNEE-JOINT.  413 

upon    the    thigh.       This   is   aided  in   dorsal  decubitus  by  gravitation,    which  also 
favors  the  outward  rotation  of  the  leg  that  commonly  occurs  at  the  same  time. 

The  swelling  of  synovitis,  whether  acute  or  chronic,  is  limited,  until  the  capsule 
gives  way,  by  the  attachments  of  the  synovial  membrane, — that  is,  it  extends  upward 
beneath  the  rectus  for  from  two  to  three  finger-breadths  or  from  four  to  five  centi- 
metres (one  and  a  half  to  two  inches)  above  the  summit  of  the  patella  ;  laterally,  it 
reaches  the  same  level  under  the  vastus  internus,  but  is  not  quite  so  high  on  the 
other  side,  under  the  vastus  externus.  Downward,  it  descends  to  nearly  the  middle 
of  the  ligamentum  patellae,  attaining  the  same  level  on  the  inner  side,  but  stopping 


FIG.  426. 


Tendon  of  extensor  quadriceps 
. — Suprapatellar  bursa 


• — Cavity  of  joint 


-Patella 


External  condyle— 


— Prepatellar  bursa 


External  lateral  ligament — 
Tendon  of  popliteus 
Popliteal  bursa — 

Head  of  fibula  - 


— External  semilunar 
cartilage 

Ligamentum  patellae 


Subpatellar  bursa 


-Tubercle  of  tibia 


_  Tibia 


Rit,rht  knee-joint.    The  joint-cavity  and  several  bursae  have  been  distended  with  injection  mass  before  dissection. 

(Spalteholz.) 

just  above  the  head  of  the  fibula  on  the  outer  side.  The  patella  is  separated  from 
the  trochlea  of  the  femur — "  floated  up."  In  testing  for  this  symptom,  it  is  impor- 
tant to  grasp  the  anterior  muscles  of  the  thigh  firmly  and  draw  them  towards  the 
knee  so  as  to  relax  the  pull  of  the  quadriceps,  which  is  occasionally  great  enough  to 
hold  the  patella  in  contact  with  the  femur,  even  in  the  presence  of  considerable 
effusion  (Fig.  426). 

The  condition  is  usually  unmistakable,  but  may  have  to  be  differentiated  from 
periarticular  abscess  or  haematoma.  In  the  latter  cases  the  swelling  will  not  be 
uniform  ;  the  inner  depression  at  the  side  of  the  patella  may  be  obliterated,  and  not 


HUMAN   ANATOMY. 


FIG.  427. 


the  outer,  or  vice  versa ;  fluctuation  cannot  be  obtained  in  every  direction, — i.e., 
from  side  to  side  under  the  patella  or  obliquely  ;  the  patella  will  lie  directly  upon 
the  femur. 

The  diagnosis  from  bursal  enlargements  will  be  considered  in  relation  to  those 
structures. 

Syphilitic  disease  of  the  gummatous  type  is  apt  to  begin  in  the  subcutaneous 
tissue  without  the  joint,  which  it  involves  secondarily.  In  its  earlier  stages  the 
swelling  would  therefore  be  periarticular,  and  recognizable  by  the  foregoing  symp- 
toms. Later,  as  it  extends  in  both  directions,  there  will  usually  be  ulceration  of 
the  skin. 

The  knee  is  more  often  the  seat  of  the  so-called  loose  bodies  than  is  any  other 
joint.  They  are  sometimes  the  result  of  osteo-arthritis  (which  affects  the  knee  by 

preference),  causing  thickening  and  fibrinous 
or  calcareous  change  in  some  of  the  syno- 
vial  fringes  ;  or  they  may  be  produced  in 
those  fringes  from  embryonic  remnants,  and 
are  then  composed  of  hyaline  cartilage  or 
nbro-cartilage  ;  or  they  may  result  from  the 
organization  of  inflammatory  lymph  after  an 
acute  arthritis- ;  or  they  may  be  portions  of 
an  interarticular  or  articular  cartilage  de- 
tached by  violence,  although  this  is  rare. 

In  a  case  of  suppurative  arthritis  the 
incisions  for  drainage  should  be  made  on 
either  side  of  the  patella  and  a  little  below 
its  middle,  and  should  be  placed  towards 
the  posterior  aspect  of  the  lateral  pouches 
of  the  synovial  membrane. 

Genu  I'algum  —  "  knock-knee"  —  in 
young  children  may  be  directly  due  to 
rickets,  or  may  follow  Charcot's  disease,  in- 
fantile paralysis,  or  any  sprain  or  dislocation 
of  the  knee  that  leaves  the  internal  lateral 
ligament  weak  or  defective.  In  children 
and  adolescents  without  these  antecedents 
its  essential  cause  is  still  a  matter  of  dispute. 
There  can  be  no  doubt,  however,  that  in 
the  great  majority  of  cases  the  production 
of  the  deformity  is  favored  by  static  modi- 
fications of  certain  anatomical  conditions 
which  are  probably  the  cause  and  not  the 
result  of  the  diaphyseal  overgrowth  of 
femur  and  tibia  (Mikulicz),  of  the  contrac- 
tion of  the  biceps  and  tensor  vaginae  femoris 
(Duchenne),  of  the  elongation  of  the  in- 
ternal lateral  ligament  (Stromeyer),  and  of 
the  atrophy  of  the  external  condyle  (Oilier) 
which  are  found  in  most  cases  of  this  de- 
formity, and  each  of  which  has  been  given  etiological  importance. 

The  angle  between  the  femoral  and  tibial  axes  (corresponding  to  that  between 
the  arm  and  forearm)  opens  outward  at  the  knee.  It  results  not,  as  in  the  upper 
extremity,  from  an  outward  obliquity  of  the  lower  segment  of  the  limb,  but  from  the 
inward  slant  of  the  thighs  from  the  pelvis  to  the  knees,  the  tibiae  (like  the  humerus) 
being  parallel  to  the  longitudinal  axis  of  the  body  and  to  each  other.  That  the  line 
of  the  knee-joint  may  be  hori/oiital,  the  internal  condyle  of  the  femur  is  longer  than 
the  external.  In  a  normal  person  standing  erect  in  the  military  attitude  of  "atten- 
tion" the  weight  of  the  trunk  is  transmitted  downward  from  the  head  of  the  femur 
in  a  vertical  line  which  passes  through  the  external  condyle  (Fig.  427).  The  erect 
position  must  therefore  be  maintained,  not  merely  through  the  approximation  of  the 


Line  of  pressure  between  hip  and  knee. 


FIG.  428. 


PRACTICAL   CONSIDERATIONS:    THE   KNEE-JOINT.  415 

bones,  as  would  be  the  case  if  the  axis  of  the  whole  lower  limb  were  a  perpendicular 
running  through  the  acetabulum  and  the  centre  of  the  ankle-joint,  but  by  the  help 
of  muscular  and  ligamentous  structures. 

The  tendency  (which  is  so  common  a  factor  in  the  production  of  deformities) 
to  assume  an  attitude  which  will  transfer  strain  from  a  tired  muscle  to  the  neighboring 
ligaments  operates  here  to  cause  stretching  and  elongation  of  the  internal  lateral 
ligament,  as  the  ' '  attitude  of  rest' '  with  the  feet  separated  and  everted  is  the  one 
usually  adopted.  The  evil  effects  are,  of  course,  favored  by  much  standing,  and  are 
most  marked  in  young  persons  of  feeble  physique  whose  weight  has  increased  dis- 
proportionately to  their  muscular  strength.  The  outer  side  of  the  knee  shows  the 
changes  due  to  increased  pressure  and  to  long-continued  approximation  of  musculo- 
tendinous  points  of  origin  and  insertion, — i.e.,  atrophy  of  the  outer  condyle  and 
outer  tuberosity  ;  contraction  and  shortening  of  the  ilio-tibial  band  of  fascia,  of  the 
external  lateral  ligament,  of  the  tendon  of  the  biceps,  and  of  the  tensor  vaginae 
femoris.  The  inner  side  shows  the  effects  of  removal  of  normal  pressure  from  grow- 
ing bones  and  of  chronic  strain  of  fibrous  and  periosteal  tissue, — i.e. ,  overgrowth  of 
the  femoral  diaphysis  just  above  the  inner  end  of  the  epiphyseal  line  and  of  the  tibial 
diaphysis  just  below  the  corresponding  level  ;  lengthening  of  the  internal  lateral 
ligament  ;  bony  outgrowth  at  its  tibial  insertion  from  chronic  periostitis. 

The  tibia  is  apt  to  be  rotated  outward,  possibly  through  the  action  of  the  short- 
ened biceps.  Talipes  valgus  (q.v. )  may  be  either  a  cause  or  a  result  of  genu  valgum. 
The  disappearance  of  the  deformity  when  the  knees  are  flexed 
is  probably  due  to  the  outward  rotation  of  the  femur  that  ac- 
companies flexion,  and  not,  as  is  generally  stated,  to  the  fact 
that  the  antero-posterior  diameter  of  the  condyles  is  unaffected 
by  the  disease. 

The  clinical  symptoms  and  results  and  the  treatment  by 
apparatus  cannot  be  described  here. 

In  Maceweri  s  osteotomy  the  femur  is  divided  from  the  inner 
side  of  the  thigh  at  a  point  twelve  millimetres  (half  an  inch) 
above  the  adductor  tubercle  and  in  a  line  at  right  angles  to 
the  long  axis  of  the  femur.  Osteotomy  may  also  be  done  from 
the  outside  of  the  thigh  and  at  the  same  level.  These  opera- 
tions are  usually  safe,  but  the  popliteal  artery,  the  anastomotica 
magna,  the  external  peroneal  nerve,  and  other  important  struc- 
tures have  been  accidentally  divided. 

Genu  varum — "  bow-leg" — is  almost  always  rhachitic  in  its 
origin.  A  child  with  rickets  and  having  lumbar  lordosis  of  the 
spine  stands  with  its  thighs  slightly  flexed,  either  as  a  secondary 
result  of  the  shortening  of  the  ilio-femoral  ligaments  produced 
by  backward  rotation  of  the  pelvis  (to  compensate  for  the  for- 
ward rotation  of  the  sacrum)  or  more  simply  as  an  easy  method 
of  relaxing  the  weak  ilio-psoas  muscles  and  preserving  the 
centre  of  gravity.  As  the  thighs  flex  the  knees  separate,  the 
femurs  rotate  outward  on  their  own  axes,  the  line  of  gravity 
falls  to  the  inside  of  the  centre  of  the  knee-joint  (Fig.  428),  the 
pressure  is  greatest  on  the  inner  condyle  and  tuberosity,  the  strain  comes  upon  the 
external  lateral  ligament,  and  the  outward  bowing  begins  and  is  continued  by  the 
leverage  of  the  body  weight. 

Genu  recurvattim — "  back-knee" — is  a  deformity  in  which,  as  a  result  of  intra- 
uterine  malposition,  or  of  congenital  paralysis  of  the  flexors  and  popliteus,  or  of 
pressure  brought  upon  the  posterior  and  crucial  ligaments  in  walking  in  a  case  of 
partial  paralysis  of  the  quadriceps,— the  limb  being  swung  forward,  the  heel  coming 
to  the  ground  in  full  extension,  and  the  weight  of  the  body  reaching  the  joint  in 
front  of  its  centre  of  gravity, — the  knee  is  bent  backward  and  the  whole  limb  presents 
a  long  curve  with  its  concavity  forward. 

In  excision  of  the  knee  the  lines  of  the  epiphysis  should  be  remembered  if  the 
patient  is  under  twenty  or  twenty-one  years  of  age  (page  365),  the  relation  of  the 
femoral  vessels  to  the  posterior  ligament,  the  situation  and  extent  of  the  synovial 


Showing  the  form  of  the 
bones  in  bow-legs. 


416 


HUMAN    ANATOMY. 


pouches  (which  in  infectious  cases  are  usually  involved),  the  direction  of  the  articular 
line  (with  which  the  saw  cut  should  be  parallel),  and  sometimes  the  possibility  of 
infection  of  the  neighboring  bursae. 

Landmarks. — The  synovial  membrane  rises  from  four  to  five  centimetres 
(one  and  a  half  to  two  inches)  above  the  upper  border  of  the  patella  ;  it  is  higher 
on  the  inner  than  on  the  outer  side  of  the  thigh  ;  its  upper  limit  descends  in  flexion 
of  the  knee. 

The  bony  points  have  been  described  in  connection  with  the  femur  and  tibia 
(pages  367,  390)  ;  the  bursae  will  be  described  later. 

The  Patella. —  Congenital  absence  of  the  patella  on  one  or  both  sides  has  been 
noted  in  a  number  of  instances,  and  has  in  some  cases  been  observed  in  several 
members  of  the  same  family.  The  functional  disability  was  slight  or  altogether 
unnoticeable. 

Fracture  by  muscular  action  is  more  common  in  this  bone  than  in  any  bone  of 
the  skeleton.  It  occurs  usually  with  the  leg  in  partial  flexion  upon  the  knee.  In 
this  position  fracture  is  favored  because  (i)  the  ligamentum  patellae  is  then  taut 
and  fixes  the  lower  edge  of  the  bone  ;  (2)  the  patella  is  in  contact  only  through  the 
upper  third  of  its  convex  under  surface  with  the  most  prominent  part  of  the  articu- 
lar surface  of  the  condyles  (Fig.  429);  and  (3)  at  this  time  the  quadriceps  extensor 


FIG.  429. 


Rectus  muscle 


tella 


Subpatellar  tissue 
Tendo  patellae 


Tibia 


Femur 

Showing  position  of  patella  in  relation  to  condyles  of  femur  with  knee  partially  flexed. 


has  the  greatest  advantage  of  leverage  upon  the  patella,  as  when  the  knee  is  fully 
bent  the  muscle  gets  its  leverage  for  the  beginning  of  extension  through  the  projec- 
tion of  the  front  of  the  condyles,  and  the  patella  lies  on  the  pad  of  fat  between  the 
femur  and  tibia  (Fig.  430),  and  when  the  knee  is  almost  or  quite  extended,  the 
patella — or  three-fourths  of  it — occupies  the  depression  of  the  trochlea,  or  even  that 
just  above  it.  As  a  result  of  the  cross-strain  brought  to  bear  in  the  partially  flexed 
position  the  bone  usually  breaks  transversely  a  little  below  its  mid-line, — i.e.,  through 
the  area  unsupported  by  the  femur  beneath  (Fig.  429).  Occasionally  it  gives  \\av 
at  a  higher  level. 

The  accident  may  happen  as  the  result  of  a  fall,  but  the  fall  is  more  apt  to 
follow  than  to  precede  the  fracture.  In  ordinary  falls  upon  the  knee  the  force  is 
received  upon  the  tubercle  of  the  tibia,  not  upon  the  patella. 

Direct  violence  often  causes  an  irregular,  comminuted,  or  stellate  fracture. 

Fracture  never  occurs  in  children  and  is  extremely  rare  before  adult  lik-. 
When  the  bone  is  broken  the  fragments  arc  immediately  separated  by  the  action 
of  the  quadriceps  upon  the  upper  one.  The  degree  of  their  separation  will  de- 
pend upon  the  amount  of  laceration  of  the  lateral  aponeurotic  expansions  of  the 
conjoined  tendon.  Unless  that  fibrous  structure  is  torn,  no  great  separation  of 
the  fragments  can  occur,  as  it  is  inserted  into  the  borders  and  front  of  the  patella, 


PRACTICAL   CONSIDERATIONS  :   THE   PATELLA. 

which  is  thus  embedded,  as  it  were,  in  a  hood  spread  out  over  the  front  of  the  joint 
and  extending  to  the  lateral  ligaments  and  to  the  oblique  lines  running  up  from  the 
tubercle  to  the  tuberosities  (Fig.  424).  The  force  causing  the  fracture  in  cases  of 
direct  violence,  or  atmospheric  pressure  on  the  front  of  the  knee  if  the  fracture  was 
from  muscular  action,  drives  in  between  the  fragments,  as  they  separate,  in  the 
shape  of  shreds  or  of  an  irregular  fringe,  portions  of  that  part  of  the  rectus  tendon 
which  was  inserted  into  the  longitudinal  grooves  or  striae  on  the  anterior  surface  of 
the  bone.  These  offer  an  obstacle  to  bony  union.  As  the  synovial  membrane  of 
the  knee-joint  lies  in  contact  with,  and  is  attached  to,  the  under  surface  of  the 
patella,  it  will  usually  be  lacerated, — i.e. ,  the  knee-joint  will  be  opened  and  the 
fragments  surrounded  by  bloody  synovial  fluid.  The  synovial  membrane  is  re- 
flected from  the  patella  some  distance  above  the  apex  of  the  bone  ;  hence  a  fracture 
may  occur  at  that  level  without  involvement  of  the  joint.  The  pad  of  fat  on  which 

FIG.  430. 


Patella 


Subpatellar  tissue 


Showing  position  of  patella  in  relation  to  condyles  of  femur  with  knee  flexed  at  right  angle. 


the  tip  of  the  bone  rests,  and  over  which  the  membrane  is  reflected,  may  aid  in 
saving  the  joint  from  injury. 

The  common  failure  to  get  bony  union  by  non-operative  methods  is  thus  seen 
to  be  due  to  (i)  separation  of  the  fragments  by  the  quadriceps,  (2)  the  interposition 
of  portions  of  the  capsule,  (3)  the  presence  of  blood-clot  and  synovial  fluid,  and  is 
supposed  to  be  further  favored  by  (4)  the  sesamoid  character  of  the  bone  inclining 
it  to  unite  by  fibrous  rather  than  by  bony  tissue.  It  has  been  asserted,  however 
(Wirth),  that  the  patella  is  a  detached  portion  of  the  upper  tibial  epiphysis  and  not 
a  true  sesamoid  bone. 

As  non-union  is  common  on  account  of  the  above  anatomical  conditions,  oper- 
ative measures  are  often  resorted  to.  In  the  open  operations  used  in  old  united 
fractures  the  fragments  are  drilled  obliquely  from  a  half-inch  above  and  below  the 
line  of  fracture  to  just  above  the  cartilaginous  under  surface,  so  that  the  wire  used 
to  hold  them  together  does  not  lie  in  the  joint. 

27 


418  HUMAN    ANATOMY. 

To  approximate  the  fragments  elevation  of  the  limb  sometimes  suffices,  but 
occasionally  partial  section  of  the  lateral  expansions  of  the  quadriceps,  of  the  rectus 
tendon,  and  of  the  muscle  itself  will  be  required  as  successive  steps. 

In  the  best  of  the  operations  used  in  recent  fractures,  and  which  do  not  widely 
open  the  joint,  a  silk  or  silver  ligature  is  carried  through  an  incision  at  the  lower 
border  of  the  patella  behind  that  bone  and  between  it  and  the  trochlear  groove 
in  the  femur,  is  brought  out  through  an  incision  at  the  upper  border,  rethreaded 
on  a  needle  with  an  eye  near  the  point,  brought  down  in  front  of  the  patella, — 
beneath  the  skin, — and  tied  or  twisted  so  as  to  hold  the  fragments  together.  The 
blood-clot  and  synovial  exudate  are  squeezed  out  through  the  two  incisions  ;  the 
entangled  capsular  fibres  are  removed  by  attrition  of  the  fractured  surfaces  against 
each  other.  These  operations  are,  of  course,  not  applicable  to  old  fractures  in 
which  shortening  of  the  muscle  has  taken  place  and  approximation  and  forcible  rub- 
bing together  of  the  fragments  are  impossible. 

Operations  for  recent  fracture  by  open  arthrotomy  permit  the  direct  removal  of 
the  fringe  of  interposed  tendinous  and  capsular  fibres  and  the  repair  by  suture 
of  the  rents  in  the  capsule  and  in  the  lateral  expansions  of  the  quadriceps.  The 
patellar  fragments  may  also  be  sutured,  but  this  is  not  always  necessary. 

Dislocation  of  the  patella  usually  occurs  from  muscular  action  and  as  a  conse- 
quence of  sudden  contraction  of  the  quadriceps. 

The  displacement  is  commonly  in  the  outward  direction  because  the  long  axis 
of  the  quadriceps  muscle  and  tendon  is  inclined  to  that  of  the  ligamentum  patellae 
in  such  a  way  that  the  bone  is  situated  at  the  apex  of  an  obtuse  angle  which  opens 
outward.  When  the  quadriceps  contracts  the  tendency  is  to  straighten  this  angle, 
— i.e.,  to  carry  the  patella  outward, — and  this,  aided  by  the  greater  strength  of 
the  vastus  externus  as  compared  with  that  of  the  inner  vastus,  is  more  than  suf- 
ficient to  overcome  the  resistance  offered  by  the  greater  prominence  of  the  external 
condyle,  as  well  as  the  relatively  more  extensive  insertion  of  the  vastus  interims  into 
the  inner  margin  of  the  patella.  The  bone  may  even,  as  in  one  recorded  case, 
be  carried  entirely  past  the  condyle,  so  as  to  lie  behind  the  centre  of  motion  of  the 
knee  when  the  joint  is  bent,  thus  causing  the  quadriceps  extensor  to  act  as  a  flexor 
of  the  leg  on  the  thigh. 

The  external  articular  facet  on  the  under  surface  of  the  patella  is  larger  than  the 
internal.  The  patella  is  in  relation,  therefore,  chiefly  with  the  external  condyle,  and 
even  if  dislocation  occurs  from  direct  violence,  it  is  more  likely  to  be  driven  in  that 
direction  (Humphry).  If  it  has  once  passed  beyond  the  edge  of  the  outer  condyle 
— a  "complete"  luxation  necessarily  attended  by  laceration  of  the  capsule — it  is 
less  likely  to  be  replaced  than  if  it  had  gone  in  the  opposite  direction,  because  of  (a) 
the  resistance  offered  by  the  prominence  of  the  condyle  itself  and  (£)  the  greater 
comparative  strength  of  the  vastus  externus. 

Outward  luxation  is  not  very  rare  in  cases  of  genu  valgum,  and,  per  contra,  in 
congenital  cases  of  patella  luxation  and  in  unreduced  traumatic  luxations  genu 
valgum  has  followed  (Makins). 

The  patella  may  be  displaced  inward  by  direct  force.  It  is  sometimes  turned 
on  edge  by  a  force  insufficient  to  dislocate  it  completely,  and  is  held  in  that  position 
by  the  tension  of  the  soft  parts  attached  to  it  and  by  the  pressure  of  the  over- 
lying fascia,  "like  a  stick  on  end  under  a  tightly  stretched  sheet"  (Stimson).  In 
flexion  of  the  knee  the  patella  lies  deeply  in  the  depression  between  the  condyk-s 
and  the  quadriceps  tendon  is  on  the  stretch.  The  bone  is  therefore  somewhat 
removed  from  danger  of  direct  violence,  and  is  steadied  and  fixed  by  the  quadri- 
ceps muscle.  In  extension  the  patella  rests  on  the  trochlear  surface  of  the  femur 
only  by  its  lower  margin  ;  it  is  more  prominent  and  thus  more  exposed  to  force 
directly  applied  ;  the  quadriceps  is  relaxed,  leaving  the  bone  freely  movable. 
For  these  reasons  extension  is  the  position  in  which  dislocation  most  commonly 
occurs. 


THE   TARSAL    BONES.  419 


THE   FOOT. 

The  framework  of  the  foot  consists  of  the  tarsus,  metatarsus,  and.  phalanges, 
which  differ  in  their  proportionate  size  from  the  corresponding  divisions  of  the  hand. 
Thus,  in  the  latter  the  carpal  region  is  the  shortest  and  that  of  the  phalanges  the 
longest,  equalling  almost  precisely  the  other  two  ;  in  the  foot,  on  the  contrary,  the 
region  of  the  phalanges  is  the  shortest  and  that  of  the  tarsus  makes  about  half  the 
entire  length.  The  tarsus  differs  also  in  its  arrangement  more  than  the  carpus  from 
the  primitive  type.  The  tarsal  bones  may  be  considered  as  divided  into  two  lateral 
divisions  :  an  outer  series  of  two  bones  bearing  the  two  outer  toes,  and  an  inner 
series  of  five  bearing  the  three  inner  toes,  so  placed  that  the  proximal  bone  of  the 
inner  part  rests  on  top  of  the  proximal  of  the  outer.  The  outer  side  of  the  skeleton 
of  the  foot  rises  but  little  from  the  ground,  while  the  inner  is  highly  arched. 

THE   TARSAL    BONES. 

The  tarsal  bones  are  the  calcaneum,  or  os  calcis,  the  heel-bone  ;  the  cuboid,  which 
with  it  forms  the  outer  division  ;  the  astragalus,  or  talus,  which  joins  the  leg  ;  the 
scaphoid,  placed  between  the  astragalus  and  the  three  cuneiform,  which  bear  the 
three  inner  metatarsals. 

THE   CALCANEUM. 

The  calcaneum1  is  a  narrow  elongated  bone  forming  the  heel,  supporting  the 
astragalus,  and  joining  the  cuboid  in  front.  It  has  six  surfaces.  The  inferior  sur- 
face presents  at  the  back  a  swelling  subdivided  into  the  internal  and  external  plan- 
tar tubercles,  of  which  the  former  is  much  the  larger,  forming  the  posterior  pier  of 
the  foot.  These  tubercles  are  continuous  at  the  posterior  border,  in  front  of  which 
a  deep  notch  divides  them.  Each  appears  on  its  side  of  the  bone.  In  front  of 
these  the  lower  surface,  convex  from  side  to  side,  is  marked  by  longitudinal  grooves. 
Near  the  front  is  the  anterior  tubercle,  a  small  swelling,  from  which  and  from  a 
depression  near  it  arise  calcaneo-cuboid  ligaments.  The  posterior  surface  is 
roughly  oval  with  the  small  end  up.  The  tendo  Achillis  is  attached  to  a  roughness 
occupying  its  lower  half,  above  which  the  bone  slants  forward  and  is  smooth  for  a 
bursa  between  it  and  the  tendon.  The  lower  part  of  the  posterior  surface  is  con- 
tinuous with  the  plantar  tubercles.  The  internal  surface  is  smooth  and  concave  ; 
for  the  internal  tubercle  projects  strongly  inward,  while  in  front  and  above  there  is 
a  shelf-like  process,  the  sustentaculum  tali,  to  support  the  head  of  the  astragalus, 
slanting  downward  and  forward.  Beneath  this  is  a  slight  groove  for  the  tendon  of 
the  long  flexor  of  the  great  toe.  Lower  down  near  the  front  border  a  depression 
for  a  ligament  to  the  cuboid  runs  down  in  front  of  the  anterior  tubercle.  The  ex- 
ternal surface  is  the  longest.  It  presents  about  its  middle  a  vague  tubercle  for 
the  middle  bundle  of  the  outer  lateral  ligament  of  the  ankle,  and  nearer  the  front 
a  larger  one,  the  peroneal  spine.  When  well  marked  this  is  a  ridge,  covered  with 
cartilage,  slanting  downward  and  forward,  separating  two  grooves  for  the  tendons  of 
the  peroneus  longus  and  brevis.  The  outer  posterior  plantar  tubercle  projects 
somewhat  on  this  side.  Rather  more  than  the  anterior  two-thirds  of  the  superior 
surface  are  devoted  chiefly  to  the  joints  with  the  astragalus  ;  the  posterior  portion 
is  convex  from  side  to  side  and  concave  from  before  backward.  There  are  two 
articular  facets  :  the  posterior  facet,  the  larger,  a  vaguely  four-sided  swelling,  occu- 
pies the  middle  of  this  surface.  Its  long  axis  runs  forward,  downward,  and  out- 
ward. It  is  convex  in  this  direction.  The  upper  inner  end  is  the  broader,  and 
near  it  the  facet  is  very  often  concave  at  right  angles  to  the  long  axis,  but  in  the 
main  it  is  about  plane  in  that  direction  and  may  be  even  slightly  convex.  The  anterior 
facet,  long  and  narrow,  concave  from  before  backward,  runs  forward  and  outward, 
nearly  parallel  to  the  long  axis  of  the  former.  It  begins  internally  on  the  top  of  the 
sustentaculum  and  ends  at  the  most  anterior  point  of  the  bone.  In  about  half  the 
cases  this  surface  is  subdivided  into  two,  and,  as  a  rule,  when  it  is  not  there  is  a 

1  Calcanciis. 


420 


HUMAN    ANATOMY. 
A  FIG.  431. 


B 


Bones  of  right  foot,  dorsal  aspect.     A,  outer  series  ;  /?,  inner  series. 


THE   CALCANEUM. 


421 


notch  in  the  free  border  just  at  the  end  of  the  sustentaculum.  Occasionally  the 
facet  in  front  of  the  interruption  is  rudimentary  or  wanting,  in  which  case,  instead 
of  articular  cartilage,  merely  synovial  membrane  is  beneath  the  head  of  the  astraga- 
lus. In  200  feet  we  have  found  the  facet  single  in  95,  divided  in  94,  and  in  n  the 
front  was  wanting.  The  two  chief  facets  (counting  the  anterior  as  one,  even  if  sub- 
divided) are  separated  by  a  deep  groove  for  the  interosseous  ligament  to  the  astrag- 
alus. This  gutter  broadens  in  front  into  a  rough  depression,  the  sinus  tarsi,  for 
ligaments.  At  its  outer  part  there  is  a  tubercle  for  the  origin  of  the  extensor  brevis 
digitorum.  The  anterior  surface,  turned  somewhat  inward,  is  wholly  articular 
for  the  cuboid.  It  is  three-sided  with  rounded  angles.  The  longest  diameter  is 
from  above  downward  and  outward,  nearly  parallel  with  the  inner  border.  The 
upper  border  is  straight  or  convex,  overhanging  the  joint  at  the  inner  side.  The 
outer  border  slants  a  little  inward  as  it  descends.  The  surface  is  concave  from 
above  downward  and  convex  transversely.  Both  these  curves  are  most  marked  at 


FIG.  432. 

Cuboid 


Astragalus 


Sustentaculum  tal 


Interosseous  groov 


Sinus  tarsi 


Peroneal  spine 


Astragalus 


Internal  tubercle 


For  bursa 

i 

Tendo  Achillis 
Right  calcaneum  from  above. 

the  upper  inner  angle,  where  they  form  almost  a  groove  for  the  plantar  process  of 
the  cuboid.  The  general  effect  is  of  a  screw  surface  twisting  upward  and  inward. 
The  calcaneum  articulates  with  two  bones,  the  cuboid  and  the  astragalus,  and  excep- 
tionally with  the  scaphoid,  to  which  it  may  be  united  by  cartilage. 

Variations. — The  hind  end  of  the  sustentaculum  is  very  rarely  a  separate 
piece  :  os  sustentaculi  proprium.  The  inner  edge  of  the  front  of  the  bone,  which 
normally  comes  very  near  to  the  scaphoid,  may  meet  it.  Sometimes  the  two  bones 
are  fused.  The  calcaneum  secundarium  is  a  small  ossicle  rarely  present  on  the 
dorsum  between  the  calcaneum,  the  cuboid,  the  scaphoid,  and  the  head  of  the 
astragalus.  Fusion  of  the  calcaneum  and  astragalus  has  been  observed  at  the  sus- 
tentaculum. 

Structure. — The  walls  are  thin,  the  cancellated  tissue  filling  the  bone,  with  a 
tendency  to  the  formation  of  large  spaces  at  the  middle.  The  architectural  arrange- 
ment is  very  clear  in  an  antero-posterior  section,  which  shows  diverging  plates  from 


422 


HUMAN   ANATOMY. 


the  greater  articular  facet  for  the  astragalus  and  a  system  of  loops  connecting  them. 
The  large  spaces  are  at  the  neutral  point. 

FIG.  433- 


Longitudinal  section  of  calcaneum,  showing;  arrangement  of  lamellae. 

Development. — The  chief  nucleus  is  said  to  appear  in  the  sixth  month  of 
foetal  life.  We  have  twice  seen  it  earlier, — once  at  about  the  fourth  month.  An 
epiphysis  for  the  back  of  the  bone  and  the  posterior  plantar  tubercles  appears  from 
the  seventh  to  the  tenth  year.  It  begins  to  fuse  by  fifteen,  completing  the  process 
in  a  year  or  so. 

THE   CUBOID. 

The  cuboid '  is  a  six-sided  bone,  flattened  from  above  downward,  interposed 
between  the  calcaneum  and  the  fourth  and  fifth  metatarsal  bones.  It  is  important 
to  remember  that  the  dorsal  surface  faces  almost  as  much  outward  as  it  does  upward. 
The  dorsal  surface,  slightly  rough,  has  the  following  outline  :  an  oblique  posterior 
border  against  the  calcaneum,  which,  though  most  often  convex,  may  be  concave, 
sinuous,  or  straight  ;  a  short  outer  concave  one  ;  an  internal  one,  at  first  straight 
when  against  the  scaphoid,  and  slanting  outward  when  against  the  external  cunei- 
form ;  and  an  anterior  one,  slanting  outward  and  backward.  The  plantar  surface 


FIG.  434. 


External  cuneiform 


Calcaneum 


lalcaneum 


Groove 


Promontory 
Right  cuboid. 


For  inf.  calcaneo-cuboid  ligament  Promontory 

A,  inner  aspect ;  B,  posterior,  outer,  and  inferior  surfaces. 


has  essentially  the  same  shape,  only  the  angle  between  the  posterior  and  r 
borders  is  drawn  out.  Owing  to  the  oblique  position  of  the  bone,  this  tits  into  the 
upper  inner  an^le  «>f  the  anterior  surface  of  the  calcaneum.  Just  below  this  angle  is 
a  prominence,  the  plantar  tubercle.  A  thick,  rounded,  oblique  ridgi-,  the  promon- 
tory or  tnbnosity,  starting  at  the  back  of  the  outer  border,  runs  forward  and  inward 
across  the  bone  behind  a  groove  between  it  and  the  anterior  border.  The  tendon  of 
the  peroneus  longus  lies  on  the  smooth  anterior  slope  of  the  promontory,  the  outer 

1  IK  cuboideuin. 


THE   ASTRAGALUS. 


423 


part  of  which  is  coated  with  cartilage.  The  external  surface  of  the  bone  is  deeply 
notched.  The  internal  surface  is  mostly  rough,  but  presents  at  about  the  middle 
an  articular  facet for  the  external  cuneiform,  broad  above,  narrow  below,  and  not  usu- 
ally reaching  the  plantar  surface.  Commonly  another  smaller  facet  for  the  scaphoid 
is  found  behind  this  one,  from  which  it  is  separated  sometimes  completely,  but  more 
often  merely  by  a  ridge,  which  makes  no  real  interruption.  The  anterior  surface, 
articular  for  the  bases  of  two  metatarsals,  has  an  inner,  an  upper,  and  a  lower  border, 
the  two  latter  meeting  at  a  rounded  angle  externally.  A  faint  vertical  ridge,  nearer 
the  inner  than  the  outer  border,  usually  divides  this  facet  into  an  inner  oblong  and 
an  outer  triangular  part  for  the  fourth  and  fifth  bones.  The  curves  of  these  articu- 
lations vary  greatly  :  sometimes  both  parts  are  concave  from  above  downward  ; 
sometimes  both  are  practically  plane.  The  posterior  surface,  entirely  articular, 
is  the  complement  of  the  front  of  the  os  calcis.  The  cuboid  articulates  with  the 
calcaneum,  the  external  cuneiform,  the  fourth  and  fifth  metatarsal  bones,  often  with 
the  scaphoid,  and  at  times  with  the  astragalus. 

Development. — There  is  but  one  centre,  appearing  at  about  birth  ;  in  our 
experience,  more  often  after  than  before. 

For  Secondary  Cuboid,  see  Scaphoid. 


ASTRAGALUS, 
is  a  very  irregular  bone  devoted  almost  wholly  to 


THE 

The  astragalus,  '  or  talus, 

articular  surfaces.  It  is  enclosed  above  by  the  socket  of  the  leg  bones.  Its  main 
part,  or  body,  rests  on  the  calcaneum,  and  presents  in  front  a  constricted  neck 
bearing  a  rounded  head,  projecting  forward  and  inward  into  the  hollow  on  the  back  of 
the  scaphoid.  The  upper  surface  presents  a  pulley-like  articular  facet  covering  the 
greater  part  of  the  bone,  convex  from  before  backward,  slightly  concave  transversely, 
decidedly  broader  in  front  than  behind.  The  cartilage  covering  it  is  continued 
down  on  either  side  to  meet  the  articular  surfaces  of  the  malleoli.  The  inner  border 


FIG.  435. 

Scaphoid 


FIG.  436. 


Head 


For  calcaneo- 
aphoid  lig. 

Calcaneum 


Internal  tubercle 


External 

tubercle 
Groove  for  tendon  of  flex.  long.  hall. 

Right  astragalus  from  above. 


Groove  for  flex, 
long.  hall. 


External  tubercle 
Right  astragalus  from  below. 


of  the  upper  articular  surface  is  distinct,  but  generally  not  sharp  ;  the  outer,  which 
reaches  higher,  is  better  defined  in  the  region  just  anterior  to  its  middle,  but  behind 
on  the  dry  bone  it  seems  rounded.  A  very  well-marked  bone  shows  (what  is  very 
striking  in  the  freshly  opened  joint)  that  this  blunted  edge  is  really  a  narrow  tri- 
angular area  belonging  to  the  superior  surface,  broadest  behind,  made  apparently 
by  the  pressure  of  the  posterior  tibio-fibular  ligament  from  the  external  malleolus  to 

1  Talus. 


424 


HUMAN    ANATOMY. 


the  back  of  the  tibia.  A  much  smaller  similar  surface  is  found  at  the  front,  made 
by  the  corresponding  anterior  ligament.  The  direction  of  the  anterior  border  of  the 
articular  surface  is  very  uncertain.  It  usually  projects  forward  at  the  outer  end,  the 
rest  being  either  transverse,  posteriorly  concave,  or  oblique.  Just  anterior  to  it  is  a 
deep  transverse  hollow  on  the  upper  surface  of  the  neck,  which  receives  the  edge  of 
the  tibia  in  extreme  dorsal  flexion  of  the  foot.  The  posterior  border  of  the  articular 
surface  is  also  of  uncertain  shape.  Its  inner  end  is  usually  somewhat  farther  back 
than  the  outer.  Behind  it  two  rough  tubercles  project  backward,  slanting  down  to 

FIG.  437. 


Sustentaculum 


For  scaphoid 


For 

sustentaculum 


For  ligament 


Calcaneum  Astragalus 

Type  of  calcaneo-astragaloid  joint  with  an  undivided  anterior  articular  facet  on  calcaneum. 

a  posterior  sharp  edge.  Between  them  is  a  deep  groove  for  the  tendon  of  the  flexor 
longus  hallucis,  running  obliquely  downward  and  inward.  The  outer  tubercle, 
which  is  much  the  larger,  is  sometimes  separated  by  a  suture  from  the  rest  of  the 
bone,  and  is  then  known  as  the  os  trigonum.  The  inner  tubercle  may  be  barely 
distinguishable.  This  region  behind  the  superior  articular  facet  is  sometimes  de- 
scribed as  the  posterior  surface  of  the  bone.  The  external  surface  of  the  body 
shows  the  triangular  facet  for  the  outer  malleolus,  concave  from  above  downward, 


FIG.  438. 


Synovial  not  cartilaginous 


Sustentaculum 


For  scaphoid 


For  internal  cak-aneo- 
scaphoid  ligament 


For  sustentaculum 


Calcaneum 


Astragalus 


Type  of  calcaneo-astragaloid  joint  when  anterior  facet  on  calcaneum  is  not  only  divided  but  has  front  portion 

rudimentary. 


with  the  lower  end  projecting  outward,  plane  or  convex  from  before  backward. 
This  is  bounded  before  and  behind  by  a  rough  strip,  with  a  hollow  at  the  upper 
ends  for  the  front  and  back  bundles  of  the  external  ligament  of  the  ankle.  The 
internal  surface  has  at  the  top  a  narrow  curved  facet  for  the  inner  malleolus,  with 
a  concave  lower  border,  deepest  in  front  and  pointed  behind.  A  part  of  the  intrrnal 
lateral  ligament  is  inserted  into  a  hollow  below  it.  The  inferior  surface  of  the 
body  presents  a  four-sided  facet,  concave  in  the  line  of  its  long  axis,  which  is  oblique, 
corresponding  to  that  of  the  greater  surface  on  the  top  of  the  calcaneum.  In  front 
of  and  parallel  to  this  is  a  di-rp  groove  for  the  interosseous  ligament,  expanding  at 
the  outer  end  into  a  triangular  hollow  on  the  under  side  of  the  neck.  This  is  a 


THE   SCAPHOID.  425 

constricted  portion,  much  broader  transversely  than  vertically,  connecting  the  head 
with  the  body.  It  often  presents  a  groove  along  the  upper  and  inner  aspect  near 
the  articular  surface  of  the  head  for  the  insertion  of  the  ligament  passing  to  the 
scaphoid.  The  head,  which  points  forward  and  inward,  is  articular  in  front  and 
below.  The  anterior  surface,  which  fits  into  the  hollow  on  the  back  of  the  scaph- 
oid, is  vaguely  oval,  with  its  long  axis  running  downward  and  inward.  The  upper 
edge,  parallel  with  this,  is  nearly  straight.  The  articular  surface  of  the  head  ex- 
tends onto  the  under  side,  reaching  to  the  deep  groove  separating  the  neck  from 
the  posterior  facet  for  the  calcaneum.  On  a  fresh  bone  the  cartilage  shows  the 
following  facets,  which  are  less  well  marked  on  a  macerated  one  :  a  facet  on  the 
front  of  the  head  to  fit  into  the  scaphoid  ;  one  on  the  lower  and  inner  side  to 
rest  on  the  anterior  articular  facet  of  the  top  of  the  calcaneum  ;  one  partly  between 
these,  which  in  the  dried  bones  would  be  free,  appearing  between  the  sustentaculum 
and  the  scaphoid,  but  in  life  resting  on  the  inferior  calcaneo-scaphoid  ligament, 
which  is  partly  covered  with  cartilage  and  elsewhere  with  synovial  membrane, 
forming  a  part  of  the  socket.  The  cartilage  on  this  surface  is  distinguished  by  its 
thinness.  These  facets  are  modified  according  to  the  arrangement  of  those  on  the 
calcaneum.  If  there  be  but  one  long  anterior  facet  on  both  sustentaculum  and  on 
the  end  of  the  body  of  the  calcaneum,  the  facet  on  the  head  for  the  anterior  facet 
of  the  calcaneum  reaches  that  for  the  concavity  of  the  scaphoid  in  front,  leaving 
internally  a  triangular  interval  between  the  two,  occupied  by  the  facet  for  the  liga- 
ment (Fig.  437).  In  the  other  extreme  (Fig.  438),  where  the  anterior  facet  on 
the  calcaneum  does  not  reach  beyond  the  sustentaculum,  the  area  of  the  head  rest- 
ing against  the  ligament  completely  separates  the  two  others  and  plays  on  that  part 
of  the  calcaneum  where  the  anterior  articular  cartilage  should  be.  Finally,  when 
the  anterior  facet  on  the  calcaneum  is  divided  into  two,  the  corresponding  facet  may 
be  completely  subdivided  by  an  interruption  of  the  cartilage,  or  in  less  marked 
forms  there  may  be  merely  a  ridge  breaking  the  surface  into  two,  but  without  sepa- 
ration ;  such  a  ridge  is  often  found  even  when  the  opposed  articular  surface  is  not 
divided.  The  lines,  however,  on  the  head  of  the  astragalus  do  not  strictly  correspond 
to  the  boundaries  of  these  surfaces.  The  astragalus  articulates  with  four  bones, — the 
tibia,  fibula,  calcaneum,  and  scaphoid. 

Development. — The  nucleus  probably  appears  at  about  the  seventh  month  of 
fcetal  life.  When  the  os  trigonum  occurs,  that  implies  another  centre  for  the  ex- 
ternal tubercle  and  the  part  of  the  articular  surface  under  it. 

The  deviation  of  the  axis  of  the  neck  from  that  of  the  long  axis  of  the  bone 
varies  considerably  among  individuals,  but,  nevertheless,  changes  during  develop- 
ment. In  the  adult  the  angle  varies  from  o  to  24°,  the  mean  of  forty-three  bones 
being  12.32°.  In  the  foetus  (presumably  at  term)  the  angle  ranges  from  17.5°  to 
45.5°,  the  mean  of  twenty-two  bones  being  35-760.1 

THE   SCAPHOID. 

The  scaphoid,2  or  navicular,  may  be  compared  to  a  disk,  concave  behind  where 
it  fits  onto  the  head  of  the  astragalus,  convex  in  front  where  it  rests  on  the  three 
cuneiform  bones.  It  is  thinner  at  the  outer  end,  where  it  touches  the  cuboid,  than 
at  the  inner,  where  it  presents  the  tuberosity.  The  superior,  or  dorsal,  surface 
is  long  transversely.  Its  posterior  border  is  regularly  concave,  the  anterior  slightly 
scalloped,  presenting  two  small  points  projecting  forward  on  either  side  of  the  mid- 
dle cuneiform.  When  in  position  the  highest  point  on  the  scaphoid  is  behind  that 
bone.  The  greater  part  of  the  dorsal  surface  slants  downward  on  the  inner  side  of 
the  foot.  The  inferior,  or  plantar,  surface  is  rough,  and  in  the  main  transversely 
concave.  The  tuberosity  at  the  inner  border  for  the  attachment  of  a  part  of  the  tibi- 
alis  posticus  muscle  is  a  knob  formed  by  the  junction  of  the  dorsal  and  plantar  sur- 
faces, and  projecting  downward  chiefly  into  the  sole  of  the  foot.  The  end  of  the 
knob  is  sometimes  distinct  from  the  scaphoid,  and  is  known  as  the  tibia  le  externum. 

1  C.  L.  Scudder  :  Congenital  Talipes  Equino-Varus,  Boston  Med.  and  Surg.  Journ.,  vol. 
ii.,  1887.     Parker  and  Shattock  :  The  Pathology  and  Etiology  of  Congenital  Club-Foot,  London, 

1884. 

2  Os  naviculare  pcdis. 


426 


HUMAN   ANATOMY. 


Its  identity  is  quite  evident  in  cases  in  which,  though  fused,  it  projects  as  a  hook. 
It  may  be  represented  by  the  sesamoid  bone  in  the  tendon  of  the  tibialis  posticus. 
Near  the  outer  end  of  the  plantar  surface  there  is  almost  always  a  slight  projection 
by  the  side  of  the  cuboid  which  may  be  very  much  developed,  extending  to  near 
the  notch  in  front  of  the  sustentaculum  of  the  calcaneum,  in  which  case  it  is  known  as 
the  secondary  cuboid.  The  external  surface  is  narrow  and  rough,  resting  against 
the  cuboid,  with  which  it  articulates  in  about  half  the  cases  by  a  facet  near  the  dor- 
sum,  which  rarely  extends  far  towards  the  sole.1  The  posterior  surface  is  con- 
cave, in  the  main  oval  and  completely  articular.  Usually  the  regularity  of  the 
lower  border  is  interrupted  near  the  outer  part  by  the  external  knob  of  the  plantar 
surface.  If  this  be  much  developed  the  shape  of  the  posterior  surface  is  changed 
from  oval  into  quadrilateral,  but  it  is  always  articular  throughout.  The  anterior 
surface  is  slightly  convex  and  entirely  articular,  except  when  the  process  just  men- 
tioned is  so  large  as  to  appear  below  it.  The  articular  surface  is  divided  into  three 


FIG.  439. 

Dorsal  surface 


FIG.  440. 

Dorsal  surface 


For  head  of  astragalus 
Right  scaphoid  from  behind,  proximal  aspect. 


External        Middle       Internal      Tuberosity 
cuneiform    cuneiform    cuneiform 

Right  scaphoid  from  in  front. 


facets,  in  the  main  triangular,  corresponding  to  the  outline  of  the  bases  of  the  three 
cuneiform  bones.  The  character  of  these  facets  is  not  constant  :  the  inner  is  usually 
convex  and  the  outer  concave. 

The  scaphoid  articulates  with  the  astragalus,  the  three  cuneiform  bones,  often 
with  the  cuboid,  and  exceptionally  it  touches  or  joins  the  calcaneum.  The  secondary 
cuboid,  above  alluded  to,  has  but  once  been  seen  isolated,  although  we  have  met  with 
one  foot  in  which  it  seemed  possible  that  it  might  have  been  distinct  earlier.  It  is 
fused  with  either  the  cuboid  or  the  scaphoid,  but  apparently  much  more  frequently 
with  the  latter,  in  which  it  occupies  the  position  above  described,  lying  at  the  weak 
part  of  the  inferior  calcaneo-scaphoid  ligament. 

Development. — It  is  generally  held  that  the  process  begins  in  the  fourth  or 
fifth  year,  but,  according  to  Gegenbaur,  it  begins  in  the  first.  The  tibiale  externum 
exists  as  a  separate  cartilage  at  the  second  month  of  foetal  life.  Usually  this  fuses 
with  the  rest,  but  it  may  have  a  centre  of  its  own. 

THE  THREE  CUNEIFORM  BONES. 

These  wedge-shaped  bones,  placed  between  the  scaphoid  and  the  three  inner 
metatarsals,  and  abutting  externally  on  the  cuboid,  form  an  important  part  of  the 
transverse  arch  of  the  foot.  The  thin  edge  of  the  internal  cuneiform,  which  is  much 
the  largest,  points  up,  that  of  the  others  down.  The  middle  cuneiform  is  the  smallest 
and  shortest,  so  that  the  second  metatarsal  bone  lies  in  a  mortise  between  the  inner 
and  outer. 

THE   INTERNAL   CUNEIFORM. 

The  internal  cuneiform,2  besides  the  proximal  and  distal  surfaces,  has  an  internal, 
an  external,  and  an  inferior.  The  posterior,  or  proximal  surface,  rounded  below 
and  pointed  above,  is  slightly  concave  and  wholly  articular.  The  anterior,  or  distal, 
surface,  also  articular,  is  kidney-shaped,  with  the  notch  in  the  outer  border.  The 
inner  surface  has  a  small  ridge  in  its  distal  half,  pointing  upward,  which  is  the 
'I'tit/m-r:  Morph.  Arbritcn,  Bel.  vi.,  1896. 

20»  cunciforine  priniiim. 


THE   CUNEIFORM    BONES. 


427 


highest  part  of  the  bone,  but  almost  the  whole  of  this  surface  is  on  the  inner  side  of 
the  foot.  Its  outer  border  runs  obliquely  forward  and  outward  with  a  sinuous 
course  till  it  reaches  the  end  of  the  middle  cuneiform,  when  it  turns  forward.  It 
has  a  short  concave  posterior  border  for  the  scaphoid  and  a  long,  nearly  straight 
one  for  the  first  metatarsal  bone.  It  passes  without  a  sharp  boundary  into  the 
lower  surface.  It  is  crossed  by  a  faint  groove,  which  exceptionally  is  deep,  running 
obliquely  downward  and  forward  to  a  smooth  swelling  for  a  bursa  under  the  tendon 


FIG.  441. 


FIG.  442. 


Dorsal 


Dorsal 


Mid.  cuneiform 


Scaphoid 


Right  internal  cuneiform,  outer  aspect. 


Right  internal  cuneiform,  inner  aspect. 


of  the  tibialis  anticus  just  before  its  insertion.  The  inferior  surface,  rough  and 
round,  has  a  tubercle  near  the  proximal  end  for  a  part  of  the  tibialis  posticus.  The 
external  surface  is  mostly  rough,  with  a  smooth  articular  strip  for  the  middle 
cuneiform  following  its  upper  and  posterior  border.  The  internal  cuneiform  articu- 
lates with  the  scaphoid,  middle  cuneiform,  and  first  and  second  metatarsal  bones. 

Development. — A  centre  appears  in  the  third  year.  Very  exceptionally  it  is 
double,  and  the  bone  is  divided  by  a  suture  into  two, — a  dorsal  and  a  plantar. 

THE   MIDDLE   CUNEIFORM. 

The  middle  cuneiform  l  has  a  sharp  ridge  below  and  an  oblong  surface  above. 
The  latter,  or  superior  surface,  is  very  little  longer  than  broad.  The  lateral 
borders  of  this  surface  have  an  outward  inclination.  The  inner  of  them  corresponds 
to  the  proximal  part  of  the  outer  border  of  the  first  cuneiform.  The  outer  border, 
for  its  proximal  two-thirds,  rests  against  the  external  cuneiform,  beyond  which  there 
is  a  small  space  between  the  bones.  The  proximal  side  of  this  surface  is  a  little 
convex  and  the  distal  about  straight.  The  posterior  surface,  wholly  articular, 

FIG.  443. 


Scaphoid 


Right  middle  cuneiform.     A,  inner  aspect ;  B,  outer  aspect. 


is  slightly  concave.  It  is  triangular,  with  the  dorsal  border  rounded,  the  outer 
concave,  and  the  inner  straight  or  slightly  convex.  The  anterior  surface,  ar- 
ticular for  the  second  metatarsal,  is  narrower.  It  has  a  slight  convexity  in  the  upper 
part  in  a  vertical  plane.  The  internal  surface  has  an  articular  facet  corresponding 
to  that  on  the  internal  cuneiform  and  a  rough  depression  for  an  interosseous  liga- 
ment. The  external  surface  has  a  facet  along  the  hind  border,  broader  above 
than  below,  and  rarely  a  small  one  at  the  front  lower  angle,  both  for  the  external 

1  Os  cuneifor me  secundum. 


428 


HUMAN   ANATOMY. 


cuneiform.      The  middle  cuneiform  articulates  with  the  scaphoid,  the  internal  and 
external  cuneiforms,  and  the  second  metatarsal. 

Development. — One  centre  appears  in  the  fourth  year. 

THE    EXTERNAL    CUNEIFORM. 

The  external  cuneiform,1  seen  from  above,  is  much  longer  than  broad,  with  a 
very  oblique  proximal  border  slanting  outward  and  backward,  an  anterior  border 
running  less  obliquely  in  the  same  direction,  an  inner  one  close  against  the  middle 
bone  in  its  proximal  third  or  one-half,  then  receding  from  it  and  extending  onto  the 
outer  side  of  the  second  metatarsal,  and  an  outer  border  first  running  forward  and 
outward  against  the  cuboid,  and  then  forward  not  quite  against  it,  but  overlapping 
the  fourth  metatarsal.  The  ridge  constituting  the  inferior  surface  does  not  quite 
reach  the  proximal  end.  The  posterior  surface,  wholly  articular,  is  oblong,  with 
the  long  axis  vertical,  and  often  a  little  convex.  The  anterior  surface,  articular  for 
the  third  metatarsal,  is  triangular  and  about  plane.  Its  inner  border  rises  higher 
than  the  outer.  The  internal  surface  articulates  with  the  second  cuneiform  bone  by 

FIG.  444. 


Cuboid 


Fourth 

metatarsal 
Third 

metatarsal 


Right  external  cuneiform.    A,  inner  aspect ;  B,  outer  aspect. 


one  or  two  corresponding  facets,  as  the  case  may  be,  and  has,  in  addition,  a  facet  for 
the  outer  side  of  the  base  of  the  second  metatarsal  at  the  front  upper  angle,  and 
often  extending  down  the  border  ;  or  the  middle  portion  may  be  wanting.  In  the 
middle  of  the  surface  is  a  roughness  for  the  interosseous  ligament.  The  external 
surface  is  chiefly  rough,  giving  origin  to  an  interosseous  ligament  for  the  cuboid  ; 
at  the  upper  proximal  angle  is  a  large  facet  for  the  same  bone,  and  at  the  distal 
upper  angle  there  may  or  may  not  be  a  small  one  for  the  side  of  the  fourth  meta- 
tarsal. The  external  cuneiform  articulates  with  the  scaphoid,  the  middle  cuneiform, 
the  cuboid,  and  the  second,  third,  and  fourth  metatarsals. 

Development. — Ossification  begins  in  the  first  year. 

The  Intercuneiform  Bone. — On  the  dorsum  there  is  a  little  pit  which  we 
have  called  the  intercuneiform  fossa,  situated  between  the  proximal  portions  of  the 
internal  and  middle  cuneiform  bones,  usually  more  at  the  expense  of  the  latter  than 
of  the  former.  We  have  at  least  twice  seen  a  separate  ossicle,  the  intercuneiform 
6one,*  in  this  fossa.  The  better  specimen  was  wedge-shaped,  its  length  exceeding 
one  centimetre.  It  clearly  was  more  intimately  related  to  the  middle  than  to  the 
internal  cuneiform.  Pfitzner  has  since  seen  it  fused  with  the  former. 

THE   METATARSAL   BONES. 

Of  these  five  bones3  the  first  is  very  much  the  largest,  although  the  shortest. 
The  second  is  the  longest,  and  the  others  of  about  equal  length. 

The  first  metatarsal  bone  has  a  concave  base  corresponding  to  the  facet  on 
the  internal  cuneiform,  which  is  prolonged  down  into  a  point  (tuberosity}  rather 
to  the  outer  side,  on  the  external  aspect  of  which  the  prroneus  longus  is  inserted 
into  a  round  impression.  On  the  inner  side  of  the  base  is  a  small  prominence  for 
the  tibialis  anticus.  A  smooth  facet  for  the  second  metatarsal  is  often  found  on  the 
outer  side.  A  groove  for  the  capsular  ligament  more  or  less  perfectly  encircles  the 

?Anat.  An/eiger,  Bel.  xx.,  1902. 

1  Os  runcifonnv  tcrtiuin.     ;'0ssa  mctatnrsalin  1-V. 


THE   METATARSAL    BONES. 


429 


base.     The  strong  shaft  has  three  sides  :  an  internal,  looking  also  upward,  in  the 
main  convex  ;  an  external,  concave  and  nearly  vertical  ;  and  an  inferior,  or  plantar, 


FIG.  445. 

Grooves  for  sesamoid  bones 


Internal 
cuneiform 

External  surface 


Plantar 


C 
Phalangeal  surface 


Head 


Internal  surface 
Inferior  surface 


Tibialis  anticus 


Impression  of  peroneus  longus          Tuberosity  Internal  cuneiform 

Right  first  metatarsal.     A,  proximal  aspect ;  B,  plantar  aspect ;  C,  dorsal  aspect. 

also  concave.      The  borders  bounding  the  outer  surface  are  the  most  distinct.      One 
or  two  nutrient  foramina  enter  this  surface,  running  distally.     The  enlarged  and 


Lateral  ligament 


Ext.  cuneiform 
Third  metatarsal 

Mid.  cuneiform 

Third  metatarsal 
Ext.  cuneiform 


Plantar 


Middle 
cuneiform 


External  cuneiform 
Right  second  metatarsal.     A,  proximal  aspect ;  B,  outer  aspect ;  C,  inner  aspect. 

rounded  distal  end,  the  head,  is  articular  except  at  the  sides,  where  it  is  flattened. 
The  facet  extends  farther  onto  the  plantar  aspect,  where  it  expands  laterally.      It 


430 


HUMAN   ANATOMY. 


has  there  a  median  elevation,  with  a  groove  on  either  side  for  a  sesamoid  bone. 
There  is  a  rough  surface  for  ligaments  on  each  side  of  the  head. 


Middle  cuneiform 


External 
cuneiform 


Plantar 


Fourth  metatarsal 


Second  inetatarsa 


External  cuneiform 
Right  third  metatarsal.    A,  proximal  aspect ;  B,  outer  aspect ;  C,  inner  aspect. 

The  four  outer  metatarsal  bones  are  distinguished  by  their  bases.  That 
of  the  second  is  concave  at  the  end,  and  fits  the  middle  cuneiform  ;  on  the  inner 
side  a  small  facet  at  the  top  meets  the  outside  of  the  first  cuneiform  ;  on  the  outer 
side  there  are  two,  an  upper  and  a  lower,  with  a  deep  cut  between  each,  resting 

FIG.  448. 


Cuboid 


Plantar 


Third  metatarsal 

External  cuneiform 
-Fifth  metatarsal 


Cuboid 
iRht  fourth  metatarsal.     .•(,  proximal  aspect  ;   /,'.  outer  aspect  ;   (.'.  inner  aspect. 


Ligament 


on  both  the  outer  cuneiform  and  the  third  metatarsal.      The  occasional  facet  for  the 
first  metatarsal  is  on  the  shaft  rather  than  on  the  end.      It  is  often  wanting  on  the 


THE   METATARSAL    BONES. 


431 


second  when  present  on  the  first,  implying  the  presence  of  a  bursa  rather  than  of  a 
joint.  The  base  of  the  third  metatarsal  fits  the  outer  cuneiform,  and  is  nearly 
plane.  The  posterior  upper  border,  seen  from  the  dorsum,  is  oblique,  running 


Dorsal  Tuberosity 


Cuboid 


Plantar 


Fourth  metatarsal 


Cuboi 


Tuberosity 


Cuboid 


Right  fifth  metatarsal.    A,  distal  aspect ;  B,  dorsal  aspect ;  C,  plantar  aspect. 

outward  and  backward.      The  inner  surface  has  two  facets  for  the  second,  and  the 

outer  surface  one  at  the  top  for  the  fourth  metatarsal.      The  base  of  the  fourth 

metatarsal  is  also  oblique.      It  has  an  oblong  facet  for  the 

cuboid,  and   a  single  internal  one  at  the  top  for  the  third,  FIG.  450. 

which  is  separated  from  the  proximal  end  by  a  rough  space 

for  the  insertion  of  an  interosseous  ligament  from  the  tarsus. 

There    is   externally  a   triangular  facet  at  the  upper  angle 

for  the  fifth.      This  last  facet  is  bounded  in  front  by  a  deep 

groove  which  receives   the  edge   of    the  facet  on  the  fifth. 

The  fifth  metatarsal  has  an  even  more  oblique  base,  the 

inner  two-thirds  of  which  bear  a  facet  for  the  cuboid.      The 

outer  part  is  prolonged  as  the  tuberosity  beyond  the  edge 

of   the  foot,  overhanging  the   joint.      The  inner  side  has  a 

facet  for  the  fourth  metatarsal  bone. 

The  shafts  of  the  metatarsal  bones  are  flattened  lat- 
erally, but  theoretically  three-sided,  like  the  first.  The 
second  has  an  external  surface  looking  directly  outward  ;  a 
superior  one  at  the  base,  which  twists  so  as  to  become  in- 
ternal. This  is  separated  from  the  former  in  the  distal  two- 
thirds  of  the  shaft  by  a  sharp  ridge.  The  third  side  is  internal 
at  the  base,  but  soon  becomes  inferior.  The  shaft  of  the 
third  differs  only  slightly,  the  external  surface  looking  some- 
what upward  and  there  being  more  of  a  ridge  below.  In 
the  fourth  it  seems  as  if  the  proximal  part  of  the  shaft  had 
been  bent  outward  on  its  axis,  so  that  the  outer  side  looks 
more  upward  and  the  other  two  are  less  twisted.  In  the 
fifth  this  process  has  gone  farther  ;  the  originally  outer  side 
is  now  the  upper,  separated  by  one  border  from  the  inner  and  by  another  from  the 
inferior.  This  last  border,  now  external,  represents  the  one  that  was  the  inferior 
of  the  third  metatarsal.  The  nutrient  foramina  of  the  four  outer  metatarsals  are 
in  the  external  surfaces,  running  upward.  They  are  not  very  constant. 


Fifth 
metatarsal 


Cuboid 


Right  fifth  metatarsal,  inner 
aspect. 


432 


HUMAN   ANATOMY. 


FIG.  451. 

Os  intermetatarseum 


The  heads  of  the  metatarsal  bones  are  compressed,  like  the  shafts,  from  side 
to  side,  and  have  each  a  pair  of  lateral  tubercles  at  the  dorsal  aspect  of  the  end  of 
the  shaft,  separated  by  a  groove  from  the  articular  surface.  Lateral  ligaments  are 
attached  both  to  the  tubercles  and  the  grooves.  The  ar- 
ticular surface  is  oblong,  extending  well  onto  the  plantar 
side,  where  it  ends  in  two  lateral  prolongations,  of  which 
the  outer  is  the  more  prominent.  A  line  connecting  their 
ends  would  be  oblique  to  the  shaft,  especially  in  the  outer 
toes. 

Fusion  of  the  outer  cuneiform  with  its  metatarsal  occurs 
occasionally  at  the  plantar  aspect.  It  is  probably  con- 
genital. Pfitzner  has  seen  it  at  seventeen  and  we  at 
nineteen. 

Development. — Centres  for  the  shafts  of  the  meta- 
tarsals  appear  towards  the  end  of  the  third  month  of  foetal 
life.  A  proximal  epiphysis  for  the  first  and  distal  ones  for 
the  others  appear  in  the  third  year,  fusing  at  about  seven- 
teen. Occasionally  the  metatarsals,  especially  the  first, 
have  an  epiphysis  at  each  end. 
Os  Intermetatarseum. — This  is  an  occasional  wedge-shaped  bone  found  on 
the  dorsal  aspect  of  the  foot,  between  the  internal  cuneiform  and  the  first  and  second 
metatarsals.  It  may  articulate  with  all  three,  or  with  any  of  them,  or  be  attached  to 
them  by  connective  tissue.  More  often  it  is  connected  by  bone  with  one  of  the  three 
neighbors,  especially  with  the  internal  cuneiform,  of  which  it  may  seem  to  be  a  pro- 
cess (Fig.  451).  It  is  found  in  some  form  once  in  ten  feet  (Pfitzner). 

THE   PHALANGES. 


Intermetatarsal  bone  fused  with 
right  internal  cuneiform. 


FIG.  452. 


Third,  distal 
or  ungual. 
phalanx 


Second,  or 
middle, 
phalanx 


There  are  two  for  the  great  toe  and  three  for  each  of  the  others.  Although  of 
very  different  proportions,  they  present  the  features  which  have  been  described  for 
those  of  the  hand,  especially  the  shape  of  the  articular  sur- 
faces. The  first  phalanx  of  the  great  toe  is  about  as 
long  as  that  of  the  thumb  and  nearly  twice  as  broad.  There 
is  a  tubercle  for  muscular  insertion  at  each  side  of  the  pal- 
mar aspect  of  the  base.  The  terminal  phalanx  of  the 
great  toe  is  also  very  massive.  The  first,  or  proximal,  pha- 
langes of  the  other  toes  diminish  in  length  from  within  out- 
ward. Those  of  the  second  row  are  so  short  as  to  be 
almost  cubical,  although  they  are  broader  than  thick.  The 
terminal,  or  distal,  phalanges  are  very  rudimentary. 
Pfitzner1  has  shown  that  in  about  one-third  of  the  cases  the 
terminal  phalanx  of  the  little  toe  is  fused  with  the  middle 
one,  even  before  birth.  Presumably  they  never  were  distinct 
in  the  embryo.  As  he  has  found  this  condition  in  Egyptian 
mummies,  certain  very  pessimistic  views  as  to  the  degener- 
ation in  store  for  the  human  foot  are  probably  unwarranted. 

Sesamoid  Bones. — Those  of  the  first  metatarso-pha- 
langeal  joint  are  large  and  constant  ;  those  of  the  same  joint 
in  the  other  toes  very  rare.  The  least  uncommon  are  those 
of  the  fifth  toe,  of  which  the  inner  sesamoid  is  found  in  5.5 
per  cent,  and  the  outer  in  6.2  per  cent.  A  sesamoid  of  the 
interphalangeal  joint  of  the  great  toe  is  found  in  50.6  per 
cent.  (Pfitzner*). 

Development. — The  first  nucleus  to  appear  is  that  of 
the  distal  phalanx  of  the  great  toe  at  the  end  of  the  third 
fcetal  month.     Those  of  the  other  distal  phalanges,  except  the  fifth,  come  some  two 
weeks  later.     The  bones  of  the  proximal  row  seem  to  ossify  rather  later  than  the 

1  Arch,  fur  Anat.  und  Entwick.,  1890. 
*  Morph.  Arbeiten,  Bd.  i. 


First,  or 
proximal, 
phalanx 


Phalanges  of  right  second 
toe,  plantar  surface. 


THE   PHALANGES. 


433 


distal  ones,  but  this  order  is  not  constant.  According  to  Bade,1  the  middle  phalanges 
have  begun  to  ossify  in  the  eighteenth  week  of  foetal  life,  but  we  have  found  bone 
wanting  considerably  later.  The  process  of  ossification  in  the  fourth  and  fifth  toes 
is  decidedly  later  than  at  the  inner  side  of  the  foot.  It  does  not  begin  in  the  middle 
phalanx  of  the  fifth  till  near  term,  and  we  have  sometimes  seen  no  sign  of  it  in  the 


Ossification  of  bones  of  tHe  foot.  A,  during  sixth  fcetal  month;  B,  at  eighth  foetal  month;  C,  at  birth;  Z>, 
during  first  year  ;  7?,  between  three  and  four  years  ;  f,  at  about  fifteen  years,  a,  for  shaft  of  metatarsals ;  6,  for  cal- 
caneuin  •  c,  for  proximal  phalanges  ;  d,  for  distal  phalanges  ;  e,  for  astragalus  \f,  for  middle  phalanges  ;  g,  for  cuboid  ; 
h,  for  external  cuneiform  ;  /,  for  heads  of  metatarsal  bones  and  base  of  first  proximal  phalanx ;  /,  for  base  of  first 
distal  phalanx;  k,  for  internal  cuneiform  ;  /,  for  base  of  first  metatarsal. 

fifth,  and  even  in  the  fourth  at  birth.  Proximal  epiphyses  appear  from  the  fourth  to 
the  sixth  year,  and  fuse  at  about  sixteen.  The  terminal  phalanges  have  distal  caps 
like  those  of  the  hand.  The  fifth  toe,  according  to  Pfitzner,  has  the  following  pecu- 
liarities :  the  proximal  epiphysis  of  the  second  phalanx  and  the  centre  for  the  shaft 
of  the  terminal  one  are  wanting,  the  proximal  epiphysis  of  the  latter  being  greatly 
exaggerated. 

1  Arch,  fur  Mik.  Anat.,  Bd.  lv.,  1900. 
28 


434 


HUMAN   ANATOMY. 


FIG.  454. 


Abductor  hallucis 

Internal  tuberosity 

Flexor  brevis  digitorum 


Groove  for  tendon  of 
flexor  longus  hallucis 

Sustentaculum  tali 
Astragalus ) 

Scaphoid 

Tibialis  posticus 

External  cuneiform 
Middle  cuneiform 
Internal  cuneiform 

Tibialis  anticus 

Peroneus  longus 

First  metatarsal 


Sesamoid  bones 


Abductor  and  flexor 

brevis  hallucis 
Adductores  obliquus 
et  transversus 


Flexor  longus  hallucis 


Postero-inferior  surface  of  calcaneum 


Abductor  minimi  digiti 

External  tuberosity 

Abductor  ossis  metatarsi  quinti 


Accessorius 
(outer  head) 

Inferior  surface  of  calcaneum 


Flexor  brevis  hallucis 
Cuboid  ridge 

Groove  for  pe roneu s  longus 

Abductor  ossis  metataisi 
quinti 

Flexor  brevis  minimi  dijftti 


Abductor  obliquus  hallucis 
Third  plantar  interosseus 

Second  plantar  interosseus 
First  plantar  interosseus 


Abductor  brevis 
minimi  digiti 
Third  plantar  interosseus 


Second  plantar 
tnterosseus 


First  plantar  interosseus 


Flexor  fi>  >"  I* 
digitoi  inn 

Flexor  longus  digital  urn 


Bones  of  right  foot,  plantar  aspect. 


BONES   OF   THE   FOOT. 


FIG.  455. 


Tendo  Achillis 
Bursal  surface 


Calcaneum 

Lateral  articular  surface  for  fibula. 
Groove  for  peroneus  longits 

Groove  for  peroneus  brevis 
Extensor  brevis  digit  or  um 

Groove  for  peroneus  longus 
Peroneus  brevis 

Peroneus  tertius 


Fourth  dorsal  interosseus 


Extensor  brevis  digitorum 


Extensor  longus  digitorum 


Groove  for  flexor  longus  hallucis 


Superior  articular  surface  of 
astragalus 


Lateral  articular  surface  for 
tibia 


Cuboid 
Scaphoid 

External  cuneiform 
Middle  cuneiform 

Internal  cuneiform 


First  metatarsal 


First  dorsal  interosseus 


Extensor  brevis  hallucis 


Extensor  longits  hallucis 


Bones  of  right  foot,  dorsal  aspect. 


436  HUMAN   ANATOMY. 


PRACTICAL   CONSIDERATIONS. 

The  union  of  the  foot  with  the  leg  at  a  right  angle,  while  necessitated  by  the 
erect  attitude  of  man,  makes  it  essential  that  the  bones  of  the  foot  shall  be  so  shaped 
and  united  that  they  may  afford  a  basis  for  both  support  and  propulsion,  all  pre- 
hensile function  being  sacrificed  to  those  ends.  Accordingly,  we  find  the  tarsus 
proportionately  much  larger,  both  it  and  the  metatarsus  stronger,  and  the  pha- 
langes much  smaller  and  less  mobile  than  the  corresponding  parts  of  the  hand. 
The  strength  of  the  foot  and  its  comparative  freedom  from  injury,  in  spite  of  its  con- 
stant exposure  to  traumatisms  of  various  grades  of  severity,  are  due  to  the  arrange- 
ment of  its  component  bones  into  the  form  of  an  arch,  which  is  well  adapted  not  only  to 
sustain  weight  and  to  provide  leverage  for  motion,  but  also  to  resist  and  distribute 
excessive  force  received,  as  in  falls  upon  the  feet.  The  posterior  pillar  of  the  arch, 
composed  of  the  os  calcis  and  the  hinder  portion  of  the  astragalus,  has  but  one  joint 
— the  calcaneo-astragaloid — with  a  very  limited  range  of  motion.  The  action  of  the 
calf  muscles  upon  the  heel  is  thus  applied  to  the  elevation  of  the  hinder  pillar  with 
the  least  possible  expenditure  of  force,  as  there  are  no  unnecessary  movements 
between  their  point  of  insertion  and  the  ankle-joint. 

The  anterior  pillar  beginning  at  the  top  of  the  astragalus — the  summit  of  the 
arch — may  be  said  to  include  practically  most  of  the  foot  anterior  to  the  ankle  and  to 
separate  naturally  into  ( I )  a  larger  and  stronger  inner  division  consisting  of  the  neck 
and  head  of  the  astragalus,  the  scaphoid,  the  three  cuneiforms,  and  the  three  inner 
metatarsals  ;  and  (2)  a  weaker  and  smaller  outer  division  composed  of  the  cuboid 
and  the  remaining  metatarsals. 

The  anterior  pillar  thus  secures  in  the  wide  surface  of  the  distal  extremities  of 
the  metatarsal  bones  a  broad  basis  of  support ;  its  inner  division  carries  most  of  the 
weight,  and  is  enabled  to  do  this  by  the  thickness  and  strength  of  the  metatarsal  bone 
of  the  great  toe  and  by  the  parallelism  of  the  latter  with  the  great  toe  ;  its  outer 
division  bears  less  weight,  but  supports  the  inner  division  laterally  and  broadens  the 
surface  in  contact  with  the  ground.  The  normal  foot  thus  rests  directly  upon  the  os 
calcis  and  the  anterior  extremities  of  the  metatarsals,  the  outer  side  of  the  foot  aiding 
more  in  preserving  balance  than  in  carrying  weight. 

An  imperfect  transverse  arch — including  the  scaphoid,  cuboid,  and  cuneiforms — 
adds  to  the  elasticity  of  the  foot  and  aids  the  main  arch  in  affording  a  pressure-free 
area  for  the  plantar  vessels  and  nerves.  Both  arches  depend  for  their  integrity  not 
only  upon  the  shape  of  the  bones,  but  also  upon  the  fasciae,  ligaments  and  tendons, 
and  to  some  extent  upon  the  small  plantar  muscles.  Still  another  transverse  arch  is 
formed  by  the  bases  of  the  metatarsal  bones,  and  a  third,  but  less  distinct  one,  by 
their  heads. 

Perhaps  the  most  accurate  conception  of  the  foot  mechanically  is  as  a  semi-dome 
(Ellis),  the  whole  dome  being  completed  in  well-shaped  feet  when  the  inner  borders 
are  approximated. 

The  epiphysis  of  the  os  calcis  occupies  the  posterior  rounded  extremity  of  the 
bone,  and  has  inserted  into  it  the  tendo  Achillis.  No  positive  clinical  evidence  of 
separation  exists,  but  it  is  probable  that  the  X-rays  will  show  that  in  young  persons 
lesions  heretofore  supposed  to  be  fractures  of  the  os  calcis  from  muscular  action  are 
actually  epiphyseal  disjunctions. 

The  epiphyses  of  the  remaining  bones  of  the  foot  have  but  little  surgical  interest. 
The  first  metatarsal,  like  that  of  the  thumb,  has  its  epiphysis  at  the  proximal  end, 
and  to  that  extent  resembles  a  phalanx.  The  other  four  metatarsals  have  their  epiph- 
yses at  the  distal  ends.  All  the  phalangeal  epiphyses  are  at  the  proximal  ends. 
In  the  metatarso-phalangeal  joints  the  synovial  membrane  is  in  close  relation  to  the 
epiphyseal  lines  ;  in  the  phalangeal  joints  it  is  not.  A  knowledge  of  these  farts  may 
occasionally  be  useful  in  cases  of  disease  or  injury  limited  to  a  particular  bone. 

Fracture  of  the  hones  of  the  tarsus  is  rare,  except  as  a  result  of  crushing  injuries 
or  of  falls  from  considerable  heights.  If  the  bones  of  the  anterior  pillar  are  broken, 
it  is  usually  by  direct  violence,  as  the  numerous  joints  and  ligaments  of  this  region 
render  it  so  elastic,  and  so  diffuse  forces  applied,  as  in  jumps  or  falls,  as  effectually  to 


PRACTICAL   CONSIDERATIONS:   THE   FOOT   BONES.  437 

prevent  fracture.  The  bones  of  the  posterior  pillar  are  broken  in  both  ways.  In 
falls  the  astragalus  is  apt  to  break  about  its  neck, — the  weakest  portion  ;  or  if  the 
foot  is  strongly  dorsiflexed,  the  anterior  articular  edge  of  the  tibia  may  act  as  a 
wedge  and  split  it  across.  The  os  calcis  may  be  broken  between  the  astragalus  and 
the  ground, — compression  fracture  ;  or  it  may  be  broken  behind  the  insertion  of  the 
inferior  calcaneo-scaphoid  ligament,  the  anterior  arch  being  flattened  by  the  fall,  but 
the  ligament  resisting  rupture.  A  few  cases  of  fracture  of  the  sustentaculum  tali  have 
been  reported,  the  foot  having  been  in  forcible  inversion,  the  lesser  process  (susten- 
taculum) being  broken  off  against  the  edge  of  the  astragalus.  In  each  case  this  was 
followed  by  eversion  and  sinking  of  the  inner  border  of  the  foot  (valgus),  the  support 
given  by  the  internal  articulating  surface  to  the  astragalus  having  been  removed. 

Of  the  metatarsal  bones,  the  first,  although  the  strongest,  is  most  frequently  broken 
because  it  carries  so  large  a  proportion  of  the  body  weight  and  because  it  receives  an 
undue  share  of  the  violence  in  falls  associated  with  eversion  of  the  foot.  The  fifth 
comes  next  in  frequency  because  of  its  exposed  position  on  the  outer  side  of  the  foot 
and  the  added  violence  in  cases  of  inversion. 

Dislocation  of  separate  bones,  especially  of  the  astragalus,  is  rare.  It  is  always 
the  result  of  the  application  of  considerable  crushing  force,  is  usually  associated  with 
other  injuries,  and  is  influenced  but  little  by  anatomical  factors. 

Disease  of  the  bones  of  the  foot,  and  especially  tuberculous  disease  of  the  tarsus, 
is  common  because  of  :  (i)  the  frequency  of  traumatism  ;  (2)  the  exposure  to  cold 
and  damp  and  the  scanty  protection  afforded  by  the  superjacent  tissues  ;  (3)  the 
remoteness  from  the  centre  of  circulation  and  the  dependent  position  of  the  part, 
both  favoring  congestions  ;  (4)  the  preponderance  of  cancellous  tissue  in  the  bones  ; 
and  (5)  the  difficulty  in  securing  perfect  rest,  especially  after  minor  injuries,  which 
are  those  most  often  followed  by  tuberculous  osteitis.  It  affects  most  frequently  those 
bones  that  bear  most  of  the  weight  of  the  body, — the  os  calcis,  the  head  of  the 
astragalus,  and  the  base  of  the  first  metatarsal.  It  is  more  likely  to  remain  localized 
when  situated  in  the  os  calcis  or  in  the  hinder  part  of  the  astragalus  ;  in  the  anterior 
portions  of  the  tarsus  the  number  and  complexity  of  the  synovial  cavities  (often 
intercommunicating)  tend  to  prolong  and  to  spread  the  disease.  In  disease  of  the 
tarsal  bones — excepting  the  astragalus,  to  which  no  muscle  is  attached — the  tendon 
sheaths  in  the  vicinity  may  be  involved  by  direct  extension  from  the  periosteum. 

Any  metatarsal  bone  may  be  involved  in  cases  of  ' '  perforating  ulcer, ' '  the  situa- 
tion of  the  latter  being  determined  usually  by  the  degree  of  pressure  upon  the  sole  in 
cases  in  which  anaesthesia  is  already  present  ;  hence  the  frequency  with  which  the  first 
metatarsal  is  involved  in  this  disease. 

Excision  of  the  separate  bones  has  frequently  been  performed,  especially  of  the 
astragalus  and  os  calcis. 

Landmarks. — On  the  inner  side  of  the  foot  can  be  felt  :  (#)  the  ridge  between 
the  inner  and  posterior  surfaces  of  the  os  calcis  ;  (£)  the  tubercle  of  the  os  calcis  ;  (r) 
the  sustentaculum  tali,  one  inch  directly  below  the  tip  of  the  malleolus  ;  (d)  from  one- 
half  to  three-quarters  of  an  inch  in  front  of  the  latter  the  head  of  the  astragalus,  very 
noticeable  in  flat-foot ;  (<?)  from  one-half  to  three-quarters  of  an  inch  more  anterior 
the  prominent  tuberosity  of  the  scaphoid,  the  space  between  it  and  the  sustentaculum 
being  filled  by  the  inferior  calcaneo-scaphoid  ligament  and  the  tibialis  posticus  tendon  ; 
from  the  tuberosity  the  tendon  may  be  traced  to  the  back  of  the  inner  malleolus  ; 
(/")'  the  internal  cuneiform  ;  (g*)  the  base  (one  and  a  half  inches  in  front  of  the 
scaphoid  tuberosity),  the  shaft,  and  the  expanded  head  of  the  first  metatarsal  ;  (h) 
the  base  of  the  first  phalanx  with  the  internal  sesamoid  bones  just  beneath  ;  (z)  the 
phalanges. 

On  the  outer  side  are  to  be  felt  :  (#)  the  ridge  between  the  outer  and  posterior 
surfaces  of  the  os  calcis  ;  (<5)  the  external  tubercle  of  the  os  calcis  ;  (c*)  the  peroneal 
tubercle,  three-quarters  of  an  inch  below  and  a  little  in  front  of  the  tip  of  the  external 
malleolus,  lying  between  the  long  and  short  peroneal  tendons  ;  (^)  the  external 
surfaces  of  the  os  calcis  and  (when  the  foot  is  inverted)  the  edge  of  its  anterior 
extremity,  lying  just  above  the  cuboid  ;  (c)  the  prominent  base  of  the  fifth  metatarsal 
(about  two  and  a  half  inches  in  front  of  the  malleolus),  the  shaft,  and  the  expanded 
head  of  that  bone  ;  (  /")  the  phalanges. 


438 


HUMAN   ANATOMY. 


On  the  sole  of  the  foot  between  the  tuberosity  of  the  os  calcis  and  the  heads  of 
the  metatarsals  the  bones  cannot  be  felt  distinctly.  The  internal  sesamoids  are 
directly  beneath  the  first  metatarso-phalangeal  articulation. 

On  the  dorsum  of  the  foot,  when  at  right  angles  to  the  leg,  the  bones  of  the 
tarsus  form  a  smooth  rounded  convexity,  with  a  slight  elevation  between  its  middle 
and  inner  thirds,  made  up  of  the  head  of  the  astragalus,  the  scaphoid,  the  middle 
cuneiform,  and  the  second  metatarsal.  With  the  foot  in  full  extension  the  head  of 
the  astragalus  projects,  and  the  extreme  anterior  ends  of  the  ridges  between  the  upper 
and  lateral  articular  surfaces  of  that  bone  can  be  felt.  The  internal  cuneiform  at  the 
summit  of  the  instep  is  easily  recognized.  The  other  cuneiforms,  the  cuboid,  and 
the  metatarsals  can  be  felt  in  thin  feet. 


THE   ANKLE-JOINT. 

The  articulation  is  between  the  bones  of  the  leg  and  those  of  the  foot  as  a 
whole, — i.e.,  between  the  tibia  and  fibula  above  and  the  astragalus  below.  It  is  a 
hinge-joint,  although  the  mortise  of  the  leg  bones  and  the  top  of  the  astragalus  are 
both  broader  in  front  than  behind.  The  ligaments  are  :  the  capsular,  supporting 


FIG.  456. 


Superior  astragalo- 
scaphoid  ligament 


Tibialis  posticus 

Groove  for  tibialis  posticus 

Sustentaculum  tali 
Groove  for  flexor  cotnmunis  digitorum 

Groove  for  flexor  longus  hallucisl 


Right  ankle-joint,  inner  aspect. 


the  synovial  membrane,  and  itself  strengthened  by  very  strong  bands  at  the  sides 
(lateral  ligaments}  and  by  a  weak  one  at  the  back.  There  is  also  a  middle  external 
lateral  ligament  quite  distinct  from  the  capsule. 

The  capsule  (Fig.  456)  arises  from  the  front  of  the  tibia  nearly  one  centi- 
metre above  the  lower  border,  from  the  edge  of  the  anterior  tibio-fibular  ligament, 


THE   ANKLE-JOINT. 


439 


from  the  front  of  both  malleoli  at  some  distance  from  the  anterior  border,  and  from 
the  under  side  of  both  malleolar  articular  surfaces.  The  posterior  half  of  the 
superior  origin  is  closer  to  the  articular  border  both  of  the  back  of  the  tibia  and  that 
of  the  inner  malleolus,  but  it  arises  from  the  posterior  border  of  the  outer  malleolus, 
so  as  to  leave  a  deep  pocket  behind  the  outer  articular  surface.  The  inferior  inser- 
tion surrounds  the  articular  surface  on  the  top  and  sides  of  the  astragalus,  being 
close  to  the  cartilage,  except  in  front,  where  the  distance  may  be  one  centimetre, 
and  behind,  where  the  separation  is  less.  This  capsule  consists  in  front  of  longi- 
tudinal fibres  of  no  great  strength,  often  with  fat  between  them.  The  posterior  part 
of  the  capsule  is  extremely  thin. 


Tendo  Achillis 


Transverse  tibio-fibular  ligament 


Posterior  fasciculus  of  external  lateral 
ligament 

Middle  fasciculus  of 
external  lateral  ligamen 


Anterior  inferior  tibio- 
fibular  ligament 


Anterior  fasciculus  of 
external  lateral 
ligament 


Astragalo-calcaneal 
ligament 

^llnterosseous  ligament 


Peroneal  spine  with 
fibrous  tissue 


Right  ankle-joint,  outer  aspect. 

The  internal  lateral '  or  deltoid  ligament  (Fig.  456)  is  an  extremely  strong 
part  of  the  capsule,  arising  from  the  notch  in  the  posterior  border  and  from^the 
tip  of  the  inner  malleolus,  the  former  portion  being  almost  one  centimetre  thick, 
running  downward  and  backward  to  the  astragalus  below  the  inner  articular  surface 
by  its  deeper  fibres  and  to  the  sustentaculum  tali  by  the  superficial  ones.  The 
great  strength  of  this  part  of  the  ligament  is  appreciated  by  examining  it  after 
division.  The  anterior  part,  thinner  but  still  strong,  runs  to  the  inferior  calcaneo- 
scaphoid  ligament,  and,  joining  the  superior  astragalo-scaphoid  ligament,  may  be 
traced  to  the  scaphoid.  It  has  no  line  of  separation  from  the  front  of  the  capsule. 

The  external  lateral  ligament  (Fig.  457)  is  described  as  consisting  of  three 
bands  which  radiate  from  the  external  malleolus,  although  only  two  are  really  parts  of 


1  Li«.  dcltoidcum. 


440  HUMAN   ANATOMY. 

the  capsule.  The  anterior  band1  (Fig.  457)  passes  forward  and  inward  from  the 
front  border  of  the  malleolus  to  the  astragalus  in  front  of  the  lateral  articular  surface. 
It  is  made  tense  in  plantar  flexion.  The  posterior  band*  (Fig.  457) — a  very  strong 
one — arises  from  the  hollow  on  the  inside  of  the  tip  of  the  outer  malleolus  and  runs 
inward  and  backward  to  the  astragalus  behind  the  posterior  outer  angle  of  the 
articular  surface.  It  is  made  tense  in  dorsal  flexion.  With  the  transverse  tibio- 
fibular  ligament  it  considerably  strengthens  the  back  of  the  capsule.  The  middle 
band*  (Fig.  457),  more  superficial  and  tending  to  be  free  from  the  capsule,  runs  down- 
ward and  backward  to  a  faint  tubercle  on  the  outer  side  of  the  calcaneum.  It  can 
be  made  fully  tense  by  no  motion  in  the  ankle-joint  alone,  but  restrains  certain 
motions  of  the  astragalus  on  the  calcaneum.  The  capsule  between  these  bands  is 
excessively  thin. 

The  synovial  membrane  lining  the  capsule  is  in  the  main  perfectly  simple, 
following  the  latter  ;  it  presents,  however,  a  prominent  fold  on  the  inside  of  the 
joint  over  the  posterior  band  of  the  external  lateral  ligament,  and  makes  something 
of  a  pouch  above  this,  below  the  transverse  ligament.  It  covers  the  pad  of  fat  be- 
tween the  bones  of  the  leg. 

Movements. — The  articulation  at  the  ankle  is  essentially  a  hinge-joint,  although 
not  a  pure  one,  since  the  fibula  moves  on  the  tibia,  and  the  astragalus,  being  more 
closely  fastened  to  the  fibula,  follows  the  latter  in  its  movements  ;  thus,  the  outer 
end  of  the  transverse  axis  of  rotation  is  subject  to  displacement.  When  the  foot  is 
midway  between  flexion  and  extension,  it  is  possible  in  the  dead  body  to  impart  a 
certain  lateral  motion  to  the  astragalus,  the  lateral  ligaments  being  apparently  not 
tense  ;  but  it  is  highly  improbable  that  this  ever  occurs  during  life,  unless  under 
accidental  circumstances,  for  the  muscles  supplement  the  ligaments.  As  the  foot 
moves  into  dorsal  flexion  the  broadest  part  of  the  astragalus  comes  into  the  broadest 
part  of  the  socket,  forcing  the  malleoli  somewhat  apart.  In  some  cases  it  would 
appear  that  the  fibula  rotates  on  a  longitudinal  axis,  while  the  head  slips  backward, 
but  both  the  degree  and  even  the  nature  of  the  movement  are  uncertain.  The  foot 
is  held  firm  and  immovable  by  the  spring  of  the  bones,  by  the  tension  of  the  pos- 
terior ligament  and  of  the  posterior  and  middle  divisions  of  the  external  lateral  one, 
and  especially  by  the  strong  posterior  part  of  the  internal  lateral.  In  extreme 
plantar  flexion  the  narrowest  part  of  the  astragalus  is  in  the  socket,  of  which  the 
bones  are  in  the  greatest  possible  approximation,  so  that  the  pad  of  fat  between 
them  is  squeezed  into  the  joint  and  rests  against  the  sickle-shaped  facet  of  the 
superior  surface,  except  that  the  hind  end  of  the  latter  is  against  the  posterior  tibio- 
fibular  ligament.  The  fold  in  the  posterior  ligament  is  brought  against  the  back  of 
the  bone.  The  anterior  ligament  and  the  anterior  parts  of  the  lateral  ones  are  tense. 
Further  support  is  gained  by  the  back  of  the  astragalus  below  the  articular  facet 
resting  against  the  back  of  the  tibia  so  as  to  lock  the  joint.  The  front  bands  of  both 
outer  and  inner  lateral  ligaments  are  tense.  The  action  of  the  numerous  muscles 
crossing  the  ankle  is,  of  course,  greatly  to  strengthen  it  and  to  prevent  any  giving 
between  the  bones  when  the  ligaments  are  not  stretched  to  the  utmost.  Moreover, 
the  elasticity  of  the  fibula  is  an  important  element  in  the  mechanics  of  the  ankle- 
joint,  and  one  that  makes  it  impossible  to  contrive  a  model  that  will  represent  the 
conditions  actually  existing. 

THE   ARTICULATIONS   OF   THE   FOOT. 

As' has  been  shown,  the  bones  of  the  foot  are  so  arranged  (Fig.  431)  that  the 
astragalus,  placed  on  the  calcaneum,  carries  with  it  the  three  inner  toes.  while  the  two 
outer,  resting  on  the  cuboid,  are  more  under  the  influence  of  the  movements  of  the 
calcaneum.  It  is,  however,  possible  for  the  scaphoid  and  cuboid  to  move  together 
on  the  two  proximal  bones.  The  essential  joints  for  the  movements  of  the  foot, 
besides  the  ankle-joint,  are  those  between  the  ca  I  cane  tun  and  astragalus  and  those 
between  the  astragalus  and  scaphoid  and  the  ca/canennt  and  cuboid  respectively. 
The  joints  between  the  smaller  bones  at  the  front  of  the  tarsus  are  mechanically  un- 
important, being  chiefly  to  break  shocks  and  to  allow  an  indefinite  giving  in  the 
arch  of  the  foot.  As  certain  ligaments  are  concerned  in  the  protection  of  several 

1  Llg.   talolibulnrc  nntcrius.     "Liu.   tiili.libulnrc  posterius.         l.i«.    ,  .iU  .iiu.ilil.ul.ii  i-. 


THE   INTEROSSEOUS    LIGAMENTS. 


441 


joints,  it  is  best  first  to  study  the  ligaments  of  the  foot  all  together,  beginning  with 
such  as  are  essential  parts  of  the  framework  ;  then  to  examine  the  joints  seriatim; 
and,  finally,  to  discuss  the  motions  of  the  foot  as  a  whole.  In  the  case  of  the  smaller 

FIG.  458. 


Tibia 


Posterior  tibio-fibular — j 
ligament 


Fibula 


InterosseousV 
astragalo-calca--\ 
neal  ligament        \ 
Calcaneo-scaphoid 
ligament 
Cubo  scaphoid  lig. 


Cubo-cuneiform  ligament 


Cuneiform  bones 

Intercuneiform 
^S^         and  inner  tarso- 
metatarsal 
ligaments 

First 
metatar- 
sal 


Second 
metatarsal 

Third  metatarsal 
Fourth  metatarsal 
Fifth  metatarsal 


Oblique  section  through  the  right  foot. 

ligaments  it  is  our  object  to  avoid  pedantic  attention  to  useless  details.     We  shall 
consider  first  the  interosseous  ligaments,  then  the  dorsal,  and  lastly  the  plantar  ones. 


THE   INTEROSSEOUS    LIGAMENTS. 

The  astragalo-calcaneal  (Fig.  457)  is  a  thick  layer  of  fibres  filling  the 
groove  between  the  two  adjacent  articular  surfaces  of  each  bone.  At  the  outer 
part,  where  the  groove  widens,  it  tends  to  divide  into  two  layers.  A  considerable 
quantity  of  fat  is  found  in  its  meshes.  Each  side  of  it  is  lined  by  the  synovial  mem- 
brane of  the  joints  which  it  separates.  An  occasional  superficial  band — the  external 
astragalo-calcaneal  (Fig.  457) — may  be  continuous  with  this  ligament. 

The  calcaneo-cubo-scaphoid  (Fig.  460)  (seen  by  removing  the  astragalus 
and  the  synovial  membrane  covering  it)  is  a  series  of  short,  strong  fibres,  collected 
into  bundles,  joining  the  front  of  the  calcaneum  with  the  outer  border  of  the  scaph- 
oid, and  by  a  weaker  division  with  the  inner  side  of  the  cuboid.  It  forms  the  outer 
part  of  the  capsule  for  the  head  of  the  astragalus,  reaching  to  the  dorsum.  This 
capsule  is  completed  by  the  superior  and  inferior  calcaneo-scaphoid  ligaments. 


442  HUMAN   ANATOMY. 

The  cubo-scaphoid  (Fig.  458)  passes  crosswise  between  these  bones,  close 
to  the  last  ligament.  Its  size  varies,  being  in  inverse  ratio  to  the  articular  facet 
between  the  bones  it  unites. 

The  cubo-cuneiform  (Fig.  458)  is  a  strong  band  connecting  the  non-articular 
surfaces  of  the  cuboid  and  the  outer  cuneiform  at  their  distal  ends  from  the  plantar 
to  the  dorsal  border. 

The  intercuneiform  (Fig.  458)  are  strong  ligaments  connecting  the  distal 
non-articular  surfaces  of  these  bones.  That  from  the  inner  side  of  the  middle 
cuneiform  does  not  completely  separate  the  joints  before  and  behind  it.  The 
arrangement  between  the  middle  and  outer  cuneiforms  is  variable  in  this  respect. 

The  interosseous  tarso-metatarsal  ligaments  (Fig.  458)  are  an  inner  and 
an  outer,  with  an  occasional  middle  one.  The  inner,  a  strong  band  arising  from 
the  outer  side  of  the  internal  cuneiform  where  it  overlaps  the  second  metatarsal,  runs 
obliquely  outward  and  forward,  most  of  its  fibres  going  to  that  bone,  but  a  few  to  the 


Astragalo-calcaneal  ligament 


Articular  surface  for  cuboid 


Articular  surfaces  for  astragalus 

Sustentaculum 
The  inner  part  of  the  right  astragalus  has  been  removed. 

outer  side  of  the  first  metatarsal.  The  outer  interosseous  ligament  arises  from  the 
adjacent  sides  of  the  external  cuneiform  and  the  cuboid,  mingling  with  the  fibres  of 
the  ligament  already  described  as  passing  between  them,  and  runs  forward  to  the 
inner  side  of  the  base  of  the  fourth  metatarsal,  to  the  rough  surface  proximal  to  the 
facet,  and  to  the  plantar  half  of  the  outer  side  of  the  third.  The  middle  interosseous 
ligament  is  inconstant  and  small.  It  runs  from  the  outer  cuneiform  to  the  second 
metatarsal. 

The  interosseous  intermetatarsal  ligaments  (Fig.  458)  are  strong 
bands,  best  seen  on  section,  between  the  bases  of  the  four  outer  bones.  The  few 
fibres  between  the  bases  of  the  first  and  second  do  not  deserve  the  name. 

The  distal  intermetatarsal  ligament  is  not  an  interosseous  one,  properly 
speaking,  but  is  mentioned  here  as  it  is  an  important  piece  of  the  general  framework. 
It  is  a  fibrous  band  connecting  the  glenoid  cartilages  at  the  metacarpo-phalangeal 
joints  precisely  as  in  the  hand,  except  that  it  goes  to  the  great  toe  as  well  as  to  the 
others. 


THE   DORSAL    LIGAMENTS. 


The  dorsal  ligaments  of  the  tarsus  are  a  number  of  bands  of  varying  degro 
of  distinctness,  all  of  which,  in  part  at  least,  assist  in  forming  the  capsules  of  the 
various  joints,  although  they  may  extend  farther. 

The  superior  astragalo-scaphoid  (Fig.  460)  might  be  divided  into  an  inner 
part,  composed  of  fibres  running  from  the  inner  side  of  the  former  bone  to  the  inner 
and  dorsal  aspect  of  the  latter,  and  into  a  dorsal  part,  running  from  the  margin  of 
the  head  of  the  astragalus  forward,  with  an  inclination  either  inward  or  outward. 


- 

k. 


THE   DORSAL    LIGAMENTS. 


443 


A  series  of  well-marked  but  not  strong  ligaments  radiate  forward  and  outward 
from  the  scaphoid  (Fig'.  460):  three  dorsal  scapho-cuneiform  and  one  scapho- 
cuboid  ligament. 

The  dorsal  calcaneo-cuboid  ligament  (Fig.  460)  is  a  thin  band  of  little 
note.  The  interosseous  calcaneo-cubo-scaphoid  reaches  the  dorsum  by  the  part 
going  to  the  scaphoid.  The  ligament  just  mentioned  is  sometimes  continuous  with 
it  at  its  origin,  and  the  two  have  been  called  by  French  anatomists  the  Y-ligament, 
to  which  much  consequence  has  been  ascribed.  The  interosseous  ligament  is  the 
important  one. 

FIG.  460. 


Dorsal  tarso-metatarsal 
ligaments 


Dorsal  scapho-cuneiform 
ligaments 


Astragalo-scaphoid 
ligament 

Scaphoid 

Calcaneo-cubo-scaphoid 
ligament 

Inferior  calcaneo- 
scaphoid  ligament 

Fibro-cartilage 


Sustentaculum 


Interosseous  astragalo- 
calcaneal  ligament 


Dorsal  intermetatarsal 
ligament 


Peroneus  tertius 


Superior  scapho- 
cuboid  ligament 


Dorsal  calcaneo-cuboid 
ligament 


Peroneus  brevis 


-Astragalo-calcaneal  ligament 


Upper  aspect  of  the  right  tarsus,  the  astragalus  having  been  removed. 


The  dorsal  tarso-metatarsal  ligaments  (Fig.  460)  are  simple  for  the  first 
metatarsal,  being  bands  running  from  the  internal  cuneiform.  For  the  others  they 
are  more  irregular,  and  there  is  an  interlacing  with  transverse  dorsal  ligaments 
between  the  metatarsals  connecting  the  outer  four  bones  and  the  second  to  the 


444 


HUMAN   ANATOMY. 


internal  cuneiform.  The  bands  over  the  cuboid  and  the  two  outer  metatarsals  are 
closely  interwoven  with  the  tendon  of  the  peroneus  tertius  when  that  muscle  is 
present.  These  ligaments  constitute  an  interrupted  series  of  bands  converging  for- 
ward from  either  side  of  the  foot. 

The  dorsal  ligaments  are  weak,  and  need  the  help  of  the  extensor  muscles  of 
the  toes  to  resist  the  strain  of  the  strong  muscles  of  the  sole. 

THE   PLANTAR    LIGAMENTS. 

The  plantar  ligaments  are  of  three  kinds  :   (a)  those  passing  from  one  bone  to 
the  next,  and  therefore  nothing  but  thickenings  of  the  capsule  ;   (6)  those  passing 

FIG.  461. 


Intermetatarsal  ligament 


Tendon  of  peroneus 
longus 


Short  plantar 
ligament 


Long  plantar  ligam 
Peroneal  s 


Calcaneum 


Tendo  Achillis 

Ri^ht  tarsus,  inferior  aspect. 


from  one  bone  to  one  or  several  distant  ones  ;   (V)  and  those  continuous  with  the 
tendon  of  the  tibialis  posticus,  which  is  very  strong  and  has  a  far-reaching  action. 


THE   CALCANEO-ASTRAGALOID   JOINT.  445 

The  plantar  calcaneo-cuboid  ligaments  are  the  long  and  the  short.  The 
former,  known  as  the  long  plantar  ligament  (Fig.  461),  arises  from  the  perios- 
teum of  the  under  side  of  the  calcaneum  in  front  of  the  posterior  tubercles,  and  runs 
forward  as  a  flat  band,  at  first  some  two  centimetres  broad,  to  the  whole  length  of 
the  ridge  of  the  cuboid,  except  its  inner  end.  It  passes  beyond  this  to  the  bases  of 
the  outer  three  metatarsals  in  a  somewhat  broken  and  weak  layer  of  fibres  forming 
a  bridge  over  the  groove  for  the  tendon  of  the  peroneus  longus.  The  short 
plantar  ligament  (Fig.  461)  is  in  part  hidden  by  the  longer,  but  is  seen  at  its 
inner  side.  It  arises  from  the  anterior  tubercle  of  the  calcaneum  and  the  bone  in 
front  of  it  and  goes  to  the  under  side  of  the  cuboid,  between  the  posterior  border 
and  the  ridge.  The  inner  fibres  run  obliquely  forward  and  inward. 

The  inferior  calcaneo-scaphoid  ligament  (Fig.  461)  fills  the  gap  on  the 
plantar  side  of  the  foot  between  the  sustentaculum  and  the  scaphoid.  It  is  more  or 
less  divisible  into  two  parts,  which  have  a  common  origin  from  the  anterior  border 
of  the  sustentaculum.  The  inner  and  stronger  part  runs  obliquely  forward  and 
inward  to  the  lower  border  of  the  scaphoid  near  the  tuberosity.  The  outer  part 
runs  more  nearly  straight  forward  to  the  outer  part  of  the  same  border.  There  is 
generally  a  small  interspace  between  them.  The  upper  surface  of  the  inner  portion 
of  the  ligament  is  covered  by  a  coating  of  articular  cartilage  completing  the  joint 
for  the  head  of  the  astragalus.  This  cartilage  is  usually  wanting  at  the  anterior 
outer  angle  of  the  space  between  the  bones.  Beneath  and  to  the  inner  side  of  the 
ligament  runs  the  tendon  of  the  tibialis  posticus.  On  the  inner  side  of  the  foot 
this  ligament  is  continuous  with  a  part  of  the  superior  astragalo-scaphoid  and  with 
the  termination  of  the  deltoid  ligament. 

The  inferior  scapho-cuboid  ligament  (Fig.  461)  is  an  insignificant  group 
of  fibres. 

The  inferior  scapho-cuneiform  ligaments  (Fig.  461)  are  three  distinct 
bands,  of  which  the  inner  is  the  broadest,  the  others  being  more  cord-like,  diverging 
from  the  under  side  of  the  scaphoid  to  the  three  cuneiform  bones.  They  are  all 
continuous  with  the  fibres  of  the  tendon  of  the  tibialis  posticus. 

On  the  plantar  side  there  is  a  very  irregular  arrangement  of  fibres  passing  from 
the  tarsus  to  the  metatarsus  and  a  considerable  system  of  oblique  fibres  running 
inward  and  forward  from  the  cuboid  and  the  fifth  metatarsal  to  the  external  cunei- 
form and  to  the  bases  of  several  metatarsal  bones. 

The  joints  of  the  phalanges  are  on  the  same  plan  as  in  the  hand  and  require  no 
further  description.  The  sesamoid  bones  at  the  tarso-metatarsal  joint  of  the  great 
toe  are  very  large  and  connected  by  the  glenoid  ligament. 

THE   POSTERIOR   CALCANEO-ASTRAGALOID   JOINT. 

This  joint  (Fig.  460)  is  separated  from  the  anterior  by  the  interosseous  ligament, 
which  is  continuous  with  the  capsule  that  completely  surrounds  the  articulation. 
This  capsule  is  in  most  parts  weak,  but  is  strengthened  behind  by  the  posterior 
astragalo-calcaneal  ligament. 

THE   ANTERIOR    CALCANEO-SCAPHO-ASTRAGALOID   JOINT. 

This  articulation  (Fig.  460)  may  be  called  a  ball-and-socket  joint,  although  the 
head  of  the  astragalus  is  not  a  part  of  the  surface  of  a  sphere.  The  articular  surfaces 
have  been  described  with  the  bones.  The  socket  is  made  by  the  anterior  articular 
facet  or  facets  of  the  calcaneum,  by  the  posterior  facet  of  the  scaphoid,  by  the  inter- 
osseous  ligament  joining  these  externally,  and  by  the  inferior  calcaneo-scaphoid  liga- 
ment, with  its  cartilaginous  plate,  which  fuses  on  the  inner  side  with  the  superior 
calcaneo-scaphoid  and  the  deltoid  ligament,  all  of  which  make  a  capsule  around  the 
head,  completed  by  the  interosseous  astragalo-calcaneal  ligament.  A  fold  of  syno- 
vial  membrane,1  variously  developed,  which  may  contain  fibrous  tissue,  is  generally 
found  on  the  floor  of  this  socket,  extending  back  from  the  interruption  of  the  anterior 
facet  on  the  calcaneum,  or  from  a  corresponding  place  when  it  is  simple,  to  the  inferior 

1  E.  Barclay  Smith  :  Journal  of  Anatomy  and  Physiology,  vol.  xxx.,  1896. 


446  HUMAN    ANATOMY. 

border  of  the  head  of  the  astragalus.     The  tendon  of  the  tibialis  posticus  directly 
beneath  and  internal  to  the  joint  adds  to  its  security. 

The  motions  of  the  two  subastragaloid  joints  must,  of  course,  be  considered 
together.  They  are  resolved  into  turning  on  an  oblique  axis  running  through  the 
interosseous  ligament,  somewhat  internal  to  its  middle,  downward  with  something 
of  a  backward  and  inward  inclination.  Rotating  on  this,  the  posterior  concave 
articular  surface  of  the  astragalus  twists  with  a  screw  motion  on  the  opposed  surface 
of  the  calcaneum.  As  the  back  of  the  astragalus  moves  upward  and  outward,  the 
head  passes  downward  and  inward  in  the  socket.  This  movement  is  stopped  by  the 
front  of  the  posterior  articular  surface  of  the  astragalus  catching  in  the  hollow  at  the 
front  of  the  convex  surface  of  the  calcaneum  that  it  plays  on.  This  is  a  most  efficient 
device  for  locking  the  joint.  The  opposite  motion  is  stopped  by  the  inner  posterior 
tubercle  of  the  astragalus  striking  the  back  of  the  sustentaculum  tali.  In  the  anterior 
joint  there  is  also  to  be  considered  the  motion  between  the  head  of  the  astragalus 
and  the  scaphoid.  The  strong  interosseous  and  inferior  calcaneo-scaphoid  ligaments 
do  not  allow  much  displacement  of  the  scaphoid,  but  it  seems  that  it  can  travel  for 
a  short  distance  up  or  down  and  in  or  out,  and  can  therefore  be  slightly  circum- 
ducted  ;  the  chief  motion,  however,  is  one  of  rotation  on  the  above-mentioned  axis 
through  the  astragalus.  Variations  in  the  slant  of  the  posterior  articular  surface  of 
the  os  calcis  must,  of  course,  modify  the  position  of  the  axis. 

THE   CALCANEO-CUBOID   JOINT. 

The  calcaneo-cuboid  joint  (Fig.  458),  surrounded  by  a  capsule  the  inner  side 
of  which  is  formed  by  the  interosseous  calcaneo-cubo-scaphoid  ligament,  is  a  modi- 
fication of  the  saddle-joint.  Apart  from  some  indefinite  gliding,  the  nature  and 
amount  of  which  vary  in  different  feet,  the  chief  motion  is  rotation  on  an  approxi- 
mately antero-posterior  axis  running  through  the  joint.  It  might,  perhaps,  be  more 
accurately  defined  as  a  screw  motion.  This  movement,  however,  is  very  limited. 
Rotation  of  the  cuboid  in  a  direction  that  would  raise  its  outer  border  is  checked  by 
the  interosseous  and  dorsal  ligaments  at  its  inner  side.  Rotation  in  the  opposite 
direction,  if  not  sooner  arrested  by  the  ligaments,  is  effectually  checked  by  the 
plantar  tubercle  of  the  cuboid  catching  on  the  overhanging  lip  of  the  articular  surface 
of  the  os  calcis,  thus  locking  the  joint. 

'  THE   SCAPHO-CUBO-CUNEIFORM   JOINT. 

This  articulation  is  a  synovial  cavity  bounded  behind  by  the  scaphoid,  extending 
forward  to  varying  distances  between  the  different  bones.  Thus,  between  the  first 
and  second  cuneiforms  it  communicates  with  the  joint  of  the  second  metatarsal,  it  is 
usually  bounded  by  the  interosseous  ligament  between  the  second  and  third  meta- 
tarsals,  and  finally  by  that  between  the  latter  with  the  cuboid.  The  motions  are 
very  slight  in  each  joint  and  of  no  great  importance  when  combined.  There  is  next 
to  no  motion  of  the  internal  cuneiform  of  the  scaphoid  and  very  little  of  the  second. 
The  external  moves  more  freely,  sliding  slightly  up  and  down.  The  interosseous 
ligaments  resist  the  undue  spreading  of  the  transverse  arch  of  the  foot. 


THE  TARSO-METATARSAL   JOINTS. 


nd. 

!*• 


That  of  the  first  metatarsal  bone  (Fig.  458)  is  an  independent  joint  with  its 
own  capsule,  the  interosseous  ligament  between  the  internal  cuneiform  and  the 
second  metatarsal  shutting  it  off.  The  front  of  the  cuneiform  is  convex  from  side  to 
side  and  about  plane  from  above  down.  Rarely  it  is  subdivided  into  an  upper  and  a 
lower  compartment.  It  may  be  prolonged  onto  the  side  of  the  second  metatarsal. 
An  articular  facet  coated  with  cartilage  is  common  on  the  outer  side  of  the  first  meta- 
tarsal, but  that  on  the  second  is  indistinct  or  wanting.  It  seems  that  this  is  simply 
a  bursa  in  most  cases  just  beyond  the  joint,  but  they  sometimes  communicate  Lat- 
eral motion  with  this  metatarsal  is  the  most  free,  and  there  is  a  certain  sliding  up 
and  down. 


THE   METATARSAL   JOINTS.  447 

The  second  tarso-metatarsal  joint  opens  at  the  inner  side  into  the  great 
tarsal  joint,  and  usually  with  that  of  the  external  cuneiform  and  third  metatarsal. 
The  motions  of    these   joints  are  slight  and 
indefinite.  FIG.  462. 

The  fourth  and  fifth  tarso-metatarsal  Head  of  first  metatarsal 

joints,  between  the  cuboid  and  the  two  outer 
metatarsal  bones,  are  nearly  or  quite  separated 
from  the  preceding  by  the  interosseous  liga- 
ment  from  between  the  outer  cuneiform  and 
the  cuboid  to  the  third  and  fourth- metatarsals  ; 
practically  they  form  a  distinct  joint.  The 
motion  is  much  more  free  than  in  the  others  Tendon  of  fiexor 
The  fourth  metatarsal  bone  plavs  on  the  third  Glenoid  ligament 

by  a  facet  distal  to  the  interosseous  ligament  Transverse  sect'lor\^l^ead  °f  first  meta" 
just  mentioned.  The  fifth  plays  still  more 

freely  both  on  the  fourth  and  on  the  cuboid.  The  motion  is  of  a  nature  to  permit 
the  drawing  of  the  outer  side  of  the  foot  downward  and  inward  so  as  to  deepen  the 
hollow  of  the  sole.  It  also  allows  the  outer  metatarsals  to  be  displaced  dorsally 
when  the  transverse  arch  is  flattened. 

THE   METATARSO-PHALANGEAL   JOINTS. 

These  articulations  in  the  foot  are  similar  to  the  corresponding  ones  of  the  hand, 
the  capsule  including  the  glenoid  and  lateral  ligaments ;  the  latter  arise  from  both 
the  tubercles  and  the  depressions  on  the  heads  of  the  metatarsals.  That  of  the  great 
toe  is  large  and  distinguished  by  the  large  size  of  the  sesamoid  bones,  which  are 
interposed  between  the  head  of  the  metatarsal  and  the  ground.  As  in  the  hand,  there 
is  no  glenoid  ligament  in  this  joint.  The  transverse  metatarsal  ligament  differs  from 
that  of  the  hand  in  connecting  all  the  toes.  The  motions  correspond  to  those  of 
the  hand,  but  the  range  of  dorsal  extension  is  greater.  Lateral  motion  is  possible 
only  when  the  toes  are  nearly  straight. 

The  structure  and  motions  of  the  interphalangeal  joints  are  as  in  the  hand. 

SYNOVIAL  CAVITIES. 

The  following  synovial  cavities  are  found  (Figs.  458,  463).  (i)  That , of  the 
ankle-joint  proper  ;  (2)  the  posterior  calcaneo-astragaloid ;  (3)  the  anterior  calcaneo- 
astragaloid  completed  by  the  scaphoid  ;  (4)  the  calcaneo-cuboid ;  (5)  the  scapho- 
cuneiform  cuboid,  the  great  tarsal  cavity  which  communicates  with  the  joints  at  the 
bases  of  the  second  and  third  metatarsals  by  a  passage  at  the  inner  side  of  the  middle 
cuneiform  and  sometimes  by  one  on  its  outer  side.  This  may  also  open  into  the 
preceding  synovial  cavity  ;  (6)  the  joint  between  the  internal  cuneiform  and  the 
first  metatarsal ;  (7)  that  of  the  ciiboid  and  the  outer  two  metatarsals. 

The  arrangement  of  the  synovial  sacs  about  the  bases  of  the  second  and  third 
metatarsals  is  variable. 

THE   FOOT   AS   A   WHOLE. 

The  foot  is  a  vault  which  may  be  considered  as  composed  of  an  indefinite  number 
of  arches  diverging  from  the  internal  tuberosity  of  the  calcaneum  and  ending  in 
front  at  the  heads  of  the  metatarsals.  The  highest  arch  is  that  in  the  line  of  the 
great  toe,  a  fact  in  some  degree  due  to  the  sesamoid  bones  which  are  between  the  head 
of  the  first  metatarsal  and  the  ground.  The  arch  at  the  outer  side  of  the  foot  is  the 
lowest.  It  is  clear  from  this  conception  that  transverse  sections  of  the  foot  must 
also  show  an  arched  structure  the  details  of  which  must  vary  with  the  line  of  section. 
The  shape  of  the  three  cuneiforms  is  an  essential  element  in  this  construction.  This 
vault  is,  however,  not  rigid,  but  elastic  and  capable  of  considerable  modification  of 
shape  under  varying  pressure. 

In  the  motions  of  the  foot  the  essential  joints  below  the  ankle  are  the  subastraga- 
loid  and  those  between  the  astragalus  arid  the  scaphoid  and  the  calcaneum  and  the 
cuboid. 


448 


HUMAN    ANATOMY. 


The  bones  in  front  of  the  astragalus  and  os  calcis  move  very  much  as  a  unit, 
although  there  may  be  some  play  between  the  scaphoid  and  cuboid  and  between  the 
latter  and  the  fifth  metatarsal.  The  astragalus,  having  no  muscle  inserted  into  it,  is 
acted  on  in  the  ankle-joint  by  the  other  bones,  as  is  the  first  row  of  the  carpus,  its 
motions  depending  on  the  pressure  it  receives.  When  the  foot  is  in  extreme  dorsal 
flexion,  all  the  joints  of  the  tarsus  are  locked  and  no  motion  is  possible.  Starting 


FIG.  463. 


Tibia 


Astragalus 

Calcaneo- 

astragaloid 

ligament 


Internal  sesatnoid  bone  posticus  Sustentaculum 

Inferior  calcaneo-scaphoid  ligament 

Longitudinal  section  through  right  foot  in  axis  of  first  metatarsal  bone. 

from  a  position  of  moderate  flexion,  the  motions  (excepting  those  of  simple  flexion 
and  extension  which  occur  in  the  ankle)  are  combinations  of  adduction  and  abduction, 
inversion  and  eversion.  Adduction  is  generally  combined  with  inversion,  and  these 
two  motions  are  more  extensive  than  the  opposite  ones.  They  practically  never 
occur  pure.  Inversion  and  eversion  occur  chiefly  in  the  joints  below  the  astragalus, 
but  in  part  in  the  mid-tarsal  joint.  Adduction  and  abduction  are  perhaps  about 
equally  divided  between  the  two  ;  but  if  the  calcaneum  be  held  by  one  hand  and  the 


FIG.  464. 

Middle  cuneiform 

External  cuneiform 


FIG.  465. 


Middle  cuneiform 


External  cuneiform 


Cuboid 


Cuboid 


Transverse 


Interosseous  ligament 

section  through  cuneiform  bones  of  right  foot, 
seen  from  behind. 


Fifth 


.     nu-ta- 
tarsal 


Interosseous  ligaments 


Oblique  section  through  cuneiform  bones  of  right  foot, 
seen  from  behind. 


front  of  the  foot  moved  by  the  other,  it  is  clear  that  the  mid-tarsal  joint  allows  much 
more  abduction  and  adduction  than  eversion  and  inversion,  which  therefore  occur 
chiefly  between  the  calcaneum  and  astragalus. 

In  the  ordinary  position  of  supporting  the  body  it  appears  that  tin-  essential  arch 
is  through  the  calcaneum,  the  cuboid,  tin-  external  cuneiform,  joined  to  the  latter  by 
a  firm  interosseous  ligament,  and  the  third  metatarsal.1  This  can  be  proved  by 

1  H.  v.  Meyer  :  Der  menschliche  Fuss. 


THE   FOOT   AS   A   WHOLE. 


449 


FIG.  466. 


removing  the  first  and  fifth  metatarsals  with  their  phalanges  and  the  first  cuneiform 
bone,  without  impairing  the  stability  of  the  foot.  The  fourth  metatarsal  may  next  be 
taken  away  without  trouble.  If  the  second  with  its  cuneiform  be  detached  with  care, 
the  arch  is  still  reasonably  firm.  It  is  possible  to  preserve  the  arch  after  taking  out 
the  astragalus,  and  then  removing  the  scaphoid.  Although  the  arch  still  stands,  it 
will  bear  little  weight,  the  third  cuneiform  being  inadequately  supported  behind  ;  but 
with  the  scaphoid  and  astragalus  retained  the  arch  is  a  good  one.  The  arches 
depend  very  much  for  their  stability  on  the  action  of  the  peroneus  longus  and  the 
tibialis  posticus,  which  pull  against  each  other  from  opposite  sides.  The  former  is 
efficient  in  maintaining  the  transverse  arch,  the  latter  in  maintaining  both  the  trans- 
verse and  the  antero-posterior.  To  these  should  be  added  the  plantar  fascia  and 
the  muscles  to  the  toes  arising  from  the  calcaneum.  When  in  life  the  weight  is 
equally  divided  between  the  feet,  the  part  in  contact  with  the  ground  is  the  heel,  the 
outer  border  of  the  foot,  the  region  of  the  heads  of  the  metatarsals,  and,  separated 
from  the  rest,  the  balls  of  the  toes,  which  bear  no  weight.  The  outer  border  also,  as 
a  rule,  is  doing  no  work  and  often  does  not  even  touch  the  ground,  It  is  easy  to 
pass  a  thin  spatula  under  the  head  of  the  fifth  metatarsal,  and  usually  not  hard  to 
pass  it  under  that  of  the  first,  thus  showing  that  in  this  position  they  are  not  essential 
parts  of  the  arch.  When  the  whole  or  nearly  the  whole  weight  is  transferred  to 
one  foot  the  following  changes  occur.  The  head  of  the  astragalus  turns  inward,  at 
the  same  time  sinking  under  the  weight  of  the  body  so  as  to  make  a  prominence  at 
the  inner  side  of  the  foot.  The  internal  malleolus  follows  this  movement.  The 
outer  malleolus  advances,  but  does  not  descend.  Thus  the  relation  of  the  front  part 
of  the  foot  to  the  posterior  is  one  of  abduction  and  eversion.1  The  weight-bearing 
region  changes  both  its  shape  and  position.  The  line  at  the 
outer  part  of  the  heel  is  the  only  part  that  remains  stationary. 
The  surface  of  pressure  (Fig.  466)  is  broader  at  the  heel  and 
still  more  so  at  the  heads  of  the  metatarsals.  The  connecting 
strip  moves  inward,  but  becomes  no  broader  ;  sometimes  it 
even  narrows.  The  chief  agent  in  resisting  this  change, 
which  is  greater  after  fatigue,  is  the  tibialis  posticus,  which 
opposes  the  inner  turn  of  the  head  of  the  astragalus  which 
precedes  its  descent.  When  this  is  inadequate,  the  change 
of  position  is  exaggerated  and  the  foot  breaks  down. 

As  the  heel  is  raised,  under  normal  conditions,  the 
weight  is  transmitted  through  the  astragalus  chiefly  to  the 
bones  and  soft  parts  forming  the  socket  for  its  head,  the 
calcaneum  receiving  little  of  it.  The  strain  comes  chiefly 
on  the  ligaments  securing  the  scaphoid,  for  that  bone  is  roost 
directly  in  the  line  of  pressure,  which  it  transmits  through 
the  front  of  the  tarsus  to  the  heads  of  the  metatarsals,  chiefly 
to  the  first  ;  but  in  this  last  respect  individuals  vary.  Usu- 
ally the  region  of  the  heads  of  the  metatarsals  narrows,  the 
weight  being  borne-  chiefly  at  the  inner  side,  but  in  some 
cases  by  all  the  heads.  When  the  weight  is  borne  by  the 
toes,  the  foot  being  inverted  and  abducted,  the  locking  by 
the  catching  of  the  plantar  tubercle  of  the  cuboid  in  the  os  calcis  is  an  important 
factor  of  stability. 

Surface  Anatomy. — The  malleoli  are  easily  felt,  the  inner  being  square,  the 
outer  longer  and  more  pointed  ;  the  latter  is  the  lower  and  the  more  posterior.  The 
ankle-joint  is,  therefore,  more  easily  opened  from  the  inner  side.  The  front  lower 
border  of  the  tibia  is  hard  to  examine  on  account  of  the  extensor  tendons  ;  the  line 
of  the  joint  is  from  one  to  two  centimetres  above  the  tip  of  the  inner  malleolus,  run- 
ning transversely.  The  general  features  of  the  os  calcis  can  be  made  out.  The  sus- 
tentaculum  is  distinct  and  the  peroneal  spine  can  be  recognized.  Along  the  inner 
side,  the  head  of  the  astragalus  can  be  felt  at  the  dorsum  where  it  enters  the  hollow 
of  the  scaphoid.  The  tubercle  of  the  latter  is  lower  down  and  farther  forward.  The 


Surface  of  pressure  on 
sole  of  foot  as  seen  through 
a  glass  plate  supporting  the 
body. 


1  Lovett :  New  York  Medical  Journal,  1896. 
29 


450  HUMAN   ANATOMY. 

first  "cuneiform  and  the  joint  behind  and  before  it,  the  first  metatarsal  and  perhaps 
the  inner  sesamoid  come  in  order.  A  very  moderate  swelling  obscures  most  of  these 
points.  On  the  outer  side  the  joint  between  the  calcaneum  and  the  cuboid  can  be 
found.  A  little  in  front  of  this  is  the  tuberosity  of  the  fifth  metatarsal,  the  only  dis- 
tinct landmark  on  the  outer  side.  The  general  dorsal  outline  of  the  tarsal  bones  is 
to  be  recognized,  but  only  under  favorable  circumstances.  The  dorsal  surfaces  of 
the  metatarsals  are  distinct.  The  joint  between  the  astragalus  and  calcaneum  behind 
and  the  scaphoid  and  cuboid  in  front  is  sinuous  :  convex  forward  at  the  inner  part 
and  tending  to  concavity  at  the  outer,  the  two  ends  of  the  line  being  nearly  in  the 
same  transverse  plane.  The  tarso- metatarsal  joint  is  very  oblique,  running  from 
within  outward  and  backward.  It  is  repeatedly  irregular,  the  chief  interruption  of 
the  direction  being  at  the  mortise  of  the  second  metatarsal  between  the  inner  and 
outer  cuneiforms.  The  joints  of  the  first  phalanges  with  the  metatarsal  bones  are 
about  2.5  centimetres  behind  the  web  of  the  toes. 

PRACTICAL   CONSIDERATIONS. 

The  Ankle-joint. — Uncomplicated  dislocations,  inward  or  outward,  are  almost 
unknown  because  of  (a)  the  close  lateral  approximation  of  the  malleoli,  which  are  held 
to  the  sides  of  the  astragalus  by  the  strong  inferior  tibio-fibular  ligaments  ;  (3)  the 
further  support  of  the  lateral  ligaments,  especially  the  inner  ;  and,  (c)  to  a  very 
minor  extent,  the  wavy  outline  of  the  upper  surface  of  the  astragalus,  which  slightly 
resists  sidewise  movements. 

Lateral  dislocations  are  accordingly  almost  always  associated  with  fracture  of 
one  or  other  of  the  bones  of  the  leg,  and  have  been  sufficiently  described  in  that 
connection  (page  395).  They  are  incomplete.  In  addition  to  the  inward  or  out- 
ward movement  of  the  astragalus  it  undergoes  a  partial  rotation  on  an  antero-posterior 
axis,  so  that  its  tibial  surface  points  obliquely  upward  in  a  direction  opposite  to  that 
of  the  displacement. 

Reduction  is  easy  and  the  after-treatment  is  that  appropriate  to  the  fracture. 

Backward  dislocations  of  the  astragalus — i.e. ,  of  the  foot  (which  are  etiologically 
forward  dislocations  of  the  tibia) — are  resisted  by  (a)  the  shape  of  the  upper  articular 
surface  of  the  astragalus,  which  is  about  one-fourth  narrower  behind  than  in  front ; 
(d)  the  corresponding  shape  of  the  irregular  arch  in  which  the  astragalus  rests  ;  (r) 
the  outward  slope  from  behind  forward  of  the  lateral  facets  of  the  astragalus  ;  (</)  the 
lower  level  of  the  posterior  as  compared  with  the  anterior  articular  edge  of  the  tibia  ; 
and  (e~)  the  reinforcement  of  the  posterior  ligament  by  the  tendon  of  the  flexor  longus 
pollicis.  If  it  were  not  for  these  provisions,  the  frequency  with  which,  in  alighting  on 
the  ground  in  running  or, jumping,  the  foot  is  fixed  and  the  tibia  is  driven  forward 
against  the  weak  anterior  ligament  would  render  these  luxations  much  more  common. 
An  even  more  powerful  leverage  is  produced  in  the  same  direction  when,  the  foot 
being  fixed,  a  fall  backward  thrusts  the  lower  end  of  the  tibia  forward.  As  it  is,  the 
backward  far  exceed  in  frequency  the  forward  luxations  because,  although  the  above- 
mentioned  anatomical  factors  favor  the  latter,  the  weight  of  the  body  is  scarcely 
ever  brought  upon  the  limb  in  such  a  direction  and  with  such  force  as  to  induce 
them  (Humphry). 

In  backward  luxation  the  tibia  rests  upon  the  scaphoid  and  cuneiform,  the 
anterior  ligament  is  ruptured,  and  the  posterior  and  lateral  ligaments  are  lacerated. 
The  foot  is  shortened  from  the  lower  anterior  edge  of  the  tibia  to  the  web  of  the  great 
toe,  the  heel  is  lengthened,  the  tendo  Achillis  describes  a  marked  curve  backward, 
and  the  depressions  on  either  side  of  it  are  exaggerated. 

Strains  of  the  ankle,  on  account  of  its  position,  where,  in  lateral  twists,  it  can 
receive  through  the  leverage  of  the  whole  lower  extremity  the  weight  of  the  entire 
body,  are  more  common  than  of  any  other  joint. 

This  force  is  nearly  always  applied  through  eversion  or  inversion  (abduction  or 
adduction)  of  the  foot,  usually  the  former,  and  the  injury  consists  in  laceration  of  the 
fibres  of  a  lateral  ligament  with  strain  of  some  of  the  tendons  in  relation  to  the 
malleoli,  and  bruising  and  pinching  of  loose  synovial  membrane.  More  ran  ly 
extreme  dorsiflexion  will  injure  the  posterior  ligament  and  the  posterior  portions  of 


PRACTICAL   CONSIDERATIONS:   THE   ANKLE-JOINT.  451 

the  lateral  ligaments  (which  limit  that  movement),  and  further  injury  may  be  done  to 
the  synovial  sac  or  to  the  periosteum  or  to  the  bones  themselves  by  the  forcible 
impact  of  the  anterior  articular  edge  of  the  tibia  upon  the  astragalus.  Sprain  from 
hyperextension  (plantar  flexion)  is  still  rarer. 

In  sprains  from  abduction  there  may  be  in  the  severe  forms  a  momentary  slight 
outward  subluxation  of  the  astragalus,  as  the  shaft  of  the  fibula  is  elastic  enough  to 
permit  of  this  without  fracture. 

The  looseness  of  the  synovial  sac  (which  is  said  to  contain  normally  a  relatively 
larger  amount  of  synovia  than  any  joint  in  the  body),  the  dependent  position  of  the 
region,  and  the  remoteness  from  the  centre  of  circulation  make  the  swelling  and 
therefore  the  tension  of  the  joint  and  the  pain  following  sprain  very  noticeable. 

Disease  of  the  joint  is  frequent  for  the  same  reasons  that  sprains  are  frequent  and 
severe. 

In  simple  (traumatic)  synovitis  the  swelling  is  marked.  It  appears  first  in  front 
beneath  the  thin  anterior  ligament,  especially  towards  the  outer  side  just  in  advance 
of  the  lateral  ligament,  because  there  the  membrane  is  less  bound  down  by  extensor 
tendons.  Later  the  swelling  extends  downward  towards  the  dorsum  of  the  foot  for 
an  inch  or  more,  the  extensor  tendons  are  pushed  forward,  and  a  fulness  appears  on 
either  side  of  the  tendo  Achillis  which,  still  later,  extends  below  the  malleoli.  The 
posterior  swelling  is  perhaps  the  most  valuable  for  diagnosis,  as  it  is  not  so  likely  as 
the  anterior  swelling  to  be  confused  with  that  produced  by  disease  of  tendon-sheaths 
or  of  separate  bones  or  joints  of  the  tarsus. 

It  may  be  remembered  in  this  connection  that  the  general  shape  of  the  swelling 
in  ankle-joint  disease  is,  rudely,  like  that  of  an  "anklet," — horizontal, — while  the 
swelling  of  teno-synovitis  is  more  or  less  vertical  in  direction. 

No  early  distortion  of  the  foot  is  produced,  as  the  capacity  of  the  joint  is  but 
little  influenced  by  position  ;  but  later  the  calf  muscles  are  apt  to  overcome  the 
anterior  tibial  group  and  to  draw  up  the  heel,  causing  ' '  pointing' '  of  the  toes. 

Tuberculosis  is  common,  and  is  unfavorable  in  its  course  because  of  the  ana- 
tomical conditions  above  recited,  the  proximity  of  the  numerous  tendon-sheaths,  the 
complex  synovial  sacs  of  the  tarsus,  and  the  large  amount  of  cancellous  tissue  in  the 
neighboring  bones,  and  also  because  of  the  difficulty  of  securing  complete  rest  and  at 
the  same  time  keeping  up  the  general  health. 

Excision  is  rarely  performed,  and  is  unsatisfactory  ;  but  arthrectomy,  done 
through  longitudinal  incisions  in  front  of  both  malleoli,  and  with  division  of  the 
malleoli  themselves,  or  removal  of  the  astragalus,  if  it  is  diseased,  has  been  followed 
by  good  results.  If  the  astragalus  is  to  be  removed  and  the  malleoli  spared  (which 
is  often  desirable  on  account  of  the  proximity  of  the  epiphyseal  lines),  the  lateral 
ligaments  will  have  to  be  divided.  By  one  or  other  of  these  plans  ample  access  to 
the  interior  of  the  joint  can  be  obtained.  Syme's  amputation  is,  however,  pre- 
ferred by  many  surgeons,  if  ankle-joint  disease  is  at  all  extensive. 

The  horizontal  line  of  the  ankle-joint  is  about  half  an  inch  above  the  tip  of  the 
internal  malleolus  and  therefore  an  inch  above  the  tip  of  the  external  malleolus. 

The  Joints  of  the  Tarsus,  Metatarsus,  and  Phalanges. — Dislocations  of 
the  astragalus — tibio-tarsal  dislocations — have  been  described  in  connection  with  the 
ankle-joint. 

Subastragaloid  dislocations — i.  e. ,  of  the  calcaneum  and  scaphoid  from  the  astrag- 
alus— are  almost  always  either  inward  and  backward  or  outward  and  backward, 
chiefly  because  of  the  shape  of  the  opposing  articular  surfaces  of  the  calcaneum  and 
astragalus.  The  upper  surface  of  the  os  calcis,  as  it  advances  forward,  descends 
suddenly  from  a  superior  to  an  inferior  level,  giving  the  articular  processes  an  oblique 
— i.e.,  approximately  vertical — direction,  to  which,  of  course,  the  direction  of  the 
articular  facets  on  the  under  surface  of  the  astragalus  corresponds. 

It  is  obvious  that  much  more  resistance  is  offered  to  anterior  displacement  of 
the  calcaneum  than  to  displacement  in  the  opposite  direction,  <md,  in  fact,  only  two 
examples  of  forward  subastragaloid  dislocation  have  been  recorded. 

The  astragalo-scaphoid  joint  is  involved  also,  but  the  rounded  head  of  the 
astragalus  offers  but  little  resistance  to  the  backward  or  lateral  movement  of  the 
scaphoid,  which,  moreover,  is  held  firmly  in  connection  with  the  os  calcis,  and  carried 


452 


HUMAN   ANATOMY. 


with  it  because  of  the  greater  strength  of  the  calcaneo-scaphoid  as  compared  with  the 
astragalo-scaphoid  ligaments.  As,  owing  to  the  width  of  the  pelvis,  the  obliquity  of 
the  femur,  and  the  curve  of  the  tibia,  the  weight  of  the  body  is  transmitted  to  the 
astragalus  in  an  inward  direction,  it  would  be  displaced  inward  (i.e. ,  there  would  be 
an  outward  luxation  of  the  os  calcis  and  scaphoid)  far  more  frequently  than  in  the 
opposite  direction  were  it  not  for  the  resistance  offered  by  the  projection  of  the  sus- 
tentaculum  and  the  lesser  articular  process  on  the  inner  side  and  the  outward  obliquity 
of  both  the  processes  of  the  posterior  calcaneo-astragaloid  joint.  The  two  lateral 
dislocations  associated  with  some  displacement  backward  are,  therefore,  about  equal 
in  frequency.  The  extensive  opposed  articular  surfaces  of  the  os  calcis  and  astragalus 
are  not,  as  a  rule,  completely  separated  ;  the  smaller  surfaces  of  the  astragalo-scaphoid 
joint  are,  so  that  the  one  is  a  subluxation,  the  other  a  complete  luxation. 

The  ligaments  uniformly  torn  are  the  interosseous  calcaneo-astragaloid,  the 
astragalo-scaphoid,  and  one  or  other  of  the  lateral  ligaments  of  the  ankle. 

In  inward  and  backward  luxation  the  symptoms  are  (a)  shortening  of  the  line 
between  the  mid-point  of  the  ankle  and  the  web  of  the  great  toe  ;  (6)  projection  and 
lengthening  of  the  heel  ;  (c)  inversion  and  adduction  of  the  foot,  the  inner  border 
shortened  and  concave,  the  outer  lengthened  and  convex  ;  (d)  partial  disappearance 
of  the  internal  malleolus  ;  (e)  projection  of  the  sustentaculum  tali  beneath  and  behind 
it ;  (/")  projection  of  the  external  malleolus  and  of  the  head  of  the  astragalus  on  the 
outer  side  of  the  dorsum,  with  yielding  spaces  in  the  soft  parts  beneath  each.  The 
axis  of  the  leg,  when  continued  downward,  falls  to  the  outer  side  of,  or  even  external 
to,  the  foot.  The  scaphoid  can  be  felt  on  the  inner  side  of  the  foot.  The  deformity 
resembles  that  of  talipes  varus. 

In  outward  and  backward  luxation  a  and  b  are  the  same  ;  there  are  abduction  and 
eversion  of  the  foot,  and  disappearance  of  the  outer  and  prominence  of  the  inner 
malleolus  ;  the  deformity  resembles  that  of  talipes  valgus. 

The  medio-tarsal — astragalo-scaphoid  and  calcaneo-cuboid — articulation  usually 
escapes  injury  on  account  of  the  elasticity  of  the  anterior  pillar  of  the  arch  of  the  foot 
(into  which  it  enters)  and  because  of  the  numerous  joints  of  the  anterior  tarsal  and 
the  metatarso-phalangeal  regions  which  take  up  and  diffuse  force  applied  to  the 
anterior  part  of  the  foot. 

The  first  metatarsal  bone  is  more  frequently  dislocated  from  the  tarsus  than  any 
of  the  others,  as,  relatively  to  the  other  phalanges,  are  the  proximal  phalanx  and  the 


FIG.  467. 


First  metatarsal 


Fourth  metatarsal 


Sesamoid  bones 


Section  of  right  foot  through  heads 


g  support  by  first  and  fourth. 


terminal  phalanx  of  the  same  toe.     These  dislocations  are  nearly  always  upwan 
Dislocation  of  the  proximal  phalanx  of  the  great  toe  may  be  as  difficult  to  reduce 
as  is  that  of  the  thumb.      Morris  thinks  that  the  sesamoid   bones  may  act  as   1  In- 
anterior  ligament  does  in  the  latter  case, — i.e.,  being  more  firmly  attached  to  the 

phalanx  than  to  the  metatarsal  bone,  they  may  be  torn  away  with  the  former,  and  by 
their  interposition  prevent  reduction. 

The  painful  affection  known  as  inclatarsalgia  has  been  thought  (Morton)  to  be 
due  to  the  position  of  the  fifth  nietatarso-phalan^eal  joint,  so  much  posterior  to  the 
fourth  that  tin-  base  of  the  first  phalanx  of  the  little  toe  is  opposite  the  head  and  neek 
of  the  fourth  metatarsal.  As  the-  fourth  and  fifth  metataisal  bones  have  greater 
mobility  than  their  fellows,  it  was  supposed  that  this  relation  afforded  opportunity  for 


PRACTICAL   CONSIDERATIONS:   THE   FOOT-JOINTS.  453 

accidental  compression  of  the  branches  of  the  external  plantar  nerve.  R.  Jones 
thinks  that  it  is  often  a  communicating  branch  between  the  fourth  division  of  the 
internal  plantar  and  the  external  plantar  that  is  compressed  between  the  bone  and  the 
ground  as  it  passes  beneath  the  head  of  the  fourth  metatarsal.  A  transverse  section 
of  the  foot  through  the  heads  of  the  metatarsals  shows  that  the  first  and  fourth  bear 
the  most  pressure  (Fig.  467).  The  situation  of  the  plantar  digital  nerves,  superficial 
to  and  not  between  the  bones,  and  the  collapse  of  the  transverse  arch  in  most  cases  of 
metatarsalgia,  broadening  the  intervals  between  the  bones,  but  increasing  pressure  on 
the  structures  beneath  them,  support  the  latter  view. 

Flat-foot  is  so  closely  associated  in  its  anatomical  deformities  with  talipes  valgus 
that  it  will  be  considered  in  relation  with  the  latter,  which,  with  the  other  varieties  of 
club-foot,  can  best  be  understood  after  the  muscles  and  fasciae  of  the  leg  and  foot 
have  been  described. 

Disease  of  the  tarsal  joints,  like  that  of  the  bones,  is  most  frequently  tuberculous 
in  character,  and  is  more  apt  to  remain  localized  when  it  is  situated  in  the  posterior 
pillar  of  the  main  arch, — i.e. ,  in  the  posterior  half  of  the  calcaneo-astragaloid  joint. 
If  in  front  of  the  interosseous  ligament  dividing  that  articulation,  or  if  in  either  of  the 
mid-tarsal  joints  (with  which  it  communicates),  or  in  any  of  the  remaining  four 
synovial  cavities,  it  is  apt  to  extend  much  beyond  its  original  limits.  The  circum- 
stances that  favor  the  origin  (page  437)  and  influence  unfavorably  the  course  of  bone 
disease  in  this  region  apply  in  the  main  to  disease  of  the  joints.  In  whichever  tissue 
— bony  or  synovial — it  originates,  it  is  apt  to  spread  to  the  other.  The  astragalo- 
scaphoid  joint,  on  account  of  its  superficial  position  and  its  range  of  motion  (which  is 
greater  than  that  of  any  of  the  joints  below  the  ankle),  is  most  apt  to  be  affected. 
The  situation  of  the  swelling  and  tenderness  will  usually  differentiate  it  from  ankle- 
joint  disease  (page  450).  Probably  on  account  of  the  diffuse  infection  of  the  abundant 
cancellous  tissue  of  the  tarsal  bones  (either  primary  or  secondary  to  joint  disease), 
remote  tuberculous  infection — phthisis — follows  or  accompanies  disease  of  the  ankle 
and  tarsus  more  frequently  than  it  does  disease  of  any  other  part  except  possibly  the 
wrist  (Cheyne). 

Gout  affects  peculiarly  the  metatarso-phalangeal  joint  of  the  great  toe.  In  516 
cases  of  gout,  341  were  of  one  or  both  of  the  great  toes  alone  and  373  of  the  great 
toe  with. some  other  part  (Scudamore).  This  is  due  to  (a)  the  abundance  in  that 
region  of  dense  fibrous  tissue  of  little  vascularity  ;  (3)  its  remoteness  from  the  heart, 
the  force  of  the  circulation  being  at  its  minimum  ;  (Y)  the  large  share  of  the  body 
weight  which  it  sustains,  as  the  anterior  extremity  of  the  main  arch  of  the  foot  ;  (d~) 
the  frequency  of  trauinatism  ;  (e~)  the  constant  exposure  to  cold  and  damp  ;  (_/)  its 
dependent  position. 

Landmarks. — The  ankle-joint  (<?.v.)  lies  about  half  an  inch  above  the  tip  of 
the  inner  malleolus.  Syme's  amputation  is  done  through  this  joint,  the  incision 
being  made  from  the  tip  of  one  malleolus  to  the  tip  of  the  other,  and  at  right  angles 
to  the  long  axis  of  the  foot. 

The  mid-tarsal  joint  (through  which  Chopart's  amputation  is  done)  runs  out- 
ward from  a  point  just  back  of  the  scaphoid  tuberosity,  and  passes  directly  over  the 
dorsum  of  the  foot  to  a  point  a  little  in  advance  of  the  middle  of  a  line  between  the 
tip  of  the  external  malleolus  and  the  tuberosity  of  the  fifth  metatarsal. 

The  tarso-metatarsal  joint  begins  at  a  point  about  one  and  a  half  inches  in  front 
of  the  tubercle  of  the  scaphoid, — i.e.,  just  back  of  the  base  of  the  first  metatarsal,— 
passes  at  first  directly  outward,  then  passes  irregularly  around  the  three  sides  of  the 
mortise  between  the  internal  and  external  cuneiforms  in  which  the  base  of  the  second 
metatarsal  rests,  and  then  slopes  slightly  backward  to  its  easily  recognized  termination 
on  the  outer  side  of  the  foot,  just  behind  the  base  of  the  fifth  metatarsal. 

Key's  amputation  begins  and  ends  at  the  two  extremities  of  this  joint-line,  but 
the  projection  of  the  internal  cuneiform  is  sawn  across.  In  Lisfranc's  amputation  the 
joint-line  is  followed  throughout.  The  metatarso-phalangeal  joints  lie  an  inch  behind 
the  interdigital  web. 


THE  MUSCULAR  SYSTEM. 

Muscular  Tissue  in  General. — Contractility,  although  exhibited  to  some 
degree  by  all  living  protoplasm,  is  possessed  especially  by  muscular  tissue,  the  sum 
of  the  contractions  of  such  tissue  being  expressed  in  motion,  the  most  conspicuous 
characteristic  of  all  the  higher  forms  of  animal  life.  Muscular  tissue  represents  a  high 
specialization  in  which  contraction  takes  place  along  definite  lines  corresponding  to 
•the  long  axes  of  the  component  cells,  in  contrast  to  the  uncertain  contractility  occurring 
within  other  elements. 

The  simplest  form  of  contractile  tissue,  as  seen  in  some  of  the  low  invertebrates, 
is  represented  by  elements  of  which  the  superficial  part  is  related  to  the  integument, 
the  deeper  being  differentiated  into  contractile  fibres.  Although  such  musculo-epithe- 
lial  cells  may  form  an  almost  complete  contractile  layer,  the  muscular  fibres  do  not 
exist  as  an  independent  tissue.  The  differentiation  of  certain  cells  into  definite  mus- 
cular tissue,  however,  soon  appears  in  the  members  of  the  zoological  scale,  although 
the  existence  of  a  distinct  muscular  system  is  deferred  until  an  adequate  nervous 
system  is  developed. 

In  the  higher  animals  muscular  tissue  appears  in  two  chief  varieties,  the  striated 
and  non-striated,  depending  upon  the  respective  histological  characteristics  of  their 
constituent  elements.  The  former  makes  up  the  muscles  controlled  by  the  will,  and 
is,  therefore,  also  termed  voluntary  muscle  ;  the  latter,  which  constitutes  the  contrac- 
tile tissue  within  the  walls  of  the  hollow  viscera,  blood-vessels  and  other  tubes,  acts 
independently  of  volition,  and  is  spoken  of  as  involuntary  muscle.  The  last  named 
is  sometimes  also  designated  vegetative  muscle,  since  the  organs  in  which  it  is  present 
are  largely  concerned  in  the  nutritive  processes  ;  the  term  animal  may  be  applied  in 
contrast  to  voluntary  muscle.  The  association  of  the  striated  muscle  with  response 
to  volition  and,  on  the  contrary,  of  the  non-striated  variety  with  involuntary  action 
must  be  accepted  with  certain  reservations,  since  in  some  animals  the  development  of 
marked  striation  never  takes  place  within  the  fibres  of  voluntary  muscle.  There  is, 
indeed,  not  a  little  evidence  going  to  show  that  the  structural  differences  which  exist 
between  the  striated  and  non-striated  musculature  are  correlated  with  their  physio- 
logical activities,  and  that  no  fundamental  distinction  can  be  drawn  between  them 
on  purely  morphological  grounds.  Muscles  which  in  one  group  of  animals  possess 
the  characteristics  of  striated  muscle-tissue  may,  in  another  group,  be  represented 
by  non-striated  fibres  (the  muscles  of  the  oesophagus,  for  instance),  and  it  seems 
probable  that  the  greater  portion  of  the  voluntary  cranial  musculature  is  serially 
equivalent  to  the  involuntary  musculature  of  the  trunk. 

The  non-striated  or  involuntary  muscle  represents  a  tissue  less  highly  specialized 
than  the  striped,  the  latter  exhibiting  to  a  conspicuous  degree  histological  differentia- 
tion. Constituting,  in  a  way,  a  separate  and  intermediate  group  stands  heart  muscle, 
which,  while  beyond  the  control  of  the  will,  presents  striated  fibres  ;  the  latter  occupy 
histologically  a  place  between  the  fibre-cell  of  the  involuntary  and  the  elongated 
striated  fibre  of  the  voluntary  muscle.  It  is  desirable,  therefore,  to  consider  the  sim- 
pler type  of  contractile  tissue  before  examining  the  more  complex  voluntary  muscle. 

NON-STRIATED  OR  INVOLUNTARY  MUSCLE. 

This,  the  less  highly  differentiated  variety  of  muscular  tissue,  occurs  in  the  form 
of  bundles  and  thin  sheets  principally  within  the  \v;ills  of  the  organs  and  vessels, 
although  enjoying  a  wide  distribution,  seldom  presenting  robust  masses,  and  bein^ 
entirely  unconnected  with  the  skeleton.  Even  when  present  in  considerable  amount, 
this  tissue  is  usually  inconspicuous,  presenting  a  faint  yellowish  tint. 

The  distribution  of   non-striped   muscle   includes  :    i.   The  digestive  tract, — the 

muscularis  mucosre  from  the  oesophagus  to  the  anus  and  delicate  bundles  within  the 

454 


NON-STRIATED   OR   INVOLUNTARY    MUSCLE. 


455 


mucosa  and  villi ;  the  muscular  tunic  from  the  lower  half  of  the  oesophagus  to  the  anus  ; 
in  the  large  excretory  ducts  of  the  liver,  pancreas,  and  some  salivary  glands,  as  well 
as  in  the  gall-bladder.  2.  The  respiratory  tract, — in  the  posterior  part  of  the  trachea, 
encircling  bundles  in  the  bronchial  tubes  as  far  as  their  terminal  divisions.  3.  The 
urinary  tract, — in  the  capsule  and  pelvis  of  the  kidney,  ureter,  bladder,  and  urethra. 

FIG.  468. 


Involuntary  muscle  from  intestine ;  several  isolated  fibre-cells  are  seen  above.     X  200. 

4.  The  male  generative  organs, — in  the  epididymis,    vas  deferens,  seminal  vesicles, 
prostate  body,  Cowper's  glands,  and   cavernous  and  spongy   bodies  of  the  penis. 

5.  The  female  generative  organs, — in  the  oviducts,  uterus,  and  vagina  ;  in  the  broad 
and  round  ligaments  ;  in  the  erectile  tissue  of  the  external  genitals  and  of  the  nipple. 

6.  The  vascular  system, — in   the  coats  of  the  arteries,  veins,  and  larger  lymphatics. 

7.  The  lymphatic  glands, — in  the  capsule  and  trabeculae  of  the  spleen  ;  sometimes  in 
the    trabeculae    of  the  larger  lymph-nodes.      8.   The   eye, — in   the   iris   and    ciliary 
body  ;    in  the  eyelids.      9.   The   integument, — in  the  sweat-    and    some  sebaceous 
glands,  as  the  minute  erector  muscles  of  the  hair-follicles  and  in  the  skin  covering 
the  scrotum  and  parts  of  the  external  genitals. 

Structure. — Non-striated,  unstriped,  pale  or  involuntary  muscle  consists  of 
an  aggregation  of  structural  units  known  as  the  fibre-cells.  These  are  deli- 
cate spindle,  often  prismatic,  elements  which  terminate  in  oblique  surfaces  at  either 
end  for  contact  with  adjacent  cells.  They  vary  greatly  in  size,  measuring  from  .  050- 

.225  mm.  in    length  and  .003-. 008  mm. 

FIG.  469.  in  width.     The  muscle-cells  found  in  the 

skin  and  blood-vessels  are  short  (.015- 
.020  mm.)  and  broad;  those  in  the  in- 
testinal wall  are  more  elongated  (.215— 
.220  mm.)  and  delicate.  The  largest 
elements  are  encountered  in  the  gravid 
uterus,  in  which  they  attain  a  length  of 
.500  mm.  and  a  breadth  of  .030  mm. 
Occasionally  the  cells  are  bifurcated  at 
the  ends,  especially  among  the  lower  ver- 
tebrates. 

FIG.  470.     • 


Portions  of  intestinal  muscle-cells,  showing  nucleus  and 
centrosome  (c).     Highly  magnified.     (Lenhossek.) 


Bundles  of    involuntary   muscle   in   transverse    section, 
showing  the  fibre-cells  cut  crosswise.     X  400. 


More  recent  critical  examinations  of  the  fibre-cells  have  demonstrated  the 
existence  of  greater  structural  complexity  than  was  formerly  recognized.1  According 
to  these  later  views,  each  fibre-cell  consists  of  a  protoplasmic  mass  in  which  lie 
embedded  the  nucleus  and  the  contractile  fibrilla.  The  former  is  appropriately 

1  An  exhaustive  review  of  the  literature  and  various  opinions  concerning  the  structure  of 
unstriped  muscle  is  given  by  M.  Heidenhain  :  Ergebnisse  der  Anatomic  und  Entwick.,  Bd.  x., 
1900. 


456 


HUMAN   ANATOMY. 


FIG.  471. 


Section  of  uterus,  showing  bundles  of  involuntary  muscle  cut 
various  directions,     yi.  220. 


described  as  rod-shaped,  being  cylindrical  with  rounded  ends.  Its  position  is  fre- 
quently eccentric  with  regard  to  the  axis  of  the  cell,  as  well  as  often  somewhat  nearer 
one  pole  than  the  other.  The  nuclei  of  these  muscle-cells  are  rich  in  chromatin, 
which  usually  presents  a  reticular  arrangement.  Under  the  influence  of  contraction, 

the  nuclei  present  more  or  less 
variation  from  their  typical  rod 
form.  Centrosomes  (Fig.  469) 
may  be  distinguished  in  favorable 
preparations  lying  within  the  cy- 
toplasm close  to  the  nucleus  (Zim- 
mermann,  Lenhossek). 

The  contractile  fibrilla  rep- 
resent differentiated  anisotropic 
threads  within  the  cell-body,  in 
their  property  of  double  refraction 
resembling  the  fibrillae  of  striped 
muscle.  They  are  most  conspicu- 
ous at  the  periphery  of  the  fibre- 
cell,  where  they  lie  closely  related 
to  the  condensed  boundary  zone 
(Heidenhain)  which  forms  the 
exterior  of  the  fibre  and  fulfils  the 
purpose  of  a  limiting  membrane 

or  sarcolemma,  although  no  such  definite  structure  encloses  the  muscle-cell  as  in  the 
case  of  the  striated  fibre.  The  demonstration  of  contractile  fibrillae  within  the  muscle- 
cells  of  the  higher  vertebrates  is  unsatisfactory  on  account  of  the  small  size  of  the 
elements  ;  in  the  large  cells  of  the  amphibia,  especially  in  the  huge  elements  of  the 
amphiuma,  their  presence  is  readily  established.  Although  lying  usually  within  the 
periphery  of  the  fibre-cell,  the  existence  of  a  conspicuous  axial  fibre  is  seen  in  certain 
cases,  as  in  the  large  isolated  muscle-cells  within  the  mesentery  of  newts. 

The  individual  elements  of  unstriped  muscle  are  held  together  by  delicate  mem- 
branous expansions  of  connective  tissue  prolonged  from  the  more  robust  septa  investing 
and  uniting  the  bundles  and  fasciculi  of  the  fibre- 
cells.  On  cross-section  (Fig.  470),  these  inter- 
cellular membranous  partitions  appear  as  delicate 
lines  between  the  transversely  cut  cells,  which 
were  formerly  interpreted  as  tracts  of  cement- 
substance  uniting  the  muscular  elements.  The 
appearances  of  intercellular  bridges,  described  by 
several  authors  (Barfuth,  de  Bruyne,  Werner, 
Bohemann,  Apathy)  as  connecting  the  adjacent 
cells,  depend  probably  upon  the  shrinkage  of 
the  latter  due  to  the  action  of  reagents  (Stohr, 
Heidenhain). 

The  blood-vessels  supplying  involuntary 
muscle  are  guided  in  their  distribution  by  the 
septa  of  interfascicular  connective  tissue  in  which 
the  larger  twigs  run.  The  latter  give  off  minute 
branches  which  terminate  in  capillaries  that  ex- 
tend between  the  primary  bundles  of  the  muscle- 
cells.  The  blood-supply  of  npn-striated  muscle 
is  meagre  when  compared  with  that  of  the  striped 
muscles. 

The  lymphatics  occur  closely  associated 
with  the  muscular  tissue  in  localities  in  which 
the  latter  exists  in  considerable  quantity,  as  in  the  wall  of  the  stomach  and  intestine, 
the  interfascicular  connective  tissue  containing  plexuses  of  lymph-channels, 

The  nerves  supplying  involuntary  muscle  are  intimately  related  to  the  sympa- 
thetic system.     The  larger  trunks  form  plexuses,  in  close  association  with  microscopic 


FIG.  472. 


Portion  of  injected  intestinal  wall,  showing 
isels  supplying  invol- 
untary  muscle;    upper    longitudinally,    lower 


arrangement  of  Dlood-vessela 


transversely  cut.     X  50. 


STRIATED   OR   VOLUNTARY    MUSCLE. 


457 


ganglia,  from  which  delicate  twigs  pass  between  the  bundles  of  muscle-cells.  The 
mode  of  their  ultimate  termination  is  described  in  connection  with  nerve-endings 
(page  1015). 

Development. — All  muscular  tissue  in  the  higheV  types,  with  the  exception  of 
that  found  within  the  sweat-glands  and  the  iris,1  may  be  regarded  practically  as  a 
derivation  of  the  meso blast.  Reference  to  Fig.  34  (page  29)  recalls  the  division 
of  the  mesoblast  into  the  parietal  and  visceral  layers,  the  latter,  in  conjunction  with 
the  entoblast,  constituting  the  splanchno-pleuric  folds  by  the  union  of  which  the 
gut-tube  is  formed.  The  subsequent  differentiation  of  the  visceral  mesoblast  contributes 
the  layers  of  the  wall  of  the  digestive  canal  outside  the  epithelial  structures  derived  from 
the  entoblast  ;  in  typical  parts  of  the  tube  these  layers  are  the  submucous,  muscular, 
and  serous  coats.  The  muscular  tunic  consists  of  the  unstriped  involuntary  variety, 
the  component  fibre-cells  representing  specialized  mesoblastic  elements. 

FIG.  473. 


ithelium  of  serous  cont 


Mesenten 


w 

' '  .-J®* 

Differentiating  muscular  tissue' 

Young  connective  tissue 
Epithelium  lining  gut-tube 


Section  of  developing  intestinal  wall,  showing  earliest  differentiation  of  involuntary  muscular  tissue  from  splanchnic 

mesoblast.    X  200. 

The  details  of  the  development  of  the  muscular  tissue  include  condensation  of 
the  young  mesoblast  produced  by  conspicuous  proliferation  and  increase  in  the  cells, 
followed  by  their  gradual  elongation  and  conversion  into  spindle  elements.  These 
are  at  first  short,  but  become  extended  as  the  tissue  assumes  its  fully  developed 
character.  In  localities  in  which  the  involuntary  muscle  occurs  in  sparingly  dis- 
tributed bundles  and  net-works  the  mesoblastic  elements  gradually  assume  the  form 
of  spindle-cells  which  for  a  time  are  inconspicuous  and  difficult  to  distinguish  from 
ordinary  young  connective  tissue.  The  formation  of  the  muscular  tissue  within  the 
walls  of  blood-vessels  is  closely  identified  with  the  intramesodermic  origin  of  the 
vascular  channels,  the  entire  walls  of  which  tubes  are  contributions  of  the  middle 
germinal  layer. 

STRIATED   OR   VOLUNTARY   MUSCLE. 

The  striped  muscular  tissue  constitutes  the  conspicuous  masses  known  as  the 
"  muscles"  or  "flesh"  attached  to  the  bony  framework  of  the  body.  These  organs 
are  also  termed  the  skeletal  muscles,  and  supply  the  active  agents  in  moving  the 
passive  levers  represented  by  the  bones  in  producing  the  movements  of  the  animal. 

The  muscles  are  usually  elongated  in  form,  and  consist  of  aggregations  of  bundles 

of  the  ultimate  contractile  elements,  \\-\G.  fibres,  grouped  into  fasciculi  ;  upon  the  size 

of  the  latter  depends  the  texture  of  the  muscles,  coarse  or  fine,  as  distinguished  in  the 

dissecting-room.      In  localities  in  which  the  fasciculi  are  of  large  size,  as  in  the  gluteus 

1  Szili :  Archiv  fiir  Ophthalmol.,  Bd.  liii.,  1902. 


HUMAN   ANATOMY. 


maximus,  the  muscles  are  conspicuous  on  account  of  their  coarse  texture  ;  a  fine- 
grained muscle,  on  the  contrary,  is  composed  of  small  fasciculi.  In  addition  to 
variations  in  the  thickness  of  the  fasciculi,  the  latter  differ  greatly  in  length  irrespec- 
tive of  the  extent  of  the  entire  muscle,  since  the  length  of  the  fasciculi  depends  largely 

upon  the  arrangement  of  the  ten- 
FIG.  474.  dons.      A  long  muscle  may  be 

f  composed  of  short  fasciculi,  since 

^     \  the  latter  may  be  attached  to  ten- 


Perimysium -i__^_  U- 


Muscle-fibres 


Several  primary  muscle-bundles  in  transverse  section,  showing  the 
arrangement  of  component  fibres.     X  40. 


dons  which  cover  ts  opposite 
sides  or  extend  within  its  sub- 
stance  as  septa.  In  such  cases, 
as  in  the  rectus  femoris  or  the 
deltoid,  the  short  fasciculi  run 
obliquely,  thereby  producing  a 
pennate  arrangement  which  often 
characterizes  muscles  of  great 
strength.  When,  on  the  con- 
trary, the  tendons  are  limited  to 
the  ends  of  a  muscle,  the  fascic- 
uli are  relatively  long  and  may 
extend  its  entire  length.  The 
sartorius  contains  fasciculi,  as 
well  as  fibres,  of  conspicuous  ex- 
tent, some  bundles  stretching 
the  entire  distance  between  the 
tendons. 

General  Structure  of 
Striated  Muscle. — The  histo- 
logical  unit  of  voluntary  muscular 
tissue  is  the  transversely  striated 
or  striped  muscle-fibre,  which 
represents  a  highly  specialized 
single  cell.  The  fibres  are  the 
contractile  elements  by  the  shortening  of  which  the  length  of  the  entire  muscle  is 
decreased  and  the  force  exerted.  The  fibres  are  cylindrical,  or  prismatic  with  rounded 
angles,  in  form,  and  vary  from  .01-.  t  mm.  in  diameter  ;  no  constant  relation  exists 
between  the  thickness  of  the  fibres  and  the  size  of  the  muscle  of  which  they  are  the 
components,  and,  indeed,  their  diameter  varies  even  within  the  same  muscle.  In 
general  the  limb  muscles  are  composed  of  large  fibres,  those  of  the  mature  male  sub- 
ject usually  exceeding  the  corresponding  fibres  of  the  female.  The  length  of  the 
muscle-fibres  is  likewise  subject  to  great  variation.  As  a  rule,  the  fibres  composing 
a  muscle  are  of  limited  length,  generally  not  exceeding  from  4-5  cm. ;  in  exceptional 
instances,  however,  as  in  the  sartorius,  they  may  attain  a  length  of  over  1 2  cm.  and 
a  width  of  from  1-5  cm.  (Felix).  The  fibres 
are  usually  somewhat  spindle-shaped,  being 
slightly  larger  in  the  middle  than  at  the  ends, 
which  are  usually  more  or  less  pointed  ;  blunted 
or  club-shaped  and,  more  rarely,  branched  ex- 
tremities are  not  uncommon.  Branched  and 
anastomosing  fibres  occur  in  certain  localities, 
as  in  the  tongue,  facial  and  ocular  muscles. 

The  individual  fibres,  each  invested  in  its 
own  sheath,  or  sarcolemma,^  are  grouped  into 
small  primary  bundles,  the  component  fibres  of 
which  are  held  together  by  a  meagre  amount  of 
connective  tissue,  the  endomysiutn.  The  latter  is  continuous  with  the-  pcriniysintn 
investing  the  primary  bundles.  These  are  associated  into  uncertain  groups,  the 
secondary  handles,  which  are  united  and  enclosed  by  extensions  and  subdivisions  of 
the  general  connective-tissue  envelope  of  the  entire  muscle,  the  epiniysimn.  In  muscles 


FIG.  475. 


Portion  of    muscle-fibre,   showing   sarcok-mnia 
bridging  break  in  sarcous  substance.     X  370. 


STRIATED   OR   VOLUNTARY   MUSCLE. 


459 


possessing  a  fine  grain  the  secondary  bundles  correspond  with  the  fasciculi,  but  in 
muscles  of  coarse  texture  each  fasciculus  includes  a  number  of  secondary  bundles 
between  which  the  ramifications  of  the  epimysium  extend.  The  characteristic  picture 
presented  in  transverse  sections  of  muscles  (Fig.  474)  illustrates  the  relation  of  the 
fibres  to  the  larger  groupings  of  the  muscular  elements. 

Structure  of  the  Muscle-Fibre. — Each  fibre  corresponds  to  a  greatly 
elongated  multinucleated  muscle-cell,  and  consists  of  a  sheath,  or  sarcolemma,  and 
the  contained  sarcous  substance. 

The  sarcolemma  forms  a  complete  investment  of  the  fibre  and  alone  comes 
into  contact  with  the  surrounding  connective  tissue  by  which  the  muscle-fibres  are 
attached  either  to  one  another  or  to  the  tendinous  structures  upon  which  they  exert 
their  pull.  The  sarcolemma  is  a  transparent,  homogeneous,  elastic  membrane  which 
so  closely  invests  the  contained  sarcous  substance  as  to  be  almost  invisible  under 
ordinary  conditions.  Being  of  greater  toughness  than  the  muscle-substance,  it  often 
withstands  mechanical  disturbance,  as  teasing,  while  the  latter  becomes  broken  ; 
where  such  breaks  occur  the  sarcous  substance  sometimes  contracts  within  the  sarco- 
lemma, which  at  the  points  of  fracture  then  becomes  visible  as  a  delicate  tubular 
sheath  stretching  across  the  space  separating  the  broken  ends  of  the  more  friable 


J— 

Q- 

M- 
Q- 
J 
z- 


iii 


S . 


Diagrams  illustrating  structure  of  striated  muscle-fibre.  A,  usual  view;  ff,  correct  view,  showing  sustentacular 
septa  continued  across  fibre  from  sarcolemma;  C,  septa  shown  after  vanadium-haematoxylin  staining.  Z,  interme- 
diate disk  (Zwischenscheibe)  ;  /,  light  band  ;  Q,  transverse  disk  (Querscheibe) ;  M,  median  disk  (Mittelscheibe)  ; 
S,  sarcolemma.  (After  M.  Heidcnkain.) 

sarcous  substance  (Fig.  475).  In  teased  preparations  the  sarcolemma  is  sometimes 
also  seen  projecting  beyond  the  sarcous  substance,  as  a  coat  sleeve  covers  the  stump 
of  an  arm. 

The  sarcous  or  muscular  substance  within  the  sarcolemma  in  turn  consists 
of  two  parts,  the  less  differentiated  passive  sarcoplasm  and  the  highly  specialized 
contractile  fibrill&  in  which  the  active  changes  take  place  resulting  in  the  contraction 
of  the  muscle-fibre. 

Since  the  highly  characteristic  appearance  of  cross-striation  which  distinguishes 
the  fibres  of  voluntary  muscle,  as  well  as  supplies  the  reason  for  its  designation  as 
striped  or  striated,  depends  upon  the  arrangement  of  the  contractile  fibrillae,  the 
details  of  the  latter  first  claim  attention. 

The  cross-striation  consists  of  alternate  dark  and  light  bands  which  extend  the 
entire  width  of  the  fibre  and  depend  upon  the  differentiation  of  the  contractile  fibrillae 
into  segments  of  greater  or  less  density.  Close  lateral  approximation  of  the  more 
dense  and  deeply  staining  segments  in  the  fibrillae,  lying  side  by  side  within  the  sarco- 
lemma, produces  the  dark  band  ;  the  similar  relation  of  the  less  dense  and  non-staining 
segments  produces  the  impression  of  the  light  band.  If  it  were  possible  to  isolate  the 
individual  contractile  fibrillce,  each  would  present  the  details  shown  in  the  accompany- 
ing diagram  (Fig.  476).  The  dark,  broad  transverse  disk  (Q*)  of  doubly  refracting, 


460 


HUMAN    ANATOMY. 


FIG.  477. 


or  anisotropic ;  substance  is  succeeded  at  either  end  by  the  light  band  (JJ}  of  singly 
refracting,  or  isotropic,  substance.  The  light  band  is  subdivided  by  a  delicate  line, 
the  intermediate  disk  (Z  ),  also  known  as  Krause  s  membrane.  The  sequence  which 
by  repetition  makes  up  the  contractile  fibrilla  consists,  therefore,  of  Z  +J-T  Q  -\-J~rZ- 
Under  favorable  conditions  for  examination  the  transverse  disk  exhibits  less  density 
midway  between  its  ends  ;  this  zone  is  traversed  by  a  delicate  line  (M~),  the  median 
disk  (Hensen,  Merkel)  or  middle  membrane  (M.  Heidenhain ). 

The  interpretation  of  these  appearances,  shown  as  usually  seen  under  moderate 
amplification  in  the  accompanying  photograph  (Fig.  477),  has  been  the  subject  of 
much  laborious  investigation  and  vexed  discussion  ;  even  at  the  present  time  authorities 
are  far  from  accord  as  to  the  significance  of  the  observed  details  in  their  relations  to  the 
architecture  of  the  muscle-fibre.  It  is  beyond  the  purpose  of  these  pages  to  review 
the  various  theories  concerning  the  ultimate  structure  of  striped  muscle  ; *  suffice  it  to 
point  out  that,  apart  from  the  conclusions  of  those  observers  who  from  time  to  time 
have  contended  that  the  appearances  are  entirely  optical  and  do  not  correspond  to 

actual  structural  details,  two  chief 
views  regarding  the  architecture  of 
the  muscle-fibre  have  been  held. 
According  to  the  one,  championed 
by  Krause,  the  intermediate  zone 
is  regarded  as  the  expression  of 
a  membranous  septum  which 
stretches  entirely  across  the  mus- 
cle-fibre as  an  inward  extension  of 
the  sarcolemma  and  thus  subdi- 
vides the  fibre  into  a  number  of 
minute  compartments,  or  contrac- 
tile disks,  by  the  longitudinal  ap- 
position of 'which  the  entire  fibre 
is  built  up.  The  other  view,  early 
accepted  by  Kolliker,  regards  the 
fibre  as  made  up  of  fibrillce  ex- 
tending the  length  of  the  fibre, 
the  transverse  cleavage  into  disks 
being  secondary  and  artificial.  The 
fibrillar  theory  as  advanced  by  Rol- 
let  has  received  wide  acceptance 
and  deserves  brief  mention.  Ac- 
cording to  this  authority,  the  con- 
tractile fibrillae  are  to  be  conceived 
as  forming  anisotropic  rods  consisting  of  alternating  thicker  and  thinner  segments 
(Fig.  478),  the  former  corresponding  in  position  with  the  broad,  dark,  transverse 
disk,  the  latter  with  the  lighter  band,  since  the  meagre  amount  of  doubly  refracting 
substance  in  this  zone  is  masked  by  the  large  quantity  of  isotropic  sarcoplasm. 
Rollet  recognized  the  intermediate  disk  as  consisting,  not  of  a  continuous  membrane, 
but  as  an  interrupted  line  representing  a  row  of  minute  beads  which  exist  as  local 
accumulations  on  the  thinner  segments  of  the  fibrillse.  Rollet' s  conception  of  the 
fibre,  therefore,  included  the  sarcolemma  containing  the  sarcoplasm  in  which  the  con- 
tractile fibrillae  were  embedded. 

More  recent  investigations  with  the  aid  of  improved  differential  stains  have  led 
to  a  modification  of  the  fibrillar  view  in  so  far  that  the  intermediate  disk  is  to  be 
regarded  as  a  structure  that  is  attached  to  the  sarcolemma  and  extends  between  the 
fibrilke.  M.  Heidenhain  believes  the  median  disk  to  be  an  additional  membrane  that 
likewise  meets  the  sarcolemma  at  the  periphery  of  the  fibre.  The  later  conception 
of  muscle  architecture  in  no  wise  questions  the  existence  of  the  fibrilla-  as  the  con- 
tractile elements  of  the  fibre,  but  regards  them  as  held  in  place  by  the  lateral  braces 

1  An  exhaustive  review  of  the  literature  and  various  opinions  regarding  tin-  structure  of 
striped  muscle  is  given  by  M.  Heidenhain:  Ergebnisse  der  Anatomic  und  Kntwick.,  Bd.  ix.. 
1899. 


Photograph   of   striated  muscle,   showing  the  usual   appearance 
under  moderately  high  magnification.     X  700. 


STRIATED   OR   VOLUNTARY    MUSCLE. 


461 


represented  by  the  intermediate  and  median  bands.  The  foregoing  diagram  (Fig. 
476),  modified  from  Heidenhain,  indicates  the  relations  of  the  several  bands  to  be 
seen  in  muscle  when  examined  under  the  most  favorable  conditions.  That  various 
reagents  produce  marked  changes  in  the  details  of  the  muscle-picture  admits  of  no 
question  ;  this  has  been  graphically  represented  by  the  last-quoted  author. J  The  fact 
that  the  intermediate  disk  is  attached  to  the  sarcolemma  is  shown  by  the  constrictions 
or  scalloped  margin  in  the  outline  of  the  fibre  during  contraction,  the  constrictions 
corresponding  in  position  to  the  attachment  of  the  membranes  of  Krause.  The 
striped  muscle  of  certain  insects  exhibits  an  additional  band,  the  accessory  disk,  sub- 
dividing the  light  zone  (J). 

The  distribution  of  the  contractile  fibrillae  throughout  the  fibre  is  not  uniform, 
since  the  fibrillae  are  grouped  into  bundles,  the  muscle-columns  or  sarcostyles.  This 
arrangement  is  well  shown  in  suitably  prepared  transverse  sections  of  muscular  tissue 
(Fig.  479),  in  which  the  individual  fibres  are  seen  to  be  made  up  of  minute  stippled 
areas  separated  by  clear  lines.  These  areas  are  known  as  Cohnheim'  s  fields,  and 
represent  the  transversely  cut  groups  of  contractile  fibrillae.  The  clear  lines  indicate 
the  distribution  of  the  sarcoplasm  ;  in  addition  to  forming  the  net-work  dividing 
Cohnheim's  fields,  the  sarcoplasm  separates  the  groups  of  individual  fibrillae,  each 
muscle-column  being  entirely  surrounded  by  the  less  highly  differentiated  substance. 


FIG.  478. 


-Sarcolemma 


FIG.  479. 


Cohnheim's — - 
field 


Diagram  illustrating  Rollet's  view  of  structure  of 
muscle-fibre  and  relations  of  assumed  details  to  usual 
appearances  of  tissue. 


Endomysium 


Nuclei  of  interfibrillar_ 
tissue 


Muscle-fibres  of  lizard  in  transverse  section,  showing 
fields  of  Cohnheim  and  muscle-nuclei.    X  650. 


When  seen  in  longitudinal  section,  the  sarcoplasm  between  the  groups  of  fibrillae 
appears  as  lines  extending  the  entire  length  of  the  fibre,  to  which  an  inconspicuous 
longitudinal  striation  is  thus  imparted. 

The  muscle-fibre  has  already  been  spoken  of  as  a  multinucleated  cell.  The 
nuclei  resulting  from  the  division  of  the  nucleus  of  the  embryonal  cell  remain  within 
the  sarcoplasm  and  are  termed  muscle-nuclei.  Their  position  in  mammalian  muscle 
is  usually  immediately  beneath  the  sarcolemma  ;  in  certain  fibres,  however,  as  those 
composing  the  semitendinosus  of  the  rabbit  (Fig.  480),  and  of  uncertain  distribution 
in  man,  the  nuclei  lie  more  deeply  embedded  within  the  sarcoplasm,  therein  agreeing 
in  location  with  the  position  occupied  by  the  nuclei  in  the  muscular  tissue  of  many 
of  the  lower  vertebrates  (Fig.  479). 

Variations  in  the  color  and  contractility  of  muscular  tissue  have  been  described 
by  Ranvier  and  Krause,  Klein,  Griitzner,  and  others.  While  the  skeletal  muscles 
are  usually  of  a  pale  tint  and  contract  energetically  when  stimulated,  particular  mus- 
cles of  certain  animals,  as  the  semitendinosus  and  the  soleus  in  the  rabbit,  possess  a 
deeper  color  and  contract  more  slowly  and  prolongedly  under  stimulation.  Such 
red  muscles,  as  they  have  been  named,  are  composed  of  fibres  which  are  thinner  than 
common  and  possess  a  relatively  larger  amount  of  sarcoplasm,  in  which  the  muscle- 
nuclei  are  embedded  not  only  immediately  beneath  the  sarcolemma,  but  also  in  the 

1  M.  Heidenhain  :  Anatom.  Anzeiger,  Bd.  xx.,  Nos.  2  and  3,  1901. 


462 


HUMAN   ANATOMY. 


deeper  parts  of  the  fibre  (Fig.  480).  The  longitudinal  striation  is  also  unusually  con- 
spicuous, due  to  the  exceptional  amount  of  interfibrillar  sarcoplusm.  Although  not 
present  in  mammals  generally  in  sufficient  quantity  to  affect  the  appearance  of  entire 
muscles,  the  peculiar  ' '  red' '  fibres  are  found  in  many  localities  intermingled  with  the 
more  usual  pale  variety.  Klein  has  described  such  fibres  in  the  diaphragm,  and. 
according  to  the  investigations  of  Griitzner  and  of  J.  Schaffer,  it  is  probable  that  they 
are  found  in  all  muscular  tissue  upon  which  devolves  prolonged  effort.  These  fibres 
are,  therefore,  present  in  the  heart,  the  eye  muscles,  and  the  muscles  of  respiration  and 
of  mastication.  The  red  fibres  must  be  regarded  as  representing  a  less  complete 
differentiation  of  the  muscle-cell  and  as  possessing  consequently  a  larger  proportion 
of  reserve  protoplasm  ;  they  are  better  able  to  withstand  the  fatigue  of  contractions 
than  those  in  which  the  specialization  of  a  larger  part  of  the  cytoplasm  has  occurred. 
The  pale  fibres  gain  in  rapidity  of  contraction  at  the  expense  of  early  exhaustion. 

Attachment  of  the  muscular  fibres,  whether  to  other  fibres  or  to  tendons,  is 
accomplished  by  the  union  of  the  sarcolemma  with  the  connective  or  tendinous  tissue 


FIG.  480. 


FIG.  481. 


Portion  of  the  soleus  muscle  of  the  rabbit  in  trans- 
verse section.  The  more  coarsely  stippled  fibres  are  of 
"red"  muscle;  they  "also  contain  nuclei  within  the  sar- 
cous  substance.  X  160. 


Section  of  tendon,  showing  termination  of  muscle- 
fibres.     X  200. 


and  never  by  direct  fusion  of  the  connective  tissue  with  the  sarcous  substance,  the 
latter  remaining  completely  invested  by  its  sheath.  On  joining  a  muscle  (Fig.  481), 
the  tendon-tissue  subdivides  into  small  bundles  which  receive  and  surround  the  pointed 
ends  of  the  muscle-fibres,  the  fibrous  tissue  becoming  attached  to  the  sarcolemma, 
while  the  areolar  tissue  between  the  tendon-bundles  blends  with  that  separating  the 
muscle-fibres. 

Cardiac  Muscle. — The  striped  muscle  of  the  heart,  in  addition  to  the  pecu- 
liarity of  being  beyond  the  control  of  the  will,  although  striated,  presents  certain 
modifications  in  the  form  and  arrangement  of  its  fibres  which  call  for  special  con- 
sideration. According  to  the  views  formerly  held,  the  histological  unit  of  the  myo- 
cardium was  the  branched  fibre-cell  (Fig.  482),  by  the  apposition  of  which  the  sheets 
of  muscular  tissue  were  formed.  The  fibre-cell  was  regarded  as  a  short  branched 
fibre,  devoid  of  a  sarcolemma  and  possessing  a  nucleus  surrounded  by  a  consideral  (It- 
area  of  undifferentiated  sarcoplasm.  The  investigations  of  M.  Heidenhain1  have 
shown  that  the  constitution  of  the  heart-fibres  corresponds  more  closely  to  that  of 

1  Anatom.  An/eiger,  Bd.  xx.,  Nos.  2  and  3,  1901. 


STRIATED   OR   VOLUNTARY   MUSCLE. 


463 


ordinary  muscle,  the  chief  difference,  in  addition  to  their  shorter  length,  being  the 
complicated  partial  longitudinal  division  which  these  fibres  undergo.      Fig.  483  repre- 
sents diagrammatically  the  peculiar  step- 

FIG.  482.  like  relation  of  the  fibres  and  their  nu- 

4v' ;,  merous  secondary  or  intercalated  limbs. 

}  M-.:V:!  Each  fibre  possesses  a  sarcolemma  which, 

„&  however,   is  less   firm  and  resistant  than 

that  usually  seen.     The  heart  muscle  pos- 

>i%".'  .  FIG.  483. 


•'••'  •'    i 


Muscle-fibres  of  human  heart.     X  375- 


Diagram  showing  the  form  and  arrangement  of  the  fibres 
of  heart  muscle.     (M.  Heidenhain.) 


sesses  a  relatively  large  amount  of  sarcoplasm,  as  evidenced  by  the  considerable 
accumulation  surrounding  the  nucleus,  as  well  as  the  thicker  strata  separating  the 
muscle-columns.  The  unusual  quantity  of  sarcoplasm  accounts  for  the  conspicuous 

FIG.  484. 


Capillary  blood-vessel 


Undifferentiated  sarcoplasm 


Nucleus 


Fibres  of  cardiac  muscle  in  transverse  section.     X  375. 


longitudinal  striation  of  cardiac  muscle  and  agrees  with  what  may  be  expected  in 
muscular  fibres  subjected  to  such  constant  activity. 


464 


HUMAN   ANATOMY. 


FIG 


The  blood-vessels  of  striped  muscle  are  very  numerous  to  insure  adequate 
nutrition  to  a  tissue  of  great  functional  activity.  The  larger  arteries  and  accompany- 
ing veins  penetrate  the  muscle  along  the  septal  extensions  of  the  epimysium  and 
divide  into  smaller  branches  which  run  between  the  fasciculi.  These  vessels  undergo 

further  subdivision  into  twigs  which  pass  between 
the  finer  bundles  of  muscle-fibres  and  ultimately 
break  up  into  the  capillaries  enclosing  the  indi- 
vidual fibres. 

The  capillary  vessels  of  voluntary  muscle 
form  a  characteristic  net-work  consisting  of  nar- 
row rectangular  meshes  (Fig.  485),  the  longer 
sides  of  which  correspond  to  the  direction  of 
the  muscle-fibres  between  which  they  run  ;  the 
shorter  sides  of  the  meshes  are  formed  by  the 
capillaries  which  extend  across  or  may  encircle 
the  individual  fibres.  The  capillaries  supplying 
muscles  subjected  to  prolonged  and  powerful 
contractions  often  exhibit  local  dilatations,  which 
may  serve  for  temporary  reservoirs  for  the  blood 
during  contraction.  The  closeness  of  the  capil- 
lary net-work  is  determined  by  the  size  of  the 
muscle-fibres,  muscles  composed  of  fine  fibres 
possessing  the  smallest  vascular  meshes. 

The  relation  of  the  blood-vessels  to  cardiac 
muscle  is  unusually  intimate,  the  capillaries  not 
only  enclosing  the  muscle-fibres  with  a  rich  net- 
work, but  lying  within  depressions  on  the  surface 
of  the  fibres,  or  even  in  channels  surrounded  by 
the  muscular  tissue  (Meigs). 
The  lymphatics  of  striated  muscular  tissue  are  represented  by  the  interfascicular 
clefts,  which  extend  within  the  connective  tissue  between  the  muscle-fibres,  and  the 
more  definite  channels  within  the  septa.  The  larger  lymph-vessels  formed  by  the 
confluence  of  those  lying  between  the  fasciculi  pass  to  the  sheath  of  the  muscle  and 
tendon  and  carry  off  the  lymph  from  the  muscular  tissue. 

The  nerves  supplying  striped  muscle  include  both  motor  and  sensory  fibres. 
The  former  terminate  in  specialized  arborizations,  the  motor  nerve-endings,  which 


Longitudinal 


Transverse 


Injected  voluntary  muscle,  showing  arrange- 
ment of  interfascicular  vessels  and  capillaries. 


FIG.  486. 


Neural  canal 


Ectoblast 
Lateral  plate  of  myotome  — -^f^  . 

JT 

Medial  plate  of  myotome—  -fgffi. 


Wolffian  body — fff, 

Parietal  mesoblast  of {£, 

somatopleura  /'•' 

t     ;-%• 


,•'      • ' ' 


•  —  Wolffian  body 
-  Parietal  mesoblast 

b 

-Umbilical  vein 


Body-cavity  Aorta  Body-cavity 

Transverse  section  of  rabbit  embryo,  showing  differentiation  of  myotomes.    X  90. 

are  usually  regarded  as  lying  beneath  the  sarcolemma  upon  the  sarcous  substance. 
The  sensory  fibres  are  connected  with  the  neuro-muscular  end  organs  or  »u<sf/c- 
spindles,  from  which  the  afferent  nerves  proceed  centrally.  The-  ck  tailed  description 


STRIATED   OR    VOLUNTARY    MUSCLE. 


465 


of  both  varieties  of  terminations  in  striped  muscle  will  be  found  under  nerve-endings 
(page  1014). 

Development  of  Striped  Muscle.— The  early  appearance  of  a  series  of 
quadrilateral  segmental  areas,  the  somites,  within  the  tract  of  the  paraxial  mesoblast 
on  each  side  of  the  neural  tube  has  been  described  (page  29).  Likewise  the  sub- 
sequent breaking  up  of  each  somite  into  the  centrally  situated  sclerotome  and  the 
peripheral  myotome  ( Fig.  34).  The  latter  soon  becomes  a  compressed  C-shaped 
mass,  in  which  the  more  compact  lateral  part  is  usually  described  as  the  cutis-platc 
and  the  medial  portion  as  the  muscle-plate.  The  histological  characters  of  these  parts 
of  the  myotome  differ,  the  cutis-plate  consisting  of  several  layers  of  closely  packed 
cells  resembling  epithelial  elements,  while  the  muscle-plate  is  composed  of  more 
loosely  disposed  spindle-cells,  between  which  lie  irregularly  round  cells,  many  of 


FIG.  487. 


Neural  canal 


Lateral  plate 


Intersegmental 
blood-vessel 


Ectoblast 


FIG.  488. 
. 


Wall  of  neural 

tube 


Developing 
muscle-fibres 


Intersegm 
blood-ves 


Frontal  section  of  rabbit  embryo,  showing 
myotomes.     X  100. 


.  • . 

ental_    Vffi.  '     &&&&• 

ssel  Y//.V  ^l^KM.-'i'' 

I 


Frontal  section  of  two  myotomes  of  rabbit  embryo, 
showing  developing  muscle.     X  130. 


which  are  actively  engaged  in  division.  The  less  differentiated  round  cells,  or 
wyoblasts,  become  elongated  and  transformed  into  the  spindle-cells,  the  elements 
which  are  directly  converted  into  the  young  muscle-fibres.  The  spindle-cells,  at  first 
mononuclear,  rapidly  increase  in  length,  the  round  or  oval  nucleus  at  the  same  time 
undergoing  division.  In  consequence  the  elongated  muscle-cells  become  multinuclear. 
The  cytoplasm  of  the  cells  early  exhibits  differentiation  into  a  peripheral  and  a 
central  zone.  During  the  second  foetal  month  the  former  manifests  a  disposition  to 
become  fibrillar,  while  the  central  zone  for  a  time  remains  undifferentiated  and  contains 
the  muscle-nuclei. 

On  cross-section  the  young  muscle-fibres  at  this  stage  appear  as  stippled  rings 
enclosing  an  indifferent  core  surrounding  the  nuclei,  the  stippling  being  due  to  the 
partially  differentiated  fibrillae.  The  latter  appear  first  as  marginal  groups,  but 
later  form  a  continuous  peripheral  zone.  This  gradually  widens,  and  by  the  close 
of  the  sixth  foetal  month  the  fibres  composing  the  muscles  of  the  upper  extremity 


466  HUMAN    ANATOMY. 

have  become  fibrillar  throughout  their  entire  thickness  ;  those  of  the  lower  ex- 
tremity acquire  a  similar  condition  a  month  later.  With  the  deeper  extension  of 
the  fibrillae  the  characteristic  cross-striation  appears,  the  nuclei  migrating  to  the 
periphery  of  the  fibre  as  the  less  differentiated  cytoplasm  becomes  invaded.  The 
sarcolemma  appears  by  the  time  the  entire  fibre  has  become  fibrillar.  The  sarcoplasm 
surrounding  the  nuclei  of  the  mature  fibre  represents  the  remains  of  the  less  highly 
differentiated  cytoplasm  of  the  original  muscle-cell  ;  that,  however,  separating  the 

muscle-columns  must  be  regarded 

FIG.  489  as  the  product  of  a  secondary  dif- 

ferentiation. 

T-*>    __.  The  designation  ' '  cutis-plate, ' ' 

applied  to  the  compact  outer  epi- 
thelioid  portion  of  the  myotome, 
expresses  the  relation  to  the  in- 
tegument which  has  been  widely 
accepted,  since  this  part  of  the 
l^  t  myotome  is  generally  regarded  as 
concerned  in  the  formation  of  the 
connective-tissue  portion  of  the 
skin.  This  fate  of  the  ' '  cutis- 
plate"  was  long  age  denied  by 
Balfour,  who  held  that  both  layers 

Developing  voluntary  muscle;  the  fibres  are  still  unstnated.    X  525.       of    the   myotome  are  Concerned   in 

the  formation  of  muscular  tissue. 

Kaestner l  arrived  at  similar  conclusions,  and  more  recently  Bardeen 2  has  shown  that 
in  the  pig  practically  the  entire  epithelial  lamella  is  converted  into  muscle.  According 
to  this  investigator,  while  some  of  the  epithelial  elements  of  the  skin-plate  degenerate, 
the  greater  number  undergo  mitosis  and  give  rise  to  myoblasts  which,  in  turn,  become 
the  spindle-cells  from  which  the  muscle-fibres  are  developed.  The  outer  margin  of 
the  epithelial  lamella  is  sharply  defined  by  a  limiting  membrane  formed  by  the  adja- 
cent cells  ;  a  somewhat  similar  but  less  pronounced  boundary  guards  the  inner  con- 
tour of  the  lamella.  The  external  limiting  membrane  persists  until  the  conversion  of 
the  epithelioid  elements  into  myoblasts  and  spindle-cells  has  been  well  established,  by 
which  time  the  mesoblastic  tissue  surrounding  the  myotomes  has  grown  in  between 
the  latter  and  the  adjacent  ectoblast  ;  it  is  from  this  source,  therefore,  and  not  from 
the  "  cutis-plate,"  that  the  connective-tissue  layer  of  the  integument  is  derived. 

The  masses  of  embryonal  muscle,  or  myomeres,  derived  from   the  somites  are 
early  separated  by  the  ingrowth  of  intersegmental  septa  of  connective  tissue  which 

FIG.  490. 

, 


Developing  muscle-fibres  in  which  striation  is  just  appearing.     X  375. 

later  support  the  intersegmental  blood-vessels  and  nerves  and,  in  the  thoracic  region, 
the  costal  elements,  and,  by  the  ingrowth  of  a  connective-tissue  partition,  each  urn- 
is  further  divided  into  a  dorsal  and  a  ventral  portion,  from  which,  in  a  general  way, 
the  muscles  associated  with  the  spine  and  the  antero-lateral  body-walls  are  derived 
respectively. 

In  this  primitive  condition  the  trunk  musculature  is  represented  by  a  series  of 

1  Archiv  fiir  Anat.  u.  Phys.,  Suppl.  Hd.,  1890. 
'Johns  Hopkins  Hospital  Reports,  vol.  ix.,  1900. 


STRIATED    OR   VOLUNTARY    MUSCLE.  467 

bands, — the  myomeres, — each  of  which  consists  of  a  dorsal  and  a  ventral  portion, 
and  which  succeed  one  another  regularly  and  segmentally  throughout  the  entire 
length  of  the  trunk.  The  muscle-fibres  of  which  each  myomere  is  composed  extend 
from  the  intersegmental  septum  in  front  to  that  behind,  having  thus  a  regular  antero- 
posterior  direction.  In  the  lower  vertebrates  this  condition  persists  with  but  little 
modification  throughout  life,  producing  the  flake-like  arrangement  of  the  muscles 
characteristic  of  the  fishes.  In  the  higher  vertebrates,  however,  numerous  secondary 
modifications  supervene,  whereby  the  myomeres  are  broken  up  into  individual  mus- 
cles, their  original  segmental  arrangement  becoming  at  the  same  time  greatly  ob- 
scured, although  it  still  persists  in  those  regions  in  which  the  muscles  are  intimately 
associated  with  segmental  skeletal  structures  such  as  the  vertebrae  and  ribs. 

These  changes  are  of  several  kinds,  and,  as  a  rule,  several  varieties  of  modi- 
fication cooperate  in  the  differentiation  of  a  muscle.  Some  of  the  more  important 
are  as  follow  : 

1.  An  end-to-end  fusion  of  several  myomeres  or  portions  of  myomeres  takes 
place,  producing  a  muscle-sheet  or  band  which  extends 'interruptedly  through  sev- 
eral primary  segments.      Such  a  modification  gives  rise  to  muscles  supplied  by  a 
number  of  segmental  nerves  ;  just  as  many,  indeed,  as  there  are  myomeres  partici- 
pating in  the  formation  of  the  muscle.      Examples  of  muscles  formed  in  this  way  are 
to  be  seen  in  the  musculature  of  the  abdominal  walls,  the  oblique  muscles,  the  trans- 
versalis,  and  the  rectus,  for  instance,  being  all  polymeric  muscles,  as  are  also  many 
of  the  longitudinal  muscles  of  the  back.      Not  infrequently  the  origin  of  these  mus- 
cles by  the  fusion  of  portions  of  successive  myomeres  is  shown,   independently  of 
their  nerve-supply,  by  the  persistence  in  their  course  of  some  of  the  intermuscular 
septa,  these  forming  transverse  tendinous  bands  traversing  the  muscle  in  a  horizontal 
direction.      Such  tendinous  inscriptions  (inscriptiones  tendinecB^,  as  they  are  termed, 
occur  normally  in  the  rectus  abdominis,  and  are  also  frequently  found  in  the  internal 
oblique,  the  sterno-hyoid,  and  the  sterno-thyroid  muscles. 

2.  A  longitudinal  division  of  the  myomeres  into  a  number  of  distinct  and  origi- 
nally parallel  portions  may  occur.      Examples  of  this  modification  combined  with  the 
end-to-end  fusion  of    the  portions  so  formed  from  successive  myomeres   are  very 
abundant.     Thus,  the  rectus  abdominis  is  the  result  of  the  splitting  off  of  the  ventral 
portion  of  a  number  of  successive  myomeres,  whose  remaining  portions  are  largely 
represented  in  the  oblique  and  transverse  abdominal  muscles.      So,  too,  in  the  neck, 
the  differentiation  of  the  sterno-hyoid  and  omo-hyoid  is  due  to  the  same  process, 
and  it  has  also  acted  in  the  differentiation  of  the  various  muscles  of  the  transverso- 
costal  group  of  the  dorsal  musculature. 

3.  A  tangential  splitting  of  the  myomeres  is  again  an  occurrence  of  great  fre- 
quency, producing  superposed  muscles,  and  is  clearly  shown  in  the  dorsal  muscula- 
ture and  in  the  ventro-lateral  muscles  of    the  thoracic   and  abdominal  walls.       It 
does  not  necessarily  involve  all  portions  of  a  myomere  when  this  has  already  divided 
longitudinally,  but  may  be  confined  to  only  certain  of  the  parts  so  formed.      Thus, 
while  it  affects  the  ventro-lateral  abdominal  muscles,  it  does  not  affect  the  rectus 
abdominis,  this  muscle  representing  the  entire  thickness  of  the  ventral  borders  of  a 
number  of  successive  myomeres. 

4.  Associated  with  the  change  just  described  there  is  frequently  a  modification 
in  the  direction  of  the  fibres  in  one  or  more  of  the  superposed  muscles.      Primarily 
the  fibres  of  each  myomere  have  an  antero-posterior  direction, — a  condition  which  is 
still  retained  in  the  rectus  abdominis,  for  instance.      In  the  ventro-lateral  abdominal 
and  thoracic  muscles,  however,  the  original  direction  of  the  fibres  has  been  greatly 
altered,  those  of  the  superficial  layer  being  directed  in  general  downward  and  inward, 
those  of  the  middle  layer  to  a  considerable  extent  downward  and  outward,  while 
those    of    the    deepest   layer   are    directed    almost    or  quite  transversely, — that   is 
to  say,  in  a  direction  which  is  90°  different  from  that  taken  by  the  fibres  of  the 
myomere. 

5.  An  exceedingly  interesting  modification  is  that  which  results  from  the  migra- 
tion of  some  of  the  myomeres  over  their  successors,  so  that  a  muscle  formed  from 
certain  of  the  cervical  myomeres,  for  example,  may  in  the  adult  condition  be  super- 
posed upon  muscles  derived  from  the  thoracic  segments.     In  such  cases  of  migration 


468  HUMAN   ANATOMY. 

the  segmental  nerve,  or  at  least  those  fibres  of  it  which  originally  supplied  the  por- 
tions of  the  myomeres  in  question,  retains  its  connection  and  is  consequently  drawn 
out  far  beyond  its  usual  territory,  a  ready  explanation  being  thus  afforded  for  the 
extended  course  of  the  long  thoracic,  long  subscapular,  and  phrenic  nerves.  The 
muscles  supplied  by  these  nerves,  as  well  as  the  pectoralis  major  and  minor  muscles, 
are  all  derived  from  cervical  myomeres,  their  adult  position  being  due  to  the  process 
of  migration,  of  whose  existence  they  form  convincing  examples. 

6.  Finally,  portions  of  one  or  several  successive  myomeres  may  undergo  degen- 
eration, becoming  converted  into  connective  tissue,  which  may  have  the  form  of 
fascia,  aponeurosis,  or  tendon.  Examples  of  this  degeneration  are  to  be  found  in 
practically  all  muscles,  since  the  tendons  by  which  they  make  their  bony  attachments 
have  resulted  from  its  action.  In  the  lower  vertebrates  and  in  the  foetus  tendons 
and  aponeuroses  are  much  less  developed  than  in  the  higher  forms  or  in  the  adult, 
being  represented  by  muscular  tissue  which  later  becomes  converted  into  tendon  or 
aponeurosis.  The  intermuscular  septa  between  the  muscles  of  the  limbs  seem  to 
have  arisen  in  this  way,  and  occasionally  relatively  large  aponeurotic  sheets  have  so 
arisen,  as  in  the  case  of  the  aponeurosis  which  unites  the  two  posterior  serratus 
muscles.  Of  especial  interest  in  this  connection  are  the  degenerations  into  liga- 
ments of  muscle-tissue  primarily  occurring  in  the  neighborhood  of  many  of  the 
joints,  the  accessory  ligaments  being  in  many  cases  formed  in  this  manner.  Thus, 
the  external  lateral  ligament  of  the  knee-joint,  the  ligamentum  teres  of  the  hip-joint, 
and  even  the  great  sacro-sciatic  ligament  owe  their  origin  to  this  process,  and  many 
other  of  the  ligaments  may  also  be  referred  to  it. 

As  a  result  of  these  various  modifications  and  their  combinations  the  individual 
muscles  of  the  adult  body,  together  with  the  aponeurotic  sheets  which  are  frequently 
associated  with  them,  are  formed. 

GENERAL   CONSIDERATION    OF   THE   VOLUNTARY    MUSCLES. 

The  voluntary  or  striated  muscles  constitute  a  very  considerable  portion  of  the 
entire  mass  of  the  body,  their  weight  in  an  average  adult  male  having  been  esti- 
mated at  about  43.4  per  cent,  of  the  total  body  weight  (Vierordt).  Each  muscle 
is  a  distinct  organ  composed  of  a  number  of  contractile  fibres  united  into  bundles  or 
fasciculi  surrounded  by  a  delicate  sheath  of  connective  tissue,  the  pcrinn'siitin,  in 
which  blood-vessels  and  nerves  ramify  to  the  various  fasciculi,  and  which,  at  the 
surface  of  the  muscle,  is  continuous  with  the  fascia  which  encloses  the  entire  organ. 

At  each  extremity  of  the  muscle  the  contractile  tissue  is  united  with  dense 
connective  tissue,  the  general  structure  of  which  resembles  that  of  the  muscle,  its 
fibres  being  arranged  in  distinct  bundles  separated  and  enclosed  by  looser  tissue 
comparable  to  the  perimysium.  By  means  of  these  tendons,  as  they  may  generi- 
cally  be  termed,  the  attachment  of  the  muscle  to  portions  of  the  skeleton  or  other 
structures  is  effected.  The  extent  to  which  the  tendon  is  developed  varies  greatly 
in  different  muscles,  in  some  being  hardly  noticeable,  so  that  the  muscle-tissue 
appears  to  be  directly  attached  to  the  bone  (Fig.  496),  at  other  times  forming  a 
long  rounded  or  flattened  band  (Fig.  576),  to  which  the  term  tendon  is  usually 
applied,  or  again  forming  a  broad,  flat  expansion,  termed  an  aponeurosis  (Fig.  525). 
Both  the  tendons  and  aponeuroses  are  to  be  regarded  as  representing  portions  of  the 
original  muscle  converted  into  connective  tissue,  and,  indeed,  comparative  anatomy 
shows  that  many  of  the  ligaments  and  aponeuroses  of  the  body,  even  although  they 
may  not  seem  to  be  directly  related  to  neighboring  muscles,  are  really  to  be  regarded 
as  muscles  which  have  undergone  a  tendinous  degeneration. 

Attachments. — The  great  majority  of  the  voluntary  muscles  are  attached  at 
either  end  to  portions  of  the  skeleton,  passing  over  one  or  more  joints,  in  which 
thcv  effect  movement  by  their  contraction.  Occasionally,  however,  a  muscle  may 
be  attached  at  one  of  its  extremities,  in  part  or  entirely,  to  fascia,  as,  for  instance, 
the  glutens  maximus  and  the  tensor  fasciae  late,  or  both  of  its  attachments  may  be 
to  fascia,  as  is  the  case  with  some  of  the  muscles  of  expression  and  with  the  muscles 
of  the  palate  and  the  intrinsic  musculature  of  the  tongue.  Others,  again,  may  have 
one  or  both  of  their  attachments  to  tendons  of  other  muscles, — e.g.,  the  accessorius 


GENERAL  CONSIDERATION  OF  THE  VOLUNTARY  MUSCLES.     469 

and  the  lumbricales, — while  others  may  pass  between  portions  of  the  skeleton  and 
special  organs  upon  which  they  act,  as  is  exemplified  by  the  muscles  of  the  eyeball. 
Whatever  may  be  the  nature  of  the  structure  to  which  the  attachment  is  made, 
it  is  convenient  for  'purposes  of  description  to  regard  one  of  the  points  of  attachment 
of  each  muscle  as  the  fixed  point  from  which  it  acts  in  contraction,  and  to  speak  of 
this  as  its  origin,  and  to  regard  the  other  as  the  point  upon  which  it  acts,  speaking 
of  it  as  the  insertion.  It  must  be  understood,  however,  that  this  distinction  between 
the  two  attachments  is  somewhat  arbitrary,  since  what  is  usually  the  fixed  point  may 
under  certain  circumstances  become  the  movable  one.  For  instance,  in  the  case  of 
a  muscle  passing  from  the  pelvis  to  a  leg  bone,  if  the  body  be  erect,  the  contraction 
of  the  muscle  will  cause  an  inclination  of  the  trunk  on  the  hip-joint,  the  attachment 
to  the  leg  bone  being  then  the  fixed  point  and  that  to  the  pelvis  the  movable  one. 
In  other  positions  of  the  body,  however,  the  contraction  of  the  muscle  will  produce 
a  movement  of  the  leg,  the  fixed  and  movable  points  being  exactly  reversed.  Since, 
however,  the  movement  of  the  leg  may  be  regarded  as  the  more  usual  result  of  the 
contraction  of  the  muscle,  the  pelvic  attachment  is  arbitrarily  regarded  as  the  origin 
and  the  attachment  to  the  femur  or  tibia  the  insertion  of  the  muscle  in  question. 

FIG.  491. 


Central  portion 


Tendon  o 

Diagrams  showing  semi-pinnate  (A)  and  pinnate  (£)  arrangement  of  muscle-fibres,  which  pass  from  tendon  01 
origin  above  to  that  of  insertion  below.  C,  compound  pinnate  arrangement,  as  in  central  division  of  deltoid  muscle. 
(After  Poirier.) 

Form. — The  muscles  assume  various  forms,  dependent  to  some  extent  upon 
the  structures  to  which  they  are  attached.  Some  are  thin  sheets  with  almost  parallel 
fibres,  others  are  more  or  less  band-like,  while  others  may  have  considerable  thick- 
ness, and  be  quadrate,  triangular,  or  spindle-shaped.  Surrounding  certain  of  the 
orifices  of  the  body  are  what  are  termed  orbicular  or  sphincter  muscles  (Figs.  495, 
499),  consisting  of  a  muscular  sheet  whose  fibres  have  a  crescentic  course  around 
either  side  of  the  orifice,  the  lips  of  which  will  tend  to  be  drawn  together  by  the  con- 
traction of  the  muscle. 

Where  the  surfaces  for  attachment  are  considerable,  the  fibres  composing  a 
muscle  have  a  more  or  less  parallel  course  ;  but  where  a  comparatively  small  area  is 
all  that  is  available  for  the  attachment  of  a  strong  muscle,  as  is  the  case  with  many 
of  the  limb  muscles,  it  is  clear  that  such  an  arrangement  cannot  obtain.  The  muscle- 
fibres  then  converge  from  either  one  or  both  sides  to  be  inserted  one  above  the  other 
into  the  tendon,  forming  what  is  termed  a  scmipinnate  (e.  g. ,  many  of  the  muscles 
of  the  leg,  Fig.  609),  or  pinnate  muscle  (e.  g. ,  mterossei  dorsales,  Fig.  590.)  This 
convergence  may  take  place  towards  either  one  or  both  tendons  of  attachment,  and 
occasionally  these  may  spread  out  over  opposite  surfaces  of  the  muscle  to  form  apo- 
neurotic  sheets  which  overlap,  so  that  the  muscle-fibres  pass  obliquely  from  the  sur- 
face of  one  tendon  to  that  of  the  other  (e.g. ,  gastrocnemius,  semitendinosus,  Fig. 
635).  Finally,  in  some  of  the  broader  muscles  (e.g. ,  deltoid  and  subscapularis)  the 
muscle-fibres  may  arise  from  and  converge  to  a  series  of  tendinous  bands  which 


470  HUMAN   ANATOMY. 

alternate  with  one  another,  the  muscle  having  thus  a  compound  pinnate  arrangement 
(Fig.  491,  C). 

As  a  rule,  the  tendons  occur  in  connection  with  the  extremities  of  the  muscle, 
but  occasionally  one  or  more  tendinous  intersections  may  occur  in  the  course  of  the 
muscle,  which  thus  becomes  divided  into  two  or  more  bellies.  This  condition  may 
be  the  result  of  the  end-to-end  union  of  the  tendons  of  attachment  of  two  primarily 
distinct  muscles  {e.g.,  digastric,  Fig.  497)  or  to  the  persistence  of  some  of  the 
dividing  lines  which  separate  the  various  embryonic  segments  of  which  a  muscle 
may  be  composed  {e.g.,  rectus  abdominis,  Fig.  523)  ;  or  it  may  be  due  to  a  sec- 
ondary attachment  formed  by  a  muscle  in  its  course,  it  being  bound  down  to  a 
neighboring  bone  by  a  band  of  fascia  {e.g.,  omo-hyoid). 

Certain  muscles  present  the  peculiarity  of  possessing  two  or  more  separate 
heads  of  origin,  attached  to  different  bones  and  uniting  to  form  a  common  tendon  of 
insertion.  In  certain  cases  {e.g.,  biceps  femoris,  pronator  radii  teres)  this  condition 
indicates  the  union  of  two  primarily  distinct  muscles  which  had  a  common  insertion, 
or  which  were,  at  all  events,  originally  inserted  close  together,  but  in  other  cases  it 
has  resulted  from  a  separation  of  an  original  muscle  into  two  portions.  The  ana- 
tomical nomenclature  is  not  quite  consistent  as  regards  such  muscles,  since  it 
describes  the  biceps  femoris  as  a  two-headed  muscle,  although  its  two  heads  are 
fundamentally  distinct  organs  ;  while,  on  the  other  hand,  it  usually  regards  the 
psoas  and  iliacus  and  the  gastrocnemius  and  soleus  as  distinct  muscles,  notwith- 
standing their  common  insertion. 

Fasciae. — Connecting  the  various  muscles  and  uniting  them  into  groups,  and 
also  surrounding  the  entire  musculature  of  the  body  and  separating  it  from  the 
deeper  layers  of  the  integument,  are  sheets  of  connective  tissue  known  as  fascia. 
These  sheets  are  by  no  means  isolated  portions  of  connective  tissue,  but  are  rather 
to  be  regarded  as  parts  of  the  general  interstitial  connective-tissue  net-work  which 
traverses  all  parts  of  the  body,  thickened  to  form  more  or  less  definite  sheets  stand- 
ing in  relation  to  the  neighboring  organs.  The  density  of  the  sheets  varies  greatly  ; 
in  some  regions  they  are  imperfectly  developed  and  may  contain  considerable 
amounts  of  fat,  while  in  others  they  form  dense,  glistening  sheets  resembling  the 
expansions  of  tendons  mentioned  above,  and  termed,  like  these,  aponeuroses. 

It  is  convenient  to  recognize  two  principal  layers  of  fasciae,  the  superficial  and 
the  deep. 

The  superficial  fascia  immediately  underlies  the  skin  of  the  entire  body,  and  is 
sometimes  considered  a  portion  of  it  and  termed  the  panniculus  adiposus,  since, 
except  in  the  eyelids,  penis,  scrotum,  and  labia  minora,  it  contains  considerable  quan- 
tities of  fat.  It  is  connected  with  the  subjacent  deep  fascia  by  a  more  or  less  exten- 
sively developed  layer  of  areolar  tissue,  which,  however,  is  lacking  in  certain  regions, 
such,  for  instance,  as  the  face,  the  palmar  surface  of  the  hand,  and  the  plantar 
surface  of  the  foot,  where  the  superficial  and  deep  fasciae  are  intimately  united. 

The  deep  fascia,  on  the  other  hand,  immediately  covers  and  invests  the  muscles, 
and  in  the  intervals  between  them  becomes  continuous  with  the  periosteal  connec- 
tive tissue  enclosing  the  bones.  Those  lamellae  of  the  fascia  which  dip  down 
between  the  muscles  of  the  limbs — the  intermuscu'lar  septa — are  frequently  of  con- 
siderable firmness  and  serve  for  the  origin  of  fibres  of  the  neighboring  muscles,  and 
occasionally  muscles  {e.g.,  soleus,  levator  ani)  take  their  origin  in  part  directly 
from  portions  of  the  deep  fascia,  which  then  becomes  thickened  along  the  line  of 
the  origin  to  form  strong  bands,  termed  arcus  tendinei,  attached  at  either  extremity 
to  neighboring  bones. 

Certain  portions  of  the  deep  fascia,  and  especially  of  the  intermuscular  septa, 
represent  portions  of  the  muscular  system  which  have  undergone  tendinous  degen- 
eration,  and  are  represented  by  muscular  tissue  in  the  lower  vertebrates.  Indeed, 
the  relative  amount  of  aponeurotic  and  tendinous  tissue,  as  compared  with  the  mus- 
cular, is  very  much  greater  in  the  higher  than  in  the  lower  forms,  and  is  appre- 
ciably greater  in  the  human  embryo  than  in  the  adult,  indicating  a  transformation 
of  one  tissue  into  the  other  (hiring  the  life  of  the  individual. 

Tendon-Sheaths.—  Where  tendons  run  in  grooves  of  bones,  bands  of  dense 
connective  tissue  extend  across  between  the  lips  of  the  grooves,  being  continuous 


GENERAL  CONSIDERATION   OF   THE   VOLUNTARY  MUSCLES.    471 

there  with  the  periosteum,  and  convert  the  grooves  into  canals  within  which  the  ten- 
dons are  enclosed,  although  capable  of  free  movement  to  and  fro.  These  connective- 
tissue  bands  are  the  tendon-sheaths,  and  the  canals  which  they  assist  in  forming 
may  contain  one  or  more  tendons.  Each  sheath  is  lined  on  its  deeper  surface  by  a 
synovial  membrane  similar  to  those  occurring  in  the  joints,  and  at  either  extremity 
of  the  sheath  this  membrane  is  reflected  upon  the  tendon  which  it  encloses,  so  that 
the  tendon  is  contained  within  a  double-walled  cylinder  whose  cavity  is  filled  with  a 
fluid  serving  to  diminish  friction  during  the  movements  of  the  tendon  (Fig.  492).  It 
is  customary  to  distinguish  the  synovial  portion  of  a  tendon-sheath  as  the  serous  or 
synovial  sheath  {vagina  mucosa)  from  the  fibrous  sheath 
(vagina  fibrosa)  with  which  it  is  always  closely  con-  FIG.  492. 

nected. 

Strands  of  connective  tissue  pass  at  intervals  across 
the  synovial  cavity  of  the  sheath  from  the  floor  of  the 
groove  on  the  bone  and  transmit  blood-vessels  to  the 
tendon  ;  these  strands  constitute  what  are  termed  v in-        Phalanx 
cula  tendinum,  or,  from  their  general  similarity  to  the 

mesentery,  mesotendons.  Diagram  showing  relations  of  ten- 

T  j  i        ,  i  don  to  tendon-sheath  as  in  cross-section 

In  some  cases  a  tendon-sheath  may  serve  to  a  cer-     of  finger. 
tain  extent  as  a  pulley,  affording  a  smooth  surface  over 

which  the  tendon  changes  its  direction,  as  in  the  case  of  the  extensor  tendons  of  the 
hand  when  this  is  partly  extended.  A  special  development  of  this  condition  is  to  be 
seen  in  the  tendinous  loop  (trochlea  muscularis}  over  which  the  tendon  of  the  superior 
oblique  muscle  of  the  eyeball  is  reflected  (Fig.  516). 

Bursae. — The  intervals  between  the  various  muscles  and  between  these  or  their 
tendons  and  the  bone  are  occupied  by  loose  areolar  tissue.  In  situations  in  which 
a  muscle  or  tendon  in  its  movements  comes  in  contact  with  a  bony  prominence,  or  in 
which  two  tendons  glide  upon  each  other,  the  spaces  of  the  areolar  tissue  enlarge  and 
become  filled  by  a  fluid  resembling  that  of  the  synovial  cavities,  the  result  -being  the 
formation  of  what  is  termed  a  bursa,  whose  purpose  is  to  diminish  the  friction  between 
the  muscle  or  tendon  and  the  bone.  Examples  of  such  bursae  are  to  be  found  abun- 
dantly in  connection  with  the  muscles  of  the  limbs,  and  some  of  those  which  occur 
in  the  vicinity  of  joints  frequently  fuse  with  the  adjacent  synovial  cavities  ;  the  bursa 
of  the  subscapularis,  situated  between  that  muscle  and  the  neck  of  the  scapula,  for 
instance,  uniting  with  the  synovial  cavity  of  the  shoulder-joint,  and  the  bursa  supra- 
patellaris,  between  the  tendon  of  the  quadriceps  femoris  and  the  femur,  fusing  with 
the  cavity  of  the  knee-joint. 

Bursae  are  also  developed  in  the  areolar  tissue  intervening  between  the  superficial 
and  deep  fasciae  in  situations  in  which  the  integument  rests  directly  upon  a  bone,  as, 
for  instance,  over  the  olecranon  process,  and  is  frequently  subjected  to  pressure  in 
that  region.  Such  bursae  are  termed  subcutaneous  burs&  to  distinguish  them  from 
those  developed  in  connection  with  the  muscles. 

Classification  of  the  Muscles. — The  muscles  may  be  classified  according 
to  three  plans  :  they  may  be  arranged  according  to  their  topographical  relations, 
according  to  their  physiological  significance,  or,  finally,  upon  a  morphological  basis, 
their  embryological  or  developmental  significance  forming  the  guide  for  their  arrange- 
ment in  groups.  In  the  following  pages  the  last-named  plan  will  be  followed  as  far 
as  possible. 

Embryologically  the  skeletal  muscles  are  formed,  for  the  most  part,  from  a  series 
of  segmentally  arranged  masses  of  mesoblast^-the  mesoblastic  somites — which  appear 
at  an  early  stage  of  development  on  either  side  of  the  notochord  and  later  extend 
ventrally  towards  the  mid- ventral  line  (page  465).  That  portion  of  the  musculature 
which  has  such  an  origin  may  be  regarded  as  consisting  primarily  of  a  series  of  plates 
arranged  segmentally  along  each  side  of  the  body,  each  plate  corresponding  to  and 
being  supplied  by  one  of  the  segmental  nerves  and  by  those  fibres  of  it  which  arise 
from  the  cells  of  the  anterior  horn  of  the  spinal  cord  or  their  homologues  in  other 
portions  of  the  central  nervous  system.  A  diagrammatic  representation  of  this  mus- 
culature in  its  primary  condition  is  shown  in  Fig.  493,  and  from  this  it  will  be  per- 
ceived that  the  series  of  muscle-plates  extends  throughout  the  entire  trunk  and  neck 


HUMAN    ANATOMY. 


FIG.  493. 


regions  of  the  body  and  to  a  certain  extent  into  the  head  region,  there  being,  how- 
ever, in  this  last  region  a  considerable  area  in  which  the  muscle-plates  are  unrepre- 
sented. 

Throughout  this  area  of  the  head  region  muscles  occur  which  arise  in  relation 
to  the  branchial  arches  and,  accordingly,  in  a  much  more  ventral  position  than  the 
mesodermic  somites.  Furthermore,  these  muscles  are  supplied  by  branches  from 
the  mixed  cranial  nerves,  arising  from  cells  situated  in  a  portion  of  the  medulla 
oblongata  which  is  comparable  to  the  lateral  horn  of  the  spinal  cord  and  con- 
stituting what  are  termed  lateral  motor  roots,  in  contradistinction  to  the  median 
or  anterior  motor  roots  which  supply  the  muscles  derived  from  the  mesodermic 
somites. 

There  are  thus  two  sharply  defined  systems  of  musculature  :  the  one,  primarily 
confined  to  the  cranial  region,  is  supplied  by  lateral  motor  nerves,  and  from  its  rela- 
tion to  the  branchial  arches  maybe  termed  the  branchiomeric  musculature ;  the  other, 

supplied  by  anterior  motor  nerves,  is  arranged 
primarily  in  a  series  of  segmental  (metameric) 
plates,  and  may  be  termed  the  metameric  mus- 
culature. These  two  systems  constitute  the 
first  divisions  in  the  morphological  classifica- 
tion of  the  musculature. 

The  further  subdivision  of  the  branchio- 
meric  muscles  is  most  conveniently  made  with 
reference  to  the  various  cranial  nerves  by 
which  they  are  supplied.  For  the  metameric 
musculature  a  more  complicated  subdivision  is 
both  necessary  and  convenient,  and  in  the  first 
place  it  may  be  divided  into  the  axial  and 
the  appendiciilar  musculature.  For  the  latter 
group,  which  includes  all  the  muscles  of  the 
limbs,  a  derivation  from  the  mesodermic  so- 
mites seems  probable,  outgrowths  from  certain 
somites  extending  into  the  limb-buds  when 
these  develop  ;  but  it  has  not  yet  been  possi- 
ble to  demonstrate,  that  this  is  the  case,  the 
limb  muscles  really  making  their  appearance 
in  an  unsegmented  mass  of  mesoblast  in  the 
limb-bud  which  appears  to  have  no  connection 
with  the  mesoblastic  somites,  these  structures 
apparently  not  being  continued  into  the  limb- 
bud,  but  seeming  to  stop  short  at  its  base.  In- 
deed, it  is  quite  possible  that  the  limb  muscles 
should  not  be  included  under  the  metameric 
musculature  ;  but  until  it  is  demonstrated  that 
their  mode  of  development  is  not  a  secondary 
condensation  of  the  embryological  history,  it 
seems  preferable  to  retain  them  as  members  of 
that  group.  . 

The  later  development  of  the  cranial  mes- 
oblastic  somites  is  somewhat  different  from  that  of  the  others,  and  it  is  consequently 
convenient  to  group  the  axial  muscles  derived  from  them  by  themselves.  And  since 
the  somites  form  in  the  embryo  two  clearly  defined  groups,  it  seems  well  to  place 
the  derived  muscles  in  two  groups  which  may  be  termed  respectively  the  orbital  and 
the  hypoglossal  groups. 

The  remaining  somites,  which  maybe  grouped  together  as  the  trunk  somites,  in 
their  later  development  undergo  numerous  modifications,  some  of  which  may  be 
regarded  as  fundamental  and  primarily  affecting  all  of  the  series,  and  thus  affording 
.1  lusis  for  a  further  subdivision.  The  most  fundamental  of  these  modifications  is  a 
division  of  each  somite  into  a  dorsal  and  a  ventral  portion,  corresponding  respectively 
to  the  primary  divisions  of  the  spinal  nerves,  and  permitting  the  recognition  of  a 


Diagram  showing  grouping  of  head  and  trunk 
myotomes.  Ill,  IV,  VI,  orbitalgroup  (supplied  by 
cranial  nerves  indicated  by  Roman  numerals)  rep- 
resenting persisting  first  three  cephalic  myoloim-s  ; 
XII,  hypoglossal  group,  representing  persisting 
last  three  cephalic  myotomes,  intervening  ones 
having  disappeared;  i,  i,  i,  i.  I,  first  niyotome  of 
cervical,  'thoracic,  lumbar,  sacral,  and  coccygeal 
groups  of  trunk  myotomes.  Each  niyotome  is  di- 
vided into  dorsal  and  ventral  segments. 


GENERAL   CONSIDERATION    OF   THE   VOLUNTARY   MUSCLES.    473 

dorsal  and  a  ventral  group  of  trunk  muscles.      The  portions  of  the  ventral  divisions 
on  either  side  of  the  mid-ventral  line  separate  to  form  a  subordinate  group  of  mus- 
cles which  may  be  termed  the  rec- 
tus group    (Fig.    494),   the   more  FIG.  494. 

lateral      portions    giving     rise     tO     a  Dorsal  division  of  spinal  nerve 

group   which,  from  the  prevailing 

oblique   course  of  its   fibres,   may  Dorsal  group 

be    termed    the    obliquus    group ;     ventral  divi-  ^-— ?**-£. 

and,  finally,  from  the  more  dor-  «"""""- 
sal  portions  of  the  ventral  muscu- 
lature there  are  developed  in  cer- 
tain regions  of  the  body  muscles 
which  lie  ventral  to  the  bodies 
or  processes  of  the  vertebrae,  and 
may  be  termed  the  hyposkeletal 
muscles,  in  contrast  to  the  re- 
maining musculature  which  ex- 
tends between  the  skeletal  ele- 
ments or  lies  dorsal  to  them,  and  N^^^^~^^^P^- Rectus  group 
hence  is  termed  the  episkeletal  mus- 

r  il^r  irp>  Diagrammatic  cross-section  of  body,  showing  primary  groups  oJ 

re-  trunk  muscles. 

To    sum  up  the  classification 
proposed  it  may  be  represented  in  the  following  manner  : 

I.   BRANCHIOMERIC  MUSCLES. 
II.   METAMERIC  MUSCLES. 

A.  Axial  Muscles. 

1.  Orbital  muscles. 

2.  Hypoglossal  muscles. 

3.  Trunk  muscles. 

a.  Dorsal, 

b.  Ventral. 

a.  Rectus  set. 

b.  Obliquus  set. 

c.  Hyposkeletal  set. 

B.  Appendicular  Muscles. 

Nerve-Supply. — The  segmental  regularity  of  the  mesodermic  somites  is  but 
slightly  retained  in  the  adult,  numerous  modifications,  such  as  fusion,  tangential  and 
longitudinal  splitting,  migration,  and  even  obliteration  taking  place  in  them  to  pro- 
duce the  various  muscles  of  the  adult.  The  various  modifications  have  not  in  all 
cases  been  traced,  but  a  study  of  the  nerve-supply  of  a  muscle  gives  in  many,  if  not 
all,  cases  an  important  clue  to  its  origin.  This  depends  upon  the  fact  that  the 
muscles  may  be  regarded  as  the  end-organs  of  the  motor  nerves,  and  that  the  seg- 
mental relation  established  in  the  embryo  between  a  nerve  and  the  muscle-tissue 
derived  from  a  given  mesodermic  somite  is  not  disturbed  in  later  development,  no 
matter  what  changes  of  relation  the  muscle- tissue  may  undergo.  Thus,  when  a 
muscle,  such  as  the  rectus  abdominis,  is  found  to  be  supplied  by  a  number  of  spinal 
nerves,  it  is  because  it  has  been  formed  by  the  fusion  of  portions  of  a  corresponding 
number  of  mesodermic  somites  ;  and  when  a  muscle,  such  as  the  latissimus  dorsi, 
lying  mainly  in  the  lumbar  region,  is  found  to  be  supplied  by  a  cervical  nerve,  it  is 
because  it  has  wandered  from  its  original  point  of  formation  in  the  cervical  region. 

Variations  in  the  nerve-supply  are  occasionally  seen,  especially  in  the  limb  mus- 
cles; but  it  seems  probable  that  such  variations  are  only  apparent,  the  nerve-fibres 
supplying  the  muscle  being  in  all  cases  strictly  equivalent,  arising  from  the  same 
region  of  the  spinal  cord,  even  although  they  may  pursue  in  different  individuals 
somewhat  different  paths  in  order  to  reach  their  destination.  Thus,  a  muscle  which 
normally  is  supplied  by  fibres  from  the  median  nerve  may  sometimes  be  found  to  be 


474  HUMAN   ANATOMY. 

supplied  by  the  ulnar  nerve,  the  nerve-fibres  using  the  ulnar  nerve  as  a  pathway  by 
which  to  reach  their  destination,  instead  of  the  median  nerve. 

It  is  important,  therefore,  both  from  the  morphological  and  clinical  stand-points, 
that  not  only  should  the  nerve  along  which  the  fibres  pass  to  reach  their  destination 
be  known,  but  also  the  nerve-roots  by  which  they  issue  from  the  central  nervous 
system. 


THE   BRANCHIOMERIC   MUSCLES. 

The  branchiomeric  muscles  are  those  skeletal  muscles  which  are  derived  from 
the  mesoderm  associated  with  the  branchial  arches,  and  are  supplied  by  those  cranial 
nerves  whose  motor  fibres  constitute  what  are  termed  lateral  motor  roots.  These 
nerves  are  the  trigeminus,  facialis,  and  glosso-pharyngeo-vago-accessorius  groups, 
and  the  classification  of  the  muscles  may  well  be  according  to  their  innervation  by 
these  three  nerve-groups. 

I.     THE   TRIGEMINAL   MUSCLES. 

The  trigeminal  muscles  stand  in  relation  primarily  to  the  first  embryonic  or  jaw- 
arch,  and  in  the  adult  to  the  structures  developed  in  association  with  this, — i.e.,  to 
the  mandible  and  the  malleus.  The  mandibular  muscles  are  represented  by  the 
muscles  of  mastication  and  two  muscles,  the  mylo-hyoid  and  the  anterior  belly  of 
the  digastric,  which  extend  between  the  mandible  and  the  hyoid  bone,  and  may  be 
termed  the  submental  muscles.  Connected  with  the  malleus  is  a  single  muscle,  the 
tensor  tympani,  and  an  additional  trigeminal  muscle  is  found  in  association  with  the 
soft  palate,  the  tensor  palati. 

(a)  THE  MUSCLES  OF  MASTICATION. 

1.  Masseter.  3.    Pterygoideus  Externus. 

2.  Temporalis.  4.    Pterygoideus  Internus. 

i.   MASSETER  (Fig.  495). 

The  masseter  is  a  strong  quadrilateral  muscle  composed  of  two  portions,  sep- 
arated at  their  origin  and  posteriorly  by  a  quantity  of  loose  areolar  tissue,  but 
united  towards  their  insertion  into  the  mandible. 

Attachments. — The  superficial  portion  arises  by  a  strong  aponeurosis  from 
the  anterior  two-thirds  of  the  lower  border  of  the  zygoma,  while  the  deeper  part 
arises  directly  from  the  posterior  third  of  the  lower  border  and  the  whole  of  the  inner 
surface  of  the  zygoma.  The  fibres  of  the  superficial  portion  pass  downward  and 
slightly  backward  to  be  inserted  into  the  outer  surface  of  the  angle  of  the  mandible, 
while  those  of  the  deeper  portion  pass  more  directly  downward  and  are  inserted  into 
the  outer  surface  of  the  ascending  ramus  as  high  as  the  bases  of  the  articular  and 
coronoid  processes,  encroaching  to  a  certain  extent  upon  the  insertion  of  the  temporal 
muscle. 

Nerve-Supply. — By  the  masseteric  branch  of  the  anterior  portion  of  the  man- 
dibular division  of  the  trigeminus. 

Action. — To  raise  the  mandible  and,  by  its  superficial  portion,  to  draw  it  for- 
ward to  a  slight  extent.  Owing  to  the  fibres  of  the  muscle  being  directed  almost 
perpendicularly  to  the  lever  upon  which  it  acts,  the  masseter  works  at  much  less 
mechanical  disadvantage  than  is  usual,  and  its  action  is  therefore  exceedingly  powerful. 

Relations. — A  considerable  portion  of  the  masseter  is  subcutaneous.  Poste- 
riorly, however,  the  parotid  gland  rests  upon  its  outer  surface-,  and  it  is  crossed  by 
the  parotid  duct,  the  transverse  facial  artery,  and  branches  of  the  facial  nerve. 
Anteriorly  its  deep  surface  is  separated  from  the  buccinator  muscle  by  a  well-devel- 
oped mass  of  fat,  the  buccal  fat-pad  (  page  489). 

The  Parotido-Masseteric  Fascia.— Covering  the  anterior  surface  of  the 
masseter  is  a  thin  layer  of  fascia,  the  masseteric  fasti*,  attached  above  to  the  zygoma 


THE   TRIGEMINAL   MUSCLES. 


475 


and  fading  out  anteriorly  beneath  the  facial  muscles.  Posteriorly  it  becomes  thicker 
and  divides  into  two  layers  to  enclose  the  parotid  gland  {parotid  fascia),  the  super- 
ficial layer  becoming  continuous  behind  with  the  layer  of  the  deep  cervical  fascia 
which  encloses  the  sterno-mastoid  muscle,  while  the  deeper  layer  is  connected  inter- 
nally with  the  styloid  process  and  joins  the  deep  cervical  fascia  below.  A  thickening 
of  this  deeper  layer  forms  a  flat  band,  the  stylo-mandibular  ligament,  which  passes 
downward  and  outward  from  the  styloid  process  to  the  angle  of  the  jaw. 

2.  TEMPORALIS  (Fig.  495). 

The  temporal  fascia  forms  a  strong  aponeurotic  membrane  attached  above  to  the 
superior  temporal  line  and  the  portion  of  bone  between  this  and  the  inferior  line, 
being  along  this  attachment  continuous  with  the  periosteum.  Below  it  divides  into 
two  layers  which  are  separated  by  a  quantity  of  adipose  tissue,  through  which  the 

FIG.  495. 


Temporal- 
fascia  (cut) 


Temporal 
muscle, 
partially 
exposed 


Buccinator 


Massi'tt-r. 
deep  portion 


Masseter,  superficial  portion  — 


Lateral  aspect  of  skull  with  temporal,  masseter,  buccinator,  and  oral  muscles  in  place. 


middle  temporal  artery  may  run,  and  is  attached  to  the  zygoma,  its  superficial  layer 
inserting  into  the  upper  border  of  the  arch  and  its  deeper  layer  into  the  inner  surface. 

Attachments. — The  temporal  muscle  arises  from  the  upper  half  of  the  deep 
surface  of  the  temporal  fascia  and  from  the  whole  extent  of  the  floor  of  the  temporal 
fossa.  Its  fibres  converge  to  an  exceedingly  strong  tendon,  which  inserts  into  the 
coronoid  process  of  the  mandible,  occupying  both  its  borders,  the  whole  of  its  inner 
surface,  and  a  varying  amount  of  its  outer  surface. 

Nerve-Supply. — By  the  anterior  and  posterior  deep  temporal  branches  from 
the  anterior  portion  of  the  mandibular  division  of  the  trigeminus. 

Action. — To  raise  the  mandible.  The  more  posterior  fibres  serve  to  retract 
the  jaw,  acting  thus  as  an  antagonist  of  the  external  pterygoid. 


476 


HUMAN    ANATOMY. 


FIG.  496. 


i  bone  (cut) 


'uncivil'  of 
mandible 


Upper  head)  External 
^Lower  head     j  pteryfjoid 


Relations.  -  —  Superficial  to  the  temporal  fascia  are  branches  of  the  superficial 
temporal  vessels  and  the  auriculo-temporal  nerve.  Beneath  the  muscle  is  in  relation 
to  the  internal  maxillary  artery  and  the  external  pterygoid  muscle. 

3.   PTERYGOIDEUS  EXTERNUS  (Fig.  496). 

Attachments.  -.-The  external  pterygoid  arises  by  two  heads.  The  upper 
head  takes  its  origin  from  the  under  surface  of  the  great  wing  of  the  sphenoid,  inter- 
nal to  the  infratemporal  crest  (pterygoid  ridge),  while  the  lower  head  arises  from 
the  outer  surface  of  the  lateral  pterygoid  plate.  The  two  heads  are  at  first  separated 
by  a  triangular  interval  through  which  the  internal  maxillary  artery  frequently  passes, 
but,  passing  backward  and  outward,  they  soon  unite  to  be  inserted  into  the  anterior 
border  of  the  interarticular  fibro-cartilage  of  the  mandibular  articulation  and  into  the 

neck  of  the  condyloid  process  oi  the 
mandible. 

Nerve-Supply.  —  By  the  exter- 
nal  pterygoid  branch  of  the  anterior 
portion  of  the  mandibular  division  of 
the  trigeminus. 

Action.  —  When  both  muscles 
act  together,  they  draw  the  jaw  and 
the  interarticular  fibro-cartilage  for- 
ward, a  movement  which  always 
accompanies  and  assists  in  the  de- 
pression of  the  jaw.  \Yhen  but  one 
muscle  acts,  the  ramus  to  which  it  is 
attached  is  drawn  forward,  while  the 

internal  pterygoid  other  pivots  in  its  articular  surface, 

the  result  being  an  apparent  lateral 
movement  of  the  jaw  towards  the 
pivotal  side. 

Relations.  —  The  outer  surface 
of  the  external  pterygoid  is  in  rela- 
tion to  the  coronoid  process  of  the 
mandible  and  the  temporal  muscle, 

its  lower  head  is  frequently  crossed.  by  the  internal  maxillary  artery  and  the  buccal 
nerve,  and  anteriorly  it  is  separated  from  the  masseter  by  the  buccal  fat-pad.  The 
deep  surface  rests  upon  the  upper  part  of  the  internal  pterygoid  muscle,  and  is  in 
relation  to  the  internal  maxillary  artery  and  the  inferior  dental  and  lingual  branches 
of  the  mandibular  division  of  the  trigeminus. 

4.     PTERYGOIDKl'S    IXTERNUS  (Fig.   496). 

Attachments.  —  The  internal  pterygoid  arises  from  the  walls  and  floor  of  the 
pterygoid  fossa,  the  majority  of  its  fibres  being  attached  to  the  inner  surface  of  the 
external  pterygoid  plate  and  to  the  tuberosity  of  the  palate  bone.  A  smaller  bundle 
of  fibres,  forming  what  may  be  termed  a  second  head,  separated  from  the  main  por- 
tion of  the  muscle  by  the  lower  head  of  the  external  pterygoid,  frequently  arises 
from  the  tuberosity  of  the  maxilla  and  the  adjacent  portion  of  the  palate  bone. 
From  these  origins  the  fibres  are  directed  downward  and  somewhat  outward  and 
backward  to  be  inserted  into  the  inner  surface  of  the  angle  and  ramus  of  the  mandi- 
ble below  the  mylo-hyoid  groove. 

Nerve-Supply.  —  By  the  internal  pterygoid  branch  from  the  trunk  of  the 
mandibular  division  of  the  trigeminus. 

Action.  —  Its  chief  action  is  to  raise  the  jaw,  having  in  this  respect  almost  as 
powerful  action  as  the  massrter.  Owing  to  the  direction  of  its  fibres,  it  will  also 
assist  the  external  pterygoid  in  protruding  the  jaw  and  in  producing  its  lateral 
movements. 

Relations.  —  The  outer  surface  of  the  muscle  is  in  relation  with  tin-  ramus  of 
the  mandible,  the  internal  maxillary  artery,  and  the  inferior  dental  and  lingual  nerves 


Mylo-hyoid,  stump 
External  and  internal  pterygoid  muscles,  seen  from  within. 


THE   TRIGEMINAL    MUSCLES.  477 

passing  between  the  muscle  and  the  bone.  Above  its  larger  head  is  covered  by  the 
external  pterygoid.  Its  inner  surface  is  in  contact  above  with  the  tensor  palati,  the 
superior  constrictor  of  the  pharynx,  and  the  ascending  palatine  artery,  while  towards 
its  insertion  it  is  in  relation  with  the  stylo-hyoid  and  posterior  belly  of  the  digastric 
and  with  the  submaxillary  gland. 

Variations  of  the  Muscles  of  Mastication. — The  muscles  of  mastication  are  all  derivatives 
of  a  single  muscular  mass  represented  by  the  adductor  mandibulce  of  fishes,  and  indications 
of  their  common  origin  are  not  infrequently  to  be  seen  in  partial  unions  of  the  various  muscles. 
Thus,  fibres  from  the  posterior  portion  of  the  deeper  head  of  the  masseter  may  join  the  tem- 
poral, fibres  from  both  the  temporal  and  masseter  sometimes  pass  to  the  anterior  border  of  the 
fibro-cartilage  of  the  mandibular  articulation,  and  connections  have  also  been  observed  between 
the  temporal  and  the  external  pterygoid. 

Additional  independent  muscles  apparently  belonging  to  this  group  sometimes  occur  in 
the  pteiygoideus  proprius,  which  extends  from  the  infratemporal  crest  of  the  sphenoid  to  the 
posterior  edge  of  the  external  pterygoid  plate,  and  in  the  pterygo-spinosus,  which  has  for  its 
attachments  the  spine  of  the  sphenoid  and  the  posterior  border  of  the  external  pterygoid  plate. 
The  significance  of  these  muscles  passing  between  points  which  are  immovable  is  somewhat 
obscure.  The  close  relationship  which  the  pterygo-spinosus  bears  to  the  spheno-mandibular 
ligament  seems  to  indicate  that  it  represents  the  musculature  of  that  portion  of  the  mandibular 
arch  which  has  become  transformed  into  the  ligament,  and  that  usually  it  is  represented  by  the 
connective  tissue  enclosing  the  ligament. 

(6)  THE  SUBMENTAL  MUSCLES, 
i.    Mylo-hyoideus.  2.    Digastricus  (Anterior  Belly). 

This  group  of  trigeminal  muscles  contains  but  two  representatives,  the  mylo- 
hyoid  and  the  anterior  belly  of  the  digastric.  This  latter  muscle,  as  ordinarily 
described,  consists  of  two  distinct  muscles  united  at  their  attachment  to  the  hyoid 
bone,  the  anterior  of  the  two  muscles  belonging  to  the  trigeminal  group,  while  the 
posterior  is  a  member  of  the  facial  group.  It  will  be  convenient  to  describe  the 
muscle  as  a  whole,  even  although  it  belongs  only  in  part  to  the  group  under  con- 
sideration. 

i.   MYLO-HYOIDEUS  (Fig.  497). 

Attachments. — The  mylo-hyoid  arises  irom.  practically  the  entire  length  of  the 
mylo-hyoid  ridge  of  the  mandible,  from  which  the  fibres  pass  inward  and  slightly 
backward  to  be  inserted  for  the  most  part  into  a  median  fibrous  raphe  common  to 
the  two  muscles  of  opposite  sides,  the  posterior  fibres,  however,  being  attached  to 
the  upper  border  of  the  body  of  the  hyoid  bone.  The  two  muscles,  taken  together, 
form  a  muscular  floor  for  the  mouth,  the  diaphragma  oris,  upon  which  the  tongue 
may  be  said  to  rest. 

Nerve -Supply. — By  the  mylo-hyoid  from  the  inferior  dental  branch  of  the 
mandibular  division  of  the  trigeminus. 

Action. — To  draw  the  hyoid  bone  upward  and  at  the  same  time  to  raise  the 
floor  of  the  mouth,  pressing  the  tongue  against  the  palate. 

Relations. — The  superficial  surface  of  the  mylo-hyoid  is  in  relation  with  the 
anterior  belly  of  the  digastric  and  with  the  facial  artery.  The  submaxillary  gland 
curves  around  its  posterior  free  margin  and  is  thus  in  relation  with  both  its  surfaces, 
the  submaxillary  duct  running  forward  upon  its  deeper  surface.  This  latter  surface 
is  also  in  relation  with  the  genio-hyoid,  genio-glossal,  hyo-glossal,  and  stylo-glossal 
muscles,  with  the  sublingual  gland,  and  with  the  lingual  branch  of  the  trigeminus 
and  the  hypoglossal  nerve. 

2.   DIGASTRICUS  (Figs.  497,  502). 

Attachments. — The  digastric,  as  its  name  indicates,  consists  of  two  bellies 
which  are  united  by  a  strong  cylindrical  tendon.  The  anterior  belly,  which  alone 
belongs  to  the  trigeminal  group  of  muscles,  arises  from  the  digastric  fossa  of  the 
mandible,  and  is  directed  downward,  backward,  and  slightly  outward  to  become  con- 


478 


HUMAN   ANATOMY. 


tinuous  with  the  intermediate  tendon.  This  is  bound  down  to  the  greater  horn  and 
body  of  the  hyoid  bone  by  a  pulley-like  band  of  the  cervical  fascia  and  to  a  certain 
extent  by  the  stylo-hyoid  muscle,  which  divides  near  its  insertion  into  the  hyoid  into 
two  slips,  between  which  the  tendon  of  the  digastric  passes. 

The  posterior  belly  (Fig.  502)  takes  its  origin  from  the  mastoid  groove  of  the 
temporal  bone,  and  passes  downward  and  forward  to  become  connected  with  the 
intermediate  tendon. 

Nerve-Supply. — The  anterior  belly  is  supplied  by  the  mylo-hyoid  nerve  from 
the  inferior  dental  branch  of  the  mandibular  division  of  the  trigeminus,  the  posterior 
belly  by  the  digastric  branch  of  the  facial. 

Action. — The  digastric  either  raises  the   hyoid  bone  or  depresses  the  jaw, 


FIG.  497. 


Mandible 


Mylo-hyoid — * 


Hyoid  bon 


Thyro-hyoid  membrane 

Stylo-glossus— 
Internal  pterygoid 


Thyro-hyoid 
Thyroid  cartilagi 
Stylo-pharyngeu 


Crico-thyroid- 


Genio-hyoid 
(mylo-hyoid  removed) 


Digastric, 
anterior  belly    • 


Fascial  loop  binding 
tendons  to  hyoid  bone 


.Stylo-glossus 

Stylo-hyoid 
Masseter 


Digastric, 
posterior  belly 


^Thyroid  gland 


Submental  muscles  from  below  ;  trachea  has  been  displaced  downward  and  backward. 

according  as  one  or  other  of  the  bones  is  fixed  by  the  antagonizing  muscles.  By  raising 
the  hyoid  when  the  mandible  is  fixed,  it  assists  the  mylo-hyoid  in  pressing  the  tongue 
against  the  palate  during  the  first  portion  of  the  act  of  deglutition,  and  in  the  second 
portion  of  that  act  the  posterior  belly  will  assist  the  stylo-hyoid  in  drawing  the  hyoid 
upward  and  backward  and  so  help  in  elevating  the  larynx. 

Relations. — The  anterior  belly  rests  upon  the  mylo-hyoid  muscle.  The  pos- 
terior belly  is  covered  by  the  sterno-mastoid  and  splenius  muscles,  and  crosses  both 
the  external  and  internal  carotid  arteries,  the  internal  jugular  vein,  and  the  pneumo- 
gastric  and  spinal  accessory  nerves. 


Variations. — A  close  relationship  exists  between  the  mylo-hyoid  and  the  anterior  belly  of 
the  digastric,  and  there  is  usually  more  or  K-ss  i-xrhange  of  fibres  between  the  two  muscles, 
sometimes  amounting  to  a  complete  fusion.  A  duplicity  of  the  anterior  belly  is  a  rather  fre- 


THE   FACIAL   MUSCLES.  479 

quent  variation,  and  the  anterior  bellies  of  opposite  sides  may  be  united  by  the  more  or  less 
complete  conversion  of  the  fascia  which  typically  passes  between  them  into  muscular  tissue. 
An  independent  muscle  extending  between  the  body  of  the  hyoid  and  the  symphysis  of  the 
mandible,  and  termed  the  mento-hyoid,  occasionally  is  found  running  alongside  of  the  medial 
border  of  the  anterior  belly,  and  is  to  be  regarded  as  a  separated  portion  of  that  muscle. 

As  regards  the  posterior  belly,  it  may  take  its  origin  from  any  part  of  the  mastoid  groove 
or  even  from  the  outer  portion  of  the  superior  fluchal  line,  and  occasionally  it  fuses  completely 
with  the  stylo-hyoid.  In  certain  cases  in  which  there  is  a  failure  of  the  anterior  belly  to  differ- 
entiate from  the  mylo-hyoid,  the  posterior  belly  is  inserted  into  the  angle  of  the  mandible 
instead  of  into  the  hyoid  bone, — a  condition  recalling  the  arrangement  typical  in  the  majority 
of  the  mammalia,  in  which  the  posterior  belly  of  the  digastric  is  represented  by  a  depressor 
mandibula. 

(c}   THE   TRIGEMINAL   PALATAL   MUSCLE, 
i.  TENSOR  PALATI  (Fig.  509). 

Attachments. — The  tensor  palati  (tensor  veil  palatini)  takes  its  origin  from 
the  scaphoid  fossa  and  spine  of  the  sphenoid  and  from  the  outer  surface  of  the  car- 
tilaginous portion  of  the  Eustachian  tube.  It  descends  along  the  outer  surface  of  the 
internal  pterygoid  plate,  and,  becoming  tendinous,  bends  at  right  angles  around  the 
hamulus  and  is  continued  inward  to  be  inserted  into  the  posterior  border  of  the  palate 
bone  and  into  the  aponeurosis  of  the  soft  palate. 

Nerve-Supply. — By  fibres  from  the  mandibular  division  of  the  trigeminus, 
which  traverse  the  otic  ganglion. 

Action. — It  tends  to  draw  the  soft  palate  to  one  side.  The  two  muscles  acting 
together  will  stretch  the  soft  palate. 

(d)   THE  TRIGEMINAL  TYMPANIC   MUSCLE, 
i.  TENSOR  TYMPANI  (Fig.  1252). 

Attachments. — The  tensor  tympani  is  a  small  bipenniform  muscle  which  lies 
in  a  bony  canal  situated  above  the  Eustachian  tube.  Its  fibres  take  their  origin  from 
the  cartilaginous  portion  of  the  Eustachian  tube,  the  adjacent  portions  of  the  great  wing 
of  the  sphenoid,  and  also  to  a  certain  extent  from  the  walls  of  the  bony  canal.  The 
tympanic  end  of  the  Eustachian  tube  is  separated  from  the  opening  of  the  canal  for 
the  tensor  by  a  bony  ridge,  the  processus  cochleariformis,  over  which  the  tendon  of 
the  tensor  bends  almost  at  right  angles  and  passes  outward  across  the  tympanic 
cavity  to  be  inserted  into  the  manubrium  mallei  near  its  attachment  to  the  head  of  the 
bone. 

Nerve-Supply. — By  fibres  from  the  mandibular  division  of  the  trigeminus, 
which  traverse  the  otic  ganglion. 

Action. — The  muscle  draws  the  handle  of  the  malleus  inward  and  so  tenses 
the  membrana  tympani. 

II.     THE   FACIAL    MUSCLES. 

The  muscles  supplied  by  the  facial  nerve  are  readily  divisible  into  two  groups. 
Primarily  this  musculature  is  associated  with  the  second  branchial  or  hyoid  arch, 
represented  in  the  adult  by  the  lesser  cornu  of  the  hyoid  bone,  the  stylo-hyoid  liga- 
ment, styloid  process,  and  stapes,  and  a  small  group  of  muscles — the  stylo-hyoid,  the 
posterior  belly  of  the  digastric,  and  the  stapedius — are  still  found  in  relation  to  these 
structures.  From  the  surface  of  the  mass  from  which  these  muscles  differentiate 
there  is  separated  at  an  early  stage  a  layer  which  gradually  increases  in  extent  and 
eventually  covers  all  the  neck  and  head  in  a  cowl,  as  it  were,  its  progress  from  the 
hyoid  arch  being  followed  by  a  branch  of  the  facial  nerve,  which  eventually,  with  the 
growth  of  the  muscle,  increases  to  such  an  extent  as  to  appear  to  be  the  main  stem 
of  the  nerve.  From  the  muscular  sheet  numerous  superficial  muscles  of  the  head 
and  neck  develop,  and  the  entire  group  so  formed  may  be  termed,  from  one  of  its 
principal  members,  the  platysma  group,  the  group  retaining  the  primary  relationships 
forming  the  hyoidean  group. 


480 


HUMAN    ANATOMY. 


(a)  THE    HYOIDEAN   MUSCLES. 

I.   Stylo-hyoideus.      2.    Digastricus  (Posterior  Belly).      3.   Stapedius. 
i.   STYLO-HYOIDEUS  (Figs.  497,  502). 

Attachments. — The  stylo-hyoid  forms  a  slender  spindle-shaped  muscle  which 
arises  from  the  upper  portion  of  the  styloid  process  and  passes  obliquely  downward 
and  forward  to  be  inserted  into  the  base  of  the  greater  cornu  of  the  hyoid  bone, 
usually  dividing  before  its  insertion  into  two  slips,  between  which  the  intermediate 
tendon  of  the  digastric  passes. 

Nerve-Supply. — By  a  branch  from  the  digastric  branch  of  the  facial  nerve. 

Action. — To  raise  and  draw  backward  the  hyoid  bone. 

Relations. — Above  the  stylo-hyoid  descends  along  the  inner  border  of  the 
posterior  belly  of  the  digastric,  passing  in  front  of  that  muscle  below.  Internal  to 
it  is  the  stylo-pharyngeus,  and  below  the  hyo-glossus  and  the  glosso-pharyngeal  and 
hypoglossal  nerves,  passing  forward  between  it  and  the  stylo-pharyngeus. 

2.    DIGASTRICUS  (Posterior  Belly).     See  page  478. 
3.   STAPEDIUS  (Fig.  1254). 

Attachments. — The  stapedius  arises  from  the  walls  of  the  cavity  contained 
within  the  pyramidal  eminence,  and  its  tendon,  entering  the  tympanic  cavity  through 
the  aperture  at  the  apex  of  the  eminence,  is  inserted  into  the  neck  of  the  stapes. 

Nerve-Supply. — By  a  small  branch  arising  from  the  facial  nerve  during  its 
course  through  the  lower  part  of  the  facial  ( Fallopian)  canal. 

Action. — By  its  contraction  it  draws  the  head  of  the  stapes  towards  the  pos- 
terior wall  of  the  tympanic  cavity,  depressing  the  posterior  part  of  the  foot-plate  of 
the  bone  while  it  raises  the  anterior  part,  thus  tensing  the  membrane  which  closes 
the  fenestra  ovalis. 

Variations  of  the  Hyoidean  Muscles. — A  close  relationship  exists  between  the  stylo-hyoid 
and  the  posterior  belly  of  the  digastric,  the  one  or  the  other  occasionally  failing  to  separate 
from  the  common  mass  from  which  they  are  derived.  A  bundle  of  muscle-fibres  sometimes 
passes  from  the  tip  of  the  styloid  process  to  the  angle  of  the  mandible,  forming  what  may  be 
termed  the  stylo-rnandibularis,  and  recalling  by  its  insertion  the  condition  presented  in  certain 
cases  by  the  posterior  belly  of  the  digastric  (page  479). 

A  duplication  of  the  stylo-hyoid  has  also  been  observed,  the  second  slip,  which  has  been 
termed  the  stylo-hyo ideus  profundus,  varying  considerably  in  its  insertion,  sometimes  accompa- 
nying the  stylo-hyoid  proper  and  sometimes  inserting  into  the  lesser  cornu  of  the  hyoid,  and  in 
some  cases  replacing  the  stylo-hyoid  ligament. 

The  division  of  the  stylo-hyoid  near  its  insertion  for  the  passage  of  the  intermediate  tendon 
of  the  digastric  does  not  always  occur,  the  insertion  being  by  a  single  head  which  may  pass 
either  to  the  outer  or  the  inner  side  of  the  tendon. 


(6)    THE 
(a)   SUPERFICIAL  LAYER. 

1 .  Platysma. 

2.  Occipito-frontalis. 

3.  Auricularis  posterior. 

4.  Auricularis  superior. 

5.  Auricularis  anterior. 

6.  Orbicularis  palpebrarunf. 

7.  Zygomaticus  major. 

8.  Levator    labii    superioris   alaeque 

nasi. 

9.  Depressor  labii  inferioris. 
10.    Levator  mrnti. 


PLATYSMA   MUSCLES. 

(6)   DEEP  LAYER. 

1.  Orbicularis  oris. 

2.  Nasalis    (compressor    nasi 

depressor  ala-  nasi  i. 

3.  Levator  labii  superioris. 

4.  Levator  anguli  oris. 

5.  Risorius. 

6.  Depressor  anguli  oris. 

7.  Buccinator. 


et 


The  comparative  and  embryological   study  of  the  platysma  muscles  have  shown 
their  origin  from  the  musculature  of  the  second  or  hyoid   arch  and  their  extension 


THE   FACIAL   MUSCLES. 


481 


thence  over  the  head  and  neck.  At  first  they  are  confined  entirely  to  the  neck  region, 
but  even  in  the  lower  mammals  the  extension  upon  the  head  has  begun,  and  in  the 
higher  members  of  this  group  two  portions  can  be  distinguished  in  the  muscle-sheet. 
The  more  superficial  of  these  is  situated  in  the  lateral  and  posterior  portions  of  the 
neck,  and  extends  thence  upon  the  sides  of  the  face  and  over  the  vertex  of  the  skull 
to  the  orbital  and  nasal  regions  of  the  face.  The  deeper  one  lies  more  anteriorly  in 
the  neck,  and  extends  upward  over  the  jaw  to  the  region  around  the  mouth. 

In  the  higher  forms  a  differentiation  of  both  layers  to  form  a  number  of  more 
or  less  separate  muscles  takes  place  and  reaches  its  highest  development  in  man, 
whose  mobility  of  facial  expression  is  due  to  the  existence  of  a  considerable  number 
of  platysma  muscles.  These  muscles  have  arisen  from  the  common  sheets  by  the 
partial  conversion  of  these  into  connective  tissue,  by  the  secondary  attachment  of 
portions  of  the  sheets  to  the  skeleton,  by  various  modifications  of  the  primary  direc- 
tion of  the  fibres,  and  by  the  obliteration  of  certain  portions  of  the  sheet  found  in  the 

FIG.  498. 


Depressor  anguli  oris TEJA 

Mandible  - 
Raphe  of  mylo-hyoid 

Sterno-hyoid ^ 


Platysma-"1 


—.Depressor  labii  inferioris 
—Levator  menti 


Mylo-hyoid 

Hyoid  bone 
Thyroid  cartilage 


Sterno-mastoid 


Sterno-thyroid* 


Inner  end  of  clavicle 


Superficial  muscles  of  neck. 


lower  animals,  the  cervical  portion  of  the  deep  layer,  for  instance,  being  normally 
lacking  in  man,  the  layer  being  represented  only  by  the  muscles  of  the  lips. 

The  platysma  musculature  is  characterized  for  the  most  part  by  the  pale  color  of 
its  fibres,  by  their  aggregation  to  form  thin  bands  or  sheets  usually  more  or  less  inter- 
mingled with  connective-tissue  strands,  so  that  their  margins  are,  as  a  rule,  ill-defined, 
and  by  their  attachment  in  frequent  cases  to  the  integument.  These  peculiarities, 
together  with  a  considerable  amount  of  variation  which  occurs  in  the  differentiation  of 
the  various  muscles,  have  brought  about  not  a  little  difference  in  the  number  of  muscles 
recognized  in  the  group  by  various  authorities,  some  recognizing  as  distinct  muscles 
what  others  regard  as  merely  more  or  less  aberrant  or  unusually  developed  slips. 

(a]    THE   MUSCLES   OF  THE  SUPERFICIAL   LAYER. 
i.   PLATYSMA  (Figs.  498,  499). 

Attachments. — The  platysma  takes  its  origin  from  the  skin  and  subcutaneous 
tissue  over  the  pectoralis  major  and  deltoid  muscles  on  a  line  extending  from  the  car- 
tilage of  the  second  rib  to  the  tip  of  the  acromion  process.  Its  fibres  are  directed 


482  .  HUMAN    ANATOMY. 

upward  and  inward  and  are  inserted  into  the  body  of  the  mandible  from  the  sym- 
physis  to  the  insertion  of  the  masseter,  the  more  posterior  fibres  extending  upward 
upon  the  face  towards  the  angle  of  the  mouth  and  becoming  lost  partly  in  the  fascia 
of  the  cheeks  and  partly  among  the  muscles  of  the  lips. 

Nerve-Supply. — By  the  inframandibular  branch  of  the  facial  nerve. 

Action. — The  contraction  of  the  platysma  results  in  drawing  the  lower  lip 
downward  and  outward  and  at  the  same  time  raising  the  skin  of  the  neck  from 
the  underlying  parts.  It  is  one  of  the  most  important  muscles  employed  in  the 
expression  of  horror  and  intense  surprise.  It  does  not  seem  probable  that  the 
muscle  has  much  effect  in  producing  depression  of  the  mandible,  an  action  which 
it  might  be  expected  to  possess  on  account  of  its  upper  attachment. 

Relations. — The  platysma  rests  upon  the  deep  fascia  of  the  neck  and  covers 
all  the  structures  at  the  front  and  sides  of  that  region.  Upon  its  deep  surface  lie  the 
external  jugular  vein,  the  superficial  lymph-nodes  of  the  neck,  and  the  superficial 
branches  of  the  cervical  plexus.  It  covers  also  the  sterno-mastoid  muscle  and  the 
depressors  of  the  hyoid  bone,  and,  above,  the  digastric  and  mylo-hyoid  muscles, 
together  with  the  submaxillary  gland  and  the  lower  portion  of  the  parotid. 

Variations.— There  is  usually  more  or  less  decussation  of  the  two  muscles  across  the 
median  line,  especially  in  their  upper  parts,  where,  indeed,  a  certain  amount  of  decussation  may 
be  considered  a  normal  condition.  The  muscle  is  subject  to  considerable  amounts  of  variation 
in  its  development,  sometimes  forming  a  very  thin,  pale  layer  largely  interspersed  with  connective 
tissue,  and  at  other  times  it  is  composed  of  strong,  deeply  colored  bundles  with  much  less  inter- 
mixture of  connective  tissue.  Its  extension  upon  the  face  may  also  vary  considerably,  some- 
times being  traceable  as  high  up  as  the  zygoma  and  extending  backward  to  behind  the  ear.  On 
the  other  hand,  it  may  be  very  considerably  reduced  in  size,  especially  below,  a  complete  absence 
of  the  lower  half  of  the  muscle  having  been  observed. 

2.    OCCIPITO-FRONTALIS  (Fig.   499). 

Attachments. — The  occipito-frontalis  (m.  epicranius)  is  a  muscular  and  aponeu- 
rotic  sheet  which  covers  the  entire  vertex  of  the  skull  from  the  occipital  region  to  the 
root  of  the  nose.  It  consists  of  two  muscular  portions,  one  of  which,  the  occipitalis, 
arises  from  the  superior  nuchal  line  and  inserts  after  a  short  course  into  the  posterior 
border  of  the  epicranial  aponeurosis,  while  the  other,  thefrontatis,  taking  its  origin 
from  the  anterior  border  of  the  galea,  is  inserted  into  the  skin  in  the  neighborhood 
of  the  eyebrows,  over  the  glabella,  and  into  the  superciliary  arches,  a  portion  of  it 
being  frequently  prolonged  downward  upon  the  nasal  bone,  forming  what  has  been 
termed  the pyramidalis  nasi  (m.  procerus),  which  is  frequently  described  as  a  distinct 
muscle. 

The  epicranial  aponeurosis  (galea  aponeurotica)  (Fig.  499)  is  a  dense  aponeu- 
rotic  sheet  which  covers  the  entire  vertex  of  the  cranium  and  is  prolonged  laterally 
over  the  temporal  fascia  as  a  thin  layer  which  extends  almost  to  the  zygoma.  On 
its  superficial  surface  it  is  intimately  associated  with  the  integument,  being  united  to 
its  deeper  surface  by  a  thin  but  close  and  resistant  layer  of  fascia  which  represents 
the  superficial  fascia  of  other  regions  of  the  body  and  in  which  are  embedded  the 
vessels  and  nerves  of  the  scalp.  The  under  surface  of  the  galea  is,  however,  smooth, 
and  is  connected  with  the  periosteum  by  a  lax  layer  of  connective  tissue,  so  that  it  is 
capable  of  considerable  movement  to  and  fro  upon  the  periosteum,  the  skin  being 
carried  with  it  in  such  movements.  A  section  through  the  scalp  at  the  vertex  would 
show  from  without  inward  ( i  )  the  skin,  (2)  the  dense  superficial  fascia  with  its  vessels 
and  nerves,  (3)  the  epicranial  aponeurosis,  (4)  loose  connective  tissue,  and  (5) 
periosteum  (Fig.  504). 

Nerve-Supply. — The  occipitalis  is  supplied  by  branches  from  the  posterior 
auricular  branch  of  the  facial,  the  frontalis  by  branches  from  the  rami  temporales  of 
the  same  nerve. 

Action. — The  occipitalis  acting  alone  will  draw  backward  the  galea  aponeurotica, 
while  the  frontalis  draws  it  forward.  If,  however,  the  galea  be  fixed  by  the  occipitales, 
the  action  of  the  frontales  is  to  raise  the  eyebrows  and  throw  the  skin  of  the  forehead 
into  transverse  wrinkles,  both  of  these  actions  being  greatly  increased  by  the  simul- 
taneous contraction  of  both  the  occipitales  and  the  frontales.  It  is  consequently  the 


THE   FACIAL    MUSCLES. 


483 


muscle  employed  in  the  expression  of  interrogation  and  surprise  and  also,  in  con- 
junction with  the  platysma,  in  that  of  horror. 

v 

The  transversus  micha-  is  a  thin  muscular  band,  frequently  present,  arising  from  the 
occipital  protuberance  and  extending  laterally  to  terminate  in  various  attachments  ;  sometimes, 
for  instance,  uniting  with  the  posterior  border  of  the  sterno-cleido-mastoid  or  with  the  auricu- 
laris  posterior.  It  may  take  its  origin  either  superficial  to  or  beneath  the  attachment  of  the 
trapezius  to  the  superior  nuchal  line,  and  in  the  former  case  is  to  be  regarded  as  a  portion  of  the 
platysma  group  of  muscles,  while  in  the  latter  it  is  more  probably  a  relic  of  the  primary  con- 
nection between  the  trapezius  and  the  sterno-cleido-mastoid  and  belongs  to  that  group  of 
muscles  (page  501). 

3.   AURICULARIS  POSTERIOR  (Fig.  499). 

Attachments. — The  posterior  auricular  (retrahens  aureni)  is  composed  of  a  few 
bundles  of  fibres  which  arise  from  the  outer  extremity  of  the  superior  nuchal  line  and 
the  base  of  the  mastoid  process  and  pass  horizontally  forward  to  be  inserted  into  the 
posterior  surface  of  the  concha.  It  is  frequently  imperfectly  separated  from  the 
occipitalis. 

Nerve-Supply. — By  the  posterior  auricular  branch  of  the  facial  nerve. 

Action. — To  draw  the  auricle  backward. 

FIG.  499. 


-Frontalis 


Auricula ris  superior 

Occipitalis 
Auricularis  anterior 

Auricularis  posterior 

Zygomaticus  m 
Zygomaticus  mil 
Levator  ang 
Levator  labii  superioris 
Buccinator 

Risorius 


Co 


Orb 


•ugator  supercilii 

cularis  palpebrarum 
bital  part  of  same  muscle 
ramidalis  nasi 

Lev.  labii  sup.  alaeque  nasi 
Compressor  narium 


Dilatores  naris 
Depressor  alae  nasi 
Orbicularis  oris 


Depressor  anguli  oris 
Depressor  labii  inferioris 
Levator  menti 


Platysma 


Superficial  dissection  of  head,  showing  platysma  muscles. 

4.  AURICULARIS  SUPERIOR  (Fig.  499). 

Attachments. — The  superior  auricular  (attollens  aurem)  is  a  triangular  muscle 
which  arises  from  the  lateral  portion  of  the  galea  aponeurotica  or  from  the  temporal 
fascia  and  converges  to  be  inserted  into  the  upper  part  of  the  cartilage  of  the 
auricle. 

Nerve-Supply. — By  fibres  from  the  rami  temporales  of  the  facial  nerve. 

Action. — To  draw  the  auricle  upward. 


5.   AURICULARIS  ANTERIOR  (Fig.  499). 

Attachments. — The  anterior  auricular  (attrahens  aurem}  is  frequently  con- 
tinuous with  the  preceding  muscle,  lying  immediately  anterior  to  it.  It  arises  from 
the  lateral  part  of  the  galea  aponeurotica  or  from  the  temporal  fascia  and  is  inserted 
into  the  upper  anterior  part  of  the  auricular  cartilage  or  into  the  fascia  immediately 
anterior  to  the  cartilage. 


4*4  HUMAN   ANATOMY. 

Nerve-Supply. — By  fibres  from  the  rami  temporales  of  the  facial  nerve. 
Action. — To  draw  the  auricle  upward  and  forward. 

it 

6.   ORBICULARIS  PALPEBRARUM  (Figs.  499,  500). 

The  orbicularis  palpebrarum  (m.  orbicularis  oculi)  is  an  elliptical  sheet  whose 
fibres  have  their  origin  in  the  neighborhood  of  the  inner  angle  of  the  eye  and  curve 
thence,  some  upward  and  outward  and  some  downward  and  outward,  around  the 
rima  palpebralis  to  terminate  in  the  neighborhood  of  the  external  angle.  The  course 
of  the  fibres  lies  partly  in  the  substance  of  the  upper  and  lower  eyelids  and  partly  over 
the  bones  surrounding  the  margin  of  the  orbit.  In  accordance  with  these  relations,  it 
is  customary  to  regard  the  muscle  as  consisting  of  two  main  portions,  the  pars  palpe- 
bralis and  the  pars  orbitalis. 

The  internal  pafpcbral  ligament  (ligamentum  palpebrale  mediate).  Where  the 
fibres  of  the  orbicularis  arise  at  the  inner  angle  of  the  eye  there  is  a  dense  band  of 
fibrous  tissue  which  is  attached  at  one  extremity  to  the  frontal  process  of  the  maxilla. 
Thence  it  is  directed  outward  across  the  outer  surface  of  the  lachrymal  sac  and  bifur- 
cates to  be  inserted  into  the  inner  border  of  each  tarsal  plate.  Just  before  its  bifur- 
cation the  ligament  gives  off  from  its  posterior  surface  a  bundle  which  is  reflected 

inward  over  the  lachrymal  sac  and 
FIG.  500.  passes  behind  this  to  be  attached  to  the 

Internal  palpebral  ligament        Orbicularis  palpebrarum  crest  of    the  lachrymal  bone. 

Tensor  tarsi       \  Upper  tarsal  plate  --ri_-    i-  /       i  •    t_  •     'i       i 

\  This  ligament,  which  is  also  known 

—it  . 

as  the  tcnao  oath,  may  be  regarded  as 

the  tendon  of  origin  of  the  fibres  of  the 
orbicularis  oculi.      At  the  outer  angle 
of  the  eye  there  is  a  certain  amount  of 
decussation  of  the  fibres  of  the  muscle 
to  form  a  raphe  palpebralis  lateralis, 
NLower  tarsal          ^ut  there  's  no  distinct  formation  of  a 
\      Plate  •  fibrous  band  comparable  to  the  inter- 

0paTplebrarum  nal  ligament. 

Orbicularis  palpebrarum  has  been  dissected  from  its  deeper  "aTS   ralpeDrallS. 1  fie  palpe- 

porSon  or  fenrsoretaersi.inward  wkh  eyelids' showing  Iachr> mal  bral  portion  of  the  muscle  arises  partly 

from  the  internal  palpebral  ligament 

and  partly  from  the  crest  of  the  lachrymal  bone.  The  fibres  which  take  origin  from 
the  ligament  arch  outward  in  the  upper  and  lower  eyelids  to  terminate  in  the  lateral 
palpebral  raphe,  forming  a  thin,  pale  sheet  in  the  subcutaneous  tissue  of  the  eyelid. 
Its  marginal  fibres,  sometimes  more  or  less  distinct  from  the  others,  form  what  has 
been  termed  the  pars  ciliaris  or  muscle  of  Riolan. 

The  fibres  which  arise  from  the  posterior  lachrymal  crest  are  usually  regarded  as 
forming  either  a  distinct  muscle,  which  has  been  termed  the  tensor  tarsi  or  Homer' s 
muscle,  or  else  as  a  separate  part  of  the  orbicularis,  the  pars  lacrimalis.  It  is 
directed  horizontally  outward  behind  the  lachrymal  sac,  resting  upon  the  posterior 
surface  of  the  reflected  bundle  of  the  internal  palpebral  ligament.  Towards  its  outer 
end  it  bifurcates,  sending  a  slip  to  each  eyelid  partly  to  be  inserted  into  the  tarsal 
plates  and  partly  to  fuse  with  the  rest  of  the  pars  palpebralis. 

Pars  Orbitalis. — The  orbital  portion  of  the  muscle  is  usually  of  a  deeper  color 
and  somewhat  thicker  than  the  palpebral,  and  the  fibres  towards  its  periphery  tend 
to  scatter  themselves  among  the  adjacent  platysma  muscles  and  to  make  numerous 
connections  with  these.  Some  bundles  from  the  lateral  and  lower  parts  of  the  muscle 
which  extend  downward  and  forward  upon  the  cheek  have  been  regarded  as  a  dis- 
tinct muscle,  the  malaris. 

The  main  muscle  arises  from  the  internal  palpebral  ligament,  the  frontal  process 
of  the  maxilla,  and  the  inner  portions  of  the  upper  and  lower  margins  of  tin-  orbit. 
The  fibres  arch  outward  to  tin-  lateral  palpebral  raphe,  a  portion  of  those  arising  Irom 
the  maxilla  inserting  into  the  integument  of  the  eyebrow  and  forming  \\hat  has  been 
termed  the  cor  ruga  tor  snf>ercilii  (  Fig.  499). 

Nerve-Supply. — By  the  rami  tempo'-ales  and  zygomatici  of  the  facial  nerv 


THE   FACIAL    MUSCLES.  485 

Action. — The  principal  action  of  the  orbicularis  palpebrarum  is  to  approximate 
the  upper  and  lower  eyelids,  closing  the  palpebral  fissure.  In  addition,  the  attach- 
ment of  the  orbital  portion  to  the  skin  draws  the  eyebrow  downward  and  the  skin  of 
the  cheek  upward  to  form  a  fold  around  the  margin  of  the  orbit,  giving  increased 
protection  to  the  eyeball.  The  corrugator  supercilii  draws  the  eyebrow  downward 
and  inward,  producing  vertical  wrinkles  of  the  integument  over  the  glabellaand  giving 
a  thoughtful  expression. 

The  pars  lacrimalis  draws  the  tarsal  plates  inward  and  backward  and  so  tenses 
the  internal  palpebral  ligament,  causing  it  to  compress  the  lachrymal  sac. 

7.   ZYGOMATICUS  MAJOR  (Figs.  499,  502). 

Attachments. — The  zygomaticus  major  (m.  zygomaticus)  is  a  slender  muscle 
which  arises  above  from  the  outer  surface  of  the  zygomatic  bone,  near  its  articulation 
with  the  zygomatic  process  of  the  temporal,  and  passes  obliquely  downward  and  for- 
ward towards  the  angle  of  the  mouth.  Its  fibres  interlace  with  those  of  the  depressor 
and  levator  anguli  oris,  and  terminate  by  blending  with  the  orbicularis  oris  and  by 
inserting  into  the  subcutaneous  tissue  of  the  lips. 

Nerve-Supply. — By  fibres  from  the  zygomatic  branch  of  the  facial  nerve. 

Action. — To  draw  upward  and  outward  the  angles  of  the  mouth,  as  in  smiling 
and  laughing. 

Variations. — A  slender  muscle  is  very  frequently  found  arising  from  the  zygomatic  bone 
anterior  to  the  zygomaticus  and  passing  downward  to  be  inserted  into  the  upper  lip.  It  lias 
been  termed  the  zygomaticus  minor,  and  appears  to  be  a  separation  of  a  portion  of  the  zygo- 
matic muscle. 

8.   LEVATOR  LABII  SUPERIORIS  AL^EQUE  NASI  (Figs.  499,  501). 

Attachments. — This  muscle  takes  its  origin  from  the  outer  surface  of  the 
frontal  process  of  the  maxilla,  and  descends  along  the  angle  which  marks  the  junction 
of  the  nose  and  the  cheek  to  be  inserted  into  the  integument  of  the  upper  lip  and 
into  the  posterior  part  of  the  ala  nasi. 

Nerve-Supply. — From  the  rami  zygomatici  of  the  facial  nerve. 

Action. — The  principal  action  of  this  muscle  is  to  raise  the  upper  lip,  although 
its  insertion  into  the  ala  nasi  enables  it  to  assist  in  the  dilatation  of  the  nostrils. 

Variations. — This  muscle  is  subject  to  considerable  variation  in  its  development,  and 
frequently  comes  into  continuity  with  neighboring  muscles,  especially  with  the  zygomaticus 
minor,  when  this  is  present,  and  with  the  levator  labii  superioris  proprius.  Indeed,  these  two 
muscles  are  often  associated  with  it  to  form  what  is  termed  the  qnadratus  labii  superioris,  of 
which  the  levator  labii  superioris  alaeque  nasi  forms  the  cap/if  angnlare,  the  levator  labii  superi- 
oris proprius  the  caput  infraorbitale,  and  the  zygomaticus  minor  the  capnt  zygomaticus.  Since, 
however,  the  levator  labii  superioris  proprius  belongs  to  the  deep  layer  of  the  platysma  muscles, 
and  therefore  to  a  different  group  than  the  other  heads  of  the  quadratics,  it  seems  preferable  to 
regard  all  the  heads  as  distinct  muscles. 

9.   DEPRESSOR  LABII  INFERIORIS  (Figs.  498,  499). 

Attachments. — The  depressor  of  the  lower  lips  (in.  quadratus  labii  inferioris) 
arises  from  the  body  of  the  mandible  beneath  the  canine  and  premolar  teeth,  its 
origin  being  covered  by  the  depressor  anguli  oris.  It  forms  a  thin  quadrate  sheet 
which  is  directed  upward  and  forward  and  is  inserted  in  the  skin  of  the  lower  lip,  its 
fibres  mingling  also  with  those  of  the  orbicularis  oris. 

Nerve-Supply. — From  the  supramandibular  branch  of  the  facial  nerve. 

Action. — To  draw  down  the  lower  lip. 

10.   LEVATOR  MENTI  (Fig.  498). 

Attachments. — The  levator  menti  (m.  mentalis)  arises  from  the  body  of  the 
mandible  below  the  incisor  teeth,  and  its  fibres  descend,  diverging  as  they  go,  to  be 
inserted  into  the  integument  above  the  point  of  the  chin. 

Nerve-Supply. — From  the  supramandibular  branch  of  the  facial  nerve. 


486  HUMAN   ANATOMY. 

Action. — To  draw  upward  the  skin  of  the  chin,  thereby  causing  protrusion  of 
the  lower  lip,  as  in  pouting.  When  its  action  is  combined  with  contraction  of  the 
depressors  of  the  angles  of  the  mouth,  it  gives  an  expression  of  haughtiness  or  con- 
tempt, and  has  thence  been  termed  the  m.  superbus.  When  slightly  contracted,  it 
gives  an  expression  of  firmness  or  decision. 

Belonging  to  the  superficial  layer  of  the  platysma  musculature  are  a  number  of 
additional  more  or  less  rudimentary  muscles  attached  at  both  extremities  to  various 
parts  of  the  cartilage  of  the  concha.  These  muscles  will  be  considered  in  connection 
with  the  description  of  the  ear  (page  1499). 

(6)   THE   MUSCLES  OF  THE   DEEP   LAYER, 
i.  ORBICULARIS  ORIS  (Figs.  499,  501,  503). 

Attachments. — The  orbicularis  oris  is  a  rather  strong  elliptical  muscle  whose 
fibres  occupy  the  thickness  of  both  the  upper  and  lower  lips  between  the  skin  and 
the  mucous  membrane  of  the  mouth.  For  the  most  part  the  fibres  composing  the 
muscle  are  forward  prolongations  of  the  buccinator,  but  mingled  with  these  there  are 
fibres  from  all  the  muscles  which  are  inserted  in  the  vicinity  of  the  mouth,  such  as 
the  zygomaticus,  levator  anguli  oris,  levator  labii  superioris,  depressor  anguli  oris, 
depressor  labii  inferioris,  and  risorius. 

It  possesses,  however,  some  slight  attachment  to  skeletal  structures  by  three 
groups  of  fibres  which  have  frequently  been  regarded  as  distinct  muscles.  These 
groups  are  :  ( i )  the  incisivi  labii  superioris,  a  series  of  bundles  of  fibres  which  arise 
from  the  incisive  fossae  of  the  maxillae  and  pass  downward  and  outward  to  mingle 
with  the  other  fibres  of  the  orbicularis  at  the  angles  of  the  mouth  ;  (2)  the  incisivi 
labii  inferioris,  which  arise  from  the  alveolar  border  of  the  mandible  beneath  the 
canine  teeth  and  unite  with  the  orbicularis  at  the  angles  of  the  mouth  ;  and  (3)  the 
depressor  septi,  composed  of  the  uppermost  fibres  of  the  orbicularis,  which  bend  up- 
ward from  either  side  in  the  median  line  and  are  inserted  into  the  margin  of  the  septal 
cartilage  of  the  nose. 

Nerve-Supply. — From  the  rami  buccales  and  supramandibular  branch  of  the 
facial  nerve. 

Action. — The  main  action  of  the  orbicularis  oris  is  to  bring  the  lips  together, 
closing  the  mouth,  and  if  its  action  be  continued,  it  will  press  the  lips  against  the  teeth. 

Its  more  peripheral  fibres,  aided  by 
FIG.  501.  the  incisive  bundles,  will  tend  to  pro- 

Pyramidalis  nasi  trude  the  lips. 

2.   NASALIS  (Fig.  501). 

m  Attachments. — The     nasalis 

.    .  ^K      nariumess  forms  a  thin  sheet  which  arises  from 

;Diiatores  naris  the  maxilla  in  close  association  with 

Levator  iabii_       '^B*F  M  ^jf  \/7  the  incisive  bundles  of  the  upper  lip. 

napsialnaqsua1                     I^*  The  more  medial  fibres,  the  pars  alaris 

portion  cut                    mm  <*Lm  )  ( depressor  alte  nasi} ,  are  inserted  into 

away  'Sffw^/  ,  •  ,  ,  •. 

ILg^f  the  alar  cartilage  ot  the  nose,  while 

BlJaf^nenH^nr^nti         the  more  lateral  ones,  the  pars  trans- 
orbicuiaris oris — ^pUP^  versa  ( compressor  nariuni) ,  often  re- 

ceiving slips  from  the  adjacent  levator 
labii  superioris  alaeque  nasi  and  the 
Muscles  of  the  nose.  levator  anguli   oris,   extend  forward 

over  the  ala  of  the  nose  to  terminate 

upon  its  dorsal  surface  in  a  thin  aponeurosis  which  unites  it  to  the  muscle  of  the 
opposite  side. 

Nerve-Supply. — From  the  zygomatic  and  buccal  rami  of  the  facial  nerve. 
Action. — The  more  median  fibres  draw  the  alar  cartilage  downward  and  in- 
ward, while  the  more  lateral  ones  slightly  depress  the  tip  of  the  nose  and  at  the  same 
time  compress  the  nostril. 


THE   FACIAL    MUSCLES.  487 

Variations. — Fibres  from  the  nasalis  sometimes  pass  upward  upon  the  nasal  bones  and 
may  enter  into  the  formation  of  the  pyramidalis  nasi  ( page  482 ) .  Frequently  the  pars  alaris  and 
pars  transversa  are  recognized  as  distinct  muscles,  the  former  being  termed  the  depressor  alee 
nasi  or  myrtiformis,  while  the  latter  is  named  the  compressor  narium.  Uncertain  and  at  best 
feeble  muscular  slips  on  the  outer  margin  of  the  nostrils  are  sometimes  described  as  distinct 
muscles,  the  dilatores  naris  anterior  et posterior. 

3.   LEVATOR  LABII  SUPERIORIS  (Fig.  499). 

Attachments. — The  elevator  of  the  upper  lip  (m.  levator  labii  superioris  pro- 
prius)  arises  above  from  the  infraorbital  margin  of  the  maxilla  and  extends  almost 
vertically  downward  over  the  infraorbital  vessels  and  nerve  to  join  with  the  orbicu- 
laris  oris  and  also  to  be  inserted  into  the  skin  of  the  upper  lip  between  the  insertions 
of  the  levator  labii  superioris  alseque  nasi  and  the  levator  anguli  oris. 

Nerve-Supply. — From  the  zygomatic  branches  of  the  facial  nerve. 

Action. — To  raise  the  upper  lip.  Acting  in  conjunction  with  the  levator  labii 
superioris  alaeque  nasi,  it  plays  an  important  part  in  the  expression  of  grief. 

4.   LEVATOR  ANGULI  ORIS  (Figs.  499,  502). 

Attachments. — The  elevator  of  the  angle  of  the  mouth  (m.  caninus)  arises  from 
the  canine  fossa  of  the  maxilla  by  a  rather  broad  origin,  from  which  its  fibres  con- 
verge to  be  inserted  into  the  skin  at  the  angle  of  the  mouth,  partly  mingling  with  the 
fibres  of  the  depressor  anguli  oris. 

Nerve-Supply. — From  the  zygomatic  branches  of  the  facial  nerve. 

Action. — To  raise  the  angle  of  the  mouth. 

5.   RISORIUS  (Fig.  499). 

Attachments. — The  risorius  is  a  triangular  sheet  of  muscle  which  arises  from 
the  outer  surface  of  the  parotido-masseteric  fascia  and  from  the  integument  of  the 
cheek  and  passes  forward  towards  the  angle  of  the  mouth,  where  it  unites  with  the 
triangularis  and  orbicularis  oris. 

Nerve-Supply. — From  the  rami  buccales  of  the  facial  nerve. 

Action. — To  draw  the  angle  of  the  mouth  outward.  Its  contraction  imparts 
a  tense  and  strained  expression  to  the  face  which  is  termed  the  risus  sardonicus. 

Variation. — The  risorius  is  frequently  absent,  and  may  be  represented  only  by  some 
scattered  muscular  bands.  Its  intimate  association  with  the  depressor  anguli  oris  indicates  its 
derivation  from  that  muscle. 

6.   DEPRESSOR  ANGULI  ORIS  (Figs.  498,  499). 

Attachments. — The  depressor  of  the  angle  of  the  mouth  (m.  triangularis) 
takes  its  origin  from  the  outer  surface  of  the  body  of  the  mandible  and  from  the  skin 
and  passes  upward  to  the  angle  of  the  mouth,  where  its  fibres  are  inserted  into  the 
skin  and  also  mingle  with  those  of  the  caninus,  risorius,  and  orbicularis  oris. 

Nerve-Supply. — From  the  supramarginal  branch  of  the  facial  nerve. 

Action. — To  draw  the  angle  of  the  mouth  downward  and  slightly  outward, 
giving  an  expression  of  sorrow. 

Variations. — A  bundle  of  fibres  not  infrequently  arises  from  the  anterior  border  of  the 
depressor  anguli  oris  near  its  origin  and  passes  obliquely  downward  and  inward  towards  the 
median  line  beneath  the  chin,  either  losing  itself  in  the  superficial  fascia  of  that  region  or  uniting 
with  its  fellow  of  the  opposite  side.  This  slip  has  been  regarded  as  a  distinct  muscle  and 
termed  the  transversus  menti.  It  seems  exceedingly  probable  that  both  this  bundle  and  the 
risorius  are  derivatives  of  the  depressor,  and  this  muscle,  notwithstanding  its  position  super- 
ficial to  both  the  depressor  labii  inferioris  and  the  platysma,  is  really  a  portion  of  the  deeper 
layer  of  the  platysma  musculature,  its  present  position  having  been  acquired  by  a  migration  from 
the  region  of  the  upper  lip. 


488 


HUMAN    ANATOMY. 


7.   BUCCINATOR    (Fig.  502). 

Bucco-Pharyngeal  Fascia. — The  buccinator  alone  of  the  platysma  group  of 
muscles  is  covered  by  a  distinct  layer  of  fascia  which  forms  the  anterior  part  of  the 
fascia  buccopharyngea  and  is  a  dense,  resistant  sheet  of  connective  tissue  intimately 


FIG.  502. 


Temporal 


\ 


—  Corrugator  supercilii 

Orbic.  palp.,  palpebral  part 

—  Pyramidalis  nasi 

—  Orhic.  palp.,  orbital  part 

Lev.  labii  sup.  al.  nasi  (cut) 
Levator  labii  superioris  (cut) 

Compressor  narium 
Levator  anguli  oris 
^  Zygomaticus 


Buccinator 
Orbicularis  oris 

Depressor  labii  inferioris 
Levator  tnenti 


atysma 


Tensor  palati 

Levator  palati 

Styloid  process ; — 

Hamular  process  — - — : 
Digastric,  posterior  belly 

Superior  constrictor 

Stylo-gloss  us 
Pterygo-mandibular  ligament 

Stylo-phyarynneus 

Stylo-hyoid 

Mandible  (cut) 

Hyo-glossus 

Greater  hyoid  cornu 

Middle  constrictor 


Thyro-hyoid 
Inferior  constrictor 


Oral,  pharyngeal,  and  styloid  groups  of  muscles;  part  of  mandible  has  been  removed  to  show  deeper  structures. 

adherent  to  the  outer  surface  of  the  muscle.  Anteriorly  the  fascia  thins  out  to  disap- 
pear in  the  tissue  of  the  lips  ;  above  it  is  attached  to  the  alveolar  portion  of  the 
maxilla  and  to  the  internal  pterygoid  plate  of  the  sphenoid,  and  -thence  is  continued 

backward  over  the  superior  con- 

FIG.  503.  stricter  muscle  of  the  pharynx 

to  meet  with  its  fellow  of  the 
opposite  side  behind  the  phar- 
ynx ;  below  it  is  attached  to  the 
posterior  part  of  the  mylo-hyoid 
ridge  of  the  mandible.  Along 
a  line  which  descends  vertically 
from  the  tip  of  the  hamulus  of 
the  sphenoid  to  the  posterior 
extremity  of  the  mylo-hyoid 
ridge  of  the  mandible  the  fascia 
is  greatly  thickened,  forming 
the  ptcrygo-fnandibular  Hga- 
nicnt,  from  which  fibres  of  the 
buccinator  arise  anteriorly,  while 
posteriorly  it  gives  origin  to  a 
portion  of  the  superior  constric- 
tor of  the  pharynx. 

Attachments. — The  buc- 
cinator forms  a  thick  quadrilateral  muscle  lying  immediately  exterior  to  the  mucous 
membrane  of  the  cheek.  Its  line  of  origin  is  horseshoe-shaped,  extending  above 
along  the  alveolar  border  and  tuberosity  of  the  maxilla  and  thenre  upon  the  hamulus 


Levator  anguli  oris 


Buccinator 


1  U-pn-ssor  anguli  oris 


Diagram  showing  course  ..I   <-onipi>nrnt   lilurs  loiming 

orbicu' 


Lilians  oris  nmsrU-. 


PRACTICAL   CONSIDERATIONS  :    THE   SCALP. 


489 


of  the  internal  pterygoid  plate  of  the  sphenoid.  It  then  descends  upon  the  anterior 
border  of  the  pterygo-mandibular  raphe,  whence  it  passes  forward  along  the  body 
of  the  mandible,  above  the  mylo-hyoid  ridge,  as  far  as  the  premolar  teeth.  From 
this  extensive  origin  its  fibres  are  directed  forward  to  become  continuous  with  those 
of  the  orbicularis  oris,  also  inserting  to  a  certain  extent  into  the  integument  of  the  lips. 

Nerve-Supply. — From  the  buccal  branch  of  the  facial  nerve. 

Action. — The  buccinator  draws  the  angle  of  the  mouth  laterally,  pressing  the 
lips  against  the  teeth.  When  the  cheeks  are  distended  the  muscle  serves  to  com- 
press the  contents  of  the  mouth,  and  plays  an  important  part  in  mastication  in  pre- 
venting the  accumulation  of  the  food  between  the  cheek  and  the  jaws,  forcing  it 
back  between  the  teeth. 

Relations. — Superficially  with  the  bucco-pharyngeal  fascia,  which  is  separated 
from  the  anterior  part  of  the  masseter  and  from  the  zygomaticus  and  risorius  by  an 
extensive  pad  of  fat, — the  buccal  fat-pad.  This  is  prolonged  backward  into  the  zygo- 
matic  fossa  between  the  temporal  and  pterygoid  muscles,  and  is  traversed  by  the  facial 
vessels  and  the  buccal  branches  of  the  trigeminal  and  facial  nerves. 

The  buccinator  is  pierced  from  without  inward  by  the  parotid  duct  and  by  the 
buccal  branch  of  the  trigeminal  nerve  on  its  way  towards  its  distribution  to  the 
mucous  membrane  of  the  cheek. 


PRACTICAL  CONSIDERATIONS  :     MUSCLES   AND    FASCIAE   OF    THE 

CRANIUM. 

The  Scalp. —  The  Occipito- Frontal  Region. — The  layers  of  the  scalp  from 
within  outward  are  : 

i.  The  pericranium — as  the  periosteum  covering  this  part  of  the  skull  is 
termed — closely  invests  the  underlying  bones  and  is  firmly  attached  at  the  sutures 
through  which,  so  long  as  these  remain  ununited,  it  is  continuous  (intersutural  mem- 
brane) with  the  outer  layer  of  the  dura, — the  endosteum  of  the  cranium.  A  similar 

FIG.  504. 


Hair-follicle 
Fibrous  septa 
Outer  compact  bone-  „ 

Diplo< 
Inner  compact  bone 


uperficial  fascia 

Aponetirosis 

Subaponeurotic 

ssue 
Pericranium 


••• — Bone 

— Dura  mater 


Pacchionian  bodies 


Superior  longitudinal  sinus 
Portion  of  frontal  section  of  head  hardened  in  formalin,  showing  layers  of  scalp,  skull,  and  meninges.     X  2'A 

and  more  constant  continuity  exists  through  the  foramina.  As  the  dura  is  the  chief 
source  of  blood-supply  of  the  cranial  bones,  they  rarely  necrose  after  accidents  which 
strip  the  pericranium  from  their  surface  (page  237).  Subpericranial  effusions  of 
blood,  or  collections  of  pus,  are  limited  and  outlined  by  the  lines  of  the  sutures. 
Cephalhaematomata' '  in  this  situation  correspond  in  shape  to  that  of  one  bone ;  they 
are  commonly  congenital,  constituting  a  form  of  caput  succedaneum,  following  head 
presentations,  and  are  then  apt  to  be  found  over  a  parietal  bone,  since  that  region  is 
most  exposed  to  pressure  during  child-birth.  Tillaux  suggests  that  in  early  life  they 
may  be  encouraged  by  the  softness  and  vascularity  of  the  cranial  bones  and  the 


490  HUMAN   ANATOMY. 

laxity  of  the  pericranium,  and  that  their  greater  frequency  in  male  children  may 
depend  upon  the  larger  size  of  the  head  in  the  male  foetus.  The  close  association  of 
the  bloody  effusion  with  the  pericranium — an  osteogenetic  membrane — sometimes 
results  in  the  development  of  bone  at  the  periphery  of  the  swelling.  The  hard 
ridge  which  is  usually  present  at  this  situation  may  give  rise,  through  contrast  with 
the  relatively  depressed  centre,  to  the  mistaken  diagnosis  of  fracture  of  the  skull. 

Occasionally  a  collection  of  blood  beneath  the  pericranium  communicates  with 
the  diploic  sinuses,  when  it  will  probably  be  situated  to  one  side  of  the  cranium  ;  or 
with  the  superior  longitudinal  sinus,  when  it  will  be  in  the  mid-line.  No  traumatic 
history  may  be  obtainable.  The  swelling  will  be  soft,  reducible,  of  varying  tension, 
and  may  receive  from  the  brain  a  feeble  pulsatile  impulse. 

The  importance  of  the  emissary  veins  in  transmitting  extracranial  infection  to 
the  venous  channels  of  the  dura  may  be  mentioned  here,  but  can  better  be  under- 
stood after  the  venous  system  has  been  described  (page  876). 

2.  The  subaponeurotic  connective  tissue  between  the  pericranium  and  the  apo- 
neurosis  of  the  occipito-frontalis.     This  is  so  loose,  thin,  and  elastic  that  the  union 
between  these  layers  is  not  a  close  one.     The  motion  of  the  ' '  scalp' '  upon  the  skull 
is  a  motion  of  the  parts  above  upon  the  parts  beneath  this  layer.      Movable  growths 
will,  therefore,  be  found  to  occupy  the  former  region  and  immovable  swellings  will 
probably  have  deeper  attachments.      Effusions  of   blood,   suppuration,   or  infective 
cellulitis  occurring  in   the  subaponeurotic  space  may  extend  widely,    and  may   be 
limited  only  by  the  attachments  of  the  musculo-fibrous  layer.     They  may  reach,  there- 
fore, posteriorly  to  the  superior  curved  line  of  the  occipital  bone,  anteriorly  to  a  little 
above  the  eyebrows,  and  laterally  to  a  level  somewhat  above  the  zygoma.      Exten- 
sive haematomata  are  uncommon,  as  the  vessels  in  this  cellular  tissue  are  few  and 
small.      If  they  are  large,  they  suggest  fracture  of  the  skull  with  laceration  of  a  branch 
of  the  middle  meningeal  artery  or  of  a  venous  sinus.      They  may,  however,  by  reason 
of  a  hard  border  and  soft  centre,  be  mistaken  for  depressed  fracture  when  the  skull 
itself  is  uninjured. 

Suppuration  and  cellulitis  are  often  serious  on  account  of  the  tendency  to  spread, 
the  possible  extension  to  the  meninges,  and  the  difficulty  in  applying  antisepsis,  in 
securing  drainage,  or,  later,  in  obtaining  the  rest  necessary  for  rapid  healing.  In 
abscess  the  diffusion  of  the  pus  is  favored  by  the  density  and  the  vitality  of  the  super- 
jacent  layers,  which,  in  consequence  of  the  former  property,  do  not  soften  and  permit 
pointing,  and,  because  of  the  latter,  do  not  slough  and  thus  give  exit  to  the  pus,  which 
therefore  may  extend  in  the  line  of  least  resistance, — i.e.,  along  the  loose  subapo- 
neurotic layer.  Wounds  involving  either  the  muscle  or  its  aponeurosis,  if  transverse 
to  the  direction  of  their  fibres,  gape  widely.  Their  healing  will  be  hastened  by 
firm  bandaging  of  the  whole  cranium  so  as  to  control  and  limit  the  movements  of 
the  scalp. 

3.  The  occipito-frontalis  muscle  and  aponeiirosis  ;  4,  the  superficial  fascia ;  5, 
the  skin.     These  three  layers   are  so  intimately  blended  that  from  the  practical 
stand-point  they  may  be  considered  together.     The  thin  aponeurosis  is  tied  to  the 
skin  (which  is  here  thicker  than  anywhere  else  in  the  body)  by  dense,  inelastic, 
perpendicular  and  oblique  fibres  of  connective  tissue,  enclosing  little  shot-like  masses 
of  fat.     This  area  is  very  vascular,  almost  all  the  vessels  of  the  scalp  being  found  in 
it  adherent  to  the  cellular-tissue  walls  of  the  fat-containing  compartments.     As  a 
result  of  these  anatomical  conditions  it  is  found  that  (i)  suppuration  is  very  limited 
in  extent  ;   (2)  superficial  infections  (such  as  erysipelatous  dermatitis)  are  accom- 
panied by  but  little  swelling  ;   (3)  incised  wounds  do  not  gape  ;  (4)  lacerated  and 
contused  wounds  are  not  followed  by  sloughing,  which  is  also  rare  as  a  result  of 
continuous  pressure,  as  from  bandages  ;  (5)  hemorrhage  after  wounds  is  abundant 
and  is  persistent  because  of  the  adherence  of  the  vessel-walls  to  the  subcutaneous 
layer  of  fascia,  which  prevents  both  their  retraction  and  contraction  ;   (6)  collections 
of  blood  after  contusions  may,  like  the  deeper  ones  already  described,  become  very 
firm  at  the  periphery, — in  this  case  from  an  excess  of  fibrinous  exudate  and  from 
the  presence  of  particles  of  displaced  fat, — while  the  inelastic  fibres  of  cellular  tissue 
(from  among  which  the  fat  particles  have  been  driven  out  by  the  force  of  the  blow) 
remain  depressed  in  the  centre  ;  these  appearances  have  not  infrequently  led  to  a 


PRACTICAL   CONSIDERATIONS:    THE   SCALP.  491 

mistaken  diagnosis  of  fracture  of  the  skull  ;  (7)  lipomata  are  rare,  as  in  the  only 
layer  in  which  fat  is  found  its  abnormal  growth  is  resisted  by  the  density  of  the 
surrounding  connective  tissue. 

Baldness  affects  especially  the  area  $f  the  scalp  which  directly  overlies  the 
occipito-frontal  aponeurosis.  It  is  attributed  (Elliott)  largely  to  the  lack  of  muscular 
fibres  in  this  region,  so  that  the  skin  is  not  ' '  exercised' '  and  the  lymph-current  is 
made  to  depend  chiefly  on  gravity.  The  density  of  the  superficial  fascia  connecting 
the  skin  and  the  aponeurosis  allies  it  with  that  of  the  palmar  and  plantar  regions,  in 
both  of  which  similarly  dense  fascia  is  found  and  hair  is  absent. 

Dermoids  are  common  over  the  anterior  fontanelle  and  the  occipital  protuber- 
ance because  the  early  contact  of  the  skin  and  dura  mater  continues  longest  in  these 
regions.  "Should  the  skin  be  imperfectly  separated,  or  a  portion  remain  persist- 
ently adherent  to  the  dura  mater,  it  would  act  precisely  as  a  tumor  germ  and  give 
rise  to  a  dermoid  cyst"  (Sutton). 

Wens  are  also  common  on  account  of  the  presence  of  large  numbers  of  seba- 
ceous glands.  In  removing  such  growths,  if  the  dissection  is  carried  close  to  the 
sac,  the  subaponeurotic  layer  will  not  be  opened  and  all  danger,  even  in  case  of 
infection,  will  be  minimized. 

So-called  ' '  horns' '  are  found  here  with  relative  frequency  by  reason  of  the 
number  of  sebaceous  glands. 

Emphysema  of  the  scalp  may  occur  as  a  complication  of  fractures  involving  the 
pharynx,  the  frontal  sinuses,  or  the  ethmoid  or  nasal  bones.  The  air  infiltrates 
either  the  subaponeurotic  or  subcutaneous  cellular  tissue. 

Pneumatocele  of  the  frontal  region  is  very  rare,  but  has  occurred  in  a  few  cases 
as  a  result  of  a  communication  between  the  nasal  cavity  and  bony  defects  in  the 
anterior  wall  of  the  frontal  sinuses.  The  swelling  is  soft,  elastic,  and  resonant,  and  is 
made  more  tense  by  forced  expiration,  less  so  by  pressure.  The  entrance  and  escape 
of  air  may  be  heard  on  auscultation.  The  air  is  always  beneath  the  pericranium. 

Syphilis,  tuberculosis,  carcinoma,  and  sarcoma  may  affect  the  scalp  primarily, 
and  are  mentioned  in  the  order  of  frequency  of  occurrence. 

Cirsoid  aneurism  is  especially  frequent  upon  the  scalp. 

The  Temporal  Region. — Here  the  skin  is  thinner  and  less  intimately  adherent 
to  the  subcutaneous  fascia  than  in  the  occipito-frontal  region  ;  that  fascia  also  is 
somewhat  less  closely  connected  to  the  aponeurosis  beneath.  Hemorrhage  between 
these  layers  is  therefore  .more  easily  controlled  by  the  usual  process  of  picking  up 
and  tying  the  vessel,  the  walls  of  which  will  be  found  freer  from  attachments  to  the 
bundles  of  fascia. 

The  fascia  over  the  temporal  muscle  itself  is  of  such  strength  and  thickness  that 
abscesses  beneath  it  rarely  point  above  the  zygoma,  but  are  directed  into  the  pterygo- 
maxillary  region  and  thence  into  the  pharynx  or  into  the  neck,  or  along  the  anterior 
temporal  muscular  fibres  to  the  coronoid  process  and  thence  into  the  mouth. 
Abscesses  above  it  have  no  special  anatomical  peculiarities. 

The  fat  in  the  temporal  fossa  is  abundant,  and  is  found  in  the  subcutaneous 
fascia,  between  the  two  layers  of  the  temporal  fascia,  and  directly  upon  the  muscle 
itself.  The  disappearance  of  this  fat  in  diseases  attended  by  emaciation  causes  the 
characteristic  unnatural  prominence  of  the  zygoma  and  apparent  deepening  of  the 
temporal  fossae. 

The  temporal  muscle  should  be  considered  with  the  pterygoids  in  their  relation 
to  fracture  of  the  ramus  and  coronoid  process  (pages  245,  493),  to  dislocation  of 
the  inferior  maxilla  (pages  246,  493),  and  to  resection  of  that  bone. 

The  pericranium  of  this  region  is  thinner  and  more  adherent  than  that  of  the 
occipito-frontal  region,  and  the  subpericranial  connective  'tissue  is  absent  ;  hence 
subperiosteal  abscess  or  haematoma  is  practically  unknown. 

The  region  may  be  invaded  by  tumors  originating  in  the  orbit  and  spreading 
through  the  spheno-maxillary  fissure  or  through  the  thin  orbital  process  of  the 
malar  bone. 

Trephining  and  other  operations  in  this  region  are  so  closely  related  to  intra- 
cranial  diseases  and  middle-ear  disease  that  they  will  be  considered  in  that  relation 
(page  1509). 


492 


HUMAN   ANATOMY. 


The  Mastoid  Region. — For  the  same  reasons  the  practical  anatomy  of  the  soft 
parts  covering  the  remaining  region  of  the  skull — the  mastoid — will  be  taken  up 
later  (page  1508). 

The  Face. — The  skin  of  the  forehead  and  cheeks  is  thin  and  vascular  and  the 
cellular  tissue  beneath  is  loose.  Therefore  wounds  bleed  freely  but  unite  rapidly  ; 
sloughing  is  rare  ;  cellulitis  tends  to  spread  ;  oedema  is  common  ;  superficial  infections 
(favored  by  the  constant  exposure  of  the  region)  are  attended  by  much  redness  and 
swelling  and  little  pain  ;  if  they  result  in  abscess,  it  is  not  apt  to  attain  a  large  size, 
as  the  delicacy  of  the  skin  permits  of  early  pointing.  On  the  other  hand,  necrotic 
processes  (as  in  cancrum  oris)  once  established  in  the  loose  cellular  tissue  and  fat  of 
the  cheeks,  run  a  rapid  and  destructive  course,  and  may  be  followed  by  great  dis- 
figurement and  by  limitation  of  the  motions  of  the  inferior  maxilla. 

Abscesses  beneath  the  buccinator  aponeurosis,  like  fatty  growths  in  the  same 
situation,  project  towards  the  cavity  of  the  mouth  ;  they  should  be  opened  through 
the  mucous  membrane. 


FIG.  505. 


Upper  cut  edge  of  masseter  _ 

Temporal 
External  pterygoid 


Internal  pterygoid 
Masseter  (cut) 


Parotid  gland 
partly  removed 


Buccinator 


•'osterior  fragment 

Line  of  fracture 
Anterior  fragment 
Digastric,  anterior  belly 
•Mylo-hyoid 
I  lyo-glossus 
Body  of  hyoid  bone 


Thyro-hyoid 

Omo-hyoid 

—Sterno-hyoid 


Dissection  of  fracture  of  body  of  mandible,  showing  displacement  produced  by  muscular 


action. 


Over  the  lower  third  of  the  nose  the  skin  is  closely  adherent,  as  it  is  over  the 
chin,  where  it  is  also  very  dense.  Infections  in  those  regions  are  therefore  exception- 
ally painful  (page  246).  The  vascularity  and  mobility  of  the  skin  of  the  forehead 
and  of  the  cheeks  make  it  especially  useful  in  plastic  operations  upon  tin  n-gion  of 
the  nose  and  mouth. 

On  account  of  the  rich  blood-supply,  naevi  are  common  on  all  parts  of  the  fan  •, 
as,  by  reason  of  the  numerous  sweat  and  sebaceous  glands,  are  acneiform  eruptions. 

Lupus  and  malignant  pustule  are  frequent  and  grave  forms  of  local  infection  : 
rodent  ulcer  (epithelioma)  is  common  ;  while  on  the  forehead  the  early  syphilitic- 
roseola  or  papule  (corona  veneris)  and  about  the  lips  and  nose  the  later  tubercular 
syphilide  are  often  seen. 

Lipomata,  in  spite  of  the  considerable  quantity  of  fat  in  the  subcutaneous  tissue, 
are  very  rare.  The  mass  of  fat  between  the  buccinator  and  masseter  muscles  — 


PRACTICAL   CONSIDERATIONS  :    THE   FACE. 


493 


FIG.  506. 


Upper  joint-cavity 

Interarticular 
cartilage 


Ram  us  of 
mandible 


"  boule  de  Bichat,"  "sucking  cushion" — is  believed  to  receive  and  distribute  the 
increased  atmospheric  pressure  which  follows  the  establishment  of  a  partial  vacuum 
in  the  mouth  during-  sucking.  It  thus  aids  in  preventing  the  buccinator  from  being 
carried  in  between  the  alveoli.  It  is  relatively  smaller  in  adults  than  in  infants  and 
in  the  latter  does  not  much 
diminish  in  size,  even  in  the 
presence  of  emaciation,  when 
the  general  subcutaneous  fat 
has  largely  disappeared 
(  Ranke) .  Sutton  says,  ' '  The 
sucking  cushions  sometimes 
enlarge  in  adults  and  simulate 
more  serious  species  of  tu- 
mors, and  it  is  curious  that  in 
some  of  the  recorded  cases 
the  enlargement  has  been  as- 
sociated with  the  impaction  of 
a  salivary  calculus  in  the  duct 
of  the  parotid  gland. ' ' 

The  importance  of  avoid- 
ing conspicuous  scars  on  the 
face  leads  the  surgeon  to  make 
his  incisions,  whenever  possi- 
ble, either  in  or  parallel  with 
the  lines  of  the  natural  furrows  due  to  the  insertion  of  some  of  the  facial  muscles  into 
the  skin  itself,  or  in  the  shadow  of  overhanging  parts,  as  beneath  the  upper  brow 
or  the  lower  edge  of  the  inferior  maxilla.  For  a  reason  not  understood,  but  possibly 
associated  with  the  difficulty  in  securing  rest,  combined  with  the  large  vascular  sup- 
ply, cicatricial  overgrowth  and  true  keloid  are  both  relatively  common  after  wounds 
of  the  face. 

In  fracture  of  the  inferior  maxilla  the  irregularity  in  the  horizontal  planes  of  the 
two  fragments  (the  anterior  being  the  lower)  is  due  to  (a)  the  weight  of  the  chin  and 

opposite  side  of    the  jaw 
FIG.  507. 

Articular  eminence 


Dissection  showing  relations  when  mandible  rests  within  glenoid 
fossa  ;  outer  part  of  capsular  ligament  has  been  cut  away,  exposing  upper 
and  lower  joint-cavities. 


I'pper  joint-cavity 


Tendon  of-    .7 
temporal    .  ;ji 
muscle       ;  V; 
Coronoid' 
process 


<  the  action  on  the  an- 
terior fragment  of  the  di- 
gastric and  other  depressors 
of  the  chin  ;  and  (c)  the 
effect  of  the  posterior  fibres 
of  the  temporal,  the  internal 
pterygoid,  and  the  super- 
ficial fibres  of  the  masseter 
in  elevating  the  posterior 
fragment  (Fig.  505). 

In  fracture  of  the  ramus 
there  is  little  displacement, 
as  the  bone  lies  between  the 
two  muscular  planes  of  the 
masseter  and  internal  ptery- 
goid and  is  splinted  by 
them.  In  fracture  of  the 
neck  of  the  condyle  the 
upper  fragment  is  drawn 
upward  and  forward  by  the 
external  pterygoid  ;  the  re- 
mainder of  the  jaw  is  some- 
what elevated  by  the  masseter,  temporal,  and  internal  pterygoid.  The  difficulty  in 
approximation  of  the  fragments  may  result  in  excess  of  callus,  which  greatly  interferes 
with  the  subsequent  movements  of  the  temporo-maxillary  articulation. 

The  mechanism  of  dislocation  of  the  lower  jaw  has  already  been  described  (page 


Ramus  of 
mandible 


Dissection  showing  relations  when  mandible  is  depressed  and  carried 
forward  upon  articular  eminence;  capsular  ligament  is  stretched  in  con- 
sequence. 


494 


HUMAN    ANATOMY. 


..Temporal  muscle 


'ondyle 
of  jaw 


246),  but  can  now  be  better  understood.  It  should  be  remembered  that  the  muscles 
of  mastication  are  exceptionally  irritable  and  are  all  supplied  by  the  motor  branch  of 
the  mandibular  division  of  the  fifth  nerve.  When  the  mouth  is  opened  very  widely, 
as  in  yawning,  or  in  an  effort  to  take  an  unusually  large  bite,  the  deep  posterior  ver- 
tical fibres  of  the  masseter  (which  are  the  only  ones  attached  to  the  ramus  and  aiding 
in  closing  the  mouth  that  do  not  run  forward  as  well  as  upward)  are  carried  behind 
the  centre  of  motion,  so  that  their  contraction  tends  still  further  to  open  the  mouth 
or  to  keep  it  open.  Reflex  contraction  from  overstretching  is  excited  in  the  general 
group,  and  the  external  pterygoid  acting  with  most  advantage  in  that  position, 
draws  the  condyle  into  the  zygomatic  fossa,  where  it  is  held  by  the  masseter  and 
internal  pterygoid. 

' '  Noisy  movement' '  of  the  temporo-maxillary  joint  is  often  due  to  weakness  of 
the  muscles  of  mastication,  permitting  the  joint  surfaces  to  fall  apart  as  the  result  of 
the  slight  lengthening  of  the  ligaments  produced  in  time  by  the  weight  of  the  jaw. 

Paralysis  and  spasm  of  the  facial  and  masticatory  muscles  will  be  considered  in 
relation  to  the  nerves  supplying  them  (pages  1255,  1248). 

The  most  frequent  congenital  defect  of  the  muscles  of  the  face  is  in  connection 

with  harelip,  in  which  deformity 

FIG.  508.  the   portion   of   the   orbicularis 

oris  corresponding  to  the  cleft 
is  absent. 

Dermoids  are  not  infre- 
quently found  at  the  angles  of 
the  orbit,  in  the  cheeks  near 
the  corner  of  the  mouth,  in  the 
naso-labial  furrows,  at  the  root 
of  the  nose,  and  in  the  mid-line 
of  the  chin.  Reference  to  the 
embryology  of  the  face  will  show 
that  these  are  localities  in  which 
epiblastic  inclusion  is  likely  to 
occur. 

Marked  congenital  asym- 
metry of  the  face  may  occur 
from  failure  of  developmental 
processes. 

Landmarks. — Just  within 
the  mid-point  of  a  line  drawn 
from  the  mastoid  process  to  the 
external  occipital  protuberance 
the  occipital  artery  can  be  felt  as,  with  the  great  occipital  nerve,  it  enters  the  scalp 
on  its  way  to  the  vertex. 

The  superficial  temporal  artery  can  be  felt,  and  often  can  be  seen  where  it  runs 
over  the  base  of  the  zygoma  in  front  of  the  ear.  Its  vein  and  the  auriculo-temporal 
nerve  are  just  behind  it.  The  division  of  the  artery  into  its  anterior  and  posterior 
branches  takes  place  about  5  cm.  (2  in.)  above  the  zygoma.  These  branches  are 
easily  palpable  on  the  firm  underlying  structures,  and  thus  afford  testimony  as  to  the 
presence  or  absence  of  arterial  degeneration.  In  old  persons  they  are  often  tortuous 
and  plainly  visible,  especially  the  anterior  branch  where  it  crosses  the  anterior  por- 
tion of  the  temporal  muscle.  The  region  is  a  frequent  seat  of  cirsoid  aneurism. 

At  the  junction  of  the  middle  with  the  inner  third  of  the  supra-orbital  bony 
margin  the  supra-orbital  notch  may  be  felt.  From  this  point  the  supra-orbital  nerve 
and  artery  pass  almost  directly  upward,  crossing  the  orbital  margin.  Between  that 
point  and  the  root  of  the  nose  the  frontal  artery  and  supratrochlear  nerve  ascend 
and  the  frontal  vein  descends. 

The  movement  of  the  condyle  of  the  inferior  maxilla  up  to  the  summit  of  the 
eminentia  articularis  when  the  mouth  is  open  and  the  external  pterygoid  contracts, 
and  its  return  into  the  glenoid  cavity  when  that  muscle  is  relaxed  and  the  mouth 
closed,  can  plainly  be  felt. 


Masseter 
muscle,  partly 
cut  away 


Dissection  showint 
slipped 


Mandible 


position  of  dislocated  jaw,  condyle  having 
in  front  of  articular  eminence. 


THE   VAGO-ACCESSORY    MUSCLES.  495 

The  relation  of  many  of  the  bony  points  to  the  overlying  soft  parts  has  been 
described  (page  246). 

The  shape  of  most  of  the  muscles  cannot  be  separately  distinguished.  Com- 
parison of  a  skull  with  a  partially  dissected  head  will  show,  however,  that  over  the 
vault  of  the  cranium  from  the  supra-orbital  ridges  to  the  nucha  the  general  shape  of 
the  skull  determines  the  surface  form  during  life,  the  flattened  muscles  and  aponeu- 
rosis  closely  conforming  to  it.  In  the  temporal  regions,  in  spite  of  the  deep  bony 
fossa,  the  triangular  muscle  and  the  accompanying  fat  (page  491)  make  the  surface 
in  vigorous,  well-nourished  persons  slightly  convex.  The  outlines  of  the  muscle  can 
be  seen  when  it  is  in  contraction,  especially  the  portion  anterior  to  the  hairy  scalp. 

On  the  face  the  characteristics  that  distinguish  the  individual  are  due  largely 
to  the  presence  of  muscles  and  of  subcutaneous  fat.  The  edge  of  the  orbit  and  the 
naso-frontal  junction  are  covered  and  given  rounded  outlines  by  the  orbicularis 
palpebrarum  and  the  pyramidalis  nasi.  The  muscles  running  from  the  malar  bone 
and  maxilla  to  the  upper  lip  aid  the  buccinator  and  the  fat  of  the  cheek  in  rilling  up 
the  great  hollows  beneath  the  malar  prominences.  The  orbicularis  oris  gives  shape 
and  expression  to  the  mouth.  The  masseter  fills  out  the  posterior  portion  of  the 
cheek  and  becomes  visible  in  outline  when  in  firm  contraction,  especially  the  vertical 
anterior  border,  just  in  front  of  which  the  facial  artery  crosses  the  inferior  maxilla. 

As  nearly  all  the  facial  muscles  have  fibres  of  insertion  into  the  facial  integument, 
their  influence  upon  expression  and  upon  the  creases  and  folds  that  become  perma- 
nent as  ' '  wrinkles, "  "  crows'  feejt, ' '  etc. ,  is  apparent. 

III.    THE  VAGO-ACCESSORY   MUSCLES. 

The  muscles  supplied  by  the  glosso-pharyngeal,  vagus,  and  spinal  accessory 
nerves  may  be  grouped  together  both  on  account  of  their  relations  in  the  adult  and 
on  account  of  the  intimate  relations  which  exist  between  the  three  nerves.  The 
glosso-pharyngeal  and  vagus  correspond  to  the  posterior  branchial  arches,  the  glosso- 
pharyngeal  to  that  represented  in  the  adult  by  the  greater  cornu  of  the  hyoid  bone 
and  the  vagus  to  those  represented  by  the  laryngeal  cartilages.  Consequently  we 
find  the  muscles  supplied  by  these  nerves  to  be  those  associated  with  the  pharynx 
and  larynx,  one  of  the  muscles  of  the  soft  palate,  the  levator  palati,  being  also 
included  in  the  group.  The  pharyngeal  muscles,  for  the  most  part,  are  supplied  from 
the  pharyngeal  plexus,  into  which  fibres  from  both  the  glosso-pharyngeal  and  vagus 
nerves  enter.  The  laryngeal  muscles,  however,  are  supplied  by  branches  coming 
directly  from  the  stem  of  the  vagus  nerve. 

The  spinal  accessory  nerve  stands  in  such  intimate  relations  with  the  vagus  that 
its  nucleus  of  origin  may  well  be  regarded  as  an  extension  of  that  of  the  vagus,  and 
by  the  union  of  a  portion  of  its  fibres  with  those  of  the  vagus  to  form  a  common 
trunk  opportunity  is  afforded  for  its  fibres  to  participate  in  the  formation  of  the 
pharyngeal  plexus,  and  there  is  evidence  pointing  to  the  origin  of  the  fibres  of  the 
inferior  laryngeal  nerve,  which  supplies  the  majority  of  the  laryngeal  muscles,  from 
the  spinal  accessory  nucleus. 

In  addition,  however,  to  its  participation  in  the  supply  of  the  pharyngeal  and, 
possibly,  the  laryngeal  muscles,  the  spinal  accessory  also  innervates  the  trapezius 
and  sterno-mastoid  muscles,  and  these,  on  account  of  their  relations,  must  constitute 
a  subgroup  distinct  from  the  other  vago -accessory  muscles. 

(a)  THE  MUSCLES  OF  THE  PALATE  AND  PHARYNX. 

1.  Stylo-pharyngeus.  5.  Palato-pharyngeus. 

2.  Levator  palati.  6.  Constrictor  pharyngis  superior. 

3.  Azygos  uvulae.  7.  Constrictor  pharyngis  medius. 

4.  Palato-glossus.  8.  Constrictor  pharyngis  inferior. 

i.    STYLO-PHARYNGEUS  (Figs.  502,  509). 

Attachments. — The  stylo-pharyngeus  arises  from  the  inner  surface  of  the 
styloid  process  near  its  base.  It  is  directed  downward,  the  glosso-pharyngeal  nerve 


496 


HUMAN    ANATOMY. 


covering  its  outer  surface,  passes  between  the  middle  and  superior  constrictors  of  the 
pharynx,  and,  being  joined  by  fibres  from  the  palato-pharyngeus,  is  inserted  into 
the  posterior  border  of  the  thyroid  cartilage  and  the  posterior  wall  of  the  pharynx. 

Nerve-Supply. — By  a  branch  of  the  glosso-pharyngeal  nerve. 

Action. — To  draw  upward  the  posterior  wall  of  the  pharynx  and  the  thyroid 
cartilage. 

2.    LEVATOR  PALATI  (Fig.  509). 

Attachments. — The  elevator  of  the  soft  palate  (m.  levator  veli  palatini)  arises 
from  the  under  surface  of  the  apex  of  the  petrous  portion  of  the  temporal  bone  and 
from  the  cartilaginous  portion  of  the  Eustachian  tube.  It  descends  obliquely  down- 


Salpingo- 
pharyngeus — 


Levator  palati- 


Superior — ^ 
constrictor 


Palato-pharynge 


Palato-pharyngeus 


Stylo-pharyngeus ! 


FIG.  509. 


Nasal  septum 


Eustachian  tube 


— External 
pterygoid 


Posterior  crico-arytenoid 


-(Esophagus 


Muscles  of  palate  and  pharynx,  seen  from  behind  ;  pharynx  laid  o'pen. 

ward  and  forward,  and,  broadening  out,  enters  the  substance  of  the  soft  palate,  into 
the  aponeurosis  of  which  it  is  inserted. 

Nerve-Supply. — From  the  pharyngeal  plexus  by  fibres  which  probably  have 
their  origin  in  the  anterior  part  of  the  nucleus  of  the  spinal  accessory  nerve. 

Action. — To  elevate  the  soft  palate. 

3.    A/v<;os  UVUL^:  (Fig.  509). 

Attachments. — The  azygos  uviihr  (m.  uvulae"),  so  named  <>n  the  supposition 
that  it  was  an  unpaired  muscle,  consists  of  two  narrow  slips  which  arise  from  the 


THE   VAGO-ACCESSORY   MUSCLES.  497 

aponeurosis  of  the  soft  palate  and  from  the  posterior  nasal  spine.  They  pass  back- 
ward and  downward,  almost  parallel  with  each  other,  into  the  uvula  to  be  inserted 
into  its  aponeurosis. 

Nerve-Supply. — From  the  pharyngeal  plexus. 

Action. — To  raise  the  uvula. 

4.    PALATO-GLOSSUS  (Fig.  1339). 

Attachments. — The  palato-glossus  (m.  glossopalatinus)  is  a  thin  sheet  which 
arises  from  the  under  surface  of  the  aponeurosis  of  the  soft  palate  and  descends  in 
the  anterior  pillar  of  the  fauces  (arcus  glossopalatinus)  to  be  inserted  into  the  sides 
of  the  tongue,  mingling  with  the  fibres  of  the  stylo-glossus. 

Nerve-Supply. — From  the  pharyngeal  plexus,  probably  by  fibres  from  the 
anterior  part  of  the  nucleus  of  the  spinal  accessory  nerve. 

Action. — To  raise  the  back  part  of  the  tongue  and  at  the  same  time  to  narrow 
the  fauces  by  causing  an  approximation  of  the  anterior  pillars.  Acting  from  below, 
it  will  depress  the  soft  palate. 

5.    PALATO-PHARYNGEUS  (Fig.  509). 

Attachments. — The  palato-pharyngeus  (m.  pharyngopalatinus)  arises  from  the 
aponeurosis  of  the  soft  palate,  from  the  posterior  border  of  the  hard  palate,  and  also 
from  the  lower  portion  of  the  cartilage  of  the  Eustachian  tube.  It  passes  downward 
and  backward  in  the  posterior  pillar  of  the  fauces  (arcus  pharyngopalatinus),  internal 
to  the  superior  and  middle  constrictors  of  the  pharynx,  and  is  inserted  into  the  pos- 
terior border  of  the  thyroid  cartilage  and  into  the  posterior  wall  of  the  pharynx. 
That  portion  of  the  muscle  which  arises  from  the  cartilage  of  the  Eustachian  tube  is 
often  regarded  as  a  distinct  muscle  which  has  been  termed  the  salpingo-pharyngeus. 

Nerve-Supply. — From  the  pharyngeal  plexus,  probably  by  fibres  from  the 
anterior  part  of  the  nucleus  of  the  spinal  accessory  nerve. 

Action. — It  draws  the  pharynx  and  thyroid  cartilage  upward  and  at  the  same 
time  approximates  the  two  posterior  pillars  of  the  fauces.  Acting  from  below,  it 
will  depress  the  soft  palate. 

6.    CONSTRICTOR  PHARYNGIS  SUPERIOR  (Figs.  501,  510). 

Attachments. — The  superior  constrictor  of  the  pharynx  forms  a  thin  quadri- 
lateral sheet  whose  origin  is  closely  associated  with  part  of  that  of  the  buccinator, 
there  being  usually  some  interchange  of  fibres  between  the  two  muscles.  It  arises 
from  the  lower  part  of  the  posterior  border  of  the  internal  pterygoid  plate  and 
from  its  hamulus,  from  the  posterior  border  of  the  pt'erygo-mandibular  ligament,  and 
is  thence  continued  upon  the  internal  oblique  line  of  the  mandible,  the  mucous  mem- 
brane of  the  mouth,  and  the  side  of  the  tongue.  The  uppermost  fibres  pass  in  a 
curve  backward  and  upward  and  are  inserted  into  the  pharyngeal  tubercle  of  the 
occipital  bone,  while  the  remainder  unite  with  the  muscle  of  the  opposite  side  in  a 
median  raphe  on  the  posterior  wall  of  the  pharynx. 

Nerve-Supply. — From  the  pharyngeal  plexus  by  fibres  which  probably  arise 
from  the  anterior  portion  of  the  nucleus  of  the  spinal  accessory  nerve. 

Action. — To  compress  the  pharynx. 

Relations. — Between  the  uppermost  fibres  of  the  muscle  and  the  base  of  the 
skull  is  an  interval  in  which  may  be  seen  the  levator  palati  and  the  Eustachian  tube. 
This  interval  has  been  termed  the  sinus  of  Morgagni,  and  is  closed  by  a  sheet  of 
connective  tissue  termed  the  fascia  pharyngobasilaris,  which  is  an  upward  prolonga- 
tion to  the  base  of  the  skull  of  the  pharyngeal  portion  of  the  bucco-pharyngeal 
fascia  (page  488). 

Externally  the  superior  constrictor  is  in  relation  above  with  the  internal  carotid 
artery,  the  vagus  nerve,  and  the  cervical  sympathetic,  and  below  with  the  upper 
part  of  the  middle  constrictor  and  the  stylo-pharyngeus.  Internally  it  is  lined  by 
mucous  membrane  throughout  the  greater  part  of  its  extent,  being  in  relation,  how- 
ever, with  the  tonsil  and  the  palato-pharyngeus  muscle. 

32 


498 


HUMAN   ANATOMY. 


Variations. — A  considerable  amount  of  independence  may  exist  between  the  bundles  of 
fibres  coming  from  different  portions  of  the  line  of  origin,  and  the  muscle  has  consequently  been 
described  as  consisting  of  various  portions  to  which  the  terms  pterygo-pharyngeus,  bucco- 
pharyngeus,  mylo-pharyngeus,  and  glosso-pharyngeus  have  been  applied. 

Not  infrequently  a  bundle  of  fibres  is  to  be  found  arising  from  the  basilar  portion  of  the 
occipital  bone  or  even  from  the  inferior  surface  of  the  petrous  portion  of  the  temporal  or  the  spine 
of  the  sphenoid,  and  passing  downward  to  be  inserted  along  with  the  pharyngo-palatinus.  A 
bundle  which  passes  from  the  cartilaginous  portion  of  the  Eustachian  tube  to  be  inserted  with 
the  palato-pharyngeus  has  been  termed  the  sal  ping  o-pharyngeus. 


Internal  carotid  artery 
Internal  jugular  vein 


Central  attachment  of  pharynx 


Mastoid— f^s 
process 

Internal 
pterygoid 


Styloid  process L 

Digastric, 
posterior  belly 

Stylo- 

pharyngeus 
Stylo-glossus 


Stylo-hyoid 

Stylo-hyoid 
ligament 


Lateral 
expan- 
sion of 
pharynx 


Tip  of  great  cprnu  of 

hyoid  bone 

Thyro-hyoid  ligament 

Superior  cornu  of  thyroid 

cartilage 


Middle 
constrictor 


ndible 


Inferior  constrictor 


ongitudinal  muscle  of  oesophagus    . 


Muscles  of  pharynx  from  behind  ;  portion  of  ink-i  ior  constrictor  has  be?n  removed. 


7.    CONSTRICTOR  PHARYNGIS  Mr.nirs  (Fi^.  510). 

Attachments. — The  middle  constrictor  of  the  pharynx  is  a  fan-shaped  sheet 
which  arises  from  the  stylo-hyoid  ligament  and  both  cornua  of  the  hyoid  bone.  The 
lil. res  pass  backward  to  be  inserted  into  the  pharyngeul  raphe,  the  upper  fibres 


THE   VAGO- ACCESSORY    MUSCLES.  499 

overlapping  the  lower  part  of  the  superior  constrictor  and  extending  in  some  cases 
almost  to  the  occipital  bone,  while  the  lower  fibres  are  overlapped  by  the  inferior 
constrictor. 

Nerve-Supply. — From  the  pharyngeal  plexus,  probably  by  fibres  from  the 
anterior  portion  of  the  spinal  accessory  nucleus.  It  is  said  to  be  supplied  also  by 
the  glosso-pharyngeal  nerve. 

Action. — To  compress  the  pharynx. 

Variations. — As  in  the  case  of  the  superior  constrictor,  the  fibres  from  different  parts  of 
the  origin  may  have  considerable  independence.  Thus  the  fibres  from  the  greater  cornu  of  the 
hyoid  have  been  recognized  as  a  muscle,  the  cerato-pharyngeus,  distinct  from  the  remainder,  to 
which  the  term  chondro-pharyngeus  has  been  applied. 

8.    CONSTRICTOR  PHARYNGIS  INFERIOR  (Figs.  501,  510). 

Attachments, — Like  the  middle  constrictor,  the  inferior  is  also  a  fan-shaped 
sheet  and  arises  from  the  outer  surface  of  the  thyroid  and  cricoid  cartilages  of  the 
larynx.  The  fibres  radiate  backward  to  be  inserted  into  the  pharyngeal  raphe,  the 
upper  ones  overlapping  the  lower  part  of  the  middle  constrictor,  while  the  lower 
ones  mingle  with  the  musculature  of  the  oesophagus. 

Nerve-Supply. — From  the  pharyngeal  plexus,  probably  through  fibres  from 
the  anterior  part  of  the  nucleus  of  the  spinal  accessory.  It  is  said  to  receive  also 
fibres  from  the  vagus  through  both  the  superior  and  inferior  laryngeal  nerves. 

Action. — To  compress  the  pharynx.  The  three  constrictors  of  the  pharynx 
play  important  parts  in  the  final  acts  of  deglutition,  forcing  the  food  towards  the 
oesophagus.  They  are  also  important  agents  in  producing  modulations  of  the  voice, 
since  the  pharynx  may  be  regarded  as  forming  a  resonator,  alterations  of  whose  form 
will  naturally  result  in  modifications  of  voice. 

Variations.— The  portions  of  the  muscle  arising  from  each  of  the  two  laryngeal  cartilages 
may  be  more  or  less  distinct  and  have  been  termed  the  thyro-pharyngeus  and  crico-pharyngeus. 

(6)   THE  MUSCLES  OF  THE  LARYNX. 

The  muscles  of  the  larynx  will  be  considered  in  connection  with  the  description 
of  that  organ  (page  1824). 

(c)  THE  TRAPEZIUS  MUSCLES, 
i.    Sterno-cleido-mastoideus.  2.    Trapezius. 

This  group  includes  but  two  muscles,  the  trapezius  and  sterno-cleido-mastoid, 
which  extend  from  the  skull  to  the  pectoral  girdle.  Both  are  in  reality  compound 
muscles,  formed  by  the  fusion  of  fibres  derived  from  the  branchiomeres  supplied  by 
the  spinal  accessory  with  portions  of  the  myotomes  supplied  by  the  second,  third, 
and  fourth  cervical  nerves.  Strictly  speaking,  therefore,  they  belong  only  partially 
to  the  series  of  branchiomeric  muscles,  but  the  union  of  the  elements  derived  from 
the  two  sources  is  so  intimate  that  any  attempt  to  distinguish  them  in  a  brief  descrip- 
tion of  the  muscles  would  tend  to  confusion. 

i.    STERNO-CLEIDO-MASTOIDEUS  (Fig.  541). 

Attachments. — The  sterno-mastoid  is  attached  below  by  two  heads  to  the 
sternum  and  the  clavicle.  The  sterna/  ht ad  arises  by  a  strong  rounded  tendon  from 
the  anterior  surface  of  the  manubrium  sterni,  while  the  clavicular  head  is  more  band- 
like,  and  takes  origin  from  the  upper  surface  of  the  sternal  end  of  the  clavicle. 
The  two  heads  are  directed  upward  and  backward,  the  clavicular  head  gradually 
passing  beneath  the  sternal  one,  and  the  two,  eventually  fusing,  are  inserted  into  the 
mastoid  process  of  the  temporal  bone  and  into  the  outer  part  of  the  superior  nuchal 
line. 


5oo 


HUMAN    ANATOMY. 


Nerve-Supply. — The  external  branch  of  the  spinal  accessory  and  the  second 
and  third  cervical  nerves. 

Action. — The  two  muscles  of  opposite  sides,  acting  together,  will  draw  the 
head  forward,  thus  bending  the  neck.  Acting  singly,  each  muscle  will  tend  to  draw 
the  head  towards  its  own  side  and  at  the  same  time  to  rotate  it  towards  the  opposite 
side. 

Relations. — Superficially  the  muscle  is  covered  by  the  platysma,  and  is  crossed 
obliquely  by  the  external  jugular  vein  and  in  varying  directions  by  the  superficial 

branches  of   the  cervical   plexus.      It  covers, 

FIG.  511.  above,  the  upper  part  of  the  posterior  belly  of 

the  digastric,  the  splenius  capitis,  the  levator 
scapulae  and  the  scaleni,  and  below  it  crosses 
the  omo-hyoid  and  covers  the  lower  attach- 
ments of  the  sterno-hyoid  and  sterno-thyroid. 
It  also  covers  the  common  carotid  artery  and 
the  lower  portions  of  the  e"xternal  and  internal 
carotids,  the  facial  and  internal  jugular  veins, 
the  cervical  plexus,  and  the  lateral  lobe  of  the 
thyroid  gland. 

erno-occipita! 


Sterno-mastoid,  su- 
perficial and  deep 


Variations.— Considerable  variation  exists  in  the 
amount  of  fusion  of  the  two  heads,  their  complete 
distinctness  being  of  so  frequent  occurrence  as  to  be 
regarded  as  normal  by  some  authors.  But,  in  ad- 
dition to  these-  two  portions,  the  muscle  presents  fre- 
quently a  separation  into  other  parts,  and  compara- 
tive anatomy  reveals  a  primary  constitution  of  the 
muscle  from  at  least  five  distinct  portions,  any  one 
or  more  of  which  may  appear  as  distinct  bundles 
(Fig.  511).  These  portions  are  arranged  in  two 
layers,  the  superficial  one  consisting  of  a  superficial 
sterno-mastoid,  a  sterno-occipital,  and  a  cleido- 
occipital  portion,  while  the  deep  one  is  formed  by 
a  deep  sterno-mastoid  and  a  cleido-mastoid  portion, 
the  names  applied  indicating  the  attachments  of  the 
various  bundles. 

Occasionally  the  lower  portion  of  the  muscle 

is  traversed  by  a  tendinous  intersection,  a  peculiarity  of  interest  in  connection  with  the  formation 
of  the  muscle  by  the  fusion  of  portions  derived  from  different  myotomes. 


Cleido-occipi- 
tal,  lower 
part  turin-d 
downward 

Quadricipital  type  of  sterno-mastoid,  showing  the 
components  of  the  muscle.     (After  Maubrac.) 


2.    TRAPEZIUS  (Figs.  512,  559). 

Attachments. — The  trapezius  is  the  most  superficial  muscle  upon  the  dorsal 
surface  of  the  body,  and  is  a  triangular  sheet  whose  base  corresponds  with  the  mid- 
dorsal  line.  The  two  muscles  of  opposite  sides  being  thus  placed  base  to  base,  form 
a  rhomboidal  sheet  which  covers  the  nape  of  the  neck  and  the  upper  part  of  the  back 
and  shoulders,  resembling  somewhat  a  monk's  cowl,  whence  the  name  cucnllaris 
sometimes  applied  to  the  muscle. 

It  arises  above  from  the  superior  nuchal  line  and  the  external  occipital  pro- 
tuberance, and  thence  along  the  ligamentum  nuchae  and  the  spinous  processes  of 
the  seventh  cervical  and  all  the  thoracic  vertebrae,  together  with  the  supraspinous 
ligaments.  The  upper  fibres  pass  downward  and  outward,  the  middle- ones  directly 
outward,  and  the  lower  ones  upward  and  outward,  and  are  inserted,  the  upper  ones 
into  the  outer  third  of  the  posterior  border  of  the  clavicle,  the  middle  ones  into  the 
inner  border  and  upper  surface  of  the  acromion  process  and  the  upper  border  of  the 
spine  of  the  scapula,  and  the  lower  ones  into  a  tubercle  at  the  base  of  the  scapular 
spine.  * 

Throughout  the  greater  part  of  its  length  the  origin  of  the  muscle  is  by  short 
tendinous  fibres  intermingled  with  muscle-tissue,  but  from  about  the  middle  of  the 
ligamentum  imch;r  t<  >  the  spinous  process  of  the  second  thoracic  vertebra  it  is  entirely 
tendinous.  Furthermore,  throughout  the  upper  half  of  this  portion  of  the  origin  the 
tendinous  fibres  gradually  increase  in  length  and  throughout  its  lower  half  they  again 
diminish,  so  that  there  is  formed  by  the  two  muscles  of  opposite  sides,  in  this  region, 


THE   VAGO-ACCESSORY    MUSCLES. 


501 


a  well-marked  oval  or  rhomboidal  tendinous  area,  which  has  been  termed  the  oval 
aponeicrosis. 

In  their  course  to  their  insertion  the  lower  fibres  pass  over  the  smooth  surface 
at  the  base  of  the  spine  of  the  scapula,  and  sometimes  a  bursa  mucosa  is  developed 
between  the  bone  and  the  muscle. 

Nerve-Supply. — From  the  external  branch  of  the  spinal  accessory  and  from 
the  third  and  fourth  cervical  nerves. 

Action. — Acting  from  above,  the  upper  fibres  draw  upward  the  point  of  the 
shoulder,  while,  acting  from  below,  they  draw  the  head  backward.  The  middle  and 

lower  fibres  draw  the  scapula  towards  the 
mid-dorsal  line  and  at  the  same  time 
rotate  it  so  as  to  raise  the  point  of  the 
shoulder. 

Variations. — Like  the  sterno-mastoid,  the 
trapezius  is  a  compound  muscle  consisting  of 
three  distinct  portions.  That  portion  of  the 
muscle  which  inserts  into  the  tuberosity  of  the 

FIG.  513. 


FIG.  512. 

Sterno-mastoid 

-  Aponeurosis  of  trapezius 
.Trapezius 

-Acromion 

Scapular 

spine 

Infraspinatus 

omboideus  major 

Teres  major 


o-occipitalis 

lius 


Latissimus  dorsi 


Superficial  dissection  of  back,  showing  trapezius 
and  adjacent  muscles. 


.Cleido-occipitalis  cervicalis 
Clavicle 

Acromion 

Dorso-scapularis 
superior 

Tuberosity  of  spine 


Tendinous  slip  to 

infraspinous  fascia 
Dorso-scapularis  inferior 


Latissimus  dorsi 


Components  of  human  trapezius  muscle. 
(Streissler. ) 


scapular  spine  represents  what  is  termed  in  the  lower  mammals  the  dorso-scapularis  inferior, 
while  the  portion  which  inserts  into  the  spine  and  acromion  process  represents  the  dorso-scap- 
ularis superior.  The  clavicular  portion,  on  the  other  hand,  is  in  the  lower  forms  associated  with 
the  cleido-occipitalis  element  of  the  sterno-cleido-mastoid,  and  may  therefore  be  termed  the 
cleido-occipitalis  cervicalis. 

Indications  of  this  triple  constitution  are  to  be  seen  in  a  more  or  less  distinct  separation  of 
the  clavicular  portion  of  the  muscle  from  the  rest  and,  less  frequently,  by  a  separation  of  the 
lower  from  the  middle  portion  (Fig.  513).  Occasionally,  too,  bundles  pass  from  the  anterior 
border  of  the  clavicular  portion  to  join  the  cleido-occipitalis  portion  of  the  sterno-cleido-mastoid, 
indicating  the  common  origin  of  the  two  muscles.  Variations  likewise  occur  in  the  extent  of 
the  spinal  attachment  of  the  trapezins,  owing  to  the  reduction  of  one  or  other  of  its  parts,  and  it 
may  be  remarked  that  this  attachment  usually  extends  lower  in  the  muscle  of  the  right  side 
than  in  that  of  the  left. 

Of  especial  interest  from  the  comparative  stand-point  is  the  occasional  existence  of  a  bundle 
of  fibres  which  lies  beneath  the  cervical  portion  of  the  trapezius,  and  is  attached  at  one  extremity 
to  the  outer  end  of  the  clavicle  or  to  the  acromion  process  and  above  to  the  transverse  processes 
of  some  of  the  upper  cervical  vertebrae,  usually  the  atlas  and  axis.  It  is  apparently  the  equivalent 
of  the  omo-transversarius  of  the  lower  mammals,  a  muscle  which  is  closely  associated  with  the 
members  of  the  trapezius  group. 


502 


HUMAN    ANATOMY. 


THE   METAMERIC   MUSCLES. 

A.     THE   AXIAL    MUSCLES. 

As  has  been  pointed  out.  the  history  of  the  anterior  two  groups  of  myotomes, 
supplied  by  cranial  nerves,  differs  somewhat  from  that  of  the  remaining  ones,  and 
it  is  convenient,  therefore,  to  consider  the  muscles  derived  from  these  myotomes 
separately  from  the  rest. 

I.     THE   ORBITAL   MUSCLES. 


1.  Levator  palpebrae  superioris. 

2.  Rectus  superior. 

3.  Rectus  internus. 


4.  Rectus  inferior. 

5.  Rectus  externus. 

6.  Obliquus  superior. 


7.    Obliquus  inferior. 

The  most  anterior  of  the  persistent  myotomes  are  three  in  number,  supplied  by 
the  oculo-motor,  trochlear,  and  abducent  nerves.  They  give  rise  to  the  muscles 
situated  in  the  orbit. 


FIG.  514. 


i.    LEVATOR  PALPEBRAE  SUPERIORIS  (Fig.  516). 

Attachments. — The  levator  palpebrae  superioris  is  a  rather  slender  muscle 
which  lies  in  the  greater  portion  of  its  course  immediately  beneath  the  periosteal 
lining  of  the  roof  of  the  orbit.  It  arises  at  the  back  of  the  orbit,  a  short  distance 

above  the  upper  margin  of 
the  optic  foramen,  and  is 
directed  forward,  broad- 
ening as  it  goes,  to  be  in- 
serted by  a  broad  aponeu- 
rosis  principally  into  the 
upper  border  of  the  tarsal 
plate  of  the  upper  eye- 
lid, the  uppermost  til>iv> 
mingling  somewhat  with 
those  of  the  palpebral 
portion  of  the  orbicularis 
oculi. 

The  aponeurosis  by 
which  the  levator  inserts 
into  the  tarsal  plate  is 
largely  composed  of  non- 
striated  muscular  fibres, 
which  constitute  what  has 
been  termed  the  orbito- 
palpcbral  muscle.  This 
is  triangular  in  shape. 
with  the  truncated  apex 
united  to  the  levator  and 
with  the  base  attached 
to  the  external  palpebral 

raphe,  the  tarsal  plate  of  the  upper  eyelid,  and  the  internal  palpebral  ligament. 
Nerve-Supply. — From  the  oculo-motor  nerve. 
Action. — To  draw  the  upper  eyelid  upward  and  backward. 
Relations. — Immediately  above  the  levator  palpebrae  superioris,  between  it  and 
the  periosteum  of  the  roof  of  the  orbit,  are  the  trochlear  and  frontal  nerves  and  the 
supra-orbital  vessels.      Below  it  rests  upon  the  medial  half  of  the  rectus  superior. 


Tendinous  loop 
for  sup.  oblique 

Superior  oblique, 
distal  part 

Internal  rectus__ 


Superior  oblique._; 
proximal  part 


Optic  nerve, 


vator  palpebrae  sup. 
.tipper  tarsal  plate 
Palpebral  fissure 

Superior  rectus 

Inferior  oblique 

External  rectus 


.Stutni)  of  levator 
palpebrse  superioris 


Ocular  muscles  seen  from  above  after  removal  of  roof  of  orbit ;  elevator  of 

uppt-r  o\vlid  has  been  rut  and  reflected  forward. 


THE   AXIAL   MUSCLES. 


2.  RECTUS  SUPERIOR  (Fig.  514). 

Attachments. — The  superior  rectus  arises  from  the  upper  portion  of  a  fibrous 
ring  termed  the  annulus  of  Zinn  (annulus  tendincus  communis),  which  surrounds  the 
optic  foramen  and  is  formed  by  a  thickening  of  the  orbital  periosteum  in  that  region. 
Thence  the  muscle  is  directed  forward  over  the  eyeball  and  is  inserted  into  the 
sclera  a  little  above  the  upper  margin  of  the  cornea. 

Nerve-Supply. — From  the  oculo-motor  nerve. 

Action. — To  rotate  the  eyeball  so  that  the  pupil  is  directed  upward  and  at  the 
same  time  somewhat  inward. 

3.  RECTUS  INTERNUS  (Fig.  514). 

Attachments. — The  internal  rectus  (m.  rectus  medialis)  arises  from  the  inner 
portion  of  the  annulus  tendineus  communis  and  passes  forward  along  the  inner  wall 
of  the  orbit  to  be  inserted  into  the  sclera  a  short  distance  behind  the  inner  margin  of 
the  cornea. 

Nerve-Supply. — From  the  oculo-motor  nerve. 

Action. — To  rotate  the  eyeball  so  that  the  pupil  is  directed  inward. 

FIG.  515. 

Superior  rectus  Levator  palpebra;  superioris 

/  Superior  oblique 

/  Trochlea,  tendon  of  superior 


Sphenoidal  fissure 
External  rectus 


Optic  nerve  (cut)  __ 


Spheno-inaxillary  fissure. 


Inferior  oblique 


oblique  in  place 


Internal  vectus 


Inferior  rectus 


Right  orbit  seen  from  before,  showing  stumps  of  ocular  muscles  attached  to  common  tendinous  ring  of  origin. 

4.  RECTUS  INFERIOR  (Fig.  516). 

Attachments. — The  inferior  rectus  arises  from  the  lower  portion  of  the  com- 
mon tendinous  ring,  its  line  of  origin  being  continuous  with  that  of  the  rectus  interims. 
It  is  inserted  into  the  sclera  a  short  distance  below  the  inferior  margin  of  the  cornea. 

Nerve-Supply. — From  the  oculo-motor  nerve. 

Action. — To  rotate  the  eyeball  so  that  the  pupil  is  directed  downward  and  at 
the  same  time  somewhat  inward. 

5.  RECTUS  EXTERNUS  (Fig.  514). 

Attachments. — The  external  rectus  (m.  rectus  lateralis)  arises  by  two  heads, 
one  of  which  is  attached  to  the  lower  and  outer  portion  of  the  common  tendinous  ring 
and  to  the  spine  on  the  lower  border  of  the  sphenoidal  fissure,  and  the  other  to  the 
upper  and  outer  part  of  the  common  tendinous  ring.  It  passes  along  the  outer  wall 
of  the  orbit  and  is  inserted  into  the  sclera  a  little  behind  the  outer  border  of  the  cornea. 

Nerve-Supply. — From  the  abducens  or  sixth  nerve. 

Action. — To  rotate  the  eyeball  so  that  the  pupil  is  directed  outward. 

Relations. — Between  the  two  heads  of  the  external  rectus  there  pass  the  oculo- 
motor, nasal,  and  abducent  nerves  and  the  ophthalmic  vein. 


504 


HUMAN    ANATOMY. 


6.    OBLIQUUS  SUPERIOR  (Figs.  514,  516). 

Attachments. — The  superior  oblique  muscle  of  the  eyeball  arises  a  little  in 
front  of  the  inner  part  of  the  optic  foramen  and  passes  forward  along  the  upper  and 
inner  wall  of  the  orbit  to  terminate  in  a  round  tendon  which  passes  through  a  ten- 
dinous loop,  the  trochlea,  attached  to  the  fovea  trochlearis  of  the  frontal  bone. 
Thence  it  is  reflected  outward,  downward,  and  backward,  and,  passing  beneath  the 
superior  rectus,  is  inserted  into  the  sclera  beneath  the  outer  margin  of  that  muscle 
and  at  about  the  equator  of  the  eyeball. 

Nerve-Supply. — From  the  trochlearis  or  fourth  nerve. 

Action. — To  rotate  the  eyeball  so  that  the  pupil  is  directed  inward  and 
downward. 

FIG.  516. 


Levator  palpebrae  superioris  — 


Superior  oblique 
Superior  rectus 
External  rectus  (cut) 

Internal  rectus 
Optic  nerve 
Stump  of  external  rectus 


,- Insertion  of  levator  palpebra- 
superioris  into  upper  larval 
plate 


Inferior  oblique 


Inferior  rectus 


Lateral  view  of  ocular  muscles  after  removal  of  outer  wall  of  orbit ;  elevator  of  upper  lid  has  been  pulled 

upward  and  inward. 

7.    OBLIQUUS  INFERIOR  (Fig.  516). 

Attachments. — The  inferior  oblique  muscle  arises  near  the  margin  of  the 
orbit  from  a  small  depression  on  the  orbital  surface  of  the  maxilla.  It  is  directed  out- 
ward, backward,  and  upward,  and,  passing  between  the  inferior  rectus  and  the  floor 
of  the  orbit,  is  inserted  into  the  sclera  a  little  behind  the  equator  of  the  eyeball  and 
under  cover  of  the  external  rectus. 

Nerve-Supply. — From  the  oculo-motor  nerve. 

Action. — To  rotate  the  eyeball  so  that  the  pupil  is  directed  upward  and  outward. 

Fasciae  of  the  Orbit. — The  muscles,  nerves,  and  vessels  of  the  orbit  are  em- 
bedded in  a  mass  of  loose  areolar  tissue  which,  abundantly  intermingled  with  a  soft 
fat,  completely  fills  the  orbital  cavity.  Around  the  vessels,  nerves,  and  muscles  this 
areolar  tissue  condenses  to  form  their  sheaths,  and  a  special  condensation,  the 
capsule  of  Tenon  (fascia  bulbi),  surrounds  the  posterior  four-fifths  of  the  eyeball, 
forming  a  socket  for  it.  The  inner  surface  of  this  capsule  is  smooth  and  is  united  to 
the  outer  surface  of  the  sclera  only  by  lax  and  slender  bands  of  fibres  which  traverse 
a  distinct  lymph-space  termed  the  space  of  Tenon  (spatium  intcrfasciale),  which  inter- 
venes between  the  capsule  and  the  eyeball,  thus  facilitating  the  movements  of  the 
latter  in  the  socket.  Posteriorly  the  capsule  is  continuous  with  the  sheath  of  the 
optic  nerve  and  anteriorly  it  joins  with  the  conjunctiva  anterior  to  the  line  of  insertion 
of  the  rectus  muscles  into  the  sclera.  The  tendons  of  the  rectus  muscles  conse- 
quently perforate  the  capsule,  which  is  prolonged  backward  upon  the  tendons  for  a 
short  distance, — in  the  case  of  the  superior  oblique  as  far  as  the  trochlea. — and  then 
becomes  continuous  with  the  areolar  sheaths  of  the  muscles  which  arc  intimately 


THE   AXIAL   MUSCLES. 


505 


adherent  to  the  muscle-tissue  and  constitute  the  fasciae  rausculares.  These  fasciae  are 
somewhat  thicker  in  their  anterior  portions  than  more  posteriorly,  and  give  off  pro- 
longations to  neighboring  parts.  From  the  fascia  of  the  rectus  superior  a  prolonga- 
tion passes  to  join  the  tendon  of  the  levator  palpebrae  superioris,  and  one  from  the 
rectus  inferior  passes  to  the  lower  border  of  the  tarsal  plate  of  the  lower  eyelid,  these 
two  recti  thus  acquiring  a  certain  amount  of  action  upon  the  eyelids.  From  the 
lateral  surface  of  the  fascia  of  the  external  rectus  a  rather  strong  prolongation  is 
given  off  which  attaches  to  the  orbital  surface  of  the  zygomatic  bone,  forming  what 
has  been  termed  the  external  check  ligament  of  the  eyeball,  while  from  the  medial 
surface  of  the  fascia  of  the  internal  rectus  a  similar,  although  somewhat  laxer,  prolon- 
gation passes  to  the  crest  of  the  lachrymal  bone  and  the  reflected  portion  of  the 
internal  palpebral  ligament. 

The  Movements  of  the   Eyeball. — The  four  recti  muscles  of  the  eyeball 
may  be  regarded  as  forming  a  cone  whose  apex  is  at  the  annulus  tendineus  communis 

FIG.  517. 

Levator  palpebrse  superioris 

Fat 

Superior  rectus 
Capsule  of  Tenon 
Superior  oblique  (cut)   \ 

c-^»  \         \     s 


Fat 


Optic  nerve 

\ 


Inferior  rectus 


-ri — Septum  orbitale 


Upper  tarsal  plate 

Lower  tarsal  plate 

Space  of  Tenon 
Septum  orbitale 


Inferior  oblique 


Diagrammatic  sagittal  section  through  orbit,  showing  relations  of  fascia  to  muscles,  eyeball,  and  orbital  wall. 

and  the  base  at  the  insertions  of  the  muscles  into  the  sclera.  The  line  joining  the 
insertions  of  the  muscles  is  not,  however,  a  circle,  but  rather  a  spiral,  the  insertion 
of  the  internal  rectus  being  nearest  to  and  that  of  the  rectus  superior  farthest  from 
the  edge  of  the  cornea.  The  axis  of  the  cone  does  not  correspond  in  direction  with 
the  antero- posterior  axis  of  the  eyeball,  but,  owing  to  the  divergence  of  the  axes  of 
the  two  orbits,  is  inclined  to  it  from  within  outward  at  an  angle  of  about  20°. 

It  follows  from  this  that  during  the  contraction  of  either  the  superior  or  infe- 
rior rectus  the  axis  of  rotation  of  the  eyeball  will  not  coincide  with  its  transverse 
axis,  but  will  be  inclined  to  it  (Fig.  518),  and  consequently  the  action  of  either  of 
these  muscles  in  directing  the  pupil  upward  or  downward  will  be  complicated  by  a 
certain  amount  of  oblique  movement,  in  the  one  case  inward  and  in  the  other  case 
outward.  In  producing  purely  upward  or  downward  movements  of  the  pupil  the 
rectus  muscles  are  associated  with  the  oblique  ones,  the  coordination  of  the  inferior 
oblique  with  the  superior  rectus  producing  a  purely  upward  rotation,  while  that  of  the 
superior  oblique  with  the  inferior  rectus  produces  a  purely  downward  movement. 


5o6 


HUMAN   ANATOMY. 


FIG.  518. 


It  has  been  demonstrated  also  that  the  oblique  movements  of  the  eyeball  are  by 
no  means  due  to  the  action  of  the  superior  and  inferior  oblique  muscles  acting  alone', 

but  that  in  every  such  movement  there  is 
a  coordination  of  two  of  the  recti  muscles 
with  one  of  the  obliques.  Thus,  in  rotations 
which  direct  the  pupil  upward  and  inward 
the  superior  and  internal  recti  cooperate  with 
the  inferior  oblique,  and  in  the  downward 
and  outward  movements  the  inferior  and 
external  recti  cooperate  with  the  superior 
oblique. 

A  purely  outward  or  inward  rotation 
can  be  produced  by  the  action  of  the  external 
or  internal  rectus,  as  the  case  may  be.  But 
it  is  to  be  noted  that  the  movements  of  the 
eyeball  are  always  bilateral,  and  that  the  in- 
ward rotation  of  the  one  eye  is  generally  as- 
sociated with  the  outward  rotation  of  the 
other,  the  combined  movements  thus  re- 
quiring the  cooperation  of  different  muscles. 
In  all  movements  of  the  eyeballs  there 
is,  accordingly,  a  coordination  of  various 
orbital  muscles,  and  when  the  combined 
oblique  movements  are  performed  this  co- 
ordination becomes  somewhat  complicated. 
The  direction  of  both  pupils  upward  and  to 
the  right  requires  the  coordination  in  the 
right  eye  of  the  inferior  oblique  and  the  su- 
perior and  external  recti  and  in  the  left  eye  of  the  inferior  oblique  and  the  superior 
and  internal  recti. 

Variations. — But  few  variations  have  been  observed  in  the  orbital  muscles.  Absence 
of  the  levator  palpebrae  superioris  has  been  noted,  and  a  slip  from  this  muscle,  termed  the 
tensor  trochlece,  sometimes  passes  to  the  trochlea. 


E  i 

Diagram  showing  action  of  ocular  muscles.  S,  S\, 
Q,Q\,  sagittal  and  transverse  axes  of  eyeball;  di- 
rection of  pull  of  muscles  is  indicated  by  lines ; 
dotted  lines  indicate  axes  around  which  superior 
and  inferior  recti  and  oblique  muscles  rotate  eye- 
ball ;  vertical  axis  (O)  corresponds  to  axis  of  rota- 
tion of  internal  and  external  recti.  (Landois.) 


II.   THE   HYPOGLOSSAL   MUSCLES. 


1.  Genio-glossus. 

2.  Hyo-glossus. 


3.  Stylo-glossus. 

4.  Lingualis. 


It  is  well  known  that  the  hypoglossal  nerve  represents  the  anterior  roots  of 
three  spinal  nerves  which  have  secondarily  been  taken  up  into  and  consolidated  with 
the  cranial  region.  Corresponding  to  these  three  nerves  are  three  myotomes  which 
combine  to  give  rise  to  muscles  connected  with  the  tongue. 

i.   GEMO-GLOSSUS  (Fig.  1339). 
The  genio-glossus  is  described  with  the  tongue  (page  1578). 

2.   HYO-GLOSSUS  (Fig.  1339). 
The  hyo-glossus  is  described  with  the  tongue  (page  1578). 

Variations. — The  fibres  which  arise  from  the  lesser  cornn  of  tin-  hyoid  hone  are  frequently 
separate  from  the  rest  of  the  muscle  and  have  been  described  as  the  ckottdro-gloSSUS^  and  the 
fibres  arising  from  the  body  of  the  hyoid  are  frequently  separated  by  a  distinct  interval  from 
those  arising  from  tin-  greater  cornu,  the  former  constituting  a  muscle  which  has  been  termed 
the  Inixio-g/osstis  and  the  latter  the  t-t'ni/i)-^r/oxxnx.  A  bundle  of  fibres,  forming  what  has  been 
termed  the  />  i/icco-gti>ssns.  sometimes  arises  from  the  carti'la^o  triticea.  situated  in  the  lateral 
hvo-thyroid  ligament,  and  passes  upward  and  forward  to  insert  nloiiii  with  tin-  posterior  fibres 
of  the  hyo-glossus. 


THE   TRUNK    MUSCLES.  507 

3.   STYLO-GLOSSUS  (Fig.  1339). 
The  stylo-glossus  is  described  with  the  tongue  (page  1579). 

Variations. — The  stylo-glossus  is  occasionally  absent,  and  may  in  such  cases  be  replaced 
by  a  mylo-glossus,  which  arises  from  the  inner  surface  of  the  angle  of  the  mandible  or  from  the 
stylo-mandibular  ligament  and  is  inserted  into  the  sides  and  under  surface  of  the  tongue. 
This  muscle  is  usually  present  in  the  form  of  some  small  bundles  of  fibres  having  the  attach- 
ments described. 

4.   LINGUALIS  (Fig.  1340). 
The  lingualis  is  described  with  the  tongue  (page  1579). 

III.    THE   TRUNK   MUSCLES. 

THE  DORSAL  MUSCLES. 

In  employing  the  term  dorsal  to  indicate  a  group  of  muscles  it  must  be  clearly 
understood  that  the  group  does  not  include  all  the  muscles  which,  in  the  adult  con- 
dition, are  found  upon  the  dorsal  surface  of  the  body.  The  term,  so  far  as  it  has 
a  topographic  significance,  refers  to  a  phylogenetic  stage  in  which  the  muscles  it  is 
intended  to  designate  were  the  only  dorsal  muscles,  and,  as  here  employed,  it  indi- 
cates only  those  muscles  which  are  derived  from  the  dorsal  portions  of  the  embryonic 
myotomes  and  are  supplied  by  the  posterior  divisions  (dorsal  rami)  of  the  spinal 
nerves. 

An  examination  of  the  muscles  of  the  back  readily  shows  that  they  consist  of 
two  distinct  sets.  There  is  a  superficial  set,  consisting  of  broad  and  flat  muscles, 
which  are,  with  few  exceptions,  attached  to  the  skeleton  of  the  fore-limb,  and  a 
deeper  set,  consisting  of  elongated  and  relatively  thick  muscles,  whose  attachments 
are  confined  to  portions  of  the  axial  skeleton.  The  muscles  of  the  former  set,  which 
may  conveniently  be  designated  the  spino-humeral  muscles,  are  all  supplied  by 
branches  from  the  ventral  rami  of  the  spinal  nerves  ;  they  have  reached  their 
present  position,  in  which  they  almost  completely  cover  in  the  true  dorsal  muscles, 
by  a  secondary  migration  from  the  more  ventral  portions  of  the  trunk,  and  prop- 
erly belong  to  the  system  of  limb  muscles,  in  connection  with  which  they  will  be 
described. 

The  true  axial  dorsal  muscles  are  all  included  in  the  deeper  set.  Viewed  from 
the  surface,  they  appear  to  form  elongated  columns  of  muscle-tissue,  extending  con- 
tinuously, more  or  less  parallel  with  the  spinal  column,  over  considerable  stretches 
of  the  back  ;  but  when  the  more  superficial  portions  of  the  columns  are  removed,  it 
will  be  seen  that  the  deeper  portions  are  associated  with  the  individual  vertebrae, 
their  fibres  possessing  a  more  or  less  distinct  segmental  arrangement.  The  columns, 
indeed,  are  to  be  regarded  as  formed  by  the  fusion  of  a  number  of  originally  inde- 
pendent muscle-segments,  derived  from  the  dorsal  portions  of  a  corresponding 
number  of  myotomes,  a  mode  of  formation  also  indicated  by  the  fact  that  the 
columns  are  supplied  by  nerves  from  a  greater  or  less  number  of  successive  spinal 
nerves,  from  just  as  many,  indeed,  as  there  are  myotomes  entering  into  their 
composition. 

Comparative  anatomy  demonstrates  that  the  dorsal  musculature  may,  further- 
more, be  regarded  as  consisting  of  two  parallel  portions  or  tracts,  a  median  and  a 
lateral.  The  former  portion,  which  includes  the  majority  of  the  dorsal  muscles,  is 
composed  of  those  muscles  which  fundamentally  arise  from  the  transverse  processes 
of  the  vertebrae  and  are  inserted  into  the  spinous  processes,  and  may  therefore  be 
termed  the  transverso-spinal  portion  ;  while  the  more  lateral  tract  consists  of  mus- 
cles which,  taking,  their  origin  primarily  from  the  transverse  processes,  are  inserted 
into  the  ribs  or  their  homologues,  and  may  accordingly  be  termed  the  transverso- 
costal  portion.  A  certain  amount  of  overlapping  of  the  median  tract  by  the  lateral 
one  occurs  in  man  ;  indeed,  in  the  lumbar  region  the  two  tracts  fuse  to  a  certain 
extent  to  form  the  sacro-spinalis  ;  but  throughout  the  thoracic  and  cervical  regions 
they  are  fairly  distinct. 


5o8 


HUMAN    ANATOMY. 


Psoas  magnus 
Lumbar  vertebra 


Subperitoneal  tissue 
1     Fascia        Peritoneum 


The  deep  fascia  of  the  back  invests  all  the  muscles  of  the  dorsal  group, 
separating  them  from  the  spino-humeral  group.  Above,  the  fascia  is  not  especially 
strong,  and  in  the  cervical  and  upper  thoracic  regions  forms  what  is  termed  the 
fascia  nuchae,  which  lies  beneath  the  trapezius  and  rhomboid  muscles.  In  the  lower 
thoracic  and  lumbar  regions,  however,  the  fascia  becomes  considerably  thickened, 
especially  that  portion  which  invests  the  sacro-spinalis  (vertebral  aponcurosis),  form- 
ing a  strong  rhomboidal  sheet  extending  from  about  the  level  of  the  sixth  thoracic 
vertebra  to  the  tip  of  the  sacrum,  its  anterior  borders  giving  attachment  to  various 
muscles,  while  the  posterior  ones  are  attached  to  the  posterior  portions  of  the  iliac 

crests,  where  it  becomes  contin- 

FIG.  519.  uous  with  the  fascia  lata  covering 

the  gluteal  muscles. 

This  dense  layer  is  termed 
the  fascia  lunibo-dorsalis  (Fig. 
559),  and  is  generally  regarded 
as  consisting  of  two  lateral  por- 
tions which  are  practically  united 
in  the  mid-dorsal  line  by  their 
common  attachment  to  the  spi- 
nous  processes  of  the  vertebrae 
and  the  supraspinous  ligaments. 
Each  of  these  lateral  portions  is 
again  considered  as  consisting 
of  two  layers  which  together 
invest  the  sacro-spinalis  ( Fig. 
519),  the  posterior  layer  being 
that  which  has  already  been  described,  while  the  anterior  layer  is  attached  medially 
to  the  tips  of  the  transverse  processes  of  the  lumbar  vertebrae,  above  to  the  lower 
border  of  the  twelfth  rib,  and  below  to  the  crest  of  the  ilium.  It  passes  outward 
beneath  the  sacro-spinalis,  separating  it  from  the  quadratus  lumborum,  and  at  the 
outer  border  of  the  former  muscle  it  fuses  with  the  posterior  layer  to  form  a  strong 
aponeurotic  band,  from  which  the  latissimus  dorsi  and  the  internal  oblique  and  trans- 
verse abdominal  muscles  take  partial  origin,  and  which  is  continued  ventrally  over 
the  inner  surface  of  the  transversus  abdominis  as  \hzfascia  transversalis. 


Lumbar  spine 

Skin 


.Transversalis  fascia; 

;. ..'..- Transversalis  muscle 

Internal  oblique 
— External  oblique 

/--Triangle  of  Petit 
^Quadratus  lumborum 

Latissimus  dorsi 
Ant.  layer  of  lumbo-dorsal  fascia 

r  Superficial  fascia 

Posterior  layer  of  lumbo-dorsal  fascia 
Sacro-spinalis 


Diagram  showing  formation  and  relations  of  lumbo-dorsal  fascia 
to  muscles  of  body-wall. 


(a)    THE  TRANSVERSO-COSTAL  TRACT. 

1 .  Sacro-spinalis. 

2.  Ilio-costalis. 


3.  Longissimus. 

4.  Splenius. 


i.    SACRO-SPINALIS  (Fig.  520). 

Attachments. — The  sacro-spinalis,  sometimes  termed  the  erector  spina,  forms 
a  large  muscular  mass  occupying  the  lumbar  portion  of  the  vertebral  groove.  It 
takes  its  origin  from  the  under  surface  of  the  lumbo-dorsal  fascia,  the  crest  of 
the  ilium,  the  posterior  surface  of  the  sacrum,  and  the  spines  of  the  lumbar  ver- 
tebrae. Anteriorly  it  divides  into  three  separate  muscles,  two  of  which,  the  ilio- 
costalis  and  the  longissimus,  belong  to  the  transverso-costal  group,  while  the  third, 
the  spinalis,  is  a  member  of  the  transverso-spinal  series. 

Nerve-Supply. — The  posterior  divisions  of  the  lumbar  nerves. 


2.      ILIO-COSTALIS  (Fig.   520). 

Attachments. — The  ilio-costalis,  also  termed  the  sacro-/u^tba/is,  is  the  most 
lateral  of  the  three  muscles  into  which  the  sacro-spinalis  divides,  and  is  the  forward 
continuation  of  the  portion  of  that  muscle  which  arises  from  the  crest  of  the  ilium. 
The  muscle  is  continued  upward  in  the  vertebral  groove  immediately  internal  to  the 
angles  of  the  ribs  as  far  as  the  fourth  cervical  vertebra,  receiving,  however,  acces- 
sions from  the  ribs  as  it  passes  over  them.  The  fibres  which  arise  from  the  iliac 


THE   TRUNK    MUSCLES. 


509 


FIG.  520. 


Obliquus  superior 


Trachelo-mastoi  d 
Levator  anguli  scapulae 

;  colli 

Cervicalis  ascendens 
Transversalis  cervicis 


Rectus  capitis  posticus  minor 
Rectus  capitis  posticus  major 

Obliquus  inferior 


Semispinalis  capitis 

(complexus  and  biventer) 

Levator  anguli  scapulse 
Semispinalis  colli 


Accessor!  us 
(ilio-costalis  dorsi) 


Spinalis  dorsi 


I.ongissimus  dorsi 


Ilio-costalis 
(ilio-costalis  lumborum) 


Sacro-spinalis 
(erector  spinae) 


Quadratus  lumborum 
Multifidus  spinae 


Dissection  c>f  muscles  of  back,  showing  transverso-costal  and  transverso-spinal  tracts. 


5io  HUMAN   ANATOMY. 

crest  are  mainly  inserted  into  the  lower  six  or  seven  ribs,  and  form  what  is  termed  the 
ilio-costalis  lumborum.  With  the  remainder  of  the  iliac  fibres  bundles  arising  from 
the  lower  five,  six,  or  seven  ribs  associate  themselves  to  form  the  ilio-costalis  dorsi, 
also  termed  the  accessorius,  which  inserts  into  the  upper  five  or  six  ribs  ;  and,  finally, 
the  uppermost  portion  of  the  muscle,  the  ilio-costalis  cervicis  or  cervicalis  ascendens,  is 
formed  by  the  union  of  bundles  arising  from  the  upper  six  or  seven  ribs,  and  is  in- 
serted into  the  posterior  tubercles  of  the  transverse  processes  of  the  fourth,  fifth,  and 
sixth  cervical  vertebrae. 

Nerve-Supply. — From  the  posterior  divisions  of  the  spinal  nerves  from  the 
lower  cervical  to  the  first  lumbar. 

Action. — The  various  portions  of  the  ilio-costalis  tend  to  bend  the  spinal 
column  backward  in  the  lower  cervical,  thoracic,  and  lumbar  regions,  and  also  to 
draw  it  somewhat  to  one  side.  They  may  likewise  have  some  action  in  drawing 
down  the  ribs,  assisting  in  forced  expiration. 

3.    LONGISSIMUS  (Fig.  520). 

Attachments. — -The  longissimus  represents  the  upward  prolongation  of  that 
portion  of  the  sacro-spinalis  which  arises  from  the  dorso-lumbar  fascia  and  the 
lumbar  vertebrae.  It  is  continued  upward  immediately  medial  to  the  ilio-costalis  to 
be  inserted  into  the  mastoid  process  of  the  temporal  bone,  but,  like  the  ilio-costalis, 
it  receives  in  its  course  accessory  bundles  and  also  gives  off  bundles  which  are 
inserted  into  the  skeletal  parts  over  which  it  passes. 

The  fibres  which  represent  the  direct  continuation  of  the  sacro-spinalis  are  con- 
tinued as  far  upward  as  the  first  thoracic  vertebra,  and  are  reinforced  by  short  acces- 
sory bundles  from  the  transverse  processes  of  the  lower  six  thoracic  vertebrae  to  form 
what  is  termed  the  longissimus  dorsi.  The  fibres  of  this  portion  of  the  muscle  are 
inserted  along  two  lines,  the  medial  of  which  passes  along  the  accessory  processes  of 
the  lumbar  vertebrae  and  the  transverse  processes  of  all  the  thoracic  vertebrae,  while 
the  lateral  line  passes  along  the  transverse  processes  of  the  lumbar  vertebrae  and  the 
angles  of  the  ribs  as  far  forward  as  the  second.  From  the  transverse  processes  of 
the  upper  six  thoracic  vertebrae  bundles  arise  which  unite  to  form  the  longissimtis 
cervicis  or  transversalis  cervicis,  which  continues  the  line  of  the  longissimus  to  an 
insertion  into  the  posterior  tubercles  of  the  transverse  processes  of  the  second  to 
the  sixth  cervical  vertebrae  ;  and,  finally,  the  longissimus  capitis  or  trachelo-mastoid 
is  formed  by  bundles  arising-  from  the  transverse  processes  of  the  three  upper 
thoracic  vertebrae  and  the  articular  processes  of  the  three  lower  cervical,  and  passes 
upward  to  be  inserted  into  the  mastoid  process  of  the  temporal  bone. 

Nerve-Supply. — From  the  posterior  divisions  of  the  spinal  nerves  from  the 
third  cervical  to  the  second  sacral. 

Action. — The  thoracic  and  cervical  portions  of  the  longissimus  will  draw  the 
spinal  column  backward  and  to  one  side  ;  the  longissimus  capitis  will  have  a  similar 
action  on  the  head. 


4.    SPLENIUS  (Fig.  520). 


10US 


Attachments. — The  splenius  forms  a  flat  muscle  which  arises  from  the  spino 
processes  of  the  upper  four  or  six  thoracic  and  the  seventh  cervical  vertebrae  and 
from  the  lower  half  of  the  ligamentum  nuclue.  It  passes  upward  and  slightly 
laterally  and  divides  into  two  portions,  the  lower  of  which,  curving  around  the  outer 
edge  of  the  upper  portion,  passes  to  an  insertion  in  tin-  posterior  tubercles  of  the 
upper  three  cervical  vertebrae,  forming  the  s/>/cniits  cervicis.  The  upper  portion, 
which  is  termed  the  splenius  cn/iitis,  continues  upward,  and  is  inserted  by  a  short 
tendon  into  the  posterior  border  of  the  mastoid  process  of  the  temporal  bone  and 
into  the  outer  part  of  the  superior  nuchal  line. 

Nerve-Supply. — From  the  posterior  divisions  of  the  second  to  the  eighth  cer- 
vical nerves. 

Action. — The  splenius  cervicis  will  draw  the  upper  cervical  vertebra-  backward 
and  will  rotate  the  atlas  towards  the  side  of  the  muscle  in  actiori.      The  action  of 


THE   TRUNK   MUSCLES.  511 

the  splenius  capitis  upon  the  head  will  be  similar  ;  the  simultaneous  action  of  the  two 
muscles  of  opposite  sides  will  bend  the  head  backward,  each  muscle  neutralizing  the 
rotatory  effect  of  the  other. 

(6)    THE  TRANSVERSO-SPINAL  TRACT. 

1.  Spinalis.  6.  Intertransversales. 

2.  Semispinalis.  7.  Rectus  capitis  posticus  major. 

3.  Multifidus.  8.  Rectus  capitis  posticus  minor. 

4.  Rotatores.  9.  Obliquus  capitis  superior. 

5.  Interspinales.  10.  Obliquus  capitis  inferior. 

i.    SPINALIS  (Fig.  520). 

Attachments. — The  spinalis  in  its  lower  portion  is  the  continuation  of  the 
deeper  and  innermost  fibres  of  the  sacro-spinalis,  and,  like  the  longissimus,  with 
which  it  is  partly  associated,  it  is  regarded  as  consisting  of  a  thoracic,  a  cervical, 
and  a  cranial  portion.  The  spinalis  dorsi  arises  from  the  spinous  processes  of  the 
upper  two  lumbar  and  the  lower  two  or  three  thoracic  vertebrae  by  tendons  common 
to  it  and  the  longissimus  dorsi.  It  forms  a  thin,  flat  muscle  which  passes  upward, 
inserting  as  it  goes  into  the  spinous  processes  of  the  thoracic  vertebrae  from  the 
second  to  the  eighth  or  ninth,  but  one  vertebra  intervening  between  its  uppermost 
tendon  of  origin  and  its  lowermost  tendon  of  insertion.  The  spinalis  cervicis  arises 
from  the  spinous  processes  of  the  upper  two  or  four  thoracic  and  the  lower  two 
cervical  vertebras,  and  ascends  alongside  the  spinous  processes  of  the  cervical  ver- 
tebras to  be  inserted,  into  those  of  the  second,  third,  and  fourth  vertebras.  The 
spinalis  capitis  consists  of  bundles  arising  from  the  spinous  processes  of  the  upper 
thoracic  and  last  cervical  vertebrae,  and  passes  upward  to  be  inserted  with  the  semi- 
spinalis  capitis. 

Nerve-Supply. — From  the  posterior  divisions  of  the  spinal  nerves  from  the 
third  cervical  to  the  last  thoracic. 

Action. — To  extend  the  spinal  column. 

2.    SEMISPINALIS    (Fig.  520). 

Attachments. — The  semispinalis  forms  the  superficial  layer  of  the  muscles 
lying  in  the  groove  between  the  spinous  and  transverse  processes  of  the  vertebras. 
Three  portions  may  be  recognized  in  it.  The  semispinalis  dorsi  arises  from  the  trans- 
verse processes  of  the  lower  six  or  seven  thoracic  vertebrae  ;  its  fibres  are  directed 
obliquely  upward  and  medially  and  are  inserted  into  the  spinous  processes  of  the  five  or 
six  upper  thoracic  and  last  two  cervical  vertebrae.  The  semispinalis  cervicis  arises 
from  the  transverse  processes  of  the  five  or  six  upper  thoracic  vertebrae  and  is  inserted 
into  the  spinous  processes  of  the  second,  third,  fourth,  fifth,  and  sometimes  the  sixth 
cervical  vertebras.  This  portion  of  the  muscle  is  almost  concealed  beneath  the  upper- 
most portion,  the  semispinalis  capitis,  which  arises  from  the  transverse  processes  of  the 
upper  six  thoracic  vertebrae  and  the  articular  and  transverse  processes  of  the  lower 
three  or  four  cervical  vertebras.  The  fibres  are  directed  almost  vertically  upward, 
and  are  joined  by  the  spinalis  capitis  to  form  a  broad  muscle-sheet  which  is  inserted 
into  the  under  surface  of  the  squamous  portion  of  the  occipital  bone  between  the 
superior  and  inferior  nuchal  lines. 

An  intermediate  tendinous  intersection  usually  divides  the  semispinalis  capitis 
into  an  upper  and  a  lower  portion,  and  is  much  more  distinct  in  the  more  medial 
bundles  than  in  the  lateral  ones.  Frequently  these  more  medial  bundles  are  sep- 
arated somewhat  from  the  others,  and  they  have  been  considered  a  distinct  muscle 
and  termed  the  biventer,  the  lateral  portion  of  the  muscle  being  named  the  complexus. 

Nerve-Supply. — From  the  posterior  divisions  of  the  spinal  nerves  from  the 
second  cervical  to  the  last  thoracic. 

Action. — The  semispinalis  dorsi  and  cervicis  extend  the  vertebral  column  and 
rotate  it  somewhat  towards  the  opposite  side.  The  semispinalis  capitis  draws  the 
head  backward  and  also  rotates  it  slightly  towards  the  opposite  side. 


512 


HUMAN   ANATOMY. 


3.     MULTIFIDUS    (FigS.   520,   52l). 

Attachments.  —  The  multifidus  (multifidus  spina}  constitutes  the  middle  layer 
of  the  muscles  occupying  the  groove  between  the  transverse  and  spinous  processes 


;.  521 


Intertrans 
poste 


Interspinales 


Levatores  costarum 


Rotatores 


Levatores  costarum 


Interspinales. 


Intertransversales 
laterales 


Deep  muscles  of  kick. 


Multifidus 


Multifidus 


of  the  vertebra,  and  is  covered,  in  the  thoracic  and  cervical  regions,  by  tin-  si-mi- 
spinalis.     It  takes  its  origin  from  the  dorsal  surface  of  the  sacrum  and  from  the  trans- 


THE   TRUNK    MUSCLES.  513 

verse  or  articulating  processes  of  all  the  vertebrae  as  far  up  as  the  fourth  cervical. 
The  fibres  from  each  vertebra  pass  over  from  two  to  four  of  the  succeeding  vertebrae 
and  are  inserted  into  the  spinous  processes  of  the  third  to  the  fifth,  the  entire  insertion 
of  the  muscle  extending  from  the  spinous  process  of  the  last  lumbar  vertebra  to  that 
of  the  axis. 

Nerve-Supply. — From  the  posterior  divisions  of  the  spinal  nerves  from  the 
third  cervical  to  the  last  lumbar. 

Action. — To  bend  the  spinal  column  backward  and  rotate  it  towards  the  op- 
posite side. 

4.     ROTATORES    (Fig.    52l). 

Attachments. — The  rotatores  (rotatores  dorsi)  form  the  deepest  layer  of  the 
muscles  occupying  the  spino-transverse  groove.  They  form  a  series  of  small  muscles 
hardly  distinguishable  from  the  bundles  of  the  multifidus,  beneath  which  they  lie. 
They  are  to  be  found  along  the  entire  length  of  the  spinal  column  from  the  sacrum  to 
the  axis,  arising-  from  the  transverse  process  of  one  vertebra  and  passing,  some  of  the 
fibres  to  the  base  of  the  spinous  process  of  the  next  succeeding  vertebra  {rotatores 
breves)  and  the  rest  to  a  corresponding  point  of  the  second  vertebra  above  {rotatores 
longi) . 

Nerve-Supply. — From  the  posterior  divisions  of  the  spinal  nerves  from  the 
third  cervical  to  the  last  lumbar. 

Action. — To  bend  the  spinal  column  backward  and  rotate  it  towards  the  op- 
posite side. 

5.   INTERSPINALES  (Fig.  521). 

Attachments. — The  interspinales  are  relatively  small  muscles  which  pass  be- 
tween the  spinous  processes  of  succeeding  vertebrae.  They  are  usually  absent 
throughout  the  greater  portion  of  the  thoracic  region,  occurring  only  in  connection 
with  the  first  and  the  last  two  spines,  but  they  are  exceptionally  well  developed  in 
the  lumbar  region  and  are  usually  paired  in  the  cervical  region,  where  they  stop  at 
the  axis. 

Nerve-Supply. — From  the  posterior  divisions  of  the  spinal  nerves  from  the 
third  cervical  to  the  fifth  lumbar. 

Action. — Acting  together  to  bend  the  cervical  and  lumbar  portions  of  the  spinal 
column  backward. 

6.    INTERTRANSVERSALES  (Fig.  521). 

Attachments. — The  name  intertransversales  (mm.  intertransversarii)  has  been 
applied  to  a  series  of  small  muscles  occurring  in  the  cervical  and  lumbar  regions  and 
extending  between  the  transverse  or  mammillary  processes  of  successive  vertebrae. 
In  each  of  the  regions  named  two  sets  of  intertransversales  are  recognized,  but  it 
seems  probable  that  only  one  of  the  sets  in  such  region  belongs  to  the  dorsal  group 
of  muscles.  This  set  will  alone  be  considered  here,  the  other  (anterior)  one  being 
described  with  the  ventral  muscles  of  the  regions  in  which  it  occurs. 

The  intertransversarii  posteriores  occur  only  in  the  cervical  region  and  extend 
between  the  posterior  tubercles  of  the  transverse  processes  of  succeeding  vertebrae. 
The  intertransversarii  mediales  occur  only  in  the  lumbar  region  and  extend  between 
the  mammillary  processes  of  successive  vertebrae. 

Nerve-Supply. — Probably  by  fibres  belonging  to  the  posterior  divisions  of  the 
cervical  and  lumbar  nerves,  but  it  is  at  present  insufficiently  determined. 

Action. — To  bend  the  cervical  and  lumbar  portions  of  the  vertebral  column 
laterally. 

7.    RECTUS  CAPITIS  POSTICUS  MAJOR  (Fig.  522). 

Attachments. — The  greater  straight  muscle  (m.  rectus  capitis  posterior  major) 
an'ses  from  the  apex  of  the  spinous  process  of  the  axis  and  passes  upward  and  out- 
ward, broadening  as  it  goes,  to  be  inserted  into  the  middle  portion  of  the  inferior 
nuchal  line. 

33 


5i4  HUMAN   ANATOMY. 

Nerve-Supply. — By  a  branch  from  the  posterior  division  of  the  suboccipital 
nerve. 

Action. — To  draw  the  head  backward  and  to  rotate  it  towards  the  same  side. 

8.    RECTUS  CAPITIS  POSTICUS  MINOR    (Fig.  522). 

Attachments. — The  lesser  straight  muscle  (m.  rcctus  capitis  posterior  minor) 
arises  from  the  posterior  tubercle  of  the  atlas  and  passes  upward,  broadening  as  it 
goes,  to  be  inserted  into  the  inner  portion  of  the  inferior  nuchal  line. 

Nerve-Supply. — By  a  branch  from  the  posterior  division  of  the  suboccipital 
nerve. 

Action. — To  draw  the  head  backward. 


FIG.  522. 


Rectus  capitis  posticus_iL_ 

minor 
Rectus  capitis  posticus — 3L- 

major 

Obliquus  superior » 

Suboccipital  triangle 5 

Obliquus  inferior 


Supraspinous  ligament 


Posterior  tubercle  of  atlas 
Transverse  process  of  atlas 


ilnterspinales 


Multifidus 


Deep  dissection  of  neck,  showing  suboccipital  group  of  muscles. 

9.    OBLIQUUS  CAPITIS  SUPERIOR  (Fig.  522). 

Attachments. — The  superior  oblique  muscle  of  the  head  arises  horn  the  trans- 
verse process  of  the  atlas  and  passes  upward  to  be  inserted  into  the  squamous  portion 
of  the  occipital  immediately  above  the  outer  part  of  the  inferior  nuchal  line. 

Nerve-Supply. — By  a  branch  from  the  posterior  division  of  the  suboccipital 
nerve. 

Action. — To  draw  the  head  backward  and  slightly  laterally. 

10.    OBLIQUUS  CAPITIS  INKKKIOK   (Fig.  522). 

Attachments. — The  inferior  oblique  muscle  of  the  head  arises  from  the  tip  of 
the  spinous  process  of  the  axis  and  is  directed  outward  and  upward  to  be  iiiti'rti'd  into 
the  transverse  process  of  the  atlas. 

Nerve-Supply. — By  a  branch  from  the  posterior  division  of  the  suboccipital 
nerve. 

Action. — To  rotate  the  axis  towards  the  same  side. 


THE   VENTRAL    MUSCLES.  515 

The  Sacro-Coccygeus  Posterior. — The  reduction  of  the  caudal  vertebrae  in  man,  indicated 
by  the  condition  of  the  coccygeal  vertebra;,  has  brought  about  a  reduction  of  the  terminal 
portion  of  the  dorsal  axial  musculature,  it  being,  as  a  rule,  represented  only  by  the  ligaments 
upon  the  dorsal  surface  of  the  coccyx.  Quite  frequently,  however,  muscular  fibres  occur  inter- 
mingled with  the  connective  tissue,  and  occasionally  a  distinct  muscle,  the  sacro-coccygeus 
posterior,  may  be  found,  extending  from  the  last  sacral  vertebra  or  even  from  the  greater  sacro- 
sciatic  ligament  to  the  coccyx. 

THE    VENTRAL    MUSCLES. 

The  ventral  trunk  musculature  includes  all  those  axial  muscles  which  are  supplied 
from  the  anterior  divisions  (ventral  rami)  of  the  spinal  nerves.  As  already  indicated 
(page  473),  it  is  divisible  into  three  subgroups  :  a  group  of  more  median  muscles,  char- 
acterized by  their  fibres  retaining  more  or  less  perfectly  a  longitudinal  direction  and 
constituting  the  rcctus  group ;  a  more  lateral  group,  in  which  the  fibres  possess  a 
distinctly  oblique  or  transverse  direction,  and  may  consequently  be  termed  the 
obliqiius  group  ;  and,  finally,  a  hyposkcletal group,  whose  fibres  have  a  longitudinal 
direction,  and  which  is  situated  anterior  or  ventral  to  the  spinal  column. 

Instead  of  considering  the  various  muscles  belonging  to  each  of  these  groups  in 
succession,  it  seems  more  convenient  to  combine  a  topographic  classification  with 
the  morphological  one,  and  to  describe  the  various  groups  as  they  occur  in  the  neck, 
thoracic,  abdominal,  and  perineal  regions.  It  must  be  understood,  however,  that 
the  delimitations  of  these  regions  are  somewhat  arbitrarily  chosen,  and  that  there  is, 
so  far  as  the  muscles  are  concerned,  a  considerable  amount  of  overlapping  of  certain 
regions,  portions  of  myotomes  which  strictly  belong  to  the  thoracic  region,  for 
instance,  being  found  within  the  limits  of  what  is  recognized  as  the  abdominal  region. 
In  many  cases  these  overlapping  myotomes  have  united  with  myotomes  of  the  lower 
region  to  form  a  continuous  muscle,  and  it  is  consequently  impossible  to  refer  them  to 
their  proper  topographic  position  without  doing  violence  to  the  individuality  of  the 
muscles  which  they  help  to  form  ;  but  when  they  remain  practically  distinct  from  the 
muscles  of  their  adopted  region,  they  will  be  referred  to  the  region  from  which  they 
have  come. 

It  will  be  convenient  to  consider  first  the  muscles  of  the  abdominal  region,  there- 
after taking  up  in  succession  those  of  the  thoracic  and  cervical  regions,  those  of  the 
perineal  region  being  left  until  the  last. 

THE    ABDOMINAL    MUSCLES. 

The  Superficial  Fascia  of  the  Abdomen. — The  superficial  fascia  of  the 
abdomen  is  usually  described  as  consisting  of  two  layers.  These,  however,  are  well 
marked  only  over  the  anterior  and  especially  the  lower  part  of  the  abdominal  wall, 
losing  their  distinctness  laterally  and  above,  where  they  pass  over  into  the  superficial 
fasciae  of  the  back  and  thorax.  The  superficial  layer  (  Camper  s  fascia}  usually  con- 
tains a  considerable  amount  of  fat,  except  at  the  umbilicus,  and  may  occasionally 
reach  a  great  thickness  owing  to  the  development  of  that  tissue.  The  deeper  layer 
immediately  underlies  the  fatty  layer,  and  is  a  connective-tissue  membrane  of  vary- 
ing density,  containing  a  considerable  amount  of  yellow  elastic  tissue.  It  is  con- 
nected to  the  deep  abdominal  fascia  which  covers  the  muscles  of  the  abdominal  wall 
by  loose  areolar  tissue,  except  along  the  median  line,  where  it  is  firmly  adherent 
along  the  linea  alba  and  around  the  umbilicus.  A  short  distance  above  the  sym- 
physis  pubis  it  gives  off  a  band  which  is  largely  composed  of  elastic  tissue  and  is 
inserted  below  into  the  fascia  of  the  penis,  forming  the  suspensory  ligament  of  that 
organ  (Fig.  528). 

In  the  inguinal  region  the  deep  layer  of  the  superficial  fascia  is  especially  well 
defined,  forming  what  has  been  termed  the  fascia  of  Scarpa.  Laterally  it  passes 
down  over  Poupart's  ligament  to  unite  with  the  fascia  lata  of  the  thigh,  the  super- 
ficial vessels  and  lymph-nodes  of  this  region  lying  between  it  and  the  superficial 
layer.  More  medially  it  is  continued  down  over  the  spermatic  cord,  becoming  con- 
tinuous below  partly  with  the  deep  layer  of  the  superficial  fascia  of  the  perineum 
(fascia  of  Colles}  and  partly,  after  fusing  with  the  superficial  layer,  which  loses  its 
fat,  with  the  dartos  of  the  scrotum. 


HUMAN   ANATOMY. 


(a)  THE   RECTUS  MUSCLF:S. 
I.    Rectus  abdominis.  2.    Pyramidalis. 

i.   RECTUS  ABDOMINIS  (Fig.  523). 

Attachments. —  The  rectus  abdominis  forms  a  flat  but  strong  muscle  which 
traverses  the  entire  length  of  the  ventral  abdominal  wall  immediately  lateral  to  the 
linea  alba.  It  arises  from  the  anterior  surface  of  the  xiphoid  process  of  the  sternum 
and  from  the  cartilages  of  the  fifth,  sixth,  and  seventh  ribs,  and  is  inserted  by  a  strong 
tendon  into  the  crest  and  symphysis  of  the  pubis. 

FIG.  523. 


Pectoralis  major 


Tendon  of  rectus 


Rectus,  cut  and  turned 
up 


Cut  edge  of  anterior 
sheath  of  rectus 


Posterior  sheath  of  rectus 
External  oblique 

Semilunar  fold 

Transversalis  fascia 

Deep  epigastric  artery 

Rectus,  stump 

Saphenous  opening 


Sheath  of  rectus,  turned  over 


Tendinous  intersection 


Rectus 


Crest  of  ilium 


^•__Anterior  superior  iliac 
<K        spine 

I 

_^M_Pyramidalis 

External 

^B abdominal  ring 

_1 Cribriform  fascia 

rinsing  saphftious 
opening 
— J__Spermatic  cord 


Muscles  of  anterior  abdominal  wall. 


The  fibres  are  directed  longitudinally,  and  are  interrupted  along  three  and 
occasionally  four  transverse  lines  by  tendinous  intersections  of  the  muscle.  One  of 
these  inscrif>tioiifs  trndincic  oecurs  about  the  U-vel  of  the  umbilicus,  another,  often 
alfi-ctmg  only  the  medial  portion  of  the  muscle,  corresponds  approximately  to  the 
lourr  margin  of  the  thorax,  and  the  third  lies  about  midway  between  tin'  two.  The 
fourth,  when  present,  frequently  is  limited  to  the  lateral  portion  of  the  muscle,  and 
occurs  about  midwav  between  the  level  of  the  umbilicus  and  the  crest  of  the  pubis. 


THE   VENTRAL    MUSCLES.  517 

Nerve-Supply. — From  the  anterior  divisions  of  the  thoracic  nerves  from  the 
fifth  to  the  twelfth. 

Action. — The  recti  act  as  flexors  of  the  thorax  upon  the  pelvis  or,  acting  from 
above,  they  flex  the  pelvis  on  the  thorax.  They  also  aid  in  the  compression  of  the 
abdominal  viscera  in  defecation  and  parturition  and  in  strong  expiratory  efforts. 

Variations. — The  origin  of  the  rectus  sometimes  ascends  to  the  fourth  or  third  rib  or  even 
higher.  The  tendinous  inscriptions  are  probably  the  persistent  representatives  of  the  connective-' 
tissue  partitions  between  certain  of  the  myotomes  of  which  the  muscle  is  composed.  They  are 
subject  to  a  certain  amount  of  variation  in  number,  five  or  six  occasionally  occurring,  while,  on 
the  other  hand,  they  may  be  reduced  to  two. 

2.   PYRAMIDALIS  (Fig.  523). 

Attachments. — The  pyramidalis  is  a  somewhat  variable  muscle  which  arises 
below  from  the  upper  surface  of  the  body  of  the  pubis  and  from  the  symphysis  and  is 
inserted  above  into  the  linea  alba,  somewhere  between  the  umbilicus  and  the  sym- 
physis. 

Nerve-Supply. — From  the  anterior  divisions  of  the  eleventh  and  twelfth 
thoracic  nerves. 

Action. — To  tense  the  linea  alba. 

Variations. — The  extent  to  which  the  muscle  is  developed  varies  greatly,  its  insertion  some- 
times extending  well  up  towards  the  umbilicus,  while,  on  the  other  hand,  it  is  not  infrequently 
absent.  This  latter  condition  has  been  estimated  to  occur  in  over  16  per  cent,  of  cases. 

(6)  THE   OBLIQUUS   MUSCLES. 

1.  Obliquus  externus.  4.   Transversalis. 

2.  Obliquus  internus.  5.   Quadratus  lumborum. 

3.  Cremaster.  6.    Intertransversales  lateral es. 

1.  OBLIQUUS  EXTERNUS  (Fig.  524). 

Attachments. — The  external  oblique  forms  a  muscular  sheet  in  the  lateral 
portions  of  the  anterior  abdominal  wall.  It  arises  by  seven  or  eight  fleshy  digitations 
from  the  corresponding  number  of  lower  ribs,  the  upper  digitations  alternating  with 
digitations  of  the  serratus  magnus,  while  the  lower  three  alternate  with  those  of  the 
latissimus  dorsi.  The  fibres  from  the  lowest  ribs  pass  vertically  downward  to  be  in- 
serted into  the  crest  of  the  ilium  ;  the  remainder  are  directed  mainly  downward  and 
forward  and ,  above,  directly  forward  to  join  a  broad  aponeurotic  sheet  which  con- 
tributes to  the  formation  of  the  ventral  abdominal  aponeurosis. 

Nerve-Supply. — From  the  anterior  divisions  of  the  eighth  to  the  twelfth 
thoracic  nerves  and  from  the  ilio-hypogastric  and  ilio-inguinal  nerves. 

Action. — Since  the  external  oblique  is  a  curved  sheet  which  passes  from  the 
lateral  portions  of  the  abdominal  wall  towards  the  mid-ventral  line,  contraction  of  its 
fibres  will  tend  to  compress  the  abdominal  contents  and  so  assist  in  micturition,  defe- 
cation, parturition,  and  expiration,  its  action  in  the  last-named  process  being  increased 
by  the  power  which  it  possesses  of  drawing  the  lower  ribs  downward.  Furthermore, 
according  as  it  acts  from  below  or  above,  it  will  flex  the  thorax  and  spinal  column 
upon  the  pelvis  or  the  pelvis  upon  the  spinal  column,  at  the  same  time  producing  a 
slight  rotation  of  the  thorax  to  the  opposite  side  and  the  pelvis  to  the  same  side. 
When  the  two  muscles  of  opposite  sides  act  together,  the  rotatory  action  of  each  will 
be  neutralized.  By  the  most  lateral  fibres  a  lateral  flexion  of  the  thorax  or  pelvis 
will  be  produced. 

2.  OBLIQUUS  INTERNUS  (Fig.  525). 

Attachments. — The  internal  oblique  muscle  lies  immediately  beneath  the  ex- 
ternal one.  It  arises  from  the  outer  two-thirds  of  Poupart's  ligament,  from  the 
whole  length  of  the  middle  lip  of  the  crest  of  the  ilium,  and  from  the  lumbo-dorsal 
fascia.  From  this  extended  origin  its  fibres  spread  out  in  a  fan-shaped  manner,  the 
more  posterior  ones  passing  upward  and  slightly  forward  to  be  inserted  into  the 


HUMAN    ANATOMY. 


lower  three  ribs,  while  of  the  rest  the  more  anterior  ones  pass  forward  and  upward, 
those  from  the  neighborhood  of  the  anterior  superior  iliac  spine  directly  forward,  and 
those  from  Poupart's  ligament  forward  and  downward,  all  joining  in  a  flat  aponeu- 
rosis  which  unites  with  the  anterior  abdominal  aponeurosis  at  the  linea  semilunaris. 
In  its  lowermost  portion  the  aponeurosis  unites  with  that  of  the  transversalis  to  form 
what  is  termed  the  conjoined  tendon,  and  by  this  it  is  attached  to  the  crest  of  the  pubis. 


FIG.  524. 


Serratus  magnu 


Latissimus  dorsi  - 


Gluteus  maximum 


External  oblique 


Petit's  triangle- — 


Fascia  lata 


Pectoralis  major 


Origin  of  pectoralis  major 
from  sheath  of  rectus 


Line  of  subcostal  arch 


Linea  transversa 

l.inea  semilunaris 
I'mbilicus 


Anterior  superior  iliac  spine 


Suspensory  ligament  of  penis 
Poupart's  ligament 

Spermatic  cord 


Dissection  of  lateral  body-wall,  showing  external  oblique  and  adjoining  muscles. 

Nerve-Supply. — From  the  anterior  divisions  of'  the  eighth  to  the  twelfth 
thoracic  nerves  and  from  the  ilio-hypogastric  and  ilio-inguinal  nerves. 

Action. — The  internal  oblique  acts  very  similarly  to  the  external  in  compressing 
the  abdominal  contents,  in  drawing  the  lower  ribs  downward,  and  in  flexing  the 
thorax  or  pelvis  laterally.  It  will  also  Hex  the  thorax  and  vertebral  column  upon  the 
pelvis  or  the  pelvis  upon  the  vertebral  column,  but  in  these  actions  the  accompanying 
rotation  will  be  in  a  direction  contrary  to  that  caused  by  the  external  oblique,  the 
thorax  being  rotated  to  the  same  side  and  the  pelvis  to  the  opposite  side.  It  may  be 
remarked  that  the  rotatory  action  of  the  external  oblique  of  the  one  side  and  the 
internal  oblique  of  the  other  will  be  in  the  same  direction. 


Variations. — The  internal  oblique  may  he  crossed  by  one  or  more  tendinous  intersections 
which  have  probably  the  same  significance  as  those  of  the  rectus  abdoniinis. 


THE   VENTRAL   MUSCLES. 


3.   CREMASTER  (Figs.  525,  1671). 

Attachments. — The  cremaster  muscle  consists  of  a  series  of  somewhat  scat- 
tered loops  of  muscle-tissue  derived  from  the  lower  part  of  the  internal  oblique  and 
to  a  slight  extent  from  the  transversalis.  It  is  attached  laterally  to  Poupart's  liga- 
ment and  medially  to  the  anterior  layer  of  the  sheath  of  the  rectus.  The  loops  de- 
scend through  the  inguinal  canal  along  with  the  spermatic  cord,  the  muscle  being 

FIG.  525. 


Pectoralis  major 


Serratus  magnus 


Latissimus  dorsi 


Edge  of  cut  external  oblique 


Internal  oblique 

Posterior  aponeurosis  of  internal 
oblique 


Iliac  crest 
Fascia  lata 


Cut  edge  of  fascia  lata 
Gluteus  maximus 


Edge  of  cut  aponeurosis  of 
external  oblique 


_  Linea  alba 


_  Anterior  aponeurosis  of  internal 
oblique 


Anterior  superior  iliac  spine 


Conjoined  tendon 

Suspensory  ligament 
Cremaster  fibres 


Dissection  of  lateral  body-wall,  showing  internal  oblique  muscle. 

well  developed  only  in  the  male,  and  spread  out  in  the  tunica  vaginalis  communis  of 
the  testis  and  spermatic  cord.  The  loops  are  united  by  connective  tissue  which  forms 
part  of  the  cremasteric  fascia. 

Nerve-Supply. — By  the  genital  branch  of  the  genito-crural  nerve. 

Action. — To  draw  the  testis  upward  towards  the  external  abdominal  ring. 

4.  TRANSVERSALIS  (Fig.  526). 

Attachments. — The  transversalis  (m.  transversus  abdominis)  is  the  deepest 
layer  of  muscle  on  the  lateral  abdominal  wall  and  immediately  underlies  the  internal 
oblique.  It  arises  from  the  cartilages  of  the  lower  six  ribs,  from  the  lumbo-dorsal 


520 


HUMAN   ANATOMY. 


fascia,  the  inner  lip  of  the  crest  of  the  ilium,  and  the  outer  two-thirds  of  Poupart's 
ligament.  Its  fibres  pass  horizontally  inward  to  join  the  ventral  abdominal  aponeu- 
rosis  along  the  linea  semilunaris  ;  the  lower  ones,  however,  bending  somewhat  down- 
ward, pass  into  an  aponeurosis  which  unites  with  that  of  the  internal  oblique  to  form 
the  conjoined  tendon  attached  to  the  crest  of  the  pubis. 

Nerve-Supply. — From  the  anterior  divisions  of  the  seventh  to  the  twelfth 
thoracic  nerves  and  from  the  ilio-hypogastric  and  ilio-inguinal  nerves. 

Action. — To  compress  the  contents  of  the  abdomen. 

FIG.  526. 


Pectoralis  major 


Serratus  magnu 


Latissimus  dorsi 


Edge  of  cut  external  oblique 


Edge  of  cut  internal  oblique 
Lumbo-dorsal  fascia 


Fascia  lata 

Cut  edge  of  fascia  lata 

Gluteus  maximus 

Tensor  fasciae  latae 


Edge  of  aponeurosis  of  external 
oolique 


.      of  aponeurosis  of  internal 
oblique 


Tjj* Aponeurosis  of  transversalis 


Rectus,  covered  by  sheath 


Conjoined  tendon 


(.'mna^ter  fibres 


Dissection  of  lateral  body-wall,  showing  transversalis  muscle. 

The  fascia  transversalis  is  a  thin  layer  of  connective  tissue  which  lines  the 
inner  (  deeper  )  surface  of  the  transversalis  muscle.  Posteriorly  it  is  continuous  with 
the  strong  aponeurotic  band  formed  by  the  fusion  of  the  superficial  and  deep  layers  of 
the  lumbo-dorsal  fascia,  anteriorly  it  combines  with  the  deeper  layer  of  the  ventral 
abdominal  aponeurosis  to  form  the  posterior  layer  of  the  sheath  of  the  rectus  muscle, 
and  above  it  unites  with  the  fascia  covering  the  lower  surface  of  the  diaphragm. 
Below  its  lateral  portion  is  attached  to  the  crest  of  the-  ilium  and  the  outer  part  of 
Poupart's  ligament  where-  it  becomes  continuous  with  the  iliac  fascia,  but  more  medially 
it  is  continued  downward  beneath  Poupart's  ligament  to  form  the  anterior  wall  of  the 
sheath  of  the  femoral  vessels,  the  portion  of  it  immediately  above  the  vessels  being 


THE   VENTRAL    MUSCLES. 


521 


thickened  somewhat  to  form  the  deep  crural  arch  (Fig.  1773).  More  medially  still  it 
is  attached  to  the  free  edge  of  Gimbernat's  ligament  and  to  the  upper  surface  of  the 
superior  ramus  and  body  of  the  pubis. 

A  little  over  i  cm.  above  Poupart's  ligament,  and  about  half-way  between  the 
anterior  superior  iliac  spine  and  the  symphysis  pubis,  the  transversalis  fascia  is  per- 
forated by  the  spermatic  cord  in  the  male  and  by  the  ligamentum  teres  of  the  uterus  in 
the  female.  The  fascia  is  continued  downward  and  forward  over  the  cord  or  ligament 
to  form  a  somewhat  funnel-like  investment  for  it  termed  the  infundibuliform  fascia,  the 
inner  margin  of  the  funnel  marking  the  position  of  the  internal  abdominal  ring. 

5.      QUADRATUS    LUMBORUM   (Fig.    527). 

Attachments. — The  quadratus  lumborum  is  a  flat  quadrilateral  muscle  which 
lies  towards  the  back  part  of  the  ab- 
dominal wall,   extending  between  the  FIG.  527. 
crest  of  the  ilium  and  the  lower  bor- 
der of  the  twelfth  rib.      It  consists  of         i^.     i^^toM^AV 
two  layers  of  fibres  which  frequently                                °v     v  v,\\ 
are   distinguishable    from   each    other      {£  ^>^ 
only   with    difficulty.       The    anterior 
layer,  which    arises    from    the   trans- 
verse processes  of  the  lower  four  lum- 
bar vertebrae  and  from  the  posterior 
part  of  the  iliac  crest,  is  inserted  into 
the  lower  border  of  the  twelfth  rib  ; 
the  posterior  layer  (Fig.    527)  arises 
from  the  crest  of  the  ilium  and  is  in- 
serted into  the    lower   border  of   the 
twelfth    rib    and    into    the  transverse 
processes  of   the   upper  four  lumbar 
vertebrae. 

Nerve-Supply. — By  branches 
from  the  lumbar  plexus. 

Action. — To  draw  downward  the 
last  rib  and  to  bend  the  lumbar  por- 
tion of  the  spinal  column  laterally. 

Relations. — The  quadratus  lum- 
borum rests  behind  upon  the  deep 
layer  of  the  fascia  lumbo-dorsalis  (Fig. 
519),  which  separates  it  from  the  spino- 
sacral  muscle.  Its  anterior  surface  is 
in  relation  to  the  kidney  and  the  as- 
cending or  descending  colon,  is  crossed 
by  the  lumbar  arteries,  and  is  covered  towards  its  inner  margin  by  the  psoas  major. 


XII  rib 


Quadratus  lumborum 


Iliac  crest 


—  Dorsal 
surface 
of  ilium 


Quadratus  iumborum  muscle  of  right  side,  seen  from  behind. 


6.   INTERTRANSVERSALES  LATERALES  (Fig.  521). 

Attachments. — The  lateral  intertransversales  are  a  series  of  small  quadrilateral 
muscles  which  extend  between  successive  transverse  processes  of  the  lumbar  vertebrae. 

Nerve-Supply. — Probably  from  the  anterior  rami  of  the  lumbar  nerves. 

Action. — To  bend  laterally  the  lumbar  portion  of  the  spinal  column. 

The  Ventral  Abdominal  Aponeurosis  (Fig.  528). — The  broad  aponeurotic 
sheets  into  which  the  oblique  and  transverse  muscles  of  the  abdomen  are  continued 
at  their  anterior  (medial)  edges  unite  more  or  less  intimately  with  one  another  and 
with  the  fascia  transversalis  to  form  the  ventral  abdominal  aponetirosis.  Laterally  the 
various  layers  of  which  this  aponeurosis  is  composed  are  to  a  certain  extent  discerni- 
ble, since  the  lines  along  which  the  fibres  of  the  three  muscles  pass  into  the  apo- 
neurosis do  not  coincide,  that  of  the  external  oblique  extending  from  the  outer  border 
of  the  rectus  muscle  above  obliquely  downward  and  laterally  to  the  anterior  superior 
spine  of  the  ilium,  while  those  of  the  internal  oblique  and  transversus  follow  essen- 


522 


HUMAN   ANATOMY. 


dally  the  outer  border  of  the  rectus,  except  below,  where  they  lie  a  little  lateral  to 
that  muscle.  More  medially,  however,  the  layers  become  intimately  associated  and 
can  only  be  separated  artificially. 

At  the  outer  border  of  the  rectus  muscle  the  aponeurosis  divides  into  two  layers 
(Fig.  529,  A)  which  pass  one  in  front  and  the  other  behind  the  rectus,  thus  forming  a 
sheath  for  it  (vagina  musculi  recti).  The  line  of  the  division  is  indicated  on  the  surface 
of  the  abdomen  by  a  slight  groove,  and  constitutes  what  is  termed  the  linea  scmi- 
lunaris.  When  they  reach  the  mesial  border  of  the  rectus  the  two  layers  unite  and 
become  continuous  in  the  middle  line  with  the  aponeurosis  of  the  opposite  side  to 
form  a  strong  fibrous  band  which  extends  from  the  front  of  the  xiphoid  process  of  the 

sternum  above  to  the 

FIG.  528.  symphysis   pubis   be- 

low, and  is  termed  the 
linea  alba.  In  its 
upper  part  this  band 
is  fairly  broad,  but 
below  the  umbilicus, 
which  is  situated  in 
the  band,  it  suddenly 
narrows  to  a  thin  line 
which  becomes  con- 
tinuous below  with  the 
superior  pubic  liga- 
ment, behind  the  in- 
sertion of  the  recti,  by 
a  triangular  expansion 
which  occasionally 
contains  muscle-fibres 
and  is  termed  the  ad* 
miniculum  lineae  albac. 
7t\\Qposterio  r  layer 
of  the  aponeurosis, 
which  forms  the  poste- 
rior wall  of  the  sheath 
of  the  rectus,  is  fairly 
thick  above,  but  a  lit- 
tle below  the  level  of 
the  umbilicus  it  sud- 
denly becomes  very 

Superficial  dissection  of  abdomen,  showing  ventral  aponeurosis. 

arched  line,  the  con- 
cavity of  which  is  downward,  and  may  sometimes  be  represented  by  a  distinct  fold. 
This  margin  is  termed  the  line  or  fold  of  Douglas  (linea  semicircularis)  (Fig.  523). 


Uncovered^ 
fibres  of  exter-  v 
nal  oblique 


Anterior,^ 
sheath  of  rec- 
tus muscle 


Anterior  superior i 

iliac  spine 
Intercolumnar    I 
fibres 

External  abdomi-_ajB 
nal  ring 

Spermatic  cord       \ 


>Lineae 

transversae 
-Linea  alba 


>vered  ex- 
crnal  oblique 


9 — Linea 

*        semilunaris 


— Suspensory 
\         ligament 
of  penis 


Various  suggestions  have  been  made  in  explanation  of  this  sudden  change  in  the  thickness 
of  the  posterior  layer  of  the  sheath  of  the  rectus.  It  has  been  supposed  that  it  was  connected 
with  the  passage  of  the  inferior  epigastric  artery  into  the  substance  of  the  muscle  (Henle),  a 
somewhat  inack-qnate  cause  even  if  the  point  of  passage  of  the  artery  through  the  sheatli  cor- 
responded with  the  semicircular  line.  The  thinness  of  tin-  portion  of  the  sheath  below  the  line 
has  been  explained  on  the  ground  that  it  represents  the  portion  with  which  the  urinary  bladder 
was  in  contact  in  fatal  life  (Gegenbaur),  and  also  by  the  view  that  the  strain  exerted  on  this 
portion  of  the  sheath  is  less  than  that  placed  upon  the  upper  part,  since  the  latter  is  acted  on 
by  fibres  of  the  oblique  and  transverse  muscles  which  have  bony  attachments  drawn  upuard 
during  inspiration,  while  the  lower  part  is  in  relation  to  the  less  active  fibres  attached  to  the 
inguinal  ligament  (Solgert. 

Kinally,  it  may  be  slated  that  the  immediate  cause  for  the  sudden  change  in  thickness  lias 
been  assigned  to  the  development  of  the  processus  vaginalis  peritoncei,  the  pouch  of  peritoneum 
which  in  the  embryo  descends  into  the  genital  swelling  and  gives  rise  in  the  male  to  the  ttmi.'a 
vaginalis  testis.  The  formation  of  this  peritoneal  pouch  is  held  to  prevent  the  lower  portions 
of  the  posterior  layer  of  the  abdominal  aponeurosis  which  are  derived  from  tin-  aponeuroses  of 
the  internal  oblique  and  transversalis  from  passing  behind  the  rectus  muscle,  the  posterior  wall 
of  its  sheath  being  formed  only  by  the  fascia  transversalis  (Kisler). 


THE   VENTRAL    MUSCLES. 


523 


In  the  lower  part  of  the  anterior  abdominal  wall  the  lowermost  fibres  of  the 
abdominal  aponeurosis — those  extending  between  the  anterior  superior  spine  of  the 
ilium  and  the  pubic  spine — form  a  strong  ligamentous  band,  the  ligament  of  Pou- 
part  (ligamentum  injjuinale)  (Figs.  524,  530,),  the  outer  portion  of  which  gives  rise  to 
some  of  the  fibres  of  the  internal  oblique  and  transversalis  muscles,  while  the  fascia 
lata  of  the  thigh  is  attached  to  it  below.  Near  its  medial  end  some  of  its  fibres  pass 
inward  to  be  attached  to  the  ilio-pectineal  line  of  the  pubis,  forming  a  horizontal  trian- 
gular sheet  whose  free  concave  lateral  border  forms  the  medial  boundary  of  ti\e  femo- 
ral ring  (annulus  fcmoralis)  through  which  the  femoral  hernias  make  their  exit  from 
the  pelvis.  This  reflection  (Fig.  531)  is  the  ligament  of  Gimbernat  (ligamentum 
lacunare).  Furthermore,  a  sheet  of  fibres,  variable  in  its  development  and  termed  the 
triangular  fascia  (ligamentum  inguinale  reflexum),  or  ligament  of  Colles  (Fig.  1485), 
is  reflected  upward  and  medially  from  the  inner  portions  of  Poupart's  and  Gimbernat' s 
ligaments  in  front  of  the  lower  medial  portions  of  the  aponeuroses  of  the  internal 
oblique  and  transversalis  muscles  to  the  anterior  layer  of  the  sheath  of  the  rectus. 

The  Inguinal  Canal. — At  an  early  stage  in  the  development  of  the  foetus  an 
outpouching  of  the  lower  part  of  the  abdominal  wall  occurs  on  each  side  to  form  the 
genital  swellings,  which  later  become  the  scrotum  in  the  male  and  the  labia  majora 

FIG.  529. 

A 


Transversalis  muscle 


Transversalis  fascia 

Peri-  Division  of  aponeurosis  of  internal  oblique 

, — Rectus — • , 


External  oblique 

Internal  obliq 

Skin 
Aponeurosis  of  internal  oblique 


Transversalis  muscle 
Internal  oblique 


Linea  alba 

/      Anterior  sheath  of  rectus 
Superficial  fascia 
Aponeurosis  of  external  oblique 


B 


Transversalis  fascia 

Peritoneum        Rectus 
fusion 


Linea  alba        Rectus 


\\i. 


Superfic 

Skin 
Aponeurosis  of  external  oblique  Anterior  sheath  of  rectus 

Diagrams  showing  constitution  of  sheath  of  rectus  muscle.     A,  in  upper  three-fourths;  B,  in  lower  fourth. 

in  the  female.  The  points  at  which  the  outpouchings  occur  are  those  at  which  the 
lower  ends  of  a  ligament  descending  from  the  primitive  kidneys  (mesonephri)  are 
attached  to  the  abdominal  wall,  and  these  ligaments,  consequently,  are  carried  through 
the  length  of  the  outpouching  beneath  its  peritoneal  lining  to  attach  to  the  walls  of 
the  scrotum  or  the  labia.  In  the  female  the  ligaments  become  in  part  the  round 
ligaments  of  the  uterus,  but  in  the  male  the  relations  of  the  outpouchings  become 
more  complicated.  Owing  to  the  descent  into  them  of  the  testes  (page  2040),  the 
ligaments  are  drawn  completely  into  the  pouch,  forming  the  gubernacula  of  the  testes, 
while  the  vasa  deferentia  and  the  vessels  and  nerves  of  the  testes  are  also  carried 
into  the  pouch,  uniting  to  form  the  spermatic  cord.  There  are,  consequently,  pass- 
ing from  the  abdominal  cavity  into  each  pouch,  in  the  female  the  round  ligaments  of 
the  uterus  and  in  the  male  the  spermatic  cord. 

At  first,  and  in  the  male  for  a  considerable  time  after  birth,  the  communication  of 
the  pouch  with  the  abdominal  cavity  is  widely  open  ;  but  later,  in  the  upper  part  of  the 
pouch  in  the  male  and  throughout  its  entire  length  in  the  female,  the  lumen  becomes 
reduced,  and  finally  is  completely  obliterated  by  the  union  of  its  walls  to  the  sper- 
matic cord  or  the  round  ligament,  its  lower  portion  persisting  in  the  male  as  the  space 
which  exists  between  the  visceral  and  parietal  layers  of  the  tunica  vaginalis  testis. 


524 


HUMAN    ANATOMY. 


As  a  result  of  these  processes  the  lower  portion  of  the  abdominal  wall  is 
traversed  on  either  side  by  the  spermatic  cord  or  by  the  ligamentum  teres  of  the 
uterus,  and  it  is  customary  to  regard  the  space  occupied  by  the  one  or  the  other  of 
these  structures  as  a  canal,  which  is  termed  the  inguinal  canal.  It  should  be 
understood,  however,  that  an  actual  space  surrounding  the  cord  or  ligament  does 
not  exist,  the  walls  of  the  canal  being  united  to  the  structure  contained  within  it. 
Nevertheless,  the  union  is  by  no  means  a  strong  one,  the  region  of  the  abdominal 
wall  traversed  by  the  ligamentum  teres  or  especially  by  the  spermatic  cord  being 
relatively  weak  and  not  infrequently  the  seat  of  an  inguinal  hernia. 

The  inguinal  canal  is  somewhat  over  3  cm.  ( i  ^  in. )  in  length  and  is  situated 
immediately  above  Poupart's  ligament,  which  it  crosses  obliquely  from  above  down- 
ward, medially,  and  forward.  Its  upper  or  inner  end  is  about  midway  between  the 
anterior  superior  spine  of  the  ilium  and  the  spine  of  the  pubis,  and  lies  about  12  mm. 
(l/z  in. )  above  the  line  of  Poupart's  ligament.  It  is  marked  by  a  more  or  less  distinct 
depression  on  the  posterior  surface  of  the  abdominal  wall  surrounding  the  spermatic 
cord  or  round  ligament,  termed  the  internal  abdominal  ring  (annulus  inguinalis 

FIG.  530. 


Anterior  superior  iliac  spine- 


Poupart's  ligament — 

Falciform  process 

Iliac  portion  of  fascia  lata. 

Saphenous  opening 

Femoral  artery-"-" 
Femoral  vein 


Internal  saphenous  vein 


-Aponeurosis  of  external  oblique 


. Intercolumnar  fibres 

— External  abdominal  ring 

. External  pillar 

Internal  pillar 

r.inibernat's  ligament,  inner 
boundary  of  femoral  ring 


Pubic  portion  of  fascia  lata 
Spermatic  cord 


—  — Scrotum 


Dissection  of  right  inguinal  region,  showing  external  abdominal  ring  and  saphenous  opening. 


abdominis).  The  depression  (Fig.  532)  is  due  to  the  transversalis  fascia  bring  pro- 
longed downward  over  the  spermatic  cord  as  a  funnel-like  sheath,  the  infnndibidi- 
fonn  fascia.  The  lower  or  medial  end  of  the  canal  corresponds  to  the  external 
abdominal  ring  (annulus  abdominnlis  subcutaneus)  (Figs.  523,  530),  and  lies  just 
lateral  to  and  a  little  above  the  spine  of  the  pubis  and  is  surrounded  by  the  lower 
nudial  portion  of  the  aponeurosis  of  the  external  oblique.  The  fibres  of  the  aponeu- 
rosis  which  bound  this  ring  are  somewhat  thickened,  forming  what  are  termed  the 
pillars  Centra)  of  the  ring,  the  uppermost  of  which,  the  internal  pillar  Cents  superior  ), 
consists  of  fibres  passing  to  the  symphysis  pubis  ;  the  lower  one,  the  external  pillar 
(cms  inferior),  is  formed  by  the  fibres  passing  to  the  pubic  spine,  and  corresponds 
to  the  medial  end  of  Poupart's  ligament.  Stretching  across  between  the  two  crura 
are  numerous  obliquely  arching  intcrcoltannar  fibres  ( librae  interenirales  )  which  extend 
laterally  almost  as  far  out  as  the  anterior  superior  spine  of  the  ilium.  From  the 
margins  of  the  external  ring  an  attenuated  prolongation  of  the  aponeurosis  of  the 
external  oblique  is  continued  downward  over  the  spermatic  cord  as  a  thin  membrane 
known  as  the  intcrcolionnar  or  external  spermatic  fascia. 


THE   VENTRAL   MUSCLES. 


525 


Owing  to  the  oblique  direction  of  the  canal,  that  portion  of  the  aponeurosis  of 
the  external  oblique  which  is  strengthened  by  the  intercolumnar  fibres,  together  with 
a  portion  of  the  internal  oblique,  forms  its  anterior  wall,  while  its  posterior  wall  is 
formed  by  the  aponeurosis  of  the  transversalis,  together  with  the  more  medial  lower 
portion  of  that  of  the  internal  oblique,  these  two  layers  of  fascia  uniting  in  this  region 
to  form  what  is  termed  the  conjoined  tendon,  which  is  attached  below  to  the  body  and 
superior  ramus  of  the  pubis,  and  medially  is  especially  thickened  to  form  a  band,  the 
falx  in«uinalis,  firmly  attached  along  its  medial  border  to  the  tendon  of  the  rectus. 
More  laterally,  where  it  forms  the  medial  boundary  of  the  internal  abdominal  ring,  it 
is  also  thickened  (Fig.  531),  forming  the  ligament  of  Hesse/bach  (ligamentum  inter- 
foveolare).  Between  these  two  thickenings  the  abdominal  wall  is  weaker  (Fig.  1493) 
and  may  give  way  to  internal  pressure,  permitting  a  hernia,  which  conies  to  the  sur- 
face at  the  external  abdominal  ring  without  having  traversed  the  inguinal  canal,  and  is 
therefore  spoken  of  as  a  direct  hernia,  in  contradistinction  to  the  more  usual  oblique 
hernia  which  enters  the  canal  at  the  internal  abdominal  ring. 


FIG.  531. 


Rectui 


Deep  epigastric  artery. 

Interfoveolar  or 

Hesselbach's  ligament 

Weak  area. 

Conjoined  tendon 

Muscular  fibres 

Lower  end  of  Poupart's  ligament 

Urachus 
Bladder 


—  Poupart's  ligament 
— Transversalis  muscle 
—  Spermatic  vessels 
..External  iliac  artery 
-External  iliac  vein 

-Deep  epigastric  artery  (cut) 
-_Vas  deferens 


'^-Femoral  ring 
Gimbernat's  ligament 


Dissection  of  posterior  surface  of  anterior  abdominal  wall,  showing  relations  of  conjoined  tendon  and  its  expansions 

to  internal  abdominal  ring. 

A  small  fasciculus  of  muscle-tissue  is  sometimes  found  close  to  the  medial  border  of  the 
internal  abdominal  ring.  It  is  the  m.  interfoveolaris  (Fig.  531),  and  arises  from  the  superior 
ramus  of  the  pubis,  passing  almost  directly  upward  to  spread  out  on  the  posterior  surface  of  the 
transversalis.  It  is  generally  regarded  as  an  aberrant  portion  of  the  transversalis  muscle. 

The  Posterior  Surface  of  the  Anterior  Abdominal  Wall. — Throughout 
its  entire  extent,  with  the  exception  of  a  small  area  in  the  median  line  below,  the 
posterior  surface  of  the  anterior  abdominal  wall  is  lined  by  peritoneum.  In  the 
exceptional  area  the  peritoneum  is  kept  from  actual  contact  with  the  wall  by  a 
band  of  fibrous  tissue,  the  urachus,  which  extends  from  the  apex  of  the  urinary 
bladder  to  the  umbilicus  and  supports  the  peritoneum  somewhat  in  the  manner 
of  a  ridge-pole  of  a  tent,  so  that  between  it  and  the  abdominal  wall  there  is  an 
interval  occupied  only  by  loose  areolar  tissue  and  termed  the  prevesical  space  of 
Ret z i us  (page  1906). 

Laterally  from  the  urachus  a  fibrous  cord,  the  lateral  ligament  of  the  umbilicus, 
may  be  seen  on  each  side,  passing  from  the  side  of  the  bladder  to  the  umbilicus  and 
representing  the  obliterated  hypogastric  arteries  of  the  foetus  ;  while  still  more  laterally 
there  may  be  seen  coming  from  the  external  iliac  artery  the  inferior  or  deep  epigas- 
tric artery,  which,  passing  immediately  to  the  inner  side  of  the  internal  abdominal 
ring  and  posterior  to  the  interfoveolar  ligament  (Fig.  532),  extends  upward  and 
inward  to  penetrate  the  posterior  layer  of  the  sheath  of  the  rectus  a  short  distance 
below  the  level  of  the  umbilicus.  Both  these  structures  produce  a  slight  ridging  or 
told  of  the  peritoneum,  that  formed  by  the  obliterated  hypogastric  artery  being  termed 
the  />//(•({  umbilicalis  latcralis,  while  the  other  is  the  plica  epigastrica.  These  two 
tolds,  together  with  the  urachus,  mark  off  the  lower  portion  of  the  abdominal  wall 


526 


HUMAN   ANATOMY. 


into  three  areas  or  foveae  (Fig.  532).  The  median  of  these  foveae  lies  between  the 
urachus  and  the  lateral  umbilical  fold  and  forms  the  supravesical  fossa,  having  for 
its  floor  the  rectus  muscle.  Between  the  lateral  umbilical  and  the  epigastric  folds 
is  the  inner  inguinal  fossa,  having  for  its  floor  the  conjoined  tendon,  and  being 
therefore  the  region  in  which  direct  inguinal  hernias  arise  ;  ano*  lateral  to  the  epi- 

FIG.  532. 


Peritoneal  surface 


Plica  epigastrica 1 

Hesselbach's  triangle 
Vas  deferens. 


External  iliac  artery. 
External  iliac  vein 

Plica  hypogastrica^ 


Outer  edge  of  rectus 
muscle 


Supravesical  fossa 

Outer  inguinal  fossa 
Inner  inguinal  fossa 


Bladder,  somewhat 
distended 


Median  umbilical  ligament 

Posterior  surface  of  anterior  abdominal  wall  of  formalin  subject. 

gastric  fold  is  the  outer  inguinal  fossa,  in  whose  floor  is  found  the  internal  abdominal 
ring,  just  to  the  outer  side  of  the  deep  epigastric  artery. 

The  triangular  area  bounded  by  Poupart's  ligament  below,  the  lateral  edge  of 
the  rectus  muscle  medially,  and  the  plica  epigastrica  laterally  has  been  termed  the 
triangle  of  Hesselbdch.  It  is  almost  identical  with  the  middle  inguinal  fossa,  and 
defines  a  little  more  precisely  the  seat  of  the  direct  hernias. 

(c)    THE   HYPOSKELETAL  MUSCLES. 

It  seems  probable  that  the  psoas  major  and  the  psoas  minor  muscles  are,  in  part 
at  least,  assignable  to  the  group  of  abdominal  hyposkeletal  muscles.  The  close 
associatio'n  of  the  psoas  major  with  the  iliacus  and  its  attachment  to  the  femur  make  it 
convenient,  however,  to  defer  their  description  until  later  (page  623). 


PRACTICAL  CONSIDERATIONS. 

THE  ABDOMEN. 

The  abdominal  cavity  is  bounded  above  by  the  diaphragm  ;  below  by  the  floor 
of  the  pelvis  ;  laterally  by  the  diaphragm,  the  lower  ribs,  the  abdominal  muscles,  and 
the  lateral  expansions  of  the  ilia  ;  posteriorly  by  the  diaphragm,  the  tenth,  eleventh, 
and  twelfth  ribs,  the  lumbar  muscles  and  vertebrae,  the  posterior  portions  of  the  ilia, 
and  the  ischial,  sacral,  coccygeal,  and  pubic  bones  ;  and  interiorly  by  the  levatores 
ani  and  coccygei  muscles.  It  should  be  noted  that  the  roof,  the  floor,  and  much  of 
the  remaining  parietes  of  the  abdomen  are  made  up  of  muscular  tissue-  which,  by 
contraction  or  by  relaxation  or  stretching,  can  alter  the  si/.e  of  the  cavity,  affect  the 
relations  of  the  contained  viscera,  and  vary  the  compression  to  which  they  are  subject. 
The  tonicity  of  the  muscular  walls  brings  about  a  normal  intra-abdominal  pressure 
which  serves  in  health  to  retain  in  position  and  to  give  support  to  the  viscera. 
This  pressure  is  increased  in  inspiration  and  by  straining,  lifting,  or  coughing.  It 
then,  by  increasing  the  outward  pressure  of  the  viscera  upon  the  internal  sur- 
face of  the  parietes,  favors  the  production  of  hernia,  the  protrusion  of  the  intestine 


PRACTICAL   CONSIDERATIONS  :    THE   ABDOMEN. 


527 


through  a  wound,  the  stretching  of  scars,  and  some  forms  of  dystocia  and  of  uterine 
displacement. 

The  pelvic  cavity — "  a  recess  leading  downward  and  backward  from  the  abdomi- 
nal cavity  proper"  (Cunningham) — is  divided  from  the  latter  by  an  imaginary  plane 
extending  from  the  promontory  of  the  sacrum  to  the  upper  edge  of  the  pubes.  It 
will  be  considered  separately. 

The  general  shape  of  the  abdominal  cavity  is  described  on  page  1615  as  are  also 
the  regions  into  which,  for  convenience,  the  abdomen  proper  may  be  divided  by  cer- 
tain arbitrary  lines  (page  1615). 

The  structures  and  organs  underlying  the  spaces  thus  marked  out  are  approxi- 
mately as  follows  : 


RIGHT  HYPOCHONDRIAC. 

Greater  part  of  right  lobe  of 
liver,  hepatic  flexure  of  colon, 
and  part  of  right  kidney. 


EPIGASTRIC. 

Greater  part  or  whole  of  left 
lobe  and  part  of  right  lobe  of 
liver,  with  gall-bladder,  part  of 
stomach,  including  both  ori- 
fices, first  and  major  portion 
of  the  second  parts  of  duo- 
denum, duodeno-jejunal  flex- 
ure, pancreas,  upper  or  inner 
end  of  spleen,  parts  of  kid- 
neys, and  suprarenal  bodies. 


LEFT  HYPOCHONDRIAC. 

Part  of  stomach,  portion  of 
spleen,  tail  of  pancreas,  splenic 
flexure  of  colon,  part  of  left 
kidney,  and  sometimes  part  of 
left  lobe  of  liver. 


RIGHT  LUMBAR. 

Ascending  colon,  part  of 
right  kidney,  and  sometimes 
part  of  ileum. 


UMBILICAL. 

Greater  part  of  transverse 
colon,  lower  portion  of  second 
and  much  of  third  part  of  duo- 
denum, some  convolutions  of 
jejunum  and  ileum,  with  por- 
tions of  mesentery  and  greater 
omentum,  part  of  right,  often 
of  left,  and  sometimes  of  both 
kidneys,  and  part  of  both 
ureters. 


LEFT  LUMBAR. 

Descending  colon,  part  of 
jejunum,  and  sometimes  part 
of  left  kidney. 


RIGHT  ILIAC. 

Caecum  with  vermiform  ap- 
pendix and  termination  of 
ileum. 


HYPOGASTRIC. 

Convolutions  of  ileum,  blad- 
der in  children,  and  when  dis- 
tended in  adults  also,  uterus 
when  in  the  gravid  state,  and, 
behind,  sigmoid  flexure. 


LEFT  ILIAC. 

Sigmoid  colon,  convolutions 
of  jejunum  and  ileum. 


The  contents  of  the  various  regions  and  the  structures  intersected  by  the  different 
planes — if  the  arbitrary  lines  are  continued  into  planes — vary  considerably  within 
normal  limits  and  greatly  in  the  presence  of  disease. 

The  shape  and  size  of  the  abdomen  are  also  extremely  variable.  In  the  normal 
adult  male  it  is  irregularly  cylindrical,  with  a  central  bulging,  an  antero-posterior 
flattening,  and  a  greater  width  near  the  pelvis  than  near  the  ribs.  In  the  adult  female 
the  larger  relative  size  of  the  lower  abdomen  is  due  to  the  greater  development  of  the 
pelvis,  and  usually  to  flabbiness  of  abdominal  muscles  and  accumulation  of  fat  from 
want  of  exercise,  and  to  compression  of  the  upper  segment  by  corsets  ;  it  is  increased 
by  the  stretching  of  repeated  pregnancies.  In  infancy  and  childhood  the  abdomen  is 
prominent  on  account  of  the  undeveloped  condition  of  the  pelvis,  the  pelvic  viscera 
being  then  practically  within  the  abdomen,  and  is  broader  above  than  below  by 
reason  of  the  relatively  great  bulk  of  the  liver. 

In  obesity  the  weight  of  the  intra-abdominal  and  subcutaneous  fat  carries  the 
lower  part  of  the  abdominal  wall  downward  by  gravity,  stretches  it,  and  produces  a 
pendulous  abdomen.  This  condition  is  also  favored  by  ascites,  pregnancy,  etc.  In 


528  HUMAN   ANATOMY. 

emaciation  the  whole  anterior  abdominal  wall  becomes  concave  (scaphoid},  especially 
the  upper  portion  bounded  by  the  ensiform  cartilage  and  the  subcostal  angle, — the 
scrobiculus  cordis  (page  171), — which,  with  the  patient  supine,  may  appear  to  rest 
directly  upon  the  vertebral  column,  with  walls  more  nearly  vertical  than  horizontal. 

Congenital  deformities  of  the  abdominal  wall  usually  consist  in  a  failure  of  the 
ventral  plates  to  unite  in  the  middle  line,  producing  various  degrees  of  umbilical 
hernia  (q.  v. )  or  leaving  the  contents  of  the  abdomen  uncovered  over  a  considerable 
area. 

Contusions  of  the  anterior  abdominal  wall,  bounded  laterally  by  the  outer  free 
border  of  the  external  oblique, — i.e.,  by  a  line  just  external  to  a  vertical  line  dropped 
from  the  lowest  part  of  the  ninth  rib, — are  of  importance  in  relation  to  the  effect 
upon  the  organs  contained  within  the  abdomen.  As  the  skin  over  the  abdomen  and 
the  abdominal  muscles  receive  their  nerve-supply  from  the  lowest  six  intercostal 
nerves  and  the  branches  of  the  anterior  division  of  the  first  lumbar,  the  contraction 
of  the  muscles  upon  the  approach  of  danger,  if  not  voluntary,  may  be  reflexly 
hastened  at  the  moment  of  external  application  of  force,  and  a  protecting  elastic 
barrier  may  thus  be  interposed  between  the  latter  and  the  abdominal  contents.  The 
rigidity  caused  by  the  contact  of  a  cold  hand  with  the  abdominal  surface,  preventing 
palpation  of  the  viscera  beneath,  affords  a  familiar  illustration  of  the  close  relation 
between  skin  and  muscles.  The  relation  of  the  nerve-supply  of  the  muscles  and 
that  of  the  underlying  viscera  explains  the  rigidity  of  the  belly  so  usually  seen  in 
injury  or  disease  of  abdominal  organs  (page  1683).  Finally  the  relation  of  the  cuta- 
neous and  muscular  branches  of  the  intercostal  nerves  is  well  shown  by  the  sudden 
inspiratory  effort  caused  by  a  dash  of  cold  water  on  the  lower  thoracic  or  abdominal 
region,  six  of  these  nerves  supplying  the  intercostal  muscles  as  well  as  the  antero- 
lateral  surface  of  the  chest  and  belly. 

The  injurious  effect  of  contusions  is  diminished  by  the  presence  of  a  thick  layer 
of  subcutaneous  fat  or  by  the  interposition  of  a  fleshy  omentum.  If  the  abdominal 
muscles  are  relaxed,  serious  injury  to  the  viscera  may  be  done  without  obvious 
damage  to  the  parietes.  Absence  of  ecchymosis  or  other  visible  sign  of  injury  should 
therefore  not  lead  to  an  absolutely  favorable  prognosis  until  after  the  lapse  of  suffi- 
cient time  to  permit  of  the  development  of  visceral  symptoms. 

Wounds. — The  thinness  and  loose  attachment  of  the  skin  of  the  abdomen  favor 
the  occurrence  of  cellulitis  as  a  result  of  infection  from  superficial  wounds.  The 
superficial  layer  of  the  superficial  fascia  contains  the  greater  part  of  the  subcutaneous 
fat  and  covers  the  superficial  blood-vessels.  The  thickness  of  the  abdominal  wall 
depends  chiefly  upon  the  thickness  of  this  fatty  layer,  which  may  be  of  several  inches. 
An  abdominal  wound  may  therefore  be  of  considerable  depth  and  yet  be  attended  by 
little  or  no  bleeding  and  be  practically  ' '  superficial. ' '  The  deeper  layer  of  the  super- 
ficial fascia  (page  515)  is  firmer,  is  elastic,  and  in  its  lower  part  is  the  vestige  of  the 
"  tunica  abdominalis,"  well  developed  in  the  horse  and  some  other  quadrupeds  for 
reinforcement  of  the  abdominal  muscles,  on  which  the  weight  of  the  viscera  comes 
more  directly  than  in  man.  It  is  attached  in  the  middle  line  to  the  deeper  struc- 
tures and  to  the  iliac  crest,  and  below  Poupart's  ligament  blends  with  the  fascia  lata 
of  the  thigh.  It  is  not  attached  over  the  space  between  the  pubic  spine  and  symphysis, 
but,  being  carried  downward  over  the  spermatic  cord,  becomes  continuous  with  the 
dartos  layer  of  the  scrotum  and  with  the  fascia  of  Colles.  Cellulitis  superficial  to  this 
layer  may  therefore  spread  in  all  directions,  but  beneath  it  is  likely  to  be  at  least  tempo- 
rarily arrested  at  the  lines  of  attachment  indicated.  General  emphysema,  effusions  of 
blood,  and  collections  of  pus  have  for  a  time  similar  limitations.  They  are  apt  to  be 
guided  by  this  fascia  into  the  space  between  the  spine  and  the  symphysis  and  to  descend 
into  the  scrotum  and  towards  the  perineum,  where  the  lateral  attachments  of  Colles's 
fascia  to  the  margins  of  the  pubic  arch  and  posteriorly  to  the  base  of  the  triangular 
ligament  prevent  their  spreading  in  those  directions.  More  usually  the  extravasa- 
tion— blood,  pus,  or  urine — gains  this  subfascial  space  below,  as  from  rupture  of  the 
urethra  anterior  (inferior)  to  the  triangular  ligament  (page  1932),  and  ascends  to  the 
abdomen  by  the  same  route,  being  prevented  from  crossing  the  mid-line  or  descend- 
ing to  the  thighs  by  the  attachments  of  the  deep  layer  of  the  superficial  fascia  that 
have  been  described. 


PRACTICAL   CONSIDERATIONS:    THE   ABDOMEN.  529 

Wounds  involving  the  muscular  layers  of  the  abdominal  wall  may  gape  widely, 
but  the  differing  directions  of  the  fibres  of  the  external  oblique,  internal  oblique, 
and  transversalis  tend  to  limit  this  just  as  they  lessen  the  after-risk  of  ventral  hernia 
and  favor  certain  physiological  acts,  as  the  emptying  of  the  bladder,  the  bowels,  or 
the  uterus.  This  difference  of  direction  is  taken  advantage  of  in  gaining  access  to  the 
abdominal  cavity  in  some  operations  (page  535). 

Infection  in  the  lateral  intcrmuscular  spaces  usually  spreads  rapidly  on  account 
of  the  abundance  of  loose  cellular  tissue.  The  cellulitis  or  resulting  abscess  (or 
collection  of  blood  or  air)  will  be  limited  by  the  semilunar  line  in  front,  by  the  costo- 
chondral  arch  above,  by  Poupart's  ligament  and  the  crest  of  the  ilium  below,  and  by 
the  edge  of  the  erector  spinae  behind  ;  in  other  words,  by  the  attachments  of  the 
muscles  between  which  they  spread  (Treves). 

Beneath  the  abdominal  wall,  practically  making  a  portion  of  it,  lies  a  layer  of 
loose  connective  tissue — the  subperitoneal  or  subserous  areolar  tissue — which  connects 
the  peritoneum  with  the  parietes.  ' '  Extraperitoneal  connective  tissue' '  has  been  sug- 
gested (Eccles)  as  a  better  name  for  it.  Infection  of  this  tissue,  whether  from  without, 
as  in  the  case  of  wounds,  or  by  extension  from  some  of  the  viscera  lying  wholly  or 
partly  behind  the  peritoneum,  as  in  perirenal  abscess  or  certain  forms  of  appendiceal 
abscess,  is  likely  to  spread  widely.  Abscesses,  especially  if  chronic,  often  gravi- 
tate into  the  iliac  fossa  and  are  arrested  at  Poupart's  ligament  by  the  junction  of  the 
transversalis  and  iliac  fasciae,  constituting  a  form  of  iliac  abscess.  If  they  are  incised 
here,  it  will  usually  be  necessary  to  go  through  only  the  abdominal  muscles  and 
aponeuroses,  including  the  transversalis  fascia,  as  the  looseness  and  abundance  of 
the  subserous  tissue  will  have  permitted  the  abscess  to  dissect  off  and  push  upward 
the  peritoneum.  If  the  patient  is  supine,  pus  in  the  iliac  fossae — i.e.,  in  the  shallow 
lower  zone  of  the  abdomen — may  gravitate  into  the  deep  lateral  recesses  of  the 
middle  zone  (page  1615),  and  it  often  takes  this  direction  in  cases  in  which  the 
source  of  infection  is  an  appendix  situated  behind  the  caecum.  It  should  be  noted 
that  a  true  iliac  abscess  is  beneath  the  iliac  fascia,  and  is  therefore  more  apt  to 
be  guided  by  that  fascia  to  the  lowest  point  of  the  ilio-psoas  space  and  to  pass 
with  the  ilio-psoas  muscle  into  the  thigh,  pointing  at  the  outer  side  of  the  femoral 
vessels. 

The  laxity  of  the  subserous  tissue  favors  certain  retroperitoneal  operations — 
e.g. ,  uretero-lithotomy — by  permitting  the  stripping  forward  of  the  peritoneum 
itself.  The  relatively  great  resistant  power  of  the  side  of  the  peritoneum  in  contact 
with  this  tissue  is  subsequently  described  (page  1754).  The  fat  contained  in  this 
layer — greatest  in  the  lumbar  region  (perinephric  fa£)  and  in  front  of  the  bladder  in 
the  space  of  Retzius  (the  triangular  interval  defined  by  the  symphysis  pubis,  the 
bladder,  and  the  peritoneum),  and  abundant  in  the  inguinal  and  iliac  regions — 
may  serve  as  a  guide  in  approaching  the  peritoneum  by  incision,  or  may  mislead  if 
mistaken  for  the  omental  fat.  The  latter  error  has  resulted,  as,  for  example,  in 
operation  for  ovarian  cyst,  in  regarding  the  peritoneum  as  the  cyst-wall,  and  in 
detaching  it  from  the  parietes  over  a  wide  area.  This  fat  occasionally  works  its  way 
through  intervals  between  the  fibres  of  the  overlying  fascia  or  muscles,  especially 
along  the  linea  alba,  and  constitutes  the  subserous  lipomata,  which,  if  large  enough, 
are  sometimes  thought  to  be  irreducible  ventral  herniae.  The  laxity  of  the  subse- 
rous areolar  layer  between  the  bladder  and  the  posterior  surface  of  the  symphysis 
pubis  permits  the  peritoneum  to  be  carried  up  on  the  summit  of  a  distended  bladder 
as  it  rises  into  the  abdomen  and  thus  facilitates  extraperitoneal  access  to  the  an- 
terior vesical  wall  (page  1912).  Its  looseness  over  the  iliacus  muscle  is  a  factor 
in  the  formation  of  the  sac  of  inguinal  hernia  (page  1767).  Wounds  of  the  abdom- 
inal wall  dividing  this  subserous  layer,  but  leaving  the  peritoneum  untouched, 
should  practically  be  classified  among  non-penetrating  wounds,  although  in  a  sense 
the  abdominal  cavity  has  been  opened.  The  symptoms  and  dangers  of  infec- 
tion will  be  as  above  enumerated.  Wounds  involving  the  peritoneum  are  called 
penetrating  wounds,  the  dangers  of  which  have  been  considered  in  the  section  on 
the  peritoneum. 

In  the  closing  of  abdominal  wounds  the  irregularities  that  may  result  from  the 
differing  directions  of  the  muscular  fibres  involved — causing  greater  retraction  at  one 

34 


530  HUMAN   ANATOMY. 

point  than  at  another — should  be  remembered.  This  may  make  accurate  suturing 
in  layers  difficult,  but  such  suturing,  together  with  careful  approximation  of  the  edges 
of  the  peritoneal  layer,  is  necessary  to  lessen  the  risk  of  ventral  hernia. 

The  respiratory  movements  prevent  the  attainment  of  absolute  rest  during  the 
healing  of  abdominal  wounds,  as  they  do  after  fractures  of  ribs  ;  but  in  both  cases 
approximate  rest,  as  secured  by  strapping  with  adhesive  plaster  or  by  abdominal 
binders,  gives  excellent  average  results. 

THE  LOIN. 

The  posterior  abdominal  wall  is  in  far  less  intimate  association  with  the  peri- 
toneum or  the  small  intestine,  and  is,  in  its  relation  to  injury  or  disease,  of  less 
importance  than  the  antero-lateral  walls,  but  it  will  be  convenient  to  consider  it  and 
the  loin  here.  Contusions,  if  over  the  ilio-costal  space, — the  posterior  segment  of 
that  portion  of  the  abdominal  wall  which  has  no  bony  protection, — are  apt,  if  severe 
enough,  to  result  in  injury  to  the  friable  kidneys  (page  1891')  rather  than  to  the  rela- 
tively strong  and  elastic  ascending  or  descending  colon.  Wounds,  if  they  pass 
through  the  entire  thickness  of  the  wall,  may  involve  either  of  these  structures. 
When  they  become  infected,  the  resulting  cellulitis  or  abscess  will  be  influenced  as  to 
the  direction  it  takes  and  in  its  limitations  by  the  various  fasciae  and  muscular  sheaths. 
The  subcutaneous  connective  tissue  is  loose  and  abundant,  and  is  frequently  the  seat 
of  suppuration  or  of  extensive  collections  of  blood  which  gravitate  towards  the  iliac 
crest  or  pass  below  it.  The  boundaries  of  effusion  into  the  intermuscular  spaces 
external  to  the  edge  of  the  erector  spinae  have  already  been  described  (vide  supra). 
Within  the  musculo-aponeurotic  compartments  made  by  the  splitting  of  the  strong 
lumbar  fascia  into  three  layers  (page  508)  and  enclosing  the  erector  spirue  and 
quadratus  lumborum  muscles  the  products  of  suppuration  may  for  a  time  be  con- 
fined. The  middle  and  posterior  layers  are,  however,  very  dense  and  resistant,  and 
therefore,  as  they  form  the  sheath  of  the  erector  spinae,  that  muscle  is  rarely  the  scat 
of  abscess  of  other  than  vertebral  origin  ;  beginning  in  caries  of  the  neural  arches, 
however,  an  abscess  may  directly  penetrate  the  muscle  between  its  fibres  of  origin  or 
insertion.  The  anterior  layer,  separating  the  quadratus  lumborum  from  the  sub- 
serous  areolar  tissue,  is  very  thin  and  is  continuous  with  the  transversalis  fascia.  For 
this  reason,  abscesses  originating  about  the  kidney  or  around  the  caecum  or  sigmoid 
not  infrequently  perforate  this  layer  and  pass  either  directly  through  the  outer  third 
of  the  thin  quadratus  lumborum  external  to  the  erector  spinae  (which  buttresses  its 
inner  two-thirds)  or  through  the  transversalis  fascia  external  to  the  quadratus.  If 
they  are  high  (perirenal),  they  may  follow  the  last  dorsal  nerve,  which  pierces  this 
fascia  and  the  transversalis  muscle  just  below  the  last  rib,  and  may  then  make  their 
way  through  the  internal  oblique  and  appear  at  the  outer  border  of  the  erector 
spime  ;  or  they  may  gravitate  to  the  triangle  of  Petit, — the  interval  between  the 
crest  of  the  ilium  (its  base)  and  the  converging  edges  of  the  external  oblique  and 
latissimus  dorsi, — where,  as  the  floor  of  the  triangle  is  formed  by  the  internal 
oblique,  they  will  be  subcutaneous  as  soon  as  they  have  perforated  the  latter  muscle. 
An  abscess  of  lower  origin  (pericaecal,  pericolic)  may  reach  the  same  space  by  fol- 
lowing the  ilio-hypogastric  branch  of  the  first  lumbar  nerve. 

Abscesses  in  the  lumbar  subserous  areolar  f issue  are  more  frequent  on  the  right 
side,  on  account  of  the  presence  of  the  appendix.  Like  abscesses  of  perinephrie 
origin  occupying  the  same  situations,  they  may  open  into  the  colon  or  sigmoid.  As 
this  tissue  is  continuous  below  with  the  corresponding  layer  in  the  pelvis,  abscesses 
originating  there  may  ascend  and  appear  at  one  or  other  of  the  various  points  de- 
scribed. True  iliac  abscesses  (vide  supra)  are  beneath  the  iliac  fascia,  which  is  con- 
tinuous with  the  transversalis  fascia  at  Ponpart's  ligament,  but  encloses  the  ilio-psoas 
muscle  in  a  definite  compartment,  weak  below,  where  the  fascia  accompanies  the 
muscle  beneath  Poupart's  ligament  to  become  the  pectineal  fascia.  The  upper  part 
of  this  fascia,  covering  the  psoas  muscle,  is  thinner  and  less  resistant  than  the  lower. 
Abscesses  beginning  in  disease  of  the  lumbar  spine  may  penetrate  directly  into  the 
muscular  substance.  Those  beginning  in  the  thoracic  spine  are  often  so  limited  an- 
teriorly by  the  internal  arcuate  ligament  and  posteriorly  by  the  spine  and  last  rib 


I 


PRACTICAL   CONSIDERATIONS  :    THE   ABDOMEN.  531 

that  they  are  diverted  into  the  psoas  sheath  between  those  slips  of  origin  of  the 
muscle  which  come  from  the  bodies  of  the  vertebrae  and  those  which  come  from 
the  transverse  processes.  Often  the  pus  descends,  as  in  iliac  abscess,  to  point  on 
the  thigh  external  to  the  femoral  vessels,  but  not  infrequently  it  passes  under  the 
external  arcuate  ligament  or  penetrates  the  psoas  sheath  at  its  outer  edge  and 
the  anterior  layer  of  the  lumbar  aponeurosis  (to  which  it  is  there  attached)  and 
points  in  the  loin,  in  which  case  it  may  be  mistaken  for  one  of  the  abscesses  origi- 
nating in  or  spreading  through  the  subserous  areolar  tissue. 

In  the  typical  psoas  abscess  the  thigh  is  flexed  to  relax  the  muscle  and  its 
sheath  and  to  lessen  the  compression  of  the  lumbar  nerves  which  are  contained 
within  it.  It  will  be  observed  that  a  psoas  or  a  true  iliac  abscess  is  in  close  relation 
to  these  nerves,  but  is  separated  from  the  iliac  vessels  and,  except  at  the  upper  por- 
tion, from  the  genito-crural  nerve  by  the  thick  iliac  fascia.  Iliac  aneurism  may, 
however,  by  pressure  cause  flexion  of  the  thigh  and  pain  in  the  course  of  the  same 
nerves. 

LANDMARKS   AND  TOPOGRAPHY    OF   THE   ABDOMEN. 

1.  The  bony  and  cartilaginous  structures  that  constitute  the  apparent  limits  of 
the  abdomen,  and  that  are  either  visible  or  palpable,  are  as  follows  : 

(a)  The  tip  of  the  ensiform  cartilage,  on  a  level  with  the  lower  part  of 
the  body  of  the  tenth  dorsal  vertebra.  (b)  The  seventh,  eighth,  ninth,  and  tenth 
costal  cartilages,  forming  the  lateral  boundaries  of  the  infrasternal  fossa  (Fig.  173, 
page  171;.  A  notch  that  may  be  felt  on  the  costal  border  indicates  the  point  of 
union  of  the  tip  of  the  tenth  to  the  edge  of  the  ninth  cartilage  (Woolsey).  (<r)  The 
tips  of  the  eleventh  and  twelfth  costal  cartilages  are  free,  except  as  they  are  con- 
nected with  each  other  by  the  intercostal  and  abdominal  muscles.  Sometimes  the 
twelfth  rib  is  rudimentary  and  does  not  project  beyond  the  external  edge  of  the 
erector  spinae  muscle.  Hence  in  planning  operations  that  open  the  abdominal  cavity 
just  below  that  rib — as  in  nephrotomy — it  is  well  to  count  the  ribs  from  above  ;  other- 
wise the  pleura  might  be  opened  by  mistake  (Fig.  1581).  (  d~)  The  spines  of  the 
lumbar  vertebrte,  corresponding  to  their  bodies  and  representing  the  posterior  bony 
wall  of  the  abdomen,  are  useful  landmarks.  Their  relation  to  the  abdominal  con- 
tents as  to  level  has  been  described  (page  148).  (<?)  The  crest  of  the  ilium,  the 
anterior  and  posterior  iliac  spines,  and  the  pubic  spine  and  svmphysis  have  been 
described  (page  349). 

2.  The   skin   is   usually  creased    or  furrowed  in  proportion   to   the  amount  of 
subcutaneous  fat  or — in  thin  persons — to  the  muscular  development.     In   fat   per- 
sons two  deep  transverse  furrows  form  across  the  abdomen.      In  the  upper  one, 
which  intersects  the  umbilicus,  the  latter  may  be  completely  concealed.      The  lower 
one  runs   just  above  the  crest  of   the  pubes.        Its  point  of    intersection   with   the 
linea  alba  is  a  convenient  landmark  for  the  introduction  of  the  trocar  in  suprapubic 
tapping  of  a  distended   bladder.      It  is   of  use   in   the  diagnosis  of  femoral  hernia 
(page  1774). 

In  cases  of  ankylosis  of  the  hip-joint  transverse  creases  may  be  seen  running 
across  the  belly  between  the  umbilicus  and  the  pubes.  They  are  produced  by  the 
freer  bending  of  the  spine  that  is  apt  to  occur  in  such  cases,  the  absence  of  some  of 
the  simpler  movements  of  the  hip-joint  in  flexion  and  extension  being  compensated 
for  by  increased  motion  of  the  vertebral  column  (Treves). 

The  stricc  gravidarum  are  sinuous,  silvery  streaks,  resembling  scars,  that  follow 
atrophy  of  the  connective-tissue  layers  of  the  skin  from  stretching  due  to  abdom- 
inal distention,  as  in  pregnancy,  ovarian  cysts,  or  ascites. 

3.  Interrmiscular  or  Interfascial  Markings. — The  linea  alba — the  fibrous  raphe 
formed  by  the  union  of  the  sheaths  of  the  recti  at  their'inner  borders — may  be  seen 
as  a  very  shallow  groove  extending  from  the  ensiform  cartilage  to  the  umbilicus. 
Below  the  tip  of  the  xiphoid  this  may  be  a  quarter  of  an  inch  in  breadth,  and  it 
is  apt  to  be  slightly  wider  just  above  the  umbilicus.      From  a  little  below  that  level 

one  to  t\vo  inches — it  cannot  be  seen,  as  until  it  nears  the  symphysis  it  is  merely 
a   line  of  fibrous  tissue  resulting   from  the  coalescence  of    the  sheaths.       A  little 


532 


HUMAN    ANATOMY. 


above  the  symphysis  it  widens  into  a  narrow  triangle  (adminiculum),  but  is  still 
not  visible  on  account  of  the  suprapubic  fat.  It  may  be  congenitally  much  wider 
than  normal,  or  may  be  stretched  by  abdominal  swellings,  and  in  either  case  may 
be  the  seat  of  ventral  hernia.  The  absence  of  blood-vessels  in  and  over  the  linea 
alba  and  its  thinness  lead  to  its  selection  as  the  site  of  the  incision  in  many 
abdominal  operations. 

The  linea  semilunaris,  corresponding  to  the  other  border  of  the  sheath  of  the 
rectus  muscle,  may  be  seen  when  the  rectus  contracts  as  a  curved  line  from  6.5  to 
7.5  cm.  (2^-3  in.)  external  to  the  linea  alba,  at  the  level  of  the  umbilicus,  with  its 

FIG.  533- 


Infraclavicular  fossa 
Coracoid  process        — ^-  -\ 


Groove  between  deltoid — r 
and  pectoral  is  major     ' 


Suprasternal  notch 

Clavicle 
Sternum 

Acromion 


Deltoid 


X-rib  cartilage 


Linea 
semilunaris 


Anterior  superior  iliac  spine 
Line  of  Poupart's  ligament 


Ensiform  cartilage 


Infrasternal 
-depression 


Linea  alba 


Linea 
-trans  versa 


Spermatic  cord  emerging 

at   external    abdominal 
ring 


Anterior  surface  of  trunk,  from  photograph  of  living  model ;  bony  landmarks  have  been  somewhat  exaggerated. 

concavity  inward,  extending  from  the  tip  of  the  ninth  costal  cartilage  to  the  spine  of 
the  pubes.  As  it  marks  the  point  of  division  of  the  abdominal  aponeuroses 
(Fig.  529)  to  form  the  sheath  of  the  rectus,  it  also  marks  a  frequent  line  of  limita- 
tion of  emphysematous,  hemorrhagic,  or  purulent  extravasations  in  the  lateral  inter- 
muscular  spaces  (vide  supra}. 

The  lineee  transvcrsce,  which  may  also  be  seen  as  shallow  grooves  when  the 
rectus  is  in  action,  and  are  most  marked  in  muscular  persons,  correspond  to  the 
tendinous  intersections  that  interrupt  the  longitudinal  fibres  of  the  rectus.  They 
are  the  representatives  of  the  intersegmental  septa  which  separate  the  original 


PRACTICAL   CONSIDERATIONS  :    THE   ABDOMEN.  533 

myotomes  giving  rise  to  the  muscles  of  the  abdomen  ;  in  some  of  the  lower  verte- 
brates (reptiles)  these  intersections  are  replaced  by  bony  bars,  as  seen  in  the 
abdominal  ribs  of  crocodiles  and  some  lizards  {Hatteria).  The  highest  is  about  the 
level  of  the  tip  of  the  ensiform  cartilage,  the  next  at  that  of  the  tenth  rib,  the  third 
at  the  umbilicus.  Very  rarely  a  fourth  line  is  seen  below  this  level.  The  second 
and  third  are  the  most  constant,  and  divide  the  upper  part  of  each  rectus  into  two 
nearly  quadrilateral  portions,  easily  seen  in  athletic  subjects.  These  bands  tend  to 
prevent  overstretching  or  rupture  of  the  rectus  in  cases  of  great  abdominal  swelling 
or  of  violent  contraction.  The  anterior  sheath  of  the  rectus  is  adherent  to  these 
fibrous  bands.  Hence  an  abscess  or  a  collection  of  blood  on  that  aspect  of  the 
muscle  may  be  confined  to  the  space  between  any  two  of  them.  Posteriorly  this  is 
not  the  case.  Spasmodic  contraction  of  the  rectus  fibres  in  one  of  these  divisions  of 
the  rectus  is  the  cause  of  one  variety  of  "phantom  tumor,"  the  swelling  appearing 
and  vanishing  with  contraction  and  relaxation  of  the  fibres, — a  phenomenon  most 
frequently  seen  in  neurasthenics,  but  which  in  this  instance  may  occasionally  indicate 
a  reflex  disturbance  based  on  some  deep-seated  source  of  irritation.  Treves  has 
seen,  for  example,  this  condition  associated  with  cancer  of  the  stomach,  duodenal 
ulcer,  and  malignant  disease  of  the  peritoneum. 

The  inguinal  groove  runs  with  a  slight  downward  curve  from  the  anterior 
superior  iliac  spine  to  the  pubic  spine  and  corresponds  to  Poupart's  ligament.  As 
this  latter  structure  results  from  a  thickening  of  the  lowest  fibres  of  the  aponeurosis 
of  the  external  oblique,  and  as  the  internal  oblique  and  transversalis  muscles  arise 
from  its  outer  half,  it  follows  that,  by  reason  of  its  direct  continuity  with  the  fascia 
lata,  extension  of  the  thigh  on  the  trunk  increases  the  tension  of  the  anterior 
abdominal  wall.  Hence  in  abdominal  examinations  the  thighs  are  flexed  on  the 
abdomen  to  lessen  this  tension.  At  the  same  time  the  shoulders  and  trunk  should 
be  slightly  elevated  to  relax  the  recti. 

Posteriorly  the  spinal  furrow  marks  the  interval  between  the  erector  spinae 
muscles  and  the  line  of  attachment  of  the  skin  to  the  tips  of  the  lumbar  spines. 
Farther  out  the  outer  edge  of  the  erector  spinae  is  palpable  and  often  visible,  except 
in  very  fat  persons.  Occasionally  the  posterior  free  edge  of  the  external  oblique  may 
be  seen  when  it  is  not  overlapped  by  the  latissimus  dorsi. 

4.  The  umbilicus,  except  as  a  landmark,  is  of  chief  interest  in  relation  to  hernia, 
in  connection  with  which  it  will  be  described.      The  creases  around  and  between  the 
folds  of  skin  forming  the  umbilical  papilla  are  difficult  to  sterilize,  and  should  receive 
especial  attention  before  operation. 

Fistulae  at  the  umbilicus  may  be  urinary  and  due  to  a  patent  urachus  (page  1911), 
or  fecal,  resulting  from  a  persistent  vitello-intestinal  duct, — Meckel's  diverticulum 
(page  1652). 

5.  The    Vessels. — The  most    important    artery  is   the   deep  epigastric   (q.v.~}, 
but  branches  of  the  deep  circumflex  iliac,  the  last  two  intercostals,  and  the  abdominal 
branches  of  the  lumbars  may  require  ligation  during  various  abdominal  operations. 
The  course  of  the  deep  epigastric  artery,  which  is  sometimes  the  source  of  trouble- 
some hemorrhage,   should   be  remembered    in    studying  the   anterior    wall    of   the 
abdomen.      A  line  drawn  with  a  slight  inward  curve  from  the  junction  of  the  inner 
and  middle  thirds  of  Poupart's  ligament  towards  the  umbilicus,  crossing  the  outer 
edge  of  the  rectus  muscle  about  one-third  the  distance  between  the  level  of  the  sym- 
physis  pubis  and  that  of  the  navel,  will  indicate  the  course  of  the  lower  part  of  this 
\<-s>el.      At  the  internal  abdominal  and  the  femoral  rings  it  has  important  relations 
to  hernial  sacs  (page  1493);  it  lies  at  first  at  the  side  of  the  rectus  in  the  subserous 
areolar  tissue,   then  in  the  transversalis  fascia,  then  within  the  .sheath  of  the  rectus 
(above  the  fold  of  Douglas)  behind  the  middle  of  the  muscle,  and   finally  in  the 
muscle  itself.      It  therefore  runs  from  without  inward  and  becomes  more  superficial 
as  it  ascends. 

With  the  exception  of  the  superior  epigastric  and  ascending  lumbar,  all  the 
abdominal  and  pelvic  veins  empty  directly  or  indirectly  into  the  inferior  vena  cava 
and  are  therefore  affected  by  the  conditions  that  obstruct  that  vessel  ;  «hence  the 
superficial  veins  are  often  varicose.  Although  their  varicosity  is  usually  a  result  of 
obstruction  in  the  portal  vein  or  inferior  vena  cava,  it  may  occur  independently  of 


534 


HUMAN    ANATOMY. 


Dytptp, 


obstructive  cause,  as  do   many  cases  of  varicose  veins  of  the  lower  extremity,  and 
may  be  very  large  and  extremely  tortuous  (.capnt  mcdus(e). 

The  mechanism  of  the  production  of  this  form  of  varicosity  by  portal  obstruc- 
tion will  be  more  readily  understood  by  reference  to  Fig.  534,  which  also  explains 
other  phenomena  associated  with  that  condition. 

The  superficial  epigastric  vein  is  often  visible.  Through  its  anastomosis  with 
the  deep  and  superior  epigastric  veins  it  is  connected  with  the  portal  and  parumbilical 
veins  and  may  be  enlarged  as  a  symptom  of  hepatic  disease  (page  1727). 

The  area  of  redness  about  the  umbilicus  seen  in  some  forms  of  peritonitis  is 
probably  due  to  inflammation  extending  along  the  obliterated  umbilical  veins 
(page  1757). 

The  surface  veins  above  the  umbilicus  empty  into  the  axilla  and  those  below  that 
level  into  the  groin,  but  the  venous  currents  may  be  reversed  by  disease.  For 
example,  the  superficial  epigastric  and  superficial  circumflex  iliac  normally  empty 
into  the  internal  saphenous  vein  a  little  below  Poupart's  ligament.  In  cases  of 
obstruction  of  the  inferior  vena  cava  the  blood-current  is  reversed  (as  it  is  in  the 
corresponding  deep  veins),  they  enlarge,  and,  by  anastomosing  with  the  superior 
epigastric,  internal  mammary,  and  thoraco-epigastric  veins,  carry  blood  from  the 
lower  limbs  into  the  axillary  or  innominate,  and  so  into  the  superior  vena  cava. 

In  hepatic  obstruction,  although  the  superficial  epigastric  may  become  varicose 
(through  its  connection  with  the  parumbilical  and  portal  veins),  this  reversal  of  the 

blood-current  does  not  occur 

FIG.  534.  in  it,   as  may  be  shown    by 

emptying  the  vein  by  press- 
ure and  observing  the  di- 
rection of  the  current  as  it 
refills. 

The  superficial  lymphatics 
of  the  abdominal  wall  below 
the  umbilical  level  empty  into 
the  nodes  at  the  groin,  those 
above  that  level  into  the 
nodes  in  the  axilla. 

6.  The  nerves  of  the 
abdominal  wall  (page  535) 
have  already  been  described 
in  their  relation  to  various 
clinical  phenomena  (pages 
1683,1755).  In  addition,  it 
should  be  said  here  that  the 
definiteness  of  the  relation 
in  nerve-supply  between  cu- 
taneous areas  and  abdominal  organs  is  often  of  great  value  in  diagnosis.  As  the 
sixth  to  the  twelfth  thoracic  and  the  first  lumbar  spinal  segments  aid  in  the  nerve- 
supply  to  the  abdominal  viscera,  and  as  the  corresponding  spinal  nerves  supply  the 
skin  of  the  abdomen,  pain  due  to  visceral  disease  is  often  referred  (through  the  com- 
municating branches  with  the  splanchnic  and  the  sympathetic  visceral  nerves )  to  the 
peripheral  terminations  on  the  skin  of  the  abdomen,  which  may  even  be  sensitive  to 
the  touch. 

It  is  possible  to  map  out  approximately  on  the  surface  the  area  of  distribution 
of  the  cutaneous  branches  from  each  of  these  segments  (Fig.  535). 

Head  has  associated  as  follows  these  areas  (  which  are  almost  identical  with  the 
arras  of  distribution  of  the  corresponding  spinal  nerves)  and  the  viscera  in  closest 
connection  with  them  : 

The  sixth,  seventh,  eighth,  and  ninth  thoracic  segments  with  the  stomach  ;  tin- 
ninth,  tenth,  eleventh,  and  twelfth  thoracic  segments  with  the  intestinal  tract  :  tin- 
seventh,  eighth,  ninth,  and  tenth  thoracic  segments  with  the  liver  and  gall-bladder  ; 
the  tenth,  eleventh,  and  twelfth  thoracic  and  the  first  lumbar  segment  with  the  kid- 
ney and  ureter  ;  the  second,  third,  and  fourth  sacral  with  the  rectum. 


CAPUT 
MEDUSAE 

Diagram  showing  anatomical  relations  of  certain  clinical  phenomena  in 
cirrhosis  of  liver.     (After  Hart  and  Taylor.) 


PRACTICAL   CONSIDERATIONS  :    THE   ABDOMEN. 


535 


The  distribution  to  the  pelvic  organs  will  be  considered  later,  but  it  may  be  said 
here  that  the  pelvic  viscera  are  supplied  from  the  fifth  lumbar  to  the  fourth  sacral 
segment  and  that  no  visceral 

branches    emerge  from    the  FIG.  535. 

second,  third,  or  fourth  lum- 
bar segments. 

Division  of  any  of  the 
motor  nerves  interferes  with 
the  function  and  ultimately 
with  the  nutrition  of  that 
portion  of  the  musculature 
of  the  abdominal  wall  that  is 
supplied  by  them,  giving  rise 
to  weakness  over  that  area, 
favoring  the  development  of 
ventral  hernia,  and,  if  ex- 
tensive, interfering  with  the 
physiological  action  of  those 
muscles  in  defecation,  urina- 
tion, or  parturition. 

For  clinical  purposes 
these  nerves  may  be  divided 
into  three  groups  (Eads): 
(a)  the  seventh  and  eighth 
intercostals  ascend  obliquely 
and  supply  the  upper  third 
of  the  abdominal  wall  ;  (£) 
the  ninth  and  tenth  intercos- 
tals run  horizontally  inward 
and  supply  the  middle  third  ; 
(c)  the  eleventh  intercostal, 
the  last  thoracic,  and  the  ilio- 
hypogastric  and  ilio-inguinal 
nerves  run  obliquely  down- 
ward and  inward  and  supply 
the  lower  third. 

It  is  obvious  that  verti- 
cal incisions  elsewhere  than 
in  the  linea  alba  (the  nerves 
do  not  cross  the  mid-line) 
will  divide  a  larger  number 
of  these  nerves  and  result 
in  more  extensive  atrophy  of 
abdominal  wall  than  will  in- 
cisions more  nearly  parallel 
with  the  nerves  and,  when 
possible,  with  the  chief  mus- 
cular fibres  of  the  region  in- 


volved. 


Diagram  of  distribution  of  cutaneous  nerves,  based  on  figures  of  Hasse 


™,  ,-       ..,         and  of  Cunningham.    On  right  side,  areas  supplied  by  indicated  nerves  are 

1  He     Anatomy     OJ     /iO-       shown;  on  left  side,  points  at  which  nerves  pierce  the  deep  fascia.     V\ 


dominal  Incisions. — A  dia- 
grammatic representation  of 
the  structures  of  the  abdom- 
inal wall  in  their  relation  to 


V-,  V3,  divisions  of  fifth  cranial  nerve;  GA,  great  auricular;  GO,  SO, 
greater  and  smaller  occipital ;  SC,  superficial  cervical  ;  St,  Cl,  Ac,  sternal, 
clavicular,  and  acromial  branches  of  supraclavicular  (Scl)  ;  Ci,  circumflex  ; 
MS,  musculo-spiral ;  Iff,  intercosto-humeral ;  LIC,  1C,  lesser  internal  and 
internal  cutaneous  ;  EC,  external  cutaneous  ;  IH,  ilio-hypogastric  ;  //,  ilio- 
inguinal  ;  r1-,  last  thoracic  ;  GC,  genito-crural ;  EC,  external  cutaneous  ; 
MC,  middle  cutaneous  ;  1C,  internal  cutaneous  ;  P,  pudic  ;  -S'-S,  small  sciatic  ; 
the  most  important  incisions  O,  obturator;  C,  T,L,  and  S,  cervical,  thoracic,  lumbar,  and  spinal  nerves. 

may    help    to   elucidate    the 

practical  application  of  some  of  the  above-mentioned  facts.  It  should  be  noted  that 
in  many  of  these  incisions  the  approximately  parallel  fibres  of  the  internal  oblique 
and  transversalis  (when  they  are  both  muscular)  may  be  regarded  as  one  layer  and 


536 


HUMAN    ANATOMY. 


FIG.  536. 


8 


separated  on  the  same  line.      No  effort  has  been  made,  therefore,  to  show  the  latter 
muscle  in  the  diagram. 

Incisions  Nos.  i,  2,  and  3  are  through  the  linea  alba,  No.  2  being  carried 
around  the  umbilicus  to  the  left  to  avoid  the  parumbilical  vein  and  the  round  liga- 
ment of  the  liver.  The  chief  advantage  is  the  accessibility  to  the  whole  cavity 
afforded  by  prolonging  the  incision.  The  slight  vascularity  of  the  median  raphe 
and  the  thinness  of  the  abdominal  wall,  while  operative  advantages,  tend  to  favor 
the  later  production  of  hernia. 

Incision  No.  4  combines  the  disadvantages  of  the  incisions  through  the  linea 
alba  with  the  added  interference  with  the  nerve-supply  to  the  rectus. 

Incision  No.  5  (McBurney)  has  been  described  (page  1685).  It  represents 
merely  the  separation  of  the  aponeurotic  fibres  of  the  external  oblique  ;  the  deeper 
wound  separates  the  internal  oblique  and  transversalis  fibres  transversely.  It  may 
be  noted  that  its  inward  extension  (Weir),  even. if  it  involves  division  instead  of 

retraction  of  the  rectus  (page  1685), 
would  equally  avoid  nerve-trunks,  but 
might  involve  ligation  of  the  deep  epi- 
gastric. The  resulting  scar  in  the 
rectus  would,  however,  merely  add  in 
effect  another  linea  transversa  and 
would  not  impair  the  efficiency  of  that 
muscle. 

Incision  No.  6  (Eads)  separates 
the  same  structures,  but  affords  a  bet- 
ter opportunity  for  approach  to  many 
appendicular  abscesses  without  going 
through  the  peritoneal  cavity  (page 
1685). 

The  incision  for  inguinal  colos- 
tomy  (page  1688)  may  be  made  on  the 
same  lines  as  those  just  described. 

Incision  No.  7,  after  division  of 
the  external  oblique,  permits  the  sepa- 
ration of  the  fibres  of  the  internal  ob- 


lique and  of  the  upper  abdominal  in- 
tercostal nerves,  which,  like  the  others, 
run  beneath  that  muscle,  and  is  used 
to  gain  access  to  the  gall-bladder 
region. 

Incision  No.  8  also  respects  the 

internal  oblique  fibres  and  the  seventh  and  eighth  intercostal  nerves  and,  when 
used  for  gastrostomy,  permits  the  development  of  a  valvular  or  sphincteric  action 
about  the  orifice  (page  1633). 

Incision  No.  9 — the  vertical  incision  through  the  rectus  recommended  for  gas- 
trostomy (Howse) — must  divide  the  terminal  branches  of  the  intercostal  nerves,  and 
consequently  that  portion  of  the  muscle  distal  to  the  line  of  division  will  be  weakened 
or  paralyzed  and  unable  to  contribute  to  the  formation  of  a  sphincter  (Eads). 

The  incision  for  lumbar  colostomy  has  been  described  (page  1688).  The  re- 
maining incisions  through  the  loin  may  be  more  appropriately  considered  in  relation 
to  the  approach  to  the  kidneys  or  ureters  (page  1894). 

Anatomical  Relations  bearing  on  the  It.vamiuation  of  the  Abdomen.  —  Harris  lias 
suggested  utilizing  the  fixed  and  circuitous  route  of  the  colon  (Fig.  1383)  to  subdi- 
vide the  abdominal  cavity  by  taking  the  inner  or  mesial  layers  of  the  longitudinal 
mesocolons  and  the  inferior  layer  of  the  transverse  mesocolon  as  the  dividing  lines. 
We  would  thus  obtain  four  regions, — namely,  (i)  the  central  region  surrounded  by 
mesocolon,  (2)  the  superior  region  lying  above  the  transverse  mesocolon,  (3)  the 
right  postero-lateral  and  (41  the  left  postero-lateral  regions  lying  external  to  and 
behind  the  longitudinal  mesocolons. 

Tumors  of  special  viscera  begin,  as  a  rule,  in  the  region  normally  occupied  by 


Diagram  illustrating  relations  of  various  incisions  to 
structures  of  abdominal  walls. 


PRACTICAL   CONSIDERATIONS:   THE   ABDOMEN.  537 

those  organs,   and  often,  when   they  overlap  its  boundaries,  displace   the  colon  in 
definite  directions. 

The  course  of  the  colon  being  made  apparent  by  inflating  it  with  air,  it  may 
therefore  be  said  that  : 

1.  Growth  in  the  central  region  would  include  tumors  of  the  omentum,  mesen- 
tery, small  intestine,  and  peritoneum,  many  retroperitoneal  tumors,  and  such  growths 
affecting  the  female  generative  apparatus  as  rise  from  the  pelvis  into  the  abdomen. 
In  the  latter  case  the  caecum  and  sigmoid  would  be  displaced  upward  and  outward. 

2.  Tumors  beginning  in  the  superior  region  would  include  those  of  the  liver, 
gall-bladder,  stomach,  lesser  omentum,  spleen,  and  pancreas.      Harris  calls  attention 
to  the  fact  that   pancreatic   cysts   have    usually  been    mistaken    for  ovarian   cysts, 
although  the  former  almost  always  displace  the  transverse  colon  downward.      They 
also,  being  retroperitoneal,  carry  it  forward,  while  tumors  of  the  spleen,  although 
they  cause  downward  displacement  of  the  colon,  especially  of  the  splenic  flexure, 
override  it  and  hug  the  anterior  abdominal  wall.      Enlargement  of  the  gall-bladder 
similarly  tends  to  depress  and  to  overlap  the  right  half  of  the  transverse  colon. 

3  and  4.  In  the  postero-lateral  or  external  regions  the  most  common  tumors  are 
those  of  the  kidneys  ;  but  as  they  are  all  retroperitoneal,  they  tend  to  carry  the 
ascending  or  descending  colon  forward  as  well  as  inward.  There  are,  of  course, 
exceptions  to  these  relations, — as,  for  example,  in  the  case  of  a  movable  kidney, 
which  may  be  displaced  so  as  to  carry  the  inner  layer  of  the  mesocolon  forward  and 
inward  and  so  have  the  colon  lying  to  the  outer  side, — but  they  are  rare,  and  the 
anatomical  relations  described  are  of  distinct  diagnostic  value. 

Bowlby  has  formulated  the  anatomical  reasons  for  first  exploring  the  right  lower 
half  of  the  abdomen  in  cases  of  intestinal  obstruction  of  doubtful  origin.  He  says 
that  here  are  to  be  found  :  (a)  the  appendix  ;  (d)  intestinal  diverticula  perhaps 
attached  to  the  umbilicus  or  to  the  neighboring  mesentery  ;  (c)  a  common  site  for 
volvulus, — that  is,  the  caecum  ;  (d  )  a  usual  site  for  the  lodgment  of  an  impacted  gall- 
stone,— that  is,  the  lower  part  of  the  ileum  ;  (e)  a  common  place  for  adhesions  due 
to  caseous  mesenteric  glands  ;  (  f)  the  sites  of  right-sided  inguinal,  femoral,  and 
obturator  herniae.  Further,  if  the  obstruction  is  in  the  small  intestine,  it  is  in  the 
right  iliac  fossa  that  undistended  intestine  will  be  found,  and  if  this  can  be  secured 
and  traced  upward,  it  is  the  surest  guide  to  the  seat  of  obstruction. 

A  brief  resume  of  some  of  those  symptoms  of  abdominal  disease  having  a  definite 
anatomical  basis  will  serve  to  complete  the  consideration  of  this  important  region. 
The  patient  being  supine  with  the  thighs  flexed  : 

1.  Inspection  may  show  :   (a)  an  asymmetrical  swelling  referable  to  a  particular 
organ  or  region  (vide  supra]  ;   (6)  general  distention,  which,  if  due  to  ascites,  will 
cause  bulging  of  the  flanks,  the  fluid  settling  in  the  deep  lateral  recesses  of  the  middle 
zone  ;  if  to  flatulence  or  intestinal  paresis,  a  more  symmetrical  enlargement,  usually 
somewhat  emphasized  in  the  central  region  on  account  of  the  presence  there  of  the 
coils  of  thin  and  easily  dilatable  small  intestine  ;  if  to  pregnancy,  a  rounded  cen- 
tral prominence  in  the  lower  abdomen  ;   (_c)  retraction,  which  if  extreme  (scaphoid), 
might  be  due  to  tuberculous  meningitis,  to  lead  poisoning,  or  to  other  cause  of  great 
emaciation  ;    (d)  cedema   of  the  skin,    indicating,  if   local,   an   abscess   underlying 
and  close  to  or  in  the  abdominal  wall  ;   (<?)  enlarged  veins  (vide  supra)  ;   (  /")  a  flat- 
tened umbilicus  in  ovarian  or  uterine  growth,  or  a  pouting  umbilicus  in  ascites  or 
tuberculous  peritonitis. 

2.  Palpation  may  disclose  :   (a)  rigidity  of  the  abdominal  wall,  which,  if  in  the 
right  hypochondriac  region,  would  suggest  gall-bladder  disease  ;  if  in  the  epigastric 
region,  stomach  ulcer  or  pancreatitis  ;  if  in  the  right  iliac  fossa,  disease  of  the  appen- 
dix or  caecum.      The  entire  absence  of  rigidity  in  a  case  of  acute  abdominal  pain, 
especially  if  the  latter  is  relieved  by  pressure,  indicates  an  absence  of  inflammation 
and  suggests  irregular  or  spasmodic  peristalsis  (colic)  as  the  cause  ;   (6)  pulsation 
due  to  the  upheaval  of  a  growth  by  vessels  beneath  it,  to  an  aneurismal  swelling,  or, 
in  the  line  of  the  vessel  and  in  thin  persons,  to  the  pulse  in  a  normal  aorta  ;   (c)  tender- 
ness, which  is  sometimes  misleading  on  account  of  the  association  of  visceral  disease 
and  reflected  surface  pain  (vide  supra).      For  example,  the  characteristic  tenderness 
of  appendicitis  is  over  McBurney's  point,  but  there  may  be  not  only  pain  but  also 


538  HUMAN   ANATOMY. 

tenderness  in  the  umbilical  region.  The  reflected  pain  of  ovaritis  may  be  beneath 
the  costal  margin  or  along  the  crural  branch  of  the  genito-crural  nerve,  where  super- 
ficial tenderness  may  be  elicited,  whereas  the  deep  pain  is  in  the  ovary  itself  (Mayo 
Robson). 

3.  Pain  due  to  abdominal  disease  has  been  described  in  connection  with  the 
various  viscera  (page  1756). 

4.  Much  information  may  be  elicited  by  percussion,  as  the  dulness  in  the  flanks 
(movable  on  change  of  position)  due  to  ascites,  or  the  localized  tympany  due  to 
volvulus  or  to  the  escape  of  gas  from  a  ruptured  appendix  into  a  surrounding  abscess  ; 
or  by  auscultation,  as  the  absence  of  the  usual  intestinal  sounds  when  a  general  peri- 
tonitis has  arrested  peristalsis  ;  or  by  inflation  of  the  stomach,  as  on  distinguishing 
between  a  growth  of  that  viscus  and  a  retroperitoneal  tumor,  or  of  the  colon  ( ride 
supra),  which  will  then  lie  below  and  perhaps  behind  an  enlarged  gall-bladder  and 
in  front  and  probably  to  the  inner  side  of  an  enlarged  kidney. 

These  and  other  procedures  are  too  technical  to  be  described  here  in  detail,  but 
are  mentioned  that  they  may  be  associated  with  the  anatomical  relations  on  which 
they  depend. 

It  should  be  noted  that  Treves  and  Keith  state  that  the  ileo-caecal  valve  corre- 
sponds to  the  spino-umbilical  line,  that  the  region  of  the  valve  in  a  normal  person 
is  usually  tender  to  pressure,  and  that  the  root  of  the  appendix  is  placed  more  than 
one  inch  lower  and  perhaps  more  internally.  This  statement  if  confirmed  will  have 
a  most  important  bearing  on  the  value  of  certain  symptoms  thought  to  indicate  the 
existence  of  appendicitis  (page  1683). 


THE   THORACIC   MUSCLES. 

(a)    THE   RECTUS  MUSCLES. 

The  rectus  abdominis,  being  supplied  by  the  lower  intercostal  nerves,  is  evi- 
dently a  derivative  of  the  thoracic  myotomes.  That  portion  of  the  rectus  group 
of  muscles  which  should  be  derived  from  the  upper  thoracic  myotomes  is  normally 
unrepresented,  although  the  occasional  extension  of  the  rectus  abdominis  to  the  upper 
costal  cartilages  or  even  to  the  clavicle  is  probably  an  indication  of  it. 

(6)    THE   OBLIQUUS   MUSCLES. 

1.  Intercostales  externi.  4.    Levatores  costarum. 

2.  Intercostales  interni.  5.   Serratus  posticus  superior. 

3.  Triangularis  sterni.  6.   Serratus  posticus  inferior. 

Here,  again,  a  considerable  portion  of  the  obliqui  and  transversalis  abdominis 
is  derived  from  thoracic  myotomes.  In  addition,  however,  a  number  of  muscles 
belonging  to  the  group  occur  in  connection  with  the  ribs. 


her. 


i.    INTERCOSTALES  EXTERNI  (Fig.  537). 

Attachments. — The  external  intercostal  muscles  are  eleven  in  number, 
stretching  across  all  the  intercostal  spaces  from  the  lower  border  of  one  rib  to  the 
upper  border  of  the  next.  The  fibres,  which  are  largely  interspersed  with  strands  of 
connective  tissue,  are  directed  downward  and  forward,  and  form  in  each  intercostal 
space  a  sheet  which  extends -in  the  upper  spaces  from  the  tubercle  of  the  rib  to  the 
junction  of  the  rib  with  its  costal  cartilage  and  in  the  lower  spaces  is  continued  upon 
the  cartilages.  The  interval  between  the  medial  borders  of  the-  upper  muscles  and 
the  border  of  the  sternum  is  occupied  by  a  sheet  of  connective  tissue  known  as  the 
external  intercostal  fascia  or  anterior  intercostal  aponenrosis. 

Nerve-Supply. — By  the  anterior  divisions  (intercostal  nerves)  of  the  thoracic 

nerves. 

Action. — To  draw  the  ribs  upward. 


THE   THORACIC   MUSCLES. 


539 


2.   INTERCOSTALES  INTERN:  (Fig.  537). 

Attachments. — The  internal  intercostals  lie  immediately  beneath  the  external 
and,  like  these,  extend  across  each  of  the  intercostal  spaces.  The  fibres  have  a 
direction  almost  at  right  angles  to  those  of  the  external  intercostals,  being  directed 
obliquely  downward  and  inward  from  the  lower  border  of  one  rib  and  its  costal  car- 
tilage to  the  upper  border  of  the  next.  The  muscle-sheets  so  formed  extend  from 
the  medial  extremity  of  each  intercostal  space  as  far  back  as  the  angles  of  the  ribs, 
becoming  there  continuous  with  an  internal  intercostal  fascia  or  posterior  intercostal 


FIG.  537. 


I  rib        Clavicle 


External  intercostal  fascia 


Internal  intercostal  mus- 
cles, anterior  part  covered 
In  external  fascia 


Internal  intercostal  muscles, 
exposed  after  removal  of  external 


Upper  external  intercostal 
muscles 


Internal  intercostal  fascia 


Lower  external  intercostal 
muscles 


Dissection  of  thoracic  wall  of  left  side,  showing  intercostal  muscles  and  fasciae. 


aponeurosis  which  continues  backward  to  the  tubercles  of  the  ribs.  The  medial  fibres 
of  the  muscles  of  the  lower  two  intercostal  spaces  become  continuous  with  the  upper 
portion  of  the  internal  oblique  muscle  of  the  abdomen. 

Nerve-Supply. — The  anterior  divisions  (intercostal  nerves)  of  the  thoracic 
nerves. 

Action. — To  drawr  the  ribs  upward. 

The  Subcostal  Muscles. — Posteriorly  the  fibres  of  the  various  internal  intercostals  do  not 
confine  themselves  to  a  single  intercostal  space,  but  extend  downward  to  the  next  space  below, 
spreading  put  in  the  muscle-sheet  of  that  space.  These  fibres,  which  vary  greatly  in  the  ex- 
tent of  their  development,  form  what  are  termed  the  subcostal  muscles. 


540 


HUMAN   ANATOMY. 


3.    TRIANGULARIS  STERNI  (Fig.  538). 

Attachments. — The  triangularis  sterni  (m.  transversus  thoracis)  forms  a  thin 
sheet  situated  upon  the  posterior  surface  of  the  medial  portion  of  the  anterior 
thoracic  wall.  It  arises  at  one  edge  by  a  series  of  slips  from  the  costal  cartilages  of 
the  second  or  third  to  the  sixth  or  seventh  rib  ;  the  upper  fibres  are  directed  obliquely 
downward  and  medially  and  the  lower  ones  transversely  to  be  inserted  by  a  thin,  flat 
tendon  to  the  sides  of  the  lower  portion  of  the  sternum  and  to  the  xiphoid  process. 
The  lower  fibres  of  the  muscle  are  practically  continuous  with  those  of  the  transversus 
abdominis. 

Nerve-Supply. — By  the  anterior  divisions  (intercostal  nerves")  of  the  second 
or  third  to  the  sixth  or  seventh  thoracic  nerve. 


FIG.  538. 


Internal  mammary  artery 


Attach- 
ment of 

iaphragm 


Dissection  of  anterior  thoracic  wall  from  behind,  showing  triangularis  sterni  and  intercostal  muscles. 

Action. — To  draw  downward  the  anterior  portions  of  the  ribs  and  so  assist  in 
expiration. 

Relations. — The  internal  mammary  vessels  pass  downward  upon  the  anterior 
surface  of  the  muscle,  separating  it  from  the  fibres  of  the  internal  intercostals. 

4.    LEVATORES  COSTARUM  (Fig.  521). 

Attachments. — The  levatores  costarum  form  a  series  of  thin  triangular  m 
cles  which  arise  from  the  transverse  processes  of  the  seventh  cervical  and  all  the 
thoracic  vertebrae  except  the  twelfth.  They  are  directed  downward  and  laterally  to 
IK-  iusi-rtcil  into  the  posterior  surface  of  the  next  succeeding  rib  (Icvatores  costarum 

/'/VTV.V  )  between  the  tubercle  and  the  angle,  some  of  the  fibres  of  the  lower  mus- 
cles passing  over  a  rib  to  be  inserted  into  the  next  but  one  below  (Irratores  costarum 
longi). 


THE   THORACIC    MUSCLES. 


Nerve-Supply. — From  the  anterior  divisions  of  the  eighth  cervical  and  the 
first  to  the  eleventh  thoracic  nerves. 

Action. — To  assist  in  drawing  the  ribs  upward.  Acting  from  the  ribs,  they 
will  assist  in  bending  the  spinal  column  backward  and  laterally  towards  the  same  side 
and  in  rotating  it  towards  the  opposite  side. 

5.    SERRATUS  POSTICUS  SUPERIOR  (Fig.  539). 

Attachments. — The  superior  posterior  serratus  is  a  quadrangular,  flat  muscle 
which  arises  by  a  flat  tendon  from  the  lower  part  of  the  ligamentum  nuchse  and  from 
the  spinous  processes  of  the  seventh  cervical  and  upper  two  or  three  thoracic  ver- 

FIG.  539. 


Com 


Splenius  c 


Levator  ang 
Serratus  posticus  sup. 


Trachelo-mastoid 

Internal  pterygoid 

pmplexus 
Biventer  cervicis 

calenus  medius 


VII  cervical  spinous  process 

.Complexus 

"calenus  posticus 


Trapezius 

(cut) 


— -Accessorius 


Semispmalis  dorsi 


Ilio-costalis 


Longissimus  dorsi 


Dorsal,  cervical,  and  thoracic  muscles. 

tebrae.  Its  fibres  are  directed  downward  and  laterally  to  be  inserted  into  the  outer 
surface  of  the  second  to  the  fifth  ribs,  lateral  to  their  angles. 

Nerve-Supply.  —  From  the  anterior  divisions  of  the  first  to  the  fourth  thoracic 
nerves. 

Action.  —  To  raise  the  ribs  to  which  it  is  attached  and  accordingly  assist  in 
inspiration. 

6.   SERRATUS  POSTICUS  INFERIOR  (Fig.  559). 

Attachments.  —  The  inferior  posterior  serratus  arises  by  a  broad  but  thin 
tendon  from  the  posterior  layer  of  the  lumbo-dorsal  fascia  from  about  the  level  of 
the  second  lumbar  to  that  of  the  tenth  or  eleventh  thoracic  vertebra.  Its  fibres  are 


542 


HUMAN    ANATOMY. 


directed  upward  and  laterally  and  are  inserted  into  the  outer  surfaces  of  the  lower 
four  ribs. 

Nerve-Supply. — From  the  anterior  divisions  of  the  ninth  to  the  twelfth 
thoracic  nerves. 

Action. — To  draw  the  ribs  to  which  it  is  attached  downward  and  outward. 
The  muscle  contracts  during  inspiration  and  assists  in  this  act  by  counteracting  the 
tendency  which  the  costal  part  of  the  diaphragm  has  to  expend  a  portion  of  its  con- 
traction in  drawing  the  lower  ribs  upward  and  inward. 

Variations. — Variations  in  the  extent  of  their  origin  are  not  uncommon  in  both  the  posterior 
serrati.  Stretching  between  them  there  is  an  aponeurosis,  termed  the  vertebral  aponcurosis, 
which  represents  the  degenerated  portion  of  a  large  muscle-sheet  present  in  the  lower  mam- 
malia, of  which  the  two  posterior  serrati  are  the  persistent  upper  and  lower  portions. 

(0    THE   HYPOSKELETAL   MUSCLES. 

The  hyposkeletal  group  of  muscles  is  practically  unrepresented  in  the  thoracic 
region. 

THE   CERVICAL    MUSCLES. 

The  Deep  Cervical  Fascia. — The  deep  cervical  fascia  (fascia  colli)  is  a 
well-marked  sheet  of  connective  tissue  which  lies  beneath  the  platysma  and  forms  a 
complete  investment  for  the  neck  region,  giving  off  from  its  deeper  surface  numer- 
ous thin  lamellae  which  surround  the  various  structures  of  the  neck  region.  Pos- 


FIG.  540. 


Sterno-hyoid 
Thyro-hyoid 
Omo-hyoid's. 
Arytenoideus 


Thyroid  cartilage 
.Vocal  cord 


Inferior  constrictor 
Carotid  sheath  - 
Prevertebral  layer 

Platysma 
Sterno-mastoid 
Longus  colli 
Scalenus  aiiticus 
Scalonus  mcdins 
Scalenus  posticus  i 
Trachelo-mastoid- 
Levator  anguli  scapulae-' 
Splenius  colli-! 
Multifidus  spinse-' 

Semispinalis  cervicis- 


Trapezius- 

Splenius  capitis-- ' 

Complexus 


.Arytenoid  cartilage 
.Pharynx 
^ — Right  carotid  artery 

.Right  internal  jugular 

vein 
i—Vertebral  arterv 

! 

—V  cervical  vertebra 


Spinal  cord 


Ligamentum  nuchae 


Section  across  neck  at  lower  border  of  fifth  cervical  vertebra. 

teriorly  the  fascia  is  attached  to  the  ligamentum  micha?  and,  traced  laterally,  it  is 
found  to  divide  into  two  layers  which  enclose  the  trapexius  and.  uniting  again  at  its 
outer  border,  arc'  continued  foruanl  over  the  posterior  triangle  of  the  neck  t<>  tin- 
lateral  border  of  the  sterno-cleido-mastoid,  where  it  again  divides  into  two  layers  to 
enclose  that  muscle.  The  two  layers  again  unite  at  the  medial  border  o)  the  muscle 
and  are  continued  over  the  anterior  triangle  of  the  neck  to  the  median  line,  where 
the  fascia  be.-onx-s  continuous  with  that  of  the  opposite  side. 

This  is  the  superficial  layer  of  the  deep  cervical   fascia.      Above  it  is  attached 
to  the  superior  nuchal  line  and   the  mastoid  process,  whence  it  is  continued  along 


mg 


THE   CERVICAL    MUSCLES.  543 

the  greater  cornu  and  body  of  the  hyoid  bone,  to  which  it  is  firmly  attached,  and 
where  it  becomes  continuous  above  with  the  deep  fascia  of  the  submental  region. 
This  fascia  covers  in  the  anterior  belly  of  the  digastric,  the  mylo-hyoid,  and  the 
submaxillary  gland,  and  is  attached  above  to  the  lower  border  of  the  mandible, 
where  it  becomes  continuous  with  the  parotido-masseteric  fascia. 

Below  the  cervical  fascia  ends  over  the  anterior  surface  of  the  clavicle,  and, 
more  medially,  in  the  interval  between  the  lower  portions  of  the  two  sterno-cleido- 
mastoid  muscles,  it  splits  into  two  lamellae,  enclosing  what  is  termed  the  spatium 
suprasternale  or  space  of  Burns.  Both  the  lamelke  pass  down  to  be  attached  to  the 
upper  part  of  the  manubrium  sterni,  so  that  the  suprasternal  space  is  completely 
closed.  It  contains  some  fatty  tissue,  usually  some  lymphatic  nodes,  and  the  lower 
portions  of  the  anterior  jugular  veins  ;  a  diverticulum  from  it  is  prolonged  laterally 
behind  the  insertion  of  the  sterno-cleido-mastoid  along  each  vein  as  it  passes  towards 
its  point  of  union  with  the  subclavian  vein. 

From  the  under  surface  of  this  superficial  layer  a  deeper  or  middle  layer  is 
given  off  at  the  sides  of  the  neck,  and,  passing  forward,  assists  in  the  formation  of 
the  sheath  for  the  carotid  artery  and  internal  jugular  vein,  and  then  divides  to 
enclose  the  omo-hyoideus  and  the  other  depressors  of  the  hyoid  bone,  a  special 
thickening  of  it  extending  downward  from  the  intermediate  tendon  of  the  omo-hyoid 
to  the  clavicle.  Above,  the  middle  layer  is  attached  to  the  greater  cornu  and  body 
of  the  hyoid  bone  along  with  the  superficial  layer,  but  below  it  is  continued  down 
into  the  thorax  in  front  of  the  oesophagus  and  trachea  and  becomes  lost  upon  the 
upper  part  of  the  pericardium. 

A  third  or  deep  layer  of  the  cervical  fascia,  also  termed  the  prevcrtcbral  fascia, 
is  given  off  from  the  under  surface  of  the  superficial  layer  about  on  the  line  of  the 
transverse  processes  of  the  vertebrae.  It  passes  almost  directly  inward  over  the 
scalene  and  hyposkeletal  muscles  of  the  neck,  enclosing  the  cervical  portion  of  the 
sympathetic  trunk  and  contributing  to  the  formation  of  the  carotid  sheath.  It 
unites  with  the  corresponding  layer  of  the  opposite  side  over  the  bodies  of  the 
vertebrae.  This  fascia  is  continued  downward  into  the  thorax  in  front  of  the  verte- 
bral column  and  above  it  extends  to  the  base  of  the  skull.  Towards  the  median 
line  in  its  upper  part  it  is  separated  from  the  pharyngeal  portion  of  the  fascia 
bucco-pharyngea  by  some  loose  areolar  tissue  which  occupies  the  so-called  retro- 
pharyngeal  space.  This  is  continued  downward  in  the  loose  tissue  surrounding  the 
•  esophagus,  but  is  bounded  laterally  by  the  union  of  the  pharyngeal  and  prevertebral 
fasciae. 

The  carotid  sheath  is  formed  by  the  union  of  portions  from  the  middle  and  deep 
layers  of  the  cervical  fascia.  It  forms  an  investment  for  the  common  carotid  artery, 
the  internal  jugular  vein,  and  the  vagus  nerve. 


(a)  THE  RKCTUS  MUSCLES. 

1.  Sterno-hyoideus.  3.   Sterno-thyroideus. 

2.  Omo-hyoideus.  4.   Thyro-hyoideus. 

5.    Genio-hyoideus. 

i.   STERNO-HYOIDEUS  (Fig.  541). 

Attachments. — The  sterno-hyoid  is  a  flat  band-like  muscle  situated  in  the 
front  of  the  neck  close  to  the  median  line.  It  arises  from  the  posterior  surface  of 
the  sternal  end  of  the  clavicle  and  from  the  manubrium  sterni  and  passes  upward  to 
be  inserted  into  the  lower  border  of  the  body  of  the  hyoid  bone.  A  mucous  bursa, 
more  constant  in  the  male  than  in  the  female,  usually  occurs  beneath  the  upper 
part  of  the  muscle,  resting  upon  the  hyo-thyroid  membrane  near  the  median  line 
and  immediately  below  the  hyoid  bone. 

Nerve-Supply. — From  the  first,  second,  and  third  cervical  nerves,  through 
the  ansa  hypoglossi. 

Action. — To  draw  the  hyoid  bone  downward. 


544 


HUMAN   ANATOMY. 


Variations. — The  sterno-hyoid  may  arise  entirely  from  the  clavicle  or  it  may  extend  its  origin 
to  the  cartilage  of  the  first  rib.  It  is  often  divided  transversely  by  a  tendinous  band  which  may- 
occur  either  in  its  lower  part  on  a  line  with  the  intermediate  tendon  of  the  omo-hyoid  or,  more 
rarely,  in  its  upper  part  on  a  level  with  the  insertion  of  the  sterno-thyroid. 

2.   OMO-HYOIDEUS  (Fig.  541). 

Attachments. — The  omo-hyoid  is  a  long,  flat  muscle  consisting  of  two  bellies 
united  by  an  intermediate  tendon.  The  inferior  belly  arises  from  the  lateral  portion 
of  the  superior  border  and  the  superior  transverse  ligament  of  the  scapula,  and  is 
directed  forward,  medially,  and  slightly  upward  to  terminate  in  the  intermediate 
tendon.  This  lies  behind  the  clavicular  portion  of  the  sterno-cleido-mastoid,  and  is 
enclosed  by  the  middle  layer  of  the  deep  cervical  fascia,  a  specially  thickened 
portion  of  which  binds  it  down  to  the  posterior  surface  of  the  clavicle  and  to  the 
first  rib.  The  superior  belly  arises  at  the  medial  end  of  the  intermediate  tendon  and 
passes  upward  and  slightly  medially  to  be  inserted  into  the  lower  border  of  the  hyoid 
bone,  lateral  to  the  sterno-hyoid. 

FIG.  541. 


Styloid  proce 

Stylo-glossus- 
Stylo-pharyngeu 

Stylo-hyoid 

Digastric,  posterior  belly. 
Rectus  capitis  anticus  major. 

Spleni 
Sterno-cleido-mastoid 


Levator  anguli  scapulae 


Scalenus  anticus 

Omo-hyoid, 
posterior " 


Buccinator 


Orbicularis  oris 
Depressor  anguli 
Depressor  labii 

inferioris 
Hyo-glossus 

Digastric,  anterior  belly 
Mylo-hyoid 
Hyoid  bone 

Inferior  pharyngeal  constrictor 
Thyro-hyoid 

Sterno-hyoid 
Thyroid  body 

Omo-hyoid,  anterior  belly 


Sterno- 
thyroid 


Muscles  of  the  neck ;  larynx  has  been  drawn  forward. 

NerverSupply. — From  the  first,  second,  and  third  cervical  nerves,  through 
the  ansa  hypoglossi. 

Action. — To  draw  downward  the  hyoid  bone.  Acting  from  above,  it  will 
assist  slightly  in  drawing  the  scapula  upward.  This  muscle  may  also  act  as  a 
tensor  of  the  cervical  fascia,  thereby  preventing  undue  pressure  on  the  great  vessels 
of  the  neck. 

Relations. — At  its  attachment  to  the  scapula  the  inferior  belly  is  coven-d  l>y 
the  trapezius  and  the  muscle  is  crossed  in  the  middle  part  of  its  course  by  the 
sterno-cleido-mastoid.  The  inferior  belly  is  in  relation  posteriorly  with  the  scalene 
muscles  and  the  roots  of  the  brachial  plexus  and  sometimes  with  the  third  portion  of 
the  subclavian  artery,  the  transx crsalis  colli  and  transverse  scapular  arteries,  and  the 
-upruscapular  nerve.  The  superior  belly  crosses  the  common  carotid  artery  and 
the  internal  jugular  vein  at  the  level  of  the  cricoid  cartilage. 


THE   CERVICAL   MUSCLES.  545 

Variations. — The  omo-hyoid  and  the  sterno-hyoid  are  derived  from  a  muscular  sheet 
which,  in  the  lo\ver  vertebrates,  invests  the  anterior  portion  of  the  neck  region,  lying  beneath 
the  platysma.  This  sheet  is  represented  in  man  by  the  two  muscles  and  the  middle  layer  of 
the  deep  cervical  fascia.  The  omo-hyoid  or  one  or  other  of  its  bellies  may  be  absent,  or,  on 
the  other  hand,  an  accessory  omo-hyoid  may  be  developed.  The  superior  belly  not  infre- 
quently fuses  more  or  less  completely  with  the  sterno-hyoid  and  the  inferior  belly  has  some- 
times a  clavicular  origin.  Occasionally  the  band  which  binds  the  intermediate  tendon  to  the 
clavicle  remains  muscular,  and,  uniting  at  the  tendon  with  the  superior  belly,  produces  what 
lias  been  termed  the  cleido-hyoideus. 

3.   STERNO-THYROIDEUS  (Fig.  541). 

Attachments. — The  sterno-thyroid  is  a  band-like  muscle  which  lies  immedi- 
ately beneath  the  sterno-hyoid.  It  arises  from  the  posterior  surface  of  the  manu- 
brium  sterni  and  from  the  cartilages  of  the  first  and  second  ribs,  and  passes  upward 
to  be  inserted  into  the  oblique  line  of  the  thyroid  cartilage. 

Nerve-Supply. — From  the  first,  second,  and  third  cervical  nerves,  through 
the  ansa  hypoglossi. 

Action. — To  draw  the  larynx  downward. 

Relations. — Superficially  the  sterno-thyroid  is  covered  by  the  sterno-hyoid. 
Deeply  it  is  in  relation  with  the  inferior  constrictor  of  the  pharynx,  the  crico- 
thyroid  muscle,  the  cricoid  cartilage,  the  lobes  of  the  thyroid  gland,  the  inferior 
thyroid  veins,  the  trachea,  and  the  common  carotid  artery,  and  it  crosses  the  left 
vena  anonyma. 

Variations. — The  lower  portion  of  the  muscle  is  often  crossed  by  a  tendinous  intersection, 
and  frequently  some  of  its  fibres  are  continued  directly  into  the  thyro-hyoid  muscle.  The  two 
muscles  of  opposite  sides  are  frequently  united  in  the  median  line,  sometimes  throughout  the 
greater  portion  of  their  length,  at  other  times  merely  by  scattered  bundles. 

4.  THYRO-HYOIDEUS  (Fig.  541). 

Attachments. — The  thyro-hyoid  lies  beneath  the  upper  portion  of  the  omo- 
hyoid.  It  arises  below  from  the  oblique  line  of  the  thyroid  cartilage  and  is 
inserted  above  into  the  lateral  portion  of  the  body  and  into  the  greater  cornu  of  the 
hyoid  bone. 

Nerve-Supply. — From  the  first  and  second  cervical  nerves,  by  fibres  which 
run  with  the  hypoglossal  nerve. 

Action. — To  draw  down  the  hyoid  bone,  or,  if  that  be  fixed,  to  draw  the 
larynx  upward. 

Relations. — As  the  muscle  passes  across  the  hyo-thyroid  membrane  it  covers 
the  superior  laryngeal  nerve  and  artery.  A  bursa,  the  b.  musculi  thyro-hyoidei,  is 
interposed  between  the  muscle  and  the  upper  part  of  the  hyo-thyroid  membrane. 

Variations. — The  thyro-hyoid  is  often  practically  continuous  with  the  sterno-thyroid.  A 
bundle  of  fibres  is  sometimes  to  be  found  passing  either  from  the  lower  border  of  the  hyoid  or 
from  the  thyroid  cartilage  to  the  lobe,  isthmus,  or  pyramid  of  the  thyroid  gland.  It  is  termed 
the  levator  glandule  thyroidece,  under  which  name  are  also  comprised  fibres  which  are  exten- 
sions of  the  inferior  constrictor  of  the  pharynx  to  the  thyroid  gland. 

5.  GENIO-HYOIDEUS  (Fig.  497). 

Attachments. — The  genio-hyoid  is  the  superior  portion  of  the  rectus  group 
of  muscles.  It  is  a  rather  narrow  band  which  arises  from  the  lower  genial  tubercle 
of  the  mandible  and  extends  backward  and  downward  to  be  inserted  into  the 
anterior  surface  of  the  body  of  the  hyoid  bone.  It  is  situated  close  to  the  median 
line,  under  cover  of  the  mylo-hyoid  and  immediately  beneath  the  lower  border  of 
the  genio-glossus. 

Nerve-Supply. — From  the  first  and  second  cervical  nerves,  by  fibres  which 
accompany  the  hypoglossal. 

Action. — If  the  hyoid  bone  be  fixed,  the  genio-hyoid  depresses  the  mandible  ; 
if  the  mandible  be  fixed,  it  draws  the  hyoid  bone  forward  and  upward. 

35 


546 


HUMAN   ANATOMY. 


(6)     THE  OBLIQUUS   MUSCLES. 

1.  Scalenus  anticus.  3.   Scalenus  posticus. 

2.  Scalenus  medius.  4.    Rectus  capitis  lateralis. 

5.    Intertransversales  anteriores. 

i.  SCALENUS  ANTICUS  (Fig.  542). 

Attachments. — The  anterior  scalene  (m.  scalenus  anterior)  arises  by  four 
tendinous  slips  from  the  anterior  tubercles  of  the  transverse  processes  of  the  third 
to  the  sixth  cervical  vertebrae.  The  four  slips  unite  to  form  a  rather  flat  muscle 
which  extends  downward  and  forward  to  be  inserted  into  the  scalene  tubercle  on  the 
upper  surface  of  the  first  rib. 

FIG.  542. 


Levator  anguli  scapulae. 


Subscapularis 


Serratus  magnus, 
middle  portion 


Sterno-mastoid,  stump 
Rectus  capitis  anticus  major 


Scalenus  anticus 
Scalenus  medius 

Scalenus  posticus, 
Rhomboidei 


— Sternum 


I  rib 


Serratus  magnus,  upper  portion 


Dissection  of  right  side  of  neck,  showing  scalene  and  adjacent  muscles. 

Nerve-Supply. — By  branches  from  the  fourth,  fifth  and  sixth  cervical  nerves. 

Action. — To  bend  the  neck  forward  and  to  the  same  side  and  to  rotate  it  to 
the  opposite  side.  If  the  cervical  vertebrae  be  fixed,  it  will  then  raise  the  first  rib, 
assisting  in  inspiration. 

Relations. — The  anterior  scalenus  lies  in  front  of  the  roots  of  the  brachial 
plexus,  and  near  its  insertion  it  passes  over  the  second  portion  of  the  subclavian  artery 
and  under  the  subclavian  vein.  The  phrenic  nerve  rests  upon  its  anterior  surfac 
during  its  course  down  the  neck. 

2.  SCALENUS  MEDIUS  (Figs.  541,  542). 

Attachments. — The  middle  scalene  is  situated  behind  the  scalenus  anterior. 
It  arises  by  six  or  seven  tendinous  slips  from  the  transverse  processes  of  the  lower 
six  or  of  all  the  cervical  vertebrae  and  extends  downward  and  outward  to  be  inserted 


THE   CERVICAL   MUSCLES.  547 

into  the  upper  surface  of  the  first  rib,  behind  the  groove  for  the  subclavian  artery. 
Some  fibres  of  the  muscle  may  extend  across  the  first  intercostal  space  to  be  inserted 
into  the  outer  surface  of  the  second  rib. 

Nerve-Supply. — By  branches  from  the  anterior  divisions  of  the  cervical 
nerves. 

Action. — To  bend  the  neck  laterally,  or,  if  the  cervical  vertebrae  be  fixed,  to 
raise  the  first  rib,  assisting  in  inspiration. 

Relations. — As  the  middle  scalene  passes  downward  to  its  insertion  it  diverges 
from  the  scalenus  anterior,  so  that  a  triangular  interval  exists  between  the  two 
muscles  through  which  the  subclavian  artery  and  the  brachial  plexus  pass,  these 
structures  lying  in  front  of  the  insertion  of  the  scalenus  medius. 

3.    SCALENUS  POSTICUS   (Fig.  542). 

Attachments. — The  posterior  scalene  (ra.  scalenus  posterior)  lies  immediately 
behind  the  scalenus  medius  and  anterior  to  the  ilio-costalis  cervicis.  It  arises  by 
two  or  three  tendinous  slips  from  the  transverse  processes  of  the  lower  two  or  three 
cervical  vertebrae  and  passes  downward  and  laterally  to  be  inserted  into  the  outer 
surface  of  the  second  rib. 

Nerve-Supply. — From  the  anterior  divisions  of  the  lower  three  cervical 
nerves. 

Action. — To  bend  the  neck  laterally,  or,  if  the  cervical  vertebrae  be  fixed,  to 
raise  the  second  rib. 

Variations  of  the  Scalene  Muscles. — There  is  not  a  little  variation  in  the  extent  of  the 
upper  attachments  of  the  scalene  muscles,  the  origins  being  increased  or,  more  usually,  dimin- 
ished in  number.  A  certain  amount  of  fusion  may  also  occur,  especially  between  the  medius 
and  posterior,  so  that  it  is  not  always  possible  to  distinguish  these  two  muscles.  Occasionally 
the  subclavian  artery  perforates  the  lower  portion  of  the  anterior  scalene,  and  the  portion  so 
separated  may  form  a  distinct  muscle,  the  scalenus  minimus,  which  lies  in  the  interval  between 
the  anterior  and  middle  scalenus,  and  is  attached  above  to  the  transverse  processes  of  the  sixth 
or  the  sixth  and  seventh  cervical  vertebrae  and  below  to  the  upper  surface  of  the  first  rib  and  to 
the  dome  of  the  pleura. 

A  muscle  occasionally  occurs  between  the  upper  part  of  the  pectoralis  major  and  the 
upper  external  intercostals,  from  both  of  which  it  is  separated  by  a  lamella  of  areolar  tissue. 
It  is  termed  the  supracostalis,  and  takes  its  origin  from  the  first  rib  and  sometimes  also  from  the 
fascia  which  covers  the  anterior  scalene,  and  passes  downward  to  be  inserted  into  the  outer 
surface  of  the  third  and  fourth  ribs,  sometimes  attaching  also  to, the  second  rib  and  sometimes 
descending  as  low  as  the  fifth.  It  has  been  regarded  as  an  aberrant  portion  of  the  pectoralis 
major  or  rectus  abdominis,  but  it  seems  to  be  more  probably  a  portion  of  the  obliquus  muscu- 
lature and  is  apparently  related  to  the  scaleni. 

4.    RECTUS  CAPITIS  LATERALIS. 

Attachments. — The  rectus  capitis  lateralis  is  a  short,  flat  muscle  which  arises 
from  the  transverse  process  of  the  atlas  and  is  inserted  into  the  inferior  surface  of 
the  jugular  process  of  the  occipital  bone. 

Nerve-Supply. — From  the  suboccipital  nerve. 

Action. — To  bend  the  head  laterally. 

5.    INTERTRANSVERSALES  ANTERIORES. 

Attachments. — The  anterior  intertransversales  are  a  series  of  small  muscles 
which  pass  between  the  anterior  tubercles  of  the  transverse  processes  of  the  cervical 
vertebrae. 

Nerve-Supply. — From  the  anterior  divisions  of  the  cervical  nerves. 

Action. — To  bend  the  head  laterally. 

The  Triangles  of  the  Neck. — The  sterno-cleido-mastoid  muscle,  on  account 
of  its  position  somewhat  superficial  to  the  remaining  muscles  of  the  neck,  serves  to 
divide  that  region  into  two  triangular  areas  which  are  of  considerable  importance 
from  the  stand-point  of  topographic  anatomy. 


54« 


HUMAN   ANATOMY. 


- 


Ster 


ic,  anterior  belly 


Trape 


ROTID  TRIANGLE 


anterior  belly 


ROTID 

R)  THIANQI  F 


One  of  these  triangles,  the  posterior,  is  bounded  by  the  lateral  border  of 
the  upper  part  of  the  trapezius  behind  and  by  the  lateral  border  of  the  sterno- 
cleicio-mastoid  in  front,  and  has  for  its  base  the  upper  border  of  the  clavicle 
between  the  insertion  of  these  two  muscles.  The  anterior  triangle  is  reversed  with 
respect  to  the  posterior  one,  having  its  apex  downward  and  its  base  above.  Its  lateral 
boundary  is  the  medial  border  of  the  sterno-cleido-mastoid,  its  medial  boundary  is 
the  median  line  of  the  neck,  and  its  base  is  formed  by  the  lower  border  of  the 

mandible    and    a    line 

FIG    543.  extending    horizontally 

backward  from  the  an- 
gle of  the  mandible  to 
the  mastoid  process. 

Each  of  these  two 
triangles  is  again  di- 
visible into  subordinate 
triangles  by  the  mus- 
cles which  cross  them. 
Thus  the  posterior  tri- 
angle is  divided  by  the 
inferior  belly  of  the  omo- 
hyoid,  which  crosses  it 
obliquely,  into  an  upper 
or  occipital  triangle  and 
a  lower  or  subclavian 
triangle,  while  the  an- 
terior triangle  is  divisi 
ble  into  three  triangles 
by  the  superior  belly  of 
the  omo-hyoid  and  tin- 
posterior  belly  of  the 
digastric.  The  lowest  of 
these  triangles,  termed 
the  muscular 'or  inferior 
carotid  triangle,  has  its 
base  along  the  median 
line  and  its  apex  directed  laterally,  its  sides  being  formed  by  the  sterno-cleido- 
mastoid  below  and  the  superior  belly  of  the  omo-hyoid  above.  The  superior  carotid 
triangle  has  its  base  along  the  upper  part  of  the  sterno-cleido-mastoid  and  its  apex 
directed  medially  ;  its  sides  are  formed  by  the  superior  belly  of  the  omo-hyoid  below 
and  the  posterior  belly  of  the  digastric  above.  Finally,  the  submaxillary  or  digastric 
triangle  is  the  basal  portion  of  the  original  anterior  triangle,  and  is  bounded  below 
by  the  two  bellies  of  the  digastric  muscle  and  above  by  the  line  of  the  lower  border 
of  the  mandible  and  its  continuation  posteriorly  to  the  sterno-mastoid  muscle. 

(c)  THE   HYPOSKELETAL   MUSCLES. 

i.    Longus  colli.  2.    Rectus  capitis  anticus  major. 

3.    Rectus  capitis  anticus  minor. 

i.   LONGUS  COLLI  (Fig.  544). 

Attachments. — The  longus  colli  forms  an  elongated  triangular  band  whose 
base  is  towards  the  median  line  and  the  wide-angled  apex  directed  laterally.  It  may 
be  regarded  as  consisting  of  three  portions.  The  medial  portion  consists  of  fibres 
which  arise  from  the  bodies  of  the  upper  three  thoracic  and  lower  two  cervical 
vertebra,  forming  a  muscular  band  which  is  inserted  into  the  bodies  of  the  three  or 
four  upper  cervical  vertebrae,  the  slip  to  the  atlas  being  inserted  into  its  anterior 
tubercle.  From  the  lower  part  of  the  medial  portion  slips  arc  ^i\cn  off  which  con- 
stitute the  inferior  oblique  portion,  and  are  inserted  into  the  transverse  processes  of 
the  fifth  and  sixth,  and  sometimes  also  of  the  fourth  and  seventh,  cervical  vertebr.e. 


SUBCLAVIAN  TRIANGLE 


Omo-hyoid,  posterior  belly- 


Clavicle 


Triangles  of  neck. 


THE   CERVICAL    MUSCLES.  549 

And,  finally,  the  superior  oblique  portion  is  formed  by  slips  arising  from  the  trans- 
verse processes  of  the  sixth  to  the  third  cervical  vertebrae  and  joining  the  upper  part 
of  the  medial  portion. 

Nerve-Supply. — From  the  anterior  divisions  of  the  second,  third,  and  fourth 
cervical  nerves. 

Action. — To  bend  the  neck  ventrally  and  laterally. 

FIG.  544. 


Anterior  tubercle  of  atlas 


Longus  colli,  superior  oblique 
portion 


W  I 

Rectus  capltis  anticus  major — — 2 


Longus  colli,  median  portion 


ongus  colli,  inferior  oblique 
portion 


Scalenus  medius — j— *•  Jj 
Scalenus  anticus 
I  rib 


Clavicle_ 


L_VII  cervical  vertebra 


I  thoracic  vertebra 


Deep  dissection  of  neck,  showing  prevertebral  muscles. 


2.   RECTUS  CAPITIS  ANTICUS  MAJOR  (Fig.  544). 

Attachments. — The  rectus  capitis  anticus  major  (m.  longus  capitis)  partly 
covers  the  upper  part  of  the  longus  colli.  It  arises  by  four  tendinous  slips  from  the 
transverse  processes  of  the  third  to  the  sixth  cervical  vertebrae,  and  passes  directly 
upward  to  be  inserted  into  the  basilar  portion  of  the  occipital  bone,  lateral  to  the 
pharyngeal  tubercle. 

Nerve-Supply. — From  the  anterior  divisions  of  the  second,  third,  and  fourth 
cervical  nerves. 

Action. — To  flex  the  head  and  rotate  it  slightly  towards  the  opposite  side. 


550  HUMAN    ANATOMY. 

3.   RECTUS  CAPITIS  ANTICUS  MINOR. 

Attachments. — The  rectus  capitis  anticus  minor  (m.  rectus  capitis  anterior) 
is  a  short,  flat  muscle  which  arises  from  the  anterior  surface  of  the  lateral  mass  of 
the  atlas  and  is  directed  obliquely  upward  and  medially  to  be  inserted  into  the 
basilar  portion  of  the  occipital  bone,  immediately  behind  the  insertion  of  the  longus 
capitis. 

Nerve-Supply. — By  the  first  cervical  (suboccipital)  nerve. 

Action. — To  flex  the  head. 

PRACTICAL   CONSIDERATIONS  :    THE  NECK. 

The  skin  of  the  front  and  sides  of  the  neck  is  thin  and  movable.  The  platysma 
myoides  is  closely  connected  to  it  by  the  thin  superficial  fascia.  The  edges  of  wounds 
transverse  to  the  fibres  of  that  muscle  are  therefore  often  inverted. 

In  the  region  of  the  nape  of  the  neck  the  skin  is  thicker  and  much  more  closely 
adherent  to  the  deep  fascia;  it  is  poorly  supplied  with  blood  ;  hair-follicles  and 
sebaceous  glands  are  numerous  ;  it  is  frequently  exposed  to  minor  traumatisms  and 
to  changes  of  surface  heat,  and  is '  often  at  a  lower  temperature  than  the  parts 
immediately  above,  which  are  covered  with  hair,  or  than  those  directly  below,  which 
are  protected  by  clothing;  the  nerve-supply  is  abundant.  For  these  reasons  furun- 
cles and  carbuncles  are  of  common  occurrence  and  are  apt  to  be  exceptionally  painful. 

The  subcutaneous  ecchymosis  which  follows  fracture  through  the  posterior  cerebral 
fossa  first  appears  anterior  to  the  tip  of  the  mastoid  and  spreads  upward  and  back- 
ward on  a  curved  line  ;  the  blood  is  prevented  from  reaching  the  surface  more 
directly  by  the  cervical  fascia,  and  therefore  goes  laterally  in  the  intermuscular 
spaces,  being  directed  towards  the  mastoid  tip  by  the  posterior  auricular  artery. 

In  the  submaxillary  region  the  looseness  of  the  skin  makes  it  available  for 
plastic  operations  on  the  cheeks  and  mouth.  In  the  submental  region  the  accu- 
mulation of  subcutaneous  adipose  tissue  seen  in  stout  persons  gives  rise  to  the 
so-called  "  double  chin."  In  both  the  latter  regions  (covered  by  the  beard  in  men) 
furuncles  and  sebaceous  cysts  are  common. 

The  surgical  relations  of  the  fascia  of  the  neck  can  best  be  understood  by  refer- 
ence to  a  horizontal  section  at  the  level  of  the  seventh  cervical  vertebra  (Fig.  545). 

The  superficial  layer  (a,  a')  will  then  be  seen  to  envelop  the  entire  neck.  Pos- 
teriorly it  is  attached  between  the  external  occipital  protuberance  and  the  seventh 
cervical  spinous  process  to  the  ligamentum  nuchae  ;  anteriorly  it  is  interlaced  with 
the  same  layer  of  fascia  from  the  other  side  of  the  neck  ;  superiorly  between  the 
external  occipital  protuberance  and  the  middle  of  the  chin  it  is  attached  on  each  side 
to  the  superior  curved  line  of  the  occipital  bone,  the  mastoid,  the  zygoma,  and  the 
lower  jaw  ;  inferiorly  between  the  seventh  spine  and  the  suprasternal  notch  it  is 
attached  on  each  side  to  the  spine  of  the  scapula,  the  acromion,  the  clavicle,  and  the 
upper  edge  of  the  sternum.  After  splitting  to  enclose  the  trapezius  and  covering  in 
the  posterior  triangle,  this  fascia  divides  again  at  the  hinder  border  of  the  sterno- 
cleido-mastoid.  The  superficial  layer  continues  over  the  surface  of  that  muscle, 
covers  in  the  anterior  triangle,  and  blends  with  its  fellow  of  the  opposite  side. 

From  its  under  surface,  after  reaching  the  sterno-mastoid,  the  deeper  layer  gives 
off  from  behind  forward  (£)  a  process — prevertebral  fascia — which  begins  near  the 
posterior  border  of  the  sterno-mastoid,  passes  in  front  of  the  scalenus  anticus,  the 
phrenic  nerve,  the  sympathetic  nerve,  and  the  longus  colli  muscle,  and  behind  the 
great  vessels,  the  pneumogastric  nerve,  and  the  oesophagus  to  the  front  of  the  base 
of  the  skull  and  the  bodies  of  the  cervical  vertebrae.  In  the  mid-line  this  descends 
behind  the  gullet  into  the  thorax.  At  the  sides  of  the  neck  it  helps  to  form  the  pos- 
terior wall  of  the  carotid  sheath,  spreads  out  over  the  scalene  muscles,  and  passes 
down  in  front  of  the  subclavian  vessels  and  the  brachial  plexus,  until  it  dips  beneath 
the  clavicle,  ft  is  then  applied  closely  to  the  under  surface  of  the  costo-coracoid 
membrane  and  splits  to  become  the  sheath  of  the  axillary  vessels.  A  second  process 
(f),  leaving  the  sterno-mastoid  more  anteriorly,  aids  in  forming  the  anterior  wall  of 
the  carotid  sheath,  and  joins  the  preceding  layer  just  internal  to  the  vessels.  It  is 


PRACTICAL   CONSIDERATIONS  :    THE  NECK. 


usually  described  as  part  of  (af)  a  process — tracheal — which  leaves  the  sterno-mastoid 
nearer  its  anterior  border,  and,  running  behind  the  sterno-hyoid  and  sterno-thyroid 
muscles,  descends  in  front  of  the  trachea  and  the  thyroid  gland  to  become  connected 
with  the  fibrous  layer  of  the  pericardium. 

The  adhesion  of  the  deep  fascia  to  the  blood-vessels,  by  preventing  contraction 
and  collapse  of  their  walls,  favors  hemorrhage  and  increases  the  risk  of  the  entrance 
of  air  into  divided  veins. 

Tracing  the  layers  of  fascia  vertically  and  from  the  surface  inward,  it  will  be 
useful  to  remember  that  the  superficial  layer  (a,  Fig.  546)  passes  to  the  top  of  the 
sternum  (sending  a  slip  to  be  attached  to  its  posterior  border)  and  to  the  clavicle. 
The  second  layer  (£)  descends  behind  the  depressors  and  in  front  of  the  thyroid 
gland  and  trachea  to  merge  into  the  pericardium,  and  farther  out  to  form  a  sheath  for 
the  omo-hyoid  and  for  the  subclavian  vein,  and  is  lost  in  the  sheath  of  the  subclavius. 


FIG.  545. 


Fusion  of  superficial  layer  in  mid-line 


Trachea 


Space  3a 

Thyroid  body 

CEsophagu 
Carotid  artery 


Internal  jugular  vein 
Vertebral  vessels 


Space  i 
Extern,  jugular  vein 

Spinal  nerves,  cut 
obliquely- 


Spinal  cord 

Trapezius  muscle. 

Vertebral  spin 


i\  M 
'.  n     Fascia  covering 

posterior  triangle 


Fascia  passing 
beneath  trapezius 


Ligamentum  nuchoe 


Section  across  neck  at  level  of  seventh  cervical  vertebra. 


This  relation  of  the  omo-hyoid  is  of  value  in  enabling  that  muscle,  when  the 
hyoid  is  fixed,  to  increase  the  tension  of  this  layer  of  fascia,  and  thus  hold  open  and 
prevent  atmospheric  pressure  upon  the  walls  of  the  vessels — especially  the  veins — 
and  the  soft  parts  (including  the  pulmonary  apices)  at  the  base  of  the  neck. 
Hilton  uses  this  function  of  the  muscle — which  connects  it  with  the  act  of  respiration — 
to  illustrate  the  precision  of  the  nerve-supply  to  muscles  generally.  The  omo-hyoid 
arises  in  close  proximity  to  the  suprascapular  notch,  and  therefore  to  the  supra- 
scapular  nerve.  Yet  it  never  receives  a  filament  from  that  nerve,  but  is  supplied 
by  the  hypoglossal  to  associate  it  with  the  movements  of  the  tongue,  the  cervical 
plexus  to  bring  it  in  relation  to  the  movements  of  the  other  neck  muscles,  and  the 
pneumogastric  to  enable  it  to  act  as  above  described  during  forced  respiration,  when 
the  rush  of  air  into  the  thorax  might  otherwise  cause  harmful  increase  of  atmospheric 
pressure  in  the  lower  cervical  or  supraclavicular  region. 

The  pretracheal  layer  is  found  between  the  depressors  and  the  trachea  passing 
down  to  its  pericardial  insertion.  Hilton  thus  explains  this  insertion  :  ' '  The  peri- 
cardium is  most  intimately  blended  with  the  diaphragm,  distinctly  identified  with  it, 
and  capable  of  being  acted  upon  by  it  at  all  times.  It  is  also  attached  above  to  the 
deep  cervical  fascia.  It  is  thus  kept  tense  by  the  action  of  the  respiratory  muscles 
in  the  neck  attached  to  the  cervical  fascia  above  and  the  diaphragm  attached  to  it 


552 


HUMAN   ANATOMY. 


Hyoid  bone 


below  ;  or,  in  other  words,  these  two  muscular  forces  are  acting  on  the  interposed 
pericardium  in  opposite  directions,  and  so  render  it  tense  and  resisting.  And  the 
special  object,  no  doubt,  of  this  piece  of  anatomy  is  that  during  a  full  inspiration, 
when  the  lungs  are  distended  with  air  and  the  right  side  of  the  heart  gorged  with 
blood  from  a  suspension  of  respiration,  the  heart  should  not  be  encroached  upon  by 
the  surrounding  lungs. ' ' 

The  prevertebral  layer  (c,  Fig.  546)  lying  between  the  oesophagus  and  spine 
passes  in  the  mid-line  directly  into  the  posterior  mediastinum;  laterally — beyond  the 
scalenus  anticus — it  aids  in  forming  the  sheath  of  the  subclavian  vessels  and  accom- 
panies them  into  the  axilla. 

Another  way  of  elucidating  the  practical  effect  of  the  somewhat  complex  dis- 
tribution of  the  cervical  fascia  is  to  regard  the  three  chief  layers — superficial,  middle, 
and  deep — as  dividing  the  neck  into  four  anatomical  spaces  (Tillaux). 

1.  Subcutaneous  (Space    i,  Fig.  545)  :    between  the  skin  and  the  superficial 
layer.      The  most  important  structure  in  this  space  is  the  external  jugular  vein,  which 
perforates  the  fascia  just  above  the  middle  of  the  clavicle. 

2.  Intra-aponeurotic  (Space   2,  Fig.  546)  :    between  the  superficial  and  mid- 

dle (sterno-clavicular)  layers.     This 

FIG.  546.  space  does  not  exist  in  fact  at  the 

summit  of  the  neck  where  the  two 
layers  are  one,  but  at  the  base  its 
depth  is  equal  to  the  thickness  of 
the  sternum.  It  may  be  continuous 
with  the  space  left  at  the  top  of  the 
sternum  between  the  two  leaflets  of 
the  superficial  layer  attached  to  the 
anterior  and  posterior  borders  of  the 
sternum,  —  Griiber's  ' '  suprasternal 
intra-aponeurotic  space,"  "  Burns' s 
space."  It  contains  fat  and  lym- 
phatic glands,  the  sternal  head  of 
the  sterno-mastoid,  and  the  anterior 
jugular  veins.  It  is  not  infrequently 
the  seat  of  abscess. 

3.  Visceral  (Space  3  =  $a  -\-  3^, 
Fig.  545):  between  the  pretracheal 
and  prevertebral  layers.  This  in- 
cludes all  the  principal  structures  of 
the  neck.  As  it  communicates  di- 
rectly with  the  thorax  and  axilla, 
suppuration  may  travel  in  those  di- 
rections. It  is  divided  into  minor 
spaces  (30  and  3^)  by  a  layer  of  fascia  coming  from  the  under  surface  of  the  sterno- 
mastoid  muscle  and  by  the  bucco-pharyngeal  fascia,  a  thin  layer  that  comes  off  from 
the  prevertebral  fascia  where  it  leaves  the  carotid  sheath,  and  which  lines  the 
constrictors  of  the  pharynx,  leaving  between  it  and  the  layer  applied  to  the  spinal 
column  a  small  but  easily  distended  space — retropharyngeal — in  which  infection 
from  pharyngeal  lesions  occasionally  occurs. 

4.  Retrovisceral  (Space  4,  Fig.  546):  the  space  between  the  prevertebral  fascia 
and  spinal  column,  including  the  longus  colli  and  rectus  capitis  anticus,  the  sympa- 
thetic nerve,  etc. 

It  is  obvious  in  a  general  way  that  all  infections  beneath  the  middle  layer  of 
fascia  are  more  likely  to  be  serious  than  those  superficial  to  it. 

Hut  to  summarize  in  a  little  more  detail  the  practical  relations  of  the  cervical 
fascia,  we  may  conclude  that  superficial  to  the  outer  layer  (a,  Fig.  545)  there  might 
occur  from  traumatism  a  wound  of  the  external  jugular,  or  from  infection  a  spread 
ing  cellulitis.  The  space  is  the  seat  of  superficial  phlegmons,  which  tend  to  spread 
under  the  skin  only  (Space  i,  Fig.  545),  and,  in  the  absence  of  tension,  are  unat- 
tended by  throbbing  pain  or  marked  constitutional  symptoms. 


Space  2 


Burns's  space 
Space  4 

Left 

in  nominate  vein 
Aortic  arch  -44 


Diagram  showing  relations  of  cervical  fascia  in  longitudinal 
section. 


PRACTICAL   CONSIDERATIONS  :    THE    NECK.  553 

The  space  between  c  and  b  (3^,  Fig.  545)  is  occupied  only  by  the  great  vessels 
and  the  pneumogastric.  Infection  there — i.e.,  within  the  sheath — may  mean  de- 
scending thrombosis  from  original  infection  of  a  cerebral  sinus,  or  may  have  spread 
directly  .through  the  sheath  from  infected  tracts  of  cellular  tissue  outside.  Behind 
b,  Fig.  545  (retrovisceral  space),  suppuration  is  not  uncommon  as  a  result  of  verte- 
bral disease.  Direct  infection  through  the  pharyngeal  wall  usually  involves  the 
retropharyngeal  space.  In  either  case  dysphagia  and  dyspnoea  are  usual  for  obvious 
reasons. 

Between  b  and  c,  Fig.  546  (pretracheal  and  prevertebral  layers),  abscess  would 
spread  most  readily  along  the  line  of  the  trachea  and  in  front  of  the  vessels  into  the 
superior  mediastinum. 

In  the  intra-aponeurotic  space  (Space  2,  Fig.  546)  an  abscess  would  probably 
point  superficially,  as  the  fascia  in  front  of  it  is  very  thin.  If  it  were  influenced  by 
gravity,  however,  it  would  follow  the  hyoid  depressors  and  their  intermuscular  spaces 
to  the  root  of  the  neck,  and  might  enter  the  superior  mediastinum. 

Two  additional  and  important  spaces  are  formed  by  extensions  or  reduplications 
of  the  cervical  fascia.  That  portion  of  the  superficial  layer  above  the  level  of  the 
angle  of  the  inferior  maxilla,  and  passing  from  that  bone  to  the  zygoma,  constitutes 
the  parotid  fascia,  which  on  the  surface  is  continuous  with  that  over  the  masseter, 
while  beneath  it  becomes  thickened  to  constitute  the  stylo-maxillary  ligament,  sep- 
arating the  parotid  and  submaxillary  glands  and  resisting  overaction  of  the  external 
pterygoid  muscle.  As  the  outer  fascial  investment  of 
the  gland  is  dense  and  resistant,  and  as  internal  to  this  FIG.  547. 

ligament  the  inner  layer  is  thinner  and  weaker  than 
elsewhere, — a  positive  gap  existing  between  the  styloid 
process  and  the  pterygoid  muscle, — suppuration  within 

the  gland  may  result  in  extension  to  the  retropharyngeal       / '  '^L  \     Myio-hyoid  muscle 
region.      It  may  follow  the  external  carotid  downward  to 
the  chest,  or,  as  the  fascial  investment  is  also  incomplete 
above,  may  extend  upward  to  the  base  of  the  skull,  or 
even  into  the  skull.      It  sometimes  follows  the  branches  ~f~/^^^~- Hv°id  b<>"e 

of  the  third  division  of  the  fifth  nerve  through  the  fora-  /   /  Outer  layer  of  fascia 

men  Ovale  into  the  Cranium.  /     Inner  layer  of  fascia 

The  second  space  alluded  to  is  formed  by  that  por-        Submaxillary  gland 
tion  of  the   superficial   layer    between    the   jaw  and  the         Portion  of  frontal  section  across 

1    .  J  J  mandible,  showing  relations  of  cer- 

hyoid  bone  and  in  front  of  the  stylo-mandibular  ligament,      vicai  fascia. 
As  it  passes  forward  from  the  latter  structure  it  splits  and 

envelops  the  submaxillary  gland,  and  becomes  firmly  attached  below  to  the  hyoid 
and  above  to  the  lower  jaw  externally  and  the  under  surface  of  the  mylo-hyoid 
muscle  internally  (Fig.  547).  Infection — "  Ludwig's  angina,"  "submaxillary 
phlegmon,"  "deep  cervical  phlegmon" — in  this  space,  which  contains  the  salivary 
gland  and  its  attendant  lymphatics,  is  rendered  exceptionally  grave  by  the  density 
of  these  fascial  layers.  The  infecting  organisms — usually  streptococci — may  gain 
access  through  a  lesion  of  the  floor  of  the  mouth  near  the  frenum,  or  from  an  alveo- 
lar abscess,  or  by  way  of  the  digastric  muscle  from  a  focus  of  disease  in  the  middle 
ear.  Once  established,  they,  with  their  secondary  products,  are  forced  along  the 
lines  of  least  resistance — by  the  side  of  the  mylo-hyoid  usually — towards  the  base 
of  the  tongue,  involving  the  cellular  tissue  about  the  glottis  and  along  the  vessels 
that  perforate  the  fascia,  causing  infective  venous  thrombosis  and  involving  the 
deeper  planes  of  connective  tissue.  Under  the  latter  circumstances,  if  tension  is  not 
promptly  relieved,  large  vessels  may  be  opened  by  the  necrotic  process.  Jacobson 
long  ago  called  attention  to  the  interesting  fact  that  communications  between  ab- 
scesses and  deep  vessels  have  usually  taken  place  beneath  the  cervical  fascia  and 
the  fascia  lata,  two  of  the  strongest  fasciae  of  the  body. 

Tumors  of  the  neck  may  originate  in  any  of  the  diverse  structures  of  that 
region.  It  may  be  mentioned  here  that  their  situation  above  or  beneath  the  cervical 
fascia  is  an  important  'factor  in  determining  their  mobility,  and  hence  the  probable 
ease  or  difficulty  of  their  removal.  In  the  latter  situation  associated  pressure- 
symptoms  are  common. 


554  HUMAN   ANATOMY. 

Lipoma  is  frequent  ;  fibroma  and  enchondroma  are  occasionally  seen  in  the 
region  of  the  ligamentum  nuchae  ;  primary  carcinoma  is  rare. 

Congenital  cysts — "  hydroceles" — of  the  neck  are  found  beneath  the  deep  fascia, 
usually  in  the  anterior  triangle  and  below  the  level  of  the  hyoid.  They  may  arise 
from  dilatation  of  the  lymphatic  vessels,  or,  as  Sutton  suggests,  they  may  originate, 
as  do  the  cervical  air-sacs  in  some  monkeys,  especially  the  chimpanzees,  by  the 
formation  of  diverticula  from  the  laryngeal  mucous  membrane.  In  any  event,  they 
ramify  in  the  various  intermuscular  spaces,  and  their  complete  removal  is  therefore 
very  difficult. 

Branchial  cysts  and  dermoids  are  not  infrequent.  They  should  be  studied  in 
connection  with  the  embryology  of  the  region. 

Congenital  tumor  of  the  sterno-mastoid  is  a  condition  resulting  from  either  rup- 
ture of  muscular  fibres  or  bruising  of  the  muscle  against  the  under  surface  of  the 
symphysis  during  delivery.  It  may  be  a  cause  of  torticollis. 

Torticollis — "wry-neck" — maybe  due  to  spasm  of  the  sterno-mastoid  either 
alone  or  associated  with  a  similar  condition  of  the  trapezius,  especially  the  clavicular 
portion,  and  often  of  the  scaleni  or  the  complexus.  Later  there  is  apt  to  be  second- 
ary contraction  of  the  deep  fascia  and  of  the  posterior  cervical  muscles.  Tenotomy 
of  the  muscle  for  the  relief  of  this  affection  is  performed  at  a  level  just  above  its 
sternal  and  clavicular  insertion.  The  subcutaneous  method  has  been  largely  dis- 
carded in  favor  of  division  through  an  open  wound.  By  the  former  plan,  not  only 
were  the  anterior,  and  sometimes  also  the  external,  jugular  veins  endangered,  but  the 
cervical  space  described  as  "visceral"  was  occasionally  opened,  and,  if  infection 
occurred,  with  fatal  results  from  septic  cellulitis  or  pleurisy. 

Section  of  the  spinal  accessory  nerve  may  be  resorted  to  when  the  spasm  is 
limited  to  the  sterno-mastoid  and  trapezius,  or  of  the  posterior  primary  divisions 
of  the  first,  second,  and  third  cervical  nerves  when  the  posterior  muscles  are  involved. 

Landmarks. — Athough  but  few  organs  belong  exclusively  to  the  neck,  a  great 
many  structures  of  mueh  diversity,  and  connecting  the  trunk  and  head,  pass  through 
it.  The  "landmarks"  will  therefore  be  found  in  relation  to  different  systems, — vas- 
cular, nervous,  etc., — those  given  here  referring  chiefly  to  the  muscles  and  their  effect 
upon  surface  form. 

The  mid-line  posteriorly  has  already  been  described  in  its  relation  to  the  spines 
of  the  cervical  vertebrae  (pages  146—148). 

On  the  sides  of  the  neck  the  platysma,  when  in  action,  produces  inconspicuous 
wrinkling  of  the  skin.  Its  fibres  are  in  a  line  from  the  chin  to  the  shoulder.  The 
sterno-mastoid,  running  obliquely  from  the  skull  to  the  sternum  and  clavicle,  divides 
each  lateral  half  of  the  neck  into  two  triangles.  The  anterior  of  these  is  boundi-d 
above  by  the  lower  border  of  the  inferior  maxilla  and  a  line  extending  from  the  angle 
of  that  bone  to  the  mastoid  process  ;  anteriorly  by  a  straight  line  between  the  middle 
of  the  chin  and  the  sternum  ;  posteriorly  by  the  anterior  border  of  the  sterno-mas- 
toid. Its  apex  is  at  the  middle  of  the  upper  edge  of  the  manubrium.  The  posterior 
triangle  is  bounded  posteriorly  by  the  anterior  edge  of  the  trapezius,  the  hinder 
edge  of  the  sterno-mastoid  in  front,  and  the  middle  of  the  clavicle  below.  Its  apex 
is  just  behind  the  mastoid  process. 

It  will  be  seen  that  by  this — the  usual — description  those  structures  lying  imme- 
diately beneath  the  sterno-mastoid  would  be  excluded  from  both  triangles.  It  is  cus- 
tomary, however,  to  include  the  common  carotid  and  internal  jugular  vein  in  the 
anterior  triangle,  although  they  are  both  under  cover  of  the  anterior  edge  of  the 
sterno-mastoid. 

The  anterior  triangle  is  divided  into  three — the  superior  carotid,  the  inferior 
carotid,  and  the  submaxillary — by  the  digastric  muscle  and  the  anterior  belly  of  the 
omo-hyoid.  The  posterior  belly  of  the  omo-hyoid  divides  the  posterior  triangle  into 
a  lower  or  subclavian  and  an  upper  or  occipital  triangle.  The  structures  included 
within  these  various  triangles  will  be  described  in  connection  with  the  vessels, 
nerves,  etc. 

The  dividing  line  between  the  two  main  triangles — the  sterno-mastoid — can  be 
both  seen  and  felt  if,  with  the  mouth  closed,  the  chin  is  depressed  and  the  skull  is 
rotated  towards  the  opposite  shoulder.  The  thick,  prominent,  rounded  anterior  bor- 


PRACTICAL   CONSIDERATIONS  :    THE   NECK. 


555 


der  can  then  be  made  out  from  mastoid  to  sternum,  but  is  more  accentuated  below, 
where  the  sternal  head  is  salient  and  sharply  denned.  This  thin  posterior  border  may- 
be felt  vaguely  at  the  upper  part,  but  cannot  be  seen.  *  At  about  the  lower  third  it 
becomes  visible  and  is  continued  into  the  broader  and  flatter  clavicular  head.  The 
middle  of  the  muscle  is  seen  throughout  most  of  its  length  as  a  fleshy,  rounded 
elevation.  Over  it,  and  usually  plainly  visible,  is  the  external  jugular  vein,  running 
between  the  platysma  and  the  deep  fascia  in  a  line  from  the  angle  of  the  jaw  to  the 
centre  of  the  clavicle.  In  rest  the  anterior  border  is  still  visible.  The  position  of 
the  muscle  on  the  side  towards  which  the  head  is  turned  is  indicated  by  a  slight 
furrow  in  the  skin.  The  muscles  partly  overlapped  by  the  sterno-mastoid  are,  from 
above  downward,  the  splenius,  levator  scapulae,  digastric,  omo-hyoid,  sterno-thyroid,. 
and  sterno-hyoid. 

FIG.  548. 


External  jugular  vein 


Submaxillary  gland 


Digastric,  anterior  belly 
Hyoid  bone 


Trapezius 

Acromio-clavicular  joint 
Acromion  process 


Lesser  supraclavicular  fossa 

Suprasternal  notch 
(jugular  fossa) 


Coracoid 
process 


Omo-hyoid,  posterior  belly 
Supraclavicular  fossa 
Infraclavicular  fossa 


Surface  markings  of  neck,  from  living  subject. 

The  interval  between  the  sternal  and  clavicular  heads  of  the  muscle  is  indicated 
by  a  slight  depression, — the  lesser  supraclavicular  fossa, — and  is  bounded  below  by 
the  upper  edge  of  the  inner  third  of  the  clavicle.  Beneath  it,  about  on  a  line  with 
the  sternal  end  of  the  clavicle,  lie  on  the  right  side  the  bifurcation  of  the  innominate 
artery  and  on  the  left  the  common  carotid  artery. 

Between  the  outer  edge  of  the  clavicular  head  of  the  sternp-mastoid  and  the 
base  of  the  anterior  edge  of  the  trapezius  is  a  broad,  flat  depression, — the  supracla- 
vicular fossa, — which  is  made  very  evident  by  shrugging  the  shoulders,  and  across 
which  the  posterior  belly  of  the  omo-hyoid  runs  and  can  often  be  seen  and  felt  in 
thin  persons,  especially  during  inspiration  or  when  the  head  is  turned  towards  the 
opposite  side  (Fig.  548).  The  line  of  the  muscle  is  from  the  suprascapular  notch, 
slightly  ascending  to  the  anterior  margin  of  the  sterno-mastoid  at  a  level  with  the 
cricoid  cartilage  and  then  rapidly  ascending  to  the  body  of  the  hyoid.  Below  is. 


556  HUMAN   ANATOMY. 

posterior  belly  run  the  brachial  plexus,  which  can  often  be  felt  and  sometimes  seen, 
and,  near  the  clavicle,  the  subclavian  artery. 

Farther  out  the  anterior  border  of  the  trapezius  may  be  seen  passing  from  the 
occiput  to  its  insertion  at  the  outer  end  of  the  middle  third  of  the  clavicle.  The 
triangular  interval  between  it  and  the  posterior  border  of  the  sterno-mastoid  is  filled 
— from  below  upward — by  the  scalenus  medius,  the  levator  anguli  scapulae,  and  the 
splenius,  but  none  of  them  is  recognizable  through  the  deep  fascia. 

In  the  mid-line  behind,  in  addition  to  the  bony  points  already  given  (pages 
146—148),  the  line  of  origin  of  the  trapezii  can  be  seen  as  a  slight  elongated  de- 
pression. None  of  the  deeper  muscles  can  be  seen  or  felt  upon  the  surface. 

In  the  mid-line  in  front  the  hyoid  bone  and  its  cornua  can  be  felt  in  the  angle 
between  the  under  surface  of  the  chin  and  the  front  of  the  neck.  From  the  hyoid 
bone  on  either  side  the  anterior  bellies  of  the  digastric  run  up  towards  the  symphysis 
and  with  the  subcutaneous  fat  give  convexity  to  the  submental  region.  Farther  out 
on  this  level  the  submaxillary  salivary  glands  can  be  felt  and  often  seen. 

The  thyro-hyoid  depression,  the  prominence  of  the  thyroid  cartilage  (pomum 
Adami},  the  crico-thyroid  space,  the  cricoid  cartilage,  and  sometimes  the  upper 
rings  of  the  trachea  may  be  felt  from  above  downward.  The  relations  of  these  parts 
to  important  vascular  and  nervous  structures  will  be  considered  later. 

The  sterno-thyroid  and  sterno-hyoid  muscles,  while  not  visible,  cover  over  and 
obscure  the  outlines  of  the  trachea,  as  does  also  the  thyroid  isthmus.  The  thyroid 
lobes  may  be  felt  on  each  side  of  the  larynx.  The  average  distance  from  the 
cricoid  to  the  upper  edge  of  the  manubrium  is  about  one  and  a  half  inches  when 
the  head  is  erect.  In  full  extension  three-quarters  of  an  inch  additional  can  be 
gained. 

The  trachea  recedes  as  it  approaches  the  sternum,  so  that  it  is  fully  an  inch  and 
a  half  behind  the  upper  border  of  the  latter.  In  this  position  between  the  two 
sternal  heads  of  the  sterno-mastoid  is  the  deep,  V-shaped  suprasternal  notch  (fossa 
jugularis),  the  depth  of  which  is  noticeably  affected  by  forced  respiration,  being 
much  increased  in  obstructive  dyspnoea. 

All  the  surface  appearances  above  described  differ  in  different  individuals,  and 
vary  in  the  same  person  in  accord  with  many  conditions,  as  the  amount  of  subcu- 
taneous fat,  the  muscular  vigor  and  development,  the  pulmonary  capacity,  the  state 
of  repose  or  of  violent  exertion,  etc.  This  should  be  remembered  in  looking  for 
landmarks  in  this  region,  which  is  in  that  respect  one  of  the  most  variable  of  the 
body,  and  most  unlike  that  of  the  cranium,  which  perhaps  typifies  the  other  extreme 
of  unchangeability. 

DlAPHRAGMA    (Fig.   549). 

The  diaphragm  is  a  dome-shaped  muscular  sheet  which  separates  the  thoracic 
and  abdominal  cavities.  Notwithstanding  its  position  in  the  adult,  it  is  a  derivative 
of  the  cervical  myotomes.  It  represents  the  upper  portion  of  a  structure  which  is 
termed  in  embryology  the  septum  transversum  (page  1701),  a  connective-tissue 
partition  which  extends  between  the  ventral  and  lateral  walls  of  the  body  and  the 
heart,  and  serves  to  convey  venous  trunks  to  that  organ.  Like  the  heart,  when 
first  formed  it  lies  far  forward  in  the  uppermost  part  of  the  cervical  region,  but  I.IUT 
it  descends  with  the  heart  until  it  reaches  its  final  position.  As  it  passes  the  third 
and  fourth  cervical  myotomes  in  its  descent,  it  receives  from  them  some  muscle-tissu< 
which  eventually  forms  all  the  muscle-tissue  of  the  diaphragm,  that  structure,  so  fai 
as  it  is  to  be  regarded  as  a  muscle,  being  a  derivative  of  the  cervical  myotom< 
named. 

The  diaphragm  is  a  muscular  sheet  composed  of  fibres  radiating  from  the  l 
border  of  the  thorax  and  from  the  upper  lumbar  vertebrae  towards  a  central  trndi- 
nous  area,  termed  the  centrum  tendineum.  According  to  their  origin,  the  muscle- 
fibres  may  be  grouped  into  three  portions.  The  sternal  portion  consists  of,  usually, 
two  bands  which  arise  from  the  posterior  surface  of  the  xiphoid  process  of  the 
sternum  and  are  separated  from  one  another  by  a  narrow  interval  filled  with  con- 
nective tissue.  Laterally  they  are  separated  by  a  similar  interval,  through  which 
the  superior  epigastric  artery  enters  the  sheath  of  the  rectus  abdominis,  from  the 


THE   CERVICAL    MUSCLES. 


557 


costal  portion,  the  fibres  of  which  take  their  origin  from  the  cartilages  of  the  lower 
six  ribs,  interdigitating  with  the  origins  of  the  transversalis  abdominis.  In  conti- 
nuity with  the  costal  part  is  the  lumbar  part,  whose  fibres  take  origin  (i)  from  two 
tendinous  arches,  the  internal  and  external  arcuate  ligaments,  which  pass  over  the 
upper  portions  of  the  psoas  (arcus  lurabocostalis  medialis)  and  the  quadratus  lum- 
borum  muscles  (arcus  lumbocostalis  lateralisj  respectively,  stretching  between  the 
twelfth  rib  and  the  transverse  process  of  the  first  lumbar  vertebra,  and  (2)  by  two 
downward  prolongations,  the  crura,  from  the  anterior  and  lateral  surfaces  of  the 
upper  three  or  four  lumbar  vertebra1. 

The  right  crus  usually  extends  somewhat  farther  downward  than  the  left,  whose 
attachment  does  not  pass  below  the  second  or  third  vertebra.  Each  crus  has  been 
divided  into  three  portions,  medial,  intermediate,  and  lateral,  which  are  not,  how- 
ever, always  clearly  recognizable,  although  indicated  by  the  passage  of  certain  struc- 
tures from  the  thorax  to  the  abdomen.  Thus,  between  the  medial  and  intermediate 


FIG.  5/19. 


Interval  between  sternal  and  costal  portions 


Lower  end  of  sternum 


Inferior  vena  cava 


/ 

tight  portion  of  ..(. 


Right  p 
central  tendon 


Right  crus — 

Right  greater 
splanchnic  nerve_ 
XII  rib 


Middle  portion  of 
central  tendon 


—  (Esophagus 


_  Left  portion  of 
central  tendon 


Aorta 
Thoracic  duct 


Inferior  vena  cava 
Bifurcation  of  aorta,  turned  forward 


Left  crus 


XII  rib 

External  arcuate  ligament 
Quadratus  lumborum 
Internal  arcuate  ligament 
Psoas  magnus 


Diaphragm,  viewed  from  below  and  the  left. 

crura  the  greater  splanchnic  nerve  and  the  azygos  (or  hemiazygos)  veins  pass,  while 
between  the  intermediate  and  lateral  crura  is  the  sympathetic  trunk. 

The  two  crura,  as  they  pass  upward,  leave  between  them  an  opening,  the  hiat^ls 
aorticus,  which  is  bridged  over  by  a  tendinous  band  (median  arcuate  ligament}  and 
gives  passage  to  the  aorta  and  thoracic  duct.  Just  behind  the  posterior  margin  of 
the  centrum  tendineum  the  crural  fibres  diverge  to  surround  in  a  sphincter-like 
manner  the  hiatus  a'sophageus,  through  which  pass  the  oesophagus  and  the  vagus 
nerves  and  oesophageal  branches  from  the  gastric  artery  and  veins. 

The  centrum  tendineum,  into  which  the  fibres  of  the  three  portions  insert,  is 
situated  somewhat  nearer  the  anterior  than  the  posterior  margin  of  the  diaphragm, 
so  that  the  fibres  of  the  sternal  muscular  portion  are  considerably  shorter  than  the 
others.  It  has  a  trefoil  shape,  possessing  a  central  and  two  lateral  lobes,  the  right 
one  of  these  being  perforated  by  a  somewhat  quadrate  foramen,  the  foramen  vena: 
cavce  (foramen  quadratum),  which  transmits  the  vena  cava  inferior. 

The  centrum  tendineum  forms  the  centre  of  the  dome  of  the  diaphragm,  and 
from  its  borders  the  muscular  fibres  slope  downward  towards  their  insertion,  the 
slope  of  the  crural  fibres  being  much  steeper  than  those  of  the  other  portions. 


558 


HUMAN   ANATOMY. 


The  dome  does  not,  however,  form  a  simple  curve,  but  is  divided  by  a  median 
depression,  which  traverses  it  from  before  backward,  into  two  secondary  lateral 
domes  which  are  unequally  developed,  that  of  the  right  side  extending  upward  as 
far  as  the  level  of  the  junction  of  the  fourth  costal  cartilage  and  rib,  while  that  of 
the  left  reaches  only  to  the  fifth  costo-cartilaginous  junction. 

Nerve-Supply. — From  the  third,  fourth,  and  sometimes  the  fifth  cervical 
nerves,  by  the  phrenic  nerves. 

Action. — To  increase  the  vertical  diameter  of  the  thorax,  a  contraction  of  the 
muscle-fibres  depressing  the  summit  of  the  dome. 

Relations. — The  upper  surface  of  the  diaphragm  forms  the  floor  of  the  thoracic 
cavity  and  is  in  contact  with  the  pleurae  and  pericardium,  the  latter  being  adherent  to 
the  centrum  tendineum.  Below,  the  diaphragm  is  largely  invested  by  peritoneum,  and 
is  in  relation  with  the  liver,  stomach,  spleen,  kidneys,  suprarenal  bodies,  duodenum, 
pancreas,  inferior  vena  cava,  and  the  branches  of  the  coeliac  artery. 

Variations. — Occasionally  the  diaphragm  is  incomplete  in  its  posterior  portion,  a  condition 
which  permits  the  formation  of  congenital  diaphragmatic  hernias.  Embryologically  the  pos- 
terior portion  of  the  diaphragm  is  the  last  to  form,  and  in  this  fact  is  probably  to  be  found  an 
explanation  of  the  location  of  this  imperfection  and  also  of  the  course  of  the  phrenic  nerves 
anterior  to  the  roots  of  the  lungs  to  reach -the  earlier  formed  anterior  portion  of  the  diaphragm. 

Fibres  which  arise  from  the  crura  and  pass  to  neighboring  structures  are  frequently  present. 
Among  the  more  constant  of  these  are  fibres  which  arise  from  the  inner  borders  of  both  crura 
and  pass  to  the  lower  portion  of  the  oesophagus,  mingled  with  dense  connective-tissue  fibres, 
and  others  which  pass  from  one  crus  or  the  other  into  the  mesentery  of  the  upper  part  of  the 
jejunum.  Probably  the  suspensory  muscle  of  the  duodenum,  or  muscle  of  Treitz,  which  passes 
from  the  left  crus  to  the  terminal  portion  of  the  duodenum,  belongs  to  this  latter  group  of  fibres, 
although  it  has  been  stated  to  be  formed  by  non-striated  muscle-fibres. 

THE    PELVIC   AND    PERINEAL   MUSCLES. 

The  ventral  portions  of  the  myotomes  succeeding  the  first  lumbar  and  from  that 
as  far  down  as  the  third  (or  second)  sacral  are  almost  entirely  unrepresented  in  the 
trunk,  being  devoted  to  the  formation  of  the  musculature  of  the  lower  limb.  Below 


FIG.  550. 


Iliac  crest 


Iliacu 

Ilio-pectineal  line 
Acetabulum 
Levator  ani 

Obturator  interim 
Alcock's  ca 


Iliac  fascia 

ternal  iliac  vessels 

vie  fascia 
lite  line 

vie  fascia 
Obturator  fascia 
Anal  fascia 


Ischio-rectal  fossa 

Seminal  vesirk 

External  sphincter 

Internal  sphincter     Rectum 

Diagrammatic  frontal  section  through  pelvis,  showing  relations  of  fasdal  layers  to  pelvic  wall  an 


\    Fascia  endopeh 

1'i-K  ir  fascia 
Recto-vesical  layer 


the  point  mentioned,  however,  the  ventral  musculature  again  appears  in  the  trunk 
in  the  pelvic,  the  perineal,  and  occasionally  the  coccygeal  region.  Owing  to  the 
conditions  under  which  it  appears,  it  is  not  possible  to  refer  the  muscles  derived  from 
it  to  the  various  subdivisions  into  which  the  ventral  musculature  of  other  regions  is 
divisible,  and  they  will  therefore  be  considered  in  sequence  without  any  attempt  at 
classification  other  than  regional. 

The  Pelvic  Fascia. — The  pelvic  fascia  is  attached  above  to  the  promontory 
of  the  sacrum  and  the  ilio-pectineal  line  (linea  terminalis)  of  the  pelvis,   where  it 


THE    PELVIC   AND    PERINEAL    MUSCLES.  559 

becomes  continuous  with  the  iliac  fascia.  It  descends  over  the  surface  of  the  pyri- 
formis  and  laterally  over  the  upper  portion  of  the  obturator  internus  and  the  pelvic 
surface  of  the  pelvic  diaphragm.  In  the  upper  part  of  its  course  over  the  pelvic  dia- 
phragm it  is  crossed  by  a  curved  thickening,  the  arcus  tendinous,  which  is  attached 
behind  to  the  spine  of  the  ischium  and  passes  in  front  upon  the  sides  of  the  prostate 
gland  or,  in  the  female,  upon  the  bladder,  and  is  continued  thence  to  the  anterior 
pelvic  wall  to  be  attached  on  either  side  of  the  symphysis  pubis,  a  little  above  its 
lower  border,  as  a  lateral  pubo-prostatic  {pubo-vesical}  ligament.  Along  this  tendi- 
nous arch  the  pelvic  fascia  gives  off  a  layer  which  passes  inward  to  the  pelvic  viscera, 
and  is  termed  the  fascia  endopelvina.  In  its  anterior  portion  this  forms  an  investment 
of  the  prostate  in  the  male  and  of  the  base  of  the  bladder  in  the  female,  and  its  under 
surface  in  this  region  is  in  contact  with,  and  indeed  may  be  regarded  as  being  fused 
with,  the  superior  layer  of  the  triangular  ligament  (page  563).  That  portion  of  the 
layer  which  intervenes  between  the  prostate  (or  bladder)  and  the  posterior  surface 
of  the  body  of  the  pubis  forms'what  is  termed  the  median  pubo-prostatic  (pubo-vesical} 
ligament. 

The  continuation  of  the  pelvic  fascia  passes  downward  over  the  surface  of  the 
pelvic  diaphragm,  and  is  termed  the  superior  fascia  of  that  structure  (fascia  dia- 
phragmatis  pelvis  superior). 

The  Obturator  Fascia. — From  the  line  along  which  the  pelvic  fascia  leaves  the 
surface  of  the  obturator  internus  muscle  to  pass  upon  the  pelvic  diaphragm  a  sheet  of 
fascia  is  continued  downward  over  the  surface  of  the  obturator  internus  muscle  to  be 
attached  below  to  the  tuberosity  and  ramus  of  the  ischium  and  the  ramus  inferior  of 
the  pubis.  This  is  the  obturator  fascia. 

Along  its  upper  border,  nearly  corresponding  with  the  arcus  tendineus  of  the 
pelvic  fascia,  but  lying  above  this  thickening  and  ending  anteriorly  farther  from  the 
median  line,  is  a  similar  curved  thickening  extending  from  the  spine  of  the  ischium, 
or  in  some  cases  from  the  ilio-pectineal  line  behind  to  the  posterior  surface  of  the 
body  of  the  os  pubis  in  front.  From  this  thickening  the  greater  portion  of  the  levator 
ani  muscle  arises  ;  it  is  consequently  termed  the  arcus  tendineus  m.  levatoris  ani,  or 
more  briefly  the  white  line.  From  the  line  a  thin  layer  of  fascia  is  continued  inward 
upon  the  under  surface  of  the  levator  ani,  forming  what  is  termed  the  anal  fascia 
(fascia  diaphragmatis  pelvis  inferior). 

This  latter  fascia  forms  the  inner  and  the  obturator  fascia  the  outer  wall  of  the 
ischio-rectal  fossa.  Near  its  lower  border  the  obturator  fascia  splits  into  two  layers  to 
form  a  canal,  the  canal  of  Alcock,  along  which  the  pudic  vessels  and  nerve  pass 
towards  the  perineum. 

In  the  above  description  the  term  pelvic  fascia  is  applied  to  the  layer  of  fascia  which  lines 
the  entire  true  pelvic  cavity, — that  is  to  say,  the  funnel-shaped  cavity  included  between  the  pel- 
vic brim  and  floor.  This  conception,  employed  by  the  German  authors,  differs  somewhat  from 
that  usually  held  by  English  anatomists,  in  that  the  latter  restrict  the  term  to  that  portion  of 
the  fascia  extending  from  the  ilio-pectineal  line  to  the  white  line,  the  continuation  down- 
ward over  the  pelvic  diaphragm  being  termed  the  recto-vesical  fascia,  from  which  extensions 
pass  to  the  bladder,  prostate  gland,  and  rectum.  The  term  recto-vesical  has  also  been  restricted 
to  the  portion  of  the  sheet  which  extends  between  the  rectum  and  the  bladder  and  encloses  the 
seminal  vesicles  (Cunningham),  and  if  the  term  is  to  be  employed  at  all,  this  application  of  it 
seems  to  be  the  preferable  one. 

Confusion  has  also  existed  in  the  application  of  the  term  "white  line,"  since  it  has  been 
made  to  include  both  the  arcus  tendineus  proper  and  the  thickened  band  from  which  the  leva- 
tor  ani  takes  its  origin  (arcus  tendineus  m.  levatoris  ani}.  These  two  bands  are,  however,  quite 
distinct,  especially  anteriorly,  as  a  careful  inspection  of  the  subject  will  demonstrate,  and  it  seems 
preferable  to  restrict  the  term  "white  line"  to  that  from  which  the  levator  ani  arises,  naming 
that  at  which  the  fascia  endopelvina  begins  the  arcus  tendineus. 

(a)    THE   PELVIC   MUSCLES. 

i.    Levator  ani.  2.   Coccygeus. 

3.    Pyriformis. 

The  floor  of  the  pelvis  is  formed  by  two  muscles  which  constitute  an  almost 
complete  partition,  the  pelvic  diaphragm,  separating  the  pelvic  from  the  perineal 
region.  The  more  anterior  and  larger  of  these  muscles  is  the  levator  ani,  the  coccy- 


560 


HTM  AN    ANATOMY. 


geus  lying  along  its  posterior  margin.  Above  the  upper  margin  of  the  latter,  and 
forming  the  posterior  wall  of  the  pelvis,  is  the  pyriformis.  Slight  intervals  occupied 
by  connective  tissue  usually  exist  between  the  coccygeus  and  the  other  two  muscles, 
presenting  opportunities  for  pelvic  hernias. 

i.    LEVATOR  AM  (Fig.  551). 

Attachments. — The  levator  ani  arises  from  the  posterior  surface  of  the  body  of 
the  os  pubis  in  front,  from  the  spine  of  the  ischium  behind,  and  in  the  interval  between 
these  two  points  from  a  thickening  of  the  upper  border  of  the  obturator  fascia,  the 
white  line.  From  this  long  line  of  origin  the  fibres  converge  downward  and  medially 
to  be  inserted  into  the  sides  and  tip  of  the  coccyx,  into  a  tendinous  raphe  extending 
in  the  median  line  between  the  tip  of  the  coccyx  and  the  anus,  and  into  the  sides  of 
the  lower  part  of  the  rectum.  The  fibres  from  the  most  anterior  portion  of  the  origin 
pass  almost  directly  backward  and  downward  to  reach  the  sides  of  the  rectum,  and 
between  them  and  the  corresponding  fibres  of  the  muscle  of  the  opposite  side  is  a 

FIG.  551- 


Pyriformis 


Coccygeus 


Ischial  spine 


Levator  ani 


Tip  of  coccyx 

-  Ischial  spine 

' —  Rectum  (cut) 

,-  — .Obturator  inter- 
ims i-overeit  by 
pelvic  fascia 

-Urethra  (cut) 


Muscular  floor  of  pelvis,  viewed  from  above. 

space,  occupied  in  the  male  by  the  lower  part  of  the  prostate  gland  and  in  the 
by  the  base  of  the  bladder  and  lower  part  of  the  vagina,   the  fascia  enclopelvina  in 
this  region  coming  into  contact  with  the  upper  surface  of  the  superior  layer  of  the 
triangular  ligament  of  the  perineum. 

Nerve-Supply. — The  posterior  portion  of  the  muscle  is  supplied  by  a  special 
branch  from  the  third  and  fourth  sacral  nerves,  the  anterior  portion  by  twigs  from  the 
inferior  hemorrhoulal  branches  of  the  pudic  nerve. 

Action. — To  bend  the  coccyx  forward  and  to  raise  the  pelvic  floor  and  viscera. 

Variations. — The  levator  ani  is  always  a  well-developed  muscle,  although  the  extent  of  its 
attachment  to  the  sides  of  the  coccyx  varies  inversely  to  the  attachment  of  the  coccygeus  to  that 
bone.  There  is  usually  to  be  found  a  dividing  line  extending  across  the  muscle  on  a  level  with 
the  junction  of  the  superior  ramus  of  the  pubis  with  the  ilium  and  separating  those  fibres  which 
are  inserted  into  the  coccyx  and  the  posterior  portion  of  the  fibrous  raphe  from  those  which 
pass  to  the  anterior  part  of  the  raphe  and  the  rectum.  Kach  of  the  portions  so  separated  is  sup- 
plied by  a  separate  nerve,  and  this,  combined  with  the  results  of  comparative  anatomy,  seems 
to  show  that  the  posterior  portion  of  the  levator  is  really  a  muscle  quite  distinct  from  tin-  ante- 
rior portion.  It  has  been  termed  the  ;//.  i/io-cofty^i-iis.  Furthermore,  it  seems  probable  that 


THE   PELVIC   AND    PERINEAL   MUSCLES. 


the  anterior  portion  is  composed  of  two  morphologically  distinct  muscles,  one  of  which  arises 
from  the  pubis  and  anterior  part  of  the  white  line  and  is  inserted  into  the  median  fibrous  raphe, 
whence  it  is  termed  the  ;«.  pubo-coccygeus ;  while  the  other,  situated  beneath, — i.ef,  superficial  to 
the  pubo-coccygeus, — consists  of  those  fibres  which  arise  from  the  pubis  and  are  inserted  into 
the  rectum,  and  is  termed  the  m.  pubo-rectalis, 

It  may  be  added  that  in  the  lower  mammals  the  muscles  corresponding  to  the  ilio-coc- 
cygeus  and  pubo-coccygeus  are  inserted  into  the  caudal  vertebrae  and  act  as  lateral  flexors  of 
the  tail. 

2.     COCCYGEUS    (FigS.    551,   603). 

Attachments. — The  coccygeus,  which  forms  the  posterior  and  lesser  portion 
of  the  diaphragma  pelvis,  lies  immediately  behind  the  levator  ani.  It  arises  from 
the  spine  of  the  ischium  and  is  inserted  into  the  sides  of  the  sacrum  and  coccyx. 

Nerve-Supply. — From  the  third  and  fourth  sacral  nerves. 

Action. — To  assist  the  levator  ani  in  raising  the  pelvic  floor.  It  also  flexes 
the  coccyx  laterally. 

Variations. — Occasionally  the  insertion  of  the  coccygeus  is  confined  to  the  sides  of  the 
sacrum,  in  which  cases  its  coccygeal  area  is  occupied  by  fibres  of  the  levator  ani.  The  muscle 
is  sometimes  termed  the  ischio-coccygeus,  and  is  represented  in  the  lower  mammals  by  a  muscle 
attached  to  the  caudal  vertebrae  and  acting  as  a  lateral  flexor  of  the  tail. 

The  Sac ro-  Coccygeus  Anterior. — Occasionally  muscular  fibres  are  to  be  found  arising  from 
the  ventral  surface  of  the  sacrum  and  inserting  into  the  coccyx.  They  form  what  is  termed  the 
sacro-coccygeus  anterior  or  curvator  coccygis,  and  apparently  belong  to  the  hyposkeletal  group 
of  muscles. 

3.   PYRIFORMIS  (Figs.  551,  552,  602.) 

Attachments. — The  pyriformis  (m.  piriformis)  arises  from  the  ventral  surface 
of  the  sacrum,  between  the  first,  second,  third,  and  fourth  sacral  foramina.  It 
passes  laterally  through 

the  great   sciatic  fora-  FIG.  552. 

men,  receiving  a  bundle 
of  fibres  from  the  upper 
margin  of  the  foramen, 
and  is  inserted  into  the 
summit  of  the  great 
trochanter,  its  tendon 
shortly  before  its  inser- 
tion becoming  closely 
united  with  that  of  the 
obturator  internus. 

Nerve  -  Supply. 
—By  branches  from  the 
sacral  plexus  from  the 
first  and  second  sacral 
nerves. 

Action. — To  ro- 
tate the  thigh  outward 
and  to  draw  it  slightly 
outward  and  back- 
ward. 


Obturator  internus 
Greater  sacrosciatic 
ligament 


its 


Relations.  —  By 

anterior     surface, 


Greater  sacro- 
sciatic foramen 
Dorsum  of  ilium 

Greater  sacro- 
sciatic foramen 
Pyriformis 

Obturator  internus 
Capsule  of  hip-joint 


Deep  dissection,  showing  insertion  of  pyriform,  internal  and  external  obturator 

muscles. 


while  within  the  pelvis, 

the  pyriformis  is  in  relation  to  the  sacral  plexus,  the  anterior  branches  of  the  internal 
iliac  vessels,  and  the  rectum.  It  lies  immediately  above  the  upper  border  of  the 
coccygeus  muscle.  Outside  the  pelvis  it  is  usually  separated  from  the  capsule  of  the 
hip-joint  by  the  gluteus  minimus  and  is  covered  by  the  gluteus  medius.  Above  the 
upper  border  of  the  muscle  at  its  exit  from  the  greater  sciatic  foramen  are  the  gluteal 
vessels  and  the  superior  gluteal  nerve,  while  below  its  lower  border,  between  this  and 
the  superior  gemellus,  are  the  sciatic  and  internal  pudic  vessels  and  the  pudic,  sciatic, 
small  sciatic,  and  inferior  gluteal  nerves.  A  bursa,  the  bursa  m.  pyriformis,  inter- 
venes between  the  tendon  of  the  muscle  and  the  summit  of  the  great  trochanter. 

36 


562 


HUMAN   ANATOMY. 


Variations. — The  pyriformis  is  occasionally  absent,  and  it  may  be  more  or  less  fused  with 
the  gluteus  minimus  or  medius.  Frequently  it  is  divided  into  two  or  more  portions  by  being 
perforated  by  the  sciatic  nerve. 

From  the  comparative  stand-point  the  pyriformis  is  to  be  regarded,  in  part  at  all  events,  as 
a  portion  of  the  musculature  extending  between  the  axial  skeleton  and  the  pelvic  girdle  or  limb, 
and  is  represented  in  the  lower  vertebrates  by  the  caudo-femoralis. 

(6)   THE   PERINEAL  MUSCLES. 


1.  Sphincter  ani  externus. 

2.  Transversus  perinaei  superficialis. 

3.  Ischio-cavernosus. 


4.  Bulbo-cavernosus. 

5.  Transversus  perinaei  profundus. 

6.  Compressor  urethrae. 


In  the  early  stages  of  development,  while  the  urogenital  ducts  and  the  digest- 
ive tract  open  into  a  common  terminal  cavity,  the  cloaca,  muscle-fibres  derived 
from  the  second,  third,  and  fourth  sacral  myotomes  arrange  themselves  in  a  flat 
layer  around  the  external  aperture  of  the  cavity,  forming  what  is  termed  the 
sphincter  cloacce.  Later,  with  the  division  of  the  cloaca  into  a  urogenital  and  a 
rectal  portion  and  the  resulting  formation  of  the  perineum,  this  primary  sphincter 
becomes  divided  into  two  portions,  one  of  which  forms  a  sphincter  ani,  while  the 
more  anterior  portion  gives  rise  to  the  muscles  of  the  perineum.  The  fibres  of  this 
latter  portion  undergo  various  modifications  in  accordance  with  the  changes  which 

FIG.  553- 


Urachus. 
Supravesical  space 


Symphysis  pubis 

Suspensory  ligament  of  penis 
Triangular  ligament,  sup.  layer 

Deep  perineal  interspac 
Triangular  ligam't,  inf.  layer 

Urethra 
Penis,  corpus  cavernosum 


Scrotum 


Rectum 

—  Prostate 

Cowper's  gland 


IViiiK-al  centre 
Colles's  fascia 
Superficial  perineal  interspace 


Continuation  of  Colles's  fascia 


Diagrammatic  sagittal  section,  showing  relations  of  fascia!  layers  of  perineum. 


take  place  in  the  urogenital  sinus,  and  a  horizontal  separation  of  the  original 
sphincter  into  two  layers  also  occurs,  whereby  the  perineal  muscles  are  arranged  in 
two  layers  separated  by  the  superior  fascia  of  the  urogenital  trigone. 

The  muscles  formed  during  these  changes  retain  the  original  sheet-like  form  of 
the  sphincter  cloacae  and  are  for  the  most  part  pale  in  color,  resembling  not  a  little  in 
their  general  character  the  platysma  muscles  of  the  face.  They  show  a  considerable 
amount  of  difference  in  their  development  in  different  individuals,  numerous  acces- 
sory muscles  having  been  described  by  various  authors,  some  of  which  will  be 
referred  to  in  the  succeeding  descriptions. 

The  Superficial  Perineal  Fascia. — The  superficial  perineal  fascia,  being 
continuous  anteriorly  with  the  superficial  fascia  of  the  lower  portion  of  the  anterior 
abdominal  wall,  is,  like  this,  composed  of  two  layers.  The  more  superficial  layer 
usually  contains  a  certain  amount  of  fat,  and,  as  in  the  abdomen,  is  really  the  pan- 
niculus  adiposus  of  the  skin.  The  deeper  layer,  which  has  been  termed  the  fascia 
of  Colics,  forms  a  continuous  membrane  which  is  attached  at  the  sides  to  the  rami 
of  the  pubes  and  ischia  and  in  front  becomes  continuous  with  the  dartos  of  the 


THE    PELVIC   AND    PERINEAL    MUSCLES.  563 

scrotum  (or  fascia  of  the  labia  majora)  and  on  either  side  of  this  with  the  corre- 
sponding layer  of  the  abdomen.  Behind  it  unites  with  the  posterior  border  of  the 
trigonum  urogenitale  on  a  line  extending  between  the  two  ischial  tuberosities,  and 
thence  is  continued  backward,  forming  a  single  sheet  with  the  superficial  layer,  to 
unite  with  the  superficial  fascia  of  the  gluteal  region.  This  posterior  portion  of  the 
superficial  perineal  fascia  may  conveniently  be  termed  the  circumanal  fascia. 

By  the  union  of  the  deep  layer  of  the  superficial  fascia  with  the  triangular  liga- 
ment behind,  an  almost  completely  enclosed  space  is  formed  between  the  two  struc- 
tures ;  it  is  open  only  anteriorly  where  it  communicates  with  the  areolar  spaces 
between  the  superficial  and  deep  layers  of  the  abdominal  fasciae.  This  space  is  the 
superficial  perineal  interspace,  and  contains  the  bulb  and  spongy  portion  of  the 
urethra,  the  corpora  cavernosa,  and  certain  of  the  perineal  muscles. 

The  Trigonum  Urogenitale, — The  trigonum  urogenitale,  more  usually  called 
the  triangular  ligament  of  the  perineum,  is  formed  by  the  deep  fascia  of  the  peri- 
neum, and,  like  the  superficial  fascia,  is  composed  of  two  layers,  the  superior  and 
inferior  (fasciae  trigoni  urogenitalis  superior  et  inferior).  At  the  sides  both  layers  are 
attached  to  the  rami  of  the  pubes  and  ischia,  in  front  to  either  edge  of  the  lower 
border  of  the  pubis,  and  behind  they  unite  with  each  other  and  with  the  deep  layer 
of  the  superficial  fascia  along  a  line  extending  transversely  across  the  perineum 
between  the  tuberosities  of  the  ischia.  Between  the  two  layers  there  is  a  completely 
closed  space,  the  deep  perineal  interspace,  in  which  are  to  be  found  the  membranous 
portion  of  the  urethra,  the  bulbo-urethral  glands,  the  pudic  vessels  and  nerves,  and, 
in  front,  the  subpubic  or  arcuate  ligament  of  the  pubis. 

At  their  lateral  insertions  the  layers  of  the  trigone  are  continuous  with  the 
obturator  fascia,  and  the  superior  layer  is  fused  above  with  the  portion  of  the  fascia 
endopelvina  which  invests  the  lower  surface  of  the  prostate  gland  (or  the  base  of  the 
bladder).  The  trigone  is  perforated  by  the  urethra  and,  in  the  female,  by  the  vagina, 
and  anteriorly  the  dorsal  vein  of  the  penis  passes  through  it  immediately  behind  the 
subpubic  ligament  of  the  pubis,  the  fibres  of  the  trigone  immediately  behind  the 
opening  for  the  vein  being  thickened  to  form  a  transverse  band  known  as  the  trans- 
verse ligament  of  the  pelvis. 

i.  SPHINCTER  ANI  EXTERNUS  (Fig.  554). 

Attachments. — The  external  sphincter  of  the  anus  consists  of  a  group  of 
fibres  which  surround  the  terminal  portion  of  the  rectum,  the  superficial  fibres 
standing  in  close  relationship  with  the  integument.  Its  fibres  arise  posteriorly 
from  the  coccyx  and  from  the  raphe  extending  from  that  bone  to  the  anus,  and, 
passing  forward  around  the  anus,  are  inserted  into  the  superficial  fascia  and  the 
central  tendon  of  the  perineum,  and  may  in  some  cases  be  continued  forward  to 
join  with  the  fibres  of  the  superficial  transverse  perineal  and  bulbo-cavernosus 
muscles. 

The  central  tendon  of  the  perineum  is  situated  in  the  median  line  about  2. 5  cm. 
in  front  of  the  anus,  and  is  the  point  of  union  of  five  muscles, — namely,  the  external 
sphincter  ani,  the  two  superficial  transversi  perinei,  and  the  bulbo-cavernosi. 

Nerve-Supply. — From  the  fourth  sacral  nerve  and  the  inferior  hemorrhoidal 
branches  of  the  pudic. 

Action. — To  close  the  anal  aperture.  It  also  serves  to  fix  the  central  tendon 
of  the  perineum  during  the  contraction  of  the  bulbo-cavernosi. 

Variations. — The  common  embryological  origin  of  the  external  sphincter  ani  and  the  perineal 
muscles  is  indicated  by  the  extension  forward  of  the  fibres  of  the  former  to  join  the  bulbo-caver- 
nosus, and  occasionally  a  fasciculus  of  it  extends  as  far  forward  as  the  base  of  the  scrotum, 
forming  what  has  been  termed  the  retractor  scroti. 

The  longitudinal  muscle-fibres  of  the  lower  portion  of  the  rectum  pass  below  into  a  sheet 
of  connective  tissue,  which  divides  into  three  more  or  less  distinct  layers  extending  to  the 
integument.  The  outer  two  of  these  layers  traverse  the  substance  of  the  external  sphincter 
ani,  a  portion  of  the  outermost  one  being  continued  backward  to  the  region  of  the  coccyx  on 
each  side  of  the  median  line  as  a  moderately  strong  band  known  as  the  ano-coccygeal  ligament. 
By  these  layers  of  fibrous  tissue  the  external  sphincter  is  divided,  sometimes  quite  distinctly, 
into  three  portions  which  have  been  regarded  as  distinct  muscles.  One  of  these  lies  imme- 
diately beneath  the  skin  surrounding  the  anus,  and  has  consequently  been  termed  the  sphincter 


564 


HUMAN   ANATOMY. 


subcutaneus.  The  sphincter  superficialis  is  that  portion  of  the  muscle  which  lies  above  and  to 
the  outer  side  of  the  sphincter  subcutaneus,  while  more  deeply  still,  and  forming  a  ring-like 
mass  of  fibres  closely  encircling  the  rectal  wall,  is  the  sphincter  profundus.  It  is  from  the 
sphincter  subcutaneus  that  the  retractor  scroti,  when  present,  is  derived,  and  fibres  from  the 
sphincter  superficialis  are  frequently  prolonged  in  front  of  the  anus  to  various  insertions,  as,  for 
instance,  to  the  tuber  ischii,  the  lower  layer  of  the  trigomim  urogenitale,  or  even  the  sheath  of 
the  corpora  cavernosa.  This  layering  of  the  external  sphincter  is  probably  a  relic  of  the  separa- 
tion of  the  sphincter  cloacae  into  two  layers,  the  subcutaneous  and  superficial  sphincters  repre- 
senting a  portion  of  the  superficial  layer,  while  the  deeper  one  is  responsible  for  the  sphincter 
profundus. 

2.  TRANSVERSUS  PERIN^EI  SUPERFICIALIS  (Fig.  554). 

Attachments. — The  superficial  transverse  perineal  muscle  is  an  exceedingly 
variable  sheet  of  muscle-fibres  situated  in  the  posterior  portion  of  the  superficial 
perineal  interspace.  In  its  typical  form  it  may  be  described  as  a  band  of  fibres  which 

FIG.  554. 


Bulbo-cavernosus  — 


Ischio-cavernosus  — 


Trans,  perinwi. 
superficialis 


Obturator, 
interims 

White  line- 

Levator  ani_ 

Coccygeus  . 


Triangular  liga- 
ment, inf.  lu\er 
_  Tendinous 

perineal  centre 
Tuberpsity  of 
ischium 

_  Anus 

_  Obturator  fascia 


l .  _  Sphincter 

externus 
I Levator  ani 

Gluteus 
7       maxitnus  (cut) 

-Greater  sacro-sciatic 
ligament 


Tip  of  coccyx 

Muscles  of  male  perineum  and  pelvic  floor,  seen  from  below. 

arises  from  the  medial  surface  of  the  ischial  tuberosity  and  passes  directly  medially 
to  be  inserted  into  the  central  tendon  of  the  perineum. 

Nerve-Supply. — From  the  perineal  branches  of  the  pudic  nerve. 

Action. — To  assist  in  fixing  the  central  tendon  of  the  perineum  during  the 
contraction  of  the  bulbo-cavernosi. 

Variations. — The  muscle  may  occasionally  be  entirely  absent.  It  frequently  receives  fibres 
from  the  anterior  ( pu bo-recta  1 )  portion  of  the  levator  ani  and  from  the  external  sphincter  ani 
and  makes  connections  with  the  bulbo-cavernosi. 

3.    ISCHIO-CAVERNOSUS  (Fig.  554). 

Attachments. — The  ischio-cavernosus,  also  named  the  erector  penis  (erector 
c/iforidis),  represents  the  lateral  portion  of  the  sphincter  cloacae.  The  two  muscles 
occupy  the  lateral  parts  of  the  superficial  perineal  interspace,  each  arising  from  the 
base  of  the  tuberosity  of  the  ischium,  enclosing  the  base  of  the  cms  penis  (clito- 
ridis)  as  in  a  sheath,  and  passing  forward  to  be  inserted  into  the  corpus  cavernosu m. 
The  muscle  in  the  female  differs  from  that  of  the  male  only  in  si/e. 

Nerve-Supply. — From  the  perineal  branches  of  the  pudie  nerve 


THE   PELVIC   AND    PERINEAL    MUSCLES.  565 

Action. — To  compress  the  corpus  cavernosum  and  thus  assist  in  producing  or 
maintaining  erection  of  the  penis  (or  clitoris). 

4.    BULBO-CAVERNOSUS  (Fig.  554). 

Attachments. — The  bulbo-cavernosus  differs  somewhat  in  its  relations  in  the 
two  sexes.  In  the  male,  in  which  it  is  also  termed  the  accelerator  urines,  the  two 
muscles  of  opposite  sides  are  united  in  a  median  fibrous  raphe  which  extends  forward 
from  the  central  tendon  of  the  perineum  over  the  bulb  and  corpus  spongiosum. 
Arising  from  this  raphe,  the  fibres  are  directed  laterally  and  forward  over  the  bulb 
and  corpus  spongiosum  and  are  inserted  into  the  under  surface  of  the  inferior  layer 
of  the  urogenital  trigone  and  into  the  fibrous  sheath  of  the  corpus  cavernosum,  some 
of  the  more  anterior  fibres  being  continued  dorsally  to  insert  into  the  fascia  covering 
the  dorsum  of  the  penis  and  forming  what  has  been  termed  the  muscle  of  Houston, 
or  compressor  vence  dor salis  penis. 

In  the  female,  in  which  the  muscle  has  been  termed  the  sphincter  vagina  (Fig. 
1732),  the  two  muscles  of  opposite  sides  are  widely  separated  from  each  other  by  the 
vagina,  which  they  surround.  They  arise  from  the  central  tendon  of  the  perineum, 
pass  forward,  investing  the  bulbi  vestibuli,  and  are  lost  in  the  fascia  covering  the 
corpora  cavernosa  and  the  dorsal  surface  of  the  clitoris. 

Nerve-Supply. — From  the  perineal  branches  of  the  pudic  nerve. 

Action. — To  compress  the  bulb  and  corpus  spongiosum  and  so  tend  to  expel 
any  fluid  contained  in  the  urethra.  The  fibres  which  pass  to  the  dorsum  of  the  penis 
(or  clitoris)  may  aid  slightly  in  the  erection  of  that  organ,  either  directly  or  by 
compressing  the  dorsal  vein. 

Variations. —The  posterior  portion  of  the  muscle,  that  surrounding  the  bulb,  is  unrepre- 
sented in  the  female  and  is  frequently  distinctly  separable  from  the  anterior  part  in  the  male  ; 
it  has  been  termed  the  compressor  biilbi.  The  deeper  fibres  of  this  part  of  the  muscle  are  sep- 
arated from  the  more  superficial  ones  by  a  thin  layer  of  areolar  tissue,  and  have  been  regarded 
as  forming  a  distinct  muscle,  the  compressor  hemisphericum  bn/bi,  which  closely  surrounds  the 
bulb,  the  two  muscles  of  either  side  interlacing  above  the  bulb  so  as  to  form  practically  a  single 
muscle  very  variable  in  its  development.  Finally,  fibres  may  arise  from  the  ischial  tuberosities 
in  common  with  those  of  the  transversi  superficiales  and  pass  forward  and  medially  to  unite 
with  the  bulbo-cavernosi  forming  what  have  been  termed  the  ischio-bulbosi. 

5.    TRANSVERSUS  PERIN^I  PROFUNDUS  (Fig.  1629). 

Attachments. — The  deep  transverse  perineal  muscle  is  situated  in  the  poste- 
rior part  of  the  deep  perineal  interspace.  It  arises  from  the  medial  surface  of  the 
inferior  ramus  of  the  ischium  and  passes  transversely  inward  to  the  median  line, 
where  it  partly  unites  with  its  fellow  of  the  opposite  side  and  partly  inserts  into  the 
central  tendon  of  the  perineum. 

Nerve-Supply. — From  the  perineal  branches  of  the  pudic  nerve. 

Action. — To  assist  in  fixing  the  central  tendon  of  the  perineum. 

6.    COMPRESSOR  URETHRA  (Fig.  1629). 

Attachments. — The  compressor  or  constrictor  of  the  urethra  (m.  sphincter 
urethrae  membranaceae)  in  the  male  is  a  thin  sheet  of  muscle-tissue  situated  in  the  deep 
perineal  interspace  anterior  to  the  deep  transversus  perinaei.  It  arises  from  the  inner 
surface  of  the  inferior  ramus  of  the  pubis  and  is  inserted  by  passing  medially  to  sur- 
round the  membranous  portion  of  the  urethra,  its  anterior  fibres  forming  a  median 
raphe  with  those  of  the  opposite  side.  The  posterior  fibres  of  the  muscle  enclose  the 
bulbo-urethral  gland. 

In  the  female  the  fibres  are  inserted \x\Xo  the  walls  of  the  vagina  as  it  traverses  the 
deep  perineal  interspace. 

Nerve-Supply. — From  the  perineal  branches  of  the  pudic  nerve. 

Action. — To  constrict  the  membranous  urethra  and,  in  the  female,  also  to 
flatten  the  wall  of  the  vagina. 

The  m.  ischio-pubicus  is  a  small  muscle  situated  at  the  side  of  the  deep  perineal  interspace. 
It  arises  from  the  inferior  rami  of  the  ischium  and  pnbis  and  passes  anteriorly  to  be  attached  to 
the  arcuate  ligament  of  the  pubis.  It  is  frequently  wanting. 


566  HUMAN   ANATOMY. 


THE  APPENDICULAR   MUSCLES. 

The  limbs  make  their  appearance  as  two  pairs  of  flat  buds  (Fig.  69),  the  upper 
pair  being  situated  in  the  lower  cervical  and  the  lower  pair  in  the  lower  lumbar  and 
upper  sacral  regions.  Into  the  buds  processes  extend  from  the  myotomes  of  the 
regions  concerned  and  apparently  give  rise  to  the  more  proximal  muscles  of  the 
limb,  but  that  they  are  the  source  of  all  the  limb  musculature  is  as  yet  undetermined. 
The  greater  mass  of  this  musculature  develops  from  a  blastema  which  occupies  the 
interior  of  the  limb-bud  and  which  cannot  at  first  be  distinguished  from  that  which 
gives  rise  to  the  limb  skeleton,  and  whether  it  represents  a  condensation  of  tissue 
whose  fundamental  derivation  is  the  myotomes  or  is  a  derivative  of  the  ventral 
mesoderm  has  not  yet  been  definitely  decided. 

However  that  may  be,  the  limb  musculature  stands  in  relation  to  the  anterior 
divisions  of  definite  spinal  nerves,  that  of  the  upper  limb  being  supplied  by  the  lower 
five  cervical  and  the  first  thoracic  nerves  and  that  of  the  lower  limb  by  the  lower  four 
lumbar  and  upper  three  sacral  nerves,  and,  furthermore,  there  is  a  distribution  of 
these  nerves  to  the  muscles  which  may  well  be  regarded  as  segmental.  It  is  also 
worthy  of  note  that  in  those  regions  of  the  trunk  in  which  the  limbs  develop  the 
ventral  musculature  is  either  very  much  reduced  or,  as  in  the  lower  limb,  practically 
wanting. 

An  examination  of  the  limb  muscles  shows  that  they  may  be  regarded  as  being 
arranged  in  a  ventral  or  pre-axial  group  and  a  dorsal  or  post-axial  group,  and  in 
harmony  with  this  arrangement  the  nerve-fibres  which  pass  to  the  muscles  arrange 
themselves  in  ventral  or  pre-axial  and  dorsal  or  post-axial  groups.  In  the  fore-limb 
the  dorsal  group  is  represented  by  the  posterior  fasciculus  or  cord  of  the  brachial 
plexus,  while  the  ventral  one  is  distributed  between  the  lateral  and  medial  fasciculi. 
In  the  lower  limb  the  correct  relationships  of  the  two  groups  of  muscles  and  their 
nerves  are  less  readily  perceivable,  owing  to  the  forward  rotation  which  the  limb  has 
undergone  in  order  to  bring  its  axis  into  a  plane  parallel  with  that  of  the  sagittal 
plane  of  the  body,  a  rotation  which  brings  it  about  that  in  the  adult,  except  in  the 
more  proximal  portion  of  the  limb,  the  pre-axial  musculature  is  on  the  posterior  and 
the  post-axial  on  the  anterior  surface.  The  pre-axial  nerve-fibres  are  distributed 
mainly  by  the  obturator  and  greater  sciatic  (internal  popliteal)  nerves,  while  the 
post-axial  ones  pass  to  their  destinations  by  way  of  the  anterior  crural  and  greater 
sciatic  (external  popliteal)  ;  and  in  this  connection  it  is  interesting  to  note  that  the 
fibres  of  the  external  popliteal  or  peroneal,  if  traced  to  their  exit  from  the  spinal 
foramina,  will  be  found  to  lie  dorsal  to  those  of  the  internal  popliteal  or  tibial,  not- 
withstanding that  the  former  are  supplied  to  the  anterior  and  the  latter  to  the  pos- 
terior muscles  of  the  leg. 

In  this  arrangement  into  pre-axial  and  post-axial  groups  there  is,  accordingly, 
to  be  found  a  clue  to  the  proper  understanding  of  the  relations  of  the  nerves  to  the 
muscles  of  the  limbs,  and  a  further  examination  of  the  two  groups  will  reveal  indica- 
tions of  a  segmental  distribution  of  the  nerves  and  muscles  in  each.  This  arrange- 
ment may  be  most  satisfactorily  understood  by  means  of  a  diagram  (  Fig.  555) 
showing  the  arrangement  of  the  muscles  and  nerves  in  what  may  be  regarded  as  its 
fundamental  condition.  The  limb-bud  may  be  regarded  as  a  flat  plate  whose  surfaces 
are  directed  dorsally  and  ventrally.  Into  the  upper  portion  of  this  plate  the  upper- 
most of  the  spinal  nerves  which  are  associated  with  it  is  prolonged,  its  post-axial 
and  pre-axial  fibres  passing  respectively  to  either  side  of  its  frontal  plane,  and  the 
succeeding  nerves  are  similarly  prolonged  into  it  in  succession  from  above  downward. 
The  nerves,  however,  which  lie  along  the  upper  and  in  the  lower  limb  also  along 
the  lower  borders  of  the  bud  are  not  prolonged  into  it  quite  so  far  as  the  others,  the 
free  edge  of  the  plate  being,  as  it  were,  rounded  off,  so  that  it  is  only  the  more  cen- 
tral (or  upper)  nerves  of  the  series  that  reach  that  portion  of  the  bud  from  which 
the  foot  (or  hand)  and  digits  will  be  developed. 

It  follows  from  this  arran^< -im-nt  that  in  the  adult  each  spinal  nerve  concerned 
supplies  a  portion  of  both  the  pre-axial  and  post-axial  groups  of  muscles,  and, 


THE   APPENDICULAR   MUSCLES.  567 

furthermore,  that  the  muscle-fibres  in  succession  from  one  border  of  the  limb  to  the 
other  are  supplied  by  successive  nerves,  those  supplied  by  the  uppermost  and,  in 
the  pelvic  limb  at  least,  the  lowermost  nerves  extending  only  to  the  neighborhood 
of  the  knee  (or  elbow)  or  even  a  shorter  distance  into  the  limb.  Thus,  in  the  fore- 
limb  one  may  expect  to  find  the  more  lateral  muscles  of  the  shoulder  and  arm 
supplied  by  fibres  from  the  uppermost  nerves  of  the  brachial  plexus,  those  lying 
towards  the  middle  of  the  shoulder  and  brachial  regions  and  in  the  lateral  portion 
of  the  antibrachium  and  hand  regions  by  the  middle  nerves,  and  those  along  the 
medial  portion  of  the  limb  by  the  lower  ones.  In  the  lower  limb,  however,  owing 
to  the  rotation  which  it  has  undergone,  the  arrangement  is  to  a  certain  extent 
reversed,  and  although  in  the  more  proximal  muscles  the  fibres  are  supplied  by  suc- 
cessive nerves  from  above  downward,  lower 

down  the  fibres  from  the  upper  nerves  are  FIG.  555. 

to  be  found  along  the  inner  side  of  the  leg         _^ — 3~^r\    xDorsai  muscles 
and  those  from  the  lower  nerves  along  the 
outer  side. 

Tp     . .  •    •       11  i.   1  8»N\    Intermuscular  septum 

If,  then,  an  originally  segmental  ar-          ^rffN^       P^.  V 
rangement  of  the  muscle-fibres  of  the  limbs         •  £*  '  >^^**'  Mesobiastic 

is  to  be  recognized,  the  segments  must  run      jg^    9       *|PPBfc  rSfoi^    /"^"post-axial 
parallel  to  the  long  axis  of  the  limb,  and  -  ^  Q  <•  ^  ^JBffi\^&MkX    ^muscles 

this  arrangement  has  permitted  their  free 
consolidation  to  form  the  various  muscles 
found  in  the  adult,  very  few  indeed  of 
which  are  supplied  by  a  single  nerve,  and 
represent,  accordingly,  portions  of  a  sin- 
gle primitive  segment.  Furthermore,  the 

j    J        •  c  ,1  i  rr      .•      1  ^&sjS         Latero-        Pre-axial  muscles 

adaptation  of  the  muscles  to  act  effectively  ^Pc/        ventral 

on    the   various   joints  of   the   limbs   has  **^\od'      muscles 

brought  about  a  transverse  division  of  the 

Diagram  of  ore-  and  post-axial  groups  of  limb-muscles. 

segments,  and  has  also  led  to  a  complete  (Koiimann.) 

degeneration  of  the  portions  of  some  of  the 

segments  in  one  part  of  the  limb  while  they  are  retained  in  another.  Thus,  for 
example,  in  the  pre-axial  musculature  of  the  brachial  region  no  trace  is  to  be  found 
of  the  segments  supplied  by  the  eighth  cervical  and  first  dorsal  nerves,  although 
the  eighth  cervical  is  represented  in  the  post-axial  musculature  and  both  in  the 
pre-axial  musculature  of  the  forearm. 

On  account  of  the  occurrence  of  both  fusion  and  degeneration,  little  trace  of  an 
original  segmental  arrangement  of  the  muscle-fibres  is  to  be  found  in  the  adult  limb 
muscles,  and  their  classification  according  to  the  segments  from  which  they  may  be 
derived  is  not  feasible.  Comparative  anatomy,  however,  shows  that  primarily  the 
limb  muscles  were  arranged  with  relation  to  the  various  joints  of  the  limb,  each 
muscle,  as  a  rule,  passing  over  but  a  single  joint,  and  in  this  relation  may  be  found  a 
basis  for  classification.  In  man  the  original  relations  have  been  modified  in  many 
cases  by  an  alteration  in  one  of  the  original  points  of  attachment  of  a  muscle  so  that 
it  passes  over  two  joints,  or  by  the  end-to-end  union  of  originally  distinct  muscles 
so  that  the  same  result  is  brought  about.  Making  allowance  for  these  modifications, 
however,  the  muscles  of  the  upper  limb  may  be  classified  into  ( i )  those  passing  from 
the  axial  skeleton  to  the  pectoral  girdle,  (2)  those  passing  from  the  girdle  to  the 
brachium  or  arm,  (3)  those  passing  from  the  brachium  to  the  antibrachium  or  fore- 
arm, (4)  those  passing  from  the  antibrachium  to  the  carpus,  and  (5)  the  digital  mus- 
cles. Similarly  in  the  lower  limb,  in  which,  however,  owing  to  the  firm  articulation 
of  the  pelvis  to  the  sacrum,  the  first  group  of  muscles  is  practically  unrepresented, 
or  at  least  may  be  placed  with  those  of  the  second  group  extending  from  the  pelvic 
girdle  to  the  femur.  With  this  grouping  there  may  be  combined  a  recognition  of 
the  pre-axial  and  post-axial  musculature,  these  terms  being  used  in  the  lower  limb  as 
well  as  in  the  upper  to  indicate  the  relationships  which  obtained  before  the  rotation 
of  the  limb. 


568 


HUMAN   ANATOMY. 


THE   MUSCLES   OF  THE   UPPER   LIMB. 

THE   MUSCLES    EXTENDING   BETWEEN   THE   AXIAL   SKELETON 
AND   THE    PECTORAL   GIRDLE. 

(a)     THE   PRE-AXIAL  MUSCLES. 

i.    Pectoralis  major.  2.    Pectoralis  minor. 

3.   Subclavius. 

The  Pectoral  Fascia.  —  The  superficial  pectoral  fascia  is  continuous  above 
with  the  superficial  cervical  and  below  with  the  superficial  abdominal  fasciae,  and 
covers  the  entire  anterior  wall  of  the  thorax.  It  usually  contains  a  considerable 
amount  of  fat  and  has  embedded  in  it  the  mammary  gland. 

The  deep  fascia  is  attached  above  to  the  clavicle,  and  forms  a  thin  membrane 
closely  adherent  to  the  surface  of  the  pectoralis  major,  at  the  lower  border  of  which 


FIG.  556. 


t 


External  anterior  thoracic  nerve 

Cephalic  vein 
Branch  of  acromio-thoracic  artery 

Deltoid 


Distal  stump  of 
pectoralis  major 

Cut  edge  of  deep- 
pectoral  fascia 


Pectoralis  minor  enclosed  in 
clavi-pectoral  fascia 


Pectoralis  major,  cut  edge 
of  clavicular  portion 


Pectoralis  major,  cut 
edge  of  sterno-costal 
portion 


Dissection  of  thoracic  wall  after  removal  of  greater  part  of  pectoralis  major,  showing  clavi-pectoral  fascia 
enclosing  pectoralis  minor  and  continuous  with  axillary  fascia. 

it  becomes  continuous  with  the  axillary  fascia.  Medially  it  is  attached  to  the  ventral 
surface  of  the  sternum  and  laterally  it  is  continuous  with  the  fascia  covering  the  deltoid. 
Beneath  the  deep  fascia  there  arises  from  the  clavicle  a  second  sheet  of  fascia 
(clavi-pectoral  fascia}  (Fig.  556)  which  encloses  the  subclavius  muscle  and  is  then 
continued  downward  to  the  upper  border  of  the  pectoralis  minor.  There  it  divides 
into  two  sheets  which  enclose  the  muscle  and  at  its  lower  margin  unite  to  form  a 
single  sheet  which  becomes  continuous  with  the  axillary  fascia  close  to  the  lower 
border  of  the  pectoralis  major.  The  portion  of  this  fascia  which  intervenes  between 
the  clavicle  and  the  subclavius  muscle  and  the  upper  border  of  the  pectoralis  minor 
is  termed  the  coraco-clavic ular  fascia  or  costo-coracoid  membrane.  It  is  prolonged 
laterally  along  the  upper  border  of  the  pectoralis  minor,  over  the  upper  portion  of 
the  axillary  vessels,  to  the  coracoid  process,  its  outer  portion  being  thickened  to  form 


THE   PECTORAL   MUSCLES. 


569 


a  band,  the  costo-coracoid  ligament  (Fig.  560),  which  passes  obliquely  downward 
and  laterally  from  the  clavicle  to  the  coracoid  process.  The  coraco-clavicular  fascia 
occasionally  contains  muscle-fibres  (the  m.  coraco-clavicularis},  and  is  usually  perfo- 
rated by  the  cephalic  vein  on  its  way  to  join  the  axillary,  by  the  thoraco-acromial 
artery,  and  by  the  external  anterior  thoracic  nerve. 

i.    PECTORALIS  MAJOR  (Fig.  557). 

Attachments. — The  pectoralis  major  is  a  strong  fan-shaped  muscle  situated 
on  the  anterior  thoracic  wall.  It  is  composed  of  three  portions  :  (i)  the  pars  da- 
vicularis,  which  arises  from  the  inner  half  of  the  anterior  border  of  the  clavicle  ; 
(2)  the  pars  sterno-costalis ,  which  arises  from  the  anterior  surface  of  the  sternum 
and  the  upper  six  costal  cartilages  ;  and  (3)  the  portio  abdominalis,  which  arises  from 


FIG.  557. 


Deltoid 


Clavicle 


Pectoralis  major, 
clavicular  portion 


Brachial 
fascia 


Pectoralis 
major,  sterno- 
costal  portion 


Serratus  magnus 


Sternum 


Latissimus  dorsi 


Pectoralis  major, 
abdominal  portion 


Dissection  of  thoracic  wall,  showing  pectoralis  major. 


the  upper  part  of  the  anterior  layer  of  the  sheath  of  the  rectus  abdominis.  From 
these  origins  the  fibres  are  directed  laterally  to  be  inserted  into  the  external  bicipital 
ridge  which  extends  downward  from  the  greater  tuberosity  of  the  humerus,  the  lower 
fibres  of  the  sterno-costal  and  the  abdominal  portions  of  the  muscle  passing  behind 
those  of  the  clavicular  and  upper  portions,  so  that  the  tendon  of  insertion  is  U-shaped 
in  section,  consisting  of  two  layers  separated  above  but  continuous  below.  A  bursa 
is  usually  interposed  between  the  posterior  surface  of  the  tendon  and  the  anterior 
surface  of  the  long  head  of  the  biceps  humeri. 

Nerve-Supply. — From  the  external  and  internal  anterior  thoracic  nerves  by 
fibres  from  the  lower  four  cervical  and  the  first  thoracic  nerves. 


570  HUMAN   ANATOMY. 

Action. — When  the  arm  is  abducted  to  a  position  at  right  angles  to  the  body, 
the  pectoralis  major  will  draw  the  arm  forward  and  at  the  same  time  will  adduct  it. 
As  the  arm  approaches  the  vertical  position,  the  adductor  action  becomes  more 
pronounced  and  the  flexor  action  less  so,  and  a  slight  amount  of  internal  rotation 
appears.  When  the  arm  is  raised  above  the  level  of  the  shoulder  and  fixed,  the 
muscle  will  assist  in  drawing  the  trunk  upward,  as  in  climbing,  and  it  will  also  assist 
in  raising  the  ribs  in  forced  inspiration. 

Variations. — In  the  lower  mammals  the  pectoralis  major  is  represented  by  a  number  of 
distinctly  separate  portions,  a  condition  which  may  be  indicated  in  man  by  a  more  than  usual 
distinctness  of  the  three  portions  of  the  muscle  and  by  the  occurrence  of  accessory  slips.  The 
sterno-costal  and  abdominal  portions  may  be  greatly  reduced  or  even  absent. 

The  m.  sternalis  is  present  in  something  over  4  per  cent,  of  all  cases  examined.  It  is  very 
variable  in  its  development,  and  consists  of  fibres  which  arise  anywhere  from  the  third  to  the 
seventh  costal  cartilage,  or  even  from  the  sheath  of  the  rectus,  and  extends  upward  to  be  attached 
to  the  anterior  surface  of  the  sternum,  the  clavicle,  or  the  tendon  of  the  sterno-cleido-mastoid. 
Usually  the  fibres  are  directed  vertically,  but  sometimes  they  may  have  a  more  or  less  oblique 
course. 

The  muscle  has  been  variously  regarded  as  a  portion  of  the  platysma,  a  downward  pro- 
longation of  the  sterno-cleido-mastoid,  an  upward  prolongation  of  the  rectus  abdominis,  and 
as  a  displaced  portion  of  the  pectoralis  major.  The  fact  that  in  the  majority  of  cases  it  is  sup- 
plied by  branches  from  the  anterior  thoracic  nerves  indicates  clearly  its  usual  derivation  from  the 
pectoralis,  but  it  is  asserted  that  in  certain  cases  it  received  its  nerve-supply  from  the  third  and 
fourth  intercostal  nerves,  in  which  cases  it  is  more  probably  to  be  regarded  as  representing  a 
thoracic  portion  of  the  rectus  trunk  muscles. 

The  chondro-epitrochlearis  is  a  slip  derived  from  the  pectoralis  major  which  takes  its 
origin  from  the  lower  costal  cartilages  or  the  abdominal  portion  of  the  pectoralis  and  is  inserted 
into  the  brachial  fascia  or  the  medial  epicondyle  of  the  humerus. 

2.   PECTORALIS  MINOR  (Fig.  560). 

Attachments. — The  pectoralis  minor  lies  beneath  the  pectoralis  major.  It 
arises  from  the  outer  surface  of  the  third,  fourth,  and  fifth  ribs  and  from  the  ascia 
covering  the  intervening  intercostal  muscles,  and  passes  obliquely  upward  and  later- 
ally to  be  inserted  into  the  coracoid  process  of  the  scapula. 

Nerve-Supply. — By  branches  of  the  external  and  internal  anterior  thoracic 
nerves  fronv  the  seventh  and  eighth  cervical  and  first  thoracic  nerves. 

Action. — To  draw  the  lateral  angle  of  the  scapula  downward  and  forward  ;  if 
the  scapula  be  fixed,  to  raise  the  ribs  to  which  it  is  attached. 

Relations. — The  pectoralis  minor  is  completely  covered  by  the  pectoralis 
major.  It  covers  the  outer  surface  of  the  upper  ribs  and  their  intercostal  spaces,  and 
near  its  insertion  it  passes  over  the  middle  portion  of  the  axillary  vessels  and  the 
cords  of  the  brachial  plexus. 

3.   SUBCLAVIUS  (Fig.  560). 

Attachments. — The  subclavius  is  an  almost  cylindrical  muscle  attached  at  one 
extremity  to  the  anterior  surface  of  the  first  costal  cartilage  and  at  the  other  to  the 
under  surface  of  about  the  middle  third  of  the  clavicle. 

Nerve-Supply. — By  a  special  nerve  from  the  brachial  plexus  from  the  fifth  and 
sixth  cervical  nerves. 

Action. — To  draw  the  outer  end  of  the  clavicle  downward  and  forward. 

Variations. — The  subclavius  seems  to  be  the  persistent  representative  of  a  group  of 
muscles  more  perfectly  developed  in  the  lower  mammals  and  especially  in  those  in  which  tin- 
clavicle  is  more  or  less  rudimentary.  Muscle-bands,  which  represent  portions  of  the  group 
normally  degenerated,  are  occasionally  found  in  man,  and  on  account  of  their  variable  relations 
have  been  described  under  various  names.  They  may  all  be  grouped,  however,  under  three 
terms,  the  stemo-chondro-scapttlaris,  the  scapuio-cfavuvlaHs,  and  the  stento-clavicularis  ( Le 
Double).  In  the  mammals  which  lack  a  clavicle — in  many  Ungulates,  for  example— a  strong 
muscle-band  passes  transversely  across  the  upper  part  of  the  thorax  from  the  sternum  and  first 
costal  cartilage  to  the  scapula.  This  is  thesterno-chondro-scapnlaris,  and  it  occasionally  occurs 
in  man  as  a  baud  arising  from  the  points  named,  or  from  either  one  of  them,  or  from  the  first 
ril),  and  inserting  into  the  coracoid  process  of  the  scapula. 

In  those  mammals  which  possess  a  rudimentary  clavicle,  such  as  the  Rodents,  only  the 
terminations  of  the  sterno-chondro-scapnlar  persist,  each  inserting  into  the  clavicle,  and  forming 


THE   SCAPULAR   MUSCLES.  571 

the  scapulo-clavicularis  and  the  sterno-clavicularis.  Each  of  these  may  occur  as  an  anomaly  in 
man,  the  sterno-clavicularis  appearing  under  various  forms,  and  passing  either  above,  behind, 
or  in  front  of  the  clavicle.  It  should  be  stated,  however,  that  there  is  a  possibility  that  some  of 
the  varieties  of  the  sterno-clavicularis  may  really  represent  persisting  portions  of  the  muscular 
sheet  which  has  given  rise  to  the  middle  layer  of  the  cervical  fascia  and  to  the  sterno-hyoid  and 
the  omo-hyoid  (page  545). 

In  the  lower  mammals  a  thin  muscular  sheet  invests  a  greater  or  less  portion  of  the  trunk 
in  intimate  association  with  the  integument,  resembling  in  this  respect  the  platysma.  It  is 
termed  the  panniculus  carnosits,  and  in  man  is  normally  unrepresented.  Occasional  traces  of 
it  are  found,  however,  and  of  these  the  most  frequent  is  the  muscle  of  the  axillary  arch,  a 
somewhat  variable  band  of  muscle-tissue  which  passes  across  the  anterior  portion  of  the  axillary 
cavity  from  the  lateral  border  of  the  latissimus  dorsi  to  the  tendon  of  the  pectoralis  major.  It 
presents  considerable  variation  in  its  insertion,  being  connected  sometimes  with  the  biceps,  the 
coraco-brachialis,  the  pectoralis  minor,  or  the  chondro-epitrochlearis,  or  being  united  with  slips 
from  the  abdominal  portion  of  the  pectoralis  major,  or  being  inserted  into  the  coracoid  process 
of  the  scapula.  It  is  supplied  by  branches  from  the  anterior  thoracic  nerves. 

(b)   THE  POST-AXIAL  MUSCLES. 

1.  Serratus  magnus.  3.    Rhomboideus  minor. 

2.  Levator  anguli  scapulae.         4.    Rhomboideus  major. 

5.    Latissimus  dorsi. 

i.  SERRATUS  MAGNUS  (Fig.  558). 

Attachments. — The  serratus  magnus  (m.  serratus  anterior)  forms  a  large 
muscular  sheet  covering  the  lateral  wall  of  the  thorax.  It  arises  by  nine  or  ten 
fleshy  digitations  from  the  outer  surfaces  of  the  eight  or  nine  upper  ribs,  the  second 
rib  giving  attachment  to  two  slips.  Its  fibres  may  be  regarded  as  arranged  in  three 
groups  :  the  uppermost  group  consists  of  fibres  from  the  first  and  second  ribs  and  is 
inserted  into  the  ventral  surface  of  the  medial  angle  of  the  scapula  ;  the  middle  group, 
from  the  second  and  third  ribs,  is  inserted  into  the  ventral  surface  of  the  vertebral 
border  of  the  scapula  ;  while  the  remaining  fibres,  constituting  the  strongest  portion 
of  the  muscle,  converge  to  the  inferior  angle  of  the  same  bone. 

Nerve-Supply. — By  the  long  thoracic  nerve  from  the  fifth,  sixth,  and  seventh 
cervical  nerves. 

Action. — It  serves  to  keep  the  scapula  closely  applied  against  the  thoracic 
wall  and  draws  it  laterally.  Since  the  portion  inserted  into  the  inferior  angle  is  the 
strongest,  a  rotation  of  the  scapula  is  produced  whereby  its  lateral  angle  is  raised. 
By  this  action  the  serratus  plays  an  important  part  in  the  elevation  (abduction)  of 
the  arm,  since,  in  the  first  place,  by  fixing  the  scapula  it  allows  the  deltoid  to  expend 
all  its  action  on  the  humerus  instead  of  wasting  part  of  it  in  tilting  the  acromion 
downward,  and,  in  the  second  place,  after  the  deltoid  has  completed  its  action  and 
has  raised  the  arm  through  about  90°,  the  further  elevation  through  another  right 
angle  is  accomplished  by  a  rotation  of  the  scapula  resulting  from  the  action  of  the 
serratus  magnus  and  trapezius. 

Variations. — Absence  of  a  portion  or  the  whole  of  the  muscle  has  been  observed.  Its 
origin  may  extend  as  low  as  the  tenth  rib,  and  it  may  receive  slips  from  the  transverse  processes 
of  the  cervical  vertebrae  and  from  the  levator  scapulae. 

2.   LEVATOR  ANGULI  SCAPULAE  (Fig.  559). 

Attachments. — This  (m.  levator  scapulae)  is  an  elongated  muscle  on  the  lateral 
surface  of  the  neck.  It  arises  from  the  transverse  processes  of  the  upper  four  cer- 
vical vertebrae  and  passes  downward,  forward,  and  laterally  to  be  inserted  into  the* 
medial  angle  and  outer  surface  of  the  vertebral  border  of  the  scapula  as  far  down  as 
the  base  of  the  spine. 

Nerve-Supply. — By  the  dorsal  scapular  nerve  from  the  fifth  cervical  nerve. 

Action. — To  draw  upward  the  medial  angle  of  the  scapula,  producing  a  rota- 
tion of  the  bone  contrary  to  that  effected  by  the  serratus  anterior.  If  the  scapula 
be  fixed,  the  action  is  to  bend  the  cervical  portion  of  the  spinal  column  laterally, 
rotating  it  slightly  to  the  opposite  side. 


572 


HUMAN    ANATOMY. 


Variations. — The  origin  may  extend  to  the  transverse  processes  of  all  the  cervical  ver- 
tebrae, and  may  be  continued  upon  the  mastoid  process  above  and  upon  the  upper  ribs  below. 
Slips  may  occur  connecting  the  levator  with  various  neighboring  muscles,  the  most  interesting 
of  these  connections  being  that  with  the  serratus  magnus,  since  comparative  anatomy  shows 
that  the  levator  was  primarily  continuous  with  that  muscle. 

A  separated  portion  of  the  outer  part  of  the  muscle  is  occasionally  inserted  into  the  outer 
end  of  the  clavicle,  forming  what  is  termed  the  levator  claviculce. 

3.   RHOMBOIDEUS  MINOR  (Fig.  559). 

Attachments. — The  rhomboideus  minor  is  a  band-like  muscle  which  arises 
from  the  lower  part  of  the  ligamentum  nuchae  and  from  the  spinous  process  of  the 

FIG.  558. 

Serratus  posticus  superior 


Coracoid  process 
Tendon  of  supraspinatus 
Acromion 
process 


Lesser, 
tuberosity  of 
humerus 

Subscapularis 


Levator  anguli  scapulae 


Superior  angle  of  scapula 
Supraspinatus 


Scalenus  posticus 
Scalenus  medius 


Scalenus  anticus 
First  rib 


Serratus  mag- 
nus, upper, 
middle,  and 
lower  por- 
tions 


Latissimus  dorsi,  cut  edge 


Dissection  of  thoracic  wall,  showing  serratus  magnus;  clavicle  has  been  removed  and  scapula  drawn  outward. 

last  cervical  vertebra  and  passes  laterally  and  downward  to  be  inserted  into  the  ver- 
tebral border  of  the  scapula  at  the  base  of  the  spine. 

Nerve-Supply. — By  the  dorsal  scapular  nerve  from  the  fifth  cervical  nerve. 

Action. — To  draw  the  scapula  upward  and  medially,  at  the  same  time  rotating 
it  so  that  the  lateral  angle  is  moved  downward. 

4.   RHOMBOIDEUS  MAJOR  (Fig.  559). 

Attachments. — The  rhomboideus  major  immediately  succeeds  the  rhom- 
boideus minor,  and  is  a  quadrilateral  sheet  which  arises  from  the  spinous  processes 
of  the  four  upper  thoracic  vertebrae  and  from  the  intervening  interspinous  liga- 


THE  SCAPULAR   MUSCLES, 
FIG.  559. 


573 


Semispinalis  capitis 
(complexes) 


Splenius  capitis  et  colli 


— Sterno-cleido-mastoideus 


Supraspinatus 

A 


nfraspinatus 


Rhomboideus  major 
Vertebral  aponenrosis 
Serratus  magnus 


Serratus  posticus 
inferior 


Oluteus  medius 


Gluteus  maximus 


Deltoid 

Infraspinatus 
Rhomboideus  major 
Teres  major 


Aponeurosis  of  trapezius 
Trapezius 


Levator  anguli  scapulae 
Rhomboideus  mino 


Latissimus  dorsi 


Aponeurosis  of  latissimus 
dorsi  (vertebral  aponeurosis) 


Superficial  muscles  of  the  back. 


574  HUMAN    ANATOMY. 

ments.  It  is  directed  downward  and  laterally  and  is  inserted  into  the  lower  two- 
thirds  of  the  vertebral  border  of  the  scapula. 

Nerve-Supply. — By  the  dorsal  scapular  nerve  from  the  fifth  cervical  nerve. 

Action. — To  draw  the  scapula  upward  and  medially,  at  the  same  time  rotating 
it  so  that  the  lateral  angle  is  moved  downward. 

Variations  of  the  Rhomboidei. — The  rhomboidei  are  sometimes  entirely  wanting,  and 
the  origins  of  both  muscles  may  be  extended  beyond  the  usual  limits. 

The  occipito-scapularis  is  a  muscle  occasionally  present  which  is  intimately  associated  in 
its  derivation  with  the  rhomboids.  It  arises  from  the  inner  part  of  the  superior  nuchal  line  and 
passes  downward  between  the  trapezius  and  splenius  to  join  the  rhomboideus  minor,  inserting 
with  it  into  the  vertebral  border  of  the  scapula. 

5.   LATISSIMUS  DORSI  (Fig.  559). 

Attachments. — The  latissimus  dorsi  is  a  large  triangular  muscle  which  arises 
from  the  spinous  processes  of  the  last  six  thoracic  vertebrae  and  the  intervening 
interspinous  ligaments  beneath  the  origin  of  the  trapezius,  from  the  lumbo-dorsal 
fascia,  from  the  posterior  portion  of  the  crest  of  the  ilium,  and  by  fleshy  digitations 
from  the  outer  surfaces  of  the  lower  three  or  four  ribs.  Its  fibres  pass  upward  and 
laterally  over  the  inferior  angle  of  the  scapula,  from  which  an  additional  slip  is  usu- 
ally added  to  the  muscle.  It  then  curves  around  the  lower  border  of  the  teres 
major  and  is  inserted,  ventrally  to  that  muscle,  into  the  crest  of  the  inner  tuberosity 
of  the  humerus.  A  mucous  bursa  (bursa  m.  latissimi  dorsi  )  lies  between  the  tendons 
of  insertion  of  the  latissimus  dorsi  and  teres  major. 

Nerve-Supply. — By  the  long  subscapular  nerve  from  the  seventh  and  eighth 
cervical  nerves. 

Action. — To  draw  the  humerus  downward,  backward,  and  inward,  at  the  same 
time  rotating  it  inward,  the  action  being  that  of  the  arm  in  swimming.  If  the 
humerus  be  fixed,  as  in  climbing,  it  draws  the  pelvis  and  lower  portion  of  the  trunk 
upward  and  forward. 

Variations. — The  latissimus  dorsi,  like  the  serratus  anterior  and  pectorales,  is  a  muscle 
which  has  migrated  extensively  from  the  region  of  its  first  formation,  the  lower  cervical  region, 
and  this  migration  can  be  witnessed  in  the  ontogeny  of  the  muscle.  Consequently  variations 
may  be  expected  and  do  occur  in  the  extent  of  the  origin  of  the  muscle,  whose  descent  and 
backward  migration  to  the  vertebral  column  may  be  interrupted  at  various  stages. 

A  great  amount  of  variation  of  this  nature  is  seen  in  its  attachment  to  the  crest  of  the  ilium. 
In  some  cases  this  attachment  extends  so  far  forward  as  to  meet  the  posterior  extremity  of  the 
attachment  of  the  external  oblique  of  the  abdomen,  but  usually  this  does  not  occur,  and  a  tri- 
angular interval,  known  as  the  triangle  of  Petit,  occurs  between  the  borders  of  the  two  muscles 
and  above  the  crest  of  the  ilium.  The  floor  of  the  triangle  is  formed  by  the  internal  obliquus 
abdominis,  and,  since  the  abdominal  wall  is  here  thinner  than  elsewhere,  the  triangle  may  occa- 
sionally be  the  seat  of  a  lumbar  hernia. 

Closely  allied  to  the  latissimus  dorsi  is  a  muscle,  the  m.  dorso-epitrochlearis,  which  occurs 
in  18  or  20  per  cent,  of  cases.  It  takes  its  origin  from  the  body  or  tendon  of  insertion  of  the 
latissimus  and  passes  to  the  brachial  fascia  or  to  the  medial  epicondyle  of  the  humerns.  It  has 
been  regarded  as  an  aberrant  portion  of  the  pectoralis  group  of  muscles,  but  its  supply  by  tlit- 
musculo-spiral  nerve  places  it  among  the  post-axial  muscles. 

The  Axillary  Fascia. — The  axillary  fascia  is  a  firm  sheet  which  extends 
across  from  the  lower  border  of  the  pectoralis  major  to  that  of  the  latissimus  dorsi 
and  teres  major,  forming  the  floor  of  the  axilla.  Laterally  it  passes  over  into  the 
deep  fascia  of  the  arm,  medially  into  the  fascia  covering  the  serratus  magnus,  and 
near  the  border  of  the  pectoralis  major  it  has  inserted  into  it  the  downward  continu- 
ation of  the  fascia  which  encloses  the  pectoralis  minor  (Fig.  556).  It  is  pierced  by 
numerous  lymphatic  vessels,  and  along  its  medial  edge  is  considerably  thickened 
to  form  a  curved  hand,  whose  concavity  is  directed  laterally,  and  which  stretches 
across  between  the  tendons  of  the  pectoralis  major  and  the  latissimus,  forming 
what  is  termed  the  axillary  arch.  Muscle-fibres  are  occasionally  found  in  this  arch 
(page  571). 

The  axilla  is  a  pyramidal  space  intervening  between  the  upper  part  of  the 
brachium  and  the  lateral  wall  of  the  thorax.  Its  apex  is  directed  upward  and  the 


THE   SHOULDER    MUSCLES.  575 

base,  which  is  formed  by  the  axillary  fascia,  downward.  Its  ventral  wall  is  formed 
by  the  pectoralis  major  and  pectoralis  minor,  its  dorsal  wall  by  the  latissimus  dorsi, 
teres  major,  and  subscapularis,  and  its  medial  wall  by  the  serratus  magnus.  In  the 
angle  formed  by  the  junction  laterally  of  its  ventral  and  dorsal  walls  lies  the  m.  coraco- 
brachialis,  and  in  the  groove  between  that  muscle  and  the  posterior  wall  are  the 
axillary  vessels  and  the  cords  of  the  brachial  plexus.  The  cavity  of  the  axilla  con- 
tains a  considerable  amount  of  fat  and  a  variable  number  of  lymphatic  nodes  ;  it  is 
traversed  by  the  thoracic  branches  of  the  axillary  vessels  and  by  the  intercosto- 
humeral  nerve,  and  the  long  thoracic  nerve  passes  downward  along  its  medial  wall  to 
the  serratus  magnus. 

THE  MUSCLES  PASSING  FROM  THE  PECTORAL  GIRDLE  TO 

THE  BRACHIUM. 

PKE-AXIAL.  Posx-AxiAL. 

i.   Coraco-brachialis.  i.  Supraspinatus.        4.   Teres  major. 

2.  Infraspinatus.          5.   Subscapularis. 

3.  Teres  minor.  6.    Deltoideus. 

(a)    THE  PRE-AXIAL  MUSCLES. 

i.    CORACO-BRACHIALIS  (Figs.  560,  570). 

Attachments. — The  coraco-brachialis  arises  from  the  tip  of  the  coracoid  pro- 
cess of  the  scapula  by  a  tendon  common  to  it  and  the  short  head  of  the  biceps.  It 
extends  downward  along  the  humerus  and  is  inserted  at  about  the  middle  of  its 
medial  border. 

Nerve-Supply. — By  the  musculo-cutaneous  nerve  from  the  seventh  cervical 
nerve. 

Action. — To  draw  the  upper  arm  forward. 

Relations. — It  is  crossed  ventrally  by  the  pectoralis  major,  and  dorsally  it  is  in 
relation  with  the  tendons  of  the  latissimus  dorsi,  the  teres  major,  and  the  subscapu- 
laris, from  the  last  of  which  its  tendon  is  separated  by  a  mucous  bursa  (dursa  m, 
coraco-brachialis^).  Laterally  the  muscle  is  in  contact  with  the  short  head  of  the 
biceps.  It  is  usually  pierced  by  the  musculo-cutaneous  nerve,  and  is  in  relation 
medially  with  the  axillary  artery  and  the  median  and  ulnar  nerves. 

Variations. — Comparative  anatomy  shows  that  the  coraco-brachialis  is  primarily  an  ex- 
tensive muscle  consisting  of  three  portions,  of  which  only  the  middle  one  and  a  part  of  the 
inferior  are  normally  present  in  man.  The  variations  which  occur  usually  consist  in  the 
appearance  of  one  or  other  of  the  missing  portions.  Thus  the  upper  portion  is  sometimes 
represented  by  a  coraco-brachialis  superior,  which  arises  from  the  coracoid  process  and  passes 
laterally  to  be  inserted  into  the  lesser  tuberosity  of  the  humerus  or  into  the  capsule  of  the 
shoulder-joint,  while  the  lower  portion  may  be  more  completely  represented  by  the  insertion 
of  the  muscle  extending  as  far  down  as  the  medial  epicondyle  of  the  humerus. 

(*)    THE  POST-AXIAL  MUSCLES. 

i.    SUPRASPINATUS  (Fig.  561). 

Attachments. — The  supraspinatus  occupies  the  supraspinous  fossa  of  the 
scapula,  arising  from  the  inner  two-thirds  of  this  and  from  the  supraspinous  fascia. 
Its  fibres  pass  laterally  and  converge  to  a  tendon  which  is  inserted  into  the  upper  facet 
upon  the  greater  tuberosity  of  the  humerus  and  into  the  capsule  of  the  shoulder- 
joint. 

Nerve-Supply. — By  the  suprascapular  nerve  from  the  fifth  and  sixth  cervical 
nerves. 

Action. — To  abduct  the  arm. 

The  supraspinous  fascia  is  the  layer  of  connective  tissue  which  covers  the 
supraspinatus  muscle.  It  is  attached  to  the  superior  border  of  the  scapula  above,  to 
the  vertebral  border  medially,  to  the  spine  below,  and  gradually  fades  out  laterally. 


the  vert 


576 


HUMAN   ANATOMY. 


2.    INFRASPINATUS  (Figs.  561,  572). 

Attachments. — The  infraspinatus  occupies  the  infraspinous  fossa  of  the  scapula 
and  arises  from  the  entire  extent  of  the  fossa,  with  the  exception  of  a  portion 
towards  the  axillary  border  of  the  bone.  It  also  arises  from  the  infraspinous  fascia 
which  covers  it.  The  fibres  pass  laterally  and  converge  to  a  strong  tendon,  which 
is  frequently  separated  from  the  capsule  of  the  shoulder-joint  by  a  small  bursa  (bursa 


FIG.  560. 


Axillary  vein 
Axillary  artery 


•Subclavius 
— -Costo-coracoid  ligament 


Deltoid 
Long  head  of  biceps 

Short  head  of  bice; 

Insertion  of 
pectoralis  major 


Deltoid 


Biceps 4 


Pectoralis  minor 


Serratus  magnus 


Latissimus  dorsi 

Subscapularis 


Bicipital 
fascia 


m.  infraspinati)  and  is  inserted  into  the  middle  facet  of 
the  greater  tuberosity  of  the  humerus. 

Nerve-Supply. — By  the  suprascapular  nerve  from 
the  fifth  and  sixth  cervical  nerves. 

Action. — When  the  arm  is  hanging  vertically,  it  is 
the  chief  outward  rotator  of  the  humerus.  When  the 
arm  is  abducted  to  a  horizontal  position,  the  muscle 
draws  it  backward. 

Variations. — The  upper  portion  of  the  muscle  is  sometimes 
distinctly  separated  from  the  rest,  and  has  been  termed  the 
infras/>hnitus  minor.  On  the  other  hand,  the  separation  which 
usually  exists  between  the  infraspinatus  and  the  teres  minor  tuny 
be  entirely  wanting. 

The  infraspinous  fascia  is  a  strong  fascia  which  covers 
the  infraspinatus  and  the  teres  minor,  giving  origin  to 
some  of  the  fibres  of  both  muscles.  It  is  attached  above 

to  the  spine  of  the  scapula,  medially  to  its  vertebral  border,  and  fades  out  laterally 

into  the  brachial  fascia. 

3.    TERES  MINOR  (Fig.  561). 

Attachments. — The  teres  minor  arixt-s  from  the  upper  two-thirds  of  tin-  dorsal 
surface  of  the  scapula,  close  to  its  axillary  border,  and  from  the  infraspinous  fascia. 


tion  of  thoracic  wall  and 
imuiior  surface  of  arm. 


THE   SHOULDER   MUSCLES. 


577 


It  passes  laterally  along  the  lower  border  of  the  infraspinatus  to  be  inserted  into  the 
capsule  of  the  shoulder-joint  and  into  the  lower  facet  of  the  greater  tuberosity  of  the 
humerus. 

Nerve-Supply. — By  the  circumflex  nerve  from  the  fifth  and  sixth  cervical 
nerves. 

Action. — When  the  arm  is  vertical,  it  rotates  the  humerus  outward  ;  when  it 
is  horizontal,  it  draws  it  backward. 

FIG.  561. 

Clavicle 


Supraspinatus 


Spine  of 
scapula 


Infraspinatus 


Subscapularis 


Sectional  surface  of 
acromion 

i — Supraspinatus 


Greater  tuberosity 


Teres  minor 


uadrilateral  space 
Tendon  of  latissimus  dorsi 


Triangular  space 

Long  (middle)  head  of 

triceps 

Outer  head  of  triceps 


Teres  major 


Triceps 


\ 
Posterior  scapular  muscles  and  part  of  triceps ;  outer  part  of  acromion  has  been  removed. 

4.  TERES  MAJOR  (Figs.  561,  572). 

Attachments. — The  teres  major  arises  from  the  dorsal  surface  of  the  scapula, 
along  the  lower  third  of  its  axillary  border,  and  passes  laterally  to  be  inserted  into  the 
crest  of  the  lesser  tuberosity  of  the  humerus  immediately  dorsal  to  the  insertion  of 
the  latissimus  dorsi. 

Nerve-Supply. — By  the  lower  subscapular  nerve  from  the  fifth  and  sixth  cervi- 
cal nerves. 

Action. — To  draw  the  arm  backward  and  medially,  at  the  same  time  rotating  it 
inward. 

Relations. — The  teres  major  is  in  relation  below  with  the  latissimus  dorsi,  which 
><-n  Is  around  its  under  surface  so  as  to  lie  ventral  to  it  at  its  insertion.  Above  it  is 
relation  with  the  teres  minor  at  its  origin,  but  separates  from  it  as  it  passes  later- 

37 


578  HUMAN    ANATOMY. 

ally,  so  that  a  triangular  interval,  the  base  of  which  is  the  humerus,  lies  between 
the  two  muscles.  This  interval  is  crossed  by  the  long  head  of  the  triceps,  which 
overlies  the  dorsal  surface  of  the  teres  major,  and  is  thus  divided  into  a  more  medial 
triangular  space,  occupied  by  the  dorsal  scapular  artery,  and  a  more  lateral  quad- 
rangular space,  through  which  the  posterior  circumflex  vessels  and  the  circumflex 
nerve  pass. 

Variations. — Considerable  variation  occurs  in  the  size  of  the  teres  major,  an  increase  in 
the  size  of  that  muscle  being  associated  with  a  diminution  of  that  of  the  latissimus  dorsi,  and  rice 
versa.  The  teres  major  is,  indeed,  to  be  regarded  as  fundamentally  a  portion  of  the  latissimus. 

5.     SUBSCAPULARIS    (Fig.   558). 

Attachments. — The  subscapularis  is  a  powerful  muscle  occupying  the  ventral 
(costal)  surface  of  the  scapula.  It  arises  from  the  whole  of  that  surface,  with  the  ex- 
ception of  a  small  portion  near  the  neck  of  the  bone,  some  fibres  also  taking  origin 
from  the  subscapular  fascia.  The  fibres  pass  laterally,  converging  to  a  strong  tendon 
which  is  inserted  into  the  lesser  tuberosity  of  the  humerus  and  to  a  certain  extent  into 
the  capsule  of  the  shoulder-joint. 

Nerve-Supply. — By  the  upper  and  lower  subscapular  nerves  from  the  fifth 
and  sixth  cervical  nerves. 

Action. — When  the  arm  is  vertical,  the  subscapularis  acts  as  a  powerful  inward 
rotator  of  the  humerus  ;  when  the  arm  is  abducted  to  a  right  angle  with  the  body, 
the  muscle  serves  to  draw  it  forward. 

Relations. — The  subscapularis  forms  a  considerable  portion  of  the  dorsal  wall 
of  the  axilla,  and  is  in  relation,  by  its  ventral  surface,  with  the  axillary  vessels  and  the 
cords  of  the  brachial  plexus,  and  laterally  with  the  coraco-brachialis  and  short  head  of 
the  biceps.  Its  lower  border  is  in  contact  with  the  teres  major  and  with  the  dorsal 
scapular  vessels  and  the  circumflex  nerve.  Dorsally  it  is  in  contact  with  the  long 
head  of  the  triceps,  and  is  separated  from  the  neck  of  the  scapula  by  the  large 
subscapular  bursa  (bursa  m.  subscapularis)  which  frequently  is  continuous  with  the 
synovial  cavity  of  the  shoulder-joint. 

Variations. — The  subscapularis  differentiates  in  the  embryo  from  the  same  sheet  which 
gives  rise  to  the  teres  major  and  the  latissimus  dorsi.  It  is  occasionally  divided  into  two  or 
more  fasciculi,  and  sometimes  there  is  separated  from  its  lower  portion  a  small  muscle,  termed 
the  subscapularis  minor,  which  arises  from  the  axillary  border  of  the  scapula  and  is  inserted  into 
the  crest  of  the  lesser  tubercle  of  the  humerus  and  sometimes  into  the  capsule  of  the  shoulder- 
joint. 

The  subscapular  fascia  is  a  firm  sheet  of  connective  tissue  which  covers  the 
ventral  surface  of  the  subscapularis.  It  is  attached  above,  medially,  and  below  to  the 
border  of  the  scapula  and  fades  out  laterally  into  the  brachial  fascia. 

6.   DELTOIDEUS  (Fig.  562). 

Attachments. — The  deltoid  is  a  large  triangular  muscle  which  covers  the 
shoulder  as  with  a  pad.  It  arises  from  the  ventral  border  of  the  outer  third  of  the 
clavicle  and  from  the  acromion  process  and  lower  border  of  the  spine  of  the  scapula. 
Its  fibres  pass  downward,  and  converge  to  be  inserted  into  the  deltoid  tubercle  of  the 
humerus.  Where  the  muscle  passes  over  the  greater  tuberosity  of  the  humerus  a 
mucous  bursa  (bursa  subdeltoidea)  is  interposed  between  it  and  that  prominence. 

Nerve-Supply. — By  the  circumflex  nerve  from  the  fifth  and  sixth  cervical 
nerves. 

Action. — To  abduct  the  arm  to  a  position  at  right  angles  to  the  body.  Fur- 
ther abduction  is  accomplished  by  a  rotation  of  the  scapula  by  the  contraction  of 
the  trapezius  and  the  serratus  anterior,  whereby  the  lateral  angle  of  the  bone  is  tilted 
upward. 

Relations. — The  deltoid  is  in  relation  by  its  deep  surface  with  the  coraroid 
process  and  the  capsule  of  the  shoulder-joint  and  with  the  various  muscles  attached 
to  or  in  the  neighborhood  of  these  structures.  The  cephalic  vein  passes  upward 
along  its  anterior  border. 


PRACTICAL   CONSIDERATIONS  :    AXILLA   AND   SHOULDER.     579 

Variations. — The  portion  of  the  deltoid  which  arises  from  the  clavicle  is  subject  to  con- 
siderable variation,  either  being  greatly  reduced  in  size  or  even  entirely  suppressed,  or  else 
being  more  extensively  developed  than  usual,  so  that  it  is  in  contact  or  even  fused  with  the 
clavicular  portion  of  the  pectpralis  major.  It  may  also  be  distinctly  separated  from  the  remain- 
der of  the  muscle,  and  not  infrequently  a  separation  of  the  acromial  and  spinal  portions  may 
also  occur,  so  that  the  muscle  becomes  three-headed. 

FIG.  562. 


Trapeziu 

Spine  of  scapula 
Acromio 

Deltoid,  spinal  portion 
Deltoid,  acromial  portion 


Sterno-cleido-mastoid 


— '—Clavicle 


Pectoralis  major 


Deltoid,  clavicular 
portion 


Deltoid  muscle  viewed  from  side 

Accessory  bundles  of  fibres  are  occasionally  found  arising  from  the  fascia  infraspinata  or 
from  some  point  along  the  axillary  border  of  the  scapula,  and  either  insert  with  the  deltoid 
(in.  basio-dettoideus)  or  join  with  the  upper  part  of  the  muscle,  being  continued  onward  as 
tendinous  fibres  which  pass  to  the  acromion  process  and  lateral  extremity  of  the  clavicle  (m. 
costo-deltoideus] .  These  fibres  represent  a  portion  of  the  deltoid  which  in  the  anthropoid  apes 
arises  from  the  borders  of  the  scapula  and  in  some  ot  the  lower  mammals  forms  a  distinct 
muscle. 

PRACTICAL   CONSIDERATIONS:    THE   MUSCLES   AND    FASCIA   OF 
THE   AXILLA   AND   SHOULDER. 

The  practical  relations  of  the  fascia  descending  to  the  superior  borders  of  the 
clavicle  and  scapula  have  been  sufficiently  described  (page  551). 

Fracture  of  the  Clavicle. — The  action  of  the  muscles  which  move  the  arm  and 
shoulder  and  of  those  attached  to  the  clavicle  (page  259)  should  be  considered  with 
reference  to  the  common  form  of  displacement  in  cases  of  fracture  of  the  latter  bone. 

The  acromial  fragment,  as  it  moves  with  the  shoulder,  is  the  more  markedly 
affected.  It  is  carried  downward  by  gravity  acting  on  the  upper  extremity  and 
aided  by  the  two  pectoral  muscles  and  the  latissimus  dorsi.  It  is  drawn  inward  by 


HUMAN    ANATOMY. 


the  sternal  fibres  of  the  pectoralis  major  and  by  all  the  muscles  passing  from  the 
trunk  to  the  humerus  and  scapula.  It  is  rotated  on  a  vertical  axis  so  that  its  inner 
end  points  backward  and  its  outer  end  forward.  The  cause  of  the  rotation  is  the 
action  of  the  two  pectorals  upon  the  shoulder  and  the  contraction  of  the  serratus, 
which  (the  support  of  the  clavicle  having  been  removed)  draws  the  scapula  (and 
with  it  the  point  of  the  shoulder)  inward  and  forward  instead  of  more  directly  for- 
ward, and  so  causes  an  anterior  projection  of  the  acromial  end  of  the  outer 
fragment. 

Theoretically  the  inner  fragment  is  displaced  upward  by  the  clavicular  fibres  of 
the  sterno-mastoid,  but  this  action  is  so  strongly  resisted  by  the  costo-clavicular 
(rhomboid)  ligament  and  by  the  upper  and  inner  fibres  of  the  pectoralis  major,  as 
well  as  by  the  subclavius,  that  it  is  not  often  productive  of  much  deformity  (Fig.  563). 
The  rationale  of  the  good  effect  of  recumbency  with  the  head  slightly  elevated 
is  evident.  The  weight  of  the  upper  extremity  ceases  to  drag  the  outer  fragment 
downward.  The  vertebral  border  of  the  scapula  is  pressed  closely  to  the  thorax 
by  the  weight  of  the  trunk.  Its  outer  border,  therefore,  cannot  be  drawn  forward  by 
the  pectorals  and  serratus,  but  tends  to  fall  backward  and  outward,  correcting  both 

the  rotation   and    the   inward 

FIG.  563.  displacement.      The  slight  ele- 

vation of  the  head  relaxes  the 
sterno-cleido-mastoid  and  re- 
moves whatever  influence  it 
may  have  in  raising  the  outer 
end  of  the  inner  fragment. 

Fractures  within  the  limits 
of  the  rhomboid  ligament  at 
the  inner  end  or  within  those 
of  the  conoid  and  trapezoid 
ligaments  at  the  outer  end  are 
attended  by  but  little  displace- 
ment. 

Fractures  of  the  scapula 
have  already  been  dealt  with 
(page  254).  Muscular  action 
influences  them  but  little  be- 
yondwhat  has  been  mentioned. 
The  fascia  beneath  and 
connected  with  the  clavicle  is 
of  much  surgical  importance. 
The  superficial  fascia  of  the 

thorax  splits  to  enclose  the  breast.  The  processes  which  pass  from  it  to  the  skin 
(Cooper's  "  ligamenta  suspensoria"),  by  their  involvement  and  contraction  in 
carcinoma,  produce  the  characteristic  adhesion  and  dimpling  of  the  skin. 

The  deep  pectoral  fascia  splits  to  form  the  sheath  of  the  pectoralis  major  muscle. 
Carcinoma  of  the  mamma  will  usually  be  found  adherent  to  this  layer  on  the  anterior 
surface  of  the  muscle.  Such  adhesion  can  best  be  demonstrated  by  attempting  to 
move  the  tumor  and  breast  in  the  direction  of  the  pectoral  fibres.  Motion  trans- 
verse to  that  line  may,  even  in  cases  in  which  the  tumor  and  muscle  are  inseparably 
connected,  appear  to  be  free,  because  the  muscle  itself  is  moved  on  the  subjacent 
structures. 

Beneath  the  deep  pectoral  fascia  an  additional  sheet,  the  clavi-pectoral  fascia. 
extends  as  a  continuation  downward  of  the  sheath  of  the  subclavius,  the  two  layers 
of  which  begin  above  at  the  two  lips  of  the  subclavian  groove  on  the  inferior  surface 
of  the  clavicle  and  unite  into  one  layer  at  the  lower  edge  of  the  subclavius.  This 
layer  is  continuous  towards  the  sternum  with  the  deep  fascia  covering  in  the  first  and 
second  intercostal  spaces  ;  externally  it  is  attached  to  the  coracoid  process  ;  inferiorly, 
after  splitting  to  enclose  the  pectoralis  minor  muscle,  it  blends  with  the  axillary  fascia. 
The  portion  of  the  clavi-pectoral  fascia  above  the  upper  border  of  the  pectoralis 
minor  is  known  as  the  costo-coracoid  membrane.  It,  together  with  the  subclavius 


Dissection  of  fracture  of  middle  of  clavicle 


PRACTICAL   CONSIDERATIONS:    AXILLA   AND   SHOULDER.     581 

muscle  (which  it  invests),  forms  the  floor  of  the  so-called  superficial  infradavicular 
triangle,  the  roof  of  which  is  made  by  the  clavicular  fibres  of  the  great  pectoral,  the 
base  by  the  anterior  fibres  of  the  deltoid,  the  upper  side  by  the  sternal  half  of  the 
clavicle,  and  the  lower  side  by  a  line  parallel  to  the  uppermost  sternal  fibres  of  the 
great  pectoral.  Its  apex  is  at  the  sterno-clavicular  angle  of  junction.  The  floor  of 
this  space  is  pierced  by  the  external  anterior  thoracic  nerve,  the  acromio-thoracic 
vessels,  and  the  cephalic  vein  (Fig.  556).  Fat  containing  a  few  lymphatic  glands, 
often  involved  in  carcinoma  of  the  breast,  is  found  there.  It  is  closed  in  above  by 
the  clavicle,  but  is  continuous  below  with  the  space  between  the  two  pectoral  muscles 
down  to  the  level  where  the  superficial  layer  of  the  deep  fascia  and  the  clavi-pectoral 
fascia  (which  has  invested  the  pectoralis  minor  and  continued  downward  as  a  single 
layer  again)  unite  at  the  lower  border  of  the  pectoralis  major  to  form  the  axillary 
fascia.  Effusions  of  blood  or  collections  of  pus  occupying  this  space  between  the  two 
muscles  are  therefore  prevented  from  passing  upward  by  the  clavicle,  forward  by  the 
pectoralis  major,  and  backward  by  the  clavi-pectoral  fascia  and  pectoralis  minor. 


FIG.  564. 


Humeral  branch  of  acromio-thoracic  artery 
Pectoralis  minor  \ 

Deltoid 

Pectoralis  major, 
distal  stump 


Cephalic 


Axillary  artery 
and  vein 


Cut  edge  of 

superficial  pec- 
toral fascia 


Cut  edge  of  superficial  la 
clavi-pectoral  fascia 

Teres  major  covered  by  axillary  fascia 


Pectoralis  major, 
clavicular  origin 

Costo-coracoid 
membrane 

Deep  layer  of 
clavi-pectoral 
fascia 

Thoracic  branch 
of  acromio- 
thoracic  artery 


Pectoralis  minor, 
cut  edge 


Dissection  of  thoracic  wall ;  pectoralis  minor  has  been  partly  removed,  exposing  deep  layer  of  clavi-pectoral 

fascia. 


Consequently  they  are  apt  to  approach  the  surface  near  the  anterior  axillary  margin 
or  in  the  groove  between  the  great  pectoral  and  deltoid, — i.e. ,  at  either  the  lower 
border  of  the  sternal  portion  of  that  muscle  or  the  upper  border  of  its  clavicular  fibres. 
Beneath  the  costo-coracoid  membrane  is  a  region  described  as  the  deep  infra- 
clavicular  triangle.  Although  continuous  with  the  axilla,  this  space  is  conveniently 
studied  as  a  separate  region  on  account  of  the  important  structures  which  it  contains 
and  the  frequency  with  which  it  is  invaded  by  disease.  Its  floor  is  formed  by  the 
first  and  second  ribs  and  the  intercostal,  serratus  magnus,  and  subscapularis  muscles. 
Its  apex  is  at  the  angle  made  by  the  line  of  the  upper  border  of  the  small  pectoral 
and  that  of  the  clavicle  at  the  coracoid  process,  those  two  lines  constituting  its  sides. 
The  base  is  towards  the  sternum  at  the  line  where  the  costo-coracoid  membrane  is 
fused  with  the  deep  fascia  over  the  upper  intercostal  spaces.  Through  this  triangle 
pass  the  axillary,  superior  thoracic,  and  acromio-thoracic  vessels,  the  cephalic  vein, 
the  external  and  internal  anterior  thoracic  and  long  thoracic  nerves,  and  the  brachial 
plexus.  It  contains  fat,  with  numerous  lymphatic  glands  and  vessels.  It  is  obvious 


582 


HUMAN   ANATOMY. 


that  it  is  continuous  above  with  the  neck  and  inferiorly  with  the  axilla.  The  latter 
space  is  shut  in  below  by  the  continuation  of  the  axillary  fascia  from  the  lower  bor- 
der of  the  pectoralis  major  backward  to  the  latissimus  dorsi,  outward  to  the  deep 
fascia  of  the  arm,  and  inward  to  the  deep  fascia  of  the  thorax. 

Abscess  or  effusion  of  blood,  as  its  progress  in  all  these  directions  is  resisted, 
may  therefore  point  in  the  neck,  following  the  vessels  and  the  trunks  of  the  plexus 
up  from  the  axilla  through  the  deep  infraclavicular  triangle,  to  make  its  appearance 
above  the  clavicle. 

The  skin  over  the  fascia  at  the  base  of  the  axilla  is  thin  and  richly  supplied 
with  hair-follicles  and  with  sebaceous  and  sudoriparous  glands  ;  hence  superficial 
infections  are  frequent  and  secondary  glandular  abscesses  are  common.  The  con- 
nective tissue  of  the  axillary  space  is  loose  and  abundant,  permitting  of  free  motion 
of  the  arm,  but  also  favoring  the  occurrence  of  large  collections  of  blood  or  of  pus. 


FIG.  565. 


FIG.  566. 


Acrotnion 

Coracoid 
process 

Glenoid 
cavity 

Head  of 
huincrus 


Shoulder  of  subject  in  which  subcoracoid  lux- 
ation has  been  produced,  showing  characteristic 
deformity. 


Showing  relation  of  bones  in  preceding  subcoracoid 
luxation. 


The  fascia  over  the  scapular  muscles — supraspinous  and  infraspinous  fascia 
has  already  been  described  in  reference  to  caries,  necrosis,  and  abscess  (pag 
255.  279). 

Dislocation  of  the  Shoulder- Joint.  — The  circumstances  that  favor  or  resist  dislo- 
cation of  the  shoulder-joint  have  been  enumerated  (pages  278,  279),  but  the  ana- 
tomical symptoms  of  that  lesion  may  now  be  considered  with  especial  reference  to 
the  muscles  involved.  Shoulder  dislocation  is  either  subglenoid  or  subcoracoid  in 
the  vast  majority  of  cases,  the  former  being  almost  invariably  the  primary  form,  for 
reasons  previously  given  (page  278). 

A  luxation,  subglenoid  primarily,  usually  becomes  subcoracoid  from  the  con- 
tinuance of  the  force  producing  it,  aided  strongly  by  the  pectoralis  major  ;  hence 
the  subcoracoid  is  the  most  common.  The  subclavicular,  in  which  the  head  passes 
farther  inward  and  lies  on  the  second  and  third  ribs  beneath  the  pectoralis  major, 


= 


PRACTICAL   CONSIDERATIONS:    AXILLA   AND   SHOULDER.     583 


FIG.  567. 


Acromion 


and  the  supracoracoid  ,  in  which,  owing  to  fracture  of  the  coracoid  or  the  acromion, 
the  head  is  displaced  upward,  are  so  uncommon  that  they  need  merely  be  mentioned 
here.  The  backward  (subspinous)  luxation  is  resisted  so  strongly  by  the  subscapu- 
laris,  and  especially  by  the  long  head  of  the  triceps,  that  it  also  is  a  surgical  rarity. 

In  the  subglenoid  and  subcoracoid  varieties  (Figs.  565,  566)  it  will  be  found  : 
i.  That  the  normal  curve  of  the  shoulder  is  replaced  by  a  straight  line,  because  of 
(a}  the  absence  of  the  head  of  the  bone  and  the  tuberosities  beneath  the  deltoid  ; 
(^)  the  stretching  of  that  muscle.  2.  For  the  same  reasons  it  will  be  found  that 
(a)  a  ruler  applied  to  the  outer  side  of  the  arm  will  touch  both  the  acromion  and  the 
external  condyle  at  the  same  time  (Hamilton)  ;  and  (<£)  the  edge  of  the  acromion  is 
unnaturally  prominent,  while  beneath  it  is  a  palpable  depression  instead  of  the  nor- 
mal resistance  of  the  tuberosities.  3.  The  elbow  is  abducted  because  of  the  tension 
of  the  deltoid.  4.  The  forearm  is  flexed  on  account  of  the  tension  of  the  biceps. 
5.  The  vertical  measurement  of  the  axilla 
is  increased  (Callaway),  because  of  (a) 
the  presence  of  the  head  or  upper  por- 
tion  of  the  shaft  in  the  line  of  meas- 
urement ;  and  (£)  the  lowering  of  the 
axillary  folds  (Bryant),  the  insertions 
of  the  pectoralis  major  and  latissimus 
dorsi  being,  of  course,  carried  down- 
ward with  the  humerus.  6.  The  elbow 
cannot  be  made  to  touch  the  chest-wall 
while  the  hand  is  placed  on  the  oppo- 
site shoulder  (Dugas),  because  the  head 
of  the  bone  is  held  in  contact  with  that 
wall  by  the  tense  muscles  and  overlying 
structures,  and  its  lower  extremity  — 
the  other  end  of  a  straight,  inflexible 
axis  —  cannot  be  made  at  the  same  time 
to  touch  at  a  second  point  the  curve 
represented  by  the  wall  of  the  thorax. 
7.  There  is  rigidity  because  of  the  ten- 
sion or  spasm  of  the  muscles  moving 
the  humerus,  especially  of  the  sub- 
scapularis,  the  deltoid,  the  supra-  and 
infraspinatus,  the  biceps,  and  the  coraco- 
brachialis.  8.  In  the  subcoracoid  luxa- 
tion the  prominence  of  the  head  may  be 
felt  beneath  the  coracoid  or  outer  third 
of  the  clavicle  where  it  lies,  the  anatom- 
ical neck  resting  on  the  anterior  border 
of  the  glenoid  cavity.  There  is  a  little 
real  lengthening,  —  i.e.  ,  the  distance  between  the  glenoid  surface  and  the  lower  end 
of  the  humerus  must  be  increased,  —  but  this  may  be  converted  into  apparent  short- 
ening by  abduction,  which  approximates  the  tip  of  the  acromion  and  the  external 
condyle.  9.  In  the  subglenoid  variety  the  head  may  be  felt  low  in  the  axilla,  the 
anterior  wall  of  which  is  widened.  It  rests  on  the  upper  part  of  the  outer  border  of 
the  scapula  just  below  the  glenoid  cavity.  Lengthening  is  apt  to  be  marked,  and, 
when  the  arm  is  adducted  somewhat,  may  exceed  an  inch.  The  stretching  and 
'  '  hollow  tension'  '  of  the  deltoid  and,  therefore,  the  abduction  of  the  arm  are 
marked.  10.  There  is  usually  (a)  pain  from  direct  pressure  upon  or  from  stretch- 
ing of  the  brachial  plexus,  and  frequently  (6)  cedema  from  similar  involvement  of 
the  axillary  vessels. 

In  all  luxations,  but  especially  in  the  subglenoid  and  subspinous,  the  circumflex 
nerve  is  apt  to  be  injured  ;  hence  obstinate  paresis  or  paralysis  of  the  deltoid  is  a 
not  infrequent  sequel. 

In  all  methods  of  reduction  of  shoulder  luxations  the  humerus  is  used  as  a 
lever,  and  in  all  it  is  desirable  to  secure  fixation  of  the  scapula  by  means  of  (a)  the 


V.  ,,- ' 

Superficial  dissection  of  preceding  subcoracoid  luxation, 
showing  muscles  after  removal  of  skin  and  fasciae. 


HUMAN    ANATOMY. 


Clavicle 

Coracoid 
process 

Long  head 
of  biceps 

Supraspinatus 
Infraspinatus 

Teres  minor 
Deltoid 


weight  of  the  trunk  in  the  supine  and  recumbent  position  ;  (£)  pressure  on  the 
acromion  and  clavicle  ;  (c)  the  use  of  a  folded  sheet  placed  high  in  the  axilla,  so 
that  it  presses  upon  the  axillary  border  in  front  and  the  dorsum  posteriorly  when 
the  two  ends  are  carried  across  the  body  and  made  taut ;  or  (d  )  by  dragging  on 
the  opposite  arm,  "which,  by  making  tense  the  trapezius  of  the  opposite  side,  pro- 
vokes contraction  of  the  muscle  on  the  injured  side"  (Makins). 

The  use  of  the  heel  or  foot  in  the  axilla  as  a  fulcrum  while  manual  extension  is 
made — the  long  arm  of  the  lever,  the  shaft  of  the  humerus,  being  carried  inward  so 
as  to  move  the  short  arm,  the  head,  outward — requires  no  anatomical  explanation. 

Kocher's  method  (applicable  especially  to  subcoracoid  luxation)  is  more  com- 
plex in  its  mode  of  action.  There  is  some  difference  of  opinion  as  to  its  exact 
mechanism,  but  it  is  safe  to  say  that  in  its  various  stages  it  acts  approximately  as 
follows,  i.  The  elbow  is  flexed,  relaxing  the  biceps,  and  the  arm  is  pressed  closely 
to  the  side,  making  tense  the  untorn  posterior  portion  of  the  capsule  extending 
between  the  posterior  lip  of  the  glenoid  fossa  and  the  under  and  back  part  of  the 

neck    of    the   humerus.     This 

FIG.  568.  portion  of  the  capsule  and  the 

tendons  of  the  posterior  scapu- 
lar muscles  are  drawn  tightly 
across  the  glenoid  fossa.  2. 
The  arm  is  rotated  outward 
until  the  forearm  is  parallel 
with  the  transverse  axis  of  the 
body,  the  hand  pointing  di- 
rectly outward.  This  rolls  the 
head  of  the  bone  outward  on 
the  tense  portion  of  the  cap- 
sule, which  is  partly  wound, 
as  it  were,  upon  the  neck,  and 
at  the  same  time  relaxes  the 
scapular  tendons  and  removes 
them  from  the  fossa.  3.  The 
elbow  is  raised  until  the  arm 
is  parallel  with  the  antero- 
posterior  axis  of  the  body. 
This  relaxes  the  anterior  fibres 
of  the  deltoid,  the  coraco- 
brachialis,  and  the  upper  por- 
tion of  the  capsule,  and  perhaps 
widens  the  space  between  the 
margins  of  the  rent,  although 
no  obstacle  to  reduction  is  usu- 
ally met  with  there.  The  lower 

portion  of  the  capsule  is  still  tense.  4.  Rotation  inward  on  this  portion  as  a  fulcrum 
now  moves  the  articular  face  of  the  head  towards  the  comparatively  free  glenoid 
cavity  and  relaxes  the  subscapularis  ;  as  the  elbow  is  then  lowered  in  adduction  the 
lower  capsular  segment  relaxes  and  the  head  re-enters  through  the  rent  by  which  it 
originally  emerged.  These  details  can  be  worked  out  satisfactorily  in  i-xprrinu'iital 
luxations  on  the  cadaver,  and  have  apparently  been  demonstrated  as  to  the  main 
points  by  Faraboeuf,  Helferich,  and  others. 

Recurrent  or  "habitual  dislocation" — i.e.,  dislocation  occurring  from  trifling 
causes,  such  as  abduction  of  the  arm — may  be  a  remote  result  of  the  rupture  or  for- 
cible separation  of  the  tendons  of  the  supra-  and  infraspinatus  muscles  from  the  cap- 
sule of  the  joint,  with  rupture  of  the  capsule  at  its  upper  portion,  and  the  formation 
of  a  free  communication  between  the  joint-cavity  and  that  of  the  subcoracoid  bursa 
(Jossel,  quoted  by  Stimson).  It  is,  however,  usually  due  to  the  injury  to  the  capsule 
and  to  the  weakness  of  the  shoglder  muscles  resulting  from  the  original  accident. 

linrs(c. — The  large  subacromial  bursa  and  the  subdeltoid  bursa  have  been  de- 
scribed in  relation  to  their  possible  enlargements  (page  279).  The  subscapular  bursa 


Pectoral  is 
major  (cut) 


Deeper  dissection  of  preceding  subcoracoid  luxation,  showing 
displacement  of  head  of  humerus  and  muscles  involved. 


THE   BRACHIAL    MUSCLES. 


585 


and  the  bursa  beneath  the  infraspinatus  often  communicate  with  the  shoulder-joint, 
and  disease  of  the  latter  may  spread  to  them. 

An  infraserratus  bursa  has  been  described  (Terrillon),  situated  between  the  infe- 
rior scapular  angle  and  the  chest-wall.  Its  enlargement  gives  rise  to  friction-like 
crepitation  or  creaking,  which  has  been  mistaken  for  fracture  of  ribs  or  scapula  or 
for  an  arthritis  of  the  shoulder.  Nancrede  says  that  this  symptom  is  due  to  (a)  an 
exosto.sis  on  the  ribs  or  scapula  which  has  caused  such  atrophy  of  the  subscapular 
and  serratus  magnus  muscles  as  to  allow  the  two  bony  surfaces  to  come  in  contact  ; 
or  (<£)  a  localized  projection  of  the  ribs  due,  for  example,  to  a  post-pleuritic  con- 
traction of  the  chest,  and  with  the  same  muscular  atrophy  ;  or  (c )  a  primary  atrophy 
of  the  muscles,  as  in  ankylosis  of  the  scapulo-humeral  joint,  which  will  admit  of  the 
normal  scapula  and  ribs  becoming  apposed.  This  latter  condition  especially  causes 
increased  movements  of  the  scapula  over  the  thoracic  wall  and  favors  the  development 
of  this  bursa. 

THE   BRACHIAL   MUSCLES. 


PRE-AXIAL. 

1.  Biceps 

2.  Brachialis  anticus. 


POST-AXIAL. 

1 .  Triceps. 

2.  Anconeus. 


Cephalic  vein 


Biceps 


Skin 


The  brachial  group  includes  those  muscles  which  act  primarily  upon  the  fore- 
arm and  form  the  muscular  substance  of  the  arm.  Some  of  them,  however,  take 
origin  in  whole  or  in  part  from  the  pectoral  girdle  and  thus  have  some  effect  on  the 
movements  which  occur  about  the  shoulder-joint,  although  their  principal  action  is 
upon  the  forearm. 

The  Brachial  Fascia. — The  deep  layer  of  the  fascia  of  the  arm  forms  a  com- 
plete investment  of  the  muscles  of  the  brachial  region.  Above  it  passes  over  into 
the  thin  fascia  covering  the 

deltoid   muscle,    and    me-  -    ...      .    FlG-  569- 

dially  it  becomes  continu- 
ous with  the  axillary  fascia, 
while  below  it  is  continuous 
with  the  fascia  of  the  fore- 
arm, adhering  firmly  to  the 
periosteum  covering  the 
subcutaneous  portions  of 
the  humerus  and  the  ole- 
cranon  process,  and  being 
reinforced  by  tendinous 
prolongations  from  the  bi- 
ceps and  triceps  muscles. 

From  its  lateral  and 
medial  surfaces  it  sends 
sheet-like  prolongations  in- 
ward to  be  attached  to  the 
humerus.  These  sheets, 
termed  the  intermuscular 
septa,  are  of  considerable 
strength  and  give  attach- 
ment to  adjacent  muscles. 
They  pass  to  the  humerus 

between  the  lateral  and  medial  borders  of  the  triceps  and  the  remaining  muscles  of  the 
arm,  and  it  is  to  be  noted  that,  while  the  medial  or  inner  septum  marks  the  boundary 
between  the  pre-axial  and  post-axial  muscles,  this  is  not  the  case  with  the  lateral  or 
external  septum.  In  the  lower  part  of  their  extent  the  septa  are  attached  to  the  supra- 
condylar  ridges  of  the  humerus  and  terminate  at  the  condyles,  a  number  of  post-axial 
muscles  of  the  forearm  arising  from  the  outer  condyle  anterior  to  the  external  septum. 

A  number  of  subcutaneous  bursse  occur  between  the  integument  and  the  bra- 
chial fascia  in  those  regions  in  which  the  fascia  is  adherent  to  the  subjacent  perios- 
teum covering  so-called  subcutaneous  portions  of  the  skeleton.  Thus  there  is  a 


Superficial  fascia^ 
Deep  fascia 


Musculo- 

spiral  nerve 

Brachio- 

radialis 


External 
intermuscular — 
septum 


Humerus 


Musculo- 
cutaneous  nerve 

Brachialis 
anticus 
Brachial 
vessels 

Median  nerve 


Basilic  vein 

i      Internal 
1 — intermuscular 
septum 


Dinar  nerve 


Triceps,  inner 
head 


Triceps,  outer  head 

/     ^~~~- -'"' 

Triceps,  middle  head        .  Tendon  of  triceps 

Section  across  right  arm  in  lower  third. 


586  HUMAN   ANATOMY. 

bursa  acromialis  over  the  acromion  process  of  the  scapula,  a  bursa  olecrani  over  the 
olecranon  process  of  the  ulna,  and  a  bursa  may  occur  over  each  condyle  of  the 
humerus. 

(a)  THE  PRE-AXIAL  MUSCLES, 
i.    BICEPS  (Figs.  560,   570). 

Attachments. — The  biceps  (m.  biceps  brachii),  as  its  name  indicates,-  takes 
origin  by  two  heads.  The  long  head  arises  from  the  upper  border  of  the  glenoid 
cavity  of  the  scapula  by  a  slender  round  tendon,  which  traverses  the  cavity  of  the 
shoulder-joint  invested  by  the  synovium  and  then  bends  downward  into  the  bicipital 
groove  (intertubercular  sulcus)  of  the  humerus,  accompanied  by  a  prolongation  of  the 
joint  capsule  (vagina  mucosa  intertubercularis),  and  then,  becoming  muscular,  unites 
with  the  short  head,  which  arises  from  the  tip  of  the  coracoid  process  of  the  scapula 
in  common  with  the  coraco-brachialis.  By  the  union  of  the  two  heads  a  strong 
muscle  is  formed  which  descends  in  front  of  the  humerus  and  a  short  distance  above 
the  elbow-joint  passes  over  into  a  flat  tendon,  which  is  continued  downward  to  be 
inserted  into  the  tuberosity  of  the  radius,  a  mucous  bursa  (bursa  bicipitoradialis) 
being  interposed  between  the  anterior  surface  of  the  tuberosity  and  the  tendon. 
Some  of  the  fibres  of  the  muscle,  instead  of  passing  into  the  tendon,  are  continued 
into  a  flat  tendinous  expansion,  the  semilunar  or  bicipital  fascia  (lacertus  fibrosus), 
which  passes  downward  and  medially  to  become  lost  in  the  fascia  of  the  forearm. 

Nerve-Supply. — By  the  musculo-cutaneous  nerve  from  the  fifth  and  sixth 
cervical  nerves. 

Action. — To  flex  the  forearm  on  the  brachium,  and  when  the  forearm  is  in  pro- 
nation  to  supinate  it.  It  will  also  act  to  a  slight  extent  in  movements  of  the  arm  at 
the  shoulder-joint,  assisting  the  coraco-brachialis  in  drawing  the  arm  forward. 

Relations. — The  biceps  is  crossed  on  its  ventral  surface  by  the  tendon  of  the 
pectoralis  major  and  is  covered  above  by  the  lateral  portion  of  the  deltoid.  Deeply 
it  is  in  relation  with  the  humerus,  the  brachialis  anticus,  and  the  supinator.  Upon 
its  inner  side  lie  the  coraco-brachialis  above  and  below,  in  the  groove  between  it  and 
the  triceps  (sulcus  bicipitalis  medialis),  the  brachial  vessels,  and  the  median  nerve. 

Variations. — The  biceps  presents  numerous  variations.  Its  long  head  is  occasionally  want- 
ing, but  more  frequently  additional  heads  occur.  Of  these  the  most  frequent,  occurring  in  some- 
thing over  10  per  cent,  of  cases,  is  a  head  which  arises  from  the  medial  surface  of  the  humerus, 
between  the  insertions  of  the  deltoid  and  coraco-brachialis.  Other  heads  may  arise  from  the 
external  tuberosity  of  the  humerus  or  from  the  outer  border  of  that  bone,  between  the  deltoid 
and  brachio-radial  muscles. 

2.    BRACHIALIS  ANTICUS  (Fig.  571). 

Attachments. — The  brachialis  anticus  (m.  brachialis)  occupies  the  anterior  sur- 
face of  the  lower  part  of  the  humerus  and  is  for  the  most  part  covered  by  the  biceps. 
It  arises  from  the  intermuscular  septa  and  the  anterior  surface  of  the  humerus  imme- 
diately below  the  insertion  of  the  deltoid,  which  it  partly  surrounds.  It  passes 
downward,  and  the  fibres  converge  to  a  short  tendon  which  is  inserted  into  the 
anterior  surface  of  the  coronoid  process  of  the  ulna. 

Nerve-Supply. — The  main  mass  of  the  muscle  is  supplied  by  branches  from 
the  musculo-cutaneous  nerve.  The  fibres  which  arise  from  the  lateral  intermuscular 
septum  and  are  covered  by  the  brachio-radialis  are  supplied  by  a  branch  from  the 
musculo-spiral  nerve.  The  nerve-fibres  come  in  both  cases  from  the  fifth  and  sixth 
cervical  nerves. 

Action. — To  flex  the  forearm. 

Variations. — The  nerve-supply  shows  the  brachialis  anticus  to  be  a  composite  muscle  the 
major  portion  of  which  is  derived  from  the  pre-axial  muscle-sheet,  while  the  lateral  portion  of 
it  conies  from  the  post-axial  sheet.  In  correspondence  with  this  derivation  of  the  muscle,  its 
lateral  portion  is  occasionally  separate  from  the  rest  and  may  terminate  below  on  the  fascia  of 
the  forearm  or  on  the  radius.  A  longitudinal  separation  of  ilk-  pre-axial  portion  of  the  muscle 
may  also  occur,  and  it  seems  probable  that  the  most  frequently  occurring  third  head  of  the 
biceps  (see  above  i  is  a  derivative  of  this  portion  of  the  brachialis. 

The  epitrochteo-ancon«M$i&a  small,  usually  quadrangular  muscle  which  is  present  in  about 
25  per  cent,  of  cases.  It  arises  from  the  posterior  surface  of  the  inner  condyle  of  the  humerus 


THE   BRACHIAL   MUSCLES. 


587 


and  passes  downward  and  laterally  to  be  inserted  into  the  external  surface  of  the  olecranon 
process  of  the  ulna.     Notwithstanding  its  position  upon  the  posterior  surface  of  the  arm,  it  is  a 

FIG.  570. 


Clavicle— 7 
Subclavius 


Biceps 


Tendon  of  in- 
sertion of  pec- 
toralis  major 


Coraco- 
brachialis 


Tendon  of  latissimus 


* 


Pectoralis  minor 


FIG.  571. 


Brachialis  anticus 


Inner  head  of  triceps 


Int.  intermuscular 

septum  ..      ,    , 

Brachialis  anticus     J 

radius 

Bicipital 

tuberosity  of  radius 
Insertion  of  biceps 


Brachialis  anticus 


Tendon  of  insertion 
of  biceps 

Brachio-radialis 


Supinator 


Bicipital  fascia 


Coronoid  pro- 
cess of  ulna 


Muscles  of  anterior  surface  of  arm. 


Brachialis  anticus  and  supinator, 
seen  from  in  front. 


derivative  of  the  pre-axial  muscle-sheet  and  is  supplied  by  the  ulnar  nerve,  whose  main  stem, 
as  it  passes  down  between  the  olecranon  and  the  inner  condyle,  is  covered  by  the  muscle. 
When  absent,  the  muscle  is  represented  by  a  strong  fibrous  band. 


HUMAN    ANATOMY. 


(6)    THE   POST-AXIAL  MUSCLES, 
i.    TRICEPS  (Figs.  570,  572). 

Attachments.     The  triceps  (m.  triceps  brachii)  is  a  strong  muscle  which  occu- 
pies the  entire  dorsal  surface  of  the  arm.      It  arises  by  three  heads.     The  scapular  or 

FIG.  572. 


Supraspinatus 

Spine  of  scapula 


Infraspinatus 


Infraspinatus, 
cut  edge 


Teres  minor  (cut) 


Inferior  angle  of 
scapula 


Teres  major. 
Serratus  magnus 


•Acromion  process 


Head  of  humerus  covered  by 
capsular  ligament 

Tendon  of  insertion  of  teres 
minor 


Axillary  border  of 
scapula 


Pectoralis 

major 

Triceps, 
long  head 


Triceps 


Latissimus  dorsi 

long  head  takes  its  origin  by  a  tendon  from  the  infra- 
glenoid  tuberosity  of  the  scapula  ;  the  inner  or  medial 
head,  from  the  posterior  (dorsal)  surface  of  the  humerus 
and  from  both  intermuscular  septa  below  and  medial 
to  the  groove  for  the  musculo-spiral  nerve  ;  and  the 
outer  or  lateral  head,  from  the  external  intermuscular 
septum  and  the  posterior  surface  of  the  humerus  above 
and  lateral  to  the  groove  for  the  musculo-spiral  nerve. 
The  three  heads  unite  to  form  a  strong,  broad  tendon 
which  is  inserted  into  the  olecranon  process  of  the 
ulna.  The  common  tendon  of  insertion  tfegins  as  a 
broad  aponeurosis  upon  the  anterior  surface  of  the 
long  head,  the  fibres  of  which  are  attached  to  the 
upper  border  and  the  upper  part  of  the  posterior  sur- 
face of  the  aponeurosis.  The  fibres  of  the  lateral  head 
are  attached  to  the  lateral  border  of  the  aponeurosis, 
while  those  of  the  medial  head,  which  is  much  stronger 
than  the  lateral  one,  pass  to  its  anterior  surface. 

Nerve-Supply. — By  the   musculo-spiral   nerve 
fn.m   the-  sixth,   seventh,   and  eighth  cervical  nerves. 

Action. — To  extend  the  forearm  on  the  upper  arm  and  to  draw  the  entire  arm 
backward. 


Tricep 


postt  rioi  M  apular  m 

clt-s  ;  portions  (it  infraspinatus  and  teres 
minor  cut  :i\\a>  . 


Variations. — The  triceps  occasionally  possesses  an  additional  head  arising  either  from  the 
coracoid  process  of  the  scapula  or  from  the  capsule  of  the  shoulder-joint. 


PRACTICAL   CONSIDERATIONS  :    MUSCLES   AND    FASCIA.      589 

2.    ANCONEUS  (Fig.  581). 

Attachments. — The  anconeus  is  a  short  muscle  which  arises  from  the  posterior 
surface  of  the  external  condyle  of  the  humerus.  Its  fibres  diverge  to  form  a  triangu- 
lar sheet  which  is  inserted  into  the  upper  part  of  the  posterior  surface  of  the  ulna  and 
into  the  outer  surface  of  the  olecranon  process. 

Nerve-Supply. — By  the  musculo-spiral  nerve  from  the  seventh  and  eighth 
cervical  nerves. 

Action. — To  assist  the  triceps  in  extending  the  arm. 


PRACTICAL   CONSIDERATIONS:    MUSCLES   AND   FASCIA   OF   THE 

ARM. 

The  deep  fascia  of  the  arm,  continuous  above  with  that  over  the  deltoid  and  with 
the  clavi-pectoral  fascia,  closely  embraces  all  the  muscular  structures  and  resists  the 
outward  passage  of  subfascial  collections  of  blood  or  pus,  which  therefore,  under  the 
influence  of  gravity,  tend  for  a  time  to  follow  the  intermuscular  spaces  downward. 
OZdema  and  swelling  above  the  elbow  are  thus  not  uncommon  as  a  result  of  disease 
or  injury  at  a  higher  level.  Blood  or  pus  may  reach  the  surface  by  following  the 
structures  that  pierce  the  fascia, — viz.,  the  basilic  vein  and  the  internal  and  external 
cutaneous  nerves.  The  ecchymosis  after  fracture  sometimes  takes  this  course.  The 
intermuscular  septa  (page  585)  divide  the  space  enclosed  by  the  brachial  aponeurosis 
into  an  anterior  and  a  posterior  compartment  extending  from  the  level  of  the  deltoid 
and  coraco-brachialis  insertions  to  that  of  the  two  condyles.  They,  too,  have  some 
effect  in  limiting  effusions,  but  the  latter,  especially  if  due  to  infection,  can  readily 
pass  from  one  space  to  the  other  by  following  the  musculo-spiral  nerve  or  the  superior 
profunda  artery  through  the  outer  septum,  or  the  ulnar  nerve,  inferior  profunda  artery, 
or  anastomotica  magna  through  the  inner  septum. 

In  selecting  a  method  of  amputation  through  the  arm  it  should  be  remembered 
that  above  the  middle  most  of  the  muscles  that  it  would  be  necessary  to  divide  are 
free  to  retract, — i.e.,  the  deltoid,  the  long  head  of  the  triceps,  the  coraco-brachialis, 
and  the  biceps.  Below  the  middle  the  biceps  is  the  only  muscle  unattached.  In 
the  former  situation,  therefore,  the  circular  method  is  apt  to  lead  to  a  "conical 
stump' '  from  the  too  free  retraction  of  the  flaps  and  from  the  activity  of  the  upper 
humeral  epiphysis  (page  272).  In  amputation  just  above  the  elbow  the  circular 
method  is  applicable,  but  the  incision  should  be  a  little  lower  at  the  antero-internal 
aspect  of  the  limb  to  allow  for  the  greater  retraction  in  the  bicipital  region. 

Inward  dislocation  of  the  tendon  of  the  long  head  of  the  biceps  muscle  has 
probably  occurred  from  direct  violence  as  an  uncomplicated  lesion  in  a  few  cases. 
The  symptoms  are  said  to  be  (White)  :  (a)  the  recognition  of  the  bicipital  groove 
empty  ;  (£)  inward  rotation  due  to  the  pressure  of  the  tendon  on  the  lesser  tuberosity 
and  on  the  tendon  of  the  subscapularis  ;  (c~)  adduction  of  the  humeral  head,  leaving 
a  slight  depression  beneath  the  tip  of  the  acromion  ;  (d)  obvious  tension  along  the 
inner  edge  of  the  biceps  muscle  when  the  forearm  is  extended  ;  (<?)  diminution  in  the 
vertical  circumference  of  the  shoulder  ;  and  (_/")  shortening  of  the  distance  between 
the  acromion  and  external  condyle  ;  both  of  the  last  two  symptoms  are  due  to  the 
elevation  of  the  humeral  head  under  the  influence  of  the  deltoid,  the  supraspinatus, 
and  the  clavicular  fibres  of  the  pectoralis  major,  that  of  the  biceps  tendon  being  with- 
drawn. These  and  other  symptoms  of  this  lesion  (although  it  is  extremely  rare) 
should  be  studied  in  connection  with  the  anatomy  of  the  muscles  involved,  as  an  aid 
in  elucidating  their  action.1 

Riipture  of  the  biceps  tendon  has  always  been  caused  by  violent  muscular  action, 
and  is  usually  accompanied  either  by  the  sudden  appearance  of  a  more  or  less  firm 
tumor  on  the  front  of  the  arm  or  by  complete  relaxation  and  flabbiness  of  the  whole 
muscle.  The  symptoms  mentioned  as  characteristic  of  dislocation  of  the  tendon 
have  not  been  noted  in  any  recorded  case  of  rupture,  with  the  exception  of  those  due 
to  the  elevation  of  the  head  of  the  humerus. 

1  J.  William  White  :  American  Journal  of  the  Medical  Sciences,  January,  iSSj. 


590 


HUMAN   ANATOMY. 


FIG.  573. 


Fractures  of  the  humerus  are  much  influenced  by  muscular  action,  although  the 
controlling  force  in  the  production  of  the  deformity  is  often  that  which  causes  the 
fracture. 

In  fracture  of  the  tuberosities  the  theoretical  displacement  is  upward  and  back- 
ward for  the  greater  tuberosity  under  the  action  of  the  supra-  and  infraspinatus  and 
teres  minor,  and  forward  and  inward  for  the  lesser  tuberosity,  which  is  supposed 
to  be  drawn  in  that  direction  by  the  subscapularis.  The  injury  is  extremely  rare  ; 
the  clinical  signs  are  obscure.  Increased  breadth  of  the  shoulder,  localized  tender- 
ness and  disability,  occurring  after  the  application  of  direct  force  or  after  violent 
action  of  the  shoulder  muscles,  would  be  suggestive  ;  recognition  of  a  preternaturally 
mobile  or  displaced  fragment  would  be  conclusive  ;  but  the  X-rays  will  usually  be 
essential. 

In  fracture  of  the  surgical  neck  of  the  humerus — i.e.,  between  the  tuberosities 
and  the  insertions  of  the  axillary  muscles — and  in  separation  of  the  upper  epiphysis 
the  fragments  are  similarly  influenced  by  muscular  action.  The  upper  fragment  is 
held  in  place,  is  a  little  elevated,  and  is  obliquely  tilted  by  the  supra-  and  infraspinatus, 

subscapularis,  and  teres  minor. 
The  upper  end  of  the  lower 
fragment  is  drawn  towards  the 
chest-wall  by  the  pectoralis 
major,  latissimus  dorsi,  and 
teres  major.  Their  action  may 
be  aided  by  that  of  the  deltoid, 
which  may  fix  the  middle  of 
the  bone  so  that  it  acts  as  a 
fulcrum,  or  may  actually  abduct 
the  elbow.  The  biceps,  triceps, 
and  coraco-brachialis  and  del- 
toid draw  the  lower  fragment 
upward,  causing  shortening 

(Fig-  573)- 

Epiphyseal 'disjunction  may 
be  suspected  if  (a)  the  patient 
is  a  child  or  an  adolescent  ; 
(6}  the  anterior  projection  of 
the  upper  end  of  the  lower  frag- 
ment is  at  an  unusually  high 
level, — i.e.,  about  that  of  the 
coracoid ;  (c)  the  crepitus  is 
muffled  ;  (d )  the  shortening 
is  slight  (page  272).  The  ap- 
plication of  the  tests  mentioned 
above  (page  583)  will  distin- 
guish this  lesion  from  luxation  of  the  shoulder,  which,  moreover,  is  very  rare  before 
adult  life  (page  306). 

In  fracture  of  the  shaft  of  the  humerus  between  the  insertions  of  the  axillary 
muscles  and  that  of  the  deltoid  the  upper  fragment  is  drawn  inward  by  the  former 
muscles  ;  the  lower  fragment  is  drawn  upward  by  the  biceps,  triceps,  and  coraco- 
brachialis,  and  upward  and  outward  by  the  deltoid  (Fig.  573). 

In  fracture  just  below  the  deltoid  insertion  that  muscle  acts  to  such  advantage  in 
abducting  the  upper  fragment  as  to  counteract  the  pull  of  the  axillary  muscles  in  the 
contrary  direction.  The  relation  of  the  fragments  will  therefore  chiefly  depend  upon 
the  direction  of  the  line  of  fracture  ;  the  shortening,  under  the  influence  of  the  biceps, 
triceps,  and  coraco-brachialis,  will  depend  on  its  degree  of  obliquity.  In  this  fracture 
it  is  sometimes  necessary  to  dress  the  arm  in  abduction  to  overcome  the  deltoid  con- 
traction. 

In  fracture  just  above  the  condyles  (page  273)  the  line  of  fracture  is  usually 
oblique  from  above  downward  and  forward  (Fig.  288).  The  short  lower  fragment 
will  be  drawn  upward  by  the  biceps  and  triceps  and  backward  by  the  latter  muscle. 


Deltoid 

Upper 

fragmen 

Long  head 

of  biceps 

Lower 

fragment 


Pectoral  i 
major,  cut 
and  turned 
down 


Latissimus  dorsi 
and  teres  major 


Dissection  of  fracture  of  surgical  neck  of  humerus. 


THE   ANTIBRACHIAL   MUSCLES. 


The  lower  end  of  the  upper  fragment  will  then  arrest  flexion  of  the  forearm  by  contact, 
or  may  puncture  the  brachialis  anticus,  the  bicipital  fascia,  and  even  the  skin. 

The  diagnosis  of  this  fracture  from  luxation  of  the  elbow  (Fig.  575)  can  be 
made  by  (a)  the  recognition  of  the  relations  of  the  three  bony  points, — the  tips  of  the 
two  condyles  and  of  the  olecranon  (page  306)  ;  (£)  the  presence  of  crepitus  ;  (c)  the 
disappearance  of  the  deformity  on  extension  and  counterextension,  and,  usually,  its 
reappearance  when  extension  is  discontinued  ;  and  (</)  the  greater  freedom  of  exten- 
sion of  the  forearm  on  the  arm  in  fracture  ;  flexion  may  be  limited,  as  above  men- 
tioned, by  the  contact  of  the  upper  fragment  with  the  forearm  at  the  bend  of  the  elbow 
and  other  points  ;  (e)  the  arm  is  shortened  in  fracture  ;  the  forearm  in  dislocation. 

In  separations  of  the  lower  humeral  epiphysis  (page  273)  (a)  the  patient  is  a 
child  or  an  adolescent ;  (3)  there  is  muffled  crepitus  ;  (c)  the  lower  end  of  the  upper 


FIG.  574. 


FIG.  575. 


Olecrationl 


Triceps 


Olecranon 


irachialis  anticus 
Biceps 


External  condyle 


Posterior  luxation  of  elbow  of  right  side. 


Displaced  head  of  radius 


Dissection  of  preceding  luxation,  showing  position 
of  bones. 


fragment  has  greater  breadth  and  is  more  rounded  than  in  fracture  ;  (</)  the  line  of 
separation  is  nearer  the  end  of  the  bone,  and  the  anterior  projection  of  the  diaph- 
ysis  is  on  a  level  with  the  fold  of  the  elbow  ;  in  fracture  it  is  usually  above  it 
(Poland). 

Condylar  fractures  have  been  described  (page  273),  but  it  may  be  mentioned 
here  that  the  elevation  of  the  internal  condyle,  if  not  corrected,  causes  the  line  of  the 
joint  to  incline  inward  instead  of  outward.  If  union  takes  place  in  that  malposition, 
the  so-called  "gun-stock  deformity,"  or  "  cubitus  varus"  (in  which  the  "carrying 
angle"  of  the  forearm  with  the  arm  is  obliterated  or  changed  to  a  similar  angle 
opening  inward)  results. 

The  bursae  about  the  elbow  have  been  described  (page  307). 

THE   ANTIBRACHIAL   MUSCLES. 

The  muscles  which  belong  to  this  group  act  primarily  upon  the  bones  of  the 
forearm  or  of  the  carpus  and  constitute  the  muscular  substance  of  the  forearm.  Some 
of  them,  however,  have  undergone  a  secondary  extension  into  the  hand  and  act  as 


592  HUMAN   ANATOMY, 

i 

flexors  or  extensors  of  the  digits,  this  extension  being  due  in  some  cases  to  the 
differentiation  of  the  fascia  of  the  hand  into  tendons  continuous  with  those  of  the  an- 
tibrachial  muscles,  in  other  cases  to  end-union  of  antibrachial  and  hand  muscles.  It 
will  be  convenient,  however,  to  regard  the  long  flexors  and  extensors  of  the  digits, 
formed  in  this  way,  as  antibrachial  muscles. 

Comparatively  studied,  an  arrangement  of  the  antibrachial  muscles  in  distinct 
layers  is  clearly  perceivable,  three  layers  being  found  in  the  pre-axial  and  two  in  the 
post-axial  muscles.  In  both  cases  the  superficial  layer  takes  its  origin  from  the 
humerus,  while  the  remaining  layers  are  attached  above  to  the  bones  of  the  forearm. 
Secondary  adaptations  have  in  some  cases  interfered  with  the  distinctness  of  the 
layers,  but  the  primary  conditions  will  be  taken  as  the  basis  for  the  classification  of 
the  muscles. 

The  antibrachial  fascia  completely  invests  the  muscles  of  the  forearm  and  is 
the  downward  continuation  of  the  brachial  fascia.  It  is  especially  strong  upon  the 
dorsal  surface  of  the  forearm,  where  it  is  attached  to  the  olecranon  process  and  the 
entire  length  of  the  posterior  border  of  the  ulna,  and  anteriorly  it  is  strengthened  in 
its  upper  part  by  the  fibres  of  the  semilunar  fascia  of  the  biceps.  At  the  wrist  it  is 
attached  to  the  bones  of  the  forearm  and  carpus,  and  becomes  thickened  by  trans- 
verse fibres  to  form  the  dorsal  and  volar  carpal  ligaments. 

The  anterior  annular  ligament  (ligamentum  carpi  volare)  lies  on  the  anterior  sur- 
face of  the  wrist,  covering  the  flexor  muscles  in  that  region  (Fig.  577).  Laterally 
and  medially  it  is  connected  with  the  dorsal  ligament.  This,  the  posterior  annular 
ligament  (ligamentum  carpi  dorsale),  is  a  stronger  transverse  band  on  the  posterior 
surface  of  the  wrist,  and  is  attached  laterally  to  the  outer  surface  and  to  the  styloid 
process  of  the  radius,  and  passes  inward  and  slightly  downward  to  the  styloid  process 
of  the  ulna  and  to  the  pisiform  and  cuneiform  bones,  making  attachments  to  the  ridges 
on  the  posterior  surface  of  the  radius  and  ulna  and  thus  converting  the  six  intervening 
grooves  into  canals  which  lodge  the  tendons  of  the  long  extensor  muscles  (Fig.  579). 
Beginning  at  the  radial  side,  the  first  canal  transmits  the  tendons  of  the  extensor  ossis 
metacarpi  pollicis  and  the  extensor  brevis  pollicis  ;  the  second,  the  tendons  of  the  two 
extensores  carpi  radiales  ;  the  third,  that  of  the  extensor  longus  pollicis  ;  the  fourth, 
those  of  the  extensor  communis  digitorum  and  the  extensor  indicjs  ;  the  fifth,  that  of 
the  extensor  minimi  digiti  ;  and  the  sixth,  that  of  the  extensor  carpi  ulnaris.  Each 
of  the  canals  is  lined  by  an  independent  synovial  membrane. 

(a)    THE   PRE-AXIAL  MUSCLES. 
(aa)    THE  SUPERFICIAL  LAYER. 

1.  Pronator  radii  teres.  3.    Palmaris  longus. 

2.  Flexor  carpi  radialis.  4.    Flexor  carpi  ulnaris. 

5.    Flexor  sublimis  digitorum. 

i.    PRONATOR  RADII  TERES  (Fig.  576). 

Attachments. — This  muscle  (m.  pronator  teres),  thick  and  band-like,  arises  by 
two  heads  (a)  from  the  inner  condyle  of  the  humerus,  the  adjacent  intermuscular 
septa,  and  the  deep  fascia,  and  (£)  from  the  medial  border  of  the  coronoid  process  of 
the  ulna.  It  passes  downward  and  laterally  and  is  inserted  into  about  the  middle  of 
the  outer  surface  of  the  radius.  The  median  nerve  passes  downward  between  the 
two  heads. 

Nerve-Supply. — By  the  median  nerve  from  the  sixth  cervical  nerve. 

Action. — To  pronate  and  flex  the  forearm. 

Variations. — The  pronator  teres  is  formed  by  a  combination  of  portions  from  the  super- 
ficial and  deep  layers  of  the  forearm  musculature,  the  condylar  head  representing  the  superficial 
portion  and  the  coronoid  head  the  deep  one.  In  the  lower  mammals  the  pronator  quadratus 
frequently  extends  well  up  towards  the  dhow-joint,  and  the  coronoid  head  of  the  pronator 
teres  represents  the  uppermost  portion  of  this  muscle,  its  lower  portion  persisting  as  the  pro- 
nator  (jiiadratus.  Not  infrequently  the  coronoid  portion  of  tin-  muscle  is  completely  separate 
from  the  condylar  head,  or  it  may  IK-  rudimentary  or  represented  only  by  a  connective-tissue 


THE   ANTIBRACHIAL   MUSCLES. 


593 


band.  The  entire  muscle  is  some- 
times incompletely  separated  from 
the  neighboring  muscles  of  the  su- 
perficial layer,  receiving  accessory 
heads  from  the  pal  mar  is  longus  or 
the  flexor  sublimis  digitorum. 

2.   FLEXOR  CARPI  RADIALIS 

(Fig-  576)- 

Attachments. — The  flexor 
carpi  radialis  arises  from  the  inner 
condyle  of  the  humerus,  by  a 
tendon  common  to  it  and  the 
neighboring  muscles  of  the  super- 
ficial layer,  from  the  adjoining 
intermuscular  septa  and  the  deep 
fascia.  It  passes  downward  and 
slightly  laterally  and  is  inserted 
into  the  bases  of  the  second  and 
third  metacarpal  bones. 

Nerve-Supply.  —  By  the 
median  nerve  from  the  sixth  cer- 
vical nerve. 

Action. — To  flex  the  hand 
and  to  assist  in  pronating  the 
forearm. 

Relations. — In  its  course 
down  the  forearm  the  flexor  carpi 
radialis  passes  obliquely  across 
the  flexor  sublimis  digitorum  and 
the  lower  part  of  the  flexor  longus 
pollicis.  At  the  wrist  it  passes 
through  a  special  sheath  within 
the  superficial  part  of  the  anterior 
annular  ligament,  and  just  before 
its  insertion  it  is  crossed  by  the 
tendon  of  the  flexor  longus  pol- 
licis. A  bursa  (bursa  m.  tlexoris 
carpi  radialis)  is  interposed  be- 
tween the  tendon  and  the  base 
of  the  second  metacarpal  bone. 
Laterally  the  muscle  is  in  contact 
above  with  the  pronator  radii 
teres  and  below  with  the  brachio- 
radialis,  from  which  it  is  sepa- 
rated near  the  wrist  by  the  radial 
artery. 

3.   PALMARIS  LONGUS 
(Fig.  576). 

Attachments. — The  pal- 
maris  longus  arises  with  the 
neighboring  superficial  muscles 
by  the  common  tendon  from  the 
inner  condyle  of  the  humerus, 
from  the  adjoining  intermuscular 
septa,  and  from  the  deep  fascia. 
It  forms  a  short  spindle-shaped 
belly  which  is  continued  into  a 


FIG.  576. 


Brachialis  anticus 


Biceps 


Brachio-radialis 


Flexor  carpi 
radialis 


Extensor  carpi - 
radialis  longior 


Palmaris  brevis 


Palmar  fascia 


Superficial  dissection  of  forearm  and  palm,  anterior  surface; 
portion  of  antibrachial  fascia  covering  origin  of  superficial  muscles 
has  been  left  in  place. 

38 


594 


HUMAN   ANATOMY. 


FIG.  577. 


Brachialis  anticr.s 


iidon  of  biceps — JE 


Extensor  carpi 
radialis  longior 


Brachio-radialis 


Insertion  of  pronator. 
radii  teres 


f  lexor  sublimi 
digitorum 


Flexor  longus  pollicis 


Tendon  of  flexor  carpi  — Ll 
radialis,  cut 


Abductor  pollicis 


Flexor  hrevls  polHc 
Adductor  pollic 

Tendon  of— 

flexor  lonxu    /• 

pollicis      /" 


Lumbricales 


•Flexor 

profundus 

digitorum 


Tendon  of  flexor 
1 — carpi  ulnaris 

| — Pisiform  bone 

\        Abductor  minimi 
Ifr— digiti 


lexor  brevis 
minimi  digiti 


Lumbricales 


Dissection  of  muscles  of  f»rr:mn  and 


ham!,  atilrrioi   surface;  most  supci  lit  ial 

lii-i-n  removed 


long,  slender  tendon  that 
passes  in  front  of  the  an- 
terior annular  ligament 
of  the  \vrist,  and  is  in- 
serted into  the  palmar 
fascia. 

Nerve-Supply.— 
By  the  median  nerve 
from  the  sixth  cervical 
nerve. 

Action. — To  tense 
the  palmar  fascia  and  flex 
the  hand. 

Variations. — The  pal- 
maris  longus  is  a  very  vari- 
able muscle.  It  is  not  in- 
frequently absent,  and  may 
present  various  modifica- 
tions in  its  structure,  being 
sometimes  entirely  tendi- 
nous, or  entirely  fleshy,  or 
tendinous  above  and  fleshy 
below.  It  is  occasionally 
double. 

4.  FLEXOR  CARPI  UL- 
NARIS (Fig.  576). 

Attachments.  — 
The  flexor  carpi  ulnaris 
arises  from  the  medial 
condyle  of  the  humerus 
in  common  with  the 
neighboring  superficial 
muscles,  from  the  inter- 
muscular  septa  and  deep 
fascia,  and  also  from  the 
posterior  surface  of  the 
olecranon  process,  and 
from  the  upper  part  of 
the  posterior  border  of 
the  ulna  by  means  of  an 
aponeurosis  common  to 
it  and  the  flexor  pro- 
fundus digitorum  and 
the  extensor  carpi  ul- 
naris. It  descends  along 
the  ulnar  border  of  the 
forearm  and  is  inserted 
into  the  pisiform  bone, 
its  tendon  being  contin- 
ued on  to  be  attached  to 
the  hook  of  the  unciform 
and,  often,  to  tin-  base  of 
the  fifth  metacarj  >al  bone. 

Nerve-Supply.— 
Hy  the-  ulnar  nerve  from 
the  eighth  cervical  and 
first  thoracic  ner\  < 

Action. —  To  flex 
and  adduct  the  hand. 


THE   ANTIBRACHIAL   MUSCLES.  595 

Relations. — By  its  deep  surface  this  muscle  is  in  relation  with  the  sublimis  and 
profundus  digitorum  and  with  the  ulnar  vessels  and  nerve.  The  ulnar  nerve  and 
posterior  recurrent  ulnar  artery  pass  beneath  a  tendinous  band  which  stretches  across 
between  the  two  heads  of  the  muscle,  and  towards  the  wrist  the  ulnar  artery  comes 
to  lie  along  the  lateral  border  of  the  tendon.  A  mucous  bursa  (bursa  m.  flexoris 
carpi  ulnaris )  is  frequently  to  be  found  between  the  tendon  and  the  upper  part  of  the 
pisiform  bone. 

Variations. — The  flexor  carpi  ulnaris  frequently  passes  distally  to  be  inserted  into  the  base 
of  the  fifth  metacarpal.  The  conversion  of  the  ulnar  head  into  connective  tissue  has  been 
observed. 

5.   FLEXOR  SUBLIMIS  DIGITORUM  (Fig.  577). 

Attachments. — The  superficial  flexor  (m.  flexor  digitorum  sublimis)  arises  from 
the  inner  condyle  of  the  humerus  in  common  with  the  neighboring  superficial  mus- 
cles, from  an  oblique  line  on  the  anterior  surface  of  the  radius,  and  from  the  tendi- 
nous arch  extending  between  these  two  bony  points  and  beneath  which  the  median 
nerve  and  ulnar  artery  pass.  The  fibres  arising  from  these  origins  form  four  bellies, 
prolonged  below  into  as  many  tendons,  which  at  the  wrist  pass  beneath  the  ante- 
rior annular  ligament  and  then  diverge  towards  the  bases  of  the  second,  third,  fourth, 
and  fifth  fingers  and  enter  the  corresponding  digital  sheaths.  Here  each  tendon 
divides  over  the  surface  of  the  first  phalanx  into  two  slips,  which  pass  one  on  either 
side  of  the  subjacent  tendon  of  the  flexor  profundus  digitorum  and  partially  unite 
beneath  it  to  be  inserted  into  the  base  of  the  second  phalanx.  Slight  tendinous 
bands,  vincula  tendinum,  pass  between  the  tendons  of  the  profundus  and  the  terminal 
portions  of  those  of  the  sublimis. 

Nerve-Supply. — By  the  median  nerve  from  the  seventh  and  eighth  cervical 
and  first  thoracic  nerves. 

Action. — Primarily  to  flex  the  second  phalanx  of  the  four  medial  digits,  but  a 
continuation  of  its  action  will  flex  the  first  phalanges  of  the  same  digits  and  eventually 
the  hand. 

Relations. — Superficially  the  flexor  sublimis  is  covered  by  the  remaining 
muscles  of  the  superficial  layer  ;  deeply  it  is  in  relation  with  the  flexor  profundus 
digitorum,  the  flexor  longus  pollicis,  the  ulnar  vessels,  and  the  median  nerve. 

Variations. — Occasionally  the  portion  of  the  muscle  which  gives  rise  to  the  tendon  of  the 
fifth  digit  appears  to  be  wanting,  the  tendon  arising  from  the  palmar  fascia,  the  anterior  annular 
ligament,  or  the  flexor  profundus.  An  explanation  of  this  anomaly  is  found  in  the  developmental 
history  of  the  muscle.  In  the  lower  vertebrates  the  superficial  flexor  inserts  into  the  palmar 
fascia,  which  gives  origin  to  a  set  of  superficial  digital  muscles,  whose  relations  are  similar  to 
those  of  the  digital  portions  of  the  sublimis  tendons.  In  the  mammalia  these  digital  muscles  de- 
generate into  tendinous  bands,  with  which  the  tendon  of  the  antibrachial  portion  of  the  muscle 
becomes  continuous.  The  origin  of  the  tendon  for  the  fifth. digit  from  the  palmar  aponeurosis 
or  transverse  carpal  ligament  is,  therefore,  a  persistence  of  a  phyletic  stage,  as  is  also  its  origin 
from  the  flexor  profundus,  since  in  the  lower  mammals  the  antibrachial  portions  of  the  two 
muscles  are  united  to  form  a  single  mass  (page  597). 

(bb)    THE  MIDDLE  LAYER. 
:.   Flexor  profundus  digitorum.  2.    Flexor  longus  pollicis. 

i.    FLEXOR  PROFUNDUS  DIGITORUM  (Fig.  578). 

Attachments. — The  deep  flexor  (m.  flexor  digitorum  profundus)  arises  from  the 
anterior  and  outer  surfaces  of  the  ulna  and  from  the  inner  half  of  the  interosseous 
membrane.  Its  fibres  are  directed  downward,  and  at  about  the  middle  of  the  fore- 
arm are  continued  into  four  tendons,  which  pass  beneath  the  anterior  annular  liga- 
ment along  with  the  tendons  of  the  flexor  sublimis  to  enter  the  digital  sheaths  of  the 
second,  third,  fourth,  and  fifth  fingers.  Opposite  the  first  phalangeal  joint  each 
tendon  passes  between  the  two  slips  of  the  corresponding  tendon  of  the  flexor  sub- 
limis and  is  inserted  into  the  base  of  the  terminal  phalanx. 

Nerve-Supply. — The  lateral  half  of  the  muscle  is  supplied  by  branches  from 
the  anterior  interosseous  branch  of  the  median  nerve  and  the  medial  half  by  the 


596 


HUMAN   ANATOMY. 


FIG.  578. 


Brachialis  anticus— r^B 


Supinator 


Insertion  of  pronator  radii  teres — i- 


Flexor  longus  pollicis- 


Flexor  carpi 
ulnaris 


Abductor 

minimi  digit! 
Anterior 

annular 

ligament 


Pronator  quadratus 


Tendon  of  flexor  carpi  radial  is 


Abductor  pollicis,  cut 
Opponens  pollici 


Flexor 

brevis  pollicis 

Adductor  pollicis,    /  * 
oblique  portion  ,/>•  -- 


,       V 

Adductor  pollicis, 
transverse  portion 


ulnar  ;  the  fibres  come  from 
the  seventh  and  eighth  cer- 
vical and  the  first  thoracic 
nerves. 

Action. — The  primary 
action  of  the  flexor  pro- 
fundus  is  to  flex  the  ter- 
minal 'phalanges  of  the 
second,  third,  fourth,  and 
fifth  fingers,  but,  continu- 
ing its  action,  it  also  flexes 
the  remaining  phalanges  of 
those  digits  and  finally  the 
hand. 

Relations.  —  In  the 
arm  the  muscle  is  covered 
by  the  flexor  sublimis  digi- 
torum  and  the  flexor  carpi 
ulnaris,  and  has  resting 
upon  its  anterior  surface 
the  ulnar  vessels  and  the 
median  and  ulnar  nerves. 
Posteriorly  it  is  in  relation 
to  the  pronator  quadratus 

digitorum  j  .  i  T      4.U 

and  the  wrist-joint.  In  the 
hand  its  tendons  are  cov- 
ered by  those  of  the  flexor 
sublimis  and  by  the  lum- 
brical  muscles  ;  they  rest 
upon  the  adductor  pollicis 
and  interosseous  muscles 
and  cross  the  deep  palmar 
arch. 


Flexor 
profundus 


Opponens 
minimi  digit! 
exor  brevis 
linimi  digiti 

Lumliri- 
cales 


Tendons 
of  flexor 

suliliniis 
digitorutn 


Dissection  of  muscles  of  forearm  and  hand,  anit-i  i»i  Miiia,.-; 
inusi  k's  liavt-  IK-IMI  removed. 


n  l'u  i.tl 


Variations. — The  flexor 
profundus  frequently  receives 
additional  slips  from  the  flexor 
sublimis  and  may  be  united  to 
the  flexor  longus  pollicis.  A 
slip  which  has  been  termed 
the  accessorius  ad  Jie. \~orcm 
profundnni  digitornin  not  in- 
frequently occurs,  arising  from 
the  coronoid  process  of  the 
ulna  and  joining  with  one  of 
the  tendons  of  the  profundus. 
The  significance  of  the  varia- 
tions of  the  profundus  will  be 
considered  in  connection  with 
those  of  the  flexor  longus  pol- 
licis. 

2.  FLEXOR  LONGUS  POL- 
LICIS (Fig.  578). 

Attachments. — The 

long  flexor  of  the  thumb 
(  m.  flexor  pollicis  Ionics ) 
lies  to  the  lateral  side  of 
the  flexor  profundus  disj- 
torum  and  arises  from  tin- 
anterior  surface  of  the  ra- 
dius and  the  adjacent  hall 


THE   ANTIBRACHIAL   MUSCLES.  597 

of  the  interosseous  membrane.  It  usually  possesses  also  an  origin  by  means  of  a 
slender  slip  from  the  coronoid  process  of  the  ulna  or  the  medial  epicondyle  of  the 
humerus.  The  muscle-fibres  pass  into  a  strong  tendon  at  the  middle  of  the  forearm, 
and  this  passes  downward  beneath  the  lateral  part  of  the  annular  ligament  and 
extends  along  the  volar  surface  of  the  thumb  to  be  inserted  into  the  base  of  its  ter- 
minal phalanx. 

Nerve-Supply.  —  By  the  anterior  interosseous  nerve  from  the  eighth  cervical 
and  first  thoracic  nerves. 

Action. — To  flex  the  terminal  phalanx  of  the  thumb  ;  continuing  its  action,  it 
will  also  flex  the  proximal  phalanx  and  assist  in  the  flexion  of  the  hand. 

Relations.— In  the  forearm  it  is  covered  by  the  flexor  sublimis  digitorum,  the 
flexor  carpi  radialis,  and  the  brachio-radialis,  and  has  resting  upon  it  the  radial  ves- 
sels. Deeply  it  is  in  relation  with  the  pronator  quadratus  and  the  wrist-joint.  In 
the  hand  its  tendon  is  covered  by  the  opponens  pollicis  and  the  flexor  brevis  pollicis, 
and  it  rests  upon  the  adductor  pollicis. 

Variations.— The  head  from  the  coronoid  process  or  medial  epicondyle  of  the  humerus  is 
sometimes  absent  and  the  muscle  is  frequently  connected  with  the  flexor  profundus  digitorum  or 
even  fused  with  it. 

Occasionally  there  arises  from  the  lower  part  of  the  anterior  and  external  surfaces  of  the 
radius  a  muscle  which  has  been  termed  theyfe.ror  carpi  radialis  brevis.  Its  insertion  varies  some- 
what, being  sometimes  on  one  of  the  carpal  bones,  at  other  times  on  either  the  second,  third,  or 
fourth  metacarpals,  and  at  others,  again,  into  the  transverse  carpal  ligament.  Although  asso- 
ciated by  name  with  the  flexor  carpi  radialis,  it  is  more  probably  a  derivative  of  the  deeper  layer 
of  the  flexor  musculature  and  is  supplied  by  the  volar  interosseous  branch  of  the  median  nerve. 

The  majority  of  the  variations  of  the  flexor  longus  pollicis  and  flexor  profundus  digitorum 
find  an  explanation  in  the  historical  development  of  the  muscles.  In  the  lowest  group  of  the 
mammalia,  the  mpnotremata,  the  two  muscles  are  fused  with  each  other  and  also  with  the 
flexor  sublimis  to  form  a  common  long  flexor,  from  the  tendon  of  which  the  tendons  of  the  flexor 
sublimis  arise.  In  slightly  higher  forms  this  common  flexor  can  be  seen  to  be  composed  of  five 
portions,  which,  from  their  points  of  origin  and  relations,  may  be  termed  the  condylo-ulnaris, 
condylo-raclialis,  centralis,  ulnaris,  and  radialis,  and  as  the  scale  is  ascended  one  finds  at  first  a 
part  of  the  condylo-ulnaris  and  later  the  whole  of  that  portion  separating  from  the  common  mass 
and  joining  the  tendons  of  the  sublimis.  In  still  higher  forms  the  centralis  and  condylo-radialis 
portions  follow  the  example  of  the  condylo-ulnaris,  the  flexor  sublimis  digitorum  in  man  being 
composed  of  these  portions  of  the  common  mass. 

The  ulnaris  and  radialis  portions  remain,  as  a  rule,  united  and,  after  the  separation  of  the 
superficial  portions  is  completed,  constitute  the  flexor  profundus.  In  man  and  a  few  other  forms 
the  radialis  separates  from  the  ulnaris  to  form  the  flexor  longus  pollicis. 

The  connections  which  occur  between  the  sublimis,  profundus,  and  flexor  longus  pollicis 
are  consequently  to  be  regarded  as  relics  of  the  historical  development  of  the  muscles,  as  the 
incomplete  separation  of  a  common  flexor  mass. 

In  the  lower  terrestrial  vertebrata  the  superficial  and  deeper  layers,  corresponding  practi- 
cally to  the  sublimis  and  profundus  (plus  the  flexor  longus  pollicis),  are  distinct,  their  fusion  in 
the  monotremes  being  a  secondary  condition,  which  forms  the  starting-point  for  the  differentia- 
tion of  the  mammalian  arrangement  of  the  muscles.  In  these  lower  forms  both  layers  insert 
into  tin.-  palmar  aponeurosis,  the  extension  of  the  deeper  layer  to  the  digits  being  due  to  the 
separation  of  the  layer  of  the  aponeurosis  to  which  the  deeper  muscle-layer  is  attached  and  its 
differentiation  into  tendons. 

It  may  be  added  that  in  the  lower  vertebrates  the  palmaris  longus  is  not  represented  as  a 
separate  muscle,  and  it  is  to  be  regarded  as  a  portion  of  the  superficial  sheet  which  has  retained 
its  original  relations  to  the  palmar  aponeurosis,  its  occasional  absence  being  ascribed  to  its 
sharing  the  history  of  the  flexor  sublimis  and  being  incorporated  in  that  muscle. 

(rr)  THE  DEEP  LAYER. 
i.    Pronator  quadratus. 

i.    PROXATOR  QUADRATUS  (Fig.  588). 

Attachments. — The  pronator  quadratus  is  a  flat  quadrangular  sheet  extending 
across  between  the  lower  portions  of  the  radius  and  ulna.  It  arises  from  the  volar 
surface  of  the  ulna  and  passes  laterally  and  slightly  clistally  to  be  inserted  into  the 
lateral  and  anterior  surfaces  of  the  lower  end  of  the  radius. 

Nerve-Supply. — By  the  anterior  interosseous  branch  of  the  median  nerve  from 
the  seventh  and  eighth  cervical  and  the  first  thoracic  nerves. 

Action. — To  pronate  the  forearm. 


598  HUMAN   ANATOMY. 

Variations. — The  pronator  quadratus  usually  occupies  about  the  lower  fourth  of  the  fore- 
arm, but  it  may  be  considerably  reduced  or,  on  the  contrary,  may  extend  as  high  as  the  middle 
of  the  forearm  or  even  higher.  It  represents  the  lower  portion  of  a  muscle-sheet  which  extends 
in  some  of  the  lower  mammals  almost  the  entire  length  of  the  forearm,  the  upper  portion  of 
this  sheet  being  represented,  as  already  pointed  out,  by  the  coronoid  head  of  the  pronator  teres. 

(6)    THE  POST-AXIAL  MUSCLKS. 

The  post-axial  muscles  of  the  forearm  may  be  regarded  as  consisting  of  two 
layers,  the  more  superficial  of  which  arises  from  the  external  condyle  of  the  humerus, 
while  the  deeper  one  is  attached  to  the  bones  of  the  forearm.  As  was  the  case  with 
the  pre-axial  muscles,  constituents  of  both  layers  have  extended  into  the  hand  to  act 
as  extensors  of  the  digits. 

(aa)  THE  SUPERFICIAL  LAYER. 

1.  Brachio-radialis.  4.    Extensor  communis  digitorum. 

2.  Extensor  carpi  radialis  longior.  5.    Extensor  minimi  digiti. 

3.  Extensor  carpi  radialis  brevior.  6.    Extensor  carpi  ulnaris. 

i.    BRACHIO-RADIALIS  (Fig.   576). 

Attachments. — The  brachio-radialis,  sometimes  termed  the  supinator  longus> 
arises  from  the  external  condylar  ridge  of  the  humerus  and  from  the  lateral  inter- 
muscular  septum.  Its  fibres  form  a  strong  muscle  which,  at  about  the  middle  of  the 
forearm,  passes  into  a  tendon  which  is  inserted  into  the  base  of  the  styloid  process  of 
the  radius. 

Nerve-Supply. — By  the  musculo-spiral  nerve  from  the  fifth  and  sixth  cervical 
nerves. 

Action. — To  flex  the  forearm.  If  the  arm  be  in  a  position  of  complete  prona- 
tion,  it  will  produce  a  slight  amount  of  supination. 

Relations. — In  its  upper  part  it  is  in  contact  medially  with  the  brachialis  anti- 
cus,  a  portion  of  whose  lateral  border  it  covers,  and  with  the  radial  nerve.  Below  it 
rests  upon  the  upper  portion  of  the  extensor  carpi  radialis  longior,  the  supinator,  the 
pronator  teres,  the  flexor  sublimis  digitorum,  and  the  radial  artery  and  nerve.  It  is 
crossed  near  its  insertion  by  the  tendons  of  the  abductor  longus  pollicis  and  extensor 
brevis  pollicis. 

Variations. — The  brachio-radialis  is  sometimes  wanting.  It  may  be  inserted  a  consider- 
able distance  above  the  base  of  the  styloid  process  of  the  radius,  a  condition  characteristic  of 
the  lower  mammals,  or  it  may  pass  as  far  down  as  the  carpal  bones  or  even  to  the  base  of  tin- 
third  metacarpal. 

2.    EXTENSOR  CARPI  RADIALIS  LONGIOR  (Figs.  576,  579). 

Attachments. — The  longer  of  the  radial  carpal  extensors  (ra.  extensor  carpi 
radialis  longus )  lies  immediately  posterior  to  the  brachio-radialis.  It  arises  from  tin- 
lower  third  of  the  external  supracondylar  ridge  of  the  humerus,  the  external  inter- 
muscular  septum,  and  the  extensor  tendon  common  to  it  and  the  neighboring  super- 
ficial muscles.  About  the  middle  of  the  forearm  it  is  continued  into  a  tendon  which 
passes  beneath  the  posterior  annular  ligament  in  the  second  compartment,  along  with 
the  extensor  carpi  radialis  brevior,  ana  is  inserted  into  the  base  of  the  second  meta- 
carpal. 

Nerve-Supply. — By  the  deep  division  of  the  musculo-spiral  nerve  from  the 
sixth  and  seventh  cervical  nerves. 

Action. — To  extend  and  slightly  abduct  the  hand. 

Variations. — The  extensor  carpi  radialis  longior  is  occasionally  fused  with  the  extensor 
carpi  radialis  brevior.  It  may  send  tendinous  slips  to  the  first  and  third  metacarpals  and  to  the 

trapezium. 

3.    KXTKNSOK  CARIM   RADIALIS  BKKVIOK   <  l;i-.   579). 

Attachments. — The  shorter  radial  carpal  extensor  (  in.  extensor  carpi  radialis 
lux-vis  )  is  fused  with  the  neighboring  superficial  extensors  where  it  arises  from  tin- 


THE   ANTIBRACHIAL   MUSCLES. 


599 


external  condyle  of  the  hu- 
merus,  from  the  adjacent  in- 
termuscular  septa,  and  from 
the  deep  fascia  of  the  fore- 
arm. Its  fibres  converge  at 
about  the  middle  of  the  fore- 
arm into  a  flat  tendon,  which 
passes  with  the  long  exten- 
sor carpi  radialis  beneath  the 
posterior  annular  ligament 
in  the  second  compartment 
and  is  inserted  into  the  base 
of  the  third  metacarpal,  a 
bursa  (bursa  m.  extensoris 
carpi  radialis)  being  inter- 
posed between*  the  tendon 
and  the  bone. 

Nerve-Supply.  —  By 
the  posterior  interosseous 
branch  of  the  musculo-spiral 
nerve  from  the  sixth  and 
seventh  cervical  nerves. 

Action. — To  extend 
the  hand. 

Variations. — It  may  be  fused 
to  a  greater  or  less  extent  with 
the  extensor  carpi  radialis  lon- 
gior and  may  be  inserted  into 
the  bases  of  both  the  second 
and  third  metacarpals. 

4.   EXTENSOR  COMMUNIS 
DIGITORUM  (Fig.  579). 

Attachments.  —  The 
common  extensor  of  the 
fingers  (m.  extensor  digitorum 
communis)  arises  in  com- 
mon with  the  neighboring 
superficial  extensors  from 
the  external  condyle  of  the 
humerus,  from  the  septa  be- 
tween it  and  the  adjoining 
muscles,  and  from  the  deep 
fascia  of  the  forearm.  At 
about  the  middle  of  the 
forearm  its  fibres  go  over 
into  four  tendons,  which  pass 
through  the  fourth  compart- 
ment beneath  the  posterior 
annular  ligament  and  diverge 
to  be  inserted  into  the  bases  of 
the  middle  and  terminal  pha- 
langes of  the  second,  third, 
fourth,  and  fifth  fingers.  Just 
before  they  pass  over  the 
metacarpo-phalangeal  joints 
of  their  digits  the  four  ten- 
dons are  usually  united  by 


FIG.  579. 


Anconeus 


Brachio-radialis 


External  condyle 


Extensor  carpi 
radialis  longior 


.Extensor  carpi 
radialis  brevior 


Flexor  carpi  ulnat 


Extensor  carpi  ulnaris 


Extensor 
communis 
digitorum 


Extensor  ossis 
metacarpi  pollicis 

Extensor  brevis 

pollicis 
Extensor  longus 

pollicis 


Tendon  of  extensor 
carpi  radialis  longior 
Tendon  of  extensor 
carpi  radialis  brevior 


Abductor 
pollicis 

First  dorsal 
interosseus 


Dissection  of  posterior  surface  of  forearm  and  hand,  showing  superficial 
extensor  muscles. 


6oo 


HUMAN   ANATOMY. 


FIG.  580. 


Olecranon  process 


Anconeus 


Extensor  carpi 

radialis  longior 
External  condyle 


Flexor  carpi  ulnaris 


Extensor  ossis 
metacarpi  pollicis 


Extensor  carpi  radi- 
alis brevior  tendon 


Extensor  carpi  radi- 
alis longior  tendon 


Dissection  of  posterior  surface  of  forearm  and  hand,  showing  deep 

IIIUM  ll'S. 


three  obliquely  transverse  ten- 
dinous bands  (juncturae  ten- 
(linum),  the  one  between  the 
index  and  median  digits  being, 
however,  frequently  wanting. 
As  each  tendon  passes  upon 
the  dorsum  of  the  first  phalanx 
of  its  digit  it  spreads  out  into  a 
membranous  expansion,  which 
receives  the  insertions  of  the 
interosseous  and  lumbrical 
muscles  and  then  divides  into 
three  more  or  less  well-defined 
slips.  The  median  slip  passes 
to  the  base  of  the  second  pha- 
lanx, while  tne  lateral  ones, 
passing  over  the  first  interpha- 
langeal  joint,  unite  over  the 
dorsum  of  the  second  phalanx 
and  are  inserted  into  the  base 
of  the  first  phalanx. 

Nerve-Supply. — By  the 
posterior  interosseous  branch 
of  the  musculo-spiral  nerve 
from  the  sixth,  seventh,  and 
eighth  cervical  nerves. 

Action. — To  extend  the 
phalanges  of  the  second,  third, 
fourth,  and  fifth  fingers  and, 
continuing  its  action,  to  extend 
the  hand. 

Variations.  —  The  principal 
variations  of  the  common  extensor 
consist  in  the  absence  of  one  or 
other  of  the  tendons,  usually  that 
to  the  fifth  digit  and  more  rarely 
that  to  the  second,  or  else  in  the 
occurrence  of  additional  tendons, 
due  to  the  division  of  one  or  more 
of  those  typically  occurring,  cer- 
tain of  the  digits  then  receiving 
two  or  even  three  tendons.  Oc- 
casionally an  additional  tendon  is 
present  which  passes  to  the  thumb 
to  unite  with  the  tendon  of  its  long 
extensor. 

5.    EXTENSOR    MINIMI    Pi<;- 
m  (Fig.  579). 

Attachments. — The  ex- 
tensor of  the  little  finger  ( in. 
extensor  diijiti  quinti  proprius  ) 
arises  in  common  with  the 
preceding  muscle  from  the  lat- 
eral epicondyleof  tin-  humerus 
and  from  the  antibrachial  fas- 
cia. Its  tendon  passes  beneath 
the  posterior  annular  ligament 
in  the  fifth  compartment  and 
fuses  over  the  fifth  metacarpal 


THE   ANTIBRACHIAL   MUSCLES. 


60 1 


Brachialis  anticus 


with    the  tendon  of    the  extensor  communis  digitorum  which  passes    to   the  little 
finger. 

Nerve-Supply. — By  the  posterior  interosseous  branch  of  the  musculo-spiral 
nerve  from  the  sixth,  seventh,  and 
eighth  nerves.  FIG.  581. 

Action. — To  extend  the  lit- 
tle finger. 

Variations. — This  muscle  is  some- 
times absent,  probably  remaining  in- 
corporated in  the  extensor  communis. 
Its  tendon  occasionally  sends  a  slip  to 
the  fourth  finger. 

6.    EXTENSOR  CARPI  ULNARIS 

(Figs.  577,  579). 

Attachments. — The  exten- 
sor carpi  ulnaris  arises  in  common 
with  the  adjacent  superficial  ex- 
tensors from  the  external  condyle 
of  the  humerus,  from  the  deep 
fascia,  and,  usually,  from  the  apo- 
neurosis  attached  to  the  posterior 
border  of  the  ulna  common  to 
this  muscle,  the  flexor  profundus 
digitorum,  and  the  flexor  carpi  ul- 
naris. Its  tendon  passes  through 
the  sixth  compartment  beneath 
the  posterior  annular  ligament  and 
is  inserted  into  the  base  of  the 
fifth  metacarpal  bone. 

Nerve-Supply.  —  By  the 
posterior  interosseous  branch  of 
the  musculo-spiral  nerve  from  the 
sixth,  seventh,  and  eighth  cervical 
nerves.  '  ;>, Radius 

Action. — To  extend  and  ad- 
duct  the  hand. 

Variations. — A  fibrous  band  is 
Often  given  off  from  the  tendon  of  the  Dissection  of  arm,  showing  deep  muscles  „,  vicinhy  of  elbow. 

muscle  to  be  inserted  somewhere  over 

the  fifth  metacarpal  into  the  sheath  of  the  tendon  of  the  extensor  of  the  little  finger  ;  it  has 

been  termed  the  m.  ulnaris  quinti  digiti. 

(bb)  THE  DEEP  LAYER. 

1.  Supinator.  3.    Extensor  brevis  pollicis. 

2.  Extensor  ossis  metacarpi  pollicis.  4.    Extensor  longus  pollicis. 

5.    Extensor  indicis. 

i.   SUPINATOR  (Figs.   580,  581). 

Attachments. — The  supinator,  also  termed  the  supinator  radii  brevis,  is  a  flat 
triangular  muscle  which  arises  partly  from  the  outer  condyle  of  the  humerus  and  the 
orbicular  ligament  of  the  elbow-joint,  and  partly  from  the  upper  part  of  the  lateral 
border  of  the  ulna  and  the  smooth  surface  beneath  the  lesser  sigmoicl  cavity  of  that 
bone.  Its  fibres  pass  obliquely  downward  and  outward,  diverging  as  they  go,  and 
are  inserted  into  the  posterior,  lateral,  and  anterior  surfaces  of  the  radius,  curving 
around  that  bone.  The  insertion  extends  downward  to  about  the  middle  of  the 
radius. 


Head  of  radius 


Supinator 


6O2 


HUMAN    ANATOMY. 


Nerve-Supply. — By  the  posterior  interosseous  branch  of  the  musculo-spiral 
nerve  from  the  sixth  cervical  nerve. 

Action. — To  supinate  the  forearm. 

Variations. — The  posterior  interosseous  nerve  perforates  the  supinator  and  occasionally 
marks  the  line  of  separation  of  the  muscle  into  two  portions,  which  correspond  to  the  epicon- 
dylar  and  ulnar  portions  of  the  muscle.  The  muscle  is  indeed  a  composite  one,  a  portion  of  it 
being  derived  from  the  superficial  extensor  layer  and  the  rest  of  it  from  the  deep  layer. 


2.    EXTENSOR  Ossis  METACARPI  POLLICIS  (Fig.  580). 

Attachments. — The  extensor  of  the  metacarpal  bone  of  the  thumb  (m.  abduc- 
tor pollicis  longus)  arises  from  the  middle  third  of  the  posterior  surfaces  of  the  ulna, 

the  interosseous  membrane,  and 

FIG.  582.  the    radius.      It    passes    down- 

ward and  laterally,  and  its  ten- 
don passes  through  the  first 
compartment  beneath  the  pos- 
terior annular  ligament  to  be 
inserted  into  the  outer  side  of 
the  base  of  the  first  metacarpal 
bone. 

Nerve-Supply. — By  the 
posterior  interosseous  branch  of 
the  musculo-spiral  nerve  from 
the  sixth,  seventh,  and  eighth 
cervical  nerves. 

Action. — To  abduct  and 
slightly  extend  the  thumb  and, 
continuing  its  action,  to  abduct 
the  hand. 

Relations. — It  is  covered 
by  the  muscles  of  the  superficial 
layer  and  is  crossed  obliquely  by 
the  dorsal  interosseous  artery. 
Below  it  crosses  obliquely  the 
tendons  of  the  extensores  carpi 
radiales  and  the  radial  artery. 

Variations. — It  may  be  par- 
tially or  wholly  fused  with  the  ex- 
tensorbrevis  pollicis.  Occasionally 
it  possesses  two  tendons,  one  of 
which  may  be  inserted  into  the  dor- 
sal carpal  ligament,  the  abductor 
brevis  pollicis,  or  the  trapezium. 


-Brachio-radialis 


Flexor  sublitnis  digitorum 


Radial  artery 


Extensor  ossis 
jnetacarpi  pollicis 
.Kxtensor  brevis  pollicis 

^ Extensor  carpi  radialis  longior 

sor  longus  pollicis 
arpi  radialis  brevior 

al  artery 


First  dorsal 
interosseus 
Radialis  indicis 
artery 


Superficial  dissection  of  hand,  virwcd  from  radial  side,  showing 
extensor  tendons  of  thumb. 


3.    EXTENSOR  BREVIS  POLLI- 
CIS (Fig.   580). 

Attachments.— The  short 
extensor  of  the  thumb  (m.  exten- 
sor pollicis  brevis),  also  termed 

the  extensor  print!  internodii  pollicis,  lies  along  the  medial  border  of  the  extensor 
ossis  metacarpi  pollicis.  It  arises  from  the  interosseous  membrane  and  the  pos- 
terior surface  of  the  radius,  partly  under  cover  of  the  extensor  longus  pollicis,  and  its 
tendon,  after  passing  with  that  <>f  the  abductor  through  the  first  compartment  of  the 
posterior  annular  ligament,  is  inserted  into  the  base  of  the  first  phalanx  of  the  thumb. 
Nerve-Supply. — By  the  posterior  interosseous  branch  of  the  musculo-spiral 
ncrvr  from  the  sixth,  seventh,  and  eighth  cervical  nerves. 

Action. — -To  abduct  the  thumb  and  extend  its  first  phalanx. 


PRACTICAL   CONSIDERATIONS  :    THE   FOREARM.  603 

Relations. — The  relations  of  the  muscle  are  essentially  the  same  as  those  of 
the  extensor  ossis  metacarpi  pollicis. 

Variations. — The  extensor  brevis  and  the  metacarpal  extensor  of  the  thumb  are  differen- 
tiations of  a  common  muscle  and  show  indications  of  this  in  their  partial  or  complete  fusion. 
The  tendon  of  the  extensor  brevis  is  sometimes  continued  onward  to  the  terminal  phalanx  of 
the  thumb  or  may  send  a  slip  to  the  base  of  the  second  metacarpal. 

4.   EXTENSOR  LONGUS  POLLICIS  (Fig.  580). 

Attachments. — The  long  extensor  of  the  thumb  (m.  extensor  pollicis  longus), 
also  known  as  the  extensor  sccundi  internodii  pollicis,  is  an  elongated  fusiform  mus- 
cle lying  along  the  medial  border  of  the  extensor  brevis  pollicis,  which  it  partly 
covers.  It  arises  from  the  interosseous  membrane  and  posterior  surface  of  the  ulna  ; 
its  tendon  passes  downward  in  the  third  compartment  beneath  the  posterior  annular 
ligament  and,  crossing  over  the  tendons  of  the  extensores  carpi  radiales,  is  inserted 
into  the  base  of  the  terminal  phalanx  of  the  thumb. 

Nerve-Supply. — By  the  posterior  interosseous  branch  of  the  musculo-spiral 
nerve  from  the  sixth,  seventh,  and  eighth  cervical  nerves. 

Action. — To  extend  the  terminal  phalanx  of  the  thumb  and,  continuing  its 
action,  to  extend  and  at  the  same  time  slightly  adduct  the  thumb. 

5.   EXTENSOR  INDICIS  (Fig.  580). 

Attachments. — The  extensor  of  the  index-finger  (m.  extensor  indicis  proprius) 
lies  along  the  medial  border  of  the  extensor  longus  pollicis.  It  arises  from  the  in- 
terosseous membrane  and  the  dorsal  surface  of  the  ulna.  Its  tendon  passes,  along 
with  the  tendons  of  the  extensor  communis  digitorum,  through  the  fourth  compart- 
ment beneath  the  posterior  annular  ligament,  and  eventually  is  inserted  with  the 
tendon  of  the  common  extensor  which  passes  to  the  index-finger. 

Nerve-Supply. — By  the  posterior  interosseous  branch  of  the  musculo-spiral 
nerve  from  the  seventh  and  eighth  cervical  nerves. 

Action. — To  extend  the  index-finger. 

Variations. — The  extensor  indicis  may  be  wanting,  or  its  tendon  may  send  slips  to  the 
third  and  fourth  digits.  Occasionally  a  muscle  arises  from  the  ulna,  below  the  origin  of  the  ex- 
tensor indicis,  and  passes  to  the  third  or  fourth  finger,  forming  what  has  been  termed  the  extensor 
digiti  niedii  (vel  annularis}  pro  firms.  This  muscle  represents  an  additional  portion  of  the  deep 
extensor  layer  which  normally  disappears. 

PRACTICAL  CONSIDERATIONS  :    THE   FOREARM. 

The  fascia  descending  from  the  arm  to  the  forearm  should  be  studied  anteriorly 
with  relation  to  the  expansion  known  as  the  bicipital  aponeurosis  (Fig.  570), — one 
of  the  "  two  inferior  tendons  of  the  biceps"  of  the  older  anatomists, — which  becomes 
continuous  with  the  deep  fascia  of  the  forearm,  and  thus,  through  the  origin  from  its 
under  surface  of  fibres  of  many  of  the  superficial  muscles  of  that  region,  associates 
their  action  with  that  of  the  biceps  itself.  Partly  for  this  reason  injuries  and  diseases 
affecting  the  bicipital  region  are  sometimes  associated  with  a  certain  weakness  of 
grasp  and  feebleness  of  wrist  flexion.  The  facts  that  only  this  aponeurotic  expansion 
separates  the  median  basilic  vein  from  the  brachial  artery,  and  that  in  persons  of  poor 
muscular  development  it  is  often  so  thin  as  scarcely  to  constitute  a  recognizable 
layer,  were  of  practical  importance  when  phlebotomy  of  the  median  basilic  was  fre- 
quent. Arterio-venous  aneurism  from  accidental  puncture  of  the  artery  was  then 
quite  common. 

Posteriorly  the  outer  aponeurotic  expansion  of  the  triceps,  running  over  the 
anconeus  to  become  continuous  with  the  deep  fascia  of  the  forearm,  is  of  importance 
in  its  relation  to  the  power  of  extension  of  the  forearm  after  excision  of  the  elbow 
(page  308). 

The  fascia  of  the  forearm,  besides  giving  origin  to  many  fibres  of  the  subjacent 
muscles,  as  lias  been  noted  above,  envelops  the  forearm  completely,  being  continu- 


604 


HUMAN    ANATOMY. 


Flexor  longus  pollicis 
Median  nerve 

IJlnar  artery 

Flexor  sublimis 
Ulnar  nerve 


kin 


ous  at  the  wrist  with  the  anterior  and  posterior  annular  ligaments.  The  septa  which 
run  in  from  it  to  be  attached  to  the  sides  of  the  ulna  and  radius  divide  the  forearm, 
with  the  aid  of  the  interosseous  membrane,  into  two  musculo-aponeurotic  spaces,  an 
antero-external  and  a  posterior  (Fig.  583).  The  former  contains  numerous  muscles 
and  the  main  vessels  and  nerves,  the  latter  is  almost  entirely  muscular. 

The  interpenetration  of  these  main  septa  and  of  the  intermuscular  fascia  by 
nervo-vascular  structures  renders  them  of  slight  importance  in  limiting  the  spread  of 
infectious  disease  or  of  collections  of  blood  or  pus.  But  in  the  not  infrequent  cases 
of  incised  wounds  severing  the  muscles  and  tendons  of  this  region  it  may  systematixe 
the  search  for  and  reunion  of  the  divided  structures  if  the  somewhat  artificial  topog- 
raphy, as  described  by  Tillaux,  is  borne  in  mind.  The  antero-external  compart- 
ment is  thus  regarded  as  including  four  spaces.  i.  That  between  the  skin  and  the 
first  muscular  layer, — the  palmaris,  flexor  carpi  ulnaris,  pronator  radii  teres,  etc., — 
and  containing  the  internal  cutaneous  and  musculo-cutaneous  nerves,  the  perforating 
branches  of  the  radial  and  ulnar  nerves,  the  superficial  veins,  and  sometimes  the 
ulnar  artery  when  there  is  a  high  bifurcation  of  the  brachial.  2.  That  between  the  first 
muscular  layer  and  the  flexor  sublimis,  with  the  brachio-radialis  and  short  supinator 

externally.     This  contains 

FIG.  583.  the  radial   nerve,   artery, 

and  veins.  3.  That  be- 
tween the  flexor  sublimis 
and  the  flexor  profundus 
and  flexor  longus  pollicis. 
This  contains  the  median 
nerve  and  the  ulnar  nerve 
and  vessels.  4.  That  be- 
tween the  last-named  mus- 
cles and  the  interosseous 
membrane,  containing  the 
anterior  interosseous  ves- 
sels and  the  interosseous 
nerve. 

In  the  posterior  com- 
partment are  to  be  found, 
in  addition  to  the  exten- 
sors and  the  anconeus, 
only  the  posterior  inter- 
osseous vessels  and  nerve 
(Fig.  5X3). 

Fractures  of  the  neck 

of  the  radius  (between  the  head  and  the  tuberosity)  are  very  rare,  as  it  is  covered  and 
protected  from  direct  violence  by  the  long  and  short  supinators  and  the  long  and 
short  radial  extensors.  Angular  displacement  forward  is  thought  to  be  caused  by 
the  action  of  the  biceps  on  the  upper  end  of  the  lower  fragment.  The  upper  frag- 
ment is  rotated  outward  by  the  supinator  brevis.  Fracture  of  the'  radius  below  its 
tubercle  and  above  the  insertion  of  the  pronator  radii  teres  (a  little  above  the  middle 
of  the  outer  side  of  the  bone)  is  followed  by  supination  and  flexion  of  the  upper  frag- 
ment by  the  biceps  and  supinator  brevis.  The  lower  fragment  is  pronated  and  drawn 
towards  the  ulna  by  the  pronators. 

It  is  well  to  treat  cases  of  this  fracture  with  the  forearm  in  mode-rate  supinatio 
so  as  to  approximate  the  fragments  and  preserve  the  axis  of  the  bone  and  the  tutu 
use-fulness  of  the  supinators. 

In  fracture  of  the  radius  below  the  insertion  of  the  pronator  radii  teres  the 
upper  fragment  is  flexed  by  the  biceps,  so  that  its  lower  end  can  sometimes  !>,•  seen 
and  felt  on  the  front  of  the  forearm  just  above  the  middle,  and  is  sometimes  pronated 
by  the  pronator  radii  teres  ;  the  lower  fragment  is  drawn  towards  the  ulna  by  the 
pronator  quadratus,  aided  by  the  action  of  the  brachio-radialis  on  the  styloid  process 

(Fig,5»A). 

In  the  usual  position  in  which  such  fractures  are  treated,  the  flexion  of  the  elbow 


Palmaris  longus 
Flexor  carpi  radialis 
Pronator  radii  teres 
Radial  artery 
Radial  nerve 


Extensor 
carpi  rad. 
long. 

Radius 


Extenso 
carpi  rad. 
brev. 

Supinator 

Extensor  cotnmunis 
I'ust.  inteross.  vessels 
and  nerve 

Interosseous  membrane  \  \        Extensor  carpi  ulnaris 

Extensor  ossis  metacarpi  pollicis  Extensor  longus  pollicis 

Section  across  middle  of  right  forearm. 


I 


PRACTICAL   CONSIDERATIONS  :    THE   FOREARM. 


605 


and  the  mid-position  between  pronation  and  stipulation  sufficiently  relax  the  biceps 
and  the  pronator  radii  teres.  The  weight  of  the  hand  in  adduction  overcomes  the 
pull  of 


FIG.  584. 


FIG.  585. 


the    brachio-radialis 
and  pronator  quadratus. 

Fracture  of  both  bones, 
from  either  direct  or  indirect 
violence,  usually  takes  place 
below  the  middle  of  the  fore- 
arm, as  there  the  muscular 
masses  which  protect  the 
upper  half  of  the  radius  from 
direct  violence  have  largely 
been  replaced  by  tendons, 
the  ulna  is  slender  and  weak, 
and  the  opposing  forces  rep- 
resented by  the  biceps  and 
brachialis  anticus  above  and 
the  weight  or  force  applied 
through  the  hand  expend 
themselves.  Thus  Malgaigne 
(quoted  by  Agnew)  reports 
a  case  in  which  both  bones 
were  broken  by  muscular 
action  alone  while  the  patient 
was  carrying  weight  in  the 
form  of  a  shovelful  of  dirt. 
When  the  resulting  deform- 
ity is  due  chiefly  to  the  con- 
traction of  muscles,  it  is  apt 
to  consist  in  flexion  of  both 
upper  fragments  by  the  bi- 
ceps and  brachialis  anticus, 
supination  of  the  upper  frag- 
ment of  the  radius  by  the 
biceps  and  supinator  brevis, 
and  approximation  of  the  two 
lower  fragments  by  the  pronator  quadratus.  Much  overlapping  and  shortening  are 
usually  prevented  by  the  untorn  fibres  of  the  interosseous  membrane. 

During  the  period  of  repair  the  mid-position — between  pronation  and  supination 
— preserves  the  parallelism  of    the  two  bones,   maintains  the  interosseous  space  at 

almost  its  greatest 

FIG.  586.  width,    relaxes   (in 

conjunction  with 
the  flexion  of  the 
elbow)  the  muscles 
involved  so  far  as 
is  possible,  and  by 
the  weight  of  the 
hand  dropping  to 
the  ulnar  side  over- 
comes the  resist- 
ance of  others,  espe- 
cially of  the  brachio- 
radialis. 

The  large  pro- 
portion of  the  re- 
turn current  of 

blood  that  is  carried  by  the  superficial  veins  of  the  forearm  makes  it  especially  impor- 
tant that  the  splints  used  should  be  so  broad  that  the  bandage  does  not  unduly  com- 


Dissection  of  fracture  of  radius  between 
the  two  pronator  muscles. 


Dissection  of  fracture  of  ole- 
cranon  process  of  left  ulna  ;  joint 
opened  from  behind. 


Ext.  carpi  radialis  long. 
Ext.  carpi  radialis  brev. 


Lower  end  of  fragment 
Brachio-radialis 
Ext.  longus  pollicis 


Radial  artery 
Flexor  tendons 
Lower  fragment 

Ext.  brevis  and  ext.  ossis  met.  poll., 
cut  and  turned  forward 

Dissection  of  Colles's  fracture  of  radius,  showing  relation  of  tendons  and  radial 

artery. 


6o6 


HUMAN    ANATOMY. 


press  the  soft  tissues  ;  while  the  ease  with  which  both  veins  and  arteries  may  be 
obstructed  at  the  bend  of  the  elbow  should  lead  to  careful  avoidance  of  pressure  in 
that  region  from  the  upper  end  of  the  palmar  splint. 

The  preservation  of  the  interosseous  space  is  favored  by  the  omission  of  the 
primary  roller  bandage  and  by  the  avoidance  of  direct  pressure  upon  the  soft  parts 
by  the  bandage  used  to  retain  the  splints. 

THE    MUSCLES   OF   THE   HAND. 

The  Deep  Fascia  of  the  Hand. — The  deep  fascia  of  the  palmar  surface 
of  the  hand  is  usually  regarded  as  being  represented  by  the  pa/mar  aponeurosis,  a 
firm  sheet  of  connective  tissue  which  occupies  the  palm  of  the  hand  and  lies  imme- 

FIG.  587. 


Thenar  eminence  covered 
with  lateral  portion  oi 
palmar  fascia 


Hypothenar  eminence 


^=~  Palmar  fascia,  central 
portion 

Palmar  fascia,  lateral  portion 


=- — Digital  nerves 

-  Superficial  transverse  ligament 


Digital  arteries 


Superficial  dissection  of  hand,  showing  palmar  fascia. 

diately  beneath  the  skin.  This  structure  represents,  however,  the  superficial  layer 
of  a  thick  aponeurosis  which  occurs  in  the  lower  vertebrates,  receiving  the  insertion 
of  the  antibrachial  flexors  and  giving  origin  to  the  digital  flexors.  From  the  proxi- 
mal portion  of  this  aponeurosis  there  is  formed,  however,  the  anterior  annular  liga- 
ment, and  this  may  be  considered  as  a  portion  of  the  palmar  aponcurosis. 

The  latter  (Fig.  587),  often  called  the  palmar  fascia,  is  a  fan-shaped  sheet 
whose  apex  is  directed  proximally,  receiving  the  insertion  of  the  palmaris  longusand 
being  to  a  certain  extent  continuous  with  the  anterior  annular  ligament.  It  reaches 


THE    MUSCLES    OF   THE    HAND.  607 

its  greatest  breadth  over  the  distal  portions  of  the  metacarpals,  and  is  continued 
onward  as  four  more  or  less  distinct  bands,  which  are  inserted  into  the  integument  at 
the  bases  of  the  second,  third,  fourth,  and  fifth  fingers.  A  little  below  the  lower 
edge  of  the  aponeurosis  transverse  bands  of  fascia  (fasciculi  transversi)  stretch  across 
between  the  same  fingers,  lying  immediately  beneath  the  skin  and  being  connected 
to  a  greater  or  less  extent  with  one  another.  These  bands  constitute  the  superficial 
transverse  metacarpal  ligament  beneath  the  webs  of  the  fingers. 

The  anterior  annular  ligament  (ligamentura  carpi  transversum)  (Fig.  578)  is  a 
strong  band  wrhich  stretches  across  from  the  trapezium  and  scaphoid  bones  of  the 
carpus  on  the  radial  side  to  the  pisiform  and  unciform  bones  on  the  ulnar  side, 
forming  a  bridge  across  the  groove  on  the  anterior  surface  of  the  carpus  which  trans- 
mits the  tendons  of  the  long  flexors  and  of  the  flexor  carpi  radialis  and  the  median 
nerve.  The  canal  so  formed  is  divided  by  a  partition  into  a  small  radial  compart- 
ment through  which  the  flexor  carpi  radialis  passes,  and  a  large  ulnar  one  which 
gives  passage  to  the  other  structures  mentioned.  The  tendons  are  enclosed  within 
synovial  sacs  which  extend  downward  to  about  the  middle  of  the  palm  and  upward 
to  a  short  distance  above  the  upper  edge  of  the  ligament.  The  sac  which  surrounds 
the  flexor  longus  pollicis  is  usually  separate  from  that  which  surrounds  the  remaining 
tendons  of  the  ulnar  compartment  ;  occasionally  the  portion  surrounding  the  tendons 
of  the  index-finger  is  also  separate. 

Towards  either  side  of  the  palmar  surface  of  the  hand  the  palmar  fascia  forms  a 
thin  covering  for  thenar  and  hypothenar  eminences  formed  by  the  superficial  muscles 
of  the  thumb  and  the  little  finger  respectively.  Upon  the  dorsal  surface  the  fascia  is 
thin,  and  is  continued  downward  from  the  lower  border  of  the  posterior  annular 
ligament  over  the  extensor  tendons  to  the  fingers,  where  it  unites  with  the  aponeu- 
roses  of  the  tendons. 

(a)    THE  PRE- AXIAL  MUSCLES. 

The  pre-axial  muscles  of  the  hand  are  to  be  regarded,  from  the  comparative 
stand-point,  as  being  arranged  in  five  layers.  Although  these  layers  become  con- 
fused to  a  certain  extent  in  the  human  hand,  it  will,  nevertheless,  aid  in  the  proper 
understanding  of  their  relations  to  group  them  according  to  the  primary  layers  from 
which  they  are  derived. 

(aa)    THE  MUSCLES  OF  THE  FIRST  LAYER. 

1.  Palmaris  brevis.  4.    Flexor  brevis  pollicis. 

2.  Abductor  pollicis.  5.    Abductor  minimi  digiti. 

3.  Opponens  pollicis.  6.    Opponens  minimi  digiti. 

7.    Flexor  brevis  minimi  digiti. 

The  most  superficial  layer  of  the  palmar  muscles  in  the  lower  vertebrates  takes 
its  origin  from  the  palmar  aponeurosis.  The  greater  portion  of  the  layer,  as  has 
already  been  pointed  out,  becomes  converted  in  the  mammalia  into  the  palmar  por- 
tions of  the  tendons  of  the  flexor  sublimis  digitorum,  and  it  is  only  towards  either 
margin  of  the  hand  that  it  persists  as  muscles,  which  show  indications  of  their 
primary  relations  in  their  origin  from  the  palmar  aponeurosis  or  the  anterior  annular 
ligament. 

i.    PALMARIS  BREVIS  (Fig.   576). 

Attachments. — The  palmaris  brevis  is  a  thin  quadrangular  sheet  which  lies 
immediately  beneath  the  skin  of  the  hypothenar  eminence.  It  arises  from  the 
proximal  portion  of  the  ulnar  border  of  the  palmar  aponeurosis  and  is  inserted  into 
the  skin  of  the  ulnar  border  of  the  hand. 

Nerve-Supply. — By  the  superficial  division  of  the  ulnar  nerve  from  the  first 
thoracic  nerve. 

Action. — To  wrinkle  the  skin  upon  the  ulnar  border  of  the  hand,  deepening 
the  hollow  of  the  hand. 

Variations. — The  muscle  may  be  greatly  reduced  in  size  and  is  occasionally  wanting. 


608  HUMAN   ANATOMY. 

2.   ABDUCTOR  POLLICIS  (Fig.   577). 

Attachments. — The  abductor  of  the  thumb  (m.  abductor  pollicis  brevis)  is  the 
most  superficial  muscle  of  the  thenar  eminence.  It  arises  from  the  anterior  annular 
ligament  and  from  the  scaphoid  bone  or  the  trapezium  and  passes  distally  to  be  in- 
serted along  with  the  flexor  brevis  pollicis  into  the  radial  side  of  the  base  ot  the  first 
phalanx  of  the  thumb  and  into  the  sheath  of  the  tendon  of  the  extensor  longus  pollicis. 

Nerve-Supply. — By  the  median  nerve  from  the  sixth  and  seventh  cervical 
nerves. 

Action. — To  flex  and  abduct  the  thumb. 

Variations. — The  portion  of  the  muscle  arising  from  the  carpus  is  sometimes  separate  from 
that  taking  origin  from  the  transverse  carpal  ligament.  Slips  are  occasionally  sent  to  the  abduc- 
tor from  the  extensores  carpi  radiales,  the  extensor  ossis  metacarpi  pollicis,  the  opponens  pol- 
licis, and  the  flexor  brevis  pollicis. 

3.    OPPONENS  POLLICIS  (Figs.   578,  588). 

Attachments. — The  opponens  pollicis  is  almost  completely  covered  by  the 
abductor  pollicis.  It  arises  from  the  anterior  annular  ligament  and  from  the  trape- 
zium, and  is  inserted  into  the  whole  length  of  the  radial  border  of  the  first  metacarpal. 

Nerve-Supply. — By  the  median  nerve  from  the  sixth  and  seventh  cervical 
nerves. 

Action. — To  flex  and  adduct  the  thumb,  opposing  it  to  the  other  fingers. 

4.    FLEXOR  BREVIS  POLLICIS  (Figs.   578,   588). 

Attachments. — The  flexor  brevis  pollicis  lies  along  the  lower  (ulnar)  border 
of  the  opponens  pollicis.  It  arises  from  the  lower  border  of  the  anterior  annular 
ligament  and  is  inserted,  along  with  the  abductor  pollicis,  into  the  radial  side  of  the 
base  of  the  first  phalanx  of  the  thumb. 

The  muscle  above  described  is  usually  regarded  by  English  anatomists  as  representing  t In- 
cuter  or  radial  head  of  the  flexor  brevis,  a  second  inner  or  ulnar  head  being  included  as  part  of 
that  muscle.  Concerning  the  inner  head  three  views  are  held  :  (a)  no  inner  head  is  recognized, 
the  small  slip  arising  from  the  ulnar  side  of  the  base  of  the  first  metacarpal  bone  and  passing 
downward  to  be  inserted  with  the  adductor  pollicis  into  the  base  of  the  first  phalanx,  which  by 
many  English  anatomists  is  regarded  as  a  small  inner  head  of  the  flexor  brevis,  being  described 
as  an  additional  (first)  palmar  interosseus  (page  612)  ;  (6)  the  small  slip  just  noted  is  the  iniu-r 
or  ulnar  head  of  the  flexor  brevis  ;  (r)  the  small  slip  and  all  the  fibres  described  as  forming  tin- 
adductor  obliquus  (page  610)  are  regarded  as  the  inner  head  of  the  flexor  brevis.  The  first 
view,  adopted  by  German  anatomists,  is  here  followed. 

Nerve-Supply. — By  the  median  nerve  from  the  sixth  and  seventh  cervical 
nerves. 

Action. — To  flex  the  first  phalanx  of  the  thumb. 

Variations. — The  muscle  is  sometimes  intimately  connected  with  the  abductor  pollicis  and 
opponens  pollicis. 

5.    ABDUCTOR  MINIMI  DIGITI  (Fig.   577). 

Attachments. — The  abductor  of  the  little  finger  (m.  abductor  di^iti  quinti) 
occupies  the  ulnar  border  of  the  hand.  It  arises  from  the  anterior  annular  ligament 
and  from  the  pisiform  bone  and  is  inserted  into  the  ulnar  side  of  the  base  of  the-  fust 
phalanx  of  the  little  finger. 

Nerve-Supply. — By  the  deep  division  of  the  ulnar  nerve  from  the  eighth  cer- 
vical and  first  thoracic  nerves. 

Action. — To  abduct  the  fifth  finger. 


6.    OPPONENS  MINIMI  DIGITI  (Fig.   578). 

Attachments. — This  muscle  (m.  opponens  digiti  quinti )  is  almost  completely 
covered  by  the  abductor  and  short  flexor  of  the  little  finger.  It  arises  from  the 
anterior  annular  ligament  and  the  uncinate  process  of  the  unciform  bone  and  is  in- 
serted into  the  whole  of  the  ulnar  border  of  the  fifth  metacarpal  bone. 


THE   MUSCLES   OF   THE   HAND. 


609 


Nerve-Supply. — By  the  deep  division  of  the  ulnar  nerve  from  the  eighth  cer- 
vical and  first  thoracic  nerves. 

Action. — To  flex  and  at  the  same  time  adduct  the  fifth  metacarpal. 

7.    FLEXOR  BREVIS  MIXIMI  DIGITI  (Figs.  577,  578;. 

Attachments. — The    short    flexor  of  the  little  ringer  (m.  tlexor    brevis    di»iti 
quinti)  lies  along  the  lateral  (radial)  border  of  the  abductor  minimi  digiti.      It  arises 

FIG.  588. 


Radius — 
Anterior  interosseous  artery   _' 


Cut  edge  of 
anterior  annular  ligament 


Opponens  pollicis 
Abductor  pollicis 


Flexor  brevis  pollicis 

l-'irsi  palmar  interosseus  __ 


Flexor  longus 
pollicis  tendon 


-Ulna 


I'ronator  quadratus 


Flexor  carpi  ulnaris  tendon 


Cut  edge  of 
anterior  annular  ligament 


I'isilorm  Ixmr 

Adductor  pollicis,  oblique  portion 

Third  palmar  interosseus 

Fourth  palmar  inU-nisseus 
_  Fourth  dorsal  interosseus 


Deep  dissection  of  wrist  and  hand,  showing  pronator  quadratus  and  short  muscles  of  thumb. 

from  the  anterior  annular  ligament  and  the  uncinate  process  of  the  uncinate  bone 
and  is  inserted  into  the  ulnar  side  of  the  base  of  the  first  phalanx  of  the  little  finger. 

Nerve-Supply.— By  the  de,ep  division  of  the  ulnar  nerve  from  the  eighth  cer- 
vical and  first  thoracic  nerves. 

Action. — To  flex  and  slightly  abduct  the  first  phalanx  of  the  little  finger. 

Variations. — The  flexor  brevis  and  opponens  minimi  digiti  are  often  united  by  muscle- 
bundles  and  may  even  be  completely  fused. 

39 


6io  HUMAN   ANATOMY. 

(bb)  THE  MUSCLES  OF  THE  SECOND  LAYER. 

In  the  lower  vertebrates  the  second  layer  also  arises  from  the  palmar  aponeu- 
rosis,  but  from  its  deeper  layers.  These,  as  has  been  stated  (page  597),  differentiate 
into  the  palmar  portions  of  the  tendons  of  the  flexor  profundus  digitorum,  and  in 
the  mammalia  the  muscles  retain  their  primary  origin  and  arise  from  those  tendons 
forming  the  lumbrical  muscles. 

I.     LUMBRICALES    (Fig.    578). 

Attachments. — The  lumbricals  are  four  slender,  band-like  muscles,  situated 
in  the  palm  of  the  hand.  Counting  from  the  radial  side  of  the  hand,  the  first  and 
second  lumbricals  arise  from  the  radial  side  of  the  flexor  profundus  tendons  to  the 
index  and  middle  fingers  respectively,  while  the  third  one  arises  from  the  adjacent 
sides  of  the  tendons  to  the  middle  and  ring  fingers,  and  the  fourth  from  those  of  the 
tendons  to  the  ring  and  little  fingers.  The  muscles  pass  distally  into  slender  tendons 
which  are  continued  to  the  radial  side  of  the  first  phalanges  of  the  second,  third, 
fourth,  and  fifth  fingers,  and  are  inserted  into  the  membranous  expansions  of  the 
tendons  of  the  extensor  communis  digitorum  to  those  fingers. 

Nerve-Supply. — The  first  and  second  lumbricals  are  supplied  by  the  median 
nerve  from  the  sixth  and  seventh  cervical  nerves  ;  the  third  and  fourth  by  the  deep 
division  of  the  ulnar  nerve  from  the  eighth  cervical  and  first  thoracic  nerves. 

Action. — To  flex  the  first  phalanges  of  the  second,  third,  fourth,  and  fifth 
fingers.  At  the  same  time,  by  their  traction  upon  the  extensor  tendons,  they  will 
tend  to  keep  the  second  and  third  phalanges  extended. 

Variations. — Variations  in  the  arrangement  of  the  lumbricals,  and  especially  of  the  third 
and  fourth,  are  not  uncommon.  The  tendon  of  each  of  these  muscles  may  bifurcate  and  be  in- 
serted iato  the  adjacent  sides  of  the  third  and  fourth  or  fourth  and  fifth  fingers,  and  more 
rarely  the  sole  insertions  may  be  into  the  ulnar  sides  of  the  first  phalanges  of  the  middle 
and  ring  fingers.  The  third  lumbrical  is  frequently  supplied  wholly  or  in  part  from  the  median 
nerve. 

(cc)  THE  MUSCLE  OF  THE  THIRD  LAYER. 

In  the  lower  vertebrates  the  third  layer  consists  of  muscles  which  arise  from  the 
carpal  and  metacarpal  bones  and  pass  to  each  of  the  digits.  In  the  mammalia  they 
become  greatly  reduced  in  number,  frequently  persisting,  however,  in  connection 
with  the  thumb,  index,  and  little  fingers,  but  in  man  they  are  represented  only  by 
an  adductor  pollicis. 

i.  ADDUCTOR  POLLICIS  (Figs.  578,  588). 

Attachments. — The  adductor  pollicis  is  a  flat  triangular  muscle  which  rests 
upon  the  metacarpal  bones  and  the  interosseous  muscles.  It  may  be  regarded  as 
consisting  of  two  portions.  The  portio  obliqua  (often  described  as  a  distinct  muscle, 
the  adductor  obliquus  pollicis}  arises  from  the  trapezium,  trapezoid,  and  os  magnum 
and  from  the  bases  of  the  second  and  third  metacarpals.  Its  fibres  are  directed  dis- 
tally and  radially,  and  are  inserted  by  a  tendon,  in  which  a  sesamoid  bone  is  usually 
developed,  into  the  ulnar  side  of  the  base  of  the  first  phalanx  of  the  thumb.  It 
also  sends  off  a  slip  which  passes  beneath  the  tendon  of  the  flexor  longus  pollicis  to 
be  inserted  into  the  radial  side  of  the  base  of  the  first  phalanx  of  the  thumb  along 
with  the  flexor  brevis  pollicis. 

The  portio  transvcrsa  (often  described  as  the  adductor  transversus  poll  ids  \ 
arises  from  the  lower  two-thirds  of  the  volar  surface  of  the  third  metacarpal,  and  its 
fibres  pass  almost  directly  radially  to  be  inserted  into  the  ulnar  side  of  the  base  of 
the  first  phalanx  of  the  thumb. 

Nerve-Supply. — By  the  deep  division  of  the  ulnar  nerve  from  the  eighth 
cervical  and  first  thoracic  nerves. 

Action. — To  adduct  the  thumb. 

Relations. — The  adductor  pollicis  is  covered  by  the  tendons  of  the  flexor 
profundus  digitorum  for  the  second  and  third  fingers  and  by  the  first  and  second 
lumbricals.  It  conceals  the  interosseous  muscles  of  the  two  radial  intermetacarpal 
intervals  and  also  the  radial  artery  and  the  arteria  princcps  pollicis.  The  deep 
palmar  arch  passes  between  the  two  portions  of  the  muscle,  near  their  origins. 


THE    MUSCLES   OF   THE   HAND. 


611 


Flexor  carpi  radialis  tendon 


Tuberosity  of  scaphoid 


.Flexor  carpi 
ulnaris  tendon 


Pisiform  bone 


_Unciform  process 
of  unciform 


(dd)  THE  MUSCLES  OF  THE  FOURTH  AND  FIFTH  LAYERS. 
i.    Interossei  volares.          2.    Interossei  dorsales. 

In  the  lower  vertebrates  the  musculature  of  the  fourth  palmar  layer  consists  of 
a  pair  of  muscles  for  each  digit,  arising  from  the  carpal  and  metacarpal  bones  and 
inserting  into  either  side  of  the  base  of  the  first  phalanx.  The  fifth  layer  lies 
dorsal  to  these,  and  consists  of  four  muscular  bands,  which  extend  slightly  obliquely 
across  the  four  inter- 
metacarpal  spaces.  FIG.  589. 

In  the  mammalia 
a  shifting  of  the  in- 
sertion of  one  of  the 
muscles  of  the  pairs 
belonging  to  the  first 
and  fifth  digits  takes 
place,  so  that  they  are 
attached  to  the  radial 
and  ulnar  sides  re- 
spectively of  the  ad- 
jacent second  and 
fourth  digits,  uniting 
with  the  correspond- 
ing members  of  the 
pairs  belonging  to 
those  digits.  With 
the  compound  mus- 
cles so  formed  the 
first  and  fourth  inter- 
metacarpal  muscles 
unite  to  form  the  first 
and  fourth  dorsal  in- 
terossei,  these  two 
muscles  being  com- 
posed, accordingly, 
by  the  fusion  of  three 
primary  muscles. 

The  second  and 
third  intermetacarpal 
muscles  unite  with  the 
radial  and  ulnar  mem- 
bers respectively  of 
the  pair  belonging  to 
the  third  digit,  and 
form  with  these  the 
second  and  third  dor- 
sal interossei. 

The  remaining 
members  of  the  pairs 
belonging  to  the  first, 
second,  fourth,  and 


\J 


\   .. 

Deep  dissection  of  hand,  showing  interosseous  muscles  as  seen  in  palm. 


fifth  digits  persist  as 

independent  muscles,  forming  what  are  termed  the  volar  interossei,  whose  arrange- 
ment is  consequently  complementary  to  that  of  the  dorsal  interossei. 

The  intermetacarpal  muscles  occupy  the  most  dorsal  position  of  all  the  palmar 
muscles,  and  it  is  probably  owing  to  their  participation  in  the  formation  of  the 
dorsal  interossei  that  these  possess  an  almost  dorsal  position  in  the  hand.  They  are 
clearly,  however,  of  palmar  origin  and  are  supplied  by  pre-axial  nerves. 


612 


HUMAN   ANATOMY. 


i.   INTEROSSEI  VOLARES  (Fig.  589). 

Attachments. — The  volar  or  palmar  interossei  are  four  slender  muscles 
situated  in  the  intervals  between  the  metacarpal  bones  and  resting  upon  the  in- 
terossei dorsales.  Thejirst  and  second  muscles,  counting  from  the  radial  side,  arise 
from  the  ulnar  side  of  the  bases  of  the  first  and  second  metacarpals,  and  are  inserted 
into  the  ulnar  side  of  the  base  of  the  first  phalanx  and,  in  the  case  of  the  second 
muscle,  also  into  the  membranous  expansion  of  the  long  extensor  tendon  of  the 

FIG.  590. 


Extensor  carpi  ulnaris 
tendon 


Extensor  carpi  radialis  longior  tendon 


Extensor  carpi  radialis  brevior 
tendon 


Extensor  longus  pollicis 
tendon 


Second  dorsal  interosseus 

Third  dorsal  interosseus 
Fourth  dorsal  interosseus 


Extensor  communis 
digitorum  tendons 


Dissection  of  hack  of  hand,  showing  dorsal  interossei  and  insertion  of  extensorteiuluiis. 


corresponding  digit.  The  third  m&  fourth  muscles  arise  from  the  radial  side  of  the 
fourth  and  fifth  metacarpals,  and  are  inserted  similarly  to  the  second  muscle,  but 
into  the  radial  sides  of  the  fourth  and  fifth  digits. 

Only  three  palmar  interossei  are  usually  described  by  Kn-lish  anatomists,  the  muscle  in- 
cluded in  the  series  by  tin-  ( ierman  school  as  the  first  interosseus  ( ;//.  interosseus  f>i -hints  volaris} 
being  regarded  as  the  small  ulnar  head  of  the  flexor  hrevis  pollicis  (page  608).  The  inclusion 
of  this  muscle  in  the  series  of  palmar  interossei  is  warranted  by  its  morphological  relations. 

Nerve-Supply. — By  the  deep  division  of  the  ulnar  nerve  from  the  eighth 
cervical  and  first  thoracic  nerves. 

Action.— To  draw  the  first,  second,  fourth,  and  fifth  digits  towards  the  middle 
finger  and  to  flex  the  first  phalanx  of  the  same  digits. 


PRACTICAL   CONSIDERATIONS  :    WRIST   AND    HAND.          613 

Variations. — The  first  volar  interosseus  is  the  most  slender  of  the  series  and  is  covered  by 
the  oblique  portion  of  the  adductor  pollicis,  with  which  it  may  be  practically  incorporated. 
( )ccasionally  it  is  so  reduced  in  si/e  as  to  appear  to  be  wanting. 

2.    INTEROSSEI  DORSALES  (Fig.  590). 

Attachments. — The  dorsal  interossei  are  also  four  in  number  and  lie  in  the 
intervals  'between  the  metacarpal  bones,  dorsal  to  the  volar  interossei.  Each  is  a 
bipinnate  muscle  arising  from  the  adjacent  surfaces  of  the  metacarpals  which  bound 
the  interspace  in  which  the  muscle  lies.  The  first  and  second  muscles,  counting 
from  the  radial  side,  are  inserted  into  the  radial  side  of  the  base  of  the  rirst  phalanx 
and  into  the  membranous  expansion  of  the  extensor  tendons  of  the  second  and 
third  fingers,  while  the  third  and  fourth  are  inserted  similarly  into  the  radial  sides 
of  the  third  and  fourth  fingers. 

Nerve-Supply. — By  the  deep  division  of  the  ulnar  nerve  from  the  eighth 
cervical  and  first  thoracic  nerves. 

Action. — The  first  and  fourth  muscles  draw  the  second  and  fourth  fingers 
away  from  the  third,  while  the  second  and  third  draw  the  third  finger  radially  or 
ulnarly,  as  the  case  may  be.  All  the  muscles  flex  the  first  phalanx  of  the  digits  to 
which  they  are  attached. 

Variations. — Occasionally  the  second  dorsal  interosseus  is  inserted  into  the  base  of  the  first 
phalanx  of  the  index-finger,  upon  its  ulnar  side. 

(*)  THE   POST-AXIAL   MUSCLE. 

Normally  no  post-axial  muscles  exist  in  the  human  hand.  Occasionally,  however,  an  ex- 
tensor brevis  digitomtn  uianus  is  more  or  less  perfectly  developed.  It  arises  from  the  dorsum 
of  the  carpus,  or  sometimes  from  the  lower  end  of  the  radius  and  ulna,  and  passes  distally  into 
a  varying  number  of  tendons.  Most  frequently  the  muscle  is  small  and  gives  rise  to  but  a  single 
tendon,  which  joins  with  the  tendon  of  the  extensor  digitorum  communis  of  either  the  second 
or  third  digit.  Sometimes  two  tendons  occur,  passing  to  the  second  and  third  digits,  and  more 
rarely  three  have  been  observed,  passing  to  the  second,  third,  and  fourth  fingers.  In  a -single 
case  a  fourth  tendon  was  observed  which  terminated  upon  the  dorsal  surface  of  the  fifth 
metacarpal. 

PRACTICAL   CONSIDERATIONS. 

The  Wrist  and  Hand. — The  skin  of  the  wrist  and  of  the  back  of  the  hand  is 
thin  and  freely  movable  and  contains  numerous  hair-follicles  and  sebaceous  glands. 
These  structures  are  absent  in  the  palm  and  on  the  palmar  and  lateral  surfaces  of  the 
fingers,  as  well  as  on  the  dorsal  surface  of  the  terminal  phalanges.  Sudoriparous 
glands  are,  on  the  contrary,  relatively  more  numerous  in  the  palms  of  the  hands 
than  on  any  other  part  of  the  body  surface. 

These  anatomical  conditions  and  the  existence  of  the  subungual  and  periungual 
spaces  and  irregularities  render  the  sterilization  of  the  hands  for  surgical  purposes 
very  difficult. 

The  absence  of  hair-follicles  and  of  sebaceous  glands  explains  the  freedom  of 
the  palm  from  the  superficial  furuncular  infections  that  are  so  common  on  the  dorsum. 

In  the  palm  the  subcutaneous  connective  tissue,  like  that  in  the  plantar  region 
and  in  the  scalp  between  the  skin  and  aponeurosis,  is  very  dense.  This  similarity 
has  already  been  alluded  to  (page  491)  in  relation  to  the  absence  of  hair-follicles  in 
the  Uvo  former  regions  and  the  frequency  of  baldness  in  the  latter. 

On  the  dorsal  surface  the  subcutaneous  tissue  is  loose.  As  a  result,  in  whitlow, 
in  palmar  abscess,  in  hemorrhagic  extravasation,  in  oedema  or  cellulitis,  the  swelling 
is  apt  to  be  much  more  marked  on  the  dorsum  and  may  be  misleading  as  to  the 
real  seat  of  the  trouble.  Abscesses  immediately  beneath  the  palmar  fascia  will 
sometimes  point  in  a  metacarpal  space  on  the  dorsum. 

The  thickness  and  close  adhesion  of  the  skin  to  the  dense  fascia  beneath,  while 
admirably  protecting  the  vessels  and  nerves  of  the  palm  and  enabling  it  to  withstand 
pressure  and  friction,  greatly  increase  the  pain  in  cutaneous  or  subcutaneous  infections. 
On  account  of  this  same  adhesion,  superficial  wounds  of  the  palm  do  not  gape,  and 
heal  readily  if  non-infected  and  kept  at  rest. 


614 


HUMAN   ANATOMY. 


Ext.  carp,  ulnarls 

Posterior 
annular  ligamen 


Ext.  min.  digiti 

Ext.  communis 
et  indicis 


Extens.  carp.  rad. 
— long,  et  brev. 
r — Ext.  brevis  pollicis 
Ext.  ossis 
etacarpi  pollicis 

Ext.  Ipngus 
pollicis 


"  It  must  be  noted  that  the  front  of  the  hand,  and  especially  the  palm,  is  singu- 
larly free  from  surface  veins.  Indeed,  the  great  bulk  of  the  blood  from  the  hand  is 
returned  by  the  superficial  veins  on  the  dorsum  of  the  fingers  and  hand"  (Treves). 

The  annular  ligaments  at  the  wrist  are  of  importance  in  their  relation  to  the 
tendons  and  their  sheaths.  The  tendon-sheaths  (Fig.  591)  which  pass  through  the 
six  compartments  in  or  under  the  posterior  ligament  behave  as  follows.  .  i.  That 
for  the  short  extensors  and  the  extensor  of  the  metacarpal  bone  of  the  thumb  runs 
from  the  joint  between  the  first  metacarpal  and  the  trapezium  to  a  point  almost  an 
inch  above  the  styloid  process  of  the  radius.  2.  That  for  the  long  and  short  radial 

extensors  of  the  carpus  runs 

FIG.  591.  from  the  insertions  of  those 

muscles  to  a  point  a  half  inch 
above  the  ligament.  3.  That 
for  the  extensor  longus  pol- 
licis runs  from  the  insertion 
to  the  upper  border  of  the 
ligament.  4.  That  for  the 
extensor  indicis  extends  from 
the  upper  border  of  the  met- 
acarpus, and  that  for  the  ex- 
tensor communis  from  the 
middle  of  the  metacarpus, 
both  to  the  upper  border  of 
the  ligament.  5.  That  for 
the  extensor  minimi  digiti 
runs  from  the  middle  of  the 
metacarpus  ;  and  6,  that  for 
the  ulnar  extensor  of  the  car- 
pus from  the  insertion,  both 
to  the  upper  border  of  the 
ligament. 

Infective  disease  of  the 
dorsum  of  the  wrist  and  hand 
is  rare  as  compared  with  the 
palmar  surface.  The  dense 
connective-tissue  fibres  of  the 
palm  run  vertically  down- 
ward to  the  palmar  fascia 
and  tendon-sheaths,  and  thus 
convey  infection  directly  to 
the  deeper  parts.  This  layer 
is  often  described  as  the  su- 
perficial palmar  fascia.  The 
subcutaneous  connective-tis- 
sue fibres  on  the  dorsum  run 
horizontally,  and  infective  in- 
flammation is  therefore  more 
likely  to  remain  superficial 
(Warren).  If,  however,  it 
does  penetrate  and  gains 

access  to  the  tendon-sheaths,  the  natural  anatomical  limitations  are  those  indicated 
above. 

Teno-synovitis  from  strain,  from  gout,  or  from  rheumatism  is  especially  frequent 
in  these  sheaths,  on  account  of  their  exposure  to  wet  and  cold,  and  also  because  the 
muscles  connected  with  them  are  relatively  weak  and  are  less  often  used  than  those 
on  the  palmar  surface  of  the  forearm.  They  are  thus  more  liable  to  strain  from 
unaccustomed  exertion. 

(ianglion  of  the  simple-  (non-tuberculous)  variety  is  also  frequent  here,  pronably 
lor  the  same  reasons. 


\ 


Dissection  ot  dorsum  of  hand,  showing  artifi 

extensor  tendons. 


•ially  distended  sheaths  of 


PRACTICAL   CONSIDERATIONS  :    WRIST   AND    HAND. 


Bursa  surrounding  ten-, 
don  of  flexor  longus 
pollicis 


One  of  the  most  common  and  most  serious  of  the  sequelae  of  fracture  of  the 
lower  end  of  the  radius  is  stiffness  of  the  wrist  and  fingers  from  adhesions  of  these 
extensor  tendons  and  their  sheaths  to  the  bone,  to  each  other,  and  to  the  surrounding 
structures. 

It  is  important  to  remember,  as  Treves  has  pointed  out,  that  '  '  the  tendons  do 
not  lie  free  within  the  sac,  but  are  bound  to  it  by  folds  of  synovial  membrane  in 
much  the  same  way  as  the  bowel  is  bound  to  the  abdominal  parietes  by  its  mesen- 
tery (Fig.  492).  These  folds  may  be  ruptured  in  severe  sprains,  when  the  nutrient 
vessels  for  the  tendon,  which  are  contained  in  them,  may  be  torn.  Rupture  is  fol- 
lowed by  effusion  into  the  sac.  These  folds  are  almost  absent  within  the  digital  sheaths, 
the  slight  ligamenta 

longa  and  brevia,  near  FIG.  592. 

the  insertion  of  the 
tendons,  being  the  sole 
representatives.  Sy- 
novial sacs  are  lined  by 
endothelium,  and  have 
extremely  free  com- 
munication with  the 
lymphatic  vessels  of 
the  part.  Hence  the 
free  absorption  of  in- 
fective matter  from 
such  cavities.  '  ' 

The  arrangement 
of  the  synovial  sheaths 
beneath  the  anterior 
annular  ligament  is 
of  great  practical  im- 
portance (Fig.  592). 
There  are  two  sacs, 
one  for  the  tendons  of 
the  superficial  and  the 
deep  flexors  ;  one  for 
the  long  flexor  of  the 
thumb.  They  extend 
upward  to  about  two 
finger-breadths  above 
the  annular  ligament. 
Downward,  that  for 
the  thumb  extends  to 
the  insertion  of  the 
tendon  in  the  terminal 
phalanx  ;  the  divertic- 
ula  for  the  index,  mid- 
dle, and  ring  fingers 
end  about  the  mid- 
die  of  the  metacarpal 

4-U    4-  £        4.U      1'j.      Dissection  of  palmar  surface 

bones  ;  that  for  the  lit- 

tie  finger  accompanies 

the  tendon  of  the  deep   flexor  to   its   insertion   in  the  last  phalanx.     The  synovial 

sheaths  for  the  digital  portions  of  the  flexors  for  the  index,  middle,  and  ring  fingers 

extend  upward  only  to  about  the  necks  of  the  corresponding  metacarpal  bones.     They 

are  thus  separated  by  an  interval  of  from  half  an  inch  to  an  inch  from  the  synovial 

sac,  extending  up  under  the  annular  ligament  to  the  forearm  (Fig.  592). 

It  results  from  this  that  infections  (felons,  wounds,  etc.  )  of  the  thumb  or  little 
finger  are  especially  apt  to  extend  upward  above  the  wrist  and  involve  the  forearm. 

Compound  ganglion  (tuberculous  teno-synovitis)  frequently  affects  the  common 
svnovial  sac  of  the  flexor  tendons  and  not  infrequently  that  of  the  longus  pollicis. 


Digital  sheath: 
of  long  flexor 
tendons 


Anterior  annu- 
lar ligament 
(cut) 


-Palmar  bursa  sur- 
rounding long 
flexor  tendons 


Prolongation 

into  tendon 
sheath  of  lit- 
tle finger 


right  hand,  showing  artificially  distended  sheaths 

of  flexor  tendons. 


616  HUMAN   ANATOMY. 

The  two  sacs  occasionally  communicate  with  each  other.  On  account  of  the  density 
of  the  annular  ligament,  the  distention  has  a  central  constriction  and  expansions  in 
the  palm  and  above  the  wrist, — "  hour-glass  shape."  These  tendons  also  are  often 
involved  in  fractures  of  the  lower  end  of  the  radius,  although,  on  account  of  the  fact 
that  the  extensors  are  in  closer  relation  to  that  bone  than  is  the  deep  flexor,  and 
that  the  other  flexors — excepting  the  longus  pollicis — are  still  farther  separated  from 
it,  limitation  of  their  motion  is  neither  so  frequent  nor  so  marked. 

In  the  palm  of  the  hand  the  thenar  and  hypothenar  eminences  are  covered  in 
by  their  fasciae,  which  separate  them  from  the  central  space  of  the  palm  through 
which  the  flexor  tendons  run,  and  over  which  is  spread  the  fan-shaped,  deep  palmar 
fascia,  beginning  at  the  tendon  of  the  palmaris  longus  above,  and  spreading  out  to 
be  divided  below  into  the  slips  for  the  fingers  (Fig.  587).  Transverse  fibres  unite 
and  strengthen  these  slips,  which  send  fibres  also  to  the  sheaths  of  the  flexor  tendons 
and  to  the  skin. 

It  may  be  noted  here  that  progressive  muscular  atrophy  usually  begins  in  the 
hand  muscles,  affecting  first  those  of  the  thenar,  then  those  of  the  hypothenar  emi- 
nence, and  next  the  interossei.  When  the  latter  are  greatly  wasted  the  hand  assumes 
the  appearance  of  a  bird's  claw, — the  main  en  griff e  (Duchenne). 

Dupuytreri  s  contraction  affects  chiefly  the  digital  prolongations  of  the  palmar 
fascia,  although  it  extends  secondarily  to  the  bundles  of  fibres  uniting  the  skin  and  the 
aponeurosis.  It  begins  usually  as  a  dense  thickening  of  the  fascia  near  the  line  of 
the  metajcarpo-phalangeal  articulation.  It  extends  in  both  directions,  the  concomitant 
shortening  slowly  drawing  down  first  the  disfal  and  then  the  intermediate  phalanx. 
The  skin  becomes  closely  adherent  to  the  contracted  fascia.  The  condition  is  seen 
oftenest  in  hands  subjected  to  frequent  slight  tcaumatism,  as  in  laborers,  or  in  those 
of  gouty  or  rheumatic  persons  past  middle  age. 

Beneath  the  flexor  tendons,  and  above  the  interossei,  the  metacarpal  bones,  and 
the  radial  arch,  lies  another  layer  of  fascia  (interosseous)  which  resists  but  feebly 
the  passage  of  pus  towards  the  dorsum  of  the  hand.  It  is  connected  with  the  thenar 
and  hypothenar  fasciae. 

Several  varieties  of  palmar  abscess  have  been  described  (Tillaux)-  in  accord- 
ance with  the  original  site  of  the  infection,  the  spread  of  which  will  be  determined  by 
the  above-mentioned  anatomical  considerations,  (a)  Infection  just  beneath  the 
thick-  epidermis  causes  a  superficial  pustule  or  abscess  (subepidermic)  which,  if 
promptly  and  freely  opened,  gives  rise  to  no  difficulty.  (£)  Infection  beneath  the 
skin  (subdermic)  is  attended  by  more  pain,  and,  if  neglected,  may  penetrate  the 
aponeurosis  ;  but  it  is  separated  by  that  structure  from  the  synovial  sheaths  and 
cavities  ;  it  may  be  widely  opened  with  no  reference  to  the  latter  or  to  vessels  ;  it  is 
accompanied  by  little  or  no  swelling  on  the  dorsum  ;  it  has.  no  tendency  to  extend  up 
to  the  wrist  ;  movements  of  the  fingers  are  not  very  painful,  (r)  Subdermic  infec- 
tion beginning  in  the  spaces  just  above  the  interdigital  clefts  (i.e.,  between  the 
digital  slips  of  the  palmar  fascia)  may  extend  by  continuity  of  connective  tissue  very 
rapidly  to  the  dorsum  of  the  hand,  which  may  then  appear  to  be  thex  chief  seat  of  the 
infection  ;  the  symptoms  are  relatively  mild,  as  the  toxic  exudate  is  not  under  great 
pressure.  (d)  Subaponeurotic  infection  —  true  palmar  abscess  —  is  excessively 
painful,  extends  rapidly  to  the  dorsum  by  perforating  the  interosseous  fascia,  and 
often  to  the  front  of  the  wrist  and  forearm  by  following  up  the  flexor  tendons  ;  move- 
ments of  the  fingers  are  painful  ;  the  dorso-palmar  diameter  of  the  hand  is  vastly 
increased  ;  the  constitutional  symptoms  are  often  marked. 

Such  abscess  may  also  point  just  above  the  interdigital  webs  or  near  the  ulnar  or 
radial  borders  of  the  hand.  Early  incision  is  imperative  and,  if  made  over  the  line  of 
a  metacarpal  bone  and  limited  in  an  upward  direction  by  a  transverse  line  correspond- 
ing to  that  of  the  web  of  the  fully  extended  thumb  (to  avoid  the  digital  vessels  and 
palmar  arches),  may  be  made  freely.  Above  the  wrist  the  region  of  safety  is  just  to 
the  ulnar  side  of  the  palmaris  longus.  i 

On  the  fingers  the  skin  resembles  in  its  characteristics  that  of  the  hand.  On  the 
palmar  surface  of  the  first  and  second  phalanges  the -skin  and  the  subcutaneous  fat  are 
connected  with  the  dense  fibrous  sheath  of  the  flexor  tendons  by  vertical  connective- 
tissue  fibres,  and  at  the  level  of  the  joints — where  the  sheaths  are  lax  and  thinner— 


PRACTICAL   CONSIDERATIONS  :    WRIST   AND    HAND. 


617 


Head  of 
metacarpal  bone 

Abductor  poll 

Flexor. 
brevis  poll. 


Tendon  of  flex,  longus  poll. 

Adductor  poll.,  obi.  portion 


Dissection  of  metacarpo-phalangeal  dislocation  of  thumb. 


by  vessels  which  penetrate  the  sheath  to  supply  the  tendons.  Over  the  last  phalanx 
the  fibro-fatty  subcutaneous  layer — the  ' '  pulp' '  of  the  finger — lies  directly  upon  the 
periosteum. 

Infection  of  the  dorsum  of  a  finger  often  originates  near  or  about  the  root  of  a  nail 
(onychia)  and  may  involve  the  matrix  of  the  latter.  It  is  not  under  much  pressure, 
and  is  therefore  not  usually 

serious,  although  through  the  FIG.  593. 

veins  and  lymphatics  it  may 
exceptionally  extend  rapidly 
up  the  arm. 

Infection  of  the  palmar 
surface  of  a  finger  (panaritium, 
paronychia,  whitlow,  felon)  is 
of  two  chief  varieties  :  (a) 
subcutaneous,  in  which  the 
symptoms  are  at  first  limited 
to  the  seat  of  infection  and  are 
superficial,  although,  as  it  is  a 
true  cellulitis,  they  may  ex- 
tend to  the  dorsum  or  towards 
the  palm  ;  and  (b)  thecal,  with 
more  severe  pairi,  greater  lim- 
itation of  flexion,  and  more 
rapid  extension  upward. 

If  the  felon  involves  the 
distal  portion  of  the  finger,  the  close  relation  of  the  "pulp"  and  the  periosteum  of 
the  last  phalanx  makes  necrosis  of  that  bone  frequent,  although  its  upper  part  usually 
escapes  because  (a')  it  is  an  epiphysis  ;  (<£)  the  insertion  of  the  tendon  of  the  deep 
flexor  probably  keeps  up  its  blood-supply  (Treves). 

The  absence  of  the  tendon-sheath  over  the  body  and  tip  of  the  last  phalanx  pre- 
vents the  conversion  of  the  subcutaneous  into  the  thecal  variety,  unless  the  infection, 
extends  upward  as  far  as  the  base  of  the  phalanx. 

Elsewhere  the  thecal  variety  often  results  from  extension  from  a  subcutaneous 
focvis  by  the  vertical  connective-tissue  fibres  and  the  vessels  already  mentioned.  The 
interphalangeal  joints  are  often  affected  because  it  is  opposite  them  that  (a)  the 

tendon-sheaths    are    thinnest    and 

FIG.  594.  ((£)  the  vessels  enter.      In  infection 

of  the  tendon-sheaths  of  the  index, 
middle,  and  ring  fingers  the  upward 
extension  is  arrested,  at  .least  for 
a  time,  about  opposite  the  necks 
of  the  metacarpal  bones.  If  the 
thumb  or  little  finger  is  involved, 
the  infection  is  likely  to  spread  to 
a  higher  level  (page  615). 

The  so-called  ' '  subcuticular' ' 
felon  is  a  superficial  pustule,  while 
the  "  subperiosteal"  felon  may 
either  result  from  extension  of  the 
foregoing  varieties  or  may  be  origi- 
nally an  infective  osteo-periostitis 
or  osteo-myelitis. 

In  relation  to  amputation  of 
the  finger  it  may  be  noted  that  the 
insertion  of  the  flexor  sublimis  tendon  into  the  sides  of  the  second  phalanx  renders 
amputation  at  the  metacarpo-phalangeal  joint  often  more  satisfactory  in  its  results 
than  one  done  through  the  first  phalanx  or  first  interphalangeal  joint. 

Dislocation  of  the  first  phalanx  of  the  thumb  upon  the  dorsum  of  its  metacarpal 
bone  requires  special  mention  on  account  of  the  difficulty  of  reduction.  It  has  been 


Dissection  showing  position  of  bones  in  dislocation  of  thumb 


618  HUMAN   ANATOMY. 

attributed  (a)  to  the  gripping  of  the  neck  of  the  metacarpal  bone  between  the 
flexor  brevis  pollicis  and  the  oblique  portion  of  the  adductor  pollicis  (these  often 
being  considered  as  the  two  heads  of  the  flexor  brevis  pollicis)  ;  (b)  to  a  similar 
entanglement  of  the  head  and  neck  in  the  slit  in  the  capsule  ;  (c)  to  the  winding  of 
the  tendon  of  the  flexor  longus  pollicis  around  the  neck  of  the  bone  ;  and  (d)  to 
the  interposition  of  the  gleno-sesamoid  plate.  Of  these  theories  the  last  two  seem 
to  offer  the  most  satisfactory  explanation  of  the  difficulties  met  with  in  attempts  at 
replacement. 

The  Surface  Landmarks  of  the  Upper  Extremity. — The  axilla  (page  574) 
is  very  distinctly  bounded  anteriorly  by  the  lower  border  of  the  pectoralis  major,  which 
runs  in  the  line  of  the  fifth  rib  from  the  sixth  costal  cartilage  to  the  external  bicipital 
ridge  ;  posteriorly  by  the  lower  edge  of  the  latissiums  dorsi  and  teres  major,  extend- 
ing to  the  bicipital  groove.  The  shape  of  the  axillary  fossa  varies  with  the  position 
of  the  arm,  becoming  deeper  when  the  arm  is  raised  at  a  right  angle  to  the  trunk  or 
when  the  great  pectoral  and  latissimus  are  contracted.  With  the  arm  still  farther 
elevated,  the  depth  of  the  space  decreases  as  traction  on  those  muscles  approximates 
the  axillary  borders  and  the  humeral  head  enters  and  partly  obliterates  the  cavity. 
With  the  arm  close  to  the  thorax,  the  third  rib  may  be  reached  by  the  exploring 
finger.  The  concavity  of  the  space  is  lessened  or  effaced  by  glandular  tumors,  effu- 
sions of  blood,  or  collections  of  pus  (page '582).  In  opening  an  axillary  abscess  it 
should  be  remembered  that  the  inner  or  thoracic  wall  is  the  direction  of  safety  so  far 
as  the  great  vessels  are  concerned. 

In  the  region  of  the  shoulder  the  rounded  surface  is  produced  by  the  thick 
deltoid  muscle  spread  over  the  greater  tuberosity  of  the  humerus.  It  is  fuller  anteri- 
orly than  posteriorly,  partly  on  account  of  the  presence  of  the  lesser  tuberosity  in 
the  former  position,  but  chiefly  because  the  hinder  portion  of  the  muscle  is  thinner 
than  the  fore  part  and  because  of  its  close  attachment  to  the  infraspinatus  fascia  and 
muscle.  The  greatest  width  of  the  shoulders  does  not  correspond  to  the  points  at 
which  the  deltoid  muscles  overlap  the  head  of  the  humerus,  but  is  at  the  level  of  the 
lower  border  of  the  anterior  axillary  fold, — i.e. ,  on  the  level  of  the  point  at  which 
the  various  bundles  of  deltoid  fibres  are  gathered  together  to  pass  to  their  insertion 
(Thomson).  The  bony  points  in  this  region  have  been  described  (pages  270,  279, 
280).  The  anterior  border  of  the  deltoid  presents  a  rounded  eminence  bounded 
internally  above  by  the  infraclavicular  fossa  (vide  infra}  and  below  by  the  closely 
applied  outer  margin  of  the  pectoralis  major.  In  the  shallow  groove  between  these 
two  muscles  the  cephalic  vein  and  a  branch  of  the  acromio-thoracic  artery  are  to  be 
found.  Just  external  to  the  groove  under  the  inner  fibres  of  the  deltoid  is  the  cora- 
coid  process  (page  255).  The  infraclavicular  fossa  is  the  triangular  interval'bounded 
by  the  outer  fibres  of  the  pectoralis  major  internally,  the  inner  fibres  of  the  deltoid 
externally,  and  the  clavicle  above.  The  surface  depression  known  by  this  name  may 
be  much  larger  than  this  intermuscular  interval,  and  may  almost  correspond  in  extent 
to  the  roof  of  the  superficial  infraclavicular  triangle  (page  581).  It  is  not  very  marked 
in  muscular  subjects.  It  is  effaced — owing  to  tension  of  fascia  and  muscles — in  sub- 
coracoid  luxation  of  the  humerus,  or  in  fracture  of  the  clavicle  with  marked  displace- 
ment of  the  fragments.  It  may  be  converted  into  a  rounded  elevation  by  glandular 
growths  extending  upward  from  the  axilla,  or  by  the  head  of  the  humenis  in  intra- 
coracoid  (infraclavicular)  luxation.  At  the  bottom  of  this  fossa,  just  within  the  cora- 
coid  process, — i.e.,  not  far  from  the  middle  of  the  clavicle, — the  first  portion  of  the 
axillary  artery  may  be  compressed  against  the  second  rib  by  pressure  directed  back- 
ward and  a  little  inward,  the  patient  being  supine. 

The  posterior  border  of  the  deltoid  above  is  tendinous,  is  closely  attached  tc 
the  infraspinatus  muscle  beneath  it,  and  is  scarcely  discernible.      Below  it  is  thick* 
and  presents  a  well-marked  rounded  eminence  which  inclines  from  behind  forward  t< 
meet  the  anterior  border  at  the  middle  of  the  outer  side  of  the  arm,  where  a  distinct 
depression  indicates  the  insertion  of  the  deltoid  (Fig.  595).     This  depression  is  a  valu- 
able practical  landmark  for  the  reasons  that  :   (  i  )   It  corresponds  to  the  middle  of  the 
shaft  of  the  hunicnis,  where  tin-  two  curves  of  the  bone  unite  and  where  the  cylin- 
drical joins  the  prismatic  part  of  the  shaft,  which  is  there  smallest,  hardest,  and  least 
elastic  (page  272),  and  hence  is  most  frequently  broken.     (  2)  It  indicates  the  region 


PRACTICAL   CONSIDERATIONS  :    SURFACE   LANDMARKS.     619 


of  insertion  of  the  deltoid  and  coraco-brachialis,  and  embraces  part  of  the  origin 
of  the  brachialis  anticus  and  internal  head  of  the  triceps,  and  is  therefore,  and  on 
account  of  the  intimate  attachment  of  the  periosteum  (page  272),  a  not  uncommon 
seat-of  exostoses.  (3)  The  region  is — by  reason  of  the  close  relation  of  these  mus- 
cles to  the  bone — a  frequent  seat  of  ununited  fracture  (page  273).  (4)  The  nutrient 
artery  enters  the  bone  and  the  superior  profunda  artery  and  musculo-spiral  nerve 
wind  around  its  posterior  surface  at  that  level,  at  which  also  the  lesser  internal  cuta- 
neous nerve  and  the  basilic  vein  penetrate  the  deep  fascia,  the  median  nerve  crosses 
the  brachial  artery,  and  the  ulnar  nerve  leaves  it. 

On  the  outer  surface  of  the  arm  below  the  insertion  of  the  deltoid  can  be  seen 
the  shallow  furrow  (Fig.  596)  between  the  outer  head  of  the  triceps  and  the  brachio- 
radialis  which  indicates  the  position  of  the  external  intermuscular  septum  and  of  the 
external  supracondyloid  ridge  (page  273)  . 

On  the  posterior  surface  of  the  arm  the  three  heads  of  the  triceps  can  be  seen 
when  the  forearm  is  strongly  extended  (Fig.  596).  The  outer  head  makes  a  distinct 
prominence  just  beneath  the  posterior  border  of  the  deltoid  ;  the  inner  head 
is  less  distinct  ;  the  long  head  conies  into  view  where  it  descends  from  between  the 
two  teres  muscles,  and  lower  in  the  arm — where  it  has  become  tendinous — is  indi- 
cated by  a  broad,  shallow  depression  ending  at  the  olecranon.  The  long  and  outer 
heads  cover  the  musculo-spiral  nerve  and  superior  profunda  artery  from  just  beneath 
the  posterior  axillary  fold  to  the  point  where  they  perforate  the  external  septum. 

On  the  anterior  and  inner  surfaces  of  the  arm  the  rounded  swell  of  the  biceps 
and  the  external  and  internal  bicipital  furrows  are  the  most  important  landmarks. 


FIG.  595. 


Deltoid 


U   Tendon  of  palmaris 

longus 
Transverse  furrows 


Brachial 

Triceps,  long      artery 
and  inner  heads 


Pectoralis 
major 


Antero-median  surface  of  right  arm,  showing  modelling  on  living  subject. 


The  elevation  of  the  biceps  shades  off  superiorly  into  the  narrower  and  less  distinct 
prominence  of  the  coraco-brachialis  where  it  comes  into  view  below  and  beneath  the 
anterior  axillary  fold.  Inferiorly  it  narrows  externally  and  merges  into  the  biceps 
tendon,  easily  seen  passing  into  the  forearm  in  the  deep  interval  between  the  rounded 
supinator  and  extensor  mass  on  the  radial  side  and  the  pronator  and  flexor  mass  on 
the  ulnar  side  (Fig.  595).  Internally  the  broader  flat  slip  of  bicipital  fascia — the 
inner  tendon — may  be  seen  with  its  sharp  upper  edge  when  the  forearm  is  semi- 
flexed  and  the  biceps  is  in  strong  action.  The  outer  bicipital  furrow  indicates  the  posi- 
tion of  the  subcutaneous  cephalic  vein.  The  inner  and  deeper  furrow  marks  the 
line  of  the  basilic  vein  (subcutaneous  in  its  lower  half,  then  subfascial),  of  the  median 
nerve  and  the  brachial  vessels,  and  in  its  upper  half  of  the  ulnar  nerve.  To  the  outer 
side  of  the  outer  furrow  from  above  downward  lie  the  deltoid,  the  outer  head  of  the 
triceps,  the  outer  portion  of  the  brachialis  anticus  and  the  brachio-radialis,  and  the 
common  extensor  mass  (Fig.  596).  To  the  inner  side  of  the  inner  furrow  are  seen  the 
coraco-brachialis,  the  long  head  and  then  the  inner  head  of  the  triceps,  the  brachialis 
anticus,  and  the  pronato-flexor  mass. 

At  the  bend  of  the  elbow  anteriorly  the  subcutaneous  veins  are  often  visible. 
Their  arrangement  is  sufficiently  described  and  figured  elsewhere  (page  892, 
Fig.  764).  The  bicipital  fascia  passes  between  the  median  basilic  vein  and  brachial 
artery,  and,  by  springing  from  the  inner  edge  of  the  biceps  tendon,  makes  that  edge 


620 


HUMAN   ANATOMY. 


less  distinct  to  both  sight  and  touch  than  the  outer  edge.  Just  within  the  inner 
edge  is  the  brachial  artery  and  farther  in  the  median  nerve. 

The  fold  of  the  elbow  is  a  transverse  crease  in  the  skin,  seen  in  flexion,  convex 
downward,  and  running  from  the  tip  of  one  condyle  to  the  tip  of  the  other.  lulies 
above  the  line  of  the  elbow-joint.  In  dislocation  of  the  radius  and  ulna  backward 
the  lower  end  of  the  humerus  is  below  this  crease  ;  in  fracture  of  the  humerus  above 
the  condyles  the  lower  end  of  the  upper  fragment  is  either  on  a  line  with  or  above 
the  crease.  This  relation  will  not  be  demonstrable  in  the  presence  of  much  swelling, 
as  this  fold  is  then  obliterated. 

On  the  front  of  the  forearm,  below  the  apex  of  the  triangular  space  resulting  from 
the  convergence  of  the  two  muscular  masses  descending  from  the  condylar  regions, 
there  are  no  salient  surface  landmarks,  and  none  of  great  practical  importance  until 
the  wrist  is  reached.  Many  of  those  of  that  region  and  of  the  hand  have  been  de- 
scribed (pages  228,  229,  230,  320).  It  should,  however,  be  noted  that,  instead  of 
being  flattened  from  before  backward  and  widest  from  side  to  side  as  when  in  the 
supine  position,  the  forearm  when  the  hand  is  pronated  becomes  rounded  and  its 
antero-posterior  slightly  exceeds  its  lateral  thickness  (Thomson).  This  is  due  to 
the  fact  that  the  tendons  of  the  supinator  and  extensor  masses  are  held  in  grooves 
in  the  lower  end  of  the  radius  by  the  posterior  annular  ligament,  and  are  thus  car- 
ried towards  the  ulna  when  the  radius  moves  in  that  direction. 


Outer  head  of  triceps 


FIG.  596. 

Brachialis  anticus 

External  bicipital  furrow 
Brachio-raclialis 

Common  extensor 


Anconeus 


Extensors 
of  thumb 


Extensor  longus  pollicis 


Olecranon   Ulna 
Internal  condyle 

Posterior  surface  of  arm  shown  in  preceding  figure. 


Ulnar  styloid  process 


Of  the  two  transverse  furrows  on  the  flexor  surface  of  the  wrist  the  lower  is  the 
more  marked.  It  is  almost  three-quarters  of  an  inch  below  the  summit  of  the  upward 
curve  of  the  wrist-joint,  is  on  the  line  of  the  intercarpal  joint  and  of  the  upper  border 
of  the  anterior  annular  ligament,  and  is  about  a  half-inch  above  the  carpo-metacarpal 
joint.  'At  the  wrist  the  palmaris  tendon — when  present — is  made  prominent  by 
extending  the  digits,  slightly  flexing  the  wrist,  and  closely  approximating  the  thenar 
and  hypothenar  eminences.  To  its  radial  side  from  within  outward  lie  the.  median 
nerve,  the  tendon  of  the  flexor  carpi  radialis,  and  the  radial  artery.  To  its  ulnar 
side  lie  first  the  rounded  elevation  made  by  the  flexor  sublimis  tendons,  then  the  ulnar 
artery,  and  then  the  flexor  carpi  ulnaris  tendon,  made  easily  palpable,  although  not 
very  prominent,  by  strong  flexion  of  the  wrist  and  little  linger. 

On  the  postero-lateral  aspect  of  the  forearm  may  be  seen  : 

1.  The  elevation  of  the  anconeus,  triangular  in  shape,  to  the  radial  side  of  tin- 
posterior  subcutaneous  surface  of  the   olecranon   and   separated    from    tin-   common 
extensor  mass  by  a  well-defined  depression.     This  muscle  and  the  expansion  of  the 
triceps  tendon  that  covers  it  are  of  great  value  in  the  movement   of  extension  of  the 
forearm  after  excision  of  the  elbow. 

2.  The  curved  border  of  the  ulna  (subcutaneous  in  stipulation),  at  the  bottom 
of   the-   it  I iiar  ft/ >>•(>;>',  between  the  flexor  carpi  ulnaris  and  the    common   extensor 
group,  is  easily  accessible  for  examination  through  its  whole  length  (page  289). 

3.  The    very    important  depression  just  below  the  external   condyle  and  exter- 
nal to  the  olecranon  has  been  described  (page  296). 


PRACTICAL   CONSIDERATIONS  :    SURFACE    LANDMARKS.      621 

4.  The  oblique  elevation  beginning  at  the  lower    third    of  the  forearm  in  the 
interval  left  by  the  divergence  of  the  supinator  and  the  common  extensor  muscles, 
and    running   do\vmvard   and   outward,  to   be   lost   on    the   posterior   surface   of   the 
thumb,    represents  the  extensors  of    the  thumb    crossing  over  the  tendons  of   the 
extensores  carpi  radialis  longior  and  brevior  to  their  points  of  insertion  (Fig.  582). 

5.  The  bony  points  to  be  seen  and  felt  at  the  elbow  and  wrist  have  been  de- 
scribed in  their  practical   relations  in  connection  with  the  bones  and  joints   (pages 
287,  296,  308,  320,  330).      The  tendon  most  easily  identified  on  the  dorsum  of  the 
wrist  is  that  of  the  extensor  longus  pollicis  when  the  thumb  is  strongly  extended  and 
abducted.      It  is  the  posterior  or  inner  boundary  of  the  hollow  at  the  base  of  the 
thumb  (  vide  infra),  and  its  groove  in  the  lower  end  of  the  radius  is  about  the  middle 
of  the  posterior  surface  and  just  to  the  ulnar  side  of  the  prominent  middle  thecal 
tubercle, — a  useful  landmark  (page   296).      The  tendon,  just  before   it  reaches  the 
radius,  corresponds  approximately  to  the  scapho-semilunar  joint. 

The  surface  markings  of  the  palm  of  the  hand  are  often  valuable  landmarks. 

The  most  important  are  :  (i)  The  triangle  called  the  "  hollow  of  the  hand,"  the 
"  cup  of  the  palm,"  etc.,  the  base  of  which  corresponds  to  the  three  elevations  oppo- 
site the  interdigital  clefts, — formed  by  protrusion  of  fat  between  the  flexor  tendons 
and  the  digital  slips  of  the  palmar  fascia  and  by  the  distal  extremities  of  the  lumbri- 
cales, — and  seen  best  when  the  metacarpo-phalangeal  joints  are  extended  and  the 
interphalangeal  joints  are  flexed.  The  sides  of  the  triangle  are  formed  by  the  thenar 
and  hypothenar  eminences.  Over  this  palmar  hollow  the  intimate  connection  of  the 
skin  and  fascia  is  of  practical  importance  (page  613).  (2)  The  chief  cutaneous 
creases  (Fig.  597)  are  four  in  number  :  (a)  from  just  above  the  apex  of  the  palmar 
triangle  to  the  radial  side  of  the  hand  above  the  base  of  the  index-finger  ;  (b)  from 
the  lower  end  of  a  to  a  point  a  little  above  the  middle  of  the  ulnar  border  of  the  palm, 
which  it  does  not  quite  reach  ;  (_c)  from  about  the  junction  of  the  lower  fourth 
with  the  upper  three-fourths  of  the  ulnar  border  of  the  palm  to  a  point  a  little  above 
the  cleft  between  the  index  and  middle  fingers;  (d)  from  b  tor,  often  extending 
upward  towards  the  wrist  and  downward  towards  the  base  of  the  middle  finger. 
a  and  d  are  longitudinal,  the  former  being  caused  by  adduction  of  the  first  meta- 
carpal,  the  latter  by  adduction  of  the  fifth  metacarpal  bone,  both  movements  being 
towards  the  mid-line  of  the  hand  ;  b  and  c  are  transverse,  and  are  produced  chiefly 
by  flexion  (6)  of  the  first  and  second  (r)  of  the  three  inner  metacarpo-phalangeal 
joints. 

a  represents  the  inner  border  of  the  thenar  eminence  and  therefore,  approxi- 
mately, of  the  outer  group  of  the  short  muscles  of  the  thumb  and  the  inner  margin  of 
the  fascia  intervening  between  them  and  the  palmar  space  through  which  run  the 
flexor  tendons.  It  intersects  the  deep  palmar  arch  at  about  the  highest  point  where 
it  crosses  the  metacarpal  bone  of  the  middle  finger. 

b,  at  the  centre  of  the  palm,  where  it  is  intersected  by  d,  crosses  the  same 
metacarpal  bone  a  line  or  two  below, — i.e. ,  nearer  the  fingers  than  the  superficial 
palmar  arch,  which  runs  about  on  a  curved  line  from  the  lower  border  of  the  thumb, 
when  it  is  at  right  angles  to  the  hand,  to  the  pisiform  bone.  The  deep  palmar  arch 
is  from  a  quarter  to  a  half  an  inch  nearer  the  wrist. 

c  represents  the  upper  limits  of  the  synovial  sheaths  of  the  flexor  tendons  of 
the  index,  middle,  and  ring  fingers,  is  a  little  above  the  division  of  the  palmar  fascia 
into  the  digital  slips  and  the  bifurcation  of  the  digital  arteries,  crosses  the  necks  of 
the  three  inner  metacarpal  bones,  and  is  as  much  above  the  corresponding  meta- 
carpo-phalangeal joints  as  they  are  above  the  webs  of  the  fingers. 

d,  at  its  upper  portion,  irregularly  outlines  the  outer  border  of  the  hypoth- 
enar eminence, — i.e.,  of  the  short  muscles  of  the  little  finger  and  of  the  fascia  sepa- 
rating them  from  the  central  space  of  the  palm, — but  it  is  the  most  irregular  and 
unimportant  of  these  creases.  The  transverse  folds  on  the  palmar  surfaces  of  the 
fingers  correspond,  the  highest  to  the  web  of  the  fingers, — i.e. ,  from  one-half  to  three- 
quarters  of  an  inch  below  the  metacarpo-phalangeal  joint, — the  middle  to  the  proxi- 
mal interphalangeal  joint,  and  the  lowest  to  a  line  a  little  above  the  distal  interpha- 
langeal joint.  On  .the  thumb  the  line  of  the  radial  side  of  the  index-finger,  if 
continued  upward,  almost  coincides  with  the  higher  of  the  creases,  which  crosses  the 


622 


HUMAN    ANATOMY. 


metacarpo-phalangeal  joint  obliquely.  The  lower  crease  corresponds  to  the  inter- 
phalangeal  joint.  The  papillary  ridges  of  the  skin  covering  the  terminal  phalanges 
assume  varied  curves  and  form  patterns, — immutable  and  characteristic  in  the  indi- 
vidual,— impressions  of  which  have  been  used  of  late  years  for  purposes  of  identifica- 
tion of  criminals. 

On  the  dorsum  of  the  hand  the  hollow  at  the  base  of  the  thumb  (the  so-called 
"snuff-box")   is  bounded  externally  ( radially )  by  the  tendon  of  the  extensor  of  the 

FIG.  597. 


VI 


Surface  markings  of  rijfht   palm. 


metacarpal  bone  of  the  thumb  and  the  short  extensor,  and  internally  by  the  tendon  of 
the  long  extensor  (Fig.  ,s*-M.  The  radial  artery,  a  large  vein, — cephalic  vein  of 
the  thumb  (Treves), — and  the  inner  division  of  the  radial  nrrvr  cross  this  space. 
Beneath  it  are  the  scaphoid  and  trapezium  and  the  articulation  between  the  latter 
and  the  first  metacarpal  bone. 

The  abductor  indicis  muscle  makes  a  distinct  fusiform  prominence  when  the 
thumb  is  adducted.  The  tendons  of  the  common  extensor  and  of  the  extensor  of  the 
little  finger  and  the  slip  connecting  them  may  be  seen. 

It  should  be  remembered  that  the  "knuckles"  are  at  each  joint,  the  distal 
extremities  of  the  proximal  bones  entering  into  the  articulation. 


THE   MUSCLES   OF   THE   LOWER    LIMB.  623 


THE  MUSCLES  OF  THE   LOWER   LIMB. 

In  describing  the  muscles  of  the  lower  limb  a  classification  similar  to  that  which 
was  employed  for  the  upper  limb  muscles  will  be  followed.  Owing,  however,  to  the 
firm  articulation  of  the  innominate  bones  to  the  sacrum,  the  muscles  extending 
between  the  axial  skeleton  and  the  pelvic  girdle  are  greatly  reduced,  and  those 
(such  as  the  psoas)  which  might  be  included  in  this  group  are  continued  to  the 
femur,  and  for  present  purposes  are  more  conveniently  grouped  with  the  muscles 
extending  from  the  girdle  to  the  femur. 

There  is  also,  in  the  lower  limb,  a  greater  number  of  muscles  passing  over  two 
joints  ;  indeed,  many  of  the  muscles  which  are  inserted  into  the  upper  portions  of 
the  leg  bones  take  their  origin  from  the  pelvic  girdle.  Most  of  these  seem  to  be, 
primarily,  members  of  the  femoral  group  of  muscles  and  will  be  so  classified  in  the 
succeeding  pages,  but  one  (the  gracilis),  at  least,  appears  to  belong  to  the  group 
extending  from  the  girdle  to  the  femur. 

THE   MUSCLES    EXTENDING   FROM   THE   PELVIC   GIRDLE 

TO  THE  FEMUR. 

(a)   THE   PRE-AXIAL  MUSCLES. 

1.  Psoas  magnus.  6.  Adductor  brevis. 

2.  Iliacus.  7.  Adductor  magnus. 

3.  Pectineus.  8.  Quadratus  femoris. 

4.  Gracilis.  9.  Obturator  externus. 

5.  Adductor  longus.  10.  Obturator  internus. 

ii.    Gemelli. 

i.    PSOAS  MAGNUS  (Fig.   598). 

Attachments. — This  muscle  (m.  psoas  major)  arises  from  the  sides  of  the 
bodies  of  the  twelfth  thoracic  and  all  the  lumbar  vertebrae  and  from  the  transverse 
processes  of  the  lumbar  vertebrae.  Its  fibres  pass  directly  downward  and  slightly 
forward  over  the  superior  ramus  of  the  pubis  and  are  inserted  by  a  tendon,  in  com- 
mon with  the  iliacus,  into  the  lesser  trochanter  of  the  femur. 

Nerve-Supply. — By  branches  from  the  lumbar  plexus  from  the  second,  third, 
and  fourth  lumbar  nerves. 

Action. — To  bend  the  spinal  column  laterally  and  to  flex  the  body  and  pelvis 
upon  the  femur.  Acting  from  above,  it  flexes  the  thigh  and  rotates  it  outward. 

Relations. — The  psoas  magnus  lies  along  the  side  of  the  lumbar  vertebrae, 
resting  upon  their  transverse  processes  and  the  medial  portion  of  the  quadratus 
lumborum.  Extending  as  high  as  the  last  thoracic  vertebra,  it  passes  beneath  the 
internal  arcuate  ligament,  or  medial  lumbo-costal  arch,  of  the  diaphragm,  and  below 
it  passes  beneath  Poupart's  ligament  to  reach  the  thigh.  In  its  abdominal  portion 
it  is  in  relation  ventrally  with  the  peritoneum,  on  the  right  side  with  the  ascending 
colon  and  duodenum,  and  on  the  left  side  with  the  descending  colon  and  pancreas. 
The  inner  border  of  the  kidney  overlaps  the  lateral  portion  of  the  muscle,  and  the 
ureter  and  spermatic  (or  ovarian)  arteries  descend  obliquely  along  it.  The  inferior 
vena  cava  lies  in  front  of  the  right  muscle.  The  nerves  formed  by  the  lumbar 
plexus  perforate  the  muscle,  and  the  genito-crural  nerve  passes  down  on  its  anterior 
surface.  In  the  pelvis  the  external  iliac  vessels  lie  along  its  medial  border,  and  it  is 
crossed,  just  before  it  passes  beneath  Poupart's  ligament,  by  the  vas  deferens.  In 
the  thigh  it  forms  a  portion  of  the  floor  of  the  femoral  or  Scarpa's  triangle,  and  lies 
between  the  iliacus  and  pectineus  muscles,  behind  the  femoral  vessels.  As  the  ten- 
don which  is  common  to  it  and  the  iliacus  passes  over  the  hip-joint  it  rests  upon  a 
rather  large  bursa  Omrsa  iliopectinea) ;  just  above  the  insertion  a  second  bursa  (bursa 
iliaca  subtendinea)  intervenes  between  the  tendon  and  the  femur. 


624 


HFMAN   ANATOMY. 


The  psoas  magnus  appears  to  be  formed  by  the  union  of  a  hyposkeletal  trunk  muscle  with 
a  femoral  muscle,  the  remaining  portions  of  which  are  represented  by  the  iliacus  and  pectineus. 
It  is  interesting  to  note  in  tliis  connection  that  in  those  mammalia  in  which  the  quadratus  lum- 
borum  is  well  developed  the  psoas  magnus  is  correspondingly  weak,  and  vice  versa. 

The  psoas  parrns  or 

FIG    SQ8  minor  ( Fig.  .598  )  is  a  long, 

flat  muscle  which  lies  upon 
the  ventral  surface  of  the 
psoas  magnus,  represent- 
ing a  separated  portion  of 
it,  and  is  present  in  sonic- 
thing  over  50  per  cent,  of 
cases.  It  arises  from  the 
bodies  of  the  last  thoracic 
and  first  lumbar  vertebrae 
and  is  inserted  into  about 
the  middle  of  the  ilio-pec- 
tineal  line  (linea  termina- 
lis)  of  the  pelvis. 


External 
arcuate  ligament 


XII  rib 


Internal 
arcuate  ligament 


Psoas 
parvus 


Quadratus  — 
lumborum 


superior  spine 
of  ilium 


Pyriformis 


Gluteus  medius — 


Tensor  fasciae  - 
latae 


— Symphysis 
pubis 


2.  ILIACUS  (Fig.  598). 

Attachments. — 
The  iliacus  arises  from 
about  the  upper  half  of 
the  anterior  surface  of 
the  ilium.  Its  fibres 
converge  downward  to 
form  a  common  tendon 
with  the  psoas  major, 
which  is  inserted  into 
the  lesser  trochanter  of 
the  femur. 

Nerve-Supply.— 
By  the  anterior  crural 
nerve  from  the  second, 
third,  and  fourth  lum- 
bar nerves. 

Action. — To  flex 
the  thigh  and  rotate  it 
slightly  outward ;  when 
the  thigh  is  fixed,  to 
flex  the  pelvis  and  trunk 
upon  the  femur. 

Relations. —  The 
iliacus  covers  the  pos- 
terior wall  of  the  false 
pelvis,  and  upon  the 
right  side  has  resting 
upon  it  the  caecum  and 
on  the  left  side  the 
sigmoid  colon.  It  is 
crossed  obliquely  by 

the  external  cutaneous  and  the  anterior  crural  nerves ;  its  inner  border  is  covered 
by  the  psoas  magntis.  It  passes  beneath  Poupart's  ligament  external  to  the  psoas 
magnus,  its  relations  in  the  thigh  being  identical  with  those  of  that  muscle.  ' 

Variations. — The  iliacus  and  psoas  magnus  are  not  infrequently  extensively  united,  and 
the  two  muscles,  together  with  tin- psoas  parvus,  when  this  is  present,  are  frequently  spoken  of 
as  the  m.  i/io-/>soas.  The  fibres  of  the  iliacus  which  arise  from  the  posterior  superior  spine 
of  tlie  ilium  are  often  separated  from  the  rest  of  the  muscle  to  form  an  ///</< ~ns  minor,  which  is 
inserted  into  the  capsule  of  the  hip-joint  or  into  the  anterior  intertrochanteric  line. 

The  Iliac  Fascia. — This  fascia  is  a  strong  sheet  of  connective  tissue  which 
covers  the  entire  ilio-psoas.  Above  it  is  attached  to  the  internal  arcuate  ligament  oi 


•IVVtineus.  cut  and 
turned  down 


—  Aclductor  magnus 


Deep  dissection  of  posterior  body-wall  and  iliac  fossa  of  right  side. 


THE   MUSCLES   OF   THE    LOWER   LIMB. 


625 


the  diaphragm,  and  thence  descends  over  the  anterior  surface  of  the  psoas.  On  reach- 
ing the  level  of  the  crest  of  the  ilium,  it  is  prolonged  outward  along  that  structure, 
where  it  is  in  connection  with  the  lower  edge  of  the  transversalis  fascia.  It  descends 
thence  over  the  anterior  surface  of  the  psoas  and  iliacus,  at  the  inner  border  of  the 
former  muscle  passing  over  into  the  pelvic  fascia.  Below  it  is  attached  in  its  lateral 
two-thirds  to  Poupart's  ligament,  more  medially  it  remains  in  contact  with  the  ilio- 
psoas  and  passes  down  into  the  thigh  behind  the  femoral  vessels,  separating  these 
structures  from  the  muscle  and  the  anterior  crural  nerve  and  forming  the  posterior 
wall  of  the  sheath  for  the  femoral  vessel.  It  thus  divides  the  space  beneath  Pou- 
part's ligament  (Fig.  599)  into  a. muscular  compartment  (lacuna  musculorum)  which 
contains  the  ilio-psoas  muscle  and  the  anterior  crural  and  external  cutaneous  nerves, 
and  a  vascular  compartment  (lacuna  vasorum)  which  contains  the  femoral  artery  and 
vein  and  the  crural  branch  of  the  genito-crural  nerve,  its  innermost  portion,  between 
the  femoral  vein  and  the  free  edge  of  Gimbernat's  ligament,  transmitting  only  a  few 
loosely  arranged  lymphatic  vessels  and  forming  what  is  termed  the  femoral  ring 
(annulus  femoralis). 

This  ring  (Fig.  599),  which  is  covered  over  by  a  portion  of  the  transversalis 
fascia,  known  as  the  septum  crurale  or  femoralc,  is  the  upper  end  of  a  space,  occu- 

FIG.  599. 


Anterior  superior  iliac  spine 


Iliac  fascia  attached  to  Poupart's  ligam 

Aponeurosis  of  external  oblique  — 

Iliacus  muscle 
Anterior  crural  nerve 

Femoral  artery 

Femorai  vein 

External  abdominal  ring 

Gimbernat's  ligament 


L.  ( )bturator  nerve 
Artery 
Vein 


Femoral  ring 

Iliac  fascia  continued  as^ 
posterior  wall  of  femo- 
ral sheath 

Pudic  branch  of  obturator 

Obturator  membrane 

Dissection  showing  structures  contained  within  the  muscular  and  vascular 
compartments  formed  by  attachments  of  iliac  fascia. 

pied  by  loose  areolar  tissue  and  lymphatic  vessels,  which  extends  a  short  distance 
downward  along  the  inner  side  of  the  felnoral  vein,  forming  what  is  termed  the 
femoral  canal.  Owing  to  the  nature  of  its  contents  and  to  its  upper  end  being 
closed  only  by  the  relatively  thin  septum  femorale,  this  canal  may  allow  of  the 
escape  of  a  portion  of  the  intestine  from  the  abdominal  cavity  downward  into  the 
thigh,  producing  a  femoral  hernia. 

Medially  the  portion  of  the  iliac  fascia  which  forms  the  posterior  wall  of  the 
sheath  for  the  femoral  vessels  is  continued  over  the  anterior  surface  of  the  pectineus 
muscle  (Fig.  1496),  this  portion  of  it  being  sometimes  termed  the  pectineal  or  ilio- 
pectineal  fascia.  Above  it  is  attached  to  the  ilio-pectineal  eminence  and  below 
becomes  continuous  with  the  deep  layer  of  the  fascia  lata. 

3.   PECTINEUS  (Fig.  600). 

Attachments. — The  pectineus  arises  from  the  anterior  surface  of  the  superior 
ramus  and  ilio-pectineal  line  of  the  pubis  and  passes  downward  and  laterally  to  be 
inserted  into  the  pectineal  line  of  the  femur,  a  bursa  intervening  between  it  and 
the  bone. 

40 


626 


HUMAN   ANATOMY. 


Nerve-Supply. — From    the  anterior   crural   nerve  by  the  second  and  third 
lumbar  nerves.  f 

Action. — To  adduct  and  flex  the  thigh  and  rotate  it  slightly  outward. 


FIG.  600. 


Anterior 
superior 
spine  of 
ilium 


Tensor  fasciae' 
latae 


Femoral  artery 
Femoral  vein 


Cut  edge  of 
fascia  lata 


Aponeu- 
rosis  of 
external 
oblique 

Poupart's 
ligament 


Spine  of 
pubis 

Pectineus 


•Vastus  internus 


Tendon  of 
extensor 
quadriceps 


Aponeurosis 
di  i-xtensor 
quadriceps 


Tendo  pati'lhr 


Variations. — The  fibres  which  in- 
nervate the  pectineus  sometimes  pass 
to  it  wholly  or  partly  by  the  obturator 
nerve. 

4.   GRACILIS  (Fig.  600). 

Attachments.  —  The  gra- 
cilis  is  a  long  band-like  muscle 
which  arises  from  the  anterior 
surface  of  the  body  and  inferior 
ramus  of  the  pubic  bone.  It  de- 
scends along  the  inner  surface  of 
the  thigh,  passes  behind  the  inner 
condyle  of  the  femur,  and  then, 
bending  slightly  forward,  is  in- 
serted into  the  inner  surface  of 
the  tibia  near  the  tuberosity,  just 
above  the  semitendinosus  and  be- 
hind and  beneath  the  expanded 
tendon  of  the  sartorius. 

Nerve-Supply.  —  By  the 
anterior  division  of  the  obturator 
nerve  from  the  second,  third,  and 
fourth  lumbar  nerves. 

Action. — To  adduct  the  leg 
and  flex  the  thigh.  It  will  also 
assist  in  rotating  the  leg  inward, 
especially  if  the  thigh  be  flexed. 

5.  ADDUCTOR  LONGUS  (Fig. 
600). 

Attachments. — The  ad- 
ductor longus  arises  from  the  an- 
terior surface  of  the  body  and 
superior  ramus  of  the  pubis  and 
passes  downward  and  laterally  to 
be  inserted  into  about  the  middle 
third  of  the  inner  lip  of  the  linea 
aspera  of  the  femur. 

Nerve-Supply.  —  By  the 
anterior  division  of  the  obturator 
nerve  from  the  second  and  third 
lumbar  nerves. 

Action. — To  adduct,  flex, 
and  outwardly  rotate  the  thigl 


6.  ADDUCTOR  BREVIS  (Fig. 
601). 


Muscles  of  right  thigh,  antero-medinn  aspect. 


Attachments. — The  ad- 
ductor brevis  arises  from  the  body 
and  inferior  ramus  of  the  pubic 
bone,  below  and  partly  external 
to  the  origin  of  the  adductor  longus.  It  passes  laterally  and  obliquely  downward  to 
be  inserted  into  the  upper  third  of  the  medial  lip  of  the  linea  aspera  of  the  femur. 


THE   MUSCLES   OF   THE    LOWER   LIMB. 


627 


FIG.  601. 


Greater  sacro-sciatic____/_ 
ligament 


m  j 


HFTTB— Dorsum  of  iliur 


Pyriformis,  cut- 


Obturator-, — 
interims 
Tuber  ischii- 


Origin  of  semimeny- 
branpsus,  semi- 
tendinosus.and 
biceps 


Adductor  brevis 
Adductor  tnagnus 


Femoral  vein 
Femoral  artery 


Internal  condyle 


Gluteus  maximus,  insertion 


Gluteus  minimus 
Greater  trochanter 


Quadratus  femoris,  insertion 
Obturator  externus 


Perforating  arteries 


/astus  externus 


Fourth  perforating  artery 


Biceps,  short  head 


Biceps,  long  head,  cut 


Popliteal  surface  of  femur 


External  condyle 


Deep  dissection  of  posterior  surface  of  right  thigh. 


628 


HUMAN   ANATOMY. 


Nerve-Supply. — By  the  anterior  ramus  of  the  obturator  nerve  from  the  third 
and  fourth  lumbar  nerves. 

Action. — To  adduct,  flex,  and  outwardly  rotate  the  thigh. 

7.    ADDUCTOR  M.u;xrs  (Fig.  601). 

Attachments. — The  adductor  magnus  arises  from  the  inferior  rami  of  the 
pubis  and  ischium,  as  far  laterally  as  the  base  of  the  tuber  ischii.  Its  anterior  fibres 
are  directed  laterally  and  downward  to  be  inserted  into  nearly  the  whole  length  of 
the  inner  lip  of  the  linea  aspera  by  a  series  of  tendinous  arches  which  give  passage 
to  the  perforating  branches  of  the  profunda  femoris  artery  on  their  way  to  the  back 
of  the  thigh.  Its  posterior  fibres  converge'  downward  to  a  strong  tendon  which  is 
inserted  into  the  adductor  tubercle  on  the  inner  condyle  of  the  femur. 

Nerve-Supply. — By  the  posterior  division  of  the  obturator  nerve  from  the 
third  and  fourth  lumbar  nerves. 

Action. — To  adduct  the  thigh. 

Relations. — The  adductor  muscles,  together  with  the  gracilis,  occupy  the 
medial  surface  of  the  thigh,  intervening  between  the  extensor  and  flexor  muscles. 
The  adductor  brevis  and  adductor  longus  enter  into  the  formation  of  the  floor  of 
Scarpa's  triangle  (page  639),  and  from  the  apex  of  the  latter  the  femoral  vessels  are 

FIG.  602. 


Sacrum 
Greater  sacro-sciatic  foramen 

Greater  sacro-sciatic  ligament 

Lesser  sacro-sciatic  ligamet 
Lesser  sacro-sciatic  forame 


Gemellus  superior 

Obturator  interims 

C'icmellus  inferior 


Crest  of  ilium 


Gluteus  minimus 
Pyriformis 


Greater  trochanter 

Tendon  of  obturator  externus 


Tuber  ischiis 
Quadratus  femoris 


Deep  dissection  of  right  buttock,  showing  muscles  attached  to  greater  trochanter  of  femur. 


continued  downward  upon  the  longus  and  magnus  close  to  their  insertion,  and, 
together  with  the  internal  saphenous  nerve,  are  bridged  over  by  an  aponeurotic 
membrane  which  passes  from  the  longus  and  magnus  to  the  surface  of  the  vastus 
internus.  By  this  membrane  the  space  occupied  by  the  vessels  and  nerve  is  con- 
verted into  a  closed  passage-way  termed  Hunter's  canal  (canalis  adductorius)  (  Fig. 
606),  the  lower  end  of  which  corresponds  to  the  interval  (  hiatus  tendinous)  between 
the  tendons  of  the  anterior  and  posterior  portions  of  the  adductor  magnus. 

The  perforating  branches  of  the  deep  femoral  artery  pierce  the  adductor  magnus 
near  its  insertion,  the  first  one  passing  above  and  the  second  below  the  adductor 
brevis,  or  both  perforate  that  muscle  also,  while  the  third  passes  through  the  magnus 
a  little  above  the  hiatus  tendineus. 


THE   MUSCLES   OF   THE   LOWER    LIMB. 


629 


Variations. — A  separation  of  any  of  the  adductor  muscles  into  distinct  portions  may  occur, 
and  indeed  the  upper  part  of  the  anterior  portion  of  the  magnus  is  usually  quite  separate  from 
the  rest  of  the  muscle  and  has  been  termed  the  adductor  minimus.  The  posterior  fibres  of  the 
magnus  frequently  receive  their  nerve-supply  through  the  great  sciatic  nerve. 

8.   QUADRATUS  EEMORIS  (Figs.  602,  608). 

Attachments. — The  quadratus  femoris  arises  from  the  lateral  border  of  the 
tuber  ischii  and  passes  almost  directly  outward  to  be  inserted  into  the  femur  along 
the  linea  quadrati,  which  extends  a  short  distance  downward  from  about  the  middle 
of  the  intertrochanteric  line. 

Nerve-Supply. — By  a  special  nerve  from  the  fourth  and  fifth  lumbar  and  first 
sacral  nerves. 

Action. — To  rotate  the  thigh  outward. 

Relations. — The  quadratus  femoris  is  concealed  by  the  lower  portion  of  the 
glutens  maximus,  and  its  posterior,  surface  is  crossed  by  the  great  and  small  sciatic 
nerves.  Beneath  it  lie  the  obturator  externus  and  the  termination  of  the  internal 

FIG.  603. 


V  lumbar  vertebra 


Anterior  surface — I— 
of  ilium 


Obturator  foramen 


Symphysis  pubis 


.Greater  sacro-sciatic  foramen 


^  Anterior  sacral  foramina 

— Pyriformis 
— Sacral  canal 

Greater  sacro-sciatic  foramen 
Spine  of  ischium 
"occygeus 


ccyx 


er  sacro-sciatic  foramen 
.ter  sacro-sciatic  ligament 
'Obturator  interims 
1'uber  ischii 


Dissection  of  right  postero-lateral  wall  of  pelvis  from  within,  showing  pyriformis  and  obturator  internus  muscles. 

circumflex  artery.      Its  upper  border  is  in  contact  with  the  gemellus  inferior  and  its 
lower  border  with  the  adductor  magnus. 

Variations. — The  muscle  is  not  infrequently  apparently  absent,  being  fused  with  the 
adductor  magnus. 

9.    OBTURATOR  EXTKRXUS  (Figs.  552,  601). 

Attachments. — The  obturator  externus,  a  thick  triangular  muscle,  arises  from 
the  anterior  surface  of  the  lower  half  of  the  obturator  membrane  and  from  the  rami 
of  tlie  pubis  and  ischium  which  bound  the  lower  half  of  .the  obturator  foramen.  The 
fibres  are  directed  outward,  and  converge  to  a  rounded  tendon  which  is  inserted  into 
the  floor  of  the  digital  fossa  of  the  femur. 

Nerve-Supply. — By  the  posterior  division  of  the  obturator  nerve  from  the 
third  and  fourth  lumbar  nerves. 

Action. — To  rotate  the  thigh  outward. 

10.   OBTURATOR  INTERNUS  (Figs.  602,  603). 

Attachments. — The  obturator  internus  arises  from  (i)  the  inner  surface  of 
the  rami  of  the  pubis  and  ischium  which  bound  the  obturator  foramen,  (2)  from  the 


630  HUMAN    ANATOMY. 

smooth  surface  of  bone  immediately  behind  the  foramen,  corresponding  to  the 
acetabulum  externally,  and  (3)  from  the  whole  of  the  inner  surface  of  the  obturator 
membrane.  Its  fibres,  passing  downward  and  backward,  converge  to  a  strong 
tendon,  which  gains  the  lesser  sacro-sciatic  foramen,  and  there,  bending  around  the 
margin  of  the  foramen,  a  bursa  (bursa  tn.  obturatoris  interni)  intervening  between 
the  tendon  and  the  bone,  passes  outward  through  the  foramen  to  be  inserted  into 
a  facet  on  the  inner  surface  of  the  greater  trochanter  of  the  femur  just  above  the 
digital  fossa. 

Nerve-Supply. — By  a  special  nerve  from  the  first,  second,  and  third  sacral 
nerves. 

Action. — To  rotate  the  thigh  outward. 

ii.   GEMELLI  (Fig.  602). 

Attachments. — The  gemelli  are  two  slender  muscles  which  lie  one  on  either 
side  of  the  tendon  of  the  obturator  internus.  The  gemellus  superior  arises  from  the 
spine  of  the  ischium  and  the  gemellus  inferior  from  the  upper  part  of  the  tuber  ischii. 
Both  muscles  are  inserted  into  the  inner  surface  of  the  greater  trochanter  of  the  femur 
along  with  the  obturator  internus. 

Nerve-Supply. — The  superior  gemellus  by  the  nerve  to  the  internal  obturator 
from  the  fourth  and  fifth  lumbar  and  first  sacral  nerves  ;  the  inferior  by  the  nerve  to 
the  quadratus  femoris  from  the  first,  second,  and  third  sacral  nerves. 

Action. — To  assist  in  rotating  the  thigh  outward. 

Variations. — One  or  other  of  the  gemelli,  usually  the  superior,  is  occasionally  wanting. 
This  is  very  probably  due  to  fusion  with  adjacent  muscles,  the  gemellus  superior  with  the 
pyriformis  and  the  inferior  with  the  quadratus  femoris. 

(6)   THE  POST- AXIAL  MUSCLES. 

1.  Gluteus  maximus.  3.    Glutens  medius. 

2.  Tensor  fascias  latae.  4.   Gluteus  minimus. 

i.   GLUTEUS  MAXIM*US  (Figs.  604,  607). 

Attachments. — The  gluteus  maximus  is  an  exceedingly  thick,  coarse  muscle 
which  forms  the  principal  mass  of  the  buttock.  It  arises  from  the  lateral  surface  of 
the  posterior  portion  of  the  ilium,  behind  the  superior  gluteal  line,  from  the  pos- 
terior surface  of  the  sacrum  and  coccyx,  and  from  the  posterior  sacro-iliac  and  greater 
sacro-sciatic  ligaments.  The  fibres  pass  laterally  and  downward,  the  upper  ones 
curving  over  the  lateral  surface  of  the  greater  trochanter  of  the  femur  and  the  lower 
ones  over  the  tuberosity  of  the  ischium,  and  are  inserted  by  a  broad  tendon  partly 
into  the  ilio-tibial  band  of  the  fascia  lata  and  partly  into  the  gluteal  tuberosity  of  the 
femur. 

Nerve-Supply. — By  the  inferior  gluteal  nerve  from  the  fifth  lumbar  and  fi 
and  second  sacral  nerves. 

Action. — To  draw  the  thigh  backward  and  rotate  it  slightly  outward.     Actin 
from  below,  it  extends  the  trunk. 

Relations. — The  gluteus  maximus  is  covered  by  the  upper  posterior  portio 
of  the  fascia  lata.      It  covers  the  gluteus  medius,    pyriformis,  obturator  interims, 
gemelli,  quadratus  femoris  and  the  origin  of  the  hamstring  muscles,   and  also  the 
gluteal,  sciatic,  and  pudic  vessels  and  nerves. 

It  is  separated  from  the  lateral  surface  of  the  trochanter  major  by  a  large  bursa 
(bursa  trochantcrica  in.  glutaci  inaximi).  two  or  three  additional  small  bursae  (bursae 
glutacofctnoralcs )  separating  the  lower  portion  of  the  muscle  from  the  shaft  of  the 
femur.  A  bursa  is  also  frequently  present  beneath  the  muscle  where  it  passes  over 
the  ischial  tuberosity  (bursa  ischiadica  in.  glutaei  maxirai). 

Variations. — The  lower  border  of  the  glutens  maximus  is  occasionally  separated  from  the 
rest  of  the  muscle,  forming  what  may  be  termed  the  tocCygeo-fftnoraKs,  and  it  occasionally 
receives  a  slip  from  the  ischial  tuherosity,  which  has  been  named  the  isektO-fetttoroKs, 


THE   MUSCLES   OF  THE   LOWER    LIMB. 


631 


2.  TENSOR  FASCIAE  LAT.-E  (Figs.  600,  604). 

Attachments. — The  tensor  fasciae  latae,  also  termed  the  tensor  vagina  femo- 
ris,  is  a  flat  muscle  which 

arises  from  the  crest  of  the  p,G    6o4 

ilium,  immediately  behind 
the  anterior  superior  spine, 
and  passes  downward  and 
slightly  backward  to  be 
inserted  into  the  upper 

portion    of    the    ilio-tibial  ^^M£jHMHMHPiBlik 

band  of  the  fascia  lata. 

Nerve-Supply.-By  M-'gr  Anterior 

the  superior  gluteal  nerve  M  nor  spine  of 

from   the  fourth  and  fifth  jfl 

lumbar  and  first  sacral 
nerves. 

Action. — To  tense  the 
fascia  lata  and  at  the  same 
time  to  flex  the  thigh  and 
rotate  it  slightly  inward. 


3.  GLUTEUS  MEDIUS 
(Figs.  604,  609). 


Gluteus  medius 


ilium 


Sartorius 


Rectus  femoris 


Vastus 
externus 


Biceps, 


Tensor     fasciae 
latae,    cut    at 
insertion  into 
fascia 

Attachments. — The 

glutens  medius  arises  from 
the  outer  surface  of  the 
ilium,  between  the  superior 
and  middle  gluteal  lines. 
Its  fibres  pass  downward, 
converging  to  a  tendon 
which  is  inserted  into  the 
lateral  surface  of  the  great 
trochanter  of  the  femur 
near  its  summit. 

Nerve-Supply. — By 
the  superior  gluteal  nerve 
from  the  fourth  and  fifth 
lumbar  and  first  sacral 
nerves. 

Action. — To  abduct 
the  thigh  and  by  its 
stronger  anterior  fibres  to 
rotate  it  inward.  Acting 
from  below,  to  flex  the 
pelvis  laterally. 

Relations. — The  an- 
terior portion  of  the  mus- 
cle is  covered  by  the  fascia 
lata  and  the  tensor  fasciae 
latae,  the  posterior  portion 
by  the  gluteus  maxim  us. 
Beneath  it  are  the  gluteus 
minimus  and  the  superior 
gluteal  vessels  and  nerve, 
its  tendon  passing  over  that 
of  the  pyriformis  near  its 
insertion. 

A  bursa  (bursa  trochanterica  m.  glutaei  medii  anterior)  is  interposed  between  the 


Biceps 


Tendon  of  quadriceps 

extensor 

r — Ilio-tibial  band,  cut 


Muscles  of  right  thigh,  lateral  aspect. 


HUMAN   ANATOMY. 


FIG.  605. 


Gluteus  maxim 


Crest  of  ilium 


Tendon  of  hici-p*- 


^     Gluteus  niedius  covered  by  fascia  lata 
fc-Anterior  superior  spine  of  ilium 

Tensor  fascise  latae 

Fascia  lata,  cut  edges 


— Symphysis  pubis 


Fascia  lata 


Ilio-tibial  band 


Patella 


„••/ 


Lateral  surface  of  rijjht  thigh  invested  by  tascia  lata. 


THE   FEMORAL   MUSCLES. 


633 


tendon  of  the  muscle  and  the  upper  part  of  the  great  trochanter,  and  another  (bursa 
trochanterica  ra.  glutaei  medii  posterior)  is  usually  present  between  the  tendon  and  that 
of  the  pyriformis. 

4.   GLUTEUS  MINIMUS  (Figs.  601,  602). 

Attachments. — The  gluteus  minimus  is  the  most  deeply  situated  of  the  gluteal 
muscles.  It  arises  from  the  lateral  surface  of  the  ilium,  between  the  middle  and 
inferior  gluteal  lines,  and  passes  downward  and  laterally  to  a  strong  tendon  which  is 
inserted  into  the  anterior  surface  of  the  great  trochanter  of  the  femur. 

Nerve-Supply. — By  the  superior  gluteal  nerve  from  the  fourth  and  fifth 
lumbar  and  first  sacral  nerves. 

Action. — To  abduct  the  thigh  and,  acting  from  below,  to  flex  the  pelvis 
laterally. 

Relations. — Superficially  it  is  covered  by  the  gluteus  medius  and  crossed  by 
the  superior  gluteal  vessels  and  nerve.  Deeply  it  rests  upon  the  capsule  of  the  hip- 
joint.  A  bursa  (bursa  trochanterica  m.  glutaei  minimi)  is  interposed  between  the 
tendon  and  the  great  trochanter. 

Variations.  — The  anterior  portion  of  the  muscle  is  sometimes  distinctly  separated  from 
the  rest,  forming  a  muscle  frequently  present  in  the  lower  mammals  and  termed  the  scansorius. 


THE   FEMORAL    MUSCLES. 

Many  of  the  muscles  which  belong  to  this  group  extend  the  entire  length  of 
the  thigh,  taking  their  origin,  in  whole  or  in  part,  from  the  pelvis. 

The  Fascia   Lata    (Fig.    605). — This,    the   deep  fascia  of    the  thigh,   is   a 


FIG.  606. 

Rectus  femoris 


Internal  intermuscular  septum 
Sartorius 

Internal  saphenous  nerve 


Linea  aspera, 
external  lip 


Fetnoral  vessels 

Internal  saphenous  vein 

Adductor  longus 

Hunter's  canal 
Gracilis 


Vastusexternus- * 

Deep  fascia 
Subcutaneous  tissue 

Skin 
External  intermuscular  septum 

Biceps,  long  head    Greater  sciatic  nerve    Setnitendinosus 
Section  across  right  thigh  through  Hunter's  canal,  seeti  from  below. 

strong  layer  which  completely  encloses  the  muscles  of  the  thigh  and  covers  the  glu- 
teal region.  Its  upper  attachment,  beginning  from  behind,  is  to  the  coccyx  and 
sacrum  ;  thence  forward  along  the  entire  length  of  the  crest  of  the  ilium  and  me- 


634 


HUMAN  -ANATOMY. 


Crest  of  ilium 


Sacral  and — T 
ligamentous       » 
origin  of  glu- 
teus  maxnnus    , 


Gluteu 
maxima 


luteus  maxi- 
mus,  insertion 


dially  along  Poupart's  ligament  to  the  body  of  the  pubis  ;  thence  it  passes  backward 
and  downward  along  the  inferior  rami  of  the  pubis  and  ischium  to  the  ischial  tuberos- 

ity,  where  it  passes  upon 

FIG.  607.  the    greater    sacro-sciatic 

ligament  and  so  back  to 
the  starting-point.  Below 
it  is  attached  to  the  bor- 
ders of  the  patella  and  be- 
comes continuous  with  the 
fascia  of  the  leg. 

The  fascia  lata  varies 
considerably  in  thickness 
in  different  regions.  Over 
the  gluteal  region  it  is  thin, 
but  over  the  great  tro- 
chanter  of  the  femur  it 
becomes  greatly  thick- 
ened, and  this  thickening 
is  continued  downward 
upon  the  lateral  surface  of 
the  thigh  (Fig.  605)  as 
far  as  the  external  tuber- 
osity  of  the  tibia,  forming 
what  is  termed  the  ilio- 
tibial  band  (tractus  ilio- 
tibialis).  This  receives  at 
its  upper  part  the  inser- 
tions of  the  tensor  fasciae 
latae  and  part  of  the  glu- 
teus  maximus,  and  from 
the  posterior  edge  of  its 
upper  portion  a  much 
smaller  and  feebler  band 
can  be  traced  backward  at 
first  across  and  then  below 
the  lower  portion  of  the 
gluteus  maximus  to  the 
ischial  tuberosity  ;  it  pro- 
duces the  gluteal  sit/cits. 

In  its  lower  posterior 
part,  where  it  forms  the 
roof  of  the  popliteal  space, 
the  fascia  is  also  somewhat 
thickened. 

Anteriorly,  just  below 
the  inner  end  of  Poupart's 
ligament,  a  prolongation 
of  the  fascia  passes  deeply 
to  join  with  the  ilio-pec- 
tineal  portion  of  the  iliac 
fascia,  and  so  assists  in  the 
formation  of  the  slu-ath  for 
the  femoral  vessels.  O\n 
an  oval  area,  situated 
immediately  external  to 
win-re  this  prolongation, 
which  is  termed  the/WvV- 
portion  (Fig.  530)  of  the  fascia  lata,  is  given  off,  the  fascia  lata  is  quite  thin  and  is 
perforated  by  the  internal  saplu-nous  vein,  superficial  blood-vessels,  and  lymphatics  ; 


.Vastus  externus 


Semitendinosus 


Semimembranosus 


Sartorius 


Gracilis,  tendon 


.Gastrocnemius 


Superficial  dissection  of  posterior  MIH';I.,    c,f  right  buttock  and  thigh, 
•howipg  iniisck-s  undisturbed. 


THE   FEMORAL   MUSCLES. 


635 


whence  it  is  termed  the  cribriform  fascia  (fascia  cribrosa),  the  area  which  it  covers 
being  \\\e  fossa  ovalis.     The  cribriform  fascia  is  readily  ruptured,  the  fossa  ovalis  then 


FIG.  608. 


Tuberosity  of  ischium H 


Quadratus  fetnoris 


Adductor  magnus 


Semitendinosus 


-Biceps,  long  head 


Semimembranosus 


Sartorius 
Gracilis 


Gastrocnemius,  inner  head 


-Pyriformis 


jfiL, — Gemellus  superior 

—Obturator  interims 
iemellus  inferior 
Greater  trochanter 


Gluteus  maximus, 
reflected 


Biceps,  short  head 
Vastus  externus 


Iff — _____J^  Biceps 


Popliteal  surface  of  femur 


Tendon  of  biceps, 
Gastrocnemius,  outer  head 


Muscles  of  posterior  surface  of  right  buttock  and  thigh,  gluteus  maximus  and  medius  having  been  reflected. 

appearing  as  a  perforation  in  the  fascia  lata,  termed  the  saphcnous  opening  (Fig. 
523).  The  fossa  ovalis  lies  immediately  over  (i.e.,  in  front  of)  the  lower  end  of  the 
femoral  canal,  and  is  consequently  of  importance  in  connection  with  femoral  herniae 


636  HUMAN   ANATOMY. 

(page  1773),  which,  descending  in  the  canal,  press  against  the  thin  fascia  cribrosa  and 
may  cause  it  to  bulge  forward. 

The  part  of  the  fascia  lata  lying  to  the  outer  side  of  the  fossa  ovalis,  or  the 
saphenous  opening,  is  known  as  the  iliac  portion  (Fig.  530),  which  at  the  lateral 
margin  of  the  fossa  ovalis,  where  the  fascia  cribrosa  joins  the  fascia  lata,  is  somewhat 
thickened  to  form  a  curved  band  termed  the  falciform  process  (margo  falciformis). 
The  latter  is  prolonged  downward,  as  the  cornu  inferius,  to  join  the  pubic  portion 
of  the  fascia  lata,  and  upward,  as  the  cornu  super  ins,  also  termed  the  femoral  liga- 
ment or  Hey' s  ligament,  which  is  somewhat  stronger  and  continued  medially  to  join 
the  inner  end  of  Poupart's  and  Gimbernat's  ligaments. 

Septa  of  connective  tissue  are  continued  from  the  deep  surface  of  the  fascia  lata 
to  the  femur  separating  the  various  muscles  of  the  thigh.  Two  are  especially  strong  ; 
one,  the  internal  intermuscular  septiiin  (septum  intermuscularis  medialis),  passing  to 
the  inner  lip  of  the  linea  aspera,  between  the  vastus  internus  and  adductor  magnus 
muscles,  and  the  other,  the  external  intermuscular  septum  (septum  intermuscularis 
lateralis),  to  the  external  lip  between  the  short  head  of  the  biceps  and  the  vastus 
externus.  To  a  certain  extent  these  septa  furnish  surfaces  of  origin  for  some  of  the 
adjacent  muscles. 

(a)   THE  PRE-AXIAL  MUSCLES. 

i.    Biceps  femoris.          2.   Semitendinosus. 
3.   Semimembranosus. 

These  muscles  are  popularly  known  as  the  hamstring  muscles. 

i.  BICEPS  FEMORIS  (Figs.  608,  609). 

Attachments. — The  biceps  femoris  takes  its  origin  by  two  distinct  heads. 
The  long  head  arises  from  lower  and  inner  facet  upon  the  tuberosity  of  the  ischium 
in  common  with  the  semitendinosus,  while  the  short  head  arises  from  the  whole 
length  of  the  outer  lip  of  the  linea  aspera  and  from  the  adjacent  septum  intermus- 
culare.  The  fibres  of  both  heads  are  directed  downward,  and  at  about  the  knee 
unite  in  a  common  tendon  which  passes  behind  the  outer  condyle  of  the  femur 
and  is  inserted  into  the  head  of  the  fibula,  bifurcating  to  embrace  the  long  external 
lateral  ligament  of  the  knee-joint.  Tendinous  bands  usually  extend  also  from  the 
tendon  to  the  outer  tuberosity  of  the  tibia. 

Nerve-Supply. — Both  heads  are  supplied  by  the  greater  sciatic  nerve.  The 
fibres  for  the  short  head,  however,  pass,  by  way  of  the  external  popliteal  division  of 
the  nerve,  from  the  fifth  lumbar  and  the  first  and  second  sacral  nerves,  while  those 
for  the  long  head  pass  by  the  internal  popliteal  division,  coining  from  the  first, 
second,  and  third  sacral  nerves. 

Action. — To  extend  the  thigh  and  flex  the  leg.  When  the  leg  is  flexed  the 
biceps  will  rotate  it  outward,  and  the  long  head  acting  from  below  assists  in  extend- 
ing the  trunk  upon  the  hip-joints. 

Relations. — The  common  tendon  of  origin  of  the  biceps  and  semitendinosus 
is  sometimes  separated  from  the  tendon  of  the  semimembranosus  by  a  bursa  (  bursa 
m.  bicipitis  superior).  More  rarely  a  bursa  is  to  be  found  between  the  tendon  of 
insertion  of  the  biceps  and  the  lateral  head  of  the  gastrocnemius,  and  almost  con- 
stantly a  bursa  (bursa  m.  bicipitis  inferior)  separates  the  tendon  of  insertion  from  the 
fibular  collateral  ligament  of  the  knee-joint. 

Variations. — The  most  important  variations  of  the  biceps  are  an  occasional  absence  of  the 
short  head  and  an  extension  of  the  insertion  to  the  crural  fascia.  Both  these  anomalies  are 
explained  by  the  composition  of  the  muscle,  the  two  heads  not  only  representing  two  originally 
distinct  muscles,  but,  as  is  indicated  by  the  nerve-supply,  the  long  head  is  a  portion  of  the  pre- 
axial  musculature  of  the  thigh,  while  the  short  head  belongs  to  the  post-axial  group.  The  com- 
parative anatomy  of  the  muscle  shows  that  the  short  head  is  a  modified  representative  of  a 
muscle  belonging  to  the  gluteal  set,  which  extended  from  the  caudal  vertebra?  to  the  fascia  of 
the  cms  and  has  only  secondarily  become  united  with  the  pre-axial  muscle,  sharing  in  its 
insertion. 


THE   FEMORAL   MUSCLES. 

FIG.  609. 


637 


Sacrum 


Greater  sacro-sciatic- — - 
ligament 


Tuberosity  of  ischiurr. — *^H 


Biceps,  origin 
Semitendinosus,  origin 


Adductor  magnus 


Crest  of  ilium 


Gluteus  medius 


•Pyriformis,  cut 


— Obturator  internus 


Greater  trochanter 

Quaclratus  femoris 
Tendon  of  vastus  externus 


Gluteus  maximus,  insertion 


— Yastus  externus 


Biceps,  short  head 


Biceps,  long  head,  cut 


Adductor  magnus 

Sartori  us- 
Tendon  of  semitendinosus 


Poplite 


Aponeurotic  expansion  from  tendon  of 

semimembranpsus  to  posterior  liga- 
ment of  knee-joint 


Fibula 


Tibia 


Deeper  dissection  of  posterior  surface  of  right  buttock  and  thigh,  exposing  semimembranosus 
and  short  head  of  biceps  muscles. 


638  HUMAN    ANATOMY. 

2.   SEMITENDINOSUS  (Fig.  608). 

Attachments. — The  semitendinosus  arises  from  the  tuberosity  of  the  ischipm 
in  common  with  the  long  head  of  the  biceps.  Its  fibres  extend  downward  to  a  long, 
slender  tendon,  which  passes  behind  the  inner  condyle  of  the  femur  and  then  curves 
forward  along  with  the  tendon  of  the  gracilis  to  be  inserted,  below  that  tendon  and 
under  cover  of  the  expanded  tendon  of  insertion  of  the  sartorius,  into  the  inner 
surface  of  the  tibia  near  the  tuberosity. 

Nerve-Supply. — By  the  internal  popliteal  division  of  the  greater  sciatic  nerve 
from  the  fifth  lumbar  and  first  and  second  sacral  nerves. 

Action. — To  extend  the  thigh  and  flex  and  rotate  inward  the  leg.  Acting  from 
below  it  will  extend  the  trunk  upon  the  hip-joints. 

Relations. — A  large  bursa  (bursa  anserina)  intervenes  between  the  tendons 
of  the  gracilis  and  semitendinosus  and  the  tibia. 

3.   SEMIMEMBRANOSUS  (Fig.  609). 

Attachments. — The  semimembranosus  arises  by  a  broad,  flat  tendon,  which 
extends  from  upper  and  outer  facet  upon  the  tuberosity  of  the  ischium  downward 
along  the  outer  border  of  the  muscle  to  about  the  middle  of  the  thigh.  The  muscle- 
fibres  pass  downward  and  inward  from  this  tendon  to  a  tendon  of  insertion,  which 
occupies  the  medial  border  of  the  muscle  and  passes  behind  the  inner  condyle  of  the 
femur  and  curves  forwardto  the  inner  surface  of  the  internal  condyle  of  the  tibia, 
into  which  it  is  inserted.  An  extension  of  the  tendon  of  insertion  usually  passes 
downward  and  outward  to  the  portion  of  the  deep  fascia  of  the  leg  which  covers  the 
popliteus  muscle  ;  another  band  extends  upward  and  outward  towards  the  outer  con- 
dyle of  the  femur,  blending  with  and  materially  strengthening  the  posterior  part  of 
the  capsular  ligament  of  the  knee-joint. 

Nerve-Supply. — By  the  internal  popliteal  division  of  the  greater  sciatic  nerve 
from  the  fourth  and  fifth  lumbar  and  first  sacral  nerves. 

Action. — To  flex  the  leg  and  assist  somewhat  in  rotating  it  inward.  Acting 
from  below  it  will  extend  the  trunk  upon  the  hip-joints. 

Relations. — The  semimembranosus  is  situated  in  front  of  the  long  head  of  the 
biceps  and  the  semitendinosus  and  behind  the  adductor  magnus.  The  greater 
sciatic  nerve  lies  along  its  lateral  border  (Fig.  606).  The  tendon  of  insertion  is 
separated  from  the  inner  head  of  the  gastrocnemius  by  a  bursa  (bursa  m.  semimem- 
branosi  medialis),  which  often  communicates  with  the  synovial  cavity  of  the  knee- 
joint  ;  the  bursa  m.  semimembranosi  lateralis  intervenes  between  the  tendon  and  the 
inner  condyle  of  the  tibia. 

(*)  THE   POST-AXIAL   MUSCLES. 

1.  Sartorius.  4.   Crureus. 

2.  Rectus  femoris.  5.   Vastus  internus. 

3.  Vastus  externus.  6.   Subcrureus. 

i.   SARTORIUS  (Fig.  610). 

Attachments. — The  sartorius  is  a  long  band-like  muscle  which  arises  from 
the  anterior  superior  spine  of  the  ilium  and  the  adjacent  part  of  the  notch  below  it. 
It  descends  obliquely  downward  and  inward  across  the  front  of  the  thigh,  in  the 
groove  between  the  rectus  femoris  and  the  vastus  internus,  on  the  one  hand,  and  the 
adductor  muscles,  on  the  other,  and  then  passes  directly  downward  behind  the 
inner  condyle  of  the  femur.  It  finally  bends  forward  to  be  inserted  into  the  inner 
surface  of  the  tibia  near  the  tuberosity,  covering  the  insertions  of  the  gracilis  and 
semitendinosus. 

Nerve-Supply. — By  the  anterior  crural  nerve  from  the  second  and  third 
lumbar  nerves. 

Action. — To  flex  the  thigh  and  log  and  to  rotate  the  thigh  outward  ;  when 
the  leg  is  flexed,  the  muscle  will  assist  in  rotating  the  thigh  inward. 


THE   FEMORAL   MUSCLES. 


639 


FIG.  610. 


Relations. — As  it  passes  obliquely  across  the  upper  part  of  the  thigh,  the  sar- 
torius  forms  the  lateral  boundary  of  a  triangular  depression  which  is  known  as 
Scarpd s  triangle  (trigonum  femorale).  The  inner  boundary  of  this  triangle  is  formed 
by  the  adductor  longus,  its  base  by 
Poupart's  ligament,  its  floor  by  the 
ilio-psoas  and  pectineus  and  often  to 
a  slight  extent  by  the  adductor  brevis, 
and  its  roof  by  the  fascia  lata  and 
the  cribriform  fascia.  The  space  so 
bounded  is  traversed  from  above  down- 
ward, from  the  middle  of  its  base  to 
its  apex,  by  the  femoral  vessels  and 
the  anterior  crural  and  crural  branch 
of  the  genito-crural  nerve,  and  con- 
tains a  number  of  lymphatic  nodes. 
At  its  apex  it  is  continuous  with  the 
adductor  or  Hunter's  canal. 

A  mucous  bursa  (bursa  ra.  sar- 
torii  propria)  intervenes  between  the 
tendon  of  the  sartorius  and  those  of 
the  gracilis  and  semimembranosus, 
and  occasionally  communicates  with 
the  bursa  anserina  (page  638). 

The  remainder  of  the  post-axial 
musculature  of  the  thigh  is  almost  en- 
tirely represented  by  four  large  mus- 
cles, more  or  less  separable  above, 
but  united  below  in  a  common  tendon, 
which  is  inserted  into  the  upper  bor- 
der of  the  patella,  and  through  this 
and  the  ligamentum  patellae  acts  upon 
the  tuberosity  of  the  tibia.  These 
muscles  have  been  grouped  together 
as  the  extensor  quadriceps  femoris, 
and  include  the  rectus  femoris,  the 
vastus  externus,  the  crureus,  and  the 
vastus  internus. 

Vastus  internus 


Pectineus 


Tendon  of 
extensor 
quadriceps 


2.   RECTUS  FEMORIS  (Fig.  610). 

Attachments. — The  rectus  fem- 
oris has  a  double  origin,  the  one,  or 
straight  head,  arising  from  the  an- 
terior inferior  spine  of  the  ilium,  and 
the  other,  or  reflected  head,  from  the 
surface  of  the  ilium  a  short  distance 
above  the  acetabulum.  The  two 
heads  give  rise  to  a  single  tendon 
which  descends  for  some  distance 
along  the  front  of  the  muscle  and,  in 
conjunction  with  a  median  septum, 
gives  origin  to  the  muscle-fibres. 
These  present  a  bipinnate  arrange- 
ment, and  pass  over  below  into  the 
common  tendon  to  be  eventually  in- 
serted by  the  ligamentum  patellae  into 
the  tubercle  of  the  tibia. 

Nerve-Supply. — By  the  anterior  crural  nerve  from  the  third  and  fourth  lumbar 
nerves. 


—  Tendo  patellae 


Muscles  of  right  thigh,  anterior  aspect. 


640  HUMAN   ANATOMY. 

Action. — To  flex  the  thigh  and  extend  the  leg.  Acting  from  below  it  will  flex 
the  trunk  on  the  hip-joints. 

Relations. — The  rectus  femoris  rests  upon  the  capsule  of  the  hip-joint  above 
and  the  crureus  below.  A  bursa  frequently  intervenes  between  the  surface  of  the 
ilium  and  the  head  which  is  inserted  above  the  acetabulum. 


3.  VASTUS  EXTERNUS  (Fig.  610). 

Attachments. — The  vastus  extern  us  (m.  vastus  lateralis)  arises  from  the  ante- 
rior intertrochanteric  line,  the  lateral  surface  of  the  greater  trochanter,  and  the  outer 
lip  of  the  linea  aspera.  The  fibres  curve  downward  and  inward  to  unite  with  the 
crureus  and  to  be  inserted  into  the  common  tendon. 

Nerve-Supply. — By  the  anterior  crural  nerve  from  the  third  and  fourth  lumbar 
nerves. 

Action. — To  extend  the  leg. 

4.   CRUREUS  (Fig.  606). 

Attachments. — The  crureus  (m.  vastus  intermedius)  lies  below  the  rectus 
femoris  and  between  the  vastus  externus  and  vastus  intern  us.  It  arises  from  the 
anterior  surface  of  the  femur  and  passes  downward  into  a  flat  tendon  which  is  inserted 
into  the  common  tendon  a  short  distance  above  the  patella. 

Nerve-Supply. — By  the  anterior  crural  nerve  from  the  third  and  fourth  lumbar 
nerves. 

Action. — To  extend  the  leg. 

5.  VASTUS  INTERNUS  (Fig.  600). 

Attachments. — The  vastus  internus  (m.  vastus  medialis)  is  usually  so  blended 
with  the  crureus  as  to  be  hardly  separable  from  it.  It  arises  from  the  spiral  line  and 
from  the  inner  lip  of  the  linea  aspera  of  the  femur,  the  fibres  curving  downward  and 
outward  to  be  partly  united  with  the  crureus  and  partly  inserted  into  the  common 
tendon. 

Nerve-Supply. — By  the  anterior  crural  nerve  from  the  third  and  fourth  lumbar 
nerves. 

Action. — To  extend  the  leg.  Owing  to  the  oblique  direction  of  the  femur 
downward  and  inward  the  action  of  the  quadriceps  femoris  would  be  to  draw  the 
patella  outward  as  well  as  upward,  thus  tending  towards  an  outward  dislocation  of 
that  bone.  This  is  obviated,  however,  by  the  vastus  internus,  the  bulk  of  whose 
fibres  arise  from  the  lower  part  of  the  femur  and  are  directed  more  or  less  trans- 
versely outward  to  the  inner  border  of  the  common  tendon. 

Relations. — The  medial  border  of  the  vastus  internus  forms  the  outer  wall  of 
Hunter's  canal  (Fig.  606),  the  fascia  which  forms  the  roof  of  the  canal  extending 
across  between  this  muscle  and  the  adductor  magnus. 

6.    SUBCRUREUS. 

Attachments. — The  subcrureus  (m.  articularis  «emi)  is  frequently  so  insepara 
bly  blended  with  the  crureus  that  it  may  well  be  regarded  as  the  deepest  layer  o 
the  latter  rather  than  as  a  distinct  muscle.      It  arises  from  the  lower  part  of  the 
anterior  surface  of  the  femur  and  passes  downward  to  be  inserted  into  the  upper 
border  of  the  capsule  of  the  knee-joint. 

Nerve-Supply. — By  the  anterior  crural  nerve  from  the  third  and  fourth  lumbar 
nerves. 

Action. — To  tense  the  capsule  of  the  knee-joint. 


PRACTICAL   CONSIDERATIONS:     THE   BUTTOCKS.  641 

PRACTICAL    CONSIDERATIONS  :    MUSCLES    AND    FASCIAE 
OF   THE   BUTTOCKS,   HIP,  THIGH,  AND  KNEE. 

i.  The  Buttocks. — The  skin  over  this  region  is  thick  and  is  closely  connected 
with  the  superficial  fascia,  which  is  abundant,  loose,  and  contains  much  fat.  The  skin 
is  richly  supplied  with  nerves  from  the  small  sciatic,  the  external  and  the  perforating 
cutaneous,  the  ilio-hypogastric,  and  the  external  branches  of  the  posterior  division  of 
the  lumbar  and  sacral  nerves.  It  is  poorly  supplied  with  blood  as  compared  with 
other  cutaneous  areas,  and  hence  usually  has  a  relatively  low  surface  temperature.  It 
is  coarse,  with  numerous  sebaceous  follicles,  and  is  the  site  of  frequent  minor  forms  of 
irritation, — chafes,  bruises,  etc., — and  is  for  these  reasons  a  common  seat  of  superficial 

FIG.  611. 


N 


Glutens  maximus, 
turned  forward 


j.  Pyriformis 

4— Dislocated  head  of  femur 

j— Obturator  interims 


-Greater  sciatic  nerve 


Quadratus  femoris 


Dissection  of  posterior  luxation  of  left  femur  towards  dorsum  of  ilium. 

furuncles,  which,  on  account  of  its  intimate  union  with  the  underlying  fascia  and  its 
plentiful  nerve-supply,  are  apt  to  be  very  painful. 

The  presence  of  a  large  quantity  of  poorly  organized  fat  in  the  superficial  fascia 
and  the  frequency  of  local  irritation  render  the  region  a  favorite  seat  of  lipomata. 

The  laxity  of  the  superficial  fascia  permits  effusions  of  pus  or  of  blood  to  attain 
exceptionally  large  dimensions,  and  this  is  encouraged  by  gravity  in  the  usually 
dependent  position  of  the  part. 

The  deep  fascia  attached  to  the  back  of  the  sacrum  and  coccyx  and  to  the  crest 
of  the  ilium  covers  in  the  glutens  medius  and  holds  it,  with  the  gluteus  minimus,  in 
an  osseo-fascial  space,  as  the  ilio-psoas  is  held  anteriorly  by  the  iliac  fascia  (page  624). 
The  posterior  space,  however,  is  completely  closed  superiorly  and  is  open  only 
inferiorly,  towards  the  thigh,  and  antero-internally,  towards  the  sciatic  foramina. 
Abscesses  or  extravasations  of  blood  in  this  space  may  originate  in,  or  may  find  their 


642 


HUMAN   ANATOMY. 


Dislocated  head  of  femur 
Femoral  artery 
Femoral  vein 


Pectineus- 


Pubic  hone • 


way  into  the  pelvic  cavity  ;  or,  guided  by  gravity,  they  may  travel  long  distances 
down  the  thigh  before  pointing.  They  are  apt  to  be  associated  with  much  pain 
because  of  the  compression  of  the  gluteal  and  other  branches  of  the  sacral  plexus 
between  the  bone  anteriorly  and  the  musculo-aponeurotic  wall  of  the  space  posteriorly. 
The  gluteus  maximus  is  embraced  by  a  sheath  formed  by  the  splitting  of  this 
fascia  into  two  layers,  the  superficial  one  of  which  is  thinner  and  less  dense  than  the 
deep  layer.  Abscess  or  hemorrhagic  extravasation  within  the  substance  of  that 
muscle  is,  therefore,  likely  to  give  more  external  evidence  of  its  presence  and  to  be 
less  painful  than  if  in  or  beneath  the  gluteus  medius.  The  gluteus  maximus  itself 
may  be  ruptured  by  violent  exertion  in  extending  the  pelvis  and  trunk  on  the  thigh, 
the  latter  being  fixed,  as  in  raising  a  heavy  weight  on  the  back  and  shoulders  while 
passing  from  a  stooping  to  an  erect  position,  or  in  carrying  a  similar  burden  upstairs, 
the  pelvis  and  femur  having  then  the  same  relative  position  at  each  upward  step  that 
they  have  when  the  thigh  is  vertical  and  the  trunk  and  pelvis  are  flexed.  In  the 
erect  position  the  muscle  is  relaxed.  When  it  is  paralyzed  the  patient  can  walk 
easily  on  a  level,  but  has  trouble  in  going  upstairs  or  in  exchanging  a  sitting  for  a 
standing  posture.  Wounds  of  the  buttock  without  fracture  of  the  bones  may  enter 
the  pelvic  cavity  through  the  sacro-sciatic  foramina,  and  Treves  has  recorded  a  case 

of  stab  wound  of  the 

FIG.  612.  buttock  in  which  the 

patient  died  from  peri- 
tonitis, the  wound 
having  involved  the 
bladder  and  caused  in- 
traperitoneal  extrava- 
sation of  urine. 

A  subgluteal  tri- 
angle has  been  de- 
scribed (Guiteras),  the 
boundaries  of  which 
are  externally  the  fem- 
oral and  trochanteric 
insertion  of  the  glu- 
teus maximus,  inter- 
nally the  long  head 
of  thebiceps,  the  tuber 
ischii,  and  part  of  the 
sacro-sciatic  ligament, 
superiorly  the  pyri- 
formis.  The  floor  of 
the  triangle  is  made 
by  the  external  rota- 
tors and  the  adductor 
magnus.  It  is  the  re- 
gion of  aneurism  of 

or  occasional  hemorrhage  from  the  sciatic  artery,  of  emergence  of  the  sciatic  nerv 
and  of  one  form  of  sciatic  hernia,  below  the  pyriformis.     The  ' '  triangle' '  is  an  arti- 
ficial one,  and  is  mentioned  merely  as  an  aid  to  localization  of  the  above  structures. 

The  subgluteal  bursae  are  of  considerable  importance.  One  is  found  interposed 
between  the  trochanter  and  each  of  the  gluteal  muscles  (page  630).  Inflammation 
and  enlargement  of  these  bursae  will  be  followed  by  adduction  and  flexion  of  the 
thigh,  because  active  extension  of  the  thigh,  in  which  the  glutei  aid,  and  rotation  in- 
ward, putting  them  on  the  stretch,  are  painful.  Flattening  of  the  buttock  and  oblit- 
eration of  the  gluteo-femoral  crease  may  follow  atrophy  of  the  muscles  from  disease 
(page  381).  Caries  of  the  trochanter  has  resulted  from  suppuration  in  these  bursae. 
The  bursae  over  the  tuberosities  of  the  ischium  frequently  enlarge  and  may  cause 
two  solid  symmetrical  swellings — "weavers'  bottom" — which  require  removal. 

2.   Trie   Hip  and  Thigh.-  The  skin  over  the  hip  is  less  dense  than  over  the 
buttock,  and  is  still  thinner  below  Poupart's  ligament  and  in  the  region  of  Scarpa's 


Gracilis        Adductor  longus 


Dissection  of  pubic  luxation  of  hip-joint. 


PRACTICAL   CONSIDERATIONS  :    THE   HIP   AND   THIGH.       643 

triangle.  Over  all  the  lower  portion  of  the  thigh  it  is  loosely  connected  by  abundant 
connective  tissue  with  the  fascia  lata,  its  attachment  being  closest  along  the  line  of 
the  external  intermuscular  septum,  between  the  vastus  externus  and  the  hamstring 
muscles,  li  is  coarse  externally  and  thinner  over  the  abductor  surfaces.  It  is  easily 
stripped  up  by  effusions  or  retracted  during  operations. 

The  superficial  fascia  in  the  subinguinal  region  is  in  two  layers,  in  the  more 
superficial  of  which  is  the  subcutaneous  fat.  The  deeper  layer  is  the  denser,  and  on 
it  lie  the  lymphatic  nodes  occupying  the  saphenous  opening.  It  offers,  however,  in 
this  region,  but  little  resistance  to  the  progress  of  pus  towards  the  surface,  as  it  is 
perforated — hence  "  cribriform  fascia" — by  the  lymph- vessels  passing  from  the  super- 
ficial to  the  deep  set  of  inguinal  nodes,  by  the  superficial  epigastric  and  external 
puclic  vessels,  and  by  the  internal  saphenous  vein  to  empty  into  the  femoral. 

Lipomata  are  not  infrequent  in  this  fascia,  especially  on  the  front,  but  sometimes 
on  the  back  of  the  thigh,  and  on  account  of  its  laxity  and  of  the  absence  of  firm 
attachments  of  their  capsules,  are  apt  to  travel  downward  by  gravity. 

FIG.  613. 


Femoral  artery 
Femoral  vein. 


Pectineus, 
ujijicr  portion 

Obturator  nerve 


Internal  saphenous  vein 


\          Pectineus,  lower  portion 

Adductor  longus  and  brevis,  lower  portion 
Ligamentum  teres 
Pectineus,  lower  portion 


Dissection  of  thyroid  luxation  of  femur,  showing  muscles  ruptured. 

The  deep  fascia  or  fascia  lata  (page  633),  attached  above  to  the  lower  edge  of 
the  great  sacro-sciatic  ligament,  the  tuberosity  and  ramus  of  the  ischium,  the  crest  of 
the  ilium,  Poupart's  ligament,  and  the  body  and  ramus  of  the  pubes,  and  below  to 
the  lateral  margins  of  the  patella  and  to  the  tibia,  and  continuous  posteriorly  with  the 
deep  fascia  of  the  leg,  forms  an  almost  unbroken  sheath  around  the  thigh.  Its  con- 
tinuity is  interrupted  only  by  the  saphenous  opening  (page  635).  It  is  of  sufficient 
strength  and  density  everywhere  to  influence  the  course  of  abscesses  and  to  modify 
the  surface  appearance  or  feel  of  deep  growths.  A  lipoma  beneath  the  fascia  lata  may 
apparently  have  the  density  of  a  malignant  growth.  A  psoas  abscess  (page  H3)> 
after  it  has  followed  the  muscle  under  and  below  Poupart's  ligament,  usually  perfo- 
rates the  sheath  and  the  fascia  lata  and  points  external  to  the  vessels  at  the  upper  part 
of  the  thigh  ;  but  after  escaping  from  the  sheath  it  may  be  unable  to  penetrate  the 
fascia,  and  may  be  guided  by  it  to  the  lower  third  of  the  thigh,  the  knee,  or  even  as 
low  as  the  leg  or  ankle. 

The  fascia  has  been  torn  or  wounded,  and,  as  it  embraces  the  subjacent  muscles  so 
closely,  the  latter  have  bulged  through  the  opening,  appearing  on  the  surface  of  the 
thigh  as  rounded  elevations  varying  in  size  and  tension  with  the  position  of  the  limb. 


644  HUMAN   ANATOMY. 

Rupture  of  the  fascia  has,  in  recorded  instances,  been  associated  with  rupture  of 
the  ilio-psoas,  the  rectus,  and  the  biceps  femoris.  The  outer  and  inner  intermuscular 
septa  (page  636)  are  of  less  surgical  importance  than  the  corresponding  structures  in 
the  arm,  and  have  but  little  effect  in  limiting  or  determining  the  course  of  a  cellulitis 
or  an  abscess. 

On  the  outer  side  of  the  thigh,  running  from  the  forepart  of  the  crest  of  the  ilium 
above  to  the  outer  tuberosity  of  the  tibia  and  the  head  of  the  fibula  below,  is  the 
thickening  of  the  fascia  lata  known  as  the  ilio-tibial  band,  the  dense,  glistening  fibres 
of  which  bridge  over  the  supratrochanteric  space  between  the  summit  of  the  trochan- 
ter  and  the  iliac  crest.  Normally  at  this  point  the  band  offers  distinct  resistance  to 
pressure  with  the  fingers.  In  fracture  of  the  neck  of  the  femur,  with  shortening,  it 
must  be  relaxed  and  less  resistant  (Allis),  and  this  sign  is  of  especial  value  in  obscure 
cases  of  impacted  fracture  of  the  neck  in  which  crepitus,  preternatural  mobility,  and 
other  of  the  conventional  symptoms  of  fracture  are  lacking  (pages  364,  367,  390). 

The  relations  of  the  muscles  about  the  hip  to  dislocation  (Figs.  395,  396,  pages 
377,  378)  and  to  hip  disease  (page  381)  have  been  described.  Suppuration  affecting 
the  iliacus  or  the  ilio-psoas  has  also  been  dealt  with  (page  381). 

Strains  of  the  ilio-psoas  muscle  are  not  infrequent,  and  may,  especially  in  chil- 
dren, give  rise  to  a  mistaken  diagnosis  of  hip-joint  disease.  In  sprains,  however, 
the  movements  of  the  joint  that  do  not  affect  the  ilio-psoas  will  be  painless  and  most 
of  the  other  anatomical  symptoms  (page  380)  will  be  absent. 

The  extensive  bursa  between  the  capsule  of  the  hip-joint  and  the  ilio-psoas 
muscle  (ilio-psoas  bursa}  may  enlarge  and  become  visible  at  the  front  of  the  thigh 
below  the  middle  of  Poupart's  ligament.  The  thigh  will  be  found  flexed  from  reflex 
irritation  of  the  ilio-psoas  and  to  lessen  pressure  on  the  bursa  (page  381).  As  the 
latter  not  infrequently  communicates  with  the  hip-joint,  infectious  disease  of  one  may 
extend  to  the  other. 

The  adductors  are  also  often  strained  or  overworked,  particularly  during  horse- 
back exercise,  and  are  sometimes  sprained  or  stretched  close  to  their  pelvic  origins. 
The  latter  injury  may  result  in  a  sclerosis  of  one  of  the  adductor  tendons,  possibly 
going  on  to  true  ossification,  and  producing  a  condition  seen  oftenest  in  cavalrymen, 
and  known  as  "  rider's  bone." 

Fractures  of  the  femur  situated  below  the  neck  (page  363)  and  above  the  con- 
dyles  (page  366)  are  much  influenced  by  muscular  action,  as  might  be  expected  from 
the  number  and  strength  of  the  muscles  concerned.  Three  of  these  fractures  may 
be  considered  in  this  relation  : 

1.  Fracture  just  below  the  trochanters  (subtrochanteric  fracture).     This  is  one 
of  the  most  difficult  of  femoral  fractures  to  manage  because  of  the  flexion,  abduc- 
tion, and  outward  rotation  of  the  upper  fragment,  caused  by  the  action  of  the  ilio- 
psoas,  the  gluteus  minimus  and  medius,  the  obturators,  quadratus,  pyriformis,  and 
gemelli.      The  lower  fragment  is  drawn  upward  by  the  rectus,  gracilis,  tensor  fascia- 
latae,    and    sartorius,   upward    and   inward    by  the   adductors,   upward   and  a  little 
backward  by  the  hamstrings.     In  the  treatment,  elevation  and  abduction  of  the  thigh 
— i.e.,  of  the  lower  fragment — are  often  resorted  to  for  obvious  reasons. 

2.  Fracture   of  the   middle  of  the  shaft  is  very  frequent   (page  365).      It 
usually  moderately  oblique  from  behind  downward  and  forward.      The  upper  frag- 
ment is  almost  always  in  advance  of  the  lower  fragment  because  (a)  the  fracturing 
force  is  more  apt  to  be  applied  from  in  front  and  to  the  lower  rather  than  the  upper 
part  of  the  thigh  ;   (&}  the  weight  of  the  limb  in  the  supim-  position  would  favor  a 
posterior  position  of  the  lower  fragment  ;  (Y)  the  ilio-psoas  tends  to  advuna-  the 
upper  fragment,   and  the  adductor  magnus  and  gastrocnemius  draw  the  lower  frag- 
ment somewhat  backward  (Fig.  614).     Then-  is  often  a  forward  angulation  or  bow- 
ing in  the  direction  of  the  normal  curve  of  the  femoral  shaft  (page  365),  thought  to 
In-  din-  to  the  action  of  the  adductors  which  subtend  the  arc  of  the  curve. 

The  shortening  is  produced,  as  usual,  by  the  muscles  running  from  the  pelvis 
to  the  thigh  and  leg. 

3.  Fracture  just  above  the  eondyles  (  supraeondylar  fracture).      This  is  usually 
the  result  of  seven-   injury  or  of  direct    violence.      It  is  commonly  oblique   from   be- 
hind forward  and  downward.      The  fracture  takes  place  at  about  the  point  of  junction 


PRACTICAL   CONSIDERATIONS:    THE   KNEE. 


645 


of  the  compact  tissue  of  the  shaft  with  the  cancellated  tissue  of  the  expanded  lower 
extremity.  It  is  from  one  to  two  inches  higher  than  the  epiphyseal  line.  The  same 
backward  rotation  of  the  lower  fragment  occurs  as  in  disjunction  of  the  epiphysis 
(page  365),  and  in  both  cases  from  the  action  of  the  gastrocnemius.  In  the  fracture, 
however,  the  sharp  lower  end  of  the  upper  fragment  is  far  more  apt  to  project  ante- 
riorly than  is  the  diaphysis  in  cases  of  epiphyseal  disjunction.  It  is  not  infrequently 
entangled  in  fibres  of  the  rectus  and  may  lacerate  the  suprapatellar  synovial  pouch. 
The  difference  probably  results  from  the  character  of  the  fracturing  force,  which  in  the 
epiphyseal  accident  is,  in  the  majority  of  cases,  hyperextension  of  the  leg  on  the 
thigh.  The  action  of  the  ilio-psoas  tends  to  advance  the  lower  end  of  the  upper 
fragment,  but  must  be  feeble.  The  pectineus  slightly  and  the  adductors  quite  strongly 
•draw  it  inward.  The  shortening  is  produced  by  the  hamstrings,  rectus,  sartorius, 
etc.  The  most  difficult  element  of  the  deformity  to  do  away  with  is  the  posterior 
rotation  of  the  lower  fragment,  which  may  also  result  in  serious  pressure  upon  or 
injury  to  the  popliteal  vessels  and  nerves.  In  setting  such  a  fracture  it  may  be  neces- 
sary to  relax  the  chief  muscles  concerned  by  flexing  the  thigh  to  a  right  angle  with 


FIG.  614. 


FIG.  615. 


— "Iliacus 
— Psoas  major 


Lower  fragment  -f- 
Popliteal  artery 


Cast  rocnem  ins. - 
outer  head 


Patella 


Tibia 


Gastrocnemius, 
inner  head 


Dissection  of  fracture  of  upper  third  of  right  femur, 
showing  forward  and  inward  displacement. 


Dissection  of  fracture  of  lower  third  of  left  femur,  show- 
ing displacement  of  popliteal  artery  by  lower  fragment. 


the  pelvis  to  relax  the  ilio-psoas,  drawing  the  knee  inward  a  little  to  relax  the  ad- 
ductors, and  flexing  the  leg  on  the  thigh  to  relax  the  gastrocnemius,  and  then  to 
make  extension  by  means  of  the  forearm  placed  in  the  ham.  Not  uncommonly  the 
displacement  recurs  so  obstinately  that  it  becomes  necessary  to  treat  the  case  with 
the  leg  fully  flexed  on  the  thigh,  and  even  to  divide  the  tendo  Achillis. 

3.  The  Knee. — The  skin  over  the  front  of  the  knee  is  dense,  coarse,  and 
loose,  qualities  that  diminish  the  gravity  of  the  frequent  injuries  to  the  integument 
itself  and  also  serve  to  protect  the  underlying  joint,  "  especially  in  stabs  with  bluntish 
instruments"  (Treves)  and,  in  fact,  in  many  forms  of  accident  in  which  the  free 
movement  of  the  skin  over  the  subjacent  structures  serves  to  make  the  application  of 
force  to  the  latter  much  less  direct. 

In  full  flexion  the  skin,  in  spite  of  its  laxity,  is  drawn  tensely  over  the  patella, 
and  a  fall  may  result  in  an  extensive  wound. 

The  relation  of  the  cutaneous  nerves  and  vessels  over  the  knee  to  those  supply- 
ing the  articulation  should  be  studied  in  connection  with  the  common  application  of 
counterirritants  or  of  blisters  to  the  region. 


646 


HUMAN   ANATOMY. 


FIG.  616. 


Vastus  ititernus 


The  quadriceps  tendon  is  separated  from  the  femur  by  a  large  bursa,  which,  in 
from  70  to  80  per  cent,  of  cases,  communicates  with  the  knee-joint  and  may  be  in- 
volved in  its  diseases.  When  separate  from  the  joint  and  distended  by  effusion,  it 
may  be  mistaken  for  synovitis  of  the  knee,  but  the  patella  will  not  be  floated  up  and 
the  concavities  at  either  side  of  that  bone  and  those  at  the  sides  of  the  ligamentum 
patellae  will  not  be  effaced. 

The  prepatellar  bursa,  separating  the  patella  from  the  skin,  is  frequently  enlarged 
in  persons  who  spend  much  time  kneeling, — "  housemaid's  knee." 

The  bursa  between  the  ligamentum  patellae  and  the  tubercle  of  the  tibia  may  be 
enlarged  or  inflamed,  and  is  then  apt  to  be  painful  on  account  of  its  compression 
between  two  non-distensible  structures,  the  bone  and  the  ligament.  The  little  pad 
of  fat  (page  400)  between  the  tubercle  and  the  ligament,  which  protrudes  at  the  sides 
of  the  latter  when  the  quadriceps  extensor  is  in  action  (page  405),  should  not  be  mis- 
taken for  enlargement  of  this  bursa. 

Posteriorly — over  the  ham — the  skin  is  thinner  and  less  movable.  The  deep 
fascia — here  the  popliteal  fascia — is  dense  and  exerts  marked  obstruction  to  the  exten-* 

sion  of  abscess,  growth,  or  aneurism  towards 
the  surface,  in  this  way  causing  severe  pain 
from  the  pressure  upon  the  nerves  that  run 
through  the  space.  As  the  latter  is  open 
above  and  below,  abscesses  may  extend  in 
either  direction. 

Pus  or  infection  may  be  guided  to  the 
subfascial  region  in  the  ham  from  the  pelvis 
or  the  buttock  by  the  great  sciatic  nerve,  or 
from  the  thigh  by  the  femoral  vessels,  or 
from  the  leg  by  the  short  saphenous  vein, 
or  by  the  deeper  vessels  and  the  lymphatics. 
The  relations  of  the  fascia  and  muscles 
of  the  thigh  to  the  patella  and  the  knee- 
joint  and  to  their  injuries  and  diseases  have 
been  sufficiently  described  (Figs.  424-430, 
pages  409-418). 

The  hamstring  tendons  are  not  infre- 
quently divided,  as,  for  reasons  already 
given,  ankylosis  of  the  knee-joint  is  usu- 
ally in  the  position  of  flexion  (page  412). 
They  are  made  very  tense  when  the  pelvis  is  strongly  flexed  on  the  thigh,  the  knee 
remaining  extended.  They  may  be  ruptured  if  excessive  force  is  applied  under 
these  circumstances. 

The  biceps  tendon  is  easily  felt  on  the  outer  side  of  the  ham,  with  the  peroneal 
nerve,  also  readily  palpable,  lying  against  its  inner  and  posterior  border.  At  the  inner 
side  of  the  ham  the  semitendinosus  tendon  is  nearer  the  mid-line,  nearer  the  surface, 
more  easily  outlined,  thinner,  and  more  cord-like  than  the  semimembranosus  tendon, 
which  is  the  most  deeply  situated  of  the  three  hamstrings.  The  line  for  dividing 
these  tendons  is  preferably  a  little  above  the  level  of  the  knee-joint  and  about  opposite 
the  most  salient  parts  of  the  femoral  condyles. 

In  the  popliteal  region  there  are  several  bursae  :  (a)  the  largest  is  between  the 
inner  head  of  the  gastrocnemius  and  the  semimembranosus  and  the  inner  condyle  of 
the  femur,  extending  downward  to  the  inner  tibial  tuberosity  and  even  as  low  as  the 
upper  margin  of  the  popliteus  ;  it  communicates  with  the  joint  in  50  per  cent,  or 
more  of  cases  (Foucher,  Gruber);  (£)  a  smaller  bursa  is  found  between  the  st-mi- 
membranosus  and  the  internal  tuberosity  of  the  tibia,  communicating  usually  with 
the  above-described  bursa.  Externally  there  are  :  (r)  a  bursa  brtwoen  the  lateral 
ligament  and  the  tendon  of  the  popliteus  ;  (</)  a  bursa — a  diverticulum  of  the  syno- 
vial  membrane  of  the  knee  (Nancrede) — between  the  same  tendon  and  the  external 
tibial  tuberosity  ;  (<•)  a  bursa  between  the  external  lateral  ligament  and  the  biceps 
tendon,  in  close  relation  to  the  external  popliteal  nerve  ;  and  (/)  a  bursa  between 
the  outer  head  of  the  gastrocnemius  and  the  external  condyle  of  the  femur. 


Fractured  surfaces 
of  patella 


Torn  fibrous  expansion 
from  patella  to  capsu- 
lar  ligament  of  knee- 
joint 


Dissection  of  fracture  of  patella. 


THE   CRURAL   MUSCLES.  647 

Nancrede  says,  that  of  the  six  popliteal  bursae,  one — the  subpopliteal  (d) — 
always  communicates  with  the  joint,  and  occasionally  with  the  upper  tibio-fibular 
joint  (Gruber)  ;  one — that  between  the  gastrocnemius  arid  the  semimembranosus 
(a) — generally  does  so  ;  and  one  (V)  occasionally  does  so. 

Enlargement  of  these  bursae  leads  to  stiffness  and  disability  in  the  use  of  the 
knee.  Extension  may  be  painful  and  may  show  the  presence  of  a  tense,  rounded, 
fluctuating  swelling.  This  will  usually  be  at  the  inner  side  of  the  popliteal  region, 
because  the  bursa  beneath  the  gastrocnemius  and  semimembranosus — the  largest  of 
the  bursae — is  the  one  most  often  enlarged. 

It  may,  on  account  of  the  transmitted  pulsation,  be  mistaken  for  an  aneurism, 
but  should  be  distinguished  by  the  facts  that,  if  due  to  bursal  enlargement,  the  swell- 
ing— unlike  that  of  aneurism — may  (#)  lessen  or  quite  disappear  when  the  knee  is 
slightly  flexed,  the  narrow  passage  between  the  bursa]  sac  and  the  joint  being  com- 
pressed when  the  posterior  ligament  is  tense  and  patulous  when  it  is  relaxed  ;  (£) 
reappear  slowly  and  not  almost  instantly  ;  (<:)  become  tenser  and  more  prominent  on 
fult  extension  ;  (V)  will  have  a  transmitted,  not  an  expansile  pulsation  ;  and  (<?) 
will  be  unaffected  as  to  bulk  by  digital  compression  of  the  femoral  artery. 

A  popliteal  lipoma — the  only  other  condition  likely  to  be  confused  with  a  non- 
suppurating,  enlarged  bursa — occupies  no  definite  position  in  the  ham,  has  no  sharply 
defined  outline,  undergoes  little  or  no  increase  of  tension  when  the  leg  is  extended, 
and  is  apt  to  have  attachments  to  the  deep  surface  of  the  skin  (Nancrede). 

THE   CRURAL    MUSCLES. 

The  crural  muscles  are  primarily  inserted  into  the  bones  of  the  leg  or  into  the 
tarsus,  but,  like  the  antibrachial  muscles,  many  of  them  have  been  extended  into 
the  foot  and  act  upon  the  digits. 

The  crural  fascia  is  a  strong  aponeurotic  sheath  investing  the  muscles  of  the 
leg,  at  the  knee  being  continuous  with  the  fascia  lata  and  below  with  the  fascia  of 
the  foot.  Over  the  external  and  internal  malleoli  and  along  the  entire  inner  surface 
of  the  tibia  the  fascia  blends  with  the  subjacent  periosteum  ;  from  the  last  of  these 
attachments  a  deep  layer  is  given  off  which  passes  across  to  the  fibula,  between  the 
superficial  and  deeper  muscles  of  the  back  of  the  leg.  That  portion  of  the  fascia 
which  covers  the  muscles  of  the  front  of  the  leg  is  exceedingly  strong,  but  it  is 
thinner  over  the  calf.  The  upper  part  of  its  posterior  portion  is  somewhat  thickened, 
and  forms  part  of  the  roof  of  the  popliteal  space.  Below  the  fascia  is  strengthened 
by  transverse  fibres  which  form  bands  that  bind  down  the  tendons  passing  over  the 
ankle-joint. 

Of  these  bands  two  are  situated  upon  the  anterior  surface  of  the  ankle-joint, 
together  forming  the  structure  termed  the  anterior  anmilar  ligament  (Fig.  623). 
The  upper  or  vertical  portion  of  this  (ligamentum  transversum  cruris)  extends  trans- 
versely across  between  the  lower  ends  of  the  tibia  and  fibula,  a  little  above  the  ankle- 
joint.  The  space  beneath  this  band  is  divided  by  a  partition  into  two  compartments, 
the  more  lateral  of  which  contains  the  extensor  longus  hallucis  and  the  extensor 
longus  digitorum,  enclosed  by  separate  synovial  sheaths,  while  the  more  medial  one 
contains  the  tibialis  anticus.  The  lower  or  horizontal  portion  of  the  ligament  (liga- 
mentum cruciatum)  is  Y-shaped.  Externally  it  is  attached  to  the  outer  surface  of 
the  calcaneum  and  passes  inward,  enclosing  the  tendons  of  the  extensor  longus  digi- 
torum, and  then  divides  into  two  limbs,  the  upper  of  which  passes  upward  and 
inward,  over  the  tendons  of  the  extensor  longus  pollicis  and  the  tibialis  anticus,  to 
be  inserted  into  the  inner  malleolus,  just  below  the  medial  end  of  the  ligamentum 
transversum.  The  lower  limb  passes  downward  and  inward  to  be  attached  to  the 
inner  border  of  the  plantar  fascia. 

On  the  posterior  surface  three  bands  occur.  Two  of  these  serve  to  bind  down 
the  tendons  of  the  peroneus  longus  and  brevis  as  they  pass  behind  the  external  mal- 
leolus, together  forming  the  lateral  annular  ligament  (retinacula  mm.  peronaeorum). 
The  upper  band  extends  downward  and  backward  from  the  outer  malleolus  to  the 
calcaneum,  while  the  lower  one,  arising  from  the  calcaneum  at  the  point  at  which 
the  outer  end  of  the  cruciate  ligament  is  attached,  extends  backward  over  the 


648 


IITMAN   ANATOMY. 


peroneal  tendons  to  be  attached  to  the  tuberosity  of  the  same  bone.  The  other 
band,  the  internal  annular  ligament  (ligamentum  laciniatumj  passes  downward  and 
backward  from  the  inner  malleolus  to  the  calcaneum,  bridging  over  a  groove  which 
is  divided  into  four  compartments  by  partitions  extending  from  the  ligament  to  the 
subjacent  bone.  The  innermost  of  these  compartments  is  occupied  by  the  posterior 
tibial  muscle  ;  the  second  one  contains  the  tendon  of  the  flexor  longus  digitorum  ; 
the  third,  the  posterior  tibial  vessels  and  nerve  ;  and  the  outermost,  the  tendon  of 
the  flexor  longus  hallucis. 

From  the  deep  surface  of  that  portion  of  the  crural  fascia  which   covers  the 
peroneus  longus  and  brevis  two  strong  expansions  of  connective  tissue  pass  deeply, 

FIG.  617. 


Anterior  tibial  artery 
Anterior  tibial  nerve 

Extensor  longus  digitorum 
Musculo-cutaneous  nerv< 

Extensor  longus  halluci 

Peroneus  longu 

Peroneus  brevi 

Fibula 

Extern,  intermuscular  septum 

Flexor  longus  halluci 

Peroneal  vesse 
Deep  fascial  sept 

Gastrocnemius,  outer  hea< 


Tibialis  anticus 

Interosseous  membrane 


\ 


d/ 


Tibia 


Tibialis  posticus 

Flexor  longus  digitorum 
Internal  saphenous  vein 

Posterior  tibial  vessels 
Internal  saphenous  nerve 
Posterior  tibial  nerve 


Soleus 

Tendon  of  plantaris 
-Gastrocnemius,  inner  head 

Deep  fascia 


Superficial  fascia 
Section  across  right  leg  at  junction  of  upper  and  middle  thirds,  viewed  from  below. 


one  in  front  of  and  one  behind  the  muscles,  to  be  attached  to  the  fibula.  These  are 
the  anterior  and  posterior  intermuscular  septa  ;  they  serve  for  the  origin  of  portions 
of  the  adjacent  muscles. 

In  regions  in  which  the  crural  fascia  is  adherent  to  subjacent  bony  structures  a 
number  of  subcutaneous  bursa  occur  between  the  deep  fascia  and  the  integument 
Thus,  over  the  patella  there  is  usually  to  be  found  a  bursa  (bursa  prepatellaris  sub- 
cutanca)  ;  occasionally  one  (bursa  prepa$llaris  subfascialis )  occurs  between  the 
patella  and  the  fascia.  Another  (bursa  infrapatellaris  subcutanea)  frequently  lies  over 
the  ligamentum  patellae,  and  immediately  below  it  the  bursa  subcutanea  tubcrositatis 
tibiae.  Again,  over  each  malleolus  a  bursa  often  exists  ( bursae  malleoli  latcralis  et 
medialis) ;  finally,  a  bursa  frequently  occurs  over  the  tendo  Achillis  at  its  insertion 
into  the  tuberosity  of  the  calcaneum  (bursa  subcutanea  temlinis  calcanei). 


(a)  THE   PRE- AXIAL  MUSCLES. 

As  is  the  case  with  the  antibrachial  pre-axial  muscles,  those  of  the  crus  are 
primarily  arranged  in  three  layers,  the  most  superficial  sheet  being  attached  above 
to  the  condyles  of  the  femur,  for  the  most  part  to  the  outer  one.  A  further  simi- 
larity to  the  arrangement  in  the  fore-arm  is  to  be  found  in  the  continuation  of  the 
muscles  of  the  middle  layer  into  the  foot,  to  act  as  flexors  of  the  digits. 


THE   CRURAL   MUSCLES.  649 

(aa)  THK   SUPERFICIAL   LAYER. 

i.    Gastrocnemius.          2.   Soleus. 
3.    Plantaris. 

The  main  mass  of  the  calf  of  the  leg  is  formed  by  two  muscles,  the  gastroc- 
nemius  and  the  soleus,  which  unite  below  in  a  common  tendon,  the  tendo  Achillis 
(tendo  calcaneus),  inserted  into  the  posterior  surface  of  the  tuberosity  of  the  calca- 
neum,  a  bursa  (bursa  tendinis  calcanei)  intervening  between  the  tendon  and  the  upper 
part  of  the  tuberosity.  Since  the  gastrocnemius  arises  by  two  heads,  these  two 
muscles  together  are  sometimes  spoken  of  as  the  triceps  surcc. 

GASTROCNEMIUS  (Fig.  618). 

Attachments. — The  gastrocnemius  takes  origin  by  two  heads.  The  outer 
head  arises  from  the  posterior  surface  of  the  femur,  just  above  the  lateral  condyle, 
by  a  short,  strong  tendon  which  sometimes  contains  a  sesamoid  cartilage  ;  the  inner 
head  arises  also  by  a  short  tendon  just  above  the  .medial  condyle  of  the  femur. 
Above,  the  two  heads  are  separated  from  each  other  by  a  groove,  but  below  they 
unite  to  form  a  thick  belly,  the  fibres  of  which  pass  over  into  a  broad,  flat  tendon 
inserted  below  with  the  tendo  Achillis. 

Nerve-Supply. — By  the  internal  popliteal  (tibial)  division  of  the  greater  sciatic 
nerve  from  the  first  and  second  sacral  nerves. 

Action. — To  extend  the  foot  and  to  assist  in  flexing  the  knee-joint. 

Relations. — The  gastrocnemius  is  in  relation  by  its  posterior  surface  with  the 
short  saphenous  vein  and  nerve.  On  its  deep  surface  it  is  in  contact  with  the 
plantaris  and  soleus  muscles  (Fig.  617),  and  in  its  upper  part  with  the  capsule  of 
the  knee-joint,  the  popliteus,  and  the  popliteal  vessels  and  nerves. 

A  bursa  (bursa  in.  gastrocnemii  medialis)  intervenes  between  the  inner  head  and 
the  capsule  of  the  knee-joint,  with  the  synovial  cavity  of  which  it  is  frequently 
continuous;  the  bursa  m.  gastrocnemii  lateralis  frequently  presents  similar  relations  to 
the  outer  head. 

Variations. — Absence  of  the  entire  muscle  or  of  the  outer  head  has  been  observed,  but  the 
most  frequent  anomaly  is  the  occurrence  of  a  third  head  which  arises  from  some  portion  of  the 
popliteal  surface  of  the  femur. 

2.    SOLEUS  (Fig.   619). 

Attachments. — The  soleus  is  a  broad,  flat  muscle  which  arises  from  the  head 
and  upper  posterior  portion  of  the  fibula,  from  the  oblique  line  of  the  tibia,  and  from 
a  tendinous  arch  which  passes  across  between  the  tibial  and  fibular  origins.  Its 
fibres  pass  downward  to  a  broad  tendon  which  joins  with  the  tendo  Achillis  below. 

Nerve-Supply. — By  the  internal  popliteal  (tibial)  division  of  the  greater  sciatic 
nerve  from  the  first  and  second  sacral  nerves. 

Action. — To  extend  the  foot. 

» 

3.    PLAXTARIS  (Fig.   619). 

Attachments. — The  plantaris  is  a  small  spindle-shaped  muscle  which  passes 
over. into  a  long,  slender  tendon  extending  downward  between  the  gastrocnemius 
and  soleus.  The  muscle  arises  from  the  femur,  just  above  the  outer  condyle,  internal 
to  the  lateral  head  of  the  gastrocnemius,  and  from  the  adjacent  part  of  the  posterior 
ligament  of  the  knee-joint.  The  tendon  traverses  almost  the  entire  length  of  the'  leg 
and  is  inserted  either  into  the  tuberosity  of  the  calcaneum  along  with,  but  to  the 
inner  side  of,  the  tendo  Achillis,  sending  also  some  fibres  to  the  internal  annular  liga- 
ment, or  into  the  tendo  Achillis  itself. 

Nerve-Supply. — By  the  internal  popliteal  (tibial)  division  of  the  greater  sciatic 
nerve  from  the  fifth  lumbar  and  first  sacral  nerves. 


650 


HUMAN   ANATOMY. 


FIG.  6 i 8. 


Internal 
condyle 


Gastrocnemius, 
inner  head 


Gastrocnemius, 
outer  head 


Tendo  Achilli 


External  condyle  FlG.   619. 


Gastrocnemius, 
outer  head 


Plantaris 


Popliteus 


Intermuscular  septum 
(to  posterior  border 
of  fibula) 


Gastrocnemius, 
tendon 


Intermuscular  septum 

Tendo  Achillis 
External  malleolus 


Superficial  dissection  of  posterior  sur- 
face of  right  leg,  showing  muscles  undis- 
turbed. 


Muscles  o 
leg;  K:i>u<K-n 
pofting  plantaris  and  soleus. 


erior  surface  of  right 
luis  been  removed,  ex- 


THE   CRURAL   MUSCLES.  651 

Action. — To  assist  in  extending  the  foot  and  to  tense  the  crural  fascia  at  the 
ankle-joint. 

Variations. — The  plantaris  is  absent  in  about  7  per  cent,  of  cases.  Its  insertion  may  be 
into  the  calcaneum,  the  tendo  Achillis,  the  crural  fascia,  or  even  into  the  plantar  aponeurosis. 

(bb)  THE  MIDDLE  LAYER. 
i.   Flexor  longus  digitorum.      2.   Flexor  longus  hallucis. 

i.    FLEXOR  LONGUS  DIGITORUM  (Figs.  620,  628). 

Attachments. — The  long  flexor  of  the  toes  (m.  flexor  digitorum  longus)  arises 
from  almost  the  whole  of  the  posterior  surface  of  the  tibia  below  the  oblique  line  and 
from  the  deep  surface  of  the  deep  layer  of  the  crural  fascia.  Its  fibres  converge  in  a 
bipinnate  manner  to  a  tendon  which  passes  laterally  to  the  tendon  of  the  tibialis 
anticus  beneath  the  internal  annular  ligament,  and  so  reaches  the  plantar  region  of 
the  foot.  There  it  is  directed  somewhat  laterally,  receiving  the  insertion  of  the  flexor 
accessorius,  and  divides  into  four  tendons  which,  passing  through  the  divided  ten- 
dons of  the  flexor  brevis,  are  inserted  into  the  base  of  the  third  or  distal  phalanx  of 
the  second,  third,  fourth,  and  fifth  toes. 

Nerve-Supply. — By  the  posterior  tibial  nerve  from  the  fifth  lumbar  and  first 
sacral  nerves. 

Action. — To  flex  the  second,  third,  fourth,  and  fifth  toes  ;  continuing  its  action, 
to  extend  the  foot  and  to  cause  slight  inversion  of  the  sole. 

Relations. — In  the  leg  (Fig.  617)  the  flexor  longus  is  covered  by  the  soleus 
and  has  resting  upon  it  the  lower  portions  of  the  posterior  tibial  vessels  and  nerve. 
It  rests  upon  the  tibialis  posticus,  crossing  it  obliquely  in  the  lower  part  of  the  leg. 
In  the  foot  its  tendons  are  covered  by  the  flexor  brevis  digitorum,  and  pass  between 
the  two  terminal  slips  of  the  tendons  of  that  muscle  over  the  first  phalanges.  Its 
tendon  is  also  covered  by  the  abductor  hallucis,  and  crosses  obliquely  the  tendon  of 
the  flexor  longus  hallucis  and  the  oblique  portion  of  the  adductor  hallucis.  The 
lumbricales  take  their  origin  from  its  tendons,  and  it  receives  the  insertion  of  the 
flexor  accessorius. 

Variations. — ^flexor  digitorum  longus  accessorius  is  occasionally  found  arising  indepen- 
dently from  the  tibia  or  from  the  fibula  and  joining  the  tendon  of  the  long  flexor  below,  or  else 
uniting  with  the  flexor  accessorius. 

2.  FLEXOR  LONGUS  HALLUCIS  (Figs.  620,  628). 

Attachments. — The  long  flexor  of  the  great  toe  (m.  flexor  hallucis  longus)  arises 
from  the  posterior  surface  of  the  fibula,  from  the  posterior  intermuscular  septum, 
and  from  the  deep  surface  of  the  deep  layer  of  the  crural  fascia.  Its  fibres  converge 
bipinnately  to  a  tendon  which  passes  beneath  the  internal  annular  ligament,  pos- 
terior to  the  posterior  tibial  vessels  and  nerve,  and  so  enters  the  plantar  surface 
of  the  foot.  There  it  passes  beneath  the  tendon  of  the  flexor  longus  digitorum, 
to  which  it  sends  a  slip,  and  continues  distally  to  be  inserted  into  the  base  of  the 
distal  phalanx  of  the  great  toe,  passing  between  the  flexor  brevis  hallucis  and  the 
first  plantar  interosseous. 

Nerve-Supply. — By  the  posterior  tibial  nerve  from  the  fourth  and  fifth  lumbar 
and  first  sacral  nerves. 

Action. — To  flex  the  hallux  and  extend  and  slightly  supinate  the  foot. 

Variations. — The  principal  variations  of  the  flexor  longus  hallucis  concern  its  union  with 
the  tendon  of  the  flexor  longus  digitorum.  The  passage  of  a  slip  between  the  two  tendons  is 
constant,  but  its  distribution  to  the  tendons  of  the  flexor  digitorum  varies  considerably.  Usually 
it  separates  into  two  slips  which  pass  to  the  tendons  for  the  second  and  third  toes,  but  it  may  also 
pass  to  the  tendons  for  the  second,  third,  and  fourth  toes,  to  that  of  the  second  alone,  or  even 
to  all  the  tendons  of  the  flexor  longus  digitorum.  It  may  also  completely  replace  the  tendon 
usually  passing  from  the  flexor  longus  digitorum  to  the  second  digit. 


652 


HUMAN    ANATOMY. 


These  variations  of  the  flexor  longus  hallucis  are  explicable  on  the  basis  that  its  history, 
together  with  that  of  the  flexor  longus  digitorum,-  has  been  very  similar  to  that  of  the  flexor 


FIG.  620. 


Internal  condyle  of  femur 


Tendon  of  semimembranosus- 


Popliteus 


Soleus,  cut ^ 


Tibia 


Flexor  longus  digitorum  — 


Soleus,  cut 


Gastrocnemius 


Plantaris,  cut 
<* -^-Headoi  fibula 


Peroneus  longus 
Soleus,  cut 


Tibialis  posticus 


Flexor  longus  hallucis 


Abductor  and 

flexor  brevis  hallucis. 


Tendon  of  peroneus  longus 


Peroneus  brevis 

Tibia  and  posterior  inferior  tibio- 
fibular  ligament 

Tendo  Achillis,  stump 
Internal  lateral  ligament 


Abductor  halluci 
Insertion  of  tibialis  posticus 

Insertion  of  tibialis  ant 


Inner  tubercle  of  os  calcis 
Outer  tubercle  of  os  calcis 

Flexor  brevis  digitorum,  stump 
Abductor  minimi  digit! 

Flexor  accessor!  us 

Flexor  brevis  minimi  digit! 
Interosseus 

I.umbricales 

•  Tendons  of  flexor  brevis  digitorum 
Deeper  .lissr,  tiun  of  right  leg,  showing  flexors  passing  into  foot. 

snblimis  digitorum  and  flexor  longus  pollicis  of  the  forearm.  In  other  words,  these  muscles 
represent  a  I.IY<T  of  niii^rlc-tissuc  \\liicli  primarily  arose  from  the  bones  of  the  leg  and  was  in- 
serted into  the  deeper  layers  of  the  plantar  aponeurosis.  Later  tendons  differentiated  from  the 


THE   CRURAL   MUSCLES. 


653 


Elantar  aponeurosis  and  the  muscles  were  continued  to  the  digits.     The  separation  of  the  flexor 
allucis  from  the  rest  of  the  muscle  took  place  later,  and  even  yet  is  somewhat  incomplete,  the 


FIG.  621. 


Internal  condyle— £^3 


Internal  lateral  ligament 


External  condyle 

Tendon  of  popliteus 
Head  of  fibula 


Anterior  tibial  artery 
Fibula 

Peroneus  longus 


Tibialis  posticus 


Flexor  longus  digitorum, 
drawn  aside 


Flexor  longus  hallucis, 
drawn  aside 


Internal  lateral  ligament 

Tibialis  anticus__^;, 
Abductor  hallucis,  stump_ 
Insertion  of  tibialis  posticus 


Insertion  of  tibialis  anticus. 
Tendon  of  flexor  longus  hallucis  _ 


Peroneus  longus 

Fibula 

.Posterior  inf.  tibio-fibular  ligament 

Tendo  Achillis,  stump 


Inner  tubercle  of  os  calcis 
Outer  tubercle  of  os  calcis 
Flexor  brevis  digitorum,  stump 

Flexor  longus  digitorum  tendon 
Flexor  accessorius 
Abductor  minimi  digiti 


Deep  dissection  of  right  leg;  flexors  have  been  turned  aside  to  expose  tibialis  posticus. 


connections  between  its  tendon  and  that  of  the  flexor  longus  digitorum  being  indications  of  its 
developmental  history. 


654 


HUMAN   ANATOMY. 


(cc)   THE  DEEP  LAYER. 

i.   Tibialis  posticus.          2.   Flexor  accessorius. 
3.    Popliteus. 

i.  TIBIALIS  POSTICUS  (Fig.  621). 

Attachments. — The  posterior  tibial  (m.  tibialis  posterior)  arises  from  the  pos- 
terior surface  of  the  interosseous  membrane  and  from  the  adjacent  surface  of  both 
the  tibia  and  fibula.  Its  fibres  pass  into  a  tendon,  situated  along  its  inner  border, 
which  passes  obliquely  downward  and  inward  beneath  the  flexor  longus  digitorum. 
It  is  continued  onward  beneath  the  most  central  portion  of  the  internal  annular  liga- 
•  ment  to  the  plantar  surface  of  the  foot,  where  it  is  inserted  into  the  tuberosity  of  the 
scaphoid  bone,  sending  prolongations  to  all  the  other  tarsal  bones,  except  the  astra- 
galus, and  to  the  bases  of  the  second,  third,  and  fourth  metatarsals. 

Nerve-Supply. — By  the  posterior  tibial  nerve  from  the  fourth  and  fifth  lumbar 
and  first  sacral  nerves. 

Action. — To  extend  the  foot  and  to  slightly  invert  the  sole. 
Relations. — The  posterior  tibial  is  the  deepest  muscle  upon  the  posterior  sur- 
face of  the  leg.  It  is  covered  by  the  soleus  and  by  the  flexor  longus  digitorum,  and 
has  resting  upon  it  the  upper  portion  of  the  posterior  tibial  and  peroneal  vessels  (Fig. 
617).  The  anterior  tibial  vessels  pass  through  the  interosseous  membrane  immedi- 
ately above  the  origin  of  the  muscle..  A  bursa  sometimes  intervenes  between  its 

tendon  and  the  tuberosity  of 

FIG.  622.  the  scaphoid  bone,    and  the 

tendon  usually  contains  a  ses- 
amoid  cartilage  or  bone  where 
vastus  intemus— »  /        -,.     V Va  ft  passes  over  the  head  of  the 

Popliteal  surface  of  femur       nctracra1n<5 
External  condyle  aSiragaiUb. 

Variations. — A  portion  of  the 
muscle  is  sometimes  inserted  into 
the  internal  annular  ligament. 

A  muscle,  which  has  been 
called  the  peroneo-tibialis,  not  in- 
frequently extends  across  between 
the  fibula  and  tibia,  immediately 
beneath  the  tibio-fibular  articula- 
tion and  above  the  anterior  tibial 
vessels  as  they  pass  towards  the 
front  of  the  leg.  It  is  usually  ru- 
dimentary, but  may  form  a  well- 
marked  triangular  sheet. 


Inner  condyle 


Insertion  of 
semimembranosus 


Poplite 


Cut  edge  of  capsular 

ligament 
Long  external 
lateral  ligament 
Short  external 

lateral  ligament 


Interosseous  membrane 


Tibia 


—  Fibula 


Deep  dissection  of  leg,  showing  popliteus  muscle. 


2.   FLEXOR  ACCESSORIUS 
(Fig.  628). 

Attachments. — The  ac- 
cessory flexor  of  the  toes  (m. 
quadratus  plantae)  arises  by  two  heads  from  the  medial  and  inferior  surfaces  of  the 
calcaneum  and,  passing  distally,  is  inserted  into  the  tendon  of  the  flexor  longus 
digitorum. 

Nerve-Supply. — By  the  external  plantar  nerve  from  the  first  and  second  sacral 
nerves. 

Action. — By  acting  on  the  long  flexor  tendons,  to  flex  the  second,  third,  fourth, 
and  fifth  toes,  and  to  counteract  the  oblique  pull  of  the  long  flexor. 

The  flexor  accessorius,  although  apparently  located  entirely  in  the  foot,  is,  nevertheless,  a 
rrural  muscle,  since  the  tendon  of  the  flexor  longus  digitorum,  into  which  it  is  inserted,  repre- 
sents, as  has  already  been  pointed  out.  a  portion  of  the  plantar  aponeurosis.  Into  this  many 
of  the  muscles  of  the  leg  were  primarily  inserted,  and  the  accessorius  represents  the  most  distal 
portion  of  the  original  deep  sheet  of  the  crural  musculature. 


THE   CRURAL   MUSCLES.  655 

3.    POPLITEUS   (Fig.   622). 

Attachments. — The  popliteus  arises  by  a  narrow  tendon  from  the  outer  con- 
dyle  of  the  femur  and  by  a  slip  from  the  posterior  ligament  of  the  knee-joint.  It 
passes  inward  and  downward  to  be  inserted  into  the  posterior  surface  of  the  tibia 
above  the  oblique  line. 

Nerve-Supply. — By  the  internal  popliteal  (tibial)  division  of  the  greater  sciatic 
nerve  from  the  fifth  lumbar  and  first  sacral  nerves. 

Action. — To  flex  the  leg  and  rotate  it  inward. 

Relations. — On  its  posterior  surface  it  is  covered  by  the  plantaris  and  gas- 
trocnemius,  and  it  is  crossed  by  the  popliteal  vessels  and  internal  popliteal  nerve. 
By  its  deep  surface  it  is  in  relation  to  the  capsule  of  the  knee-joint,  a  bursa  (bursa  ra. 
poplitei)  intervening. 

Variations. — The  most  frequent  anomaly  in  connection  with  the  popliteus  is  the  occurrence 
of  a  second  head,  which  arises  from  the  sesamoid  cartilage  of  the  lateral  head  of  the  gastroc- 
nemius.  The  occurrence  of  this  head  is  frequently  associated  with  the  absence  of  the  plantaris. 

(b}    THE  POST-AXIAL  MUSCLES. 

1.  Tibialis  anticus.  4.    Extensor  longus  hallucis. 

2.  Extensor  longus  digitorum.          5.    Peroneus  longus. 

3.  Peroneus  tertius.  6.    Peroneus  brevis. 

TIBIALIS  ANTICUS  (Fig.  623). 

Attachments. — The  anterior  tibial  muscle  (m.  tibialis  anterior)  arises  from  the 
outer  tuberosity  and  surface  of  the  tibia  and  also  from  the  interosseous  membrane 
and  the  crural  fascia.  Its  fibres  extend  downward  to  a  strong  tendon  which  passes 
through  the  inner  compartment  of  the  anterior  annular  ligament  and  is  inserted 
into  the  inner  surface  of  the  internal  cuneiform  and  the  base  of  the  first  metatarsal 
bone. 

Nerve-Supply. — By  the  anterior  tibial  nerve  from  the  fourth  and  fifth  lumbar 
and  first  sacral  nerves. 

Action. — To  flex  the  foot  ;  to  draw  up  the  inner  border  and  hence  invert  the 
sole. 

Relations. — The  anterior  tibial  rests  upon  the  lateral  surface  of  the  tibia  and 
upon  the  interosseous  membrane,  and  is  in  contact  externally  with  the  extensor 
longus  digitorum,  the  extensor  longus  hallucis,  and  the  anterior  tibial  vessels  and 
nerve  (Fig.  617).  A  bursa  (bursa  subtendinea  m.  tibialis  anterioris)  intervenes 
between  its  tendon  and  the  medial  cuneiform  bone. 

Variations. — Not  infrequently  a  bundle  is  detached  from  the  muscle  to  be  inserted  into  the 
anterior  annular  ligament,  into  the  dorsal  fascia  of  the  foot,  or,  in  some  cases,  into  the  astragalus. 
It  forms  what  has  been  termed  the  tibio-fascialis  anterior  or  tibio-asiragalus. 

2.    EXTENSOR  LONGUS  DIGITORUM  (Fig.  623). 

Attachments. — The  long  extensor  of  the  toes  (m.  extensor  digitorum  longus) 
arises  from  the  external  condyle  of  the  tibia,  the  upper  part  of  the  fibula,  the  in- 
terosseous membrane,  the  intermuscular  septum,  and  the  crural  fascia.  Its  fibres 
pass  downward  and  terminate  at  about  the  middle  of  the  leg  in  a  tendon  which  passes 
through  the  outer  compartment  of  the  anterior  annular  ligament  and  divides  into  four 
tendons  which  pass  to  the  second,  third,  fourth,  and  fifth  toes.  Over  the  metatarso- 
phalangeal  joint  of  its  digit  each  tendon  spreads  out  into  a  membranous  expansion 
which  covers  the  dorsum  of  the  first  phalanx  and  receives  the  insertions  of  the  inter- 
ossei  and  lumbricales,  and,  in  the  case  of  the  second,  third,  and  fourth  toes,  those  of 
the  extensor  brevis  digitorum.  Distally  each  membranous  expansion  divides  into 
three  slips,  of  which  the  middle  one  is  inserted  into  the  second  phalanx  and  the 
lateral  ones  into  the  third  phalanx  of  its  digit. 

Nerve-Supply. — From  the  anterior  tibial  nerve  from  the  fourth  and  fifth  lum- 
t  ar  and  first  sacral  nerves. 

Action.— To  extend  the  second,  third,  fourth,  and  fifth  toes  and  to  flex  the  foot. 


656 


HUMAN   ANATOMY. 


Relations. — By  its  deep  surface  and  medially  the  muscle  is  in  relation  with 
the  extensor  longus  hallucis,  medially  with  the  tibialis  anticus,  the  anterior  tibial  ves- 
sels and  nerve,  and  deeply  with  the 
deep  peroneal  nerve  above  and  the 
ankle-joint  below.  Laterally  it  is  in 
contact  with  the  peroneus  longus 
above,  with  the  peroneus  tertius  be- 
low, and  with  the  musculo-cutaneous 
nerve,  which  passes  downward  be- 
tween it  and  the  peroneus  longus 
(Fig.  617). 


Tubercle  of  tibia 


Portion  of  deep 
fascia  of  leg 


Intermuscular 
septum  attached 
to  fibula 


Peroneus  brevi 


Fibula — 


Peroneus  brevis 
tendon 


Outer  malleolus_ 


Extensor 
brevis  digitornni 

Peroneus  tertius 
tendon 

Base  of  fifth 
metatarsus 


Tibialis  anticus 


Extensor  longus 
digitorum 


Extensor 

longus  hallucis 

IT — Peroneus  tertius 

f\      Inner  malleolus 
j Anterior  annu- 
lar ligament, 
J£  j        vertical  por- 
tion 

Anterior  an- 
nular ligament, 
horixontal  por- 
tion 

Kxtensorhrevis 
digitorum 


Variations. — Considerable  variation 
occurs  in  the  arrangement  of  the  terminal 
tendons,  one  of  the  most  usual  departures 
from  the  typical  condition  being  a  duplica- 
tion of  the  tendon  to  one  or  more  of  the 
toes,  the  additional  tendon  either  passing 
to  the  same  digit  as  its  fellow  or  to  an 
adjacent  one.  Occasionally  a  slip  passes 
from  the  innermost  tendon  to  that  of  the 
extensor  longus  hallucis,  and  slips  may 
pass  from  any  of  the  tendons  to  the  meta- 
tarsal bones. 


3.   PERONEUS  TERTIUS   (Fig.  623). 

Attachments. — The  peroneus 
tertius  arises  from  the  lower  part  of 
the  anterior  surface  of  the  fibula  and 
from  the  interosseous  membrane,  the 
intermuscular  septum,  and  the  crural 
fascia.  At  about  the  level  of  the 
ankle  its  fibres  pass  over  into  a  ten- 
don which  continues  through  the 
lateral  compartment  of  the  anterior 
annular  ligament,  together  with  the 
tendon  of  the  extensor  longus  digi- 
torum, and  is  inserted  into  the  base 
of  the  fifth  metatarsal  bone. 

Nerve-Supply. — By  the  ante- 
rior tibial  nerve  from  the  fourth  and 
fifth  lumbar  and  first  sacral  nerves. 

Action. — To  flex  and  evert  the 
foot. 

Variations. — The  peroneus  tertius  is 
quite  frequently  absent,  and  is  usually  more 
or  less  closely  united  with  the  extensor 
longus  digitorum  above.  Its  tendon  some- 
times splits  into  two  portions,  the  additional 
one  passing  either  to  the  fifth  toe  or  to  the 
fourth  metatarsal. 

Notwithstanding  its  name,  which  has 
reference  to  its  origin  from  the  fibula. 
the  peroneus  tertius  has  morphologically 
nothing  to  do  with  the  other  peroneal 
muscles,  but  is  a  separated  portion  of  the 
extensor  longus  digitorum,  whose  connec- 
tions with  the  metatarsals  are  interesting 
in  this  regard. 


Superficial  dissection  of  anterior  surface  of  right  leg, 
•bowing  muscles  undisturbed. 

4.    EXTENSOR  LONGUS  HALLUCIS  (Fig.  624). 

Attachments. — The  long  or  proper  extensor  of  the  great  toe  ( in.  extensor  hallucis 

lon»us)  arises  from  the  inner  surface-  of  tin1  fibula  and  from  the  interosseous  membrane. 


THE   CRURAL   MUSCLES. 


657 


FIG.  624. 


Its  fibres  are  collected  into  a  tendon  which  passes  through  the  middle  compartment 
of  the  anterior  annular  ligament  and  is  continued  distally  to  the  great  toe.  Over  the 
metatarso-phalangeal  joint 
it  spreads  out  into  a  mem- 
branous expansion  which 
receives  a  tendon  of  the 
extensor  brevis  digitorum 
and  is  then  continued  dis- 

Outer  tuberos-- 

ity  of  tibia 
Head  of  fibula- 


tally  to  be  inserted  into  the 
first  and  second  phalanges. 

Nerve-Supply. —  By 
the  anterior  tibial  nerve  from 
the  fourth  and  fifth  lumbar 
and  first  sacral  nerves. 

Action. — To  extend 
the  great  toe  and  flex  the  foot. 

Relations. — The  ex- 
tensor longus  hallucis  is  cov- 
ered in  its  upper  part  by 
the  tibialis  anticus  and  the 
extensor  longus  digitorum. 
Near  the  ankle  it  crosses 
obliquely  over  the  anterior 
tibial  artery  and  passes  upon 
the  foot  between  the  ten- 
dons of  the  extensor  longus 
digitorum  and  the  tibialis 
anticus,  internal  to  the  ar- 
teria  clorsalis  pedis. 

Variations. — The  muscle 
is  occasionally  inserted  at  its 
origin  with  the  extensor  longus 
digitorum,  and,  in  addition  to 
the  connections  which  may  ex- 
ist between  its  tendon  and  that 
of  the  long  extensor,  it  may  also 
be  connected  with  one  of  the 
tendons  of  the  extensor  brevis 
digitorum. 

A  small  muscle  is  some- 
times to  be  found  passing  down- 
ward alongside  of  the  extensor 
brevis  hallucis  to  be  inserted 
into  the  base  of  the  first  meta- 
tarsal.  It  may  be  termed  the 
abductor  longus  hallucis,  and 
takes  its  origin  either  from  the 
fibula  close  to  the  origin  of 
the  extensor  longus  hallucis,  or 
from  that  muscle,  or  from  the 
extensor  longus  digitorum  or 
the  tibialis  anticus. 

What  has  been  termed  an 
extensor  brevis  hallucis  is  fre- 
quently represented  by  a  slip 
from  the  extensor  longus  hal- 
lucis, the  extensor  longus  digi- 
torum, or  even  from  the  tibialis 
anticus  inserting  into  the  base  of 
the  first  phalanx  of  the  hallux. 


Calf  muscles 


Peroneus 

longus 


Intermuscular 

septum 


Extensor  longus 
digitorum 


Extensor  longus 
hallucis 


Tubercle  of  tibia 


muscles 


Tibialis  anticus 


Crest  of  tibia 


Peroneus  brevis 


Peroneus  tertius 


Anterior  annular  ligame 
cut  edge 

Outer  malleo 


Peroneus  brevis  tend 
Base  of  fifth  metatars 

Abductor  minimi  dig 


malleolus 


Muscles  of  anterior  surface  of  right  leg;  extensor  longus  digitorum  has 
been  drawn  aside  to  expose  extensor  longus  hallucis. 


5.    PERONEUS  LONGUS  (Figs.  625,  629). 

Attachments. — The  peroneus  longus  arises  from  the  upper  part  of  the  lateral 
surface  of  the  fibula  and  from  the  intermuscular  septa  and  crural  fascia.      Its  fibres 

42 


658 


HUMAN   ANATOMY. 


extend  obliquely  downward  to  a  tendon  which  passes  behind  the  outer  malleolus  and 

then  runs  forward  in  a  groove  on  the 


FIG.  625. 


ead  of  fibula 
ubercle  of  tibia 

ExU-nsor  longus 
digitorum,  cut 


ibialisanticus 


Abductor  minimi  <lij;iti 


Flexor  brevis  minimi  digiti 


Superficial  dissection  of  right  leg,  antero-lateral  aspect, 
showing  peroneal  muscles. 


nerve  from  the  fourth  and  fifth  lumbar  and  first  sacral  nerves. 


calcaneum,  in  which  it  is  held  by 
fibrous  bands  (retinacula  mm.  pero- 
naeorum).  On  the  cuboid  it  again 
changes  its  direction,  passing  upon 
the  plantar  surface  of  the  foot  in  a 
groove  upon  that  bone  which  is  cov- 
ered in  by  the  long  plantar  liga- 
ment, and  then,  running  obliquely 
across  the  foot,  it  is  inserted  into  the 
internal  cuneiform  and  the  base  of 
the  first  metatarsal  bone.  In  front 
of  the  tuberosity  of  the  cuboid  the 
tendon  usually  contains  a  sesamoid 
cartilage. 

Nerve-Supply. —  By  the  mus- 
culo-cutaneous  nerve  from  the  fourth 
and  fifth  lumbar  and  first  sacral  nerves. 

Action. — To  extend  the  foot  and 
evert  the  sole. 

Relations. — The  peroneus  lon- 
gus occupies  the  lateral  surface  of  the 
leg  (Fig.  617).  It  is  in  contact  pos- 
teriorly with  the  soleus  and  internally 
with  the  extensor  longus  digitorum, 
being  separated  from  these  muscles  by 
the  intermuscular  septa.  The  musculo- 
cutaneous  nerve  passes  through  the 
substance  of  the  upper  part  of  the  mus- 
cle and  is  continued  downward  between 
the  peroneus  longus  and  the  extensor 
longus  digitorum.  In  the  foot  the  ten- 
don of  the  peroneus  longus  is  deeply 
placed,  resting  directly  upon  the  plan- 
tar surfaces  of  the  cuboid,  the  external 
cuneiform,  and  the  bases  of  the  second 
and  third  metatarsal  bones. 

PERONEUS  BREVIS  (Fig.  624). 

Attachments. — The   peroneus 
brevis  lies  beneath  the  peroneus  lon- 
gus and  arises  from  the  lower  portion 
of    the   lateral   surface   of    the   fibula 
and  from  the  intermuscular  septa.    Its 
fibres  join  a  tendon  which 
Tendons  of  ex-  passes  behind  the  external 
malleolus    and    then    dis- 
tally,  along  with  the  ten- 
don of  the  |>en>neus   lon- 
gus, beneath    the   fibrous 
bands  or  retinacula  to  be 
inserted  into  the  tuberos- 
ity of  the  fifth  metatarsal 
bone. 

Nerve-Supply. — By 
the      musculo  -  cutaneous 


THE   MUSCLES   OF   THE   FOOT. 


659 


FIG.  626. 


alcis,  inner  tubercle 


eo-metatarsal 


Action. — To  extend  and  evert  the  foot. 

Variations. — A  slip  is  very  frequently  given  off  from  the  tendon  of  the  short  peroneus 
which  is  inserted  either  into  the  tendon  of  the  extensor  longus  digitorum  passing  to  the  fifth  toe 
or  directly  into  that  digit.  In  some  cases  the  slip  arises  from  the  belly  of  the  muscle,  from  that 
of  the  peroneus  longus,  or  even  from  the  fibula  directly,  and  represents  what  has  been  termed 
the  peroneus  quiiitus. 

\peroneusquartiis,  where  distinctness  from  the  quintus  seems  doubtful,  sometimes  occurs  as 
a  muscle  arising  from  the  lower  part  of  the  fibula  and  inserting  into  the  calcaneum  or  the  tuber- 
osity  of  the  cuboid. 

THE   MUSCLES   OF   THE   FOOT. 

The  plantar  fascia  or  aponeurosis  (Fig.  626)  is  a  dense  sheet  of  connective 
tissue  lying  immediately  beneath  the  skin  of  the  plantar  surface  of  the  foot  and 
covering  the  pre-axial  mus- 
cles. It  is  attached  behind 
to  the  tuberosity  of  the  cal- 
caneum, and  extends  dis- 
tally  in  a  fan-like  manner  to 
be  attached  by  five  processes 
to  the  skin  over  the  meta- 
tarso-phalangeal  joints  of 
the  digits.  The  aponeuro- 
sis is  much  thicker  in  its 
middle  portion  than  at  the 
sides,  where  it  is  continued 
dorsally  over  the  sides  of 
the  foot  to  become  continu- 
ous with  the  fascia  of  the  dor- 
sum  of  the  foot  and  with  the 
crural  fascia.  Between  its 
cutaneous  insertions  trans- 
verse bands  of  fibres  stretch 
across  to  form  the  super- 
ficial transverse  metatarsal 
ligament  (fasciculi  trans- 
versi ) ;  from  its  deep  sur- 
face strong  sheets  are  given 
off  which  pass  to  the  sheaths 
of  the  flexor  tendons.  Ex- 
pansions are  also  given  off 
from  its  deep  surface  which 
invest  the  flexor  brevis  digi- 
torum and,  on  either  side, 
the  abductor  hallucis  and 
abductor  minimi  digiti. 

Between  the  aponeu- 
rosis and  the  integument 
over  the  inferior  surface  of 
the  tuberosity  of  the  calca- 
neum a  bursa  (Imrsa  subcu- 
tanea  calcanea )  is  constantly 
present. 

The  dorsal   surface  of 
the  foot  is  covered  by  the  fascia  dorsalis  pedis,  a  rather  thin  sheet  continuous  with 
the  crural  fascia  above.      It  covers  the  long  extensor  tendons. 

(a)    THE  PRE-AXIAL  MUSCLES. 

Like  the  pre-axial  muscles  of  the  hand,  those  of  the  foot  may  be  regarded  as 
derived  from  five  primary  layers,  which  have  undergone  a  considerable  amount  of 
modification,  including  some  fusion. 


Plantar  fascia, 
central  portion 


Plantar  fascia, 
inner  lateral 
portion 


Plantar  fascia, 
slip  for  great  toe 

Flexor  longus 
hallucis  tendon 

Superficial 
transverse  met- 
atarsal ligament 


Plantar  fascia, 
outer  lateral 
portion 


Plantar  fascia, 
digital  slips 


Superficial  dissection  of   sole  of   right  foot  (subject  lying 
on  belly),  showing  plantar  fascia. 


66o 


HUMAN    ANATOMY. 


(aa)   THE  MUSCLES  OK  THE  FIRST  LAYER. 

1.  Flexor  brevis  digitorum.          3.   Abductor  hallucis. 

2.  Flexor  brevis  hallucis.  4.   Abductor  minimi  digiti. 


i.    FLEXOR  BREVIS  DIGITORUM  (Fig.  627). 

Attachments. — The  short  flexor  of  the  toes  (m.  flexor  digitorum  brevis)  arises 
from  the  inner  process  of  the  calcaneal  tuberosity  and  from  the  plantar  aponeurosis. 
It  extends  distally,  beneath  the  aponeurosis,  as  a  thick  quadrangular  muscle,  the 

fibres  of  which  are  collected 

FIG.  627.  over    the    metatarsal    bones 

into  four  tendons  which  pass 
to  the  second,  third,  fourth, 
and  fifth  toes.  Over  the 
first  phalanx  of  the  toe  each 
tendon  divides  into  two  ter- 

Oscaids — /JMfc  j ~WKI  minal  slips,  between  which 

the  corresponding  tendon  of 
the  flexor  longus  digitorum 
passes  and  which  are  in- 
setted into  the  second  pha- 
lanx. 

Nerve-Supply. —  By 
the  internal  plantar  nerve 
from  the  fourth  and  fifth 
lumbar  and  first  sacral 
nerves. 

Action. — To  flex  the 
second,  third,  fourth,  and 

Flexor  brevis         fifth  tOCS. 
minimi  digiti 

Variations. — The  most  fre- 
quent variation  in  this  muscle  is 
the  absence  of  the  tendon  to 
the  fifth  toe,  an  absence  which 
occurs  in  somewhat  over  21  per 
cent,  of  cases  examined.  Some- 
times the  tendon  is  replaced  by 
a  slip  or  muscle  which  arises 
from  the  tendon  of  the  flexor 
longus  digitorum. 

The  flexor  brevis  repre- 
sents the  middle  portion  of  the 
superficial  flexor  layer,  and  cor- 
responds, accordingly,  to  the 
terminal  portions  of  the  ten- 
dons of  the  flexor  sublimis  of 
the  hand.  Its  origin  is  primarily 
from  the  plantar  aponeurosis, 
and  hence  the  occasional  origin 
of  the  portion  for  the  fifth  toe 
becomes  intelligible,  since  the 
tendon  of  the  ilexor  longus  is 
a  differentiation  of  the  dccpet 
layer  of  the  aponeurosis. 


Ab'ductor  hallucis 


Flexor  brevis 
digitorum 


Flexor  brevis 
hallucis 


Flexor  longus 
hallucis  tendon 


Abductor 
minimi  digiti 


Flexor  longus 
digitorum  ten- 
dons 

Flexor  brevis 
digitorum  ten- 
dons 


Flexor  tendons 
in  sheath 


Flex.  brcv.  digi- 
tonmi  tendon 


Flexor  longus  digitorum 
tendon 


Superficial  muscles  of  sole  of  right  foot. 


2.    FLEXOR  BREVIS  HALLUCIS  (Fig.  628). 

Attachments. — The  short  flexor  of  the  great   toe  (m.  flexor  hallucis  brevis) 

from  the  plantar  surface  of  the  internal  cuneiform  bone  and  the  adjacent  liga- 
mentous  structures.  Its  libn-s  pass  distally  to  a  tendon  which  contains  a  sesamoid 
bone,  and  is  inserted  into  the  inner  surface  of  the  base  of  the  first  phalanx  of  the 
great  toe. 

Nerve-Supply. — By  the  internal  plantar  nerve  from  the  fourth  lumbar  ner 

Action. — To  tle\  the  !4 real  toe. 


THE   MUSCLES   OF   THE   FOOT. 


66 1 


Variations. — The  flexor  b.revis  hallucis  is  frequently  intimately  fused  with  the  abductor 
hallucis. 

A  portion  of  the  deeper  fibres  of  the  flexor  brevis  hallucis  is  frequently  inserted  into  the 
whole  length  of  the  first  metatarsal.  Occasionally  these  fibres  are  quite  distinct  from  the  rest 
of  the  muscle,  forming  what  has  been  termed  an  opponens  hallucis. 

In  the  description  of  the  muscle  given  above,  account  has  been  taken  only  of  what  is  usually 
described  as  the  inner  portion,  the  flexor  brevis  pollicis  being  usually  regarded  as  consisting 
of  two  bellies,  the  second  of  which  is  inserted  into  the  lateral  side  of  the  base  of  the  first 
phalanx  of  the  great  toe.  The  relations  of  this  outer  belly  and  its  nerve-supply,  however,  indi- 
cate that  it  belongs  to  an  entirely  different  layer  than  the  medial  belly.  It  will,  therefore,  be 
considered  later  in  connection  with  the  interossei  (page  663). 

FIG.  628. 


Os  calcis,  inner  tubercle  -j 

Abductor  hallucis,  — Itt-J 
calcaneal  origin 
Internal  annular  ligament — •%• 

Flexor  brevis  digitorum,  origin 
Flexor  longus  hallucis  tendon  —  \£2 

Tibialis  posticus  tendon-: ^ 

Flexor  longus  digitorum  tendon 

Abductor  hallucis,  part  of  origin. 


Abductor  hallucis,  cut 


First  plantar  interosseu.s 
Flexor  brevis  hallucis 


Lumbricales 


Flexor  longus  hallucis  tendon 


Flexor  brevis  digitorum 
Flexor  longus  digitorum 


Os  calcis,  outer  tubercle 

Abductor  minimi  digiti,  origin 
Long  plantar  ligament 

Peroneus  longus  tendon 

Abductor  minimi  digiti,  occasional 
insertion  (Abductor  ossis  metatarsi 
quinti) 

Flexor  accessorius 
Tubercle  of  fifth  metatarsus 
Flexor  brevis  minimi  digiti, 
part  of  its  origin 

Flexor  longus  digitorum 


Flexor  brevis  minimi  digiti 


Abductor  minimi  digiti, 
insertion 


Flexor  longus  digitorum 
tendons 

Flexor  brevis  digitorum 
tendons,  cut 


Long  and  accessory  flexors  of  right  sole,  exposed  by  removal  of  superficial  muscles. 


3.    ABDUCTOR  HALLUCIS  (Fig.   627). 

Attachments. — The  abductor  hallucis  extends  along  the  inner  border  of  the 
foot,  arising  from  the  inner  tubercle  and  surface  of  the  calcaneum  and  from  the 
plantar  aponeurosis  and  being  inserted,  along  with  the  flexor  brevis  hallucis,  into  the 
inner  side  of  the  base  of  the  first  phalanx  of  the  great  toe. 

Nerve-Supply. — By  the  internal  plantar  nerve  from  the  fourth  and  fifth  lumbar 
and  first  sacral  nerves. 

Action. — To  abduct  and  flex  the  hallux. 


662  HUMAN   ANATOMY. 

ABDUCTOR  MINIMI  DIGITI  (Fig.  627). 

Attachments. — The  abductor  of  the  little  toe  (m.  abductor  digiti  quinti)  is 
situated  along  the  outer  border  of  the  foot.  It  arises  from  the  under  surface  of  the 
calcaneum  and  from  the  plantar  aponeurosis,  and  extends  distally  and  laterally  to  be 
inserted  partly  into  the  tuberosity  of  the  fifth  metatarsal  bone  and  partly  into  the 
lateral  side  of  the  base  of  the  first  phalanx  of  the  little  toe. 

Nerve-Supply. — By  the  external  plantar  nerve  from  the  first  and  second 
sacral  nerves. 

Action. — To  abduct  and  flex  the  little  toe. 

Variations — A  portion  of  the  abductor  digiti  quinti  frequently  separates  from  the  rest  of 
the  muscle  to  form  a  fusiform  belly  which  has  been  termed  the  abductor  ossis  metatarsi  quinti. 
It  arises  from  the  lateral  part  of  the  inferior  surface  of  the  os  calcis  and  is  inserted,  either  inde- 
pendently or  in  common  with  the  abductor,  into  the  tuberosity  of  the  fifth  metatarsal. 

(bb)   THE  MUSCLES  OF  THE  SECOND  LAYER. 
I.      LUMBRICALES    (Fig.    628). 

Attachments. — The  lumbricales  are  four  spindle-shaped  muscles  which  arise 
from  the  adjacent  borders  of  the  tendons  of  the  flexor  longus  digitorum  and  from  the 
inner  border  of  its  first  tendon.  They  pass  distally  to  the  inner  surfaces  of  the  first 
phalanges  of  the  second,  third,  fourth,  and  fifth  digits,  where  they  are  inserted  into  the 
membranous  expansions  of  the  tendons  of  the  extensor  longus  digitorum. 

Nerve-Supply. — The  first  or  first  and  second  muscles,  counting  from  the  tibial 
side,  are  supplied  by  the  internal  plantar  nerve  ;  the  remaining  three  or  two  are  sup- 
plied from  the  external  plantar  from  the  fourth  and  fifth  lumbar  and  first  sacral  nerves. 

Action. — To  flex  and  draw  medially  the  second,  third,  fourth,  and  fifth  toes. 

Variations. — Absence  of  one  or  other  of  the  lumbricales  has  been  noted,  the  fourth  and  third 
being  those  most  frequently  lacking  ;  these  same  muscles  are  frequently  bifid  at  their  insertions. 
Small  bursae  may  intervene  between  the  tendons  and  the  first  phalanges. 

The  significance  of  the  lumbricales  is  similar  to  that  of  the  corresponding  muscles  of  the 
hand.  They  arise  primarily  from  the  deeper  layers  of  the  plantar  aponeurosis,  and  when  these 
differentiate  into  the  tendons  of  the  flexor  longus  digitorum  they  come  to  arise  from  those 
structures. 

(cc)    THE  MUSCLES  OF  THE  THIRD  LAYER. 
i.    ADDUCTOR  HALLUCIS  (Fig.  629). 

Attachments. — The  adductor  hallucis  consists  of  two  portions,  often  described 
as  two  distinct  muscles,  united  orlly  at  their  insertions.  The  oblique  portion  (caput 
obliquum),  or  adductor  obliquus,  arises  from  the  bases  of  the  second,  third,  and 
fourth  metatarsals  and  from  the  long  plantar  ligament  and  passes  distally  and  inward 
along  the  interval  between  the  first  and  second  metatarsals,  its  fibres  converging  to  a 
strong  tendon  which  unites  with  that  of  the  transverse  portion  (caput  transversum),  or 
adductor  transversus.  This  extends  almost  transversely,  under  cover  of  the  three 
medial  tendons  of  the  long  and  short  flexors  and  the  lumbricales,  over  the  heads  of 
the  fourth,  third,  and  second  metatarsals.  It  arises  from  the  capsules  of  the  four 
lateral  metatarso-phalangeal  joints  and  passes  medially  to  join  the  tendon  of  the 
oblique  portion.  The  common  tendon  so  formed  unites  with  the  tendon  of  the  first 
plantar  interosseous  and  is  inserted  into  the  sesamoid  bone  of  that  tendon  and  into  the 
lateral  surface  of  the  base  of  the  first  phalanx  of  the  great  toe. 

Nerve-Supply. — By  the  deep  branch  of  the  external  plantar  nerve  from  the 
fifth  lumbar  and  first  and  second  sacral  nerves. 

Action. — To  flex  and  adduct  the  hallux. 

Variations. — Some  variation  occurs  in  the  extent  of  the  origin  of  both  portions  of  the 
adductor  hallucis.  The  oblique  portion  may  be  limited  to  the  long  plantar  ligament,  or  may 
receive  an  accessory  slip  from  the  shaft  of  the  second  metatarsal,  wade  the  origin  of  the  trans- 
verse portion  from  the  fifth  metatarso-phalangeal  joint  may  be  lacking. 

It  is  to  be  noted  that  in  the  fa-tus  the  two  portions  of  the  adductor  are  not  separated  by  a 
wide  interval  as  in  the  adult,  but  lie  in  contact  with  each  other. 


THE   MUSCLES   OF   THE   FOOT. 


663 


A  small  muscular  slip  has  occasionally  been  observed  passing  from  the  long  plantar  liga- 
ment to  the  lateral  surface  of  the  base  of  the  first  phalanx  of  the  second  toe.  It  appears  to 
represent  an  adductor  secundi  digiti. 

FIG.  629. 


Os  calcis,  inner  tubercle- — 

Flexor  brevis  digitorum 

Flexor  longus  hallucis  tendon 

Flexor  longus  digitorum  tendon 

Flexor  accessorius,  inner  head 

Tibialis  posticus  tendon 


Abductor  hallucis,  cut 

Flexor  brevis  hallucis 

First  plantar  interosseus 

Adductor  hallucis,  oblique  portion 


Tendon  of  flexor  longus 

digitorum 
Tendon  of  flexor  brevis  _ 

digitorum 


Flexor  longus  hallucis  tendon 


Os  calcis,  outer  tubercle 


Abductor  minimi  digiti 


Flexor  accessorius,  outer  head 
-Peroneus  longus  tendon 

Long  plantar  ligament 

k Abductor  ossis  metatarsi  quinti 

7W  (part  of  abductor  minimi  digiti) 


Tendon  of  peroneus  longus 
in  sheath 


Flexor  brevis  minimi  digiti 


Abductor  minimi  digiti 


Adductor  hallucis, 
transverse  portion 


Deep  dissection  of  sole  of  right  foot,  showing  short  flexors 
of  great  and  little  toes  and  adductor  muscles. 

(dd)    THE  MUSCLES  OF  THE  FOURTH  AND  FIFTH  LAYERS. 

i.    Interossei  plan  tares.          2.    Interossei  dorsales. 
3.    Flexor  brevis  minimi  digiti. 

As  in  the  hand,  the  fourth  and  fifth  layers  of  the  pre-axial  musculature  become 
united  to  form  the  dorsal  interossei,  portions  of  the  fourth  layer  remaining  distinct  to 
form  the  plantar  interossei.  The  arrangements  in  the  hand  and  foot  differ,  however, 
in  this  respect,  that  in  the  foot  the  lateral  muscle  derived  from  the  fourth  layer  forms 
a  large,  well-developed  structure  termed  the  flexor  brevis  minimi  digiti. 

i.   INTEROSSEI  PLANTARES  (Fig.  630). 

Attachments. — The  plantar  interossei  are  four  spindle-shaped  muscles.  The 
first  is  very  much  stronger  than  the  others,  and  is  often  described  as  the  outer  head 
of  the  flexor  brevis  hallucis  (page  661).  It  arises,  in  common  with  the  flexor  brevis 


664 


HUMAN    ANATOMY. 


hallucis,  from  the  inner  cuneiform  bones  and  the  adjacent  ligamentous  structures. 
It  extends  distally  along  the  lateral  surface  of  the  first  metatarsal  bone  and  passes 
over  into  a  strong  tendon,  which  contains  a  sesamoid  bone,  and  is  inserted  into  the 
outer  surface  of  the  base  of  the  first  phalanx  of  the  great  toe,  along  with  the 
adductor  hallucis. 

The  remaining  three  muscles  are  much  smaller  and  arise  in  succession  from  the 
medial  surfaces  of  the  third,  fourth,  and  fifth  metatarsals,  and,  passing  distally,  are 

inserted  by    slender   ten- 

FIG.  630.  dons  into  the  membranous 

expansions  of  the  long  ex- 
tensor tendonsof  the  third, 
fourth,  and  fifth  toes,  on 
the  medial  sides  of  their 
first  phalanges. 

Nerve -Supply. — By 
the  external  plantar  nerve 
from  the  first  and  second 
sacral  nerves. 

Action. — To  flex  the 
first,  third,  fourth,  and  fifth 
toes  and  to  draw  the  last 
three  medially. 

Variations. — As  above 
stated,  the  first  plantar  inter- 
osseus  is  usually  describee]  as 
a  second  head  of  the  flexor 
brevis  hallucis.  It  is  some- 
times more  or  less  insepara- 
ble from  the  oblique  portion 
of  the  adductor  hallucis. 

2.  INTEROSSEI  DORSALES 

(Figs.  623,  630). 

Attachments. — The 
dorsal  interossei  are  also 
four  in  number.  They 
arise  from  the  adjacent 
sides  of  each  pair  of  nut- 
atarsals  and  pass  distally 
in  the  interspaces  between 
these  bones.  The  fibres 
of  each  muscle  converge 
to  a  narrow  tendon  which 
is  inserted  into  the  mem- 
branous expansions  of  the 
extensor  tendons  over  the 
first  phalanges  of  the  sec- 
ond, third,  and  fourth  toes. 
The  first  and  second  mus- 


Insertion  of 
peroneus  longus 

Insertion  of. 
tibialis  anticus 

Adductor, 
obliquus  hallucis 


Long  plantar  ligament 


Peroneous  brevis 
tendon 


Peroneus  longus 
tendon 

.Superficial  fibres 
of  long  plantar  lig. 
Tubercle  of  fifth 
metatarsus 


Flexor  brevis 
minimi  digiti, 
stump 


Tendons  of  flex- 
or brevis  hallucis 
and  first  plantar 
inter os seus  re- 
flected, with  ab- 
ductor and  ad- 
ductor tendons, 
showing  the  two 
sesamoid  bones 


Deep  dissection  of 


>f  right  foot,  showing  interosseous  muscles. 


cles  insert  into  the  opposite  sides  of  the  second  toe  and  the  third  and  fourth  into  the 
lateral  sides  of  the  third  and  fourth  toes. 

Nerve-Supply. — By  the  external  plantar  nerve  from  the  first  and  second  sac 
nerves. 

Action. — To  flex  the  second,  third,  and  fourth  toes;  the  first  also  draws  the 
second  toe  medially  and  the  rest  the  second,  third,  and  fourth  toes  laterally. 


3.   FLEXOR  BREVIS  MINIMI  DIGITI  (Fig.  629). 

Attachments. — The  short  flexor  of  the  little  toe  (m.  flexor  digiti  quinti  brevis), 

which  really  represents  a  fifth  plantar  interosseus,  arises  from  the  base  of  the  fifth 


PRACTICAL   CONSIDERATIONS  :    THE   LEG.  665 

metatarsal  and  passes  distally  along  the  outer  side  of  the  fourth  plantar  interosseus 
to  be  inserted  by  a  tendon  into  the  outer  surface  of  the  base  of  the  rirst  phalanx  of 
the  fifth  toe  and  also  into  the  distal  portion  of  the  fifth  metatarsal. 

Nerve-Supply. — From    the    external    plantar    nerve  from  the  second   sacral 

nerve. 

Action. — To  flex  the  fifth  toe  and  draw  it  lateralward. 

Variations. — The  portion  of  the  flexor  brevis  minimi  cligiti  which  passes  to  the  fifth  meta- 
tarsal is  frequently  more  or  less  distinct  from  the  rest  of  the  muscle,  and  has  then  been  termed 
the  opponent  quinti  digiti. 

(f>)    THE  POST-AXIAL  MUSCLES, 
i.    EXTENSOR  BREVIS  DIGITORUM  (Fig.   624). 

Attachments. — The  short  extensor  of  the  toes  (m.  extensor  digitorum  brevis) 
(irises  from  the  lateral  and  superior  surfaces  of  the  calcaneum.  It  passes  distally 
beneath  the  tendons  of  the  extensor  longus  digitorum  and  divides  into  four  portions, 
the  outer  three  of  which  soon  become  tendinous  and  are  inserted  by  fusing  with  the 
tendons  of  the  extensor  longus  to  the  second,  third,  and  fourth  toes  over  the  first 
phalanges  of  those  toes;  the  innermost  tendon  is  inserted  into  the  base  of  the  first 
phalanx  of  the  great  toe. 

Nerve-Supply. — By  the  anterior  tibial  nerve  from  the  fourth  and  fifth  lumbar 
and  first  sacral  nerves. 

Action. — To  extend  and  draw  laterally  the  first,  second,  third,  and  fourth  toes. 

Variations. — Occasionally  one  or  other  of  the  tendons  of  the  extensor  brevis  may  be 
doubled,  this  condition  being  most  frequent  in  the  tendon  to  the  second  toe  ;  sometimes  a  fifth 
tendon  passes  to  the  little  toe. 

The  innermost  tendon  is  nearly  always  much  stronger  than  the  others  ;  the  fibres  which 
insert  into  it  are  occasionally  separate  from  the  remainder  of  the  muscle,  then  forming  the 
e.v  tensor  brei'is  liallucis. 

PRACTICAL    CONSIDERATIONS:    MUSCLES   AND    FASCIAE 
OF  THE  LEG,   ANKLE,  AND  FOOT. 

i.  The  Leg. — The  skin  over  the  leg  is  everywhere  more  adherent  to  the  un- 
derlying fascia  than  it  is  in  the  thigh.  Its  inability  at  certain  places,  as  over  the  spine 
and  antero-internal  surface  of  the  tibia,  to  glide  away  when  force  is  applied  partly 
accounts  for  the  frequency  with  which  bruising  or  laceration,  superficial  ulceration, 
or  even  periostitis  or  caries  follows  injuries  to  the  ' '  shin. 

The  deep  fascia  blends  with  the  periosteum  at  the  head  and  inner  and  anterior 
borders  of  the  tibia,  at  the  head  of  the  fibula,  and  at  the  two  malleoli.  It  is  thicker 
and  denser  above  and  anteriorly  than  below  and  posteriorly.  The  two  septa  (Figs. 
627,  623)  that  run  inward  from  it  on  the  outer  side  of  the  leg  and  are  attached  to  the 
anterior  and  external  borders  of  the  fibula  constitute  an  osseo-aponeurotic  space  that 
contains  the  peroneal  muscles  and  that  may,  for  a  time,  limit  the  spread  of  infection 
or  of  suppuration.  The  peronei,  in  their  compartment,  and,  farther  in,  the  bones  and 
interosseous  membrane,  separate  the  anterior  group  of  muscles — the  tibialis  anticus, 
extensor  communis,  etc. — from  the  posterior  group.  The  fascia  over  the  anterior 
group  embraces  them  so  closely,  that  when  it  is  wounded  or'  torn  the  muscle-fibres 
protrude  and  approximation  of  the  edges  of  the  fascial  wound  may  be  difficult.  In 
the  anterior  compartment  the  muscles  are  intimately  adherent  to  its  fibrous  walls,  as 
is  the  case  in  the  forearm,  but  not  in  the  arm  or  thigh  (Tillaux).  In  the  posterior 
compartment,  on  the  contrary,  a  loose  layer  of  connective  tissue  intervenes  between 
the  gastrocnemius  and  the  deep  fascia,  and  permits  the  greater  degree  of  motion 
between  the  muscle  and  the  aponeurosis  necessitated  by  the  greater  range  of  motion 
in  plantar,  as  compared  with  dorsal,  flexion  of  the  foot. 

The  difference  will  be  noted  in  dealing  with  wounds  involving  these  regions,  or 
in  some  operations,  as  amputation  of  the  leg. 

The  septum,  anteriorly,  at  the  upper  third  of  the  leg,  between  the  tibialis  anticus 
and  extensor  longus  digitorum,  is  of  variable  density,  gives  no  indication  of  its  pres- 


666 


HUMAN   ANATOMY. 


FIG.  631. 


ence  on  either  the  skin  or  fascial  surface,  and  although  described  as  a  guide  to  the 
anterior  tibial  artery  (g.v.),  is  untrustworthy  on  account  of  the  difficulty  of  recog- 
nizing it  (Treves). 

Posteriorly  the  deep  layer  of  fascia  that  holds  down  the  deep  muscles  to  the 
tibia  and  fibula  and  runs  transversely  beneath  the  soleus  and  gastrocnemius,  is  weaker 

above,  where  it  is  covered  and  reinforced  by  the  latter 
muscles,  and  stronger  below,  where  it  loses  their  sup- 
port. It  is  continued  downward  and  separates  the 
tendo  Achillis  from  the  deeper  structures.  In  ap- 
proaching the  vessels  behind  the  malleolus,  one  finds, 
therefore,  two  layers  of  deep  fascia. 

Growths  originating  in  the  head  of  the  tibia  or 
occupying  the  interosseous  space  are  much  influenced 
by  the  resistance  of  the  deep  fascia,  which,  as  is  the 
case  with  the  fascia  lata,  may  for  a  time  determine 
their  shape  and  direction  and  alter  their  surface  ap- 
pearance and  their  apparent  density. 

Cellulitis  and  abscess  are  for  a  while  confined 
beneath  the  fascia,  but,  like  the  coloring  matter  of 
the  blood  after  fracture,  may  soon  find  their  way  to 
the  surface  by  following  the  vessels  that  perforate  it. 

Some  fibres  of  the  gastrocnemius  or,  more  fre- 
quently, the  tendo  Achillis  at  its  weakest  point,  on  a 
level  with  the  internal  malleolus,  may  be  ruptured 
during  strong  effort,  as  in  raising  the  body  on  the 
toes  while  bearing  a  weight.  Sometimes,  however, 
this  accident  follows  comparatively  trifling  exertion. 

2.  The  Ankle  and  Foot. — The  skin  around 
the  ankle  and  upon  the  dorsum  of  the  foot  is  thin 
and  lax.  The  absence  of  a  fatty  or  muscular  layer 
between  it  and  the  subjacent  bones  and  the  distance 
of  the  region  from  the  centre  of  circulation  make 
gangrene  from  relatively  slight  contusion,  or  from  the 
pressure  of  splints  or  dressings,  more  common  here 
than  elsewhere. 

Over  the  sole,  especially  at  those  places  which 
normally  bear  the  weight  of  the  body, — the  heel,  the 
ball  of  the  great  toe,  the  line  of  the  heads  of  the  metatarsal  bones  (page  452),  and 
the  outer  side  of  the  foot, — the  skin  is  much  denser.  It  often  contains  callosities 
which  cause  pain  by  pressure  and  are  usually  the  result  of  friction  between  the  sole 
and  an  ill-fitting  shoe.  Its  close  connection  with  the  underlying  plantar  fascia  is 
similar  to  that  between  the  skin  of  the  palm  and  the  palmar  fascia,  "and  between  the 
skin  of  the  scalp  and  the  occipito-frontalis  aponeurosis,  in  all  of  which  regions  the 
integument  is  exceptionally  thick  and  dense,  and  in  the  former  two  hairless  (pa£ 
491).  Under  the  heel  the  thick  skin  and  the  pad  of  subcutaneous  fascia  containii 
fat  are  especially  valuable  in  lessening  the  force  of  falls  upon  that  part  of  the  foot 
where  there  is  no  elastic  arch  composed  of  a  number  of  bones  and  joints  to  take 
and  distribute  the  force,  as  do  both  the  transverse  arch  and  the  anterior  pillar  of 
the  main  arch  (page  436).  This  tissue,  vertical  and  scanty  in  the  sole,  is  loose  and 
abundant  on  the  dorsum  and  around  the  tendo  Achillis,  in  which  latter  region  it 
contains  some  fat.  Its  laxity  over  the  dorsum,  while  it  somewhat  protects  the  inst€ 
from  the  effects  of  direct  violence,  adds  greatly  to  the  ease  with  which  swelling 
oedema  may  occur  in  cellulitis  or,  on  account  of  the  dependent  position  of  the  pai 
and  its  remoteness  from  the  heart,  in  anasarca. 

The  deep  fascia  at  the  ankle  is  thickened  on  the  dorsum  and  sides  to  form  the 
annular  ligaments,  the  chief  function  of  which  is  to  hold  in  place  the  tendons  that 
move  the  foot  and  toes.  Anteriorly  this  is  done  by  two  bands,  beneath  the  upper  of 
which  the  tendon  of  the  tibialis  anticus  runs,  while  the  lower  covers  in  the  tendon  of 
the  same  muscle  and  those  of  the  extensor  proprius  pollicis  and  of  the  extensor  coin- 


Dissection  of  fracture  of  left  tibia, 

showing  effect  of  muscular 

action  on  fragments. 


PRACTICAL   CONSIDERATIONS:    ANKLE   AND    FOOT.          667 

munis  and  peroneus  tertius,  the  last  two  running  in  one  sheath.  Internally — i.e., 
between  the  heel  and  the  internal  malleolus — the  tendons  of  the  flexor  longus  pol- 
licis,  the  flexor  longus  digitorum,  and  the  tibialis  posticus  run  beneath  the  internal 
annular  ligament,  the  last  named  being  the  deepest  and  in  the  closest  proximity  to 
the  ankle-joint,  disease  of  which  may  originate  in  the  tendon.  The  relation  of  the 
flexor  longus  pollicis  tendon  to  the  posterior  ligament  is  intimate,  and  is  believed  to 
be  of  advantage  in  resisting  posterior  luxation  of  the  astragalus  (page  450). 

The  peroneus  longus  tendon  is  thought  to  be  more  frequently  displaced  than 
anv  other  tendon  in  the  body.  When  this  accident  happens,  the  tendon  slips  from 
its  groove  behind  the  external  malleolus  and  over  the  thin  posterior  border  of  the 
latter  to  its  anterior  face.  This  dislocation  is  favored  by  (a)  the  length  and  slender- 
ness  of  the  tendon  ;  (£)  the  shallowness  of  the  groove  in  which  it  runs  ;  (c~)  the 
relative  weakness  of  the  single  slip  of  the  external  annular  ligament  that  covers  the 
tendon;  (d)  the  fact  that  it  changes  its  direction  twice  between  the  lower  third  of  the 
leg  and  its  insertion, — i.e. ,  once  at  the  malleolus  and  once  at  the  margin  of  the  cuboid. 

Disease  of  the  sheaths  of  the  tendons  about  the  ankle-joint  is  not  rare,  is  apt  to 
be  tuberculous,  and  is  favored  by  the  frequent  strains  and  the  exposure  to  cold  and 
wet  to  which  they  are  subjected,  and  by  their  dependent  position  and  remoteness 
from  the  heart. 

Their  relation  to  disease  of  the  tarsal  bones  should  be  remembered  (page  437). 
The  approximately  vertical  direction  of  the  swelling  in  the  early  stages  is  some- 
times of  use  in  differentiating  teno-synovitis  from  ankle-joint  disease  (page  451). 

The  involvement  of  the  tendon-sheaths  in  sprain  of  the  ankle-joint  (page  450) 
adds  to  the  duration  of  the  disability  produced  by  that  accident. 

On  the  sole  of  the  foot  the  dense  plantar  fascia  is  of  importance  in  relation  to 
infection  or  suppuration  beneath  it.  Of  its  three  divisions  (page  659),  the  central 
one  is  much  the  strongest.  With  the  intermuscular  septa  that  run  from  its  lateral  bor- 
ders into  the  sole  and  separate  the  flexor  brevis  digitorum  from  the  abductor  minimi 
digiti  externally  and  from  the  abductor  hallucis  internally,  it  makes  a  compartment 
the  floor  of  which  is  rarely  penetrated  by  inflammatory  or  purulent  effusions.  An 
abscess  beginning  in  the  mid-region  of  the  sole  beneath  the  plantar  fascia  may  pass 
forward  between  the  digital  slips  or  upward  through  the  interosseous  spaces,  or 
along  the  tendon-sheaths  to  the  ankle.  More  rarely  apertures  in  the  plantar  fascia 
permit  suppuration  to  spread  through  it  to  the  subcutaneous  region  of  the  sole. 
The  abscess  cavity  then  consists  of  two  portions  connected  by  a  narrow  neck,  abces 
en  bouton  de  chemise  (Tillaux). 

The  lateral  progress  of  such  an  abscess — through  the  intermuscular  septa  above 
described — is  easier  than  penetration  of  the  strong  central  leaflet  of  the  plantar  fascia. 

It  will  be  noted  that  the  three  compartments  into  which  the  sole  is  then  divided 
are  analogous  to  the  thenar,  hypothenar,  and  central  divisions  of  the  palm.  Con- 
traction of  the  plantar  fascia,  which  aids  in  maintaining  the  curve  of  the  arch  of  the 
foot,  as  a  string  would  that  of  its  bow,  increases  that  arch,  is  often  associated  with 
the  different  forms  of  talipes,  and  is  thought  to  be  one  of  the  common  causes  of  a 
subvariety, — pes  cavus.  Relaxation  or  elongation  of  the  plan  tar  fascia  favors  depres- 
sion of  the  normal  arch,  and  hence  contributes  to  the  development  of  the  condition 
known  as  "flat-foot"  (pes  planus}  (vide  infra). 

Club- Foot. — The  mechanics  of  the  normal  foot  have  already  been  sufficiently 
described  (pages  436,  447). 

Of  the  deformities,  either  congenital  or  acquired,  which  are  grouped  under  the 
name  club-foot,  it  is  necessary  to  describe,  from  the  anatomical  stand-point,  only  the 
chief  varieties. 

i.  Talipes  equino-varns,  when  congenital,  is  believed  to  result  from  retention 
of  the  foetal  position, — i.e. ,  from  defective  development.  The  inward  rotation  of  the 
flexed  and  crossed  limbs  in  utero,  which  in  the  later  periods  of  fcetal  life  removes  the 
pressure  from  the  fibular  side  of  the  legs  and  the  dorsum  of  the  feet  and  puts  the 
latter  in  the  position  of  extreme  flexion  with  the  soles — instead  'of  the  tops — of  the 
feet  against  the  uterine  walls  (Berg),  does  not  take  place.  This  is  the  commonest 
of  all  the  forms  of  club-foot.  When  it  is  acquired,  it  may  be  due  to  paralysis  of 
those  muscles  that  oppose  the  adduction  and  extension  of  the  foot, — i.e.,  chiefly  of 


668  HUMAN    ANATOMY. 

the  extensor  longus  digitorum  and  the  peronei.  The  muscles  that  draw  up  the  heel, 
— the  gastrocnemius  and  soleus, — the  muscles  that  elevate  the  inner  border  of  the 
foot  and  adduct  it, — the  tibalis  anticus  and  posticus  and  the  flexor  longus  digitorum, 
— are  not  resisted  ;  or,  if  the  case  is  congenital,  are  assisted  by  the  position  of  the 
foot,  which  is  therefore  found  with  (a)  the  heel  elevated  ;  (6)  the  inner  edge  of  the 
sole  drawn  upward  ;  (c)  its  axis  turned  inward  ;  (d)  the  sole  shortened,  partly 
through  contraction  of  the  plantar  fascia. 

In  marked  cases  the  calcaneum  will  be  almost  vertical,  as  will  the  astragalus, 
which  will  also  be  rotated  forward  so  that  its  head  may  have  two  articular  facets,  one 
of  them  projecting  on  the  dorsum ;  the  scaphoid  is  atrophied  and  is  close  to  the 
inner  malleolus;  the  cuneiform  bones  accompany  it,  and  the  cuboid  becomes  the 
chief  point  of  support  of  the  weight  of  the  body. 

Corresponding  changes  occur  in  the  metatarsal  bones  and  phalanges,  which  may 
be  at  right  angles  to  the  line  of  the  inner  side  of  the  leg. 

Pure  talipes  varus,  in  which  the  elevation  of  the  heel  is  absent,  is  very  rare.  The 
other  varieties  of  club-foot  are  seldom  congenital. 

2.  Talipes   Valgus. — The  foot  is  abducted  and  the  outer  border  elevated  by  the 
peronei,  the  inner  side  being  correspondingly   depressed  and  the  arch  of  the  foot 
flattened  out. 

3.  Talipes  Equinus. — The  heel  is  drawn  up  by  the  gastrocnemius  and  soleus  ; 
the  patient  walks  on   the  balls  of  the  toes  ;  the  os  calcis  and   the  astragalus  are 
changed   in   position   as    in   equino-varus.      The  astragalo-scaphoid  and    calcaneo- 
cuboid  joints  are  much  flexed,  so  that  the  scaphoid  may  even  be  in  contact  with  the 
os  calcis. 

4.  Talipes  Calcaneus. — The  extensor  longus  digitorum  and  the  extensor  pro- 
prius  pollicis  raise  the  toes  and  with  them  the  foot,  so  that  the  anterior  portion  of  the 
os  calcis  is  elevated  and  the  astragalus  is  rotated  backward  until  its  articular  sur- 
face points  in  that  direction.     The  patient  walks  on  the  heel. 

Flat-foot  results  from  weakness  or  relaxation  of  plantar  muscles,  fascia?,  and 
ligaments,  especially  the  inferior  calcaneo -scaphoid  (page  445).  When,  in  persons 
who  stand  much  of  their  time,  or  in  those  with  defective  ankles  originally,  this  liga- 
ment yields,  the  head  of  the  astragalus  is  carried  downward  and  inward  by  the  body 
weight,  which,  owing  to  the  width  of  the  pelvis,  the  obliquity  of  the  femur,  and  the 
curve  of  the  tibia,  is  transmitted  to  the  astragalus  somewhat  from  without  inward. 
This  is  associated  with  abduction  of  the  foot,  resisted  by  the  internal  lateral  and 
calcaneo-astragaloid  ligaments.  This  sinking  of  the  astragalus  and  increased  promi- 
nence of  the  internal  malleolus  may  be  seen  in  many  normal  feet  when  the  weight  of 
the  body  is  thrown  on  one  foot  (page  449).  In  well-marked  cases  of  flat-foot  the 
tibialis  posticus  fails  to  resist  this  change  effectually,  the  peronei  add  to  the  abduction 
or  shortening,  the  arch  of  the  sole  of  the  foot  entirely  disappears  or  may  even  become 
a  rounded  downward  curve,  the  deltoid  ligament  stretches,  as  do  the  long  and  short 
plantar  ligaments,  and  the  head  of  the  astragalus,  the  scaphoid  tubercle,  and  the 
sustentaculum  tali  (page  449)  become  unduly  prominent  and  may  be  the  main  poin 
of  support. 

Two  bursae  about  the  foot  are  of  enough  importance  to  demand  attention. 

The  retrocalcaneal  bursa  lies  between  the  os  calcis  and  the  tendo  Achillis,  the 
depressions  at  the  sides  of  which  are  effaced  when  the  bursa  is  distended.  The  cor- 
responding obliteration  of  the  anterior  depressions  just  beneath  the  malleoli  (page 
451),  which  occurs  in  ankle-joint  disease,  does  not  take  place.  Flexion  or  extension 
of  the  foot  or  contraction  of  the  calf  muscles  is  painful. 

/>  unions. — There  may  be  normally  a  bursa  over  the  metatarso-phalangeal  join 
of  the  great  toe,  or  an  "adventitious"  bursa — formed  by  dilatation  of  lymph-spaces, 
condensation  of  connective  tissue,  and  localized  effusion — may  develop  there,  as  a 
result  of  pressure  and  friction  from  badly  fitting  shoes.  The  great  toe  is  forced  out- 
ward, the  internal  lateral  ligament  of  the  articulation  is  elongated,  the  joint  is  made 
unduly  prominent,'  the  head  of  the  first  metatarsal  bone  sometimes  enlarges,  and  the 
cartilage  over  its  inner  surface  not  uncommonly  atrophies  and  disappears,  leaving  a 
communication  between  the  bursal  sac  and  the  synovial  cavity  of  the  joint.  Mat- 
foot  and  all  degrees  of  valgus  tend  to  produce  a  similar  condition  by  exposing  the 


; 


SURFACE   LANDMARKS  :   THE   LOWER    EXTREMITY. 


669 


inner  border  of  the  foot — and  thus  the  first  metatarso-phalangeal  joint — to  excessive 
pressure. 

Adventitious  burs;e  are  found  over  the  external  inalleolus,  — "  tailor's  bursa,"  — 
over  the  cuboid  in  equino-varus,  and  at  other  points  exposed  to  pressure  in  the 
different  forms  of  club-foot. 


Crest  of  ilium 


SURFACE    LANDMARKS   OF   THE   LOWER    EXTREMITY. 

i.  The  Buttocks  and  Hip. — The  iliac  furrow  (page  349 )  indicating  the  line 
of  the  crest  of  the  ilium,  with  the  external  oblique  above  and  the  gluteus  medius 
below,  passes  forward  to  the  anterior 

superior  spine,    and    is    more    or  less  FIG.  632. 

effaced  posteriorly  where  the  crest  is 
covered  by  the  flat  tendon  of  the  erec- 
tor spincE.  The  posterior  superior 
spine  is  always  indicated  by  a  surface 
depression. 

In  women  the  continuous  layer  of 
fat  passing  from  the  loin  to  the  but- 
tock blends  the  surface  forms  of  these 
regions  into  one  uniform  curve  (Thom- 
son i ,  and  there  is  no  such  marked  defi- 
nition of  them  as  is  seen  in  the  male. 

The  rounded  prominence  of  the 
buttock  (Fig.  632)  is  clue  partly  to 
subcutaneous  fat,  partly  to  the  thick 
muscular  mass  of  the  gluteus  maximus, 
especially  developed  in  man  by  reason 
of  his  assumption  of  the  upright  po- 
sition. It  is  more  prominent  posteri- 
orly, becomes  flattened  as  it  passes 
outward,  and  ends  in  a  distinct  de- 
pression (  Fig.  632  )  at  the  tendinous 
insertion  of  that  muscle  just  behind 
and  below  the  greater  trochanter.  Al- 
though the  trochanter  is  on  a  plane 
external  to  that  of  the  iliac  crest,  the 
hollow  between  it  and  the  ilium  is  so 
obliterated  by  the  gluteus  medius  and 
minimus  muscles  that  it  ordinarily  does 
not  appear  as  a  surface  prominence. 
Its  upper  border — on  a  level  with  the 
centre  of  the  acetabulum — is  indistinct 
on  account  of  the  presence  of  the  glu- 
teus medius  tendon  which  passes  over 
it  to  be  inserted  into  the  outer  surface 
of  the  trochanter. 

In  front  the  muscular  eminences 
where  the  region  of  the  buttock  passes 
into  that  of  the  hip  are  due  to  the  glu- 
teus medius  above  and  more  anteriorly 
to  the  tensor  facise  latre  (Fig.  632), 
which  shows  as  a  broad  elevation 
just  behind  a  vertical  line  drawn 

through  the  anterior  superior  spine  and  just  below  the  forepart  of  the  iliac  crest. 
It  can  be  best  seen  if  the  thigh  is  in  abduction  and  inward  rotation. 

As  the  skin  of  the  buttock  is  made  tense  when  the  thigh  is  flexed  on  the  pelvis, 
the  fold  of  the  nates  ( gluteo-femoral  crease),  due  to  creasing  or  drawing  in  of  the 
skin,  is  formed  when  the  thigh  is  extended.  It  begins  just  below  the  level  of  the 


Extensor 

brevis 

digitorum 


—  Extensor  longus  digitorum 


Lateral  surface  of  right  leg.  showing 
mock-Hint;  on  living  subjrct. 


670  HUMAN   ANATOMY. 

tuberosity  of  the  ischium,  runs  horizontally  outward,  and  crosses  the  middle  of  the 
lower  edge  of  the  gluteus  maximus,  part  of  which — the  inner — is  therefore  above  it 
and  part — the  outer — below  it.  In  flexion  of  the  hip  the  gluteus  maximus  is  flattened 
and  the  skin  stretched  over  it,  and  hence  this  fold  is  more  or  less  completely  effaced. 
As  flexion  is  an  almost  constant  early  symptom  of  hip-joint  disease  (page  381),  and 
is  usually  associated  with  atrophy  of  the  muscles  moving  the  joint,  the  obliteration  of 
the  gluteo-femoral  crease,  characteristic  of  this  disease,  can  readily  be  understood. 

In  women,  on  account  of  the  thickness  of  the  supragluteal  layer  of  fat,  the  gluteo- 
femoral  crease  is  longer  and  deeper  than  in  men. 

The  various  bony  points  of  this  region  have  been  described  (pages  345,  349),  as 
have  the  different  lines  and  measurements  employed  in  the  diagnosis  of  fractures  of 
the  neck  of  the  femur  and  of  dislocation  (pages  362,  364,  367). 

2.  The  Thigh. — (a)  Anterior  criiral  region.  The  hip  passes  insensibly  in 
front  and  below  into  the  region  of  the  thigh.  The  inguinal  furrow,  a  valuable  land- 
mark, separates  the  surface  of  the  abdomen  from  that  of  the  thigh  (page  1774).  It 
indicates  the  line  of  Poupart's  ligament,  which  may  be  felt,  in  the  absence  of  much 
subcutaneous  fat,  from  the  iliac  spine  to  the  pubic  spine,  more  easily  over  its  inner 
half,  and  still  more  easily  if  the  thigh  is  in  extension,  abduction,  and  outward  rotation. 

The  ligament  is  relaxed  by  flexion,  adduction,  and  inward  rotation  of  the  thigh, 
and  with  it,  to  some  extent,  the  deep  fasciae  of  the  thigh  and  abdomen  ;  therefore 
that  position  is  the  one  most  favorable  to  reduction  of  either  inguinal  or  femoral 
hernia  by  taxis  (pages  1770,  1774). 

Below  this  a  second  furrow — "  Holden's  line" — is  sometimes  seen  with  the  thigh 
in  slight  flexion,  beginning  at  the  scroto-femoral  angle  and  becoming  less  distinct  until 
it  is  lost  at  or  over  the  supratrochanteric  space.  It  runs  across  the  front  of  the  cap- 
sule of  the  hip-joint  and  is  lost  in  the  presence  of  synovitis  of  that  joint.  It  is  often 
indistinct,  and  in  some  subjects  cannot  be  made  out  at  all  (Treves). 

On  the  line  of  this  furrow,  and  just  external  to  a  vertical  line  drawn  through  the 
middle  of  Poupart's  ligament,  the  head  of  the  femur  can  sometimes  be  made  palpable 
by  extension  and  rotation  of  the  thigh,  but  this  is  rarely  possible  in  fat  or  muscular 
persons. 

The  depression  or  flattening  of  Scarpa's  triangle  (page  639)  can  usually  be  seen. 
The  tendon  of  origin  of  the  adductor  longus — made  prominent  by  abduction — and 
the  upper  portion  of  the  sartorius,  emphasized  by  flexion  and  outward  rotation  of  the 
thigh  with  the  knee  bent,  mark  its  inner  and  outer  borders  respectively.  The  sar- 
torius, continued  downward,  becomes  flattened  and  is  lost  in  the  rounded  fulness  on 
the  inner  side  of  the  knee.  Just  internal  to  a  line  bisecting  the  triangle  the  femoral 
artery  may  be  felt  and  its  pulsations  sometimes  seen.  A  very  trifling  depression  is 
occasionally  present  near  the  inner  angle  at  the  base  of  the  triangle,  and  then  indi- 
cates the  position  of  the  saphenous  opening  (page  635),  the  centre  of  which  is  from 
one  to  one  and  a  half  inches  below  and  the  same  distance  external  to  the  pubic  spine, 
which  is  on  a  transverse  line  drawn  through  the  upper  margin  of  the  greater  trochan- 
ter.  From  the  apex  of  the  triangle  the  shallow  groove,  extending  towards  the  inner 
side  of  the  knee,  marks  the  course  of  the  sartorius  and  the  interval  between  the  quad- 
riceps extensor  and  the  adductors.  To  the  outer  side  of  the  triangle  the  rectus  can  be 
seen,  showing  below  the  anterior  superior  spine  in  the  interval  between  the  sartorius 
and  the  tensor  fasciae  latse  ;  it  runs  down  the  front  of  the  thigh,  giving  it  its  convex 
fulness,  and  narrowing  to  its  ending  in  the  flattened  quadriceps  tendon,  the  edges  of 
which  stand  out  when  the  leg  is  strongly  extended  on  the  thigh.  The  obliteratior 
of  Scarpa's  triangle,  in  full  extension  of  the  thigh,  is  due  to  the  thrusting  forwar 
of  the  overlying  tissues  by  the  neck  and  the  upper  end  of  the  shaft  of  the  femur. 

To  the  inner  side  of  Scarpa's  triangle,  below  and  posteriorly  to  the  adductc 
longus,  the  other  adductors  and  thegrudlis  give-  the  rounded  outline  to  the  inner  side 
of  the  upper  thigh.  Near  the  knee,  when  the  leg  is  flexed,  the  tendon  of  insertion  of 
the  adductor  magnus  can  be  plainly  felt  between  the  sartorius  and  vastus  internus. 
The  latter  muscle  stands  out  along  the  lower  half  of  the  thigh  and  is  still  more  promi- 
nent near  the  knee,  where  it  becomes  superficial  between  the  rectus  and  the  sartorius. 

On  the  outer  side  the  vastus  externus  gives  the  thigh  its  broad,  slightly  convex 
surface,  down  the  centre  of  which  there  is  sometimes  a  slight  vertical  groove  im" 


FIG.  633. 


Poupart's  ' 
ligament 


Sartorius- 


Rectus  - 
femoris 


—  Femoral 
artery 

— Scarpa's 
triangle 


Quadriceps •— 

tendon 


Patella- 


Tubercle  of  tibia 


Subcutaneous- 
surface  of  tibia 


SURFACE   LANDMARKS  :    THE   LOWER   EXTREMITY.         671 

eating  the  position  of  the  ilio-tibial  band  of  fascia  between  the  insertions  of  the  tensor 
fasciae  latae  and  gluteus  maximus  and  the  external  tibial  tuberosity.  More  pos- 
teriorly a  distinct  longitudinal  depression  corresponds  to  the  external  intermuscular 
septum,  between  the  vastus  externus  and  the  short  head  of  the  biceps.  At  the 
lower  third  of  the  thigh  this  groove  indicates  the  line  of  nearest  approach  of  the  shaft 
of  the  femur  to  the  surface.  Elsewhere  it  is 
usually  so  covered  by  muscular  masses  that 
it  is  not  to  be  felt,  even  indistinctly.  The 
corresponding  internal  septum—  between  the 
vastus  iuternus  and  the  adductors  and  pecti- 
neus — produces  no  surface  marking. 

(&)  Posterior  crural  region.  The  ham- 
strings, descending  from  beneath  the  lower 
edge  of  the  gluteus  maximus,  cannot  at  first 
be  separately  identified.  Lower,  a  very  slight 
depression  may  mark  the  interval  between 
the  semimembranosus  and  the  semitendino- 
sus,  and  the  biceps  tendon  becomes  a  salient 
rounded  cord. 

When  the  limbs  are  straight  with  the 
knees  together  there  should  be  but  a  slight 
interval  between  the  thighs,  and  that  only 
where  the  sartorius  muscles  curve  back  to 
lie  along  the  inner  surface  of  the  limb.  In 
women,  owing  to  the  greater  quantity  of  sub- 
cutaneous fat,  the  thighs  may  be  in  contact 
all  the  way  down  (Thomson). 

3.  The   Knee. — On  the  anterior  sur- 
face the  quadriceps  tendon  and  the  ligamen- 
tum   patellae  are   made   more  prominent  by 
strong  extension  of  the  leg,  and  on  each  side 
of  the  ligament  the  little  eminence  made  by  the 
protrusion  of  the  soft  subpatellar  fat  becomes 
visible.     The  angle  made  by  the  axes  of  the 
tendon  and  ligament  should  be  noted  (page 
418). 

The  outline  of  the  patella  is  easily  felt 
and  can  usually  be  seen.  Above  it  is  a  slight 
depression.  At  its  sides  are  two  concavities 
— the  inner  of  which  is  a  little  more  marked, 
as  the  inner  border  of  the  patella  is  the 
more  prominent — which  in  fat  persons  may 
disappear,  as  they  do,  together  with  the  su- 
prapatellar  depression,  in  synovitis  of  the 
knee-joint  (page  413).  Both  anteriorly  and 
laterally  the  landmarks  have  been  sufficiently 
described  (pages  367,  390). 

Posteriorly  the  popliteal  space — the  ham 
— is  slightly  convex  during  extension  of  the 
leg  and  deeply  concave  when  it  is  flexed. 
The  boundaries,  the  relations  of  the  ham- 
string tendons,  of  the  ilio-tibial  band  externally  and  of  the  sartorius  tendon  internally 
have  been  described  (pages  409,  646).  At  the  lower  portion  of  the  space  the  con- 
verging fleshy  bellies  of  the  gastrocnemius  may  be  felt. 

4.  The   Leg. — The  landmarks  relating  to  the  tibia  (page  390)  and  fibula  (page 
396)  have  been  described.      Between  these  bones  the  belly  of  the  tibialis  anticus  causes 
a  distinct  prominence,  to  the  fibular  side  of  which  is  the  narrower  and  less-marked 
elevation  due  to  the  extensor  longus  digitorum.      Below  the  middle  third  of  the  leg 
these  muscles  are  tendinous,  but  by  dorsal  flexion  of  the  foot  and  of  the  toes  (exten- 


<• —  Muscles 
of  calf 


.Ankle- 
joint 


Abductor 
and  tlcxor 
breyis  hal- 
lucis 


Antero-median  surface  of  right  leg,  showing 
modelling  on  living  subject. 


672  HUMAN   ANATOMY. 

sion)  they  can  be  made  to  stand  out  with  the  tendon  of  the  extensor  proprius  hallucis 
between  them  ;  to  the  outer  side  of  the  extensor  longus  digitorum  tendon  a  slight 
groove  indicates  the  interval  between  that  muscle  and  the  peroneus  tertius.  The 
latter — as  a  muscle  peculiar  to  man  and  probably  developing  as  a  result  of  his  assump- 
tion of  the  erect  posture — is  not  invariably  present.  Above,  between  the  extensor 
longus  digitorum  and  the  soleus,  the  peroneus  longus  makes  a  longitudinal  elevation 
shading  off  below — where  the  fleshy  fibres  become  tendinous — into  the  flatter  pero- 
neus brevis. 

Posteriorly  the  swell  of  the  calf  is  formed  by  the  gastrocnemius,  and  its  surface 
markings  are  due  to  the  peculiar  arrangement  of  the  fleshy  and  tendinous  portions  of 
that  muscle.  When  the  calf  muscles  are  in  action,  as  in  standing  on  the  toes,  it  will 
be  seen  that  the  inner  head  is  the  larger  and  descends  somewhat  lower  than  the  outer 
head  ;  and  the  lateral  borders  of  the  soleus  will  be  seen  coming  to  the  surface  beyond 
the  lower  part  of  the  gastrocnemius  and  the  tendo  Achillis  and  showing  as  curved 
eminences,  of  which  the  outer  is  the  longer. 

5.  The  Ankle  and  Foot. — The  bony  landmarks  have  been  described  (pages 
390,  396,  437,  449,  453). 

At  the  front  of  the  ankle  the  extensor  tendons  are  easily  recognized.  The 
largest  and  most  internal  is  that  of  the  tibialis  anticus  ;  then,  in  order,  the  extensor 
proprius  hallucis,  extensor  longus  digitorum,  and — when  present — the  peroneus  ter- 
tius. Beneath  the  tendons  of  the  long  extensor  and  just  below  the  external  mal- 
leolus,  the  fleshy  belly  of  the  short  extensor  of  the  toes,  filling  the  space  between  the 
os  calcis  and  astragalus,  can  easily  be  felt  as  a  soft  swelling  over  the  outer  part  of  the 
tarsal  region,  and  is  distinctly  visible  when  in  action.  On  either  side  of  the  tendi- 
nous elevation,  on  a  level  with  the  line  of  the  ankle-joint  and  in  front  of  each 
malleolus,  is  a  little  depression.  This  is  effaced  when  the  capsule  is  distended 
by  effusion  (page  451).  The  two  fleshy  masses  on  the  inner  and  outer  border  of 
the  foot  are  due  respectively  to  the  abductor  and  flexor  brevis  hallucis  and  the  ab- 
ductor and  flexor  brevis  minimi  digiti.  The  dorsal  interossei  project  upward  slightly 
between  the  metatarsal  bones.  The  lines  on  the  dorsum  of  the  foot  corresponding 
to  the  various  joints  have  been  described  (page  453). 

Behind  the  ankle  and  at  the  sides  of  the  tendo  Achillis— between  it  and  the  pos- 
terior surfaces  of  the  malleoli — are  two  concavities,  of  which  the  outer  is  the  deeper. 
In  it  the  tendons  of  the  peroneus  longus  and  brevis  may  be  felt,  the  latter  the  nearer 
to  the  fibula.  In  the  inner  concavity  lie,  in  order  from  the  malleolus  backward,  the 
tendons  of  the  tibialis  posticus,  the  flexor  longus  digitorum,  and  the  flexor  longus 
pollicis. 

On  the  sole  of  the  foot  the  abductors  of  the  great  and  little  toes  show  somewhat 
on  the  surface,  but  the  chief  outlines  are  determined  by  the  arch  of  the  foot,  the 
strong  plantar  fascia,  and  the  thick  integument.  The  digital  creases  have  but  little 
practical  value. 

As  the  foot,  taken  as  a  whole,  acts  as  a  lever,  and  as  the  calf  muscles  are 
attached  to  the  heel, — the  short  end  of  such  a  lever, — it  follows  that  the  develop- 
ment of  these  muscles  will  stand  in  some  relation  to  the  length  or  projection  of  the 
heel.  As  a  short  lever  will  require  the  application  of  a  greater  force  to  produce 
the  same  result  than  will  a  long  lever,  we  find  the  most  marked  muscular  develop- 
ment of  the  calf  associated  with  a  short  foot  and  a  short  heel,  while-  a  long  foot  and 
a  long  heel  are  the  usual  concomitants  of  a  poorly  developed  calf  (Thomson  ).  The 
athletic  feats  of  some  runners  with  poorly  developed  calves  may  sometimes  be 
explained  by  observing  the  unusual  length  and  projection  of  the  heel. 


THE  VASCULAR  SYSTEM. 

THE  vascular  system  is  composed  of  the  organs  immediately  concerned  in  the 
circulation  throughout  the  body  of  the  fluids  which  convey  to  the  tissues  the  nutritive 
substances  and  oxygen  necessary  for  their  metabolism  and  carry  from  them  to  the 
excretory  organs  the  waste  products  formed  during  metabolism. 

The  system  is  usually  regarded  as  being  composed  of  two  portions,  the  one  con- 
sisting of  organs  in  which  circulates  the  red  fluid  which  we  term  'blood,  while  the 
organs  of  the  other  contain  a  colorless  or  white  fluid  known  as  lymph  or  chyle  ;  the 
former  of  these  subsystems  is  the  blood-vascidar  system,  and  the  latter  is  the  lymphatic 
system.  It  must  be  recognized,  however,  that  the  two  systems  communicate,  and  that 
the  lymphatic  system  develops  as  an  outgrowth  from  the  blood-vascular  system  ;  so 
that  while  it  proves  convenient  for  descriptive  purposes  to  regard  the  two  systems  as 
distinct,  nevertheless,  they  are  intimately  associated  both  anatomically  and  embryo- 
logically. 

THE  BLOOD-VASCULAR  SYSTEM. 

The  blood-vascular  system  consists  of  ( i )  a  system  of  canals  known  as  blood- 
vessels, traversing  practically  all  parts  of  the  body,  and  (2)  of  a  contractile  organ,  the 
heart,  by  whose  pulsations  the  blood  is  forced  through  the  vessels.  The  vessels  are 
again  divisible  into  ( i )  vessels,  which  carry  the  blood  from  the  heart  to  the  tissues 
and  are  known  as  arteries,  (2)  exceedingly  fine  vessels  which  form  a  net-work  in  the 
tissues  and  are  termed  capillaries,  and  (3)  vessels  which  return  the  blood  from  the 
tissues  to  the  heart  and  are  known  as  veins. 

THE   STRUCTURE   OF    BLOOD-VESSELS. 

Although  passing  into  one  another  insensibly  and  without  sharp  demarcation, 
where  typically  represented  the  arteries,  capillaries,  and  veins  present  such  character- 
istic histological  pictures  that  they  are  readily  distinguished  from  one  another. 

All  blood-vessels,  including  the  heart,  possess  an  endothelial  lining  which  may 
constitute  a  distinct  inner  coat,  the  tunica  intima,  or,  as  in  the  capillaries,  even  the 
entire  wall  of  the  vessel.  Usually,  however,  the  intima  consists  of  the  endothelium 
reinforced  by  a  variable  amount  of  fibre-elastic  tissue  in  which  the  elastica  predomi- 
nates. Except  within  the  walls  of  capillaries,  external  to  the  intima  lies  a  thick 
middle  coat,  the  tunica  media,  which  typically  is  composed  of  intermingled  lamellae 
of  involuntary  muscle  and  elastica  and  fine  fibrillae  of  fibrous  tissue.  Outside  the  media 
follows  the  tunica  externa  or  advcntitia,  which,  although  usually  thinner  than  the 
middle  coat,  is  of  exceptional  strength  and  toughness — characteristics  conferred  by 
its  fibre-elastic  tissue  and  upon  which  the  integrity  of  a  ligature  often  depends. 

It  should  be  noted  that  the  endothelial  tube  is  the  fundamental  and  primary 
structure  in  all  cases,  the  outer  coats  being  secondary  and  variable  according  to  the 
size  and  character  that  the  vessel  attains.  The  customary  division  into  the  three 
coats  is  more  or  less  artificial  and  in  the  larger  vessels  is  often  uncertain.  The 
recognition  of  an  inner  endothelial  and  an  outer  musculo-elastic  coat  often  more  closely 
corresponds  to  the  actual  arrangement  of  the  tissues  than  the  conventional  subdivision 
into  three  tunics. 

The  endothelial  lining  of  the  arteries  consists  of  elongated  spindle-shaped 
plates  united  by  narrow  sinuous  lines  of  cement  substance  which,  after  silver-staining, 
map  out  the  irregular  contours  of  the  cells  with  diagrammatic  clearness  (Fig.  634). 
At  the  junction  of  the  plates,  occasional  accumulations  of  the  cement  substance  mark 
minute  intercellular  areas,  the  stigmata,  that  indicate  points  of  less  accurate  apposi- 
tion. Within  the  veins,  the  endothelial  plates  are  shorter  and  broader  than  in  the 
arteries,  approaching  somewhat  irregular  polygons  in  outline.  The  demarcation  of 

43  673 


674 


HUMAN   ANATOMY. 


the  endothelium  into  distinct  cells  is  less  evident  in  the  capillaries  than  in  the  larger 
vessels,  in  some  cases  a  continuous  syncytial  sheet  replacing  the  definitely  outlined 
plates.  The  presence  of  a  relatively  small  oval  nucleus  is  readily  demonstrated  by 
suitable  stains. 

The  involuntary  muscle  varies  in  amount,  from  the  imperfect  single  layer  of 
muscle-cells  found  in  the  arterioles,  to  the  robust  muscular  coat  of  many  lamellae  in 
the  larger  arteries.  It  is  relatively  best  developed  in  arteries  of  medium  size,  where 
the  muscle  occurs  in  distinct  broad  or  sheet-like  bundles  between  the  strands  of  elastic 
tissue.  The  component  fibre-cells  are  short  and  often  branched  and,  for  the  most 
part,  circularly  disposed.  The  distribution  of  the  muscular  tissue  is  much  less 
regular  and  constant  in  the  veins  than  in  the  arteries,  since  in  many  it  is  scanty, 
in  some  entirely  .wanting,  and  in  a  few  veins  excessive,  occurring  in  both  circular  and 
longitudinal  layers.  The  striated  tmiscle  found  in  the  large  vessels  communicating 
with  the  heart  resembles  that  of  the  cardiac  wall  from  which  it  is  derived. 

Connective-tissue  is  represented  in  the  arteries  and  veins  by  both  fibrous  and 
elastic  tissue.  The  former  is  present  as  delicate  or  coarser  bundles  of  fibrillae  that 
extend  between  the  other  components  of  the  vascular  wall. 


FIG.  634. 


B. 


A. 


A,  endothelium  of  aiteriole  after  silver-staining ;  X  200.     B,  endothelial  cells 
more  highly  magnified.     X  500. 

The  elastic  tissue  is  very  conspicuous  in  all  arteries  save  the  smallest,  and  in 
many  veins.  It  presents  all  variations  in  amount  and  arrangement  from  loose  net- 
works of  delicate  fibres  in  the  smaller  vessels  to  robust  plates  and  membranes  in  the 
largest  arteries.  Within  the  intima  of  the  latter,  the  elastica  often  occurs  as  sheets 
broken  by  pits  and  perforations,  which  are,  therefore,  known  as  fene strated 
branes. 

Nutrient  blood-vessels  are  present  within  the  walls  of  all  the  larger  vessel 
down  to  those  of  i  mm.  in  diameter,  and  provide  nourishment  for  the  tissues  com- 
posing the  tubes.  These  vasa  vasorum,  as  they  are  called,  are  usually  branches  from 
some  neighboring  artery,  their  favorite  situation  being  the  external  coat  within  which 
they  ramify,  breaking  up  into  capillaries  that,  in  the  larger  vessels,  invade  the  adja- 
cent media.  The  blood  from  the  vascular  wall  is  collected  by  small  veins  that  accom- 
pany the  nutrient  arteries,  or,  as  in  the  case  of  the  veins,  empty  directly  into  the 
venous  trunk  in  whose  walls  they  course. 

Lymphatics  are  represented  by  spaces  both  within  the  muscular  tissue  and 
beneath  the  endothelium.  In  certain  situations,  conspicuously  in  the  brain  and  the 
retina,  the  blood-vessels  are  enclosed  within  lymph-channels,  the  pcrivascular  lymph- 
sheaths,  that  occupy  the  adventitia. 

The  nerves  distributed  to  the  walls  of  blood-vessels,  especially  to  the  arteries, 
are  numerous  and  include  both  sympathetic  and  spinal  fibres.  The  former  are  des- 


STRUCTURE   OF    BLOOD-VESSELS 


675 


tined  particularly  for  the  muscular  tissue  and,  therefore,  are  directed  to  the  media, 
although  vessels  in  which  muscle  is  wanting,  as  in  certain  veins  and  the  capillaries, 
are  not  without  nerves.  From  the  plexus  that  surrounds  the  vessel,  notably  rich 
about  the  arteries,  nerve-fibrillae  penetrate  the  media  and  end  among  the  muscle- 
fibres  in  the  manner  usual  in  such  tissue  (page  1015).  Special  sensory  nerve- 
endings  have  been  described  in  both  the  external  and  internal  tunics. 

The  Arteries. — Since  the  arrangement  of  the  component  tissues  is  most 
typical  in  arteries  of  medium  size  (from  4-6  mm.  in  diameter),  the  radial  artery  may 
appropriately  serve  for  description.  Seen  in  cross-section  (Fig.  635),  after  the  usual 
methods  of  preservation  and  staining,  the  intima  presents  a  plicated  contour  as  it 
follows  the  foldings  of  the  internal  elastic  membrane  that  appears  as  a  conspicuous 
corrugated  light  band  marking  the  outer  boundary  of  the  inner  tunic.  The  lining 
endothelial  cells  are  so  thin  that  in  profile  their  presence  is  indicated  chiefly  by  the 
slightly  projecting  nuclei.  Between  the  endothelium  and  the  elastic  membrane  the 


FIG.  635. 


Intima    .-,f 


Media 


Endothelium 
Internal  elastic 
membrane 

•^S^^sgy^"' ' 

"  *^^~.r 


Involuntary  muscle 


Elastic  tissue 


Ad  vent  it  ia 


—  External  elastic 
membrane 


—  Elastica 

Vasa  vasorum 


Transverse  section  of  artery  of  medium  size.     X  150. 

intima  includes  a  thin  layer  of  fibrous  and  elastic  fibrillae.  The  media,  thick  and 
conspicuous,  consists  of  circularly  disposed  flat  bundles  of  involuntary  muscle  sepa- 
rated by  membranous  plates  of  elastic  tissue,  that  in  the  section  appear  light  and 
unstained.  After  the  action  of  selective  dyes,  as  orcein,  the  elastica  is  very  con- 
spicuous (Fig.  636).  Delicate  fibrillae  of  fibrous  tissue  course  among  the  musculo- 
elastic  strands.  Beneath  the  outer  coat,  the  elastica  becomes  condensed  into  a  more 
or  less  distinct  external  elastic  membrane  that  marks  the  outer  boundary  of  the  media. 
The  adventitia  varies  in  thickness,  in  the  medium-sized  arteries  being  relatively  better 
developed  than  in  the  larger  ones.  It  consists  of  bundles  of  fibrous  tissue  intermingled 
with  elastic  fibres  of  varying  thickness.  The  adventitia  contains  the  vasa  vasorum 
and  chief  lymph-channels  of  the  vascular  wall. 

Followed  towards  the  capillaries,  the  coats  of  the  artery  gradually  diminish  in 
thickness,  the  endothelium  resting  directly  upon  the  internal  elastic  membrane  so 
long  as  the  latter  persists,  and  afterwards  upon  the  rapidly  attenuating  media.  The 
elastica  becomes  progressively  reduced  until  it  entirely  disappears  from  the  middle 


HUMAN   ANATOMY. 


coat,  which  then  becomes  a  purely  muscular  tunic  and,  before  the  capillary  is  reached, 
is  reduced  to  a  single  layer  of  muscle-cells.  In  the  precapillary  arterioles  the  muscle 
no  longer  forms  a  continuous  layer,  but  is  represented  by  groups  of  fibre-cells  that 


Intima 


External  elastic 

membrane 


Adventitia 


Transverse-section  of  artery  of  medium  size,  stained  to  show  elastic  tissue.     X  too. 

partially  wrap  around  the  vessel,  and  at  last  are  replaced  by  isolated  elements.  After 
the  disappearance  of  the  muscle-cells,  the  blood-vessel  has  become  a  true  capillary. 
The  adventitia  shares  in  the  general  reduction  and  gradually  diminishes  in  thickness 
until,  in  the  smallest  arteries,  it  consists  of  only  a  few  fibre-elastic  strands  outside  the 
muscle-cells. 

In  the  large  arteries,  on  the  other  hand,  the  intima  and  media  chiefly  undergo 
augmentation.  Although  the  inner  coat  greatly  thickens  and  contains  a  large 
amount  of  fibrous  tissue  and  elastica,  a  conspicuous  internal  elastic  membrane,  as 
seen  in  the  smaller  vessels,  is  lacking,  since  the  elastic  plates  and  membranes  are 
now  so  abundant  that  the  local  accumulation  is  no  longer  striking,  the  boundary 
between  the  inner  and  middle 
coats  being,  therefore,  less 
sharply  defined.  The  character 
of  the  thickened  media  also 
changes,  the  muscular  tissue  be- 
ing relatively  reduced  and  over- 
shadowed by  the  excessive  de- 
velopment of  the  fibro-elastic 
tissue,  which  is  arranged  in  reg- 
ularly disposed  lamellae  separa- 
ting the  muscle-bundles  and 
conferring  a  more  compact  and 
denser  character  to  the  wall  of 
the  vessel.  The  adventitia, 
while  relatively  thinner  than  in 
arteries  of  medium  size,  is  also 
increased  and  consists  of  robust 
fibres  and  plates  of  elastica,  many  of  \\hirh  are  longitudinally  disposed  and  irreg- 
ular, although  strong,  bundles  of  fibrous  tissue.  Exceptionally,  longitudinal  strands 
of  muscle  appear  in  the  outer  coat  next  the  media.  In  the  roots  of  the  aorta  and 


FIG.  637. 


Small  aiteries  in  which  muscular  coat  is  reduced  to  single 
layer  of  cells.     X  150. 


STRUCTURE   OF   BLOOD-VESSELS. 


677 


g£?  Intima 


Media 


pulmonary  artery,  the  media  consists  chiefly  of  striated  muscle  which  resembles  that 
of  the  myocardium  with  which  it  is  continuous,  both  vessels  having  been  derived  from 
a  common  trunk,  the  bulbus  arteriosus,  the  anterior  segment  of  the  primary  heart-tube. 

The  Veins. — The  walls  of  the  veins  are  always  thinner  than  those  of  corre- 
sponding arteries  and  are  more  flaccid  and  less  contractile  in  consequence  of  the 
smaller  amount  of  elastic  and  muscular  tissue  that  they  contain. 

In  veins  of  medium  size  (from  4-8  mm.  in  diameter),  the  intima  consists  of  the 
lining  endothelium,  the  cells  of  which  are  relatively  broad  and  short,  a  thin  layer  of 
fibrous  connective  tissue  and  net-works  of  fine  elastic  fibres.  A  distinct  internal 
elastic  membrane  is  seldom  pres- 
ent, at  most  a  condensation  of  FIG.  638. 
elastic  fibrillae  marking  the  outer 
limit  of  the  inner  coat.  In  some 
veins,  as  the  cephalic,  basilic, 
femoral,  long  saphenous,  and  pop- 
liteal, bundles  of  smooth  muscle 
occur  within  the  intima.  In  ad- 
dition to  the  circularly  disposed 
thin  sheets  of  muscular  and  fibro- 
elastic  tissue,  the  media  contains 
fibro-elastic  plates,  sometimes 
mingled  with  a  few  bundles  of 
muscle-cells,  that  extend  longi- 
tudinally. In  certain  veins,  as  in 
the  saphenous,  deep  femoral,  and 
popliteal,  the  longitudinal  fibres 
may  constitute  a  zone  beneath  the 
intima  to  the  exclusion  of  the  mus- 
cular tissue.  The  adventitia  is 
often  thicker  than  the  media,  and 
consists  of  interlacing  fibres  and 
net-works  of  fibro-elastic  strands, 
the  general  direction  of  which  is 
lengthwise.  In  many  veins,  par- 
ticularly in  those  of  the  lower  ex- 
tremity, the  outer  coat  contains 
bundles  of  longitudinally  disposed 
muscle-cells. 

The  valves  with  which  many 
veins  are  provided  consist  of 
paired  crescentic  folds  (Fig.  641) 
of  the  intima,  covered  on  both 
sides  with  endothelium,  containing 
a  small  amount  of  fibro-elastic  tis- 
sue. The  attached  border  of  the 
leaflets  ends  in  narrow  prolonga- 
tions that  extend  beyond  the  free 
margin  of  the  valve.  Between  the 
leaflets  of  the  valve  and  the  wall 
of  the  vein  lie  the  pocket-like  si- 
nuses, which  the  blood  distends  when  the  valve  is  closed. 


Adventitia 


Transverse  section  of  abdominal  aorta.    X  90. 


In  the  structure  of  their 

walls,  the  large  veins  present  many  deviations  from  the  typical  arrangement.  While 

;  intima  is  only  exceptionally  increased,  as  in  the  hepatic  part  of  the  inferior  vena 
cava  and  the  beginning  of  the  portal  vein,  the  media  is  often  markedly  thickened. 
I  his  increase  is  chiefly  due  to  augmentation  of  the  elastic  and  fibrous  tissue,  the  mus- 

2  remaining  comparatively  scanty.  The  splenic  and  portal  veins,  however,  are 
particularly  rich  in  muscular  tissue  ;  on  the  other  hand,  the  media  may  be 
almost  wanting,  as  in  the  greater  part  of  the  inferior  vena  cava  and  the  larger 
hepatic  veins. 


678 


HUMAN   ANATOMY. 


~. —  Intima 


Adventitia 


Lack  of  muscle  within  the  media  is  often  compensated  by  an  unusual  develop- 

ment of  such  tissue  in  the  adventitia;  in  some  large  veins,  as  in  the  hepatic  portion  of 

the    inferior    cava,   su- 

FIG.  639.  perior    mesenteric,    or 

external  iliac,  the  in- 
ner half  or  two-thirds 
of  the  outer  coat  is 
occupied  by  robust 
bundles  of  longitudi- 
nally arranged  muscle. 
In  some  cases,  how- 
ever, as  in  the  renal 
and  portal  veins,  the 
longitudinal  muscle  in- 
vades the  entire  thick- 
ness of  the  adventitia, 
or,  as  in  the  supra- 
renal vein,  the  muscle 
of  the  outer  tunic  may 
include  both  circular 
and  longitudinal  layers. 
The  walls  of  the 
small  veins  (less  than 
.040  mm.  in  diameter) 
consist  of  only  endo- 
thelium  and  connective 
tissue.  The  latter  rep- 
resents a  relatively  ro- 
bust adventitia  and  a 
feebly  developed  me- 
dia, muscle-fibres  being 
wanting.  Traced  tow- 

ards the  capillaries,  the  connective  tissue  gradually  diminishes  until  the  endothelial 

coat  alone  remains.      In  passing  into  veins  of  medium  size,  at  first  the  muscle-cells  are 

short  and  scattered  and  only 

partly  encircle  the  tube.     Far- 

ther along  the  elastica  appears 

in  the  form  of  delicate  fibres 

and  net-works  that  increase  in 

size  and  density  as  the  muscu- 

lar tissue  becomes  more  pro- 

nounced.     It    is    worthy    of 

mention  that  certain  veins,  no- 

tably those  of  the  brain  and  pia 

mater,  the  dural  sinuses,  and 

the  blood-spaces  of  cavernous 

tissue,     are    usually    entirely 

devoid    of    muscle,    although 

in  the  walls  of  some  of  the 

larger    cerebral    veins,    small 

strands  of  such  tissue  occur. 
The  Capillaries.  —  The 

most    favorable    arrangement 

for  efficient  nutrition  is  mani- 

festly one  insuring  the  passage 

of     the    blood-Stream    at    a    re- 

duced    rate  of   speed  in  inti- 

mate relations  with  the  tissue-elements.     These  requirements  are  met  in  the  capil- 

laries whose  collectively  increased  calibre  and  thin  walls  favor  slowing  of  the  blood- 


Transverse  section  of  pulmonary  artery  near  its  root, 
showing  striated  muscle.     X  15°- 


FIG.  640. 


Intima 


Media    - 


, 


Adventitia 


Transverse  section  of  vein  of  medium  size.     X  250. 


STRUCTURE   OF   BLOOD-VESSELS. 


679 


FIG.  641. 


Portion  of  fem- 
oral vein,  opened 
to  show  bicuspid 
valve. 


stream  and  the  passage  of  the  plasma  and  oxygen  into  the  surrounding  tissues. 
The  walls  of  the  capillaries  consist  of  only  the  lining  plates,  the  entire  vessel  being  in 
fact  a  delicate  endothelial  tube.  The  cells  composing  the  latter  are 
elongated  lanceolate  plates,  possessing  oval  nuclei,  united  by  nar- 
row lines  of  cement  substance.  Although  the  transition  from  the 
arterioles  is  gradual,  the  final  disappearance  of  the  muscle-cells  marks 
the  beginning  of  the  true  capillaries  ;  the  passage  of  the  latter  into 
the  veins  is  less  certain,  since  muscular  tissue  is  wanting  in  those 
of  small  size.  In  the  smallest  capillaries  two  endothelial  plates  may 
suffice  to  encircle  the  entire  lumen;  in  the  larger  three  or  four  cells 
may  be  required  to  complete  the  vessel.  Preformed  openings  (sto- 
mata)  in  the  walls  of  the  capillaries  do  not  exist,  the  passage  of  the 
leucocytes  and,  under  certain  conditions,  also  of  the  red  blood-cells 
(diapedesis)  and  of  small  particles  of  foreign  substances,  being  effected 
between  the  endothelial  plates.  In  some  capillaries,  as  in  those  of 
the  choroid,  liver,  or  renal  glomeruli,  the  usual  demarcation  of  the 
wall  into  distinct  cells  is  wanting,  the  individual  endothelial  plates 
being  replaced  by  a  continuous  nucleated  sheet  or  syncytial  layer. 
Where  the  capillaries  course  within  fibrous  tissue,  not  uncommonly  the 
vessel  is  accompanied  by  delicate  strands  of  connective  tissue  (adventitia  capillaris) 
that  suggest  an  external  sheath. 

The  capillaries  are  usually  arranged  as  net-works,  of  which  the  channels  are  of 
fairly  constant  size  within  the  tissue  to  which  they  are  distributed.  During  life  it  is  prob- 
able that  none  are  too  small  to  permit  the  passage  of  the  red  blood-cells,  while  many 
admit  two  or  even  three  such  elements  abreast.  Their  usual  diameter  varies  between 
.008  and  .020  mm.  The  capillary  net- works  in  various  parts  of  the  body  differ  in  the 
form  and  closeness  of  their  meshes,  since  these  details  are  influenced  by  the  arrange- 
ment of  the  component  elements  and  by  the  function  of  the  structures  supplied.  Thus, 
in  muscles,  tendons,  and  nerves  the  meshes  are  elongated  and  narrow;  in  glands,  the 
lungs,  and  adipose  tissue  they  are  irregularly  polygonal;  in  the  liver-lobules  converg- 
ingly  or  radially  disposed;  while  in  the  subepithelial  papillae  of  the  mucous  membranes 
and  the  skin  the  capillaries  commonly  form  loops.  In  general,  it  may  be  assumed  that 

FIG.  642. 

>  v^  (  ;  / 

WV-E?^WI    ;  " .:••:.  •  'J    •'$ 


\,   /  <•/  !A,    .  V»^» 

Jt 

'       i  ;  \     'fr  / 


ff*jti*  ,;,  \.  r  V-  \^^&,'^?:-:^ 

c  <--<•••  ^SH-wj«r W-  '^*,3*&£ 

4  >     '  I     &  a^  .  -^  •'•••-.  ^-^^  -/'~.:,.^-^' 


c^<~,     m^^^m^^^^^M^ 

•  ^^Jj^^^^^^m    { 

>  * 


:-*&^^*?l&~^*^jm^ >v-  <  \ - 

rteHo,e    ^&(QI^^  LU    ^  ! 

^^^^^M^^'^jf  \-^ih,  *  ^ 


?%?*£'•:%     '       -if 

U_/  ¥       ^KwifeM1^* 


Capillaries  arising  from  arteriole  and  ending  in  small  vein  in  omentum.     X  200. 

the  greater  the  functional  activity  of  an  organ,  the  closer  is  its  capillary  net-work. 
Organs  actively  engaged  in  excretion,  as  the  kidneys,  or  the  elimination  of  substances 


68o  HUMAN   ANATOMY. 

from  the  blood,  as  the  lungs  or  liver,  as  well  as  those  producing  substances  directly 
entering  the  circulation  (organs  of  internal  secretion),  as  the  thyroid  gland,  are  pro- 
vided with  exceptionally  rich  and  close  net-works.  The  mesh-works  within  the  walls 
of  the  pulmonary  alveoli  are  of  remarkable  closeness  and  are  often  narrower  than  the 
capillaries  surrounding  them. 

Under  the  name,  sinusoids,  Minot1  has  grouped  the  circulation  occurring  in 
certain  organs,  as  the  liver,  in  which  the  capillaries  are  formed  by  the  invasion  and 
subdivision  of  the  large  original  blood-channel  by  the  tissue-cords.  The  resulting 
sinusoids  differ  from  ordinary  capillaries,  therefore,  in  connecting  afferent  and  efferent 
vessels  of  the  same  nature,  both  being  either  venous  or  arterial.  Capillaries,  on  the 
contrary,  form  communications  between  arteries  and  veins.  In  consequence  of  the 
invagination  of  the  original  vessel,  its  endothelium  bears  an  unusually  intimate  rela- 
tion to  the  tissue-trabeculae,  little  or  no  connective  tissue  intervening.  F.  T.  Lewis 2 
has  shown  that  the  Wolffian  body  and  the  developing  heart  also  present  examples  of 
sinusoidal  formation,  and  suggests  the  significance  of  sinusoids  as  representing  a 
primitive  type  of  circulation. 

THE   BLOOD. 

The  fluid  circulating  within  all  parts  of  the  blood-vascular  system  consists  of  a 
clear,  almost  colorless  plasma  or  liquor  sa^^g^^,^n^s  in  which  are  suspended  vast 
numbers  of  small  free  corpuscular  elements,  the  blood-cells.  The  latter  are  of  two 
chief  kinds,  the  colored  cells,  or  erythrocytes,  and  the  colorless  or  leucocytes.  The 
characteristic  appearance  of  the  blood  is  due  to  the  presence  of  hemoglobin  con- 
tained within  the  erythrocytes  which,  while  individually  only  faintly  tinted,  collect- 
ively impart  the  familiar  hue  as  well  as  a  certain  degree  of  opacity.  That  the 
characteristic  pigment  is  limited  to  the  cells  is  shown  by  the  lack  of  color  and  the 
transparency  of  the  plasma  when  examined  under  the  microscope,  although  to  the 
unaided  eye  the  blood  appears  uniformly  red  and  somewhat  opaque.  The  most  im- 
portant property  of  hemoglobin  is  its  great  affinity  for  oxygen  which,  taken  up  from 
the  air  during  respiration  and  combined  as  oxyhemoglobin,  is  carried  by  the  red 
cells  to  all  parts  of  the  body.  When  rich  in  oxygen  (containing  about  twenty  vol- 
umes) the  blood  possesses  the  bright  scarlet  hue  characteristic  of  arterial  blood;  after 
losing  approximately  one-half  of  its  oxygen  and  acquiring  about  an  equal  volume  of 
carbon  dioxide  during  its  intimate  relations  with  the  tissues,  the  blood  returned  by 
the  veins  is  dark  purplish-blue  in  color.  If  the  hemoglobin  escapes  from  the  eryth- 
rocytes into  the  plasma,  the  latter  becomes  deeply  tinged  and  the  blood  loses  its 
opacity  and  becomes  transparent  or  ' '  laked. ' ' 

The  specific  gravity  of  normal  blood  is  about  1060;  its  reaction  is  alkaline  and 
due  chiefly  to  the  presence  of  sodium  carbonate.  Immediately  after  withdrawal  from 
the  body  the  blood  possesses  a  characteristic  odor  that  probably  depends  upon  cer- 
tain volatile  fatty  acids.  When  fresh  it  is  slippery  to  the  feel,  but  after  exposure 
to  air  becomes  sticky.  Upon  standing  it  undergoes  coagulation,  whereby  the  cor- 
puscles become  entangled  among  the  innumerable  delicate  filaments  of  fibrin,  a  pro- 
teid  substance  that  appears  in  the  plasma  after  withdrawal  of  the  blood  from  the 
body.  As  the  result  of  this  entanglement  the  corpuscles  are  collected  into  a  dark- 
colored,  jelly-like  mass,  the  blood-clot  or  crassamentum,  that  separates  from  the  sur- 
rounding clear  straw-colored  serum.  The  latter  possesses  an  alkaline  reaction  and 
a  specific  gravity  of  1028.  The  serum  closely  resembles  the  liquor  sanguinis,  con- 
taining about  ten  per  cent,  of  solid  substances,  of  which  about  three-fourths  are  pro- 
teids — serum-albumin,  serum-globulin,  and  fibrin-ferment,  the  latter  replacing  the 
fibrinogen  present  in  the  plasma  before  coagulation  occurs. 

Blood-Crystals. — The  chief  constituent  of  the  red  cells,  the  hemoglobin,  prob- 
ably exists  within  the  corpuscles  as  an  amorphous  mass  in  combination  with  other 
substances  (Hoppe-Seyler)  from  which  it  must  be  freed  by  solution  before  crystal- 
lization can  occur.     After  laking,  the  coloring  matter  of  the  blood,  in  the  form  of 
oxyhemoglobin,  separates  into  microscopic  crystals  that  belong  to  the  rhombic  sys- 
tem,  usually  appearing    as    elongated    rhombic   or    rectangular    plates  (Fig.   643). 
1  Proceedings  Boston  Sor.  Nat.  History,  vol.  xxix,  1900. 
*  Anatomischer  Anzeiger,  Bd.  xxv.,  1904. 


THE   BLOOD. 


681 


When  unusually  large  or  superimposed  they  exhibit  the  characteristic  crimson  hue, 
but  when  single  and  small  the  hemoglobin  crystals  are  colorless  or  of  a  faint  greenish- 
yellow  tint.  On  mixing  dried  blood  with  a  few  grains  of  sodium  chloride  and  a  small 
quantity  of  acetic  acid  and  heating  until  bubbles  appear,  minute  brown  crystals  are 
formed  in  large  numbers.  These  are  known  as  Tcichmanri  s  or  hemin  crystals  and  re- 
present one  of  the  products  derived  from  the 

reduction    of   hemoglobin.      Being  yielded  by  FIG.  643. 

blood  from  various  sources,  they  are  indica- 
tive only  of  the  presence  of  blood  and  are 
valueless  in  differentiating  the  blood  of  man 
from  that  of  other  animals.  In  blood-clots 
of  long  standing  minute  hematoidin  crystals 
often  appear  as  yellowish-red  plates.  This 
substance  is  likewise  a  reduction-product  of 
hemoglobin. 

The  Colored  Blood-Cells.— The  ma- 
ture colored  blood -cells,  erythrocytes,  or  red 
corpiiscles,  of  man  and  other  mammals  (ex- 
cept those  of  the  camel  family,  which  are 
elliptical  in  outline)  are  small,  biconcave, 
circular,  nonnucleated  discs,  with  smooth 
contour  and  rounded  edges.  When  viewed 
by  transmitted  light,  the  individual  "red" 
cells  possess  a  pale  greenish-yellow  tint,  and 
only  when  they  are  collected  in  masses  or 
superimposed  in  several  layers  is  the  distinc- 
tive blood-color  evident.  The  peculiar  form 
of  the  corpuscle — biconcave  in  the  centre  and  biconvex  at  the  periphery — 
renders  accurate  focussing  of  all  parts  of  its  broader  surface  in  one  plane  impossible  ; 
hence  under  the  high  amplification  necessary  for  their  satisfactory  examination, 
the  entire  cells  are  never  sharply  defined  and,  according  to  focal  adjustment, 
appear  either  as  light  rings  enclosing  dark  centres  or  vice  versa.  Viewed  in 
profile,  the  thicker  convex  marginal  areas  are  connected  by  the  thinner 
concave  centre,  the  corpuscle  presenting  a  general  figure  somewhat  resembling 
a  dumb-bell. 

After  fresh  blood  has  been  distributed  as  a  thin  layer  and  allowed  to  remain 
unshaken  for  some  time,  the  red  cells  exhibit  a  peculiar  tendency  to  become  arranged 

in  columns,  with  their  broad  surfaces  in  contact,  similar 
to  piles  or  rouleaus  of  coin  (Fig.  646).  Agitation  dis- 
perses the  corpuscles,  which,  however,  may  resume  their 
former  grouping  when  again  undisturbed.  The  columns 
may  join  one  another  until  a  net-work  of  rouleaus  is 
formed.  If  the  stratum  of  blood  be  thin,  the  red  cells 
f  usually  later  separate,  but  they  may  retain  their  columnar 
grouping. 


Crystals  of  oxyhemoglobin  from  human 
blood.     X  160. 


FIG.  644. 


)  ^ 


Hemin  crystals  from  human 
blood.      X  250. 


The  long-accepted  biconcave  discoidal  form  of  the  mam- 
malian erythrocytes  has  been  questioned  by  Dekhuyzen  *  and, 
more  recently,  by  Weidenreich  2  and  by  F.  T.  Lewis,3  who  be- 
lieve that  the  normal  form  of  the  red  blood-cells  is  cup-shaped, 
similar  to  a  sphere  more  or  less  deeply  indented,  thus  reviving 
the  conception  held  by  Leeuwenhoek  nearly  two  centuries  ago. 
Although  such  cupped  corpuscles  are  familiar,  they  are  generally 

regarded  as  changed  cells  resulting  from  modification  of  the  density  of  the  plasma.  The  posi- 
tive testimony  of  so  careful  an  observer  as  Lewis  as  to  the  occurrence  of  the  cup-shaped  red  cells 
within  the  circulation  during  life  entitle  these  views  to  consideration.4 

1  Anatomischer  Anzeiger,  Bd.  xv.,  1899. 
3  Archiv.  f.  mikrps.  Anatom.,  Bd.  Ixi.,  1902. 

3  Journal  of  Medical  Research,  vol.  x.,  1904. 

4  A  critical  review  concerning  the  form  and  structure  of  the  red  cells  is  given  by  Weiden- 
reich in  Ergebnisse  d.  Anat.  u.  Entwick.,  Bd.  xiii.,  1904. 


682 


HUMAN   ANATOMY. 


Dresbach 1  has  recorded  the  presence  of  elliptical  red  cells  in  the  blood  of  an  apparently 
healthy  mulatto.  The  oval  corpuscles,  which  measured  .010  mm.  by  .004  mm.,  were  approxi- 
mately constant  in  size,  slightly  biconcave,  and  constituted  ninety  per  cent,  of  all  the  red  cells. 
They  were  observed  over  a  period  of  four  months,  during  which  time  the  number  of  erythro- 

cytes  and  leucocytes  and  the  amount  of 

FIG.  645.  hemoglobin  were  normal.     Dresbach  con- 

cludes that  the  oval  form  was  not  an  arti- 
fact, but  probably  due  to  developmental 
variation. 

The  average  diameter  of  the  red 
blood-cells  of  man  is  .0x378  mm. 
(STTHF  m-)>  some  corpuscles  meas- 
uring as  little  as  .0045  mm.  and 
others  as  much  as  .0095  mm.  Their 
average  thickness  is  about  .0018  mm. 
It  is  probable  that  the  average  diam- 
eter is  uninfluenced  by  sex  and  is 
constant  for  all  races,  although  ac- 
cording to  Gram,  the  size  of  the  cor- 
puscles is  somewhat  greater  in  the 
inhabitants  of  northern  countries. 
The  number  of  red  cells  normally 
contained  in  one  cubic  millimeter  of 
blood  is  approximately  5,000,000  in 
the  male  and  something  less  (4,500,- 
ooo)  in  the  female.  The  number  of 
corpuscles  is  practically  the  same 
whether  the  blood  be  taken  from  the  arteries,  capillaries,  or  veins,  but  is  lower  in  the 
blood  from  the  vessels  of  the  lower  extremity  than  of  the  upper,  probably  owing  to 
the  greater  proportion  of  plasma  in  the  more  dependent  parts  of  the  body.  Within 
the  first  day  after  birth,  the  number  of  erythrocytes  is  normally  very  high;  in  ad- 
vanced old  age  it  is  usually  diminished. 

In  general,  the  red  blood-cells  of  mammals  are  small  and  their  size,  which  greatly  varies  in 
different  orders,  bears  no  relation  to  that  of  the  animal.  The  corpuscles  of  man,  which  are  among 
the  largest  and  exceeded  by  only  those  of  the  elephant  (.0094  mm.)  and  the  two-toed  sloth 
(.0091  mm. ),  are  approximated  by  those  of  the 

guinea-pig  (.0075  mm.),  dog  (.0073  mm.),  rab-  FIG.  646. 

bit  (.0069  mm. ),  and  cat  (.0065  mm.).  Those 
of  many  familiar  mammals  are  distinctly 
smaller,  as  the  hog  (.006  mm.),  horse  (.0056 
mm.),  sheep  (.005  mm.)  and  goat  (.004  mm. ).  ,  ,  ^X 

The  smallest  mammalian  corpuscles  are  those  of 
the  musk-ox,  with  a  diameter  of  only  .0025  mm. 

It  is  obvious  that  a  positive  differentiation  .    >, 

of  human  blood  from  that  of  some  of  the  do- 
mestic animals,  based  on  the  measurement  of 

the  red  cells,  is  uncertain  and  often  impossible.  ,•'&•••••. 

The  application  of  the  "biological"  test  has 
placed  a  much  more  reliable  and  even  specific 
means  in  the  hands  of  the  medico-legal  expert. 
This  test  depends  upon  the  fact,  demonstrated 
by  Bordet,  Uhlenmuth,  and  others,  that  the 
blood-serum  of  an  animal  that  has  been  repeat- 
edly injected  with  small  quantities  of  human 


Red  cells  from  human  blood  ; 
near  centre  of  field. 


leucocyte  seen 

X865. 


Human  blood  corpuscles ;  two  leucocyte 
seen  among  the  red  cells,  most  of  whicl 
grouped  in  rouleaus.  X  625. 


blood  will  produce  a  distinct  cloudy  precipitate 
or  turbidity  when  added  to  a  dilute  solution 
of  human  blood,  but  will  yield  no  result  when 

added  to  similar  solutions  of  blood  from  other  animals.     An  important  advantage  of  this  test 
is  that  even  when  the  blood  is  putrid,  contaminated,  or  derived  from  old  dried  dots,  the  char- 
acteristic changes  occur.     Certain  exceptional  disturbing  conditions,  such  as  the  presence  of 
1  Science,  March  18,  1904,  and  March  24,  1905,. 


THE   BLOOD. 


683 


monkey's  blood,  human   lachrymal  or  nasal   secretion,  being  eliminated,  a  positive  reaction 
with  the  serum-test  is  strong  evidence  of  the  presence  of  human  blood. 

The  nonnucleated  condition  of  the  mature  erythrocytes  is  the  distinguishing  characteristic 
of  mammalian  blood  as  contrasted  with  the  colored  corpuscles  of  other  vertebrates,  since  even 
in  the  exceptional  oval  red  cell  of  the  camel  family  the  nucleus  is  wanting.  The  mammalian 
red  corpuscles,  however,  must  be  regarded  as  a  secondary  deviation  from  the  fundamental  type 
represented  by  the  oval  nucleated  erythrocyte  of  the  other  vertebrates,  the  nucleated  embryonic 
red  cell  losing  its  nucleus  as  maturity  is  acquired.  In  general,  the  oval  nucleated  red  cells  are 
larger  than  the  mammalian  nonnucleated  discs.  The  largest  erythrocytes  are  found  in  the 
tailed  amphibians,  those  of  the  amphiuma,  the  largest  known,  attain  the  gigantic  length  of  .080 
mm.,  and  are  approximately  ten  times  as  large  as  the  human  red  blood-cell. 

The  structure  of  the  red  blood-cell  has  long  been  and  still  is  a  subject  of  dis- 
cussion, two  opposed  views  finding  ardent  supporters.  According  to  the  one,  held 
by  Schaefer,1  Weidenreich,  and  others,  the  erythrocyte  consists  of  a  membranous 
external  envelope  inclosing  the  colored  fluid  contents.  On  the  other  hand,  Rollett 
and  many  others  regard  the  corpuscle  as  composed  of  an  insoluble  uniform  spongy 
stroma  of  great  delicacy,  occupied  by  the  coloring  matter  or  hemoglobin.  Although 
no  definite  envelope  is  present,  in  the  sense  of  a  distinct  cell-membrane,  it  is  highly 
probable  that  a  peripheral  condensation  of  the  stroma  exists.  The  fact  that  the 


FIG.  647. 


B. 


Nucleated  amphibian  red  blood-cells;  A,  from  newt ;  B,  from  amphiuma.     X  75P. 

fragments  into  which  the  red  blood-cells  may  be  broken  up  after  certain  treatment, 
as  by  heating,  retain  the  appearance  and  structure  identical  with  the  larger  original 
cell,  is  strong  evidence  that  the  hemoglobin  has  not  escaped  and,  therefore,  does 
not  exist  in  a  fluid  condition  within  the  cell,  notwithstanding  the  ingenious  but 
scarcely  convincing  explanations  of  the  phenomena  advanced  by  the  supporters  of 
the  vesicular  structure  of  these  cells.  The  further  evidence  afforded  by  those 
parts  of  the  corpuscles  that  remain  after  abstraction  of  the  hemoglobin  by  water, 
ether,  and  other  reagents,  points  to  the  existence  of  a  distinct  stroma,  the  thicker 
edges  of  which  appear  in  profile  as  outlines  of  the  ' '  ghosts ' '  that  then  represent 
the  former  colored  cells. 

The  erythrocytes  are  extremely  sensitive  to  a  wide  range  of  reagents  and  conditions  and, 
therefore,  require  great  care  in  their  collection  and  examination  if  distortions  are  to  be  avoided. 
Exposure  to  even  a  current  of  air  often  suffices  to  produce  conspicuous  changes  in  the  red  blood- 
cells.  Alterations  in  form  may  be  grouped  into  those  resulting  from  the  action  of  solutions  of 
lower  and  of  higher  density  than  that  of  the  normal  plasma.  The  latter  is  conveniently  sub- 
stituted by  an  .85  per  cent,  solution  of  sodium  chloride.  If  the  proportion  of  salt  be  grad- 
ually reduced,  the  corpuscles  show  evidences  of  swelling,  at  first  by  losing  their  concavity  on 
one  side  and  later,  as  the  density  of  the  reagent  approaches  that  of  water,  assuming  the 
spherical  form  and  parting  with  the  hemoglobin  and  becoming  colorless.  On  the  other  hand, 

1  Anatomischer  Anzeiger,  Bd.  xxvi.,  1905. 


684 


HUMAN   ANATOMY. 


FIG.  648. 


when  subjected  to  saline  solutions  stronger  than  the  "normal,"  the  exterior  of  the  corpuscles 
becomes  irregular  and  beset  with  knob-like  projections  or  spines.  When  the  concentration 
of  the  medium  is  increased,  the  "crenation"  gives  place  to  marked  shrinkage  and  distortion, 
until  the  cells  lose  all  resemblance  to  their  normal  form. 

Upon  treatment  with  water,  aqueous  dilutions  of  acetic  acid,  ether,  and  other  reagents,  the 
erythrocytes  are  promptly  decolorized  by  the  extraction  of  the  hemoglobin.  An  interesting 
modification  of  the  phenomenon  may  be  produced  by  solutions  of  tannic  acid  or  potassium 
bichromate  of  varying  strength.  When  the  reaction  is  vigorous,  the  decomposed  hemoglobin 
is  caught  within  the  cell  and  appears  as  a  mass  somewhat  resembling  a  nucleus.  When  tin- 
reaction  is  feeble,  as  with  very  weak  solutions,  the  hemoglobin  is  less  suddenly  precipitated,  and 
appears  as  a  minute  projection  attached  to  one  part  of  the  exterior  of  the  decolorized  corpuscle. 
Alkaline  solutions  effect  the  complete  destruction  of  the  red  cells.  Among  the  reagents 
employed  in  histological  investigations,  osmic  acid  (i  per  cent.)  deserves  especial  confidence  as 
preserving  the  form  of  the  red  corpuscles.  Fixation  by  heat,  so  commonly  used  in  the  prepara- 
tion of  blood  specimens  for  clinical  examinations,  produces  alterations  and  often  marked  changes 
in  the  red  cells,  and,  therefore,  is  unsuitable  for  histological  study  of  these  elements.  Attenua- 
tion of  the  central  parts  of  the  cells  produces  appearances  that  have  been  mistaken  for  a  nucle- 
ated condition  of  the  erythrocytes.  Upon  cautious  application  of  heat,  with  precautions  against 
evaporation  and  drying,  the  corpuscles  extrude  portions  of  their  substance  which,  after  separation, 
resemble  miniature  red  cells. 

The  Colorless  Blood-cells. — It  may 
at  once  be  emphasized  that  the  colorless  cells 
observed  within  the  blood  are  only  incident- 
ally related  to  the  red  cells  and,  further,  that 
they,  in  part  at  least,  primarily  circulate  within 
the  lymph-vascular  system,  from  which  they 
are  poured  into  the  blood. 

When  examined  in  fresh  and  unstained 
preparations,  the  colorless  cells  or  leuco- 
cytes appear  as  pale  nucleated  elements 
which,  by  their  pearly  tint  and  refracting 
properties,  are  readily  distinguished  from  the 
much  more  numerous  surrounding  erythro- 
cytes. Their  shape  is  very  variable,  but 
when  first  withdrawn  from  the  body  is  usually 
irregularly  spherical  or  oval.  When  placed 
on  a  warmed  slide  and  maintained  at  the 
temperature  of  the  body,  many  of  these  cells 
soon  exhibit  amoeboid  motion,  whereby  are 
produced  not  only  alterations  in  their  form,  but  often  also  changes  in  their  actual 
position. 

A  nucleus  is  always  present,  but  may  be  obscured  in  the  contracted  spherical 
condition  of  the  cell  by  the  overlying  granular  cytoplasm.  In  the  expanded  con- 
dition, as  when  the  cell  is  undergoing  amoeboid  change,  the  nucleus  is  very  evi- 
dent and  the  cytoplasm  often  differentiated  into  a  homogeneous  peripheral  zone 
(exoplasm)  and  a  central  granular  area  (endoplasni)  surrounding  the  nucleus.  A 
distinct  cell-wall  is  absent,  although  it  is  probable  that  a  slight  peripheral  condensa- 
tion serves  to  outline  the  corpuscle.  That  such  condensation  does  not  constitute  a 
definite  envelope  is  shown  by  the  readiness  with  which  foreign  particles  may  be  taken 
into  the  body  of  the  cell. 

Although  the  size  of  the  colorless  corpuscles  varies  with  the  type  of  the  cell,  as 
presently  described,  in  general  the  diameter  of  these  elements  is  larger  than  that  of 
the  erythrocytes,  and  is  commonly  from  .oio-.oi2  mm.  Their  number  is  much  U-ss 
than  that  of  the  red  corpuscles,  the  usual  ratio  between  the  white  and  red  cells  being 
about  i :  600.  Even  within  physiological  limits  this  ratio  varies  considerably,  from 
5000  to  10,000,  with  an  average  of  7500,  white  cells  being  normally  found  in  one 
cubic  millimeter  of  blood. 

Critical  examination  of  the  colorless  cells,  after  fixation  and  staining,  has  shown  that  among 
the  elements  collectively  designated  as  the  "white  cells"  or  "leucocytes,"  five  varieties  are 
usually  present  in  normal  blood.  Since  the  recognition  of  these  forms  is  sometimes  of  practical 


Varieties   of   colorless   blood-cells   seen    in 
normal    human    blood ;    a,  small  lymphocytes ; 

b,  large  lymphocyte  or  mononuclear  leucocyte; 

c,  transitional  leucocyte ;    rf,  polymorphonuclear 
leucocytes ;  e,  eosinophile  ;  /,  red  cells.     X  900. 


THE   BLOOD.  685 

importance,  a  brief  resum£  of  their  characteristics,  based  on  the  descriptions  of  Ehrlich  and  of 
Da  Costa,1  may  appropriately  here  find  place. 

It  should  be  noted  that  the  differentiation  of  these  cells  is  founded  upon  not  only  their 
morphological  characters,  but  also  the  behavior  of  the  granules  embedded  within  their  cyto- 
plasm when  subjected  to  certain  combination  stains.  A  generation  ago  Ehrlich  divided  the 
aniline  dyes  into  three  groups — acid,  basic,  and  neutral.  The  first  includes  such  dyes  as  acid 
fuchsin,  orange  G  or  eosin,  in  which  the  coloring  principle  acts  or  exists  as  an  acid  and  exhibits 
an  especial  affinity  for  the  cytoplasm.  The  second  group,  the  basic  stains,  includes  dyes,  as 
hematoxylin,  methylene-blue,  methyl-violet,  methyl-green  or  thionin,  in  which  the  coloring  prin- 
ciple exists  chemically  as  a  base  in  combination  with  a  colorless  acid  and  particularly  affects  the 
chromatin  ;  hence,  such  are  nuclear  stains.  Neutral  dyes,  produced  by  mixture  of  solutions  of 
an  acid  and  a  basic  stain,  have  a  selective  affinity  for  certain  so-called  neutrophilic  granules. 

Assuming  that  the  blood-film  has  been  fixed  by  heat  and  tinged  with  Ehrlich's  "triacid 
stain"  (a  combination  of  solutions  of  acid  fuchsin,  orange  G,  and  methyl-green)  the  following 
varieties  of  colorless  cells  are  distinguishable  in  normal  blood  : 

1.  Small  Lymphocytes. — These  are  non-granular  cells,  with  an  average  diameter  of  .0075 
mm.  or  about  that  of  the  erythrocytes,  distinguished  by  a  large  deeply  staining  nucleus  that 
occupies  almost  the  entire  cell.     The  meagre  cytoplasm  is  reduced  to  a  narrow  peripheral  zone, 
so  inconspicuous  that  it  may  be  overlooked.     The  small  lymphocytes,  which  constitute  from 
20-30  per  cent,  of  all  the  white  corpuscles,  are  the  most  common  derivative  from  the  lymphoid 
tissues. 

2.  Large  Lymphocytes,  or  Mononuclear  Leucocytes. — These  elements,  about  .012  mm.  in 
diameter,  possess  a  relatively  small  round  or  oval  nucleus,  which  is  usually  eccentrically  placed 
and  so  poor  in  chromatin  that  it  stains  faintly.     The  cytoplasm  is  non-granular  and  comparatively 
large  in  amount. 

3.  Transitional  Leucocytes. — Assuming  that  the  lymphocytes  and  leucocytes  are  related 
and  not  distinct  elements,  the  transitional  forms  represent  the  developmental  stage  linking  the 
large  lymphocytes  with  the  mature  leucocytes.     Their  distinguishing  feature  is  the  indented  or 
kidney-shaped  nucleus  which  usually  occupies  an  eccentric  position  within  the  non-granular 
cytoplasm.     The  latter,  as  well  as  the  diameter  of  the  transitional  forms,  corresponds  with  that 
of  the  large  mononuclear  leucocyte. 

4.  Polymorphonuclear  Leucocytes. — These  represent  by  far  the  most  common  type  of 
white  cells,  of  which  they  constitute  about  70  per  cent.     Their  diameter  is  approximately  .010 
mm.,  hence  they  are  somewhat  smaller  than  the  transitional  forms,  but  larger  than  the  red  cells. 
Their  cytoplasm  is  relatively  large  in  amount  and  contains  fine  neutrophilic  granules.     On 
account  of  the  great  diversity  of  the  forms  that  they  assume,  the  nuclei  are  very  conspicuous 
features  of  this  type  of  leucocyte.     At  first  sight  the  nuclei  appear  multiple;  closer  examination, 
however,  shows  the  seemingly  distinct  nuclei  to  be  connected  by  delicate  processes,  so  that, 
although  exceptionally  two  or  more  isolated  nuclei  exist  and  the  cells  are  truly  polynuclear, 
their  actual  condition  is  appropriately  designated  as  polymorphonuclear. 

5.  Eosinophiles. — Leucocytes  of  this  type  are  conspicuously  distinguished  by-  the  coarse, 
highly  refractive  granules  within  the  cytoplasm  that  display  an  especial  affinity  for  acid  dyes, 
particularly  for  eosin.     These  resemble  the  polymorphonuclear  leucocytes  in  size  (.010  mm.) 
and  in  the  character  of  their  nuclei,  the  latter,  however,  in  general  being  less  distorted  and 
commonly  eccentrically  placed.     The  eosinophiles  are  prone  to  rupture,  after  which  the  pale 
nucleus  lies  in  the  midst  of  a  swarm  of  brightly  tinged  granules. 

Although  other  types  of  colorless  cells,  as  myelocytes  and  mast  cells,  are  of  clinical  interest, 
they  do  not  occur  in  normal  blood  and,  hence,  need  not  be  here  discussed.  An  occasional  addi- 
tional type  of  leucocyte,  the  basophile  cells,  is  rarely  present  in  normal  blood.  These  elements 
resemble  the  polymorphonuclear  leucocytes,  but  are  distinguished  from  the  latter  by  the  presence 
within  the  cytoplasm  of  closely  packed  fine  granules  that  possess  a  strong  affinity  for  basic  dyes. 

In  the  foregoing  grouping  the  varieties  of  white  cells  are  regarded  as  different  stages  of 
elements  genetically  related  and  derived  from  the  same  sources— a  view  supported  by  the  early 
development  of  the  leucocytes.  It  should  be  mentioned,  however,  that  Ehrlich  and  many  other 
hematologists  consider  the  lymphocytes  and  the  leucocytes  as  entirely  distinct  elements,  believing 
the  former  to  be  derived  from  lymphoid  tissues  and  the  leucocytes  exclusively  from  bone-marrow. 
Accordingly,  the  large  lymphocytes  and  the  large  mononuclear  leucocytes  are  of  different  nature, 
although,  as  universally  admitted,  their  assumed  differentiation  is  at  best  uncertain.  The  presence 
of  all  forms  of  white  cells  in  the  circulation  of  the  embryo  long  before  the  appearance  of  bone- 
marrow  ( Ebner)  seems  conclusive  evidence  that  the  origin  of  the  leucocytes  is  not  limited  to  the 
marrow  tissue. 

The  Blood  Plaques. — In  addition  to  the  erythrocytes  and  leucocytes,  the 
blood  of  man  and  other  mammals  regularly  contains  small  bodies,  the  blood  plaques 

'Clinical  Hematology.     Phila.,  1901. 


686  HUMAN   ANATOMY. 

or  blood  platelets.  As  they  are  extraordinarily  sensitive  to  exposure,  even  to  entire 
disappearance,  special  precautions  are  necessary  to  insure  their  presence  in  an  unal- 
tered condition  in  preparations  examined.  If  blood  be  drawn  directly  into  and  mixed 
with  a  drop  of  .7  per  cent,  salt  solution,  or,  still  better,  into  one  of  weak  osmic  acid 
solution,  the  blood  plaques  appear  as  round  or  oval  discs,  from  .002-.  004  mm.  in 
diameter,  usually  somewhat  less  than  one-third  of  the  size  of  the  red  cells.  From 
these  they  further  differ  in  being  colorless  and  devoid  of  hemoglobin  and  in  staining 
readily  in  very  dilute  solutions  of  methyl-violet.  The  blood  plaques  are  homogeneous 
or  faintly  granular,  nonnucleated,  never  exhibit  amoeboid  movement,  and  may  be 
directly  observed  as  free  bodies  circulating  within  the  vessels.  On  withdrawal  from 
the  latter,  without  precautions  for  their  preservation,  they  at  once  collect  in  irregular 
masses  and  undergo  disintegration,  their  remains  usually  being  centres  from  which 
radiate  the  fibrillae  of  the  fibrin  net-works.  Notwithstanding  the  attention  bestowed 
upon  these  bodies,  the  source  and  significance  of  the  blood  plaques  are  still  unde- 
termined, although  numerous  theories  have  been  advanced.  Their  source  has  been 

variously  attributed    to    disintegration   of   the 

FIG.  649.  leucocytes,   to  extrusion    from    the  red   cells, 

to  precipitation  of  globulin  or  to  destruction 
of  the  endothelial  lining  of  the  vessels.  None 
of  these  assumptions  can  be  regarded  as  es- 
tablished, or  even  probable,  in  view  of  their 
constant  presence  and  large  normal  quota — 
an  average  of  300,000  plaques  in  one  cubic 
millimeter  of  blood. 

Granules. — In  addition  to  the  corpus- 
cles and  the  plaques,  extremely  minute  gran- 
ules occur  in  varying  numbers  in  normal 
human  blood.  The  nature  of  these  particles 
differs.  Some  are  undoubtedly  finely  divided 
fat;  others,  described  by  H.  F.  M  tiller  under 
the  name,  hemoconia,  are  of  uncertain  compo- 
sition, but  not  fatty;  while  a  certain  propor- 

Human  Woodp,  showing^cells  ^  .g  probably  derived  from  the  disintegration 

of  endothelial  and  blood-cells.  The  destruc- 
tion of  the  latter  is  accountable  for  the  minute  particles  of  pigment  that  are  constant, 
if  not  numerous,  constituents  of  the  circulation. 

DEVELOPMENT  OF  THE  BLOOD-VESSELS  AND  CORPUSCLES. 

The  earliest  blood-vessels  appear  within  the  extra  embryonic  mesoblast  covering 
the  vitelline  sac  and,  therefore,  beyond  the  limits  of  the  embryo  proper  and  entirely 
independent  of  the  heart  and  axial  trunks.  In  the  lower  mammals,  the  formation 
of  the  primary  vessels  takes  place  towards  the  periphery  of  a  limited  field,  known  as 
the  vascular  area,  that  encircles  only  a  portion  of  the  vitelline  sac;  in  man  the 
limited  proportions  of  the  latter  enable  the  net-work  of  developing  blood-channels  to 
extend  completely  over  the  vesicle,  so  that  the  vascular  area  becomes  coextensive 
with  the  yolk  sac.  Although  the  earliest  stages  in  the  formation  of  the  primary 
blood-vessels  have  never  been  observed  in  man,  since  the  vessels  were  already 
present  over  the  vitelline  sac  in  the  youngest  embryo  so  far  examined,  it  is  probable 
that  the  development  of  the  human  vascular  tissues  is  essentially  the  same  as  t1" 
seen  in  other  mammals. 

In  the  rabbit,  the  first  indications  of  the  developing  blood-vessels  are  cords  or 
groups  of  spherical  cells  that  appear  within  the  deeper,  later  splanchnic,  layer  of  the 
mesoblast  covering  the  vitelline  sac.  These  tracts  become  larger  in  consequence 
not  only  of  proliferation,  but  also  of  separation  of  the  component  cells.  The  meso- 
blastic  elements  surrounding  the  tracts  soon  become  disposed  as  enclosing  walls, 
within  which  the  separated  cells,  now  suspended  in  a  clear  fluid  that  has  meanwhile 
appeared,  represent  the  earliest  blood-cells. 

The  channels  thus  established  unite  into  a  net-work  of  primary  blood-vessels  that 
at  first  occupies  the  periphery  of  the  vascular  area,  but  later  extends  towards  the 


DEVELOPMENT  OF  BLOOD-VESSELS  AND  CORPUSCLES.       687 


embryo  and,  after  the  appearance  of  the  large  converging  trunks,  the  vitelline  veins 
and  arteries,  joins  the  intra-embryonic  trunks  that  coincidently  have  been  formed. 

Although  the  generally  accepted  current  views  relating  to  the  independent  origin 
of  the  primary  blood-vessels  within  the  vascular  area  have  not  escaped  challenge,  it 
may  be  regarded  as  established  that  the  development  of  subsequent  blood-vessels 
proceeds  from  the  cells  constituting  the  walls  of  pre-existing  channels.  The  walls 
of  the  growing  capillaries  consist  of  delicate  endothelial  plates  from  which  pointed 
sprouts  grow  into  the  surrounding  tissue  (Fig.  651).  These  outgrowths,  direct  pro- 
longations of  the  cytoplasm  of  the  endothelial  cells,  are  at  first  solid,  but  later  become 
hollowed  out  by  the  gradual  extension  of  the  lumen  of  the  capillary.  Vascular  loops 
are  often  formed  by  the  meeting  and  fusion  of  the  outgrowths  proceeding  in  opposite 
directions,  the  communication  being  established  by  the  final  disappearance  of  the  sep- 
tum in  consequence  of  the  extension  of  the  lumen  of  the  parent  vessels.  At  first  rep- 
resented by  only  a  single  layer  of 

endothelial  cells,  the  walls  of  the  FIG.  650. 

larger  blood-vessels  become  rein- 
forced by  the  additional  layers 
derived  from  the  surrounding 
mesoblast. 

Development  of  the 
Erythrocytes. — The  first,  and 
for  a  time  the  only,  blood-cells 
present  within  the  embryo  are 
the  primary  nucleated  erythro- 
cytes  derived  probably  directly 
from  the  mesoblastic  elements 
within  the  angioblastic  areas  in 
which  the  earliest  vessels  appear. 
These  cells,  separated  by  the 
colorless  plasma  which  appears 
between  them  and  in  which  they 
henceforth  float,  undergo  mitotic 
division,  producing  nucleated 
elements  that,  in  turn,  give  rise 
to  other  corpuscles.  The  pri- 
mary erythrocytes  are  spherical, 
nucleated,  and  larger  (about  .01 2 
mm.  in  diameter)  than  the  adult 
red  cells.  At  first  their  cyto- 
plasm is  colorless  and  slightly 
granular,  but  soon  becomes  ho- 
mogeneous and  tinged  with 
hemoglobin. 

After  the  earlier  fcetal 
months,  during  which  prolifera- 
tion of  the  blood-cells  occurs 
in  all  parts  of  the  circulation,  the  corpuscles  engaged  in  division  withdraw  to 
localities  in  which  the  blood-current  is  sluggish  and,  therefore,  favorable  for  mitosis. 
Such  localities  are  particularly  the  liver,  spleen,  and  bone-marrow,  the  large  capil- 
laries and  tissues  of  which  afford  temporary  resting  places  during  proliferation.  After 
a  time  the  primary  erythrocytes  lose  their  nuclei,  diminish  in  size,  and  assume  their 
definite  form.  These  changes  begin  during  the  second  fcetal  month,  more  and  more 
nonnucleated  discoidal  red  cells  appearing  as  gestation  advances,  so  that  at  birth 
almost  all  the  nucleated  erythrocytes  have  disappeared  from  the  circulation. 

Since  the  red  cells  possess  only  a  limited  vitality,  their  constantly  occurring 
death  requires  the  production  of  new  corpuscles.  Preceding  the  development  of  the 
spleen  and  bone-marrow,  the  liver  is  the  principal  centre  of  blood-formation.  Later 
the  splenic  and  marrow  tissues  share  this  function,  while  after  birth  the  red  bone- 
marrow  is  the  chief  seat  in  which  the  continual  additions  of  new  erythrocytes  necessary 


. .  -•  • 


Surface  view  of  vascular  area  of  chick  embryo  with  twelve 
somites  (29  hours)  ;  net-work  of  developing  blood-vessels,  most 
distinct  in  periphery  of  area,  is  connected  with  vitelline  veins 
from  embryo  by  faint  channels ;  cephalic  segment  of  neural 
tube  shows  brain-vesicles  and  eye-buds  ;  caudal  segment  still 
widely  open.  X  16. 


,' 


688  HUMAN   ANATOMY. 

to  maintain  the  normal  quota  are  made.      The  production  of  the  new  red  cells  within 
the  marrow  proceeds  from  colorless  nucleated  elements,   the  erythroblasts,  that  by 
division  give  rise  to  the  nucleated  erythrocytes  or  normoblasts  which,  upon  the  appear- 
ance of    hemoglobin  and  the 

FIG.  651.  disappearance  of  their  nuclei, 

are  transformed  into  the  usual 
red  cells,  and  as  such  enter 
the  circulation. 

The  disappearance  of  the 
nucleus  of  the  normoblasts  has 
long  been  a  subject  of  discus- 
sion and  speculation.  Accord- 
ing to  the  older  view  —  still, 
however,  accepted  by  many — 
the  nucleus  is  extruded  from 
^  the  erythrocyte  and  under- 

_  _^7 ._  goes  disintegration,  thus,  in 
the  opinion  of  some,  supply- 
ing the  source  of  the  blood 
plaques.  According  to  the 
more  recent  views,  held  by 

Developing  blood-vessels  in  embryonal  subcutaneous  tissue;  Neumann,    Kolliker,    Pappen- 

a,  larger  capillary;    b,  young  capillaries;  c,  solid  protoplasmic  T         i    -r-i 

outgrowths  forming  new  vessels,   x  300.  heim,  Israel,  Ebner,  and  others, 

the  disappearance  of  the  nu- 
cleus is  due  to  its  solution  and  absorption  within  the  erythrocyte.  Under  normal 
conditions  nucleated  red  cells  or  normoblasts  do  not  occur  in  the  circulation.  After 
severe  hemorrhage  or  in  other  conditions  requiring  unusual  activity  of  the  blood- 
forming  processes,  they  may  be  present  in  large  numbers  until  the  normal  quota  of 
erythrocytes  has  been  once  more  established.  In  view  of  the  constant  presence  of 
erythroblasts  and  nucleated  erythrocytes  within  the  splenic  pulp,  the  spleen  must  be 
regarded  as  an  additional,  although  under  usual  conditions  limited,  source  of  the  red 
blood-cells.  When,  however,  the  necessity  for  rapidly  augmenting  the  number  of 
red  cells  arises,  the  spleen  may  assume  the  r61e  of  an  active  blood-producing  tissue. 
Since  such  cells  are  found  also  in  the  thymus,  this  body  probably  must  be  included 
among  the  blood-forming  organs  of  early  life.  There  is  no  satisfactory  evidence  that 
the  erythrocytes  are  derived  from  the  colorless  cells  or  from  the  blood  plaques. 

Development  of  the  Leucocytes. — During  the  first  weeks  succeeding  the 
appearance  of  the  primary  red  cells,  the  latter  are  the  only  elements  within  the  circu- 
lation.     In  the  second  foetal  month,   however,   leuco- 
cytes  appear,   and  henceforth  are  companions  of  the  FIG.  652. 
erythrocytes.     As   already  noted,   the  white  cells  are 
elements  that  primarily  belong  to  the  lymphatic  sys- 
tem,   from   which   they   are   poured    into    the   blood-                 _          © 
channels.      Genetically   the   red   and   white   cells   are 
entirely  distinct  and  unrelated.  M$ 

Concerning  the  origin  of  the  first  leucocytes  much  @        Q       ^' 

uncertainty  exists,  although  it  is  generally  assumed  that  ©  ® 

they  arise  from  mesoblastic  cells,  and,  therefore,  to  that  «* 

extent,  share  with  the  erythrocytes  a  common  source.  • 

Suggestive  as  are  the  views  of  Beard,1  Retterer,  Nus- 
baum  and  Prymak,2  and  others,  supporting  the  origin 

Of   leucocytes  within  the  early  thymUS    in  loco  and    not,  Nucleated  embryonal  erythro- 

,,       ,     i  i      ,        .  .          r  i-vtcs;    two  dividing  cells  exhibit 

as  generally  held,   by  invasion  from    the  surrounding       mttotk  figures,    x  600. 
mesoblast,  they  cannot  be  regarded  as  established.     The 

conclusion  of  Beard,  that  the  first  leucocytes  to  appear  within  the  embryo  o\\v  tlu-ir 
production  to  the  metamorphosis. of  the  entoblastic  epithelium  of  the  primary  thymus, 
and  that  the  subsequent  migration  of  the  leucocytes  so  derived  establishes  foci  from 

1  Anatom.  Anzeiger,  Bd.  xviii.,  1900. 

2  Anatom.  Anzeijjer,  Bd.  xix.,  1901. 


THE   HEART. 


689 


Megakaryocyte 


Leucocytes 


which  are  developed  the  various  masses  of  lymphoid  tissue  occurring  throughout  the 
body,  has  been  challenged  by  Hammar, '  who  found  leucocytes  in  the  blood  and  con- 
nective tissues  of  the  human  foetus  before  they  appear  in  the  thymus.  In  any  event 
it  is  probable  tha"t  the  first  leucocytes  originate  as  amoeboid  cells  outside  the  ves- 
sels, which  they  later  enter,  aided  by  their  migratory  powers.  Their  subsequent 
multiplication  is  effected  by  division,  for  the  most  part  mitotic,  of  the  pre-existing 
cells.  This  proliferation  occurs  chiefly  within  the  lymphoid  tissue  throughout  the 
body,  the  lymph-nodules,  spleen  and  bone-marrow  being  the  most  important  local- 
ities. The  germ-centres  of  the  lymph-nodules  (page  936)  are  seats  of  especial 
activity  for  the  formation  of  the  types  of  colorless  cell  known  as  the  mononuclear 
lymphocyte,  although  whether  the  proliferating  cells  originate  within  the  germ- 
centres,  or  only  complete  their  division  in  these  situations  after  being  carried  from 
other  points  (Stohr),  is  still  unsettled. 

From  the  developmental  standpoint,  the  sharp  separation  of  the  colorless  blood- 
cells  into  lymphocytes  and  leucocytes,  as  insisted  upon  by  Ehrlich  and  his  supporters, 
based  on  the  assumption  that  the  leucocytes  originate  exclusively  within  bone-marrow, 
is  not  well  founded  in  view  of  the  presence  of  all  the  typical  forms  of  white  cel.s,  in- 
cluding the  polymorphonuclear  leucocytes,  shortly  after  the  first  appearance  of  the 
white  corpuscles  and  long  before 

the  advent  of   the  earliest    bone-  FIG.  653. 

marrow  (Ebner).  For  the  pres- 
ent, at  least,  it  seems  most  reason- 
able to  regard  the  various  forms 
of  the  white  cells  as  constituting 
a  genetic  sequence  in  which  the 
lymphocyte,  leucocyte,  and  eosin- 
ophile  represent  different  stages  in 
the  development  of  elements  hav- 
ing a  common  origin. 

In  addition  to  the  red  blood- 
cells  in  various  stages  of  develop- 
ment and  the  different  types  of 
leucocytes,  peculiar  huge  elements 
early  appear  in  the  embryonic 
blood-forming  organs,  and  after 
birth  in  bone-marrow.  These 
giant  cells,  or  megakaryocytes 
(Howell),  are  distinguished  by 
their  large,  irregularly  lobulated 
but  single  nucleus  from  the  osteo- 
clasts,  since  the  nuclei  of  the  latter  are  usually  oval  and  multiple.  The  'megakaryo- 
cytes are  often  observed  containing  within  their  substance  the  remains  of  both  white 
and  red  cells;  they  are,  therefore,  regarded  as  phagocytes  upon  which  devolves  the 
removal  of  effete  blood-corpuscles.  Their  origin  is  uncertain,  by  some  (Howell,  van 
der  Stricht,  Heidenhain)  being  referred  to  the  leucocytes,  and  by  others  (Kolliker, 
Kuborn)  to  the  endothelium  of  the  vessels,  while  Ebner  regards  those  within  the  bone- 
marrow  as  probably  derived  from  fixed  connective-tissue  cells  of  the  reticulum.  Nei- 
ther form  of  these  giant  marrow-cells  is  normally  found  within  the  post-natal  circulation. 

THE  HEART. 

General  Description. — The  heart  is  a  hollow,  muscular  organ  of  a  somewhat 
conical  shape,  situated  in  the  lower  part  of  the  thoracic  cavity,  behind  the  lower  two- 
thirds  of  the  sternum.  It  is  enclosed  within  a  double-walled  serous  sac,  \hapericar- 
diuin,  and  has  a  somewhat  oblique  position  in  the  thorax,  its  base  (basis  cordis)  looking 
upward,  dorsally,  and  to  the  right,  while  its  apex  (apex  cordis)  points  downward,  ven- 
trally,  and  to  the  left.  In  consequence  of  this  obliquity  about  two-thirds  of  the  organ 
lies  to  the  left  and  one-third  to  the  right  of  the  median  plane  of  the  body. 

1  Anatom.  Anzeiger,  Bd.  xxvii.,  1905. 
44 


Osteoclast 


Bone 
trabecula 


Osteoblasts 


Section  of  embryonal  bone-marrow,  showing 
nucleated  erythrocytes,  leucocytes  and  mega- 
karyocyte.  X  625. 


690 


HUMAN   ANATOMY. 


It  may  be  regarded  as  possessing  two  surfaces,  which  are  not,  however,  distinctly 
separated,  but  pass  into  each  other  with  rounded  edges,  especially  upon  the  left  side. 
One  of  these  surfaces  looks  forward  and  somewhat  upward,  and  is  separated  by  the  peri- 
cardium and  some  loose  areolar  tissue  from  contact  with  the  sternum  and  the  lower 
costal  cartilages,  the  thin  anterior  edges  of  the  lungs  and  pleurae  also  intervening  to 
a  considerable  extent;  this  is  the  antcro-superior  surface  (facies  sternocostalis),  and 
for  convenience  it  may  be  more  briefly  termed  the  anterior  surface.  The  other,  the 
postero-inferior  or  posterior  surface  (facies  diaphragmatica),  rests  directly  upon  the 
upper  surface  of  the  diaphragm. 

At  about  one-third  of  the  distance  from  the  base  to  the  apex  a  deep  circular 
groove,  more  distinct  upon  the  posterior  surface,  surrounds  the  heart,  separating  an 

FIG.  654. 


Superior  vena  cava 


Systemic  aorta  (aorta) 


Right  auricular 
appendage 


Right  auricle 

Auriculo-ventricular 
groove 


Line  of  reflection  of 
pericardium 

Ductus  arteriosus 


Pulmonary  aorta 
(pulmonary  artery) 


Right  ventricle 


Anterior  interventricu 
lar  groove 


Anterior  aspect  of  heart  hardened  in  situ  ;  probe  lies  in  transverse  sinus  of  pericardium. 


upper  thin-walled  auricular  portion  of  the  organ  from  a  lower  thick-walled  ventricular 
one  :  this  groove  is  termed  the  auricuh-ventricular  groove  (sulcus  coronaritts),  and 
contains  the  proximal  portions  of  the  coronary  vessels  which  supply  the  heart's  sub- 
stance. Extending  towards  the  apex  from  this  groove,  two  other  shallower  grooves 
are  to  be  observed,  one  situated  towards  the  right  side  of  the  anterior  surface  and  the 
other  upon  the  posterior  surface.  These  grooves,  which  also  lodge  portions  of  the 
coronary  vessels,  are  the  anterior  and  posterior  interventricular  grooves  (sulci  limui- 
tudinalcs),  and  mark  the  line  of  separation  of  the  ventricular  portion  of  the  heart  into 
two  chambers  known  as  the  right  and  left  ventricles.  From  the  base  of  tin-  right  ven- 
tricle a  large  blood-vessel,  \\\v  pn/)HO)iary  aorta  ^\  pulmonary  artery,  arises,  while  from 
the  base  of  the  lett  ventricle,  and  almost  immediately  posterior  to  the  root  of  the  pul- 
monary aorta,  the  systemic  aorta  takes  its  origin.  The  orifices  by  which  each  of  these 


THE   HEART. 


691 


vessels  communicates  with  its  ventricle  are  guarded  by  special  valves  known  as 
the  scniilitnar  rak'cs. 

The  auricular  portion  of  the  heart  rests  upon  the  posterior  part  of  the  base  of  the 
ventricular  portion,  and  is  best  viewed  from  the  posterior  surface  (Fig.  655),  since 
it  is  almost  completely  hidden  anteriorly  by  the  two  aortae.  Like  the  ventricular 
portion,  it  is  composed  of  two  separate  chambers,  which  are  not,  however,  very 
apparent  on  surface  view.  These  chambers  are  the  right  and  left  auricles,  and  com- 
municate with  the  corresponding  ventricles  by  auricula-ventricular  orifices  guarded 
by  special  auricula-ventricular  valves.  From  the  lateral  part  of  the  anterior  sur- 
face of  each  auricle  a  process,  the  aw  icular  appendix,  arises.  These  appendices  are 


FIG.  655. 


Left  common  carotid  artery" 
Left  subclavian  artery 


Innominate  artery 


Left  pulmonary 
artery 


Vestigial  fold 

Sup.  left  pulm.  vein 
Left  auricular 
appendix 


Inf.  left  pulm.  vein  — 


Coronary  sinus    / 


Left  ventricle 


Azygos  vein 
Superior  vena  cava 


Right  pulmonary 
artery 


Superior 


Inferior 


right 

pulmonary 

veins 


Left  auricle 
Right  auricle 

Inferior  vena  cava 


Right  ventricle 


Apex    x 
Posterior  aspect  of  heart  hardened  in  situ  ;  showing  lines  of  reflection  of  pericardium. 


slightly  flattened  prolongations  of  the  auricles,  and  bend  forward  around  the  bases  of 
the  aortae,  which  they  slightly  overlap  in  front  ;  they  are  the  only  portions  of  the 
auricles  visible  upon  the  anterior  surface  of  the  heart.  Upon  its  superior  surface  the 
right  auricle  receives  the  termination  of  a  large  venous  trunk,  the  vena  cava 
superior,  which  returns  to  the  heart  blood  from  the  head,  neck,  upper  extremities, 
and  walls  of  the  thorax  ;  while  upon  its  posterior  surface  is  the  opening  of  another 
large  vessel,  the  vena  cava  inferior,  which  returns  blood  from  the  abdominal  and 
pelvic  walls  and  viscera  and  from  the  lower  limbs.  The  left  auricle  receives  upon 
its  surface  the  four  pulmonary  veins  arranged  in  pairs,  one  pair  situated  towards  the 
left  portion  of  the  auricle  and  the  other  towards  the  right. 


692 


HUMAN   ANATOMY. 


FIG.  656. 


Position. — The  heart  may  vary  considerably  in  position  without  being  regarded 
as  abnormal,  but  what  may  be  considered  its  typical  position  with  reference  to  the 
anterior  thoracic  wall  may  be  stated  about  as  follows  :  The  apex  is  situated  behind 
the  fifth  intercostal  space,  about  8  cm.  (3^  in.)  from  the  median  line,  this  position 
being  median  to  and  slightly  below  the  junction  of  the  fifth  costal  cartilage  with  its 
rib.  The  level  of  the  base  may  be  approximately  indicated  by  a  line  drawn  from  a 
point  slightly  above  the  upper  border  of  the  third  costal  cartilage  of  the  left  side, 
about  4. 5  cm.  (i^4  m-)  ^rom  t^6  median  Hire  of  the  sternum,  to  a  point  upon  the 
upper  border  of  the  third  costal  cartilage  of  the  right  side,  about  3  cm.  (i^  in.) 
from  the  middle  line.  If  now  the  left  end  of  the  base-line  be.  united  to  the  apex 
point  by  a  line  which  is  slightly  convex  towards  the  left,  and  a  line,  markedly  convex 
towards  the  right,  be  drawn  from  the  right  end  of  the  base-line  to  the  junction  of 
the  seventh  costal  cartilage  of  the  right  side  with  the  sternum  and  thence  to  the 

apex  point,  a  heart-area  will  be  en- 
closed which  corresponds  to  the  out- 
line of  the  organ  as  seen  from  in 
front. 

Considerable  importance  at- 
taches to  the  location  of  the  auriculo- 
ventricular  and  aortic  orifices  with 
reference  to  the  anterior  thoracic  wall. 
The  right  auriculo-ventricular  ori- 
fice in  a  typical  heart  lies  on  a  level 
with  the  attachment  of  the  fifth  costal 
cartilages  to  the  sternum,  almost  be- 
hind the  median  line  of  that  bone  and 
opposite  the  fourth  intercostal  space, 
while  the  left  auricuh-ventriculaf 
orifice  is  opposite  the  sternal  end  of 
the  left  third  intercostal  space.  In 
other  words  these  openings  lie  along 
a  line  which  corresponds  with  the 
auriculo-ventricular  groove,  and  this 
may  be  represented  by  a  line  drawn 
from  the  upper  border  of  the  junc- 
tion of  the  seventh  costal  cartilage  of 
the  right  side  with  the  sternum  to  the 
sternal  end  of  the  third  left  costal 
cartilage.  The  right  orifice  is  lo- 
cated upon  the  line  where  it  is  inter 
sected  by  a  line  joining  the  sternal 
ends  of  the  fifth  costal  cartilages. 
while  the  left  one  is  situated  at  its 
upper  end. 

The    systemic    and    pulmonary 
aortic   orifices  are  situated  at  about 

the  level  of  the  attachment  of  the  third  costal  cartilages  to  the  sternum,  the  pulmon- 
ary orifice  being  behind  the  sternal  end  of  the  third  left  cartilage-,  while  the  aortic 
orifice  is  behind  the  left  half  of  the  sternum,  a  little  below  and  to  the  right  of  the  pul- 
monary one,  the  two  orifices  overlapping  for  about  one-quarter  of  their  diameters 
It  is  to  be  noted,  however,  that  the  pulmonary  aorta  is  directed  upward  and  to  the 
left,  while  the  systemic  aorta  inclines  decidedly  towards  the  right  in  the  first  part  of 
its  course;  and  since  the  sounds  caused  by  the  valves  which  guard  the  orifices  are 
carried  in  the  direction  of  the  blood-stream,  auscultation  of  the  pulmonary  seinilnnar 
valves  may  be  practised  over  the  sternal  end  of  the  second  left  intercostal  space, 
while  that  of  the  systemic  valves  is  best  performed  over  the  sternal  end  of  the  second 
right  space. 

Similarly  the  close  proximity  of  the  areas  of  the  left  auriculo-ventricular  and 
systemic  aortic  orifices,  as  projected  upon  the  thoracic  wall,  might  lead  to  confusion, 


Positicn  of  heart  and  valves  in  relation  to  anterior  thoracic 
wall.  A,  aortic  valve;  P,  valve  of  pulmonary  aon a;  T,  tri- 
cuspid  valve  ;  M,  mitral  valve. 


THE   CHAMBERS   OF   THE    HEART.  693 

were  it  not  that  the  course  of  the  blood  passing  through  the  two  orifices  is  in  opposite 
directions,  and  the  auscultation  of  the  auriculo-ventricular  orifice  is  consequently 
satisfactorily  performed  towards  the  apex  of  the  heart. 

Considerable  variation  from  the  position  of  the  heart  indicated  above  may  be  found.  Thus, 
the  apex  may  be  situated  behind  the  fifth  costal  cartilage,  or  more  rarely  the  sixth,  and  the  pul- 
monary aortic  orifice  may  occur  as  high  up  as  the  second  intercostal  space,  or  as  low  as  the  level 
of  the  fourth  costal  cartilage. 

The  heart  naturally  has  its  position  altered  somewhat  during  its  contraction  and  during  the 
respiratory  acts,  and  the  position  of  the  body  will  also  have  some  effect  in  modifying  its  location. 
Resting,  as  it  does,  upon  the  diaphragm,  the  heart  will  alter  its  position  somewhat  with  altera- 
tions <>f  that  muscle  ;  and  since  in  the  child  the  diaphragm  is  somewhat  higher  and  in  the  aged 
somewhat  lower  than  in  the  middle  period  of  life,  corresponding  changes  according  to*age  will 
be  found  in  the  position  of  the  heart.  It  may  be  noted,  furthermore,  that  the  position  of  the 
heart  as  determined  in  the  cadaver  will,  as  a  rule,  be  slightly  higher  than  in  the  living  body, 
owing  to  post-mortem  tissue  changes  which  allow  the  diaphragm  to  assume  a  more  vaulted  form 
than  is  usual  in  life. 

Relations. — As  regards  its  relations  the  heart  is  completely  enclosed  within  the 
pericardium,  with  which  alone  surrounding  organs  come  into  contact.  In  what  fol- 
lows it  is  really  the  relations  of  the  pericardium  that  will  be  described,  although  of 
necessity  these  relations  are  indirectly  those  of  the  heart  and  will  be  spoken  of  as 
such. 

Anteriorly  the  greater  part  of  the  heart  is  covered  by  the  anterior  borders  of 
the  lungs  and  pleurae,  which  separate  it  from  contact  with  the  anterior  thoracic  wall. 
As  a  rule,  the  anterior  borders  of  the  pleurae  are  in  contact  from  the  level  of  the 
scvond  costal  cartilage  to  that  of  the  fourth,  but  below  the  latter  level  they  separate, 
the  border  of  the  left  pleura  diverging  from  the  median  line  more  rapidly  than  that 
of  the  right.  In  consequence,  throughout  an  irregularly  triangular  area  (Fig.  1580), 
whose  vertical  diameter  extends  from  the  level  of  the  fourth  to  that  of  the  sixth 
costal  cartilages,  the  heart  is  uncovered  by  the  pleurae  and  lies  directly  behind  the 
thoracic  wall.  This  area  forms  what  is  termed  by  clinicians  the  area  of  absolute  dul- 
ncss.  Laterally  the  heart  is  in  relation  with  the  lungs,  the  phrenic  nerves  passing 
downward  on  either  side  between  the  pericardium  and  the  pleura.  Posteriorly  the 
relations  are  again  with  the  lungs  and  with  the  oesophagus  and  the  thoracic  aorta. 
Infcriorly  the  heart  rests  directly  upon  the  diaphragm,  beneath  which  is  the 
stomach. 

Size  and  Weight. — There  is  considerable  individual  variation  in  the  size  of 
the  heart,  and  marked  discrepancies  exist  in  the-  observations  that  have  been  re- 
corded. It  may  be  said  that  in  the  adult  the  heart,  on  an  average,  will  possess  a 
length  of  from  12-15  cm-  (4?4~6  in.),  a  greatest  breadth  of  from  9-11  cm. 

•-4%  in.)  and  a  thickness  of  from  5-8  cm.  (2-3^  in.). 

Its  weight  has  been  given  at  from  266-346  gm.  (9^-12^  oz. )  for  males  and 
from  230-340  gm.  (8^5-12  oz.  )  for  females,(  the  average  of  a  series  of  observations  by 
different  authors  giving  312  gm.  ( 1 1  oz. )  for  the  male  and  274  gm.  (9^  oz.  )  for  the 
female.  The  proportion  of  heart  to  the  weight  of  the  entire  body,  according  to  an 
average  drawn  from  several  observers,  is  i  :  169  in  the  male  and  i  :  162  in  the  female. 
It  must  be  remembered,  however,  that  the  weight  of  the  heart  increases  with  age  up 
to  about  the  seventieth  year,  probably  a  slight  diminution  taking  place  after  that 
period. 

THE  CHAMBERS  OF  THE  HEART. 

It  has  already  been  noted  that  the  heart  is  composed  of  four  chambers,  a  right 
and  left  auricle  and  a  right  and  left  ventricle.  As  the  heart  lies  in  position,  little  of 
the  auricles,  with  the  exception  of  the  auricular  appendices,  can  be  seen,  since  they 
have  in  front  of  them  the  roots  of  the  aortae.  In  the  ventricular  portion  the  greater 
part  of  the  anterior  surface  is  formed  by  the  right  ventricle,  a  small  portion  only 
of  the  left  ventricle  showing  to  the  left  and  at  the 'apex,  the  whole  of  which  is  formed 
by  the  left  ventricle.  The  four  chambers  will  now  be  considered  in  succession,  begin- 
ning with  the  auricles. 

The  Right  Auricle. — The  right  auricle  (atrium  dcxtrunO  is  a  relatively  thin- 
walled  chamber  having  in  cross-section  a  roughly  triangular  form,  the  various  sur- 


694 


HUMAN   ANATOMY. 


faces,  however,  passing  into  one  another  almost  insensibly  without  forming  distinct 
angles.  Viewed  externally,  the  roof  of  the  chamber  is  directed  upward,  backward, 
and  somewhat  to  the  right,  and  near  its  junction  with  what  may  be  termed  the  poste- 
rior wall  receives  the  superior  vena  cava.  The  posterior  wall,  also  smooth  and 
rounded,  receives,  near  its  junction  with  the  median  wall,  the  inferior  vena  cava,  and 
below  and  to  the  left  of  this,  in  the  posterior  auriculo- ventricular  groove,  is  the  ter- 
minal portion  of  a  vein  which  winds  around  the  heart  from  the  left  and  is  termed  the 
coronary  sinus.  The  antero-lateral  wall  is  prolonged  into  a  somewhat  triangular 
diverticulum  with  crenulated  edges,  which  winds  anteriorly  around  the  proximal  por- 
tion of  the  pulmonary  aorta  and  is  known  as  the  right  auricular  appendix  (auricula 
dextra}.  The  median  wall  is  not  visible  on  surface  view,  and  is  formed  by  a  rather 
thin  muscular  partition,  the  auricular  septiim  (septum  atriorum),  which  is  common  to 
both  auricles  ;  and  the  floor,  also  invisible  from  the  exterior,  corresponds  to  the  base 
of  the  right  ventricle,  and  is  perforated  by  an  oval  aperture,  the  right  auricula-ven- 
tricular orifice,  which  places  the  cavity  of  the  auricle  in  communication  with  that  of 
the  right  ventricle. 

FIG.  657. 


Vena  azygos 


Right  pulmo- 
nary artery 


Systemic  aorta 
Pulmonary  aorta  or  artery 


Right  auricular  appendage 

Right  ventricle,  conus 
arteriosus 


Sup.  pulm.  vein 


Right  auriculo- 
Inf.  pulm.  vein      )M»     •  Hit  HHL  ventricular 

valve 

'•'^fc^^Bfek^    /  ii^k\  .v    -aa      •  m\"% 

Fossa  oval  is, 
surrounded 
by  annulus 
Inferior 
vena  cava 


Orifice  of  coronary  sinus,  guarded  by  Thebesian  valve 
Eustachian  valve  Depression  receiving  Thebcsian  veins 

Interior  of  right  auricle  exposed  after  removal  of  part  of  heart  wall. 

When  the  interior  of  the  right  auricle  is  examined  (Figs.  657,  661),  tin- 
surface  is  found  to  be  for  the  most  part  smooth,  being  lined  throughout  by  a  delicate 
shining  membrane  covered  by  flattened  cells  and  termed  the  endocardium.  The 
general  smoothness  of  the  surface  is,  however,  interrupted  here  and  there  by  minute 
depressions  (foramina  venarum  minimarum)  into  some  of  whi«h  open  the  orifices  of 
Thebesian  veins  that  traverse  the  walls  of  the  heart.  The  cavity  of  tin-  auricular 
appendix  is  crossed  by  a  net-work  of  anastomosing  fibre-muscular  trabeculse,  the 
muscnli  pectiuati,  which  are  everywhere  lined  upon  their  free  surfaces  by  endocardium 
and  give  to  the  appendix  a  somewhat  spongy  texture.  In  the  roof  of  the  auricle  is 
seen  the  circular  orifice  of  the  superior  voni  /vrrvr,  unguarded  bv  valves  and  having  a 
diameter  of  from  18-22  mm.,  and  on  the  posterior  wall  is  the  somewhat  oblique 
opening  of  the  inferior  re)ia  eara,  somewhat  larger  than  that  of  the  superior  one, 
measuring  from  27-36  mm.  in  diameter.  The  lower  and  lateral  margins  of  this 
orifice  are  guarded  'by  a  crescentic  fold,  the  I'".itsiachian  ;-alre  ( valvula  venae  cavae 
inferiors  ),  which  tends  to  direct  the  blond  entering  by  the  vein  upward  and  medially. 
and  is  the  remains  of  a  structure  of  considerable  importance-  during  fu-tal  life 


TH-E   CHAMBERS    OF   THE    HEART. 


695 


FIG.  658. 


onary  aorta 


708).  Between  the  superior  and  inferior  venae  cavse  there  may  sometimes  be  seen 
a  more  or  less  marked  prominence  of  the  posterior  wall,  the  tubercle  of  Lower 
(tuberculum  intervenosum),  the  remains  of  a  structure  also  of  importance  in  the  foetal 
circulation.  Below  and  somewhat  median  to  the  opening  of  the  inferior  vena  cava 
is  the  circular  orifice  of  the  coronary  sinus,  measuring  about  12  mm.  in  diameter, 
and  guarded,  like  the  inferior  caval  orifice,  by  a  crescentic  valve  which  surrounds  its 
lateral  margin  and  is  termed  the  Thebesian  valve  (valvula  sinus  coronarii). 

The  median  wall,  in  addition  to  a  number  of  Thebesian  orifices,  presents  at  about 
its  centre  an  oval  depression,  the  fossa  ovalis,  whose  superior  and  anterior  borders 
are  surrounded  by  a  thickening  or  slight  fold  termed  the  annulus  ovalis  (limbus  fossae 
ovalis). 

The  fossa  ovalis  indicates  the  position  of  what  was  in  foetal  life  the  foramen  ovale,  through 
which  the  blood  entering  the  right  auricle  froni  the  inferior  vena  cava  passed  directly  into  the 
left  auricle  and  so  joined  at  once  the  systemic  circulation  (page  929).  This  foramen  traversed 
the  auricular  septum  obliquely,  the  septum  really  consisting  of  two  folds,  one  of  which  projected 
backward  from  the  anterior  wall  of  the  auricular  portion  of  the  heart,  and  the  other  forward  from 
the  posterior  wall,  the  plane  of  the  latter  fold  lying  slightly  to  the  left  of  that  of  the  former  one. 
After  birth  these  two  folds  increase  in  size  so  that  their  free  margins  overlap  and  event- 
ually fuse,  closing  the  foramen,  and 
the  original  free  edge  of  the  ante- 
rior fold  becomes  the  annulus  of 
Vieussens,  while  the  floor  of  the 
fossa  ovalis  is  formed  by  the  pos- 
terior fold. 

It  occasionally  happens  that 
the  foramen  ovale  fails  to  close 
after  birth,  remaining  sufficiently 
open  to  permit  of  serious  disturb- 
ances of  the  circulation  which  are 
usually,  although  not  always,  early 
fatal.  Very  frequently,  however, 
the  fusion  of  the  overlapping  sur- 
iaces  of  the  two  folds  is  not  quite 
•complete,  and  a  small,  oblique,  slit- 
like  opening  persists  between  the 
two  auricles.  In  such  cases  during 
the  contraction  of  the  auricles  the 
pressure  of  the  blood  on  the  over- 
lapping walls  of  the  slit  brings 
them  into  close  apposition  and  effectually  closes  the  slit,  so  that  no  disturbances  of  the  circula- 
tion result  from  its  presence.  This  slit-like  opening  has  been  found  to  be  present  in  somewhat 
over  30  per  cent,  of  the  adult  hearts  examined. 

The  Left  Auricle. — The  left  auricle  (atrium  sinistrura)  has  the  same  general 
external  form  as  the  right  one,  and,  as  in  the  latter,  its  antero-lateral  wall  is  prolonged 
into  an  auricular  appendix  which  curves  forward  around  the  left  side  of  the  proximal 
portion  of  the  systemic  aorta.  Upon  its  posterior  surface  the  auricle  receives  the  four 
pulmonary  veins  arranged  in  pairs,  one  of  which  is  situated  nearer  the  medial  and  the 
other  towards  the  lateral  edge  of  the  surface,  and  passing  obliquely  over  this  surface 
towards  the  coronary  sinus  is  a  small  vein,  known  as  the  oblique  vein  of  the  left 
auricle  (vena  obliqua  atrii  sinistri  [Marshalli]  ),  which  represents  the  proximal  end  of 
the  left  vena  cava  superior  present  during  early  embryonic  life  (page  927). 

Viewed  from  the  interior,  the  walls  of  the  left  auricle,  like  those  of  the  right  one, 
are  everywhere  lined  by  a  smooth,  shining  endocardium  ;  in  the  appendix  the  spongy 
structure  due  to  the  existence  of  anastomosing  muscidi  pcctinati  also  occurs,  and 
occasional  depressions  of  the  surface  mark  the  openings  of  ven<z  Thebesii,  which  are, 
however,  much  less  abundant  than  in  the  right  auricle.  The  openings  of  the  pul- 
monary veins  on  the  posterior  wall  are  circular,  and  each  measures  from  14-15  mm. 
in  diameter  ;  they  are  unguarded  by  valves,  although  a  slight  horizontal  fold  sepa- 
rates the  portion  of  the  auricular  cavity  into  which  the  left  veins  open  from  the 
entrance  into  the  auricular  appendix. 

Upon  the  median  wall,  over  the  area  occupied  by  the  fossa  ovalis  of  the  right 
auricle,  a  slight  depression  is  frequently  to  be  observed,  and  immediately  anterior  to 
it  there  is  usually  a  small  crescentic  fold,  the  semilunar  fold,  whose  concavity  is 


Eustachian 
valve 


Inferior 
vena  cava 


Heart  of  foetus  just  before  birth  ;  wall  of  right  auricle 
has  been  cut  away,  showing  foramen  ovale. 


696 


HUMAN   ANATOMY. 


directed  forward,  and  which  represents  the  free  edge  of  the  posterior  segment  or  fold 
of  the  auricular  septum  (page  708).  In  the  floor  is  situated  the  large  circular 
auriculo-ventricular  orifice  by  which  the  cavity  of  the  auricle  communicates  with  that 
of  the  left  ventricle. 

The  Ventricles. — The  two  ventricles  present  many  features  in  common  and 
may  be  described  together,  such  differences  as  exist  between  them  being  pointed  out 
as  the  description  proceeds.  Each  has  a  form  which  may  be  likened  to  a  three-sided 
pyramid  whose  base  is  directed  upward  and  the  apex  downward.  The  edges  of  the 
left  ventricle  are,  however,  somewhat  more  rounded  than  those  of  the  right,  so  that 
its  form  approaches  more  nearly  that  of  a  cone  ;  and,  furthermore,  it  is  somewhat 

FIG.  659. 


Systemic  aorta 


Left  pulmonary  artery 


Superior  left  pulmonary  vein 


Left  auricular 

appendix 


Part  of  posterior 
leaflet  of  mitral 
valve 

Anterior  (aortic) 
leaflet  of  mitral 
valve 


Left  ventricle 


Superior  vena  cava 


Azygos  vein 


Right  pulmonary 
artery 


Superior  right 
pulmonary  vein 


Inferior  right 
pulmonary  vein 

Left  auricle, 
opened 


Inferior  vena  cava 


Coronary  sinus,  cut 


Interior  of  left  auricle  and  ventricle,  seen  from  behind  ;  posterior  wall  of  heart 
has  been  partially  removed  by  frontal  section. 

longer  than  the  right,  its  apex  alone  forming  the  apex  of  the  heart.  The  surfaces 
presented  by  each  ventricle  may  be  termed  antero-lateral,  posterior,  and  median,  but 
in  using  these  terms  the  heart  is  to  be  regarded  as  placed  so  that  its  long  axis  is  ver- 
tical ;  in  situ  the  antero-lateral  surfaces  look  largely  upward  and  the  posterior  sur- 
faces downward.  The  median  wall  is  a  partition,  the  inlet-ventricular  septum  (septum 
ventriculorum),  common  to  the  two  ventricles,  and  completely  separates  their  cavities. 
Throughout  the  greater  part  of  its  extent  this  septum  is  muscular,  but  towards  its 
upper  border  it  becomes  fibrous  (pars  inrmbrancca'}  and  is  continuous  with  the 
septum  of  the  auricles  ;  the  position  of  its  edges  are  indicated  upon  the  external  sur- 
face of  the  heart  by  the  anterior  and  posterior  interventricular  grooves.  The  bases  of 


THE  CHAMBERS  OF  THE  HEART. 


697 


the  ventricles  are  directed  upward,  backward,  and  to  the  right,  and  each  is  perforated 
by  two  orifices.  One  of  these  in  each  ventricle  is  the  auricula-ventricular  orifice, 
while  the  other,  in  the  case  of  the  right  ventricle,  is  the  opening  of  the  pulmonary 
aorta,  and  is  placed  in  front  and  a  little  to  the  left  of  the  auriculo-ventricular  orifice 
upon  the  summit  of  a  slight  conical  elevation  of  the  base  of  the  ventricle,  termed 
the  conns  arteriosus  or  infundibuhim.  The  second  orifice  of  the  left  ventricle  is  the 
opening  of  the  systemic  aorta,  and  is  situated  in  front  and  a  little  to  the  right  of  the 
corresponding  auriculo-ventricular  orifice,  immediately  adjoining  it. 

Compared  with  those  of  the  auricles,  the  walls  of  both  ventricles  are  very  thick, 
that  of  the  left  especially  so,  being  from  two  and  a  half  to  three  times  as  thick  as  the 
right  one.  Unlike  the  auricles  in  another  way,  the  inner  surfaces  of  the  ventricles. 

FIG.  660. 


Systemic  aorta 


Superior  vena  cava 


Inferior  vena  cava 
Eustachian  valve 

Pectinate  muscles 

Thebesian  valve 
guarding  opening 
of  coronary  sinus 
Posterior  leaflet  o: 

tricuspid  valve 


Pulmonary  aorta 
(pulmonary  artery) 


Left  coronary  artery 


Leaflet  of  aortic  valve 

Anterior(aortic) 
leaflet  of  mitral 
valve 


Membranous  part 
of  interventricu- 
lar  septum 


Medial  leaflet  of 
tricuspid  valve 


Interventricular 
septum 


Septal  papillary  muscles 

Posterior  papillary  muscle,  cut 

Posterior  portion  of  heart,  hardened  in  situ  and  sectioned 
parallel  to  posterior  surface ;  viewed  from  before. 

instead  of  being  even,  are  very  irregular,  being  everywhere  covered  by  muscular 
ridges  or  columns,  over  and  around  which  the  endocardium  is  folded.  These  mus- 
cular elevations  are  usually  regarded  as  consisting  of  three  varieties  :  ( i )  ridges 
which  are  attached  throughout  their  entire  length  to  the  wall  of  the  ventricle,  upon 
which  they  stand  out  like  bas-reliefs  ;  (2)  columns  which  are  attached  at  either 
extremity  to  the  wall  of  the  ventricle,  but  are  free  from  it  throughout  the  intervening 
portion  of  their  length  ;  and  (3)  columns  which  are  attached  only  by  one  extremity 
to  the  ventricular  wall  and  by  their  other  extremity  give  attachment  to  slender  ten- 
dons, chorda;  tendinea;,  which  pass  to  the  edges  of  the  valves  guarding  the  auriculo- 
ventricular  orifices.  To  the  columns  belonging  to  the  first  and  second  of  these 
groups  the  term  columnar  carnece  is  applied,  while  those  of  the  third  group  are  known 


698 


HUMAN   ANATOMY. 


as  the  musculi papillares.  Quite  frequently  in  the  right  ventricle  and  more  rarely  in 
the  left,  a  muscular  band  occurs,  which  passes  across  the  cavity  from  one  wall  to  the 
other  near  the  apex  ;  such  a  structure  constitutes  what  has  been  termed  a  moderator 
band.  Here  and  there  between  the  columnae  carneae  of  both  ventricles  minute  orifices 
of  the  Thebesian  vessels  occur. 

Around  the  orifices  situated  at  the  bases  of  the  ventricles  the  muscular  sub- 
stance of  the  heart's  walls  passes  over  into  dense  fibrous  tissue,  of  which  the  portion 

FIG.  661. 


"Pulmonary  aorta  (pulmonary  artery) 


Leaflets  of 

pulmonary  semilunar  valve 


Corpus  Arantii  on  posterior  leaflet 

Anterior  leaflet  of 

aortic  valve,  cut 


Septal  chordae  of 
tricuspid  valve- 


Interventricular  / 

septum — — f= 


Muscle 
left  ventricl 


Moderator  bam 


Anterior 
papillary  muscle. 


Superior  vena  cava 


Systemic  aorta 


Right  coronary 

artery 

Right  auricular 
appendage 


Pectinate  muscles 


Anterior  leaflet  of 

tricuspid  valve- 
Margin  of  tricuspid 

valve 


Chorda:  tendineae 


Columnae  carneae 


Anterior  wall  of  heart  hardened  in  situ  and  sectioned  parallel  to  posterior  surface, 
viewed  from  behind  ;  only  very  small  part  of  left  ventricle  is  seen  ;  probe  passes  from 
pulmonary  aorta  (artery)  into  right  ventricle. 

surrounding  the  auriculo-ventricular  orifices  serves  to  connect  the  auricles  and  ven- 
tricles. If  the  auricles  and  the  proximal  portions  of  the  aorta?  be  removed,  the 
fibrous  tissue  \\ill  be  seen  to  form  four  rings  (annnli  fibrosi),  one  corresponding  to 
each  of  the  basal  orifices  of  the  ventricles;  and,  furthermore,  three  of  the  rinses — 
those  surrounding-  the  two  auriculo-ventricular  orifices  and  that  of  the  systemic  aorta 
—will  be  seen  to  be  directly  in  contact,  while  the  fourth — that  surrounding  the  pul- 
monary aortic  orifice — is  separate  from  the  others,  although  connected  with  the  right 
auriculo-ventricular  ring  by  a  narrow  fibrous  band  which  descends  in  the  posterior 


THE   CHAMBERS   OF   THE   HEART.  699 

wall  of  the  conns  arteriosus.  The  ring  surrounding  the  left  auriculo-ventricular 
orifice  is  somewhat  thicker  than  that  of  the  right,  and  is  fused  with  the  systemic  aortic 
ring  throughout  about  the  medial  third  of  its  circumference,  whereas  the  correspond- 
ing fusion  of  the  right  ring  is  of  much  less  extent.  In  the  angle  formed  by  the 
junction  of  the  right  auriculo-ventricular  ring  at  the  side  with  the  systemic  aortic 
ring  in  front  a  special  thickening  of  the  fibrous  tissue  occurs,  so  that  it  becomes  of 
almost  cartilaginous  consistency,  and  a  similar,  although  smaller,  thickening  also 
occurs  in  the  angle  formed  by  the  junction  of  the  anterior  walls  of  the  left  auriculo- 
ventricular  and  systemic  aortic  rings.  These  thickenings  form  what  are  termed  the 
right  and  left  auriculo-ventricular  nodes  (trigona  fibrosa),  and  they  are  of  interest  as 
being  occasionally  the  seat  of  a  calcareous  deposit  or  of  a  fatty  infiltration,  a  condi- 
tion which  may  be  shared  by  fibre-like  prolongations  of  the  nodes  (_/?/#  coronaria) 
which  extend  into  adjacent  portions  of  the  auriculo-ventricular  rings. 

The  Auriculo-Ventricular  Valves. — Attached  by  its  base  to  each  auriculo- 
ventricular  fibrous  ring,  and  projecting  downward  into  the  cavity  of  the  correspond- 
ing ventricle,  is  a  valve  having  the  general  form  of  a  membranous  cone,  whose  walls 
are  of  thin  but  strong  fibrous  tissue  covered  on  both  sides  by  the  endocardium.  Each 
cone,  however,  is  divided  by  deep  incisions  into  triangular  segments,  of  which  there 
are  three  in  the  valve  of  the  right  ventricle,  whence  it  is  usually  termed  the  tricuspid 
•valve,  while  two  incisions  divide  the  left  valve  into  two  segments  and  procure  for  it 
the  name  of  the  bicuspid  or  mitral  valve,  the  latter  term  being  suggested  by  its 
resemblance  to  a  bishop's  mitre.  Of  the  three  segments  of  the  tricuspid  valve, 
one  (cuspis  anterior),  larger  than  the  others  and  also  known  as  the  infundibular 
cusp  is  attached  to  the  anterior  border  of  the  auriculo-ventricular  orifice  ;  a  second 
•one  (cuspis  posterior)  is  attached  to  the  posterior  border  ;  while  the  third  or  septa! 
(cuspis  medialis)  occupies  the  interval  between  the  medial  edges  of  the  other  two, 
and  is  attached  to  that  portion  of  the  auriculo-ventricular  fibrous  ring  which  is 
united  to  the  right  auriculo-ventricular  node  and  to  the  upper  part  of  the  ventricular 
septum.  In  the  mitral  valve  one  segment  (cuspis  posterior)  is  attached  to  the 
posterior  border  of  the  auriculo-ventricular  fibrous  ring,  while  the  other  (cuspis 
anterior)  or  aortic  cusp  is  situated  anteriorly,  and  depends  from  that  portion  of 
the  ring  which  is  united  to  the  ring  surrounding  the  systemic  aortic  orifice,  and 
consequently  appears  to  be  a  downward  prolongation  from  the  posterior  border  of 
that  orifice.  It  is  to  be  noted  that  the  depths  of  the  incisions  separating  the  seg- 
ments of  both  valves  vary  considerably,  and  additional  incisions  may  occur,  resulting 
in  the  formation  of  additional  segments.  Not  infrequently  a  small  accessory  segment 
occupies  the  apex  of  one  or  more  of  the  incisions. 

These  valves,  while  permitting  the  free  passage  of  blood  from  the  auricles  into  the 
ventricles,  prevent  its  passage  in  the  reverse  direction  during  the  contraction  of  the 
ventricles  ;  for  the  pressure  of  the  blood  within  the  ventricles  forces  the  segments  up- 
ward so  that  they  completely  occlude  the  auriculo-ventricular  orifices,  the  chordae 
tendineae  which  are  attached  to  them,  and  which  are  rendered  taut  by  the  contraction 
of  the  papillary  muscles,  preventing  them  from  being  forced  back  into  the  auricles. 
The  musculi  papillares  of  each  ventricle  are  arranged  in  two  groups,  one  consisting 
of  small  papillae,  situated  near  the  upper  portion  of  the  ventricle  behind  the  segments 
of  the  valves,  and  the  other,  composed  of  larger  conical  muscles,  situated  nearer  the 
apex.  The  chordae  tendineae  which  arise  from  the  upper  group  are  short,  and  are 
attached  to  the  ventricular  surface  of  the  valve  near  its  base  ;  those  which  arise  from 
the  lower  group  are  much  larger,  and  are  attached  to  the  edges  of  the  valve  and  to 
its  ventricular  surface  near  its  free  edge.  The  papillary  muscles  belonging  to  this 
lower  group  tend  to  be  arranged  in  sets  corresponding  in  position  with  the  incisions 
which  separate  the  segments  of  the  valves,  and  there  are,  accordingly,  three  sets  in 
the  right  ventricle  and  two  in  the  left  ;  but  this  arrangement  is  not  quite  definite,  and 
there  is  also  considerable  variation  in  the  number  of  papillary  muscles  in  each  set, 
only  one  being  present  in  some  cases  and  several  in  others.  However  that  may  be, 
the  chorda:;  tendineae  arising  from  the  apices  of  the  muscles  of  each  set  diverge  as 
they  p;iss  upward  and  are  attached  to  both  the  adjacent  segments  of  the  valve.  When 
distinct  accessory  segments  occur,  they  also  receive  the  insertion  of  some  of  the 
chordae  tendineoe. 


700 


HUMAN   ANATOMY. 


The  Semilunar  Valves. — Although  really  belonging  to  the  pulmonary  and 
systemic  aortae,  it  is  convenient  to  consider  these  valves  along  with  the  heart,  since 
they  prevent  the  regurgitation  of  the  blood  contained  in  the  aortae  into  the  ventricles 
at  the  completion  of  their  contraction. 

The  segments  guarding  these  valves  are  three  in  number  in  each  aorta  and  are 
attached  to  the  fibrous  ring  of  the  aortic  orifices.  Each  segment  is  a  crescentic 
pouch-like  structure,  whose  cavity  is  directed  away  from  the  heart,  so  that  any  ten- 
dency for  the  blood  to  return  from  the  aortae  into  the  ventricles  will  result  in  the  fill- 
ing of  the  pouches  so  that  the  three  are  brought  into  apposition  and  effectually  close 
the  orifice.  Their  efficiency  is  increased  by  ( i )  the  occurrence  at  the  middle  of  the 
free  edge  of  each  segment  of  a  small  fibro-cartilaginous  nodule,  the  nodule  of  Aran- 
tius,  which  fills  the  small  gap  which  might  otherwise  be  left  at  the  point  of  meeting  of 
the  free  edges  of  all  three  segments  ;  and  by  (2)  the  aorta  being  pouched  out  behind 
each  segment  to  form  a  small  pocket,  a  sinus  of  Valsalva,  greater  opportunity  being 
thus  allowed  for  the  blood  to  enter  the  cavities  of  the  valves  and  so  force  their  free 
edges  together. 

The  segments  of  thesemilunar  valves  of  the  systemic  aorta  (valvulae  semilunares 
aortae)  are  somewhat  stronger  than  those  of  the  pulmonary  aorta  (valvulae  semilu- 

FIG.  662. 


Post,  leaflet  of  pulm.  valve 

Left  coronary  artery, 
behind  left  posterior  leaflet 


Anterior  cusp  of  left 

auriculo-ventricular  valve 


Posterior  cusp 

Fibrous  ring  surrounding 
mitral  valve 


Right  coronary  artery, 
behind  anterior  leaflet 


Right  posterior  leaflet  of 
aortic  valve 


Anterior  cusp  of  right 

auriculo-ventricular  valve 


Medial  cusp 


Posterior  cusp 

Fibrous  ring  surrounding 
tricuspid  valve 


Valves  of  heart  viewed  from  above,  after  removal  of  auricles  and  greater  part  of  aortae. 


nares  a,  pulmonalis),  and  are  arranged,  if  considered  with  reference  to  the  plains  of 
the  body,  the  heart  being  in  situ,  so  that  one  is  situated  anteriorly  and  the  other 
two  right  and  left  posteriorly.  In  the  pulmonary  aorta  one  valve  segment  will  be 
posterior  and  the  others  right  and  left  anteriorly.  If,  however,  the  heart  be  held 
so  that  its  ventricular  septum  lies  in  the  sagittal  plane,  then  the  valve  segments  dilh-r 
by  60°  from  the  relative  position  given  above,  those  of  the  pulmonary  artery  being 
arranged  so  that  one  lies  anteriorly  and  the  other  two  right  and  left  posteriorly, 
while  in  the  systemic  aorta  one  is  posterior  and  the  other  two  right  and  left  anter- 
iorly, an  arrangement  to  be  expected  from  the  manner  of  development  of  the 
valves  (page  710). 

The  Architecture  of  the  Heart  Muscle. — The  musculature  of  the  walls 
of  the  auricles  is  relatively  very  thin,  and  it  is  difficult  to  distinguish  any  definite 
arrangement  of  its  fibres  in  layers.  Groups  of  fibers  can,  however,  be  distin- 
guished, and  of  these  certain  are  confined  to  each  auricle,  while  others  are  common 
to  the  two. 

Of  the  fasciculi  proper  to  each  auricle  two  principal  groups  can  be  recogm/e 
I.   Annular  fasciculi,  which   surround   the   orifices  of  the  veins   entering    the 
auricles,  and  represent  the  continuation  of  the  circular  muscle  layer  of  the  veins  into 
the  auricular  walls. 


THE   CHAMBERS   OF   THE   HEART. 


701 


FIG.  663. 

Anterior  cusp  of  aortic  valve 


Portion  of  left  ventricle,  showing  position  (  +  ) 
of  auriculo-yentricular  muscle  bundle  in  membran- 
ous part  of  interventricular  septum.  (Rttzer.) 


2.  Ansiform  fasciculi,  which  take  their  origin  from  the  auriculo-ventricular 
fibrous  ring  anteriorly  and  extend  over  the  auricle  to  insert  into  the  fibrous  ring 
posteriorly.  These  bundles  are  situated  as  a  rule  more  deeply  than  the  annular 
fasciculi  and  produce  the  pectinate  mus- 
cles of  the  auricular  appendage,  as  well 
as  certain  columnar  elevations,  covered 
by  endocardium,  which  occur  upon  the 
inner  surfaces  of  the  walls  of  the  auricles. 
The  fasciculi  common  to  both  auri- 
cles are  developed  only  in  the  neighbor- 
hood of  the  auriculo-ventricular  groove, 
and  constitute  thin  superficial  bands, 
which  run  parallel  to  the  groove.  The 
anterior  fasciculus  is  broader  and  more 
highly  developed  than  the  posterior  one. 
The  auriculo-ventricular  fibrous  ring 
forms  an  almost  complete  separation  be- 
tween the  musculature  of  the  auricles  and 
that  of  the  ventricles,  the  only  direct  con- 
nection between  the  two  being  formed 
by  a  slender  auriculo-ventricular  fasci- 
culus. This  takes  its  origin  in  the  pos- 
terior wall  of  the  right  auricle  close  to 
the  auricular  septum  (His,  Jr.)  and  passes 
downward  towards  the  upper  border  of 
the  muscular  portion  of  the  ventricular 
septum  (Fig.  663).  Here  it  bends  forward  and  runs  across  the  septum  in  the  line 
of  junction  of  its  membranous  and  muscular  portions,  and  is  lost  anteriorly  in  the 
musculature  of  the  ventricles.  The  existence  of  this  auriculo-ventricular  fasciculus 
is  of  considerable  importance  in  connection  with  transmission  of  the  contraction  wave 
from  the  auricles  to  the  ventricles,  the  application  of  a  clamp  to  the  bundle  having 
been  shown  to  produce  heart-block  (Erlanger). 

It  can  readily  be  perceived  that  the  muscle-fibres  of  which  the  walls  of  the 
ventricles  are  composed  are  arranged  in  more  or  less  definite  layers,  and  that  the 
direction  of  the  fibres  in  the  deeper  layers  is  different  from  that  of  the  more  super- 
ficial ones.  The  descriptions  of  the  various  layers  and  of  their  relations  to  one 
another  vary  greatly  in  different  authors;  in  that  given  here  the  results  obtained  by 

MacCallum,    by  the   application 

IMG,  664.  of    more  suitable  methods  than 

were  available  to  the  earlier  ob- 
servers, will  be  followed. 

The  fibres  of  the  ventricles 
can  start  only  from  the  fibrous 
rings  surrounding  the  ventricu- 
lar orifices  or  else  from  the  sum- 
mits of  the  musculi  papillares,  to 
which  a  certain  amount  of  fixa- 
tion is  afforded  by  the  chordae 
tendineae  and  their  attachment 
to  the  auriculo-ventricular  valves. 
It  will  be  convenient  to  regard 
the  fibrous  rings  as  the  principal 
points  of  origin,  and  the  most 
superficial  layer  of  the  muscula- 
ture may  be  said  to  arise  from 
them  and  from  the  tendinous 

band  which  descends  upon  the  posterior  surface  of  the  conus  arteriosus  towards  the 
right  auriculo-ventricular  ring.  Those  fibres  which  take  their  origin  from  this  ten- 
dinous band  and  the  right  ring  wind  in  a  left-handed  spiral  over  the  surface  of  the 


Left 

auriculo- 
ventricular 
orifice 


Papillary 
muscles 
of  right 
ventricle 


Diagram  of  course  of  superficial  muscle  layers  originating 
in  right  and  left  auriculo-ventricular  rings  and  in  posterior 
half  of  tendon  of  conus  arteriosus.  (MacCallum. ) 


702 


1 1  I'M  AN   ANATOMY. 


Left 

auriculo- 
ventricular 
orifice 


Right  auriculo- 
ventricular  orifice 


Septal  papil- 
lary muscles 
Posterior 
papillary 
muscles 


Diagram  of  course  of  superficial  muscle  layers  originating  in  anterior 
half  of  tendon  of  conus  arteriosus.     (MacCallum.) 


ventricles,  and  when  they  reach  the  apex,  they  bend  upon  themselves  and  pass 
deeply  and  upward  to  terminate  in  the  papillary  muscles  of  the  left  ventricle.  Those 
fibres  which  arise  from  the  left  auriculo-ventricular  fibrous  ring  cross  the  posterior  in- 

terventricular  groove  and,  pass- 
ing beneath  the  fibres  from  the 
Tendon  of  right  ring,  encircle  the  right  ven- 

conus  arteriosus  tricle  and  finally  terminate  in  the 
papillary  muscles  of  that  ven- 
tricle. 

On  the  removal  of  these 
superficial  fibres  a  deeper  set  is 
seen,  which  seem  to  form  two 
muscular  cones,  each  surround- 
ing one  of  the  ventricles.  In 
the  adult  heart  it  is  difficult  to 
perceive  the  true  relations  of  the 
two  cones,  but  in  the  hearts  of 
young  individuals  up  to  two  or 
three  years  of  age  it  has  been 
found  that  both  the  cones  are 
formed  by  the  curving  of  a  con- 
tinuous sheet  of  fibres  in  an  S-shaped  manner.  This  deep  sheet  of  fibres  takes  its 
origin  principally  from  the  right  auriculo-ventricular  fibrous  ring  and  from  the  ten- 
dinous band  of  the  conus  arteriosus,  and  encircles  the  right  ventricle,  lying  beneath 
the  superficial  layer.  When  it  reaches  the  posterior  border  of  the  ventricular  sep- 
tum, it  passes  forward  in  that  structure,  and  then  encircles  the  left  ventricle,  termi- 
nating finally  in  the  papillary  muscles  of  that  ventricle.  The  deep  fibres  which  arise 
from  the  left  fibrous  ring  are  entirely  confined  to  the  left  ventricle,  forming  a  circular 
band  surrounding  its  basal  portion. 

Structure. — The  heart  muscle,  the  myocardium,  is  both  covered  and  lined 
with  serous  membrane,  the  epicardium,  as  the  visceral  layer  of  the  pericardium  is 
often  called,  investing  it  externally  and  the  endocardium,  continuous  with  the  intima 
of  the  large  blood-vessels,  clothing  all  parts  of  its  elaborately  modelled  inner  surface. 
The  epicardium  corresponds  in  its  general  structure  with  other  parts  of  the 
pericardium,  consisting,  as  do  other  serous  membranes,  of  a  single  layer  of  endothelial 
cells  that  covers  its  free  surface  and  rests  upon  a  stratum  of  fibro-elastic  connective 
tissue.  The  elastic  fibrillae  are  very  fine  and  numerous  and,  immediately  beneath  the 
endothelium,  form  a  dense  net-work.  When  not  separated  from  the  muscle  by 
subserous  fat,  as  it  con- 
spicuously is  in  the  in-  FIG.  666. 
terventricular  and  auric- 
ulo-ventricular grooves, 
the  epicardium  is  inti- 
mately attached  to  the 
subjacent  muscular  tis- 
sue. The  numerous 
branches  of  the  coron- 
ary vessels,  as  well  as 
the  nerve  trunks  and  -^6*. 
the  microscopic  ganglia  "^r 
connected  with  the  car- 
diac plexuses,  lie  be-  Heart  mi 
ni-ath  the  epicardium  or 
within  its  deepest  layer. 
The  endocardium 
follows  all  the  irregular- 
ities of  the  interior  of  the  heart,  lining  every  recess  and  covering  the  free  surface-;  nf 
the  valves,  tendinous  cords  and  papillary  muscles.  It  consists  of  the  endothelium 
and  the  underlying  connective  tissue.  The  latter  is  differentiated  by  the  distribution 


Subendo- 

thelial 

stratum 

Layer  rich 
in  elastica 

Deepest 
layer 


Blood-vessel 


Section  of  endocardium. 


VESSELS   OF   THE   HEART. 


7°3 


FIG.  667. 


Muscular  tissue 


Fibro- 
elastic 
tissue  of 
valve- 
leaflet 


Endo- 
thelium 


of  the  elastica  into  two  strata,  a  thin  subendothelial  layer  practically  free  from  elastic 
fibres  and  a  broad  layer  in  which  the  elastica  predominates.  The  deepest  stratum 
of  the  endocardium  is  continuous  with  the  endomysium  that  penetrates  between  the 
fibres  of  the  heart  muscle. 

The  valves  consist  of  duplicatures  of  the  endocardium,  in  their  thicker  parts 
strengthened  by  an  intermediate  middle  layer  of  fibro-elastic  tissue  prolonged  from 
the  fibrous  rings  of  attachment.  Towards  the  free  margins  of  the  valves  all  three 
layers  are  blended  and  reduced  to  a  thin  fibrous  stratum  covered  by  endothelium. 
In  the  auriculo-ventricular  leaflets,  the  fibro-elastic  tissue  of  the  chordae  tendineae  is, 
continuous  with  the  middle  layer,  while  meagre  peripheral  bundles  of  muscle  may  be 
present  beneath  the  endocardium.  Al- 
though '  thinner  than  the  auriculo- 
ventricular,  the  pulmonary  and  aortic 
semilunar  valves  possess  essentially  the 
same  structure,  the  endocardial  layer, 
however,  being  thickened  to  produce 
the  noduli  Aurantii. 

In  addition  to  the  structural  de- 
tails of  the  fibres  composing  the  myo- 
cardium already  described  in  connec- 
tion with  the  general  histology  of 
muscle  (page  462),  it  may  be  noted 
that  in  the  immediate  vicinity  of  their 
nuclei  the  fibres  of  the  heart- muscle 
constantly  contain  accumulations  of 
undifferentiated  sarcoplasm  in  which 
lie  groups  of  highly  refracting  brown- 
ish granules  that,  under  moderate 
magnification,  appear  as  pigment  at 
the  poles  of  the  nuclei.  The  muscle- 
fibres,  branching  into  net-works  with 
long  narrow  meshes,  are  held  together 
by  delicate  lamellae  of  connective  tis- 
sue, the  endomysium,  which,  together 
with  the  more  robust  septa  that  as  the 
perimysium  invest  the  muscular  bun- 
dles, support  the  blood-vessels.  The 
relation  of  the  capillaries  to  the  muscle- 
substance  is  unusually  intimate,  the 
capillary  loops  often  modelling  the  sur- 
face of  the  fibres,  lying  in  deep  grooves 
almost  completely  enclosed  by  the  sur- 
rounding sarcous  tissue  (Meigs).  Al- 
though much  less  constant  and  typical 
than  in  the  ventricular  myocardium  of 
many  of  the  lower  animals,  as  the 
sheep,  goat,  and  ox,  the  imperfectly 
differentiated  fibres,  known  as  fibres 
of  Purkinje,  are  represented  in  the 
human  heart-muscle  by  subendocardial  fibres.  There  is  reason  to  believe  that  these 
fibres  are  related  to  the  co-ordinating  auriculo-ventricular  bundle  of  His  (page  701.) 

The  Blood-Vessels  and  Lymphatics  of  the  Heart. — The  heart  receives 
its  blood-supply  through  the  two  coronary  arteries  which  arise  from  the  systemic 
aorta  immediately  above  its  origin,  the  return  flow  being  by  the  coronary  veins  which 
open  into  the  right  auricle  by  the  coronary  sinus.  Both  these  sets  of  vessels  will  be 
described  later  (page  728),  but  it  may  be  pointed  out  here  that  the  branches  of  the 
coronary  artery  upon  the  surface  of  the  heart  are,  as  a  rule,  all  end-arteries, — that  is, 
arteries  which  form  no  direct  anastomoses  with  their  neighbors.  Practically  no 
blood  can  be  carried  directly,  therefore,  by  the  left  coronary  artery  into  the  territory 


Papillary  muscle 


Longitudinal  section  of  leaflet  of 
tricuspid  valve.     X  20. 


704  HUMAN   ANATOMY. 

supplied  by  the  right  one,  or  vice  versa,  and  sudden  occlusion  of  either  of  the  arteries 
will  produce  serious  disturbances  or,  in  some  cases,  complete  arrest  of  the  contrac- 
tions of  the  heart.  Since,  however,  the  capillaries  of  the  heart's  substance,  into 
which  each  artery  is  continued,  form  a  continuous  net-work,  a  passage-way  for  the 
blood  of  one  artery  into  the  territory  normally  supplied  by  the  other  may  be  formed 
by  their  enlargement,  opportunity  for  which  may  be  afforded  in  cases  in  which  the 
occlusion  of  an  artery  has  been  very  gradual  in  its  development. 

There  is,  however,  another  way  by  which  the  tissue  of  the  heart  may  receive  nutrition  in 
cases  of  gradual  occlusion  of  the  coronary  arteries,  namely,  through  the  Thebesian  orifices  in 
the  walls  of  the  auricles  and  ventricles.  These  openings  communicate  by  means  of  capillaries 
with  the  coronary  vessels,  and  it  has  been  shown  experimentally  that  the  heart  can  be  effectively 
nourished  by  b'ood  passing  from  the  chambers  of  the  heart  through  the  Thebesian  vessels  and 
back  into  tlie  coronary  veins. 

The  lymphatic  vessels  of  the  heart  form  a  net-work  beneath  the  visceral  layer 
of  the  pericardium,  and  a  second  less  distinct  net-work  has  also  been  described  as 
occurring  beneath  the  endocardium.  These  net-works  communicate  with  two  sets  of 
principal  vessels  \vhich  lie  in  the  anterior  and  posterior  portions  of  the  auriculo-ven- 
tricular  groove.  The  anterior  set  passes  from  the  right  to  the  left,  and,  on  reaching 
the  pulmonary  aorta,  passes  around  its  left  surface  to  reach  the  systemic  aorta,  upon 
which  it  ascends  to  terminate  in  a  lymphatic  node  situated  to  the  left  of  the  trachea. 
The  posterior  set  opens  in  part  into  the  anterior  one  and  in  part  ascends  along  the 
right  side  of  the  pulmonary  aorta  to  terminate  in  one  of  the  nodes  situated  beneath 
the  bifurcation  of  the  trachea. 

The  Nerves  of  the  Heart. — The  nerves  of  the  heart  are  derived  from  the 
cardiac  plexuses  and,  passing  downward  along  the  aortae,  are  distributed  partly  to  the 
auricles  and  partly  accompany  the  coronary  arteries  along  the  auriculo-ventricular 
groove,  where  they  form  the  coronary  plexus,  from  which  branches  are  distributed 
to  the  ventricles.  Over  the  surfaces  of  the  auricles  and  ventricles  the  branches  form 
a  fine  plexus  situated  beneath  the  visceral  layer  of  the  pericardium,  and  from  this 
plexus  branches  pass  into  the  substance  of  the  heart  to  terminate  upon  the  muscle- 
fibres.  Some  nerve-fibres  are  also  distributed  to  the  pericardium  and  endocardium, 
and  these  are  regarded  as  being  afferent  in  function,  as  are  also  certain  fibres  which 
terminate  in  the  connective  tissue  of  the  heart's  walls. 

Scattered  in  the  superficial  plexuses  there  are  numerous  ganglion-cells,  some- 
times occurring  singly  and  sometimes  collected  into  small  ganglia.  They  tend  to  be 
especially  numerous  around  the  orifices  of  the  great  veins  opening  into  the  auricles, 
in  the  coronary  plexuses,  and  over  the  upper  portions  of  the  ventricles.  It  has  been 
asserted  that  ganglion-cells  also  occur  embedded  in  the  walls  of  the  ventricles,  but  at 
present  this  requires  confirmation. 

Much  has  yet  to  be  learned  concerning  the  qualities  of  the  various  nerve-fibres  which  pass  to 
the  heart  in  man,  but  it  is  presumable  that  they  resemble  in  general  those  which  have  been  deter- 
mined experimentally  for  those  of  the  lower  mammals.  In  the  latter  it  has  been  shown  that  the 
cardiac  plexuses  contain  both  afferent  and  efferent  nerve-fibres.  The  cardiac  plexuses  are  formed 
by  branches  from  the  pneumogastric  and  sympathetic  nerves,  and  among  the  fibres  from  the  former 
nerve  are  some  which,  when  stimulated,  cause  a  cessation  of  the  heart's  contractions,  whence 
they  are  termed  the  inhibitory  nerves.  Stimulation  of  sympathetic  fibres,  which,  in  the  dog,  for 
example,  pass  to  the  cardiac  plexus  from  the  first  thoracic  ganglion  of  the  ganglionated  cord, 
produces  an  increase  in  either  the  rapidity  or  the  intensity  of  the  heart-beat,  and  these  fibres  are 
consequently  termed  the  accelerator  or  ang  mentor  fibres.  Both  the  inhibitory  and  augmentor 
fibres  are  efferent, — i.e.,  they  carry  impulses  from  the  nerve-centres  out  to  the  heart  ;  in  addi- 
tion, the  existence  of  afferent  fibres  has  been  determined  among  the  pneumogastric  constituents 
of  the  plexuses.  These  are  the  depressor  .///>/ r.v.  so  called  because  their  stimulation  produces  a 
marked  fall  in  the  blood-pressure,  not  on  account  of  any  action  upon  the  heart-beat,  since  they 
lead  the  stimulus  away  from  the  heart,  but  by  acting  rellexly  upon  the  intestinal  vessels  so  as  to 
produce  their  dilatation  and,  by  thus  lessening  the  peripheral  resistance  against  which  the  heart 
must  contend,  lessen  the  work  which  the  organ  lias  to  do. 

Whether  the  various  efferent  fibres  pass  directly  to  the  muscular  tissue  of  the  heart  or  ter- 
minate upon  cardiac  ganglion-cells  which  transmit  the  impulse  to  the  muscle-fibres  is  a  point 
uhich  remains  to  be  determined,  although,  from  analogy  with  what  is  known  as  to  the  relation 
of  the  cerebro-spinal  fibres  to  other  portions  of  the  involuntary  muscular  tissue,  it  would  seem 
prob.ible  that  the  | meumogastric  efferent  fibres  terminate  primarily  upon  the  cardiac  ganglion- 
cells. 


THE    PRIMITIVE    HEART. 


7°5 


DEVELOPMENT   OF   THE   HEART. 

In  the  mammals  in  which  the  earliest  stages  in  the  development  of  the  heart  have 
been  observed,  this  organ  arises  as  two  separate  tubes  that  are  formed  by  folding  of 
the  visceral  mesoblast  near  the  margin  of  the  embryonic  area.  This  folding  occurs 
while  the  embryo  is  still  spread  out  upon  the  surface  of  the  yolk-sac  and  produces  on 
each  side  an  elevation,  a  heart-tube,  that  projects  into  the  primitive  body-cavity 
(  Fig.  668).  Each  heart-fold  differentiates  into  a  thicker  outer  or  myocardial  layer, 
which  gives  rise  to  a  portion  of  the  cardiac  muscle,  and  a  very  thin  inner  endocardial 
layer,  from  which  the  serous  lining  of  the  heart  is  derived.  The  latter  consists  of  a 
single  stratum  of  mesoblastic  cells  surrounded  by  the  muscle-layer,  but  separated  by 
a  distinct  space,  as  a  shrunken  cast  lies  within  its  mould. 

With  the  beginning  constriction  of  the  gut-tube  from  the  vitelline  sac  and  the 
associated  approximation  of  the  splanchnopleura  of  the  two  sides,  the  heart-tubes,  at 
first  widely  apart,  gradually  approach  the  mid-line  until  they  meet  beneath  the  ventral 
surface  of  the  primitive  pharynx,  in  advance  of  the  yolk-sac.  Upon  coming  into 
contact,  the  cavities  of  the  two  heart-tubes  for  a  brief  period  remain  separated  by  the 
partition  formed  by  the  opposed  portions  of  the  myocardial  layers.  Very  soon,  how- 
ever, solution  of  this  septum  occurs  and  the  two  sacs  become  a  single  heart.  The 
endothelial  tubes  are  last  to  fuse,  retaining  their  independence  after  the  myocardial 
walls  have  blended.  Upon  fusion  of  the  endothelial  layers  the  conversion  of  the  double 
tubes  into  a  single  heart  is 
complete.  FIG.  668. 

The  early  venous  trunks 
— the  body-stems  (cardinals 
and  jugulars)  within  the  em- 
bryo and  the  vitelline  and 
allantoic  (later  umbilical)  veins 
from  the  extra  embryonic  vas- 
cular net-works — converge  to- 
wards a  common  sac,  the 
sinus  venosus,  which  joins  the 
caudal  end  of  the  cylindrical 
primitive  heart.  The  slightly 
tapering  cephalic  extremity  of 
the  latter  becomes  the  truncus 
arteriosus,  from  which  two  trunks,  the  ventral  aorta,  are  prolonged  forward  beneath 
the  primitive  pharynx,  giving  off  the  aortic  bows  that  traverse  in  pairs  the  series  of 
visceral  arches.  The  primitive  heart  consists,  therefore,  of  a  cylinder,  somewhat 
contracted  at  its  anterior  end,  that  occupies  the  ventral  mid-line  in  the  later  cervical 
region.  The  blood  poured  into  the  sinus  venosus  by  the  veins  enters  its  posterior 
extremity  and  escapes  anteriorly  through  the  truncus  arteriosus. 

Although  for  a  brief  period  the  heart-tube  retains  its  median  position  and 
straight  cylindrical  form,  its  increasing  length  soon  causes  it  to  become  bent  upon 
itself  and  to  assume  the  S-like  contour  shown  in  Fig.  672  A,  from  an  embryo  of  2. 15 
mm.  in  length,  in  which  the  venous  end  of  the  tube  lies  below  and  to  the  left  and 
the  arterial  trunk  above  and  to  the  right.  The  intermediate  portion  of  the  tube, 
extending  at  first  downward  and  then  obliquely  upward  and  towards  the  left,  is  the 
primitive  ventricle,  the  early  sigmoid  heart-tube  already  suggesting  the  recognition 
of  an  arterial,  ventricular,  and  venous  segment. 

During  the  further  development  of  the  heart  a  rearrangement  of  these  three 
divisions  takes  place,  since  the  venous  segment,  orginally  below,  gradually  acquires 
a  position  above  and  behind,  while  the  primitive  ventricle  comes  to  lie  in  front  and 
below  (Fig.  672).  With  the  completion  of  this  rotation,  a  deep  external  groove 
appears  between  the  ventricular  and  venous  chamber,  now  the  primitive  auricle,  that 
indicates  the  position  of  a  contracted  passage,  the  auricular  canal  (Fig.  672,  C),  as 
the  common  auriculo-ventricular  opening  is  termed.  Coincidently  with  the  upward 
migration  of  the  venous  segment,  a  lateral  outpouching  of  the  auricular  chamber 
appears  on  each  side  of  the  truncus  arteriosus.  These  expansions,  the  primary  ait- 

45 


\.  ^    i 

X 

Myocardial 
layer 
Endocardial  layer 


Gut-tube 


Splanch- 
nopleura 


Heart-tube 


Transvetse  section  of  very  young  rabbit  em- 
bryo, showing  two  heart-tubes  widely  separated  by 
unclosed  digestive  tube.  X  150. 


706 


HUMAN    ANATOMY. 


ricular  appendages,  rapidly  increase,  until  they  form  the  most  conspicuous  part  of  the 
young  heart  (Fig.  673,  C),  embracing  the  upper  part  of  the  truncus  arteriosus  and 
overlying  the  ventricle. 

Meanwhile  the  ventricular  segment  has  assumed  the  most  dependent  and  ventral 
position,  for  a  time  appearing  as  a  transversely  expanding  sac  (Fig.  672,  B )  that  in 
form  recalls  a  greatly  dilated  stomach,  the  truncus  arteriosus  joining  the  "  pylorus," 
and  the  contracted  auricular  canal  suggesting  the  oesophagus.  Soon,  however,  the 
higher  right  end  of  the  ventricular  segment  sinks  to  the  level  and  gains  the  ventral 
plane  of  the  left  end,  the  ventricle  in  consequence  losing  in  width  but  gaining  in 
height.  A  shallow  longitudinal  crescentic  furrow,  the  later  interventricular  groove, 
now  appears  on  the  surface  of  the  ventricle  and  suggests  the  subdivision  of  this  seg- 
ment into  right  and  left 

FIG.  669.  chambers,     at     the     same 

time  indicating  the  posi- 
tion of  the  growing  inter- 
nal partition  that  leads  to 
this  separation. 

Sections  of  the  young 
heart  (  Fig.  670 )  show 
the  venous  and  ventricular 
segments  as  widely  com- 
municating portions  of  the 
sigmoid  tube,  the  walls  of 
which  are  composed  of  the 
myocardial  and  endothe- 
lial  layers.  In  somewhat 
older  embryos  (Fig.  671), 
the  communication  between 
these  divisions  of  the  heart- 
tube  exhibits  a  slight  con- 
traction, marking  the  posi- 
tion of  the  later  auricular 
canal,  which  becomes  a  nar- 
row transverse  cleft  that 
connects  the  primitive  ven- 
tricle with  the  auricular 
chamber.  The  myocar- 
dial layer  of  the  heart- 
wall,  particularly  in  the 
ventricle,  also  shows  the 
beginning  of  the  trabeculae 
that  invaginate  the  endo- 
thelial  lining  and  event- 
ually lead  to  the  conspicu- 
ous modelling  of  the 
interior  of  the  adult  heart. 
Frontal  sections  of  the 

young  human  heart  (Fig.  674,  A}  show  the  commencing  separation  of  the  ventricular 
and  auricular  chambers  into  right  and  left  halves.  This  division  is  effected  by  the 
formation  of  a  vertical  partition  consisting  of  an  upper  auricular,  a  middle  valvular, 
and  a  lower  ventricular  part,  supplemented  by  the  aortic  septum  that  appears  in  the 
truncus  arteriosus  and  subdivides  the  latter  into  the  pulmonary  and  systemic  aortae. 
The  subdivision  of  the  auricle,  which  anticipates  that  of  the  ventricle,  begins  in 
the  fourth  week  with  the  downward  extension  of  a  crescentic  fold,  the  auricular  sep- 
tum, or  septum  primum,  that  gradually  grows  from  the  postero-superior  wall  of  the 
auricle  towards  the  auricular  canal  and  fuses  with  the  partition  that,  as  tin-  septum 
intermedium,  is  formed  within  the  canal  by  local  thickening  of  its  anterior  and  pos- 
terior lips.  In  this  manner  not  only  the  common  auricular  chamber,  but  also  the 
transversely  elongated  auriculo-ventricular  opening,  is  separated  into  a  right  and  a 


Right  duct 
of  Cuvier 

Right 
cardinal 


Primitive 
ventricle 

Pericardial 

sac.  cut 

Left  urnhil- 

ical  vein 

Left  vitel- 
line  vein 


Right  umbilical  vein 

Right  vitelline  vein 

Reconstruction  of  upper  part  of  human  embryo  of  third 
weelf  (3.2  mm.),  showing  relation  of  heart  and  blood-vessels. 
X  50.  (Drawn  from  His  model.) 


DEVELOPMENT    OF   THE    HEART. 


707 


FIG.  670. 


Neural  canal 


Aorta 


Digestive 
tube 


left  half.  The  interauricular  partition,  however,  is  not  complete,  since  an  opening 
appears  in  its  upper  part  even  before  it  has  finished  its  downward  growth  and  union 
with  the  valvular  septum.  This  opening  enlarges  and  remains  as  lh^  foramen  ovale 
that  persists  until  birth  as  a  direct  passage  for  the  blood  from  the  right  into  the  left 
auricle  during  the  continuance  of  the  foetal  circulation  (page  929). 

The  subdivision  of  the  ventricular  chamber,  which  commences  a  little  later 
than  that  of  the  auricle,  is  accomplished  chiefly  by  the  formation  of  the  ventricular 
septum.  The  latter  grows  from  the  postero-inferior  wall  of  the  ventricle  as  a  cres- 
centic projection  that  continues  inward,  a  thickening  of  the  ventricular  wall  corre- 
sponding in  position  with  the  external  interventricular  groove.  The  partition  thus 
formed  extends  towards  the  auriculo-ventricular  opening,  where  it  meets  and  fuses 
with  the  septum  intermedium,  in  this  manner  insuring  the  communication  of  the 
right  and  left  auricles  with  the  corresponding  ventricles  through  the  intervening 
respective  portions  of  the  valvular  opening. 

The  isolation  of  the  two  ventricles  from  each  other,  however,  is  not  at  first  com- 
plete, owing  to  the  ventricular  partition  being  imperfect  above  and  in  front.  This 
deficiency  is  overcome  by  the  down- 
ward extension  of  the  aortic  septum 
within  the  bulbus  arteriosus  (as  the 
somewhat  dilated  lower  end  of  the  trun- 
cus  arteriosus  is  now  appropriately 
called )  until  it  meets  and  fuses  with  the 
ventricular  partition,  thus  completing 
the  separation  of  the  cardiac  chambers 
into  a  right  and  left  heart.  The  part 
of  the  ventricular  partition  contributed 
by  the  aortic  septum  always  remains 
thin  and  constitutes  the  pars  membran- 
acea  of  the  adult  organ. 

Coincidently  with  the  foregoing 
changes,  the  auricles  undergo  impor- 
tant modifications  in  their  relations  with 
the  blood-vessels  opening  into  them. 
During  the  development  of  the  auricles, 
the  oval  sinus  venosus,  into  which  is 
conveyed  the  blood  returned  by  the  vi- 
telline,  allantoic  (umbilical)  and  body- 
veins,  elongates  transversely  into  a 
crescentic  sac,  the  convexity  of  which  is 
in  contact  with  the  back  of  the  auricles, 
its  opening  into  the  latter  having  shifted 
so  that  it  is  in  relation  with  only  the 
right  half  of  the  auricular  chamber.  With  the  expanded  body  and  right  horn  of 
the  venous  crescent  communicate  the  vessels  that  later  are  represented  by  the  superior 
and  inferior  venae  cavae,  while  the  elongated  and  smaller  left  horn  receives  the  left 
duct  of  Cuvier  that  becomes  the  coronary  sinus. 

For  a  time  the  opening  of  the  sinus  venosus,  or  sinus  reuniens  (His),  into  the 
heart  occupies  the  posterior  wall  of  the  right  half  of  the  auricle.  It  is  guarded  by 
the  venous  valve,  consisting  of  a  right  and  left  leaflet,  that  is  prolonged  forward 
along  the  roof  of  the  auricle  as  a  crescentic  ridge,  the  septum  spurium  (Fig.  674,  A), 
With  the  continued  appropriation  of  the  venous  sinus  by  the  expanding  auricle,  the 
single  aperture  of  the  sinus  disappears  as  the  sac  becomes  part  of  the  auricular 
chamber,  thereupon  the  two  venae  cavae  and  the  coronary  sinus  open  directly  into  the 
right  auricle  by  an  independent  orifice.  That  of  the  superior  cava  lies  in  the  upper 
posterior  part  of  the  auricle,  that  of  the  inferior  cava  being  lower  and  more  lateral, 
with  the  smaller  orifice  of  the  coronary  sinus  slightly  below.  The  septum  spurium, 
the  greater  part  of  the  left,  and  the  upper  part  of  the  right  segment  of  the  arching 
fold  that  originaHy  surrounds  the  opening  of  the  sinus  venosus  disappear  during  the 
appropriation  of  the  venous  sac  by  the  auricle.  The  lower  part  of  the  right,  leaflet, 


docardial 
layer 


Myocardial 
layer 


Primitive  ventricle 


Transverse  section  of  early  rabbit  em- 
bryo passing  through  young  heart,  showing 
venous  segment  behind  and  arterial  in 
front.  X  75- 


708 


HUMAN   ANATOMY. 


Fig.  671. 


on  the  contrary,  persists  and  differentiates  into  the  larger  Eustachian  retire,  that 
guards  the  lower  margin  of  the  inferior  vena  cava  and  directs  its  blood-stream  towards 
the  foramen  ovale,  and  the  smaller  Thebesian  valve,  that  protects  the  orifice  of  the 
coronary  sinus. 

As  above  noted,  the  separation  of  the  two  auricles  is  incomplete  on  account  of 
the  existence  of  the  foramen  ovale  within  the  interauricular  partition.  From  the  roof 
and  anterior  wall  of  the  right  auricle  an  additional  and  relatively  thick  crescentic  ridge, 
the  septum  secundum,  arches  around  the  foramen  ovale  of  \vhich  it  forms  the  anterior 
or  ventral  boundary.  It  lies  close  to  and  parallel  with  the  auricular  septum  and 
fuses  below  with  the  lower  part  of  the  left  segment  of  the  venous  valve  to  form  the 
limbus  Vieussenii  that  later  limits  the  fossa  ovalis,  marking  the  former  position  of  the 
foramen  ovale.  The  latter,  therefore,  is  included  between  two  partially  overlapping 
crescentic  margins,  that  contributed  by  the  septum  auriculum  lying  behind  and  to  the 
left,  and  that  by  the  septum  secundum  in  front  and  to  the  right,  a  narrow  sagittal 

cleft  intervening  so  that  the  surfaces  of 
the  lunate  borders  are  not  in  contact. 

Since  the  division  of  the  heart  into 
a  right  and  left  side  is  inseparably  con- 
nected with  the  development  of  the 
lungs  and  the  consequent  necessity  for 
a  distinct  pulmonary  circulation,  provis- 
ion for  the  return  of  the  blood  from  the 
lungs  to  the  heart  is  made  by  the  early 
formation  of  the  pulmonary  veins. 
These  arise  in  pairs,  one  pair  for  each 
lung;  close  to  the  heart  each  pair  unites 
into  a  single  right  or  left  stem  that,  in 
turn,  joins  with  its  fellow  of  the  oppo- 
site side  to  form  one  short  common 
trunk.  For  a  time  none  of  these  ves- 
sels communicate  with  the  heart,  but 
later  the  common  single  pulmonary  vein 
opens  into  the  left  auricle  close  to  the 
septum.  With  the  subsequent  growth 
and  expansion  of  the  auricles  an  appro- 
priation occurs  on  the  left  side  similar  to 
that  affecting  the  sinus  venosus  on  the 
right,  in  consequence  of  which  the  short 


Aorta 


Pharynx 


,-ocar- 

i  u  in 


Truncus  arteriosus 


Transverse  section  of  somewhat  older  em- 
bryo, showing  differentiation  into  auricles, 
ventricle  and  truncus  arteriosus.  X  75- 


common  pulmonary  vein  is  first  drawn 
into  the  heart,  to  be  followed  next  by 
the  two  secondary  and,   finally,  by  the 
four    primary  pulmonary   veins,    all    of 
which    then  open    by  separate  orifices 
into  the  enlarging  left  auricle.      The  fre- 
quent variations  in  the  number  of  the  pulmonary  veins  and  in  their  relations  to  the 
heart  are  usually  to  be  referred  to  arrest  or  modification  of  this  foetal  appropriation. 

The  differentiation  of  a  right  and  left  auriculo-ventricular  valve  proceeds  from  the 
subdivision  of  the  auricular  canal  by  the  septum  intermedium.  The  latter  is  fonm-d 
by  the  approximation  and  union  of  the  median  cushion-like  projections  upon  the 
ventral  and  dorsal  walls  of  the  common  auriculo-ventricular  opening.  The  unob- 
literated  lateral  portions  of  the  latter  are  triangular  in  outline  and  guarded  by  pro- 
liferations of  the  endocardium.  Those  of  the  lower  margins  of  the  valves  elongate 
and  project  into  the  ventricles  on  the  right  side,  giving  rise  to  two  leaflets,  and  on  the 
left  to  a  single  flap.  An  additional  prolongation  from  the  partition  contributes  a 
septal  leaflet  on  each  side.  In  this  manner  the  complement  of  flaps  for  the  tricuspid 
and  bicuspid  (mitral)  valves  is  early  provided.  The  close  relation  between  thr  lc  if- 
U-ts  and  the  attached  restraining  bands,  the  chordae  tendineae,  results  from  the 
secondary  union  of  the  immature  Maps  with  the  trabeculae  of  the  spongy  myocardium 
of  the  young  heart.  The  loose  muscular  walls  undergo  partial  consolidation,  so  that 


' 


DEVELOPMENT   OF   THE   HEART. 


709 


the  outer  strata  of  the  ventricular  muscle  become  compact  while  the  inner  layers  for 
a  time  retain  their  characteristic  trabeculse.  Those  attached  to  the  valves  undergo 
thickening  and  consolidation  and  become  the  papillary  muscles;  a  few  persist  as  ties 

FIG.  672. 

A  B  C 


Reconstructions  of  developing  hearts ;  A,  from  human  embryo  of  about  14  days  (2.15  mm.  long)  ;  £,  of  21  days 
(4.2  mm.);  C  of  23  days  (4.3  mm.);  ta,  truncus  arteriosus  :  pv,  primitive  ventricle;  sv,  sinus  venosus;  aa,a'a', 
right  and  left  auricular  appendages  ;  avc,  auriculo-ventricular  canal.  X  20.  (Drawn  from  His  models.) 

FIG.  673. 

A  B 


Iv 


h> 


Iv 


Reconstructions  of  developing  hearts;  A,  from  human  embryo  of  25  days  (5  mm.  greatest  length);  £,  endo- 
thelial  heart  from  same;  C,  of  35  days  (13.7  mm.);  ra,  la,  right  and  left  auricles  represented  by  large  auricular 
appendages;  rv,  Iv,  right  and  left  ventricles;  la,  truncus  arteriosus;  e,  endothelial  tube;  ac,  auriculo-ventricular 
canal;  ag,  interventricular  groove.  X  20.  (Drawn  from  His  models.) 


or  moderator  bands ;  while  the  majority  retain  their  freedom  to  a  lesser  degree  and,  as 
the  columnar  carneae,  produce  the  conspicuous  modelling  of  the  interior  of  the  ven- 
tricles. The  muscular  tissue,  which  at  first  extended  to  and  even  within  the  valve- 


7io  HUMAN   ANATOMY. 

leaflets,  subsequently  undergoes  partial  atrophy  and  disappears  from  the  flaps  and 
adjoining  parts  of  the  attached  bands,  the  latter  thereby  being  converted  into  the 
fibrous  chordae  tendineae. 

Even  before  the  longitudinal  subdivision  of  the  bulbus  arteriosus  occurs,  the 
junction  of  this  tube  with  the  primary  ventricle  is  marked  by  four  cushion-like  thick- 
enings that  project  from  the  interior  of  the  bulb.  These  elevations,  which  consist  of 
immature  connective  tissue  covered  by  endothelium,  furnish  the  leaflets  of  the  aortic 
and  pulmonary  semilunar  valves.  The  formation  of  the  aortic  septum  within  the 
bulbus  arteriosus  begins  some  distance  above  the  valve  and  immediately  below  the 
origin  of  the  right  and  left  pulmonary  arteries.  From  this  point  the  partition  gradu- 
ally grows  downward  until  it  encounters  the  elongated  lateral  pair  of  the  original  four 
valve-cushions,  of  which  one  lies  in  front,  one  behind,  and  two  at  the  sides  of  the  bulb. 
With  the  completion  of  the  division  of  the  bulbus  arteriosus  into  the  systemic  and 
pulmonary  aortae,  the  septum  cleaves  the  two  lateral  cushions,  each  of  the  resulting 
valves  "being  guarded  by  three  leaflets  so  disposed  that  the  original  and  undivided 
flap  of  the  pulmonary  artery  lies  in  front,  and  that  of  the  aorta  behind.  The  partial 
rotation  that  later  places  the  aortic  valve  behind  and  to  the  left  of  the  pulmonary 
brings  about  the  disposition  observed  in  the  adult  (page  700),  in  which  the  single 
leaflet  of  the  aortic  semilunar  valve  lies  in  front  and  that  within  the  pulmonary  artery 
is  behind.  At  first  comparatively  thick,  the  leaflets  suffer  partial  absorption,  whereby 
they  are  converted  into  the  membranous  cusps  that  bound  crescentic  pouches,  the 
sinuses  of  Valsalva,  which  lie  between  the  leaflets  and  the  wall  of  the  vessels. 

PRACTICAL   CONSIDERATIONS  :    THE   HEART. 

It  is  possible  here  only  to  indicate  with  great  brevity  certain  changes  in  the 
position  of  the  heart  which  should  be  studied  in  connection  with  its  relations. 

The  apex  beat,  normally  to  be  found  about  one  inch  below  and  two  inches  to  the 
sternal  side  of  the  left  nipple,  is  due  to  the  recoil  of  the  left  ventricle  as  it  empties  its 
contents  into  the  aorta,  to  the  lengthening  of  that  vessel  as  the  blood  enters  it,  to  the 
consequent  straightening  of  the  arch  (carrying  the  heart  forward),  and  to  the  absence 
of  any  interposed  lung-tissue  over  the  "area  of  absolute  dulness." 

The  apex  beat  (and  usually  the  heart  itself)  is  (a)  raised  in  cases  of  ascites, 
tympanites,  large  abdominal  tumors,  and  atrophic  pulmonary  conditions  ;  (b)  de- 
pressed in  aortic  aneurism,  mediastinal  growths,  pulmonary  emphysema,  pleural 
effusion,  and  hypertrophy  or  dilatation  of  the  left  ventricle  ;  (*-)  displaced  laterally 
to  the  right  by  left  pleural  effusion,  splenic  tumors,  hypertrophy  of  the  right  ventri- 
cle, to  the  left  by  hepatic  tumors,  right  pleural  effusion,  hypertrophy  of  the  left  ven- 
tricle. The  heart  may  be  drawn  to  either  side  by  contracting  pleural  adhesions. 
As  the  area  of  absolute  dulness — "superficial  cardiac  area" — corresponds  to  that 
portion  of  the  cardiac  substance  which  is  not  separated  by  pulmonary  tissue  from 
the  thoracic  wall,  it  follows  that  its  extent  varies  inversely  with  the  size  or  expansion 
of  the  lungs.  In  emphysema  the  area  of  cardiac  dulness  may  quite  disappear  ;  in 
the  later  stages  of  fibroid  phthisis  it  may  be  much  larger  than  normal. 

In  relation  to  the  anatomy  of  the  valves  and  cavities  of  the  heart,  the  sounds 
produced  by  the  passage  of  blood  through  them  should  be  considered  in  connection 
with  at  least  a  few  of  the  modifications  caused  by  the  chief  pathological  changes  that 
affect  that  organ.  It  may  be  said  here,  for  the  sake  of  clearness,  that  the/V-y/  sound 
occurs  during  the  contraction  of  the  ventricles,  when  the  auriculo-ventricular  open- 
ings should  be  closed  by  the  mitral  and  tricuspid  valves  and  the  aortic  and  pul- 
monary orifices  should  be  open,  and  that  it  is  due  to  (#)  the  shutting  of  the  valves, 
and  (£)  the  impulse  of  the  apex  against  the  thoracic  wall,  with  possibly  some  addi- 
tion from  (r)  the  contraction  of  the  walls  of  the  ventricles,  although  this  latter  factor 
is  doubtful. 

The  second  sound  occurs  during  the  auriculo-ventricular  dilatation,  and  is  due  to 
the  closure  of  the  pulmonary  and  aortic  semilunar  valves  caused  by  the  recoil  of  the 
blood-current  brought  about  by  the  elastic  coats  of  tlu-  aorta  and  pulmonary  arteries. 

If  a  murmur  heard  over  the  chest  is  synchronous  with  the  radial  pulse  (  systolic  i, 
it  occurs  during  ventricular  contraction,  and  is  usually  due  either  (  a )  to  regUTgita- 


PRACTICAL    CONSIDERATIONS:    THE   HEART.  711 

tion  of  blood  through  an  auriculo-ventricular  valve  that  does  not  accurately  close  the 
corresponding  opening  or  (6}  to  an  obstruction  to  the  exit  of  blood  from  the  ven- 
tricle at  the  aortic  or  at  the  pulmonary  orifice. 

If  a  heart  murmur  is  not  synchronous  with  the  radial  pulse  (diastolic  or  pre- 
systolic),  it  may  be  caused  by.(«)  obstruction  to  the  passage  of  blood  from  an 
auricle  into  a  ventricle  (mitral  or  tricuspid  stenosis) ;  or  (£)  regurgitation  from  the 
pulmonary  artery  or  aorta  into  the  right  or  left  ventricle  (pulmonary  or  aortic  insuf- 
ficiency). 

Of  these  various  murmurs  those  due  to  mitral  and  aortic  insufficiency  are  by  tar 

the  most  frequent. 

Valvular  disease  of  the  left  side  of  the  heart  (90  per  cent,  of  all  cases)  is  more 
frequent  on  account  of  the  greater  work  required  of  this  side  and  the  associated 
greater  liability  to  strain,  rarely  sudden,  usually  trifling  but  oft  repeated. 

1.  Mitral  insufficiency — an  imperfect  closure  of  the  segments  of  the  left  auriculo- 
ventricular  valve — causes  a  systolic  murmur,  heard  best  (a)  over  the  apex  and  super- 
ficial cardiac  area  because  there  the  ear  can  most  nearly  approach  the  left  ventricle 
without  the  interposition  of  pulmonary  tissue  or  of  the  right  ventricle  ;  (£)  in  the 
axilla,  because  it  is  transmitted  in  the  direction  of  the  arterial  blood-current ;  and  (c) 
at  the  angle  of  the  left  scapula,  or  between  the  fifth  and  eighth  thoracic  vertebrae,  for 
the  same  reason,  and  because  at  that  point  the  left  ventricle  is  posterior.      In  addi- 
tion, the  pulmonary  second  sound  is  louder  and  sharper  than  natural  (accentuated) 
because  of  the  following  series  of  occurrences  which  should  be  studied  in  connection 
with  the  structures  and  cavities   involved  :    over-filling  and  distention  of  the  left 
auricle,  imperfect  emptying  of  the  pulmonary  veins,  pulmonary  congestion  and  re- 
sistance to  the  systole  of  the  right  ventricle,  increased  fulness  of  the  pulmonary  arter- 
ies,  and  corresponding  increase  of  the    backward  pressure   upon   the   pulmonary 
valves,  shutting  them  more  sharply  and  forcibly  (accentuation). 

Furthermore,  as  the  distention  of  both  ventricles  results  in  hypertrophy,  the 
transverse  diameter  of  the  area  of  cardiac  dulness  is  distinctly  increased. 

2.  In  mitral  stenosis  (often  associated  with  some  degree  of  mitral  insufficiency) 
a  murmur  is  usually  heard,  preceding  the  pulse-beat  (presystolic), — corresponding, 
that  is,  to  the  auricular  systole,  and,  as  the  left  auricle  is  distended — from  imperfect 
emptying — and   hence  the   pulmonary  veins   and   arteries  and   the  right  heart  are 
in  the  same  condition,  there  is  again  a  loud  accentuation  of  the  second  sound. 

3.  Aortic  insufficiency  is  characterized   by  a  murmur   that   follows  the  radial 
pulse  (diastolic),  occurs  as  the  blood  is  being  driven  back  into  the  ventricle  by  the 
elastic  aorta,  is  heard  best  over  the  sternal  end  of  the  second  right  intercostal  space 
(vide  supra),  is  often  propagated  towards  the  xiphoid  cartilage  or  down  the  left  side 
of  the  sternum,  and  is  more  rarely  heard  in  the  carotid  or  axillary  vessels, — i.e.,  as 
it  is  a  murmur  primarily  due  to  the  reflux  of  blood  from  the  aorta  into  the  ventricle, 
it  is,  in  accordance  with  well-known  laws  of  physics,  transmitted  in  the  direction  of 
the  current  causing  it. 

The  great  distention  and  subsequent  hypertrophy  of  the  left  ventricle  caused  by 
its  inability  to  empty  itself  result  in  a  marked  increase  of  percussion  dulness.  As 
the  aortic  valves  do  not  come  together  normally,  the  aortic  second  sound  is  feeble  or 
absent. 

4.  Aortic  stenosis  (much  less  frequent  than  insufficiency)  is  usually  accompanied 
by  a  systolic  murmur  heard  at  the  aortic  cartilage  and  transmitted  along  the  great 
vessels  to  the  axilla,  to  the  neck,  and  along  the  spine,  but  difficult  to  distinguish  from 
similar   murmurs   caused   by  disease   of    the    inner  coat  of    the  aorta  or  by  mere 
roughening  of  the  valves.      As  the  aorta  receives  a  diminished  quantity  of  blood, 
one  factor  in  the  production  of  the  apex  beat  is  lessened  in  effectiveness  and  the 
cardiac  impulse  is  often  also  lessened.      Dilatation  and  hypertrophy  of  the  left  ven- 
tricle with   subsequent  secondary  changes  in  the  other  cavities  may  follow,  but  are 
not  nearly  so  marked  as  in  aortic  insufficiency. 

Valvular  disease  of  the  right  side  of  the  heart  may,  on  account  of  its  relative 
infrequency  and  to  avoid  repetition,  be  even  more  briefly  summarized  : 

i.  Tricuspid  insufficiency — often  following  pulmonary  conditions  obstructing  the 
circulation — is  characterized  by  (a)  a  low  systolic  murmur  heard  well  over  the 


7i2  HUMAN    ANATOMY. 

lower  sternum  on  account  of  the  relation  of  the  right  auriculo-ventricular  orifice  to 
the  middle  of  that  bone  ;  (6)  increase  of  percussion  area  to  the  right  of  the  sternum 
because  of  the  distention  and  dilatation  of  the  right  auricle  that  follow  ;  and,  (<:)  from 
the  same  cause  and  the  resultant  backward  pressure  on  the  systemic  veins,  a  venous 
pulse-wave,  seen  best  in  the  internal  and  external  jugular  on  the  right  side,  but  not 
infrequently  recognizable  on  both  sides,  in  the  subclavian  and  axillary  veins  also,  or 
as  a  systolic  expansile  impulse  in  the  liver  transmitted  through  the  inferior  cava  and 
hepatic  veins. 

2.  Tricuspid  stenosis,  like  that  of  the  mitral  valve,  is  apt  to  cause  a  presystolic 
murmur,  and  for  the  same  physical  reasons. 

3  and  4.  Pulmonary  insufficiency  and  stenosis  (disease  of  the  pulmonary  valves) 
are  so  rare  and  so  uncertain  in  their  physical  signs  as  to  require  mention  merely  to 
complete  the  survey  of  the  group. 

The  various  forms  and  degrees  of  hypertrophy  or  dilatation  of  the  heart  which 
are  associated  with  the  foregoing  conditions  can  be  readily  understood  by  con- 
sidering the  increased  resistance  and  correspondingly  increased  exertion  which  are 
brought  about  by  the  valvular  changes.  The  essential  cause  of  hypertrophy  in  the 
heart,  as  in  other  muscles,  is  increased  work.  The  etiological  factors  which  neces- 
sitate this  should  be  studied  in  connection  with  the  anatomy  of  the  heart  and  have 
been  well  summarized  by  Osier. 

Hypertrophy  of  the  left  ventricle  alone,  or  with  general  enlargement  of  the  heart, 
is  brought  about  by — 

(a)  Conditions  affecting  the  heart  itself :  (i)  Disease  of  the  aortic  valve  ;  (2) 
mitral  insufficiency  ;  (3)  pericardial  adhesions  ;  (4)  sclerotic  myocarditis  ;  (5)  dis- 
turbed innervation  with  overaction,  as  in  exophthalmic  goitre,  in  long-continued 
nervous  palpitation,  or  as  a  result  of  the  action  of  certain  articles,  such  as  tea,  alcohol, 
and  tobacco.  In  all  of  these  conditions  the  work  of  the  heart  is  increased.  In  the 
case  of  the  valve  lesions  the  increase  is  due  to  the  increased  intraventricular  pressure  ; 
in  the  case  of  the  adherent  pericardium,  or  the  myocarditis,  to  direct  interference  with 
the  symmetrical  and  orderly  contraction  of  the  chambers. 

(^),  Conditions  acting  upon  the  blood-vessels:  (i)  General  arterio-sclerosis, 
with  or  without  renal  disease  ;  (2)  all  states  of  increased  arterial  tension  induced  by 
the  contraction  of  the  smaller  arteries  under  the  influence  of  certain  toxic  substances  ; 
(3)  prolonged  muscular  exertion,  which  enormously  increases  the  blood-pressure  in 
the  arteries  ;  (4)  narrowing  of  the  aorta,  as  in  congenital  stenosis. 

Hypertrophy  of  the  right  ventricle  is  met  with  under  the  following  conditions  : 

( i )  Lesions  of  the  mitral  valve,  either  incompetence  or  stenosis,  which  act  by  in- 
creasing the  resistance  in  the  pulmonary  vessels  ;  (2)  pulmonary  lesions  with  obliter- 
ation of  any  considerable  number  of  blood-vessels  within  the  lungs,  such  as  occurs 
in  emphysema  or  cirrhosis  ;  (3)  valvular  lesions  on  the  right  side  occasionally,  and 
not  infrequently  in  the  foetus  ;  (4)  chronic  valvular  disease  of  the  left  heart  and 
pericardial  adhesions. 

In  the  auricles  simple  hypertrophy  is  never  seen  ;  it  is  always  dilatation  with 
hypertrophy.  In  the  left  auricle  the  condition  develops  in  lesions  at  the  mitral  orifice, 
particularly  stenosis.  The  right  auricle  hypertrophies  when  there  is  greatly  increased 
blood-pressure  in  the  lesser  circulation,  whether  due  to  mitral  stenosis  or  to  pulmo- 
nary lesions.  Narrowing  of  the  tricuspid  orifice  is  a  less  frequent  cause. 

Hypertrophy  or  dilatation  of  the  cardiac  chambers  may  cause  pressure,  some- 
times injurious,  on  surrounding  structures. 

Great  enlargements  of  the  left  ventricle,  as  seen  in  the  bovine  heart  of  valvular 
disease,  may  occasion  compression  of  the  lower  portion  of  the  left  lung  when  a  devi- 
ation of  the  mediastinum  towards  the  right  is  prevented.  As  a  rule,  such  enlarge- 
ment compresses  the  lower  part  of  the  left  lung  comparatively  little.  Enlargement 
of  the  right  ventricle  frequently  causes  a  depression  and  forward  displacement  of  the 
left  lobe  of  the  liver  and  the  appearance  of  a  pulsating  mass  in  the  epigastrium. 

Dilatation  of  the  auricles  is  more  likely  to  produce  serious  compression  of  sur- 
rounding structures  than  is  that  of  the  ventricles  because  of  the  greater  fixation  of  the 
heart  at  its  upper  portion  where  the  auricles  are  placed.  Enlargement  of  the  left 
auricle  has  in  some  eases  produced  compression  of  the  left  bronchus  with  consequent 


PRACTICAL   CONSIDERATIONS:    THE    HEART.  713 

collapse  of  the  lung.  Enlargement  of  the  right  auricle  seems  to  be  the  basis  of  the 
frequently  occurring  right-sided  hydrothorax  of  valvular  heart  disease.  Compression 
of  the  azygos  vein  and  perhaps  of  the  veins  and  lymphatics  at  the  root  of  the  right 
lung  by  the  enlarged  auricle  accounts  for  the  occurrence  of  one-sided  hydrothorax 
(Stengel). 

Rupt^lre  of  the  heart  is  usually  secondary  to  fatty  degeneration  of  the  cardiac 
muscles.  It  may  follow  a  complete  embolic  obstruction  of  one  of  the  branches  of 
the  coronary  arteries.  Arterio-sclerosis  with  slow  obliteration  of  one  or  both  of 
these  arteries  may  result  in  such  atrophy  of  the  myocardium  as  to  favor  rupture,  and 
this  atrophy  is  hastened  by  the  fact  that  there  is  no  direct  anastomosis  between  the 
branches  oif  these  vessels  (page  703).  With  any  of  these  predisposing  conditions 
present,  rupture  may  follow  unusual  exertion,  or  a  heavy  fall,  or  direct  violence  to 
the  precordium,  or  may  occur  spontaneously.  The  right  side  of  the  heart  is  the 
more  frequently  involved,  the  right  auricle  especially  ;  but  the  cavities  implicated,  in 
order  of  frequency,  are  the  right  auricle,  left  ventricle,  left  auricle,  right  ventricle. 
This  order  probably  results  from  the  facts  that  (a)  the  right  auricle  is  the  weakest 
part  of  the  heart ;  (3)  the  left  ventricle,  though  normally  the  strongest  part,  stands 
second  because  it  is  specially  liable  to  the  myocardial  degenerations  that  result  from 
coronary  arterio-sclerosis  ;  (c)  the  left  auricle  and  the  right  ventricle,  though  weaker 
than  the  left  ventricle,  are  less  frequently  affected  because  they  are  not  so  liable  to 
such  degeneration. 

Wound  of  the  heart  is  not  necessarily  fatal.  A  stab  wound  may  be  followed  by 
little  or  no  hemorrhage  owing  to  the  anatomical  arrangement  of  the  muscular  fibres, 
some  of  which,  whatever  the  direction  of  the  wound,  escape  division.  The  thicker 
the  cardiac  wall  at  the  site  of  the  wound  the  more  numerous  the  fibres  and  the 
more  effective  their  action  in  preventing  hemorrhage  ;  hence  wounds  of  the  auricles 
are  more  certainly  and  more  rapidly  fatal  than  wounds  of  the  ventricles,  and  wounds 
of  the  right  ventricle  are  graver  than  those  of  the  left.  Pain  and  syncopal  attacks 
are  almost  always  present.  Hemorrhage  into  the  pericardium  will  be  attended  by 
great  precordial  oppression,  there  will  be  increase  of  the  area  of  cardiac  dulness, 
and  indistinctness  or  feebleness  of  all  the  heart  sounds. 

The  anterior  surface  of  the  heart  is  most  frequently  wounded.  The  overlapping 
of  the  pleura  (page  1860)  leads  to  its  usual  involvement  in  wounds  of  the  heart  or  peri- 
cardium, except  those  that  reach  the  latter  through  those  areas  of  the  sternum  with 
which  they  are  in  direct  relation.  Accordingly,  in  most  heart  wounds  a  pleural  cavity 
— commonly  the  left — is  found  to  contain  blood.  As  the  anterior  margin  of  the  lung 
is  also  apt  to  be  involved,  except  when  the  wound  is  within  the  bounds  of  the  area 
of  cardiac  dulness,  the  blood  in  both  the  pleural  and  pericardial  cavities  may  be  frothy. 

The  right  auricle  and  ventricle  and  the  left  coronary  vessels — running  in  the 
anterior  interventricular  groove — are  most  frequently  wounded  ;  the  right  auricle  if 
the  wound  passes  through  the  inner  end  of  the  right  third,  fourth,  or  fifth  intercostal 
space  ;  the  right  ventricle  if  it  passes  through  a  corresponding  space  to  the  left  of  the 
sternum. 

As  40  per  cent,  of  the  reported  cases  operated  upon  for  heart- wounds  have 
recovered,  it  may  be  well  to  associate  the  study  of  the  normal  heart  with  that  of  the 
best  method  of  gaining  access  to  it  for  surgical  purposes. 

The  heart  should  be  exposed  by  a  flap,  the  lower  border  of  which  corresponds 
to  the  sixth  interspace,  the  inner  border  to  the  left  border  of  the  sternum,  and  the 
upper  border  to  the  third  or,  if  the  wound  is  high  up,  to  the  second  interspace. 
The  cartilages  of  the  corresponding  ribs  are  divided  and  the  flap  is  raised,  separated 
if  possible  from  the  pleura,  and  turned  outward  by  fracturing  the  ribs.  The  pleura 
is  separated  from  the  pericardium,  to  which  it  does  not  adhere  very  closely, 
beginning  towards  the  middle  line.  The  pericardium  is  then  incised  and  the  accu- 
mulated blood  evacuated,  which  is  often  a  great  relief  to  the  heart,  to  which  the  pulse 
quickly  responds.  Two  fingers  are  now  inserted  below  and  behind  the  apex  and 
the  heart  tilted  forward  and  sutured.  If  a  second  wound — that  of  exit — is  suspected, 
it  may  be  found  by  twisting  the  heart  gently  to  the  right  or  left.  The  sutures  should 
go  down  to  the  endocardium,  but  should  not  enter  the  cavities  of  the  heart.  The 
pericardium  is  then  closed,  the  pleura  replaced,  and  the  flaps  sutured  in  position.  • 


HUMAN  ANATOMY. 


The  same  incision — or  an  extension  downward  of  this  one — will  permit  of  suffi- 
cient exposure  of  the  heart  for  cardiac  massage,  a  method  of  resuscitation  in  des- 
perate cases  of  syncope  during  anaesthesia  which  has  been  recently  employed,  but 
the  value  of  which,  if  it  has  any,  cannot  now  be  estimated. 

THE    PERICARDIUM. 

The  pericardium  is  the  serous  sac  which  encloses  the  heart  and  the  proximal  por- 
tions of  the  great  vessels.  Like  other  serous  sacs,  it  consists  of  two  layers,  one  of 
which,  the  visceral  layer,  closely  invests  the  heart  and  at  its  base  becomes  continuous 
with  the  parietal  layer,  within  which  it  is  invaginated. 

The  visceral  layer,  sometimes  termed  the  epicardium,  is  an  exceedingly  thin 
membrane,  and  is  throughout  the  greater  part  of  its  extent  so  closely  adherent  to  the 
outer  surface  of  the  heart  that  any  attempt  to  detach  it  results  in  injury  to  the  super- 
ficial layers  of  the  heart  musculature.  Over  the  right  side  and  the  anterior  surface 
of  the  ventricular  portion  of  the  heart,  however,  a  certain  amount  of  fat,  even  in  thin 
persons,  occurs  between  the  muscular  tissue  and  the  epicardium. 


FIG.  675. 


Sternum 


Right  ventricle 


Pericardia  1  sac 


—  Lung 

Parietal 

pericardium 

—  Visceral 

pericardium 

—  Pleura 


-  -  Right  auriculo- 

ventricular  valve 

—  Eustachian  valve 

—  Inferior  vena  cava 


(Esophagus 
—  Vena  azygos 

—  VIII.  thoracic  vertebra 


Thoracic  aorta 


Portion  of  cross-section  of  body  at  level  of  eighth  thoracic  vertebra,  viewed  from  above, 
showing  heart  enclosed  by  pericardium. 

The  parietal  layer,  much  stronger  than  the  visceral,  forms  a  somewhat 
conical  sac,  the  base  of  which  rests  upon  and  is  attached  to  the  diaphragm,  while  its 
apex  surrounds  the  roots  of  the  aortae.  Notwithstanding  its  greater  size,  no  cavity 
exists  normally  between  this  and  the  visceral  layer,  the  two  being  in  contact 
throughout,  except  below,  where,  towards  the  periphery  of  the  base  of  the  parietal 
cone,  a  slight  space  occurs  which  is  normally  occupied  by  a  quantity  of  pericardial 
fluid  (liquor  pericardii}. 

At  the  sides,  and  to  a  considerable  extent  on  its  anterior  surface,  the  parietal 
layer  of  the  pericardium  is  united  to  or  is  in  close  contact  with  the  adjacent  pleurae. 
At  the  upper  part  of  its  anterior  surface  where  it  covers  the  aorta  it  is  free  from  such 
contact,  and  over  a  triangular  area  near  the  base  of  the  cone  the  anterior  surface 
rests  upon  the  posterior  surface  of  the  lower  part  of  the  sternum,  to  which  it  is 
united  by  sonic  loose  areolar  tissue.  Posteriorly  it  is  free  to  a  considerable  extent 
from  the  pleurae,  that  portion  of  it  which  covers  the  posterior  surface  of  the  left 
auricle  resting  upon  the  oesophagus  and  the  thoracic  aorta.  The  base  of  the  cone 
is  firmly  united  to  the  upper  surface  of  the  diaphragm  throughout  its  entire  extent, 
the  area  of  attachment  corresponding  to  the  anterior  and  a  portion  of  the  left  lobe  of 
the  central  tendon. 


THE   PERICARDIUM. 


715' 


Above,  as  has  been  stated,  the  parietal  layer  extends  upward  some  distance  upon 
the  proximal  portions  of  the  systemic  and  pulmonary  aortae  before  passing  over  into  the 
visceral  layer,  but  the  amount  to  which  the  two  vessels  are  invested  differs  considerably. 
If  the  parietal  layer  be  cut  away  along  the  line  at  which  it  becomes  continuous  with 
the  visceral  layer,  two  distinct  lines  will  be  found  indicating  its  attachments.  One  of 
these  surrounds  the  two  aortae  (Fig.  654),  which  are  united  by  connective  tissue,  and 
extends  upward  upon  the  systemic  aorta  to  a  point  a  little  below  the  origin  of  the 
innominate  artery,  a  level  which  corresponds  very  nearly  with  the  upper  border 
of  the  second  costal  cartilage;  upon  the  pulmonary  aorta  (artery)  the  line  does  no* 
rise  quite  so  high,  reaching  to  a  point  a  little  below  where  the  vessel  divides  into 
the  right  and  left  pulmonary  arteries.  The  other  line  of  attachment  is  much  more 
extensive  and  complicated  (Fig.  655).  Starting  from  its  attachment  to  the  left 

FIG.  676. 


Scalentis  anticus  muscle 


Clavicle 

R.  com.  carotid  art., cut 
Int.  mammary  arterji 

I .  costal  cartilage 


Sterno-thyroid  muscle 
Sterno-hyoid  muscle 
Sterno-cleido-mastoid  muscle 

Right  subclavian  artery 

Trachea 

I.  costal  cartilage 


Left  phrenic  nerve 


Mesial  surface  of 
right  lung 


— — *-  Diaphragm,  central  tendo 


Recti  muscles 


Anterior  thoracic  wall  has  been  partly  removed,  leaving  left  half  of  sternum  and  some 
'  ribs  in  place ;  lungs  have  been  drawn  aside  to  expose  pericardia!  sac. 

pulmonary  veins,  upon  which  it  ascends  for  a  short  distance,  it  passes  directly  across 
the  posterior  surface  of  the  left  auricle  to  the  base  of  the  right  pulmonary  veins,  and 
is  thence  continued  downward  to  surround  the  vena  cava  inferior  close  to  its  entrance 
into  the  right  auricle.  Thence  it  passes  upward  to  regain  the  right  pulmonary  veins, 
and  is  then  continued  around  the  vena  cava  superior,  upon  which  it  rises  to  a  height 
of  about  3  cm.  It  then  passes  towards  the  left  over  the  posterior  surface  of  the 
auricles  to  reach  the  starting-point  at  the  left  pulmonary  veins. 

The  existence  of  these  two  separate  lines  of  attachment  is  due  to  a  difference  in 
the  arrangement  of  the  visceral  and  parietal  layers  in  the  interval  between  the  aortoe 
and  the  anterior  surface  of  the  auricles.  The  parietal  layer  passes  directly  across 
from  the  aortae  to  the  auricles,  while  the  visceral  layer  forms  an  investment  for  the 
vessels,  extending  downward  to  their  origin  from  the  ventricles,  and  is  thence 


716  HUMAN   ANATOMY. 

reflected  upward  over  the  anterior  surface  of  the  auricles  until  it  again  meets  the 
parietal  laytfr.  There  is  thus  produced,  between  the  aortae  in  front  and  the  auricles 
behind,  a  cavity  or  cleft,  known  as  the  transverse  sinus  of  the  pericardium  (Fig.  654), 
which  is  continuous  at  either  extremity  with  the  general  pericardial  cavity,  and  is 
roofed  in  by  the  parietal  layer,  while  its  walls  and  floor  are  formed  by  the  visceral 
layer. 

In  the  roof  of  the  sinus  transversus  a  slight  fold  is  to  be  found  towards  the  left,  which 
passes  backward  to  the  line  of  attachment  of  the  roof  to  the  left  auricle  and  thence  obliquely 
downward  in  the  visceral  layer  covering  the  posterior  surface  of  the  auricle  towards  the  coro- 
nary sinus.  This  duplicature,  known  as  the  vestigial  fold  of  the  pericardium  ( ligamentum  v. 
cavae  sinistrae),  contains  in  its  upper  part  a  fibrous  cord  and  in  its  lower  part  the  oblique  vein  of 
the  left  auricle  ;  these  two  structures,  the  vein  and  fibrous  cord,  together  with  the  coronary 
sinus,  representing  the  remains  of  an  original  left  superior  vena  cava. 

It  may  be  noted  that  the  line  of  attachment  of  the  parietal  layer  between  the  left  pul- 
monary veins  and  the  inferior  vena  cava  extends  high  up  on  the  posterior  surface  of  the  auricles, 
and  there  is  thus  formed  in  this  region  a  pouch-like  diverticulum  of  the  pericardium  whose 
mouth  looks  downward.  This  is  what  has  been  termed  the  oblique  sinus  of  the  pericardium. 
Its  parietal  wall  rests  upon  the  oesophagus  posteriorly,  and  in  case  of  extensive  effusion  into  the 
pericardial  cavity,  compression  of  the  oesophagus  sufficient  to  interfere  with  the  act  of  swallow- 
ing may  result. 

The  Ligaments  of  the  Pericardium. — The  parietal  layer  of  the  pericardium 
is  united  to  the  surrounding  structures  by  areolar  tissue  which  may  condense  to  definite 
bands  termed  pericardial  ligaments.  Thus  the  tissue  between  the  pericardium  and 
the  sternum  may  condense  to  form  a  superior  and  an  inferior  pericardio-stcrnal  liga- 
ment, the  former  passing  to  the  posterior  surface  of  the  manubrium  sterni  and  the 
latter  to  the  lower  part  of  the  gladiolus.  Similarly,  bundles  of  fibres  are  attached  to 
the  apex  of  the  pericardial  cone  and  to  the  great  vessels  of  the  heart,  taking  their 
origin  from  the  prevertebral  layer  of  the  cervical  fascia  which  is  prolonged  downward 
into  the  thorax  ;  these  are  the  pericardio-vertebral  ligaments.  And,  finally,  a  band 
has  been  described  as  extending  from  the  posterior  surface  of  the  pericardium  to  the 
upper  surface  of  the  diaphragm  on  either  side  of  the  vena  cava  inferior  :  these  form 
what  are  termed  the  pericardia-phrenic  ligaments. 

The  Vessels. — The  arteries  which  supply  the  posterior  surface  of  the  parietal 
layer  of  the  pericardium  arise  from  the  thoracic  aorta,  and  those  of  the  anterior  sur- 
face are  given  off  by  the  internal  mammary  artery.  The  veins  of  the  parietal  layer 
pursue  courses  parallel  with  those  of  the  arteries,  and  open  into  the  vena  azygos 
behind  and  the  superior  phrenic  or  superior  vena  cava  anteriorly. 

The  lymphatics  pass  to  the  nodes  lying  in  the  bifurcation  of  the  trachea.  The  vas- 
cular supply  of  the  visceral  layer  is  the  same  as  that  of  the  muscular  tissue  of  the  heart. 

The  nerves  distributed  to  the  pericardium  include  fibres  from  the  phrenic  nerve, 
especially  the  left  one,  and  also  probably  from  the  cardiac  plexus. 

PRACTICAL  CONSIDERATIONS  :  THE  PERICARDIUM. 

The  visceral  layer  of  the  pericardium  is  closely  attached,  to  and  practically  insep- 
arable from  the  heart  muscle.  It  is  continuous  with  the  parietal  layer  at  the  base  of 
the  heart  where  the  two  layers  ensheathe  the  great  vessels,  covering  in  especially 
the  first  inch  and  a  half  of  the  aorta  and  pulmonary  artery  and  leaving,  between 
those  vessels  in  front  and  the  auricles  behind,  an  open  space — the  transverse  sinus — 
which  may  be  the  seat  of  an  effusion  walled  off  by  adhesions  from  the  general  peri- 
cardial cavity.  The  least  resistant  important  structure  in  immediate  relation  to  this 
sinus  is  the  superior  vena  cava, — also  intrapericardial  at  its  lowermost  portion,- — and 
such  effusion  might  therefore  cause  fulness  of  the  veins  of  the  neck  or  even  cyanosis 
without  the  evidence  of  a  general  pericardial  dropsy  large  enough  to  give  the  usual 
concomitant  physical  >i^ns  (videinfnti).  In  artificial  distention  of  the  pericardium 
the  sac  tends  to  assume  the  shape  of  two  irregular  spheres,  the  upper  or  smaller  one 
containing  the  great  vessels  just  mentioned,  the  lower  embracing  the  heart,  the 
ascending  cava,  and  the  pulmonary  veins.  At  the  apex  of  the  In-art,  where  the  peri- 
cardium is  reflected  from  the  diaphragm,  unimportant  sinuses,  analogous  to  the 
costo-phrenic  sinus  of  the  pleura,  may  exist. 


PRACTICAL  CONSIDERATIONS:    PERICARDIUM.  717 

The  parietal  layer  of  the  pericardium  is  in  relation  with  an  external  fibrous  layer 
which  extends  beyond  the  serous  investment  of  the  roots  of  the  great  vessels,  blends 
with  their  outer  coats,  and  is  directly  continuous  with  the  deep  cervical  fascia,  thus 
connecting'  the  pericardium  with  two  respiratory  agents,  the  diaphragm  below  and 
the  cervical  muscles  (omo-hyoid)  above.  When  these  act  conjointly,  as  in  a  full 
inspiration,  they  render  the  pericardium  tense  and  resisting,  and  minimize  the  pressure 
upon  the  heart  by  the  inflated  lungs  (page  551). 

Pericarditis — probably  more  often  overlooked  than  any  other  serious  disease 
(Osier) — may  arise  from  wound  from  without,  as  in  ordinary  penetrating  wounds 
of  the  chest,  or  from  within,  as  from  the  passage  of  a  foreign  body  from  the  oesoph- 
agus into  the  pericardium  (page  1614);  or  it  may  follow  extension  of  disease  from 
contiguous  organs,  as  in  pleuro-pneumonia.  The  anatomical  relations  of  the  peri- 
cardium explain  these  occurrences.  The  more  usual  causes,  as  rheumatism,  septi- 
caemia, gout,  and  nephritis,  have  no  anatomical  bearing. 

Pericarditis  is  attended  by  certain  symptoms — well  detailed  by  Sibson — which 
should  be  studied  in  connection  with  the  anatomy  of  the  heart  and  pericardium. 

I.  Pain — (a)  spontaneous  and  directly  over  the  heart,  the  pleurae  often  being 
involved,  both  these  serous  membranes — like  the  peritoneum — becoming  painful 
when  inflamed,  although  normally  insensitive  ;  (&)  elicited  by  pressure  (tenderness), 
the  skin  over  the  precordium  sometimes  participating  on  account  of  the  connection 
between  the  upper  intercostal  nerves  and  the  ganglia  and  nerves  of  the  cardiac  plexus  ; 
(c*)  over  the  epigastric  region  and  increased  by  pressure,  because,  although  normally 
the  pericardium  below  is  in  direct  relation  with  the  thoracic  parietes  over  only  a  small 
area  behind  the  xiphoid  cartilage,  distention  'of  the  pericardial  sac,  as  in  effusion 
from  pericarditis,  carries  it  downward  so  that  it  may  be  well  below  the  tip  of  the 
xiphoid  ;  (d  )  between  the  scapulae  or  deep  in  the  chest,  increased  by  swallowing  or 
by  eructations,  and  worse  when  the  patient  is  supine,  due  to  the  relation  between  the 
oesophagus  and  pericardium  just  below  the  aortic  arch  ;  (e)  in  the  side,  usually 
pleuritic  (from  extension),  and  more  common  on  the  left  side  on  account  of  the 
greater  extent  to  which  the  inflamed  pericardium  occupies  the  left  side  of  the  chest 
than  the  right  side,  to  the  marked  backward  displacement  of  the  lower  lobe  of  the 
left  lung  by  the  distended  pericardial  sac,  and  possibly  (Sibson)  to  the  pressure 
of  the  latter  on  the  left  bronchus  increasing  in  the  left  lung  the  tendency  to  intercur- 
rent  pneumonia.  2.  Feeble  or  irregular  heart  action,  due  to  («)  direct  extension 
of  the  inflammation  from  the  visceral  layer  of  the  pericardium  to  the  heart  muscle 
(myocarditis);  (£)  implication  of  the  cardiac  nerves  ;  (<:)  pressure  by  the  pericardial 
effusion  on  the  venae  cavae  and  pulmonary  veins,  impeding  the  blood-supply  to  both 
auricles  ;  direct  pressure  upon  the  auricles  interfering  with  the  ventricular  supply  ;  and 
pressure  upon  the  whole  organ  both  directly  from  the  effusion  and  indirectly  from 
the  compressed  and  displaced  lungs  and  the  other  contiguous  structures,  embarrass- 
ing its  action,  especially  in  diastole.  3.  Dyspnoea,  due  to  the  pulmonary  congestion 
produced  by  the  previous  causes  ;  sometimes  the  result  of  a  pleurisy  or  pleuro- 
pneumonia  by  extension  ;  or  perhaps,  as  Hilton  has  suggested,  partly  from  fixation 
or  irregular  action  of  the  diaphragm  through  irritation  of  the  pericardiac  filament 
of  the  phrenic  (ramus  pericardiacus),  usually  given  off  on  the  right  side.  4.  Dys- 
phagia  (page  1614)  from  compression  of  the  oesophagus  between  the  pericardium 
and  the  vertebral  column,  usually  relieved  when  the  patient  is  put  in  an  approximately 
vertical  position.  5.  Aphonia,  from  involvement  of  the  left  recurrent  laryngeal 
nerve  by  contiguity,  or  of  both  nerves  through  their  cardiac  branches.  6.  Fulness 
of  the  cervical  veins  and  flushing  or  cyanosis  of  the  face,  due  to  pressure  upon  the 
thin  walls  of  the  right  auricle  and  of  the  superior  vena  cava.  Compression  of  the 
left  auricle  is  better  resisted  on  account  of  the  greater  thickness  of  its  walls  ;  when 
it  occurs,  it  tends  to  produce  pulmonary  congestion  or  apoplexy. 

The  physical  signs  of  pericarditis  are,  of  course,  influenced  by  the  attachment, 
surroundings,  and  physical  qualities  of  the  pericardium. 

i .  As  it  is  in  two  layers  normally  movable  upon  each  other,  the  roughening  caused 
by  inflammation  produces  a  friction-sound  which,  when  typical,  is  (a)  heard  best  over 
the  middle  and  the  lower  half  of  the  sternum,  and  over  the  adjoining  left  costal 
cartilages  or  their  interspaces,  because  there  a  greater  extent  of  the  pericardium  is 


yi8  HUMAN   ANATOMY. 

closer  to  the  ear,  with  fewer  intervening  structures  than  elsewhere  ;  (<£)  preceded  or 
accompanied  by  pain  (vide  supra}',  (c)-  usually  increased  by  pressure  with  the  stetho- 
scope, which  brings  the  two  roughened  pericardial  layers  into  closer  apposition  ;  (d) 
accompanied  by  an  extension  of  the  area  of  cardiac  dulness  (vide  infra);  (e)  is 
double, — that  is,  corresponding,  although  not  altogether  synchronously,  to  both 
systole  and  diastole  ;  and  (/")  may  disappear  when  effusion  occurs, — separating  the 
two  layers, — or  may  persist  over  a  small  area  near  either  the  diaphragmatic  attach- 
ment or  the  pericardial  reflection  at  the  base. 

2.  As  the  pericardium  is  markedly  elastic,  when  effusion  takes  place  the  parietal 
layer  may  stretch  so  that  the  pericardial  cavity  may  hold  ten  or  twelve  ounces  instead 
of  a  few  grammes,  or  in  chronic  cases  may  contain  several  pints.      As  its  cavity  is  in  the 
shape  of  that  of  a  hollow  cone  or  pear,  the  apex  corresponding  to  the  fixed  portion  of 
the  heart — held  in  place  by  the  great  vessels — and  the  base — enlarged  to  permit  the 
considerable  degree  of  motion  of  the  heart's  apex — to  the  upper  surface  of  the  dia- 
phragm, pericardial  effusions  also  take  this  general  shape,  and  the  area  of  percussion- 
dulness  will   be   found   to    have  its  base — about  on  a  level  with  the  fifth  or  sixth 
interspace — inferior,  and  its  apex — about  on  a  level  with  the  second  interspace — 
directed  upward  towards  the  first  segment  of  the  sternum.      It  is  more  marked  to  the 
left  of  the  sternum  on  account  of  the  larger  area  of  heart  and  pericardium  on  that 
side,  but  may  be  found  to  the  right  of  the  sternum,  especially  about  the  fifth  intercostal 
space  (Rotch),  because  on  the  right  side  (owing  to  the  presence  of  the  right  lobe  of 
the  liver)  the  lower  border  of  the  distended  sac  is  somewhat  higher  than  on  the  left. 

3.  As  such  enlargement  must  affect  the  contiguous  organs  and  the  overlying 
parietes,   there  will  be  found  in  full  distention  :   (a)  prominence  of  the  intercostal 
spaces,  especially  on  the  left  side,  or  of  the  left  antero-lateral  thoracic  walls,  of  the 
epigastrium  (from  depression  of  the  diaphragm  and  left  lobe  of  the  liver),  of  the 
lower  two-thirds  of  the  sternum,  or,  in  children  with  yielding  thoracic  walls,  of  the 
whole  precordia  ;   (£)  compression  of  the  left  lung,  sometimes  causing  a  tympanitic 
percussion-note  in  the  left  axillary  region  ;   (c)  compression,  between  the  relatively 
unyielding  sternum  and  the  dorsal  spine,  of  the  trachea  and  left  bronchus  (irritative 
cough),  the  oesophagus  (dysphagia),  and  the  aorta  (affecting  the  systemic  blood- 
supply);  (</)  a  backward  curve  of  the  dorsal  spine  has  been  described  (Sibson)  as 
resulting  from  the  necessity  of  limiting  pressure  on  these  important  structures  ;  (<?) 
compression  or  irritation  of  the  recurrent  laryngeal  nerve  (aphonia)  and  the  superior 
vena  cava  (venous  engorgement  of  neck  and  face)  have  been  noted  (vide  supra). 

4.  The  upward  displacement  of  the  heart  itself,  due  to  (a)  its  attachments  to 
the  great  vessels  fixing  its  upper  portion  ;  and  (b)  the  effect  of  gravity  upon  the 
effusion  which  distends  the  lower  part  of  the  sac,  separates  to  an  extent  the  chest- 
walls  and  the  inferior  portion  of  the  right  ventricle,  and  occupying  the  space  between 
the  lower  surface  of  the  heart  and  the  tendinous  centre  of  the  diaphragm,  forces  the 
former  organ  into  the  upper  part  of  the  pericardial  sac,  causes  a  corresponding 
alteration  in  the  cardiac  impulse,  which  is  diminished  or  obliterated,  and  a  change  in 
the  position  of  the  apex  beat,  which  may  be  found  at  the  third  or  fourth  interspace 
instead  of  at  the  fifth  ;  as  the  upper  portion  of  the  chest  is  the  narrower,  and  as  the 
left  lung  has  been  pushed  aside  by  the  distended  sac,  the  apex  beat  may  also  be 
found  much  nearer  a  vertical  line  drawn  through  the  nipple  than  is  normally  the  case. 

Either  paracentesis  pericardii  or  incision  of  the  pericardium  for  the  purpose  of 
tapping  or  of  draining  the  sac  in  cases  of  purulent  effusion  may  be  done  in  the  fifth 
or  sixth  intercostal  space  on  the  left  side  about  one  inch  from  the  sternum.  The 
internal  mammary  artery  descends  vertically  about  a  half  inch  from  the  margin  of 
the  sternum.  The  pleura  is  often  pushed  by  the  distended  sac  beyond  the  point 
mentioned.  If  not,  the  trocar  would  penetrate  its  two  layers  if  inserted  one  inch  from 
the  sternal  border.  In  the  sixth  interspace  there  is  somewhat  less  danger  of  wound- 
ing the  heart.  Incision  close  to  the  edge  of  the  sternum  will  usually  avoid  both  of 
these  risks.  Incision  or  puncture  in  the  fifth  space  on  the  right  side  has  been  ad- 
vised as  minimi/ing  the  danger  to  the  heart.  Deguy  (quoted  by  Treves)  advises  sub- 
periosteal  resection  of  the  xiphoid  cartilage  by  a  median  incision,  downward  detach- 
ment of  the  diaphragmatic  muscle-fibres,  and  dissection  through  the  loose  cellular 
tissue  to  the  pericardium,  which  is  seized,  drawn  down  and  forward,  and  incised. 


THE   ARTERIES.  719 

» 

THE   GENERAL    PLAN   OF   THE   CIRCULATION. 

The  blood  which  enters  the  right  auricle  of  the  heart  by  way  of  the  superior  and 
inferior  venae  cavae  and  the  coronary  sinus  is  blood  which  has  come  from  the  tissues, 
to  which  it  has  delivered  the  oxygen  and  nutritive  material  and  from  which  it  has  re- 
ceived carbon  dioxide  and  other  waste  products.  From  the  right  auricle  this  blood 
passes  through  the  right  auriculo-ventricular  orifice  into  the  right  ventricle,  and  on 
the  contraction  of  this,  which  follows  immediately  upon  the  contraction  of  the  auricle, 
it  is  forced  into  the  pulmonary  aorta  (pulmonary  artery),  the  tricuspid  valve  pre- 
venting regurgitation  into  the  auricle.  Upon  the  completion  of  the  contraction  of  the 
ventricle,  the  blood  which  has  been  forced  into  the  pulmonary  aorta  and  is  distend- 
ing its  walls  forces  together  the  pulmonary  semilunar  valves  and,  consequently,  by  the 
contraction  of  the  walls  of  the  vessel  and  by  subsequent  contractions  of  the  ventricle, 
sending  new  blood  into  the  vessel,  is  forced  onward  towards  the  lungs.  In  the  sub- 
stance of  these  organs  the  pulmonary  vessels  divide  repeatedly,  and  finally  form  a 
dense  net-work  of  capillaries,  through  the  walls  of  which  an  interchange  of  gases  be- 
tween the  blood  and  the  air  contained  in  the  cavities  of  the  lungs  takes  place.  From 
the  pulmonary  capillaries  the  pulmonary  veins  arise  and  carry  the  purified  blood  back 
to  the  heart,  emptying  it  into  the  left  auricle. 

In  this  course  the  blood  has  passed  from  the  heart  through  a  set  of  capillaries 
back  to  the  heart,  and  in  one  sense  it  has  completed  a  circuit,  which  is  termed  the  minor 
or  pulmonary  circulation.  In  reality,  however,  it  is  not  a  perfect  circuit,  since,  while 
beginning  in  the  right  side  of  the  heart,  it  terminates  in  the  left  side.  In  order  to 
reach  again  the  right  side,  it  is  necessary  for  it  to  pass  through  the  major  or  systemic 
circulation,  the  general  course  of  which  is  as  follows. 

From  the  left  auricle  the  blood  passes  through  the  left  auriculo-ventricular  orifice 
into  the  left  ventricle,  and  by  the  contraction  of  this  is  forced  into  the  systemic  aorta, 
or,  as  it  is  more  frequently  termed,  the  aorta,  the  bicuspid  valve  preventing  its  pas- 
sage back  into  the  auricle.  The  aorta  curves  backward  and  to  the  left  and  passes 
down  the  body  lying  upon  the  left  side  of  the  vertebral  column,  and  in  its  course 
gives  off  branches  which  distribute  the  blood  to  all  parts  of  the  body.  In  the  vari- 
ous organs  these  branches  break  up  into  a  net-work  of  capillaries,  from  which  veins 
lead  the  blood  into  either  the  superior  or  the  inferior  vena  cava  or  into  the  coronary 
sinus,  from  which  it  passes  to  the  right  auricle. 

In  the  systemic,  as  in  the  pulmonary  circulation,  the  blood  passes  from  the  heart, 
through  one  set  of  capillaries,  and  back  to  the  heart.  In  the  case  of  the  blood  which 
traverses  the  vessels  passing  to  the  stomach,  the  intestines  (with  the  exception  of 
the  lower  portion  of  the  rectum),  the  pancreas,  and  the  spleen,  however,  a  modifi- 
cation of  this  arrangement  occurs,  in  that  before  returning  to  the  heart  the  blood 
is  required  to  pass  through  two  sets  of  capillaries.  The  first  set  is  in  the  substance  of 
the  organs  named,  and  after  passing  through  this  the  blood  is  collected  into  a  vein, 
the  vena  porta,  which  conveys  it  to  the  liver.  Here  the  portal  vein  breaks  up  into 
the  second  set  of  capillaries,  through  which  the  blood  passes  to  the  hepatic  veins, 
which  open  into  the  vena  cava  inferior,  and  thus  return  the  blood  to  the  right 
auricle.  This  portion  of  the  major  circuit  forms  what  is  termed  tine  portal  circulation. 

THE  ARTERIES. 

The  arteries  are  those  vessels  which  conduct  the  blood  away  from  the  heart. 
Since  the  blood  is  forced  into  the  arteries  under  considerable  pressure  by  the  con- 
traction of  the  ventricles,  it  is  necessary  that  the  walls  of  these  vessels  should  be  suffi- 
ciently strong  to  withstand  pressure,  and  at  the  same  time  elastic  so  as  to  yield  to 
each  successive  injection  of  blood  from  the  heart  and  to  return  to  the  normal  calibre 
when  the  wave  has  passed.  As  the  blood  courses  from  the  main  vessels  to  the  capil- 
laries, it  passes  through  channels  of  progressively  decreasing  calibre,  and  is,  there- 
fore, constantly  encountering  increased  resistance,  whereby  the  arterial  pressure  is 
diminished,  until  finally,  when  the  capillaries  are  reached,  the  pressure  is  practically 
nothing.  As  the  pressure  is  reduced,  the  thickness  of  the  arterial  walls  diminishes, 


720  HUMAN   ANATOMY. 

so  that,  as  a  rule,  it  may  be  stated  that  the  thickness  of  the  wall  of  an  artery  is 
directly  proportional  to  the  calibre  of  the  vessel.  Exceptions  to  the  rule  exist,  how- 
ever, and  the  thickness  of  the  wall  is  not  necessarily  the  same  in  vessels  of  identical 
calibre. 

Another  general  rule,  to  which  there  are  also  exceptions,  is  to  the  effect  that  the 
calibre  of  an  artery  is  proportional  to  the  extent  of  territory  which  it  supplies.  At 
each  point  where  a  branch  is  given  off  from  an  artery  a  diminution  of  the  calibre 
occurs,  but  throughout  the  interval  between  successive  branches  the  size  of  the  vessel 
usually  remains  unchanged.  Where,  however,  a  marked  alteration  in  the  direction 
of  an  artery  occurs,  its  diameter  undergoes  a  slight  diminution,  but  is  re-established, 
or,  indeed,  increased  for  a  short  distance,  so  soon  as  the  change  of  direction  is 
accomplished.  These  constrictions,  which  are  especially  noticeable  in  large  arteries, 
such  as  the  aortic  arch  or  the  subclavian,  are  termed  arterial  isthmuses,  and  the 
enlargements  which  succeed  are  known  as  arterial  spindles. 

The  area  of  the  transverse  section  of  a  left  subclavian  artery  before  any  branches  were  given 
off  was  found  to  be  27.6  sq.  mm.,  that  of  a  section  of  the  isthmus  was  15.6  sq.  mm.,  while  that 
of  a  section  taken  about  2  cm.  beyond  the  isthmus  was  20  sq.  mm.  In  the  case  of  an  aorta  in 
which  the  spindle  was  well  marked,  the  area  of  a  transverse  section  of  the  isthmus  was  found  to 
be  46  sq.  mm.,  that  of  a  section  through  the  spindle  was  65  sq.  mm.,  and  that  of  a  section  of  the 
thoracic  aorta  a  little  below  the  spindle  was  again  46  sq.  mm.  (Stahel). 

THE  GENERAL  PLAN  OF  THE  ARTERIAL  SYSTEM. 

An  idea  of  the  general  plan  of  the  arterial  system  may  be  most  readily  obtained 
by  reference  to  the  arrangement  occurring  in  the  fishes  (Fig.  677),  in  which  respira- 
tion is  performed  by  gills  borne  upon  a  series  of  branchial  bars  which  form  the 
lateral  walls  of  the  pharynx.  In  these  forms  the  heart  consists  of  but  two  cham- 
bers, an  atrium  which  receives  the  great  veins  and  a  ventricle  from  which  a  single 
aortic  trunk,  the  truncus  arteriosus,  arises.  The  heart  contains  only  venous  blood, 
and  its  function  is  to  drive  the  blood  through  the  gills,  where  it  becomes  oxygen- 
ated, and  whence  it  passes  to  the  various  organs  of  the  body.  The  heart  is  situated 
far  forward,  beneath  the  posterior  portion  of  the  pharynx,  and  the  aorta  passes  forward 
from  it  along  the  floor  of  the  pharynx,  sometimes  dividing  early  into  two  parallel 
stems,  the  ventral  aortce.  From  these,  and  from  the  aorta  before  its  division, 
branches  pass  off  to  each  of  the  gill-arches  and,  breaking  up  into  capillaries,  traverse 
the  gill-filaments  borne  by  the  arches.  After  being  oxygenated  in  the  gill-filaments, 
the  blood  from  each  gill  is  collected  again  into  a  stem  which  joins  with  those  coming 
from  the  other  gills  of  the  same  side  of  the  body  to  form  a  longitudinal  trunk  situated 
on  the  roof  of  the  pharynx,  and  this  trunk,  passing  backward,  unites  with  its  fellow 
of  the  opposite  side  to  form  a  dorsal  aorta,  which  is  continued  throughout  the  entire 
length  of  the  body  immediately  beneath  the  vertebral  column. 

From  the  forward  part  of  each  of  the  dorsal  longitudinal  stems  branches  arc 
continued  forward  into  the  head  region,  and  throughout  the  entire  trunk  region  the 
dorsal  aorta  gives  off  laterally  paired  branches  corresponding  to  each  of  the  seg- 
ments of  the  trunk,  and  from  its  ventral  surface  one  or  two  series  of  visceral  branches 
which  are  also  arranged  segmentally. 

At  one  stage  in  the  development  of  the  human  embryo  the  arrangement  of  the 
arterial  system  is  essentially  the  same  as  that  which  has  just  been  described,  except 
that,  since  there  are  no  longer  any  gill-filaments,  the  capillaries  of  the  branchial 
vessels  are  lacking.  By  a  series  of  important  changes,  later  to  be  described  (page 
846),  this  arrangement  is  converted  into  that  found  in  the  adult,  the  relation  between 
the  human  arrangement  and  that  occurring  in  the  fishes  being  shown  by  a  comparison 
of  the  preceding  diagram  with  Fig.  678.  It  will  be  seen  that  the  fourth  branchial 
arch  of  the  left  side  is  represented  by  the  arch  of  the  aorta,  the  anterior  portion 
of  the  dorsal  aorta  becomes  what  is  termed  the  internal  carotid  artery,  the  forward 
prolongation  of  the  ventral  aorta  becomes  the  external  carotid  artery,  and  the  con- 
necting link  between  these  two  vessels  represents  the  third  branchial  vessel.  And, 
finally,  the  last  pair  of  branchial  vessels  is  represented  by  the  pulmonary  arteries. 

While  the  arteries  have  their  primary  embryonic  arrangement,  the  heart  lies  far 
forward  beneath  the  posterior  portion  of  the  pharynx.  Later,  however,  it  undergoes 


GENERAL    PLAN   OF   THE   ARTERIAL   SYSTEM. 


721 


a  regression  whereby  it  becomes  situated  in  the  thorax,  and  in  this  migration  it 
carries  backward  (downward)  with  it  the  pulmonary  arteries  and  the  arch  of  the 
aorta  and  produces  an  elongation  of  the  carotids.  As  a  result  of  the  regression  of 
the  aortic  arch,  the  lateral  branches  which  arose  from  the  anterior  portions  of  the 
dorsal  aorta  and  were  distributed  to  the  cervical  segments  of  the  body  become  sepa- 


Segmental 
Dorsal  aorta       arteries 


FIG.  677. 
Dorsal  aortic  trunks 


Gill-cleft 


Head  arteries 

~ 


Heart 


Head  arteries 
Third  aortic  (gill)  bow 


Diagram  showing  fundamental  arrangement  of  arteries  in  fish,  supposed  to  be  viewed 
from  the  side  and  above;  shaded  tube  represents  digestive  canal  with  its  gill-clefts  in  front 
surrounded  by  series  of  six  aortic  bows  and  behind  by  segmental  arteries. 

rated  from  their  origins  as  far  down  as  the  branch  to  the  seventh  cervical  segment, 
which  becomes  the  adult  subclavian  artery,  but  having  developed  anastomoses  with 
one  another,  so  that  a  longitudinal  stem,  running  parallel  with  the  internal  carotid 
and  attached  below  to  the  subclavian,  is  formed,  they  appear  in  the  adult  as  lateral 
branches  of  that  stem  which  is  termed  the  vertebral  artery.  Primarily  there  are  no 
longitudinal  arteries  in  the  body,  with  the  exception  of  the  carotids  and  the  dorsal 
aorta  ;  but  just  as  the  vertebral  artery  is  formed  in  the  neck  by  the  anastomosis  of 
upwardly  and  downwardly  directed  branches  from  lateral  vessels,  so,  too,  in  other 
regions,  such  as  the  thoracic  and  abdominal  walls,  other  longitudinal  stems  are 
secondarily  developed. 

The  dorsal  aorta  throughout  its  course  gives  off  with  almost  segmental  regular- 
ity lateral  branches  to  the  body-walls  which  form  the  intercostal  and  lumbar  arteries, 
the  fifth  lumbar  branches  becoming  greatly  enlarged  to  supply  the  lower  limb,  and 
being  termed  the  iliac  arteries.  Below  the  origin  of  these  the  aorta  is  represented 
only  by  a  comparatively  slender  vessel,  the  middle  sacral  artery,  which  is  continued 
to  the  tip  of  the  coccyx,  giving  off  lateral  branches  with  a  more  or  less  distinct  seg- 
mental arrangement.  The  visceral  branches  which  arise  from  the  aorta  do  not  retain 
their  original  segmental  arrangement  as  perfectly  as  do  the  branches  to  the  body- 
walls,  but  fuse  to  a  very  considerable  extent,  especially  in  the  abdomen,  to  form  a 
small  number  of  vessels  which  ramify  to  the  various  portions  of  the  digestive  tract 
and  to  the  genito-urinary  abdominal  organs. 

FIG.  678. 


Aortic  arch 


Left  subclavian 
Aorta 


Dorsal  aortae 


Right 
subclavian 

Pulmonary  artery 


Ascending  aorta 


Internal  carotids 

Oropharynx 
External  carotids 


Ventral  aortae 


Diagram  showing  derivation  of  arteries  in  man  by  modifications  in  preceding  plan  ; 
left  fourth  aortic  bow  becomes  aortic  arch. 

It  will  be  seen,  therefore,  that  the  arterial  system  consists  of  two  fundamental 
portions,  a  branchial  and  a  dorsal  aortic  portion.  A  classification  of  the  vessels  of 
the  adult  according  to  such  a  plan  would,  however,  result  in  considerable  confusion, 
since,  owing  to  the  secondary  modifications  which  have  occurred,  it  would  necessi- 
tate the  separation  into  different  groups  of  arteries  which  are  closely  related,  and, 

46 


722 


HUMAN   ANATOMY. 


conversely,  would  associate  quite  distinct  vessels.  It  will  be  more  convenient,  there- 
fore, to  employ  a  topographic  classification,  according  to  which  two  main  subdivi- 
sions of  the  system — that  of  \hz' pulmonary  aorta  and  that  of  the  systemic  aorta — may 
be  recognized,  the  systemic  subdivision  being  again  divided  into  the  aortic  arch,  the 
thoracic,  and  the  abdominal  portions. 

THE   PULMONARY   AORTA. 

The  pulmonary  aorta,  most  frequently  termed  the  pulmonary  artery  (a.  pul- 
monalis)  takes  its  origin  from  the  summit  of  the  conus  arteriosus  of  the  right 
ventricle.  It  is  from  4.5-5  cm.  (about  2  in.)  in  length,  and  is  directed  upward, 
backward,  and  slightly  towards  the  left,  and  beneath  the  arch  of  the  aorta  it  divides 
into  the  right  and  left  pulmonary  arteries  (Fig.  679). 

FIG.  679. 


Right  innominate  vein 


I-eft  common  carotid  artery 

/  —  I-eft  subclavian  artery 


Left  pulmonary  artery 


Pulmonary  vein 


Inferior 
pulmonary  vein 


Stump  of  superior  cava 
light  auricular  appendage' 

Aorta,  systemic 
Left  coronary  artery 
Right  coronary  vessels 


Conus  arteriosus 
Jnterventricular  branches 
of  left  coronary  vessels 


Right  ventricle 


Injected  heart  and  great  vessels,  viewed  from  before ;  part  of  superior  vena  cava  and  aorta 
have  been  removed  to  show  right  pulmonary  artery. 

Relations. — Throughout  the  greater  portion  of  its  k-ngth  tlu-  pulmonary  aorta 
is  invested  by  that  part  of  the  visceral  layer  of  the  pericardium  which  surrounds  it 
and  the  basal  portion  of  the  systemic  aorta.  At  its  origin  it  is  partly  overlapped  in 
front  by  the  tip  of  the  right  auricular  appendix,  and  posteriorly  it  is  in  relation  with 
the  base  of  the  systemic  aorta  and  the  proximal  portion  of  the  right  coronary  artery. 
More  distally  it  lies  to  the  left  of  the  systemic  aorta  and  rests  upon  the  anterior  sur- 
face of  the  left  auricle. 

Branches. — The  right  pulmonary  artery  (ramiis  dexter1)  has  an  almost  transverse  course 
from  its  origin  towards  the  base  of  the  right  lung.  It  passes  outward  above  the  right  auricle, 
behind  the  ascending  portion  of  the  systemic  aorta  and  tin-  superior  vt-na  cava  and  in  front  of 
the  right  bronchus.  At  the  root  of  the  lung  it  divides  into  three  branches  which  are  distributed 
to  the  three  lobes  of  the  lung. 

The  left  pulmonary  artery  (ramus  sinister)  is  somewhat  shorter  than  the  right,  and  passes 
outward  in  front  of  the  descending  portion  of  the  aortic  arch  and  the  left  bronchus  to  the  root 


THE   AORTIC   ARCH.  723 

of  the  left  lung,  where  it  divides  into  two  branches  to  be  distributed  to  the  lobes  of  the  lung. 
From  the  upper  border  of  the  artery  a  short  cylindrical  cord  passes  to  the  under  surface  of  the 
transverse  portion  of  the  aortic  arch,  a  little  beyond  the  point  at  which  the  left  subclavian  artery 
arises  from  its  upper  convex  surface.  This  cord  is  the  remains  of  a  communication  between 
the  pulmonary  and  systemic  aortas  which  exists  in  fcetal  life,  when  the  lungs  are  not  functional, 
and  is  termed  the  ductus  arteriosus.  It  represents  the  outer  portion  of  the  vessel  of  the  sixth 
branchial  arch  of  the  left  side,  and  its  lumen  usually  becomes  occluded  during  the  first  few 
months  after  birth,  so  that,  as  a  rule,  the  cord  is  solid  in  the  adult. 

Variations. — The  majority  of  the  variations  that  have  been  observed  in  the  pulmonary 
aorta  are  associated  with  serious  malformations  of  the  heart  which  usually  result  in  early  death, 
and  are  consequently  to  be  classed  as  pathological  rather  than  as  merely  anomalous  conditions. 
A  precocious  division  of  the  main  stem  of  the  pulmonary  aorta  occasionally  occurs,  absence  of 
the  right  pulmonary  artery  has  been  observed,  and  an  accessory  coronary  artery  has  been  noted 
arising  from  the  pulmonary  aorta. 

Failure  of  the  ductus  arteriosus  to  undergo  complete  occlusion  is  a  not  infrequent  occur- 
rence, and  is  often  associated  with  a  persistence  of  the  foramen  ovale.  The  ductus  has  also 
been  observed  to  arise  directly  from  the  right  ventricle. 

THE   SYSTEMIC   AORTA. 

The  systemic  aorta,  or,  as  it  is  more  commonly  and  more  simply  termed,  the 
aorta,  is  the  main  arterial  stem  for  the  supply  of  the  tissues  of  the  body.  It  arises 
from  the  base  of  the  left  ventricle  and  curves  in  an  arch-like  manner  to  the  left  side  of 
the  vertebral  column,  along  which  it  runs  to  the  level  of  the  fourth  lumbar  vertebra. 
There  it  gives  off  a  pair  of  large  common  iliac  arteries,  and  is  continued  onward,  much 
reduced  in  size,  along  the  ventral  surface  of  the  sacrum  and  coccyx,  being  termed  in 
this  portion  of  its  course  the  middle  sacral  artery. 

It  may  be  regarded,  for  the  purpose  of  description,  as  being  composed  of  three 
portions  :  (i)  the  aortic  arch,  which  extends  from  the  heart  to  the  left  side  of  the 
body  of  the  fourth  thoracic  vertebra  ;  (2)  the  thoracic  aorta,  extending  from  the 
lower  end  of  the  aortic  arch  to  the  diaphragm  ;  and  (3)  the  abdominal  aorta,  extend- 
ing from  the  diaphragm  to  the  fourth  lumbar  vertebra.  The  middle  sacral  artery 
may  most  conveniently  be  treated  as  a  branch  of  the  abdominal  aorta. 

THE   AORTIC    ARCH. 

The  aortic  arch  arises  from  the  base  of  the  left  ventricle  (Figs.  679,  690),  and 
in  the  first  or  ascending  portion  (aorta  ascendens)  of  its  course  is  directed  upward  and 
somewhat  forward  and  to  the  right.  It  then  curves  to  the  left  and  backward  as  the 
transverse  portion  (arcus  aortae),  and  finally  bends  downward  as  the  descending 
portion  along  the  left  side  of  the  body  of  the  fourth  thoracic  vertebra,  to  become 
continuous  with  the  thoracic  aorta. 

At  its  origin  the  aortic  arch  presents  three  rounded  swellings,  one  anterior  and  the 
other  two  postero-lateral,  marking  the  position  of  the  sinuses  of  Valsalva  (sinus  aortae). 
The  diameter  of  the  ascending  portion  is  about  2. 7  cm.  and  that  of  the  descending 
portion  about  2  cm. ,  the  diminution  appearing  rather  suddenly  below  the  origin  of 
the  left  subclavian  artery  and  forming  what  has  been  termed  the  aortic  isthmus. 
Where  the  ascending  portion  passes  over  into  the  transverse  an  enlargement  of  the 
diameter  occurs  which  is  especially  well  marked  in  older  individuals,  and  is  presuma- 
bly due  to  the  impact  of  the  blood  forced  out  of  the  ventricle  by  its  contractions. 

At  about  the  junction  of  its  transverse  and  descending  portions  the  arch  has 
attached  to  its  under  surface  the  fibrous  cord  which  represents  the  fcetal  ductus 
arteriosus. 

Relations. — The  ascending  portion  of  the  arch  is  enclosed  throughout 
almost  its  entire  length  (about  5  cm. ,  or  2  in. )  in  the  sheath,  formed  by  the  visceral 
layer  of  the  pericardium,  which  it  shares  with  the  pulmonary  aorta.  At  its  origin 
it  lies  behind  and  somewhat  to  the  left  of  that  vessel,  but  higher  up  crosses  it 
obliquely,  so  that  it  comes  to  lie  upon  its  right  side  ;  to  the  right  and  left  it  is  in 
relation  with  the  corresponding  auricles,  and  anteriorly  its  upper  portion  is  separ- 
ated from  contact  with  the  sternum  by  a  more  or  less  abundant  fatty  tissue  in  which 
are  the  remains  of  the  thymus  gland.  Posteriorly  it  is  in  relation  with  the  anterior 
surface  of  the  auricles. 


724 


HUMAN   ANATOMY. 


The  transverse  portion  is  crossed  on  its  anterior  surface  by  the  left  phrenic, 
cardiac,  and  pneumogastric  nerves,  arranged  in  that  order  from  right  to  left,  the 
pneumogastric  crossing  it  on  a  level  with  the  origin  of  the  left  subclavian  artery. 


Remains  of  thymus 
II.  costal  cartilage 


FlG.    680. 


Sternum 


Lttng. 

Left  phrenic  nerve 

Ascending  portion 

)h-node 
iral  sac 


Bronchial  lymph-node 
Pleu 


Transverse  portion  __ 

Left  pneumogastric  nerve 

Left  recurrent  laryngeal  nerve 

Descending  portion rfl^B 


(Esophagus 
Thoracic  duct 


.Pencardial  sac 


Lung 

-  Right  phrenic  nerve 
—  Superior  vena  cava 

—   Bronchial  lymph-node 

Bifurcation  of  trachea 

—  Right  pneumogastric  nerve 

—   Vena  azygos 


—  IV.  thoracic  vertebra 


FlG.  68 1. 


FIG.  682. 


Part  of  cross-section  of  body  at  level  of  fourth  thoracic  vertebra,  viewed  from  above; 
upper  part  of  aortic  arch  has  been  removed. 

More  posteriorly  the  anterior  surface  is  in  contact  with  the  left  pleura.  Behind  it  is 
in  relation  from  right  to  left  with  the  superior  vena  cava,  the  trachea,  the  oesoph- 
agus, and  the  body  of  the  fourth  thoracic  vertebra,  and  below  it  are  the  right  pul- 
monary artery,  the  left  recurrent  laryngeal  nerve,  and  the  left  bronchus,  the  arch 
crossing  this  last  structure  obliquely  from  above  downward  and  outward. 

The  descending  portion  of  the  arch  has  in  front  of  it  a  portion  of  the  left 
pleura  and  the  root  of  the  left  lung.      Behind,  it  rests  upon  the  fourth  thoracic  ver- 
tebra; to  the  right  of  it  are  the 

cesophagus  and  the  thoracic  duct 

and  also  the  body  of  the  fourth 

thoracic  vertebra,  and  to  the  left 

are  the  left  pleura  and  lung. 

Branches. — Just  above  its 

origin  the  aortic  arch  gives  off 

(i)  the  right  and  left  coronary 

arteries,  and  from  the  upper  or 

convex  surface  of  the  transverse 

portion  there  arise  in  succession, 

from  right  to  left,  (2)  the  innom- 
inate or  brachio-ccphalic*  (3)  the 

left  common  carotid,  and  (4)  the 

left  subclavian  artery. 

Variations.  ( )u  in»  to  the  com- 
plexity of  the  changes  by  which  the 
primary  arrangement  of  tin-  branchial 
arch  vessels  is  transformed  into  the 
adult  arrangement  ( Figs.  681,  682), 
and  owing  also  to  the  possibility  of 
some  of  t  In- normal  changes  remaining 
uncompleted,  tin-  variations  which  oc- 
cur in  connection  with  the  arch  of  the 
aorta  are  rather  numerous.  They  may 
be  conveniently  classed  m  live  Croups. 

Group  I.— In  the  normal  development  (Fig.  682)  the  distal  portion  of  the  right  aortic  arch 
nerates  as  tar  up  as  the  right   suhclavian  artery,  indications  of  it  persisting  as  a  nmn- or 


Diagram  showing  primary 
ait:inx<-mrnt  of  longitudinal 
stems  and  series  of  six  aortic 
bows  ;  7V},  truncus  arteriosus: 
VA,  DA,  ventral  and  dorsal 
aortic;  A,  unpaired  dorsal 
aorta;  I-VI*  aortic  bows,  of 
which  Kis  rudimentary. 


Diagram  showing  normal 
derivations  in  man  of  primary 
vessels  by  modification  of  pre- 
ceding plan  ;  A.  aorta;  A  A,  aortic 
arch;  /,  innominate  artery  ;  CC, 
common  i  annuls;  AC.  /(  .  e\te: 
nal  and  internal  carotids  ;  5.  sub- 
clavian artery  ;  /*.  puhnonatv  a:: 
ery;  /•>.-!  duct  us  arteriosus. 


degenerates  as  far  up  as  the  rigl 

less  rudimentary  rax  atx'rnins  arising  from  the  thoracic  aorta.      This  degeneration   may  not 
occur,  both   the'right  and   left  aortic  arches  persisting  in  their  entirety  (Fig.  683);  and,  since  in 


THE   AORTIC   ARCH. 


725 


such  cases  the  descending  aorta  usually  retains  its  normal  position  to  the  left  of  the  spinal 
column,  a  condition  is  produced  in  which  the  aortic  arch  appears  to  be  split  lengthwise  into 
two  portions,  one  of  which,  the  left  arch,  passes  in  front  of  the  trachea  and  oesophagus  and 
gives  origin  to  the  left  common  carotid  and  the  left  subclavian  arteries,  while  the  other  passes 


FIG-  683. 


FIG.  684. 


RAA 


Right  suhcla 


ft  common 
carotid 
ft  subclavian 

Ductus 
arteriosus 


Developmental  variations  of 
Group  I,  giving  rise  to  anomaly 
shown  in  next  figure.  1?AA,LAA, 
right  and  left  aortic  arches ;  J?S, 
LS,  subclavian  arteries;  A,  aorta; 
P,  pulmonary  artery. 


moiiary  artery 


Double  aortic  arch  through  which  trachea 
and  ossophagus  pass,     (ffommel). 


behind  the  structures  named  and  gives  origin  to  a  right  common  carotid  and  a  right  subclavian 
(Fig.  684). 

The  relative  diameters  of  the  two  portions  of  the  aortic  arch  so  formed  may  vary  con- 
siderably, that  passing  in  front  of  the  trachea  (the  true  left  arch)  being  sometimes  larger  and  at 
other  times  smaller  than  the  other  one.  In  the  latter  case  an  obliteration  of  the  distal  portion  of 
the  left  arch  may  occur,  and  the  left  common  carotid  and  left  subclavian  arteries  will  then 
appear  to  arise  close  to  the  innominate  stem,  from  a  common  trunk,  the  aortic  arch  passing 
to  the  left  behind  the  trachea. 

Group  II. — A  more  frequent  anomaly  is  the  complete  persistence  of  the  distal  portion  of 
the  right  aortic  arch  (Fig.  685)  associated  with  the  disappearance  of  a  greater  or  less  portion  of 


FIG.  685. 


FIG.  686. 


Trachea 


Left  common 
carotid 
Right 
vertebral 

Right 
subclavian 


Aorta 


Developmental  variations  of 
Group  II,  giving  rise  to  anomaly 
shown  in  next  figure.  A,  aorta; 
P,  pulmonary  artery  ;  RS,  LS,  right 
and  left  subclavian  arteries;  RV, 
right  vertebral  artery. 


:sophagus 

Left  common  carotid 

Left  vertebral 

h-Left 

subclavian 


Right 

subclavian 


Origin  of  right  subclavian  artery  from  descending  aorta. 


its  proximal  part,  the  result  being  the  apparent  origin  of  the  right  subclavian  artery  from  the 
descending  aorta,  whence  it  passes  to  the  right  behind  the  trachea  and  cespphagus.  Variations  of 
this  condition,  depending  upon  the  location  and  extent  of  the  disappearing  portion  of  the  right 
arch,  may  modify  the  relations  of  the  right  vertebral  and  subclavian  arteries.  Thus,  in  some 


726 


HUMAN   ANATOMY. 


FIG.  687. 


KAA 


DA  — 


cases  the  vertebral  may  arise  as  in  the  normal  arrangement  from  the  subclavian,  or  it  may,  as  it 

were,  exchange  positions  with  the  subclavian,  arising  from  the  descending  aorta,  while  the  sub- 

clavian arises,  in  common  with  the  right  common  carotid,  from  an  innominate   stem  ;   or  the 

vertebral  may  arise  with  the  right  common  carotid  from  the  innominate  stem,  the  subclavian 

alone  coming  from  the  descending  aorta  (Fig.  686). 

Group  III.  —  A  third  group  of  anomalies  depends  upon  the  complete  persistence  of  the 
right  aortic  arch,  associated  with  the  disappearance  of  the 
distal  portion  of  the  left  one  (Fig.  687).  In  such  cases  the 
result  is  a  complete  reversal  of  the  aortic  arch  and  its 
branches,  unaccompanied,  however,  by  a  reversal  of  any  of 
the  other  organs  of  the  body,  and  thus  differing  from  a 
true  situs  in  versus  viscerum.  The  arch  is  directed  from  left 
to  right,  and  gives  rise  to  an  innominate  stem,  from  which 
the  left  common  carotid  and  left  subclavian  arteries  arise,  a 
right  common  carotid  and  a  right  subclavian,  the  descend- 
ing aorta  lying  upon  the  right  side  of  the  vertebral  column. 
Variations  of  these  anomalies  concern  principally  the  rela- 
tions of  the  ductus  arteriosus  or  the  cord  which  represents 
it.  It  may  unite  with  the  descending  aorta,  in  which  case 
it  is  the  persistent  right  sixth  branchial  vessel,  or  it  may  be 
formed,  as  usual,  from  the  left  sixth  branchial  vessel,  com- 
municating distally  with  the  left  subclavian,  this  artery,  in 
cases  where  the  ductus  remains  patent,  appearing  to  arise  by- 
two  roots,  one  from  the  innominate  stem  and  one  from  the 
pulmonary  aorta. 

Group  IV.  —  In  the  fourth  group  there  is  a  complete 
persistence  of  the  right  aortic  arch  associated  with  a  dis- 
appearance of  the  proximal  portion  of  the  left  arch  (Fig.  688), 
the  resulting  arrangement  being  the  reverse  of  that  seen 
in  cases  belonging  to  the  second  group.  The  left  sub- 
clavian artery  appears  to  arise  from  the  descending  aorta, 
which  lies  upon  the  right  side  of  the  vertebral  column,  and 
passes  to  the;  left  behind  the  trachea  and  oesophagus.  Varia- 

tions in  the  relations  of  the  ductus  arteriosus,  similar  to  those  mentioned  as  occurring  in  the 

third  group,  may  be  found. 

Group  V.  —  A  fifth  group  includes  those   cases   in  which 

the  arch  itself  is  normal,  but  in  which  there  are  variations  in  the 

vessels  that  arise  from   it.     These   variations  may  be  either  a 

diminution  or  an  increase  of  the  normal  number  of  vessels  or 

an  abnormal  arrangement  of  a  normal,  number.     The  diminu- 

tion and  altered  arrangement   of   the  vessels  depend  upon  a 

shifting  of  more  or  fewer  of  them,  so  that,  for  example,  the  left 

common  carotid  and  left  subclavian  arteries  may  arise  from  a 

common  left  innominate  stem,  all  the  vessels  may  arise  from 

a  common  stem,  the  two   common  carotids  may  have  a  com- 

mon origin,  while  the  two  subclavians  arise  independently,  or, 

what  is  the  most  frequent  of  these   variations,  the   left  com- 

mon carotid   may   arise  from   the    innominate  stem    and  pass 

upward    and    to    the    left    obliquely    across    the   front    of    the 

trachea. 

An  increase  in  the  number  of  vessels  may  be   brought 

about  by  the   independent  origin   from   the  arch  of  both  the 

right  common  carotid  and  the  right  subclavian,  the  innominate 

being  absent.     In   other   cases,   vessels  which  normally  do   not 

come   into  relation  with  the  arch  may  take  origin  from  it,  this 

being  most  frequently  the  case  with  the  vertebral  arteries  and 

less  frequently  with  the   internal  mammaries  ;   and,  finally,  an 

addit9nal  branch  to  the  thyroid  gland,  the  art.  thyroidea  ima, 

occasionally  takes  origin  from  the  arch. 


Developmental  variations 
of  Group  III.  A,  aorta;  P, 
pulmonary  artery;  RAA, 
right  aortic  arch;  DA,  duc- 
tus arteriosus  ;  RS,  LS,  right 
and  left  subclavian  arteries. 


FIG.  688. 


Developmental  variations 
I>      J.  aorta;  P, 


of  Group 


lA* 


Practical  Considerations. — The  Aortic  Arch  and  Thoracic  Aorta.— 
Surface  Relations. — The  ascending  aorta  begins  beneath  the  sternum  just  to  the 
right  of  the  inner  end  of  the  third  left  costal  cartilage.  It  ascends  obliquely  and 
towards  the  upper  border  of  the  second  right  costal  cartilage.  The  second  (trans- 
verse) part  passes  backward  and  to  the  left,  crossing  the  mid-line  about  an  inch 
from  the  suprasternal  notch,  the  lower  (concave)  border  corresponding  in  level  with 
the  ridge  between  the  manubrium  and  the  gladiolus,  the  upper  (convex)  border  to  the 
level  of  the  third  thoracic  spinous  process,  to  the  middle  of  the  manubrium,  and  the 
middle  of  the  first  costal  cartilage.  This  border  is  about  one  inch  below  the  supra- 
sternal  notch.  The  surface  relations  of  this  portion  vary  with  the  development  of 


PRACTICAL   CONSIDERATIONS:    THE   AORTIC   ARCH.         727 

the  thorax.  In  persons  with  small  chests  the  upper  border  may  almost  reach  the 
level  of  the  top  of  the  manubrium,  while  in  those  with  large  chests  it  may  be  no 
higher  than  the  junction  of  the  first  and  second  pieces  of  the  sternum  (angulus 
Ludovici}.  The  transverse  portion  reaches  the  left  side  of  the  vertebral  column  at 
a  level  just  above  the  fourth  thoracic  spine.  The  third  (descending)  portion  and 
the  thoracic  aorta  lie  at  first  a  little  to  the  left  of  the  body  of  the  fourth  thoracic 
vertebra  and  gradually  incline  to  the  mid-line,  passing  through  the  diaphragm  at  the 
level  of  the  twelfth  thoracic  vertebra. 

Aneurisms  of  the  aorta  are  more  frequent  than  are  those  of  any  other  vessel,  on 
account  of  the  great  strains  to  which  the  aorta  is  subject.  They  may  most  con- 
veniently be  considered  here  by  following  the  anatomical  subdivisions  of  the  vessel, 
premising,  however,  that  the  symptoms  thus  described  frequently  commingle  and 
overlap. 

A.  The  ascending,  portion  is  more  subject  to  aneurism  than  are  the  remaining 
portions,  because  it  receives  the  first  and  most  vigorous  impulse  of  the  heart's  stroke, 
and  because  it  is  within — enclosed  by — the  pericardium,  and  its  walls  are  not  rein- 
forced by  blending  with  the  fibrous  pericardial  layer,  as  is  the  case  in  the  second 
and  third  portions.     Aneurism  most  frequently  involves  the  region  of  the  anterior 
sinus  of  Valsalva,  where  regurgitation  of  blood  chiefly  takes  place  ;  or,  if  higher,  the 
anterior  wall  of  the  aorta  in  the  vicinity  of  the  normal  dilatation,  probably  due  to  the 
impact  of  the  blood-current  leaving  the  heart.     The  symptoms  are  :   i .    Venous  con- 
gestion, causing  («)  lividity  of  the  face  from  pressure  on  the  descending  cava,  the 
left  innominate,  and  the  internal  jugular  veins  ;   (3)  dizziness  and  headache  from  the 
same  cause  ;  (<:)  swelling  and  oedema  of  the  right  arm  from  pressure  on  the  sub- 
clavian  vein  ;  (</)  sivelling  and  oedema  of  the  anterior  thoracic  wall  from  pressure  on  the 
internal  mammary,  azygos,  or  hemiazygos  veins.      2.    Dyspnoea  with  altered  breath 
sounds  over  the  right  chest,  from  pressure  on  the  root  of  the  right  lung.     3.   Dys- 
phonia  or  aphonia,  with  croupy  or  stridulous  respiration,  from  pressure  on  the  right 
recurrent  laryngeal  nerve  ;  sometimes  from  venous  congestion  due  to  pressure  on 
the  internal  jugular  and  innominate  acting  through  the  superior  thyroid  and  inferior 
thyroid  veins  on  the  corresponding  laryngeal  veins.      4.   Swelling  or  tumor,  often 
first  seen  at  or  about  the  sternal  end  of  the  third  right  intercostal  space.      5.   Dis- 
placement of  the  heart,  occasionally  occurring  when  the  aneurism  involves  especially 
the  concave  side  of  the  vessel  and  pushes  the  heart  downward  and  to  the  left.     6. 
Ascites  and  oedema  of  the  legs  and  feet  from  compression  of  the  ascending  cava  when 
the  aneurism  occupies  the  same  situation.      7.   Pain  in  the  sternum,  the  ribs,  or  the 
spine  from  direct  pressure  ;  encircling  the  upper  part  of  the  chest  from  pressure  on 
the  intercostal  nerves  ;  running  down  the  side  of  the  thorax  and  the  inner  surface  of 
the  arm  from  pressure  on  fibres  distributed  by  the  intercosto-humeral  nerve. 

B.  Aneurism  of  the  transverse  portion  may  cause  :   i.    Dyspnoea  and  dysphonia 
or  aphonia  from  direct  pressure  on  the  trachea  or  bronchi,  or  from  involvement  of 
the  left  recurrent  laryngeal  nerve  in  its  course  around  the  arch.      2.   Dilatation  of 
the  pupil  followed  by  'contraction   from,    first,   irritation   and  then   paralysis  of  the 
sympathetic.      3.    Inanition  from  pressure  on  the  thoracic  duct.     4.   Swelling,  often 
beginning  in  the  mid-line,  then  extending  to  the  right  (thirty-one  cases  out  of  thirty- 
five,  Browne,  quoted  by  Osier),  and  sometimes  simulating  innominate  or  common 
carotid    aneurism.      4.    Venous  congestion  of  the  head,   neck,   left  arm,   etc.,    often 
more  marked  on  the  left  side  from  the  greater  exposure  to  pressure  of  the  left  innomi- 
nate vein.     5.    Weakness  or  absence  of  radial  or  temporal  pulse — especially  on  the 
left  side — due  to  pressure  on  or  involvement  of  the  innominate,  left  subclavian,  or 
left  carotid  artery. 

C.  Aneurism  of  the  descending  portion  of  the  arch  and  of  the  thoracic  aorta 
may  cause  :   i.  Dysphagia,  which  is  common  and  apt  to  appear  earlier  on  account 
of  the  more  direct  relation  with  the  oesophagus.      2.    Great  pain  in  the  spine,  some- 
times followed  by  paralysis,  from  erosion  of  the  vertebrae  and  compression  of  the 
cord.      3.   Swelling  in  the  left  scapular  region  or  at  the  vertebral  ends  of  the  middle 
ribs  on  the  left  side.     4.   Bronchiectasis,  with  cough  and  expectoration,  from  press- 
ure on  the  left  bronchus,  or  asthmatic  attacks  from  involvement  of  the  left  pulmo- 
nary plexus. 


728 


HUMAN    ANATOMY. 


THE  CORONARY  ARTERIES. 

The  coronary  arteries,  which  supply  the  heart,  are  two  in  number,  and  arise  from 
the  right  and  left  prominences  at  the  base  of  the  aorta  which  mark  the  corresponding 
sinuses  of  Valsalva. 

The  left  coronary  artery  (a.  coronaria  sinistra)  lies  at  its  origin  (Fig.  679) 
behind  the  base  of  the  pulmonary  aorta,  and  passes  forward  between  that  vessel  and 
the  left  auricular  appendix  to  reach  the  anterior  interventricular  groove,  in  which  it 
divides  into  two  branches.  The  larger  of  these  (ramus  descendens  anterior)  descends 
in  the  groove  to  the  apex  of  the  heart,  giving  off  branches  which  supply  the  anterior 
surface  of  both  ventricles,  while  the  smaller  one  (ramus  circumtlexus)  passes  backward 
in  the  left  portion  of  the  auriculo-ventricular  groove  and  gives  off  branches  to  the 
left  auricle  and  ventricle.  Branches  to  the  left  auricle  also  arise  from  the  main  stem 
of  the  artery,  as  well  as  twigs  to  the  walls  of  the  aortae. 

FIG.  689. 


Left  pulmonary  artery 

Superior  left  pulmonary  vein 
Inferior  left  pulmonary  vein 

Termination  of  left 
coronary  vein 

Transverse  branch  of  left 
coronary  artery 


Left  ventricle 


Superior  vena  cava 

Superior  right  pulmonary  vein 
Right  pulmonary  artery 

Inferior  right  pulmonary  vein 


Inferior  vena  cava 


Coronary  sinus 

Right  coronary  vein 
Transverse  branch  of  right 

coronary  artery 
Posterior  descending  branch 
of  right  coronary  artery 


Middle  cardiac  vein 


Right  ventricle 


Postero-inferior  surface  of  injected  heart,  viewed  from  below  and  behind. 


The  right  coronary  artery  (a.  coronaria  dextra)  passes  outward  from  its  origin 
in  the  right  portion  of  the  auriculo-ventricular  groove,  in  which  it  lies,  until  it  reaches 
the  posterior  interventricular  groove,  down  which  it  (ramus  descendens  posterior)  is 
continued  towards  the  apex  of  the  heart  (Fig.  689).  In  its  course  it  gives  off  num- 
erous branches,  which  are  distributed  to  the  right  auricle  and  ventricle  and  to  the 
portion  of  the  left  ventricle  which  adjoins  the  posterior  interventricular  groove. 
Usually  a  large  branch,  the  marginal  artery,  descends  along  tin-  right  border  of  the 
heart  (Fig.  679)  and  gives  branches  to  both  surfaces  of  the  right  ventricle. 

The  peculiarities  of  the  ultimate  distribution  of  these  arteries  have  been  described 
in  connection  with  the  heart  (page  703). 

Variations. — The  two  coronary  arteries  may  arise  by  a  common  stem;  one  of  them  may 
!•••  \\  anting,  or  supernumerary  vessels  may  occur. 


THE   INNOMINATE   ARTERY.  729 

THE  INNOMINATE  ARTERY. 

The  innominate  artery  (a.  anonyma)  (Figs.  679,  690),  also  known  as  the 
brachio- cephalic,  is  the  first  as  well  as  the  largest  of  the  three  vessels  which  arise 
from  the  arch  of  the  aorta.  It  passes  directly  upward  to  the  level  of  the  right 
sterno-clavicular  articulation,  where  it  divides  into  the  right  common  carotid  and 
the  right  subclavian,  but  gives  rise  to  no  other  branches. 

Relations. — Anteriorly  it  is  separated  from  the  sternum  and  from  the  origins  of 
the  right  sterno-hyoid  and  sterno-thyroid  muscles  by  the  left  innominate  vein  and 
by  some  fatty  tissue  which  contains  the  remains  of  the  thymus  gland.  Posteriorly 
it  is  in  relation  with  the  trachea  and  the  sympathetic  cardiac  nerves  ;  on  the  right 
it  is  in  contact  with  the  right  pleura  and  on  the  left  of  it  is  the  left  common 
carotid  artery. 

Variations. — The  variations  of  the  innominate  artery  have  already  been  discussed  in 
connection  with  the  variations  of  the  aortic  arch,  since  the  vessel  represents  the  proximal 
portion  of  the  right  arch.  Jt  shows  considerable  variation  in  length,  measuring  between  2.8 
and  4.5  cm.,  although  occasionally  reaching  a  length  of  5  or  even  7  cm.  Occasionally  it  is 
absent,  the  right  common  carotid  and  the  right  subclavian  arteries  arising  directly  from  the 
aortic  arch. 

Although  the  innominate  artery  does  not,  as  a  rule,  give  origin  to  any  branches  except 
the  two  terminal  ones,  yet  in  about  10  per  cent,  of  cases  there  arises  from  it  a  vessel  which  is 
termed  the  arteria  thyroidea  ima.  This  takes  its  origin  usually  from  near  the  base  of  the 
innominate,  upon  its  medial  surface,  and  passes  directly  upward  upon  the  anterior  surface  of  the 
trachea  to  terminate  in  branches  which  are  distributed  to  the  isthmus  and  the  lower  portions  of 
the  lobes  of  the  thyroid  body.  The  presence  of  this  thyroidea  ima  is  frequently  associated  with 
a  more  or  less  extensive  reduction  of  the  size  of  one  or  other  of  the  inferior  thyroid  arteries,  and, 
indeed,  these  arteries  may  be  entirely  supplanted  by  it.  It  is  somewhat  variable  in  its  origin, 
for,  instead  of  arising  from  the  innominate,  it  may  be  given  off  by  the  aortic  arch,  by  the  right 
common  carotid,  by  either  the  right  or  left  subclavian,  or,  in  rare  cases,  by  one  of  the  branches 
of  the  subclavians. 

Practical  Considerations. — The  line  of  the  innominate  artery  is  from  the 
middle  of  the  manubrium  to  the  right  sterno-clavicular  joint.  Its  point  of  bifurca- 
tion would  be  crossed  by  a  line  drawn  backward,  just  above  the  clavicle,  through 
the  interval  between  the  sternal  and  clavicular  portions  of  the  sterno-mastoid  muscle. 

Aneurism  of  the  innominate  artery,  often  associated  with  aneurism  of  the  aortic 
arch,  causes  pressure-symptoms  easily  explained  by  the  chief  relations  of  the  vessel. 
They  may  be  summarized  as  follows  :  i.  Vascidar,  (a)  arterial,  weakness  or  irregu- 
larity of  the  right  radical  pulse  or  of  the  right  carotid  or  temporal  pulse  from  inter- 
ruption of  the  direct  blood-current  ;  (£)  venous,  duskiness  of  the  face  and  neck, 
especially  of  the  right  side,  oedema  of  the  eyelids,  protrusion  of  the  eyeballs,  lividity 
of  the  lips,  from  pressure  on  the  left  innominate,  deep  jugular,  and  transverse 
veins  lying  between  the  vessel  and  the  thoracic  wall  ;  oedema  of  the  right  arm  from 
subclavian  pressure.  2.  Nervous,  cough  and  hoarseness  or  aphonia  from  involve- 
ment of  the  right  recurrent  laryngeal  :  dilatation  or  contraction  of  the  pupil  from 
pressure  on  the  sympathetic  ;  hiccough  from  irritation  of  the  phrenic  ;  pain,  particu- 
larly severe  on  the  right  side  of  the  neck  and  head,  the  same  side  of  the  chest,  and 
down  the  right  arm  from  pressure  on  the  branches  of  the  cervical  and  brachial 
plexuses.  In  addition,  dyspnoea  and  dysphagia  from  compression  of  the  trachea 
and  oesophagus,  and  the  appearance  of  a  swelling  at  and  above  the  right  sterno- 
clavicular  articulation,  often  obliterating  the  suprasternal  depression,  are  character- 
istic symptoms. 

In  endeavoring  to  differentiate  these  aneurisms  from  those  of  the  arch  of  the 
aorta  it  may  be  well  to  remember  that  the  position  of  the  innominate  is  above,  to 
the  right,  and,  in  a  way,  cervico-thoracic,  while  that  of  the  arch  is  on  a  lower  level, 
is  median  or  to  the  left,  and  is  wholly  thoracic. 

Ligation.  —  Two  skin  incisions,  each  three  inches  in  length,  are  made  along  the 
anterior  edge  of  the  sterno-mastoid  muscle  and  the  upper  border  of  the  inner  third 
of  the  clavicle,  uniting  at  an  acute  angle  near  the  right-sterno-clavicular  articulation. 
The  sternal  portion  and  the  greater  part  of  the  clavicular  portion  of  the  sterno-mas- 


730  HUMAN   ANATOMY. 

toid  muscle  are  divided  just  above  their  origin.  The  anterior  jugular  vein  runs 
behind  the  sternal  head,  and  is  to  be  avoided  or  tied.  The  thyroid  plexus  of  veins 
may  appear  in  the  wound,  and  should  be  tied  or  drawn  out  of  the  way.  The 
sterno-hyoid  and  sterno-thyroid  muscles  are  divided  close  to  the  sternum.  The  deep 
cervical  fascia  is  divided  in  the  line  of  the  superficial  wound.  The  common  carotid 
artery  should  be  found,  its  sheath  opened,  and  the  vessel  traced  down  to  the  innomi- 
nate bifurcation.  The  internal  jugular  vein  may  be  much  engorged  and  should  be 
drawn  outward.  The  innominate  vein  may  protrude  into  the  wound.  Osteoplastic 
resection  of  the  manubrium  (Bardenheuer),  or  a  median  longitudinal  division  of  that 
bone  (Woolsey)  with  retraction  of  the  edges,  will  facilitate  the  exposure  of  the 
vessel.  The  most  important  relations  are  to  the  outer  side, — viz.,  the  vagus,  the 
pleura,  and  the  right  innominate  vein.  The  left  common  carotid  and  trachea  lie  to 
the  inner  side.  The  needle  should  be  passed  from  without  inward.  The  ligature 
should  be  placed  as  high  as  possible,  to  leave  room  between  it  and  the  aorta  for  the 
formation  of  a  satisfactory  clot.  It  is  well  to  ligate  the  common  carotid  and  the 
vertebral  at  the  same  time,  to  lessen  the  risk  of  secondary  hemorrhage  on  the  distal 
side  of  the  ligature. 

The  collateral  circulation  is  carried  on  from  the  proximal  or  cardiac  side  of  the 
ligature  by  (a)  the  first  aortic  intercostal  ;  (£)  the  upper  aortic  intercostals  ;  (c}  the 
inferior  phrenic  branch  of  the  abdominal  aorta  (within  the  diaphragm);  (d)  the 
deep  epigastric  (within  the  rectus  sheath) ;  (^)  the  vertebrals  and  internal  carotids 
of  the  left  side  (within  the  cranium — circle  of  Willis) ;  and  (/")  the  branches  of  the 
left  external  carotid  ;  anastomosing  respectively  with  (a)  the  superior  intercostal  of 
the  subclavian  ;  (£)  the  intercostals  of  the  internal  mammary  and  the  thoracic 
branches  of  the  axillary  ;  (c}  the  musculo-phrenic  branch  of  the  internal  mammary  ; 
{d  )  the  superior  epigastric  branch  of  the  internal  mammary  ;  (^)  the  vessels  in  the 
right  half  of  the  circle  of  Willis  ;  and  (/")  the  branches  of  the  right  external  carotid, 
all  receiving  their  blood-supply  from  beyond — or  to  the  distal  side  of — the  ligature. 

THE   COMMON   CAROTID    ARTERIES. 

The  right  common  carotid  artery  arises  from  the  innominate  and  the  left  one  from 
the  arch  of  the  aorta  (Fig.  690).  Both  pass  directly  upward  in  the  neck,  along  the 
side  of  the  trachea  and  larynx,  and  terminate  opposite  the  upper  border  of  the  thyroid 
cartilage  by  dividing  into  the  external  and  internal  carotid  arteries,  their  course  being 
represented  by  a  line  drawn  from  a  point  midway  between  the  angle  of  the  jaw  and 
the  mastoid  process  to  the  sterno-clavicular  articulation.  Throughout  its  course 
neither  of  the  common  carotids  gives  off  any  branches,  and  they  consequently  have 
an  almost  uniform  calibre,  except  towards  their  point  of  division,  where  they  present 
a  dilatation  frequently  continued  into  the  internal  carotid  and  usually  becoming  more 
marked  with  advancing  age. 

Relations. — The  left  common  carotid  lies  in  the  thoracic  cavity  during  the 
first  part  of  its  course,  and  in  this  respect  differs  from  the  right  artery,  whose  origin 
from  the  brachio-cephalic  is  at  the  level  of  the  sterno-clavicular  articulation.  This 
thoracic  portion  of  the  left  common  carotid  is  usually  about  3  cm.  (i^  in.)  in 
length,  and  is  crossed  obliquely  in  front,  near  its  root,  by  the  left  innominate 
(brachio-cephalic)  vein  and  by  the  cardiac  branches  of  the  pneumogastric  nerve.  It 
is  separated  from  the  sternum  and  the  origin  of  the  sterno-thyroid  muscle  by  some 
fatty  tissue  which  contains  the  remains  of  the  thymus  gland,  and  posteriorly  it  is  in 
relation  with  the  trachea  below  and  higher  up  with  the  left  recurrent  laryngeal  nerve. 
Below,  to  its  right  side  and  a  short  distance  away,  is  the  innominate  artery  ;  above 
it  is  in  close  relation  with  the  trachea,  while  to  its  left  and  somewhat  posteriorly  are 
the  left  subclavian  artery  and  the  left  pneumogastric  nerve. 

Throughout  their  cervical  portions  the  relations  of  both  arteries  are  iden- 
tical. Each  is  enclosed  within  a  fibrous  sheath  formed  by  the  deep  cervical  fascia 
(page  550),  the  sheath  also  containing  the  internal  jugular  vein  and  the  pneumo- 
gastric nerve,  the  vein  lying  lateral  to  the  artery  and  the  nerve  between  the  two 
vessels,  but  in  a  plane  slightly  posterior  to  them.  Extending  downward  for  a  vari- 
able distance  upon  the  anterior  surface  of  the  sheath  is  the  descending  hypoglossal 


THE   COMMON    CAROTID   ARTERIES. 


731 


nerve,  and  overlapping-  it  to  a  certain  extent  is  the  sterno-cleido-mastoid  muscle 
and,  below,  the  sterno-hyoid  and  sterno-thyroid.  At  about  the  level  of  the  cricoid 
cartilage  of  the  larynx  the  artery  is  crossed  obliquely  by  the  omo-hyoid  muscle,  and 
higher  up  by  the  middle  and  superior  thyroid,  the  lingual  and  sometimes  the  facial 
veins,  and  the  sterno-mastoid  branch  of  the  superior  thyroid  artery. 

Posteriorly  the  sheath  rests  upon  the  prevertebral  fascia  covering  the  longus  colli 
and  the  rectus  capitis  anticus  major  muscles,  and  is  in  relation  with  the  ganglionated 
cord  of  the  sympathetic  nervous  system  and  its  superior  and  middle  cardiac 
branches.  Lower  down,  opposite  the  sixth  cervical  vertebra,  the  branches  of  the 


FIG.  690. 


Scalenus  antic 
Thyroid  a) 

Right  common  carotid  art* 

Right  subclavian  art< 

Internal  mammary  art« 

Left  common  carotid  art. 
Innominate  artery 

Innominate  veins 

Superior  vena  cava 

Left  bronchus 
Right  pulmonary  vein 

Right  pulmonary  artery 

Branch  of  right  bronchus 

Right  pulmonary  vein 

Right  auricular  appendage 

Mesial  surface  of  lung 


Right  coronary  artery 


Vertebral  arteries 

Inferior  thyroid  artery 

msverse  cervical  artery 


rascapular  artery 


Thyroid  axis 
Clavicle 


Subclavian  artery 
Trachea 


Pericardium,  upper  limit 
Ligamentum  arteriosum 
Aorta,  systemic 
Left  pulmonary  artery 
Pulmonary  aorta  (artery) 

Pulmonary  veins 
Right  ventricle 
(conus  arteriosus) 

•£—  Mesial  surface  of  lung 
eft  coronary  artery 


Diaphragm 


Dissection  showing  aortic  arch  and  its  branches ;  lungs  have  been  pulled  aside. 

inferior  thyroid  artery  pass  behind  it.  Medially  are  the  trachea  and  the  oesophagus, 
together  with  the  recurrent  laryngeal  nerve,  the  lobe  of  the  thyroid  gland,  and, 
above,  the  larynx  and  the  pharynx. 

Variations. — The  variations  of  the  common  carotid  arteries  have  been  sufficiently  discussed 
in  connection  with  the  anomalies  of  the  aortic  arch  (page  724). 

Practical  Considerations. — Aneiirism  of  the  common  carotid  artery  is  not 
very  frequent.  It  most  commonly  occurs  near  the  bifurcation  (a)  because  of  the 
slight  dilatation  normally  existing  there  ;  (£)  because  there  the  vessel  is  more  super- 


732  HUMAN   ANATOMY. 

ficial, — i.e.,  least  supported  by  overlying  muscle  ;  and  (c)  because  of  the  increased 
resistance  to  the  blood-current  at  that  point.  It  is  seen  oftener  in  the  right  carotid 
than  in  the  left.  Pressure-symptoms :  pain  in  the  side  of  the  neck,  face,  and  head 
in  the  distribution  of  the  superficial  cervical  plexus  of  nerves  ;  duskiness  or  mottling 
of  the  skin  from  pressure  on  the  sympathetic  ;  dyspna-a  and  cough  from  lateral 
deflection  of  the  larynx  and  trachea  ;  defective  vision,  vertigo,  or  stupor  from  press- 
ure on  the  internal  jugular  ;  hoarseness  or  aphonia  from  implication  of  the  recurrent 
laryngeal  nerve  ;  dysphagia  from  direct  pressure  on  the  oesophagus,  or — possibly, 
together  with  irregular  heart  action,  vomiting,  or  asthmatic  respiration — from  press- 
ure on  the  pneumogastric. 

Digital  compression  may  be  used  in  a  case  of  stab  wound  or  in  the  treatment 
of  aneurism  (a)  by  making  pressure  backward  and  outward  beneath  the  anterior 
edge  of  the  sterno-mastoid  muscle  at  the  level  of  the  cricoid  cartilage,  so  as  to  flatten 
out  the  artery  against  the  transverse  process  of  the  sixth  cervical  vertebra  (carotid 
tubercle)  about  two  and  a  half  inches  above  the  clavicle.  As  the  vertebral  artery  at 
this  level  enters  its  canal  in  the  foramina  of  the  transverse  processes,  it  will  probably 
escape  pressure.  The  internal  jugular  vein  is  usually  displaced  laterally.  The 
common  carotid  artery  may  also  be  effectually  compressed  in  cases  of  wound  (6~)  by 
grasping  the  anterior  edge  of  the  sterno-mastoid  and  the  artery  together  between 
the  thumb  and  fingers,  or  (V)  by  placing  the  thumb  beneath  the  artery  and  the 
anterior  edge  of  the  muscle,  and  the  fingers  along  its  posterior  edge.  In  all  three  of 
these  methods  it  is  necessary  to  flex  the  head  and  turn  it  a  little  towards  the  affected 
side  so  as  fully  to  relax  the  sterno-mastoid. 

Ligation. — It  may  be  necessary  to  tie  the  common  carotid  in  cases  of  («)  aneu- 
rism, including  certain  pulsating  tumors  of  the  orbit  or  scalp  or  within  the  cranium  ; 
(6)  hemorrhage  from  wound  of  the  neck,  or  from  pharyngeal  wound  or  ulceration  ; 
or  (c)  for  the  prevention  of  bleeding  during  some  operations.  Whenever  ligation 
of  the  external  carotid  satisfactorily  meets  the  indications,  it  is  better  to  tie  that 
vessel  {q.v. ),  as  the  cerebral  circulation  is  not  thereby  interfered  with. 

The  lower  portions  of  the  common  carotids  on  both  sides  of  the  neck  are  deeply 
seated  ;  they  are  covered  by  three  planes  of  muscles  (the  sterno-mastoid,  sterno- 
hyoid,  and  sterno-thyroid)  ;  the  inferior  thyroid  artery  and  recurrent  laryngeal  nerve 
run  behind  them  on  each  side,  and  on  the  left  side  the  internal  jugular  vein  usually 
passes  from  without  inward  in  front  of  the  artery,  which  is  also  in  close  relation  to 
the  thoracic  duct,  the  innominate  artery,  and  the  left  innominate  vein. 

Two  operations  for  ligation  of  the  common  carotid  may  be  described  :  I.  The 
place  of  election  for  the  application  of  a  ligature  is  just  above  the  omo-hyoid  muscle, 
where  the  artery  has  become  more  superficial  and  is  covered  only  by  the  skin,  the 
platysma,  the  fasciae,  and  the  anterior  edge  of  the  sterno-mastoid.  The  skin  incision 
— three  inches  in  length — is  made  in  the  line  of  the  vessel,  the  centre  being  placed 
opposite  the  anterior  arch  of  the  cricoid  cartilage.  It  divides  also  the  platysma. 
The  deep  fascia  is  divided,  and  the  anterior  edge  of  the  sterno-mastoid  is  exposed 
and  followed  downward  to  the  angle  between  it  and  the  upper  edge  of  the  omo- 
hyoid  muscle.  The  former  muscle  is  then  drawn  outward,  the  latter  downward,  the 
descendens  hypoglossi  nerve  avoided,  the  sterno-mastoid  branch  of  the  superior 
thyroid  artery  and  the  superior — and  sometimes  the  middle — thyroid  vein  held  aside 
or  tied,  and  the  sheath  opened  over  the  carotid  compartment, — i.e.,  well  to  the 
inner  side, — so  as  to  avoid  injury  to  the  larger  internal  jugular  vein,  which  some- 
times— as  in  cases  of  embarrassed  respiration — bulges  over  the  artery  so  as  com- 
pletely to  obscure  it.  The  needle  should  be  passed  from  without  inward  to  avoid 
injury  to  the  vein,  care,  of  course,  being  taken  not  to  include  the  vagus. 

2.  ficlow  the  omo-hyoid  muscle  the  skin  incision — three  inches  in  length — still 
follows  the  anterior  border  of  the  sterno-mastoid,  beginning  now  a  little  below  tin- 
lower  border  of  the  cricoid  cartilage  and  ending  just  above  the  sterno-clavicular 
articulation.  A  second  incision  along  the  upper  border  of  the  clavicle  is  often  advis- 
able. The  sterno-mastoid  is  drawn  outward  and  the  outer  edge  of  the  sterno-hyoid 
muscle  exposed,  and  that  muscle,  with  the  sterno-thyroid,  drawn  downward  and 
inward.  Frequently  the  sternal  portion  of  the  sterno-mastoid,  and  occasionally  the 
sterno-hyoid  and  sterno-thyroid  muscles  also,  will  require  division  if  the  ligature  has 


THE  EXTERNAL  CAROTID  ARTERY.  733 

to  be  placed  as  near  the  root  of  the  neck  as  possible.  The  internal  jugular  vein  — 
especially  on  the  left  side— the  inferior  thyroid  artery,  and  the  recurrent  laryngeal 
nerve  must  be  avoided.  The  needle  is  passed  from  without  inward. 

The  collateral  circulation  is  carried  on  from  the  proximal  or  cardiac  side  through 
(a)  the  branches  of  the  external  carotid  on  the  opposite  side,  (£)  the  inferior  thy- 
roid, (c)  the  profunda  cervicis  (from  the  superior  intercostal  and  thus  from  the  sub- 
clavian),  (d  )  the  internal  carotid  and  the  vessels  of  the  opposite  segment  of  the 
circle  of  Willis,  and  (>)  the  vertebral,  by  anastomosing  respectively  with  (a)  the 
external  carotid  branches,  (b)  the  superior  thyroid,  (c)  the  princeps  cervicis  (from 
the  occipital),  and  (d  )  and  (<?)  the  vessels  of  the  circle  of  Willis  on  the  affected  side. 

THE  EXTERNAL  CAROTID  ARTERY. 

The  external  carotid  artery  (a  carotis  externa)  (Figs.  692,  693)  arises  from  the 
common  carotid  at  about  the  level  of  the  upper  border  of  the  thyroid  cartilage — a 
level  which  corresponds  to  the  body  of  the  fourth  cervical  vertebra.  Thence  it  is 
directed  upward  and  slightly  backward  towards  the  angle  of  the  jaw,  where  it  enters 
the  substance  of  the  parotid  gland  and  continues  upward  in  that  structure  to  just 
below  the  root  of  the  zygoma.  Here  it  gives  rise  to  a  large  branch,  the  internal 
maxillary,  and  is  then  continued  upward  over  the  root  of  the  zygoma  upon  the  side 
of  the  skull,  this  terminal  portion  of  it  being  termed  the  superficial  temporal  artery. 

Relations. —  In  the  first  portion  of  its  course  the  external  carotid  lies  in  the 
superior  carotid  triangle  (page  548),  and  is  there  crossed  by  the  hypoglossal  nerve 
and  the  facial  vein.  Higher  up  it  passes  beneath  the  posterior  belly  of  the  digastric 
and  the'stylo-hyoid  muscles  and  also  beneath  the  temporo-maxillary  vein,  and  enters 
the  substance  of  the  parotid  gland.  Posteriorly  it  is  separated  from  the  external 
carotid  artery  by  the  stylo-glossus  and  stylo-pharyngeus  muscles  and  the  glosso- 
pharyngeal  nerve  ;  the  internal  carotid  artery  lies  laterally  to  it  at  its  origin  ; 
internally  it  is  in  relation  with  the  inferior  and  middle  constrictors  of  the  pharynx 
and  the  superior  laryngeal  nerve. 

Branches. — From  the  anterior  surface  of  the  external  carotid  arise,  from 
below  upward,  (i)  the  superior  thyroid,  (2)  the  lingual,  (3)  \.\\e  facial,  and  (4) 
the  internal  maxillary  arteries.  From  its  posterior  surface,  in  the  same  order  of 
succession,  arise  (5)  the  ascending  pharyngeal,  (6)  the  sterno-mastoid,  (7)  the 
occipital,  (8)  the  posterior  auricular  arteries.  Finally,  (9)  the  superficial  temporal 
artery  is  to  be  regarded  as  a  branch  which  is  the  continuation  upward  of  the 
main  stem. 

Variations. — Occasionally  the  external  carotid  artery  is  absent,  its  branches  arising  from 
the  common  carotid,  which  is  continued  directly  into  the  internal  carotid.  The  number  of  its 
branches  may  be  reduced  by  certain  of  them,  the  lingual  and  facial,  for  instance,  arising  by  a 
common  stem,  or  they  may  be  increased  by  the  occurrence  of  various  accessory  branches  pass- 
ing to  regions  supplied  by  the  regular  ones 

Practical  Considerations. — The  external  carotid  is  rarely  the  subject  of 
aneurism,  except  as  a  result  of  trauma.  The  tumor  is  situated  below  the  angle  of 
the  jaw.  Pressure  on  the  hypoglossal  and  glosso-pharyngeal  nerves  and  on  the 
internal  jugular  vein  causes  various  symptoms  which  are  not  usually  definitely  diag- 
nostic. In  one  case  there  was  unilateral  atrophy  of  the  tongue  (Heath)  probably 
from  involvement  of  the  hypoglossal.  If  the  aneurism  is  situated  near  the  origin  of 
the  vessel,  it  may  be  indistinguishable  from  aneurism  of  the  common  carotid  at  its 
usual  location,  just  below  the  bifurcation.  The  vessel  is  not  infrequently  tied  for 
wound  of  the  neck,  for  aneurism  of  one  of  its  branches",  and  occasionally  as  a  pre- 
liminary to  certain  operations,  as  excision  of  the  superior  maxilla  or  removal  of  a 
malignant  tonsillar  or  parotid  tumor.  In  cases  of  stab  or  cut-throat  wound  it  is 
better,  when  possible,  to  find  and  tie  both  ends  of  the  bleeding  vessel,  as  the  free 
anastomosis  between  the  branches  of  the  two  external  carotids  renders  a  recurrence 
of  hemorrhage  probable  after  ligation  of  the  main  trunk. 

Ligation. — That  part  of  the  line  for  the  common  carotid  extending  from  the 
level  of  the  angle  of  the  lower  jaw  to  that  of  the  middle  of  the  thyroid  cartilage  is  the 


734  HUMAN   ANATOMY. 

line  for  the  skin  incision.  The  artery  is  usually  tied  below  the  digastric  muscle — 
i.e.,  in  the  superior  carotid  triangle  (page  548) — and  between  the  origins  of  the  supe- 
rior thyroid  and  the  lingual  arteries — because  that  is  the  longest  interval  without 
branches.  After  the  skin,  superficial  fascia,  platysma,  and  deep  fascia  have  been 
divided,  the  anterior  edge  of  the  sterno-mastoid  cleared  and  drawn  outward  at  the 
lower  portion  of  the  wound,  and  the  facial,  lingual,  or  superior  thyroid  veins — if  they 
present — drawn  aside  or  tied  and  cut,  the  posterior  belly  of  the  digastric  muscle 
above  should  be  identified.  Just  beneath  it  the  hypoglossal  nerve  crosses  the  artery, 
and  a  little  lower — about  the  middle  of  the  incision — the  tip  of  the  greater  cornu  of 
the  hyoid  bone  may  be  felt.  At  this  level — above  the  origin  of  the  superior  thyroid 
and  below  that  of  the  lingual — the  artery  lies  just  to  the  inner  side  of  the  internal 
carotid  (but  somewhat  superficial  to  it)  and  of  the  internal  jugular  vein,  and  has  the 
superior  laryngeal  nerve  in  close  relation  behind  it. 

The  internal  carotid  has  been  tied  at  this  level  by  mistake  for  the  external 
carotid.  To  avoid  this  it  should  be  remembered  that  the  external  carotid  (a)  is 
more  anterior  ;  (6)  is  more  superficial  ;  (r)  is  usually  smaller,  especially  in  the 
young  ;  (af)  gives  off  branches  ;  (e)  is  close  to  the  tip  of  the  hyoid  bone  ;  (_/")  is  in 
contact  with  the  hypoglossal  nerve  ;  and  (  g}  that  compression  of  the  isolated  vessel 
arrests  the  temporal  and  facial  pulses.  The  needle  is  passed  from  without  inward  to 
avoid  the  internal  jugular. 

The  ligature  has  been  applied  just  below  the  parotid  gland — i.e.,  above  the 
digastric  muscle.  The  incision  (on  the  same  line)  should  extend  from  the  lobe  of 
the  ear  to  the  hyoid  bone,  the  sterno-mastoid  should  be  drawn  outward,  the  poste- 
rior belly  of  the  digastric  and  the  stylo-hyoid  muscle  downward,  and  the  parotid 
upward  and  inward. 

The  collateral  circulation  is  carried  on  from  the  cardiac  side  through  (a)  the 
branches  of  the  opposite  external  carotid  ;  (3)  the  inferior  thyroid  on  the  affected 
side  ;  (e)  the  branches  of  the  ophthalmic  of  the  same  side  ;  and  (df )  the  profunda 
cervicis,  anastomosing  respectively  with  (a)  the  branches  of  the  ligated  external 
carotid  ;  (&*)  the  superior  thyroid  ;  (c)  the  facial  (from  the  same  vessel — the  external 
carotid)  ;  and  (a?)  the  princeps  cervicis. 

i.  The  Superior  Thyroid  Artery. — The  superior  thyroid  artery  (a.  thy- 
roidea  superior)  (Fig.  692)  arises  from  the  anterior  surface  of  the  external  carotid,  a 
short  distance  above  its  origin,  and  is  at  first  directed  almost  horizontally  anteriorly, 
but  soon  turns  downward  and,  passing  over  the  superior  laryngeal  nerve  and  beneath 
the  omo-hyoid  and  thyro-hyoid  muscles,  breaks  up  into  a  number  of  branches  which 
enter  the  substance  of  the  thyroid  gland.  It  possesses  always  a  calibre  of  consider- 
able size,  but  varies  directly  according  to  the  size  of  the  gland,  and  inversely 
according  to  the  amount  of  blood  reaching  the  gland  from  other  sources.  It  anas- 
tomoses abundantly  with  its  fellow  of  the  opposite  side  and  with  the  inferior  thyroid 
branch  of  the  subclavian. 

Branches. — From  its  horizontal  portion  are  given  off — 

(a)  An  infrahyoid  branch  (ramus  hyoideus),  which   passes  along  the  lower  border  of  the 
hyoid  bone,  supplying  the  muscles  inserting  into  that  bone. 

(b)  A  sterno-mastoid  branch  (ramus  sternodeidomastoideus),  always  small  and  occasionally 
wanting,    which  passes  downward  and  backward   across  tin-  sheath   enclosing  the  common 
carotid  to  enter  the  substance  of  the  sterno-cleido-mastoid  muscle. 

(c)  A  superior  laryngeal  branch  (a.  laryngea  superior),  which  passes  forward  and  downward 
beneath  the  thyro-hyoid  muscle  and,  piercing  the  thyro-hyoid  membrane  along  with  the  supennr 
laryngeal  nerve,  is  distributed  to  the  intrinsic  muscles  and  mucous  membrane  of  the  larynx. 

From  its  descending  portipn  it  gives  ofT — 

(d)  The  crico-thyroid  branch  (ramus  cricothyroideus),  usually  of  small   si/e,  which  passes 
horizontally  forward  over  the  crico-thyroid  membrane  and  anastomoses  with  its  fellow  of  the 
opposite  side,  giving  off  branches  which  perforate  the  membrane  and  are  distributed  to  the 
muscles  and  mucous  membrane  of  the  lower  part  of  the  larynx. 

Variations.— The  superior  thyroid  may  give  origin  to  both  the  asi-ending  ph.iryngeal  and 
the  ascending  palatine.  The  crico-thyroid  'not  infrequently  arises  from  the  superior  laryngeal, 
and  may  appear  to  be  the  main  stem  of  that  artery,  and  the  superior  laryngeal  may  arise  directly 
from  the  external  carotid. 


THE   LINGUAL   ARTERY. 


735 


Practical  Considerations. — The  superior  thyroid  artery  or  one  of  its  branches 
is  frequently  divided  in  cut- throat  wounds.  The  sterno-mastoid  branch  may  have 
to  be  tied  in  the  operation  of  ligation  of  the  common  carotid  at  the  place  of  election 
and  the  crico-thyroid  branch  during-  the  performance  of  laryngotomy. 

Ligation. — The  skin  incision,  two  inches  in  length,  with  its  centre  opposite  the 
thyro-hyoid  space,  is  made  along  the  carotid  line.  After  the  superior  thyroid  veins 
have  been  dealt  with  and  the  external  carotid  has  been  recognized,  the  vessel  may 
most  easily  be  found  in  the  sulcus  between  the  upper  border  of  the  thyroid  cartilage 

FIG.  691. 


•  branch  of  temporal 

Anterior  branch  of  temporal 

Middle  temporal  artery 


Branches  of  posterior 
auricular  artery 


Transverse  facial  artery 

Superficial  temporal  artery 

Great  occipital  nerve 

Trajiezius 

Splenius 
Occipital  artery 

Internal  carotid  artery 

iscending  cervical 
External  carotid  artery 
I.evator  anj,'uli  scapul:e 

Common  carotid  artery 
Scalenus  medius 

Transverse  cervical — -     _ 
Posterior  scapular ^ 


Supra-orbital  artery  (shown 
thro'  cut  in  the  muscles) 


Frontal  artery 
.isal  artery 

Angular  artery 


Facial  vein 
Lateral  nasal  artery 

Termination  <>f 

infra-orbital  artery 
Septal  artery 

Superior  cor.  .nary 

Buccinator 
Inferior  labial  artery 

Masseteric  branch 
Facial  artery 


Submental  artery 
^-Muscular  branch 
Submaxillary  branch 


Superior  thyroid  artery 
Thyro-hyoid  muscle 

Sterno-mastoid  branch 
Omo-hyoid  muscle 
'Sterno-hyoid  muscle 

Sterno-thyroid  muscle 


Subclavian  artery 

Subclavian  vein 

Superficial  dissection,  showing  arteries  of  neck,  face  and  scalp. 

and  the  great  vessels,  where  for  a  short  distance  it  is  superficial  and  run's  almost 
horizontally. 

The  needle  should  be  passed  from  above  downward  with  the  point  directed  some- 
what towards  the  mid-line.  The  close  proximity  posteriorly  of  the  superior  laryngeal 
nerve  should  be  remembered. 

2.  The  Lingual  Artery.— The  lingual  artery  (a.  lingualis)  (Fig.  692)  usually 
arises  from  the  anterior  surface. of  the  external  carotid,  between  the  origins  of  the 
superior  thyroid  and  the  facial,  although  it  is  sometimes  given  off  from  a  trunk 


736  HUMAN   ANATOMY. 

common  to  it  and  one  or  other  of  these  arteries,  especially  the  facial.  In  the  first  part 
of  its  course  it  passes  forward  and  slightly  upward  and  inward  towards  the  tip  of  the 
lesser  cornu  of  the  hyoid  bone,  and  is  crossed  by  the  posterior  belly  of  the  digastric 
and  the  stylo-hyoid  muscles  and  by  the  hypoglossal  nerve.  On  reaching  the  p<»- 
terior  border  of  the  hyo-glossus,  it  passes  beneath  that  muscle  and  is  continued 
almost  directly  forward  beneath  the  mucous  membrane  covering  the  under  surface  of 
the  tongue  and  between  the  genio-hyo-glossus  and  the  inferior  lingualis  muscles.  In 
this  terminal  portion  it  has  a  sinuous  course,  and  is  frequently  termed  the  ranine 
artery  (a.  profunda  linguae);  it  gives  branches  to  the  adjacent  muscular  substance 
and  mucous  membrane  of  the  tongue,  and  near  its  termination  anastomoses  with  its 
fellow  of  the  opposite  side. 

Branches. — (a)  The  suprahyoid  branch  (ramus  hyoideus),  given  off  from  the  first  portion, 
passes  horizontally  forward  over  the  hyoid  bone,  sending  branches  to  the  muscles  which  are 
inserted  into  that  bone  from  below. 

(A)  The  dorsal  lingual  branch  (rami  dorsales  linguae),  from  the  second  portion,  arises 
under  cover  of  the  posterior  border  of  the  hyo-glossus  and,  passing  upward  medial  to  the  stylo- 
glossus,  breaks  up  into  branches  which  are  distributed  to  the  mucous  membrane  of  the  dorsum 
of  the  tongue,  as  far  back  as  the  epiglottis,  and  also  to  the  tonsil.  Occasionally  a  branch  unites 
with  a  corresponding  one  from  the  artery  of  the  opposite  side,  immediately  in  front  of  the  fora- 
men caecum,  and  is  continued  forward  in  the  median  line,  immediately  beneath  the  mucous 
membrane  of  the  dorsum  of  the  tongue,  as  far  as  the  tip. 

(c)  The  sublingual  branch  (a.  sublingualis)  is  given  off  near  the  anterior  border  of  the  hyo- 
glossus  muscle  and  runs  forward  in  the  same  plane  as  the  ranine  artery,  but  on  a  lower  level, 
resting  upon  the  mylo-hyoid  muscle  and  lying  between  the  genio-hyoid  laterally  and  the  genio- 
hyo-glossus  medially.  It  is  accompanied  by  thesubmaxillary  (Wharton's)  duct,  which  lies  upon 
its  medial  side,  and  it  terminates  in  the  sublingual  gland,  also  sending  branches  to  the  neighbor- 
ing muscles  and  to  the  alveolar  border  of  the  mandible. 

Anastomoses. — The  various  branches  of  the  lingual  artery  anastomose  exten- 
sively with  their  fellows  of  the  opposite  side.  The  anastomoses  of«  the  two  aa.  dor- 
sales  linguae  take  place,  however,  only  through  exceedingly  fine  twigs,  so  that  the 
tongue  may  be  divided  longitudinally  in  the  median  line  without  any  great  loss  of 
blood,  except  towards  the  tip,  where  a  larger  anastomosis  of  the  ranine  arteries  occurs. 
In  addition  to  these  contra-lateral  anastomoses,  the  lingual  also  anastomoses  through 
its  suprahyoid  branch  with  the  infrahyoid  of  the  superior  thyroid  artery,  through 
its  sublingual  branch  with  the  submental  branch  of  the  facial,  and  through  the  a. 
dorsalis  linguae  with  the  various  tonsillar  arteries. 

Variations. — The  lingual  artery  sometimes  arises  from  a  common  trunk  with  the  facial, 
and  it  has  been  observed  to  terminate  at  the  root  of  the  tongue,  being  replaced  in  the  rest  of  its 
course  by  branches  from  the  internal  maxillary  or  by  the  submental  branch  of  the  facial.  The 
sublingual  branches  are  not  infrequently  lacking,  being  replaced  by  branches  of  the  submental, 
and,  in  addition  to  its  normal  branches,  the  main  artery  may  give  rise  to  a  superior  laryngeal  and 
an  accessory  superior  thyroid  branch. 

Practical  Considerations. — The  lingual  artery  is  tied  most  frequently  as  a 
preliminary  to  excision  of  the  whole  or  part  of  the  tongue,  but  one  or  both  arteries 
may  be  ligated  to  stop  bleeding  following  wound  or  malignant  ulceration  of  that 
organ,  or  in  an  effort  to  arrest  growth  by  cutting  off  Wood-supply,  as  in  cases  of 
cancer  of  the  tongue  or  of  macroglossia. 

f.itration. — The  artery  is  for  convenience  divided  into  three  portions,  the //Y.v/ 
between  its  origin — about  opposite  the  greater  cornu  of  the  hyoid — and  the  posterior 
edge  of  the  hyo-glossus  muscle,  lying  upon  the  middle  constrictor  of  the  pharynx  ; 
the  st-fond  beneath  the  hyo-glossus  muscle,  lying  upon  the  genio-glossus  :  the  third, 
( ranine }  from  the  anterior  border  of  the  hyo-glossus  along  the  under  surface  of  the 
tongue  to  its  termination. 

The  place  of  election  is  in  the  second  part.  The  skin  incision,  two  inches  in 
length,  curved,  with  the  concavity  upward,  begins  a  half- inch  below  and  external  to 
the  mandibular  symphysis  and  ends  a  little  below  and  internal  to  the  point  where 
the  facial  artery  crosses  the  lower  edge  of  the  inferior  maxilla  ;  its  centre  is  just 
above  the  greater  cornu  of  the  hyoid.  If  the  incision  is  carried  too  far  backward, 


*  THE   FACIAL   ARTERY.  737 

the  facial  vein  may  be  cut.  The  remainder  of  the  operation  may  be  described  as  if 
it  were  done  in  four  stages.  i.  That  portion  of  the  deep  fascia  constituting  the 
anterior  layer  of  the  capsule  of  the  submaxillary  gland  is  divided  in  the  line  of  the 
incision,  the  lower  edge  of  the  gland  exposed,  and  the  gland  itself  cleared  and  ele- 
vated over  the  lower  jaw,  with  due  care  to  avoid  injury  to  the  facial  artery  which 
passes  through  its  substance  and  the  facial  vein  which  runs  upon  its  surface.  2. 
The  thin  posterior  leaf  of  the  capsule  of  the  gland  being  divided,  the  white,  shining 
aponeurotic  loop  attaching  the  digastric  tendon  to  the  greater  cornu  of  the  hyoid 
will  be  seen.  The  tendon  near  the  bone  or  the  digastric  aponeurosis  should  be  fixed 
by  a  blunt  hook  or  tenaculum  and  drawn  downward  and  towards  the  surface.  3. 
After  the  division  of  the  posterior  layer  of  the  capsule  of  the  submaxillary  gland,  the 
posterior  edge  of  the  mylo-hyoid  muscle,  the  fibres  running  upward  and  slightly 
backward,  can  be  recognized  at  the  anterior  angle  of  the  wound  and  should  be 
clearly  defined.  4.  The  hypoglossal  nerve  separates  from  the  artery  at  the  poste- 
rior border  of  the  hyo-glossus  muscle,  where  the  vessel  disappears  to  run  between 
that  muscle  and  the  middle  .constrictor.  The  nerve,  accompanied  by  the  ranine 
vein,  runs  almost  horizontally  across  the  surface  of  the  hyo-glossus,  and  in  its  turn 
disappears  under  the  edge  of  the  mylo-hyoid  muscle.  It  will  have  been  brought 
into  view  when  the  submaxillary  gland  has  been  raised,  the  posterior  layer  of  its 
capsule  divided,  and  a  little  fatty  connective  tissue  picked  away.  In  the  irregular 
triangle  formed  by  the  nerve  above,  the  mylo-hyoid  anteriorly,  and  the  posterior 
belly  and  tendon  of  the  digastric  posteriorly,  the  lingual  artery  runs  beneath  the 
hyo-glossus  muscle  and  near  the  apex  of  the  triangle — i.e.,  near  the  hyoid  bone. 
The  nerve  and  vein,  which  are  on  a  slightly  higher  level — a  few  millimetres — 
having  been  raised  and  the  fibres  of  the  hyo-glossus  divided  parallel  with  the  hyoid 
and  just  above  it,  the  artery  will  be  brought  into  view. 

In  ligation  of  the  lingual  for  carcinoma  of  the  tongue,  the  state  of  the  salivary 
gland,  which  varies  in  size,  in  density,  and  in  the  closeness  of  its  attachments,  is  the 
main  element  of  uncertainty  (Treves). 

3.  The  Facial  Artery. — The  facial  artery  (a.  maxillaris  externa)  (Fig.  691) 
arises  usually  a  short  distance  above  the  lingual,  from  the  anterior  surface  of  the 
external  carotid.  It  passes  at  first  forward  and  slightly  upward,  lying  beneath  the 
posterior  belly  of  the  digastric  and  the  stylo-hyoid  muscles  and  the  hypoglossal  nerve, 
and  is  then  continued  almost  horizontally  forward  in  a  groove  in  the  submaxillary 
gland.  When  it  reaches  the  level  of  the  anterior  border  of  the  masseter  muscle,  it 
assumes  a  vertical  direction  and  passes  over  the  ramus  of  the  mandible,  and  is  then 
continued  in  a  sinuous  course  obliquely  across  the  face  towards  the  naso-labial  angle, 
resting  upon  the  buccinator  and  levator  anguli  oris  muscles,  and  being  crossed  by  the 
risorius  and  zygomatic  muscles  and  by  some  branches  of  the  facial  nerve.  Arrived  at 
the  naso-labial  angle,  it  again  takes  an  almost  vertical  course,  passing  upward  beneath 
(or  sometimes  over)  the  levator  labii  superioris  and  the  levator  labii'superioris  alaeque 
nasi  towards  the  inner  angle  of  the  orbit,  where  it  terminates  by  anastomosing  with 
the  nasal  branch  of  the  ophthalmic  artery.  This  terminal  vertical  portion  of  the 
vessel  is  usually  termed  the  angular  artery  (a,  angularis). 

Branches. -The  branches  of  the  facial  artery  (  Figs.  691,  693)  may  be  arranged  in  two 
groups  according  to  their  origin  from  the  cervical  or  facial  portions  of  the  artery. 

From  the  cervical  portion  arise  :  (a)  The  ascending  palatine  branch  (a.  palatina  ascen- 
dens),  a  small  artery  which  passes  upward  between  the  stylo-glossus  and  stylo-pharyngeus  mus- 
cles, to  which  it  sends  branches,  and  then  comes  to  lie  upon  the  outer  surface  of  the  superior 
constrictor  of  the  pharynx.  It  terminates  by  sending  branches  to  the  soft  palate,  the  tonsil, 
and  the  Eustachian  tube. 

[b]  The  tonsillar  branch  (ramus  tonsillaris)  is  another  small  branch  which  passes  verti- 
cally upward.  It  arises  close  to  the  ascending  palatine  and,  passing  over  the  stylo-glossus 
muscle,  pierces  the  superior  constrictor  of  the  pharynx  to  be  distributed  to  the  tonsil. 

(r)  The  glandular  branches  (raini  glandulares),  two  or  three  in  number,  are  distributed  to 
the  submaxillary  gland. 

(of)  The  submental  branch  fa.  submentalis)  arises  just  before  the  artery  bends  upward 
over  the  mandible,  and  continues  onward  in  the  horizontal  course  followed  by  the  facial, 

47 


738  HUMAN   ANATOMY.  * 

through  the  submaxillary  gland.  It  passes  forward  upon  the  mylo-hyoid  muscle,  close  to  its 
origin,  until  it  reaches  the  insertion  of  the  anterior  belly  of  the  digastric,  when  it  passes  upward 
•upon  the  ramus  of  the  mandible  to  supply  the  depressor  labii  mferioris  and  to  anastomose  with 
the  mental  branches  of  the  inferior  dental  artery  and  with  the  interior  labial  branches  of  the 
facial.  It  sends  branches  to  the  muscles  in  its  vicinity  and  also  to  the  integument,  and  branches 
perforate  the  mylo-hyoid  muscle  to  anastomose  with  the  sublingual  brandies  of  the  lingual. 

From  the  facial  portion,  (e)  The  masseteric  branches  arise  from  the  posterior  surface  of 
the  artery — and  are  directed  upward  to  supply  the  masseter  muscle  and  to  anastomose  with 
branches  of  the  internal  maxillary  and  transverse  facial  arteries. 

(f)  The  inferior  labial  branch  (a.  labialis  inferior)  passes  forward  along  the  outer  surface 
of  the  horizontal  ramus  of  the  mandible,  supplying  the  depressor  angiili  oris,  the  depressor 
labii  inferioris,  and  the  integument,  and  anastomosing  with  the  mental  branches  of  the  inferior 
dental  and  submental  arteries. 

(g)  The  inferior  coronary  artery  passes  forward  in  the  substance  of  the  lower  lip  between 
the  mucous  membrane  and  orbicularis  oris,  supplying  the  latter,  and  terminates  by  anastomosing 
with  its  fellow  of  the  opposite  side. 

(h)  The  superior  coronary  artery  (a.  labialis  superior)  has  the  same  course  and  relations  in 
the  upper  lip  that  the  inferior  coronary  has  in  the  lower  one.  •  It  anastomoses  with  its  fellow  of 
the  opposite  side,  and  near  its  termination  usually  sends  a  small  branch  upward  to  the  septum 
of  the  nose,  the  a.  septi  narium. 

(i)  The  lateral  nasal  takes  its  origin  just  as  the  artery  reaches  the  naso-labial  angle  ;  it 
passes  forward  over  the  ala  of  the  nose,  supplying  its  muscles  and  integument. 

(j)  The  angular  artery  (a.  angularis)  is  the  terminal  portion  of  the  facial  artery  beyond 
the  naso-labial  angle.  It  passes  directly  upward  in  the  angle  between  the  nose  and  the  cheek, 
and  gives  branches  to  the  adjacent  muscles,  the  lachrymal  sac,  and  the  orbicularis  palpebrarum, 
anastomosing  with  the  nasal  branch  of  the  ophthalmic  artery  and  with  the  infra-orbital  branch 
of  the  internal  maxillary. 

Anastomoses. — The  facial  artery,  by  means  of  its  facial  branches  and  the  sub- 
mental  arteries,  makes  abundant  anastomoses  with  its  fellow  of  the  opposite  side. 
In  addition,  it  is  connected  with  other  branches  of  the  external  carotid;  with  the 
dorsalis  linguae  and  submental  branches  of  the  lingual  by  its  tonsillar  and  inferior 
labial  branches  respectively;  with  the  descending  palatine,  infra-orbital  branches,  and 
mental  branches  of  the  internal  maxillary  by  its  tonsillar,  angular,  and  inferior  labial 
branches;  and  with  the  transverse  facial  branch  of  the  superficial  temporal  by  its 
masseteric  branches.  Finally,  it  is  connected  with  the  ophthalmic  branch  of  the 
internal  carotid  by  the  angular  artery. 

Variations. — The  facial  artery  may  arise  by  a  trunk  common  to  it  and  the  lingual,  or  it 
may  arise  above  the  level  of  the  angle  of  the  jaw.  Quite  frequently  it  does  not  extend  upon  the 
face  beyond  the  angle  of  the  mouth,  being  replaced  in  the  upper  part  of  its  course  by  branches 
from  the  transverse  facial  or  internal  maxillary  artery. 

The  ascending  palatine  branch  frequently  arises  directly  from  the  external  carotid,  or  it 
may  take  its  origin  from  the  ascending  pharyngeal  or  from  the  occipital,  and  the  tonsillar  is 
frequently  a  branch  of  it.  The  submental  branch  may  be  greatly  reduced  in  size  or  even 
absent,  being  replaced  in  whole  or  in  part  by  the  sublingual,  these  two  arteries  being  inversely 
proportionate  to  each  other  so  fai  as  their  development  is  concerned. 

Practical  Considerations. — The  facial  artery  may  require  ligation  on  account 
of  division  of  one  of  its  branches,  as  the  coronary,  but  whenever  direct  ligation 
of  the  wounded  vessel  is  possible,  it  is  preferable  on  account  of  the  very  free 
anastomosis  betwreen  the  branches  of  opposite  sides,  leading  usually,  after  ligation 
of  the  main  trunk,  to  recurrence  of  the  hemorrhage.  In  bleeding  after  tonsillotomy 
(page  1608),  either  the  tonsillar  branch  of  the  facial  or  the  main  vessel  (where  it  runs 
between  the  posterior  belly  of  the  digastric  and  the  stylo-glossus  muscles)  may  be 
involved  ;  but  as  the  blood  may  also  be  furnished  by  the  ascending  pharyngral. 
ligation  of  the  external  carotid  itself  rather  than  of  the  facial  would  be  more  likely  to 
be  efficient. 

legation. — (#)  The  cervical  portion  of  the  vessel  maybe  reached  through  an 
incision  like  that  for  the  lingual,  placed  a  little  higher,  and  not  extending  so  far 
anteriorly.  When  the  submaxillary  gland  is  drawn  upward,  the  artery  will  be  drawn 
with  it  and  made  prominent.  This  portion  may  also  be  reached  near  its  origin  by 
uncovering  the  external  carotid  (q.t>. )  and  identifying  the  vessel  where  it  runs 


THE    INTERNAL   MAXILLARY   ARTERY. 


between  the  posterior  belly  of  the  digastric  above  and  the  hypoglossal  nerve  below. 
(£)  The  facial  portion  is  easily  exposed  where  it  crosses  the  mandible  at  the  ante- 
rior border  of  the  masseter,  either  by  a  vertical  cut  parallel  with  that  muscle  and  the 
artery  or  by  a  horizontal  cut  crossing  the  vessel  and  placed  under  the  inferior  margin 
of  the  jaw  so  as  to  leave  the  scar  in  an  inconspicuous  position.  Beneath  the  skin 
and  the  superficial  fascia  the  platysma  and  deep  fascia  are  the  only  structures  that 
require  division.  The  vein  lies  in  the  groove  between  the  artery  and  the  edge  of  the 
masseter. 

4.   The  Internal  Maxillary  Artery. — The  internal  maxillary   (a.  maxillaris 
interna)  (Fig.  692)  is  a  large  branch  which  arises  from  the  anterior  surface  of  the 

FIG.  692. 


Small  meningeal  branch 
Middle  meningeal 

Tympanic  ti:anch 
Superficial  tem]>oral 

Stylo-mastoid 
Meningeal  branch 

Posterior  auricular 

Trach< 

O 

Sterno-m 


of  internal  maxillary 
y  to  superior  maxilla 


Posterior  superior  dental 

Internal  maxillary  artery 
Inferior  dental  arlery 
Buccal  branch 
Internal  pterygoid  muscle 


>Ranine  artery 
.Tonsilar  artery 
.Ascending  palatine 
Facial  artery,  cut 
"ublingual  artery 
Dorsalis  linguae 


Scalenus  anticus 

Longus  colli 

Superficial  cervical 

Posterior  scapular 


Scalenus  niedius 
Tendinous  origin  of  Scalenus  medius 


oid  artery 
Thyroid  axis 
Vertebral  artery 
Subclavian  artery 


ammary  artery. 


Sterno-mastoid  brancn  Suprascapular  artery 

Deeper  dissection,  showing  carotid  and  subclavian  arteries. 


external  carotid,  opposite  the  neck  of  the  mandible.  It  passes  forward  with  a  flexuous 
course,  lying  at  first  between  the  neck  of  the  mandible  and  the  spleno-mandibular 
ligament,  and  then  passing  either  between  the  two  pterygoid  muscles,  in  which  case  it 
crosses  the  inferior  dental  and  lingual  nerves,  or  else  over  the  external  surface  of  the 
external  pterygoid,  between  that  muscle  and  the  temporal.  It  then  passes  between 
the  two  heads  of  the  external  pterygoid,  in  the  one  case  passing  from  below  upward 
and  in  the  other  from  without  inward,  and  enters  the  spheno-maxillary  fossa,  in 
which  it  is  directed  upward  and  inward  towards  the  spheno-palatine  foramen,  which 
it  traverses  under  the  name  of  the  spheno-palatine  artery. 

Branches. — For  convenience  in  description  it  is  customary  to  regard  the  internal  maxillary 
artery  as  consisting  of  three  portions.     Its  first,  or  mandibular  portion,  is  that  which  lies  inter- 


740  HUMAN   ANATOMY. 

nal  to  the  neck  of  the  mandible  ;  the  second,  or  pterygoid  portion,  is  that  which  traverses  the 
pterygoid  fossa,  and  is  in  relation  with  the  pterygoid  muscles  ;  and  the  third,  or  spheno-nia.Yil- 
lary  portion,  extends  from  where  it  passes  between  the  two  heads  of  the  external  pterygoid  mus- 
cle to  its  entrance  into  the  spheno-palatine  foramen.  Of  the  sixteen  named  branches  arising  from 
the  internal  maxillary  artery,  five  arise  from  the  first  portion,  five  from  the  second,  and  six  from 
the  third. 

From  the  first  or  mandibular  portion  arise  (i)  the  deep  auricular,  (2)  the  tympanic,  (3) 
the  middle  meningeal,  (4)  \\\<z  small  meningeal,  and  (5)  the  inferior  denial  arteries. 

(a)  The  deep  auricular  (a.  auricularis  profunda)  is  a  small  branch  which  passes  behind  the 
temporo-mandibular  articulation,  to  which  it  sends  branches,  and  perforates  the  anterior  wall  of 
the  external  auditory  meatus  to  supply  the  skin  lining  that  passage  and  the  outer  surface  of  the 
tympanic  membrane. 

(6)  The  tympanic  (a.  tympanica  anterior),  also  a  small  branch,  passes  upward,  giving  off 
branches  to  the  temporo-mandibular  articulation,  and  enters  the  Glaserian  fissure.  Thence  it 
traverses  the  iter  chordae  anterius  along  with  the  chorda  tympani,  and  reaches  the  middle  ear,  to 
whose  mucous  membrane  it  is  distributed,  anastomosing  with  the  tympanic  branches  of  the  stylo- 
mastoid  artery. 

(c)  The  middle  meningeal  (a.  meningea  media)  is  the  largest  of  all  the  branches.     It  as- 
cends vertically  towards  the  base  of  the  skull  and  enters  the  cranium  by  the  foramen  spinosum, 
and,  after  passing  outward  and  upward  for  a  short  distance  upon  the  great  w  ing  of  the  sphenoid, 
divides  into  an  anterior  and  a  posterior  terminal  branch,  which  ramify  over  the  surface  of  the 
dura  and  supply  nearly  the  whole  of  its  lateral  and  superior  surfaces,  making  abundant  anasto- 
moses with  the  vessel  of  the  opposite  side.     The  anterior  branch,  the  larger  of  the  two  terminal 
branches,  passes  obliquely  forward  over  the  greater  wing  of  the  sphenoid,  crosses  the  anterior 
inferior  angle  of  the  parietal,  and  then  ascends  along  the  anterior  border  of  that  bone  almost  to 
the  superior  longitudinal  sinus,  sending  off  numerous  branches.     The  posterior  branch  passes 
backward  and  upward  over  the  squamous  portion  of  the  temporal  bone,  and  then  over  the  pos- 
terior part  of  the  parietal  bone,  giving  off  numerous  branches  which  pass  upward  as  far  as  the 
superior  longitudinal  sinus  and  backward  as  far  as  the  lateral  sinus.     In  addition  to  these  ter- 
minal branches,  the  main  stem  within  the  cranium  also  gives  origin  to  (aa)  a petrosal  branch 
(a.  petrosus  superficialis)  which  enters  the  hiatus  Fallopii  and  anastomoses  with  the  terminal  por- 
tion of  the  stylo-mastoid  arteries  ;  to  (bb)  Gasserian  branches,  minute  twigs  which  pass  to  the 
Gasserian  ganglion  and  the  fifth  nerve  ;  to  (rr)  a  tympanic  branch  (a.  tympanica  superior)  which 
descends  through  the  petro-squamous  suture  to  the  mucous  membrane  of  the  middle  ear  and  the 
mastoid  cells  ;  and,  finally,  to  (dd )  an  orbital  branch,  a  small  vessel  that  passes  into  the  orbit 
through  the  outermost  portion  of  the  sphenoidal  fissure  and  anastomoses  with  the  lachrymal 
branch  of  the  ophthalmic. 

(d)  The  small  meningeal  (r.  meningeus  accessorius)   is  an  inconstant  branch,  sometimes 
arising  from  the  middle  meningeal.     It  passes  upward  along  the  mandibular  division  of  the  fifth 
nerve,  and  enters  the  cranium  through  the  foramen  ovale  to  be  distributed  to  the  Gasserian 
ganglion  and  the  dura  mater  in  its  neighborhood. 

(e)  The  inferior  dental  (a.  alveolaris  inferior)  is  given  off  from  the  lower  surface  of  the  artery 
and  descends  along  with  the  inferior  dental  nerve  to  the  mandibular  foramen.     Before  reaching 
the  foramen  it  gives  off  (aa)  a  lingual  branch,  which   accompanies  the  lingual  nerve  to  the 
tongue,    and   (bb)  a  mylo-hyoid  branch  (ramus  mylohyoideus),  accompanying  the   mylo-hyoid 
nerve  to  the  muscle  of  that  name.     Entering  the  mandibular  foramen,  it  traverses  the  man- 
dibular canal,  giving  off  branches  to  the  roots  of  the  lower  teeth  as  it  passes  them,  and  finally 
emerges  at  the  mental  foramen  as  (cc)  the  mental  artery  (a.  mentalis),  supplying  the  neighboring 
muscles  and  integument  and  anastomosing  with  the  subnu-ntal  and  inferior  labial  branches  of  tin- 
facial.     Just  before  issuing  from  the  mental  foramen  it  gives  off  (dd)  an  incisive  branch  which 
distributes  twigs  to  the  incisor  teeth. 

From  the  second,  or  pterygoid  portion,  arise  branches  distributed  chiefly  to  the  adjacent 
muscles;  they  are  (i)  the  massctcric,  (2)  the  deep  temporal,  (3  and  4)  the  internal  and  <•.»/,;- 
nal  pterygoid,  and  (5)  the  bnccal  artery. 

(/)  The  masseteric  branch  (a.  masseterica)  passes  with  the  corresponding  nerve  through 
the  sigmoid  notch  of  the  mandible  to  enter  the  deep  surface  of  the  masseter. 

(ff)  The  deep  temporal  branches  are  two  in  number,  the  anterior  and  the  posterior.  The 
posterior  branch  (a.  temporalis  profiuKla  posterior  t  arises  close  to  or  in  common  with  the  mas 
sftc-rir,  while  the  anterior  one  (a.  tempnralis  profunda  anterior1)  is  given  off  near  tin-  termination 
of  the  pterygoid  portion  of  the  artery.  They  both  pass  upward  between  tin-  temporal  muscle 
and  the  bone,  supplying  the  muscle  and  anastomosing  with  the  middle  temporal  branch  of  tin 
temporal  artery. 

(A  and  i)  The  internal  and  external  pterygoid  branches  (ram i  pterygoidei )  are  short  and 
variable  in  number.  They  pass  dirvctly  into  the  muscles  of  the  same  names. 


THE    INTERNAL    MAXILLARY   ARTERY. 


(y)  The  buccal  branch  (a.  bucdnatoria )  passes  downward  and  forward  with  the  buccal 
nerve  along  the  anterior  border  of  the  tendon  of  the  temporal  muscle,  and  supplies  the  bucci- 
nator muscle  and  the  mucous  membrane  of  the  mouth. 

From  the  third  or  spheno-maxillary  portion  arise  (i)  the  alveolar,  (2)  the  infraorbital, 
(3)  the  descending  palatine,  (4)  the  I'idian,  (5)  the  pterygo-palatine,  and  (6)  the  spheno- 
t>alatine. 

(&)  The  alveolar  branch  (a.  alveolaris  superior  posterior)  descends  upon  the  tuberosity  of 
the  maxilla,  giving  off  branches  which  penetrate  small  foramina  in  that  bone  and  are  distributed 
to  the  molar  and  premolar  teeth  and  the  gums  of  the  upper  jaw  and  to  the  mucous  membrane 
lining  the  antrum  of  Highmore.  The  main  stem  terminates  upon  the  tuberosity  of  the  maxilla 
by  breaking  up  into  a  plexus  with  which  branches  from  the  buccal  artery  unite. 

FIG.  693. 


Anterior  temporal 
Posterior  temporal 

Middle  temporal 

Transverse  facial 

Great  meningeal 

Superficial  temporal 

Small  meningeal 

Tympanic 

Internal  maxillary 

Inferior  dental  artery 

Mylo-hyoid  artery 

Posterior  auricular 

Inferior  dental  nerve 

Sterno-mastoid  artery 

Occipital  artery 

Tonsillar  artery 

Ascending  palatine 

Hypoglossal  nerve 

Facial  artery 

Internal  carotid 

External  carotid 

Superior  thyroid 

Common  carotid 

Sterno-mastoid  arterv 


Coronoid  process 
of  mandible  with 
insertion  of  tem- 
poral muscle 

-  Buccinator 

-Superior  coro- 
nary artery 

Inferior  coro- 
nary artery 

Inferior  labial 
artery 

Mental  branch  of 
facial  emerging 
from  mental  for- 
amen 

Submental  artery 


Genio-hyoid 

muscle 
Lingual  artery 

Hyoglossus  mus- 
cle, cut 

Mylo-hyoid   mus- 
cle of  left  side 

Superior  laryn- 
geal  artery 

Thyro-hyoid 
muscle 


External  carotid,  internal  maxillary  and  inferior  dental  arteries  ;  condyle  and 
outer  table  of  mandible  have  been  removed. 

(/)  The  infraorbital  artery  (a.  infraorbitalis)  frequently  arises  in  common  with  the  alveolar. 
It  passes  forward  and  upward  through  the  spheno-maxillary  fossa  and  the  spheno-maxillary 
foramen  to  traverse  the  infraorbital  groove  and  canal  along  with  the  infraorbital  nerve.  In  this 
part  of  its  course  it  gives  off  (aa)  orbital  branches,  distributed  to  the  adipose  tissue  of  the  orbit 
and  to  the  neighboring  muscles  of  the  eye,  and  (bb)  anterior  dental  branches  (aa.  alveolares 
superiores  anteriores)  which  pass  down  the  anterior  wall  of  the  antrum  of  Highmore,  along  with 
the  anterior  and  middle  superior  dental  nerves,  to  supply  the  mucous  membrane  lining  the 
antrum  and  the  canine  and  incisor  teeth  of  the  upper  jaw.  The  main  stem  emerges  upon  the 
face  at  the  infraorbital  foramen  and  divides  into  (cc)  palpebral,  (dd)  nasal,  and  fee]  labial 
branches,  whose  distribution  is  indicated  by  their  names,  and  which  anastomose  with  the  nasal 
and  lachrymal  branches  of  the  ophthalmic  artery,  the  transverse  facial  branch  of  the  superficial 
temporal,  and  the  superior  coronary  and  angular  branches  of  the  facial. 

(in)  The  descending  palatine  artery  fa.  palatina  descendens)  accompanies  the  anterior  pala- 
tine nerve  from  the  spheno-palatine  ganglion  through  the  posterior  palatine  canal,  and,  on  its 


742  HUMAN   ANATOMY. 

emergence  from  the  posterior  palatine  foramen,  divides  into  an  anterior  and  a  posterior  branch. 
The  former  passes  forward  beneath  the  mucous  membrane  of  the  hard  palate,  which  it  supplies, 
and  at  the  anterior  palatine  foramen  anastomoses  with  the  spheno-palatine  artery;  the  latter 
passes  backward  to  supply  the  soft  palate  and  the  tonsil,  anastomosing  with  the  ascending 
palatine  branch  of  the  facial. 

I  //)  The  Vidian  artery  (;i.  canalis  pterygoidei )  is  a  small  branch  which  passes  backward  along 
tiie  Yidian  nerve  through  the  Yidian  canal,  and  sends  branches  to  the' roof  of  the  pharynx  and 
to  the  Eustachian  tube. 

(o)  The  pterygo-palatine  artery  (a.  palatina  major)  is  also  a  somewhat  slender  branch.  It 
passes  backward  through  the  pterygo-palatine  foramen  along  with  the  pharyngeal  nerve  from 
the  spheno-palatine  ganglion,  and  supplies  the  roof  of  the  pharynx,  the  Eustachian  tube,  and 
the  mucous  membrane  lining  the  sphenoidal  cells. 

(/>)  The  spheno-palatine  artery  (a.  sphenopalatina )  is  the  terminal  branch  of  the  internal 
maxillary.  It  passes  into  the  nasal  cavity  through  the  spheno-palatine  foramen  along  with  the 
spheno-palatine  nerve  from  the  spheno-palatine  ganglion.  Shortly  after  traversing  the  foramen 
it  divides  into  an  internal  and  an  external  branch.  The  internal  branch,  sometimes  termed  the 
naso-palatine,  passes  transversely  across  the  roof  of  the  nasal  cavity  to  reach  the  septum,  upon 
which  it  passes  downward  and  forward,  giving  off  numerous  branches  which  anastomose  to  form 
a  rich  net-work  beneath  the  mucous  membrane  of  the  septum.  It  finally  reaches  the  anterior 
palatine  foramen,  where  it  anastomoses  with  the  anterior  branch  of  the  descending  palatine. 
Throughout  its  course  it  is  accompanied  by  the  naso-palatine  nerve.  The  external  branch 
ramifies  downward  and  forward  over  the  lateral  wall  of  the  nasal  fossa,  forming  a  rich  plexus 
beneath  the  mucous  membrane  lining  the  meatuses  and  the  turbinate  bones. 

It  will  be  observed  that  all  the  branches  arising  from  the  first  and  third  portions  of  the 
internal  maxillary  artery  traverse  bony  canals  or  foramina,  while  those  of  the  second  portion 
do  not,  but  are  distributed  directly  to  muscles. 

Anastomoses. — The  communications  of  the  internal  maxillary  artery  are  with 
the  branches  of  the  artery  of  the  opposite  side,  with  other  branches  of  the  artery  of  the 
same  side,  with  other  branches  of  the  external  carotid,  and  with  branches  of  the 
internal  carotid.  The  most  abundant  anastomoses  with  the  artery  of  the  opposite 
side  are  made  through  the  branches  of  the  middle  meningeal;  the  alveolar  branch 
anastomoses  with  the  dental  branches  of  the  infraorbital  of  the  same  side  and  with 
the  buccal  artery,  and  the  anterior  branch  of  the  descending  palatine  makes  a  large 
anastomosis  with  the  naso-palatine  branch  of  the  spheno-palatine  at  the  anterior 
palatine  foramen.  The  other  branches  of  the  external  carotid  with  which  anastomoses 
are  made  are  the  facial,  the  temporal,  and  the  posterior  auricular;  the  facial  com- 
municates by  means  of  its  submental  and  inferior  labial  branches  with  the  mental 
branch  of  the  inferior  dental,  by  its  superior  coronary  and  angular  branches  with  the 
terminal  branches  of  the  infraorbital,  by  its  superior  coronary  with  branches  of  the 
naso-palatine,  and  by  its  ascending  palatine  with  branches  of  the  descending  palatine. 
The  deep  temporal  arteries  anastomose  with  branches  of  the  superficial  temporal  and 
the  infraorbital  with  the  transverse  facial  branch  of  the  same  artery;  while  the 
posterior  auricular  communicates  by  means  of  its  stylo-mastoid  branch  with  the 
tympanic  branch  and  with  the  petrosal  branch  of  the  middle  meningeal. 

Of  the  anastomoses  with  the  internal  carotid  arteries  the  most  important  are 
those  between  the  orbital  branch  of  the  middle  meningeal  and  the-  lachrymal  artery. 
between  the  terminal  branches  of  the  infraorbital  and  the  terminal  branches  of  the 
ophthalmic,  and  between  the  spheno-palatine  branches  and  the  ethmoidal  arteries. 

Variations. — In  the  early  stages  of  development  the  main  portion  of  the  internal  maxillary 
is  represented  by  a  Stem  which  arises  from  tin-  internal  carotid  (Tandler).  This  is  known  as 
the  a.  stapedia  (Fig.  694,  Ast},  since  it  traverses  the  middle  ear,  passing  through  the  foramen 
of  the  stapes  (st}\  it  makes  its  exit  from  the  middle  ear  by  the  ('.laserian  fissure  and  divides  into 
two  stems,  one  of  which  (  Rs~]  passes  through  the  foramen  spinosnm  (.As/)  and  is  distributed  to 
tin-  snpraorbital  region,  while  the  other  divides  into  two  branches  which,  from  their  distribution, 
are  termed  the  infraorbital  (  A'/  )  and  the  mandibular  (inferior  dental)  (/\in).  A  branch  i_  A'(/.v . 
arises  later  from  tin-  external  carotid  which  anastomoses  with  the  lower  stem  \\  here  it  divides 
into  tin-  two  brandies  just  mentioned,  and  the  main  stein  of  the  stapedius  disappears,  except 
in  its  distal  portion,  which  persists  as  the  tympanic  branch  of  the  internal  maxillary,  which  tre- 
(liientlv  arises  in  the  adult  from  the  middle  'meningeal  instead  of  directlv  from  the  internal  max- 
illary '  By  these  changes,  as  mav  be  seen  from  the  accompanying  diagrams,  the  adult  internal 
maxillary  is  formed,  the  snpraorbital  branch  becoming  the  middle  meningeal  (  M»i  \  and  the 
mandibular  branch  the  inferior  dental,  while  the  infraorbital  branch  (A1/,  becomes  the  main 
stein  of  the  artery  from  which  the  remaining  branches  gradually  develop. 


THE   OCCIPITAL    ARTERY. 


743 


FIG.  694. 


Ast 


In  correspondence  with  this  history,  a  persistence  of  the  stapedial  artery  is  occasionally 
found  ;  but  the  majority  of  the  usual  variations  of  the  internal  maxillary  are  due  to  the  second- 
ary anastomoses  which  its  branches  make  with  other  vessels.  Thus,  by  an  enlargement  of 
the  anastomoses  between  the  middle  meniirgeal  and  the  branches  of  the  ophthalmic  artery,  that 
vessel  or  some  of  its  branches,  notably 
the  lachrymal,  may  come  to  arise  from 
the  middle  meningeal  (page  749).  And, 
similarly,  by  the  anastomoses  with  the 
facial  or  transverse  facial  arteries,  the 
terminal  branches  of  the  infraorbital 
may  be  transferred  to  those  vessels,  the 
infraorbital  itself  stopping  in  the  middle 
of  the  infraorbital  groove. 

5.  The  Ascending  Pharyn- 
geal  Artery. — The  ascending 
pharyngeal  artery  (a.  pharyngea 
ascendens)  (Fig.  695)  differs  from 
all  the  other  branches  of  the  external 
carotid  by  its  vertical  course.  It 
is  a  comparatively  small  stem  which 
arises  close  to  or  immediately  at  the 
origin  of  the  external  carotid  and 
passes  upward,  at  first  between  that 
vessel  and  the  internal  carotid,  and 
later  between  the  internal  carotid 
and  the  internal  jugular  vein. 


Diagrams  illustrating  development  of  internal  max- 
illary artery  ;  A,  early  stage ;  £,  later  stage;  C,  common 
carotid;  Ce,  Ci,  external  and  internal  carotid.  For  ex- 
planation of  other  letters,  see  text.  (  Tandler.) 


Branches. — (a)  A  prevertebral  branch  which  supplies  the  prevertebral  muscles  of  the  neck 
and  anastomoses  with  the  ascending  cervical  branch  of  the  inferior  thyroid  artery. 

(b)  Pharyngeal  branches  (rami  pharyngei),  two  or  three  in  number,  which  supply  the  con- 
strictor muscles  and  the  mucous  membrane  of  the  pharynx. 

(e)  Meningeal  Branches. — A  number  of  small  twigs,  into  which  the  artery  breaks  up  as  it 
approaches  the  base  of  the  skull,  pass  through  the  jugular  and  anterior  condyloid  foramina  to 
supply  the  dura  mater  of  the  posterior  fossa  of  the  skull,  and  through  the  cartilage  of  the  middle 
lacerated  foramen  to  simply  the  dura  of  the  middle  fossa. 

Variations. — The  ascending  pharyngeal  frequently  gives  origin  to  the  ascending  palatine 
and  more  rarely  to  the  superior  laryngeal  artery.  It  is  very  variable  in  its  origin,  not  infre- 
quently being  given  off  from  one  or  other  of  the  neighboring  branches  of  the  external  carotid. 

6.  The   Sterno-Mastoid    Artery. — The    sterno-mastoid    artery    (a.    sterno- 
cletdomastoidea)  arises  from  the  posterior  surface  of  the  external  carotid,  near  its  origin, 
and  passes  downward  and  backward  to  enter  the  sterno-cleido-mastoid  muscle  along 
with  the  spinal  accessory  nerve.      It  is  a  comparatively  small  vessel  and  is  not  infre- 
quently absent,  being  replaced  by  branches  passing  to  the  muscle  from  other  arteries. 
When  it  is  present,  the  hypoglossal  nerve  bends  around  to  it  to  pass  forward  to  the 
lingual  muscles. 

7.  The   Occipital  Artery. — The  occipital  artery  (a.  occipitalis)  (Figs.  691, 
692)  arises  from  the  posterior  surface  of  the  carotid,  opposite  or  a  little  below  the 
facial.      It  passes  upward  and  backward,  and  is  at  first  partly  covered  by  the  posterior 
belly  of  the  digastric  and  the  stylo-hyoid  muscles,  the  parotid  gland,  and  the  temporo- 
maxillary  vein.      It    crosses    in   succession,   from  before  backward,   the  hypoglossal 
nerve,  which,  when  the  sterno-mastoid  artery  is  wanting,  winds  around  it  to  pass  for- 
ward to  the  tongue,  the  pneumogastric  nerve,  the  internal  jugular  vein,  and  the  spinal 
accessory  nerve.      It  then  passes  more  deeply,  lying  in  a  groove  on  the  posterior  sur- 
face of   the  mastoid   process  and  beneath  the  origin  of  the  posterior  belly  of  the 
digastric,  the  sterno-cleido-mastoid,  and  the  splenius  capitis.     Emerging  from  beneath 
these  muscles,  it  reappears  in  the  upper  part  of  the  occipital  triangle,  and  then  ascends 
in  a  tortuous  course  over  the  back  of  the  skull,  sometimes  perforating  the  trapezius 
near   its    origin,   and    breaks    up    into    numerous   branches  which  anastomose  with 
branches  from  the  artery  of  the  opposite  side  and  with  those  of  the  posterior  auricular 
and  superficial  temporal.      In  this  last  part  of  its  course  it  is  superficial,  lying  beneath 


744  HUMAN    ANATOMY. 

the  integument  upon  the  aponeurosis  of  the  occipito-frontalis.  The  artery  pierces 
the  deeper  structures,  accompanied  by  the  great  occipital  nerve,  a  short  distance 
lateral  to  and  a  little  below  the  external  occipital  protuberance. 

Branches. — In  addition  to  its  terminal  branches,  the  occipital  artery  gives  off  : 

(a)  A  superior  sterno-mastoid  branch  which  supplies  the  upper  part  of  the  sterno-cleido- 
mastoid. 

(o)  Posterior  meningeal  branches,  one  or  more  slender  vessels  which  pass  upward  along 
the  internal  jugular  vein  and,  entering  the  skull  by  the  jugular  foramen,  are  supplied  to  the 
dura  mater  of  the  posterior  fossa. 

(f )  An  auricular  branch  (ramus  auricularis)  which  passes  upward  over  the  mastoid  process 
to  supply  the  pinna  of  the  ear. 

(d )  A  mastoid  branch  (ramus  mastoideus)  which  enters  the  skull  by  the  mastoid  foramen 
and  supplies  the  mucous  membrane  lining  the  mastoid  cells,  the  diploe,  and  the  dura  mater. 

(e)  An  arteria  princeps  cervicis  (ramus  descendens)  which  arises  from  the  artery,  just  as  it 
passes  out  from  beneath  the  splenius  and  descends  the  neck,  supplying  the  adjacent  muscles  and 
anastomosing  with  the  superficial  cervical  branch  of  the  transversalis  colli  and  with  the  pro- 
funda  cervicis  from  the  superior  intercostal. 

(_/")  Muscular  branches  (rami  musculares)  which  are  given  off  all  along  the  course  of  the 
artery  to  the  neighboring  muscles. 

Anastomoses. — The  occipital  artery  makes  comparatively  large  and  abundant 
anastomoses  in  the  scalp  with  the  stylo-mastoid  and  temporal  arteries,  and  also, 
by  means  of  its  art.  princeps  cervicis,  with  branches  of  the  transversalis  colli  and 
superior  profunda  arteries,  which  arise  from  the  subclavian.  These  latter  anastomoses 
are  of  considerable  importance  in  the  development  of  a  collateral  circulation  after 
ligation  of  either  the  common  carotid  or  the  subclavian  arteries. 

Variations. — The  occipital  artery  occasionally  passes  superficial  to  the  sterno-cleido-mas- 
toid  muscle  instead  of  beneath  it,  and  it  not  infrequently  gives  origin  to  the  ascending  pharyn- 
geal  artery  or  to  the  stylo-mastoid. 

Practical  Considerations. — The  occipital  artery  is  rarely  formally  ligated. 
The  cervical  portion  may  be  reached  through  an  incision  along  the  anterior  border 
of  the  sterno-mastoid,  beginning  midway  between  the  ramus  of  the  mandible  and  the 
lobe  of  the  ear  and  extending  downward  two  and  a  half  inches.  The  deep  fascia  at 
the  upper  angle  of  the  wound  (parotid  fascia)  is  spared  on  account  of  the  risk  of 
salivary  fistula.  At  the  lower  angle  it  is  divided,  the  parotid  and  sterno-mastoid 
are  separated,  and  the  digastric  and  stylo-hyoid  muscles  recognized  and  drawn 
upward.  The  occipital  artery,  near  its  origin,  will  then  be  seen  crossing  the  internal 
carotid  artery  and  internal  jugular  vein  and  in  contact  with  the  curve  of  the  hypo- 
glossal  nerve  where  it  turns  to  cross  the  neck.  The  artery  may  be  ligated  close 
behind  the  nerve,  the  needle  being  passed  from  without  inward  to  avoid  the  jugular 
vein.  The  occipital  portion  is  approached  through  an  almost  horizontal  incision  two 
inches  in  length,  beginning  at  the  tip  of  the  mastoid  apophysis  and  extending  back- 
ward and  a  little  upward.  The  outer  fibres  of  the  sterno-mastoid  and  its  aponeu- 
rotic  expansion,  the  splenius,  and  often  the  complexus,  must  then  be  divided  and 
the  pulsation  of  the  artery  sought  for  in  the  space  between  the  mastoid  and  the 
transverse  process  of  the  atlas,  whence  the  vessel  may  be  traced  outward.  If  it  is 
isolated  near  to  the  mastoid,  great  care  must  be  taken  not  to  injure  the  important 
mastoid  venous  tributaries  of  the  occipital  vein  which  in  this  region  connect  it  with 
the  lateral  sinus. 

S.  The  Posterior  Auricular  Artery. — The  posterior  auricular  artery  <  a. 
aiirkularis  posterior)  (Fig.  693  )  arises  from  tin-  external  carotid  after  it  has  passed 
beneath  the  posterior  belly  of  the  digastric.  It  passes  upward  and  backward,  cov- 
ered at  first  by  the  parotid  gland,  which  it  supplies,  and  divides  in  the  angle  between 
the  pinna  and  the  mastoid  process  into  terminal  branches,  some  of  which  supply  the 
pinna,  while  others  anastomose  with  branches  from  the  occipital  and  superficial 
temporal 


THE   SUPERFICIAL   TEMPORAL   ARTERY.  745 

Branches. — In  addition  to  branches  to  the  parotid  gland  and  to  neighboring  muscles,  it 
gives  rise  to  the  stylo-mastoid  artery  (a.  stylomastoidea).  This  vessel  enters  the  stylo-mastoid 
foramen  and  traverses  the  facial  canal  (aqueduct  of  Fallopius)  as  far  as  the  point  at  which  the 
hiatus  Fallopii  passes  off  from  it.  During  its  course  through  the  canal  it  gives  off  branches  to 
the  mucous  membrane  lining  the  mastoid  cells,  to  the  stapedius  muscle,  and  to  the  mucous 
membrane  of  the  middle  ear,  those  twigs  which  pass  to  the  inner  surface  of  the  tympanic  mem- 
brane anastomosing  with  the  tympanic  branch  of  the  internal  maxillary.  Arrived  at  the  hiatus 
Fallopii,  the  artery  accompanies  the  great  superficial  petrosal  nerve  through  that  canal  and 
enters  the  cranium,  supplying  the  dura  mater  and  anastomosing  with  branches  of  the  middle 
meningeal  artery. 

Variations.— The  stylo-mastoid  artery  may  arise  from  the  occipital  or  its  place  may  be 
taken  by  the  petrosal  branch  of  the  middle  meningeal,  with  which  the  stylo-mastoid  normally 
anastomoses. 

9.  The  Superficial  Temporal  Artery. — The  superficial  temporal  artery 
(a.  temporalis  superficialis)  (Fig.  693)  is  the  continuation  of  the  external  carotid  after 
it  has  given  off  the  internal  maxillary.  At  its  origin  it  is  embedded  in  the  substance 
of  the  parotid  gland,  and  is  directed  upward  over  the  root  of  the  zygoma  and  imme- 
diately in  front  of  the  pinna.  After  ascending  a  short  distance,  usually  about  2  cm. , 
upon  the  aponeurosis  covering  the  temporal  muscle,  it  divides  into  an  anterior  and  a 
posterior  branch,  which,  diverging  and  branching  repeatedly,  pass  upward  over  the 
temporal  and  occipito-f rental  aponeuroses  almost  to  the  vertex  of  the  skull,  anasto- 
mosing with  the  supra-orbital  branches  of  the  ophthalmic  branch  of  the  internal 
carotid,  with  the  posterior  auricular  and  occipital  branches  of  the  external  carotid, 
and  with  the  artery  of  the  opposite  side. 

Branches. — 

(a)  Parotid  branches  (rami  parotidei),  small  branches  to  the  parotid  gland. 

(b)  Articular  branches  to  the  temporo-mandibular  articulation. 

(c)  Muscular  branches  to  the  masseter  muscle. 

(d)  The  anterior  auricular  branches  (rami  auriculares  anteriores)  supply  the  outer  surface 
of  the  pinna  and  the  outer  portion  of  the  external  auditory  meatus. 

(e)  The  transverse  facial  artery  (a,  transversa  faciei)  arises  just  below  the  main  stem  of  the 
artery,  crosses  the  zygoma,  and  is  directed  forward  parallel  with  the  zygoma  and  between  it 
and  the  parotid  duct.     It  gives  off  branches  to  neighboring  muscles  and  to  the  integument  of 
the  cheek,  and  anastomoses  with  the  masseteric  branches  of  the  facial  and  with  the  buccal, 
alveolar,  and  infra-orbital  branches  of  the  internal  maxillary. 

(_/)  The  middle  deep  temporal  (a,  temporalis  media)  arises  just  above  the  zygoma,  and 
after  perforating  the  temporal  aponeurosis  and  muscle,  it  ascends  upon  the  surface  of  the  skull 
to  anastomose  with  the  deep  temporal  branches  of  the  internal  maxillary  artery. 

(g)  The  orbital  branch  (a.  zygomaticoorbitalis)  runs  forward  along  the  upper  border  of  the 
zygoma,  supplying  the  orbicularis  palpebrarum  and  also  sending  branches  into  the  cavity  of 
the  orbit. 

Anastomoses. — The  superficial  temporal  artery  makes  extensive  anastomoses 
in  the  scalp  with  its  fellow  of  the  opposite  side,  with  the  occipital  and  posterior  auricu- 
lar branches  of  the  external  carotid,  and  with  the  supra-orbital  branch  of  the  oph- 
thalmic. By  means  of  the  transverse  facial  it  makes  anastomoses  with  the  facial  and 
internal  maxillary  arteries. 

Variations. — The  principal  variations  of  the  superficial  temporal  are  its  division  into  the 
terminal  branches  below  the  level  of  the  zygomatic  arch  and  the  absence  of  its  posterior  ter- 
minal branch  ;  in  the  latter  case  the  area  of  distribution  of  the  posterior  branch  is  supplied  by 
the  posterior  auricular  or  the  occipital  artery. 

Practical  Considerations. — The  superficial  temporal  artery  may  require 
ligation  on  account  of  wound  of  the  vessel,  or  of  one  of  its  branches,  or  in  cases  of 
aneurism.  It  or  one  of  its  chief  subdivisions  used  frequently  to  be  selected  for  the 
now  rare  operation  of  arteriotomy.  The  vessel  never  becomes  very  superficial  imme- 
diately after  emerging  from  beneath  the  upper  part  of  the  parotid.  In  the  first  por- 
tion of  its  track  of  ascent  its  pulsations  are  difficult  to  perceive.  In  the  presence  of 
the  least  swelling  of  the  region  they  become  incapable  of  serving  as  a  guide  for  the 
incision  (Farabeuf  ). 


746 


HUMAN   ANATOMY. 


Ligation. — The  skin,  superficial  fascia,  and  some  fibres  of  the  attrahens  aurem 
muscle  are  divided  for  an  inch  on  a  vertical  line  between  the  tragus  and  the  condyle 
of  the  mandible,  a  little  nearer  the  latter.  The  artery  will  be  found  closely  bound  by 
connective-tissue  bands  to  the  temporal  aponeurosis. 

THE  INTERNAL  CAROTID  ARTERY. 

The  internal  carotid  (Figs.  693,  695)  is  the  second  terminal  branch  of  the  com- 
mon carotid,  from  which  it  arises  on  a  level  with  the  upper  border  of  the  thyroid 

FIG.  695. 


Branch  of  left  middle 
tneningeal  artery 

Posterior  cerebral 

arteries 


Branch  of  left  middle 

meningeal 


Basilar  artery 


Posterior  inferior 

cerebellar  artery  — 


Left  vertebral  artery 
Right  vertebral  artery 


Deep  cervical  artery 

Vertebral  artery 
Transverse  process  of 

I.  thoracic  vertebra 


Superior  intercostal  artery 

Branch  to  II.  intercostal  space 

1 1.  rib 

I.  aortic  intercostal 

II.  aortic  intercostal 


Middle  cerebral  artery 


Atlas 

Arteria  princeps  cervicis 

Axis 

Left  complexus 


Lingual  artery 
Superior  thyroid  artery 
Thyro-hyoid  muscle 
Thyroid  cartilage 

Inferior  constrictor  of  pharynx 


Common  carotid  artery 


Anterior  cerebral  artery 
Anterior  clinoid  process 

Middle  fossa  of  skull 
Int.  carotid,  cav.  portion 
Sup.  maxilla,  malar  process 
Int.  carotid,  petrous  portion 

Internal  maxillary  artery 
Eustachian  tube 


Transverse  process  of  atlas 
Sup.  constictorof  pharynx 
Int.  carotid,  cervical  portion 
Ascending  pharyngeal 
•Stylo-glossus 
-Stylo-phangeus 

External  carotid  artery 
•Stylo-hyoid  muscle,  cut 


Suhclavian  artery 
Innominate  artery 


Internal  n  ammary  artery 


Deep  dissection,  showing  internal  carotid,  vertebral  and  superior  intercostal  arteries. 

cartilage.  In  tin-  first  or  cervical  portion  of  its  course  it  lies  upon  the  outer  side  of  tin- 
external  carotid,  but.  as  it  passes  upward,  it  comes  to  lie  behind  and  then  internal 
to  that  vessel,  from  which  it  is  separated  by  the  stylo -hyoid,  digastric,  and  stylo- 
pharyugeus  muscles.  It  passes  almost  vertically  up  the  neck  to  the  entrance  to  the 
carotid  canal,  ivstin-  posteriorly  on  the  prevertebral  fascia  covering  the  rectus  capitis 


THE   INTERNAL   CAROTID   ARTERY.  747 

anticus  major,  and  having  upon  its  median  side  the  wall  of  the  pharynx  and  laterally 
the  internal  jugular  vein,  between  which  and  the  artery,  and  on  a  plane  slightly  pos- 
terior to  both,  is  the  pneumogastric  nerve.  It  is  also  in  relation  in  the  upper  part 
of  this  cervical  portion  of  its  course  with  the  glosso-pharyngeal  nerve,  which  lies  at 
first  behind  it,  but  crosses  its  external  surface  lower  down  as  it  bends  forward  towards 
the  tongue,  and  with  the  superior  sympathetic  ganglion,  whose  cardiac  branch 
descends  along  its  internal  surface,  while  the  pharyngeal  branches  cross  it  and 
the  carotid  branch  ascends  with  the  artery  to  the  carotid  canal,  in  which  it  breaks 
up  to  form  the  carotid  plexus. 

In  the  second  or  petrosal  portion  of  its  course  the  internal  carotid  traverses  the 
carotid  canal,  to  whose  direction  it  conforms,  passing  at  first  vertically  upward  and 
then  bending  so  as  to  run  forward  and  inward  to  enter  the  cranial  cavity  at  the 
foramen  lacerum  medium. 

It  then  enters  upon  the  third  or  intracranial  portion  of  its  course,  ascending  at 
first  towards  the  posterior  clinoid  process,  but  soon  bending  forward  and  entering  the 
outer  wall  of  the  cavernous  sinus.  In  this  it  passes  forward,  accompanied  by  the 
sixth  nerve  (abducens),  and  at  the  level  of  the  anterior  clinoid  process  bends  upward, 
pierces  the  dura  mater,  and  quickly  divides  into  its  terminal  branches. 

Branches. — Throughout  its  cervical  portion  the  internal  carotid  normally  gives 
off  no  branches,  in  its  petrosal  portion,  in  addition  to  some  small  twigs  to  the  peri- 
osteum lining  the  carotid  canal,  it  gives  origin  to  (i)  a  tympanic  branch.  In  its 
intracranial  portion,  in  addition  to  small  branches  to  the  walls  of  the  cavernous  sinus 
and  the  related  cranial  nerves,  to  the  Gasserian  ganglion,  and  to  the  pituitary  body, 
there  arise  (2)  anterior  meningeal  branches,  (3)  the  ophthalmic,  (4)  posterior  commu- 
nicating, (5)  anterior  choroid  arteries.  And,  finally,  its  terminal  branches,  (6)  the 
middle  and  (7)  the  anterior  cerebral  arteries. 

Variations. — In  its  cervical  portion  the  internal  carotid  occasionally  takes  a  somewhat 
sinuous  course,  and,  especially  in  its  upper  part,  may  be  thrown  into  a  pronounced  horseshoe- 
shaped  curve.  It  may  give  rise  to  branches  which  normally  spring  from  the  external  carotid, 
as,  for  example,  the  ascending  pharyngeal  and  the  lingual,  and  accessory  branches  may  arise 
from  its  intracranial  portion. 

Practical  Considerations. — The  internal  carotid  artery,  on  account  of  its 
deeper  position,  is  not  so  often  wounded  as  the  external  carotid.  It  has  been  punc- 
tured through  the  pharynx  and  has  been  wounded  in  tonsillotomy  (page  1608). 

Aneurism  of  the  internal  carotid  is  not  common.  When  it  involves  the  petrosal 
or  intracranial  portion  of  the  vessel  it  causes  symptoms  referrible  to  those  regions 
and  better  dealt  with  after  the  venous  system  has  been  described  (page  873).  In 
its  cervical  portion  it  shows  a  tendency  to  become  tortuous  in  elderly  persons, 
owing  doubtless  to  its  fixity  above,  where  it  enters  the  carotid  canal,  and  to  the  rela- 
tive lack  of  fixation  below  (Taylor). 

As  the  artery  is  crossed  externally  by  the  dense  layers  of  the  deep  cervical 
fascia,  and  by  the  stylo-hyoid,  stylo-glossus,  stylo-pharyngeus,  and  digastric  mus- 
cles, the  progress  of  a  swelling  in  this  direction  is  strongly  resisted.  Internally  the 
middle  constrictor  and  mucous  membrane  of  the  pharynx  offer  far  less  obstruction  to 
the  extension  of  the  aneurism,  and  in  many  of  the  recorded  cases  a  pulsating  pha- 
ryngeal protrusion  has  been  the  chief  symptom.  The  effects  of  pressure  on  surround- 
ing structures,  the  internal  jugular  vein,  and  the  pneumogastric  and  sympathetic 
nerves,  for  example,  are  not  unlike  those  observed  in  other  carotid  aneurisms.  The 
direct  interference  with  cerebral  circulation  is  greater  in  aneurism  of  the  internal 
carotid,  and  vertigo,  headache,  drowsiness,  etc. ,  are  apt  to  be  more  conspicuous  as 
early  symptoms. 

Ligation.  — The  vessel  may  be  reached  close  to  its  origin  and  tied  through  the 
same  incision  as  that  used  in  ligating  the  external  carotid  (page  733).  The  sterno- 
mastoid  muscle  is  drawn  outward,  the  digastric  muscle  and  hypoglossal  nerve 
(which  are  usually  seen)  upward,  and  the  external  carotid  artery  inward.  The  two 
vessels  should  be  carefully  distinguished.  The  needle  should  be  passed  from  with- 


HUMAN   ANATOMY. 


out  inward,  avoiding  the  internal  jugular  vein,  the  pneumogastric  and  sympathetic 
nerves,  and  the  ascending  pharyngeal  and  external  carotid  arteries. 

The  collateral  circulation  is  carried  on  through  the  vertebrals  and  the  vessels  of 
the  circle  of  Willis  and  is  freely  re-established. 

i.  The  Tympanic  Artery. — The  tympanic  artery  (ramus  caroticotympani- 
cus)  is  a  small  vessel  which  arises  from  the  petrosal  portion  of  the  internal  carotid. 
It  passes  through  a  foramen  in  the  wall  of  the  carotid  canal  to  supply  the  mucous 
membrane  .of  the  middle  ear,  anastomosing  with  the  tympanic  branches  of  the  stylo- 
mastoid  and  internal  maxillary  arteries. 

FIG.  696. 


Facial  artery 


Frontal  arter 


Internal  branch  of 

supraorbital 

Superior  oblique  muscle 
Superior  palpebral 

branch 
Inferior  palpebral 

branch 

Frontal  artery 
Nasal  artery 
Anterior  ethmoidal 

branch 
Supraorbital  artery 

"  Posterior  ethmoidal 
branch 

Superior  oblique 

Superior  rectus 
Optic  nerve 

Ophthalmic  arterj 


Internal  carotid  artery 
Posterior  clinoid  process 


Internal  carotid, 

cavernous  portion 


—Nasal  artery 

—  Supraorbital  artery 


Iff — Superior  rectus 


Levator  palpebrae  superions 


Lachrymal  artery 


Lachrymal  ^land 

Temporal  branch 
Arteria  centralis  retina; 
Lone  |>"-tc-M.>r 

.  iliary  arteries 
'  Short  jwsterior 

ciliary  arteries 

Middle  fossa  of  skull 


Branches  of  right  ophthalmic  artery,  sei-n  from  above  after  removal  of  roof  of  orbit. 


2.  The    Anterior    Meningeal    Arteries. — The    anterior   meningeal  arteries 
are  a  number  of  small  branches  which  arise  from  the  intracranial  portion  of  the  inter- 
nal carotid  and  are  supplied  to  the  neighboring  dura  mater,  anastomosing  with  the 
branches  of  the  anterior  ramus  of  the  middle  meningeal  artery. 

3.  The  Ophthalmic  Artery. — The  ophthalmic  artery  (a.  ophthalmica  )  i.  Fi^s. 
696,  697)  arises  from  the  internal  carotid  immediately  after  it  has  issued  from  the-  roof 
of  the  cavernous  sinus.      It  passes  forward  beneath  the  optic  nerve  and  traverses  the 
optic  foramen  with  that  structure.  v   In  the  orbit  it  ascends  to  the  outer  side  of  the 
optic  nerve  and,  crossing  over  it,  passes  in  a  sinuous  course  towards  the  inner  wall 


THE    OPHTHALMIC   ARTERY.  749 

of  the  orbit,  along  which  it  runs  between  the  superior  oblique  and  internal  rectus 
muscles  to  the  inner  angle,  where  it  terminates  by  dividing  into  palpcbral,  frontal, 
and  nasal  branches. 

Branches. — (a)  The  arteria  centralis  retinae  arises  from  the  ophthalmic  while  that  vessel 
is  still  below  the  optic  nerve.  It  runs  forward  along  the  under  surface  of  the  nerve  to  a  point 
about  15  mm.  from  the  posterior  surface  of  the  eye,  where  it  passes  into  the  substance  of  the 
nerve  and  continues  its  course  forward  in  the  centre  of  that  structure.  Arrived  at  the  retina, 
the  artery  divides  into  two  main  branches,  one  ascending  and  the  other  descending,  and  these, 
branching  repeatedly,  form  an  arterial  net-work  upon  the  surface  of  the  retina.  The  finer 
branches  of  the  net-work  extend  deeply  into  the  substance  of  the  retina,  although  none  reach 
the  layer  of  visual  cells.  They  pass  over  directly  into  the  corresponding  veins  without  making 
connections  with  any  of  the  other  arteries  supplied  to  the  eyeball.  Just  after  its  entrance  into 
the  eyeball,  however,  the  main  stem  of  the  artery  anastomoses  with  the  short  ciliary  vessels. 

(£)  The  ciliary  arteries,  \\  hich  are  distributed  to  the  choroid  coat,  the  ciliary  processes,  and 
the  iris,  are  somewhat  variable  in  their  number  and  origin.  Two  sets  are  distinguishable,  and 
are  named  from  their  relative  position  the  posterior  and  anterior  ciliary  arteries. 

(aa)  The  posterior  ciliary  arteries  (aa.  ciliares  posteriores)  arise  from  the  ophthalmic  artery 
as  it  crosses  over  the  optic  nerve,  either  as  two  trunks  which  pass  forward,  the  one  on  the  inner 
and  the  other  on  the  outer  side  of  the  optic  nerve,  or  else  as  a  variable  number  of  small  vessels. 
Eventually  the  vessels  break  up  into  from  ten  to  twenty  branches,  which  surround  the  distal 
portion  of  the  optic  nerve,  and,  piercing  the  sclerotic,  are  distributed  to  the  choroid  coat  of  the 
eye.  Two  of  the  vessels,  lying  one  on  either  side  of  the  optic  nerve,  are  usually  stronger  than 
the  others,  pierce  the  sclerotic  some  distance  nearer  the  equator  of  the  eyeball,  and  are 
termed  the  long  posterior  ciliary  arteries  (aa.  ciliares  posteriores  longae).  They  pass  forward 
between  the  sclerotic  and  choroid  coats,  send  branches  to  the  ciliary  muscle,  and  divide  at  the 
peripheral  border  of  the  iris  into  two  stems,  which,  passing  around  the  iris,  unite  with  their 
fellows  of  the  opposite  side  and  with  branches  of  the  anterior  ciliary  arteries  to  form  the 
circulus  arteriosus  iridis,  from  which  branches  radiate  to  the  iris  and  the  ciliary  processes. 

(f>6)  The  anterior  ciliary  arteries  (aa.  ciliares  anteriores)  usually  take  their  origin  from  the 
muscular  branches  of  the  ophthalmic  and  accompany  the  tendons  of  the  recti  muscles  (two 
arteries  being  associated  with  each  muscle,  except  in  the  case  of  the  external  rectus,  where 
there  is  only  one)  to  the  sclerotic,  where  they  send  off  perforating  branches  which,  after 
piercing  the  sclerotic,  unite  with  the  long  ciliaries  to  form  the  arterial  circle  of  the  iris.  The 
main  stems  are  continued  onward  towards  the  margin  of  the  cornea,  where  they  divide  and 
anastomose  to  form  a  narrow  net-work  surrounding  that  portion  of  the  eyeball  and  also  give 
branches  to  the  conjunctiva.  An  anterior  ciliary  vessel  is  frequently  contributed  by  the 
lachrymal  artery. 

(c)  The  lachrymal  artery  (a  lacrimalis)  arises  from  the  ophthalmic  as  it  passes  upward  over 
the  external  surface  of  the  optic  nerve  and  passes  forward  and  outward,  in  company  with  the 
lachrymal  nerve,  along  the  upper  border  of  the  external  rectus  muscle.  It  traverses  the  substance 
of  the  lachrymal  gland,  to  which  it  gives  branches,  and  terminates  in  small  branches  to  the  eye- 
lids. In  its  course  it  gives  off  a  number  of  small  twigs  to  the  external  rectus  muscle  ;  a  menin- 
gcal  branch,  which  passes  back  into  the  cranium  through  the  sphenoidal  fissure  and  anasto- 
moses with  the  middle  meningeal  ;  and  a  malar  branch,  which  passes  to  the  temporal  fossa 
through  a  small  canal  in  the  malar  bone  and  anastomoses  with  the  anterior  deep  temporal  and 
the  transverse  facial  arteries. 

(if)  The  muscular  branches  (rami  musculares)  are  somewhat  irregular  in  their  number  and 
origin.  Usually  there  are  two  principal  stems  and  a  variable  number  of  small  twigs,  but  occa- 
sionally the  two  principal  stems  arise  by  a  common  trunk.  When  the  two  are  distinct,  the  in- 
ferior one  arises  close  to  the  lachrymal,  and  is  distributed  to  the  inferior  and  internal  recti  and 
the  inferior  oblique  muscles  ;  while  the  superior,  smaller  and  less  constant,  arises  after  the  oph- 
thalmic has  crossed  over  the  optic  nerve,  and  is  distributed  to  the  superior  and  external  muscles 
of  tlit-  orbit.  In  addition  to  branches  to  the  muscles,  these  arteries  also  give  origin  to  the 
anterior  ciliary  arteries  described  above. 

(e)  The  supraorbital  artery  (a.  supraorbitalis)  arises  as  the  ophthalmic  passes  over  the  optic 
nerve.  It  is  at  first  directed  upward,  and  then  passes  forward  between  the  periosteum  of  the 
roof  of  the  orbit  and  the  levator  palpebrae  superioris,  and,  making  its  exit  from  the  orbit  through 
the  supraorbital  notch  or  foramen,  terminates  in  branches  which  ascend  over  the  frontal  bone 
towards  the  vertex  of  the  skull,  supplying  the  integument  and  periosteum  and  anastomosing 
with  the  superficial  temporal  artery.  In  its  course  through  the  orbit  it  gives  off  periosteal, 
diploic,  and  muscular  twigs,  and,  after  its  exit  from  the  supraorbital  notch,  a  palpebral  branch 
to  the  upper  eyelid. 

(f)  The  ethmoidal  arteries  are  two  in  number,  and  arise  from  the  ophthalmic  as  it  passes 
along  the  inner  wall  of  the  orbit.     The  posterior  ethmoidal  (a.  ethmoidalis  posterior) ,  which  is  the 


HUMAN   ANATOMY. 


smaller  and  less  constant  of  the  two,  passes  through  the  posterior  ethmoidal  foramen  and  is 
distributed  to  the  mucous  membrane  lining  the  posterior  ethmoidal  cells  and  the  upper  poste- 
rior part  of  the  nasal  septum,  where  it  anastomoses  with  the  spheno-palatine  branch  of  the 
internal  maxillary.  It  sometimes  arises  from  the  supraorbital  artery.  The  anterior  ethmoidal 
(a.  ethmoidalis  anterior)  passes  through  the  anterior  ethmoidal  foramen  along  with  the  nasal 
nerve,  and,  entering  the  cranium,  passes  forward  over  the  cribriform  plate  of  the  ethmoid  to  the 
nasal  slit  at  the  side  of  the  crista  galli.  Through  this  slit  it  enters  the  nasal  cavity  and  passes 
downward  in  a  groove  upon  the  under  surface  of  the  nasal  bone,  supplying  the  nasal  mucous 
membrane.  While  within  the  cranium  it  gives  off  a  small  meningeal  branch  to  the  dura  mater 
of  the  anterior  portion  of  the  cranium,  and  it  also  sends  branches  to  the  mucous  membrane 
lining  the  anterior  and  middle  ethmoidal  cells  and  the  frontal  sinuses. 

(  g)  The  palpebral  branches  (aa.  palpebrales  mediales)  are  two  in  number,  and  are  distrib- 
uted to  the  upper  and  lower  eyelids  respectively.  They  arise  opposite  the  pulley  of  the  superior 
oblique  muscle  and  descend  towards  the  inner  canthus  of  the  eye.  Each  artery  then  bends  out- 
ward towards  the  outer  canthus  along  the  free  border  of  the  lid,  between  the  tarsal  cartilage 
and  the  orbicularis  muscle,  forming  the  palpebral  arches  (arcus  tarseus  superior  et  inferior}, 

FIG.  697. 


Lacrimal  artery 
Anterior  ethmoidal 


Posterior  ethmoidal 
Ophthalmic  artery 
Optic  nerve 


Supraorbital 
artery 

Frontal  artery- 
Nasal  artery 
Superior  and  in- 
ferior palpebral 
arteries 
Angular  artery 
Anterior  ciliary 
arteries 


Internal  carotid  artery 
Posterior  clinoid 
process 

Int.  carotid  artery, 
cavernous  portion 


Infraorbital 
artery 
Facial  artery 

/  ^    I^M         '^M 

Arteria  centralis  retinae 
Long  posterior  ciliary  artery 
Short  posterior  ciliary  arteries 

Internal  maxillary  artery 
Branches  of  ophthalmic  artery,  seen  from  side  after  removal  of  lateral  orbital  wall. 

from  which  branches  pass  upward  or  downward,  as  the  case  may  be,  to  supply  the  orbicularis, 
the  Meibomian  glands,  and  the  integument  of  the  lid.  As  they  approach  the  outer  canthus,  the 
arches  anastomose  with  the  palpebral  branches  of  the  lachrymal  artery. 

(A)  The  frontal  branch  (a.  frontalis)  is  usually  small,  and  is  distributed  to  the  integument 
over  the  glabella  and  to  the  pyramidalis  nasi  and  frontalis  muscles.  It  also  sends  some  twigs 
to  the  eyelids. 

(i)  The  nasal  artery  (a.  dorsalia  nasi)  is  the  true  terminal   branch  of  the  ophthalmii 
passes  downward  in  the  angle  formed  by  the  nose  and  the  lower  eyelid  and  becomes  directly 
continuous  with  the  angular  portion  of  the  facial  artery.     In  its  course  it  gives  branches  to  the 
walls  of  the  lachrymal  sac  and  to  the  integument  of  the  root  of  the  nose. 

Anastomoses.— The  principal  communications  of  the  ophthalmic  artery  are 
with  the-  superficial  temporal,  internal  maxillary,  and  farial  branches  of  tin-  external 
carotid.  With  the  first  of  these  it  communicates  extensively  l>y  means  of  the  supra- 
orbital  branch  and  less  importantly  through  the  anastomosis  of  the  malar  branch  of 
the  lachrymal  with  the  transverse  facial  artery.  It  makes  a  very  important  anasto- 


THE    POSTERIOR   COMMUNICATING   ARTERY. 


751 


rnosis  with  the  middle  meningeal  branch  of  the  internal  maxillary  through  the  lachry- 
mal branch,  and  communicates  also  with  the  spheno-palatine  artery  by  means  of  the 
ethmoidal  branches.      The  anastomosis 
of  the  nasal  branch  with  the  angular  ar- 
tery from  the  facial  is  also  a  large  one,  the 
two  vessels  being  practically  continuous. 


FIG 


Supraorbital 


Variations. — In  addition  to  the  varia- 
tions in  the  number  and  origins  of  its 
branches,  the  ophthalmic  artery  also  presents 
variations  in  its  course,  in  that,  instead  of  pass- 
ing to  the  inner  wall  of  the  orbit  above  the  op- 
tic nerve,  it  sometimes  passes  below  that 
structure.  The  most  striking  variation  which 
it  presents,  however,  is  associated  with  the 
development  of  the  branch  of  the  lachrymal 
artery,  which  passes  back  through  the  sphe- 
noidal  fissure  to  anastomose  with  the  middle 
meningeal  (Fig.  698).  Occasionally  this 
branch  becomes  exceptionally  large  and  forms 
the  main  stem  of  the  lachrymal  artery,  the 
connection  of  that  vessel  with  the  ophthalmic 
vanishing,  so  that  it  seems  to  be  a  branch  of 
the  middle  meningeal.  A  further  step  in  this 
process  which  sometimes  occurs  results  in  the 
origin  of  the  entire  ophthalmic  system  of  ves- 
sels from  the  middle  meningeal  artery. 


Degenera- 
ted portion 


middle 
meningeal 


Variations  of  ophthalmic  artery  ;  lachrymal  coming 
chiefly  from  middle  meningeal.     (Meyer.) 


4.   The  Posterior  Communicating  Artery. — The  posterior  communicating 
artery  (a.  communicans  posterior)  (Fig.  702)  arises  from  the  posterior  surface  of  the 

FIG.  699. 

Branch  of  ascending  frontal  artery        Precentral  sulcus 
Parietal  artery  /      / 

Ascending  frontal  artery 

Branches  of 
anterior  cere- 
bral artery  from 
mesial  surface 


Anterior  inferior 
cerebellar  artery 


Branches 
of  anterior 
cerebral 
artery 

External 

orbital  arterv 


Inferior  frontal  artery 

Middle  cerebral 
artery 

Temporal  branches  of 
middle  cerebral  artery 

Parieto-temporal  arteries 
Basilar  artery 
Pons 

Left  vertebral  artery 
Middle  cerebellar  peduncle 

Right  vertebral  artery 


Lateral  surface  of  brain,  showing  cortical  branches  of  middle  cerebral  artery;  those  of  anterior  and  posterior 
rebral  arteries  are  seen  curving  over  supero-mesial  border  of  cerebral  hemisphere. 

internal  carotid,   opposite    the  sella  turcica.      It    is  directed  backward  beneath  the 
optic  tract  and  the  inner  border  of  the  crus  cerebri,  and  terminates  posteriorly  by 


752 


HUMAN    ANATOMY. 


opening  directly  into  the  posterior  cerebral  artery.      In  its  course  it  gives  off  twigs 
to  the  tuber  cinereum,  the  corpora  albicantia,  and  the  crus  cerebri. 

5.  The    Anterior  Choroid  Artery. — The  anterior  choroid  artery  ( a.  choroi- 
dea)    (Fig.  702)  arises  from   the  posterior  surface  of  the   internal  carotid,  slightly 
distal  to  the  posterior  communicating  artery.      It  is  directed  outward  and  backward 
at  first,  and  then,  curving  upward  between  the  brain-stem  and  the  temporal  lobe,  it 
gives  branches  to  the  hippocampus  major.      It   is  then  continued  upward  and  for- 
ward as  the  artery  of  the  choroid  plexus  of  the  lateral  ventricle,  and  anastomoses  at 
the  foramen  of  Monro  with  the  artery  of  the  choroid  plexus  of  the  third  ventricle, 
which  comes  from  the  superior  cerebellar  branch  of  the  basilar  artery. 

6.  The  Middle  Cerebral  Artery. — The    middle  cerebral  artery  (a.    cerebri 
media)  (Figs.  699,  702)  is  one  of  the  terminal  branches  of  the  internal  carotid.      It 
passes  at  first  outward  to  the  lower  end  of  the  Sylvian  fissure,  and  is  then  directed 
backward  and  upward,  lying  at  first  deeply  in  the  fissure  close  to  the  surface  of  the 

FIG.  700. 

Middle  internal  frontal  artery 


Posterior  internal 
frontal  artery 


Internal  carotid  artery 

External  orbital  artery 

Middle  cerebral  artery 
From  temporal  branch  of  middle  cerebral 

Posterior  communicating  artery      Ant 


l  brain  lies  .if 
erebral 


Posterio 


ebral  artery 


Mesial  surface  of  cerebral  hemisphere,  showing  cortical  branches  of  anterior 
and  posterior  cerebral  arteries. 

island  of  Reil,  but  gradually  becoming  more  superficial  until  at  the  posterior  ex- 
tremity of  the  horizontal  limb  of  the  fissure  it  reaches  tlu  surface  and  divides  intc 
branches  which  ramify  over  the  lateral  surface  of  the  cerebral  hemisphere. 

Branches. — In  its  course  outward  to  enter  the  Sylvian  fissure  it  gives  off  a  number  of  small 
central  branches  which  penetrate  the  substance  of  the  cerebral  hemisphere  at  the  anterior  per- 
forated space,  and,  as  the  striate  arteries,  supply  the  corpus  striatum.  These  antero-lateral 
»anglionic  branches,  as  they  are  often  called,  are  arranged  as  two  groups  :  (a)  the  internal 
striate  arteries,  which  pass  upward  through  the  lenticular  nucleus  (globus  pallidus)  and  the 
internal  capsule  and  end  in  the  caudate  nucleus,  supplying  the  anterior  part  of  the  structures 
traversed  ;  (t>)  the  external  striate  arteries,  which  after  traversing  the  putamen  and  the  internal 
capsule  terminate  in  either  the  caudate  nucleus  or  the  optic  thalamus.  One  of  the  former 
(leiiticiilo-striatc}  vessels,  which  passes  around  the  outer  border  of  the  lenticular  nucleus  before 
traversing  its  substance,  is  larger  than  the  others  and,  since  it  frequently  ruptures,  is  known  as 
the  artery  of  cerebral  hemorrhage.  While  in  the  Sylvian  fissure  the  middle  cerebral  artery 
gives  off  numerous  branches  to  the  cortex  of  the  island  of  Reil  and  continues  into  the  cortical 
branches,  which  are  distributed  to  the  lateral  surface  of  the  hemisphere  and  are  usually  four  i 


THE   SUBCLAVIAN   ARTERY.  753 

number,  (a)  The  inferior  frontal  is  distributed  to  the  inferior  frontal  convolutions,  (6)  the 
ascending  frontal  passes  to  the  lower  portion  of  the  ascending  frontal  convolution,  (c)  the 
parietal  supplies  the  whole  of  the  ascending  parietal  convolution  and  the  neighboring  portions 
of  the  inferior  parietal,  and  (d)  the  parieto-temporal  passes  to  all  the  convolutions  around  the 
posterior  limb  of  the  fissure  of  Sylvius. 

7.  The  Anterior  Cerebral  Artery. — The  anterior  cerebral  artery  (a.  cerebri 
anterior)  (Fig.  700)  is  the  smaller  of  the  terminal  branches  of  the  internal  carotid. 
It  passes  forward  above  the  optic  chiasma  to  the  anterior  end  of  the  great  longitudi- 
nal fissure,  and,  bending  upward  around  the  rostrum  of  the  corpus  callosum,  is  con- 
tinued backward  along  the  medial  surface  of  the  cerebral  hemisphere  to  the  posterior 
portion  of  the  parietal  lobe.  At  its  entrance  into  the  great  longitudinal  fissure  it  is 
connected  with  its  fellow  of  the  opposite  side  by  a  short  transverse  vessel  termed 
the  anterior  communicating  artery  (Fig.  702). 

Branches. — Immediately  after  it  has  crossed  the  optic  chiasma  the  anterior  cerebral  artery 
gives  off  a  number  of  small  central  branches  (antero-mesial  ganglionic) ,  which  penetrate  the 
base  of  the  brain  and  are  distributed  to  the  lamina  cinerea,  the  rostrum  of  the  corpus  callosum, 
the  septum  lucidum,  and  the  tip  of  the  caudate  nucleus.  Throughout  its  course  in  the  great 
longitudinal  fissure  it  gives  branches  to  the  corpus  callosum  and  also  cortical  branches  to  the 
medial  and  lateral  surfaces  of  the  cerebral  hemisphere.  These  branches  are  (a)  the  orbital, 
which  vary  in  number  and  are  distributed  to  the  orbital  surface  of  the  frontal  lobe,  also  sup- 
plying the  olfactory  bulb  ;  (b)  the  anterior  internal  frontal,  which  supplies  the  anterior  and 
lower  part  of  the  marginal  convolution  and  sends  branches  to  the  lateral  surface  of  the  hemis- 
phere supplying  the  superior  and  middle  frontal  convolutions  ;  (c)  the  middle  internal  frontal, 
which  is  distributed  to  the  middle  and  posterior  parts  of  the  marginal  convolution  and  to  the 
adjacent  portions  of  the  superior  and  ascending  frontal  and  ascending  parietal  convolutions  ; 
and  (d}  the  posterior  internal  frontal  or  quadrate,  which,  in  addition  to  sending  branches  to  the 
corpus  callosum,  supplies  the  quadrate  lobe  and  the  upper  part  of  the  superior  parietal  convo- 
lution. These  branches  anastomose  upon  the  inferior  and  lateral  surfaces  of  the  hemisphere 
with  the  branches  of  the  middle  cerebral  artery,  the  main  stem  of  the  artery  anastomosing 
posteriorly  with  branches  of  the  posterior  cerebral. 

Anastomoses  of  the  Carotid  System. — Although  the  majority  of  the 
anastomoses  of  the  branches  of  the  carotid  arteries  are  with  one  another,  yet  there  is 
a  sufficient  amount  of  communication  with  other  vessels  to  allow  of  the  establishment 
of  a  collateral  circulation  after  ligation  of  the  common  carotid  of  one  side.  .  The  con- 
nections which  are  available  for  the  circulation  in  such  a  case  are  as  follows.  ( i ) 
There  is  abundant  communication  between  the  branches  of  the  right  and  left  external 
carotids  across  the  median  line  ;  (2)  the  anterior  communicating  artery  forms  an 
important  communication  between  the  internal  carotids  of  opposite  sides  ;  (3) 
anastomoses  exist  between  the  ascending  cervical  branch  of  the  inferior  thyroid,  the 
superficial  cervical  branch  of  the  transversalis  colli,  and  the  deep  cervical  branch  of 
the  superior  intercostal,  on  the  one  hand,  all  of  these  being  branches  of  the  sub- 
clavian  artery,  and  the  a.  princeps  cervicis,  a  branch  of  the  occipital  artery  ;  (4) 
abundant  communications  exist  between  the  terminal  branches  of  the  inferior  thyroid 
from  the  subclavian  and  the  superior  thyroid  from  the  external  carotid  ;  and,  finally, 
(5)  by  means  of  the  posterior  communicating  artery  the  internal  carotid  may 
receive  blood  from  the  posterior  cerebral  artery,  which,  through  the  basilar  and 
vertebral  arteries,  belongs  to  the  subclavian  system. 

THE  SUBCLAVIAN  ARTERY. 

In  the  primary  arrangement  of  the  branchial  blood-vessels,  while  there  are  two 
aortic  arches  (Fig.  678),  the  two  subclavian  arteries  arise  symmetrically  from  these 
arches  as  lateral  segmental  branches  corresponding  to  the  seventh  cervical  segment. 
With  the  disappearance  of  the  lower  portion  of  the  right  arch,  however,  an  apparent 
lack  of  symmetry  in  their  origin  supervenes,  the  vessel  of  the  right  side  arising  from 
the  innominate  stem,  while  that  of  the  left  side  springs  directly  from  the  persist- 
ing aortic  arch.  As  a  matter  of  fact,  however,  the  proximal  portion  of  the  right  aortic 
arch  is  represented  by  the  innominate  stem,  together  with  a  small  portion  of  the 
proximal  end  of  the  right  subclavian  artery,  so  that  the  original  morphological  sym- 


754 


HUMAN   ANATOMY. 


metry  is  retained  ;  but,  since  a  portion  of  the  original  right  aortic  arch  is  included  in 
the  adult  right  subclavian,  this  vessel  is  a  little  more  than  equivalent  to  its  fellow 
of  the  opposite  side.  Furthermore,  since  the  innominate  stem  ascends  directly 
upward  from  its  origin,  a  topographical  asymmetry  of  the  two  vessels  results. 

The  origin  of  the  right  subclavian  is  opposite  the  right  sterno-clavicular  articula- 
tion, and  from  that  point  the  artery  ascends  upward  and  outward  in  a  gentle  curve 
over  the  dome  of  the  pleura  to  the  inner  border  of  the  scalenus  anticus.  The  origin 
of  the  left  subclavian  is  from  the  termination  of  the  transverse  portion  of  the  aortic 
arch,  and  is  consequently  much  deeper  in  the  thorax  (Fig.  690).  From  its  origin 
it  ascends  at  first  almost  vertically  and  then  curves  outward  and  slightly  forward  to 
reach  the  inner  border  of  the  scalenus  anticus.  From  this  point  onward  the  course  of 
the  two  arteries  is  the  same.  Passing  behind  the  anterior  scalene  muscle,  each  artery 
continues  its  course  outward  across  the  root  of  the  neck,  curving  downward  to  the 
outer  border  of  the  first  rib,  at  which  point  it  becomes  known  as  the  axillary  artery. 

FIG.  701. 


Traoezius 

Descending 
branches  of 
cervical  plexus 

Transverse 
cervical  vessels 

Omohyoid 

muscle 

Brachial  plexus 
Suprascapular 

vessels 


Subclavian  artery  - 


Subclavian  vein 


Clavicle 


Clavicular  portion  of 
sterno-mastoid 

External  jugular  vein 


Anterior  scalene  muscle 
Phrenic  nerve 

Internal  jugular  vein 
Sternal  portion  of 

sterno-mastoid 
Common  carotid  artery 

•Sterno-hyoid  muscle 
irst  rib 


Dissection  of  neck,  showing  relations  of  blood-vessels  and  nerves ;  clavicle 
disarticulated  from  sternum  and  drawn  down. 

In  consequence  of  the  difference  in  origin,  the  right  subclavian  artery  is  usually 
approximately  7.5  cm.  (3  in.)  in  length,  or  about  one  inch  shorter  than  the  left. 
In  its  course  across  the  root  of  the  neck  the  height  which  the  subclavian  artery 
may  reach  varies  considerably  in  different  individuals  ;  in  some  it  never  rises  above 
the  clavicle,  while  in  others  its  highest  point  may  be  from  2.5-3  cm-  O"1/^  nl-  ^ 
above  that  bone.  Most  frequently  it  reaches  a  point  about  1.5  cm.  (s/g  in. )  above  the 
clavicle,  this  highest  point  being  reached  as  it  passes  beneath  the  scalenus  muscle. 
As  it  commences  its  downward  Course  towards  the  first  rib,  the  artery  undergoes  a 
more  or  less  pronounced  diminution  in  diameter,  which  persists  for  a  distance  of  from 
0.5-1  cm.,  and  is  followed  by  an  enlargement  to  about  its  original  si/e,  what  has 
been  termed  an  arterial  isthmus  and  spindle  thus  resulting  (page  720). 

Relations. — For  convenience  in  description,  the  subclavian  artery  is  usually 
regarded  as  consisting  of  three  portions.  The  first  portion  extends  from  its  origin 
to'  the  inner  edge  of  the  scalenus  anticus,  the  second  portion  lies  behind  that  muscle, 


THE   SUBCLAVIAN    ARTERY.  755 

while  the  third  portion  extends  from  the  outer  border  of  the  scalenus  to  the  con- 
ventional termination  of  the  artery  at  the  lower  border  of  the  first  rib.  On  account 
of  the  difference  in  their  origins,  the  relations  of  the  first  portions  of  the  right  and 
left  vessels  differ  somewhat. 

The  first  portion  of  the  right  subclavian  artery  lies  behind  the  clavicular 
portion  of  the  sterno-cleido-mastoid,  and  is  crossed  in  front  by  the  internal  jugular 
and  vertebral  veins  and  by  the  right  pneumogastric,  phrenic,  and  superior  sympa- 
thetic cardiac  nerves.  Behind,  it  is  in  relation  with  the  transverse  process  of  the 
seventh  cervical  vertebra,  with  the  inferior  cervical  sympathetic  ganglion,  and  with 
the  right  recurrent  laryngeal  nerve,  which  winds  around  its  under  surface  from  in 
front.  Below,  it  is  in  contact  with  the  dome  of  the  right  pleura. 

The  first  portion  of  the  left  subclavian  artery,  at  its  origin,  is  deeply  seated 
in  the  thoracic  cavity  and  ascends  almost  vertically  through  the  superior  mediastinum. 
Behind,  and  somewhat  medial  to  it,  are  the  cesophagus,  the  thoracic  duct,  and  the 
longus  colli  muscle,  and  at  its  emergence  from  the  thorax  the  lower  cervical  sympa- 
thetic ganglion.  Medial,  or  internal  to  it,  are  the  trachea  and  the  left  recurrent  laryn- 
geal nerve,  and  lateral  to  it,  on  its  left  side,  are  the  left  pleura  and  lung,  which  also 
overlap  it  in  front.  Near  its  origin  it  is  crossed  by  the  left  innominate  (brachio- ceph- 
alic) vein,  and,  shortly  before  it  passes  over  into  the  second  portion,  it  is  crossed  by  the 
internal  jugular,  vertebral,  and  'subclavian  veins,  as  well  as  by  the  phrenic  nerve  and 
the  thoracic  duct,  the  latter  arching  over  it  to  reach  its  termination  in  the  subclavian 
vein.  The  left  pneumogastric  and  cardiac  sympathetic  nerves  descend  into  the 
thorax  in  front  of  it,  the  pneumogastric,  before  passing  over  the  aortic  arch,  coming 
into  contact  with  the  anterior  surface  of  the  vessel.  As  it  emerges  from  the  thorax 
the  subclavian  lies  behind  the  clavicular  portion  of  the  sterno-cleido-mastoid.  In  the 
neck  it  rests  below  upon  the  dome  of  the  left  pleura. 

The  second  portion  of  the  subclavian  artery,  the  relations  of  which 
and  of  the  succeeding  portion  of  the  vessel  are  the  same  on  both  sides,  in  front 
is  covered  by  the  scalenus  anticus  muscle,  anterior  to  which  and  on  a  slightly  lower 
plane  is  the  subclavian  vein.  Behind  and  above  it  are  the  trunks  of  the  brachial 
plexus,  which  separate  it  from  the  scalenus  medius,  and  below  it  is  in  contact  with 
the  pleura. 

The  third  portion  of  the  subclavian  artery  lies  in  the  supraclavicular  fossa, 
and  is  covered  only  by  the  skin,  the  platysma,  and  that  part  of  the  deep  cervical 
fascia  which  contains  the  external  jugular  vein  and  the  supraclavicular  branches  of 
the  cervical  plexus,  and  encloses  a  quantity  of  fatty  tissue,  in  which  the  suprascapular 
artery  passes  outward.  Behind,  it  is  in  contact  with  the  scalenus  medius  and  the 
brachial  plexus,  and  above  it  are  the  brachial  plexus  and  the  posterior  belly  of  the 
omo-hyoid.  Below,  it  rests  upon  the  first  rib,  at  the  lower  border  of  which  the  vessel 
becomes  the  axillary  artery. 

Branches. — Considerable  variation  exists  in  the  arrangement  of  the  branches 
of  the  subclavian,  but  in  what  is  probably  the  most  frequent  arrangement  the 
branches  are  as  follows  : 

From  the  first  portion  arise  (i)  the  vertebral,  (2)  the  internal  mammary,  (3) 
the  superior  intercostal,  and  (4)  the  thyroid  axis  ;  from  the  second  portion  no 
branches  are  given  off  ;  from  the  third  portion.  (5)  the  transverse  cervical. 

Variations. — The  variations  in  the  origin  of  the  subclavian  artery  have  already  been  consid- 
ered in  describing  the  variations  of  the  aortic  arch  (page  725).  Other  anomalies  occur  in  its 
relation  to  the  scalenus  anticus,  in  front  of  which  it  sometimes  passes,  and  it  may  also  traverse 
the  substance  of  the  muscle  obliquely.  More  rarely  the  artery  divides  at  the  inner  border  of  the 
muscle,  the  two  branches  so  formed  continuing  onward  through  the  axilla  and  down  the  arm 
to  become  the  radial  and  ulnar  arteries. 

Numerous  supernumerary  branches  may  arise  from  the  subclavian.  These  may  be  either 
(i)  accessory  to  the  branches  normally  arising  from  the  artery,  such  as  an  accessory  vertebral, 
an  accessory  internal  mammary,  or  an  accessory  inferior  thyroid  ;  (2)  they  may  be  branches, 
such  as  the  long  thoracic,  dorsal  scapular,  subscapular,  and  the  anterior  and  posterior  circum- 
flexes, which  normally  arise  from  the  axillary  artery,  but  have  secondarily  shifted  to  the  sub- 
clavian as  the  result  of  the  enlargement  of  anastomoses  which  they  make  with  branches  of  that 
vessel  ;  or  (3)  they  may  be  branches  to  neighboring  organs,  such  as  a  bronchial  or  a  pericar- 
dial  branch,  or  occasionally  the  thyroidea  ima  (page  729). 


756  HUMAN   ANATOMY. 

Practical  Considerations. — The  subclavian  artery  may  require  ligation,  on 
account  of  stab  wounds,  as  a  preliminary  to  the  removal  of  growths — axillary  or 
scapular — or  to  an  interscapulo-thoracic  amputation,  or  in  cases  of  axillary  or  sub- 
clavian aneurism,  or,  together  with  the  common  carotid  artery,  in  aortic  or 
innominate  aneurism. 

On  the  surface  of  the  neck  the  subclavian  artery  is  represented  by  a  curve-, 
convex  upward,  beginning  at  the  sterno-clavicular  articulation  and  ending  beneath 
the  middle  of  the  clavicle,  its  highest  point  being  on  an  average  about  five-eighths 
of  an  inch  above  that  bone.  The  vein  is  lower,  is  in  front  of  the  artery  ( separated 
from  it  by  the  scalenus  anticus  muscle),  and  is  usually  nearly  or  quite  under  cover 
of  the  clavicle. 

Aneurism  of  the  subclavian  is  more  frequent  on  the  right  side,  probably  because 
of  the  greater  use  and  consequent  greater  exposure  to  strain  of  the  right  upper 
extremity.  It  may  affect  any  portion  of  the  vessel,  but  the  third  portion — external 
to  the  scaleni,  where  it  is  least  supported  by  surrounding  muscles — is  most  com- 
monly involved  either  primarily  or  by  extension  of  an  aneurismal  dilatation  upward 
from  the  axillary  or  downward  from  the  arch  of  the  subclavian.  The  thoracic- 
portion  of  the  left  subclavian  is  never  the  primary  seat  of  aneurism. 

The  symptoms  are:  (a)  pain  or  numbness  and  loss  of  pou<tr  in  the  arm  and 
hand  from  pressure  on  the  brachial  plexus  ;  (£)  swelling  and  ccdema  of  the  arm  and 
hand  from  pressure  on  the  subclavian  vein  ;  (c)  hiccough  or  irregular,  jerky  res- 
piration from  pressure  on  the  phrenic  nerve  ;  (d)  vertigo,  somnolence,  defective 
vision,  from  compression  of  the  internal  jugular  ;  (>)  tumor,  usually  appearing  in 
the  posterior  inferior  cervical  triangle,  with  its  long  diameter  approximately  parallel 
with  the  clavicle,  and  extending  upward  and  outward  ;  exceptionally  it  grows  down- 
ward, but  this  is  rare  on  account  of  the  resistance  offered  by  the  clavicle,  the  first 
rib,  and  the  structures  filling  the  costo-clavicular  space. 

Digital  compression  of  the  first  and  second  portions  of  the  artery  is  practically 
impossible.  The  third  portion  may  be  imperfectly  occluded  by  making  strong 
pressure  directly  backward  just  above  the  clavicle,  a  little  external  to  its  middle,  so 
that  the  artery  may  be  flattened  out  or  narrowed  against  the  scalenus  medius  muscle 
and  the  seventh  cervical  transverse  process.  Much  more  effectual  pressure  may  be 
made  at  the  same  point,  especially  if  the  tip  of  the  shoulder  can  be  lowered  so  as  to 
carry  the  clavicle  downward  and  make  the  upper  surface  of  the  first  rib  more 
accessible,  in  a  direction  downward,  backward,  and  inward, — i.e. ,  in  a  line  nearly  or 
quite  perpendicular  to  the  plane  of  that  surface.  The  vessel  is  thus  compressed 
against  it,  and  is  not  pushed  off  of  it.  It  will  be  useful  to  recall  that  the  outer  border 
of  the  scalenus  anticus  and  the  posterior  border  of  the  sterno-mastoid — the  latter 
palpable  and  often  visible — are  approximately  on  the  same  line,  immediately  outside 
of  which  is  the  third  portion  of  the  vessel.  The  scalene  tubercle — the  elevation  or 
roughening  on  the  upper  surface  of  the  first  rib  between  the  shallow  depression  for 
the  subclavian  vein  and  the  deeper  groove  for  the  subclavian  artery — gives  attach- 
ment to  the  scalenus  anticus  and,  when  recognized,  serves  as  a  valuable  guide  to  tin- 
vessel. 

Ligation. — The  first  portion — between  the  origin  of  the  vessel  and  the  inner  side 
of  the  scalenus  anticus — has  been  ligated  with  uniformly  fatal  results.  On  tin-  left 
side  it  is  so  situated  as  to  depth,  origin  of  branches — the  vertebral,  internal  mammary, 
thyroid  axis,  and  superior  intercostal — and  contiguity  of  important  structures — the 
heart,  the  aorta,  the  pleura,  the  innominate  vein,  the  thoracic  duct,  tin  pneumogastric, 
<-an liar,  recurrent  laryngeal  and  phrenic  nerves — that  its  ligation  has  only  once 
been  accomplished  (Rodgers).  On  the  right  side  the  operative  procedure  is  some- 
\\hat  less  difficult,  but  many  of  the  relations  are  identical  (vide  .W//VYM,  and  the 
procedure  is  still  so  formidable  that  its  description  is  included  in  some-  works  on 
operative  surgery  only  because  the  ligation  "affords  good  practice  on  the  dead 
subject  "  (Jacobson). 

Tin-  steps  of  the  operation  are  the  same  as  those  in  ligation  of  the  innominate 
f  pa-e  7^())  until  the  carotid  sheath  is  reached  and  opened.  The  internal  jugular 
vein  and  pneumOgastric  nerve  should  be  drawn  aside  ( inward,  Agnew  :  outward, 
Harwell  )  and  tin-  subclavian  recoiMii/.ed,  springing  from  the  bifurcation  of  the  innom- 


PRACTICAL  CONSIDERATIONS:    SUBCLAVIAN  ARTERY.        757 

inate  at  an  acute  angle  with  the  carotid  and  deeper  by  the  full  diameter  of  the 
latter.  The  needle  should  be  passed  from  below  upward,  while  the  pleura  is  gently 
depressed  with  the  finger. 

The  second  portion — behind  the  scalenus  anticus — has  in  a  few  cases  been  suc- 
cessfully ligated  for  aneurism  external  to  it,  but  the  operation  does  not  require 
special  description.  It  is  identical  with  that  for  tying  the  third  portion,  with  the 
addition  of  more  extensive  division  of  the  clavicular  portion  of  the  sterno-mastoid 
and  a  partial  division  of  the  scalenus  anticus,  having  due  regard  to  the  position  of 
the  phrenic  nerve  on  the  inner  part  of  the  anterior  surface  of  that  muscle. 

The  third  portion — from  the  outer  edge  of  the  scalenus  anticus  to  the  lower 
border  of  the  first  rib— has  been  frequently  and  successfully  ligated.  Three  methods 
may  be  described  : 

1.  By  the  first  and  usual  one  it  is  approached  by  a  transverse  incision,  parallel 
with  the  clavicle  and  extending  along  the  base  of  the  posterior  cervical  triangle  from 
the  middle  of  the  clavicular  head  of  the  sterno-mastoid  to  the  anterior  border  of  the 
trapezius.      This  is  best  made  by  drawing  the  skin  down  and  incising  it  directly 
upon  the  bone,  in  this  way  easily  avoiding  the  external  jugular  vein.      The  platysma 
muscle  and  the  supraclavicular  nerves  are  divided  at  the  same  time.     On  releasing  the 
skin  the  wound  will  be  placed  about  a  half-inch  above  the  clavicle.      The  shoulder  is 
then  well  depressed  so  as  to  lower  this  bone  and  increase  the  supraclavicular  space. 
The  deep  fascia,  which,  as  it  is  attached  to  the  superior  border  of  the  clavicle,  is  not 
pulled  down  with  the  skin  and  platysma,  is  then  divided,  the  external  jugular  vein 
drawn  aside  or  tied  and  cut,  the  loose  cellular  tissue,  and  possibly  the  omo-hyoid 
aponeurosis,  scratched  through  or  cut,  and  one  or  the  other  of  four  landmarks  iden- 
tified :  (a)  the  tense  outer  edge  of  the  anterior  scalene  muscle  or  (6)  the  scalene 
tubercle  at  the  insertion   of  that   muscle   into  the  first  rib,   the  artery  lying  just 
outside  these  on  the  rib;   (c~)  the  first  rib  itself  traced  inward  with  the  finger  from  the 
outer  angle  of  the  wound  until  the  artery  is  reached  ;   (d}  the  lowest  cord  of  the 
brachial  plexus,  lying  immediately  above,  or  sometimes  slightly  overlapping  the  artery. 
The  cord  has  been  mistaken  for  the  vessel,  but  compression  between  the  finger  and 
the  rib  does  not  flatten  it  out,  as  in  the  case  of  the  artery,  and,  of  course,  does  not 
arrest  the  radial  pulse.      The  tubercle  is  often  poorly  developed,  and  has  a  less  close 
relation  to  the  vessel  when  the  latter  rises  high  above  the  clavicle.      The  process  of 
cervical  fascia  reaching  from  the  posterior  border  of  the  scalenus  to  the  sheath  of  the 
artery  may  be  so  tense  as  to  obscure  to  both  sight  and  touch  the  line  of  the  outer 
edge  of  the  muscle 

The  artery  is  cautiously  denuded,  care  being  taken  to  avoid  injury  to  the 
pleura  or  to  the  subclavian  vein.  The  transverse  cervical  artery  is  usually  above 
and  the  suprascapular  artery  below  the  line  of  incision.  The  phrenic  nerve  has 
been  known  to  pass  directly  over  the  third  portion  of  the  subclavian  (Agnew), 
and  the  possibility  of  the  presence  of  this  rare  anomaly  should  be  remembered. 
The  needle,  the  tip  kept  between  the  artery  and  the  rib,  is  passed  from  above  down- 
ward, and  from  behind  forward  and  a  little  inward.  In  the  case  of  a  high  arch  of  the 
subclavian  the  third  portion  is  nearly  vertical,  and  it  would  then  be  more  correct  to 
speak  of  passing  the  needle  from  without  inward. 

2.  The  middle  of  the  clavicle  for  two  or  more  inches,  or  the  whole  clavicle,  may 
be  resected  subperiosteally,   as    in    interscapulo-thoracic  amputations,   and  the    ap- 
proach to  the  artery  greatly  facilitated. 

3.  By  strongly   elevating — instead   of   depressing — the  shoulder  and    clavicle, 
using  the  arm  as  a  tractor,  the  artery  may  be  exposed  by  an  incision  just  below  and 
parallel  with  the  middle  of   the  clavicle.      A  portion  of  the  outer  edge  of  the  pec- 
toralis  major  and  some  of  the  inner  deltoid  fibres  will  usually  have  to  be  divided, 
although  it  may  be   possible  to  gain  sufficient  room  by  drawing  the  margin  of  the 
former  muscle  inward  and  that  of  the  latter  outward.      The  cephalic  vein  dipping  in 
through  this   intermuscular  depression   (Mohrenheim's  fossa)    to  join   the  axillary 
vein  must  be  avoided.     The  artery  is  found  lying  between  the  vein  internally  and 
the  close  bundle  of  the  cords  of  the  brachial  plexus  externally.      The  point  at  which 
the  vessel  is  tied  is  said  to  be  identical  with  that  at  which  it  is  ligated  through  the 
usual  incision  (Dawbarn). 


758  HUMAN   ANATOMY. 

The  collateral  circulation  after  ligation  of  the  third  portion  of  the  subclavian 
artery  is  carried  on  from  the  proximal  or  cardiac  side  of  the  ligature  by  (a)  the 
suprascapular  and  posterior  scapular  ;  (6)  the  aortic  intercostals,  the  superior  inter- 
costals,  and  the  internal  mammary  ;  and  (c)  numerous  subdivisions  of  subclavian 
branches  running  through  the  axilla,  anastomosing  respectively  with  (a)  the  sub- 
scapular,  and  the  acromio-thoracic  ;  (£),  the  subscapular,  long  thoracic,  infrascap- 
ular,  and  dorsalis  scapulae  ;  (c)  the  axillary  trunk  or  its  branches. 

i.  The  Vertebral  Artery. — The  vertebral  artery  (a.  vertebralis)  (Figs.  695, 
704),  the  first  and  largest  branch  of  the  subclavian  artery,  is  destined  chiefly  for  the 
supply  of  the  spinal  cord  and  the  brain,  joining  with  the  internal  carotid  arteries  to 
form  the  remarkable  intracranial  anastomotic  circle  of  Willis.  In  view  of  its  peculiar 
course,  the  vertebral  artery  may  be  conveniently  divided  into  four  parts. 

The  first  portion  arises  from  the  upper  surface  of  the  first  part  of  the  sub- 
clavian artery,  opposite  the  interval  between  the  longus  colli  and  scalenus  anticus, 
and  courses  upward  and  somewhat  backward,  between  these  muscles  and  in  front 
of  the  transverse  process  of  the  seventh  cervical  vertebra,  to  the  foramen  in  the 
transverse  process  of  the  sixth  cervical  vertebra,  which  it  enters.  The  artery  is 
surrounded  by  a  plexus  of  sympathetic  nerve-fibres,  and  in  front  is  crossed  by  the 
inferior  thyroid  artery  and  covered  by  the  vertebral  and  internal  jugular  veins. 
The  second  portion  includes  the  ascent  of  the  artery  through  the  foramina  in  the 
transverse  process  of  the  upper  six  cervical  vertebrae,  surrounded  by  plexiform  net- 
works of  sympathetic  nerve-fibers  and  of  veins,  and  Lying  in  front  of  the  trunks  of 
the  cervical  nerves.  As  the  artery  traverses  the  foramen  in  the  axis  it  abandons  its 
previous  almost  vertical  course  and  passes  upward  and  outward  to  reach  the  foramen 
in  the  atlas.  As  the  artery  emerges  from  this  opening,  between  the  suboccipital 
nerve  and  the  rectus  capitis  lateralis  muscle,  the  third  portion  begins,  which  winds 
horizontally  to  the  outer  side  and  back  of  the  superior  articular  surface  of  the  atlas 
to  enter  the  suboccipital  triangle  (Fig.  522)  where  the  artery  rests  in  the  vertebral 
groove  upon  the  posterior  arch  of  the  atlas,  separated  from  the  bone,  however,  by 
the  suboccipital  nerve.  The  artery  then  perforates  the  lower  border  of  the  posterior 
occipito-atlantoid  ligament  and  enters  the  spinal  canal.  The  fourth  portion  of 
the  artery  pierces  the  spinal  dura  mater,  passes  between  the  roots  of  the  hypoglossal 
nerve  and  the  dentate  ligament  and  enters  the  cranial  cavity  by  traversing  the  fora- 
men magnum.  Passing  forward  along  the  medulla  oblongata  and  gradually  inclin- 
ing towards  the  mid-ventral  line,  at  the  posterior  border  of  the  pons  the  vertebral 
artery  unites  with  its  fellow  of  the  opposite  side  to  form  the  basilar  artery  ( a.  basi- 
laris),  which  extends  forward  along  the  median  line  of  the  pons  to  the  anterior 
border  of  that  structure,  where  it  terminates  by  dividing  into  the  two  posterior 
cerebral  arteries. 

Branches. — In  its  course  up  the  neck  the  vertebral  artery  gives  off,  opposite  each  inter- 
vertebral  space  which  it  passes,  lateral  and  medial  branches  which  represent  the  original  seg- 
mental  arteries  by  the  anastomoses  of  whose  branches  the  vertebral  \vas  formed  (  page  721 ). 

(a)  The  lateral  or  muscular  branches  pass  to  the  muscles  of  the  neck  and  form  anasto- 
moses with  the  ascending  and  deep  cervical  branches  of  the  subclavian  and  with  the  arteria 
princeps  cervicis  of  the  occipital. 

(b)  The  medial  or  spinal  branches  ( rami  spinales)  pass  through  the  intervertebral  foramina 
into  the  spinal  canal,  accompanying  the  spinal  nerves,  and  are  distributed  to  the  bodies  of  the 
vertebrae  and  to  the  membranes  and  substance  of  the  spinal  cord.     Each  branch  gives  off  an 
</.v, , 'iii/in^  and  a  </i'\ci-//ifi//^  rtumis  upon   the  posterior  surface  of  the  spinal  cord,  and  these, 
anastomosing  with  each  other  and  with  twigs  from   the  spinal  branches  of  the  intercostal,  lum- 
bar, and  lateral  sacral  arteries  below  and  with  the  posterior  spinal  branches  of  the  upper  part 
of  the  vertebral,  assist  in  the  formation   of  the  posterior  spinal  arteries,  which   run   the  entire 
length  of  the  spinal  cord  upon  its  posterior  surface  on  each  side  of  the  median  line.     Ante- 
riorly the  spinal   branches  of   the  vertebral    unite  with   the  anterior  spinal    artery,   reinforcing 
that  vessel. 

(c}  The  posterior  meningeal  artery  frnmus  ineninneus)  arises  from  the  vertebral,  just  after 
it  has  pierced  the  dura  mater,  and  supplies  the  portion  of  that  membrane  which  lines  the  pos- 
terior portion  of  the  posterior  fossa  of  the  skull. 


THE    VERTEBRAL   ARTERY. 


759 


(d)  The  posterior  spinal  artery  (a.  spinalis  posterior)  is  a  slender  vessel  which  anasto- 
moses below  with  the  posterior  ascending  ramus  of  the  uppermost  spinal  branch  from  the 
cervical   portion  of  the  vertebral  and  forms  the  uppermost  part  of  the  posterior  spinal  artery. 

(e)  The  anterior  spinal  artery  (a.  spinalis  anterior),  much  larger  than  the  preceding,  arises 
from  the  inner  surface  of  the  vertebral,  a  short  distance_  before  the  latter  unites  with  its  fellow 
to  form  the  basilar.     It  passes  downward  and  towards  the  ventral  median  line,  and  unites  with 
its  fellow  to  form  a  single  median  longitudinal  stem  which  extends  the  entire  length  of  the 
spinal  cord  along  the  line  of  the  anterior  median  fissure,  receiving  reinforcing  branches  from 
the  various  spinal  branches  of  the  vertebral,  intercostal,  lumbar,  and  lateral  sacral  arteries. 

(f)  The  posterior  inferior  cerebellar  artery  (a.  cerebelli  inferior  posterior)  arises  at  about  the 
same  level  as   the   preceding  vessel,  but   from  the  outer  surface  of  the  vertebral.     It  passes 
upward  over  the  sides  of  the  medulla  oblongata  to  supply  the  lower  surface  of  the  cerebellum, 

FIG.  702. 


Anterior  cerebral  artery- 


Olfactory  tract,  cut 


Anterior  cerebral 

artery 


Internal  carotid  artery 


Pituitary  body 
Anterior  choroid 

artery 

Posterior  communi- 
cating artery 

Corpora  nianunillaria 
Posterior  cerebral 

artery 
Superior  cerebellar 

artery 

A  pontine  artery 
Auditory  artery 

Trigeminal  nerve 


Vertebral  artery  - 


Right  lobe  of 
cerebellum 


Anterior  communicating 
artery 

Optic  chiasm 

Internal  carotid  artery 
Middle  cerebral  artery 


Antero-lateral  gang- 
lionic  arteries 
Posterior  com.  arteries 
Anterior  choroid  artery 
Trochlear  nerve 
Posterior  cerebral  artery 
Sup.  cerebellar  artery 

Basilar  artery 
Pons 

Anterior  inferior  cerebel- 
lar artery 


Anterior  spinal  artery 
Medulla  oblongata 

Posterior  inferior  ecre- 
bellar  artery 

Vertebral  artery 


Inferior  surface  of  brain,  showing  internal  carotid,  vertebral  and  basilar  arteries  and  circle  of 
Willis;  apex  of  left  temporal  lobe  has  been  removed  to  expose  ganglionic  arteries. 


giving  branches  to  the  medulla  and  to  the  choroid  plexus  of  the  fourth  ventricle  and  anasto- 
mosing with  the  superior  cerebellar  artery. 

From  the  basilar  artery,  (Fig.  702)  the  anterior  median  continuation  of  the  vertebrals. 

(,?•)  Numerous  transverse  arteries  are  given  off  and  pass  outward  over  the  pons  to  supply 
that  structure  and  the  adjacent  portions  of  the  brain. 

(//)  The  internal  auditory  arteries  (aa.  auditivae  internae),  one  on  each  side,  are  additionally 
given  off,  and  accompany  the  auditory  nerve  through  the  internal  auditory  meatus  to  supply  the 
internal  ear. 

(t)  The  anterior  inferior  cerebellar  arteries  (aa.  cerebelli  inferiores  anteriores),  pass  out- 
ward on  either  side  over  the  surface  of  the  pons  to  the  lower  surface  of  the  anterior  portion  of  the 
cerebellum,  supplying  that  structure  and  anastomosing  with  the  superior  cerebellar  arteries. 

(/)  The  superior  cerebellar  arteries  (aa.  cerebelli  superiores),  These  arise  from  the  basilar, 
immediately  behind  its  division  into  the  posterior  cerebral  arteries.  They  pass  outward  and 
backward  over  the  pons  and  the  crura  cerebri,  immediately  behind  the  roots  of  the  oculo-motor 


760  HUMAN   ANATOMY. 

nerves,  and,  curving  upward  in  the  tentorial  fissure  almost  parallel  with  the  trochlear  nerves, 
are  distributed  to  the  upper  surface  of  the  cerebellum  and  anastomose  with  the  inferior  cere- 
bellar  arteries. 

(£)  The  posterior  cerebral  arteries  (aa.  cerebri  posteriores)  (Fig.  702)  are  the  terminal 
branches  of  the  basilar.  From  its  origin  at  the  anterior  border  of  the  pons  each  artery  passes 
outward  and  slightly  forward,  curving 'around  the  crus  cerebri,  immediately  in  front  of  the  root 
of  the  oculomotor  nerve,  which  separates  it  from  the  superior  cerebellar  artery.  It  then 
passes  ui)on  the  inferior  surface  of  the  cerebral  hemisphere,  where  it  breaks  up  into  cortical 
branches  which  ramify  over  the  surface  of  the  temporal  and  occipital  lobes,  anastomosing  with 
one  another  and  with  the  branches  of  the  anterior  and  middle  cerebrals.  The  cortical  branches 
(Fig.  700)  include  the  anterior  temporal,  which  supplies  the  anterior  parts  of  the  uncinate  and 
occipito-temporal  convolutions;  the  posterior  temporal,  distributed  to  the  posterior  part  of  the 
uncinate  and  the  occipito-temporal  convolutions  and  the  adjoining  gyms  lingualis  ;  the  calca- 
tine,  the  continuation  of  the  posterior  cerebral  along  the  calcarine  fissure,  which  passes  to  the 
cuneus  and  the  gyms  lingualis,  and  winds  to  the  outer  surface  ;  and  fazparieto-occipita.lt  which 
follows  the  parieto-occipital  fissure  to  the  cuneus  and  the  quadrate  lobe. 

Immediately  at  their  origin  the  posterior  cerebrals  give  rise  to  a  number  of  small  central 
branches  (posfero-mesial  and  postero-lateral  ganglionic}  which  dip  down  into  the  substance 
of  the  posterior  perforated  space  to  supply  the  optic  thalamus  and  the  adjacent  parts  of  the 
brain-stem,  and  somewhat  more  laterally  each  gives  off  a  posterior  choroidal  branch,  which 
passes  forward  in  the  transverse  fissure  to  the  choroid  plexus  of  the  third  ventricle.  Near 
where  it  passes  in  front  of  the  oculo-motor  nerve,  each  posterior  cerebral  receives  the  posterior 
communicating  artery  which  passes  back  to  it  from  the  internal  carotid,  and  more  laterally  it 
gives  off  some  small  branches  which  are  distributed  to  the  corpora  quadrigemina  and  the 
posterior  part  of  the  optic  thalamus. 

Variations. — The  vertebral  artery  may  arise  from  a  trunk  common  to  it  and  one  of  the 
other  branches  of  the  subclavian,  and  sometimes  it  arises  directly  from  the  arch  of  the  aorta  or, 
on  the  right  side,  from  the  innominate  artery  or  the  common  carotid.  It  may  traverse  a  foramen 
in  the  transverse  process  of  the  seventh  cervical  vertebra,  or  the  lowest  vertebrarterial  foramen 
through  which  it  passes  may  be  the  fifth,  fourth,  third,  or  even  the  second.  Very  rarely  the  two 
vertebrals  fail  to  unite  to  form  a  single  median  basilar,  that  artery  being  thus  represented  by  two 
longitudinal  trunks  united  by  transverse  anastomoses.  Occasionally  the  basilar  divides  into  two 
longitudinal  stems  which  reunite  farther  forward,  and  its  formation  by  the  fusion  of  two  parallel 
vessels  is  frequently  indicated  by  the  presence  in  its  interior  of  a  more  or  less  perfect  median 
sagittal  partition. 

The  vertebral  may  give  origin  to  an  inferior  thyroid  artery  or  to  the  deep  cervical,  and  oc- 
casionally, in  its  upper  part,  to  a  branch  which  anastomoses  with  the  occipital.  One  of  the  pos- 
terior inferior  cerebellar  arteries  may  be  wanting,  as  is  also  not  infrequently  the  case  with  one 
of  the  anterior  inferior  cerebellars,  or  these  latter  vessels  may  arise  from  the  posterior  cerebral. 
Occasionally  the  proximal  portion  of  one  or  other  of  the  posterior  cerebral  arteries  is  reduced  to 
a  mere  thread,  the  blood  reaching  the  terminal  portions  of  the  vessel  from  the  internal  carotid, 
through  the  posterior  communicating  artery. 

The  Circle  of  Willis. — The  circle  or,  as  it  is  more  properly  called,  the 
polygon  of  Willis  (circulus  artcriosus)  is  a  continuous  anastomosis  at  the  base  of  the 
brain  (Fig.  702)  between  branches  of  the  internal  carotids  and  subclavians  (verte- 
brals). It  surrounds  the  posterior  perforated  space  and  the  floor  of  the  thalamen- 
cephalon.  Posteriorly  it  is  formed  by  the  proximal  portions  of  the  posterior  cerebral 
arteries,  at  the  sides  by  the  posterior  communicating  and  internal  carotid  arteries 
behind,  and  by  the  proximal  portions  of  the  anterior  cerebrals  in  front,  and  it  is 
completed  anteriorly  by  the  anterior  communicating  artery  which  unites  the  two 
anterior  cerebrals. 

By  means  of  these  connections  free  communication  is  established  at  the  base  of 
the  brain  between  the  two  internal  carotids  and  also  between  these  vessels  and  the 
vertebrals.  It  maybe  noted  that  a  further  communication  between  these  sets  <»f 
vessels  exists  upon  the  lateral  surfaces  of  the  cerebral  hemispheres  where  branches 
of  the  posterior  cerebral  arteries  anastomose  with  branches  of  both  the  middle  and 
anterior  cerebrals. 

In  marked  contrast  to  this  abundant  anastomosis  of  the  larger  vessels  upon  the 
surface  of  the  cerebrum  is  the  lack  of  direct  communication  between  the  small  vessels 
which  penetrate  its  substance.  These  ar^  all  terminal  or  end-arteries, — that  is, 
vessels  which  have  no  communication  with  others  except  through  the  general  capil- 
lary net-work,  which  offers  but  little  opportunity  foe  the  establishment  of  an  efficient 
collateral  circulation  in  the  case  of  occlusion  of  one  of  the  arteries. 


PRACTICAL  CONSIDERATIONS:   VERTEBRAL  ARTERY.         761 

Practical  Considerations. — The  vertebral  artery  may  require  ligation  on 
account  of  wounds,  or  of  traumatic  aneurism  of  the  vessel  itself,  or  (in  addition  to  the 
ligation  of  other  vessels)  in  aortic  or  innominate  aneurism,  or  to  prevent  or  arrest 
secondary  hemorrhage  after  ligation  of  the  innominate. 

Aneurism — except  from  wound — is  excessively  rare,  the  vessel  being  well  sup- 
ported, first  between  the  scalenus  anticus  and  the  longus  colli  muscles  and  then  in  the 
bony  canal  in  the  transverse  processes.  Only  one  case  of  spontaneous  aneurism  of 
the  cervical  portion  of  the  artery  has  been  reported  (Hufschmidt). 

Traumatic  aneurism  is  more  frequent,  but,  on  account  of  the  vessel's  depth,  is  rare. 

Paralysis  of  some  of  the  tongue  muscles  has  been  attributed  to  pressure  on  the 
hypoglossal  nerve  by  a  vertebral  aneurism  and  severe  occipital  headache  to  pressure 
on  the  suboccipital  nerve. 

Digital  compression  of  the  vertebral  is  possible  below  Chassaignac' s  carotid 
tubercle  (q.v.~), — i.e.,  below  the  level  of  the  cricoid  cartilage,  if  pressure  is  made  in 
the  line  of  the  great  vessels.  Alternating  pressure  above  and  below  this  level  is  of 
great  diagnostic  value  in  distinguishing  the  source  of  the  bleeding,  or  of  the  supply  of 
blood  to  a  pulsating  tumor,  after  a  deep  wound  of  the  neck.  Pressure  along  the  line 
of  the  common  carotid  below  the  tubercle — i.e. ,  for  from  two  to  two  and  a  half  inches 
above  the  clavicle — will  usually  arrest  such  bleeding  and  pulsation,  no  matter  whether 
the  vertebral  or  either  of  the  carotids  is  involved.  Pressure  above  the  tubercle  will 
affect  only  the  carotids  and  their  branches,  but — except  in  the  presence  of  an  anomaly 
— will  leave  unchanged  a  flow  of  blood  or  an  aneurismal  pulsation  proceeding  from 
the  vertebral.  Furthermore,  as  in  one  of  the  not  infrequent  vertebral  variations 
(vide  supra),  the  artery  may  not  enter  its  vertebrarterial  foramen  until  it  reaches  the 
fifth,  fourth,  third,  or  even  the  second  transverse  process,  and  as,  in  such  a  case,  it 
would  be  effectually  compressed  when  pressure  was  applied  higher  than  the  carotid 
tubercle,  it  would  be  well  always  to  supplement  the  above  test  by  the  method  of 
"lateral  compression"  (Rouge), — i.e.,  by  pressing  together  between  the  thumb  and 
fingers  the  anterior,  portion  of  the  relaxed  sterno-mastoid  muscle  and  the  carotid 
sheath  and  its  contents.  This  avoids  all  risk  of  coincident  compression  of  the  verte- 
bral, and  if  it  arrests  the  temporal  pulse  without  affecting  materially  the  bleeding  or 
the  pulsation  on  account  of  which  the  examination  is  made,  it  greatly  increases  the 
probability  that  the  latter  are  of  vertebral  origin  (Matas).  The  importance  of  making* 
the  diagnosis  is  shown  by  the  fact  that  in  sixteen  out  of  thirty-six  cases  of  injuries  to 
the  vertebral  artery  the  common  carotid  had  been  ligated,  aggravating  the  hemor- 
rhage by  increasing  the  strain  on  the  vertebral  circulation  and,  of  course,  also  increas- 
ing the  risk  from  shock,  and  later  from  cerebral  complications  (Matas). 

Ligation  of  the  vertebral  has  been  effected  through  variously  placed  incisions  : 
i.  Low  in  the  neck,  one  of  three  inches  in  length  along  the  posterior  border  of  the 
sterno-mastoid  and  with  its  lower  end  at  the  clavicle,  with  division  of  some  of  the  clav- 
icular fibres  of  that  muscle  and  of  the  deep  fascia,  will  permit  the  recognition  of  the 
carotid  tubercle,  the  displacement  inward  of  the  sterno-mastoid  and  internal  jugular 
vein,  the  definition  of  the  space  between  the  scalenus  anticus  and  the  longus  colli, 
and  the  identification  of  the  artery  by  its  pulsation.  The  vertebral  vein  lies  in  front 
of  the  artery.  The  pleura,  the  inferior  thyroid  vessels,  the  phrenic  nerve,  and  on  the 
left  side  the  thoracic  duct  must  be  avoided.  The  fibres  of  the  cervical  sympathetic 
will  be  almost  necessarily  disturbed,  and  may  be  included  in  the  ligature.  Contrac- 
tion of  the  corresponding  pupil,  through  the  then  unopposed  action  of  the  oculo- 
motor, will  indicate  that  the  vessel  has  been  secured;  it  will  be  only  temporary. 

2.  For  a  ligation  in  continuity,  as  for  wound  or  aneurism  in  the  suboccipital 
region,  the  artery  may  be  much  more  easily  reached  through  an  incision  identical 
with  that  used  for  ligating  the  common  carotid  above  the  omo-hyoid  (page  732). 
When  the  carotid  sheath  is  well  exposed  it  is  drawn  outward  with  its  contents. 
Chassaignac' s  tubercle  is  felt  (on  the  cricoid  level  or  one  centimetre  above  it)  and 
the  longus  colli  fibres  below,  overlying  the  artery,  are  seen.  A  transverse  division 
of  that  muscle  exposes  the  vertebral  artery  in  a  much  safer  region  than  below  and  at 
a  less  depth  (Dawbarn). 

The  collateral  circulation  is  very  freely  re-established  through  the  vessels  of  the 
circle  of  Willis. 


762 


HUMAN   ANATOMY. 


FIG.  703. 


Cephalic  vein  f 

Humeral  branch  of 
acromial  thoracic  artery 

Branch,  long  thoracic  artery 

I.  and  III. ant.  perforating  arteries 

IV.  aortic  intercostal  artery 

Lower  branch  of  III.  aortic  intercostal 
Internal  intercostal  muscle 
Musculo-phrenic  artery  •< 


IX.  aortic  intercostal  artery 
Transversalis  muscle 


Internal  oblique  muscle 
Subcostal  artery 


- 1.  chondro-sternal  articulation 
-Internal  mammary  artery 
—  I.  ant.  perf.  artery  of  left  side 

^Anterior  intercostal  arteries  of 
II.,  111..  IV.  and  V.  interspaces 


Anterior  superior  spine  of  ilium 
Deep  epigastric  artery 


Superficial  circumflex  iliac  artery 
Superficial  epigastric  artery 


-Superior  epigastric  artery 


Kectus  abdomini» 


Semilunar  fold  of  Douglas 


Superficlalexternalpudu  artery 


Deep  external  pudic  artery 
Dorsalis  penis  arteries 


Internal  mammary  and  deep  epigastric  arteries. 


THE    INTERNAL    MAMMARY  ARTERY.  763 

2.  The  Internal  Mammary  Artery. — The  internal  mammary  artery  (a.  mam- 
maria  interna)  (Figs.  692,  703)  arises  from  the  lower  surface  of  the  subclavian, 
usually  a  few  millimetres  lateral  to  the  origin  of  the  vertebral.  It  is  at  first  directed 
downward,  inward  and  slightly  forward  to  reach  the  posterior  surface  of  the  first 
costal  cartilage,  about  half-an-inch  lateral  to  the  border  of  the  sternum,  and  is  thence 
continued  vertically  downward  upon  the  inner  surface  of  the  anterior  thoracic  wall 
to  the  sixth  intercostal  space,  opposite  which  it  terminates  by  dividing  into  the 
musculo-phrenic  and  superior  epigastric  arteries. 

In  the  upper  part  of  its  course  the  artery  rests  upon  the  dome  of  the  pleura, 
crosses  the  posterior  surface  of  the  subclavian  vein,  and  is  crossed  obliquely  from 
above  downward  and  inward  by  the  phrenic  nerve.  In  the  thorax  it  is  in  con- 
tact behind  with  the  parietal  layer  of  the  pleura  as  far  down  as  the  third  costal  carti- 
lage, and  below  that  with  the  triangularis  sterni  muscle.  Anteriorly  it  rests  upon 
the  posterior  surfaces  of  the  upper  five  costal  cartilages,  and,  in  the  intercostal 
spaces,  upon  the  anterior  portions  of  the  internal  intercostal  muscles. 

Branches. — -The  internal  mammary  gives  off  the  following  branches:  (i)  the  superior 
phrenic,  or  comes  nervi  phrenici,  (2)  the  mediastinal  branches.  (3)  the  anterior  intercostals, 
(4)  the  anterior  perforating  branches  and  the  two  terminal  branches,  (5)  the  inusculo-phrenic, 
and  (6)  the  superior  epigastric. 

(a)  The  superior  phrenic  artery  or  comes  nervi  phrenici  (a.  pericardiacophrenica)  arises  from 
the  upper  part  of  the  internal  mammary,  and  is  a  long,  slender  branch  which  accompanies  the 
phrenic  nerve  to  the  diaphragm,  where  it  anastomoses  with  the  inferior  phrenic  and  musculo- 
phrenic  vessels.  In  its  course  it  gives  off  numerous  small  branches  to  the  pleura  and  peri- 
cardium, which  anastomose  with  the  mediastinal  branches  and  the  bronchial  vessels  from  the 
thoracic  aorta. 

(6)  The  mediastinal  branches  (aa.  mediastinales  anteriores)  area  number  of  small  vessels 
which  are  distributed  to  the  sternum,  the  remains  of  the  thymus  gland,  the  pericardium,  and  the 
adipose  tissue  of  the  anterior  mediastinum. 

(r)  The  anterior  intercostal  arteries  (rami  intercostales)  arise  from  the  internal  mammary 
opposite  each  of  the  five  upper  intercostal  spaces,  and  are  two  in  number  for  each  space.  They 
pass  outward  and  slightly  downward  upon  the  posterior  surface  of  the  intercostal  muscles,  one 
along  the  upper  border  of  each  of  the  intercostal  spaces  concerned  and  the  other  along  its  lower 
border,  and  after  having  pierced  the  internal  intercostal  muscles,  they  terminate  by  becoming 
continuous  with  the  upper  and  lower  divisions  respectively  of  the  intercostal  branches  of  the 
superior  intercostal  artery  and  of  the  three  uppermost  aortic  intercostals.  These  branches  really 
represent  ventral  prolongations  of  the  aortic  intercostal  arteries  from  which  arose  the  upward 
and  downward  branches  whose  anastomosis  resulted  in  the  formation  of  the  internal  mammary 
(compare  page  848). 

(d]  The  anterior   perforating   branches  (rami  perforantes)   arise   from  the  internal  mam- 
mary, one  opposite  each  intercostal  space  that  it  crosses,  and  represent  the  ventral  ends  of  the 
original  aortic  intercostal.    They  pierce  the  internal  intercostal  muscles,  the  anterior  intercostal 
membrane,  and  the  pectoralis  major,  to  supply  branches  to  the  sternum  and  to  the  integument. 
The  arteries  of  the  third  and  fourth  intercostal  spaces  are  larger  than  the  others  and  send 
branches  to  the  mammary  gland. 

(e)  The  musculo-phrenic  artery  (a.  musculophrenica)  is  the  lateral  terminal  branch  of  the 
internal  mammary.     It  arises  opposite  the  anterior  end  of  the  sixth  intercostal  space  and  passes 
downward  and  outward  along  the  attachments  of  the  diaphragm  to  the  seventh  and  eighth  costal 
cartilages,  and  then,  piercing  the  diaphragm,  is  continued  onward  upon  the  under  surface  of  that 
muscle  to  the  level  of  the  tenth  or  eleventh  rib,  where  it  terminates  by  anastomosing  with  the 
inferior  phrenic  arteries  and  with  the  ascending  branch  of  the  deep  circumflex  iliac.     In  addition 
to  branches  to  the  diaphragm,  it  gives  off  two  anterior  intercostal  branches  opposite  each  of  the 
intercostal  spaces  that  it  crosses  as  far  down  as  the  ninth  ;  these  branches   have   the  same 
arrangement  and  significance  as  the  anterior  intercostal  branches  of  the  internal  mammary. 

( /)  The  superior  epigastric  artery  (a  epigastrica  superior)  is  the  medial  terminal  branch 
of  the  internal  mammary.  It  continues  the  course  of  that  artery  downward,  and  passes  through 
the  diaphragm  in  the  interval  between  its  costal  and  sternal  origins  and  enters  the  sheath  of 
the  rectus  abdominis.  Lower  down  it  passes  into  the  substance  of  that  muscle,  where  it  termi- 
nates by  anastomosing  with  branches  of  the  deep  epigastric  artery. 

Anastomoses. — By  means  of  its  terminal  branches  the  internal  mammary 
makes  a  double  anastomosis  in  the  anterior  abdominal  walls  with  branches  from  the 
iliac  vessels, — namely,  with  the  deep  epigastric  and  deep  circumflex  iliac  branches  of 


764  HUMAN   ANATOMY. 

the  external  iliac,  and  thus  connects  the  superior  and  inferior  portions  of  the  aortic 
system  of  vessels.  In  addition,  by  means  of  the  anterior  intercostals,  it  makes 
extensive  connections  with  the  thoracic  aorta  through  the  aortic  intercostals. 

Variations.— The  internal  mammary  may  arise  from  the  second  or  even  the  third  portion 
of  the  subclavian,  or  it  may  take  its  origin  from  the  thyroid  axis  or  from  the  superior  intercostal. 
In  its  course  down  the  anterior  thoracic  wall  it  varies  considerably  in  its  relation  to  the  lateral 
border  of  the  sternum,  its  distance  from  it  varying  in  different  cases  from  5-20  mm. 

Of  the  supernumerary  branches  to  which  it  may  give  rise,  one  of  the  most  important  is  the 
lateral  internal  mammary  (ramus  costalis  lateralis).  This  arises  from  the  internal  mammary 
above  the  first  rib,  or  in  some  cases  directly  from  the  subclavian,  and  descends  upon  the  inner 
surfaces  of  the  upper  four  or  six  ribs  and  the  intervening  intercostal  spaces,  parallel  with  the 
internal  mammary,  but  some  distance  lateral  to  it.  It  gives  off  branches  in  each  intercostal 
space,  which  anastomose  ventrally  with  the  anterior  intercostal  branches  of  the  internal 
mammary  and  dorsal  ly  with  the  aortic  intercostals. 

Practical  Considerations. — The  internal  mammary  is  not  infrequently 
involved  in  stab  wounds  of  the  chest,  and  this  accident  may  be  suspected  if  after  such 
a  wound  there  are  threatening  symptoms  of  internal  hemorrhage  with  no  evidence  of 
injury  to  the  lung  itself.  The  bleeding  may  take  place  into  the  pleural  cavity,  causing 
the  characteristic  symptoms  of  haemothorax  (page  1866). 

Compression. — In  emergencies  the  bleeding  may  sometimes  be  arrested  by 
pushing  through  the  wound  into  the  intrathoracic  space  or  pleural  cavity  a  pouch  of 
antiseptic  gauze,  packing  it  with  other  strips  of  gauze  so  as  to  distend  the  portion 
within  the  ribs,  and  then  making  traction  upon  it  so  as  to  compress  the  wounded 
vessel  against  the  costal  cartilages  and  the  chest-wall. 

This  same  method  is  applicable  in  some  cases  of  intercostal  hemorrhage  when  it 
is  not  possible  or  desirable  to  approach  the  vessel  directly  in  its  groove  on  the  under 
and  inner  border  of  the  rib  by  incision  or  by  resection  of  a  portion  of  the  rib. 

Ligation. — In  some  cases  it  may  be  necessary  to  ligate  the  vessel  in  its  con- 
tinuity, although  its  free  anastomoses  make  it  very  desirable  to  find  and  tie  it  on  both 
sides  of  the  wound.  It  may  be  reached  through  an  incision  parallel  with  the  sternum 
and  a  half-inch  from  its  margin  or  through  a  transverse  incision  extending  outward 
along  an  intercostal  space.  In  either  event,  the  skin,  superficial  fascia,  sternal  fibres 
of  the  great  pectoral  muscle,  the  external  intercostal  aponeurosis  (connecting  the 
external  intercostal  muscle  with  the  sternum),  and  the  internal  intercostal  muscle 
must  be  divided.  The  artery  with  its  accompanying  veins  will  be  found  in  loose 
cellular  tissue  lying,  in  the  first  two  spaces,  upon  the  endothoracic  fascia,  which  sepa- 
rates it  from  the  pleura  ;  in  the  lower  spaces  the  vessel  rests  upon  the  triangularis 
sterni  muscle.  Below  the  third  or  fourth  space  resection  of  a  cartilage  will  usually 
be  necessary  for  the  purpose  of  gaining  room,  and  at  any  level  is  often  resorted  to 
to  permit  direct  access  to  the  bleeding  ends. 

3.  The  Superior  Intercostal  Artery. — The  superior  intercostal  artery 
(truncus  costocervicalis)  (Fig.  695)  arises  from  the  upper  posterior  surface  of  the 
subclavian  artery,  usually  about  opposite  the  origin  of  the  internal  mammary,  but  quite 
frequently,  and  especially  upon  the  right  side,  under  cover  of  the  scalenus  anticus. 
It  passes  at  first  upward  and  medially,  and  then  curves  backward  and  downward  over 
the  dome  of  the  pleura  to  reach  the  anterior  surface  of  the  neck  of  the  first  rib, 
where  it  divides  into  two  terminal  branches  which  pass  laterally  in  the  first  and 
second  intercostal  spaces.  As  it  enters  the  thorax,  the  superior  intercostal  lies  be- 
tween the  first  thoracic  sympathetic  ganglion  and  the  first  thoracic  spinal  nerve. 

Branches.— The  superior  intercostal  gives  rise  to  (i)  the  deep  cervical  artery,  and  to 
two  terminal  branches,  (2)  they?™/ and  (3)  the  second  intercostal  arte ries. 

(a)  The  deep  cervical  artery  (a.  cervicalis  profunda)  arises  just  as  the  superior  intercostal 
reaches  the  upper  border  of  the  neck  of  the  first  rib,  although  occasionally  it  takes  origin 
directly  from  the  subclavian.  It  is  directed  upward  and  backward,  passing  between  the  last 
cervical  and  first  thoracic  nerves  and  beneath  the  transverse  process  of  the  last  cervical  verte- 
bra,  and  ascends  the  neck  between  the  complexus  and  the  semispinalis  colli,  to  which  it  sends 
branches.  It  anastomoses  with  branches  of  the  ascending  cervical,  vertebral,  and  princeps  cer- 
vicis  arteries,  and  gives  off  a  spinal  branch  which  passes  along  the  eighth  cervical  nerve  to  the 


THE   THYROID   AXIS. 


765 


spinal  canal,  where  it  anastomoses  upon  the  surface  of  the  spinal  cord  with  the  spinal  branches 
of  the  vertebral  and  of  the  intercostal  arteries. 

In  all  its  relations  the  deep  cervical  is  comparable  to  a  posterior  branch  of  an  intercostal 
artery,  and  is  to  be  regarded  as  the  posterior  branch  of  the  seventh  cervical  segmental  artery, 
which  is  the  subclavian. 

(6)  The  first  intercostal  artery  passes  outward  and  forward  in  the  first  intercostal  space, 
and  resembles  in  its  course  and  distribution  an  aortic  intercostal  (page  792). 

(c)  The  second  intercostal  artery  arises  at  the  bifurcation  of  the  superior  intercostal  and 
passes  downward  over  the  neck  of  the  second  rib  to  the  second  intercostal  space,  in  which  it 

FIG.  704. 


Deltoid 


Biceps,  long  head 

Anterior  circumflex 

Biceps,  short  head 

Axillary  artery 

Posterior 

circumflex 

Subscapular 

Dorsalis  scapulae  ' 

Long  thoracic 
Subscapularis 

Teres  major 
Latissimus  dorsi 

Serratus  magnus 


Common  carotid 
Suprascapular 

-  Inferior  thyroid 
-Thyroid  axis 


Vertebral 
Thyroid  body 
Common  carotid 
Trachea 

Subclavian  artery 
Clavicular  facet 

of  sternum 
Int.  mammary 

First  rib 
Superior  thoracic 


Alar  thoracic 


Pectoralis  minor, 
cut 


Deep  dissection  exposing  subclavian  and  axillary  arteries  and  their  branches. 


courses  similarly  to  an  aortic  intercostal  (page  792).  It  usually  receives  an  anastomosing  branch 
from  the  third  intercostal  artery  or  else  directly  from  the  thoracic  aorta,  and  may  be  replaced 
by  it. 

Variations. — The  superior  intercostal  may  arise  from  the  vertebral  artery  and  may  termi- 
nate in  the  first  intercostal  alone,  the  second  arising  from  the  third  or  from  the  thoracic  aorta. 
Anastomoses  occur  between  the  first  and  second  intercostals  and  the  arteria  aberrans  ( page 
792),  when  that  vessel  is  present. 

4.  The  Thyroid  Axis. — The  thyroid  axis  (triinctts  thyreoccrvicalis)  (Fig.  704) 
arises  from  the  upper  border  of  the  subclavian,  usually  just  medial  to  the  medial 
border  of  the  scalenus  anticus.  It  ascends  vertically  upward  for  from  2—10  mm., 


766  HUMAN   ANATOMY. 

and  terminates  by  dividing  into  three  branches:   (i)   the  inferior  thyroid,  (2)  the 
superficial  cervical,  and  (3)  the  suprascapular. 

(a)  The  inferior  thyroid  artery  (a.  thyreoidea  inferior;  (Fig.  692)  is  the 
largest  of  the  branches  which  arise  from  the  thyroid  axis.  It  passes  at  first  verti- 
cally upward  to  about  the  level  of  the  transverse  process  of  the  sixth  cervical 
vertebra,  and  then  bends  medially.  It  passes  behind  the  common  carotid  artery, 
the  internal  jugular  vein,  and  the  pneumogastric  nerve,  either  behind  or  in  front  of 
the  recurrent  laryngeal  nerve  and  in  front  of  the  vertebral  artery,  and  finally  breaks 
up  into  branches  which  supply  the  lower  part  of  the  thyroid  gland  and  anastomose 
with  their  fellows  of  the  opposite  side  and  with  the  superior  thyroid  artery. 

Branches. — In  addition  to  these  terminal  branches,  the  inferior  thyroid  gives  origin  to  the 
following  arteries  : 

(aa)  Muscular  branches  to  the  scalenus  anticus  and  the  inferior  constrictor  of  the  pharynx. 

(66)  The  ascending  cervical  artery  (a  cervicalis  ascendens)  frequently  arises  directly  from 
the  thyroid  axis  and  passes  vertically  upward,  parallel  to  the  phrenic  nerve,  in  the  interval  be- 
tween the  scalenus  anticus  and  the  rectus  capitis  anticus  major.  It  supplies  the  deep  muscles 
of  the  neck,  sends  branches  through  the  spinal  foramina  which  accompany  the  spinal  branches 
of  the  vertebral  artery,  and  anastomoses  with  the  vertebral,  the  occipital,  the  ascending  pharyn- 
geal,  and  the  deep  cervical  arteries. 

(cc )  The  inferior  laryngeal  artery  (a.  laryngea  inferior)  passes  upward  in  the  groove  be- 
tween the  trachea  and  oesophagus  in  company  with  the  recurrent  laryngeal  nerve.  It  passes 
beneath  the  lower  border  of  the  inferior  constrictor  of  the  pharynx  and  enters  the  larynx,  to 
whose  mucous  membrane  and  muscles  it  is  distributed.  It  anastomoses  with  the  superior 
laryngeal  branch  of  the  superior  thyroid. 

Finally,  it  gives  off  small  branches  to  the  pharynx,  oesophagus,  and  trachea,  one  of  those 
to  the  last-named  structure  extending  down  upon  its  lateral  surface  to  anastomose  below  with 
the  bronchial  arteries. 

The  anastomoses  which  the  inferior  thyroid  makes  by  its  thyroid  branches  with  the  supe- 
rior thyroid  and  by  its  ascending  cervical  branch  with  the  occipital  constitute  important  connec- 
tions between  the  subclavian  and  carotid  systems  and  play  an  important  part  in  the  establish- 
ment of  the  collateral  circulation  after  ligation  of  the  common  carotid  artery. 

Variations. — The  thyroid  axis  occasionally  arises  under  cover  of  or  even  lateral  to  the 
scalenus  anticus,  and  it  may  be  entirely  wanting,  its  branches  arising  directly  from  the  subcla- 
vian. The  inferior  thyroid  maybe  absent  on  one  side  or  on  both,  and  its  size  varies  inversely 
to  the  development  of  its  fellow  of  the  opposite  side  or  to  that  of  the  superior  thyroid  arteries. 

Practical  Considerations. — The  inferior  thyroid  may  be  tied  for  a  wound  or 
during  the  operation  of  thyroidectomy.  It  has  been  frequently  tied,  in  conjunction 
with  the  superior  thyroid,  in  various  forms  of  goitre,  but  the  procedtire  has  been 
abandoned.  It  may  be  reached  through  the  incision  for  tying  the  carotid  below  the 
omo-hyoid  (page  732).  The  sterno-mastoid  and  the  carotid  sheath  and  its  contents 
are  drawn  outward.  The  carotid  tubercle  being  found,  the  inferior  thyroid  should 
be  sought  for  at  a  slightly  lower  level, — opposite  the  body  of  the  sixth  cervical  ver- 
tebra or  about  the  level  of  the  omo-hyoid  crossing, — coming  out  from  behind  the 
sheath  of  the  great  vessels  and  running  in  front  of  the  vertebral  artery  obliquely 
upward  and  inward  towards  the  gland.  It  should  be  remembered  that  before  enter- 
ing the  gland  it  lies  for  a  short  distance  close  to  its  posterior  surface,  and  that  the 
recurrent  laryngeal  nerve  is  in  intimate  relation  to  this  part  of  the  vessel  or  to  its 
terminal  branches.  It  should  therefore  be  tied  in  the  fissure  between  the  oesophagus 
and  the  great  vessels,  as  close  to  the  carotid  sheath — i.e.,  as  far  from  the  inferior 
angle  of  the  gland — as  possible,  to  avoid  inclusion  of  this  nerve.  The  middle  cer- 
vical ganglion  of  the  sympathetic,  the  phrenic  and  the  descendens  hypoglossi  nerves, 
and,  on  the  left  side,  the  thoracic  duct  should  be  carefully  avoidi -d. 

(b}  The  superficial  cervical  artery  (a.  cervicalis  superiicialis)  (Fig.  "I'.s) 
passes  almost  directly  laterally  from  the  thyroid  axis,  passing  in  front  of  the  scalenus 
anticus  and  then  across  the  lower  part  of  the  posterior  triangle  of  the  neck  at  a  lc\el 
of  about  25  cm.  above  the  clavicle.  Arrived  at  the  anterior  border  of  the  trape/ius, 
it  j Kisses  beneath  that  muscle  and  breaks  up  into  ascending  and  descending  branches 
which  supply  the  trapezius,  the  levator  anguli  scapula-,  the  rhomboidei,  and  the 


THE   AXILLARY  ARTERY.  767 

splenii.  The  ascending  branches  anastomose  with  the  deep  and  ascending  cervical 
arteries,  and  with  the  princeps  cervicis  of  the  occipital  and  the  descending  branches 
with  the  suprascapular  and  transverse  cervical. 

(V)  The  suprascapular  artery  (a.  transversa  scapulae)  (Fig.  704),  like  the 
superficial  cervical,  passes  almost  directly  laterally  across  the  lower  part  of  the  pos- 
terior triangle  of  the  neck.  It  lies,  however,  on  a  somewhat  lower  level  than,  and 
anterior  to,  the  superficial  cervical,  lying' usually  behind  the  clavicle,  in  front  of  the 
subclavian  artery,  and  resting  below  upon  the  subclavian  vein.  It  is  continued  later- 
ally beneath  the  trapezius,  to  which  it  sends  branches,  and,  having  reached  the 
upper  border  of  the  scapula,  it  passes  over  the  transverse  ligament  of  that  bone, 
or  occasionally  through  the  suprascapular  notch,  into  the  supraspinous  fossa.  Here 
it  gives  branches  to  the  supraspinatus  muscle,  and,  winding  around  the  lateral 
border  of  the  spine,  passes  through  the  scapular  notch  into  the  infraspinous  fossa, 
where  it  breaks  up  into  branches  supplying  the  infraspinatus  muscle  and  anastomos- 
ing abundantly  and  widely  with  the  branches  of  the  dorsal  scapular  artery. 

5.  The  Transverse  Cervical. — The  transverse  cervical  (a.  transversa  colli) 
is  the  only  branch  which  arises  from  the  third  portion  of  the  subclavian.  It  also  is 
directed  laterally,  parallel  with  the  superficial  cervical  and  suprascapular  arteries, 
about  midway  between  them,  but  on  a  much  deeper  level.  It  rests  upon  the  anterior 
surface  of  the  scalenus  medius  muscle,  and  upon  the  trunks  of  the  brachial  plexus, 
and,  passing  beneath  the  posterior  belly  of  the  omo-hyoid,  reaches  the  lower  portion 
of  the  levator  anguli  scapulae,  beneath  which  it  terminates  by  dividing  into  ascending 
and  posterior  scapular  branches. 

Branches. — In  addition  to  the  two  terminal  branches,  the  transverse  cervical  gives  off 
branches  to  the  trapezius,  the  supraspinatus,  and  the  levator  anguli  scapulae  muscles. 

(a)  The  ascending  terminal  branch  (ramus  ascendens)  passes  upward  to  supply  the  splenius 
muscles,  and  forms  anastomoses  with  the  superficial  cervical. 

(6)  The  posterior  scapular  artery  (ramus  descendens)  descends  along  the  entire  length  of  the 
vertebral  border  of  the  scapula  beneath  the  rhomboid  muscles.  It  supplies  these  muscles  and 
the  serratus  posticus  superior,  and  sends  branches  laterally  upon  both  the  dorsal  and  ventral 
surfaces  of  the  scapula,  supplying  the  infraspinatus  and  subscapular  muscles  and  anastomosing 
with  the  dorsal  scapular  and  subscapular  arteries 

Anastomoses. — The  anastomoses  which  the  suprascapular  and  transverse  cer- 
vical arteries  make  with  the  branches  of  the  subscapular  artery  from  the  axillary  are 
of  considerable  importance  in  the  establishment  of  the  collateral  circulation  from  the 
arm  after  ligation  of  the  third  portion  of  the  subclavian.  Additional  paths  which 
may  be  employed  for  the  same  purpose  are  afforded  by  the  anastomoses  which 
occur  between  the  thoracic  branches  of  the  axillary  artery  and  the  intercostal 
branches  of  the  superior  intercostal,  and  more  especially  the  perforating  branches  of 
the  internal  mammary. 

Variations. — Very  frequently  indeed  the  anastomosis  which  exists  between  the  ascending 
branch  of  the  transverse  and  the  superficial  cervical  develops  to  such  an  extent  that  it  forms 
the  principal  channel  by  which  the  blood  reaches  the  posterior  scapular  from  the  subclavian, 
and  in  such  cases  the  main  stem  of  the  transverse  cervical  disappears,  the  posterior  scapular 
then  becoming  a  terminal  branch  of  the  superficial  cervical.  This  arrangement  (Fig.  705)  is  of 
such  frequent  occurrence  that  it  is  regarded  as  the  normal  one  by  many  authors.  When  this  is 
done,  the  name,  transverse  cervical,  is  applied  to  the  main  stem  of  the  superficial  cervical,  the 
latter  term  being  retained  for  and  limited  to  the  ascending  branch  of  the  original  artery.  When 
this  arrangement  obtains,  there  is  no  branch  from  the  third  portion  of  the  subclavian  artery. 

THE   AXILLARY  ARTERY. 

The  axillary  artery  (a.  axillaris)  (Figs.  704,  705)  is  the  continuation  of  the 
subclavian  through  the  axillary  space.  It  begins  at  the  lower  border  of  the  first 
rib,  at  the  apex  of  the  axillary  space,  and  passes  downward  along  the  outer 
wall  of  the  space  to  the  lower  border  of  the  teres  major,  where  it  becomes  the 
brachial  artery.  When  the  arm  is  abducted  to  a  position  at  right  angles  to  the 
axis  of  the  trunk,  the  artery  has  an  almost  straight  course,  which  may  be  repre- 
sented by  a  line  drawn  from  the  middle  of  the  clavicle  to  a  point  midway  between 


768 


HUMAN   ANATOMY. 


the  two  condyles  of  the  humerus.  When,  however,  the  arm  hangs  vertically,  the 
vessel  is  slightly  curved,  the  convexity  of  the  curve  looking  upward  and  outward. 

Relations. — For  convenience  in  description  it  is  customary  to  regard  the  axil- 
lary artery  as  consisting  of  three  portions,  the  first  of  which  is  above  the  upper 
border  of  the  pectoralis  minor,  the  second  behind  that  muscle,  and  the  third  tic-low 
its  lower  border. 

The  first  portion  of  the  artery  is  covered  anteriorly  by  the  clavicular  portion 
of  the  pectoralis  major,  by  the  costo-coracoid  membrane  which  separates  it  from  the 
cephalic  vein  and  the  branches  of  the  acromio-thoracic  artery,  and  by  the  subclavius 
muscle.  The  artery  is  enclosed  along  with  its  accompanying  vein  and  the  cords  of 


FIG.  705. 

Superficial  cervical 


Posterior 
Pectoralis  major,  cut  and  everted  Deltoid^  scapular        Trapezius 

DettotcL 


Biceps,  long  head 


Brachial  plexus 

Transverse  cervical 
/      Subcla\  ian  artery 
/      /     Scalenus  anticus 


Anterior  circumflex 

Axillary  artery,  third  |x>rtion 

Biceps,  short  head 

Coraco-brachialis 
Posterior  circumflex 

Dorsal  scapular 
Subscapular 

Teres  major 
Latissimus  dors! 

I-onjj  thoracic 
Serratus  inagnus 


VertrlT.il 

Inferior  thyroid 
_'lhyr"M  ,i\i- 
_  Subclavius  mus. 

ni.-il 
thor.i.  it 
Buperlcc 
thoracic 


_  Alar  thoracic 


Suliscapi 
laris 


\ 


Subclavian  and  axillary  arteries   pectoralis  minor  still  in  place. 

the  brachial  plexus  in  a  downward  prolongation  of  the  cervical  fascia  known  as  the 
a.vil/arv  sheath,  and  rests  behind  upon  the  upper  serration  of  the  serratUS  inagnus  and 
up  >n  the  first  intercostal  space.  The  internal  anterior  thoracic  and  the  posterior 
thoracic  nerves  cross  it  obliquely  behind,  the  latter  nerve  intervening  between  it 
and  tlu-  serratus  niagnus.  Above,  at  the  outer  side,  are  the  ronls  of  the  brachial 
plexus  and  the  external  anterior  thoracic  nerve,  and  below  and  to  the  inner  side  is 
the  axillary  vein,  between  which  and  the  artery  is  the  internal  anterior  thoracic  nerve. 
In  its  second  portion  the  artery  is  covered  anteriorly  by  both  the  pectoralis 
major  and  the  pectoralis  minor.  Posteriorly  it  lies  in  contact  with  the  posterior  cord 
of  the  brachial  plexus,  and  is  separated  by  a  quantity  of  aro.lar  and  fatty  tissue  from 


PRACTICAL  CONSIDERATIONS:    AXILLARY  ARTERY.          769 

the  anterior  surface  of  the  subscapularis  muscle.  External  to  it  is  the  outer  cord  of  the 
brachial  plexus,  and  internally  the  inner  cord,  which  separates  it  from  the  axillary  vein. 
In  its  third  portion  the  artery  is  covered  in  its  upper  half  by  the  lower  part  of 
the  pectoralis  major,  but  in  its  lower  half  only  by  the  integument  and  the  superficial 
and  deep  fascue.  The  inner  head  of  the  median  nerve  passes  obliquely  across  its 
anterior  surface.  Posteriorly  it  is  in  relation  with  the  subscapularis,  latissimus  dorsi, 
and  teres  major,  in  that  order  from  above  downward,  a  considerable  amount  of  areolar 
tissue,  in  which  run  the  circumflex  and  musculo-spiral  nerves,  intervening,  however, 
between  the  artery  and  the  muscles.  To  the  outer  side  are  the  median  and  musculo- 
cutaneous  nerves  and  the  coraco-brachialis  muscle,  while  internally  are  the  internal 
cutaneous  and  ulnar  nerves  and  the  axillary  vein. 

Branches. — Much  variation  occurs  in  the  arrangement  of  the  branches  of  the 
axillary  artery.  It  is  customary  to  recognize  seven  branches,  but  one  or  more  of 
them  is  frequently  absent  as  a  distinct  branch  arising  directly  from  the  artery. 
These  branches  are  arranged  as  follows  :  from  the  first  part  are  given  off  (i)  the 
superior  thoracic  and  (2)  the  acromial  thoracic  ;  from  the  second  part  (3)  the  long 
thoracic  and  (4)  the  alar  thoracic  ;  and  from  the  third  part  (5)  the  subscapular, 
(6)  the  anterior  circumflex,  and  (7)  the  posterior  circumflex. 

Variations. — As  stated  in  the  description  of  the  variations  of  the  subclavian,  the  axillary 
artery  may  be  represented  by  two  parallel  vessels  which  arise  from  the  first  portion  of  the  sub- 
clavian and  are  continued  below  into  the  radial  and  ulnar  arteries.  The  more  frequent  varia- 
tions, however,  concern  the  occurrence  of  additional  branches  from  the  axillary,  and  of  these 
there  may  be  mentioned  the  occurrence  of  the  superior  profunda,  normally  a  branch  of  the 
brachial,  but  not  infrequently  arising  from  the  axillary  "in  common  with  the  subscapular. 

Practical  Considerations. — The  axillary  artery  may  require  to  be  ligated  on 
account  of  wounds,  of  rupture,  of  high  aneurism  of  the  brachial,  or,  rarely,  in  distal 
ligation  for  subclavian  aneurism. 

Wounds  of  the  axillary  are  not  uncommon  when  the  vulnerating  body — a  knife- 
blade,  a  bullet,  etc. — is  directed  from  within  outward,  the  artery  in  all  positions  of 
the  arm  maintaining  a  much  closer  relation  to  the  outer,  or  humeral,  wall  of  the 
axilla  than  to  the  inner,  or  thoracic,  wall,  which  is  therefore  known  as  the  wall  of 
safety.  It  is  always  well  in  such  cases  to  expose  the  artery  and  to  tie  both  ends,  as 
the  exact  source  of  the  bleeding  is  often  necessarily  in  doubt  and  the  free  anastomosis 
of  its  branches  is  likely  to  lead  to  secondary  hemorrhage  from  the  wound  if  the  vessel 
is  tied  in  continuity. 

Rupture  of  the  axillary  artery  has  occurred  in  a  considerable  number  of  cases  as 
an  accident  due  to  the  movements  employed  in  attempted  reduction  of  old  dislocations 
of  the  shoulder.  The  preponderance  of  arterial  as  compared  with  venous  rupture 
(twenty-six  out  of  twenty-eight  cases,  Stimson  ;  or  forty  out  of  forty-four,  Korte) 
is  striking,  the  greater  thinness  of  the  vein  and  its  attachment  to  the  costo-coracoid 
membrane — circumstances  that  would  seem  to  favor  its  rupture — being  more  than 
counterbalanced  by  the  greater  frequency  and  extent  of  atheromatous  degeneration 
and  consequent  loss  of  elasticity  in  the  artery,  and  possibly  by  the  greater  liability 
of  the  latter  to  undergo  tension  during  the  movements  of  abduction,  elevation,  and 
circumduction  (which  are  those  chiefly  associated  with  the  accident  in  question),  and 
— as  the  outermost  or  rather  uppermost  vessel — to  contract  adhesion  to  the  displaced 
humeral  head. 

Aneurism  of  the  axillary  is  comparatively  frequent,  as  might  be  expected  from 
the  number,  variety,  and  range  of  the  movements  of  the  shoulder-joint,  during  which 
the  vessel  is  subjected  to  strains  and  to  a  variety  of  flexures.  It  is  more  common  on 
the  right  side  on  account  of  the  more  general  use  of  the  right  arm,  and  affects  oftenest 
the  third  portion  of  the  vessel,  or  that  least  supported  by  surrounding  structures  and 
most  subjected  to  changes  in  tension  and  position  and  to  certain  injuries,  as  those 
which  occur  during  luxation  of  the  shoulder  or  during  efforts  at  reduction  (vide 
supra}.  On  account  of  the  looseness  of  the  tissue  in  which  it  lies,  such  an  aneurism 
rapidly  attains  a  large  size  and,  by  reason  of  the  minor  traumatisms  inflicted  during 
the  shoulder  movements,  is  especially  prone  to  inflammation. 

49 


770 


HUMAN   ANATOMY. 


The  symptoms  are  (a)  swelling  showing  immediately  below  the  clavicle  (in 
Mohrenheim's  fossa)  and  pushing  that  bone  upward  if  the  first  portion  is  involved, 
or  pushing  the  pectoral  muscles  forward  if  the  aneurism  is  lower,  or  appearing  as  a 
pulsating  tumor  in  the  axilla  if  the  third  portion  is  involved  ;  (b)cedema  of  the  arm 
and  hand  from  pressure  on  the  axillary  vein  ;  (<:)  pain  down  the  arm,  in  the  shoulder 
and  neck,  and  down  the  side  of  the  chest,  and  feebleness  and  limitation  of  shoulder 
and  arm  movements  from,  first,  spasm,  then  paresis  of  the  associated  muscles,  all  due 
to  pressure  on  the  brachial  plexus  and  its  branches. 

Digital  compression  of  the  axillary  artery  is  only  effectively  possible  in  the  lower 
part  of  the  third  portion,  where,  with  the  fingers  beneath  the  anterior  axillary  fold, 

FIG.  706. 


Cut  fibres 
of  pectoral  is 

major    Clavicle    Subclavius    Axillary  artery 

Brachial  plexus 


Pectoralis  minor 


Pectoralis 


First  intercostal  space 


Subclavian  vein     Pecioraiis 
major,  cut 

Second  rib 

Dissection  showing  relations  of  axillary  artery  in  first  part  of  its  course. 

the  vessel,  if  the  effort  is  made  with  due  care  and  gentleness,  may  be  flattened  against 
the  humerus  just  within  the  edge  of  the  coraco-brachialis  and  biceps. 

Ligation  of  the  first  portion  may  be  effected  in  two  ways  :  i.  With  the-  arm 
abducted  to  a  right  angle,  an  incision  three  inches  long,  slightly  convex  downward, 
and  with  its  centre  about  an  inch  below  the  middle  of  the  clavicle,  is  made  through 
the  skin,  superficial  fascia,  and  platysma.  The  cephalic  vein  and  the  descending 
branch  of  the  acromial  thoracic  artery  will  be  seen,  just  beneath  the  fascia,  in  the 
groove  between  the  deltoid  and  greater  pectoral  muscles.  The  outer  clavicular  fibres 
of  the  pectoralis  major  are  then  divided  close  to  the  clavicle  ;  the  interpectoral  and 
axillary  fascia  and  some  loose  connective  tissue  are  broken  up  ;  the  upper  border  of 
the  pectoralis  minor  is  identified  and  traced  to  the  coracoid  process  ;  the  costo-rora- 
roid  membrane  is  cautiously  cut  through  by  a  vertical  incision  close  to  the  coracoid  ; 
the  artery  is  then  sought  for,  lying  between  the  brachial  plexus  of  nerves  externally  and 


AXILLARY   ARTERY:    BRANCHES.  771 

the  vein  internally.  The  internal  anterior  thoracic  nerve  is  sometimes  seen  coming 
out  between  the  vein  and  the  artery.  The  arm  should  be  brought  to  the  side  to 
relieve  tension  on  the  vessels,  especially  the  vein,  which  in  that  position  will  be  least 
prominent.  The  needle  should  be  passed  from  within  and  below  outward  and  upward. 

2.  With  the  arm  abducted,  so  as  to  make  evident  the  fissure  between  the  sternal 
and  clavicular  portions  of  the  pectoralis  major,  an  oblique  incision  is  made  over  this 
space  and  will  usually  begin  about  a  half-inch  from  the  sterno-clavicular  joint.  The 
muscular  interspace  having  been  exposed,  its  sides  are  separated,  not  directly  back- 
ward, but  backward  and  upward  towards  the  clavicle.  The  arm  is  brought  to  the 
side  to  relax  the  pectoral  fibres.  The  pectoralis  minor  and  the  space  between  it  and 
the  clavicle  are  reached^^  and  if  the  latter  is  too  contracted,  the  muscle  may  be  divided 
close  to  the  coracoid  process.  The  artery  is  then  exposed  and  secured  as  in  the 
method  above  given. 

The  second  portion  is  not  formally  ligated,  but  may  have  a  ligature  applied  when- 
ever, as  in  the  last-mentioned  method,  the  lesser  pectoral  has  been  divided. 

Ligation  of  the  third  portion  of  the  subclavian  artery  is,  on  account  of  its  ease 
of  performance,  almost  invariably  preferred  to  any  of  these  operations. 

The  third  portion  of  the  axillary  is  that  almost  always  selected  for  ligation  of 
that  vessel,  for  a  similar  reason. 

The  line  of  the  vessel,  the  arm  being  at  right  angles  to  the  trunk,  is  from  the 
junction  of  the  anterior  and  middle  thirds  of  the  summit  of  the  axilla  to  the  middle  of 
the  bend  of  the  arm  at  the  elbow.  This  line  will  be  found  to  follow  the  inner  margin 
of  the  coraco-brachialis  muscle,  the  prominence  of  which  may  be  seen  just  internal  to 
the  swell  of  the  biceps  where  it  emerges  from  beneath  the  anterior  axillary  fold.  An 
incision  is  made  on  this  line  through  the  skin  and  superficial  and  deep  fasciae,  and  the 
fibres  of  the  coraco-brachialis  margin  are  exposed  and  cleared.  Internally  to  them 
lies  the  vessel,  the  median  and  musculo-cutaneous  nerves  external  to  it,  and  the  inter- 
nal cutaneous  nerve  and  axillary  vein  on  its  inner  side. 

The  needle  should  be  passed  from  within  outward. 

The  collateral  circulation  is  established  after  ligation  of  the  first  portion  above 
the  origin  of  the  acromial  thoracic  precisely  as  after  ligation  of  the  third  portion  of 
the  subclavian  (page  757).  After  ligation  of  the  third  portion  above  the  origin  of 
the  subscapular  the  anastomoses  take  place  between  (a)  the  intercostals,  long  thoracic, 
posterior  scapular,  and  suprascapular,  and  (<£)  the  acromial  thoracic,  on  the  cardiac 
side  of  the  ligature  ;  and  (a)  the  subscapular,  and  (^)  the  posterior  circumflex  on 
the  distal  side. 

When  the  vessel  has  been  tied  between  the  origins  of  the  subscapular  and  the 
two  circumflex  arteries — probably  the  point  of  election  (Taylor) — the  anastomoses 
occur  between  the  branches  of  the  axillary  and  those  of  the  thyroid  axis, — i.e. ,  the 
suprascapular  and  acromial  thoracic  above  and  the  posterior  circumflex  below.  Still 
lower, — i.e.,  below  the  circumflex  arteries — the  collateral  circulation  is  established 
just  as  after  ligation  of  the  brachial  above  the  superior  profunda  (q.v.}. 

1.  The    Superior    Thoracic    Artery. — The  'superior  or  short  thoracic   (a. 
thoracalis  suprema)  (Fig.  704)  arises  just  after  the  axillary  has  emerged  from  beneath 
the  subclavius  muscle,  and  is  directed  downward  and  forward  to  the  first  intercostal 
space,  the  muscles  of  which  it  supplies.      Not  infrequently  it  gives  off  a  branch  which 
supplies  the  muscles  of  the  second  intercostal  space  also.      Its  branches  anastomose 
with  those  of  the  internal  mammary  and  acromial  thoracic,  and  occasionally  its  place 
is  caken  by  a  branch  from  the  latter  vessel. 

2.  The    Acromial   Thoracic   Artery. — The    acromial    thoracic    (a.  thoraco- 
acromialis)  (Fig.  705)  is  a  very  constant  branch  which  arises  from  the  front  of  the 
axillary  artery,  a  short  distance  below  the  superior  thoracic.      It  is  directed  forward 
for  a  short  distance,  but  soon  divides  into  thoracic,  clavicular,  and  acromio-humeral 
branches. 

Branches. — (a)  The  thoracic  branches  (rami  pectorales)  pass  downward  and  forward  to  the 
side  of  the  thorax,  supplying  the  muscles  of  the  second  and  third,  and  sometimes  of  the  fourth 
and  fifth  intercostal  spaces,  and  also  giving  branches  to  the  pectoralis  major  and  the  pectoralis 
minor.  It  anastomoses  with  the  intercostal  arteries  and  the  superior  and  long  thoracics. 


772 


iir.MAN    ANATOMY. 


(t>)  The  clavicular  branch,  which  is  the  smallest  of  the  three,  passes  upward  to  supply  the 
subclavius  muscle,  and  anastomoses  with  the  suprascapular  artery. 

(c)  The  acromio-humeral  branch  passes  upward  and  outward  across  the  costo-coracoid 
membrane  and  over  the  coracoid  process  of  the  scapula,  and  then  divides  into  an  acroinial  and 
a  liuincral branch.  The  former  (ramus  acromialis)  passes  upward  towards  the  acromial  process 
to  supply  the  deltoid  muscle,  while  the  latter  (ramus  dcltoideus)  turns  downward  in  the  groove 
between  the  deltoid  and  the  clavicular  portion  of  the  pectoralis  major,  accompanying  the  cephalic 
vein.  It  sends  branches  to  the  two  adjacent  muscles  and  to  the  integument,  and  anastomoses 
with  the  anterior  circumflex  artery. 

3.  The  Long  Thoracic  Artery. — The  long  thoracic  (a.  thoracica  latcralis j 
(Fig.  704)  is  a  somewhat  inconstant  branch,  whose  place  is  very  frequently  taken  by 
the  thoracic  branch  of  the  acromial  thoracic  or  by  a  branch  from  the  subscapular.  It 
passes  downward  and  forward  upon  the  serratus  magnus,  sending  branches  to  that 
muscle,  the  pectoralis  minor,  and  the  muscles  of  the  third,  fourth,  and  fifth  intercostal 


FIG.  707. 


Transverse  cervical  artery 
Superficial  Cervical  branch 
Posterior  scapular  branch 
Trapeztus,  cut 


Acromion 
Deltoid,  everted 
Triceps 


Rhom- 
boideus 
niajo 


_'ost.  circumflex  art. 
Infraspinatus 
Triceps,  scapular  head 
Teres  minor 
Spine  of  scapula 
Dorsal  scapular  artery 

Subscapularis 
Teres  major 


Latissimus  dorsi 


Arteries  of  posterior  aspect  of  shoulder. 

spaces.      It  also  sends  branches  to  the  mammary  gland  (mini   maniniarii  extern! ), 
whence  it  has  been  termed  the  external  mam  man'  artery.      It  anastomoses  with  t 
thoracic  branch  of  the  acromial  thoracic,  with  the  subscapular  and  the  mtercostals. 
and  with  the  perforating  branches  of  the  internal  mammary. 

4.  The  Alar  Thoracic  Artery.— The  alar  thoracic  (  Fig.  7"4  >  '*  :l  very  " 
slant  small  branch  which  passes  to  the  fascia  and  lymphatic-  glands  of  the  axillary 
space.     Its  place  may  be  taken  by  brandies  from  the  subscapular,  the  long  thoracic, 
or  tin-  thoracic  branch  of  the  acromial  thoracic. 

5.  The    Subscapular    Artery.— Tin-    subscapular    (a.    suhscapulans 
704) 'is  the  largest  branch  of  tin-  axillary  and   arises  just  as  that  artery  crosses 
lower  border  of  the  subscapularis  muscle.      It  passes  downward  and  inward,  accon 
named   by   the  long  subscapular  nerve,   along  the  lower  border  of  tin-  subscapiiiar 
musde  as  far  as  the  lower  angle  of  the  scapula,  and  distributes  branches  through 
out   its  course  to  the  subscapularis  and   tens  major  and  to  the  latissnmis  dorsi. 
also  gives  off — 


THE   BRACHIAL   ARTERY.  773 

(a)  Thoracic  branches   (rami  thoracodorsales) ,  which  supply  the  serratus  magnus  and  the 
muscles  of  some  of  the  intercostal  spaces,  and  not  far  from  its  origin  it  gives  off — 

(b)  The  dorsal  scapular  (a.  circumflex  scapulae).     This  vessel,  of  large  size,  winds  around 
the  axillary  border  of  the  scapula  in  the  triangular  space  bounded  by  the  teres  major,  the  teres 
minor,  and  the  long  head  of  the  triceps,  and  is  distributed  to  the  infraspinatus  and  the  teres 
minor. 

The  subscapular  artery  anastomoses  through  its  thoracic  branches  with  the  intercostals  and 
with  the  long  thoracic,  and  through  the  dorsal  scapular  with  the  suprascapular  and  posterior 
scapular  arteries. 

Variations. — The  subscapular  artery  varies  somewhat  in  its  origin.  Occasionally  it  springs 
from  the  second  portion  of  the  axillary,  and  may  also  arise  from  the  brachial.  Quite  frequently 
it  arises  from  a  trunk  common  to  it  and  one  or  other  or  both  circumflex  arteries,  and  the  supe- 
rior profunda  brachii,  normally  a  branch  of  the  brachial  artery,  may  also  arise  from  this  common 
trunk. 

The  subscapular  has  been  observed  to  give  rise  to  an  aberrant  artery  which  passes  down 
the  arm  and  either  unites  with  the  brachial  or  else  becomes  the  ulnar,  or  may  even  extend  to 
the  neighborhood  of  the  wrist,  where  it  unites  with  a  branch  of  the  anterior  interosseous  artery 
to  form  the  radial. 

6.  The  Anterior  Circumflex  Artery. — The  anterior  circumflex   (a.  circura- 
tlexa  huraeri  anterior)  (Fig.  704)  is  the  smallest  of  the  three  branches  of  the  third 
portion  of  the  axillary,  and  arises  either  directly  from  the  artery  or  from  a  common 
trunk  with  the  posterior  circumflex  ;  more  rarely  it  arises  from  the  subscapular.      It 
passes  outward  beneath  the  coraco-brachialis  and  the  heads  of  the  biceps,  and  winds 
around  the  surgical   neck  of  the  humerus,  lying   close  to  the  bone.      Opposite  the 
bicipital  groove  it  gives  off  a  branch  which  ascends  along  the  groove  to  be  distributed 
to    the   capsule    of   the  shoulder-joint,   and  it    also  sends  branches  to   the    coraco- 
brachialis  and  biceps.      It  terminates  by  anastomosing  with  the  posterior  circumflex 
and  with  the  humeral  branch  of  the  acromial  thoracic. 

7.  The    Posterior    Circumflex    Artery. — The  posterior  circumflex  (a.  cir- 
cumtlexa  humeri  posterior)  (Fig.  704)  arises  from  the  axillary,  almost  opposite  the 
anterior  circumflex,  or  from  a  common  trunk  with  that  vessel  or  with  the  subscap- 
ular.    More  rarely  it  may  arise  from  the  upper  part  of  the  brachial  artery.     It  passes 
backward  and  outward  through  the  quadrilateral  space  bounded  by  the  subscapularis 
above,  the   teres    major  below,    the  long  head    of    the    triceps  internally,    and    the 
humerus  externally,  and  winds  around  the  posterior  surface  of  that  bone  at  the  level 
of  its  surgical  neck.      Passing  under  the  deltoid  muscle  externally,  it  divides  into 
a  number  of  branches,  most  of  which  pass  into  the  muscle  to  supply  it,  while  some 
pass  to  the  shoulder-joint.      It  anastomoses  with  the  acromial  branch  of  the  acromial 
thoracic,  with  the  anterior  circumflex,  and  with  the  superior  profunda  branch  of  the 
brachial. 

THE   BRACHIAL   ARTERY. 

The  brachial  artery  (a,  brachialis)  (Figs.  708,  709)  is  the  continuation  of  the 
axillary  down  the  arm.  It  begins  at  the  lower  border  of  the  teres  major  and  termi- 
nates a  little  below  the  bend  of  the  elbow  by  dividing  into  the  radial  and  ulnar 
arteries.  In  the  upper  part  of  its  course  the  vessel  lies  along  the  inner  side  of  the 
arm,  but  as  it  passes  downward  it  inclines  somewhat  outward,  so  that  in  its  lower 
part  it  is  on  the  anterior  surface  of  the  brachium.  Its  course  may  be  indicated  by  a 
line  drawn  from  the  junction  of  the  outer  and  middle  thirds  of  the  folds  of  the  axilla 
to  a  point  midway  between  the  condyles  of  the  humerus. 

Relations. — Anteriorly  the  brachial  artery  is  covered  throughout  the  greater 
part  of  its  course  by  only  the  deep  and  superficial  fasciae  and  the  integument.  About 
the  middle  of  its  length  it  is  crossed  obliquely,  from  without  inward,  by  the  median 
nerve,  and  at  the  bend  of  the  elbow  it  passes  beneath  the  aponeurotic  slip,  the 
so-called  bicipital  fascia  (lacertus  fibrosus)  from  the  tendon  of  the  biceps,  and  is 
separated  by  it  from  the  median  basilic  vein.  Posteriorly  it  rests  in  succession,  from 
above  downward,  upon  the  long  head  of  the  triceps,  the  inner  head  of  the  triceps, 
the  insertion  of  the  coraco-brachialis,  and  the  brachialis  anticus.  The  musculo-spiral 
nerve  and  the  superior  profunda  artery  pass  downward  and  inward  between  the 
vessel  and  the  long  head  of  the  triceps.  Externally  to  it,  above,  is  the  median  nerve 


774 


HUMAN    ANATOMY. 


and  the  coraco-brachialis  muscle,  and,  lower  down,  the  biceps  and  its  tendon. 
Internally  it  is  in  relation,  above,  with  the  ulnar,  internal  cutaneous,  and  lesser 
internal  cutaneous  nerves,  and,  in  its  lower  third,  with  the  median  nerve.  The  basilic 
vein  is  somewhat  superficial  to  it  and  to  its  inner  side. 

Two  venae  comites  accompany  the  artery,  lying  respectively  upon  its  inner  and 
outer  sides,  and  cross  branches  pass  between  the  two.  It  is  also  accompanied  by  two 
lymphatic  vessels  which  have  in  their  course  three  or  four  lymphatic  nodes,  usually 
of  small  size. 

Branches. — The  brachial  artery  gives  off  muscular  branches  to  the  biceps, 
coraco-brachialis,  brachialis  anticus,  triceps,  and  pronator  radii  teres,  and  a  small 

FIG.  708. 


Deltoid 


Cephalic  vein 
Humeral  branch  of  acromial  thoracic  artery 


Pectoralis  majo: 


Axillary  vein 
Muscular  vein 

Outer  head'of  median  nerve 
Inner  head  of  median  nerve 
Axillary  artery 
Musculo-cutaneous  ne 


Brachial  artery 

Superior  profunda  artery 

Median  nerve 


I.atissiimis  dorsi 
tendon 


Teres  major 


Inferior  profunda  artery 
Internal  intermuscular  septum 

Anastomotic  artery 


Biceps  tendon 
Ant.  cutaneous 
hr.of  musculo- 
cutaneous  nrv. 
Bicipital  fascia 


•Musculo-spiral  nerve 
Inner  head  of  triceps 


Inner  condyle 
ilecranon 


Brachial  artery  in  relation  to  nerves  of  arm. 


nutrient  artery  for  the  humerus  (a.  nutriciac  humeri)  arises  either  directly  from  the 
brachial  or  from  one  of  its  muscular  branches  or  from  the  inferior  profunda.  It 
enters  the  nutrient  foramen  upon  the  inner  surface  of  the  shaft  of  the  humerus.  In 
addition,  there  arise  from  the  brachial  (i)  the  superior  profunda,  (2)  the  inferior 
Profunda,  and  (3)  the  anastomotica  magna. 

Variations. — Tin-  variations  which  the  hrachial  artery  presents  are  both  numerous  and 
important,  in  that  they  affect  materially  the  origin  of  the'  two  terminal  branches,  the  radial 
and  ulnar. 

In  cases  in  which  there  is  a  well-developed  supracondyloid  process  on  the  humerus  i  page 
268),  the  hrarhial  artery  accompanies  the  median  nerve  behind  it,  and  only  jtassrs  upon  the  an- 
terior surface  of  the  arm  after  it  lias  passed  it.  In  such  cases  there  generally  arises  from  the 
upper  part  of  the  brachial,  or  even  from  the  axillary,  a  vessel  which  descends  upon  the  anterior 
surface  of  the  arm,  lying  superficially  and  sending  branches  to  the  biceps  and  brachialis  anticus 


THE  BRACHIAL  ARTERY:  BRANCHES. 


775 


muscles.  This  has  been  variously  termed  the  vas  aberrans,  the  a.  brachialis  superficialis,  or  the 
a.  radia/is  super jicialis,  and  it  appears  to  be  normally  present,  but  much  reduced  in  size  and 
included  among  the  muscular  branches. 

The  majority  of  the  modifications  of  the  brachial  artery  are  due  to  an  extraordinary  devel- 
opment of  the  superficial  brachial.  Thus  it  may  enlarge  and  become  continuous  below  with 
the  radial  artery,  giving  rise  to  a  condition  usually  termed  a  "  high"  origin  of  the  radial  ;  more 

FIG.  709. 


Humeral  branch  of  acromial  thoracic  artery  • 
Pectoralis  minor,  stump. 

Biceps  and  coraco-brachialis,  stump 

Axillary  artery 

Anterior  circumflex  artery 
Tendon  of  long  head  of  biceps 

Insertion  of  pectoralis  major 
Deltoid 


Coraco-brachialis 


Brachialis  anticus 


Tendon  of  biceps 


[dorsi 

Teres  major  and  latissimus 
lUperior  profunda  artery 

Brachial  artery 


Triceps 


Inferior  profunda  artery 


Anastomotic  artery 


Inner  condyle 
—  Olecranon 

Origin  of  superficial  flexors 
Anterior  ulnar  recurrent  artery 
Posterior  ulnar  recurrent  artery 


Jlnar  artery 


Radial  artery 


Brachial  artery  and  its  branches. 


rarely  it  may  unite  with  the  ulnar  artery,  producing  a  "  high"  origin  for  that  vessel ;  occasion- 
ally it  gives  rise  to  both  the  radial  and  ulnar,  the  true  brachial  being  continuous  below  with  the 
common  interosseous  ;  or,  finally,  it  may  unite  with  the  lower  part  of  the  brachial  artery  proper, 
the  portion  of  the  latter  between  the  origin  and  anastomosis  of  the  superficial  brachial  disap- 
pearing, so  that  what  is  termed  a  brachial  artery  is  formed,  which  passes  behind  instead  of  in 
front  of  the  median  nerve. 


776  HUMAN    ANATOMY. 

Comparative  anatomy  and  embryology  both  indicate  that  the  occurrence  of  a  well-devel- 
oped superficial  brachial,  continuous  below  with  the  radial,  is  the  primary  condition,  and  that 
the  origin  of  the  radial  as  a  terminal  branch  of  the  brachial  proper  is  a  secondary  condition, 
due  to  an  anastomosis  between  the  lower  part  of  the  original  superficial  stem  and  the  brachial 
and  to  the  subsequent  diminution  or  partial  obliteration  of  the  former  above  this  anastomosis 
(Fig.  748  E  ). 

Another  branch,  normally  present  but  usually  insignificant,  which  may  reach  an  extraor- 
dinary development,  is  the  a.  plica:  cubiti  superficialis.  It  arises  from  the  lower  portion  of  the 
brachial  and,  passing  inward  and  downward  beneath  the  tendon  of  the  biceps,  is  distributed  to 
the  flexor  carpi  radialis  and  the  palmaris  longus.  When  abnormally  developed,  it  forms  what 
has  been  termed  the  accessory  ulnar  artery,  and  passes  down  the  forearm,  immediately  beneath 
the  deep  fascia  and  between  the  two  muscles  just  mentioned,  and  terminates  by  anasto- 
mosing with  the  ulnar,  or  in  some  cases  replaces  it  and  enters  into  the  formation  of  the  palmar 
arches. 

Supernumerary  branches  accessory  to  the  branches  usually  present  may  also  occur,  and, 
in  addition,  the  brachial  may  give  rise,  in  its  upper  part,  to  the  subscapular  and  the  posterior 
circumflex,  normally  branches  of  the  axillary  ;  in  its  lower  part,  to  the  radial  recurrent;  and,  at 
its  bifurcation,  to  the  interosseous  artery  or  to  the  median,  which  is  usually  a  branch  of  the 
interosseous. 

Practical  Considerations. — Spontaneous  aneurism  of  the  brachial  artery  is 
rare,  and  is  usually  associated  with  marked  arterio-sclerosis  or  with  cardiac  disease. 
Wounds  and  traumatic  aneurism  are  common,  though  lessened  in  frequency  by  the 
protected  position  of  the  upper  two-thirds  of  the  artery  on  the  inner  side  of  the  arm. 
Aneurism  has,  however,  followed  a  stab-wound  from  the  outer  side,  which,  after 
passing  through  the  biceps,  involved  the  vessel.  Arterio-venous  aneurism  just 
above  the  bend  of  the  elbow  was  formerly  often  met  with  as  a  result  of  the  accidental 
wounding  of  the  artery  during  phlebotomy  of  the  median '  basilic  vein,  parallel  with 
the  vessel  at  that  point  and  separated  from  it  only  by  the  lacertus  fibrosus. 

The  line  of  the  artery  is  from  the  junction  of  the  anterior  and  middle  thirds  of 
the  axilla  to  the  middle  of  the  bend  of  the  elbow  when  the  arm  is  abducted  and  the 
forearm  extended  and  supinated. 

The  artery  in  the  upper  two-thirds  of  its  course  may  be  compressed  against  the 
inner  side  of  the  humerus  by  pressure  directed  outward  and  a  very  little  backward 
along  the  internal  border  of  the  coraco-brachialis  and  biceps.  This  muscular  border 
may  be  visible,  or  may  be  recognized  by  picking  it  up  between  the  thumb  and  finger. 
The  artery  may  be  overlapped  by  this  inner  edge  of  the  biceps,  especially  in  mus- 
cular subjects.  At  the  middle  of  the  arm,  over  the  insertion  of  the  coraco-brachialis 
into  the  flat  surface  above  the  beginning  of  the  internal  supracondyloid  ridge,  it  may 
most  easily  be  subjected  to  compression.  In  the  lower  third  the  pressure  must  be 
directed  backward,  as  the  humerus — separated  from  it  by  the  brachialis  anticus 
muscle — then  lies  behind  it. 

Ligation  of  the  vessel  at  its  upper  third  is  effected  through  an  incision  made 
along  the  inner  border  of  the  muscular  ridge  of  the  coraco-brachialis  muscle,  the 
fibres  of  which  may  with  advantage  be  exposed  and  identified.  Nothing  lies  between 
the  artery  and  the  muscle  except  the  median  nerve.  The  basilic  vein  is  to  the  inner 
side  of  the  vessel  and  may,  before  the  incision  is  made,  be  identified  and  avoided  by 
compression  of  the  axillary  vein  above.  The  ulnar  nerve  also  lies  to  the  inner  side. 
The  needle  may  be  passed  in  either  direction. 

In  ligation  at  the  middle  of  the  arm,  the  limb  should  be  abducted  with  the  elbow 
slightly  flexed,  and  should  be  supported  by  an  assistant.  If  the  arm  is  allowed  to 
rest  upon  a  flat  surface,  the  triceps  is  pushed  upward  and  may  be  mistaken  for 
the  biceps,  and  the  dissection  may  bring  into  view  the  inferior  profunda  artery 
and  the  ulnar  nerve  instead  of  the  brachial  and  the  median  (Heath  |.  It  is  well 
to  see  and  identify  the  innermost  fibres  of  the  biceps.  After  they  are  displaci-d 
outward,  the  median  nerve  (beginning  to  bear  to  the  inner  side)  should  be  separated 
from  the  vessel,  the  sheath  opened,  the  venae  comites  (the  inner  of  which  is  usually 
the  larger)  drawn  aside,  and  the  needle  passed  from  the  nerve.  jucobson  calls 
attention  to  the  fact  that  this  usually  easy  ligation  may  be  difficult  when  the  artery 
is  concealed  by  the  median  nerve  at  the  point  at  which  it  is  sought,  and  when  its 
calibre  is  small  and  its  beat  feeble  as  the  result  of  hemorrhage.  The  median  nerve 
(from  transmitted  pulsation),  the  inferior  profunda  artery,  ami  even  the  basilic  vein 
have  been  mistaken  for  the  brachial. 


THE    BRACHIAL   ARTERY:    BRANCHES.  777 

In  ligation  at  the  lower  third — above  the  bend  of  the  elbow — the  inner  edge 
of  the  biceps  tendon  should  be  distinctly  recognized,  and  the  position  of  the 
superficial  veins,  especially  the  median  basilic,  should  be  made  apparent  by  com- 
pression above. 

The  incision  should  lie  just  within  the  edge  of  the  tendon  and  should  be  parallel 
with  it,  running  therefore  obliquely  from  within  outward.  It  will  usually  be  just 
outside  of  the  median  basilic  vein.  Its  centre  is  about  on  a  level  with  the  transverse 
fold  of  the  bend  of  the  elbow.  The  fibres  of  the  bicipital  fascia  are  divided  in  the 
line  of  the  skin  incision, — i.e.,  diagonally,  as  they  run  downward  and  inward.  The 
needle  may  be  passed  from  within  outward  so  as  to  avoid  the  median  nerve,  which, 
however,  is  here  some  distance  to  the  inner  side.  In  all  ligations  of  the  brachial,  its 
frequent  variations  (vide  supra}  should  be  remembered,  and  the  possibility  of  the 
presence  of  a  "  vas  aberrans' '  or  an  "  accessory  ulnar' '  should  be  borne  in  mind,  as 
should  the  occasional  occurrence  of  a  muscular  slip  crossing  the  vessel  and  derived 
from  the  pectoralis  major  or  from  one  of  the  humeral  muscles. 

The  collateral  circulation  is  carried  on  after  ligation  above  the  superior  profunda 
between  the  ascending  or  recurrent  branches  of  that  vessel  and  the  circumflex  (espe- 
cially the  posterior)  and  subscapular  arteries.  After  ligation  below  the  origin  of  the 
inferior  profunda,  the  circulation  is  carried  on  through  the  anastomosis  between  the 
branches  of  the  profunda  from  above  and  those  of  the  anastomotic  and  the  recurrents 
from  the  radial,  ulnar,  and  posterior  interosseous  from  below.  After  ligation  below 
the  anastomotic,  the  branches  of  that  vessel,  as  well  as  those  of  the  profundae,  carry 
the  blood  to  the  recurrents. 

1.  The   Superior  Profunda  Artery. — The  superior  profunda   (a.   profunda 
brachii)  (Fig.  709)  arises  from  the  upper  part  of  the  brachial,  on  its  posterior  surface, 
and  is  directed  downward  and  outward,  between  the  inner  and  long  heads  of  the 
triceps,  to  reach  the  posterior  surface  of  the  humerus.     Accompanied  by  the  musculo- 
spiral  nerve,  it  curves  around  to  the  outer  surface  of  the  bone,  lying  in  the  musculo- 
spiral  groove,  and  having  arrived  at  the  external  supracondylar  ridge,  it  pierces  the 
external  intermuscular  septum  and  continues  downward  between  the  brachialis  anticus 
and  the  supinator  longus,   to   terminate  by  anastomosing  in   front  of   the  external 
condyle  with  the  radial  recurrent  artery. 

Branches. — In  its  course  the  superior  profunda  gives  off  a  number  of  branches,  among 
which  may  be  mentioned  : 

(a)  A  deltoid  branch   (ratnus  deltoideus),  which  passes  transversely  outward  to  the  inser- 
tion of  the  deltoid,  and  then  bends  upward  in  the  substance  of  that  muscle. 

(b)  Muscular  branches  to  the  triceps. 

(c)  A  median  collateral  branch  (a,  collateralis  media),  which  passes  downward  in  the  sub- 
stance of  the  inner  head  of  the  triceps  to  the  olecranon  process,  where  it  anastomoses  with  the 
posterior  ulnar  recurrent,  the  posterior  interosseous  recurrent,  and  the  anastomotica  magna. 

(d)  An  articular  branch,  which  is  given  off  from  the  lower  portion  of  the  artery,  just  before 
it  pierces  the  external  intermuscular  septum,  and  is  distributed  to  the  elbow-joint. 

(<?)  Cutaneous  branches,  which  accompany  the  external  cutaneous  branches  of  the  mus- 
culo-spiral  nerve. 

Variations. — The  superior  profunda  occasionally  arises  from  the  axillary  artery  either 
directly  or  in  common  with  the  posterior  circumflex.  That  portion  of  its  main  stem  which 
traverses  the  musculo-spiral  groove  beyond  the  point  where  the  medial  collateral  branch  is  given 
off  is  sometimes  termed  the  radial  collateral,  the  profunda  being  regarded  as  dividing,  after 
a  short  course,  into  the  two  collateral  branches.  The  deltoid  artery  not  infrequently  arises 
directly  from  the  brachial  artery  or  else  from  the  inferior  profunda. 

2.  The    Inferior    Profunda  Artery. — The   inferior   profunda  (a.  collateralis 
ulnar  is  superior)  (  Fig.  709)  arises  from  the  inner  surface  of  the  brachial,  at  about  the 
middle  of  its  course.      It  passes  downward  and  backward,  accompanying  the  ulnar 
nerve,   through  the  internal  intermuscular  septum,   and   then  downward  along  the 
anterior  surface  of  the  inner  head  of  the  triceps  to  the  back  of  the  internal  condyle, 
where  it  terminates  by  anastomosing  with  the  anastomotica  magna  and  the  posterior 
ulnar  recurrent.      It  gives  branches  to  the  triceps  and  to  the  brachialis  anticus. 


778  HUMAN   ANATOMY. 

3.  The  Anastomotica  Magna. — The  anastomotica  magna  (a.  collateralis 
ulnaris  inferior)  (Fig.  709)  arises  from  the  inner  surface  of  the  brachial  artery,  about 
4  cm.  (1^6  in.)  above  its  termination.  It  passes  inward  over  the  brachialis  anticus 
and  beneath  the  median  nerve,  and,  piercing  the  internal  intermuscular  septum,  winds 
around  the  inner  border  of  the  humerus  and  passes  transversely  across  its  posterior 
surface,  just  above  .the  olecranal  fossa.  It  anastomoses  with  the  posterior  ulnar  recur- 
rent and  with  both  the  superior  and  inferior  profunda  arteries,  and  also,  by  means  »i  ;t 
branch  given  off  before  it  pierces  the  intermuscular  septum,  with  the  anterior  ulnar 
recurrent. 

Anastomoses  around  the  Elbow. — The  brachial  artery  forms  rich  anasto- 
moses around  the  elbow-joint  with  both  the  radial  and  ulnar  arteries  by  means  of  its 
superior  and  inferior  profunda  branches  and  the  anastomotica  magna,  abundant 
opportunity  being  thus  afforded  for  a  collateral  circulation  to  the  forearm  after  ligation 
of  the  brachial.  Thus,  the  superior  profunda  anastomoses  in  front  of  the  external 
condyle  of  the  humerus  with  the  radial  recurrent,  and  its  medial  collateral  branch 
anastomoses  in  the  neighborhood  of  the  olecranon  process  with  the  posterior  inter- 
osseous  and  the  posterior  ulnar  recurrents.  The  inferior  profunda  also  anastomoses 
with  the  posterior  ulnar  recurrent  behind  the  internal  condyle,  while  the  anastomotica 
magna  makes  connections  in  front  of  the  internal  condyle  with  the  anterior  ulnar 
recurrent;  and  posteriorly,  with  the  posterior  ulnar  and  the  posterior  interosseous 
recurrents. 

THE  ULNAR   ARTERY. 

The  ulnar  artery  (a.  ulnaris)  (  Figs.  710,  712)  is  the  larger  of  the  two  terminal 
branches  of  the  brachial.  It  arises  just  below  the  bend  of  the  elbow  and  passes  at 
first  distally  and  inward,  in  a  gentle  curve,  beneath  the  muscles  which  arise  from  the 
internal  condyle  of  the  humerus,  and  at  the  junction  of  the  upper  and  middle  thirds 
of  the  forearm  assumes  a  more  vertical  direction.  Arrived  at  the  wrist,  it  passes  over 
the  anterior  annular  ligament  to  the  radial  side  of  the  pisiform  bone  and  then  passes 
across  the  palmar  surface  of  the  hand,  forming  the  superficial  palmar  arch  (arcus 
volaris  superficialis),  whose  convexity  looks  distally,  and  terminates  opposite  the 
second  intermetacarpal  space  by  anastomosing  with  the  superficial  volar  branch  of 
the  radial. 

For  convenience  in  description,  the  ulnar  artery  may  be  regarded  as  consisting 
of  three  parts  :  ( i )  an  antibrachial portion  extending  from  the  origin  of  the  vessel  to 
the  upper  border  of  the  anterior  annular  ligament,  (2)  a  carpal  portion  resting  upon 
the  annular  ligament,  and  (3)  a  palmar  portion  in  the  hand.  The  course  of  the 
lower  two-thirds  of  the  antibrachial  portion  may  be  represented  by  a  line  drawn  from 
the  front  of  the  internal  condyle  of  the  humerus  to  a  point  immediately  to  the  radial 
side  of  the  pisiform  bone,  while  the  course  of  the  upper  third  may  be  indicated  by  a 
line  drawn  from  the  middle  of  the  bend  of  the  elbow  to  meet  the  first  line  at  the 
junction  of  its  upper  and  middle  thirds.  The  superficial  palmar  arch  is  on  a  U-vi ' 
with  the  thumb  when  the  digit  is  abducted  to  a  position  at  right  angles  to  the  axis 
of  the  hand. 

Relations. — The  antibrachial  portion  of  the  ulnar  in  its  upper  third  is  cov- 
ered by  the  pronator  radii  teres,  the  flexor  carpi  radialis,  the  palmans  longus,  and  the 
flexor  sublimis  digitorum,  and  is  crossed  obliquely  by  the  median  nerve.  Behind,  it 
rests  upon  the  tendons  of  the  brachialis  anticus  and  upon  the  flexor  profundus  di.ui 
torum.  In  its  lower  two-thirds  it  is  overlapped  above  by  the  flexor  carpi  ulnaris,  I  nit 
below  it  lies  entirely  to  the  radial  side  of  the  tendon  of  that  muscle,  and  is  covered 
only  by  the  skin  and  fasciae.  It  rests  upon  the  flexor  profundus  digitorum,  and  to  its 
radial  side  is  the  tendon  of  the  flexor  sublimis  digitorum,  while  to  its  ulnar  side  it  is  in 
close  relation  with  the  ulnar  nerve,  as  well  as  with  the  tendon  of  the  flexor  carpi  ulnaris. 

In  its  carpal  portion  it  rests  upon  the  anterior  surface  of  the  anterior  annular 
ligament,  immediately  to  the  radial  side  of  the  pisiform  bone,  and  is  covered  In  an 
expansion  from  the  tendon  of  the  flexor  carpi  ulnaris. 

The  palmar  portion,  in  the  upper  part  of  its  course,  is  covered  by  the  palmaris 
brevis  and  rests  upon  the  flexor  brevis  minimi  digiti.  The  superficial  palmar  arch, 
as  it  passes  radialwards,  is  crossed  successively  by  the  palmar  branch  of  the  ulnar 


THE   ULNAR   ARTERY. 


779 


nerve,  the  palmar  fascia,  and  the  palmar  branch  of  the  median  nerve.  It  rests  upon 
the  digital  branches  of  the  ulnar  nerve,  the  long  flexor  tendons,  and  the  digital 
branches  of  the  median  nerve. 

Branches. — From  its  antibrachial  portion  the  ulnar  artery  gives  rise  to 
numerous  muscular  branches  supplying  the  muscles  of  the  forearm,  and,  in  addition, 
to  ( i )  the  anterior  idnar 

recurrent,    (2)  the  POS-  FlG-  7io. 

terior  ulnar  recurrent, 
(3)  the  common  interos- 
seous, (4)  a  nutrient 
branch,  (5)  the  poster- 
ior ulnar  carpal,  and 
(6)  the  anterior  ulnar 
carpal. 

From  the  carpal 
portion  arise  no 
branches  of  considera- 
ble size. 

From  the  palmar 
portion  arise  (7)  the 
superior  and  (8)  the  in- 
ferior deep  palmar 
branches  and  (9)  the 
digital  branches,  and,  in 
addition,  muscular 

branches     to     Superficial     Brachialis  anticus 

muscles  of  the  palm  and 
cutaneous  branches. 


Superficial 
branch  of 

sup.  profunda 

Musculo- 

spiral  nerve 


Radial  recurrent 
artery 


Brachio-radialis 


Pronator 
radii  teres 


Va  r  i  a  t  i  o  n  s . — From 
the  developmental  stand- 
point the  ulnar  artery  (page 
848),  although  earlier  in  its 
appearance  than  the  radial, 
is,  nevertheless,  preceded 
as  the  principal  artery  of 
the  forearm  by  two  others. 
In  the  most  primitive  con- 
dition the  brachial  is  con- 
tinued down  the  forearm, 
resting  upon  the  interos- 
seous membrane  and  giving 
rise  at  the  base  of  the  hand 
to  a  leash  of  digital 
branches.  Later  there  de- 
velops from  the  brachial  a 
second  artery,  which  passes  Anterior 


Radial  nerve 

Radial  artery 
Flexor 

longus  pollicis 


Inferior  profunda  artery 

Origin  of  superficial  flexors 
Median  nerve 
Brachial  artery 
Tendon  of  biceps 

Brachialis  anticus 
Origin  of  superficial  flexors 
Ant.  ulnar  recurrent  artery 
Post,  ulnar  recurrent  artery 

Common  interosseous  artery 
Ulnar  nerve 

Median  nerve 


carpal  artery. 

Flexor  carpi 
radialis 

Superficial 
volar  artery 


Ulnar  artery 

Flexor  profundus  digitorum 


Flexor  sublitnis  digitorum 


Palmaris  longus  tendon 
Anterior  carpal  artery 
Posterior  carpal  artery 

Flexor  carpi  ulnaris 


Pisiform  bone 


distally  in  a  plane  superfi- 
cial to  the  original  vessel, 
accompanying  the  median 
nerve  through  the  interval 
between  the  flexor  sublimis 
digitorum  and  the  flexor 
profundus  digitorum.  This 
median  artery,  near  the 
wrist  anastomoses  with  the 
original  one,  and  the  latter 
then  begins  to  diminish  in 
size  and  separates  from  the 
median  above  the  point  of  its  anastomosis,  forming  the  anterior  interosseous  artery.  In  this 
condition  it  is  the  median  artery  which  gives  origin  to  the  digital  branches.  Finally,  the  ulnar 
arises  as  another  distinct  branch  from  the  brachial  and  gradually  supplants  the  median,  which 
now  appears  as  a  branch  of  the  interosseous  known  as  the  a.  comes  nervi  mediani. 

As  is  frequently  the  case  where  the  development  passes  through  a  series  of  well-marked 
stages,  its  arrest  may  occur  at  any  one  of  these,  and  consequently  an  anomaly  may  occur  in 
which  the  ulnar  artery  is  represented  only  by  some  muscular  branches,  its  place  being  taken  by 


Radial  and  ulnar  arteries  :  superficial  dissection. 


7  So 


HUMAN   ANATOMY. 


a  persistent  median  or  interosseous  artery,— a  condition  of  which  indications  are  to  be  seen  in 
the  participation  of  the  interosseous  or  median  artery  in  the  formation  of  the  superficial  palmar 
arch  (page  7X5).  An  interesting  condition  in  which  indications  are  clearly  retained  of  all  the 
Stages  which  the  forearm  arteries  pass  through  in  their  evolution  is  shown  in  Fig.  711.  An 
artery  which  is  the  superficial  brachial,  and  which  arose  from  the  axillary,  descends  the  arm 
parallel  to  the  brachial  proper  and  terminates  by  becomiitg  the  radial.  A  distinct  ulnar  has 
developed  and  the  anterior  interosseous  has  acquired  its  typical  arrangement,  but  there  is  a 
well-developed  median  artery  which  sends  a  strong  branch  across  to  the  radial  and  termi- 
nates by  anastomosing  with  the  superficial  palmar  branch  of  the  ulnar  to  form  the  superficial 
palmar  arch. 

Another  variation  may  occur  in  the  form  of  a  "high  origin"  of  the  ulnar  artery,  a  condi- 
tion which  results  from  the  anastomosis  of  the  superficial  brachial  artery  (page  774)  with  the 
ulnar.  In  such  cases  the  ulnar  frequently  passes  down  the  forearm  in  a  much  more  superficial 

position  than  usual,  passing  over,  instead  of  under, 

FIG.  711.  the   muscles    arising    from   the    internal    condyle. 

Such  a  superficial  course  may  also  be  followed  when 

fc/'/;i''&     'Ml  ^e  artery  nas  a  norni«il    origin,  and   occasionally 

IJi  f  jj/      -toi  it  passes  to  the  ulnar  border  of  the  forearm   be- 

tween the  palmaris  longus  and  the  flexor  sublimis 
digitorum. 


Brachial 


Ulnar 


Median 


Superficial 
palmar 
arch 


Anterior 
interosseous 


Variation  of  artorics  of  left  arm,  showing 
retention  of  developmental  conditions. 


the 


Practical  Considerations. — The  ul- 
nar artery  may  be  ligated  for  wound  or  for 
aneurism — of  which  it  is  rarely  the  subject — 
either  ( i )  about  the  middle  of  the  forearm  or 
(2)  just  above  the  wrist. 

i.  With  the  forearm  supinated,  an  in- 
cision on  the  line  indicated  (vide  supra) 
through  the  skin  and  the  thin  deep  fascia 
should  expose  either  a  white  line — the  ten- 
dinous edge  of  the  flexor  carpi  ulnaris — which 
is  not  always  present  (Treves),  or  a  yellow 
(fatty)  interspace  (Farabeuf)  between  that 
muscle  and  the  flexor  sublimis  digitorum.  It 
is  best  marked  at  the  lower  part  of  the  wound. 
If  more  than  one  white  line  should  be  present. 
the  one  sought  for  would  be  nearer  the  ulnar 
margin  of  the  limb.  At  the  bottom  of  the 
interspace  thus  identified,  which  runs  oblique- 
ly inward  towards  the  ulna,  the  artery  will  be 
found  lying  on  the  flexor  profundus  digitorum, 
with  the  ulnar  nerve  to  its  inner  side.  It 
is  often  overlapped  by  the  inner  deep  edge 
of  the  flexor  sublimis,  so  that  that  muscle 
must  be  lifted  up  and  drawn  outward  before 
the  vessel  can  be  fully  exposed.  In  sepa- 
rating the  muscles  care  must  be  taken  not  to 
go  beyond  the  vessel  and  nerve — pushing 
them  to  the  radial  side — and  open  up  the  in- 
terspace between  the  flexor  carpi  ulnaris  and 
the  flexor  profundus.  The  space  between 
the  flexor  sublimis  and  the  palmaris  longus 
proper  space,  but  is  much  more  shallow  and  even 


Deep 

palmar 
arch 


lies  to  the  outer  side  of 
less  well  marked. 

2.  Forcibly  extend  the  hand  so  as  to  bring  into  prominence  the  fleshy  swell  of 
the  flexor  sublimis  muscle  and  tendons,  just  to  the  ulnar  side  of  the  palmaris  longus 
page  620).  The  incision,  beginning  about  one  inch  above  the  flexure  of  the  wrist, 
should  be  made  in  the  groove  to  the  inner  side  of  this  prominence,  and  is  immedi- 
ately in  line  with  the  pisiform  bone.  After  the  deep  fascia  is  divided  the  tendon  of 
the  flexor  carpi  ulnaris  is  seen  and,  after  it  is  relaxed  by  flexion  of  the  wrist,  is  drawn 
a  little  inward,  when  the  artery  will  be  found  still  lying  upon  the  flexor  profundus 
and  bound  to  it  by  a  definite  layer  of  fascia,  which  must  be  carefully  divided 
(Treves).  The  ulnar  nerve  lies  in  close  proximity  to  the  vessel  on  the  ulnar  side. 


THE   ULNAR   ARTERY.  781 

The  ven£e  comites  of  the  ulnar  are  closely  attached  to  it,  but  may  be  included  in 
the  ligature  without  danger,  as  the  other  venous  channels  of  the  forearm  are  amply 
sufficient  to  carry  on  the  circulation. 

The  collateral  circulation  is  maintained  by  means  of  the  free  anastomosis  between 
the  branches  of  the  radial  and  ulnar,  those  of  the  interosseous  vessels,  and  those  of 
the  carpal  and  palmar  arches. 

1.  The  Anterior  Ulnar  Recurrent  Artery. — The  anterior  ulnar  recurrent 
(a.  recurrens  ulnaris  anterior)    (Fig.    712)  arises  from  the  upper  part  of  the  ulnar 
artery,   frequently  in  common  with  the  posterior  recurrent.      It  is  usually  a  rather 
slender  branch,  and  is  directed  upward  in  the  groove  between  the  brachialis  anticus 
and  the  pronator  radii  teres  towards  the  internal  condyle,  over  which  it  terminates 
in  branches  which  anastomose  with  the  inferior  profunda  and  anastomotica  magna  of 
the  brachial.      It  gives  off  branches  to  the  neighboring  muscles  and  a  branch  to  the 
anterior  inner  portion  of  the  capsular  ligament  of  the  elbow-joint. 

2.  The  Posterior  Ulnar  Recurrent  Artery. — The  posterior  ulnar  recurrent 
(a.  recurrens  ulnaris  posterior)  (Fig.  712)  arises  either  immediately  below  the  anterior 
recurrent  or  by  a  common  trunk  with  it.      It  is  usually  considerably  larger  than  the 
anterior  recurrent,  and  passes  at  first  almost  horizontally  inward  and  backward  be- 
tween the  flexor  sublimis  and  the  flexor  profundus  digitorum,  and  then  bends  upward 
along  the  side  of  the  ulnar  nerve  between  the  two  heads  of  the  flexor  carpi  ulnaris.      It 
terminates  upon    the  posterior  surface  of   the  internal    condyle  of    the  humerus  in 
branches  which  anastomose  with  the  posterior  branch  of  the  inferior  profunda  and 
with  the  anastomotica  magna  of  the  brachial. 

It  gives  branches  to  the  adjacent  muscles,  to  the  skin,  and  to  the  posterior  in- 
ternal portion  of  the  capsule  of  the  elbow-joint. 

3.  The    Common    Interosseous   Artery. — The   common    interosseous    (a. 
interossea  coramunis)  (Fig.  710)  arises  from  the  outer  and  back  part  of  the  ulnar 
artery,   a  short  distance  below  the  posterior  ulnar  recurrent.      It  is  a  short,   stout 
trunk  which  passes  downward  and  outward  and,  having  reached  the  upper  border 
of   the   interosseous    ligament,   divides  into  the  anterior  and  posterior  interosseous 
arteries. 

Variations. — In  cases  in  which  a  superficial  brachial  artery  (page  774)  exists,  the  true 
brachial  may  be  directly  continuous  below  with  the  common  interosseous,  the  radial  and  ulnar 
arteries  arising  by  the  bifurcation  of  the  superficial  brachial.  Such  cases  form  what  are  usually 
termed  "  high"  origins  of  the  common  interosseous  ;  and,  since  the  superficial  brachial  may  arise 
from  the  axillary,  owing  to  the  anastomosis  with  it  of  the  aberrant  branch  of  that  artery,  the 
common  interosseous  may  also  appear  to  arise  from  the  axillary. 

In  cases  of  high  origin  of  the  radial  the  common  interosseous  may  arise  from  that  vessel 
and  give  origin  to  the  recurrent  ulnar  branches,  and  it  may  also  give  rise  to  these  branches  when 
it  lias  a  normal  origin.  When  it  has  a  high  origin,  it  may  give  off  both  the  radial  and  ulnar 
recurrent  branches. 

a.  The  Anterior  Interosseous  Artery. — The  anterior  interosseous  (a.  inter- 
ossea volaris)  (Fig.  712)  descends  from  the  point  of  bifurcation  of  the  common  inter- 
osseous artery,  along  the  anterior  surface  of  the  interosseous  membrane,  between  the 
adjacent  edges  of  the  flexor  profundus  digitorum  and  the  flexor  longus  pollicis,  and 
divides  at  the  upper  border  of  the  pronator  quadratus  into  an  anterior  and  a  pos- 
terior terminal  branch  (Fig.  715). 

Branches. — In  addition  to  muscular  branches  to  the  adjacent  muscles  and  to  the  ex- 
tensor muscles  of  the  thumb, — the  latter  perforating  the  interosseous  membrane  to  reach  their 
destinations, — the  anterior  interosseous  artery  gives  off  a  number  of  more  or  less  important 
branches. 

(aa)  The  median  artery  (a.  comes  nervi  mediani)  arises  from  the  anterior  surface  of  the  ante- 
rior interosseous,  immediately  below  the  origin  of  that  vessel.  It  passes  forward  to  join  the 
median  nerve,  which  it  accompanies  down  the  arm,  and  in  whose  substance  it  is  frequently 
embedded.  It  continues  its  course  with  the  nerve  beneath  the  anterior  annular  ligament,  and, 
when  well  developed,  may  terminate  by  anastomosing  directly  with  the  superficial  palmar 
arch. 

(bb}  A  nutrient  branch  is  usually  given  off  to  the  radius  and  occasionally  also  to  the  ulna. 


782  HUMAN   ANATOMY. 

(cc}  The  anterior  terminal  branch  passes  either  over  or  beneath  the  pronator  quadratus, 
and  terminates  usually  by  anastomosing  with  branches  of  the  anterior  radial  and  ulnar  carpal 
and  with  the  palmar  recurrent  arteries.  Occasionally  it  anastomoses  directly  \vith  the  super- 
ficial palmar  arch. 

(dd )  The  posterior  terminal  branch  is  larger  than  the  anterior.  It  perforates  the  inter- 
osseous  membrane,  anastomoses  with  the  posterior  interrosseous  artery,  and  terminates  in 
branches  which  anastomose  with  the  posterior  radial  and  ulnar  carpals  to  form  the  dorsal  carpal 
net-work. 

Variations. — The  anterior  interosseous  artery  may  arise  from  the  radial,  and  it  may  form 
anastomoses  below  with  the  radial  or  with  both  the  radial  and  ulnar.  The  relations  which  it 
sometimes  possesses  with  the  superficial  palmar  arch  will  be  considered  later, 

The  median  artery  is  occasionally  of  considerable  size  and  frequently  arises  from  the 
common  interosseous.  Its  relations  to  the  superficial  palmar  arch  will  also  be  considered 
later  (page  785). 

b.  The  Posterior  Interosseous  Artery. — The  posterior  interosseous  (a.  inter- 
ossea  dorsalis)  (Fig.  715)  passes  backward  between  the  radius  and  ulna,  above  the 
concave  upper  margin  of  the  interrosseous  membrane.  It  thus  reaches  the  posterior 
portion  of  the  forearm  and  turns  abruptly  downward  between  the  superficial  and  deep 
layers  of  the  extensor  muscles,  and  breaks  up  at  the  wrist  into  branches  which  anas- 
tomose with  the  posterior  radial  and  ulnar  carpals  and  with  the  posterior  terminal 
branch  of  the  anterior  interosseous,  assisting  in  the  formation  of  the  dorsal  carpal 
net-work. 

Just  as  it  reaches  the  posterior  surface  of  the  forearm  it  gives  off  a  posterior 
interosseous  recurrent  branch  (a.  interossea  recurrens),  which  ascends  between  the 
anconeus  and  the  supinator  brevis  to  the  posterior  surface  of  the  external  condyle  of 
the  humerus,  where  it  anastomoses  with  the  superior  profunda  and  the  anastomotica 
magna.  In  its  course  down  the  arm  the  posterior  interosseous  gives  branches  to  the 
extensor  muscles,  and,  through  the  dorsal  carpal  net-work,  it  takes  part  in  the  supply 
of  the  articulations  of  the  wrist  and  carpus. 

4.  The  Ulnar  Nutrient  Artery. — The  nutrient  branch  for  the  ulna  arises 
from  the  upper  third  of  the  ulnar  artery  or  from  one  of  its  muscular  branches,  or 
from  the  anterior  interosseous.      It  enters  the  nutrient  foramen  situated  upon  the 
anterior  surface  of  the  bone,  near  its  outer  border. 

5.  The  Posterior  Ulnar  Carpal  Artery. — The  posterior  ulnar  carpal  (ramus 
carpeus  dorsalis)  (Fig.  715)  is  small.      It  arises  from  the  inner  surface  of  the  ulnar 
artery,  just  above  the  pisiform  bone,  and  winds  inward  beneath  the  tendon  of  the 
flexor  carpi  ulnaris  to  the  back  of  the  carpus,  where  it  anastomoses  with  the  posterior 
radial  carpal  and  the  posterior  interosseous  to  form  the  dorsal  carpal  net-work. 

6.  The  Anterior  Ulnar  Carpal  Artery. — The  anterior  ulnar  carpal  (ramus 
carpeus  volaris)  (Fig.  712)  is  also  small.      It  arises  from  the  ulnar  artery,  just  above 
the  upper  border  of  the  anterior  annular  ligament,  and  passes  outward  upon  the  car- 
pal ligaments  and  beneath  the  long  flexor  tendons  to  anastomose  with  the  anterior 
radial  carpal  and  anterior  interosseous  to  form  the  anterior  carpal  net-work. 

7  and  8.  The  Deep  Palmar  Arteries. — The  deep  palmar  branches  (rami 
volares  profundi)  (Fig.  712)  are  given  off  from  the  ulnar  artery,  just  after  it  has 
entered  the  palm.  The  superior  branch  arises  just  after  the  ulnar  artery  has  passed 
the  pisiform  bone,  and  passes  dorsally  in  the  interval  between  the  flexor  brevis  minimi 
digiti  and  the  abductor  minimi  digiti.  It  then  perforates  theopponens  minimi  digiti. 
and  terminates  by  inosculating  with  the  deep  palmar  arch. 

'l"h<  inferior  branch  arises  just  as  the  ulnar  artery  is  bending  to  pass  trans- 
versely across  the  palm.  It  passes  dorsally  between  the  flexor  brevis  minimi  digiti 
and  the  long  flexor  tendon  for  the  little  finger,  and  terminates  by  inosculating  with 
the  deep  palmar  arch,  near  the  superior  branch. 

Frequently  one  or  other  of  these  branches,  more  usually  the  superior  one,  is 
lac-king,  and  only  one  communication  between  the'  ulnar  and  the  deep  palmar  arch 
r  \ists.  In  their  passage  dorsally,  both  arteries  give  off  branches  to  the  adjacent 
muscles. 


THE   ULNAR   ARTERY. 


783 


FIG.  712. 


Musculo-spiral  nerve 

Superficial  branch  of  superior  profunda 

Tendon  of  biceps 

Radial  nerve,  cut 

Posterior  interosseous  nerve 

Supinator  brevis 

Radial  recurrent  artery 


Radial  artery" 

Posterior  interosseous  artery 

Pronator  radii  teres 

Extensor  carpi  radialis  longior 

Brachio-radialis  — 


Flexor  longus  pollicis 


Anterior  radial  carpal  artery 


Radial  artery 
Princeps  pollicis 

Branch  to  superficial  palmar  arch 


Radialis  indicis 


Median  nerve 


—  Brachial  artery 

1 

y^\ Inferior  profunda  art 


ery 


Origin  of  superficial  flexors 
Inner  condyle 

Brachialis  anticus 

Anterior  ulnar  recurrent  artery 

Posterior  ulnar  recurrent  artery 
Ulnar  artery 

Common  interosseous  artery 


—  Ulnar  portion  of  flexor  profundus 
Ulnar  artery 
Anterior  interosseous  artery 

Anterior  interosseous  nerve 


Pronator  quadratus 

Anterior  ulnar  carpal  artery 
Wrist  joint 


Pisiform  bone 

Deep  branch  of  ulnar  artery 
Ulnar  artery 
Deep  palmar  arch 
Palmar  interosseous  arteries 

Digital  arteries 


Deep  arteries  of  right  forearm  and  hand  ;  flexor  surface. 


734 


HUMAN   ANATOMY. 


9.  The  Digital  Arteries. — The  digital  branches  (aa.  di»itales  volares  com- 
munes) arise  from  the  portion  of  the  ulnar  artery  which  passes  transversely  across 
the  palm  of  the  hand  and  is  termed  the  superficial  palmar  arch  (amis  volaris 
superficial  is).  They  are  four  in  number;  the  first  of  the  four,  starting  from  the 
ulnar  border  of  the  hand,  passes  obliquely  downward  and  inward  across  the  hypoth- 
enar  muscles  and  continues  distally  along  the  ulnar  border  of  the  little  finger.  The 

FIG.  713. 


Radial  artery 
Superficial  volar  artery  - 


Abductor  pollicis 
Opponeus  pollicis 

Flexor  brevis  pollicis 


Flexor  longus 

pollici  tendon 

Princeps  pollicis 


Radialis  indicis 


Ulnar  nerve 

-  I'lnar  artery 
—  Pisiform  bone 


Anterior  annular  ligament 
Deep  branch  of  ulnar  artery 
Digital  branches  of  median  nerve 

Abductor  minimi  digiti 
Flexor  brevis  minimi  digiti 

Digital  arteries 


Superficial  palmar  arch  and  its  branches. 

remaining  three  pass  downward  in  the  second,  third,  and  fourth  intermetacarpal 
spaces  resting  upon  the  lumbrical  muscles,  and,  just  before  reaching  the  clefts  of  the 
fingers,  each  receives  the  corresponding  palmar  interosseous  artery  and  then  divides 
into  two  branches,  the  collateral  digital  branches  (aa.  diyitales  volares  propriac 
which  extend  distally  upon  the  adjacent  sides  of  the  neighboring  digits.  These  col- 
lateral branches  make  numerous  transverse  anastomoses  with  one  another,  especially 
in  the  neighborhood  of  the  interphalangeal  joints,  and  terminate  in  fine  branches 
which  supply  the  bulb  of  the  finger  and  the  bed  of  the  nail. 


Variations. — The  variations  of  the  digital  arteries  depend  principally  ( i )  upon  their  pro- 
portional development  with  regard  to  the  palmar  interosseoiis  vessels  from  the  deep  palmar 
arch,  and  (2)  upon  variations  in  the  mode  of  formation  of  the  superficial  palmar  arch. 

The  palmar  interosseous  branches  of  the  radial  anastomose  with  the  digitals  just  before 
the  division  of  the  latter  into  their  collateral  branches,  and  if  the  iuU-rossea-  are  strongly  devel- 
oped, the  digitals  are  apt  to  be  of  small  calibre,  and  may  be  so  much  reduced  in  si/e  that  the 
collaterals  of  one  or  more  of  them  mav  be  regarded  as  continuations  of  the  corresponding 
palmar  interosswe.  Conversely,  although  normally  tin-  supply  for  tin-  radial  side  of  the  index- 
finger  and  the  thumb  is  from  the  deep  palmar  arch,  yet  occasionally  it  is  derived  from  the 
superficial  arch,  the  princeps  pollicis  and  the  radialis  indicis,  the  branches  from  the  deep 
palmar  arch,  being  much  reduced  in  size. 


THE   RADIAL   ARTERY. 


735 


The  variations  in  the  formation  of  the  superficial  palmar  arch  are  frequent  and  numerous, 
and  may  be  grouped  in  two  classes  :  (i)  those  in  which  additional  branches  from  the  forearm 
participate  in  the  formation  of  the  arch  or  replace  the  radial  in  its  composition,  and  (2)  those  in 
which  there  is  no  true  arch,  the  arteries  which  should  participate  in  its  formation,  and  in  some 
cases  additional  ones  also,  failing  to  anastomose  and  each  giving  rise  independently  to  a  certain 
number  of  digital  branches.  To  the  first  of  these  classes  belong  the  cases  in  which  the  median 
or  anterior  interosseous  artery  anastomoses  directly  with  the  arch  formed  by  the  superficial 
volar  and  the  ulnar,  and  also  those  in  which  the  superficial  volar  fails  to  reach  the  ulnar,  the  arch 
being  formed  by  the  union  of  the  latter  vessel  with  the  median  or  the  anterior  interosseous. 
And,  finally,  the  arch  may  be  formed  by  the  ulnar  artery  alone,  no  direct  communication  taking 
place  between  it  and  the  arteries  mentioned. 

In  the  second  class  of  cases — that  in  which  there  is  no  true  arch — the  ulnar  and  the  super- 
ficial volar,  on  reaching  the  palm,  divide  in  a  somewhat  fan-like  manner  to  give  rise  to  the  digital 
branches.  The  superficial  volar  may  contribute  the  fourth  digital,  as  well  as  the  vessels  to  the 


Variations  of  palmar  arteries  replacing  superficial  arch.     (  faschtschinski). 

thumb  and  radial  side  of  the  index  (Fig.  714,  A  ),  or  it  may  be  limited  to  the  latter  vessels,  all 
four  normal  digitals  being  derived  from  the  ulnar.  With  the  absence  of  the  arch  there  may  be 
associated  an  extra  development  of  the  median  artery,  which  continues  distally  into  the  palm 
as  the  fourth  digital  vessel,  the  remaining  digitals  and  the  radialis  indicis  and  princeps  pollicis 
being  supplied  by  the  ulnar  and  radial  respectively  (  C).  Or,  finally,  with  the  extra  development 
of  the  median  there  is  associated  an  absence,  more  or  less  complete,  of  the  superficial  volar, 
the  median  giving  off  the  branches  to  the  radial  digit  as  well  as  the  fourth  digital  (£ ) . 

THE    RADIAL   ARTERY. 

The  radial  artery  (a.  radialis)  (Figs.  710,  712)  is  the  smaller  of  the  two  terminal 
branches  of  the  brachial,  whose  course  it  continues  downward  through  the  forearm. 
It  arises  at  the  bend  of  the  elbow  and  passes  down  the  outer  border  of  the  forearm  to 
the  level  of  the  styloid  process  of  the  radius,  where  it  bends  outward,  curving  around 
the  external  lateral  ligament  of  the  wrist.  It  then  extends  downward  over  the  pos- 
terior surface  of  the  trapezium  until  it  reaches  the  interval  between  the  first  and  second 
metacarpal  bones,  and  here  it  again  changes  its  direction  and  passes  forward  into  the 
palmar  surface  of  the  hand,  across  which  it  is  continued  inward  over  the  anterior  sur- 
faces of  the  second,  third,  and  fourth  metacarpals,  forming  what  is  termed  the  deep 
palmar  arch  (arcus  volaris  profundus).  It  terminates  opposite  the  proximal  part 
of  the  fourth  metacarpal  interspace  by  anastomosing  with  the  deep  palmar  branch  of 
the  ulnar. 

In  accordance  with  its  position  with  reference  to  the  bony  axis  of  the  forearm 
and  hand,  the  radial  artery  may  be  regarded  as  consisting  of  three  parts.  In  its  first 
or  antibrachial  portion  it  is  preaxial  in  position,  in  the  second  or  carpal  portion  it  is 
postaxial,  and  in  the  third  or  paltnar  portion  it  is  again  preaxial. 

Relations. — In  its  antibrachial  portion  the  course  of  the  artery  may  be  indi- 
cated by  a  line  drawn  from,  a  point  midway  between  the  two  condyles  of  the  humerus 
to  a  point  about  i  cm.  internal  to  the  styloid  process  of  the  radius.  In  its  upper 
half  it  is  overlapped  in  front  by  the  inner  border  of  the  brachio-radialis  (supinator 
longus)  muscle,  but  lower  down  it  is  covered  only  by  the  deep  and  superficial  fascia; 

50 


786  HUMAN   ANATOMY. 

and  the  skin.  Posteriorly  it  rests  successively,  from  above  downward,  upon  the 
tendon  of  the  biceps,  the  supinator  brevis,  the  pronator  radii  teres,  the  radial  portion 
of  the  flexor  sublimis  digitorum,  the  flexor  longus  pollicis,  the  outer  border  of  the 
pronator  quadratus,  and  the  anterior  surface  of  the  lower  end  of  the  radius.  Inter- 
nally it  is  in  contact  with  the  pronator  radii  teres  in  its  upper  third,  and  throughout 
the  rest  of  its  course  with  the  outer  border  of  the  flexor  carpi  radialis.  Externally  it 
is  in  relation  throughout  its  entire  length  with  the  brachio-radialis,  and  in  the  middle 
third  of  its  course  it  is  in  contact  with  the  radial  nerve.  Two  venae  comites  accom- 
pany the  artery,  lying  to  its  inner  and  outer  sides. 

In  its  carpal  portion  the  radial  artery  rests  at  first  upon  the  external  lateral 
ligament  of  the  wrist  and  then  upon  the  posterior  surface  of  the  trapezium.  It  passes 
beneath,  successively,  the  tendons  of  the  extensor  ossis  metacarpi  pollicis,  the  exten- 
sor brevis  pollicis,  and  the  extensor  longus  pollicis,  being  covered  in  the  interval 
between  the  last  two  and  to  the  ulnar  side  of  the  extensor  longus  pollicis  only  by  the 
skin  and  fasciae,  in  which  are  some  branches  of  the  radial  nerve  and  tributaries  of  the 
radial  vein. 

In  its  palmar  portion,  as  it  passes  forward  through  the  proximal  portion  of  the 
first  intermetacarpal  space,  the  artery  lies  between  the  two  heads  of  the  first  dorsal 
interosseous  muscle.  It  then  bends  inward  beneath  the  oblique  head  of  the  adductor 
pollicis,  and,  either  penetrating  that  muscle  or  passing  between  it  and  the  transverse 
head  of  the  same  muscle,  is  continued  ulnarward  beneath  the  tendons  of  the  long 
flexors,  resting  upon  the  bases  of  the  metacarpal  bones  and  upon  the  interosseous 
muscles. 

Branches. — From  its  antibrachial  portion  the  radial  artery  gives  off  numer- 
ous muscular  branches  to  the  muscles  on  the  radial  side  of  the  forearm,  and,  in 
addition,  gives  origin  to  (i)  the  radial  recurrent,  (2)  the  anterior  radial  carpal,  and 
(3)  the  superficial  volar, 

From  its  carpal  portion  it  gives  rise  to  (4)  the  posterior  radial  carpal,  (5)  the 
dor  salts  pollicis,  and  (6)  the  dorsalis  indicis. 

From  its  palmar  portion  its  branches  are  (7)  the  princeps  pollicis,  (8)  the 
palmar  interosseous  (of  which  there  are  three),  and  (9)  the  recurrent  carpals. 

Variations. — The  high  origin  of  the  radial  has  already  been  considered  in  discussing  the 
variations  of  the  brachial  artery  (page  774).  It  is  the  last  of  the  forearm  arteries  to  be  devel- 
oped in  the  comparative  series,  and  its  relations  with  the  arterial  supply  to  the  hand  is  due  to 
secondary  anastomoses  which  it  makes  with  vessels  originally  present,  whereby  it  has  come  to 
give  origin  to  many  branches  formed  before  its  appearance.  Thus  the  dorsalis  indicis  and  the 
dorsalis  pollicis  are  primarily  digital  branches  from  the  dorsal  interosseous  artery  of  the  first 
intermetacarpal  space,  and  this  artery  arose  from  the  posterior  carpal  arch  and  has  become  a 
portion  of  the  radial  by  the  anastomosis  of  that  artery  with  the  arch.  Similarly  the  portion  of 
the  radial  which  passes  forward  between  the  first  and  second  metacarpals  to  join  the  deep 
palmar  arch  is  primarily  the  first  posterior  perforating  vessel,  which  has  secondarily  become  the 
deep  palmar  apparent  continuation  of  the  radial,  and  has  brought  that  vessel  into  direct  con- 
tinuity with  the  arch  and  given  it  the  branches  which  originally  arose  from  that  vessel. 

The  secondary  anastomoses  of  the  original  radial  with  pre-existing  vessels  have,  how«-\er, 
become  well  established,  and  variations  of  the  radial,  other  than  its  high  origin,  are  rather 
uncommon.  It  has  been  observed  to  terminate  in  an  anastomosis  with  an  enlarged  posterior 
carpal  arch,  or  in  the  lower  part  of  the  forearm  by  anastomosis  with  the  anterior  interosseous 
artery.  Its  absence  below  the  point  where  the  radial  recurrent  is  given  off  has  also  been  ob- 
served, its  territory  in  such  cases  being  supplied  by  the  interosseous. 

Occasionally  it  passes  to  the  dorsal  surface  of  the  arm  much  higher  up  than  usual,  and  in 
such  cases  the  superficial  volar  branch  also  arises  at  a  much  higher  level  than  usual  and  passt-s 
downward  along  the  line  usually  occupied  by  the  radial  artery.  It  is  an  exceedingly  slender  ves- 
sel, and,  being  felt  at  the  place  where  the  pulse  is  usually  examined,  may  give  rise  to  erroneous 
conclusions  as  to  the  quality  of  that  phenomenon. 

Practical  Considerations. — The  radial  artery,  like  the  ulnar,  is  the  subject 
of  idiopathic  aneurism  only  with  great  rarity,  but  a  stab-wound  may  result  in  a  trau- 
matic aneurism,  or  may  necessitate  immediate  ligation  for  control  of  hemorrhage. 
The  vessel  may  be  tied  in  any  part  of  its  course. 

i.  At  the  upper  third  of  its  antibrachial  portion  it  is  reached  through  an  incision 
made  on  the  line  described  (ride  supra],  which,  after  the  deep  fascia  is  opened  up, 
should  disclose  the  interspace  between  the  brachio-radialis  and  the  pronator  radii 


THE    RADIAL   ARTERY.  787 

teres.  This  is  often  indicated  by  a  yellowish  (cellulo-fatty)  line.  The  fibres  of  the 
former  muscle  are  almost  parallel  with  the  long  axis  of  the  forearm  and  overlie  the 
artery  ;  those  of  the  latter  are  oblique  and  lie  close  to  the  inner  side  of  the  vessel. 
The  nerve  is  so  far  external  that  it  is  not  likely  to  be  seen.  The  artery,  with  its 
vena?  comites,  lies  on  the  supinator  brevis. 

2.  At  the  middle  of  the  forearm  the  incision  is  made  on  the  same  line.      The 
same  relations  exist,  except  that  there  the  nerve  is  usually  very  near  to  the  outer  side 
of  the  artery,  which  now  lies  on  the  tendon  of  insertion  of  the  pronator  radii  teres. 

As  the  brachio-radialis  is  not  very  wide  at  this  part  (especially  if  the  artery  is 
sought  for  at  the  lower  end  of  the  middle  third),  it  is  very  easy  to  expose  the  outer 
instead  of  the  inner  border  of  the  muscle,  in  which  case  the  muscle  is  apt  to  be  drawn 
inward,  and  when  the  depths  of  the  wound  are  opened  up  the  radial  nerve  is  reached. 
This  is  the  common  error  of  beginners. 

The  tendon  of  the  brachio-radialis,  as  a  rule,  first  makes  its  appearance  at  the 
outer  border  of  the  muscle,  so  that  if  this  tendinous  edge  is  exposed  the  operator 
will  know  that  he  has  laid  bare  the  wrong  side  of  the  muscle.  The  inner  border 
of  the  latter  remains  muscular,  until  it  ends  somewhat  abruptly  in  the  tendon 
(Treves). 

3.  At  the  lower  third  the  incision  should  be  made  midway  between  the  tendon 
of  the  brachio-radialis  and  that  of  the  flexor  carpi  radialis,  the  latter  of  which  may 
be  made  prominent  by  strongly  extending  the  hand.      The  vessel  is  very  superficial, 
and  is  disclosed  as  soon   as  the   thin   fascia   is   divided.      The   nerve  has  left  the 
vessel  altogether   (at  a  level  of  from  three  inches  above  the  wrist  to  the  middle 
of  the  forearm)   and  has  passed  under  the  brachio-radialis  tendon  to  the  dorsum 
of  the  hand. 

4.  In  the  triangular  fossa  between  the  lower  end  of  the  radius  and  the  root  of  the 
thumb  (tabatiere  anatomique) ,   bounded  externally  by  the  tendon  of  the  extensor 
longus   pollicis,   internally  by  the  tendons  of   the  extensor  brevis  pollicis  and   the 
extensor  ossis  metacarpi  pollicis,  and  superiorly  by  the  inferior  margin  of  the  posterior 
annular  ligament  (Fig,  716),  the  radial  artery  may  occasionally  require  ligation  on 
account  of  wound  or  of  aneurism.      An  incision  one  inch  and  a  half  long  should  be 
made  obliquely  across  the  fossa,  observing  to  avoid  one  of  the  chief  radicles  of  the 
radial  vein,  which  lies  in  the  superficial  fascia  immediately  in  the  course  of  the  wound. 
After  opening  the  fascia,  and  displacing  some  loose  adipose  tissue,  the  artery  will  be 
reached  at  the  bottom  of  the  depression  between  the  tendons  of  the  thumb.      It  is 
desirable  to  avoid  opening  the  sheaths  of  the  tendons  or  the  joint  between  the  scaph- 
oid and  trapezium  ;  these  bones  together  with  the  base  of  the  first  metacarpal  form 
the  floor  of  the  space. 

The  collateral  cirailation  after  ligation  of  the  radial  is  carried  on  as  after  ligation 
of  the  ulnar,  q.  v. 

Wounds  of  a  palmar  or  carpal  arch  are  apt  to  be  troublesome  on  account  of  the 
occasional  difficulty  in  finding  and  securing  both  ends  of  the  divided  vessel,  and 
because  of  the  very  free  anastomosis  between  the  palmar  and  carpal  arches  and  the 
interosseous  vessels,  which  leads  to  recurrent  hemorrhage,  even  after  ligation  of  both 
radial  and  ulnar.  Compression  over  the  wound,  firm  bandaging  from  the  finger-tips 
to  the  axilla,  and  elevation  of  the  limb,  are,  for  these  reasons,  the  methods  usually 
first  employed,  and  if  applied  thoroughly  will  generally  be  effectual.  Ligation  of  the 
brachial  is  indicated  when  these  have  failed,  on  account  of  the  necessity  for  getting 
above  the  interosseous  anastomotic  supply  (vide  supra}. 

i.  The  Radial  Recurrent  Artery. — The  radial  recurrent  (a.  recurrens  radialis) 
(Fig.  712)  arises  from  the  outer  surface  of  the  radial,  shortly  below  its  origin.  It  is 
at  first  directed  downward  upon  the  surface  of  the  supinator  brevis,  but  quickly 
bends:  upward  towards  the  external  condyle  of  the  humerus,  passing  between  the 
radial  and  posterior  interosseous  nerves  and  lying  beneath  the  supinator  longus. 
It  gives  numerous  branches  to  the  supinator  longus  and  brevis  and  to  the  extensor 
carpi  radialis  longior  and  the  extensor  carpi  radialis  brevior,  and  terminates  at  the 
external  condyle  by  anastomosing  with  the  superior  profunda  from  the  brachial 
artery. 


788 


HUMAN   ANATOMY. 


2.   The  Anterior  Radial  Carpal  Artery.— 
carpca  volarisj  (Fig.  712)  is  usually  a  small  branch 


Triceps,  cut 


Olecranon  process ~m 


Anconeus  — 


Interosseous 

recurrent  artery 
Extensor  carpi 

ulnaris,  cut 


__  Superior  profunda 

artery 
-  Brachio-radialis 

—  Extensor  carpi 

radialis  lonKtor 
External  condyle 


Head  of  radius 


Supinator  brevis 


Posterior  interosse- 
ous artery 

Posterior  interosse- 
ous nerve 

Extensor  carpi 

radialis  brevior 


The  anterior  radial  carpal  (  ramus 
which  arises  from  near  the  lower 
end  of  the  antibrachial  portion 
of  the  radial.  It  passes  inward 
beneath  the  flexor  tendons  at 
about  the  lower  border  of  the 
pronator  quadratus,  and  breaks 
up  into  a  number  of  small 
branches  which  anastomose 
with  branches  from  the  anterior 
ulnar  carpal,  the  anterior  inter- 
osseous, and  the  recurrent  car- 
pals  to  form  an  anterior  carpal 
net-work.  From  this  net-work 
branches  pass  to  the  wrist  and 
to  the  carpal  articulations. 

3.  The  Superficial  Vo- 
lar Artery. — The  superficial 
volar  (ramus  volaris  supcrtici- 
alis)  (Fig.  713)  arises  usually 
just  where  the  radial  bends  out- 
ward and  backward  to  reach  the 
posterior  surface  of  the  wrist. 
It  is  usually  rather  slender, 
although  variable  in  size,  and 
is  directed  downward,  passing 
either  over,  through,  or  beneath 
the  adductor  pollicis,  supplying 
that  and  the  other  muscles  of  the 
thenar  eminence,  and  terminates 
usually  by  anastomosing  with 
the  superficial  palmar  branch  of 
the  ulnar  to  form  the  superficial 
palmar  arch. 

Variations.  —  The  superficial 
volar  is  somewhat  variable  both  as 
tosize,  origin,  and  mode  of  termina- 
tion. It  occasionally  arises  high  up 
upon  the  radial,  and  in  such  cases 
that  vessel  passes  to  the  posterior 
surface  of  the  arm  at  a  much  higher 
level  than  usual.  Not  infrequently 
it  takes  no  part  in  the  formation  of 
the  superficial  palmar  arch,  and 
may  terminate  m  the  muscles  of 
the  thenar  eminence,  the  digital 
branches  being  all  given  off  by  the 
superficial  palmar  branch  of  the 
ulnar;  or,  on  the  contrary,  appear- 
ing as  a  well-developed  stem,  it 
may  divide  distally  into  from  one 
to  four  digital  arteries,  the  remain- 
ing ones  arising  directly  from  the 
superficial  palmar  branch  of  the 
ulnar  or  partly  from  that  and  partly 
from  the  median  artery  (page  7*4 

4.  The  Posterior  Ra- 
dial Carpal  Artery. — The 

posterior  radial  carpal  (ramus 
carpeus  dorsalis)  (Fig.  715  )  is  a 
small  branch  which  is  given  off  from  the  radial  just  as  that  vessel  passes  beneath  the 
tendon  of  the  extensor  ossis  metacarpi  pollicis.  It  passes  horizontally  inward  beneath 


Extensor 

longus  pollicis 


Extensor  indicis 


Posterior  ulnar 

carpal  artery 


Dorsal 

interosseous 

arteries 


Extensor  ossis 
metacarpi  pollicis 


Extensor  brevis 

pollicis 

Anterior  interosse- 
ous artery 


Posterior  radial 

carpal  artery 
Radial  artery 

Dorsalis  pollicis 

artery 
Dorsalis 
indicis  artery 


ArUTK-s  of  extensor  suilan-  "t  t..i>ami  and  hand. 


THE    RADIAL   ARTERY.  789 

the  tendons  of  the  extensor  carpi  radialis  longior  and  the  extensor  carpi  radialis 
brevior,  and  anastomoses,  either  directly  or  by  means  of  a  number  of  small  branches, 
with  the  posterior  ulnar  carpal,  forming  a  posterior  carpal  a)  ch  or  net-work. 

Branches. — From  the  posterior  carpal  arch  or  net-work  a  longitudinal  stem  passes  distally 
in  each  of  the  three  inner  intermetacarpal  spaces.  These  are  the  dorsal  interosseous  arteries 
(aa.  metacarpeae  dorsales).  At  the  upper  extremity  of  its  intermetacarpal  space  each  interosseous 
artery  receives  the  corresponding  perforating  branch  from  the  palmar  interosseous  artery, 
and  when  it  reaches  the  interval  between  the  bases  of  the  proximal  phalanges,  it  divides  into 
two  branches,  which  run  forward  upon  the  inner  and  outer  surfaces  respectively  of  the  proximal 
phalanges  of  the  adjacent  digits  and  terminate  in  small  branches  upon  these  phalanges. 

A  slender  branch,  which  arises  either  directly  from  the  dorsal  carpal  arch  or  from  the  in- 
terosseous artery  of  the  fourth  intermetacarpal  space,  passes  along  the  inner  border  of  the  metacar- 
pal  and  proximal  phalanx  of  the  little  finger.  It  terminates  upon  the  proximal  phalanx  of  its  digit. 

Variations. — Considerable  variation  occurs  in  the  size  of  the  dorsal  interosseous  arteries. 
That  which  traverses  the  fourth  intermetacarpal  space  is  sometimes  wanting,  while  that  of  the 
second  space  is  sometimes  of  considerable  size  and  may  arise  directly  from  the  radial  artery. 
Occasionally  each  artery  undergoes  a  sudden  increase  of  calibre  at  the  point  where  it  is  joined 
by  the  perforating  branch  from  the  deep  palmar  arch,  and  may  appear  to  be  the  continuation  of 
the  perforating  branch.  Where  it  divides  into  its  two  terminal  branches,  each  interosseous  gives 
off  an  inferior  perforating  branch,  which  passes  forward  to  communicate  with  the  corresponding 
palmar  digital  artery  ;  but  these  perforating  branches  are  frequently  wanting,  with  the  exception 
of  that  given  off  from  the  artery  of  the  second  intermetacarpal  space. 

5.  The    Dorsalis    Pollicis   Artery. — The    dorsalis    pollicis  (Fig.    715)  is  a 
slender  artery  which  arises  from  the  radial  just  before  it  passes  beneath  the  tendon  of 
the  extensor  longus  pollicis.      It  passes  distally  along  the  dorsal  surface  of  the  first 
metacarpal  and  terminates  upon  the  dorsum  of  the  first  phalanx  of  the  thumb. 

6.  The  Dorsalis  Indicis  Artery. — The    dorsalis    indicis    (Fig.    715)   arises 
from  the  radial  just  as  it  passes  between  the  two  heads  of  the  first  dorsal  interosseous 
muscle  to  enter  the  palm  of  the  hand.      It  passes  distally  along  the  radial  border  of  the 
second  metacarpal,  resting  upon  the  first  dorsal  interosseous  muscle,  and  terminates 

FIG.  716. 

Extensor  carpi  radialis  longior        Extensor  longus  pol]icis 
Lower  extremity  of  radius      \      \  Dorsalis  indicis 

Radial  artery    v 


Extensor  ossis  metacarpi  pollicis 

Extensor  brevis  pollicis 


Dissection  showing  relation  of  radial  artery  to  extensor  tendons  in  "snuff  box." 

upon  the  first  phalanx  of  the  index-finger.     It  frequently  gives  off  a  small  branch  which 
passes  along  the  inner  border  of  the  metacarpal  and  first  phalanx  of  the  thumb. 

Variations. — The  dorsalis  indicis,  together  with  the  carpal  portion  of  the  radial  distal  to 
the  point  at  which  the  posterior  radial  carpal  is  given  off,  represents  the  dorsal  interosseous 
artery  of  the  first  intermetacarpal  space  The  branch  to  the  inner  border  of  the  thumb  repre- 
sents one  of  the  terminal  branches  of  that  artery,  and  frequently  arises  directly  from  the  radial 
opposite  the  main  stem  of  the  dorsalis  indicis. 

7.  The  Princeps  Pollicis  Artery. — The  a.  princeps  pollicis  (Fig.  717)  arises 
from  the  radial  just  as  it  emerges  from  between  the  two  heads  of  the  first  dorsal  inter- 
osseous muscle  and  is  bending  horizontally  inward  to  form  the  deep  palmar  arch.  The 
artery  passes  directly  distally,  resting  upon  the  palmar  surface  of  the  first  dorsal  inter- 
osseous muscle  and  being  covered  by  the  adductor  pollicis.  While  still  beneath  the 


790 


HUMAN   ANATOMY. 


caput  obliquum  of  the  adductor,  the  vessel  frequently  divides  into  two  branches,  one  of 
which  is  continued  distally  along  the  radial  border  of  the  index-finger,  forming  what 
has  been  termed  the  a.  radialis  indicis  (a.  volaris  indicis  radialis),  while  the  other 
extends  along  the  first  metacarpal  and,  passing  between  the  two  heads  of  the  adductor, 
divides  beneath  the  tendon  of  the  flexor  longus  pollicis  into  two  branches,  which 
pass  distally  along  the  palmar  surface  of  the  thumb,  one  along  the  inner  and  the 
other  along  the  outer  border,  anastomosing  with  the  branches  of  the  dorsalis  pollicis. 

Variations. — The  a.  princeps  pollicis  is  in  reality  the  palmar  interosseous  artery  of  the  first 
intermetacarpal  space,  and,  when  developed  as  described,  corresponds  in  the  arrangement  of 
its  branches  with  the  dorsalis  indicis,  together  with  the  dorsalis  pollicis.  Frequently,  however, 
the  branch  to  the  radial  border  of  the  index-finger  is  lacking,  or,  on  the  other  hand,  it  may  be 
well  developed  and  arise  directly  from  the  deep  palmar  arch,  or  sometimes  both  it  and  the 
princeps  pollicis  are  derived  from  the  superficial  palmar  arch  (page  784). 

8.  The  Palmar  Interosseous  Arteries. — The  palmar  interosseous  arteries 
(aa.  metacarpeae  volares)  are  three  in  number,  and  arise  from  the  deep  palmar  arch  as 

FIG.  717. 


Radial  artery 

Anterior  carpal  branch 
Superficial  volar 


Posterior  carpal  branch 
Metacarpal 
Dorsales  pollicis 
Radial  artery. 
Princeps  pollicis 
Radialis  indicis 
Dorsalis  indicis 
Branch  from  radialis  in 
dicis  for  superficial  arcl 


Ulnar  artery 

Anterior  carpal  branch 


'osterior  carpal  branch 


.Posterior  carpal  branch 


Posterior  carpal  arch 

Deep  branch  of  ulnar 
A  perforating  branch  of 

deep  palmar  arch 
Superficial  palmar  arch 
Dorsal  interosseous 

arteries 
Palmar  interosseous 

arteries 


Digital  arteries 


Semidiagrammatic  reconstruction  of  right  hand,  viewed  from  palm,  showing  relations  of  arteries 
to  surface  and  to  bones;  vessels  on  dorsal  surface  are  represented  in  outline. 

it  crosses  the  second,  third,  and  fourth  intermetaearpal  spaces.      Each  artery  pasdea 
distally    in    its   intrnm-tararpal   spare,    resting  upon  the  interosseous   muscles,    and 


THE   THORACIC   AORTA.  791 

nates  by  anastomosing  with  the  corresponding  digital  artery  from  the  superficial  palmar 
arch  just  before  the  digital  divides  into  its  two  terminal  branches.  Immediately  at 
its  origin  each  palmar  interosseous  gives  off  a  perforating  branch  (ramus  perforans) 
which  passes  dorsally  between  the  adjacent  metacarpals  to  communicate  directly  with 
the  corresponding  dorsal  interosseous  artery. 

Variations. — The  palmar  interosseous  arteries  vary  considerably  in  size,  according  as  the 
digital  branches  from  the  superficial  palmar  arch  are  well  or  poorly  developed  (page  784). 
When  the  ulnar  palmar  digital  is  small,  an  extra  branch  may  arise  from  the  deep  palmar  arch, 
passing  along  the  ulnar  border  of  the  little  finger. 

9.  The  Radial  Recurrent  Arteries. — The  radial  recurrent  arteries  (Fig.  717) 
are  two  or  three  small  branches  which  arise  from  the  concave  surface  of  the  deep 
palmar  arch  and  pass  proximally  over  the  carpus  to  anastomose  with  the  terminal 
branches  of  the  anterior  interosseous  and  of  the  anterior  radial  and  ulnar  carpal 
arteries.  By  the  anastomosis  of  these  various  arteries  there  is  formed  upon  the 
anterior  surface  of  the  carpus  a  net-work,  the  rete  carpale  volare,  from  which  branches 
are  distributed  to  the  wrist  and  to  the  carpal  articulations. 

The  Collateral  Circulation  in  the  Forearm. — The  brachial  artery,  after 
being  ligated,  will  convey  blood  to  the  forearm  arteries  by  means  of  its  superior  and 
inferior  profunda  branches  and  by  the  anastomotica  magna,  which  form  a  rich  anas- 
tomosis at  the  elbow-joint  with  the  radial  recurrent,  the  anterior  and  posterior  ulnar 
recurrent,  and  the  posterior  interosseous  recurrent.  The  collateral  circulation  in  the 
parts  supplied  by  the  ulnar  and  radial  arteries,  after  ligation  of  one  or  other  of  these 
vessels,  will  be  carried  on  by  means  of  the  direct  anastomoses  between  the  two 
arteries  in  the  superficial  and  deep  palmar  arches  and  also  by  way  of  the  anterior  and 
posterior  carpal  net-works.  To  the  former  of  these  net-works  the  radial  artery  sends 
contributions  from  its  posterior  carpal  branch  and  the  ulnar  from  its  posterior  carpal 
and  anterior  and  posterior  interosseous  branches,  while  to  the  latter  the  radial  sends 
its  anterior  carpal  branch  and  the  ulnar  its  anterior  carpal  and  anterior  interosseous 
branches. 

THE   THORACIC   AORTA. 

The  thoracic  aorta  (aorta  thoracalis)  (Fig.  718)  is  the  continuation  of  the 
descending  limb  of  the  aortic  arch,  and  begins  upon  the  left  side  of  the  body 
of  the  fourth  thoracic  vertebra.  It  passes  downward  through  the  thorax  in  the 
posterior  mediastinum  and  terminates  below  at  the  diaphragm,  behind  which  it 
passes  to  become  continuous  with  the  abdominal  aorta.  In  the  upper  part  of  its 
course  it  lies  a  little  to  the  left  of  the  median  line,  but  it  tends  slightly  to  the  right 
as  it  descends,  and  eventually  occupies  the  median  line  just  before  it  reaches  the 
diaphragm. 

Relations. — Anteriorly  it  is  in  relation  with  the  left  bronchus  and  the  root  of 
the  left  lung  in  its  upper  part,  and  it  is  crossed  very  obliquely  by  the  cesophagus, 
which  separates  it  from  the  pericardium  and  the  posterior  surface  of  the  left  auricle 
of  the  heart.  Posteriorly  it  rests  upon  the  bodies  of  the  eight  lower  thoracic  ver- 
tebrae, or  rather  throughout  the  greater  part  of  its  extent  upon  the  anterior  common 
ligament  of  the  thoracic  vertebrae,  and  at  about  the  level  of  the  fifth  vertebra  has 
passing  obliquely  upward  behind  it  the  thoracic  duct  and,  at  the  level  of  the  eighth 
vertebra,  the  vena  hemi-azygos. 

Upon  the  right  side  are,  above,  the  cesophagus  and  lower  down  the  right  pleura. 
The  thoracic  duct  passes  upward  upon  its  right  side  and  slightly  behind  it  as  far  as 
the  fifth  thoracic  vertebra,  and  the  vena  azygos  also  lies  upon  its  right  side,  but  on  a 
plane  slightly  posterior  to  it.  On  the  left  side  are  the  left  lung  and  pleura  above, 
and  below,  the  cesophagus,  while  the  vena  hemi-azygos  also  lies  upon  its  left  side,  but 
on  a  somewhat  posterior  plane. 

Branches. — The  branches  which  arise  from  the  thoracic  aorta  may  be  divided 
into  two  groups,  according  as  they  are  distributed  to  the  thoracic  viscera  or  to  the 
parietes.  The  visceral  branches  are  (i)  the  bronchial,  (2)  the  cesophageal,  and  (3) 
the  mediastinal.  The  parietal  branches  are  (4)  the  aortic  intercostal  arteries,  and 
(5)  the  diaphragmatic  branches. 


792  HUMAN   ANATOMY. 

Variations. — The  passage  of  the  thoracic  aorta  down  the  right  side  of  the  vertebral  column 
in  the  upper  part  of  its  course  and  the  origin  from  it  of  the  right  subclavian  artery  have  already 
been  discussed  in  connection  with  the  variations  of  the  aortic  arch  (page  724].'  It  was  there 
pointed  out  that  both  these  abnormalities  depend  upon  the  more  or  less  perfect  persistence  of  the 
lower  portion  of  the  right  primitive  aortic  arch.  Not  infrequently  a  modification  of  this  condi- 
tion is  to  be  seen  in  the  existence  of  a  small  branch  arising  from  the  upper  part  of  the  thoracic 
aorta  and  passing  obliquely  upward  and  to  the  right  behind  the  (esophagus.  This  is  the  arteria 
aberrans,  and  it  is  to  be  regarded  as  a  persistence  in  a  rudimentary  condition  of  the  distal  por- 
tion of  the  right  primitive  aortic  arch.  It  is  regarded  by  some  authors  as  a  normal  branch  of  the 
thoracic  aorta,  but  it  is  somewhat  inconstant  in  its  occurrence.  Occasionally  it  anastomoses 
with  the  first  or  second  intercostal  branches  of  the  superior  intercostal  artery  ( page  765). 

1.  The  Bronchial  Arteries. — The  bronchial  arteries  (aa.  hronchialcs)  (Fig. 
718)  are  somewhat  variable  in  number;    while   three  are   usually   described,  they 
may  be  reduced  to  two  or  increased  to  four.     They  arise  from  the  upper  portion 
of  the  thoracic  aorta  and  pass  to  the  right  and  left  bronchi,  and  are  continued  along 
these  to  supply  the  tissue  of  the  lungs.     The  right  bronchial  artery,  which  very 
frequently  arises  from  the  first  right  aortic  intercostal,  passes  to  the  right  in  front 
of  the  oesophagus  and  applies  itself  to  the  posterior  surface  of  the  right  bronchus, 
along  which  it  passes  to  the  lung.      In  its  course  it  gives  off  minute  branches  to 
the  oesophagus,  bronchus,  and  pericardium,  and  to  the  lymphatic  nodes  in  its  neigh- 
borhood. 

The  left  bronchial  arteries,  which  are  usually  two  in  number,  apply  them- 
selves at  once  to  the  posterior  surface  of  the  left  bronchus  as  it  passes  in  front  of  the 
aorta  and  are  continued  along  this  to  the  lung.  They  give  off  small  branches  to  the 
oesophagus  and  to  neighboring  lymphatic  nodes.  The  upper  of  the  two  vessels  fre- 
quently arises  by  a  common  stem  with  the  right  bronchial,  and  may  be  the  only  one 
that  is  present. 

2.  The  CEsophageal  Arteries. — The  oesophageal  branches  (aa.  asophageae) 
(Fig.  718)  of  the  thoracic  aorta  are  also  variable  in  number,  forming  a  series  of  four  or 
sometimes  five  or  six  small  vessels  which  arise  in  succession  from  above  downward 
from  the  anterior  surface  of  the  aorta.     After  a  short  but  somewhat  tortuous  course, 
they  reach  the  oesophagus,  in  the  wall  of  which  they  branch  to  form  a  net-work  which 
receives  branches  from  the  bronchial  arteries,  from  the  inferior  thyroid  above  and  the 
gastric  artery  below. 

3.  The    Mediastinal  Arteries. — The  mediastinal  arteries  (rami  pericardiaci) 
are  a  number  of  small  vessels  which  arise  from  the  anterior  surface  of  the  thoracic 
aorta  and  are  distributed  to  the  mediastinal  lymph-nodes  and  the  posterior  surface  of 
the  pericardium. 

4.  The    Aortic  Intercostal  Arteries. — The    aortic    intercostals    (aa.  inter- 
costales)  (Fig.  718)  supplying  the  tissues  of  the  lower  intercostal  spaces,  are  usually 
nine  in  number  on  each  side,  while  a  tenth,  sometimes  termed  the  subcostal  artery, 
runs  along  the  lower  border  of  the  last  rib,  supplying  the  upper  part  of  the  abdom- 
inal wall.     The  arteries  arise  in  pairs  from  the  posterior  surface  of  the  thoracic  aorta 
and  pass  outward  over  the  bodies  of  the  vertebrae  to  the  intercostal  spaces,  those  of 
the  right  side  being,  for  the  most  part,   somewhat    longer  than  those  of   the  left, 
owing  to  the  position  of  the  thoracic  aorta  to  the  left  of  the  vertebral  column  through- 
out the  greater  portion  of  its  length.      Arrived  at  the  intercostal  space,  each  artery 
passes  obliquely  outward  and  upward  across  the  space  towards  the  angle  of  the  rib 
next  above,  resting  upon  the  internal  intercostal  fascia,  and  covered  by  pleura.      It 
then  pierces  the  intercostal  fascia  and,  as  far  as  the  angle  of  the  rib,  runs  between  the 
fascia  and  the  external  intercostal  muscle.      On  reaching  the  angle  of  the  rib  the  artery 
passes  beneath  the  internal  intercostal  muscle  and  is  continued  around  the  thoracic 
wall  in  the  subcostal  groove  of  the  rib,  and  between  the  two  intercostal  muscles,  to 
terminate  usually  by  inosculating  in  front  with  the  upper  of  the  two  Anterior  inter* 
costal  arteries  given  off  by  the  internal  mammary  or  the  musculo-phrenic  to  each 
intercostal   space.     The  arteries  which    pass  to  the  tenth  and    eleventh  intercostal 
spaces  continue  onward   beyond  the  extremities  of    their  corresponding  ribs,   and, 
passing   between  the  oblique  muscles  of   the  abdomen,   anastomose  with  the  deep 
epigastric  artery.      The  same  arrangement   occurs  in  the  case  of  each  of  the  tenth 
aortic  intercostal  (subcostal)  arteries.     These,  however,  throughout  that  portion  of 


THE   THORACIC   AORTA.  793 

their  course  in  which  they  are  in  relation  to  the  twelfth  ribs,  rest  upon  the  quadratus 
lumborum  muscles,  beneath  the  transversalis  fascia,  and  at  the  outer  border  of  that 
muscle  pass  beneath  the  fibres  of  the  transversalis  abdominis,  and,  more  laterally, 
perforating  the  internal  oblique,  come  to  lie  between  that  muscle  and  the  external 
oblique. 

Relations. — In  the  first  portion  of  their  course,  while  passing  over  the  bodies 
of  the  vertebrae,  the  right  aortic  intercostals  are  crossed  by  the  thoracic  duct  and  by 
the  vena  azygos,  and  the  upper  ones  are  also  crossed  by  the  oesophagus.  Those 
of  the  left  side  are  crossed  by  the  vena  hemiazygos,  and  both  sets  are  covered 
by  the  pleura.  Opposite  the  heads  of  the  ribs  they  are  crossed  by  the  ganglionated 
cord  of  the  sympathetic  nervous  system,  the  lower  ones  also  by  the  splanchnic  nerves, 
and  in  their  course  through  the  intercostal  spaces  they  are  in  relation  to  the  inter- 
costal veins  and  nerves,  each  artery  lying  below  its  corresponding  vein  and  above  the 
nerve,  but  on  a  plane  slightly  posterior  to  both.  The  arteries  of  the  upper  spaces  lie 
at  first  below  the  corresponding  nerves,  but  as  they  approach  the  lower  borders  of 
their  ribs  they  cross  the  nerves  obliquely,  and  throughout  the  greater  part  of  their 
course  possess  the  relation  described. 

Branches. — Each  artery  gives  off  small  branches  to  the  bodies  of  the  vertebras  and  to  the 
pleura,  and  throughout  its  course  through  the  intercostal  space  numerous. 

(a)  Muscular  branches,  which  supply  the  intercostal  muscles,  the  serratus  magnus,  and 
the  pectorales  major  and  minor,  anastomosing  with  the  thoracic  branches  from  the  axillary 
artery.     The  vessels  of  the  lower  spaces  and  the  subcostal  also  supply  the  upper  portions  of 
the  abdominal  muscles,  the  subcostal  anastomosing  with  branches  of  the  uppermost  lumbar 
artery  and  with  the  ascending  branch  of  the  superficial  circumflex  iliac  ;  the  lower  vessels  also 
give  off  numerous  branches  to  the  diaphragm  which  anastomose  with  the  phrenic  arteries 
from  the  abdominal  aorta.     Some  of  the  muscular  branches  which  arise  from  the  vessels  of  the 
third,  fourth,  and  fifth  spaces  send  branches  to  the  mammary  gland,  assisting  the  perforating 
branches  of  the  internal  mammary  and  the  long  thoracic  branch  of  the  axillary  in  the  supply  of 
that  structure.     These  intercostal  mammary  branches  (rami  mammarii  laterales)   may  become 
greatly  enlarged  during  lactation,  and  may  give  rise  to  considerable  hemorrhage  in  the  operation 
for  removal  of  the  gland. 

In  addition,  each  aortic  intercostal  gives  off  a  dorsal,  a  lateral  cutaneous,  and  a  collateral 
branch. 

(b)  The  dorsal  branch  (ramus  posterior)  arises  from  each  artery,  just  as  it  enters  its  inter- 
costal space,   and  passes  directly  backward,   in  company  with  the  posterior  division  of  the 
corresponding  spinal  nerve,  between  the  necks  of  the  adjacent  ribs  and  internal  to  the  superior 
costo-transverse  ligament.     Having  reached  the  vertebral  groove,  it  divides  into  a  spinal  and  a 
muscular  branch.     The  former  (ramus  spinalis)  passes  through  the  intervertebral  foramen  in 
company  with  the  root  of  the  spinal  nerve,  and,  within  the  spinal  canal,  gives  'off  branches  to 
the  body  of  the  vertebra  and  its  neural  arches  and  to  the  dura  mater,  and  also  branches  which 
pass  to  the  spinal  cord  and  anastomose  with  the  anterior  and  posterior  spinal  arteries.     The 
muscular  branch  (ramus  muscularis)  continues  posteriorly  in  the  direction  of  the  main  stem  of 
the  vessel  and  divides  into  an  external  and  an  internal  branch  which  pass  between  the  principal 
masses  of  the  dorsal  musculature,  supplying  these  and  terminating  in  branches  to  the  integu- 
ment of  the  back. 

(c)  The  lateral  cutaneous  branch  ( ramus  cutaneus  lateralis)  arises  at  about  the  axillary  line 
and  perforates  the  external  intercostal  muscle  in  company  with  the  lateral  cutaneous  branch  of 
the  corresponding  intercostal  nerve.     It  is  distributed  with  the  nerve  to  the  integument  of  the 
lateral  portions  of  the  thorax,  also  supplying  the  serratus  magnus  and  the  pectoral  muscles 
and  anastomosing  with  the  perforating  branches  of  the  internal  mammary  and  with  the  thoracic 
branches  of  the  axillary  artery. 

(d)  The  collateral  branch  arises  as  the  intercostal  approaches  the  angle  of  its  rib.     It 
s  obliquely  outward  and  downward  to  the  upper  border  of  the  rib  next  below,  along  which 

ms  to  terminate  by  anastomosing  with  the  lower  of  the  two  anterior  intercostal  branches 
given  off  by  the  internal  mammary  or  the  musculo-phrenic  to  each  intercostal  space.  The 
collateral  branches  of  the  three  lower  intercostals  are  small  and  inconstant  and,  when  present, 
terminate  in  the  abdominal  wall. 

Variations.— The  intercostal  arteries  of  the  first  and  second  spaces  usuallv  arise  from  the 

.upenor  intercostal  branch  of  the  subclavian,  but  occasionally  the  artery  of  the  second  space, 

ana  more  rarely  that  of  the  first,  may  arise  from  the  thoracic  aorta.     Or,  conversely,  the  arteries 

he  third  and  fourth  intercostal  spaces,  as  well  as  those  of  the  first  and  second,  may  arise 

superior  intercostal,  the  aortic  intercostals  being  correspondingly  reduced  in  number. 


794  HUMAN   ANATOMY. 

Occasionally  the  second  intercostal  is  formed  by  a  branch  from  the  first  aortic  intercostal 
which  runs  upward  to  the  second  space  over  the  neck  of  the  third  rib,  and  a  similar  condition 
may  be  met  with  in  the  lower  arteries,  two  or  more  intercostal  spaces  being  supplied  from  a 
common  stem.  Finally,  the  right  and  left  arteries  of  one  or  all  of  the  pairs  may  arise  from  a 
common  stem,  springing  from  the  posterior  median  line  of  the  aorta. 

Practical  considerations  of  the  thoracic  aorta  are  discussed  with  those  of  the  aortic  arch 
on  page  726. 

THE  ABDOMINAL   AORTA. 

The  abdominal  aorta  is  the  continuation  below  the  diaphragm  of  the  thoracic 
aorta.  It  may  be  said  to  begin,  therefore,  at  the  lower  border  of  the  twelfth  thoracic 
vertebra,  and  passes  downward  upon  the  bodies  of  the  four  upper  lumbar  vertebra 
lying  almost  in  the  median  line.  It  is  usually  described  as  terminating  opposite  the 
fourth  lumbar  vertebra  by  dividing  into  the  right  and  left  common  iliac  arteries, 
although  it  is  really  continued  onward  beyond  that  point  as  a  relatively  feeble  \ 
which  is  termed  the  middle  sacral  artery.  It  seems  advisable,  however,  to  adhere  to 
the  classic  definitions  of  the  artery,  and  to  regard  the  middle  sacral,  for  purposes  of 
description,  as  one  of  its  branches. 

Relations. — Posteriorly,  the  abdominal  aorta  rests  upon  the  anterior  com- 
mon ligament  of  the  four  upper  lumbar  vertebrae  and  crosses  the  left  lumbar  veins. 
Anteriorly,  in  its  uppermost  part,  it  is  invested  by  the  sympathetic  solar  plexus,  from 
which  branches  pass  downward  along  the  vessel,  forming  the  aortic  plexus.  A  little 
lower  it  is  crossed  by  the  splenic  vein,  the  pancreas,  the  left  renal  vein,  and  the 
third  portion  of  the  duodenum,  and  still  lower  it  is  in  relation  with  the  coils  of 
the  small  intestine,  from  which,  however,  it  is  separated  by  the  peritoneum.  Upon 
a  more  anterior  plane  there  are,  above,  the  left  lobe  of  the  liver,  and  the  stomach 
and  transverse  colon.  To  the  right,  it  is  in  contact,  in  its  upper  part,  with  the 
thoracic  duct  and  the  receptaculum  chyli,  which  lie  partly  covered  by  it,  and  with 
the  right  crus  of  the  diaphragm,  which  separates  it  from  the  inferior  vena  cava  ; 
lower  down  it  is  in  direct  contact  with  the  vena  cava.  To  the  left,  is  the  left  crus 
of  the  diaphragm  and  the  fourth  portion  of  the  duodenum  above,  while  below  it 
is  separated  by  the  peritoneum  from  coils  of  the  small  intestine,  and  has  running 
alongside  the  left  spermatic  (ovarian)  artery  and  vein,  and  still  more  laterally  the 
left  ureter. 

Branches. — The  branches  of  the  abdominal  aorta,  like  those  of  the  thoracic, 
may  be  divided  into  two  sets,  visceral  and  parietal. 

The  Visceral  branches  are  (i)  the  cceliac  axis,  (2)  the  superior  mesenteric, 
and  (3)  the  inferior  'mesenteric  artery.  These  are  median  unpaired  branches  which 
arise  from  the  anterior  surface  of  the  aorta;  in  addition,  there  are  a  number  of  paired 
visceral  branches:  (4)  the  inferior  phrenic,  (5)  the  suprarenal,  (6)  the  renal,  and  (7  i 
the  spermatic  or  ovarian  arteries. 

The  parietal  branches  are  (8)  the  lumbar  arteries,  of  which  there  are  four 
pairs,  (9)  the  middle  sacral,  and  (i°)  the  common  iliac  arteries.     With  the  excep 
tion  of  the  middle  sacral,  the  parietal  branches  are  all  paired. 

Considered  in  the  order  of  their  origin  from  the  aorta,  the  branches  are  ar- 
ranged thus:  (i)  The  inferior  phrenics,  (2)  the  cceliac  axis,  (3)  the  suprarenal s. 
(4)  the  superior  mesenteric,  (5)  the  first  pair  of  lumbar  arteries,  (6)  the  renal s, 
(7)  the  spermatics  or  ovarians,  (8)  the  second  pair  of  lumbars,  (9)  the  inferior 
mesenteric,  ( 10  and  1 1 )  the  third  and.  fourth  pairs  of  lumbars,  (12)  the  middle  sacral, 
and  (13)  the  common  iliacs. 

Variations  of  the  abdominal  aorta  are  not  common.  In  cases  in  which  tin- aortic  arch 
bends  to  the  right,  the  abdominal  aorta  may  lie  somewhat  to  tin-  right  of  the  median  line,  and  i: 
has  been  observed  to  pass  downward  upon  the  right  of  the  inferior  vena  cava.  Variations  also 
occur  in  the  level  at  which  the  aorta  bifurcates  Into  the  common  iliacs.  In  the  majority  of  cases 
the  bifurcation  is  opposite  the  middle  of  the  fourth  lumbar  vertebra,  but  it  is  not  infrequently 
lower,  taking  place  opposite  the  lower  half  of  that  vertebra,  opposite  the  succeeding  interver- 
tebral  disc,  or,  in  rare  cases,  opposite  the  upper  portion  of  the  fifth  vertebra.  Bifurcation  at  a 
higher  level  than  usual  is  less  t"iv<|m-nt,  but  it  lias  been  observed  as  high  as  opposite  the  inter- 
vertebral  disc  between  the  third  and  fourth  vertebra',  and,  in  very  rare  cases,  the  artery  has 
been  found  to  divide  as  high  as  the  second  lumbar  vertebra. 


THE   ABDOMINAL   AORTA 


795 


FIG.  718. 


Vertebral  artery 

Common  carotid  artery 

Superior  intercostal  artery 

Subclavian  artery 

Innominate  artery 

1   aortic  intercostal  artery 

Right  bronchus 

II.  and  III  aortic  intercostal 

arteries 

Right  and  left  coronary 

arteries 

Leaflets  of  aortic  semilunar 

valve 

IV. -VII  aortic  intercostal 
arteries 


Vena  azygos 
Thoracic  duct 


Subcostal  artery 
Part  of  right  crus  of 

diaphragm 

I.  lumbar  artery 
Quadratus  lumborum 

Superior  mesenteric  artery 

Suprarenal  artery 

Renal  artery 


Inferior  mesenteric 
artery 


Psoas  magnus          /  •  i 
muscle 


Iliac  branch  of 
ilio-lumbar  arterv 


Trachea 

Left  common  carotid  artery 
Scalenus  anticus  muscle 
Vertebral  artery 
Sectional  surface  of  I.  rib 
Superior  intercostal  artery 

I.  and  II.  aortic  intercostal 

Left  bronchus  arteries 

Aorta 

Upper  left  bronchial  artery 

(Esophagus 

Lower  left  bronchial  artery 


III.,  IV.  and  V.  aortic 

intercostals 
A  pericardia!  branch 

CEsophageal  branches 


VI. -X.  aortic  intercostal 

arteries 


An  cesophageal  branch 
Inferior  phrenic  arteries 
•Subcostal  artery 

•Coeliac  axis 

I.  lumbar  artery 

Lumbar  fascia — middle  layer 
Suprarenal  artery 
Renal  artery 

II.  lumbar  artery 


Spermatic  arteries 
III.  lumbar  artery 
Origin  of  quadratus  lumborum 


IV.  lumbar  arterv 


•Ji Middle  sacral  artery 


Left  common  iliac  artery 


Internal  iliac  artery 

-Ilio-lumbar  artery 
Posterior  trunk  ot int.  iliac 
-Anterior  trunk  of  int.  iliac 

-  External  iliac  artery- 


Aorta  and  its  branches  :  ten  intercostal  arteries  are  present,  first  supplying  second  space  ;  on  right 
side  internal  intercostal  muscles  are  in  position,  on  left  they  have  been  removed. 


796  HUMAN   ANATOMY. 

Although  the  abdominal  aortic  stem  is  very  constant  in  its  relations,  considerable  variation 
occurs  in  the  origin  of  its  branches.  Most  of  these  will  be  considered  in  connection  with  the 
description  of  the  branches  concerned,  but  it  may  be  noted  here  that  very  frequently  a  number 
of  small  branches,  terminating  in  the  neighboring  organs  or  connective  tissue  and  lymph-nodes, 
arise  from  the  abdominal  aorta,  in  addition  to  the  branches  which  have  already  been  named. 
These  small  branches  are  rather  inconstant,  and  may  arise  from  either  the  anterior  surface  of 
the  aorta,  in  which  case  they  are  unpaired  vessels,  or  in  pairs  from  its  sides. 

Their  existence  seems  to  indicate  the  occurrence  of  a  primitively  strictly  segmental  arrange- 
ment of  the  branches  of  the  abdominal  aorta,  and  a  type-condition  has  been  supposed  to  occur 
in  which  the  aorta  gives  off,  opposite  each  segmental  interval  that  it  passes,  three  pairs  of  ves- 
sels, which   arrange  themselves  in  three  distinct   sets 

FIG   710  (I'lR   7'9)'     One  set  arises  from  the  anterior  surface  of 

the  aorta,  and  is  usually  reduced,  either  by  fusion  or 
by  the  degeneration  of  one  or  other  of  each  pair,  to  a 
single  unpaired  vessel  for  each  segment ;  a  second  set 
arises  from  the  sides  of  the  aorta  and,  like  the  first  set, 
is  distributed  to  the  abdominal  viscera;  and  a  third  set 
arises  from  the  posterior  surface  of  the  aorta  and  is  dis- 
tributed to  the  abdominal  parietes. 

Of  the  unpaired  set  of  vessels,  only  three  persist 
until  adult  life,  becoming  the  cceliac  axis  and  the  sup- 
erior and  inferior  mesenteric  arteries,  the  position  oc- 
cupied by  these  vessels  in  the  adult  being  due  to  a 
downward  migration  which  they  undergo,  the  cu-liac 
axis  representing  the  ventral  visceral  branch  of  the 
fourth  thoracic  or  possibly  a  higher  segment,  the  sup- 
erior mesenteric  that  of  the  seventh  thoracic,  and  the 
inferior  mesenteric  that  of  the  twelfth  thoracic.  The 
paired  visceral  branches  are  developed  mainly  in  con- 
nection with  the  embryonic  kidney,  and  on  the  replace- 
ment  of  this  by  the  adult  organ  the  majority  of  them 
body-trunk  (aorta) ;  s,  somatic  branch  to  body-  disappear,  the  suprarenal,  renal,  and  spermatic  arteries 
walls,  C  paired  visceral  branches;  Z>, unpaired  and  certain  inconstant  branches  which  are  lost  in  the 

neighboring  connective  tissue  representing  them  in  the 
adult.  Of  the  parietal  paired  set,  the  four  pairs  of 

lumbar  arteries  correspond  to  the  four  upper  lumbar  segments,  while  the  common  iliacs  are 
the  branches  of  the  fifth  lumbar  segment.  The  lumbar  arteries  are  evidently  serially  homolo- 
gous with  the  thoracic  intercostals  and  present  many  similarities  to  the  lower  members  of  that 
series,  but  the  common  iliacs  are  peculiar  in  that  they  give  rise  to  branches  which  pass  to  the 
pelvic  viscera,  a  condition  which  may  be  explained  by  the  fact  that  the  paired  visceral  branches 
of  the  third  lumbar  segment  unite  with  them  and  are  represented  by  the  hypogastric  artery 
and  its  branches. 

Practical  Considerations. — The  abdominal  aorta  is  the  subject  of  aneurism 
much  more  rarely  than  is  the  thoracic  aorta,  because  of  the  relatively  less  powerful 
cardiac  impulse  which  reaches  it.  The  sac  is  most  often  situated  in  the  neighbor- 
hood of  the  cceliac  axis  because  (#)  in  this  region  the  artery  has  lost  the  support 
afforded  by  the  tendinous  arch  of  the  diaphragm,  which  produces  a  constriction  in 
its  walls  at  each  ventricular  systole  ;  (£)  it  rather  suddenly  contracts  about  one  and 
a  half  inches  below  this  level  (after  having  given  off  a  number  of  large  branches), 
so  that  the  intervening  portion  is  somewhat  fusiform  or  pouched  (Agnew)  ;  (Y)  the 
pressure  on  this  aortic  segment  is  increased  by  the  sudden  alteration  in  the  direction 
of  the  blood-current  caused  by  the  presence  of  these  branches  (the  inferior  phn-nics, 
the  cceliac  axis,  the  suprarenals,  superior  mesenteric,  etc.);  and  (</)  the  walls  at 
this  point  are  said  to  be  intrinsically  weak,  often  giving  way  (Woolsey)  during  injec- 
tions of  the  cadaver.  The  aneurism  may  occupy  any  aspect  of  the  vessel,  but  is 
more  commonly  on  the  anterior  wall,  which  receives  less  support.  As  it  enlarges  it 
will  cause  some  or  all  of  the  following  symptoms  : 

i.  Tumor  in  the  epigastric  or  hypochondriac  region  (usually  the  left  because 
there  is  less  resistance  from  surrounding  organs  and  because  the  artery  inclines  in 
that  direction),  having  the  characteristic  bruit  and  expansile  pulsation,  commonly 
capable  of  being  outlined  by  palpation  or  grasped  (distinguishing  it  from  a  "  throb- 
bing aorta"),  and  unchanged  as  to  pulsation  and  impulse  when  the  patient  is  put  in 
the  knee-elbow  position  (eliminating  growths  of  the  left  lobe  of  the  liver,  the  pylorus, 
or  the  pancreas,  in  which  the  tumor  falls  forward — />,  downward — and  the  impulse 
lessens  or  disappears)  (Osier).  2.  Dyspnoea  from  interference  with  the  descent  of 
the  diaphragm.  3.  Dysphagia  from  pressure  on  the  cesophageal  opening.  4.  Dys- 


THE   VISCERAL    BRANCHES.  797 

pepsia  and  vomiting  directly  from  pressure  upon  the  stomach,  and  indirectly  from 
involvement  of  the  solar  plexus.  5.  Jaundice  from  compression  of  the  common 
duct  and  duodenum.  6.  Polyuria  followed  by  albuminuria  and  hcematuria  or  anuria 
from  pressure  on  the  renal  nerves.  7.  Oedema  of  the  legs  and  feet  from  pressure  on 
the  ascending  cava.  If  the  tumor  enlarges  posteriorly  there  is  apt  to  be  also  : 
8.  Pain  in  the  buttocks,  thighs,  and  loins  from  pressure  on  the  lumbar  nerves,  and 
in  the  back  from  pressure  on  the  solar  plexus  and  splanchnics,  or  from  erosion  of  the 
vertebra  ;  and  rarely  there  may  be  :  9.  Weakness  or  paralysis  of  the  lower  extremities 
from  involvement  of  the  cord.  As  a  rule,  the  pain,  distress,  and  disability  are  not  so 
great  in  abdominal  as  in  thoracic  aneurism,  because  of  the  greater  mobility  of  the 
abdominal  contents,  which  can  be  much  more  easily  displaced  than  those  of  the 
middle  or  posterior  mediastinum  and  with  consequences  not  so  directly  threatening  life. 

Abdominal  aneurisms  rupture  into  the  retroperitoneal  space,  the  peritoneal 
cavity,  the  intestines  (most  often  the  duodenum),  or — after  ulcerating  through  the 
diaphragm — into  the  pleura. 

Compression  of  the  abdominal  aorta  may  be  effected  by  special  tourniquets,  the 
intestines  being  first  well  emptied  and  then  got  out  of  the  way,  as  far  as  possible, 
by  rolling  the  patient  on  the  right  side  before  applying  the  pad,  between  which  and 
the  skin  a  soft  sponge  should  be  interposed.  The  pad  is  placed  a  little  to  the  left 
of  the  umbilicus,  or,  better — as  the  aorta  may  be  median  in  position — directly  over 
the  pulsation  of  the  vessel.  Macewen  has  effectively  controlled  the  abdominal  aorta 
by  throwing  the  weight  of  the  body  on  the  aorta  through  the  closed  right  hand  placed 
a  little  to  the  left  of  the  middle  line,  the  knuckle  of  the  index-finger  just  touching 
the  upper  border  of  the  umbilicus.  With  the  left  hand  the  arrest  of  the  blood-cur- 
rent is  ascertained  by  feeling  the  femoral  at  the  brim  of  the  pelvis.  Only  enough 
weight  to  arrest  the  femoral  pulse  is  required.  If  the  patient  vomits  or  coughs,  the 
pressure  must  be  increased,  lest  the  hand  be  lifted  from  the  aorta  by  the  abdominal 
muscles. 

Of  course  these  methods  would  be  applicable  only  to  aneurisms  situated  near 
the  bifurcation.  Compression  has  cured  at  least  one  such  case.  They  have,  how- 
ever, been  applied  in  iliac  and  common  femoral  aneurism  and  to  control  hemorrhage 
during  inter-ilio-abdominal  or  hip-joint  amputation. 

Ligation  of  the  abdominal  aorta  has  been  done  in  about  a  dozen  cases  with 
uniformly  fatal  results.  The  ligature  has  been  applied  between  the  bifurcation  and  the 
origin  of  the  inferior  mesenteric  artery — one  and  a  half  to  two  inches  higher.  A  median 
incision  with  its  centre  at  the  umbilicus  is  made,  the  peritoneal  cavity  opened,  and 
the  intestines  displaced.  The  layer  of  peritoneum  over  the  artery  is  carefully  divided 
— or  scratched  through — and  the  vessel  isolated,  avoiding  the  sympathetic  fibres 
connecting  the  aortic  plexus  (lying  above  the  origin  of  the  inferior  mesenteric) 
with  the  hypogastric  plexus  (lying  between  the  common  iliacs)  (Astley  Cooper, 
Jacobson).  The  dense  areolar  tissue  surrounding  the  vessel  is  penetrated  and  the 
aneurism  needle  is  passed  through  it  from  right  to  left  to  avoid  injury  to  the  vena 
cava.  The  extraperitoneal  operation  closely  resembles  that  for  ligation  of  the  common 
iliac  (page  808). 

THE   VISCERAL    BRANCHES. 

i.  The  Coeliac  Axis. — The  cceliac  axis  (a.  coeliaca)  (Figs.  720,  721)  arises 
from  the  anterior  surface  of  the  abdominal  aorta,  a  short  distance  below  the  aortic 
opening  of  the  diaphragm,  and  is  a  short,  stout  trunk  from  1-1.5  cm.  in  length, 
which  projects  forward  above  the  upper  border  of  the  pancreas.  It  terminates  by 
dividing  simultaneously  into  (i)  the  gastric,  (2)  hepatic,  and  (3)  splenic  arteries.  . 

Variations. — The  cceliac  axis  may  be  wanting,  the  three  branches  to  which  normally  it 
gives  origin  arising  independently  from  the  aorta.  Occasionally  it  gives  rise  to  but  two  terminal 
branches,  usually  the  hepatic  and  splenic,  although  more  rarely  they  may  be  the  gastric  and 
splenic  ;  or,  while  dividing  into  three  terminal  branches,  these  may  be  the  gastric,  hepatic,  and 
a  common  stem  from  the  two  inferior  phrenics  ;  the  gastric,  splenic,  and  the  right  suprarenal ; 
or  the  gastric,  splenic,  and  the  right  gastro-epiploic.  It  may  also  give  rise  to  additional  branches, 
such  as  one  or  both  of  the  inferior  phrenics,  a  gastro-duodenal,  the  superior  mesenteric,  the 
colica  media,  or  the  pancreatica  magna,  this  last  being  normally  a  branch  of  the  splenic  artery. 


798 


HUMAN   ANATOMY. 


(a)  The  Gastric  Artery. — The  gastric  artery  (a  gastrica  sinistra)  (Fig.  720)  is 
the  smallest  of  the  three  branches  given  off  from  the  coeliac  axis.  In  the  first  portion 
of  its  course  it  passes  to  the  left  and  slightly  upward,  across  the  left  crus  of  the 
diaphragm,  lying  behind  the  posterior  layer  of  the  lesser  sac  of  peritoneum.  It  reaches 
the  lesser  curvature  of  the  stomach  near  the  opening  of  the  oesophagus  into  that 
viscus,  where  the  upper  part  of  the  posterior  wall  of  the  lesser  sac  of  peritoneum  passes 
over  upon  the  stomach  to  become  continuous  with  the  posterior  layer  of  the  lesser 


Right  lobe  of  liver 


Gall  bladder 

Common  bile  duct 

Inferior  vena  cava 

Castro-duodenal  artery 

Right  kidney 

Pyloric  branch 

of  hepatic  artery 

Duodenum 

Pancreas 
Ascending  colon 

Crest  of  ilium 

Right  gastro-epiploic 
artery 


Abdominal  aorta 
Spleen 
Cceliac  axis 
Gastric  artery 

Cut  edge  of  diaphragm 


Splenic  Iiranches 
of  splenic  artery 

Splenic  artery 

Superior  mesenteric 
artery 


Left  gastro- 
epiploic  artery 


pStomach 
-«if— Transverse  colon 


Branches  of 

mi.  idle  colic 
artery 


Coeliac  axis  and  its  branches. 

(gastro-hepatic)  omentum.  It  then  curves  forward,  downward,  and  to  the  right 
along  the  lesser  curvature  of  the  stomach,  lying  between  the  two  lavrrs  of  the  lesser 
omentum,  frequently  dividing  into  two  parallel  stems  in  this  portion  of  its  course, 
and  terminates  near  the  pyloric  end  of  the  stomach  by  anastomosing  with  the  pyloric 
branch  of  the  hepatic  artery. 

Branches. — Just  at  the  point  where  the  gastric  artery  reaches  the  stomach  it  gives  off — 
(aa)  OEsophageal  branches   (rami  resophagci )   which   pass  upward    to  supply   tin-   lower 
portion  of  the  u-sophagus,  anastomosing  with  the  usophageal  branches  of  the  thoracic  aorta 
and  with  branches  of  the  inferior  phrenic  arteries.     Throughout  the  entire  length  of  its  course 
along  the  lesser  curvature  of  the  stomach  the  gastric  artery  gives  rise  to — 


THE   VISCERAL    BRANCHES.  799 

(bb)  Gastric  branches  which  pass  downward  over  both  surfaces  of  the  stomach,  anasto- 
mosing with  the  short  gastric  branches  from  the  splenic  artery  and  with  the  gastric  branches 
which  pass  upward  from  the  gastro-epiploic  arch  which  passes  along  the  greater  curvature  of 
the  stomach.  Some  of  the  branches  which  arise  from  the  more  proximal  portion  of  the  artery 
and  ramify  over  the  cardiac  portion  of  the  stomach  are  frequently  described  as  the  cardiac 
branches. 

(cc)  A  small  hepatic  branch  passes  upward  between  the  two  layers  of  the  lesser  omentum 
towards  the  left  end  of  the  transverse  fissure  of  the  liver,  where  it  anastomoses  with  the  left 
branch  of  the  hepatic  artery. 

Variations. — The  gastric  artery  occasionally  arises  directly  from  the  abdominal  aorta,  in 
which  case  it  may  give  rise  to  one  or  both  of  the  inferior  phrenic  arteries.  Its  hepatic  branch  is 
not  infrequently  enlarged,  and  then  constitutes  the  main  stem  of  the  left  branch  of  the  hepatic 
artery,  which  thus  seems  to  arise  from  the  gastric 

(<$)  The  Hepatic  Artery. — In  the  first  portion  of  its  course  the  hepatic  artery 
(a.  hepatica)  (Figs.  720,  721)  passes  from  left  to  right  and  slightly  forward,  over  the 
right  crus  of  the  diaphragm,  lying  beneath  the  posterior  wall  of  the  lesser  sac  of  perito- 
neum. Where  this  passes  over  into  the  posterior  layer  of  the  lesser  (gastro-hepatic) 
omentum  towards  the  right,  the  artery  bends  upward  and  ascends,  in  the  free  edge  of 
the  lesser  omentum,  towards  the  transverse  fissure  of  the  liver,  where  it  divides  into 
two  terminal  branches. 

Relations. — In  the  first  portion  of  its  course  the  hepatic  artery  rests  below 
upon  the  upper  border  of  the  head  of  the  pancreas  and  is  in  contact  above  with  the 
lower  surface  of  the  Spigelian  lobe  of  the  liver,  upon  which  it  frequently  makes  a 
distinct  impression.  It  lies  at  first  upon  a  plane  posterior  to  the  portal  vein,  but 
later  it  crosses  the  left  surface  of  the  vein  and  comes  to  lie  in  front  of  it.  In  its 
course  upward  in  the  free  edge  of  the  lesser  omentum  the  artery  lies  anteriorly  to  the 
portal  vein  and  upon  the  left  side  of  the  common  bile-duct. 

Branches. — As  the  hepatic  artery  passes  between  the  two  layers  of  the  lesser  omentum  it 
gives  origin  to  two  branches,  the  pyloric  and  the  gastro-duodenal. 

(aa)  The  pyloric  branch  (a  gastrica  dextra)  is  the  smaller  of  the  two.  It  descends  to  the 
pyloric  end  of  the  stomach  and  then,  bending  to  the  left,  runs  along  the  lesser  curvature  of  the 
stomach,  between  the  two  layers  of  the  lesser  omentum,  and  terminates  by  anastomosing  with 
the  gastric  artery,  It  gives  branches  to  either  side  of  the  pyloric  extremity  of  the  stomach  and, 
like  the  gastric  artery,  is  frequently  represented  by  two  parallel  vessels. 

(bb)  The  gastro-duodenal  (a.  gastroduodenalis),  the  larger  branch,  descends  behind  the 
first  portion  of  the  duodenum  and  terminates  at  its  lower  border  by  dividing  into  two  branches, 
the  superior  pancreatico-duodenal  and  the  right  gastro-epiploic, 

(aaa)  The  superior  pancreatico-duodenal  branch  (a  pancreaticoduodenalis  superior)  descends 
to  the  head  of  the  pancreas,  upon  the  surface  of  which  it  anastomoses  with  branches  of  the 
inferior  pancreatico-duodenal  branch  of  the  superior  mesenteric  artery.  It  sends  branches  into 
the  substance  of  the  gland  and  to  the  walls  of  the  duodenum. 

(bbb)  The  right  gastro-epiploic  artery  (a.  gastroepiploica  dextra)  passes  to  the  left  along  the 
greater  curvature  of  the  stomach,  between  the  folds  of  the  greater  omentum,  and  inosculates 
with  the  left  gastro-epiploic  branch  of  the  splenic  artery.  It  sends  branches  upward  upon  both 
surfaces  of  the  stomach,  which  anastomose  with  branches  from  the  gastric  artery  and  from  the 
pyloric  branch  of  the  hepatic,  and  other  branches  pass  downward  into  the  greater  omentum 
(epiploon). 

(cc)  The  terminal  branches  are  two  in  number  and  pass  the  one  to  the  right  and  the  other 
to  the  left  lobe  of  the  liver  The  right  branch  (  ramus  dexter)  passes  towards  the  right  extremity 
of  the  transverse  fissure  of  the  liver,  its  course  lying  either  in  front  of  the  hepatic  and  cystic 
ducts  or  between  these  two  structures.  At  the  extremity  of  the  fissure  it  divides  into  a  number 
of  branches  which  enter  the  substance  of  the  right  lobe  of  the  liver.  As  it  passes  across  the 
hepatic  duct  it  gives  off  a  cystic  branch  (a  cystica)  which  runs  downward  and  forward  along 
the  cystic  duct  to  the  gall-bladder,  whose  walls  it  supplies,  also  giving  some  small  branches  to 
the  liver.  The  left  branch  (ramus  sinister)  is  directed  towards  the  left  end  of  the  transverse 
fissure,  and.  after  giving  off  one  or  two  branches  which  enter  the  substance  of  the  Spigelian 
lobe,  terminates  by  dividing  into  a  number  of  branches  which  enter  the  left  lobe  of  the  liver. 

Variations. — Variations  of  the  hepatic  artery  are  exceedingly  frequent.  The  artery  itself 
may  arise  directly  from  the  aorta  instead  of  from  the  coeliac  axis.  or.  by  the  enlargement  of  its 
anastomoses  and  the  diminution  of  the  normal  main  stem,  it  may  appear  to  be  a  branch  of  the 


8oo 


HUMAN   ANATOMY. 


gastric  or  more  frequently  of  the  superior  mesenteric  artery.  It  has  also  been  described  as 
arising  from  the  right  renal  artery.  Further,  by  the  enlargement  of  anastomoses,  associated 
with  a  persistence  of  the  normal  mam  stem,  accessory  hepatic  arteries  from  the  gastric  or 
superior  mesenteric,  or  both,  may  be  present,  and  an  accessory  stem  may  arise  from  the  aorta. 
Great  variation  occurs  in  the  point  at  which  the  artery  divides  into  its  two  terminal 
branches.  This  division  may  occur  as  low  down  as  the  origin  of  the  gastro-duodenal  branch 
so  that  in  its  course  up  the  free  edge  of  the  lesser  omentum  the  artery-  may  be  represented  by 
two  parallel  stems  which  pass  respectively  to  the  right  and  left  lobes  of  the  liver.  Indeed,  not 
only  may  there  be  a  precocious  division  into  the  two  terminal  branches,  but  each  of  these  may 
again  divide,  almost  at  their  origin,  into  two  or  more  stems,  so  that  a  number  of  parallel  vessels". 
one  of  which  usually  represents  the  cystic  branch,  ascend  to  the  liver.  Occasionally  the  cystic 
branch  or  an  accessory  cystic  branch  arises  from  the  gastro-duodenal,  and  this  latter  vessel  may 
arise  from  the  cxjeliac  axis,  while  the  liver  and  gall-bladder  are  supplied  by  a  stem  which  arises 
from  the  superior  mesenteric  (Brewer). 

(V)  The  Splenic  Artery.— The  splenic  artery  (a.  lienalis)  (Figs.  720,  721; 
is  the  largest  branch  of  the  cceliac  axis.  It  passes  in  a  more  or  less  tortuous  course 
over  the  left  crus  of  the  diaphragm  and  along  the  upper  border  of  the  pancreas,  lying 
behind  the  posterior  wall  of  the  lesser  sac  of  the  peritoneum.  It  crosses  the  anterior 

FIG.  721. 


Under  surface  of  left  lobe  of  liver        Gastric  artery 


CEsophajjeal  branches 


Abdominal  aorta 


Coeliac  axis 

Cystic  branch  of  hepatic 

Common  Me  duct 

End  of  renal  vein  in  vena  cava 

IIe|ntic  artery 

Portal  vein 

Gastro-duodenal  artery  — 
Duodenum  *" 
Splenic  vein  " 
Superior  mesenteric  vein  - 
Right  gastro-epiploic  artery 
Superior  pancreatico-  ' 
duodenal  artery 


Inferior  pancreatico- 

duodenal  artery 


Ascending  colon 
Middle  colic 


Superior  mesenteric  artery 
Splenic  artery 

Transverse  colon,  turned  up 
Left  kidney- 


t;astro-epipl.)ic 
artery 

lirnncli  to  jjreatomentu 


-  Descending  colon 
Duodenum 


Right  col 


Coeliac  axis  and  its  branches  :  stomach  has  been  removed  and 
transverse  colon  turned  up. 

stirface  of  the  left  suprarenal  capsule  and  the  upper  part  of  the  left  kidney,  and, 
passing  between  the  two  layers  of  the  lieno-renal  ligament,  reaches  the  hilum  of  the 
spleen,  where  it  breaks  up  into  a  number  of  branches  which  pass  to  the  substance  <>f 
that  organ. 

Branches. — (aa)  Pancreatic  branches  (rami  pancreatic!)  are  given  off  from  the  splenic  artery 
throughout  the  entire  extent  of  its  course  along  the  upper  border  of  the  panm-as  and  supply 
that  organ.  One  branch,  much  larger  than  the  others  (a.  pancrcaiica  manna),  arises  at  about 
the  junction  of  the  middle  and  left  thirds  of  the  artery  and.  entering  the  substance  of  the  gland 
obliquely,  passes  from  left  to  right  along  with  the  pancreatic  duct. 

(bk]  Short  gastric  branches  (aa  gastricac  breves  V  variable  in  number,  are  ,i;i\en  off  either 
from  the  terminal  portion  of  the  artery  or  from  some  of  its  terminal  branches  'They  p.is^ 
between  the  layers  of  the  gastro-splenic  omentum  to  the  left  end  of  the  greater  curvature  of  the 
stomach,  and.  passing  upon  the  surfaces  of  that  organ,  supplv  it,  and  anastomose  with  the  cardiac 
branches  of  the  gastric-  artery  and  with  the  branches  of  the  left  gastro-epiploic. 


THE   VISCERAL    BRANCHES, 


80 1 


(cc)  The  left  gastro-epiploic  artery  (a.  gastroepiploica  sinistra )  arises  close  to  the  termination 
of  the  splenic  and  passes  between  the  layers  of  the  gastro-splenic  omentum  to  the  greater  curvature 
of  the  stomach,  along  which  it  runs  between  the  layers  of  the  greater  omentum,  and  terminates  by 
inosculating  with  the  right  gastro-epiploic  branch  of  the  hepatic  artery.  Throughout  its  course  it 
gives  off  numerous  branches  which  pass,  on  the  one  hand,  upward  upon  both  surfaces  of  the 
stomach  to  anastomose  with  branches  of  the  gastric  artery,  and,  on  the  other  hand,  downward 
into  the  greater  omentum. 

Variations.— The  splenic  is  remarkably  constant  in  its  course  and  branches.  It  may  arise 
directly  from  the  aorta,  and  it  has  been  observed  to  give  off  the  gastric  artery,  a  large  branch 
to  the  left  lobe  of  the  liver,  and  the  middle  colic  artery. 

2.  The  Superior  Mesenteric  Artery.  — The  superior  mesenteric  artery 
(a.  mesenterica  superior)  (Figs.  721,  722)  arises  from  the  anterior  surface  of  the 
abdominal  aorta,  about  1.5  cm.  below  the  cceliac  axis.  It  lies  at  first  behind  the 
pancreas,  but,  passing  downward  and  forward,  it  emerges  between  that  organ  and 
the  upper  border  of  the  third  portion  of  the  duodenum  and  enters  the  mesentery. 

FIG.  722. 


Transverse  colon 


Pancreas 
Superior  mesenteric 

artery 

Middle  colic  artery 
Duodenum 


Right  colic  artery 
Ascending  colon 

Ileo-colic  artery 

Anterior  superior 
spine  of  ilium 

Branches  to 

small  intestine 

Caecum 


Posterior  surface 
of  stomach 


Left  colic  artery 
Duodenum 

:^  Crest  of  ilium 


Branches  to  small 
intestine 


Anterior  superior 
spine  of  ilium 

Part  of  jejunum 


Parts  of  ileum 


Superior  mesenteric  artery  and  its  branches  ;  transverse  colon  and 
stomach  have  been  drawn  upward. 

It  passes  downward  between  the  two  layers  of  the  mesentery,  gradually  curving 
towards  the  right,  and  terminates  near  the  junction  of  the  ileum  with  the  caecum  by 
anastomosing  with  its  own  ileo-colic  branch. 

Branches. — The  superior  mesenteric  artery  supplies  the  whole  length  of  the  small  intestine, 
with  the  exception  of  the  upper  part  of  the  duodenum,  and  also  a  considerable  portion  of  the 
large  intestine,  including  the  caecum  and  appendix,  the  ascending  colon,  and  about  half  the 


802  HUMAN   ANATOMY. 

transverse  colon.  The  lower  portions  of  the  duodenum  and  ileum  and  the  large  intestine  are 
supplied  by  branches  given  off  from  the  concave  surface  of  the  artery,  while  the  rest  of  the  small 
intestine  receives  its  supply  from  a  somewhat  variable  number  of  branches  which  arise  from 
the  convex  surface. 

(a)  The  inferior  pancreatico-duodenal  (a.  pancreaticoduodenalis  inferior)   is  a  small  vessel 
which  usually  arises  from  the  superior  mesenteric  just  as  it  emerges  from  beneath  the  pancreas, 
although  it  occasionally  is  given  off  by  the  uppermost  of  the  intestinal  branches.    It  passes  towards 
the  right  along  the  upper  border  of  the  third  portion  of  the  duodenum,  and  supplies  that  portion 
of  the  intestine,  as  well  as  the  neighboring  portions  of  the  pancreas,  and  anastomoses  with  the 
superior  pancreatico-duodenal  branch  of  the  hepatic  artery. 

(b)  The  intestinal  branches  (tami  iniestinales),  also  called  rasa  intestini  tennis,  are  from 
ten  to  sixteen  in  number,  and  arise  from  the  convex  surface  of  the  artery,  those  branches  which 
arise  from  the  upper  portion  of  the  parent  stem  being,  in  general,  larger  than  the  lower  ones. 
The  first  two  or  three  branches,  as  they  pass  towards  the  intestine  between  the  two  layers  of 
the  mesentery,  divide  into  an  ascending  and  a  descending  branch,  and  these  branches  inosculate 
to  form  a  series  of  primary  arches,  which  run,  in  a  general  way,  parallel  with  the  intestine. 
Lower  down,  in  addition  to  these  primary  arches,  secondary  ones  are  formed  by  the  inosculation 
of  branches  given  off  proximally  to  those  which  form  the  primary  arches  ;  still  later,  tertiary  arches 
make  their  appearance,  and  finally  the  arrangement  becomes  so  complicated  as  to  resemble 
a  net-work  rather  than  a  definite  series  of  arches.     From  the  convex  surfaces  of  the  primary 
arches  a  large  number  of  parallel  straight  branches  pass  to  the  intestine  and  are  distributed  to 
its  walls.     They  rarely  branch  in  their  course  through  the  mesentery,  and  are  usually  distributed 
to  one  side  of  the  intestine  and   then  to  the  other  alternately.     The  rich  anastomosis  which 
occurs  between  the  various  intestinal  branches,  and  which  varies  greatly  in  its  complexity,  serves 
to  equalize  the  supply  of  blood  to  the  entire  length  of  the  intestine  and  to  permit  of  abundant 
and  rapidly  collateral  circulation  to  any  portion  of  the  tract  from  which  the  direct  supply  may- 
be cut  off  by  pressure  exerted  during  peristalsis. 

(r)  The  ileo-colic  artery  (a.  ileocolica)  arises  about  half-way  down  the  concave  surface  of 
the  superior  mesenteric  either  independently  or  in  common  with  the  right  colic  branch.  It 
passes  downward  and  outward,  beneath  the' peritoneum,  towards  the  ileo-C£ecal  junction,  giving 
off  branches  which  inosculate  with  the  right  colic  above,  with  the  terminal  portion  of  the  supe- 
rior mesenteric  below,  and,  in  the  interval,  with  one  another  to  form  a  series  of  arches  from 
which  branches  are  supplied  to  the  terminal  portion  of  the  ileum,  to  the  ccecum  and  the  vermi- 
form appendix  (a.  appendicularis)  and  to  the  lower  third  of  the  ascending  colon. 

(d  )  The  right  colic  artery  (a.  colica  dextra)  arises  from  the  concave  surface  of  the  superior 
mesenteric  either  a  short  distance  above  or  in  common  with  the  ileo-colic.  It  runs  towards  the 
right,  behind  the  peritoneum,  passing  over  the  right  psoas  muscle,  the  ureter,  and  the  spermatic 
(or  ovarian)  vessels,  and  as  it  approaches  the  ascending  colon  it  divides  into  an  ascending  and 
a  descending  branch.  These  inosculate  respectively  with  the  middle  colic  and  the  ileo-colic  to 
form  arches,  from  which  branches  pass  to  the  upper  two-thirds  of  the  ascending  and  to  a  portion 
of  the  transverse  colon. 

(e)  The  middle  colic  artery  (a.  colica  media)  arises  from  the  concave  surface  of  the  superior 
mesenteric  a  little  below  the  origin  of  the  inferior  pancreatico-duodenal  branch.  It  passes  for- 
ward and  downward  between  the  two  layers  of  the  transverse  mesocolon,  and  divides  into  a 
right  and  left  branch  which  inosculate  respectively  with  the  right  colic  and  with  the  left  colic 
branch  of  the  inferior  mesenteric  to  form  arches,  from  which  branches  pass  to  the  transverse 
colon. 

Variations. — Considerable  variation  occurs  in  the  number  and  position  of  the  branches  of 
the  superior  mesenteric  artery  and  also  in  the  complexity  of  the  anastomoses  which  occur 
between  these.  In  addition  to  those  usually  present,  branches  may  be  sent  to  any  of  the  neigh- 
boring organs,  such  as  the  liver,  stomach,  and  spleen,  and  the  artery  may  give  rise  to  the  hepatic, 
as  already  pointed  out,  or  to  the  gastro- duodenal,  or  even  the  gastric  or  renal  artery.  It  has 
been  observed  to  supply  the  place  of  the  inferior  mesenteric  artery  when  that  vessel  was  lacking, 
giving  off  left  colic,  sigmoid,  and  superior  hemorrhoidal  branches. 

From  the  embryologieal  stand-point  the  superior  mesenteric  represents  the  intestinal 
branch  of  the  omphalo-niesenteric  artery,  which,  during  the  early  months  of  fatal  lite,  passes 
outward  through  the  umbilicus  to  be  distributed  upon  the  surface  of  the  yolk-sac.  Usually  this 
artery  disappears,  except  in  so  far  as  it  is  concerned  in  the  formation  of  the  superior  mesenteric 
artery;  but  it  has  been  observed  to  persist,  appearing  as  a  branch  of  the  superior  mesenteric 
which  is  continued  forward  in  a  strand  of  connective  tissue  from  the  ileum  to  the  umbilicus, 
where  it  anastomoses  with  the  epigastric  artery -and  sends  a  branch  upward  along  with  the 
round  ligament  of  the  liver. 

3.  The  Inferior  Mesenteric  Artery. — The  inferior  mesenteric  artery  (a. 
mesenterica  inferior)  (Fit;.  723)  arises  from  the  anterior  surface  of  the  abdominal 
aorta  from  3-40111.  above  the  bifurcation  of  that  vessel  into  the  two  common  iliacs. 


THE   VISCERAL    BRANCHES. 


803 


It  passes  downward  and  to  the  left,  beneath  the  peritoneum  and  resting  upon  the 
left  psoas  muscle,  and,  after  having  crossed  the  left  common  iliac,  it  terminates  upon 
the  upper  portion  of  the  rectum,  this  terminal  portion  being  called  the  superior  hem- 
orrhoidal artery. 

Branches.— (a)  The  left  colic  artery  (a.  colica  sinistra)  arises  shortly  below  the  origin  of 
the  artery  and  passes  upward  and  to  the  left.  It  divides  into  an  ascending  and  a  descending 
branch,  the  former  of  which  passes  between  the  two  layers  of  the  transverse  mesocolon  to  inos- 
culate with  the  middle  colic  branch  of  the  superior  mesenteric,  while  the  descending  branch, 
filtering  the  sigmoid  mesocolon,  anastomoses  with  the  sigmoid  arteries.  From  the  arches  thus 
formed  branches  pass  to  the  left  portion  of  the  transverse  colon  and  to  the  whole  of  the  descend- 
ing colon. 

(b)  The  sigmoid  branches  (aa.  sigmoideae ),  two  or  three  in  number,  are  given  off  as  the 
inferior  mesenteric  crosses  the  left  common  iliac.  They  run  downward  and  to  the  left  over  the 

FIG.  723. 


Transverse  colon,  turned  upward 


Part  of  transverse 
mesocolon 

Splenic  artery 
Parcreatica  niagna 

Inferior  pancre- 
atico-duodenal 

artery 


Left  kidney 

Inferior  mesenteric  artery 
Left  colic 
Descending  colon 
Sigmoid  artery 


Middle  hemorrhoidal 
branches  of 

internal  iliac 


Termination  of 

ileum,  cut 


-Sigmoid  flexure 


Superior  hemorrhoidal  artery- 
Ion  posterior  surface  of  rectuin) 


Anterior  surface  of  rect 


Superior  and  inferior  mesenteric  arteries ;   small  intestine  has  been  removed. 

left  psoas  muscle  and,  passing  between  the  two  layers  of  the  sigmoid  mesocolon,  give  off  as- 
cending and  descending  branches  which  anastomose  with  one  another  and  with  the  left  colic 
and  superior  hemorrhoidal  arteries,  forming  with  them  arches  from  which  branches  pass  to  the 
sigmoid  colon. 

(c)  The  superior  hemorrhoidal  artery  (a.  haemorrhoidalis  superior )  is  the  terminal  portion 
of  the  superior  mesenteric.  It  descends  into  the  pelvis  lying  between  the  folds  of  the  mesentery 
of  the  pelvic  portion  of  the  colon-,  and  at  the  junction  of  the  colon  and  rectum  divides  into  two 
branches  which  continue  down  the  sides  of  the  rectum,  supplying  that  viscus  and  making  anas- 
tomoses with  the  middle  hemorrhoidal  from  the  internal  iliac  and  with  the  inferior  hemorrhoidal 
from  the  internal  pudic. 


804  HUMAN   ANATOMY. 

Variations. — The  inferior  mesenteric  artery  may  be  wanting,  its  place  being  supplied  by 
branches  from  the  superior  mesenteric.  It  occasionally  gives  rise  to  the  middle  colic  artery  or 
to  an  accessory  renal  vessel. 

4.  The    Inferior    Phrenic    Arteries. — The    inferior    phrenic   arteries    (aa. 
phrenicac  inferiores)  (Fig.  718)  most  frequently  arise  from  the  abdominal  aorta,  cithcr 
singly  or  by  a  common  trunk,  immediately  beneath  the  aortic  opening  of  the  dia- 
phragm and  above  the  cceliac  axis.      They  are  directed  upward  and  laterally  over 
the  crura  of  the  diaphragm,  to  which  they  supply  branches,  and  in  this  portion  of 
their  course  they  also  give  off  superior  suprarenal  branches   (  ranii  stiprarenalcs 
superiores)  to  the  suprarenal  bodies.      Over  the  region  where  the  crura  pass  into  the 
diaphragm    proper,   each  inferior  phrenic  divides  into  an  internal  and  an  external 
branch.     The  former  is  the  smaller  of  the  two,  and  passes  inward  towards  the  ceso- 
phageal  opening  of  the  diaphragm,  where  it  anastomoses  with  its  fellow  of  the  oppo- 
site side  to  form  an  arterial  ring  from  which  branches  descend  upon  the  oesophagus, 
supplying  the  lower  portion  of  that  structure  and  anastomosing  with  the  cesophageal 
branches  of  the  gastric  artery. 

The  external  branches  are  directed  laterally  upon  the  under  surface  of  the  dia- 
phragm, supplying  it.  They  pass  as  far  forward  as  the  costal  and  sternal  origins  of 
the  diaphragm,  anastomosing  with  the  musculo-phrenic,  superior  epigastric,  and 
superior  phrenic  branches  of  the  internal  mammary  arteries,  while  other  branches 
ramify  over  the  lateral  portions  of  the  diaphragm,  anastomosing  with  the  lower  inter- 
costals  and  perforating  the  central  tendon  to  anastomose  with  the  pericardial  arteries 
and  with  the  diaphragmatic  branches  of  the  thoracic  aorta. 

Variations. — The  inferior  phrenic  arteries  are  very  variable  in  their  origin.  One  fre- 
quently takes  its  origin  from  the  cceliac  axis  or  from  one  of  its  branches,  or  both  may  arise  from 
the  axis.  They  have  also  been  observed  to  arise  from  the  superior  mesenteric  or  the  renal,  or 
from  the  abdominal  aorta  below  the  superior  mesenteric.  They  also  vary  considerably  in  volume. 

5.  The  Suprarenal  Arteries. — The  suprarenal  arteries,  sometimes  termed  the 
middle  suprarenal*  (aa  suprarenales  mediae)  (Fig.  718)  to  distinguish  them  from  the 
suprarenal  branches  of  the  inferior  phrenic  and  renal  arteries,   are  a  pair  of  small 
but  constant  branches  which  arise  from  the  sides  of  the  abdominal  aorta,  almost  oppo- 
site the  origin  of  the  superior  mesenteric  artery.     They  pass  outward  and  slightly 
upward  over  the  crura  of  the  diaphragm  to  the  suprarenal  bodies,  where  they  anasto- 
mose with  the  other  suprarenal  branches. 

6.  The  Renal  Arteries. — The  renal  arteries  (aa.  renales)  (Figs.  718,  1591) 
are  two  large  stems  which  arise  from  the  sides  of  the  abdominal  aorta  a  little  below 
the  origin  of  the  superior  mesenteric.      Usually  the  two  arteries  are  opposite  each 
other,  but  frequently  that  of  the  right  side  arises  a  little  lower  down  than  that  of 
the  left  side.      They  are  directed  outward  and  slightly  downward  towards  the  kidneys, 
each  artery,  before  reaching  the  hilum,  dividing  into  from  three  to  five  branches, 
which  enter  the  substance  of  the  kidney  independently  at  the  hilum. 

Relations. — In  their  course  towards  the  kidneys  the  renal  arteries  rest  upon  the 
lower  portions  of  the  crura  of  the  diaphragm  and  more  late-rally  upon  the  upper  part  of 
the  psoas  muscles.  The  right  artery  is  somewhat  longer  than  the  left,  owing  to  the 
position  of  the  abdominal  aorta  a  little  to  the  left  of  the  median  line,  and  it  passes  behind 
the  inferior  vena  cava.  Both  vessels  are  almost  concealed  beneath  the  corresponding 
renal  veins,  and  at  the  hilum  of  the  kidney  the  majority  of  the  terminal  branches  pass 
in  front  of  the  upper  portion  of  the  ureter,  only  one  or  two  passing  behind  it. 

Branches. — Near  its  termination  each  artery  gives  off  branches  which  pass  to  the  adipose 
tissue  sum  mnding  the  kidney,  and  a  ureteral  branch  which  supplies  the  upper  part  of  the  ureter. 
anastomosing  with  the  ureteral  branch  of  the  spermatic  (or  ovarian)  artery.  More  proximally 
it  gives  origin  to  an  inferior  suprarenal  branch  (a  suprarenalis  inferior  I  which  passes  upward  to 
the  lower  part  of  the  suprarenal  body  and  anastomoses  with  the  other  brandies  which  go  to 
that  structure. 

Variations. — Not  infrequently  the  division  of  the  renal  arteries  into  their  terminal  branches 
takes  place  <-;irl\,  sometimes  immediately  at  their  origin,  several  stems  arising  directly  from  the 
aorta  and  passing  outward  to  the  kidney.  Accessory  renal  branches  may  arise  from  theabdomi- 


THE   VISCERAL    BRANCHES.  805 

nal  aorta  or  from  the  middle  sacral,  the  common  iliac,  the  internal  iliac,  or  the  inferior  mesen- 
tcric,  and  occasionally  the  renal  artery  proper  may  be  lacking  and  its  place  taken  by  a  vessel 
from  one  or  other  of  these  origins.  These  accessory  arteries  frequently  enter  the  substance  of 
the  kidney  elsewhere  than  at  the  hilum. 

The  two  renal  arteries  may  arise  by  a  common  trunk  from  the  anterior  surface  of  the  aorta, 
and  they  occasionally  give  off  branches  which  are  either  accessory  to  or  replace  vessels  normally 
arising  elsewhere.  Thus  they  have  been  observed  to  give  rise  to  the  inferior  phrenics,  the  right 
branch  of  the  hepatic,  the  spermatics.  branches  to  the  pancreas  and  colon,  and  one  or  more  of 
the  lumbar  arteries. 

•ja.  The  Spermatic  Arteries. — The  spermatic  arteries  (aa.  sperraaticae  internae) 
(Figs.  718,  1591)  are  two  slender  vessels  which  arise  from  the  anterior  surface  of  the 
aorta  a  little  below  the  renals.  They  are  directed  downward,  and  slightly  outward  and 
forward,  towards  the  lower  part  of  the  anterior  abdominal  wall,  and  as  they  approach 
this  each  vessel  curves  inward  towards  the  median  line  to  reach  the  internal  abdominal 
ring.  Here  it  comes  into  relation  with  the  vas  deferens  and  becomes  enclosed  with 
it  in  the  spermatic  cord.  Embedded  in  this  structure,  it  traverses  the  inguinal  canal 
and  passes  into  the  scrotum,  terminating  just  above  the  testis  by  dividing  into 
branches  which  pass  to  that  organ  and  to  the  epididymis. 

Relations. — In  its  course  through  the  abdomen  the  left  spermatic  artery  lies 
behind  the  peritoneum  and  rests  upon  the  psoas  muscle.  About  the  middle  of  this 
portion  of  its  course  it  crosses  obliquely  in  front  of  the  ureter,  and  lower  down  has 
resting  upon  it  the  sigmoid  colon.  The  right  artery  at  first  lies  in  the  root  of  the 
mesentery  ;  it  descends  obliquely  upon  the  anterior  surface  of  the  inferior  vena  cava 
and  then,  crossing  the  ureter  obliquely,  comes  to  lie  behind  the  terminal  portion  of 
the  ileum  and  frequently  behind  the  vermiform  appendix. 

In  the  pelvic  and  inguinal  portions  of  their  course  the  relations  of  both  arteries 
are  the  same.  The  vessels  rest  upon  the  psoas  muscle  to  the  outer  side  of  the  ex- 
ternal iliac  artery,  and  cross  the  lower  part  of  that  vessel  and  the  accompanying  vein 
to  reach  the  internal  abdominal  ring.  In  their  course  down  the  spermatic  cord  the 
arteries  lie  behind  the  anterior  group  of  the  spermatic  veins  and  in  front  of  the  vas 
deferens. 

Branches. — In  addition  to  the  terminal  (a)  testicular  and  (d)  epididymal  branches,  each 
spermatic  artery  gives  off — 

(c)  An  ureteral  branch  which  is  distributed  to  the  middle  portion  of  that  duct,  anastomosing 
with  the  ureteral  branch  of  the  renal  artery  above  and  with  branches  from  the  inferior  vesical 
artery  below. 

(d)  Cremasteric  branches  are  given  off  in  the  course  through  the  spermatic  cord  and  sup- 
ply the  cremaster  muscle,  anastomosing  with  the  cremasteric  branch  of  the  deep  epigastric 
artery. 

Variations. — The  spermatic  arteries  occasionally  arise  by  a  common  trunk,  or,  on  the 
other  hand,  they  may  arise  at  different  levels.  They  have  been  observed  to  arise  from  the 
renals,  especially  the  left  one,  from  the  suprarenals,  or  from  the  superior  mesenteric  artery. 

•jb.  The  Ovarian  Arteries. — The  ovarian  arteries  (aa.  ovaricae)  (Fig.  726) 
correspond  in  the  female  to  the  spermatic  arteries  of  the  male,  and  have  a  similar 
origin  and  similar  relations  in  the  abdominal  portion  of  their  course.  Arrived  at 
the  pelvis,  however,  they  cross  the  common  iliac  arteries  and  veins  and,  traversing 
the  suspensory  ligament  of  the  ovary,  pass  inward  between  the  folds  of  the  broad 
ligament  of  the  uterus,  terminating  beneath  the  ovary  by  inosculating  with  the  uterine 
artery. 

Branches. — Like  the  spermatic  arteries,  the  ovarian  give  off  (a)  ureteral  branches.  In  ad- 
dition, they  give  rise  to  (b)  tubal  branches,  which  pass  to  the  distal  portions  of  the  Fallopian 
tubes  ;  (r)  ligamentous  branches,  which  accompany  and  supply  the  round  ligament  of  the 
uterus  ;  and  (d )  ovarian  branches,  which  enter  the  hilum  of  the  ovary  and  are  distributed  to  its 
substance. 

8.  The  Lumbar  Arteries. — The  lumbar  arteries  (aa.  lumbales)  (Fig.  718)  are 
arranged  in  four  pairs,  and  take  origin  from  the  sides  of  the  abdominal  aorta,  opposite 
the  four  upper  lumbar  vertebrae.  They  are  directed  outward  upon  the  bodies  of  the 
vertebrae,  the  lumbar  portion  of  the  sympathetic  cord  descending  in  front  of  them,  and 


8o6  HUMAN   ANATOMY. 

those  of  the  right  side  also  pass  beneath  the  inferior  vena  cava,  while  the  two  upper 
ones  of  the  same  side  pass  beneath  the  receptaculum  chyli.  They  then  pass  beneath 
the  psoas  muscle  and  the  branches  of  the  lumbar  plexus,  the  two  upper  ones  H!M> 
passing  beneath  the  crura  of  the  diaphragm  ;  and  then,  farther  out,  they  pass  beneath 
the  quadratus  lumborum,  except  in  the  case  of  the  last  pair,  which  lies  upon  the  ante- 
rior surface  of  that  muscle.  At  the  outer  border  of  the  quadratus  they  pass  between 
the  transversalis  and  the  internal  oblique  muscles  of  the  abdomen,  and  are  continued 
onward  in  the  abdominal  wall,  eventually  piercing  the'  internal  oblique  and  reaching 
the  rectus  muscle. 

Branches. — The  lumbar  arteries  are  to  be  regarded  as  continuations  of  the  scries  of  inter- 
costal vessels,  and,  like  the  thoracic  members  of  the  series,  each  gives  off  a  dorsal  branch  (  ramus 
dorsalis).  This  arises  when  the  vessel  lies  behind  the  psoas  muscle  and  is  directed  posteriorly, 
soon  dividing  into  (a)  a  spinal  branch  (ramus  spinalis).  which  enters  the  spinal  canal  through 
the  intervertebral  foramen  and  anastomoses  with  the  anterior  and  posterior  spinal  arteries  ;  and 
(b)  a  muscular  branch,  which  is  distributed  to  the  muscles  and  skin  of  the  back.  In  addition, 
each  lumbar  artery  gives  off  numerous  branches  to  the  muscles  with  which  it  comes  into  relation. 

Variations. — One  or  more  of  the'  lumbar  arteries  may  be  wanting  and  two  or  more  of  them 
may  arise  by  a  common  stem 

9.  The  Middle  Sacral  Artery. — The  middle  sacral  artery  (a.  sacralis  media  ) 
(Fig.  718),  which  is  to  be  regarded  as  the  continuation  of  the  abdominal  aorta,  is 
a  small  vessel  arising  from  the  posterior  surface  of  the  aorta  immediately  above  its 
bifurcation  into  the  two  common  iliacs.  It  passes  downward  in  the  median  line  over 
the  last  two  lumbar,  the  sacral  and  the  coccygeal  vertebrae,  and  terminates  opposite 
the  tip  of  the  coccyx  by  sending  branches  to  the  coccygeal  body  or  Luschka's  gland 
(glomus  coccygeum). 

Branches. — It  sometimes  gives  rise  to  a  fifth  pair  of  lumbar  arteries  (aa.  lumbales  imae),  and 
lower  down  it  sends  off  small  lateral  branches  which  send  branches  inward  to  the  spinal  canal 
through  the  anterior  sacral  foramina  and  anastomose  with  the  lateral  sacral  branches  of  the 
internal  iliac  artery.  These  lateral  branches  appear  to  represent  a  continuation  of  the  inter- 
costal and  lumbar  series  of  arteries,  the  branches  which  enter  the  anterior  sacral  foramina  cor- 
responding to  the  dorsal  branches  of  those  vessels. 

Variations. — The  middle  sacral  occasionally  arises  from  one  or  other  of  the  common  iliac 
arteries,  and  it  may  give  origin  to  an  accessory  renal  artery. 

Practical  Considerations. — Some  of  the  branches  of  the  abdominal  aorta, 
including  the  splenic,  hepatic,  renal,  superior  and  inferior  mesenteric,  and  the  ovarian, 
have  been  the  subject  of  aneurism. 

These  aneurisms  do  not  usually  attain  any  great  bulk,  seldom  exceeding  the 
size  of  a  hen's  egg.  They  are  apt  to  be  round  or  oval  in  shape.  Occasionally — espe- 
cially in  the  aneurisms  of  the  renal  artery — they  may  almost  fill  the  abdominal 
cavity.  Except  when  connected  with  the  hepatic,  the  renal,  or  the  cceliac  axis,  they 
are  movable,  changing  their  position  in  the  various  movements  of  the  body.  They 
may  possess  also  the  characteristics  of  pulsation  and  bruit.  When  the  cu-liac 
artery  is  affected  the  disease  cannot  be  distinguished  from  aneurism  of  the  parent 
trunk. 

In  cases  of  implication  of  the  hepatic  artery,  the  pressure-effects  of  the  tumor 
give  rise  to  pain  in  the  right  side  and  to  jaundice  from  obstruction  of  the  hepatic, 
cystic,  and  common  bile-ducts  (Agnew). 

The  renal  artery  has  been  found  to  be  aneurismal  in  a  small  number  of  instances, 
the  majority  being  of  traumatic  origin.  The  chief  symptoms  have  been :  (  a  )  tumor. 
varying  in  size,  situated  in  the  region  of  the  kidney,  immovable  with  respiration  or 
with  change  <>f  posture,  and  almost  always  without  impulse  or  bruit,  on  account  prob- 
ably of  the  usual  disproportion,  in  renal  aneurisms,  between  the  large  aneurismal 
cavity  and  the  size  of  the  vessel  involved  ;  (/>)  h<rmaturin  often  but  not  invariably 
present  ;  (c}  pain  elicited  by  pressure,  or  felt  in  the  loin  or  extending  to  the  genitalia, 
and  sometimes  accompanied  by  retraction  of  the  testis. 


THE    COMMON    ILIAC   ARTERIES.  807 

These  abdominal  aneurisms  are  not  uncommonly  unsuspected  until  they  have 
reached  a  late  stage,  and  may  even  rupture  and  cause  death  from  hemorrhage  with- 
out having  caused  more  than  trifling  inconvenience.  In  a  number  of  cases  the  pain 
— especially  apt  to  be  felt  in  the  back — has  been  the  only  symptom  complained  of. 
If  a  pulsating  tumor,  or  one  with  a  bruit,  can  be  felt,  it  would  be  proper  to  approach 
the  region  by  an  intraperitoneal  or — in  the  case  of  the  renals — possibly  an  extra- 
peritoneal  incision,  and  ligate  the  artery  on  the  cardiac  and  distal  sides  of  the  sac. 

THE   COMMON    ILIAC   ARTERIES. 

The  common  iliac  arteries  (aa.  iliacae  communes)  (Figs.  724,  726)  are  usually 
regarded  as  the  terminal  branches  of  the  abdominal  aorta,  although  in  reality  the 
middle  sacral  artery  forms  the  morphological  continuation  of  that  vessel,  the  common 
iliacs  being  lateral  segmental  branches  comparable  to  a  pair  of  lumbar  or  intercostal 
arteries.  They  arise  opposite  the  body  of  the  fourth  lumbar  vertebra  and  pass 
obliquely  outward,  downward,  and  forward  to  about  the  level  of  the  sacro-iliac  articu- 
lation, where  they  terminate  by  dividing  into  the  internal  and  external  iliac  arteries. 

The  two  common  iliacs  diverge  from  each  other  at  an  angle  of  from  6o°-65°  in 
the  male  and  somewhat  more  (68°-75°)  in  the  female.  On  account  of  the  position  of 
the  abdominal  aorta  being  slightly  to  the  left  of  the  median  line,  the  right  artery  is 
slightly  longer  than  the  left,  and  is  inclined  to  the  median  line  at  a  slightly  greater  angle. 

Relations. — The  common  iliac  arteries  are  covered  by  peritoneum,  which  sepa- 
rates them  on  the  right  from  the  terminal  portion  of  the  ileum  and  on  the  left  from 
the  sigmoid  colon.  Anteriorly,  each  artery  is  crossed  by  the  ureter,  and  in  the  female 
by  the  ovarian  artery  and  vein,  and  by  the  branches  of  the  sympathetic  cord  which 
pass  downward  to  the  hypogastric  plexus.  The  left  common  iliac  is,  in  addition, 
crossed  by  the  superior  hemorrhoidal  branch  of  the  inferior  mesenteric  artery. 
Behind,  the  vessel  of  the  left  side  rests  upon  the  bodies  of  the  fourth  and  fifth 
lumbar  vertebrae,  that  of  the  right  side  being  separated  from  them  by  the  right 
common  iliac  vein  and  by  the  upper  end  of  the  corresponding  vein  of  the  left  side. 
Lower  both  vessels  rest  upon  the  psoas  muscle.  Laterally,  they  are  also  in  relation 
with  the  psoas  and  with  the  spermatic  artery  in  the  male  and,  in  the  case  of  the 
vessel  of  the  right  side,  with  the  upper  part  of  the  right  common  iliac  vein. 
Medially,  are  the  common  iliac  veins  and  the  hypogastric  plexus. 

Branches. — The  common  iliac  arteries  terminate  by  dividing  into  the  external 
and  internal  iliac  arteries.  In  addition,  they  give  rise  only  to  small  vessels  which 
pass  to  the  subjacent  psoas  muscles  and  to  the  neighboring  peritoneum  and  lymph- 
nodes  and  the  ureters. 

Variations. — A  certain  amount  of  variation  occurs  in  the  length  of  the  common  iliac  arte- 
ries, depending  largely  upon  the  level  at  which  the  bifurcation  of  the  abdominal  aorta  occurs. 
One  or  other  vessel  may  give  rise  to  the  middle  sacral  artery  or  to  an  accessory  renal  artery. 

Practical  Considerations. — The  common  iliac  artery  is  very  rarely  the  sub- 
ject of  aneurism.  Direct  compression  of  the  artery  may  be  made  by  either  of  the 
plans  described  as  applicable  to  the  abdominal  aorta,  and  should  be  applied  about 
one  inch  below  and  a  half  inch  to  the  right  or  left  of  the  umbilicus.  While  it  is 
easier  to  get  rid  of  the  intestines,  as  the  vessel  is  placed  more  laterally,  it  is  not 
always  easy  to  avoid  compression  of  the  aorta  itself. 

Ligation  of  the  common  iliac  may  be  required  for  aneurism  lower  down,  espe- 
cially of  the  upper  part  of  the  external  iliac,  or  for  wound,  or  as  a  preliminary  to  or 
part  of  the  procedure  in  the  removal  of  pelvic  growths. 

It  may  be  effected  by  either  :  (i)  The  transperitoneal  method,  or  (2)  the  extra- 
peritoneal  method,  i.  A  median  incision  from  umbilicus  to  symphysis,  opening  the 
peritoneal  cavity,  the  intestines  being  kept  in  the  upper  segment  of  the  abdomen  by 
pads  or  by  placing  the  patient  in  the  Trendelenburg  position,  will  give  easy  access 
to  the  vessel.  On  each  side  it  lies  directly  beneath  the  peritoneum,  but  there  are 
anatomical  differences  to  which  Makins  has  called  attention.  On  the  right  side 
the  vessel  is  uncovered  by  any  structure  of  importance,  and  may  be  reached  by 
dividing  the  peritoneum  directly  over  it  vertically.  On  this  side  the  vena  cava 


8o8  HUMAN   ANATOMY. 

and  both  common  iliac  veins  are  in  close  relation  with  the  artery,  the  latter  two 
passing  beneath  it.  On  the  left  side,  the  inferior  mesenteric  vessels  as  they  enter 
the  sigmoid  mesocolon  and  pass  downward  to  the  rectum  cover  practically  the 
whole  of  the  artery,  and  to  reach  the  common  iliac  comfortably  and  safely  the 
peritoneum  would  need  to  be  divided  close  to  the  left  of  the  median  line  of  the 
sacrum  and  be  displaced  outward.  The  vein  usually  lies  on  the  inner  side  of 
and  somewhat  behind  the  artery.  This  manoeuvre  has  the  disadvantage  of  ex- 
posing the  vein  freely,  but  this  would  probably  give  far  less  trouble  than  would  the 
numerous  mesenteric  vessels  when  swollen  by  reason  of  the  loss  of  their  peritoneal 
support. 

2.  By  the  extraperitoneal  method  the  vessel  is  approached  through  various 
incisions  ;  the  best  (Crampton)  (especially  if  it  is  desirable  to  apply  the  ligature  at 
the  highest  possible  point)  begins  at  the  tip  of  the  last  rib  and  extends  downward  to 
the  ilium  and  forward  to  the  anterior  superior  spinous  process.  The  abdominal 
muscles  and  transversalis  fascia  are  divided  at  the  lower  extremity  of  the  wound,  the 
peritoneum  separated  with  the  finger  from  the  iliac  fascia  in  a  direction  corresponding 
to  the  line  of  the  crista  ilii,  the  abdominal  muscles  severed  on  the  same  line,  and  the 
separation  of  the  peritoneum  continued  until  it  is  pushed  off  the  psoas  and  the  iliac 
vessels,  which  lie  on  the  inner  aspect  of  that  muscle.  The  ureter  is  raised  with  the 
peritoneum  and  remains  attached  to  it. 

The  artery  may  be  similarly  approached  through  an  incision  placed  just  above 
Poupart's  ligament  and  very  like  that  used  for  the  exposure  of  the  external  iliac.  The 
needle  is  passed  from  the  vein — i.e. ,  from  left  to  right — in  ligating  the  right  common 
iliac,  and  from  right  to  left  if  the  vessel  of  the  left  side  is  the  subject  of  operation. 

The  collateral  circulation  is  carried  on  from  above  the  ligature  by  (a)  the  inter- 
nal mammary;  (£)  the  superior  hemorrhoidal  ;  (c~)  the  lumbar;  (d}  the  middle 
sacral  ;  and  (V)  the  pudic  and  obturator  of  the  opposite  side,  anastomosing  respect- 
ively with  (a)  the  deep  epigastric  ;  (£)  the  middle  hemorrhoidal  (internal  iliac)  ;  (c) 
the  deep  circumflex  iliac  ;  and  (e)  the  pudic  and  obturator  of  the  other  side  (/.<•., 
the  side  of  the  ligature)  from  below. 

THE    INTERNAL    ILIAC  ARTERY. 

The  internal  iliac  artery  (a.  hypogastrica)  (Fig.  724)  arises  from  the. common 
iliac  and  passes  almost  directly  downward  in  front  of  the  sacro-iliac  articulation  into 
the  pelvis.  Opposite  the  upper  border  of  the  great  sacro-sciatic  foramen  it  divides 
into  two  main  stems,  the  anterior  and  posterior  divisions,  from  which  branches  of 
distribution  are  given  off. 

Relations. — Posteriorly  the  internal  iliac  artery  is  covered  by  peritoneum  and 
is  crossed  obliquely  by  the  ureter.  More  anteriorly  the  vessel  of  the  right  side  is  in 
relation  with  some  coils  of  the  ileum,  while  that  of  the  left  side  is  in  relation  to  the 
upper  part  of  the  rectum.  Posteriorly  each  artery  rests  upon  the  upper  part  of  the 
external  iliac  vein,  which  separates  it  from  the  inner  border  of  the  psoas  muscle,  and  is 
accompanied  throughout  its  course  by  the  internal  iliac  vein. 

Branches. — From  the  main  stem  of  the  artery,  before  its  division,  there  arises 
(i)  the  ilio-lumbar  artery,  and  from  its  posterior  division  (2)  the  lateral  sacra /s, 
usually  two  in  number,  and  (3)  the  gluteal.  From  the  anterior  division  there'  art- 
given  off  a  hypogastric  a.rr's,  which  divides  into  (4)  the  superior  vcsical,  (5)  inferior 
vesical,  and  (6)  prostatic  or  vaginal  branches,  and  (7)  the  vfsicido-deferential  or 
uterine  artery,  and,  in  addition,  (8)  the  obturator  and  (9)  middle  hemorrhoidal 
arteries,  the  main  stem  terminating  by  dividing  into  ( 10)  the  internal  pudic  and 
( 1 1 )  sciatic  arteries. 

Variations. — The  internal  iliac  arteries  represent  tin- proximal  part  of  the  fu  tal  umbilical 
Of  hypogastric  arteries  which  return  the  blood  from  the  tutus  to  the  placenta.  During  intra- 
uteriiie  life  these  vessels  are  ]ari;e  and  appear  to  be  the  continuation  of  the  common  iliacs,  pass- 
ing forward  beneath  the  peritoneum  to  the  lateral  walls  of  the  bladder  and  thence  upward  upon 
the  anterior  abdominal  wall  to  the  umbilicus,  and  thence  in  the  substance  of  the  umbilical  cord 
to  the  placenta.  After  birth  the  arteries  diminish  in  si/e,  and  those  portions  of  them  which  pass 
across  the  lateral  walls  of  the  urinary  bladder  and  up  the  abdominal  wall  become  converted  into 
solid  fibrous  cords  which  persist  throughout  life  and  are  known  as  the  obliterated  hypogastric 


THE    INTERNAL    ILIAC   ARTERY. 


809 


arteries.  The  portions  of  the  arteries  which  remain  patent  form  the  main  stems  of  the  internal 
iliacs,  the  hypogastric  axes  and  the  superior  vesical  arteries  ;  what  are  spoken  of  as  the  main 
stems  of  the  anterior  divisions  of  the  internal  iliacs  are  really  the  common  trunks  by  which 
the  sciatic  and  internal  pudic  arteries  arise  from  the  hypogastric. 

In  the  arrangement  of  the  branches  of  the  foetal  hypogastric  arteries  four  types  may 
be  recognized,  and  corresponding  to  each  of  these  is  an  arrangement  of  the  adult  internal 
iliac  branches.  Leaving  out  of  consideration  for  the  present  the  smaller  branches,  the  first 
type  is  that  in  which  two  large  trunks  arise  from  the  hypogastric,  the  posterior  one  being 
the  gluteal  and  the  anterior  a  trunk  which  divides  into  the  pudic  and  sciatic.  The  adult 

FIG.  724. 


Obturator  artery 

Anterior  supenoi 

spine  of  iliun 


Deep  circumflex 
iliac  artery 


External  iliac  arten 

External  iliac  vei 
Obturator  vei 


Deep  epigastric  arte 

Vas  deferens 


Artery  of  vas  deferens 


Middle  sacral  artery 
Right  common  iliac  artery 


Ilio-lumbar  artery 

Internal  iliac  artery 

Posterior  trunk  of  internal  iliac 

Superior  gluteal  artery 

Single  trunk  dividing  into 
two  lateral  sacral  arttrries 

Pyriformis  muscle 

.Anterior  trunk  of 

internal  iliac 
Superior  hemorrhoidal 
from  inferior  mescnteric 


Rectum 


vesical  artery 


Middle  vesicul  artery 
Inferior  vesical  artery 
Sciatic  artery 

Internal  pudic 
artery 

Right  and  left 
middle  hem- 
orrhoidal arteries 


Spine  of  ischium 

Seminal  vesicles 
Left  ureter 
Anus 

Prostate 


Internal  pudic 
artery,  in  ischii 


Symphysis  pubis. 

Bladder 
Right  dorsal  artery  of  penis 


Left  dorsal  artery  of  penis  ' 

Left  corpus  cavernosum  Corpus    Membranous      Bulbo-cavernosus  muscle 

spongiosum     urethra 

Dissection  of  pelvis  of  male,  showing  right  internal  iliac  artery  and  its  branches. 


condition  which  results  from  this  arrangement  is  that  described  above,  the  main  stem  of  the 
internal  iliac  appearing  to  divide  into  two  divisions,  from  the  anterior  of  which  the  hypogastric 
axis  arises. 

The  second  type  is  that  in  which  the  three  large  vessels  arise  independently  from  the  hypo- 
gastric,  the  resulting  adult  condition  closely  resembling  that  produced  from  the  first  type,  except 
that  the  hypogastric  axis  seems  to  arise  from  the  internal  pudic,  the  separation  of  the  anterior 
division  into  its  two  terminal  branches  occurring  high  up. 

The  third  type  is  that  in  which  the  gluteal  and  sciatic  arteries  arise  by  a  common  trunk 
from  the  hypogastric,  the  pudic  remaining  distinct.  In  the  adult,  in  such  cases,  the  anterior 
division  gives  rise  to  the  hypogastric  axis  and  the  internal  pudic,  the  sciatic  arising  from  the 
posterior  division. 

Finally,  in  the  fourth  type,  which  is  of  rare  occurrence,  all  three  large  vessels  arise  from  a 
common  stem,  in  which  case  there  will  be  no  apparent  separation  of  the  adult  internal  iliac  into 
an  anterior  and  a  posterior  division. 


8io 


HUMAN   ANATOMY. 


The  variations  of  the  smaller  branches,  which  are  quite  numerous,  will  be  considered  in 
connection  with  their  description.  It  may  be  pointed  out,  however,  that,  since  the  superior 
vesical  artery  is  the  persistent  portion  of  the  original  hypogastric  artery  and  primarily  the 
direct  continuation  of  the  hypogastric  axis,  some  of  the  visceral  branches  which  normally 
arise  from  the  axis  may  take  their  origin  from  the  superior  vesical.  Furthermore,  vessels  which 
embryologically  arise  from  one  or  other  of  the  great  branches  of  the  hypogastric  may,  on  account 
of  the  variations  in  the  origin  of  these,  come  to  arise  from  the  hypogastric  axis. 

Practical  Considerations.— The  internal  iliac  artery  is  almost  never  the  seat 
of  aneurism.  It  has  been  ligated  for  hemorrhage,  for  gluteal  and  sciatic  aneurism, 
and  in  the  treatment  of  inoperable  pelvic  growths.  It  may  be  approached  intraperi- 
toneally  by  the  same  incision  and  the  same  general  procedure  as  employed  in 
ligation  of  the  common  iliac  (g.v.).  The  vein  lies  behind  and  to  the  inner  side,  and 

FIG.  725. 


Diagram  illustrating  four  types  of  arrangement  of  branches  from  hypogastric  (internal  iliac)  artery  :  cc,  <•;, 
ii,  common,  external  and  internal  iliac  artery;  »'/,  ilio-lumbar;  Is,  lateral  sacral;  g,  gluteal;  s,  sciatic;  ip, 
internal  pudic  ;  ha,  hypogastric  axis. 

by  reason  of  its  size  and  its  close  proximity  to  the  vessel  must  be  very  carefully  dealt 
with.  The  needle  should  be  passed  from  within  outward.  The  relation  of  the  ureter, 
which  crosses  the  vessel  obliquely  from  without  inward  and  downward,  and  of  the 
hypogastric  plexus  should  be  borne  in  mind. 

In  the  extraperitoneal  method  the  incision  and  procedure  are  just  as  in  extra- 
peritoneal  ligation  of  the  external  iliac  (page  819),  except  that  the  separation  of  the 
peritoneum  from  the  iliac  fascia  must  be  carried  to  a  higher  level. 

The  collateral  circulation  is  carried  on  chiefly  through  (a)  the  inferior  mesen- 
teric  ;  (£)  the  circumflex  iliac  ;  (V)  the  middle  sacral  ;  (d)  the  deep  femoral  ;  (e)  the 
obturator  and  internal  pudic  of  the  opposite  side,  all  of  which  carry  blood  from  above 
the  ligature  into  (a)  the  hemorrhoidal  branches  of  the  internal  iliac  ;  (&')  the  ilio- 
lumbar  ;  (r)  the  lateral  sacral  ;  (</)  the  sciatic  and  gluteal  ;  and  (>)  the  corresponding 
vessels  of  the  other  side  (/.  e. ,  the  side  of  the  ligature). 

1.  The    Ilio-Lumbar    Artery. — The  ilio-lumbar  artery   (a.  ilio-lumbalis) 
(Fig.    724)  is  most  frequently  given  off  from  the  main  stem  of  the  internal  iliac, 
shortly  above  its  separation  into  the  anterior  and   posterior  divisions.     Not  infre- 
quently, however,  it  is  a  branch  of  the  posterior  division.      It  passes  upward  and 
outward  towards  the  brim  of  the  pelvis,  crossing  in  front  of  the  lumbo-sacral  nerve 
and   behind    the  external    iliac  artery,  beyond  which  it  passes   beneath  the  psoas 
muscle.     On  reaching  the  crest  of  the  ilium  it  divides  into  two 

Branches.— (a)  The  lumbar  branch  (ramus  luml.alis ')  is  directed  upward  and  backward  be- 
neath the  psoas  and  supplies  that  muscle  and  the  quadratus  lumborum.  It  sends  a  spinal  branch 
(ramus  spina/is}  through  the  intervertebral  foramen  between  the  last  lumbar  and  (MM  s;u T.I! 
vertebrae,  and  anastomoses  with  branches  of  the  last  lumbar  artery. 

(t>)  The  iliac  branch  (ramus  iliacus)  passes  outward  beneath  the  psoas  and  ramifies  upon 
t IK-  surface  of  the  iliacus  muscle,  supplying  it  and  usually  giving  off  a  nutrient  branch  to  the 
ilium. 

2.  The  Lateral  Sacral  Arteries. — The  lateral  sacral  arteries   (aa.  sacrales 
laterales")  (Fig.  724)  are  usuallv  two  in  number,  and  arise  from  the  posterior  division  of 
the  internal  iliac.     The  superior  one  passes  downward  and  inward  to  the  first  anterior 
sacral  foramen,  and  passes  through  it  to  supply  the  spinal  membranes  and  anastomose 


THE    INTERNAL    ILIAC   ARTERY.  811 

with  the  other  spinal  arteries.  The  inferior  artery  passes  at  first  inward  and  then 
downward  upon  the  surface  of  the  sacrum,  parallel  to  the  middle  sacral  artery,  with 
which  it  anastomoses  at  the  tip  of  the  coccyx  and  also,  by  delicate  transverse  branches, 
opposite  each  sacral  vertebra.  Opposite  each  anterior  sacral  foramen  that  it  passes 
— i.e.,  opposite  the  second,  third,  and  fourth — it  gives  off  a  branch  (ramus  spinalis) 
which  enters  the  foramen  and  behaves  like  the  spinal  branch  of  the  superior  artery. 
In  its  downward  course  the  inferior  lateral  sacral  lies  to  the  outer  side  of  the  sacral 
portion  of  the  sympathetic  cord  and  crosses  the  slips  of  origin  of  the  pyriformis 
muscle. 

Variations. — Very  frequently  the  two  lateral  sacral  arteries  arise  by  a  common  stem,  and 
occasionally  the  branch  which  enters  the  second  anterior  sacral  foramen  arises  independently. 
In  all  probability  the  longitudinal  stem  of  the  inferior  artery  is  to  be  regarded  as  having  been 
formed  by  the  direct  anastomosis  of  ascending  and  descending  twigs  from  the  lateral  branches 
of  the  middle  sacral,  each  of  which  is  serially  homologous  with  the  lumbar  and  intercostal  arte- 
ries. The  process  is  similar  to  what  has  occurred  in  the  formation  of  the  vertebral  artery 
(page  721). 

3.  The  Gluteal  Artery. — The  gluteal  artery  (a.  glutaea  superior)  (Fig.  727)  is 
the  continuation  of  the  posterior  division  of  the  internal  iliac.      It  is  the  largest  of  all 
the  branches  of  that  vessel,  and  passes  backward  between  the  lumbo-sacral  cord  and 
the  first  sacral  nerve  to  the  upper  border  of  the  great  sacro-sciatic  foramen.      It  passes 
through  the  foramen,  in  company  with  the  superior  gluteal  nerve,  above  the  pyriformis 
muscle,  and  soon  after  making  its  exit  from  the  pelvis  divides  into  a  superficial  and  a 
deep  branch. 

Branches. — (a)  The  superficial  branch  (ramus  superior)  soon  divides  into  a  number  of 
branches  which  enter  the  upper  portion  of  the  gluteus  maximus,  some  supplying  that  muscle, 
while  others  traverse  it  to  supply  the  skin  over  the  upper  part  of  the  gluteal  region.  One 
branch,  larger  than  the  others,  passes  outward  along  the  upper  border  of  the  origin  of  the 
glutens  medius  almost  to  the  anterior  superior  spine  of  the  ilium,  anastomosing  with  branches  of 
the  external  circumflex  iliac  artery. 

(b)  The  deep  branch  (ramus  inferior)  soon  divides  into  two  branches,  (aa)  The  superior 
branch  passes  outward  along  the  upper  border  of  the  gluteus  minimus  almost  to  the  anterior 
inferior  spine  of  the  ilium,  where,  under  cover  of  the  tensor  vaginae  femoris,  it  anastomoses 
with  tlie  descending  branch  of  the  external  circumflex  iliac  ;  it  sends  branches  to  both  the  glu- 
tens medius  and  minimus,  (bb)  The  inferior  branch  passes  outward  and  downward,  over  the 
surface  of  the  gluteus  medius,  towards  the  greater  trochanter  of  the  femur,  and  gives  branches 
to  both  the  gluteus  medius  and  minimus  and  to  the  hip-joint. 

4.  The  Superior  Vesical  Artery. — The  superior  vesical  artery  (a.  umbilicalis) 
(Fig.  724)   represents  the  original  main  stem  of  the  foetal  hypogastric  artery,  and 
consequently  takes  its  origin  from  the  hypogastric  axis  and  is  continuous  anteriorly 
with  the  fibrous  cord  which  represents  the  obliterated  hypogastric  artery  (Fig.  728). 
It  passes  forward,  beneath  the  peritoneum,  towards  the  urinary  bladder,  and  as  it 
approaches  that  structure  gives  off  branches  to  it  (aa.  vesicales  superiores)  which  ramify 
over  its  surface  and  sides  and  supply  its  upper  and  middle  portions.      They  anasto- 
mose below  with  branches  of  the  prostatic  and  inferior  vesical  arteries. 

Variations.— Not  infrequently  an  accessory  branch  arising  from  the  superior  vesical  is  dis- 
tributed to  the  middle  and  lower  portions  of  the  bladder,  forming  what  has  been  termed  the 
•middle  vesical  artery  ( Fig.  724) . 

5.  The   Inferior  Vesical   Artery. — The  inferior  vesical  artery   (a.  vesicalis 
inferior)  (Fig.  724)  may  arise  from  the  hypogastric  axis,  from  the  anterior  division  of 
the  internal  iliac  below  the  axis,  from  the  middle  hemorrhoidal,  or  quite  frequently 
from  the  prostatic.      It  descends  towards  the  lower  portion  of  the  bladder,  supplying 
the  base  and  neck  of  that  structure,  and  also  sending  branches  to  the  prostate  gland 
and  the  seminal  vesicles  in  the  male.      It  anastomoses  with  branches  of  the  prostatic 
and  superior  vesical  arteries. 

Variations. — The  inferior  vesical  is  usually  a  rather  slender  branch,  and  ma)-  be  replaced 
by  vesical  branches  from  the  prostatic  or  by  branches  of  the  superior  vesical. 


812 


HUMAN    ANATOMY. 


6a.  The  Prostatic  Artery. — The  prostatic  artery  arises  either  from  the  hypo- 
gastric  axis,  or,  more  usually,  from  a  trunk  common  to  it  and  the  inferior  vesical  or  the 
middle  hemorrhoidal.  It  passes  downward,  forward,  and  inward  to  the  lateral  surface 
of  the  prostate  gland,  and  sends  branches  into  the  interior  of  that  structure  and  also 
to  the  base  of  the  bladder,  anastomosing  with  branches  of  the  inferior  vesical  artery. 

66.  The  Vaginal  Artery. — The  vaginal  artery  (a.  vaginalis)  (Fig.  726),  the 
homologue  of  the  prostatic  artery,  arises  either  from  the  hypogastric  axis,  more  usually 
from  a  trunk  common  to  it  and  the  inferior  vesical  or  middle  hemorrhoidal,  or  from 
the  anterior  division  of  the  internal  iliac,  below  the  hypogastric  axis.  It  passes  down- 
ward and  inward  towards  the  lower  part  of  the  sides  of  the  vagina,  where  it  divides  into 
numerous  branches  which  ramify  over  the  anterior  and  posterior  surfaces  of  that  organ, 
anastomosing  with  the  corresponding  branches  of  the  artery  of  the  other  side.  It  also 
anastomoses  above  with  the  cervical  branches  of  the  uterine  artery  and  below  with  the 
perineal  branches  of  the  internal  pudic.  By  these  anastomoses  there  is  usually  formed 
along  the  median  line  of  both  the  anterior  and  posterior  surfaces  of  the  vagina  a  more 
or  less  regular  vessel  which  is  known  as  the  azygos  artery  of  the  vagina. 


FIG.  726. 


Deep  circumflex  iliac  artery 

Round  ligament 

External  iliac  artery 
Ova'ian  artery 
External  -liac  vein 
•arian  veins 


Deep  epigastric 

artery  — — 


Obliterated 

hypogastri 


Bladder 

Symphysis  puliis 

( ibturator  nerve 
Vulva 


Dorsal  artery  of 

clitori 


Artery  to  corpi 
caver 


Right  ureter 
•Common  iliac  arter\ 


I-eft  common  iliac 

Bowel 

Obturator  artery 
•Superior  \  esii  al  arterv 
.Middle  vesical  arter\ 
;  Oviduct 

Inferior  vesical  artery 

Jterine  artery 
'Stump  of  round  liga- 
'Ovary  [ment 

arian  artery 


•Uterine  artery 
Superior  vesical  artery 
Vaginal  artery 

Anterior  trunk  of 

internal  iliac  arten 


Middle  hemorrhoidal  artery 


Artery  to  bulb 


Vaginal  branch  Left  Vaginal  artery 

of  uterine  artery  ureter 

Arteries  of  female  pelvis,  seen  from  left  side. 


Variations. — The  vaginal  artery  occasionally  arises  from  a  common  trunk  \\  ith  the  uterine. 
Frequently,  as  a  result  of  its  precocious  division,  it  is  represented  by  two  or  more  vessels. 

•ja.  The  Vesiculo-Deferential  Artery. — The  vesiculo-deferential  artery 
(a.  deferentialis )  usually  arises  from  the  hypogastric  axis,  but  sometimes  from  the 
proximal  part  of  the  superior  vesical  or  from  the  anterior  division  of  the  internal  iliac, 
below  the  hypogastric  axis.  It  passes  downward,  forward,  and  inward,  and,  crossing 
the  ureter,  gives  a  branch  to  the  vas  deferens  and  then  breaks  up  into  a  number  of  small 
branches  which  are  distributed  to  the  vesicula  seminalis.  The  deferential  branch, 
on  reaching  the  vas,  divides  into  an  ascending  and  a  descending  branch.  The  former 
passes  upward  along  the  vas  to  the  internal  abdominal  ring  and  thence  through  the 
inguinal  canal  to  the  neighborhood  of  the  epididymis,  anastomosing  with  branches  of 
tin-  spermatic  artery.  The  descending  branch  accompanies  the  vas  to  the  prostate. 

-,b.  The  Uterine  Artery. — The  uterine  artery  (a.  utcrina)  (Fig.  726)  corres- 
ponds to  the  vesiculo-deferential  antl  has  a  similar  origin.  It  passes  at  first  down\\  aid 
and  inward  upon  the  surface  of  the  levator  ani,  and  then  inward  in  a  tortuous  course 


THE   INTERNAL    ILIAC   ARTERY.  813 

along  the  base  of  the  broad  ligament  towards  the  neck  of  the  uterus.  Just  before 
reaching  the  uterus,  usually  about  2  cm.  ( ^  in. )  from  it,  the  artery  crosses  in  front 
of  the  ureter  and  then  bends  upward  between  the  two  layers  of  the  broad  ligament 
along  the  side  of  the  uterus.  Arrived  at  the  junction  of  the  Fallopian  tube  with  the 
uterus,  it  bends  outward  along  the  lower  border  of  the  tube,  and  then,  passing 
beneath  the  hilum  of  the  ovary,  terminates  by  inosculating  with  the  ovarian  artery. 
In  its  course  between  the  layers  of  the  broad  ligament  the  artery  is  accompanied 
by  the  large  uterine  veins,  which  almost  conceal  it,  and  both  artery  and  veins  are 
enclosed  in  a  rather  dense  sheath  of  areolar  tissue.  During  pregnancy  the  artery 
becomes  much  enlarged,  and  its  course,  as  well  as  that  of  its  branches,  becomes 
exceedingly  sinuous  and  even  spiral. 

Branches. — (a)  As  the  uterine  artery  crosses  the  renal  duct,  a  ureteral  branch  is  supplied 
to  the  ureter.  On  reaching  the  sides  of  the  uterus,  it  gives  off — 

(b)  One  or  several  cervical  branches.  These  pass  to  the  cervix  and  divide  into  numerous 
branches  which  supply  that  portion  of  the  uterus  and  the  upper  part  of  the  vagina.  They  are 
relatively  long  and  tortuous,  and  anastomose  below  with  the  branches  of  the  vaginal  arteries. 
Throughout  the  rest  of  its  course  along  the  sides  of  the  uterus  it  gives  off  numerous — 

(f)  Uterine  branches,  which,  although  tortuous,  yet  differ  from  the  cervical  branches  in 
being  rather  short.  They  pass  to  both  the  anterior  and  posterior  surfaces  of  the  uterus  and 
supply  its  body  and  fundus,  and  it  is  to  be  remarked  that  both  these  branches  and  the  cervical 
ones  diminish  rapidly  in  calibre  as  they  branch  upon  the  surface  of  the  uterus,  so  that  at  the 
middle  line  of  the  organ  only  exceedingly  minute  twigs  are  to  be  found. 

From  the  portion  of  the  artery  that  runs  outward  along  the  lower  border  of  the  Fallopian 
tube — 

(d]  Tubal  branches  (rami  tubarii)  are  given  off.     One  of  these,  much  stronger  than  the 
others,  arises  just  before  the  uterine  inosculates  with  the  ovarian  artery,  and  passes  outward 
along  the  tube  to  its  fimbriated  extremity,  sending  branches  to  it  through  its  entire  course. 

(e)  Ovarian  branches   (rami  ovarii)  to   the  ovary  are  finally  given   off  from  the  uterine 
artery  in  the  vicinity  of  its  anastomosis  with  the  ovarian. 

8.  The  Middle    Hemorrhoidal  Artery. — The  middle  hemorrhoidal  artery 
(a.  haemorrhoidalis  media)  (Fig.  726)  is  somewhat  variable  both  in  its  origin  and  in 
its  size.      It  arises  either  from  the  anterior  division  of  the  internal  iliac,  below  the 
hypogastric  artery,  or,  as  frequently  happens,  from  the  inferior  vesical  or  occasionally 
from  the  internal  pudic.      It  passes  along  the  lateral  surface  of  the  middle  portion  of 
the  rectum,  giving  off  branches  which,  in  addition  to  aiding  in  supplying  the  vagina 
and  communicating  with  the  vaginal  arteries,  anastomose  above  with  the  superior 
hemorrhoidal  from  the  inferior  mesenteric  and  below  with  the  inferior  hemorrhoidal 
from  the  internal  pudic. 

9.  The  Obturator  Artery. — The  obturator  artery  (a.  obturatoria)  (Fig.  724) 
arises  from  the  anterior  division  of  the  internal  iliac,  below  the  hypogastric  axis.      It 
passes  forward  along  the   lateral  wall  of  the  pelvis,  resting  upon  the  pelvic  fascia 
which   covers  the  upper   portion   of  the  internal  obturator  muscle,  and  having  the 
obturator  nerve  immediately  above  it  and  the  vein  below.      Just  before  reaching  the 
anterior  wall  of  the  pelvis  it  is  crossed  by  the  vas  deferens  in  the  male,  as  it  passes 
downward  from  the  internal  abdominal  ring,  and  then  it  pierces  the  pelvic  fascia  and 
makes  its  exit  from  the  pelvic  cavity  through  the  obturator  canal,  on  emerging  from 
which  it  divides  into  two  terminal  branches,  an  internal  and  an  external. 

Branches.—  Within  the  pelvis  the  obturator  artery  gives  off  several  small  branches,  of 
which  the  more  important  are — 

( a )  An  iliac  branch,  which  is  given  off  near  the  origin  of  the  obturator  and  passes  up  to 
the  iliac  fossa,  supplying  the  ilio-psoas  muscle,  giving  nutrient  branches  to  the  ilium  and  anasto- 
mosing with  the  iliac  branch  of  the  ilio-lumbar  artery. 

(b)  Muscular  branches,  which  are  distributed  to  the  obturator  interims  and  the  levator  ani. 

(c)  Vesical  branches,  which  pass  to  the  bladder  beneath  the  false  lateral  ligament  and 
anastomose  with  branches  from  the  superior  vesical  ;  and 

(d)  A  pubic  branch   (ramus  puhicus)  which  arises  just  before  the  artery  enters  the  obtu- 
rator canal  and  ascends  upon  the  posterior  surface  of  the  os  pubis  to  anastomose  above  with  the 
pubic  branch  of  the  deep  epigastric  artery. 

Outside  the peh ~is  the  obturator  artery  divides  into  an  external  and  an  internal  branch. 


8 14  HUMAN    ANATOMY. 

(e)  The  external  branch  passes  around  the  external  border  of  the  obturator  foramen, 
beneath  the  external  obturator  muscle,  and  terminates  by  anastomosing  with  the  internal  branch 
and  with  the  internal  circumflex  from  the  deep  femoral.  Near  its  origin  it  gives  off — 

(aa)  An  internal  branch,  which  passes  downward  on  the  posterior  surface  of  the  obturator 
membrane,  under  cover  of  the  internal  obturator  muscle,  to  the  tuberosity  of  the  ischium,  and 
it  also  gives  rise  to — 

(bb)  An  acetabular  branch  (ramus  acetabuli),  which  passes  through  the  cotyloid  notch  and 
supplies  the  fatty  tissue  occupying  the  bottom  of  the  acetabulum. 

(/)  The  internal  branch  runs  around  the  inner  border  of  the  obturator  foramen,  beneath 
the  external  obturator  muscle,  and  terminates  by  anastomosing  with  the  external  branch. 

Variations. — The  obturator  artery  varies  greatly  in  its  origin,  and  these  variations  may  In- 
divided  into  two  groups,  according  as  the  origin  is  from  the  internal  or  the  external  iliac  system 
of  arteries.  While  the  origin  of  the  vessel  from  the  anterior  division  of  the  internal  iliac  is  the 
most  frequent,  yet,  when  compared  with  all  the  variations  taken  together,  it  occurs  in  some- 
what less  than  50  per  cent,  of  cases.  Of  other  origins  from  the  system  of  the  internal  iliac  there 
may  be  mentioned  those  from  the  main  stem  of  the  iliac  before  its  division,  from  its  posterior 
division,  and  from  the  gluteal  artery.  Furthermore,  its  origin  may  occur  from  either  the  sciatic 
or  the  internal  pudic  artery,  although  such  cases  are  rare. 

More  frequent  and  of  greater  importance  from  the  practical  stand-point  is  the  origin 
from  the  external  iliac  system,  which  occurs  in  about  30  per  cent,  of  cases.  In  the  immense 
majority  of  such  cases— in  almost  twenty-nine  out  of  every  thirty — the  origin  is  from  the  deep 
epigastric  artery,  being  in  the  remaining  cases  from  the  external  iliac  distal  to  the  deep  epigas- 
tric or  from  the  upper  part  of  the  common  femoral  artery.  Undoubtedly  the  primary  relations 
of  the  obturator  artery  are  with  the  internal  iliac  system  of  vessels,  and  the  origin  from  the  ex- 
ternal iliac  system  is  to  be  regarded  as  due  to  the  secondary  enlargement  of  an  anastomosis  nor- 
mally present  and  the  diminution  or  inhibition  of  the  original  stem  of  the  obturator.  Possibilities 
for  such  a  process  are  furnished  by  the  normal  anastomosis  between  the  pubic  branches  of  the 
obturator  and  the  external  circumflex,  and  all  gradations  may  be  found  between  the  normal  ar- 
rangement and  the  complete  replacement  of  the  original  intrapelvic  portion  of  the  obturator  by 
the  pubic  anastomosis. 

The  origin  of  the  obturator  from  the  deep  epigastric  artery  ( Fig.  728)  becomes  of  importance 
from  the  fact  that,  in  order  to  reach  its  point  of  exit  from  the  pelvis,  the  obturator  canal,  the 
vessel  must  come  into  intimate  relations  with  the  crural  ring,  and  mav  thus  add  an  important 
complication  to  the  operation  for  the  relief  of  femoral  hernia  (page  *775)-  There  are  three  possi- 
ble courses  for  the  vessel  in  relation  to  the  ring  :  ( i )  it  may  pass  inward  from  its  origin  over  the 
upper  border  of  the  ring  and  then  curve  downward  and  inward  along  the  free  border  of  (iim- 
bernat's  ligament  to  reach  the  obturator  canal  ;  (2)  it  may  bend  downward  abruptly  at  its  origin 
and  pass  m  an  almost  direct  course  to  the  obturator  canal,  passing  over  the  inner  surface  of 
the  external  iliac  vein,  and  therefore  down  the  outer  border  of  the  crural  ring;  or  (3)  it  may 
pass  directly  across  the  ring.  As  regards  the  relative  frequency  of  each  of  these  courses  it  is 
interesting  to  note  that,  according  to  observations  made  by  Jastschinski,  the  course  along  the 
outer  border  of  the  ring  is  much  the  most  frequent,  occurring  in  60  per  cent,  of  cases,  and  being 
more  frequent  in  females  than  in  males.  The  course  across  the  ring  occurs  in  about  22.5  per 
cent,  of  cases,  and  is  again  more  frequent  in  females  than  in  males  ;  while  the  course  along  the 
free  edge  of  Gimbernat's  ligament  occurs  in  only  17.5  per  cent,  of  cases,  and  is  more  common 
in  males  than  in  females.  The  differences  in  the  two  sexes  are  associated  with  the  differences  in 
the  form  of  the  pelvis  and  of  the  obturator  foramen. 

Practical  Considerations. — The  gluteal  and  sciatic  arteries  have  not  uncom- 
monly been  affected  by  aneurism  which  has  shown  itself  as  a  pulsating  compressible 
tumor  in  the  gluteal  region,  often  with  a  bruit,  and  usually  causing  pain  over  the 
nates,  extending  down  the  posterior  aspect  of  the  thigh — from  pressure  on  tin-  sciatic 
nerve — and  causing  lameness. 

The  gluteal  aneurism  is  situated  somewhat  farther  back  in  the  buttock  than  the 
sciatic,  which  is  apt  to  be  farther  forward  and  downward,  near  the  gluteo-femoral 
crease  (Agnew). 

Either  of  these  vessels  or  the  internal  pudic  may  require  ligature  on  account  of 
stab-wounds.  Serious  hemorrhage  from  a  wound  in  the  upper  part  of  the  glutens 
maxinr.is,  i.e.,  a  little  below  a  line  from  the  posterior  superior  iliac  spine  to  the  top 
of  the  great  trochanter,  is  likely  to  proceed  from  the  gluteal  artery.  Lower,  nearer 
to  the  fold  of  the  buttock,  it  may  come  from  the  sciatic.  The  gluteal  may  be  tied 
through  an  incision  made  along  the  line  just  mentioned,  from  the  posterior  superior 
spine  to  the  trochanter.  With  the  thigh  in  inward  rotation,  the  junction  of  the  middle 
with  the  upper  third  of  that  line  indicates  about  the  point  where  the  gluteal  artery 
comes  out  through  the  sciatic  notch.  The  fibres  of  the  glutens  maximus  are  sepa- 
rated, the  muscle  is  relaxed  by  full  extension  of  the  thigh,  and  the  upper  bony  margin 


THE   INTERNAL   ILIAC   ARTERY.  815 

of  the  sciatic  notch  is  felt  for  with  the  finger  through  the  interspace  between  the  pyri- 
formis  and  the  gluteus  medius.  The  artery  may  be  found  as  it  turns  over  the  bony 
tip  of  the  sacro-sciatic  foramen  towards  the  dorsum  ilii.  The  sciatic  artery  may  be 
reached  through  the  same  incision,  the  finger  then  being  carried  below  the  pyriformis 
muscle,  when  the  spine  of  the  ischium  and  the  sharp  edge  of  the  sacro-sciatic  ligament 
will  serve  as  landmarks. 

The  point  of  emergence  of  both  the  sciatic  and  internal  pudic  arteries  is  indicated 
with  sufficient  accuracy  by  the  junction  of  the  lower  and  middle  thirds  of  a  line  drawn 
from  the  tuberosity  of  the  ischium  to  the  posterior  superior  spine  of  the  ilium.  The 
incision  employed  should  follow  the  direction  of  the  fibres  of  the  greater  gluteal 
muscle. 

10.  The  Sciatic  Artery. — The  sciatic  artery  (a.  glutaea  inferior)  (Fig.  727)  is 
one  of  the  two  terminal  branches  of  the  anterior  division  of  the  internal  iliac.      It  lies 
at  first  internal  and  posterior  to  the  internal  pudic  artery,  and  is  directed  downward 
and  backward  towards  the  lower  part  of  the  great  sacro-sciatic  foramen,  passing  usu- 
ally below  the  fourth  sacral  nerve.      It  makes  its  exit  from  the  pelvis  through  the  great 
sacro-sciatic  foramen,  below   the  pyriformis   muscle,   and  bends  downward   beneath 
the  gluteus  maximus.      It  crosses  the  internal  pudic  artery  at  about  the  level  of  the 
spine  of  the  ischium,  and  in  the  rest  ot  its  course  lies  to  the  inner  side  of  the  great 
sciatic  nerve.      It  descends  upon  the  gemelli,  the  internal  obturator,  and  the  quad- 
ratus  femoris,  and,  after  giving  off  its  principal  branches,  is  continued  down  the  leg 
as  a  slender  vessel,  the  comes  nervi  ischiadici. 

Branches. —  Within  the  pelvis  the  sciatic  artery  gives  off  some  small  and  inconstant  branches 
to  the  internal  obturator  and  pyriformis  muscles  and  to  the  trunks  of  the  sacral  pelvis. 

Outside  the  pelvis  it  gives  rise  to  several  larger  branches. 

(a)  The  coccygeal  branch  passes  inward  and  pierces  the  great  sacro-sciatic  ligament  and 
the  gluteus  maximus  near  its  origin,  terminating  in  the  tissues  over  the  lower  part  of  the  sacrum 
and  coccyx. 

(f>)  Muscular  branches,  variable  in  number,  pass  to  the  neighboring  muscles,  some  of 
them  being  continued  beneath  the  quadratus  femoris  to  reach  the  capsule  of  the  hip-joint. 
One  branch  somewhat  larger  than  the  rest  can  frequently  be  seen  entering  the  deep  surface  of 
the  gluteus  maximus  in  company  with  the  inferior  gluteal  nerve  ;  it  supplies  the  muscle  and 
forms  anastomoses  with  the  gluteal  artery. 

(c)  An  anastomotic  branch  passes  transversely  outward,  usually  beneath  the  great  sciatic 
nerve,  towards  the  greater  trochanter  of  the  femur.     It  gives  twigs  to  the  gemelli  muscles,  and 
in  the  neighborhood  of  the  trochanter  anastomoses  with  the  terminal  branch  of  the  internal  cir- 
cumflex, with  the  transverse  branch  of  the  external  circumflex,  and,  below,  with  the  first  per- 
forating artery,  completing  what  is  termed  the  crucial  anastomosis, 

(d)  Cutaneous  branches,  variable  in  number,  wind  around  the  lower  border  of  the  gluteus 
maximus  in  company  with  branches  of  the  small  sciatic  nerve,  and  supply  the  integument  over 
the  lower  part  of  the  gluteal  region. 

(e)  The  a.  comes  nervi  ischiadici  is  the  continuation  of  the  sciatic  artery.     It  is  a  long, 
slender  branch  which  passes  downward  upon  or  in  the  substance  of  the  great  sciatic  nerve,  sup- 
plying it  and  anastomosing  with  the  perforating  branches  of  the  profunda  femoris. 

Variations. — The  occasional  origin  of  the  sciatic  from  the  gluteal  artery  or  from  the 
hypogastric  axis  has  already  been  described  in  connection  with  the  variations  of  the  internal 
iliac  (page  808).  Occasionally  it  has  a  double  origin  from  both  the  gluteal  and  the  anterior 
division  of  the  internal  iliac,  or  it  may  be  double,  owing  to  the  existence  of  stems  from  each  of 
these  vessels  which  pursue  independent  courses. 

In  addition  to  its  normal  branches,  it  may  give  origin  to  the  lateral  sacral,  the  inferior 
vesical,  and  the  uterine  or  the  middle  hemorrhoidal.  Especial  interest  attaches  to  the  comes 
nervi  ischiadici,  which  occasionally  traverses  the  entire  length  of  the  thigh  to  unite  below  with 
the  popliteal  artery.  It  represents  the  original  main  stem  of  the  sciatic  artery,  of  which  the 
popliteal  was  primarily  the  continuation,  the  connection  of  that  artery  with  the  femoral,  and  the 
subsequent  diminution  of  the  sciatic  being  secondary  arrangements  (page  824). 

11.  The    Internal    Pudic   Artery. — The   internal   pudic  artery  (a.  pudenda 
interna)  (Fig.  727)  is  the  other  terminal  branch  of  the  anterior  division  of  the  internal 
iliac.      It  is  directed  downward  in  front  of  the  sciatic  artery  to  the  lower  portion  of  the 
great  sacro-sciatic  foramen,  where  it  makes  its  exit  from  the  pelvis,  passing  between 


8i6 


HUMAN   ANATOMY. 


FIG.  727. 


Superior  gluteal  artery 

Superficial  branch  of 
superior  uluteal 

Gluteus  maximus 
Sciatic  arter;- 


Coccygeal  artery  - 
Internal  purlic  artery 


Tuber  ischii  ^ 
Biceps,  stump 


Transverse  branch  of 
internal  circumflex 


Perforating  branches  of  deep  femoral  artery 


Semimembranosus 
Popliteal  artery 

Muscular  branches 
Superior  internal  articular  artery 


Gluteus  medius,  cut 

Upper  ramus  of  deep  branch  of 

superior  gluteal  artery 
Gluteus  minimus 

Muscular  branch  of  sup.  gluteal 
Lower  ramus  of  deep  branch 
Pyriformis  (of  sup.  gluteal 


Gluteus  medius 

Greater  sciatic  nerve 
Tendon  of  obturator  internus 

Articular  branch  from  ascending 

branch  of  internal  circumflex 

Articular  branch  of  sciatic  artery 

Anastomotic  branch 

Comes  nervi  ischiadici 
Gluteus  maximus 

From  external  circumflex 
Superior  perforating  artery 

From  external  circumflex 

Vastus  externus 

Middle  perforating  artery 


Inferior  perforating  artery 

Biceps— short  head 
Biceps— long  head 


Muscular  branch  of  femoral 
artery 


Popliteal  vein 


Superior  external  articular  artery 

Hxternal  sural  artery 

Inferior  external  articular  artery 

Gastrocnemius 


Arteries  of  gluteal  region  and  posterior  surface  of  right  thigh. 


THE   INTERNAL   ILIAC   ARTERY.  817 

the  pyriformis  and  coccygeus  muscles.  It  then  bends  forward,  under  cover  of  the 
gluteus  maximus,  and,  curving  beneath  the  spine  of  the  ischium,  passes  through  the 
lesser  sacro-sciatic  notch  to  enter  the  ischio-rectal  fossa.  Its  course  is  then  forward 
along  the  lateral  wall  of  the  fossa,  lying  with  its  accompanying  vein  and  the  pudic 
nerve  in  a  fibrous  canal  known  as  AlcocK1 s  canal,  formed  by  a  splitting  of  the  obtu- 
rator fascia  near  its  lower  border.  At  the  anterior  portion  of  the  ischio-rectal  fossa 
the  artery  perforates  the  triangular  ligament  of  the  perineum  and  passes  forward 
between  the  two  layers  composing  that  structure,  finally  perforating  the  superficial 
layer  and  becoming  the  dorsal  artery  of  the  penis  (or  clitoris). 

Branches. — In  the  pelvic  and  gluteal  portions  of  its  course  the  internal  pudic,  as  a  rule, 
gives  off  only  slender  muscular  branches  to  the  neighboring  muscles.  In  its  ischio-rectal  por- 
tion its  branches  are  more  important. 

(a)  The  inferior  hemorrhoidal  arteries  (aa.  haemorrhoidales  inferiores),  usually  two  in  num- 
ber, but  frequently  only  one,  which  early  divides  into  two  or  three  stems,  arise  from  the  internal 
pudic,  just  after  it  has  traversed  the  lesser  sacro-sciatic  foramen.  They  perforate  the  inner  wall 
of  Alcock's  canal  and  pass  through  the  fat-tissue  which  occupies  the  ischio-rectal  fossa  towards 
the  lower  part  of  the  rectum.  They  give  branches  to  the  ischio-rectal  fat-tissue,  to  the  sphincter 
and  levator  am,  to  the  gluteus  maximus,  to  the  skin  over  the  ischio-rectal  and  anal  regions,  and 
to  the  lower  part  of  the  rectum,  anastomosing  above  with  the  middle  hemorrhoidal  branches  of 
the  internal  iliac. 

(&}  The  superficial  perineal  artery  (a.  perinei)  arises  just  before  the  internal  pudic  enters  the 
space  between  the  layers  of  the  triangular  ligament  of  the  perineum.  It  is  at  first  directed 
almost  vertically  downward,  but  quickly  bending  around  the  posterior  border  of  the  superficial 
transverse  muscle  of  the  perineum,  near  its  origin  from  the  ischial  tuberosity,  it  is  directed  for- 
ward and  inward  in  the  interval  between  the  ischio-cavernosus  and  bulbo-cavernosus  muscles. 
In  this  portion  of  its  course  it  is  covered  only  by  the  superficial  perineal  fascia  and  the  integu- 
ment, and  passes  forward  to  be  distributed  to  the  posterior  portion  of  the  scrotum  in  the  male 
and  to  the  labia  majora  in  the  female.  In  its  course  it  gives  off  numerous  cutaneous  branches 
as  well  as  branches  to  the  neighboring  muscles.  One  of  these  latter,  usually  somewhat  larger 
than  the  rest,  passes  inward  towards  the  median  line,  beneath  the  superficial  transverse  muscle 
of  the  perineum,  which  it  supplies,  as  also  the  bulbo-cavernosus  and  external  sphincter  ani. 
This  is  what  has  been  termed  the  transverse  artery  of  the  perineum.  It  anastomoses  at  the 
central  point  of  the  perineum  with  its  fellow  of  the  opposite  side,  with  other  branches  from  the 
superficial  perineal  artery  anteriorly  and  with  branches  of  the  inferior  hemorrhoidals  posteriorly. 

In  its  perineal  portion  also  the  internal  pudic  gives  off  important  branches. 

(c)  The  artery  to  the  bulb  (a.  bulbi  urethrae  or  a.  bulbi  vestibuli)  arises  from  the  internal 
pudic  a  short  distance  after  it  has  entered  the  deep   perineal   interspace.      It  is  a  relatively 
large  vessel   in  the   male,  and   passes   almost  horizontally  inward  towards  the  median  line. 
Before  reaching  this,  however,  it  perforates  the  superficial  layer  of  the  triangular  ligament, 
enters  the  substance  of  the  bulbus  urethrae  about  15  mm.  in  front  of  its  posterior  extremity, 
and  is  distributed  to  that  structure  and  to  the  posterior  third  of  the  corpus  spongiosum  and 
urethra.      In  the  female  it  is  of  a  lesser  calibre  than  in  the  male,  and  is  distributed  to  the  bulbus 
vestibuli. 

(d)  The  urethral  artery  (a.  urethralis)  arises  usually  some  distance  anteriorly  to  the  artery 
of  the  bulb,  and,  like  it,  is  directed  medially,  and  penetrates  the  superficial  layer  of  the  tri- 
angular ligament  to  enter  the  substance  of  the    corpus  spongiosum.     It  reaches  the  corpus 
spongiosum  just  behind  the  symphysis  pubis,  where  the  two  corpora  cavernosa  come  together 
to  form  the  penis,  and  is  continued  forward  in  the  spongiosum  to  the  glans.     It  is  a  somewhat 
inconstant  branch,  and  is  quite  small  in  the  female. 

(e)  The  artery  of  the  corpus  cavernosum  (a.  profunda  penis  s.  clitoridis)  arises  from  the 
internal  pudic,  just  posterior  to  the   lower  border  of  the  symphysis  pubis,  and   is   directed 
outward  towards  the  bone.      It  penetrates  the  superficial   layer  of  the  triangular   ligament 
close  to  its  attachment  to  the  pubic  ramus,  artd  enters  the  corpus  cavernosum  at  about  the 
junction  of  its  middle  and  posterior  thirds.     It  passes  to  the  centre  of  the  corpus  and  there 
divides  into  a  posterior  branch  which  supplies  blood  to  the  posterior  third  of  that  structure, 
and  an  anterior  one  which  distributes  to  its  anterior  two-thirds.     It  is  much  smaller  in  the 
female  than  in  the  male. 

(f)  The  dorsal  artery  of  the  penis  or  clitoris  (a.  dorsalis  penis  s.  clitoridis)  is  the  continua- 
tion of  the  main  stem  of  the  internal  pudic  beyond  the  origin  of  the  artery  to  the  corpus  cav- 
ernosum.    It  penetrates  the  superficial  layer  of  the  triangular  ligament  near  its  apex,  and  passes 
upward  in  the  suspensory  ligament  of  the  penis  or  clitoris  to  the  dorsal  surface  of  that  organ, 
along  which  it  passes,  lying  to  the  side  of  the  median  line  and  separated  from  its  fellow  of  the 
opposite  side  by  the  single  median  dorsal  vein.     Laterally  to  it  is  situated  the  dorsal  nerve  of 

52 


8i8  HUMAN   ANATOMY. 

the  penis  (or  clitoris),  and  still  more  laterally  the  deep  external  pudic  branch  of  the  common 
femoral  artery.  On  reaching  the  glans,  it  forms  an  anastomotic  circle  around  the  base  of  that 
structure,  uniting  with  its  fellow  of  the  opposite  side.  Throughout  its  course-  it  gives  branches  to 
the  corpus  cavernosum  and  the  integument  of  the  penis  or  the  prepuce  of  the  clitoris 

Variations. — The  occasional  origin  from  the  internal  pudic  of  the  inferior  vesical,  middle 
hemorrhoidal,  and  uterine  arteries  has  already  been  noted.  The  internal  pudic.  instead  of 
passing  out  of  the  pelvis  by  the  great  sacro-sciatic  foramen,  may  be  directed  forward  upon  the 
tloor  of  the  pelvis  and  pass  out  beneath  the  pubic  symphysis  to  become  the  dorsal  artery  of  the 
penis.  More  frequently  this  course  is  taken  by  an  accessory  internal  pudic  which  arises  from 
the  pudic  in  cases  where  this  vessel  appears  to  arise  from  the  hypogastric  axis,  a  condition 
which  results  in  the  early  division  of  the  common  stem  from  which  the  sciatic  and  internal 
pudic  arteries  normally  arise. 

The  artery  of  the  bulb  may  arise  opposite  the  ischial  tuberosity  and  pass  obliquely  forward 
and  medially  across  the  ischio-rectal  fossa,  and  in  some  cases  it  passes  at  first  directly  across 
towards  the  anus  and  then  bends  forward  to  reach  the  bulb. 

The  dorsal  artery  of  the  penis  or  clitoris  occasionally  unites  with  its  fellow  of  the  opposite 
side  to  form  a  single  median  artery,  or  the  two  arteries  of  opposite  sides  may  be  united  by  trans- 
verse anastomoses.  Sometimes  a  third  vessel  arises  either  directly  from  the  anterior  division 
of  the  internal  iliac  or  from  the  obturator,  even  when  this  vessel  takes  its  origin  from  the  deep 
epigastric. 

Anastomoses  of  the  Internal  Iliac. — The  internal  iliac  makes  anastomoses 
with  branches  of  the  abdominal  aorta,  of  the  external  iliac,  and  with  its  fellow  of  the 
opposite  side,  and  it  is  through  these  connections  that  the  collateral  circulation  may 
be  established. 

Of  branches  communicating  with  the  abdominal  aortic  system  there  are  the 
hemorrhoidal  branches  which  anastomose  with  the  superior  hemorrhoidal  from  the 
inferior  mesenteric,  the  uterine  which  anastomoses  with  the  ovarian,  and  the  lateral 
sacrals  which  anastomose  with  the  middle  sacral.  Communications  with  the  system 
of  the  external  iliac  are  through  the  sciatic  with  branches  of  the  profunda  femoris, 
through  the  ilio-lumbar  and  gluteal  with  the  external  and  internal  circumflex  iliacs, 
and  through  the  obturator  with  the  deep  epigastric  through  the  pubic  branches.  The 
anastomoses  across  the  middle  line  occur  between  the  vesical,  prostatic  (vaginal), 
obturator,  and  internal  pudic  branches. 

THE   EXTERNAL   ILIAC   ARTERY. 

The  external  iliac  artery  (a.  iliaca  externa)  (Figs.  724,  728)  extends  from  the 
bifurcation  of  the  common  iliac,  opposite  the  sacro-iliac  articulation,  to  a  point  beneath 
Poupart's  ligament'miclway  between  the  anterior  superior  spine  of  the  ilium  and  the 
symphysis  pubis.  It  there  becomes  the  femoral  artery.  In  the  adult  the  external 
iliac  is  usually  larger  than  the  internal  and  is  directed  more  nearly  in  the  line  of  the 
common  iliac,  downward,  forward,  and  outward  along  the  brim  of  the  true  pelvis. 

Relations. — Anteriorly,  the  artery  is  covered  by  peritoneum  and  is  enclosed, 
together  with  the  vein,  in  a  moderately  dense  sheath  derived  from  the  subperitoneal 
tissue  and  termed  Abernethy1  s  fascia.  By  the  peritoneum  it  is  separated  on  the 
right  side  from  the  terminal  portion  of  the  ileum  and  sometimes  from  the  vermiform 
appendix,  and  on  the  left  from  the  sigmoid  colon.  Near  its  origin  it  is  crossed  by 
the  ovarian  vessels  in  the  female  and  sometimes  by  the  ureter  ;  near  its  lower  end  it 
is  crossed  obliquely  by  the  genital  branch  of  the  genito-crural  nerve  and  by  the  deep 
cpi-astric  vein.  Some  lymph-nodes  are  also  found  resting  upon  its  anterior  surface. 
Posteriorly,  it  rests  upon  the  iliac  fascia  which  separates  it  from  the  psoas  muscle  . 
ni<'dially~\\.  is  crossed  near  its  lower  end^  by  the  vas  deferens  in  the  male  and  the 
n .mid  ligament  of  the  uterus  in  the  female,  and  is  accompanied  throughout  its 
course  by  the  external  iliac  vein,  which  lies,  however,  on  a  slightly  posterior  plane. 
I ., it, nilly,  it  is  in  relation  to  the  genito-crural  nerve. 

Branches. — In  addition   to  sonic  small   twigs  to  the  psoas  muscle  and  to  th 
neighboring  lymphatic  glands,  the  external  iliac  gives  origin  to  (l)  the  </,•</> 
.ind  (  2  )  the  <i<r/>  <i)cinnjlr\   iliac  arteries. 

Variations. -The  external  iliac  varies  considerably  in  length,  according  to  the  level  at 
which  the  abdoiiiin.il  aorta  and  the  common  iliac  bifurcate  Independently  of  •  this,  however, 
and  especially  in  ai;ed  individuals,  it  is  fre<|iientlv  longer  than  is  necessary  to  reach  in  a  direct 


THE   EXTERNAL    ILIAC    ARTERY.  819 

line  from  the  common  iliac  to  beneath  Poupart's  ligament,  and  in  such  cases  it  makes  a  more 
or  less  pronounced  bend  which  may  dip  below  the  brim  of  the  pelvis.  In  the  embryo  it  is  a 
comparatively  small  vessel,  the  main  supply  of  the  lower  limb  being  through  the  sciatic,  which 
is  continuous  below  with  the  popliteal  .  page  -;  ;  -  nally  this  condition  is  retained,  the 

artery  then  terminating  by  becoming  the  deep  instead  of  the  common  femoral. 

In  addition  to  the  usual  branches  it  may  give  off  the  obturator  i  page  814),  or  an  accessory 
deep  epigastric  or  deep  circumflex  iliac.  Or  branches  usually  arising  from  the  common  femoral, 
such  as  the  superficial  external  pudic  or  even  the  profunda  iemoris,  may  arise  from  it. 

Practical  Considerations. — The  external  iliac  artery  is  occasionally  the  seat 

eurism,  and  such  tumors  have  been  mistaken  for  malignant  growths  or  for 
abscess.  A  swelling  with  expansile  pulsation  and  bruit  can  usually  be  found  in  the 
line  of  the  vessel  near  the  brim  of  the  pelvis,  and  the  patient  will  be  unable  to  extend 
freely  the  thigh  or  the  trunk,  and  will  lean  forward  in  walking  or  standing  to  relieve 
the  ilio-psoas  from  pressure.  There  is  apt  to  be  pain  in  the  groin  and  down  the  front 
of  the  thigh  from  pressure  on  the  anterior  crural  nerve,  or  on  the  crural  branch 
of  the  genito-crural. 

It  may  be  imperfectly  compress fd  just  above  its  termination  at  the  middle  of 
Poupart's  ligament,  but,  as  is  the  case  with  the  common  and  internal  iliacs.  the 
circulation  through  it  is  better  controlled  by  pressure  on  the  abdominal  aorta.  The 
line  of  the  vessel  extends  from  a  point  half-way  between  the  pubic  symphysis  and  the 
anterior  superior  spinous  process  to  a  point  a  little  below  and  to  the  left  of  the 
umbilicus.  The  course  of  the  external  iliac  corresponds  to  the  lower  third  of  this 
line,  the  upper  two-thirds  representing  the  line  of  the  common  iliac, 

Ligation  of  the  vessel  has  been  done  for  aneurism  of  the  common  femoral,  for 
hemorrhage,  and  as  a  palliative  in  malignant  growths  or  in  elephantiasis  of  the 
extremity. 

Like  the  other  iliacs.  it  may  be  approached  by  either:  (i)  the  intraperitoneal; 
the  extra  peritoneal  route. 

i.  The  incision  should  be  made  in  the  semilunar  line,  and  will  thus  cross  the 
line  of  the  vessel  obliquely.  Its  lower  end  should  reach  Poupart's  ligament.  Its 
i  will  vary  with  the  thickness  of  the  abdominal  wall)  from  three  inches  to  four 
inches.  The  superficial  circumflex  ilii  and  the  deep  epigastric  arteries  may  require 
ligation.  The  intestines  are  displaced  upward.  At  the  left  side  the  sigmoid  flexure, 
and  on  the  right  the  termination  of  the  ileum,  may  be  found  in  close  relation  to  the 

1.  On  both  sides  the  spermatic  vessels  cross  it.  and  their  distention  (analogous 
to  that  of  the  mesenteric  vessels  spoken  of  in  connection  with  ligation  of  the  left 
common  iliac)  (page  808),  when  deprived  of  their  peritoneal  support,  has  been  noted 

M.ikins  \ 

The  peritoneum  over  the  vessel — on  the  left  side  possibly  a  part  of  the  sigmoid 
colon — is  divided  parallel  with  the  long  axis  of  the  artery,  and  the  needle  is 
—  d  from  the  vein. 

2.  Ligation  by  the  extraperitoneal  method — still  preferred  by  many  surgeons  in 
the  case  of  this  vessel — is  done  through  an  incision  parallel  with  Poupart's  ligament, 
but  slightly  convex  downward,  beginning  one  inch  above  the  anterior  superior  spinous 
process  of  the  ilium  and  ending  at  the  outer  pillar  of  the  external  abdominal  ring. 
After  dividing  the  abdominal  muscles  and  the  transversalis  fascia,  the  separation  of 
the  peritoneum  from  the  iliac  fascia  is  begun  near  the  outer  extremity  of  the  wound, 
where  the  subperitoneal  areolar  tissue  is  more  abundant  and  the  connection  of  the 
peritoneum  and  the  fascia  less  intimate.     After  the  detachment  has  been  effected 

rly  by  means  of  a  ringer \  the  vessel  is  exposed  with  the  vein  lying  behind 
it  above  and  to  the  inner  side  near  Poupart's  ligament,  and  the  anterior  crural 
nerve  some  distance  to  the  outer  side.  The  needle  should  be  passed  from  within 
outward. 

The  collateral  circulation  is  carried  on  from  above  the  ligature  by  (a}  the  lumbar; 

he  obturator;  (r)  the  sciatic;  (</)  the  gluteal;  (<^  the  internal  pudic;  and  (/") 
the  internal  mammary  and  lower  intercostals  anastomosing  respectively  with  \a'>  the 
deep  circumflex  iliac:  (P~)  the  internal  circumflex:  .  the  perforating  \proiu: 

the  external  circumflex:  ^ )  the  external  pudic  (femoral);  and  (_/")  the  deep 
epigastric  from  below. 


820  HUMAN   ANATOMY. 

i.  The  Deep  Epigastric  Artery. — The  deep  epigastric  artery  (a.  epigastrica 
inferior)  (Fig.  728)  arises  from  the  anterior  surface  of  the  external  iliac,  a  short 
distance  above  where  it  passes  beneath  Poupart's  ligament.  Immediately  after  its 
origin  it  bends  downward  and  medially  to  pass  the  lower  border  of  the  internal 
abdominal  ring,  being  crossed  in  this  situation  by  the  vas  deferens  in  the  male  and  the 
round  ligament  of  the  uterus  in  the  female.  It  then  curves  upward  and  medially 
along  the  medial  border  of  the  internal  abdominal  ring  and  ascends  along  the  outer 
border  of  Hesselbach's  triangle  (page  526),  of  which  it  forms  the  lateral  boundary. 
Throughout  this  portion  of  its  course  it  lies  between  the  peritoneum  and  the  trans- 
versalis  fascia,  but  at  about  the  level  of  the  fold  of  Douglas,  in  the  posterior  surface 
of  the  sheath  of  the  rectus  abdominis,  it  pierces  the  fascia  and  ascends  between  the 
muscle  and  the  posterior  layer  of  its  sheath,  eventually  entering  the  substance  of  the 
muscle,  where  it  terminates  by  anastomosing  with  the  superior  epigastric  branch  of 
the  internal  mammary  artery. 

Branches. — Throughout  its  course  the  deep  epigastric  artery  gives  off  a  number  of  branches. 

(a)  The  cremasteric  branch  (a.  spermatica  externa  in  the  male,  a.  ligamenti  teretis  in  the 

female)  is  given  off  a  short  distance  beyond  the  origin  of  the  deep  epigastric  and  accompanies 

FIG.  728. 

Anterior  superior  spine  of  ilium 

Deep  circumflex  iliac  artery 


Rectus  abdominis, 
turned  dowmv.int 
with  part  of  ab- 
dominal wall 


External  iliac  artery 
External  iliac  vein 


ternal  iliac  artery  as  the  in 

"Murator 
bliterated  hypo- 

mttiM^A"-  c^:  .*•  .jur>i<i"  i — 1_         rSiul0" 

•Vesical  branch  of 
Edge  of  ovary. 


Round  ligament  of  ut< 

Cut  edge  of  broad  ligament 


Obturator  vein 


Portion  of  left  half  pelvis  of  female  subject  viewed  from  above  and  right 
side,  showing  obturator  artery  arising  from  deep  epigastric. 

the  spermatic  cord  or  round  ligament  of  the  uterus  through  the  inguinal  canal.  In  the  male  it 
supplies  the  cremaster  muscle  and  the  spermatic  cord,  anastomosing  with  the  spermatic  and 
deferential  arteries,  and  in  the  female,  in  which  it  is  small,  it  supplies  the  lower  part  of  the 
round  ligament  and  terminates  in  the  labia  majora  by  anastomosing  with  branches  of  the  super- 
ficial  perineal  artery. 

(b}  The  pubic  branch  (ramiis  pulticus)  arises  a  short  distance  beyond  the  cremasteric  and, 
passing  cither  above  or  below  the  femoral  ring,  passes  downward  and  inward  upon  tin-  posterior 
surface  of  the  os  pubis,  where  it  may  anastomose  with  the  pubic  branch  of  tin-  obturator.  It  is 
by  the  anastomosis  and  enlargement  of  this  artery  and  the  pubic  branch  of  the  obturator 
that  the  latter  vessel  comes  to  arise  so  frequently  from  the  deep  epigastric  i  page  814).  And 
even  when  the  obturator  has  its  normal  origin,  the  anastomosis  may  render  the  pubic  branch  of 
the  deep  epigastric  of  considerable  importance  in  the  operation  for  the  relief  of  femoral  hernia. 

(c]  Muscular  branches,  variable  in  number,  are  given  off,  for  the  most  part,  from  tin- 
outer  side  of  the  artery  and  supply  the  muscles  of  the  abdominal  walls.     They  anastomose  with 
branches  of  the  lower  intercostal  and  lumbar  arteries. 

(d)  Cutaneous  branches,  also  variable  in  number,  pierce  the  rectus  and  the  anterior  wall 
of  its  sheath  and  supply  the  skin  of  the  abdomen  near  the  median  line. 


THE   FEMORAL   ARTERY.  821 

Variations.— The  deep  epigastric  may  arise  from  the  external  iliac  higher  up  than  usual, — 
as  high,  indeed,  as  a  point  6  cm.  (2^  in.)  above  Poupart's  ligament.  In  such  cases  it  passes 
downward  and  forward  upon  the  anterior  surface  of  the  external  iliac  to  reach  the  abdominal 
wall.  It  may  also  arise  below  its  usual  position, — that  is  to  say,  from  the  common  femoral 
artery, — and  it  may  be  given  off  from  a  trunk  common  to  it  and  the  deep  circumflex  iliac. 

In  addition  to  being  frequently  the  origin  of  the  obturator  (page  814),  it  may  be  given  off 
from  that  artery  as  a  result  of  the  enlargement  of  the  anastomosis  of  the  pubic  branches  of  the 
two  arteries  and  the  subsequent  degeneration  of  the  proximal  portion  of  the  deep  epigastric. 
Occasionally  it  gives  origin  to  the  dorsal  artery  of  the  penis  or  clitoris,  an  arrangement  which 
also  results  from  its  relation  to  the  obturator,  from  which  this  artery  sometimes  arises. 

2.  The  Deep  Circumflex  Iliac  Artery. — The  deep  circumflex  iliac  artery  (a. 
circumflexa  ilium  profunda)  (Fig.  728)  arises  from  the  outer  surface  of  the  external 
iliac,  a  little  below  the  deep  epigastric.  It  passes  outward  along  the  lower  border 
of  Poupart's  ligament,  enclosed  in  a  sheath  formed  by  the  iliac  fascia,  and  opposite  the 
anterior  superior  spine  of  the  ilium,  or  it  may  be  a  little  beyond  it,  divides  into  an 
ascending  and  a  horizontal  branch. 

Branches. — In  its  course  it  gives  branches  to  the  muscles  of  the  abdominal  wall  and,  at 
the  anterior  superior  spine  of  the  ilium,  to  the  upper  part  of  the  sartorius  and  to  the  tensor 
vaginae  femoris. 

(a)  The  ascending  branch  pierces  the  transversalis  muscle  and  ascends  directly  upward 
between  that  muscle  and  the  internal  oblique.     It  sends  branches  to  both  these  muscles,  as  well 
as  to  the  external  oblique  and  the  integument,  and  terminates  by  anastomosing  with  the  lumbar 
arteries  and  with  the  tenth  aortic  intercostal  (subcostal). 

(b)  The  horizontal  branch  continues  the  course  of  the  main  stem.     It  lies  at  first  a  little 
below  the  crest  of  the  ilium,  but  later  ascends  and  perforates  the  transversalis  muscle,  passing 
onward  upon  the  crest  of  the  ilium  between  that  muscle  and  the  internal  oblique.     It  gives  off 
branches  which  supply  the  abdominal  muscles  and  anastomose  with  the  lumbar  arteries,  and 
terminates  by  anastomosing  with  the  lumbar  branches  of  the  ilio-lumbar. 

Variations. — The  deep  circumflex  iliac  artery  may  arise  from  a  common  stern  with  the  deep 
epigastric  or  from  the  upper  part  of  the  common  femoral  artery.  Not  infrequently  it  gives  rise 
to  a  branch,  shortly  after  its  origin,  which  passes  upward  upon  the  anterior  abdominal  wall,  un- 
derneath the  transversalis  fascia,  parallel  and  lateral  to  the  deep  epigastric.  This  lateral  epi- 
gastric artery,  as  it  has  been  termed,  is  occasionally  of  considerable  size,  in  which  case  the 
ascending  branch  of  the  circumflex  iliac  may  be  more  or  less  reduced.  It  may  ascend  to  the 
level  of  the  umbilicus  or  even  above  that  point,  sending  branches  to  the  muscles  of  the  abdom- 
inal wall. 

Anastomoses  of  the  External  Iliac. — Opportunities  for  the  development  of 
a  collateral  circulation  after  ligation  of  the  external  iliac  artery  are  afforded  by  the 
anastomoses  of  its  deep  epigastric  branch  with  the  superior  epigastric  branch  of  the 
internal  mammary,  with  the  lower  aortic  intercostals,  and  with  the  lumbar  arteries. 
The  deep  circumflex  iliac  also  makes  connections  with  the  lumbar  arteries  by  its 
ascending  and  lateral  epigastric  branches,  and,  furthermore,  anastomoses  with  the 
ilio-lumbar  and  gluteal  branches  of  the  internal  iliac.  Another  connection  with  the 
internal  iliac  system  is  made  by  the  anastomoses  of  the  pubic  branches  of  the  deep 
epigastric  and  obturator  arteries. 

Anastomoses  between  branches  of  the  internal  iliac  and  the  femoral  arteries  are 
also  of  importance  in  this  connection,  but  will  be  described  in  connection  with  the 
femoral  artery  (page  831). 

THE   FEMORAL   ARTERY. 

The  femoral  artery  (a.  femoralis)  (Figs.  729,  732)  is  the  continuation  of  the 
external  iliac  below  Poupart's  ligament.  Its  course  is  almost  vertically  downward, 
with  a  slight  inclination  inward  and  backward,  and  may  be  indicated  by  a  line  drawn 
from  a  point  in  Poupart's  ligament  midway  between  the  symphysis  pubis  and  the 
anterior  superior  spine  of  the  ilium  to  the  adductor  tubercle  upon  the  inner  condyle 
of  the  femur,  when  the  thigh  is  flexed  upon  the  pelvis  and  rotated  outward.  It  ter- 
minates at  about  the  junction  of  the  middle  and  lower  thirds  of  the  thigh,'  where  it 
passes  through  the  adductor  magnus  muscle,  close  to  the  inner  surface  of  the  femur, 
to  become  the  popliteal  artery. 


822 


HUMAN    ANATOMY. 


FIG.  729. 


Sartorius,  stump 

Anterior  crural  nerve 

Superficial  circumflex  iliac 

Rectus  femoris,  stump 

Iliacus 

Ascending  branch  of 

external  circumflex 
Deep  femoral  artery 

External  circumflex  artery 
Transverse  branch  of 

external  circumflex 
Descending  branch  of 

external  circumflex 


Rectus  femoris,  cut 


Vastus  externus 


Superficial  epigastric 
Femoral  artery 
Deep  external  pudic 

•Superficial  ex- 
ternal pudic 
Femoral  vein 


Pectineus 


Adductor  longus 


Aponeurotic  roof  of  Hunter's  canal 


Adductor  magnus 


Anastomotica  magna— 

superficial  branch 
Inner  hamstring  muscles 


•Vastus  interims 


From  anastomotica  magna 


Trillion  of  sartorius 
Anastomotica  magna 


Arteries  of  front  of  thigh  ;  superficial  dissection. 


THE   FEMORAL   ARTERY.  823 

Relations. — In  its  uppermost  part,  for  a  distance  of  about  3  cm.  (i^  in.),  the 
femoral  artery,  together  with  the  accompanying  vein,  is  enclosed  within  a  sheath 
formed  by  a  prolongation  of  the  transversalis  and  iliac  fasciae  below  Poupart's  liga- 
ment. This  femoral  sheath  is  funnel-shaped  and  is  divided  by  partitions  into  three 
compartments,  the  most  lateral  of  which  contains  the  artery,  the  middle  one  the 
femoral  vein,  while  the  medial  one  forms  what  is  termed  the  femoral  or  crural  canal 
(page  625).  Below,  the  walls  of  the  sheath  gradually  pass  over  into  the  con- 
nective tissue  which  invests  the  vessels. 

In  the  upper  half  of  its  course  the  femoral  artery  lies  in  Scarpa's  triangle  (page 
639),  while  in  its. lower  half  it  is  contained  within  a  space  known  as  Hunter' s  canal, 
situated  between  the  adductor  magnus  and  vastus  medialis  muscles  and  covered  in 
by  the  sartorius. 

In  Scarpa's  triangle  the  relations  of  the  artery  are  as  follows.  Anteriorly,  it 
is  covered  by  the  integument,  the  superficial  fascia,  and  the  fascia  lata,  the  inner 
margin  of  the  attenuated  portion  of  the  latter  fascia,  which  is  known  as  the  cribriform 
fascia,  overlapping  it  at  about  the  junction  of  its  upper  and  middle  thirds.  Superficial 
to  the  fascia  lata  are  some  of  the  superficial  inguinal  lymphatic  nodes  and  the  superfi- 
cial circumflex  iliac  vein,  while  deeper  and  resting  upon  the  upper  part  of  the  artery  is 
the  crural  branch  of  the  genito-crural  nerve,  and  towards  the  apex  of  the  triangle  the 
internal  cutaneous  nerve.  Posteriorly,  the  artery  rests  upon  the  tendon  of  the  ilio- 
psoas  muscle,  which  separates  it  from  the  capsule  of  the  hip-joint,  and  lower  down  it 
lies  upon  the  pectineus  muscle.  Throughout  the  lower  part  of  the  triangle  it  is  sep- 
arated from  the  adductor  longus  muscle  by  the  femoral  vein  and  by  the  deep  femoral 
artery  and  vein.  Medially,  it  is  in  relation  above  with  the  femoral  vein  and  below 
with  the  adductor  longus;  laterally,  with  the  ilio-psoas  muscle  and  the  leash  of 
nerves  formed  from  the  anterior  crural  nerve. 

In  Hunter's  canal  the  artery  lies  beneath  the  sartorius  muscle  and  is  crossed 
obliquely  from  without  inward  by  the  long  saphenous  nerve.  Posteriorly  it  rests  upon 
the  adductor  longus  and  the  adductor  magnus, 'and  also  upon  the  femoral  vein  which, 
below,  comes  to  lie  somewhat  laterally  as  well  as  posterior  to  it  and  is  firmly  united 
to  the  artery  by  dense  connective  tissue.  To  the  inner  side  of  the  artery  is  the  ad- 
ductor longus  above  and  the  adductor  magnus  below,  while  to  its  outer  side,  and 
partly  overlapping  it,  is  the  vastus  internus. 

Branches. — In  Scarpa's  triangle  the  femoral  artery  gives  off  (i)  the  super- 
ficial epigastric,  (2)  the  superficial  circumflex  iliac,  (3)  the  siiperficial  external 
pudic,  (4)  the  deep  external  pudic,  (5)  the  profunda  femot is,  and  (6)  muscular 
branches.  In  Hunter's  canal  it  gives  off  additional  muscular  branches  and,  just 
before  perforating  the  adductor  muscle,  (7)  the  anastomotica  magna. 

The  profunda  femoris  so  much  surpasses  in  size  the  other  branches  of  the  femoral 
that  the  latter  artery  is  frequently  regarded  as  bifurcating  at  the  point  where  this 
vessel  arises.  The  portion  of  the  artery  above  the  bifurcation  is  then  termed  the 
common  femoral,  while  its  continuation  through  Scarpa's  triangle  and  Hunter's  canal 
is  known  as  the  superficial  femoral. 

Variations. — A  comparative  study  of  the  arteries  of  the  thigh  reveals  the  fact  that  the  exist- 
ence of  a  well-developed  femoral  artery  forming  the  main  blood-channel  for  the  leg  is  a  condi- 
tion characteristic  of  the  mammalia.  In  the  lower  vertebrate  groups  the  sciatic  is  the  principal 
artery  of  the  thigh,  extending  throughout  the  whole  length  of  its  flexor  surface  and  becoming 
continuous  below  with  the  popliteal  artery,  the  femoral  artery  being  comparatively  insignificant 
and  terminating  as  the  profunda  femoris.  The  peculiar  course  of  the  mammalian  femoral,  start- 
ing, as  it  does,  as  an  artery  of  the  extensor  surface  of  the  limb  and  later  perforating  the  adductor 
magnus  to  become  continuous  with  the  popliteal  upon  the  flexor  surface,  is  to  be  regarded, 
therefore,  as  a  secondary  arrangement,  and  its  history  is  somewhat  as  follows. 

While  the  sciatic  is  still  the  principal  vessel  of  the  thigh  and  retains  its  connection  with  the 
popliteal  below,  a  branch  is  given  off  from  the  femoral  which  accompanies  the  long  saphenous 
nerve  through  Hunter's  canal  and  down  the  inner  surface  of  the  crus,  having  in  this  lower  por- 
tion of  its  course  a  superficial  position  corresponding  with  that  of  the  nerve.  Near  the  lower 
part  of  Hunter's  canal  this  vessel,  which  is  known  as  the  saphenous  artery,  gives  off  a  branch 
which  perforates  the  adductor  magnus  and  unites  with  the  sciatic,  producing  an  arrangement 
which,  in  various  degrees  of  development,  may  be  regarded  as  characteristic  of  the  mammalia 
as  a  group.  In  man,  however,  the  process  goes  a  step  further  in  that,  correlatively  with  an 
enlargement  of  the  anastomosis  between  the  saphenous  and  the  sciatic,  there  is  a  diminution  of 
the  main  stem  of  the  latter  vessel,  so  that  eventually  it  becomes  reduced  to  the  slender  a.  comes 


824  HUMAN   ANATOMY. 


i'i  ischiadici  which  loses,  as  a  rule,  its  continuity  with  the  popliteal.  That  artery  now  appears 
to  be  the  continuation  of  the  saphenous  (femoral),  since  there  occurs  a  degeneration  of  the 
saphenous  below  the  point  where  the  anastomosing  branch  is  given  off.  These  chan— 
shown  diagrammatical!}-  in  Fig.  748,  (page  849)  from  which  it  will  be  seen  that  the  femoral  artery 
below  the  origin  of  the  profunda  is  the  upper  part  of  the  original  a.  saphena,  the  continuation  of 
that  vessel  down  the  cms  being  represented  only  by  the  superficial  branch  of  the  anastomotica 
magna. 

The  principal  variations  which  are  shown  by  the  femoral  artery  are  associated  with  these 
changes  which  it  has  passed  through  in  its  development,  and  represent  a  cessation  of  the  devel- 
opment at  one  stage  or  other  of  its  progress.  Thus,  as  already  pointed  out  i  page  8151,  the 
comes  nen'i  ischiadici  may  remain  the  principal  vessel  of  the  thigh,  the  femoral  terminating  in 
the  profunda  femoris.  Or  the  development  may  proceed  to  the  formation  of  the  a.  saphena, 
which  may  arise  either  immediately  above  the  profunda  femoris,  in  such  case  the  superficial 
femoral  being  wanting  and  the  comes  nervi  ischiadici  still  well  developed,  or  else  from  the  lower 
part  of  the  femoral,  just  before  it  pierces  the  adductor  muscle.  From  this  point  the  \ 
when  fully  developed,  is  continued  onward  with  the  long  saphenous  nerve  between  the  adductor 
magnus  and  the  vastus  medialis,  and  below  the  knee-joint  perforates  the  crural  fascia  and  is 
continued  superficially  down,  the  inner  side  of  the  crus,  accompanying  the  long  saphenous  nerve 
and  vein  to  the  internal  malleolus,  where  it  makes  connections  with  the  posterior  tibial  artery 
and  may  sometimes  persist  as  a  branch  of  that  vessel. 

In  addition  to  these  anomalies,  the  femoral  artery  frequently  gives  off  branches  which  nor- 
mally arise  from  other  vessels.  Thus  it  may  give  rise  to  the  deep  epigastric  or  the  deep  cir- 
cumflex iliac,  normally  branches  of  the  external  iliac,  or  to  the  external  or  internal  circumflex, 
normally  branches  of  the  profunda  femoris.  It  has  also  been  observed  to  give  origin  to  the  ilio- 
lumbar  artery. 

Practical  Considerations.  —  The  femoral  artery  is  more  often  wounded  than 
the  brachial  on  account  of  the  position  of  its  upper  half  —  in  Scarpa's  triangle  —  on 
the  anterior  surface  of  the  limb,  and  of  its  relatively  more  intimate  relation  to  the 
femur  at  its  lower  end.  In  the  latter  region  it  has  been  opened  by  spicules  of  necrotic 
bone.  Next  to  the  popliteal,  it  is  more  frequently  the  subject  of  aneurism  than  any 
other  external  arterial  trunk.  On  account  of  the  close  relation  of  the  lymphatic 
glands  in  and  near  the  groin,  the  vessel  has  been  opened  by  ulceration  and  sloughing 
in  bubo  or  in»carcinoma,  and  has  been  involved  in  sarcomatous  growths.  The  same 
relation  has  caused  the  aneurism  to  be  mistaken  for  a  glandular  abscess,  an  error 
which  has  occurred  oftener  in  connection  with  this  vessel  than  with  any  other. 

Compression  of  the  femoral  artery  has  yielded  very  satisfactory  results  in  the 
treatment  of  popliteal  aneurism.  The  pressure  is  best  applied  in  a  direction  backward 
and  outward  just  below  the  inferior  edge  of  Poupart's  ligament  where  the  vessel  can 
be  flattened  against  the  brim  of  the  pelvis  —  the  upper  margin  of  the  acetabulum  — 
just  outside  the  ilio-pectineal  eminence,  only  a  very  thin  portion  of  the  ilio-psoas 
muscle  intervening.  A  little  lower,  a  more  fleshy  portion  of  that  muscle  separates  it 
from  the  head  of  the  femur,  and  yet  lower  the  artery  has  back  of  it  the  still  less 
resistant  mass  of  the  pectineus  and  adductor  brevis  muscles,  and  more  force  will  be 
required  to  obliterate  its  lumen.  At  the  apex  of  Scarpa's  triangle  the  pressure  must 
be  directed  backward  and  somewhat  more  outward,  and  a  little  lower  still  more 
directly  outward,  the  artery  at  these  places  being  compressed  against  the  femur,  the 
vastus  internus  intervening. 

Extreme  flexion  of  the  thigh  upon  the  trunk  will  occlude  the  femoral,  and 
been  used  successfully  in  the  cure  of  popliteal  aneurism  and  for  the  temporary  am 
of  hemorrhage. 

Ligation  of  the  vessel  may  be  done  :   i.    Between  Poupart's  ligament  and  tl 
origin  of  the  profunda  —  the  common  femoral   (vide  sitpra}.     2.   At  the   apex 
Scarpa's  triangle.     3.    In  Hunter's  canal. 

i.  The  common  femoral  is  rarely  ligated  except  as  a  preliminary  to  some  ton 
of  hip-joint  amputations,  or  for  the  relief  of  hemorrhage.  In  aneurism  of  the  upper 
portion  of  the  superficial  femoral  the  external  iliac  is  ordinarily  preferred  because  of 
(a)  the  possibility  of  a  high  origin  of  the  profunda.  The  common  femoral  is  normally 
only  about  one  and  a  half  inches  in  length.  If  its  bifurcation  occurs  above  the  usual 
level  —  the  most  common  variation  —  the  ligature  would  be  in  dangerously  close 
proximity  to  so  large  a  trunk.  (£)  The  presence  of  a  number  of  smaller  branches— 
the  deep  epigastric  and  deep  circumflex  iliac  coming  off  immediately  above  Poupart's 
ligament,  the  superficial  epigastric,  circumflex  iliac,  and  external  pudic,  the 
external  pudic,  and  occasionally  one  of  the  circumflex  arteries  (especially  the  internal 


THE   FEMORAL   ARTERY. 


825 


Ilio-p: 


Adductor  longus 
muscle 


arising  from  the  femoral.  This  circumstance  likewise  interferes  with  the  firmness  and 
security  of  the  clot  formation  after  ligature,  (c)  The  fact  that  ligature  of  the 
common  femoral  cuts  off  the  chief  blood-supply  to  the  lower  limb  also  militates 
against  its  selection  and  leads  to  the  choice  of  the  superficial  femoral  whenever  pos- 
sible, so  as  to  permit  the  profunda  and  its  branches  to  maintain  a  sufficient  vascular 
current.  The  incision  should  be  begun  on  the  abdomen  a  little  above  Poupart's 
ligament,  midway  between  the  anterior  superior  spine  and  the  symphysis  pubis,  and 
extend  downward  to  about  two  inches  below  the  ligament  in  the  line  of  the  vessel — 
vide  supra.  The  structures  to  be  avoided  in  approaching  the  artery  are  the  glands 
and  veins  that  lie  in  the  fat  over  the  cribriform  fascia,  the  superficial  epigastric  artery 
and,  when  the  sheath  is  exposed,  the  crural  branch  of  the  genito-crural  nerve  lying 
upon  it  near  its  outer  side.  The  vein  is  in  close  contact  with  the  inner  side  of  the 
artery.  The  needle  should  be  passed  from  within  outward. 

The  collateral  circulation  will  be  carried  on  from  above  the  ligature  by  («)  the' 
internal  pudic  (from  the  internal  iliac);  (3)  the  gluteal  and  sciatic  (from  the  same 
vessel);  (c)  the  deep  cir- 
cumflex iliac,  from  the  FIG.  730. 
external  iliac ;  (d}  the  ob- 
turator, and  (e)  the  comes 
nervi  ischiadici,  anasto- 
mosing respectively  with 
(«)  the  superficial  and 
deep  external  pudic :  (b) 
the  circumflex  and  per- 
forating arteries  ;  (<:)  the 
external  circumflex  ;  {d} 
the  internal  circumflex  ; 
and  (e)  the  perforating,  all 
from  either  the  common, 
superficial,  or  deep  fem- 
oral. 

2.  At  the  apex  of 
Scarpa's  triangle  an  inci- 
sion with  its  centre  at  the 
apex   of    the    triangle    is 
made  on  the  line  of   the 
vessel,  the  thigh  being  ab- 
ducted and   rotated  out- 
ward,  the  hip  a  little 
flexed,    the  knee  well 
flexed,  and  the  leg  resting 
on  its  outer  surface.      Be- 
fore   reaching    the   deep 
fascia,  the  long  saphenous 
vein  or  the  external  super- 
ficial femoral  vein,  may  be 

met  with  and  should  be  avoided.  After  opening  the  deep  fascia  the  fibres  of  the 
inner  edge  of  the  sartorius  should  be  exposed,  and  may  be  recognized  by  their  oblique 
course.  That  muscle  should  be  displaced  outward,  the  vascular  groove  containing 
the  vessel  and  some  fatty  areolar  tissue  identified,  and  the  sheath  exposed.  The 
internal  cutaneous  branch  of  the  anterior  crural  nerve  in  front,  and  the  nerve  to  the 
vastus  internus  and  the  long  saphenous  nerve  externally,  should  be  avoided,  and  the 
sheath  opened.  The  needle  should  be  passed  from  without  inward  to  avoid  the  vein, 
which  here  lies  behind  and  to  the  outer  side  of  the  artery. 

3.  To  reach  the  vessel  in  Hunter's  canal,  the  limb  being  in  the  position  above 
described,  an  incision  is  made  on  the  line  of  the  vessel  extending  from  the  apex  of  the 
triangle  to  about  three  inches  above  the  internal  condyle.     The  long  saphenous  vein 
should  be  avoided.      The  deep  fascia  is  opened,  and  the  outer  edge  of  the  sartorius 
identified.      The  only  structure  that  could  be  mistaken  for  it  is  the  vastus  internus, 


Internal  saphe- 
nous vein 


Superficial  dissection  of  Scarpa's  triangle,  showing 
relations  of  femoral  vessels. 


826 


HUMAN   ANATOMY. 


FIG.  731. 


Kectus  mi 
Nerve  to  vastus 

internus 
Sartorius  muscle 


Adductor  longus  muscle 
Femoral  vein 

^-Internal  cutaneous  nerve 
Internal  saphenous  nerve 
-Femoral  artery 

-—Roof  of  Hunter's  canal 


Internal  saphenous  vein 


the  fibres  of  which  run  obliquely  outward  instead  of  inward.  The  sartorius  is 
displaced  inward  and  the  thigh  more  strongly  abducted,  when  the  tension  on  the 
adductor  fibres — the  adductor  magnus  and  the  lower  edge  of  the  adductor  longus — 
will  clearly  define  the  lower — inner — border  of  Hunter's  canal.  The  aponeurotic  roof 

of  the  canal  stretch- 
ing across  to  the 
vastus  internus  is 
pierced  by  the  in- 
ternal saphenous 
nerve,  which  may  be 
a  useful  guide.  This 
aponeurosis  is  di- 
vided and  the  vessel 
exposed.  The  vein 
lies  behind  and 
somewhat  to  the 
outer  side.  The 
needle  should  be 
passed  from  without 
inward. 

The  collateral 
circulation  after  liga- 
tion  of  the  superficial 
femoral  is  carried  on 
from  above  by  (  a  > 
the  perforating  and 
terminal  branches  of 
the  profunda  ;  and 
(^)  the  descending 
branch  of  the  exter- 
nal circumflex  anas- 
tomosing respectively  with  (a)  the  superior  articular  and  muscular  branches  of  the 
popliteal  ;  and  (b)  the  anastomotica  magna  and  superior  articular  from  below. 

1.  The  Superficial   Epigastric   Artery. — The  superficial   epigastric  artery 
(a.  epigastrica  superticialis)  (Fig.  729)  arises  from  the  anterior  surface  of  the  femoral, 
about  i  cm.  below  Poupart's  ligament.      It  is  directed  at  first  forward,  but,  after  per- 
forating the   fascia  lata  or  sometimes  the  cribriform   fascia,    it  bends  upward  over 
Poupart's  ligament  and  ascends  between  the  superficial  and  deep  layers  of  the  super- 
ficial abdominal  fascia  to  the  neighborhood  of  the  umbilicus.      It  gives  branches  to 
adjacent  inguinal  lymphatic  nodes  and  to  the  integument,  anastomosing  with  the 
cutaneous  branches  of  the  deep  epigastric  artery. 

2.  The  Superficial   Circumflex    Iliac   Artery. — The  superficial  circumflex 
iliac  artery  (a.  circumtlexa  ilium  superticialis)  (Fig.  729)  arises  from  the  anterior  surface 
of  the  femoral,  a  little  below  the  superficial  epigastric,  or  from  a  common  trunk  with 
that  artery.      It  perforates  the  fascia  lata  or  the  cribriform  fascia  and  is  then  directed 
laterally  more  or  less  parallel  with  Poupart's  ligament,  extending  almost  as  far  as  the 
anterior  superior  spine  of  the  ilium.      It  gives  branches  to  the  adjacent  inguinal  lym- 
phatic   nodes   and   to   the   sartorius    muscle,  and   anastomoses  with    the  cutaneous 
branches  of  the  deep  circumflex  iliac. 

3.  The  Superficial  External  Pudic  Artery.— The  superficial  external  pudic 
artery  (a.  pudenda  externa  superticialis)  (Fig.  729)  arises  from  the  inner  surface  of  the 
femoral  artery  and  is  directed  inward  and  slightly  upward  towards  the  spine  of  the 
pubis.      It  pierces  the  cribriform  fascia  and,  crossing  over  the  spermatic  cord  or  round 
ligament,  sends  branches  to  the  integument  above  the  pubes..     It  is  then  continued 
along  the  dorsal  surface  of  the  penis  or  clitoris,  lateral  and  external  to  the  dorsal  artery 
of  that  organ,  with  which  it  anastomoses  at  the  glans.      It  supplies  branches  to  the 
integument  of  the  penis  and  to  the  preputium  clitoridis,   and   also  gives  brain  lie- 
to  the  scrotum  or  labium  majus. 


Dissection  showing  femoral  vessels  in  Scarpa's  triangle 
and  disappearing  in  Hunter's  canal. 


THE   FEMORAL   ARTERY. 


827 


FIG.  732. 


Stump  of  sartorius 
Superficial  circumflex  iliac  artery 

Rectus  tendon 
Femoral  artery 


Ascending  branch  of  external 
circumflex  artery 

Deep  femoral  artery 

Transverse  branches  of  external 

circumflex  artery 
Descending  branch  of  external 
circumflex  artery 

Vastus  externus 


Crureus 


Rectus 


Tendon  of  quadriceps 
extensor,  cut 


Patella,  detached  and  displaced 
outward 


Superficial  epigastric  artery 

_  Superficial  ext.  pudic  artery- 
Deep  external  pudic  artery 
Femoral  vein 
Pectineus 

—  Penis — sectional  surface 

—  Buttock 


Adductor  longus 

.Semitendinosus 

.Gracilis 
Adductor  tnagnus 


nastomotica  magna 

nastomotica  magna — 
deep  portion 

Anastomotica  magna— 
superficial  branch 

Popliteal  artery 
Semimembranosus 


Inferior  internal  articular  artery 


Arteries  of  front  of  thigh  ;  deeper  dissection. 


828  HUMAN   ANATOMY. 

4.  The   Deep  External  Pudic  Artery. — The  deep  external  puclic  artery  (a. 
pudenda  cxterna  profunda)  (Fig.  732)  arises  from  the  inner  surface  of  the  femoral, 
either  a  little  below  the  superficial  external  pudic  or  in  common  with  that  vessel.      It 
passes  medially  beneath  the  fascia  lata  across  the  femoral  vein  and  the  pectineus  and 
adductor  longus  muscles.      It  then  pierces  the  fascia  lata  close  to  the  ramus  of  the 
pubis  and  is  distributed  to  the  sides  of  the  scrotum  or  labium  majus,  anastomosing 
with  branches  of  the  superficial  external  pudic  and  of  the  superficial  perineal  branch 
of  the  internal  pudic. 

5.  The    Deep    Femoral    Artery. — The   deep    femoral    artery    (a.    profunda 
feraoris)    (Fig.    733)   arises  from   the   outer  surface   of   the  femoral,   usually   about 
4  cm.  below  Poupart's  ligament,  and  at  first  is  directed  downward  parallel  to  the 
femoral  and  to  the  outer  side  of  that  vessel.      It  then  bends  medially  and  passes 
obliquely  behind  the  femoral  artery  and  vein,  and  on  arriving  at  the  upper  border  of  the 
adductor  longus,  passes  behind  that  vessel  and  is  continued  downward  between  it 
and   the  adductor  magnus,  rapidly  diminishing  in  size.      Finally  it   perforates   the 
adductor  magnus  and  terminates  in  branches  to  the  lower  portions  of  the  hamstring 
muscles. 

Relations. — At  first  the  profunda  lies  alongside  the  femoral  and  is,  like  it,  su- 
perficial, having  in  front  of  it  only  the  fasciae  and  integument,  together  with  some- 
branches  of  the  anterior  crural  nerve.  Later  it  lies  behind  the  femoral  artery  and 
the  femoral  and  profunda  veins,  and  still  later  the  adductor  longus  and  the  adductor 
magnus.  Posteriorly  it  rests  at  first  upon  the  ilio-psoas  and  then  successively  upon 
the  pectineus,  the  adductor  brevis,  and  the  adductor  magnus. 

Branches. — The  profunda  femoris  gives  origin  to  the  following  branches  :  ( i )  the  external 
circumflex,  (2)  the  internal  circumflex,  (3)  the  three  perforating  arteries.  The  terminal  por- 
tion of  the  profunda,  after  it  has  pierced  the  adductor  magnus,  is  sometimes  spoken  of  as  the 
fourth  perforating  artery. 

(a)  The  external  circumflex  artery  (a.  circumflexa  femoris  lateralis)   is  the  largest  of  the 
branches  of  the  profunda  and  arises  from  it  a  short  distance  beyond  its  origin.     It  is  directed 
horizontally  outward  across  Scarpa's  triangle,  resting  upon  the  ilio-psoas  muscle  and  passing 
between  the  superficial  and  deep  branches  of  the  anterior  crural  nerve.     It  then  passes  beneath 
the  sartorius  and  rectus  muscles  and  terminates  by  dividing  into  an  ascending,  a  transverse,  and 
a  descending  branch.     The  ascending  branch  passes  upward  and  outward  to  beneath  the  tensor 
vaginae  femoris,  running  along  the  anterior  trochanteric  line  of  the  femur,  and  terminates  by  anas- 
tomosing with  the  gluteal  and  the  deep  circumflex  iliac  arteries.     It  sends  twigs  to  the  neigh- 
boring muscles  and  to  the  hip-joint.     The  transverse  branch  is  small  and  runs  directly  outward 
to  below  the  greater  trochanter,  passing  between  the  rectus  and  the  crureus  muscles  and  through 
the  substance  of  the  vastus  lateralis.     It  unites  with  branches  of  the  sciatic,  internal  circumflex, 
and  first  perforating  arteries  to  form  the  crucial  anastomosis.     The  descending  branch  runs 
downward  beneath  the  rectus  muscle,  along  with  the  nerve,  to  the  vastus  lateralis,  and  usually 
extends  to  the  neighborhood  of  the  knee-joint,  where  it  anastomoses  with  the  superior  external 
branch  of  the  popliteus  and  assists  in  the  formation  of  the  circumpatellar  anastomosis.     It  gives 
branches  to  the  rectus,  crureus,  and  vastus  lateralis. 

(b)  The  internal  circumflex  artery  (a.  circumflexa  femoris  medialis)   arises  from  the  inner 
surface  of  the  profunda,  very  nearly  opposite  the  external  circumflex.     It  passes  over  the  surface 
of  the  ilio-psoas  and  beneath  the  pectineus  to  reach  the  anterior  surface  of  the  neck  of  the 
femur.     It  then  crosses  the  upper  portion  of  the  adductor  brevis  and  adductor  magnus  and 
passes  along  the  lower  border  of  the  obturator  externus  and,  finally,  upon  the  anterior  surface 
of  the  quadratus  femoris,  where  it  divides  into  its  terminal  branches. 

(aa)  The  ascending  branch  (ramus  ascendens)  passes  upward  towards  the  digital  fossa  of 
the  femur,  sending  branches  to  the  capsule  of  the  hip-joint  and  anastomosing  with  the  sciatic 
and  external  circumflex  arteries. 

(bo)  The  descending  branch  (ramus  descendensl  passes  downward  and  curves  around  the 
lower  border  of  the  quadratus  femoris  to  terminate  in  the  upper  portion  of  the  hamstring  mus- 
cles. This  branch  anastomoses  with  the  sciatic,  external  circumflex,  and  first  perforating  ves- 
sels to  form  the  crucial  anastomosis.  In  addition,  the  internal  circumflex  in  its  course  sends 
muscular  branches  to  the  adjacent  muscles  and  also  an  articular  branch  (rnmus  acetatuili)  to  the 
hip-joint. 

(r)  The  three  perforating  branches  arise  in  succession  from  the  profunda  and  pass  back- 
ward, curving  around  the  inner  surface  of  the  femur.  They  perforate  the  adductor  muscles 
close  to  the  bone,  and  supply  the  hamstring  muscles  and  the  vastus  externus,  anastomosing  with 
one  another  and  with  neighboring  vessels. 


THE   FEMORAL   ARTERY. 


829 


(aa)  The  first  or  superior  perforating  artery  (a.  perforans  prima)  is  generally  the  largest  of 
the  three,  and  arises  just  as  the  profunda  passes  behind  the  adductor  longus.  It  either  passes 
through  the  adductor  brevis  or  between  that  muscle  and  the  pectineus  and  pierces  the  adductor 

FIG.  733. 


Superficial  circumflex  iliac 
Iliacus  muscle 

Femoral  artery 

Tendon  of  rectus 

Tensor  vaginae  femori 
Ascending  branch  of 

external  circumflex 

Profunda  femoris 
External  circumflex 

Transverse  branches  of 

external  circumflex 

Descending  branch  of 

external  circumflex 

Vastus  externus 
First  perforating  artery 

Adductor  brevis 
Second  perforating  artery 

Vastus  internus 
Third  perforating  artery 


Adducto 


Fourth  perforating  artery. 


Deep  branch  of 

anastomotica  magna 


Adductor  niagnus 
Gracilis 


Superficial  epigastric  artery 

Psoas  muscle 
Pectineus 

-  Spermatic  cord 

—  Obturator  artery 
Adductor  longus 
Adductor  brevis 
Corpus  spongiosum  of  penis 

•  Obturator  externus 

~  Internal  circumflex  artery 

Articular  branch  of 

internal  circumflex 


Adductor  magnus 


Femoral  artery 


Semimembranosus 


Superficial  branch  of 

anastomotica  magna 


Deep  femoral  artery  and  its  branches. 

magnus,  and  then  divides  into  an  ascending  and  a  descending  branch,  the  latter  of  which  anasto- 
moses with  the  ascending  branch  of  the  second  perforating,  while  the  former  assists  in  the  for- 
mation of  the  crucial  anastomosis. 


830 


HUMAN    ANATOMY. 


(bb)  The  second  or  middle  perforating  artery  (a.  perforans  secunda)  arises  a  little  below  the 
first  and,  after  piercing  the  adductor  brevis  and  the  adductor  magnus,  divides  into  an  ascending 
and  a  descending  branch  which  anastomose  respectively  with  the  descending  branch  of  the  first 
and  the  ascending  branch  of  the  third  perforating.  A  nutrient  artery  to  the  femur  is  usually 
given  off  from  this  vessel,  although  frequently  it  comes  from  the  third  perforating. 

(cc)  The  third  or  inferior  perforating  artery  (a.  perforans  tertia)  arises  usually  on  a  level 
with  the  lower  border  of  the  adductor  brevis.  It  pierces  the  adductor  magnus  and  terminates, 
like  the  other  perforating  arteries,  by  dividing  into  an  ascending  and  a  descending  branch.  The 
ascending  branch  anastomoses  with  the  descending  branch  of  the  second  perforating,  while  the 
descending  one  anastomoses  with  branches  from  the  terminal  portion  of  the  profunda.  The 
nutrient  artery  to  the  femur  is  frequently  given  off  by  this  branch. 

Variations. — The  variations  of  the  profunda  and  its  branches  are  somewhat  numerous,  and 
to  a  very  considerable  extent  are  largely  associated  with  one  another.  In  other  words,  there 
may  be  more  or  less  dissociation  of  the  various  vessels  of  the  profunda  complex,  one  or  other 
of  them  having  an  independent  origin  from  the  femoral,  and,  indeed,  this  process  may  occur  to 
such  an  extent  that  a  profunda  femoris  as  a  definite  vessel  can  hardly  be  said  to  exist. 

The  point  of  origin  of  the  profunda  from  the  femoral  is  stated  to  be  usually  about  4  cm. 
distant  from  Poupart's  ligament,  but  the  figure  must  be  taken  as  a  general  average  from  which 
there  may  be  wide  departures.  Thus,  in  430  limbs  Quain  found  that  the  distance  from  Poupart's 
ligament  of  the  origin  of  the  profunda  was  between  2.5  and  5.1  cm.  in  68  per  cent.,  and  of 
this  number  it  was  between  2.5  and  3.8  cm.  in  42.6  per  cent.  It  was  distant  less  than  2.5  cm.  in 
24.6  per  cent,  of  the  limbs  and  more  than  5.1  cm.  in  only  7.4  per  cent.  Quain's  figures  are  as 
follows : 

Origin  at  Poupart's  ligament 7  cases. 

0-1.3  cm-  below  Poupart's  ligament 13  cases. 

1.3-2.5  cm.  below  Poupart's  ligament 86  cases. 

2.5-3.8  cm.  below  Poupart's  ligament           .        183  cases. 

3.8-5.  i  cm.  below  Poupart's  ligament    .    . 109  cases. 

5.1-6.3  cm.  below  Poupart's  ligament 19  cases. 

6.3-7.6  cm.  below  Poupart's  ligament 12  cases. 

1 1. 6  cm.  below  Poupart's  ligament i  case. 

Essentially  similar  results  have  been  obtained  by  Srb  and  other  observers,  and  it  seems 
evident  from  the  statistics  that  the  origin  of  the  profunda  is  more  apt  to  be  above  than  below  the 
point  taken  as  the  average. 

One  or  other  of  the  circumflex  arteries  may  arise  independently  from  the  femoral,  this  con- 
dition occurring  somewhat  more  frequently  in  the  case  of  the  internal  circumflex  than  in  that  of 

the  outer  one,  and  the  point  of  origin  of  the  inde- 
pendent vessel  may  be  either  above  or  be-low  that 
of  the  profunda.  When  it  is  the  internal  circum- 
flex which  is  the  independent  vessel,  its  origin  is 
most  frequently  above  that  of  the  profunda;  or  per- 
haps'it  would  be  more  correct  to  say  that  with  an 
independent  internal  circumflex  the  origin  of  the 
profunda  is  apt  to  be  somewhat  below  the  typical 
point.  With  a  high  origin  of  the  profunda,  the 
external  circumflex  may  be  represented  by  two 
vessels,  one  of  which  arises  from  the  profunda, 
while  the  accessory  one  springs  from  the  femoral 
lower  down.  Occasionally  both  circumflexes  may 
arise  independently  from  the  femoral,  the  profunda 
in  such  cases  having  usually  a  low  origin,  and  one 
or  other  of  the  perforating  arteries  may  arise  from 
the  circumflexes.  An  extreme  case  of  this  nature, 
representing  an  almost  complete  dissociation  of  the 
profunda,  has  been  described  by  Ruge,  (Fig.  734) 
in  which  the  superior  perforating  arises  from  the 
internal  circumflex  and  the  middle  one  from  the 
external  circumflex,  what  may  be  termed  the  pro 
funda  arising  9.7  cm.  below  Poupart's  ligament 
and  giving  off  only  the  inferior  perforating. 

The  internal  circumflex  may  be  very  much 
reduced  in  size  or  even  absent,  its  territory  being 
supplied  by  branches  from  the  obturator  artery.  Occasionally,  although  rarely,  one  or  other 
of  the  perforating  branches  arises  directly  from  the  femoral,  and  a  similar  origin  has  also  been 
observed  for  the  descending  branch  of  the  external  circumflex. 

6.   The   Muscular  Branches. — The  muscular  branches  (rami  musculares)  of 

the  femoral  artery  are  rather  numerous  and  are  distributed  to  all  the  muscles  upon  tin- 
front  of  the  thijrh.  They  are  variable  in  number  and  position  and  do  not  call  lor  any 
special  description. 


FIG.  734. 


iliac 


Superficial 

circumflex 


External 

circumflex 


Middle 

perforating? 


Inferior  perforating 
(profunda  femoris) 


Diagram  showing  almost  complete  dissociation 
of  profunda  femoris.     (Ruge). 


Superficial 
epigastric 


Internal 
circumflex 

Superior 
perforating 


THE   POPLITEAL   ARTERY.  831 

7.  The  Anastomotica  Magna. — The  anastomotica  magna  (a.  genu  suprema) 
(Fig.  733)  arises  from  the  femoral,  just  before  it  passes  through  the  adductor  magnus. 
It  passes  downward  a  short  distance  in  front  of  the  adductor  magnus  and  divides  into 
two  branches,  a  superficial  and  a  deep. 

Branches. — (a)  The  superficial  branch  (ramus  saphenus)  follows  the  course  of  the  long 
saphenous  nerve  and,  perforating  with  it  the  crural  fascia,  is  supplied  to  the  integument  over  the 
inner  side  of  the  knee  and  the  upper  portion  of  the  leg.  It  anastomoses  with  the  inferior  in- 
ternal articular  branch  of  the  popliteal,  then  entering  into  the  formation  of  the  circumpatellar 
anastomosis, 

(6}  The  deep  branch  (ramus  musculo-articularis)  enters  the  substance  of  the  vastus  interims 
and  passes  downward  to  take  part  in  the  formation  of  the  circumpatellar  plexus,  also  sending 
branches  to  the  capsule  of  the  knee-joint. 

Variations. — The  anastomotica  magna  is  occasionally  given  off  from  the  upper  portion  of  the 
popliteal  artery.  Occasionally  it  is  continued  some  distance  down  the  leg  with  the  long  saphe- 
nous nerve,  representing  in  such  cases  more  perfectly  the  original  saphenous  artery  (page  849)  ; 
or  this  vessel  may  be  indicated  by  a  series  of  anastomoses  which  accompany  the  nerve  and  vein 
and  begin  with  the  superficial  branch  of  the  anastomotica. 

Anastomoses  of  the  Femoral  Artery. — In  the  case  of  obliteration  of  the 
external  iHac  artery,  blood  may  reach  the  femoral  by  means  of  the  anastomoses  of  the 
iliac  arteries  already  noted  (page  821),  and,  in  addition,  byway  of  the  anastomoses 
between  the  superficial  and  deep  epigastrics  and  between  the  superficial  circumflex 
iliac  artery  and  the  deep  vessel  of  the  same  name  and  the  gluteal.  The  anastomoses 
between  the  external  and  internal  pudics  would  also  assist. 

If  the  obliteration  of  the  femoral  artery  be  above  the  origin  of  the  profunda 
femoris,  a  collateral  circulation  may  be  established  by  the  union  of  the  branches  of  that 
vessel  with  the  sciatic  in  the  crucial  anastomosis  and  also  by  the  communication  exist- 
ing between  the  external  circumflex  and  the  gluteal  and  the  deep  circumflex  iliac. 

If  the  obliteration  be  below  the  origin  of  the  profunda,  circulation  will  be  main- 
tained through  the  anastomoses  around  the  knee-joint,  in  which  the  descending 
branch  of  the  external  circumflex  and  the  terminal  portion  of  the  profunda,  on  the 
one  hand,  and  the  anastomotica  magna,  on  the  other,  participate. 

THE   POPLITEAL   ARTERY. 

The  popliteal  artery  (a.  poplitea)  (Fig,  736)  is  the  continuation  of  the  femoral, 
and  extends  from  the  point  where  the  latter  pierces  the  adductor  magnus  to  the  lower 
border  of  the  popliteus  muscle,  where  it  divides  into  the  anterior  and  posterior  tibial 
arteries.  Its  course  is  at  first  downward  and  slightly  outward,  but  it  soon  becomes 
almost  vertical,  corresponding  practically  with  the  long  axis  of  the  popliteal  space. 

Relations. — Anteriorly,  the  popliteal  artery  is  in  relation  to  the  posterior  sur- 
face of  the  lower  part  of  the  femur,  from  which  it  is  separated,  however,  by  a  layer 
of  adipose  tissue.  Lower  down  it  rests  upon  the  posterior  ligament  of  the  knee-joint, 
and  still  lower  upon  the  fascia  covering  the  posterior  surface  of  the  popliteus  muscle. 
Posteriorly,  it  is  somewhat  overlapped  in  the  upper  part  of  its  course  by  the  border  of 
the  semimembranosus,  and  below  by  the  inner  head  of  the  gastrocnemius.  In  its  pas- 
sage through  the  popliteal  space,  however,  it  is  covered  only  by  the  integument  and 
fascue,  beneath  which  is  a  considerable  amount  of  fatty  tissue.  About  the  middle  of  its 
course  it  is  crossed  obliquely  from  without  inward  by  the  internal  popliteal  nerve,  and 
throughout  its  entire  length  it  has  resting  upon  and  firmly  adherent  to  it  the  popliteal 
vein,  which  lies,  however,  slightly  to  its  outer  side  above  and  to  its  inner  side  below. 
Internally,  it  is  in  relation  from  above  downward  with  the  semimembranosus,  the 
internal  condyle  of  the  femur,  the  internal  popliteal  nerve,  and  the  inner  head  of  the 
gastrocnemius,  and  externally  with  the  internal  popliteal  nerve,  the  external  condyle 
of  the  femur,  the  outer  head  of  the  gastrocnemius,  and  the  plantaris. 

Branches. — The  branches  which  arise  from  the  popliteal  artery  are  all  small 
and  may  be  arranged  in  three  groups  :  (i)  muscular,  (2)  articular,  (3)  cutaneous. 

Variations. — The  popliteal  artery  occasionally  divides  into  the  tibial  arteries  above  the 
upper  border  of  the  popliteus  muscle,  and  more  rarely  the  division  is  delayed  until  the  artery 
has  reached  a  point  almost  half-way  down  the  leg. 


HUMAN   ANATOMY. 


reater  sciatic  nerve 


Popliteal  artery 
Popliteal  vein 


Practical  Considerations. — The  popliteal  artery  is  rarely  wounded  because 
of  its  protected  position  on  the  posterior  aspect  of  the  limb  and  in  the  hollow  of  the 
ham.  Its  upper  portion  is  overlapped  by  the  outer  border  of  the  semimembranostis 
muscle,  and  its  lower  portion  by  the  inner  head  of  the  gastrocnemius  ;  the  inter- 
mediate portion,  covered  only  by  skin,  fascia,  and  areolo-fatty  tissue,  is  very  deeply 
placed  and  is  not  more  than  an  inch  in  length.  It  may  be  torn  in  luxation  of  the 
knee,  or  wounded  in  fracture  of  the  lower  end  of  the  femur,  or  during  certain  opera- 
tions, as  osteotomy  of  the  femur  for  genu  valgum.  Laceration  or  wound  of  this 
vessel  is  more  dangerous  than  a  corresponding  injury  to  the  brachial  at  the  bend  of 
the  elbow,  because  of  the  greater  proximity — in  the  case  of  the  popliteal — of  the 
branches  on  which  the  chief  anastomotic  supply  depends  ;  and  because  of  the 
unyielding  character  of  the  walls  of  the  space  in  which  the  effused  blood  is  confined. 
Aneurism  of  the  popliteal  artery  comes  next  in  frequency  to  aneurism  of  the 
thoracic  aorta.  This  is  due  (#)  to  the  frequent  minor  strains  occurring  during 
flexion  and  extension  of  the  knee.  If  extreme,  the  former  movement  bends  th~ 
artery  at  such  an  acute  angle  that  the  flow  of  blood  through  it  is  arrested  and 

the    pressure    abo,ve    this 

FIG-  735-  point    greatly    increased  ; 

and  the  latter"  may  so 
stretch  the  vessel  longi- 
tudinally that  if  its  elasticity 
is  at  all  diminished  by  ather- 
omatous  changes  the  inner 
and  middle  coats  are 
thinned  or  ruptured.  (^) 
The  lack  of  muscular  sup- 
port which  the  artery — sur- 
rounded by  loose  cellular 
tissue — receives  also  favors 
the  development  of  aneur- 
ism. (V)  The  artery  is  said 
to  be  unusually  liable  to  ath- 
eromatous  degeneration. 
(d}  It  divides  a  short  dis- 
tance below  into  two 
vessels,  thus  increasing  the 
blood-pressure  above  the 
bifurcation.  (>)  Its  course 
is  curved  (like  that  of 
the  aortic  arch),  and  hence 
the  pressure  is  irregularly 
distributed.  (/")  The  ten- 
dinous opening  in  the 
adductor  magnus,  through 
which  the  vessel  runs,  con- 
stricts it  slightly  at  each  pulse-beat  and  tends — as  in  the  case  of  the  abdominal  aorta 
below  the  hiatus  aorticus — to  produce  a  little  dilatation  below  that  level.  As  both 
these  vessels  have  been  said  to  be  especially  weak  in  these  regions,  it  may  be 
possible  that  some  trifling  but  oft-repeated  interference  with  the  vasa  vasorum 
favors  degenerative  changes  by  slightly  diminishing  the  blood-supply  to  the  vessel 
walls. 

Aneurism  may  occur  suddenly,  with  a  sensation  resembling  that  produced  by  a 
blow  with  a  whip.  It  may  develop  slowly,  and,  if  it  takes  a  forward  direction,  with 
symptoms  simulating  rheumatism  on  account  of  the  pressure  upon  the  posterior 
ligament oi  the  knee-joint — i.e.,  dull  pain,  stiffness,  semi-flexion  of  the  knci-,  inability 
to  extend  the  joint  freely.  If  it  develops  in  the  opposite  direction,  the  absence  of 
resistance  causes  the  early  appearance  of  a  characteristic  pulsating  tumor  with  bru:t 
and  the  usual  signs  of  aneurism.  It  should  not  be  confused  with  an  enlarged  bursa 
(page  647),  the  subject  of  transmitted  pulsation,  or  with  tumor  or  abscess  overlying 


Semitendin. 
Semimembrani 


Inner  head  of 
gastrocnemius 


Communicans 
peronei  nerve 


External 
saphenous  nerve 

External 
saphenous  vein 


Dissection  of  right  popliteal  region,  showing 
relation  of  vessels  and  nerves. 


THE   POPLITEAL   ARTERY.  833 

the  artery  and  similarly  influenced.  Ultimately  there  is  apt  to  be  oedema  of  the  leg 
from  interference  with  the  venous  circulation,  or  erosion  of  the  posterior  lower  sur- 
face of  the  femur,  or  great  pain  with  weakness  of  the  leg  from  pressure  on  the  inter- 
nal popliteal  nerve,  or  even  moist  gangrene  if  the  aneurism  has  leaked  or  burst  and 
the  venous  current  has  been  cut  off  by  the  pressure  of  the  effused  blood  confined  for 
a  time  within  narrow  limits  and  under  great  pressure  by  the  fascia  of  the  region 
(page  646). 

Compression  of  the  popliteal  may  be  effected  directly  at  its  upper  end  by  pres- 
sure forward,  so  that  it  is  flattened  out  against  the  femur,  only  a  little  fatty  connective 
tissue  intervening.  It  is  almost  impossible,  however,  to  avoid  including  the  thick- 
walled  vein  which  is  nearer  the  surface  and  very  closely  attached  to  the  artery. 
Compression  is  therefore  almost  invariably  applied  to  the  common  femoral  (page 
824).  On  account  of  the  shortness  of  the  popliteal — and  the  consequent  proximity 
of  a  ligature  to  the  diseased  portion,  if  the  vessel  itself  is  tied — the  superficial  femoral 
at  the  point  of  election — the  apex  of  Scarpa's  triangle — is"  usually  selected  for  liga- 
tion  when  that  becomes  necessary. 

Ligation  of  the  popliteal  artery  is  effected  at  either  :  (i)  its  upper,  or  (2)  its 
lower  third,  the  depth  of  the  middle  portion  and  the  density  of  the  lateral  fascial 
border  of1  the  space  in  which  it  lies  rendering  it  unsuitable  for  operation. 

1.  The  patient  being  prone  with  the  leg  extended,  an  incision  is  made  along  the 
external  border  of   the  semimembranosus  muscle,  beginning  at  the  junction  of  the 
middle  and  lower  thirds  of  the  thigh.      The  skin  and  fascia  and  some  fatty  tissue 
having  been  divided,  the  muscle  is  drawn  inward,  and  the  vessel  will  be  found  with 
the  internal  popliteal  nerve  external  to  it  and  much  more  superficial,  and  the  vein 
external  and  behind  it, — i.e. ,  nearer  the  surface  of  the  popliteal  space — and  closely 
adherent.     The  needle  is  passed  from  without  inward. 

2.  An  incision  is  made  beginning  opposite  the  line  of  the  articulation  a  little 
external  to  the  middle  of  the  popliteal  space,  the  inner  head  of  the  gastrocnemius 
being  slightly  larger  than  the  outer  head.      The  external  saphenous  vein  lying  in  the 
superficial  fascia  is  drawn  to  one  side,  the  fascia  is  divided,  and  the  two  heads  of  the 
gastrocnemius  are  exposed  and  separated  with  the  finger,   the  knee  being  a  little 
flexed  so  as  to  relax  them.      At  the  bottom  of  the  interval  between  them  will  be  found 
the  nerve  and  vein  lying  to  the  inner  side  of  the  artery  and  somewhat  superficial  to  it. 
The  needle  is  passed  from  within  outward. 

The  collateral  circulation  is  carried  on  from  above  the  ligature  by  means  of  (a) 
the  superior  articulars  ;  (b)  the  anastomotica  magna  ;  (c*)  the  descending  branch  of 
the  external  circumflex  and  the  terminal  portion  of  the  profunda  anastomosing 
respectively  with  (#)  the  inferior  articulars  ;  (£)  the  tibial  recurrent  ;  and  (r)  the 
superior  fibular  and  branches  of  the  popliteal.  The  rete  patellae  takes  part  in  this 
anastomosis. 

1.  The  Muscular  Branches. — These  (Fig.  736)  are  arranged  in  two  groups, 
and  are  supplied  to  the  muscles  which  bound  the  popliteal  space.      The  superior  group 
consists  of  a  variable  number  of  small  vessels  which  pass  to  the  biceps,  semimembra- 
nosus,   and  semitendinosus,   while   the   inferior  group  is  composed  of  some  small 
branches  which  pass  to  the  popliteus  muscle,  and  two  larger  vessels,  the  largest  of  all 
the  vessels  which  arise  from  the  popliteal,  which  pass  respectively  to  the  inner  and 
outer  heads  of  the  gastrocnemius,   and  are  termed  the  sural  arteries  (aa.  surales). 
They  arise  just  as  the  popliteal  is  passing  beneath  the  inner  head  of  the  gastrocnemius. 

2.  The  Articular    Branches. — These   (Fig.   736)  are  five  in  number,   four 
being  arranged  in  pairs,   two   above  and  two  below,  while  the  fifth  is  unpaired  or 
azygos.      The  paired  branches  wind  around  the  femur  and  the  capsule  of  the  knee- 
joint  towards  the  front,  where  they  anastomose  with  one  another  and  with  adjacent 
vessels  to  form  a  rich  circumpatellar  anastomosis.      They  give  off  branches  to  the 
capsule  of  the  knee-joint  and  also  to  the  neighboring  muscles. 

(a  and  d)  The  internal  and  external  superior  articular  branches  (aa.  genu  superior  medialis 
et  lateralis)  arise  opposite  each  other  and  pass  transversely  above  the  corresponding  heads  of  the 
gastrocnemius.  The  external  one  then  passes  beneath  the  biceps  and  winds  around  the  femur 

53 


834  HUMAN   ANATOMY. 

above  its  external  condyle,  embedded  in  the  substance  of  the  vastus  externus,  dividing  finally 
into  branches  which  take  part  in  the  formation  of  the  circumpatellar  anastomoses.  The  termi- 
nation of  the  internal  branch  is  similar,  and  its  course  is  beneath  the  semimembranosus  and 
through  the  tendon  of  the  adductor  magnus  into  the  substance  of  the  vastus  interims. 

(c)  The  internal  inferior  articular  branch  (a.  gemi  inferior  medialis)  arises  about  opposite 
or  a  little  above  the  line  of  the  tibio-femoral  articulation  and  courses  downward  and  inward 
over  the  surface  of  the  popliteal  muscle,  beneath  the  inner  head  of  the  gastrocnemius.  It  passes 
beneath  the  internal  lateral  ligament  of  the  knee-joint  and  winds  around  the  tuberosity  of  the 
tibia  to  join  the  circumpatellar  anastomosis. 

(d  )  The  external  inferior  articular  branch  ( a.  gemi  inferior  lateralis)  arises  a  little  lower  down 
than  its  fellow  and  passes  almost  transversely  outward,  at  first  beneath  the  external  head  of  the 
gastrocnemius  and  the  plantaris,  and  winds  around  the  outer  tuberosity  of  the  tibia,  beneath 
the  long  internal  lateral  ligament  of  the  knee-joint,  to  join  the  circumpatellar  anastomosis. 

(e)  The  azygos  articular  branch  (a.  gemi  media )  is  the  smallest  of  all  the  articular  branches. 
It  arises  either  from  the  anterior  surface  of  the  popliteal  or  from  the  external  superior  articular 
branch,  and  pierces  the  posterior  ligament  of  the  knee-joint  to  be  distributed  to  the  crucial, 
mucous,  and  alar  ligaments.  " 

The  circumpatellar  anastomosis  (rete  patellae)  (Fig.  732)  is  a  rich  net-work 
of  vessels  which  occurs  in  the  superficial  fascia  surrounding  the  patella,  and  from  which 
branches  are  sent  to  the  patella,  the  capsule  of  the  knee-joint,  and  the  neighboring 
muscles.  The  following  vessels  take  part  in  its  formation.  From  above,  the  anasto- 
motica  magna  from  the  femoral  and  the  descending  branch  of  the  external  circumflex ; 
from  the  sides,  the  internal  and  external  superior  and  the  internal  and  external  inferior 
articular  branches  of  the  popliteal  and  the  muscular  branches  of  the  same  artery ;  and 
from  below,  the  anterior  tibial  recurrent. 

3.  The  Cutaneous  Branches. — These  are  variable  in  origin  and  number  and 
are  distributed  to  the  integument  covering  the  popliteal  space  and  the  upper  part  of 
the  calf  of  the  leg.  One  of  them  occasionally  attains  a  considerable  size  and  is 
termed  the  posterior  saphenous  artery.  It  accompanies  the  short  saphenous  vein 
down  the  back  of  the  crus,  sending  off  branches  to  the  adjacent  integument. 

The  Collateral  Circulation  of  the  Popliteal  Artery. — The  passage  of 
blood  to  the  leg  after  ligation  of  the  popliteal  artery  is  effected  by  means  of  the  ricli 
anastomosis  which  exists  around  the  knee-joint,  and  in  .which  the  branches  of  the 
popliteal  take  part.  In  addition  to  these,  however,  it  also  receives  from  above  the 
anastomotica  magna,  the  descending  branch  of  the  external  circumflex,  and  the 
terminal  portion  of  the  profunda  artery,  while  there  pass  to  it  from  below  the  superior 
fibular  and  the  anterior  and  posterior  tibial  recurrent  arteries. 

THE    POSTERIOR   TIBIAL   ARTERY. 

The  posterior  tibial  artery  (a.  tibialis  posterior)  (Fig.  736)  is  the  direct  con- 
tinuation of  the  popliteal  down  the  posterior  surface  of  the  leg.  It  begins  at  the 
bifurcation  of  the  popliteal  at  the  lower  border  of  the  popliteus  muscle  and  passes 
almost  vertically  downward,  under  cover  of  the  more  superficial  muscles  of  the  calf, 
to  the  groove  between  the  inner  malleolus  and  the  os  calcis,  where,  opposite  the  tip 
of  the  malleolus,  it  terminates  by  dividing  into  the  internal  and  external  plantar 
arteries.  Its  course  may  be  indicated  by  a  line  drawn  from  the  centre  of  the  popli- 
teal space  to  a  point  midway  between  the  inner  malleolus  and  the  os  calcis. 

Relations. — Anteriorly,  the  artery  rests  in  succession,  from  above  downward, 
upon  the  tibialis  posticus,  the  flexor  longus  digitorum,  the  posterior  surface  of  the 
lower  part  of  the  tibia,  and  the  internal  lateral  ligament  of  the  ankle-joint.  It  is 
closely  bound  down  to  the  muscles  upon  which  it  rests  by  the  layer  of  the  deep  fascia 
which  covers  them,  the  thickness  and  density  of  this  fascia  increasing  towards  tin- 
lower  part  of  the  leg.  Posteriorly,  it  is  covered  by  the  soleus  and  gastrocnemiufl 
throughout  the  greater  part  of  its  course,  but  in  the  lower  third  of  the  le^  it  is  super- 
ficial, being  covered  only  by  the  skin  and  fasciae,  except  just  before  its  termination, 
where  it  lies  beneath  the  internal  annular  ligament  and  the  origin  of  the  abductOf 
hallucis.  A  short  distance  below  its  commencement  it  is  crossed  obliquely,  from 
within  outward,  by  the-  posterior  tibial  nerve.  Internally,  it  is  in  relation  with  the 
posterior  tibial  nerve  for  a  short  distance  above,  and  in  the  malleolar  groove  it  has 


THE   POSTERIOR   TIBIAL   ARTERY. 
FIG.  736. 


835 


Semimembranosus 

Semitendinosus 
Superior  internal 

articular  artery 


Sartorius 
Gracilis 


Sural  branches 


Gastrocneinius — 

inner  head 


Inferior  internal  articular 

Internal  lateral  ligament 
Posterior  tibial  artery 

Soleus,  cut 


Flexor  longus  digitorum — 


External  plantar  artery 
Internal  plantar  artery 


Flexor  longus  hallucis  tendo 


Tibialis  posticus 


Popliteal  artery 

Superior  external  articular  artery 

Azygos  articular  artery 

Sural  branches 

Inferior  external  articular 

Plantaris 

Gastrocneinius — outer  head 

Tendon  of  popliteus 


Anterior  tibial  artery 


Peroneal  artery 
Soleus,  turned  aside 


Flexor  longus  hallucis 


Anterior  peroneal  artery 
Communicating  branch 
Tendon  of  peroneus  longus 

Peroneus  brevis 

Flexor  longus  hallucis 
Tendo  Achillis 

External  calcanean  (posterior 

peroneal)  branches 
Internal  calcanean  branch 


Plantar  fascia  and  flexor  brevis 

digitorum 
rendon  of  flexor  longus  digitorum 


Arteries  of  posterior  surface  of  right  leg. 


836  HUMAN   ANATOMY. 

internally  and  in  front  of  it  the  tendon  of  the  flexor  longus  digitorum,  and  internal  to 
that  the  tendon  of  the  tibialis  posticus.  Externally,  the  posterior  tibial  nerve  accom- 
panies it  throughout  the  greater  portion  of  its  course,  and  at  the  ankle-joint  the  nerve 
lies  external  and  posterior  to  the  artery,  between  it  and  the  tendon  of  the  flexor  longus 
pollicis.  The  artery  is  accompanied  throughout  its  course  by  two  venae  comites 
which  lie  respectively  to  its  outer  and  inner  side. 

Branches. — In  addition  to  numerous  muscular  branches  which  are  distributed 
to  the  neighboring  muscles,  and  cutaneous  branches  to  the  inner  and  posterior  sur- 
faces of  the  leg,  the  posterior  tibial  gives  origin  to  ( i )  a  nutrient  branch  to  the  tibia, 
(2)  the  peroneal  artery,  (3)  a  communicating  branch,  (4)  an  internal  malleolar 
branch,  (5)  an  internal  calcaneal  and  the  two  terminal  branches,  (6)  the  internal, 
and  (7)  the  external  plantar  arteries, 

Variations. — Although  apparently  the  principal  artery  of  the  flexor  surface  of  the  leg  and 
the  direct  continuation  of  the  popliteal,  developmentally  the  posterior  tibial  is  a  secondary 
vessel,  the  original  main  vessel  being  the  peroneal.  The  history  of  the  posterior  tibial  seems  to 
have  been  somewhat  as  follows.  The  saphenous  artery,  whose  origin  has  been  mentioned  in 
connection  with  the  variations  of  the  femoral  artery  (page  823),  in  the  lower  part  of  the  leg 
winds  around  to  the  posterior  surface  and  passes  behind  the  internal  malleolus,  where  it  termi- 
nates by  dividing  into  the  plantar  arteries.  From  the  upper  part  of  the  peroneal  artery  a  branch 
arises  which  passes  down  the  tibial  side  of  the  leg,  beneath  the  superficial  flexor  muscles,  and 
at  the  internal  malleolus  anastomoses  with  the  saphenous.  This  vessel  is  the  posterior  tibial, 
and,  its  calibre  enlarging,  exceeds  that  of  the  peroneal,  which  thus  sinks  to  the  rank  of  a  branch 
of  the  artery  to  which  it  gave  birth.  A  reason  for  this  increase  of  calibre  in  the  posterior  tibial 
is  to  be  found  in  the  degeneration  of  the  saphenous  artery  (page  849),  whereby  the  tibial  be- 
comes the  channel  of  supply  for  the  plantar  arteries,  which  seem  to  be  its  continuation. 

The  majority  of  the  principal  variations  of  the  posterior  tibial  are  readily  explained  in  the 
light  of  such  a  history.  Thus  there  may  be  no  posterior  tibial,  or  it  may  be  represented  by  a 
small  vessel  whose  distribution  is  confined  to  the  upper  part  of  the  leg.  In  such  a  case,  as 
the  saphenous  artery  degenerates,  anastomoses  between  it  and  the  terminal  portion  of  the  pero- 
neal may  enlarge  so  that  the  plantar  arteries  come  to  take  their  origin  from  that  vessel.  Or, 
again,  the  development  of  the  posterior  tibial  may  proceed  normally,  but  the  lower  portion  of 
the  saphenous  may  not  degenerate  completely,  but  persists,  as  has  been  observed,  as  a  branch 
of  the  tibial,  passing  upward  upon  the  leg  in  company  with  the  long  saphenous  nerve. 

Other  variations  of  the  posterior  tibial  which  have  been  observed,  however,  cannot  appar- 
ently be  explained  as  resulting  from  modifications  of  the  normal  course  of  development,  but  are 
rather  to  be  regarded  as  progressive  variations  due  to  the  enlargement  of  what  are  usually  more 
or  less  insignificant  anastomoses.  Of  this  nature  is  the  origin  from  the  posterior  tibial,  at  about 
the  middle  of  the  leg,  of  a  branch  which  pierces  the  interosseous  membrane  and  divides  into 
an  ascending  and  a  descending  branch,  which  together  represent  the  anterior  tibial  artery.  Or, 
again,  the  posterior  tibial  has  been  observed  to  perforate  the  lower  part  of  the  interosst-ou-. 
membrane  and  to  be  continued  down  the  dorsum  of  the  foot  as  the  dorsalis  pedis  artery, 
the  plantar  arteries  arising  from  the  peroneal.  Occasionally,  also,  the  posterior  tibial  may 
terminate  by  inosculating  with  the  peroneal,  probably  by  the  enlargement  of  the  communicating 
branch,  the  peroneal  in  this  case  also  giving  rise  to  the  plantar  arteries. 

The  high  and  low  origins  of  the  posterior  tibial  have  already  been  mentioned  in  connection 
with  the  variations  of  the  popliteal  (page  831). 

Practical  Considerations. — The  posterior  tibial  artery  on  account  of  its  deep 
position  beneath  the  large  superficial  calf  muscles  is  rarely  wounded  and,  by  reason 
of  the  support  which  it  receives  in  its  upper  two-thirds  from  those  muscles  and  the 
deeper  muscular  layer  on  which  it  lies,  and  in  its  lower  third  'from  the  dense  fascia 
covering  it,  it  is  seldom  the  subject  of  aneurism.  Except  for  a  short  portion  of  its 
course  immediately  above  the  ankle,  it  is  separated  from  the  tibia  by  the  deep  calf 
muscles,  and  is  therefore  not  often  involved  in  fractures  of  that  bone. 

The  bifurcation  of  the  popliteal  is  not  infrequently  the  region  at  which  an  em- 
bolus  carried  down  from  the  popliteal  is  arrested,  and  such  a  clot  may  block  both 
the  tibial  arteries.  Their  free  anastomosis  prevents  gangrene  if  only  one  of  them  is 
occluded  ;  but  if  both  are  involved,  and  especially  if  tin-  succeeding  additions  to  the 
clot  invade  the  anterior  tibial  recurrent — interfering  with  anastomosis  from  above — 
gangrene  almost  certainly  follows. 

Compression  of  the  posterior  tibial  is  scarcely  possible  above  its  lower  third. 
Above  the  ankle  and  behind  the  inner  malleolus  it  may  be  flattened  against  the  tibia 
by  pressure  directed  outward  and  a  little  forward. 

I.igatiou  of  the  posterior  tibial  may  be  done  at  any  part  of  its  course,  but  in  its 
upper  third  is  an  operation  of  some  difficulty. 


THE   POSTERIOR   TIBIAL   ARTERY. 


837 


FIG.  737. 


Gastrocnemius, 
outer  head 

-Venae  comites 

Flexor  longus 
"digitorujn 
-Post,  tibial  artery 

Post,  tibial  nerve 

Cut  edge  of 

soleus  muscle 


— '?  /       Tendon  of 


plantaris 


VA 


i.  The  artery  is  best  approached  from  the  inner  side  of  the  leg.  The  leg  being 
flexed,  the  limb  is  laid  on  its  outer  side,  and  an  incision  three  and  a  half  or  four  inches 
in  length  is  made  along  the  inner 
margin  of  the  tibia,  beginning  two 
and  a  half  inches  from  the  upper  end  of 
that  bone.  The  skin  being  divided, 
care  must  be  exercised  in  opening 
the  superficial  fascia  not  to  injure  the 
internal  saphenous  vein  or  nerve,  both 
of  which  lie  directly  in  the  track  of  the 
wound.  These  structures  being  dis- 
placed, the  deep  fascia  must  be  slit  up 
to  the  full  extent  of  the  incision.  It 
should  also  be  cut  transversely,  so  as 
to  allow  a  freer  access  to  the  intermus- 
cular  parts.  The  next  step  consists 
in  detaching  the  origin  of  the  soleus 
muscle  from  the  tibia.  It  is  at  this 
stage  of  the  operation  that  one  of  two 
errors  is  often  committed, — the  inter- 
muscular  space  between  the  inner 
head  of  the  gastrocnemius  and  the 
soleus  muscle  is  opened,  or  all  the 
muscular  tissue  is  separated  from  the 
bone,  the  tibialis  posticus  muscle  be- 
ing raised  along  with  the  soleus. 
The  first  mistake  leads  the  operator 
above  the  vessel  and  the  second  leads 
him  underneath.  There  is,  however, 
a  guide  which  will  afford  important 
assistance.  If  the  soleus  has  been 
properly  detached  and  raised,  its 
under  surface  will  present  a  white,  shining  sheet  of  tendinous  material,  beneath 

which  will  be   seen   a 
FIG.  738.  ,  .    ,      .      ,.   , 

layer  of  fascia  (inter- 
muscular)  covering  the 
tibialis  posticus  muscle. 
If  search  is  now  made 
externally  and  towards 
the  middle  of  the  leg, 
the  artery  will  be  found 
covered  by  the  inter- 
muscular  fascia,  the 
nerve  lying  to  its  outer 
side.  After  the  vessel 
has  been  separated 
from  the  investing  con- 
nective tissue  and  the 
accompanying  veins, 
the  needle  must  be 
passed  from  without 
inward  (Agnew). 

2.  At  the  middle 
third  the  artery  is 
reached  through  an 
incision  parallel  with 
the  inner  edge  of  the 
tibia  and  a  half  inch  from  its  border.  Avoiding  the  saphenous  vein  and  nerve,  the 
superficial  fascia  and  the  deep  fascia  (with  its  fibres  running  transversely)  are 


Dissection  of  back  of  right  leg,  showing  relations  of  pos- 
terior tibial  vessels  and  nerve ;  gastrocnemius  and  soleus 
muscles  have  been  cut  and  drawn  aside. 


'Post,  tibial  artery 

Post,  tibial  nerve 
Tendo  Achillis 
Flex.  long,  halluci: 


Dissection  of  inner  side  of  right  ankle,  showing  relation  of  tendons,  vessels 
and  nerves  as  they   pass  between  calcanium  and  internal  malleolus. 


838  HUMAN   ANATOMY. 

divided  in  the  line  of  the  skin  wound,  the  inner  margin  of  the  soleus  displaced 
outward,  and  the  vessel,  with  its  venie  comites,  exposed,  the  posterior  tibial  nerve 
lying  to  its  outer  side.  A  little  lower — i.e. ,  in  the  lower  third  of  the  leg — the 
incision  should  be  made  midway  between  the  inner  edge  of  the  tibia  and  the  inner 
edge  of  the  tendo  Achillis,  and  the  artery  will  be  found  lying  on  the  fibres  of  the 
flexor  longus  digitorum,  the  tendon  to  the  inner  side,  and  the  nerve  external. 

3.  To  ligate  the  vessel  at  the  inside  of  the  ankle  the  incision  should  be  semi- 
lunar  in  shape,  parallel  with  the  margin  of  the  inner  malleolus,  and  about  half-way 
between  it  and  the  margin  of  the  tendo  Achillis.  After  dividing  the  deep  fascia- 
internal  annular  ligament — the  artery  will  be  found,  with  its  accompanying  veins, 
lying  between  the  flexor  longus  digitorum  and  tibialis  posticus  tendons  on  the  inside 
— each  in  a  separate  synovial  sheath  and  the  latter  near  the  malleolus — and  the 
nerve  and  flexor  longus  pollicis  tendon  on  the  outside.  The  sheaths  of  these  tendons 
should  not  be  opened. 

The  collateral  circulation  is  carried  on  from  above  the  ligature  by  («)  the 
anterior  and  posterior  peroneal  arteries  and  their  muscular  and  communicating 
branches  ;  (£)  the  external  malleolar  branch  of  the  anterior  tibial ;  (c)  the  internal 
malleolar  (anterior  tibial);  (a?)  the  dorsalis  pedis.  Anastomosing  respectively 
with  (a)  the  muscular  branches  and  the  communicating  branch  of  the  posterior 
tibial  ;  (£)  the  external  plantar  branch  of  the  posterior  tibial  ;  (c)  the  internal  malle- 
olar (posterior  tibial)  ;  and  (a?)  the  internal  and  external  plantars. 

1.  The  Nutrient  Artery. — The  nutrient  artery  to  the  tibia  (a.  nutritia  tibiae  > 
may  arise  from  the  posterior  tibial,  either  above  or  below  the  origin  of  the  peroneal 
artery,  or  sometimes  it  arises  from  that  vessel.      It  pierces  the  tibialis  posticus  and 
enters  the  nutrient  foramen  on  the  posterior  surface  of  the  tibia,  sending  off,  before 
it  does  so,  some  small  muscular  branches. 

2.  The  Peroneal  Artery. — The  peroneal  artery  (a.  peronaea)  (Fig.  736)  is  by 
far  the  largest  of  the  collateral  branches  of  the  posterior  tibial.      It  arises  about  2.5  cm. 
below  the  lower  border  of  the  popliteus  muscle  and  is  at  first  directed  outward  and 
downward  towards  the  fibula,  and  then  passes  vertically  downward  along  the  inner 
surface  of  that  bone  to  a  point  about  2.5  cm.  above  the  ankle-joint,  where  it  termi- 
nates by  dividing  into  the  anterior  and  posterior  peroneal  arteries. 

Relations. — In  the  upper  part  of  its  course  it  is  covered  posteriorly  by  the 
soleus,  lying  between  that  muscle  and  the  tibialis  posticus.  Lower  down  it  passes 
beneath  the  flexor  longus  hallucis  or  else  traverses  the  substance  of  that  muscle,  and 
just  before  its  termination  it  emerges  from  beneath  the  muscle  and  becomes  super- 
ficial. It  is  accompanied  by  two  venae  comites. 

Branches. — In  addition  to  numerous  muscular  branches  to  the  neighboring  muscles  and 
cutaneous  branches  to  the  integument  of  the  outer  border  of  the  cms,  the  peroneal  artery  gives 
off  the  following  vessels  : 

(a)  The  nutrient  artery  to  the  fibula  (a.  nutritiae  fibulae)  enters  the  nutrient  foranu-n  of  that 
bone. 

(A)  The  communicating  branch  (ramus  communicans)  passes  inward  over  tin-  lower  end  of 
the  tibia  and  beneath  the  tendo  Achillis,  a  short  distance  above  the  terminal  bifurcation  of  the 
peroneal.  It  inosculates  with  the  communicating  branch  of  the  posterior  tibial. 

(c)  The  anterior  peroneal  artery  ( ramus  perfonms)  is  one  of  the  terminal   branches  of  the 
peroneal.     It  passes  directly  forward  and,  perforating  the  interosseous  membrane,  bends  down- 
ward over  the  ankle-joint  to  the  dorsum  of  the  foot.      It  sends  branches  to  the  ankle-joint  and 
to  the  inferior  tibio-libular  articulation,  as  well  as  to  the  peroneiis  tertius  muscle,  beneath  which 
it  ] tasses,  and  terminates  by  anastomosing  with  the  tarsal  and  metatarsal  branches  of  the  dorsalis 
pedis  and  with  the  external  plantar  artery  upon  the  side  of  the  foot. 

(d)  The  posterior  peroneal  artery  is  the  other  terminal   branch  of  the  peroneal,  of  which 
it  is  the  direct  continuation.      It   gives  origin  to  the  r.vternal  calcancal  branch   which  ramifies 
over  the  outer  surface  of  the  os  calcis  and   terminates  by  anastomosing  with   the  internal  cal- 
caneal  branch  of  the  posterior  tibial   artery  and  with  the  tarsal  and  metatarsal   branches  of  the 
dorsalis  pedis. 

Variations. — The  peroneal  artery  is  exceedingly  subject  to  variation.  It  is  rarely  absent, 
but  not  infrei|iiently  it  terminates  over  the  outer  malleolus,  its  lower  portion  being  given  off  from 
a  branch  which  passes  across  from  the  posterior  tibial  and  represents  the  enlarged  anastomosis 


THE   POSTERIOR   TIBIAL   ARTERY. 


839 


FIG.  739. 


Internal  annular 

ligament,  cut  edge 


Inner  malleolus— i- 
Abductor  hallucis 

Internal  plantar 


Flexor  longus 

hallucis  tendon 


From  external  calcanean 


Internal  calcaneal  ot 
external  plantar 
Plantar  fascia,  cut 


Flexor  brevis  digitorum 

Abductor  minimi  digiti 
External  plantar  artery 


of  the  posterior  tibial  and  peroneal  communicating  branches.  Conversely,  when  the  lower  por- 
tion of  the  posterior  tibial  is  wanting',  it  may  be  replaced  by  the  peroneal,  which  then  gives  rise 
to  the  plantar  arteries.  Occasionally  the  peroneal  is  larger  than  usual,  and  may  give  origin  to 
the  anterior  tibial  artery,  and  it  may  give  off  the  nutrient  artery  for  the  tibia. 

The  anterior  peroneal  artery  is  sometimes  absent,  but  more  frequently  it  is  larger  than 
usual  and  inosculates  with  the  anterior  tibial.  Occasionally  the  lower  portion  of  this  latter  ves- 
sel is  wanting,  and  the  anterior  peroneal  may  then  take  its  place,  being  continued  downward 
upon  the  dorsum  of  the  foot  as  the  dorsalis  pedis  and  giving  off  the  branches  which  normally 
arise  from  that  vessel. 

3.  The  Communicating  Artery. — The  communicating  artery  (r.  communicans) 

(Fig.  736)  extends  transversely  outward  across  the  posterior  surface  of  the  tibia,  beneath 
the  tendon  of  the  flexor 
longus  hallucis  and  the 
tendo  Achillis,  and  an- 
astomoses   with    the 
communicating  branch      Internal  calcanein  of 
of  the  peroneal.  ^sterior  tlbial- 

4.  The  Internal 
Malleolar  Artery.— 
The  internal  malleolar 
artery   (a.    malleolaris 
posterior  medialis)  (Fig. 
740)  passes  directly  in- 
ward, beneath  the  ten- 
dons   of     the     flexor 
longus   digitorum  and 
tibialis     posticus,     to 
ramify  over  the  internal 
surface    of    the     inner 
malleolus,    anastomos- 
ing  with   the    internal 
malleolar  branch  of  the 
anterior  tibial  artery. 

5.  The  Internal 
Calcaneal  Artery.— 
The  internal   calcaneal 
artery   (raraus   calcanei 
medialis)    (Fig.    736) 
arises  from  the   lower 
part    of    the    posterior 
tibial,     just    before     it 
divides    into    the    two 
plantar  vessels.      It  is 
frequently  represented 
by    several    branches 
which    descend    along 
the  inner  side   of   the 

tuberosity  of  the  os  calcis,  supplying  the  neighboring  parts  of  the  integument  and 
anastomosing  with  branches  of  the  internal  malleolar  and  posterior  peroneal  arteries. 

6.  The  Internal  Plantar  Artery. — The   internal  plantar  artery  (a.  plantaris 
medialis)  (Fig.  740)  is  the  smaller  of  the  two  terminal  branches  of  the  posterior  tibial. 
It  arises  in  the  groove  between  the  internal  malleolus  and  the  os  calcis  and  is  directed 
at  first  downward  and  forward,  under  cover  of  the  abductor  hallucis,  and  then  forward 
along  the  inner  border  of  the  foot,  between  the  abductor  hallucis  and  the  flexor  brevis 
digitorum,  terminating  opposite  the  head  of  the  first  metatarsal  bone  by  anastomosing 
with  one  or  other  of   the  two   branches   distributed    to  the    plantar  surface    of  the 
great  toe. 

Branches. — In  its  course  it  gives  off  muscular  branches  to  the  abductor  hallucis  and  the 
flexor  brevis  digitorum,  cutaneous  branches  to  the  integument  over  the  inner  border  of  the  foot, 
and  articular  branches  to  the  neighboring  tarsal  joints.  In  addition,  it  usually  gives  off  near  its 


Princeps  halluc 


Interosseous  arteries 
dividing  into 

digital  branches 


Arteries  of  plantar  surface  of  right  foot ;    superficial  dissection. 


84o  HUMAN   ANATOMY. 

origin  a  larger  branch,  the  anastomotic  branch,  which  passes  beneath  the  abductor  hallucis  to 
gain  the  upper  border  of  that  muscle,  along  which  it  courses  forward,  giving  off  numerous 
branches  to  the  abductor  and  the  adjacent  integument  and  anastomosing  with  the  tarsal  and 
metatarsal  branches  of  the  dorsalis  pedis.  More  distally  it  gives  off  from  its  outer  surface  a 
varying  number  of  slender  superficial  digital  branches,  which  pass  obliquely  forward  and  out- 
ward across  the  sole  of  the  foot  to  anastomose  with  one  or  more  of  the  plantar  interosseous 
branches  from  the  plantar  arch. 

Variations. — Occasionally  the  superficial  digital  branches  of  the  internal  plantar  arise  from 
a  common  stem  which  anastomoses  with  a  branch  from  the  external  plantar  to  form  a  superfi- 
cial plantar  arch  beneath  the  superficial  fascia.  This  is  the  equivalent  of  the  superficial  palmar 
arch  of  the  hand. 

7.  The  External  Plantar  Artery. — The  external  plantar  artery  (a.  plantaris 
lateralis)  (Fig.  740)  is  the  larger  of  the  terminal  branches  of  the  posterior  tibial.  It 
passes  forward  and  outward  across  the  sole  of  the  foot,  at  first  between  the  flexor 
brevis  digitorum  and  the  flexor  accessorius,  and  then  in  the  interval  between  the  flexor 
brevis  digitorum  and  the  abductor  minimi  digiti.  Opposite  the  base  of  the  fifth  meta- 
tarsal bone  it  turns  somewhat  abruptly  inward  and  again  crosses  the  sole  of  the  foot, 
forming  the  plantar  arch  (arcus  plantaris),  which  terminates  at  the  proximal  end  of 
the  first  intermetatarsal  space  by  uniting  with  the  communicating  branch  from  the 
dorsalis  pedis. 

Relations. — In  the  first  part  of  its  course  the  external  plantar  lies  beneath  the 
abductor  hallucis  and  the  flexor  brevis  digitorum,  but  as  it  approaches  the  fifth  meta- 
tarsal it  becomes  more  superficial,  being  covered  only  by  the  skin  and  the  superficial 
and  plantar  fasciae.  It  rests  upon  the  flexor  accessorius  and  the  flexor  brevis  minimi 
digiti,  and  is  accompanied  by  the  external  plantar  nerve. 

The  plantar  arch,  on  the  contrary,  occupies  a  much  deeper  position.  It  passes 
beneath  the  tendons  of  the  flexor  longus  digitorum,  the  lumbricales,  and  the  oblique 
portion  of  the  adductor  hallucis,  resting  upon  the  proximal  ends  of  the  second,  third, 
and  fourth  metatarsals  and  upon  the  interosseous  muscles  which  occur  between  those 
bones. 

Branches. — The  external  plantar  artery  gives  rise  to  (a)  numerous  muscular  branches 
which  supply  the  various  muscles  of  the  plantar  surface  of  the  foot,  and  in  its  first  part  to 

(b)  Cutaneous  branches  which  supply  the  skin  over  the  sole  and  outer  border  of  the  foot, 
some  of  them  forming  anastomoses  with  branches  of  the  tarsal  and  metatarsal  branches  of  the 
dorsalis  pedis.     In  addition,  there  are  given  off  from  the  first  portion  of  the  artery — 

(c )  Calcaneal  branches,  one  or  more  in  number,  which  arise  near  the  commencement  of 
the  external  plantar  and  ramify  over  the  inner  surface  of  the  os  calcis,  anastomosing  with  the 
internal  calcaneal  branches  of  the  posterior  tibial. 

From  the  plantar  arch  a  number  of  vessels  are  given  off. 

(d)  The  articulating  branches  are  given  off  from  the  posterior  or  concave  surface  of  the 
arch  and  supply  the  tarsal  articulations. 

(e)  The  posterior  perforating  branches,  four  in  number,  arise  either  from  the  plantar  arch 
or  from  the  plantar  digital  branches  of  the  fourth  intermetatarsal  space.     They  ascend  in  the 
intermetarsal  spaces  between  the  heads  of  the  dorsal  interosseous  muscles  and  terminate  by  inos- 
culating with  the  first,  second,  and  third  dorsal  interosseous  arteries.     The  branch  which  passes 
through  the  first  intermetatarsal  space  is  much  larger  than  the  rest  and  inosculates  with  the  dor- 
salis pedis  artery  ;  it  is  sometimes  regarded  as  the  terminal  branch  of  that  vessel. 

(/)  The  plantar  interosseous  arteries  ( aa.  metatarsae  jdantares)  are  five  in  number,  and  are 
usually  numbered  in  succession  from  the  outer  side  of  the  foot  inward, — that  is  to  say,  in  tin- 
opposite  direction  to  the  intermetatarsal  spaces  in  which  they  lie.  The  first  arises  just  where 
the  external  plantar  artery  is  bending  inward  to  form  the  -plantar  arch  and  passes  forward 
along  the  inner  border  of  the  abductor  minimi  digiti,  later  crossing  over  the  flexor  brevis  minimi 
digiti  to  reach  the  outer  surface  of  the  little  toe,  along  which  it  runs. 

The  second,  third,  and  fourth  plantar  interosseous  arteries  arise  in  succession  from  the 
plantar  arch  as  it  crosses  the  fourth,  third,  and  second  intermetatarsal  spaces,  and  pass  forward, 
resting  upon  the  interosseous  muscles  and  covered  by  the  tendons  of  the  flexor  longus  digitorum 
and  the  lumbricales,  and  more  distally  by  the  transverse  adductor  of  the  great  toe.  Just  before 
reaching  the  line  of  the  metatarso-phalangeal  articulations  each  artery  gives  off  an  anterior  per- 
forating branch,  which  passes  dorsally  to  communicate  with  the  corresponding  dorsal  interos- 
seous artery,  and  then  divides  into  two  plantar  digital  branches,  which  pass  onward  upon  the 
adjacent  sides  of  neighboring  digits. 


THE    POSTERIOR   TIBIAL   ARTERY. 


The  fifth  plantar  interosseous  artery  is  considerably  larger  than  the  others,  and  arises  from 
the  inner  end  of  the  plantar  arch,  opposite  the  communicating  branch  which  passes  between  the 
plantar  arch  and  the  dorsalis  pedis.  It  runs  forward  at  first  along  the  first  intermetatarsal  space 
and  then  upon  the  first  metatarsal  bone,  and  gives  off  a  digital  branch  which  passes  to  the  inner 
surface  of  the  great  toe  and  continues  on  towards  the  metatarso-phalangeal  joint  of  that  digit. 
Before  reaching  this,  however,  it  gives  off  an  anterior  perforating  branch  and  then  divides  into 
two  plantar  digital  branches,  which  supply  respectively  the  inner  side  of  the  second  and  the 
outer  side  of  the  great  toe. 

Since  the  communicating  branch  which  traverses  the  first  intermetatarsal  space  is  some- 
times regarded  as  the  terminal  portion  of  the  dorsalis  pedis  artery,  and  the  fifth  plantar  inter- 
osseous artery  seems  to  be,  upon  such  a  view,  the  branch  of  the  communicating  vessel,  the  fifth 
plantar  has  been  de- 
scribed as  a  branch  of  FIG.  740. 
the  dorsalis  pedis  ar-  Tendo  Achiiiis 
tery,  under  the  name  of 
the  a.  princeps  hallucu. 
There  can  be  no  doubt, 
however,  that  both  the 
communicating    and 
the  princeps  are  equiv- 
alent to  the  other  pos- 
terior perforating  and 
plantar    interosseous 
arteries. 


Posterior  tibial 


Internal  malleola 


Internal  lateral 
ligam 


Internal  plantar 


Flexor  longus 

hallucis  tendon 


Adductor 

obliquus,  cut 


Princeps  hallucis 
(V.  interosseous) 
dividing  into 
digital  branches 


Internal  calcanean 
Abductor  hallucis 
Internal  calcanean  of  ext. 
External  [plantar 

plantar 

Flexor  brevis  digitorum 

Flexor  accessorius 
Superficial  fascia 

—  Abductor  minimi  digit! 


II.  and  III.  plantar 
interossei  and  flexor 
brevis  minimi  digit! 


I.-IV.  interosseous 
arteries  dividing  into 
digital  branches 


Variations. — The 
external  plantar  artery 
may  be  quite  small,  in 
which  case  the  plantar 
arch  seems  to  be  a 
continuation  from  the 
anterior  tibial  artery 
through  the  posterior 
perforating  branch  of 
the  first  intermetatar- 
sal space.  The  arch 
is  occasionally  double, 
owing  to  its  division 
at  its  origin  into  two 
stems  which  reunite 
opposite  the  first  inter- 
metatarsal space.  The 
first  plantar  interosse- 
ous may  arise  by  a 
common  stem  with  the 
second,  and,  con- 
versely, one  or  more 
of  the  plantar  digital 
branches  may  have  an 
independent  origin 
from  the  arch. 

Anastomoses 
of  the  Posterior 
Tibial  Artery. — A 

collateral  circulation 

for  the  posterior  tibial  after  interruption  of  that  vessel  below  the  origin  of  the 
peroneal  may  readily  be  established  through  the  anastomoses  which  its  branches 
form  with  those  of  the  peroneal  and  those  of  the  anterior  tibial.  The  anasto- 
moses with  the  peroneal  are  between  the  communicating  branches  of  the  two 
arteries,  between  the  anterior  peroneal  and  the  external  plantar,  and  between  the 
posterior  peroneal  and  the  internal  calcaneal.  With  the  anterior  tibial  artery  there 
is  communication  through  the  malleolar  branches  of  the  two  arteries,  through  the 
anastomotic  branch  of  the  external  plantar  and  the  tarsal  and  metatarsal  branches 
of  the  dorsalis  pedis,  and  through  the  union  of  anterior  and  posterior  perforating 
branches  of  the  plantar  arch  and  the  plantar  interosseous  arteries  with  the  dorsalis 
pedis  and  dorsal  interosseae. 


Arteries  of  plantar  surface  of  right  foot ;  deeper  dissection. 


842 


HUMAN    ANATOMY. 


FIG.  741. 


THE   ANTERIOR  TIBIAL   ARTERY. 

The  anterior  tibial  artery  (a.  tibialis  anterior)  (Figs.  742,  743)  is  the  other  terminal 
branch  of  the  popliteal.  It  begins  at  the  lower  border  of  the  popliteus  muscle,  and  is  at 
first  directed  forward,  passing  between  the  tibia  and  fibula  and  the  two  uppermost  slips 
of  origin  of  the  tibialis  posticus,  above  the  upper  border  of  the  interosseous  membrane. 
It  then  bends  downward  and  traverses  the  entire  length  of  the  crus  to  the  front  of  the 
ankle-joint,  where  it  becomes  the  dorsalis  pedis  artery.  Its  course  may  be  represented 
by  a  line  drawn  from  the  head  of  the  fibula  to  a  point  half-way  between  the  two  malleoli. 

Relations. — In  its  course  down  the  leg  the  anterior  tibial  artery  rests  posteriorly 
upon  the  interosseous  membrane,  to  which  it  is  more  or  less  firmly  united  by  fibrous 
bands  ;  in  the  lower  quarter  of  its  course  it  rests  upon  the  front  of  the  tibia.  Anteriorly, 
in  the  upper  two-thirds  of  its  course,  it  is  overlapped  by  the  tibialis  anticus,  lying  along 
the  deep  edge  of  the  connective-tissue  partition  which  separates  that  muscle  from  the  ex- 
tensor longus  digitorum  and  the  extensor  proprius  hallucis.  Lower,  however,  it  is 
superficial,  and  just  above  the  ankle-joint  it  is  crossed  obliquely,  from  without  inward, 
by  the  tendon  of  the  extensor  proprius  hallucis,  and  then  passes  beneath  the  anterior 
annular  ligament.  Internally  to  it  is  the  tibialis  anticus,  and  at  the  ankle-joint  the  ten- 
don of  the  extensor  proprius  hallucis  ;  externally  it  has  in  its  upper  third  the*  extensor 
longus  digitorum,  in  its  middle  third  the  extensor  proprius  hallucis,  and  at  the  ankle  the 
inner  tendon  of  the  extensor  longus  digitorum.  The  anterior  tibial  nerve  lies  to  tin- 
outer  side  of  the  artery  in  its  upper  and  lower  thirds  ;  in  the  middle  third  of  the  leg  it 
is  usually  in  front  of  the  vessel. 

Variations. — The  anterior  tibial  artery,  as  it  occurs  in  man,  appears  to  be  the  result  of  a  union 
of  two  originally  distinct  vessels,  both  of  which  arise  from  the  primitive  peroneal  artery  and  pass  to 

the  front  of  the  leg.  The-  up- 
permost of  these  forms  tin- 
greater  portion  of  the  artery, 
while  the  lower  one,  which 
is  represented  by  the  anterior 
peroneal  artery,  forms  only 
the  lower  part  of  the  anterior 
tibial  and  its  continuation 
upon  the  dorsurn  of  the  foot, 
the  dorsalis  pedis.  In  case  of 
failure  in  the  union  of  these 
two  vessels,  the  anterior  tibial 
may  appear  to  terminate  in 
muscular  branches  a  short 
distance  above  the  ankle- 
joint,  the  dorsalis  pedis  being 
the  continuation  of  the  an- 
terior peroneal.  This  ar- 
rangement is  not  infrequent  ; 
more  rarely  the  upper  portion 
of  the  vessel  is  greatly  re- 
duced, being  represented 
only  by  a  small  stem  which 
gives  off  the  posterior  and 
anterior  recurrent  branches 
as  well  as  branches  to  the 
popliteus  muscle,  the  front  of 
of  the  leg,  in  such  cases,  being 
Sometimes  supplied  by  an  in- 
dependent perforating  branch 
from  the  posterior  tibial. 

Practical  Consid- 
erations.— The  anterior 
tibial  artery  is  more  often 

Dissection  of  middle  third  of  right  leg,  showing  relations  of  anterior  tibial  -  , 

vessels  and  nerves;   extensor  muscles  have  been  drawn  aside.  WOUImCU      tiKll!     tin.     po 

tenor  tibial  because  of  its 

in.  ire  exposed  position  on  the  front  of  tin-  limb  and  its  close  relation  to  the  tibia.     It  is  not 
infrequently  lacerated  by  the  sharp  edge  of  a  fragment  in  fracture  of  that  bone.      It  is 


Peroneus  brevis  — 


Ext.  longus  hallucis  — 


Ext.  longus 

digitorum 


Tibialis 

anticus  muscle 


— Tibia 

Ant.  tibial  nerve 

—  Ant.  tibial  artery 

—  Companion  vein 


THE   ANTERIOR   TIBIAL   ARTERY. 


843 


Superior  external  articular 


External  condyle  — 


Anterior  tibial  recurrent 


Peroneus  longus — 


Extensor  longus  digitoruin — 


Extensor  proprius  halluci: 


Branch  of  superior 

internal  articular 

—  Tendo  patellce 

•  Inferior  internal  articular  artery 

^=>Tibialis  anticus 

Interosseous  membrane 


.Anterior  tibial  artery 


ribialis  anticus 


rarely  the  subject  of  aneurism.  Ligation  may  be  done  at  ( i)  the  upper;  (2)  the  middle; 
or  ( 3 )  the  lower  third.  The  line  of  the  artery  is  from  a  point  midway  between  the  exter- 
nal tibial  tuberosityand 
the  head  of  the  fibula  to 
the  middle  of  the  anteri- 
or inter  malleolar  space, 
i.  When  through 
an  incision  made  at 
this  line  the  deep  fascia 
is  reached  and  divided, 
the  interspace  in  which 

the     artery     lieS     Should  Inferior  external  articular 

be     SOUght     for.  It     is  Tendon  of  biceps- 

that  between  the  tibi- 
alis  anticus  and  the 
extensor  longus  digi- 
torum, is  the  only  in- 
termuscular  interstice 
in  the  upper  anterior 
tibial  region,  is  about 
an  inch  or  an  inch  and 
a  quarter  external  to 
the  tibial  crest,  and  a 
half  to  three-quarters 
of  an  inch  internal  to 
the  septum  which  di- 
vides the  extensor  lon- 
gus from  the  peroneus 
longus.  This  septum 
is  often  marked  by  a 
white  line  visible  before 
the  deep  fascia  is  di- 
vided ,  or  it  may  be 
recognized  by  slipping 
a  director  outward  be- 
neath the  aponeurosis 
until  its  point  is  firmly 
arrested.  The  inter- 
space containing  the 
anterior  tibial  artery 
will  then  be  internal  to 
this  and  can  be  felt  as 
a  line  of  lessened  resist- 
ance when  the  fore- 
finger is  pressed  length- 
wise along  the  muscles 
(Treves).  On  the 
other  hand,  the  apon- 
eurotic  partition  be- 
tween the  extensor 
and  the  peroneus  — 
external  to  the  inter- 
space sought  for  — 
resists  and  vibrates 
under  the  point  of  the 
director  or  the  fore- 
finger (Farabeuf).  At 
the  bottom  of  the  interspace  the  artery  will  be  found  lying  upon  the  interosseous 
membrane  to  the  outer  side  of  the  tibia  and  with  the  nerve  external  to  it.' 


Peroneus  brevis 
Peroneus  longus  tendon 

Aaterior  peroneal  artery 
External  malleolar  artery 


External  calcanean  or 
posterior  peroneal  arter; 
External  malleolu 


Tarsal  artery 
Extensor  brevis  digitoruin 


Peroneus  brevis  tendon 
Metatarsal  artery 


Posterior 

perforating  arteries 

Dorsal  interosseous  arteries 


Internal  malleolar  artery 
Inner  malleolus 


— —  Innermost  tendon  of 

extensor  brevis  digitorum 

Dorsalis  pedis 


Communicating  artery 

Dorsalis  hallucis 

Anterior  perforating  arteries 


Tendons  of  extensor 
longus  digitoruin 


Arteries  of  front  of  leg  and  dorsum  of  foot. 


844  HUMAN   ANATOMY. 

2.  At   the   middle   of   the   limb  the   same  interspace  is  found — usually  more 
easily,  as  there  is  often  some  yellowish-white  fatty  tissue  lying  between  the  muscles 
and  seen  as  a  line  on  the  surface  of  the  deep  fascia — and  is  opened.      The  artery 
which  still  lies  on  the  interosseous  membrane  will  be  found  in  the  deeper  space  thus 
disclosed  between  the  extensor  proprius  pollicis  and  the  tibialis  anticus. 

3.  At  the  lower  third  an  incision  on  the  same  line  will  expose  the  vessel  lying 
usually  in  the  innermost  of  the  two  interstices  found  at  that  part  of  the  limb,  viz., 
that  between  the  tibialis  anticus  and  the  extensor  proprius  pollicis.      Occasionally 
it  will  be  found  to  the  outer  side  of  the  tendon  of  the  extensor  proprius — the  second 
tendon  from  the  tibia — in  the  space  between  that  muscle  and  the  extensor  longus 
digitorum.     The  vessel  lies  on  .the  front  of  the  tibia,  with  the  nerve  external. 

The  collateral  circulation  is  carried  on  from  above  the  ligature  by  (a)  the  pero- 
neals  ;  and  (<5)  the  posterior  tibial,  anastomosing  respectively  with  (a)  the  external 
malleolar,  the  branches  of  the  dorsalis  pedis  and  the  plantar  ;  and  (fr)  the  internal 
malleolar  from  below,  assisted  by  the  many  small  anastomotic  vessels  piercing  the 
interosseous  membrane  and  derived  from  the  two  tibials. 

Branches. — In  addition  to  numerous  muscular  branches  which  supply  the 
adjacent  muscles,  the  anterior  tibial  artery  gives  off  the  following  : 

i.  The  superior  fibular  branch  (ramus  fibularis)  is  a  small  vessel  which  arises 
from  the  anterior  tibial  immediately  below  its  origin  ;  occasionally  it  arises  by  a  com- 
mon trunk  with  the  posterior  tibial  recurrent  or  else  from  the  lower  part  of  the 
popliteal.  It  passes  upward  behind  the  neck  of  the  fibula,  traversing  the  substance 
of  the  soleus,  and  sends  branches  to  that  muscle  and  to  the  peroneus  longus,  and 
anastomoses  with  the  external  inferior  articular  branch  of  the  popliteal. 

2. '  The  posterior  recurrent  tibial  artery  (a.  recurrens  tibialis  posterior)  arises 
while  the  anterior  tibial  is  still  upon  the  posterior  surface  of  the  leg.  It  passes  upward 
between  the  popliteal  muscle  and  the  posterior  ligament  of  the  knee-joint,  both  of 
whicn  it  supplies,  and  terminates  by  anastomosing  with  the  external  and  internal 
inferior  articular  branches  of  the  popliteal. 

3.  The  anterior  recurrent  tibial  artery  (a.  recurrens  tibialis  anterior)  is  given 
off  just  after  the  anterior  tibial  has  reached  the  front  of  the  leg.      It  runs  upward  in 
the  substance  of  the  tibialis  anticus  and  oyer  the  outer  tuberosity  of  the  tibia,  and 
terminates  by  taking  part  in  the  formation  of  the  circumpatellar  anastomosis.      It 
gives  branches  to  the  tibialis  anticus,  the  extensor  longus  digitorum,  the  capsule  of 
the  knee-joint,  and  the  adjacent  integument.     This  artery  is  of  importance  in  the 
establishment  of  a  collateral  circulation  after  ligation  of  the  popliteal  artery  (page  834), 
on  account  of  its  anastomoses  with  the  descending  branch  of  the  external  circumflex 
artery  and  with  the  anastomotica  magna. 

4.  The  internal  malleolar  artery  (a.  malleolaris  anterior  medialis)  arises  from 
the  inner  surface  of  the  anterior  tibial,  a  little  above  the  ankle.      It  passes  inward 
beneath  the  tibialis  anticus,  over  the  surface  of  the  inner  malleolus,  and  terminates 
by  anastomosing  with  the  malleolar  branch  of  the  posterior  tibial,  the  internal  plantar,, 
and  the  internal  calcaneal  arteries. 

5.  The  external  malleolar  artery  (a.  malleolaris  anterior  lateralis)  arises  from 
the  outer  surface  of  the  anterior  tibial,  usually  a  little  below  the  internal  malleolar. 
It  is  directed  outward  and  downward  beneath  the  extensor  longus  digitorum  and  the 
peroneus  tertius,  over  the  surface  of  the  external  malleolus,   and  anastomoses  with 
branches  from  the  anterior  and  posterior  peroneal  arteries. 

Anastomoses  of  the  Anterior  Tibial  Artery. —  Collateral  circulation  is 
readily  established,  in  cases  of  interruption  of  the  anterior  tibial  artery,  by  means 
of  its  abundant  anastomoses  with  branches  of  the  posterior  tibial.  Thus  there  art- 
rich  anastomoses  between  the  internal  malleolar  branch  of  the  anterior  tibial  and  the 
malk-olar  branch  of  the  posterior  tibial,  and  between  the  external  malleolar  branch  of 
the  anterior  tibial  and  the  anterior  and  posterior  peroneal  branches.  Further,  since 
the  dorsalis  pedis  artery  is  the  continuation  of  the  anterior  tibial,  it  will  assist  mate- 
rially in  the  collateral  circulation  by  the  anastomoses  of  its  tarsal  and  metatarsal 
branches  with  the  plantar  and  peroneal  arteries  and  by  its  connections  with  the 
plantar  arch*. 


THE   DORSAL   ARTERY. 


845 


Tendon  of 

tibialis  anticus 


Branch  of  musculo- 

cutaneous  nerve 


Ant.  tibial  artery 
Ant    tibial  nerve 


Tendon  of  extensor 

longus  hallucis 


Musculo- 
cutaneous  nerve 


— Peroneus  brevis 
Peroneus  longus 


Dorsalis  pedis  artery 


THE  DORSAL  ARTERY  OF  THE  FOOT. 

The  dorsal  artery  of  the  foot  (a.  dorsalis  pedis)  (Fig.  743)  is  the  continuation  of 
the  anterior  tibial  beyond  the  ankle-joint.  It  extends  to  the  proximal  portion  of  the 
first  intermetatarsal  space,  where  it  receives  the  large  fourth  perforating  branch  of  the 
plantar  arch,  and  is  thence  continued  forward  along  the  intermetatarsal  space  as  the 
a.  dorsalis  hallucis. 

Relations. — The  dorsalis  pedis  is  covered  in  the  proximal  portion  of  its  course  by 
the  anterior  annular  ligament,  and  is  crossed  just  before  it  reaches  the  intermetatarsal 
space  by  the  tendon  of  the  extensor  brevis  digitorum  which  passes  to  the  great  toe.  It 
rests  successively  upon 
the  anterior  ligament  of 
the  ankle-joint,  the  head 
of  the  astragalus,  the 
astragalo-scaphoid  liga- 
ment, the  dorsal  surface 
of  the  scaphoid  bone,  the 
dorsal  scapho-cuneiform 
ligament,  and  the  in- 
tercuneiform  ligaments 
which  extend  between 
the  middle  and  internal 
cuneiform  bones.  Ex- 
ternally it  is  separated 
from  the  innermost  ten- 
don of  the  extensor  lon- 
gus  digitorum  and  from 
the  extensor  brevis  digi- 
torum by  the  inner  termi- 
nal branch  of  the  anterior 
tibial  nerve,  and  inter- 
nally it  is  in  relation  with 
the  tendon  of  the  exten- 
sor hallucis  proprius. 

Branches.  —  In 
addition  to  numerous  cu- 
f a  11  cons  branches  to  the 
skin  of  the  dorsum  of 
the  foot  and  muscular 
branches  to  the  extensor 
bn.-vis  digitorum,  the 
dorsalis  pedis  gives  rise 
to  the  following  vessels. 

1.  The    internal 
tarsal    branches    (aa. 
tarseae  mediates )  are  one 

or  more  small  vessels  which  pass  over  the  outer  border  of  the  foot,  supplying  the 
integument  and  the  tarsal  articulations  and  anastomosing  with  the  internal  malleolai 
and  internal  plantar  arteries. 

2.  The  external  tarsal  branch  (a.  tarsea  lateralis)  arises  opposite  the  head 
of  the  astragalus  and  passes  outward  and  forward  over  the  scaphoid  and   cuboid 
bones,   under  cover  of  the  extensor  brevis  digitorum.      It  gives  branches  to  that 
muscle,  to  the  skin,  and  to  the  tarsal  articulations,  and  anastomoses  with  the  external 
malleolus  and  anterior  peroneal  arteries  above,  with  the  external  plantar  laterally,  and 
with  the  metatarsal  below. 

3.  The  metatarsal  branch  (a.  arcuata)  arises  over  the  internal  cuneiform  bone 
and  is  directed  at  first  laterally  forward  and  then  laterally  over  the  bases  of  the  four 
outer  metatarsal  bones  and  beneath  the  tendons  of  the  extensor  longus  and  extensoi 


Dissection  showing  relations  of  vessels  and  nerves  in  vicinity  of  left  ankle  ; 
portion  of  anterior  annular  ligament  still  in  place. 


846  HUMAN   ANATOMY. 

brevis  digitorum.  It  thus  forms  an  arch  upon  the  dorsal  surface  of  the  foot  corres- 
ponding in  position  with  the  plantar  arch  below.  It  anastomoses  laterally  with  the 
external  tarsal  and  with  the  external  plantar,  and  opposite  each  of  the  intermetatarsal 
spaces  which  it  passes — the  second,  third  and  fourth — gives  off  a  dorsal  interosse- 
ous  artery  (a.  metatarsea  dorsalis). 

Each  of  these  passes  forward  along  its  intermetatarsal  space,  and,  immediately 
beyond  its  origin,  gives  off  a  posterior  perforating  branch  which  communicates  directly 
with  the  corresponding  posterior  perforating  branch  of  the  plantar  arch.  At  the  distal 
end  of  its  intermetatarsal  space  each  artery  gives  off  an  anterior  perforating  branch 
which  unites  with  the  similar  branch  of  the  corresponding  plantar  interosseous,  and 
then  divides  into  two  dorsal  digital  branches  (aa.  digitales  dorsales)  which  pass  along 
the  adjacent  surfaces  of  two  neighboring  digits  and  anastomose  with  one  another  and 
with  the  plantar  digital  branches. 

4.  The  dorsal  interosseous  branch  of  the  first  intermetatarsal  space 
appears  to  be  the  continuation  of  the  dorsalis  pedis,  and  is  usually  termed 
the  a.  dorsalis  hallucis.  Its  course  is  exactly  similar  to  that  of  each  of  the 
other  dorsal  interosseous  arteries,  except  that,  in  addition  to  the  anterior  dorsal 
perforating  and  terminal  dorsal  digital  branches,  it  gives  off,  not  far  from  its 
origin,  a  third  digital  branch  which  passes  forward  along  the  outer  surface  of  the 
great  toe.  The  posterior  communicating  artery  which  should  arise  from  this  vessel 
is  represented  by  the  large  branch  by  which  the  dorsalis  pedis  communicates  with  the 
plantar  arch. 

Variations. — The  origin  of  the  dorsalis  pedis  from  the  peroneal  by  means  of  the  anterior 
peroneal  branch  has  already  been  noted  in  connection  with  the  variations  of  the  anterior  tibia! 
artery.  Another  origin  which  has  been  observed  is  from  the  external  plantar  artery,  \vhich 
sends  upward  through  the  astragalo-calcaneal  canal  a  large  branch  which  is  continued  distally 
upon  the  dorsum  of  the  foot  and  gives  off  the  tarsal  and  metatarsal  branches.  This  vessel  is 
represented  in  the  adult  by  a  small  branch  which  arises  from  the  external  tarsal  artery  and  pur- 
sues the  course  indicated  to  anastomose  with  the  external  plantar  ;  it  appears  to  be  much  more 
highly  developed  in  the  embryo  than  in  the  adult  (Leboucq). 

Other  variations  in  the  dorsalis  pedis  and  its  branches  depend  upon  a  correlation  which 
exists  between  the  development  of  the  dorsal  and  plantar  system  of  vessels.  If,  for  example, 
the  plantar  interossese  are  well  developed,  they  will,  through  the  anterior  perforating  branches, 
furnish  the  main  blood-supply  for  the  dorsal  digital  branches,  and  the  dorsal  interosseous  ves- 
sels, as  well  as  the  metatarsal,  may  be  much  reduced.  Or  the  plantar  arch,  through  the  pos- 
terior perforating  branches,  may  be  the  main  supply  for  the  dorsal  interosseous  vessels,  and  the 
dorsalis  pedis  itself  may  be  diminished  in  size  or  may  even  terminate  in  a  net-work  of  small 
vessels  over  the  dorsal  surface  of  the  tarsus. 

DEVELOPMENT  OF  THE  ARTERIES. 

In  the  preceding  pages  some  of  the  more  important  facts  regarding  the  development  of  the 
arteries  have  been  mentioned  in  connection  with  the  anomalies  in  whose  production  they  are 
concerned  ;  these  facts  may  now  be  briefly  restated  in  a  more  connected  manner. 

At  an  early  stage  of  development,  while  the  heart  lies  far  forward  beneath  the  pharyngeal 
region  and  its  ventricle  is  still  undivided,  the  blood  leaves  it  by  a  single  vessel  which  passes  forward 
along  the  mid-ventral  line  of  the  pharynx  and  divides  to  form  two  ventral  longitudinal  stems,  from 
each  of  which  six  lateral  branchial  vessels  arise,  the  fifth  vessel  of  each  stem,  counting  from 
before  backward,  being  quite  rudimentary  and  closely  associated  with  the  fourth.  These 
branchial  vessels  pass  dorsally  in  the  branchial  arches  to  the  dorsal  surface  of  the  pharynx,  where 
those  of  each  side  unite  to  form  a  longitudinal  stem  which  passes  backward,  and  at  about  the 
level  of  the  eighth  cervical  vertebra  unites  with  its  fellow  of  the  opposite  side  to  form  a  single 
longitudinal  trunk,  the  dorsal  aorta  (Fig.  677).  This  is  continued  backward  to  the  posterior 
extremity  of  the  trunk,  lying  immediately  ventral  to  the  vertebral  column.  From  the  anterior 
ends  of  the  ventral  and  dorsal  longitudinal  steins  brandies  pass  forward  into  the  cranial  region; 
and  from  the  dorsal  longitudinal  stems  and  the  dorsal  aorta  lateral  and  ventral  branches  are 
given  off  in  regular  segmental  succession.  The  modifications  undergone  by  the  branchial  arch 
vessels  in  the  course  of  development  may  first  be-  traced  and  then  the  arrangement  and  modifica- 
tions of  the  segmental  branches  will  be  considered. 

The  first  modification  of  the  branchial  arch  vessels  consists  in  the  disappearance  of  the  two 
anterior  ones  on  either  side,  and  then  follow  a  number  of  changes  which  may  be  briefly  stated  as 
follows,  (i)  The  portions  of  the  dorsal  longitudinal  stems  intervening  between  the  third  and 
fourth  branchial  vessels  disappear  ;  (2)  the  fifth  branchial  vessels  disappear  ;  (T,)  the  sixth  loses 
its  connection  with  the  dorsal  longitudinal  stem  on  the  right  side  5(4)  the  proximal  portion  of 


DEVELOPMENT   OF   THE   ARTERIES. 


847 


Fro.  744. 


Diagrams  illustrating  primary  arrangement  (A)  and  second- 
ary modifications  (S)  in  branchial  arch  vessels.  TA,  truncus 
arteriosus;  I-VI,  aortic  bows;  VA,  DA,  ventral  and  dorsal 
aortae  ;  A,  aorta;  AA,  aortic  arch;  7,  innominate  artery;  CC, 
C£,  Cf,  common,  external  and  internal  carotids;  5,  subclavian  ; 
P,  pulmonary  artery ;  da.  ductus  arteriosus. 


the  ventral  longitudinal  stem  divides  in  the  frontal  plane  into  two  portions,  one  of  which  is  con- 
nected with  the  sixth  branchial  vessels,  while  the  other  retains  the  remaining  ones  ;  and  (5)  the 
posterior  portion  of  the  right  dorsal  longitudinal  stem  disappears,  so  that  the  dorsal  aorta  is 
formed  only  by  the  left  stem  (Fig.  678).  As  the  result  of  these  changes  the  anterior  portion  of  the 
ventral  longitudinal  stem  becomes  the  external  carotid  artery  ;  the  anterior  portion  of  the  dorsal 
longitudinal  stem  the  internal  carotid  ; 
the  third  branchial  vessel  becomes  the 
connection  between  the  two  carotids  ; 
the  fourth  branchial  vessel  of  the  left 
side,  together  with  the  left  dorsal  longi- 
tudinal stem,  becomes  the  arch  of  the 
aorta  ;  the  right  fourth  branchial  vessel 
and  the  persisting  portion  of  the  right 
dorsal  longitudinal  stem  become  the 
proximal  portion  of  the  right  subclav- 
ian  artery  ;  the  sixth  branchial  vessels 
become  the  pulmonary  arteries,  the 
persisting  connection  of  the  left  one 
with  the  aortic  arch  being  the  ductus 
arteriosus  ;  the  proximal  portion  of  the 
ventral  longitudinal  trunk  which  re- 
mains connected  with  the  sixth  vessels 
becomes  the  pulmonary  aorta,  while 
the  other  portion  becomes  the  prox- 
imal part  of  the  aortic  arch.  These 
changes  are  shown  diagrammatically 
in  Fig.  744,  A  and  B. 

From  the  forward  prolongations 
of  the  carotid  arteries  the  vessels  which 
supply  the  cranial  structures  are  de- 
veloped, and  lateral  branches  also  pass  from  the  carotids  to  the  structures  which  are  formed 
from  the  branchial  arches.  Of  these  branches  the  superior  thyroid,  lingual,  and  facial  arteries  are 
probably  from  the  beginning  connected  with  the  external  carotid,  but  the  greater  part  of  the 
internal  maxillary  takes  its  origin  from  the  internal  carotid  and  only  secondarily  becomes  con- 
nected with  the  external  one  (page  743). 

From  the  dorsal  longitudinal  stems,  posterior  to  the  point  at  which  the  sixth  branchial 
vessels  join  them,  branches  pass  off  laterally  to  each  of  the  cervical  segments,  the  most  anterior 
pair  accompanying  the  hypoglossal  nerve  and  passing  to  the  occipital  segments  with  which  the 
nerve  is  associated.  Later,  as  the  heart  recedes  towards  its  final  position  in  the  thorax,  carrying 

with  it  the  dorsal  longitudinal  stems,  the  majority  of 
the  cervical  lateral  branches  separate  from  the  stems 
and  are  represented  in  the  adult  by  the  segmental 
muscular  and  spinal  branches  which  arise  from  the 
vertebral  artery.  The  seventh  branches,  however, 
retain  their  connection  with  the  longitudinal  stems 
and  become  the  subclavian  arteries  of  the  adult. 

Throughout  the  entire  length  of  the  dorsal  aorta 
segmental  branches  are  distributed  not  only  to  the 
body-wall,  but  also  to  the  viscera,  and  in  each  seg- 
ment two  typical  sets  of  visceral  branches  may  be 
distinguished, — a  pair  of  lateral  branches  which  pass 
laterally  beneath  the  peritoneum  to  the  paired  viscera, 
and  a  single  median  branch  which  passes  ventrally  in 
the  mesentery  and  is  supplied  to  the  digestive  tract 
and  its  derivatives  (Fig.  745).  The  lateral  branches 
to  the  body-wall  persist  in  the  adult  as  the  inter- 
costal lumbar  and  lateral  sacral  branches,  the  fifth 
lumbar  branches  entering  into  the  formation  of  the 
iliac  arteries.  The  visceral  branches  belonging  to 
both  sets,  however,  undergo  much  modification, 

some  disappearing  and  others  fusing,  so  that  little  trace  of  their  primary" segmental  arrangement 
5  to  be  recognized  in  the  adult.  Representatives  of  the  paired  visceral  branches  are  to  be 
found  in  the  bronchial,  suprarenal,  renal,  and  spermatic  (ovarian)' arteries,  and  in  the  fa-tus 
the  umbilical  arteries  represent  the  paired  branches  of  the  third  lumbar  segment.  At  an 
early  stage,  however,  these  vessels  make  connections  with  branches  of  the  iliac  arteries  and 


FIG.  745. 


Diagram  showing  fundamental  arrangement 
of  branches  from  aorta  (A)  ;  £,  lateral  branches 
to  body-wall;  C,  paired  visceral,  D,  unpaired 
visceral  branch  ;  E.  peritoneum. 


848 


HUMAN   ANATOMY. 


FIG.  746. 


then  lose  their  original  connections  with  the  aorta,  so  that  they  seem  in  the  foetus  to  arise 
from  the  iliac  vessels,  and  these  latter,  although  primarily  somatic  in  their  distribution,  give  off 
a  number  of  visceral  branches. 

Of  the  unpaired  visceral  branches  representatives  are  to  be  found  in  the  thoracic  region  in 
the  cesophageal  and  mediastinal  vessels  and  in  the  abdomen  in  the  coeliac  axis  and  the  superior 
and  inferior  mesenteric  arteries,  the  superior  mesenteric  representing  the  omphalo-mesenteric 
or  vitelline  arteries  of  the  embryo  which  primarily  arise  by  several  roots,  only  the  lowest  of  which 
persists  to  form  the  adult  vessel. 

According  to  the  general  plan  of  the  embryonic  arterial  system  thus  outlined,  the  only  ves- 
sels which  have  primarily  a  longitudinal  course  are  the  dorsal  and  ventral  longitudinal  stems, 
the  dorsal  aorta,  and  its  prolongation,  the  a.  sacra  media.  In  the  adult  however,  several  other 
longitudinal  vessels  exist,  such,  for  instance,  as  the  vertebrals,  the  internal  mammaries,  and  the 
superficial  and  deep  epigastrics.  All  these  vessels  are  secondary  formations  due  to  the  end-to- 
end  anastomoses  of  upwardly  and  downwardly 
directed  branches  of  the  lateral  segmental  ves- 
sels. The  internal  mammaries  and  the  epigas- 
trics (Fig.  746)  are  formed  in  this  manner  from 
branches  of  the  intercostal  arteries,  with  which 
they  remain  connected  to  a  greater  or  less  ex- 
tent ;  the  vertebrals  are  formed  from  branches 
of  the  lateral  cervical  vessels,  and  become  inde- 
pendent stems  by  the  separation  of  these  vessels 
from  the  dorsal  longitudinal  stems,  as  already 
described. 

The  arteries  of  the  limbs  are  formed,  as 
already  stated,  by  the  lateral  somatic  brandies 
of  the  seventh  cervical  and  fifth  lumbar  segments 
respectively,  but  in  both  limbs  a  series  of  changes 
is  necessary  before  the  adult  arrangement  is 
acquired.  In  the  arm  the  subclavian  artery  at 
first  extends  as  a  single  main  stem  as  far  as  the 
carpus,  where  it  terminates  by  dividing  into 
digital  branches  for  the  fingers  (Fig.  747,  A\. 
Throughout  its  course  in  the  forearm  it  lies 
between  the  two  bones,  resting  on  the  interos- 
seous  membrane,  in  the  position  occupied  by 
the  adult  anterior  interosseous  artery  ;  from 
the  upper  part  of  this  portion  of  its  course  a 
branch  is  given  off  which  takes  a  more  super- 
ficial course,  accompanying  the  median  nerve. 
This  median  artery  gradually  becomes  larger. 
Trunk-arteries  of  embryo  of  six  weeks,  showing  whjje  the  anterjOr  interosseous  undergoes  a  cor- 
origin  of  internal  mammary  (tm)  and  epigastric  arteries 
(se,  superficial,  de,  deep);  a.  aorta ;  v,  vertebral;  ct,  responding  retrogression,  and  eventually  the 

median,  by  fusing  with  the  lower  portion  of  the 
interosseous,  forms  the  main  channel  for  the  digi- 
tal branches  and  becomes  the  principal  artery  of 
the  forearm  (Fig.  747,  B\  A  further  stage  is  marked  by  the  development  of  the  ulnar  artery  as  a 
branch  from  the  brachial,  and  this,  extending  down  the  ulnar  side  of  the  forearm,  unites  with  the 
median  to  form  a  carpal  arch  from  which  the  digital  branches  arise  (  C).  Later  there  develops 
high  up  upon  the  brachial  a  superficial  brachial  artery,  which,  after  traversing  the  brachiiim, 
passes  down  the  radial  side  of  the  forearm  and  near  the  wrist  passes  to  the  posterior  surface, 
dividing  over  the  carpus  into  branches  for  the  d«  >rsum  of  the  thumb  and  index-finger.  After  tin- 
appearance  of  the  ulnar  artery  a  retrogression  of  the  median  begins,  whereby  it  becomes  the 
a.  comes  nervi  mediani  of  the  adult ;  a  branch,  the  superficial  volar,  arises  from  the  lower  part  <>f 
the. superficial  brachial  and  passes  downward  into  the  palm  to  unite  with  the  palmar  arch  already 
present  (D)  ;  and,  finally,  a  branch  arising  from  the  lower  part  of  the  brachial  anastomoses  with 
the  superficial  brachial  just  below  the  bend  of  the  elbow  and  together  with  the  antibrachial  part 
of  the  superficial  brachial,  forms  the  radial  artery.  The  upper  part  of  the  superficial  brachial 
then  degenerates  until  it  is  normally  represented  in  the  adult  by  a  small  branch  of  the  brachial 
which  passes  to  the  biceps  muscle  (E). 

In  the  leg  the  changes  are  equally  complicated.  Primarily  it  is  the  sciatic-  artery  which 
forms  the  main  stein,  extending  the  entire  length  of  the  posterior  surface  of  the  limb  into  the 
plantar  surface  of  the  foot,  where  it  divides  into  the  digital  branches  (Fig.  71s.  -"'>•  Tin- ex- 
ternal iliac  at  this  stage  is  a  relatively  slender  vessel  which  extends  but  a  short  distance  down  the 
thigh  and  terminates  in  what  is  later  the  profunda  femoris.  In  a  later  stage  there  arises  from 


common  iliac,  continuing  as  large  hypogastric  (ft) ; 
external  iliac,  giving  off  deep  epigastric  and  femoral, 
is  still  small.  X  5-  (Mall.) 


DEVELOPMENT  OF  THE  ARTERIES. 


849 


the  external  iliac  a  vessel  (saph}  which  accompanies  the  internal  saphenous  nerve  down  the 
leg  aiid,  entering  the  foot,  takes  from  the  original  main  stem  its  digital  branches  (B).  From  this 
saphenous  artery  a  branch  is  given  off  which  pierces  the  substance  of  the  adductor  magnus  mus- 

FIG.  747 


b  — 


b  — 


Diagrams  illustrating  development  of  arteries  of  upper  limb  ;  b,  brachial ;  i,  interosseous  ; 
rf,  digital ;  m,  median;   «,  ulnar;  sb,  superficial  brachial  ;  r,  radial. 


-saph 


Diagrams  illustrating  development  of  arteries  of  lower  limb;  s.  sciatic  ;  d,  digital ;  f,  femoral ; 
saph,  saphenous  ;  pop,  popliteal ;  per,  peroneal ;  pt,  at,  posterior  and  anterior  tibial. 

cle  and  anastomoses  with  the  sciatic  artery  just  above  the  upper  end  of  the  popliteal  space  (C), 
whereupon  the  portion  of  the  sciatic  artery  immediately  above  the  anastomosis  degenerates  and 

54 


850  HUMAN   ANATOMY. 

the  vessel  becomes  reduced  to  the  slender  a.  comes  nervi  ischiadici  of  the  adult.  Its  lower  por- 
tions, which  become  the  popliteal  and  peroneal  arteries,  now  seem  to  be  the  continuation  of  the 
femoral  (i.e.,  the  saphenous). 

From  the  lower  part  of  the  popliteal  a  branch  arises  which  anastomoses  with  the  saphenous 
and,  together  with  the  lower  part  of  that  artery,  forms  the  posterior  tibial,  the  upper  part  of  the 
saphenous  then  disappearing  except  in  so  far  as  it  is  represented  by  one  of  the  branches  of  the 
anastomotica  magna.  The  anterior  tibial  is  a  late  formation  resulting  from  the  fusion  of  an  upper 
and  lower  branch  from  the  peroneal  which  perforate  the  interosseous  membrane  (C),  the  con- 
nection of  the  lower  branch  with  the  peroneal  degenerating  after  the  anastomosis,  except  in  so 
far  as  it  persists  as  the  anterior  peroneal  artery 


THE  VEINS. 

The  veins  are  those  vessels  which  receive  the  blood  from  the  capillary  net-work 
and  return  it  to  the  heart. 

Compared  with  the  arteries,  they  present  many  differences,  both  of  structure 
(page  677)  and  arrangement.  Their  walls  are  much  thinner,  so  that  the  color  of 
the  blood  which  they  contain  shows  through,  and  they  are  readily  compressible  to  the 
extent  of  a  complete  obliteration  of  their  lumen  and  are  also  exceedingly  dilatable. 
Notwithstanding  their  thinness,  they  are  less  easily  ruptured  by  over-distention  than 
are  the  arteries  and  are  capable  of  undergoing  a  remarkable  elongation,  those  of  an 
adult  withstanding  an  extension  to  at  least  50  per  cent,  more  than  their  original  length 
without  losing  their  elasticity  —  a  property  which  explains  the  more  direct  course 
taken  by  the  veins  as  compared  with  the  arteries  in  mobile  portions  of  the  body  (e.g., 
the  facial  vein  as  compared  with  the  artery).  Indeed,  it  seems  that  the  veins  when 
in  place  in  the  body  are  always  stretched  to  a  considerable  extent,  .the  cephalic  vein, 
for  example,  contracting  when  removed  from  the  body  to  40  per  cent,  of  its  length 
in  the  extended  arm  (Bardeleben). 

The  most  striking  structural  peculiarity  of  the  veins,  however,  is  the  occurrence 
in  them  of  semilunar  valves,  arranged  usually  in  pairs,  with  their  cavities  directed 
towards  the  heart.  These  valves  resemble  in  their  general  form  the  semilunar  valves 
of  the  systemic  and  pulmonary  aortae,  and,  as  in  those  vessels,  the  veins  are  somewhat 
enlarged  immediately  above  the  attachment  of  each  pair,  so  that  the  blood  may 
readily  flow  behind  the  valves,  force  their  free  margins  together  and  so  occlude 
the  vessel.  These  valves  play  an  important  part  in  directing  the  flow  of  blood  in 
the  veins  towards  the  heart,  since,  in  the  event  of  any  pressure,  such  as  that  exerted 
by  a  contracting  muscle,  acting  on  the  vein,  they  will  prevent  a  backward  flow  of 
blood  towards  the  capillaries.  Valves  do  not  occur  in  veins  of  less  than  i  mm.  in 
diameter  and  are  also  lacking  in  many  of  the  larger  trunks,  such  as  the  superior  and 
inferior  venae  cavae,  the  pulmonary  and  the  portal  veins.  In  general  they  are  more 
numerous  in  the  veins  of  the  limbs  than  in  those  of  the  trunk  and  in  the  deep  than  in 
the  superficial  vessels. 

Their  number  in  any  vessel  in  which  they  normally  occur  is  subject  to  con- 
siderable variation  in  different  individuals  and  even  on  opposite  sides  of  the  body  in 
the  same  subject.  It  seems  probable  that  this  variation  is  brought  about  by  a 
degeneration  of  a  greater  or  less  number  of  the  pairs  originally  present,  since  in  the 
majority  of  the  veins  the  number  of  valves  diminishes  with  age  (Bardeleben),  and 
even  in  adult  bodies  evidence  of  degeneration  may  be  seen  in  the  insufficiency  of 
some  of  the  valves  or  even  in  their  perforation.  It  is  possible,  therefore,  that  the 
arrangement  of  the  valves  in  the  adult  is  a  secondary  condition,  derived  from  one  in 
which  the  valves  were  much  more  numerous  and  were  situated  at  regular  intervals 
along  the  vessels.  In  favor  of  this  view  it  has  been  found  (Bardeleben)  that  in  certain 
veins  the  valves  in  the  adult  are  separated  by  intervals  either  of  a  definite  length  or  of 
a  multiple  of  this,  the  length  of  the  intervals  stand'ng  in  relation  to  the  length  of  the 
part  or,  in  general,  to  the  height  of  the  individua1  in  which  the  vein  occurs.  Thus,  in 
a  man  measuring  160  mm.  in  height,  the  valves  of  the  right  long  saphenous  vein  were 
separated  by  intervals  which  were  all  approximately  multiples  of  6.Ss  mm.  in  length, 
while  the  intervals  separating  the  valves  of  the  right  cephalic  vein  were  approximately 
multiples  of  s-2  mm.;  and  in  a  male  child  81  cm.  in  height,  the  valves  of  the  right 
long  saphenous  vein  were  separated  by  intervals  of  3  mm.  or  some  multiple  of  this. 


THE    VEINS.  851 

A  more  readily  appreciable  relation  of  the  valves  is  that  which  they  bear  to  the 
branches  which  open  into  the  vein,  a  pair  of  valves  being  found  immediately  distal  to 
the  entrance  of  each  collateral  vein  ;  and,  furthermore,  a  pair,  or  at  least  a  single  valve, 
very  generally  occurs  at  the  termination  of  a  vein,  where  it  enters  either  a  larger 
stem  or  the  heart.  These  terminal  valves  are  present  in  certain  veins  which  other- 
wise are  quite  destitute  of  valves,  as,  for  instance,  in  the  internal  jugular,  the  internal 
maxillary,  and  the  vertebral  veins. 

It  has  already  been  noted  that  valves  are  entirely  wanting  in  certain  veins.  Among  these 
are  the  sinuses  of  the  cranium,  the  cerebral,  ophthalmic,  periosteal,  pulmonary,  bronchial, 
portal,  renal,  uterine,  ovarian,  and  innominate  (brachio-cephalic)  veins,  and  the  superior  and 
inferior  venae  cavae.  Furthermore,  they  are  usually  absent  in  the  common  and  internal  iliacs 
and  in  the  facial  veins,  although  occasionally  they  occur  in  all  three. 

In  their  position  and  arrangement  also  the  veins  differ  noticeably  from  the 
arteries.  While  veins  are  usually  to  be  found  accompanying  the  arteries,  enclosed  with 
them  in  a  common  fibrous  sheath,  additional  veins  of  considerable  size  are  abundant 
immediately  beneath  the  skin — a  condition  which  is  almost  entirely  foreign  to  the 
arteries.  Furthermore,  although  in  a  general  way  a  vein  may  pursue  the  same 
course  as  an  artery,  it  may  lie  at  some  little  distance  from  the  latter  and  fail  to  follow 
its  course  exactly.  This  is  true,  for  instance,  of  the  facial  and  the  lingual  veins 
and  also  of  the  subclavian  vein,  which  is  separated  from  the  corresponding  artery  by 
the  scalenus  anticus  muscle  ;  this  likewise  applies  to  the  veins  at  the  root  of  the  neck 
which  accompany  in  a  general  way  the  branches  of  the  subclavian  artery,  but  open  into 
the  innominate  vein  instead  of  the  subclavian.  In  many  cases  the  veins  which  accom- 
pany arteries  are  double,  one  lying  on  either  side  of  the  artery  and  forming  what  are 
generically  known  as  venae  comites  (venae  comitantes ).  The  causes  which  determine 
this  double  condition  are  obscure.  The  arrangement  is  not  found  in  the  larger 
venous  trunks,  occurring,  for  instance,  in  the  leg  only  below  the  knee  and  in  the 
arm  only  as  far  up  as  the  middle  of  the  brachium  ;  size  alone,  however,  does  not 
seem  to  be  the  determining  factor,  since  the  internal  mammary  and  epigastric  veins 
are  double,  while  the  intercostal  and  lumbar  veins,  almost  of  the  same  size  as  the 
former,  are  single.  Nor  does  the  quality  of  the  tissue  in  which  the  veins  occur 
determine  their  duplication,  for  those  which  are  embedded  within  the  muscles  of  the 
tongue  are  doubled,  while  those  within  the  heart  musculature  are  single  ;  again, 
while,  as  a  rule,  the  veins  which  occur  in  fibrous  tissue — as,  for  instance,  the  menin- 
geal  veins — are  double,  yet  those  of  the  skin  are  single.  Finally,  it  may  be  noted 
that  there  are  exceptions  to  the  rule  that  the  veins  which  occur  in  the  cavities  of  the 
body  are  single,  since  a  duplication  is  found  in  the  spermatic  veins  and  also  in  those 
of  the  gall-bladder. 

Not  only  doubling  of  many  of  the  veins  occurs,  but  a  prevailing  tendency  exists 
towards  extensive  anastomoses  far  surpassing  that  displayed  by  any  of  the  arteries. 
Even  in  the  cases  of  the  larger  proximal  trunks  communications  exist,  those  between 
the  pulmonary  and  bronchial  veins  and  that  between  the  superior  and  inferior  venae 
cavae  by  way  of  the  azygos  being  examples.  In  the  smaller  vessels  the  anastomoses 
are  often  so  numerous  as  to  result  in  the  formation  of  plexuses.  Venae  comites  are 
united  by  frequent  cross-connections,  sometimes  so  numerous  as  to  present  the  ap- 
.pearance  of  a  plexus  surrounding  the  artery.  Complicated  venous  plexuses  also 
accompany  the  various  ducts  of  the  body,  as,  for  example,  the  parotid  ducts,  the 
ureters,  and  the  vasa  deferentia.  In  addition,  extensive  venous  plexuses  occur  in 
various  regions  of  the  body,  as  in  the  neighborhood  of  its  orifices,  in  the  terminal 
phalanges  of  the  fingers  and  toes,  in  the  diplo£  of  the  skull,  in  the  spinal  canal,  in 
the  pelvis,  and  in  connection  with  the  genito-urinary  organs.  Since  the  larger 
trunks  usually  arise  at  several  points  both  from  these  and  from  the  wider-meshed 
plexuses  occurring  elsewhere,  opportunity  is  thus  afforded  for  the  return  of  the 
blood  to  the  heart  by  different  paths — an  arrangement  explaining  the  frequent  ineffi- 
ciency of  a  ligation  of  even  large  trunks  to  prevent  venous  hemorrhage. 

Special  mention  should  be  made  of  one  set  of  the  venous  channels — namely, 
the  sinuses  of  the  dura  mater — which  establish  communication  between  the  cerebral 
and  ophthalmic  veins  and  the  internal  jugular.  They  are  channels  contained  within 


852  HUMAN    ANATOMY. 

the  dura  mater,  lined  by  an  endothelium  similar  to  and  continuous  with  that  of  the 
cxtracranial  veins,  but  lack  any  extensive  development  of  elastic  fibres  in  their 
walls,  which  are  formed  by  the  dura.  They  possess  no  valves,  although  in  certain 
of  them,  as  in  the  superior  longitudinal  and  cavernous  sinuses,  the  lumen  is 
traversed  by  irregular  trabeculae  of  fibrous  tissue.  These  are  especially  well 
developed  and  almost  tendinous  in  character  in  the  superior  longitudinal  sinus, 
while  in  the  cavernous  sinus  they  are  softer,  and  from  them  and  from  the  walls  of  the 
sinus  fringe-like  prolongations,  .5-2  mm.  in  length,  project  freely  into  the  lumen. 
Connected  with  certain  of  these  sinuses  and  developed  from  certain  of  the  smaller 
veins  which  open  into  them  are  so-called  blood-lakes  ( lacunae) — cavities  or  plexuses 
in  the  dura  mater,  lined  with  endothelium,  and  connecting  either  directly  or  by  means 
of  a  short  canal  with  an  adjacent  sinus.  They  are  usually  situated  more  or  less  sym- 
metrically with  reference  to  the  sinus  with  which  they  are  connected,  and  some  are 
very  constant  in  occurrence.  Thus,  a  certain  number  usually  occur  on  either  side 
of  the  superior  longitudinal  sinus  (page  1199),  others  in  the  tentorium  cerebelli  con- 
necting with  the  lateral  sinus,  others  in  the  middle  fossa  of  the  skull  along  the  course 
of  the  meningeal  veins,  and  others  in  the  vicinity  of  the  straight  sinus.  They  occasion- 
ally reach  a  considerable  size,  bulging  outward  the  dura  which  encloses  them  and 
excavating  by  absorption  irregular  depressions  upon  the  inner  surface  of  the  skull. 
Occasionally  this  absorption  of  the  cranial  bones  proceeds  so  far  that  bulging  of  the 
outer  table  of  the  skull  over  a  lake  takes  place,  and,  in  the  case  of  those  occurring 
along  the  course  of  the  superior  longitudinal  sinus,  Pacchionian  bodies  developed  from 
the  subjacent  arachnoid  tissue  may  invade  them,  pushing  before  them  the  attenuated 
floors  of  the  lakes. 

Classification  of  the  Veins. — Theoretically  a  description  of  the  veins  should 
start  with  the  peripheral  vessels  and  proceed  towards  the  great  trunks,  following  the 
course  of  the  blood.  Such  a  method  would  prove,  however,  somewhat  confusing, 
largely  on  account  of  the  numerous  anastomoses  that  occur  ;  it  is  preferable,  therefore, 
to  base  a  classification  primarily  upon  the  great  trunks  and  to  consider  their  afferents 
topographically,  according  to  the  areas  which  they  drain. 

From  the  embryological  stand-point,  there  are  primarily  four  great  systems  of 
veins  :  (  r )  the  cardinal  system,  represented  by  the  vena  cava  superior  and  its  tributa- 
ries ;  (2)  the  inferior  caval  system;  (3)  the  portal  system  ;  and  (4)  the  pulmonary 
system.  Owing  to  subsequent  changes,  it  is  necessary  to  recognize  in  the  cardinal 
system  three  sub-systems  :  (i)  that  of  the  cardiac  veins  ;  (2)  that  of  the  superior 
vena  cava  and  its  tributaries,  except  (3)  the  azygos  veins.  In  all,  then,  six  great 
systems  of  veins  may  be  recognized  in  the  adult.  They  are  as  follows  : 

1.  The  pulmonary  system. 

2.  The  cardiac  system.  ) 

3.  The  superior  caval  system.    V  The  cardinal  system. 

4.  The  azygos  system.  ) 

5.  The  inferior  caval  system. 

6.  The  portal  system. 

In  the  descriptions  which  follow  the  veins  are  considered  on  the  basis  of  this 
classification. 

THE    PULMONARY    SYSTEM. 
THE  PULMONARY  VEINS. 

The  pulmonary  veins  (venae  pulmonales)  (Figs.  749,  750)  are  four  in  number, 
two  passing  from  the  hilum  of  each  lung  to  the  posterior  surface  of  the  left  auricle  <>f 
the  heart.  Each  vein  is  formed  at  the  hilum  of  its  lung  by  the  union  of  a  number 
of  smaller  vessels  which  take  origin  ultimately  from  the  capillary  net-work  formed  by 
the  branches  of  the  pulmonary  artery  and  to  a  certain  extent  from  that  formed  by  the 
bronchial  arteries.  The  arrangement  of  the  afferent  branches  in  the  substance  of  the 
lungs  is  described  in  connection  with  the  anatomy  of  these  organs  (page  1854),  aml  it 
will  be  sufficient  to  note  here  that  they  correspond  i'i  number  to  the  branches  of  the 
pulmonary  artery  and  of  the  bronchi,  and  pursue  a  course  more  or  less  independent 
of  these,  which  He  side  by  side.  Converging  and  uniting  as  they  pass  towards  the 
hilum.  the  branches  from  the  superior  lobe  of  each  lung  unite  to  form  the  superior 


THE    PULMONARY    VEINS. 


853 


pulmonary  vein  of  that  side,  those  from  the  inferior  lobe  unite  to  form  the  in- 
ferior pulmonary  vein,  while  those  from  the  middle  lobe  of  the  right  lung  unite 
to  form  a  single  trunk  which  usually  opens  into  the  right  superior  vein,  although  it 
occasionally  opens  independently  into  the  left  auricle,  forming  what  is  then  termed 
the  middle  pulmonary  vein. 

Each  of  the  four  pulmonary  veins  has  a  length  of  about  15  mm.,  and  for  about 
one-third  of  its  course  is  partially  invested  by  the  visceral  layer  of  the  pericardium 
(page  715).  The  right  superior  vein  is  usually  slightly  the  largest  of  the  four,  while 
the  left  superior  is  the  smallest,  the  right  and  left  inferior  veins  being  about  the  same 
size.  No  valves  occur  either  throughout  the  course  or  at  the  orifices  of  the  pulmonary 
veins. 

Relations. — The  superior  pulmonary  veins  have  a  course  which  is  obliquely 
downward  and  inward.  In  their  extraperitoneal  portion  they  lie  anterior  to  and 
below  the  pulmonary  arteries,  and  are  separated  by  them  from  the  bronchi ;  the 


FIG.  749. 


Right  innominate  vein 


on  carotid  artery 

Left  subclavian  artery 


Left  pulmonary  artery 


Left  auric- 
ular ap- 
pendage 
Conus 
arteriostis 
tricular 
'branches  of  left 
coronary  vessels 
Left  ventricle 


Aorta,  systemic 
Left  coronary  artery 
Right  coronary  vessels 


Right  ventrid 


Injected  heart  and  great  vessels,  viewed  from  before ;  parts  of  superior  vena  cava  and  aorta 
have  been  removed  to  show  right  pulmonary  artery. 

vein  of  the  right  side  is  crossed  from  above  downward  by  the  phrenic  nerve  and  by 
the  vena  cava  superior.  In  its  intrapericardial  portion  the  right  superior  vein  lies 
behind  the  terminal  portion  of  the  superior  vena  cava  and  the  left  one  behind  the 
pulmonary  aorta  (pulmonary  artery),  while  posteriorly  each  is  in  relation  with  its 
corresponding  inferior  vein. 

The  inferior  veins  are  more  horizontal  in  position,  but  are  directed  forward 
as  well  as  inward.  They  lie  in  a  plane  considerably  posterior  to  that  of  the 
corresponding  superior  veins  and  are  situated  internally  to  and  behind  an  anterior 
descending  branch  of  each  bronchus. 

Anastomoses. — In  addition  to  serving  for  the  return  flow  of  the  blood  carried 
to  the  lungs  by  the  pulmonary  arteries,  the  pulmonary  veins  also  receive  a  certain 
amount  of  the  blood  carried  by  the  bronchial  arteries.  Communications  between 


854  HUMAN    ANATOMY. 

the  bronchial  and  pulmonary  veins  in  the  region  of  the  smaller  bronchi  are  abundant, 
and,  in  addition,  the  main  stems  of  the  pulmonary  veins  receive  at  the  hilum  of  the 
lung  one  or  more  branches  from  the  larger  bronchial  veins.  They  also  receive  com- 
munications from  the  venous  plexus  which  surrounds  the  thoracic  aorta  in  the  pos- 
terior mediastinum,  and  occasionally  also  a  vein  from  the  pericardium.  There  is 
thus  a  certain  commingling  of  venous  blood  with  the  arterialized  blood  which  forms 
the  principal  contents  of  the  pulmonary  veins. 

Variations. — At  one  stage  in  the  development  of  the  embryo  the  veins  from  each  lung 
converge  to  a  single  short  trunk  before  opening  into  the  portion  of  the  atrium  which  corresponds 
to  the  left  auricle.  As  the  development  of  the  heart  proceeds,  this  trunk  is  gradually  taken  up 
into  the  auricle,  until  the  two  stems  which  unite  to  form  it  open  independently  into  that 
structure.  An  inhibition  of  this  process  occasionally  obtains,  so  that  but  a  single  vein,  repre- 
senting the  original  terminal  trunk,  opens  into  the  auricle  from  one  lung  or  from  both.  On  the 
other  hand,  the  taking  up  of  the  pulmonary  vein  into  the  wall  of  the  auricle  may  proceed  further 
than  usual,  or,  to  state  it  perhaps  more  correctly,  the  union  of  the  various  stems  emerging  from 
the  hilum  of  the  lung  may  be  partly  delayed  until  they  have  reached  the  original  terminal  trunk, 
so  that  when  this  is  taken  up  into  the  auricle  an  additional  vein  will  open  independently  into  the 
latter.  This  extra  vein  is  most  frequently  that  from  the  middle  lobe  of  the  right  lung,  but  three 
distinct  veins  have  also  been  observed  upon  the  left  side. 

THE   CARDINAL    SYSTEM. 

The  cardinal  system  of  veins  is  so  named  because  its  main  trunks  are  the  repre- 
sentatives of  the  cardinal  veins  of  the  embryo.  These  veins  are  four  in  number, 
disposed  symmetrically  in  pairs,  two  returning  the  blood  from  the  head,  neck,  and 
upper  extremities,  while  the  other  two  return  that  from  the  thoracic  and  abdominal 
walls,  from  the  thoracic  viscera,  and  from  the  lower  extremities.  Just  before  they 
reach  the  heart,  the  superior  and  inferior  or  posterior  cardinal  veins  of  each  side 
unite  (Fig.  776)  to  form  trunks  known  as  the  ducts  of  Cuvier,  the  two  ducts  opening 
independently  into  the  primitive  right  auricle.  By  a  series  of  changes,  which  are 
described  more  fully  in  the  section  on  the  development  of  the  veins  (page  927),  the 
left  superior  cardinal  becomes  connected  with  the  right  at  the  base  of  the  neek,  the  stem 
so  formed  constituting  what  is  termed  the  superior  vena  cava.  The  portion  of  the 
left  superior  cardinal  between  the  connecting  .vessel  and  the  heart  becomes  greatly 
reduced  in  size,  indeed,  almost  completely  degenerates ;  the  left  duct  of  Cuvier, 
however,  persisting  as  the  coronary  sinus,  which  receives  the  coronary  veins  returning 
the  blood  from  the  heart's  walls.  On  the  development  of  the  vena  cava  inferior  the 
veins  of  the  lower  extremity  make  connection  with  it,  separating  from  the  inferior 
cardinals;  these  latter  become  considerably  reduced  in  size,  especially  in  the  abdominal 
region,  a  cross-connection  develops  between  the  left  and  right  veins,  and  the  former 
severs  its  connection  with  the  left  ductus  Cuvieri,  the  final  result  being  the  formation 
of  the  venae  azygos  and  hemi-azygos  of  the  adult. 

There  are,  then,  developed  from  the  cardinal  veins  of  the  embryo  three  sub- 
systems of  yeins  :  (i)  that  of  the  cardiac  veins  ;  (2)  that  of  the  superior  vena  cava, 
which  includes  the  jugular  and  subclavian  groups  of  veins,  the  original  superior 
cardinals  being  represented  by  the  internal  jugular  veins  ;  and  (3)  the  azygos  sub- 
system. These  will  be  considered  in  the  order  in  which  they  have  been  named. 

THE   CARDIAC    VEINS. 
THE  CORONARY  SINUS. 

The  coronary  sinus  (sinus  coronarius)  (Fig.  750)  is  a  short  venous  trunk  about 
3  cm.  (a  little  over  an  inch)  in  length,  which  occupies  the  right  half  of  that  portion  of  the 
posterior  auriculo-ventricular  groove  which  lies  between  the  left  auricle  and  ventricle. 
At  its  right  end  it  opens  into  the  right  auricle,  its  orifice  (Fig.  657)  being  situated 
upon  the  posterior  surface  of  the  auricle-,  below  that  of  the  inferior  vena  cava,  and  beinu 
guarded  by  tin-  Tln-bcsian  ;vi/;r  (  valvula  sinus  coronarii).  At  its  left  end  it  receives  tin 
great  coronary  vein,  from  whose  proximal  portion  it  is  not  always  clearly  distinguish* 
able  upon  superficial  examination.  A  close  inspection  usually  reveals,  ho\\ever, 
either  a  constriction  or  a  slight  dilatation  at  the  union  of  the  two  vessels,  and  on 


THE   CARDIAC   VEINS. 


855 


laying  them  open  a  distinct  valve,  of  either  one  or  two  cusps,  but  usually  insuffi- 
cient, will  be  found  at  their  line  of  junction.  This  valve  is  known  as  the  valve  of 
Vieussens.  Furthermore,  the  walls  of  the  sinus  differ  from  those  of  the  vein  in  pos- 
sessing a  complete  layer  of  muscular  fibres,  both  oblique  and  circular,  continuous 
with  the  musculature  of  the  auricle. 

In  addition  to  the  great  coronary  vein,  the  coronary  sinus  also  receives  the 
posterior  vein  of  the  left  ventricle  and  the  middle  cardiac  vein,  which  open  into  it 
from  below,  and  the  oblique  vein  of  the  left  auricle,  which  passes  to  it  from  above. 

Variations. — The  coronary  sinus,  as  already  stated,  represents  the  left  ductus  Cuvieri  of 
the  embryo.  It  varies  somewhat  in  length,  reaching  in  extreme  cases  a  length  of  5.4  cm.  It  has 
been  observed  to  be  obliterated  at  its  entrance  into  the  right  auricle,  the  great  coronary  vein 
then  opening  into  the  left  innominate  ( brachio-cephalic)  vein,  and,  in  addition  to  the  veins 
already  noted  as  emptying  into  it,  it  frequently  receives  the  marginal  vein  of  the  left  ventricle. 

i.  The  Left  Coronary  Vein. — The  great  cardiac  or  left  coronary  vein  (v.  cor- 
dis  magna)  (Fig.  749)  begins  upon  the  anterior  surface  of  the  heart  at  the  apex, 
where  it  anastomoses  with  the  veins  of  the  posterior  surface,  and  ascends  the  anterior 

FIG.  750. 


Left  pulmonary  artery 


Superior  left  pulmonary  vein 

Inferior  left  pulmonary  vein 

Termination  of  \ eft 
coronary  vein 

Transverse  branch  of 
left  coronary  artery 


Left  ventricle 


Superior  vena  cava 

Superior  right  pulmonary  vein 
Right  pulmonary  artery 

nferior  right  pulmonary  vein 


Inferior  vena  cava 


Coronary  sinus 

Right  coronary  vein 
Transverse  branch  of  right 

coronary  artery 
Posterior  descending  branch 
of  right  coronary  artery 


Middle  cardiac  vein 


Right  ventricle 


Posterior-inferior  aspect  of  injected  heart,  showing  blood-vessels. 

interventricular  groove  in  company  with  the  left  coronary  artery,  to  the  anterior 
auriculo-ventricular  groove,  in  which  it  passes  to  the  left  and,  curving  around  the  left 
border  of  the  heart  to  the  posterior  surface,  terminates  by  opening  into  the  left  end 
of  the  coronary  sinus. 

In  the  vertical  portion  of  its  course  it  receives  veins  from  the  anterior  surface  of 
both  ventricles,  and  in  its  course  in  the  auriculo-ventricular  groove,  throughout  which  it 
is  embedded  in  the  fat  which  usually  occupies  the  groove,  it  receives  a  number  of  small 
veins  from  the  surfaces  of  both  the  left  auricle  and  ventricle.  Among  those  from  the 
ventricle  there  is  especially  to  be  mentioned,  as  larger  and  more  constant  than  the 
rest,  the  vena  marginalis  sinistra,  which  ascends  along  the  left  border  of  the  heart 
and  empties  into  the  great  coronary  vein  shortly  before  its  opening  into  the  sinus. 


856  HUMAN    ANATOMY. 

2.  The  Posterior  Cardiac  Vein. — The  posterior  cardiac  vein  (v.  posterior 
ventriculi  sinistri)  ascends  along  the  posterior  surface  of  the  left  ventricle,  lying  about 
midway  between  the  left  border  of  the  heart  and  the  posterior  interventricular  groove 
and  receiving  collateral  branches  from  the  walls  of  the  ventricle.      It  opens  above 
into  the  coronary  sinus  near  the  point  of  entrance  of  the  great  coronary  vein  and 
occasionally  unites  with  that  vessel. 

3.  The  Middle  Cardiac  Vein. — The  middle  cardiac  vein   (v.  cordis  media; 
(Fig.  750)  occupies  the  posterior  interventricular  groove,  accompanying  the  right 
coronary  artery.      It  arises  in  the  vicinity  of  the  apex  of  the  heart  and  ascends, 
receiving  collateral  branches  from  the  posterior  surfaces  of  both  ventricles,  to  open 
into  the  coronary  sinus  near  its  termination.      This,  next  to  the  great  coronary  vein,  is 
the  largest  vein  of  the  heart,  and  occasionally  opens  independently  into  the  right 
auricle  close  to  the  entrance  of  the  coronary  sinus. 

4.  The   Right  Coronary  Vein. — The  small  cardiac  or  right  coronary  vein 
(v.  cordis  parva)  (Fig.  750)  occupies,  when  present,  the  right  half  of  the  posterior 
auriculo-ventricular  groove  and  opens  into  the  coronary  sinus  just  before  its  termi- 
nation.     Occasionally  it  opens  into  the  middle  cardiac  vein,   or   directly  into   the 
right  auricle,   and  is  not   infrequently  lacking  as  a  distinct  vessel,   the  tributaries 
which  empty  into  it  from  the  posterior  surface  of  the  right  auricle  and  the  upper 
part  of  the  posterior  surface  of  the  right  ventricle  then  opening  directly  into  the 
auricle.      One  of  the  largest  and  most  constant  of  these  tributaries  ascends  along 
the  right  border  of  the  right  ventricle  and  is  termed  the  right  marginal  vein  or 
vein  of  Galen. 

5.  The  Oblique  Vein  of  the   Left  Auricle. — The  oblique  vein  of  the  left 
auricle  (v.  obliqua  atrii   sinistri),  also  known   as  Marshall' s  vein,  is  a  small  vein  of 
variable  development  which  descends  obliquely  over  the  posterior  surface  of  the  left 
auricle  and  opens  below  into  the  coronary  sinus.      Above,  it  is  continuous  with  a 
fibrous  cord  contained  within  the  vestigial  fold  of  the  pericardium  (page  716),  the 
cord  and  vein  together  representing  the  lower  part  of  an  original  left  superior  vena 
cava.     The  degree  of  development  of  the  vein  varies  greatly,  and  occasionally  the 
fibrous  cord  retains  its  original  lumen,  so  that  a  more  or  less  developed  left  superior 
vena  cava  is  really  present.     This  anomaly  may,   however,   be  more  conveniently 
considered  in  connection  with  those  of  the  superior  caval  system  of  veins  (page  859). 

In  addition  to  these  principal  veins  of  the  heart  there  is  a  varying  number  of 
others  which  open  directly  into  the  right  auricle  and  are  situated  upon  the  anterior 
surface  of  the  right  ventricle,  whence  they  have  been  termed  the  anterior  cardiac 
veins  (vv.  cordis  anteriores).  They  are  all  comparatively  short  vessels  and  usually 
accompany  descending  branches  of  the  right  coronary  artery.  Owing  to  the  fre- 
quency with  which  it  opens  directly  into  the  auricle,  the  vein  of  Galen  is  usually 
regarded  as  one  of  this  group  of  veins. 

Finally,  the  Thebesian  veins  ( vv.  cordis  minimae)  form  part  of  the  cardiac 
venous  system.  These  are  minute  veins,  imbedded  in  the  substance  of  the  In  art 
walls,  and  communicating  with  the  heart  cavities  by  means  of  the  Thebesian  foramina 
(page  716), -which  occur  most  abundantly  upon  the  walls  of  the  right  auricle,  though 
also  upon  those  of  the  left  auricle,  and,  less  abundantly,  upon  those  of  the  ventricles. 
At  their  other  ends  these  veins  communicate  in  the  heart's  substance  with  the  radicles 
of  the  other  cardiac  veins,  and,  in  cases  of  stenosis  of  the  coronary  arteries,  may 
consequently  contribute  to  some  extent  to  the  nutrition  of  the  heart  musculature, 
carrying  blood  to  it  directly  from  the  heart  cavities. 

Valves  of  the  Cardiac  Veins. — The  Thebesian  vafae,  which  guards  the  right 
auricle,  may  be  considered  as  the  ostial  valve  of  that  vessel,  which  throughout 
course  is  destitute  of  valves.  So,  too,  throughout  the  extent  of  the  cardiac  veil 
valves  are  entirely  lacking,  but  certain  of  those  which  open  into  the  coronary  si 
are  provided  with  ostial  valves.  That  of  the  threat  coronary  vein  is  the-  ra/rc  o 
VieitsscHs,  and  others  are  usually  present  at  the  mouths  of  the  middle  vein  and  tin 
posterior  vein  of  the  left  ventricle,  and  less  constantly  at  the  mouths  of  the  marginal 
and  the  small  coronary  veins.  These  valves  may  be  either  single  or  paired  and  are 
frequently  insufficient.  No  valves  are  present  either  throughout  the  course  or  at  the 
orifice  of  the  oblique  vein  of  the  left  auricle. 


THE   SUPERIOR   CAVAL   SYSTEM.  857 

Variations. — The  principal  variations  which  occur  in  connection  with  the  cardiac  veins  have 
been  noted  in  the  description  of  the  vessels,  and  it  need  only  be  added  that  the  oblique  vein  of 
the  left  auricle  is  not  infrequently  entirely  lacking,  except  in  so  far  as  it  is  represented  by  a 
fibrous  cord,  that  absence  of  the  great  coronary  vein  has  been  observed,  and  that  the  middle 
vein  occasionally  opens  directly  into  the  right  auricle. 


THE   SUPERIOR   CAVAL   SYSTEM. 
THE  VENA  CAVA  SUPERIOR. 

The  superior  or  descending  vena  cava  (Figs.  749,  751)  is  the  main  venous  trunk 
which  delivers  to  the  heart  the  blood  returning  from  the  head,  neck,  upper  limbs,  and 
thorax.  It  measures  7-8  cm.  (3  in.  )  in  length,  and  has  a  diameter  at  its  termination 
of  about  2. 2  cm.  (a  little  less  than  i  in.  ).  It  is  situated  throughout  its  entire  course  in 
the  thoracic  cavity,  lying  in  the  superior  mediastinum,  and  is  formed  immediately 


FIG.  751. 


Anterior  jugular  \e 
Transverse  cervical  vein 

Clavicl. 
Suprascapular  v 


Right  inferior 

thyroid  vein 
1.  right  posterior 
intercostal 

mammary  vein 


Left  internal  jugular  vein 
Scalenus  anticus  muscle 
External  jugular  vein 


Left  subclav 
Clavicle 


Right 

auricular  append 


Right  coronary  or 
small  cardiac  vein 


Right  lung, 

mesial  surface 


Left  inferior  thyroid  vein 
I.  rib 

Left  innominate  vein 
Superior  intercostal  vein 
•I.  left  posterior  intercostal 
•^•Internal  mammary  vein 
Aorta 

Line  of  pericardia!  reflection 
R.  and  L.  pulmonary  arteries 
A  division  of  left  bronchus 
—Pulmonary  artery 

'Left  pulmonary  vein 

•Bronchus 

Left  auricular  appendix 


I  .eft  coronary  or  great 
cardiac  vein 


Left  lung,  mesial  surface 


Diaphragm,  thoracic  surface 


Dissection  showing  innominate  veins  and  superior  vena  cava  in  position ; 
lungs  have  been  pulled  aside. 

below  the  lower  border  of  the  first  costal  cartilage  of  the  right  side  by  the  union  of  the 
right  and  left  innominate  (brachio-cephalic)  veins.  Its  course  is  downward  and 
slightly  backward,  with  a  curvature  corresponding  to  the  first  portion  of  the  arch  of 
the  aorta,  with  which  it  is  in  relation.  Below,  it  opens  into  the  upper  posterior  portion 
of  the  right  auricle  on  a  level  with  the  third  costal  cartilage  of  the  right  side. 

Relations. — The  lower  portion  of  the  superior  vena  cava  is  invested  by  the  peri- 
cardium to  an  extent  varying  from  a  few  to  40  mm. ,  on  an  average,  perhaps  to  about 
one-third  its  length.  The  upper  extrapericardial  portion  is  in  relation  anteriorly 


858 


HUMAN   ANATOMY. 


with  the  thymus  gland  or  the  fatty  tissue  which  replaces  it,  and  is  overlapped  by 
the  right  pleura  and  lung.  Behind,  it  crosses  the  origin  of  the  right  bronchus  and 
the  structures  at  the  root  of  the  right  lung,  from  which  it  is  separated  by  numerous 
lymphatic  nodes  ;  to  the  right  it  is  in  contact  with  the  pleura  covering  the  inner  surface 
of  the  right  lung  and  with  the  right  phrenic  nerve  ;  and  to  the  left  it  lies  alongside  the 
ascending  portion  of  the  aortic  arch. 

In  its  lower  intrapericardial  portion  it  has  to  the  left  the  systemic  aorta:  anteriorly, 
the  right  auricle;  posteriorly,  the  right  pulmonary  artery,  the  right  superior  pul- 
monary vein,  and  the  right  bronchus,  while  upon  the  right  it  is  free. 

The  vena  cava  superior  contains  no  valves. 

Tributaries. — In  addition  to  the  right  and  left  innominate  veins,  by  the  union 
of  which  it  is  formed,  the  vena  cava  superior  receives  the  vena  azygos  major  and 
small  veins  from  the  mediastinum  and  pericardium. 

Variations. — Cases  have  been  recorded  in  which  the  vena  cava  superior  received  the  right 
internal  mammary  or  the  right  superior  intercostal  vein  which  normally  open  into  the  right 
innominate  vein.  It  may  also  receive  the  vena  thyreoidea  ima,  a  vein  only  occasionally  present 
and  draining  the  territory  supplied  by  the  art.  thyreoidea  ima. 

A  more  remarkable  and  rarer  variation  is  the  union  with  the  superior  vena  cava  of  a  com- 
paratively large  vein  which  issues  from  the  right  lung.  A  similar  condition  has  been  observed 
in  connection  with  the  innominate  veins,  and  its  probable  significance  will  be  considered  in 
connection  with  the  variations  of  those  vessels. 

Practical  Considerations. — The  superior  vena  cava  would  be  involved  in  a 
stab-wound  passing  through  either  the  first  or  the  second  intercostal  space  on  the 
right  side,  close  to  the  sternum.  The  vessel  is  subject  to  compression  in  aneurism 
of  the  ascending  aorta  (<?.  v. ),  producing  venous  congestion  in  the  veins  of  the  neck 
and  of  the  upper  extremities. 

THE  INNOMINATE  VEINS. 

The  innominate  or  brachio-cephalic  veins  (vv.  anonymae)  (Fig.  751)  are  two  in 
number,  a  right  and  a  left.  They  are  situated  in  the  upper  portion  of  the  thoracic 
cavity,  being  formed  by  the  union  of  the  internal  jugular  and  subclavian  veins,  and 
terminate  by  uniting  opposite  the  first  costal  cartilage  of  the  right  side  to  form  the 
vena  cava  superior.  The  union  of  the  internal  jugular  and  subclavian  vein  takes 
place  on  each  side  opposite  the  sternal  end  of  the  clavicle  ;  but,  since  the  vena  cava 
superior  lies  entirely  to  the  right  of  the  median  line  of  the  body,  the  left  innominate 
vein  has  a  much  greater  distance  to  traverse  in  order  to  reach  its  point  of  termination 
than  has  the  right  one,  and  consequently  it  will  be  necessary  to  describe  each  vein 
separately. 

The  right  innominate  vein  has  a  length  of  2-4  cm.  (Y^-il/>  in.)  and  an 
almost  vertical  course,  opening  directly  downward  into  the  vena  cava  superior.  It 
lies  behind  the  inner  end  of  the  right  clavicle,  from  which  it  is  separated  by  the  lower 
portions  of  the  sterno-hyoid  and  sterno-thyroid  muscles,  and  a  little  lower  it  is  behinc 
the  first  right  costal  cartilage.  ...To  the  right  it  is  in  relation  with  the  inner  surfac 
of  the  right  pleura  and  with  the  right  phrenic  nerve,  to  the  left  with  the  brachic 
cephalic  artery  and  right  pneumogastric  nerve,  and  behind  with  the  pleura. 

The  left  innominate  vein  has  a  length  almost  double  that  of  the  right,  meas- 
uring 5-9  cm.  (2-3^-2  in.)  from  its  origin  behind  the  sternal  end  of  the  left  clavicle 
to  its  union  with  the  right  vein  to  form  the  vena  cava.  Its  course  is  transverse 
from  left  to  right  and  at  the  same  time  slightly  downward,  and  it  extends  completely 
across  the  uppermost  part  of  the  thoracic  cavity,  resting  below  upon  the  aortic  arch, 
and  passing  in  front  of  the  left  subclavian  and  common  carotid  arteries,  the  trachea, 
the  brachio-cephalic  artery,  and  the  pneumogastric  nerve.  It  is  separated  from  the 
manubrium  sterni  by  the  insertion  of  the  sterno-hyoid  and  sterno-thyroid  muscles  and 
by  the  fatty  tissue  representing  the  thymus  gland,  and,  being  on  a  level  with  or 
slightly  above  the  upper  border  of  the  manubrium,  it  can  usually  be  felt  in  the  supra- 
sternal  fossa. 

Neither  of  the  innominate  veins  possesses  valves.  The  left  is  of  somewhat  greater 
diameter  than  the  right,  owing  to  the  greater  number  of  tributaries  which  it  receives. 


THE   SUPERIOR   CAVAL  SYSTEM. 


859 


Variations. — As  pointed  out  in  the  account  of  the  development  of  the  great  veins  (page  926), 
there  is  at  one  stage  a  symmetrical  arrangement  of  the  vessels  which  open  into  the  right  auricle 
from  above  ;  in  other  words,  the  left  internal  jugular  is  continued  directly  downward  from  the 
point  where  the  left  subclavian  vein  opens  into  it  to  the  auricle,  this  downward  continuation 
bein°"  usually  termed  the  left  superior  vena  cava.  Later  a  cross-connection,  the  left  innominate 
veinrforms  between  the  right  and  left  jugulars  at  the  root  of  the  neck,  and  the  left  superior  vena 
cava  then  normally  undergoes  degeneration,  traces  of  it  only  persisting  as  the  oblique  vein  of 
the  left  auricle  and  the  coronary  sinus. 

Occasionally  this  normal  progress  of  events  fails  to  occur,  the  result  being  the  complete 
absence  or  imperfect  development  of  the  left  innominate  vein  together  with  a  persistence  of  the 
Irft  superior  vena  cava  ;  or  else,  even  with  the  perfect  development  of  the.left  innominate,  there 
may  be  a  failure  of  the  left 

superior  vena  cava  to  degen-  pIG   7^2. 

erate.  Various  gradations 
between  the  embryonic  and 
adult  conditions  may  occur, 
and  the  annexed  diagram 
(Fig.  752)  shows  the  nature 
of  the  anomaly.  It  may  be 
noted  that  with  the  persist- 
ence of  the  left  superior  vena 
cava  there  is  frequently  a 
retention  of  the  communica- 
tion with  it  of  the  left  cardinal 
vein,  which  normally  be- 
comes the  v.  hemi-azygos,  —a 
condition  which  will  be  more 
especially  considered  in  con- 
nection with  the  anomalies  of 
the  azygos  veins  ( page  893 ) . 


Left  internal  jugular 


L.  subclavian 
L.  innominate 


L.  sup.  vena  cava 
L.  azygos 


L.  pulmonary 

arter 


Coronary  sinus 


Right  int.  jugular 

R.  subclavian 
R.  innominate 

R.sup.  vena  cava 
R.  azygos 

julmonary  artery 
ulmonary  veins 


Practical  Consid- 
erations.—  The  left  in- 
nominate vein,  running 
horizontally  just  below  the 
upper  border  of  the  ma- 
nubrium,  lies  immediately 
above  the  aortic  arch. 

When  the  latter  is  unusually  high,  and  occasionally  in  children,  the  vein — especially 
if  engorged — may  project  above  the  level  of  the  suprasternal  notch  and  may  be 
endangered  during  a  thyroidectomy,  the  removal  of  a  tumor,  or  a  low  tracheotomy. 


Inf.  vena  cava 


Posterior  aspect  of  heart  and  great  vessels,  showing  persistence 
of  left  superior  vena  cava  ;  (semidiagrammatic). 


Tributaries.  —  In  addition  to  the  subclavian  and  internal  jugular  veins,  by 
whose  union  they  are  formed,  each  innominate  vein  receives  (i)  the  deep  cervical, 
(2)  the  vertebral,  (3)  the  internal  mammary,  and  (4)  the  inferior  thyroid  veins  of 
its  side.  The  left  innominate  vein  receives  in  addition  (5)  the  superior  phrenic, 
(6)  the  thymic,  (7)  the  pericardial,  (8)  the  anterior  mediastinal,  and  (9)  the 
left  superior  intercostal  vein.  Of  these'  the  left  superior  intercostal  vein  will  be 
described  with  the  other  intercostals. 

i.  The  Deep  Cervical  Vein. — The  deep  cervical  vein  (v.  cervicalis  profunda) 
takes  its  origin  in  a  plexus  situated  in  the  occipital  triangle  and  having  also  con- 
nected with  it  the  vertebral  and  occipital  veins.  It  passes  down  the  neck,  lying  be- 
tween the  semispinalis  cervicis  and  the  splenius  cervicis,  and  in  the  upper  part  of  its 
course  accompanies  the  deep  branch  of  the  art.  princeps  cervicis.  Lower  down  it 
accompanies  the  deep  cervical  branch  of  the  superior  intercostal  artery  and  bends 
slightly  outward  and  forward,  passes  between  the  transverse  process  of  the  seventh 
cervical  vertebra  and  the  first  rib,  and  opens  into  the  innominate  vein  either  behind 
the  vertebral  vein  or  by  a  common  trunk  with  that  vessel. 

Tributaries. — In  its  course  down  the  neck  it  receives  numerous  tributaries  from  the  deeper 
cervical  muscles,  and  opposite  each  intervertebral  foramen  which  it  passes  it  makes  connections 
with  the  vertebral  vein  and  the  veins  of  the  spinal  canal. 

The  most  important  of  its  tributaries  is,  however,  the  occipital  vein,  which  arises  in  a 
plexus  covering  the  occipital  portion  of  the  skull  and  communicating  with  branches  of  the  pos- 
terior auricular  and  temporal  veins.  It  passes  downward  with  the  occipital  artery,  pierces  the 


86o  HUMAN   ANATOMY. 

trapezius  muscle  near  its  origin  from  the  superior  nuchal  line,  and  enters  the  suboccipital  tri- 
angle where  it  opens  into  the  deep  cervical  vein.  Occasionally,  however,  it  either  unites  with 
the  posterior  auricular  vein  or  opens  directly  into  the  external  jugular  below  the  posterior 
auricular.  The  mastoid  emissary  vein  (page  876)  usually  opens  into  one  of  its  branches. 

2.  The  Vertebral  Vein. — The  vertebral  vein    (v.    vertebralis)   accompanies 
the  artery  of  the  same  name  through  all  but  the  cranial  portion  of  its  course,  and  is 
usually  a  single  trunk,  although  frequently  it  is  double  or  occasionally  even  plexiform 
throughout  more  or  less  of  its  course.      It  arises  in  the  suboccipital  triangle  from  a 
plexus  of  small  veins  with  which  the  occipital  and  deep  cervical  veins  also  communi- 
cate, and  passes  downward  through  the  foramina  in  the  transverse  processes  of  the  six 
(occasionally  seven  or  five  or  even  only  four)  upper  cervical  vertebne.      At  its  exit 
from  the  foramen  of  the  sixth  vertebra  it  is  continued  obliquely  forward  and  down- 
ward behind  the  inferior  thyroid  artery  and  the  internal  jugular  vein,  and,  passing 
usually  in   front  of,  but  occasionally  behind,   the  subclavian  artery,   opens  into  the 
innominate  vein  near  its  origin. 

The  opening  into  the  innominate  is  guarded  by  a  pair  of  valves.  Throughout 
its  course  the  vein  is  connected  to  the  periosteum,  lining  each  of  the  vertebra-arterial 
canals  it  traverses,  by  fibrous  bands,  and  in  its  terminal  portion  it  is  adherent  to  the 
deep  cervical  fascia,  so  that  its  walls  do  not  collapse  even  when  it  is  emptied  of  blood. 

Tributaries. — Like  the  vertebral  artery,  the  vein  receives  tributaries  from  the  deep  mus- 
cles of  the  neck  and,  at  each  intervertebral  foramen  which  it  passes,  communicating  branches 
from  the  plexuses  in  the  spinal  canal  on  the  one  hand,  and  from  the  posterior  spinal  plexus  and 
the  deep  cervical  vein  on  the  other.  In  its  terminal  portion,  after  it  has  issued  from  the  fora- 
men in  the  transverse  process  of  the  sixth  cervical  vertebra,  it  receives  the  ascending  cervical 
vein,  which  arises  in  the  plexus  upon  the  anterior  surfaces  of  the  bodies  of  the  upper  cervical 
vertebrae,  and  accompanies  the  ascending  cervical  artery  down  the  neck.  Very  frequently  it 
also  receives,  shortly  before  its  termination,  the  deep  cervical  vein. 

3.  The  Internal  Mammary  Vein. — The  internal  mammary  vein  (v.  niamma- 
ria  interna)  is  formed  by  the  union  of  the  venae  comites  of  the  musculo-phrenic  and 
superior  epigastric  arteries,  and  throughout  the  greater  part  of  its  course  is  double,  one 
stem  lying  along  the  outer  and  the  other  along  the  inner  side  of  the  artery  in  its 
course  along  the  inner  surface  of  the  anterior  thoracic  wall.      Opposite  the  second 
or  third  intercostal  space  the  two  stems  unite,  the  single  vein  so  formed  lying  to  tin- 
inner  side  of  the  artery  and  opening  above  into  the   innominate  vein  of  the  same 
side.      Numerous  valves  occur  in  the  course  of  the  vein. 

Tributaries. — The  tributaries  of  the  internal  mammary  veins  correspond  in  general  with 
the  branches  of  the  internal  mammary  artery,  with  the  exception  of  the  superior  phrenic,  medi- 
astinal,  pericardia!,  and  thymic  branches,  which  usually  open  independently  into  the  left  innom- 
irtate  vein.  Its  sternal  branches  form  plexuses  upon  both  surfaces  of  the  sternum,  and  so  form 
communication  with  the  vein  of  the  opposite  side,  and  the  anterior  intercostal  branches  unite 
with  the  posterior  intercostals  ( page  896) .  The  perforating  branches  assist  in  returning  the  blood 
from  the  pectoral  muscles,  those  of  the  first  and  second  intercostal  spaces  being  larger  than  the 
rest  in  the  female,  and  serving  to  return  a  considerable  portion  of  the  blood  from  the  mammary 
gland.  By  means  of  the  superior  epigastric  branches  the  internal  mammary  makes  connection 
with  the  subcutaneous  veins  of  the  abdomen,  and,  since  these  are  also  connected  with  the 
epigastric  and  circumflex  iliac  branches  of  the  iliac  veins,  an  anastomosis  is  formed  between  the 
superior  and  inferior  caval  systems  of  veins. 

4.  The  Inferior  Thyroid  Veins. — The  inferior  thyroid  veins  (vv.  thyreoideae 
inferiores)  have  their  origin  in  a  venous  plexus  (plexus  thyrcoidcus  impar )  which  covers 
the  anterior  surface  and  sides  of  the  trachea  immediately  below  the  isthmus  of  the 
thyroid  gland,  the  vessels  which  form  the  plexus  issuing  from  the  substance  of  the  thy- 
roid gland,  or  in  some  cases  being  downward  prolongations  of  the  branches  of  origin 
of  the  superior  thyroid  veins.      From  the  plexus  two  or  sometimes  three  veins  descend 
the  neck,  following  paths  quite  distinct  from  those  of  the  inferior  thyroid  arteries, 
and  open  below  into  the  innominate  veins,  their  orifices  being  guarded  by  valves. 
When  three  veins  are  present,  the  odd  one  occupies  a  median  position  and  is  known 


THE   SUPERIOR   CAVAL  SYSTEM.  86 1 

as  the  vena  thyreoidea  ima,  corresponding  to  the  artery  of  the  same  name,  which, 
however,  need  not  be  present  with  it.  It  opens  usually  into  the"  left  innominate 
vein,  but  occasionally  is  prolonged  inward  to  terminate  in  the  superior  vena  cava. 

Tributaries. — The  plexus  thyreoideus  impar  receives  communications  from  the  superior 
thyroid  veins  and  also  has  opening  into  it  the  inferior  laryngeal  veins  (vv.  laryngeae  inferiores) 
which  descend  from  the  larynx.  The  inferior  thyroid  veins  receive  directly  branches  from  the 
trachea  (vv.  tracheales)  and  from  the  oesophagus  (vv.  cesophageae). 

Practical  Considerations. — An  incision  across  the  inferior  thyroid  vein, 
whose  walls,  being  imbedded  in  inflamed  tissue,  could  not  collapse,  has  caused 
sudden  death  by  the  entrance  of  air.  Parise,  in  attempting  to  seize  the  divided 
inferior  thyroid  vein  during  tracheotomy,  lifted  the  superficial  wall  only,  thus  per- 
mitting air  to  enter  the  vein  with  a  fatal  result  (Allen). 

5.  The  Superior  Phrenic  Vein. — The  superior  phrenic  vein  (v.  phrenica 
superior)  has  its  origin  upon  the  upper  surface  of  the  diaphragm  and  ascends  through 
the  thorax,  lying  between  the  pericardium  and  pleura  and  accompanying  the  phrenic 
nerve  and  the  superior  phrenic  artery,  of  which  it  is  a  companion  vein.      Usually  the 
veins  of  both  sides  are  double.      They  open  above  into  the  left  innominate  vein,  fre- 
quently uniting  with  the  thymic,  pericardial,  and  mediastinal  veins  before  their  termi- 
nation.    They  are  provided  with  valves  both  at  their  orifice  and  along  their  course. 

6.  The  Thymic  Veins. — The  thymic  veins  (vv.  thymicae)  are  rather  insig- 
nificant in  the  adult  and  are  usually  two  or  three  in  number.      They  arise  in  the 
adipose  tissue  which  replaces  the  thymus  gland  and  empty  above  into  the  left  innomi- 
nate vein,   frequently  uniting  with  the  superior  phrenic  veins.      In  the  child  they  are 
of  considerable  size  in  correlation  with  the  development  of  the  thymus  gland. 

7.  The  Pericardial  Veins. — The  pericardial  veins    (vv.  pericardiacae)  vary 
considerably  in  number.      They  are  all  small,  and  empty  in  part  into  the  left  innomi- 
nate vein  and  in  part  into  the  azygos  and  internal  mammary  veins. 

8.  The  Anterior  Mediastinal  Veins. — The  anterior  mediastinal  veins  (vv. 
mediastinales  anteriores ) ,'  like  the  preceding,  are  variable  in  number  and  small.     They 
arise  in  the  anterior  mediastinum  and  open  above  into  the  left  innominate  vein. 

THE  INTERNAL  JUGULAR  VEIN. 

The  internal  jugular  vein  (v.  jugularis  interna)  (Figs.  753,  760)  is  the  principal 
venous  trunk  of  the  neck.  It  is  the  continuation  of  the  lateral  sinus  at  the  jugular 
foramen,  and  descends  the  neck  in  company  with  the  internal  and  common  carotid 
arteries  to  a  point  a  little  external  to  the  sterno-clavicular  articulation,  where  it  unites 
with  the  subclavian  to  form  the  innominate  vein.  At  its  origin  it  rests  upon  the  anterior 
sloping  surface  of  the  jugular  process  of  the  occipital  bone,  .and  usually  presents  at 
this  point  a  distinct  bulbous  enlargement  (bulbus  venae  jugularis  superior)  measuring 
about  1.5  cm.  in  diameter.  Below  the  bulbus  superior,  at  its  exit  from  the  jugular 
foramen,  the  diameter  of  the  vein  averages  about  9  mm.,  although  subject  to  consider- 
able variation,  and  usually  differing  on  the  two  sides,  since  the  lateral  sinuses,  of 
which  the  veins  are  the  continuations,  differ  on  the  two  sides,  that  of  the  right  being 
in  the  majority  of  cases  the  larger.  As  it  descends  the  neck  the  vein  gradually 
increases  in  size  as  it  receives  its  various  tributaries,  and  just  before  its  union  with  the 
subclavian  vein  it  presents  a  more  or  less  pronounced  spindle-shaped  enlargement 
(bulbus  venae  jugularis  inferior).  This  dilatation  is  usually  much  more  distinct  in  the 
right  vein  than  in  the  left,  and  at  its  upper  end  is  provided  with  a  pair  of  valves  or  else 
with  a  single  one,  the  cavities  of  the  valves  being  directed  downward  as  if  to  prevent 
an  upward  flow  of  blood.  Even  when  a  pair  is  present  they  are  insufficient,  but  they 
may  nevertheless  play  an  important  part  in  preventing  the  blood  from  flowing  into 
the  innominate  through  the  subclavian  vein  and  from  producing,  during  the  systole 
of  the  auricle,  a  back  pressure  in  the  cerebral  veins  which  are  in  connection  with  the 
internal  jugular.  Since  the  right  innominate  is  much  more  nearly  in  a  line  with  the 
vena  cava  superior  than  is  the  left,  the  greater  development  of  the  inferior  bulb  in 
the  right  internal  jugular  can  be  readily  understood. 


862 


HUMAN    ANATOMY. 


Relations. — In  the  upper  part  of  its  course  the  internal  jugular  rests  upon  the 
rectus  capitis  lat'eralis  and  the  transverse  processes  of  the  upper  cervical  vertebrae. 
To  its  inner  side  and  somewhat  in  front  of  it  is  the  internal  carotid  artery,  the  glosso- 
pharyngeal,  pneumogastric,  spinal  accessory,  and  hypoglossal  nerves  separating  the 
two  vessels  above.  The  external  branch  of  the  spinal  accessory  crosses  it  obliquely 
either  in  front  or  behind,  and  somewhat  lower  it  is  crossed  anteriorly  by  the  stylo- 
hyoid  muscle  and  the  posterior  belly  of  the  digastric  and  also  by  the  occipital  and 
posterior  auricular  arteries.  To  its  inner  side  is  the  wall  of  the  pharynx,  with  which  it 
is  not,  however,  directly  in  contact. 

Throughout  the  neck  it  lies  beneath  the  sterno-cleido-mastoid  muscle,  imme- 
diately to  the  outer  side  of  the  common  carotid  artery,  being  enclosed  in  a  common 


Superficial  temporal  veta\ 


FIG.  753- 


Posterior  auricular  vein- 


External  auditory  meatu 

Mastoid  vein 

Occipital  vein 

Internal  maxillary  vein 

Temporo-maxillary  vein 

Posterior  trunk  of  temporo- 

maxillary  vein 

Anterior  trunk  of  temporo- 

maxillaryvem 

External  jugular  vein 

Lingual  vein 

Internal  carotid  artery 

Internal  jugular  vein 

Posterior  external  jugular  vein 

Superior  thyroid  vein 

Common  carotid  artery 


\ 


Temporal  muscle,  cut 

Internal  maxillary  vein 


Facial  vein 


Communication  bel  lin- 
gual and  anterior  jugulai 
Middle  thyroid  vein 


Left  innominate  veil 


Subclavian  vein 
Innominat 


Left  snierior 
intercostal  vein 


e  artery 


Right  innominate  vein 


Dissection  showing;  deep  veins  of  neck  and  hea'd. 


sheath  with  it,  as  is  also  the  pneumogastric  nerve,  which  lies  behind  and  between  the 
two  vessels.  Below  the  omohyoid  muscle  the  vein  tends  to  separate  from  the  artery, 
passing  somewhat  more  anteriorly.  In  this  part  of  its  course  it,  or,  to  be  more  pre- 
cise, tin-  inferior  bulb,  is  situated  immediately  behind  the  space  which  separates  the 
two  heads  of  the  sterno-cleido-mastoid.  Behind,  it  rests  upon  the  inner  border  of  the 
scalenus  anticus,  crosses  the  subclavian  artery,  and  has  the  pneumogastric  and  phrenic 
nerves  passing  downward  on  either  side. 

Variations. — Variations  of  the  internal  jus^'hir  vein  are  not  numerous.  It  may  be  noted, 
however,  that  in  its  course  down  the  neck  it  occasionally  overlaps  tin-  carotid  artery  to  a  con- 
siderable extent, — a  condition  which  is  especially  marked  in  the  region  of  the  inferior  bulb  when 
this  is  well  developed. 


THE   SUPERIOR    CAVAL  SYSTEM.  863 

The  left  internal  jugular  has  been  observed  much  reduced  in  size,  there  being  a  compen- 
satory enlargement  of  the  corresponding  external  jugular,  and  it  may  be  doubled  throughout  a 
greater  or  less  portion  of  its  course,  although  always  single  at  either  extremity.  In  addition 
to  the  normal  tributaries  described  below,  it  may  receive  the  temporo-maxillary  vein,  the  verte- 
bral superior  laryngeal,  or  left  superior  intercostal,  a  bronchial  vein,  the  suprascapular,  or  the 
transverse  cervical  vein. 

Practical  Considerations. — The  internal  jugular  vein — the  largest  of  the 
superficially  placed  veins  of  the  body — may  be  involved  in  cut-throat  or  other  wounds 
of  the  neck.  Like  the  carotid,  it  usually  escapes  in  attempts  at  suicide  on  account  of  the 
usual  position  assumed — with  the  chin  elevated  and  the  head  thrown  back  so  that  the 
muscles  are  rendered  tense  and  prominent  and  the  vessels  are  protected.  If  the 
wound  is  above  the  thyroid  cartilage  they  are  still  safer  on  account  of  their  inclination 
backward,  and  such  a  wound  may  reach  the  spinal  column  without  injuring  them.  In 
wounds  below  the  thyroid  if  the  air  passages  are  opened  in  attempted  suicide,  the 
sudden  exit  of  air  from  the  lungs,  accompanied  by  collapse  of  the  chest,  may,  it  has 
been  suggested,  result  in  the  dropping  of  the  arm  carrying  the  weapon  before  the 
wound  has  reached  the  level  of  the  vessels,  although  they  are  here  more  vulnerable 
than  they  are  above.  The  internal  jugular,  the  other  veins  of  the  neck,  and  the 
subclavian  and  axillary  veins,  are  greatly  influenced  by  respiration,  emptying  during 
inspiration,  distending  during  expiration — the  ' '  respiratory  wave, ' '  or  "  venous 
pulse."  Their  attachments  to  the  fascia  keep  them  from  entirely  collapsing.  This 
is  especially  noticeable  in  the  internal  jugular.  After  the  carotid  sheath  has  been 
opened  the  vein  will  vary  in  appearance  from  a  distended  thin-walled  tube  perhaps 
half  an  inch  in  diameter,  (expiration),  to  a  flaccid,  ribbon-like  structure  with  walls 
apparently  in  contact  (inspiration).  During  inspiration  air  may  thus  be  readily  drawn 
into  one  of  these  veins  if  it  has  been  wounded,  and  if  the  wound  is  dry,  or  if  pressure 
is  not  immediately  applied  to  the  vein  on  the  cardiac  side  of  the  wound.  If  the  air  is 
in  large  quantity  it  may  cause  instant  death  when  it  reaches  the  right  auricle  by  over- 
distension  and  paralysis  of  the  right  side  of  the  heart  ;  or  sometimes  less  rapidly  by 
asphyxia  following  air  embolism  of  the  pulmonary  veins. 

The  internal  jugular  vein  may  be  infected  secondarily  to  infective  intracranial 
sinus  thrombosis,  especially  of  the  sigmoid.  Phlebitis  or  thrombosis  of  the  internal 
jugular  is  attended  by  pain  and  tenderness  along  the  course  of  the  vein;  and  later  by 
the  development  of  a  cord-like-  mass  to  the  inner  side  of  the  sterno-mastoid  muscle 
and  the  outer  side  of  the  carotid  artery.  This  may  involve  the  whole  length  of  the 
vein  but  is  apt  to  be  confined  to  the  upper  third.  When  an  infected  thrombus  in  the 
sigmoid  sinus  has  undergone  such  extensive  disintegration  that  it  is  unlikely  to  be 
entirely  removed  by  operative  obliteration  of  the  upper  two-thirds  of  the  sinus,  or 
when  in  a  thrombosed  internal  jugular,  giving  the  sensation  of  a  hard  cord-like  struc- 
ture, its  upper  part  becomes  soft  from  disintegration  of  the  thrombus  and  this  disin- 
tegration descends,  ligation  of  the  vessel  below  this  point  usually  becomes  necessary 
(Macewen).  The  ligation  shuts  off  the  main  channel  between  the  sigmoid  sinus  and 
the  lungs,  although  the  latter  may  still  be  infected  by  way  of  the  occipital  sinus  and 
condylar  veins  and  the  subclavian  vein. 

The  vessel  is  approached  by  the  same  incision  as  that  made  for  ligation  of  a  caro- 
tid. The  vascular  sheath  is  opened  well  to  the  outer  side  so  that  the  carotid  com- 
partment may,  if  possible,  be  left  intact.  The  vein  should  be  tied  in  two  places  and 
divided  between  the  ligatures. 

After  occlusion  of  the  vein  either  by  ligature  or  by  pressure  from  a  growth,  the 
blood  from  the  corresponding  side  of  the  head  passes  by  a  transverse  vein  to  the 
internal  jugular  of  the  opposite  side. 

Tributaries. — In  addition  to  the  lateral  and  the  inferior  petrosal  sinuses,  which 
will  be  described  with  the  other  cranial  sinuses,  the  internal  jugular  receives  the 
following  tributaries  :  (i)  the  pharyngeal,  (2)  the  facial,  (3)  the  lingual,  (4)  the 
superior  thyroid,  and  (5)  the  middle  thyroid  veins. 

i.  The  Pharyngeal  Veins. — The  pharyngeal  veins  (vv.  pharyngeae)  are  small 
vessels,  varying  in  number,  which  open,  either  independently  or  after  having  united 
to  a  single  stem,  either  directly  into  the  internal  jugular  or  indirectly  by  way  of  the 


864  HUMAN    ANATOMY. 

lingual  or  superior  thyroid  vein.  They  take  their  origin  from  a  venous  plexus 
(plexus  pbaryngetts)  which  covers  the  outer  surface  of  the  pharynx,  lying  between 
the  constrictor  muscles  and  the  pharyngeal  portion  of  the  bucco-pharyngeal  fascia. 
In  addition  to  branches  from  the  pharyngeal  wall,  this  plexus  also  receives  tributaries 
from  the  anterior  recti  and  longus  colli  muscles,  and  from  the  soft  palate,  the  tonsillar 
plexus  and  the  Eustachian  tube,  and  has  opening  into  it  branches  from  a  plexus  which 
surrounds  the  internal  carotid  artery  in  its  course  through  the  carotid  canal,  communi- 
cating above  with  the  cavernous  sinus.  It  also  receives  the  veins  (  vv.  canal  is  pterygoidei) 
which  accompany  the  Vidian  artery  through  its  canal,  and  communicates  with  the 
pterygoid,  cesophageal,  and  vertebral  plexuses. 

2.  The  Facial  Vein. — The  facial  vein  (v.  facialis  anterior)  (Fig.  754)  is 
formed  at  about  the  inner  extremity  of  the  eyebrow  by  the  union  of  the  frontal  and 
supraorbital  veins.  From  its  point  of  origin  it  skirts  around  the  inner  border  of  the 
orbit  and  is  then  directed  obliquely  downward  and  backward  across  the  face,  crosses 
over  the  anterior  inferior  angle  of  the  masseter  muscle  and  the  ramus  of  the  mandible 
a  short  distance  in  front  of  the  angle,  and  is  thence  continued  onward  across  the 
posterior  part  of  the  submaxillary  and  the  upper  part  of  the  superior  carotid  triangles 
to  open  into  the  internal  jugular  at  about  the  level  of  the  hyoid  bone.  It  follows 
in  a  general  way  the  course  of  the  corresponding  artery,  lying  posterior  to  it,  but 
the  path  across  the  face  is  much  more  direct  than  that  followed  by  the  artery. 

That  portion  of  the  vein  which  extends  from  the  junction  of  the  frontal  and  supra- 
orbital  arteries  to  the  lower  border  of  the  orbit  is  usually  termed  the  angular  vein, 
and  branches  arise  from  this  which  pass  backward  into  the  orbit  to  communicate 
with  the  ophthalmic  vein.  Just  below  the  ramus  of  the  mandible  it  usually  receives 
a  large  communicating  branch  from  the  external  jugular,  and  the  portion  which  in- 
tervenes between  this  communication  and  the  internal  jugular  is  termed  the  common 
facial  vein  (v.  facialis  communis).  Both  the  facial  and  the  angular  veins  are  usually 
described  as  being  destitute  of  valves  ;  these  structures  do  occur,  however,  but  they 
are  always  insufficient  and  form  no  bar  to  the  passage  of  blood  in  an  inverse  direc- 
tion— i.e.,  from  the  facial  and  angular  backward  into  the  ophthalmic  veins. 

Relations. — The  angular  vein  rests  upon  the  nasal  process  of  the  maxillary 
vein  internal  to  the  lachrymal  sac.  In  its  upper  portion  the  facial  vein  lies  under 
cover  of  the  orbicularis  palpebrarum,  and  it  also  passes  beneath  the  zygomatic  muscles, 
but  is  superficial  to  the  other  muscles  of  the  face.  In  its  inframandibular  or  cervical 
portion  it  lies  beneath  the  platysma  in  a  groove  in  the  submaxillary  gland. 

Variations. --The  upper  portion  of  the  facial  vein  may  be  greatly  reduced  in  size.  Below, 
it  frequently  unites  with  the  lingual  vein  to  form  a  linguo-facial  trunk,  which  may  also  be  joined 
by  the  superior  thyroid.  Instead  of  opening  into  the  internal  jugular,  it  occasionally  passes 
across  the  sterno-cleido-mastoid  muscle  to  unite  with  the  external  or  anterior  jugular. 

Practical  Considerations. — Allen  has  called  attention  to  the  fact  that  the 
venous  supply  of  the  face  differs  in  some  important  particulars  from  that  of  the  trunk 
and  limbs.  In  the  last-named  localities,  both  deep  and  superficial  currents  flow  in 
the  same  direction  towards  the  heart.  The  facial  trunk,  however,  is  not  formed  by 
primal  venules,  as  is  commonly  the  case,  but  by  branches  communicating  with  the 
frontal  and  supraorbital  veins,  and  by  a  transverse  branch  found  at  the  bridge  of 
the  nose. 

The  two  most  important  communications  with  the  cavernous  sinus  are  through 
the  ophthalmic  vein,  which  receives  tributaries  from  the  angular  vein,  and  the  deep 
facial  vein,  which  empties  into  the  pterygoid  plexus,  which  in  its  turn  communicates 
with  the  cavernous  sinus  by  veins  passing  through  the  foramen  ovale.  The  veins 
corresponding  to  the  deep  parts  of  the  face,  other  than  those  mentioned,  also  seek 
an  outlet  in  the  same  direction,  so  that  much  of  the  superficial  blood  of  the  upper 
part  and  side  of  the  face  passes  inward  to  the  brain-case  and  to  the  interior  of  the 
facial  region,  while  the  remaining  portion  flows  downward  to  join  the  jugular  veins. 

The  facial  vein  at  its  lower  end  receives  a  large  communicating  branch  from  the 
external  jugular,  and  therefore  at  or  below  that  point  carries  a  considerable  volume 
of  blood,  making  wounds  of  the  vein  dangerous. 


THE   SUPERIOR   CAVAL  SYSTEM.  865 

The  facial  vein  is  said  to  be  less  flaccid  than  most  superficial  veins,  and  there- 
fore to  remain  more  patent  after  section  ;  it  possesses  either  imperfectly  developed 
or  rudimentary  valves,  or  none  at  all.  As  a  consequence  of  these  facts,  septic  dis- 
ease— malignant  pustule,  furuncle,  carbuncle,  cancrum  oris — involving  the  face  or 
forehead,  is  exceptionally  dangerous,  as  the  infection  may  spread  by  way  of  the 
ophthalmic  vein  or  the  pterygoid  plexus  to  the  cavernous  sinus  and  result  in  a  fatal 
thrombosis  or  meningitis. 

The  relations  existing  between  the  venous  blood  of  the  face  and  that  of  the 
brain-case  are  rendered  evident  by  the  fact  that  the  state  of  the  circulation  of  the 
external  nose  is  sometimes  an  index  of  the  condition  of  the  vessels  of  the  brain. 
Moreover,  in  cases  of  orbital  or  intracranial  tumors,  the  ophthalmic,  angular,  and 
facial  veins  become  congested,  dilated,  and  tortuous  from  pressure-interference  with 
the  venous  current. 

The  line  of  the  facial  vein  is  from  the  canthus  of  the  eye  to  a  point  on  the  mandible 
at  the  anterior  border  of  the  masseter  muscle  and  just  behind  the  facial  artery.  This 
line  is  straight  instead  of  tortuous,  as  is  the  case  with  that  of  the  latter  vessel. 

Tributaries. — The  tributaries  of  the  facial  vein  are  (a)  thefronta/and  (b]  the  supraorbitai ', 
by  the  union  of  which  it  is  formed.  In  addition  it  receives  in  its  course  across  the  face  (c)  the 
palpebral,  (d )  the  lateral  nasals,  (e)  the  superior  labial,  (f)  the  inferior  labial,  ( g)  the  deep 
facial,  (A)  the  masseteric,  and  (i  )  the  anterior  parotid  veins.  In  its  cervical  portion  it  has  open- 
ing into  it  (j)  the  inferior  or  descending  palatine,  and  (k)  the  submental  veins. 

(a)  The  frontal  veins  (vv.  frontales)  descend  over  the  forehead  on  either  side  of  the  median 
line,  lying  immediately  beneath  the  skin  upon  the  frontalis  muscle.     The  branches  from  which 
they  take  origin  communicate  at  the  sides  and  vertex  of  the  skull  with  tributaries  of  the  occip- 
ital and  temporal  veins,  and  also  through  small  foramina  in  the  frontal  bone  with  the  superior 
longitudinal  sinus.     The  two  veins  are  connected  by  numerous  cross-branches,  and  not  infre- 
quently unite  more  or  less  completely  to  form  a  single  median  stem  which  bifurcates  below. 
Kach  vein  terminates  at  the  inner  angle  of  the  orbit  by  uniting  with  the  corresponding  supraor- 
bitai vein  to  form  the  angular. 

At  the  root  of  the  nose  the  two  veins  are  usually  united  by  a  distinct  cross-branch,  the 
nasal  arch,  which  receives  from  below  the  dorsal  nasal  veins. 

(b)  The  supraorbitai  vein  (v.  supraorbitalis)  is  a  relatively  large  trunk  which  runs  trans- 
versely above  the  superior  margin  of  the  orbit  and  consequently  is  quite  distinct  from  the  artery 
of  the  same  name.     It  arises  at  the  external  angle  of  the  orbit,  where  it  communicates  with 
affluents  of  the  temporal  veins,  and  passes  inward  beneath  the  orbicularis  palpebrarum,  and, 
piercing  that  muscle  just  above  the  inner  angle  of  the  orbit,  unites  with  the  frontal  vein  to  form 
the  angular. 

It  receives  numerous  small  branches  from  neighboring  regions  and  from  the  diploic  vein 
of  the  frontal  bone,  and  at  the  supraorbitai  notch  it  communicates  with  the  ophthalmic  system 
of  veins. 

(c)  The  palpebral  veins  (vv.  palpebrales  superiores  et  inferiores)  are  small  vessels  which  take 
their  origin  from  the  venous  plexus  of  the  eyelids  and  open  into  the  angular  vein:     The  palpe- 
bral plexus  also  communicates  laterally  with  the  affluents  of  the  temporal  veins. 

(d ')  The  lateral  nasal  veins  ( vv.  nasales  externae)  arise  in  a  rich  plexus  which  occupies  the 
alae  and  tip  of  the  nose  and  with  which  the  dorsal  nasal  vein  communicates  and  also  branches  from 
the  extensive  pituitary  plexus,  these  latter  branches  emerging  along  the  line  of  junction  of  the 
nasal  bones  and  cartilage.  The  veins  extend  upward  and  backward  and  open  into  the  lower 
part  of  the  angular  vein. 

(e)  The  superior  labial  or  coronary  vein  (v.  labialis  superior)  takes  its  origin  in  a  plexus  in 
the  substance  of  the  upper  lip  with  which  branches  from  the  septum  and  ala;  of  the  nose  com- 
municate.    The  course  of  the  vein  is  independent  of  that  of  the  artery  of  the  same  name,  passing 
backward  and  somewhat  upward  to  the  naso-labial  groove,  and  opening  into  the  facial  vein 
about  opposite  the  ala  of  the  nose. 

(f)  The  inferior  labial  vein  (v.  labialis  inferior)  arises  from  a  venous  plexus  in  the  lower  lip 
and  passes  downward  and  outward  to  open  into  the  facial  just  after  it  has  crossed  the  ramus  of  the 
mandible.     Usually  a  second  vein,  the  inferior  coronary,  also  arises  from  the  inferior  labial  plexus 
and  passes  almost  horizontally  outward  to  open  into  the  facial  a  little  below  the  angle  of  the  mouth. 

(g)  The  deep  facial  vein,  also  termed  the  anterior  internal  maxillary,  takes  its  origin  from 
the  pterygoid  plexus  (page  882)  over  the  tuberosity  of  the  maxilla,  through  which  it  receives 
branches  from  a  net-work  lying  beneath  the  mucous  membrane  lining  the  antrum  of  Highmore. 
It  passes  forward  and  downward  between  the  buccinator  and  masseter  muscles,  and  opens  into 
the  outer  surface  of  the  facial  where  that  vein  passes  beneath  the  zygomatic  muscle. 

55 


866 


HUMAN   ANATOMY. 


(h)  The  masseteric  veins  (vv.  massetericae )  are  several  small  veins  which  return  the  blood 
from  the  masseteric  and  buccinator  muscles,  opening  into  the  outer  surface  of  the  facial  vein. 

(i  )  The  anterior  parotid  veins  (\\.  parotiikne  jinu-riorcs  i  consist  of  several  small  veins  which 
issue  from  the  anterior  border  of  the  parotid  gland  and  from  the  socia  parotidis.  They  follow 
the  parotid  duct,  around  which  they  form  a  net-work,  and  open  into  the  outer  surface  of  the 
.facial  vein. 

(j  )  The  inferior  or  descending  palatine  vein  (v.  palatina)  accompanies  the  ascending  palatine 
or  tonsillar  branch  of  the  facial  artery.  It  takes  its  origin  in  the  tonsillar  plexus  and  descends 
upon  the  side  of  the  pharynx  to  open  into  the  facial  after  it  has  crossed  the  ramus  of  the  mandible. 

FJG.  754. 


Temporal  fascia 


Superficial 

tem|x>ral  vein 

Middle  temporal 

vein 


Occipital  vein 

Internal  maxillary 
vein 

Temporo- 
maxillary  vein 
Posterior  auricular 
vein 


Sterno-cleido- 
mastoid 

Communication 

between  facial 

and  external 

jugular  vein 

External  jugular 

vein 

Tril nitary  of  trans- 
Terse  cervical  vein 
Posterior  external 
jugular  vein 

Trapezius 


Frontal  veins 

Suprai.rtiital  vein 
Branch  of 

cation  with  ophthal- 
mic vein 
Angular  vein 


Deep  facial  vein 


Subinental  vein 
Common  facial  vein 

Anterior  jugular  vein 


Platysma 


Superficial  veins  of  head  and  neck;  external  jujjular  lies  beneath  platysma  muscle, 
winch  has  been  partly  iumov<.-<l. 

(£)  The  submental  vein  (\:  siihinenialis)  accompanies  the  artery  of  tin    same  name. 
rests  upon  tlie  superficial  surface  of  the  mylo-hyoid  muscle  and  passes  backward  and  outward 
the  submaxillary  triangle,  beneath  the  platysma,  to  open  into  the  cervical  portion  of  the  fad. 
It  i-omnmnicates  with   the  siiblingual  vein  by  several  branches  which  perforate  the  mylo-hyoi 
muscle,  and,  in  addition  to  cutaneous  and  muscular  branches,  also  receives  tributaries  from  t 
siibmaxillary  gland,  these   latter  vessels,  however,  frequently  opening  directly  into  the  facial 
it  traverses  the  groove  upon  tin-  -laud. 


THE   SUPERIOR   CAVAL  SYSTEM.  867 

-j.  The  Lingual  Vein. — The  lingual  vein  (v.  lingualis)  is  a  short  trunk  which 
either  opens  directly  into  the  internal  jugular  or  unites  with  the  facial  vein  to  form  a 
linguo-facial  trunk.  It  is  formed  by  the  union  of  two  vessels,  the  deep  lingual  veins, 
which  are  the  venae  comites  of  the  lingual  artery,  and  the  subh'ngual. 

The  deep  lingual  veins  are  of  small  calibre  and  accompany  the  lingual  artery 
throughout  its  entire  course,  numerous  cross-connections  between  them  involving  the 
artery  as  in  a  plexus.  Shortly  before  opening  into  the  lingual  stem  the  two  veins  unite, 
and  into  the  vessel  so  formed  the  companion  veins  of  the  dorsal  artery  of  the  tongue 
(vv.  dorsales  linguae)  open,  these  vessels  communicating  with  the  tonsillar  plexus  and 
the  superior  laryngeal  vein. 

The  sublingual  vein,  also  termed. the  ranine,  has  its  origin  on  the  under  sur- 
face of  the  tip  of  the  tongue,  beneath  the  mucous  membrane.  It  passes  backward, 
at  first  in  company  with  the  submaxillary  duct,  and,  after  receiving  communicating 
branches  from  the  deep  lingual  and  the  submental  veins,  it  passes  to  the  outer  side 
of  the  hyoglossus  muscle  and  continues  backward  in  company  with  the  hypoglossal 
nerve,  whence  it  has  been  termed  the  v.  comitans  n.  hypoglossi. 

All  the  branches  of  the  lingual  vein  are  provided  with  valves. 

Variations. — Considerable  variation  exists  in  the  extent  to  which  the  lingual  vein  is  de- 
veloped, both  its  constituent  tributaries  as  well  as  the  dorsales  linguae  sometimes  opening  inde- 
pendently into  the  internal  jugular.  It  may  open  into  either  the  external  or  anterior  jugular 
instead  of  the  internal,  and  the  deep  linguals  may  open  into  the  pharyngeal  vein.  Occasionally, 
by  the  enlargement  of  the  connection  normally  occurring,  the  submental  vein  becomes  a  tribu- 
tary of  the  sublingual. 

4.  The  Superior  Thyroid  Vein. — The  superior  thyroid  vein  (v.  thyreoidea 
superior )  accompanies  the  artery  of  the  same  name.      It  arises  in  the  upper  portion 
of  the  plexus  which  encloses  the  thyroid  gland,  communicating  through  it  with  its  fellow 
of  the  opposite  side  and  with  the  middle  and  inferior  thyroid  veins.      It  is  directed  up- 
ward and  backward,  and  opens  either  directly  into  the  internal  jugular  or  more  usually 
into  the  lingual  or  the  linguo-facial  trunk. 

Tributaries. — The  following  are  received  by  the  superior  thyroid  vein,  (a)  The  superior 
laryngeal  vein  ( v.  laryngea  superior),  which  arises  in  the  pharyngo-laryngeal  recess  from  a  plexus 
which  receives  the  blood  from  the  aryepiglottidean  fold  and  the  laryngeal  musculature  and  com- 
municates with  the  vv.  dorsales  linguae  above  and  also  with  the  lower  portion  of  the  pharyngeal 
plexus.  It  passes  upward  and  backward  in  company  with  the  corresponding  nerve  and  artery 
ami  opens  into  the  superior  thyroid  vein  or  occasionally  into  the  linguo-facial  trunk  or  the 
anterior  jugular,  (b)  The  crico-thyroid  vein  is  a  slender  vessel  which  accompanies  the  artery 
of  the  same  name,  (c)  The  sterno-mastoid  vein  (v.  sternocleidomastoidea)  receives  blood  from 
the  sterno-cleido-mastoid  muscle  and  is  associated  with  the  artery  of  the  same  name. 

5.  The    Middle    Thyroid  Vein. — The  middle   thyroid  vein    is  not   always 
present  and  may  be  regarded  as  accessory  to  the  superior  thyroid.      It  issues  from 
the  thyroid  plexus,  opposite  the  lower  part  of  the  lateral  lobe  of  the  gland,  and  passes 
downward  and  outward,  independently  of  any  artery,  to  open  into  the  internal  jugular 
at  the  junction  of  its  middle  and  lower  thirds. 

THE  SINUSES  OF  THE  DURA  MATER. 

The  sinuses  of  the  dura  mater  (sinus  durae  matris)  form  a  series  of  channels, 
frequently  of  considerable  size,  occupying  clefts  in  the  substance  of  the  dura  mater. 
They  receive  the  cerebral,  meningeal,  and  diploic  veins  and,  in  addition,  communicate 
with  the  extracranial  veins  by  numerous  connecting  veins  known  as  emissary  veins,  the 
largest  and  most  important  of  which  are  the  ophthalmic  veins.  They  are  drained 
mainly  by  the  internal  jugular.  A  statement  of  their  general  structure  and  a  brief 
description  of  the  blood-lakes  associated  with  them  have  already  been  given  (page  851). 

i.  The  Lateral  Sinus. — The  lateral  sinus  (sinus  transversus)  (Figs.  756,  757) 
has  its  origin  opposite  the  internal  occipital  protuberance,  at  which  point  there  is  a 
meeting  of  five  sinuses,  the  two  lateral,  the  superior  longitudinal,  the  straight,  and 


868 


HUMAN   ANATOMY. 


the  occipital.  From  this  meeting-point,  which  is  termed  the  torcular  Herophili  (con- 
fluens  sinuum),  each  lateral  sinus  passes  outward  over  the  squamous  portion  of  the 
occipital  bone  along  the  line  of  the  attachment  of  the  tentorium  cerebelli,  and,  passing 
over  the  posterior  inferior  angle  of  the  parietal,  is  continued  inward  upon  the  inner 
surface  of  the  mastoid  portion  of  the  temporal  and  the  jugular  process  of  the  occipital 
to  reach  the  jugular  foramen,  where  it  opens  into  the  internal  jugular  vein.  As  it  passes 
upon  the  mastoid  portion  of  the  temporal,  it  leaves  the  line  of  attachment  of  the  ten- 
torium cerebelli,  passing  somewhat  downward  as  well  as  inward,  and  follows  the  line 
of  junction  of  the  petrous  and  mastoid  portions  of  the  bone  in  a  somewhat  S-shaped 
course,  whence  this  portion  of  it  is  frequently  termed  the  sigmoid  sinus. 

A  difference  in  size  is  usually  noticeable  in  the  sinuses  of  the  opposite  sides, 
that  of  the  right  being  usually  the  larger,  and  this  difference  is  due  to  the  mode  in 
which  the  various  sinuses  meet  at  the  torcular  Herophili.  Most  frequently  the 
superior  longitudinal  sinus  communicates  mainly  with  the  right  lateral,  while  the 


FIG.  755. 


Skin 


Superior  longitudinal  sinus 


Falx  cerebri 


Cerebral 
hemisphere 


Posterior  horn  of 
lateral  ventricle 


Tentorium 
Left  lateral  sinus 


Superior  worm 


Fibro-aponeurotic  layers  of  scalp 
Parietal  layer  of  dura 
Bone 


f— Inferior  longitudi- 
nal sinus,  cut 
obliquely 


Posterior  horn  of 
lateral  ventricle 


Tentorium 

Right  lateral  sinus 

Cerebellum 
Inferior  worm 


Occipital  sinus 


Frontal  section  of  head,  viewed  from  behind,  showing  relations  ot  dura  mater  to  sinusc* 
and  to  cerebral  hemispheres  and  ceit-tn-llum. 

straight  sinus  opens  principally  into  the  left,  the  greater  amount  of  blood  carried  by 
the  superior  longitudinal,  as  compared  with  that  transmitted  by  the  straight,  resulting 
in  the  larger  size  of  the  right  lateral  sinus.  Indeed,  in  some  cases  the  right  lateral 
sinus  is  practically  the  direct  continuation  of  the  superior  longitudinal  and  the  left 
lateral  of  the  straight,  the  two  laterals  being  connected  only  by  a  short  and  relatively 
small  connecting  arm,  which  represents  the  torcular  Herophili.  Throughout  that 
portion  of  their  course's  in  which  the  lateral  sinuses  lie  in  the  line  of  attachment  of  the 
tentoriiim  cerebelli  they  are  triangular  in  cross-section  (Fig.  755),  but  in  their  mastoid 
f  sigmoid)  portion  they  are  semi-ciivular  ;  the  right  sinus  has  a  diameter  of  from 
9-12  mm.,  while  the  left  varies  from  3-5  mm.  At  the  jugular  foramen  each  sinus 
makes  a  sudden  bend  and  opens  either  directly  into  the  summit  of  the  superior  jugular 
bulb,  or  else  at  a  varying  distance  downward  upon  the  anterior  surface  of  the  bulb, 
the  upper  extremity  of  which  then  forms  a  dome-shaped  structure  projecting  upward 
into  the  jugular  foramen. 


THE   SUPERIOR   CAVAL  SYSTEM.  869 

Tributaries. — The  lateral  sinuses,  in  addition  to  the  sinuses  which  communicate  with  them 
at  the  torcular  Herophili,  receive  the  following  tributaries,  most  of  which  will  be  described  in 
greater  detail  later:  (a)  the  posterior  inferior  cerebral  veins,  which  pass  backward  from  the 
temporo-sphenoidal  regions  of  the  cerebral  hemispheres  ;  (b)  some  of  the  inferior  cerebellar  veins  ; 
(c)  the  superior  petrosal  sinus,  this  latter  communicating  with  it  just  where  it  leaves  the  line  of 
attachment  of  the  tentorium  cerebelli.  Into  the  sigmoid  portion  there  open  (d )  the  internal  au- 
ditory veins  ( vv.  auditivae  internae ),  which  issue  from  the  internal  auditory  meatus  ;  (e)  the  mastoid 
emissary  vein  (page  876)  ;  and  (f)  some  of  the  veins  of  the  medulla  oblongata  and  pons. 

Variations. — Considerable  variation  exists  in  the  relative  sizes  of  the  right  and  left  lateral 
sinuses,  in  accordance  as  the  superior  longitudinal  sinus  opens  more  or  less  directly  into  one 
or  the  other.  As  stated,  the  tendency  is  for  the  superior  longitudinal  to  open  into  the  right 
lateral  ;  quite  often,  however,  it  opens  into  the  left,  and  occasionally  it  may  communicate  equally 
with  both.  In  100  crania,  Riidinger  found  that  the  right  lateral  sinus  was  the  larger  in  70  cases, 
the  left  in  27,  and  the  two  were  equal  in  size  in  only  3  cases. 

The  horizontal  portion  of  the  left  sinus  has  been  observed  to  be  lacking  or  reduced  to  an 
exceedingly  fine  channel,  and  one  or  botli  of  the  sinuses  have  been  observed  to  pass  through  a 
greatly  enlarged  mastoid  foramen  to  open  into  the  posterior  auricular  vein,  the  sigmoid  sinus 
being  represented  only  by  a  very  small  channel. 

In  a  considerable  number  of  cases  a  small  sinus,  known  as  the  petro-squamosal  shuts,  opens 
into  the  lateral  just  as  it  bends  downward  and  inward  upon  the  mastoid  portion  of  the  temporal. 
This  sinus  passes  downward  over  the  anterior  surface  of  the  petrous  portion  of  the  temporal, 
along  the  line  of  its  junction  with  the  squamous  portion,  and  occasionally  passes  through  a 
foramen — the  foramen  jugulare  spurium — which  opens  to  the  exterior  just  behind  the  articular 
eminence  of  the  zygomatic  process.  The  sinus  represents  the  original  terminal  portion  of  the 
lateral  sinus,  the  sigmoid  portion  of  that  sinus  being  a  secondary  formation,  and  opened  after 
its  exit  from  the  foramen  jugulare  spurium  into  the  internal  jugular,  although  its  connection  in  the 
adult  is  with  the  temporal  vein. 

Practical  Considerations. — By  reason  of  its  proximity  to  the  middle  ear, 
mastoid  antrum  and  cells,  the  sigmoid  portion  of  the  lateral  sinus  is  more  often  the 
subject  of  thrombosis  than  any  other  sinus  (page  1509).  This  may  arise  in  the 
following  six  ways,  mentioned  in  the  order  of  frequency,  the  first  outnumbering  all  the 
others:  (i)  Extension  from  chronic  purulent  inflammation  of  the  middle  ear;  (2) 
extension  of  acute  inflammatory  disease  from  the  mouth,  pharynx,  and  tonsils  into 
the  middle  ear,  antrum,  and  cells  ;  (3)  extension  of  thrombosis  from  other  sinuses, 
especially  the  so  closely  associated  superior  petrosal  ;  (4)  trauma,  such  as  fracture  of 
the  base  extending  through  the  middle  ear  to  the  sinus  ;  (5)  pressure  of  tumors  or 
discharge  associated  with  them  ;  (6)  infection  from  septic  wounds  of  the  head,  neck, 
or  mastoid  region  (Macevven). 

The  anatomical  symptoms  of  thrombosis  of  this  sinus  may  be  due  to  (a)  obstruc- 
tive distension  of  the  superficial  veins  communicating  with  the  sinus,  chiefly  the 
mastoid  vein  (q.v.)  ;  (£)  mastoid  inflammation  (osteitis)  resulting  from  contiguity 
and  from  the  venous  connection  ;  (e)  phlebitis  .of  the  veins  communicating  with  the 
sinus,  especially  the  internal  jugular  (page  863),  condyloid  (page  876),  and,  occasion- 
ally, the  mastoid. 

The  subject  of  sigmoid  sinus  thrombosis  is  further  considered  in  relation  to  the 
mastoid  (page  1508). 

The  knee  (genu)  of  the  sigmoid  portion  of  the  lateral  sinus  extends  further 
inward  and  forward  on  the  right  side  than  on  the  left,  and  this  fact,  together  with  the 
larger  size  of  the  right  lateral  sinus  as  compared  with  the  left,  aids  in  explaining  the 
greater  frequency  of  sinus  thrombosis,  septic  meningitis,  and  cerebral  abscess  as 
sequelae  of  otitis  media  on  the  right  side  (page  1509).  The  infection  is  carried 
by  the  veins  which  connect  the  mastoid  cells  and  antrum  with  the  genu  of  the 
sigmoid  sinus. 

On  the  surface  the  top  of  the  curve  represented  by  the  horizontal  and  descending 
(sigmoid)  portion  of  the  lateral  sinus  should  correspond  to  a  point  (asteric)  2.5  cm. 
above  and  3.8  cm.  (i}4  in.)  behind  the  centre  of  the  auditory  meatus.  This  is 
about  the  infero-posterior  parietal  angle.  The  superior  limit  of  the  horizontal  portion 
of  the  sinus  is  represented  by  a  line  from  this  asteric  point  to  3.8  cm.  (i  ^  in.)  above 
the  inion.  The  superior  and  anterior  boundary  of  the  sigmoid  portion  is  indicated 
by  a  line  from  the  same  point  curving  downward  and  forward  along  the  skin 
groove  at  the  auriculo-mastoid  junction  to  a  little  below  the  level  of  the  external 


870  HUMAN   ANATOMY. 

auditory  meatus.  Here  the  sinus  turns  inward  and  forward  to  reach  the  jugular 
foramen  and  has  no  further  close  relation  to  the  lateral  cranial  wall.  A  curved  line 
drawn  1 2  mm.  ( ^  in. )  below  the  horizontal  and  behind  the  vertical  portions  of  the 
curved  line  last  described  represents  approximately  the  inferior  and  posterior 
boundary  of  the  sinus.  The  width  thus  indicated — a  half  inch — varies  ;  it  is  usually 
greater  in  the  descending  part  of  the  sinus.  So,  too,  the  space  intervening 
between  the  genu  and  the  posterior  wall  of  the  external  auditory  meatus  may  vary 
from  2-12  mm. 

The  direction  of  the  sinuses  is  also  indicated  (Macewen)  by  a  line  from  the 
upper  edge  of  the  external  meatus  to  the  asterion,  and  by  one  from  the  tip  of  the 
mastoid  to  the  parieto-squamo-mastoid  junction,  the  latter  corresponding  to  the 
midportion  of  the  sinus,  or  that  most  often  involved  in  middle-ear  disease.  The 
region  of  danger  in  trephining  is  enclosed  (Birmingham)  by  two  lines,  one  from  a 
point  3.3  cm.  (i^  in.)  above  and  3.8cm.  (\Y>  in.)  behind  the  centre  of  the 
external  auditory  meatus  to  a  point  12  mm.  ()4  in.)  above  the  inion  ;  the  other 
from  a  point  3. 8  cm.  ( i  */£  in. )  behind  the  meatus  and  on  the  same  level  to  a  point 
12  mm.  (^  in.)  below  the  inion.  The  sinus  almost  never  overpasses  these  limits 
in  either  a  downward  or  an  upward  direction,  and  hence  the  trephine  or  chisel  may 
be  safely  applied  either  below  or  above  these  lines. 

Fracture  of  the  base  of  the  skull  may  extend  into  the  lateral  sinus,  in  which 
case  the  blood  may  pass  outward  into  the  tympanum  and  thence  by  way  of  the  Eusta- 
chian  tube  to  the  pharynx,  or — if  the  tympanic  membrane  is  torn — may  find  exit, 
mingled  with  cerebro-spinal  fluid,  at  the  external  auditory  meatus  (page  1505). 

For  further  remarks  on  the  practical  relations  of  this  important  sinus,  see 
page  1508. 

2.  The  Superior  Longitudinal  Sinus. — The  superior  longitudinal  sinus 
(sinus  sagittalis  superior)  (Fig.  756)  is  an  unpaired  sinus  which  lies  along  the  line  of 
attachment  of  the  falx  cerebri  to  the  cranial  vault.  It  begins  blindly  anteriorly  by  a 
small  vein-like  portion  which  lies  in  the  foramen  caecum  between  the  frontal  and 
ethmoidal  bones,  but  soon  becomes  a  true  sinus  which  passes  upward  and  backward  in 
the  median  line  of  the  frontal  bone,  beneath  the  sagittal  suture  of  the  parietals,  and  down 
the  median  line  of  the  squamous  portion  of  the  occipital  to  terminate  at  the  internal 
occipital  protuberance  by  opening  into  the  torcular  Herophili,  or,  usually,  more  or 
less  directly  into  the  right  lateral  sinus. 

The  sinus  is  triangular  in  section  and  increases  gradually  in  size  from  before  back- 
ward, measuring  about  1.5  mm.  in  diameter  at  the  level  of  the  apex  of  the  crista 
galli  and  1 1  mm.  at  its  termination.  Its  lumen  is  usually  traversed  by  numerous 
irregular  bands  of  connective  tissue  known  as  chorda  Willisii,  and  frequently,  espe- 
cially in  aged  persons,  Pacchionian  bodies,  which  are  numerous  along  its  course, 
project  into  it  (Fig.  1039). 

Tributaries.— In  the  fcetus  and  in  early  childhood  the  superior  longitudinal  sinus  communi- 
cates with  the  veins  of  the  nasal  cavity  through  the  foramen  caecum,  but  this  connection  is  diss.  >1  ved 
in  the  adult.  In  addition,  it  communicates  with  the  neighboring  blood-lakes  and  through  these 
with  the  meningeal  veins,  and  receives  (a)  branches  from  the  adjacent  portions  of  the  dura 
mater  ;  (t>)  the  superior  cerebral  veins,  from  ten  to  fifteen  in  number  (page  877)  ;  and  (c)  diploic 
veins,  some  of  which  traverse  the  parietal  bone  and  constitute  emissary  veins,  the  most  noticeable 
of  these  being  one  which  traverses  the  parietal  foramen  (page  876). 

Variations.— The  superior  longitudinal  sinus  varies  considerably  in  size  and  is  occasionally 
exceedingly  small,  the  tributaries  which  normally  open  into  it   passing  downward   in  the  talx 
to  open  into  the  inferior  longitudinal  sinus.      It  lias  been  observed  to  divide  into  two  trunk 
throughout  a  portion  of  its  course,  and  also  to  divide  at  the  apex  of  the  occipital  bone  into  tv 
trunks  which  followed  the  lines  of  tin-  lambdoid  suture  to  open  into  the  lateral  sinuses, 
as  stated,  the  sinus  communicates  more  or  less  directly  with  the  right  lateral  sinus,  but  pCCfil 
ally  it  may  bend  to  the  left  of  the  internal  occipital  protuberance  and  open  into  the  left  lateral. 

Practical  Considerations. — The  superior  longitudinal  sinus  may  become 
infected  (a  from  the  scalp  through  the  diploic  veins  :  (  h )  from  foci  of  cerebral  or 
meningeal  disease  through  the  contiguous  blood-lakes  or  through  the  cerebral  veins  : 
(<r)  in  childhood  from  the  nose  through  the  veins  traversing  the  foramen  caecum. 


THE   SUPERIOR   CAVAL  SYSTEM. 


871 


When  the  latter  veins  are  patent  epistaxis  may  be  a  symptom  of  cerebral  hyperaemia 
(as  in  congestive  headaches)  and  may  relieve  it.  In  children  epistaxis,  in  infants 
cedema  of  the  scalp  over  the  anterior  fontanelle,  and  in  adults  oedema  over  the  parie- 
tal and  occipital  regions  are  common  symptoms  of  thrombosis  of  this  sinus,  and  are 
easily  understood  in  view  of  its  venous  tributaries. 

Naevi  in  the  scalp  in  the  mid-line  sometimes  communicate  directly  with  the  sinus 
by  veins  passing  between  the  parietals  or  directly  through  them  near  the  medial  edge. 

Traumatic  or  inflammatory  thrombosis  may  follow  a  depressed  fracture  of  the 
cranial  vault  if  the  fragment  invades  the  lumen  of  the  sinus  and  obstructs  or  arrests 
the  flow  of  blood. 

A  noninfective  form  of  thrombosis  is  sometimes  observed  in  connection  with 
this  sinus.  It  has  received  the  name  of  marasmic  thrombosis,  as  it  has  usually  been 
associated  with  weakness  and  debility. 

The  construction  of  all  the  sinuses  predisposes  them  to  thrombosis.  Their 
rigidity,  their  width,  the  trabeculae  which  occasionally  cross  them,  the  peculiar 
manner  in  which  they  are  prevented  from  being  too  rapidly  depleted  during  inspira- 


FIG.  756. 


Superior  longitudinal  sinus 


Superficial  Syl 


of  striate  body 
Falx  cerebri 
Inferior  longitudinal  sinu 


Internal  cerebral  veins,  uniting  to 
form  great  cerebral   (Galen's) 


Straight  sinus 

Tentorium  cerebellt  (under 

surface,  right  half) 

Right  superior  petrosal  sinus 

Internal  auditory  meatus 

Torcular  Herophili 

Lateral   superior  cerebellar  vein; 

Right  lateral  sinus 

Falx  cerebelli 

Right  inferior  petrosal  sinus 


Head  has  been  sectioned  to  left  of  mid-sagittal  plane  and  brain  removed,  showing  dural  septa  in  position; 
terminal  portions  of  some  superior  cerebral  veins  are  seen  upon  the  surface  of  falx  cerebri. 

tion  when  the  lowering  of  pressure  takes  place  in  the  great  cervical  veins  (page  878), 
and,  in  the  case  of  the  longitudinal  sinus,  the  direction  in  which  the  blood  from  the 
cerebral  veins  enters  at  an  obtuse  or  right  angle  against  the  current,  all  tend  to  retard 
the^  flow  of  blood  and  favor  coagulation.  When  to  these  conditions  is  added  a 
deficient  supply  of  possibly  defective  blood,  as  in  exhaustion  or  depletion  from  pro- 
fuse diarrhoea,  marasmic  thrombosis  is  apt  to  occur  (Macewen). 

The  line  of  the  sinus  begins  at  the  root  of  the  nose  and  runs  in  the  mid-line  to 
the  external  occipital  protuberance. 

Rarely  there  are  found  in  the  mid-line  of  the  vertex  small  reducible  swellings  to 
which  are  feebly  transmitted  the  brain  pulsations.  They  are  subpericranial,  contain 
venous  blood,  and  connect  with  the  longitudinal  sinus  through  apertures  in  the  skull, 
either  congenital,  the  result  of  bone  disease  or  atrophy,  or  due  to  accident. 

3.  The  Inferior  Longitudinal  Sinus.— The  inferior  longitudinal  sinus  (sinus 
sagittalis  inferior)  (Fig.  756)  is  an  unpaired  sinus  which  lies  in  the  inferior  or  free  edge 
of  the  falx  cerebri.  It  begins  at  about  the  middle  of  the  border  of  the  falx  and  passes 


872  HUMAN   ANATOMY. 

backward,  gradually  increasing  in  size,  to  the  junction  of  the  falx  with  the  tentorium 
cerebelli,  where  it  opens  into  the  straight  sinus.  It  receives  small  tributaries  from  the 
falx  and  sometimes  also  from  the  corpus  callosum. 

4.  The  Straight  Sinus. — The  straight  sinus  (sinus  rectus)   (Fig.   756),  also 
unpaired,  lies  along  the  line  of  junction  of  the  falx  cerebri  with  the  tentorium  cerebelli. 
It  is  formed  at  the  anterior  border  of  the  tentorium  by  the  junction  of  the  inferior  longi- 
tudinal sinus  and  the  great  cerebral  vein  (vena  Galcni)  (page  877),  and  is  directed 
backward  to  open  into  the  torcular  Herophili  or  more  usually  into  the  left  lateral 
sinus. 

In  addition  to  the  two  trunks  by  whose  union  it  is  formed,  it  receives  a  number 
of  small  branches  from  the  tentorium,  branches  from  the  posterior  portion  of  the 
medial  surfaces  of  the  cerebral  hemispheres,  and  sometimes  a  median  superior  cere- 
bellar  vein. 

5.  The  Occipital  Sinus. — The  occipital  sinus  (sinus  occipitalis)  (Fig.  757)  is 
an  unpaired,  or  in  some  cases  a  paired,  sinus  which  descends  from  the  torcular  Herophili 
along  the  line  of  attachment  of  the  falx  cerebelli  to  the  posterior  border  of  the  foramen 
magnum.      There   it    divides    into    two  trunks,    the  marginal  sinuses,    which  pass 
forward  along  the  margin  of  the  foramen  magnum,   one  on  one  side  and  one  on 
the  other,   to  open  into  the  bulbus  superior  of  the  corresponding  internal  jugular 
vein. 

The  occipital  sinus  receives  as  tributaries  branches  from  the  falx  cerebelli  and 
the  adjacent  portions  of  the  dura,  and  also  some  veins  from  the  inferior  surface  of  the 
cerebellum.  At  the  posterior  border  of  the  foramen  magnum,  where  it  bifurcates  to 
form  the  marginal  sinuses,  it  makes  connection  with  the  veins -of  the  posterior  spinal 
plexus. 

Variations. — The  occipital  sinus  is  occasionally  wanting,  and  frequently  extends  only  as  far 
as  the  posterior  border  of  the  foramen  magnum,  the  marginal  sinuses  being  undeveloped.  It 
may  open  above  into  either  the  right  or  left  lateral  sinus,  or  into  the  straight  sinus  a  short 
distance  before  its  termination. 

6.  The  Cavernous  Sinus. — The  cavernous  sinus  (sinus  cavernosus)  (Fig.  757) 
is  a  paired  sinus  of  considerable  size  which  extends  along  the  sides  of  the  body  of  the 
sphenoid  bone  from  the  sphenoidal  fissure  in  front  to  the  apex  of  the  petrous  portion  of 
the  temporal.      It  measures  about  2  cm.  in  length  and  has  a  diameter  of  about  i  cm. 
and  is  almost  quadrilateral  in  cross-section.      Its  external  diameter  does  not,  however, 
represent  the  actual  capacity  of  its  lumen,  since  this  is  greatly  reduced  in  size  (i)  by 
being  traversed  by  numerous  trabeculse  from  which  fringe-like  prolongations  hang 
freely  into  the  blood-current,  a  section  of  the  sinus  having  very  much  the  appearance 
of  a  section  of  the  corpus  cavernosum  penis,  whence  the  name  bestowed  upon  it  by 
Winslow  ;    and  (2)  by  the  fact  that  the  internal  carotid  artery  and  the  abducent 
(sixth)  nerve  traverse  it,  while  certain  other  of  the  cranial  nerves  are  embedded  in  its 
outer  wall.     These  nerves  are  the  oculomotor,  the  pathetic,  and  the  ophthalmic  and 
maxillary  divisions  of  the  trigeminus,  which  lie  in  that  order  from  above  downwarc  . 

Tributaries. — At  the  sphenoidal  fissure  the  cavernous  sinus  receives  the  ophthalmic  vein 
and,  farther  back,  occasionally  the  basilar  vein,  both  of  which  are  described  later  on  (page  877  I. 
In  addition,  it  receives  veins  from  the  neighboring  portions  of  tin-  dura  mater,  and  has  connecting 
with  it  the  spheno-parietal  and  the  intercavernous  sinuses.  These  latter  are  transverse  simisis 
which  pass  across  between  the  two  cavernous  sinuses,  the  one  (sinus  intercavernosus  anterior) 
passing  in  front  of  the  sella  turcica  and  the  other  (sinus  intercavernosus  posterior)  behind  th;.t 
cavity,  and  they  receive  branches  from  the  dura  mater  and  from  the  pituitary  body.  The  two 
sinuses,  together  with  the  portion  of  the  cavernous  sinus  between  their  terminations  on  each  side, 
form  what  is  usually  termed  the  circular  sinus  (sinus  circnlaris). 

Besides  the  vessels  which  are  truly  tributaries,  the  cavernous  sinus  also  has  connected 
with  it  certain  vessels  which  are  emissary  in  function,  leading  blood  away  from  it.  The  two 
petrosal  sinuses  in  which  it  terminates  are  of  this  nature.  In  addition,  veins  pass  from  its  undt  r 
surface  (i)  through  the  foramen  ovale,  along  with  the  mandibular  division  of  the  trigeminal 
nerve,  to  communicate  with  the  pterygoid  plexus;  (2)  through  the  fibrous  tissue  which  closes 
the  foramen  lacernm  medium  ;  (;0  through  the  foramen  of  Yesalius,  when  this  exists  ;  and  (4) 
occasionally  through  the  foramen  rotnndum  with  the  maxillary  division  of  the  trigeminal  nerve. 


THE   SUPERIOR   CAVAL  SYSTEM. 


873 


Where  the  internal  carotid  enters  the  cavernous  sinus  at  the  internal  orifice  of  the  carotid 
canal  the  sinus  projects  downward  around  the  artery  in  a  funnel-shaped  manner,  and  from  it 
there  arises  a  close  net-work  of  veins,  the  carotid  plexus  or  carotid  sinus,  which  completely 
invests  the  artery  throughout  its  course  through  the  carotid  canal,  at  the  lower  opening  of 
which  it  is  continued  into  one  or  two  veins  which  open  into  the  internal  jugular. 

Practical  Considerations. — The  cavernous  sinus,  though  less  frequently 
affected  with  thrombosis  than  any  other  large  sinus,  may  become  infected  from 
foci  apparently  far  removed,  through  the  extra-orbital  communications  of  the 
ophthalmic  veins  (pages  879,  880).  Thus,  carbuncle  of  the  face,  cancrum 
oris,  alveolo-dental  periostitis,  ulceration  of  the  Schneiderian  mucous  membrane, 
empyema  of  the  maxillary  antrum,  abscess  of  the  frontal  sinus,  osteomyelitis  of 

FIG.  757. 


Eyeball 
Superior 

ophthalmic  vein 
Inferior 

ophthalmic  vein 


Optic  nerve 
Ophthalmic  vein 

Anterior 

clinoid  process 


Cavernous  sinus 


Inferior 

petrosal  sinus 

Superior  petrosal 
sinu 

Lateral  sinu: 

Inferior 

cerebral  vei 

Occipital  sinus 


Lateral  sin 


Optic  nerve 


Circular  sinus 
Cavernous  sinus 


Transverse  sinus 
Inferior 


Superior 

petrosal  sinus 

Foramen  magnum 
Tentorium  cerebelli 

Inferior  cerebral  vein 

Inferior  longitudinal 

sinus  in  cross 

section 

Lateral  sinus 
Torcular  Herophili 


Dural  sinuses  at  base  of  skull ;   falx  cerebri  and  left  half  of  tentorium  have  been  removed. 

the  frontal  diploic  tissue,  may  each  be  followed  by  cavernous  sinus  thrombosis. 
In  the  presence  of  thrombosis,  there  are  two  groups  of  pressure  symptoms  (a) 
venous,  causing  exophthalmos,  oedema  of  the  eyelids  and  of  the  corresponding  side 
of  the  root  of  the  nose,  and  some  chemosis  ;  (£)  nervous,  causing  ptosis,  strabismus, 
variations  in  the  pupil,  pain,  etc. 

Arterio-venous  aneurism  between  this  sinus  and  the  internal  carotid,  in  addition 
to  similar  symptoms  of  venous  obstruction  (page  863),  often  likewise  causes  paralyses 
in  the  distribution  of  the  third,  the  fourth,  and  the  ophthalmic  division  of  the  fifth 
cranial  nerves,  which  lie  in  the  dura  mater  on  the  outer  wall  of  the  sinus,  and  of  the 
sixth  nerve,  which  is  in  close  relation  to  the  internal  carotid. 

The  bulk  of  the  blood  of  the  contents  of  the  anterior  and  lower  portions  of  the 
skull  empties  into  the  cavernous  sinus;  that  of  the  remaining  portion, — including  the 
greater  part  of  the  cerebrum,  the  cerebellum,  the  pons,  and  the  cerebral  peduncles 


874  HUMAN   ANATOMY. 

— chiefly  into  the  tributaries  of  the  lateral  sinus.  The  two  sinuses  through  the 
superior  petrosal  sinus  and  other  venous  channels,  have  free*  anastomotic  connection 
which  effectually  tends  to  equalize  or  distribute  blood-pressure. 

The  communication  between  the  two  cavernous  sinuses  through  the  basilar  sinus 
— or  plexus — and  the  circular  sinus,  is  an  important  portion  of  the  mechanism  by 
which  the  pressure  of  venous  blood  within  the  skull  is  equalized.  This  same  com- 
munication may,  however,  in  a  case  of  anterio- venous  aneurism  (vide  supra)  bring 
about  involvement  of  the  orbit  on  the  other  side,  the  blood  from  the  aneurism  entering 
the  opposite  sinus  by  way  of  these  intercommunicating  sinuses,  or  infection  may 
follow  the  same  channel. 

7.  The  Spheno-Parietal  Sinus. — The  spheno-parietal  sinus  (sinus  spheno' 
parietalis),  also  known  from  its  position  as  the  sinus  alee  pan vz-,  arises  at  the  outer 
extremity  of  the  lesser  wing  of   the  sphenoid  from  one  of  the  meningeal  veins  and 
passes  horizontally  inward,  under  cover  of  the  posterior  border  of  the  lesser  wing,  to 
reach  the  cavernous  sinus  near  its  anterior  extremity.      It  receives  dural,  diploic,  and 
some  of  the  anterior  cerebral  veins. 

8.  The  Superior  Petrosal  Sinus. — The  superior  petrosal  sinus  (sinus  petrosus 
superior)  is  the  smaller  of  the  two  sinuses  into  which  the  cavernous  divides  at  the 
apex  of  the  petrous  portion  of  the  temporal.      It  passes  outward  and  backward  along 
the  superior  border  of  the  petrous  bone  and  opens  into  the  lateral  sinus  just  at  the 
point  where  it  leaves  the  line  of  attachment  of  the  tentorium  cerebelli  to  become  the 
sigmoid  sinus.      The  superior  petrosal  sinuses  receive  some  small  tympanic  veins  and 
some  branches  from  the  cerebellum  and  cerebrum. 

9.  The  Inferior  Petrosal  Sinus. — The  inferior  petrosal  sinus  (sinus  petrosus 
inferior)  is  the  larger  terminal  branch  of  the  cavernous  sinus,  and  extends  from  the 
posterior  extremity  of  that  sinus,  at  the  apex  of  the  petrous  portion  of  the  temporal 
bone,  along  the  petro-occipital  suture  to  the. jugular  foramen,  where  it  opens  into  the 
superior  bulb  of  the  jugular  vein,  or,  frequently,  into  the  vein  below  the  bulb. 

In  addition  to  small  branches  from  the  neighboring  portions  of  the  dura  and 
from  the  cerebellum,  pons,  and  medulla  oblongata,  the  inferior  petrosal  sinus 
receives,  some  internal  auditory  veins  and  an  anterior  condyloid  vein  which  arises 
from  a  plexus  surrounding  the  hypoglossal  nerve  in  its  course  through  the  anterior 
condyloid  foramen.  In  its  anterior  portion  the  sinus  is  also  in  communication  with 
the  basilar  sinus. 

10.  The  Basilar  Sinus. — The  basilar  sinus  (plexus  basilaris),  also  termed  the 
transverse  sinus,  is  usually  a  plexus  of  sinuses  rather  than  a  single,  distinct  sinus. 
It    occupies   the   dura   mater   which    covers   the    basilar   process   of    the   occipital 
bone   and   communicates   with  the   inferior   petrosal   and    posterior   intercavernous 
sinuses  in  front,  and  behind,  at  the  anterior  border  of  the  foramen  magnum,   with 
the  anterior  spinal  plexus.      It  receives  branches  from  the  medulla  oblongata  and 
from  the  diploe. 

Practical  Considerations. — Fracture  of  the  base  of  the  skull  through  the 
posterior  (cerebellar)  fossa  may  involve  the  basilar  plexus  of  sinuses  and  be  followed 
by  an  intracranial  hemorrhage  which  slowly  oozes  through  the  line  of  fracture  and, 
following  the  lines  of  vessels  or  nerves,  ultimately  causes  swelling  and  ecchymosis  of 
the  skin  of  the  neck  ;  the  latter  is  apt  to  show  first  anterior  to  the  tip  of  the  mastoid, 
to  which  region  the  blood  is  conducted  by  the  cellular  tissue  around  the  auricular 
artery.  It  spreads  thence  upward  and  backward  in  a  curved  line. 

THE  DiPLOir  VEINS. 

The  spaces  of  the  diploe  are  traversed  by  a  rich  plexus  of  veins,  characterized 
by  the  thinness  of  their  walls  and  opening  by  numerous  small  communicating 
branches  either  into  the  veins  of  the  seal]),  the  middle  meninoe.il  veins.  <>r  the 
cranial  sinuses.  Some  larger,  although  rather  inconstant,  stems  also  arise  from  the 
plexus  and  fonn  what  are  termed  the  diploic  veins.  Of  these,  four  are  usually 
recognized  (Fig.  758). 


THE   SUPERIOR   CAVAL  SYSTEM. 


875 


1.  The  anterior  diploic  vein  (v.  diploica  frontalis)  descends  in  the  diploe  of  the  frontal  bone 
and  at  the  level  of  the  supra-orbital  notch  opens  either  into  the  supra-orbital  or  ophthalmic  vein. 
It  communicates  with  the  anterior  temporal  diploic  vein  and  also  with  the  frontal  veins  and  the 
superior  longitudinal  sinus. 

2.  The  anterior  temporal  diploic  vein  (v.  diploica  temporalis  anterior)  passes  downward  and 
forward  in  the  diploe  of  the  anterior  portion  of  the  parietal  bone  and  opens  either  into  a  deep 
temporal  vein  or  into  the  spheno-parietal  sinus. 

3.  The  posterior  temporal  diploic  vein  (v.  diploica  temporalis  posterior)  passes  downward  in 
the  diploe  of  the  posterior  part  of  the  parietal  bone  and  usually  opens  into  the  mastoid  emissary 
vein,  thus  communicating  with  the  lateral  sinus.     It  also  communicates  with  the  posterior  auric- 
ular vein  and  may  open  into  it. 

4.  The  occipital  diploic  vein  ( v  diploica  occipitalis )  passes  downward  in  the  squamous  portion 
of  the  occipital  bone,  not  far  from  the  median  line,  and  opens  either  into  the  occipital  vein  or  into  the 
occipital  emissary  vein,  by  which  it  communicates  with  the  torcular  Herophili  or  the  lateral  sinus. 

FIG.  758. 


Occipital  diploic  vein 


Posterior 

temporal  diploic  vein 


•Anterior  or  frontal 
diploic  vein 


'rental  vein 
Supra-orbital  vein 
Frontal  diploic  vein 
Angular  vein 


Anterior  temporal 

diploic  vein 
Deep  temporal  vein 


Outer  table  of  skull  has  been  removed  to  expose  venous  spaces  of  diploe. 


Practical  Considerations. — The  diploic  veins  being  incapable  of  effective 
contraction,  bleed  very  freely  and  persistently,  and  -are  sometimes  a  source  of 
embarrassment  during  operations  on  the  skull.  Through  their  communications 
with  the  veins  of  the  scalp  on  the  one  hand,  and  with  the  endo-cranial  sinuses 
and  meningeal  veins  on  the  other,  they  may,  as  in  some  cases  of  compound  fracture, 
convey  infection  from  the  surface  to  the  diploe,  causing  osteomyelitis  and  necrosis, 
or  within  the  cranium,  causing  septic  meningitis  or  sinus  thrombosis.  Pyaemia 
has  followed  an  infective  phlebitis  of  the  diploic  veins  themselves.  Diploic  infection 
introduced  from  without — pyogenic — or  through  the  blood— tuberculous — is  apt 
to  spread  rapidly  within  the  diploic  tissue  itself,  as  well  as  to  the  underlying 
structures. 

THE  EMISSARY  VEINS. 

The  term  emissary  vein  is  applied  to  those  branches  which  place  the  sinuses  of 
the  dura  mater  in  communication  with  veins  external  to  the  cranial  cavity.  Using 
the  term  in  its  broadest  sense,  the  emissary  veins  are  very  numerous,  since  both  the 
diploic  and  the  meningeal  veins  might  be  regarded  as  such,  as  well  as  the  carotid 


876  HUMAN   ANATOMY. 

plexus  (page  873)  and  the  ophthalmic  vein  (page  879),  all  these  making  connections 
with  the  sinuses,  on  the  one  hand,  and  with  extracranial  veins,  on  the  other.  It  is 
customary,  however,  to  limit  the  term  to  certain  veins  which,  for  the  most  part, 
traverse  special  foramina  in  the  cranial  walls,  a  few,  however,  passing  through 
foramina  whose  principal  content  is  one  of  the  cranial  nerves. 

1.  The  parietal  emissary  vein  (emissarium  parietale  ),  rather  variable  in  size,  traverses  the  cor- 
respondingly variable  parietal  foramen,  placing  the  superior  longitudinal  sinus  in  communication 
with  the  veins  of  the  scalp. 

2.  The  occipital  emissary  vein  (emissarium  occipkale)  traverses  the  occipital  protuberance 
and  places  the  torcular  Herophili  or  one  or  the  other  of  the  lateral  sinuses  in  communication  with 
the  occipital  veins.     Its  size  is  variable  ;  it  usually  receives  the  occipital  cliploic  vein,  and  may 
perforate  only  the  external  or  the  internal  table  of  the  occipital  bone,  representing  in  such  cases 
the  terminal  portion  of  the  diploic  vein  rather  than  a  true  emissary. 

3.  The  mastoid  emissary  vein  (emissarium  mastoideum )  passes  through  the  mastoid  foramen 
and  places  the  lateral  sinus  in  communication  with  either  the  occipital  or  the  posterior  auricular 
veins.     It  is  occasionally  wanting,  and,  on  the  other  hand,  may  be  so  large  as  to  appear  to  be 
the  continuation  of  the  lateral  sinus,  the  terminal  portion  of  that  vessel  between  the  mastoid  and 
jugular  foramina  being  greatly  reduced  in  size. 

4.  The  posterior  condyloid  emissary  vein  (emissarium  condyloideum )  is  very  inconstant,  and 
when  present  traverses  the  posterior  condyloid  foramen,  extending  between  the  lateral  sinus  near 
its  termination  and  the  vertebral  veins. 

5.  The  anterior  condyloid  emissary  vein  (rete  canalis  hypoglossi)  is  a  net-work  which  sur- 
rounds the  hypoglossal  nerve  in  its  course  through  the  anterior  condyloid  foramen.     From  the 
plexus  two  veins  arise,  one  of  which  passes  to  the  inferior  petrosal  sinus  and  the  other  to  the 
vertebral  veins. 

6.  The  emissaries  of  the  foramen  ovale  (  rete  foraminis  ovalis)  are  formed  by  two  veins  which 
communicate  above  with  the  cavernous  sinus  and  pass  to  the  foramen  ovale,  where  they  form  a 
plexus  surrounding  the  mandibular  division  of  the  trigeminal  nerve  and  communicate  with  the 
pterygoid  plexus  of  veins.     Occasionally,  also,  a  similar  plexus  accompanies  the  maxillary  division 
of  the  trigeminus  through  the  foramen  rotundum. 

7.  The  emissary  vein  of  the  foramen  of  Vesalius  is,  like  the  foramen,  inconstant,  occurring 
only  about  once  in  three  cases.      It  extends  between  the  cavernous  sinus  and  the  pterygoid 
plexus  of  veins. 

8.  Finally,  a  variable  number  of  small  veins   pass  through  the  connective  tissue  which 
closes  the  foramen  lacerum  medium  and  place  the  cavernous  sinus  in  communication  with  the 
pterygoid  plexus. 

Practical  Considerations. — The  relations  of  the  emissary  veins  explain  many 
cases  of  spread  of  extra-cranial  infection  to  the  meninges  and  the  sinuses.  If  there 
were  no  emissary  veins,  injuries  and  diseases  of  the  scalp  and  skull  would  lose 
half  their  seriousness  (Treves).  Infected  wounds  of  the  scalp,  cellulitis  or  erysipelas 
involving  that  structure,  osteomyelitis,  or  necrosis  of  the  cranial  bones  may  through 
the  emissary  veins  result  in  serious  intra- cranial  disease.  The  largest  of  these  veins 
is  usually  the  mastoid,  the  communication  between  the  lateral  sinus  and  the  occipital 
or  posterior  auricular  vein  {vide  supra}.  This  relation  and  the  considerable  quan- 
tity of  blood  carried  by  the  mastoid  vein  are  thought  to  explain  the  supposed  effect 
of  leeches  or  blisters  applied  behind  the  ear  in  cerebral  hyperaemia  or  inflammation, 
especially  as  nearly  all  the  blood  of  the  brain  leaves  it  through  the  lateral  sinuses. 
They  also  explain  the  extensive  oedema  behind  the  ear  and  around  the  mastoid 
region  often  seen  in  lateral  sinus  thrombosis.  Pus  has  formed  in  the  cerebellar 
fossa  outside  of  the  sigmoid  sinus,  made  its  exit  through  the  mastoid  foramen  and 
appeared  as  an  occipito-cervical  abscess  (Erichsen).  The  escape  of  pus  by  the 
mastoid  foramen  indicates  extradural  pus  in  the  cerebellar  fossa  about  the  sigmoid 
groove,  with  the  probability  that  sigmoid  sinus  thrombosis  exists,  especially  if  the 
mastoid  vein  is  itself  thrombosed  (Macewen). 

In  suppurative  sigmoid  sinus  disease  the  posterior  condyloid  vein  may  convey 
infection  to  the  cellular  tissue  in  the  upper  part  of  the  posterior  cervical  triangle, 
causing  abscess  beneath  the  deep  fascia  ;  or,  as  a  result  of  cerebellar  pachymen- 
ingitis,  there  may  be  phlebitis  of  this  vein,  with  marked  tenderness  in  the  saint- 
region.  The  emissary  veins  are  important  agents  in  the  equalization  of  intra-cranial 
pressure. 


THE   SUPERIOR    CAVAL  SYSTEM.  877 

THE  CEREBRAL  VEINS. 

The  cerebral  veins  (vv.  cerebri)  convey  the  blood  carried  to  the  brain  by 
the  cerebral  arteries  to  the  sinuses  of  the  dura  mater.  They  differ  from  most 
of  the  other  veins  in  that  they  contain  no  valves,  their  walls  are  very  thin  and 
destitute  of.  muscle-tissue,  and  their  arrangement  does  not  usually  follow  that  of  the 
arteries. 

1.  The  Superior  Cerebral  Veins. — The  superior  cerebral  veins  (vv.  cerebri 
superiores)  are  from  eight  to  twelve  in  number,  draining  the  upper,  lateral  and  medial 
surfaces  of  the  cerebral  hemispheres.      They  follow,  for  the  most  part,  the  sulci  of  the 
hemispheres,  although  connected  across  the  gyri  by  numerous  anastomoses,  and  they 
open  above  into  the  superior  longitudinal  sinus.      The  various  veins  show  a  tendency 
to  increase  in  size  from  before  backward,  and  while  the  anterior  ones  have  a  course 
almost  at  right  angles  to  the  superior  longitudinal  sinus,  the  more  posterior  ones  are 
directed  forward  as  well  as  upward  and  open  obliquely  into  the  sinus  and  in  a  direc- 
tion contrary  to  the  flow  of  the  blood  contained  within  it. 

2.  The  Middle  Cerebral  Vein. — The  middle  cerebral  vein  (v.  cerebri  media), 
also  termed  the  superficial  Sylvian  vein,  lies  superficially  along  the  line  of  the  Sylvian 
fissure  and  opens  below  into  either  the  cavernous  or  the  spheno-parietal  sinus.      It 
receives  affluents  from  the  surface  of  the  brain  on  either  side  of  the  fissure  and  through 
these  anastomoses  with  both  the  superior  and  inferior  cerebral  veins.      One  of  these 
affluents  which  lies  approximately  along  the  line  of  the  fissure  of  Rolando  is  usually 
of  large  size  and  communicates  directly  with  one  of  the  superior  cerebral  veins,  the 
two  forming  what    is  known  as  the  great  anastomotic  vein  of  Trolard,  uniting  the 
superior  longitudinal  sinus  with  the  median  cerebral  vein. 

3.  The    Inferior   Cerebral  Veins. — The  inferior  cerebral  veins  (vv.  cerebri 
inferiores)  are  a  number  of  small  veins  which  occupy  the  inferior  surfaces  of  the  hemi- 
spheres.    They  are  somewhat    irregular  in  their  arrangement,  those  of  the    frontal 
lobes  anastomosing  with  the  superior  cerebrals  and  opening  into  the  anterior  portion 
of   the   superior   longitudinal    sinus,  while    those  of  the  temporo-sphenoidal  region 
anastomose  with  the  middle  cerebral  and  open  into  the  spheno-parietal,  cavernous  and 
superior  petrosal  sinuses  and  into  the  basilar  vein. 

4.  The  Great  Cerebral  Vein. — The  great  cerebral  vein  (v.  cerebri  magna), 
also  known  as  the  great  vein  of  Galen,  is  a  short  stem  about  i  cm.  in  length  which 
is  formed  beneath  the  splenium  of  the  corpus  callosum  in  the  neighborhood  of  the 
pineal  body,  by  the  union  of  the  two  internal  cerebral  veins.      It  passes  backward 
and  upward,   curving  around  the  posterior  extremity  of  the  corpus  callosum,   and 
terminates  (Fig.  756)  by  opening  into  the  anterior  end  of  the  straight  sinus. 

Tributaries. — The  great  cerebral  vein  is  formed  by  the  union  of  the  two  (a)  internal  cerebral 
•veins  (vv.  cerebri  interns),  also  known  as  the  small  veins  of  Galen.  These  are  situated,  one  on 
either  side  of  the  median  line,  in  the  velum  interpositum,  which  forms  the  roof  of  the  third 
ventricle.  Each  is  formed  at  the  foramen  of  Monro  by  the  union  of  three  veins,  the  choroid  vein, 
the  vein  of  the  septum  lucidum,  and  the  vein  of  the  corpus  striatum.  The  choroid  vein  ( v.  chori- 
oidea )  seems  to  be  the  direct  continuation  of  the  internal  cerebral  vein.  It  begins  at  the  junc- 
tion of  the  body  and  descending  horn  of  the  lateral  ventricle,  passes  forward  along  the  floor  of 
the  ventricle  in  the  outer  edge  of  the  choroid  plexus,  and  opens  at  the  foramen  of  Monro  into  the 
internal  cerebral  vein  of  its  side.  The  vein  of  the  septum  lucidum  (v.  septi  pellucidi)  passes 
backward  along  the  outer  (ventricular)  surface  of  the  septum  lucidum,  returning  the  blood  from 
the  head  of  the  caudate  nucleus  and  neighboring  parts,  and  the  vein  of  the  corpus  striatum  (v. 
terminalis),  which  drains  the  lenticular  nucleus  and  to  a  certain  extent  the  caudate  nucleus  also, 
passes  backward  in  the  groove  between  the  corpus  striatum  and  the  optic  thalamus  (stria  termi- 
nalis). 

(b]  The  posterior  vein  of  the  corpus  callosum  passes  backward  from  about  the  middle  of 
the  superior  surface  of  the  corpus  callosum  and,  bending  around  the  splenium,  empties  into  the 
great  cerebral  vein  or  into  the  internal  cerebral  vein  near  its  termination.     It  receives  blood 
from  the  corpus  callosum  and  from  the  median  surface  of  the  hemisphere. 

(c)  The  basilar  vein  (v.  basalis)  is  a  large  paired  vein  which  arises  at  the  anterior  per- 
forated space  by  the  junction  of  the  deep  Sylvian  vein  with  the  anterior  vein  of  the  corpus  cal- 
losum.    It  passes  backward  over  the  optic  tract  of  its  side  and  then  curves  upward  around  the 
crus  cerebri  to  reach  the  dorsal  surface  of  the  brain-stem,  where  it  opens  into  either  the  great  or 
the  internal  cerebral  vein.     Occasionally  the  terminal  portion  which  bends  upward  around  the 


878  HUMAN   ANATOMY. 

crus  is  lacking,  the  vein  then  emptying  into  the  cavernous  sinus.  The  deep  Sylvian  vein,  which 
is  its  main  stem  of  origin,  begins  in  a  number  of  vessels  which  ramify  over  the  surface  of  the 
insula  (island  of  Reil)  and  passes  downward  and  forward  at  the  bottom  of  the  Sylvian  fissure  to 
become  continuous  with  the  basilar  at  the  anterior  perforated  space.  Occasionally  it  unites 
with  the  lower  portion  of  the  middle  cerebral  vein  or  opens  with  it  into  the  spheno-parietal 
sinus.  The  anterior  vein  of  the  corpus  callosum  corresponds  to  the  anterior  cerebellar  artery, 
sometimes  termed  the  anterior  central  vein  ;  it  arises  on  the  anterior  part  of  the  upper  surface 
of  the  corpus  callosum  and  bends  downward  around  the  genu  to  unite  with  the  deep  Sylvian 
vein  at  the  anterior  perforated  space. 

The  basilar  vein  drains  all  the  central  part  of  the  base  of  the  brain,  and,  in  addition  to  the 
two  veins  which  are  regarded  as  its  stems  of  origin,  it  receives  branches  from  the  optic  tract, 
the  olfactory  bulb,  the  anterior  perforated  space,  the  tuber  cinereum,  the  corpora  mammillaria, 
and  the  posterior  perforated  space,  and  it  furthermore  receives  a  vein  from  the  superior  vt-rmis 
of  the  cerebellum.  The  veins  of  the  anterior  perforated  space  are  from  ten  to  fifteen  in  number 
and  have  their  origin  in  the  nuclei  of  the  corpus  striatum  and  in  the  internal  capsule,  while  those 
of  the*  posterior  perforated  space  drain  the  optic  thalami. 

Practical  Considerations.— The  free  communication  of  the  thin-walled 
valveless  cerebral  veins  with  one  another  is  one  of  the  agents  for  the  equalization  of 
intracranial  venous  pressure.  An  anastomotic  trunk  unites  the  middle  cerebral  vein 
with  the  posterior  cerebral,  thus  permitting  the  passage  of  venous  blood  by  means 
of  the  anterior  basilar  vein  into  the  sinuses  about  the  foramen  magnum.  Relief  from 
excessive  intracranial  blood-pressure  may,  in  addition,  be  effected  by  the  escape  of 
blood  from  within  the  cranium  (a}  in  the  occipital  region  through  the  internal 
jugular  and  mastoid  vein  ;  (^)  in  the  frontal  region  through  the  ophthalmic  vein 
and  the  vein  traversing  the  foramen  ovale  ;  (c)  in  the  basal  region  through  the 
petrosal  sinuses  and  the  posterior  condyloid  vein  ;  and  {d}  at  the  vertex  through  the 
diploic  veins  and  the  venules  penetrating  the  outer  table  of  the  cranium  to  join  those 
of  the  scalp  (Allen). 

The  avoidance  of  sudden  depletion  of  the  intracranial  venous  channels  through 
the  inspiratory  emptying  of  the  large  extracranial  veins  is  admirably  provided  for 
and  the  mechanism  should  be  understood,  as  it  has  practical  relation  to  many  phe- 
nomena of  cerebral  anaemia  and  hyperaemia,  to  shock  and  syncope  and  concussion, 
to  sinus  thrombosis,  and  to  many  other  intracranial  conditions.  The  chief  factors 
in  equalizing  the  flow  in  the  sinuses — and  thus  practically  throughout  the  brain — 
may  be  briefly  summarized  as  follows  : 

(a)  The  oblique  entrance  into  the  longitudinal  sinus  of  its  tributaries — the 
larger  middle  and  posterior  cerebral  veins — pouring  their  blood  into  it  against  the 
stream  ;  (b)  the  division  of  the  sinus  at  the  Torcular  Herophili  into  two  trunks 
diverging  at  right  angles  ;  (r)  the  course  of  the  blood-current  in  the  lateral  sinus — 
first  horizontal,  with  a  convexity  outward  ;  then — in  the  first  part  of  the  sigmoid — 
vertical  ;  then  horizontal,  with  a  convexity  downward,  and  then  a  quick  upward  and 
outward  turn,  with  narrowing  of  its  calibre  before  entering  the  jugular  fossa  ;  (</) 
the  widening  of  the  upper  part  of  this  fossa — which  is  above  the  outlet  of  the  sig- 
moid— and  the  narrowing  of  its  exit  (Macewen).  Were  it  not  for  these  and  other 
subsidiary  anatomical  arrangements  contributing  to  the  same  end,  the  effect  of  a 
deep  inspiration  on  the  cervical  veins  (page  863)  would  be  so  to  aspirate  the  venous 
channels  of  the  brain  as  to  cause  faintness  or  momentary  unconsciousness. 

The  cerebral  veins  are  so  delicate  that  in  operations  upon  the  brain  it  is  often 
better  to  arrest  bleeding  by  gauze-pressure  than  to  attempt  to  seize  and  tie  separate 
vessels. 

5.  The  Cerebellar  Veins. — The  cerebellar  veins  form  a  net-work  over  the 
surface  of  the  cerebellum,  the  course  of  the  larger  stems  being,  for  the  most  part,  at 
right  angles  to  that  of  the  folia-. 

The  superior  cerebellar  veins  (vv.  cerebelli  superiorcs)  open  in  part  laterally 
into  the  lateral  and  superior  petrosal  sinuses,  while  others  pass  medially  and  unite  to 
form  a  superior  median  cerebellar  vein,  which  passes  forward  and  downward  along 
the  superior  vermis  and  opens  either  into  the  great  cerebral  vein  or  the  terminal 
portion  of  the  basilar  vein. 


THE   SUPERIOR   CAVAL   SYSTEM.  879 

The  inferior  cerebellar  veins  (vv.  cerebelli  inferiores),  somewhat  larger  than 
the  superior,  pass  in  part  forward  and  outward  to  open  into  the  lateral  or  superior 
petrosal  sinuses,  and  in  part  backward  to  unite  with  the  occipital  sinus. 

THE  OPHTHALMIC  VEINS. 

The  ophthalmic  veins  take  their  origin  from  the  contents  of  the  orbit  and  pass  from 
before  backward,  uniting  to  form  two  principal  trunks,  a  large  superior  and  a  smaller 
inferior  ophthalmic  vein,  which  open  at  the  sphenoidal  fissure  into  the  anterior 
extremity  of  the  cavernous  sinus.  At  the  margin  of  the  orbit  both  veins  form 
important  connections  with  the  angular  vein,  and,  since  no  valves  occur  in  any  of 
the  branches  of  the  ophthalmic  veins,  they  form  important  emissaries  connecting 
the  cavernous  sinus  with  the  facial  vein. 

1.  The  Superior  Ophthalmic  Vein. — The  superior  ophthalmic  vein  (v.  oph* 
thalmica  superior)  (Fig.  757)  is  formed  at  the  inner  angle  of  the  orbit  by  the  fusion  of 
usually  two  vessels  which  come  from  the  supra-orbital  and  angular  veins  and  pass 
respectively  above  and  below  the  pulley  of  the  superior  oblique  muscle  of  the  eye 
and  unite  a  short  distance  posterior  to  that  structure.      The  anterior  portion  of  the 
superior  ophthalmic  vein  so  formed  is  sometimes  termed  the  v.  naso-frontalis ,  and  in 
its  further  course  it  is  directed  somewhat  tortuously,  at  first  obliquely  backward  and 
outward,  passing  across  the  optic  nerve  and   beneath   the  superior  rectus  muscle, 
and  then  more   directly  backward  to  the  sphenoidal  fissure. 

Tributaries. — The  superior  ophthalmic  receives  numerous  tributaries  from  both  the  eyeball 
and  the  other  contents  of  the  orbit,  most  of  the  branches  from  the  latter  sources  corresponding 
to  branches  of  the  ophthalmic  artery.  Thus  it  receives  (a)  the  anterior  and  (6)  the  posterior 
ethmoidal  veins  (vv.  ethmoidales  anterior  et  posterior)  which  return  blood  from  the  sphenoidal 
sinus  and  the  superior  meatus  and  turbinate  bone  of  the  nose,  communicating  with  the  other 
veins  of  the  nasal  cavity  and  entering  the  orbit  by  the  ethmoidal  foramina  ;  (c)  the  lachrymal 
vein  (v.  lacrimalis),  a  vein  of  considerable  size  arising  in  the  lachrymal  gland  and  accompanying 
the  artery  of  the  same  name  ;  and  (d)  muscular  veins  (vv.  musculares)  which  return  the  blood 
from  the  levator  palpebrae  superioris,  the  superior  and  internal  recti,  and  the  superior  oblique,  the 
veins  from  the  other  muscles  of  the  orbit  usually  opening  into  the  inferior  ophthalmic  vein. 

From  the  eyeball  it  receives  (e)  the  two  superior  venae  vorticosae.  These  veins  return  the 
blood  from  the  choroid  coat,  the  ciliary  body,  and  the  iris,  and  are  four  in  number,  each  having 
its  origin  from  a  rich  plexus  which  occupies  one  of  the  four  quadrants  of  the  choroid,  the  prin- 
cipal stems  of  the  plexus  radiating  from  all  directions  towards  the  central  point  of  its  quadrant. 
Here  they  unite  to  form  a  single  trunk  which  pierces  the  sclera  obliquely  at  about  the  equator 
of  the  eyeball,  the  veins  from  the  two  superior  quadrants  emptying  into  the  superior  ophthalmic, 
while  the  two  from  the  inferior  quadrants  connect  with  the  inferior  ophthalmic.  Occasionally 
five  or  six  venae  vorticosae  exist,  and  they  open  sometimes  into  the  muscular  veins  instead  of 
directly  into  the  ophthalmic  stems.  (/)  The  anterior  ciliary  veins  (vv,  ciliares  anteriores)  are 
very  slender  veins  which  leave  the  eyeball  at  the  points  where  the  recti  muscles  are  inserted 
into  the  sclerotic  ;  two  or  three  veins  are  associated  with  each  muscle-tendon  and  open  into  the 
muscular  veins,  (g]  The  posterior  ciliary  veins  (vv.  ciliares  posteriores)  accompany  the  poste- 
rior or  short  ciliary  arteries.  The  territory  supplied  by  the  arteries  is,  however,  drained  by  the 
venae  vorticosae,  and  the  posterior  ciliary  veins,  which  are  very  small,  take  their  origin  only  from 
the  posterior  portion  of  the  sclerotic  and  from  the  sheath  of  the  optic  nerve.  ( h )  The  vena  cen- 
tralis  retinas  is  a  single  stem  which  accompanies  the  corresponding  artery  through  the  centre  of  the 
optic  nerve,  and  has  its  origin  in  branches  which  ramify  over  the  surface  of  the  retina.  The  vein 
leaves  the  optic  nerve  usually  before  the  artery  and  opens  either  into  the  superior  ophthalmic 
vein  or,  more  frequently,  directly  into  the  cavernous  sinus. 

2.  The  Inferior  Ophthalmic  Vein. — The  inferior  ophthalmic  vein  (v.  oph- 
thalmica  inferior)  (Fig.  757)  takes  its  origin  from  a  net-work  of  small  veins  situated 
on  the  inner  portion  of  the  floor  of  the  orbit  near  its  border.      This  plexus  communi- 
cates with  the  facial  vein  and  is  continued  backward  towards  the  fundus  of  the  orbit, 
more  frequently  as  a  coarse  net-work  than  as  a  definite  stem.      The  vein,  when  it 
exists,  or  the  net- work,  anastomoses  with  branches  of  the  superior  ophthalmic. 

Tributaries. — (a)  Muscular  branches  from  the  inferior  and  external  recti  and  the  inferior 
oblique  muscles  and  (b)  the  inferior  venae  vorticosae  from  the  lower  half  of  the  eyeball. 
It  opens  posteriorly  either  directly  into  the  cavernous  sinus  or  else  unites  with  the  superior 
ophthalmic  vein. 


88o  HUMAN    ANATOMY. 

Anastomoses  of  the  Ophthalmic  Veins. — The  ophthalmic  veins  are  throughout  destitute 
of  valves  and  open  posteriorly  into  the  cavernous  sinus,  and,  since  they  also  communicate  with 
peripheral  veins,  they  may  well  be  regarded  as  emissary  channels  through  which  the  blood  may 
flow  either  from  the  cavernous  sinus  to  the  peripheral  veins  or  in  the  reverse  direction,  as  may 
be  determined  by  the  relative  pressure  within  and  without  the  cranium.  The  principal  connec- 
tions which  the  veins  make  are  (  i )  with  the  facial  vein,  which  is  itself  practically  devoid  of 
valves,  through  their  branches  of  origin  ;  (2)  with  the  veins  of  the  nasal  cavity  through  the  eth- 
moidal  branches  ;  and  (3)  with  the  pterygoid  plexus  by  means  of  a  branch  of  the  inferior  ophthal- 
mic which  passes  downward  through  the  spheno-maxillnry  fissure. 

Practical  Considerations. — The  communication  between  the  superior 
ophthalmic  vein — the  largest  channel  in  the  adult  between  the  vessels  of  the  venous 
system  of  the  head  and  face  and  the  sinuses  of  the  dura  mater — and  the  facial  vein, 
while  adding  to  the  danger  of  intracranial  complications  as  a  result  of  infectious  disease 
situated  upon  the  face  (page  873),  affords  relief  to  intraocular  tension  in  cases  ot 
pressure  upon  the  cavernous  sinus,  as  from  an  inflammatory  exudate  or  an  intra- 
orbital  or  intracranial  growth.  Such  relief  delays  the  appearance  of  "choked  disc" 
(page  1471),  due  to  the  distension  of  the  tributaries  of  the  vein,  especially  the  poste- 
rior ciliary  veins  and  the  vena  centralis  retinae.  In  arterio-venous  aneurism  of  the 
cavernous  sinus  and  internal  carotid  artery — due  to  basal  cranial  fracture,  a  bullet- 
or  stab-wound,  or  to  idiopathic  vascular  degeneration — the  ophthalmic  veins  are 
usually  compressed  and  may  transmit  pulsation  from  the  sinus  to  the  dilated  veins 
of  the  eyelids  and  of  the  frontal  region.  The  conjunctiva?  are  congested.  Exoph- 
thalmos  (page  1439).  bruit  and  thrill  are  not  uncommonly  present  as  a  result  of 
involvement  of  the  intraorbital  veins.  Nervous  symptoms — noise  in  the  head, 
intracranial  or  frontal  pain  and  paralyses — are  rarely  absent. 

These  symptoms  may  be  simulated  by  those  caused  by  traumatic  aneurism  of 
an  orbital  artery  or  by  the  direct  pressure  of  an  internal  carotid  aneurism  on  the 
ophthalmic  vein  as  it  empties  into  the  sinus. 

THE  EXTERNAL  JUGULAR  VEIN. 

The  external  jugular  vein  (v.  jugularis  externa)  (Fig.  759),  notwithstanding  its 
usual  connection  with  the  subclavian,  is  closely  related  both  in  its  development  and 
topographical  relations  with  the  internal  jugular,  and  may  be  most  conveniently  con- 
sidered here.  It  is  formed  in  the  neighborhood  of  the  angle  of  the  mandible  by  the 
union  of  the  temporo-maxillary  and  posterior  auricular  veins,  and  courses  downward 
immediately  below  the  platysma,  crossing  the  sterno-cleido-mastoid  muscle  obliquely. 
In  the  lower  part  of  the  neck  it  pierces  the  superficial  layer  of  the  deep  cervical 
fascia,  sometimes  above  and  sometimes  below  the  posterior  belly  of  the  onio-hyoid, 
and  opens  into  the  subclavian  vein  near  its  junction  with  the  internal  jugular.  A 
short  distance  below  its  origin  it  gives  off  a  large  branch  which  passes  forward  and 
downward  to  communicate  with  the  facial  vein. 

At  its  entrance  into  the  subclavian  it  is  provided  with  a  pair  of  valves,  and  usually 
a  second  pair  occurs  at  about  the  middle  of  the  neck.  A  third  pair  is  occasionally 
present  in  the  interval  between  the  other  two.  and  all  of  them  are  insufficient. 
The  superficial  layer  of  the  deep  cervical  fascia  is  intimately  adherent  to  the  walls 
of  the  vein  at  the  point  where  the  latter  perforates  it,  and  sometimes  the  fascia 
is  especially  thickened  immediately  below  and  to  the  inner  side  of  the  vein.  This 
attachment  of  the  fascia  prevents  any  collapse  of  the  walls  of  the  lower  part  of  the 
vein,  if  for  any  reason  there  is  a  deficiency  in  the  amount  of  blood  it  contains,  and 
predisposes,  therefore,  to  the  entrance  of  air  in  case  the  vein  is  severed. 

Variation*.— Considerable  differences  of  opinion  exist  as  to  tin-  definition  of  the  external 
jugular  vein.  Some  authors  describe  it  as  formed  by  the  union  of  the  posterior  auricular  and 
occipital  veins,  the  communicating  branch  described  above  as  occurring  between  it  and  the 
facial  being  tlu-n  regarded  as  the  main  stem  of  the  temporo-maxillary  ;  others,  again,  regard  it 
as  formed  by  the  union  of  the  temporal  and  maxillary  veins,  the  temporo-maxillary  then  con- 
stituting its  upper  portion. 

The  vein  is  subject  to  considerable  variation  in  si/e,  an  inverse  correlation  existing  between 
it  and  the  anterior  jugular.  It  may  even  be  entirely  wanting  or.  on  the  other  hand,  it  may  be 
double  throughout  a  portion  of  its  course.  It  occasionally  divides  below,  one  branch  passing, 
as  usual,  to  the  subclavian.  while  the  other,  passing  over  the  clavicular  attachment  of  the  sterno- 
cleido-mastoid,  opens  into  either  the  anterior  or  the  internal  jugular. 


THE  SUPERIOR  CAVAL  SYSTEM. 


881 


In  connection  with  the  abundant  variation  shown  in  the  size  of  the  external  jugular  it  is 
interesting  to  note  that  in  the  majority  of  mammals  it  is  the  most  important  vein  of  the  neck, 
surpassing  the  internal  jugular  in  size.  It  is,  however,  of  later  development  than  the  latter, 
and  its  later  importance  is  due  largely  to  the  union  with  it  of  the  facial  vein  or  of  the 
linguo-facial  trunk.  In  man,  however,  a  new  connection  of  the  facial  with  the  internal  jugular 
occurs,  whereby  the  importance  of  the  external  jugular  becomes  reduced,  and  its  variation 
in  size  is  largely  dependent  upon  the  extent  to  which  the  original  direct  connection  of 
the  facial  with  it  is  retained. 

FIG.  759. 


Temporal  fa 


Superficial 

temporal  i 
Middle  temp 


Occipital  vein 
Internal  maxillary 

maxillary  vein 
Posterior  auricular 


Sterno-cleido- 
mastoid 

Communication 

between  facial 

and  external 

jugular  vein 

External  jugular 

vein 

Tributary  of  trans- 
Terse  cervical  vein 
Posterior  external 
jugular  vein 

Trapezius 


Frontal  veins 

Supraorbital  vein 
Branch  of  communi- 
cation with  ophthal- 
mic vein 
Angular  vein 


Lateral  nasal  vein 


Deep  facial  vein 


Submental  vein 


Superficial  veins  of  head  and  neck  ;  external  jugular  lies  beneath  platysma 
muscle,  which  has  been  partly  removed. 


Practical  Considerations. — The  line  of  the  external  jugular  vein  is  from  the 
angle  of  the  jaw  to  the  centre  of  the  clavicle.  Backward  pressure  made  about 
an  inch  above  the  latter  point  will  cause  the  vein  to  become  visible  through- 
out its  length.  For  that  reason  it  was  at  one  time  selected  for  phlebotomy  in 
congestions  or  inflammations  about  the  face  and  neck.  The  vein  is  in  the 
superficial  fascia  and  therefore  courses  over  the  sterno-mastoid  muscle.  In  all 
operations  on  the  side  of  the  neck  its  size  and  its  course  should  be  borne  in  mind. 

56 


882  HUMAN   ANATOMY. 

Tributaries. — The  tributaries  of  the  external  jugular  are  (i)  the  temporo- 
maxillary,  (2)  the  posterior  auricular,  (3)  the  posterior  external  jugular,  (4)  the 
suprascapular ,  and  (5)  the  anterior  jugular  vein.  It  may  also  receive  the  occipital 
vein  (page  859). 

i.  The  Temporo-Maxillary  Vein. — The  temporo-maxillary  vein  (v,  facialis 
posterior)  (Fig.  753)  is  formed  in  the  substance  of  the  parotid  gland  by  the  union  of  the 
temporal  and  internal  maxillary  veins.  It  passes  directly  downward,  and  at  about  the 
angle  of  the  jaw  unites  with  the  posterior  auricular  vein  to  form  the  external  jugular. 

The  temporal  vein  accompanies  the  temporal  artery  and  is  formed  just  above 
the  zygoma  by  the  union  of  the  superficial  and  middle  temporal  veins.  The  super- 
ficial temporal  vein  (v.  temporalis  superficialis)  (Fig.  759)  is  formed  by  the 
union  of  an  anterior  and  a  posterior  branch,  which  take  their  origin  in  a  plexus 
covering  the  greater  portion  of  the  skull-cap  and  communicate  anteriorly  with 
branches  of  the  frontal  vein  and  posteriorly  with  the  posterior  auricular  and  occipital 
veins.  The  middle  temporal  (v.  temporalis  media)  arises  from  a  plexus  which 
lies  upon  the  outer  surface  of  the  temporal  muscle,  beneath  the  temporal  fascia  and 
above  the  zygoma.  Branches  of  the  plexus  pierce  the  temporal  fascia  near  the 
external  angle  of  the  eye  and  communicate  with  branches  of  the  facial  and  lachrymal 
nerves,  while  other  branches  pass  deeply  into  the  substance  of  the  temporal  muscle 
and  anastomose  with  the  deep  temporal  veins.  The  middle  temporal,  from  its  origin 
in  the  plexus,  passes  backward  parallel  with  the  upper  border  of  the  zygoma, 
perforates  the  temporal  fascia,  and  joins  with  the  superficial  temporal  vein. 

Tributaries. — The  temporal  vein  receives  the  following  tributaries,  (a)  The  anterior 
auricular  veins  (vv.  auriculares  anteriores)  are  four  or  five  small  vessels  which  come  from  the 
anterior  surface  of  the  pinna.  (6)  The  posterior  parotid  veins  (vv.  parotideae  posteriores),  small 
branches  which  drain  the  parotid  gland,  communicating  with  the  anterior  parotid  branches  of 
the  facial,  (c)  The  articular  veins  (vv.  articulares  mandibulae),  several  in  number,  arise  in  a  rich 
plexus  which  surrounds  the  synovial  membrane  of  the  temporo-mandibular  articulation. 
This  plexus  receives  tympanic  branches  (vv.  tympanicae),  which  accompany  the  tympanic 
artery  through  the  Glaserian  fissure,  and  communicates  anteriorly  with  the  pterygoid  plexus. 
(d)  The  transverse  facial  vein  (v.  transversa  faciei)  which  accompanies  the  artery  of  the 
same  name. 

The  internal  maxillary  vein  (v.  maxillaris  interna)  (Fig.  760)  appears 
sometimes  as  a  distinct  vessel  accompanying  the  internal  maxillary  artery  and 
receiving  as  tributaries  veins  corresponding  to  the  arterial  branches.  In  other  cases 
it  is  represented  by  a  plexus  of  veins,  frequently  exceedingly  dense,  occupying  the 
pterygoid  fossa  and  communicating  anteriorly  with  the  facial  vein  and  posteriorly 
with  the  temporo-maxillary.  This  pterygoid  plexus  (plexus  pterygoideus)  (Fig. 
760)  is  embedded  in  the  adipose  tissue  which  occupies  the  pterygoid  fossa  and 
consists  of  two  portions,  one  situated  upon  the  outer  surface  of  the  external 
pterygoid  muscle  and  the  other  between  the  two  pterygoids,  this  latter  plexus 
being  somewhat  more  extensive  than  the  other,  with  which  it  is  united  by  branches 
passing  through,  above,  and  beneath  the  external  pterygoid  muscle.  It  is  also 
continued  forward  as  a  fine  plexus  surrounding  the  infra-orbital  nerve,  and  that 
portion  which  rests  upon  the  tuberosity  of  the  maxilla  is  occasionally  more  or  less 
distinct  from  the  remainder,  and  has  been  termed  the  plexus  ahcolaris. 

The  pterygoid  plexus  communicates  with  the  facial  vein  through  the  deep 
facial  or  anterior  internal  maxillary  vein,  with  the  pharyngeal  plexus,  and  with  the 
articular  plexus  of  the  temporo-mandibular  articulation.  It  further  receives  the 
emissary  veins  from  the  cavernous  plexus  which  traverse  the  foramen  ovale,  the  fora- 
men of  Vesalius,  and  the  foramen  lacerum  medium,  and  also  a  branch  from  the 
inferior  ophthalmic  vein  which  passes  through  the  spheno-maxillary  fissure. 

Tributaries. — The  tributaries  of  the  internal  maxillary  vein  or  the  pterygoid  plexus  may  be 
described  as  follows. 

(a)  The  spheno-palatine  vein  has  its  origin  in  the  rich  venous  plexus  which  underlies  tin- 
mucous  membrane  of  the  nasal  cavity  and  with  which  the  ethmoidal  veins  also  communicate. 
It  traverses  the  spheno-palatine  foramen  with  the  artery  of  the  same  name,  and  is  joined  by  the 
Vidian,  ptetygo-palatine,  and  superior  palatine  reins,  all  small  vessels  whose  origin  is  indicated 


THE   SUPERIOR    CAVAL  SYSTEM. 


883 


by  their  names.     It  then  passes  between  the  two  heads  of  the  external  pterygoid  muscle  and 
opens  into  the  pterygoid  plexus  or  into  the  internal  maxillary  vein. 

(d)  The  superior  dental  veins  open  into  the  infra-orbital  and  alveolar  portions  of  the  plexus. 

(c)  Muscular  veins  from  the  masseter,  buccal,  and  pterygoid  muscles. 

(d)  The  deep  temporal  veins  (vv.  temporales  profundae)  descend  from  the  substance  of  the 
temporal  muscle,  where  they  anastomose  with  the  superficial  temporals,  between  the  muscle 
and  the  bone. 

(e)  The  middle  meningeal  veins  (vv.  meningeae  mediae)  accompany  the  main  stem  and 
branches  of  the  middle  meningeal  artery  as  venae  comites  and  return  the  blood  from  the  dura  mater 
lining  the  sides  and  vertex  of  the  cranium.     Lying  in  the  substance  of  the  dura  mater,  these  veins 


FIG.  760. 


Temporal  fascia 


Supraorbital  vein 


Temporal  muscle  — 

Superficial 

temporal  vein^ 


temporal  vei 

Middle 

meningeal  veir. 

1'l'per  |>,irt  of 
pterygoid  plexu: 

Internal 

maxillary  vein 

Temporal  vein 


Pterygoid  plexus' 

Internal  pterygoid  muscle 
Temporo-maxillary  vein 
Posterior  auricular  vein 

Posterior  trunk  of 

teinporo-maxillary  vein 
Anterior  trunk  of 

temporo-maxillary  vein 

Sterno-cleido-mastoid  muscl 

External  jugular  vein 
Internal  carotid  artery 


Internal  jugular  vei 


Frontal  veins 


Angnlar  vein 


Communicating 
branch  to 
ophthalmic 
vein 


One  of  deep 

temporal  veins 

External 

pterygoid  muscle 

Buccal  vein 

Deep  facial  vein 
Inferior  dental  vein 


Facial  vein 
Submental  vein 
iubmaxillary  gland 


Common  facial  vein 

ommunicating  branch  to 

anterior  jugular  vein 
oimiiuu  carotid  anery 


Veins  of  head ;   part  of  mandible  and  associated  muscles  have  been  removed 
to  expose  pterygoid  plexus.      . 

resemble  the  sinuses  of  the  dura  in  their  structure,  and  they  communicate  with  the  blood-lakes  of 
the  dura,  with  the  superior  longitudinal,  spheno-parietal  and  petro-squamosal  sinuses,  and  with 
the  superficial  Sylvian  vein.  They  open  below  into  the  deeper  portion  of  the  pterygoid  plexus. 
(f)  The  inferior  dental  vein  follows  the  course  of  the  inferior  dental  artery,  opening  above 
into  the  more  superficial  portion  of  the  plexus. 

2.  The  Posterior  Auricular  Vein. — The  posterior  auricular  vein  (v.  auricularis 
posterior)  arises  from  a  plexus  situated  over  the  mastoid  portion  of  the  temporal  bone 
and  communicating  with  branches  of  the  occipital  and  temporal  veins.  It  descends 


884  HUMAN   ANATOMY. 

behind  the  pinna,  occasionally  receiving  the  mastoid  emissary  vein,  and  terminates  near 
the  angle  of  the  jaw  by  uniting  with  the  temporo-maxillary  to  form  the  external  jugular. 

3.  The   Posterior  External  Jugular  Vein. — The  posterior  external  jugular 
vein  arises  from  the  integument  and  muscles  of  the  upper  and  back  part  of  the  neck, 
just  below  the  occipital  region,  and  descends  obliquely  behind  the  sterno-cleido- mastoid 
muscle  to  open  into  the  external  jugular  just  after  it  has  crossed  the  muscle. 

4.  The  Suprascapular  Vein. — The  suprascapular  vein  (v.  transversa  scapulae) 
is  really  a  double  vein,  being  represented  by  two  vessels  provided  with  valves  which 
accompany  the   suprascapular   artery    as    its  venae    comites.      They  arise  upon  the 
upper  part  of  the  dorsal  surface  of  the  scapula,  pass  over  the  transverse  ligament  of 
that  bone,  and  are  continued  inward,  parallel  with  the  clavicle  and  behind  it,  to  open 
into  the  external  jugular  near  its  termination  or  else  directly  into  the  subclavian. 
Just  before  their  termination  the  two  venae  comites  unite  to  a  single  stem. 

The  suprascapular  vein  is  usually  joined  either  at  or  near  its  termination  by  the 
transverse  cervical  veins  which  form  the  venae  comites  of  the  transversalis  colli  artery. 
These  veins  may  also  open,  however,  directly  into  the  subclavian. 

5.  The  Anterior  Jugular  Vein. — The  anterior  jugular  vein  (v.  jugularis 
anterior)  (Fig.  753)  arises  beneath  the  chin,  upon  the  mylo-hyoid  muscle,  by  branches 
which  come  from  the  integument  and  superficial  muscles  of  that  region,  communicating 
with  the  submental  branches  of  the  facial.  The  vein  passes  almost  vertically  down  the 
neck,  resting  upon  the  sterno-hyoid  muscle  a  short  distance  lateral  from  the  median  line, 
until  it  meets  the  anterior  (inner)  border  of  the  sterno-cleido-mastoid  near  its  sternal 
attachment.  There  it  makes  an  abrupt  bend,  passing  almost  horizontally  outward 
beneath  the  muscle  to  open  into  the  external  jugular  immediately  above  its  termination. 

The  anterior  jugular  receives  a  communicating  branch,  occasionally  of  con- 
siderable size,  from  the  facial  subcutaneous  veins,  and  tributaries  from  the  median 
region  of  the  neck  also  open  into  it ;  it  may  also  receive  small  branches  from  the  larynx 
and  thyroid  gland. 

It  contains  no  valves.  At  its  origin  it  is  superficial  to  the  deep  cervical  fascia.  Inn 
below  the  hyoid  bone  it  is  embedded  in  the  superficial  layer  of  that  fascia,  and  below 
lies  in  the  spatium  suprasternale  (space  of  Burns)  formed  by  the  splitting  of  the  fascia 
into  two  lamellae.  In  this  space  there  occurs  a  transverse  anastomosis  between  tin- 
two  veins,  forming  what  is  termed  the  arcus  venosus  juguli,  and  into  this  a  number 
of  small  branches  from  neighboring  structures  open.  The  horizontal  portion  of  the 
vein  eventually  pierces  the  posterior  layer  of  the  space  to  reach  the  external  jugular. 

Variations. — The  anterior  jugular  varies  considerably  in  size,  inversely  to  the  external 
jugular.  Occasionally  the  two  veins  of  opposite  sides  unite  throughout  the  vertical  portion  o; 
their  course  to  form  a  single  stem,  which  passes  down  the  median  line  of  the  neck  and  has  con- 
sequently been  termed  the  v,  mediana  colli. 

The  communicating  branch  from  the  facial  vein,  which  passes  downward  along  the  anterior 
border  of  the  sterno-cleido-mastoid,  is  sometimes  quite  large,  functioning  as  the  direct  continua- 
tion of  the  facial,  which  may  thus  pour  its  blood  mainly,  if  not  entirely,  into  the  anterior  jugular. 
Below,  while  the  anterior  jugular  usually  opens  into  the  external  jugular,  yet  it  sometimes  opens 
directly  into  the  subclavian,  and  occasionally  it  receives  near  its  termination  an  e.rft'rna/  thoracic 
TV/;/,  which  ascends  from  the  region  of  the  mammary  ghmd  over  the  clavicle,  posterior  to  the 
attachment  of  the  sterno-cleido-mastoid. 

THE  SUBCLAVIAN  VEIN. 

The  subclavian  vein  (v.  subclavia)  (Fig.  753)  is  the  terminal  portion  of  the  venous 
system  of  the  upper  extremity.  It  begins  at  the  anterior  border  of  the  first  rib,  where 
it  is  directly  continuous  with  the  axillary  vein,  and  passes  almost  horizontally  inward, 
anterior  to  the  scalenus  anticus  muscle  and  behind  the  clavicle,  to  the  junction 
of  that  bone  with  the  sternum,  where  it  unites  with  the  internal  jugular  to  form  the 
innominate  vein.  Its  course  is  very  similar  to  that  of  the  subclavian  artery,  but  it 
is  more  horizontal  and  somewhat  anterior  to  the  artery,  from  which  it  is  separated 
by  the  scalenus  anticus. 

It  is  provided  with  a  pair  of  valves  at  its  junction  with  the  internal  jugular  and  with 
another  pair  at  its  junction  with  the  axillary  vein.  In  the  first  portion  of  its  course  it 
is  in  relation  anteriorly  with  the  suhcluvins  muscle,  and  its  anterior  wall  is  united  to 


THE   SUPERIOR    CAVAL  SYSTEM.  885 

the  fascia  which  encloses  that  muscle  ;  near  its  termination  it  is  united  to  the 
middle  layer  of  the  deep  cervical  fascia,  behind  which  it  lies.  As  a  result  of  these 
connections  the  vein  does  not  collapse  when  empty,  and,  furthermore,  its  lumen  is 
enlarged  by  movements,  such  as  those  of  inspiration  or  the  raising  of  the  arm, 
which  affect  the  fascia. 

With  the  exception  of  the  external  jugular  and  occasionally  the  anterior 
ingular,  the  subclavian  vein  receives,  as  a  rule,  no  tributaries,  the  veins  which 
<-om-spond  to  the  branches  of  the  subclavian  artery  opening  either  into  the 
innominate  or  the  external  jugular.  Occasionally,  however,  it  receives  the  supra- 
-rapular  and  the  superior  intercostal  vein  (page  896),  and  the  acromial  thoracic 
vrin  may  open  into  it  near  its  beginning. 


Trapez                                                                  */£*•  Clavicular  portion  of 

^^^.iding                                            ~~~~~~-—Jrs  j^J^^Bi  ~\     sterno-mastoid,  cut  and 

'branches  of                                                                    ,    '        .            '•,  .                                                      turned  forward 

i  t-rvical  plexus  ~""'a=jgg-                             •              '•''  ;  ">                            I    1 

"^N^r                                 •               \  :X.         "4^^         '  ^~- External  jugular  vein 

Transverse  ^***\  ~ — ~jf  %     '        ^K\-        ^ 

cervical  vessels  •                             -X,,^..                                 '',-,,  '•,-••;            \ 

•  -.,    ,    '.  -,          v                              _____Anterior  scalene  muscle 
Omo-hyoid                                            '^V'         "•Hft^S'3 

muscle    -                                                                    \  -J&tor          ,                 'Phrenic  nerve 

Krachial  plexus  -  z5fe=t'*r   '  -  4P«f  '  r-^vlllternal  Jugular  vein 

Vsternal  portion  c 
sterno-mastoid 
— 4-Common  carotid 

I^^^^H^r^^L^^'"'" N          * 

Subclavian  artery 


Suprascapular        ^^^==-  '  ,J^V  ~H -Vsternal  portion  of 

•       .       :-  ••»     1      K       \      sterno-mastoid 

artery 

•Sterno-hyoid  muscle 


LFirst  rib 
Subclavian  vein" 


Clavicle 

Dissection  of  neck,  showing  relations  of  subclavian  vein  ;   clavicle  has  been 
disarticulated  from  sternum  and  drawn  down. 

Variations. — Occasionally  the  course  of  the  subclavian  vein  has  the  form  of  a  curve  which 
rises  above  the  level  of  the  clavicle  and  may  even  bring  the  vein  to  lie  above  the  artery.  It  may 
pass  with  the  artery  behind  the  scalenus  anticus,  the  artery  and  vein  may  exchange  places  with 
reference  to  that  muscle,  or  the  vein  may  divide  to  form  a  ring  encircling  the  muscle.  Rarely  it 
passes  between  the  subclavius  muscle  and  the  clavicle. 

Practical  Considerations. — The  subclavian  vein  occupies  the  acute  inner 
angle  between  the  clavicle  and  the  first  rib,  and  therefore — and  on  account  of  its 
slight  resistance — in  periosteal  or  osseous  growths  from  those  bones  is  especially 
likely  to  suffer  compression.  The  interposed  subclavius  muscle  usually  protects  it, 
as  it  does  the  artery  and  the  brachial  plexus,  from  injury  in  case  of  fracture  (page  259). 
The  vein  barely  rises  above  the  clavicle,  and  therefore  usually  escapes  in  stab- 
wounds  involving  the  supraclavicular  fossa,  while  the  artery  which  arches  an  inch 
to  an  inch  and  a  half  above  that  line  suffers  much  oftener. 

The  connection  of  the  anterior  wall  of  the  vein  with  the  fascia  of  the  subclavius 
muscle,  causing  an  increase  in  its  calibre  during  forced  inspiration  or  an  elevation  of 
the  arm  (vide  supra),  should  be  remembered  in  case  of  wound  of  this  vessel  during 


886  HUMAN   ANATOMY. 

operation,  as  elevation  of  the  clavicle  may  then  be  followed  by  the  entrance  of  air 
into  the  vein  (Henle).  Obstruction  of  the  subclavian  at  the  point  of  junction  with 
the  internal  jugular  results  in  compression  of  the  orifice  of  the  thoracic  duct. 

THE   VEINS   OF   THE   UPPER    EXTREMITY. 

Instead  of  following  distally  the  various  branches  which  return  the  blood  from 
the  upper  limb  it  will  be  more  convenient  to  begin  with  the  peripheral  branches  and 
trace  the  vessels  proximally  towards  the  subclavian. 

The  veins  of  the  upper  extremity  may  be  divided  into  a  superficial  and  a  deep 
set.  The  latter  follow  in  general  the  course  of  the  arteries,  of  which  they  are,  as  a 
rule,  the  venae  comites.  They  anastomose  frequently  with  the  superficial  veins  and 
are  more  richly  supplied  with  valves  than  are  the  latter. 

THE    DEEP  VEINS. 
THE  DEEP  VEINS  OF  THE  HAND. 

The  deep  veins  of  the  hand  are  all  relatively  small  and  are  of  less  importance 
than  the  superficial  ones  in  returning  the  blood.  Each  of  the  palmar  arterial 
arches  is  accompanied  by  venae  comites,  and  into  those  of  the  superficial  arch  (arcus 
volaris  venosus  superficialis)  the  superficial  digital  veins  (vv.  digitales  volares  com- 
munes) open,  while  those  of  the  deep  arch  (arcus  volaris  venosus  profundus)  receive 
the  veins  (vv.  metacarpeae  volares)  which  accompany  the  aa.  princeps  pollicis,  radialis 
indicis,  and  interossei  palmares. 

Upon  the  dorsum  of  the  hand  even  more  than  on  its  volar  surface  the  chief 
part  is  played  by  the  superficial  veins.  Three  or  four  pairs  of  dorsal  interosseous 
veins  occur,  however,  accompanying  the  corresponding  arteries  and  opening  event- 
ually partly  into  the  radial  veins  and  partly,  through  the  veins  corresponding  to  the 
posterior  carpal  net-work,  into  the  superficial  veins  of  the  dorsum  of  the  wrist  (rete 
venosura  dorsale  manus).  As  in  the  case  of  the  arteries,  the  deep  veins  of  the  dorsal 
and  volar  surfaces  of  the  hand  are  connected  by  perforating  veins,  and  both  make 
numerous  connections  with  the  superficial  veins. 

THE  DEEP  VEINS  OF  THE  FOREARM. 

The  deep  veins  of  the  forearm  are  the  venae  comites  which  accompany  the  radial 
and  ulnar  arteries  and  their  branches.  The  radial  veins  (vv.  radiales)  are  the 
upward  continuation  of  the  veins  of  the  deep  palmar  arch  and  are  relatively  slender. 
The  ulnar  veins  (vv.  ulnares)  are  larger  and  are  formed  by  the  union  of  the  ulnar 
ends  of  the  venae  comites  of  both  the  superficial  and  deep  palmar  arches.  Usually 
they  have  a  large  communication  from  the  superficial  veins  of  the  dorsum  of  the  hand, 
and  receive  near  the  elbow  the  veins  which  accompany  the  interosseous  artery  and 
its  branches,  and  also  a  strong  communicating  branch,  the  deep  median  vein,  from 
the  superficial  median  (page  890).  Both  the  ulnar  and  radial  veins  are  well  supplied 
with  valves,  and  they  unite  at  the  elbow  to  form  the  brachial  veins. 

THE  BRACHIAL  VEINS. 

The  brachial  veins  (vv.  brachiales)  (Fig.  762)  are  the  companion  veins  of  the 
brachial  artery  and  receive  tributaries  corresponding  to  the  branches  of  the  artery. 
They  are  formed  at  about  the  elbow-joint  by  the  union  of  the  radial  and  ulnar  veins, 
and  extend  upward,  one  on  either  side  of  the  brachial  artery,  to  the  lower  border  of  the 
pectoralis  major  muscle,  at  about  which  level  they  unite  to  form  a  single  trunk,  termed 
the  axillary  vein. 

As  is  usual  with  venae  comites,  the  two  brachial  veins  are  united  by  numerous 
anastomoses  and  occasionally  unite  through  portions  of  their  course,  especially  above,  to 
form  a  single  trunk.  At  the  elbow  one  of  the  veins  frequently  lies  in  front  of  the  artery 
and  sometimes  the  two  veins  pursue  a  spiral  course  around  it.  In  addition  to  the 
tributaries  which  accompany  the  branches  of  the  brachial  artery,  the  brachial  veins,  <>i 
rather  the  inner  one  of  the  two,  receive  near  their  termination  the  basilic  vein  (page  890). 


VEINS   OF   THE   UPPER    EXTREMITY. 


887 


THE  AXILLARY  VEIN. 


The  axillary  vein  (v. 
axillaris)  (Fig.  762)  is 
formed  by  the  union  of 
the  two  brachial  veins, 
usually  at  about  the  lower 
border  of  the  pectoralis 
major.  It  lies  along  the 
inner  side  of  the  axillary 
artery,  and  at  the  lower 
border  of  the  first  rib 
passes  directly  into  the 
subclavian  vein.  In  the 
lower  part  of  its  course  it  is 
separated  from  the  artery 
by  the  ulnar  nerve  and  the 
inner  head  of  the  median  ; 
above,  it  is  more  nearly  in 
contact  with  it. 

The  axillary  vein 
possesses  a  pair  of  valves, 
usually  situated  at  the 
level  of  the  lower  border  of 
the  subscapularis  muscle. 
Its  walls  are  intimately 
connected  with  the  fascia 
of  the  axillary  space,  so 
that,  as  in  the  case  of  the 
subclavian,  its  lumen 
remains  patent  even  when 
empty  of  blood,  and  con- 
sequently air  may  possibly 
enter  in  cases  where  the 
vein  is  wounded. 

Tributaries . — 
These  correspond  in 
general  with  the  branches 
of  the  artery,  except  that 
the  axillary  vein  receives 
the  cephalic,  which  is  un- 
represented by  an  artery, 
and,  furthermore,  the 
acromial  thoracic,  which 
corresponds  to  the  artery 
of  the  same  name,  instead 
of  opening  into  the  axil- 
lary, connects  with  the 
cephalic.  Of  especial 
importance  among  the 
tributaries  is  the  long 
thoracic  vein  (v.  thorac- 
alis  lateralis)  which  brings 
to  the  axillary  the  blood 
from  the  lateral  walls  of 
the  thorax.  Its  branches 
of  origin  are  the 


FIG.  762. 


Costo-coracoid 

ligament 


Pectoralis  minor 


Subscapular  veil 


'eres  major 
Posterior  circumflex  vein 

.Venae  comites  of  brachial  artery- 


Median  cephalic  vein 
Superficial  radial  vei: 


Inner  vena  comes  or 
radial  artery. 


Superficial  veins  of  anterior  surface  of  rig;ht  forearm  and 
axillary  vein  and  its  tributaries. 


comites  of  the  branches  of  the  thoracic  arteries,  and  they  return  the  blood  from  the 


888  HUMAN    ANATOMY. 

pectoral  and  serratus  magnus  muscles  and  in  part  from  the  intercostals.  They  are 
abundantly  supplied  with  valves,  and  unite  to  a  single  stem  which  presents  variations 
in  its  connections  with  the  axillary  vein  similar  to  those  described  for  the  corresponding 
artery.  By  means  of  the  costo-axillary  veins  ( vv.  costo-axillares),  which  pass  from 
the  middle  portions  of  the  upper  six  or  seven  intercostal  spaces,  it  forms  anastomoses 
with  the  intercostal  veins  which  open  into  the  azygos  system. 

These  costo-axillary  veins  open  either  directly  into  the  long  thoracic  or  into 
the  thoraco-epigastric  vein  (v.  thoraco-epigastrica),  a  more  or  less  definite  stem 
which  extends  upward  along  the  lateral  walls  of  the  thorax,  subcutaneously,  to  open 
into  the  long  thoracic  near  its  termination.  It  receives  numerous  tributaries  from  the 
rich  subcutaneous  venous  net-work  which  occurs  upon  the  anterior  and  lateral 
walls  of  the  thorax  (vv.  cutaneae  pectoris),  and  communicates  directly  below  with  epi- 
gastric branches  from  the  femoral  vein,  thus  forming  an  important  communication 
between  the  superior  and  inferior  caval  systems.  It  also  receives  the  veins  coming 
from  the  region  of  the  mammary  gland,  where  the  pectoral  cutaneous  veins  form  a 
net-work  surrounding  the  nipple,  the  plexus  venosus  mammillae.  The  deeper 
veins  of  the  gland  open  in  part  directly  into  the  long  thoracic,  whence  this  lias 
been  termed  the  external  mammary  vein,  and  partly  into  the  internal  mammary 
by  branches  which  accompany  the  perforating  branches  of  the  internal  mammary 
artery  (page  860). 

Practical  Considerations. — When  the  axillary  vein  is  formed  by  the  junc- 
tion of  the  two  brachial  veins  with  the  basilic  vein,  the  union  occurs  usually  at  the 
inferior  border  of  the  subscapularis  muscle.  The  vein  is  then  somewhat  shorter 
than  the  artery.  Occasionally  the  coalescence  of  these  tributaries  does  not  take 
place  until  a  level  just  beneath  the  lower  border  of  the  clavicle  has  been  reached. 
When  this  is  the  case,  operations  in  the  axilla  will  involve  the  ligation  of  many  com- 
municating transverse  veins  crossing  the  artery  to  join  the  venae  comites  lying  upon 
either  side  of  it. 

Phlebitis  of  the  veins  of  the  upper  extremity  is'  but  seldom  transmitted  to  the 
axillary  vein,  rarely  to  the  subclavian,  and  never  to  the  internal  jugular  or  innomi- 
nate (Allen).  This  immunity  is  supposed  to  be  due  to  disproportionately  greater 
size  of  a  main  venous  trunk  as  compared  with  its  tributaries  ;  any  of  the  radicles  of 
the  veins  of  the  hand,  forearm,  and  arm — whose  calibres  are  nearly  equal — readily 
transmitting  infection.  Phlebitis  of  the  axillary  vein  may,  through  the  costo-axillary 
branches  of  the  long  thoracic  vein,  extend  to  within  the  thorax  and  result  in  a  septic 
pleurisy. 

Accidental  wounds  of  the  axillary  vein — especially  of  its  upper  portion — are 
dangerous  on  account  of  its  size,  its  nearness  to  the  thorax — so  that  it  markedly 
shows  the  respiratory  wave — and  its'  attachment  to  the  costo-coracoid  membrane, 
preventing  its  collapse,  favoring  hemorrhage,  or,  when  it  is  empty,  permitting  the 
entrance  of  air.  It  lies  within  and  a  little  below  the  artery,  which  it  overlaps, 
particularly  towards  its  upper  and  lower  portions,  and  when  it  is  distended  during 
expiration.  As  it  is  straighter  than  the  artery,  the  curve  of  the  latter  carries  it  a  little 
away  from  the  vein  at  the  middle  portion.  Abduction  of  the  arm  brings  the  vein  to 
a  higher  level  and  often  almost  in  front  of  the  artery  so  as  partly  to  hide  it.  It  will 
therefore  be  found  with  this  relationship  in  many  operations  upon  the  axilla,  and  it  is 
on  account  of  it — i.e. ,  its  more  superficial  position — and  of  its  larger  size  that  the  vein  is 
more  frequently  wounded  than  is  the  artery.  On  the  other  hand,  the  axillary  artery 
is  oftener  ruptured,  as  in  the  manipulations  for  the  reduction  of  old  luxations  of  the 
shoulder,  probably,  as  such  luxations  are  more  frequent  in  old  persons,  on  account 
of  the  greater  loss  of  elasticity  of  its  thicker  walls,  and  possibly  on  account  of  greater 
traction  upon  it  by  reason  of  its  deeper  and  more  external  position  (page  769). 

The  close  relation  of  the  vein  to  the  deep  chain  of  axillary  glands  makes  it  the 
chief  source  of  danger  in  operations  for  the  removal  of  the  breast  and  cleaning  out 
the  axilla  in  cases  of  mammary  cancer,  especially  if  the  axillary  nodes  are  already 
notably  involved.  It  is  well,  therefore,  to  expose  the  vein  at  an  early  stage  of  the 
operation.  If  the  walls  have  been  invaded  by  the  disease,  or  if  extirpation  of  the 
cancerous  mass  is  impossible  without  resection  of  the  vein,  the  latter  operation  may 


VEINS   OF   THE   UPPER   EXTREMITY. 


FIG.  763. 


Olecranon 


External  condyle 


Radial  vein 


be  performed.  The  resulting  swelling  and  oedema  of  the  upper  limb  are  minimized 
by  the  consecutive  enlargement  of  the  cephalic  vein.  Such  swelling  and  cedema  are 
common  symptoms  of  pressure  upon  the  axillary  vein  by  cancerous  lymph-nodes  in 
the  later  stages  of  mammary  cancer  (page  770).  Suture  of  the  wall  of  the  vein  in 
cases  of  accidental  and  of  operative  wound  has  been  successfully  performed. 

THE   SUPERFICIAL  VEINS. 
THE  SUPERFICIAL  VEINS  OF  THE  HAND. 

The  veins  upon  the  dorsal  surface  (Fig.  763)  form  the  principal  superficial 
channels  for  the  return  of  blood  from  the  hand.  They  begin  in  a  plexus  upon  the 
dorsum  of  the  first  phalanges,  surrounding 
the  nail,  and  are  continued  over  the  suc- 
ceeding phalanges  as  a  coarser  plexus  in 
which  longitudinal  trunks  (vv.  digitales 
dorsales  propriae)  can  be  more  or  less 
distinctly  perceived.  At  about  the  middle 
of  the  dorsum  of  the  proximal  phalanges 
transverse  arches  (arcus  venosi  digitales), 
one  for  each  digit,  connect  the  various 
dorsal  digital  veins  ;  each  arch  is  concave 
proximally,  and  at  either  end  unites  with 
the  extremities  of  the  neighboring  arches 
to  form  four  dorsal  metacarpal  veins 
;  vv  metacarpeae  dorsales)  which  pass 
upward  along  the  lines  of  the  intermeta- 
carpal  spaces.  Just  before  joining  with 
its  neighbors  each  digital  arch  receives 
intercapitular  veins  (vv.  intercapitu- 
lares)  which  ascend  in  the  web  of  the 
fingers  from  the  volar  surface  and  assist  in 
the  passage  of  the  blood  of  the  superficial 
volar  veins  into  those  of  the  dorsal  surface. 

The  four  dorsal  metacarpal  veins  are 
abundantly  connected  by  anastomosing 
branches  which  pass  obliquely  from  one 
vein  to  the  other,  a  net- work  (rete  venosum 
dorsale  raanus)  with  elongated  meshes 
being  thus  formed.  The  veins  of  the  first 
and  fourth  intermetacarpal  spaces,  as  a 
rule,  however,  retain  a  greater  amount  of 
individuality  than  the  other  two,  and  have 
consequently  received  special  names,  that 
of  the  first  interspace  being  sometimes 
termed  the  vena  cephalica  pollicis, 
while  that  of  the  fourth  interspace  is  the 
vena  salvatella.  The  dorsal  net-work 
is  drained  by  two  veins  which  pass  up  the 
fore'arm,  the  cephalic  and  basilic  veins. 

The  superficial  veins  of  the  volar 
surface  of  the  hand  are  small  and  for  the 
most  part  open  into  the  dorsal  veins. 
They  arise  as  a  plexus  in  the  balls  of  the 
fingers  and  pass  along  the  volar  surfaces 

i-     ..  |  •          i  •    11  •.     j-  Superficial  veins  of  right  hand  and 

Of  the  digits  as  a  pleXUS  in  which  longltlldl-  forearm  ;  posterior  surface. 

nal  trunks  (vv.  digitales  volares  propriae) 

can  be  distinguished.  From  the  plexus  of  each  finger  branches  wind  around  the  sides  of 
the  digits  to  open  into  the  dorsal  digital  veins,  and  at  the  roots  of  the  fingers  important 
connections  in  a  similar  direction  are  made  by  the  intercapitular  veins  (see  above). 


890 


HUMAN   ANATOMY. 


The  superficial  veins  of  the  palm  of  the  hand  are  situated  superficially  to  the 
palmar  aponeurosis.  They  are  for  the  most  part  small,  and  form  a  net-work  which 
is  open  over  the  central  part  of  the  palm,  but  much  closer  over  the  thenar  and 
hypothenar  eminences.  These  lateral  portions  communicate  with  the  dorsal  net-work 
as  well  as  the  net-work  of  the  anterior  surface  of  the  forearm,  into  which  the  central 
portion  opens. 

THE  BASILIC  VEIN. 

The  basilic  vein  (v.  basilica)  (Fig.  762)  takes  its  origin  from  the  ulnar  side  of 
the  dorsal  net- work  of  the  hand,  and  is  sometimes  described  as  the  direct  continuation 
of  the  dorsal  metacarpal  vein  of  the  fourth  interspace.  It  passes  obliquely  upward  and 
inward,  winding  around  the  border  of  the  hand  towards  the  anterior  surface  of  the  fore- 
arm, up  which  it  ascends.  Beyond  the  bend  of  the  elbow  it  continues  its  way  upward 
along  the  inner  border  of  the  biceps  muscle  as  far  as  the  upper  third  of  the  brachium, 
at  which  level  it  pierces  the  fascia  of  the  arm,  and  after  a  usually  short  subfascial 
course  terminates  by  opening  into  the  internal  brachial  vein. 

The  basilic  is  the  largest  of  all  the  superficial  veins  of  the  arm,  and  is  provided 
with  from  ten  to  fifteen  pairs  of  valves.  It  receives  tributaries  from  the  superficial 
plexus  of  the  thenar  eminence  and  from  the  anterior  and  posterior  surfaces  of  the 
forearm.  Near  the  elbow  it  receives  from  the  cephalic  vein  the  median  vein,  and 
also  communicates  with  the  cephalic  higher  up  by  branches  which  pass  across  the 
biceps  muscle,  and  with  the  brachial  veins  by  small  branches  which  pierce  the  brachial 
fascia. 

Variations. — The  basilic  is  little  subject  to  variation  except  in  regard  to  its  termination, 
which  is  frequently  in  the  axillary  and  sometimes  in  the  subclavian  ;  in  both  these  cases  the  sub- 
fascial portion  of  its  course  is  considerably  longer  than  usual.  Occasionally  it  is  accompanied 
throughout  its  course  by  an  accessory  basilic. 

The  portion  of  the  vein  extending  from  its  origin  to  the  bend  of  the  elbow  is  frequently 
spoken  of  as  the  superficial  ulnar  vein,  the  term  basilic  being  limited  to  the  brachial  portion  of 
the  vein  as  described  above. 

THE  CEPHALIC  VEIN. 

The  cephalic  vein  (v.  cephalica)  (Fig.  762)  takes  its  origin  from  the  radial  portion 
of  the  dorsal  net- work  of  the  hand,  and  especially  from  the  dorsal  metacarpal  vein 
of  the  first  interspace.  It  passes  upward,  inclining  forward  over  the  surface  of  the 
brachio-radialis  muscle,  and  so  reaches  the  anterior  surface  of  the  forearm.  Arrived 
at  the  bend  of  the  elbow,  it  ascends  along  the  groove  which  marks  the  outer  border  of 
the  biceps  muscle  and  then  in  the  groove  between  the  deltoid  and  the  pectoralis  major, 
and  at  the  upper  border  of  the  latter  muscle  it  passes  between  it  and  the  clavicle,  per- 
forates the  costo-coracoid  membrane,  and,  crossing  in  front  of  the  axillary  artery, 
empties  into  the  axillary  vein. 

It  is  provided  with  from  twelve  to  fifteen  pairs  of  valves,  of  which  from  four  to 
seven  occur  in  its  antibrachial  portion,  seven  in  its  brachial  portion,  and  one  at  its 
union  with  the  axillary. 

Tributaries. — The  cephalic  vein  receives  numerous  branches  from  the  super- 
ficial net-work  of  the  posterior  surface  of  the  forearm  and,  indeed,  plays  a  much 
more  important  part  in  the  drainage  of  this  region  than  does  the  antibrachial  portion 
of  the  basilic.  Quite  frequently  it  is  accompanied  in  its  course  up  the  forearm  by  an 
accessory  cephalic  vein  (v.  cephalica  accessoria),  which  arises  in  the  posterior  super- 
ficial net- work  and  opens  into  the  main  cephalic  vein  at  the  bend  of  the  elbow.  It 
also  receives  branches  from  the  superficial  net-work  of  the  anterior  surface  of  the 
forearm  and,  a  short  distance  below  the  bend  of  the  elbow,  gives  off  a  strong  branch, 
the  median  vein  (v.  mediana  cuhiti),  which  passes  obliquely  upward  and  inward  to 
open  into  the  basilic,  giving  off  in  its  course  a  communicating  branch  to  one  or  other 
of  the  deep  veins  of  the  forearm. 

In  its  brachial  portion  it  is  connected  with  the  basilic  by  branches  which  pass 
across  the  biceps  muscle,  and  just  before  opening  into  the  axillary  it  receives  the 
acromial  thoracic  vein  (v.  thoracoacromialis),  which  corresponds  to  the  artery  of 
the  same  name. 


VEINS  'OF   THE   UPPER   EXTREMITY.  891 

Variations. — Unlike  the  basilic,  the  cephalic  vein  frequently  presents  variations  which  affect 
principally  its  brachial  portion.  One  of  the  most  important  of  these  is  the  complete  absence  of 
this  portion  of  the  vein,  the  antibrachial  portion  emptying  its  blood  into  the  basilic  by  means 
of  the  median  vein.  In  other  cases  it  is  only  the  uppermost  part  of  the  brachial  portion  that  is 
lacking,  the  lower  part  in  such  cases  either  making  connection  with  the  brachial  veins  or  else 
conveying  its  blood  downward  to  the  median  vein,  by  which  it  passes  to  the  basilic. 

Another  interesting  anomaly  consists  in  the  occurrence  of  a  branch  which  is  given  off  just 
as  the  vein  dips  downward  to  pierce  the  costo-coracoid  membrane.  It  is  termed  the  jugulo- 
cephalic  vein,  and  passes  up  over  the  clavicle  to  open  above  into  the  external  jugular  near  its 
communication  with  the  subclavian. 

These  variations  find  an  explanation  in  the  changes  undergone  by  the  superficial  veins  of 
the  arm  during  their  development,  both  the  absence  of  the  brachial  portion  of  the  vein  and  the 
occurrence  of  a  jugulo-cephalic  being  the  persistence  of  conditions  normally  passed  through  in 
development.  It  would  seem  that  three,  or  perhaps  better  four,  stages  are  to  be  recognized  in 
the  development  of  the  superficial  veins  of  the  arm.  In  the  first  stage  the  basilic  vein  forms  the 
only  great  superficial  trunk,  extending  up  the  inner  side  of  the  arm  from  the  wrist  to  the  axilla  and 
opening  into  the  axillary  vein  above.  Later,  however,  this  condition  is  modified  by  the  de- 
velopment of  the  antibrachial  portion  of  the  cephalic,  which  increases  in  size  at  the  expense  of 
the  antibrachial  portion  of  the  basilic  until  it  becomes  the  most  important  vein  of  the  forearm. 
At  the  bend  of  the  elbow  this  vein  receives  a  short  transverse  branch  formed  by  the  union  of  an 
ascending  and  descending  limb,  and  then  bends  obliquely  inward  to  join  the  brachial  portion  of 
the  basilic.  Higher  up  in  the  groove  between  the  pectoralis  major  and  deltoid  muscles  is  a 
small  deltoid  vein,  which  is  unconnected  with  the  veins  already  described.  Such  a  stage  as  this 
gives  a  clue  to  the  variations  in  which  the  brachial  portion  of  the  cephalic  is  either  absent  or 
only  partially  developed.  The  ascending  limb  of  the  transverse  branch  of  the  elbow,  and  this 
branch  itself,  together  represent  what  will  later  be  the  lower  part  of  the  brachial  portion  of  the 
cephalic,  while  the  deltoid  vein  represents  its  upper  part  ;  the  descending  limb  of  the  trans- 
verse branch  represents  the  accessory  cephalic  vein,  and  the  oblique  portion  of  the  antibrachial 
cephalic,  between  the  transverse  branch  and  the  basilic,  represents  the  median  vein.  Indeed, 
relics  of  this  condition  are  to  be  seen  even  in  the  normal  arrangement,  for  while  the  antibrachial 
portion  of  the  cephalic  usually  exceeds  in  size  the  corresponding  portion  of  the  basilic,  the  con- 
ditions are  reversed  in  the  brachial  portions  of  the  two  veins,  the  antibrachial  portion  of  the 
cephalic  and  the  brachial  portion  of  the  basilic  (connected  by  the  median)  forming  the  main 
channel  for  the  return  of  blood  from  the  superficial  portions  of  the  arm. 

A  third  stage  is  brought  about  by  the  completion  of  the  cephalic  vein  by  the  union  of  the 
ascending  limb  of  the  transverse  branch  with  the  deltoid,  the  vein  so  formed  being  continued  up 
over  the  clavicle  to  open  into  the  external  jugular  ;  and,  finally,  the  fourth  or  adult  stage  is  pro- 
duced from  this  by  the  degeneration  of  that  portion  of  the  cephalic  which  corresponds  to  what 
is  termed  the  jugulo-cephalic. 

The  antibrachial  portion  of  the  cephalic  is  frequently  termed  the  superficial  radial  vein,  the 
accessory  cephalic  being  then  the  accessory  superficial  radial.  Furthermore,  it  is  to  be  noted 
that  quite  frequently  one  or  more  strong  longitudinal  stems  are  developed  in  the  superficial  net- 
work of  the  anterior  surface  of  the  forearm,  and  to  one  of  these  the  term  median  vein  has  been 
applied.  This  condition  has  generally  been  accepted  by  the  English  and  French  anatomists  as 
typical,  and  their  description  of  the  origin  of  the  basilic  and  cephalic  veins  is  as  follows.  The 
median  vein  when  it  reaches  the  bend  of  the  elbow  divides  into  two  divergent  stems  (Fig.  764) 
which  are  termed  the  median  basilic  and  median  cephalic  veins.  The  median  basilic,  which 
corresponds  with  what  has  been  termed  above  the  median  vein,  unites  with  the  superficial  ulnar 
to  form  the  basilic  vein,  while  the  median  cephalic,  which  represents  the  foetal  transverse  branch 
of  the  elbow,  similarly  unites  with  the  superficial  radial  to  form  the  cephalic.  Such  an  arrange- 
ment is  undoubtedly  of  frequent  occurrence  ;  but  since  the  median  vein,  as  understood  in  such  a 
description,  is  so  variable  and  so  manifestly  a  secondary  formation,  and  since  the  arrangement 
taken  above  as  typical  is  not  only  also  of  frequent  occurrence,  but  furthermore  follows  more 
closely  the  embryonic  relations  of  the  various  vessels,  it  has  been  given  the  preference. 

PRACTICAL  CONSIDERATIONS. — THE  VEINS  OF  THE  UPPER  EXTREMITY. 

The  Deep  Veins. — The  venae  comites  of  the  radial  artery  have  been  said, 
when  distended,  to  alter,  by  pressure,  the  character  of  the  pulse.  The  numerous 
short  anastomotic  branches  which  unite  the  venae  comites  of  the  brachial  artery 
cross  in  front  of  that  vessel  and  may  have  to  be  tied  as  a  preliminary  to  ligation 
of  the  artery. 

The  Superficial  Veins. —  The  Hand. — The  veins  of  the  dorsal  surface  are 
subcutaneous,  prominent,  and,  in  order  that  the  circulation  may  not  be  inter- 
rupted during  prehension,  are  much  larger  than  those  of  the  palmar  surface.  Like 
the  other  superficial  veins  of  the  upper  extremity,  they  are  scantily  supplied  with 
valves  and  are  therefore  easily  distended  by  the  effects  of  gravity  or  by  any  constric- 
tion of  the  limb  above. 

The  Forearm. — The  large  size  of  the  superficial  veins  in  the  forearm^  their  sub- 
cutaneous position,  the  small  number  of  valves  they  contain,  and  the  fact  that  most 


892 


HUMAN    ANATOMY. 


FIG.  764. 


Cephalic  vein 


Musculo- 

cutaneous  ner 


Tendon  of  biceps 


Median 

cephalic  vein 


Superficial 

r.nii.xl  vein 


Basilic  vein 
Part  of  |>osterior 
Brachial  artery 
Median  nerve 
Brachial  vein 


ilnar 

vein 


Internal 

cutaneous  nerve 


—  Posterior  ulnar 


• Median  basilic 


il  it.il  fascia 


of  the  venous  blood  of  the  limb  is  returned  by  them,  make  circular  constriction  of 
the  arm  or  forearm — as  in  cases  of  poorly  applied  splints — especially  dangerous. 
Swelling  and  oedema  distal  to  the  constriction  are  sure  to  result  speedily  and,  if  the 
pressure  is  continued,  to  be  followed  by  ulceration  or  gangrene. 

On  the  extensor  surface  of  the  forearm  the  superficial  veins  are  less  conspicuous 
than  on  the  flexor,  and  between  the  olecranon  and  the  level  of  the  pronator  teres 
insertion  are  almost  completely  lacking.  This  is  the  surface  most  exposed  to  trau- 
matism,  and  along  it  main  arteries  and  nerve-trunks  are  also  absent. 

The  Elbow. — The  vein  given  off  by  the  median  vein  when  it  reaches  the  bend  of 
the  elbow,  and  known  by  the  English  and  French  anatomists  (vide  supra)  as  the 
median  basilic,  is  of  the  greatest  practical  importance  among  the  veins  at  the  bend  of 
the  elbow.  The  M-like  figure  made  by  the  superficial  ulnar  and  superficial  radial  in 
uniting  respectively  with  the  median  basilic  and  median  cephalic  to  form  the  basilic 

and  cephalic  veins  is  by 
no  means  constant,  but  is 
present  in  only  from  one-half 
to  two-thirds  of  all  cases 
(Treves).  Even,  however, 
if  the  basilic  and  cephalic 
veins  do  not  originate  in 
this  way,  the  median  vein 
(if  from  the  cephalic),  the 
median  basilic  (if  from  the 
median),  will  be  found  begin- 
ning a  short  distance  below 
the  elbow,  to  the  outer  side 
of  the  biceps  tendons,  and 
crossing  the  tendon,  the 
brachial  artery,  the  brachial 
veins,  and  the  median  nerve, 
from  all  of  which  it  is 
separated  by  the  bicipitul 
aponeurosis,  the  inner  of  the 
two  lower  biceps  tendons  of 
the  old  anatomists.  The 
vein  may,  however,  run 
either  more  transversely  or 
more  vertically  and  so  have 
different  relations  to  the 
artery  and  nerve  ;  it  is 
usually  the  largest  of  the 
anticubital  veins,  but  may 
be  smaller  than  the  median 
cephalic,  which  is  commonly  the  second  in  size,  followed  by  the  median,  ulnar,  and 
radial,  in  the  order  mentioned. 

For  reasons  explained  above,  abnormalities  and  even  absence  of  the  cephalic 
and  radial  veins  are  more  frequent  than  those  of  the  basilic. 

For  this  reason,  and  on  account  of  its  large  size,  the  greater  quantity  of  blood 
it  carries — as  it  is  above  the  entrance  of  the  deep  median  vein,  and  thus  receives 
blood  from  the  deep  veins  of  the  forearm — its  superficial  position,  its  prominence, 
and  its  relative  fixation  to  the  bicipital  fascia  by  cellular  tissue,  the  median  basilic  is 
the  vein  selected  for  either  intravenous  transfusion  or  phlebotomy.  In  opening  the 
vein,  certain  dangers  are  to  be  avoided  :  ( i )  Wound  of  the  brachial  artery,  if  it 
results  in  a  direct  communication  between  the  vein  and  artery,  will  cause  an  aneu- 
rismal  varix  ;  if  it  results  in  the  formation  of  an  intervening  sac  in  the  perivaseular 
connective  tissue,  through  which  the  blood  from  the  artery  flows  before  entering  the 
vein,  it  will  cause  a  varicose  aneurism.  (2)  A  septic  wound  may  cause  a  lymphan- 
gitis from  jnfection  of  the  lymph-vessels  accompanying  the  vein,  and  may  result  in 
axilary  abscess.  (3)  I'nnecessary  damage  to  the  filaments  of  the  internal  cuta- 


Superficial  dissection  of  region  of  elbow,  showing 
relation  of  veins  and  nerves. 


THE   AZYGOS   SYSTEM.  893 

neous  nerve  (lying  in  front  of  the  vein)  may  give  rise  to  chronic  traumatic  neuritis 
(Tillaux),  while  injury  of  the  cutaneous  branches  of  the  musculo-cutaneous  nerve 
(in  closer  relation  to  the  median  cephalic  vein),  or  entanglement  of  those  branches 
in  the  cicatrix,  may,  by  reflex  irritation  acting  through  the  motor  fibres,  cause  tonic 
spasm  of  the  biceps  and  brachialis  anticus,  "  bent  arm"  (Hilton). 

The  Arm.  — The  cephalic  vein  and  its  anomalies  should  be  studied  in  relation 
to  ligation  of  the  axillary  artery  (q.v.\  the  first  portion  of  which  it  crosses  (sepa- 
rated from  it  by  the  clavi-pectoral  fascia),  on  its  way  to  reach  the  axillary  vein. 

It  may  be  remembered  that  the  basilic  vein  pierces  the  brachial  aponeurosis  a 
little  below  the  middle  of  the  arm  and  ceases  to  be  superficial. 

THE   AZYGOS   SYSTEM. 

The  principal  trunks  of  the  azygos  system  of  veins  are  persistent  portions  of 
the  embryonic  cardinal  veins  which  drained  the  thoracic  and  abdominal  walls,  as  well 
as  the  paired  viscera  of  the  abdomen,  and  united  above  with  the  jugular  trunks  to 
form  the  Cuvierian  ducts  (page  926).  On  the  development  of  the  inferior  vena 
cava  their  importance  diminished  greatly,  and  in  the  adult  they  serve  principally  to 
collect  the  blood  from  the  intercostal  spaces.  The  reduction  of  the  lower  part  of  the 
left  jugular  vein  (page  927)  brought  about  further  modifications  of  the  left  cardinal, 
its  original  connection  with  the  left  jugular  being  dissolved  and  a  new  one  formed 
with  the  right  cardinal.  This  latter  vein  forms  what  is  termed  the  azygos  vein  of  the 
adult,  while  what  persists  of  the  left  one  is  known  as  the  hemiazygos  and  accessory 
hemiazygos. 

THE  AZYGOS  VEIN. 

The  azygos  vein  (v.  azygos)  (Fig.  765),  sometimes  called  the  azygos  major, 
begins  immediately  below  the  diaphragm,  where  it  is  directly  continuous  with  the  right 
ascending  lumbar  vein,  formed  by  the  anastomosis  of  branches  of  the  lumbar  veins  and 
connecting  below  with  the  ilio-lumbar  or  common  iliac.  The  azygos  vein  passes  up- 
ward into  the  thoracic  cavity,  traversing  the  diaphragm  either  by  the  cleft  between  the 
medial  and  intermediate  portions  of  the  right  crus  or  else  by  the  aortic  opening.  It 
then  continues  its  way  upward  in  the  posterior  mediastinum,  resting  upon  the  ante- 
rior surfaces  of  the  bodies  of  the  thoracic  vertebrae  a  little  to  the  right  of  the  middle 
line,  passing  over  the  right  intercostal  arteries  and  having  the  thoracic  aorta  and  the 
thoracic  duct  immediately  to  the  left  of  it.  When  it  reaches  the  level  of  the  fourth 
vertebra  it  bends  forward  and  somewhat  to  the  right,  and,  curving  over  the  right 
bronchus  and  the  right  pulmonary  artery,  it  descends  slightly  to  open  into  the  pos- 
terior surface  of  the  superior  vena  cava,  just  above  the  level  at  which  that  vessel 
becomes  invested  by  the  pericardium,  The  terminal  portion  of  the  vein  from  the 
fourth  vertebra  onward  is  sometimes  termed  the  azygos  arch. 

The  azygos  vein  in  a  considerable  proportion  (22  per  cent.,  Gruber)  of  cases  is 
entirely  destitute  of  valves,  and  when  present  they  rarely  exceed  four  in  number,  are, 
apparently,  never  exactly  paired,  and  are  usually  insufficient.  They  occur  more  fre- 
quently in  the  arch  than  in  the  vertical  portion  of  the  vein. 

Tributaries. — The  azygos  vein  at  its  origin  has  usually  some  small  connections 
with  the  vena  cava  inferior,  but  its  principal  tributaries  are  the  right  intercostal  veins. 
In  addition  it  receives  branches  from  the  oesophagus  (vv.  oesophageae),  from  the  are- 
olar  tissue  and  lymph-nodes  of  the  posterior  mediastinum  and  from  a  plexus  which 
surrounds  the  thoracic  aorta,  from  the  posterior  surface  of  the  pericardium,  and  from 
the  substance  of  the  right  lung,  these  last  bronchial  veins  (vv.  bronchiales  posted- 
ores  )  issuing  from  the  hilum  of  the  lung  and  opening  into  the  azygos  at  the  beginning 
of  its  arch.  They  anastomose  with  the  pulmonary  veins  both  along  the  course  of  the 
smaller  bronchi  and  also  outside  the  lung,  and  they  receive  some  smaller  bronchial 
veins  (vv.  bronchiales  anteriores)  situated  upon  the  anterior  surface  of  the  bronchi. 
The  azygos  vein  furthermore  receives  the  hemiazygos  vein  ;  this  and  the  intercostal 
veins  will  be  described  below. 

Variations. — Since  the  cardinal  veins,  from  which  the  azygos  and  hemiazygos  are  formed, 
are  primarily  symmetrical,  it  may  happen,  just  as  was  the  case  with  the  aortic  arches,  that  it  is 
the  left  one  that  is  more  fully  retained  and  therefore  becomes  the  azygos  vein,  the  right  becoming 


894 


HUMAN   ANATOMY. 


FIG.  765. 


Internal  jugular  vein 
Right  vertebral  vein 

Right  subclavian  vein 

Right  innominate  vein 

Right  inferior  thyroid  vein 

Right  internal  mammary  vein 

Superior  vena  cava 

Right  bronchial  vein 
Right  superior  intercostal  vein 


Vena  azygos 


Hepatic  veins 
Inferior  vena  cava 


Suprarenal  vein 


Renal  vein 

Vena  azygos 

Right  spermatic  vein 

Quadratus  lumborum 
Branch  of  communi- 
cation to  vena  azygos 
Ascending  lumbar  vein 


Right  common  Iliac  vein 
Ilio-Iumbar  vein 


Thoracic  duct 

Left  vertebral  vein 

Left  inferior  thyroid  vein 


Left  innominate  vein 

Left  internal  mammary  veil 

Left  superior  intercostal  veil 


fena  hemiazygos  accessoria 


Left  common  iliac  vein 

Ilio-Iumbar  vein 
Internal  iliac  vein 

External  iliac  vein 


Portion  of  posterior  body-wall,  showing  azyjjos  veins,  superior  and  inferior 
vena  cava,  and  their  tributaries. 


THE  AZYGOS   SYSTEM.  895 

the  hemiazygos.  Occasionally,  instead  of  opening  into  the  superior  vena  cava,  the  azygos 
terminates  in  the  right  subclavian,  the  right  innominate  vein,  or  even  opens  directly  into  the  right 
auricle.  A  further  anomaly  is  sometimes  presented  by  the  azygos,  in  its  upper  part,  being  situated 
at  the  bottom  of  a  deep  groove  upon  the  surface  of  the  right  lung,  which  thus  comes  to  have  an 
accessory  lobe  known  as  the  azygos  lobe  or  lobule. 

Practical  Considerations. — The  azygos  veins  are  the  connecting  links  be- 
tween the  cardinal  and  the  inferior  caval  systems.  In  cases  of  obstruction  of  the 
inferior  cava  they  are  able  to  carry  on  the  collateral  circulation  very  effectively, 
through  their  communication  with  the  common  iliac,  renal,  lumbar,  and  ilio-lumbar 
veins.  Growths  in  the  posterior  mediastinum,  enlarged  bronchial  glands,  or  aortic 
aneurisms  may  so  compress  these  veins  as  to  cause  oedema  of  the  chest  wall  by 
interference  with  the  intercostal  veins  which  empty  into  them. 

THE  HEMIAZYGOS  VEIN. 

The  hemiazygos  vein  (v.  hemiazygos)  (Fig.  765),  also  called  the  azygos  minor 
inferior,  is  the  counterpart,  on  the  left  side  of  the  body,  of  the  lower  part  of  the  azygos. 
It  arises  just  below  the  diaphragm  as  the  continuation  upward  of  the  left  ascending 
lumbar  vein  (page  901),  also  receiving  usually  a  communicating  branch  from  the  left 
renal  vein.  It  passes  upward  into  the  thorax  between  the  medial  and  intermediate 
portions  of  the  left  crus  of  the  diaphragm,  and  then  ascends  upon  the  left  side  of  the 
bodies  of  the  lower  thoracic  vertebrae,  passing  in  front  of  the  lower  left  intercostal 
arteries  and  having  the  thoracic  aorta  to  its  right.  At  about  the  level  of  the  eighth 
or  ninth  vertebra  it  bends  towards  the  right  and,  passing  behind  the  aorta  and  the 
cesophagus,  opens  into  the  azygos  vein. 

In  its  course  it  receives  the  lower  five  or  four  left  intercostal  veins,  which  con- 
stitute its  principal  tributaries,  and  in  some  cases  it  also  receives  the  accessory  hemi- 
azygos vein.  It  also  receives  some  branches  from  the  cesophagus  and  from  the 
posterior  mediastinum. 

THE  ACCESSORY  HEMIAZYGOS  VEIN. 

The  accessory  hemiazygos  vein  (v.  hemiazygos  accessoria)  (Fig.  765),  also  called 
the  azygos  minor  superior,  is  a  descending  stem  which  lies  upon  the  left  side  of  the 
bodies  of  the  upper  thoracic  vertebrae  and  receives  the  upper  left  intercostal  veins.  It 
begins  above  at  about  the  second  intercostal  space  by  the  union  of  a  small  vein,  which 
connects  it  with  the  left  innominate,  with  the  left  superior  intercostal.  When  it  has 
reached  the  level  of  the  seventh  or  eighth  thoracic  vertebra  it  bends  to  the  right  and, 
passing  beneath  the  aorta  and  the  cesophagus,  opens  into  the  azygos  vein.  Quite 
frequently  it  opens  below  into  the  hemiazygos  just  as  that  vein  bends  towards  the 
right,  and  even  when  it  has  an  independent  connection  with  the  azygos  it  may  be 
connected  with  the  hemiazygos  by  an  anastomotic  branch. 

It  receives  the  upper  seven  or  eight  left  intercostal  veins  and  in  addition  the  left 
posterior  bronchial  vein. 

Variations. — The  hemiazygos  and  accessory  hemiazygos  veins  together  represent  the  left 
cardinal  vein  of  the  embryo  which  primarily  opened  into  the  left  Cuvierian  duct.  With  the  dis- 
appearance of  the  lower  part  of  the  left  jugular  vein  the  relations  of  the  left  cardinal  change, 
the  vein  making  a  connection  across  the  middle  line  with  the  right  cardinal  (the  azygos).  Indi- 
cations of  the  original  condition  are  occasionally  seen  in  a  fibrous  cord  which  connects  the  left 
superior  intercostal  vein,  which  is  strictly  a  portion  of  the  accessory  hemiazygos,  with  the 
oblique  vein  of  the  left  auricle  (page  856). 

As  already  pointed  out  in  speaking  of  variations  of  the  azygos,  cases  have  been  observed 
in  which  the  hemiazygos  and  accessory  hemiazygos  occur  upon  the  right  side  of  the  body,  being 
formed  from  the  right  cardinal,  while  the  left  cardinal  gives  rise  to  the  azygos.  And  more 
rarely  the  two  veins  have  been  observed  fused  to  form  a  single  trunk  lying  upon  the  anterior 
surface  of  the  thoracic  vertebrae  and  receiving  all  the  intercostal  arteries. 

A  considerable  amount  of  variation  exists  in  the  number  of  intercostal  veins  received  by  the 
hemiazygos  and  the  accessory  hemiazygos  respectively.  Usually  they  divide  between  them  the 
intercostals,  since  they  either  unite  or  cross  the  median  line  to  the  azygos  over  successive 
vertebrae.  The  hemiazygos  has  been  observed  to  cross  the  vertebral  column  anywhere  from  the 
sixth  to  the  eleventh  vertebra,  and  the  accessory  may  descend  as  far  as  the  tenth  or  may  cross  at 
the  third.  In  cases  where  it  makes  its  crossing  high  up  a  number  of  intercostal  spaces  may  inter- 


896  HUMAN   ANATOMY. 

vene  between  it  and  the  hemiazygos,  and  the  veins  of  these  then  open  directly  into  the  azygos 
passing,  each  independently,  across  the  vertebral  column  beneath  the  aorta  and  oesophagus! 
Absence  of  the  accessory  hemiazygos  has  been  observed,  the  upper  six  or  eight  iiiVr- 
costal  veins  uniting  to  form  a  common  ascending  trunk  which  opens  into  the  left  innominate 
In  all  probability,  however,  this  common  ascending  stem  is  properly  to  be  regarded  as  the 
accessory  hemiazygos,  whose  normal  connection  with  the  innominate  has  increased  in  size  while 
its  connection  with  the  azygos  or  hemiazygos  has  either  degenerated  or  failed  to  form. 

THE  INTERCOSTAL  VEINS. 

The  intercostal  veins  (vv.  intercostales)  (Fig.  765),  sometimes  designated  as 
posterior  intercostal  as  distinguished  from  the  anterior  intercostal  tributaries  of  the 
internal  mammary  vein,  accompany  the  intercostal  arteries  and  are  twelve  in  number 
on  each  side,  one  occurring  in  each  intercostal  space  and  one,  sometimes  termed  the 
subcostal  vein,  running  along  the  lower  border  of  each  twelfth  rib.  They  lie  along 
the  upper  border  of  the  spaces  to  which  they  belong,  in  a  groove  on  the  lower  border 
of  the  rib,  and  are  above  the  corresponding  arteries.  The  upper  nine  or  ten  veins 
open  anteriorly  into  the  internal  mammary  or  musculo-phrenic  veins,  but  the  lower 
three  or  two,  which  are  somewhat  larger  than  the  rest,  have  no  anterior  communica- 
tion and  receive  tributaries  from  the  abdominal  muscles  and  the  diaphragm.  In  the 
middle  portion  of  their  course  the  upper  six  or  seven  veins  give  off  branches,  the 
costo-axillary  veins,  which  ascend  towards  the  axilla  and  open  into  either  the  long 
thoracic  or  the  thoraco-epigastric  vein  and  so  into  the  axillary,  and,  as  it  approaches 
the  vertebral  column  behind,  each  vein  receives  a  dorsal  branch  (ramus  dorsalis)  which 
accompanies  the  spinal  branch  of  the  intercostal  artery  and  returns  the  blood  from  the 
skin  and  muscles  of  the  back  and  also  from  the  spinal  column  and  its  contents,  this 
latter  drainage  being  by  means  of  a  spinal  branch  (ramus  spinalis)  which  connects 
with  the  intervertebral  veins  (page  898). 

Their  posterior  termination  varies  considerably  in  different  individuals,  especially 
as  regards  the  upper  members  of  the  series.  It  may  be  supposed  that  primarily  ail 
the  intercostal  veins  of  the  right  side  opened  into  the  azygos  vein  and  all  of  those  of 
the  left  side  into  the  hemiazygos  or  accessory  hemiazygos,  and  this  condition  holds 
in  the  adult  with  all  but  the  upper  two  or  three  veins.  On  the  right  side  the  vein 
of  the  first  space — that  of  the  second  space  sometimes  uniting  with  it — frequently 
accompanies  the  superior  intercostal  artery  as  a  right  superior  intercostal  vein, 
and  opens  above  into  either  the  right  innominate  or  one  of  its  branches,  usually  the 
vertebral;  on  the  left  side  the  vein  of  the  first  space  opens  into  the  left  innominate  vein, 
being  sometimes  termed  the  accessory  left  superior  intercostal  vein,  while  the 
veins  of  the  second,  third,  and  sometimes  the  fourth  spaces  unite  to  a  common  trunk 
which  crosses  the  arch  of  the  aorta  and  opens  into  the  left  innominate  vein,  forming 
the  left  superior  intercostal  vein.  It  is  to  be  noted  that  this  last  is  connected 
with  the  accessory  hemiazygos  vein  and  really  represents,  in  part  at  least,  its  upper 
portion, — a  fact  which  is  all  the  more  evident  from  its  frequent  connection  by  means 
of  a  fibrous  cord  with  the  oblique  vein  of  the  left  auricle  ;  and,  furthermore,  it  may 
also  be  pointed  out  that  the  veins  of  the  second,  third,  and  sometimes  the  fourth  spaces 
of  the  right  side  usually  unite  to  a  common  trunk  which  opens  into  the  azvi;<» 
vein. 

The  principal  tributaries  and  connections  of  the  intercostal  veins  have  already 
been  mentioned,  but  there  remain  to  be  described  the  interesting  arrangement  shown 
by  the  valves  in  those  veins  which  connect  anteriorly  with  the  internal  mammary  or 
musculo-phrenic  veins.  So  far  as  this  arrangement  is  concerned,  each  vein  may  he- 
regarded  as  consisting  of  three  portions  :  ( i )  an  anterior  portion,  in  which  the  con- 
cavities of  the  valves  look  towards  the  internal  mammary  or  musculo-phrenic  veins  ; 
(2)  a  posterior  portion,  in  which  the  valves  look  towards  the  azygos  or  hemiaxy^os 
veins  ;  and  (3)  an  intermediate  portion,  which  is  destitute  of  valves.  As  a  result  of 
this  arrangement  the  blood  of  the  anterior  portion  of  each  vein  must  pass  to  the  internal 
mammary  veins  (page  860),  that  of  the  posterior  portion  to  the  azygos  or  hemiax\  L;<  s, 
while  in  the  intermediate  portion  it  may  puss  in  either  direction.  Hut  it  is  with  this 
intermediate  portion  that  the  costo-axillary  veins  are  connected,  so  that  in  the  upper 
six  or  seven  veins,  in  addition  to  passing  partly  anteriorly  and  partly  posteriorly,  some 
of  the  blood  takes  an  ascending  direction  ;'iul  empties  into  the  axillary  vein. 


THE   AZYGOS    SYSTEM.  897 

In  the  two  or  three  lower  veins  there  is  no  such  double  flow,  the  valves  all 
looking  towards  the  azygos  veins.  Valves  occur  at  the  opening  of  practically  all  the 
intercostals  into  the  azygos  veins,  the  last  intercostal  forming  an  exception  to  this 
rule,  and,  furthermore,  the  valves  of  the  lower  veins  are  apt  to  be  insufficient. 

THE  SPINAL  VEINS. 

The  spinal  veins,  which  return  the  blood  from  the  vertebral  column  and  the 
adjacent  muscles  and  also  from  the  membranes  enclosing  the  spinal  cord,  present  in  a 
high  degree  the  plexiform  arrangement  which  is  characteristic  of  the  veins  as  com- 
pared with  the  arteries.  They  form  a  series  of  longitudinal  plexuses  which  extend 
practically  the  entire  length  of  the  spinal  column,  communicating  extensively  with  one 
another,  and  may  be  divided  primarily  into  those  which  lie  external  to  the  spinal 
canal  and  those  which  lie  within  the  canal. 

The  external  spinal  plexuses  (plexus  venosi  vertebrales  externi)  are  two  in 
number,  anterior  and  posterior.  The  anterior  external  plexus  (plexus  venosus 
vertebralis  anterior)  rests  upon  the  anterior  surfaces  of  the  bodies  of  the  vertebrae, 
and  presents  considerable  differences  in  the  amount  of  its  complexity  in  different 
portions  of  the  spinal  column.  In  the  thoracic  and  lumbar  regions  it  forms  a  net- 
work with  large  meshes,  in  the  sacral  region  it  is  represented  by  transverse  anasto- 
moses between  the  lateral  and  middle  sacral  veins,  and  in  the  cervical  region  it  reaches 
its  greatest  degree  of  complexity,  forming  a  close  net-work,  especially  dense  above 
and  resting  partly  upon  the  bodies  of  the  vertebrae  and  partly  upon  the  longus  colli 
muscles.  At  each  intervertebral  foramen  the  plexus  communicates  with  the  veins 
issuing  from  the  internal  spinal  plexuses  and  also  with  the  posterior  external  plexus, 
and  in  addition  sends  branches  to  the  vertebral  veins  in  the  cervical  region  and  to 
the  rami  spinales  of  the  intercostal  and  lumbar  veins  in  the  corresponding  regions. 

The  posterior  external  plexuses  (plexus  venosi  vertebrales  posteriores)  lie  partly 
upon  the  posterior  surfaces  of  the  laminae  of  the  vertebrae  and  the  ligamenta  subflava 
and  partly  between  the  deeper  dorsal  muscles.  As  in  the  case  of  the  anterior  plexus, 
they  are  more  complicated  in  the  cervical  than  in  the  thoracic  and  lumbar  regions. 
In  the  latter  their  meshes  are  somewhat  elongated  longitudinally,  and  they  communi- 
cate with  the  internal  plexuses  at  the  intervertebral  foramina  and  also  by  branches 
which  traverse  the  ligamenta  subflava,  and  they  have  further  communications  with 
the  anterior  external  plexus  and  with  the  spinal  rami  of  the  intercostal  and  lumbar 
veins.  In  the  cervical  region,  in  correspondence  with  the  greater  differentiation  of 
the  dorsal  musculature,  the  plexuses  become  divided  into  several  layers,  and  in  the 
region  between  the  occiput  and  the  axis  vertebra  their  deep  layers  form  an  especially 
dense  net-work,  the  suboccipital  plexus,  with  which  the  occipital,  vertebral,  deep 
cervical,  and  posterior  external  jugular  veins  communicate.  Throughout  its  course 
the  cervical  portion  of  the  plexus  communicates  with  the  internal  and  anterior  ex- 
ternal plexuses  and  also  with  the  vertebral  vein. 

The  internal  spinal  plexuses  (plexus  venosi  vertebrales  interni)  are  situated  in 
the  dura  mater  lining  the  spinal  canal  and  are  much  closer  than  the  external  plexuses. 
The  veins  which  form  them  have  a  general  longitudinal  direction  and  anastomose 
abundantly,  but  nevertheless  four  subordinate  longitudinal  lines  of  vessels  can  be 
recognized,  two  of  which  are  upon  the  anterior  wall  of  the  spinal  canal  and  two  upon 
the  posterior  wall. 

The  anterior  internal  plexuses  lie  one  on  each  side  of  the  median  line  on  the 
posterior  surfaces  of  the  bodies  of  the  vertebrae  and  the  intervertebral  disks,  from  the 
foramen  magnum  to  the  sacral  region.  They  are  composed  of  rather  large  veins, 
between  which  are  frequent  anastomoses,  and  transverse  connecting  vessels  run  across 
the  body  of  each  vertebra  between  the  two  plexuses,  passing  beneath  the  posterior 
common  vertebral  ligament.  Into  these  transverse  connections  open  the  basivertebral 
reins  (vv.  basi vertebrales)  which  return  the  blood  from  the  bodies  of  the  vertebrae, 
traversing  these  to  a  certain  extent  to  communicate  with  the  anterior  external  plexus. 
The  anterior  internal  plexuses  also  communicate  opposite  each  vertebra  with  the  pos- 
terior internal  plexuses,  rings  of  anastomosing  veins  thus  surrounding  the  spinal  canal 
opposite  each  vertebra  and  constituting  what  are  termed  the  retia  venosa  vertebrarum. 

57 


898  HUMAN    ANATOMY. 

The  posterior  internal  plexuses  are  situated  one  on  either  side  of  the  median  line 
on  the  anterior  surfaces  of  the  laminae  and  on  the  ligamenta  subflava,  through  which 
they  send  branches  to  communicate  with  the  posterior  external  plexus.  They  are 
connected  by  transverse  plexuses  which  complete  the  retia  venosa  vertebrarum,  and 
are  composed  of  smaller  vessels  than  the  anterior  plexuses,  and  the  net-work  which 
they  form  is  more  open. 

Laterally,  at  each  intervertebral  foramen  the  internal  plexuses  send  branches  out 
from  the  spinal  canal  along  the  nerve-trunks,  and  by  means  of  these  intervertebral 
veins  ( vv.  intervertebrales),  which  have  the  form  of  plexuses  at  their  origin  and  receive 
communicating  branches  from  the  external  vertebral  plexuses  and  from  the  veins  of  the 
spinal  cord,  the  internal  plexuses  pour  their  blood  into  the  vertebral,  intercostal,  lum- 
bar, and  lateral  sacral  veins,  the  connection  with  the  intercostals  being  through  their  rami 
spinales.  Above,  the  internal  plexuses  form  an  especially  rich  rete  or  plexus  around 
the  foramen  magnum  and  communicate  with  the  occipital,  marginal,  and  basilar  sinuses. 

Practical  Considerations. — The  posterior  external  spinal  plexuses,  by  means 
of  their  communication  through  the  intervertebral  foramina  and  the  ligamenta  sub- 
flava with  the  internal  plexuses,  may  convey  infection  from  without — septic  wounds 
of  the  back,  severe  bed-sores,  osteitis  of  the  vertebral  laminae — to  the  interior  of  the 
spinal  canal.  External  pachy meningitis  has  thus  originated.  In  operations  upon 
the  spine,  these  veins  bleed  so  freely  that  it  is  often  well  after  severing  them  upon 
one  side  to  control  them  by  packing  and  proceed  to  the  exposure  of  the  spine  on 
the  opposite  side,  repeating  the  packing  there.  The  internal  plexuses,  interposed 
between  the  theca  of  the  cord  and  the  interior  walls  of  the  vertebral  column,  may, 
as  a  result  of  trauma,  furnish  blood  enough  to  cause  compression  of  the  cord.  The 
symptoms  are  usually  relatively  slow  in  developing — as  compared  with  those  due  to 
injury  to  the  cord  itself  or  to  its  vessels — and  are  referable  mainly  to  the  lower  spinal 
segments,  the  blood  gravitating  to  that  portion  of  the  canal. 

Hemorrhage  may  occur  within  the  membranes  (haematorrhacis),  when  the 
blood  will  likewise  tend  to  gravitate  toward  the  lower  end  of  the  cord,  and,  unless 
in  large  amount,  may  cause  no  definitely  localizing  symptoms.  Bleeding  from  the 
venae  medulli  spinales  may  take  place  into  the  substance  of  the  cord  (haemato- 
myelia),  and  is  most  likely  to  occur  in  the  segments  from  the  fourth  cervical  to  tin 
first  dorsal  (Thorburn),  because  of  the  degree  of  motion  of  that  portion  of  the  spine, 
the  union  toward  its  base  of  a  fixed  and  a  movable  segment,  and  the  frequency  with 
which  forces  causing  excessive  flexion  or  over-extension  are  applied  to  the  head. 
If  the  lesion  causes  compression  only,  the  paralysis,  anaesthesia,  etc.,  will  be  only 
temporary.  If  it  is  associated  with  disorganization  of  the  cord,  they  will  be  permanent. 

THE  VEINS  OF  THE  SPINAL  CORD. 

The  veins  of  the  spinal  cord  (vv.  medulli  spinales)  occur  as  six  longitudinal  stems 
situated  upon  the  surface  of  the  cord  and  connected  by  a  fine  net-work  very  much  as 
are  the  arteries.  One  of  these  stems  traverses  the  entire  length  of  the  cord  along  tin- 
line  of  the  anterior  median  fissure,  and  has  on  either  side  of  it  another  stem  which 
lies  immediately  posterior  to  the  line  of  exit  of  the  anterior  nerve-roots.  These  three 
stems  together  form  the  anterior  medulli-spinal  veins  ( vv.  shinnies  externae 
anteriores).  The  posterior  veins  (vv.  spinales  extcrnae  posteriores )  have  a  similar 
arrangement,  one  lying  along  the  line  of  the  posterior  longitudinal  fissure  and  one 
posterior  to  each  of  the  lines  of  entrance  of  the  posterior  nerve-roots. 

All  these  stems,  together  with  the  plexus  which  connects  them,  lie  in  the  pia 
mater  and  receive  branches  (vv.  spinales  internae)  from  the  substance  of  the  cord. 
From  them  branches  pass  out  along  the  nerve-roots  to  join  the  intervertebral  veins, 
and  at  the  upper  extremity  of  the  cord  they  join  the  veins  of  the  medulla  oblongata. 

THE  INFERIOR  CAVAL  SYSTEM. 

The  inferior  caval  system  includes  all  the  veins  from  the  body- wall  below  the 
level  of  the  diaphragm  ;  those  from  the  abdominal  and  pelvic  cavities,  with  the 
exception  of  those  from  the  stomach,  intestines  (except  the  lower  part  of  the  rectum), 


THE   INFERIOR    CAVAL   SYSTEM. 


pancreas,  and  spleen  ;   and  those  from  the  lower  limb.      It  receives  its  name  from  its 
principal  vessel,  the  inferior  vena  cava,  which  conveys  its  blood  to  the  right  auricle. 

THE  INFERIOR  VENA  CAVA. 

The  inferior  or  ascending  vena  cava  (vena  cava  inferior)  (Figs.  765,  766)  is  formed 
by  the  union  of  the  two  common  iliac  veins  either  on  the  right  side  of  the  intervertebral 
disk  separating  the  fourth  and  fifth  lumbar  vertebras  or  on  the  right  side  of  the  fifth 
lumbar  vertebra.  From  this  point  it  ascends  directly  upward  to  the  level  of  the  first 


Hepatic  veins 


FIG.  766. 


Right  suprarenal  '.,.-. 
body  17 j 


Vena  cava-i 
Right  renal  vein 

Right  kidney \ 

Right  ureter 


Right  spermatic 
vein 

Right  spermati 
artery 


Vas  deferens  J 
Spermatic  cord  i-  S^ 


Cceliac  axis 

CEsophagus    /         ^Superior  mesenteric  artery 
Left  suprarenal 
body 


[  Left  renal  vein 


/-Left  kidney 
I — Left  renal  artery 


Inferior  mesen- 

teric  artery 
Left  ureter 

Quadratus 
lumborum 

Left  spermatic 
artery 

Common  iliac 
artery 

Common  iliac 
vein 

Psoas  magnus 


_Left  ureter, 
pelvic  portion 

i_ Rectum  (cut) 


4  Vas  deferens 
Bladder 


Inferior  vena  cava  and  iliac  veins. 

lumbar  vertebra  and  there  begins  to  bend  slightly  to  the  right  to  reach  the  fissure 

the  liver  which  separates  the  Spigelian  and  right  lobes.      Passing  upward  in  this 

issure,  it  reaches  the  diaphragm  and  perforates  the  left  lobe  of  the  centrum  tendineum 

that  structure,  so  entering  the  cavity  of  the  thorax,  then  bends  slightly  forward  and 

the  left,  and  opens  into  the  lower  and  back  part  of  the  right  auricle  of  the  heart. 

It  is  the  largest  vein  of  the  body,  measuring  at  its  entrance  into  the  auricle  about 

33  mm.  in  diameter.      It  increases  in  size  from  below  upward  with  the  accession  of  its 

various  tributaries,  somewhat  sudden  increases  succeeding  the  entrance  into  it  of  its 

largest  tributaries,  the  renal  and  hepatic  veins.      It  contains  no  valves,  unless  the 

Eustachian  valve  guarding  its  entrance  into  the  auricle  be  regarded  as  belonging  to  it. 


900  HUMAN   ANATOMY. 

Relations. — For  convenience  in  description  the  vena  cava  inferior  may  be 
regarded  as  consisting  of  an  abdominal  and  a  thoracic  portion.  The  former,  which 
constitutes  by  far  the  greater  part  of  its  length,  has  the  following  relations.  Poste- 
riorly it  rests  upon  the  right  side  of  the  lumbar  vertebrae,  upon  the  origins  of  the 
psoas  major  and  minor  muscles,  and  above  upon  the  right  crus  of  the  diaphragm  ; 
it  crosses  in  its  course  the  right  lumbar  and  right  renal  arteries.  Medially  it  is  in 
close  relation  with  the  abdominal  aorta  throughout  the  greater  portion  of  its  course, 
but  separates  from  it  slightly  above,  the  right  crus  of  the  diaphragm  intervening. 
Laterally  it  is  in  contact  with  the  psoas  major  muscle  below,  and  at  about  the  middle 
of  its  course  it  is  in  close  relation  with  the  inner  border  of  the  right  kidney.  Ante- 
riorly it  is  covered  at  its  origin  by  the  right  common  iliac  artery  and  in  the  lower 
part  of  its  course  by  peritoneum.  At  the  level  of  the  third  lumbar  vertebra  it  lies 
beneath  the  third  portion  of  the  duodenum,  and  immediately  above  that  beneath  the 
head  of  the  pancreas  and  the  main  stem  of  the  portal  vein,  which  crosses  it  obliquely. 
Finally,  it  lies  in  the  vena  caval  fissure  of  the  liver,  having  to  the  right  the  right 
lobe  and  to  the  left  the  Spigelian  lobe,  and  being  sometimes  completely  surrounded  by 
liver-tissue,  owing  to  a  thin  portion  of  it  bridging  over  the  fissure.  Throughout  this 
part  of  its  course  it  is  firmly  united  to  the  walls  of  the  fissure  by  fibrous  bands. 

In  its  thoracic  portion,  which,  is  quite  short,  measuring  not  more  than  3  cm.  in 
length,  it  is  in  relation  at  first  with  the  right  lung  and  pleura,  and  in  the  upper  part 
is  enclosed  for  about  1.2  cm.  in  the  pericardium. 

Variations. — The  development  of  the  inferior  vena  cava  (page  927)  shows  it  to  be  formed 
by  the  union  of  three  primarily  distinct  structures.  Its  upper  part,  between  the  entrance  of  tin- 
hepatic  veins  and  the  right  auricle,  is  the  upper  part  of  the  embryonic  ductus  venosus,  then  fol- 
lows a  considerable  portion  derived  from  the  right  subcardinal  vein,  and,  finally,  its  lower  part  is 
formed  from  the  right  cardinal  vein.  Of  these  embryonic  veins  the  ductus  venosus  is  unpaired, 
the  other  two  are  the  right  members  of  paired  veins,  whose  fellows  undergo  almost  complete 
degeneration. 

Anomalies  of  the  vena  cava,  which  are  not  uncommon,  are  for  the  most  part  explicable  as 
a  persistence  or  modification  of  the  embryonic  conditions.  Thus,  that  portion  of  the  vessel  which 
is  formed  from  the  right  subcardinal  and  right  cardinal  may  fail  to  develop,  in  which  case  what 
is  termed  a  persistence  of  the  cardinals  occurs.  Up  to  a  point  above  the  level  of  the  ren.1l  veins 
the  vena  cava  is  represented  by  two  parallel  trunks  lying  one  on  either  side  of  the  aorta,  the  one 
receiving  the  right  common  iliac  vein  and  the  other  the  left.  These  represent  the  abdominal 
portions  of  the  cardinal  veins  or,  in  the  majority  of  cases,  more  probably  the  subcardinals,  and  unite 
above  with  the  unpaired  ductus  venosus,  which  carries  their  blood  to  the  heart.  In  other  w<  >rds, 
such  cases  are,  as  a  rule,  to  be  regarded  as  a  similar  development  of  both  subcardinal  veins. 

Occasionally,  however,  the  development  of  the  right  subcardinal  to  form  the  vena  cava 
may  proceed  as  usual,  but  it  fails  to  make  a  connection  with  the  ductus  venosus,  one  of  its  con 
nections  with  the  right  cardinal  enlarging  so  that  this  vein  receives  the  caval  blood,  carries  it 
through  the  aortic  opening  of  the  diaphragm,  and.  as  the  a/ygos  vein,  empties  it  int.  >  the  superior 
vena  cava.  The  hepatic  veins  open  as  usual  into  the  ductus  venosus,  which  passes  to  the  righl 
auricle  in  the  normal  manner,  and  the  vena  cava  inferior  is  thus  represented  by  two  distinct  veins. 
the  upper  part  of  the  ductus  venosus.  which  in  such  cases  is  termed  the  common  hepatic  vein  (  r. 
hepatica  communis),  and  the  subcardinal  and  cardinal  portion. 

Another  variation  may  be  produced  by  a  reversal  of  the  roles  of  the  two  subcardinals  in 
forming  the  vena  cava,  the  left  being  the  one  which  develops,  while  the  right  degenerates. 
Such  a  condition  is  found  in  all  cases  of  situs  inversus  viscerum,  but  it  has  also  been  observed 
in  cases  in  which  there  was  otherwise  a  normal  arrangement  of  the  organs.  In  such  cases  the 
vena  cava  in  the  lower  part  of  its  course  lies  to  the  left  of  the  aorta  instead  of  to  the  right,  and  at 
the  level  of  the  renal  arteries  it  crosses  to  the  right  side  in  front  of  the  aorta,  its  further  course 
being  normal.  But  just  as  the  lower  part  of  the  inferior  vena  cava,  when  normally  formed  from 
the  right  subcardinal,  may  fail  to  unite  with  the  ductus  venosus  but  retain  its  primary  connection 
with  the  azygos,  so,  too,  when  formed  from  the  left  subcardinal,  it  may  retain  its  connection  with 
the  hemiazygos  and  drain  through  that  vessel  into  the  a/ygos  and  so  into  the  superior  vena  cava. 

These  various  cases  include  the  principal  variations  which  occur  in  connection  with  the 
vena  cava  inferior.  It  may  be  pointed  out  that  normally  connections  exist  between  tin-  ;I/\LM>S 
vein  and  the  vena  cava  below  the  diaphragm  ;  by  means  of  the  ascending  lumbar  veins,  and 
also  by  the  thoraco-epigastric  veins,  connection  is  established  between  tributaries  of  the  interior 
cava  and  the  external  iliac  veins  and  the  axillary  vein.  My  means  of  these  normally  subordinate 
channels  opportunity  is  afforded  for  the  maintenance  of  the  circulation  in  case  of  obliteration  of 
the  vena  cava. 

Practical  Considerations. — The  inferior  cava  may  be  ruptured  in  severe 
abdominal  injuries,  as  in  the  case  of  a  weight  falling  upon,  or  a  wagon  passing  over, 
the  belly.  The  site  of  rupture  is  most  often  in'  the  portion  lying  in  the  hepatic 


THE    INFERIOR   CAVAL   SYSTEM.  901 

fissure.  Its  relation  to  the  right  psoas  major  muscle  has  resulted,  in  cases  of  psoas 
abscess,  in  ulceration  and  opening  of  the  vein,  with  fatal  hemorrhage.  Its  relation 
to  the  inner  border  of  the  right  kidney  has  resulted  in  its  compression  by  a 
movable  kidney,  or  by  a  cancerous  growth  of  the  kidney,  causing  caval  thrombosis, 
a  condition  which  has  also  been  noted  in  connection  with  chronic  nephritis  and 
with  infarction  of  the  renal  parenchyma.  Its  relation  to  the  liver  results,  in 
some  cases  of  hepatic  enlargement,  in  compression  of  the  vena  cava  with  oedema 
of  the  lower  limbs,  and  other  symptoms  of  obstruction.  Its  close  proximity  to 
the  lower  end  of  the  bile-duct  necessitates  caution  in  cutting  operations  for  the 
removal  of  impacted  stones  from  the  duct  (choledochotomy)  (page  1732).  Enlarge- 
ment or  growth  involving  the  head  of  the  pancreas  may  compress  the  cava 
sufficiently  to  cause  obstructive  symptoms,  and  the  nearness  of  the  vein  constitutes 
one  of  the  very  serious  obstacles  to  removal  of  pancreatic  tumors.  In  ureterotomy 
or  other  operation  on  the  right  ureter,  the  close  relationship  of  the  vena  cava  at 
the  point  of  crossing  should  be  remembered.  Thrombosis  of  the  cava,  from 
whatever  cause,  though  it  may  extend  the  entire  length  of  the  vessel,  is  apt  to 
be  limited  to  a  portion  of  the  vessel,  as  that  between  the  renal  veins  and  the 
auricle,  or  that  extending  from  the  iliac  veins  to  the  renal  veins.  The  collateral 
circulation  after  occlusion  may  be  carried  on  through  the  saphenous,  superficial 
abdominal,  spermatic,  pudic,  and  deep  epigastric  veins,  and  the  obturator,  inferior 
mesenteric,  external  mammary,  and  azygos  veins. 

Tributaries. — In  addition  to  the  common  iliac  veins  by  whose  union  it  is 
formed,  the  vena  cava  inferior  receives  a  number  of  tributaries  from  the  abdominal 
walls  and  organs.  These  may  be  arranged  into  two  groups  according  as  they  drain 
t\\& parietes  of  the  abdomen  (radices  parietales)  or  its  viscera  (radices  viscerales).  Of 
the  former  there  are  :  (i)  the  inferior  phrenic  and  (2)  the  lumbar  veins,  and  of  the 
latter  (3)  the  hepatic,  (4)  the  renal,  (5)  the  suprarenal,  and  (6)  the  spermatic  or 
ovarian  veins. 

1.  The  Inferior  Phrenic  Vein. — The  inferior  phrenic  (v.  phrenica  inferior) 
•  is  a  paired  vein  which  corresponds  to  the  similarly  named  artery.      It  is  formed  by 

the  union  of  a  number  of  tributaries  which  ramify  upon  the  under  surface  of  the 
diaphragm,  and  ope'ns  into  the  vena  cava  just  before  it  passes  through  the  diaphragm. 
It  receives  tributaries  from  the  upper  portion  of  the  suprarenal  capsule,  and  the  left 
vein,  by  the  enlargement  of  an  anastomosis  of  its  suprarenal  tributaries  with  the 
suprarenal  vein,  may  open  through  the  latter  into  the  left  renal  vein.  The  right 
vein  occasionally  opens  into  the  right  hepatic  vein. 

2.  The  Lumbar  Veins. — The  lumbar  veins  (vv.  lumbales)  are  usually  four  in 
number  on  each  side,  and  accompany  the  corresponding  arteries,  lying  above  them. 
They  resemble  closely  in  their  relations  and  tributaries  the  intercostal  veins,  of  which 
they  are  serial  homologues.      Each  vein  arises  in  the  muscles  of  the  abdominal  wall 
and  passes  backward  and  inward  towards  the  vertebral  column,  passing  beneath  the 
psoas  muscle.     Shortly  before  reaching  the  vena  cava  it  receives  a  ram  us  dorsal  is. 
This  has  its  origin  in  the  dorsal  integument  and  muscles,  communicating  with  the 
posterior  external  spinal  plexus,  and  receives  a  ramus  spinalis  which  communicates 
with   one   of    the    lumbar    intervertebral    veins    and    so    with   the    internal    spinal 
plexuses.     The  veins  then  continue  their  course  towards  the  vena  cava,  those  of  the 
left  side  passing  beneath   the  abdominal  aorta,  and   they  open   into   the  posterior 
surface  of  the  vena  cava. 

As  it  passes  upon  the  lateral  surface  of  its  corresponding  lumbar  vertebra,  each 
of  the  three  lower  veins  is  connected  with  the  one  above  by  an  ascending  stem,  which 
also  places  the  lowest  vein  in  communication  with  the  ilio-lumbar  or  the  common  iliac 
vein,  while  from  the  uppermost  vein  it  is  continued  on  upward  to  join  with  the  azygos 
or  hemiazygos  as  the  case  may  be.  This  ascending  stem  is  the  ascending  lumbar 
vein  (v.  lumbalis  ascendens),  and  is  of  especial  interest  as  forming  an  important 
collateral  channel  between  the  inferior  and  superior  venae  cavae. 

Each  lumbar  vein  possesses  one  or  two  valves  in  its  course,  and  sometimes 
also  valves  at  its  entrance  into  the  vena  cava.  The  concavities  of  these  valves  are 
directed  towards  the  vena  cava,  but  the  valves  are  nearly  always  insufficient  and 


902  HUMAN   ANATOMY. 

consequently  will  not  prevent  a  flow  of  blood  from  the  vena  cava  outward  to  the 
ascending  lumbar  veins  in  cases  of  occlusion  of  the  upper  part  of  the  vena  cava. 

3.  The  Hepatic  Veins. — The  hepatic  veins  (vv.  hcpaticae)  (Fig.  765)  return 
the   blood  which    has   been   carried   to   the  liver   both   by   the  hepatic  artery  and 
by  the  portal  vein.       They  are  two  or  three  in  number,   and  are  formed   by   the 
union  of  the  intralobular  veins  of  the  liver  (page  920).      They  emerge  from  the 
substance  of   the  liver  at   the  upper  part  of   the  groove*  in   which   the   vena   cava 
lies,  and,  passing  obliquely  upward,  enter  that  vessel  at  an  angle  shortly  before  it 
passes  through  the  diaphragm. 

One  of  the  hepatic  veins  drains  the  substance  of  the  right  lobe  of  the  liver, 
the  other,  when  there  are  but  two,  the  remaining  lobes.  Quite  frequently  this 
second  or  left  vein  is  replaced  by  two  vessels,  one  of  which  drains  the  left 
lobe  alone,  while  the  other  drains  the  Spigelian  and  quadrate  lobes.  Usually, 
in  addition  to  these  principal  veins,  a  varying  number  of  small  hepatic  veins 
occur,  which  make  their  exit  from  the  liver-substance  on  the  walls  of  the  groove 
for  the  vena  cava  and  open  directly  into  that  vessel  without  joining  the  principal 
hepatic  veins. 

The  hepatic  veins  possess  no  valves  in  the  adult,  and  are  characterized  by  the 
thickness  of  their  walls,  which  are  provided  with  both  circular  and  longitudinal 
muscles. 

Variations. — Occasionally,  the  right  vein,  more  rarely  the  left,  perforates  the  diaphragm 
and  opens  either  into  the  thoracic  portion  of  the  inferior  vena  cava  or  else  directly  into  the  right 
auricle.  The  two  (or  three)  veins  sometimes  unite  to  a  single  trunk  before  joining  the  vena 
cava,  and  this  trunk  has  been  observed  to  penetrate  the  diaphragm  and  open  direct!)  into  the 
right  auricle  without  communicating  with  the  vena  cava. 

4.  The  Renal  Veins. — The  renal  veins  (vv.  renales)  (Fig.  766)  are  two  in 
number,  one  returning  the  blood  from  each  kidney.      Each  vein  is  formed  at  the 
hilum,  or  some  little  distance  from  it,  by  the  union  of  from  three  to  five  branches 
which  come  from  the  kidney  substance,  and  is  directed  medially  and  slightly  upward, 
lying  in  front  of  the  corresponding  artery.      On  account  of  the  position  of  the  vena 
cava  to  the  right  of  the  median  line,  the  left  vein  is  somewhat  longer  than  the  right, 
and  passes  in  front  of  the  abdominal  aorta,  just  below  the  origin  of  the  superior 
mesenteric  artery,  to  reach  its  point  of  entrance  into  the  vena  cava,  this  point  being 
usually  a  little  higher  than  that  of  the  right  vein. 

Tributaries. — In  addition  to  the  vessels  by  whose  union  it  is  formed,  each  renal  vein  receives 
(a)  an  inferior  suprarenal  vein  from  the  lower  part  of  the  suprarenal  capsule,  accompanying  tin 
corresponding  artery  ;  (b]  adipose  veins,  which  pass  transversely  across  both  surfaces  of  the 
kidney,  taking  their  origin  in  its  adipose  capsule  ;  (c)  a  ureteric  vein,  frequently  more  or  less 
plexiform  in  structure,  which  returns  the  blood  from  the  upper  part  of  the  ureter,  anastomosing 
below  with  the  ureteric  tributaries  of  the  spermatic  vein.  In  addition,  the  left  renal  vein  receives 
the  left  spermatic  (ovarian)  and  the  left  middle  suprarenal  veins,  both  of  which  will  be 
considered  with  their  fellows  of  the  opposite  side. 

The  adipose  veins  ramifying  in  the  kidney  fat  penetrate  the  renal  fascia  and  so  come 
into  connection  with  the  tributaries  of  the  lumbar  veins,  and  'they  also  send  branches  to  the 
spermatic  or  ovarian  veins.  A  more  important  communication  is,  however,  made  through 
a  vein  which  arises  from  the  lower  surface  of  each  renal  and  empties  on  the  right  side 
into  the  first  lumbar  vein,  while  on  the  left  side  it  bifurcates,  sending  one  branch  downward 
to  the  first  lumbar  and  the  other  upward  to  open  into  the  hemia/ygos.  Since  valves  occur 
hut  rarely  in  the  renal  vein,  and  its  tributaries  are  likewise  either  without  valves  or  with 
insufficient  ones,  the  circulation  of  the  kidney  may  be  maintained  by  means  of  these 
communications  of  the  renal  veins,  even  in  cases  of  obliteration  of  the  vena  cava  inferior  in 
its  upper  portion. 

Variations. — The  renal  veins  are  occasional  I  v  replaced  by  from  two  to  seven  \essels  which 
open  independently  into  the  vena  cava, — a  condition  which  probably  depends  upon  the  failure  of 
tin-  vessels  from  the  different  portions  of  the  kidneys  to  unite  to  a"  common  stem.  _  Accessory 
veins,  which  communicate  with  the  vena  cava  below  the  level  of  the  renals  or  even  with  the  com- 
mon iliac,  sometimes  occur,  but  more  rarely  than  the  similar  arteries.  The  left  renal  vein  has 
been  observed  in  several  cases  to  pass  almost  vertically  downward  parallel  to  the  vertebral 
column,  opening  into  the  vena  cava  at  the  level  of  the  fourth  lumbar  vertebra 


THE    INFERIOR   CAVAL   SYSTEM.  903 

5.  The  Middle  Suprarenal  Veins.  —  The  middle  suprarenal  veins  (vv. 
stiprarenales )  are  the  principal  veins  of  the  suprarenal  bodies,  from  which,  however, 
the  superior  suprarenals,  emptying  into  the  phrenics,  and  the  inferior,  opening 
into  the  renals,  also  arise.  Each  vein  occupies  a  groove  on  the  anterior  surface 
of  the  suprarenal  body,  and  descends  obliquely  inward  to  open  on  the  right 
side  into  the  inferior  vena  cava  above  the  right  renal,  and  on  the  left  side  into  the 
left  renal. 

6a.  The  Spermatic  Veins. — The  spermatic  veins  (vv.  spermaticae)  begin  at 
the  internal  abdominal  ring,  whence  they  pass  upward  and  inward  along  with  the 
spermatic  arteries  and  are  the  continuation  upward  of  the  venous  plexuses  which 
surround  the  spermatic  cords. 

Each  of  these  plexuses  has  its  origin  in  the  testicular  veins  (vv.  testiculares) 
which  return  the  blood  from  the  tunica  albuginea  testis  and  from  the  seminiferous 
tubules,  these  latter  branches  passing  towards  the  hilum  of  the  organ  in  the  trabeculae. 
They  make  their  exit  from  the  testis  at  about  the  middle  of  its  superior  border,  and 
are  joined  very  shortly  by  the  veins  of  the  epididymis.  They  are  then  continued 
up  the  spermatic  cord  in  the  form  of  from  ten  to  twenty  flexuous  stems,  which 
anastomose  abundantly  to  form  what  is  termed  the  pampiniform  plexus  (plexus 
pampiniformis),  surrounding  the  spermatic  artery.  As  the  cord  enters  the  inguinal 
canal  the  plexus  is  reduced  to  some  three  or  four  stems,  which,  at  the  internal 
abdominal  ring,  become  the  spermatic  veins. 

These  are  two  or  three  stems  which  anastomose  abundantly  with  one  another 
and  consequently  present  a  plexiform  arrangement.  They  surround  the  abdominal 
portion  of  the  spermatic  artery  and,  shortly  before  reaching  their  termination,  unite 
to  a  single  stem,  which  on  the  right  side  opens  at  an  acute  angle  into  the  vena  cava 
inferior  below  the  right  renal  vein,  while  on  the  left  side  it  opens  almost  at  a  right 
angle  into  the  lower  border  of  the  left  renal  vein. 

The  spermatic  veins  proper  possess  no  valves,  except  that  there  is  usually 
a  pair  at  the  entrance  of  the  right  vein  into  the  vena  cava.  In  the  stems  of  the 
pampiniform  plexus,  however,  valves  are  usually  to  be  found,  but  they  are  very 
frequently  insufficient. 

Tributaries. — The  spermatic  veins  receive  a  ureteric  branch  from  the  lower  part  of  the 
ureter  and  also  peritoneal  branches  and  renal  branches  from  the  adipose  capsule  of  that  organ. 
In  the  scrotum  the  pampiniform  plexus  makes  connections  with  the  branches  of  the  external  pudic 
veins,  and  at  their  entrance  into  the  external  abdominal  ring  the  two  plexuses  of  opposite  sides 
are  connected  by  transverse  anastomoses  which  pass  in  front  of  the  symphysis  pubis.  A  deeper 
transverse  anastomosis  also  occurs  between  the  two  spermatics  as  they  emerge  from  the  internal 
abdominal  rings,  and  they  communicate  by  means  of  their  peritoneal  branches  with  the  branches 
of  the  right  and  left  colic  veins. 

Variations. — Occasionally  the  left  vein  as  well  as  the  right  opens  directly  into  the  vena  cava, 
and  in  cases  in  which  that  vessel  is  situated  upon  the  left  side  it  is  the  left  vein  which  opens 
directly  into  it,  the  right  one  opening  into  the  right  renal  vein.  They  communicate  sometimes  on 
one  side  or  the  other  with  a  lumbar  vein  or  with  the  middle  suprarenal,  and  the  left  vein  has 
been  observed  to  open  into  the  hemiazygos. 

The  spermatic  veins  are  very  apt  to  become  varicose,  and  it  is  well  known  that  this  con- 
dition is  more  apt  to  occur  in  the  left  vein  than.in  the  right.  Various  reasons  have  been  assigned 
for  this  difference  in  the  two  veins,  the  chief  of  these  being  ( i )  that  the  left  vein  opens  at  prac- 
tically a  right  angle  into  the  renal,  while  the  right  opens  at  an  acute  angle  into  the  vena  cava  ; 
(2)  the  left  vein  is  destitute  of  valves  at  its  opening  into  the  renal,  while  the  right  one  usually 
possesses  a  pair  at  its  orifice  ;  and  (3)  that  the  left  vein  in  its  course  up  the  abdominal  wall  lies 
beneath  the  sigmoid  colon,  while  the  right  has  only  coils  of  the  small  intestine  with  their  more 
fluid  contents  in  front  of  it. 

66.  The  Ovarian  Veins. — The  ovarian  veins  (vv.  ovaricae)  correspond  to 
the  spermatic  veins  of  the  male.  They  take  their  origin  from  the  veins  which 
issue  at  the  hilum  of  the  ovary  and  are  also  connected  by  wide  anastomoses 
with  the  veins  of  the  fundus  of  the  uterus.  They  form  a  close  plexus,  the  pam- 
piniform plexus  (plexus  pampiniformis),  which  accompanies  the  ovarian  artery 
between  the  two  layers  of  the  broad  ligament  parallel  with  the  Fallopian  tube, 
receiving  branches  from  the  latter  structure  and  from  the  round  ligament  of  the 


904  HUMAN   ANATOMY. 

uterus.  Leaving  the  broad  ligament  with  the  ovarian  artery,  they  ascend  along 
that  vessel,  the  number  of  trunks  becoming  reduced  to  two  and  eventually  to  one, 
and  they  open  above  in  the  same  manner  as  the  spermatic  veins,  the  right  one 
into  the  inferior  vena  cava  and  the  left  one  into  the  left  renal  vein.  They  possess 
no  valves. 

Their  variations  are  essentially  similar  to  those  presented  by  the  spermatic  veins. 

Practical  Considerations. —  The  Tributaries  of  the  Inferior  Cava. — In  a 
case  of  occlusion  of  the  inferior  cava  by  thrombus  extending  from  the  renal  vein  to 
the  right  auricle,  the  phrenic  and  renal  veins  opened  into  the  lumbar  and  azygos 
veins,  the  blood  of  the  abdomen  thus  gaining  the  superior  cava  (Allen). 

The  intralobular  branches  of  the  hepatic  veins  may  be  the  source  of  profuse 
hemorrhage  in  cases  of  wound  or  rupture  of  the  liver,  because  (a)  they  are  thin- 
walled  ;  (b}  they  are  not  encircled  by  cellular  tissue,  but  are  closely  attached  to  the 
liver  substance  and  thus  cannot  collapse  or  retract,  a  condition  which  also  predisposes 
to  the  entrance  of  air  into  the  divided  veins  ;  (/)  they  are  valveless,  and  the  main 
trunks  open  direct  into  the  vena  cava,  any  obstruction  of  which  would  therefore  result 
in  the  escape  of  great  quantities  of  blood  ;  (d  )  the  flow  in  the  main  trunks — from  the 
vein  to  the  cava — is  influenced  by  the  movements  of  the  diaphragm,  the  descent  of 
this  muscle  tending  to  constrict  the  opening  through  which  the  veins  pass,  and  thus 
to  obstruct  the  current  and  favor  bleeding.  Hemorrhage  from  the  liver  after  a  wound 
or  during  an  operation  is  very  difficult  to  arrest  by  ligature  on  account  of  the  thinness 
of  the  walls  of  the  intralobular  veins  and  the  friability  of  the  liver  tissue  itself.  It  is 
usually  controlled  by  gauze-pressure  or  by  the  galvano-cautery.  The  branches  of  the 
portal  vein  may  also  bleed  freely,  but  are  surrounded  by  a  quantity  of  lax  cellular 
tissue,  as  they  run  in  the  ' '  portal  canals' '  with  the  branches  of  the  biliary  ducts  and 
of  the  hepatic  artery,  and  can  thus  retract  or  collapse  when  torn  or  divided.  More- 
over, the  blood -pressure  within  the  portal  vein  is  low,  favoring  the  spontaneous  arrest 
of  hemorrhage.  In  obstruction  of  the  common  duct,  preventing  the  escape  of  bile 
into  the  intestine,  the  radicles  of  the  hepatic  veins  take  up  the  bile-stained  exudate 
that  results  from  the  increased  intra-hepatic  tension.  Its  entrance  into  the  general 
circulation  through  the  vena  cava  gives  rise  to  jaundice. 

The  relative  shortness  of  the  right  renal  vein  occasionally  adds  to  the  difficulties 
of  a  right-sided  nephrectomy,  the  pedicle — the  vein,  artery,  ureter,  etc. — being 
shorter  and  less  easily  controlled  by  ligature.  As  the  veins  are  subject  to  variation 
as  well  as  the  arteries — though  less  frequently — supernumerary  or  misplaced  vessels 
should  be  carefully  looked  for.  They  may  be  found  emerging  from  the  kidney  at 
either  pole,  or  from  the  hilum  behind  the  pelvis.  Fatal  results  have  followed  the 
failure,  during  a  nephrectomy,  to  find  and  secure  such  aberrant  vessels.  At  times 
the  left  renal  vein  passes  behind  the  aorta,  to  which  occurrence  may  be  attributed 
the  greater  frequency  of  hyperaemia  of  the  left  kidney  (Allen).  The  renal  veins 
may  be  obstructed  by  pressure  from  retroperitoneal  growths,  or — in  the  supine 
position — from  movable  abdominal  tumors  or  the  gravid  uterus,  or  from  traction 
caused  by  displacements  of  the  kidney  itself,  or  as  a  result  of  congestion  in  the 
cardio-pulmonary  system,  as  in  pneumonia  or  valvular  heart  disease.  By  whatever 
cause  produced,  the  congestion,  if  sufficiently  long-continued,  may  give  rise  to  a  form 
of  chronic  interstitial  nephritis.  The  communication  (ride  supra)  between  the  renal 
veins  and  the  first  lumbar  vein  and — on  the  left  side — the  hemiazygos  vein,  accounts 
for  the  undoubted  good  effect  often  produced  in  renal  congestions  by  counter- 
irritation,  blisters,  cupping,  or  leeching  in  the  loin. 

The  spermatic  veins  are  of  chief  practical  interest  in  their  relation  to  varicocele. 
The  anatomical  reasons  for  the  frequency  of  this  condition,  and  for  its  occurrence  by 
preference  on  the  left  side,  are  given  on  page  1961. 

The  veins  of  the  pampiniform  plexus  proper  are  usually  distinct  from  those 
which  accompany  the  vas  deferens  and  its. artery.  In  excision  of  the  former  set  for 
varicocele,  the  vas  deferens  is  always  pushed  to  the  rear  and  held  out  of  harm's  way. 
It  carries  with  it  its  artery  and  veins,  and  the  anastomotic  communications  of  the 
former  with  the  spermatic  artery — almost  always  cut  or  tied  with  its  venous  plexus — 
and  with  the  scrotal  arteries  suffice  to  maintain  the  nutrition  of  the  testis,  while  the 


THE    INFERIOR    CAVAL    SYSTEM.  905 

veins  of  this  smaller  and  posterior  group  enlarge  to  carry  on  the  return  circulation. 
Elevation  is  of  especial  value  in  testicular  inflammation,  as  the  dependent  position  of 
the  spermatic  veins  and  their  lack  of  adequate  support  greatly  intensify  the  engorge- 
ment and  venous  obstruction  of  inflammatory  processes. 

THE  COMMON  ILIAC  VEINS. 

The  common  iliac  veins  (vv.  iliacae  communes)  (Fig.  765)  are  two  in  number, 
and  are  formed  opposite  the  sacro-iliac  articulations  by  the  union  of  the  internal  and 
external  iliac  veins.  They  pass  upward,  converging  as  they  go,  and  unite  at  about 
the  level  of  the  intervertebral  disk  between  the  fourth  and  fifth  lumbar  vertebrae  to 
form  the  vena  cava  inferior. 

Since  their  point  of  union  lies  somewhat  to  the  right  of  the  median  line,  the  right 
vein  is  shorter  than  the  left  and  its  course  is  more  directly  upward.  Neither  vein 
possesses  valves. 

Relations. — The  union  of  the  two  veins  takes  place  beneath  the  right  common 
iliac  artery,  and  the  right  vein,  at  its  origin,  lies  behind  that  vessel,  although,  since  its 
course  is  more  vertical  than  that  of  the  artery,  it  gradually  comes  to  lie  somewhat 
lateral  to  it  above.  The  left  vein  near  its  termination  is  crossed  from  without  inward 
by  the  right  common  iliac  artery,  and  throughout  its  course  lies  medially  to  the  left 
common  iliac  artery  and  on  a  plane  somewhat  posterior  to  it. 

Variations. — Occasionally  the  external  and  internal  iliac  veins  do  not  unite  to  form  a  common 
stem,  but  open  directly  into  the  inferior  vena  cava.  This  may  occur  on  one  or  both  sides. 

Tributaries. — In  addition  to  the  external  and  internal  iliacs,  by  whose  union 
they  are  formed,  the  common  iliacs  receive  but  a  single  tributary,  the  middle  sacral 
vein  (v.  sacralis  media),  and  this  opens  into  the  left  vein.  It  accompanies  the  middle 
sacral  artery,  and  in  the  lower  part  of  its  course  it  is  frequently  double,  one  vessel 
lying  on  each  side  of  the  artery.  Opposite  each  sacral  vertebra  it  receives  a 
transverse  connecting  branch  from  the  lateral  sacral  veins  and  so  forms  with  these 
what  is  termed  the  anterior  sacral  plexus.  At  its  origin  it  communicates  with 
the  hemorrhoidal  veins. 

THE  INTERNAL  ILIAC  VEIN. 

The  internal  iliac  vein  (v.  hypogastrica)  (Fig.  767)  of  each  side  is  a  short  but 
rather  large  vessel,  which  accompanies  the  internal  iliac  artery,  lying  to  its  medial 
side  and  in  a  plane  somewhat  posterior  to  it.  It  extends  from  the  neighborhood  of 
the  great  sacro-sciatic  foramen  to  the  level  of  the  sacro-iliac  synchondrosis,  where  it 
unites  with  the  external  iliac  to  form  the  common  iliac  vein. 

Tributaries. — Its  tributaries  correspond  in  general  with  the  branches  of  the 
internal  iliac  artery,  but  those  which  arise  in  the  pelvic  viscera  present  the  peculiarity 
that  they  take  their  origin  from  more  or  less  extensive  plexuses  which  communicate 
with  one  another.  The  stems  which  pass  from  these  plexuses  to  the  internal  iliac 
also  anastomose  to  a  considerable  extent,  the  result  being  that  it  is  not  possible  in  all 
cases  to  recognize  definite  veins  corresponding  to  the  visceral  arteries. 

The  following  are  the  tributaries  that  are,  as  a  rule,  to  be  recognized  :  ( i )  the 
gluteal,  (2)  the  lateral  sacral,  (3)  the  ilio-lumbar,  (4)  the  sciatic, _(s)  the  internal 
pudic,  (6)  the  obturator,  (7)  the  middle  hemorrhoidal,  (8)  the  uterine,  and  (9)  the 
vesical  veins. 

i.  The  Gluteal  Vein. — The  gluteal  vein  (v.  glutaea  superior)  accompanies  the 
artery  of  the  same  name.  Throughout  its  extrapelvic  course  its  tributaries  accom- 
pany the  branches  of  the  artery  as  valved  venae  comites,  and  at  the  upper  part  of  the 
greater  sacro-sciatic  foramen  the  veins  accompanying  the  two  main  branches  of  the 
artery  unite  to  form  a  double  trunk,  united  by  numerous  anastomoses.  This  trunk, 
which  is  occasionally  single,  passes  through  the  greater  sacro-sciatic  foramen  above 
the  pyriformis  muscle  and,  after  a  short  intrapelvic  course,  opens  int©  the  internal 
iliac  vein. 

Where  they  pass  through  the  greater  sacro-sciatic  foramen  both  artery  and  vein 
are  surrounded  by  a  dense  connective  tissue  which  renders  their  separation  difficult 
and  brings  it  about  that  the  lumen  of  the  vein  remains  patent  when  emptied  of  blood. 


906 


HUMAN   ANATOMY. 


2.  The  Lateral  Sacral  Veins. — The  lateral  sacral  veins  (vv.  sacrales  laterales) 
are  usually  double,  and  pass  upward  with  their  arteries  upon  the  anterior  surface 
of  the  sacrum  just  medial  to  the  anterior  sacral  foramina,  and  open  above  either 
directly  into  the  internal  iliacs  or  into  the  gluteal  veins.      As  they  pass  each  sacral 
foramen  they  receive  tributaries  from  the  internal  spinal  plexuses,  and  opposite  each 
sacral  vertebra  are  connected  by  transverse  branches  with  the  middle  sacral  veins, 
these  anastomoses  forming  the  anterior  sacral  plexus. 

3.  The    Ilio-Lumbar    Vein. — The  ilio-lumbar  vein  (v.  iliolumbalis)  follows 
the  course  of  the  corresponding  artery  and  its  branches  and  is  richly  supplied  with 


FIG.  767. 


Aorta 


Vena  cava  inferior 


Genito-crural  nerve 


Internal  iliac  vein 

Anterior  superior 

spine  of  ilium 


Obturator  nerve 
External  iliac- 
artery  and  vein 
Superior  gluteal  vein 


Dorsal  vein  of  penis 

Sup.  and  deep  layers  of 
triangular  ligament 


Ischio-cavemosus  muscle, 
cut  edge 


Cowper's  gland 


Bulbo-cavernosus 

muscle,  cut  edge 


.Right  and  left  common  iliac  arteries 
Left  common  iliac  vein 

Internal  iliac  vein 


Lateral  sacral  vein 


Superior 

hemorrhoidal 


Lateral  sacral  vein 


Sciatic  vein 


Internal  pudL  vein 


Vesical  veins  i 

ing  to  a  single  trilmt  : 
of  internal  iliac  vein 

TriUitaries  of  intern  i 
iliac  from  vesical 
plexus 


Middle  hemorrhoidal  \ein 
Vesico-prostatic  |  : 
Prostate 

Superficial  anal  sphincter.  « 
venous  plexus  trilmt  ir;   t<> 
inferior  hemorrhoidal  veins 

Anus 


Transverse  perinea!  muscle 


Bulb  of  corpus  spongiosum 


•wt-(l  from  left  side. 


valves.  Its  lumbar  tributary  receives  some  of  the  lower  intervertebral  veins  ami 
occasionally  the  last  lumbar,  and  anastomoses  with  the  lower  portion  of  the  ascending 
lumbar  vein.  The  iliac  tributary,  which  begins  over  the  crest  of  the  ilium  and  in 
the  substance  of  the  iliacus  muscle,  makes  anastomoses  with  tributaries  of  the  drrp 
circumflex  iliac  vein  and  thus  establishes  an  important  collateral  venous  path  between 
the  external  and  internal  iliars. 

The  main  stem  of  the  vein  is  a  single  trunk  which  opens  into  the  internal  iliac 
or  occasionally  into  the  common  iliac. 

4.  The  Sciatic  Vein. — The  sciatic  vein  <  v.  ulutaea  interior)  of  either  side  of  the 
body  has  essentially  the  same  course  as  the  corresponding  artrry.  Its  extrapelvic 


THE    INFERIOR   CAVAL   SYSTEM.  907 

tributaries  are  venae  comites  of  the  branches  of  the  artery,  and  its  usually  single 
main  stem  passes  through  the  greater  sacro-sciatic  foramen  below  the  pyriformis  to 
empty  into  the  internal  iliac. 

Anastomoses  of  comparatively  large  calibre  occur  between  the  extrapelvic 
portions  of  the  sciatic  vein  and  the  internal  circumflex  and  first  perforating  tribu- 
taries of  the  deep  femoral  vein,  thus  establishing  a  collateral  venous  path  between 
the  tributaries  of  the  internal  and  external  iliacs. 

5.  The  Internal  Pudic  Vein. — The  internal  pudic  vein  (v.  pudenda  interim)  is 
associated  throughout  the  greater  part  of  its  course  with  the  artery  of  the  same  name. 
It  differs,  however,  somewhat  in  its  origin,  since  it  is  not  the  direct  continuation  of  the 
dorsal  vein  of  the  penis  (or  clitoris),  although  it  communicates  with  that  vessel  by  a 
small  branch  immediately  below  the  symphysis  pubis,  but  is  rather  the  continuation 
of  the  veins  of  the  corpus  cavernosum  which  accompany  the  artery  to  that  structure. 
It  is  throughout  the  most  of  its  length  double,  anastomoses  between  the  two  stems 
surrounding  the  internal  pudic  artery.      It  has  its  origin  between  the  two  layers  of  the 
triangular  ligament  of  the  perineum  and  passes  backward  into  the  ischio-rectal  fossa, 
lying  with  the  artery  at  the  side  of  that  cavity  in  a  canal  (Alcock1  s  canal)  formed  by  a 
splitting  of  the  lower  edge  of  the  obturator  fascia.      It  leaves  the  ischio-rectal  fossa  by 
the  lesser  sacro-sciatic  foramen  and,  curving  around  the  spine  of  the  ischium,  enters 
the  pelvis  through  the  lower  part  of  the  greater  sacro-sciatic  foramen  and  empties 
into  the  internal  iliac. 

In  addition  to  the  communication  with  the  dorsal  vein  of  the  penis  (or  clitoris) 
already  mentioned,  the  internal  pudic  vein  makes  near  its  origin  a  connection  with  the 
pudendal  plexus  and,  as  it  curves  over  the  spine  of  the  ischium,  with  the  sciatic  vein. 

It  possesses  several  valves  arranged  in  a  rather  characteristic  manner.  Through- 
out its  course  through  the  perineum  it  is  valveless,  but  both  its  terminal  portion  and 
its  communication  with  the  pudendal  plexus  possess  valves  whose  concavities  look  in 
the  one  case  towards  the  internal  iliac  and  in  the  other  towards  the  plexus.  Blood 
contained  in  the  perineal  portion  of  the  vein  may  flow,  therefore,  either  towards  the 
internal  iliac  directly  or  to  the  pudendal  plexus  (Fenwick),  and  the  communication 
with  the  latter  cannot  well  be  regarded  as  the  origin  of  the  vein,  as  is  sometimes 
done. 

Tributaries. — In  addition  to  (a)  the  vein  of  the  corpus  cavernosum  (v.  profunda  penis  vel 
clitoridis)  already  mentioned,  the  internal  pudic  vein  receives  numerous  tributaries  which  cor- 
respond with  the  branches  of  the  artery.  Among  these  may  be  mentioned  :  (b)  the  veins  of  the 
bulb  ( vv.  bulbi  urethrae),  which  are  quite  numerous  and  issue  from  the  bulb  of  the  urethra  or  from 
the  bulbus  vestibuli  in  the  female,  these  latter  vessels  being  quite  large  ;  (c )  the  superficial  peri- 
neal veins  (vv.  scrotales  posteriores),  which  return  the  blood  from  the  integument  and  superficial 
muscles  of  the  perineum  and  from  the  posterior  surface  of  the  scrotum  and  the  posterior  portion 
of  the  labia  majora,  anastomosing  in  these  structures  with  the  tributaries  of  the  external  pudic 
veins;  (d)  the  inferior  hemorrhoidal  veins  (vv.  haemorrhoidales  inferiores),  which  traverse  the 
ischio-rectal  space  from  the  neighborhood  of  the  anus,  where  they  make  communications  with 
the  hemorrhoidal  plexus  of  the  rectum. 

6.  The  Obturator  Vein. — The  obturator  vein  (v.  obturatoria)  accompanies  the 
obturator  artery  and  shares  in  the  variations  which  that  vessel  presents  (page  814). 
It  takes  its  origin  in  the  adductor  muscles  of  the  thigh,  its  tributaries  uniting  to  form 
an  internal  and  an  external  branch,  which  curve  around  the  margins  of  the  obturator 
foramen.      The  vein  formed  by  the  union  of  these  two  branches  passes  through  the 
opening  in  the  upper  part  of  the  obturator  membrane  and  passes  across  the  lateral 
pelvic  wall,  lying  immediately  below  the  artery.      It  opens,  as  a  rule,  into  the  internal 
iliac  vein. 

Its  communications  are  somewhat  extensive  and  important.  Its  external  tribu- 
tary branch  receives  branches  from  the  scrotum  or  labia  majora  and  through  these 
communicates  with  the  external  pudic  veins.  At  its  passage  through  the  opening 
in  the  obturator  membrane  it  receives  branches  from  the  obturator  plexus,  which 
cover  both  surfaces  of  the  membrane  and  drain  the  obturator  muscles,  and  also  a 
branch  which  passes  downward  and  inward  upon  the  inner  surface  of  the  os  pubis, 
frequently  communicating  above  with  the  pubic  tributary  of  the  deep  epigastric  vein. 


908  HUMAN   ANATOMY. 

Additional  communications  are  made  with  the  vesico-prostatic  (vesico- vaginal) 
plexus  and  the  internal  pudic  vein,  and  also  with  the  internal  circumflex  branch  of 
the  deep  femoral  and  with  the  sciatic. 

7.  The   Middle   Hemorrhoidal  Vein. — The  middle  hemorrhoidal  vein  (v. 
haemorrhoidalis  media)  has  its  origin  in  the  hemorrhoidal  plexus  of  the  rectum,  and 
after  receiving  tributaries  from  the  seminal  vesicles,  the  prostate  gland,  and  the  urinary 
bladder  in  the  male  and  from  the  vagina  in  the  female,  opens  into  the  internal  iliac 
or  one  of  its  tributaries.     It  is  a  comparatively  large  vein,  and  of  importance  in  that 
it    forms  through   its   connection  with    the   hemorrhoidal   plexus  a   communication 
between  the  portal  and  inferior  caval  systems  of  veins. 

The  hemorrhoidal  plexus  (plexus  haemorrhoidalis)  which  surrounds  the  rectum 
is  composed  of  two  venous  net-works,  one  of  which,  the  internal  hemorrhoidal  plexus, 
lies  in  the  submucosa  of  the  rectum,  while  the  other,  \heexternal  hemorrhoidal  plexus, 
rests  upon  its  outer  surface.  The  internal  plexus  is  characterized  in  the  adult,  in  that 
portion  of  it  which  lies  just  above  the  anal  opening,  by  the  occurrence  of  round  or 
elongated  bunches  (glomera  haemorrhoidalia)  formed  by  a  number  of  small  veins  coiled 
together  into  a  mass  resembling  somewhat  a  Malpighian  glomerulus.  Upon  the  veins 
which  form  the  glomera,  or  upon  those  extending  between  adjacent  glomera,  ampullar 
dilatations  occur  which  have  been  regarded  both  as  the  cause  and  as  the  result  of  the 
glomera  formation.  Be  that  as  it  may,  the  internal  hemorrhoidal  plexus  presents  in 
the  adult,  slightly  above  the  anus,  a  distinct  band  characterized  by  the  occurrence 
of  glomera  and  dilatations,  and  forming  what  is  termed  the  annulus  haemorrhoidalis. 

The  internal  plexus  opens  partly  at  the  anal  orifice  into  the  branches  of  the 
inferior  hemorrhoidal  veins  and  partly,  by  branches  which  traverse  the  muscular  coats 
of  the  rectum,  into  the  external  plexus.  This  has  three  sets  of  efferent  veins  : 
(i)  the  inferior  hemorrhoidals,  which  open  into  the  internal  pudic  ;  (2)  the  middle 
hemorrhoidals,  which  pass  to  the  internal  iliac  or  one  of  its  branches  ;  and  (3)  the 
superior  hemorrhoidal,  which  leads  to  the  inferior  mesenteric  and  so  to  the  portal 
vein.  The  external  plexus  also  communicates  with  "the  vesico-prostatic  plexus  in 
the  male  and  the  vaginal  plexus  in  the  female. 

8.  The    Uterine  Vein. — The  uterine  vein   (v.  uterina)    arises   opposite   the 
external  os  uteri  from  the  plexus  utero-vaginalis.      It  is  at  first  a  double  vein,  its  two 
trunks  accompanying  the  uterine  artery,  and  where  that  vessel  crosses  the  ureter  one 
of  the  trunks  passes  with  the  artery  in  front  of  the  duct  and  the  other  behind  it. 
The  two  trunks  then  usually  unite  to  a  single  vein,  which  passes  into  the  internal 
iliac,  frequently  receiving  the  vesical  veins  or  the  obturator. 

The  utero-vaginal  plexus  is  formed  by  the  veins  which  return  the  blood  from 
the  uterus  and  vagina.  The  veins  in  the  substance  of  the  uterus  are  exceedingly 
thin-walled,  appearing  as  clefts  in  sections,  and  form  a  more  or  less  distinct  layer 
(stratum  vasculare)  in  the  muscular  wall  of  the  organ.  From  this  vessels  pass  to 
both  the  anterior  and  posterior  surfaces  of  the  organ  and  follow  a  course  which  is 
outward  and  more  or  less  downward  towards  the  lateral  borders,  where,  between  the 
two  layers  of  the  broad  ligament,  they  form  a  rich  plexus,  the  uterine  plexus,  the 
vessels  of  which  converge  towards  the  origin  of  the  uterine  vein,  opposite  the  external 
os  uteri.  The  vaginal  veins  form  a  rich  plexus  in  the  walls  of  the  vagina,  the 
emissaries  from  which  are  directed  laterally  and  more  or  less  upward,  forming  along 
the  lateral  walls  of  the  organ  a  rich  vaginal  plexus  whose  stems  also  convener  to 
the  uterine  vein  at  the  level  of  the  external  os  uteri.  These  two  plexuses,  the  uterine 
and  vaginal,  are  continuous  at  the  level  of  the  external  os  uteri  and  form  together 
the  extensive  plexus  utero-vaginalis. 

At  the  fundus  of  the  uterus  this  plexus  makes  abundant  connections  with 
the  pampiniform  plexus  of  the  ovarian  veins  and  with  the  funicular  veins  which 
accompany  the  ligamentum  teres.  Lower  down,  throughout  its  uterine  portion,  it 
receives  affluents  from  the  plexus  of  veins  which  occurs  between  the  layers  of  the  broad 
ligament,  and  the  lower  part  of  its  vaginal  portion  makes  connections  anteriorly 
with  the  vesico- vagina]  plexus  and  posteriorly  with  the  external  hemorrhoidal  plexus. 

9-  The  Vesical  Veins. — The  vesical  veins  (vv.  vesicales )  vary  somewhat  in 
number,  but  together  represent  a  vessel  of  considerable  size.  They  arise  at  the  sides 
of  the  bladder  from  a  well-marked  plexus  which  occupies  in  the  male  the  groove 


THE    INFERIOR   CAVAL   SYSTEM.  909 

between  the  prostate  gland  and  the  bladder  and  is  termed  the  vesico -pro static  plexzts. 
In  the  female  the  plexus  lies  at  the  sides  and  base  of  the  bladder,  and  from  its 
relations  posteriorly  is  known  as  the  vesico-vaginal  plexus.  From  their  origin 
the  vesical  veins  pass  upward,  outward,  and  backward  to  open  into  the  internal 

iliac. 

The  vesico-prostatic  or  vesico-vaginal  plexus  (plexus  vesicalis),  occupying 
the  position  indicated  above,  is  formed  principally  by  the  veins  which  drain 
the  urinary  bladder  and,  in  the  male,  the  prostate  gland.  Posteriorly,  in  the 
male,  the  plexus  communicates  with  the  external  hemorrhoidal  plexus,  and  in  the 
female  with  the  vaginal  plexus,  and  anteriorly,  in  both  sexes,  it  communicates 
extensively  with  the  pudendal  plexus.  In  addition  to  the  drainage  which  it 
possesses  through  the  vesical  veins,  it  also  drains  by  way  of  the  obturator  veins, 
branches  from  it  joining  those  vessels  just  after  they  have  passed  through  the 
obturator  foramina. 

The  pudendal  plexus  (plexus  pudendalis),  also  known  as  the  plexus  of  Santo - 
riui,  occupies  the  space  between  the  lower  part  of  the  pelvic  surface  of  the  symphysis 
pubis  and  the  anterior  surface  of  the  neck  of  the  bladder,  becoming  continuous 
posteriorly  at  the  sides  with  the  vesico-prostatic  (vesico-vaginal)  plexus.  Its  chief 
tributary  is  the  deep  dorsal  vein  of  the  penis  (clitoris)  (v.  dorsalis  penis  vel 
clitoridis),  which  is  a  single  large  vein  (sometimes  partly  double  in  the  female)  which 
passes  along  the  dorsal  mid-line  of  the  penis  or  clitoris,  beneath  the  deep  fascia 
(Fig.  767),  in  the  groove  between  the  two  corpora  cavernosa,  and  hasten  either  side 
of  it  one  of  the  two  dorsal  arteries.  It  receives  branches  from  the  corpora  cavernosa 
and  has  its  origin  in  two  veins  which  curve  from  below  upward  around  the  base  of 
the  glans  penis  (clitoridis).  At  the  root  of  the  penis  (clitoris)  it  leaves  the  dorsal 
surface  and  perforates  the  triangular  ligament  of  the  perineum,  .usually  just  below  the 
border  of  the  subpubic  ligament,  so  entering  the  pelvis.  It  then  bifurcates,  each  of 
the  branches  passing  into  the  pudendal  plexus.  Before  entering  the  pelvis  it  gives 
off  on  either  side  a  small  branch  which  unites  with  the  internal  pudic  vein,  thus 
representing  the  course  of  the  artery. 

In  addition  to  the  dorsal  vein  of  the  penis  (clitoris),  the  pudendal  plexus  also 
receives  branches  from  the  internal  pudic  vein  and  from  the  anterior  surfaces  of  the 
bladder  and,  in  the  male,  the  prostate.  It  communicates  posteriorly  and  at  the 
sides  with  the  vesico-prostatic  (vesico-vaginal)  plexus,  and  through  it  finds  its  chief 
efferents  in  the  vesical  veins,  although  it  is  also  drained  by  the  obturator  veins,  with 
each  of  which  it  communicates  by  one  or  two  branches. 

THE  EXTERNAL  ILIAC  VEIN. 

The  external  iliac  vein  (v.  iliaca  externa)  (Figs.  766,  767)  begins  at  Poupart's 
ligament,  where  the  femoral  vein  becomes  continuous  with  it,  and  passes  upward, 
backward,  and  inward  to  the  level  of  the  sacro-iliac  articulation,  where  it  unites  with 
the  internal  iliac  to  form  the  common  iliac. 

Its  course  is  along  the  line  of  junction  of  the  false  and  the  true  pelvis,  and  it  lies 
upon  the  inner  border  of  the  psoas  muscle  and  internal,  or  in  its  upper  part  internal 
and  posterior,  to  the  external  iliac  artery.  Near  its  termination  it  is  crossed  by  the 
internal  iliac  artery,  on  the  left  side  almost  at  a  right  angle,  on  the  right  more 
obliquely.  Valves  are  present  in  about  35  veins  out  of  100,  but  in  a  third  of 
such  cases  they  are  insufficient. 

Tributaries. — The  tributaries  of  the  external  iliac  vein  are  :  (i)  the  deep  epi- 
gastric and  (2)  the  deep  circumflex  iliac  veins. 

i.  The  Deep  Epigastric  Vein. — The  deep  epigastric  vein  (v.  epigastrica 
inferior)  has  its  origin  above  the  umbilicus  in  the  substance  of  the  rectus  abdominis 
muscle,  where  it  anastomoses  with  the  superior  epigastric  vein.  It  accompanies  the 
deep  epigastric  artery  as  two  venae  comites  which  unite  below  to  form  a  single  trunk 
opening  into  the  external  iliac  a  short  distance  above  Poupart's  ligament. 

Below  the  level  of  the  umbilicus  the  vein  is  provided  with  valves  whose  concav- 
ities are  directed  downward,  but  above  the  umbilicus  it  is  said  to  be  destitute  of 
valves.  It  receives  tributaries  from  the  rectus  muscle  and,  as  it  passes  beneath  the 


910  HUMAN   ANATOMY. 

internal  abdominal  ring,  from  the  spermatic  cord  or  round  ligament  of  the  uterus. 
The  connections  which  it  makes  with  other  veins  are  numerous  and  important. 
Its  connections  with  the  superior  epigastric  vein  have  already  been  noted  ;  by  this 
communication  is  established  between  the  superior  and  inferior  venae  cavae.  In 
addition,  by  means  of  branches  which  traverse  the  sheath  of  the  rectus  muscle, 
it  communicates  with  the  subcutaneous  and  subperitoneal  veins  of  the  abdominal 
wall  and  with  the  parumbilical  veins,  forming  through  these  latter  a  connection 
with  the  portal  system  of  veins.  Finally,  by  means  of  a  pubic  branch,  which  is 
frequently  a  tributary  of  the  external  iliac  rather  than  of  the  deep  epigastric,  it 
communicates  with  the  obturator  vein,  and  by  the  enlargement  of  this  communication 
the  obturator  vein,  just  as  is  the  case  with  the  artery,  may  become  a  tributary  of  the 
deep  epigastric. 

2.  The  Deep  Circumflex  Iliac  Vein. — The  deep  circumflex  iliac  vein  (v. 
circumflexa  ilium  profunda)  has  the  same  course  as  the  corresponding  artery,  which 
it  surrounds  in  a  plexiform  manner.  It  possesses  valves  and  communicates  with  the 
iliolumbar  veins.  Near  its  termination  it  becomes  a  single  trunk  and  opens  into  the 
external  iliac  a  little  above  the  deep  epigastric  ;  occasionally  it  opens  into  the  latter 
vessel. 

THE   VEINS    OF   THE    LOWER    LIMB. 

The  external  iliac  vein  is  the  channel  by  which  the  blood  returning  from  the 
lower  limb  is  conveyed  to  the  inferior  vena  cava  and  is  the  direct  upward  continuation 
of  the  femoral  vein.  Instead,  however,  of  proceeding  to  a  description  of  this  latter 
vessel  and  so  down  the  leg,  it  will  be  more  convenient  to  begin  the  account  of  the 
veins  of  the  lower  limb  with  those  of  the  foot  and  proceed  upward  to  the  femoral. 

As  in  the  upper  limb,  two  practically  distinct  sets  of  veins  can  be  recognized  in 
the  leg  ;  one  set  is  more  or  less  deeply  seated  and  accompanies  the  arteries,  while  the 
other  is  superficial  and,  in  the  adult,  has  a  course  quite  independent  of  the  arterial 
distribution.  The  deep  veins  will  first  be  considered.. 

THE   DEEP  VEINS. 
THE  DEEP  VEINS  OF  THE  FOOT. 

The  deep  veins  of  the  sole  of  the  foot  have  their  origin  in  a  net-work  with 
more  or  less  distinctly  elongated  meshes,  which  occurs  upon  the  plantar  surfaces 
of  the  digits.  These  are  the  plantar  digital  veins  (vv.  dictates  plantares),  and 
in  the  webs  of  the  toes  the  vessels  of  each  digit  unite  with  those  of  the  neighboring 
ones  to  form  a  series  of  plantar  interosseous  veins  (vv.  metatarseae  plantares) 
occupying  the  metatarsal  interspaces  and  forming  venae  comites  for  the  plantar 
interosseous  (metacarpal)  arteries.  Just  as  the  digital  veins  unite  to  form  the 
interosseous,  they  send  dorsal  branches  (vv.  intercapitulares),  which  unite  with 
the  dorsal  interosseous  veins,  and,  in  addition,  make  connections  with  the  superficial 
plantar  veins,  and  might,  indeed,  be  classed  with  these  quite  as  appropriately  as  with 
the  deep  set. 

The  plantar  interosseous  veins  pass  backward,  receiving  branches  from  the 
neighboring  muscles,  and  open  into  a  venous  plantar  arch  (arcus  vcnosus  plantaris), 
formed  by  the  venae  comites  of  the  arterial  plantar  arch.  These  are  continued  pos- 
teriorly into  the  external  plantar  veins,  which  pass  obliquely  across  the  loot  along 
with  the  corresponding  artery  and  unite  behind  the  inner  malleolus  with  the  internal 
plantar  veins  to  form  the  companion  veins  of  the  posterior  tibia!  artery.  Both 
plantar  veins  give  off  branches  which  perforate  the  plantar  aponeurosis  and  communi- 
cate with  the  superficial  plantar  veins,  and  connecting  vessels  also  pass  across  the 
sole  of  the  foot  between  the  two  veins. 

Upon  the  dorsum  of  the  foot  there  exist  the  dorsal  digital  veins  ( vv.  dinitales 
dorsalesi,  which,  like  the  corresponding  plantar  veins,  may  be  equally  classified  with 
superficial  or  deep  veins,  since  they  make  connections  with  both  sets.  In  the  wd>s  of 
the  toes  the  vessels  of  adjoining  digits  unite  to  form  the  four  dorsal  interosseous 
veins  (  vv.  metatarseae  dorsalcs  ).  which  occupy  the  metatarsal  interspaces  and  com- 
municate with  the  corresponding  plantar  veins  by  the  intercapitular  and  perforating 


THE  VEINS   OF   THE   LOWER    LIMB.  911 

veins.  They  form  the  venae  comites  of  the  dorsal  interosseous  (metatarsal)  arteries  and 
open  into  the  companion  veins  of  the  metatarsal  artery.  These,  together  with  the  veins 
accompanying  the  tarsal  arteries,  open  into  the  venae  comites  of  the  art.  dorsalis  pedis, 
and  these  in  turn  are  continuous  with  the  venae  comites  of  the  anterior  tibial  artery. 

THE  DEEP  VEINS  OF  THE  LEG. 

The  deep  veins  of  the  leg  are  the  venae  comites  of  the  posterior  and  anterior 
tibial  arteries  and  their  branches.  The  posterior  tibial  vein  (v.  tibialis  posterior) 
is  formed  behind  the  internal  malleolus  by  the  union  of  the  internal  and  external 
plantar  veins,  and  consists  of  two,  or  in  many  cases  three,  veins  accompanying  the 
posterior  tibial  artery.  It  terminates  at  the  lower  border  of  the  popliteus  muscle  by 
uniting  with  the  anterior  tibial  veins  to  form  the  popliteal,  and  possesses  in  its  course 
from  eight  to  twenty  valves.  A  short  distance  below  the  popliteus  muscle  it  receives 
the  peroneal  veins  (vv,  peroneae)  which  accompany  the  peroneal  artery.  They  are 
usually  of  larger  calibre  than  the  posterior  tibial  veins,  receiving  a  larger  share  of  the 
vessels  which  come  from  the  posterior  crural  muscles,  and  they  anastomose  with  the 
posterior  tibials  by  frequent  transverse  branches,  and  also  with  the  anterior  tibials. 
They  possess  from  eight  to  ten  valves. 

The  anterior  tibial  veins  (vv.  tibiales  anteriores)  are  the  upward  continuation 
of  the  venae  comites  of  the  art.  dorsalis  pedis.  They  accompany  the  anterior  tibial 
artery,  and  are  united  across  the  artery  by  numerous  transverse  anastomoses.  They 
pass  with  the  artery  to  the  posterior  surface  of  the  crus  above  the  interosseous  mem- 
brane and  unite  with  the  posterior  tibials  to  form  the  popliteal  vein.  They  make 
communications  with  both  the  peroneal  and  posterior  tibial  veins  by  branches  which 
perforate  the  interosseous  membrane,  and  are  furnished,  on  the  average,  with  about 
eleven  valves. 

THE  POPLITEAL  VEIN. 

The  popliteal  vein  (v.  poplitea)  (Fig.  768)  is  a  single  trunk  formed  by  the  union 
of  the  anterior  and  posterior  tibial  veins  at  the  lower  border  of  the  popliteus  muscle, 
and  it  extends  from  that  point  to  the  opening  in  the  adductor  magnus  which  transmits 
the  femoral  artery.  It  is  throughout  closely  bound  down  by  dense  connective  tissue 
to  the  popliteal  artery,  and  lies  between  that  vessel  and  the  internal  popliteal  nerve. 
Its  course,  however,  is  not  quite  parallel  to  that  of  the  artery,  but  in  its  lower  part 
it  is  slightly  internal  to  the  artery  and  in  its  upper  part  somewhat  external  to  it. 
The  popliteal  vein  possesses  from  one  to  four  valves  and  is  directly  continuous  above 
with  the  femoral  vein. 

In  addition  to  the  popliteal  vein,  the  popliteal  artery  has  two  other  smaller  veins 
accompanying  it.  The  external  one  (v.  comitans  lateralis)  has  its  origin  from  the 
veins  issuing  from  the  outer  head  of  the  gastrocnemius  and  the  soleus,  and  passes 
upward  along  the  outer  surface  of  the  artery  to  open  into  the  popliteal  vein  at  about 
the  middle  of  its  course.  The  inner  vena  comitans  (v.  comitans  medialis)  is  formed 
by  the  veins  issuing  from  the  inner  head  of  the  gastrocnemius  and  ascends  along  the 
inner  side  of  the  artery,  making  connections  with  the  inferior  and  superior  internal 
articular  veins,  to  open  into  the  popliteal  vein  just  below  the  opening  in  the  adductor 
magnus. 

Tributaries. — The  majority  of  the  tributaries  of  the  popliteal  vein  correspond 
to  the  branches  of  the  popliteal  artery, — that  is  to  say,  they  are  articular  and 
muscular.  In  addition  it  receives  the  short  saphenous  vein  at  about  the  middle  of 
its  course. 

Variations. — The  popliteal  vein  may  be  considerably  shorter  -than  usual  owing  to  the  fail- 
ure of  the  tibial  veins  to  unite  at  the  customary  level.  Not  infrequently  the  vein  is  double 
throughout  a  portion  of  its  course,  more  rarely  throughout  its  entire  length,  and  it  occasionally 
lies  beneath  (i.e.,  anterior  to)  the  artery. 

It  normally  communicates  by  means  of  its  tributaries  with  branches  of  the  deep  femoral 
vein,  and  occasionally  this  communication  becomes  so  large  that  the  popliteal  seems  to  bifurcate 
above,  one  branch  becoming  continuous  with  the  femoral  and  the  other  with  the  deep 
femoral.  More  interesting  from  the  historical  stand-point  are  the  rare  cases  in  which  the  vein 


912 


HUMAN   ANATOMY. 


ascends  the   back  of  the  thigh  along  with  the  sciatic  nerve,  either  uniting  above  with  c 
the  branches  of  the  deep  femoral  or  continuing  into  the  pelvis  with  the  nerve  to  become  a 

FIG.  768. 


Tibial  nerve 

Semitendinosus  muscle 

Popliteal  artery 
Semimembranosus  muscle 

Azygos  articular  vein 
Communication  with 

internal  saphenous  vein 

Popliteal  vein 
External  saphenous  vein 

Sural  veins 


Gastrocnemius  muscle, 

inner  head 


Popliteus  muscle 


Posterior  tibial  artery 

Communication  between 
anterior  and  posterior 

tibtel  veins 


Posterior  tibial  veins 


Communication  with 

deep  femoral  vein 


Biceps  muscle 


Superior  external 

articular  veins 


Plantaris  muscle 


Gastrocnemius, 

outer  head 


Anterior  tibial  vein 
Anterior  tibial  artery 
Soleus,  cut  surface 


Gastrocnemius, 

cut  surface 


Deep  fascia,  cut  edge 


Veins  of  right  popliteal  space. 


tributary  of  the  internal  iliac  vein.     This  last  arrangement  recalls  ;m  anomaly  occasionally  pre- 
sented by  the  sciatic  artery  (page  815),  and  is  probably  clue  to  the  same  embryological  conditions. 


THE  VEINS   OF   THE   LOWER   LIMB. 


THE  FEMORAL  VEIN. 

The  femoral  vein  (v.  femoralis)  (Fig.  769)  accompanies  the  femoral  artery 
from  the  opening  in  the  adductor  muscle  through  Hunter's  canal  and  Scarpa's 
triangle  to  its  beginning  at  the  lower  border  of  Poupart's  ligament.  It  is  a  single 

FIG.  769. 


Anterior 

superior  spine  of  ilium 

Superficial 

circumflex  iliac  vein 

Sartorius,  cut 

Femoral  artery 

Rectus  femoris,  cut 

Femoral  vein 


External  circumflex  vein 
Deeo  femoral  vein 


Vastus  externus 


Rectus  femoris,  cut 


Anastomotica  magna  vein 


Quadriceps 

extensor  tendot 


Patella, 

displaced  outwardly 


Superficial  epigastric  vein 
Poupart's  ligament 
External  pudic  vein 

Pectineus  muscle 
Dorsal  vein  of  penis 

Internal  saphenous  vein 


—  Superior  perforating  vein 
Deep  femoral  vein 
Middle  perforating  vein 

Inferior  perforating  vein 


Muscular  vein 


Femoral  artery 

Tendon  of  adductor  magnus 


Internal  saphenous  vein 


Popliteal  vein 


Right  femoral  vein  and  its  tributaries. 
58 


914  HUMAN   ANATOMY. 

trunk  and  is  the  direct  continuation  of  the  popliteal  vein  below,  and  it  terminates  by 
becoming  continuous  with  the  external  iliac  vein  above.  In  its  lower  part  it  lies 
slightly  external  to  the  artery,  but  throughout  the  greater  part  of  its  course  it  rests 
upon  the  posterior  surface  of  the  artery  and  is  enclosed  in  a  common  sheath  with  it. 
Above  it  inclines  somewhat  inwardly  and  comes  to  lie  upon  the  inner  surface  of  the 
artery,  between  it  and  the  femoral  canal.  It  possesses  from  one  to  five  pairs  of 
valves,  the  most  constant  pair,  present  in  81  per  cent,  of  cases,  being  situated  in  the 
upper  5  cm.  of  the  vein  and  consequently  controlling  the  flow  from  all  the  veins  of 
the  lower  limb. 

Tributaries. — The  tributaries  of  the  femoral  vein  correspond  with  the  branches 
of  the  femoral  artery,  although  some  of  them  communicate  with  the  vein  only  indirectly, 
opening  primarily  into  the  long  saphenous  vein,  which  is  itself  a  tributary  of  the 
femoral.  Thus,  the  long  saphenous  usually  receives  the  external  pudic,  superficial 
circumflex  iliac,  and  superficial  epigastric  veins,  and  these  will  be  described  later 
with  the  saphenous  veins.  Of  the  remaining  tributaries,  (  i  )  the  deep  femoral,  (  2  > 
the  vents  comites,  and  (3)  the  anastomotica  magna,  the  first  two  deserve  special 
mention. 

1.  The  Deep  Femoral  Vein. — The  deep  femoral  vein  (v.  profunda  fcnioi  is  t 
accompanies  the  deep  femoral  artery,  and,  like  it,  receives  as  tributaries  perforating 
veins  (vv.  perforantes)  which  take  their  origin  upon  the  posterior  surface  of  the 
adductor  muscles  and  anastomose  with  one  another,  with  tributaries  of  the  popliteal 
below  and  with  the  sciatic  above.      The  lowest  perforating  vein,  which  represents  the 
actual  beginning  of  the  deep  femoral,  has  communicating  with  it  one  of  the  terminal 
branches  of  the  short  saphenous  vein.      The  deep  femoral  vein  also   receives   the 
internal    and    external    circumflex    veins    (vv.  circumllexa    femoris    medialis  et 
lateralis)    which  accompany  the  corresponding  arteries  as  their  venae  comites,   the 
internal    circumflex    anastomosing    with    the    sciatic   and    obturator    veins   and    so 
providing  for  a  possible  collateral  circulation  between  the  internal  and  external  iliac 
veins.     The    deep    femoral    opens    into  the   femoral    usually  about  4-5  cm.   In-low 
Poupart's    ligament,    but    not    infrequently   at    a    somewhat    higher   level,   and  the 
circumflex  veins  may  open  directly  into  the  femoral  instead  of  into  the  deepe'r  vein. 

2.  The  Vense  Comites. — The  venae  comites  of  the  femoral  artery  are  two  or 
three  small  stems  which  run   parallel  with   the  artery  and  vein  through  Hunter's 
canal.      One  lies  to  the  inner  side  of  the  artery  (v.  comitans  medialis)  and  the  other 
to  the  outer  side  (v.  comitans  lateralis),  and  when  a  third  is  present  it  accompanies 
the  long  saphenous  nerve.      They  communicate  with,  or  in  some  cases  receive,  the 
veins  issuing  from  the  adjacent  muscles  and  open  into  the  femoral  vein,  usually  a 
little  below  the  point  where  it  receives  the  deep  femoral  vein. 

Variations. — The  portion  of  the  femoral  vein  above  the  entrance  of  the  deep  femoral  is 
sometimes  termed  the  common  femoral  vein  and  the  rest  of  it  the  superficial  femoral,  the 
common  femoral  being  formed  by  the  union  of  the  superficial  and  deep  veins. 

Occasionally  the  vein  lies  anterior  to  the  artery  throughout  a  considerable  portion  <>f  its 
course,  and  it  may  be  double  to  a  greater  or  less  extent,  the  two  veins  in  such  cases  either  lying 
posterior  to  the  artery  or  one  on  either  side  of  it. 

It  occasionally  passes  up  the  leg  behind  the  adductor  niagmis.  passing  through  the  muscle 
where  it  is  normally  perforated  by  one  of  the  perforating  veins,  this  arrangement  being 
apparently  due  to  the  enlargement  of  a  connection  with  the  deep  femoral  and  of  the  anastomosis 
between  the  perforating  veins.  In  such  cases  the  femoral  artery-  is  accompanied  by  one  or  two 
small  stems,  perhaps  representing  the  venae  comites,  and  in  those  cases  in  which  the  popliteal 
vein  passes  up  the  back  of  the  thigh  (page  911)  the  femoral  is  also  greatly  reduced  in  size. 

THE  SUPERFICIAL  VK1NS. 
THE  SUPERFICIAL  VEINS  OF  THE  FOOT. 

It  has  already  been  pointed  out  (page  910)  that  the  dorsal  and  plantar  digital 
veins  may  be  grouped  either  with  the  superficial  or  deep  veins  of  the  foot,  since  they 
communicate  extensively  with  both  sets.  The  superficial  connections  of  the  plantar 
digitals  are  with  an  arcus  vcnosus  plantaris  cutaneus  which  runs  across  the  foot  at  the 
bases  of  the  toes  and,  bending  upward  over  the  edges  of  the  foot,  communicates  with 
the  dorsal  veins.  Posteriorly  to  this  arch  is  a  subcutaneous  net-work  (rete  venosum 


THE  VEINS   OF   THE   LOWER   LIMB. 


9*5 


Biceps 
Popliteal  vein 


plantare  cutaneum)  which  is  especially  close  in  the  fatty  pad  beneath  the-heel,  but  more 
open  towards  the  bases  of  the  toes.  This  net-work  makes  numerous  connections 
with  the  deep  plantar  veins,  and  to  a  great  extent  is  drained  by  superhcial  emissaries 
which  pass  upward  over  the  borders  of  the  foot  and  open  into  the  superficial  dorsal 
veins.  These  emissaries  are  larger  on  the  inner  than  on  the  outer  side  of  the  foot,  and 
they  all  have  a  somewhat  backward  as  well  as  an  upward  direction,  those  from  the 
most  posterior  portions  of  the  plexus  passing  directly  backward  and  upward  over 
the  tuberosity  of  the  heel.  Anteriorly  the  more  central  portions  of  the  net-work  drain 
into  the  superficial  plantar  arch  and  communicate  through  this  with  the  dorsal  veins. 
The  dorsal  digital  veins  form  by  their  union  in  pairs  the  common  digital  veins 
\  v.  digitales  communes  pcdis),  which  correspond  in  position  to  the  dorsal  interosseous 
veins,  except  that  they  are  subcutaneous.  Posteriorly  these  veins  anastomose  to  from 
a  more  or  less  regular  dorsal  subcu- 
taneous arch  (arcus  venosus  dorsalis  FIG.  770. 
pedis),  which  extends  across  the  dorsal 
portions  of  the  metatarsal  bones,  being 
convex  distally  and  increasing  in  size 
from  the  outer  to  the  inner  border  of 
the  foot.  Proximally  to  this  arch  there 
is  an  irregular  net- work  of  veins  (rete 
venosum  dorsale  pcdis)  which  makes 
numerous  connections  with  the  deep 
veins  and  passes  proximally  into  the 
net-work  of  the  anterior  surface  of  the 
crus.  Towards  the  borders  of  the  foot,  M~~shortu 

...  ,.   '  f>  n\        saphenous  vein 

and  forming  the  lateral  and  medial 
boundaries  of  the  net-work,  a  more  or 
less  distinct  longitudinal  marginal 
vein  can  be  seen  on  each  side  (vv. 
margijialcs  lateralis  et  mcdialis),  and  it  is 
into  these  that  the  superficial  emissaries 
from  the  plantar  net-work  open  from 
below.  The  internal  marginal  vein  is 
somewhat  larger  than  the  external  and 
joins  the  dorsal  arch  to  form  the  long 
saphenous  vein,  while  the  external  is  the 
principal  origin  of  the  short  saphenous. 

THE  SHORT  SAPHENOUS  VEIN. 

The  short  or  external  saphenous 
vein  (v.  saphena  parva)  (Fig.  770)  is  the 
superficial  vein  of  the  back  of  the  crus. 
It  begins  behind  the  external  malleolus 
at  the  Upward  continuation  of  the  ex- 
ternal marginal  vein  of  the  foot.  It  lies 
at  first  upon  the  outer  border  of  the 
tendo  Achillis,  but  later  takes  a  more 
median  position  and  ascends  the  pos- 
terior surface  of  the  leg  almost  in  the 
median  line.  At  about  the  middle  of 
the  leg  it  perforates  the  crural  fascia 
and  continues  its  upward  course  in  the 
groove  between  the  two  heads  of  the 
gastrocnemius,  and,  entering  the  pop- 
liteal space,  terminates  by  dividing  into 
two  branches,  one  of  which  opens  into  the  posterior  surface  of  the  popliteal  vein 
about  on  a  level  with  the  origins  of  the  gastrocnemius,  while  the  other  passes 
farther  upward  to  communicate  with  the  beginning  of  the  deep  femoral  vein. 


Superficial  veins  on  dorsum  of  right  toot  and 
posterior  surface  of  leg. 


916  HUMAN   ANATOMY. 

The  short  saphenous  vein  possesses  from  nine  to  ten  valves  in  its  course  up  the 
leg.  In  its  lower  part  it  accompanies  the  external  or  short  saphenous  nerve,  which 
lies  beneath  (i.e.,  anterior  to)  it,  and  above  it  accompanies  a  branch  of  the  small 
sciatic  nerve. 

Tributaries. — The  short  saphenous  vein  drains  the  outer  border  of  the  foot 
and  the  whole  of  the  posterior  superficial  portion  of  the  crus.  Near  its  origin  it 
receives  the  posterior  emissaries  from  the  superficial  plantar  net-work,  and  throughout 
its  course  up  the  crus  it  receives  numerous  branches  from  the  superficial  net-work  of 
the  posterior  surface  of  that  portion  of  the  leg,  and  through  this  net-work  makes 
communications  with  the  long  saphenous  vein.  The  terminal  branch  which  com- 
municates with  the  deep  femoral  vein  receives  a  stem  known  as  the  v  femoropoplitea, 
which  runs  downward  upon  the  back  of  the  thigh,  superficially,  receiving  branches 
from  the  posterior  superficial  net-work  of  the  thigh  and  communicating  above  with 
the  sciatic  and  gluteal  veins. 

Variations. — The  short  saphenous  vein  occasionally  opens  into  the  long  saphenous  by  the 
enlargement  of  one  of  the  anastomoses  between  the  two  veins,  only  a  small  vessel  representing 
its  communication  with  the  popliteal.  It  has  been  observed  to  continue  up  the  thigh  without 
or  with  but  a  small  communication  with  the  popliteal  and  deep  femoral  veins,  and,  entering  the 
pelvis  with  the  great  sciatic  nerve,  to  open  into  the  internal  iliac  vein.  In  such  cases  its  femoral 
portion  probably  represents  the  original  femoral  portion  of  the  sciatic  vein,  and  has  the  same 
significance  as  the  prolongation  of  the  popliteal  up  the  thigh,  of  which  mention  has  already  been 
made  (page  911). 

THE  LONG  SAPHENOUS  VEIN. 

The  long  or  internal  saphenous  vein  (v.  saphena  magna)  (Fig.  771)  has  its 
origin  in  the  junction  of  the  inner  end  of  the  dorsal  arch  of  the  foot  with  the  inner 
marginal  vein.  It  passes  upward  in  front  of  the  inner  malleolus  and  then  in  the 
groove  between  the  medial  border  of  the  tibia  and  the  inner  border  of  the  gastrocne- 
mius  muscle.  As  it  approaches  the  knee-joint  it  bends  slightly  backward  to  pass 
behind  the  internal  condyle  of  the  femur,  and  then  continues  up  the  thigh  in  an 
almost  direct  course  to  the  fossa  ovalis,  where  it  pierces  the  cribriform  fascia  and 
opens  into  the  femoral  vein. 

It  is  subcutaneous  throughout  its  entire  course  and  possesses  from  twelve  to 
eighteen  valves,  some  of  which,  especially  in  old  individuals,  are  apt  to  be  insufficient. 
Throughout  its  course  up  the  crus  it  accompanies  the  long  saphenous  nerve,  and  in 
the  thigh  it  lies  at  first  along  the  line  of  the  outer  (anterior)  edge  of  the  sartorius, 
but  later  crosses  that  muscle  obliquely  so  as  to  lie  internal  to  it  above. 

Tributaries. — At  its  origin  the  long  saphenous  vein  receives  some  of  the  more 
posterior  internal  emissaries  of  the  plantar  net-work,  and  in  its  course  up  the  crus  it 
receives  the  blood  from  all  those  portions  of  the  superficial  crural  net-work  which  do 
not  communicate  with  the  short  saphenous.  In  the  thigh  it  is  the  collecting  stem 
for  all  the  superficial  veins,  those  from  the  posterior  surface  frequently  uniting  to  form 
an  accessory  saphenous  vein  (v.  saphena  accessoria),  while  those  from  the 
anterior  surface  may  form  an  external  superficial  femoral  vein  (Fig.  771). 

Throughout  its  entire  course  it  makes  numerous  connections  with  the  deep  veins. 
with  the  anterior  tibial  by  some  five  or  six  branches  (TT.  sapheno-tibiales  a  uteri  ores), 
with  the  posterior  tibial  by  usually  three  (rr.  sdfihoio-tibia/cs  postcn'tvrs ),  and  with 
the  femoral  or  one  of  its  tributaries  by  usually  a  single  one.  Various  communications 
with  the  small  saphenous  also  occur. 

In  addition  to  these  various  connections,  the  long  saphenous  receives,  just 
before  its  entrance  into  the  femoral,  a  number  of  vessels  which  accompany  some  of 
the  superficial  branches  of  the  femoral  artery.  They  are  by  no  means  constant 
tributaries  of  the  saphenous,  but  frequently  pass  through  the  cribriform  fascia  to 
open  directly  into  the  femoral  vein. 

i.  The  External  Pudic  Veins. — The  external  pudic  veins  (vv.  pudcndac 
externae)  are,  like  the  corresponding  arteries,  two  in  number,  one  superficial  and 
one  deep.  They  have  their  origin  in  the  external  genitals,  receiving  nunierou> 
veins  from  the  anterior  surface  of  the  scrotum  (vv.  scrotalcs  antcriorcs)  or  tin- 
anterior  portions  of  the  labia  majora  (vv.  labialcs  antcriorcs ).  They  also  receive  a 


THE  VEINS    OF   THE    LOWER    LIMB. 


917 


Anterior  superior 
spine  of  ilium 


Superficial 
epigastric  vein 


Femoral  vein 


External  superficial 
femoral  vein 


Patella 


;;• 


single  or  paired  vein  which  runs  along  the  dorsal  surface  of  the  penis  or  clitoris 
immediately  beneath  the  integment  (v.  dorsalis  penis  (  clitoridis)  subcutanea  j,  and  at 
the  symphysis  pubis  bends  later- 
ally to  join  the  external  pudics.  i'ic;. 

2.  The    Superficial    Cir- 
cumflex    Iliac     Vein. — The 
superficial    circumflex   iliac    vein 
(v.  circumilexa  ilium  superficialis) 
accompanies    the   artery    of    the 
same    name,    receiving   subcuta- 
neous branches   from  the  lower 
lateral   portions  of  the  abdomen 
and  from  the  anterior  hip  region. 
It    frequently    unites    with    the 
superficial  epigastric  vein  before 
opening  into  the  saphenous. 

3.  The   Superficial   Epi- 
gastric Vein. — The  superficial 
epigastric     vein     (v.     epigastrica 
superficialis  )  takes  its  origin  from 
the   subcutaneous   veins    of    the 
lower  part  of  the  anterior  abdom- 
inal wall  as  high  as  a  little  above 
the  umbilicus.      It  is  joined  at  a 
varying     level     by    the    thoraco- 
epigastric  vein  (Fig.  775),  which 
opens    above    into    the    axillary 
vein,    and    is    occasionally    pro- 
longed    downwaid     to     open 
independently     into     the     long 
saphenous. 

Variations. — The  long  saphe- 
nous vein  may  perforate  the  fascia 
lata  some  distance  below  the  fossa 
ovalis.  It  is  not  infrequently  replaced 
in  the  crural  portion  of  its  course  by  a 
net-work  of  veins  in  which  no  special 
main  stem  can  be  recognized,  and  in 
the  thigh  it  is  occasionally  double. 

PRACTICAL  CONSIDERATIONS. 
— THE  ILIAC  VEINS  AND 
THE  VEINS  OF  THE  LOWER 
EXTREMITY. 

The  common  iliac  veins 

illustrate  the  rule  (Owen)  that 
below  the  diaphragm  the  veins  of 
the  trunk  are  on  a  plane  posterior 
to  the  arteries  (except  the  renal) 
and  incline  generally  to  the 
venous — the  right — side.  Thus 
the  left  common  iliac  is  always 
on  the  inner  fright)  side  of  the 
corresponding  artery  and  ulti- 
mately crosses  the  right  artery, 
on  a  posterior  plane.  The  right 

vein  begins  slightly  to  the  inner  side  of  the  right  artery,  which  it  crosses — 
on  a  posterior  plane — to  reach  the  right  side  of  the  fifth  lumbar  vertebra.  These 
relations  are  important  in  operations  on  the  common  iliac  arteries  (page  808). 


Dorsal 

venous  arch 


Inner  malleolus 


Superficial  veins  of  right  lower  limb;  internal 
aspect . 


9i8  HUMAN    ANATOMY. 

The  internal  iliac  veins  may  become  involved  in  infections  of  any  of  the 
numerous  plexuses  from  which  their  tributaries  arise.  Thus,  puerperal  metritis 
may  not  only  lead  to  pelvic  cellulitis  (page  2014),  but  may  set  up  a  thrombophlebitis 
in  the  intra-uterine  veins  which,  spreading  to  the  internal  and  common  iliac  veins, 
will  obstruct  the  venous  current  from  the  whole  lower  extremity,  bringing  about  a 
wide-spread  oedema,  with  aching  and  tenderness  (phlegmasia  alba  dolens,  milk  leg). 
Similar  conditions  sometimes  follow  septic  infection  of  the  prostatic  vesical  and 
hemorrhoidal  plexuses.  The  practical  relations  of  these  venous  channels  have  been 
described  in  connection  with  the  prostate,  bladder,  and  rectum.  The  branches 
of  the  internal  iliac  vein  aid  indirectly  in  supporting  the  pelvic  viscera.  They  are 
apt  to  be  varicose  in  the  aged,  especially  in  females.  They  supply  the  blood  in 
cases  of  pelvic  haematocele. 

The  external  iliac  vein  is  frequently  involved  in  femoral  phlebitis,  the 
continuity  of  direction  and  calibre  between  it  and  the  femoral  being  practically 
unbroken. 

The  femoral  vein  is  not  infrequently  the  subject  of  thrombo-phlebitis,  descend- 
ing, as  a  result  of  some  form  of  pelvic  infection  (vide  supra},  or  ascending,  following 
septic  infection  of  the  soft  parts  or  bones  of  the  lower  extremity  ;  or  occasionally 
directly  caused  by  contusion  of  the  vessel  just  below  the  groin,  or  by  its  bruising 
during  forced  flexion  of  the  thigh.  Femoral  phlebitis  is  not  uncommonly  a  sequel 
of  enteric  fever  and  of  other  exhausting  diseases,  and  is  a  familiar  post-operative 
complication  of  operations  for  the  removal  of  the  appendix,  the  uterus,  the  tubes  and 
ovaries,  and  other  abdomino-pelvic  procedures,  even  when  apparently  unattended  by 
infection.  The  predisposing  causes  are  thought  to  be  the  relative  immobility  of  the 
patient  and  the  consequent  sluggishness  of  the  circulation,  especially  in  the  lower 
extremities,  the  dependent  position  of  the  limb  in  bed,  and  the  altered  constitution 
of  the  blood  (in  the  case  of  fever)  ;  the  exciting  cause  is  probably  a  very  slight 
degree  of  infection.  Pain  and  oedema  follow,  but  such  cases  almost  always  do  well. 
On  account  of  its  nearness  to  the  artery,  both  vessels  are  often  wounded  at  the  same 
time,  with  the  resulting  formation — if  the  communication  between  them  is  direct — 
of  an  aneurismal  varix  ;  or  if  it  is  indirect — an  aneurismal  sac  intervening — of  a 
varicose  aneurism.  Wounds  requiring  ligation  and  sudden  occlusion  of  the  vein 
from  any  cause  are  dangerous  from  the  risk  of  development  of  moist  gangrene. 
Lateral  suture  of  wounds  in  this  vein  has  been  successfully  employed  in  a  number  of 
instances.  The  femoral  vein  is  not  infrequently  involved  in  ulcerative  malignant 
or  phagedenic  processes  implicating  the  skin  of  the  groin  and  upper  thigh,  or  the 
inguinal  lymphatic  nodes. 

After  ligation,  the  collateral  circulation  is  established  between  the  veins  of  the 
buttocks  and  the  internal  circumflex  veins,  and  between  the  veins  of  the  pdvis  and 
the  external  pudic  veins. 

The  practical  relations  of  the  femoral  vein  to  femoral  hernia  have  been  described 
(page  1773). 

The  popliteal  vein,  together  with  the  artery  (which  is  closer  to  the  bone,  and 
therefore  more  easily  compressed  or  torn),  has  been  lacerated  in  supracondyloid 
fracture  of  the  femur.  It  has  been  so  compressed  by  a  popliteal  aneurism  as  to  cause 
thrombosis  and  enormous  distention  of  the  veins  and  of  the  leg.  Owing  to  tin- 
unyielding  character  of  the  boundaries  of  the  ham,  it  may  also  be  sufficiently  com 
pressed  by  inflammatory  exudates,  by  abscess,  or  by  enlarged  bursae,  to  cause 
swelling  and  oedema  of  the  foot  and  leg.  The  vein  is  so  exceptionally  thick -walled 
that  in  spite  of  its  more  superficial  position  it  is  never  ruptured  alone,  but  only  when 
the  force  is  sufficient  to  tear  the  artery  also.  The  involvement  of  both  may  be  favt  >red 
by  the  fact  that  the  two  vessels  are  so  closely  united  that  it  is  difficult  to  separate  them, 
and  this  also  favors  the  occasional  production  of  aneurismal  varix  or  varicose 
aneurism  after  stab- wounds.  This  close  connection  makes  the  denudation  of  the 
artery  difficult  in  the  operation  for  its  ligation. 

The  veins  of  the  leg  are,  with  the  possible  exception  of  the  veins  of  the 
pampiniform  and  hemorrhoidal  plexuses,  more  often  the  subject  of  varicosity  than 
any  other  veins  of  the  body.  This  is  due  to  (i)  the  high  blood-pressure  in  these 
veins,  resulting  from -(a)  the  erect  posture  of  the  human  species  and  the  consequent 


THE    PORTAL  SYSTEM.  919 

vertical  position  of  these  veins  ;  (6)  the  length  of  the  column  of  blood  they  carry, 
extending,  in  the  case  of  the  long  saphenous  vein,  from  its  beginning  at  the  ankle  to 
the  upper  orifice  of  the  inferior  vena  cava  ;  (V)  in  many  cases  to  compression  above, 
as  from  abdominal  or  pelvic  growths,  or  the  gravid  uterus,  or  from  garters.  (2)  In 
the  superficial  veins  the  frequency  of  varicosity  is  also  due  to  the  lack  of  adequate 
external  support  to  their  thin  and  distensible  walls,  the  saphenous  veins,  for  example, 
lying  outside  of  the  deep  fascia  in  loose  connective  tissue.  (3)  To  the  increased 
resistance  that  must  be  overcome  at  the  points  where  the  deep  and  superficial  vessels 
communicate,  and  where  in  many  cases  the  varicosity  seems  to  begin.  At  such 
points  the  upward  current  of  blood  has  to  overcome — and  the  walls  of  the  veins  to 
support — not  only  the  downward  pressure  of  the  vertical  column  of  blood  in  the 
vessels  above  it,  but  also  the  resistance  of  the  blood-stream  driven  out  of  the  deep 
vein  by  the  contracting  muscles  between  which  it  lies,  and  entering  the  superficial 
vein  at  a  right  angle.  The  valve  next  below  this  point  of  entrance  prevents  the  relief 
that  might  be  obtained  from  temporary  distention  of  a  long  lower  section  of  the  vein 
and  limits  these  forces  to  a  circumscribed  area,  which  yields  and  becomes  varicose. 

The  venous  plexus  between  the  two  layers  of  the  muscles  of  the  calf  is  often  the 
seat  of  varices  of  great  size.  The  six  chief  veins  which  pass  from  the  soleus  muscle 
alone  to  enter  into  the  posterior  tibial  and  peroneal  trunks  have  a  united  diameter 
of  not  less  than  one  inch  (Treves). 

The  fact  that  each  of  the  saphenous  veins  is  accompanied  by  a  sensory  nerve 
accounts  for  the  aches  and  pains  associated  with  varicosity. 

THE  PORTAL  SYSTEM. 

The  portal  system  is  composed  of  all  the  veins  which  have  their  origin  in  the 
walls  of  the  digestive  tract  below  the  diaphragm  (with  the  exception  of  those  of  the 
lower  part  of  the  rectum)  and  includes  also  the  veins  which  return  the  blood  from 
the  pancreas,  spleen,  and  gall-bladder.  It  presents  a  marked  peculiarity  in  that  the 
system  begins  and  ends  in  capillaries,  the  blood  which  it  contains  having  entered  its 
constituent  veins  from  the  capillaries  of  the  intestine,  stomach,  and  the  other  organs 
mentioned  above,  and  passing  thence  to  the  liver,  where  it  traverses  another  set 
of  capillaries,  by  which  it  reaches  the  hepatic  veins  and  so  the  heart.  Coming  as 
it  does  principally  from  the  intestine,  the  portal  blood  is  more  or  less  laden  with 
nutritive  material,  which  has  been  digested  and  absorbed  through  the  intestinal 
walls,  but  is  not  yet  in  a  condition,  so  far  as  some  of  its  constituents  are  concerned, 
suitable  for  assimilation  by  the  tissues.  To  undergo  the  changes  necessary  for  its 
conversion  into  assimilable  material  it  is  carried  by  the  portal  vein  to  the  liver,  and  as  it 
passes  through  the  capillaries  of  that  organ  it  undergoes  the  necessary  modifications. 

In  other  words,  the  portal  vein  stands  in  a  somewhat  similar  relation  to  the  liver 
that  the  pulmonary  vein  does  to  the  lungs.  Its  purpose  is  not  to  convey  material  to 
the  organ  for  its  nutrition,  that  being  accomplished  by  the  hepatic  arteries  for  the 
liver  just  as  it  is  accomplished  by  the  bronchial  arteries  for  the  lungs,  but  to  carry  to 
the  liver  crude  material  upon  which  the  organ  may  act,  elaborating  it  and  returning 
it,  as  required,  to  the  circulation  in  a  purified  and  assimilable  condition. 

The  inclusion  of  the  veins  of  the  spleen,  gall-bladder,  and  pancreas,  or  even  of 
those  of  the  rectum,  in  the  portal  system  is  to  be  explained  on  the  ground  of  topo- 
graphic relationship  rather  than  on  the  basis  indicated  above. 

The  main  stem  of  the  portal  system  will  first  be  described  and  then  its  tributaries 
in  succession. 

THE  PORTAL  VEIN. 

The  portal  vein  (v.  portae)  (Figs.  772,  774)  is  formed  behind  the  head  of  the 
pancreas  by  the  union  of  the  superior  mesenteric  and  splenic  veins,  the  latter  receiving 
the  inferior  mesenteric  vein  shortly  before  its  union  with  the  superior  mesenteric. 
The  two  veins  unite  almost  at  a  right  angle,  and  from  their  point  of  union  the  portal 
vein  passes  obliquely  upward  and  to  the  right,  along  the  free  edge  of  the  lesser 
omentum,  towards  the  transverse  fissure  of  the  liver.  There  it  divides  into  two 
trunks,  of  which  the  right  is  the  larger  and  shorter  and  quickly  bifurcates  into 
an  anterior  and  a  posterior  branch.  It  is  distributed  to  the  whole  of  the  right 


920 


HUMAN   ANATOMY. 


lobe  of  the  liver  and  to  the  greater  part  of  the  Spigelian  and  quadrate  lobes,  the 
remainder  of  these  lobes  and  the  left  lobe  receiving  branches  from  the  left  trunk. 

The  trunks  of  the  vein  or  their  branches  enter  the  substance  of  the  liver  and 
divide  in  a  more  or  less  distinctly  dichotomous  manner  to  form  interlobidar  veins, 
which,  as  their  name  indicates,  occupy  a  position  between  the  lobules  of  the  organ, 
and  give  of?  capillaries  which  traverse  the  lobule  and  empty  into  the  intralobular 
veins,  the  origins  of  the  hepatic  veins. 

The  portal  vein  measures  about  8  cm.  (3^  in. )  in  length  and  has  a  diameter  of 
from  1.5  to  2  cm.  Its  walls,  especially  in  its  upper  portion,  contain  a  considerable 
quantity  of  muscle-tissue  and  it  is  destitute  of  valves. 

Relations. — At  its  origin  the  portal  vein  lies  behind  the  head  of  the  pancreas 
and  to  the  left  of  the  vena  cava  inferior.  As  it  ascends  it  comes  to  lie  at  first  behind 


FIG.  772. 


Round  ligament  of  liver 


Hepatic  duct 
Cystic  duct 


Spigelian  lobe  of  liver 

Kiyht  crus  of  diaphragm 
Hepatic  artery 

'^Spleen 


Cystic 
Portal 

Common  bile-duct 

Pyloric  vein 
Superior  mesenteric  vein 


Right 

gastro-epiploic  vei 


Tributaries  of 

middle  colic  vein 


Gastric  artery 
Coeliac  axis 
Stomach 
Splenic  artery 
Gastric  vein 

Splenic  vein 

Inferior  mesentery  \ciii 
Left  jjastro-epiploic  vein 
Pancreas 


Portal  vein  and  its  tributaries;  liver  has  been  pulled  upward. 

the  first  portion  of  the  duodenum  and  then  between  the  two  layers  of  the  lesser 
omentum.  In  this  latter  portion  of  its  course  it  is  associated  with  the  hepatic  artery 
and  the  common  bile-duct,  both  of  which  lie  anterior  to  it,  the  artery  to  the  left  and  the 
duct  to  the  right.  It  enters  the  transverse  fissure  towards  its  right  extremity,  hence 
the  shortness  of  the  right  trunk  compared  with  the  left,  and  its  trunks  have  in  front 
of  them  the  branches  of  the  hepatic  artery,  the  hepatic  ducts  lyini;  anterior  to  these. 
Tributaries. — The  tributaries  of  the  portal  vein  are  :  (i)  the  superior  mescn- 
teric,  (2)  tin-  splenic,  (3)  the  inferior  nicscntcric,  (4)  the  gastric,  (5)  the pyloric, 
and  (6)  the  cystic  reins.  In  addition  to  these  principal  tributaries,  the  portal  vein,  or 
IN  1  Handles  within  the  liver,  also  receives  a  number  of  small  veins  which  have  their 
origin  in  the-  falciform  ligament  of  the  liver  and  in  the  lesser  omentum,  and,  further- 
more, it  receives  at  the  transverse  fissure  (7)  some  panitnbilical  reins  which  ascend 
the  anterior  abdominal  wall  along  with  the  round  ligament. 


THE   PORTAL  SYSTEM.  921 

i.  The  Superior  Mesenteric  Vein. — The  superior  mesenteric  vein  (v.  mesen- 
terica  superior)  (Fig.  773)  accompanies  the  artery  of  the  same  name,  lying  upon  its 
right  side.  It  has  its  beginning  somewhere  in  the  neighborhood  of  the  terminal 
portion  of, the  ileum  and  ascends  in  the  line  of  attachment  of  the  mesentery.  Above, 
it  passes  over  the  third  portion  of  the  duodenum  and  then  between  that  portion 
of  the  intestine  and  the  lower  border  of  the  pancreas,  uniting  behind  the  head  of  the 
pancreas  with  the  splenic  vein  to  form  the  portal  vein.  It  possesses  no  valves. 

Tributaries. — The  tributaries  of  the  superior  mesenteric  vein  correspond  with  the  branches 
of  the  corresponding  artery,  except  that  it  receives  in  addition  the  pancreatico-duodenal  and 
right  gastro-epiploic  veins  which  accompany  the  similarly  named  branches  of  the  hepatic  artery. 

(a)  The  veins  of  the  small  intestine  (vv.  intestinales)  have  their  origin  in  the  walls  of  the 
small  intestine  from  the  last  portion  of  the  duodenum  to  within  a  short  distance  of  the  ileo-csecal 
valve.  Their  arrangement  is  essentially  similar  to  that  of  the  arteries  of  the  small  intestine,  the 
numerous  small  branches  which  emerge  from  the  intestine  being  united  "by  transverse  anasto- 
moses, as  a  rule  more  numerous  than  those  of  the  arteries,  and  forming  one  or  more  series  of 
venous  arcades  lying  between  the  two  layers  of  the  mesentery.  From  these  arcades  branches 
arise  which  pass  towards  the  superior  mesenteric  vein,  gradually  uniting  to  form  about  twenty 
stems  which  open  independently  into  the  superior  mesenteric.  The  branches  of  origin  of  the 
intestinal  veins,  just  after  they  emerge  from  the  intestine  are  provided  with  valves  in  the  child, 
but  they  usually  degenerate  more  or  less  completely  before  adult  life. 

(6)  The  ileo-colic  vein  (v.  ileocolica)  arises  at  the  junction  of  the  ileum  and  caecum  by  the 
union  of  a  caecal  and  an  ileal  branch,  the  latter  of  which  anastomoses  with  the  origin  of  the 
superior  mesenteric.  The  caecal  branch  receives  an  appendicular  vein  from  the  appendix  vermi- 
formis,  and  the  main  stem  passes  upward  between  the  two  layers  of  the  mesentery  to  open  into 
the  superior  mesenteric  just  before  it  passes  over  the  duodenum. 

(c)  The  right  colic  veins  (vv.  colicae  dextrae)  originate  in  the  walls  of  the  ascending  colon 
and  are  two  or  three  in  number.    They  anastomose  by  transverse  branches  with  the  ileo-colic  and 
middle  colic  veins  and  pass  almost  horizontally  medially  to  open  into  the  superior  mesenteric. 

(d)  The   middle   colic   vein    (v.  colica    media)    emerges  from  the  transverse  colon   by   a 
number  of  small  branches  which  anastomose  to  the  right  and  left  with  the  right  and  left  colic 
veins,  and  unite  to  a  single  stem  which  opens  into  the  superior  mesenteric  just  before  it  passes 
beneath  the  pancreas. 

(e)  The  right  gastro-epiploic  vein  (v.  gastroepiploica  dextra)  runs  from  left  to  right  along 
the  greater  curvature  of  the  stomach,  communicating  directly  with  the  left  gastro-epiploic  at 
about  the   middle  of  the  curvature.     It  receives  tributaries  from  the  lower  portions  of  the 
anterior  and  posterior  surfaces  of  the  stomach  and  from  the  greater  omentum,  and  opens  into 
the  superior  mesenteric  shortly  before  its  union  with  the  splenic.     It  occasionally  receives  a 
pancreatico-duodenal  vein,  and  may  unite  with  the  middle  colic  vein  to  form  a  gastro-colic 
vein  instead  of  opening  directly  into  the  superior  mesenteric. 

(_/)  The  pancreatico-duodenal  veins  (vv.  pancreaticoduodenales),  like  the  arteries,  may  be 
two  in  number,  one  of  which  opens  directly  into  the  superior  mesenteric  and  the  other 
into  the  right  gastro-epiploic.  Frequently,  however,  they  are  broken  up  into  a  number  of 
separate  vessels  arising  independently  from  each  of  the  two  viscera  concerned,  the  duodenum 
(vv.  duodenales)  and  the  head  of  the  pancreas  (vv.  pancreaticae). 

2.  The  Splenic  Vein. — The  splenic  vein  (v.  lienalis)  (Fig.  774)  is  formed  by 
the  union  of  five  or  six  branches  which  emerge  from  the  hilum  of  the  spleen.  It  passes 
almost  horizontally  to  the  right  below  the  splenic  artery,  resting  at  first  upon  the 
upper  border  of  the  pancreas,  but  later  coming  to  lie  behind  that  organ.  Behind  the 
head  of  the  pancreas  it  unites  with  the  superior  mesenteric  to  form  the  portal  vein. 

Tributaries. — These  correspond  with  the  branches  of  the  artery,  and  in  addition  it  receives 
near  its  termination  the  inferior  mesenteric  vein,  which  for  purposes  of  description  will,  however, 
be  regarded  as  independent. 

(a)  The  short  gastric  veins  (vv.  gastricae  breves)  arise  from  the  fundus  of  the  stomach  and 
pass  between  the  layers  of  the  gastro-splenic  omentum  to  open  partly  into  the  splenic  vein  and 
partly  into  its  branches  of  origin  as  they  emerge  from  the  hilum. 

(b)  The  left  gastro-epiploic  vein  (v.  gastroepiploica  sinistra)  passes  from  right  to  left  along 
the  greater  curvature  of  the  stomach,  communicating  directly  with  the  right  gastro-epiploic  about 
half-way  along  the  curvature.     It  receives  branches  from  the  lower  portions  of  both  surfaces  of 
the  stomach  and  from  the  greater  omentum,  and  opens  into  the  splenic  vein  near  its  formation. 

(c)  The  pancreatic  veins   (vv.  pancreaticae),  which  may  be  five  or  more  in  number,  open 
into  the  splenic  vein  at  various  points  in  its  passage  behind  the  pancreas. 


922 


HUMAN   ANATOMY. 


3.  The  Inferior  Mesenteric  Vein. — The  inferior  mesenteric  vein  (v.  mesen- 
terica  inferior)  (Fig.  774)  is  formed  by  the  junction  of  the  superior  hemorrhoidal  and 
sigmoid  veins  opposite  the  sigmoid  flexure  of  the  colon,  and  passes  upward  in 
company  with  the  corresponding  artery.  It  is  continued  on,  however,  beyond  the 
point  where  the  artery  arises  from  the  abdominal  aorta,  lying  behind  the  peritoneum 
slightly  medial  to  the  ascending  colon,  and,  finally,  it  passes  beneath  the  pancreas 


IMC;.  773. 


Ascending  colon 
Middle  colic  veil 
Right  colic  vein 


Superior 

mesenteric  vein 


lleo-colic  vein 


-  Transverse  colon 


Descending  colon 

-Left  colic  vein 

Pancreas 

Inferior  mesenteric  vein 

Superior  mesenteric  arterj 

Duodenum,  transverse  par 

Jejunum 

Veins  of  the  small  intestim 


Cofls'of  lleum 


Superior  mesenteric  vein  and  its  tributaries;    transverse  colon 
has  been  pulled  upward. 

to  open  usually  into  the  splenic  vein  not  far  from  its  union  with  the  superior 
mesenteric.  Occasionally  it  opens  into  the  latter  vein  (Fig.  774)  or  else  equally 
into  both,  thus  taking  a  direct  part  in  the  formation  of  the  portal  vein. 

Tributaries. — Its  tributaries  correspond  to  tin-  branches  of  the-  artery. 

(a)  The  superior  hemorrhoidal  vein  i  v.  haemorrhoidalis  superior)  has  its  origin  from  the 
upper  part  of  the  hemorrhoida!  plexus  by  several  branches,  and,  passing  upward,  unites  with  the 
si-moid  veins  to  form  the  inferior  mesenteric.  Through  the  hemorrhoidal  plexus  it  communi- 
cates with  the  middle  and  inferior  hemorrhoidal  veins,  thus  placing  the  portal  and  inferior  caval 
systems  in  communication. 

(t>)  The  sigmoid  veins  (vv.  sinmoideae)  are  variable  in  number  and  pass  from  the  sigmoid 
flexure  and  the  lower  portion  of  the  descending  colon  to  the  inferior  mesenteric,  the  lowest  one 
uniting  with  the  superior  hemorrhoidal  to  form  that  vein. 


THE   PORTAL  SYSTEM.  923 

(c)  The  left  colic  vein  (v.  coiica  sinistra)  has  its  origin  in  the  walls  of  the  descending  colon, 
anastomosing  above  with  the  middle  colic  and  below  with  the  sigmoid  veins.  It  passes  medially 
to  open  into  the  upper  part  of  the  inferior  mesenteric. 

4.  The  Gastric  Vein. — The  gastric  vein  (v.  coronaria  ventriculi)  (Fig.  772) 
accompanies  the  gastric  artery  along  the  lesser  curvature  of  the  stomach.      It  has  its 
origin  at  the  pyloric  end  of  the  stomach,  where  it  anastomoses  with  the  pyloric  vein, 
and  passes  at  first  from  right  to  left  along  the  lesser  curvature,  receiving  tributaries 
from   the   upper   part  of    both   surfaces  of   the  stomach.      At  the   opening   of   the 
oesophagus  into   the  stomach  it  makes  connections  with  the  cesophageal  veins,  and 
then  bends  upon  itself  and  passes  from  left  to  right  behind  the  posterior  wall  of  the 
lesser  sac  of  the  peritoneum,  and  terminates  either  in  the  portal  vein  or  in  the  splenic 
shortly  before  its  union  with  the  superior  mesenteric. 

The  peculiar  reflected  course  of  the  gastric  vein  is  readily  understood  if  it  be  remembered 
that  the  adult  position  of  the  stomach  is  a  secondary  one.  When  first  formed  the  long  axis  of 
the  stomach  is  practically  vertical,  the  pyloric  end  being  directed  downward,  and  a  vein  starting 
at  the  pylorus  will  have  a  direct  ascending  course  to  the  portal  vein.  When  the  stomach  as- 
sumes its  adult  position  the  course  of  the  vein  with  reference  to  the  viscus  does  not  alter,  and 
consequently  it  passes  from  pylorus  to  cardia,  and  must  then  bend  back  upon  itself  to  reach  the 
portal  vein. 

5.  The  Pyloric  Vein. — The  pyloric  vein  (v.  pylorica)  (Fig.  772)  accompanies 
the  pyloric  branch  of  the  hepatic  artery.      It  takes  its  origin  at  the  pyloric  end  of  the 
stomach,  where  it  anastomoses  with  the  gastric  vein,  and  passes  downward  to  open 
into  the  portal. 

6.  The   Cystic  Vein. — The  cystic  vein    (v.  cystica)   (Fig.   772)   returns  the 
blood  from  the  walls  of  the  gall-bladder  and  opens  usually  into  the  right  trunk  of  the 
portal  vein.      It  is  frequently  represented  by  two  separate  stems. 

7.  The  Parumbilical  Veins. — The  parumbilical  veins  (vv.  parumbilicales)  are 
a  number  of  small  veins  which  have  their  origin  in  the  anterior  abdominal  wall  in  the 
neighbourhood  of  the  umbilicus  and  pass  upward  in  the  fold  of  peritoneum  which 
contains  the  round  ligament  of  the  liver.     They  anastomose  below  with  both  the 
superficial  and  deep  epigastric  arteries  and  also  with  small  vessels  which  pass  down- 
ward alongside  of  the  urachus  to  empty  into  the  vesical  plexus.      Above,  the  majority 
of  them  enter  the  quadrate  and  left  lobes  of  the  liver,  but  one  of  them,  the  vena 
supraumbilicalis,  enters  the  substance  of  the  round  ligament  at  a  varying  level  and 
opens  into  the  more  or  less  extensive  lumen  of  that  structure,  which  represents  the 
umbilical  vein  of  foetal  life.      This  lumen  appears  to  persist  in  the  majority  of  cases, 
although  greatly  reduced  in  size  from  that  of  the  umbilical  vein,  and  may  extend 
throughout  almost  the  entire  length  of  the  round  ligament,  although  perhaps,  more 
usually,  it  is  limited  to  its  upper  part,  and  opens  into  the  right  trunk  of  the  portal 
vein.     When  the  lumen  is  entirely  obliterated  it  is  possible  that  the  supraumbilical 
vein,  which  has  also  been  termed  the  accessory  portal  vein,  may  open  directly  into 
the  portal  vein. 

Collateral  Circulation  of  the  Portal  Vein. — Considering  the  fact  that  the  portal  vein 
terminates  in  capillaries  in  the  substance  of  the  liver,  it  is  evident  that  certain  pathological 
conditions,  such  as  cirrhotic  changes,  which  may  occur  in  that  organ,  will  more  or  less  completely 
interfere  with  the  return  of  the  blood  to  the  heart  from  the  intestine,  spleen,  and  pancreas,  by 
producing  an  obliteration  of  the  capillaries.  The  possibilities  of  a  collateral  circulation  are 
therefore  important,  and  a  number  of  routes  occur  by  which,  under  stress,  the  blood  of  the 
portal  venous  system  may  pass  around  the  liver  and  reach  the  heart  through  one  of  the  other 
systems.  The  functional  capabilities  of  these  various  routes  are  furthered  by  the  fact  that  none 
of  the  tributaries  of  the  portal  vein  possess  valves  except  in  their  finer  branches,  and  the  blood 
can  therefore  flow  in  them  in  a  reverse  direction  if  necessary.  The  principal  collateral  routes 
are  as  follows  : 

1.  Through  the  gastric  vein  the  blood  may  pass  to  the  cesophageal  veins  and  thence  to  the 
azygos  and  hemiazygos  veins.     When  this  route  is  functional  the  oesophageal  veins  become 
enlarged  and  frequently  varicose,  forming  contorted  elevations  upon  the  surface  of  the  oesophagus. 

2.  Through  the  superior  hemorrhoidal  veins  connections  are  made  by  way  of  the  hemor- 
rhoidal  plexus  with  the  hemorrhoidal  branches  of  the  internal  iliac.     These  connections  seem, 
however,  to  be  less  frequently  functional  than  either  the  cardiac  or  parumbilical  routes. 


HUMAN   ANATOMY. 


3.  Through  the  umbilical  and  suprauuibilical  veins  to  the  superficial  or  deep  epigastrics  and 
so  to  the  external  iliac  veins.  It  is  interesting  to  note  that  in  cases  where  this  route  is  functional 
the  enlargement  of  the  superficial  epigastric  veins  is  usually  accompanied  by  a  development  of 
varicosities  upon  them,  while  this  is  not  the  case  with  the  deep  epigastrics.  An  explanation  of 
this  difference  has  been  found  in  the  fact  that  the  deep  veins,  before  opening  into  the  external 
iliac,  bend  slightly  backward,  so  that  their  orifices  are  directed  in  the  same  way  as  the  flow  of 
blood  in  the  larger  stem,  whereas  the  superficial  epigastrics  open  from  above  into  the  long 
saphenous  veins,  their  orifices  being  opposed,  therefore,  to  the  flow  of  blood  in  the  saphenous, 
— a  condition  which  naturally  predisposes  towards  stasis  of  the  blood  in  the  epigastrics  and,  it 
may  be  remarked,  also  of  that  in  the  saphenous. 

These  are  the  principal  routes,  but  it  must  be  noted  that  anastomoses  also  exist  between 
the  portal  system  and  the  phrenic  veins  by  means  of  the  small  veins  which  descend  towards  the 


Liver,  uiuler  surface 

Spigelian  lobe  uf  Iher 

Crura  of  diapliragr 


Round  ligament 


Vena  cava  inferior 

1'ortal  vein 

Pyloric  vein 

Cystic  -duct 

Cueliac  axis 

Gall-bladder 

Castro-duodenal   vein 

Common  bile-duct 

Renal  vein 


Superi 


mesenteric  vein 


Superior 

mesenteric  artery 


Ascending  colon 


Aorta 


Inferior 

mesenteric  artery 


Superior 

hemorrlioidal  \ein 


Sigmoid  colon 


Termination 
of  ileuiii         Cut 

edge  of     Cavity  ot 
mesentery 


Inferior  mesenteric  and  splcni.    \rins  and  tributaries  of  portal  vein;  stomarli  and 
transverse  colon  have  been  removed  and  liver  pulled  upward. 


liver  in  the  falciform  ligament,  and  communications  with  the  interior  caval  system  also  occur 
by  means  of  anastomoses  between  the  peritoneal  and  mesenteric  veins,  both  of  which  are  (|uite 
small. 

Finally,  it  may  be  mentioned  that  anomalous  and  therefore  inconstant  communications  of 
the  portal  branches  with  those  of  other  systems  have  been  observed.  Thus  the  gastric,  tin- 
short  gastrics.  or  the  pyloric  vein  may  anastomose  with  the  phivnics  ;  the  splenic  or  the  lelt 
-astro-epiploic  with  the  n-nals  ;  the  right  or  left  colic  with  the  branches  from  the  fatty  capsule  of 
the  corresponding  kidney;  and  the  duodenal  branches  may  open  into  the  inferior  vena  cava. 


THE   PORTAL  SYSTEM. 


925 


Practical  Considerations. — The  portal  system  may  be  obstructed  by  (a) 
tumors  or  swellings  involving  the  liver  itself,  as  carcinoma,  hydatids,  or  abscess  ;  (6) 
enlargement  of  the  gall-bladder  from  new  growth  or  from  concretions  ;  (c)  tumors 
of  contiguous  structures,  as  disease  of  lymph-nodes  in  the  portal  fissure  or  between 
the  layers  of  the  lesser  omentum,  or  carcinoma  of  the  head  of  the  pancreas  ;  (d) 
disease  of  the  liver  tissue,  especially  cirrhosis  (chronic  interstitial  hepatitis)  in 
which  the  interlobular  veins  are  compressed  by  the  contraction  of  the  connective 


FIG.  775. 


External  jugular  vein 


Subscapula 


III.,  IV..  and  V 
anterior  i«rforatin<; 
veins  and  tribut; 


Tributaries  of 
superior  epigastric  vein 


Tributary  of 

deep  epigastric  veia 


Thoraco-epigastric  vein 


Superficial 

circumflex   iliac  vein 


Saphenous  opening 
Internal  saphenous  vein 


External  jugular  vein 

Cephalic  vein 

Axillary  artery 
Axillary  veil 


Brachial 
veins 


V'.,  VI.,  and  VII. 

intercostal  vein 


Tributary    of 

musculo-plirenic  vein 


—Thoraco-epigastric  vein 


Tributary  of 

deep  epigastric  vein 


Superficial  epigastric  ven 


Femoral  vein 

Deep  dorsal  vein  of  penis 


•Superficial 

dorsal  vein  of  penis 

Internal  saphenous  vein 


Superficial  veins  of  anterior  body-wall ;    pectoralis  and  external  intercostal  muscles  (of 

fifth  to  seventh  intercostal  spaces)  on  left  side  have  been   removed.  • 

tissue  in  the  spaces  between  the  lobules  ;  (<?)  valvular  disease  of  the  heart  leading  to 
backward  pressure  through  the  cava  and  hepatic  and  intralobular  veins  which  finally 
reaches  the  terminal  capillaries  of  the  portal  vein  and  then  the  interlobular  veins 
and  the  entire  portal  system,  resulting  in  some  cases  in  the  so-called  nutmeg  liver 
(cyanotic  atrophy).  The  consequences  of  portal  obstruction  are  various,  but  may,  as 
a  rule,  easily  be  understood  by  referring  each  symptom  to  its  anatomical  basis  in 


926 


HUMAN    ANATOMY. 


obstruction  of  one  or  the  other  of  the  venous  tributaries.  The  chief  results  are  : 
(i)  Enlargement  of  the  liver  itself,  at  first  congestive,  later  from  hyperplasia. 
Diminution  in  the  quantity  of  bile  or  alteration  in  its  character  may  cause  constipa- 
tion and  indigestion  ;  or  escape  of  its  coloring  matter  and  its  absorption  by  the 
hepatic  veins  may  give  rise  to  jaundice.  (2)  From  congestion  of  the  gastric  and 
intestinal  mucosa  (through  the  superior  and  inferior  mesenteric,  splenic,  and  gastric 
tributaries)  there  may  develop  indigestion,  flatulence,  eructations,  and  vomiting,  often 
bloody  ;  serous  exudation  into  the  bowel — intestinal  indigestion,  and  diarrhoea,  some- 
times with  black  stools  from  decomposed  blood — or  into  the  general  peritoneal 
cavity — ascites  ;  enlargement  and  tenderness  of  the  spleen  ;  hemorrhoids  (from  the 
communication  between  the  middle  and  inferior  hemorrhoidal  veins — systemic — and 
the  superior  hemorrhoidal  vein — portal)  ;  varicosities  in  the  lower  extremities,  possibly 
from  the  same  communication  between  the  caval  and  portal  systems,  but  oftener  from 
the  direct  interference  by  an  enlarged  liver  with  the  current  in  the  inferior  cava. 

Septic  inflammation  of  the  liver  may  reach  that  organ  through  any  of  the  portal 
tributaries.  It  is  not  uncommonly  the  result  of  infection  originating  during  a  dysen- 
teric attack.  Cancer  may  also  reach  the  liver  by  venous  channels,  usually  by  the 
gastric  or  hemorrhoidal  tributaries. 

As  the  number  of  extraperitoneal  anastomoses  between  the  branches  of  the 
parietal  vessels  (lower  intercostal,  phrenic,  lumbar,  ilio-lumbar,  epigastric  and  circum- 
flex iliac)  and  branches  of  vessels  that  supply  viscera  without  a  complete  peritoneal 
covering  (liver,  kidneys,  suprarenals,  duodenum,  pancreas,  ascending  and  descending 
colon)  are  of  great  importance  in  case  of  obstruction  to  the  visceral  arterial  supply, 
so  the  corresponding  venous  anastomoses  are  of  equal  or  greater  importance  in 
obstruction  of  the  portal  vein  or  of  the  inferior  cava.  The  occasional  connection 
between  a  parumbilical  vein  and  the  external  iliacs — through  the  epigastrics — may 
also  relieve  portal  obstruction.  The  above  anastomoses  explain  the  effect  of  leeches 
or  wet  cups  or  counter-irritation  of  the  surface  in  congestions  or  inflammations  of 
the  partly  extraperitoneal  viscera.  (Woolsey.) 

DEVELOPMENT  OF  THE  VEINS. 

The  embryonic  venous  system  may  be  regarded  as  consisting  of  three  sets  of  vessels. 
One  of  these  becomes  the  pulmonary  veins,  another  gives  rise  to  the  portal  and  umbilical  veins, 
while  the  third  is  represented  by  what  are  termed  the  cardinal  veins.  It  is  to  these  last  that 
attention  may  first  be  directed. 

The  Cardinal  Veins. — The  cardinal  veins  (Fig.  776)  are  two  longitudinal  stems  which 
extend  the  entire  length  of  the  body,  one  on  either  side  of  the  median  line,  receiving  throughout 

their  course  lateral  somatic  and  visceral  branches 

FIG.  776.  in  more  or  less  perfect  segmental  succession. 

From  each  vein  a  branch  passes  medially  towards 
the  heart,  and  the  portion  of  the  longitudinal 
vein  anterior  to  this  cross-branch  is  termed  the 
anterior  cardinal  or  primitive  jugular,  while 
that  behind  it  is  known  as  \!(\^ posterior  cardinal. 
The  cross-branch,  which  is  usually  described  as 
formed  by  the  union  of  the  anterior  and  pos- 
terior cardinals,  is  termed  the  duct  of  Cnvier. 

The  anterior  cardinals  take  their  origin 
from  veins  which  ramify  over  the  surface  of  the 
brain  and  receive  at  first  both  the  ophthalmic  and 
facial  veins.  The  cerebral  veins  later  condense 
to  form  the  superior  and  inferior  longitudinal, 
the  straight,  and  the  lateral  sinuses,  with  the  last 
of  which  the  ophthalmic  veins  unite,  their  intra- 
cranial  portions  becoming  the  cavernous  and 
inferior  petrosal  sinuses  The  facial  veins,  how- 
ever, sever  their  connection  with  the  cerebral 
veins  and  unite  with  other  superficial  veins  to 
form  the  external  jugular — a  vessel  which  in 
some  mammalia  reaches  a  high  degree  of  dev«-l 

opment,  almost  or  entirely  replacing   the  internal   jugular,  which    represents   tin-   mai.i   st 
of  the  cardinal.      In  man  the  original  condition,  in  which  the  external  jugular  is  of  subordin 


—Anterior  cardinal 


—Venous  sinus  of  heart 
—  Duct  of  Cuvier 
— Vitelline  vein 

— I'n.liilical  vein 
— Posterior  cardinal 


Diagram  showing  primary  symmetrical 
ent  of  i 


venous  system. 


DEVELOPMENT   OF   THE   VEINS. 


927 


importance,  is  more  nearly  retained,  but  indications  of  a  transference  of  blood  from  the  intracranial 
portions  of  the  internal  jugular  system  to  the  external  vessel  are  to  be  seen  in  the  emissary  veins. 
At  first  each  internal  jugular  opens  independently  into  the  right  auricle  through  the 
corresponding  duct  of  Cuvier  (Fig.  777,  A),  but  later  a  communicating  branch  extending 
obliquely  across  from  the  left  to  the  right  vein  is  developed  (Fig.  777,  £),  and  thereafter  the 


Superior  cardinal 

(internal  jugular) 


Cuvierian  duct 
Primary  inf.  cava 
Posterior  cardinal 


Internal  jugular 
External  jugular 
Subclavian 


•Left  innominate 


I  Oblique  vein  of 

left  auricle 
Coronary  sinus 


Inferior  vena  cava 


I          .  I  | 

Diagrams  illustrating  development  of  superior  vena  cava;  A,  primary  symmetrical  arrangement ;  B,  establishment 
of  transverse  connection  ;  C,  atrophy  on  left  side  and  persistence  on  right  side  of  superior  vena  cava. 

lower  portion  of  the  left  vein  degenerates  until  it  is  represented  only  by  the  small  oblique  vein  of 
the  left  auricle,  opening  into  the  coronary  sinus,  which  is  the  persisting  left  ductus  Cuvieri 
(Fig.  777.  C).  The  oblique  connecting  branch  becomes  the  left  innominate  vein  of  adult 
anatomy,  and  the  portion  of  the  left  anterior  cardinal  below  the  point  where  it  is  joined  by  the 
innominate,  together  with  the  right  ductus  Cuvieri,  becomes  the  superior  vena  cava. 

The  Inferior  Vena  Cava. — The  posterior  cardinals  persist  in  part  as  the  azygos  veins,  but 
their  history  is  so  intimately  associated  with  that  of  the  inferior  vena  cava  that  an  account  of  the 
development  of  the  latter  may  first  be  presented.  In  the  early  stages  of  development  the  only 
portion  of  the  inferior  vena  cava  which  exists  is  the  portion  which  intervenes  between  the  entrance 
of  the  hepatic  veins  and  the  right  auricle,  this  portion  representing  the  terminal  part  of  the  ductus 

FIG.  778. 


•t —   Coronary  sinus 


Hemiazygos 


Inferior   vena   cava 


Diagrams  illustrating  developmental  changes  leading  to  formation  of  inferior  caval  and  azygos  veins. 

venosus  (page  705).  Branches  which  pass  to  the  posterior  cardinal  veins  from  the  mesentery 
anastomose  longitudinally  to  form  on  each  side  of  the  body  a  venous  stem  which  has  a  course 
parallel  to  that  of  the  cardinals,  with  which  it  unites  below  ( Fig.  778,  A}.  This  is  the  subcardinal 
vein,  the  two  vessels  of  opposite  sides  of  the  body  being  united  with  one  another  and  with  the 
cardinals  by  a  strong  cross-branch  which  joins  the  cardinals  opposite  the  point  of  entrance, into 


928 


HUMAN   ANATOMY. 


DC 


DC 


those  of  the  renal  veins.  The  portion  of  the  right  subcardinal  which  lies  anterior  to  the  cross- 
branch  then  enlarges  and  unites  with  the  existing  portion  of  the  inferior  vena  cava,  and  the  lower 
portion  of  the  right  cardinal,  together  with  the  portion  of  the  cross-branch  which  intervenes 
between  it  and  the  right  subcardinal,  also  enlarges,  and  these  three  elements  eventually  come 
into  line  with  one  another  and  with  the  terminal  portion  of  the  ductus  venosus  to  form  the 
inferior  vena  cava. 

The  lower  portions  of  both  subcardinals  now  degenerate,  and  the  upper  portion  of  the  left 
vein,  diminishing  in  size,  becomes  the  left  suprarenal  vein.  A  cross-branch  forms  between 
the  two  posterior  cardinals  at  the  level  of  the  common  iliac  veins,  and  the  lower  part  of  the  left 
cardinal  then  disappears  (Fig.  778,  C),  a  small  portion  below  the  original  renal  cross-branch 
alone  persisting  to  form  the  terminal  part  of  the  left  spermatic  (ovarian)  vein,  which  thus  comes 
to  open  into  the  left  renal  vein,  since  the  terminal  portion  of  that  vessel  represents  the  original 
renal  cross-branch.  As  a  result  of  this  degeneration  the  left  common  iliac  vein  comes  to  open 
into  the  lower  part  of  the  right  posterior  cardinal  by  way  of  the  iliac  cross-branch. 

The  Azygos  Veins. — While  these  changes  have  been  taking  place  the  anterior  portions  of 
the  posterior  cardinals  have  undergone  degeneration  immediately  anterior  to  the  renal  cross- 
branch  (Fig.  778),  so  that  they  form  independent  vessels,  receiving  the  intercostal  veins  and 
terminating  above  in  the  ductus  Cuvieri.  They  now  constitute  the  azygos  veins,  and,  on  the 

degeneration  of  the  lower  part  of  the  left 

FIG.  779.  anterior  cardinal,  the  left  azygos  develops 

connection  with  the  right  by  one  or  two 
transverse  branches  and  then  separates 
from  the  coronary  sinus,  the  adult  condi- 
tion of  the  hemiazygos  vein  being  thus 
acquired. 

The  Portal  Vein. — Passing  along  the 
umbilical  cord  to  the  body  of  the  embryo 
are  two  vitelline  or  omphalo-mesenteric 
veins,  which  have  their  origin  in  the  yolk- 
sac,  and  the  umbilical  vein,  which  brings 
back  the  blood  from  the  placenta.  When 
it  reaches  the  umbilicus,  the  umbilical 
vein  divides  into  two  stems  which  pass 
upward  upon  the  inner  surface  of  the 
anterior  abdominal  wall  and  unite  above 
with  the  corresponding  vitelline  veins  to 
open  into  the  ductus  Cuvieri.  The  vitel- 
line veins  pass  from  the  umbilicus  to  the 
intestine  and  ascend  along  it,  receiving 
tributaries  from  it ;  above,  they  traverse 
the  liver,  breaking  up  into  a  net-work  in  its 
substance,  and  are  then  continued  on  to 
unite  with  the  umbilicals  (Fig.  779,  . /i. 
By  the  enlargement  of  certain  portions  of 
the  hepatic  net-work  a  well-marked  venous 
stem  is  formed,  extending  from  the  point 
where  the  left  vitelline  vein  enters  the  liver 
to  the  junction  of  the  common  stem  formed 
by  the  right  vitelline  and  umbilical  veins 
with  the  duct  of  Cuvier.  This  new  stem  is 
the  ductus  rcnosns  (Figs.  779,  B  and  C), 

and  it  later  forms  a  connection  with  the  left  umbilical  vein  and  becomes  the  continuation 
of  that  vessel  as  the  result  of  the  degeneration  of  the  upper  part  of  the  umbilical  (/)}. 

In  the  meantime  three  cross-connections  have  developed  between  the  two  vitelline  veins 
(Fig.  779,  A,  /?,  C),  two  of  them  passing  ventral  to  the  intestine  and  one  dorsal  to  it,  the 
intestine  thus  becoming  surrounded  by  two  venous  rings.  The  right  half  of  the  lower  ring 
and  the  left  half  of  the  upper  one  now  degenerate  (/?),  and  the  persisting  portions,  which 
terminate  partly  in  the  hepatic  net-work  and  partly  in  the  ductus  venosus,  become  the  portal 
vein.  The  upper  portion  of  the  right  umbilical  vein  has  in  the  meantime  made  a  connection 
with  the  upper  ring  of  the  vitelline,  and  the  part  above  the  connection  then  degenerates,  the 
lower  part  becoming  much  reduced  in  si/e  and  persisting  as  a  small  parumbilical  vein  in  the 
anterior  abdominal  wall.  This  arrangement  persists  until  birth,  the  placenta!  blood  passing  by 
way  of  the  left  umbilical  vein  partly  to  the  ductus  venosus  and  thence  by  the  inferior  vena  cava  to 
the  heart  and  partly  through  the  hepatic  net-work  by  way  of  the  communication  between  the  left 
umbilical  and  vitelline  veins.  At  birth  the  placenta!  supply  of  blood  is  of  course  cut  off,  the  ductus 


DC 


DC 


•-lu 


DC 


!r 


Diagrams  illustrating  transformations  of  vitelline  and 
umbilical  veins  during  development  of  liver-veins.  DC,  ducts 
of  Cuvier;  h,  heart;  ru,  lu,  right  and  left  umbilical  veins; 
rv,  Iv,  right  and  left  vitelline  veins  ;  civ,  ductus  venosus  ;  pv, 
portal  vein.  (Hochstetter.) 


THE   FCETAL  CIRCULATION.  929 

venosus  degenerates  to  a  solid  cord  up  to  the  point  where  the  hepatic  veins,  developed  from  the 
hepatic  net-work,  unite  with  it.  The  umbilical  vein  also  degenerates  to  form  the  round  ligament 
of  the  liver,  which  frequently  presents  more  or  less  distinct  evidences  of  its  original  lumen. 

The  Veins  of  the  Limbs. — The  details  of  the  development  of  the  limb  veins  are  not  as  yet 
thoroughly  known.  The  superficial  veins  are  the  first  to  form,  the  basilic  vein  of  the  arm  and 
the  long  saphenous  of  the  leg  being  the  primary  vessels  and  the  axillary  and  subclavian  and  the 
iliac  veins  their  respective  continuatipns.  The  remaining  superficial  veins  and  the  deep  veins 
are  later  formations. 

The  Pulmonary  Veins. — The  pulmonary  veins  make  their  exit  from  the  lungs  as  four 
vessels,  two  belonging  to  each  lung,  but  as  they  approach  the  heart  they  unite  first  in  pairs  and 
then  to  form  a  single  trunk  which  opens  into  the  right  auricle.  Later  a  considerable  portion  of 
the  original  veins  is  taken  up  into  the  wall  of  the  auricle,  the  absorption  eventually  extending 
beyond  the  point  of  the  union  of  the  original  veins  in  pairs,  so  that  in  the  adult  all  four  veins 
open  independently  into  the  auricle. 

THE  FCETAL  CIRCULATION. 

The  primary  or  vitelline  circulation  of  the  mammalian  embryo,  formed 
by  the  ramifications  of  the  vitelline  arteries  and  veins  over  the  yolk-sac  (umbilical 
vesicle),  must  be  regarded  as  an  inheritance  from  ancestors  in  whom  the  yolk 
provided  the  nutrition  for  the  developing  animal.  While  in  birds  and  reptiles 
the  vitelline  veins  are  important  channels  for  the  conveyance  of  the  nutritive 
materials  taken  up  from  the  yolk,  in  mammals  in  this  respect  they  are  of  little 
consequence,  thus  affording  an  example  of  structures  that,  although  no  longer 
useful,  recur  in  the  development.  The  vitelline  circulation  is  soon  followed  by  a 
second,  the  allantoic  circulation,  which  in  man  and  the  higher  mammals  provides 
the  vessels  connecting  the  foetus  with  the  placenta — the  organ  whereby  respiration 
and  nutrition  are  secured  to  the  foetus  during  the  greater  part  of  its  sojourn  within 
the  uterus. 

The  blood  is  carried  from  the  foetus  to  the  placenta  by  the  hypogastric  arteries 
and  their  prolongations,  the  two  umbilical  arteries.  After  passing  through  the 
vascular  tufts  of  the  chorionic  villi  that  constitute  the  essential  structures  of  the  foetal 
part  of  the  placenta,  the  fcetal  blood,  renewed  in  oxygen  and  laden  with  nutritive 
material  derived  from  the  maternal  circulation,  is  carried  by  venous  tributaries  that 
unite  into  the  single  umbilical  vein.  The  latter  vessel  accompanies  the  umbilical 
arteries  within  the  umbilical  cord  as  far  as  the  umbilicus,  from  which  point  it  then 
passes  along  the  free  margin  of  the  crescentic  peritoneal  fold,  the  falciform  ligament, 
to  the  under  surface  of  the  liver  to  join  the  portal  vein  and  pour  its  stream  of  freshly 
oxygenated  blood  into  the  current  of  venous  blood  returned  from  the  digestive  tract 
to  the  liver.  For  a  short  time  the  rapidly  growing  liver  is  capable  of  transmitting 
all  the  blood  brought  to  it  by  the  vitelline  (later  portal)  and  the  umbilical  veins, 
and  this  blood  is  returned  to  the  heart  after  making  the  circuit  of  the  vessels  of  the 
liver.  Soon,  however,  the  latter  organ  can  no  longer  accommodate  the  entire 
volume  of  blood  conveyed  to  it  by  the  portal  and  umbilical  veins,  and  the  necessary 
relief  is  afforded  by  the  development  of  a  short  vessel,  the  ductus  venosus,  or 
ductus  Arantii,  that  extends  from  the  portal  vein  to  the  inferior  vena  cava  and 
thus  establishes  a  by-pass  for  the  greater  part  of  the  oxygenated  blood  returned 
from  the  placenta.  On  reaching  the  inferior  cava,  this  pure  blood  is  mingled  with 
the  venous  blood  being  returned  from  the  lower  half  of  the  body  and  the  abdominal 
viscera,  the  mixed  stream  so  formed  being  poured  into  the  right  auricle.  On  entering 
the  heart  the  current  is  directed  by  the  Eustachian  valve  towards  the  foramen 
ovale  in  the  auricular  septum  and  enters  the  left  auricle.  After  receiving  the 
meagre  additions  returned  by  the  pulmonary  veins  from  the  uninflated  lungs,  the 
blood  passes  through  the  left  auriculo-ventricular  opening  into  the  left  ventricle. 
Contraction  of  this  chamber  forces  the  blood  into  the  systemic  aorta  and  thence  to 
all  parts  of  the  body. 

After  traversing  the  vessels  of  the  head,  neck,  upper  extremities,  and  thorax, 
the  venous  blood  from  these  parts  is  returned  to  the  heart  by  the  superior  vena  cava, 
but  on  entering  the  right  auricle  does  not  mingle  to  any  extent  with  the  current 
returned  by  the  inferior  cava,  but  passes  through  the  auriculo-ventricular  orifice  into 
the  right  ventricle.  With  contraction  of  the  ventricles  the  blood  is  propelled  into 

59 


930 


HUMAN   ANATOMY. 


FIG.  780. 


the  pulmonary  artery  and  towards  the  lungs.  Being  uninflated  these  organs  can 
appropriate  only  a  small  part  of  the  entire  volume  of  blood  brought  by  the  pulmonary 
artery,  hence  the  necessity  of  a  second  by-pass,  the  ductus  arteriosus,  or  dnctns 
Botalli,  that  extends  from  the  beginning  of  the  left  pulmonary  artery  to  the 
adjacent  aorta  and  represents  the  still  pervious  distal  portion  of  the  last  aortic  arch 

on  the  left  side  (page  847).  By  means 
of  the  ductus  arteriosus,  the  venous  blood 
returned  from  the  head  and  upper 
extremities  is  poured  into  the  great 
descending  trunk,  the  aorta,  and  carried 
to  the  abdominal  viscera  and  the  lower 
extremities.  On  reaching  the  bifurcation 
of  the  common  iliac  arteries,  the  blood- 
stream divides,  that  part  going  into  the 
internal  iliacs  being  of  much  greater 
importance,  so  far  as  the  general  nutri- 
tion of  the  foetus  is  concerned,  since  it 
is  carried  by  the  continuations  of  these 
vessels — the  hypogastrics  and  umbilical 
arteries — to  the  placenta,  to  be  once  more 
purified  and  again  returned  to  the  foetus 
by  the  umbilical  vein. 

From  the  foregoing  sketch  of  the 
foetal  circulation  it  is  evident  that,  with 
the  exception  of  the  umbilical  vein,  no 
vessel  within  the  foetus  conveys  strictly 
arterial  or  fully  oxygenated  blood,  since 
on  entering  the  inferior  cava  the  pure 
blood  is  mixed  with  the  venous  returning 
from  the  lower  half  of  the  body.  It  is 
further  evident  that  the  blood  distributed 
to  the  head  and  upper  extremities  is  less 
contaminated  than  that  passing  to  the 
lower  half  of  the  body  from  branches  of 
the 
the 

ductus  arteriosus.  It  may  be  borne  in 
mind  that  the  umbilical  vein  and  the 
ductus  venosus  carry  arterial  blood  and 
the  pulmonary  artery  and  the  ductus 
arteriosus  purely  venous  blood,  the  aorta 
distributing  mixed.  Upon  the  assumption 
of  the  respiratory  function  at  birth,  the 
three  anatomical  structures  peculiar  to 
the  foetal  circulation — the  ductus  venosus, 
the  foramen  ovale,  and  the  ductus  arteri- 
osus— become  useless  and  soon  undergo 
occlusion  and  atrophy,  the  two  former 
ducts  being  represented  by  the  fibrous  cords  seen  on  the  posterior  surface  of  the  liver 
and  terminal  part  of  the  aortic  arch  respectively.  Closure  of  the  foramen  ovale 
proceeds  more  slowly,  a  week  or  more  being  usually  consumed  in  effecting 
obliteration  of  the  opening  ;  indeed,  in  a  large  proportion  complete  closure  never 
occurs  (page  695). 


aorta   gven   off   after    junction    with 
venous    stream     conveyed     by    the 


Diagram  of  foetal  circulation  shortly  before  birth : 
courseof  blood  is  indicated  by  arrows.  P, placenta;  UA, 
UV,  umbilical  arteries  and  vein  ;  U,  umbilicus ;  DV, 
ductus  venosus  ;  IVC,  inferior  vena  cava  ;  PV,  portal 
vein ;  HV,  hepatic  veins ;  RV,  LV,  right  and  left 
ventricle;  PA,  pulmonary  artery;  DA.  ductus  arteri- 
osus; SVC.  superior  vena  cava  ;  AA,  abdominal  aorta; 
HA,  hypogastric  arteries  (internal  iliac) ;  EIA,  ex- 
ternal iliac  arteries;  I,  intestine;  L,  lungs;  K,  kidney. 


THE  LYMPHATIC  SYSTEM. 

THE  lymphatic  system  is  a  system  of  vessels  which  occur  abundantly  in  almost 
all  portions  of  the  body  and  converge  and  anastomose  to  form  two  or  more  main 
trunks,  which  open  into  the  subclavian  veins  just  before  they  are  joined  by  the 
internal  jugular.  The  vessels  contain  a  fluid  termed  lymph,  usually  colorless,  and 
containing  numerous  corpuscles  known  as  lymphocytes.  Since  the  latter  usually 
come  under  observation  as  they  circulate  within  the  blood-vessels,  the  detailed 
account  of  the  lymphocytes  is  given  in  connection  with  blood-corpuscles  (page  684). 
In  those  vessels  which  have  their  origin  in  the  wall  of  the  small  intestine, 
however,  the  contained  fluid  has,  especially  during  digestion,  a  more  or  less  milky 
appearance,  owing  to  the  lymphocytes  being  loaded  with  particles  of  fat  which  they 
have  taken  up  from  the  intestinal  contents.  On  this  account,  these  vessels  are 
usually  spoken  of  as  ladcals,  although  it  must  be  recognized  that  they  are  merely 
portions  of  the  general  lymphatic  system. 

In  certain  respects  the  vessels  of  the  system  strongly  resemble  the  veins,  closely 
associated  with  which  they  take  their  origin  embryologically  and  into  which  they 
finally  pour  their  contents  in  the  adult.  They  arise  from  a  capillary  net-work,  their 
walls  have  a  structure  closely  resembling  that  of  the  veins,  they  are  abundantly 
supplied  with  valves,  and  it  may  be  said  that  the  fluid  which  they  contain  flows  from 
the  tissues  towards  the  heart.  With  these  similarities  there  are  combined,  however, 
marked  differences.  One  of  the  most  important  of  these  consists  in  the  fact  that 
the  capillaries  are  closed  and  do  not  communicate  with  any  centrifugal  set  of  vessels, 
as  the  venous  capillaries  do  with  the  arterial  ;  and  another  important  difference  is 
to  be  found  in  the  frequent  occurrence  upon  the  lymphatic  vessels  of  character- 
istic enlargements,  the  lymphatic  nodes  or  so-called  glands  (lyraphoglandulae),  quite 
different  from  anything  ^occurring  in  connection  with  the  veins. 

Lymph-Spaces. — Throughout  practically  all  regions  of  the  body  spaces  of 
varying  size,  occupied  by  a  clear,  more  or  less  watery  fluid,  exist,  and  to  these 
the  term  lymph-spaces  has  been  applied  (Fig.  781).  It  was  long  believed  that 
they  were  directly  continuous  with  the  lymphatic  capillaries,  that  the  latter,  indeed, 
opened  out  from  them,  the  spaces  forming  the  origins  of  the  capillaries.  There  is, 
however,  a  growing  tendency  to  dispute  this  view  and  to  regard  the  lymphatic 
capillaries  as  being  quite  independent  of  the  spaces, — the  entire  lymphatic  system, 
in  fact,  being  a  closed  system,  except  for  its  communications  with  the  subclavian 
veins.  Since,  however,  the  lymphatic  capillaries  form  net-works  in  the  tissues 
which  bound  these  spaces,  interchange  of  their  contents  with  those  of  the  capillaries 
is  by  no  means  difficult,  the  lymphocytes,  even,  passing  on  occasion  through  the 
walls  of  the  capillaries  into  the  spaces  and  returning  again  to  the  interior  of  the 
capillaries. 

If  a  colored  fluid  be  injected  into  the  portal  vein  it  will  pass  through  the  walls  of 
the  venous  capillaries  and  invade  the  spaces  of  the  interlobular  hepatic  connective 
tissue,  and  later  it  will  flow  away  by  the  hepatic  lymph-capillaries.  By  varying  the 
extent  of  the  injection  it  will  be  found  that  the  lymphatic  vessels  will  be  injected  when 
the  lymph-spaces  are  completely  filled,  but  will  not  be  when  the  spaces  are  only 
partially  injected  (Mall),  so  that  it  may  be  concluded  that  the  extravasation  from  the 
portal  capillaries  is  primarily  into  the  hepatic  lymph-spaces  and  thence  makes  its  way 
into  the  lymph-capillaries. 

The  spaces  vary  greatly  in  size,  existing  in  certain  tissues  even  between  the 
individual  cells.  They  are  more  evident,  however,  in  the  connective  tissues,  reaching 
a  considerable  size  in  areolar  tissue,  where  they  form  a  continuous  net-work,  and, 
since  the  blood-vessels  are  usually  surrounded  by  a  greater  or  less  amount  of  con- 
nective tissue,  lymph-spaces  are  quite  distinct  along  their  courses,  forming  what  are 
known  as  the  perivascular  lymph-spaces  (Fig.  782).  In  other  regions  of  the  body 
somewhat  extensive  spaces  occur  which  have  been  regarded  as  belonging  to  the 


932 


HUMAN   ANATOMY. 


category  of  lymph-spaces,  and  among  these  there  may  be  mentioned  the  subarachnoid 
and  subdural  spaces  of  the  meninges,  Tenon's   space  in    the  orbit,  and  even    the 

FIG.  781. 


Valve 


Peri  vascular 

lymph-space 


Lymph-space 


Deeply  stained 
ground  substance 


Portion  of  central  tendon  of  rabbit's  diaphragm,  treated  with  silver  nitrate;  lymphatic  vessels  are  shown  as  light 
irregular  tracts ;  lymph-spaces  are  seen  within  stained  ground  substance.    X  120. 

spaces    occupied  by  the  aqueous  and  vitreous  humors  of*the  eye,  as  well  as  the 
smaller  spaces  of  that  organ.      So,  too,  the  spaces  surrounding  that  enclosed  by  the 

membranous  labyrinth  of 

FIG.  782.  the  ear  have  been  regarded 

as  lymph-spaces,  as  is 
indicated  by  their  names. 
Finally,  it  may  be 
mentioned  that  the  syn- 
ovial  cavities  of  the  artic- 
ulations and  the  greater 
serous  cavities  of  the  body 
enclosed  by  the  pleura, 
pericardium,  and  perito- 
neum have  been  regarded 
as  being  in  direct  com- 
munication with  the  lym- 
phatic capillaries;  but  this 
view  is  also  in  all  proba- 
bility erroneous. 

Notwithstanding  tin- 
independence  of  these 
spaces  from  the  lymphatic 
capillaries,  it  must  be 
recognized  that  some  of 
them  at  least  play  im- 

Perivascular  lymph-spaces  surrounding  retinal  blood-vessels.    X  230.  pot'tailt      FOlCS      from      the 

physiological   standpoint, 

in  serving  as  middle-men  between  the  tissues  and  the  lymphatics,  and,  furthermore. 
those  of  the  eyeball,  by  their  communication  with  neighboring  spaces,   permit  of  a 


THE   LYMPHATIC   SYSTEM. 


933 


Lymphatic  capillary  net-works  within  connective-tissue  layer  of  skiti  ;  smaller 
vessels  belong  to  superficial  net-work,  larger  to  deeper.     (Teichmann*) 


rapid  compensation  for  variations  in  the  intraocular  tension.      From  the  anatomical 

standpoint,  however,  they  are  not  to  be  regarded  as  actually  parts  of  the  lymphatic 

system,  and  the  mention  that  they  here  receive  is  merely  a  tribute  to  their  historical 

importance  in  the  problem  of  the  origin  of  the  lymphatic  capillaries. 

The  Capillaries. — The  lymphatic  capillaries  (Fig.  783),  which  are  arranged 

in  the  form  of  net-works  of  very  different  degrees  of  fineness  and  complexity,  closely 

resemble  in  structure  the 

blood  -  capillaries,     their  FIG.  783. 

walls     consisting     of     a 

single  layer  of  endothelial 

plates,   which,   however, 

are    usually   larger    and 

less    regularly    disposed 

than    those    lining     the 

blood  -  channels.      They 

differ  from  those  of  the 

blood  -  vascular     system 

not  only  in  their  ultimate 

branches    being    closed, 

but  also  in  their  general 

appearance.     Thus,  they 

are     of     much     greater 

calibre,    their     diameter 

varying  from  .030— .060 

mm.,  while   that   of   the 

blood-capillaries  may  be 

as    little   as   .008    mm.  ; 

they  do  not  present  the  regularity  of  size  and  gradual  increase  or   diminution  of 

calibre  noticeable  in  the  blood-capillaries,  but  larger  and  smaller  stems  are  indefinitely 

interspersed,  and  spindle-shaped  or 
nodular  enlargements  may  occur  at 
irregular  intervals  throughout  the 
net-work.  And,  finally,  as  a  result 
of  these  peculiarities,  the  meshes  of 
the  net-work  are  of  very  varying  size 
and  form. 

The  arrangement  assumed  by 
a  net-work  depends  largely  upon 
the  tissue  and  Qrgan  in  which  it 
occurs.  In  the  integument,  for  in- 
stance, the  lymph- capillaries  arrange 
themselves  in  two  more  or  less 
distinct  layers,"  a  more  superficial 
one,  composed  of  smaller  capillaries, 
and  a  deeper,  coarser  one, — numer- 
ous communications  necessarily 
existing  between  the  two.  Both  net- 
works are  confined  to  the  dermis, 
the  more  superficial  one  lying  close 
to  its  epidermal  surface,  while  the 
deeper  one  is  situated  in  its  deeper 


layers,  the  distance  between  the  two 
varying  according  to  the  develop- 
ment of  the  dermis  in  different 
portions  of  the  body  and  in  different 
individuals.  From  the  superficial  layer  loops  or  single  capillaries  project  upward  into 
the  dermaj  papillae,  and  special  portions  of  the  net-work  surround  each  hair-follicle  and 
sudoriparous  gland. 

*  Das  Saugadersystem.     Leipzig,  1861. 


FIG.    784. 


Lymph-cells 


Transverse  section  of  small  lymph-vessel.     X  210. 


934 


HUMAN   ANATOMY. 


FIG.  785. 


The  mucous  membranes  have  essentially  the  same  arrangement,  the  net-work  with- 
in the  small  intestine,  for  instance,  being  arranged  in  two  more  or  less  distinct  layers,  one 
of  which  lies  in  the  submucosa  and  sends  loops  or  blindly  ending  processes  into  the  villi, 
while  the  other  is  situated  in  the  muscular  coat.  What  may  be  regarded  as  a  third  net- 
work, lying  beneath  the  serous  or  connective-tissue  investment,  is  formed  by  the  anas- 
tomosis of  the  stems  arising  from  the  deeper  net-works  and  it  is  from  this  last  net-work 
that  the  efferent  stems  arise.  In  most  other  organs  lined  by  mucous  membrane  a 
similar  arrangement  occurs,  although  in  the  uterus,  bladder,  and  ureters  the  submucous 
net-work  seems  to  be  wanting,  the  muscular  set  alone  being  demonstrable.  Through- 
out the  serous  membranes  the  net-works  possess  naturally  a  layered  arrangement,  but 
in  the  more  massive  organs,  such  as  the  liver  and  pancreas,  they  are  arranged  with 
reference  to  the  constituent  lobules,  each  being  invested  by  an  interlobular  net-work. 
Considerable  variation  exists  in  the  closeness  of  the  net-work  in  different  organs, 
and,  indeed,  in  different  parts  of  the  same  organ,  but  everywhere  the  lymph- 
capillaries  are  exceedingly  thin-walled  and  possess  no  valves.  As  has  been  pointed 
out,  the  view  formerly  prevailed  that  the  capillaries  communicated  directly  with  the 
great  serous  cavities  of  the  body,  with  the  spaces  of  the  connective  tissues,  and  even 
with  the  pericellular  spaces  which  occur  in  the  more  compact  tissues,  all  these  being 
regarded  as  radicles  of  the  lymphatic  vessels.  It  is  now  believed,  however,  that 
such  is  not  the  case,  but  that  the  net-works,  which  are  everywhere  continuous,  are 
completely  closed  except  for  their  communications  with  the  efferent  vessels. 

The  Lymph-Vessels. — The  lymph-vessels, 
which  issue  from  the  capillary  net-works  and  convey 
the  lymph  ultimately  to  the  subclavian  veins,  have 
an  arrangement  closely  resembling  that  of  the  veins, 
and,  indeed,  the  larger  ones  are  usually  situated 
alongside  and  accompany  the  course  of  blood-vessels. 
Just  as  it  is  possible  over  the  surface  of  the  body  and 
limbs  to  distinguish  between  superficial  and  deep 
veins,  so  there  can  be  recognized  a  superficial  set 
of  lymphatic  vessels  (vasa  lymphatica  superficialia), 
situated  superficially  to  the  fascia  which  encloses  the 
musculature,  and  a  deep  set  (vasa  lymphatica  profunda), 
the  vessels  of  which  lie  beneath  the  fascia  ;  numerous 
communications,  however,  exist  between  the  two  sets. 
Just  as  the  veins  unite  to  form  larger  trunks 
as  they  pass  from  the  capillaries  toward  their  termi- 
nation, so,  too,  the  lymphatics ;  but  the  latter 
present  two  peculiarities  which  distinguish  them 
from  the  veins.  They  do  not  anastomose  as  abun- 
dantly as  the  latter  and  there  is  not  the  same 
proportional  increase  in  the  size  of  a  lymphatic 
vessel  formed  by  the  junction  of  others  as  in  the 
veins,  so  that,  while  the  lymphatics  at  their  origin 
from  the  capillary  net-works  may  have  the  same 
calibre  as  the  corresponding  veins,  yet  their  terminal 
trunks  are  of  much  smaller  diameter. 

As  a  rule,  several  lymphatic  vessels  arise  from 
the  capillary  net-work  of  any  organ  or  region  of  the 
body,  and,  since  the  net-work  is  to  be  regarded  as 
practically  continuous  over  large  areas,  it  would 
appear  that  the  flow  of  lymph  from  any  circumscribed 
area  might  take  place  through  widely  separated 
stems  and  be  carried  along  very  different  paths. 
And  such,  to  a  certain  extent,  is  the  case  ;  but  it 
has  been  found  by  experiment  and  by  the  observation 
of  pathological  conditions  that  for  each  organ  or  region  there  is  a  more  or  Iocs  definite 
lymphatic  path,  each  vessel  or  group  of  vessels  tending  to  drain  a  somewhat  definite 
area  of  the  net-work,  a  fact  of  considerable  importance  from  the  diagnostic  standpoint. 


Shaded  part  of  figure  shows  area 
ili.iincil  by  right  lymphatic  duct;  lym- 
phatics of  remaining  teYritory  reci-ivil 
by  thoracic  dm  t. 


THE   LYMPHATIC   SYSTEM. 


935 


All  the  lymphatic  vessels  terminate  directly  or  indirectly  in  one  of  two  main 
trunks,  which,  as  already  stated,  open  respectively  into  the  right  and  left  subclavian 
veins.  The  left  trunk,  the  thoracic  duct  (ductus  thoracicus),  is  much  larger  than 
the  right,  beginning  in  the  abdominal  region  and  traversing  the  entire  length  of  the 
thorax  to  reach  its  destination.  It  receives  all  the  lymph  returned  from  the  lower 
limbs,  the  pelvic  walls  and  viscera,  the  abdominal  walls  and  viscera,  the  lower  part  of 
the  right  half  and  the  whole  of  the  left  half  of  the  thoracic  wall,  the  left  half  of  the 
thoracic  viscera,  the  left  side  of  the  neck  and  head,  and  the  left  arm.  The  other 
trunk,  the  right  lymphatic  duct  (ductus  lymphaticus  dexter),  is  very  short,  and, 
indeed,  is  frequently  wanting,  the  vessels  which  typically  unite  to  form  it  opening 
independently  into  the  vein.  It  receives  the  lymph  from  the  upper  part  of  the  right 
side  of  the  thoracic  wall,  from  the  right  half  of  the  thoracic  viscera  and  the  upper  surface 
of  the  liver,  the  right  side  of  the  neck  and  head,  and  from  the  right  arm  (Fig.  785). 

In  structure  the  larger  lymphatic  vessels  are  similar  to  the  veins,  but,  as  a  rule, 
their  walls  are  thinner  than  those  of  veins  of  corresponding  calibre  and  their  valves 
are  more  numerous.  The  walls  of  the  most  robust  trunks,  particularly  those  of  the 
thoracic  duct,  consist  of  three  coats.  From  within  outward  these  are  :  (a)  the 
intima,  composed  of  the  endothelial  lining  and  the  fibre-elastic  subendothelial  layer  ; 
(^)  the  media,  made  up  of  involuntary  muscle  interspersed  with  fibro-elastic  tissue  ; 
and  (c)  the  adventitia,  consisting  of  fibro-elastic  tissue  and,  frequently,  of  longitudinal 
bundles  of  involuntary  muscle. 

The  Lymphatic  Nodes. — Scattered  along  the  course  of  the  lymphatic  vessels 
are  to  be  found  in  various  regions  of  the  body  elliptical  flattened  nodules  (Fig.  796) 
of  varying  size,  some- 
times singly  but  more  FIG-  786- 
frequently  in  chains  or 
groups  ( plexus  lym- 
phatic!) of  from  three 
to  six  or  even  ten  to 
fifteen.  These  are  the 
lymphatic  nodes  (lym- 
phoglandulae).  As  it 
approaches  a  node,  a 
lymph  -  vessel  divides 
into  a  number  of  stems, 
the  vasa  afferentia, 
which  enter  the  sub- 
stance of  the  node  and 
communicate  with  a 
capillary  net-work  in 
its  interior,  from  which 
a  somewhat  smaller 
number  of  vessels,  the 
vasa  efferentia,  arise 
(Fig.  786).  These, 
leaving  the  node,  the 
surface  of  which  fre- 
quently presents  a 
slight  depression,  the 
hilum,  at  their  point  of  emergence,  unite  to  form  the  continuation  of  the  vessel. 
The  lymph  conveyed  by  any  of  the  vessels  traverses  one  or  more  nodes  before 
emptying  into  the  thoracic  or  right  lymphatic  duct,  and  in  those  cases  in  which 
a  plexus  occurs  in  a  lymph-path  a  number  of  nodes  must  be  traversed.  The 
passage  through  the  intranodular  net -work  produces  a  greater  or  less  retardation  of 
the  flow  of  the  fluid  and  affords  opportunity  for  the  accumulation  of  lymphocytes. 
Moreover,  since  these  possess  a  phagocytic  function,  in  cases  of  infection  of  any 
part  of  the  body  the  nodes  along  the  lymph-paths  leading  from  it  become  more 
or  less  engorged  with  lymphocytes  and  enlarged,  and  in  case  the  lymphocytes  are 
unable  to  contend  successfully  with  the  infective  material,  the  nodes  may  serve  as 


Cortical  follicle 


Lymph-sinus 


Capsule 


Afferent 

lymphatics 


Lymph-sinus 


Diagram  illustrating  architecture  of  lymph-node. 


936 


HUMAN   ANATOMY. 


foci  for  its  distribution  to  other  parts  of  the  system.  The  nodes  therefore,  sen  -ing 
as  traps  for  the  infective  material,  possess  a  high  degree  of  importance  from  the 
surgical  standpoint,  an  accurate  knowledge  of  their  location  and  of  the  lymph-paths 
along  which  each  group  is  situated  being  of  great  value. 

In  addition  to  the  ordinary  lymph-nodes  there  occur  in  various  regions  of  the 
body,  especially  in  the  prevertebral  regions  of  the  abdomen,  structures  which 
resemble  lymph-nodes  in  their  form  and  size,  but  differ  from  them  in  color.  In 
general  the  lymph-nodes  are  of  a  pale  pinkish  color,  although  those  in  the  vicinity 
of  the  lungs  are  usually  blackish,  from  the  deposition  in  them  of  dust  particles  from 
the  lungs,  and  those  in  connection  with  the  vessels  arising  from  the  small  intestine  are 
milky  white  during  digestion.  The  structures  in  question,  however,  are  of  a  deep 
red  color,  owing  to  the  presence  of  abundant  blood-vessels  in  their  cortical  portion. 
These  bodies  have  been  termed  the  hemolymph  nodes,  but  their  exact  nature  and 
function  have  not  yet  been  definitely  ascertained.  By  some  they  are  regarded  as 
special  structures,  quite  different  from  the  lymph-nodes,  perhaps  partaking  somewhat 
of  the  character  of  the  spleen  ;  while  others  regard  them  as  ordinary  lymph-nodes 
with  an  especially  rich  blood  supply,  transitional  forms  between  them  and  the  usual 
lymph-nodes  being  believed  to  exist.  Whether  or  not  direct  communication  exists 
between  the  cortical  blood-vessels  and  the  medullary  lymphatics  within  these 
hemolymph  nodes  is  also  a  question  concerning  which  differences  of  opinion  exist. 
Structure  of  Lymphoid  Tissue. — Wherever  found,  whether  as  diffuse  masses, 
simple  nodules,  or  as  the  larger  and  more  complex  lymph-nodes,  lymphoid  or  adenoid 

tissue  is  composed  of  two  chief  con- 

FIG.  787.  stituents,  the  supporting  reticulum 

and  the  lymphoid  cells  contained 
within  the  meshes  of  the  framework. 
The  reticidum  varies  in  the  thickness 
of  the  component  fibres  and  the  size 
of  its  meshes,  but  in  the  denser  types 
of  lymphoid  tissue,  as  seen  in  the 
periphery  of  the  solitary  nodules  and 
in  the  cortical  follicles  and  medullary 
cords  of  the  lymph-nodes,  it  is  so 
masked  by  the  innumerable  oxer- 
lying  cells  that  only  after  removal 
of  the  latter  can  the  supporting 
framework  be  satisfactorily  demon- 
strated. The  reticulum,  the  nature 
of  which  is  still  a  subject  of  discus- 
sion, may  be  regarded  as  modified 
fibrous  connective  tissue,  upon  the 
trabeculae  of  which,  particularly  at 
the  points  of  junction,  flattened  con- 
nective tissue  cells  are  closely  applied 
as  a  more  or  less  complete  invest- 
ment. In  certain  localities  where  of 
exceptional  delicacy,  the  reticulum 
may  be  formed  almost  entirely  by 
the  anastomosing  processes  of  stellate 
connective-tissue  elements. 
The  cells  composing  lymphoid  tissue,  exceedingly  numerous  and  closely  packed, 
present  the  general  characteristics  that  distinguish  the  lymphocytes,  being  small 
elements  with  comparatively  large  nuclei,  which  exhibit  a  strong  affinity  for  nuclear 
(basic)  stains. 

The  simple  lymph-nodules,  of  varying  size  but  seldom  more  than  2  mm.  in 
diameter,  are  irregularly  spherical  or  elliptical  masses  of  lymphoid  tissue  in  which  a 
denser  peripheral  /one  encloses  and  blends  with  a  core  of  less  compact  texture. 
Within  the  looser  and  therefore  lighter  central  area,  lymphoid  cells  in  various  Stages 
of  mitotic  division  are  frequently  seen,  such  foci,  known  as  ^,>-»/-iriiftrs,  indicating 


Mucous 

glands 


Germ-centre 
of  nodule 


Submucous 
layer 


Simple  lymph-nodule  from  large  intestine.     X  120. 


THE   LYMPHATIC   SYSTEM. 


937 


FIG.  788. 


the  birthplaces  of  new  lymphocytes.  Although  the  limits  of  the  lymph-nodules  are 
commonly  imperfectly  defined  by  a  condensation  of  the  surrounding  connective 
tissue,  a  distinct  capsule  is  usually  wanting. 
Definite  lymph-channels  are  found  neither 
upon  the  surface  nor  within  the  simple 
nodules  ;  the  latter  are  provided,  however, 
with  a  generous  net-work  of  capillary 
blood-vessels  (Fig.  792): 

Intermediate  in  their  complexity  of 
arrangement,  between  the  simple  nodules 
on  the  one  hand  and  the  typical  lymph- 
nodes  on  the  other,  stand  such  structures 
as  Peyer's  patches  and  the  faucial  and 
pharyngeal  tonsils,  in  which  groups  of 
simple  nodules  are  blended  into  a  single 
organ,  the  component  follicles  only  partly 
retaining  their  individuality. 

The  lymph-nodes  interposed  along 
the  lymphatic  vessels,  usually  embedded 
within  fatty  tissue,  represent  still  higher 
differentiation  as  distinct  organs.  In  form 
and  size  they  vary  from  minute  bodies 
resembling  millet-seeds  to  flattened  oval  or 
bean-shaped  organs,  that  may  measure  almost  an  inch  in  their  longest  diameter. 
They  are  invested  by  a  distinct  fibrous  capsule,  in  which  elastic  fibres  constantly  and 
unstriped  muscle  occasionally  are  present.  From  the  deeper  surface  of  this  envelope 
numerous  radially  directed  trabeculae  penetrate  the  outer  zone,  or  cortex,  which  is 
thus  subdivided  into  a  series  of  pyramidal  compartments.  On  reaching  the  inner 
limits  of  the  cortical  zone,  the  trabeculae  are  less  regularly  disposed  and  more  freely 
united,  thereby  breaking  up  the  deeper  parts,  or  medulla,  of  the  node  into  uncertain 
cylindrical  compartments.  The  spaces  thus  imperfectly  defined  by  the  trabeculae  are 


Portion  ot  lymph-nodule,  showing  details 
of  germ-centre.    X  350. 


Germ-centre 
Lymph-sinus 


Fat 


FIG.  789. 

Lymph-sinus 


Capsule 
Trabecula 


Cortical  follicles 


Lymph-sinus 


Hilum  Vasa  efferentia  Medullary  cords 

Section  of  small  lymph-node  through  hilum.      X  25. 


incompletely  filled  by  masses  of  compact  lymphoid  tissue,  the  general  form  and 
arrangement  of  which  correspond  to  the  compartments  in  which  they  lie.  The  masses 
contained  within  the  peripheral  spaces  are  spherical  or  pyriform  and  constitute 


HUMAN   ANATOMY. 


the  cortical  nodules ;  those  within  the  communicating  central  compartments  form  a 
net-work  of  irregular  cylinders,  the  medullary  cords,  which  are  continuous  with  one 

another  and  with  the  deeper 
i at; — '^..•j.c-Tjqs*^.  * 1U-  79° 


Capsule  — 


Lymph-sinus 


Cortical  follicle 


Lymph-sinus 


Lymph-sinus 


Medullary  cord 


Portion  of  periphery  of  lymph-node,  showing  relation  between  trabecula, 
sinus,  and  lymphoid  tissue.     X  50. 


part  of  the  cortical  nodules 
(Fig.  789). 

The  intervals  between 
the  tracts  of  lymphoid 
tissue  and  the  trabecular 
frame-work  constitute  a 
system  of  freely  intercom- 
municating channels,  the 
lymph  -  sinuses,  through 
which  passes  the  lymph 
brought  to  the  node  by  the 
afferent  lymphatic  vessels. 
The  latter  pierce  the  capsule 
on  the  convex  surface  of 
the  node  and  empty  into 
the  sinuses  that  surround 
the  outer  and  lateral  surfaces 
of  the  cortical  nodules. 
After  traversing  the  periph- 
eral sinuses,  the  lymph 
passes  into  the  irregular 
channels  of  the  medulla 
and  towards  the  point  at 
which  the  efferent  lymph- 
vessels  leave  the  nodule. 
The  position  of  this  exit  is 
usually  indicated  by  a  more 


FIG.  791. 


*> 


Trabecula 


or  less  pronounced  indentation,   known  as  the  hilum,  on  the  surface  of  the  node 
opposite    the    entrance    of    the 
afferent  lymph-vessels. 

The  lymph-sinuses,  there- 
fore, are  bounded  on  one  side  '  *.L*i!£i?«§3^'  H. 
by  the  capsule  or  the  trabeculae 
and  on  the  other  by  the  masses 
of  dense  lymphoid  tissue.  The 
lumen  of  these  channels,  however, 
is  not  free,  but  occupied  by  a 
delicate  wide-meshed  reticulum 
consisting  of  fine  strands  of 
connective  tissue  where  most 
marked,  or  of  the  processes  of 
stellate  cells  where  very  delicate 
(Ebner).  The  sinuses  are  lined 
by  an  imperfect  layer  of  flattened 
plate-like  cells,  that  represent 
the  endothelium  of  the  adjoining 
lymphatic  vessels  and  also  cover 
the  more  robust  trabeculae  cross- 
ing the  channels.  The  reticulum 
occupying  the  sinuses  is  continu- 
ous with  the  closer  and  more 
delicate  net-work  within  the  adja- 
cent dense  lymphoid  tissue. 
Although  both  the  afferent  and 

efferent  lymphatics  are  provided  ^  ^          details  of  lym,)h.,inus 

with  valves,  the  lymph-channels  and  medullary  cords,   x  250. 


Lymph-sinus 


THE   LYMPHATIC   SYSTEM. 


939 


FIG.  792. 


Cross-section  of  small  lymph-node,  injected  to  show  rich  vascular 
supply.     X  10. 


within  the  node  are  destitute  of  such  folds.  The  passage  of  the  lymph  through  the 
nodes  is  retarded  by  the  reticulum  within  the  sinuses,  thus  favoring  the  entrance  of 
the  young  lymphocytes  from  the  surrounding  lymphoid  tissue  into  the  sluggishly 
circulating  fluid.  Germ-centres,  the  particular  foci  for  the  production  of  the  lympho- 
cytes, usually  are  present  within  the  cortical  nodules,  but  are  not  found  within 
medullary  cords. 

The  blood-vessels  for  the  nutrition  of  the  lymph-nodes  are  numerous.  Entering 
at  the  hilum,  they  divide  into  arterioles  which  follow  the  trabeculae,  giving  off  smaller 
branches  that  pene- 
trate the  medullary 
cords  and  the  cortical 
nodules  and  break  up 
into  rich  capillary  net- 
works for  the  supply 
of  the  denser  lym- 
phoid tissue. 

Both  medullated 
and  non-medullated 
nerves  enter  the 
node  at  the  hilum  in 
company  with  the 
blood-vessels.  They 
are  chiefly  sympa- 
thetic fibres  destined 
for  the  involuntary 
muscle  of  the  vessels 
and  of  the  capsule. 
The  distribution  of  the 
medullated  fibres  is 

uncertain.  According  to  Tonkoff,  fibrillae  are  traceable  into  the  lymphatic  tissue  of 
the  medulla. 

Development. — The  origin  of  the  first  lymph-cells,  the  lymphocytes,  is  uncer- 
tain, these  elements  appearing  outside  the  vessels  as  derivatives  from  the  mesoblast 
(page  688).  After  the  establishment  of  the  lymphoid  tissue  new  cells  are  continually 
being  formed  within  the  various  lymph-nodes  and  nodules. 

The  development  of  the  lymphatic  vessels  has  generally  been  believed  to 
proceed  from  the  veins  by  a  process  of  budding  (Ranvier),  similar  to  that  followed 
in  the  extension  of  the  blood-vessels  ;  and  certain  recent  investigators, — Sabin,1 
who  studied  the  development  of  the  lymphatics  in  pig  embryos,  and  F.  T.  Lewis,2 
who  worked  with  rabbit  embryos, — while  differing  as  to  details  of  the  development 
of  the  definitive  lymphatic  stems,  agree  as  regards  their  origin  in  this  manner. 

Sabin,  by  employing  a  method  of  injection,  found  that  the  first  traces  of  a 
lymphatic  system  appear  in  pig  embryos,  14.5  mm.  in  length,  as  two  small  out- 
growths, which  develop,  one  on  each  side,  at  the  junction  of  the  subclavian  and 
jugular  veins  ;  from  these,  by  a  process  of  endothelial  budding,  vessels  gradually 
grow  towards  the  skin,  radiating  and  anastomosing  in  all  directions  to  form  a 
subcutaneous  net-work,  which  gradually  extends  throughout  the  anterior  half  of  the 
body.  Later  two  additional  outgrowths  develop  at  the  junction  of  the  femoral  and 
post-cardinal  veins,  and  give  rise  to  a  subcutaneous  net-work  throughout  the  posterior 
half  of  the  body,  the  two  sets  of  net-works  thus  formed  eventually  uniting. 

Lewis's  studies  of  serial  sections  of  rabbit  embryos  gave  somewhat  different 
results  and  indicated  that  Sabin' s  method  of  study  did  not  suffice  to  reveal  the  actual 
origin  of  the  lymphatics.  He  found  the  first  of  these  vessels  along  the  course  of  the 
internal  jugular  vein  as  a  series  of  spaces,  each  of  which  he  supposed  to  represent  an 
independent  outgrowth  from  the  vein.  These  spaces  eventually  fused  to  form  a 
single  lymph-channel  accompanying  each  vein,  and  other  channels  were  found  to 
arise  in  a  similar  manner  in  connection  with  the  subcardinal,  mesenteric,  and  azygos 

1  Amer.  Jour,  of  Anatomy,  vol.  i.,  1902. 

2  Amer.  Jour,  of  Anatomy,  vol.  v.,  1905. 


940 


HUMAN   ANATOMY. 


FIG.  793- 


veins.  The  various  channels  finally  unite  to  form  a  continuous  system  which  acquires 
new  openings  with  the  venous  system  near  the  termination  of  the  subclavian  veins, 
the  condition  found  in  the  adult  being  thus  established. 

More  recently  Huntington  and  McClure,1  working  with  cat  embryos,  have  also 
found  the  earliest  traces  of  the  lymphatic  system  in  a  series  of  spaces  which  appear  in 
the  tissue  surrounding  the  intima  of  the  anterior  cardinal  veins,  but  they  found  that 
these  spaces  have  at  first  no  connection  with  the  veins,  nor  are  they  outgrowths 
from  them.  The  anterior  cardinal  vein  of  each  side  is  early  divided  longitudinally 
into  two  portions  by  the  passage  through  it  of  the  cervical  nerves,  and  the  dorso- 

lateral  portion  of  the  vein  later 
undergoes  retrogression,  the 
ventro-medial  portion  persisting 
as  the  internal  jugular.  As  the 
dorso-lateral  portion  shrinks,  the 
lymphatic  spaces  along  its  course 
rapidly  enlarge,  fuse  together, 
and  form  a  large  lymphatic  stem, 
which  subsequently  makes  con- 
nection with  the  subclavian  vein, 
and  thus  forms  the  primary 
lymphatic  trunk  of  the  body 

(Fig-  793)- 

Later,  spaces  develop  along 
the  course  of  the  anterior  cardinal 
veins  below  the  point  where  the 
subclavians  open  into  them,  but 
it  is  noticeable  that  those  occur- 
ring in  association  with  the  left 
vein,  which  undergoes  retrogres- 
sion, develop  more  rapidly  than 
those  accompanying  the  same 
portion  of  the  right  vein  and  form 
the  thoracic  duct  (Fig.  794),  this 
structure  thus  belonging  essen- 
tially to  the  left  half  of  the  body, 
since  the  principal  persistent  veins 
occur  on  the  right  side.  Similar 
spaces  appear  in  the  peri-intimal 
tissue  of  other  veins,  and  in  all 
cases  those  associated  with  retro- 
gressive veins  are  the  most  rapidly 
developed.  While  most  of  the 
principal  lymphatic  trunks  unite  with  the  thoracic  duct,  yet  they  may  also  form 
temporary  or  even  permanent  communications  with  other  veins  than  the  subclavian, 
certain  of  the  adult  anomalies  being  results  of  these  connections. 

From  these  observations  it  seems  that  the  lymphatics  arise  from  spaces  which 
are  primarily  independent  of,  although  associated  with,  the  veins,  and  that,  while  this 
mode  of  origin  of  the  lymphatics  applies  to  those  following  the  primitive  systemic 
veins,  yet  the  more  peripheral  portions  of  the  system  are  developed  by  a  process  of 
budding  from  the  main  stems,  just  as  is  the  case  with  the  smaller  branches  of  the 
blood-vessels.  By  this  budding  process  the  system  gradually  extends  throughout  the 
body,  invading  the  various  tissues,  the  invasion,  however,  failing  to  affect  certain  of 
the  tissues,  such  as  cartilage  and  the  central  nervous  system. 

The  development  of  the  lymph-nodes  has  been  recently  studied  by  Kling'  and 
by  Sabin.:i  According  to  the  latter  investigator,  the  lymph-nodes  may  be  regarded 
as  formed  by  two  fundamental  parts — the  Iytnf>hoid  element^  consisting  of  lympho- 
cytes in  a  reticulum  surrounding  the  terminal  artery  and  its  capillaries  within  the 

1  Anu-r.  Jour,  of  Anatomy,  vol.  vi.,  1907.         *  Archiv  f.  mikros.  Anat.,  Bd.  63,  1904. 
:l  Amer.  Jour,  of  Anatomy,  vol.  v.,  1905.  *  Amer.  Jour,  of  Anatomy,  vol.  v.,  1905. 


Developing  lymphatics  in  rabbit  embryo  of  11  mm.  (14  days); 
X  9.  Lymphatic  vessels  are  heavily  shaded  ;  veins  are  light.  In.J., 
Ex.J..  internal  and  external  jugular  veins;  Pr.U,,  primitive  ulnar; 
Ex.M.,  external  mammary;  Az.,  azygos;  KC/.,  inferior  vena  cava  ; 
G.,  gastric;  S.Af.,  superior  mesenteric  ;  V.,  vitelline  ;  Sc.,  subcar- 
dinal;  K.A.,  renal  anastomosis  of  subcardinals  ;  JPr.Fi.,  primitive 
fibular;  c.6.,  connecting  branch  ;  An.  T.,  anterior  tibial ;  c.,  caudal; 
j.  4>5^  6,  position  of  corresponding  cervical  nerves,  (f.  T.  Lewis.*) 


THE   THORACIC    DUCT. 


941 


cords  and  germ-centres  respectively,  and  the  sinus-element,  represented  by  channels 
resulting  from  the  multiplication  of  the  lymph-vessels.  The  former,  or  vascular  factor, 
is  constant  and  present  in  the  simplest  nodule  ;  the  sinus-element,  on  the  contrary, 
varies,  sometimes  (as  in  the  usual  type  of  node)  being  developed  from  numbers 
of  closely  packed  lymph-ducts 

and,    therefore,    of   lymphatic  FIG.  794. 

origin,  and  at  other  times  (as 
in  the  hemolymph  nodes) 
being  venous  channels  occu- 
pied by  blood.  By  the  sub- 
sequent intergrowth  of  the 
lymphoid  element  and  the 
greatly  multiplied  lymph- 
capillaries,  the  intervening 
bridges  of  connective  tissue 
are  reduced  in  thickness  until 
finally  only  the  reticulum 
remains  and  the  lymphoid 
tissue  is  ultimately  brought 
into  intimate  relation  with 
the  surrounding  sinus.  In 
certain  nodes  the  sinus  retains 
its  character  as  a  direct  out- 
growth from  the  veins  and 
becomes  filled  with  erythro- 
cytes.  Such  nodes  assume  the 
peculiarities  of  hemolymph 
nodes,  in  which  the  blood- 
sinuses  replace  those  that 
convey  lymph.  As  Sabine 
has  emphasized,  the  follicle 
is  the  anatomical  as  well  as 
the  vascular  unit,  the  simplest 
nodule  consisting  of  a  single 
follicle.  The  latter  may  be 
without  a  sinus,  or  surrounded 
by  one  which  is  either  a  lym- 
phatic or  a  venous  channel. 


Developing  lymphatics  in  rabbit  embryo  of  21  mm.  (ry  days);  X  6. 
Lymphatic  vessels  are  heavily  shaded  ;  veins  are  light;  for  significance 
of  lettering  see  preceding  figure;  in  addition,  Ce.,  cephalic;  Br.,  bra- 


chial;    /?.,  radial  ;    Ss.,  subscapular;    Set.,  sciatic  ; 
iliolumbar.     (f.    T.  Lewis.*) 


In  describing  the  various 
lymphatic  vessels  and  nodes  it 
will  be  convenient  to  consider 
first  the  great  terminal  trunks 
of  the  system,  the  thoracic 
and  right  lymphatic  ducts, 
and  then  discuss  the  remaining 
portions  of  the  system  from 
the  topographical  standpoint.  Attention  will  be  directed  primarily  to  the  nodes 
of  each  region,  the  course  of  the  lymph-paths  from  each  organ  and  their  relations 
to  the  nodes  being  subsequently  considered. 

THE  THORACIC  DUCT. 

The  thoracic  duct  (ductus  thoracicus)  (Fig.  795)  extends  from  the  lower  border 
of  the  second  lumbar  vertebra,  through  the  entire  length  of  the  thorax,  to  open  into 
the  left  subclavian  vein  close  to  the  point  where  it  is  joined  by  the  left  internal 
jugular.  Its  entire  length  is  from  43—46  cm.  (17—18  in.).  The  duct  lies  at  first  in 

*  Amer.  Jour,  of  Anatomy,  vol.  v.,  1905. 


942 


HUMAN   ANATOMY. 


front  of  the  first  and  second  lumbar  vertebrae,  and  passes  upward  through  the  aortic 
opening  of  the  diaphragm.      In  the  thorax  its  course,  although  slightly  sinuous,  in 


FIG.  795. 


Internal  jugular  vein 


Trachea 

Vertebral  vein 
Right  lymphatic  duct 

Subclavian  vein 
I.  rib 

Right  innominate  veil 


(Esophagus 


Vena  azygos 


Right  lumbar  lymph  trunk 


Crest  of  ilium 


Left  common  carotid  artery 

Left  innominate  vein 
Thoracic  duct 
Left  subclavian  vein 
Scalenus  anticus 
Left  subclavian  artery 
Thyroid  axis 
I.  rib 
Vertebral  artery 


Thoracic  duct 


Aorta 


Intercostal  arteries 


Receptaculum  chyli 
Intestinal  lymph  trunk 


Left  lumbar  lymph  trunk 


Crest  of  ilium 


Dissection  of  posterior  body-wall,  seen  from  in  front,  showing  thoracic  duct  and  right  lymphatic  duct ; 
veins  have  been  laterally  displaced  to  expose  terminations  of  thoracic  duct. 

general  is  at  first  almost  directly  upward,  a  little  to  the  right  of  the  median  line  of 
the  bodies  of  the  thoracic  vertebrae  ;   at  the  level  of  from  the  sixth  to  the  fourth 


THE  THORACIC   DUCT.  943 

vertebrae,  however,  it  begins  to  incline  slightly  towards  the  left,  and,  finally,  at  about 
the  lower  border  of  the  seventh  cervical  vertebra  it  changes  its  direction  somewhat 
abruptly,  passing  upward,  forward  and  to  the  left,  and  then  downward  and  forward, 
thus  forming  an  arch  whose  convexity  is  directed  upward  and  whose  extremity 
opens  into  the  subclavian  vein. 

The  thoracic  duct  is  formed  by  the  union  of  the  right  and  left  lumbar  trunks 
(trunci  lumbales)  which  drain  the  lumbar  nodes.  The  left  trunk,  shortly  before  its 
union  with  the  right,  is  usually  joined  by  an  unpaired  intestinal  trunk  (truncus  intes* 
tinalis)  that  drains  the  cceliac  and  mesenteric  nodes.  Just  above  its  commencement 
the  thoracic  duct  usually,  although  not  always,  presents  a  pyriform  enlargement,  the 
receptaculum  chyli  (cisterna  chyli),  which  extends  upward  as  far  as  the  level  of 
the  eleventh  thoracic  vertebra,  and  measures  from  5-7.5  cm.  (2-3  in.)  in  length  and 
from  6-8  mm.  in  diameter.  Above  the  eleventh  thoracic  vertebra  the  duct  gradually 
diminishes  in  calibre  until  about  the  middle  of  its  course,  where  it  again  enlarges. 
The  thoracic  duct  possesses  few  valves  in  comparison  with  other  lymphatic  vessels, 
those  which  do  occur  being  frequently  insufficient.  Its  entrance  into  the  subclavian 
vein,  however,  is  guarded  by  two  well-developed  leaflets,  which  prevent  the  passage 
of  blood  into  the  duct. 

Relations. — In  its  abdominal  portion  the  thoracic  duct  lies  almost  in  the  median 
line  in  front  of  the  bodies  of  the  first  two  lumbar  and  twelfth  thoracic  vertebrae,  and 
between  the  crura  of  the  diaphragm,  or  under  cover  of  the  right  crus.  Anteriorly,  it 
is  in  relation  with  the  right  side  of  the  abdominal  aorta,  with  the  greater  azygos  vein 
to  the  right. 

In  its  thoracic  portion  it  lies  at  first  within  the  posterior  mediastinum,  but 
above,  it  enters  the  superior  mediastinum.  In  the  former  it  lies  anterior  to  the 
bodies  of  the  eleventh  to  the  fifth  thoracic  vertebrae,  and  has  in  front  of  it,  from 
below  upward,  the  pericardium,  the  oesophagus,  and  the  arch  of  the  aorta.  The 
thoracic  aorta  lies  to  the  left  of  it,  and  to  the  right  are  the  right  pleura  and  the 
greater  azygos  vein.  The  lower  right  intercostal  arteries  pass  between  it  and  the 
bodies  of  the  vertebrae,  as  does  also  the  terminal  portion  of  the  hemiazygos  vein. 
In  the  superior  mediastinum  it  rests  upon  the  lower  part  of  the  left  longus  colli 
muscle,  being  separated  by  it  from  the  bodies  of  the  upper  three  thoracic  vertebrae. 
Anteriorly,  it  is  in  relation  with  the  origin  of  the  left  subclavian  artery  and  with  the 
vertebral  vein  ;  to  the  left  is  the  left  pleura  and  to  the  right  are  the  oesophagus  and 
the  left  recurrent  laryngeal  nerve. 

Its  arch  is  in  relation  below  with  the  apex  of  the  left  lung  and  with  the  left  sub- 
clavian artery  ;  to  the  left  and  posterior  to  it  is  the  vertebral  vein  and  to  the  right 
and  anteriorly  are  the  left  common  carotid  artery,  the  left  internal  jugular  vein,  and 
the  left  pneumogas.tric  nerve. 

Tributaries. — In  addition  to  the  right  and  left  lumbar  and  the  intestinal  trunks 
by  whose  union  it  is  formed,  the  thoracic  duct  receives  on  either  side  ( i )  near  its 
origin,  a  descending  trunk  which  drains  the  posterior  nodes  of  the  lower  six  or  seven 
intercostal  spaces  ;  (2)  an  ascending  stem  from  the  upper  lumbar  nodes  which  trav- 
erses the  crus  of  the  diaphragm  and  joins  the  duct  at  about  the  level  of  the  ninth  or 
tenth  thoracic  vertebrae  ;  (3)  the  efferent  vessels  from  the  upper  posterior  intercostal 
nodes,  which  sometimes  unite  to  form  a  single  ascending  stem  opening  into  the  upper 
part  of  the  duct ;  (4)  the  efferent  vessels  of  the  posterior  mediastinal  nodes  ;  (5)  the 
left  jugular  trunk  ;  and,  occasionally,  (6)  the  left  subclavian  and  (7)  the  leftbroncho- 
mediastinal  trunks,  these  last  three  uniting  with  the  duct  just  before  it  opens  into  the 
subclavian  vein. 

Variations. — The  thoracic  duct  is  subject  to  numerous  variations,  so  much  so  that 
certain  authors  have  regarded  as  typical  arrangements  which  others  have  considered  to  be 
abnormal. 

Its  origin  is  frequently  opposite  the  body  of  the  first  lumbar  vertebra  or  even 
opposite  the  last  thoracic  ;  and  rarely  it  is  below  the  lower  border  of  the  second  lumbar. 
Instead  of  being  formed  by  the  union  of  only  two  trunks,  three  are  frequently  found 
participating  in  its  origin,  the  odd  one  being  the  intestinal  trunk  which  usually  opens  into 
the  left  lumbar  trunk.  Occasionally  all  three  trunks  are  represented  by  a  number  of  smaller 
stems  which  anastomose  with  one  another  as  well  as  with  the  descending  stems  from  the 
posterior  intercostal  nodes,  the  plexus  so  formed  communicating  by  a  number  of  efferents 


944 


HUMAN    ANATOMY. 


with  the  receptaculum  chyli.  It  must  be  remembered  that  embryologically  what  are  usually 
termed  the  origins  of  the  thoracic  duct  are  in  reality  its  prolongations,  that  is  to  say,  outgrowths 
from  it,  so  that  possibilities  for  variation  in  these  stems  are  abundant. 

In  another  respect  the  embryological  history  of  the  duct  probably  throws  light  upon  its 
anomalies.  In  the  rabbit  the  spaces  formed  along  the  course  of  the  left  posterior  cardinal  vein 
frequently  unite  to  form  two  more  or  less  distinct,  parallel  stems,  which  together  represent  the 
thoracic  duct  (Fig.  794).  Whether  this  condition  also  exists  in  man  is  unknown,  but  if  it  does 
then  an  explanation  is  afforded  for  one  of  the  most  frequent  anomalies  of  the  duct,  namely,  its 
division  in  its  lower  part  into  two  parallel  stems  which  unite  again  after  a  longer  or  shorter  inde- 
pendent course.  This  condition  is  so  frequent  that  it  has  been  regarded  as  typical  by  some 
authors  ;  usually  the  union  of  the  two  stems  occurs  at  about  the  level  of  the  seventh  thoracic 
vertebra,  but  occasionally  they  remain  separate  throughout  the  entire  length  of  the  thorax  and 
may  be  connected  by  transverse  anastomoses. 

Another  group  of  anomalies,  probably  having  a  quite  different  embryological  basis,  includes 
cases  in  which  there  are  either  two  distinct  thoracic  ducts,  or  else  a  single  one  which  branches 
in  its  upper  part,  one  of  the  two  stems  in  either  case  passing  to  the  left  subclavian  vein  and  the 
other  to  the  right.  This  condition  is  due  to  the  fact  that  the  lymphatic  system  is  symmetrical  in 
its  embryological  origin,  a  trunk  arising  in  connection  with  the  right  azygos  vein  as  well  as  with 
the  left.  Ordinarily  the  left  trunk,  developing  more  rapidly  than  the  right,  becomes  the  thoracic- 
duct,  while  the  right  outgrowth  remains  short  and  forms  the  right  lymphatic  duct.  Conditions 
might  occur,  however,  in  which  the  right  trunk  would  undergo  a  more  extensive  development 
and  either  unite  with  the  left  trunk  or  grow  downward  to  form  a  second  thoracic  duct,  thus 
producing  the  conditions  under  discussion.  A  further  modification  along  the  same  line  would 
lead  to  the  development  of  the  thoracic  duct  from  the  right  trunk,  the  left  giving  rise  only  to 
a  short  lymphatic  duct,  an  exact  reversal  of  the  normal  arrangement  being  thus  produced. 
Several  such  cases  have  been  recorded,  and  it  is  interesting  to  note  that  they  frequently 
accompany  abnormalities  of  the  aortic  arch,  such  as  the  origin  of  the  right  subclavian  from  the 
descending  portion  ;  the  anomaly  also  occurs,  however,  independently  of  any  variation  in  the 
blood-vessels. 

Considerable  variation  exists  in  the  level  to  which  the  arch  of  the  thoracic  duct  rises  in  the 
neck,  and  it  is  stated  that  it  may  lie  anywhere  between  the  levels  of  the  fifth  cervical  and  first 
thoracic  vertebrae. 

Likewise,  variations  in  the  mode  of  termination  of  the  thoracic  duct  are  often  observed. 
It  may  open  into  the  subclavian  vein  at  some  distance  from  the  junction  of  the  internal  jugular. 
or,  occasionally,  into  its  posterior  surface,  and  not  infrequently  it  divides  near  its  termination 
into  two  or  more  stems  (Fig.  795),  which  may  open  into  the  internal  or  the  external  jugular 
or  into  the  azygos  or  vertebral  veins  as  well  as  into  the  subclavian.  The  connection  with  the 
azygos  vein  is  probably  of  frequent  occurrence. 

Practical  Considerations. — The  thoracic  duct  may  be  obstructed  by  («) 
aneurism  of  the  arch  of  the  aorta;  (b)  enlarged  mediastinal  nodes  (tuberculous, 
lymphadenomatous,  or  carcinomatous)  ;  (c}  mediastinal  neoplasms — especially  if  in 
the  anterior  mediastinum  ;  (</)  exophthalmic  goitre  (very  rarely)  ;  (e)  thrombosis 
of  the  left  innominate  vein  or  of  the  subclavian  at  its  junction  with  the  internal  jugular  ; 
(/)  tricuspid  incompetence  (through  backward  pressure)  ;  (g}  cardiac  hyper- 
trophy ;  (k)  dense  pancreatic  growths  (Agnew)  ;  (/')  thrombosis  (tuberculous)  of 
the  duct  itself ;  (j  )  filarial  disease  (obstruction  by  the  parent  worms)  ;  (£)  cicatri- 
cial  contraction  or  adhesion  involving  the  duct  ;  (/)  disease  (tuberculous,  carcino- 
matous) of  the  walls  of  the  duct. 

The  duct  may  be  injured  (a)  during  operations — as  for  growths  or  enlarged 
glands — or  by  stab  or  bullet  wounds  (usually  in  its  cervical  portion)  ;  or  (b)  by 
grave  trauma,  as  fracture  dislocation  of  the  spine  (usually  in  the  thoracic  or  abdomi- 
nal portion),  or  violent  compression  of  the  thorax  ;  or  (r)  by  muscular  effort  or 
during  a  paroxysm  of  vomiting  (Busey),  or  whooping-cough  (Wilhelm). 

The  fact  that  the  duct  as  a  rule  extends  upward  but  little  if  at  all  above  the 
level  of  the  junction  of  the  internal  jugular  and  subclavian  renders  operative  injury  of 
it  rare,  but  as  it  occasionally  is  found  higher,  and  may  even  extend  to  5.5  cm. 
(2^  in.)  above  the  upper  border  of  the  sternum,  its  possible  presence  and  its  rela- 
tions and  variations  (vide  supra]  should  not  be  forgotten  during  extensive  operations 
at  the  base  of  the  neck  on  the  left  side. 

The  results  of  obstruction  of  the  thoracic  duct  are  (a)  increased  pressure 
and  dilatation  of  the  vessels  behind  the  obstruction  ;  (£)  the  establishment  of 
collateral  circulation  and  entrance  of  lymph  into  the  general  circulation;  or— if 
such  collateral  circulation  is  not  established — (f)  leakage  by  transudation  int.. 
the  surrounding  tissues,  into  the  pleura!  cavity  (rare),  or  into  the  peritoneal 
cavity  ;  or  (d  >  rupture  of  the  duct  or  its  tributaries.  The  stomata  of  the  thin-walled 


THE   LYMPHATICS    OF   THE    HEAD.  945 

lymphatic  vessels  offer  little  obstacle  to  free  transudation,  which,  when  it  follows 
obstruction,  may  be  compared  to  the  hematemesis  seen  in  hepatic  cirrhosis  (Rolleston). 

The  symptoms  of  obstruction  are  neither  so  constant  nor  so  marked  as  they 
would  be  if  it  were  not  that  (a)  the  lymphatic  system  is  not,  like  the  veins,  a  series  of 
closed  vessels,  but  is  practically  continuous  with  the  interstices  of  the  tissues;  and  that 
(6)  it  communicates  with  the  venous  system,  the  duct  itsdf  with  the  azygos  vein  in  the 
posterior  mediastinum,  and  the  smaller  lymphatics  with  venules  elsewhere — certainly, 
for  example,  in  the  inguinal  region,  and  probably  in  other  parts  of  the  body  (Leaf). 

The  effects  of  obstruction  are  most  often  noticeable  when  the  interference  with 
the  flow  of  lymph  takes  place  near  the  termination  of  the  duct  on  the  outer  side  of 
the  internal  jugular  vein,  near  its  junction  with  the  subclavian.  This  is  probably 
due  to  (a)  the  frequency  of  tumor  or  of  injury  in  this  situation  ;  (b~)  the  consolida- 
tion of  the  lymph-vessels  here  into  a  single  trunk  ;  (V)  the  greater  difficulty  in  estab- 
lishing a  compensatory  collateral  circulation  between  the  parts  of  the  duct  above  and 
below  the  obstruction  than  if  the  latter  were  lower  down  (Rolleston). 

Chylous  ascites  may  be  due  either  to  obstruction  with  transudation  of  chyle 
from  distended  lacteals  into  the  peritoneal  cavity,  or  to  wound  or  rupture  of  the 
thoracic  duct,  or  of  the  larger  lymph-vessels,  or  of  varicose  lymph-vessels,  or  of 
lymphangiomata.  Chylous  pleural  effusions  may  similarly  result,  or  an  effusion  fol- 
lowing wound  or  rupture  may  be  partly  thoracic  and  partly  abdominal,  as  in  a  case 
in  which,  after  extreme  compression  of  the  chest,  death  followed  in  three  weeks,'  and 
the  thoracic  duct  was  found  ruptured  where  it  traversed  the  hiatus  aorticus  (Bellamy). 

When  the  receptaculum  chyli  is  involved,  the  thoracic  duct  above  may  be  quite 
healthy,  and  lymph  may  pass  into  it  by  anastomotic  channels  and  no  chylous  ascites 
be  produced. 

Carcinoma  of  the  aortic  or  mesenteric  nodes  may  cause  enough  dilatation  of  the 
lymphatics  to  bring  about  chylous  ascites. 

THE  RIGHT  LYMPHATIC  DUCT. 

The  right  lymphatic  duct  (ductus  lymphaticus  dexter)  (Fig.  795)  opens  into  the 
right  subclavian  vein  and  is  a  very  short  stem,  rarely  having  a  length  of  more  than 
from  IO-I2  mm.  It  is  formed  by  the  union  of  the  right  jugular  and  subclavian 
lymphatic  trunks,  the  right  broncho-mediastinal  trunk  rarely  contributing  to  its 
formation,  but  having  usually  an  independent  opening  into  the  subclavian  vein. 
Very  frequently  no  right  lymphatic  duct  exists,  the  jugular  and  subclavian  trunks, 
as  well  as  the  broncho-mediastinal,  opening  independently  into  the  vein. 

THE   LYMPHATICS   OF   THE   HEAD. 
THE  LYMPH-NODES. 

The  lymphatic  nodes  of  the  head  are  arranged  in  groups,  which,  for  the  most 
part,  are  situated  along  the  line  of  junction  of  the  head  and  neck  regions,  that  is  to 
say,  along  a  line  extending  from  the  external  occipital  protuberance  to  the  temporo- 
mandibular  articulation  and  thence  along  the  rami  of  the  mandible.  A  few  small  nodes 
also  occur  upon  the  cheeks,  and  others  which  lie  upon  the  surfaces  of  the  hyo-glossus 
and  genio-hyo-glossus  muscles  and  upon  the  upper  part  of  the  posterior  surface  of 
the  pharynx  may  be  regarded  as  belonging  to  the  head  region.  Including  these, 
the  various  groups  recognizable  in  the  region  are  (i)  the  occipital,  (2)  the  posterior 
auricular,  (3)  the  anterior  auricular,  (4)  the  parotid,  (5)  the  submaxillary ,  (6)  the 
submcntal,  (7)  the  facial,  (8)  the  lingual,  and  (9)  the  retropharyngeal  groups. 

The  occipital  nodes  (1)  mphoglandulae  occipitales)  are  from  one  to  three  in  num- 
ber and  are  situated  at  the  base  of  the  occipital  triangle,  immediately  lateral  to  the 
border  of  the  trapezius  muscle  and  resting  upon  the  upper  part  of  the  semispinalis 
capitis  (Fig.  796).  Their  afferents  come  from  the  occipital  portion  of  the  scalp  and 
their  efferents  pass  to  the  upper,  nodes  of  the  superior  deep  cervical  group. 

The  posterior  auricular  or  mastoid  nodes  (lymphoglandulae  auriculares 
posteriores)  are  usually  two  in  number  and  are  of  small  size  ;  they  rest  upon  the 
mastoid  portion  of  the  insertion  of  the  sterno-cleido-mastoid  muscle  (Fig.  796). 

60 


946 


HUMAN   ANATOMY. 


Their  afferents  are  from  the  temporal  region  of  the  scalp,  from  the  posterior  surface 
of  the  pinna  and  of  the  external  auditory  meatus.  Their  cffcrents  pass  to  the  upper 
nodes  of  the  superior  deep  cervical  group. 

Tin-  anterior  auricular  nodes  (lymphoglandulae  auricularcs  antcriores)  vary  from 
one  to  three  in  number  and  are  situated  immediately  in  front  of  the  tragus,  beneath 
the  parotid  fascia.  Their  afferents  come  from  the  anterior  surface  of  the  pinna  and 
of  the  external  auditory  meatus,  from  the  integument  of  the  temporal  region,  and 
from  the  outer  portions  of  the  eyelids.  Their  efferents  pass  to  the  superior  deep 
cervical  nodes. 

The  parotid  nodes  (lymphoglandulae  parotideae)  are  situated  in  the  substance 
of  the  parotid  gland  (Figs.  796,  801).  They  are  quite  numerous  and  vary 

greatly    in   size.      They 

FIG.  796.  receive    afferents    from 

the  same  regions  as  the 
anterior  auricular  nodes, 
and  the  lower  nodes  of 
the  group  also  receive 
stems  from  the  soft 
palate.  Their  efferents 
pass  to  the  superior 
deep  cervical  nodes. 

The  submaxillary 
nodes  (lymphoglandulae 
subniaxillares)  are  from 
three  to  eight  or  more 
in  number,  forming  a 
chain  along  the  lower 
border  of  the  horizontal 
ramus  of  the  mandible, 
as  far  forward  as  the 
attachment  of  the  ante- 
rior belly  of  the  digastric 
muscle  (Fig.  796).  One 
node  which  rests  upon 
the  facial  artery  just 
before  it  passes  over  the 
ramus  of  the  mandible  is 
larger  than  the  rest,  and 
this,  together  with  two 
others,  which  are  some- 
what smaller  and  lie  one 
either  side  of  the 


Posterior 
auricular  node 


on 


Superficial  lymphatic  vessels  and  nodes  of  head  and 
neck  ;    semidiagrammatic. 


larger  node,  are  the 
most  constant  represen- 
tatives of  the  group,  the 
remaining  nodes  being 
usually  still  smaller  and 
varying  both  in  number  and  position.  Occasionally  a  small  node  occurs  imbedded 
in  the  substance  of  the  submaxillary  gland.  These  nodes  receive,  as  afferents, 
vessels  from  the  submental  and  facial  nodes  and  also  directly  from  the  territory 
drained  by  the  latter,  namely,  the  upper  lip,  the  outer  surface  of  the  nose  and  the 
cheek,  from  the  inner  portions  of  the  eyelids,  from  the  lower  lip,  the  gums  of 
both  jaws,  and  from  the  anterior  part  of  the  tongue.  Their  efferents  descend  upon 
the  surface  of  the  submaxillary  gland  to  open  into  the  superior  deep  cervical  nodes, 
especially  into  those  situated  in  the  neighborhood  of  the  bifurcation  of  the  common 
carotid  artery. 

The  submental  nodes  are  two  or  sometimes  three  in  number,  and  are  situated 
in  tin-  triangular  space  included  between  the  anterior  bellies  of  the  two  digastric 
muscles,  each  of  the  two  principal  nodes  resting  upon  the  inner  border  of  one  of  the 


THE   LYMPHATICS   OF   THE   HEAD. 


947 


FIG. 


Submental 
node 


Superior 
deep 
cervical 
node 


Sterno- 
niastoid 
muscle 


Submaxillary  and  submental   lymph-nodes,  new-born  child.     (Stahr.*) 


muscles  (Figs.  796,  797).     They  receive  afferents  from  the  integument  of  the  chin, 

from  the  lower  lip,  and  from  the  floor  of  the  mouth  ;  their  efferents  pass  partly  to  the 

submaxillary  nodes  and 

partly  to  a  node  of  the 

superior    deep     cervical 

group    situated    on    the 

internal    jugular    vein    a 

little  above  the  level  at 

which    it   is    crossed    by 

the    omo-hyoid    muscle. 
The   facial   nodes 

(lymphoglandulae  faciales 

profundae)  consist  of  sev- 
eral small  groups  (Fig. 

798).      One  of   these   is 

composed  of  two  or  three 

nodes  situated  upon  the 

outer     surface     of      the 

horizontal  ramus  of  the 

mandible,     in     front     of 

the    anterior    border   of 

the     masseter     muscle  ; 

these    may    be     termed 

the  mandibular  nodes. 

A  second  group  is  to  be 

found   resting  upon   the 

surface  of  the  buccinator 

muscle,  and  its  nodes  are  therefore  termed  the  buccinator  nodes.     They  are  three 

or  four  in  number  and  are  situated  in  the  interval  between  the  facial  vein  and  artery, 

or  posterior  to  the  vein,  almost  opposite  the  angle  of  the  mouth  and  either  beneath 

or     slightly     below     the 

FIG.  798.  zygomaticus    major.       A 

third  group  is  formed  by 
the  maxillary  nodes, 
which  are  somewhat 
scattered,  one  or  two 
occurring  in  the  groove 
formed  by  the  junction  of 
the  nose  and  cheek,  while 
another  rests  upon  the 
malar  bone  near  the  lower 
border  of  the  orbit.  These 
maxillary  nodes  are  nor- 
mally quite  small  and  may 
readily  be  overlooked. 

The  afferents  for  the 
various  groups  of  facial 
nodes  take  their  origin 
in  the  upper  lip,  in  the 
integument  and  mucous 
membrane  of  the  nose 
and  cheek,  and  probably 
also  in  the  eyelids,  the 

conjunctiva,  and  the  lachrymal  gland.    Their  efferents  pass  to  the  submaxillary  nodes. 
The  lingual  nodes  (lymphoglandulae  linguales)  are  a  number  of  small  enlarge- 
ments situated  upon  the  vessels  which  drain  the  lymphatic  capillaries  of  the  tongue. 

They  do  not  possess  any  very  definite  grouping  and  are  to  be  found   upon  both 

*Archivf.  Anat.  u.  Physiol.,  1898. 
t  Beitrage  zur  klin.  Chirurgie,  Bd.  39. 


I 

Facial  lymph-nodes.     ( Trendel.\) 


948 


HUMAN   ANATOMY. 


surfaces  of  the  hyo-glossus  muscle  and  in  the  interval  between  the  two  genio-hyo- 
glossi.  From  the  surgical  standpoint  they  are  of  comparatively  little  importance, 
and  have  been  termed.  "  intercalated  nodes,"  to  distinguish  them  from  the  true 
terminal  nodes  of  the  lingual  lymphatics  (page  954),  in  which  enlargement  occurs  in 

cases  of  cancerous  or 
FIG.  799. 


Longus  colli  muscle,  stump 


the 


Internal 

•otid 
artery 


Retropharyngeal  lymph-nodes.     ( Most.*) 


other   infection  of 
tongue. 

The  retro-phar- 
yngeal  nodes  are  for 
the  most  part  small, 
appearing  as  slight  en- 
largements of  the  lym- 
phatics which  drain  the 
posterior  surface  of  the 
pharynx.  In  addition 
to  these  ' '  intercalated 
nodes,"  however,  one 
or  two  much  larger 
nodes  occur  at  the  junc- 
tion of  the  lateral  and 
posterior  surfaces  of 
the  pharynx,  about  on 
a  level  with  the  anterior 
arch  of  the  atlas.  They 
are  imbedded  in  the 
bucco-pharyngeal  fas- 
cia and  rest  upon  the 
lateral  portions  of  the 

rectus  capitis  anticus  major.  Afferents  come  to  them  from  the  upper  part  of  the 
pharynx  and  from  the  mucous  membrane  of  the  nose,  and  their  efferents  pass  to  the 
upper  deep  cervical  nodes  (Fig.  799). 

THE  LYMPHATIC  VESSELS. 

The  Scalp. — The  lymphatics  of  the  scalp  form  a  rich  net-work,  which  is  espe- 
cially dense  in  the  neighborhood  of  the  vertex,  the  meshes  becoming  more  elongated 
as  the  vessels  pass  away  from  the  median  line.  From  the  frontal  region  some  ten  to 
twelve  vessels  pass  downward  and  backward  to  terminate  in  the  parotid  nodes  ;  from 
the  parietal  and  temporal  regions  from  six  to  ten  vessels  pass  downward,  some  in 
front  of  the  external  auditory  meatus  to  terminate  in  the  anterior  auricular  and  paro- 
tid nodes,  and  some  behind  the  meatus  to  reach  the  posterior  auricular  nodes  ;  and 
from  the  occipital  region  the  more  posterior  vessels  pass  downward,  partly  to  the 
occipital  and  partly  to  the  superior  deep  cervical  nodes,  while  the  more  anterior  five  or 
six  converge  to  form  a  single  large  trunk  which  descends  along  the  posterior  border 
of  the  sterno-cleido-mastoid  muscle  and  terminates  in  the  inferior  deep  cervical  nodes. 

The  Brain  and  the  Meninges. — No  lymphatic  vessels  have  as  yet  been  cer- 
tainly demonstrated  either  in  the  central  nervous  system  or  in  the  meninges,  although 
they  have  been  described  as  accompanying  the  middle  meningeal  artery  in  the  dura 
mater  and  the  middle  cerebral  artery  in  the  pia  (Poirier).  Lymph-spaces,  how- 
ever, some  of  them  of  considerable  size,  are  abundantly  present.  Of  these  there  may 
be  mentioned,  first,  \\\a periccllular  s/xiccs  which  surround  the  individual  cells  of  the 
brain  and  spinal  cord,  both  the  actual  nerve-cells  and  the  neuroglia-cells,  those 
accompanying  the  latter  extending  along  their  processes  to  communicate  with  an 
epicerebral  space  believed  to  exist  between  the  surface  of  the  brain  and  the  pia  (His), 
and  also  with  spaces  which  occur  along  the  course  of  the  cerebral  blood-vessels.  Of 
this  second  group  of  spaces,  the  pcrivascitlar  spaa-s,  two  sets  have  been  described, 
one  occurring  in  the  adventitia  surrounding  tin-  vessels  and  the  other  between  the 
adventitia  and  the  brain  substance,  and,  accompanying  the  blood-vessels  into  the  pia, 

*  Archiv  f.  klin.  Chirurjjie,  Bd.  41,  1900. 


THE   LYMPHATICS   OF   THE    HEAD. 


949 


they  communicate  with  the  subarachnoid  spaces.  The  third  group  of  spaces  is 
formed  by  the  subdural  and  subarachnoid  spaces,  but  no  special  description  need  here 
be  given  of  these,  since  they  are  more  properly  described  (-page  1197)  as  portions  of 
the  meninges  than  as  parts  of  the  lymphatic  system.  By  some  authors  an  epidural 
space,  situated  between  the  dura  and  the  skull,  is  also  recognized. 

Lymph-spaces  have  been  described  as  occurring  in  the  substance  of  both  the  dura 
and  the  pia,  forming  in  the  latter  a  rather  close  net-work  with  which  the  perivascular 
spaces  communicate.  The  spaces  of  both  membranes  communicate  with  the  subdural 
space,  and  those  of  the  dura  are  said  also  to  communicate  with  the  epidural  space. 

Practically  nothing  is  yet  known  concerning  the  lymphatics  of  the  spinal  cord. 

The  Eye  and  Orbit. — No  lymphatic  vessels  have  as  yet  been  described  as 
occurring  in  the  orbital  tissues,  nor  do  they  occur  in  the  eyeball.  But,  on  the  other 
hand,  numerous  lymph-spaces  occur  in  connection  with  the  latter  structure,  one  of 
the  most  important  of  these  being  the  space  of  Tenon  (spatium  interfasciale),  with 
which  the  remaining  spaces  communicate  more  or  less  directly  (Fig.  800).  A 
description  of  this  space  has  already  been  given  (page  504),  but  it  may  be  recalled 
that,  in  the  first  place,  the  space  is  continued,  by  means  of  the  supravaginal  lymph- 


FIG.  800. 


Conjunctiva!  sac 
Space  of  Tenon 


Diagram  showing  relation  of  space  of  Tenon  to  intracranial  lymph-spaces. 

path  surrounding  the  optic  nerve,  along  the  latter  to  the  apex  of  the  orbit,  where 
it  communicates  with  the  subdural  space  of  the  cranium,  injection  of  that  space 
resulting  in  the  injection  of  the  space  of  Tenon  (Schwalbe),  and,  secondly,  that  the 
sheaths  of  the  anterior  portions  of  the  orbital  muscles  are  formed  by  reflections  of  the 
capsule  of  Tenon,  so  that  no  obstacles  exist  in  the  way  of  the  passage  of  lymph 
from  the  muscles  into  the  space. 

The  cavities  occupied  by  the  vitreous  and  aqueous  humors  have  also  been  re- 
garded as  lymph-spaces,  and  pericellular  spaces  in  the  cornea,  which  come  into  rela- 
tion with  the  lymphatic  vessels  of  the  conjunctiva  at  the  corneal  margin,  are  readily 
demonstrable.  In  the  tissue  of  the  sclerotic  spaces  also  occur,  communicating  on 
the  one  hand  with  the  space  of  Tenon  and  on  the  other  with  suprachoroid  spaces 
which  are  abundantly  present  in  the  lamina  fusca  of  the  choroid  coat  and,  by  means 
of  spaces  accompanying  the  venae  vorticosae,  communicate  with  the  space  of  Tenon. 

In  the  eyelids,  conjunctiva,  and  lachrymal  apparatus  true  lymphatic  vessels  occur. 
In  the  eyelids  three  net-works  have  been  distinguished,  one  of  which  is  subcutaneous, 
the  second  lies  immediately  external  to  the  tarsal  plate,  and  the  third  is  subconjunctival. 
Communicating  branches  pass  between  adjacent  plexuses,  especially  between  the 


950 


HUMAN    ANATOMY. 


subcutaneous  and  praetarsal  ones,  and  all  three  are  united  at  the  palpebral  margins 
in  a  rather  finely  meshed  plexus.  Efferents  pass  both  toward  the  inner  and  the 
outer  angle  of  the  orbit,  and  the  former  pass  downward,  obliquely  across  the  cheek, 
in  company  with  the  facial  vein,  to  terminate  in  the  submaxillary  nodes,  possibly 
making  connections  with  some  of  the  facial  nodes  on  their  way  (Fig.  798).  The 
outer  ones  pass  partly  to  the  anterior  auricular  and  partly  to  the  upper  parotid  nodes. 
In  the  conjunctiva  two  net-works  occur,  one  situated  in  the  superficial  and  the 
other  in  the  deeper  layers  of  the  conjunctival  dermis.  Communicating  stems  pass 
between  the  net-works,  which  are  much  finer  in  the  neighborhood  of  the  corneal 
margin  than  more  peripherally.  They  come  into  relation  with  the  pericellular 
lymph-spaces  of  the  cornea,  and  their  efferents  pass  toward  the  outer  and  inner 
angles  of  the  orbit,  to  accompany  the  palpebral  efferents  to  the  submaxillary, 
posterior  auricular,  and  parotid  nodes. 

Of  the  lymphatic  vessels  of  the  lachrymal  gland  but  little  is  known,  but  in  ma- 
lignant diseases  of  the  gland  enlargement  of  some  of  the  facial  and  anterior  auricular 
nodes  has  been  observed,  and  it  is  probable  that  vessels  from  the  gland  accompany 
the  palpebral  and  conjunctival  efferents.  The  vessels  from  the  nasal  duct  probably 
partly  accompany  branches  of  the  facial  vein  to  the  facial  nodes,  while  those  from  its 
lower  portion  pass  with  the  efferents  from  the  nasal  mucous  membrane  to  the  retro- 
pharyngeal  and  superior  deep  cervical  nodes. 

The  Ear. — No  true  lymphatics  have  yet  been  observed  in  the  tissues  of  the 
internal  ear,  but  the  space  which  intervenes  between  the  osseous  wall  of  the  ear 
cavity  and  the  membranous  ear  has  been  regarded  as  a  lymph-space,  and  on  that 

account    has    been    termed    the 

FIG.   801.  perilymphatic    space.       It    com- 

municates with  the  subdural 
space  of  the  cranium  by  the 
aqueductus  cochleae  and  by  the 
prolongations  of  it  which  accom- 
pany the  ductus  endolymphaticus 
and  the  auditory  nerve. 

In  the  middle  ear  spaces 
have  been  observed  in  the  con- 
nective tissue  lining  the  bony 
walls,  as  well  as  in  that  of  the 
tympanic  membrane.  In  addi- 
tion a  feebly  developed  net- work 
has  been  described  as  occurring 
beneath  the  epithelium  lining  the 
inner  (tympanic)  surface  of  the 
tympanic  membrane,  efferents 
from  it  accompanying  the  tym- 
panic artery  and  terminating  in 
the  parotid  nodes. 

Much  more  extensively 
developed  are  the  lymphatic 
vessels  of  the  external  car. 
Beneath  the  epithelium  covering 
the  outer  (meatal)  surface  of  the 
tympanic  membrane  there  is  a 
very  fine  net- work,  whose  effer- 
ents accompany  the  blood-vessels, 
radiating  toward  the  periphery  of  the  membrane,  and  eventually  open  partly  into  the 
posterior  and  partly  into  the  anterior  auricular  nodes.  A  net-work  also  occurs 
throughout  the  entire  extent  of  the  external  auditory  meatus,  its  efferents  having 
the  same  destination  as  those  of  the  pinna. 

The  vessels  of  the  last  named  portion  of  the  ear  form  a  rich  net-work  extending 
throughout  the  whole  extent  of  the  organ,  and  from  it  stems  pass  in  three  principal 

*An;itom.  An/ri^rr,  I'd.  \v.,  1899. 


Great 

auricular 

nerve 


SupraclavicuUr  node 


Lymphatics  of  posterior  surface  of  auricle  of  new-born 
child.     (Stahr.*) 


THE    LYMPHATICS   OF   THE   HEAD. 


directions  ;  it  must  be  recognized,  however,  that  this  classification  of  the  stems  into 
three  groups  does  not  imply  a  corresponding  division  of  the  net-work  into  distinct 
areas,  since  there  is  a  considerable  overlapping  of  the  areas  drained  by  the  various 
stems)  and,  indeed,  stems  from  the  same  region  may  pass  in  some  cases  with  one  of 
the  group,  and  in  others  with  another.  From  the  outer  (anterior)  surface  the 
stems  pass  mainly  to  the  anterior  auricular  nodes,  a  few  bending  backward  over  the 
helix  and  terminating  in  the  posterior  auricular  nodes.  Froiii  the  upper  part  of  the 
posterior  surface  (Fig.  80 1)  the  stems  pass  mainly  to  the  posterior  auricular  nodes, 
some,  however,  continuing  past  them  to  terminate  in  the  external  jugular  nodes. 
From  the  lower  part  of  the  pinna,  including  the  lobule,  a  number  of  stems  pass  to 
the  parotid  nodes. 

The  Nasal  Region. — The  lymphatic  vessels  of  the  integument  of  the  nose 
(Fig.  802)  form  numerous  anastomoses  with  those  of  the  mucous  membrane,  especially 
with  those  of  the  middle  and  inferior  meatuses,  and  those  of  the  one  side  of  the  nose 
are  also  continuous  with  those  of  the  other  side.  Some  of  the  vessels  which  drain 
the  upper  portion  of 

the  nasal  integument  FIG.  802. 

pass  almost  directly 
backward  to  the 
parotid  nodes,  but 
the  principal  path, 
followed  by  vessels 
from  all  parts  of  the 
nasal  integument, 
is  downwards  and 
backwards  across 
the  cheek,  in  com- 
pany with  the  facial 
blood  -  vessels.  In 
their  course  some  of 
them  traverse  some 
of  the  facial  nodes, 
which  appear  as  if 
intercalated  in  their 
course,  but  the  ma- 
jority pass  directly 
to  the  submaxillary 
nodes. . 

A  rich  1  y  m- 
phatic  net-work  lies 
beneath  the  mucous 
membrane  of  the 

nasal  cavities,  and  from  it  vessels  pass  in  two  directions.  Those  of  the  anterior  and 
lower  portions  of  the  fossae  pass  forward  and,  partly  at  the  external  nares  and  partly  by 
passing  between  the  nasal  bones  and  the  cartilages,  communicate  with  the  superficial 
nasal  lymphatics.  The  majority  of  the  vessels,  however,  take  a  backward  course, 
terminating  in  different  node  groups.  Some  join  the  vessels  draining  the  palate  and 
tonsils  to  pass  to  the  superior  deep  cervical  nodes  and  especially  to  that  one  which  is 
situated  in  the  angle  formed  by  the  union  of  the  facial  and  internal  jugular  veins, 
while  the  rest  unite  to  form  from  two  to  four  stems  which  pass  over  the  lateral  surface 
of  the  pharynx  and  terminate  in  the  retropharyngeal  nodes. 

The  lymphatics  of  the  sinuses  which  open  into  the  nasal  cavities  follow,  in  part 
at  least,  the  same  courses  as  those  of  the  nasal  mucous  membrane,  their  principal 
termination  being  in  the  larger  retropharyngeal  nodes. 

The  Cheeks,  Lips,  Gums,  and  Teeth. — The  lymphatics  from  the  more 
posterior  portions  of  the  cheeks  empty  into  the  parotid  nodes  ;  those  from  the 
more  anterior  portions  pass  to  the  submaxillary  nodes,  and  the  deeper  ones 
communicate  with  the  facial  nodes. 

*  Beitrage  f.  klin.  Chirurgie,  Bd.  xxv.,  1899. 


llary 


Lymphatics  of  nose  and  cheek.     (Kiittner.*) 


952 


HUMAN    ANATOMY. 


The  vessels  from  the  submucous  tissues  of  the  lips  pass  mainly  to  the  submaxil- 
lary  nodes,  two  or  three  stems  passing  from  the  lower  lip  and  one  or  two  from  the 
upper.  Those  of  the  lower  lip  pass  downward  and  outward  toward  the  facial  artery 
and  follow  its  course  into  the  submaxillary  region,  while  those  from  the  upper  lip  are 
directed  at  first  almost  horizontally  outward  toward  the  facial  vein,  whose  course 
they  follow  toward  their  termination.  No  anastomoses  occur  between  the  submucous 
vessels  of  the  two  sides  in  either  lip. 

The  subcutaneous  vessels  of  the  upper  lip  (Fig.  803)  have  a  course  similar  to 
that  of  the  corresponding  submucous  stems,  with  which  they  may  unite,  and  they 
terminate  principally  in  the  submaxillary  nodes,  although  communication  may  also  be 
made  with  one  of  the  lower  parotid  nodes.  The  subcutaneous  vessels  of  the  lower  lip 
are  from  two  to  four  in  number,  and  pass  principally  to  the  submental  nodes,  from  which 

efferents  pass  to  the  sub- 

FIG.  803.  maxillary     and     superior 

deep  cervical  nodes.  A 
noteworthy  peculiarity  of 
these  lower  lip  vessels, 
which  is  in  marked  con- 
trast with  what  obtains  in 
the  submucous  stems,  is 
that  those  of  the  right 
and  left  halves  of  the  lip 
anastomose,  so  that  an 
injection  may  pass  from 
the  vessels  of  the  right 
half  into  the  left  sub- 
mental  and  submaxillary 
nodes. 

The  lymphatics  of 
the  lower  gums  form  a 
very  rich  net-work  from 
which  from  fourteen  to 
seventeen  stems  arise. 
These  empty  into  a  single 
large  collecting  stem  on 
either  side,  which  passes 
outward  over  the  outer 
surface  of  the  mandible 
and,  opposite  the  last 
molar  tooth,  dips  down- 
ward to  terminate  in 
the  submaxillary  nodes. 
Whether  or  not  the  pulp 
of  the  teeth  contains  lymphatic  capillaries  is  a  disputed  question.  All  attempts  to 
inject  them  have  failed,  but  it  has  been  maintained  that  their  existence  has  been 
demonstrated  by  histological  methods.  Enlargement  of  the  submaxillary  nodes  lias 
been  observed  to  follow  dental  lesions,  but  this  may  be  due  to  the  involvement  of  the 
tissues  of  the  gums  rather  than  to  that  of  the  tooth  pulp. 

The  Tongue. — The  lymphatics  of  the  tongue  (Fig.  804)  are  divisible  into  two 
groups  according  as  they  arise  in  the  submucous  tissue  or  in  the  musculature.  The 
submucous  vessels  take  their  origin  from  an  exceedingly  rich  net-work  which  extends 
throughout  the  entire  surface  of  the  tongue.  It  is  especially  close  toward  the  tip, 
the  meshes  becoming  larger  posteriorly,  and  that  portion  of  it  which  lies  posterior  to 
the  circumvallate  papillae  is  independent  of  that  of  the  more  anterior  portions  of  the 
tongue.  The  vessels  of  the  muscular  portion  of  the  organ  are  much  less  extensively 
developed  and  the  efferent  stems  which  pass  from  them  early  unite  with  those  of 
the  submucous  net-work.  These  latter  are  quite  numerous  and  for  purposes  of 
description  may  be  arranged  in  four  groups. 

*  Ink-mat.  Monatssclirift  f.  Anal.  u.  1'hysiol.,  1900. 


Deep 

•cervical 

nodes 


Subcutaneous  lymphatics  of  lips  and  superior  deep  cervical  nodes, 
new-born  child.     (Dorrendorjf.*) 


THE   LYMPHATICS   OF   THE   HEAD. 


953 


Faucial 
tonsil 


The  first  or  apical  group  (Fig.  805)  consists  of  from  two  to  four  stems  which 
arise  from  the  net-work  at  the  tip  of  the  tongue  and  pass  downward  and  backward, 
half  of  them  lying  on  one  side  of  the  frenum  and  half  on  the  other  side.  They  follow 
at  first  the  anterior  border  of  the  genio-hyo-glossus  muscle  and  then  pass  upon  the 
outer  surface  of  that  muscle  and  are  continued  downward  and  backward,  either 
external  or  internal  to  the  hyo-glossus,  until  they  reach  the  greater  cornu  of  the 
hyoid  bone,  just  below  the  attachment  of  the  stylo-hyoid.  They  then  cross  obliquely 
over  the  outer  surface  of  the  greater  cornu,  and  are  continued  down  the  neck  along 
the  outer  border  of  the  omo-hyoid  muscle  to  open  into  one  of  the  inferior  deep 
cervical  nodes  situated  upon  the  jugular  vein  just  above  the  point  where  it  is  crossed 
by  the  omo-hyoid  muscle.  Sometimes  an  additional  apical  stem  passes  down  the 
frenum  in  company  with  those  just  described,  but  continues  on  downward  to 
perforate  the  mylo-hyoid  muscle  and  terminate  in  one  of  the  submental  nodes. 

A  second  or  lateral  group  consists  of  a  number  of  vessels  which  emerge  from  the 
net- work  along  the  borders  of  the  tongue  (Fig.  804).  There  are  from  eight  to  twelve 
stems  in  this  group  on 
either  side,  and  all  are  at 
first  directed  almost  verti- 
cally downwards,  a  few, 
three  or  four,  passing  later- 
ally to  the  sublingual  gland 
and  the  rest  medial  to  it. 
The  former  continue  their 
downward  course,  perforate 
the  mylo-hyoid  muscle,  and 
terminate  in  the  submaxil- 
lary  nodes,  while  the  others 
take  a  course  obliquely 
downward  and  backward, 
and,  passing  some  upon 
the  median  and  others 
upon  the  lajteral  surface 
of  the  hyo-glossus  muscle, 
terminate  in  the  superior 
deep  cervical  nodes  and 
especially  in  one  situated  a 
little  above  the  level  of  the 
bifurcation  of  the  common 
carotid  artery.  This  node, 
on  account  of  its  relations  to 
these  lingual  stems,  has  been 
termed  the  principal  node 
of  the  tongue  (Fig.  805). 

A  third  or  basal  group  takes  its  origin  from  the  dense  portion  of  the  submucous 
net-work  which  surrounds  the  circumvallate  papillae  and  the  foramen  caecum.  Four 
stems  issue  from  the  net-work  in  the  neighborhood  of  the  median  line,  and  two  on  each 
side  more  laterally.  The  median  stems  pass  at  first  directly  backward  and  then  bend 
outward  in  the  glosso-epiglottidean  folds,  two  on  either  side,  and  join  the  lateral  stems 
beneath  the  tonsils.  The  lateral  stems,  which  drain  the  regions  of  the  lateral  circum- 
vallate papillae,  the  foliate  papillae,  and  the  glandular  region  of  the  tongue,  are  directed 
backward  towards  the  lower  border  of  the  tonsil,  and,  after  being  joined  in  that  situation 
by  the  median  stems,  they  pass  deeply  to  terminate  in  the  superior  deep  cervical  nodes. 

Finally,  a  fourth  or  median  group  arises  from  the  net-work  of  the  median 
portion  of  the  tongue,  anterior  to  the  circumvallate  papillae.  These  stems  are  five 
or  six  in  number,  and  pass  at  first  directly  downward  through  the  substance  of  the 
tongue  and  through  the  interval  which  separates  the  two  genio-hyo-glossal  muscles. 
One  or  two  of  them  then  continue  in  their  downward  course  and  pass,  in  some  cases 


Apical 
net-work  of 
lymphatics 


Lymphatics  of  dorsum  ar 


of  tongue.     (Kiittner.*) 


*  Beitrage  f.  klin.  Chirurgie,  Bd.  xxi.,  1895. 


954 


HUMAN   ANATOMY. 


Basal  vessel 


FIG.  805 , 


Apical 

vessels 


Lateral 

vessels 
Apical 

vessels 


to  the  right  and  in  some  to  the  left,  between  the  genio-hyo-glossus  and  the  genio- 
hyoid  muscles,  perforate  the  mylo-hyoid,  and  terminate  in  the  submaxillary  nodes. 
The  remaining  three  or  four  stems  pass  backward  along  the  mylo-hyoid  muscle 
and,  emerging  at  its  posterior  border,  pass  to  the  superior  deep  cervical  nodes. 

From  this  account  it  will  be  seen  that  four  different  groups  of  nodes  stand  in 
relation  to  the  lymphatics  of  the  tongue.  ( i )  The  submental  nodes  receive  a  stem 
from  the  tip  ;  (2)  the  submaxillary  nodes  receive  stems  from  the  marginal  and  cen- 
tral regions  ;  (3)  the  superior  deep  cervical  nodes  receive  stems  from  the  marginal, 
central,  and  basal  regions  ;  and  (4)  the  inferior  deep  cervical  nodes  receive  a  stem 

from  the  apical  region. 
In  addition  it  may  be 
mentioned  that  many 
of  the  stems  have  upon 
their  course  one  or  more 
of  the  small  ' '  inter- 
calated ' '  lingual  nodes 
(  page  948  ).  Special 
importance,  however, 
attaches  to  that  supe- 
rior deep  cervical  node 
already  mentioned  as 
occurring  at  about  the 
level  of  the  bifurcation 
of  the  common  carotid 
artery,  on  account  of 
the  numerous  afferents 
it  receives  from  the 
tongue. 

The  lymphatics  of 
the  floor  of  the  mouth 
have  essentially  the  same 
terminations  as  those  of 
the  tongue.  The  stems 
which  arise  from  its 
anterior  half  pass  with 
the  stems  from  the  tip 

of  the  tongue  to  the  inferior  deep  cervical  nodes,  while  from  its  entire  surface  stems 
pass  to  the  submaxillary  and  superior  deep  cervical  nodes. 

The  Palate,  Pharynx,  and  Tonsils. — The  lymphatics  of  the  hard  palate  form 
a  fine  net- work  in  the  superficial  portions  of  the  mucous  membrane  and  are  continuous 
laterally  with  those  of  the  upper  gum.  They  empty  into  several  stems  which  pass 
backward  in  the  median  line  of  the  palate  and  at  about  the  level  of  the  last  molar 
teeth  bend  outward  to  the  right  and  left,  and,  passing  in  front  of  the  anterior  pillars 
of  the  fauces,  pierce  the  superior  constrictor  of  the  pharynx  to  terminate  in  those 
superior  deep  cervical  nodes  which  are  situated  on  the  internal  jugular  vein  above  the 
level  at  which  it  is  crossed  by  the  posterior  belly  of  the  digastric  muscle. 

The  net-work  of  the  soft  'palate  is  exceedingly  close  and  especially  so  in  the 
uvula,  which  in  a  successful  injection  of  the  lymphatics  may  treble  its  volume,  be- 
coming exceedingly  turgid  (Sappey).  Stems  emerging  from  the  net-work  pass 
toward  both  surfaces  of  the  palate,  those  lying  below  the  upper  surface  passing  l>ack- 
ward  and  outward  to  join  the  stems  from  the  nasal  mucous  membrane  just  below 
the  orifice  of  the  Eustachian  tube,  whence  their  course  is  similar  to  that  of  the  nasal 
stems.  Some  of  them  pnss  upward  and  backward  to  perforate  the  superior  con- 
strictor of  the  pharynx  and  terminate  in  the  lateral  PetTOpharyngeal  nodes,  while 
others  descend  beneath  the  mucous  membrane  covering  the  posterior  pillars  of  the 
fauces  and,  after  perforating  the  superior  constrictor,  terminate  in  the  upper  nodes 
of  the  superior  deep  cervical  group. 

*  Gazette  hebdomadaire,  1902. 


Lymphatics  of  tongue.     (Puttier* , 


THE   LYMPHATICS   OF   THE   HEAD.  955 

The  lymphatics  of  the  tonsil,  which  resemble  those  of  the  soft  palate  in  their 
abundance,  pass  with  the  stems  from  the  basal  region  of  the  tongue  to  the  superior 
deep  cervical  nodes. 

Those  of  the  pharynx  are  also  abundant,  especially  above  (Fig.  799).  The 
stems  which  arise  from  the  roof  and  upper  part  pass  principally  to  the  retro- 
pharyngeal  nodes,  although  some  reach  the  superior  deep  cervical  nodes  directly  by 
following  the  course  of  the  ganglionated  cord.  The  stems  which  have  their  origin 
in  the  lower  part  of  the  pharyngeal  net-work  pass  downward  toward  the  larynx 
and  unite  with  its  vessels  to  be  distributed  to  the  superior  deep  cervical  nodes  as  far 
down  as  opposite  the  level  of  the  second  or  third  tracheal  ring. 

Practical  Considerations. —  The  Lymph-Nodes  of  the  Head. — The  lymphatics 
of  the  scalp  pass  from  the  plexus  of  fine  radicles  on  the  vertex  into  the  suboccipital 
(occipital),  mastoid  (postauricular),  parotid  (preauricular),  and  superficial  cervical 
nodes,  and  a  few — from  the  frontal  region — into  the  submaxillary  node,  into  one  or 
the  other  of  which  infection  may  be  carried  from  any  portion  of  the  scalp. 

The  suboccipital  nodes — one  to  three  on  each  side — lie  on  a  line  drawn  from  the 
junction  of  the  upper  and  middle  thirds  of  the  ear  to  the  inion  and  about  two  inches 
external  to  that  point.  They  are  often  enlarged  as  a  result  of  wounds  or  irritation 
of  the  occipital  and  postauricular  portion  of  the  scalp  and — especially  in  neglected 
children — as  a  consequence  of  eczema  affecting  the  skin  back  of  the  ear.  The  close 
relation  of  the  node  to  the  great  occipital  nerve,  on  which  it  usually  lies,  gives  rise 
to  marked  tenderness  on  pressure,  the  nerve  being  compressed  between  the  node 
and  the  bone.  The  source  of  infection  of  these  nodes  may  be  intracranial — e.g. , 
suppurative  meningitis  of  the  cerebellar  fossa  (Macewen). 

The  mastoid  node,  found  directly  over  the  mastoid  insertion  of  the  sterno-cleido- 
mastoid,  is  likewise  usually  infected  from  the  same  scalp  region.  It  may  also  be 
involved  alone  or  together  with  the  suboccipital  and  deep  cervical  nodes  in  localized 
tuberculous  mastoiditis  or  even  in  tuberculous  otitis  media. 

The  parotid  nodes,  lying  both  in  and  upon  the  gland,  receive  lymph  from  and 
consequently  may  be  infected  by  lesions  of  the  scalp,  the  outer  portion  of  the  lids, 
the  orbit,  the  cheeks,  the  nasal  fossae,  the  naso-pharynx,  the  external  auditory 
meatus,  the  tympanum,  or  the  temporo-mandibular  joint.  Chronic  enlargement  of 
these  nodes,  especially  of  the  deeper  ones  in  the  substance  of  the  gland  and  beneath 
the  parotid  capsule,  may  lead  to  a  mistaken  diagnosis  of  parotid  tumor.  Suppura- 
tive inflammation  of  these  deeper  nodes  gives  rise  to  a  true  parotid  abscess,  which,  on 
account  of  the  resistance  of  the  strong  parotid  fascia,  will  be  under  great  tension. 
Sloughing  of  the  parotid  tissue  may  occur.  There  will  be  shooting  pains  in  the 
head,  neck,  and  ear,  from  pressure  on  the  branches  of  the  trigeminus  accompanying 
the  facial,  or  on  the  auriculo-temporal  and  great  auricular  nerves.  The  contiguity  of 
the  temporo-mandibular  joint — into  which  the  abscess  may  open — makes  movement 
of  the  lower  jaw  painful.  The  relative  weakness  of  the  capsule  anteriorly  and  on  its 
inner  aspect  causes  the  pus  to  travel  forward  towards  the  cheek,  or  inward  towards 
the  pharynx,  following  sometimes  the  pharyngeal  process  of  the  parotid  and  giving 
rise  to  a  retropharyngeal  abscess.  Gravity  and  the  cervical  process  of  the  parotid 
may  conduct  the  pus  into  the  neck. 

The  lymphatics  of  the  face  empty,  the  superficial  set — accompanying  the  facial 
vein  —into  the  parotid  and  submaxillary  nodes  ;  the  deep  set,  with  some  of  those  of 
the  orbit,  palate,  nasal  fossse,  and  upper  jaw,  are  said  to  end  in  the  internal  maxil- 
lary nodes  situated  at  the  sides  of  the  pharynx  anteriorly.  According  to  Leaf,  these 
are  only  exceptionally  present.  Their  involvement  in  infections  spreading  from  the 
above  regions  may  give  rise  to  "  latero-pharyngeal  abscess,"  causing  a  swelling 
externally  behind  the  angle  of  the  mandible,  and  an  inward  projection  of  the  pharyn- 
geal wall  posterior  to  the  tonsil.  The  proximity  of  the  internal  carotid  should  be 
remembered,  and  the  fact  that  an  aneurism  of  that  vessel  has  been  opened  under  the 
impression  that  it  was  an  abscess  of  this  variety  (page  747). 

Some  lymphatics  from  the  chin  and  the  mid-portion  of  the  lower  lip  empty  into 
the  suprahyoid  (submental)  nodes  lying  on  the  mylo-hyoid  between  the  two 
anterior  bellies  of  the  digastrics.  Enlargement  of  these  nodes  may  be  distinguished 


956  HUMAN   ANATOMY. 

from  a  bursal  tumor  (thyro-hyoid)  by  the  fact  that  the  former  is  above,  the  latter 
below,  the  hyoid  bone. 

Enlargement  of  a  submaxillary  node,  as  of  a  parotid  node,  may,  particularly 
if  it  lies  within  the  sheath  of  the  gland,  be  mistaken  for  a  growth  of  the  gland  itself. 
The  latter — as  compared  with  the  parotid — is,  however,  much  less  closely  and  firmly 
enveloped  by  its  capsule,  is  more  superficial,  and  is  not  in  near  relation  to  such 
important  structures.  On  the  other  hand,  the  wide  area  which  drains  into  the  sub- 
maxillary  nodes — the  middle  of  the  forehead  and  of  the  face,  the  inner  portions  of 
the  lids,  the  mouth,  pharynx,  anterior  portion  of  the  tongue,  gums  and  teeth  of  the 
lower  jaw — renders  them  especially  liable  to  pyogenic  or  tuberculous  or  syphilitic 
infection,  or  to  secondary  involvement  in  carcinoma  of  any  of  these  regions — espe- 
cially of  the  tongue  or  lower  lip.  In  examining  for  enlargement  of  these  nodes,  the 
chin  should  be  lowered  so  as  to  relax  the  depressors  of  the  lower  jaw  and  the  deep 
cervical  fascia  and  permit  of  more  accurate  palpation  of  the  region.  When  these 
submaxillary  nodes  require  removal  for  infectious  or  malignant  disease,  the  salivary 
gland  is  often  involved  and  must  be  removed  with  them.  On  account  of  its  accessi- 
bility and  the  laxity  of  its  capsular  connections,  enucleation  of  this  gland  is  easily 
accomplished.  The  relation  of  the  facial  artery  lying  close  to  the  upper  part  of  its 
deep  aspect — which  it  grooves — before  crossing  the  jaw  in  front  of  the  masseter 
muscle  should  be  remembered. 

The  efferent  vessels  from  all  these  nodes — suboccipital,  mastoid,  parotid,  and 
submaxillary — enter  into  the  superficial  cervical  nodes,  the  efferent  vessels  from 
which,  in  their  turn,  enter  the  deep  cervical  nodes  (page  957).  Extracranial  lesions 
of  an  irritative  kind  will  thus  first  show  themselves  in  enlargement  of  the  first 
mentioned  groups  ;  if  the  irritation  is  continued,  the  superficial  cervical  nodes  will 
enlarge  ;  and  if  it  persists  and  is  sufficiently  severe,  the  deep  cervical  will  also 
participate  in  the  enlargement  (Macewen).  As  the  intracranial  lymph-paths,  having 
their  origin  in  the  cerebral  pia  mater  and  the  choroid  plexuses  of  the  ventricles, 
pass  out  of  the  skull  in  company  with  the  internal  carotid  and  vertebral  arteries  and, 
lower,  the  internal  jugular  vein  and  empty  into  the  deep  cervical  nodes,  these  latter 
are,  theoretically,  first  affected  by  intracranial  irritation.  As  they  lie  beneath  the 
cervical  fascia,  their  enlargement  may  not  be  early  noticed.  These  variations  in  the 
seat  of  glandular  swelling  cannot,  however,  be  relied  upon  as  a  basis  for  a  positive 
differential  diagnosis  between  intracranial  and  more  superficial  (extracranial)  sources 
of  irritation  or  infection. 

THE    LYMPHATICS    OF   THE    NECK. 
THE  LYMPH-NODES. 

The  principal  group  of  nodes  in  the  neck  region  is  that  which  is  situated  along 
the  course  of  the  internal  jugular  vein,  forming  the  jugular  plexus  ( plexus  jugularis). 
It  consists  of  a  variable,  but  usually  large,  number  of  nodes  and  is  interposed  in  the 
pathway  followed  by  the  entire  lymphatic  system  of  the  head  and  neck.  It  is  prac- 
tically a  continuous  chain  of  nodes,  extending  the  entire  length  of  the  neck,  but  for 
convenience  in  description  it  is  convenient  to  regard  the  nodes  as  forming  two  sub- 
groups which  are  named  the  superior  and  inferior  deep  cervical  nodes.  In  addition 
to  these  some  smaller  groups  occur  more  superficially,  forming  what  are  termed  the 
superficial  cervical  nodes,  so  that  altogether  there  are  three  main  groups  of  nodes  in 
the  cervical  region. 

The  superficial  cervical  nodes  (lymphoiilandulae  cervicalcs  stipcrficinlcs ) 
may  conveniently  be  divided  into  two  subgroups,  both  of  which  are  composed 
of  rather  small  and  somewhat  inconstant  nodes.  The  external  jugular  nodes,  as 
their  name  indicates,  are  situated  along  the  course  of  the  external  jugular  vein, 
and  consequently  rest  upon  the  outer  surface  of  the  sterno-cleido-mastoid  muscle. 
They  occur  a  little  below  the  lower  extremity  of  the  parotid  gland  (Fig.  796), 
and  are  usually  two  or  three  in  number,  one  or  two  additional  nodes  sometimes 
being  present  at  a  somewhat  lower  level.  They  receive  afferent s  from  the  pinna 
of  the  ear  and  from  the  parotid  region,  and  their  efferent*  pass  over  the  anterior 
border  of  the  sterno-cleido-mastoid  to  open  into  the  superior  deep  cervical  nodes. 


THE   LYMPHATICS   OF   THE   NECK. 


957 


FIG. 


Digastric  muscle 


Anterior 

cervical 

node 


Recurrential 
node 


Anterior  cervical  and   recurrential  nodes  and  lymphatics 
of  larynx.     (Most.*) 


The  second  subgroup  is  that  of  the  anterior  cervical  nodes,  which  are  both  variable 

and  inconstant  and  are  situated  beneath 

the   depressor    muscles    of    the    hyoid 

bone,  resting  upon  the  anterior  surface 

of  the  larynx  and  on  the  anterior  and 

lateral  surfaces  of  the  trachea.      Those 

which  rest  upon  the  trachea  are  some- 
what more  constant  than  the  others,  but 

like   them  they  are   usually  small    and 

are  therefore  likely  to  be  overlooked  in 

normal    conditions.      The   more    lateral 

members  of  the  series,  from  three  to  six 

in    number,    are   arranged    in    a    chain 

which  follows  the  course  of  the  recurrent 

(inferior)  laryngeal  nerve  and  are  some- 
times   spoken    of    as    the    recurrential 

nodes.       The    anterior    cervical    nodes 

receive  afferents   from  the    larynx  and 

trachea,  and  their  efferents  pass  to  the 

lower  superior  deep  cervical  nodes. 

The     superior    deep     cervical 

nodes  (lymphoglandulae  cervicales   pro- 

fundae    superiores)    vary    from    ten    to 

sixteen  in   number,   and    extend   along 

the  course  of  the  internal  jugular  vein 

from  the  tip  of  the  mastoid  process  to 

the  level  at  which  the  vein  is  crossed 

by    the    omo-hyoid    muscle.     They  lie 

either  directly  upon  the  vein  or  slightly  posterior  to  it,  beneath  the  sterno-cleido- 

mastoid  muscle,   and  are 

FIG.  807.  all    united    by    numerous 

connecting  stems  so  that 
they  form  a  veritable 
plexus.  Some  of  the 
nodes  are  exceedingly 
constant  in  position,  one, 
especially,  which  receives 
numerous  afferents  from 
the  lingual  region  and  has 
therefore  been  termed  the 
principal  node  of  the 
tongue,  occurring  at  about 
the  level  of  the  bifurcation 
of  the  common  carotid 
artery,  and  a  second  is 
situated  just  above  the 
ofno-hyoid  muscle.  The 
afferents  of  the  group  are 
very  numerous,  and  may 
be  divided  into  two  classes 
according  as  they  take 
their  origin  in  nodes 
belonging  to  other  groups 
or  come  directly  from 
the  lymphatic  net-works. 
Belonging  to  the  first 
class  and  terminating  in 

the  more  posterior   nodes  are  the    efferent  stems   for  the   posterior  auricular  and 

*Anatom.  Anzeiger,  Bd.  xv.,  1899. 


\ 


Sterno-mastoid 
muscle,  cut 


Deep  cervical  lymph-nodes. 


958  HUMAN   ANATOMY. 

occipital  nodes,  while  in  the  more  anterior  nodes  efferents  from  the  retropharyn- 
geal,  parotid,  submaxillary,  submental,  and  superficial  cervical  nodes  terminate. 

Belonging  to  the  second  class  and  terminating  in  the  more  posterior  nodes  are 
(i)  a  vessel  which  descends  directly  from  the  occipital  region  of  the  scalp  ;  (2)  some 
stems  from  the  posterior  surface  of  the  pinna  ;  and  (3)  stems  from  the  upper  part 
of  the  back  of  the  neck.  To  the  more  anterior  nodes  pass  ( I )  the  majority  of  the 
stems  descending  from  the  tongue  ;  (2)  stems  from  the  nasal  mucous  membrane, 
the  palate,  and  the  upper  portions  of  the  pharynx  ;  (3)  stems  from  the  cervical 
portion  of  the  oesophagus  ;  (4)  the  majority  of  the  stems  from  the  larynx  and  those 
which  come  from  the  cervical  portion  of  the  trachea,  and  (5)  the  stems  from  the 
thyroid  gland. 

The  efferents  from  the  lower  nodes  of  the  plexus  pass  partly  to  the  inferior  deep 
cervical  nodes,  and  partly  unite  with  the  efferents  of  these  to  form  the  jugular  trunk, 
which  is  described  below. 

The  inferior  deep  cervical  nodes  (lymphoglandulae  cervicales  profundae 
inferiores),  also  termed  the  supraclavicular  nodes,  occupy  the  supraclavicular  triangle 
of  the  neck,  resting  upon  the  scalene  muscles  and  upon  the  trunks  of  the  brachial 
plexus.  They  are  fewer  in  number  and,  as  a  rule,  smaller  than  the  superior  deep 
cervical  nodes.  In  addition  to  the  afferents  from  the  superior  nodes  they  receive  ( i ) 
a  stem  which  passes  directly  downward  from  the  occipital  region  of  the  scalp  along 
the  posterior  border  of  the  sterno-cleido-mastoid  muscle  ;  (2)  vessels  from  the 
integument  and  muscles  of  the  lower  portion  of  the  neck  ;  (3)  vessels  from  the 
integument  of  the  upper  portion  of  the  pectoral  region  ;  (4)  occasionally  some 
vessels  from  the  arm  which  follow  the  course  of  the  cephalic  vein  ;  (5)  some  efferents 
from  the  brachial  groups  of  the  axillary  nodes  ;  and  (6)  vessels  which  pass  to  the 
lower  nodes  of  the  left,  rarely  the  right,  side  from  the  liver,  ascending  in  the 
suspensory  ligament  of  that  organ,  piercing  the  diaphragm,  and  following  the  course 
of  the  internal  mammary  vessels  upward  through  the  thorax. 

Their  efferents  unite  with  some  of  those  from  the  superior  deep  cervical  nodes  to 
form  a  single  stem,  the  jugular  trunk  (truncus  jugularis),  which  on  the  left  side 
opens  into  the  arch  of  the  thoracic  duct  and  on  the  right  unites  with  the  subclavian 
trunk  to  form  the  right  lymphatic  duct.  Both  the  right  and  the  left  trunks,  how- 
ever, frequently  open  directly  into  the  subclavian  vein. 

THE  LYMPHATIC  VESSELS. 

The  Integument  and  Muscles  of  the  Neck. — The  lymphatic  stems  arising 
from  the  subcutaneous  and  muscular  net-works  of  the  neck  open  into  the  posterior 
nodes  of  the  superior  deep  cervical  chain. 

The  Larynx  and  Trachea. — The  lymphatic  net-work  of  the  larynx  is  very 
well  developed  over  the  greater  portion  of  the  mucous  membrane  and  is  especially 
rich  in  the  regions  of  the  false  vocal  cords  and  the  ventricles.  Over  the  true  vocal 
cords,  however,  it  is  very  feebly  developed,  and  the  entire  net-work  may  therefore  be 
regarded  as  consisting  of  two  portions,  one  of  which  is  situated  above  the  level  of  the 
true  cords  and  the  other  below  them.  The  two  portions  are  not,  it  is  true,  perfectly 
distinct,  since  they  are  connected  by  the  feeble  net-work  of  the  true  cords  ;  but  it  has 
not  been  found  possible  to  force  an  injection  from  one  portion  into  the  other  and, 
furthermore,  each  portion  gives  rise  to  a  special  set  of  efferent  stems. 

The  stems  which  arise  from  the  upper  net-work  are  from  three  to  six  in 
number  on  each  side,  and  make  their  exit  from  the  larynx  through  the  lateral 
portions  of  the  thyro-hyoid  membrane,  in  close  proximity  to  the  superior  laryngeal 
artery  (Fig.  806).  They  then  pass  outward  to  the  anterior  nodes  of  the  superior 
deep  cervical  chain,  some  opening  into  the  nodes  situated  in  the  neighborhood 
of  the  bifurcation  of  the  common  carotid  artery,  while  others,  bending  downward, 
terminate  in  lower  nodes. 

The  stems  from  the  lower  net- work  pass  in  two  directions  ;  a  few  small  ones 
perforate  the  crico-thyroid  membrane  near  the  median  line,  while  the  rest  are  directed 
posteriorly  and  make  their  exit  below  the  lower  border  of  the  cricoid  -cartilage.  The 
anterior  stems  pass  partly  to  an  anterior  cervical  node  situated  usually  in  the  median 


THE    LYMPHATICS    OF   THE   NECK.  959 

line  between  the  two  crico-thyroid  muscles,  another  descends  over  the  isthmus  of 
the  thyroid  gland  to  terminate  in  one  of  the  nodes  which  rest  upon  the  anterior 
surface  of  the  trachea,  while  one  or  two  pass  outward  -along  the  upper  border 
of  the  lobes  of  the  thyroid  gland  and  then  descend  to  terminate  in  one  of  the 
superior  deep  cervical  nodes  situated  about  opposite  the  middle  of  the  sterno-cleido- 
mastoid  muscle.  The  posterior  stems,  which  are  from  three  to  six  in  number,  after 
making  their  exit  from  the  larynx,  follow  the  course  of  the  recurrent  laryngeal 
nerves  and  terminate  in  the  recurrential  nodes  situated  in  the  course  of  those  nerves, 
some  of  the  stems  frequently  anastomosing  to  form  a  plexus  which  descends  along 
the  vagus  nerve  and  may  be  followed,  in  some  cases,  to  the  inferior  deep  cervical 
nodes. 

The  net-work  of  the  trachea  is  formed  of  delicate  and  slender  vessels  arranged  so 
as  to  form  elongated  meshes,  and  the  stems  which  arise  from  it  emerge  from  the 
lateral  surfaces  of  the  trachea,  passing  between  the  tracheal  cartilages.  Those  from 
the  upper  part  of  the  trachea  pass  to  the  recurrential  nodes,  while  the  lower  ones 
pass  to  the  bronchial  nodes  situated  in  the  neighborhood  of  the  bifurcation  of  the 
trachea. 

The  Thyroid  Gland. — The  lymphatic  stems  from  the  thyroid  gland  pass  for 
the  most  part  to  the  superior  deep  cervical  nodes,  following  the  course  of  the  superior 
thyroid  artery,  some  of  them,  however,  passing  at  first  directly  upward  and  coming 
into  relation  with  an  anterior  cervical  node  situated  upon  the  crico-thyroid 
membrane.  Those  which  arise  from  the  lower  border  of  the  isthmus  and  from  the 
neighboring  portions  of  the  lobes  are  directed  downward,  and  terminate  in  the 
anterior  cervical  nodes  which  are  situated  upon  the  anterior  surface  of  the  trachea 
and  in  the  recurrential  nodes. 

The  CEsophagus. — The  cervical  portion  of  the  oesophagus  will  be  considered 
together  with  its  thoracic  portion  (page  971). 

Practical  Considerations. —  The  Lymph- Nodes  of  the  Neck. — i.  The  super- 
ficial cervical  nodes — not  invariably  present — are  found  over  the  sterno-mastoid, 
along  the  external  jugular  vein,  between  the  deep  fascia  and  the  platysma,  and  may 
be  enlarged  in  various  affections  of  the  external  ear  and  of  the  skin  of  the  face  and 
neck,  or  consecutively  to  infections  of  the  suboccipital  (occipital),  mastoid  (post- 
auricular),  parotid  (preauricular),  or  submaxillary  nodes.  Those  found  posteriorly 
near  the  anterior  border  of  the  trapezius  muscle  enlarge  early  in  the  secondary  stage 
of  syphilis  and,  on  account  of  their  accessibility  for  palpation,  are  then  of  diagnostic 
value.  2.  The  deep  cervical  nodes  are  divisible,  for  convenience,  into  two  groups  :  (<z) 
an  upper  group,  situated  about  and  above  the  bifurcation  of  the  common  carotid  artery 
and  the  upper  part  of  the  internal  jugular  vein,  some  of  which  lie  partly  beneath  the 
posterior  edge  of  the  sterno-mastoid  and  partly  projecting  into  the  posterior  cervical 
triangle  ;  (b)  a  lower  group,  found  near  the  lower  portions  of  the  internal  jugular, 
external  jugular,  subclavian,  and  transverse  cervical  veins,  and  lying  almost  com- 
pletely beneath  the  sterno-mastoid.  At  the  root  of  the  neck  this  group  is  continuous 
externally  with  the  subclavian  and  axillary,  and  internally  with  the  mediastinal  nodes. 
All  these  deep  cervical  nodes  lie  in  or  beneath  the  deep  fascia  and  receive  the 
efferent  vessels  from  the  superficial  nodes  (and  thus  from  their  tributaries  mentioned 
above)  as  well  as  all  other  lymphatics  of  the  head  and  neck — retrophar/hgeal, 
suprahyoid,  etc. — that  do  not  directly  communicate  with  the  superficial  group. 

The  deep  cervical  nodes  are  accordingly  found  to  be  inflamed  or  enlarged 
consecutively  to  a  great  variety  of  conditions, — e.g. ,  eczema,  wounds  or  ulcers  of 
any  portion  of  the  scalp  or  face,  dental  caries,  alveolo-dental  abscess,  pharyngeal 
or  buccal  or  tonsillar  inflammation  or  ulceration,  fissures  or  ulcers  or  carcinoma 
of  the  tongue,  otitis  (external  or  medial),  rhinitis,  hordeolum,  labial  herpes  or 
chancre  or  epithelioma.  They  may  also  be  enlarged — though  with  great  rarity — 
from  primary  carcinoma  and — less  rarely — from  lympho-sarcoma  or  from  Hodgkin's 
disease.  Furthermore,  various  intracranial  conditions  may  be  followed  by  involve- 
ment of  the  cervical  nodes,  both  superficial  and  deep.  In  most  cases  the  infection 
comes  from  the  same  side  of  the  head,  face,  or  neck,  as  the  enlarged  glands,  but 
occasionally  the  original  lesion  is  on  the  opposite  side. 


960  HUMAN   ANATOMY. 

Swellings  of  this  deep  chain  of  glands — especially  of  those  beneath  the  sterno- 
mastoid — may  be  present  without  being  distinctly  palpable,  and  are  apt,  in  any  case 
severe  enough  to  come  to  operation,  to  involve  many  more  nodes  than  were 
previously  suspected. 

One  node  of  the  upper  group  lies  behind  the  posterior  belly  of  the  digastric  in 
the  angle  between  the  internal  jugular  and  facial  veins.  Leaf  has  suggested  that 
it  be  called  the  "  jugulo-digastric"  node.  In  some  affections  of  the  tonsil  and  of 
the  base  of  the  tongue,  it  enlarges  and  projects  in  front  of  the  anterior  border  of  the 
sterno-mastoid,  its  contents  being  about  half  an  inch  below  and  somewhat  internal  to 
the  angle  of  the  jaw. 

Other  glands  of  this  group,  which  are  very  constant  in  position,  lie  over  the 
insertion  of  the  splenius  capitis  under  cover  of  the  upper  end  of  the  sterno-mastoid 
and  surround  the  spinal  accessory  nerve  before  it  perforates  the  latter  muscle.  En- 
largement of  these  glands  would  compress  the  nerve  against  the  transverse  process 
of  the  atlas  (Leaf). 

The  retropharyngeal  nodes  lie  in  the  space  of  that  name  (page  552),  about 
opposite  the  axis,  on  the  rectus  capitis  anticus  major  and  to  the  inner  side  of  the 
glosso-pharyngeal  nerve  where  it  curves  around  the  lower  border  of  the  stylo- 
pharyngeus.  They  communicate  with  the  upper  group  of  the  deep  nodes.  They 
may  be  enlarged  from  infection  through  the  overlying  mucosa,  as  they  are  in  close 
relation  to  the  buccal  portion  of  the  pharynx,  which,  on  account  of  its  many  crypts 
or  recesses,  the  large  amount  of  adenoid  tissue  present,  its  relatively  direct  exposure 
to  mechanical  injury  and  to  the  current  of  inspired  air  (drying  it,  reducing  its 
temperature,  and  possibly  conveying  microbic  irritants),  is  especially  susceptible  to 
inflammation.  They  may  also  enlarge  as  a  result  of  caries  of  the  bodies  of  the 
cervical  vertebrae.  In  either  case,  there  may  be  pharyngeal  and  tonsillar  pain,  ear- 
ache, and  other  evidence  of  glosso-pharyngeal  irritation.  If  suppuration  occurs,  a 
fluctuating  swelling  appears  which  pushes  the  posterior  wall  of  the  pharynx  forward 
(the  retropharyngeal  connective  tissue  being  lax  to  permit  of  the  free  movement  of 
the  pharynx  during  deglutition),  depresses  the  soft  palate,  and  causes  dysphagia  ; 
or,  if  lower,  causes  dysphonia  and  dyspncea  by  obstructing  the  laryngeal  opening. 
Such  an  abscess  may  gravitate  along  the  oesophagus  into  the  mediastinum  and  may 
even  reach  the  diaphragm  ;  or  it  may  extend  laterally  behind  the  parotid  and  great 
vessels  to  the  side  of  the  neck,  or,  reaching  the  cords  of  the  brachial  plexus,  may  be 
conducted  by  them  to  the  posterior  cervical  triangle  or  down  into  the  axilla.  Such 
an  abscess  should  not  be  left  to  spontaneous  evacuation,  on  account  of  the  danger 
of  its  extension  in  these  directions,  or — if  the  abscess  should  suddenly  burst  into  the 
pharynx — of  suffocation  or  of  septic  pneumonia  if  the  pus  entered  the  air-passages. 
It  may  be  opened  through  the  mouth,  in  the  mid-line  of  the  pharynx  (the  head 
being  bent  over  so  that  the  pus  would  not  run  toward  the  glottis),  or  externally  by 
an  incision  along  the  posterior  margin  of  the  sterno-mastoid,  the  great  vessels  being 
pushed  forward  as  the  wound  is  deepened. 

The  lower  group  of  deep  cervical  nodes  enlarge  most  frequently  consecutively 
to  infection  or  disease  of  the  upper  group.  They  also  receive  the  lymphatics  from 
the  supraspinous  fossa  which  follow  the  suprascapular  artery,  and  those  from  the 
upper  part  of  the  deltoid.  *  Those  that  lie  at  the  very  base  of  the  neck,  in  the  sub- 
claviari  triangle,  or  on  the  omo-hyoid  muscle,  are  not  uncommonly  affected  in  the  latter 
stages  of  mammary  carcinoma  (page  2035).  They  are  continuous  with  the  axillary 
nodes,  while  those  to  their  inner  side — lying  on  the  levator  anguli  scapulae  and 
scalenus  medius  just  external  to  the  internal  jugular  vein — are  also  often  involved  in 
the  upward  extension  of  cancer.  Both  sets  communicate  with  the  mediastinal  nodes. 
On  the  left  side  they  are  in  close  proximity  to  the  thoracic  duct.  The  branches  of 
the  cervical  plexus  pass  among  the  nodes  of  this  deep  cervical  group. 

In  cases  of  chronic  inflammation  and  enlargement  of  these  nodes  they  will  usually 
be  found  adherent  to  the  internal  jugular  vein,  which  is  in  close  relation  to  most  of 
them.  As  the  majority  of  them  lie  beneath  the  sterno-cleido-mastoid,  that  muscle 
will  often  have  to  be  divided  either  partially  or  completely  in  operations  for  tln-ir 
removal.  Certain  cysts,  in  most  cases  congenital,  usually  sulu'iitaiu'ous  but  with  <Kvp 
prolongations  into  the  intermuscular  spaces,  are  found  in  the  neck,  and  are  believed 


THE    LYMPHATICS    OF   THE   UPPER    EXTREMITY.  961 

to  be  of  lymphatic  origin,  because  (a)  they  are  often  associated,  and  sometimes 
anatomically  connected  with  other  congenital  defects  of  the  lymphatic  system, 
such  as  macroglossia  (cavernous  lymphangioma  of  the  tongue)  and  macrocheilia 
(labial  lymphangioma)  ;  and  (£)  they  are  in  communication  with  the  lymphatic 
trunks  (Rolleston). 

THE  LYMPHATICS  OF  THE  UPPER  EXTREMITY. 
THE  LYMPHATIC  NOUKS. 

The  lymphatic  nodes  of  the  arm  are  for  the  most  part  confined  to  its  upper 
portions,  the  principal  group  occurring  in  the  axilla  and  consisting  of  a  considerable 
number  of  nodes  united  by  connecting  stems  to  form  a  plexus  axillaris.  A  few 
scattered  nodes  also  occur  in  the  brachial  region  and  some  are  occasionally  to  be 
found  in  the  antibrachium,  but  they  are  entirely  lacking  in  the  hand.  An  especial 
interest  attaches  to  the  axillary  nodes  on  account  of  the  extensive  area  from  which 
they  receive  afferents,  for,  in  addition  to  almost  the  entire  lymphatic  drainage  of  the 
arm,  they  also  receive  the  vessels  from  the  anterior  and  lateral  thoracic  walls,  from 
the  mammary  gland,  and  from  the  scapular  region.  The  brachial  and  antibrachial 
nodes,  on  the  other  hand,  are  rather  to  be  regarded  as  ' '  intercalated  ' '  nodes  inter- 
posed in  the  course  of  certain  of  the  lymphatic  vessels  ;  some  of  them  lie* superficial 
to  the  deep  fascia,  while  others  are  situated  more  deeply  along  the  course  of  the 
principal  blood-vessels,  and,  consequently,  it  is  convenient  to  divide  them  into  two 
sets  according  as  they  are  superficial  or  deep. 

The  superficial  brachial  nodes  (lymphoglandttlae  cubitales  superficiales)  are 
arranged  in  two  principal  groups.  One  of  these  rests  upon  the  brachial  fascia  imme- 
diately over  the  internal  condyle  of  the  humerus,  and  may  be  termed  the  epitrochlear 
group  (Fig.  809).  It  consists  of  from  one  to  four  nodes,  of  which  one,  the  lowest  of 
the  group,  is  especially  constant  and  is  termed  the  epitrochlear  node.  The  remaining 
nodes,  if  present,  are  situated  along  the  course  of  the  basilic  vein,  one  frequently 
lying  almost  in  the  median  line  of  the  arm  a  short  distance  above  the  bend  of  the 
elbow.  The  afferents  of  the  epitrochlear  nodes  are  the  superficial  vessels  of  the 
forearm  and  hand,  especially  those  which  pass  upward  along  the  ulnar  border  of 
the  forearm  ;  their  efferents  pass  upward  along  the  basilic  vein  and  join  the  deep 
vessels  where  the  basilic  vein  dips  down  to  join  the  brachial. 

A  second  group,  which  may  be  termed  the  delto-pedoral  group,  consists  of  from 
one  to  four  nodes  situated  along  the  course  of  the  cephalic  vein,  in  the  groove 
between  the  deltoid  muscle  and  the  clavicular  portion  of  the  pectoralis  major 
(Fig.  809).  They  are  not  always  distinguishable  and  are  usually  quite  small. 
They  are  interposed  in  the  course  of  the  delto-pectoral  lymphatic  stem  which  passes 
upward  in  the  groove  and  opens  into  the  subclavicular  group  of  axillary  nodes 
or  occasionally  into  the  inferior  deep  cervical  nodes. 

The  deep  brachial  nodes  sometimes  include  some  small  nodes  occurring  on 
the  lymphatic  stems  which  accompany  the  ulnar  and  radial  blood-vessels,  but  these 
nodes  are  relatively  inconstant.  Of  more  frequent  occurrence  is  a  group  of  two 
or  three  small  nodes  (1)  mphoglandulae  cubitales  profundae)  which  occur  upon  the  stems 
accompanying  the  brachial  artery  and  are  situated  at  about  the  middle  part  of  its 
course.  Their  afferents  are  the  deep  lymphatics  of  the  forearm  and  their  efferents 
pass  upward  to  terminate  in  the  humeral  nodes  of  the  axillary  group. 

The  axillary  nodes,  which  are  embedded  in  the  areolar  tissue  occupying  the 
axillary  space,  vary  in  number  from  sixteen  to  thirty-six.  Some  of  them  are  usually 
of  considerable  size,  especially  in  those  cases  in  which  their  number  approaches  the 
lower  limit  mentioned,  for  it  is  a  general  rule  that  the  size  of  the  nodes  in  any  group  is 
inversely  proportional  to  their  number  ;  but  it  seems  probable  that  in  addition  to  those 
which  may  be  observed  macroscopically,  exceedingly  small  ones,  approaching  micro- 
scopic size,  also  occur,  and  that  these,  under  pathological  conditions  or  after  removal 
of  the  larger  ones,  may  increase  in  size  and  form  additional  or  new  foci  of  infection. 

Although  united  by  connecting  stems  to  form  a  plexus,  the  axillary  nodes  may 
be  divided,  according  to  their  position  and  the  source  from  which  their  afferents 
come,  into  a  number  of  more  or  less  distinct  subgroups  (Figs.  808,  814),  and  of 

61 


962 


HUMAN   ANATOMY. 


these,  four  are  terminals  for  lymphatic  stems  coming  from  the  arm  and  the  thoracic 
walls,  while  two  others  form  relays  between  these  terminal  nodes  and  the  subclavian 
trunk  by  which  the  lymph  from  the  entire  axillary  plexus  is  conveyed  to  the  right 
lymphatic  duct  or  to  the  arch  of  the  thoracic  duct. 

1.  The  brachial  subgroup  is  composed  of   a  number  of    usually  large  nodes, 
arranged  in  a  chain  along  the  axillary  vein,  for  the  most  part  along  its  inner  surface, 
although  a  node  is  to  be  found  behind  it,  between  it  and  the  subscapular  muscle. 
The  affcrents  of  this  group  come  from  the  arm  and  include  almost  the  entire  set 
of  collecting  stems  from  that  region,   only  one  of  them,   that  which    accompanies 
the  cephalic  vein,   passing  to  another  group.      Their  efferents  pass  partly  to  the 
intermediate  subgroup  of  the  axillary  plexus,  partly  to  the  subclavicular  subgroup, 
and  partly  to  the  lower  nodes  of  the  inferior  deep  cervical  group. 

2.  The  anterior  pectoral  subgroup  is  composed  of  two  or  three  usually  small 
nodes   situated   over   the  second  and  third   intercostal  spaces,  beneath  the  lower 

FIG.  808. 


Brachial  plexus 
Subclavian  artery. 

Intermediate  nodes 


Subclavicular  nodes 


Mammary  gland 


Brachial  nodes 
Subscapular  nodes 
Anterior  pectoral  nodes 

Inferior  pectoral  nodes 


Axillary  lymph-nodes,  new-born  child.     (Oelsitfi.*) 

border  of  the  pectoralis  major  muscle  and  anterior  to  the  long  thoracic  artery. 
They  receive  afferents  from  the  integument  of  the  anterior  surface  of  the  thorax, 
from 'the  pectoral  muscles,  and  from  the  mammary  gland.  Their  efferents  pass 
partly  to  the  intermediate  and  partly  to  the  subclavicular  subgroup  of  the  axillary 
nodes. 

3.  The  inferior  pectoral  subgroup  is  composed  of  two  or  three  small   nodes, 
situated  either  upon  or  posterior  to  the  long  thoracic  artery  over  the  fourth  and  fifth 
intercostal  spaces  or  even   higher.     They  receive  their  affcrents  mainly  from  the 
integument  of  the  lateral  wall  of  the  thorax  and  from  the  subjacent  muscles,   and 
their  efferents  pass  to  the  nodes  of  the  intermediate  subgroup. 

4.  The  subscapnlar  subgroup  (  lympho^landuhic  subscapulares  )  consists  of  a  chain 
of  six  or  more  nodes  situated  along  tin-  course  of  the-  subscapular  artery,  and,  in 
addition,  includes  two  or  three  nodes  which    rest   upon   the  dorsal   surface  of  the 
scapula  in  the  groove  between  the  teres  major  and  minor  muscles.      The  ajfe  rents 


*Archiv  f.  klin.  Chirurgie,  lid.  Ixiv.,  1901. 


THE   LYMPHATICS    OF   THE    UPPER    EXTREMITY. 


963 


come  froiii  the  integument  and  muscles  of  the  lower  part  of  the  neck,  from  the 
dorsal  surface  of  the  thorax,  and  from  the  scapular  region  ;  the  efferents  pass  mainly 
to  the  nodes  of  the  intermediate  subgroup. 

5.  The    intermediate    subgroup    consists    of  a   number    of   rather    large   nodes 
imbedded  in  the  adipose  tissue  which  occupies  the  interval  between  the  lateral  wall 
of  the  thorax  and  the  upper  part  of  the  long  thoracic  vein  as  it  bends  outward  to 
open  into  the  terminal  part  of  the  axillary  vein.     It  receives  affercnts  from  all  the 
terminal  subgroups  of  the  axillary  plexus,  and  its  efferents  pass  to  the  nodes  of  the 
subclavicular  subgroup. 

6.  The  subclavicular  subgroup  consists  of    from  six  to  twelve  nodes  situated 
near  the  apex  of  the  axillary  space,  partly  beneath  the  pectoralis  minor  and  partly 
above  the   upper   border  of   that   muscle.       They  constitute  the   final  link    in   the 
axillary  chain,  since  they  receive  as  affercnts,  either  directly  or  indirectly  through  the 
intermediate  nodes,  the  efferents  from  all  the  other  subgroups.     Their  efferents  unite 
to  form  a  trunk  of  considerable  size,  the   subclavian   trunk  (truncus  subclavius), 
which,  from  its  origin  opposite  the  first  intercostal  space,  passes  almost  vertically 
upward  over  the  subclavian  vein  to  open  into  it  near  its  junction  with  the  external 
jugular,  or  else  to  unite  with  the  jugular  trunk  on  the  right  side  or  to  open  into  the 
arch  of  the  thoracic  duct  on  the  left  side.      In  addition  to  this  principal  termination 
one  or  more  of  the  subclavicular  efferents  usually,  pass  to  one  of  the  lower  nodes  of 
the  inferior  deep  cervical  group. 

The  independent  termination  of  the  subclavian  trunk  in  the  subclavian  vein  is  probably  the 
most  frequent  arrangement,  but  the  exact  position  of  its  junction  with  the  vein  is  variable.  Most 
frequently  it  empties  at  the  angle  formed  by  the  junction  of  the  subclavian  and  internal  jugular 
veins,  but  it  may  terminate  upon  the  superior  surface  of  the  subclavian  vein  some  distance  ( i  cm. ) 
away  from  the  angle,  and  quite  frequently  it  opens  upon  the  anterior  surface  of  the  vein,  or,  in 
rarer  instances,  upon  its  posterior  surface.  Not  unfrequently  two  or  even  more  subclavian 
trunks  occur,  and  in  such  cases  one  may  unite  with  the  jugular  trunk,  or,  if  on  the  left  side,  open 
into  the  arch  of  the  thoracic  duct,  while  the  other  terminates  directly  in  the  vein. 

THE  LYMPHATIC  VESSELS. 

The  lymphatic  vessels  of  the  upper  limb  are  divisible  into  two  groups  according 
as  they  lie  superficial  to  or  beneath  the  deep  fascia. 

The  superficial  vessels,  which  are  far  more  numerous  than  the  deep  ones,  have 
their  origin  in  the  subcutaneous  net-work  which  occurs  throughout 
the  entire  extent  of  the  limb,  but  is  especially  developed  upon  the 
palmar  surface  of  the  hand  and  upon  the  fingers  (Fig.  810).      The 
net-work  of  each  digit  tends  toward  its  sides  and  at  its  base  unites 
with  those  of  the  adjacent  digits  to  form  a  number  of 
stems  which  pass  upward  upon  the  dorsal  surface  of  the   Deito-pectorai 
hand,  for  the  most  part  over  the  intermetacarpal  spaces, 
although  abun- 
dant    anasto- 
moses    occur 
between      the 
vessels      of 
neighbor  ing 
spaces  so  that 

an  open  dorsal    net-work  is    formed.      The 
stems  which. arise  from  the  net-works  of  the 
inner  border  of  the  little  finger  and  of  the  outer  border  of  the 
index  also  pass  upward  upon  the  dorsum  of  the  hand,  lying 
respectively  toward  its  inner  and  outer  borders,  and  the  net- 
work of  the  thumb  is  drained  by  vessels  which  pass  upward 
on  its  dorsal  surface.     From  the  central  portion  of  the  palmar 
net-work  some  small  stems  pass  deeply,   penetrating   the       Superficial  lymphatic  vessels  of 

i  •     •       .1        j  i  1        •  i '       i       .      upper  limb:    semidiagrammatic. 

palmar  aponeurosis  to  join  the  deep  lymphatic  vessels,  but    (Based  on  figures  of  Sappey.) 

its  remaining  portions  radiate  in  all  directions  to  join  the 

stems  of  the  dorsal  net-work.      Thus,  the  distal  portions  of  the  net-work  converge 


FIG.  SOQ. 


node 


964 


HUMAN   ANATOMY. 


toward  the  webs  of  the  fingers  and  pass  dorsally  to  join  the  stems  which  pass  upward 
over  the  intermetacarpal  spaces  ;  the  inner  portions  pass  over  into  a  number  of  small 
stems  which  curve  around  the  inner  border  of  the  hand  to  join  the  stems  coming  from 
the  little  finger  ;  the  outer  portions  similarly  empty  into  the  stems  coming  from  the 
outer  surface  of  the  index  finger  and  from  the  thumb  ;  while  the  proximal  portions 
give  rise  to  a  number  of  stems  which  pass  upward  along  the  anterior  surface  of  the 
forearm.  The  arrangement,  indeed,  is  very  similar  to  that  followed  by  the  veins. 
At  the  wrist,  then,  there  are  a  considerable  number  (about  thirty,  more  or  less) 
of  longitudinal  stems  which  are  arranged  in  two  groups,  one  of  which  is  dorsal  and 
the  other  ventral  (Figs.  810,  8n).  The  former  consists  of  the  stems  which  drain 
the  digital  net-works  and  the  distal  and  lateral  portions  of  the  palmar  net-work, 
while  the  latter  is  formed  of  stems  arising  from  the  proximal  portion  of  the  palmar 
net-work.  As  they  ascend  the  arm  these  stems  receive  afferents  from  the  sub- 

FIG.  Si i. 


Lymphatics  of  hand  :  Fig.  810,  palmar,  Fig.  811,  dorsal  surface.  Superficial  digital  net-works  (a)  empty  at  buM-s 
of  fingers  into  larger  stems  (k,  c),  which  are  tributary  to  trunks  on  forearm  (rf) ;  superficial  palmar  vessels  commu- 
nicate (Fig.  810,  *)  with  deeper  lymphatics.  (Sappey.*) 

cutaneous  net-work  of  the  forearm,  and  at  the  same  time  anastomose  with  one 
another,  so  that  their  number  diminishes  gradually  as  they  ascend,  until,  at  about 
the  middle  of  the  brachium,  they  are  reduced  almost  to  half  the  original  number. 
As  they  approach  the  elbow  (Fig.  809),  the  stems  of  the  dorsal  group  divide  into 
two  sets,  which  curve  forward,  one  around  the  outer  border  and  the  other  around 
the  inner  border  of  the  forearm,  so  that  above  the  elbow  all  the  principal  stems  are 
situated  upon  the  anterior  (ventral)  surface  of  the  arm,  an  arrangement  which  again 
recalls  that  presented  by  the  veins. 

Just  above  the  bend  of  the  elbow  one  or  two  of  the  inner  stems  pass  into  the 
epitrochlear  nodes  (Fig.  809),  whose  efferents  pierce  the  brachial  fascia  to  empty 
into  the  deep  brachial  lymphatics,  but  the  majority  of  the  remaining  stems  pass 
directly  upward  along  the  anterior  surface  of  the  brachium  to  terminate  above  in 
the  brachial  nodes  of  the  axillary  plexus.  The  most  external  stem  follows,  however, 
a  different  course  (  Fig.  -^09),  accompanying  the  cephalic  vein  along  the  groove 
between  the  deltoid  and  pectoralis  major  muscles  ;  after  traversing  the  deho-pectoral 


*  Description  et   icono^rapliir  <les  vaisseaux  lymphatiques,  1874. 


THE    LYMPHATICS    OF   THE    UPPER    EXTREMITY.  965 

nodes  it  perforates  the  costo-coracoid  membrane  and  terminates  in  one  of  the 
subclavicular  nodes  or,  more  rarely,  follows  the  course  of  the  jugulo-cephalic  vein 
over  the  clavicle  and  terminates  in  one  of  the  lower  inferior  deep  cervical  nodes. 
From  the  net-work  of  the  posterior  surface  of  the  brachium  a  number  of  small  stems 
arise  and  pass  obliquely  upward,  those  lying  towards  the  outer  border  of  the  arm 
curving  around  it  to  join  the  outer  main  stems,  while  the  inner  ones  partly  join  the 
inner  main  stems  and  partly  terminate  in  the  subscapular  nodes  along  with  the  vessels 
from  the  posterior  surface  of  the  shoulder. 

The  deep  lymphatics  of  the  arm  are  much  less  numerous  than  the  super- 
ficial ones  and  follow  the  courses  of  the  main  blood-vessels,  usually  corresponding  in 
number  with  the  venae  comites.  They  occur  in  company  with  the  radial,  ulnar, 
anterior  and  posterior  interosseous,  and  brachial  vessels. 

The  radial  lymphatics  are  formed  by  the  union  of  two  stems,  one  of  which  follows 
the  course  of  the  main  stem  of  the  artery  from  the  deep  palmar  arch,  while  the  other 
accompanies  the  superficial  volar  artery  from  the  superficial  arch.  They  come 
together,  usually  a  short  distance  above  the  wrist-joint,  to  form  two  stems  which  pass 
upward  along  the  artery  and  may  traverse  one  or  two  small  and  inconstant  nodes. 
They  terminate  by  uniting  with  the  ulnar  stems  to  form  the  brachial  lymphatics. 

The  ulnar  lymphatics  are  also  formed  by  the  union  of  two  stems,  which 
accompany  the  deep  and  superficial  branches  of  the  ulnar  artery.  They  accompany 
the  ulnar  artery  up  the  forearm,  occasionally  traversing  one  or  two  small  nodes,  and, 
near  their  union  with  the  radial  stems  below  the  bend  of  the  elbow,  they  receive  the 
stems  which  accompany  the  anterior  and  posterior  interosseous  arteries. 

The  brachial  lymphatics  are  two  in  number  and  are  formed  by  the  union  of  the 
radial  and  ulnar  stems.  They  accompany  the  brachial  artery,  traversing  three  or 
four  nodes  in  their  course  and  receiving  the  efferents  of  the  epitrochlear  nodes,  or, 
these  failing,  the  inner  sterns  of  the  forearm.  They  terminate  in  the  brachial  nodes 
of  the  axillary  plexus,  especially  in  one  which  usually  lies  between  the  axillary  vein 
and  the  subscapular  muscle. 

Practical  Considerations. —  The  Lymph-Nodes  of  the  Axilla  and  Upper 
Extremity. — The  palm  has  relatively  few  large  lymphatics  (as  it  has  few  superficial 
nerves  and  blood-vessels)  ;  hence  wounds  of  the  fingers  or  of  the  dorsum  of  the 
hand,  where  the  lymphatics  are  of  larger  size,  are  more  commonly  followed  by 
lymphangitis  than  are  wounds  of  the  palm.  Nodes  are  occasionally  found  along  the 
course  of  the  arteries  of  the  forearm  and  arm,  but  are  inconstant  and  not  of  great 
practical  importance.  One  or  two  beneath  the  deep  fascia  on  the  flexor  surface  of 
the  elbow  and  on  a  level  with  the  internal  condyle  or  an  inch  or  two  above  it,  are  less 
variable  and  are  sometimes  palpably  enlarged  in  syphilis  at  the  time  of  the  early 
general  adenopathy. 

The  axillary  nodes  will  be  almost  sufficiently  described  in  relation  to  the 
subject  of  mammary  cancer  (page  2035).  Further  reference  to  them  will  be  found  in 
the  description  of  the  axilla  (page  581). 

These  nodes  may  be  the  primary  seat  of  lympho-sarcoma,  may  be  the  subject  of 
tuberculous  or  syphilitic  enlargement,  and  are  constantly  infected  after  septic  wounds 
of  the  hand,  forearm,  or  arm,  and  less  frequently  from  wounds  in  the  remaining 
areas  which  drain  into  them,  viz. ,  the  cervical  region  over  the  trapezius  muscle,  the 
dorsal  region,  the  lumbar  region  as  far  down  as  the  level  of  the  iliac  crest,  the 
abdominal  region  above  the  umbilicus,  and  the  front  and  sides  of  the  thoracic  region. 
Their  progressive  enlargement  widens  the  axilla,  renders  it  more  shallow  by  pushing 
its  floor  downward,  makes  the  anterior  fold  prominent,  and  increases  the  space 
between  the  outer  border  of  the  scapula  and  the  thoracic  wall.  Axillary  abscess 
commonly  originates  in  these  nodes,  consecutively  to  sepsis  elsewhere,  as  in  the 
regions  mentioned,  or  after  shoulder-joint  suppuration,  or  mammary  infection,  or 
caries  of  an  upper  rib.  Such  an  abscess  will  produce  rapidly  the  same  phenomena  as 
those  caused  by  a  growth.  It  may  make  its  way  behind  the  clavicle  into  the  supra- 
clavicular  fossa  by  following  the  cords  of  the  brachial  plexus,  or  may  gravitate  down 
the  arm  along  the  course  of  the  vessels.  It  cannot  come  directly  forward  on  account 
of  the  pectoral  muscles  and  clavi-pectoral  fascia,  or  downward  on  account  of  the 


966 


HUMAN    ANATOMY. 


axillary  fascia,  or  backward  by  reason  of  the  attachment  of  the  serratus  magnus  to  the 
scapula,  or  outward  or  inward  because  of  the  upper  limb  and  the  wall  of  the  thorax. 
It  should  be  opened  half  way  between  the  anterior  and  posterior  folds  near  the 
inner  or  thoracic  wall. 


Intercostal  node 


THE   LYMPHATICS   OF   THE   THORAX. 
THE  LYMPH-NODES. 

Certain  of  the  nodes  which  have  been  described  as  belonging  to  the  axillary 
plexus,  namely,  those  forming  the  anterior  and  inferior  pectoral  subgroups,  might 
well  be  considered  as  belonging  to  the  thoracic  set,  since  their  afferents  drain  the 
anterior  and  lateral  walls  of  the  thorax.  On  account  of  their  situation,  however,  as 
well  as  their  intimate  connection  by  efferents  with  the  intermediate  and  subclavicular 
axillary  nodes,  they  are  more  conveniently  classed  with  the  axillary  set. 

The  remaining  thoracic  nodes  may  be  divided  into  two  sets  according  as  they 
occur  in  connection  with  the  thoracic  walls,  parietal  nodes,  or  with  the  viscera, 
visceral  nodes.  Of  the  parietal  nodes  there  are  two  principal  groups. 

The  sternal  or  internal  mammary  nodes  (lymphoglandulae  stcrnales)  form 
two  chains  which  extend  upwards  upon  the  inner  surface  of  the  anterior  thoracic 
wall,  along  the  course  of  the  internal  mammary  blood-vessels  (Fig.  812).  They  vary 

in  number  from  four  to  ten, 

FIG.  812.  anci  are  situated  at  the  ante- 

rior or  sternal  ends  of  three 
or  more  of  the  upper  inter- 
costal spaces,  resting  upon 
the  internal  intercostal  mus- 
cles and  being  covered,  so  far 
as  the  lower  members  of  the 
group  are  concerned,  by  slips 
of  the  triangularis  sterni. 
Their  afferents  come  from 
the  anterior  diaphragmatic 
nodes,  from  the  upper  por- 
tions of  the  rectus  abdominis, 
from  the  anterior  portions  of 
the  intercostal  muscles,  from 
the  integument  over  the  ster- 
num and  costal  cartilages, 
and,  to  a  certain  extent,  from 
the  mammary  glands.  Since 
the  nodes  are  arranged  in 
the  form  of  a  chain,  the  effer- 
ents from  the  lower  members 
of  the  series'  are  afferents  for 
the  higher  ones;  the  terminal 
efferents  usually  unite  to  form 
a  single  stem  which  joins  the  efferents  of  the  anterior  mediastinal  and  bronchial  nodes 
to  form  the  broncho-mediastinal  trunk  (page  968). 

The  intercostal  nodes  ( lymphoglandulae  intercostales)  are  situated  along  the 
courses  of  the  intercostal  arteries,  the  principal  and  most  constant  members  of  the 
series  being  situated  towards  the  posterior  extremities  of  the  intercostal  spaces. 
Some  nodes  which  occur  in  the  lateral  portions  of  the  spaces  are  inconstant  and 
always  small  ;  they  are  usually  situated,  when  present,  at  the  point  where  the 
intercostal  arteries  give  off  their  lateral  perforating  branches. 

The  afferents  of  the  intercostal  nodes  drain  the  posterior  portions  of  the  inter- 
costal spaces.  The  efferents  of  the  lower  members  of  the  series  unite  to  form  a  stem 
which  passes  downward  and  terminates  in  the  receptaculum  chyli,  while  those  from 


Lower 

interinammary 
node 


Lymph-nodes  of  anterior  thoracic  wall,  viewed  from  behind. 
(Based  upon  figure  of  Poirier  and  Cuneo.*) 


;-  -Polder  et  Cliarpy  :   Traite!  d'anatoinie  huniaim-,  Tome  ii.,  1902. 


THE  LYMPHATICS  OF  THE  THORAX. 


967 


the  nodes  of  the  upper  spaces  are  directed  more  or  less  medially  to  open  into   the 
thoracic  duct. 

The  visceral  nodes  of  the  thorax  may  be  arranged  in  three  main  groups,  one 
consisting  of  the  nodes  situated  in  the  anterior  mediastinum,  a  second  of  those 
situated  in  the  posterior  mediastinum,  and  a  third  of  those  which  occur  in  the 
neighborhood  of  the  bifurcation  of  the  trachea  and  along  the  bronchi. 

The  anterior  mediastinal  nodes  (lymphoglandulae  mediastinales  anteriores) 
are  arranged  in  two  groups,  one  of  which  occurs  in  the  lower  and  the  other  in  the 
upper  part  of  the  mediastinum.  The  nodes  of  the  lower  group,  termed  the  diaphrag- 
matic nodes,  are  from  three  to  four  in  number,  and  are  situated  upon  the  anterior 
part  of  the  upper  surface  of  the  diaphragm,  immediately  behind  the  xiphoid  process 
of  the  sternum  ;  their  afferents  come  from  the  diaphragm  and  from  the  upper  surface 
of  the  liver,  and  their  efferents  pass  to  the  lower  deep  cervical  nodes,  following  the 
course  of  the  internal  mammary  vessels. 

The  upper  group,  that  of  the  cardiac  nodes,  is  composed  of  from  eight  to  ten  nodes 
situated  upon  the  anterior  surfaces  of  the  arch  of  the  aorta  and  the  left  innominate  vein. 
They  receive  afferents  from  the  anterior  surface  of  the  pericardium  and  thymus  gland 
and  from  the  sternal  and  bronchial  nodes.  Their  efferents  pass  upward  and  unite  with 
those  from  the  bronchial  nodes  to  form  the  broncho-mediastinal  trunk  (page  968). 

The  posterior  mediastinal  nodes  (lymphoglandulae  mediastinales  posteriores), 
eight  to  twelve  in  number,  are  situated  along  the  thoracic  aorta  in  the  posterior 
mediastinum.  Their  afferents  come  from  the  cesophagus,  the  posterior  surface  of 
the  pericardium,  and  the  upper  surface  of  the  liver,  while  their  efferents  open  mainly 
into  the  thoracic  duct,  a  few  passing  to  the  bronchial  nodes. 

Two  or  three  small  nodes  which  may  be  regarded  as  belonging  to  this  group 
occur  upon  the  convex  surface  of  the  diaphragm  in  the  neighborhood  of  the  opening 
for  the  inferior  vena  cava.  They  receive  afferents  from  the  diaphragmatic  net-work 
and  also  from  the  superficial  net-work  of  the  upper  surface  of  the  liver. 

The  bronchial  nodes  (lymphoglandulae  bronchiales)  on  account  of  their  number 
and  size  are  the  most  im- 
portant  of  the  thoracic 
nodes,  and  for  the  con- 
venience of  description 
they  may  be  regarded  as 
forming  three  subgroups 
(  Fig.  813).  One  of  these 
is  formed  by  the  tracheal 
nodes  ( lymphoglandulae 
tracheales),  seven  to  ten 
in  number  and  situated 
on  either  side  of  the 
lower  part  of  the  trachea. 
Those  upon  the  right 
side  are  as  a  rule  more 
numerous  and  larger  than 
those  on  the  left  side, 
varying  from  the  size  of 
a  pea  to  that  of  a  bean 
in  the  normal  condition. 
A  second  subgroup  is 
that  of  the  bronchial  nodes 
proper,  from  ten  to  twelve 
in  number  and  situated  in 
the  angle  formed  by  the 
two  bronchi.  Thev  are  *  , 

r          ,1  i  Tracheal  and  bronchial  Ivmph-nodes,  viewed  from  behind.     (Halle.*} 

lor  the  most   part  large, 

those  beneath  the  right  bronchus  being  usually  larger  and   more   numerous   than 


Oesophagus 


Pulmonary  nodes 


*Clinique  medicale,  Tome  iv. 


968  HUMAN   ANATOMY. 

those  below  the  left  one.  The  third  subgroup  is  formed  by  the  pulmonary  nodes, 
usually  of  small  size  and  situated  in  the  hilus  of  the  lungs,  between  the  larger 
divisions  of  the  bronchi. 

The  affcrents  of  the  bronchial  nodes  are  (i)  from  the  lungs,  (2)  from  the  lower 
part  of  the  trachea  and  from  the  bronchi,  (3)  from  the  heart,  and  (4)  from  the 
posterior  mediastinal  nodes.  Their  efferent*  may  either  pass  as  a  number  of  stems 
to  the  thoracic  duct  or  directly  to  the  subclavian  vein  on  the  right  side,  but  more 
frequently  they  unite  to  form  a  single  stem,  with  which  the  stems  coming  from  the 
sternal  and  anterior  mediastinal  nodes  unite  to  form  a  single  broncho-mediastinal 
trunk  (truncus  bronchomediastinalis),  which  passes  upward  toward  the  confluence 
of  the  internal  jugular  and  subclavian  veins.  It  either  opens  independently  into  the 
subclavian  vein,  which  is  the  most  usual  arrangement,  or  else,  on  the  right  side,  it 
unites  with  the  subclavian  and  jugular  trunks  to  form  the  right  lymphatic  duct  or,  on 
the  left  side,  it  unites  with  the  subclavian  trunk  to  open  into  the  arch  of  the  thoracic 
duct,  into  which  it  may  also  open  directly. 

THE  LYMPHATIC  VESSELS. 

The  cutaneous  lymphatics  of  the  thorax  form  a  rich  net-work  extending 
throughout  the  subcutaneous  tissue  and  being  continuous  above  with  the  subcutaneous 
net-work  of  the  cervical  region  and  below  with  that  of  the  abdomen.  From  the 
net-work  of  the  anterior  surface  a  considerable  number  of  stems  arise,  which  pass 
outward,  the  upper  ones  almost  horizontally  and  the  lower  ones  obliquely  upward 
and  outward,  to  terminate  in  the  anterior  pectoral  nodes  of  the  axillary  plexus 
(Fig.  814).  These  stems  form  the  principal  path  of  the  anterior  thoracic  drainage, 
but,  in  addition,  some  stems  which  arise  from  the  upper  portion  of  the  net-work 
pass  upward  over  the  clavicle  and  terminate  in  some  of  the  lower  inferior  deep 
cervical  nodes,  and  from  the  portions  of  the  net-work  near  the  median  line  short 
stems  perforate  the  intercostal  spaces  and  terminate  in  the  sternal  nodes.  Further- 
more, it  is  to  be  noted  that  the  net-works  of  either  side  are  continuous  across  the 
median  line  over  the  surface  of  the  sternum,  and  there  may  consequently  be  a  certain 
amount  of  crossing  in  the  lymph  flow,  that  coming  from  the  more  median  portions 
of  the  net-work  of  the  right  half  of  the  anterior  thoracic  wall,  for  instance, 
terminating  in  the  left  axillary  nodes.  These  decussating  paths  are,  however,  of 
comparatively  little  importance  except  in  cases  of  stoppage  of  the  normal  flow  to 
the  axillary  nodes  of  the  same  side,  and  in  such  cases  a  collateral  drainage  may 
also  be  established  for  the  lower  portion  of  the  thoracic  walls  through  the  abdominal 
lymphatics  to  the  inguinal  nodes. 

Upon  the  lateral  portions  of  the  thorax  the  net-work  gives  rise  to  some  half 
dozen  stems  which  pass  upwards  to  terminate  in  the  inferior  pectoral  nodes  of  the 
axillary  plexus,  and  from  the  net-work  of  the  posterior  thoracic  wall  about  ten  or 
twelve  main  stems  arise  which  converge  laterally  to  terminate  in  the  subscapular 
group  of  the  axillary  plexus.  As  was  the  case  in  the  anterior  net-work,  so  in  the 
posterior  net-work  some  stems  from  the  upper  portions  of  the  dorsal  net-work  pass  to 
the  lower  inferior  deep  cervical  nodes,  and  below  more  or  less  anastomosis  occurs 
between  the  net-works  of  the  thoracic  and  abdominal  (lumbar)  regions. 

The  Mammary  Gland. — The  lymphatics  of  the  mammary  gland  arise  in  the 
deeper  portions  of  the  mammary  tissue  from  sack-like  enlargements  situated  in 
the  connective  tissue  between  the  various  lobules  of  the  gland.  The  majority  of 
the  stems  follow  in  general  the  course  of  the  ducts  and,  passing  toward  the  surface, 
communicate  with  an  exceedingly  fine  subareolar  net- work,  which  is  a  special 
development  of  the  general  subcutaneous  net-work  of  the  anterior  thoracic  wall. 
From  the  subareolar  net-work  two  or  more  stems  arise  and  form  the  principal  paths 
for  the  mammary  lymph,  l>ut  accessory  paths  are  also  furnished  by  stems  which  arise 
from  the  sack-like  enlargements  and  pass  toward  the  periphery  of  the  gland, 
avoiding  the  subareolar  net-work. 

The  stems  which  arise  from  the  subarrolar  net-work  pass  at  first  almost  directly 
outwards  until  they  reach  the  lower  border  of  the  pectoralis  major.  They  then 
ascend  along  the  lower  edge  of  this  muscle  for  a  short  distance,  and  eventually  bend 


THE  LYMPHATICS  OF  THE  THORAX. 


969 


around  it,  perforate  the  axillary  fascia,  and  terminate  in  the  anterior  pectoral  nodes 
of  the  axillary  plexus.  Occasionally  one  finds  along  the  course  of  one  or  other  of  the 
stems  a  small  intercalated  node,  and  one  or  two  small  nodes,  the  paramammillary 
nodes,  may  occur  a  short  distance  below  the  lower  border  of  the  gland  on  one  of  the 
efferents  which  passes  to  the  lower  principal  stem. 

The  accessory  paths  of  the  mammary  lymph  are  principally  two  in  number, 
(i)  In  about  ten  per  cent,  of  cases  examined  a  stem  issued  from  the  deep  surface  of 
the  gland,  perforated  the  pectoralis  major,  and  passed  upward  between  that  muscle 
and  the  pectoralis  minor  to  terminate  in  the  subclavicular  nodes.  (2)  A  varying 
number  of  small  stems  leave  the  medial  portion  of  the  periphery  of  the  gland  and 
perforate  the  sternal  border  of  the  pectoralis  major  and  the  intercostal  muscles,  to 
terminate  in  the  sternal  nodes. 

It  may  be  noted  that  the  obstacle  to  the  flow  of  lymph  presented  by  enlarged  axillary  nodes 
in  severe  affections  of  the  mammary  gland  may  lead  to  the  development  of  accessory  or 
collateral  paths  other  than  those  mentioned  above.  Thus,  since  the  subareolar  net-work  is 


Delto-pectoral  node 


FIG.  814. 

Brachial  node 


Subscapular  node 


Anterior  pectoral  node 

Vessel  passing  to  anterior 

pectoral  node 


Inferior  pectoral  node 


Subclavian  node 


Vessel  passing  to 
subclavian  node 


Intermediate  node 


-Subareolar  plexus 
over  mammary 
gland 


Lymphatics  of  mammary  gland  and  axillary  nodes.     (Poirier  and  Cuneo.*) 

continuous  with  the  general  anterior  thoracic  subcutaneous  net-work,  and  the  latter  is  continuous 
across  the  median  line,  affection  of  the  gland  of  one  side  may  cause  enlargement  of  the  axillary 
nodes  of  the  opposite  side,  and,  furthermore,  since  the  thoracic  subcutaneous  net-work  is 
continuous  with  that  of  the  abdomen,  there  is  a  possibility  for  the  establishment  of  a  collateral 
path  leading  to  the  inguinal  nodes. 

Furthermore,  it  is  to  be  remembered  that,  although  the  anterior  pectoral  nodes  are  the 
termination  of  the  principal  mammary  stems,  yet  the  connection  between  these  and  other 
axillary  nodes,  especially  those  of  the  intermediate  and  subclavicular  subgroups,  is  so  intimate 
that  practically  all  the  axillary  nodes  may  be  involved,  or  are  at  least  open  to  suspicion,  in 
cases  of  mammary  carcinoma. 

The  intercostal  lymphatics  are  arranged  in  two  sets  corresponding  to  the 
two  intercostal  muscles  (Sappey).  The  vessels  from  each  internal  intercostal  unite  to 
form  a  single  stem  which  passes  forward  along  the  lower  border  of  the  rib  forming 
the  upper  boundary  of  its  space.  The  stems  of  the  upper  spaces  open  independently 
into  the  sternal  nodes,  while  those  from  the  lower  spaces  unite  to  form  a  common 
ascending  stem  which  terminates  in  the  lowest  node  of  the  sternal  chain. 


Poirier  et  Charpy  :   Traite"  d'anatomie  humaine,  Tome  ii.,  1902. 


970  HUMAN    ANATOMY. 

The  vessels  from  the  external  intercostals  are  somewhat  larger  than  those  from 
the  internal  muscles  and  have  a  backward  direction,  terminating  in  the  intercostal 
nodes.  It  is  upon  these  stems  that  the  lateral  intercostal  nodes  are  situated  when 
present.  Anastomoses  occur  between  the  two  sets  of  vessels,  and  the  internal  set 
also  receives  communicating  stems  from  the  parietal  layer  of  the  pleura,  while  the 
external  one  receives  branches  from  the  muscles  which  cover  the  thoracic  wall, 
although  the  principal  path  for  these  leads  to  the  axillary  nodes. 

The  Diaphragm. — The  lymphatics  of  the  diaphragm  form  rich  net-works  upon 
both  its  surfaces,  that  upon  the  peritoneal  surface  being  especially  well  developed,  and 
numerous  vessels  traverse  the  substance  of  both  the  muscular  tissue  and  the  centrum 
tendineum,  uniting  the  net-work  of  the  abdominal  with  that  of  the  thoracic  surface. 
Upon  the  thoracic  surface  the  net-work  is  exceedingly  fine  and  close-meshed  in  the 
region  of  the  centrum  tendineum,  being  most  distinct  in  the  regions  of  the  lateral 
leaflets.  From  this  net-work  branches  pass  outward  parallel  to  the  muscular 
fibres  to  unite  with  a  series  of  anastomosing  stems  whose  general  direction  is  forward. 
Branches  coming  from  the  more  peripheral  portions  of  the  diaphragm  also  empty  into 
these  stems,  which  carry  the  lymph  forward  to  the  diaphragmatic  nodes,  whence  it 
passes  to  the  anterior  mediastinal  nodes.  From  the  net-works  of  the  lateral  leaflets 
•of  the  central  tendon  collecting  stems  are  also  directed  backward  and  medially  towards 
the  aortic  opening,  which  they  traverse  to  terminate  in  the  upper  coeliac  nodes. 

It  is  to  be  observed  that  the  nodes  of  the  thoracic  surface  are  for  the  most  part 
situated  anteriorly,  while  the  coeliac  nodes,  which  may  be  regarded  as  the  principal 
nodes  of  the  inferior  surface,  are  located  posteriorly.  Both  sets  of  nodes,  however, 
receive  lymph  from  both  surfaces  of  the  diaphragm  by  means  of  the  perforating 
branches  which  connect  the  upper  and  the  lower  net-works.  The  lower  net-work 
is,  furthermore,  connected  with  the  lymphatics  of  the  more  lateral  portions  of  the 
peritoneum  and  also  with  those  of  the  liver  (page  980),  while  the  upper  net-work 
makes  connections  with  the  lymphatic  vessels  of  the  pleurae.  These  communications, 
when  considered  in  connection  with  the  existence  of  the  perforating  branches,  explain 
the  occurrence  of  pleuritis  as  a  sequence  of  subphrenic  abscess  or  of  the  latter  as  a 
sequence  of  thoracic  empyema. 

The  Heart. — The  lymphatics  of  the  heart  are  arranged  in  two  principal  net- 
works, one  of  which  lies  immediately  beneath  the  endocardium,  while  the  other  is 
upon  the  outer  surface  of  the  organ  immediately  beneath  the  visceral  layer  of  the 
pericardium.  The  endocardial  net-work  communicates  with  the  superficial  one  by 
branches  which  traverse  the  heart  musculature,  and  the  flow  of  lymph  from  the 
endocardial  net-work  takes  place  only  through  these  communicating  branches.  The 
superficial  net-work  extends  over  the  whole  surface  of  the  heart,  the  vessels  of  which 
it  is  formed  being  well  supplied  with  valves  and  arranged  so  as  to  form  characteristic 
quadrate  or  rhomboidal  meshes.  From  the  net-work  longitudinal  stems  pass  up- 
ward towards  the  base  of  the  heart,  corresponding  in  a  general  way  to  the  cardiac 
veins.  Upon  the  anterior  surface  three  stems  are  to  be  found  passing  upward 
along  the  anterior  interventricular  groove,  parallel  to  the  anterior  cardiac  vein,  and, 
on  arriving  at  the  auriculo-ventricular  groove,  they  unite  to  form  a  single  trunk. 
With  this  another  stem  unites  which  has  its  origin  in  the  net-work  of  the  posterior 
surface  of  the  heart  and  ascends  along  the  posterior  interventricular  groove, 
parallel  with  the  posterior  cardiac  vein.  On  reaching  the  auriculo-ventricular  gn>o\  e 
it  bends  round  to  the  left  and,  encircling  the  base  of  the  left  ventricle,  unites  with 
the  anterior  vessels.  The  conjoined  trunk  so  formed  passes  upward  along  the  pos- 
terior surface  of  the  pulmonary  aorta,  perforates  the  parietal  layer  of  the  pericardium, 
and  terminates  in  one  of  the  bronchial  nodes. 

From  the  net-work  over  the  right  side  of  the  right  ventricle  another  longitudinal 
stem  arises  and  passes  upward  parallel  to  the  right  marginal  vein,  and,  on  reaching  the 
auriculo-ventricular  groove,  winds  around  to  the  right  and  so  reaches  the  anterior 
surface  of  the  heart.  It  then  ascends  parallel  with  the  anterior  trunk,  along  the  pos- 
terior surface  of  the  pulmonary  aorta,  and  also  terminates  in  one  of  the  bronchial  nodes. 

The  Lungs. — The  lymphatics  of  the  lungs  may  be  regarded  as  consisting  of 
two  sets,  deep  and  superficial.  The  deep  set  is  composed  of  a  number  of  stems 
which  accompany  the  branches  of  the  pulmonary  arteries  and  veins  and  of  others 


THE  LYMPHATICS  OF  THE  THORAX.          971 

which  are  associated  more  especially  with  the  bronchi.  The  bronchial  vessels  take 
their  origin  from  a  net-work  contained  in  the  walls  of  the  bronchi,  and  are  traceable 
along  the  entire  length  of  each  bronchus  and  its  branches  until  the  terminal  bronchi 
are  reached  ;  here  the  net-work  disappears  and  no  indications  of  it  are  to  be  found 
in  the  walls  of  the  atria  or  alveoli.  In  the  larger  bronchi  the  net-work  is  double, 
one  portion  of  it  occurring  immediately  beneath  the  mucous  membrane  and  the 
other  external  to  the  cartilaginous  rings,  but  in  the  finer  bronchi  only  one  layer  is 
present  and  from  this  branches  pass  to  the  stems  which  accompany  the  arteries  and 
veins.  All  the  stems  belonging  to  this  deep  set  of  lymphatics  pass  to  the  hilus  of 
the  lung  and  there  open  into  the  pulmonary  nodes. 

The  superficial  set  consists  of  a  net-work  situated  upon  the  surface  of  the  lung, 
immediately  beneath  the  visceral  layer  of  the  pleura.  The  vessels  composing  it  are  well 
supplied  with  valves  and  have  communicating  with  them  branches  from  the  visceral 
layer  of  the  pleura  and  valved  branches  which  have  their  origin  in  the  interlobular  and 
intralobular  connective  tissue.  No  communication  has  been  observed  between  the 
superficial  and  deep  pulmonary  net-works,  the  stems  from  the  superficial  net-work 
alone  passing  toward  the  hilus  of  the  lung  and  terminating  in  the  pulmonary  nodes. 

Lymphatic  vessels  have  been  demonstrated  in  the  parietal  layer  of  the  pleura. 
Those  upon  its  costal  surface  communicate  with  the  intercostal  vessels  ;  those  upon 
the  diaphragmatic  surface  with  the  diaphragmatic  net-work  ;  and  those  upon  the 
mediastinal  surface  with  the  posterior  mediastinal  nodes. 

The  CEsophagus. — The  lymphatics  of  the  oesophagus  are  arranged  in  two  net- 
works, one  of  which  is  submucous,  while  the  other  is  situated  in  the  muscular  coat. 
The  stems  which  drain  the  net-works  of  the  cervical  portion  of  the  oesophagus  pass 
to  the  superior  deep  cervical  and  the  recurrential  nodes,  while  those  draining 
the  thoracic  portions  of  the  net-works  pass  to  the  posterior  mediastinal  nodes. 
Finally,  the  stems  originating  in  the  net-works  of  the  terminal  portion  pass  to  the 
upper  nodes  of  the  cceliac  group. 

Practical  Considerations. —  The  Lymph- Nodes  of  the  Thorax  and  Medias- 
tinum. Anterior  Mediastinum.  —  The  nodes  in  close  relation  to  the  internal 
mammary  artery  are  of  practical  importance  on  account  of  their  relations  (a)  to 
the  diaphragm  ;  (b)  to  the  anterior  extremities  of  the  intercostal  spaces  ;  (c)  to  the 
inner  segment  of  the  mammary  gland.  They  may  therefore  be  involved  in  cases 
of  subpleural  (supradiaphragmatic)  abscess,  of  tuberculous  or  syphilitic  or  typhoidal 
caries  of  the  ribs  or  sternum,  or  of  carcinoma  of  the  breast  (page  2035). 

Middle  Mediastinum. — The  nodes  just  below  the  bifurcation  of  the  trachea 
(bronchial,  peribronchial),  in  close  relation  to  the  trachea,  the  bronchi,  and  the 
r6ots  of  the  lungs,  are  frequently  involved  in  tuberculous  infection  of  the  lungs. 
The  pulmonary  lymphatics,  both  perivascular  and  peribronchial,  communicate  on 
the  one  hand  indirectly  with  the  lymph-spaces  in  the  walls  of  the  alveoli  beneath 
the  epithelial  cells,  and  on  the  other  with  these  nodes.  Solid  particles — and  this 
includes  the  bacillus  tuberculosis  and  other  organisms — are  thus  enabled  to  pass  from 
within  the  alveoli  into  the  lymphatic  spaces,  and  from  these  they  are  forced  on  by 
the  respiratory  movements  of  the  lungs  to  the  bronchial  nodes,  to  which  all  the 
lymphatics  converge.  These  nodes  often  contain,  especially  in  coal  miners,  or  in  the 
inhabitants  of  large  cities,  a  large  amount  of  black  pigment,  consisting  of  minute 
particles  of  dust,  smoke  (carbon),  etc.,  that  have  been  inhaled  (Taylor). 

Caseation  and  ulceration  of  these  nodes  have  involved  the  trachea  (page  1840), 
the  bronchi  (especially  the  right  one,  with  which  the  larger  number  are  in  close 
relation),  and  the  oesophagus  (page  1614),  directly  in  front  of  which  some  of  them  lie. 
Their  enlargement  has  also  produced  various  pressure  symptoms, — dyspnoea,  dys- 
phagia,  stridulous  respiration,  etc., — which  their  relations  easily  explain. 

Posterior  Mediastinum. — A  group  of  nodes — cesophago-pericardiac  (Leaf) — 
lying  between  the  posterior  surface  of  the  pericardium  and  the  oesophagus,  are  in 
close  relation  to  the  trunk  of  the  pneumogastric  nerve  and  its  oesophageal  branches. 
Their  infection — through  their  direct  connection  with  the  not  infrequently  infected 
nodes  in  the  neck  and  thorax  lying  between  the  trachea  and  oesophagus — may  produce 
symptoms  of  vagus  irritation.  It  has  been  thought  (Guiteras)  that  these  nodes  and 


972 


HUMAN   ANATOMY. 


the  bronchial  nodes  are  especially  enlarged  in  influenza  and  that  some  of  the  anomalous 
pulmonary  symptoms  of  that  disease — simulating  congestion,  pneumonia,  etc.,  are 
thus  accounted  for.  Marked  enlargement  of  the  bronchial  nodes  may  be  indicated 
by  an  area  of  percussion  dulness  below  the  level  of  the  fourth  dorsal  vertebra  (Yeoj. 

In  cancer  of  the  oesophagus  either  the  mediastinal  nodes  or  those  at  the  root  of 
the  neck  may  be  involved,  as  both  sets  receive  lymphatics  from  that  tube.  Medias- 
tinal growth  (sarcoma)  or  abscess  may  originate  in  these  nodes.  Either  condition 
— but  especially  the  neoplasm — will  occasion  marked  symptoms  of  pressure  on 
the  trachea,  bronchi,  oesophagus,  and  superior  cava  and  innominate  veins, — e.g. , 
dyspnoea,  dysphagia,  oedema  of  the  face,  neck,  and  upper  limbs,  dilatation  of  the 
superficial  veins  of  the  abdomen  and  thorax. 

THE    LYMPHATICS   OF   THE   ABDOMEN. 

THE  LYMPH-NODES. 

The  principal  nodes  of  the  abdominal  region  are  those  associated  with  the 
viscera  and  those  situated  upon  the  posterior  wall  in  the  vicinity  of  the  aorta. 
A  few  small  and  inconstant  nodes  also  occur  upon  the  anterior  wall,  and  of  these  the 
most  important  are  the  epigastric,  the  circumflex  iliac,  and  the  umbilical  nodes. 

The  epigastric  nodes  (lymphoglandulae  epigastricae)  are  three  or  four  in 
number  and  are  interposed  in  the  course  of  the  lymphatic  stems  which  accompany 

FIG.  815, 


Umbilical  node 


Deep  epigastric 

artery 


Epigastric  node 


Iliac  node 


Umbilical   node 


Lymphatic  vessels 
accompanying  deep 

epigastric  artery 


Iliac  node 


Epigastric  and  umbilical  lymph-nodes,  seen  from  behind.     (Cuneo  and  MarciUe.*} 

the  deep  epigastric  vessels  (Fig.  815)  ;  they  occur  toward  the  lower  part  of  the 
vessels  and  their  efferent*  pass  to  the  lower  iliac  -nodes. 

The  circumflex  iliac  nodes  are  from  two  to  four  in  number  when  present, 
but  are  not  unfrequently  wanting.  They  are  situated  along  the  course  of  the  deep 
circumflex  iliac  vessels  ;  they  receive  afferent s  from  the  lower  lateral  portions  of  the 
abdominal  wall,  and  send  cffcroits  to  the  lower  iliac  nodes. 

The  umbilical  nodes  an-  situated  in  the  subserous  areolar  tissue  in  the 
neighborhood  of  the  umbilicus.  They  are  three  in  number,  one  being  situated  a 
little  below  and  to  one  side  of  the  umbilicus,  and  the  other  two  above  the  umbilicus 


Hull,  et  M£m.  Soci£t£  anatom.,  1901. 


THE    LYMPHATICS    OF   THE   ABDOMEN. 


973 


in  the  median  line  (Fig.  815).  They  occur  in  the  net-work  which  covers  the 
posterior  surface  of  the  sheath  of  the  rectus  muscles,  and  are  apparently  of  inconstant 
occurrence. 

The  remaining  abdominal  nodes  may  be  regarded  as  arranged  in  two  principal 
divisions,  one  of  which  includes  the  groups  associated  with  the  various  viscera,  while 
the  other  is  formed  by  the  groups  occurring  in  the  posterior  wall.  This  latter 
division  may  be  separated  into  the  cce/iac  and  lumbar  nodes. 

The  coeliac  nodes  vary  in  number  from  sixteen  to  twenty,  and  are  situated  in 
front  of  the  abdominal  aorta,  around  the  origins  of  the  cceliac  axis  and  the  superior 
mesenteric  artery.  They  are  extensively  connected  with  one  another  so  as  to  form 
a  distinct  cceliac  plexus  (plexus  coeliacus).  They  receive  affercnts  from  the  lower 
portions  of  the  oesophagus,  from  the  diaphragm,  and  from  the  gastric,  hepatic,  pan- 
creatico-splenic,  and  mesenteric  nodes  ;  the  efferent  s  of  the  lower  nodes  pass  to  the 
higher  members  of  the  group  and  the  efferents  of  these  either  open  independently 

FIG.  816. 


Right 

suprarenal  body 


Right  kidney 


Right  lateral 

lumbar  nodes 


Median   lumbar  node 


Right  ureter 


Iliac  node 


Left  suprarenal  body 


Left  kidney 


Left  lateral 

lumbar  nodes 


Lymphatic  vessels 

from  testis 


Lumbar  nodes,  new-born  child.     (Cuneo.*) 

into  the  receptaculum  chyli,  or,  more  usually,  unite  to  form  a  common  trunk,  the 
truncus  intestinalis,  which  joins  the  left  lumbar  trunk  to  form  one  of  the  origins  of 
the  thoracic  duct  (page  943). 

The  lumbar  nodes  (lymphoglandulae  lumbales)  are  twenty  to  thirty  in  number, 
and  form  three  irregular  longitudinal  rows  along  the  course  of  the  abdominal  aorta 
(Fig.  816),  extending  from  the  level  of  the  second  lumbar  vertebra  to  the  bifurcation 
of  the  aorta,  and  forming  with  the  aid  of  connecting  vessels  a  well-marked  plexus, 
the  plexus  lumbalis.  The  median  row  is  composed  of  some  five  or  six  large  nodes 
situated  upon  the  anterior  surface  of  the  aorta,  and  of  four  or  five  retro-aortic  nodes 
which  rest  upon  the  bodies  of  the  third  and  fourth  lumbar  vertebrae,  immediately 
below  the  lower  extremity  of  the  receptaculum  chyli.  Of  the  lateral  rows  that  of 
the  left  side  is  formed  by  a  number  of  nodes  arranged  in  an  almost  vertical  series 
upon  the  successive  heads  of  the  psoas  muscle.  The  right  lateral  nodes  occupy  a 


*  Bull,  et  Mem.  Societe  anatom.,  1901. 


974 


HUMAN    ANATOMY. 


corresponding  position  with  relation  to  the  right  psoas,  lying  posterior  to  the  vena 
cava  inferior,  but  a  varying  number  of  nodes  which  may  be  referred  to  this  group 
also  occur  upon  the  anterior  surface  of  that  vessel. 

Since  all  the  nodes  are  united  by  communicating  vessels,  they  form  a  plexus  and 
will  receive  afferents  from  and  give  efferents  to  one' another.  In  addition,  the  median 
row  receives  afferents  from  the  descending  colon  and  the  mesocolic  nodes,  while  the 
lateral  rows  receive  them  from  the  muscles  of  the  posterior  abdominal  walls,  from 
the  iliac  nodes,  from  the  testes  in  the  male  and  the  ovaries,  Fallopian  tubes,  and 
uterus  in  the  female,  and  from  the  kidneys  and  suprarenal  capsules.  The  efferents 
of  the  upper  nodes  of  the  median  row  pass  upward  to  terminate  in  the  lower  cceliac 
nodes,  while  those  of  the  lateral  rows  either  pass  to  the  nodes  of  the  median  row, 
or  unite  together  to  form  on  either  side  a  common  trunk,  the  truncus  lumbalis, 
which  unites  with  its  fellow  to  form  the  receptaculum  chyli  (page  943),  or  else 
they  perforate  the  crus  of  the  diaphragm  and  open  independently  into  the 
thoracic  duct. 

The  visceral  abdominal  nodes  are  arranged  in  groups  or  chains  which  follow 
in  general  the  principal  visceral  branches  of  the  aorta,  those  following  the  branches  of 
the  cceliac  axis  and  the  superior  mesenteric  artery  communicating  by  their  efferents 

FIG.  817. 


Superior 

gastric  nodes 


Inferior 

gastric  nodes 


Lymphatic  nodes  and  vessels  of  stomach.     (Polya  and  JVavratil.*) 

mainly  with   the  coeliac  nodes,   while  those  accompanying   the   inferior  mesenteric 
branches  communicate  with  the  median  lumbar  nodes. 

Corresponding  with  the  branches  of  the  coeliac  axis  are  the  gastric,  hepatic,  and 
pancreatico-splenic  nodes.  The  gastric  nodes  consist  of  two  chains  (hmpho- 
glandulae  gastricac  superiores  et  inferiores)  situated  respectively  along  the  lesser  and 
greater  curvatures  of  the  stomach.  The  superior  nodes,  three  to  fifteen  in  number, 
are  situated  along  the  course  of  the  gastric  artery,  principally  along  the  lesser 
curvature  of  the  stomach  between  the  two  layers  of  the  gastro-hepatic  omentum 
(Fig.  817),  although  a  few  also  occur  along"  the  course  of  the  artery  before  it 
reaches  the  stomach  and  others  upon  the  left  side  of  the  cardiac  orifice  of  the 
viscus.  The  inferior  nodes  are  situated  in  the  vicinity  of  the  pyloric  end  of  the 
stomach,  partly  along  the  right  half  of  the  greater  curvature,  accompanying 
tin-  right  gastro-cpiploic  vessels,  and  partly  on  the  posterior  surface  of  the  pylorus 
along  the  course  of  the  gastro-duodcnal  vessels.  The  gastric  nodes  receive  afferents 
from  the  stomach  and  in  tin-  case  of  the  retro-pyloric  nodes  also  from  the  first 
portion  of  the  duodenum,  and  their  eft', -rents  pass  to  tin-  coeliac  nodes,  those  of 
the  superior  group  following  the  course  of  the  gastric  vessels,  while  those  from  the 
inferior  group  accompany  the  Castro-duodenal  and  hepatic  arteries. 

*  Deutsche  Zt- itschrift  f.  Chirurgie,  Bd.  Ixix. 


THE   LYMPHATICS    OF   THE   ABDOMEN. 


975 


The  hepatic  nodes  (lymphoglandulac  hepaticae)  are  more  or  less  clearly  arranged 
in  two  series.  One  series  accompanies  the  main  stem  of  the  hepatic  artery  along  the 
upper  border  of  the  head  of  the  pancreas  and  throughout  the  vertical  portion  of  its 
course  in  the  free  margin  of  the  gastro-hepatic  omentum,  and  the  other  accompanies 
the  superior  pancreatico-duodenal  branch  and  ascends  along  the  bile-duct  to  the 
portal  fissure.  The  afferents  of  the  nodes  come  from  the  liver,  the  head  of  the 
pancreas,  and  the  first  and  second  portions  of  the  duodenum,  and  their  efferents  pass 
to  the  cceliac  nodes. 

The  pancreatico-splenic  nodes  (lymphoglandulae  pancreaticolienales)  accom- 
pany the  splenic  artery  throughout  the  greater  portion  of  its  course,  and  are 
consequently  situated  along  and  partly  behind  the  upper  border  of  the  pancreas 
(Fig.  8 1 8).  They  vary  in  number  from  four  to  ten,  and  their  afferents  come  from 
the  organs  supplied  by  the  splenic  artery, — namely,  the  stomach,  pancreas,  and 
spleen, — while  their  efferents  pass  to  the  cceliac  nodes. 

The  mesenteric  nodes  (lymphoglandulae  raesentericae)  are  from  one  hundred  to 
two  hundred  in  number,  and  are  arranged  along  the  superior  mesenteric  artery  and 
its  branches  to  the  small  intestine.  They  form  three  more  or  less  distinct  series, 
especially  towards  the  upper  portion  of  the  mesentery.  One  series,  in  which  the 

FIG.  818. 


Hepatic  node 


Retropyloric  node 


Mesocolic  nodes 


Pancreatico-splenic  nodes 


Transverse  mesocolon 


— "?~  Transverse  colon 


Pancreatico-splenic,  retropyloric,  and  mesocolic  nodes,  new-horn  child  ;   liver  drawn  upward,  stomach  and 
duodenum  laterally.     (Cuneo  and  Delamare.*) 

nodes  are  more  numerous  and  smaller  than  the  others,  lies  close  to  the  intestine, 
among  the  terminal  branches  of  the  artery  ;  a  second  consists  of  larger  scattered 
nodes  situated  along  the  primary  branches  of  the  artery  ;  while  the  third  series 
includes  the  closely  aggregated  nodes  which  surround  its  main  stem.  Towards  the 
lower  portion  of  the  ileum  the  distinction  of  the  first  and  second  series  becomes 
less  and  less  apparent,  and  at  the  junction  of  the  ileum  and  caecum  the  nodes  form  a 
single  group,  situated  a  short  distance  from  the  intestine  between  the  two  layers  of 
the  mesentery.  These  nodes  are  sometimes  termed  the  ileo-caecal  nodes,  and 
associated  with  them  by  means  of  its  efferents  is  a  variable  group  of  small  nodes, 
the  appendicular  nodes,  situated  partly  in  the  base  of  the  mesenteriole  of  the 
appendix  and  partly  in  the  immediate  vicinity  of  the  junction  of  the  ileum  and 
caecum  (Fig.  820). 

The  various  series  of  nodes  are  connected  with  one  another  by  vessels,  which  in 
this  region  are  known  as  lacteals,  and  the  nodes  of  the  first  series  receive  their 
afferents  from  the  walls  of  the  small  intestine,  and,  in  the  case  of  the  ileo-caecal  nodes, 
from  the  caecum  and  vermiform  appendix.  The  efferents  of  the  nodes  of  the  third 
series  pass  to  those  nodes  of  the  cceliac  group  which  are  situated  around  the  origin 
of  the  superior  mesenteric  artery. 

*  Jour,  de  1'anat.  et  de  la  physiol.,  Tome  xxxvi.,  1900. 


976  HUMAN    ANATOMY. 

The  nodes  which  are  associated  with  the  abdominal  portions  of  the  large  intestine 
are  known  as  the  mesocolic  nodes  ( lymphoglandnlae  mesocolicae)  and  they  consist 
of  from  twenty  to  fifty  small  nodes  which  are  situated  close  to  the  intestine  (Fig.  818). 
Their  afferents  are  received  from  the  entire  length  of  the  large  intestine,  with  the 
exception  of  the  caecum  and  appendix  and  the  rectum,  and  the  efferents  of  the  nodes 
associated  with  the  ascending  colon  and  the  right  half  of  the  transverse  colon  pass  to 
the  lower  cceliac  nodes,  while  those  of  the  nodes  associated  with  the  left  half  of  the 
transverse  colon  and  with  the  descending  and  sigmoid  colons  pass  to  the  median  row 
of  lumbar  nodes. 

In  addition  to  the  nodes  which  are  properly  included  in  the  mesocolic  group 
there  are  a  number  of  small  nodes  situated  upon  the  lateral  walls  of  the  upper  part  of 
the  rectum,  along  the  lines  of  the  superior  hemorrhoidal  vessels  (Fig.  821).  These 
ano-rectal  nodes  are  from  two  to  eight  in  number  on  each  side,  and  are  situated 
beneath  the  fibrous  investment  of  the  rectum,  resting  directly  upon  the  outer  surface 
of  the  muscular  coat.  They  receive  their  afferents  from  the  neighboring  portions  of 
the  wall  of  the  rectum  and,  in  the  female,  from  the  posterior  surface  of  the  vagina, 
and  their  efferents  pass  to  the  mesocolic  nodes  situated  in  the  lower  part  of  the 
mesentery  of  the  sigmoid  colon. 

THE   LYMPHATIC  VESSELS. 

The  Abdominal  \Afalls. — The  anterior  abdominal  wall,  as  regards  its 
lymphatic  vessels,  may  be  divided  into  a  supra-  and  an  infra-umbilical  region.  The 
lymphatics  of  the  former  area  belong  in  reality  to  the  thoracic  cutaneous  set,  passing 
upward  to  join  the  thoracic  stems  which  terminate  in  the  anterior  pectoral  nodes  of 
the  axillary  plexus.  The  vessels  of  the  infra-umbilical  region,  on  the  contrary, 
descend  to  terminate  in  the  inguinal  nodes.  Along  the  line  of  junction  of  the  two 
regions  anastomoses  occur  and  the  vessels  of  the  right  half  of  the  abdominal  wall  also 
communicate  with  those  of  the  left  half.  The  subcutaneous  vessels  of  the  posterior 
abdominal  and  lumbar  regions  anastomose  with  the  corresponding  vessels  of  the 
posterior  thoracic  region  above,  and  below  with  those  of  the  gluteal  region.  They 
form  an  extensive  net-work,  from  which  stems  pass  downward  and  forward,  parallel 
with  the  crest  of  the  ilium,  to  terminate  in  the  inguinal  nodes. 

The  lymphatic  net-work  of  the  deeper  structures  of  the  abdominal  walls  is 
drained  by  a  number  of  stems  which  follow  in  general  the  courses  of  the  blood- 
vessels. Thus,  the  stems  which  lead  away  from  the  upper  portion  of  the  abdominal 
wall  pass  upward  along  the  course  of  the  superior  epigastric  vessels  to  terminate  in 
the  lower  sternal  nodes  ;  another  set  follows  the  course  of  the  deep  epigastric  vessels 
to  terminate  in  the  lower  iliac  nodes,  after  traversing  the  epigastric  nodes  ;  another 
accompanies  the  deep  circumflex  iliac  vessels,  draining  the  lower  portions  of  the  lateral 
walls  of  the  abdomen,  traversing  the  circumflex  iliac  nodes,  and  also  terminating  in 
the  iliac  nodes  ;  while  other  sets  accompany  the  lumbar  vessels  and  terminate  in  the 
lateral  rows  of  lumbar  nodes.  Abundant  communications  exist  between  the  vessels  of 
adjacent  drainage  areas  and  from  the  region  of  the  umbilicus  the  lymph  flow  may  follow 
any  one  of  the  paths  mentioned  above.  Attention  may  be  called  to  the  occasional 
presence  of  nodes  in  the  course  of  the  vessels  arising  in  the  umbilical  region  (page  972). 

The  Stomach. — The  lymphatics  of  the  stomach  have  their  origin  in  two 
net-works,  one  of  which  is  situated  in  the  mucosa  and  the  other  in  the  muscular 
coat.  The  net-work  of  the  mucosa  occurs  uninterruptedly  throughout  the  entire 
extent  of  the  gastric  surface  and  is  continuous  with  the  corresponding  net-works  of 
both  the  oesophagus  and  duodenum.  From  its  deeper  surface  branches  pass  to  a 
more  open  net-work  situated  upon  the  outer  surface  of  the  submucosa,  and  from  this 
stems  traverse  the  muscular  coat  obliquely  to  terminate  in  a  subsenms  net-work  which 
also  receives  branches  from  the  net-work  of  the  muscular  coat.  Connections  between 
the  muscular  and  mucous  net-works  occur,  but  they  are  so  indirect  that  an  extensive 
cancerous  infection  of  the  mucosa  may  reach  the  outer  layers  of  the  stomach  only  at 
limited  areas  at  some  distance  from  one  another. 

The  subserous  net-work  with  which  both  primary  net-works  communicate  gives 
origin  to  a  number  of  stems  which  pass  to  the  gastric  nodes,  and  the  course  which  they 
follow  is  such  that  the  entire  surface  of  the  stomach  may  be  regarded  as  presenting 


THE   LYMPHATICS   OF   THE   ABDOMEN. 


977 


three  more  or  less  distinct  lymphatic  areas  (Fig.  817).  Not  that  the  areas  are 
perfectly  separated  from  one  another  ;  on  the  contrary,  the  subserous  net-work  is 
continuous  kover  the  entire  surface.  But  the  collecting  stems  from  each  area  follow 
a  definite  route  toward  different  node  groups.  The  largest  of  these  areas  occupies 
roughly  the  whole  of  the  upper  border  of  the  stomach  from  the  fundus  to  the 
pylorus,  and  extends  downward  on  either  surface  to  about  two-thirds  of  the  distance 
to  the  greater  curvature.  Its  collecting  stems  all  pass  to  the  superior  cardiac  nodes. 
The  second  area  occupies  about  the  pyloric  two-thirds  of  the  greater  curvature,  and 
its  efferents  pass  to  the  inferior  gastric  nodes,  while  the  third  and  smallest  area 
occupies  the  lower  part  of  the  fundus  and  the  cardiac  one-third  of  the  greater 
curvature,  and  sends  its  efferents  to  the  splenic  nodes.  It  may  be  remarked  that 
these  areas  correspond  in  a  general  way  with  the  areas  drained  by  the  principal  veins 
arising  in  the  stomach  walls.  Thus,  the  large  upper  area  corresponds  in  general  with 
the  drainage  area  of  the  gastric  vein,  the;  lower  pyloric  area  to  that  of  the  right 
gastro-epiploic  vein,  and  the  lower  cardiac  area  to  that  of  the  left  gastro-epiploic. 
It  may  further  be  noted  that  while  the  subserous  net-work  communicates  with  the 
superficial  net-work  of  the  oesophagus,  it  seems  to  be  completely  cut  off  from  connec- 
tion with  the  corresponding  duodenal  net-work,  an  arrangement  which  is  in  striking 
contrast  to  the  continuity  which 
exists  between  the  gastric  and 
duodenal  mucosa  net-works  and 
explains  the  rare  extension  of  a 
carcinomatous  infection  of  the 
pylorus  to  the  duodenum  by  the 
subserous  route. 

The  Small  Intestine. — 
Throughout  the  entire  length  of 
the  intestine,  both  small  and  large, 
the  lymphatic  net  -  works  are 
arranged  in  two  sets,  one  of  which 
is  situated  in  the  mucosa  and  the 
other  in  the  muscular  coat.  The 
two  net-works  are  more  or  less 
independent,  though  communicat- 
ing branches  occur,  and  both  open 
into  a  subserous  net-work  from 
which  collecting  stems  arise. 

The  stems  which  pass  from 
the  duodenum  are  divisible  into 
two  groups  according  as  they  arise  from  the  anterior  or  posterior  surface.  Those 
coming  from  the  anterior  surface  pass  to  the  chain  of  nodes  situated  along  the 
course  of  the  inferior  pancreatico-duodenal  artery,  and  so  to  the  cceliac  nodes, 
which  surround  the  origin  of  the  superior  mesenteric  artery,  while  the  posterior 
stems  pass  to  the  hepatic  nodes  situated  along  the  course  of  the  superior  pancreatico- 
duodenal  vessels  and  so  to  the  cceliac  nodes  which  surround  the  coeliac  axis.  Some 
of  the  stems  which  take  their  origin  from  the  first  part  of  the  duodenum  pass  to 
those  nodes  of  the  inferior  gastric  group  which  are  situated  upon  the  posterior 
surface  of  the  pyloric  region  of  the  stomach,  and,  since  these  nodes  also  receive 
afferents  from  the  pylorus,  they  afford  opportunity  for  the  transference  of  a  superficial 
infection  from  the  pylorus  to  the  duodenum,  a  direct  route  for  infection  in  this 
direction  being  wanting  (see  above). 

The  collecting  stems  of  the  jejunum  and  ileum  pass  to  the  first  series  of 
mesenteric  nodes,  situated  along  the  line  of  attachment  of  the  mesentery  to  the 
intestine,  and,  after  traversing  these,  are  continued  onward  to  the  second  and  third 
series  of  nodes,  whose  efferents  pass  to  the  coeliac  nodes  surrounding  the  origin  of 
the  superior  mesenteric  artery.  The  vessels  issuing  from  the  jejuno-ileum  are  usually 
spoken  of  as  the  lacteals,  on  account  of  their  contents,  especially  at  times  when 
absorption  of  food  constituents  is  proceeding  rapidly  in  the  intestine,  having  a  milky 
appearance,  owing  to  the  presence  of  numerous  fat  globules  in  the  lymphocytes. 

62 


Mesenteric  lymphatic  nodes  and  vessels ;  peritoneal  covering  of 
mesentery  has  been  removed. 


97« 


HUMAN   ANATOMY. 


The  Large  Intestine. — The  two  sets  of  lymphatic  net-works  characteristic  of 
mucous  membranes  occur  in  the  walls  of  the  large  intestine,  and  they  communicate 
with  one  another  and  finally  open  into  a  subserous  net-work  from  which  collecting 
stems  take  origin.  In  the  vermiform  appendix  (Fig.  820)  these  collecting  stems  are 
from  three  to  five  in  number  and  pass  upward  in  the  mesenteriole  to  terminate  in 
the  appendicular  nodes  or,  in  the  absence  of  these,  directly  in  the  ileo-caecal  nodes. 
The  subserous  net-work  of  the  base  of  the  appendix  communicates  freely  with  that  of 
the  caecum,  whose  collecting  stems  have  essentially  the  same  course  as  those  of  the 
appendix,  passing  primarily  to  the  appendicular  nodes  situated  in  the  neighborhood 
of  the  ileo-caecal  junction  and  thence  to  the  ileo-caecal  nodes.  The  ultimate  nodes 
of  the  appendicular  and  caecal  systems  are  situated  in  the  root  of  the  mesentery  along 
the  course  of  the  superior  mesenteric  vessels  ;  they  belong  to  the  group  of  mesenteric 
nodes  and  receive  their  afferents  in  part  from  the  ileo-caecal  nodes. 

Communications  have  been  described  as  existing  between  the  appendicular  lymphatics 
and  those  of  the  broad  ligament  of  the  uterus  as  well  as  the  iliac  nodes.  The  more  recent 
observations  have  failed,  however,  to  confirm  the  existence  of  any  direct  connection  with 

these  structures,  and  patholog- 

FIG.  820.  ical   conditions  of   the  broad 

ligament  and  iliac  nodes  asso- 
ciated with  acute  appendicitis 
may  perhaps  be  due  to  a 
dissemination  of  the  infection 
through  the  subperitoneal  net- 
work by  way  of  the  so-called 
appendiculo-ovarian  ligament. 

lleo-c.necal _L»S*^  fi^ 

The  collecting  stems 
from  the  subserous  net- 
work of  the  ascending  colon 
pass  primarily  to  some  in- 
constant mesocolic  nodes, 
situated  along  the  line  of 
attachment  of  the  colon  to 
the  abdominal  wall,  and 
thence  are  continued  along 
the  lines  followed  by  the 
right  colic  vessels  to  the 
superior  mesenteric  nodes. 
The  stems  from  the  trans- 
verse colon  have  a  more 
varied  course  in  accordance  with  the  arrangement  of  the  blood-vessels.  They  pass 
primarily  to  a  series  of  mesocolic  nodes  situated  between  the  layers  of  the  transverse 
mesocolon  close  to  the  intestine  ;  these  are  of  larger  size  and  more  numerous  than 
the  nodes  associated  with  either  the  ascending  or  descending  colon  and  are  especially 
well  developed  toward  either  angle  of  the  colon.  Their  efferents  pass  principally 
to  some  four  or  five  nodes  situated  along  the  course  of  the  middle  colic  vessels  and 
thence  to  the  third  group  of  mesenteric  nodes,  but  those  from  the  vicinity  of  the 
splenic  flexure  follow  the  course  of  the  branches  of  the  left  colic  vessels  and  so  pass 
to  the  nodes  of  the  median  lumbar  group  situated  in  the  neighborhood  of  the  inferior 
mesenteric  artery.  The  lymphatics  of  the  transverse  colon  communicate  somewhat 
extensively  with  those  of  the  great  omentum,  as  the  result  of  the  attachment  of  the 
latter  to  the  colon,  and  they  are  thus  placed  in  connection  with  the  inferior  gastric 
and  splenic  nodes. 

The  collecting  stems  from  the  descending  colon  and  sigmoid  flexure  pass 
primarily  to  mesocolic  nodes  situated  close  to  the  attached  surface  of  the  intestine, 
and  thence  follow  the  courses  of  the  left  colic  and  sigmoid  vessels  to  the  median 
lumbar  nodes  situated  in  the  vicinity  of  the  origin  of  the  inferior  mesenteric  artery. 


Vermiform  appendix 


Ileo-caecal  and  appendicular  lymphatic  nodes  and  vessels. 
(Potya  and  Navratil.*) 


*  Deutsche  Zeitschrift  f.  Chirurgie,  Bd.  Ixix. 


THE  LYMPHATICS  OF  THE  ABDOMEN. 


979 


The  mesocolic  nodes  associated  with  the  descending  colon  are  less  numerous 
and  smaller  than  those  of  the  sigmoid  flexure  and  resemble  in  appearance  and 
arrangement  those  of  the  ascending  colon. 

The  lymphatics  of  the  rectum  (Fig.  821),  although  belonging  in  large  part  to  the 
pelvic  region,  may,  for  the  sake  of  completeness  of  the  account  of  the  intestinal 
lymphatics,  be  considered  here  in  their  entirety.  Of  the  two  primary  net-works  that 
of  the  muscular  coat  is  injected  only  with  difficulty,  but  it  communicates  with  the 
mucosa  net-work  and  its  collecting  stems  follow  the  same  course  as  those  of  the 
deeper  net-work.  In  the  mucosa  net-work  two  zones  may  be  distinguished,  one  of 
which  includes  the  greater  portion  of  the  net-work  and  extends  down  to  the  lower 
ends  of  the  columns  of  Morgagni,  while  the  other  includes  that  portion  of  the  mucosa 
intervening  between  that  level  and  the  anal  integument.  The  upper  zone  may  be 
termed  the  net-work  of  the  rectal  mucosa,  while  the  lower  one  may  be  designated 
as  the  net-work  of  the  anal 

mucosa,   since  the  region  in  FIG.  821. 

which  it  occurs  forms  the 
transition  between  the  mu- 
cosa and  the  anal  integument. 

The  collecting  stems 
from  the  net-work  of  the 
rectal  mucosa  traverse  the 
muscular  coat  and  enter  into 
relation  with  the  ano-rectal 
nodes  (  page  976  ).  After 
traversing  these  they  are 
continued  onward  along  the 
course  of  the  superior  hemor- 
rhoidal  vessels  and  open  into 
the  lower  mesocolic  nodes, 
from  which  efferents  pass  to 
the  median  lumbar  nodes 
situated  in  the  neighborhood 
of  the  origin  of  the  inferior 
mesenteric  artery.  The  net- 
work of  the  anal  mucosa  sends 
numerous  branches  upward  to 
communicate  with  the  lower 
part  of  the  rectal  mucosa  net- 
work. These  branches  trav- 
erse for  the  most  part  the 
columns  of  Morgagni  in  which 
they  are  so  numerous  as  to  earn  for  themselves  the  appellation  of  glomi  lymphatici, 
while,  on  the  other  hand,  the  mucosa  of  the  depressions  between  the  columns  is 
comparatively  poor  in  lymphatics.  Some  collecting  stems  from  the  anal  mucosa 
perforate  the  muscular  coat  and  pass  to  the  ano-rectal  nodes,  and  thence  along  with 
the  stems  from  the  rectal  mucosa  to  the  lower  mesocolic  nodes,  while  others  follow 
the  course  of  the  middle  hemorrhoidal  vessels  and  terminate  in  nodes  belonging  to 
the  hypogastric  group  (page  984)  situated  at  the  point  where  the  internal  iliac 
artery  divides  into  its  leash  of  branches,  or  else  at  the  level  of  the  great  sacro-sciatic 
notch,  a  little  below  the  point  where  the  obturator  vein  joins  the  internal  iliac. 

The  lymphatics  of  the  anal  integument  will  be  considered  together  with  those  of 
the  perineal  region  (page  987). 

The  Pancreas. — The  lymphatics  of  the  pancreas  take  their  origin  from  a 
perilobular  net-work  from  which  collecting  stems  pass  to  the  neighboring  nodes, 
following  the  course  of  the  blood-vessels  which  supply  the  gland.  The  great  majority 
of  them  pass  to  the  chain  of  splenic  nodes  which  extends  along  the  upper  border  of 
the  pancreas,  but  those  of  the  head  of  the  gland  pass  in  part  to  nodes  of  the  hepatic 

*Archivf.  Anat.  u.  Physiol.,  1895. 


Net-work  in  anal 

integument 


Lymphatics  of  rectum.    (Gerota.*} 


980 


HUMAN   ANATOMY. 


group,  following  the  course  of  the  superior  pancreatico-duodenal  vessels,  while  others 
again  accompany  the  inferior  pancreatico-duodenal  vessels  to  terminate  in  nodes 
belonging  to  the  mesenteric  group. 

The  Liver. — The  lymphatics  of  the  liver  are  arranged  in  perilobular  net-works 
from  which  stems  pass  in  two  principal  directions  ;  those  which  come  from  the  deeper 
portions  of  the  net-work  follow  the  course  of  either  the  portal  or  hepatic  venous 
branches,  while  those  arising  from  the  net-works  surrounding  the  more  superficial 
lobules  pass  to  the  surface  of  the  liver,  upon  which  they  anastomose  extensively  to 
form  a  subserous  net-work  from  which  efferent  stems  arise. 

The  deep  efferents  which  accompany  the  branches  of  the  portal  vein  take  their 
course  in  the  substance  of  the  capsule  of  Glisson,  two  or  three  stems  accompanying 
each  of  the  larger  branches  of  the  vein  and  anastomosing  with  one  another  to  form 
a  plexus  around  the  vessel  and  the  accompanying  branches  of  the  hepatic  artery  and 
bile-duct.  As  the  branches  of  the  vein  are  followed  to  their  union  to  form  larger 
trunks,  the  accompanying  lymphatics  unite  to  a  considerable  extent,  so  that  from 
fifteen  to  twenty  stems  emerge  at  the  transverse  fissure  and  terminate  in  the  hepatic 

FIG.  822. 


Lymphatics  of  postero-infertor  surface  of  liver,  a,  a,  trunks  arising  from  vicinity  of  right  border  of  liver  and 
going  to  one  of  the  nodes  surrounding  inferior  cava  (C)  as  it  enters  thorax;  6,  trunk  arising  from  inferior  sur- 
face of  right  lobe  and  emptying  at  hilum  into  nodes  resting  on  neck  of  gall-bladder ;  c,  trunks  arising  near  gall- 
bladder and  going  to  lower  hilum-nodes ;  rf,  trunks  running  on  attached  surface  of  gall-bladder;  f,e,e,  trunks 
that  take  origin  from  superficial  net-works  and  disappear  in  liver  to  follow  branches  of  portal  vein  to  hilum- 
nodes ;  f)f,f*  caval  nodes  receiving  vessels  from  Spigelian  lobe  {g)\  A,  A,  principal  trunks  of  left  lobe;  «',  i,  i, 
trunks  that  arise  from  superficial  net-works  and  dip  into  liver  to  join  vessels  in  capsule  of  Glisson  ;  j.  trunks 
from  superior  surface  of  liver  which  follow  round  ligament  to  hilum-nodes;  k,  trunks  from  superior  surface  that 
end  in  nodes  in  posterior  part  of  longitudinal  fissure  (/) ;  »;,  trunks  connecting  these  nodes  with  those  in  hilum; 
n  (14),  nodes  connected  with  terminal  part  of  oesophagus;  o,  o,  o  (15),  hilum  nodes  which  receive  all  trunks 
accompanying  vena  porta  and  large  part  of  those  from  inferior  surface;  p,p,  vessels  from  quadrate  lobe  (q). 


nodes  situated  in  the  fissure.  The  stems  which  accompany  the  branches  of  the 
hepatic  vein  also  form  more  or  less  distinct  plexuses,  and,  when  they  emerge  from 
the  liver  substance,  are  from  five  to  six  in  number.  They  continue  upward  along 
the  inferior  vena  cava,  pass  with  it  through  the  diaphragm,  and  terminate  in  the  nodes 
situated  on  the  convex  surface  of  the  diaphragm  around  the  orifice  for  the  vena  cava. 
The  superficial  vessels  have  more  diversified  courses,  and  it  will  be  coim-im-nt 
to  consider  them  as  belonging  to  two  groups  according  as  they  arise  from  tin- 
superior  or  inferior  surface  of  the  liver.  And  first  those  arising  from  the  net-wot  k 
of  the  superior  surface  may  be  described.  Those  which  arise  toward  the  posterior 
portion  of  the  surface  of  both  the  right  and  left  lobes  pass  mainly  toward  the  vena  rava 
inferior  and  ascend  with  it  through  the  diaphragm  to  terminate  in  the  nodes  situated 

*  Description  et  Irono.^niphie  des  Yaisseaux  lymphatiques,  1874. 


THE  LYMPHATICS  OF  THE  ABDOMEN.          981 

around  the  opening  for  the  vena  cava.  From  the  more  lateral  portions  of  each 
lobe,  however,  the  collecting  stems  take  a  different  course,  those  from  the  right  lobe 
uniting  to  form  a  single  stem  which  passes  backward  between  the  layers  of  the  right 
lateral  (triangular)  ligament,  and  then  passes  medially  over  the  surface  of  the  right 
crus  of  the  diaphragm  to  terminate  in  the  nodes  surrounding  the  cceliac  axis.  Those 
from  the  lateral  portions  of  the  left  lobe  pass  backward  between  the  layers  of 
the  left  lateral  (triangular)  ligament  and  terminate  in  the  nodes  of  the  superior 
gastric  group  which  are  situated  in  the  neighborhood  of  the  cardiac  orifice  of  the 
stomach. 

The  collecting  stems  of  the  anterior  portion  of  the  siiperior  surface  are  relatively 
small  and  are  more  conspicuous  on  the  right  lobe  than  on  the  left.  They  pass 
forward  and  downward  to  curve  around  the  anterior  border  of  the  liver,  and  join  with 
the  stems  arising  from  the  quadrate  lobe  and  gall-bladder  to  pass  with  these  to  the 
hepatic  nodes  situated  in  the  transverse  fissure.  Finally,  much  more  important  than 
these,  is  a  group  of  vessels  which  arise  from  a  rich  subserous  net-work  situated  along 
the  line  of  attachment  of  the  suspensory  (falciform)  ligament.  Some  of  these  vessels 
take  a  backward  course  toward  the  vena  cava  and  accompany  the  other  vessels  of 
the  superior  surface  which  terminate  in  the  caval  diaphragmatic  nodes,  and  others 
pass  forward  until  they  meet  the  upper  portion  of  the  round  ligament,  which  they 
follow  to  reach  the  nodes  situated  in  the  transverse  fissure.  The  remaining  stems  of 
the  group,  from  three  to  ten  in  number,  pass  forward  and  upward,  between  the  layers 
of  the  suspensory  ligament,  toward  the  under  surface  of  the  diaphragm,  traverse 
that  structure  near  its  anterior  attachment,  and  come  into  connection  with  a 
number  of  small  nodes  situated  behind  the  xiphoid  process  of  the  sternum.  From 
these  they  are  continued  upward  along  the  course  of  the  internal  mammary  vessels 
to  terminate  in  the  lower  nodes  of  the  inferior  deep  cervical  group,  usually  upon  the 
left  side,  rarely  upon  the  right.  This  path  is  of  importance  as  furnishing  a  direct  route 
by  which  the  metastasis  of  the  left  supraclavicular  nodes,  frequently  induced  by 
abdominal  carcinomata,  may  be  produced.  It  must,  furthermore,  be  noted  that 
both  these  vessels  and  others  which  arise  from  the  superior  surface  of  the  liver  com- 
municate somewhat  extensively  with  the  net-work  occurring  on  the  under  surface  of 
the  diaphragm,  and  since  this  net-work  communicates  abundantly  with  that  of  the 
thoracic  surface  of  the  diaphragm,  and  this  again  with  the  vessels  of  the  pleurae, 
opportunity  is  afforded  for  the  development  of  pleuritis,  especially  upon  the  right 
side,  as  a  result  of  a  subdiaphragmatic  infection. 

Turning  now  to  the  stems  arising  from  the  superficial  net-work  of  the  inferior 
surface  of  the  liver,  it  will  be  found  that  they  pass  principally  to  the  hepatic  nodes 
situated  in  the  transverse  fissure,  at  least  these  nodes  form  the  termination  for  the 
vessels  passing  from  the  left  and  quadrate  lobes,  the  left  half  of  the  Spigelian  and 
the  anterior  and  middle  portions  of  the  right  lobe.  Those,  however,  which  take 
their  origin  toward  the  posterior  part  of  the  right  lobe  and  from  the  right  half  of 
the  Spigelian  pass  to  the  vena  cava  and,  ascending  along  it,  terminate  in  the  dia- 
phragmatic nodes  surrounding  its  opening  into  the  thorax. 

The  lymphatics  of  the  gall-bladder  and  common  bile-duct  have  their  origin 
in  two  net-works,  one  of  which  is  situated  in  the  mucosa  and  the  other  in  the  muscular 
coat.  Efferents  from  both  net-works  pass  to  the  surface  to  form  a  superficial 
net-work,  from  which  collecting  stems  pass,  in  the  case  of  the  gall-bladder  to  the 
nodes  situated  in  the  transverse  fissure,  and  in  the  case  of  the  duct  for  the  most 
part  to  a  chain  of  nodes  belonging  to  the  hepatic  group,  which  occurs  along  the  line 
of  the  duct  in  the  edge  of  the  gastro-hepatic  omentum  ;  those  from  the  lower  portion 
of  the  duct,  however,  associate  themselves  with  stems  from  the  duodenum  and  head 
of  the  pancreas  which  open  into  the  uppermost  nodes  situated  along  the  course  of 
the  superior  pancreatico-duodenal  vessels. 

Stated  in  brief,  the  destinations  of  the  hepatic  lymphatics  are  principally  the 
hepatic  nodes  situated  in  the  transverse  fissure  and  the  diaphragmatic  nodes  which 
surround  the  opening  of  the  inferior  vena  cava.  A  vessel  from  the  right  lobe  also 
passes  to  the  cceliac  nodes,  some  from  the  left  lobe  to  the  superior  gastric  nodes, 
and  an  important  group  passes  up  in  the  suspensory  ligament  to  communicate  with 
some  of  the  anterior  diaphragmatic  nodes  and  terminate  in  the  lower  inferior  deep 


982 


HUMAN   ANATOMY. 


cervical  nodes.  Finally,  it  is  to  be  remembered  that  numerous  communications 
exist  between  the  superficial  hepatic  lymphatics  and  those  which  form  the  net-work 
on  the  abdominal  surface  of  the  diaphragm. 

The  Spleen. — The  lymphatics  of  the  spleen  are  arranged  in  a  superficial  and 
a  deep  set,  numerous  communications  occurring  between  the  two.  The  vessels 
of  the  superficial  set  are  subserous  in  position  and  converge  toward  the  hilus  to 
terminate  in  the  adjacent  pancreatico-splenic  nodes,  to  which  the  deep  lymphatics, 
which  accompany  the  blood-vessels  of  the  spleen,  also  pass. 

The  Kidneys  and  Ureters. — The  lymphatics  of  the  kidney  form  three  net- 
works, one  of  which  is  situated  in  the  cortical  tissue  of  the  kidney,  the  second,  whose 
meshes  are  very  fine,  is  situated  immediately  beneath  the  fibrous  capsule,  while  the 
third  occurs  beneath  the  peritoneum  in  the  superficial  portions  of  the  adipose  capsule. 
The  efferents  of  the  cortical  net-work  follow  the  branches  of  the  renal  vessels 
through  the  medullary  substance  and  emerge  at  the  hilus  in  the  form  of  from  four  to 

seven  vessels,  which  pass 

FIG.  823.  j^  J^  toward  the  median  line  of 

the  posterior  abdominal 
wall  along  the  course  of 
the  renal  veins,  and  termi- 
nate in  the  upper  nodes  of 
the  lateral  lumbar  groups 
(Fig.  823).  Those  which 
come  from  the  right  kid- 
ney terminate  partly  in 
nodes  which  lie  in  front 
of  the  inferior  vena  cava, 
and  partly  in  two  or  three 
large  nodes  which  are 
situated  behind  that  vessel 
upon  the  right  crus  of  the 
diaphragm.  The  efferents 
from  these  nodes  pierce 
the  crus  and  terminate 
directly  in  the  thoracic 
duct.  The  uppermost 
nodes  to  which  the  vessels 
of  the  left  kidney  pass 
are  situated  upon  the  left 
crus  of  the  diaphragm  and 
their  efferents  also  pierce 
the  crus  to  open  into 
the  thoracic  duct  ;  the  efferents  from  the  remaining  nodes  concerned  unite  with 
those  of  the  other  lateral  lumbar  nodes  to  form  the  lumbar  trunks  which  open 
into  the  receptaculum  chyli. 

The  net-work  which  lies  beneath  the  fibrous  capsule  communicates  with  both  the 
cortical  and  subserous  net-works,  and  its  drainage  is  probably  mainly  through  these  : 
a  few  stems,  however,  pass  toward  the  hilus,  beneath  the  capsule,  and  unite  with 
the  terminal  efferents  from  the  cortical  net- work,  there  being  no  direct  connection 
between  the  net-work  and  the  lumbar  nodes.  The  case  is  different  with  the  subserous 
net-work,  its  efferents  passing  to  the  upper  lateral  lumbar  nodes  quite  independently 
of  the  cortical  efferents.  As  already  noted,  it  has  abundant  communication  with 
the  net-work  beneath  the  fibrous  capsule,  and  through  this  with  the  cortical 
net-work,  so  that  infections  of  the  kidney  tissue  are  readily  communicated  to  the 
adipose  capsule. 

The  lymphatic  net-works  of  the  ureters  appear  to  be  limited  to  the  muscular 
coat  and  the  surface  of  the  ducts  (Sakata).  The  efferents  which  arise  from  the 
upper  portions  of  the  net-works,  that  is  to  say  from  the  portions  above  the  level  at 


Ovary 


Lymphatics  of  kidneys  and  of  ovary,  new-born  child.     (Stahr.*) 


*Archivf.  Anal.  u.  Physiol.,  1900. 


THE    LYMPHATICS    OF   THE    PELVIS. 


983 


FIG.   824. 


which  the  ureter  is  crossed  by  the  spermatic  (ovarian)  artery,  pass  upward  to  unite 

with  the  renal   efferents  or  occasionally  to  terminate  directly  in  the  upper   lateral 

lumbar  nodes  (Fig.  824).     The  majority 

of  the  efferents  arise  from  those  portions  of 

the  ducts  intervening  between  the  crossing 

of  the  spermatic    (ovarian)    arteries   and 

the  level   at  which   the  ureters  cross  the 

common  iliac  vessels  to  enter  the  pelvis, 

and  these  vessels  pass  either  to  the  lower 

lateral  lumbar  nodes,  or  else,  in  the  case 

of    the    lower    ones,    to   the    upper   iliac 

nodes.      Finally,    the    efferents    from    the 

pelvic  portions  of  the  ureters  either  unite 

with  the  vessels  passing  from  the  bladder, 

or  else  communicate  directly  with  certain 

of  the  hypogastric  nodes. 

In  and  beneath  the  fibrous  capsule 
of  the  suprarenal  bodies  a  lymphatic 
net-work  occurs,  whose  efferents  on  the 
one  hand  join  the  renal  lymphatics,  and 
on  the  other  pass  into  the  substance  of 
the  organs  to  communicate  with  a  net- 
work situated  in  the  glomerular  portion 
of  the  cortex.  From  this  latter  net-work 
stems  pass  centrally  in  the  partitions 
between  the  cell  columns  of  the  cortex  to 
unite  with  a  rich  plexus  which  traverses 
all  portions  of  the  medullary  substance. 
The  main  stems  of  this  plexus  follow  the 
course  of  the  suprarenal  blood-vessels  and 
emerge  at  the  hilus  of  the  organ  as  four 
or  five  stems,  which  pass  to  the  upper 
lateral  lumbar  nodes.  Some  of  the  stems  are  also  said  to  pierce  the  crura  of  the 
diaphragm  and  terminate  in  the  lower  nodes  of  the  posterior  mediastinal  group. 

THE    LYMPHATICS    OF   THE    PELVIS. 
THE  LYMPH-NODES. 

The  pelvic  lymphatic  nodes  are  arranged  along  the  courses  of  the  principal 
vessels,  and  may  conveniently  be  divided  into  three  groups,  the  iliac,  the  hypogastric, 
and  the  sacral  nodes.  In  addition  some  small  inconstant  nodes  occur  in  association 
with  the  bladder  and  these  will  be  described  in  connection  with  the  vessels  arising 
from  that  organ  (page  985).  The  epigastric  and  circumflex  iliac  nodes,  already 
described  in  connection  with  the  abdominal  region  (page  972),  are  really  outliers 
of  the  iliac  group. 

The  iliac  nodes  (Fig.  825)  are  from  fifteen  to  twenty  in  number  and  form  a 
plexus  (plexus  iliacus  externus)  along  the  course  of  the  common  and  external  iliac 
vessels,  the  uppermost  nodes  lying  at  the  level  of  the  bifurcation  of  the  aorta  and 
the  lowermost  around  the  point  of  exit  of  the  external  iliac  vessels  beneath  Poupart's 
ligament.  Three  more  or  less  distinct  linear  series  of  nodes  can  be  recognized  in 
the  plexus,  one  of  which,  along  the  course  of  the  common  iliac  artery,  is  situated 
close  to  the  outer  surface  of  the  artery  and  along  the  medial  border  of  the  psoas  muscle. 
The  second  lies  behind  the  artery,  resting  upon  the  anterior  surface  of  the  vein,  while 
the  third  unites  with  its  fellow  of  the  opposite  side  to  form  a  group  of  three  or  four 
nodes  resting  upon  the  left  common  iliac  vein  and  the  promontory  of  the  sacrum 
in  the  angle  formed  by  the  bifurcation  of  the  aorta.  Of  the  series  along  the  line  of 
the  external  iliac  vessels  one  lies  to  the  outer  side  of  the  artery  along  the  medial 


Lymphatics  of  ureters.     (Based  on  several  figures 
by  SaAala.*) 


*Archivf.  Anatotn.  u.  Physiol.,  1903. 


984 


HUMAN   ANATOMY. 


border  of  the  psoas,  the  second  in  the  angle  between  the  vein  and  the  artery,  and 
the  third  along  the  lower  border  of  the  vein,  between  it  and  the  obturator  nerve. 

The  various  nodes  of  the  iliac  set  communicate  with  one  another  so  that  the 
efferent*  of  one  node  are  afferents  for  the  higher  ones.  In  addition  they  receive 
ajferents  from  the  inguinal  nodes  as  well  as  from  the  epigastric  and  circumflex  iliac 
nodes  as  already  stated,  and  the  group  situated  over  the  promontory  of  the  sacrum 
also  receives  afferents  from  both  the  hypogastric  and  sacral  nodes.  Furthermore, 
afferents  pass  to  the  iliac  nodes  from  the  pelvic  portions  of  the  ureters,  from  the 
bladder  and  prostate  gland,  from  the  lower  portion  of  the  uterus  and  the  upper 
portion  of  the  vagina,  from  the  glans  penis  and  clitoris,  from  the  adductor  muscles 
of  the  thigh  through  vessels  accompanying  the  obturator  artery,  and,  in  the  case  of 
the  lateral  series  of  nodes,  from  the  psoas  muscle  and  the  adjacent  subserous  tissue. 
The  efferents  pass  to  the  lower  lateral  lumbar  nodes. 

The  internal  iliac  or  hypogastric  nodes  (lymphoglandulae  hypogastricae)  are 
from  nine  to  twelve  in  number  on  each  side,  and  are  situated  on  the  lateral  walls 
of  the  pelvic  cavity,  along  the  course  of  the  internal  iliac  vessel  and  its  branches 

FIG.  825. 


Lower 

lumbar  node 


Iliac  nodes 


Iliac  node  of 

promontory  group 


Superficial 

inguinal  nodes 


Iliac  nodes.     (Cun'eo  and  Marcille.*) 


(Fig.  825).  They  are  connected  together  to  form  a  plexus  (plexus  hypogastricus), 
and  receive  afferents  from  most  of  the  regions  to  which  the  branches  of  the  internal 
iliac  artery  are  distributed.  Thus  branches  come  to  them  from  all  the  pelvic  organs, 
from  the  deeper  portions  of  the  perineum,  including  the  penial  portion  of  the  urethra, 
from  the  deep  portions  of  the  posterior  and  internal  femoral  and  the  gluteal  regions. 
Their  efferents  pass  mainly  to  the  iliac  nodes  situated  on  the  promontory  of  the 
sacrum,  those  which  arise  from  the  obturator  node,  situated  upon  the  obturator  artery 
as  it  passes  through  the  obturator  foramen,  passing,  however,  to  nodes  belonging  to 
the  inner  series  of  the  group  accompanying  the  external  iliac  vessels. 

The  sacral  nodes  are  situated  on  the  ventral  surface  of  the  sacrum,  partly 
along  the  course  of  the  middle  sacral  vessels,  and  partly  internal  to  the  second  and 
third  anterior  sacral  foramina,  along  the  course  of  the  lateral  sacral  arteries  (Fig.  829). 
All  the  nodes  are  small  and  they  are  united  together  by  lymphatic  vessels  to  form  a 
sacral  plexus  (plexus  sacralis  medius).  They  receive  ajferents  from  the  neighboring 
muscles  and  from  the  sacrum,  and  their  efferents  pass  to  the  iliac  nodes  situated 
upon  the  promontory  of  the  sacrum. 

THE  LYMPHATIC  VESSELS. 

Under  this  heading  will  be  considered  the  vessels  of  the  various  pelvic  organs, 
with  the  exception  of  those  of  the  rectum,  which  have  already  been  described 
(page  979).  In  addition  there  will  be  included  the  vessels  of  the  external  genitalia, 


*Bull.  et  M£m.  Societe*  anatom.,  1901. 


THE    LYMPHATICS   OF   THE    PELVIS. 


985 


FIG.   826. 


Obliterated  hypogastric 


and,  on  account  of  their  intimate  relation  with  these,  the  superficial  lymphatics  of 
the  perineal  and  circumanal  regions. 

The  Bladder. — It  was  for  a  long  time  a  matter  for  discussion  whether  or  not 
the  mucosa  of  the  bladder  was  provided  with  a  lymphatic  net-work,  but  the  general 
consensus  of  recent  observers  is  that  it  is  not.  Only  the  muscular  coat  possesses  a 
net-work,  and  from  this  stems  pass  to  the  surface  of  the  viscus  to  form  a  superficial 
net-work  beneath  the  peritoneal  or  fascial  investment.  This  net-work  is  continuous 
at  the  neck  of  the  bladder  with  those  of  the  urethra  and  prostate  gland,  and,  at  its 
base,  with  the  net-works  of  the  ureters  and  seminal  vesicles,  and,  in  the  female,  of  the 
vagina.  The  efferent  stems  which  take  origin  from  it  may  be  divided  into  two 
groups  according  as  they  arise  upon  the  anterior  or  posterior  surface. 

Those  passing  from  the  lower  part  of  the  anterior  surface  are  directed  laterally 
and  those  from  the  upper  part  pursue  a  flexuous  course  downward  and  laterally  to 
terminate  in  the  nodes  of  the  iliac  group  situated  along  the  external  iliac  vessels 
(Fig.  826).  In  their  course  they  usually  traverse  some  small  nodes  .situated  in 
close  proximity  to  the  bladder 
and  divisible  according  to  their 
position  into  two  groups.  One 
of  these  is  situated  upon  the 
anterior  surface  of  the  bladder, 
and  consists  of  two  or  three 
nodes,  the  anterior  vesical 
nodes,  two  of  which  are  usually 
situated  near  the  apex  of  the  vis- 
cus in  the  course  of  the  superior 
vesical  artery,  while  the  third 
occurs  lower  down  in  the  retro- 
pubic  tissue.  The  other  group 
consists  of  from  two  to  four 
nodes,  the  lateral  vesical 
nodes,  situated  on  either  side 
of  the  bladder  along  the  course 
of  the  obliterated  hypogastric 
arteries.  Both  groups  are  some- 
what inconstant,  but  occur  in  a 
large  percentage  of  cases. 

The  vessels  from  the  upper 
part  of  the  posterior  surface  of 
the  bladder  pass  downward  and 
laterally,  often  traversing  some 
of  the  lateral  vesical  nodes,  and  terminate  in  the  external  iliac  nodes  which  receive 
the  stems  from  the  anterior  surface.  Others  pass  to  the  hypogastric  nodes,  while 
others  again,  arising  from  the  base  of  the  bladder,  pass  at  first  directly  backward 
past  the  lateral  surfaces  of  the  rectum  and  then  ascend  on  the  sacrum  to  terminate 
in  the  iliac  nodes  situated  upon  the  promontory. 

The  Prostate  Gland. — The  lymphatics  of  the  prostate  have  their  origin  in 
net-works  surrounding  the  various  acini  of  the  gland.  From  these  net-works  stems 
pass  to  the  surface,  where  they  form  a  second  net-work,  and  from  this  the  efferent 
stems  pass  symmetrically  on  either  side  of  the  median  line  to  somewhat  diverse 
terminations.  One  or  two  of  the  efferents  on  either  side  ascend  in  a  tortuous  course 
upon  the  posterior  surface  of  the  bladder,  and  then  bend  laterally  over  the  obliterated 
hypogastric  arteries  to  terminate  in  one  of  the  middle  series  of  the  iliac  nodes 
which  accompany  the  external  iliac  vessels.  Another  stem  passes  backward  along 
the  prostatic  vessels  to  terminate  in  one  of  the  hypogastric  nodes  ;  others  pass  at  first 
backward  on  either  side  of  the  rectum,  and  then  ascend  upon  the  anterior  surface 
of  the  sacrum  to  terminate  in  the  lateral  sacral  nodes  or  in  the  iliac  nodes  situated 
on  the  promontory  of  the  sacrum  ;  and  from  the  anterior  surface  of  the  gland  a  stem 


Anterior  vesical  node 


Subhypogastric 
node 


Anterior 

vesical  node 


Lymph-nodes  of  bladder.     (Based  on  figures  of  Gerota.*) 


*Archiv  f.  Anatom.  u.  Physiol.,  1897. 


986 


HUMAN    ANATOMY. 


passes  downward  on  either  side  of  the  membranous  portion  of  the  urethra,  and, 
accompanying  the  urethral  lymphatics  along  the  course  of  the  internal  pudic  vessels, 
terminates  in  one  of  the  hypogastric  nodes  situated  upon  these  vessels. 

The  Urethra. — The  mucous  membrane  of  the  male  urethra  is  furnished 
throughout  its  entire  extent  with  a  lymphatic  net-work,  which  is  especially  rich  in 
the  region  of  the  glans  and  diminishes  in  complexity  in  the  membranous  and 
prostatic  portions  of  the  duct.  In  the  last  region  it  communicates  with  the  net-work 
in  the  muscular  coat  of  the  neck  of  the  bladder.  The  efferents  from  the  membranous 
portion  of  the  duct  associate  themselves  with  some  of  the  prostatic  efferents  and  pass 
to  a  hypogastric  node  situated  on  the  course  of  the  internal  pudic  vessels,  and  those 
from  the  penial  portion  accompany  the  vessels  which  arise  from  the  glans  and  will 
be  described  in  the  account  of  the  lymphatics  of  the  penis.  The  net-work  of  the 
female  urethra  corresponds  with  those  of  the  membranous  and  prostatic  portions  of 
the  male  duct. 

The  External  Reproductive  Organs  in  the  Male. — The  lymphatics  of  the 
scrotum  form  an  exceedingly  rich  net-work,  especially  well  developed  in  the  vicinity 
of  the  raphe  and  thence  extending  laterally  over  the  entire  surface.  From  six  to 

eight    stems    arise    from 

FlG-   827-  this    net-work,    and    the 

uppermost  accompany 
and  eventually  anasto- 
mose with  the  superhcial 
efferents  from  the  penis 
and  terminate  in  the  in- 
ner inguinal  nodes.  The 
remaining  stems  pass 
upward  and  outward  to 
terminate  in  the  inner 
superficial  subinguinal 
nodes. 

The  lymphatics  of 
the  penis  are  divisible 
into  a  superficial  and  a 
deep  set  which  correspond 
respectively  to  the  super- 
ficial and  deep  blood- 
vessels of  the  organ.  The 
superficial  set  forms  a 
net-work  in  the  integu- 
ment of  the  penis  which 
radiates  in  all  directions 
from  the  frenulum,  some 
stems  passing  forward  and 
upward  into  the  prepuce  and  some  especially  strong  stems  passing  dorsally  in  the 
furrow  behind  the  corona  of  the  glans.  As  they  approach  the  dorsal  mid-line  these 
latter  give  off  one  or  two  longitudinally  directed  efferents,  or  else  they  unite  to  form 
a  single  stem  which  runs  along  the  dorsal  mid-line.  Other  stems  arising  from  the 
more  proximal  portions  of  the  net-work  curve  upward  from  below  over  the  lateral 
surfaces  of  the  penis,  and  either  unite  with  the  dorsal  stems  or  form  independent 
lateral  stems  parallel  with  the  dorsal  ones.  Numerous  anastomoses  occur  between 
all  the  longitudinal  stems  throughout  their  courses,  and,  as  they  approach  the 
symphysis,  they  bend  laterally,  some  indeed  dividing  to  send  branches  to  either 
side,  and,  after  the  upper  stems  from  the  scrotum  have  united  with  them,  tiny 
terminate  in  the  inner  inguinal  nodes. 

The  deep  set  forms  a  net-work  especially  well  developed  in  tin-  glans,  in  which 
a  superficial  and  a  deep  layer  may  be  distinguished.  Both  these  layers  communicate 
at  the  meatus  with  the  urethral  net-work,  and  from  the  deeper  layer  a  special  plexus 


Superficial  lymphatic  vessels  of  penis  and  scrotum  and  inguinal 
nodes.     (Bruhns.*) 


*  Archiv  f.  Anat.  u.  Physiol.,  1900. 


THE    LYMPHATICS    OF   THE    PELVIS.  987 

is  developed  on  either  side  of  the  frenulum  (Panizzd1 s  plexus},  from  which  stems 
ascend  in  the  groove  back  of  the  corona  glandis.  Into  these  stems  the  superficial 
layer  of  the  net-work  opens,  and  they  also  receive  communications  from  the  super- 
ficial vessels  of  the  penis.  From  them  one  or  two  stems  arise  which  pass  proximally 
in  company  with  the  dorsal  vein  of  the  penis  toward  the  suspensory  ligament.  Here 
they  usually  divide  to  form  a  more  or  less  distinct  plexus,  lying  immediately  over 
the  symphysis  pubis  and  provided  with  some  small  lymphatic  nodes,  and  from  it  two 
or  three  stems  pass  off  laterally  on  either  side.  These  pass  across  the  surface  of  the 
pectineus  muscle  and  beneath  the  spermatic  cord,  and  some  then  pass  either  to  the 
inner  inguinal  or  deep  subinguinal  glands,  while  others  extend  along  Poupart's 
ligament  to  the  external  abdominal  ring  and,  traversing  the  inguinal  canal,  terminate 
in  one  of  the  lower  iliac  nodes. 

It  is  to  be  noted  that  owing  to  the  anastomoses  and  bifurcations  of  both  the 
superficial  and  deep  longitudinal  stems  it  is  possible  that  a  unilateral  infection  may 
cause  enlargment  of  the  nodes  of  both  sides. 

The  External  Reproductive  Organs  in  the  Female. — The  lymphatics  of 
the  external  female  genitalia  have  essentially  the  same  distribution  as  those  of  the 
corresponding  organs  in  the  male.  In  both  the  labia  majora  and  minora  rich 
subcutaneous  net-works  occur,  from  which  numerous  stems  arise  and  pass  to  the  inner- 
most inguinal  and  occasionally  the  inner  superficial  subinguinal  nodes.  The  stems 
from  the  upper  parts  of  the  labia  ascend  at  first  directly  upward  toward  the  mons 
veneris  and  then  bend  suddenly  outward  to  reach  their  terminal  nodes  ;  those  from 
the  lower  parts  pass  either  directly  upward  and  outward  or  else  at  first  directly 
upward  parallel  to  the  outer  edges  of  the  labia  and  then  bend  suddenly  outward. 
Some  of  the  stems  coming  from  one  or  other  of  the  labia  may  pass  to  the  nodes  of 
the  opposite  side,  and,  furthermore,  communications  exist  through  the  anterior  and 
posterior  commissures  between  the  net- works  of  the  opposite  labia,  so  that  a  unilateral 
infection  may  produce  enlargement  of  the  inguinal  nodes  on  both  sides. 

The  lymphatics  of  the  clitoris  present  essentially  the  same  arrangement  as  the 
deep  lymphatics  of  the  penis.  They  form  a  rich  net- work  in  the  glans  and  from  this 
longitudinal  stems  arise  and  pass  toward  the  symphysis  pubis,  in  front  of  which  they 
form  a  plexus  which  usually  contains  some  small  nodes.  From  the  plexus  stems 
arise  which  pass  laterally,  and  terminate  either  in  one  of  the  deep  subinguinal  nodes 
or  else  in  the  lower  iliac  nodes,  which  they  reach  by  traversing  the  inguinal  canal. 

The  Perineum  and  Circumanal  Regions. — The  deeper  lymphatics  of  these 
regions  have  been  considered  in  connection  with  the  organs  to  which  they  belong 
and  there  remain  for  consideration  only  the  subcutaneous  vessels.  These  in  the 
perineal  region  form  an  abundant  net- work  from  which  stems  pass  forward,  for  the 
most  part  in  the  furrow  between  the  perineum  and  the  inner  surface  of  the  thigh, 
and,  associating  themselves  with  the  stems  from  the  scrotum  or  labia  majora, 
terminate  in  the  inner  inguinal  or  superficial  subinguinal  nodes. 

The  subcutaneous  lymphatics  which  surround  the  anal  opening  also  form  a  rich 
net-work,  which  communicates  extensively  with  that  of  the  anal  mucosa  (page  979). 
From  it  some  two  or  three  stems  pass  forward  along  the  inner  side  of  the  thigh  to 
terminate  with  the  perineal  and  scrotal  (labial)  stems  in  the  inner  inguinal  nodes. 

The  Internal  Reproductive  Organs  in  the  Male. — Thetestis  possesses  an 
abundant  supply  of  lymphatics,  which  may  be  divided  into  a  deep  and  a  superficial  set. 
The  former  takes  its  origin  in  a  rich  net-work  which  surrounds  the  seminal  ducts,  and 
the  stems  which  compose  it  pass  toward  the  hilum  in  the  septa,  and,  issuing,  associate 
themselves  with  the  stems  arising  from  the  superficial  net-work.  This  is  double,  one 
layer  of  it  lying  beneath  the  tunica  albuginea  and  the  other  between  that  investment 
and  the  visceral  layer  of  the  tunica  vaginalis.  Both  layers  are  abundantly  connected  by 
vessels  which  traverse  the  tunica  albuginea,  and  the  deeper  layer  also  receives  numer- 
ous communicating  stems  from  the  deep  lymphatics  and  from  the  lymphatics  of  the 
epididymis.  Collecting  stems  from  both  layers  converge  toward  the  hilum,  where  they 
become  associated  with  the  stems  from  the  deep  net-work,  from  six  to  eight  or  rarely 
more  trunks  which  ascend  along  the  spermatic  cord  to  the  internal  abdominal  ring. 
They  then  follow  the  course  of  the  spermatic  veins  upward,  and  terminate  in  from  two 
to  four  of  the  lateral  lumbar  nodes  (Fig.  816).  The  nodes  to  which  the  vessels  from 


988 


HUMAN    ANATOMY. 


the  left  testis  pass  lie  immediately  beneath  the  level  of  the  renal  veins,  while  those 
in  which  the  stems  from  the  right  testis  terminate  are  lower,  being  situated  about 
midway  between  the  level  of  the  renal  vein  and  the  junction  of  the  common  iliac  veins. 

The  lymphatics  of  the  vas  deferens  are  probably  arranged  in  two  net-works, 
one  belonging  to  the  mucosa  and  the  other  to  the  muscular  coat,  although  so  far  only 
the  latter  net-work  has  been  demonstrated.  At  the  testicular  end  of  the  duct  the 
net-work  communicates  with  that  of  the  epididymis,  and  the  stems  which  arise  from 
it  accompany  those  of  the  testis  to  the  lateral  lumbar  nodes.  At  the  vesical  end 
the  net-work  communicates  with  that  of  the  seminal  vesicles  and  its  efferents  pass 
to  one  of  the  hypogastric  nodes. 

The  lymphatics  of  the  seminal  vesicles  are  much  more  readily  demonstrable 
than  those  of  the  vasa  deferentia.  They  arise  from  two  net-works,  one  of  which  is 
situated  in  the  mucosa  and  the  other  in  the  muscularis.  Stems  from  the  latter  form 
a  third  net-work  over  the  surfaces  of  the  vesicles  and  from  this  efferents,  two  or  three 
in  number,  pass  to  some  of  the  hypogastric  nodes. 

The  Internal  Reproductive  Organs  in  the  Female. — The  lymphatics  of 
the  ovary  are  very  abundant  throughout  the  substance  of  the  organ,  a  fine  net- work 


Lateral  lumbar  node 


Lymphatic  vessels  from 
fundus  of  uterus 


Iliac  node 

Lymphatic 

vessels  from  body  and 
cervix  of  uterus 


Ureter 


Lymphatic  vessels 
from  ovary  and 
upper  part  of  uterus 


Ovary 
Fallopian  tube 


Bladder 


Lymphatics  of  internal  reproductive  organs  of  female.     (Poirier.*) 

surrounding  each  of  the  Graafian  follicles.  The  stems  which  arise  from  these  net- 
works converge  toward  the  hilus,  where  they  form  a  rich  plexus  and  from  this  from 
six  to  eight  efferents  arise  and  follow  the  ovarian  blood-vessels  to  terminate  in  the 
lateral  lumbar  nodes  (Fig.  828). 

Owing  to  thinness  of  the  walls  it  is  difficult  to  distinguish  a  definitely  layered 
arrangement  of  the  lymphatic  net-work  of  the  Fallopian  tubes.  It  is,  however, 
rich,  and  communicates  with  that  of  the  fundus  of  the  uterus.  It  gives  rise-  to  two  or 
three  efferents  which  accompany  the  ovarian  efferents  to  the  lateral  lumbar  nodes. 


*Progrds  Medical,  1890. 


THE    LYMPHATICS    OF   THE    PELVIS. 


989 


In  the  uterus  (Figs.  828,  829)  the  conditions  are  much  more  favorable  for 
determining  the  existence  of  separate  net-works  in  the  mucosa  and  muscularis  than 
in  the  Fallopian  tubes,  but,  nevertheless,  much  difference  of  opinion  exists  as  to  the 
occurrence  of  a  mucosa  net-work.  That  of  the  muscularis  can  be  injected  without 
difficulty,  but  no  conclusive  injections  have  yet  been  made  of  the  mucosa,  and  while 
some  authors  (Bruhns,  Sappey,  Poirier)  are  inclined  to  admit  the  existence  of  a 
net-work  in  it,  others  (Leopold)  deny  it.  However  that  may  be,  a  well-developed 
net-work  occurs  in  the  muscular  coat,  in  the  deeper  portions  of  which  it  becomes 
especially  rich,  and,  furthermore,  it  is  more  abundant  in  the  cervix  than  in  the  body 
or  fundus.  From  it  stems  pass  to  the  surface  of  the  organ  to  form  a  subserous 
net-work,  from  which  a  number  of  efferents  arise. 

These  may  be  divided  into  three  principal  groups  according  to  their  termina- 
tions. ( I )  The  efferents  from  the  fundus,  usually  two  in  number,  pass  outward  on 
either  side  in  the  upper  portion  of  the  broad  ligament,  and,  associating  themselves 
with  the  efferents  from  the  ovary,  terminate  in  the  lateral  lumbar  nodes.  (2)  Small 
stems  pass  from  the  fundus  along  the  round  ligament  of  the  uterus  to  terminate  in  the 


FIG.   829. 


1Hyi>ogastric 
nodes 


inguinal  nodes.  (3)  The 
efferents  from  the  body 
and  cervix  pass  laterally 
to  terminate  in  the  median 
iliac  nodes  situated  in  the 
angle  between  the  external 
and  internal  iliac  arteries. 
In  the  course  of  these  last 
vessels,  at  the  point  where 
they  cross  the  ureter,  a 
small  titero-vaginal  node 
is  occasionally  placed. 

Other  efferents  have 
been  described  as  passing 
from  the  cervix  to  a  hypo- 
gastric  node  situated  at 
the  origin  of  the  uterine  or 
vaginal  artery,  and  two  or 
three  stems  have  been 
found  arising  from  the 
posterior  surface  of  the 
cervix  and  passing  back- 
ward on  either  side  of 
the  rectum  to  the  anterior 
surface  of  the  sacrum, 
up  which  they  pass  to 
terminate  in  the  iliac  nodes  situated  upon  the  sacral  promontory  (Fig.  829). 

In  the  vagina  there  is  no  question  as  to  the  existence  of  definite  net-works  in 
both  the  mucosa  and  muscularis.  That  of  the  mucosa  (Fig.  830)  is  exceptionally 
fine  and  communicates  abundantly  with  the  coarser  net-work  of  the  muscularis,  as 
well  as  with  the  net- work  of  the  vaginal  portion  of  the  cervix  above  and  with  that  of 
the  labia  minora  below.  From  the  muscularis  net-work  stems  pass  to  the  surface 
of  the  organ  to  form  a  third  net-work,  from  which  the  main  efferent  stems  arise, 
and  these  may  be  arranged  in  three  groups  according  to  their  destinations:  (i) 
those  which  arise  from  the  upper  portion  of  the  vagina  join  the  stems  which  pass 
from  .the  cervix  of  the  uterus  (Fig.  830)  and  terminate  with  these  in  the  median 
iliac  nodes  situated  in  the  angle  formed  by  the  external  and  internal  iliac  arteries  ; 
(2)  those  arising  from  the  middle  portion  accompany  the  vaginal  vessels,  passing 
obliquely  upward,  outward,  and  backward,  to  terminate  in  one  or  two  hypogastric 
nodes  situated  at  the  origin  of  the  uterine  arteries  ;  and  (3)  those  from  the  lower 
portion  associate  themselves  with  those  from  the  labia  minora  and  terminate  with  these 


Lymphatics  of  uterus.     (Cuneo  and  Marcille.*) 


*Bull.  et  Mem.  Societ^  anatom.,  1902. 


990 


HUMAN    ANATOMY. 


Efferent! 

from  infe- 
rior group 


Lymphatic  net-work  of  vaginal  mucous  membrane.     (Poirier.*) 


in  the  inner  inguinal  nodes.    Certain  of  the  stems  from  the  middle  portion  also  pass  to 
the  same  middle  iliac  nodes  which  receive  the  efferents  from  the  upper  portion,  and 

stems    have    been    observed 

FIG.  830.  (Bruhns)    passing  from  the 

posterior  surface  of  the  vagi- 
na to  the  lateral  lumbar  nodes 
and  even  to  the  iliac  nodes 
situated  on  the  promontory 
of  the  sacrum,  while  others 
have  been  traced  to  the 
anorectal  nodes  (page  976). 
Finally,  it  may  be  noted 
that  the  superficial  net-work 
of  the  anterior  surface  of  the 
vagina  communicates  with 
that  of  the  posterior  surface 
of  the  bladder. 

Practical  Considera- 
tions.—  The  Lymph-Nodes 
of  the  Abdomen  and  PC  Iris. 
— The  superficial  lymphatics 
of  the  wall  of  the  abdomen 
convey  infection,  if  the  pri- 
mary focus  is  above  the  level 
of  the  umbilicus,  to  the  axil- 
lary nodes  ;  if  it  is  below  that 
level,  to  the  inguinal  nodes. 
Hence,  in  cases  of  furuncle  or  carbuncle,  or  of  chancre,  or  of  epithelioma,  the  site 
of  the  lesion  would  determine  the  region  in  which  adenopathy  should  be  sought. 
The  cceliac  groitp  of  nodes  may  be  involved  in  diseases  of  the  greater  portion  of 
the  digestive  tract,  or  of  the  stomach,  spleen,  or  part  of  the  liver  ;  or  their  enlarge- 
ment may  follow  that  of  the  lumbar  or  of  the  mesenteric  nodes.  The  nodes  in  and 
about  the  portal  fissure,  or  between  the  layers  of  the  gastro-hepatic  omentum  may  so 
enlarge  in  cases  of  carcinoma  of  the  stomach  or  of  the  liver  as  to  compress  the  portal 
vein  (causing  ascites)  or  the  common  bile  duct  (causing  jaundice). 

The  lymphatic  relations  of  the  stomach,  liver,  spleen,  and  pancreas  have  been 
sufficiently  considered  from  the  practical  stand-point  in  connection  with  these  viscera. 
The  mesenteric  nodes  are  frequently  and  gravely  involved  in  various  intestinal 
diseases.  They  are  often  infected  and  enlarged  during  typhoid  fever.  They  are 
especially  implicated  in  peritoneal  or  intestinal  tuberculosis.  The  lymphoid  nodules 
in  the  neighborhood  of  Peyer's  patches  are  surrounded  by  lymphatic  plexuses  and 
are  a  common  site  of  tuberculous  ulceration.  The  bacilli  tuberculosis  are  carried 
directly  thence  to  the  mesenteric  glands  (tabes  mesenterica),  and  sometimes  by  way 
of  the  lymphatic  vessels  and  thoracic  duct,  may  reach  the  general  circulation  in  large 
numbers  (generalized  tuberculosis,  acute  miliary  tuberculosis).  In  some  cases  of 
tuberculous  peritonitis  associated  with  mesenteric  gland  disease,  the  mesentery 
undergoes  marked  and  extreme  contraction,  so  that  the  altered  coils  of  intestine  are 
held  closely  to  the  spine,  and  their  lumen  may  be  greatly  narrowed  (peritonitis 
deformans)  (Taylor). 

Mesenteric  cysts  (serous  or  chylous  cysts)  are  usually  of  lymphatic  origin,  and 
may  be  due  to  lymphatic  obstruction  or  to  a  degeneration  and  dilatation  of  the  mes- 
enteric nodes  analogous  to  the  varicosity  of  inguinal  nodes  in  filarial  disease.  The 
clinical  signs  of  such  cysts  are  :  i,  a  prominent,  fluctuating,  usually  spherical  swell- 
ing near  the  umbilicus  ;  2,  marked  mobility  of  the  tumor — especially  in  a  transverse 
direction  and  around  the  central  avis  ;  3,  the  presence  of  a  zone  of  resonance  around 
the  cyst  and  a  belt  of  resonance  across  it  (Moynihan).  The  symptoms  may  be 


*Progr£s  medical,  1890. 


i 


THE  LYMPHATICS  OF  THE  LOWER  EXTREMITY.     991 

either  (a)  chronic,  of  the  nature  of  colicky  pain  due  to  interference  with  the  intes- 
tine and  to  gastro-intestinal  disturbance,  the  presence  of  a  tumor  distinguishing  the 
case  from  one  of  simple  gastro-enteritis  ;  or  (6)  those  of  acute  intestinal  obstruction 
(Rolleston). 

The  lumbar  nodes  may  be  enlarged  from  septic  or  malignant  disease  of  the 
lower  extremities,  the  testes,  the  fundus  of  the  uterus,  the  ovary,  the  kidneys  and 
adrenals,  the  sigmoid  or  rectum.  The  wide  area  thus  drained  by  them  exposes 
them  frequently  to  transmitted  infection  or  disease.  Their  condition  in  the  presence 
of  carcinoma  affecting  any  of  these  regions  or  viscera  has  an  important  practical 
bearing  upon  the  question  of  operative  interference,  as,  practically  without  excep- 
tion, if  they  are  involved  only  palliation  can  be  hoped  for.  With  an  empty  intes- 
tinal tract  and  a  thoroughly  relaxed  abdomen,  even  moderate  enlargement  of  these 
nodes  may,  in  thin  persons,  be  detected  by  palpation.  In  persons  with  very  mus- 
cular or  very  fat  abdominal  walls,  they  cannot  be  felt  until  they  have  formed  a  con- 
siderable mass.  Their  great  enlargement — especially  in  carcinoma — often  results  in 
swelling  and  oedema  of  the  lower  extremities  on  account  of  the  obstruction  to  the 
current  in  the  inferior  cava  produced  by  the  pressure  of  the  dense  indurated  glands 
which  may  quite  encircle  both  that  vessel  and  the  aorta  and  may  even  interfere  with 
the  circulation  in  the  latter. 

The  lumbar  nodes  often  enlarge  consecutively  to  enlargement  of  the  pelvic  nodes 
(obturator,  gluteal,  sciatic,  internal  pudic,  external  and  internal  iliacs),  some  of  which 
are  also  palpable — in  thin  persons — when  the  subject  of  carcinomatous  infiltration. 
The  external  iliac  nodes,  for  example,  lying  along  the  anterior  and  inner  aspect  of  the 
external  iliac  vessels,  may,  when  cancerous,  be  recognizable  in  this  way,  and  may 
be  found  by  their  tenderness — though  less  distinctly  felt — in  some  septic  cases.  As 
they  receive  the  lymphatic  vessels  from  the  nodes  of  the  groin,  and  the  vessels 
accompanying  the  deep  circumflex  iliac  arteries,  their  enlargement  may  follow  that 
of  the  inguinal  nodes,  or  may  result  from  septic  or  syphilitic  or  cancerous  foci  in  the 
supra-inguinal  portion  of  the  abdominal  wall.  In  cancer  of  the  testis  the  iliac  and 
lumbar  nodes  are  in  the  closest  relation  to  the  ascending  current  of  lymph,  the 
inguinal  nodes,  as  a  rule,  being  involved  later,  after  the  skin  of  the  scrotum  has 
become  infiltrated  or  ulcerated.  In  advanced  cases  of  carcinoma  of  the  rectum  or 
uterus,  the  obturator,  epigastric  and  external  iliac  groups  become  considerably 
affected.  QEdema  of  the  legs  often  results  because  (a)  the  enlarged  nodes  press 
directly  upon  the  external  iliac  vessels  ;  and  (<5)  the  lymphatics  pass  both  over  and 
under  these  vessels  to  communicate  with  the  obturator  node  and  thus  compress  the 
vein  in  a  ring-like  carcinomatous  mass  (Leaf).  The  pain  felt  in  these  cases  is  due 
to  the  pressure  of  the  affected  glands  upon  the  nerve-trunks  arising  from  the  lumbo- 
sacral  plexus.  Similar  pains  may  be  felt  when  any  of  the  pelvic  glands  are  involved 
as  there  is  a  similarly  close  relation  between  the  obturator  node  and  the  obturator 
nerve  ;  the  gluteal,  sciatic,  and  internal  pudic  nodes  and  the  first  and  second  sacral 
and  great  sciatic  nerves  ;  and  the  external  iliac  nodes  and  the  anterior  crural 
nerve.  The  obturator  group  of  nodes  lying  between  the  external  iliac  vein  and  the 
obturator  nerve  assume  surgical  importance  because  sometimes  the  lowest  node  of 
this  group  is  found  projecting  through  the  crural  canal.  The  relation  of  this  node  to 
Gimbernat's  ligament  shows  that  when  enlarged  it  would  appear  as  a  swelling  occu- 
pying a  position  similar  to  that  of  a  femoral  hernia  (Leaf).  Cases  are  on  record 
(White)  in  which  an  inflammation  of  this  node  has  simulated  a  strangulated  femoral 
hernia. 

THE  LYMPHATICS  OF  THE  LOWER  EXTREMITY. 
THE  LYMPHATIC  NODES. 

The  Inguinal  Nodes. — The  principal  group  of  nodes  of  the  lower  extremity 
is  situated  in  the  inguinal  region  over  Scarpa's  triangle,  where  they  form  a  consider- 
able mass,  placed  for  the  most  part  between  the  layers  of  the  fascia  lata,  and  consist 
of  from  twelve  to  twenty  nodes  united  by  connecting  branches  to  form  a  plexus,  the 
plexus  inguinalis.  Though  in  reality  forming  a  single  group,  they  have  been 
divided  for  purposes  of  description  into  a  number  of  subordinate  groups  which  must 
be  recognized  to  have  merely  a  conventional  value.  The  first  of  these  divisions  is  a 


992 


HUMAN   ANATOMY. 


FIG.  831. 


separation  of  the  nodes  which  lie  respectively  above  and  below  a  horizontal  line 
drawn  through  the  point  at  which  the  long  saphenous  vein  pierces  the  cribriform 
fascia,  and  to  those  lying  above  this  line  the  term  inguinal  nodes  (lymphoglandulae 
inguinales)  is  applied,  while  those  below  it  are  termed  the  subinguinal  nodes 
(lymphoglandulae  subinguinales).  This  latter  subgroup  is  again  divided  into  a  super- 
ficial (lymphoglandulae  subinguinales  superticiales)  and  a  deep  (lymphoglandulae  sub- 
inguinales profundae)  set,  according  as  they  are  situated  in  or  beneath  the  fascia  lata. 
Finally,  by  means  of  a  vertical  line  passing  through  the  orifice  in  the  cribriform  fascia 
through  which  the  long  saphenous  vein  passes,  the  inguinal  and  superficial  subinguinal 
groups  are  each  subdivided  into  an  inner  and  an  outer  set,  a  small  central  group  of 
nodes,  surrounding  the  saphenous  orifice,  being  also  sometimes  recognizable.  It 
may,  however,  again  be  emphasized  that  these  subdivisions  are  purely  conventional 
and  cannot  always  be  clearly  distinguished,  nor  do  they  represent,  except  in  a  very 

general  way,  the  terminations  of  definite  drainage 
areas.  Indeed,  the  numerous  connections  which 
exist  between  the  nodes  of  the  various  subgroups 
cause  their  distinction  to  be  of  comparatively  little 
importance  from  the  surgical  stand-point. 

The  inguinal  nodes  are  arranged  in  a  more 
or  less  distinct  chain  over  the  base  of  Scarpa's 
triangle,  immediately  below  Poupart's  ligament. 
They  receive  as  afferents  the  superficial  lymphatics 
of  the  abdominal  walls  and  the  gluteal  region,  the 
superficial  vessels  of  the  scrotum  and  penis  in  the 
male  and  of  the  labia  majora  and  minora  in  the 
female,  as  well  as  those  from  the  perineum  and 
the  circumanal  region.  Their  efferents  perforate  the 
cribriform  fascia,  enter  the  abdomen  by  the  femoral 
ring,  and  terminate  in  the  lower  iliac  nodes. 

The  superficial  subinguinal  nodes  receive 
some  afferents  from  the  gluteal  regions  and  also 
some  from  the  perineum  and  circumanal  regions,  but 
the  principal  set  is  formed  by  the  superficial  vessels 
of  the  leg.  Their  efferents  have  essentially  the 
same  course  as  those  of  the  inguinal  nodes,  piercing 
the  cribriform  fascia  to  accompany  the  femora] 
vessels  to  the  abdomen,  where  they  terminate  in  the 
lower  iliac  nodes.  In  their  course  through  the 
femoral  sheath  some  of  them  lie  on  the  anterior 
surface  of  the  vessels,  but  the  majority  lie  on  their 
inner  side  in  the  crural  canal  and  some  of  them 
terminate  in  the  deep  subinguinal  nodes. 

The  deep  subinguinal  nodes  vary  in  number 
from  one  to  three.  They  are  placed  along  the 
course  of  the  femoral  vein,  one  occurring  immediately  beneath  the  point  of  junction 
of  the  long  saphenous  vein  with  the  femoral,  a  second  a  little  higher  up  in  the  crural 
canal,  and  the  third,  termed  by  French  authors  the  node  of  Cloquet  and  by  the 
Germans  the  node  of  Rosenmuller,  is  situated  at  the  entrance  into  the  crural  canal 
from  the  abdomen.  Their  principal  afferents  are  the  deep  lymphatics  of  the  thigh 
which  accompany  the  femoral  vessels  and  their  branches,  but  in  addition  they  receive 
stems  from  the  superficial  subinguinal  nodes  and  the  deep  vessels  of  the  penis  and 
clitoris.  Their  efferents  pass,  like  those  of  the  superficial  nodes,  to  the  lower  iliac 
nodes. 

The  popliteal  nodes  (lymphoglandulae  popliteae)  are  some  four  or  more  in 
number  and  are  embedded  in  the  adipose  tissue  of  the  popliteal  space  (Fig.  832). 
One  or  two  occur  in  the  neighborhood  of  the  short  saphenous  vein  immediately 
after  it  has  entered  the  popliteal  space,  while  the  rest  are  situated  more  deeply  upon 
the  popliteal  vessels.  The  more  superficial  nodes  receive  as  affcrenfs  the  superficial 
lymphatics  of  the  leg  which  accompany  the  short  saphenous  vein,  while  the  deeper 


Superficial 

horizontal  line  subdivides  nodes  into 
upper  and  lower  groups;  vertical  line 
into  median  and  lateral  groups 


inguinal    lymph-nodes; 
subdivi 


THE  LYMPHATICS  OF  THE  LOWER  EXTREMITY. 


993 


Popliteal  lymph-nodes.     (Poirier  and  Cuneo.*) 


ones  receive  the  vessels  which  accompany  the  branches  of  the  popliteal  vessels  and 

also  those  accompanying  the  anterior  and  posterior  tibial  vessels.      Their  efferents  for 

the    most    part    accompany    the 

femoral    vessels   to  terminate  in  FIG.  832. 

the  deep  subinguinal  nodes. 

The  anterior  tibial  node 
(lymphoglandula  tibialis  anterior) 
is  a  small  and  probably  inconstant 
node  situated  in  the  upper  part 
of  the  course  of  the  lymphatic 
vessels  which  accompany  the 
anterior  tibial  artery.  Its  effer- 
ent pass  upward  along  with 
the  anterior  tibial  and  popliteal 
blood-vessels  to  terminate  in  the 
deeper  popliteal  nodes. 

THE  LYMPHATIC  VESSELS. 

The  lymphatic  vessels  of  the 
lower  extremity  may  be  divided 
into  two  groups,  one  of  which 
consists  of  the  subcutaneous  net- 
work and  its  efferent  stems  and 
the  other  of  those  vessels  which 
accompany  the  principal  blood- 
vessels. 

The  superficial  lymphat- 
ics take  their  origin  from  a 
net-work  distributed  throughout  all  portions  of  the  subcutaneous  tissue  of  the 
extremity,  but  increasing  in  richness  and  complexity  toward  the  distal  part  of  the 
limb,  until  in  the  foot,  and  especially  in  the  plantar  region,  it  forms  a  very  close  and 
abundant  net-work.  This  plantar  net-work  extends  not  only  throughout  the  entire 
plantar  region,  but  curves  dorsally  upon  both  the  outer  and  inner  borders  of  the  foot, 
and  also  over  the  posterior  surface  of  the  heel,  and  from  these  lateral  and  posterior 
portions  of  the  net-work  as  well  as  from  the  subcutaneous  net-work  of  the  digits 
numerous  collecting  steins  arise.  These  anastomose  abundantly,  and  those  from  the 
digits,  the  whole  of  the  inner  border  of  the  foot  and  the  distal  half  of  its  outer  border 
form  an  open  plexus  upon  the  dorsum  of  the  foot.  The  stems,  several  in  number, 
which  arise  from  this  plexus  pass  upward  along  the  inner  surface  of  the  leg 
(Fig.  833),  following  in  general  the  course  of  the  long  saphenous  vein  and  receiving 
as  they  go  communications  from  the  superficial  net-works  of  the  regions  they 
traverse.  In  the  neighborhood  of  the  knee  stems  arising  from  the  net-work  over 
the  anterior  tibial  region  become  associated  with  them,  and  above  the  knee  branches 
which  drain  the  net-work  of  the  outer,  inner,  and  posterior  surfaces  of  the  thigh  also 
curve  upward  and  inward  or  forward,  as  the  case  may  be,  to  accompany  them. 
The  numerous  stems  so  formed  are  all  situated  superficially  to  the  fascia  lata,  and 
terminate  above  in  the  superficial  subinguinal  nodes,  the  more  anterior  stems  passing 
to  the  outer  and  the  more  posterior  to  the  inner  members  of  the  group. 

The  stems  which  arise  from  the  calcaneal  portion  of  the  plantar  net-work  and 
from  that  portion  of  it  which  curves  upward  over  the  posterior  half  of  the  outer 
border  of  the  foot,  pass  upward  upon  the  posterior  surface  of  the  crus  in  company 
with  the  short  saphenous  vein.  They  receive  communications  from  the  superficial 
net-work  of  the  calf  and,  as  they  approach  the  bend  of  the  knee,  they  perforate  the 
crural  fascia  and  terminate  in  the  more  superficial  popliteal  nodes. 

Finally,  from  the  net-work  over  the  gluteal  region  a  number  of  collecting  stems 
arise,  the  majority  of  which  curve  forward  and  converge  to  terminate  in  the  outer 
inguinal  nodes,  some  from  the  more  posterior  portions  of  the  net-work,  however, 


*  Poirier  et  Charpy  :  Trait£  d'anatomie  humaine,  Tome  ii.,  1902 

63 


994 


HUMAN    ANATOMY. 


FIG.  833. 


passing  forward  along  with   the   stems  from   the   circumanal    region  to  the  inner 
inguinal  or  superficial  subinguinal  nodes. 

The  deep  lymphatics  of  the  lower  extremity  take  their  origin  mainly  in  the 
muscles  and  form  stems  which  accompany  the  blood-vessels.  From  the  net-work 
of  the  plantar  muscles  one  or  two  stems  take  origin  which  follow  the  course  of  the 
plantar  arch,  ascending  to  the  dorsum  of  the  foot  between  the  first  and  second 
metatarsal  bones.  They  then  follow  the  course  of  the  dorsal  pedal  vessels,  receiving 
the  stems  which  accompany  their  branches,  and  then  accompany  the  anterior  tibial 

vessels  up  the  leg.  After  traversing  the  anterior  tibial 
nodes  they  pass  with  the  vessels  through  the  foramen  in 
the  interosseous  membrane,  and,  continuing  their  upward 
course  through  the  popliteal  space,  terminate  in  the 
deeper  popliteal  nodes. 

Other  branches  arising  in  the  plantar  musculature 
follow    the    plantar    vessels    backward,    and,    ascending 
behind  the  internal  malleolus,  accompany  the  posterior 
V aFA  tibial  vessels.      Toward  the  upper  part  of  the  crus  they 

receive  the  stems  which  accompany  the  peroneal  vessels 
and  their  branches,  and  terminate,  like  the  anterior 
stems,  in  the  deeper  popliteal  nodes. 

From  these  nodes  four  large  stems  issue,  and, 
passing  through  the  hiatus  tendineus  of  the  adductor 
magnus,  continue  their  course  up  the  thigh  in  company 
with  the  femoral  vessels.  They  receive  the  stems  which 
accompany  the  various  branches  of  the  femoral  vessels 
and  terminate  above  in  the  deep  subinguinal  nodes. 
In  addition  to  these  deep  femoral  lymphatics  others 
occur  in  the  thigh  in  company  with  the  obturator  and 
sciatic  vessels,  and  the  muscles  of  the  gluteal  region  are 
drained  by  stems  which  accompany  the  gluteal  vessels. 
All  these  stems  terminate  in  nodes  belonging  to  the 
hypogastric  group,  those  accompanying  the  sciatic  ves- 
sels traversing  some  small  and  inconstant  nodes  situated 
beneath  the  pyriformis  muscle,  while  some  ten  or  twelve 
similar  nodes  occur  along  the  course  of  the  gluteal  stems. 

Practical  Considerations. —  The  Nodes  of  the 
Lower  Extremity. — The  majority  of  the  lymphatics  of 
the  sole  of  the  foot  unite  with  those  of  the  inner  side 
of  the  dorsum  and  run  with  the  long  saphenous  vein  to 
enter  the  inguinal  nodes.  A  smaller  number  run  up  the 
fibular  side  of  the  leg,  but  most  of  these  cross  over  the 
leg  or  at  the  ham  to  join  the  inner  lymphatic  vessels. 
A  still  smaller  number  run  with  the  short  saphenous 
vein  and  empty  into  the  popliteal  nodes.  The  far  more 
frequent  occurrence  of  glandular  swellings  and  abscess  in 
the  groin  than  in  the  ham  is  thus  easily  understood. 
The  popliteal  nodes  (iuicrcondylar,  lying  on  either 
side  of  the  popliteal  artery  between  the  two  heads  of 
the  gastrocnemius,  and  supra&mdylar,  lying  deeper  and 
against  the  back  of  the  femur)  are  extremely  difficult  to  feel  unless  they  are 
enlarged,  and  even  then  the  only  one  which  can  be  detected  is  that  which  lies  over 
the  internal  popliteal  nerve.  This  node,  probably  from  the  constant  movement  of 
the  knee-joint,  is  very  apt  to  suppurate  as  a  result  of  superficial  sores  about  the  heel. 
The  intercondylar  nodes  cannot  be  felt  ;  in  the  first  place,  because  of  their  deep 
position,  and  secondly,  because  when  pressed  they  become  still  further  forced  clown 
between  the  condyles.  The  suprarondylar  nodes  lie  altogether  too  deep  to  be  felt 
by  the  fingers  (Leaf).  A  small  node  beneath  the  fascia  close  to  the  point  of  entry 
of  the  short  saphenous  receives  some  of  the  lymphatics  that  accompany  that  vein. 


Superficial  lymphatic  vessels 
of  lower  limb  ;  semiaiagrammatic. 
(Based  on  figures  of  Sappey.) 


THE   LYMPHATICS   OF   THE    LOWER   EXTREMITY.  995 

Popliteal  abscess  will  follow  pyogenic  infection  of  tlie  popliteal  nodes.  The 
pressure  effects  due  to  the  density  and  rigidity  of  the  popliteal  fascia  and  the  conse- 
quent necessity  for  early  and  free  incision  and  drainage  have  already  been  described 
(pages  646).  Enlargement  of  the  popliteal  nodes  has  been  mistaken  for  enlarged 
bursae — though  the  nodes  are  deeper  and  nearer  the  median  line — for  popliteal  aneur- 
ism, and  for  neoplasms. 

The  inguinal  nodes  are  numerous  and,  on  account  of  their  frequent  involvement 
in  diseases  of  the  lower  extremity  and  of  the  genitals,  are  important.  The  arrange- 
ment into  a  superficial  and  deep  set,  and  the  division  of  the  former  into  two  groups, 
the  horizontal,  parallel  with  and  close  to  Poupart'  s  ligament,  and  the  vertical,  parallel 
with  and  close  to  the  long  saphenous  vein,  is  of  convenience.  The  deep  set  is  found 
to  the  inner  side  of  the  femoral  vein  and  may  be  said  to  include  one  group  which  is 
embedded  in  the  fatty  layer  at  the  saphenous  opening  and  bears  the  same  relation  to 
the  fascia  lata  that  the  central  group  of  axillary  glands  bears  to  the  axillary  fascia 
(Leaf)  (page  581).  The  inguinal  nodes  receive  lymph  through  the  superficial  lym- 
phatics as  follows  :  Lower  limb — vertical  set  of  superficial  nodes  ;  lower  half  of 
abdomen — middle  nodes  of  horizontal  set  ;  outer  surface  of  buttock — external  nodes 
of  horizontal  set ;  inner  surface  of  buttock — internal  nodes  of  horizontal  set,  (a  few 
of  these  vessels  go  to  the  vertical  nodes  ;  external  genitals — horizontal  nodes,  a  few 
going  to  the  vertical  set  ;  perineum-vertical  set.  The  deep  lymphatics  of  the  lower 
limb  enter  the  deep  set  of  nodes  (Treves).  The  deep  lymphatics  of  the  penis  and 
those  that  are  found  with  the  obturator,  gluteal,  and  sciatic  vessels  enter  the  pelvic 
nodes.  The  inguinal  nodes  communicate  with  the  external  and  common  iliac  nodes, 
the  pelvic  lymphatics  with  the  internal  iliac  nodes,  and  both  the  iliac  groups  with  the 
lumbar  nodes.  The  deep  node  lying  in  the  crural  canal  and  upon  the  septum  crurale 
is  variously  described  as  one  of  the  obturator  (pelvic)  group  (Leaf)  and  as  one  of 
the  deep  set  of  inguinal  nodes  (Treves).  It  should  be  remembered  that  when  it  is 
inflamed  it  may  not  only  simulate  strangulated  hernia,  but,  on  account  of  the  density 
of  the  structures  by  which  it  is  surrounded  and  their  participation  in  the  movements 
of  the  thigh,  may  give  rise  to  pain  suggesting  coxalgia. 

The  relations  of  branches  of  the  anterior  crural  nerve  to  the  inguinal  nodes 
may,  in  cases  of  inflammation  or  enlargement,  give  rise  to  pain  or  spasm  in  the  region 
supplied  by  that  nerve.  Filariasis  (elephantiasis  arabum)  of  the  femoral  lymphatics, 
which  are  obstructed  by  the  worms,  gives  rise  to  very  great  swelling  of  the  lower 
extremity  (Cochin  leg,  Barbadoes  leg). 

In  addition  to  what  has  been  stated  above  the  practical  application  of  a  knowl- 
edge of  the  lymphatics  of  the  lower  extremity  embraces  the  following  considerations  : 

(«)  The  lymphatic  vessels  may  be  inflamed  without  involvement  of  the  veins, 
when  the  course  of  some  of  the  main  vessels  can  be  distinctly  traced  under  the  skin. 
When  chronically  inflamed,  and  obstruction  exists  at  the  nearest  lymphatic  gland,  the 
vessels  may  become  thickened,  dilated,  and  tortuous.  The  lymphatic  vessels  of  the 
sheath  of  the  penis  are,  perhaps,  more  frequently  involved  in  diseased  action  than 
those  of  any  other  portion  of  the  skin  surface.  Inflamed  lymphatic  vessels  often 
co-exist  with  a  chancre.  In  cases  of  neglected  chancre,  associated  with  an  indurated 
condition  of  the  lymphatic  nodes  of  the  groin,  they  may  even  form  bulla-like  swell- 
ings which  sometimes  rupture  and  permit  the  lymph  to  escape  externally.  Rarely 
dilatation  of  the  lymphatic  vessels  occurs  without  apparent  cause. 

(£)  The  lymphatic  vessels  may,  from  causes  imperfectly  understood,  become 
filled  with  chylous  fluid.  In  one  (Petters),  remarkable  dilatation  of  the  lymphatics 
existed  in  the  right  groin  and  in  the  abdomen,  in  a  patient  the  subject  of  valvular 
heart  disease.  The  glands  were  converted  into  cyst-like  cavities  filled  with  a  yellow 
fluid.  Rosary-like  dilatations,  similar  to  those  seen  at  the  elbow,  occur  infrequently 
•  below  the  groin. 

The  inguinal  lymphatic  glands  are  the  common  seat  of  diseased  action  dependent 
upon  the  transmission  of  the  virus  of  syphilis,  or  of  any  other  irritant  whose  point  of 
entrance  is  through  the  external  genitals.  In  the  nonsyphilitic  infections  they 
frequently  suppurate  or  excite  suppurative  cellulitis  in  the  parts  about  them.  Acute 
inflammatory  engorgement  of  one  of  them  has  been  known  to  induce  fatal  peritonitis 
by  direct  continuity  through  the  lymphatic  vessels  of  the  abdominal  wall  (Allen). 


THE  NERVOUS  SYSTEM. 

THE  nervous  system — the  complex  apparatus  by  which  the  organism  is  brought 
into  relation  with  its  surroundings  and  by  which  its  various  parts  are  united  into  one 
coordinated  whole — consists  essentially  of  structural  units,  the  neurones,  held  together 
by  a  special  sustentacular  tissue,  the  neuroglia,  assisted  by  ingrowths  of  connective 
tissue  from  the  investing  membrane,  the  pia  mater. 

The  neurone,  the  morphological  unit  of  the  nervous  system,  includes  a 
nucleated  protoplasmic  accumulation,  the  cell-body,  and  the  processes.  The  former, 
usually  spoken  of  as  the  nerve-cell,  presides  over  the  nutrition  of  the  neurone  and  is 
the  seat  of  the  subtle  changes  giving  rise  to  nervous  impulse.  The  processes  arise 
as  outgrowths  from  the  cell-body  and  provide  the  paths  along  which  impulses  are 
conveyed.  They  are  very  variable  in  length,  some  extending  only  a  fraction  of  a 
millimeter  beyond  the  cell-body,  while  others  continue  for  many  centimeters  to 
distant  parts  of  the  body.  The  longer  processes,  which  usually  acquire  protecting 
sheaths,  are  known  as  the  nerve-fibres,  and  these,  associated  in  bundles,  constitute 
the  nerve-trunks  that  pass  to  the  muscles  and  various  other  organs. 

Reduced  to  its  simplest  terms,  the  nervous  system  consists  of  the  two  parts  rep- 
resented in  the  accompanying  diagram  (Fig.  834).  The  one,  the  sensory  neurone, 

(A)    takes   up    the   stimulus   received    upon    the 

FIG.  834.  integument  or  other  sensory  surface  and,  by  means 

of  its  process  (nerve-fibre),  conveys  such  impulse 
from  the  periphery  towards  the  central  aggregations 
of  nerve-cells  that  commonly  lie  in  the  vicinity  of  the 
body-axis.  Functionally,  such  a  path  constitutes  a 
centripetal  or  off  ere  nt  fibre  (a).  The  impressions 
thus  carried  are  transferred  to  the  second  element, 
the  motor  neurone  {JB},  which  in  response  sends 
out  the  impulse  originating  within  the  cell -body 
(nerve-cell)  along  the  process  known  as  tin-  ct  iitri- 
fugal  or  efferent  fibre  (e~),  to  the  muscle-cell 
and  causes  contraction.  The  simple  relations  of 

Diagram  showing  fundamental  units     the  foregoing  apparatus  are,   in  fact,    superceded 
of  nervous  system.   A,  sensory  neurone,     Dy  much  greater  complexity  in  consequence  of  the 

conducting    afferent    impulses  by   its   pro-       .  •         ,         .  °          .         .  ,.   .*         .    J  .  1-1        i 

cess  (a)  from  periphery  (s) ;  'ft,  motor  introduction  of  additional  neurones  by  which  the 
proces1se(')'tomusc!lere"t  impulses  by  '"*  afferent  impressions  are  distributed  to  nerve-cells 

situated  not  only  in  the  immediate  vicinity  of  the 
first  neurone,  but  at  different  and  often  distant  levels. 

Although  very  exceptionally  the  relation  between  the  neurones  may  perhaps  be 
that  of  actual  continuity  in  consequence  of  a  secondary  union  of  their  processes 
(Held),  the  view  concerning  the  constitution  of  the  nervous  system  most  worthy  of 
confidence,  notwithstanding  the  bitter  attacks  by  certain  histologists,  regards  tin- 
neurones  as  separate  and  distinct  units.  While  chained  together  to  form  the  various 
paths  of  conduction,  they  are  probably  seldom,  if  ever,  actually  united  to  one  another 
but  only  intimately  related,  since  their  processes,  although  in  close  contact,  are  not 
directly  continuous, — contiguity  but  not  continuity  being  the-  ordinary  relation. 

During  the  evolution  of  the  nervous  system  from  the  simpler  type,  the  cell- 
bodies  of  the  neurones  forsake  their  primary  superficial  position  and  recede  from  the 
periphery.  In  vertebrates  this  recession  is  expressed  in  the  axial  accumulation  of 
cell-bodies  either  within  the  wall  or  in  the  immediate  vicinity  of  the  neural  tube 
(brain  and  spinal  cord),  from  or  to  which  the  processes  pass.  The  nervous  system 
is  often  divided,  therefore,  into  a  <-vv//;w/and  a  peripheral  portion.  The  former,  also 
known  as  the  ccrcbro-sf>inal  a\is<  includes  the  brain  and  spinal  cord  and  contains 
the  chief  axial  collections  of  nerve-cells  ;  the  peripheral  portion,  on  the  contrary, 
996 


THE    NERVOUS   TISSUES. 


997 


contains  the  nerve-cells  of  the  sensory  ganglia  and  is  principally  composed  of  the 
nerve-fibres  that  pass  to  and  from  the  end-organs.  Intimately  associated  with  and 
in  fact  a  part  of  the  peripheral  nervous  system,  but  at  the  same  time  possessing  a 
certain  degree  of  independence,  stands  the  sympathetic  system,  which  provides  for 
the  innervation  of  the  involuntary  muscle  and  glandular  tissue  throughout  the  body 
and  the  muscle  of  the  heart. 

When  sectioned,  the  fresh  brain  and  spinal  cord  do  not  present  a  uniform  appear- 
ance, but  are  seen  to  be  made  up  of  a  darker  and  a  lighter  substance.  The  former, 
the  gray  matter,  owes  its  reddish  brown  color  not  only  to  the  numerous  nerve-cells 
that  it  contains,  but  also  to  its  greater  vascularity  ;  the  hue  of  the  lighter  substance, 
the  white  matter,  is  due  to  its  chief  constituents,  the  medullated  nerve-fibres,  in 
conjunction  with  its  relatively  meagre  vascular  supply. 

THE  NERVOUS  TISSUES. 

The  Neurones. — The  neurones,  the  essential  morphological  units  of  the 
nervous  system,  consist  of  the  cell-body  and  the  processes.  The  latter,  as  seen  in 
the  case  of  a  typical  motor  neurone  (Fig.  835),  are  of  two  kinds  :  (a)  the  branched 
protoplasmic  extensions,  the  dendrites,  which  may  be  multiple  and  form  elaborate 
arborescent  ramifications  that  establish  relations  with  other  neurones,  and  (<£)  the 
single  unbranched  axone  (neuraxis,  neurite)  that  ordinarily  is  prolonged  to  form  the 
axis-cylinder  of  a  nerve-fibre,  and,  hence,  is  often  termed  the  axis-cylinder  process. 
The  dendrites  are  usually  uneven  in  contour  and  relatively  robust  as  they  leave 
the  cell-body,  but  rapidly  become  thinner,  due  to  their  repeated  branching,  until 

they  are  reduced  to  delicate  threads  that  con- 
stitute the  terminal  arborizations,  the  telodendria, 
formed  by  the  .end-branches.  The  latter  are 
beset  with  minute  varicosities  and  finally  end  in 
terminal  bead-like  thickenings.  The  axones, 
slender  and  smooth  and  of  uniform  thickness, 
are  much  less  conspicuous  than  the  dendrites. 
They  may  be  short  and  only  extend  to  nearby 
cells  ;  or  they  may  be  of  great  length  and  con- 
nect distant  parts  that  lie  either  wholly  within  the 

FIG.  836. 


Dendrites 


FIG.  835. 


Dendrites 


Arborization 

of  axone 


Telodendrion 
Diagram  of  typical  neurone. 


Diagram  of  nerve-cell  of  type 
II,  in  which  axone  is  not  prolonged 
as  nerve-fibre. 


cerebro-spinal  axis  (as  from  the  brain-cortex  to  the  lower  part  of  the  spinal  cord)  or 
extend  beyond  (as  from  the  lower  part  of  the  cord  to  the  plantar  muscles  of  the  foot). 


998 


HUMAN   ANATOMY. 


FIG.  837. 


On  reaching  their  destination  the  axones  terminate  in  end-arborizations  (telodendria) 
of  various  forms,  in  a  manner  similar  to  the  dendrites.      According  to  the  distribution 

of  their  axones,  the  neurones  are  divided  into  two 
classes.  In  those  of  the  first,  known  as  cells  of  type  /, 
the  axone  is  continued  as  a  nerve-fibre  and  is,  therefore, 
relatively  long.  Soon  after  leaving  the  cell-body  such 
axones  give  off  delicate  lateral  processes,  the  collaterals, 
which,  after  a  longer  or  shorter  course,  break  up  into 
arborizations  ending  in  relation  with  other  and  often 
remote  neurones.  Neurones  of  the  second  and  much 
less  frequent  class,  cells  of  type  //,  possess  short  axones 
that  are  not  continued  as  nerve-fibres,  but  almost 
immediately  break  up  into  complex  end-arborizations 
or  neuropodia  (Kolliker),  limited  to  the  gray  matter. 
The  processes  of  the  sensory  neurones,  as  in  the 
case  of  those  constituting  the  spinal  and,  other  ganglia 
connected  with  afferent  nerves,  are  so  modified  during 
development  (Fig.  839)  that  later  both  dendrites  and 
axones  arise  in  common  from  the  single  robust  stalk  of 
an  apparently  unipolar  cell.  Branching  T-like,  one 
process  (the  dendrite)  passes  towards  the  periphery 
and  the  other  (the  axone)  extends  to  and  into  the 
cerebro-spinal  axis. 

The  nerve-cells,  as  the  bodies  of  the  neurones 

Semichagrammatic  representation  of  ,,     .  .  ,     ,        •< 

structure  of  neurone;  a,  axone.         are  called,  possess  certain  structural  details  in  common, 

although  in  some  instances  they  present  characteristics 

that  suffice  to  identify  them  as  belonging  to  particular  localities.      Nerve-cells  are 
relatively  large  elements,  those  in  the  anterior  horns  of  the  spinal  cord  measuring 
from  .070-.  150  mm.    in  diameter,  and  contain  a  large  spherical   nucleus,  poor   in 
chromatin  but  usually  pro- 
vided with   a   conspicuous  FIG.  838. 
nucleolus.    Their  cytoplasm 
varies    in  appearance  with 
the  method  of  fixation  and 
staining  to  such  an  extent 
that  considerable  uncertain- 
ty exists  as  to  the  relation 
of  many  described  details  to 
the  actual  structure  of  the 
cells.      It  may  be  accepted 
as     established,     however, 
that   the   cell-body  of   the 
neurone  consists  of  aground 
substance,  homogeneous  or 
finely    granular,    in   which 
delicate  fibrHla  and  masses 
of  chromatophilic  grannies 
are  embedded  ;  in  addition, 
a  variable  amount  of  brown 
or  blackish  pigment  is  com- 
monly present  in  the  vicin- 
ity  of    the    nucleus.     The 
presence   of    the    fibrilke 
within  the  nerve-cell,  long 
aim    maintained    by    Max 
Schultze    but    later    disiv- 


Nerve-cells  of  human  spinal  cord  stained  to  show  Nissl  bodies  ;  D,  dendrites ; 
.1.  .ixoncs;   ( ',  Implantation. COM;   A',  nucleus;  A/,  nucleolus.     X  4°°. 


garded,    has    been    placed 
beyond  question  by  the  researches  of  Apathy.  Bethe,  Cajal  and  others.     The  signifi- 
cance and  relations  of  the  fibrillae  to  the  nerve-cell,  however,  have  given  rise  to  warm 


THE   NERVOUS   TISSUES. 


999 


discussion.  The  observations  based  upon  the  improved  methods  of  silver-staining 
introduced  by  Cajal  have  contributed  much  towards  the  solution  of  these  questions, 
and,  at  present,  the  most  experienced  histologists  incline  towards  the  view  that  the 
fibrillae  demonstrable  within  the  nerve-cell  are  limited  to  the  body  and  processes  of 
that  particular  neurone  and  do  not  unite  with  the  'fibrillae  of  other  neurones.  When 
adequately  differentiated  by  successful  staining,  the  fibrillae  form  .an  intracellular 
net-work  within  the  cell-body,  from  which  they  are  continued  into  the  dendrites  and 
axone  and  in  all  cases  end  free  in  the  terminal  arborizations  (Retzius). 

After  special  staining  with  methylene  blue,  or  other  basic  anilines,  the  chrom- 
atophilic  granules  appear  deeply  colored  and  arranged  in  groups  or  masses  of  vary- 
ing form  and  size.  Such  aggregations,  known  as  Nissl  bodies,  after  the  German 
histologist  whose  elaborate  studies  and  theories  concerning  the  structure  of  the  nerve- 
cell  have  given  prominence  to  these  masses  of  ' '  stainable  substance, ' '  are  usually 
most  conspicuous  in  the  vicinity  of  the  nucleus.  Collectively,  they  constitute  the 
tigroid  substance  of  Lenhossek  and  are  least  marked  at  the  periphery  of  the  nerve- 
cell.  They  are  continued  into  the  dendrites  as  elongated  flakes  or  pointed  rod-like 
tracts  that  finally  are  resolved  into  scattered  granules  along  the  processes.  The 
axone,  on  the  contrary,  is  not  invaded  by  the  Nissl  bodies,  and  usually  joins  the 
nerve-cell  at  an  area  free  from  the  stainable  substance,  the  axis-cylinder  process  com- 
monly arising  from  a  slight  elevation  known  as  the  implantation  cone.  Exception- 
ally, the  axone  may  arise  from  one  of  the  dendrites,  either  at  its  base  or  at  a  point 
some  distance  from  the  cell-body. 

Notwithstanding  the  elaborate  classification  of  nerve-cells  and  the  theories  based  upon  the 
Nissl  bodies,  their  significance  is  still  debatable,  although  in  the  light  of  the  more  recent  studies 
by  Carrier,  Holmes  and  others  it  seems  probable  that  they  are  normal  constituents  of  the  cell 
and  are  directly  related  to  functional  activity,  undergoing  increase  under  unusual  stimulus. 

The  intracellular  canals  described  by  Holmgren  as  existing  in  nerve-cells,  in  connection 
with  a  reticulum  (trophospongium)  that  appears  after  certain  treatment,  have  been  variously 
interpreted.  By  not  a  few  they  are  regarded  as  artefacts,  or  at  least  dependent  upon  the  intra- 
cellular fibrillae  for  their  exhibition.  Pewsner-Neufeld,  however,  believes  them  to  be  lymph- 
clefts  within  the  cytoplasm  that  directly  communicate  with  lymph-spaces  which  surround  the 
nerve-cell  and  thus  provide  a  means  for  the  rapid  removal  of  waste  products  from  the  neurone. 


FIG.  839. 


Every  neurone  possesses  at  least  one  process,  which  is  then  an  axone,  although 
usually  provided  with  both  dendrites  and  axone.  Very 
rarely  more  than  a  single  axone  is  present.  Depend- 
ing upon  the  number  of  their  processes,  nerve-cells  are 
described  as  unipolar,  bipolar,  or  multipolar.  The 
unipolar  condition  is  often  secondary,  since  two 
processes  may  be  so  blended  for  part  of  their  course 
that  they  form  a  single  process.  Conspicuous  examples 
of  such  relation  are  seen  in  the  spherical  nerve-cells 
composing  the  spinal  and  other  ganglia  connected  with 
the  sensory  nerves.  Primarily  such  neurones  possess 
an  axone  and  a  dendrite  that  arise  from  opposite  ends 
of  what  is  for  a  time  a  spindle-shaped  bipolar  cell. 
During  development,  however,  the  unilateral  growth 
of  the  cell-body  towards  the  surface  of  the  ganglion 
brings  about  the  gradual  approximation  of  the  two 
processes  until  they  fuse  in  the  single  extension  into 
which  the  spherical  or  flask-like  cell  is  prolonged. 
This  process  sooner  or  later  undergoes  a  Y-  or  T-  like 
division,  one  process,  usually  identified  as  the  dendrite, 
passing  to  the  periphery  to  end  in  the  free  terminal 
arborization,  whilst  the  other,  the  axone,  passes 
centrally  to  end  in  an  arborization  around  the 
neurones  lying  within  the  cerebro-spinal  axis. 

Examples  of  bipolar  neurones,  in  which  the  dendrite  and  axone  pass  from 
opposite  sides  of  the  spherical  cell-body,  are  found  in  the  retina  and  the  ganglia 


Diagram  showing  transformation 
of  young  bipolar  sensory  neurone  into 
one  of  unipolar  type. 


IOOO 


HUMAN   ANATOMY. 


FIG. 


connected  with  the  acoustic  nerve.      An  interesting  modification  of  bipolar  neurones 
is  presented  by  the  olfactory  cells,  whose  dendrites  are  represented  by  the  extremely 

short  processes  embedded  within  the  nasal  mucous 
membrane,  whilst  the  axones  are  prolonged  as  the 
fibres  of  the  olfactory  nerves  into  the  cranial  cavity 
to  end  in  telodendria  within  the  glomeruli  of  the 
olfactory  bulb. 

The  cell-bodies  of  the  multipolar  neurones, 
which  possess  one  axone  and  several  dendrites,  vary 
in  form  (Fig.  841).  Some,  as  those  within  the  sym- 
pathetic ganglia,  are  approximately  spherical  and  o£ 
moderate  size,  with  short  delicate  dendrites  ;  many 
are  of  large  size  and  irregularly  stellate  form,  the 
dendrites  passing  out  in  all  directions,  as  seen  in  the 
conspicuous  motor  neurones  within  the  gray  matter 
of  the  spinal  cord  ;  others  possess  a  regular  and 
characteristic  form,  as  the  flask-shaped  cells  of  Purkinje 
within  the  cerebellum,  or  the  pyramidal  cells  of  the 
cerebral  cortex.  '  Certain  multipolar  neurones  within 
the  cerebral  cortex,  and  especially  those  constituting 
the  chief  components  of  the  granule  layer,  of  the 
cerebellum,  are  distinguished  by  the  small  size  of 
their  cell-bodies  and  the  peculiar  ramifications  and  claw-like  telodendria  of  their 
dendrites  (Fig.  945^.  Within  the  cerebellar  cortex  are  likewise  found  examples  of 

FIG.  841. 


Bipolar  neurones;  a,  from  olfactory 
mucous  membrane — dendrite  is  above; 
b,  from  retina.  (Modified from  Cajal.) 


Multipolar  nerve-cells  of  various  forms;   A,  from  spinal  cord;   B,  from  cerebral  cortex;    C,  from  cerebellar  cortex 
(Purkinje  cell)  ;  a,  axone  ;  c,  implantation  cone. 

the  multipolar  neurones  of  Golgi's  type  II,  whose  axones  almost  immediately 
undergo  elaborate  branching  within  the  gray  matter  to  which  they  are  confined. 
The  Nerve-Fibres. — From  the  foregoing  considerations  it  is  evident  that  tin: 
nerve-fibres  are  not  independent  elements,  but  that  all  are  the  processes  of  neurones 
—  either  the  axones  of  those  that  are  prolonged  into  fibres  (type  I),  or  the  dendrites 
of  those  situated  within  the  spinal  and  other  sensory  peripheral  ganglia.  Although 
neurones  exist  which  are  not  continued  as  nerve-fibres,  the  latter  are  always  connected 


THE   NERVOUS   TISSUES. 


1001 


FIG. 


Axis-cylinders 


Axolemma 


Medullary  sheath 


-  Node  of  Ranvier 


Xeurilemma 


Medullated  nerve-fibres,  as  seen  in  longi- 
tudinal sections  of  spinal  nerve.    X  500. 


with  neurones.  Recognizing,  therefore,  that  the  nerve-fibres  are  only  processes  of 
neurones,  their  separate  description  is  justified  only  as  a  matter  of  convenience. 
The  fundamental  part  of  every  nerve-fibre  is  the  central  cord,  commonly  known 
as  the  axis-cylinder,  which  is  composed  of  threads  of  great  delicacy,  the  axis- 
fibrilhc,  prolonged  from  the  nerve-cell  and  embedded  within  a  semifluid  interfibrillar 
substance,  the  neuroplasm,  the  entire  cord  so  con- 
stituted being  enclosed  by  a  delicate  structureless 
sheath,  the  axolemma.  The  existence  of  the 
axolemma  as  a  distinct  sheath,  however,  is  ques- 
tionable, the  appearance  of  such  investment  not 
improbably  being  due  to  a  local  condensation  of 
the  framework  of  the  medullary  coat  immediately 
around  the  axis-cylinder. 

In  the  case  of  the  typical  fibres,  such  as  form 
the  chief  constituents  of  the  peripheral  nerves 
distributed  to  various  parts  of  the  body,  the  axis- 
cylinder  is  surrounded  by  a  relatively  thick  coat, 
known  as  the  medullary  sheath,  outside  of  which 
lies  a  thin  structureless  envelope,  the  neurilemma 
or  sheath  of  Schwann,  that  invests  the  entire 
nerve-fibre.  In  the  case  of  fibres  proceeding  from 
neurones  composing  the  sensory  ganglia,  the 
neurilemma  is  continuous  with  the  nucleated 
sheath  enclosing  the  individual  ganglion-cells. 
The  medullary  sheath  consists  of  two  parts, 
a  delicate  reticular  framework  and  a  fatty  substance,  the  myelin,  that  fills  the  meshes 
of  the  supporting  reticulum.  The  latter,  arranged  for  the  most  part  as  anastomosing 
membranous  lamellae,  that  in  transverse  sections  of  the  nerve-fibre  appear  as  faint 
concentric  lines,  resists  pancreatic  digestion  and  fat-dissolving  reagents,  and  was 
regarded  by  Ewald  and  Kiihne  as  possessing  properties  similar  to  the  keratin  of 
horny  substances  and,  hence,  was  named  by  them  ncnrokcratin.  The  blackening 
after  treatment  with  osmic  acid  and  other  reactions  exhibited  by  myelin  indicate  its 
fatty  nature,  and  it  is  probable  that  this  substance  exists  during  life  in  the  form  of  a 
fine  emulsion  supported  by  the  framework.  When  fresh,  myelin  appears  highly 
refracting  and  homogeneous,  and  confers  upon  the  medullated  nerve-fibres  their 
characteristic  whitish  color.  It  is,  however,  prone  to  post-mortem  changes,  so  that 
after  death  it  loses  its  former  uniformity  and  presents  irregular  contractions  and 
collections,  or  at  the  broken  end  of  the  fibre  extrudes  in  irregular  globules,  due 
probably  to  fusion  of  the  normal  individual  minute  droplets  into  larger  masses. 

The  medullary  sheath  is  not  uniformly  continuous,  but  almost  completely  inter- 
rupted at  regular,  although  in  different  fibres  variable,  intervals  marked  by  annular 

constrictions.  These  constrictions,  the  nodes 
of  Ranvier,  correspond  to  narrow  zones  at 
which  the  medullary  sheath  is  practically 
wanting  and  the  neurilemma  dips  in  and,  some- 
what thickened,  lies  in  close  relation  with  the 
axis-cylinder.  According  to  Hardesty  *  the 
medullary  sheath  does  not  suffer  complete 
suppression  at  the  nodes,  but  is  represented 
by  part  of  its  reduced  framework  which  trans- 
verses  the  constriction,  a  conclusion  which 
we  can  confirm.  The  nodes  occur  at  regular 
intervals  along  the  fibre,  which  they  thus  divide 
In  general,  the  latter  are  longer  in  large  fibres, 

where  they  have  a  length  of  about  i  mm.,  and  shorter  in  those  of  small  diameter,  in 
which  they  may  measure  .  i  mm.  or  less  in  length.  The  axis-cylinder  passes  uninter- 
ruptedly across  the  nodes,  although  it  often  presents  a  slight  fusiform  enlargement 


FIG. 


Axis-cylinder 
Neurilemma 


Medullary  sheath 


Medullated  nerve-fibres  in  transverse 
section.     X  550. 

into  a  series  of  interned  a  I  segments. 


.  Journal  of  Anatomy,  vol.  iv.,  1905. 


1002 


HUMAN   ANATOMY. 


opposite  each  constriction    (Ranvier).     The  neurilemma  also  suffers  no  break  at 

the  nodes,  but  is  continuous  from  one  segment  to  the  other. 

In  addition  to  the  partial  interruptions  at  the 
nodes,  the  medullary  sheath  after  treatment  with 
osmic  acid  frequently  appears  broken  by  clear 
narrow  clefts  that  extend  obliquely  from  the  neuri- 
lemma to  the  axolemma  and  thus  subdivide  each 
internodal  segment  into  a  number  of  smaller 
tracts,  known  as  the  Schmidt- Lantermann  segments 
(Fig.  844).  The  oblique  clefts  do  not  all  extend 
in  the  same  direction,  even  within  the  same  inter- 
nodal  segment,  since  they  are  usually  directed  from 
without  inward  and  towards  the  nodal  constrictions 
and,  therefore,  have  an  opposed  disposition  at  the 
ends  of  the  same  as  well  as  of  the  adjoining  seg- 
ments. The  significance  of  this  subdivision  is  un- 
certain ;  many  regarding  the  details  as  artefacts. 
According  to  Capparelli l,  however,  the  apparent 
clefts  are  in  reality  unstained  membraneous  septa 
that  pass  obliquely  from  the  axolemma  to  the  inner 
surface  of  the  neurilemma  and  serve  to  hold  the 
axis-cylinder  in  place  and  to  enclose  the  myelin. 
The  studies  of  Hatai 2  on  the  arrangement  of  the 
neurokeratin  seem  to  support  these  conclusions. 
Within  each  internodal  segment,  beneath  the  sheath 
of  Schwann,  lies  a  single  (sometimes  more  than 
one)  small  neiirilemma-cell  which  consists  of  an 
elongated  oval  nucleus  surrounded  by  a  meagre 
amount  of  cytoplasm.  These  cells  represent  the 

remains  of  the  mesoblastic  elements  (sheath-cells}  that  during  the  growth  of  the 

jierve-fibre  were  active  in  providing  its  envelope  (page  ion). 


Schmidt- 

Lantermann 

segment 


Axis-cylinder 


Cleft 


Node  of  Ranvier 


Medullated  nerve-fibres  after  treatment 
with  osmic  acid;  A,  fibre  showing  reticu- 
lum  within  medullary  coat ;  B,  one  showing 
same  coat  divided  into  segments.  X  5°°- 


FIG.  845. 


> 


Medullated  nerve-fibres  becoming  nonmedullated  on  approaching 
their  termination.     X  235. 

Depending  upon  the  presence  or  absence  of  the  medullary  sheath  throughout 
the  greater  part  of  their  course,  nerve-fibres  a  re  distinguished  as  medullated  or  non- 

1  Archiv  f.  mikros.  Anat.  u.  Entwick.,  Bd.  66,  1905. 
*  Journal  of  Comparative  Neurology,  vol.  xiii.,  1903. 


THE   NERVOUS   TISSUES. 


1003 


medullated.  The  medullated  fibres  constitute  the  great  majority  of  those  making 
up  the  peripheral  nerves  and  the  tracts  of  the  cerebro-spinal  axis  ;  the  component 
fibres  of  the  latter,  however,  while  medullated  are  without  the  neurilemma.  The 
nonmedullated  fibres,  on  the  other  hand,  are  chiefly  prolongations  (axones)  from 
the  ganglion  cells  of  the  sympathetic  system,  although  in  the  case  of  the  olfactory 
nerves  the  fibres  are  also  without  a  myelin-coat.  The  dis- 
tinction between  these  two  classes  of  fibres  is  relative  rather  than 
absolute,  since  every  medullated  nerve-fibre  becomes  nonmed- 
ullated before  reaching  its  termination,  central  or  peripheral. 

Medullary  nerve-fibres  vary  greatly  in  thickness,  the  smallest  hav- 
ing a  diameter  of  only  .001  mm.,  whilst  the  largest  may  measure  as 
much  as  .020  mm.  According  to  their  diameter,  as  determined  by 
Kolliker,  the  medullated  fibres  may  be  grouped  as  fine  (.oo2-.oo4 
mm.),  medium  (.oo^-.oog  mm.),  and  coarse  (.oio-.o2o  mm.).  In 
general,  the  thicker  fibres  are  the  longer  and  are  the  processes  of  large 
nerve-cells  ;  conversely,  the  finer  have  shorter  courses  and  belong  to 
small  cells.  Although  subject  to  many  exceptions,  the  motor  fibres 
are  usually  the  thicker  and  the  sensory  the  smaller. 

.Since  there  are  many  more  nerve-fibres  than  nerve-cells,  it  is  evi- 
dent that  the  former  must  undergo  division  along  their  course.  Such 
doubling  always  occurs  at  a  point  corresponding  to  a  node  of  Ranvier, 
never  within  the  internodal  segment,  the  sheaths  being  continued  over 
the  two  resulting  fibres.  On  approaching  their  peripheral  termination 
the  branching  becomes  more  frequent  and  the  medullary  sheath  thinner 
until  it  ends,  after  which  the  axis-cylinder  continues  invested  with  only 
the  attenuated  neurilemma.  The  latter,  now  reduced  to  an  extremely 

delicate  covering  beset  with  occasional  nuclei,  sooner  or  later  disappears,  the  naked  axis-cylinder 
alone  being  prolonged  to  end  finally  in  the  varicose  threads  of  the  telodendrion. 

The  nonmedullated  nerve-fibres  proper,  also  termed  pale  fibres  or  fibres  of  Remak,  include 
those  that  are  without  the  myelin  sheath  throughout  their  course.  They  are  chiefly  the  axones 
of  sympathetic  neurones.  Devoid  of  medullary  sheath,  these  fibres,  often  .002  mm.  or  less  in 
diameter,  consist  of  only  the  axis-cylinder  and  the  neurilemma,  the  latter  being  thinner  and 
more  delicate  than  on  the  medullated  fibres.  Like  the  latter,  the  pale  fibres  end  in  telodendria 
composed  of  naked  axis-cylinders,  bearing  irregular  varicosities. 


Nonmedullated  nerve- 
fibres  in  longitudinal  section 
of  splenic  nerve.  X  310. 


FIG.  847. 


Neuroglia. — The  neurones  (nerve-cells  and  fibres)  within  the  cerebro-spinal 
axis  are  everywhere  held  together  by  a  special  supporting  tissue  known  as  neuroglia. 

The  latter  is  primarily  derived  from  the  invagi- 
nated  ectoblast  lining  the  neural  tube,  certain 
elements,  the  sporigioblasts,  being  devoted  to  the 
production  of  the  neuroglia,  while  others,  the 
neuroblasts,  give  rise  to  the  neurones.  At  first 
the  supporting  tissue  is  represented  by  greatly 
elongated,  radially  disposed  fibre-cells  that  often 
extend  the  entire  thickness  of  the  wall  of  the 
neural  canal.  Later,  the  neurogliar  elements 
become  differentiated  into  (#)  those  bordering 
the  lumen  of  the  canal,  which  are  partly  retained 
as  the  ependymal  cells,  and  (<£)  those  which  have 
early  migrated  to  more  peripheral  locations  and 
given  rise  to  stellate  cells  that  are  converted 
into  spider-like  elements,  the  astrocytes.  Seen 
in  chrome-silver  preparations  (Fig.  847)  these 
appear  as  irregular  triangular  or  quadrilateral 
cells  from  whose  angles  numerous  delicate 
fibrillae  extend  between  the  surrounding  nervous 
elements.  According  to  Rubaschkin,1  the  astro- 
cytes are  transformations  from  larger  branched  gliogenetic  cells,  by  the  conversion  of 
whose  robust  protoplasmic  processes  the  delicate  fibrillcz  that  later  form  the  chief 

1  Archiv  f.  mikros.  Anat.  u.  Entwick.,  Bd.  64,  1904. 


Young  neuroglia  cells ;   astrocytes,  from  brain 
of  child.    X  300. 


IOO4 


HUMAN  ANATOMY. 


constituents  of  the  neuroglia  arise.  So  long  as  neuroglia  is  being  produced,  as  in 
the  nervous  axis  of  young  animals,  the  large  gliogenetic  cells  are  present  and  directly 
concerned  in  the  production  of  additional  fibrillae,  their  cytoplasm  becoming  pro- 
gressively less  granular  and  reduced  through  the  various  transition  phases  until  in 
the  final  condition,  as  the  small  glia  cells,  little  more  than  the  nucleus  remains. 
During  these  changes  very  many  fibrillae  lose  their  connection  with  the  cells  and,  in 
conjunction  with  the  glia  threads  still  attached  to  the  astrocytes,  form  an  elaborate 
interlacement  in  which  the  neuroglia  cells,  now  reduced  and  for  the  most  part  devoid 
of  processes,  lie  scattered  at  uncertain  intervals. 

In  all  parts  of  the  central  nervous  system  the  mature  neuroglia  consists  of 
essentially  the  same  tissue,  the  differences  presented  in  certain  localities  depending 
largely  upon  variations  in  its  compactness.  Everywhere  the  chief  part  of  the  sup- 
porting tissue  consists  of  the  intricate  felt-work  of  fibrillae,  glia-fibrcs,  as  they  are 
called,  wrhich  are  usually  free  but  to  some  extent  connected  with  the  spider-cells  or 
astrocytes.  Where,  however,  the  neuroglia  borders  the  neural  tube  (the  ventricles 
of  the  brain  and  the  central  canal  of  the  spinal  cord)  as  the  ependymal  layer,  its 
arrangement  exhibits  peculiarities  that  call  for  later  special  mention. 

In  the  immediate  vicinity  of  the  neurones  the  felt-work  of  the  fibrillse  is  unusually  close,  so 
that  the  cell-bodies  and  the  roots  of  the  processes  are  surrounded  by  a  protecting  sheath,  the 
glia-capsulc.  This  diminishes  along  the  dendrites,  and  after  these  begin  to  branch  the  neuroglia 
no  longer  forms  a  complete  special  investment.  The  medullated  nerve-fibres  within  the  brain 
and  spinal  cord  are  also  provided  with  delicate  neurogliar  sheaths  which  replace  the  neurilemma 
which  on  these  fibres  is  wanting.  These  sheaths  are  prolonged  for  some  distance  on  the  fibres 

of  the  roots  of  the  spinal  nerves.  The  fibres  of  the  optic 
nerve  and  of  the  olfactory  tract  are  accompanied  through- 
out their  length  by  neurogliar  sheaths,  those  of  the 
remaining  cranial  nerves  losing  these  envelopes  shortly 
after  leaving  the  brain  (Rubaschkin). 

Beneath  the  pia  mater  the  neuroglia  is  especially 
dense  and  forms  the  external  subpial  layer  that  every- 
where invests  the  nervous  mass,  following  all  the  inequali- 
ties of  its  surface.  In  this  manner  the  pia  mater  is  excluded 
and,  except  where  its  connective-tissue  strands  accompany 
the  blood-vessels  that  enter  the  nervous  mass,  takes  no 
part  in  the  make-up  of  the  supporting  stroma.  The 
subpial  layer  consists  of  a  dense  felt-work  of  glia-fibres, 
disposed  in  various  planes,  which  are  partly  free  and  partly 
the  processes  of  spider  cells.  Internally  the  layer  fades 
into  the  adjoining  diffuse  neuroglia  without  demarcation. 
At  the  periphery  the  fibres  often  exhibit  a  radial  disposi- 
tion, their  outer  ends  usually  being  somewhat  expanded. 
\Yithin  the  white  matter  the  neuroglia,  both  in  its  distri- 
bution and  density,  is  fairly  uniform,  although  special 
tracts  often  separate  the  larger  bundles  of  nerve-til >n-s. 
Its  arrangement  within  the  gray  matter  presents  less 
uniformity,  since  more  or  less  marked  condensations 
occur  where  the  nerve-cells  are  collected  into  nuclei,  as 
conspicuously  seen  in  the  inferior  olive. 


FIG.  848. 


Ependymal  cells  and  adjacent  neuro- 
glia surrounding  central  canal  of  spinal 
cord  of  cat.  X  75.  (Rubaschkin.) 


Where  the  neuroglia  borders  the  neural  tube 
(especially  the  central  canal  of  the  spinal  cord)  it 
constitutes  the  ependymal  layer,  the  peculiari- 
ties of  which  call  for  special  mention.  The  imme- 
diate lining  of  the  tube  consists  of  a  single  layer  of 

pyramidal  epithelial  elements,  the  ^nidynial  celts,  whose  free  surfaces  or  bases  look 
towards  the  lumen,  and  the  apices  towards  the  surrounding  nervous  tissue.  At  least 
during  the  earlier  years  in  man,  and  throughout  life  in  many  lower  mammals,  the 
free  surface  of  each  cell  is  beset  with  a  number  of  hair-like  processes  that  in  their 
relations  with  the  cytoplasm  correspond  to  ordinary  cilia.  The  pointed  distal  end  of 
the  epemlvmal  cell  is  prolonged  into  a  conical  process  that  is  directly  continued 
into  usually  a  single  neurogliar  fibre  which,  after  a  course  of  uncertain  length  becomes 


THE   NERVOUS   TISSUES.  1005 

lost  in  the  surrounding  complex  of  glia-fibres.  In  young  tissue  the  apical  processes 
often  exhibit  evidences  of  breaking  up  into  a  number  of  fine  fibrillae.  Where  the 
processes  enter  robust  tracts  of  neuroglia,  as  in  the  posterior  longitudinal  septum  of 
the  spinal  cord,  they  are  of  unusual  length.  In  addition  to  the  radially  directed 
fibres  connected  with  the  ependymal  cells,  the  fibre-complex  of  the  ependymal  zone 
includes  many  fibrillae  that  are  circularly  and  longitudinally  disposed.  Scattered 
glia  cells,  some  stellate  but  mostly  small,  are  also  present  and  represent  the  elements 
from  which  the  neuroglia-fibrillae  have  been  derived. 

In  the  preceding  account  of  the  elements  composing  the  nervous  tissues  the  neurones  have 
been  regarded  as  the  morphological  units,  each  retaining  its  individual  anatomical  indepen- 
dence, although  functionally  closely  related  with  other  similar  units.  This  conception,  com- 
monly referred  to  as  the  Neurone  Doctrine  and  strikingly  formulated  by  Waldeyer  in  1891, 
stands  in  contrast  to  the  prior  views  by  which  actual  continuity  was  attributed  to  the  nerve-cells 
by  means  of  the  union  assumed  to  exist  within  the  terminal  net-works  of  their  processes.  The 
independence  and  true  relation  of  the  neurone  was  established  largely  through  the  convincing 
embryological  investigations  of  His  and  the  renewed  study  of  the  nerve-cells  as  demonstrated 
by  the  improved  applications  of  the  Golgi  silver-impregnations,  supplemented  by  the  method 
of  vital  staining  by  methylene  blue  introduced  by  Ehrlich.  The  Neurone  Doctrine  has  gained 
wide  acceptance  and  the  support  of  the  most  distinguished  anatomists,  among  those  who  have 
materially  strengthened  its  position  being  Kolliker,  Ramon  y  Cajal,  Retzius,  Lenhosse'k, 
Waldeyer,  van  Gehuchten,  and  Edinger. 

The  neurone  conception,  securely  founded  as  it  is  upon  a  vast  mass  of  evidence  collected 
from  a  wide  field  by  the  most  painstaking  and  accurate  observation,  has  not  escaped  challenge, 
and  at  present  is  assailed  by  a  group  of  histologists  headed  by  Apathy  and  Bethe,  who  not  only 
bitterly  oppose  the  integrity  of  the  neurone  as  an  independent  unit,  but  also  strive  to  depose  the 
nerve-cell  from  its  dignity  as  the  fundamental  physiological  factor.  In  1897  Apathy1  published 
his  observations  on  the  structure  of  the  ganglia  of  certain  invertebrates,  as  revealed  by  a  new 
mercuric  gold-chloride  method,  and  thereby  established  the  important  fact  that  the  cell-body 
and  processes  of  the  neurone  are  pervaded  by  fine  neurofibrillae,  thus  confirming  the  fibrillar 
structure  of  the  nerve-cell  advanced  by  Max  Schultze  more  than  a  quarter  of  a  century  before. 
Following  Apathy,  Bethe2  investigated  the  tissues  of  the  higher  animals  and  succeeded  in  dem- 
onstrating the  existence  of  the  neurofibrilke  within  the  neurones  of  man.  According  to  these 
observers,  the  neurofibrillae,  although  interlaced  without  junction  within  the  cell-bodies,  are 
independent  threads,  that  are  not  confined  to  the  neurones  but  pass  beyond  and  unite  with 
fibres  from  other  sources.  The  neurofibrillae,  therefore,  and  not  the  nerve-cells,  are  the  essen- 
tial elements  of  the  nervous  system,  the  cells  being  only  interposed  along  the  path  of  conduc- 
tion. Indeed,  according  to  these  views,  the  neurofibrillae  are  independent  of  and,  in  a  sense, 
foreign  to  the  nerve-cells,  leaving  or  entering  the  latter  at  pleasure  and  constituting  by  their 
union  a  continuous  path  of  conduction  from  the  receptive  element  to  the  muscle-fibre.  Apdthy, 
moreover,  assumes  the  existence  throughout  the  central  nervous  system  of  a  fibrillar  net-work 
formed  outside  and  between  the  nerve-cells  by  the  neurofibrillae  from  which  the  axones  may 
arise  independently  of  the  nerve-cells.  It  is  evident  that  if  such  be  the  case  the  conception  of 
the  neurone  as  an  individual  unit  falls. 

The  criticism  made  by  the  newer  school,  that  the  supporters  of  the  neurone  theory  relied 
upon  methods  which  inadequately  demonstrated  the  ultimate  terminal  relations  (the  assumed 
union  in  net-works)  has  been  met  by  the  introduction  of  the  still  newer  methods  of  Beilschow- 
sky  and  especially  of  Cajal,  which  have  yielded  preparations  that  demonstrate  that  the  neuro- 
fibrillae everywhere  form  net- works  within  the' cell-bodies  of  the  neurones,  are  confined  to  their 
processes,  and  even  in  their  ultimate  endings  form  ununited  terminal  arborizations.  It  seems, 
indeed,  that,  at  present  at  least,  the  defenders  of  the  neurone  theory  may  with  justice  charge 
their  opponents  in  turn  with  depending  upon  methods  that  only  partially  show  the  relations  of 
the  neurofibrillae  within  the  neurones.  Retzius,  than  whom  no  more  experienced  and  competent 
authority  in  this  difficult  field  of  research  can  be  consulted,  has  recently  reviewed  the  entire 
question  and  presented3  most  convincingly  the  facts  that  enable  him,  as  well  as  the  most 
distinguished  anatomists  of  to-day,  still  vigorously  to  champion  the  Neurone  Doctrine.  After 
a  critical  and  scientific  discussion  of  the  arguments  advanced  by  Apathy,  Bethe  and  Nissl,4 
Retzius  rests  his  case  with  little  concern  as  to  the  verdict  of  those  to  whom  facts  and  not 
speculation  most  appeal. 

1  Mitteilungen  aus  d.  Zoolog.  Station  zu  Neapel,  Bd.  xii.,  1897. 

2  Allgemeine  Anat.  u.  Physiol.  des  Nervensystems,  1903. 

3  Biologische  Vntersuchungen,  N.  F.,  Bd.  xii.,  1905. 

4  Die  Neuronenlehre  und  ihre  Anhjinger,  1903. 


ioo6 


HUMAN    ANATOMY. 


The  Nerve-Trunks. — The  fibres  composing  the  peripheral  nervous  system  are 
grouped  into  the  larger  and  smaller  nerve-trunks  which  extend  to  various  parts  of  the 
body.  In  the  make-up  of  those  that  supply  both  muscles  and  sensory  surfaces 
(integument  or  mucous  membranes),  as,  for  example,  the  median  or  the  third  division 
of  the  trigeminal  nerve,  three  sets  of  fibres  are  included  :  ( i )  the  efferent  axones  of 
motor  neurones  whose  cell-bodies  are  situated  within  the  spinal  cord  or  brain  ;  (2)  the 
afferent  dendrites  of  sensory  neurones  within  the  spinal  and  other  sensory  ganglia  ; 
and  (3)  the  efferent  axones  of  neurones  within  the  sympathetic  ganglia  that  accompany 
the  spinal  fibres  to  the  periphery  and  serve  for  the  innervation  of  the  involuntary 
muscle  of  the  blood-vessels  and  of  the  skin  and  the  glands. 

The  nerve-fibres,  the  various  kinds  usually  more  or  less  intermingled,  are 
grouped  into  bundles,  the  funiculi,  which  differ  in  number  and  diameter  according 
to  the  size  of  the  entire  trunk  that  they  form.  Each  funiculus  is  surrounded  by  a 
definite  sheath  of  dense  connective  tissue,  the  perineurium,  which  is  directly  con- 
tinuous with  the  delicate  fibre-elastic  tissue  prolonged  between  the  individual  nerve- 
fibres  as  the  endoneurium.  When  well  represented,  the  sheath  of  the  funiculus 
consists  of  concentric  lamellae  of  fibrous  tissue  which  enclose  perineurial  lymph-spaces. 

FIG.  849. 


Epineurium 


_^—  Blood-vessels 

•  ''iV-p.   '» 

^~ — — Perineurium 


- 


.Funiculus  of 
nerve-fibres 


•SBBfi 

' 

Transverse  section  of  small  nerve-trunk  composed  of  loosely  united  funiculi.    X  20. 

The  latter,  lined  by  flattened  connective-tissue  plates,  are  in  relation  with  the  clefts 
between  the  nerve-fibres,  on  the  one  hand,  and  with  the  lymphatics  within  the  inter- 
funicular  tissue  on  the  other.  Where,  as  usual,  the  nerve  is  composed  of  several 
funiculi,  these  are  loosely  bound  together  and  the  entire  trunk  so  formed  is  invested 
by  a  general  fibre-elastic  envelope,  the  cpinci(riuin<  in  which  course  the  blood-vessels 
and  lymphatics.  These  envelopes  of  the  nerve-trunk  are  continued  over  its  branches, 
even  onto  its  smallest  subdivisions.  The  last  representative  of  these  coverings 
is  seen  on  the  individual  fibres  as  the  sheath  of  Hcnlc,  that  surrounds  the  fibre 
and  consists  of  flattened  cells  and  delicate  strands  of  connective  tissue  outside  the 
neurilemma. 

In  cross-sections  of  the  nerve-trunk  (Fig.  850),  the 'transversely  cut  individual 
medullated  nerve-fibres  appear  as  small  circles,  sharply  defined  by  a  tine  outline  (the 
neurilemma),  each  enclosing  a  deeply  stained  dot  (the  axis-cylinder  in  section). 
The  interval  between  the  latter  and  the  neurilemma,  corresponding  to  the  space 
occupied  by  the  myelin,  usually  appears  clear  and  unstained  with  the  exception  of 
delicate  and  uncertain  suggestions  of  membranous  septa.  In  contrast  with  its 
unstained  appearance  in  sections  tinged  with  carmine,  after  the  action  of  osmic  acid 
or  special  hematoxylin  staining  ( Wcigert  )  the  medullary  substance  exhibits  a  dark 
color  and  the  axis-cylinder  appears  surrounded  by  a  deeply  tinted  ring.  The  neuri- 


THE   NERVOUS    TISSUES. 


1007 


lemma  nuclei  are  occasionally  seen  as  deeply  stained  crescentic  figures  that  partially 
embrace  the  nerve-fibre,  lying  beneath  the  neurilemma  within  depressions  in  the 
medullary  substance. 

FIG.  850. 


Perineurium 


';.j,,"<t£^'-   -•  Endoneurium 


Nerve-fibre 


Epineurium 


Blood-vesse 


Transverse  section  of  funiculus  composed  of  nerve-fibres  held  together  by  endoneurium  and 
surrounded  by  perineurium.     X  175. 

Viewed  in  cross-section,  the  nonmedullated  fibres  appear  as  small  irregularly 
round  figures  arranged  in  groups  that  .correspond  to  bundles  (Fig.  851).  When 
numerous,  the  latter  are  aggregated 

FIG.  851. 

Epineurium 


into  secondary  bundles  between 
which  extend  delicate  connective- 
tissue  septa,  continuous  with  the 
general  envelope  investing  the  nerve- 
trunk.  The  medullary  substance 
being  wanting,  the  pale  fibres  are 
of  small  size  and  often  possess  a 
diameter  of  less  than  .001  mm. 

The  Ganglia.— The  cell- 
bodies  of  the  neurones  that  consti- 
tute the  sensory  pathways  within  the 
peripheral  nerves  and  of  the  neu- 
rones of  the  sympathetic  system 
are  collected  at  various  points  into 
aggregations  known  as  ganglia. 
Familiar  examples  of  the  latter  are 
the  spinal  ganglia  on  the  posterior 
roots  of  the  spinal  nerves,  certain 
cranial  ganglia  (as  the  Gasserian 
connected  with  the  fifth  nerve,  the 
acoustic  with  the  eighth,  and  those  on  the  trunks  of  the  seventh,  ninth  and  tenth 
cranial  nerves),  and  the  sympathetic  ganglia  along  the  gangliated  cords  and  within 
various  plexuses  of  the  sympathetic. 

A  longitudinal  section  of  a  spinal  ganglion  (Fig.  852),  which  may  be  taken 
as  a  type  of  such  collections,  shows  the  entire  ovoid  mass  to  be  enclosed  by  a  fibrous 
capsule  continuous  with  that  ensheathing  the  nerves.  Immediately  beneath  the 
capsule  the  ganglion-cells  are  arranged  in  a  fairly  continuous  layer  of  varying  thick- 
ness, while  the  cells,  more  deeply  placed,  are  broken  up  into  groups  by  the  tracts  of 


Inter-fascicular 
septum 


Transverse  section  of  small  splenic  nerve  consisting  chiefly  of 
nonmedullated  fibres.     X  200. 


ioo8 


HUMAN   ANATOMY. 


intervening  nerve-fibres,  a  small  amount  of  connective  tissue  prolonged  from  the 
endoneurium  of  the  nerve-bundles  and  accompanying  the  blood-vessels  being  also 


FIG.  852. 


Posterior  root  (sensory ) 


Spinal  cord 


Spinal  ganglion 


FIG.  853. 

Nerve-fibres,  cut  transversely 
Nerve-cell 


Anterior  (motor)  root 

Common  trunk  of  spinal  nerve 
Anterior  division 

Section  of  spinal  nerve,  showing  its  roots,  ganglion,  common  trunk  and  primary  divisions.    X  10. 

present.      The  chief  ganglion-cells  are  from  .060-. 080  mm.  in  diameter,  but  some 
measure   as    much    as  .170    mm.    and    others   as    little   as  .025   mm.      In    sections 

(Fig.  853)  they  usually  appear  round  or  oval, 
since  only  exceptionally  are  their  processes  to 
be  seen.  Each  cell  is  enclosed  by  a  richly 
nucleated  capsule  which  is  continuous  with  the 
sheath  of  the  nerve-fibres.  Most  of  the  many 
other  oval  nuclei  that  are  conspicuous  in  sections 
of  the  ganglia  belong  to  the  neurilemma  of  the 
nerve-fibres  and,  hence,  are  seen  as  chains  ex- 
tending in  different  planes.  Although  by  far 
the  greater  number  of  the  nerve-cells  within 
the  spinal  ganglia  are  (a}  the  cell-bodies  of 
the  sensory  neurones,  whose  processes  course 
within  the  spinal  nerves,  additional  nervous  ele- 
ments are  also  present.  According  to  Pogicl ' 
among  these  are  (&}  cells  of  type  II,  which, 
while  closely  resembling  the  chief  neurones  in 
the  form  and  appearance  of  their  cell-bodies, 
differ  from  them  in  possessing  processes  that 
are  confined  to  the  ganglion  and  end  in  fine 
ramifications  over  or  beneath  the  capsules  of  other  ganglion-cells.  The  cell-bodies 
of  the  neurones  of  type  II  are  in  turn  surrounded  by  end-plexuses  of  probably 

1  Anatomischer  Anzeiger,  I'.d.  \ii.,  iSg6. 


Capsule 


•t>  '-  ~~~^  Nerve-fibres 

Section   o!   s)iin;il   ganglion,  showing  nerve-cells 
surrounded  by  inn  k-ati  .1  capsules.     X 


DEVELOPMENT   OF   THE   NERVOUS   TISSUES. 


1009 


Diagram  of  constituents  of  spinal  ganglion  ;  blue  lines  repre- 
sent efferent  fibres ;  black,  afferent ;  red,  sympathetic;  a,  sensory 
ganglion  cells;  c,  cells  of  type  II,  whose  axones  end  (6)  around 
sensory  cells;  3,  sympathetic  neurone;  AR,  P/f,  anterior  and 
posterior  roots;  AD,  PD,  anterior  and  posterior  primary  divi- 
sions of  spinal  nerve;  RC,  ramus  communicans. 


sympathetic  fibres  (Dogiel).  Finally  (<:)  a  few  multipolar  nerve-cells  are  usually 
found  within  the  spinal  ganglia  that  in  shape  and  structure  resemble  the  cell-bodies 
of  the  sympathetic  neurones. 

The  sympathetic  ganglia  are  represented  by  those  of  the  great  gangliated  cords, 
certain  cranial  ganglia  (ciliary,  spheno-palatine,  otic,  and  submaxillary),  the  ganglia 
within  the  three  prevertebral  plexuses,  and  the  innumerable  small  and  often  micro- 
scopic ganglia  associated  with  the  muscular  tissue  of  the  digestive,  respiratory  and 
uro-genital  tracts,  in  the  heart  and  in  the  various  glands. 

In  their  general  structure  the  sympathetic  ganglia  are  similar  to  those  connected 
with  the  spinal  nerves,  forming  definite  masses  enclosed  by  a  fibrous  capsule,  from 
which  connective-tissue  processes  pass  into  the  interior  of  the  ganglion  for  the  support 
and  separation  of  the  nervous 

elements.     The   individual    gangli-  FIG.  854. 

on-cells — unipolar,  bipolar  or  multi- 
polar — are  ensheathed  by  nucleated 
capsules  continuous  with  the  neuri- 
lemma  of  the  nerve-fibres.  The 
sympathetic  ganglion-cells  are  vari- 
ously related  to  the  terminal  ramifi- 
cations of  (a)  other  sympathetic 
neurones  and  of  (^)  the  neurones 
of  the  central  nervous  system  (by 
way  of  the  white  rami  fibres  or  their 
equivalents).  In  both  cases,  the 
ramification  of  the  nonmedullated 
and  fine  fibre  in  the  one  and  of  the 
medullated  fibre  in  the  other,  a 
pericellular  plexus,  commonly  en- 
closes the  cell-body.  In  the  lower 
vertebrates  (amphibians  and  reptiles),  the  spinal  fibre  frequently  winds  spirally  around 
the  single  process  of  the  ganglion-cell  before  breaking  up  into  the  pericellular  plexus 
(Huber1).  The  broader  relations  of  the  component  nervous  elements  of  the  spinal 
ganglia  are  considered  in  connection  with  the  Sympathetic  System  (page  1354). 

DEVELOPMENT  OF  THE  NERVOUS  TISSUES. 

Reference  to  the  account  of  the  early  development  of  the  nervous  system  (page  26)  will 
recall  the  fact  that  the  neural  groove,  later  the  neural  tube,  is  lined  by  invaginated  and  thickened 

ectoblast  from  which  the  essential  nervous  tissues  are 
derived.  For  the  fundamental  facts  concerning  the  histo- 
genesis  of  these  tissues  we  are  in  large  measure  indebted 
to  the  labors  of  His,  whose  account,  supplemented  by  the 
important  contributions  of  Kolliker,  Cajal,  Lenhosse'k, 
Schaper  and  others,  forms  the  basis  of  our  knowledge 
concerning  these  processes.  Although  in  its  principal 
features  the  histogenesis  is  similar  in  all  parts  of  the 
neural  tube,  in  that  portion  which  becomes  the  spinal 
cord  the  changes  are  most  typical  and  will,  therefore,  be 
here  described. 

During  the  approximation  and  closure  of  the  neural 
tube  the  cells  composing  its  wall  undergo  active  prolife- 
ration, whereby  the  wall,  at  first  composed  of  only  one 
or  two  rows  of  definitely  outlined  cells,  is  converted  into 
a  multinucleated  tract  in  which  the  cell  boundaries  dis- 
appear and  the  nuclei  lie  embedded  within  a  general 
protoplasmic  sheet  or  syncytium  (Hardesty2).  The 
large  dividing  elements  within  the  latter,  the  germinal 
cells  of  His,  are  conspicuous  on  account  of  their  mitotic 
figures  and  are  situated  close  to  the  lumen  of  the  neural  tube.  His  regarded  them  as  special 
cells  directly  concerned  in  the  production  of  the  neurones,  a  conclusion,  however,  that  has  not 

1  Journal  of  Morphology,  1899. 
"Arner.  Journal  of  Anatomy,  vol.  iii.,  1904. 
64 


FIG 


Segment  from  lateral  wall  of  neural  tube 
of  pig  embryo  of  5  mm. ;  syncytium  replacing 
distinctly  outlined  cells,  a,  inner  zone;  g, 

ferminal  cells;   ilm,  internal  limiting  mem- 
rane ;   m,  peripheral  zone ;   r,  radial  strands 
of  cytoplasm.     X  690.     (Hardesty.) 


IOIO 


HUMAN    ANATOMY. 


been  sustained  (Kolliker,  Schaper  and  others)  since  the  primary  germinal  cells  probably  only 
represent  proliferating  elements  engaged  in  forming  what  for  a  time  is  an  undifferentiated  tissue. 
The  cells  composing  the  neural  wall  are  at  first  in  close  contact,  their  blended  cytoplasm 
(syncytium)  forming  an  almost  unbroken  sheet.  Soon,  however,  this  continuity  is  interrupted 
in  consequence  of  the  longitudinal  expansion  of  the  tissue  and  the  appearance  of  spaces,  and  the 
cell-substance  is  resolved  into  a  delicate  reticulum,  the  myelospongium  of  His,  which  becomes 
condensed  at  the  inner  and  outer  margins  of  the  wall  of  the  neural  tube  into  the  internal  and 
external  limiting  membrane. 

The  meshes  of  the  reticulum  enlarge,  the  intervening  nucleated  tracts  of  cytoplasm  elongate 
and  the  increasing  nuclei  become  radially  disposed.  By  reason  of  these  changes  the  elements 
next  the  lumen  of  the  tube  assume  a  columnar  form  and  radial  arrangement  and  become  the 
primary  ependymal  cells.  The  remaining  elements,  appropriately  named  the  indifferent  cells 
(Schaper),  increase  in  number  in  consequence  of  the  continued  division  of  the  germinal  cells  and 
gradually  become  collected  as  the  nuclear  layer  at  some  distance  beyond  the  ependymal  zone. 
Meanwhile  and  very  early,  the  peripheral  portion  of  the  supporting  framework  adjoining 
the  outer  border  of  the  neural  wall  becomes  denser  and  free  from  nuclei  and  is  converted  into 

the  marginal  zone  ( Randschleier  of 

FIG.  856.  His),  that  is  continuous  with  the 

delicate  reticulum  pervading  the 
other  parts  of  the  wall.  The  in- 
different cells  later  differentiate 
into  (a)  the  spongioblasts  from 
which  the  characteristic  constitu- 
ents of  the  definite  supporting 
tissue,  the  neuroglia,  are  derived, 
and  (£)  the  neuroblasts  that  are 
directly  converted  into  the  neu- 
rones. Within  the  resulting  cell- 
complex  that  for  a  time  occupies 
the  greater  part  of  the  wall  of 
the  neural  tube,  it  is  difficult  to 
distinguish  with  certainty  between  the  neuroglia  and  neuron-producing  elements,  since  both 
are  often  elongated  in  shape  and  prolonged  into  processes. 

Histogenesis  of  the  Neuroglia. — In  addition  to  the  extension,  condensation  and  moulding 
(by  the  developing  nerve-cells  and  fibres)  that  the  primary  syncytial  meshwork  undergoes 

FIG.  857. 


elm 


Segment  of  wall  of  neural  tube  of  pig  embryo  of  10  mm.;  radial 
strands  (r)  of  syncytium  and  differentiation  of  ependymal  (a),  nuclear 
(6)  and  marginal  (m)  layers;  tint,  elm,  internal  and  external  limiting 
membrane ;  g,  dividing  cell ;  /,  pia  mater.  X  690.  (Hardesty.) 


Transverse  section  of  ventro-lateral  segment  of  developing  spinal  cord  from  pig  embrvo  of  .;<>  nun.,  uppei  ; 
figure  from  chrome-silver  preparation,  lower  part  trom  oiu-  stained  with  toltiiclin  hi  no  ;  r,  central  canal  ;  ff>.  ependymai 
lavi-r  •     H.   nuclear   layer;    m,  marginal    layer;    /,   radial    fibres  ;    i'.   ventral    plate  uniting   halves   of   cord.     X  240. 
(Hardesty.} 

(Hardesty),  the  gradual  transformation  of  the  spongioblasts  and  their  descendants  into  fibrillae 
establishes  a  more  definite  framework  that  replaces  the  primary  net-work  (myelospongium),  and 
eventually,  in  conjunction  with  the  fibtilhe  derived  from  the  processes  of  the  ependymal  cells, 


DEVELOPMENT   OF   THE   NERVOUS   TISSUES. 


ion 


FIG. 


gives  rise  to  the  definite  supporting  tissue,  the  neuroglia.  According  to  Hardesty,  the  glia-fibres 
arise  within  the  syncytial  tissue  independently  of  the  neuroglia  cells,  a  view  in  direct  opposition 
to  the  observations  of  Rubaschkin,  who  attributes  to  the  descendants  of  the  spongioblasts,  the 
gliagenetic  cells,  a  positive  role  in  the  production  of  the  fibres.  Accepting  the  conclusions  of 
the  last-named  investigator,  the  successive  stages  of  the  cells  concerned  in  the  production  of 
the  general  neurogliar  tissue  are  represented  by  the  spongioblasts,  the  gliogenetic  cells,  the 
astrocytes,  and,  finally,  the  glia  cells.  The  primary  ependymal  elements  are  succeeded  by  the 
epithelium  which  lines  the  ventricles  and  the  central  canal  of  the  spinal  cord.  Their  periph- 
erally directed  processes  are  in  large  part  transformed  into  glia-fibres  and  thus,  along  with  the 
processes  of  the  spider  cells,  contribute  to  the  formation  of  the  neurogliar  felt-work.  The 
accompanying  illustration  (Fig.  857),  taken  from  Hardesty's  paper,  affords  an  instructive 
comparison  of  the  appearance  of  the  young  supporting  tissue  after  true  staining  with  approved 
reagents  (Benda)  and  after  silver  precipitation  methods  (Golgi)  upon  which  so  much  reliance 
has  been  placed.  The  silver  picture  shows  the  classic  long  neurogliar  fibres  extending  the 
entire  thickness,  but  fails  to  reveal  the  wealth  of  supporting  tissue  and  nuclei.  To  what 
extent  the  mesoblastic  ingrowths  that  follow  the  penetrating  young  blood-vessels  into  the  neural 
wall  take  part  in  the  production  of  the  distinctive  neurogliar  framework  is  admittedly  difficult  to 
determine  (Hardesty)  ;  that  such  tissue,  however,  contributes  to  the  support  of  the  nervous 
elements  is  certain. 

Histogenesis  of  the  Neurones.— The  neuroblasts  are  distinguishable  with  certainty  from  the 
spongioblasts  as  soon  as  they  are  provided  with  nerve-processes.  The  latter  appear  as  out- 
growths from  the  pointed  and 
peripherally  directed  ends  of  the 
developing  nerve-cells,  invade  the 
marginal  zone,  and  later  emerge 
from  the  wall  of  the  immature 
cord  as  the  ventral  or  anterior 
root-fibres  of  the  spinal  nerves 
(Fig.  858).  The  deeper  tint  of 
their  distal  ends  after  staining, 
their  tendency  to  collect  in  con- 
verging groups,  and  the  uniform 
width  of  the  outgrowing  nerve- 
processes  are  disinctive  character- 
istics of  the  neuroblasts  (His1). 
The  first,  and  for  a  considerable 
time  the  only  processes  with  which 
the  neurones  are  provided  cor- 
respond to  the  axones  that  be- 
come the  axis-cylinders  of  the 
efferent  (motor)  nerves.  Subse- 
quently other  processes,  the  den- 
drites,  grow  out  in  various  direc- 
tions from  the  cell-bodies  of  the 
young  neurones. 

Development  of  the  Peripheral  Nerves. — According  to  the  teaching  of  His,  accepted  by 
most  anatomists,  the  axis-cylinder  of  the  entire  future  nerve-fibre  is  formed  by  the  peripheral 
growth  of  the  original  nerve-process  of  the  neuroblast.  The  assumed  development  of  the  nerve- 
fibre  by  the  union  of  a  number  of  segments  ( Balfour,  Dohrn,  and  others,  and,  more  recently, 
Bethe  and  O.  Schultze)  is  not  in  accord  with  renewed  investigations,  and  the  findings  upon 
which  the  composite  theory  of  the  fibre  is  based  are  open  to  different  interpretation  (Kolliker, 
Retzius). 

According  to  Bardeen,2  the  development  of  the  peripheral  spinal  nerves  is  briefly  as  follows: 
The  motor  neuroblasts  and  the  sensory  spinal  ganglion-cells  send  out  processes  of  considerable 
thickness,  all  of  which  soon  begin  to  give  rise  at  their  extremities  to  groups  of  fibril/a:,  which 
increase  in  thickness  and  length  and,  in  turn,  at  their  extremities  give  rise  to  new  groups  of 
fibrils.  At  first  these  proceed  as  naked  bundles,  but  soon  become  surrounded  with  sheath-cells 
of  mesoblastic  origin  which  thus  enclose  the  early  embryonic  nerve,  that  may  contain  hundreds 
of  fibrillas.  After  a  nerve  has  become  distended  by  ingrowth  of  new  fibrils  from  behind,  the 
proliferating  sheath  cells  begin  to  wander  from  the  periphery  in  among  the  fibrillae  and  give  rise 
by  anastomosis  of  their  processes  to  a  net-work  that  divides  the  original  fasciculus  into  a  number 
of  secondary  bundles.  The  intrafascicular  cells  increase  rapidly,  the  process  of  subdivision 


Neuroblasts 


Efferent  axones 


Portion  of  spinal  cord  of  human  enibiyo,  showing  development  of 
ventral  root-axones  as  outgrowths  from  ventral  neuroblasts.  X  300. 
(After  His.} 


1  Die  Entwickelung  des  menschlichen  Gehirns,  1904. 
2Amer.  Journal  of  Anatomy,  vol.  ii.,  1903. 


IOI2 


HUMAN   ANATOMY. 


FIG. 


Developing  intercostal  nerve  of  pig 
embryo  of  10  mm. ;  tip  of  nerve  is  composed 
of  fibrils  surrounded  by  sheath-cells.  X  360. 
(Bardeen.) 


FlG.  860. 


fe  .  ' 


continues  and  the  bundles  of  fibrilke  become  progressively  smaller  and  more  compact  until, 
surrounded  by  membranous  septa,  they  correspond  to  the  axis-cylinders  of  the  individual  nerve- 
fibres,  enclosed  by  the  neurilemma  and  its  cells.  The  endoneurium  appears  comparatively  late 

and,  like  the  neurilemma,  is  a  product  of  the  mesoblast. 
Later,  condensations  of  the  mesoblast  around  the  definite 
bundles  of  nerve-fibres  and  about  the  entire  nerve-trunk 
provide  the  perineiirium  and  the  epineurium  respectively. 
During  its  course  to  the  periphery  the  young  nerve  gives 
rise  to  numerous  branches,  the  points  of  outgrowth  being 
indicated  by  a  preparatory  increase  of  the  peripheral  cells 
which  often  form  a  tubular  projection  into  which  the  nerve- 
fibrillae  grow.  The  proximal  plexuses  (such  as  the 
brachial  or  lumbar)  are  formed  during  the  outgrowth  of 
the  nerves  from  the  region  of  the  central  nervous  system  ; 
the  coarser  distal  plexuses  arise  during  the  extension  of 
the  branches  to  the  various  parts  for  which  they  are 
destined  ;  whilst  the  finer  terminal  plexuses  are  established  during  the  development  of  functional 
unity  between  the  nerve-fibres  and  the  structures  to  which  they  are  distributed. 

The  medullary  sheath  is  a  comparatively  late  acquisition,  since  it  does  not  appear  until 
about  the  fourth  month  of  foetal  life.  Within  the  central  nervous  system  the  tracts  of  nerve- 
fibres  obtain  their  medullary  coat  at  different  times  (some  not  until  after  birth),  a  variation  that 
is  of  much  service  in  enabling  the  anatomist  to  trace  the  course  of  the  individual  paths  of  con- 
duction. The  origin  and  method  of  formation  of  the  medullary  substance  has  been,  and  in  fact 
still  is,  a  subject  of  discussion.  It  is,  however,  certain  that  its  production  is  not  dependent 
upon  the  neurilemma,  since  the  medullated  fibres  within  the 
cerebro-spinal  axis  are  devoid  of  this  sheath,  and,  further, 
that  the  myelin  sometimes  appears  before  the  neurilemma 
( Roister,  Bardeen).  While  it  is  doubtful  whether  the  myelin 
is  directly  formed  from  the  outer  part  of  the  axis-cylinder, 
as  suggested  by  Kolliker,  it  is  probable  that  this  structure 
exerts  some  influence  resulting  in  the  deposit  of  the  myelin- 
droplets  either  from  the  blood  (Wlassak),  or  from  the 
apparently  fluid  substance  that  after  a  time  surrounds 
the  axis-cylinder  (Bardeen).  Regarding  the  formation  of 
\hzframework  supporting  the  droplets  of  myelin,  Hardesty1 
inclines  to  the  view  that  certain  sheath  cells,  which  appear 
during  medullation,  are  probably  concerned.  From  the 
foregoing  account  it  is  evident  that  the  axis-cylinder  is 
derived  from  the  ectoblast  and  the  neurilemma  from  the 
mesoblast ;  the  origin  of  the  medullary  sheath  is  still 
undetermined,  but  most  probably  is  mesoblastic. 

Development  of  the  Ganglia. — The  origin  of  the  afferent 
(sensory)  neurones,  whose  cell-bodies  are  situated  within 
the  spinal  and -other  ganglia,  is  entirely  different  from  that 
of  the  efferent  (motor)  ones  above  described.  In  the  case 
of  the  spinal  nerves,  the  development  of  the  ganglia  pro- 
ceeds from  a  group  of  ectoblastic  cells  that  form  a  ridge,  the 
ganglion-crest^  on  the  margin  of  either  lip  of  the  still  open 
neural  tube  (Fig.  860),  just  where  the  general  ectoblast 
passes  into  that  lining  the  groove.  On  approximation  of 
the  lips  of  the  latter,  the  cells  of  the  ganglion-crests  fuse 
into  a  wedge-shaped  mass  that  completes  the  closure  of  the 
neural  tube  and  constitutes  a  centre  of  proliferation  from 
which  the  cells  migrate  outward  over  the  dorso-lateral  wall 
of  the  tube.  The  proliferation  is  not  uniform  but  most 
marked  at  points  that  correspond  to  the  mesoblastir 
somites,  in  consequence  of  which  a  series  of  segmentally 
arranged  cell-aggregations  appears  on  each  side  of  the 
neural  tube.  These  collections  are  the  anlages  of  the 
spinal  ganglia.  Within  them  certain  cells  soon  become  fusiform  and,  assuming  the  role  of 
neuroblasts,  send  out  a  process  from  either  end.  One  process — the  axom-  grows  centrally, 
while  the  other— the  dendrite— extends  peripherally  and  becomes  the  chief  part  of  a  sensory 
nerve-fibre.  The  subsequent  growth  of  the  neurone  is  not  symmetrical,  but  to  one  side,  and  so 


Transverse  sections  of  dorsal  region 
of  human  embryos,  showini;  curly  differ- 
entiation of  spinal  ganglion  ;  A,  K,  neural 
tube  still  open;  C,  f>,  tube  rl<>M.-<l;  ", 
ganglion-ridges;  ft, faaed  tidgi-s;  c,  out- 
growth to  form  ganglion  ;  d,  ectoblast. 
X  230.  (Lenhosstk.) 


1  Amer.  Journal  of  Anatomy,  vol.  iv.,  1905. 


DEVELOPMENT   OF   THE    NERVOUS   TISSUES. 


1013 


FIG-  861. 


.'.  ^VT-*--     • 


Cross-'-ection  of  part  of  dorsal  region  of  human 
embryo,  showing  developing  spinal  ganglion ;  dz, 
vz,  mz,  dorsal,  ventral  and  marginal  zones  of 
spinal  cord ;  dr,  vr,  dorsal  and  ventral  root-fibres 
of  spinal  nerve  («)  ;  sg,  spinal  ganglion  on  dorsal 
root.  X 


ordered  that  the  two   processes  are  approximated  and  finally  joined  to  the  cell-body  by  a 

common  stalk  (Fig.  839),  the  neurone  being  thus  converted  into  an  unipolar  ganglion-cell. 

The  centrally  directed  processes,  the  later  posterior 

root-fibres  of  a  spinal  nerve,  grow  into  the  develop- 
ing cord  and  enter  the  peripheral  zone  (later  the 

white  matter)  to  end,  when  their  development  is 

completed,  at  various  levels  in  relation  with  neu- 
rones formed  within  the  neural  axis.  The  peri- 
pherally directed  processes  of  the  spinal  sensory 

neurones,    on    the   other  hand,    mingle    with   the 

axones  from  the  motor  neurones  to  form  the  mixed 

nerves  distributed  to  the  various  parts,  of  the  body. 

The  essential  parts  of  the  sensory  neurones,  the 

cell-body    and  the    processes,    are    derived  from 

ectoblastic  elements,  whilst  the  sheaths,  whether 

of  the  nerve-cells,  of  the  fibres  or  of  the  entire 

ganglion,  are  contributed  by  the  mesoblast. 

The  development  of  the  sympathetic  ganglia, 

which  include  essentially  three  sets — those  of  the 

gangliated  cords,  those  of  the  prevertebral  plexuses 

(cardiac,  solar  and  hypogastric ) ,  and  the  terminal 

— has  given  rise  to  much  discussion.     According 

to  one  view,  the   sympathetic   neurones   have  an 

independent  origin  and  only  secondarily  form  con- 
nections with  the  cerebro-spinal  nerves.  The  other 

view,    on   the   contrary,    regards  the  sympathetic 

neurones  as  the  direct  descendents  of  neurogenetic 

elements  derived  from  the  developing  spinal  nerves. 

The  evidence  in  support  of  the  last  view  is   so 

convincing  that  there  is  little  question  as  to  the 

correctness  of  its  principle,  although  many  details 

of  the   process,    as   relating  to  man,   are  still  to 

be  studied.     It  is,  however,  equally  true  that  the 

sympathetic  ganglia  are  neither  produced  by  constriction  and  isolation  of  parts  of  the  spinal 

ganglia,  as  sometimes  assumed, 

FIG.  862.  nor  bv  the  migration'  of  fully 

differentiated  ganglion -cells, 
but,  as  emphasized  by  Neu- 
mayer,  from  undifferentiated 
neuroblasts  which  undergo  in 
loco  their  development.  The 
earliest  suggestions  of  definite 
sympathetic  ganglia  in  the 
human  embryo  appear  about 
the  beginning  of  the  second 
fcetal  month  as  aggregations  of 
cells  at  the  distal  ends  of  the 
visceral  rami  of  the  developing 
spinal  nerves.  From  these  cells 
are  derived  the  definite  sympa- 
thetic neurones  of  thegangliated 
cord,  as  well  as  those  which 
follow  the  mesial  ingrowth  of 
the  spinal  fibres  for  the  pro- 
duction of  the  prevertebral  and 
terminal  ganglia.  The  lateral 
ganglia  thus  formed  constitute 
for  a  time  a  series  of  isolated 
nodes  ;  subsequently  these  are 
connected  by  the  differentiation 
of  sympathetic  axones  which 
grow  from  one  ganglion  to  the 

next  and,  in  conjunction  with  the  spinal  fibres,  establish  the  longitudinal  commissural  strands 

of  the  gangliated  cord.      Other  sympathetic  cells  send  axones  centrally  and  give  rise  to  the 

efferent  splanchnic  nerves,  whilst  the  axones  of  still  others  pass  to  the  growing  spinal  nerves. 


&&'  I    ;;'^, 


Spinal 
ganglia 


A 


Sagittal  section  ot  rabbit  embryo  showing  several  developing  spinal  ganglia 
and  nerve-trunks  ;  A,  aorta;  .S,  intersegmental  artery.     X  52. 


HUMAN   ANATOMY. 


NERVE-TERMINATIONS. 

The  terminations  of  the  fibres  composing  the  peripheral  nerves — the  axones  of 
certain  motor  neurones  situated  within  the  cerebro-spinal  axis  and  the  sympathetic 
system  and  the  dendrites  of  the  neurones  of  the  sensory  ganglia — supply  the  means 
by  which  the  various  structures  of  the  body  are  brought  into  intimate  relation 
with  the  nervous  system.  Some  of  these  terminations  transfer  impulses  resulting  in 
muscular  contractions  ;  others  convey  impressions  that  produce  various  sensations 

(pain,  pressure,  muscle-sense, 

PIG.  863.  temperature).       The    nerve- 

terminations,   therefore,  may 

V  .  be  grouped  according  to  func- 

tion into  motor  and  sensory 
endings. 

MOTOR  NERVE-ENDINGS. 

The  motor  endings  in- 
clude (a)  terminations  of  the 
axones  of  neurones  situated 
within  the  motor  nuclei  of 
the  spinal  cord  and  brain- 
stem  that  pass  to  voluntary 
muscle  ;  (d)  terminations  of 
sympathetic  neurones  that 
end  in  involuntary  muscle  and 
(c)  in  cardiac  muscle. 

Endings  in  Voluntary 
Muscle. — On  approaching 
their  peripheral  destination 
the  medullated  nerve-fibres 
branch  repeatedly,  each  fibre 
in  this  manner  coming  into 
relation  with  a  number  of  mus- 
cle-fibres. When  the  med- 
ullated nerve- fibre  reaches  the 
muscle-fibre  which  it  supplies,  its  medullary  sheath  abruptly  ends  and  the  neurilemma 
becomes  inseparably  fused  with  the  sarcolemma,  whilst  the  axis-cylinder  passes  beneath 
this  sheath  to  terminate  in  an  end-plate.  The  latter  appears  as  an  oval  area,  from 
.040— .060  mm.  in  its  greatest  diameter,  which  is  applied 
to  the  muscle-substance  ;  in  profile  it  shows  a  slight 
projection  beyond  the  contour  of  the  muscle-fibre, 
known  as  the  eminence  of  Doyere.  Embedded  within 
a  general  nucleated  sheet  of  granular  protoplasm,  the 
sole-plate,  lie  the  brush-like  terminal  arborizations  of  the 
axis-cylinder  formed  of  irregular  varicosites  and  club- 
shaped  ends.  From  the  details  of  the  development  of 
the  motor  end  plates,  as  described  by  Bardeen,  it  is 
probable  that  the  granular  sole-plate  and  its  nuclei  are 
differentiated  from  the  sarcoplasm  and  the  nuclei  of  the 
muscle-fibre  respectively.  The  much  discussed  relation 
of  the  end-plate  to  the  sarcolemma — whether  outside  or 
beneath — seems  to  be  decided  in  favor  of  a  subsarco- 
lemmal  position,  since  the  muscle-sheath  appears  sub- 
sequently to  the  formation  of  the  motor-ending,  a  fact 
that  explains  the  apparent  piercing  of  the  sarcolemma 
by  the  axis-cylinder.  Usually  each  muscle-fibre  is  pro- 
vided with  a  single  motor  end-plate,  which  may  lie  at  an 
equal  or  uiu-qual  distance  from  the  ends  of  the  fibre.  Exceptionally  two  end-plates 
may  be  found  on  one  muscle-fibre,  in  which  case  the  endings  lie  near  each  other. 


.End- 
plate 


Motor  nerve-endings  in  voluntary  muscle ;  bundle  of  nerve-fibres 
seen  separating  to  supply  the  individual  muscle-fibres.     X  160. 


FIG.  864. 


- 


Motor  in -i  \  r -ending  in  voluntary 
muscle  ;  a,  axonc  terniiiiatinv;  in  end- 
plate  ;  »,  neurilemma  ;  j.  sole-plate. 
X  4°o- 


NERVE-TERMINATIONS.  1015 

Endings  in  Involuntary  Muscle. — The  terminations  of  the  axones  of  the 
sympathetic  neurones  supplying  the  nonstriated  muscle  are  comparatively  simple. 
The  neurones  contributing  the  immediate  fibres  of  distribution 
usually  occupy  the  nodal  points  of  plexuses  from  which  bundles  FIG.  865. 

of  nonmedullated  nerve-fibres  extend  to  and  enclose  the  muscle 
fasciculi.  Entering  the  latter  the  nerve-fibres  divide  into 
delicate  varicose  threads  that  pass  between  the  muscle-cells, 
parallel  with  their  long  axes.  As  they  course  within  the 
intercellular  substance,  the  varicose  fibrils  give  off  short  lateral 
branches  that  end,  as  does  also  the  parent  fibre,  in  minute 
terminal  knots  on  the  surface  of  the  muscle-cells,  often  in  the 
vicinity  of  the  nucleus.  Probably  by  no  means  every  muscle- 
cell  individually  receives  a  nerve-ending,  a  longitudinal  group 
including  three  or  four  rows  of  muscle-cells  lying  between 
two  adjoining  terminal  nerve-fibrils  (Huber). 

Endings  in  Cardiac  Muscle. — These,  also  the  termi- 
nations of  sympathetic  neurones,  have  been  studied  by,  among     Nerve.ending  in'  invo,untary 
others,   Cajal,   Retzius,   Berkley  and   Huber.      According  to  muscle.0  (Huber.) 

the  last-named  investigator,  the  varicose  nerve-fibrils  may  be 

followed  between  the  muscle-cells,  during  which  course  side  branches  arise  that,  as 
well  as  the  main  fibril,  terminate  on  the  muscle  elements  in  endings  of  varying  com- 
plexity. In  some  cases  these  are  merely  minute  simple  end-knots,  resembling  those 
found  in  involuntary  muscle  ;  in  other  cases  they  are  more  elaborate  and  consist  of  a 
group  of  secondary  fibrillae  bearing  nodular  endings,  the  whole  recalling  somewhat 
the  motor  end-plates  in  striped  muscle.  It  is  probable  that  most  of  the  cardiac 
muscle-cells  are  in  direct  relation  with  nerve-endings  (Huber). 

SENSORY  NERVE-ENDINGS. 

Since  the  sensory  endings  are  the  peripheral  terminal  arborizations  of  the 
neurones  whose  cell-bodies  lie  in  the  spinal  and  other  sensory  ganglia,  such  teloden- 
dria  are  functionally  the  beginnings  of  the  paths  conducting  the  sensory  stimuli  to 
the  central  nervous  system.  According  to  their  relations  to  the  surrounding  tissue, 
the  sensory  endings  are  broadly  grouped  into  free  and  encapsulated. 

Free  Sensory  Endings. — These  endings  include  vast  numbers  of  nerve- 
terminations  found  in  the  skin  and  the  mucous  membranes,  chiefly  within  the 
epithelium  but  to  some  extent  also  within  the  connective  tissue  strata.  As  a  rule 
the  sensory  (afferent)  nerve-fibres  do  not  branch  to  any  extent  until  near  their 
peripheral  destination,  where  they  undergo  repeated  divisions,  always  at  a  node  of 
Ranvier  and  in  various  directions.  The  medullary  sheath  of  the  main  fibre  is 
retained  until  close  to  its  termination,  although  some  of  its  branches  may  course 
as  nonmedullated  fibres  for  a  considerable  distance  before  ending  or  entering  the 
epithelium.  In  the  skin — and  the  same  general  plan  applies  to  the  mucous  mem- 
branes— the  fibres  destined  for  the  epidermis  lose  their  myelin  coat  beneath  the 
basement  membrane  and  enter  the  epithelium  as  vertically  coursing  nonmedullated 

fibrils.  Within  the  epidermis  they  break  up  into 
numerous  delicate  fibrils  which  undergo  further  divi- 
sion into  still  finer  varicose  threads  that  ramify 
between  the  cells  of  the  stratum  germinativum  and 
terminate  in  minute  free  end-knobs  (Fig.  866). 
Although  an  intracellular  position  of  these  nerve- 
endings  has  been  described  by  various  writers,  it 
is  probable  that  the  endings  are  extracellular  and  lie 
upon  the  surface  of  and  not  within  the  epithelial 
Free  sensory  endings  within  epidermis  elements.  Similar,  but  far  less  numerous,  free  end- 

^&Si^^kSb£(^flS^rfi^ril!>e     in£s>  varicose  and  club-like  in  form,   occur  within 

the  connective  tissue  layers  of  the  skin   and   the 

tunica  propria  of  mucous  membranes.  Within  the  integument,  conspicuous  end- 
ramifications  of  sensory  neurones  surround  the  hair  follicles,  lying  upon  the  outer 
surface  of  the  glassy  membrane. 


ioi6 


HUMAN   ANATOMY. 


FIG.  867. 


Tactile  cells  of  Merkel   lying  'within  inter- 


papillary  epithelium;  broken  line  (e)  indicates 
junction  of  epithelium  and  connective  tissue 
layer;  (»)  nerve  passing  into  epithelium.  X  160. 
(  Worthmann.  ) 


FlG.  868. 


The  tactile  cells  of  Merkel,   found  in  the  deeper  layers  of  the  epidermis, 
represent  a  somewhat  more  differentiated  form  of   intraepithelial   terminations  and 

suggest  transitions  to  the  more  specialized  end- 
organs.  In  these  endings  the  nerve-fibrils 
terminate  in  cup-shaped  expansions  or  menisci, 
against  which  rest  the  modified  epithelial  cells. 
The  latter  may  be  regarded  as  an  imperfectly 
differentiated  newrofpithtlium^  examples  of 
which  are  seen  in  the  gustatory  cells  in  the 
taste  buds  and  in  the  highly  specialized  visual 
and  auditory  cells  in  the  retina  and  in  the 
organ  of  Corti  respectively. 

Encapsulated  Sensory  Endings. — In 
their  most  highly  developed  forms  these  end- 
ings (corpuscula  nervorum  terminalia)  are 
represented  by  relatively  large  special  end- 
organs  in  which  the  terminations  of  the  axis- 
cylinder  are  enclosed  within  an  elaborate 
laminated  capsule.  The  latter,  however,  is 
more  often  present  as  a  much  simpler  and 
thinner  envelope  consisting  of  strands  of  fibrous 
tissue. 

Transition  forms  between  the  intraepithelial  tactile  cells  above  noted  and  the 
more  specialized  encapsulated  end-organs,  always  within  the  connective  tissue,  are 
seen  in  the  corpuscles  of  Grandry  (not  found  in  man 
but  conspicuous  in  the  skin  covering  the  bill  and  in 
the  tongue  of  many  water-fowl),  in  which  the  nerve 
ends  in  a  disc-like  expansion  enclosed  between  large 
modified  epithelial  cells  and  the  neuromuscular  and 
neurotendinous  end-organs,  presently  to  be  described 
(page  1020). 

The  group  of  simpler  encapsulated  endings 
includes  three  well-known  examples  :  the  end-bulbs 
and  the  genital  corpuscles  of  Krause  and  the  cor- 
puscles of  Meissner,  all  of  which  possess  a  common 
structural  plan — interwoven  telodendria  embedded 
within  a  semifluid  interfibrillar  substance  and  surrounded  by  a  thin  fibrous  envelope. 

The  End-Bulbs  of  Krause. — These  endings 
include  a  variety  of  irregularly  spherical  or  ellipsoidal 
bodies  found  in  the  edge  of  the  eyelid,  the  conjunctiva 
and  corneal  margin,  the  lips  and  the  oral  mucous 
membrane,  the  glans  penis  and  clitoridis  and  probably 
other  parts  of  the  integument  highly  endowed  with 
sensibility.  Within  the  conjunctiva,  as  described  by 
Dogiel1,  they  lie  superficially  placed  within  the  con- 
nective tissue  near  the  summit  of  the  papillae  and 
folds,  when  such  elevations  exist,  but  always  close 
beneath  the  epithelium.  They  vary  considerably  in 
size,  often  being  small  (.002-. 004  mm.),  but  some- 
times measuring  from  .05-.  10  mm.  in  diameter. 
Usually  a  single  nerve-fibre,  exceptionally  two  or  even 
more,  enters  each  bulb,  losing  its  medullary  sheath  as 
it  pierces  the  thin  fibrous  capsule.  Within  the  latter 
the  nerve,  now  represented  by  the  naked  axis-cylinder, 
divides  into  from  two  to  four  branches,  which,  after 
describing  several  annular  or  spiral  turns,  give  off 

varicose  fibrils  that  undergo  further  division,  the  terminal  threads  forming  a  more  or 
less  intricate  maze  within  the  semifluid  substance  enclosed  by  the  fibrous  capsule. 

'Archivf.  mik.  Anat.,  Bd.  xliv.,  1895. 


i    ('.ruiulry  from 


Two  corpiiM  k- 
bill  of  duck  ;    nerve  is  seen  entering 
corpuscle  on  right.    X  265. 


Two  end-bulbs  of  Krause  from  human 
conjunctiva.    (Dogitl.) 


NERVE-TERMINATIONS. 


1017 


FIG.  871. 


Genital  corpuscle  from  integument 
of  penis;  nerve  divides  before  piercing 
capsule  and  terminates  in  intricate  end- 
windings.  (Dogicl.) 


Genital  corpuscle  from  integ- 
ument of  human  clitoris.  X  350. 
(  Worthmann. ) 


FIG.  872. 


The  Genital  Corpuscles. — These  endings,  most  numerous  (from  one  to  four 
to  the  square  millimeter)  in  the  deeper  strata  of  the  corium  covering  the  glans  penis 
and  clitoridis,  but  occurring  also  in  the  neighboring  parts  of  the  genitalia,  are  of 
irregular  oval  or  lobulated 
outline  and  from  .02  to  .35 
mm.  in  diameter.  They 
present  the  same  general 
architecture  as  the  end- 
bulbs,  but  are  of  larger  size, 
possess  a  somewhat  thicker 
capsule,  and  contain  a  more 
intricate  interlacement  of 
the  terminal  nerve-fibrillae. 
The  latter  are  derived  from 
the  subdivision  of  two  or 
three  medullated  fibres  that 
enter  near  the  base  of  the 
corpuscle  and  are  beset  with 
varicosities  and  club-shaped 
terminal  enlargements. 
The  fibrous  capsule,  consisting  of  several  connective  tissue  lamellae  possessing  flat- 
tened fusiform  nuclei,  encloses  the  semifluid  or  granular  interfibrillar  substance  in 
which  the  end-arborizations  are  embedded. 

The  Corpuscles  of  Meissner. — In  man  these  are  most  numerous  in  the 
corium  of  the  skin  covering  the  flexor  surface  of  the  fingers  and  toes.  They  are  also 
found  in  other  regions  possessing  sensibility  in  a  high  degree,  such  as  the  lips, 
margin  of  the  eyelid,  nipple,  penis  and  clitoris,  as  well  as  on  the  dorsum  of  the  hand 

and  foot  and  the  radial  surface  of  the  forearm. 
On  the  volar  surface  of  the  distal  phalanx  of  the 
fingers,  where  they  occur  in  greatest  numbers, 
some  twenty  are  found  to  the  square  millimeter 
(Meissner).  The  corpuscles  occupy  the  summit 
of  the  papillae  and  ridges  of  the  connective  tissue 
stratum  of  the  skin,  and  lie  close  beneath  the 
cuticle,  with  their  long  axes  perpendicular  to  the 
latter.  In  shape  they  are  elongated  irregular 
ellipsoids,  often  somewhat  sinuous  in  outline, 
and  in  the  larger  papillae  may  be  joined  at  the 
deeper  end  with  others  to  form  a  compound 
corpuscle.  They  are  relatively  large,  being  from 
.12-.  1 8  mm.  long  and  about  one-third  as  wide. 
Depending  upon  the  size,  each  corpuscle  is  sup- 
plied by  one  or  more  nerve-fibres  which  enter  in 
the  vicinity  of  the  base,  as  the  deeper  end  is 
called,  and,  on  piercing  the  capsule  and  losing 
the  medullary  sheath,  divide  into  a  number  of 
naked  axis-cylinders.  These  pass  across  the 
corpuscle  in  parallel  or  spiral  windings  and  are 
beset  with  fusiform  and  pyriform  varicosities, 
similar  enlargements  marking  the  ends  of  the 
terminal  threads.  The  entire  fibrillar  interlace- 
ment is  embedded  within  a  semifluid  substance 
and  enclosed  by  a  thin  nucleated  fibrous  capsule. 
The  Corpuscles  of  Ruffini. — These  end- 
ings are  also  found  within  the  skin,  but  at  deeper  levels,  near  and  sometimes  within 
the  subcorium.  They  are  of  large  size,  sometimes  measuring  as  much  as  1.35  mm. 
in  length,  and  of  an  elongated  fusiform  contour.  The  nerve-fibres,  often  two  or 
more,  which  usually  join  the  capsule  on  the  side,  less  frequently  near  one  end,  retain 
the  medullary  sheath  for  some  distance  after  penetrating  the  capsule  and  throughout 


Corpuscle  of  Meissner  lying  within  papilla 
of  corium  of  skin  from  finger;  only  deeper 
layers  of  overlying  epidermis  are  shown;  «, 
entering  nerve-fibre.  X  270. 


ioi8 


HUMAN   ANATOMY. 


FIG.  873. 


Cylindrical  end-bulb  from  con- 
nective tissue  layer  of  skin.  X  180. 
(Szymonowicz.) 


a  number  of  bold  curves  and  twistings.      After  the  disappearance  of  their  sheaths, 
the  naked  axis-cylinders  undergo  repeated  divisions,  the  resulting  fibrillae  becoming 

varicose  and    intertwined   and    ending   in   free   terminal 
knob-Jike  enlargements. 

In  contrast  to  the  foregoing  end-organs,  in  which 
the  axis-cylinder  subdivides  into  numerous  terminal 
threads  disposed  as  more  or  less  elaborate  intertwinings, 
a  second  group  is  distinguished  by  the  possession  of  a 
thick  laminated  capsule  that  encloses  a  cylindrical  core  or 
inner  bulb  containing  the  slightly  branched  axis-cylinder. 
These  endings,  of  which  the  Pacinian  corpuscle  is  repre- 
sentative, are  relatively  large  and  ellipsoidal. 

A  transitional  form,  connecting  them  with  the 
spherical  end-bulbs,  is  presented  by  the  cylindrical 
end-bulbs  of  Krause.  These  are  found  in  various 
parts  of  the  corium,  the  oral  mucous  membrane  and 
between  the  bundles  of  striped  muscle  and  of  tendon. 
They  are  irregularly  cylindrical  in  form,  often  more  or 
less  bent,  and  consist  of  a  thin  laminated  capsule  that  encloses  a  core  of  semifluid 
substance  in  which  lies  the  centrally  placed  axis-cylinder.  The  latter,  after  losing 
the  medullary  sheath  on  entering  at  .the  proximal  end  of  the  capsule,  traverses  the 
core  without  branching  until  near  the  distal  pole,  where  it  ends  in  a  single  or  slightly 
subdivided  terminal  enlargement. 

The  Vater-Pacinian  Corpuscles. — These  structures,  the  most  highly  special- 
ized sensory  end-organs,  are  relatively  large  ellipsoidal  bodies,  from  .05-.  15  mm.  in 
length  and  about  one-third  as  much  in  breadth,  situated  within  the  connective  tissue 
in  many  parts  of  the  body. 

In  man  they  are  found  in  FIG-  874- 

the  deeper  layers  of  the 
connective  tissue  layer  of 
the  skin,  especially  on  the 
palmar  and  plantar  aspects 
of  the  fingers  and  toes,  in 
the  connective  tissue  in  the 
vicinity  of  the  joints,  in 
tendons,  in  the  sheath  of 
muscles,  in  the  periosteum 
and  in  the  tunica  propria 
of  the  serous  membranes, 
the  peritoneum,  pleura  and 
pericardium.  They  are 
particularly  large  in  the 
mesentery  of  the  cat,  where 
they  may  be  readily  de- 
tected with  the  unaided  eye 
as  oval  pearly  bodies  some- 
times two  millimeters  or 
more  in  length. 

The  most  conspicuous 
part  of  the  Pacinian  body 
is  the  robust  capsule  that 
constitutes  almost  the  en- 
tire bulk  of  the  corpuscle 
and  consists  of  from  one 

tO    three    dozen     thin     COn-  Vater-Pacinian  corpuscles  from  skin  of  ohikt  s  fin.m-i  ;    ,1.  lonKit..,lmal  ; 

Centric    lamelke    of    fibrOUS       A',  transverse  section  ;   «,  nerve  entci  ini;  capsule  t..  n-:i.  h  timer  bulb. 

tissue.     The  surfaces  of  the 

lamella  are  covered  with  emlothdial  plates  whose  nuclei  appear  as  fusiform  thicken- 
ings, alting  the  concentric  striae  of  the  corpuscle.     The  axis  of  the' Pacinian  body 


, 


NERVE-TERMINATIONS. 


1019 


Corpuscles  of  Herbst  from  bill  of  duck  ;  a,  longitudinal,  b,  transverse 
section  ;  n,  nerve  traversing  lamellae  of  capsule  ;  axis-cylinder  within  core 
is  surrounded  by  cells.  X  360. 


is  occupied  by  a  core  or  inner  bulb  of  semifluid  substance  in  which  the  naked 
axis-cylinder  is  embedded. 

On  joining  the  proximal  pole  of  the  corpuscle,  the  fibrous  (Henle's)  sheath  of 
the  nerve-fibre  blends  with  the  outer  lamellae  of  the  capsule,  while  the  medullary 
coat  is  retained  during  the  somewhat  tortuous  path  of  the  fibre  through  the  capsule 
as  far  as  the  core.  Here  the  remaining  envelope  of  the  nerve-fibre  disappears,  the 
terminal  part  of  its  course, 

through  the  core,   being  as  FIG.  875. 

the  naked  axis-cylinder.  At 
a  variable  distance  but  often 
just  before  gaining  the  distal 
pole  of  the  core,  the  axis- 
cylinder  divides  into  from 
two  to  four  branches,  each  of 
which  terminates  in  a  slightly 
expanded  end-knot.  Some- 
times shortly  after  penetrat- 
ing the  capsule,  the  nerve- 
fibre  splits  into  two  or  more 
axis-cylinders  which  then 
share  the  common  envelope 
of  semifluid  axial  substance. 

Similar  end-organs,  the 
corpuscles  of  Herbst, 
occur  in  the  velvety  skin 
covering  the  bill  and  in  the 
tongue  of  water-fowl.  They 
closely  resemble  the  Pacinian 
bodies  of  mammals,  but  differ 

in  being  generally  smaller,  relatively  broader,  and  in  exhibiting  a  row  of  cubical  cells 
within  the  core  and  around  the  axis-cylinder.  These  cells  are  regarded  as  corres- 
ponding to  the  large  cells  enclosing  the  tactile  discs  in  the  Grandry's  corpuscles. 

The  Golgi-Mazzoni  corpuscles,  found  in  the  subcutaneous  tissue  of  the  pulp 
of  the  fingers,  are  modifications  of  the  ordinary  Pacinian  end-organs.  They  differ 
from  the  latter  in  possessing  fewer  lamellae,  a  relatively  larger  core  and  a  more 
branched  axis-cylinder. 

Neuromuscular  Endings. — First  described  by  Kolliker  and  by  Kiihne, 
although  previously  seen  by  Weissmann,  these  end-organs,  often  termed  muscle- 
spindles,  are  now  regarded  as  sensory  endings  that  are  probably  concerned  in  afford- 
ing impressions  as  to  tension  or  ' '  muscle-sense  ' ' .  They  lie  within  the  connective 
tissue  separating  the  bundles  of  voluntary  muscle-fibres  and  are  long  spindle-shaped 
structures,  varying  in  length  from  1-5  mm.  or  more  and  in  width  from  .  I-.3  mm. 
where  broadest.  They  are  widely  distributed,  being  probably  present  in  all  the 
skeletal  muscles,  and  are  especially  numerous  in  the  small  muscles  of  the  hand  and 
foot.  They  have  not  been  found,  however,  in  the  intrinsic  muscles  of  the  tongue 
and  in  the  eye  muscles,  although  within  the  tendons  of  the  latter  very  similar  (neuro- 
tendinous")  end-organs  have  been  demonstrated. 

Each  spindle  consists  of  a  capsule,  composed  of  a  half-dozen  concentric  layers 
of  fibrous  tissue,  which  encloses  a  group  of  usually  from  three  to  ten,  but  sometimes 
as  many  as  twenty,  striped  muscle-fibres,  medullated  nerves,  blood-vessels  and  inter- 
spersed connective  tissue.  These  intrafusal  fibres,  as  they  are  called,  differ  from 
those  of  the  surrounding  muscle  in  being  much  smaller  in  diameter  and  length, 
markedly  tapering  towards  either  end,  more  coarsely  but  less  distinctly  striated,  and 
in  possessing  nuclei  within  the  sarcous  substance.  The  striations  are  not  equally 
distinct  in  all  parts  of  the  fibres,  being  much  less  evident  in  the  middle  zone  than 
towards  the  ends.  The  fibres  are  more  numerous  and  of  greater  diameter  in  the 
equatorial  region  than  near  the  poles  of  the  spindle. 

The  intrafusal  fibres  collectively  are  surrounded  by  a  thin  special  connective 
tissue  envelope,  the  axial  sheath,  between  which  and  the  capsule  lies  the  periaxial 


IO2O 


HUMAN   ANATOMY. 


Nerve-fibre- 


Sheath- 


Capsule 


lymph-space.  Each  spindle  receives  usually  several  medullated  nerve-fibres,  which, 
after  incorporation  of  their  sheaths  of  Henle  with  the  capsule,  pierce  the  latter  at 
various  points  and  proceed  to  the  individual  muscle-fibres.  The  terminal  relations 
of  the  nerves  to  the  intrafusal  fibres  have  been  studied  by  means  of  the  newer 

methods  especially  by  Ruffini, 
FIG.  876.  Huber  and  DeWitt  and  Dogiel. 

After  repeated  division  during 

*^eir  course  tnrough  the  cap- 
sule and  periaxial  space,  the 
nerve-fibres  pierce  the  axial 
sheath,  lose  their  medullary 
coat  and  terminate  either  as 
one  or  more  ribbon-like 
branches  that  encircle  the  mus- 
cle-fibres in  annular  or  spiral 
windings,  or,  after  further 
subdivision,  as  branched  telo- 
dendria  in  which  the  ultimate 
fibrils  end  in  irregular  spherical 
or  pyriform  enlargements. 

Neurotendinous  End- 
ings.— These  end-organs, 
described  by  Golgi  and  sub- 
sequently more  fully  investi- 
gated by  Kolliker,  Ciaccio,  and 
Huber  and  DeWitt,  in  their 
general  architecture  resemble 
closely  the  sensory  endings  in 
muscle.  They  lie  embedded 
within  the  intrafascicular  con- 
nective tissue  and  are  usually 
found  in  the  vicinity  of  the 
junction  of  muscle  and  tendon. 
Like  the  neuromuscular  end- 
ings, the  tendon- spindles  are 
long  fusiform  structures,  from 
i. -i. 5  mm.  in  length,  sur- 
rounded by  a  fibrous  capsule. 
The  latter  encloses  a  group  of 
from  eight  to  twenty  intrafusal 
tendon  fasciculi,  which  are 
smaller  and  apparently  less 
mature  than  those,  of  the  sur- 
rounding tendon -tissue.  The 
intrafusal  fasciculi  are  invested 
by  a  fibrous  axial  sheath  be- 
tween which  and  the  capsul( 
lies  a  periaxial  Lymph-space. 

On  reaching  the  spindle, 
after  repeated  branching,  the 
medullated  nerve-fibres  pene- 
trate  the  capsule,  with  whicl 
their  fibrous  (Henle's)  sheaths 
blend,    and    undergo    furtht 
division.     The  medullary  coat  is  lost  after  they  pierce  the  axial  sheath,  the  naked  axis- 
cylinders  breaking  up  into  smaller  fibrils  that  extend  along  tin-  intrafusal  fasciculi, 
terminal  ramifications,  applied  to  the  surface  of  the  fasciculi,  vary  in  details  (Huber). 
Some  arise  as  short  lateral  branches  that  partly  encircle  the  fasciculi   and   end 
im -ular  plate-like  expansions,  while  others  terminate  between  the  smaller  fasciculi. 


J 

m 


Axial 
sheath' 


,. 


Nerve-fibre 


A,  neuromuscular  ending;  />',  neurotendinous  ending  in  longitudi- 
nal section,  imahyli-nc-blue  staining.  •  260.  (  Drawn  from  preparation 
made  by  Professor  Huber.) 


THE  CENTRAL  NERVOUS  SYSTEM. 

THE  central  nervous  system  includes  the  spinal  cord  and  the  brain.  In  principle 
these  parts  are  to  be  regarded  as  the  walls  of  the  primary  neural  tube,  modified  by 
unequal  growth  and  expansion,  which  even  after  acquiring  their  definite  relations 
enclose  the  remains  of  the  canal,  as  represented  by  the  system  of  ventricular  spaces. 
In  contrast  to  the  spinal  segment  of  the  neural  tube,  which  always  remains  a  rela- 
tively simple  cylinder,  the  spinal  cord,  the  cephalic  segment  early  differentiates  into 
three  primary  cerebral  vesicles,  the  anterior  and  posterior  of  which  subdivide,  so  that 
five  secondary  brain-vesicles  are  present.  Coincidently  marked  flexure  of  the 
cephalic  segment  occurs  at  certain  points  and  in  consequence  this  part  of  the  neural 
tube  becomes  bent  upon  itself  to  such  a  degree  that  the  axis  of  the  anterior  vesicle 
lies  almost  parallel  with  that  of  the  spinal  segment  (Fig.  912).  From  the  five 
secondary  divisions  of  the  flexed  and  sinuously  bent  cephalic  segment  of  the  neural 
tube  are  developed  the  fundamental  parts  of  the  brain  in  the  manner  presently  to  be 
described  (page  1060),  whilst  from  the  relatively  straight  spinal  segment  proceeds  the 
development  of  the  spinal  cord,  in  which  process  growth  and  differentiation  convert 
the  originally  thin-walled  tube  into  an  almost  solid  cylinder,  the  minute  central  canal 
alone  remaining  as  the  representative  of  the  once  conspicuous  lumen. 

THE  SPINAL  CORD. 

The  spinal  cord  (medulla  spinalis)  is  that  part  of  the  central  nervous  system,  or 
cerebro-spinal  axis,  which  lies  within  the  vertebral  canal.  Its  upper  limit,  where  it 
becomes  continuous  with  the  medulla  oblongata,  is  in  a  measure  conventional,  since 
there  is  no  demarcation  on  the  cord  itself  to  indicate  exactly  its  junction  with  the  brain. 
Accurately  considered,  the  superior  limit  of  the  cord  may  be  assumed  to  correspond 
with  the  emergence  of  the  uppermost  root-fibres  of  the  first  spinal  nerve  which  pass 
out  between  the  atlas  and  the  skull  ;  this  level  also  corresponds  to  the  lowest  strands 
of  the  pyramidal  decussation  of  the  medulla  oblongata  and  to  the  upper  border  of  the 
posterior  arch  of  the  atlas.  For  practical  purposes,  however,  the  lower  margin  of 
the  foramen  magnum  defines  with  sufficient  accuracy  the  upper  limit  of  the  spinal 
cord.  Below,  the  spinal  cord  terminates  somewhat  abruptly  in  a  pointed  end,  the 
conus  medullaris,  that  usually  ends  opposite  the  disc  between  the  first  and  second 
lumbar  vertebrae.  The  level  to  which  the  cord  extends  inferiorly,  however,  is  subject 
to  considerable  variation,  very  rarely  being  as  high  as  the  middle  of  the  body  of  the 
last  thoracic  vertebra  (Moorhead),  or  as  low  as  the  upper  border  of  the  body  of  the 
third  lumbar  vertebra  (Waring).  In  the  female  subject  the  spinal  cord,  although 
absolutely  shorter  than  in  the  male,  extends  to  a  relatively  lower  level  hi  the  vertebral 
canal.  Marked  bending  of  the  spine  produces  slight  alterations  in  the  position  of  the 
cord,  during  strong  flexion  an  appreciable  ascent  of  the  lower  end  taking  place.  The 
relation  of  the  cord  to  the  vertebral  canal  varies  at  different  periods.  Until  the  third 
month  of  foetal  life  the  cord  occupies  the  entire  length  of  the  canal,  but  subsequently, 
owing  to  the  more  rapid  lengthening  of  the  spine  than  of  the  spinal  cord,  the  latter  no 
longer  reaches  to  the  lower  limit  of  the  canal  and,  therefore,  apparently  rises,  so  that 
by  the  sixth  fcetal  month  the  lower  end  of  the  cord  lies  opposite  the  first  sacral  vertebra, 
and  at  birth  terminates  usually  on  a  level  with  the  body  of  the  third  lumbar  vertebra. 

Measured  from  its  upper  conventional  limit  to  the  lower  end  of  the  conus  medullaris,  the 
spinal  cord  in  the  adult  male  has  an  average  length  of  45  cm.  (17%"  in.),  and  in  the  female  of 
43.7  cm.  (i7>(  in.),  in  both  sexes  the  proportion  of  the  length  of  the  cord  to  that  of  the  pre- 
sacral  spine  being  approximately  as  64  : 100  (Ziehen).  The  cord-length  bears  no  constant  rela- 
tion to  stature,  although  in  a  general  way  tall  individuals  may  possess  long  cords.  The  weight 
of  the  spinal  cord,  stripped  of  its  membranes  and  nerves,  is  something  less  than  30  grammes 
(i  oz.),  or  about  1-2000  of  the  body-weight.  Its  proportion  to  the  weight  of  the  brain  is  i  143. 
When  fresh  the  spinal  cord  possesses  a  soft  cheesy  consistence  and  a  specific  gravity  of  1.035. 

102 1 


IO22 


HUMAN    ANATOMY. 


FIG.  877. 


Skull 


Pedicles,  cut 


Medulla 


•Laminae,  cut 


» Transverse 

processes 


Pedicles. 


— Dural  sheath 


XII  T- 


i  in rJn 


.1  In 


Pedicles, 


.  End  of 

dural  sheath 


Posterior 
divisions  of 
sacral  nerves< 


Sin-nth  of  filiini 


End  of  Ilium 


.  Coccyx 


S|nn:il  i-i.nl  i-nrlosi-d  in  iiu(,|,,-,ir,|  dural  slu-atli  lying  within 
vertebral  canal ;  m-ma:  an  tiei  > •i>ni|iU-u-lv  n-nuived  on  right  side, 

partially  On   left,  to  expose  doml   aspivt   <>l   duia:    first  and   last 

hiinharand  lacral  groupa  are  indicated 
by  Italic  BgOrcaj    corresponding  v.-iU-hn-  l,\  Roman  mnm-iaK. 


The  Membranes  of  the 
Cord. — The  spinal  cord,  together 
with  the  roots  of  the  thirty-one  pairs 
of  spinal  nerves,  lies  within  the 
vertebral  canal  enclosed  by  three 
protecting  membranes,  ormeninges, 
which,  from  without  inward,  arc  i 
the  dura  mater,  (2)  the  arachnoidca, 
and  (3)  the/>/a  mater,  all  of  which 
are  directly  continuous  through  the 
foramen  magnum  with  the  corres- 
ponding coverings  of  the  brain. 
The  external  sheath,  or  thcca,  formed 
by  the  dura,  is  a  robust  fibro-elastic 
tubular  envelope,  much  longer  and 
considerably  wider  than  the  cord, 
that  does  not  lie  against  the  wall  of 
the  vertebral  canal,  -but  is  separated 
by  an  interval  containing  thin-walled 
plexiform  veins  and  loose  fatty  con- 
nective tissues  (Fig.  879). 

The  dural  sheath,  about  .5 
mm.  in  thickness,  extends  to  the 
level  of  the  second  sacral  vertebra 
and  is,  therefore,  considerably  longer 
than  the  spinal  cord.  The  part  of 
the  sac  not  occupied  by  the  cord 
encloses  the  longitudinal  bundles 
of  root-fibres,  that  pass  obliquely  to 
the  levels  at  which  the  correspond- 
ing nerves  leave  the  vertebral  canal, 
and  a  fibrous  strand,  they?////;/  tcr- 
minale,  prolonged  from  the  cord  to 
the  lower  end  of  the  spine. 

The  pia  constitutes  the  imme- 
diate investment  of  the  cord  and 
supports  the  blood-vessels  destined 
for  the  nutrition  of  the  enclosed 
nervous  cylinder.  The-  pial  sheath 
is  composed  of  an  outer  fibrous 
and  an  inner  vascular  layer,  the 
connective  tissue  of  the  latter  ac- 
companying the  blood-vessels  into 
the  substance  of  the  cord. 

The  arachnoid,  a  delicate  veil- 
like  structure  made-  up  of  interlacing 
bundles  of  fibro-elastic  tissue,  lies 
between  the  other  two  membranes 
and  invests  loosely  the  inner  surface' 
of  the  dura  and  closely  the  outer 
surface  of  the  pia.  It  effectually 
Subdivides  the  considerable  space 
between  the  external  and  internal 
sheaths  into  two  compartments,  the 
one  beneath  the  dura,  the  subdnral 
space,  being  little  more  than  a  capil- 
lary cleft  filled  with  modified  lymph, 
and  the  other,  the  siibaniclnwid 
s/Hrcc,  between  the  arachnoid  and 


THE   CENTRAL    NERVOUS   SYSTEM. 


1023 


The  spinal    cord,    therefore,    hangs 
FIG.  878. 


-  Pons 


•Arachnoid 


Medulla 


Ligamenta 
denticulata 


the  pia,  containing  the  cerebro- spinal  fluid. 
suspended  within  the  tube  of  dura, 
surrounded  by  a  cushion  of  fluid — 
an  arrangement  well  adapted  to  insure 
the  nervous  cylinder  against  the  inju- 
rious effects  of  shocks  and  of  undue 
pressure  during  changes  in  the  position 
of  the  spine.  Both  spaces,  but  par- 
ticularly the  subarachnoid,  are  crossed 
by  fibrous  trabeculae  and  thus  imper- 
fectly subdivided  into  secondary  com- 
partments, all  of  which  are  lined  with 
endothelium. 

The  spinal  cord  is  fixed  within  the 
loose  dural  sheath  not  only  by  the  root- 
fibres  of  the  spinal  nerves  that  pass 
between  the  cord  and  the  outer  envelope, 
but  also  by  two  lateral  fibrous  bands,  the 
ligamenta  denticulata,  that  are  continu- 
ous with  the  pia  along  the  cord,  one  on 
each  side.  Mesially  they  are  attached 
between  the  anterior  and  posterior  root- 
fibres  and  externally  to  the  inner  surface 
of  the  dura  by  the  tips  of  pointed  pro- 
cesses, about  twenty-one  in  all,  that 
stretch  across  the  subarachnoid  space, 
which  they  imperfectly  divide  into  a 
general  anterior  and  a  posterior  com- 
partment. The  ligaments,  covered  by 
prolongations  of  the  arachnoid,  extend 
the  entire  length  of  the  cord,  the  first  pro- 
cess being  attached  to  the  margin  of  the 
foramen  magnum,  immediately  above 
the  vertebral  artery  as  it  pierces  the  dura. 
The  succeeding  ones  meet  the  dura 
between  the  pairs  of  spinal  nerves,  the 
lowest  process  lying  between  the  last 
thoracic  and  the  first  lumbar  nerve. 
In  the  cervical  and  thoracic  region,  a 
median  fibrous  band,  the  septum  posticum,  connects  the  posterior  surface  of  the  cord 


Spinal  cord, 
covered  with 

I arachnoid 

I  and  pia 

Upper  part  of  spinal  cord  within  dural  sheath,  which 
has  been  opened  and  turned  aside ;  ligamenta  denticulata 
and  nerve-roots  are  shown  as  they  pass  outward  to  dura. 


Dural  sheath 
Periosteum  \ 


Spinal  cord 

Posterior  root 


Ligamentutn 
denticulatum 


Anterior  root 


Spinal  ganglion 


Spinal  nerve 


Extradural 

areolar  tissue 


Vertebral  artery 
Body  of  fourth  cerv 

Transverse  section  of  vertebral  canal  at  level  of  fourth  cervical  vertebra,  spinal  cord  in  position. 


with  the  dura  and  partially  subdivides  the  subarachnoid  space.     Lower,  this  partition, 


IO24 


HUMAN   ANATOMY. 


FIG.  880. 


Skull 

Vertebral  artery 
/  en 

Spinal 
accessory  nerve" 


Pedicles,  cut  • 


Sen- 


Pedicles  < 


12  tn- 


•  Medulla 
-/  en 


-Spinal  accessory 

,        nerve 
•  Edge  of 
cut  dural  sheath 


-Spinal  cord 


-Edge  of  cut 

dural  sheath 


.  Spinal  cord 


Pediclesr 


5  /«. 


Posterior 
divisions    of 
sacral  nerves ' 


-End  of  conus 

medulla  ris 


-Filum  terminale 

-Descending 

nerves 


End  of  dural 

sheath 
,  2  sn 


. I'iluiii  rxternum 
.Cn 


Posterior  wall  of  vertebral  canal  has  been  removi-.l  and 
dural  sheath  opened  to  expose  spinal  cord  mid  dorsal  roots 
of  attached  nerves ;  /  en,  I  C,  first  cervical  nerve  and  vertebra 
iivrlv  ;  Cn,  eoccygeal  nerves. 


which  may  transmit  blood-vessels,  is 
imperfect  or  altogether  absent.  As 
they  cross  the  subarachnoid  space  the 
bundles  of  root-fibres  of  the  spinal 
nerves  are  enclosed  by  prolongations 
of  the  pia  and  arachnoid.  These 
sheaths  are  retained  by  the  nerves  for 
only  a  short  distance  after  the  latter 
receive  an  additional  investment  from 
the  dura  as  they  leave  the  vertebral 
canal.  The  dural  sheath  becomes 
continuous  with  the  epineurium  of  the 
spinal  nerves. 

The  Cord  -  Segments.— 
Although  no  suggestion  of  such  sub- 
division is  to  be  seen  as  constrictions 
on  its  surface,  in  principle  tine  spinal 
cord  consists  of  a  series  of  segments, 
each  of  which  gives  origin  to  the 
anterior  (motor)  and  receives  the  pos- 
terior (sensory)  root-fibres  of  one 
pair  of  spinal  nerves.  These  nerves, 
usually  thirty-one  pairs  in  number, 
are  classified  as  eight  cervical,  twelve 
thoracic,  five  lumbar,  five  sacral,  and 
one  coccygeal.  Corresponding  to  the 
attachment  of  the  nerves  the  cord  is 
conventionally  divided  into  cervical, 
thoracic,  lumbar,  and  sacral  regions. 
Of  the  entire  length  of  a  cord  measur- 
ing 43  cm.,  approximately  10  cm.,  or 
about  23.5  per  cent.,  belonged  to  the 
cervical  region;  24  cm.,  or  55.5  per 
cent.,  to  the  thoracic;  6  cm.,  or  14 
per  cent,  to  the  lumbar;  and  3  cm., 
or  7  per  cent.,  to  the  sacral  region. 

The  spinal  nerves  are  attached 
to  the  lateral  surfaces  of  the  cord  by 
fan-shaped  groups  of  anterior  and  pos- 
terior root-fibres  that  are  gathered  into 
compact  strands  as  they  converge  to 
form  a  common  trunk  (Fig.  884). 
The  portion  of  the  spinal  cord  with 
which  the  root-fibres  of  a  spinal  nerve 
are  connected  constitutes  its  cord- 
segment,  the  limits  of  which  lie  in  the 
interval  separating  the  extreme  fibres 
of  the  nerve  and  those  of  the  adjacent 
nerves.  In  the  thoracic  cord  these 
intervals  are  very  evident,  since  the 
segments  are  relatively  long  ;  in  the 
cervical  and  lumbar  regions,  on  the 
contrary,  the  groups  of  root-fibres 
are  so  crowded  that  they  form  almost 
unbroken  rows. 

.  The  length  of  the  individual  cord- 
segments  varies  ;  thus,  according  to  the 
measurements  of  Liideritz,  those  of  the 
cervical  region,  are  from  11-13.5  mm.  ; 


THE  CENTRAL   NERVOUS   SYSTEM. 


1025 


those  of  the  thoracic  re- 
gion from  12-26  mm.,  the 
longest  belonging  to  the 
V-VII  thoracic  nerves; 
those  of  the  lumbar  region 
rapidly  decrease  from  15.5 
-5.5  cm.,  followed  by  a 
more  gradual  diminution 
to  less  than  4  cm.  in  the 
sacral  region. 

In  consequence  of  the 
disproportion  between  the 
length  of  the  spinal  cord 
and  that  of  the  vertebral 
canal,  the  discrepancy  be- 
tween the  level  at  which 
the  nerves  are  attached 
to  the  cord  and  that  of 
the  intervertebral  foramina 
through  which  they  leave 
the  canal  becomes  more 
marked  towards  the  lower 
end  of  the  series.  The 
growth  of  the  cord,  how- 


FIG.  881. 


Ye 


Transverse  section  of  vertebral  canal,  at  level  of  middle  of  first  lumbar 
vertebra;  spinal  cord  (conus  medullaris),  surrounded  by  nerve-bundles,  is  seen 
within  dural  sheath. 


'Conus 


i  In 


medullaris 


ever,  is  not  uniform  since,  as  shown  by  Pfitzner,  during  the  later  years  of  childhood  elongation 
FIG.  882.  of  the  thoracic  region  occurs  to  such  an  extent 

that  this  part  of  the  cord  once  more  equals, 
if  indeed  not  exceeds,  the  corresponding 
portion  of  the  spine.  While  the  cervical  cord 
keeps  fairly  abreast  the  cervical  portion  of 
the  vertebral  column,  the  lumbar  and  sacral 
segments  are  left  far  behind.  The  results  of 
these  changes  are  seen  in  the  course  of  the 
root-fibres,  which  in  the  neck,  below  the  third 
nerve,  run  somewhat  downward  to  their  points 
of  emergence,  and  in  the  thoracic  region  pass 
more  horizontally,  while  those  of  the  lumbar 
and  sacral  nerves  descend  almost  vertically 
for  a  considerable  distance — in  the  case  of  the 
last  sacral  nerve  28  cm.  (Testut) — before 
reaching  their  appropriate  levels. 

The  large  and  conspicuous  leash  of 
descending  root-fibres,  seen  upon  open- 
ing the  dural  sheath,  constitutes  the 
cauda  equina,  in  the  midst  of  which 
the  glistening  silvery  filum  terminale 
is  distinguishable.  It  is  evident,  there- 
fore, that  in  most  cases  the  level  of  the 
cord-segment  and  that  of  the  vertebra 
bearing  the  same  designation  do  not 
correspond.  Likewise,  it  must  be  re- 
membered that,  although  in  general  the 
spinal  nerves  are  named  in  accordance 
with  the  vertebrae  immediately  below 
which  they  escape,  in  the  neck  there 
are  eight  cervical  spinal  nerves  and 
only  seven  vertebrae,  the  first  or  sub- 
occipital  nerve  emerging  between  the 
atlas  and  the  skull,  and  the  eighth 
between  the  last  cervical  and  first  thoracic 

End  of  spinal  cord  with  roots  of  lower  nerves  descend-      vertebra  •  hence    evrpnr  rhp  lasr  nnp    rhpv 
ing  in  cauda  equina  to  gain  their  respective  foramina ;  .    '  exCePt  ne<  tnev 

7~J  In,  f-s  sn,  en,  lumbar,  sacral  and  coccygeal  nerves.  Correspond  With  the  Vertebra  below. 

65 


Filum 
externum, 
in  sheath 


Coccvx 


IO26 


HUMAN   ANATOMY. 


FIG.  883. 


Medulla 


Cervical 


Thoracic 


Lumbar 


Sacral 


Coccygeal 


Form  of  the  Cord. — After  removal  of  its  membranes  and  the  root-fibres,  the 
spinal  cord  is  seen  to  differ  from  a  simple  cylinder  in 
the  following  respects.  It  is  somewhat  flattened  in  the 
antero-posterior  direction,  so  that  the  sagittal  diameter  is 
always  less  than  the  transverse  diameter,  and  its  outline 
in  cross-sections,  therefore,  is  not  circular  but  more  or 
less  oval  ;  its  width  is  not  uniform  on  account  of  two 
conspicuous  swellings  that  are  associated  with  the  origin 
and  reception  of  the  large  nerves  supplying  the  limbs. 
The  upper  or  cervical  enlargement  (intumescentia 
cervicalis)  begins  just  below  the  upper  end  of  the  cord 
and  ends  opposite  the  second  thoracic  vertebra,  having 
its  greatest  expansion  at  the  level  of  the  fifth  and  sixth 
cervical  vertebrae,  where  the  sagittal  diameter  is  about 
9  mm.  and  the  transverse  from  13-14  mm.  The  lower 
or  lumbar  enlargement  (intumescentia  lumbalis)  begins 
opposite  the  tenth  thoracic  vertebra,  slightly  above  the 
origin  of  the  first  lumbar  nerve,  and  fades  away  in  the 
conus  medullaris  below.  It  appears  very  gradually 
and  reaches  its  maximum  opposite  the  twelfth  thoracic 
vertebra,  where  the  cord  has  a  sagittal  diameter  of  8. 5  mm. 
and  a  transverse  diameter  of  from  11-13  mm.  (Ravenel). 
The  lumbar  enlargement  is  associated  with  the  great 
nerve-trunks  supplying  the  lower  limbs.  The  inter- 
vening part  of  the  thoracic  region  is  the  smallest  and  most 
uniform  portion  of  the  cord  and  is  almost  circular  in  out- 
line. Where  least  expanded,  opposite  the  middle  of  the 
thoracic  spine,  the  cord  measures  8  mm.  in  its  sagittal 
and  10  mm.  in  its  transverse  diameter.  These  enlarge- 
ments appear  coincidently  with  the  formation  of  the  limbs, 
are  relatively  small  during  foetal  life,  and  acquire  their 
full  dimensions  only  after  the  limbs  have  attained  their 
definite  growth.  In  a  general  way,  a  similar  relation 
between  the  size  of  the  enlargements  and  the  degree  of 
development  of  the  limbs  is  observed  in  the  lower  animals. 
At  the  tip  of  the  conus  medullaris  the  spinal  cord 
is  prolonged  into  a  delicate  tapering  strand,  the  filum 
terminale,  that  consists  chiefly  of  fibrous  tissue  con- 
tinued from  the  pia  mater  and  invested  by  arachnoid. 
It  extends  to  the  bottom  of  the  pointed  and  closed  end 
of  the  dural  sac,  which  it  pierces  at  the  level  of  the  second 
sacral  vertebra  and,  ensheathed  by  a  prolongation  of  dura 
(vagina  terminalis),  as  the  fihan  terminate  c.\/cr)ii/ni, 
proceeds  downward  through  the  lower  end  of  the  sacral 
canal  for  a  distance  of  about  8  cm.  (3^  in.),  finally  t<> 
be  attached  to  the  periosteum  covering  the  posterior 
surface  of  the  coccyx.  The  part  within  the  dural  sac, 
the  filum  terni/na/c  intcrnum,  is  about  16  cm.  (6%  in.) 
in  length  and  surrounded  by  the  nerve-bundles  of  the 
cauda  equina*(Fig.  882),  from  which  it  is  readily  dis- 
tinguished by  its  glistening  silvery  appearance. 

The  upper  half  or  less  of  the  internal  filum  contains  the 
Spinal  >,,ni  >Mmdrd  ,,i  mom-      terminal  part  of  the  central  canal  of  the  spinal  cord  walled  by 
l)t:m,-s  and  nerves,  slKiwini;  pro-  (|  •  ]  variable  layer  of  nervous  substance  in  which  small 

portions  oi  its  length  contributed  .          .  ,        ..         , 

by  diiTri.-nt  n-uions  and  position  nerve-cells  are  usually  present.  The  minute  bundles  of  ncrve- 
and  relative  si/.  >i  rniaiKi-ni.-nts.as  fibres  often  found  adhering  to  the  filum.  which  sometimes  mav  be 
viewed  from  before :  Bemidlagram-  •  ,  .  ,  .  .  .  ,  ',  , 

matic,  based  on  im-asmvin.-nts  ;  followed  to  and  even  through  the  dnral  sheath,  are  regarded  by 
mi,  -third  actual  si/..  Rauberas  representing  one  or  two  additional  (second  and  third) 

coccygeal  nerves,  homologous  with  the  caudal  nerves  of  the  lower  animals. 


THE   CENTRAL   NERVOUS   SYSTEM. 


1027 


The  Columns  of  the  Cord. — Inspection  of  the  surface  and  particularly  of 
cross-sections  of  the  spinal  cord  (Fig.  885)  shows  the  latter  to  be  partially  divided 
into  a  symmetrical  right  and  left  half  by  a  median  cleft  in  front  and  a  partition  in  the 
mid-line  behind.  The  cleft,  the  anterior  median  fissure  ( tissura  mediana  anterior) 
extends  the  entire  length  of  the  cord,  and  is  continued  on  the  upper  part  of  the 
filum  terminate.  It  is  narrow,  from  2-3.5  mm-  m  depth,  penetrating  for  less  than 
one-third  of  the  ventro-dorsal  djameter  of  the  cord,  and  occupied  by  a  process  of 
pia  mater.  Along  its  floor,  which  lies  immediately  in  front  of  the  white  commissure, 
it  is  frequently  deflected  to  one  side  of  the  mid-line  and  presents  a  slight  expansion. 

The  separation  into  halves  is  completed  by  the  posterior  median  septum 
(septum  medianiim  posteritis),  the  so-called  posterior  median  fissure.  With  the  ex- 
ception of  a  shallow  groove  in  the  upper  cervical  cord,  the  lumbar  enlargement  and 
the  conus  medullaris,  no  fissure  exists,  but  in  its  place  a  dense  partition  extends  from 
the  posterior  surface  to  the  middle  of  the  interior  of  the  cord,  ending  in  close  relation 
to  the  gray  commissure. 

The  character  of  the  septum  is  a  subject  of  dispute,  according  to  some  anatomists  con- 
sisting exclusively  of  condensed  neuroglia,  while  others  regard  it  as  composed  of  pial  tissue 
blended  with  the  neuroglia  and,  therefore,  of  both  mesoblastic  and  ectoblastic  origin.  The 
latter  view  is  substantiated  by  the  mode  of  development  of  the  posterior  septum,  the  immature 
pial  covering  of  the  developing  blood-vessels  being  imprisoned  within  and  fused  with  the  neu- 
rogliar  partition  derived  from  the  expanding  dorsal  halves  of  the  developing  cord  (page  1050). 
The  application  of  differential  stains  also  demonstrates  the  composite  nature  of  the  septum. 

Each  half  of  the  spinal  cord  is  further  subdivided  by  the  lines  along  which  the 
root-fibres  of  the  spinal  nerves  are  attached.  The  root-line  of  the  dorsal  (sensory) 
fibres  is  relatively  straight  and  narrow,  and  marked  by  a  slight  furrow,  the  postero- 
lateral  sulcus  (sulcus  lateralis  posterior)  that  lies  from  2.5-3.5  mm-  lateral  to  the 
posterior  septum  and  is  evident  even  on  the  intersegmental  intervals  where  the  root- 
fibres  are  practically  absent.  The  ventral  root-line,  marking  the  emergence  of  the 
anterior  (motor)  fibres,  is  much  less  certain,  since  the  bundles  of  fibres  of  the  indi- 
vidual nerves  do  not  emerge  in  the  same  vertical  plane,  but  overlie  one  another  to 
some  extent,  so  that  each  group  occupies  a  crescentic  area,  whose  greatest  width  cor- 
responds in  a  general  way  with  that  of  the  subjacent  ventral  horn  of  gray  matter. 
The  anterior  root-line,  which  lies  from  2-4  mm.  lateral  to  the  median  fissure,  is 
neither  indicated  by  a 

distinct  furrow  nor  con-  FIG.  884. 

tinuous. 

In  this  manner  two 
longitudinal  tracts,  the 
posterior  columns 
(funiculi  posteriores)  are 
marked  off  between 
the  posterior  median 
septum  and  the  sulci 
of  the  posterior  root- 
lines.  These  columns 
include  something  less 
than  one-third  of  the 
circumference  of  the 
cord,  and  are  about 
6  mm.  in  width  in  the 
thoracic  cord  and  8mm. 
and  7  mm.  in  the  cervi- 
cal and  lumbar  enlarge- 
ments respectively. 
The  tracts  included 

between  the  dorsal  and  ventral  root-lines  constitute  the  lateral  columns  (funiculi 
laterales)  and  those  between  the  ventral  root-lines  and  anterior  median  fissure  are  the 
anterior  columns  (funiculi  anteriores).  Such  subdivision  into  anterior  and  lateral 


Skull 

Vertebra 

artery 

i  cerv.  nerve 


Medulla 


Ganglion 
on  4  nerve 


Dorsal  roots  of  5  cerv.  nerve 


Upper  end  of  spinal  cord,  viewed  from  behind  after  partial  removal  of  dnral 
sheath  ;  cord-segments  are  indicated  by  groups  of  converging  bundles  of  posterior 
root-fibres;  spinal  ganglia  are  seen  lying  within  the  intervertebral  foramina; 
spinal  accessory  nerve  is  seen  ascending  on  each  side. 


1028 


HUMAN   ANATOMY. 


columns  is,  however,  largely  artificial,  since  neither  superficially  nor  internally  is  there 
a  definite  demarcation  between  these  tracts.  They  may  be,  therefore,  conveniently 
regarded  as  forming  a  common  antero- lateral  column,  that  on  each  side  embraces 
something  more  than  two-thirds  of  the  semicircumference  of  the  cord.  In  the  lower 
cervical  and  upper  thoracic  cord,  each  posterior  column  is  subdivided  by  a  shallow 
furrow  that  lies  from  1.5-2  mm.  lateral  to  the  posterior  medium  septum.  This,  the 
paramedian  sulcus  (sulcus  intermedius  posterior), corresponds  in  position  with  the 
peripheral  attachment  of  a  radial  septum  of  neuroglia  that  penetrates  the  white  matter 
for  a  variable  distance,  sometimes  almost  as  far  as  the  gray  matter,  and  subdivides  the 
posterior  column  into  two  unequal  tracts,  of  which  the  inner  and  smaller  is  the  pos- 
tero-median  column  (funiculus  gracilis),  or  column  of  Goll,  and  the  outer  and 
larger  is  the  postero-lateral  column  (funiculus  cuneatus),  or  column  of  Burdach. 
The  Gray  Matter. — Inspection  of  the  transversely  sectioned  spinal  cord,  even 
with  the  unaided  eye,  shows  it  to  be  composed  of  an  irregular  core  of  gray  substance 
enclosed  by  a  mantle  of  white  matter.  Within  each  half  of  the  cord  the  gray 


FIG.  885. 


Caput  cornu 


Cervix  cornu 


Lateral  cornu 


Basis  cornu 


Caput  cornu 


Posterior  median  septum 


rior  column 

Posterior  root-furrow 


^%i^ Posterior 

3L  root-fibres 


-ateral  column 


Central  canal 
in  gray 
commissure 


Anterior  median  fissure        Anterior 


Anterior  white  commissure 


Transverse  section  of  thoracic  cord,  showing  disposition  of  gray  and  white  matter  and  division  of  latter  into 
anterior,  lateral  and  posterior  columns.     X  13. 

matter  forms  a  comma-shaped  area,  the  broader  end  of  which  lies  in  front  and  the 
narrower  behind,  with  the  concavity  directed  laterally.  The  convex  surfaces  of  the 
tracts  of  the  two  sides,  which  look  towards  each  other  and  the  mid-line,  are  connected 
by  a  transverse  band  of  gray  matter,  the  gray  commissure  (cominissiira  «risea)  that 
extends  across  the  mid-line,  usually  sonu-what  in  advance  of  the  middle  of  the  sagittal 
diameter,  and  encloses  the  minute  central  canal  of  the  cord.  By  this  canal  the 
connecting  band,  or  central  gray  matter,  is  divided  into  a  dorsal  and  a  ventral  part, 
the  posterior  and  the  anterior  gray  commissure,  which  lie  behind  and  in  front  of  the 
tube  respectively. 

While  the  posterior  median  septum  reaches  the  dorsal  surface  of  the  gray  com- 
missure, the  ventral  margin  of  the  latter  is  separated  from  the  anterior  median  fissure 
by  an  intervening  bridge  of  white  matter,  the  anterior  white  commissure  (com- 
inissnni  anterior  alba)  which  connects  the  anterior  columns  of  the  cord  and  provides 
an  important  pathway  for  fibres  passing  from  one  side  to  the  other.  A  zone  of  mod- 
ified neuroglia  immediately  surrounding  the  central  canal  is  known  as  the  substantia 
gelatinosa  centralis  (substantia  urisea  ccntralis). 


THE   CENTRAL    NERVOUS   SYSTEM. 


1029 


FIG.  886. 


I  C— 


Each  crescent  of  gray  matter  is  divisible  into  three  parts — the  ventral  and  the 
dorsal  extremity,  that  project  beyond  the  transverse  gray  commissure  and  constitute 
the  anterior  and  posterior -horns  or  cornua  of  the  gray  matter  (columnae  griseae),  and 
the  intermediate  portion  (pars  intermedia)  that  connects  the  cornua  and  receives  the 
commissure.  The  two  horns  differ  markedly  from  each  other  and,  although  varying 
in  details  in  different  levels,  retain  their  distinctive  features  throughout  the  cord. 

The  anterior  cornu  (columna  grisea  anterior)  is  short,  thick  and  rounded,  and 
separated  by  a  considerable  layer  of  white  matter  from  the  surface  of  the  cord,  through 
which  the  ventral  root-fibres  proceed  to  their  points  of  emergence  in  the  root-areas. 
The  blunt  tip  of  the  anterior  horn  is  known  as  the  caput  cornu,  and  the  dorsal  por- 
tion by  which  it  joins  the  commissure  and  the  pars  intermedia  as  the  basis  cornu. 

The  posterior  cornu  (columna  grisea  posterior)  presents  a  marked  contrast  in 
being  usually  relatively  long,  narrow  and  pointed,  and 
in  extending  peripherally  almost  to  the  postero-lateral 
sulcus.  The  tip  or  apex  of  the  dorsal  horn  is  formed 
of  a  A-shaped  stratum  of  peculiar  character,  the  sub- 
stantia  gelatinosa  Rolandi,  that  appears  lighter  in 
tint  (Fig.  885)  and  somewhat  less  opaque  than  the 
subjacent  and  broader  portion  of  the  horn,  caput  cornu, 
which  it  covers  as  a  cap.  More  ventrally  the  posterior 
horn  is  usually  somewhat  contracted,  to  which  portion 
the  term,  cervix  cornu  (cervix  columnae  posterioris)  is 
applied.  In  the  lower  thoracic  cord,  however,  this 
constriction  is  replaced  by  a  slight  bulging  located  on 
the  mesial  side  of  the  junction  of  the  posterior  cornu 
with  the  gray  commissure.  This  enlargement  corres- 
ponds to  the  location  of  a  longitudinal  group  of  nerve- 
cells  constituting  the  column  of  Clarke. 

The  fairly  sharp  demarcation  between  the  gray 
and  white  matter  is  interrupted  along  the  lateral  border 
of  the  crescent  by  delicate  prolongations  of  gray  matter 
into  the  surrounding  lateral  column  (Fig.  888).  The 
subdivisions  of  these  processes  unite  to  form  a  reticulum 
of  gray  matter,  the  meshes  of  which  are  occupied  by 
longitudinally  coursing  nerve-fibres,  the  whole  giving 
rise  to  an  interlacement  known  as  fae,  processus  or  for- 
matio  reticularis.  Although  to  some  extent  present 
in  the  greater  part  of  the  cord,  this  structure  is  most 
marked  in  the  upper  cervical  region,  where  it  exists  as 
a  conspicuous  net-work  filling  the  recess  that  indents 
the  lateral  border  of  the  pars  intermedia  and  the  neck 
of  the  posterior  horn  of  the  gray  crescent.  In  the 
thoracic  and  upper  parts  of  the  cervical  cord,  therefore 
in  regions  in  which  the  enlargements  are  wanting,  the 
formatio  reticularis  is  condensed  into  a  compact  process 
of  gray  matter  that  is  directed  outward  (Fig.  885)  and 
known  as  the  lateral  cornu  (columna  lateralis). 


i  T— 


Taken  as  a  whole,  the  gray  matter,  which  in  cross-sections 
appears  as  the  H -shaped  area  formed  by  the  two  crescents 
and  the  commissure,  constitutes  a  continuous  column,  whose 
irregular  contour  depends  not  only  upon  the  peculiar  disposi- 
tion of  the  gray  matter,  but  also  upon  the  variations  in  its 
amount  at  different  levels  of  the  cord.  Thus,  at  the  level  of 
the  third  cervical  nerve  the  gray  matter  constitutes  somewhat 
more  than  one-fourth  of  the  entire  area  of  the  cord ;  at  that  of 
the  seventh  nerve  about  one-third,  while  in  the  thoracic  region, 
between  the  second  and  eleventh  nerves,  it  is  reduced  to  about  one-sixth.  At  the  last  thoracic 
nerve  it  again  forms  one-fourth,  and  at  the  third  and  fifth  lumbar  two-fifths  and  three-fifths 
respectively.  In  the  sacral  cord  the  relative  amount  of  gray  matter  increases  until,  at  the  level 


Diagram  showing  amount  of  gray 
and  white  matter  in  relation  to  entire 
area  of  cord,  and  relative  lengths  of 
cord-segments;  the  latter  are  indicated 
by  divisions  on  left  margin  of  figure — 
I  C,  I  T,  I  L,  I  S,  first  segment  of  cervi- 

respectively ;  dark  zone  next  left  bor- 
der represents  the  gray  matter,  light 
zone  the  white  matter,  outer  dark  zone 
the  entire  area  of  cord.  (Donaldson.) 


1030 


HUMAN   ANATOMY. 


of  the  last  sacral  nerve,  it  reaches  three-fourths.  The  absolute  amount  of  gray  matter  is  greatest 
within  the  cervical  and  lumbar  enlargements  of  the  cord,  where  it  is  directly  related  to  the  large 
nerves  supplying  the  lirhbs.  On  comparing  the  tracts  of  white  matter  and  the  gray  column  it 
follows  that  while  in  the  lower  third  ot  the  lumbar  cord  these  are  of  approximately  equal  area, 
below  this  level  the  gray  matter  exceeds  the  white.  In  the  remaining  regions,  on  the  other 
hand,  the  white  matter  predominates,  in  the  greater  part  of  the  thoracic  cord  exceeding  the  gray 
from  four  to  five  fold  and  in  the  cervical  cord  being  from  two  to  three  times  greater. 

The  Central  Canal. — Where  well  represented,  the  central  canal  (canalis  cen- 
tralis),  the  remains  of  the  once  conspicuous  neural  tube,  appears  as  a  minute 
opening  in  the  gray  commissure,  about  .2  mm.  in  diameter  and  barely  visible  with 
the  unaided  eye.  In  the  child  it  extends  the  entire  length  of  the  cord  and,  below, 
ends  blindly  in  the  upper  half  of  the  filum  terminale.  Above,  it  opens  into  the  lower 
end  of  the  fourth  ventricle,  from  which  it  is  prolonged  downward  through  the  lower 
half  of  the  medulla  oblongata  into  the  spinal  cord.  In  not  over  one-fifth  of  adult 
subjects,  however,  is  the  canal  retained  as  a  pervious  tube  throughout  the  cord,  its 
lumen  usually  being  partially  or  completely  obliterated  for  longer  or  shorter  stretches, 
the  lumen  last  disappearing  in  the  lower  part  of  the  cord.  Within  the  conus 
medullaris,  the  central  canal  regularly  exhibits  an  expansion,  the  sinus  terminalis, 
that  begins  below  the  origin  of  the  coccygeal  nerve  and  extends  caudally  for  from 
8-10  mm.,  with  a  maximum  frontal  diameter  of  i  mm.  or  over. 

The  obliteration  of  the  central  canal,  complete  in  about  50  per  cent,  of  subjects  beyond 
middle  life  (Schulz),  is  to  be  regarded  as  a  physiological  accompaniment  of  advancing  age.  It 
is  effected  by  displacement  and  proliferation  of  the  ependyma-cells  lining  the  canal,  in  conjunc- 
tion with  ingrowth  of  the  surrounding  neurogliar  fibres  (Weigert).  The  form  of  the  canal,  as 
seen  in  cross-sections,  is  very  variable  and  uncertain  owing  to  the  changes  incident  to  the  use 
of  hardening  fluids.  In  a  general  way  when  well  preserved  the  lumen  is  round  or  oval  and 
smallest  in  the  thoracic  region  ;  in  some  places,  as  in  the  upper  cervical  cord  and  in  the  lumbar 
enlargement,  it  is  larger  and  often  appears  pentagonal  in  outline,  whilst  in  others  the  calibre 
may  be  reduced  to  a  sagittal  slit.  The  position  of  the  central  canal  varies  at  different  levels  in 
relation  to  the  ventral  and  dorsal  surfaces  of  the  cord.  In  the  middle  of  the  lumbar  region  it 
occupies  approximately  the  centre  of  the  cord,  but  above,  in  the  thoracic  and  cervical  segments, 
it  lies  much  nearer  the  ventral  than  the  dorsal  surface,  while  below  it  gradually  approaches  the 
dorsal  surface,  but  always  remains  closed. 

Mention  may  be  made  of  a  remarkable  structure  named  Reissner* s  fibre,  after  its  discov- 
erer, that  as  a  longitudinal  thread  of  great  delicacy  lies  free  within  the  central  canal  of  the  cord 
and  the  lower  ventricle  of  the  brain,  extending  from  the  cavity  of  the  mesencephalon  above  to 
the  lowest  part  of  the  cordrcanal  below.  The  interpretation  of  this  structure  as  an  artefact, 
which  considering  its  extraordinary  position  is  most  natural,  seems  untenable  in  view  of  the 
positive  testimony,  confirming  its  existence  as  a  preformed  and  true  structure  in  many 
vertebrates,  given  by  several  subsequent  observers  and  especially  by  Sargent.1  Its  nature  and 
significance  are  problematic.  Although  the  existence  of  this  fibre  has  been  established  in  many 
vertebrates,  even  in  birds,  it  has  not  yet  been  discovered  in  man. 

MICROSCOPICAL  STRUCTURE  OF  THE  SPINAL  CORD. 

The  three  chief  components  of  the  spinal  cord — the  nerve-cells,  the  nerve-fibres 
and  the  neuroglia — vary  in  proportion  and  disposition  in  the  white  and  gray  matter. 
It  is,  therefore,  desirable  to  consider  the  general  structure  of  the  cord  before  describ- 
ing its  detailed  characteristics  at  different  levels. 

The  Gray  Matter. — The  most  distinctive  elements  of  the  gray  matter  are  the 
ni ult if>olar  nerve-cells  which  lie  embedded  within  a  complex  sponge-like  matrix  formed 
by  the  various  processes — dendrites,  axones  and  collaterals — from  other  neurones,  the 
supporting  neuroglia  and  the  blood-vessels.  In  two  localities — immediately  around  the 
central  canal  and  capping  the  dorsal  cornu — the  gray  matter  varies  in  its  appearance 
and  constitution  and  exhibits  the  modifications  peculiar  to  the  central  and  Rolandic 
substantia  gelatinosa,  the  details  of  which  call  for  later  description  (page  1034). 

Tin  nerve-cells  of  the  anterior  horn  are  multipolar,  in  cross-sections  the 
cell-bodies  appearing  irregularly  polygonal  and  in  longitudinal  sections  fusiform  in  out- 

1  Bulletin  of  Harvard  Museum  of  Comp.  Zoology,  vol.  xlv.,  1904. 


MICROSCOPICAL   STRUCTURE    OF   SPINAL    CORD.  1031 

line.  They  may  vary  from  .065-.  135  in  diameter,  unless  unusually  small,  when  they 
measure  from  .030-. 080  mm.  (Kolliker).  In  a  typical  example,  as  represented  by 
one  of  the  ventral  radicular  cells  giving  origin  to  anterior  root-fibres,  from  three 
to  ten  dendritic  processes  radiate  in  various  planes,  divide  dichotomously  with 
decreasing  width  and  finally  end  in  terminal  arborizations.  In  contrast  to  the  robust 
dendrites  beset  with  spines,  the  axone  is  smooth,  slender  and  directly  continuous 
with  the  axis-cylinder  of  a  root-fibre  of  a  spinal  nerve  and  unbranched,  with  the 
exceptions  of  delicate  lateral  processes  that  are  given  off  almost  at  right  angles.  These 
processes,  the  collaterals,  arise  at  a  variable  distance  from  the  cell-body,  but  usually 
close  to  the  latter  and  always  before  leaving  the  gray  matter.  They  repeatedly 
divide  and  follow  a  recurrent  course  within  the  anterior  horn.  After  appropriate 
staining  the  cytoplasm  of  the  nerve-cells  exhibits  conspicuous  accumulations  of  the 
deeply  staining  tigroid  substance  that  lie  within  the  meshes  of  the  reticulum  formed  by 
delicate  neurofibrillae, 

which  not  only  occupy  FIG.  887. 

the    cell-body   but  also 

extend  into  the  various  jy^  -\ 

processes.  The  fibrillse, 
however,  do  not  pass 
beyond  the  limits  of  the 
neurone  to  which  they 
belong  (Retzius).  Each 
nerve-cell  possesses  a 
spherical  or  ellipsoidal 
nucleus,  from  .010  to 
.020  mm.  in  its  greatest 
diameter,  which  is  en- 
closed by  a  distinct 
nuclear  membrane  and 
usually  contains  a  single 
nucleolus,  exceptionally 
two  or  three.  Within 
the  cytoplasm  an  accu- 
mulation of  brownish- 
yellow  pigment  granules 
is  usually  present  near 
one  pole,  often  in  the 
vicinity  of  the  implanta- 
tion cone  from  which 
the  axone  springs. 


In  addition  to  the  con- 
spicuous ventral  radicular 
cells  above  described,  the 
anterior  horn  contains  Nerve-fibres  of  white  matter  Anterior  root-fibres 

Other     nervous      elements,  Portion  of  anterior  cornu  of  gray  matter,  showing  multipolar 

Some    Of    which,    the    Com-  nerve-cells.     X  120. 

missural  cells,  send   their 

axones  through  the  anterior  commissure  to  the  opposite  half  of  the  cord,  while  the  axones  of 
others,  the  strand-cells,  pass  into  the  columns  of  white  matter  of  the  same,  less  frequently 
opposite,  side. 

The  commissural  cells,  which  with  few  exceptions  occupy  the  median  portion  of  the 
anterior  horn,  resemble  in  size  and  contour  the  radicular  cells,  but  differ  from  the  latter  in  pos- 
sessing smaller  nuclei.  The  majority  of  the  dendrites  are  directed  towards  the  inner  part  of 
the  ventral  cornu,  but  some  pass  into  the  gray  commissure  and  a  few  end  within  the  adjacent 
white  matter.  The  axones  traverse  the  anterior  white  commissure  to  gain  the  ventral  column 
of  the  opposite  side,  in  which  they  either  divide  "f-like  into  ascending  and  descending  fibres,  or 
undivided  turn  brainward.  • 

The  strand  cells,  variable  in  form  and  generally  smaller  than  the  root-cells,  are  only 
sparingly  represented  in  the  anterior  horn.  They  are  distinguished  by  the  course  of  their 
axones,  which  usually  pass  to  the  anterior  column  of  the  same  side.  In  some  cases,  however, 


1032 


HUMAN    ANATOMY. 


the  axone  divides  into  two,  rarely  three,  fibres,  one  of  which  crosses  by  way  of  the  anterior 
white  commissure  to  the  opposite  ventral  column,  while  the  other  passes  to  the  ventral 
column  of  the  same  side. 

As  well  seen  in  cross-sections,  although  the  nerve-cells  of  the  anterior  horn  are  widely 
scattered  they  are  not  uniformly  distributed  through  the  gray  matter,  but  are  collected  into 
more  or  less  definite  groups  that  recur  in  consecutive  sections.  It  is  evident,  therefore,  that  the 
cell-groups  are  not  limited  to  a  single  plane,  but  are  continuous  as  longitudinal  tracts  or 
columns  for  longer  or  shorter  stretches  within  the  core  of  gray  matter  of  the  cord. 

The  grouping  of  the  nerve-cells  of  the  anterior  horn  includes  two  general 
collections,  a  mesial  group,  containing  many  commissural  cells,  and  a  lateral  group 
composed  chiefly  of  ventral  radicular  cells.  These  collections,  however,  vary  in 
extent  and  definition  in  different  parts  of  the  cord  and,  where  well  marked,  are  often 


FIG. 


Cells  of  substantia 
gelatinosa  Rolandi 


Posterior  horn  cells 


Accessory  dorso- 
lateral  groups 


Dorso-latcral  group 


"  Ventro-lateral  group 
Mesial  group' 

Transverse  section  of  lower  cervical  cord,  showing  grouping  of  nerve-cells  ;  Nissl  staining.    X  20. 

made  up  of  more  than  a  single  aggregation  of  cells.  This  feature  is  particularly  rvi- 
dent  in  the  lateral  collection,  in  which  an  anterior  and  a  posterior  subdivision  are 
recognized  as  the  ventro-lateral  and  the  dorso-lateral  group  that  occupy  the  corre- 
sponding angles  of  the  anterior  horn.  The  mesial  collection,  situated  within  the 
ventral  angle,  is  likewise,  but  much  less  clearly,  divisible  into  a  centre-mesial  and  a 
dorso-nn-sial  group,  of  which  the  latter  is  variable  and  at  many  levels  wanting.  In  a 
general  way  the  pronounced  presence  of  these  cell-groups  influences  the  outline  of 
the  anterior  horn,  so  that  corresponding  projections  of  the  gray  matter  mark  their 
position.  This  relation  is  conspicuously  exemplified  in  the  cervical  and  lumbo-sacral 
enlargements,  in  which  the  presence  of  large  lateral  cell-groups  is  directly  associated 
with  a  marked  increase  in  the  transverse  diameter  of  the  anterior  horn.  Conversely, 
when  these  cell-columns  become  smaller  or  disappear,  the  corresponding  rlrvations 
on  the  surface  of  the  anterior  horn  diminish  or  are  absent.  Owing  to  such  variations 
the  contours  of  the  gray  core  are  subject  to  constant  and  sometimes  abrupt  change. 


MICROSCOPICAL   STRUCTURE    OF    SPINAL   CORD.  1033 

The  ventro-median  cell-column  is  the  most  constant,  since,  as  emphasized  by  the  pains- 
taking studies  of  Bruce,1  it  is  interrupted  only  between  the  levels  of  the  fifth  lumbar  and  first 
sacral  nerve  in  its  otherwise  unbroken  course  through  the  length  of  the  cord,  as  far  as  the  level 
of  the  fifth  sacral  nerve.  An  augmentation  of  this  tract  in  the  fourth  and  fifth  cervical  segments 
is  probably  associated  with  the  spinal  origin  of  the  phrenic  nerve  (Bruce). 

The  dorso-mesial  cell-column  is  much  less  constant,  being  represented  only  in  the  thoracic 
region,  in  a  few  cervical  segments  and  at  the  level  of  the  first  lumbar  nerve.  In  agreement 
with  van  Gehuchten  and  others,  Bruce  regards  the  continuity  of  the  mesial  group  as  presump- 
tive evidence  of  its  close  relation  to  the  dorsal  extensor  muscles  of  the  trunk. 

The  ventro-lateral  cell-column  appears  first  at  the  level  of  the  fourth  cervical  nerve, 
increases  rapidly  in  the  succeeding  segments  and  fades  away  at  the  lower  part  of  the  eighth 
cervical  segment.  It  reappears  in  the  lumbar  enlargement,  reaching  its  maximum  at  the  level 
of  the  first  sacral  nerve  and,  diminishing  rapidly  through  the  upper  part  of  the  second, 
disappears  before  the  third  sacral  segment  is  reached. 

The  dorso-lateral  cell-column,  in  places  the  most  conspicuous  collection  of  the  anterior 
horn,  begins  above  at  the  lower  part  of  the  fourth  cervical  segment  and,  increasing  rapidly, 
attains  its  greatest  development  in  the  neck  in  the  fifth  and  sixth  segments.  It  suffers  a  marked 
reduction  at  the  level  of  the  seventh  cervical  nerve,  which  is  followed  by  a  sudden  increase  in 
the  next  segment  in  which  the  column  presents  an  additional  collection  of  nerve-cells  known  as 
the  accessory  dorso-lateral  or  post-postero-  lateral  group.  Below  the  level  of  the  second  thoracic 
nerve  the  dorso-lateral  cell-column  is  unrepresented  as  far  as  the  second  sacral  segment  where 
it  reappears,  somewhat  abruptly,  and  attains  its  maximum  size  in  the  fourth  and  fifth  lumbar 
segments.  The  column  then  diminishes  and  ceases  at  the  lower  part  of  the  third  sacral  seg- 
ment. Within  the  sacral  cord,  between  the  levels  of  the  first  and  third  nerve  inclusive,  the 
dorso-lateral  cell- group  is  augmented  by  an  accessory  group.  From  the  third  lumbar  to  the 
sacral  nerve-levels,  an  additional  compact  collection  of  nerve-cells  occupies  a  more  median 
position  in  the  anterior  horn  and  constitutes  the  central  group. 

From  the  position  of  the  greatest  expansions  of  the  lateral  cell-columns — within  the  cervical 
and  lumbo-sacral  enlargements — it  is  evident  that  they  are  associated  with  the  large  nerves  sup- 
plying the  muscles  of  the  limbs.  Further,  according  to  Bruce,  in  a  general  way  the  size  of  the 
radicular  cells  bears  a  relation  to  that  of  the  muscles  supplied,  the  smaller  dimensions  of  the 
cervical  cells,  as  compared  with  those  of  the  lumbo-sacral  region,  corresponding  with  the  smaller 
size  of  the  upper  limb  in  comparison  with  that  of  the  lower  one. 

In  addition  to  the  nerve-cells  assembled  within  the  foregoing  more  or  less  well  defined 
groups,  some  scattered  cells  are  irregularly  distributed  through  the  anterior  horn  and  do  not 
strictly  belong  to  any  of  the  groups. 

Below  the  level  of  the  first  coccygeal  nerve,  the  cells  of  the  anterior  horn  become  so 
diminished  in  number,  that  they  are  no  longer  grouped  with  regularity,  but,  reduced  in  size,  lie 
uncertainly  distributed  within  the  gray  matter  as  far  as  the  lower  limits  of  the  conus  medullaris. 

.  The  nerve-cells  of  the  posterior  horn  are  neither  as  large  nor  as  regularly 
disposed  as  the  anterior  horn  cells.  Only  in  one  locality,  along  the  median  border 
of  the  base  of  the  posterior  horn,  are  they  collected  into  a  distinct  tract,  the  column  of 
Clarke  ;  otherwise  they  are  scattered  without  order  throughout  the  gray  matter  of  the 
posterior  cornu.  Since,  however,  the  latter  comprises  certain  areas,  the  cells  of 
the  posterior  horn  may  be  divided  into  (i)  the  cells  of  Clarke' s  column,  (2)  the 
cells  of  the  substantia  gelatinosa  Rolandi,  and  (3)  the  inner  cells  of  the  caput  cornu. 

The  cells  of  Clarke's  column  form  a  very  conspicuous  collection  which  extends  from  the  level 
of  the  seventh  cervical  nerve  to  that  of  the  second  lumbar  nerve  and  is  best  developed  in  the 
lower  thoracic  region  of'the  cord.  Although  confined  chiefly  to  the  dorsal  portion  of  the  cord, 
and  hence  sometimes  designated  as  the  "dorsal  nucleus,"  Clarke's  column  is  represented  to  a 
slight  degree  in  the  sacral  and  upper  cervical  regions  (sacral  and  cervical  nuclei  of  Stilling) .  In 
cross-sections  the  cell-column  appears  as  a  group  of  multipolar  cells  that  occupy  the  mesial 
border  of  the  base  of  the  posterior  horn  and,  where  the  column  is  best  developed  (opposite  the 
origin  of  the  twelfth  thoracic  nerve),  correspond  to  an  elevation  on  the  surface  of  the  gray 
matter.  The  cells  usually  are  about  .050  mm.  in  diameter,  polygonal  in  outline  and  possess  a 
relatively  large  number  of  richly  branched  dendrites  that  radiate  chiefly  within  the  limits  of  the 
group  (Cajal).  The  axones  commonly  spring  from  the  anterior  or  lateral  margin  of  the  cells 
and  course  ventrally  for  a  considerable  distance  before  bending  outward  toward  the  lateral 
column  of  white  matter  within  which,  as  constituent  fibres  of  the  direct  cerebellar  tract 
(page  1044)  >  they  turn  brainward. 

'Topographical  Atlas  of  the  Spinal  Cord,  1901. 


1034 


HUMAN   ANATOMY. 


The  nerve-cells  of  the  substantia  gelatinosa  Rolandi,  also  known  as  Gierke ' s  cells,  include 
innumerable  small  stellate,  less  frequently  fusiform  or  pear-shaped  elements  that  measure  only 
from  .oo6-.o2o  mm.,  although  exceptionally  of  larger  size.  Their  numerous  short  dendrites  are 
irregularly  disposed  and  branched.  The  axones,  which  always  arise  from  the  dorsal  pole  of  the 
cell,  are  continued  partly  to  the  white  matter  of  the  posterior  column,  within  which  they  divide 
into  ascending  and  descending  limbs,  and  partly  to  the  gray  matter  itself,  within  which  they  run 
as  longitudinal  fibres.  Under  the  name  of  the  marginal  cells  are  described  the  much  larger 
(.035-.055  mm. )  nerve-cells  which  occupy  the  border  of  the  substantia  gelatinosa.  They  are 
spindle-shaped  or  pyramidal  in  form,  their  long  axes  lying  parallel  or  the  apices  directed  towards 
the  Rolandic  substance  respectively,  and  constitute  a  one-celled  layer  enclosing  the  substantia 
gelatinosa,  into  which  many  of  their  tangentially  coursing  dendrites  penetrate.  Their  axones 
pass  through  the  substantia  gelatinosa  and  probably  continue  for  the  most  part  within  the  lateral 
column,  although  some  enter  the  posterior  column  (Cajal,  Kolliker). 

The  inner  cells  of  the  posterior  horn  are  intermingled  with  numerous  nervous  elements  of 
small  size  irregularly  distributed  within  the  head  of  the  dorsal  cornu.  The  inner  cells  proper 
are  triangular  or  spindle-shaped  in  form  and,  on  an  average,  measure  about  .050  mm.;  they 
are,  therefore,  larger  than  the  ordinary  cells  of  the  Rolandic  substance.  The  dendrites  arise 

FIG.  889. 


White  matter  of 

posterior  column 


Cells  of  Clarke's  column 

Substantia  gelatinosa  centraiis 


Central  canal 
Part  of  cross-section  of  cord,  showing  cells  of  Clarke's  column  in  base  of  posterior  horn.    X'no. 

from  the  angles  or  ends  of  the  cells  and  diverge  in  all  directions.  The  axones  pass,  either 
directly  or  in  curves,  mostly  into  the  lateral  column  of  the  same  side  ;  some,  however,  have 
been  followed  into  the  posterior  or  anterior  columns  of  the  same  side  (Kolliker),  and,  rarely,  into 
the  opposite  anterior  column  (Cajal).  Exceptionally  type  II  cells  —  those  in  which  the  axone  is 
not  prolonged  as  the  axis-cylinder  of  a  nerve-fibre,  but  soon  breaks  up  into  an  elaborate  end 
arborization  confined  to  the  gray  matter  —  are  found  within  the  gray  matter  of  the  posterior  horn. 
Their  number  is,  however,  much  less  than  often  assumed  (Ziehen). 

The  nervous  character  of  most  of  the  cells  seen  within  the  substantia  gelatinosa  Rolandi  has 
been  established  only  since  the  introduction  of  the  Golgi  methods  of  silver-impregnation. 
Previously,  these  elements  were  regarded  as  glia  cells,  an  exceptionally  large  amount  of 
neuroglia  in  general  being  attributed  to  the  Rolandic  substance.  It  is  now  admitted  that 
instr.-ul  <>f  such  being  the  case,  this  region  of  the  gray  matter  is  relatively  poor  in  neurogliar 
elements  and  numerically  rich  in  nerve-cells. 

The  nerve-cells  of  the  pars  intermediate  of  the  gray  matter,  which  connects 
the  dorsal  and  ventral  horns  and  lies  opposite  the  gray  commissure,  may  be  broadly 
divided  into  two  classes,  the  lateral  and  the  middle  cells,  that  occupy  respectively  the 
outer  border  and  the  more  central  area  of  this  part  of  the  gray  matter  of  the  cord. 


MICROSCOPICAL    STRUCTURE    OF    SPINAL   CORD. 


Those  of  the  first  class,  or  intermedio-lateral  cells,  are  associated  with  the  formatio  reticu- 
laris  and  its  condensation,  the  lateral  horn,  and  hence  are  often  spoken  of  as  the  group  or 
column  of  the  lateral  horn.  These  cells  form  a  slender  tract  of  small  closely  packed  elements 
that  is  represented  through  almost  the  entire  length  of  the  cord,  although  best  marked  in  the 
upper  third  of  the  thoracic  region  and  partially  interrupted  in  the  cervical  and  lumbo-sacral 
segments.  Where  the  formatio  reticularis  is  condensed  with  a  distinct  lateral  horn,  as  in  the 
thoracic  region,  the  cells  occupy  the  projection,  but  elsewhere  lie  within  the  base  of  the  gray  net- 
work. As  a  continuous  cell-column  the  tract  extends  from  the  lower  part  of  the  eighth  cervical 
segment  to  the  upper  part  of  the  third  lumbar,  being  most  conspicuous  at  the  level  of  the  third  and 
fourth  thoracic  nerves  (Bruce).  Practically  suppressed  in  the  cervical  region  between  the  eighth 
and  third  segments,  above  the  latter  the  column  reappears  along  with  the  formatio  reticularis. 
Below,  it  is  again  seen  within  the  third  and  fourth  sacral  segments.  The  nerve-cells  are  multi- 
polar  or  fusiform  in  outline,  from  .oi5~.o45  mm.  in  their  longest  diameter,  contain  little  pigment, 
and  are  provided  with  a  variable  number  of  dendrites,  of  which  two  are  usually  larger  than  the 
others.  These  arise  from  opposite  poles  of  the  cell  and  send  branches,  for  the  most  part,  into  the 
adjacent  white  matter.  The  axones  pass  directly  into  the  lateral  columns  and  become  ascending 
or  descending  fibres  ;  a  few  axones,  however,  enter  the  anterior  column  of  the  same  side  (Ziehen). 

The  cells  of  the  second  class,  or  intermediate  cells,  are  irregularly  disposed  and  only  in  the 
upper  part  of  the  cord  present  a  fairly  distinct  middle  group  (Waldeyer).  They  are  polygonal 
or  fusiform  in  outline,  small  in  size  (seldom  exceeding  .025  mm.)  and  provided  with  irregular 
dendrites.  The  axones  are  continued  chiefly  within  the  lateral  column  of  the  same  side,  although 
some  pass  to  the  anterior  column  and  a  few  probably  cross  to  the  opposite  side. 

A  small  number  of  isolated  nerve-cells  are  usually  to  be  found  within  the  white  matter,  out- 
side but  in  the  neighborhood  of  the  gray  core.  These,  the  outlying  cells  of  Sherrington,1  by 
whom  they  have  been  studied,  occur  most  frequently  in  the  vicinity  of  the  more  superficially 
placed  cell-columns.  Within  the  anterior  columns  they  lie  in  the  paths  of  the  fibres  proceeding 
to  the  anterior  white  commissure  ;  in  the  lateral  columns  they  are  in  proximity  to  the  intermedio- 
lateral  group  of  the  lateral  horn  and  formatio  reticularis  and  to  the  cells  of  the  substantia 
Rolandi ;  and  in  the  posterior  columns,  where  they  are  relatively  numerous,  they  are  associated 
with  the  fibre-tracts  leading  to  the  column  of  Clarke.  The  outlying  cells  are  regarded  as 
elements  displaced  from  their  usual  position  during  the  course  of  the  differentiation  and  growth 
of  the  white  and  gray  matter.  Similar  displacement  sometimes  affects  the  cells  of  the  spinal 
ganglia,  which  then  may  be  encountered  within  the  cord. 


The  Neuroglia  of  the  Gray  Matter. — As  in  other  parts  of  the  cord,  so  in 
the  gray  matter  the  neuroglia  is  everywhere  present  as  the  supporting  framework  of 

the  nervous  elements,  the 

FIG.  890. 

Posterior  median 
septum 


Paraniedian  septum 
subdividing 
posterior  column 


cells  and  fibres.  The  gen- 
eral structureof  neuroglia 
having  been  described 
(page  1004),  it  only  re- 
mains to  note  here  the 
special  features  of  its 
arrangement  within  the 
gray  matter.  In  general, 
the  felt-work  of  the  neu- 
rogliar  fibrils  is  more 
compact  than  that  per- 
meating the  white  matter, 
being  somewhat  denser 
at  the  periphery  than  in 
the  deeper  parts  of  the 
gray  matter.  There  is, 
however,  no  hard  boun- 
dary between  the  sup- 
porting tissue  of  the  two, 
since  numerousglia  fibrils 
extend  outward  from  the 
frame-work  of  the  gra)'  matter  to  be  lost  between  the  nerve  fibres  of  the  adjoining 
columns.  This  feature  is  marked  in  the  anterior  horn,  where  the  glia  fibrils  form 
septa  of  considerable  thickness  that  diverge  into  the  surrounding  columns  ;  further 

1  Proceedings  Royal  Society,  vol.  30,  1890. 


Anterior  median  fissure 


Anterior  column 


Transverse  section  of  cord  slightly  magnified,  showing  general   arrangement 
of  neuroglia.     X  10. 


1036 


HUMAN   ANATOMY. 


the  conspicuous  processes  of  the  formatio  reticularis  and  the  projecting  lateral  horn 
consist  largely  of  neuroglia.  The  larger  nerve-cells  and  their  robust  processes  are 
ensheathed  by  interlacements  of  neuroglia  hbrilhe. 

In  the  several  parts  of  the  posterior  horn  the  amount  of  neuroglia  varies. 
Thus,  the  apex  consists  almost  exclusively  of  glia  tissue,  while  within  the  Rolandic 
substance  the  number  of  glia  fibres  and  cells  is  unusually  small.  Within  the 
caput  and  remaining  parts  of  the  posterior  horn  the  neurogliar  elements  are  similar 
in  quantity  and  disposition  to  those  in  the  anterior  horn. 

The  ependyma  cells  lining  the  central  canal  of  the  cord  are  the  direct  descendants  of  the 
radially  arranged  embryonal  supporting  elements  (page  1004)  ;  they  may,  therefore,  be  regarded 
as  specialized  neuroglia  cells.  Although  most  advantageously  studied  in  the  foetus  and  the 
child,  in  favorable  preparations  from  adult  cords  they  are  seen  as  a  single  row  of  pyramidal 
cells,  from  .030-.050  mm.  long  and  from  one-fourth  to  one-third  as  broad,  whose  bases  are 
directed  towards  the  lumen  of  the  canal  and  beset  with  cilia.  Their  pointed  distal  ends,  or 
apices,  are  prolonged  into  a  long  delicate  ependymal  fibre,  that  in  the  adult  is  soon  lost  in  the 
surrounding  neuroglia,  but  in  the  foetus  extends  through  the  entire  thickness  of  the  cord.  The 
ependyma  cells  are  not  all  of  equal  size,  those  occupying  the  ventral  mid-line,  especially  in  the 
cervical  region,  being  about  twice  as  long  as  those  on  the  opposite  wall  of  the  canal.  The  epen- 
dymal fibres  proceeding  from  these  cells  are  of  special  length  and  thickness,  the  ventral  ones  con- 
verging to  form  a  wedge-shaped  mass  that  in  the  young  subject  continues  as  far  forward  as  the 
bottom  of  the  anterior  median  fissure.  The  dorsal  ependymal  fibres  are  prolonged  through  the 
gray  commissure  into  the  posterior  median  septum,  some  diverging  into  the  columns  of  Goll. 


FIG.  891. 


Substantia  gelatinosa  centralis  is  the  name  given  to  a  zone  of  peculiar  trans- 
lucency  that  immediately  surrounds  the  central  canal.  This  annular  area  consists  of 

modified  neuroglia  in  which  radial  ependymal  fibers  are 
interwoven  with  circularly  disposed  neurogliar  fibrillae, 
the  whole  giving  rise  to  a  compact  stratum,  interspersed 
with  an  unusual  number  of  glia  cells,  upon  which  arrange- 
ment, in  conjunction  with  the  absence  of  nerve-fibres, 
the  characteristic  appearance  of  the  gelatinous  substance 
depends.  In  addition  to  the  branched  glia  elements,  a 
number  of  radially  directed  spindle  cells  are  present  in 
this  zone  ;  they  send  delicate  processes  between  the 
ependyma  cells,  of  which  they  are  probably  outwardly 
displaced  members.  In  marked  contrast  with  the  Ro- 
landic substance,  which  caps  the  posterior  horn,  the 
substantia  gelatinosa  centralis  contains  no  nerve-cells  but 
only  glia  elements,  in  recognition  of  which  the  term,  sub- 
stantia gliosa  centralis,  has  been  proposed  by  Ziehen. 
The  Nerve-Fibres  of  the  Gray  Matter.— 
Within  all  portions  of  the  gray  core  a  considerable  part 
of  the  intricate  ground-work  in  which  the  nerve-cells  lie 
embedded  is  contributed  by  the  processes  of  neurones 
situated  at  the  same,  different  or  even  remote  levels. 
These  processes,  which  constitute  the  nerve-fibres, 
medullated  and  nonmedullated,  that  are  seen  traversing 
the  gray  matter  in  all  directions,  include:(i)  the  collate- 
rals and  the  terminal  branches  of  the  dorsal  root-fibres  that  enter  the  gray  matter  ; 
(2)  nerve-fibres  of  the  descending  tracts  that  terminate  in  relation  with  the  ventral 
(motor)  horn  cells  ;  (3)  the  axones  and  collaterals  given  off  by  the  numerous  pos- 
terior horn  cells,  that  traverse  the  gray  matter  to  and  from  the  respective  columns  into 
which  they  pass.  The  dendritic  processes,  as  well  as  the  axones  of  the  type  II  cells, 
also  contribute  to  the  sum  of  nervous  fibrilke  encountered  within  the  gray  matter  of 
the  cord. 

WHITE  MATTER  OF  THE  SPINAL  CORD. 

The  predominating  components  of  the  white  substance  being  the  longitudinal 
nerve-fibres  which  pass  for  a  longer  or  shorter  distance  up  and  down  in  the  columns  of 
the  cord,  in  cross-sections  the  outer  field,  between  the  gray  core  and  the  periphery 


Central  canal  and  surrounding 
substantia  jrelatinosa  centralis,  from 
child's  cord ;  canal  is  lined  with 
ependyma  cells,  outside  of  which 
lies  neuroglia  with  glia  cells.  X  135. 


WHITE  MATTER  OF  THE  SPINAL  CORU. 


1037 


of  the  cord,  appears  to  be  composed  of  innumerable,  closely  set,  small  cells,  held 
together  by  delicate  supporting  tissue.  These  apparent  cells  are  the  medullated 
nerve-fibres  cut  transversely,  in  which  the  sectioned  axis-cylinders  show  as  deeply 
stained  dots,  that  commonly  lie  somewhat  eccentrically  and  are  surrounded  by  deli- 
cate irregularly  annular  striations  representing  the  framework  of  the  medullary  coat. 
The  nerve-fibres  of  the  cerebro-spinal  axis  are  without  neurilemma,  the  lack  of  this 
sheath  being  compensated  by  a  slight  condensation  of  the  neuroglia  around  the 
fibres.  Seen  in  transverse  sections  this  investment  appears  as  the  ring  that  gives 
a  definite  outline  to  the  fibre. 

The  individual  nerve-fibres  vary  greatly  in  size,  even  within  the  same  tract  large  and  small 
fibres  often  lying  side  by  side.  The  smallest  may  be  less  than  .005  mm.  and  the  largest  over 
.025  mm.  In  a  general  way,  the  diameter  of  the  fibre  bears  a  direct  relation  to  its  length,  those 


Fig.  892. 


Trabecula  of  neuroglia 


Blood-vessel  in  pia 


Subpial  layer 
of  neuroglia 


Peripheral  part  of  transverse  section  of  spinal  cord,  showing  nerve-fibres  subdivided  into  groups  by  ingrowth  of 

subpial  layer  of  neuroglia.     X  230.  , 

having  an  extended  course  being  larger  than  shorter  ones  ;  it  follows  that  the  fibres  occupying 
the  peripheral  parts  of  the  white  matter,  particularly  in  the  lateral  columns,  are  more  frequently 
of  large  diameter  than  those  near  the  gray  matter. 

The  immediate  surface  of  the  white  substance  beneath  the  pia  mater  is  formed  by  a  con- 
densed tract  of  neuroglia,  the  subpial  layer,  from  .O20-.O40  mm.  in  thickness,  that  is  devoid  of 
nervous  elements  and  forms  the  definite  outer  boundary  of  the  cord.  This  zone  consists  of  a 
dense  interlacement  of  circular,  longitudinal  and  radial  neuroglia  fibrils  among  which  numer- 
ous glia  cells  are  embedded.  From  the  deeper  surface  of  this  ensheathing  layer  numerous 
bundles  of  fibrillse  penetrate  between  the  subjacent  nerve-fibres  to  become  lost  in  the  general 
supporting  ground-work.  At  certain  places  the  bundles  are  replaced  by  robust  septa  by  which 
the  nerve-fibres  are  imperfectly  divided  into  groups  or  tracts,  as  conspicuously  seen  in  the  pos- 
terior column  where  the  paramedian  septum  effects  an  imperfect  subdivision  into  the  tract  of 
Goll  and  of  Burdach.  The  blood-vessels  that  enter  the  nervous  substance  from  the  pia,  accom- 
panied by  connective  tissue,  are  surrounded  by  tubular  sheaths  of  neuroglia,  and  the  same  is 


1038 


HUMAN   ANATOMY. 


true  of  the  bundles  of  root-fibres  of  the  spinal  nerves,  lint  apart  from  the  connective  tissue  that 
enters  with  the  blood-vessels,  the  amount  of  mesoblastic  tissue  concerned  in  the  supporting 
framework  of  the  cord  is  inconsiderable,  according  to  some  histologists,  indeed,  being 
practically  nothing. 

Fibre-Tracts  of  the  White  Matter. — Although  microscopical  examination 
of  ordinary  sections  of  the  cord  affords  slight  indication  of  a  subdivision  of  the 
columns  of  white  matter  into  areas  corresponding  with  definite  fibre-tracts,  yet  the 
combined  evidence  of  anatomical,  pathological,  embryological  and  experimental 
investigation  establishes  the  existence  of  a  number  of  such  paths  of  conduction. 
With  few  exceptions,  they  are,  however,  without  sharp  boundaries  and  illy  defined, 
adjoining  tracts  often  overlapping,  and  depend  for  their  presence  upon  the  fact  that 
nerve-fibres  having  the  same  function  and  destination  proceed  in  company  from  the 
same  group  of  nerve-cells  (nucleus)  along  a  similar  course.  In  addition  to  being  pro- 
vided with  paths  of  conduction  necessary  for  the  performance  of  its  function  as  a  centre 
for  independent  (reflex)  impulses  in  response  to  external  stimuli,  the  cord  contains 
tracts  that  connect  it  with  the  brain,  as  well  as  those  that  bring  the  various  levels  of 
the  cord  itself  into  association.  The  white  matter,  therefore,  contains  three  classes  of 
fibres  :  ( i )  those  entering  the  cord  from  the  periphery  and  other  parts  of  the  body  ; 
(2)  those  entering  it  from  the  brain  ;  and  (3)  those  arising  from  the  nerve-cells  situated 
within  the  cord  itself.  The  first  two  constitute  the  exogenous,  the  last  the  endogenous 
tracts.  It  is  evident  that  some  of  these  fibres  constitute  pathways  for  the  transmission 
of  impulses  from  lower  to  higher  levels  and  hence  form  ascending  tracts,  while  others, 
which  conduct  impulses  in  the  opposite  direction,  form,  descending  tracts. 

Since  it  is  impossible  to  distinguish  between  these  fibres  by  mere  inspection  of  sections  of 
the  adult  normal  cord,  and,  moreover,  extremely  difficult  and  practically  impossible  to  follow 
in  such  preparations  the  longer  fibres  throughout  their  course,  advantage  is  taken  of  other 
means  by  which  differentiation  of  individual  tracts  is  feasible.  Such  means  include  chiefly 
the  experimental  and  embryological  methods. 

The  experimental  method  depends  upon  the  law  discovered  by  Waller,  more  than  half  a 
century  ago,  that  when  the  continuity  of  a  nerve-fibre  is  destroyed,  either  by  a  pathological 
lesion  or  by  the  experimenter's  knife,  the  portion  of  the  nerve-fibre  (the  axone  of  a  neurone) 
beyond  the  break,  and  therefore  isolated  from  the  presiding  nerve-cell,  undergoes  secondary 
degeneration,  while  the  portion  remaining  connected  with  the  cell  usually  undergoes  little  or 
no  change.  It  should  be  pointed  out,  however,  that  occasionally  the  connected  portion  of  the 
fibre,  and  even  the  nerve-cell  itself,  undoubtedly  exhibits  changes  known  as  retrograde  degen- 
eration, which,  although  uncertain  as  to  occurrence  and  cause,  may  at  times  prove  a  source  of 
error  in  deducing  conclusions.  If  a  lateral  section  of  one-half  of  the  cord  of  a  living  animal  be 
made,  and,  after  the  expiration  of  from  three  to  four  weeks,  transverse  sections  be  cut  and 
appropriately  prepared  (by  the  methods  of  Marschi  or  of  Weigert),  certain  groups  of  nerve- 
fibres  will  present  degenerative  changes.  It  will  be  seen,  however,  that  the  degenerated  tracts 
in  sections  taken  from  above  the  lesion  are  not  the  same  as  those  in  sections  from  below  the 
division,  showing  that  certain  fibres  have  been  involved  in  opposite  directions,  those  arising 
from  nerve-cells  lying  below  the  lesion  being  affected  with  ascending  degeneration,  and  those 
from  cells  situated  above  with  descending  degeneration.  In  this  manner,  by  rare-fill  study  of 
consecutive  sections,  much  valuable  information  has  been  gained  as  to  the  origin,  course,  ter- 
mination and  function  of  many  fibre-tracts  within  the  central  nervous  system. 

The  embryological  method,  also  productive  of  important  advances  in  our  knowledge  of 
the  nervous  pathways,  is  based  on  the  fact,  first  demonstrated  by  Meckel,  that  the  nerve-fibres 
of  the  central  nervous  system  do  not  all  acquire  their  medullary   sheath  at  the  same  time 
Taking  advantage  of  such  variation,  as  suggested  by  Meynert  and  later  extensively  carried  out 
by  Flechsig  and  other?,  upon  staining  sections  of  embryonal  tissue  with  reagents  that   color 


especially  the  medullary  substance,  it  is  possible  to  differentiate  and  follow  certain  fibre-tracts 
in  the  fcetal  cord  with  great  clearness,  since  only  those  tracts  are  stained  in  which  the  myelin  is 
already  formed.  It  is  of  interest  to  note  that,  in  a  general  way,  the  order  in  which  the  different 
strands  of  the  cord  acquire  their  medullary  coat  accords  with  the  sequence  in  which  nervous 
function  is  assumed  by  the  fcetus  and  child  Thus,  the  paths  required  for  spinal  reflexes  (the 
posterior  and  anterior  root-fibres)  are  first  to  become  medullated  (fourth  and  fifth  total 
months);  those  bringing  into  association  the  different  segments  of  the  cord  next  (from  tin- 
fifth  to  the  seventh  month)  acquire  myelin;  those  connecting  the  cord  with  the  cerebellum 
follow  somewhat  later,  while  those  establishing  relations  with  the  cerebral  cortex  are  last 
do  not  begin  to  medullate  until  shortly  before  birth. 


WHITE  MATTER  OF  THE  SPINAL  CORD. 


1039 


Based  on  the  collective  evidence  contributed  by  these  methods — anatomical, 
physiological,  and  developmental — it  is  possible  to  locate  and  trace  with  fair  accuracy 
a  number  of  fibre-tracts  in  the  cerebro-spinal  axis.  Since  they  are  undergoing 
continual  augmentation  or  decrease,  their  actual  area  and  position  are  subject  to 
variation,  so  that  the  detailed  relations  in  one  region  of  the  cord  differ  from  those 
at  other  levels.  The  accompanying  schematic  figure,  therefore,  must  be  regarded 
as  showing  only  the  general  relations  of  the  most  important  paths  of  the  cord, 
and  not  as  accurately  representing  the  actual  form  and  size  of  the  fibre-tracts. 
It  must  also  be  appreciated  that  the  definite  limits  of  these  tracts  in  such  diagrammatic 

FIG.  893. 


Association  tracts 


Cerebro-spinal  tract 


\    \  V 

Vestibulo-spinal  tract 
Tecto-spinal  tract 


Rubro-spinal 

tract 
-  Vestibulo-spinal 

tract 

jfj~  Spino-thalamic 
tract 


Spino-olivary 
tract  (Helweg) 


representations  seldom  exist  in  reality,  since  the  fibres  of  the  adjacent  paths  in 
most  cases  overlap,  or,  indeed,  extensively  intermingle,  so  that  the  fields  seen  in 
cross-sections  may  be  shared  by  strands  belonging  to  different  fibre-systems. 

The  Fibre-Tracts  of  the  Posterior  Column. — The  subdivision  of  the 
posterior  column  of  white  matter  by  the  paramedian  septum  into  two  general 
parts  has  been  noted  (page  1028).  Of  these  the  inner  one  is  the  postero-median 
fasciculus,  or  tract  of  Goll  (fasciculus  gracilis),  and  the  outer  one  is  the  postero- 
lateral  fasciculus  or  tract  of  Burdach  (fasciculus  cuncatus).  These  tracts  are 
so  intimately  associated  with  the  fibres  entering  by  the  posterior  roots  of  the  spinal 
nerves,  that  the  general  relations  and  behavior  of  these  fibres  must  be  considered 
in  order  to  understand  the  composition  of  the  posterior  columns,  as  well  as  that 
of  certain  secondary  paths. 

All  sensory  impulses  that  enter  the  spinal  cord  do  so  by  way  of  the  posterior 
root-fibres.  The  latter  are  the  centrally  directed  processes  (axpnes)  of  the  neurones 
whose  cell-bodies  lie  within  the  spinal  ganglia  situated  on  the  dorsal  roots  of  the 
spinal  nerves.  They  convey  to  the  cord  the  various  impulses  collected  by  the 
peripherally  directed  processes  (the  sensory  nerves)  from  the  integument,  mucous 
membranes,  muscles,  tendons  and  joints  from  all  parts  of  the  body,  with  the 
exception  of  those  served  by  the  cranial  nerves.  The  impulses  thus  conducted  are 
transformed  into  the  impressions  of  touch,  muscle-sense,  heat,  cold  and  pain. 
The  last  being  probably  the  result  of  excessive  stimulation  that  by  its  intensity 
causes  discomfort  in  various  degrees,  the  existence  of  special  paths  for  the  conduc- 
tion of  painful  impressions  is  unlikely.  It  is  evident  that  the  larger  part  of  the 


HUMAN    ANATOMY. 


sensory  neurones  lies  outside  the  spinal  cord  ;  it  is,  however,  with  the  intramedullary 
portion  of  these  neurones,  as  constituents  of  paths  within  the  cord,  that  we  are  here 
concerned. 

On  entering  the  spinal  cord  along  the  postero-lateral  groove,  the  dorsal  root- 
fibres  for  the  most  part  penetrate  the  tract  of  Burdach,  close  to  the  inner  side  of  the 
posterior  horn.  Some  of  the  more  external  root-fibres,  however,  do  not  enter  Bur- 
dach's  tract,  but  form  a  small  adjoining  field,  the  tract  of  Lissauer,  that  lies  im- 
mediately dorsal  to  the  apex  of  the  posterior  horn.  Soon  after  gaining  the  posterior 
column,  with  few  exceptions,  each  dorsal  root-fibre  undergoes  a  >-  or  |—  like  divi- 
sion into  an  ascending  and  a  descending  limb,  which  assume  a  longitudinal  course 
and  pass  upward  and  downward  in  the  cord  for  a  variable  distance,  the  descending 
limb  being  usually  the  shorter.  During  their  course  from  both,  but  particularly  from 
the  descending  limb  and  from  the  proximal  part  of  the  ascending  fibre,  collateral 

branches  are  given  off  which  bend  sharply 

FIG.  894.  inward  and  pass  horizontally  into  the  gray 

matter  to  end  chiefly  in  relation  with  the 
neurones  of  the  posterior  horn,  from  which 
cells  secondary  paths  arise.  Not  only  the 
collaterals,  but  also  the  main  stem-fibres  of 
the  descending  and  shorter  ascending  limbs 
end  in  the  manner  just  described.  In  addi- 
tion to  the  short  collaterals  destined  for  the 
cells  of  the  dorsal  horn,  others,  the  ventral 
reflex  collaterals,  pursue  a  sigmoid  course, 
traversing  the  substantia  gelatinosa  Rolandi 
and  the  remaining  parts  of  the  posterior 
horn  and  the  intermediate  gray  matter,  to 
end  in  arborizations  around  the  radicular 
cells  of  the  anterior  horn,  and  thus  complete 
important  reflex  arcs,  by  which  impulses 
transmitted  through  the  dorsal  roots  directly 
impress  the  motor  neurones.  The  latter  are 
usually  of  the  same  side,  but  some  collaterals 
cross  by  way  of  the  anterior  commissure  to 
terminate  in  relation  with  the  anterior  horn 
cells  of  the  opposite  side.  It  is  probable 
that  a  considerable  number  of  such  anterior 
horn  reflex  collaterals  are  given  off  from  the 

fibres  that  ascend  in  the  long  tracts  of  the  posterior  column  to  the  medulla  oblongata. 
With  possibly  the  exception  of  certain  fibres  which  pass  directly  to  the  cerebellum 
(Hoche),  all  the  sensory  root-fibres  (axones  of  neurones  of  the  I  order)  end  around 
the  neurones  situated  either  within  the  gray  matter  of  the  spinal  cord  or  within  the 
nuclei  of  the  medulla  ;  thence  the  impressions  are  conveyed  by  the  axones  of  these 
neurones  of  the  II  order  to  higher  centers,  to  be  taken  up,  in  turn,  by  neurones  of 
the  III  or  even  higher  order,  in  the  sequence  of  the  chain  required  to  complete  the 
path  for  the  conduction  and  distribution  of  the  impulse. 

The  most  important  groups  of  the  collaterals  and  stem-fibres  of  the  posterior 
roots  are: 

1.  The  long  ascending  tracts  passing  chiefly  to  the  nuclei  of  the  medulla. 

2.  The  fibres  passing  to  the  cells  of  the  column  of  Clarke. 

3.  The  collaterals  passing  to  the  anterior  horn  cells. 

4.  The  fibres  entering  the   posterior   horn   from  the  tract  of   Burdach  and   of 
Lissauer  to  end  about  the  neurones  of  the  II  order  situated  within  the  gray  inattcr 
of  the  posterior  horn  and  the  intermediate  gray  matter. 

The  direct  ascending  posterior  tract  includes  the  dorsal  root-fibres  that 
pass  uninterruptedly  upward  within  the  posterior  column  as  far  as  the  nuclei  of  the 
medulla.  On  entering  the  cord  they  lie  at  first  within  the  tract  of  Burdach,  but  in 
their  ascent  are  gradually  displaced  medianly  and  dorsally  by  the  continued  addition 
of  other  root-fibres  from  the  succeeding  higher  nerves.  In  consequence,  in  cross 


Diagram  showing  division  of  posterior  root-fibres 
into  ascending  and  descending  branches;  long  fibre 
sends  collaterals  to  anterior  root  cells ;  other  fibres 
end  at  different  levels  around  cells  in  gray  matter  of 
posterior  horn  ;  S.  G.,  spinal  ganglion. 


WHITE  MATTER  OF  THE  SPINAL  CORD. 


1041 


sections  of  the  cord  in  the  cervical  region  the  long  fibres  entering  by  the  lower 
nerve-roots  occupy  the  inner  part  of  Coil's  column,  but  are  excluded  from  the  median 
septum,  except  behind,  by  a  narrow  hemielliptical  area,  which  with  its  mate  of  the 
opposite  side  forms  the  oval  field  of  Flechsig.  The  fibres  entering  by  the  lower 
thoracic  nerves  lie  more  laterally,  while  those  entering  by  the  upper  thoracic  and 
cervical  nerves  appropriate  the  adjoining  part  of  Burdach's  tract,  the  lateral  area  of 
which,  next  the  posterior  horn,  is  occupied  chiefly  by  the  posterior  root-fibres. 

It  must  be  understood  that  while  in  a  general  way  the  fibres  of  the  long  ascending  tracts 
have  the  disposition  just  indicated,  they  are  so  intertwined  and  mingled  with  the  strands  passing 
to  and  from  the  gray  matter  that  the  definite  outlines  of  their  conventional  area,  as  represented 
in  diagrams,  are  wanting.  Collectively  the 

fibres  composing  this  tract  are  of  medium  or  FIG.  895. 

small  size,  but  acquire  their  medullary  coat  .-^r---,-'^~ 

very  early,  myelination  beginning  about  the  s^f^?^          l^R^fe* 

fourth  foetal  month,  although  not  completed  -%rS.\ 

until  the  ninth  (Bechterew).  .  ''•'-%^\ 

The  termination  of  the  long  ascend- 
ing fibres  is  chiefly  in  relation  with  the 
neurones  within  the  lower  part  of  the 
medulla — the  fibres  of  Coil's  tract  end- 
ing about  the  cells  of  the  nucleus  gracilis 
and  those  of  Burdach's  tract  about  the 
cells  of  the  nucleus  cuneatus.  From 
these  stations  paths  of  the  II  order 
convey  the  impulses  to  the  cerebel- 
lum, by  way  of  the  inferior  cerebellar 
peduncle,  and  to  the  higher  sensory 
centres  by  way  of  the  mesial  fillet,  as 
later  described  (page  1115).  Whether 
certain  of  the  component  fibres  of  these 
ascending  tracts  are  directly  continued 
to  the  cerebellum,  and  perhaps  to  the 
mesial  fillet,  without  undergoing  inter- 
ruption in  the  nuclei  of  the  medulla  is  still  uncertain,  although  supported  by  the 
statements  of  Hoche,  Kolliker,  Solder  and  others. 

The  root-fibres  passing  to  Clarke's  column  occupy  the  middle  and  median 
part  of  Burdach's  tract,  mingled  with  those  of  the  long  ascending  paths.  After  cours- 
ing longitudinally,  usually  for  some  distance,  within  the  posterior  column,  they  bend 
outward,  and,  sweeping  in  graceful  curves,  enter  the  gray  matter  to  end  about 
Clarke's  cells.  It  is  noteworthy  that  the  level  at  which  they  end  is  often  considerably 
higher  than  that  at  which  the  root-fibres  enter  the  cord,  an  arrangement  which 
explains  the  fact  that  lesions  of  the  lowermost  of  these  strands  may  be  followed  as 
ascending  degenerations  into  the  thoracic  region  (Mayer).  On  entering  the  gray 
matter  the  terminal  arborization  of  a  single  root-fibre  usually  ends  in  relation  with 
several  neurones  of  Clarke's  column  (Lenhossek).  The  important  sensory  path  of 
the  II  order,  known  as  the  direct  cerebellar  tract  (page  1044),  arises  as  the  axones 
of  these  neurones. 

The  anterior  reflex  fibres  to  the  ventral  horn  are  all  collaterals,  not  continu- 
ations of  the  stem-fibres,  far  the  greater  part  of  which  come  from  the  fibres  of  the 
Hong  ascending  posterior  tract.  These  collaterals  penetrate  the  gray  matter  princi- 
pally at  the  median  border  of  the  head  of  the  posterior  horn,  behind  Clarke's 
column,  but  partly  also  through  the  substantia  Rolandi,  and  thence  pass  ventrally  or 
ventro-laterally,  with  a  slightly  curved  or  sigmoid  course,  towards  the  anterior  horn. 
As  they  enter  the  latter,  the  collaterals  diverge  more  and  more  and  are  distributed 
to  the  various  groups  of  the  anterior  horn  cells,  chiefly  in  relation  with  the  lateral 
groups  of  radicular  cells  from  which  the  ventral  root-fibres  arise  ;  they  thus  establish 
direct  reflex  paths  by  which  sensory  impulses  conveyed  by  the  posterior  root-fibres 
impress  the  motor  neurones,  while,  at  the  same  time,  these  impulses  are  transmitted 

66 


Section  of  spinal  cord  at  level  of  second  cervical  seg- 
ment; formatio  reticularis  fills  bay  between  posterior  and 
anterior  cornua;  substantia  gelatmosa  caps  apex  of  pos- 
terior cornu.  Drawn  from  Weigert-Pal  preparation  made 
by  Professor  Spiller.  X  6. 


1042 


HUMAN  ANATOMY. 


FIG.  896. 


Section  of  spinal  cord  at  level  of  sixth  cervical  segment;  anterior 
cornua  are  very  broad  ;  obliquely  cut  bundles  of  posterior  root-fibres  lie  in 
postero-lateral  sulcus.  Preparation  by  Professor  Spiller.  X  6. 


to  higher  levels  by  the  ascending  stem-fibres.  Although  the  anterior  reflex  collat- 
erals are,  for  the  most  part,  in  relation  with  the  cells  of  the  same  side,  it  is  probable 
that  some  cross  by  way  of  the  posterior  commissure,  and  possibly  also  by  the  anterior 
bridge,  to  the  opposite  ventral  horn  cells.  It  is  doubtful,  on  the  other  hand, 
whether  either  stem-fibres  or  collaterals  of  the  posterior  roots  pass  directly  to  the 
anterior  column  either  of  the. same  or  opposite  sides  (Ziehen). 

The  root-fibres  passing  to  the  posterior  horn  include  those  which  pene- 
trate the  substantia  Rolandi,  either  as  collaterals  or  stem-fibres  of  Burdach's  or 

of  Lissauer's  tracts,  to  end 
about  the  neurones  within 
the  Rolandic  substance  or 
within  the  head  of  the  pos- 
terior horn.  Their  longitudi- 
nal course  within  Burdach's 
tract  is  ordinarily  short  ; 
they  then  bend  horizontally 
and  enter  the  gray  matter 
of  the  posterior  horn,  within 
which  they  soon  terminate 
in  end-arborizations  around 
the  neurones  of  the  II  order. 
Some  fibres,  however,  do 
not  undergo  T-division  until 
after  entering  the  posterior 
horn,  where,  within  the  Ro- 
landic substance  or  caput 
cornu,  they  then  bifurcate, 
in  some  cases  the  ascending 

limbs  pursuing  a  vertical  course  within  the  gray  matter,  particularly  of  the  caput 
cornu,  for  some  distance  before  ending  about  the  head-cells  of  the  posterior  horn. 

The  tract  of  Lissauer,  or  marginal  zone,  situated  immediately  behind  the 
apex  of  the  dorsal  horn,  receives  the  lateral  group  of  the  posterior  root-fibres.  These 
are  all  of  unusually  small  size  and,  after  a  short  longitudinal  course  in  which  the 
descending  limbs  predominate,  they  turn  horizontally  and,  both  as  collaterals  and 
stem-fibres,  penetrate  the  substantia  Rolandi,  about  whose  cells  and  those  of  the 
caput  cornu  they  end. 

From  the  foregoing  description,  it  is  evident  that  the  dorsal  root-fibres  destined 
for  the  posterior  horn  terminate  in  relation  with  neurones  of  the  II  order  represented 
chiefly  by  the  cells  of  the  substantia  gelatinosa  Rolandi,  including  the  marginal  cells, 
and  the  inner  cells  of  the  caput  cornu. 

The  secondary  or  endogenous  tracts  of  the  posterior  column  arise  as  axones  from  the 
neurones  of  the  II  order  (the  marginal  cells,  the  cells  of  the  substantia  Rolandi  and  the  head- 
cells)  situated  within  the  posterior  horn  and  include  ascending  and  descending  paths. 

The  ascending  secondary  tract  is  composed  of  the  axones  derived  from  the  posterior  horn 
cells  of  the  same  and,  by  way  of  the  posterior  commissure,  opposite  side,  which  pass  into  tin- 
posterior  column.  In  a  general  way,  they  occupy  the  ventral  field,  although  sharing  it  with 
scattered  strands  of  root-fibres  and  of  descending  endogenous  fibres.  The  destination  of  tin- 
fibres  of  this  ascending  tract  is  uncertain,  sonic  fibres  pursuing  a  short  and  others  a  longer 
course,  within  the  posterior  column  before  entering  the  gray  matter  at  higher  levels  to  end  in 
relation  with  the  posterior  horn  cells,  or,  perhaps,  in  some  cases,  with  the  neurones  within 
the  nuclei  of  the  medulla  (Rothmann). 

The  descending  secondary  tracts,  as  shown  by  degenerations  following  lesions  involving 
the  posterior  column,  occupy  varying  but  fairly  well  differentiated  areas.  In  the  cervical  and 
upper  thoracic  cord  they  are  collected  into  the  comma  bundle  of  Scluilt/e,  which  extends  from 
near  the  neck  of  the  posterior  horn  dorsal ly  along  the  median  margin  of  Hurdach's  tract.  In 
the  lower  thoracic  and  lumbar  cord  they  form  an  elongated  half-ellipse  along  the  posterior 
median  septum  which,  with  the  corresponding  bundle  of  the  Opposite  side,  produces  the  oval 
field  of  Flechsig.  Still  lower,  in  the  sacral  cord,  they  lie  at  the  junction  of  the  median  septum 
and  the  posterior  surface  of  the  cord  as  the  medio-dorsal  triangular  bundle  of  C.ombault  and 
Philippe.  Additional  descending  endogenous  fibres  are  scattered  in  the  ventral  field.  It  is 


WHITE  MATTER  OF  THE  SPINAL  CORD. 


1043 


likely  that  these  areas  represent  the  principal  aggregations  of  the  downward  coursing  limbs  of 
the  axones,  after  their  T-like  branching,  derived  from  the  posterior  horn  cells  of  the  same  and 
opposite  sides.  In  the  cervical 

region   these  axones  are  col-  FIG.  897. 

lected  into  bundles  which  ap- 
pear as  the  comma  tract ;  in 
the  lower  thoracic  cord  these 
are  replaced  by,  without  being 
directly  continuous  with,  those 
forming  the  oval  field,  and 
these  in  turn  by  the  axones  of 
the  triangular  bundle.  No  one 
of  these  fields  is  exclusively 
devoted  to  the  descending 
limbs  of  endogenous  fibres, 
since  in  all  the  presence  of 
exogenous  posterior  root- 
fibres  has  been  demonstrated. 

The  Fibre  -  Tracts 
of  the  Lateral  Column. 
— These  include  :  ( i )  the 
lateral  pyramidal,  (2)  the 
direct  cerebellar,  (3)  the 

ascending"       antero-lateral  Section  of  spinal  cord  at  level  of  seventh  cervical  segment;   anterior 

.v      ,  cornua  are  less  robust ;  root-zone  is  seen  just  behind  Lissauer's  tract.     X  6. 

and  (4)  the  lateral  ground-      Preparation  by  Professor  Spiller. 

bundle. 

The  lateral  or  crossed  pyramidal  tract  (fasciculus  cerebrospinalis  lateralis) 
forms  the  chief  path  by  which  motor  impulses  originating  in  the  cerebral  cortex  are 
conveyed  to  the  spinal  cord.  It  stands  in  close  relation  with  the  direct  pyramidal 
tract  of  the  anterior  column.  Both  are  continuations  of  the  conspicuous  pyramidal 
paths  of  the  medulla  oblongata  and  may  be  followed  upward  through  the  ventral 
part  of  the  medulla,  the  pons  and  the  cerebral  peduncles  into  the  white  matter  of  the 
cerebral  hemispheres  and  on  to  the  cortical  gray  matter  where,  in  the  motor  areas 
bordering  chiefly  the  Rolandic  fissure,  lie  the  nerve-cells  from  which  the  pyramidal 
fibres  arise.  These  fibres,  therefore,  are  the  axones  of  cortical  motor  neurones  and 
extend  without  interruption  from  the  superficial  gray  matter  of  the  cerebral  hemi- 
spheres to  various  levels  in  the  cord,  constituting  long  descending  (corticifugal) 
motor  tracts.  On  reaching  the  lower  part  of  the  medulla,  from  80-90  per  cent,  of 
the  component  fibres  of  each  pyramid  cross  to  the  opposite  side  by  way  of  the 
decussation  of  the  pyramids  (page  1065)  and,  entering  the  cord,  descend  as  the 
lateral  pyramidal  tract;  the  remaining  fibres  (on  an  average,  about  15  per  cent.) 
pass  downward  into  the  ventral  column  of  the  cord  as  the  direct  pyramidal  tract. 

After  decussating,  the  crossed  pyramidal  tract  passes  outward  to  enter  the  lateral 
column  of  the  cord,  thereby  exchanging  its  former  median  and  superficial  position 
for  a  deeper  and  more  lateral  one.  Since  its  fibres  are  continually  entering  the  gray 
matter  to  end  about  the  radicular  cells  from  which  the  anterior  root-fibres  of  the 
spinal  nerves  arise,  the  tract  progressively  loses  in  size  as  it  descends,  until,  at  about 
the  level  of  the  fourth  sacral  nerve,  it  ceases  to  exist  as  a  distinct  strand,  although 
continued  by  small  scattered  bundles  of  fibres  as  far  as  the  origin  of  the  coccygeal 
nerve.  This  diminution  is  not  regular,  since  in  the  sacral  and  lumbar  enlargements 
the  loss  is  more  marked  than  elsewhere,  on  account  of  the  relations  of  the  tract-fibres 
to  the  large  motor  limb- nerves. 

The  relatioas,  as  well  as  size,  of  the  lateral  pyramidal  tract  vary  at  different  levels.  As 
seen  in  cross-sections  of  the  upper  thoracic  region  of  the  cord,  the  tract  occupies  an  area  of 
considerable  size,  that  mesially  lies  against  the  posterior  horn  and  laterally  is  in  contact  with 
the  direct  cerebellar  tract,  by  which  it  is  excluded  from  the  periphery.  In  front,  where  its  limits 
are  less  definite,  the  tract  extends  ventrally  for  a  variable  distance  into  the  lateral  column,  but 
seldom  overreaches  the  plane  of  the  gray  commissure.  With  the  diminution  and  disappear- 
ance of  the  direct  cerebellar  tract  within  the  lower  portions  of  the  cord,  the  pyramidal  field 
approaches  and  finally  reaches  the  surface,  which  relation  it  retains  as  it  grows  smaller,  the 


1044 


HUMAN   ANATOMY. 


FIG.  898. 


reduction  affecting  the  more  deeply  placed  fibres.     In  consequence  of  these  variations,  the  form 
of  the  pyramidal  tract  in  cross-section  changes  from  wedge-shape  to  triangular,  with  the  base 

lying  at  the  periphery  and  the  apex  directed 
inward.  During  their  descent  the  fibres  of  the 
pyramidal  tract  give  off  at  different  levels  col- 
laterals, which  bend  horizontally  inward  and 
forward,  enter  the  gray  matter,  and  end  in  rela- 
tion with  the  anterior  horn  cells.  A  similar 
course  is  followed  by  the  parent  fibres  on  reach- 
ing the  segment  for  which  they  are  destined,  the 
terminal  part  of  the  individual  fibres  sweeping 
in  short  curves  through  the  intervening  ground- 
bundle  of  the  lateral  column  to  gain  the  radicular 
cells  around  which  they  end.  By  means  of  its 
collaterals,  each  pyramidal  fibre  establishes  rela- 
tion with  several  cord-segments.  The  fibres  of 
this  tract  are  relatively  tardy  in  acquiring  their 
medullary  coat,  which  process  does  not  begin 
until  the  last  month  of  fcetal  life  and  is  not  com- 
pleted until  after  the  second  year. 

Section  of  spinal  cord  at  level  of  sixth  thoracic 
segment ;  slender  posterior  cornua  covered  with  sub- 


stantia  gelatinosa ;  postero-lateral  angle  marks  greatest 
Preparation  b 


width  of  anterior  cornu. 
fessor  Spiller. 


X  6. 


jy  Pro- 


The  direct  cerebellar  tract  (fas- 
ciculus cerebellospinalis),  is  an  important 
ascending  path  of  the  second  order  that 
establishes  communication  between  the  reception  sensory  cord-nucleus  formed  by 
Clarke's  cells  and  the  cerebellum.  In  cross-sections  of  the  thoracic  region,  the  tract 
forms  a  superficial  flattened  comet-shaped  field  that  occupies  the  dorsal  half  of  the  lateral 
column,  extending  from  the  apex  of  the  posterior  horn  forward  along  the  periphery 
of  the  cord,  to  the  outer  side  of  the  lateral  pyramidal  tract,  to  about  the  anterior 
plane  of  the  gray  commissure.  Its  ventral  end,  particularly  in  the  lower  cervical 
region,  is  broadest  and  projects  somewhat  into  the  lateral  column  in  advance  of  the 
lateral  pyramidal  field.  Although  as  a  compact  strand  the  direct  cerebellar  tract 
begins  at  the  tenth  thoracic  segment,  it  is  represented  by  isolated  fibres  in  the  luinbo- 
sacral  region.  The  fibres  collectively  are  large  and  become  medullated  about  the  sixth 
foetal  month  (Bechterew).  In  a  general  way  the  fibres  having  the  longest  course 
occupy  the  dorsal  part  of  the  tract  and  those  having  the  shortest  the  ventral  (Flatau). 

Arising  as  the  axones  of  the  cells  of  Clarke's  column,  the  components  of  the 
tract  pass  in  curves  almost  horizontally  outward  through  the  gray  matter  and  lateral 
column  to  the  peripheral  field,  on  gaining  which  they  bend  sharply  brainward  and 
ascend  without  interruption  to  the  medulla.  Their  further  course  includes  the  pas- 
sage through  the  dorso-lateral  field  of  the  medulla  as  far  as  the  inferior  cerebellar 
peduncle,  by  which  the  fibres  reach  the  cerebellum  to  end  in  relation  with  the  superior 
worm,  on,  probably,  both  the  same  and  the  opposite  sides. 

The  tract  of  Gowers  (fasciculus  antcrolateralis  superficialis)  constitutes  another 
pathway  of  the  II  order,  which  connects  the  cord  with  the  cerebellum  and  probably 
also  establishes  relations  with  the  cerebrum.  In  cross-sections  the  tract  appears 
somewhat  uncertainly  defined  owing  to  the  intermingling  of  its  fibres  with  those  of 
adjoining  strands,  but  in  the  main  it  includes  a  superficial  crescentic  field  that  touches 
the  direct  cerebellar  and  lateral  pyramidal  tracts  behind,  extends  along  the  margin 
of  the  cord  for  a  variable  distance,  and  usually  ends  in  front  in  the  vicinity  of  the 
ventral  nerve-roots.  The  inner  boundary,  separating  the  tract  in  question  from  the 
lateral  ground-bundle,  lacks  in  sharpness  and  is  overlaid  by  the  Adjoining  strands. 
Below,  the  tract  appears  about  the  middle  of  the  lumbar  region  and  continues 
throughout  the  remainder  of  the  cord.  As  Gowers'  tract  ascends,  it  fails  to  show 
the  considerable  increase  in  size  that  might  be  expected  in  view  of  the  continual 
additions  that  it  receives.  In  explanation  of  this,  the  probable  mingling  of  some  of 
its  fibres  with  those  of  the  direct  cerebellar  tract,  rather  than  their  ending  in  the 
cord,  seems  the  most  plausible  (/it-hen). 

The  exact  origin  of  the  constituents  of  Gowers'  tract  is  still  uncertain,  but  it  is 
very  likely  that  its  libres  are  chiefly  the  axones  of  the  neurones  (marginal  and  inner 
cells)  situated  within  the  posterior  horn,  partly  .from  the  same  and  partly  from  the 


: 


WHITE  MATTER  OF  THE  SPINAL  CORD.  1045 

opposite  sides,  with  contributions,  possibly,  from  the  cells  of  the  intermediate  gray 
matter.  After  traversing  the  cord,  the  lateral  field  of  the  medulla,  and  the  tegmental 
portion  of  the  pons,  the  tract  ascends  the  T-, 

i  ...  1-1          •      r       •  r  IG.     oQQ.  ^ 

brain  stem  to  the  vicinity  of  the  inferior  cor- 
pora quadrigemina.  Here  the  major  part  of  ;-  ^Mlii. 
the  fibres  turn  backward  and,  by  way  of  the 
superior  cerebellar  peduncle  and  the  superior 
medullary  velum,  reach  the  cerebellum  to  .'.  \  V 
end  mostly,  in  the  superior"  worm,  partly  on 
the  same  side  and  partly  crossed  (Hoche). 
Possibly  a  part  of  the  cerebellar  contingent 
may  share  the  path  of  the  direct  cerebellar 
tract  and  in  this  way  reach  the  cerebellum 
by  its  inferior  peduncle  (Ziehen).  It  is 
probable  that  all  fibres  from  Gowers'  tract  do 
not  pass  to  the  cerebellum,  but  that  some 
continue  upward  to  terminate  in  relation  with 
the  neurones  of  the  superior  corpora  quadri-  ..  ,s?cti?n  of  sP'nal  cord  at  level  of  lower  part  of 

...  .     f  •      ~,  nun  lumbar  segment ;  gray  matter  relatively  large 

gemma     and     OI      the     OptlC      thalamUS.         1  he       in  amount ;  anterior  cornua  bulky.    Preparation  by 

fibres    of   the    tract    acquire    the    medullary 

coat  about  the  beginning  of  the  eighth  month  of  foetal  life  (Bechterew). 

The  lateral  ground-bundle  (fasciculus  lateralis  proprius)  of  Flechsig  includes 
the  remainder  of  the  lateral  column.  Much  uncertainty  prevails  as  to  its  detailed 
paths,  but  beyond  question  the  composition  of  the  ground-bundle  is  very  complex 
and  comprises  a  number  of  long  exogenous  paths  that  descend  from  the  brain,  as  well 
as  one  long  ascending  and  many  shorter  endogenous  strands,  both  ascending  and 
descending.  These  short  tracts  occupy  chiefly  the  central  parts  of  the  lateral  column 
and,  in  a  general  way,  lie  close  to  the  gray  matter,  within  an  area  between  the  ante- 
rior and  posterior  horns,  known  as  the  boundary  zone.  They  are,  however,  not 
limited  to  this  field,  as  not  a  few  of  their  fibres  lie  scattered  among  the  longer 
exogenous  tracts  occupying  the  more  lateral  portions  of  the  ground-bundle. 

One  long  endogenous  path,  the  spino-thalamic  tract,  is  of  unusual  importance  since  it  estab- 
lishes a  direct  sensory  link  between  the  cord  and  higher  centres.  This  tract  arises  from  the 
cells  of  the  posterior  horn  of  the  opposite  side,  the  axones  crossing  in  the  anterior  commissure 
to  pursue  a  course  brainward  within  the  antero-lateral  ground-bundle.  Although  the  fibres  of 
this  tract  are  scattered  and  not  collected  into  a  compact  strand,  their  chief  location  is  just  medial 
to  Gowers'  tract.  Associated  with  the  fibres  destined  for  the  optic  thalamus  are  others  (tractus 
spino-tectalis)  that  end  in  the  region  of  the  corpora  quadrigemina. 

The  short  endogenous  tracts  include  both  ascending  and  descending  fibres  which  arise  as 
the  axones  chiefly  of  the  marginal  and  inner  cells  of  the  posterior  horn,  some  coming  from  the 

opposite  side  by  way  of  the  posterior  intracentral  commissure. 

FIG.  900.  Entering  the  lateral  column  the  axones  undergo  T-like  division 

with  ascending  and  descending  limbs.  The  former  pass  upward 
for  a  distance  that  usually  includes  only  from  one  to  three 
segments,  then  bend  inward  and  enter  the  gray  matter  to  end 
probably  in  relation  with  other  posterior  horn  cells.  The  down- 
wardly directed  limbs  form  the  descending  endogenous  fibres, 
which,  in  addition  to  occupying  the  boundary  zone  are  also 
scattered  among  the  longer  tracts  of  the  ground-bundle.  After 
a  relatively  long  course,  they  enter  the  gray  matter  to  end 
probably  in  relation  with  the  anterior  horn  cells.  They  are, 
therefore,  regarded  as  establishing  reflex-paths.  Since  these 
endogenous  strands  link  together  various  levels  of  the  cord,  they 
Seciton  of  spinal  cord  at  level  are  often  collectively  termed  intersegmental  association  fibres. 
c^nhuad^thraSubSi a  S'inosn  The  ^°S^ous  tracts  of  the  lateral  ground-bundle  are  closely 

are  relatively  bulky.  Preparation  related  with  those  found  in  the  ground-bundle  of  the  anterior 
by  Professor  Spiller.  )  column  and  what  may  be  said  of  the  former  largely  applies  to 

the  latter.     Notwithstanding  the  study  that  these  tracts  have 

received,  much  uncertainty  exists  as  to  their  exact  origin  and  termination  ;  it  may  be  stated  in 
a  general  way,  however,  that  they  bring  the  higher  sensory  and  coordinating  centres  into 
relation  with  the  spinal  cord  and  constitute,  therefore,  descending  paths  other  than  the 


HUMAN    ANATOMY. 


FIG.  901. 


pyramidal   tracts.      Among  those   whose  existence   within   the   antero-lateral  ground-bundle 
may  be  considered  as  established,  or  at  least  probable,  are  the  following: 

1.  Rubro-spinal  fibres  from  the  cells  of  the  red  nucleus  within  the  cerebral  peduncles. 

2.  Tecto-spinal  fibres  from  the  cells  of  the  anterior  corpora  quadrigemina. 

3.  Vestibulo-spinal  fibres  from  the  cells  of  the  lateral  vestibular  (Deiters')  nucleus. 

4.  Medullo-spinal  fibres  from  the  cells  of  the  formatio  reticularis,  arcuate  and  lateral  nuclei. 

5.  Olivo-spinal  fibres  from  the  cells  of  the  inferior  olivary  nucleus. 

Of  these  strands,  those  from  the  red  nucleus,  corpora  quadrigemina,  and  vestibular  nucleus, 
descend  chiefly  within  the  lateral  ground-bundle,  whilst  those  from  the  medulla  are  particularly 

within  the  anterior  ground-bundle.  Although  the  latter  includes 
tne  greater  part  of  the  descending  cerebello-rubro-spinal  fibres 
in  the  narrow  peripheral  sulco-marginal  zone  of  Marie,  other 
fibres  are  probably  distributed  within  the  lateral  column  in 
front  of  the  direct  pyramidal  tract.  These  descending  indirect 
cerebellar  fibres  are  often  collectively  known  as  the  tract  of 
Marchi-Lowenthal.  For  the  most  part  the  exogenous  strands 
are  so  intermingled  and  scattered  that  they  are  without  definite 
outlines;  an  exception  to  this  is  presented  by  the  olivary  fibres, 
which  are  sometimes  seen  as  a  fairly  distinct  triangular  bundle, 
Just  behind  the  anterior  root-fibres  at  the  periphery  of  the  cord, 
known  as  Helweg's  tract.  Concerning  the  exact  ending  of 
these  descending  paths  little  is  known,  but  it  is  reasonable  to 
assume  that  they  terminate  at  various  levels  in  relation  with  the 
ventral  horn  cells  which  are  thus  brought  under  the  coordinating  influence  of  the  higher  centres. 


Section  of  spinal  cord  at  level  of 
fifth  sacral  segment ;  anterior  cornua 
small  and  inconspicuous.  Prepara- 
tion by  Professor  Spiller.  X  8. 


FIG.  902. 

-  n 


The  Fibre-Tracts  of  the  Anterior  Column.  —  According  to  the  simplest 
classification  the  anterior  column  includes  two  subdivisions  :  (  i  )  the  anterior  pyra- 
midal tract  and  (2)  the  anterior  ground-bundle. 

The  anterior  pyramidal  tract  (fasciculus  cerebrospinalis  anterior),  also  called 
the  uncrossed  or  direct  pyramidal  tract,  stands  in  complemental  relation  with  the  lat- 
eral pyramidal  fasciculus,  being  composed  of  the  pyramidal  fibres  that  do  not  undergo 
decussation  in  the  medulla  oblongata.  It  usually  contains  about  15  per  cent,  of  the 
pyramidal  fibres,  but  may  include  a  much  larger  proportion  ;  on  the  other  hand,  it 
may  be  entirely  suppressed  when,  as  rarely  happens,  total  crossing  occurs. 

The  direct  pyramidal  tract  occupies  the  inner  part  of  the  anterior  column, 
forming  a  narrow  area  along  the  median  fissure  that  extends  from  the  white  commis- 
sure behind  to  near  the  ventral  margin  of  the  cord.  Ordinarily  the  tract  ends  below 
about  the  middle  of  the  thoracic  cord,  but  in  exceptional  cases,  when  a  larger  pro- 
portion of  the  pyramidal  fibres  than  usual  is  included  in  the  tract,  it  may  extend  as 
far  as  the  middle  of  the  lumbar  enlargement,  with  corres- 
ponding increase  in  its  cross  area.  If,  on  the  other  hand, 
the  number  of  uncrossed  fibres  is  unusually  small,  the  tract 
may  reach  only  as  far  as  the  cervical  enlargement,  with  a 
reduction  of  its  sagittal  dimension.  Although  often  spoken 
of  as  the  '  '  uncrossed  '  '  pyramidal  tract,  this  characteristic 
applies  only  to  the  relation  of  the  fibres  at  the  decussation 
in  the  medulla,  since  in  their  downward  journey  in  the  cord 
the  great  majority  of  the  fibres  traverse  the  anterior  white 
commissure  at  appropriate  levels  to  end  in  arborizations 
about  the  ventral  root-cells  of  the  anterior  horn  of  the 
opposite  side.  It  is  highly  probable,  however,  that  some  fibres  do  not  undergo 
decussation,  but  terminate  about  the  radicular  cells  of  the  same  side. 

The  anterior  ground-bundle  (fasciculus  anterior  proprius),  following  the  divi- 
sion of  Flechsig,  includes  the  remainder  of  the  ventral  column.  In  front,  when-  its 
lateral  limits  are  uncertain,  it  is  continuous  with  the  ground-bundle  of  the  lateral  col- 
umn, the  two  together  being  often  with  advantage  regarded  as  constituting  a  single 
antero-lati  nil  tract.  What  has  been  said  concerning  the  constitution  of  the  lateral 
ground-bundle  applies  in  the  main  to  that  of  the  anterior  column,  since,  here  as  there, 
the  region  bordering  the  gray  matter  contains  chiefly  the  short  endogenous  strands, 
while  the  more  peripheral  parts  of  the  ground-bundle  are  occupied  by  the  long 
exogenous  paths,  intermingled,  however,  with  the  longer  intrinsic  fibres. 


segment;  differentiation  of  cor- 


WHITE   MATTER  OF   THE   SPINAL   CORD.  1047 

The  endogenous  fibres  arise  as  the  axones,  chiefly  of  the  inner  cells  of  the  posterior  horn, 
as  well  as  from  the  cells  of  the  intermediate  gray  matter  (Ziehen),  and  in  great  measure  cross 
by  way  of  the  anterior  white  commissure  to  the  opposite  anterior  column.  After  undergoing 
T-division,  their  upwardly  directed  limbs  constitute  the  ascending  paths  and  those  coursing 
downward  the  descending  ones.  While  both  sets  of  fibres  for  the  most  part  pursue  only  a  short 
path,  that  of  the  descending  limbs  is  usually  the  longer,  the  fibres  entering  the  gray  matter  to 
end  in  relation  with  the  anterior  horn  cells  of  lower  levels.  They  are,  therefore,  regarded  as 
secondary  reflex  paths.  The  termination  of  the  ascending  limbs  is  uncertain,  but  probably  is 
within  the  gray  matter  of  the  posterior  horn. 

The  exogenous  tracts  of  the  anterior  ground-bundle,  have  been  mentioned  in  connection 
with  those  of  the  lateral  column.  The  investigations  of  Lowenthal,  Marchi,  Bechterew,  Thomas 
and  others,  support  the  presence  within  the  anterior  ground-bundle,  also  within  the  lateral 
column,  of  long  efferent  (cortifugal)  paths  that  arise,  at  least  indirectly,  from  neurones  within 
the  cerebellum,  and  end  in  relation  to  the  anterior  horn  cells.  These  paths,  collectively  known 
as  the  descending  cerebello-spinal  tract,  or  tract  of  Marchi- Lowenthal,  are  of  uncertain  extent 
and  outline,  and  more  or  less  mingled  with  the  constituents  of  other  strands.  In  a  general  way 
the  descending  cerebello-spinal  fibres  occupy  a  narrow  crescentic  field  that  appropriates  the 
periphery  of  the  cord  for  a  variable  distance  both  mesially  and  laterally.  In  the  anterior  column 
the  tract  includes  the  anterior  marginal  bundle,  probably  from  the  nucleus  fastigii  of  the 
cerebellum  of  the  same  and  opposite  side,  and  mesially  mingles  with  fibres  from  the  corpora 
quadrigemina  as  constituents  of  the  visual  reflex  paths.  The  termination  of  these  descending 
paths  is  assumed  to  be  in  relation  with  the  anterior  horn  cells,  which  in  this  manner  are  brought 
under  the  influence  of  the  higher  coordinating  and  reflex  centres. 

In  recapitulation  the  chief  fibre-tracts  of  the  spinal  cord  may  be  grouped  as  follows^ 

I.     Within  the  Posterior  Column — 
Ascending  Paths  : 

Direct  ascending  posterior  root-fibres. 
Ascending  endogenous  fibres. 
Descending  Paths :  • 

Descending  posterior  root-fibres. 
Descending  endogenous  fibres. 

II.     Within  the  Lateral  Column— 
Ascending  Paths  : 

Direct  cerebellar  tract. 
Gowers'  tract. 
Spino-thalamic  tract. 
Short  endogenous  fibres. 
Descending  Paths  : 

Lateral  pyramidal  tract. 

Indefinite  exogenous  tracts  (including  the  rubro-spinal,  quadri- 
gemino-spinal,    vestibulo-spinal,    cerebello-spinal    and  olivo- 
spinal). 
Descending  endogenous  fibres. 

III.     Within  the  Anterior  Column— 
Ascending  Paths  : 

Ascending  endogenous  fibres  from  posterior  horn  cells. 

Ascending  endogenous  fibres  from  anterior  horn  cells. 
Descending  Paths  : 

Direct  pyramidal  tract. 

Descending  cerebello-spinal  fibres. 

Tegmento-spinal  fibres. 

Blood-Vessels  of  the  Spinal  Cord. — The  arteries  supplying  the  cord  are 
from  many  sources — the  vertebral,  deep  cervical,  intercostal,  lumbar,  ilio-lumbar  and 
lateral  sacral  of  the  two  sides — since  the  vascular  net-work  within  the  pia  accompanies 
the  nervous  cylinder  throughout  its  length.  Above  and  within  the  skull,  the  verte- 
bral arteries  give  off  the  two  anterior  and  the  two  posterior  spinal  arteries,  of  which 
the  latter  retain  their  independence  and  descend  upon  the  dorso-lateral  surface  of  the 
cord,  one  on  each  side,  in  front  of  the  posterior  nerve-roots.  The  two  anterior 
spinal  arteries,  on  the  other  hand,  soon  unite  (somewhere  above  the  level  of  the 
third  cervical  nerve)  into  a  single  trunk,  which  descends  along  the  ventral  surface  of 
the  cord,  just  in  front  of  the  anterior  median  fissure. 


1048 


II  I'M  AN   ANATOMY. 


FIG.  903. 

Posterior  sulcal 


Parasulcal 


f 


As  these  stems  pass  downward,  they  are  joined  and  reinforced  by  the  segmcntal 
spinal  branches  given  off  by  the  vertebral,  intercostal,  lumbar  and  lateral  sacral 
arteries,  which  enter  the  spinal  canal  through  the  intervertebral  foramina  and,  after 
piercing  the  dura  and  giving  off  small  radicular  brandies  to  the  nerve-roots  them- 
selves, divide  into  ventral  and  dorsal  branches  that  follow  the  respective  nerve-roots 
to  the  cord,  where  they  join  with  the  longitudinal  trunks  which  they  thus  assist  in 
maintaining.  By  the  junction  of  horizontal  branches  arising  from  these  arteries,  a 
series  of  complete  annular  anastomoses  is  formed  around  the  cord,  which  is  still 
further  enclosed  by  additional  vertical  stems  resulting  from  the  union  of  upward  and 
downward  coursing  twigs.  In  this  manner,  in  addition  to  the  large  single  anterior 
spinal  trunk  (tractus  arteriosus  spinalis  anterior)  in  the  mid-line  in  front  and  the 
paired  postero-lateral  trunk  (tractus  arteriosus  postero-lateralis  spinalis")  just  in 
advance  of  the  dorsal  nerve-roots,  smaller  longitudinal  arteries  are  formed  at  the 
side  and  in  the  vicinity  of  the  nerve-roots. 

From  the  arterial  net- work  within  the  pia,  the  nervous  tissue  is  supplied  by  pene- 
trating twigs  that  enter  the  surface  of  the  cord  at  various  points. 

The  gray  matter  receives  its  principal  blood-supply  from  the  series  of  anterior 
Jissural  arteries,  over  two  hundred  in  number,  which  pass  from  the  anterior  spinal 
trunk  backward  within  the  median  fissure  to  its  bottom  and  there  divide  into  right 

and  left  branches,  which  traverse  the 
anterior  white  commissure  to  gain  the 
gray  matter  on  either  side  of  the  central 
canal.  These  vessels,  the  sulco-mar- 

y  Y  /Postero-lateral        ginal  arteries,  divide  into  ascending 

o  ^  VV.U  ;H  X      Penetrating          and  descending  branches  that  provide 

for  the  entire  gray  matter  with  the 
exception  of  the  most  peripheral  zone. 
The  latter,  together  with  the  white 
matter,  receives  its  supply  from 
the  penetrating  branches  that  come 
from  the  surrounding  intrapial  trunks 
and  enter  the  surface  of  the  cord. 
Unpaired  horizontal  twigs,  the  pos- 
terior sulcal  arteries,  follow  the 
posterior  median  septum  at  different 
levels  for  some  distance,  but  before 
reaching  the  posterior  commissure 
usually  break  up  into  terminal  ramifi- 
cations, some  of  which  pass  to  the 
gray  matter  of  the  posterior  horns. 
Communications  exist  between  the 
penetrating  twigs  of  the  radicular 
arteries  and  the  lateral  branches  of  tin- 
anterior  fissural.  After  entering  the  nervous  tissue,  however,  each  artery  provides 
the  sole  supply  for  some  definite  part  of  the  cord  ;  they  are  therefore  ' '  end-arteries, 
a  fact  which  explains  the  extensive  and  elaborate  system  of  vessels  necessary  to 
maintain  the  nutrition  of  the  cord. 

The  plexiform  veins  within  the  spinal  pia  are  formed  by  the  union  of  the  small 
radicles  that  collect  the  blood  from  the  intraspinal  capillaries  and,  after  an  independ- 
ent course  similar  to  that  of  the  arteries  but  not  accompanying  them,  emerge  at  the 
surface  of  the  cord.  From  the  venous  net-work  within  the  pia  six  main  longitudinal 
trunks  are  differentiated.  These  are  : — the  unpaired  anterior  median  rein,  in  front  of 
the  corresponding  fissure  ;  the  paired  antero-latcral  reins,  just  In-hind  the  ventral 
nerve-roots — these  two  sets  receiving  the  tributaries  emerging  from  the  median  fissure 
and  in  the  vicinity  of  the  anterior  root-fibres  ;  the  unpaired  posterior  median  vein, 
behind  in  the  mid-line  ;  and  the  paired  postero-lateral  reins,  just  behind  the  dorsal 
roots.  The  blood  is  conveyed  from  these  intrapial  channels  chiefly  by  the  radicular 
veins,  following  the  nerve-roots,  which  communicate  with  or  terminate  in  the  anterior 
and  posterior  longitudinal  spinal  veins  within  the  vertebral  canal,  from  which  the 


Penetrating 

artery- 


Anterior 

fissural      Anterior     Ascending  branch 
spinal  artery 

Part  of  transverse  section  of  injected   spinal   cord   showing 
vascular  supply  of  white  and  gray  matter.    X  10. 


WHITE   MATTER   OF   THE   SPINAL   CORD. 


1049 


intervertebral  efferents  carry  the  blood  into  the  vertebral,  intercostal,  lumbar  and 
lateral  sacral  veins.  A  part  of  the  blood  from  the  intrapial  plexus  is  conducted 
upward  by  the  anterior  and  posterior  median  veins  into  the  venous  net-work  covering 
the  pons  and  thence  into  the  lower  dural  sinuses. 

Definite  lymphatic  vessels  within  the  spinal  cord  are  unknown. 

Development  of  the  Spinal  Cord. — A  sketch  of  the  general  histogenetic  processes  leading 
to  the  differentiation  of  the  neurones  and  the  neuroglia  has  been  given  (page  1009)  ;  it  remains, 
therefore,  to  consider  here  the  changes  in  the  neural  tube  by  which  the  definite  spinal  cord  is 
evolved.  From  the  time  of  its  closure,  probably  about  the  end  of  the  second  week  of  foetal 
life,  the  neural  tube  presents  three  regions  : — the  relatively  thick  lateral  walls  and  the  thin  ven- 
tral and  dorsal  intervening  bridges,  the  floor-  and  roof -plates,  that  in  front  and  behind  complete 
the  boundaries  of  the  canal  in  the  mid-line.  By  the  fifth  week  the  lateral  walls  exhibit  a  distinct 
differentiation  into  three  zones — the  inner  ependymal  layer,  the  middle  nuclear  layer  and  the 
outer  marginal  layer,  surrounded  by  the  external  limiting  membrane.  In  contrast  to  the  other 
two,  the  marginal  zone  is  almost  devoid  of  nuclei  and,  beyond  affording  support  and  perhaps 
assisting  in  providing  a  medullary  coat,  plays  a  passive  role  in  the  production  of  the  nervous 
elements. 

By  this  time  the  former  general  oval  contour  of  the  developing  cord,  as  seen  in  cross-sec- 
tions, has  become  modified  by  the  conspicuous  thickening  of  the  antero-lateral  area  of  the  nuclear 
layer  into  a  prominent  mass  on  each  side,  whereby  the  reticular  marginal  layer  is  pushed  out- 


FIG.  904. 
Roof-plate 


FIG.  905. 

Roof-plate 


Dorsal  zone 


Ventral 
root-fibres 


Neuroblasts 


*  Floor-plate 


Developing;  spinal  cord  of  about  four 
weeks.     X  100.     (f/is.) 


Floor-plate 


Ventral  root-fibres 


Developing  spinal  cord  of  about  five  weeks. 
X  60.    (His.) 


ward  with  corresponding  increase  in  the  width  of  the  entire  ventral  part  of  the  cord,  which  is 
now  broadest  in  front.  Within  this  thickened  ventro-lateral  part  of  the  nuclear  layer,  later  the 
anterior  horn  of  gray  matter,  as  early  as  the  fourth  week  young  neurones  are  seen  from  which 
axones  grow  outward  through  the  marginal  zone  and  pierce  the  external  limiting  membrane  as 
the  representatives  of  the  anterior  root-fibres  of  the  spinal  nerves.  Postero-laterally  the  thin 
nuclear  layer  is  covered  by  a  somewhat  projecting  thickened  area  within  the  marginal  layer, 
known  as  the  oval  bundle,  whose  presence  is  due  to  the  ingrowth  of  the  developing  dorsal  root- 
fibres  from  the  sensory  neurones  of  the  spinal  ganglion,  which  process  begins  as  early  as  the 
end  of  the  fourth  week  (His). 

Associated  with  these  changes,  the  lumen  of  the  cord  becomes  heart-shaped  in  consequence 
of  a  conspicuous  local  increase  in  its  transverse  diameter,  with  corresponding  bulging  of  the 
lateral  wall.  In  this  manner  a  longitudinal  furrow  appears  by  which  the  side  walls  of  the  tube 
are  differentiated  into  two  tracts,  the  dorsal  and  the  ventral  zones  (the  alar  and  basal  lamina?  of 
His).  This  subdivision  is  of  much  importance,  since  in  the  cord-segment,  and  also  with  less 
certainty  in  the  brain-segment  of  the  neural  tube,  these  tracts  are  definitely  connected  with  the 
root-fibres  of  the  spinal  nerves,  the  dorsal  zone  with  the  sensory  and  the  ventral  zone  with  the 
motor  roots.  In  advance  of  the  floor-plate  the  ventrally  protruding  halves  of  the  cord  include  a 
broad  and  shallow  furrow  which  marks  the  position  of  the  anterior  median  fissure.  During  the 
sixth  week  the  form  of  the  tube-lumen  becomes  further  modified  by  the  elongation  and  narrow- 


1050 


HUMAN   ANATOMY. 


ing  of  the  dorsal  part  of  the  canal  in  consequence  of  the  approximation  of  its  walls,  which  in  the 
course  of  the  seventh  week  is  closer  and,  by  the  end  of  the  second  month  is  completed  by  the 
meeting  and  fusion  of  the  adjacent  inner  layers,  with  obliteration  of  the  intervening  cleft 
and  the  production  of  the  posterior  median  septum  in  its  place.  Since  the  partition  is  formed 
by  the  union  of  the  inner  (ependymal)  layers,  it  is  probable  that  the  septum  is  to  be  regarded 
as  essentially  neurogliar  in  origin  and  character.  It  must  be  remembered,  however,  that  a 
certain  amount  of  mesoblastic  tissue  may  be  later  introduced  in  company  with  the  blood-vessels 
which  subsequently  invade  the  septum.  The  remaining  and  unclosed  part  of  the  lumen  for 
a  time  resembles  in  outline  the  conventional  spade  of  the  playing  card,  with  the  stem  directed 
ventrally  ;  but  later  gradually  diminishes  in  size  and  acquires  the  contour  of  the  definite  central 
canal. 

During  these  alterations  in  the  extent  and  form  of  its  lumen,  the  gray  matter  of  the  develop- 
ing cord  markedly  increases,  especially  behind  where  the  posterior  horn  appears  as  a  projection 
beneath  the  broadening  mass  of  the  ingrowing  dorsal  root-fibres.  As  the  posterior  horn  becomes 
better  defined,  the  root-bundle  becomes  meso-laterally  displaced,  lying  behind  the  horn,  and 
then  constitutes  the  tract  of  Burdach.  Coil's  tract  is  formed  somewhat  later  and  at  about  the 
third  month  appears  as  a  narrow  wedge-shaped  area  that  is  introduced  between  the  mid-line  and 
Burdach' s  tract.  Towards  the  end  of  the  second  month,  the  anterior  white  commissure  is 
indicated  by  the  oblique  transverse  ingrowth  of  axones  into  the  most  ventral  part  of  the  floor- 
plate  as  they  make  their  way  to  the  opposite  side.  Meanwhile  the  anterior  median  fissure  has 


FIG.  906. 


FIG.  907. 


Coil's  tract 

Burdach's  tract 


Lateral 
column 


Anterior  column 


Developing  spinal  cord  of  about  seven  and  one-half 
weeks.     X  44-    (His.) 


Anterior  median  fissure          Anterior        Root-fibres 
with  pial  process          column 

Developing  spinal  cord  of  about  three  months.    X  30.    ( His. ) 


become  deeper  and  narrower  in  consequence  of  the  increased  bulk  of  medio-ventral  parts  of  the 
cord.  As  the  fissure  is  thus  differentiated  the  process  of  mesoblastic  tissue,  which  from  the 
earliest  suggestion  of  the  groove  occupies  the  depression,  is  correspondingly  elongated  and 
affords  a  passage  for  the  blood-vessels  destined  for  the  nutrition  of  the  interior  of  the  cord. 
Until  the  third  month  the  gray  matter,  derived  from  the  nuclear  layer,  is  much  more  voluminous 
than  the  surrounding  marginal  layer,  which,  so  far  as  the  contribution  of  nervous  elements  is 
concerned,  is  passive,  since  its  conversion  into  the  white  matter  depends  upon  the  ingrowth 
of  axones  from  the  neurones  situated  either  within  or  outside  the  cord. 

The  development  of  the  individual  fibre-tracts  includes  two  stages,  between  the  comple- 
tion of  which  a  considerable,  and  sometimes  a  long,  period  intervenes.  The  first  marks  the 
invasion  of  the  supporting  tissue  of  the  marginal  zone  by  the  ingrowing  axones  as  naked  axis- 
cylinders  ;  the  second  witnesses  the  clothing  of  these  fibres  with  myelin.  The  period  between 
the  appearance  of  the  tract  and  the  development  of  the  medullary  coat  is  variable.  In  some 
cases,  as  in  the  great  cerebro-spinal  motor  paths,  although  tin-  fibres  grow  into  the  cord  during 
the  fifth  month  of  fcrtal  life,  myelination  does  not  begin  until  shortly  before  birth  and  is  not 
completed  until  after  the  second  year.  In  other  cases,  as  in  the  direct  cerebellar,  a  period  of 
three  months,  from  the  third  to  the  sixth,  elapses.  It  is  probable  that  the  acquisition  of  the 
medullary  coat  commences  before  the  functional  activity  of  the  fibres  begins,  although  such 
stimulation  undoubtedly  assists;  further  myelination  proceeds  gradually  along  the  course  of 
the  fibres  and  in  the  direction  of  conduction. 


PRACTICAL    CONSIDERATIONS  :    SPINAL   CORD.  1051 

Based  on  the  observations  of  Flechsig,  His,  Bechterew,  and  others,  the  time  of  the 
appearance  and  of  the  development  of  the  medullary  coat  of  some  of  the  fibres  within  the 
spinal  cord  may  be  given. 

Fibres  of  Appear  Myelinate 

Anterior  root  about  4th  week  during  5th  month 

Burdach's  tract  during  4th  week  end  of  6th  month 

Coil's  tract  about  gth  week  beginning  of  yth  month 

Pyramidal  tracts  end  of  5th  month  gth  month  to  2nd  year 

Direct  cerebellar  tract  beginning  of  3rd  month  about  6th  month 

Gowers'  tract  during  4th  month  during  6th  month 

The  presence  of  the  sinus  terminalis  (page  1030)  in  the  cord  at  birth  depends  partly  upon 
the  persistence  of  the  lumen  of  the  central  canal  at  the  lower  end  of  the  conus  medullaris  and 
partly  upon  a  proliferation  of  the  wall-cells  of  the  subjacent  segment,  followed  by  secondary 
dilatation  shortly  before  birth. 

During  the  early  weeks  of  development,  the  neural  tube  extends  to  the  lowermost  limits  of 
the  series  of  somites  ;  but  after  differentiation  of  the  root-fibres  begins,  the  segment  of  the  cord 
below  the  level  of  origin  of  the  first  coccygeal  nerves  is  marked  by  feeble  proliferation,  the 
effects  of  which  are  soon  manifest  in  the  rudimentary  condition  of  the  caudal  end  of  the  cord. 
With  the  subsequent  development  of  the  other  regions,  this  histological  contrast  becomes  more 
evident,  to  which  is  soon  added  the  conspicuous  attenuation  caused  by  the  attachment  of  the 
lower  end  of  the  cord  to  the  caudal  pole  of  the  spine,  which  elongates  with  greater  rapidity 
than  the  contained  nervous  cylinder.  In  this  manner  the  lowest  segment  of  the  cord,  with  its 
mesoblastic  envelope,  is  converted  into  the  delicate  thread-like  filum  terminate,  within  whose 
upper  half  are  found  the  remains  of  the  rudimentary  nervous  tissue. 

PRACTICAL  CONSIDERATIONS  :  SPINAL  CORD. 

Congenital  Errors  in  Development. — The  spinal  cord  may  be  absent  (amyelia), 
or  it  may  be  defective  in  a  certain  portion  (ateomyelia).  In  such  conditions,  however, 
the  patient  cannot  live.  The  cord  maybe  double  from  bifurcation  {diplomyelia). 

A  spina  bifida  is  a  congenital  condition  due  to  a  deficiency  in  the  vertebrae, 
almost  always  of  the  laminae  and  spinous  processes.  There  is  usually  a  protrusion 
of  the  contents  of  the  spinal  canal,  although  in  some  cases  there  is  no  protrusion,  and 
in  others  the  vertebral  canal,  or  even  the  central  canal  of  the  cord  may  be  open  to 
the  surface.  Three  varieties  of  tumors  are  described  according  to  their  contents.  If 
the  meninges '  only  protrude  from  the  canal  in  the  form  of  a  sac  containing  cerebro- 
spinal  fluid,  it  is  called  a  meningocele ;  if  the  sac  contains  a  portion  of  the  cord  also 
it  is  called  a  meningo-myelocele.  In  the  third  variety,  syringo-myelocele,  the  cavity 
of  the  tumor  is  found  to  consist  either  of  the  dilated  canal  of  the  cord,  so  that  the 
thinned-out  substance  of  the  cord  is  in  the  wall  of  the  sac,  or  of  a  cavity  in  the  cord 
tissue  itself.  This  is  the  least  common  of  the  three  forms. 

In  the  meningo-myelocele,  which  is  the  most  common  form,  the  cord  becomes 
flattened  out  and  attached  to  the  posterior  wall  of  the  sac,  but  still  has  its  central 
canal  intact.  The  spinal  nerves  cross  the  sac  to  their  corresponding  intervertebral 
foramina.  In  this  and  in  the  syringo-myelocele  there  is  frequently  some  degree  of 
paralysis  in  the  parts  below  from  disturbance  of  the  cord  at  the  seat  of  the  tumor. 
The  most  common  seat  of  the  defect  is  in  the  lumbo-sacral  region.  It  is  rare  in 
other  parts  of  the  spine.  Therefore,  the  bowels,  bladder,  and  lower  extremities  are 
the  parts  most  frequently  affected.  If  the  lesion  is  confined  to  the  lower  part  of  the 
sacral  region,  the  extremities  usually  escape.  Paralytic  talipes  is  comparatively 
common. 

There  is  no  sharp  line  of  demarcation  between  the  medulla  oblongata  and  the 
cord.  The  beginning  of  the  latter  is  variously  given  as  at  the  origin  of  the  first 
cervical  nerve,  the  lower  margin  of  the  foramen  magnum,  or  the  decussation  of  the 
pyramids,  the  last  being  the  more  generally  accepted. 

Since  in  the  adult,  the  spinal  cord  ends  below  usually  at  the  level  of  the  disc 
between  the  first  and  second  lumbar  vertebrae,  injuries  of  the  spine  below  the  second 
lumbar  vertebra  do  not  involve  the  cord.  The  membranes  of  the  cord,  however, 
containing  cerebro-spinal  fluid  extend  as  far  as  the  second  or  third  s.acral  vertebra, 
so  that  at  this  level  injuries  with  infection  may  cause  fatal  meningitis. 


1052 


II  I'M  AN   ANATOMY. 


The  bony  canal  is  lined  with  periosteum,  unlike  the  cranium,  in  which  the 
external  layer  of  the  dura  mater  serves  that  purpose.  The  spinal  dura  is  separated 
from  the  posterior  common  ligament,  the  ligamenta  subflava,  and  the  periosteum  by  a 
fatty  areolar  tissue  containing  a  plexus  of  veins.  Extensive  extradural  hemorrhage 
may,  therefore,  occur  without  serious  pressure  on  the  cord.  The  blood  tends  to  sink 
by  gravity,  and  later  may  produce  symptoms  of  compression.  The  dura  is  thick 
and  strong  and  offers  considerable  resistance  to  the  invasion  of  disease  from  with- 
out, even  to  tuberculosis  with  caries  of  the  vertebrae,  or  to  malignant  tumors  arising 
within  the  vertebrae.  Infections  outside  the  spinal  column,  as  in  abscess  of  the  back, 
or  bed  sores,  may  extend  along  the  communicating  veins,  giving  rise  to  extradural 
abscess  and  perhaps  to  extensive  meningitis. 

The  spinal  cord,  surrounded  by  cerebro-spinal  fluid,  hangs  loosely  within  the 
dura,  being  attached  to  it  only  by  the  roots  of  the  spinal  nerves  which  receive  invest- 
ments from  the  dura  as  they  pass  outward,  by  the  ligamenta  denticulata,  and  by  the 
delicate  fibres  of  arachnoid  tissue  extending  from  the  pia  to  the  dura.  The  cord  is, 
therefore,  not  frequently  injured  from  external  violence.  The  numerous  articulations 
of  the  vertebrae  and  the  elasticity  of  the  ligaments  and  of  the  intervertebral  discs  permit 
the  distribution  of  much  of  the  force  applied  to  the  spine  before  it  reaches  the  cord. 

The  greater  part  of  the  cerebro-spinal  fluid  is  contained  in  the  subarachnoid 
space,  which  communicates  freely  with  the  same  space  in  the  cranium,  and  is  con- 
tinuous with  the  ventricular  fluid  through  the  foramen  of  Majendie. 

The  cord  is  exposed  to  the  danger  of  penetration  by  sharp  instruments  only  from 
behind,  but  even  here  the  overlapping  of  the  laminae  and  spinous  processes  offers 
an  excellent  protection.  This  protection  is  largely  lacking  above  and  below  the  atlas, 
and  the  risk  there  from  such  wounds  is  correspondingly  greater.  At  lower  levels  in 
order  that  the  canal  may  be  reached,  the  vulnerating  instrument  must  be  directed  in 
the  line  of  the  obliquity  of  the  laminae,  which  will  vary  in  the  different  portions  of 
the  spine,  being  greatest  in  the  dorsal  region. 

Conciission — shaking  with  molecular  disturbance  and  without  obvious  gross 
lesion — of  the  cord,  although  more  frequent  than  has  been  supposed,  is  rare  because 
of  (a)  the  arrangement  of  the  different  constituents  of  the  vertebral  column,  which  by 
means  of  its  curves,  the  elastic  intervertebral  discs,  its  numerous  joints,  and  the 
large  amount  of  cancellous  tissue  in  the  vertebral  bodies,  is  able  to  take  up  and 
distribute  harmlessly  forces  of  some  degree  of  violence  ;  (<£)  the  situation  of  the  cord 
in  the  centre  of  the  column,  where,  as  the  most  frequent  serious  injuries  to  the  spine 
are  caused  by  extreme  forward  flexion,  it  is  somewhat  removed  from  danger  in 
accordance  with  a  law  of  mechanics  that  "  when  a  beam,  as  of  timber,  is  exposed  to 
breakage  and  the  force  does  not  exceed  the  limits  of  the  strength  of  the  material, 
one  division  resists  compression,  another  laceration  of  the  particles,  while  the  third, 
between  the  two,  is  in  a  negative  condition"  (Jacobson)  ;  (c)  the  suspension  of  the 
cord  in  the  surrounding  cerebro-spinal  fluid  ( ' '  like  a  caterpillar  hung  by  a  thread 
in  a  phial  of  water" — Treves)  by  its  thecal  attachments  and  nerve-roots;  (d}  its 
connection  above  with  the  cerebellum,  itself  resting  on  an  elastic  "water-bed" 
which  minimizes  the  transmission  downward  of  violence  applied  to  the  cranium. 
Many  of  the  cases  reported  as  concussion  are  undoubtedly  due  to  hemorrhage'  or 
other  gross  lesions  of  the  cord. 

Contusion  of  the  cord  may  occur  from  sprains,  as  in  forced  flexion  of  the  spine. 
The  most  frequent  and  most  serious  cases  are  those  due  to  fracture-dislocations  of  the 
spine,  the  cord  being  more  or  less  crushed  between  the  upper  and  lower  fragments. 
It  is  so  delicate  a  structure  that  it  may  be  thoroughly  disorganized  without  evident 
injury  to  the  membranes  or  alteration  of  its  internal  form.  The  paralysis  of  the  parts 
below  will  be  complete  or  partial  according  to  whether  the  whole  or  only  a  part  of 
the  transverse  section  of  the  cord  at  the  seat  of  injury  is  destroyed.  Since  when 
the  lesion  is  complete  everything  supplied  by  the  cord  below  tin-  scat  of  the  lesion 
i>  paraly/.ed,  the  higher  the  injury  to  the  cord  the  greater  the  gravity  of  the  case. 
When  the  atlas  or  axis  is  fractured  and  displaced  the  vital  centres  in  the  medulla  are 
in  danger  and  death  may  result  immediately.  The  phrenic  nerves  which  arise  chiefly 
from  the  four.th  cervical  segment,  but  partly  from  the  third  and  fifth  segments, 
are  also  paralyzed  and  respiration  ceases. 


PRACTICAL   CONSIDERATIONS  :    SPINAL   CORD.  1053 

In  fracture-dislocations  of  the  spine  it  is  the  body  of  the  vertebra  which  is  most 
frequently  fractured,  the  ligaments  yielding  posteriorly  and  permitting  the  dislocation. 
The  fractured  edges  of  bone  are,  therefore,  in  front  of  the  cord ;  and,  as  the  upper 
fragment  passes  forward,  the  anterior  or  motor  portion  of  the  cord  is  pressed 
and  crushed  against  the  sharp  upper  edge  of  the  lower  fragment.  In  partial 
transverse  lesions  of  the  cord  the  paralysis  below  the  lesions  affects,  therefore,  the 
motor  columns  of  the  cord  more  than  the  sensory  columns  which  are  in  part 
posterior. 

The  most  frequent  seat  of  fracture-dislocation  of  the  spine  is  in  the  thoraco- 
lumbar  region  (page  145).  Fortunately,  it  is  this  variety  which  offers  the  best 
prognosis,  since  the  cord  ends  usually  just  below  the  lower  border  of  the  first 
lumbar  vertebra,  and  the  cauda  equina  being  more  movable  and  tougher  than  the 
cord  itself,  it  can  better  evade  the  encroachment  on  the  canal,  although  in  spite  of 
these  facts,  it  is  not  infrequently  injured  in  such  lesions.  The  bodies  of  the  lumbar 
vertebrae  are  the  largest  and  most  cancellous,  the  intervertebral  discs  the  thickest 
and  most  elastic,  so  that  crushing  of  them  occurs  with  less  tendency  to  invade  the 
canal  and  injure  the  cord  than  in  any  other  portion  of  the  spine. 

In  caries  of  the  spine  (Pott's  disease)  the  lesion  is  situated  in  the  bodies  of  the 
vertebrae,  and  therefore,  in  front  of  the  cord.  As  the  inflammatory  exudate  extends 
it  will  invade  the  spinal  canal  anteriorly,  often  producing  an  external  pachymeningitis. 
The  irritation  and  pressure  resulting  will  again  affect  the  motor  portion  of  the  cord, 
first  producing  a  paralysis  of  motion  in  the  parts  below,  varying  in  degree  according 
to  the  amount  of  pressure  on  the  cord.  If  sensation  is  impaired  it  is  a  later 
phenomenon  and  is  due  to  greater  pressure  upon  the  cord,  and  in  some  cases  to 
myelitis.  The  loss  of  motion  is  often  the  only  effect  produced.  If  the  lower  cervical 
region  is  involved  by  the  lesion  the  phrenic  nerves  will  escape  paralysis,  but  the 
arms,  trunk,  bladder,  rectum,  and  lower  extremities  will  be  affected.  Since  the 
intercostal  and  abdominal  muscles  are  involved  in  the  paralysis,  breathing  will  be 
difficult  and  will  depend  upon  the  action  of  the  diaphragm  only.  Thus  as  the  lesion 
occurs  at  successively  lower  levels,  the  highest  limits  of  the  paralyzed  area  descend, 
and  the  expectation  of  life  increases. 

In  the  cervical  and  thoraco-lumbar  regions  where  the  injuries  to  the  spine  and 
the  cord  are  most  frequent,  are  situated  the  two  enlargements  of  the  cord.  The 
cervical  begins  at  the  fourth  cervical  vertebra,  gradually  reaches  its  largest  diameter 
opposite  the  fifth  and  sixth  vertebrae,  and  then  gradually  decreases  to  the  first 
thoracic,  where  it  merges  into  the  thoracic  portion  of  the  cord.  Only  in  the  thoracic 
region  does  the  circumference  of  the  cord  remain  the  same  throughout.  The  lumbar 
enlargement  is  shorter  than  the  cervical  and  begins  opposite  the  tenth  thoracic 
vertebra,  gradually  increases  to  the  twelfth  thoracic,  after  which  it  gradually  decreases 
to  the  conus  medullaris. 

The  localization  of  lesions  of  the  cord,  producing  symptoms  of  paralysis,  will  depend 
upon  the  height  and  extent  of  the  paralyzed  areas.  It  must  be  borne  in  mind  that  the 
nerve-roots  arise  from  the  cord  usually  at  a  level  higher  than  the  foramina  through 
which  they  escape  from  the  spinal  canal.  The  first  and  second  cervical  nerve-roots 
pass  out  of  the  canal  almost  horizontally.  The  intraspinal  course  of  the  succeeding 
nerve-roots  increases  gradually  in  obliquity  so  that  the  spinous  processes  of  the  second, 
third  and  fourth  vertebrae  correspond  approximately  to  the  level  of  the  third,  fourth 
and  fifth  cervical  nerve-roots.  The  seventh  cervical  spine  corresponds  to  the  first 
thoracic  nerve-root.  The  spinous  process  of  the  fifth  thoracic  vertebra  is  on  a 
level  with  the  seventh  thoracic  nerve,  and  the  spine  of  the  tenth  thoracic  vertebra 
with  the  origin  of  the  second  lumbar  nerve.  The  first  lumbar  nerve  arises  just  below 
the  ninth  thoracic  spine,  the  second  lumbar  nerve  opposite  the  tenth  thoracic 
spine,  the  third  and  fourth  lumbar  nerves  opposite  the  eleventh  spine,  and  the 
fifth  lumbar  and  the  first  sacral  nerves  between  the  eleventh  and  twelfth  thoracic 
spines. 

Only  the  spinous  processes  can  be  our  surface  guides,  and  it  must  be  borne  in 
mind  that  they  are  not  always  on  the  level  of  their  corresponding  vertebrae.  Briefly, 
it  may  be  said  that  the  eight  cervical  nerves  arise  from  the  cord  between  the  lower 
margin  of  the  foramen  magnum  and  the  sixth  cervical  spine,  the  first  six  thoracic 


HUMAN   ANATOMY. 


First  cervical /•>/ 

vertebra 


Skull 


First  thoracic 
vertebra 


First  tlioracic  spine 


nerves  between  the  latter  spine  and  the  fourth  thoracic,  the  lower  six  thoracic  nerves 

between  the  fourth  and  ninth  dorsal  spines,   the  five  lumbar  nerves  opposite  the 

•  ninth,    tenth    and    eleventh   spines, 

and  the  five  sacral  nerves  opposite 
the  twelfth  thoracic  and  the  first 
lumbar  spine. 

A  convenient  rule  to  locate  the 
levels  of  origin  of  the  nerve-roots, 
applicable  to  the  prelumbar  nerves, 
is  given  by  Ziehen  as  follows  : — 
For  the  cervical  nerves,  subtract  one 
from  the  number  of  the  nerve,  the 


remainder  indicating  the  correspond- 
ing spinous  process  ;  for  the  upper 
( I-V)  thoracic  nerves  subtract  two  ; 
for  the  lower  (VI-XII)  thoracic 
nerves  subtract  three.  All  the  cer- 
vical nerves  pass  out  through  the 
intervertebral  foramina  above  the 
vertebrae  after  which  they  are  named, 
except  the  eighth  cervical,  which 
emerges  between  the  seventh  cer- 
vical and  the  first  dorsal  vertebrae. 
All  the  other  spinal  nerves  escape 
below  the  vertebrae  from  which  they 
are  named.  Since  the  nerve-roots 
pass  a  considerable  distance  down- 
ward within  the  spinal  canal  before 
leaving  it,  it  follows  that  a  lesion  of 
the  cord  at  a  given  level,  as  from 
a  fracture-dislocation  of  the  spine, 
may  be  associated  with  a  paralysis 
of  the  nerve-roots  passing  out  at 
or  below  that  level,  and  arising 
from  the  cord  at  a  higher  point. 
This  must  be  taken  into  account  in 
determining  the  seat  of  the  lesion, 
since  when  the  nerve-roots  are  not 
involved  the  lesion  will  be  as  much 
higher  than  its  corresponding  inter- 
vertebral  foramina  (as  indicated  by 
the  upper  limits  of  the  paralyzed 
area)  as  the  length  of  the  intraspinal 
course  of  the  corresponding  nerve- 
roots. 

Each  root-cell  in  the  anterior 
horn  of  gray  matter  is  connected 
with  a  motor  fibre,  which  passes 
out  in  the  anterior  root  of  a  spinal 
nerve  to  its  muscle.  Motor  impulses 
originating  in  the  cortex  of  the  brain, 
pass  downward  along  the  antero- 
lateral  columns  of  the  cord,  chiefly 
in  the  lateral  pyramidal  tract.  They 
first  traverse  the  ganglion  cells  of 
the  anterior  horns  before  passing 
out  in  the  anterior  or  motor  roots 

to  their  destination.      These  ganglion  cells  constitute,  at  least  functionally,  the  trophic 
centres  for  the  muscles.      Lesions  of  the  anterior  horns,  therefore,  besides  causing 


First  lumbar  spine 


Sacrum 


First  sacral  vertebra 


Coccyx. 


Diagram,  based  on  frozen  section,  showing  relations  of 
.ui«l  spines  <.t  vertebrae  to  levels  at  which  spinal  IK-IMS 
li. .111  \  riti-lnal  i  anal. 


THE    BRAIN.  1055 

paralysis  (polio-myelitis),  will  lead  to  atrophy  of  the  corresponding  muscles.  The 
vasomotor  centres  are  also  in  the  anterior  horns,  probably  in  the  intermedio-lateral 
tract. 

Sensory  impulses  pass  to  the  posterior  horns  through  the  posterior  roots,  and 
some  of  them  soon  cross  to  the  opposite  side  of  the  cord,  others  ascending  in  the 
posterior  column.  The  lemniscus  is  probably  the  chief  sensory  tract  in  the  medulla 
oblongata,  pons,  and  cerebral  peduncles. 

Every  segment  of  the  spinal  cord  contains  centres  for  certain  groups  of  muscles, 
and  for  reflex  movements  associated  with  them.  A  reflex  begins  in  the  stimulation 
of  a  sensory  nerve.  The  impulse  thus  created  passes  to  a  centre  in  the  cord  and 
thence  is  transmitted  to  a  motor  nerve,  thus  producing  a  contraction  of  the  muscle 
supplied  by  that  nerve.  The  complete  path  of  this  impulse  is  called  a  reflex  arc. 
The  sensory  impulse  may  be  transmitted  to  different  segments  of  the  cord  and  thence 
out  through  the  corresponding  motor  roots.  Thus  a  complicated  reflex  arc  is 
produced.  It  is  to  be  assumed,  however,  that  the  impulse  will  take  the  shortest 
route,  so  that  simple  reflexes  will  have  their  reflex  arc  chiefly  in  those  segments  of 
the  cord  in  which  the  posterior  root  enters. 

Each  segment  of  the  cord  is  connected  with  fibres  from  the  brain  to  which  must 
be  ascribed  the  function  of  reflex  inhibition.  If  the  inhibitory  fibres  are  irritated,  the 
reflexes  are  impaired  from  stimulation  of  inhibition.  If  the  conductivity  of  these 
fibres  is  destroyed,  the  reflexes  are  increased ;  but  if  the  reflex  arc  is  broken  at  any 
point,  the  reflexes  are  lost.  Among  the  most  important  of  these  are  the  skin  and 
tendon  reflexes. 

The  centres  for  the  bladder,  rectum,  and  sexual  apparatus,  are  located  in  the 
sacral  segment  of  the  spinal  cord  at  and  below  the  third  sacral  segment.  They 
regulate  the  functions  of  these  organs  and  are  associated  in  some  unknown  way  with 
the  brain.  (See  mechanics  of  urination,  page  1914). 

H&mato-rachis,  or  hemorrhage  into  the  membranes  of  the  cord  (extramedullary 
hemorrhage),  may  result  from  an  injury  to  the  spinal  column,  as  a  fracture  or  a  severe 
sprain.  The  bleeding  may  be  from  the  plexus  of  veins  between  the  dura  and  bony 
wall  of  the  canal  (most  frequent),  or  from  the  vessels  between  the  dura  and  the  cord. 
In  either  case  the  symptoms  will  be  much  the  same.  There  will  be  a  sudden  and 
severe  pain  in  the  region  of  the  spine,  diffused  some  distance  from  the  seat  of  the  in- 
jury, due  to  irritation  of  the  meninges,  and  pain  transferred  along  the  distribution  of 
the  sensory  nerves  coming  from  the  affected  segments  of  the  cord,  accompanied  by 
abnormal  sensations,  as  tingling  and  hyperaesthesia.  In  the  motor  distribution  there 
will  be  muscular  spasm,  or  sometimes  a  persistent  contraction  of  the  muscles.  Gen- 
eral convulsive  movements,  retention  of  urine,  and,  later,  symptoms  of  paralysis  may 
appear,  but  as  a  rule  the  latter  is  not  complete. 

Hczrnato-myelia,  or  hemorrhage  into  the  substance  of  the  cord  (intramedullary 
hemorrhage)  from  traumatism,  usually  occurs  between  the  fourth  cervical  segment 
of  the  cord  and  the  first  dorsal  (Thorburn),  and  is  commonly  due  to  forced  flexion 
of  the  spine,  which  is  most  marked  in  this  region,  as  in  falls  on  the  head  and  neck. 
The  cord  has  been  crushed  in  such  accidents  without  fracture  of  the  spine  and  with 
only  temporary  dislocation.  The  hemorrhage  is  usually  chiefly  in  the  gray  matter 
and  may  be  only  punctate  in  size,  or  may  be  large  enough  to  extend  far  into  the 
white  matter,  or  even  outside  the  cord  into  the  subarachnoid  space.  The  symptoms 
usually  appear  immediately  after  the  injury  and  are  bilateral,  suggesting  a  total 
transverse  lesion.  There  will  be  much  pain  in  the  back,  occasionally  extending  along 
the  arms  or  around  the  thorax.  Spasms,  rigidity,  and  paralysis  rapidly  ensue,  with 
loss  of  the  reflexes  in  the  segment  of  the  cord  involved.  There  may  be  the  same 
dissociation  of  sensation  as  in  syringomyelia  when  the  hemorrhage  is  confined  to  the 
centre  of  the  cord. 

THE   BRAIN. 

The  brain, or  the  encephalon,  is  the  part  of  the  cerebro-spinal  axis  that  lies  within 
the  skull.  It  is  produced  by  the  differentiation  of  the  cephalic  segment  of  the  neural 
tube.  Although  the  brain  is  often  of  great  relative  bulk  and  high  complexity,  as  in 
man  and  some  other  mammals,  it  must  not  be  forgotten  that  the  spinal  cord  is  the 


1056 


HUMAN    ANATOMY. 


fundamental  and  essential  part  of  the  nervous  axis  and  that  the  degree  to  which  the 
brain  is  developed  is,  in  a  sense,  accidental  and  dependent  upon  the  necessities  of  the 
animal  in  relation  to  the  exercise  of  the  higher  nervous  functions.  In  the  lowest 
vertebrates,  the  fishes,  in  which  association  of  the  impressions  received  from  the 
outer  world  is  only  feebly  exercised,  those  parts  of  the  brain  rendering  such  functions 
possible,  as  the  cerebral  hemispheres,  are  very  imperfectly  represented.  On  the 
other  hand,  in  man,  in  whom  the  capacity  for  the  exercise  of  the  higher  nervous 
functions  involving  association  is  conspicuous,  the  antero-superior  parts  of  the  brain, 
the  pallium,  as  the  regions  particularly  concerned  are  called,  are  so  enormously 
developed  that  the  human  brain  is  thereby  distinguished  from  all  others.  Whether  of 
low  or  high  development,  all  brains  are  evolved  from  certain  fundamental  parts,  the 
brain-vesicles,  differentiated  in  the  head-end  of  the  embryonic  neural  canal  ;  the 
underlying  conception  of  the  brain,  therefore,  is  that  of  a  tube,  bent  and  modified  to  a 
variable  degree  by  the  thickening,  unequal  growth  and  expansion  of  its  walls.  Even 
when  most  complex,  as  in  man,  the  adult  organ  exhibits  unmistakable  evidences  of 
subdivision  corresponding  more  or  less  closely  with  the  primary  brain-vesicles,  and 
contains  spaces,  the  ventricles,  that  represent  the  modified  lumen  of  these  segments. 

FIG.  909. 


Orbital  surface  of 
frontal  lobe 


Optic  commissure 

Optic  tract 

Cerebral  peduncle 

Interpeduncular  space 


Medulla 
Cerebellum 


Olfactory  tract 

Stalk  of  pituitary  body- 
Tuber  cinereum 
Mammillary  bodies 
Cerebral  peduncle 
Temporal  lobe 
Pons 


Cerebellum 


Occipital  lobe 


Spinal  cord 


Simplified  drawing  of  brain  as  seen  from  below,  showing  relations  of  brain-stem  to  spinal  cord  and  cerebrum. 


Preparatory  to  entering  upon  a  description  of  the  fully  formed  brain,  it  is  desirable 
to  consider  briefly  the  broad  plan  according  to  which  the  organ  is  laid  down  and 
the  general  lines  along  which  its  evolution  proceeds.  Before  doing  so,  however,  it 
will  l^e  necessary  to  take  a  general  survey  of  the  relations  of  the  several  divisions 
composing  the  brain. 

Denuded  of  its  investing  membranes  and  the  attached  cranial  nerves,  and  viewed 
from  below  (Fig.  909),  the  eneephalon  is  seen  to  consist  of  a  median  brain-stem,  that 
interiorly  is  directly  continuous  with  the  spinal  cord  through  tin-  foramen  magnum 
and  above  divides  into  two  diverging  arms  that  disappear  within  the  lar^e  overhang- 
ing mass  of  the  cerebrum.  The  brain-stem  includes  three  divisions,  the  inferior  of 
which,  the  medulla  obhngala,  is  the  uninterrupted  upward  prolongation  of  the  spinal 
•cord  and  above  is  limited  by  the  projecting  lower  border  of  the  quadrilateral  mass 


THE  BRAIN.  1057 

of  the  next  division,  the  pons  Varolii.  Beyond  the  upper  margin  of  the  pons  the 
brain-stem  is  represented  by  a  third  division  that  ventrally  is  separated  by  a  deep 
recess  into  two  diverging  limbs,  the  cerebral  peduncles^  or  crura  cerebri,  to  corre- 
spond with  the  halves  or  hemispheres  of  the  cerebrum,  each  of  which  receives  one 
of  the  crura  and  in  this  manner  is  connected  with  the  lower  levels  of  the  cerebro- 
spinal  axis.  The  greater  part  of  the  medulla  and  pons  is  covered  dorsally  by  the 
cerebellum,  whose  large  lateral  expansions,  or  hemispheres,  project  on  either  side 
as  conspicuous  masses,  distinguished  by  the  closely  set  plications  and  intervening 
fissures  that  mark  their  surface.  Of  the  five  component  parts  of  the  brain — medulla, 
pons,  cerebral  peduncles,  cerebrum,  and  cerebellum — the  last  two  are  coated  with 
the  cortical  gray  matter,  in  which,  broadly  speaking,  are  situated  the  neurones 
that  constitute  the  end-stations  for  the  sensory  impulses  conveyed  by  the  various 
corticipetal  paths  and  the  centres  controlling  the  lower-lying  nuclei  of  the  motor 
nerves.  The  brain-stem,  on  the  other  hand,  whilst  containing  numerous  stations 
for  the  reception  and  distribution  of  sensory  impulses,  is  primarily  the  great  pathway 
by  which  the  cerebrum  and  the  cerebellum  are  connected  with  each  other  and  with 
the  spinal  cord. 

Viewed  in  a  mesial  sagittal  section  (Fig.  910),  each  of  these  divisions  is  seen  to 
be  related  to  some  part  of  the  system  of  communicating  spaces  that,  as  the  lateral 
and  third  ventricles,  the  aqueduct  of  Sylvius  and  the  fourth  ventricle,  extend  from 
the  cerebral  hemispheres  above,  through  the  brain-stem  and  beneath  the  cerebellum, 
to  the  central  canal  of  the  spinal  cord  below.  Since  the  lateral  ventricles  are  two  in 
number,  in  correspondence  with  the  cerebral  hemispheres  in  which  they  lie,  their 
position  is  lateral  to  the  mid-plane  and  hence  only  one  of  the  openings,  the  foramina 
of  Monroe,  by  which  they  communicate  with  the  unpaired  and  mesially  placed  third 
ventricle,  is  seen  in  sagittal  sections. 

Both  the  roof  and  the  floor  of  the  irregular  third  ventricle  are  thin,  whilst  its 
lateral  walls  are  formed  by  two  robust  masses,  the  optic  thalami,  the  mesial  surface 

Corpus  callosum  FlG'    9«>. 

Septum  lucidun 

Frontal  lobe,  mesial  surface^        />\       ^^ "  j         ~^  ^  "\  /  Optic  thalamus.  <*orsal  surface 

Lateral  wall  of  third 
ventricle  (optic  thalamus) 


__  _      __  _  -Cerebral  peduncle 

Anterior  commissur 
Foramen  of  Monroe- 
Lamina  cinerea- \^^HZZ^ZZr==^t^-v  ^X^Sl        \          ^^"    ^_^&»^_- Roof  of  Sylvian  aqueduct 

Optic  commissure- 

-  Occipital  lobe 

-Superior  medullary  velum 

//      jwr  .     \  «?>K:  ".:•  ^  \  v  L.   xr 

Floor  of  third  ventricle 
Mammillary  body 


,  -  .  _,     ,  „.     ,.,., .  White  core  of  cerebellum 

Aqueduct  of  Sylvius' 


Pons 


Inferior  medullary  velun 
Fourth  ventricle 


•Simplified  drawing  of  brain  as  seen  in  mesial  section,  showing  relation  of  brain-stem,  cerebrum  and  cerebellum, 

and  ventricular  spaces. 

of  one  of  which  forms  the  background  of  the  space  when  viewed  in  sagittal  section. 
The  roof  of  the  ventricle  is  very  thin  and  consists  of  the  delicate  layer  of  ependyma, 
as  the  immediate  lining  of  the  ventricular  spaces  is  designated,  supported  by  the 
closely  adherent  fold  of  pia  mater  which  in  this  situation  pushes  before  it  the  neural 
wall  and  contains  within  its  lateral  border  a  thickened  fringe  of  blood-vessels,  the 

67 


1058  HUMAN    ANATOMY. 

choroid  plexus.  The  two  structures,  the  ependyma  and  the  pia  mater  together, 
constitute  the  membranous  velum  interposition  that  forms  the  roof  of  the  ventricle 
and  lies  beneath  the  triangular  fornix,  whose  vaulted  form  is  suggested  by  the  arching 
ridge  that  descends  in  front  of  the  thalamus  and  marks  the  position  of  the  anterior 
pillar  of  the  fornix.  Behind,  just  over  the  upper  end  of  the  Sylvian  aqueduct,  lies 
the  cone-shaped  pineal  body  that  belongs  to  the  third  ventricle,  from  which  it  is  an 
outgrowth.  The  floor  of  the  ventricle  is  also,  for  the  most  part,  relatively  thin  and 
irregular  in  contour.  It  corresponds  to  the  median  part  of  the  lozenge-shaped  area, 
the  interpeduncular  space,  which,  seen  on  the  inferior  surface  of  the  brain,  is  bounded 
behind  by  the  anteriorly  diverging  cerebral  peduncles  and  in  front  by  the  optic  chiasm 
and  the  posteriorly  diverging  optic  tracts.  The  posterior  half  of  this  area  includes 
the  deep  triangular  recess  at  the  bottom  of  which  is  seen  the  numerous  minute  open- 
ings of  the  posterior  perforated  space  through  which  small  branches  of  the  posterior 
cerebral  arteries  pass  to  the  optic  thalamus  and  the  crura.  Passing  forward,  the 
paired  corpora  mammillaria,  the  tuber  cinereum,  the  stalk  of  the  pituitary  body 
occupy  successively  the  interpeduncular  space.  Anteriorly,  between  the  trans- 
versely cut  optic  chiasm  below  and  the  recurved  portion  of  the  great  arching  com- 
missure, the  corpus  callosum,  above,  the  third  ventricle  is  closed  by  a  thin  sheet  of 
nervous  substance  known  as  the  lamina  cinerea. 

Through  the  foramina  of  Monroe  the  lateral  ventricles  open  into  the  third,  and 
the  latter  communicates  with  the  fourth  ventricle  by  way  of  the  Sylvian  aqueduct. 
This  narrow  canal  is  surrounded  below  and  laterally  by  the  dorsal  part  or  tegmentum 
of  the  cerebral  peduncles  ;  above  it  lies  a  plate  of  some  thickness  the  dorsal  surface 
of  which  is  modelled  into  two  pairs  of  rounded  elevations,  the  superior  and  inferior 
corpora  q^ladrigemina. 

In  sagittal  section,  the  fourth  ventricle  appears  as  a  triangular  space,  the 
anterior  or  basal  wall  being  formed  by  the  dorsal  surface  of  the  pons  and  medulla  and 
the  posteriorly  directed  apex  lying  beneath  the  cerebellum.  The  upper  half  of  the 
thin  tent-like  roof  of  the  ventricle  is  formed  by  the  superior  medullary  velum,  a  thin 
layer  of  white  matter  that  stretches  from  beneath  the  inferior  corpora  quadrigemina 
to  the  cerebellum.  A  similar  lamina,  the  inferior  medullary  velum  extends  from  the 
cerebellum  downward,  but  before  reaching  the  dorsal  surface  of  the  medulla  becomes 
so  attenuated  that  this  part  of  the  ventricular  roof,  known  as  the  tela  chorioidea, 
consists  practically  of  the  pia  mater,  although  the  ependyma  excludes  the  vascular 
membrane  from  actual  entrance  into  the  ventricle.  The  pia,  however,  pushes  in  the 
ependymal  layer  and  in  this  manner  produces  the  vascular  fringes  known  as  the 
choroid  plexus  of  the  fourth  ventricle.  When  viewed  from  behind,  the  ventricle 
exhibits  a  rhomboidal  outline,  the  lateral  boundaries  above  being  formed  by  two 
arms,  the  superior  cerebellar peduncles,  that  divergingly  descend  from  the  sides  of  the 
corpora  quadrigemina  to  the  cerebellum.  Similar  bands,  the  inferior  cerebellar 
peduncles,  convergingly  descend  from  the  cerebellar  hemispheres  to  the  posterior 
columns  of  the  medulla  and  form  the  lower  lateral  boundaries  of  the  fourth  ventricle. 

Seen  from  directly  above  (Fig.  984),  the  cerebrum,  divided  into  its  hemi- 
spheres by  the  deep  sagittal  fissure,  is  the  only  part  of  the  brain  visible,  the  other  four 
divisions  being  masked  by  the  enormously  developed  overhanging  cerebral  mantle. 
The  effects  of  this  expansion  in  displacing  base- ward  parts  which,  temporarily  in  man 
and  permanently  in  the  lower  vertebrates,  occupy  a  superior  position,  are  conspicuous 
when  the  sagittal  section  of  the  developing  (Fig.  913)  and  that  of  the  fully  formed 
human  brain  (Fig.  910)  are  compared.  It  should  be  noted,  that  although  in  the 
latter  the  brain-stem  and  the  cerebellum  are  completely  overhung  by  the  cerebral 
hemispheres,  they  still  are  in  relation  with  the  free  surface  of  the  brain,  and  by 
passing  beneath  the  posterior  part  of  the  cerebrum  the  dorsal  surface  of  the  cerebellum 
and  of  the  brain-stem  may  be  reached  without  mutilation  of  the  nervous  tissue. 

THE  GENERAL  DEVELOPMENT  OF  THE  BRAIN. 

Even  before  complete  closure  of  the  anterior  end  of  the  neural  tube,  which 
takes  place  probably  shortly  after  the  end  of  the  second  week  of  foetal  life,  the 
cephalic  region  of  this  tube,  slightly  flattened  from  side  to  side,  exhibits  tin-  results 


GENERAL  DEVELOPMENT  OF  THE  BRAIN. 


1059 


of  unequal  growth  in  two  slight  constrictions  separating  three  dilatations  known  as 
the  primary  brain-vesicles.  The  posterior  of  these,  the  hind-brain,1  is  much 
the  longer,  exceeding  the  combined  length  of  the  other  two  (Fig.  911);  after  a  short 
time  when  viewed  from  behind  it  presents  an  elongated  lozenge-shaped  form  and, 
hence,  is  also  called  the  rhombencephalon.  The  middle  vesicle,  the  mid-brain, 
or  mesencephalon,  is  conspicuous  on  account  of  its  rounded  form  and  prominent 
position,  lying,  as  it  does,  over  the  marked  primary  flexure  which  the  head-end  of 
the  neural  tube  very  early  exhibits. 

The  anterior  vesicle,  known  as  the  fore-brain,  or  prosencephalon,  at  first  is 
small  and  rounded,  but  soon  becomes  modified  by  the  appearance,  on  either  side, 
of  a  hollow  protuberance,  the  optic  vesicle,  that  pushes  out  from  the  lower  lateral 
wall.  For  a  time  the  optic  vesicle  communicates  with  the  main  cavity  of  the  fore- 
brain  by  a  wide  opening.  This  gradually  becomes  reduced  and  constricted  until  the 


FIG.  911. 


Fore-brain 


Pallium 


Mid-brain 


Optic  vesicle 


Fore-brain 
(thalamic  region)     f 


Pallium 


Mid-brain 


Reconstruction  of  brain  of  human  embryo  of  about  two  weeks  (3.2  mm.);  A,  outer  surface;  £,  inner  surface; 
up,  neural  pore,  where  fore-brain  is  still  open;  cs,  anlage  of  corpus  striatum ;  or,  optic  recess  leading  into  optic 
vesicle;  A/,  hypothalamic  region,  (ffis.) 

evagination  is  attached  by  a  hollow  stem,  the  optic  stalk,  which  later  takes  part  in 
the  formation  of  the  optic  nerve  that  connects  the  eye  with  the  brain,  the  vesicle 
itself  giving  rise  (page  1482)  to  the  nervous  coat  of  the  eye,  the  retina.  By  the 
time  the  optic  evagination  is  formed,  the  front  part  of  the  fore-brain  shows  a  slight 
bulging,  narrow  below  and  broader  and  rounded  above,  and  separated  from  the 
optic  outgrowth  by  a  slight  furrow.  This  is  the  first  suggestion  of  the  anlage  of  the 
hemisphere  or  pallium  (His).  The  latter  soon  gives  rise  to  two  rounded  hollow 
protrusions,  one  on  either  side  of  the  fore-brain,  that  rapidly  expand  into  the 
conspicuous  primary  cerebral  hemispheres.  The  lower  part  of  the  fore-brain  includes 
the  region  that  later,  after  differentiation  and  outgrowth  from  the  hemisphere, 
receives  the  nerves  of  smell  and  is  known  as  the  rhinencephalon. 

A  slight  ridge  (Fig.  911,  B),  projecting  inward  from  the  roof  of  the  fore-brain, 
suggests  a  subdivision  of  the  general  space  into  a  posterior  and  an  anterior  region. 

1  This  use  of  the  term  hind-brain  is  at  variance  with  its  older  significance,  still  retained  by 
sonie  German  writers,  as  indicating  the  upper  division  (metencephalon)  of  the  posterior 
primary  vesicle.  In  view,  however,  of  the  now  general  application  of  fore-brain  and  mid-brain 
to  the  other  primary  vesicles,  it  seems  more  consistent  to  include  hind-brain  in  the  series,  as  has 
been  done  by  Cunningham,  with  a  distinct  gain  not  only  in  convenience,  but  in  avoiding  terms 
which  in  their  Anglicised  form  are  at  best  awkward  and  unnecessary. 


io6o 


HUMAN   ANATOMY. 


The  latter,  the  outwardly  bulging  pallium  or  hemisphere-anlage,  is  limited  below  by 
the  optic  recess,  the  entrance  into  the  optic  vesicle,  and,  farther  front,  by  a  flattened 
triangular  elevation  that  marks  the  earliest  rudiment  of  the  corpus  striatum.  The 
posterior  or  thalamic  region  extends  backward  to  the  mid-brain,  from  which  it  is 
separated  by  the  slight  external  constriction  and  corresponding  internal  ridge. 
During  the  fourth  week  the  demarcations  just  noted  become  more  definite,  so  that 
the  primary  anterior  vesicle  is  imperfectly  subdivided  into  two  secondary  compart- 
ments, the  telencephalon,  conveniently  called  the  end-brain,  and  the  dienceph- 
alon.  Considered  with  regard  to  the  details  presented  by  the  interior  of  the  fore- 
brain,  the  four  areas  recognized  by  His  are  evident.  These  are  (Fig.  912)  the 
region  of  the  pallium  and  of  the  corpus  striatum,  respectively  above  and  below  in 
the  telencephalon,  and  the  region  of  the  thalamus  and  of  the  hypothaiamus  respec- 
tively above  and  below  in  the  diencephalon.  Between  the  protruding  hemispheres, 
the  telencephalon  is  closed  in  front  and  below  by  a  thin  and  narrow  wall,  the  lamina 
terminalis,  which  defines  the  anterior  limit  of  the  brain-tube. 

While  the  more  detailed  account  of  the  further  development  of  these  regions 
will  be  given  in  connection  with  the  description  of  the  several  divisions  of  the  brain, 


FIG.  912. 


Mid-brain 


Mid-brain 


Diencephalon 


Thalamencephalon 


Telencephalon 


bf 


Pallium 


Spinal  cord 


Reconstruction  of  brain  of  human  embryo  of  about  four  weeks  (6.9  mm.);  A,  outer  surface;  B,  inner  surface; 
/,  isthmus  ;  os,  aperture  of  optic  stalk  ;  c/>,  cerebral  peduncle ;  cj,  cervical  flexure ;  bf,  cephalic  flexure.  Drawn  from 
His  model.  . 

it  may  be  pointed  out  here,  in  a  general  way,  that  the  pallium  gives  rise  to  the  con- 
spicuous cerebral  hemispheres,  which,  joined  below  by  a  common  lamina,  expand  out- 
ward, upward  and  backward  and  rapidly  dwarf  the  other  parts  of  the  brain-tube  which 
are  thus  gradually  covered  over.  The  striate  area  thickens  into  the  corpus  striatum, 
which  appears  as  a  striking  prominence  on  the  outer  and  lower  wall  of  each  lateral 
ventricle.  The  latter  represents  a  secondary  extension  of  the  original  cavity  of  the 
fore-brain  enclosed  by  the  developing  cerebral  hemisphere,  and  at  first  is  large  and 
thin-walled  and  communicates  by  a  wide  opening  with  the  remainder  of  the  brain- 
vesicle.  The  unequal  growth  and  thickening,  which  subsequently  modify  the 
surrounding  walls,  reduce  this  large  aperture  until  it  persists  as  the  small  foramen 
of  Monroe,  by  which  the  lateral  ventricle  communicates  with  the  third  ventricle.  The 
latter  represents  what  is  left  of  the  cavity  of  the  fore-brain  and,  therefore,  the  com- 


GENERAL   DEVELOPMENT   OF   THE    BRAIN.  1061 

bined  contribution  of  the  telencephalon  and  diencephaion.  During  the  fifth  week 
the  diencephaion  expands  into  a  relatively  large  irregular  space  (Fig.  913),  whose 
roof  and  floor  are  thin  and  whose  lateral  walls  are  thickened  by  the  masses  of  the 
developing  thalami.  The  hypothalamic  region  becomes  the  most  dependent 
part  of  the  fore-brain  and  gives  rise  to  the  structures  that  later  occupy  the  inter- 
peduncular  space  on  the  base  of  the  brain.  The  roof  of  the  diencephaion  remains 
thin,  does  not  produce  nervous  tissue  and,  in  conjunction  with  the  ingrowth  of  the 
vascular  pia  mater,  forms  the  velum  interpositum  and  its  choroid  plexuses.  The 
pineal  body  and  the  posterior  lobe  of  the  pituitary  body  arise  as  outgrowths  from  the 
roof  and  floor  of  the  diencephaion.  respectively. 

The  mid-brain,  or  mesencephalon,  at  first  large  and  conspicuous  on  account 
of  its  elongation  and  prominent  position  at  the  summit  of  the  brain-tube,  does  not 
keep  pace  with  the  adjoining  vesicles,,  and  in  the  fully  formed  brain  is  represented  by 
the  parts  surrounding  the  aqueduct  of  Sylvius.  Neither  does  it  subdivide,  but,  while 
its  entire  wall  is  converted  into  nervous  tissue,  retains  its  primary  simplicity  to  a 
greater  degree  than  any  of  the  other  brain-segments.  The  lateral  and  ventral  walls 
of  the  mid-brain  contribute  the  cerebral  peduncles  ;  its  roof  gives  rise  to  the  corpora 
quadrigemina  ;  and  its  cavity  persists  as  the  narrow  canal,  the  aqueduct  of  Sylvius, 
that  connects  the  third  and  fourth  ventricles. 

The  posterior  vesicle,  the  hind-brain,  or  rhombencephalon,  the  largest  of 
the  primary  brain-segments,  is  the  seat  of  striking  changes.  These  include  thicken- 
ing and  sharp  forward  flexion  of  the  ventro-lateral  walls,  in  consequence  of  which  the 
floor  of  the  space  becomes  broadened  out  opposite  the  bend  and  assumes  a  lozenge- 
shaped  outline.  The  hind-brain  is  conventionally  subdivided  (Fig.  913)  into  a 
superior  part,  the  metencephalon,  and  an  inferior  part,  the  myelencephalon. 
Its  cavity,  common  to  both  subdivisions,  persists  as  the  fourth  ventricle. 

The  extreme  upper  part  of  the  metencephalon,  where  it  joins  the  mid-brain, 
early  exhibits  a  constriction,  which  by  His  has  been  termed  the  isthmus  rhom- 
bencephali  and  regarded  as  a  distinct  division  of  the  brain-tube.  In  the  fully  formed 
brain,  the  isthmus  corresponds  to  the  uppermost  part  of  the  fourth  ventricle,  just  below 
the  Sylvian  aqueduct,  roofed  in  by  the  superior  medullary  velum  that  stretches 
between  the  superior  cerebellar  peduncles.  The  thickened  and  markedly  bent  ventro- 
lateral  wall  of  the  metencephalon  gives  rise  to  the  pons  Varolii,  whilst  in  the  roof  of 
the  ventricle  appears  a  new  mass  of  nervous  tissue,  the  cerebellum. 

The  myelencephalon,  soon  limited  below  by  the  cervical  flexure,  shares  in  the 
ventral  thickening  seen  in  the  preceding  division.  Its  floor  and  particularly  its  sides, 
the  latter  at  the  same  time  spreading  apart,  form  the  medulla  oblongata,  which 
below  gradually  tapers  into  the  spinal  cord.  Its  roof,  in  which  thinness  is  always 
a  prominent  feature,  becomes  more  attenuated  as  development  proceeds  and  is 
converted  into  the  inferior  medullary  velum  and  the  tela  chorioidea  that  close  in  this 
part  of  the  fourth  ventricle.  The  subsequent  invagination  of  this  membranous 
portion  of  the  ventricular  roof  by  the  pia  mater  brings  about  the  production  of  a 
choroid  plexus  similar  to  that  seen  in  the  roof  of  the  third  ventricle. 

From  the  foregoing  sketch  of  the  changes  affecting  the  embryonic  brain-tube,  it 
is  evident  that  the  anterior  and  posterior  primary  vesicles  undergo  subdivision,  while 
the  mid-brain  remains  undivided,  five  secondary  brain-vesicles — the  telencepha- 
lon, the  diencephaion,  the  mesencephalon,  the  metencephalon  and  the  myelencepha- 
lon— replacing  the  three  primary  ones. 

In  consequence  of  the  unequal  growth  of  various  parts  of  the  cephalic  segment 
of  the  neural  tube,  the  latter  becomes  bent  in  the  sagittal  plane  at  certain  points, 
so  that,  when  viewed  from  the  side,  the  axis  of  the  developing  human  brain 
describes  an  S-like  curve  (Fig.  912).  These  flexures,  to  which  incidental  reference 
has  been  made,  bring  about  a  disturbance,  for  the  most  part  temporary,  in  the 
relations  of  the  brain-segments,  which  in  the  lower  vertebrates  follow  in  regular  order 
along  an  axis  practically  straight.  In  the  developing  human  brain,'  in  which  they 
are  most  conspicuous,  there  are  three  flexures — >the  cephalic,  cervical,  and  pontine. 

The  first  of  these,  the  cephalic  flexure  which  appears  towards  the  end  of 
the  second  week  and  before  the  neural  tube  has  completely  closed,  is  primary  and 
involves  the  entire  head.  It  takes  place  in  the  region  of  the  mid-brain  and  lies 


1062 


HUMAN   ANATOMY. 


Telencephalon 


Corpus  striatum 

Optic  recess 


Mesencephalon 


Isthmus 


Metencephalon 


M  yelencephaloi  i 


above  the  anterior  end  of  the  primary  gut-tube  and  of  the  notochord.      At  first  the 
axis  of  the  fore-brain  lies  about  at  right  angles  with  that  of  the  rhombencephalon, 

(Fig.  911)  but,  with  the  in- 
FIG.  913.  creasing  size  of  the  middle 

Diencephalon  i  •    i  i 

and  anterior  vesicles,  t he- 
angle  of  the  flexure  becomes 
more  acute  until  the  long 
axis  of  the  fore-brain  and 
of  the  rhombencephalon  are 
almost  parallel  (Fig.  912). 
During  the  fourth  week 
a  second  ventral  bend,  the 
cervical  flexure,  appears 
at  the  lower  end  of  the  hind- 
brain  and  marks  the  separa- 
tion of  the  encephalic  from 
the  spinal  portion  of  the 
neural  tube.  The  cervical 
flexure,  which  also  involves 
the  head,  is  most  evident 
at  the  close  of  the  fourth 
week,  when  it  is  almost  a 
right  angle  (  Fig.  912);  after 
this  it  becomes  less  pronounced  in  consequence  of  the  elevation  of  the  head  which 
succeeds  the  period  when  the  embryonic  axis  is  most  bent. 

The  third  flexure  appears  about  the  fifth  week  in  the  part  of  the  metencephalon 
in  which  the  pons  is  later  developed  and,  hence,  is  termed  the  pontine  flexure. 
It  concerns  chiefly  the  ventral  wall,  which  is  in  consequence  for  a  time  ventrally 
doubled  on  itself ;  subsequently  this  flexure  almost  entirely  disappears.  In  contrast 
to  the  preceding  bends,  this  flexure  is  only  partial  and  involves  chiefly  the  ventral 
and  only  slightly  the  dorsal  wall  of  the  neural  tube  ;  on  the  exterior  of  the  embryo  its 
presence  is  not  detectable. 

The  developmental  relations  of  the  chief  parts  of  the  fully  formed  brain  to  the 
embryonic  brain-vesicles  are  shown  in  the  accompanying  table. 

TABLE  SHOWING  RELATIONS  OF  BRAIN-VESICLES  AND  THEIR  DERIVATIVES. 


Ventral  Dorsal 

zone  of  brain-wall 

Diagram  showing  five  cerebral  vesicles  and  dorsal  and  ventral  zones  of 
their  wall ;  based  on  brain  of  embryo  of  four  and  one-half  weeks.  ( His. ) 


PRIMARY  SEGMENT 

SECONDARY  SEGMENT 

DERIVATIVES 

CAVITY 

Anterior  vesicle 

Telencephalon 

Cerebral  hemispheres 
Olfactory  lobes 
Corpora  striata 

Lateral  ventricles      \  se        i  ..... 
Foramina  of  Monroe  i  se 
Anterior  part  of  third  ventricle 

Prosencephalon 
or 
Fore-brain 

Diencephalon 

Optic  thalami 
Optic  nerves  and  tracts 
Subthalamic  tegmenta 
Interpeduncular  structures 
Pineal  and  pituitary  bodies 

Posterior  part  of  third  ventricle 

Middle  vesicle 
Mesencephalon 
or 

Mesencephalon 

Cerebral  peduncles 
Corpora  quadrigemina 

Aqueduct  of  Sylvius 

Mid-brain 


Posterior  vesicle 
Rhombencephalon 
or 

Hind-brain 

Isthmus 

Superior  cerebellar  peduncles 
Superior  medullary  velum 

Fourth  ventricle 

Metencephalon 

Pons 
Cerebellum 

M  y  elencephalon 

Medulla 
Inferior  medullary  velum 

Notwithstanding  the  great  changes  in  position  and  relation  which  many  parts  of 
the  human  brain  suffer  during  development,  chiefly  in  consequence  of  the  enormous 
expansion  of  the  pallium  and  the  correspondingly  large  size  of  its  commissure,  the 


GENERAL  DEVELOPMENT  OF  THE  BRAIN: 


1063 


corpus  callosum,  the  fundamental  relationships'  indicated  by  embryology  are  of  such 
value  that,  even  in  the  description  of  the  adult  organ,  grouping  of  the  various  parts 
of  the  brain  upon  a  develop- 
mental basis  is  found  advan-  FIG.  914. 
tageous.  Although  strict 
adherence  to  such  a  plan 
would  be  at  times  inconven- 
ient, and,  therefore,  will  not 
be  followed,  constant  refer- 
ence to  primary  relations  is 
imperative.  It  will  be  con- 
venient, therefore,  at  this 
place,  to  call  attention  to 
the  accompanying  outline 
diagrams  which  illustrate 
the  principles  established  by 
His  in  his  epoch-making 
studies  of  the  human  brain. 
In  addition  to  showing  the 
five  cerebral  vesicles,  Fig. 
913  indicates  the  relative 
position  and  extent  of  the 
two  fundamental  subdivisions  of  the  lateral  walls  of  the  neural  tube,  the  dorsal 
or  alar  and  the  ventral  or  basal  laminae,  which  play  such  important  roles  in  the 
differentiation  of  the  various  parts  of  the  brain-stem.  Fig.  914  shows  a  later 
stage,  in  which  the  genetic  relations  of  all  the  more  important  parts  of  the  brain  may 
be  recognized.  The  greatest  complexity  is  presented  in  the  development  of  the 
derivations  of  the  fore-brain,  particularly  of  those  which  are  differentiated  from  the 
diencephalon  and  later  are  found  connected  with  the  third  ventricle.  In  order  to 
set  forth  the  developmental  relations  of  the  fore-brain,  the  following  table  from  His, 
slightly  modified,  will  be  of  service  : 


Epithalamus 
Thalamus  /  Metathalamus 

ars  mammillaris  hypothalami 
Mesencephalon 

Pedunculi  cerebri 
Isthmus 
Cerebellum 
Pons 


Medulla 


Dorsal  zone 
Ventral  zone 


Rhinencephalon 


Pars  optica 
hypothalami 


Diagram  showing  chief   derivatives  from  cerebral  visicles 
brain  of  embryo  of  third  month.     (His.) 


based  on 


Fore-Brain 

or 
Prosencephalon 


(Pallium 

'  Hetnisphaerium <  Corpus  striatum 

'  TELENCEPHALON-^  (Rhinencephalon 

^Pars  optica  hypothalami 


[DlEN 


CEPHALON 


Pars  mammillaris  hypothalami 

"Thalamus 
Epithalamus 
Habenula 
Thalamencephalon 


Corpus  pineale 
Commissura  post. 
Metathalamus 

Corpora  geniculata 

PARTS  OF  THE  BRAIN  DERIVED  FROM  THE  RHOMBENCEPHALON. 
THE  MEDULLA  OBLONGATA. 

The  medulla  oblongata,  sometimes  called  the  bulb  and  usually  designated  by  the 
'convenient  but  indefinite  name  "  medulla,"  is  the  direct  upward  prolongation  of  the 
spinal  cord.  It  begins  at  the  decussation  of  the  pyramids  below,  about  on  a  level 
with  the  lower  border  of  the  foramen  magnum,  and  ends  at  the  lower  margin  of  the 
pons  above  and  is  approximately  2.5  cm.  (i  in)  in.  length.  Its  general  form  is 
tapering,  increasing  in  breadth  from  the  transverse  diameter  of  the  cord  (10  mm.) 
below,  to  almost  twice  as  much  (18  mm.)  above,  and  in  the  antero-posterior  dimen- 
sion from  8-15  mm.  Its  long  axis  corresponds  very  closely  with  that  of  the  cord  and 
is,  therefore,  approximately  vertical.  The  medulla,  surrounded  by  the  pia  and  arach- 
noid, lies  behind  the  concave  surface  of  the  basilar  portion  of  the  occipital  bone,  with 
its  dorsal  surface  within  the  vallecula  between  the  hemispheres  of  the  cerebellum. 

Superficially,  in  many  respects  the  medulla  appears  to  be  the  direct  continuation 
-of  the  spinal  cord.  Thus,  it  is  divided  into  lateral  halves  by  the  prolongation  of  the 
anterior  and  posterior  median  fissures  ;  each  half  is  subdivided  by  a  ventro-lateral 
•and  a  dorso-lateral  line  of  nerve-roots  into  tracts  that  seemingly  are  continuations  of 


1064  HUMAN    ANATOMY. 

the  anterior,  lateral  and  posterior  columns  of  the  cord.  This  correspondence,  how- 
ever, is  incomplete  and  only  superficial,  since,  as  will  be  evident  after  studying  the 
internal  structure  of  the  medulla,  the  components  of  the  cord,  both  gray  and  white 
matter,  are  rearranged  or  modified  to  such  an  extent  that  few  occupy  the  same  posi- 
tion in  the  medulla  as  they  do  in  the  cord. 

The  anterior  median  fissure  is  interrupted  at  the  lower  limit  of  the  medulla, 
for  a  distance  of  from  6-7  mm. ,  by  from  five  to  seven  robust  strands  of  nerve-fibres 
that  pass  obliquely  across  the  furrow,  interlacing  as  they  proceed  from  the  two  sides. 
These  strands  constitute  the  decussation  of  the  pyramids  (decussatio  pyramidum), 
whereby  the  greater  number  of  the  fibres  of  the  important  motor  paths  pass  to  the 
opposite  sides  to  gain  the  lateral  columns  of  the  cord,  in  which  they  descend  as  the 
lateral  pyramidal  tracts.  The  fibres  that  remain  uncrossed  occupy  the  lateral  por- 
tions of  the  pyramids  and,  converging  towards  the  median  fissure,  descend  on  either 
side  of  the  latter  within  the  anterior  columns  as  the  direct  pyramidal  tracts.  The 


Infundibulum 
•\     •* — '     /     **r- 

Optic  tract  -  _ 

^  -Cerebral  peduncle 

^^        ^T  T*.     \  ^- 

Mammillary  body 

/THKiMtX 

"Interpeduncular  space 

'    "^¥ 

Pons  (basilar  groove)  • 

•^,^—Tiigeminal  nerve 
Middle  cerebellar  peduncle  «^_      y"' 


cerebellar  peduncle 

jjjjF**1  -..,  /•'' 

Anterior  median  fissure- --^— — i^_—_  T^__.   -»^_- 

"Inferior  cerebellar  peduncle 

_  (Restiform  body) 

Cerebellum'  ~~     ^^^^^^~        ~^^~^^~ 

'\  '      \  .'VMftt  ^4        L*         "t       ~V<      *^BMh  -  1         '-mJ^^V  ^~ 

^Olivary  eminence 


Root-bundles  of  ninth s^        ^-^C^         'S     S^  Ef~~~--^  Arcuate  fibres 

and  tenth  nerves  ^•i2c^__2£i"1^  -~^_ 

Pyramidal  decussation 

Root-bundles  of  twelfth  nerve  ^  ' 

Anterior  roots  of  first  spinal  nerve 
Brain-stem  viewed  from  in  front,  showing  ventral  aspect  of  medulla,  pons  and  mid-brain. 

decussation  varies  in  distinctness,  sometimes  the  component  strands  being  so  buried 
within  the  fissure  that  they  are  scarcely  evident,  or  even  not  at  all  apparent,  on  the 
surface  and  can  be  satisfactorily  seen  only  when  the  lips  of  the  groove  are  separated. 

Above  the  decussation  the  anterior  median  fissure  increases  in  depth  in  conse- 
quence of  the  greater  projection  of  the  bounding  pyramidal  tracts.  Its  upper  end, 
just  below  the  inferior  border  of  the  pons,  is  marked  by  a  slightly  expanded  triangular 
depression,  the  foramen  c(ecnm. 

The  posterior  median  fissure,  the  direct  continuation  of  the  corresponding 
groove  on  the  cord,  extends  along  only  the  lower  half  of  the  medulla,  since  above 
that  limit  it  disappears  in  consequence  of  (a)  the  separation  and  divergence  of  the 
dorsal  tracts  of  the  bulb,  which  below  enclose  the  fissure,  to  form  the  lower  lateral 
boundaries  of  the  lozenge-shaped  fourth  ventricle  (fossa  rhomboidalis),  and  (t>) 
the  gradual  backward  displacement  of  the  central  canal  within  the  closed  part  of  the 
medulla  until,  at  the  lower  angle  of  the  ventricle,  it  opens  out  into  that  space. 

l-'.ach  half  of  the  medulla  is  superficially  subdivided  into  three  longitudinal  tracts 
or  areas  by  two  grooves  situated  at  some  distance  to  the  side  of  the  ventral  and  dorsal 
median  fissures  respectively.  One  of  these,  the  antero-lateral  furrow,  marks  tin- 
line  of  emergence  of  the  root-fibres  of  the  hypoglossal  nerve,  which,  being  entirely 


THE   MEDULLA   OBLONGATA. 


1065 


FIG.  916. 


Cerebral  cortex 


motor,  correspond  to  the  ventral  roots  of  the  spinal  nerves  with  which  they  are 
in  series.  The  other  groove,  the  postero-lateral  furrow,  continues  upward  in  a 
general  way  the  line  of  the  dorsal  spinal  root-fibres  and  marks  the  attachment  of  the 
fibres  of  the  ninth,  tenth  and  bulbar  part  of  the  eleventh  cranial  nerves.  Unlike  the 
posterior  root-fibres  of  the  cord,  which  are  exclusively  sensory,  those  attached  along 
this  groove  of  the  medulla  are  partly  efferent  and  partly  afferent,  the  fibres  belong- 
ing to  the  spinal  accessory  being  entirely  motor,  while  those  of  the  glosso-pharyngeal 
and  the  pneumogastric  include  both  and,  therefore,  are  mixed. 

The  Anterior  Area. — This  subdivision  of  the  medulla,  also  known  as  the  pyra- 
mid, includes  the  region  lying  between  the  anterior  median  fissure  and  the  antero- 
lateral  furrow.  Superficially  it  appears  as  a  slightly  convex  longitudinal  tract,  from 
6-7  mm.  in  width,  that  continues  upward 
the  anterior  column  of  the  cord.  Each 
pyramid  constitutes  a  robust  strand,  which 
belowbeginsat  thedecussationand,  increas- 
ing slightly  as  it  ascends,  above  disappears 
within  the  substance  of  the  pons.  Just 
before  its  disappearance,  or,  strictly  speak- 
ing, after  its  emergence,  the  pyramid 
is  slightly  contracted  on  account  of  the 
increased  width  of  the  bounding  furrows. 
Its  chief  components  being  the  descending 
motor  paths  formed  by  the  cortico-spinal 
fibres,  of  which  approximately  four-fifths 
pass  to  the  opposite  side  by  way  of  the 
decussation  to  gain  the  lateral  pyramidal 
tract,  it  is  evident  that  only  to  the  extent 
of  the  direct  pyramidal  fasciculus  and,  for  a 
short  distance,  the  anterior  ground-bundle, 
are  its  constituents  represented  in  the 
anterior  column  of  the  spinal  cord. 

The  fibres  destined  for  the  direct 
pyramidal  tract,  which  above  the  decussa- 
tion occupy  the  lateral  part  of  the  pyramid, 
gradually  converge  toward  the  mid-line 
as  the  decussating  fibres  disappear,  until,  at 
the  lower  limit  of  the  crossing,  they  lie 
next  the  median  fissure,  which  position 
they  retain  in  their  further  descent  within 
the  cord.  The  space  thus  afforded  at  the 
lower  end  of  the  medulla,  to  the  outer  side 
of  the  uncrossed  fibres,  is  occupied  by 
the  prolongation  of  the  anterior  ground- 
bundle,  which,  however,  soon  suffers 


Pyramidal 
decussation 

Lateral 

pyramidal  tract 
Direct 

pyramidal  tract 


Spinal  nerve 


Diagram  showing  course  and  decussation  of  cortico- 
spinal  (pyramidal)  tract ;  M,  medulla;  P,  pons;  CP, 
cerebral  peduncle;  T,  thalamus  ;  C,  L,  caudate  and 
lenticular  nuclei ;  CC,  corpus  callosum. 

displacement  as  it  encounters  the  pyramid. 

The  ground-bundle  lies  at  first  to  the  outer  side  of  the  strands  of  decussating  fibres 
and  then  behind  the  pyramid;  higher,  it  is  pushed  backward  towards  the  mid-line 
by  the  appearance  of  the  inferior  olive  and  the  mesial  fillet  until,  finally,  it  is 
continued  as  the  posterior  longitudinal  fasciculus  at  the  side  of  the  median  raphe 
beneath  the  gray  matter  covering  the  floor  of  the  fourth  ventricle. 

The  proportion  of  the  pyramidal  fibres  taking  part  in  the  motor  decussation  is 
not  always  the  same,  from  80-90  per  cent,  being  the  usual  number.  Vary  rarely  all 
the  fibres  cross,  with  suppression  of  the  direct  pyramidal  tracts — an  arrangement 
found  normally  in  many  lower  animals.  On  the  other  hand,  the  direct  pyramidal 
tracts  may  appropriate  an  unusually  large  number  of  the  fibres,  even  to  90  per  cent, 
of  the  entire  pyramid,  the  crossed  tract,  however,  never  being  entirely  unrepresented. 
Ordinarily  the  tracts  of  the  two  sides  are  approximately  of  equal  extent,  but  occasion- 
ally they  may  be  asymmetrical,  in  which  case  the  excess  of  the  one  is  offset  by  a 
corresponding  diminution  in  the  fasciculus  of  the  opposite  side  (Flechsig). 


1066 


HUMAN    ANATOMY. 


The  Lateral  Area. — This  region  is  defined  on  the  surface  by  the  antero-lateral 
and  postero-lateral  furrows  in  front  and  behind  respectively,  and  includes  a  narrow 
strip  on  the  lateral  aspect  of  the  medulla.  Below,  the  tract  is  continuous  with  the 
lateral  column  of  the  cord,  a  resemblance  which  is,  however,  only  superficial  since 
within  the  medulla  the  large  crossed  pyramidal  tract  no  longer  lies  laterally  but 
within  the  anterior  area  of  the  opposite  side.  The  upper  part  of  the  lateral  area  is 
conspicuously  modified  by  the  presence  of  an  elongated  oval  prominence,  the  olivary 
eminence  (oliva),  produced  by  the  underlying  corrugated  lamina  of  gray  matter 
composing  the  inferior  olivary  nucleus.  The  olive  measures  about  13  mm.  in  length 
and  about  half  as  much  in  its  greatest  width.  Its  upper  end,  more  prominent  and 
slightly  broader  than  the  lower,  is  separated  from  the  inferior  border  of  the  pons  by 
a  deep  groove,  which'  medially  joins  the  furrow  occupied  by  the  hypoglossal  root- 
fibres  and  laterally  is  continuous  with  a  broad  depressed  area,  the  fiarao/h'ary  fossa, 
that  separates  the  olive  from  the  restiform  body  and  lodges  the  fibres  of  the  glosso- 
pharyngeal  and  pneumogastric  nerves.  The  demarcation  of  the  lower  tapering  end 
of  the  olive  is  somewhat  masked  by  the  anterior  superficial  arcuate  fibres,  which  cover 
for  a  variable  distance  the  inferior  part  of  the  olive  in  their  course  backward  to  gain 


Thalamus 


Pulvinar 

Median  geniculate  body 
Inferior  brachium 

Superior  colliculus 
Cerebral  peduncle 
Inferior  colliculus 


Superior  cerebellar  peduncle 

Superior  medullary  velum 
Middle  cerebellar  peduncle 

Line  of  attachment  of 
roof  of  IV  ventricle 
Inferior  cerebellar  peduncle 
(restiform  body) 

Clava 

Tuberculum  cuneatum 
Tuberculum  Rolandi 


FIG.  917. 

Lateral  geniculate  body- 


Superior  brachium 

Mesial  root  of  optic  tract 
Anterior  perforated  space 

—  Optic  tract 

—  Lateral  olfactory  root 


Optic  nerve 
Optic  commissure 
•Tuber  cinereum 
Mammillary  body 


-Olivary  eminence 
-Arcuate  fibres 

Lateral  area  of  medulla 


Brain-stem  viewed  from  the  side,  showing  lateral  aspect  of  medulla,  pons,  and  mid-brain. 


the  restiform  body.  The  components  of  the  lateral  column  of  the  cord  traceable  into 
the  medulla — the  direct  cerebellar  and  Cowers'  tract  and  the  long  paths  of  the  lateral 
ground-bundle — for  the  most  part,  with  the  exception  of  the  direct  cerebellar  tract, 
pass  beneath  or  to  the  outer  side  of  the  olive.  The  superficially  placed  direct  cere- 
bellar tract  gradually  leaves  the  lateral  area  and  passes  outward  and  backward  to  join 
the  inferior  cerebellar  peduncle  by  which  it  reaches  the  cerebellum. 

The  Posterior  Area. — The  posterior  region  of  the  medulla  is  bounded  laterally 
by  the  fibres  of  the  ninth  and  tenth  nerves  ;  and  mesially,  in  the  lower  half  of  the 
bulb,  by  the  posterior  median  fissure  and,  in  the  upper  half,  by  the  diverging  sides 
of  the  fourth  ventricle.  Below,  the  posterior  area  receives  the  prolongations  of  the 
tracts  of  Goll  and  of  Burdach,  which  within  the  medulla  are  known  as  the  funic- 
ulus  gracilis  and  funiculus  cuneatus  respectively,  and  are  Separated  from  each 
other  by  the  paramedian  sulcus.  Beginning  with  a  width  of  about  2  mm.,  the  gra- 
cile  funirulus  increases  in  breadth  as  'it  ascends  until,  just  before  reaching  the  lower 
end  of  the  fourth  ventricle,  it  expands  into  a  well-marked  swelling,  the  clava,  about 
4mm.  wide,  which  is  caused  by  a  subjacent  accumulation  of  gray  matter.  'Ihrn. 
diverging  from  its  fellow  of  the  opposite  side  to  bound  the  ventricle,  after  a  short 
course  it  loses  its  identity  as  a  distinct  strand  and  becomes  continuous  with  the 


THE   MEDULLA   OBLONGATA. 


1067 


inferior  cerebellar  peduncle  or  restiform  body.  The  expansion  within  the 
upper  part  of  the  funiculus  gracilis,  the  clava,  contains  the  nucleus  gracilis  (nucleus 
funiculi  gracilis),  the  reception  station  in  which  the  long  sensory  fibres  of  Coil's  tract 
are  interrupted.  The  triangular  interval  included  between  the  gracile  funiculi,  where 
these  begin  to  diverge,  corresponds  to  the  level  at  which  the  central  canal  of  the  cord 
ends  by  opening  out  into  the  fourth  ventricle.  A  thin  lamina,  the  obex,  closes  this 
interval  and  is  continuous  with  the  ventricular  roof. 

Along  the  outer  side  of  the  gracile  fasciculus  and  separated  from  it  by  the  para- 
median  furrow,  extends  a  second  longitudinal  tract,  the  funiculus  cuneatus,  which 
at  the  lower  end  of  the  medulla  receives  the  column  of  Burdach.  Slightly  above  the 
lower  level  of  the  clava,  the  cuneate  strand  also  exhibits  an  expansion,  the  cuneate 
tubercle  (tuberculum  cinereum),  that  is  less  circumscribed,  but  extends  farther  upward 
than  the  median  elevation.  Beneath  this  prominence  lies  an  elongated  mass  of  gray 
matter,  the  nucleus  cuneatus  (nucleus  funiculi  cuneati),  around  whose  cells  the  long 
sensory  fibres  of  Burdach' s  tract  end. 

Still  more  laterally,  between  the  roots  of  the  ninth  and  tenth  nerves  and  the 
cuneate  strand,  the  posterior  area  of  the  medulla  presents  a  third  longitudinal  eleva- 
tion, the  funiculus  of  Rolando.  The  latter  is  caused  by  the  increased  bulk  of  the 


FIG.  918. 


Inferior  colliculus 
Cerebral  peduncle 

Median  fossa 

Median  sulcus 

Middle  cerebellar  peduncle 

Acoustic  strise 

Acoustic  trivone 

Restiform  body 

Attachment  of  ventricular  roof 
Obex 

Funiculus  cuneatus 


Frenulum 

Superior  trochlear  nerve 

Cerebellar  peduncle 
Floor  of  fourth  ventricle 
Fovea  superior 

Eminentia  teres 
Trigonum  hypoglossi 
Trigonum  ragi  (fovea  inferior) 

Funiculus  separens 
Area  postrema 

Funiculus  gracilis 
Lateral  area 


Medulla  and  floor  of  fourth  ventricle  seen  from  behind,  after  removal  of  cerebellum  and  ventricular  roof.   X  iH- 

underlying  substantia  gelatinosa  that  caps  the  remains  of  the  posterior  horn  of  gray 
matter,  and  is  overlaid  by  a  superficial  sheet  of  white  matter  composed  of  the  longi- 
tudinal fibres  of  the  descending  root  of  the  trigeminal  nerve.  While,  therefore,  the 
tubercle  of  Rolando  is  produced  by  the  exaggeration  of  gray  matter  represented 
within  the  spinal  cord,  the  gracile  and  cuneate  nuclei  are  new  stations  in  which  the 
posterior  root-fibres  not  interrupted  at  lower  levels  end,  and  from  which  the  sensory 
impulses  collected  by  the  cord  are  distributed  to  the  cerebellum  and  the  higher 
centres  by  neurones  of  the  second  order. 

The  upper  half  of  the  posterior  area  of  the  medulla  is  modified  by  the  presence 
of  the  fourth  ventricle,  the  lower  lateral  boundary  of  which  it  largely  forms,  into  a 
robust  rope-like  strand  that  diverges  as  it  ascends.  Above,  it  abuts  against  and  fuses 
with  the  lateral  continuation  of  the  pons  and  then,  bending  backward,  enters  the 
overhanging  cerebellum  as  the  inferior  cerebellar  peduncle.  This  strand,  also 
known  as  the  restiform  body  (corpus  restiforme),  is  seemingly  the  direct  prolongation 
of  the  gracile  and  cuneate  funiculi.  Such,  however,  is  not  the  case,  since  the  fibres 
passing  from  these  tracts  to  the  cerebellum  by  way  of  the  restiform  body  are  the  axones 
of  the  gracile  and  cuneate  nuclei  and,  therefore,  new  links  in  the  chain  of  conduction. 


io68 


HUMAN   ANATOMY. 


The  inferior  cerebellar  peduncle  is  the  most  direct  path  by  which  the  cerebellum 
is  connected  with  the  medulla  and  the  spinal  cord.  In  addition  to  the  tracts 
originating  in  the  cord  and  destined  for  the  cerebellum  (the  direct  cerebellar  and 
possibly  part  of  Gowers'  tract),  it  comprises  probably  fibres  passing  in  both  direc- 
tions; that  is,  from  the  cells  within  the  medulla  to  the  cerebellum,  and  from  the 
cerebellar  cells  to  the  medulla.  A  more  detailed  account  of  these  components  will 
be  given  in  connection  with  the  structure  of  the  medulla  (page  1072).  Upon  close 
inspection  of  the  surface  of  the  medulla,  the  direct  cerebellar  tract  is  seen  as  an 
obliquely  coursing  band  that  at  the  lower  level  of  the  olive  leaves  the  lateral  area  and 
gradually  passes  backward,  over  the  upper  and  outer  end  of  the  Rolandic  tubercle, 
to  join  the  restiform  body,  within  which  it  continues  its  journey  to  the  cerebellum. 
The  anterior  superficial  arcuate  fibres  also  enter  the  restiform  body,  after  sweeping 
around  the  inferior  pole  of  the  olive,  or  crossing  its  surface,  and  the  upper  part  of  the 
funiculus  of  Rolando.  Additional  contributions,  the  posterior  superficial  arcuate 
fibres,  proceed  to  the  restiform  body  from  the  gracile  and  cuneate  nuclei  of  the 
same  side.  Just  before  bending  backward  to  enter  the  cerebellum,  the  restiform 
body  is  crossed  by  a  variable  number  of  superficial  strands,  the  striae  acusticae, 
that  may  be  traced  from  the  floor  of  the  fourth  ventricle  and  around  the  inferior 
peduncle  to  the  cochlear  nucleus. 

INTERNAL   STRUCTURE    OF    THE    MEDULLA    OBLONGATA. 

As  already  pointed  out,  the  correspondence  between  the  spinal  cord  and  the 
medulla  is  only  superficial,  sections  across  the  medulla  revealing  the  presence  of  con- 
siderable masses  of  gray  matter  and  important  tracts  of  nerve-fibres  not  represented 


FIG.  919. 


Ventral  (A)  and  dorsal  (B)  aspects  of  brain  stem,  showing  levels  of  sections  which  follow. 

in  the  cord,  as  well  as  the  rearrangement,  modification  or  disappearance  of  spinal 
tracts  which  are  prolonged  into  the  bulb.  In  consequence,  tin-  medulla,  even  at 
its  lower  end,  presents  new  features,  and  towards  its  upper  limit  varies  so  greatly 
trom  the  eord  that  but  slight  resemblance  to  the  latter  is  retained.  The  character- 
istic features  displayed  by  transverse  sections  of  the  medulla  at  different  levels 
depend  upon  the  changes  induced  by  four  chief  factors: — (i)  the  decussation  of 
the  pyramids,  (2)  the  appearance  of  the  dorsal  nuclei,  (3)  the  production  of  the 
formatio  reticularis,  and  (4)  the  opening  out  of  the  fourth  ventricle. 


THE   MEDULLA    OBLONGATA. 


1069 


Funiculus 
'cuneatus 


Decussating 
fibres 


Anterior 
cornu 


Transverse  section  of  medulla  at  level  A,  Fig.  919;  beginning  of  pyramidal 

de 


decussation. 
Spiller. 


Weigert-Pal  staining.     X 


Preparation  made  by  Professor 


The  effects  of  the  decussation  of  the  pyramidal  tracts,  assuming  for  convenience 
that  the  latter  pass  from  below  upward,  are  conspicuous  when  followed  in  consecutive 
transverse     sections     from 
the    spino-bulbar    junction  ^IG-  920- 

,    r,  ~J          ,-.  _^. x  Funiculus  gracilis 

cerebralward.        Ihe     first  _/*3iliiSS?53vc 

suggestion  of  the  decussa- 
tion appears  (Fig.  920)  as 
strands  of  nerve-fibres,  that 
pass  from  the  field  of  the 
lateral  pyramidal  tract  in 
thelateral  column  obliquely 
through  the  adjacent  ante- 
rior horn  of  gray  matter  and 
across  the  bottom  of  the  an- 
terior median  fissure  to  gain 
the  opposite  anterior  col- 
umn. At  a  slightly  higher 
level,  where  the  decussation 
is  fully  established  (Fig. 
921),  the  large  strands  of 
•obliquely  sectional  fibres 
are  seen  cutting  through  the  gray  matter,  partly  filling  the  median  fissure,  and  collecting 
on  either  side  of  the  latter  as  the  large  ventral  bundles  which  thence  upward  constitute 
the  prominent  pyramidal  fields.  In  consequence  of  the  greater  space  required  by 
the  pyramids,  the  isolated  anterior  horns  of  the  gray  matter,  cut  off  by  the  crossing 
strands,  and  the  adjacent  anterior  ground-bundle  are  displaced  laterally  and  at  first 
lie  to  the  outer  side  of  the  decussated  fibres.  Later,  the  ground-bundle  assumes  a 
position  behind  the  pyramid  and  eventually  becomes  continuous  with  the  posterior 
longitudinal  fasciculus  (page  1116).  The  detached  anterior  cornu  of  the  gray 
matter  is  pushed  outward  and  backward  and  gradually  becomes  broken  up  by  and 
interspersed  among  the  fibres  of  the  formatio  reticularis. 

The  Posterior  Nuclei  and  the  Arcuate  Fibres. — The  robust  tracts  of 
white  matter  (nerve-fibres)  prolonged  into  the  gracile  and  cuneate  funiculi  from  the 
tracts  of  Goll  and  of  Burdach  become  invaded  by  new  masses  of  gray  matter,  the 
nucleus  gracilis  and  cuneatus.  The  gracile  nucleus,  the  first  encountered,  begins 

as   a    narrow   area    of   gray 

FIG.  921.  matter  within  the  correspond- 

ing strand,  on  a  level  with 
the  pyramidal  decussation 
(Fig.  921).  It  rapidly  in- 
creases in  bulk,  until  it 
not  only  invades  the  entire 
funiculus  gracilis,  but  also 
joins  the  gray  matter  sur- 
rounding the  central  canal. 
The  superficial  stratum  of 
spinal  fibres  gradually  dimin- 
ishes as  more  and  more  of  its 
components  end  around  the 
cells  of  the  gracile  nucleus, 
until,  finally,  all  are  inter- 
rupted. Meanwhile  the 
cuneate  nucleus  appears 
within  the  funiculus  cuneatus 
as  a  dorsally  directed  club- 
shaped  mass  of  gray  mat- 
ter (Fig.  922)  which  soon 

becomes  a   prominent  mottled  area,   sharply  defined  by  the  overlying  stratum  of 
Burdach  fibres.      The  cuneate  nucleus  extends  to  a  higher  level  than  the  nucleus 


Nucleus  gra 


Isolated 
anterior 
cornu 


Pyramidal   decussation 


Transverse  section  of  medulla  at  level  B,  Fig.  919 ;  pyramidal  decus- 
sation well  established ;  posterior  cornua  are  displaced  laterally  by 
posterior  columns.  X  5%.  Preparation  by  Professor  Spiller. 


IOJO 


HUMAN    ANATOMY. 


gracilis  and,  even  after  the  disappearance  of  the  latter,  continues  as  a  striking  collec- 
tion of  gray  matter  beneath  the  dorsal  surface  of  the  medulla,  from  which  it  is 
separated  by  the  posterior  superficial  arcuate  fibres.  Within  the  upper  part  of  the 
fasciculus  cuneatus  the  gray  matter  becomes  subdivided  into  two  masses  (Fig.  924), 
the  more  superficial  and  continuous  of  which  is  called  the  nucleus  cuneatus  extennts, 
and  the  deeper  and  more  broken  one,  the  nucleus  cuneatus  intcrnus. 

Owing  to  the  increased  bulk  of  the  fasciculi  of  the  posterior  area  occasioned  by  the 
appearance  and  expansion  of  the  contained  nuclei,  the  dorsal  horns  of  the  gray  matter 
are  displaced  laterally  and  forward,  so  that  they  come  to  lie  on  a  level  with  the  central 
canal.  Meanwhile  the  posterior  cornua  themselves,  especially  the  capping  substantia 
gelatinosa,  materially  gain  in  bulk  and  now  appear  as  two  club-shaped  masses  of  gray 
matter  that  cause  the  dorso-lateral  projections  of  the  Rolandic  tubercles  seen  on  the 


FIG.  922. 


Nucleus  gracilis 


Funiculus  gracilis 
Funiculus  cuneatus 


Spinal  root  of  V   nei 
Substantia  gelatinosa 


Accessory  olivary  nucleu 


Antero-lateral  ground-bundle 


Anterior  superficial  arcuate  fibres' 


Nucleus  cuneatus 


ffig\  Central  gray  matter 
Deep  arcuate  fibres 

Fibres  of  XII  nerve 
Sensory  decussation 

Pyramidal  tracts 


Transverse  section  of  medulla  at  level  C,  Fig.  919,  showing  sensory  decussation,  posterior  nuclei  and 
pyramidal  tracts.     X  5K-     Preparation  by  Professor  Spiller. 

surface.  Beneath  the  latter  and  closely  overlying  the  outer  border  of  the  extensive  area 
of  the  substantia  gelatinosa,  a  crescentic  tract  of  the  longitudinally  coursing  nerve- 
fibres  marks  the  position  of  the  descending  root  of  the  trigeminal  nerve  (  Fig.  922). 
The  chief  purpose  of  the  gracile  and  cuneate  nuclei  being  the  reception  of  the 
long  sensory  tracts  continued  from  the  'cord  and  the  distribution  of  impulses  so 
received  to  the  cerebellum  and  to  the  higher  centres,  it  is  evident  that  new  paths  of 
the  second  order  must  arise  within  these  nuclei.  About  on  a  level  with  the  upper  limit 
of  the  pyramidal  or  motor  decussation,  fibres  emerge  from  the  gracile  and  cuneate 
nuclei,  sweep  forward  and  inward  in  bold  curves  and  cross  the  median  raphe  to  the 
opposite  side  of  the  medulla,  immediately  behind  the  pvramids  ( Fig.  922).  They 
then  turn  sharply  upward  and  form  the  beginning  of  the  important  sensory  pathway 
known  as  the  median  fillet  (lemniscus  medial  is)  that  eonneets  the  medullary  nuclei 
with  the  higher  centres,  as  the  superior  corpora  quadrigemina  and  the  optic  thalanms. 
The  first  fibres  that  emerge  in  this  manner  from  the  gracile  and  cuneate  nuclei 
constitute  a  fairly  well  defined  strand  to  which  the  name  sensory  decussation  or 
decussation  of  the  fillet  is  given.  It  must  not  be  supposed,  however,  that  with 
this  deeussation  the  crossing  ceases,  for,  quite  the  contrary,  it  is  only  the  beginning 
of  an  extended  series  of  sensory  fibres  that  pass  across  the  raphe  at  various  levels 
throughout  the  brain-stem.  '  As  many  longitudinally  coursing  fibres  are  encountered 
by  those  sweeping  from  side  to  side,  an  interweaving  of  vertical  and  hori/ontal  fibres 
occurs,  which  results  in  the  production  of  the  characteristic  formatio  reticularis  that 
constitutes  a  large  part  of  the  medulla,  as  well  as  of  the  dorsal  or  tegmental  portions 


THE   MEDULLA    OBLONGATA. 


1071 


Nucleus  cuneatus         gracilis      Coil's  tract 


Fibres  from  Burdach's  tract 
Post,  superficial  arcuate 


of  the  pons  and  cerebral  crura.      A  feeble  expression  of  a  somewhat  similar  structure 
is  seen  in  the  reticular  formation  within  the  lateral  column  of  the  spinal  cord. 

The  Arcuate  Fibres. — These  originate  as  the  axones  of  the  cells  of  thegracile 
and  cuneate  nuclei  and  include  three  sets.     The  first,  the  deep  arcuate  fibres,  turn 
sharply   brainward    after 
crossing  the  raphe  and  FlG-  923- 

Constitute    the   Chief   COn-  Nucleus      Fibres  from 

stituents  of  the  mesial 
fillet.  The  second  set,  the 
anterior  superficial 
arcuate  fibres,  also 
cross  the  mid-line,  but 
these,  instead  of  turning 
upward,  pass  forward, 
enter  through  the  pyra- 
mid or  along  its  median 
aspect,  and,  gaining  the 
surface,  sweep  over  the 
pyramid  and  olivary  emi- 
nenceand  thenceproceed 
backward  to  the  restiform 
body  and  on  to  the  cere- 
bellum. An  oval  collection  of  small  fusiform  nerve-cells,  the  arcuate  nucleus 
(nucleus  arcuatus)  lies  in  the  path  of  these  fibres,  at  first  on  the  ventral  surface  of  the 
pyramid  and  then  along  t£e  median  fissure.  Whilst  some  additional  arcuate  fibres 
arise  from  the  cells  of  the  nucleus,  the  majority  sweep  by  without  interruption. 
The  third  set,  the  posterior  superficial  arcuate  fibres,  proceed  from  the  cells  of 
the  gracile  and  cuneate  nuclei  of  the  same  side  and  pass  beneath  the  ventricular 
floor  to  the  adjacent  restiform  body  and  thence  to  the  cerebellum. 


Deep  arcuate 


Anterior  superficial  arcuate 


Arcuate  nucleus 


Diagram  illustrating  source  and  path  of  arcuate  fibres;   RB,  restiform  body;, 
P,  pyramidal  tract ;  O,  inferior  olivary  nucleus. 


FIG.  924. 


Nucleus  gracilis 


Funiculus  cuneatus  -. 


Fasciculus  solitarius  — M- 


Nucleus  latera 


Nucleus  ambiguus 


Decussation  of 
fillet  fibres 


Median  fillet  • 


Pyramidal  tract  • 


Nucleus  cuneatus  interims 
Nuc.  cuneatus 
extern  us 


Substantia 
gelatinosa 


Spinal  root  of 
V  nerve 

Deep  arcuate  fibres 
and  formatio 
reticularis 


Dorsal  access, 
olivary  nucleus 

.Inferior  olivary 
nucleus 


Mesial  access, 
olivary  nucleus 


Anterior  superficial  arcuate  fibres' 


Arcuate  nucleus 


Transverse  section  of  medulla  at  level  D,  Fig.  919,  showing  posterior  nuclei,  inferior  olivary  nuclei,  formatio 
-eticulans  and  dorsal  displacement  of  central  canal.    X  5%.    Preparation  by  Professor  Spiller. 

The  Olivary  Nuclei.— These  include,  in  each  half  of  the  medulla,  three  masses 
of  gray  matter — the  inferior  olivary  nucleus  and  the  two  accessory  olivary  nuclei. 
Beneath  the  prominent  olivary  eminence  lies  a  corrugated  sack-like  lamina  of  gray 


1072 


HUMAN   ANATOMY. 


FIG.  925. 

Dorsal 


Ventral 

Dorso-lateral  aspect  of  inferior  olivary 
•nucleus  as  reconstructed  by  Dr.  Florence 
R.  Sabin.  X  5. 


matter,  the  inferior  olivary  nucleus  (nucleus  olivaris  inferior),  which  in  favorable 
transverse  sections  appears  as  a  conspicuous  sinuous  C-like  figure.  The  nucleus 
resembles  a  greatly  crumpled  bag,  of  which  the  closed  end  lies  beneath  the 
corresponding  superficial  protuberance  and  the  mouth,  or  hilum,  looks  mesially 

and  somewhat  dorsally.  When  reconstructed  and 
viewed  from  the  side  (Fig.  925),  the  plications  of 
the  lateral  and  dorso-lateral  surfaces  display  a 
general  antero-lateral  disposition.  On  the  ventral 
surface  the  grooves  radiate  from  the  ventral  border 
of  the  hilum  (Sabin).  The  greatest  length  of  the 
inferior  olivary  nucleus  is  from  12-15  mm.,  its 
transverse  diameter  is  about  6  mm. ,  and  its  vertical 
one  about  one  millimeter  less.  The  somewhat 
compressed  hilum  measures  sagittally  from  8-9  mm. 
The  plicated  lamina  of  gray  matter  composing  the 
wall  of  the  sac  is  from  .2-.  3  mm.  in  thickness 
and  contains  numerous  small  irregularly  spherical 
nerve-cells,  each  provided  with  a  variable  number 
of  dendrites  and  an  axone,  embedded  within  a 
compact  feltwork  of  neuroglia  fibres.  The  interior  of  the  gray  sac  is  filled  with 
white  matter  consisting  of  nerve-fibres  that,  for  the  most  part,  stream  through  the 
hilum  and  thus  constitute  the  olivary  peduncle.  These  strands,  known  as  the 
cerebello-olivary  fibres,  connect  the  cerebellar  cortex  with  the  inferior  olivary 
nucleus  and  probably  pass  in  both  directions.  Many  fibres,  the  axones  of  the  olivary 
neurones,  issue  from  the  hilum  on  the  one  side,  cross  tjie  mid-line  and,  sweeping 
through  the  opposite  olivary  nucleus  either  by  way  of  the  hilum  or  directly  traversing 
the  gray  lamina,  continue  their  course  to  the  restiform  body  and  thence  to  the 
cerebellum.  Other  fibres  originate  in  the  cells  of  the  cerebellar  cortex  and  proceed 
in  the  opposite  direction  along  the  same  pathway  to  end  in  relation  with  the  cells 
of  the  inferior  olivary  nucleus.  The  further  links  in  the  chain  of  conduction  are 

uncertain  ;     according 

FIG.  926. 

Cerebello-olivary  strands 


to  Kolliker  it  is  prob- 
able that  from  some  of 
the  olivary  cells,  fibres 
pass  downward  into  the 
antero-lateral  ground- 
bundle  of  the  cord. 

The  accessory 
olivary  nuclei  are 
two  irregular  plate-like 
masses  of  gray  matter 
that  lie  respectively 
mesially  and  dorsally 
to  the  chief  olive.  The 
first  of  these,  the  mesial 
accessory  olivary  nu- 
cleus (nucleus  olivaris 
accessorius  mesial  is) 
is  a  sagittally  placed 
lamina, from  10-1 1  mm. 
in  length,  which  lies 
between  the  tract  of  the 
fillet  and  the  root-fibres 
of  the 


tii-rvf         Tr  pYtft-irJc  t-»F>  Section  of  inferior  olivarv  nucleus,  showing  plicated  sheet  of  «ray  substance 

traversed  by  strands  of  cerebello-olivary  fibres.    X  too. 

low   the    inferior  olive 

and,  therefore,  is  encountered  in  transverse  sections  at  a  lower  level — immediately 

above  the  pyramidal  <l<vussation — than  the  main  nucleus.      According  to  the  recon- 
structions of  Sabin,  the  nucleus  comprises  three  dorso-ventral  columns  of  cells,  of 


THE    MEDULLA   OBLONGATA. 


1073 


which  the  lower  and  middle  are  continuous  and  the  upper  is  unconnected,  and  four 
small  isolated  masses  of  gray  matter  along  the  dorsal  border  of  the  nucleus.  The 
inferior  or  spinal  end  of  the  nucleus  is  thickened  and  bent  outward,  so  that  its  plane 
is  oblique  and  parallel  with  the  ventral  surface  of  the  chief  olive.  Higher,  when  the 
latter  is  well  established,  the  mesial  accessory  nucleus  is  represented  by  a  narrow 
broken  tract,  that  corresponds  more  closely  with  the  sagittal  plane.  In  this  situa- 
tion the  nucleus  lies  between  the  fillet  and  the  inner  end  of  the  chief  olive  and  across 


Dorsal  nucleus  of  vagus 


FIG.  927. 


Ventricular  roof 


Funiculus  cunea- 

tus,  overlaid  by 

restiform  body- 


Fasciculus^  ^jjg 
solitarius^ 


Substantia  gela- 

tinosa  overlaid 

by  root  of  V 

Nucleus  ambiguus 


Nucleus  lateralis — tf; 


Nucleus  cuneatus 


Post,  longitudinal 
fasciculus 

-  Root-fibres  of  XII 


Inferior  olivary 
'nucleus 


Tract  of  mesial  fillet 


Pyramidal  tract 


Anterior  superficial  arcuate  fibres 


Transverse  section  of  medulla  at  level  E,  Fig.  919  ;  central  canal  has  opened  into  fourth  ventricle  ;  restiform 
body  appearing.     X  5.     Preparation  by  Professor  Spiller. 

its  hilum.  The  dorsal  accessory  olivary  nucleus  (nucleus  olivaris  accessorius  dorsalis) 
is  less  extensive  than  the  median,  measuring  about  9  mm.  in  length,  and  lies  close  to 
and  behind  the  posterior  lip  of  the  hilum  of  the  inferior  olive. 

The  Central  Gray  Matter. — As  pointed  out,  within  the  closed  part  of  the 
medulla  the  central  canal  and  the  surrounding  gray  matter  are  gradually  displaced 
dorsally  in  consequence  of  the  increasing  space  required  by  the  pyramid,  the  fillet 
tract  and  the  posterior  longitudinal  fasciculus,  three  paired  tracts  of  longitudinally 
coursing  fibres  that  lie  close  to  the  median  raphe  and  enlarge  as  they  are  followed 
upward.  When  the  central  canal  opens  out  into  the  fourth  ventricle,  the  sur- 
rounding gray  matter  is  correspondingly  spread  out  and  forms  the  lining  of  the 
ventricular  floor.  Within  this  gray  sheet  and  near  the  mid-line,  on  each  side,  is  seen 
the  group  of  cells  constituting  the  hypoglossal  nucleus  from  which  the  fibres  of  the 
twelfth  cranial  nerve  arise.  These  strands  take  a  direct  ventro-lateral  course  through 
the  medulla  and  emerge  on  the  surface  in  the  groove  between  the  pyramid  and 
olivary  eminence.  Slightly  more  lateral,  and  to  the  outer  side  of  the  hypoglossal 
nucleus,  another  group  of  cells  marks  the  position  of  the  elongated  vago-glosso- 
pharyngeal  nucleus,  partly  sensory  and  partly  motor,  belonging  to  the  tenth  and 
ninth  cranial  nerves.  The  fibres  of  the  vagus  traverse  the  medulla  laterally  and 
meet  the  surface  at  the  junction  of  the  lateral  and  posterior  areas.  In  this  way 
the  diverging  fibres  of  the  tenth  and  twelfth  nerves  subdivide  each  half  of  the  medulla 
into  three  triangular  areas — a  mesial,  a  lateral  and  a  posterior  (Flechsig). 

Viewed  in  transverse  sections  through  the  upper  third  of  the  medulla,  the  poste- 
rior area — the  space  between  the  vagus  fibres  and  the  dorsal  surface  of  the  medulla — 
is  seen  to  contain  a  number  of  important  fibre-tracts.  ( i)  The  restiform.  body  appears 

68 


1074 


HUMAN   ANATOMY. 


as  a  large  irregularly  crescentic  tract  of  transversely  cut  fibres  that  occupies  the 
greater  part  of  the  periphery.  (2)  The  descending  root  of  the  vestibular  nerve  is  seen 
to  the  inner  side  of  the  dorso-mesial  border  of  the  restiform  body  as  a  field  of  loosely 
grouped  bundles  of  cross-sectioned  nerve-fibres.  (3)  The  fasciculus  solitarius,  or 


FIG.  928. 

Fasciculus  solitarius  Dorsal  nucleus  of  X 

\  ,  Nucleus  of  XII 

Post.  long, 
fasciculus 


Ventricular  roof 


Nucleus  ambiguus 


estiform  body 


Descending 
1  vestibular  root 


Gray  column 
of  vestibular  root 
Form.retic.grisea 
Form,  retic.  alba 
nterolivary  stratum 
(median  fillet) 


-Inferior  olivary  nucleus 


Pyramidal  tracts 

Transverse  section  of  medulla  at  level  F,  Fig.  919 ;  ventricular  floor  is  wide ;  restiform  body  well  established  ; 
descending  root  of  vestibular  nerve  is  seen.     >   5.     Preparation  by  Professor  Spiller. 

descending  root  of  the  vagus  and  glosso-pharyngeal  nerves,  shows  as  a  conspicuous 
transversely  cut  bundle  which  lies  ventro-mesially  to  the  vestibular  root.      (4)  The 
descending  root  of  the  trigeminal  nerve  is  easily  identified  as  a  superficial  crescentic 
field  that  on  its  mesial  aspect  encloses  the  remains  of  the  substantia  gelatinosa  Rolandi. 
The  lateral  area,  between  the  diverging  vagus  and  hypoglossal  root-fibres,  is 
chiefly  occupied,  in  addition  to  (i)  the  inferior  olivary  and  (2)  dorsal  accessory 
olivary  nucleus,  by  the  feltwork  of  fibres  producing  the  reticular  formation.      In  con- 
trast to  that  within  the 

FIG.  929.  anterior  area,  the  retic- 

ulum  within  the  lateral 
area  contains  a  con- 
siderable amount  of 
diffuse  gray  matter  be- 
tween its  fibres,  and, 
hence,  is  known  as  (3) 
\h&  formatio  reticular  is 
grisea.  Accessions  to 
the  irregularly  distrib- 
uted nerve-cells  occur 
as  two  moredefinitecol- 
lections  ;  one  of  these, 
(4)  the  nucleus  am- 
bi^iius.  consists  of  an 
inconspicuous  group  of 
large  cells  lying  about 
the  middle  of  the  i^ray 
reticular  substance  and  is  of  importance  as  the  nucleus  of  origin  of  at  least  part  of 
the  motor  fibres  of  the  vagus  nerve.  The  other  (5),  the  nucleus  laterally  includes 
an  uncertain  aggregation  of  medium  si/ed  cells,  situated  near  the  periphery  and  ventral 


o- 


Nerve-cell 


Transverse 
fibr 


Longitudinal _i 

fibres 


/ 


• 


Portion    of   formatio    retimhuis    K'ist-a,    showing    nerve-cells    and    interlacing 
transverse  and  longitudinal  fibres.     X  13°- 


THE   MEDULLA   OBLONGATA. 


1075 


from  the  trigeminal  root.  A  separate  group  of  somewhat  larger  cells,  nearer  the 
ventral  border  of  the  trifacial  root,  has  been  designated  the  nucleus  lateralis  dorsalis, 
and  by  Kolliker  regarded  as  belonging  to  the  origin  of  the  spinal  accessory  nerve. 


Cochlear  fibres  crossing 
restiform  body 


Kestiform  body 


Descending  root  of 
vestibular  nerve 


FIG.  930. 


Striae 
acusticae 


Nucleus 
of  IX 


Median 
btibular 
mcleus 


Deiters' 
nucleus 


ti-  Post.  long. 
f.\  fasciculus 


body 


Substantia  gelatinosa 
l;ormatio  reticularis  alba " 
Tract  of  mesial  fillet  - 


Inferior  olivary  body 


V 


i     Fibres  of  IX  nerve 
.     Spinal  root  of  V  neive 
Substantia  gelatinosa 
Formatio  reticularis  grisea 


X*5"'*'  •:'-';          '•'•'  * /     '       Pyramidal  tracts 

Transverse  section  of  medulla  at  level  G,  Fig.  919;  ventral  part  is  narrower,  whilst  dorsal  part  is  expanded  owing 
to  increased  size  of  restitorm  oodies.    X  4-     Preparation  by  Professor  Spiller. 

In  a  general  way  the  cells  of  these  nuclei  (ambiguus  and  lateralis)  of  the  Substantia 
grisea  may  be  regarded  as  the  analogues  of  the  lateral  horn-cells  of  the  cord,  just  as 
those  of  the  hypoglossal  nucleus  resemble  the  anterior  root-cells  of  the  spinal  nerves. 
The  anterior  area,  between  the  mid-line  and  the  hypoglossal  root-fibres,  is 
occupied  ventrally  by  ( r )  the  pyramidal  tract,  which  appropriates  the  entire  width 
of  the  field  with  the  exception  of  a  very  narrow  peripheral  zone  that  intervenes 


Nerve-  Longitudinal    Transverse  •/ 

cell  fibres  fibres 

Median  raphe 

Portion  of  transverse  section  of  medulla,  showing  median  raphe  and  adjacent  formatio  reticularis  alba.    X  130. 

between  the  pyramidal  fibres  and  the  surface  along  the  median  fissure  and  the  ventral 
aspect  of  the  medulla.  This  zone  is  traversed  by  (2)  the  anterior  superficial  arcuate 
fibres,  among  which  is  lodged  an  irregular  column  of  nerve-cells  that  constitute  (3) 


1076  HUMAN   ANATOMY. 

the  arcuate  nucleus.  The  latter  lies  at  first  chiefly  on  the  ventral  and,  higher,  on  the 
mesial  aspect  of  the  pyramidal  tract.  The  cells  of  this  nucleus,  small  and  fusiform, 
are  the  origin  of  not  a  few  of  the  superficial  arcuate  fibres,  although  those  from  the 
dorsal  nuclei  continue  their  course  over  the  nucleus  without  interruption.  At  the 
upper  end  of  the  medulla,  the  cells  of  the  arcuate  nucleus  increase  in  number  and 
mingle  with  those  of  the  nucleus  of  the  raphe  and  the  pontine  nucleus. 

Dorsal  to  the  pyramid  and  immediately  next  the  mid-line  lies  (4)  the  compact 
tract  of  the  median  fillet,  composed  of  longitudinal  fibres  that  are  the  upward  continu- 
ation of  the  deep  arcuate  fibres,  which,  from  the  sensory  decussation  to  the  upper 
limit  of  the  cuneate  nucleus,  bend  sharply  brainward  after  crossing  the  mid-line.  The 
fillet-tracts  are  also  known  as  the  interolivary  stratum,  as  they  constitute  a  compact 
and  laterally  compressed  field  between  the  inferior  olivary  nuclei.  Lateral  to  the 
fillet,  between  the  latter  and  the  hypoglossal  fibres,  lies  (5)  the  mesial  accessory 
olivary  nucleus.  (6)  The  posterior  longitudinal  fasciculus  appears  in  cross-section 
as  a  compact  oval  or  laterally  flattened  strand,  which  lies  next  the  raphe  and 
immediately  beneath  the  gray  matter  covering  the  floor  of  the  fourth  ventricle. 
This  important  path  will  be  later  described  (page  1116).  The  remaining  space 
of  the  anterior  compartment,  between  the  pyramid  and  the  ventricular  gray  matter, 
is  occupied  by  the  formatio  reticularis  alba,  so  designated  in  distinction  to  the 
formatio  grisea  on  account  of  its  meagre  number  of  nerve-cells,  since,  with  the  excep- 
tion of  those  scattered  in  the  immediate  vicinity  of  the  mid-line  (nucleus  raphe),  few 
cells  are  present. 

The  Formatio  Reticularis. — Repeated  mention  has  been  made  of  the  reticu- 
lar  formation  produced  by  the  interweaving  of  the  horizontal  and  vertical  fibres. 
Whilst  particularly  conspicuous  within  the  medulla  at  the  levels  occupied  by  the 
gracile,  cuneate  and  inferior  olivary  nuclei,  on  account  of  the  prominence  of  the 
arcuate  and  cerebello-olivary  fibres,  the  formatio  reticularis  does  not  end  with  the 
disappearance  of  these  nuclei  and  fibres,  but  is  prolonged  upward,  although  less 
marked,  by  transversely  coursing  fibres  derived  from  the  reception-nuclei  of  various 
cranial  nerves — the  vagus,  glosso-pharyngeal,  auditory,  facial,  and  trigeminal — from 
whose  neurones  axones  of  the  second  order  arise  that  sweep  across  the  mid-line 
to  join  chiefly  the  fillet  tract  or  to  end,  perhaps,  about  nerve-cells  of  other  nuclei. 
In  this  manner  the  formatio  reticularis  finds  representation  within  the  dorsal  or 
tegmental  areas  of  the  pons  and  the  cerebral  crura.  The  longitudinal  fibres  within 
the  formatio  reticularis  grisea  are  derived  from  many  sources.  Some  are  the 
continuation  of  Gowers'  tract ;  some  belong  to  the  long  strands  concerned  in 
establishing  reflex  paths  connecting  the  corpora  quadrigemina,  nucleus  rubrum, 
vestibular  and  olivary  nuclei  with  the  spinal  cord  ;  some  are  the  axones  of  tegmental 
neurones  and  pursue  shorter  courses,  both  descending  and  ascending,  as  association 
fibres  linking  together  different  levels  of  the  brain-stem  ;  while  still  others  an-  the 
prolongations  of  the  spino-thalamic  and  other  long  tracts  of  the  antero-lateral  ground- 
bundle  of  the  cord.  The  longitudinal  fibres  of  the  formatio  alba  are  chiefly  the 
components  of  the  mesial  fillet  and  of  the  posterior  longitudinal  fasciculus  with, 
possibly,  the  addition  of  short  association  fibres  proceeding  from  the  nerve-cells  that 
are  found  within  the  anterior  area. 

The  details  of  a  transverse  section  passing  just  beneath  the  lower  border  of  the  pons  (  I -"ig. 
932)  vary  considerably  from  those  of  the  level  shown  in  Fig.  930.  The  ventral  half  of  the 
medulla  has  lost  in  width  in  consequence  of  the  disappearance  of  the  superficial  olivary  emi- 
nence,  the  inferior  olive  being  at  this  level  represented  by  only  a  few  irregular  plications.  The 
pyramids,  likewise,  are  narrower,  and  separated  by  the  broadened  anterior  median  fissure.  The 
mesial  fillet  and  the  posterior  longitudinal  fasciculus  are  now  widely  separated  by  the  inter- 
vening nucleus  centralis  inferior  that  appears  between  them  along  the  raphe.  The  nuclei  of  the 
•hypoglossal  and  glosso-pharyngeal  nerves  are  no  longer  seen,  but  instead,  along  the  floor  of  the 
ventricle  underlying  the  area  acustica,  appears  a  large  triangular  mass  of  gray  matter,  the 
mesial  vestibular  nucleus.  External  to  the  latter  the  lateral  or  l^'Hcrs1  nucleus  and  the 
descending  or  spinal  acoustic  root  lie  close  to  the  restiform  body,  which  in  transverse  section 
presents  a  bean-shaped  outline.  Between  the  restiform  body  and  the  descending  trigeminal  root. 
the  fibres  of  the  mesial  or  rcslibular  part  of  the  auditory  nerve  pass  backward  to  gain  the  vestib- 
ular nuclei.  The  outer  surface  of  the  restiform  body  is  closely  related  to  a  considerable 


THE   PONS  VAROLII. 


1077 


tract  of  gray  matter  that  collectively  constitutes  the  reception-nucleus  of  the  cochlear  division  of 
the  auditory  nerve.  This  ganglion  is  subdivided  into  a  superior  and  an  inferior  portion,  these 
being  the  dorsal  cochlear  nucleus  and  the  ventral  cochlear  nucleus  respectively.  They  both 
receive  the  fibres  of  the  cochlear  or  lateral  division  of  the  auditory  nerve.  The  ventral  cochlear 
nucleus  is  the  starting  point  of  a  tract  of  transverse  fibres,  that  pass  horizontally  inward,  many 
traversing  the  fillet  and  crossing  the  raphe,  and  intermingle  with  those  from  the  opposite 
side.  They  thus  form  a  broad  strand,  the  corpus  trapezoides,  that  within  the  pons  occupies 
the  lower  limit  of  the  tegmental  region,  which  it  separates  from  the  ventral.  In  Fig.  932 


FIG.  932. 


Descend-     Gray  substance 
Substantia      ing  root  of  floor 

gelatinosa      ofVIII          ofventricle 


Nucleus  of 
facial 


Mesial  vestibular 

nucleus 

Post.  long.  /       > 

fasciculus  /^-^ 


Deiters '  nucleus 


Restiform  body 


Cochlear  nerve 


Dorso-lateral 
- cochlear 
nucleus 


Cochlear  nerve  • 

and  ventral  cochlear  nucleus    , 

SpimlrootofV         . 
Trapezoidal  fibres'         / 
Inferior  olivary  nucleus  , 

Median  fillet 


Superior        Ventral  cochlear  nucleus 
olive 


Tra 


Pyramidal  tract 

nsverse  section  of  medulla  at  level  H,  Fig.  919;  pyramids  are  small  and  inferior  olivary  nuclei  are  disappearing; 
roots  of  auditory  nerve  are  entering  in  relation  to  restiform  bodies.    X  4-    Preparation  by  Professor  Spiller. 

only  the  beginning  of  this  tract  is  visible,  but  slightly  higher,  in  the  pons  (Fig.  933),  the 
trapezoidal  fibres  are  shown  in  force.  Strands  of  fibres  from  the  cochlear  nuclei  arch  over  the 
restiform  body  and  proceed  beneath  the  ventricular  floor  to  the  mid-groove  ;  these  mark  the 
course  of  the  strice  acusticce  seen  crossing  the  ventricle.  Ventro-mesial  to  the  spinal  root 
of  the  trigeminus  and  the  associated  Rolandic  substance  the  nucleus  of  the  facial  nerve  appears 
as  an  irregularly  oval  and  somewhat  broken  group  of  large  stellate  cells,  from  which  the 
strands  of  root-fibres  pass  dorso-medially. 

THE  PONS  VAROLII. 

Viewed  from  in  front,  the  pons  appears  as  a  quadrilateral  prominence  on  the 
ventral  aspect  of  the  brain,  interposed  between  the  medulla  oblongata  below,  the 
cerebral  peduncles  above,  and  the  cerebellar  hemispheres  at  the  sides.  Its  lower 
and  upper  limits  are  well  defined  by  grooves  that  separate  the  corresponding  borders 
from  the  adjacent  divisions  of  the  brain -stem,  and  between  these  boundaries  the  pons 
measures  from  25-28  mm.  in  the  mid-line.  Laterally,  however,  its  limits  are 
unmarked,  as  here  the  mass  of  the  pons  narrows  and  is  directly  continued  on  each 
side  as  a  robust  arm  which  sweeps  downward  and  backward  into  the  cerebellum  as 
the  middle  cerebellar  peduncle.  The  fibres  of  the  trigeminal  nerves,  which  are 
attached  near  its  upper  and  lateral  margins,  are  taken  as  the  conventional  lateral 
limits  of  the  pons,  the  transverse  diameter  measured  between  these  points  being 
about  30  mm. 

The  ventral  surface  of  the  pons,  strongly  convex  transversely  and  less  so  in 
the  opposite  direction,  lies  behind  the  basilar  process  of  the  occipital  bone  and  the 
dorsum  sellae.  It  is  marked  by  a  shallow  median  groove  (sulcus  basilaris),  which 
broadens  as  it  ascends  and  lodges  the  basilar  artery  and  is  bounded  on  each  side  by  a 
slight  longitudinal  elevation.  Where  the  latter  meets  the  medulla,  the  pyramid  is  seen 
to  plunge  into  the  pons  beneath  its  transversely  striated  surface.  The  longitudinal 


ioy8 


HUMAN   ANATOMY. 


ridges  are  produced  by  the  underlying  pyramidal  tracts  in  their  journey  through 
the  pons  from  the  cerebral  peduncles  to  the  medulla.  The  transverse  striation 
indicates  the  general  course  of  the  superficial  fibres  towards  the  cerebellum. 

The  lateral  surface,  continued  from  the  ventral  without  interruption,  above 
is  rounded  and  sloping  and  separated  from  the  cerebral  peduncles  by  a  distinct 
furrow.  Below,  it  passes  insensibly  into  the  middle  cerebellar  peduncle,  into  which 
the  lower  and  lateral  part  of  the  pons  is  prolonged.  Whilst  the  superficial  striation 
in  a  general  way  follows  the  contour  of  the  pons,  a  broad  band .( fasciculus  obliquus 
pontis)  from  the  upper  part  of  the  ventral  surface  sweeps-obliquely  backward  and 
downward  and  overlies  the  more  horizontally  directed  middle  and  lower  fibres. 

The  free  portion  of  the  dorsal  surface  of  the  pons  contributes  the  upper  half 
of  the  floor  of  the  fourth  ventricle  and  is,  therefore,  not  visible  until  the  roof  of  that 
cavity  is  removed.  Above  the  middle  peduncle,  the  sides  of  the  pons  are  blended 
with  the  overlying  superior  cerebellar  peduncles,  which,  in  conjunction  with  the 
intervening  superior  medullary  velum,  complete  dorsally  the  ring  of  tissue  sur- 
rounding the  narrowed  superior  end  of  the  fourth  ventricle. 


INTERNAL    STRUCTURE    OF    THE    PONS    VAROLII. 

Viewed  in  transverse  sections  the  pons  is  seen  to  include  two  clearly  defined 
areas,  the  ventral  and  the  dorsal  (Fig.  933).  The  ventral  part  (pars  basilaris) 
presents  a  characteristic  picture  in  which  the  large  pyramidal  tracts  are  covered  in 


FIG-  933- 


Abducent  fibres 


Superior  cerebellar 

peduncle 

Facial  fibres 


Superior  cerebellar  peduncle 
Nucleus  Post,  long          Nucleus 

\      of  VI  fasciculus  of  VI 


Pyramidal  tracts 


[{merging  facia]  fibn 
V'estibular  fibres 


Spinal  root  of  V 
Olivary  peduncle 


Superior  olive 


1-ormatio  reticnlaris 
uftegmentum 


Transverse  fibres 


Transverse  section  of  pons  at  level  I,  Fig.  910 ;  showing  general  subdivision  into  ventral  and  dorsal  (tegmental) 
areas  and  nuclei  of  sixth  and  seventh  nerves.     X  3. 

and  excluded  from  the  surface  by  a  conspicuous  layer  of  superficial  transverse  fibres 
(  stratum  suprrticiale  pontis),  that  laterally  sweep  backward  into  the  cerebellar  peduncle 
and  are  traversed  by  the  root-fibres  of  the  seventh  and  eighth  nerves.  The  pyra- 
mids no  longer  appear  as  compact  fields,  but  are  broken  up  into  smaller  bundles  by 
the  transverse  strands  of  ponto-cerebellar  fibres.  This  subdivision  becomes  more 
marked  at  higher  levels  of  the  pons  (Fig.  936),  in  which  the  interweaving  of  the 
longitudinal  and  transverse  bundles  produces  a  coarse  feltwork  (  stratum  complexum 
At  the  upper  border  of  the  pons,  the  scattered  pyramidal  bundles  become  once  more 
collected  into  two  compact  strands,  which  are  continued  into  the  central  part  of  the 
crusta  of  the  cerebral  peduncle.  The  dorsal  limit  of  the  ventral  field  is  occupied 
by  a  well  marked  deeper  layer  of  transverse  fibres  stratum  profiimlum  pontis  K  A 
considerable  amount  of  gray  matter,  collectively  known  as  the  pontine  nucleus 


THE   PONS   VAROLII. 


1079 


Portion  of  cross-section  of  pons,  showing  cells  of  pontine 
nucleus.     X  300. 


(nucleus  pontis)  is  distributed  within  the  interstices  between  the  bundles  of  nerve- 
fibres.  The  cells  of  this  nucleus,  small  in  size  and  stellate  in  form,  are  closely 
related  to  *the  ponto-cerebellar  fibres  of  the  same  and  of  the  opposite  side,  many 
constituting  stations  of  interruption  in  the  cortico-cerebellar  paths. 

The  dorsal  or  tegmental  part  of  the  pons  (pars  dorsalis  pontis)  resembles 
to  a  considerable  extent  in  its  general  structure  the  formatio  reticularis  grisea  of 
the  medulla,  consisting  for  the  most  part  of  a  reticulum  of  transverse  and  longitudinal 
fibres,  interspersed  with  nerve-cells,  on  each  side  of  the  median  raphe.  The  appear- 
ance of  certain  new  masses 

of  gray  matter  and  of  nerve-  <IG-  934- 

fibres,  together  with  changes 
in  the  position  of  the  fillet, 
produce  details  that  vary 
with  the  level  of  the  section. 
When  this  passes  above  the 
lower  margin  of  the  pons 
(Fig.  933).  two  diverging 
and  obliquely  cut  strands  of 
fibres,  coursing  from  the 
ventricular  floor  towards  the 
ventral  aspect,  mark  the  root- 
fibres  of  the  sixth  and  seventh 
cranial  nerves  and  divide  the 
dorsal  region,  on  each  side, 
into  three  areas.  The  middle 
area,  between  the  abducent 
fibres  mesially  and  the  facial 
fibres  laterally,  contains  three 
important  collections  of  nerve- 
cells.  One  of  these,  the  nu- 
cleus of  the  sixth  nerve,  lies  close  to  the  floor  of  the  ventricle  and  beneath  the 
rounded  prominence  of  the  eminentia  teres,  which  it  helps  to  produce,  and  gives 
origin  to  the  root-fibres  of  the  abducent  nerve.  These  fibres  take  an  obliquely 
ventral  path,  slightly  bowed  towards  the  raphe,  and  cut  through  not  only  the  dorsal 
but  also  the  ventral  part  of  the  pons  to  gain  its  lower  border,  along  which  they 
emerge  a  few  millimeters  from  the  mid-line.  In  favorable  sections  the  nucleus  of  the 
sixth  is  seen  separated  from  the  floor  of  the  fourth  ventricle  by  the  arching  fibres  of 
the  facial  nerve. 

Another  conspicuous  nucleus  of  the  middle  area,  the  superior  olive  (nucleus 
olivaris  superior),  lies  near  the  ventral  limit  of  the  tegmental  area,  partly  lodged  within 
an  indentation  on  the  dorsal  surface  of  the  conspicuous  tract  of  transverse  fibres, 
known  as  the  corpus  trapezoides,  that  extends  from  the  ventral  cochlear  nucleus 
medially  and  materially  aids  in  defining  the  ventral  boundary  of  the  dorsal  area. 
The  superior  olive  (Fig.  933)  is  an  irregularly  spherical  collection  of  nerve-cells, 
interposed  in  the  path  connecting  the  auditory  nuclei  with  the  cerebral  cortex,  and 
closely  related  with  the  tract  of  the  lateral  fillet  (page  1082).  In  addition  to  contrib- 
uting numerous  fibres  to  the  latter,  the  superior  olive  sends  others  to  the  abducent 
nucleus  which  are  seen  as  delicate  strands,  the  peduncle  of  the  superior  olive,  that 
pass  towards  the  nucleus  of  the  sixth  nerve  and  bring  this  centre  into  relation  with 
auditory  impulses.  A  small  collection  of  nerve-cells  between  the  fibres  of  the  trape- 
zoidal tract,  ventro-medial  to  the  superior  olive,  constitutes  the  nucleus  trapezoides. 
Close  to  the  medial  border  of  the  superior  olive  a  small  oval  bundle  of  longitudinal 
fibres,  the  central  tegmental  fasciculus,  is  sometimes  seen.  These  fibres  are  probably 
derived  from  the  olivary  nucleus  (Obersteiner). 

The  facial  nucleus,  a  conspicuous  but  broken  oval  mass  of  gray  matter 
(Fig.  933),  includes  several  groups  of  large  stellate  cells  that  lie  dorso-lateral  to 
the  superior  olive  and  to  the  inner  side  of  the  emerging  facial  fibres.  From  the 
cells  of  this  nucleus  the  loosely  collected  root-fibres  of  the  facial  nerve  pass  back- 
ward and  inward  to  reach  the  floor  of  the  fourth  ventricle.  Here  they  converge  into 


io8o 


HUMAN   ANATOMY. 


a  compact  strand  that,  as  the  ascending  portion  of  the  nerve,  courses  beneath  the 
eminentia  teres  seen  on  the  ventricular  floor,  close  to  the  mid-line,  until  it  bends 
outward  and,  arching  around  the  abducent  nucleus,  continues  ventrally  as  the 
emerging  root-fibres. 

The  ventral  part  of  the  inner  area  and  the  adjoining  part  of  the  middle  one  are 
occupied  by  the  field  of  the  mesial  fillet  which,  at  the  level  under  consideration,  no 
longer  has  its  longest  axis  directed  dorso-ventrally,  but  approximately  horizontal. 
The  tract  now  appears  as  a  modified  oval,  somewhat  compressed  from  before  back- 
ward, the  thicker  inner  end  of  which  reaches  the  raphe  while  the  tapering  outer  end 
lies  near  the  superior  olive.  The  posterior  longitudinal  fasciculus  is  seen  as  a  com- 
pact strand,  immediately  beneath  the  gray  matter  of  the  ventricular  floor  and  at  the 
side  of  the  raphe.  To  the  outer  side  of  the  emerging  facial  fibres,  and  therefore  in 


FIG.  935. 


Mesencephalic  root  of  V 
Posterior  longitudinal  fasciculus 


Superior  cerebellar  peduncle 
Inferior  cerebellar  peduncle 

Sensory  trigeminal  nucleus 
-  Middle  cerebellar  peduncle 


.  Motor  trigeminal 
Fnucleus 


-Motor  fibres  of  V 

5^^S-"^Trigeminal  nerve 

^^  Superior  olive 
'y  *  ^"^  Median  fillet 
Deep  transverse  pontine  fibres 

Pyramidal  tracts 
Middle  transverse  pontine  fibres 


Transverse  section  of  pons  at  level  J,  Fig.  919,  showing  root  of  trigeminal  nerve  with  its  nuclei.    X  3- 

Preparation  by  Professor  Spiller. 

the  lateral  pontine  area,  appear  the  substantial  gclatinosa  and  the  associated  spinal 
root  of  the  trigeminal  nerve.  Just  behind  the  latter  the  descending  vcstibidar  root 
lies  close  to  the  inner  side  of  the  restiform  body.  The  collection  of  nerve-cells 
marking  Betters'  nucleus  is  seen  beneath  the  ventricular  floor  in  close  relation  with 
the  descending  vestibular  root. 

Sections  passing  at  the  level  of  Fig.  935,  and,  therefore,  about  three  millimeters  above 
that  of  Fig.  933,  show  interesting  details  connected  with  the  nuclei  and  roots  of  the  trigemwal 
nerve.  At  this  level  the  nuclei  and  roots  of  the  sixth  and  seventh  nerves  are  no  longer  seen. 
The  median  fillet  appears  on  each  side  as  a  compressed  oval,  the  long  axis  of  which  is  hori- 
zontal and  whose  inner  end  almost  touches  the  raphe.  Just  above  the  outer  end  of  the  fillet, 
the  cerebral  extremity  of  the  superior  olive  is  still  visible,  to  which  a  few  strands  of  transx rise 
fibres— the  last  of  the  trapezoid  body— pass.  The  lateral  boundary  of  the  ventral  part  of  the 
pons  is  defined  by  a  hugh  tract  of  obliquely  cut  fibres  that  marks  the  entering  sensory  root  of  the 
trigeminal  nerve.  On  following  this  tract  dorsally  it  is  seen  to  enter  a  large  mass  of  gray 
matter,  the  sensory  nucleus  of  the  trigeminal  nerve.  This  ganglion,  composed  of  closely 
packed  small  multipolar  cells,  corresponds  to  an  accumulation  of  the  substantia  gelatinoso, 
which,  it  will  be  remembered,  is  to  be  seen  in  all  the  preceding  lower  levels  intimately  related 


THE    PONS  VAROLII. 


1081 


to  the  descending  or  spinal  root  of  the  fifth  nerve.  A  second  and  more  compact  ganglion,  the 
motor  nucleus  of  the  trigeminus,  lies  to  the  inner  side  and  slightly  farther  back.  It  contains  large 
multipolar  cells,  extends  to  a  somewhat  higher  level  than  the  sensory  nucleus,,  and  is  separated 
from  the  latter  by  a  strand  of  fibres  which  arch  over  the  motor  nucleus  and  then  pass  mesially 
beneath  the  ventricular  floor  to  the  raphe,  where  they  cross  to  the  motor  nucleus  of  the  appo- 
site side.  These  fibres  are  part  of  the  crossed  constituents  of  the  motor  trigeminal  root.  Additional 
components  of  the  latter,  the  descending  or  mesencephalic  root,  are  seen  in  the  interval  between 
the  superior  cerebellar  peduncle  and  the  lateral  angle  of  the  ventricle.  The  motor  root  itself  is 
represented  by  several  inconspicuous  and  broken  strands  of  fibres  that  emerge  from  the  motor 
nucleus  and  lie  close  to  the  inner  side  of  the  large  sensory  root. 

Lateral  to  the  sensory  nucleus  and  root  of  the  fifth,  and  therefore  beyond  the  conventional 
limits  of  the  pons,  the  section  includes  the  three  large  fibre-tracts  of  the  three  cerebellar 
peduncles.  The  most  anterior  of  these  is  the  middle  peduncle  into  which  the  corresponding 
ventral  part  of  the  pons  is  continued.  The  next  and  middle  tract,  joining  the  tegmentum  to  the 


Fourth  ventricle 


FIG.  936. 


Superior  cerebellar  penduncle 

Substantia  ferruginea 
Tegmental  a: 


Lateral  fillet 

Nucleus  01  lateral  fillet 

Mesial  fillet 


Lingula  overlying  superior  medullary  velum 

Floor  of  fourth  ventricle 

Mesencephalic  root  of  trigeminus. 


Pyramidal  tracts 


Raphe 


Transverse  section  of  pons  at  level  K,  Fig.  919.  showing  fourth  ventricle  closed  by  superior  cerebellar  penduncles 
and  superior  medullary  velum.    X  3.    Preparation  by  Professor  Spiller. 

outer  side  of  the  sensory  trifacial  nucleus,  is  the  now  obliquely  cut  inferior  peduncle  or  resti- 
form  body.  The  third  and  dorsal  tract  is  part  of  the  superior  peduncle,  which  being  crescentic 
in  cross-section,  is  here  represented  by  its  ventral  edge.  The  three  peduncles  are  thus 
intimately  related  as  they  pass  into  the  central  core  of  white  matter  of  the  cerebellum. 

In  sections  passing  at  levels  above  the  middle  cerebral  peduncle  (Fig.  936),  the  ventro- 
lateral  surface  of  the  pons  is  free  and  unattached  and  passes  over  the  rounded  dorso-lateral 
border  onto  the  free  posterior  surface  of  the  projecting  part  of  the  pons.  Behind,  the  latter  is 
blended  with  the  robust  arms,  the  superior  cerebellar  peduncles,  that  form  the  lateral  walls  of 
the  upper  part  of  the  narrowing  fourth  ventricle.  This  latter  space  is  roofed  in  by  the  superior 
medullary  velum  which  stretches  across  the  ventricle  between  the  superior  peduncles  and  on  its 
upper  surface  supports  the  thin  lamina  of  cerebellar  cortical  gray  matter  belonging  to  the  lingula 
of  the  superior  worm. 

The  floor  of  the  ventricle  is  grooved  in  the  mid-line  by  a  furrow  bounded  on  each  side  by 
an  elevation — the  upward  prolongation  of  the  eminentia  teres.  The  depression  at  the  lateral 
angle  of  the  ventricular  floor  is  the  upper  part  of  ihefovea  superior. 

Beneath  the  latter  are  grouped  the  deeply  pigmented  nerve-cells  of  the  sub stantia  ferruginea 
that,  seen  through  the  intervening  layer  of  tissue,  confer  the  characteristic  bluish  tint  of  the 


1082 


HUMAN    ANATOMY. 


locus  caeruleus  to  this  part  of  the  ventricle  (page  1097).  Mesial  to  these  cells  the  posterior  longi- 
tudinal fasciculus  shows,  in  transverse  section,  as  a  triangular  field  close  to  and  on  each  side 
of  the  raphe. 

The  most  conspicuous  feature  of  the  dorsal  part  of  the  section  is  the  comma-shaped  fibre- 
tract,  of  the  superior  cerebellar  peduncle  (brachium  conjunct! vum).  The  thicker  part  of  the  tract 
lies  dorsally  and  its  thinner  edge  cuts  into  the  lateral  part  of  the  posterior  area  of  the  pons 
about  half  way  between  its  dorsal  and  ventral  boundaries.  Between  the  cerebellar  tract  and  the 
lateral  angle  of  the  ventricle,  a  slender  crescentic  strand  of  transversely  cut  fibres  marks  the 
descending  motor  or  mesencephalic  root  of  the  trigeminal  nerve.  The  tract  of  the  median  fillet 
no  longer  touches  the  raphe,  but  lies  as  a  compressed  and  horizontally  elongated  oval  along  the 
ventral  border  of  the  dorsal  field.  The  three-cornered  area  included  between  the  outer  end  of 
the  mesial  fillet,  the  cerebellar  arm  and  the  surface,  contains  a  curved  triangular  tract  that 
sweeps  backward  and  insinuates  its  pointed  dorsal  extremity  along  the  outer  side  of  the  cere- 
bellar strand.  This  tract  is  the  lateral  fillet  (lemniscus  lateralis),  an  important  part  of  the 
pathway  by  which  auditory  impulses  are  carried  from  the  reception-nuclei  of  the  eighth  nerve 
to  the  inferior  corpora  quadrigemina,  the  internal  geniculate  body  and  the  cerebral  cortex.  A 
collection  of  small  nerve-cells,  embedded  within  the  outer  angle  of  this  tract,  gives  rise  to  a 
number  of  its  component  fibres  and  is,  therefore,  known  as  the  nucleus  of  the  lateral  fillet 
(nucleus  lemniscus  lateralis).  An  additional  group,  between  the  lateral  fillet  and  the  cerebellar 
tract,  constitutes  the  nucleus  tegmenti  lateralis  (Kolliker).  The  remainder  of  the  tegmental 
area  is  occupied  by  the  formatio  reticularis. 

THE  CEREBELLUM. 

The  cerebellum — the  "little  brain,"  in  contrast  to  the  cerebrum  or  "great 
brain" — is  placed  in  the  posterior  fossa  of  the  skull  and  beneath  the  tent-like  shelf 
of  dura,  the  tentorium,  which  separates  it  from  the  overlying  posterior  part  of  trie 


FIG.  937. 


Pons 


Middle  cerebellar 
peduncle 

Medulla 
Accessory  flocculus 

Flocculus 
Biventral  lobule 


Anterior  crescentic  lobule 


Great  horizontal 
fissure 


Postero-superior 
lobule 


Postero-inferior 
lobule 


Tonsil 


Pyramid  Posterior  cerebellar  notch  Tuber 

Cerebellum  viewed  from  in  front  and  below ;  pons  and  medulla  occupy  greater  part  of  vallecula  and  mask  worm. 

cerebral  hemispheres.  It  lies  behind  the  pons  and  medulla  and  the  fourth  ventricle, 
with  the  roof  of  which  space  it  is  intimately  related.  By  means  of  its  three  peduncles 
— inferior,  middle  and  superior — the  cerebellum  is  connected  with  the  medulla,  the 
pons  and  the  mid-brain  respectively. 

The  general  form  of  the  cerebellum  is  that  of  an  ellipsoid,  compressed  from 
above  downward  and  constricted,  save  on  tin-  dorsal  aspect,  by  a  median  groove  of 
varying  proportions.  Its  greatest  dimension  is  the  transverse  diameter,  about  10  cm. 
(4  in.);  its  least  is  the  vertical  (3  cm.),  while  in  the  sagittal  direction  the  cerebellum 
measures  about  4  cm.  in  the  mid-line  and  about  (>  cm.  at  the  side.  The  cerebellum 
weighs  about  140  gm.  (5  oz. )  and  constitutes  approximately  one-tenth  of  the  entire 
brain-weight. 

The  conventional  division  into  a  narrow  median  part,  the  worm,  and  the  two 
lateral  expansions,  the  hemispheres,  while  convenient  for  the  description  of  the 
cerebellum  of  man,  is  not  warranted  by  recent  comparative  and  developmental 


THE    CEREBELLUM.  1083 

studies  (Stroud,  Elliott  Smith,  Bradley,  Bolk  and  others),  since  some  details  given 
prominence  in  human  anatomy  are  of  secondary  importance,  and  others  of  greater 
morphological  significance  are  only  slightly  emphasized. 

The  surface  of  the  cerebellum  is  divided  by  the  deeper  fissures  into  more  or  less 
well  defined  areas,  the  lobiiles,  each  of  which  is  subdivided  by  shallower  clefts  into 
narrow  tracts,  the  folia,  from  2-4  mm.  in  width,  that  usually  pursue  a  curved  course 
within  a  given  lobule  and,  in  a  general  way,  run  parallel  to  one  another  and  to  the 
sulci  bounding  the  tract.  On  separating  the  plate-like  folia,  or  on  making  a  section 
across  the  plications  (Fig.  943),  it  will  be  seen  that  the  pattern  of  the  folia  is  greatly 
extended  by  the  presence  of  numerous  additional  furrows  on  the  deeper  and  hidden 
aspects  of  the  leaflets,  which  are,  therefore,  ordinarily  invisible  from  the  surface. 
Whether  free  or  sunken,  the  exterior  of  the  cerebellum  is  everywhere  formed  by  a 
cortical  layer  of  gray  matter,  from  1-1.5  mm-  thick,  that  encloses  a  medullary  layer 
of  white  matter  of  variable  thickness.  Owing  to  this  arrangement,  sagittal  sections 
of  the  cerebellum  expose  an  elaborate  system  of  branching  tracts  of  white  and  gray 
matter,  designated  as  the  arbor  vita  (Fig.  938). 

The  general  ellipsoidal  mass  of  the  cerebellum,  comprising  the  narrow  central 
vermis  and  the  expanded  lateral  hemispheres,  presents  a  superior  and  an  inferior  sur- 
face and  rounded  anterior  and  posterior  borders.  Of  these  the  anterior  border  is 
indented  by  a  wide  groove,  the  anterior  notch  (incisura  cerebelli  anterior),  which  is 
much  larger  than  the  posterior  and  bounded  laterally  by  the  cerebellar  hemispheres 
and  behind  by  the  anterior  part  of  the  worm.  It  is  occupied  by  the  inferior  corpora 
quadrigemina  and  the  superior 

cerebellar   peduncles  and  FIG.  938. 

intervening     superior    medul-  /  syhian  aqueduct 

lary  velum.  The  posterior 
border  is  interrupted  by  a 
smaller  median  indentation, 
the  posterior  notch  (incisura 
cerebelli  posterior),  which  is 
bounded  on  each  side  by  the 
hemispheres  and  at  the  bottom 
by  the  hind  part  of  the  worm, 
and  contains  the  crescentic 
fold  of  dura  known  as  the  falx 


Tela  chorioidea- 

The    upper    surface    of 

the  cerebellum  is  modelled  by 
the   overlying   tentorium    and 
presents  a  slight  median  trans- 
versely furrowed  ridge  that  COr-       Mesial  sagittal  section  of  brain-stem  and  cerebellum,  showing  fourth 
responds   to   the  Upper  surface  ventricle,  Sylvian  aqueduct,  and  cerebellar  worm. 

of  the  middle  division,  or  worm, 

and  is  known  as  the  vermis  superior.      The  most  elevated  part  of  this  surface  lies 

a  short  distance  behind  the  anterior  notch.      From  this  point,  designated  the  mon- 

ticulus,  the  upper  surface  slopes  gradually  downward  on  each  side  to   the  lateral 

margins  of  the  hemispheres,  whilst  it  falls  off  more  rapidly  towards  the  posterior 

notch. 

The  lower  surface  of  the  cerebellum  is  much  less  regular,  owing  to  the  pres- 
ence of  a  wide  median  groove,  the  vallecula,  that  is  bordered  laterally  by  the 
rounded  hemispheres  and  is  continuous  in  front  and  behind  with  the  anterior  and 
posterior  notches.  The  bottom  of  the  vallecula  is  occupied  by  the  irregular  ridge-like 
surface  of  the  middle  lobe  which  is  here  known  as  the  vermis  inferior.  The  front 
of  the  valley  receives  the  dorsal  surface  of  the  medulla. 

The  cerebellum  is  incompletely  divided  into  an  upper  and  a  lower  part  by  a  deep 
cleft,  the  great  horizontal  fissure  (sulcus  horizontalis  cerebelli).  The  sulcus 
begins  in  front,  at  the  side  of  the  middle  cerebellar  peduncle,  by  the  junction  of  two 
diverging  limbs  that  embrace  the  three  cerebellar  peduncles.  It  passes  usually  con- 
tinuously around  the  circumference  of  the  cerebellum,  but  sometimes  is  interrupted 


1084 


HUMAN   ANATOMY. 


on  the  worm,  and  cuts  deeply  into  the  lateral  and  posterior  portions  of  the  hemispheres 
and  the  worm  behind.  It  is,  however,  visible  on  the  upper  aspect  of  the  cerebellum 
only  for  a  short  distance  as  it  approaches  the  posterior  notch,  the  remainder  of  its 
course  being  masked  by  the  overhanging  border  of  the  hemisphere.  Although 
of  cardinal  importance  in  the  usual  description  of  the  human  cerebellum,  the  great 
horizontal  sulcus  is  of  secondary  morphological  significance,  being  a  secondary 
fissure  that  is  developed  relatively  late  in  man  and  feebly  or  not  at  all  in  many 
other  animals. 

Both  the  vermis  and  the  hemispheres  are  subdivided  into  tracts,  or  lobules,  by 
the  deeper  fissures  ;  these  are  grouped  into  lobes,  in  the  conventional  division  of 
the  human  cerebellum,  by  regarding  each  median  division  of  the  worm  as  associated 
with  a  pair  of  lateral  lobules,  one  for  each  hemisphere. 

LOBES  AND  FISSURES  OF  THE  UPPER  SURFACE. — The  subdivisions  of  the 
superior  worm  are,  from  before  backward  : — (i)  the  lingula,  (2)  the  lobnlns  centralis, 
(3)  the  culmen,  (4)  the  clivus,  and  (5)  the  folium  cacuminis.  With  the  exception 
of  the  lingula,  which  usually  is  unprovided  with  lateral  expansions,  these  median 
tracts  are  connected  respectively  with  (i)  the  al&  lobuli  centralis,  (2)  the  anterior 
crescentic  lobule,  (3)  the  posterior  crescentic  lobule,  (4)  the  postero-siiperior  lobule. 


Lobus  Lingulae. — The  lingula,  the  extreme  anterior  end  of  the  superior  worm,  is  not  free, 
but  lies  attached  to  the  upper  surface  of  the  superior  medullary  velum,  covered  by  the  over- 
hanging adjacent  part,  lobulus  centralis,  of  the  worm,  which  must  be  displaced  to  expose  the 


FIG.  939. 


Ala  lobuli  centralis 


Anterior  notch 


Lobulus  centralis 


Anterior 
crescentic  lobule 


Posterior 
crescentic  lobule 


Postero-superior 
lobule 


Postcentral  fissure 
Culmen 

Preclival  fissure 
Postclival  fissure 


Clivus 


Great  horizontal  fissure 

Postero-inferior  lobule 


Folium  cacuminis 


Tuber 
Cerebellum  viewed  from  above. 


structure  in  question.  The  lingula  consists  of  a  tongue  of  gray  matter,  composed  of  five  or  six 
rudimentary  transverse  folia,. that  overlies  the  median  and  lower  part  of  the  superior  medullary 
velum  and,  therefore,  is  behind  the  upper  part  of  the  fourth  ventricle  (Fig.  938).  Occasionally 
the  lingula  is  prolonged  laterally  by  rudimentary  folia  onto  the  superior  cerebellar  peduncles,  in 
which  case  these  extensions,  known  as  the  alae  lingula;  (vincula  lingulae)  are  reckoned  as  tin- 
lateral  divisions  of  the  lobus  lingulae. 

Lobus  Centralis.— The  median  part  of  the  subdivision  includes  the  second  segment  of  the 
upper  worm,  the  central  lobule  (lobulus  centralis),  that  lies  chiefly  at  the  bottom  of  the  anterior 
notch  and  is  visible  to  only  a  very  limited  extent  on  the  upper  surface  of  the  cerebellum.  The 
central  lobule  consists  of  from  15-18  folia,  but  not  infrequently  is  divided  into  two  sets  of  leaflets, 
which  then  are  collectively  somewhat  more  numerous.  It  is  separated  from  tin-  lingula  by  the 
precentral  fissure  and  from  the  culmen  by  the  postcentral  fissure.  On  each  side  the  central 
folia  are  prolonged  into  a  triangular  tract  that  curves  along  the  side  of  the  anterior  notch,  form- 
ing a  lateral  wing-like  lobule,  the  ala  (ala  lobuli  centralis).  The  two  alae,  in  conjunction  with 
the  median  worm-segment,  constitute  the  lobus  centralis. 

Lobus  Culminis.— The  third  division  of  the  upper  worm  includes  the  most  prominent  part 
of  the  upper  surface  of  the  hemisphere  and,  being  the  crest  or  summit  of  the  general  elevation. 


THE    CEREBELLUM.  1085 

the  monticulus,  is  called  the  culmen  (oilmen  monticuli).  It  is  formed  by  a  half  dozen  or  more 
longer  and  shorter  folia  that  laterally  are  continuous  with  a  lunate  area  of  the  hemisphere  known 
as  the  anterior  crescentic  lobule  (pars  anterior  lobuli  quadrangularis).  The  latter  is  the  most 
anterior  division  of  the  upper  surface  of  the  hemisphere  and  is  a  broad  crescentic  tract  limited 
behind  by  the  preclival  fissure(sulcus  superior  anterior).  The  two  anterior  crescentic  lobules  and 
the  culmen  constitute  the  lobus  culminis. 

Lobus  Clivi. — The  fourth  segment  of  the  superior  worm  slopes  rapidly  downward  from  the 
culmen  and  receives  the  name  clivus  (declive  monticuli).  It  is  separated  from  the  preceding  part 
of  the  worm  by  a  deep  cleft,  the  central  part  of  the  preclival  sulcus,  which  on  account  of  its  mor- 
phological importance  has  been  called  the  fissura  prima  (Elliot  Smith).  Laterally  the  clivus  is 
connected  on  each  side  with  the  posterior  crescentic  lobule  (pars  posterior  lobuli  quadrangularis) 
which  resembles  the  lobule  in  front  and  is  separated  from  the  one  behind  by  the  postclival 
fissure  (sulcus  superior  posterior).  The  clivus  and  the  two  posterior  crescentic  lobules  constitute 
the  lobus  clivi. 

The  two  crescentic  lobules,  the  anterior  and  posterior,  are  regarded  by  German  anatomists 
as  constituting  one  tract,  the  lobulus  quadrangularis,  of  which  the  crescentic  lobes  then  become 
the  pars  anterior  and  pars  posterior  respectively. 

Lobus  Cacuminis. — The  fifth  and  last  segment  of  the  superior  worm,  the  folium  cacuminis 
(folium  vermis),  varies  greatly  in  its  details.  It  consists  of  a  narrow  plate  that  lies  between 
the  clivus  above  and  the  tuber  below  and  includes  usually  only  one  or  two,  exceptionally 
as  many  as  five  or  six,  small  folia.  Sometimes  it  reaches  the  level  of  the  adjoining  parts  of 
the  worm,  of  which  it  forms  the  posterior  end  ;  at  other  times  it  is  so  sunken  and  buried  that 
its  presence  can  be  demonstrated  only  after  separating  the  clivus  and  tuber,  with  either  of 
which  it  is  occasionally  joined.  At  best  it  is  insignificant  in  comparison  with  the  large 
crescentic  tracts,  the  postero-superior  lobules,  that  it  connects.  The  postero-superior  lobule 
(lobulus  semilunaris  posterior)  includes -the  remainder  of  the  upper  cerebellar  hemisphere  of 
which  it  forms  the  most  expanded  and  lateral  tract.  In  front  it  is  separated  from  the  posterior 
crescentic  lobule  by  the  postclival  fissure  and  behind  is  limited  by  the  great  horizontal 
sulcus,  which  it  overhangs  at  the  side.  The  folium  cacuminis  and  the  two  postero-superior 
lobules  constitute  the  lobus  cacuminis. 

LOBES  AND  FISSURES  OF  THE  LOWER  SURFACE. — The  inferior  surface  of 
the  cerebellum  is  modified  by  a  wide  depression,  the  vallecula,  in  the  broader 
upper  half  of  which  the  posterior  surface  of  the  tapering  medulla  oblongata  is 
received.  The  bottom  of  the  valley  is  occupied  by  the  irregular  projection  of 
the  inferior  worm,  which,  when  the  brain-stem  is  in  place,  is  covered  and  not 
seen,  except  at  its  posterior  third  (Fig.  940).  After  removal  of  the  pons  and 
medulla  by  cutting  through  the  cerebellar  peduncles  and  the  medullary  vela,  not 
only  the  entire  inferior  worm  is  exposed,  but  also  the  lobulus  centralis  and  its 
alse  are  seen  to  good  advantage.  The  inferior  worm  is  separated  on  each  side 
from  the  adjacent  surfaces  of  the  cerebellar  hemispheres  by  a  groove,  the  sulcus 
valleculae,  that  is  deepened  in  its  anterior  third  by  the  close  apposition  of  its  lateral 
boundary  (the  tonsil)  with  the  worm. 

The  connections  between  the  divisions  of  the  inferior  worm — from  before  back- 
ward (i)  the  nodule,  (2)  the  iivula,  (3)  the  pyramid  and  (4)  the  tuber — and  the 
related  parts  of  the  hemisphere  are  less  evident  and  direct  than  on  the  upper  surface 
of  the  cerebellum.  The  inferior  surface  includes  four  lobules  which,  from  before 
backward,  are:  (i)  the  flocculus,  (2)  the  tonsil,  (3)  the  biventral  lobule  and  (4)  the 
postero-inferior  lobule. 

Lobus  Noduli. — The  nodule  (nodulus),  the  most  anterior  segment  of  the  inferior  worm, 
varies  much  in  size  and  form,  but  frequently  appears  as  a  rounded  triangular  prominence,  made 
up  of  about  a  dozen  folia,  that  are  limited  at  the  sides  by  the  sulcus  valleculae  and  behind  by  the 
postnodular  fissure.  The  relation  of  the  nodule  to  the  inferior  medullary  velum  is  somewhat 
analogous,  but  less  intimate,  to  that  of  the  lingula  to  the  superior  velum.  The  two  structures  are 
more  or  less  extensively  united,  and  the  nodule  thus  excluded  from  the  fourth  ventricle  by  the 
inferior  velum  that  passes  beneath  the  inferior  worm  to  the  apex  of  the  posterior  recess  of 
the  ventricle  (Fig.  938). 

The  division  of  the  hemisphere  associated  with  the  nodule,  the  flocculus,  lies  at  some 
distance  from  the  worm  and  appears,  on  either  side  of  the  cerebellum,  as  a  wedge-shaped 
group  of  short  irregular  folia  that  project  between  the  .middle  cerebellar  peduncle  and  the 
anterior  border  of  the  hemisphere.  When  well  developed  it  may  touch  the  adjacent  margin 
of  the  anterior  crescentic  lobule  of  the  upper  surface.  In  addition  to  the  chief  floccules, 


io86  HUMAN   ANATOMY. 

composed  of  from  ten  to  twelve  leaflets,  a  second  and  smaller  set,  known  as  the  paraflocculus 
or  accessory  flocculus,  lies  behind  and  lateral  to  the  main  group,  often  completely  buried  beneath 
the  overhanging  margin  of  the  bi ventral  lobule.  In  the  embryo  and  in  many  mammals,  the 
paraflocculus  is  of  considerable  size  and  then  shares  the  relatively  much  greater  development 
of  the  flocculus  than  seen  in  the  adult  human  brain.  The  connection  between  the  flocculus 
and  the  nodule  is  established  by  the  lateral  part  of  the  inferior  medullary  velum,  which 
constitutes  the  peduncle  of  white  matter  for  the  floccular  folia.  In  this  manner  the  nodule 
and  the  two  flocculi,  with  the  intermediate  part  of  the  medullary  velum,  constitute  the 
lobus  noduli. 

Lobus  Uvulae. — The  uvula,  the  next  part  of  the  inferior  worm,  is  laterally  compressed 
between  the  deeper  parts  of  .the  two  tonsils.  It"  varies  in  form  and  often  appears  as  a  narrow 
ridge-like  structure,  triangular  on  section,  of  which  the  median  crest  alone  is  seen  when  the 
tonsils  are  in  place.  The  uvula  is  limited  in  front  by  the  postnodular  fissure,  and  behind  by 
the  prepyramidal,  which  laterally,  as  the  post-tonsillar  fissure,  curves  outward  along  the  postero- 
lateral  border  of  the  tonsil.  The  free  median  surface  of  the  uvula  is  usually  cleft  into  two  or 
three  major  subdivisions,  which  in  turn  are  scored  by  shallower  incisions,  so  that  from  six  to  ten 
leaflets  are  present.  Some  two  dozen  additional  folia  mark  the  hidden  lateral  surfaces,  the 
entire  number  being  thus  usually  raised  to  thirty  or  more. 

The  tonsil  or  amygdala  (tonsilla),  the  segment  of  the  hemisphere  associated  with  the  uvula, 
is  a  pyramidal  mass  lying  between  the  worm  and  the  biventral  lobule  and  forming  the  central 
zone  of  the  general  quadrant  embracing  the  lower  surface  of  the  entire  hemisphere.  The  free 
convex  inferior  surface  of  the  tonsil  is  irregularly  triangular  in  outline  and  bounded  by  a  rela- 
tively straight  median  margin  (along  the  sulcus  valleculae),  an  outwardly  arched  postero-lateral 

FIG.  940. 

Lobulus  centralis  Ala  lobuli  centralis 

Superior  cerebellar  peduncle  •  

^^^..^  f'^%m2i^^^^<^^' -—Superior  medullary  velum 

Middle  cerebellar  peduncle 


Inferior. ,,--U^  «^. Fourth  ventricle 

medullary  velum 

Great 

horizontal  fissure  ^  ^SJfl^'  -   ^^t— Ife'Z  "-r^^TIUBs^^k-  Nodule 

Accessory  flocculus 

Postero-inferior   ™   '     -     "  '        '^      '"^         •— ^»<i       •.  M-  Flocculus 

lobule      ^^^_^  im  t     t i  r    ,._^^_.,,       .          ^     ,  ,^^^^^_ 

I'vuhi 

J^^^H  Os'  .  '    .VHHHL     ~-    i  If  «•     i     i     .Vi^^m 

Biventral  lobule" 

l^W        -IT 

Pyramid 
Posterior  notch 
Tonsil 

Inferior  aspect  of  cerebellum,  after  removal  of  pons  and  medulla. 

border  (along  the  curved  posttonsillar  fissure)  and  a  notched  anterior  edge.  This,  the  chief 
surface,  is  marked  by  a  straight  furrow  that  extends  from  the  indentation  on  the  anterior  border 
backward  and  inward  and  marks  a  line  along  which  the  curved  folia,  from  nine  to  fourteen  in 
number,  abut.  Of  the  other  surfaces  bearing  folia— the  median,  posterior  and  lateral— that 
directed  towards  the  uvula  (median)  alone  is  entirely  unattached,  the  others,  with  the  superior, 
receiving  the  stalk  of  white  matter.  The  deeper  part  of  the  tonsil  is  subdivided,  so  that  on 
removing  the  larger  and  more  superficial  portion  of  the  amygdala  a  buried  and  accessory 
segment  of  its  mass  often  remains.  Beneath  (really  above)  the  tonsil,  a  narrow  ton-iu-, 
marked  with  short  transverse  folia,  stretches  from  the  posterior  part  of  tin-  uvula  across  the  roof 
of  the  space  occupied  by  the  tonsil  to  the  upper  and  lateral  part  of  the  amygdala.  This  tract, 
known  as  the  furrowed  band  (alae  uvulae)  connects  the  worm  with  the  hemisphere  and  thus 
joins  the  uvula  and  the  two  tonsils  into  the  lobus  uvula-  The  posterior  border  of  tin- 
furrowed  band  is  free,  whilst  its  anterior  one  is  continuous  with  tin-  inferior  medullary  \vhmi. 
After  removal  of  the  tonsil  by  cutting  through  its  supero-lateral  stalk,  a  deep  recess  is  left, 
which  is  bounded  medially  by  the  uvula  and  laterally  by  the  bivi-ntral  lobule  and  roofed 
in  by  the  furrowed  band  and  the  inferior  velum.  To  this  space  the  older  anatomists  gave  the 
name,  "bird's  ni-st  "  (nidus  aris}.  . 

Lobus  Pyramidis.— The-  pyramid  (pyramis)  the  segment  of  the  inferior  worm  lying  behllM 
the  uvula  and  in  front  of  the  tuber,  is  partly  covered  by  the  tonsils.     Posterior  to  the  latter 


THE    CEREBELLUM.  1087 

it  is  seen  at  the  bottom  of  the  vallecula  between  the  median  areas  of  the  bi ventral  lobules, 
where  it  forms  the  most  prominent  division  of  the  worm.  It  is  an  elongated  club-shaped 
mass,  attached  by  a  narrow  stalk  and  separated  from  the  adjacent  parts  of  the  worm  by  the 
prepyramidal  and  postpyramidal  fissures  and  from  the  hemispheres  by  the  sulci  valleculai. 
The  convex  inferior  surface  usually  presents  from  5-8  superficial  folia,  those  towards  the 
uvula  being  longer  than  those  directed  towards  the  tuber.  After  removal  of  the  tonsil,  a 
narrow  band,  the  connecting  ridge,  is  seen  passing,  on  each  side,  from  the  anterior  part  of  the 
pyramid  to  the  adjacent  mesial  end  of  the  biventral  lobe,  which,  in  this  manner,  is  brought  into 
relation  with  the  worm. 

The  biventral  lobule  (lobulus  biventer)  ordinarily  consists,  as  its  name  implies,  of  two  sub- 
divisions, which  together  appear  on  the  surface  as  a  curved  zone,  the  extremities  of  which  are 
more  contracted  than  the  intermediate  tract  that  attains  a  breadth  of  15  mm.  and  more.  The 
details  of  form  and  foliation  are  quite  variable,  the  lobule  being  not  only  sometimes  much 
broader  than  usual,  but  farther  subdivided,  so  that  three,  instead  of  two,  tracts  are  included. 
The  broader  outer  end  of  the  lobule  reaches  the  anterior  margin  of  the  hemisphere,  and  the 
narrowed  inner  end  the  vallecula,  in  consequence  of  which  the  component  superficial  concentric 
leaflets,  some  twelve  to  sixteen  in  number,  are  compressed  and  thinner  as  they  approach  the 
sulcus  valleculae.  The  biventral  lobule  is  separated  from  the  tonsil,  around  which  it  curves,  by 
the  lateral  extension  of  the  prepyramidal  or  post-tonsillar  fissure  and  is  limited  behind  by  the 
arched  postpyramidal  fissure. 

Lobus  tuberis. — The  tuber  (tuber  vermis)  forms  the  most  posterior  division  of  the 
inferior  worm  and  lies  beneath  the  great  horizontal  fissure  when  that  sulcus  is  continuous 
across  the  mid-line.  When  the  folium  cacuminis  is  small  and  buried,  the  tuber  comes 
into  close  relation  with  the  lower  end  of  the  clivus,  the  three  divisions  of  the  worm  just 
mentioned  all  springing  from  a  common  stalk  of  white  matter.  The  tuber  is  of  a  general 

FIG.  941. 

Superior  worm 
Roof  of  fourth  ventricle  (lobulus  centralis) 

Cerebellum,  seen  from  below  after  removal  of  tonsils. 

conical  form,  with  the  base  directed  towards  the  pyramid,  from  which  it  is  separated  by  the 
postpyramidal  fissure,  and  its  apex  projecting  into  the  posterior  cerebellar  notch.  It  presents 
a  few,  from  2-4,  superficial  folia,  which  model  the  posterior  pole  of  the  worm,  as  viewed  from 
behind  and  above. 

The  tuber  is  directly  connected  on  each  side  with  a  considerable  crescentic  tract,  the 
postero-inferior  lobule  (lobulus  semilunaris  inferior),  that  is  limited  in  front  by  the  lateral 
extension  of  the  postpyramidal  fissure  (sulcus  inferior  anterior)  and  behind  by  the  great  hori- 
zontal fissure.  After  emerging  from  the  sulcus  valleculae,  the  folia  rapidly  expand  into 
a  lunate  tract,  from  15-25  mm.  in  its  widest  part,  that  forms  the  immediate  posterior  border 
of  the  hemisphere.  The  postero-inferior  lobule  is  usually  described  as  divided  into  two 
parts,  an  anterior  and  a  posterior,  by  the  postgracile  fissure  (sulcus  inferior  posterior),  but 
quite  frequently  further  subdivision  of  the  superficial  folia,  from  12-18  in  number,  results 
in  defining  three  sublobules.  The  anterior  of  the  two  conventional  subdivisions  is  a  narrow 
tract  of  fairly  uniform  width  to  which  the  name  lobulus  gracilis  is  applied.  The  lunate 
posterior  area,  much  less  regular  in  contour  and  foliation,  is  known  as  the  inferior  crescentic 
lobule  (lobulus  semilunaris  inferior)  and  sometimes  presents  evidence  of  subdivision  into 
two  secondary  crescentic  areas.  The  postero-inferior  lobules  and  the  tuber  constitute  the 
lobus  tuberis. 


io88  HUMAN   ANATOMY. 

In  recapitulation,  the  foregoing  cerebellar  lobes,  with  their  component  worm-segments  and 
associated  hemisphere-tracts,  and  the  intervening  fissures  may  be  followed  in  order,  from  the 
anterior  and  superior  end  of  the  worm  to  its  front  and  lower  pole.  Although  not  agreeing 
with  a  morphological  division,  such  grouping1  is  convenient  as  applied  to  the  adult  human 
cerebellum. 

THE  LOBES  OF  THE  CEREBELLUM. 

WORM  HEMISPHERE  LOBE 

Lingula  (Vinculum  linguke)  Lobus  lingulae 

— Su/cus  precentralis — 
Lobulus  centralis  Ala  lobuli  centralis  Lobus  centralis 

-  Sulcus  postcentralis    — 

Culmen  monticuli  Lobulus  lunatus  anterior  Lobus  culminis 

—  Sulcus  preclivalis  — 

Clivus  monticuli  Lobulus  lunatus  posterior  Lobus  clivi 

—  Sulcus  postclivalis  — 

Folium  cacuminis  Lobulus  postero-superior  Lobus  cacuminis 

— Sulcus   horizontalis — 
Tuber  vermis  Lobulus  postero-inferior  Lobus  tuberis 

— Sulcus  postpyramidalis — 
Pyramidis  Lobulus  biventer  Lobus  pyramidis 

—  Sulcus  prepyramidalis  — 
Uvula  Tonsilla  Lobus  uvulae 

-  Sulcus  postnodularis  - 

Nodulus  Flocculus  Lobus  noduli 

Architecture  of  the  Cerebellum. — With  the  exception  of  where  the  robust 
peduncular  collections  of  nerve-fibres  enter  the  hemispheres  and  immediately  above 
the  dorsal  recess  of  the  fourth  ventricle,  the  cerebellum  is  everywhere  covered  by  a 
continuous  superficial  sheet  of  cortical  gray  matter  which  follows  and  encloses  the  sub- 
divisions of  the  white  core.  The  latter,  as  exposed  in  sagittal  sections  of  the  hemi- 
sphere, is  seen  to  be  a  compact  central  mass  of  white  matter,  from  which  stout  stems 
radiate  into  the  various  lobules.  From  these,  the  primary  stems,  secondary  branches 
penetrate  the  subdivisions  of  the  lobules,  and  from  the  sides  of  these,  in  turn,  smaller 
tracts  of  white  matter,  the  tertiary  branches,  enter  the  individual  folia.  Over  these 
ramifications  of  the  white  core,  the  cortical  gray  matter  stretches  as  a  fairly  uniform 
layer,  about  1.5  mm.  thick,  that  follows  the  complexity  of  the  folia  and  fissures. 
The  resulting  arborization  and  the  contrast  between  the  white  and  gray  matter  are 
particularly  well  shown  in  sections  passing  at  right  angles  to  the  general  direction  of 
the  folia.  This  disposition  is  especially  evident  in  median  sagittal  sections  (Fig.  938), 
where  the  less  bulky  medullary  substance  of  the  worm,  also  known  as  the^w/w 
irapezoidcum,  and  its  radiating  branches  produce  a  striking  picture,  to  which  the 
name,  arbor  vitce  cerebelli,  is  applied. 

The  Internal  Nuclei.— In  addition  to  and  unconnected  with  the  cortical 
layer,  four  paired  masses  of  gray  matter,  the  internal  nuclei— one  of  considerable 
size  and  three  small — lie  embedded  within  the  white  matter. 

The  dentate  nucleus  (nucleus  dentatus),  or  corpus  dentatnni.  the  largest  and 
most  important  of  the  internal  nuclei,  consists  of  a  plicated  sac  of  gray  matter 
(  Fig.  951)  and  resembles  in  many  respects  the  inferior  olivary  nucleus.  Jke  the 
latter,  it  is  a  crumpled  thin  lamina  of  gray  matter  which  is  folded  on  itself  into  a 
pouch,  enclosing  white  matter,  through  whose  medially  directed  mouth,  termed  the 
hilnm,  emerge  'many  fibre-constituents  of  the  superior  cerebellar  peduncle, 
dentate  nucleus  never  encroaches  upon  the  core  of  the  worm,  but  lies  embedded 
within  the  anterior  part  of  the  median  half  of  the  hemisphere,  with  its  long  axis 

1  Modified  from  Schafrr  and  Thane  in  Quain's  Anatomy,  Tenth  Edition. 


THE   CEREBELLUM. 


1089 


directed  forward  and  somewhat  inward  and,  therefore,  slightly  oblique  to  the  sagittal 
plane.  Anteriorly  the  nucleus  reaches  the  level  of  a  frontal  plane  passing  through 
the  precentral  fissure  ;  laterally  it  extends  to  about  the  middle  of  the  hemisphere 
(Ziehen) ;  whilst  medially  its  postero-inferior  end  comes  into  such  close  relation  with 
the  fourth  ventricle  that  a  slight  elevation,  eminentia  nuclei  dentati,  is  produced  on 
the  lateral  ventricular  wall.  In  its  longest  (antero-posterior)  dimension  the  nucleus 
measures  from  1 5-20  mm. ,  and  in  breadth  about  half  as  much. 

Of  the  other  paired  internal  collections  of  gray  matter — the  nucleus  fastigii,  the 
nucleus  emboliformis  and  the  nucleus  globosus — the  nucleus  fastigii,  or  the  roof 
nucleus,  is  the  best  defined.  It  lies  within  the  core  of  the  worm,  in  the  lower  part 
of  the  corpus  trapezoideum,  very  close  to  the  mid-line  and  to  its  fellow  of  the  oppo- 
site side.  In  its  general  form  the  nucleus  is  egg-shaped,  with  the  posterior  pole 
somewhat  prolonged,  and  in  its  sagittal  diameter  measures  about  10  mm.  and  in  the 
transverse  dimension  about  half  as  much.  The  nucleus  extends  from  the  base  of  the 


FIG.  942. 


Nucleus  fastigii 
Nucleus  globosus 


Nucleus 
emboliformis 


Restiform  body 
(external  division) 

Nucleus  deritatus 


Restiform  body  "- 
(internal  division)  •/•. 


Ventral 
cochlear  nucleus 


rt*L 


V.V 


Superior  worm 


Decussatipn  of 
roof-nuclei 


Fourth  ventricle 


va 

Vestibular  nerve 

Inferior  olivary   nucleus 


Substantia 
"  gelatinosa 

Spinal  root 
'  of  V  nerve 

Flocculus 


Posterior  longitudinal  fasciculus 


—  Pyramidal  tracts 


Section  across  upper  part  of  fourth  ventricle,  showing  internal  cerebellar  nuclei ;  new-born  child.     X  3/^. 
Weigert-Pal  staining.     Preparation  by  Professor  Spiller. 

lingula  to  the  stem  of  the  pyramid,  and  in  frontal  sections  (Fig.  942)  appears  circu- 
lar in  outline  and  closely  related  with  fibre-tracts  that  in  part  end  in  the  nucleus  of 
the  opposite  side. 

The  nucleus  emboliformis,  or  embolus,  is  an  irregular  wedge-shaped  plate 
of  gray  matter  that  partly  closes  the  hilum  of  the  dentate  nucleus,  in  much  the  same 
manner  that  the  median  accessory  olivary  nucleus  obstructs  the  mouth  of  the  chief 
olivary  nucleus.  In  its  sagittal  diameter  it  measures  about  15  mm. ,  and  in  the  vertical 
one  approximately  one-fourth  as  much  ;  it  decreases  in  thickness  from  about  3  mm. 
in  front  to  a  slender  wedge  behind.  The  embolus  rests  upon  the  superior  cerebellar 
peduncle,  its  front  end  extending  to  within  a  few  millimeters  of  the  precentral 
fissure  and  its  posterior  pole  reaching  almost  as  far  back  as  the  dentate  nucleus, 
with  which  it  is  united  by  a  limited  connection. 

The  nucleus  globosus  lies  close  to  the  medial  side  of  the  embolus,  between 
the  latter  and  the  roof  nuclei.  In  its  general  form  the  nucleus  is  comparable  to  a 
sphere  attached  to  a  sagittally  directed  stalk  (Ziehen).  The  globular  head,  about 
5  mm.  in  diameter  and  somewhat  transversely  compressed,  lies  above  the  tonsil  and 
is  continuous  with  the  stalk  that  extends  backward  for  a  distance  of  about  8  mm. 

By  means  of  uncertain  and  limited  attachments  the  nucleus  globosus  is  loosely 
connected  with  the  roof  nucleus  and  the  embolus,  and  also  joins  the  postero-inferior 


IOQO 


HUMAN   ANATOMY. 


FIG.  943. 


Molecular  layer 
Granule  layer 

White  matter 
'Cells  of  Purkinje 


part  of  the  dentate  nucleus.  Since  the  latter  and  the  embolus  are  likewise  slightly 
connected,  it  is  evident  that  all  four  internal  nuclei  are  more  or  less  continuous 
masses  of  gray  matter. 

In  structure  the  internal  nuclei  differ  markedly  from  the  cerebellar  cortex, 
since  in  the  main  they  are  composed  of  irregularly  disposed  nerve-cells  of  one  kind 
interspersed  with  numerous  nerve-fibres.  The  dentate  nucleus  contains  cells  from 
.020-.  030  mm.  in  diameter  whose  bodies  are  angular  or  stellate  in  outline  and  pig- 
mented  in  varying  degrees.  Their  processes  are  usually  so  disposed  that  the  axones 
pass  into  the  medullary  substance  enclosed  by  the  plicated  lamina  and  the  dendrites 
into  the  surrounding  white  matter  of  the  hemisphere.  Numerous  fibres  enter  the 
dentate  body  from  without,  many  being  the  axones  of  the  Purkinje  cells,  and  break 
up  into  a  rich  plexus  within  the  folded  sheet  of  gray  substance..  Since  the  nucleus 
emboliformis  and  the  nucleus  globosus  are  only  incompletely  isolated  parts  of 
the  dentate  nucleus,  their  structure  corresponds  closely  with  that  of  the  chief  mass. 

The  roof-nuclei,  on  the 
contrary,  possess  cells  of 
much  larger  size  (.040  to 
.080  mm.),  more  rounded 
form  and  greater  uniform- 
ity in  tint,  although  their 
general  yellowish  brown 
color  implies  less  intense 
pigmentation.  Numerous 
strands  of  nerve-fibres  sub- 
divide the  nucleus  into 
secondary  areas,  while 
some  large  transversely 
coursing  bundles  establish 
a  decussation  with  the  roof- 
nucleus  of  the  opposite 
side. 

The  Cerebellar 
Cortex.— When  the  folia 
are  sectioned  at  right 
angles  to  their  course,  each 
leaflet  composing  the 
characteristic  arborization 
is  seen  to  consist  of  a  cen- 
tral tract  of  white  medul- 
lary substance,  covered  in 
by  the  continuous  super- 
ficial sheet  of  cortical  gray 
matter.  The  latter,  usually  somewhat  less  than  one  millimeter  in  thickness,  includes 
two  very  evident  strata — the  outer  and  lighter  molecular  layer  and  the  inner  and 
darker  granule  layer. 

The  molecular  layer  is  of  uniform  thickness,  about  4  mm. ,  and  contains  three 
varieties  of  nerve-cells — the  Purkinje  cells,  the  basket  cells  and  the  small  cortical 
cells.  The  Purkinje  cells,  the  most  distinctive  nervous  elements  of  the  cerebellum, 
occupy  the  deepest  part  of  the  molecular  layer,  where  they  are  disposed  in  a  single 
row  along  the  outer  boundary  of  the  subjacent  granular  layer.  The  cells  are  most 
numerous  and  more  closely  placed  upon  the  summit  of  the  folium  and  fewer  and 
more  scattered  along  the  fissures,  in  which  situation  they  are  also  often  of  less  typical 
pyriform  shape.  They  possess  a  large  flask-like  body,  about  .060  mm.  in  diameter, 
from  the  pointed  and  outwardly  directed  end  of  which  usually  one,  sometimes  more, 
robust  dendritic  process  arises.  The  chief  process,  relatively  thick  and  very  short, 
soon  divides  into  two  branches,  which  at  first  diverge  and  run  more  or  less  horizontally 
and  then  turn  sharply  outwanl  to  assume  a  course  vertical  to  the  surface  and  undergo 
repeated  subdivision.  The  arrangement  of  the  larger  dendrites  is  very  striking  and 
recalls  the  branching  of  the  antlers  of  a  deer.  Tin-  smaller  processes  arise  at  varying 


Central  limb 
of  white  matter 

Transverse  section  of  cerebellar  folium,  showing  relations  of  cortex  to 
underlying  white  matter.     X  10. 


THE    CEREBELLUM. 


1091 


and  often  acute  angles,  the  completed  division  resulting,  as  displayed  by  silver 
impregnations  (Fig.  944),  in  an  arborization  of  astonishing  richness  and  extent  that 
often  reaches  almost  to  the  outer  boundary  of  the  molecular  layer.  The  dendritic 
ramification  of  each  cell  is  limited,  however,  to  a  narrow  zone  extending  across  the 
folium  and,  hence,  when  examined  in  sections  cut  parallel  with  the  plane  of  the  folium, 
these  expansions  are  found  to  be  confined  to  tracts  separated  by  zones  of  the  molecular 
layer  that  are  uninvaded  by  the  dendrites  of  the  Purkinje  cells.  The  axones  of 
the  latter  arise  from  the  rounded  basal  or  deeper  end  of  the  pyriform  body  and  at 
once  enter  the  granular  layer,  which  they  traverse  to  gain  the  white  medullary  core 
of  the  folium.  In  their  course  the  axones  give  off  a  few  recurrent  collaterals  that 
end  within  the  molecular  layer  in  the  vicinity  of  the  bodies  of  the  cells  of  Purkinje. 

The  stellate  or  basket  cells  lie  at  different  planes,  but  chiefly  within  the 
deeper  half  of  the  molecular  layer.  They  possess  an  irregular  stellate  body,  from 
.010— .020  mm.  in  diameter,  from  which  several  dendrites  radiate.  Their  chief 
feature  of  interest  is  the 

remarkable      relation     of  FIG.  944. 

the  axone,  which  extends  A  B 

across  the  folium  in  an 
approximately  horizontal 
plane  along  and  to  the 
outer  side  of  the  row  of 
the  Purkinje  cells.  During 
this  course  the  axone  gives 
off  from  three  to  six 
collaterals  that  descend 
to  the  cells  of  Purkinje, 
whose  bodies  they  sur- 
round and  enclose  with  a 
basket  -  like  arborization, 
the  terminal  ramification 
of  the  main  process  itself 
ending  in  like  manner. 
By  means,  of  this  arrange- 
ment each  basket  cell  is 
brought  into  close  relation 
with  several  of  the  larger 
elements. 

The  small  cortical 

cells  occur  at  all  depths,  but  are  most  numerous  in  the  more  superficial  planes, 
in  which  they  appear  as  diminutive  multipolar  elements  with  radiating  dendrites  and 
axones  of  uncertain  destination. 

The  granule  layer,  of  a  rust-brown  tint  when  fresh  and  deeply  colored  in 
stained  preparations,  is  thickest  on  the  summit  of  the  folia  and  thinnest  opposite  the 
bottom  of  the  sulci.  While  sharply  defined  from  the  overlying  molecular  layer,  it  is 
less  clearly  distinguished  from  the  medullary  substance.  The  granular  layer  con- 
tains two  varieties  of  nerve-cells — the  granule  cells  and  the  large  stellate  cells. 

The  granule  cells  are  very  small  (.ooy-.oio  mm.)  and  numerous  and  so  closely 
packed  that  they  confer  upon  the  stratum  its  distinctive  density.  They  are  provided 
with  from  three  to  six  short  radiating  dendritic  processes  that  end  in  peculiar  claw- 
like  arborizations  in  relation  with  other  granule  cells.  The  axpnes,  directed  towards 
the  surface,  enter  the  molecular  layer,  within  which,  at  various  levels  corresponding 
to  the  depth  of  the  cells,  they  undergo  T-like  division.  The  two  resulting  branches 
run  horizontally  and  lengthwise  and  in  the  folium — that  is,  parallel  to  the  surface  and 
at  right  angles  to  the  plane  of  expansion  of  the  dendrites  of  the  Purkinje  cells,  through 
the  arborizations  of  which  they  find  their  way  and  with  which  they  probably  come 
into  close  relation. 

The  large  stellate  cells  are  present  in  varying  number,  but  are  never  numer- 
ous. They  lie  close  to  the  outer  limit  of  the  granule  layer  and  possess  a  cell-body  of 
uncertain  and  irregular  form,  from  .030— .040  mm.  in  diameter,  from  which  usually 


Two  Purkinje  cells  from  silver  preparation  of  cerebellar  cortex;  A,  side 
view;  B,  cell  in  profile  ;  a,  axone.  X  10.  Preparation  made  by  Prof.  T.  G.  Lee. 


1092 


HUMAN   ANATOMY. 


several  richly  branched  dendrites  pass  in  various  directions,  but  largely  into  the 
molecular  layer.  The  axone  is  most  distinctive,  as  very  soon  after  leaving  the  cell  it 
splits  up  into  an  arborization  of  unusual  extent  and  complexity,  which,  however,  is 
confined  to  the  granular  layer.  These  cells,  therefore,  belong  to  those  of  type  II 
(page  998).  Since  by  their  processes  they  are  brought  into  intimate  relation  with 
a  number  of  other  neurones,  the  elements  under  consideration  are  probably  of  the 
nature  of  association  cells. 

The  nerve-fibres  encountered  within  the  cerebellar  cortex  (Fig.  945)  comprise 
three  chief  varieties,  (i)  The  first  of  these  includes  the  axones  of  the  cells  of  Purkinje 
which  contribute  no  inconsiderable  portion  of  the  fibres  passing  from  the  cerebellar 
cortex  to  other  parts,  either  of  the  cerebellum  itself  or  of  the  cerebrum  and  brain-stem. 
(2)  The  moss-fibres  destined  especially  for  the  granular  layer,  which  upon  enter- 

FIG.  945. 


Molecular  layer 


Granule  layer 


White  matter 


Moss-fibres 


Axones  of  Purkinje  cells 


Climbing  fibres 


Diagrammatic  reconstruction  of  part  of  folium,  illustrating  relations  of  nerve-cells  and  fibres  of  cerebellar  cor- 
tex ;  folium  is  shown  cut  transversely  and  longitudinally  ;  a,  Purkinje  cells  ;  b,  granule  cells ;  c ,  small  cortical  cells  ; 
d,  basket  cells  ;  e,  large  stellate  cells. 

ing  the  latter  break  up  into  a  number  of  branches  that  bear,  either  at  the  points  of 
division  or  at  their  ends,  thickenings  from  which  bundles  of  short  diverging  twigs  are 
given  off.  By  this  arrangement  each  moss-fibre  ends  in  relation  with  a  large  number 
of  granule  cells.  (3)  The  climbing-fibres,  so  named  (Cajal)  on  account  of  their 
tortuous  and  vine-like  course,  ascend  through  the  granular  to  the  molecular  layer, 
to  which  they  are  chiefly  if  not  exclusively  distributed,  where  they  entwine  and 
cling  to  the  primary  and  secondary  dendritic  processes  of  the  Purkinje  cells. 
Additional  fibres  encountered  within  the  granule  layer  are,  evidently,  the  axones  of 
t h<- granule  cells  and  the  collaterals  of  the  cells  of  Purkinje,  whilst  a  large  propor- 
tion of  the  fibres  within  the  molecular  layer  are  formed  by  the  ramifications  of  the 
axones  of  the  granule"  cells  and  of  the  basket  cells. 

The  neuroglia  forms  a  supporting  framework  of  considerable  density  both 
within  the  white  matter  and  the  cortex.  As  seen  in  preparations  colored  with  the 
usual  nuclear  stains,  the  neurogliar  elements  are  conspicuous  within  the  granule 
layer,  to  whose  numerous  small  nuclei  they  contribute  no  small  part.  The  cells 
occupying  the  outer  zone  of  the  granule  layer  exhibit  a  peculiar  arrangement  of  their 
processes  that  in  a  measure  recalls  the  disposition  of  those  of  the  Purkinje  cells.  In 


THE   CEREBELLUM.  1093 

addition  to  a  short  and  uncertain  centrally  directed  process,  the  irregular  cell  gives 
off  a  brush-like  group  of  nbrillae  which  penetrate  the  molecular  layer,  seldom  branch- 
ing, as  far  as  the  free  surface  of  the  folium,  when  they  end  beneath  the  pia  in  expan- 
sions that  become  condensed  and  unite  into  a  delicate  limiting  membrane.  The 
radial  disposition  of  the  neuroglia  fibres,  as  well  as  of  the  Purkinjean  dendrites, 
climbing  fibres  and  the  larger  blood-vessels,  confer  upon  the  molecular  layer  a 
vertical  striation  that  is  often  marked. 

The  Medullary  Substance.— The  white  matter  composing  the  core  of  the  cerebellar 
hemispheres  exhibits  several  fairly  definite  subdivisions,  among  which  may  be  distinguished  : 

1.  The  subcortical  layer,  from  .2-. 5  mm.  in  thickness,  that  extends  beneath  the  granule 
layer,  parallel  to  the  surface,  and  sweeps  around  the  bottom  of  the  deeper  fissures.     Within  the 
series  of  festoons  thus  formed  lie  the  association  tracts  that  connect  the  folia  and  lobules  of  the 
same  hemisphere. 

2.  The  commissural  tracts,  of  which  the  larger  lies  in  front  of  the  dentate  nucelus  and  the 
smaller  behind  this  nucleus,  are  continued  across  the  mid-line  and  into  the  opposite  hemisphere 
as  the  anterior  (superior)  and  the  posterior  (inferior)  cerebellar  decussations. 

3.  The  peridentate  stratum  that  comprises  a  fibre-complex  that  surrounds  the  nucleus 
dentatum. 

Within  the  medullary  substance  of  the  worm,  lie  : 

1.  The  superior  cerebellar  commissure,  a  robust  tract  of  transversely  coursing  fibres  that 
passes  in  front  of  the  roof-nucleus  and,  beyond  the  worm,  expands  on  each  side  into  the  main 
limbs  of  the  medullary  tree.     It  is  chiefly  by  the  decussating  fibres  within  this  commissure  that 
the  cortex  of  the  two  hemispheres  is  connected. 

2.  The  inferior  cerebellar  commissure  passes  behind  the  roof-nucleus  and  consists  of  a 
number  of  small  transversely  coursing  bundles. 

3.  The  decussation  of  the  roof-nuclei  constitutes  a  commissural  and  decussating  tract  distinct 
from  that  of  the  cerebellar  commissures  just  described.     The  rounded  bundles  traverse  the 
roof-nucleus,  particularly  its  superior  (anterior)  part,  more  distally  skirting  its  dorsal  margin 
and,  still  farther  backward,  invading  the  beginning  of  the  horizontal  medullary  limb. 

4.  The  median  sagittal  bundle  extends  from  the  superior  medullary  velum  beneath  the  roof- 
nucleus  into  the  medulla  of  the  worm  ;  above,  these  fibres  are  continued  upward  through  the 
velar  frenum  and  into  the  inferior  quadrigeminal  colliculus. 

In  addition  to  the  foregoing  tracts,  the  central  parts  of  the  branches  of  the  medullary  tree, 
not  only  of  the  hemispheres  but  also  of  the  worm,  are  occupied  by  longitudinally  coursing  fibres 
that  pass  directly  into  the  white  core,  and  thence  are  continued  into  the  cerebellar  peduncles  as 
the  afferent  and  efferent  paths  by  which  the  cerebellar  cortex  is  brought  into  relation  with  other 
parts  of  the  brain  and  spinal  cord. 

FIBRE-TRACTS  OF  THE  CEREBELLAR  PEDUNCLES.  . 

Repeated  mention  has  been  made  of  the  three  robust  arms  of  white  matter, 
the  peduncles,  that  enter  the  medullary  substance  of  the  cerebellum  and  serve 
to  transmit  the  fibre-tracts  that  connect  the  cerebellum  with  the  cerebrum,  the 
brain-stem  and  the  spinal  cord.  The  general  features  of  the  inferior,  middle  and 
superior  cerebellar  peduncles  are  described  in  connection  with  the  medulla,  the  pons 
and  the  mid-brain  respectively.  It  will  be  convenient  in  this  place,  in  connection 
with  the  cerebellum,  to  consider  more  in  detail  the  constituents  of  these  important 
pathways. 

The  Inferior  Cerebellar  Peduncle. — This  robust  stalk  (corpus  restiforme), 
also  known  as  the  restiform  body,  includes  not  only  the  tracts  connecting  the  cere- 
bellum with  the  spinal  cord,  but  also  those  that  link  the  cerebellum  and  the  medulla. 
Two  divisions,  the  spinal  and  the  bulbar,  are  therefore  often  recognized. 

The  chief  constituents  of  the  inferior  peduncle  are  :  • 

1.  The  direct  cerebellar  tract,  the  fibres  of  which  arise  from  the  cells  of  Clarke's  column, 
course  through  the  lateral  part  of  the  inferior  peduncle  and  end  in  the  cortex  of  the  anterior  part 
of  the  superior  worm  on  the  same  side,  some  fibres  reaching  the  opposite  side  of  the  worm  by 
way  of  the  superior  commissure. 

2.  The  arcuate  fibres  (anterior  and  posterior  superficial),  from  the  gracile  and  cuneate  nuclei 
of  the  same  and  the  opposite  side.    Additionally,  perhaps,  some  fibres  are  continued,  without  inter- 
ruption in  the  medullary  nuclei,  from  the  posterior  fasciculi  of  the  cord.    All  of  these,  direct  and 
indirect,  end  chiefly  within  the  cortex  of  the  superior  worm  of  the  same  and  the  opposite  side. 


1094  HUMAN   ANATOMY. 

3.  The  olivo-cerebellar  fibres,  chiefly  from  the  opposite  inferior  olivary  nucleus  but  to  a 
limited  extent  also  from  the  nucleus  of  the  same  side.     They  contribute  in  large  measure  to  the 
lormation  of  the  lateral  part  of  the  restiform  body  and,  on  reaching  the  cerebellum,  end  within 
the  cortex  of  the  hemisphere  and  worm,  as  well  as  within  the  fibre-complex  enveloping  the 
nucleus  dentatus.     Whilst  for  the  most  part  afferent,  it  is  probable  that  some  of  the  fibres  within 
the  tract  are  efferent  and  hence  conduct  impulses  in  the  contrary  direction. 

4.  Fibres  from  the  nucleus  lateralis  of  the  medulla,  which  pass  to  the  cortex  of  the  cere- 
bellar  hemisphere. 

5.  Fibres  from  the  arcuate  nucleus,  which  pass  to  the  cerebellar  cortex. 

6.  The  nucleo-cerebellar  tract,  comprising  fibres  from  the  cells  within  the  reception-nuclei 
of  the  trigeminal,  facial,  vestibular,  glosso-pharyngeal  and  vagus  nerves.     The  tract  occupies 
the  median  part  of  the  peduncle  and  ends  chiefly  in  the  roof-nucleus  of  the  same  and  of  the 
opposite  side. 

7.  Other  fibres  pass   in   reversed   direction   from   the   roof-nucleus   to  the  dorso-lateral 
(Deiters' )  vestibular  nucleus  of  the  auditory  nerve  and  thence,  as  the  vestibulo-spinal  tract, 
descend  through  the  medulla  into  the  antero-lateral  column  of  the  cord. 

8.  Additional  vestibular  (and,  possibly,  other  sensory-)  fibres  pass  without  interruption  by 
way  of  the  restiform  body  to  the  roof-nuclei  and  constitute  the  direct  sensory  cerebellar  tract 
of  Edinger. 

The  Middle  Cerebellar  Peduncle. — The  middle  peduncle  (brachium  pontis), 
which  continues  the  pons  laterally  into  the  medulla  of  the  cerebellum,  transmits  the 
fibres  whereby  the  impulses  arising  within  the  cerebral  cortex  are  conveyed  to  the 
cerebellum.  It  does  not  establish  direct  connections  between  the  cerebellar  hemi- 
spheres, as  it  might  be  supposed  to  do  from  its  transverse  position  and  intimate 
relation  with  the  cerebellar  hemisphere,  such  bonds  from  side  to  side  passing 
exclusively  by  way  of  the  commissures  within  the  worm. 

The  chief  constituents  of  the  middle  peduncle  are  : 

1.  The  continuations  of  the  fronto-cerebellar  and  temporo-occipito-cerebellar  tracts,  the 
fibres  of  which  arise  from  the  cortical  cells  within  the  frontal,   temporal  and  occipital  lobes 
respectively,  descend  through  the  internal  capsule  and  the  cerebral  cms,  and  end  around  the 
cells  of  the  pontine  nucleus.     From  the  latter  cells  arise  the  ponto-cerebellar  fibres,  the  imme- 
diate constituents  of  the  middle  peduncle,  that  for  the  most  part  cross  the  mid- line  and  traverse 
the  peduncle  to  be  distributed  to  all  parts  of  the  cortex  of  the  hemispheres  and  of  the  worm  and, 
possibly,  also  to  the  nucleus  dentatus.     A  small  number  of  these  fibres  do  not  decussate,  but 
pass  from  the  pontine  cells  to  the  cerebellar  cortex  of  the  same  side.     It  should  be  remembered 
that  the  pontine  nuclei  are  also  influenced  by  cortical  impulses  that  descend  by  way  of  the  pyra- 
midal tracts,  since  numerous  collaterals  from  the  component  fibres  of  these  motor  paths  end 
around  the  pontine  cells. 

2.  Efferent  cerebello-pontine  fibres,  distinguished  from  the  afferent  fibres  by  their  larger 
diameter,    originate   as   axones  of  the    Purkinje   cells   and   pass  from   the   cerebellar  cortex 
through  the  middle  peduncle  into  the  dorsal  part  of  the  pons,  where,  after  crossing  the  mid-line, 
they  are  believed  (Bechterew)  to  end  within  the  tegmentum  in  relation  with  the  cells  of  the 
nucleus  tegmenti  situated  close  to   the  raphe.     The  assumption,  often  made,  that  many  of  the 
efferent  cerebello-pontine  fibres  end  around  the  cells  of  the  nucleus  pontis,  lacks  the  support  of 
the  more  recent  observations. 

The  Superior  Cerebellar  Peduncle. — The  superior  peduncle  (brachium  con- 
junctivum)  forms,  with  its  fellow  of  the  opposite  side,  the  important  pathway  by  which 
the  cerebellar  impulses  are  transmitted  to  the  higher  centres  and,  eventually,  to 
the  cerebral  cortex,  as  well  as  indirectly  to  the  spinal  cord. 

Its  chief  constituents  are  (i)  the  cerebello-rubral  and  (2)  the  cerebello-thalamic  fibres 
collectively  known  as  the  cerebello-tegmental  tract.  The  principal  components  of  the  latter  are 
the  fibres  arising  from  the  cells  of  the  dentate  nucleus,  which,  emerging  from  the  hilum  of  the 
corpus  dentatum  and  receiving  augmentations  from  the  roof-nucleus  and,  probably,  to  a  limited 
extent  from  the  cortex  of  the  worm,  become  consolidated  into  the  rounded  arm  that  skirts  the 
supero-lateral  boundary  of  the  fourth  ventricle.  Converging  with  the  tract  of  the  opposite  side 
towards  the  mid-line,  the  peduncle  sinks  ventrally  and  disappears  beneath  the  corpora  <iuadri- 
gemina,  many  of  its  fibres  continuing  their  course  through  the  tegmentum  of  the  cerebral  peduncle 
into  the  snbthalamic  region  and  the  tli.ilamus.  On  reaching  a  level  corresponding  to  that  of 
the  upper  third  of  the  inferior  colliculi  of  the  quadrigemina  bodies,  the  tracts  of  the  two  sid<  s 
meet  and  begin  to  intermingle,  the  decussation  of  the  superior  peduncle  (Fig.  1112)  thus  estab- 


THE   CEREBELLUM. 


1095 


FIG.  946. 


lished  being  best  marked  opposite  the  superior  colliculi.  Above  this  decussation,  which,  how- 
ever, does  not  involve  all  of  its  fibres,  since  some  ascend  on  the  same  side,  the  cerebello-tegmental 
tract  is  in  large  measure  interrupted  in  the  red  nucleus  (nucleus  tegmenti  rubrum),  that  lies  within 
the  upper  part  of  the  tegmental  area  of  the  cerebral  crus  (page  1114).  The  fibres  not  ending 
around  the  cells  of  this  nucleus  are  continued  through  the  subthalamic  region  into  the  thalamus, 
in  relation  to  the  cells  of  which  they  terminate. 

Of  those  ending  within  the  red  nucleus,  the  majority  transfer  their  impulses  to  fibres  that 
arise  from  the  rubral  neurones  and  thence  proceed  to  the  thalamus  in  company  with  the  unin- 
terrupted   fibres.     From    the 
thalamus    the     impulses    are 
carried  by  the  thalamo-cortical 
paths  (page  1122)  to  the  cere- 
bral cortex,  the  cells  of  which 
are    thus    influenced    by   the 
coordinating  reflexes   of   the 
cerebellum. 

A  considerable  part  of 
the  impulses  conveyed  to  the 
red  nucleus  is  diverted  by  the 
axones  of  some  of  its  neurones 
into  an  entirely  different  path, 
namely,  the  rubro-spinal  tract, 
by  which  the  impulses  from 
the  cerebellum  are  carried 
through  the  brain-stem  and 
antero-lateral  column  of  the 
cord  to  the  anterior  root-cells 
of  the  spinal  nerves. 

From  the  foregoing 
descriptions  it  is  evident  that 
by  means  of  its  peduncles  the 
cerebellum  receives  no  small 
part  of.  the  sensory  impulses 
collected  by  the  spinal  and 
cranial  nerves  and,  in  turn, 
issues  the  impulses  necessary 
to  maintain  coordination  and 
equilibrium.  Such  impulses 
may  be  entirely  reflex,  as  in 
the  case  of  movements  per- 
formed automatically,  in  which 
instance  the  circuit  is  (a) 
from  the  spinal  cord  and  the 
medulla,  directly  or  indirectly, 
to  the  cerebellum  chiefly  by 
way  of  the  tracts  within  the 
inferior  cerebellar  peduncles  ; 
(b)  from  the  cerebellum  to  the 
motor  root-cells  within  the 
brain-stem  and  the  cord  by 
way  of  the  cerebello-vestibulo- 
spinal  tract  and  the  cerebello- 
rubro-spinal  tract. 

When  the  necessity 


teralis 


Posterior  tracts 


Diagram  illustrating  chief  components  of  cerebellar   peduncles ;    fibres 
nas 

arises    for    voluntary    efforts 

in    maintaining    equilibrium, 

the  circuit  includes   impulses 

from   the  cerebral   cortex,  in 

which   case  the  cerebello- 

rubro  -  thalamo  -  cortical    tract 

and  the  cortico-spinal  tract  form  the  most  direct  path.     As  accessory  to  this  an  indirect  path, 

impulses  by  way  of  the  cortico-ponto-cerebellar  and  the  cerebello-rubro-spinal  tracts,  may  be 

assumed  as  probably  taking  part  in  securing  the  necessary  motor  balance. 


passing  by  inferior  peduncle  (IP)  are  red  ;  those  by  superior  peduncle  (SP) 
are  blue;  those  by  middle  peduncle  (MP)  are  black;  C,  cerebrum;  T, 
thalamus;  1C,  internal  capsule;  R,  rod  nucleus;  Cb,  cerebellum;  d,  dentate 
nucleus;  p,  pontine  nucleus;  v,  l,o,  vestibular,  lateral,  and  inferior  olivary 
nuclei;  s,  reception  nuclei  of  sensory  nerves;  Sg.  spinal  ganglion;  i,  2, 
cerebello-rubral  fibres,  one  of  which  (4)  is  continued  downward  as  rubro- 
spinal  tract;  3,  cerebello-thalamic ;  5,  rubro-trialamic  ;  6,  thalamo-cortical; 
7,  fronto-pontine ;  8,  temporo-occipito-pontine ;  9,  10,  ponto-cerebellar  fibres. 


1096 


HUMAN   ANATOMY. 


THE  FOURTH  VENTRICLE. 

The  fourth  ventricle  (ventriculus  quartus),  the  persistent  and  modified  hind-brain 
segment  of  the  primary  neural  canal,  is  an  irregular  triangular  space  between  the 
pons  and  the  medulla  in  front,  and  the  inferior  cerebellar  worm  and  the  superior  and 
inferior  medullary  vela  behind.  The  lateral  boundaries  are  contributed  by  the  supe- 
rior and  inferior  cerebellar  peduncles.  Its  long  axis  is  approximately  vertical  and 
about  3  cm.  in  length,  measured  from  the  lower  extremity,  where  the  ventricle  is 
directly  continuous  with  the  central  canal  enclosed  within  the  medulla  "and  spinal 
cord,  to  the  upper  end,  where  it  passes  into  the  aqueduct  of  Sylvius.  Its  width  is 
greatest  (about  2.75  cm.)  somewhat  below  the  middle,  where  this  dimension  is 
increased  by  two  lateral  recesses,  one  on  each  side,  that  continue  the  cavity  of  the 
ventricle  over  the  restiform  body. 

The  Floor  of  the  Fourth  Ventricle. — The  floor  of  the  ventricle,  really  its 
anterior  wall,  when  viewed  from  behind  after  removal  of  the  cerebellum  and  the 
medullary  vela,  appears  as  a  lozenge-shaped  area  (fossa  rhomboidea).  The  upper  half 
of  the  floor  is  formed  by  the  dorsal  or  ventricular  surface  of  the  pons  and  is  bounded 

FIG.  947. 


Sylvian  aqueduct 


Superior 

posterior  recess 


Posterior  commissure 

Sylvian  aqueduct 
Isthmus 

Superior  median  sulcus 


Superior  lateral  sulcus 

Foramen 
of  Luschka 


Superior  posterior  recesses 


Lower  end  of  ventricle  containing  foramen  of  Majendie 

Cast  of  cavity  of  fourth  ventricle;  A,  from  the  side  ;  £,  from  above.     X   J.      (Retztus) 

laterally  by  the  upwardly  converging  superior  cerebellar  peduncles.  The  lower  half 
is  formed  by  the  ventricular  surface  of  the  open  part  of  the  medulla  and  is  bounded 
by  the  downwardly  converging  inferior  cerebellar  peduncles  and  the  clavae.  The 
narrow  lower  angle  of  the  rhombic  area,  long  known  as  the  calamus  scriptorius, 
corresponds  to  the  interval  between  the  clavae,  where  the  central  canal  of  the  cord 
communicates  with  the  fourth  ventricle.  The  upper  angle,  situated  beneath  the 
superior  medullary  velum  and,  therefore,  described  by  some  anatomists  as  belonging 
to  the  isthmus  of  the  hind-brain  (rhombencephalon),  marks  the  lower  end  of  the 
Sylvian  aqueduct.  The  length  of  the  rhombic  fossa  is  about. 3  cm.,  and  its  breadth, 
greatest  at  the  level  of  the  auditory  nerve,  is  about  2  cm. 

In  consequence  of  the  elevation  of  its  lateral  boundaries,  the  floor  appears  sunken 
and  corresponds  approximately  with  the  frontal  plane,  being  almost  vertical.  It  is 
divided  into  symmetrical  lateral  portions  by  a  median  groove  (  sulcus  medianus  longi- 
tudinalis  sinus  rhomboidalis),  and  into  an  upper  and  a  lower  half  by  transverse  mark- 
ings, the  acoustic  striae  (striae  acusticae),  which  on  each  side  arise  from  the  nuclei  of 
the  cochlear  nerve,  wind  over  the  restiform  body  and  cross  the  floor  of  the  ventricle 
to  disappear  within  the  median  furrow.  At  its  lower  end,  where  it  sinks  into  the 
central  canal  of  the  cord,  the  median  groove  becomes  somewhat  wider,  the  resulting 
depression  being  sometimes  designated  the  rcnfn'cn/ns  Aurantii.  Roofing  in  the 
ventricle  at  this  point  and  bridging  the  cleft  separating  the  posterior  columns,  lies  a 
thin  triangular  sheet  of  loose  vascular  tissue,  the  obex,  which  laterally  is  continuous 


THE   FOURTH    VENTRICLE. 


1097 


with  the  delicate  roof-membrane,  known  as  the  tela  chorioidea.  Toward  its  upper 
end  the  longitudinal  furrow  presents  a  second  expansion,  the  fossa  mediana.  The 
acoustic  stride  vary  greatly  in  distinctness  and  arrangement,  sometimes  appearing  as 
well-marked  bands  that  cross  the  ventricular  floor  with  little  divergence,  or  they  may 
constitute  a  fan-shaped  group  in  which  the  strands  may  be  irregularly  disposed  or 
even  overlap  ;  in  other  cases  they  may  be  much  less  distinct  on  one  side,  or  so  feebly 
marked  on  both  as  to  be  unrecognizable.  Quite  frequently  one  band  diverges  from 
the  others  and  crosses  the  floor  obliquely  upward  and  outward.  This  stran,d,  spe- 
cially designated  as  the  conductor  sonorus,  is  seldom  equally  distinct  on  the  two 
sides,  being  usually  better  seen  on  the  left. 

The  inferior  division  of  the  ventricular  floor,  that  lying  below  the  acoustic 
striae,  presents  three  general  fields  of  triangular  outline.  The  one  next  the  median 
groove,  with  its  base  above  and  its  apex  directed  towards  the  lower  angle  of  the 
ventricle,  which  it  almost  reaches,  is  the  trigonum  hypoglossi,  so  called  from  the 
fact  that  it  partly  overlies  the  nucleus  of  the  twelfth  nerve.  Lateral  from  the  last 

FIG.  948. 


Corpora  quadrigemina 
Sylvian  aqueduct 

Fovea  superior^  &     >*    ^       It  1      ^I"lTTl(v-  Superior  cerebellar  peduncles 

Acoustic  striae^  XY>^  "  111     \ /"*"      •   '       -1?\  <~^  Eminentia  teres 


Trigonum 
hypoglossi 


White  core  of 
cerebellum 


Trigonum  acustici 

^  ___^  Clava 

Trigonum  vagi- 

Funiculus  gracilis 

Floor  of  fourth  ventricle  exposed  after  removal  of  its  roof  by  frontal  section. 

named  area  is  a  somewhat  depressed  triangular  field  of  darker  color,  the  apex  of  which 
is  placed  above,  near  the  acoustic  striae,  and  the  base  below  ;  this  field  is  known  as  the 
ala  cinerea,  from  the  dark  tint  imparted  to  it  by  the  pigmented  cells  lying  beneath, 
and  as  the  trigonum  vagi,  in  recognition  of  the  subjacent  glosso-pharyngeo-vagus 
nucleus.  The  remainder  of  the  inferior  division  of  the  ventricular  floor  includes  an 
elevated  triangular  field,  the  trigonum  acustici,  that  is  part  of  the  larger  tract,  the 
area  acustica,  which  occupies  not  only  the  lateral  angle  of  the  rhomboidal  fossa, 
where  it  is  crossed  by  the  acoustic  striae,  but  also  the  adjacent  portion  of  the  superior 
division  of  the  ventricular  floor.  Laterally,  the  acoustic  area  presents  a  distinct 
elevation,  the  tuberculum  acusticum,  which,  together  with  the  adjacent  part  of 
the  trigonum  acustici,  is  related  to  the  nuclei  of  the  cochlear  nerve  ;  the  more  median 
portion  of  the  acoustic  area,  on  the  other  hand,  belongs  to  the  vestibular  division. 

The  superior  division  of  the  ventricular  floor,  above  the  acoustic  striae,  is 
marked  on  each  side  of  the  median  groove  by  a  prominent  elevation,  the  eminentia 
teres,  which  below  is  continuous  with  the  trigonum  hypoglossi  and  above  narrows  and 
fades  away  towards  the  floor  of  the  Sylvian  aqueduct.  Laterally  the  eminence  is 
bounded  by  a  depressed  area,  the  fovea  superior,  which  is  the  expanded  upper  part 
of  a  second  longitudinal  furrow,  the  sulcus  lateralis,  that  defines  the  outer  limit  of 
the  eminentia  teres  and  below  is  continued  into  the  depressed  trigonum  vagi,  to  which 
the  name,  fovea  inferior,  is  sometimes  applied.  Above  and  to  the  outer  side  of  the 


1098 


HUMAN   ANATOMY. 


superior  fovea,  the  ventricular  floor  presents  a  slightly  sunken  field,  the  locus 
coeruleus,  which  extends  upward  to  the  Sylvian  aqueduct  and  in  fresh  preparations 
possesses  a  bluish  gray  tint  in  consequence  of  the  deeply  pigmented  cells  of  the 
underlying  substantia  ferruginea  (page  1081)  showing  through  the  ependymal  layer. 

The  accurate  description  of  the  surface  markings  of  the  ventricular  floor  given  by  Retzius,1 
has  been  supplemented  by  Streeter's2  careful  study  of  the  relation  of  these  details  to  the  under- 
lying structures.  The  most  important  results  of  these  observations,  which  have  materially 
advance'd  our  understanding  of  this  important  part  of  the  brain-stem,  may  here  find  mention. 

The  trigonum  hypoglossi  is  seen,  especially  when  examined  under  fluid  with  a  hand-lens, 
to  include  two  subdivisions,  a  narrow  median  and  a  broader  lateral.  The  first  of  these  is  con- 
vex, about  5  mm.  long  by  i  mm.  wide,  and  corresponds  to  the  rounded  upper  end  of  the  nucleus 
of  the  twelfth  nerve  ;  it  is,  therefore,  appropriately  called  the  eminentia  hypoglossi  (Streeter). 
The  entire  hypoglossal  nucleus,  however,  is  of  much  larger  size  (about  12  mm.  long  by  2  mm. 
wide)  and  extends  some  5  mm.  below  the  tip  of  the  calamus  scriptorius,  ventral  (anterior)  to  the 

FIG.  949. 

Colliculus  inferior  IV.    nerve 

Superior  cerebellar  peduncle 

Stria  pontis 
Median  fovea 
V.  nerve 

Superior  fovea 
Eminentia  teres 

Acoustic  striae 

VIII.  nerve 

IX.  and  X.  nerves 

Trigonum  acustici 

Trigonum  hypoglossi 
Trigonum  or  fovea  vagi 

Funiculus  separens 

Area  post  re  ma 

Nucleus  cuneatus 

Nucleus  gracilis 

Floor  of  the  fourth  ventricle ;  areas  corresponding  to  nuclei  of  nerves  are  shown  on  right  half  of 

figure.     X  j.    (Streeter.) 

vagus  nucleus  and  nucleus  gracilis.  Lying  immediately  above  the  hypoglossal  eminence  is  a 
second  and  somewhat  less  pronounced  elevation,  formed  by  the  nucleus  funiculi  teres  and  meas- 
uring nearly  6  mm.  in  length  by  i  mm.  in  breadth.  Lateral  to  these  two  median  elevations  and 
limited  externally  by  the  ala  cinerea,  lies  a  wedge-shaped  field  that  is  insinuated  between  the 
hypoglossal  eminence  and  the  vagal  trigone.  It  stretches  from  the  acoustic  striae  above  to  the 
nib  of  the  calamus  scriptorius  below.  This  field,  named  the  area  plumifonnis  by  Retzius  on 
account  of  its  feather-like  markings,  is  regarded  by  Streeter  as  corresponding  to  a  group  of  cells, 
the  nucleus  intercalatus,  that  occupies  a  superficial  position  in  the  ventricular  floor  and  partly 
overlies  the  hypoglossal  nucleus. 

The  fovea  vagi  (ala  cinerea),  which  lies  lateral  to  the  nucleus  intercalatus,  corresponds  to 
the  middle  and  superficial  third  of  the  vago-glosso-pharyngeal  nucleus,  the  entire  extent  of  tin- 
latter  including  a  tract  measuring  about  13  mm.  in  length  by  2  mm.  in  breadth,  that  stretches 
from  beneath  the  vestibular  nucleus  above  to  over  2  mm.  beyond  the  inferior  angle  ot  tin- 
ventricle.  The  lower  third  of  the  area  of  the  vagus  nucleus  is  partly  within  the  ventricle  ; 
immediately  above  the  obex  this  intraventricular  portion  is  covered  by  a  layer  of  loose  vascular 
tissue  and  appears  as  an  upwardly  diverging  pointed  field,  area  postrema  of  Retzius.  This  i 
separated  from  the  ala  cinerea  by  a  translucent  ridge,  the  funiculus  separens,  composed  of 
thickened  ependymal  neuroglia  (Streeter). 

1  Pas  Menchenhirn,  1896. 

*Amer.  Journal  of  Anat.  Vol  II,  1903. 


Area  n.  trigemini 

N.  facialis 

Area  n.  abducentis 

Area  n.  vestihularis 
Area  n.  cochlearis 


Area  nuc.  funic.  teretis 
Funiculus  solitarius 
Area  n.  vagi 


Area  n.  hypoglossi 


THE   FOURTH  VENTRICLE. 


1099 


The  prominence  of  the  eminentia  teres  is  due  to  the  underlying  nucleus  of  the  sixth  nerve, 
enclosed  by  the  knee  of  the  facial  ;  for  it,  therefore,  Streeter  proposes  the  name  eminentia  abdu- 
centis.  The  longitudinal  ridge  that  continues  upward  and  bounds  the  median  fovea,  the  last 
cited  author  interprets  as  due  to  a  field  of  gray  matter,  thin  in  the  vicinity  of  the  abducent 
eminence  and  thicker  above,  to  which  the  name  nucleus  incertus  is  applied.  Lateral  to  the 
nucleus  incertus  and  the  facio-abducent  eminence,  lies  the  fovea  anterior,  which  elongated  and 
depressed  area  (nearly  6  mm.  long  by  i  mm.  wide)  is  due  to  the  exit  of  the  root  of  the  fifth 
nerve  ;  it  may,  therefore,  be  called  the  fovea  trigemini.  The  median  portion  of  the  elevated 
acoustic  area  includes  the  elongated  and  irregularly  lozenge-shaped  vestibular  area,  that 
measures  about  16  mm.  in  length  by  4  mm.  in  breadth  and  extends  from  the  fovea  anterior 
(trigemini)  to  the  nucleus  gracilis.  The  lateral  part  of  the  area  acustica  is  occupied  by  the 
cochlear  area,  which  stretches  into  the  recessus  lateralis  and  overlies  the  nucleus  cochlearis. 

The  Roof  of  the  Fourth  Ventricle. — Viewed  in  median  sagittal  section  (Fig. 
938),  the  roof  of  the  fourth  ventricle  appears  as  a  tent-like  structure,  whose  wings, 
where  they  come  together,  bound  a  space,  the  recessus  tecti,  that  penetrates  the 
cerebellar  medulla 

between  thesuperior  FIG.  950. 

and  inferior  worm. 
The  upper  wing  of 
the  tent  is  formed  by 
the  superior  med- 
ullary velum,  the 
triangular  sheet  of 
white  matter  stretch- 
ing from  beneath 
the  quadrigeminal 
bodies  above  to  the 
medullary  substance 
of  the  cerebellum 
below,  and  is  over- 
laid by  the  rudimen- 
tary cerebellar  folia 
of  the  lingula.  It 
must  be  understood 
that  the  ventricular 
surface  of  the  velum 


Corpora  quadrigemina 


Superior 
cerebellar  peduncle 


Roof  of 
fourth  ventricle 


Tela  chorioide 
and  choroid  pie 


White  core  o[ 
cerebellum 


Dorsal  portion  of  preparation  shown  in  Fig.  948 ;  roof  of  fourth  ventricle  is  seen 
from  below. 


is    clothed    by    the 

ependyma — as  are  all  other  parts  not  only  of  the  fourth  ventricle  but  of  all  the 
ventricular  cavities.  Laterally  the  superior  medullary  velum  is  attached  to  the 
superior  cerebellar  peduncles,  which  to  a  limited  extent  share  in  closing  in  this 
part  of  the  ventricle  (Fig.  936). 

The  lower  half  of  the  roof  comprises  two  parts,  an  upper  and  thicker  crescentic 
plate  of  white  matter,  the  inferior  medullary  velum,  and  a  lower  and  extremely  thin 
membrane,  the  tela  chorioidea.  Medially  the  inferior  medullary  velum  is  attached 
for  some  distance  to  the  front  and  lower  surface  of  the  nodules,  which  it  excludes, 
strictly  regarded,  from  the  ventricle,  whilst  laterally  the  velum  is  prolonged  to  the 
flocculus,  its  fibres  becoming  continuous  with  the  white  core  of  this  subdivision  of 
the  cerebellum.  The  nervous  constituents  of  the  velum  extend  only  as  far  as  its 
crescentic  lower  border,  beyond  which  the  roof  of  the  ventricle,  in  a  morphological 
sense,  is  formed  by  the  ependymal  layer  alone.  This,  however,  is  supported  by  a 
backing  of  pial  tissue,  which,  in  conjunction  with  the  ependyma,  forms  the  tela 
chorioidea.  On  nearing  the  lower  angle  of  the  ventricle,  the  roof  presents  a  trian- 
gular thickening,  the  obex,  that  closes  the  cleft  between  the  clavae  and  lies  behind 
(above)  the  nib  of  the  calamus  scriptorius. 

On  each  side  the  obex,  which  consists  of  a  layer  of  white  matter  fused  with  the 
underlying  ependyma,  is  continuous  with  the  slightly  thickened  margin  of  the  roof, 
the  taenia  ventriculi,  whose  line  of  attachment  passes  from  the  clava  upward  and 
outward  over  the  cuneate  tubercle  of  the  medulla  and  the  restiform  body  and,  farther 
upward,  runs  obliquely  across  the  dorsal  surface  of  this  peduncle  to  close  in  the  lateral 


i  ioo  HUMAN   ANATOMY. 

recess — one  of  the  pair  of  diverticula  that  overlie  the  inferior  cerebellar  peduncles 
and  add  materially  to  the  transverse  dimension  of  the  ventricle.  After  enclosing  the 
lateral  recess  the  taenia  leads  to  the  stalk  of  the  flocculus  and  the  inferior  velum. 

Within  the  triangular  field  of  the  teia  chorioidea,  the  pia  mater  takes  advantage 
of  the  attenuation  of  the  ventricular  wall  to  effect  invaginations  by  which  its  blood- 
vessels apparently  gain  entrance  into  the  ventricle.  Such  invaginations,  known  as 
the  choroid  plexus  of  the  fourth  ventricle,  occur  in  the  ventricular  roof 
on  each  side  and  in  the  immediate  vicinity  of  the  mid-line,  where  they  appear  as 
parallel  villous  or  fringe-like  stripes,  the  median  plexus,  which  extends  upward 
from  near  the  obex  to  the  inferior  medullary  velum.  Opposite  the  nodules  they 

FIG.  951. 

Roof-nuclei 


Nucleus  globosus 


Nucleus 
emboliformis 


Nucleus  dentat 


Choroid  plex 


j^Medalta 

Fibres  of  IX.  ne 

Spinal  root_ 
of  V.  nerve"  ^__     __  _„_ 

'  *•--    Cerebellum 
)         (flocculus) 


Lateral  recess  of  ventricle' 

sS^&$S$$&$ 
Inferior  olivary  nucleus 

•'¥' 1     .      ."  >  '  >  Posterior  longitudinal  fasciculus 

Pyramidal  tracts  Mesial  fillet 

Section  across  lower  third  of  fourth  ventricle,  showing  internal  cerebellar  nuclei,  choroid  plexus,  lateral  recesses  and 
medulla  ;  new-born  child.     X  3%.     Preparation  by  Professor  Spiller. 

diverge  and,  as  the  lateral  plexuses,  invaginate  the  wall  of  the  lateral  recesses. 
The  vascular  complex  lies  within  the  fold  of  pial  tissue,  the  space  between  the  pial 
layers  being  occupied  by  prolongations  of  the  arachnoid. 

Notwithstanding  its  conspicuous  thinness  during  the  first  half  of  foetal  life,  the  tela 
chorioidea  suffices  to  completely  close  the  ventricle.  From  about  the  fifth  month, 
however,  the  delicate  membrane  is  perforated  by  an  aperture  that  remains  throughout 
life.  This  opening,  the  foramen  of  Majendie  (apertura  medialis  ventriculi  quart! ') 
lies  immediately  above  the  obex  and  between  the  strands  of  the  choroid  plexus. 
Two  additional  clefts,  the  foramina  of  Luschka  (aperturae  laterales),  usually  exist, 
one  on  each  side,  in  the  wall  of  the  lateral  recesses  in  the  neighborhood  of  the  vago- 
glosso-pharyngeal  nerves.  By  means  of  these  three  openings,  and  probably  by  these 
alone,  the  system  of  ventricular  cavities  and  the  central  canal  of  the  spinal  cord  are 
brought  into  communication  with  the  subarachnoid  lymph-space.  A  path  is  thus 
provided  by  which  the  cerebro-spinal  fluid,  secreted  within  the  lateral,  third  and  fourth 
ventricles  by  the  various  choroid  plexuses,  constantly  escapes  and  thereby  prevents 
undue  accumulation  and  distension  within  the  cavities  of  the  brain  and  spinal  cord. 

THE  DEVELOPMENT  OF  THE  HIND-BRAIN  DERIVATIVES. 

In  the  general  sketch  of  the  development  of  the  brain  previously  given  (page  1061),  it  was 
pointed  out  that  the  hind-brain,  or  rhombcnccphalon,  includes  two  subdivisions,  the  myclcncef>h- 
ahnt  and  the  >n<-ti'>ncf>hii/on,  the  extreme  upper  part  of  the  latter  being  designated  the  isthmus. 
It  has  been  further  noticed  that  the  junction  of  the  cord  and  brain-segments  of  the  neural  tube 
corresponds  with  the  conspicuous  cervical  flexure,  whose  early  appearance  is  followed  by  an 


DEVELOPMENT   OF    HIND-BRAIN    DERIVATIVES. 


I  101 


FIG.  952. 


outward  bending  of  the  lateral  walls  of  the  brain-vesicle  and  the  stretching  and  flattening  of  the 

roof-plate.     In  consequence  of  these  changes  the  roof  of  the  rhombencephalon  becomes  reduced 

to  an  attenuated  sheet  which,  when  viewed  from 

above,  appears  as  a  lozenge-shaped  membrane 

that  closes  in  the  subjacent  cavity,  the  subse- 

quent fourth  ventricle.     It  has  also  been  pointed 

out  (page  1049)  tnat  t'ie  relatively  thick  lateral 

walls  of  the  neural  tube  exhibit,  even  within  the 

cord-segment,  a   differentiation   into  a  dorsal 

and  a  ventral  zone  (the  alar  and  basal  lamime 

of  His),  which  subdivisions  are  associated  with 

the  sensory  and  motor  root-fibres  of  the  nerves 

respectively.     Similar  relations,  in  a  more  pro- 

nounced degree,  are  evident  within  the  brain- 

stem  and  are  of  much  interest  as  indicating  the 

morphological   correspondence  of  the  purely 

motor    nerves    (the   third,    fourth,    sixth    and 

twelfth)   on  the  one  hand,  and  of  the  mixed 

nerves  (the  fifth,  seventh,  ninth  and  tenth)  on 

the  other. 

The  Medulla.  —  The  great  preponderance 
of  the  nervous  matter  along  the  floor  of  the 
fourth  ventricle,  as  represented  by  the  medulla, 
is  due  primarily  to  the  outward  bending  of  the 
lateral  walls  of  the  myelencephalon,  supple- 
mented by  the  accession  of  large  tracts  of 
nerve-fibres  that  later  grow  in  from  other  parts 
of  the  cerebro-spinal  axis.  In  consequence  of 

the  former  change,  the  dorsal  zones  of  the  side-walls  are  gradually  displaced  laterally  ;  at 
the  same  time  they  become  partly  folded  on  themselves  to  produce  along  their  outer  margin 
the  rhombic  lip  (His),  which  is  directly  continuous  with  the  expanded  and  thin  roof-plate. 
Later,  the  dorsal  zones  come  to  lie  almost  horizontally,  their  ventricular  surface  corresponding 
with  that  of  the  ventral  laminae,  in  conjunction  with  which  the  floor  of  the  definitive  fourth 


Mid-brain 


Right  hemisphere 


Inferior  colliculus 


Roof-plate 

Cerebellum 
Cavity  of 
hind-brain 
Lateral  recess 
Rhombic  lip 
Attachment  of 
roof 

Medulla 


Reconstruction  of  brain  of  human  embryo  of  22.8 
mm.,  showing  hind-brain  and  part  of  mid-brain  viewed 
from  behind.  X  12.  Drawn  from  model  made  by 
Dr.  Ewing  Taylor. 


FIG.  953. 

Superior  colliculus. 


y  of  mid-brain 


Superior 
medullary  velum 


Hemisphere  of 
cerebellum 


ventricle  is  later  formed.  Coin- 
cidently  with  the  outward  mi- 
gration of  the  dorsal  laminae, 
the  ventral  zones  also  thicken 
and  assume  a  much  more  hori- 
zontal position,  with  their  inner 
ends  separated  superficially  by 
a  median  furrow  and,  deeper, 
by  the  compressed  remains  of 
the  floor-plate.  Very  early  and 
before  the  flattening  out  of  the 
myelencephalon  has  advanced 
to  any  marked  extent,  the  de- 
marcation between  the  dorsal 
and  ventral  zones  is  evident  as 
a  lateral  longitudinal  groove 
on  the  ventricular  surface  of 
the  myelencephalon.  Indica- 
tions of  this  division  persist 
and  in  the  adult  medulla  are 
represented  by  the  fovea  pos- 
terior and  the  sulcus  lateralis 
seen  on  the  floor  of  the  fourth 
ventricle.  As  in  the  cord-seg- 
ment, so  in  the  myelencepha- 
lon the  lateral  walls  are  the 
only  regions  of  the  neural  tube 
in  which  neuroblasts  are  devel- 
oped, the  roof-plate  and  the  floor-plate  containing  spongioblasts  alone. 

Very  early  and  before  the  flattening  out  of  the  myelencephalon  has  advanced  to  any  marked 
extent,  within  the  ventral  zones  and  close  to  the  mid-line,  appear  groups  of  neuroblast,  from 
which  axones  grow  ventrally  to  form  the  root-fibres  of  the  motor  (hypoglossal)  nerves.  Sensory 


Cavity  of  hind-brain 
(IV  ventricle) 

Roof  of  hind-brain,  lo 


\ 


Reconstruction  of   hind-brain  of   human    embryo  ot   about  three  months 
(50  mm.),  viewed  from  side  and  behind.     Drawn  from  His  model. 


1102 


HUMAN    ANATOMY. 


fibres  are  also  early  represented  by  bundles  which  grow  centrally  from  the  ganglion  of  the  vagus 
towards  the  developing  medulla,  upon  whose  surface,  opposite  the  junction  of  the  dorsal  and 
ventral  zones,  they  appear  as  a  flattened  oval  bundle  (fasciculus  solitarius).  For  a  time  super- 
ficial and  loosely  applied,  this  bundle  gradually  becomes  more  deeply  placed  in  consequence  of 
the  extension,  ventral  folding,  and  final  fusion  of  the  rhombic  lip  with  the  remainder  of  the  dorsal 
zone.  Subsequently  the  fasciculus  solitarius  becomes  still  farther  removed  from  the  surface  by 
the  ingrowth  of  tracts  of  nerve-fibres  from  the  neuroblasts  of  the  rhombic  lip  and  from  other 

sources  until,    finally,  the  bundle  comes  to   lie 


FIG.  954. 


beneath  the  ventricular  floor  where  its  position 
permanently  indicates  the  junction  between  the 
original  dorsal  and  ventral  zones  of  the  medul- 
lary wall.  In  a  similar  manner  the  sensory  fibres 
of  the  trigeminal  nerve  are  applied  to  the  sur- 
face of  the  developing  pons ;  since,  however, 
the  bundle  is  attached  after  consolidation  of  the 
dorsal  zone  of  the  medulla  has  begun,  the 
descending  trifacial  fibres  retain  the  relatively 
superficial  position  characterizing  the  spinal  root, 
while  the  descending  root  (fasciculus  solitarius) 
of  the  glosso-pharyngeo-vagus  lies  more  deeply 
placed.  Subsequent  to  the  invasion  of  the  medulla 
by  the  sensory  parts  of  this  nerve,  the  outgrowth 
of  the  axones  from  the  neuroblasts  constitut- 
ing the  nucleus  of  origin  provide  its  motor  root- 
fibres. 

The  rhombic  lip  is  a  region  of  much  impor- 
tance, since  from  the  neuroblasts  which  appear 
within  it  are  derived  the  cells  of  the  reception 
nuclei  (substantia  gelatinosa)  of  the  sensory 
cranial  nerves,  of  the  nuclei  of  the  posterior  col- 
umns, of  the  inferior  and  accessory  olivary  nuclei 
and  of  the  arcuate  nucleus.  From  the  neuro- 
blasts many  axones  grow  medio-ventrally,  pierce 
the  median  spongioblastic  septum  derived  from 
the  primary  floor-plate,  which  later  becomes  the 
median  raphe,  and  gain  the  opposite  side  and 
thus  establish  the  systems  of  arcuate  fibres.  Other 
axones  grow  dorsally  and  take  part  in  even- 
tually producing  the  fibre-tracts  connecting  the 
olivary,  dorsal  and  arcuate  nuclei  with  the  cere- 
bellum. It  is  evident  that  the  development  of  the 
myelencephalon  primarily  contributes  the  nerv- 
ous substance  that  becomes  the  dorsal  part  of  the 
medulla  and  underlies  the  fourth  ventricle.  Later 
the  closed  part  of  the  medulla,  which  at  first 
is  wanting,  as  well  as  the  conspicuous  pyramidal 
tracts,  are  added  as  the  strands  of  ascending 
and  descending  fibres  grow  into  the  medulla 
from  the  spinal  cord  and  from  other  parts  of  the 
brain.  In  this  manner  the  important  tracts  of 
the  posterior  columns  and  the  spinal  constitu- 
ents of  the  restiform  body  and  of  the  brain-stem 
are  added  and,  still  later,  the  bulky  pyramids 
take  form  when  the  cerebro-spinal  paths  are 
established. 

In  accord  with  the  falling  apart  and  thick- 
ening that  affect  the  lateral  walls  of  the  myi- 
lencephalon  and  lead  to  the  production  of  the 
medulla,  the  roof-plate  of  the  brain-vesicle 
becomes  flattened  and  laterally  expanded  to  keep  pace  with  the  increasing  width  of  the  ventricular 
floor.  In  consequence,  the  roof-plate  is  converted  into  a  rhomboidal  sheet  of  great  delicacy,  tin- 
primary  velum,  which  histologically  consists  of  littK-  more  than  the  layer  of  ependymal  rt-lls. 
These,  however,  soon  come  into  close  relation  with  the  overlying  mesoblastir  tissue-  from  which 
tlu-  pia  is  differentiated.  During  the  third  month  a  transverse  fold,  tin-  f>lica  chorioidca,  appears 
in  the  roof-sheet,  near  the  posterior  limit  of  the  developing  cerebellum  (Fig.  955,  B}.  Into  this 


Transverse  sections  of  hind-brain  of  human  embryos, 
showing  three  stages  in  development  of  medulla ;  A, 
about  four  and  a  half  weeks;  H, about  six  weeks;  C, 
about  eight  weeks ;  rp,  roof-plate ;  r,  raphe ;  ti.  v, 
dorsal  (alar)  and  ventral  (basal)  laminze  ;  rl,  rhombic 
lip ;./»-,  lateral  recess;  fs,  fasciculus  solitarius;  cr. 
restiform  body  ;  xii,  hynoglossal  nerve  ;  sv,  spinal 
root  of  trigeminus  ;  to,  inferior  olivary  nucleus,  (ffis.) 


DEVELOPMENT   OF    HIND-BRAIN    DERIVATIVES. 


1103 


duplicature,  directed  towards  the  brain  cavity,  the  mesoblast  grows  and  later  develops  blood- 
vessels, and  is  converted  into  a  vascular  complex  that  eventually  forms  the  choroid plexus  of  the 
fourth  ventricle.  From  the  manner  of  its  development,  it  is  evident  that  the  plexus  is  excluded 
by  the  ependymal  layer  from  the  ventricular  space,  outside  of  which  the  pial  blood-vessels, 
therefore,  really  lie.  The  conversion  of  the  upper  part  of  the  primary  velum  into  the  thicker 
definite  inferior  medullary  velum  follows  the  addition  of  nervous  substance  during  the  develop- 
ment of  the  cerebellum.  Similar  thickening  of  the  roof-sheet  at  the  lower  angle  of  the  ventricle 
results  in  the  production  of  the  obex  and  the  tasniae. 

The  Pons.  —  The  pons  arises  as  a  thickening  of  that  part  of  the  metencephalon  which  forms 
the  anterior  wall  of  the  pontine  flexure.  In  its  essential  phases  the  development  of  the  pons 
probably  closely  resembles  that  of  the  medulla,  since  the  early  metencephalon  presents  the  same 
general  features  as  does  the  myelencephalon.  Thus,  the  ventral  zones  of  its  lateral  walls  play 
an  active  role  in  the  production  of  the  tegmental  portion  of  the  pons  and  the  nuclei  of  origin  of 
the  motor  root-fibres  of  the  fifth,  sixth  and  seventh  nerves,  whilst  the  floor-plate  becomes  the 
raphe.  In  addition  to  providing  the  reception-nuclei  of  the  sensory  cranial  nerves,  and,  per- 
haps, the  pontine  nuclei,  the  dorsal 

zones  contribute  the  neuroblasts  which  FIG.  955. 

become  the  nervous  elements  of  the 
cerebellum.  As  in  the  medulla,  so  in 
the  pons  the  great  ventral  tracts  are 
secondary  and  relatively  late  additions 
to  the  tegmentum,  which  must  be  re- 
garded as  the  primary  and  oldest  part 
of  this  segment  of  the  brain-stem,  the 
bulky  ventral  nervous  masses  taking 
form  only  after  the  appearance  of  the 
cerebro-spinal  and  cerebro-cerebellar 
paths.  In  a  manner  analagous  to  that 
by  which  the  sensory  part  of  the  vagus 
is  at  first  loosely  applied  and  later  in- 
corporated with  the  medulla,  the  sen- 
sory fibres  of  the  trigeminus  are  for  a 
time  attached  to  the  surface  of  the 
dorsal  zone  of  the  pons,  subsequently 
becoming  covered  in  and  more  deeply 
placed  by  the  addition  of  peripheral 
tracts.  Likewise  the  fibres  of  the  audi- 
tory nerve  come  into  relation  with  the 
superficially  situated  reception-nuclei 
of  the  cochlear  and  vestibular  nerves. 

The  Cerebellum. — The  develop- 
ment of  the  human  cerebellum  pro- 
ceeds from  the  roof-plate  and  adjacent 
parts  of  the  dorsal  zones  of  the  lateral 
walls  of  the  metencephalon.  In  an 
embryo  22.8  mm.  long,  the  cerebellar 
anlage  consists  of  two  lateral  plates 

connected  by  a  narrow  thin  intervening  lamina  representing  the  roof-plate  (Fig.  952).  After 
the  apposition  of  the  lateral  plates,  which  soon  occurs,  this  bridge  disappears,  the  developing 
cerebellum  for  a  time  appearing  as  an  arched  lamina  enclosing  the  upper  part  of  the  cavity  of 
the  hind-brain  (Kuithan1). 

The  subsequent  development  of  the  human  cerebellum  has  been  recently  carefully  studied 
by  Bolk 2  in  a  series  of  about  forty  foetuses,  hardened  in  formalin  and  ranging  from  5  to  30  cm.  in 
their  entire  (crown-sole)  length.  The  following  account  is  based  largely  on  these  investigations. 
In  a  foetus  of  5  cm. ,  about  nine  weeks  old,  the  cerebellar  anlage  is  represented  by  a  horseshoe- 
shaped  thickening  of  the  metencephalic  roof,  the  cerebellar  lamina,  whose  upper  margin  is  con- 
nected by  the  encephalic  fold  with  the  mid-brain  and  whose  lower  border  has  attached  to  it  the 
primary  velum — the  thin  rhomboidal  roof-plate  of  the  myelencephalon.  Median  sagittal  section 
of  the  cerebellar  lamina  at  this  stage  (Fig.  955,  A]  shows  its  form  to  be  asymmetrically  biconvex, 
the  more  convex  surface  encroaching  upon  the  brain-cavity.  In  a  slightly  older  foetus  ( Fig. 
955.  B)  the  cerebellar  lamina  has  become  triangular,  in  section  presenting  a  superior,  an 
anterior,  and  an  inferior  surface.  From  its  attachment  along  the  superior  margin  of  the  lamina 
the  inferior  velum  dips  forward  toward  the  pontine  flexure  and,  forming  a  transversely  cresentic 

1  Miinchner  med.  Abhand.,  1895. 
2Petrus  Camper,  36  Deel,  1905. 


Median  sagittal  sections  showing  four  early  stages  of  develop- 
ment of  human  cerebellum,  from  foetuses  from  5  to  9  cm.  long; 
nib,  mid-brain  ;  c,  cerebellum  ;  sv,  iv,  superior  and  inferior  medul- 
lary velum  ;  vc,  ventricular  cavity ;  d,  cavity  of  diencephalon ;  p, 
pons  ;  m.  medulla  ;  .r,  spinal  cord  ;  if,  incisura  fastigii ;  /,  sulcus 
primarius  ;  j,  sulcus  postnodularis.  (Drawn  from  figures  of  Bolk.) 


HUMAN   ANATOMY. 


fold,  the  plica  chorioidea,  bounds  a  narrow  recess  that  extends  along  the  inferior  surface  of  the 
cerebellar  lamina.  This  recess  is  only  temporary  and  is  soon  obliterated  by  the  subsequent  at- 
tachment of  the  roof-membrane  to  the  inferior  surface  of  the  cerebellar  lamina.  The  succeeding 
stage  (Fig.  955,  C)  emphasizes  the  alteration  in  the  planes  of  the  cerebellar  surfaces,  the  former 
superior  now  becoming  the  anterior,  the  anterior  the  inferior,  and  the  inferior  the  posterior. 
From  the  posterior  margin  of  the  dorsal  surface  the  choroid  fold  dips  into  the  brain-cavity. 
Between  the  mid-brain  and  the  cerebellum  now  stretches  the  first  definite  indication  of  the  later 
superior  medullary  velum.  In  agreement  with  His,  Bolk  recognizes  that  the  former  intraven- 
tricular  (inferior)  surface  has  now  become  an  extraventricular  one  and  that  the  permanent  attach- 
ment of  the  plica  chorioidea  corresponds  to  a  secondary  and  not  to  the  primary  line  of  union. 
The  stage  represented  in  Fig.  955,  D  is  important,  since  it  marks  the  beginning  of  the  first 
fissures.  One  of  these,  the  sulcus primarius  (the  fissura  prima  of  Elliot  Smith),  appears  as  a 
transverse  groove  on  the  upper  part  of  the  anterior  surface  and  thus  early  establishes  the  funda- 
mental division  of  the  cerebellum  into  an  anterior  and  a  posterior  lobe.  The  other  fissure 
appears  in  the  median  area  near  the  posterior  margin  of  the  cerebellum  and  is  the  sulcus  post- 
nodularis.  On  each  side  (Fig.  956,  A )  an  additional  fissure  cuts  off  a  narrow  tract  that  embraces 
the  postero-lateral  area  of  the  cerebellum.  This  fissure,  the  sulcns  flocc ularis,  for  a  time  remains 
ununited  with  the  postnodular  sulcus  ;  but  later,  with  its  fellow,  it  becomes  continuous  with 
the  postnodular  sulcus  and  thus  defines  a  narrow  band-like  tract,  the  median  part  of  which 


FIG.  956. 


4  2  2         4 

Six  stages  in  development  of  human  cerebellum,  from  foetuses  of  9  (A),  13  (B),  i§  (C),  22  (D),  25  (£),  and  32  cm. 
(F)  length;  /,  sulcus  primarius  (preclival) ;  2,  s.  floccularis ;  j,  s.  postnodulans ;  4,  s.  mfrapyramidalis ;  5,  s. 
superior  posterior  (postclival) ;  h,  great  horizontal  fissure;  mb,  mid-brain;  r,  roof-membrane;  Ir,  lateral  recess; 
«,  nodulus  ;  «,  uvula  ;  /,  pyramis  ;  t,  tuber ;/,  folum.  (Drawn  from  figures  of  Bolk.) 

eventually  becomes  the  nodule,  the  lateral  portions  the  flocculi,  whilst  the  intervening  strips 
become  the  floccular  peduncles  and  part  of  the  inferior  medullary  velum.  The  diverticulum 
bounded  on  each  side  by  the  floccular  area  is  the  beginning  of  the  lateral  recess  of  the  fourth 
ventricle  and  is  early  filled  by  the  rapidly  growing  choroid  plexus.  A  shallow  transverse 
groove,  the  incisura  fastigii,  just  suggested  in  Fig.  955,  C  but  distinct  in  the  succeeding  sketch, 
marks  the  beginning  of  the  tent-like  recess  that  later  conspicuously  models  the  roof  of  the 
fourth  ventricle.  Coincidently  with  and  about  midway  between  the  fissures  just  described,  a 
third  furrow  appears  on  the  posterior  cerebellar  lobe.  This  is  ihefasura  secunda  (Elliot  Smith) 
or  the  infra/>yniini(ln/  sn/cits.  Very  shortly  a  fourth  groove  appears  behind  the  sulcus  primarius 
and  marks  the  beginning  of  the  prepyramidal  fissure.  In  this  manner  the  median  trad  of  the 
post«rior  lobe  is  early  subdivided  by  three  fissures  into  four  areas,  which,  from  behind  touan! 
the  sulcus  priniai  !us,  give  rise  to  the  nodule,  the  uvula,  the  pyramid  and  a  still  undifferentiated 
zone.  By  the  subsequent  appearance  of  additional  furrows,  this  narrow  /one  gives  origin  to  the 
nil),  r,  the  folium  caaiminis  and  tin-  clivus.  Meanwhile  on  the  anterior  lobe  of  the  cerebellum 
three  short  transverse  fissures  appear,  by  which  the  anterior  end  of  the  worm-tract  is  broken 
up  into  areas  that,  while  establishing  subdivisions  of  morphological  value  (Bolk),  are  later  lost 
in  the  uncertain  foliation  of  the  lingnla  and  lobulus  rentralis  of  the  mature  cerebellum. 

After  the  fundamental  subdivision  of  the  median  area  (worm)  has  been  accomplished,  the 
lateral  masses  (hemispheres)  of  the  cerebellum  become  subdivided  into  definite  tracts  (lobules) 
by  fissures  that  appear  during  the  fourth  and  filth  months  of  foetal  life.  The  lateral  extensions 


THE   MESENCEPHALON.  1105 

of  the  sulcus  primarius — itself  the  later  preclival  fissure — separate  the  anterior  and  posterior 
crescentic  lobules.  During  the  fourth  month  the  postlunate  fissure  appears,  in  each  hemisphere, 
on  the  upper  surface  of  the  posterior  lobe.  By  the  extension  and  medial  union  of  these  sulci,  for 
a  time  separate,  are  established  the  posterior  limit  of  the  clivus  (postclival  fissure)  and  the 
demarcation  between  the  posterior  crescentic  and  the  postero-superior  lobule.  The  post-tonsillar 
fissure  bounds  the  conspicuous  elevation  of  the  tonsil  behind  and  medially  joins  the  infrapyram- 
idal  (later  prepyramidal)  sulcus.  The  parapyramidal  fissure  defines  the  upper  (posterior) 
limit  of  the  biventral  lobule  and  unites  with  the  suprapyramidal  (later  postpyramidal)  fissure. 
The  great  horizontal  fissure,  so  conspicuous  in  the  mature  cerebellum,  appears  relatively  late, 
about  the  end  of  the  fifth  month,  and  is  at  first  represented  by  a  shallow  transverse  median  fur- 
row that  lies  immediately  in  front  of  the  suprapyramidal  fissure  (Bolk) ,  an  origin  at  variance 
with  the  generally  accepted  formation  of  the  horizontal  fissure  by  the  union  of  two  lateral  sulci, 
that  grow  medially  from  the  hemispheres  and  meet  in  the  worm.  The  early  fissure  having  such 
history,  Bolk  identifies  as  the  postlunate  (sulcus  superior  posterior)  and  not  as  the  horizontal. 
This  author  also  emphasizes  the  fact  that  at  the  sixth  foetal  month  the  folium  cacuminis  is,  as  a 
rule,  not  only  defined,  but  forms  a  well-marked  superficial  tract  that  connects  the  adjoining 
lateral  tracts  (postero-superior  lobules).  This  part  of  the  worm,  however,  does  not  keep  pace 
with  the  cortical  expansion  of  the  surrounding  parts  and,  hence,  becomes  overgrown  by  these 
and  sinks  into  the  relative  insignificance  that  distinguishes  this  part  of  the  worm  in  the  fully 
matured  cerebellum.  In  consequence  of  the  rapid  growth  and  expansion  of  the  peripheral 
portions  of  the  human-  cerebellum,  some  fissures  of  secondary  morphological  importance,  as 
the  horizontal,  become  excessively  deepened  and  more  conspicuous  in  man  than  those  of 
fundamental  significance,  as  the  sulcus  primarius  (preclival)  and  the  postnodular  fissures.  This 
cortical  expansion,  especially  within  the  superior  region,  likewise  brings  about  prominent 
changes  in  the  position  of  the  segments  of  the  worm,  so  that  eventually  those  which  primarily 
lay  behind  later  come  to  lie  below,  the  divisions  of  the  conventional  upper  and  lower  worm  of 
the  mature  cerebellum  following  along  the  C-like  curve  seen  in  sagittal  sections. 

The  histogenesis  of  the  cerebellar  cortex  probably  primarily  proceeds  from  the  invasion  of 
the  cellular  lamina  by  the  cells  of  the  dorsal  zones  of  the  lateral  walls  of  the  metencephalon,  as 
well  as  directly  from  these  zones  themselves.  The  earliest  differentiation  results  in  the  production 
•of  three  strata  :  (a)  the  inner  ependymal  layer,  and  (d)  the  middle  mantle  layer,  and  (c)  the  outer 
marginal  layer.  Of  these  the  mantle  layer  is  the  thickest  and  richest  in  cells,  from  which  both 
neuroblasts  and  spongioblasts  arise,  although  their  differentiation  occurs  relatively  late.  The 
Purkinje  cells,  early  distinguishable  by  their  large  clear  nuclei,  appear  during  the  sixth  foetal 
month,  but  for  some  time  lack  their  characteristic  processes.  Likewise  from  the  mantle  layer 
are  derived  the  earliest  constituents  of  the  granule  layer.  Meanwhile  within  the  marginal  layer, 
immediately  beneath  the  external  surface  of  the  cerebellum,  an  additional  and  temporarily  con- 
spicuous cell-stratum,  the  external  granule  layer,  becomes  a  prominent  feature  of  the  develop- 
ing cerebellar  cortex.  This  layer  soon  exhibits  a  subdivision  into  two  zones  of  which  the  outer 
contains  many  dividing  cells,  while  the  inner  is  almost  free  from  karyokinetic  figures.  During 
the  later  months  of  foetal  life  the  inner  sublayer  disappears  and  at  birth  the  outer  one  is  greatly 
reduced  ;  finally,  this  also  disappears,  so  that  after  the  earliest  years  of  childhood  the  external 
granule  layer  is  no  longer  seen.  The  chief  factor  in  this  reduction  and  eventual  obliteration 
of  this  stratum  is,  according  to  Cajal,  the  gradual  transformation  of  its  neuroblasts  into  nerve- 
cells  that  recede  from  their  peripheral  position  to  assist  in  the  completion  of  the  granule  layer, 
as  whose  small  and  characteristically  branched  elements  they  persist.  Other  neurones  of  the 
external  granule  layer  are  transformed  into  the  basket  cells  and  the  large  stellate  cells.  The 
neuroglia  of  the  cerebellar  cortex  is  derived  chiefly  from  the  spongioblastic  elements  of  the  inner 
or  ependymal  layer,  the  conversion  of  the  cells  of  the  outer  grannie  layer  into  the  supporting 
tissue,  as  sometimes  assumed,  being  unlikely  (Ziehen).  Since  the  molecular  layer  is  composed 
to  a  considerable  extent  of  the  dendritic  processes  of  the  Purkinje  cells,  the  development  of  the 
outer  division  of  the  cerebellar  cortex  is  complete  only  after  the  growth  of  such  processes,  as 
well  as  of  the  climbing  fibres  from  the  white  core,  has  taken  place. 

The  production  of  the  superior  cerebellar  peduncles  and  of  the  definite  superior  medullary 
velum  is  dependent  upon  the  development  of  the  fibres  that  pass  from  and  to  the  dentate 
nucleus  and  the  cerebellar  cortex — an  invasion  that  occurs  during  late  foetal  and  early  post- 
natal life. 

THE    MESENCEPHALON. 

Notwithstanding  its  considerable  size  and  prominent  position  in  the  embryo,  in 
its  mature  condition  the  mesencephalon,  or  mid-brain,  forms  the  smallest  and  least  con- 
spicuous division  not  only  of  the  brain-stem  but  also  of  the  entire  brain.  Neverthe- 
less, the  many  fundamental  tracts  which  it  contains,  as  well  as  the  new  paths  and 
combinations  which  arise  within  its  substance,  confer  on  the  mid-brain  an  importance 

70 


uo6 


HUMAN   ANATOMY. 


not  suggested  by  its  size.  Its  upper  limit  corresponds  with  an  oblique  plane  passing 
through  the  base  of  the  pineal  body  and  the  posterior  border  of  the  corpora  niam- 
millaria  ;  its  lower  one  is  indicated  on  the  ventral  surface  by  the  upper  border  of  the 
pons  and  on  the  dorsal  aspect  by  the  upper  margin  of  the  superior  medullary  velum. 
As  seen  in  sagittal  sections  (Fig.  938,)  the  mid-brain  is  about  n  mm.  in  length, 
although  when  measured  on  the  ventral  surface  it  is  slightly  shorter  (9  mm.)  and 
on  the  dorsal  aspect  a  little  longer  (13  mm.).  Its  greatest  breadth  is  approximately 
23  mm.  The  mid-brain  is  traversed  longitudinally  by  a  canal,  the  Syh'ian  aqueduct, 
which,  however,  lies  much  nearer  the  dorsal  than  the  ventral  surface  of  the  brain-stem. 
When  the  several  parts  of  the  brain  are  undisturbed,  only  a  portion  of  the  ventral 
aspect  of  the  mid-brain  can  be  seen.  Its  dorsal  and  lateral  surfaces  are  hidden  by 
the  overhanging  cerebral  hemispheres,  the  splenium  of  the  corpus  callosum  and  the 
pulvinar  of  the  thalamus  being  in  close  relation  with  these  surfaces  respectively. 
Notwithstanding  its  ventral  position  and  apparent  removal  from  the  exterior  of  the 
brain  behind,  the  dorsal  surface  of  the  mid-brain  is,  in  fact,  directly  continuous  with 

FIG.  957. 


Thalamus 
Trigonum  habenulse 

Pulvinar 
Colliculus  superior 

Cerebral  peduncle 

Fourth  nerve 

Pons 

Superior  cerebellar  peduncle 


T;eiiia  thalami 

Commissura  habenulse 
"Pineal  body 


Median  geniculate  body 
Brachium  inferior 
Colliculus  inferior 

Frenulum  veli 

Lingula 

Cerebellum,  cut  surface 


Mid-brain  viewed  from  behind ;  upper  part  of  cerebellum  has  been  removed  to  expose  superior  medullary 

velum  with  lingula. 

and  a  part  of  the  free  posterior  surface  of  the  brain.  It  is,  therefore,  covered  with 
the  pia  mater,  as  may  be  demonstrated  by  drawing  aside  the  overhanging  cerebral 
hemispheres.  In  situ  the  mid-brain  occupies  the  opening  bounded  by  the  tento- 
rium  and  thus  connects  the  divisions  of  the  brain  which  lie  within  the  posterior  cra- 
nial fossa  (cerebellum,  pons  and  medulla)  with  those  (cerebral  hemispheres)  that  lie 
above.  Its  cavity,  the  Sylvian  aqueduct,  establishes  direct  communication  between 
the  third  and  fourth  ventricles.  The  mid-brain  includes  two  main  subdivisions,  a 
smaller  dorsal  part,  the  quadrigeminal plate,  which  roofs  in  the  Sylvian  aqueduct  and 
bears  the  corpora  quadrigemina,  and  a  much  larger  ventral  part,  made  up  by  the 
cerebral  pedimdes. 

The  quadrigeminal  plate  lies  behind  the  plane  of  the  roof  of  the  Sylvian 
aqueduct  and  extends  from  the  base  of  the  pineal  body  above  to  the  upper  margin 
of  the  anterior  medullary  velum  below.  Its  dorsal  surface  is  subdivided  into  four  \\hitc 
rounded  elevations,  the  corpora  quadrigemina,  by  two  grooves,  one  of  which  is 
a  median  longitudinal  furrow  and  the  other  a  transverse  furrow  that  crosses  the  first 
one  at  right  angles  and  slightly  below  its  middle  point.  The  upper  part  of  the  longi- 
tudinal groove,  between  the  upper  pair  of  elevations,  broadens  into  a  shallow  trian- 
gular depression,  the  pineal  fossa  (trii{onum  subpincnlc)  in  which  rests  the  pineal 
body.  Below,  the  mid-furrow  ends  at  the  base  of  the  frenum  of  the  superior  medul- 
lary velum. 


THE   MESENCEPHALON. 


1107 


Pulvinar 


Superior  colliculu; 


Inferior  colliculus 


Superior  medullary 
velum 

Superior  cerebellar 
peduncle 

Lingula 


Middle  cerebellar 
peduncle,  cut 


FIG.  958. 

Superior  brachium 
i       Median  geniculate  body 
/      /         Lateral  geniculate  body 

Tractus  transversus 
Cerebral  peduncle 
Optic  tract 


The  elevations  forming  the  upper  pair  of  quadrigeminal  bodies,  the  colliculi 
superiores,  are  the  larger  and  more  conspicuous,  and  measure  from  7-8  mm.  in 
length,  about  10  mm.  in  breadth,  and  6  mm.  in  height.  Laterally  each  superior  col- 
liculus is  continued  into  an  arm,  the  superior  brachium  (brachium  quadrigeminum 
superius)  which  is  denned  by  a  groove  above  and  below,  and  passes  upward  and 
outward,  between  the  optic  thalamus  and  the  median  geniculate  body,  to  be  lost 
within  an  indistinctly  circumscribed  oval  eminence,  the  lateral  geniculate  body 
(corpus  geniculatum  laterale),  which  lies  beneath  the  pulvinar.  In  like  manner,  each 
of  the  smaller  lower  pair  of  quadrigeminal  bodies,  the  colliculi  inferiores,  (about 
6  mm.  in  length  by  8  mm.  in  breadth  and  5  mm.  in  height)  is  prolonged  laterally 
into  the  inferior  brachium  (brachiura  quadrigerainum  inferius),  which  in  turn  ends 
in  the  sharply  denned  median  geniculate  body  (corpus  geniculatum  mediale),  an 
oval  elevation  about  10  mm.  in  length.  Ventrally  the  quadrigeminal  plate  becomes 
directly  continuous  with  the  adjacent  part  of  the  cerebral  peduncles. 

The  cerebral  peduncles  (pedunculi  cerebri),  also  called  the  cerebral  crura, 
constitute  the  bulky  ventral  part  of  the  mid-brain.  Dorsally,  the  two  peduncles  are 
fused  into  a  continuous  tract,  the  tegmentum,  which  contributes  the  side-walls  and 
floor  of  the  Sylvian  aqueduct  and  blends  on  each  side  with  the  overlying  quadri- 
geminal plate.  Ventrally  the  peduncles  are  unfused  and  appear  on  the  inferior  sur- 
face of  the  brain  as  two  robust  stalks  (Fig.  993).  These  emerge  from  the  upper 
border  of  the  pons  and  pass,  diverging  at  an  angle  of  from  70-85°,  upward  and  out- 
ward to  enter,  one  on  each 
side,  the  cerebral  hemi- 
spheres just  where  the 
peduncles  are  crossed  by 
the  outwardly  winding 
optic  tracts.  At  the  pons 
each  peduncle  possesses 
a  breadth  of  from  12-15 
mm.,  which  increases  to 
from  18-20  mm.  at  the 
upper  end  of  the  stalk  ;  the 
borders  of  each  peduncle 
are,  therefore,  not  quite 
parallel,  but  slightly  di- 
verging. Neither  are  the 
mesial  margins  of  the  pe- 
duncles in  contact  as  they 
issue  from  the  pons,  but 
separated  by  an  interval 
of  about  3  mm.  This 
distance  increases  until  at  their  upper  ends  the  peduncles  are  about  13  mm.  apart. 
Superficially  each  peduncle  is  formed  by  strands  of  fibres  which  do  not  pursue  a 
strictly  longitudinal  course,  but  wind  spirally  from  within  outward  ;  in  consequence 
of  this  arrangement  the  surface  of  the  peduncle  presents  a  characteristic  twisted  or 
rope-like  striation.  The  regularity  of  this  marking  is  sometimes  disturbed  by  a 
faintly  defined  strand  of  fibres  (tractus  peduncularis  transversus),  that  winds  over  the 
median  border  and  ventral  surface  of  the  peduncle,  passes  upward  and  outward  across 
the  lateral  surface  of  the  mid-brain,  to  be  lost  in  the  vicinity  of  the  medial  geniculate 
body.  The  depressed  triangular  area  included  between  the  diverging  peduncles  is  the 
interpeduncular  fossa,  the  floor  of  which  is  pierced  by  numerous  minute  openings 
that  transmit  small  blood-vessels,  and  hence  is  known  as  the  posterior  perforated 
substance.  The  blunted  inferior  angle  of  the  fossa,  immediately  above  the  pons, 
corresponds  with  a  depression,  the  recessus  posterior;  another,  but  less  marked 
depression,  the  recessus  anterior,  is  bounded  by  the  postero-median  surfaces  of 
the  mammillary  bodies.  A  shallow  lateral  groove  (sulcus  mcsencephali  lateralis) 
extends  along  the  outer  surface  of  the  peduncle,  whilst  along  its  inner  aspect,  and 
therefore  looking  into  the  interpeduncular  fossa,  runs  the  median  or  oculomotor 
groove  (sulcus  nervi  oculomotorius),  that  is  more  distinct  than  the  lateral  furrow  and 


Dorso-lateral  aspect  of  mid-brain. 


iio8 


HUMAN    ANATOMY. 


marks  the  line  along  which  the  root-fibres  of  the  third  cranial  nerve  emerge.  On 
transverse  section  (Fig.  963)  these  furrows  are  seen  to  correspond  with  the  edges  of  a 
crescentic  field  of  deeply  pigmented  gray  matter,  the  substantia  nigra,  by  which 
each  peduncle  is  subdivided  into  a  dorsal  portion,  the  tegmentum,  and  a  ventral 
part,  the  crusta  (basis  pedunculi).  The  latter  lies  ventral  to  the  superficial  lateral 
and  median  furrows,  and  contributes  largely  to  the  bulk  of  the  free  part  of  the 
peduncle.  When  traced  upward  it  is  found  to  enter  the  cerebral  hemisphere  and 
become  continuous  with  the  internal  capsule.  It  contains  the  great  motor  tracts  and 
is  the  chief  pathway  by  which  efferent  cortical  impulses  are  transmitted  to  the  lower 
lying  centres.  The  tegmentum,  on  the  contrary,  in  a  general  way  is  associated 
with  the  sensory  tracts,  and,  above,  enters  the  subthalamic  region  (page  1127). 

The  dorso-lateral  surface  of  the  mid-brain,  just  where  it  passes  into  that  of 
the  superior  cerebellar  peduncle,  shares  with  the  latter  a  triangular  area,  the  trigo- 


Emerging  fibres  of  fourth  nerve 
Fourth  nerve,  cut 

Lateral  fillet 

Posterior  longitudinal 
fasciculus 

Tegmental  field 
Mesial  fillet 


FlG.   959. 

Decussation  of  fourth  nerve 
,Sylvian  aqueduct 

gray  substance 
Mesencephalic  root  of  trigeminus 

•         Substantia  ferruginen 

Superior  cerebellar 

peduncle 

I)ecussation  of  cerebellar 

peduncle 


Pyramidal  tracts 


Transverse  fibres 


Transverse  section  of  brain-stem  at  level  L  (Fig.  919),  junction  of  pens  and  mid-brain  ;  superior  cerebellar  pt-dun- 
cles  are  beginning  to  decussate ;  trochlear  decussation  seen  above  Sylvian  aqueduct.    Weigert-1'al  staining 
Preparation  by  Professor  Spiller. 

num  lemnisci,  which,  as  implied  by  its  name,  is  related  to  the  underlying  and 
here  superficially  placed  tract  of  the  fillet  (lemniscus).  Above,  this  area  extends 
as  far  as  the  inferior  brachium  and  is  limited  in  front  by  the  sulcus  mesencephali 
lateralis,  whilst  behind  it  is  defined  from  the  superior  cerebellar  peduncle  by  a_  slight 
furrow  (sulcus  limitans  posterior).  When  closely  examined  the  triangular  field  is  seen 
to  be  subdivided  by  a  faint  groove  into  an  upper  and  a  lower  area,  which  correspond 
with  the  underlying  fibres  of  the  lateral  and  of  the  mesial  fillet  respectively.  A 
superficial  strand  of  fibres,  the  tractus  peduncularis  transversus,  is  sometimes  seen 
crossing  the  lateral  surface  of  the  mid-brain.  It  appears  on  the  dorsal  aspect  of  the 
latter,  between  the  inferior  brachium  and  the  median  genirulate  body,  winds  around 
the  latero-ventral  surface  of  the  peduncle  and  disappears  in  the  vicinity  of  the 
mammillary  body.  According  to  Marburg,  the  strand  establishes  a  connection 
between  the  optic  tract  and  a  nucleus  in  the  floor  of  the  third  ventricle  and  represents, 
in  a  rudimentary  condition,  the  basal  optic  root  found  in  many  animals. 

The  Sylvian  aqueduct  Caqu.-icductus  ccrc-bri )  represents  the  cavity  of  the  middle 
brain-vesicle  and,  there-fore,  is  lined  with  an  ependymal  layer  continuous  above  ami 
below  with  that  clothing  the  interior  of  the  third  and  fourth  ventricles.  As  seen  in 


THE   MESENCEPHALON. 


1109 


cross-sections,  (Fig.  960)  its  outline  in  a  general  way  is  triangular,  with  the  base 
above  and  the  apex  directly  below  ;  but  the  contour  of  the  canal  varies  at  different 
levels,  being  triangular  near  its  extremities  and  irregularly  cordiform  or  elliptical  in 
the  intervening  part  of  its  course. 

INTERNAL  STRUCTURE  OF  THE  MESENCEPHALON. 

Disregarding  the  several  small  nuclei,  the  nuclei  of  the  corpora  quadrigemina 
and  the  red  nuclei,  the  gray  matter  within  the  mesencephalon  is  disposed  as  three 
tracts  that  extend  the  entire  length  of  the  mid-brain.  These  are  the  tubular  mass 
of  the  central  gray  matter,  which  surrounds  the  aqueduct,  and  the  two  crescentic 
columns  of  the  substantia  nigra,  which  subdivide  the  peduncles  into  the  tegmental 
and  basal  portions. 

The  central  gray  matter  (stratum  griseum  centrale)  completely  encloses 
the  cavity  of  the  mid-brain  and  hence  is  often  called  the  Sylvian  gray  -matter.  It 
contains  numerous  irregularly  scattered  nerve-cells  of  uncertain  form  and  size, 
and,  along  its  ventral  border,  the  nuclei  of  origin  of  the  oculomotor  and  trochlear 
nerves  ;  within  its  lateral  parts  lie  the  nuclei  from  which  proceed  the  fibres  of  the 
mesencephalic  roots  of  the  trigeminal  nerves. 

FIG.  960. 


Inferior  colliculus 


Mesencephalic 
root  of  trigeminus 

Lateral  fillet 
Fibres  of  fourth  nerve  • 

Nucleus  of 
fourth  nerve 

Mesial  fillet 


Sylvian  aqueduct 


Central  gray  substance 

Posterior  longitudinal 
fasciculus 


Fountain  decussation 


Mesial  fillet 


Cerebellar  peduncle 


Decussation  of  cerebellar  peduncle 


Transverse  section  of  dorsal  part  of  mid-brain  through  lower  end  of  inferior  colliculi,  at  level  M  (Fig.  919) 
showing  nucleus  of  trochlear  nerve,  and  decussation  of  cerebellar  peduncle.  Weigert-Pal  staining.  X  3^. 
Preparation  by  Professor  Spiller. 

The  substantia  nigra  is  disposed  as  two  irregular  crescentic  columns  of  dark 
gray  matter  that  separate  the  tegmentum  from  the  crustae  of  the  peduncles.  The 
substance  begins  below  at  the  upper  border  of  the  pons  and  continues  uninterruptedly 
through  the  length  of  the  mid-brain  into  the  subthalamic  region  of  the  diencephalon, 
where  it  gradually  disappears.  The  deep  color  of  this  tract  is  due  to  the  conspicuous 
pigmentation  of  its  numerous  nerve-cells.  These  cells  are  of  medium  size  and  of 
various  form,  spindle-shaped  elements,  interspersed  with  some  of  stellate  and  a  few 
of  pyramidal  form,  predominating.  They  enclose  considerable  accumulations  of  dark 
brown  pigment  that  render  the  cells  unusually  conspicuous.  During  the  earliest 
years  of  childhood  the  pigmentation  is  absent  or  very  slight,  but  after  the  sixth 
year  it  is  marked,  and  by  the  seventeenth  has  acquired  its  full  intensity.  Seen  in 
cross-sections  (Fig.  961),  the  convexity  of  each  column,  directed  forward  and  out- 
ward, is  not  uniform,  but  broken  into  irregular  scallops  by  processes  of  gray  matter 
that  penetrate  the  subjacent  crusta.  The  concave  dorsal  margin,  on  the  contrary,  is 
unbroken  and  even.  The  horns  of  the  crescentic  areas,  of  which  the  median  is 
somewhat  the  thicker,  approach  the  free  surface  along  the  bottom  of  the  superficial 


1 1  io  HUMAN   ANATOMY. 

lateral  and  median  grooves  of  the  mid-brain.  Concerning  the  functions  and  connec- 
tions of  the  neurones  within  the  substantia  nigra  very  little  is  known. 

The  Quadrigeminal  and  Geniculate  Bodies. — The  inferior  colliculus 
consists  chiefly  of  a  biconvex  (in  section  oval)  mass  of  gray  matter,  the  nucleus 
colliculi  inferioris,  in  which  many  nerve-cells  of  varying  form  and  mostly  of  small 
size  lie  embedded  within  a  complex  of  nerve- fibres.  The  lower  end  of  the  nucleus 
stands  in  intimate  relation  with  the  acoustic  fibres  composing  the  lateral  fillet,  many 
of  which  enter  the  ventral  aspect  of  the  nucleus  colliculi  to  end  around  its  cells,  whilst 
a  considerable  number  pass  superficial  to  the  nucleus  and  thus  form  an  external  fibre- 
layer  that  intervenes  between  the  gray  nucleus  and  the  surface.  Although  many  of 
these  external  fillet-fibres  enter  the  colliculus  at  higher  levels,  not  a  few  continue, 
by  way  of  the  inferior  brachium,  to  the  median  geniculate  body,  around  whose  neu- 
rones they  end.  A  much  smaller  and  less  well  defined  tract  of  fillet-fibres  passes  to 
the  mesial  side  of  the  nucleus,  the  ventral  margin  of  which  is  thus  embraced  (Fig.  960) 
by  the  diverging  but  unequally  robust  fillet-strands  that  in  this  manner  partially 
encapsulate  the  collicular  nucleus.  From  the  supero-lateral  parts  of  the  nucleus 
fibres  proceed  which,  in  conjunction  with  those  continued  from  the  lateral  fillet, 
form  the  chief  constituents  of  the  inferior  brachium.  A  part  of  this  arm,  how- 
ever, is  composed  of  strands  of  fibres  that  pass  from  the  cerebral  cortex  (especially 
the  temporal)  to  the  inferior  colliculus.  Towards  the  upper  pole  of  the  nucleus 
some  loose  strands  of  fillet-fibres,  probably  along  with  commissural  fibres  uniting 
the  inferior  colliculi,  cross  the  mid-line  and  establish  a  decussation. 

The  internal  or  median  geniculate  body  (corpus  geniculatum  mediate), 
although  genetically  belonging  to  the  diencephalon,  is  so  closely  related  to  the 
inferior  colliculus  as  to  require  description  in  this  place.  It  consists  of  a  superficial 
layer  of  white  matter  composed  of  fibres  from  the  inferior  brachium,  which  pass 
outward  as  continuations  of  the  lateral  fillet,  as  axones  of  the  cells  of  the  inferior 
colliculus,  or  as  fibres  forming  the  lateral  root  of  the  optic  tract,  also  known  as  the 
inferior  commissure  of  Gudden.  Within  this  fibre-capsule  lies  an  oval  mass  of 
gray  matter,  the  nucleus  corporis  geniculati  medialis,  from  whose  cells  axones 
proceed  chiefly  towards  the  cerebral  cortex  in  continuation  of  the  auditory  paths 
of  which  the  inferior  colliculus  and  the  median  geniculate  body  are  important 
stations. 

Connections  of  the  Inferior  Colliculus  and  Median  Geniculate  Body. — Mention  has  been 
made,  when  describing  the  reception-nuclei  of  the  cochlear  portion  of  the  auditory  nerve  (page 
1076) ,  that  the  tract  of  the  lateral  fillet  takes  origin  to  an  important  extent  from  the  cells  of  these 
nuclei,  and,  further,  (page  1082),  that  the  fillet-fibres  end  around  either  the  cells  of  the  inferior 
colliculus,  or  those  of  the  median  geniculate  body.  It  is  evident,  therefore,  that  these  parts  of 
the  mid-brain  stand  in  intimate  relation  with  the  parts  concerned  in  conveying  auditory  impulses. 
The  more  detailed  account  of  the  chaining  together  of  the  neurones  forming  such  paths  is 
deferred  until  the  auditory  nerve  is  considered  (page  1257).  The  connection  of  the  fibres  com- 
posing the  median  root  of  the  optic  tract  with  the  median  geniculate  body  and  the  inferior  collic- 
ulus has  been  established  beyond  doubt ;  further,  that  this  part  of  the  optic  tract  is  not  concerned 
in  conducting  visual  impulses,  is  shown  by  the  fact  that  these  fibres  remain  unaffected  under 
conditions  (after  removal  of  the  eyes)  that  lead  to  degeneration  of  the  fibres  of  retinal  ori-in. 
The  destination  and  significance  of  the  fibre-systems  included  within  the  median  root  of  the 
optic  tract  are  only  imperfectly  understood,  but  it  may  be  accepted  as  certain  that  they  can  no 
longer  be  regarded  as  merely  establishing  a  bond  between  the  median  geniculate  and  indiivctly 
the  inferior  quadrigeminal  bodies  of  the  two  sides,  as  implied  by  the  name  commissure,  since 
many  of  these  fibres  are  probably  directed  after  decussation  to  the  lenticular  nucleus  (globus 
pallidus),  while  others  possibly  may  end  on  the  same  side  in  the  subthalamic  nucleus  (page  1128). 
The  gray  matter  of  the  inferior  colliculus,  like  that  of  the  superior,  gives  rise  to  fibres  of  the 
tecto-bulbar  and  tecto-spinal  tracts,  presently  to  be  described  (page  mi). 

The  superior  colliculus  is  composed  of  a  number  of  alternating  layers  of  white 
and  gray  matter.  The  latter,  however,  is  not  aggregated  into  a  definite  nucleus,  as 
in  the  case  of  the  inferior  colliculus,  but  is  broken  up  into  uncertain  zones  by  the 
tracts  of  nerve-fibres.  Although  as  many  as  seven  layers  have  been  described, 
SOUK-  of  these  are  so  blended  that  only  four  well-defined  strata  can  be  readily 
distinguished.  From  the  surface  inward  these  are : 


THE   MESENCEPHALON. 


mi 


1.  The  stratum  zonale,  a  thin  peripheral  fibre-layer  that  occupies  the  surface  of  the  collic- 
ulus,  whose  components  are  fibres  derived,  in  great  part  at  least,  from  the  optic  tract. 

2.  The  stratum  cinereum,  which  is  not  uniform,  but  thickest  and  most  marked  over  the 
convexity  of  the  colliculus,  and  appears,  therefore,  crescentic  in  transverse  sections.    The  nerve- 
cells  contained  in  this  cap-like  sheet  are  small  and  relatively  few,  their  axones  passing  for  the 
most  part  towards  the  deeper  layers,  whilst  their  dendrites  are  directed  peripherally.     The 
stratum  is  by  no  means  composed  entirely  of  gray  matter,  but  is  invaded  by  many  medullated 
nerve-fibres. 

3.  The  stratum  opticum,  which  consists  of  a  complex  of  gray  matter  and  nerve-fibres, 
the  latter  including  strands  derived  from  the  optic  tract,  which  gain  the  side  of  the  colliculus 
by  way  of  the  superior  brachium  either  as  direct  continuations  of   the  optic  fibres,  or  after 
interruption  in  the  lateral  geniculate  body.     That  this  stratum  includes  other  fibres,  is  shown 
by  the   incomplete   involvement  of  the   layer  in  conditions   producing  degeneration  of  the 

FIG.  961. 


Inferior  colliculus 


Sylvian  aqueduct 

\ 


Central  gray  substance 


Inferior  brachium 


Posterior        | 

longitudinal  — -J 

fasciculus       / 

Tegmental  field  — i. 

Lateral  sulcus  -/ 


Fountain  decussation 


Mesial  fillet 

Decussation 
.^.  of  cerebellar 
<j  peduncles 


Substantia^X 
nigra,  separat- 
ing crusta  from 
tegmentum 

Motor  tracts  ' 


Stratum 
Intermedium 


Cerebellar 
peduncle 


Pontine    Interpeduncular 
fibres  space 


Transverse  section  of  mid-brain  at  level  N  (Fig.  919);    decussation  of  cerebellar  peduncles  is  just  ending. 
Weigert-Pal  staining.     X  3.    Preparation  by  Professor  Spiller. 

optic  paths,  as  well  as  by  the  prominence  of  parts  of  the  stratum  in  animals  possessing  only 
rudimentary  visual  paths  (Edinger).  The  stratum  opticum,  however,  consists  by  no  means 
exclusively  of  fibres,  but  contains,  especially  in  its  deeper  part,  numerous  nerve-cells  of  large 
size,  around  which  the  end-arborizations  of  the  optic  fibres  terminate. 

4.  The  stratum  lemnisci,  which  likewise  includes  masses  of  gray  matter  interspersed 
between  the  strands  of  nerve-fibres.  The  latter  are  chiefly  from  that  part  of  the  median  fillet 
which  terminates  within  the  superior  colliculus  ;  a  certain  number  of  the  fibres,  however,  are 
probably  derived  from  the  lateral  fillet,  which,  while  having  its  principal  quadrigeminal  relation 
with  the  inferior  colliculus,  also  sends  a  small  contingent  to  the  upper  body.  The  deeper  part 
of  the  fillet-layer  contains  a  considerable  amount  of  gray  matter,  in  which  numerous  nerve-cells, 
usually  of  small  size,  are  irregularly  distributed. 

In  addition  to  receiving  optic  and  fillet-fibres,  the  gray  matter  of  the  colliculus  gives  origin 
to  an  important  system  of  descending  fibres  which  establishes  connections  between  the  mid-brain 
and  the  lower  levels  of  the  brain-stem  and  the  spinal  cord.  These  fibres  emerge  from  the  ven- 
tral border  of  the  colliculus  as  radially  disposed  strands  which,  on  nearing  the  gray  matter 
surrounding  the  aqueduct,  turn  ventrally.  The  more  laterally  situated  fibres,  reinforced  by 
those  from  the  opposite  side,  descend  within  the  tegmental  field  to  end  partly  in  relation  with 
the  nuclei  within  the  brain-stem  (tractus  tecto-bulbaris  lateralis)  and  partly  within  the  spinal  cord 
(tractus  tecto-spinalis  lateralis).  The  medially  situated  fibres  sweep  arovmd  the  Sylvian  gray 
matter  and,  for  the  most  part,  cross  the  raphe  immediately  ventral  to  the  posterior  longitudinal 
fasciculus,  thus  establishing  the  fountain  decussation  of  Meynert  (Fig.  960).  The  further  course 


1 1 12  HUMAN   ANATOMY. 

of  these  fibres  is  downward  through  the  brain-stem  and  into  the  anterior  column  of  the  cord 
(tractus  tecto-spinalis  medialisj.  Whether  these  fibres  are  interrupted  in  small  secondary  nuclei 
within  the  tegmentum,  or  pass  unbrokenly  from  the  collicular  cells  to  the  cord  is  undetermined. 
It  is  probable  that,  as  constituents  ol  a  spino-tectal  path,  fibres  also  ascend  from  the  spinal  cord 
to  the  quadrigeminal  bodies.  According  to  Kolliker,  some  of  the  radial  fibres  are  traceable 
through  the  tegmentum,  passing  to  the  outer  side  of  the  red  nucleus  and  piercing  the  tract  of 
the  median  fillet,  and  into  the  substantia  nigra,  whose  cells  they  probably  join  as  axones.  The 
commissure  of  the  superior  colliculi  is  formed  by  fibres  that  cross  the  mid-line  to  the  opposite 
quadrigeminal  body  and  probably  includes,  in  addition  to  the  axones  of  cells  within  the  colliculi 
themselves,  fibres  from  the  fillet  and  optic  tracts. 

The  most  important  connections  of  the  superior  colliculus,  as  may  be  anticipated  from  the 
foregoing  description  of  its  structure,  are  : 

i.  With  the  optic  tract,  directly  or  indirectly  from  the  lateral  geniculate  body,  by  way  of 
the  superior  brachium.  2.  With  the  cerebral  cortex  of  the  occipital  lobe  by  way  of  the  superior 
brachium  and  the  optic  radiation  (page  1175).  3.  With  the  posterior  sensory  columns  of  the 
spinal  cord,  indirectly  by  way  of  the  median  fillet.  4.  With  the  cochlear  nuclei  by  way  of  the 
lateral  fillet,  thus  establishing  a  path  for  audito-visual  reflexes.  5.  With  nuclei  of  the  third, 
fourth  and  sixth  cranial  nerves,  controlling  the  eye-muscles,  especially  the  oculomotor,  by  way 
of  the  posterior  longitudinal  fasciculus.  6.  With  the  lower  levels  of  the  brain-stem  and  the 
spinal  cord  by  way  of  the  tecto-bulbar  and  tecto-spinal  tracts. 

The  lateral  geniculate  body  belongs  to  the  diencephalon  and  may  be  regarded  as  a  special- 
ized part  of  the  optic  thalamus  ;  the  consideration  of  its  structure  therefore,  properly  falls  with 
that  of  the  metathalamus  (page  1126). 

The  Tegmentum. — The  tegmental  region  of  the  mid-brain  includes,  as  seen  in 
transverse  sections  (Fig.  961),  the  U-shaped  area  extending  from  the  quadri- 
geminal bodies  behind  to  the  crescents  of  the  substantia  nigra  in  front.  In  the  vicin- 
ity of  the  central  gray  matter  that  surrounds  the  Sylvian  aqueduct,  the  tegmentum 
consists  chiefly  of  a  foundation  resembling  the  formatio  reticularis  seen  at  lower 
levels.  This  substance  is  produced  by  the  intermingling  of  transverse  or  arcuate  and 
longitudinal  fibres  and  a  meagre  amount  of  gray  matter  with  irregularly  distributed 
nerve-cells,  that  fills  the  interstices  between  the  strands  of  nerve-fibres.  The  more 
lateral  and  ventral  parts  of  the  tegmentum  are  to  a  large  extent  occupied  by  the 
prominent  fibre-tracts  belonging  to  the  fillets  and  to  the  superior  cerebellar  peduncles, 
or  by  collections  of  gray  matter,  as  the  red  nuclei.  Special  groups  of  nerve-cells 
and  of  nerve-fibres  mark  the  origin  and  course  of  the  oculomotor  and  trochlear 
nerves. 

The  details  of  the  tegmentum  vary  with  the  level  of  the  plane  of  section.  Thus,  at  the  lower 
end  of  the  mid-brain  the  tracts  of  the  cerebellar  peduncles  approach  the  mid-line  as  they  ascend 
and  those  of  the  fillets  assume  a  more  lateral  position  ;  whilst  at  higher  levels  these  tracts,  which 
lower  in  the  mid-brain  are  so  conspicuous,  either  terminate  to  a  large  extent,  or  become  so 
broken  up  as  to  no  longer  form  impressive  bundles. 

In  sections  passing  through  the  lower  pole  of  the  inferior  quadrigeminal  bodies  (Fig.  960), 
the  zone  overlying  the  substantia  nigra  is  occupied  to  a  great  extent  by  the  median  fillet,  which 
here  appears  as  a  broad  but  thin  crescentic  or  comma-shaped  field,  whose  outer  and  thicker 
end  lies  at  the  periphery  and  abuts  against  the  base  of  the  dorsally  arching  tract  of  the  lateral 
fillet.  At  the  inner  end  of  the  median  fillet,  near  the  mid-line,  an  isolated  group  of  obliquely 
cut  fibres  sometimes  indicates  the  position  of  the  lemnisco-crustal  bundle  that  appears  ventrally 
among  the  robust  strands  of  the  crusta.  Taken  together,  the  two  fillets  form  a  compact  trad, 
the  outer  contour  of  which,  at  the  level  now  considered,  resembles  a  horizontally  placed  Gothic 
arch,  the  summit  of  the  curve  lying  at  the  surface  and  the  lower  and  upper  limits  of  the  arch 
being  the  median  and  lateral  fillets  respectively.  The  lateral  fillet  continues  the  sweep  of  the 
fillet-stratum  along  the  periphery  of  the  tegmentum  until  it  embraces  the  lower  pole  of  the 
inferior  colliculus  in  the  manner  previously  described  (page  mo). 

Dorsal  to  the  tract  of  the  median  fillet,  and  separated  from  the  latter  by  a  thin  layer  of  com- 
pact foundation-substance,  the  ventral  tegmental  field,  lies  the  broad  curved  band  formed  by 
the  blending  of  the  two  superior  cerebellar  peduncles.  At  lower  levels  (Fig.  936)  these  stalks 
are  separate  and  appear  as  laterally  placed  and  conspicuous  crescentic  areas  of  transversely  cut 
fibres  ;  but  opposite  the  lower  limit  of  the  inferior  qnadrigeminal  bodies  the  ventral  ends  of  these 
crescents  meet  at  the  mid-line  and  interlace  to  form  the  decussation  of  the  cerebellar  peduncles. 
At  a  slightly  higher  level,  after  their  decussation  has  been  almost  completed  (Fig.  961  K  the 
cerebellar  peduncles  appear  as  prominent  rectangular  fields,  with  rounded  corners,  on  each 
side  of  and  close  to  the  mid-line.  These  fields  of  transversely  cut  fibres  represent  the  peduncles 


THE   MESENCEPHALON. 


1113. 


as  they  pass  upward  to  the  red  nuclei,  in  which  a  large  number  of  their  component  fibres  end. 
On  each  side  of  the  median  raphe  of  the  tegmental  field  and  above  (behind)  the  peduncular 
tract,  is  seen  the  posterior  longitudinal  fasciculus,  which  here,  broader  than  in  the  pons,  passes 
close  to  the  ventral  side  of  the  nucleus  of  the  trochlear  nerve.  The  attenuated  crescentic  tract 
of  transverely  cut  fibres  which  lies  along  the  lateral  margin  of  the  central  gray  substance,  medial 
to  the  nucleus  of  the  inferior  colliculus,  represents  the  mesencephalic  root  of  the  trigeminal  nerve. 
In  sections  taken  slightly  below  the  level  of  the  trochlear  nucleus,  irregular  bundles  of  obliquely 
cut  fibres  mark  the  dorsally  directed  course  of  the  fourth-nerve  to  gain  its  decussation  in  the  roof 
of  the  aqueduct  at  the  lowest  limit  of  the  mesencephalon  (Fig.  959). 

FIG.  962. 


Caudate  nucleus 


Anterior  nucleus 


Pulvinar 
Posterior  commissure- 

Pineal  body 
Sylvian  gray  matter 

Corpora  quadrigemina 
Posterior  longitudinal 
fasciculus 

Superior 
medullary  velum 


Cerebellum 


Fourth  ventricle 


Fibres  of   ,.' 
abducent  nerve 


Thalamus 
Ventral  nucleus 


Internal  capsule 

External 
medullary  lamina 

Lenticular  nucleus 

Stratum  medullare 
hypothalamicum 
Tuber  cinereum 


Optic  commissure 


Crustaand  substantia  nigra 
(latter  to  left) 

Red  nucleus 

Fibres  of  oculomotor  nerve 
Superior  cerebellar  peduncle 
Ponto-cerebellar  tracts 


-Pyramidal  tracts 
Mesial  fillet 


Floor  of  IV  ventricle 

(medulla) 
Formatio  reticularis 


Internal  arcuate  fibres 
Nucleus  cuneatus — 

Nucleus  gracilis 
Posterior  fasciculi 


Inferior  olivary  nucleus 


Sagittal  section  of  brain-stem  ;  plane  of  section  is  somewhat  lateral  to  mid-line., 

by  Professor  Spiller. 


ij.     Preparation 


As  seen  in  cross-sections  passing  through  the  superior  quaclrigeminal  bodies,  the  details  of 
the  tegmentum  differ  considerably  from  those  at  the  levels  previously  stated.  The  lateral  fillet 
is  no  longer  present  as  a  distinct  field,  since  with  the  exception  of  a  few  strands  that  are  con- 
tinued into  the  superior  colliculus,  its  fibres  end  within  the  lower  colliculus  or  pass  into  the 
inferior  brachium.  The  median  fillet  now  shows  (Fig.  963)  as  a  somewhat  attenuated  crescentic 
field,  lying  to  the  inner  side  of  the  obliquely  cut  inferior  brachium,  in  consequence  of  many  of 
its.  fibres  having  ended  within  the  lower  part  of  the  superior  colliculus,  the  more  dorsally  situated 
of  those  remaining  being  seen  within  the  upper  colliculus  as  the  stratum  lemnisci. 


HUMAN   ANATOMY. 


The  most  conspicuous  object  within  the  tegmentum  in  the  superior  half  of 
the  mid-brain  is  a  large  round  reticulated  field  on  each  side  of  the  median  raphe, 
which  marks  the  position  of  the  red  nucleus  (nucleus  ruber).  This  body,  also 
called  the  nucleus  tegmenti,  is  of  an  irregular  ovoid  form  (Fig.  963)  and  of  a  reddish 
tint  when  seen  in  sections  of  the  fresh  brain.  Its  lower  limit  corresponds  with  the  level 
of  the  lower  margin  of  the  superior  colliculus,  whilst  its  upper  pole  extends  into  the 
subthalamic  region.  Its  diameter  increases  towards  the  upper  end  and  its  long  axis 
converges  as  it  ascends,  so  that  the  upper  enlarged  portions  of  the  two  nuclei  lie 
close  to  the  mid-line  and  nearer  each  other  than  do  the  lower  poles.  Each  nucleus 
consists  of  a  complex  of  gray  matter  and  nerve-fibres.  The  latter  preponderate 
below,  where  the  red  nucleus  receives  the  fibres  of  the  superior  cerebellar  peduncle, 
and  are  much  less  numerous  above,  since  many  fibres  come  to  an  end  around  the 
rubral  cells.  These  elements  are  very  variable  in  shape  and  size  (.020. -060  mm.), 
but  are  most  often  irregularly  triangular  or  stellate.  The  red  nuclei  constitute  not 

FIG.  963. 


Optic    JB 
thalamus— <BH 


Optic  fibres  joining 
'superior  colliculus 


Part  of  median 
geniculate  nucleus 

Median 

geniculate  body 


Emerging  fibres  of 
oculomotor  nerve 


Inter- 
peduncular 
space      Red 
nucleus 


In  i.il  geniculate  body 
"Stratum  intermedium 


rusta  of  cerebral  peduncle 
'^Substantia  nigra 


Transverse  section  of  mid-brain  at  level  O  ,  _ 
red  nucleus,  and  nuclei  and  root-fibres  of  oculomoto 
Spiller. 


(Fig.  919), passing  through  superior  colliculus  and  geniculate  bodies; 
motor  nerve.     Weigert-Pal  staining.     X  3-     Preparation  by  Professor 


only  important  stations  in  the  path  connecting  the  cerebellum  and  spinal  cord,  but 
also  probably  contribute  links  in  chains  uniting  the  cerebral  cortex  and  the  internal 
nuclei  with  the  cord.  Whilst  some  of  the  constituents  of  the  superior  cerebellar 
peduncle  pass  around  the  red  nucleus  and  continue  as  cerebeUo-thalamic  fibres  uninter- 
ruptedly to  the  optic  thalamus,  the  majority  of  the  fibres  of  this  arm  end  around  the 
cells  of  the  nucleus.  Of  these  many  give  off  axones  that  proceed  brainward  as  rubro- 
thalamic  fibres  ;  others  emerge  from  the  ventro-medial  surface  of  the  nucleus.  en>s> 
the  mid-line  (decussation  of  Forel)  and  bend  downward  as  the-  rubro-spmal  tract. 
The  latter  descends  within  the  tegmentum  of  the  mid-brain  and  pons,  traverses  the 
medulla  and  finally  enters  the  lateral  column  of  the  cord  as  one  of  the  important  but 
uncertainly  defined  descending  tracts.  Other  fibres  enter  the  red  nucleus  on  H 
lateral  aspect  and  establish  connections  between  the  cerebral  cortex  (Dejerine),  and 
probably  also  the  corpus  striatuni  (Fdin^er).  and  the  nucleus.  From  the  cells  of 
the  latter  the  path  is  continued  by  fibres  which  join  the  rubro-spinal  tract,  and 
this  manner  establish  an  indirect' motor  path  that  supplements  the  cortico-spmal 
tracts  identified  with  the  pyramidal. 


THE    MESENCEPHALON.  1115 

The  Crusta. — The  crusta,  or  pes  pedunculi,  appears  in  transverse  sections 
(Fig.  963)  as  a  bold  sickle-shaped  field  that  occupies  the  most  ventral  portion  of  the 
mid-brain.  It  consists  chiefly  of  longitudinally  coursing  fibres  which,  having  traversed 
the  internal  capsule,  are  passing  from  various  parts  of  the  cerebral  cortex  to  lower 
levels  in  the  brain-stem  and  the  spinal  cord.  The  longitudinal  fibres  are  separated 
into  bundles  by  the  invasion  of  numerous  strands  from  the  fibre-complex,  known  as 
the  stratum  intermedium,  which  lies  along  the  ventral  border  of  the  substantia 
nigra.  The  fibres  of  the  crusta  comprise  three  general  sets:  the  cortico-pontine,  the 
cortico-biilbar,  and  the  cortico-spinal. 

The  cortico-pontine  fibres  include  those  passing  from  the  cells  of  the  cerebral 
cortex  to  the  cells  of  the  pontine  nucleus  as  links  in  the  cortico-cerebellar  paths, 
They  are  represented  by  the  fronto-pontine  and  the  tempero-occipito-pontine  tracts, 
which  occupy  approximately  the  median  and  lateral  fifths  of  the  crusta  respectively. 
The  cortico-bulbar-fibres  include  the  efferent  strands  which  pass  from  the  motor 
areas  of  the  frontal  lobe  to  the  nuclei  of  the  motor  fibres  originating  in  the  bulbar  portion 
of  the  brain-stem  (trigeminal,  abducent,  facial,  glosso-pharyngeal,  vagus  and  hypo- 
glossal  nerves).  These  tracts  occupy  something  less  than  the  fifth  of  the  crusta 
lying  next  the  fronto-pontine  tract.  The  cortico-spinal  fibres  include  the  great 
motor  strands  which,  as  the  pyramidal  tracts,  are  so  conspicuous  at  lower  levels. 
These  tracts  share  with  the  fronto-bulbar  paths  the  middle  three-fifths  of  the  crusta, 
appropriating  approximately  the  lateral  three-quarters  of  this  area  (Fig.  1012 ). 

The  Median  Fillet. — Repeated  reference  has  been  made  to  the  median  fillet 
(leraniscus  medialis)  in  the  preceding  descriptions  of  the  brain-stem  ;  a  general  con- 
sideration of  this  important  sensory  tract  may  here  be  given.  It  begins  at  the  lower 
part  of  the  medulla,  about  on  a  level  corresponding  with  the  upper  limit  of  the 
pyramidal  decussation,  as  axones  of  the  cells  within  the  nucleus  gracilis.  These 
sweep  ventro-medially  as  the  deep  arcuate  fibres,  for  the  most  part  cross  the  raphe, 
and  bend  sharply  brainward.  Succeeding  the  condensation  of  the  fillet-fibres  into 
the  sensory  decussation  (Fig.  922)  which  marks  the  lowest  limit  of  the  tract,  the 
fillet  receives  continuous  additions  of  arcuate  fibres  from  the  gracile  and  cuneate 
nuclei  so  long  as  these  collections  are  present.  On  reaching  the  inferior  olivary 
nuclei  in  its  journey  brainward,  the  fillet  forms  a  laterally  compressed  tract,  the 
interolivary  stratum,  lying  immediately  dorsal  to  the  pyramids  (Fig.  928). 
Towards  the  upper  end  of  the  pons,  the  fillet  gradually  exchanges  its  sagittal  plane 
and  median  position  for  an  obliquely  horizontal  disposition,  with  an  increasing 
tendency  to  migrate  laterally.  The  fibres  arising  from  the  nucleus  cuneatus,  which 
below  occupied  the  ventral  part  of  the  fillet,  now  constitute  the  lateral  part  of  the 
tract,  whilst  those  from  the  nucleus  gracilis  form  its  medial  portion.  Within  the 
mid-brain  the  median  and  the  lateral  fillets  form  a  continuous  crescentic  tract  which, 
within  the  upper  part  of  the  tegmentum  and  after  the  disappearance  of  the  acoustic 
paths,  is  represented  chiefly  by  the  superficial  and  laterally  placed  tract  which  the 
median  fillet  has  now  become.  A  considerable  part  of  its  fibres  end  around  the  cells 
of  the  deeper  gray  stratum  of  the  superior  colliculus,  some  passing  over  the  aque- 
duct to  the  colliculus  of  the  opposite  side.  The  remaining  fibres  continue  upward 
through  the  tegmentum,  lateral  and  dorsal  to  the  red  nucleus,  and  the  subthalamic 
region,  to  terminate  chiefly  in  relation  with  the  cells  within  the  ventral  part  of  the 
optic  thalamus.  After  such  interruption  the  impulses  are  carried  by  fibres  arising 
within  the  thalamus  to  various  parts  of.  the  cerebral  cortex.  Whether  fillet-fibres 
gain  the  cortical  gray  matter  without  interruption  within  the  thalamus  is  uncertain. 
Other  fibres,  said  to  be  derived  from  the  cuneate  nucleus,  end  in  the  corpus  subtha- 
lamicum,  and  the  lenticular  nucleus  (globus  pallidus),  from  whose  cells  a  certain  num- 
ber of  fibres  proceed  by  way  of  a  strand  placed  above  the  optic  chiasm,  the  com- 
missure of  Meynert,  to  the  globus  pallidus  of  the  opposite  side.  Still  other  fibres 
are  traceable  into  the  posterior  commissure  of  the  brain  and  into  the  mammillary 
body. 

The  constituents  of  the  median  fillet,  however,  are  by  no  means  restricted  to 
the  fibres  arising  from  the  gracile  and  cuneate  nuclei  of  the  posterior  columns,  but 
include  numerous  important  accessions  from  the  reception-nuclei  of  all  the  sensory 
cranial  nerves  connected  with  the  brain-stem.  From  the  cells  within  the  more 


1 1 16 


HUMAN   ANATOMY. 


FIG.  964. 


extensive  of  such  nuclei,  as  those  within  the  column  of  substantia  gelatinosa  accom- 
panying the  spinal  root  of  the  trigeminus,  numerous  arcuate  fibres  sweep  towards  the 
raphe  and,  with  few  exceptions,  cross  to  join  the  median  fillet  of  the  opposite  side. 
In  this  manner  provision  is  made  for  the  transmission  to  the  higher  receptive  centres 
of  sensory  impulses  collected  not  only  by  the  strands  of  the  posterior  column  of  the 
cord,  but  also  by  the  sensory  fibres  of  the  cranial  nerves  attached  to  the  brain-stem. 
Although  the  principal  components  of  the  fillet-tract  are  the  bulbo-tecto- 
thalamic  strands,  some  fibres  running  in  the  opposite  direction  are  also  present. 
Some  of  these  probably  arise  from  cells  within  the  optic  thalamus  and  the  corpora 
quadrigemina.  Others  are  efferent  strands  which  establish  connections  between 

the  cortical  gray  matter  and 
the  nuclei  of  the  motor  cranial 
nerves,  especially  the  facial  and 
hypoglossal.  These  cortico- 
bulbar  tracts  descend  within 
the  crusta  to  the  lower  end  of 
the  cerebral  peduncle  ;  then, 
leaving  the  latter,  they  traverse 
the  stratum  intermedium  and  in 
the  upper  part  of  the  pons  join 
the  median  fillet  and  descend 
within  its  ventro  -  median 
part  as  far  as  the  superior  end 
of  the  hypoglossal  nucleus. 
During  their  course,  the  fibres 
of  this  crustal  fillet,  as  it  is 
called,  for  the  most  part  undergo 
decussation  on  reaching  the 
levels  of  the  motor  nucleus  for 
which  they  are  destined  ;  some 
fibres,  however,  possibly  end 
around  the  cells  of  the  nucleus  of 
the  same  side. 

The  Posterior  Longi- 
tudinal Fasciculus.  —  This 
bundle  (fasciculus  longitudinalis 
dorsalis)  is  an  association  path 
of  fundamental  importance,  be- 


Sen 


Superior  collicul 


y  part) 


eusory 


Diagram  showing  chief  afferent  constituents  of  median  fillet. 


Posterior  tract 

Spino-thalamii 
Spinal  ganglion — -.f— 7T?V  I *XT\ 

ing  present  in  all  vertebrates.  As 
a  distinct  strand  it  begins  in  the 
superior  part  of  the  mid-brain 
and  thence  is  traceable  as  a  con- 
tinuous tract  through  the  teg- 

mental  region  of  the  pons,  the  dorsal  and  lateral  ventral  field  of  the  medulla  into  the 
anterior  ground-bundle  of  the  spinal  cord.  Throughout  the  greater  part  of  its  course 
through  the  brain-stem,  its  position  is  constant,  the  fasciculi  of  the  two  sides  lying 
close  to  the  median  raphe  and  immediately  beneath  the  gray  matter  flooring  the  Sylvian 
aqueduct  and  the  fourth  ventricle  (Figs.  959,  961).  In  the  lower  part  of  the  medulla, 
the  bundle  gradually  leaves  the  ventricular  floor  and  rests  upon  the  dorsal  border  of 
the  median  fillet,  and,  at  the  level  of  the  pyramidal  decussation,  where  the  fillet  no 
longer  intervenes,  lies  behind  the  pyramid  and  at  some  distance  from  the  mid-line. 
Lower,  it  assumes  a  more  ventral  position,  to  the  medial  side  of  the  isolated  anterior 
cornu,  and,  finally,  enters  the  anterior  column  of  the  cord  to  be  lost  within  the-  upper 
part  of  the  ground  bundle. 

The  fasciculus  includes  association  fibres  of  varying  lengths,  some  of  which  are 
ascending  and  others  descending  paths.  The  constitution  of  the  bundle  is,  there- 
fore, continually  changing,  the  loss  of  certain  fibres  being  replaced  by  the  addition 
of  others.  Its  fibres  are  among  the  very  first  in  the  brain  to  become  medullated,  and 
begin  to  acquire  this  coat  during  the  fourth  foetal  month  (Hosel  ). 


THE   MESENCEPHALON. 


1117 


FIG.  965. 


CN 


Notwithstanding  the  admitted  importance  of  the  tract  and  the  prolonged  study  that  it  has 
received,  much  remains  to  be  determined  concerning  the  source  and  connections  of  the  many 
constituents  which  undoubtedly  go  to  form  the  bundle.  Among  the  more  certain  of  these  com- 
ponents the  following  may  be  mentioned  : 

1.  At  the  upper  end  of  the  fasciculus  a  considerable  number  of  fibres  arise  from  the  cells 
of  the  nucleus  of  the  posterior  commissure,  or  Darkschewitscti ' s  nucleus,  which  lies  in  advance 
of  the  oculomotor  nucleus,  within  the  gray  matter  surrounding  the  superior  end  of  the  Sylvian 
aqueduct.     According  to  Edinger  an  additional  contingent  takes  origin  from  a  nucleus  (n.  fas- 
ciculi longitudinalis  dorsalis)   within  the  gray  matter  of  the 

floor  of  the  third  ventricle  in  the  vicinity  of  the  corpus  mam- 
millare.  The  contributions  from  both  these  sources  join 
the  fasciculus  as  crossed  fibres  from  the  nuclei  of  the 
opposite  side. 

2.  The  fibres  arising  from  the  vestibular  (Deiters') 
nucleus  constitute  an  important  element  of  the  posterior 
longitudinal   bundle,  since  they  establish  reflex  paths  for 
equilibration   impulses.      These   fibres,    both  crossed  and 
uncrossed,  join  the  fasciculus  and  pass  in  both  directions. 
Those  passing  brainward  have  as  their  chief  objective  point 
the  oculomotor  nucleus,  although  the  nuclei  of  the  sixth 
and   fourth    nerves   receive   fibres   or  collaterals.     In  this 
manner  the  filaments  supplying  the  various  ocular  muscles 
are  brought  under  the  influence  of  the  vestibular  impulses. 
It  is  probable  that  the    facial  nucleus   likewise    receives 
collaterals,  if  not  main  stems,  of  the  vestibulo-nuclear  fibres. 

3.  Upon  clinical  and  experimental  evidence,  it  may  be 
assumed  that  fibres  pass  by  way  of  the  longitudinal  bundle 
from  the  abducent  nucleus  to  that  part  of  the  oculomotor 
nucleus  sending  fibres  to  the  internal  rectus  muscle  of  the 
opposite  side  (perhaps  also  from  the  nucleus  of  the  third 
nerve  to  that  of  the  abducens  of  the  same  side),  by  which 
arrangement  the  harmonious   action  of  the   internal   and 
external  recti  muscles  is  insured.     Basing  their  conclusions 
upon    similar    evidence,    many     anatomists     accept    the 
existence  of  fibres   which   pass   by    way   of  the  posterior 
longitudinal  bundle  from  the  oculomotor  nucleus  to  the  cells 
of  the  facial  nucleus  (page  1251)  from  which  proceed  the 

fibres  supplying  the  orbicularis  palpebrarum  and  the  corrugator  supercilii.  In  this  manner 
the  coordinated  action  of  these  muscles  and  the  levator  palpebrae  superioris  is  explained.  A 
similar  connection  is  probably  established  by  the  posterior  longitudinal  bundle  between  the 
nucleus  of  the  hypoglossal  and  that  of  the  facial  nerve,  whereby  the  closely  associated 
movements  of  the  lips  and  tongue  are  assured.  That  the  function  of  the  posterior  fasciculus 
is  by  no  means  limited  to  association  of  the  nuclei  of  the  ocular  nerves  is  evident  from  the 
fact  that  in  animals  or  individuals  in  which  such  centres  are  wanting  (due  to  absence  or 
imperfect  development  of  the  visual  organs)  the  bundle  is  nevertheless  well  represented. 

4.  Fibres  arise  from  the  reception-nuclei  of  the  remaining  sensory  nerves  of  the  brain-stem 
and  pass  to  the  posterior  longitudinal  fasciculus  of  the  same  and  the  opposite  side.     On  enter- 
ing the  bundle,  they  course  in  both  directions  and  by  means  of  their  collaterals  and  stem-fibres 
send  end-brushes  to  the  nuclei  of  the  motor  nerves,  in  this  manner  establishing  direct  reflex 
areas  between  the  afferent  and  efferent  paths. 

In  addition  to  linking  together  by  longer  and  shorter  association  fibres  the  various  levels  of 
the  brain-stem  and  the  latter  with  the  upper  segments  of  the  spinal  cord,  it  is  probable  that  the 
relations  of  the  posterior  longitudinal  bundle  are  far  reaching  and  may  include  connections 
with  the  thalamus  and  subthalamic  region,  the  corpora  quadrigemina,  the  red  nucleus  and  the 
cerebellum. 

DEVELOPMENT  OF  THE  MESENCEPHALON. 

Of  the  three  primary  cerebral  vesicles,  the  mid-brain  undergoes  least  change.  Although 
much  smaller  than  either  of  the  other  segments  of  the  brain-tube,  its  prominent  position,  lying 
as  it  does  at  the  summit  of  the  cephalic  flexure,  makes  it  conspicuous  in  the  early  developing 
brain.  During  the  enormous  expansion  upward  and  backward  incident  to  the  development 
of  the  cerebral  hemispheres  in  man,  the  mid-brain  becomes  covered  in  and  deposed  to  a 
dependent  position  and  a  relatively  small  size.  For  a  time  possessing  a  spacious  cavity,  it  fails 
to  keep  pace  with  the  growth  of  the  adjoining  parts  ;  its  walls  thicken  and  its  lumen  becomes 
•eventually  reduced  to  the  narrow  Sylvian  aqueduct. 


Diagram  showing  chief  constituents 
of  posterior  longitudinal  fasciculus.  Ill, 
IV,  VI,  VII,  XII,  nuclei  of  respective 
nerves;  DN,  vestibular  (Deiters1)  nu- 
cleus ;  CN,  common  nucleus  of  posterior 
commissure  and  posterior  longitudinal 
fasciculus. 


in8  HUMAN    ANATOMY. 

The  dorsal  zones  of  the  lateral  wall  of  the  mid-brain  give  rise  to  the  quadrigeminal  plate, 
whose  external  surface  is  at  first  smooth  but  later  marked  by  a  temporary-  median  longitudinal 
ridge.  About  the  third  fcetal  month,  with  the  exception  of  its  lower  end,  which  persists  as  the 
frenulum  veli,  this  ridge  is  succeeded  by  a  longitudinal  groove  bounded  on  either  side  by  an 
elevation.  The  elevations  of  the  two  sides  mark  the  appearance  of  the  corpora  bigemina,  cor- 
responding to  the  optic  lobes  of  the  lower  vertebrates.  During  the  fifth  month,  an  obliquely 
transverse  furrow  forms  on  each  side,  by  which  the  paired  elevations  are  subdivided  into  four 
eminences,  the  corpora  quadrigemina.  About  this  time  the  corpora  geniculata,  which  however 
belong  developmentally  to  the  diencephalon,  are  also  differentiated  and  for  awhile  are  rela- 
tively very  large  and  prominent. 

The  ventral  zones  greatly  thicken  and  give  origin  to  the  tegmentum,  including  the  nuclei 
of  the  oculomotor  and  of  the  trochlear  nerves  and,  perhaps,  the  red  nuclei,  and  the  mantle  layer 
of  the  cerebral  peduncles  with  the  interpeduncular  substance.  The  floor-plate  becomes  com- 
pressed between  the  expanding  ventral  zones  of  the  lateral  walls  and  probably  is  represented 
by  the  raphe.  Since  the  fibre-systems  of  the  crustae  are,  for  the  most  part,  derived  from  sources 
outside  the  brain-stem,  their  appearance  within  the  peduncles  follows  a  secondary  ingrowth, 
and  only  after  such  invasion  do  the  cerebral  crura  present  their  characteristic  ventral  prom- 
inence. The  cortico-pontine  tracts  share  with  the  pyramidial  fibres  the  characteristic  of  tardy 
myelination,  since  they  do  not  acquire  their  medullary  coat  until  some  time  after  birth.  Among 
the  earliest  of  the  cortico-bulbar  fibres  to  become  medullated  -(a  few  weeks  after  birth  i  are  those 
destined  for  the  motor  cranial  nerves  by  way  of  the  crustal  or  pyramidal  fillet  of  Flechsig. 
According  to  Kolliker,  the  stratum  intermedium,  which  is  closely  related  to  the  substantia 
nigra,  not  only  in  position  but  also  by  the  destination  of  many  of  its  fibres,  contains  a  consider- 
able number  of  medullated  fibres  by  the  ninth  fcetal  month. 

THE   FORE-BRAIN. 

It  will  be  recalled  that  the  fore-brain,  the  anterior  primary  cerebral  vesicle,  gives 
rise  to  two  subdivisions,  the  telencephalon  and  the  diencephalon  (page  1060).  Since 
the  latter  lies  immediately  in  front  of  the  mid-brain,  in  following  the  order  in  which 
the  brain-segments  have  been  described,  the  diencephalon  next  claims  attention. 

THE    DIENCEPHALON. 

Strictly  considered  upon  the  basis  of  the  classic  subdivision  suggested  by  His,  the 
diencephalon,  or  inter-brain,  includes  (i)  a  large  dorsal  portion,  the  thalamen- 
cephalon  and  (2)  a  small  ventral  portion,  the  pars  mammillaris  hypothami, 
together  with  (3)  the  enclosed  remains  of  the  posterior  part  of  the  cavity  of  the 
fore-brain,  as  represented  by  the  greater  part  of  the  third  ventricle.  The  thalamen- 
cephalon,  in  turn,  includes  :  (a)  the  thalamus,  (£)  the  epithalamus,  comprising  the 
pineal  body,  the  habenular  region  and  the  posterior  commissure,  and  (c)  the  meta- 
thalamus,  including  the  corpora  geniculata.  Since,  however,  the  description  of  the 
third  ventricle  and  its  surrounding  structures — the  essential  features  of  this  segment 
of  the  adult  brain — requires  the  inclusion  of  parts  belonging  to  the  telencephalon 
(pars  optica  hypothalami),  it  will  be  more  convenient  to  disregard  their  strict 
developmental  relations  and  include  the  representatives  of  the  pars  optica  in  the 
consideration  of  the  diencephalon. 

The  Thalamus. — After  removal  of  the  overlying  structures — the  corpus  callo- 
sum,  the  fornix  and  the  velum  interpositum — the  thalami  (thalami),  also  called 
the  optic  thalami,  are  seen  as  two  conspicuous  masses  of  gray  matter  separated  by  a 
narrow  cleft,  the  third  ventricle.  Each  thalamus  is  an  ovoid  ganglionic  mass,  blunt 
wedge-shaped,  as  seen  in  cross-sections  (Fig.  967),  whose  long  axis  extends  from 
the  narrow  anterior  pole  backward  and  outward.  Of  its  four  surfaces,  the  lateral  and 
ventral  are  blended  with  the  surrounding  nervous  tissue,  and  the  mesial  and  dorsal 
are  to  a  large  extent  free.  The  large  superior  surface  is  irregularly  triangular 
in  outline,  slightly  convex  in  the  frontal  plane  and  markedly  so  in  the  sagittal,  and 
covered  with  a  thin  layer  of  nerve-fibres,  the  stratum  zonale,  which  imparts  a 
whitish  color.  This  stratum  is  composed  of  fibres  which  are  traceable  on  the  one 
hand  to  the  optic  tract,  and  on  the  other  to  the  optic  radiation  in  the  hind  part  of 
the  internal  capsule.  Laterally,  the  superior  surface  is  separated  from  the-  caudate 
nucleus  by  a  groove  which  obliquely  crosses  the  floor  of  the  lateral  ventricle  and 
lodges  a  narrow  hand  of  fibres,  the  taenia  semicircularis  (stria  tci  minalis  i  and,  in 
its  anterior  part,  the  vein  of  the  corpus  striatum.  In  its  front  half,  where  it  hounds  the 


THE   DIENCEPHALON. 


1119 


ventricle,  the  inner  border  is  sharply  defined  from  the  mesial  surface  by  a  delicate  but 
well  defined  ridge,  tsenia  thalami,  produced  by  the  thickening  of  the  ependyma 
of  the  third  ventricle,  along  its  line  of  reflection  onto  the  membranous  roof,  and 
the  underlying  strand  of  nerve-fibres,  the  stria  medullaris.  Traced  backward,  the 
tsenia  thalami  becomes  continuous  with  the  stalk  of  the  pineal  body.  Between 
this  ridge  and  the  diverging  mesial  border  of  the  upper  surface  of  the  thalamus,  is 
included  a  narrow  depressed  triangular  area,  known  as  the  trigonum  habenulae. 
It  lies  on  a  distinctly  lower  level  than  the  adjoining  convex  upper  surface  of  the 
thalamus.  Since  it  contains  a  special  nucleus  and  belongs  to  the  epithalamus,  its. 
description  will  be  deferred  until  that  region  is  considered  (page  1123).  The  upper 
surface  is  not  quite  even,  but  subdivided  by  a  shallow  oblique  furrow,  which  runs 
from  before  backward  and  outward  and  marks  the  position  of  the  overlying  lateral 
border  of  the  fornix.  External  to  this  furrow  lies  a  free  marginal  zone  that  forms  a 
part  of  the  floor  of  the  lateral  ventricle  ;  internal  to  it  is  an  attached  inner  zone  over 
which  the  velum  interpositum  is  united  to  the  thalamus.  By  the  attachment  of  this 


FIG.  966. 


Septum  lucidum 

Tsenia    semicircularis  and 
vena   terminalis 

Tsenia  chorioidea 
Furrow  for  fornix 

Tasnia  thalami 

Trigonum  habenulse 

Pulvinar 


Corpora   quadrigemina 


Corpus  callosum 


Caudate  nucleus 

Anterior  pillars  of  fornix 
—  Foramen  of  Monroe 

Anterior  commissure 

Middle  commissure  in  III 
ventricle 

Thalamus 

Posterior  commissure 
Pineal  body 


Lingula 


Thalami,  caudate  nuclei  and  ventricles  viewed  from  above  after  removal  of  corpus  callosum,  fornix  and 
velum  interpositum  ;  third  ventricle  shows  as  narrow  cleft  between  mesial  surfaces  of  thalami. 

sheet  to  the  fornix  above  and  to  the  thalamus  below,  direct  communication  between 
the  third  and  lateral  ventricles  is  shut  off  save  through  the  foramen  of  Monroe.  In 
front,  the  superior  surface  ends  on  the  rounded  elevation  (tuberculum  anterius  thalami) 
which  marks  the  anterior  pole  of  the  ganglion,  while  behind  it  goes  over  onto 
the  prominent  posterior  projection,  the  pulvinar,  which  overhangs  the  superior 
brachium  and  the  corpora  geniculata.  The  mesial  surface  forms  the  greater  part 
of  the  lateral  wall  of  the  third  ventricle.  It  is  covered  by  a  layer  of  gray  matter 
prolonged  from  the  central  gray  of  the  Sylvian  aqueduct,  over  which  stretches  the 
immediate  lining  of  the  ventricle,  the  ependyma.  The  upper  boundary  of  the  mesial 
surface  is  sharply  defined  by  the  taenia  thalami,  which  behind  is  continuous  with  the 
stalk  of  the  pineal  body  (Fig.  966).  Its  lower  limit  is  indicated  by  an  oblique 
furrow,  the  sulcus  hypothalamicus,  which  separates  the  thalamic  from  the 
hypothalamic  regions.  Somewhat  in  advance  of  their  middle,  the  mesial  surfaces 
of  the  two  thalami  are  connected  by  a  bridge  of  gray  matter,  known  as  the 
middle  commissure  (massa  intermedia),  usually  about  7—8  mm.  in  diameter  and 
oval  in  section,  but  very  variable  in  thickness  and  form.  From  the  meagre  number 
of  medullated  nerve-fibres  that  it  contains,  its  importance,  at  least  in  man,  seems 
to  be  small.  The  lateral  surface  of  the  thalamus  is  inseparably  blended  with  the 
adjacent  thick  and  conspicuous  stratum  of  white  matter,  the  internal  capsule, 
which  intervenes  between  the  thalamus  and  the  more  laterally  placed  lenticular 


JI2O 


HUMAN    ANATOMY. 


nucleus,  and  establishes  the  important  pathway  transmitting  the  fibre-tracts  con- 
necting the  cerebral  cortex  with  the  thalamus  and  with  the  lower  levels  by  way 
of  the  crusta  of  the  cerebral  peduncle.  Since  the  innumerable  fibres  which  pass 
to  and  from  the  thalamus  along  its  ventro-lateral  surface  interlace,  this  surface  is 
•covered  by  a  distinct  reticulated  stratum,  to  which  the  name  external  medullary 
lamina  is  applied.  The  ventral  surface  is  also  attached,  but  instead  of  being 
united  with  the  internal  capsule,  as  is  the  lateral,  it  rests  upon  and  is  intimately 
blended  with  the  upward  prolongation  of  the  tegmental  portion  of  the  cerebral 
peduncle,  here  known  as  the  subthalamic  tegmental  region,  presently  to  be 
described  (page  1127). 

FIG.  967. 


Corpus  callosum 

Choroid  plexus 

Fornix 

Tsenia  thalami 

Middle  commissure 

Third  ventricle 

Manimillo-thalatnic 

tract 

Maininillary  body 

Amygdaloid 
nucleus 


Caudate  nucleus 


Thalamus, 
mesial  nucleus 


Thalamus. 
lateral  nucleus 

Lenticular  nucleus 

Subthalamic 

nucleus 

Optic  tract 

Tail  of 

caudate  nucleus 
Inferior  horn  of 
lateral  ventricle 


Hippocampus,  cut  obliquely 
Crusta  of  cerebral  peduncle 

Frontal  section  of  brain  passing  through  thalami,  middle  commissure  and  mammilla! y  bodies. 

Structure  of  the  Thalamus. — Although  composed  chiefly  of  gray  matter, 
the  thalamus  is  partially  surrounded  and  penetrated  by  tracts  of  white  matter.  In 
addition  to  being  invested  on  its  superior  and  ventro-lateral  surfaces  by  the  stratum 
zonale  and  the  external  medullary  lamina  respectively,  the  general  ganglionic  mass 
is  subdivided  by  a  vertical  internal  sheet  of  fibres,  continuous  with  the  stratum  xonale 
and  known  as  the  internal  medullary  lamina,  into  three  fairly  marked  nuclei, 
the  anterior,  the  mesial  and  the  lateral  (  Fig.  967).  Of  these  the  lateral  nucleus  is 
much  the  largest  and  is  included  between  the  external  and  internal  medullary  lamina-. 
Whilst  the  lateral  nucleus  does  not  reach  as  far  forward  as  the  anterior  pole  of  the 
thalamus,  its  caudal  extremity  includes  the  entire  pulvinar.  Tin-  lateral  nucleus 
consists  histologically  of  an  intricate  complex  of  nerve-fibres  and  cells.  The  latter 
are  in  general  of  the  multipolar  type,  although  very  variable  as  to  details  of  t<>rm 
•and  sixe.  Two  principal  types  are  recognixed  by  Kolliker,  the  one  being  elongated 
or  fusiform  and  possessed  of  relatively  few  branches,  and  the  other  being  stellate  and 
provided  with  richly  branched  dendrites.  Many  of  the  fibres  represent  paths  ending 
within  the  thalamus  and  therefore  terminate  in  arborixatioiis  around  the  thalamic 
cells  ;  others  are  the  a \ones  of  such  cells  and  pass  to  various  parts  of  the  cortex  or 
other  parts  of  the  brain.  The  historical  characteristics  of  the  lateral  nucleus,  in  the 


THE   DIENCEPHALON. 


II2I 


main  hold  good  for  the  other  nuclei,  although  the  lateral  nucleus  is  particularly 
rich  in  fibres,  and  therefore  of  a  paler  tint,  on  account  of  its  close  relations  to  the 
internal  capsule  and  the  tegmentum  of  the  cerebral  peduncle. 

The  mesial  nucleus  lies  between  the  central  gray  matter  of  the  ventricular 
wall  and  the  internal  medullary  lamina,  and  is  separated  by  the  latter  from  the  lateral 
nucleus.  Its  caudal  end  is  bordered  internally  by  the  ganglion  habenulae,  and,  behind, 
by  the  pulvinar.  The  anterior  nucleus,  the  smallest  of  the  three,  is  a  wedge-shaped 
mass,  whose  rounded  base  looks  forward  and  corresponds  to  the  anterior  tubercle, 
and  whose  apex  is  directed  backward  and  lies  between  the  front  ends  of  the  mesial 
and  lateral  nuclei,  separated  from  these  by  the  internal  medullary  lamina,  which 
divides  into  two  diverging  levels  that  embrace  the  anterior  nucleus.  In  addition  to 
its  contribution  of  radiating  fibres  which  take  part  in  the  production  of  the  thalamic 
radiation,  the  anterior  nucleus  contains  a  compact  bundle  of  fibres  traceable  into  the 
mammillary  body  on  the  base  of  the  brain.  These  are  the  constituents  of  the  mam- 
millo-thalamic  tract,  or  bundle  of  Vicq  d1  Azyr,  by  which  a  large  part  of  the  fibres 


FIG.  968. 


Corpus  callosmn 
Choroid  plexus 
Lateral  ventricle 


Stratum  zonale 
Caudate  nucleus 
Genu  of  internal  capsule 
Thalamus,  mesial  nucleus 

Thalamus,  lateral 
nucleus 

Internal  capsule 


Putamen 


Globus  pallidus 


Anterior  pillars  of  foriiix/ 

Lamina  cinerea 


Gyrus  callosus 

Cingulum 

Corpus  callosum 

.Striate  vein 


Anterior  commissure 


Caudate  nucleus 

Taenia  semicircularis 


Internal  medullary 
lamina 

External  medul- 
lary lamina 


Mammillo- 
thalamic  tract 


— Putamen 
Globus  pallidus 


Thalamo-tegmental 
tract 


Olfactory  fibres 


Oblique  frontal  section  through  thalamus  and  anterior  commissure;  Weigert-Pal  staining.     X  f- 
Preparation  by  Professor  Spiller. 


coursing  within  the  anterior  pillar  of  the  fornix  are  carried  to  the  thalamus  (page 
1159).  The  entire  ventral  part  of  the  thalamus  is  occupied  by  an  illy-defined  mass 
of  gray  matter,  known  as  the  ventral  nucleus,  which  lacks  sharp  definition  from 
the  overlying  nuclei  and  in  fact  is  continuous  with  the  lateral  nucleus.  The  ventral 
nucleus  presents  a  differentiation  into  the  nucleus  centralis  of  Luys,  which  occupies 
a  mesial  position  and  appears  round  in  section  (Fig.  970),  and  receives  fibres  from 
the  red  nucleus  and  the  posterior  commissure,  and  the  nucleus  arciformis,  which 
lies  ventro-lateral  to  the  preceding  nucleus  and  is  crescentic  in  outline.  The  ventral 
nucleus  is  of  importance,  not  only  because  it  receives  the  great  sensory  paths,  but  also 
on  account  of  its  phylogenetic  rank,  since,  according  to  Edinger,  it,  together  with  the 
ganglion  habenulas,  represents  the  oldest  of  the  thalamic  nuclei  and  is  found  through- 
out the  vertebrate  series. 

Connections  of  the  Thalamus. — Broadly  considered,  the  thalamus  may  be 
regarded  as  a  great  ganglionic  internode  interposed  in  the  corticipetal  paths  around 
whose  cells  most  of  the  constituents  of  the  important  secondary  paths  conveying 
afferent  impulses  from  the  spinal  cord,  the  brain-stem  and  the  cerebellum  end, 

7' 


1122 


HIM  AN    ANATOMY. 


and  from  whose  cells  corticipetal  fibres  pass  to  all  parts  of  the  cerebral  cortex 
and  to  the  corpus  striatum.  Further,  it  must  be  understood  that  the  thalamus 
receives  fibres  from  all  parts  of  the  cerebral  cortex,  and,  lastly,  that  from  it 
proceed  efferent  fibres  to  the  lower  centres  within  the  brain-stem  and  the  cord. 
It  is  evident,  therefore,  that  the  connections  of  the  thalamus  are  very  intricate 
and  far  reaching. 


FIG.  969. 


i.  The  lower  thalamocipetal  tracts  include :  (a)  those  passing  directly  from  the  spinal  cord, 
as  the  spino-thalanric  and  probably  a  part  of  Cowers'  tract ;  ({>)  those  passing  from  the 
various  nuclei  by  way  of  the  median  fillet ;  (c)  those  passing  from  the  cerebellum,  either 

directly,  as  the  cerebello-thalaniic 
tract,  or,  after  interruption  in  the 
red  nucleus,  as  the  nibro-thala- 
mic;  (d)  probably  other  tracts 
which  arise  within  the  tegmen- 
tal  area  of  the  brain-stem.  The 
fibres  from  the  various  sources 
enter  the  under  surface  of  the 
thalamus  to  end  within  the  ven- 
tral nucleus,  or  by  means  of  the 
internal  medullary  lamina  to  be 
distributed  to  the  other  nuclei. 

2.  The  thalamic  radiation 
comprises  the  fibres  which  stream 
from  the  latero-ventral  surface  of 
the  thalamus  to  all  parts  of  the 
hemisphere  ( thalamo-cortical ) , 
some  crossing  by  way  of  the 
corpus  callosum  to  the  oppo- 
site side,  as  well  as  those  which 
pass  in  the  opposite  direction 
(  cortico-thalamic  )  towards  the 
ganglion.  Although  as  they 
traverse  the  external  medullary 
lamina  the  fibres  are  not  particu- 
larly grouped,  their  various  rela- 
tions to  the  cortex  or  other  parts 
are  established  by  different  and 
more  or  less  definite  paths. 
These  are  designated  as  the 
stalks  of  the  thalamus,  of  which 
a  frontal,  a  parietal,  an  occipital 
and  a  ventral  are  conventionally 
distinguished.  The  anterior  or 
frontal  stalk  emerges  from  the 
fore-part  of  the  lateral  surface  of 
the  thalamus,  traverses  the  an- 
terior part  of  the  internal  capsule 
between  the  caudate  and  lentic- 
ular nuclei,  to  which  it  distributes 
fibres,  and  finally  gains  the  cortex  of  the  frontal  lobe.  From  the  cells  of  this  region,  cortico- 
thalamic  fibres  follow  in  reversed  order  the  paths  just  mentioned,  thus  establishing  a 
double  relation  between  the  cortex  and  the  basal  ganglion.  In  addition  to  the  preceding 
cortico-thalamic  fibres,  the  antero-ventral  part  of  the  thalamus  receives  a  strand  from  the 
cortex  of  the  olfactory  bulb.  The  parietal  stalk  leaves  the  lateral  surface  of  the  thalamus  and 
enters  the  internal  capsule  and  often  the  lenticular  nucleus,  in  its  course  to  the  parietal 
cortex.  Other  corticipetal  fibres,  destined  for  the  parietal  and  adjacent  parts  of  the 
frontal  lobe,  are  the  continuations  of  the  path  of  the  mesial  fillet.  To  a  large  extent 
these  fibres  pass  from  the  ventral  thalamic  nucleus  outward  to  the  under  surface  of 
the  lenticular  nuck-us,  then  bend  upward  and  traverse  the  lenticular  nucleus  by  way  of 
the  medullary  stria'  or  the  globus  pallidus  to  gain  the  cortex.  Other  fibres  continue  the  fillet- 
path  by  entering  the  internal  capsule  and  thus,  perhaps,  directly  proceed  to  the  cortex.  The 
occipital  stalk  includes  the  fibres  that  connect  the  thalamus  with  tin-  visual  cortical  areas  of  the 
occipital  and  parietal  lobes.  They  issue  from  the  lateral  surface  of  the  pulvinar,  and  as  the 


Rubro-thalamic 
Cerebello-thalamic 


Median  fillet 
Spino-thalamic 


Diagram  showing  chief  connections  of  thalamus;  black  fibres  rep- 
resent afferent  tracts  ending  in  thalamus  and  thalamo-cortical  paths  : 
red  fibres  are  the  cortico-thalamic  and  strio-thalatnic  paths ;  T,  thal- 
amus; C.  L,  caudate  and  lenticular  nuclei;  C,  C,  corpus  callosum; 
f,  P,  T,  O,  frontal,  parietal,  temporal  and  occipital  lobes;  fjr,  fornix; 
M,  mammillary  body;  Pd,  cerebral  peduncle;  SC,  /C,  superior  and  in- 
ferior colliculi ;  K,  red  nucleus ;  Ps,  pons  ;  /,  frontal  stalk  ;  2,  parietal 
stalk  ;  3,  4,  lenticular  and  temporal  parts  of  ventral  stalk  ;  ,5,  occipital 
stalk. 


THE    DIENCEPHALON. 


1123 


optic  radiations  sweep  outward  and  backward  around  the  posterior  horn  of  the  lateral 
ventricle  to  end  in  the  cortex.  The  ventral  stalk  is  complex  in  its  relations,  since  its  fibres 
include  two  systems.  Emerging  from  the  fore-part  of  the  ventral  surface  of  the  thalamus, 
from  the  lateral  and  mesial  nuclei,  the  stalk  passes  downward  and  outward  beneath  the 
lenticular  nucleus.  Its  lower  part,  known  as  the  ansa  peduncularis,  continues  laterally  into 
the  cortex  of  the  temporal  and  of  the  central  lobe  ;  its  upper  part,  the  ansa  lenticularis, 
closely  skirts  the  adjacent  border  of  the  lenticular  nucleus  which  it  enters  to  gain  the  putamen, 
or,  continuing  through  the  lenticular  nucleus  by  way  of  the  medullary  laminae,  to  reach  the 
caudate  nucleus.  Under  the  name  tractus  strio-fhalamicus,  are  included  the  fibres  which  pass 
from  the  caudate  nucleus  and  the  putamen  to  the  thalamus,  subthalamic  body  and  red  nucleus, 
a  small  number  of  fibres  probably  entering  the  thalamus  from  the  caudate  nucleus  by  the  more 
direct  route  of  the  internal  capsule. 

3.  The  stratum  zonale,  the  thin  layer  of  white  matter  which  covers  the  superior  aspect 
of  the  thalamus,  consists  in  large  part  of  thalamocipetal  fibres  derived  from  the  optic  tract  or  the 
optic  radiation.  Those  from  the  lateral  root  of  the  tract  superficially  cross  the  external  genic- 
ulate  body  and  spread  over  the  thalamus,  while  those  from  the  occipital  cortex  by  way  of  the 
optic  radiation  invest  the  pulvinar.  Other  contributions  to  the  stratum  zonale  include  fibres 
from  the  temporal  cortex  by  way  of  the  ventral  stalk. 

The  Epithalamus.  —  Under  this  subdivision  of  the  thalamencephalon  are 
included:  (i)  the  trigonum  habenulee,  (2)  the  pineal  body,  and  (3)  the  posterior 
commissure — all  structures  closely  associated  with  the  superior  and  posterior  boun- 
daries of  the  third  ventricle. 

FIG.  970. 

Veins  of  Galen  in 
Corpus        velum  interpositum  Stria 


Fornix         callosum 


medullaris         Ganglion  habenulae 


Lateral  ventricle 
Caudate  nucleus 


Thalamus, 
ventral  nucleus 


Thalamus,   /f^ 
mesial  nucleus1 


Subthalamic 
region 


Crusta  of 
cerebral  peduncles 


_ .  External 

medullary  lamina 

Thalamus 


Red  nucleus 


enticular 
ilK^  nucleus 

>S    Internal  capsule 


Subthalamic  nucleus 


Oblique  frontal  section  through  thalamus  and  subthalamic  region  ;     Weigert-Pal  staining.     X  \. 
Preparation  by  Professor  Spiller. 


The  trigonum  habenulae  is  the  narrow  triangular  area  lying  between  the 
sharply  denned  edge  (taenia  thalami)  of  the  ventricular  wall  internally  and  the 
diverging  mesial  border  of  the  upper  surface  of  the  thalamus  externally  (Fig.  966). 
Its  surface  is  depressed  and  at  a  lower  level  than  that  of  the  thalamus  and  behind  is 
continuous  with  a  mesially  curving  strand,  the  pineal  peduncle.  Beneath  the 
ridge  of  thickened  ependyma  marking  the  taenia  thalami,  lies  a  distinct  strand 
of  nerve-fibres,  the  stria  medullaris,  while  at  a  still  deeper  level  and  covered  by 
the  superficial  fibres  is  situated  an  aggregation  of  small  nerve-cells,  known  as  the 
ganglion  habenulae.  The  source  of  the  fibres  composing  the  stria  medullaris  and 
the  connections  of  the  ganglion  habenulae  are  still  uncertain.  It  is  probable,  how- 
ever, that  many  components  of  the  stria  are  associated  with  the  olfactory  centres 
and  include  :  ( i )  olfado-habenular  fibres,  which  arise  from  cells  within  the  septum 


I  I  24 


HUMAN   ANATOMY. 


lucidum  and  the  olfactory  area,  and  (2)  cortico-habenular  fibres,  which  spring  from 
the  cortical  cells  within  the  hippocampus  or  the  adjacent  region,  and  by  way  of 
the  fornix  and  its  anterior  pillar  are  carried  to  the  fore-end  of  the  thalamus,  whence 
they  pass  backward  within  the  medullary  stria.  (3)  Other  thalamo-habenular fibres 
also  probably  join  the  stria  medullaris  from  the  interior  of  the  thalamus.  Whilst  many 
of  the  fibres  composing  the  stria  end  around  the  cells  of  the  ganglion  habenulae, 
some  continue  backward,  without  interruption,  within  the  strand  known  as  the 
peduncle  of  the  pineal  body,  cross  to  the  other  side  in  the  bundle  bearing  the 
name,  commissura  habenulae,  and  end  in  relation  with  the  cells  of  the  opposite 
habenular  nucleus.  The  ganglion  habenulae  (Fig.  970),  in  turn,  gives  origin  to 
an  important  bundle,  the  fasciculus  retroflexus  of  Meynert,  which  arches  down- 
ward and  backward,  passing  at  first  between  the  central  gray  matter  of  the  third 
ventricle  and  the  thalamus  proper,  and  later  to  the  medial  side  of  the  red  nucleus, 
to  reach  the  base  of  the  brain,  and  for  the  most  part  to  end  around  the  cells  of  the 
interpeduncular  ganglion.  This  nucleus,  which  in  many  animals  is  a  well-defined 
collection  of  cells,  in  man  is  represented  by  a  more  scattered  median  cell-group 
within  the  posterior  perforated  substance  close  to  the  anterior  border  of  the  pons. 
The  fasciculus,  also  termed  the  habenulo- peduncular  tract,  receives  contribu- 
tions from  the  ganglion  habenulae  of  both  sides,  some  fibres  having  crossed  in  the 
habenular  commissure  ;  although  the  majority  -of  its  fibres  end,  mostly  crossed,  in 
the  interpeduncular  ganglion,  not  a  few  may  be  traced  farther  caudally  within  the 
tegmentum  of  the  brain-stem  (Obersteiner),  as  may  also  the  fibres  from  the  cells 
of  the  ganglion  interpedunculare. 

The  Pineal  Body. — The  pineal  body  (corpus  pincale),  also  often  called  the 
cpiphysis,  is  a  cone-shaped  organ,  from  8-10  mm.  in  length,  attached  to  the 
posterior  extremity  of  the  roof  of  the  third  ventricle.  It  is  slightly  compressed  from 

above   downward    and 


FIG.  971. 


Section  of  pineal  body  showing  calcareous  concretions  or  brain-sand.     X  130. 


rests,  with  its  apex 
pointing  backward,  on 
the  dorsal  aspect  of  the 
mid-brain  in  the  trian- 
gular pineal  depression 
between  the  superior 
corpora  quadrigemina 
(Fig.  966).  Its  base, 
as  its  anterior  end  is 
called,  is  attached 
above  to  the  commis- 
sura habenulae,  from 
which  on  each  side  a 
narrow  but  distinct 
ridge,  the  pineal  stalk, 
curves  forward  to  be- 
come continuous  with 
the  stria  medullaris. 
Below,  its  base  is  united 
with  the  posterior  com- 
missure of  the  brain 
overlying  the  entrance 
into  the  Sylvian  aque- 
duct. Between  the 


habenular  and  posterior  commissures  a  small  pointed  diverticulum,  the  pineal  recess, 
extends  from  the  third  ventricle  for  a  very  short  distance  into  the  pineal  body, 
and  thus  recalls  the  early  condition  in  which  the  organ  is.  developed  as  a  tubular 
outgrowth  in  the  roof-plate  of  the  diencephalon.  This  relation  to  the  thin  ventricular 
roof  tin  body  retains,  its  apex  later  becoming  closely  surrounded  by  and  embedded 
within  the  loose  vascular  tissue  of  the  pia  mater. 

The  structure  of  the  pineal  body,  as  seen  in  cross-section  (  Fig.  971),  includes 
a  reticular  framework  of  connective  tissue  trabeculce,  whose  meshes  are  filled  with 


THE    DIENCEPHALON. 


1125 


Lenticular  area 
Retinal  area 


rounded  or  sometimes  elongated  epithelial  cells,  which  often  contain  brownish  pig- 
ment. With  the  exception  of  a  few  nerve-filaments  in  the  anterior  part,  probably 
sympathetic  in  origin  and  destined  for  the  blood-vessels,  and  a  dense  net- work  of 
neuroglia  fibres  in  the  under  part, 

the  pineal  body  contains   no    ele-  FlG-  972. 

ments  of  a  nervous  character,  nerve- 
cells  being  absent.  Quite  com- 
monly the  adult  organ  encloses  a 
variable  number  of  concretions, 
often  called  brain- sand  (acervulus) , 
which  consist  of  laminated  particles 
composed  of  calcium  carbonate 
and  phosphate  mingled  with  or- 
ganic material.  They  may  be  of 
microscopic  dimensions,  or  reach 
the  size  of  a  millet  seed,  and  by 
aggregation  assume  a  mammillated 
form. 


Blood-vessel 


Diverticulum 

dividing  into 

tubules 


Sagittal  section  of  pineal  organ  of  lizard  (Lacerta  agilis) 
embryo.     X   175. 


The  significance  of  the  pineal 
body  long  remained  an  unsolved 
riddle  and  served  as  the  theme  for 
unrestrained  speculation.  The  em- 
bryological  and  comparative  studies  of 

Graaf,  Spencer  and  others  have  shown  that  in  many  of  the  lower  animals,  especially  in  the  reptiles 
(lizards),  the  pineal  body  reaches  a  high  degree  of  development  and  is  a  flattened  cup-shaped 
organ  connected  with  the  brain  by  a  stalk  containing  nerve-fibres.  The  structural  resemblances 
to  the  invertebrate  visual  organ  suggested  a  possible  similarity  of  purpose  in  the  higher  types, 
an  assumption  that  was  strengthened  by  the  fact  that  in  certain  lizards  the  pineal  body  not  only 
is  borne  by  a  stalk  but  reaches  an  interparietal  subcutaneous  position  on  the  head  by  passing 
through  or  lying  within  a  special  foramen  in  the  skull.  The  organ  was,  therefore,  designated 
the  pineal  eye,  although  probably  in  no  existing  animal  a  functionating  structure.  While  such  a 
superficial  position  in  the  adult  is  very  exceptional,  the  embryonic  relations  in  many  reptiles 
(Fig.  972)  are  very  suggestive  of  the  probable  significance  ot  the  pineal  body,  at  least  in  such 
form  as  a  rudimentary  sense  organ,  although  not  necessarily  an  eye.  These  conclusions  are 
likewise  suggestive  in  forming  our  conceptions  concerning  the  pineal  body  in  man,  which  is 

now  by  many  regarded  as  representing  a  very  imperfectly 
developed  and    greatly  modified  sensory  structure. 

Although  strictly  belonging  to  the  telencephalon,  men- 
tion may  here  be  made  of  a  second  evagination,  know  as  the 
paraphysis,  which  arises  from  the  roof-plate  of  the  fore-brain. 
The  pouch  appears  in  advance  of  the  pineal  outgrowth  and  is 
a  temporary  structure,  seemingly  being  in  nature  comparable 
to  an  outwardly  directed  choroid  plexus.  The  paraphysis 
has  been  described  in  the  lower  vertebrates,  including  reptiles 
and  birds,  in  some  mammals  and,  indeed,  according  to 
the  observations  of  Francotte  and  of  Ewing  Taylor,  it  is  not 
improbable  that  a  corresponding  evagination  is  recognizable 
in  the  early  human  embryo. 


FIG.  973. 


Small  portion  of  pineal  body, 
showing  constituent  cells  more  highly 
magnified.  X  600. 


The  posterior  commissure  (commissura  poste- 
rior cerebri)  is  a  narrow  but  distinct  cord-like  band  of 
white  matter  which  overlies  the  superior  entrance  into 

the  Sylvian  aqueduct  (Fig.  976)  and  is  partially  masked  by  the  habenular  commissure 
and  pineal  peduncle  above.  Behind  and  laterally  it  is  continuous  with  the  superior 
colliculi.  The  commissure  provides  the  paths  by  which  fibres  from  various  sources 
undergo  median  decussation,  but  the  details  and  connections  of  its  component  fibres 
are  only  imperfectly  understood.  Among  its  probable  constituents  are:  (i)  fibres 
originating  in  the  nucleus  of  the  posterior  commissure  and  also  from  the  nucleus  of 
the  posterior  longitudinal  fasiculus  (nucleus  fasciculi  longitudinalis  posterior),  which 
occupies  the  gray  matter  of  the  floor  of  the  third  ventricle  near  the  mammillary 
bodies  (page  1117);  (2)  fibres  from  the  posterior  part  of  the  thalamus  of  the 


1 1  26 


HUMAN    ANATOMY. 


opposite  side  which  descend  within  the  tegmentum,  lateral  and  ventral  to  the 
posterior  longitudinal  fasciculus  ;  (3)  fibres  which  cross  to  join  the  fasciculus  retro- 
flexus  ;  (4)  fibres  from  the  median  fillet  and  (5)  from  the  superior  cerebellar 
peduncle  which  traverse  the  commissure  to  reach  the  opposite  thalamus  ;  (6)  per- 
haps fibres  from  the  deeper  gray  stratum  of  the  corpora  quadrigemina  to  the  cerebral 
cortex  of  the  other  side.  Its  presence  in  all  vertebrates  and  the  very  early 
acquisition  of  a  medullary  coat  by  its  fibres  indicate,  as  pointed  out  by  Edinger, 
the  fundamental  character  of  the  commissure. 

The  Metathalamus. — This  subdivision  of  the  thalamencephalon  includes  em- 
bryologically  both  the  median  and  lateral  geniculate  bodies.      Since  in  the  fully  formed 


FIG.  974. 


Corpus  callosum 


Fornix 

Choroid  plexus 

Velum  inter- 
positum 

Nucleus  habetiuke 

Subthalamic 

nucleus 

Red  nucleus 


Substantia  nigra 


Oculomotor  nerve 


Crusta  of  cerebral  peduncle 


Caudate  nucleus 


Thalamus 


Subthalamic  region 

Crwroid  plexus  in  inferior 
horn  of  lateral  ventricle 

Caudate  nucleus,  tail 

Hippocam:>u>, 
obliquely  cut 

Gyms  detitatus 

Ciyrus  hippocampi, 
bounding  inferior 
fissure  leading  into 
choroidal  pk-\n- 


Frontal  section  of  brain  passing  through  thalami,  subthalamic  region  and  cerebral  peduncles;  inferior 
horn  of  lateral  ventricle  with  hippocampus  in  section  also  seen. 

brain  the  former  are  closely  associated  with  the  inferior  colliculi  and  their  arms,  the 
inferior  brachia,  they  may  be  conveniently  described  in  connection  with  the  mid- 
brain,  as  has  been  done  (page  nio). 

The  lateral  geniculate  bodies,  (corpora  geniculata  laterales),  one  on  each  side, 
are  two  fusiform  elevations,  about  16  mm.  in  length  and  half  as  much  in  width,  which 
project  from  the  outer  and  under  surface  of  the  posterior  part  of  the  thalamus  ( Fig. 
958).  They  are  so  buried  within  the  thalamus  that  they  are  much  less  distinct  than  the 
median  geniculate  bodies.  In  front  they  receive  the  outer  division  of  the  optic  tracts, 
while  behind  they  are  connected  by  the  superior  brachia  with  the  superior  corpora 
quadrigemina.  In  structure  the  lateral  geniculate  body  consists  of  alternating  layers 
of  white  and  gray  matter.  The  former,  somewhat  thinner  than  the  gray  substance, 
are,  to  a  large  measure  the  optic  fibres,  many  of  which  end  around  the  cells  within 
the  gray  lamina-.  Other  fibres  of  the  optic  tract  continue  without  interruption  into 
the  superior  brachium  and  so  to  the  upper  colliculus,  while  a  certain  number  end 
within  the  thalamus,  and  in  their  course  over  the  surface  of  the  latter  take  part  in  the 
production  of  the  stratum  zonale  (page  1118).  From  many  of  the  cells  within  the 
geniculate  body,  fibres  proceed  by  way  of  the  optic  radiations  to  the  cerebral  cortex. 


*e 


THE    DIENCEPHALON. 


1127 


Then,  too,  many  corticifugal  fibres  course  in  the  opposite  direction  as  the  axones  of 
the  cortical  cells,  and  end  in  relation  to  the  geniculate  neurones,  thus  establishing  a 
double  relation  between  the  lateral  geniculate  body  and  the  occipital  cortex. 

The  Hypothalamus. — Although,  strictly  regarded  according  to  its  develop- 
mental relations,  the  diencephalon  claims  only  the  posterior  or  mammillary  part  of 
the  hypothalamus,  it  is  desirable  to  consider  at  this  time  the  derivations  of  the  entire 
hypothalamic  subdivision  of  the  fore-brain.  Under  the  above  heading  will  be  de- 
scribed, therefore,  the  structures  lying  within  or  forming  the  floor  and  the  anterior 
wall  of  the  third  ventricle,  including  the  subthalamic  region. 

The  subthalamic  region  in  its  developmental  relations  stands,  as  it  were,  as  a 
link  connecting  the  diencephalon  and  the  mid-brain.  The  subthalamic  region  is  the 
upward  prolongation  of  the  tegmentum  of  the  cerebral  peduncles  and  occupies,  on  each 
side  of  the  mid-line,  the  triangular  area  between  the  thalamus  above  and  the  internal 
capsule  and  its  continuation,  the  crusta  of  the  peduncle,  below  (Fig.  974).  It  is  insepa- 

FIG.  975. 


Red  nucleus 


Substantia 
nigra 


Choroid  plexus 


Fornix 

Pulvinar 

Lateral  geniculate 
body  ( leader  crosses 
cut  tail  of  caudate 
nucleus) 

—  Median  geniculate 
body 


Hippocampus 


Superior  cerebellar 
peduncle 


Pons 
Frontal  section  of  brain  passing  through  posterior  poles  of  thalami,  pineal  body  and  brain-stem. 

rably  blended  with  the  ventral  surface  of  the  thalamus,  which  thus  obliquely  overlies 
the  termination  of  the  tegmental  or  sensory  portion  of  the  cerebral  stalk.  Through 
this  area  the  important  thalamocipetal  paths  of  the  fillet  and  of  the  superior  cerebellar 
peduncles  reach  the  thalamus,  and  within  it  are  seen  the  upper  extremities  of  the 
chief  ganglia  of  the  mid-brain,  the  substantia  nigra  and  the  red  nucleus,  and  a  new 
mass  of  gray  matter,  the  corpus  subthalamicum.  The  substantia  nigra  presents  the 
same  characteristics  here  as  in  the  peduncle,  being  conspicuously  dark  and  overlying 
the  crustal  fibres.  As  it  ascends,  it  decreases  in  bulk  from  within  outward  until,  at 
the  level  of  the  mammillary  body,  the  substantia  nigra  is  no  longer  recognizable. 
The  connections  of  the  cells  within  the  substantia  nigra  are  imperfectly  understood, 
but  it  is  probable  that  they  receive  many  fibres  from  the  caudate  nucleus  and  the 
putamen  and,  perhaps,  also  from  the  frontal  cortical  areas.  From  the  cells,  on  the 
other  hand,  fibres  pass  into  the  tegmentum  and  into  the  crusta  and  thence  to 
lower  levels.  According  to  Bechterew,  some  fibres  join  the  fillet-tract  and  thus 
reach  the  superior  quadrigeminal  bodies.  At  first  the  red  nucleus  is  a  very 
prominent  feature  in  frontal  sections  of  the  subthalamic  region  (Fig.  970),  appearing 


1128 


HUMAN    ANATOMY. 


as  a  circular  area  of  gray  matter  enclosed  by  a  zone  of  cerebello-thalamic  fibres  ; 
farther  forward  it,  too,  gradually  diminishes  and  disappears  at  a  level  somewhat 
behind  that  of  the  corpora  mammillaria.  The  connections  of  the  red  nucleus  have 
been  considered  in  connection  with  the  superior  cerebellar  peduncle  (page  1095)  ; 
suffice  it  here  to  recall  its  twofold  significance  as  an  interruption  station  for  many 
of  the  cerebello-rubro-spinal  and  for  the  cerebro-rubro-spinal  tracts. 

The  corpus  subthalamicum  (nucleus  hvpothalamicus),  or  nucleus  of  Litys,  is  a 
mass  of  deeply  tinted  gray  matter  peculiar  to  the  subthalamic  region  and  unrepresented, 
in  the  mid-brain.  It  appears  in  cross-section  (Fig.  970)  as  a  small  biconvex  area, 
immediately  dorsal  to  the  tract  of  crustal  fibres  and  lateral  to  the  red  nucleus  and  the 
substantia  nigra.  As  the  latter  diminishes,  the  subthalamic  nucleus  expands  to  take 
its  place  and,  where  fully  represented,  measures  from  3-4  mm.  in  thickness  and  from 
10-12  mm.  in  its  longest  diameter,-  and  extends  superiorly  considerably  beyond  the 
.level  of  the  red  nucleus.  Histologically  the  subthalamic  body  is  distinguished  by  a 
dense  net-work  of  fine  medullated  nerve-fibres,  enclosing  pigmented  multipolar  nerve- 
cells  of  medium  size,  and  by  an  unusually  close  mesh-work  of  capillary  blood-vessels. 
The  dorsal  surface  of  the  nucleus  is  defined  by  the  overlying  lateral  part  of  the  field 


FIG.  976. 


Septum  hicidum 
Choroid  plexus 


Foramen  of  Monroe 


Genii  of  corpus  callosum 


Rostrum   of 
corpus  callosum 


Anterior  commissure 


Lamina  cinerea1 

Optic  recess 


Optic  commissure 

Anterior  lobe  of  pituitary  body 
Posterior  lobe  of  pituitary 


y  body 
Infundibulum 


Body  of  fornix 

Velum  interpositum  covering: 
Thalamus,  [thalamus 
mesial  surface 


T;cnia  thalami 
plenium 


Commissura  habenuUe 
Pineal  recess 


Pineal  body 
Posterior  commissure 


-Quadrigeminal  plate 
Sylvian  aqueduct 
Cerebral  peduncle 
Middle  commissure 
Sulcus  hypothalamicus 
Mam  mil  la  ry  body 
Tuber  cinereum" 
Anterior  pillar  of  fornix 


Right  lateral  wall  of  third  ventricle  :  velum  interpositum  covers  superior  surface  of  thalamus. 


of  Forel,  as  the  stream  of  fibres  passing  between  the  red  nucleus  and  the  thalamus 
and  the  internal  capsule  is  called.  From  the  ventral  surface  of  the  nucleus,  fibres 
pierce  the  adjacent  crusta  and  join  the  ansa  lenticularis  to  gain,  probably,  the  globus 
pallidus ;  other  perforating  fibres  perhaps  connect  the  subthalamic  body  with 
Meynert's  and  Gudden's  commissures  (Obersteiner).  The  ventro-medial  ends 
of  the  bodies  of  the  two  sides  are  connected  by  a  bridge,  the  commissura 
hypothalamica,  which  traverses  the  floor  of  the* third  ventricle  above  the 
mammillary  bodies.  In  addition  to  connecting  the  two  subthalamic  nuclei,  the 
commissure  contains  decussating  fibres  from  the  anterior  pillars  of  the  fornix  and, 
according  to  Edinger,  probably  fibres  from  the  fore-end  of  the  posterior  longitudinal 
fasciculus. 

The  corpora  mammillaria  (corpora  mamillaria),  also  called  the  corpora  albi- 
cantia,  are  two  hemispherical  elevations,  about  5  mm.  in  diameter,  which  lit- close  to  the 
mid-line-  within  the  inter] >eduncular  space  on  the  basal  surface  of  the  brain  (Fig.  993). 
They  are  almost  but  not  quite  in  contact,  being  separated  by  a  narrow  interval  which 
immediately  behind  the  little  bodies  deepens  into  the  anterior  recess  marking  the 
front  end  of  the  shallow  median  furrow  that  grooves  the  posterior  perforated  sub- 
stance. The  posterior  surfaces  of  the  mammiilary  bodies  indicate  the  anterior  limit 
of  the  ventral  surface  of  the  mid-brain.  When  examined  in  section  (Fig.  970), 


= 


THE    DIENCEPHALON.  1129 

each  body  is  seen  to  be  composed  of  an  outer  layer  of  white  matter  enclosing  a  core 
of  gray  substance,  known  collectively  as  the  nucleus  mammillaris.  The  latter  is 
subdivided  into  a  medial  and  lateral  part  by  fibres  from  the  downward  arching  ante- 
rior pillar  of  the  fornix,  which  penetrate  the  gray  matter  as  well  as  invest  to  a  large 
extent  its  exterior.  Only  a  part  of  ( i )  the  fornix  fibres,  however,  end  directly  in 
the  mammillary  nuclei,  since  some  pass  above  and  behind  the  ganglion  to  gain  the 
hypothalamic  commissure  (page  1128)  and,  after  decussation,  to  end  in  the  mam- 
milliary  body  of  the  opposite  side.  From  the  dorsal  part  of  the  medial  nucleus, 
distinguished  from  the  lateral  one  by  its  larger  nerve-cells,  emerges  a  distinct  and 
compact  bundle  of  fibers  (Fig.  967),  which  on  clearing  the  nucleus,  separates  into  two 
strands.  One  of  these,  known  as  (2)  the  mammillo-thalamic  tract,  or  the  bundle 
of  Vicq  d'  Azyr,  courses  upward  and  forward,  and  ends  within  the  anterior  nucleus  of 
the  thalamus  ;  in  this  manner  it  completes  the  paths  by  which  the  cortical  olfactory 
centres  within  the  hippocampus  major  are  connected  (by  way  of  the  fimbria,  body 
and  anterior  pillar  of  the  fornix  and  the  mammillo-thalamic  strand)  with  the  thalamus 
(Fig.  1049).  That  fibres  pass  between  the  latter  and  the  mammillary  nucleus  in 
both  directions,  is  shown  by  the  fact  that  destruction  of  either  of  these  centres  is  fol- 
lowed in  turn  by  ascending  or  descending  degeneration  of  the  fibres.  (3)  The 
other  part  of  the  bundle  issuing  from  the  mammillary  nucleus  arches  backward  and 
downward  and,  as  the  mammillo-teg  mental  tract,  is  traceable  into  the  tegmentum  of 
the  mid-brain  to  the  vicinity  of  the  inferior  colliculus.  (4)  Under  the  name,  pednn- 
culus  corporis  mammillaris,  another  mammillo-tegmental  tract  is  described.  This 
strand  springs  from  the  lateral  mammillary  nucleus,  and,  coursing  backward  and 
downward  along  the  medial  margin  of  the  crusta,  enters  the  tegmentum.  Its  des- 
tination is  uncertain,  but  according  to  Kolliker  the  tract  probably  ends  in  the  central 
gray  matter  surrounding  the  Sylvian  aqueduct  in  proximity  with  the  trochlear 
nucleus.  Other,  but  much  less  well  established,  strands  have  been  described  by 
Lenhossek  as  proceeding  forward  from  the  peripheral  layer  of  the  mammillary  body 
over  the  tuber  cinereum.  Concerning  their  further  course  little  is  known  with 
certainty. 

The  tuber  cinereum  is  the  first  of  a  series  of  median  outpouchings  which 
model  the  thin  sheet  of  gray  matter  constituting  the  floor  and  the  anterior  wall  of 
the  third  ventricle  and  belong  to  the  pars  optica  of  the  hypothalamus.  As  seen  from 
the  exterior  (Fig.  993),  the  tuber  cinereum  is  a  median  elevation  placed  between  the 
mammillary  bodies  behind  and  the  optic  chiasm  in  front,  and  the  cerebral  peduncles 
and  the  optic  tracts  at  the  sides.  Together  with  the  infundibulum,  it  forms  the  most 
dependent  part  of  the  third  ventricle  and  consists  of  a  thin  layer  of  gray  matter,  less 
than  1.5  mm.  thick,  that  is  continued  forward  as  the  attenuated  extension  of  the  im- 
portant sheet  found  within  the  mid-brain  and  fourth  ventricle.  In  addition  to  the  fibre- 
strands  coming  from  the  mammillary  bodies  noted  by  Lenhossek,  this  investigator 
and  Kolliker  credit  the  tuber  cinereum  with  possessing  small  paired  composite  gang- 
lia, the  nuclei  tuberis  and  the  nuclei  supraoptici  of  Kolliker.  Concerning  their  con- 
nections nothing  is  definitely  known.  The  anterior  part  of  the  tuber,  immediately 
behind  the  optic  chiasm,  descends  abruptly  and  somewhat  forward  to  form  a  funnel- 
shaped  stalk,  the  infundibulum,  to  whose  lower  end  or  apex  is  attached  the  pos- 
terior lobe  of  the  pituitary  body  (Fig.  976).  Although  in  the  very  young  child  the 
infundibulum  retains  to  some  extent  its  original  character  as  a  hollow  outgrowth 
from  the  ventricle,  in  the  mature  subject  this  cavity,  the  recessus  infundibuli, 
has  mostly  disappeared  and  the  stalk  is  solid,  save  for  a  slight  diverticulum  within  its 
upper  and  widest  part. 

The  posterior  part  of  the  tuber  cinereum,  between  the  root  of  the  infundibulum 
and  the  mammillary  bodies,  exhibits  occasionally  in  the  adult  brain,  and  almost  con- 
stantly in  that  of  the  foetus,  a  small  rounded  median  projection,  flanked  on  each  side 
by  a  slight  elevation.  To  this  modelling  Retzius  has  applied  the  name,  emincnlia 
saccularis  in  recognition  of  its  similarity  to  the  evagination  (saccus  vasculosus )  found 
in  fishes.  The  eminence  encloses  a  shallow  pouch,  recessus  saccularis,  which  opens 
into  the  third  ventricle. 

The  pituitary  body  (hypophysis  cerebri)  is  attached  to  the  dependent  tip  of  the 
infundibulum,  and,  closely  invested  by  a  loose  sheath  of  connective  tissue,  hangs 


1 130 


HUMAN   ANATOMY. 


within  the  pituitary  fossa  on  the  base  of  the  skull,  just  in  advance  of  the  dorsum  sellae 
(Fig.  996).  Above,  the  fossa  is  closed  by  a  special  partition  of  dura,  the  diaphragma 
settee,  through  an  opening  in  which  the  intundibulum  passes  to  the  mushroom -shaped 
organ.  The  pituitary  body  consists  of  two  distinct  parts,  of  which  the  so-called 
anterior  lobe  is  much  the  larger  and  of  a  darker  grayish  red  color.  Its  posterior 
surface  is  concave  and  receives  the  small  posterior  lobe,  which  is  partially  embraced 
at  the  sides  by  the  expanded  lateral  margins  of  the  anterior  division.  Although  the 
two  lobes  are  closely  bound  together  by  connective  tissue,  they  are  not  only  distinct 
as  to  structure  and  probably  function,  but  are  developed  from  entirely  different 
regions.  The  anterior  lobe  is  formed  as  an  outgrowth  from  the  oral  diverticulum, 
while  the  posterior  lobe  first  appears  as  a  ventral  evagination  from  the  diencephalon 
(Fig.  1530).  The  anterior  lobe,  glandular  in  character,  has  been  described  in  con- 
nection with  the  Accessory  Organs  of  Nutrition  (page  1806)  and,  therefore,  calls 
for  no  further  consideration  in  this  place. 

FIG.  977. 


Interlobar  septum 


Posterior  or  cerebral  lobe 


Blood-vessel 


Connective-tissue 
trabecula 


Capsule 
Transverse  section  of  pituitary  body,  showing  relation  of  anterior  (oral)  and  posterior  (cerebral)  lobes.     X  7. 

The  posterior  lobe  of  the  pituitary  body  is  lighter  in  color  and  softer  in  con- 
sistence and  directly  attached  to  the  floor  of  the  third  ventricle  by  means  of  its  stalk, 
the  infundibulum.  During  the  early  stages  of  its  development,  this  lobe  is  repre- 
sented by  a  tubular  outgrowth  whose  walls  partake  of  the  general  character  of  the 
adjacent  brain-visicle.  Later  the  lumen  within  the  lower  end  of  the  diverticulum  dis- 
appears in  consequence  of  thickening  and  approximation  of  its  walls,  a  funnel-shaped 
recess  of  variable  depth  within  the  infundibulum  alone  remaining.  In  the  adult  con- 
dition, the  posterior  or  cerebral  lobe  retains  few  histological  features  suggesting  its 
nervous  origin.  Of  the  demonstrable  interlacing  fibres,  with  fusiform  enlargements 
and  elongated  nuclei,  none  can  be  identified  as  nerve-fibres,  while  of  the  numerous 
cells  which  the  lobule  contains,  only  a  few  of  large  size  and  pigmented  cytoplasm 
uncertainly  resemble  nervous  elements.  Wijh  the  exception  of  possibly  neurogliar 
cells,  the  existence  of  definite  nervous  tissue  within  the  cerebral  lobe  of  the  mature 
human  hypophysis  is  doubtful. 

The  optic  tracts  and  commissure  are  elsewhere  described  (page  1223), 
suffice  it  at  this  place  to  mention  their  relation  to  the  interpeduncular  structures. 
The  optic  tracts  diverge  backward  and  wind  around  the  ventral  surface  of  the  cere- 
bral peduncles  (Fig.  993).  Their  medial  ends  are  fused  into  a  transversely  flattened 
white  band,  the  optic  commissure  or  chiasm.  The  latter  is  connected  with  the  front 
surface  of  the  tuber  cinereum,  whilst  above  the  chiasm  the  anterior  wall  of  the  ventricle 
consists  of  a  delicate  sheet  of  gray  matter,  the  lamina  cinerea  (lamina  terminalis 
This  structure  lies  in  the  mid-line,  passes  almost  vertically  upward,  with  a  slight 
forwardly  directed  curve,  and  becomes  continuous  with  the  rostrum  of  the  corpus 


THE    DIENCEPHALON.  1131 

callosum.      Just  before  meeting  the  latter,  the  lamina  passes  in  front  of  the  anterior 
commissure  of  the  brain  (Fig.  976). 

The  Third  Ventricle. — The  third  ventricle  (ventriculus  tertius  cerebri)  is  the 
narrow  cleft-like  space  that  separates  the  medial  surfaces  of  the  thalami  (Fig.  966). 
It  is  somewhat  broader  behind  and  much  deeper  in  front,  where  it  comes  into  close 
relation  with  the  exterior  of  the  brain,  the  interpeduncular  lamina  alone  intervening. 
Seen  from  the  side,  as  in  mesial  sagittal  sections  (Fig.  996),  the  outline  of  the 
ventricle  is  irregularly  comet-shaped,  with^the  broader  end  above  and  behind  and  the 
blunted  point  directed  downward  and  forward  (Fig.  978).  Behind,  it  communicates 
with  the  Sylvian  aqueduct,  and  through  this  canal  indirectly  with  the  fourth  ventricle; 
anteriorly  it  connects  with  the  two  lateral  ventricles  by  means  of  the  foramina  of 
Monroe.  Its  sagittal  diameter,  measured  between  the  anterior  commissure  and  the 
base  of  the  pineal  body,  is  approximately  2.5  cm.  The  lateral  wall  of  the  ventricle 
(Fig.  976)  is  formed  chiefly  by  that  part  of  the  thalamus  which  lies  below  the  level 
of  the  taenia  thalami.  On  this  surface,  slightly  in  advance  of  the  middle,  is  seen  the 
small  oval  field  of  the  middle  commissure,  and  in  front  of  this  the  downward  curving 
elevation  produced  by  the  anterior  pillar  of  the  fornix.  Between  the  latter  and  the 
prominent  anterior  tubercle  of  the  thalamus  lies  the  foramen  of  Monroe  (foramen 
interventriculare),  which  establishes  communication  between  the  third  and  the  cor- 

FIG.  978. 

Middle  commissure 

Pineal  recess  / 

v  /  -Foramen  of  Monroe 

\          ^^l^fc  ^ 

Suprapineal  recess- 


.Anterior  commissure 

— -^  — — "      ^^  i_ 

Posterior  commissure 
Sylvian  aqueduct 


Mammillary  body  ^J  ^^~~~"~-  Optic  recess 

Infundibulum  • 

Optic  chiasm 

Cast  of  third  ventricle,  viewed  from  the  side.     X  \.     (Retzius.) 

responding  lateral  ventricle,  and  transmits  the  trunk  formed  by  the  union  of  the 
vein  of  the  corpus  striatum  and  the  choroid  vein.  A  shallow  furrow  on  the  ventric- 
ular wall,  the  sulcus  hypothalamicus  leads  from  the  foramen  backward  and  some- 
what downward  (Fig.  976).  It  is  of  importance  as  indicating,  even  in  the  adult 
brain,  the  demarcation  between  the  thalamencephalon  and  the  hypothalamus — parts 
derived  respectively  from  the  dorsal  and  ventral  zones  of  the  embryonic  brain-vesicle. 
The  roof  of  the  ventricle  extends  from  the  foramina  of  Monroe,  bounded  above 
and  in  front  by  the  arching  pillars  of  the  fornix,  to  the  pineal  body  behind,  over 
which  it  pouches  out  into  the  suprapincal  recess,  as  the  little  diverticulum  overlying 
the  body  is  termed.  The  immediate  and  morphological  roof  consists  of  the  delicate 
ependymal  layer,  which  is  attached  to  the  taenia  thalami  on  each  side  and,  stretching 
across  the  interthalamic  cleft,  closes  in  the  ventricle.  The  ependymal  layer,  how- 
ever, is  backed  by  a  vascular  fold  of  pia  mater,  which,  in  conjunction  with  the 
epithelial  layer,  constitutes  the  velum  interposition.  This  structure  is  more  fully 
described  in  connection  with  the  lateral  ventricles  (page  1162);  but  its  relation  to 
the  third  ventricle  finds  appropriate  mention  at  this  place.  As  in  the  roof  of  the 
fourth  ventricle  and  in  the  lateral  ventricles,  so  in  the  third  does  the  vascular  tissue 
of  the  pia  mater  invaginate  the  ependymal  layer  to  form  vascular  fringes  which 
project  into  the  ventricle  (Fig.  974).  A  double  line  of  such  invaginations  hangs 
from  the  roof  of  the  third  ventricle  and  constitutes  the  choroid  plexus  of  that  space. 
Since  the  ependyma  everywhere  covers  these  pial  processes,  it  is  evident  that  the 
fringes  are,  strictly  regarded,  outside  the  ventricle  and  excluded  by  the  continuous 
layer  of  the  epithelium. 


1 1 32  HUMAN    ANATOMY. 

The  posterior  wall  of  the  third  ventricle  is  very  short  and  includes  the  base  of 
the  pineal  body,  with  the  opening  into  the  minute  pineal  recess,  the  posterior  com- 
missure and  the  orifice  leading  into  the  Sylvian  aqueduct.  The  floor  slopes  rapidly 
downward  and  forward  (Fig.  976)  and  comprises  a  small  part  of  the  tegmentum 
of  the  cerebral  peduncles,  the  posterior  perforated  substance,  the  mammillary  bodies, 
and  the  tuber  cinereum  with  the  infundibulum  —  structures  already  described  and 
included  within  the  interpeduncular  area  on  the  base  of  the  brain.  Corresponding 
with  the  position  of  the  superficial  elevation,  the  ventricle  exhibits  the  diverticulum 
of  the  infundibulum.  The  optic  chiasm  marks  the  anterior  limit  of  the  floor  and  the 
beginning  of  the  anterior  wall.  Immediately  above  the  chiasm  the  anterior  wall 
exhibits  a  diverticulum,  the  optic  recess,  from  which  the  lamina  cinerea  ascends  to 
join  the  rostrum  of  the  corpus  callosum,  in  its  course  passing  close  to  and  in  front 
of  the  anterior  commissure.  The  latter  structure  shows  on  the  front  wall  of  the 

FIG.  979. 

Cavity  in  septum  lucidum  Corpus  callosum,  cut 

Caudate  nucleus 

•N^  X.  V 

, Lateral  ventricle 

W.      ^-^•L       ^ 

Internal  capsule 

Putamen  of 
lenticular  nucleus 

Cut  anterior  end 
of  fornix 

Anterior  pillars 
of  fornix 

Anterior  commissure  

Thalamus,  anterior  tubercle 
Optic  recess — ~~~  "  —  "^X-      '"  \  \ 

Foramen  of  Monroe 

Optic  chiasm  Lamina  cinerea 

Portion  of  frontal  section  of  brain  passing  through  foramina  of  Monroe,  showing  anterior  wall  of  third  ventricle 
modelled  by  anterior  commissure  and  pillars  of  fornix. 

ventricle  as  a  transverse  ridge  between  the  descending  and  slightly  diverging  anterior 
pillars  of  the  fornix  (Fig.  979).  Although  distinctly  modelling  the  ventricular 
walls,  all  of  these  bands  are  excluded  from  the  ventricle  by  its  ependymal  lining. 

THE  TELENCEPHALON. 

The  telencephalon,  or  end-brain,  consists  of  two  fundamental  parts,  the  hemi- 
sphaerium  and  the  pars  optica  hypothalami.  The  latter  includes:  (i)  the 
lamina  cinerea  (terminal is},  (2)  the  optic  commissure,  (3)  the  tiibcr  cinereum  and 
(4)  the  pituitary  body,  all  of  which  have  been  already  considered,  as  a  matter  of  con- 
venience, in  connection  with  the  diencephalon  and  the  third  ventricle.  The  hemi- 
sphere comprises:  (i)  the  pallium,  (2)  the  rhinencephalon,  and  (3)  the  corpus 
striafum.  The  first  of  these  subdivisions  undergoes  such  enormous  development  in 
the  anthropoid  apes  and  in  man,  that  the  pallium  becomes  the  dominating  factor  and, 
expanding  upward,  laterally  and  backward  as  the  great  cerebral  mantle,  not  only 
forms  the  chief  bulk  of  the  cerebrum,  but  overlies  the  derivatives  of  the  other  brain- 
segments  to  such  an  extent  that  these  parts  are  to  a  large  measure  covered  and 
deposed  from  their  primary  position  on  the  free  dorsal  surface  of  the  brain.  In  conse- 
quence in  man,  in  whom  the  pallium  reaches  its  highest  development,  the  thalami, 
corpora  quadrigemina  and  the  cerebellum  are  masked  by  the  hemispheres  and  occupy 
topographically  a  dependent  position.  The  rhinencephaion.  on  the  contrary,  is  in 
man  only  feebly  developed  and  rudimentary  in  comparison  with  the  conspicuous  and 
bulky  corresponding  structures  possessed  by  animals  in  which  the  sense  of  smell  is 
highly  developed.  The  corpus  striatton.  consisting  of  two  large  masses  of  gray 


THE   TELENCEPHALON.  1133 

matter,  the  caudate  and  the  lenticular  nucleus,  represents  the  internal  nucleus  of  the 
end-brain.  Certain  commissural  structures,  as  the  corpus  callosum,  the  anterior  com- 
missure and  t\\e  fornix  are  to  be  regarded  as  secondary  and  as  serving  to  connect 
the  halves  of  the  great  brain.  The  immediate  free  or  outer  surface  of  the  pallium  is 
everywhere  formed  by  a  thin  peripheral  layer  of  cortical  gray  matter,  which,  as  an 
unbroken  sheet,  clothes  the  various  ridges  and  intervening  furrows — the  convolutions 
and  fissures — which  model  the  exterior  of  the  cerebrum  and  provide  the  necessary 
extent  of  surface.  Beneath  the  cortical  gray  substance  lies  the  white  matter,  which 
constitutes  the  bulk  of  the  hemisphere  and  consists  of  the  tracts  of  nerve-fibres  pass- 
ing to  and  from  the  cortex,  as  well  as  of  those  connecting  the  various  regions  of  the 
cortex  with  one  another.  Embedded  within  the  core  of  white  matter  and  lying 
much  nearer  the  basal  than  the  superior  surface  of  the  hemisphere  (Fig.  1009),  the 
corpus  striatum  is  closely  related  to  the  ventricular  cavity  by  means  of  the  caudate 
nucleus  on  the  one  hand,  and  to  the  cortical  gray  matter  by  the  lenticular  nucleus 
on  the  other.  In  view  of  the  rudimentary  condition  of  the  rhinencephalon  and 
the  over-shadowing  development  of  the  pallium  in  man,  it  is  usual  and  convenient 
to  regard  most  of  the  parts  derived  from  the  telencephalon  as  belonging  to  the 
hemispheres,  the  latter  term  being  used  in  a  less  restricted  sense  than  warranted 
by  a  precise  interpretation  of  its  developmental  significance. 

THE  CEREBRAL  HEMISPHERES. 

Viewed  from  above,  the  human  brain  presents  an  ovoid  form,  the  narrower  end 
being  directed  forward  and  the  broader  backward,  the  greatest  width  corresponding 
with  the  parietal  eminences  (Fig.  984).  The  convex  surface  formed  by  the 
hemispheres  is  divided  by  a  deep  median  sagittal  cleft,  the  longitudinal  fissure 
(fissura  longitudinalis  cerebri),  that,  for  a  distance  less  than  one-third  of  its  length 
anteriorly  and  more  than  one-third  posteriorly,  completely  separates  the  hemi- 
spheres. In  its  middle  third  or  more,  the  fissure  is  interrupted  at  a  depth  of  about 
3.5  cm.  by  the  arched  upper  surface  of  the  corpus  callosum,  the  chief  connection 
between  the  hemispheres.  The  upper  and  back  part  of  the  longitudinal  fissure, 
throughout  its  length,  is  occupied  by  the  sickle-shaped  mesial  fold  of  dura  mater, 
the  falx  cerebri,  which  incompletely  subdivides  the  space  occupied  by  the 
cerebrum  into  two  compartments.  Under  the  name,  transverse  fissure  (fissura 
transversa  cerebri),  is  sometimes  described  the  deep  cleft  which  separates  the 
postero-inferior  surface  of  the  hemisphere  from  the  cerebellum,  the  corpora  quad- 
rigemina  and  the  pineal  body.  This  cleft,  so  evident  after  the  brain  has  been 
removed  from  the  skull,  when  the  parts  are  in  situ  is  filled  behind  by  the  tentorium 
cerebelli  and  in  front  by  a  fold  of  pia. 

The  hemispheres  are  advantageously  studied  after  being  separated  from  each 
other  by  sagittal  section,  and  from  the  brain-stem  by  cutting  across  the  mid-brain. 
When  examined  after  such  isolation,  especially  when  hardened  before  removal  from 
the  skull,  each  hemisphere  presents  a  dorso-lateral,  a  mesial  and  an  inferior  surface. 
The  dorso-lateral  surface  (Fig.  980)  is  convex  both  from  before  backward  and 
from  above  downward  and  closely  conforms  to  the  opposed  inner  surface  of  the 
cranial  vault.  The  mesial  surface  (Fig.  987)  is  flat  and  vertical  and  bounds  the 
longitudinal  fissure.  It  is  in  contact  with  the  sagittal  fold  of  dura,  the  falx  cerebri, 
except  in  front  and  below  where  the  partition  is  narrow;  here  the  mesial  surfaces 
of  the  hemispheres,  covered  of  course  by  the  pia  and  arachnoid,  lie  in  apposition. 
The  inferior  surface  (Fig.  989)  is  irregular,  its  approximate  anterior  third 
resting  in  the  anterior  cerebral  fossa  of  the  cranial  floor,  the  middle  third  in  the 
lateral  part  of  the  middle  fossa,  whilst  the  posterior  third  is  supported  by  the 
upper  aspect  of  the  tentorium,  which  separates  it  from  the  subjacent  cerebellum. 
At  the  juncture  of  its  anterior  and  middle  thirds,  the  inferior  surface  of  the 
hemisphere  is  crossed  transversely,  from  within  outward,  by  the  stem  of  the  Sylvian 
fissure  and  thus  subdivided  into  an  anterior  and  a  posterior  tract.  The  former 
and  smaller,  known  as  the  orbital  area,  rests  upon  the  orbital  plate  of  the  frontal 
bone  and  is  modelled  by  this  convex  bony  shelf  into  a  corresponding  slight  con- 
cavity from  side  to  side.  The  tract  behind  the  deep  Sylvian  cleft  is  at  first  convex 


134 


HUMAN    ANATOMY. 


and  rounded,  as  it  lies  within  the  middle  fossa,  but  traced  backward  it  passes 
insensibly  into  the  tcntorial  area,  supported  by  the  tentorium  cerebelli.  This  area 
is  concave  from  before  backward  and  directed  inward  as  well  as  downward,  in 
correspondence  with  the  characteristic  curvature  of  the  tent-like  dural  septum. 

The  borders  separating  the  surfaces  of  the  hemisphere  are  the  dorso-mesial, 
the  infero-lateral  and  the  infero-mesial.  The  dorso-mesial  border  intervenes 
between  the  mesial  and  lateral  surfaces  and,  therefore,  follows  the  arched  contour  of 
the  hemisphere  beneath  the  vaulted  calvaria.  The  infero-lateral  border,  between 
the  lateral  and  inferior  surfaces,  is  better  dehned  in  front,  where  it  separates  the  orbi- 
tal area  from  the  external  surface  as  the  arched  superciliary  border  (Cunningham), 
than  behind,  where  it  is  so  rounded  off  as  to  scarcely  be  recognizable  as  a  distinct 
margin.  The  infero-mesial  border  intervenes  between  the  mesial  and  the  inferior 
surface  of  the  hemisphere.  It  is  well  marked  in  front,  where  it  limits  the  orbital  area 
mesially,  and  again  behind,  where  it  corresponds  to  the  line  of  juncture  between 

FIG.  980. 


Lateral  aspect  of  left  cerebral  hemisphere;  dorso-median  surface  is  somewhat  foreshortened  ;  red  lines  indicate 
boundaries  separating  parietal,  temporal  and  occipital  lobes ;  r,  Rolandic  fissure ;  .$.  g ..  i.  g.,  its  superior  and  inferior 
genu;  S1,  S'2,  S*,  S*  asc.,  vertical,  horizontal,  posterior  and  ascending  limbs  of  Sylvian  fissure;  /.  p.  c.,  s.  p.  c., 
inferior  and  superior  precentral;  sf.,  if.,  superior  and  inferior  frontal;  p.m..  paramedian  ;  »/./.,  mid-frontal  ;  d., 
diagonal,  here  continuous  with  inferior  precentral;  /',  p~,  p*,  /*,  inferior,  superior,  horizontal  and  occipital  limhs 
of  inter-parietal;  p.  o.,  parieto-occipital ;  't1,  t1  asc.,  superior  temporal  and  its  upturned  limb;  f-,f-  asc.,  middle 
temporal  and  its  upturned  limb;  t.  o.,  transverse  occipital;  /.  o.,  lateral  occipital;  A.,  arm  centre;/?.  T.  O.,  pars 
basalis,  triangularis  and  orbitalis  ;  Arc.  p.-o.,  arcus  parieto-occipitalis. 

the  falx  cerebri  and  the  tentorium  and  marks  the  division  between  the  mesial  surface 
and  the  tentorial  area.  This  margin  has  been  designated  the  internal  occipital  border 
by  Cunningham. 

The  extreme  anterior  end  of  the  cerebral  hemisphere  is  known  as  the  frontal 
pole  (polus  frontalis),  and  the  most  projecting  part  of  the  posterior  end  as  the 
occipital  pole  (polus  occipitalis),  while  the  tip  of  the  subdivision  of  the  hemisphere 
which  projects  below  the  Sylvian  fissure  constitutes  the  temporal  pole  (polus  tcm- 
poralis).  A  short  distance  behind  the  latter,  the  inferior  surface  exhibits  a  well 
defined  petrosal  depression  (impressio  petrosa);  this  is  caused  by  the  elevation  cross- 
ing the  petrous  portion  of  the  temporal  bone  which  corresponds  to  the  position  of 
the  superior  semicircular  canal.  Under  favorable  conditions  of  hardening,  the  infero- 
mesial  aspect  of  the  occipital  pole  sometimes  displays  a  broad  shallow  groove  which 
marks  the  commencement  of  the  lateral  sinus.  The  groove  is  usually  better  marked 
on  the  right  side  than  on  the  left,  in  accordance  with  the  larger  size  of  the  right 
sinus  as  commonly  found  ;  occasionally  these  relations  are  reversed,  and  frequently 
no  groove  is  recognizable  on  the  side  of  the  smaller  sinus.  In  brains  hardened  in 
sil/i,  the  gently  arching  curve  of  the  hind-half  of  the  infero-lateral  border  of  the  hemi- 
sphere is  interrupted  by  a  more  or  less  evident  indentation,  the  preoccipital 
notch  ( incisura  prai-occipitalis  ),  at  a  point  about  3.75  cm.  ( 1 1A  in.)  in  front  of  the 
occipital  pole  (Fig.  980).  This  notch,  prominent  in  the  child  but  later  variable  in 


THE   TELENCEPHALON.  1135 

its  distinctness,  is  produced  by  a  fold  of  dura  over  the  parieto-mastoid  suture  and 
above  the  highest  part  of  the  lateral  sinus  (Cunningham).  It  is  of  importance 
in  the  topography  of  the  brain,  since  it  is  often  taken  as  the  lower  limit  of  the 
paricto-occipital  line,  establishing  the  conventional  division  on  the  lateral  surface  of 
the  hemisphere  between  the  parietal  and  occipital  lobes  (page  1143). 

The  complex  modelling  of  the  surface  of  the  cerebral  hemispheres,  the  charac- 
teristic feature  of  the  human  brain,  is  produced  by  the  presence  of  irregular  eleva- 
tions, the  convolutions  or  gyri,  separated  by  the  intervening  furrows,  the  fissures 
or  sulci.  Although  presenting  many  variations  in  the  details  of  their  arrangement, 
not  only  in  different  individuals  but  even  in  the  hemispheres  of  the  same  brain,  the 
convolutions  and  fissures  of  every  normal  human  brain  are  grouped  according  to  a 
general  and  definite  plan  to  which  the  brain-patterns,  whether  elaborate  or  simple,  in 
the  main  conform.  The  fissures  differ  greatly  not  only  as  to  their  depth  as  observed 
in  the  fully  formed  brain,  but  also  as  to  their  relation  with  the  developing  hemi- 
sphere, a  very  few,  known  as  the  complete  fissures,  involving  the  entire  thickness 
of  the  wall  of  the  cerebral  vesicle  and  in  consequence  producing  corresponding  eleva- 
tions on  the  internal  surface  of  the  ventricular  cavities.  Of  such  total  sulci  the  most 
important  permanent  ones  are  :  ( i )  the  hippocampal  fissure,  which  produces  the  pro- 
jection known  as  the  hipptfcampus  major  within  the  lateral  ventricle  ;  (2)  the  ante- 
rior part  of  the  calcarine  fissure,  which  gives  rise  to  the  calcar  avis  ;  and  (3)  the 
fore-part  of  the  collateral  fissure,  which  is  responsible  for  the  variable  collateral  emi- 
nence. The  choroidal  and  the  parieto-occipital  fissure  are  also  complete  fissures  of 
foetal  life,  but  give  rise  to  imaginations  which  do  not  permanently  model  the  ventric- 
ular walls.  The  remaining  furrows  merely  impress  the  surface  of  the  hemispheres 
and  are  termed  incomplete  fissures.  Their  depth  varies,  in  some  cases  being  only  a 
few  millimetres  and  in  others  as  much  as  2.5  cm.,  with  an  average  of  about  i  cm. 
The  height  of  the  convolutions  usually  exceeds  their  width,  the  latter,  in  turn,  being 
commonly  somewhat  greater  at  the  surface  than  at  the  bases  of  the  gyri.  It  is  evi- 
dent, therefore  that  the  convoluted  condition  of  the  hemispheres  provides  a  greatly 
increased  area  of  cortical  gray  matter  without  unduely  adding  to  the  bulk  of  the 
brain,  the  extent  of  the  sunken  surface  being  estimated  as  twice  that  of  the  exposed. 
The  larger  and  longer  adjacent  convolutions  are  frequently  connected  by  short 
ridges,  the  annectant  gyri,  which  have  no  place  in  the  typical  arrangement.  They 
may  cross  the  bottom  of  the  intervening  fissure  and  ordinarily  be  entirely  hidden 
from  view  (gyri  profundi);  or  they  may  be  superficially  placed  (gyri  transitivi)  and 
materially  add  to  the  complexity  of  the  surface  configuration. 

The  cause  and  origin  of  the  cerebral  convolutions  are  still  subjects  for  discussion.  The 
fact,  that  at  the  time  the  fissures  begin  to  appear,  towards  the  end  of  the  fifth  fcetal  month,  the 
surface  of  the  young  brain  is  not  in  close  contact  with  the  cranial  wall,  disproves  the  assumption 
that  the  latter  is  directly  responsible  for  the  production  of  the  fissures  and  convolutions.  It  is 
probable  that  the  immediate  cause  of  the  surface  modelling  must  be  sought  in  the  unequal 
growth  and  consequent  localized  tension  which  affect  the  hemispheres,  excessive  growth  in  the 
longitudinal  axis  resulting  in  transverse  furrows,  and  that  in  the  opposite  axis  producing  fissures 
extending  lengthwise.  Whether  the  excessive  expansion  is  caused  by  increase  in  the  gray  or 
white  matter  is  uncertain,  although  local  augmentation  of  the  cortical  gray  substance  is  prob- 
ably the  more  important  factor.  After  the  beginning  of  the  eighth  month,  when  the  growing 
brain  comes  into  contact  with  the  cranial  wall,  the  convolutions,  which  before  were  to  a  large 
extent  unrestrained  and  therefore  relatively  broad  and  rounded,  suffer  compression,  the  results 
of  which  are  seen  in  the  flattening  and  closer  packing  of  the  gyri  and  the  narrowing  and  deepen- 
ing of  the  intervening  fissures.  By  the  end  of  fcetal  life  the  salient  features  of  the  plan  of 
arrangement  have  been  established,  although  the  final  details  of  the  brain-pattern  are  not 
acquired  until  sometime  after  birth. 

The  Cerebral  Lobes  and  Interlobar  Fissures. — For  the  purposes  of 
description  and  topography,  the  cerebral  hemispheres  are  subdivided  into  more  or 
less  definite  tracts,  the  lobes,  by  certain  sulci,  appropriately  known  as  the  inter- 
lobar  fissures.  With  few  exceptions,  however,  the  lobes  so  defined  have  little 
fundamental  importance,  since  their  recognition  is  warranted  by  convenience  and  not 
by  morphological  significance,  in  most  cases  the  conspicuous  limiting  sulci  being  of 


1 136 


HUMAN    ANATOMY. 


secondary  importance,  while  those  of  primary  value  are  comparatively  obscure  in  the 
fully  formed  human  brain.  The  interlobar  fissures,  six  in  number,  are  :  ( i )  the 
fissure  of  Sylvius,  (2)  the  central  fissure,  (3)  the  parieto-occipital  fissure,  (4)  the 
collateral  fissure,  (5)  the  calloso-marginal  fissure  and  (6)  the  limiting  snlcus  of 
Reil. 

The  lobes  marked  off  by  these  fissures  with  varying  degrees  of  certainty  are  :  ( i ) 
the  frontal,  (2)  the  parietal,  (3)  the  temporal,  (4)  the  occipital,  (5)  the  limbic,  and 
(6)  the  insula.  An  additional  division,  (7)  the  olfactory  lobe,  although  of  impor- 
tance as  representing  the  peripheral  part  of  the  rhinencephalon  of  osmatic  animals  (as 
those  possessing  the  sense  of  smell  in  a  high  degree  are  called),  is  not  related  to  the 
foregoing  sulci  and  comprises  the  rudimentary  olfactory  bulb  and  tract  and  associated 
parts  (page  1151).  It  will  be  of  advantage  to  describe  the  interlobar  fissures  as  pre- 
paratory to  a  detailed  consideration  of  the  lobes. 

The  fissure  of  Sylvius  (fissura  cerebri  lateralis)  is  the  most  conspicuous  fissure 
of  the  hemisphere.  It  begins  on  the  inferior  surface  of  the  brain  in  a  depression,  the 
vallecula  Sylvii,  which  opens  out  on  the  anterior  perforated  space.  The  first  part  of 
the  fissure,  its  stem,  passes  horizontally  outward  to  the  lateral  surface  of  the  hemi- 
sphere, forming  a  deep  cleft  which  separates  the  orbital  area  from  the  underlying  tem- 


Rolandic  fissure 


FIG.  981. 

Inferior  precentral  sulcus 
.  ^^  Inferior  frontal  sulci 


Ascending  limb 


Posterior  limb 


Orbital  surface 
Horizontal  limb 


Portion  of  lateral  surface  of  right  hemisphere,  showing  ascending,  horizontal  and  posterior  limbs  of  Sylvum 
fissure  radiating  from  Sylvian  point.  B,  T,  O,  pars  basalis,  triangularis  and  orbitalis  of  inferior  frontal  gyms  ; 
.V/',  superior  temporal  gyrus. 

poral  pole.  On  reaching  the  surface  at  the  Sylvian  point,  the  fissure  divides  (Fig. 
981)  into  (a)  a  short  anterior  horizontal  branch,  (^)  a  somewhat  longer  anterior 
ascending  branch,  and  (c)  a  long  posterior  branch. 

The  anterior  horizontal  branch  (ramus  anterior  horizontalis),  about,  2  cm.  in 
length,  extends  forward  into  the  inferior  frontal  gyrus  parallel  to  and  just  above  the 
infero-lateral  border,  and  forms  the  lower  limit  of  the  pars  triangularis  (page  1141  ). 

The  anterior  ascending  branch  (ramus  anterior  ascendens)  passes  upward  and 
slightly  forward  into  the  hind-part  of  the  inferior  frontal  convolution  for  a  distance  of 
about  3  cm.  The  frequently  observed  variations  in  the  relation  and  arrangement  of 
the  anterior  branches  of  the  Sylvian  fissure — the  ascending  and  horizontal  limbs  in 
many  cases  arising  from  a  common  arm,  sometimes  being  fused  into  a  single  sulcus, 
or  again  being  absent — are  due  to  atypical  growth  of  the  opercula.  particularly  of 
the  frontal. 

The  posterior  branch  (ramus  posterior),  the  main  continuation  of  the  fissure  and 
about  8  cm.  in  length,  is  directed  horizontally  backward,  with  a  slight  inclination 
upward.  It  forms  a  very  evident  boundary  between  the  anterior  parts  of  the  parietal 
and  temporal  lobes  which  it  separates  by  a  deep  cleft  that  usually  ends  behind  in  an 
ascending  limb  surrounded  by  the  angular  gyrus  (Fig.  980).  Not  infrequently  the 
fissure  ends  by  dividing  into  two  short  anus,  one  of  which  penetrates  the  parietal 
lobe  while  the  other  arches  downward  into  the  temporal  lobe. 


THE   TELENCEPHALON. 


FIG.  982. 


The  form  and  relations  of  the  fissure  of  Sylvius  are  so  dependent  upon  the  growth  of  the 
surrounding  parts,  that  a  sketch  of  the  development  of  this  region  of  the  hemisphere  is  necessary 
for  an  understanding  of  the  significance  of  this  conspicuous  sulcus.  During  the  third  foetal 
month  the  lateral  surface  of  the  cerebral  hemisphere 
presents  a  crescentic  depressed  area,  the  fossa  Sylvii, 
whose  floor  corresponds  to  the  insitla  or  island  of  J\eil. 
The  latter  is  seen  in  the  adult  brain,  on  separating  the 
margins  of  the  Sylvian  fissure,  as  a  sunken  area  which  is 
completely  hidden  by  the  overhanging  parts,  the  opercula 
insulae,  of  the  surrounding  lobes  (Fig.  990).  During  the 
fifth  month  the  former  shallow  crescentic  Sylvian  fossa 
gives  place  to  a  more  definitely  walled  triangular  depres- 
sion, which,  during  the  succeeding  month,  begins  to  be 
enclosed  by  the  formation  of  the  opercula.  The  details  of 
this  process  have  been  carefully  studied  by  Cunningham1 
and  more  recently  by  Retzius.2  The  opercula  which 
bound  the  triangular  fossa,  named  from  the  regions 
which  contribute  them  and  at  first  three  in  number,  are 
the  upper  or  parieto-frontal,  the  lower  or  temporal,  and 
the  anterior  or  orbital.  The  upper  and  lower  walls  first 

c  jme  in  contact  and  thereby  form  the  posterior  limb  of  the  Sylvian  fissure.  Later  the  angle 
between  the  upper  and  front  walls  of  the  fossa  becomes  modified  and  is  finally  obliterated  by  the 
appearance  of  a  wedge-shaped  projection,  later  the  frontal  operculum,  which  insinuates  itself 

between  the  adjacent  end 
FIG.  983. 

Inferior  precentral  Rolandic  fissure 


Left  hemisphere  of  brain  of  five  months 
fiL-tus  ;  three-fourths  natural  size. 


Inferior  frontal 


Parieto- 
frontal 
opercultnn 


Interparietal 


Olfactory  bulb         / 
Insula 


Vivian  fissure     Superior  temporal  sulcus 


Lateral  surface  of  left  hemisphere  of  eight  months  fostus  ;  insula  is  partly  covered 
by  opercula;    three-fourths  natural  size.     (Retzius.) 


i 


of  the  parieto-frontal  and 
the  orbital  opercula.  The 
orbital  and  particularly  the 
frontal  operculum  are  late 
in  their  differentiation  and 
growth,  and  not  until 
towards  the  second  year 
after  birth  do  they  come 
into  apposition  with  each 
other  and  the  remaining 
opercula  to  complete  the 
curtain  that  overhangs  the 
insula.  Along  with  the 
closure  of  the  front  part  of 
the  Sylvian  fossa,  the  dif- 
ferentiation of  the  anterior 
limbs  of  the  fissure  pro- 
gresses, since  upon  the 

adequate  growth  of  the  frontal  operculum  depends  the  production  of  a  distinct  pars  triangularis 
and  of  two  separate  anterior  branches.  Faulty  development  of  this  intermediate  part  of  the 
opercular  wall  accounts  for  the  V  or  I  form,  as  well  as  the  occasional  absence,  of  the  anterior  limbs. 

The  central  fissure  (sulcus  centralis),  or  fissure  of  Rolando,  extends 
transversely  across  the  upper  half  of  the  convex  dorsal  surface  of  the  hemisphere  and 
therefore,  with  the  bordering  precentral  and  postcentral  convolutions,  interrupts  the 
general  longitudinal  course  of  the  gyri  and  sulci.  Bearing  this  peculiarity  in  mind, 
the  fissure  is  readily  identified  even  in  brains  exhibiting  an  elaborate  and  complex 
modelling.  It  begins  above  on  the  supero-mesial  margin  of  the  hemisphere,  a  short 
distance  behind  the  middle  of  the  border,  and  descends  with  a  slight  general  forward 
obliquity  to  the  vicinity  of  the  posterior  limit  of  the  fissure  of  Sylvius,  above  whose 
mid-point  it  usually  ends.  Its  upper  extremity  usually  extends  over  the  supero- 
mesial  border  of  the  hemisphere  and,  passing  obliquely  backward,  cuts  for  a  short 
distance  into  the  marginal  gyrus  of  the  mesial  surface  (Fig.  987).  Its  lower  ex- 
tremity usually  ends  short  of  the  Sylvian  fissure,  but  occasionally  (rarely)  opens 
into  this  cleft.  It  constitutes  a  very  definite  boundary  on  the  external  surface  of  the 
hemisphere  between  the  frontal  and  parietal  lobes.  Although  passing  obliquely 
downward  and  forward,  the  course  of  the  central  fissure  is  by  no  means  straight 

1  Contribution  to  the  Surface  Anatomy  of  the  Cerebral  Hemispheres,  Irish  Academy,  1892. 

2  Das  Menschenhirn,  1896. 

72 


U38 


HUMAN   ANATOMY. 


owing  to  a  marked  angular  backward  projection  of  the  substance  of  the  precentral 
convolution,  situated  about  the  junction  of  the  upper  and  middle  thirds  of  the  fissure. 
In  consequence,  the  fissure  presents  in  this  part  of  its  course  a  distinct  curve,  with 
the  concavity  directed  forward,  the  upper  and  lower  limits  of  this  bend  consti- 
tuting the  superior  and  the  inferior  genu  respectively  (Fig.  980).  The  cortical 
tissue  filling  this  recess  is  of  importance,  since  it  represents  the  part  of  the  precentral 
gyrus  devoted  to  the  motor  centre  for  the  arm.  Below  the  inferior  genu  the  fissure 
descends  almost  vertically,  its  lower  end  often  bending  slightly  backward.  The 
angle  which  the  general  direction  of  the  central  fissure  makes  with  the  mesial  plane 
in  the  adult  brain  is  on  an  average  71.7°  (Cunningham),  the  Rolandic  angle,  as  it 
is  called,  of  the  two  sides  subtending  therefore  about  143°  (Fig.  984). 

FIG.  984. 


Superior  aspect  of  cerebral  hemispheres;  LF,  longitudinal  fissure;  ».,  r.  Rolandic  fissuie;  s#,  /ir.  its  . 
and  inferior  genu  ;  .s.  pc.,  superior  precentral;  s.f,  i.f,  superior  ant)  inferior  frontal  ;  f>m,  paramedian  ;  />,  />-,  />',  />'. 
inferior,  superior,  horizontal  and  occipital  limbs  of  inlerparietal ;  p-o,  parieto-occipital;  /.«..  /.".,  transverse  and 
lateral  occipital;  Sasc,  ascending  limb  of  Sylvian  ;  t*asc.,  t-asc.,  ascending  limbs  of  superior  and  middle  temporal. 

Since  the  central  fissure  is  usually  developed  from  two  separate  parts,  a  longer 
lower  and  a  short  upper  (Cunningham,  Retzius)  which  later  become  continuous,  a 
deep  annectant  gyrus  is  generally  found  crossing  the  bottom  of  the  sulcus  at  the 
junction  of  its  upper  and  middle  thirds.  In  exceptional  cases  the  original  separation 
is  continued  by  the  deep  annectant  gyrus  maintaining  its  superficial  relations,  the 
adult  fissure  then  being  interrupted  by  the  bridge  which  ordinarily  is  limited  to  the 
bottom  of  the  cleft.  As  a  variation  of  very  great  variety,  completed  doubling  of  tin 
central  fissure  has  been  observed. 

The  parieto-occipital  fissure  (fissura  parieto-occipitalis )  is  seen  chiefly  on  the 
mesial  surface  of  the  hemisphere  (Fig.  987),  where  it  appears  as  a  deep  cleft  which 
extends  from  a  point  on  the  supero-niesial  border  of  the  hemisphere,  about  4  cm.  in 
front  of  the  occipital  pole,  downward  and  forward.  This  inner  part  of  the  fissure, 


THE   TELENCEPHALON.  1139 

the  so-called  internal  paricto-occipital  fissure,  separates  the  mesial  surfaces  of  the 
parietal  and  occipital  lobes  and  ends  below  by  joining  the  calcarine  fissure,  the 
two  sulci  together  forming  a  >  whose  posteriorly  directed  diverging  limbs  in- 
clude a  wedged-shaped  portion  of  the  occipital  lobe  known  as  the  cuneus.  The 
parieto-occipital  fissure  is  continued  without  interruption  across  the  upper  margin  of 
the  hemisphere  and  onto  the  external  surface  for  a  short  distance.  This  outer  exten- 
sion, usually  only  from  12-15  mm.  in  length,  constitutes  the  external  parieto-occipital 
fissure  and  terminates  after  its  limited  transverse  course  in  a  bowed  convolution,  the 
arcns  parieto-occipitalis,  which  surrounds  and  separates  its  end  from  the  occipital  part 
of  the  interparietal  fissure.  Although  sometimes  ending  in  two  short  and  somewhat 
open  branches,  the  external  limit  of  the  parieto-occipital  fissure  is  usually  relatively 
inconspicuous;  notwithstanding,  the  sulcus  is  of  much  importance  as  affording  a 
readily  recognized  upper  limit  of  the  conventional  boundary  line  between  the  occipi- 
tal and  the  parietal  and  temporal  lobes.  In  the  foetal  brain  the  parieto-occipital  sul- 
cus- produces  a  distinct  invagination  of  the  wall  of  the  cerebrum  and  corresponds, 
therefore,  to  a  complete  fissure.  In  the  adult  brain,  however,  all  trace  of  this  infold- 
ing has  disappeared  in  consequence  of  the  growth  and  thickening  of  the  ventricular 
wall  which  subsequently  takes  place  (Cunningham). 

The  collateral  fissure  (fissura  collateralis)  is  a  well  marked  sulcus  on  the 
inferior  surface  of  the  hemisphere.  It  begins  behind  a  little  to  the  outer  side  of  the 
occipital  pole  and  extends  forward,  crossing  the  tentorial  area  parallel  with,  below 
and  lateral  to,  the  calcarine  fissure,  until  opposite  the  posterior  end  of  the  corpus  callo- 
sum,  where  it  meets  the  hippocampal  gyrus.  It  is  then  directed  slightly  outward, 
forming  the  lateral  boundary  of  the  last-named  convolution,  over  the  temporal  area 
well  toward  the  temporal  pole,  near  which  it  either  embraces  or  joins  with  a  short 
curved  furrow,  the  incisura  temporalis,  which,  in  conjunction  with  the  collateral 
fissure,  separates  the  lower  or  hippocampal  part  of  the  limbic  lobe  from  the  temporal 
lobe.  According  to  Cunningham,  the  collateral  fissure  is  at  first  represented  by 
three  distinct  parts — a  posterior  or  occipital,  an  intermediate  and  a  temporal — -"which 
later  become  one  continuous  furrow.  Of  these  three  primary  divisions,  the  interme- 
diate, and  usually  also  the  temporal,  are  complete  fissures,  producing  respectively 
the  collateral  protuberance  and  the  collateral  eminence  seen  in  the  lateral  ventricle 
(page  1164).  The  occipital  portion  of  the  fissure  is  never  complete  and,  therefore, 
does  not  give  rise  to  any  elevation. 

The  calloso-marginal  fissure  (sulcus  cinguli)  is  the  most  conspicuous  sul- 
cus on  the  mesial  surface  of  the  hemisphere,  where  it  appears  as  a  curved  furrow 
running  above  and  concentric  with  the  arched  upper  surface  of  the  corpus  callosum. 
It  begins  in  front  below  the  fore-end  of  this  bridge,  just  above  the  anterior  perforated 
space,  sweeps  around  the  genu  of  the  corpus  callosum  and  arches  backward  above 
the  latter  structure  almost  as  far  as  the  splenium,  where  it  turns  upward  (ramus  mar- 
ginalis)  and  reaches  the  supero-mesial  border  of  the  hemisphere  a  short  distance  be- 
hind the  overturned  end  of  the  Rolandic  fissure.  By  its  course  the  calloso-marginal 
sulcus  marks  off  on  the  anterior  two-thirds  of  the  mesial  surface  of  the  hemisphere 
the  marginal  convolution  of  the  frontal  lobe  from  the  callosal  gyrus  of  the  limbic  lobe, 
the  somewhat  uncertain  posterior  boundary  of  the  latter  beyond  the  sulcus  being 
indicated  by  the  inconspicuous  postlimbic  fissure,  which  arches  downward  concen- 
trically with  the  splenium.  The  frequent  variations  in  the  details  of  the  calloso- 
marginal  fissure  depend  upon  irregularities  in  the  arrangement  and  fusion  of  the 
three  separate  furrows  by  the  union  of  which  a  continuous  sulcus  is  formed. 

The  limiting  sulcus  of  Reil  (sulcus  circulates  Reili)  is  a  shallow  furrow 
that  incompletely  surrounds  the  insula  and  imperfectly  separates  this  buried  portion 
of  the  central  cortex  from  the  deeper  parts  of  the  enclosing  opercula.  The  sulcus 
consists  of  three  parts — a  superior,  separating  the  island  from  the  parietal  and  fron- 
tal lobes,  an  anterior,  intervening  in  front  between  the  insula  and  the  frontal  lobe,  and 
a  posterior,  imperfectly  separating  the  hind  part  of  the  island  from  the  limbic  lobe. 

THE    LOBES    OF    THE    HEMISPHERES. 

The  Frontal  Lobe. — The  frontal  lobe  (lobus  frontalis)  is  the  largest  of  the 
subdivisions  of  the  hemisphere  and  includes  approximately  one-third  of  the  hemi- 


1140 


HTM  AX    ANATOMY. 


FIG.  985. 


cerebrum.  It  appears  on  each  of  the  three  aspects  of  the  hemisphere  and  has, 
therefore,  a  dorso-lateral,  a  mesial  and  an  inferior  surface.  On  the  external  surface 
of  the  hemisphere  it  is  bounded  behind  by  the  central  fissure,  which  separates  it  from 
the  parietal  lobe,  and  below  by  the  fore-part  of  the  Sylvian  fissure,  which  intervenes 
between  it  and  the  temporal  lobe.  On  the  mesial  surface  the  frontal  lobe  includes 
an  irregular  —> ,  marked  off  by  the  calloso-marginal  sulcus,  the  longer  upper  limb 
ending  behind  the  central  fissure.  On  the  inferior  surface  of  the  hemisphere,  the 
frontal  lobe  includes  the  concave  orbital  area,  bounded  behind  by  the  transversely 
directed  stem  of  the  Sylvian  fissure,  which  sulcus  thus  separates  it  from  the  temporal 
lobe. 

The  principal  fissures  on  the  dorso-lateral  surface  of  the  frontal  lobe  are :  ( i )  the 
inferior  precentral,  (2)  the  superior  precentral,  (3)  the  superior  frontal  and  (4)  the 
inferior  frontal.  The  inferior  precental  sulcus  which  consists  of  a  longer  vertical 
and  a  short  transverse  limb  and  has  a  general  ~|  or  T  form.  The  vertical  limb 
begins  above  the  fissure  of  Sylvius  and  in  front  of  the  central  fissure  and  extends 
upward  parallel  to  the  latter  and  separated  from  the  lower  part  of  the  precentral 

convolution.  The  horizontal  limb 
passes  obliquely  forward  and  upward 
and  cuts  for  a  variable  distance  into 
the  middle  frontal  convolution.  Fre- 
quently the  inferior  precentral  sulcus 
is  directly  continuous  with  the  inferior 
frontal  furrow;  sometimes  it  opens 
below  into  the  Sylvian  fissure  and 
above  may  join  the  superior. 

The  superior  precental  sulcus 
prolongs  upward  the  anterior  boun- 
dary of  the  precentral  convolution.  It 
lies  parallel  with  the  upper  half  of  the 
Rolandic  fissure,  but  does  not  usually, 
although  sometimes  reach  the  upper 
margin  of  the  hemisphere.  Almost 
constantly  it  receives  the  posterior 
end  of  the  superior  frontal  sulcus  with 
which  it  forms  a  —\  shaped  furrow. 

The  superior  frontal  sulcus 
extends  forward  from  the  preceding 

fissure  with  a  course  which  corresponds  in  general  with  the  supero-mesial  border 
of  the  hemisphere  and  thus  marks  off  a  longitudinal  marginal  tract,  the  superior 
frontal  convolution.  Anteriorly  the  superior  frontal  may  join  the  median  frontal 
sulcus,  while  its  posterior  end  may  incise  the  precentral  convolution.  Often  tin- 
course  of  the  fissure  is  interrupted  by  superficial  anncctant  gyri  which  connect  the 
adjacent  borders  of  the  upper  and  middle  frontal  convolutions. 

The  inferior  frontal  sulcus  begins  behind  in  the  interval  between  the  hori- 
zontal and  vertical  limbs  of  the  inferior  precentral  furrow,  <>r  in  confluence  with  one 
of  these.  In  its  general  course  it  arches  forward  and  downward  towards  the  anterior 
or  superciliary  margin  of  the  hemisphere  and  terminates  a  short  distance  behind 
this  border  by  bifurcating  into  a  transverse  limb.  The  line  of  the  fissure  is  often 
obscured  by  superficial  annectant  gyri  and  complicated  by  small  secondary  furrows 
which  pass  from  it  into  the  bordering  middle  and  inferior  frontal  convolutions, 

The  convolutions  on  the  dorso-lateral  surface  of  the  frontal  lobe  are  the  pre- 
central, the  superior  frontal,  tin-  middle  frontal  and  the  inferior  frontal. 

The  precentral  gyrus  ( nyrus  centrnlis  anterior),  also  known  as  tin-  ascending 
frontal,  is  bounded  behind  by  the  central  fissure  and  in  front  by  the  superior  and 
inferior  precentral  snlci.  Below  it  is  limited  by  the  Sylvian  fissure,  whilst  its  upper 
end  is  continuous  with  the  paracentral  lobule  of  the  mesial  surface.  Anteriorly  it  is 
connected  with  all  three  frontal  convolutions.  A  short  distance  abo\e  its  middle,  it 
s<-nds  backward  a  conspicuous  projection,  triangular  or  rounded  in  outline,  which 
encroaches  upon  the  postcentral  gyrns  and  correspondingly  modifies  the  line  of  the 


Anterior  aspect  of  cerebral  hemisplK-rcs,  liar  1cm.  1  ii 
skull;  s/',if,  superior  and  inferior  Ironta!  fissures;  />«/. 
paramedian;  tn.f,  mid-frontal;  /-»/.,  fronto-inarginal. 


THE   TELENCEPHALC  )X. 


1 141 


Rolandic  fissure.  The  observations  of  Mills  and  of  Grunbaum  and  Sherrington 
emphasize  the  predominating  importance  of  the  precentral  convolution  as  containing 
the  important  cortical  motor  areas  (page  1211),  the  backward  projection  just 
noted  containing  the  centres  controlling  the  muscles  of  the  upper  extremity. 

The  superior  frontal  gyrus  lies  between  the  supero-mesial  border  of  the  hemi- 
sphere and  the  superior  frontal  sulcus.  Since  its  course  corresponds  with  the  upper 
margin  of  the  hemisphere,  it  is  much  longer  than  the  other  frontal  convolutions  on 
the  external  surface  and  reaches  the  frontal  pole.  It  is  continuous  with  the  marginal 
gyrus,  which,  in  fact,  is  only  its  mesial  part.  Behind,  it  joins  the  precentral  convolu- 
tion by  a  narrow  bridge  between  the  upper  end  of  the  precentral  sulcus  and  that  of  a 
branch  from  the  calloso-marginal  fissure.  The  superior  frontal  convolution,  notwith- 
standing its  meagre  width,  is  frequently  imperfectly  divided  into  an  upper  and  a 
lower  part  by  a  series  of  shallow  longitudinal  furrows  collectively  termed  \.\\e  para- 
median  sulcus.  The  latter  is  regarded  as  a  distinctive  feature  of  the  human  brain, 
and  is  found  relatively  deep  and  well  marked  only  in  the  brains  of  the  higher  races. 

The  middle  frontal  gyrus,  the  broadest  of  the  three,  extends  forward  parallel 
with  the  upper  frontal  convolution  well  towards  the  frontal  pole.  It  is  bounded 

IMC;.  986. 

Inferior  frontal  sulcus  Inferior  precentral  sulcus 


Rolandic  fissure 


Ascending  limb 


Orbital  surface 

Horizontal  limb 


Posterior  limb 


Portion   of   lateral   surface  of    left   hemisphere,  showing  pars    basalis  (B),  triangularis  ( T)  and   orbitalis    (0)    of 
inferior  frontal  gyrus,    known  as  Broca's  convolution  :  ST.,  superior  temporal  gyrus. 

above  and  below  by  the  superior  and  the  frontal  sulcus  respectively  and,  in  man  and 
the  anthropoid  apes,  is  almost  constantly  subdivided  into  an  upper  and  a  lower  sub- 
division by  the  mid  frontal  sulcus  (sulcus  frontalis  medius).  The  latter  is  often  broken 
by  annectant  gyri  into  two  or  more  pieces  and  in  front  usually  bifurcates  to  form  the 
fronto-marginal  sulcus  (sulcus  transversus  anterior),  which  runs  across  the  hemi- 
sphere a  short  distance  above  the  superciliary  margin. 

The  inferior  frontal  gyrus,  the  shortest  of  the  three,  lies  below  the  inferior 
frontal  sulcus  and  arches  forward  and  downward  around  the  anterior  limbs  of  the 
Sylvian  fissure.  Below  and  behind  it  is  connected  with  the  lower  end  of  the  pre- 
central convolution  by  a  narrow  bridge  enclosing  the  lower  end  of  the  inferior  pre- 
central sulcus.  By  the  ascending  and  horizontal  limbs  of  the  Sylvian  fissure  the 
inferior  frontal  gyrus  is  incompletely  divided  into  three  portions — the  pars  basalis, 
the  pars  triangularis  and  the  pars  orbitalis  (Fig.  986).  The  pars  basalis  (pars 
opcrcularis)  occupies  the  posterior  part  of  the  convolution  and  lies  between  the 
inferior  precentral  sulcus  and  the  ascending  Sylvian  limb.  It  forms  the  fore-part  of 
the  fronto-parietal  operculum  and  is  indented  by  an  inconspicuous  although  constant 
furrow,  the  sulcus  diagonalis,  which  extends  obliquely  downward  and  forward  across 
the  gyrus  for  a  variable  distance.  Although  usually  distinct,  the  diagonal  sulcus 
may  join  the  inferior  precentral  (Fig.  986),  the  inferior  frontal  or  the  Sylvian 
fissure.  The  pars  triangularis  is  the  wedge-shaped  tract  included  between  the 
two  limbs  of  the  Sylvian  fissure.  Its  base  is  directed  upward  and  forward  and  its 


n42  HUMAN   ANATOMY. 

apex  towards  the  Sylvian  point.  The  pars  orbitalis  lies  below  the  horizontal  limb 
and  is  continued  around  the  margin  of  the  hemisphere  onto  the  orbital  surface  of 
the  frontal  lobe.  It  is  evident,  from  the  description  of  the  boundaries  of  the  Sylvian 
fissure  already  given  (page  1137),  that  the  preceding  subdivisions  of  the  inferior 
frontal  gyrus  correspond  with  certain  of  the  opercula — the  pars  basalis  with  the 
anterior  part  of  the  fronto-parietal,  the  pars  triangularis  with  the  frontal  and  the 
pars  orbitalis  with  the  orbital  operculum.  The  posterior  extremity  of  the  inferior 
frontal  gyrus  on  the  left  side  is  known  as  Broca  s  convolution  and  has  long  been 
regarded  as  the  centre  for  the  movements  for  articulate  speech,  although  the  accuracy 
of  this  view  has  been  questioned.  According  to  Marie,  Broca' s  convolution  has 
no  relation  with  speech,  a  conclusion,  however,  so  far  not  convincingly  supported. 
The  convolution  is  sometimes  better  developed  on  the  left  than  the  right  side  of 
the  brain,  the  pars  triangularis  particularly  being  increased.  As  previously  noted, 
the  development  of  this  wedge — the  frontal  operculum — bears  a  direct  relation  to 
the  degree  of  independence  of  the  two  anterior  limbs  of  the  Sylvian  fissure. 

The  mesial  surface  of  the  frontal  lobe  (Fig.  987),  includes  only  one  convolution, 
the  marginal  gyrus,  which  lies  between  the  dorso-mesial  margin  of  the  hemisphere 
and  the  calloso-marginal  sulcus  (page  1139),  and  by  the  latter  is  separated  from  the 
limbic  lobe.  It  is  — 3-shaped  and  directly  continuous  with  the  superior  frontal  gyrus 
above  and  with  the  gyrus  rectus  on  the  orbital  surface  below.  Its  posterior  end  is 
almost  completely  cut  off  from  the  rest  of  the  gyrus  by  an  ascending  limb  (sulcus  para- 
centralis)  from  the  calloso-marginal  sulcus,  the  portion  so  isolated  forming  the  front 
part  of  the  paracentral  lobule,  which  is  bounded  behind  by  the  upturned  end 
(ramus  marginalis)  of  the  calloso-marginal  sulcus  and  contains,  near  its  hind  border, 
the  termination  of  the  fissure  of  Rolando.  By  means  of  an  annectant  convolution 
passing  below  the  last-named  furrow,  the  frontal  part  of  the  paracentral  lobule  is  con- 
tinuous with  the  part  contributed  by  the  parietal  lobe.  The  middle  of  the  mar- 
ginal gyrus  is  often  incompletely  subdivided  by  a  shallow  longitudinal  groove,  the 
mesial  frontal  sulcus,  into  an  upper  and  a  lower  tract,  whilst  its  anterior  and  lower 
end  is  uncertainly  cleft  by  two  or  three  short  downward  curving  furrows,  the  sulci 
rostrales. 

The  orbital  surface  of  the  frontal  lobe  is  marked  by  two  fissures,  the  olfactory 
and  the  orbital  and  by  three  chief  convolutions,  the  inner,  the  middle  and  the  outer 
orbital.  Although  such  division  is  convenient  for  the  purposes  of  description,  it 
must  be  remembered  that  these  orbital  gyri  are  not  separate  convolutions,  but  lankly 
the  inferior  portions  of  the  upper,  middle  and  lower  frontal  convolutions  of  the  outer 
surface  of  the  lobe. 

The  olfactory  sulcus  lodges  the  olfactory  bulb,  tract  and  tubercle,  and  ex- 
tends parallel  with,  or  inclined  somewhat  towards  the  great  longitudinal  fissure.  Its 
course  being  straight,  the  sulcus  marks  off  a  narrow  strip,  about  i  cm.  in  width, 
along  the  mesial  border  of  the  lobe.  This  area,  although  specially  designated  as  the 
gyrus  rectus,  is  only  a  part  of  the  broader  longitudinal  tract  which  corresponds  to 
the  orbital  surface  of  the  superior  frontal  convolution. 

The  orbital  sulcus  includes  a  number  of  furrows  whose  arrangement  is  very 
variable,  not  only  in  different  brains  but  often  on  the  two  sides  of  the  same  brain. 
In  the  disposition  assumed  as  the  typical  one,  which,  however,  is  far  from  constant, 
the  orbital  sulcus  consists  of  two  longitudinal  limbs,  connected  by  a  shorter  trans- 
verse arm,  the  three  furrows  forming  a  common  fissure  which  corresponds  more  or 
less  closely  with  the  letter  H.  In  many  cases,  however,  the  sulcus  more  nearly  re- 
sembles  an  X  or  K,  or  it  may  be  still  further  modified  by  the  presence  of  additional 
secondary  grooves  of  variable  number  and  length.  Assuming  the  conventional  H- 
form  to  exist,  the  orbital  surface  is  divided  into  three  longitudinal  trails,  the  inner, 
middle  and  outer  orbital  gyri,  by  the  long  limbs  (sulcus  orbitalis  interims  et  cxter- 
nus).  The  inner  tract  is  subdivided  by  the  olfactory  sulcus  into  the  gyrus  rectus, 
above  mentioned,  and  an  outer  part,  the  gyrus  orbitalis  internns  in  the  more 
restricted  sense.  The  middle  orbital  gyrus  is  subdivided  by  the  curved  transverse 
limb  i  sulcus  orbitalis  transversus )  into  the  anterior  and  the  posterior  orbital  gyrus, 
which  lie;  respectively  in  front  and  behind  the  transverse  furrow.  In  many  cases  the 
latter  curves  out\vanl  and  backward  until  it  almost  re-aches  the  Svlvian  fissure-. 


THE   TELENCEPHALON. 

The  Parietal  Lobe. — This  division  includes  a  considerable  part  of  the  hemi- 
sphere and  presents  two  surfaces,  an  external  and  a  mesial.  The  external  surface, 
much  the  more  extensive  and  irregularly  quadrilateral  in  outline,  is  bounded  above, 
in  front  and  partially  below  by  well  marked  fissures,  but  behind  and  postero-infe- 
riorly  its  limits  from  the  occipital  and  temporal  lobes  are  defined  for  the  most  part 
by  imaginary  lines.  Its  upper  boundary  corresponds  with  the  supero-mesial  border 
of  the  hemisphere  ;  its  anterior  boundary  is  the  central  fissure,  by  which  the  pari- 
etal lobe  is  completely  separated  from  the  frontal  except  below,  where  the  postcen- 
tral  gyrus  is  continuous  with  the  precentral  by  the  bridge  closing  the  lower  end  of 
the  Rolandic  fissure.  Its  posterior  boundary,  which  separates  the  parietal  from  the 
occipital  lobe,  is  largely  conventional  and  indicated  by  a  line  drawn  from  the  point 
where  the  parieto-occipital  fissure  cuts  the  upper  margin  of  the  hemisphere  to  an  in- 
dentation, the  preoccipital  notch  (page  1134),  which  grooves  the  infero-lateral  border 
of  the  hemisphere  at  a  point  from  3.5-4  cm.  in  front  of  the  occipital  pole.  Its 
inferior  border,  between  the  parietal  and  the  temporal  lobes,  is  definite  where  formed 
by  the  posterior  limb  of  the  Sylvian  fissure.  Beyond  the  upturned  end  of  the  latter, 

FIG.  987. 


Infero-mesial  aspect  of  left  cerebral  hemisphere;  cm.,  calloso-marginal  fissure;  ros.,  rostral;  r.,  overturned 
end  of  Rolandic  ;  />.  /.,  post-limbic  ;  i.  p-o.,  internal  parieto-occipital ;  p.  cal.,  a.  cal.,  posterior  and  anterior  calcarine  ; 
p.  col.,  a.  col.,  posterior  and  anterior  collateral ;  i.  t.,  incisura  temporalis  or  rhinial ;  o-t.,  occipito-temporal. 

the  parietal  and  the  temporal  lobes  are  continuous  and  their  separation  is  conven- 
tionally assumed  to  be  made  by  an  arbitrary  line  prolonged  backward  in  the  direc- 
tion of  the  posterior  limb  of  the  Sylvian  fissure  until  it  meets  the  parieto-occipital 
line  previously  described. 

The  external  surface  of  the  parietal  lobe  is  subdivided  by  a  composite  fissure, 
the  interparietal  sulcus,  into  three  general  tracts,  the  postcentral,  the  superior  pari- 
etal and  the  inferior  parietal  gyrus. 

The  interparietal  sulcus,  especially  described  by  Turner,  starts  in  the  antero- 
inferior  angle  of  the  lobe  a  short  distance  above  the  Sylvian  fissure,  with  which  it  is 
rarely  continuous,  ascends  for  about  an  inch  parallel  with  the  central  fissure,  and 
then  sweeps  backward  and  slightly  upward  across  the  parietal  into  the  occipital  lobe. 
The  interparietal  sulcus  is  developed  as  four  originally  distinct  parts,  which  in  the 
fully  formed  brain,  notwithstanding  their  usual  fusion,  are  recognized  as  the  inferior 
and  the  superior  postcentral  sulcus  and  the  horizontal  and  occipital  limbs  (Cun- 
ningham). 

The  inferior  postcentral  sulcus  lies  behind  and  parallel  with  the  lower  part 
of  the  central  fissure.  Although  in  most  cases  continuous  with  either  the  superior 
postcentral  sulcus  (in  72  percent,  according  to  Retzius1),  or  with  the  horizontal  limb 

1  Biologische  Untersuchungen,  VIII.,  1898. 


1 144 


HTM  AN    ANATOMY. 


(66  per  cent.),  or  with  both  (55  per  cent.),  the  inferior  limb  may  remain  ununited 
(  17  per  cent.).  When  joined,  the  two  limbs  together  form  a  continuous  postccntral 
sulcus  which  parallels  the  fissure  of  Rolando  and  bounds  the  postcentral  convolution 
behind.  In  rare  instances  the  inferior  postcentral  sulcus  opens  below  into  the 
Sylvian  fissure. 

The  superior  postcentral  sulcus  lies  behind  and  parallel  with  the  upper  part 
of  the  fissure  of  Rolando,  gaining  the  superior  margin  of  the  hemisphere  between  the 
incisions  of  the  Rolandic  fissure  and  the  upturned  end  of  the  calloso-marginal  sulcus. 
Although  in  59  per  cent,  of  the  brains  studied  by  Retzius  the  fissure  was  confluent 
with  the  horizontal  limb,  in  24  per  cent,  it  remained  isolated. 

The  horizontal  limb  passes  backward  and  slightly  upward  and  separates  the 
superior  and  inferior  parietal  convolutions  from  each  other.  It  is  usually  continuous 
in  front  with  one  or  the  other  or  with  both  postcentral  sulci  and  behind  with  the 

FIG.  988. 


Lateral  aspect  of  left  side  of  brain.  LF,  longitudinal  fissure;  /•.,  r.,  r.,  Rolandic  fissure;  i.  /«  .,  A. /'<'.,  inferior  and 
superior  precentral;  sf.,  if.,  superior  and  inferior  frontal ;  S/>,  S.  asc..  posterior  and  ascending  limbs  of  Sylvian 
fissure;  P,p",  />;t, /4,  inferior,  superior,  horizontal  and  occipital  limbs  of  interparictal ;  />-o,  parit-to-occipital ;  /.  o., 
1.  o.,  transverse  and  lateral  occipital ;  /',  tlasc.,  superior  temporal  and  its  upturned  limb;  (-,  t-asc.,  middle  temporal 
and  its  upturned  limb. 

posterior  or  occipital  limb.  As  a  rule  it  joins  a  continuous  postcentral  sulcus,  in 
which  case  the  three  furrows  form  a  \—  shaped  fissure,  which  subdivides  the  parietal 
lobe  into  its  three  main  convolutions. 

The  occipital  limb  is  usually  attached  to  the  horizontal  one  and  then  directly 
prolongs  the  interparietal  sulcus  into  the  occipital  lobe.  Sometimes,  however,  it 
retains  its  original  independence  and  is  separated  from  the  ramus  horizontalis  by  a 
deep  annectant  gyrus.  It  is  irregularly  curved  and  marks  the  lower  boundary  of  the 
gyrus,  the  arcus  parieto-occipitalis,  which  receives  the  outer  end  of  the  parieto- 
occipital  fissure.  Beyond  the  line  of  this  furrow,  the  sulcus  lies  in  the  occipital  lobe 
and  behind  the  arcus  parieto-occipitalis  ends  by  bifurcating  into  two  widely  divergent 
arms,  which  constitute  the  transverse  occipital  sulcus. 

The  chief  convolutions  on  the  external  surface  of  tlic  parietal  lobe  are  three — the 
postcentral,  the  superior  parietal  and  the  inferior  parietal. 

The  postcentral  gyrus,  also  called  tin-  ascending  parietal^  forms  the  posterior 
wall  of  the  fissure  of  Rolando,  and  itself  is  bounded  behind  by  the  postrentral  sulcus, 
either  by  the  continuous  fissure  or  by  its  two  divisions.  The  lower  end  of  the  gyrus 
is  connected  with  the  precentral  convolution  in  front  and  with  the  inferior  parietal 
one  behind  by  the  annectant  i^yri  (-losing  the  lower  ends  of  the  central  and  postcen- 


THE   TELENCEPHALON.  1145 

tral  sulci  respectively.  Above,  the  convolution  is  continuous  with  the  preccntral 
lobule  of  the  mesial  surface  between  the  terminations  of  the  calloso-marginal  and  the 
Rolandic  fissures.  In  its  width  and  general  oblique  course  across  the  hemisphere, 
the  postcentral  convolution  strongly  resembles  the  precentral  gyrus  and  with  the 
latter  and  the  three  associated  sulci — the  precentral,  central  and  postcentral — forms 
a  conspicuous  feature  in  the  modelling  of  the  external  surface  of  the  hemisphere  and 
affords  a  ready  means  of  locating  the  Rolandic  fissure. 

The  superior  parietal  gyrus  is  the  triangular  tract  lying  between  superior 
postcentral  sulcus,  the  horizontal  limb  of  the  interparietal  sulcus  and  the  supero- 
mesial  border  of  the  hemisphere.  Behind,  it  is  limited  by  the  overturned  outer  end 
of  the  parieto-occipital  fissure,  around  which,  however,  it  is  continuous  with  the 
occipital  lobe  by  means  of  the  curved  convolution,  the  arcus  parieto-occipitalis. 
Farther  forward  it  is  frequently  deeply  incised  by  an  ascending  branch  from  the  inter- 
parietal  sulcus.  It  is  connected  with  the  postcentral  gyrus  around  the  upper  end  of 
the  superior  postcentral  sulcus  and,  in  those  cases  in  which  the  last-named  sulcus  fails 
to  unite  with  outer  segments  of  the  interparietal  fissure,  additionally  joins  the  post- 
central  gyrus  about  the  inferior  postcentral  sulcus. 

The  inferior  parietal  gyrus  is  included  between  the  curved  interparietal 
sulcus  and  the  conventional  lower  boundary  of  the  lobe.  Since  only  the  front  end  of 
this  boundary  is  defined  by  a  groove,  its  greater  part  being  the  arbitrary  line  above 
described,  it  follows  that  behind  the  Sylvian  fissure  the  inferior  parietal  convolution 
is  continuous  with  the  subjacent  temporal  gyri.  The  convolution  is  cut  into  from 
below  by  the  upturned  end  of  the  Sylvian  fissure  and  the  terminations  of  the  first  and 
second  temporal  sulci  and  by  these  incisions  is  somewhat  uncertainly  subdivided  into 
three  parts,  the  supramarginal,  the  angular  and  the  postparietal  gyri  (Fig.  988). 
The  supramarginal  gyrus  arches  around  the  upturned  extremity  of  the  Sylvian 
fissure.  It  lies  behind  and  below  the  front  part  of  the  interparietal  sulcus,  around 
whose  lower  end  it  joins  the  postcentral  gyrus,  whilst  below  it  is  continuous  with  the 
superior  temporal  and  behind  with  the  angular  gyrus.  The  angular  gyrus  surmounts 
the  upwardly  directed  end  of  the  superior  temporal  sulcus  and  below  is  prolonged  into 
the  superior  and  middle  temporal  convolutions.  It  is  commonly  imperfectly  sepa- 
rated from  the  postparietal  gyrus  by  a  shallow  furrow.  The  postparietal  gyrus 
bends  over  the  obliquely  vertical  extremity  of  the  middle  temporal  sulcus  and  below 
joins  the  middle  and  inferior  temporal  convolutions.  It  lies  approximately  opposite 
the  arcus  parieto-occipitalis  from  which  it  is  separated  by  the  occipital  branch  of  the 
interparietal  sulcus. 

The  mesial  surface  of  the  parietal  lobe  includes  an  irregularly  quadrate  area  ex- 
tending from  the  internal  limb  of  the  parieto-occipital  sulcus  behind  to  the  line  of  the 
Rolandic  fissure  in  front;  below  it  is  imperfectly  defined  from  the  limbic  lobe  by  the 
calloso-marginal  sulcus,  to  a  very  slight  extent,  and  its  continuation,  the  post-limbic 
furrow.  By  far  the  greater  part  of  this  surface  is  embraced  by  the  quadrate  lobule 
or  precuneus,  an  irregularly  quadrilateral  area  (Fig.  987)  limited  in  front  by  the 
upturned  terminal  limb  of  the  calloso-marginal  and  behind  by  the  parieto-occipital 
sulcus.  The  lobule,  the  mesial  aspect  of  the  superior  parietal  convolution,  is  usually 
marked  by  one  or  more  furrows,  the  precuneate  sulci,  which  incise  the  upper  margin 
of  the  hemisphere  and  extend  for  a  short  distance  onto  the  outer  surface. 

The  Occipital  Lobe. — The  occipital  lobe  is  pyramidal  in  form  and  includes 
the  occipital  pole  and  the  adjacent  parts  of  the  hemisphere.  It  is  represented  on  all 
of  the  aspects  of  the  hemisphere  and  possesses,  therefore,  a  lateral,  a  mesial  and  an 
inferior  or  tentorial  surface.  A  well-marked  occipital  lobe  is  found  only  in  the  brain 
of  man  and  of  the  anthropoid  apes  and  is  developed  as  a  backward  prolongation  of 
the  parietal  and  temporal  lobes,  from  which,  therefore,  it  is  but  imperfectly  sepa- 
rated. On  the  mesial  surface  its  extent  is  definitely  limited  by  the  internal  parieto- 
occipital  sulcus,  by  which  it  is  cut  off  from  the  quadrate  lobule  or  precuneus  of  the 
parietal  lobe.  On  the  lateral  surface,  on  the  contrary,  it  is  continuous  with  the  pari- 
etal and  temporal  lobes,  its  anterior  boundary  being  arbitrary  and  indicated  by  the 
parieto-occipital  line  drawn  from  the  overturned  limit  of  the  parieto-occipital  sulcus 
above  to  the  preoccipital  notch  below.  On  the  inferior  or  tentorial  aspect  its  demar- 
cation is  even  more  uncertain,  the  occipital,  limbic  and  temporal  lobes  being  here 


1146 


HUMAN   ANATOMY. 


directly  continuous,  and  depends  upon  the  recognition  of  an  arbitrary  line  which 
may  be  drawn,  as  suggested  by  Cunningham,  from  the  preoccipital  notch  on  the 
infero-lateral  border  to  the  isthmus  of  the  limbic  lobe,  just  below  the  splenium  of 
the  corpus  callosum. 

The  external  surface  of  the  occipital  lobe  is  modelled  by  two  well-defined  fissures, 
the  transverse  occipital  and  the  lateral  occipital,  and  by  two  somewhat  uncertain 
convolutions,  the  superior  and  the  inferior  occipital  (Fig.  988). 

The  transverse  occipital  sulcus  is,  as  above  pointed  out,  the  widely  diver- 
gent terminal  bifurcation  of  the  interparietal  fissure,  whose  last  segment  beyond  the 
outer  end  of  the  parieto-occipital  sulcus  enters  the  occipital  lobe  to  end  in  the  manner 
just  indicated. 

FIG.  989. 


Inferior  aspect    of  cerebral  hemispheres,      t.o.,  t.o.,  e.o.,    internal,  transverse  and   external    orbital 
i.e.,  incisura  temporalis  ;  cat.,  calcarine  ,  col.,  collateral ;  o-t.,  occipito-temporal  fissures. 


fissu 


The  lateral  occipital  sulcus  arches  horizontally  forward  below  the  lower  end 
of  the  preceding  furrow,  not  infrequently  dividing  into  an  ascending  and  a  descending 
limb. 

The  superior  and  inferior  occipital  gyri  are  the  upper  and  lower  areas  into 
which  the  outer  aspect  of  the  occipital  lobe  is  somewhat  uncertainly  subdivided  by 
the  lateral  occipital  sulcus.  Secondary  furrows  and  ridges  often  obscure  the  charae- 
teristic  modelling  of  this  surface,  whilst  annectant  convolutions  connect  its  gyri  with 
the  parietal  and  temporal  lobes. 

The  mesial  snrface  of  the  occipital  lobe  presents  one  sulcus,  the  calcarine  fissure, 
a  triangular  tract,  the  cuneus,  and  part  of  the  gyms  lingualis. 

The  calcarine  fissure  begins  by  a  forked  extremity,  the  longer  lower  limb  of 
which  incises  the  occipital  pole  in  the  impression  made  on  the  hemisphere  by  the 
lateral  sinus.  It  then  continues  forward,  slightly  arched,  a  short  distance  above  tin- 
border  of  the  lobe  formed  by  the  junction  of  the  falx  cerebri  and  the  teiitorium,  and 


THE    TELENCEPHALON.  1147 

ends,  after  a  short  bend  outward,  by  cutting  into  the  limbic  lobe  just  below  the 
splenium  of  the  corpus  callosum  (Fig.  987).  This  incision  divides  the  posterior 
extremity  of  the  hippocampal  gyrus  into  a  narrow  upper  tract,  the  isthmus,  which 
links  the  gyrus  with  the  callosal  convolution,  and  a  broader  lower  arm,  which 
establishes  continuity  between  the  hippocampal  and  fusiform  gyri.  A  short  distance 
in  front  of  its  middle,  the  calcarine  fissure  is  joined  by  the  lower  end  of  the  parieto- 
occipital  sulcus,  the  two  furrows  forming  a  >  shaped  sulcus,  between  whose 
diverging  limbs  lies  the  triangular  cuneus.  Although  usually  appearing  as  one 
continuous  fissure,  the  parieto-occipital  and  calcarine  sulci  are  incompletely  separated 
by  a  deep  annectant  gyrus,  which  connects  the  cuneus  with  the  limbic  lobe.  The 
calcarine  fissure  itself  is  subdivided  by  a  second  sunken  gyrus  into  an  anterior  and  a 
posterior  part.  The  latter,  the  posterior  calcarine  fissure,  is  shorter  and  shallower 
than  the  front  part  and  is  not  a  total  fissure.  The  other  portion,  the  anterior  calca- 
rine fissure,  is  not  only  the  deeper  but  completely  invaginates  the  brain-wall,  thereby 
giving  rise  to  the  elevation  known  as  the  calcar  avis,  seen  on  the  inner  boundary  of 
the  posterior  horn  of  the  lateral  ventricle. 

The  cuneus  forms  the  chief  part  of  the  mesial  aspect  of  the  occipital  lobe.  It 
is  triangular  in  outline  and  lies  between  the  parieto-occipital  sulcus  in  front  and  the 
posterior  limb  of  the  calcarine  fissure  below,  whilst  above  and  behind  it  reaches  the 
superior  border  of  the  hemisphere  (Fig.  987).  Its  surface  is  frequently  impressed 
by  one  or  more  shallow  vertical  furrows. 

The  lingual  gyrus,  also  called  the  infra-calcarine ',  is  the  irregular  elongated 
tract  bounded  mesially  and  above  by  the  calcarine  fissure,  and  laterally  and  below  by 
the  collateral  (Fig.  989).  Its  rounded  hind-end  lies  in  the  occipital  lobe,  whilst  its 
tapering  and  greatly  narrowed  front-end  is  continuous  with  the  hippocampal  convo- 
lution. The  gyrus  fits  into  the  angle  between  the  falx  cerebri  and  the  tentorium 
and  therefore  bears  the  internal  occipital  border  of  the  hemisphere  and  appears  on 
both  the  mesial  and  the  tentorial  surfaces.  It  is  usually  modelled  by  irregular  shallow 
furrows  which  break  up  the  larger  tentorial  aspect  into  uncertain  secondary  gyri. 

The  inferior  or  tentorial  surface  of  the  occipital  lobe  is  continuous  with  the  more 
extensive  similar  surface  of  the  temporal  lobe  resting  upon  the  tentorium.  In  addi- 
tion to  the  tentorial  part  of  the  lingual  gyrus,  this  aspect  of  the  lobe  is  occupied  by 
the  posterior  part  of  the  occipito-temporal  gyrus.  The  latter  includes  an  irreg- 
ular fusiform  tract,  bounded  by  the  collateral  fissure  internally  and  by  the  inferior 
temporal  sulcus  laterally  (Fig.  989).  As  expressed  by  its  name,  the  occipito- 
temporal  convolution  belongs  partly  to  the  occipital  and  partly  to  the  temporal 
lobe  and  extends  from  the  occipital  to  the  temporal  pole.  Its  surface  is  broken 
by  a  number  of  irregularly  disposed  furrows  which  add  to  the  uncertainty  of  its 
outer  boundary. 

The  Temporal  Lobe. — The  temporal  lobe  includes  the  irregularly  pyramidal 
division  of  the  cerebral  hemisphere,  whose  apex  is  lodged  within  the  middle  fossa  of 
the  skull  and  whose  succeeding  part  forms  the  conspicuous  dependent  mass  seen  on 
the  infero-lateral  surface  of  the  hemicerebrum.  In  front  it  is  separated  from  the 
frontal  lobe  by  the  stem  of  the  Sylvian  fissure;  above  it  is  marked  off  from  the  pari- 
etal lobe  by  the  posterior  limb  of  the  Sylvian  fissure  and  the  arbitrary  line  prolonged 
backward  in  the  direction  of  this  sulcus;  externally  and  below  it  is  defined  by  the 
infero-lateral  border  of  the  hemisphere;  and  mesially  it  is  separated  from  the  limbic 
lobe  by  the  collateral  fissure.  Its  posterior  border,  however,  on  both  the  lateral  and 
the  inferior  (tentorial)  surface  is  arbitrary  and  indicated  by  the  lines  already  men- 
tioned (page  1143)  which  afford  the  conventional  demarcation  between  the  occipital 
and  temporal  lobes. 

The  temporal  lobe  presents  three  surfaces,  the  convex  lateral,  the  inferior 
(largely  tentorial ),  and  the  buried  superior  or  opercular.  Of  these  the  lateral  and 
inferior  are  separated  by  a  border  so  broad  and  rounded  that  the  surfaces  pass  insen- 
sibly into  each  other.  Its  tip  corresponds  with  the  temporal  pole  of  the  hemisphere 
and  underlies  the  posterior  part  of  the  orbital  surface  of  the  frontal  lobe,  which  it 
partially  masks. 

The  lateral  surface  of  the  temporal  lobe  is  modelled  by  two  fissures,  the  superior 
and  the  middle  temporal,  and  three  convolutions,  the  superior,  the  middle  and  the 


H4S  Hl'MAX    AXATOMV. 

inferior  temporal  (Fig.  988),  all  of  which  correspond  in  the  general  direction  of 
their  course  with  the  posterior  limb  of  the  Sylvian  fissure  and  extend  backward 
and  slightly  upward. 

Tlu^superior  temporal  sulcus,  also  called  the  parallel  sulcus  in  recognition 
of  the  similarity  of  its  course  with  that  of  the  posterior  limb  of  the  Sylvian  fissure,  is 
the  first  in  the  series  of  longitudinal  furrows,  the  third  of  which  appears  not  on  the 
outer,  but  on  the  inferior  aspect  of  the  lobe.  It  begins  near  the  temporal  pole,  runs 
parallel  with  the  posterior  limb  of  the  Sylvian  fissure  and  ends  by  cutting  upward 
into  the  inferior  parietal  convolution,  whose  angular  gyrus  surrounds  the  upturned 
extremity  of  the  sulcus. 

The  middle  temporal  sulcus,  the  second  in  the  series,  lies  below  the  pre- 
ceding fissure,  whose  direction  in  a  general  way  it  follows.  It  is,  however,  much 
less  certainly  marked  and  in  most  cases  is  not  a  continuous  furrow,  as  is  the  superior 
sulcus,  but  broken  by  superficial  annectant  convolutions  into  a  number  of  separate 
pieces,  the  exact  sequence  of  which  is  often  difficult  to  follow.  The  upturned  end  of 
the  middle  temporal  sulcus  cuts  into  the  lower  parietal  convolution  towards  the  pos- 
terior limb  of  the  interparietal  sulcus  (Fig.  988)  from  which,  however,  it  is  separated 
by  the  arching  postparietal  gyrus. 

FIG.  990. 


Rolandic   fissure 


Right  cerebral  hemisphere,  with  opercula  displaced  to  expose  island  of  Reil. 

The  superior  temporal  gyrus  intervenes  between  the  posterior  limb  of  the 
Sylvian  fissure  and  the  superior  temporal  sulcus.  Its  lower  end  lies  at  the  temporal 
pole,  whilst  above  the  tract  is  continuous  with  the  supramarginal  and  angular  gyri 
of  the  parietal  lobe. 

The  middle  temporal  gyrus,  between  the  upper  and  middle  temporal  sulci, 
is  connected  with  the  subjacent  convolution  by  the  bridges  which  interrupt  the  sec- 
ond temporal  furrow.  Above  and  behind  it  is  continuous  with  the  angular  and 
I  x  istparietal  convolutions. 

The  inferior  temporal  gyrus  occupies  the  rounded  infero-lateral  margin  of 
the  hemisphere,  and  appears  on  both  the  lateral  and  the  inferior  surface  of  the  lobe, 
being  continuous  with  the  occipital  lobe  behind  (Fig.  988).  Its  upper  boundary, 
formed  by  the  middle  temporal  sulcus,  is  indistinct  ;  its  lower  and  mesial  limit  is 
defined  by  the  inferior  temporal  sulcus,  which  separates  it  from  the  occipito- 
temporal  gyrus. 

The  'inferior  surface  of  the  temporal  lobe  is  rounded  in  front,  where  it  rests  in 
the  anterior  cerebral  fossa,  but  behind  is  modelled  by  the  upper  surface  of  the  ten- 
tnrium  cerebelli  and  is,  therefore,  concave  from  before  backward  and  slightly  convex 
from  side  to  side.  It  presents  one  fissure,  the  inferior  temporal,  and  one  convolu- 
tion, the  anterior  part  of  the  occipito-temporal. 

The  inferior  temporal  sulcus,  also  called  the  oeeipito-temporal,  courses  LmiM 
tudinallv  a  short  distance  internal   to  the  infero-lateral  border  of  the  hemisphere  and 


THE   TELENCEPHALON.  1149 

separates  the  inferior  temporal  from  the  occipito-temporal  gyrus.  Although  for 
the  greater  part  of  its  extent  on  the  temporal  lobe,  it  is  not  confined  to  this,  but 
continues  backward  into  the  occipital  lobe  which,  therefore,  claims  it  as  one  of  its 
furrows.  The  sulcus  is  rarely  continuous,  usually  being  broken  by  annectant  gyri 
into  a  posterior,  a  middle  and  an  anterior  segment. 

The  occipito-temporal  gyrus  (gyrus  fusiformis)  is,  as  its  names  imply,  a 
fusiform  tract  belonging  partly  to  the  occipital  and  partly  to  the  temporal  lobe 
(Fig.  989).  Its  two  ends,  in  front  and  behind,  are  pointed  and  connected  by  a 
broader  intervening  tract,  which  is  commonly  broken  up  by  secondary  furrows. 
The  temporal  division  of  the  gyrus,  including  approximately  its  anterior  two-thirds, 
is  embraced  between  the  converging  collateral  fissure  mesially  and  the  inferior 
temporal  sulcus  laterally  ;  its  conventional  posterior  limit  is  the  line  drawn  from 
the  preoccipital  notch  to  the  isthmus  of  the  limbic  lobe,  immediately  beneath  the 
hind-end  of  the  corpus  callosum. 

The  superior  surface  of  the  temporal  lobe  is  directed  towards  the  insula  and 
is  therefore  an  opercular  aspect.  On  separating  the  walls  of  the  Sylvian  fissure  to 
expose  it,  this  buried  surface  of  the  temporal  lobe  often  exhibits  several  shallow 
transverse  furrows  and  indistinct  gyri  ;  the  deep  aspect  of  the  temporal  pole  being 
similarly  indented. 

FIG.  991. 

Rolandic  fissure^  Sulcus  subdividing  precentral  lobule 

/  Cut  surface  of  frontal  lobe 

"\    ^*.  J  ^M 

.--  ^      jf       -St*  i 

••'  \,      >/  '   / 

Sulcus  centralis^  X^^aaaay^.^  ,    j| 

.  Sulcus  circulans 


Gyri  breves  . 
Sulcus  centralis  insulse 

Gyrus  longus     Temporal        Apex        Limen 
lobe,  cut 

Island  of  Reil  exposed  after  cutting  away  surrounding  parts  of  right  cerebral  hemisphere. 

The  Insula. — The  insula,  or  island  of  Reil,  sometimes  also  called  the  central 
lobe,  is,  in  the  human  brain,  entirely  concealed  within  the  Sylvian  fissure  by  the 
approximation  of  the  overhanging  opercula.  The  manner  in  which  the  latter  are 
developed  from  the  wall  surrounding  the  early  Sylvian  fossa  has  been  described 
(page  1137)  ;  it  remains  here  to  note  the  chief  features  of  this  region  in  the  adult 
brain.  On  examining  the  relations  of  the  insula,  as  seen  in  frontal  sections  of  the 
brain  (Fig.  967),  it  will  be  noted  (a~)  that  the  shell  of  cortical  gray  matter  cover- 
ing the  sunken  convolutions  is  directly  continuous  along  the  Sylvian  fissure  with  that 
covering  the  convolutions  on  the  freely  exposed  parts  of  the  hemisphere  ;  (b)  that 
the  insular  cortex  lies  close  to  the  underlying  mass  of  gray  matter,  the  lenticular 
division  of  the  corpus  striatum,  a  narrow  tract  of  white  matter,  the  external  capsule, 
alone  intervening.  Since  the  corpus  striatum  is  one  of  the  earliest  of  the  funda- 
mental parts  of  the  telencephalon  to  be  developed,  it  is  probable  that  its  close  pri- 
mary relation  to  the  surface  of  the  hemisphere  is  largely  responsible  for  the  failure  of 
the  overlying  cortex  to  keep  pace  with  the  general  expansion  of  the  adjoining  parts. 

When  exposed,  by  separation  or  removal  of  the  surrounding  opercula  (Fig. 
991),  the  insula  appears  as  a  triangular  convex  field  composed  of  a  group  of  radi- 
ating convolutions,  whose  broader  ends  lie  above  and  pointed  ones  below.  The 


1 150 


HUMAN   ANATOMY. 


dependent  apex  of  the  insula  lies  close  to  the  anterior  perforated  space,  with  the 
gray  matter  of  which  the  cortical  sheet  of  the  island  is  continuous  by  way  of 
a  transitional  area,  known  as  the  limcn  insulic,  where  the  limiting  sulcus  of  the 
island  is  incomplete.  In  addition  to  being  imperfectly  separated  from  the  surround- 
ing opercula  by  the  curved  limiting  sulcus  {sulcus  circularis  insultc},  the  island 
is  divided  into  an  anterior  and  a  posterior  part  by  the  sulcus  centra/is  insithc. 
This  furrow  continues  in  a  general  way  the  downward  and  forward  direction  of  the 
fissure  of  Rolando,  the  deeper  part  of  which  is  seen  above  the  island  (Fig.  991). 
The  anterior  part,  or  precentral  lobule,  is  subdivided  by  two,  sometimes  by  three, 
shallow  grooves  into  three  or  four  short  downwardly  converging  ridges,  the  gvri 
breves,  of  which  the  front  one  is  connected  with  the  deeper  part  of  the  inferior 
frontal  convolution  by  a  small  arched  annectant  gyrus  transversus.  The  hind-part 
of  the  island,  the  postcentral  lobule,  includes  a  longer  wedge-shaped  tract,  the  gyrus 
longus,  which  below  is  continuous  with  the  limbic  lobe.  The  gyrus  longus  is 
frequently  subdivided  by  one  or  more  shallow  furrows  into  secondary  ridges. 

The  Limbic  Lobe. — The  limbic  lobe  (gyrus  fornicatus)  appears  on  the  mesial 
and  inferior  surfaces  of  the  hemisphere  (Fig.  987)    as  an  elongated  o-shapecl  tract, 


Splenium  of  corpus  callosum 
Collosal  fissure 


FIG.  992. 

Fornix,  body 

Tlialmus,  partly  cut  away 
Septum  luciduni 


Fasciola  cinerea 


Calcarine  fissure 


Isthmus' 


Khinal  fissure 


Uncus 


Collateral  fissure 

Gyrus  dentatus 


Gyrus       Fiinbria 
hippocampi 

Portion  of  infero-mesial  surface  of  left  hemisphere,  showing  lower  part  of  limbic   lobe  and   adjacent  structures. 

whose  ends  lie  closely  approximated  with  each  other  and  with  the  anterior  JKT- 
forated  space.  These  extremities  are  further  intimately  associated  with  the  two  limbs 
of  the  olfactory  tract,  in  this  manner  the  limbic  and  olfactory  lobes  becoming,  at 
least  topographically,  continuous.  The  limbic  lobe  comprises  two  parts,  an  antero- 
superior  and  an  inferior,  of  which  the  former,  the  callosal  gynts,  lies  concentric 
with  the  upper  surface  of  the  corpus  callosum,  and  the  inferior  part,  the  liippo- 
catnpal  gvnts,  forms  the  mesial  tract  of  the  tentorial  surface  of  the  hemisphere, 
The  limbic  lobe  is  separated  from  the  adjacent  convolutions  by  the  calloso-marginal 
sulcus  in  front  and  above,  by  the  postlimbic  sulcus  behind,  and  by  the  anterior 
part  of  the  collateral  fissure  below.  Its  demarcation  from  the  anterior  part  of  the 
temporal  lobe  is  effected  by  the  inconspicuous  rhinal  sulcus  ( tissura  rhinica  >.  or 
incisura  temporalis,  which  feeble  furrow  in  man  represents  the  important  and 
fundamental  ectorhinal  fissure  of  the  lower  animals. 

The  callosal  gyrus  ( <-\nis  cin«iili  >,  also  called  the  gyrus  foniicatns  (not  to  be 
mi-taken,  however,  with  the"  same  name  as  applied  to  the  entire  limbic  lobe',  begins 
at  the  anterior  perforated  space,  below  the  recurved  rostrum  of  the  corpus  callosum. 
Thence  it  winds  around  the  gi-nu  of  the  latter  and  follows  the  convex  dorsal  surface' 
of  the  corpus  callosum,  separated  however  from  it  by  the  narrow  callosal  sulcus 
(sulcus  corporis  cnllosi).  On  reaching  a  point  just  below  the  splenium,  around  which 


'c*s 

, 


THE    TELENCEPHALON.  1151 

it  bends,  the  callosal  gyrus  is  markedly  reduced  in  width  by  the  encroachment  of  the 
calcarine  fissure,  the  narrowed  tapering  tract  thus  formed  being  the  upper  part  of  the 
isthmus  (isthmus  gyri  fornicati),  which  below  joins  the  similarly  reduced  upper  end 
of  the  hippocampal  convolution  and  so  establishes  the  continuity  between  the  two 
parts  of  the  lobe. 

The  hippocampal  gyrus  (gyrus  hippocampi)  curves  forward  from  the  isthmus 
along  the  mesial  border  of  the  tentorial  surface  of  the  hemisphere  towards  the  apex 
of  the  temporal  lobe,  which,  however,  it  fails  to  reach  (Fig.  922).  Its  anterior 
extremity  is  distinctly  thickened  and  forms  a  rounded  hook-like  projection,  the 
uncus,  which  is  recurved  and  directed  backward  and  inward.  The  uncus  is 
separated  from  the  apex  of  the  temporal  lobe  by  the  incisura  temporalis  (fissura 
rhinica),  whilst  the  hippocampal  convolution  is  marked  off  laterally  by  the  anterior 
part  of  the  collateral  fissure.  Although  blended  with  the  gyrus  hippocampi  and 
seemingly  a  part  of  the  limbic  lobe,  the  uncus,  strictly  considered,  belongs  to  the 
rhinencephalon  and  not  to  the  limbic  lobe  (Turner,  Elliot  Smith).  The  posterior 
end  of  the  hippocampal  convolution  is  incised  by  the  anterior  extremity  of  the 
calcarine  fissure  and  so  divided  into  two  parts  ;  of  these  the  upper  aids  in  forming 
the  isthmus  and  is  continuous  with  the  callosal  gyrus,  whilst  the  lower  one  blends 
with  the  front  part  of  the  gyrus  lingualis  of  the  occipital  lobe. 

The  Rhinencephalon. — Although  a  division  of  fundamental  importance  and 
differentiated  at  a  very  early  period  in  the  development  of  the  human  telencephalon, 
in  the  brain  of  man  it  is  represented  by  structures,  which  to  a  great  extent  are  rudi- 
mentary and  feeble  expressions  of  the  bulky  corresponding  parts  in  the  brains  of 
many  of  the  lower  animals.  Its  small  size  in  man,  as  compared  with  the  voluminous 
structures  seen  in  some  mammals  in  which  the  rhinencephalon  constitutes  a  large 
part  of  the  entire  hemisphere,  is  no  doubt  associated  with  the  relatively  feeble  olfac- 
tory sense  possessed  by  man.  It  is  probable,  however,  that  other  and  unknown 
factors  are  responsible  for  the  development  of  this  part  of  the  hemisphere  to  a  degree 
disproportionate  to  the  olfactory  capacity  of  the  animal,  as  strikingly  observed  among 
the  lower  vertebrates.  The  conclusions  deduced  from  comparative  studies  empha- 
size the  fundamental  character  of  the  rhinencephalon  as  phylogenetically  being  the 
oldest  part  of  the  hemisphere.  Indeed  of  such  primary  morphological  significance 
is  the  rhinencephalon  that  it  is  termed  the  archipallium,  as  distinguished  from  the 
neopallium,  which  comprises  almost  the  entire  remainder  of  the  hemisphere  with  the 
exception  of  its  nucleus,  the  corpus  striatum. 

As  seen  in  the  human  brain,  the  rhinencephalon  includes  the  rudimentary  olfac- 
tory lobe — represented  by  the  olfactory  bulb,  the  olfactory  tract  with  its  roots,  the 
olfactory  trigone,  and  the  parolfactory  area — and  the  uncus  and  a  number  of  acces- 
sory parts,  including  the  anterior  perforated  space,  the  gyrus  subcallosus,  the  sep- 
tum lucidum,  the  fornix,  the  hippocampus  and  the  gyrus  dentatus.  Some  of  these 
accessory  structures  can  be  understood  only  after  their  relations  to  outer  parts  of 
the  brain  have  been  considered.  Deferring  the  details  of  certain  of  these  struc- 
tures, as  the  septum  lucidum,  the  fornix,  and  the  hippocampus  major,  until  the 
lateral  ventricles  are  described  (page  1160),  it  will  suffice  for  the  present  to  point 
out  their  general  features  as  related  to  the  rhinencephalon. 

The  Olfactory  Lobe. — This  division  of  the  adult  human  brain  is  small  and 
rudimentary  and  comprises  the  olfactory  bulb,  the  olfactory  tract,  the  olfactory 
trigone  and  the  parolfactory  area  (Fig.  993).  Of  these  all  but  the  last  lie  on  the 
inferior  surface  of  the  brain,  whilst  the  parolfactory  area  occupies  a  small  space  on 
the  mesial  aspect  of  the  hemisphere. 

The  olfactory  bulb  (bulbus  olfactorius)  is  an  elongated  irregularly  oval  swell- 
ing, about  10  mm.  long,  from  3-4  mm.  wide  and  about  2.5  mm.  thick,  which  behind 
is  continuous  with  the  olfactory  tract  and  below  receives  the  olfactory  filaments.  Its 
upper  surface  underlies  the  olfactory  sulcus  of  the  orbital  aspect  of  the  frontal  lobe, 
and  its  under  one  rests  upon  the  cribriform  plate  of  the  ethmoid  bone,  through  the 
apertures  of  which  the  bundles  of  the  olfactory  nerve-fibres  ascend  from  the  nasal 
mucous  membrane  to  the  bulb. 

The  structure  of  the  olfactory  bulb  shares  the  general  rudimentary  condition  which  charac- 
terizes the  lobe  in  man,  the  bulb  having  lost  the  central  cavity  ( ventriculus  bulbi  o/factorii) , 


1152 


I  UMAX   ANATOMY. 


which  in  many  animals  is  continuous  with  the  fore-part  of  the  lateral  ventricle,  as  well  as  some 
of  the  six  layers  that  may  be  typically  represented,  as  in  the  dog's  bulb.  The  ventral  aspect  of 
the  bulb,  receiving  the  olfactory  nerves,  retains  most  completely  its  nervous  character  and  pre- 
sents three  chief  strata  (Fig.  995).  (i)  The  stratum  of  olfactory  fibres  appears  as  a  narrow 
zone  made  up  of  the  irregularly  intermingled  bundles  of  axones  of  the  olfactory  cells  situated 
within  the  olfactory  area  of  the  nasal  mucous  membrane.  This  layer  is  succeeded  by  a  broader 
tract,  (2)  the  stratum  of  the  mitral  cells,  so  named  on  account  of  the  numerous  nerve-cells  of 
peculiar  bishop' s-hat  form  which  occupy  its  upper  border.  Along  its  lower  margin  extends  a 
narrow  zone  of  large  spherical  masses,  the  olfactory  glomeruli.  These  bodies,  from  .o65-.o9o 
mm.  in  diameter,  consist  of  an  intricate  complex  formed  by  the  intertwining  of  the  richly 
branching  axones  ascending  from  the  olfactory  cells  and  of  the  dendrites  descending  from 
the  mitral  cells.  The  interval  between  the  upper  and  lower  margins  of  the  second  stratum  is 
occupied  by  the  molecular  layer,  composed  of  small  nerve-cells  whose  dendrites  also  enter  the 
glomeruli.  (3)  The  stratum  of  central  fibres  includes  the  centrally  directed  axones  of  the 
mitral  and  other  nerve-cells  which  constitute  the  second  link  in  the  complicated  paths  by  which 
the  olfactory  stimuli  are  carried  to  the  cortical  areas.  The  outer  zone  of  this  stratum  is  known 


FIG.  993. 


Olfactory  bulb 


Olfactory  tra 

Mesial 

olfactory  ..tria 

Lateral 

olfactory  stna 

Island  of  Reil 

Anterior 
perforated  space 

Cut  surface  of 
temporal  lobe 

Cerebral  peduncle 
crossed  by 
optic  tract 

Lateral 
geniculate  body 


Olfactory  sulcus 

I'arolfactory  area 

Tnberculiiin 
olfactoriurn 


Trigomun 
olfactoriutn 


Optic  chiastn, 
~  I  artly  out  away 
—  Manimillary  body 
iu  interpeauncular 
space 
-  Oculomotor  nerve 


Cerebral  peduncle 


I'ulvinar 
Median  geniculate  body 


Sylvian  aqueduct 


Anterior  part  of  inferior  surface  of  brain,  showing  parts  of  olfactory  lobe  and  Mnictmvs   within    interpedun- 
cular  space  ;  tip  of  right  temporal  lobe  has  been  removed. 

as  the  granular  layer  and  consists  of  many  small  nerve-cells  intermingled  with  the  fibres.  The 
deeper  part  of  the  stratum  of  nerve-fibres  encloses  some  larger  nerve-cells  of  stellate  or 
enlongated  form.  The  central  part  of  the  bulb,  which  represents  the  obliterated  ventricular 
space,  is  filled  by  a  gelatinous  substance  resembling  modified  neuroglia. 

The  olfactory  tract  (tractus  olfactorius)  is  a  narrow  band  of  light  color,  which 
extends  from  the  olfactory  bulb  in  front  to  the  olfactory  trig<>ne  behind  (Fig.  993). 
It  measures  about  2  cm.  in  length  and  2.5  mm.  in  width,  but  is  broader  at  its  pos- 
terior extremity,  from  which  the  olfactory  stria,  as  its  roots  are  called,  diverge.  Its 
ventral  surface  is  flat  and  its  narrow  dorsal  one  ridged,  the  tract  appearing  in 
transverse  section  more  or  less  triangular  in  outline. 

The  structure  of  the  olfactory  tract  further  emphasi/es  the  rudimentary  condition  of  the 
part  in  man.  The  ventral  aspect  and  the  rounded  adjoining  borders  consist  of:  (i)  a  stratum 
of  >KT;'<  -fi/>n-s,  longitudinally  coursing  and  therefore  transversely  rut  in  cross-sections,  which 
OOVera  the  sides  and  dorsal  surface  of  the  tract  and  is  reduced  to  an  extremely  thin  and  rudimen- 
tarv  sheet.  Next  follows  (2)  a  gt'/titimms  stratum,  which  represents  the  obliterated  ventricular 
cavity  seen  in  main  lower  animals.  Succeeding  this  and  forming  the  thickest  layer  of  the  tract 

;  the  dorsal  stratum  <>/'» mv  matter,  which  still  retains  its  importance  as  a  tract  of  cortical 
gray  substance  from  which  fibres  pass  to  oilier  parts  of  the  hemisphere  (page  1222). 


THE   TELENCEPHALON.  1153 

The  olfactory  striae,  the  so-called  roots  of  the  olfactory  tract  (Fig.  993),  are 
usually  two,  the  mesial  and  the  lateral,  an  additional  intermediate  root  being  some- 
times represented  by  faint  strands.  The  mesial  stria  bends  sharply  inward,  passes 
along  the  inner  margin  of  the  olfactory  trigone  and  disappears  on  the  mesial  surface 
of  the  hemisphere  by  joining  probably  partly  the  callosal  and  partly  the  subcallosal 
gyri  (Fig.  994).  The  diverging  lateral  stria  obliquely  courses  along  the  antero- 
lateral  margin  of  the  perforated  space,  but  usually  disappears  as  a  distinct  tract  before 
it  can  be  traced  to  the  uncus,  its  probable  destination  (page  1222).  Occasionally  the 
lateral  root  is  represented  by  two  strands,  an  outer  and  an  inner,  the  last  one  fading 
away  in  the  substance  of  the  anterior  perforated  space.  An  additional  intermediate 
stria  is  sometimes  recognizable  for  a  short  time  before  it  too  sinks  into  the  anterior 
perforated  space. 

The  olfactory  trigone  (trigonum  olfactorium )  is  the  three-sided  slightly  convex 
area  embraced  by  the  two  roots  of  the  olfactory  tract  at  the  sides,  and  behind  sepa- 
rated from  the  anterior  perforated  space  by  a  groove  (sulcus  parolfactorius  posterior). 
The  triangular  area  seen  on  the  inferior  surface  of  the  hemisphere  (Fig.  993)  is 
really  the  under  aspect  of  a  more  extensive  pyramidal  elevation,  the  tuberculum 
olfactorium,  which,  however,  lies  in  large  part  within  the  olfactory  sulcus  and  is 
therefore  superficially  not  visible  except  at  its  base,  the  trigone.  Retzius  regards 
this  part  of  the  hemisphere 

as  a  constant  deep  convo-  '  FIG.  994. 

lution,  gyrus  tuberis  olfac- 
torius,  from  which  proceed 
two  ridges,  gyrus  olfacto- 
rius  medialis  and  lateralis. 
These  bend  respectively 
inward  and  outward  and 
support  the  white  strands  of 
nerve-fibres,  the  striae  olfac- 
torii,  which  are  usually  de- 
scribed as  the  roots  of  the 
olfactory  tract.  The  tuber-  Rostrum  of  ^  -,^ 

ir  •  rorrms    callosnm      ^^T^m  _L       .<*i       >^^  ^Lamina  cmerea 

culum  olfactorium  contains 

•111  £  Septum  lucidum      /       /    Sulcus  parolfactorius  posterior 

a    considerable   amount   or     Sulcus  paroitactonus      / 

«  .    ,    .  anterior  Gyrus  subcallosus 

gray  matter,  which  is  a  part 
of  the  peripheral  olfactory 

COrtex  ana,^V\ltn  Other  por-       Portion  ot  mesial  surface  of  right  hemisphere,  showing  gyrus  subcallosus 
tioilS    of    this    sheet,    shares  and  parolfactory  area. 

in  the  reception  of  axones 

from  the   mitral  cells  and  in   the  origin    of    fibres    passing    to    other    parts    of   the 

rhinencephalon. 

The  parolfactory  area,  Q?  field  of  Broca,  lies  as  a  small  curved  tract  upon  the 
mesial  surface  of  the  hemisphere,  just  in  front  of  and  below  the  gyrus  subcallosus 
which  extends  from  the  rostrum  to  the  corpus  callosum  (Fig.  994).  The  area 
parolfactoria  is  bounded  in  front  by  the  sidcus  parolfactorius  anterior  and  behind  by 
the  sulcus  parolfactorius  posterior,  and  is  connected  in  front  with  the  superior  frontal 
gyrus,  above  with  the  callosal  gyrus  and  below  with  the  inner  part  of  the  trigonum 
olfactorium,  the  mesial  olfactory  gyrus  above  mentioned. 

The  anterior  perforated  space  (substantia  perforata  anterior)  is  an  irregularly 
triangular  area  (Fig.  993)  lying  behind  the  trigonum  olfactorium,  from  which  it  is 
separated  by  the  obliquely  coursing  sulcus  parolfactorius  posterior,  and  in  front  of 
the  optic  commissure.  Its  inner  part  is  narrow  and  extends  as  a  point  between  the 
mesial  root  of  the  olfactory  tract  and  the  lower  end  of  the  subcallosal  gyrus.  Its 
broader  outer  part  extends  into  the  floor  of  the  stem  of  the  Sylvian  fissure  and 
behind  reaches  the  deeper  part  of  the  uncus  and,  more  medially,  the  optic  tract. 
Its  designation  as  perforated  is  justified  by  the  large  number  of  small  oval  apertures 
for  the  transmission  of  perforating  branches  from  the  antero-mesial  and  antero- 
lateral  groups  of  the  basal  arteries.  These  openings,  most  numerous  along  the 
front  margin  of  the  space,  are  disposed  with  some  regularity  in  parallel  rows  and 


"54 


HUMAN   ANATOMY. 


FIG.  995. 


Atrophic  ventricu- 
lar area 


Nerve-fibre  layer 


Granular  layer 


Layer  of  mitral 
cells 


Molecular  layer 


Olfactory 
glomeruli 


Blood-vessel 


Olfactory  fibre 
layer 


decrease  in  size  as  they  approach  the  inner  border  (Foville).  The  substance  of 
the  space  proper  consists  of  a  thin  sheet  of  gray  matter  containing  groups  of 
nerve-cells,  some  of  which  constitute  the  nuclei  of  primary  centres  interposed  in 
the  paths  connecting  the  olfactory  lobe  with  the  secondary  (cortical)  olfactory 
centres  (page  1222).  In  addition  to  the  white  strands  of  nerve-fibres  composing 
the  olfactory  striae  which  after  a  longer  or  shorter  superficial  course  sink  into  the 
substance  of  the  perforated  space,  an  obliquely  directed  narrow  ribbon-like  tract, 
the  diagonal  band  of  Broca,  may  be  sometimes  made  out  along  the  inner  margin 
of  the  area  perforata.  In  front  it  is  continuous  with  the  subcallosal  gyrus  and 
behind  passes  along  the  optic  tract  towards  the  anterior  end  of  the  hippocampal 
convolution.  The  band  is  of  interest  as  being  probably  the  beginning,  on  the 

basal  surface  of  the  brain,  of  at  least 
a  part  of  the  fibre-tracts  contained 
within  the  rudimentary  supracallosal 
gyrus  (page  1157)  that,  in  turn,  is 
prolonged  into  the  gyrus  dentatus. 
The  uncus  is  the  thickened 
anterior  extremity  of  the  gyrus 
hippocampi,  recurved  around  the 
front  end  of  the  hippocampal  fissure 
(Fig.  992).  Antero-inferiorly  it  is 
separated  from  the  adjacent  part  of 
the  temporal  lobe  by  the  inconspicu- 
ous incisura  temporalis  or  rhinal 
sulcus,  which  in  animals  possessing 
a  well  developed  rhinencephalon 
constitutes  a  definite  boundary  be- 
tween this  part  of  the  hemisphere 
and  the  pallium.  With  its  deeper 
surface  the  uncus  is  in  close  relation 
with  the  anterior  perforated  space, 
whilst  postero-mesially  it  is  connected 
with  the  fimbria  (page  1165)  and 
the  gyrus  dentatus  (page  1166). 
Although  seemingly  a  part  of  the 
limbic  lobe,  the  comparative  studies 
of  Turner  and  of  Elliot  Smith  have 
established  its  morphological  inde- 
pendence from  the  last-named  lobe 
and  emphasized  its  relation  with  the 
rhinencephalon.  With  the  lateral 
olfactory  stria,  the  uncus  constitutes 

Transverse  section  of  olfactory  bulb ;   drawing  includes  part  ',    m™    fhe    feeble    renresentation  of 

of  bulb  lying  ventral  to  atrophic  ventricular  area. 

the  large  and  conspicuous  pyramidal 
lobe,  which  in  many  animals  forms  the  most  massive  part  of  the  olfactory  brain. 

The  accessory  parts  of  the  rhinencephalon  include  structures  which,  for  the 
most  part,  constitute  collectively  an  elaborate  path  by  which  the  olfactory  cortical 
centres  are  connected  with  each  other,  on  the  one  hand,  and  with  the  optic  thalaimis 
and  lower  levels  on  the  other.  Since  these  structures  are  by  position  closely  asso- 
ciated with  parts  of  the  brain  still  to  be  described,  with  the  exception  of  the  anterior 
perforated  space  already  noted  (page  1153),  they  will  be  merely  mentioned  here,  as 
components  of  the  rhinencephalon,  their  details  being  deferred  until  the  related  parts 
are  considered. 

The  fornix  (page  1158),  the  fimbria  (page  1165)  and  the-  hippocampus 
(page  1165),  all  seen  within  the  lateral  ventricle  (page  1164),  constitute  important 
paths  by  which  fibres  pass  to  and  from  the  olfactory  cortical  centre.  The  gyrus 
subcallosus  (page  1153").  the  gyrus  supracallosus  (page  1157)  and  the  gyrus 
dentatus  (page  1 166)  together  form  an  additional  arched  tract,  which,  beginning  at 
the  base  of  the  brain,  follows  closely  the  convex  surface  of  the  corpus  callosum  as  far 


THE   TELENCEPHALON.  1155 

as  its  hind-end  and  then,  as  the  dentate  gyms,  extends  forward  along  the  inner  sur- 
face of  the  hippocampus  to  the  uncus.  The  septum  lucidum  (page  1 159),  a  sickle- 
shaped  partition  which  lies  between  the  lateral  ventricles,  the  corpus  callosum  and 
the  fornix,  is  also  a  constituent  of  the  olfactory  path,  as  are  also,  perhaps,  the  taenia 
semicircularis  (page  1162)  and  the  nucleus  amygdalae  (page  1172). 

In  the  foregoing  description  of  the  rhiiiencephalon  only  such  parts  have  been  included  as 
seem  warranted  on  morphological  grounds  (Turner,  Elliot  Smith  and  Cunningham).  It  should 
be  pointed  out,  however,  that  the  German  and  French  anatomists  include  also  the  limbic  lobe, 
the  division  and  constitution  of  the  rhinencephalon  accordingly  being  as  follows  : 

RHINENCEPHALON. 
I.     Peripheral   Portion 

Anterior  part  : 

1.  Bulbus  olfactorius 

2.  Tractus  olfactorius 

3.  Tuberculum  olfactorium 


OLFACTORY    LOBE 


II.     Central  Portion 


4.  Area  parolfactoria 
JB.     Posterior  part  : 

5.  Substantia  perforata  anterior 

6.  Gyrus  subcallosus 

Gyrus  callosus 
Gyrus  hippocampi 

3.  Gyrus  uncinatus 

4.  Hippocampus 

5.  Gyrus  dentatus 

6.  Gyrus  supracallosus 

ARCHITECTURE  OF  THE  CEREBRAL  HEMISPHERES. 

On  drawing  apart  the  walls  of  the  great  longitudinal  fissure,  it  will  be  seen  that, 
while  in  front  and  behind  this  cleft  completely  separates  the  hemispheres,  the  latter 
are  connected  in  the  intervening  part  of  their  length  by  a  robust  commissure,  the 
corpus  callosum,  which  floors  the  fissure  along  the  middle  part  of  its  course.  On 
making  sections  of  the  hemisphere  above  the  level  of  this  bridge,  either  in  the  frontal 
or  transverse  plane,  the  hemibrain  is  found  to  be  composed  of  the  thin  reddish  brown 
sheet  of  cortical  gray  matter  (substantia  corticalis),  which  everywhere  constitutes  an 
unbroken  stratum,  and  the  enclosed  large  tract  of  white  matter,  the  centrum  ovale. 
Beneath  the  corpus  callosum  lies  the  lateral  ventricle,  the  cavity  enclosed  within  the 
hemisphere,  in  whose  lateral  wall  and  floor  appears  the  mesial  division  of  the  corpus 
striature,  the  caudate  nucleus,  whilst  further  outward  is  lodged  the  lateral  division  of 
the  nuclear  mass  of  the  end-brain,  the  lenticular  nucleus.  Attached  to  the  under 
surface  of  the  posterior  half  of  the  corpus  callosum  is  the  arched  layer  of  fibres  known 
as  faefornix,  and  below  the  latter,  covering  to  a  large  extent  the  upper  surface  of 
the  thalamus  which  forms  a  part  of  the  floor  of  the  lateral  ventricle,  lies  the  thin 
highly  vascular  sheet,  the  velum  interpositum.  These  and  the  other  structures  more 
or  less  closely  related  to  the  lateral  ventricle  claim  fuller  description,  which  may  now 
be  undertaken. 

The  Corpus  Callosum.  —  This  structure  is  the  great  commissure  which  con- 
nects the  hemispheres  and,  in  addition,  affords  passage  to  fibres  that  arise  from  the 
thalamus  and,  probably,  other  nuclei  outside  the  hemisphere  and  proceed  to  the 
cerebral  cortex.  It  lies  considerably  nearer  the  anterior  than  the  posterior  end  of 
the  hemisphere  and  occupies  approximately  one  half  of  the  latter'  s  length.  Seen  in 
mesial  sagittal  section  (Fig.  996),  the  corpus  callosum  appears  as  a  robust  arched 
structure,  white  in  color  and  composed  of  nerve-fibres  transversely  cut,  whose  ends 
are  considerably  thicker  than  the  intermediate  portion,  the  body  (trunctis  corporis 
callosi).  Its  upper  surface  is  convex,  partly  free  and  partly  covered  by  the  overlying 
hemisphere,  and  its  lower  one  is  concave  and,  where  not  attached  to.  the  fornix  and 
the  septum  lucidum,  clothed  by  the  ependyma  lining  the  ventricle.  Its  length  is 
about  7  cm.  (2^  in.)  and  its  greatest  thickness,  at  its  posterior  extremity,  is  about 
8  mm.  It  is  widest  behind,  where  it  measures  about  20  mm.,  and  somewhat 
narrower  in  front.  The  thickened  front  end,  the  genu,  bends  backward  and  is 


1156 


HUMAN   ANATOMY. 


prolonged  into  the  sharply  recurved  and  tapering  rostrum,  whose  thin  edge  is 
continued  backward  and  downward  into  the  lamina  cinerea,  the  attenuated  anterior 
wall  of  the  third  ventricle  (page  1132).  The  rounded  and  massive  posterior  end  of 
the  corpus  callosum,  known  as  the  splenium,  overlies  the  pineal  body  and  the 
superior  colliculi,  and  above  bounds  the  cleft  through  which  the  pia  mater  gains 
the  velum  interpositum  (page  1162). 

The  convex  upper  surface  of  the  corpus  callosum,  where  it  forms  the  bottom  of 
the  longitudinal  fissure,  is  free,  except  behind  where  in  contact  with  the  posterior 
part  of  the  falx  cerebri ;  laterally  it  is  partially  overlaid  by  the  callosal  gyrus,  which, 

FIG.  996. 


Mesial  surface  of  cere-. 
bral  hemisphere 


»     <  >pening  of  cere- 
S  bcU  vein 


Splenium 

vein  of  Galen 


y£-'        >^Lobulus  centralis 
.^Culmen 

|vVxLiDguU 


Superior  longitudi- 

nal sinus 
Falx  cerebri.  cut 


Lamina  cinerea 

Optic  chiasm,  cut 
Infundibulum 

Pituitary  body 
Tuber  cinereum 
Interpeduncular  space 
Mammillary  body. 
Oculomotor  nerve 
Sphenoiclal  sinus 
Cerebral  peduncle 
Pineal  body 
Basilai 
Corpora  quadrigi 

Pons 

Aqueduct  of  Sylviu< 
Superior  medullary  velu 

Fourth  ventricle 

Choroidal  plexus 

Right  vertebral  artery 


Mesial  section  of  brain  in  JI/M,  showing  relations  to  skull  and  dura;   cerebral  falx  has  been  pactly  remove'!,  but 

arachnoid  and  pia  are  still  in  place. 


however,  is  separated  from  it  by  the  intervening  co/fara/JM&Kf  (sulcus  corporis  callosi  ). 
Although  consisting  practically  exclusively  of  transversely  coursing  nerve-fibres, 
which  produce  a  corresponding  cross  striatum,  the  upper  surface  of  the  corpus 
callosum  (Fig.  997)  is  covered  by  a  thin  atrophic  layer  of  _yray  matter  (induscum 
gristmill  >  which  laterally  is  continuous  with  the  cortical  substance  of  the  callosal 
gyrus  and  contains  rudimentary  strands  of  longitudinal  nerve-fibres.  These  are 
arranged  on  each  side  of  the  slight  groove  marking  the  mid-line  in  two  strands  ;  the 
nne,  the  stria  medialis,  is  placed  close  to.  the  strand  of  the  opposite  side  and  with 
it  constitutes  the  so-called  w/~v'.f  of  /^w/.v/.  The  other  strand,  the  stria  lateralis, 
or  teenia  tccfa,  lies  farther  outward  and  is  covered  by  the  overhanging  callosal  gyms. 
These  rudimentary  structures,  including  the  thin  sheet  of  gray  matter  and  the  two 


THE   TELENCEPHALON. 


"57 


stria,  represent  an  atrophic  convolution,  the  gyrus  supracallosus.  Traced  forward 
and  around  the  recurved  genu  and  rostrum,  the  mesial  stria  is  prolonged  into  the 
gyrus  subcallosus,  a  small  crescentic  cortical  tract  on  the  mesial  surface  of  the 
hemisphere  immediately  below  the  rostrum  (Fig.  994);  while  the  lateral  stria  is 
continued  into  the  area  parolfactoria  (page  1153)  and  into  the  anterior  perforated 
space.  When  followed  backward  and  around  the  splenium,  the  striae  and  gray 
matter  of  the  corpus  callosum  become  continuous  with  the  gyrus  dentatus  and,  by 
way  of  the  latter,  with  the  uncus. 

The  under  surface  of  the  corpus  callosum  (Fig.  998)  exhibits  a  very 
evident  transverse  striation  and  forms  the  roof  of  the  anterior  cornu  and  body  of 
both  lateral  ventricles.  With  the  exception  of  a  strip  of  varying  width  along  the 
mesial  plane,  where  attached  to  the  septum  lucidum  in  front  and  to  the  triangular 


FIG.  997. 


Frontal  pole 


Genu 


Mesial  longitudinal 
striae 


Upper  surface 
of  corpus  callosum 


Lateral  longitudinal 
stria 


Forceps  anterior 


Transverse  fibres 


Tapetura 


Forceps  posterior 


Splenium 


Occipital  pole 


Cerebral  hemispheres  from  which  upper  and  median  parts  have  been  removed  to  expose  corpus  callosum  ;  on  left 
side  longitudinal  striae  and  thin  layer  of  gray  matter  cover  upper  surface  of  corpus  callosum;  on  right  side  these 
have  been  scraped  away  to  expose  transverse  fibres  and  anterior  and  posterior  forceps. 

body  of  the  fornix  behind,  the  corpus  callosum  is  free  and  covered  with  the 
ependyma  which  lines  the  ventricular  spaces.  In  consequence  of  the  bridge  being 
shorter  than  the  length  of  the  hemispheres,  from  most  parts  of  which  it  receives 
fibres,  the  latter  are  consolidated  at  the  ends  of  the  corpus  callosum  and  give  rise  to 
the  genu  and  the  splenium.  On  gaining  the  lateral  margins  of  the  corpus  callosum, 
its  fibres  are  no  longer  restrained  but  radiate  in  all  directions  (radiatio  corporis  cal- 
losi)  towards  the  cortex  and  intersect  the  fibres  of  the  corona  radiata  (page  1186). 
Those  traversing  the  thinner  body  and  upper  part  of  the  splenium  of  the  com- 
missure pass  laterally  and  in  each  hemisphere  from  a  thin  but  definite  fibre-sheet, 
known  as  the  tapetum,  which  extends  over  the  lateral  ventricle,  especially  its 
posterior  horn,  and  constitutes  the  lateral  wall  of  its  posterior  cornu  and  of  the 
adjacent  part  of  the  descending  horn.  The  fibres  composing  the  fore-part  of  the 
genu  turn  forward  as  a  distinct  band,  the  forceps  anterior,  towards  the  frontal 


HUMAN   ANATOMY. 


pole  of  the  hemisphere,  whilst  those  constituting  the  greater  part  of  the  splenium 
are  consolidated  into  a  robust  strand,  the  forceps  posterior,  which  sweeps 
abruptly  backward  into  the  occipital  lobe  and  in  its  course  produces  a  curved  ridge 
on  the  fore-part  of  the  inner  wall  of  the  posterior  horn  of  the  lateral  ventricle. 

The  Fornix. — The  fornix  is  an  arched  structure,  white  in  color,  and  composed, 
for  the  most  part,  of  two  crescentic  tracts  of  longitudinally  coursing  nerve-fibres. 
The  two  ends  of  these  narrow  crescents  are  free  for  some  distance,  but  along  their 
medial  borders  the  intervening  parts  are  connected  with  the  under  surface  of  the  cor- 
pus callosum  and  with  each  other  (Fig.  998),  thus  producing  a  triangular  field,  the 
body  (corpus  fornicis),  whose  apex  is  directed  forward  and  is  prolonged  into  two 
slender  diverging  stalks,  the  anterior  pillars,  and  whose  lateral  angles  are  con- 
tinued into  the  downwardly  arching  posterior  pillars.  .  The  upper  surface  of  the 
body  is  subdivided  into  an  attached  and  an  unattached  area.  The  former  is  a  small 

FIG.  998. 


Body  of  fornix 


Mammillary  bodies 


Splenium  of 
corpus  callosum 


Lyra 


Free  margin  of 
fornix 

Under  surface  of 
corpus  callosum 

Cut  surfaces  of 

hemisphere 


Septum  lucidum 


Anterior  pillar 
T'nder  surface  of  genu  of  corpus  callosum 

Dissection  of  brain,  showing  under  surface  of  fornix  and  corpus  callosum. 

narrow  triangle,  the  posterior  and  broader  part  of  which  corresponds  with  the  attach- 
ment of  the  fornix  to  the  under  surface  of  the  corpus  callosum  ;  whilst  the  anterior 
part  is  a  mere  mesial  strip  denoting  the  line  along  which  the  arching  fornix  is  bit-mini 
with  the  septum  lucidum,  the  sickle-shaped  partition  that  fills  the  interval  betwrrn 
the  corpus  callosum  and  the  fornix  and  separates  the  anterior  horns  of  the  lateral  ven- 
tricles. On  either  side  of  the  attached  field,  the  fornix  presents  a  smooth  and  some- 
what thicker  marginal  zone,  which  forms  part  of  the  floor  of  the  lateral  ventricle  and, 
depending  upon  the  size  and  distention  of  the  ventricular  space,  either  extends  later- 
ally as  a  horizontally  directed  wing  that  overlies  a  part  of  the  thalamus,  or  descends 
obliquely  towards  the  thalamus  upon  whose  upper  surface  the  margin  of  the  fornix 
indirectly  rests.  The  triangular  central  sheet  of  the  fornix,  bounded  by  its  unattached 
margins  laterally  and  the  splenium  behind,  exhibits  transverse  striation  due  to  the 
presence  of  bundles  of  commissural  fibres  connecting  the  hippocampi  of  the  two  sides. 
This  part  of  the  fornix  constitutes  the  commissura  hippocampi,  also  known  as  the 
psalterium  or  lyra.  A  narrow  horizontal  cleft,  the  so-called  ventricle  of  }  \-rga  (  cavnm 


THE   TELENCEPHALON.  1159 

psalterii),  sometimes  intervenes  as  the  result  of  imperfect  union,  between  the  under 
surface  of  the  corpus  callosum  and  the  middle  part  of  the  body  of  the  fornix.  It 
should  be  understood,  however,  that  this  cleft  is  not  a  part  of  the  series  of  true  ven- 
tricular spaces.  The  under  surface  of  the  fornix  rests  upon  the  velum  interpositum, 
which  thus  separates  it  from  the  third  ventricle  and  the  upper  surfaces  of  the  two 
thalami  which  it  overlies. 

'The  anterior  pillars  of  the  fornix  (columnae  fornicis)  are  two  slender  cylin- 
drical strands,  which,  slightly  diverging-  as  they  leave  the  anterior  angle  of  the  body, 
arch  downward  and  forward,  then  somewhat  backward,  and  descend  to  the  basal 
surface  of  the  brain,  where  they  end  in  the  mammillary  bodies.  In  their  descent 
they  lie  in  the  extreme  front  part  of  the  lateral  walls  of  the  third  ventricle,  where 
they  show  as  ridges  (Fig.  976),  and  form  on  each  side,  the  upper  and  anterior 
boundary  of  the  foramen  of  Monroe.  A  short  distance  below  the  latter  opening, 
the  pillar  disappears  from  the  ventricular  wall  in  consequence  of  the  increasing 
divergence  from  the  mesial  plane.  On  reaching  the  mammillary  body  on  the  basal 
surface  of  the  brain,  the  fibres  composing  the  anterior  pillar  are  interrupted  to 
a  large  extent  in  the  mammillary  nuclei  (Fig.  967).  The  connections  of  these 
stations  are  described  elsewhere  (page  1129),  suffice  it  here  to  recall  that  while  a 
part  of  their  fibres  are  continued  to  lower  levels,  a  very  considerable  strand,  known 
as  the  bundle  of  Vicq  d'  Azyr,  arches  upward  and  completes  the  connection  between 
the  fornix  and  the  thalamus,  in  the  anterior  part  of  which  these  mammillo-thalamic 
fibres  end.  The  relations  of  the  anterior  pillars  to  the  olfactory  paths  are  noted  in 
connection  with  the  olfactory  nerve  (page  1222). 

The  posterior  pillars  of  the  fornix  (crura  fornicis),  the  widely  diverging 
backward  prolongations  from  the  lateral  angles  of  its  body,  are  at  first  attached  to 
the  under  surface  of  the  corpus  callosum.  They  then  turn  outward,  and,  sweeping 
around  the  posterior  ends  of  the  optic  thalami,  enter  the  descending  horns  of  the 
lateral  ventricles  and  arch  downward  along  the  dorso- mesial  border  of  the  conspicu- 
ous hippocampi,  the  elevations  which  mark  the  inferior  horns  of  the  lateral  ventricles. 
On  reaching  this  situation,  however,  the  posterior  pillar  no  longer  retains  its  previous 
form,  but  now  appears  much  reduced  in  size,  as  a  white  flattened  band,  known  as 
the  fimbria,  which,  broadest  in  the  middle  of  its  course,  narrows  as  it  descends,  and 
ends  by  joining  the  uncus  at  the  lower  extremity  of  the  ventricle.  The  progressive 
diminution  of  the  fimbria  during  its  descent  is  due  to  the  contribution  of  many  of  its 
fibres  to  the  sheet  of  white  matter,  the  alveus,  which  covers  the  hippocampus.  It  is 
evident  that  the  fornix  constitutes,  by  means  of  its  several  parts,  a  continuous  tract 
of  longitudinally  coursing  fibres,  which  convey  impulses  from  the  chief  cortical  olfac- 
tory centre,  the  uncus  and  the  hippocampus,  to  the  mammillary  nuclei  and  thence,  in 
great  part,  by  the  bundle  of  Vicq  d'  Azyr  to  the  thalamus. 

The  fornix  may  be  considered,  in  a  sense,  as  a  tract  of  white  matter  representing  the  lower 
edge  of  the  hemisphere  ;  in  front  and  behind  these  edges  remain  ununited  and  more  or  less 
widely  apart.  Beneath  the  corpus  callosum  they  become  attached  not  only  to  the  under  surface 
of  this  bridge,  but  also  to  each  other  by  the  commissural  fibres  of  the  psalterium.  The  peculiar 
course  of  the  fornix  is  referable  to  the  backward  and  downward  expansion  of  the  developing 
hemispheres,  as  the  result  of  which  the  posterior  end  of  the  fornix  follows  the  hippocampus  in 
its  migration  into  the  descending  horn  of  the  lateral  ventricle  as  the  temporal  lobe  is  devel- 
oped. Further  consideration  of  these  changes,  however,  may  be  deferred  (page  1167)  until 
the  associated  structures  have  been  described  in  connection  with  the  lateral  ventricle. 

The  Septum  Lucidum. — The  septum  lucidum  (septum  pellucidum)  is  the  thin 
median  vertical  partition  which  fills  the  interval  between  the  corpus  callosum  above 
and  in  front  and  the  fornix  behind  (Fig.  996),  with  which  structures  its  margins  are 
firmly  attached.  It  separates  the  anterior  horns  and  adjoining  parts  of  the  lateral 
ventricles  and  is,  in  a  modified  form,  triangular  in  shape  when  viewed  laterally.  The 
sides  of  the  triangle  are  all  curved  and  its  anterior  angle,  received  within  the  bend  of 
the  genu,  is  blunt  and  rounded.  Its  posterior  angle  is  narrow  and  extends  for  a 
variable  distance  between  the  under  surface  of  the  body  of  the  corpus  callosum 
and  the  upper  arched  surface  of  the  body  of  the  fornix.  The  lower  angle 
occupies  the  interval  between  the  thin  edge  of  the  rostrum  and  the  anterior  pillars 


n6o 


HUMAN    ANATOMY. 


of  the  fornix.  The  septum  consists  of  two  thin  layers  (laminae  septi  pellucidi), 
between  which  lies  a  narrow  cleft  (cavum  septi  pellucidi)  to  which  the  misleading 
name,  fifth  ventricle,  has  long  been  applied.  This  space,  very  variable  in  extent 
and  width,  is  usually  so  narrow  and  contains  such  a  small  quantity  of  modified 
lymph,  that  the  laminae  forming  its  walls  are  in  apposition.  It  is  entirely  closed  and, 
therefore,  cut  off  from  the  true  ventricular  system  ;  neither  is  it  lined  with  ependyma. 
The  septum  lucidum  in  man  is  the  rudimentary  representation  of  what  in  many 
of  the  lower  (macrosmatic)  animals  is  a  much  more  important  tract  of  cortical 
substance.  In  some  animals,  as  for  example,  the  rabbit,  cat  and  dog,  the  septum 
is  solid,  a  cleft  never  appearing  within  it.  Notwithstanding  the  reduction  which 
it  has  suffered  in  man,  the  septum  exhibits  in  its  structure  its  relation  to  the 
cortex,  comprising,  from  its  cleft  outward  :  (i)  a  thin  layer  of  nerve-fibres,  (2)  an 
uncertain  layer  of  gray  matter  containing  numerous  nerve-cells  of  pyramidal  form, 
and,  next  to  the  lateral  ventricle,  (3)  a  layer  of  nerve-fibres,  the  ventricular  surface 

of  which  is  clothed  with 
FIG.  999. 

Body  of   fornix 


It 


Corpus  callosum. 
upper  surface 


Anterior 

Eillar  of 
Drnix 


Mammil- 
lary  body 


Fimbria  I 

Hippocampus 


Uncus.  partially 
cut  away 


the  usual  ependyma. 
is  probable  that  axones 
proceeding  from  the  cells 
within  the  septum  lucidum 
are  constituents  of  the 
olfactory  strands  within 
the  fornix,  which  pass  to 
the  hippocampus  and  the 
uncus,  and  of  the  t.enia 
semicircularis  (page 
1162),  terminating  in 
the  amygdaloid  nucleus 
(page  11/2). 

The  Lateral  Ven- 
tricles.— The  lateral 
ventricles  (ventricula  late- 
rales)  are  a  pair  of  irreg- 
ular cavities  contained 
within  the  cerebral  hemi- 
spheres. They  are  devel- 
oped as  outpouchings 
from  the  original  cavity 
of  the  end-brain  and  for 
a  time  communicate  with  this  space  by  wide  openings.  The  latter,  however,  fail  to 
keep  pace  in  their  growth  with  the  expansion  of  the  hemispheres,  and  in  the  fully 
developed  brain  are  represented  by  the  small  apertures,  the  foramina  of  Monroe, 
which  maintain  communication  between  the  lateral  and  third  ventricles,  the  last- 
named  space  representing  the  primary  cavity  of  the  fore-brain. 

When  viewed  from  above,  after  removal  of  its  roof,  the  corpus  callosum  and  its 
lateral  extensions,  each  lateral  ventricle  appears  as  an  elongated,  irregularly  curved 
cavity  (Fig.  1000),  which  extends  for  about  two-thirds  of  the  entire  length  of  the 
hemisphere  and,  in  addition,  penetrates  the  temporal  lobe  almost  to  its  pole.  It 
is  lined,  as  are  all  the  other  true  ventricles,  with  a  delicate  epithelial  layer,  the 
ependyma,  which  likewise  clothes  the  structures  which  encroach  upon  its  lumen,  as 
the  caudate  nucleus  and  the  thalamus,  as  well  as  those  which  seemingly  hang  free 
within  it,  as  the  choroid  plexus  and  the  fornix.  It  is  usual  to  describe  the  ventricle 
as  consisting  of  four  parts,  the  body,  and  the-  anterior,  posterior  and  inferior  horns. 
Tin-  anterior  horn  and  the  body  are  practically  one  and  separated  by  only  an  arbi- 
trary division  ;  the  posterior  and  the  inferior  horn  extend  into  the  occipital  and  the 
temporal  lobe  respectively,  whilst  the  anterior  horn  enters  the  frontal  lobe. 

The  anterior  horn  (cormi  anterius  )  includes  from  the  tip  of  the  ventricle  to 
the  foramen  of  Monroe,  the  latter  corresponding  with  the  anterior  limit  of  the  con- 
spicuous choroid  plexus,  curves  forward  and  outward  around  the  head  of  the  caudate 
nucleus  into  the  white  substance  of  the  frontal  lobe  and  in  frontal  sections  (Fig. 


Dissection  showing  fornix  in  front  and  above  ;  drawn  from  preparation  and 
Steger  model. 


THE   TELENCEPHALON. 


1161 


1007)  appears  triangular  in  outline.  The  upper  side  or  base  of  the  triangle,  slightly 
curved  towards  the  ventricle,  is  the  lower  surface  of  the  arched  corpus  callosum  and 
its  antero-lateral  radiations  ;  the  mesial  side  is  approximately  vertical  and  formed 
by  the  septum  lucidum  ;  the  lateral  side  bulges  strongly  towards  the  ventricle  in 
correspondence  with  the  convexity  of  the  massive  head  of  the  caudate  nucleus.  The 
floor  of  this  part  of  the  ventricle  is  narrow,  often  a  mere  groove  along  the  junction  of 
the  sloping  lateral  and  vertical  mesial  wall,  and  in  front  passes  insensibly  into  the 
concave  anterior  wall,  formed  by  the  lateral  part  of  the  hind  surface  of  the  genu  of 
the  corpus  callosum. 

The  body  (pars  centralis)  of  the  lateral  ventricle  includes  that  part  of  the  space 
which  extends  from  the  foramen  of  Monroe  to  the  bifurcation  of  the  ventricle  into  its 

FIG.   1000. 


pus  callosum 


Anterior  ho 
lateral  ven' 


Caudate  nucleus,  head 
Foramen  of  Monroe 


l^enticula    nucleus, 
sectioned 


T;enia  semicircularis 

Thalamus,    up]  >er 
surface 

Hippocampus 
Collateral  eminence 
Fin. 


Collateral  protruber- 

ance  in  trii;onuiii 

ventriculi 

Bulb  of  forceps 

posterior 

Calcar  avis 


Posterior  horn  of 
lateral  ventricle 


Septum  lucidum 


Cavity  within  septum 


Fornix ,  anterior  pillar 


Posterior  horn 

of  lateral  ventricle 


Lateral  ventricles  seen  from  above  after  partial  removal  of  corpus  callosum  and  cerebral  hemispheres. 

posterior  and  inferior  horns,  opposite  the  splenium  of  the  corpus  callosum.  When 
viewed  in  frontal  sections  (Fig.  1010),  it  appears  as  a  narrow,  obliquely  horizontal 
cleft,  directed  somewhat  upward,  roofed  in  by  the  corpus  callosum.  Its  mesial 
wall  is  formed  in  front  by  the  hind  part  of  the  septum  lucidum  and  behind  the 
latter  by  the  fornix  where  it  is  attached  to  the  under  surface  of  the  corpus  callosum. 
A  distinct  lateral  wall  is  wanting,  the  ventricle  being  here  closed  by  the  meeting 
of  the  floor  and  roof.  Its  floor  is  constituted  by  several  structures  of  importance 
which,  named  from  without  inward,  are:  (i)  the  caudate  nucleus  ;  (2)  an  oblique 
groove  (sulcus  intermedius),  which  extends  from  before  backward  and  outward, 
between  the  caudate  nucleus  and  the  thalamus,  and  lodges,  in  addition  to  the  vein 
of  the  corpus  striatum,  a  white  band  of  nerve-fibres  known  as  the  Icenia 
semicircularis  ;  (3)  a  narrow  portion  of  the  upper  surface  of  the  thalamus,  which  is 


Il62 


HUMAN   ANATOMY. 


•Anterior  horn 


almost  completely  masked  by  the  overlying  choroid  plexus  ;  (4)  the  choroid plexus 
of  the  lateral  ventricle  ;  and  (5)  the  lateral  edge  of  \hefornix.  The  caudate  nucleus 
will  be  subsequently  described  (page  1169),  suffice  it  to  note  its  rapid  diminution 
in  size,  as  it  curves  backward  and  downward  on  the  roof  of  the  inferior  horn. 

The  taenia  semicircularis  is  more  or  less  hidden  by  the  superficially  placed  men 
of  the  corpus  striatum  (vena  terminalis),  which  lies  immediately  beneath  the  epen- 
dyma  and  shows  as  a  distinct  sinuous  ridge.  Receiving  tributaries  from  the  adjacent 
parts  of  the  thalamus,  the  caudate  nucleus  and  the  walls  of  the  anterior  horn,  includ- 
ing the  septum  lucidum,  the  vein  passes  to  the  foramen  of  Monroe,  where,  meeting 
with  the  choroid  vein  at  the  apex  of  the  velum  interpositum,  it  forms  with  the  last- 
named  vessel  the  vein  of  Galen. 

The  taenia  semicircularis,  the  band-like  tract  of  nerve-fibres  which  occupies 
the  sulcus  intermedius,  is  probably  a  part  of  the  complex  pathway  by  which  the  pri- 
mary and  secondary  olfactory  centres  are  united.  Its  component  fibres  arise  partly 
in  the  anterior  perforated  space  and  partly  in  the  septum  lucidum  from  which  centres, 
reinforced  by  fibres  from  the  anterior  commissure,  they  converge  towards  the  sulcus 

intermedius     which      they 

FIG.  1001.  then  follow.     After  leaving 

the  body  of  the  lateral 
ventricle  they  descend  with- 
in the  roof  of  the  inferior 
horn,  in  close  relation  to 
the  recurved  tail  of  the 
caudate  nucleus,  to  end 
within  the  amygdaloid 
nucleus  (page  1172). 

The  choroid  plexus 
(  plexus  chorioideus  ventriculi 
lateralis)  is  a  convoluted 
vascular  complex  which 
occupies  the  lateral  margin 
of  the  pial  sheet,  the  velum 
interpositum,  within  the 
body  of  the  lateral  ventricle, 
and,  in  addition,  descends 
along  the  inferior  horn  of 
the  lateral  ventricle  to  its 
tip.  In  order  to  understand 
the  relations  of  the  choroid 
plexus,  those  of  the  larger 
sheet,  of  which  it  is  part,  must  be  described.  The  velum  interpositum  (tela 
chorioidea  ventriculi  tertii)  is  a  delicate  sheet  of  pia  mater  whose  upper  surface  is 
exposed  after  removal  of  the  corpus  callosum  and  the  body  of  the  fornix.  When 
viewed  from  above  (Fig.  1102)  it  is  triangular  in  outline,  its  apex  lying  at  the 
foramina  of  Monroe  and  its  lateral  basal  angles  extending  into  the  descending  horns 
of  the  lateral  ventricles.  Its  inferior  surface  forms  the  roof  of  the  third  ventricle, 
beyond  which  on  each  side  it  covers  the  greater  part  of  the  upper  surface  of  the 
thalamus  and,  in  turn,  is  overlaid  by  the  fornix.  Behind,  the  velum  interpositum  is 
continuous  beneath  the  splenium  of  the  corpus  callosum  with  the  pia  mater  investing 
the  external  surface  of  the  hemisphere.  This  relation  readily  gives  rise  to  the 
impression  that  the  pial  tissue  has  gained  entrance  to  the  ventricles  by  growing 
forward  through  the  cleft  beneath  the  splenium  and  the  fornix.  That  such,  however, 
is  not  the  case  will  be  pointed  out  later,  when  the  development  of  this  sheet  is 
considered  (page  1194).  The  relation  of  the  velum  interpositum  to  the  ventricular 
cavities  should  be  carefully  noted  by  tracing  the  ependyma  from  the  caudate  nucleus 
inward.  Leaving  the  convex  surface  of  this  structure,  the  ventricular  lining  covers 
the  sulcus  terminalis  with  its  vein,  and  passes  for  a  short  distance  over  the  adjoining 
outer  part  of  the  upper  surface  of  the  thalamus.  This  zone  (lamina  aftixa)  narrows 
in  front  and  behind,  and  where  broadest  measures  from  5-7  mm.  Along  the 


Lateral 
recess 


Posterior 
horn 


Cast  of  ventricles,  viewed  from  above.     X  %•     (Relzius.) 


THE  TELENCEPHALON. 


1163 


inner  margin  of  this  zone  the  ependyma  leaves  the  surface  of  the  thalamus  and 
passes  onto  the  villous  projections  (Fig.  1003)  of  pia  mater  containing  the  convolu- 
tions of  blood-vessels  of  which  the  choroid  plexus  is  composed.  Each  projection, 
(glomus  chorioideum)  consists  of:  (i)  a  capillary  complex  formed  by  the  terminal 
twigs  of  the  anterior  and  posterior  choroidal  arteries,  which  gain  the  interior  of  the 
hemisphere  through  the  choroidal  fissure  in  the  inferior  horn  of  the  lateral  ventricle  ; 
(2)  the  connective  tissue  of  the  pia  ;  and  (3)  the  ependymal  layer  (lamina  chorioidea 
epithelialis),  which  everywhere  invests  the  pial  plications  and,  therefore,  excludes  the 
vascular  tissue  from  actual  entrance  into  the  ventricular  cavity.  While  inconspicuous 
and  often  overlooked,  this  ependymal  layer  is  of  much  morphological  significance, 
since  it  represents  all  that  persists  in  certain  localities  of  the  true  wall  of  the  hemi- 
sphere. After  leaving  the  surface  of  the  thalamus  and  investing  the  vascular  pro- 


FIG.  1002. 


Septum  lucidum 
Anterior  end  of  fornix,  cut 


Hippocampus 
Velum  interpositum 


Choroid  plexus  in  inferior 
horn  of  lateral  ventricle 


Splenium,  under  surface 


Posterior  horn  of  lateral 
ventricl 


Lateral  parts  of  fornix, 
under  surface 


Corpus  callosum 


Caudate  nucleus 


Choroid  plexus,  overlying 
foramen  of  Monroe 


Vein  of  corpus  striatum 
f. Choroid  vein  in  plexus 

.Veins  of  Galen 


Crus  of  fornix  and  posterior 
.forceps  of  corpus  callosum, 
cut 


Under  surface  of  fornix, 
Lyra 


^  Cut  anterior  end  of  fornix 


Dissection  of  brain,  showing  velum  interpositum  and  choroid  plexuses  of  lateral  ventricles  ;  seen  from  above 
after  removal  of  corpus  callosum  and  fornix;  latter  has  been  cut  through  in  front  and  behind  and  turned  back, 
exposing  its  under  surface. 

jections  constituting  the  choroidal  plexus,  the  ependyma  becomes  attached  along 
the  taenia  fornicis  to  the  thin  lateral  margin  of  the  fornix,  beneath  which  the  velum 
interpositum  protrudes  to  expand  into  the  choroid  plexus  within  the  body  of  the 
ventricle. 

The  plexus  is  not  confined  to  this  part  of  the  space,  but  follows  the  hippocampus 
to  the  lower  end  of  the  inferior  horn.  The  relation  of  the  vascular  pial  tissue  to 
this  extension  of  the  ventricle  is,  however,  the  same  as  within  the  body,  since  the 
glomeruli  here,  as  there,  are  completely  invested  by  the  ependyma,  which  they 
invaginate  along  a  groove,  the  choroidal  fissure,  above  the  hippocampus,  in 
the  same  manner  as  they  do  higher  in  the  ventricle.  The  line  of  attachment  of  the 
ependyma  to  the  wall  of  the  horn,  taenia  fimbriae,  follows  the  recurved  tail  of 
the  caudate  nucleus,  just  beneath  which  it  lies,  on  the  one  hand,  and  the  thin  mesial 
edge  of  the  fimbria  (the  continuation  of  the  fornix)  on  the  other.  On  pulling  out 


1164 


HUMAN   ANATOMY. 


the  entire  choroid  plexus  of  the  lateral  ventricle,  the  ependyma  is  torn  away  and  an 
artificial  opening  is  produced,  which  may  be  followed,  as  a  curved  narrow  cleft,  from 
the  lower  end  of  the  inferior  horn  upward  above  the  hippocampus  and  over  the 
dorsal  surface  of  the  thalamus,  beneath  the  fornix  and  the  splenium,  to  the  exterior  of 
the  hemisphere.  When  traced  forward  from  its  attachment  along  the  upper  surface 
of  the  thalamus,  the  line  of  the  reflection  of  the  ependyma,  taenia  chorioidea,  leads 
to  just  above  the  foramen  of  Monroe  (Fig.  1031),  where  it  is  joined  by  the  similar 
line  of  the  opposite  ventricle.  From  this  point  the  choroidal  line  of  ependymal 
reflection  is  continuous  with  the  taenia  thalami,  the  sharp  ridge  which  marks  the 
junction  of  the  superior  and  mesial  surface  of  the  thalamus  (page  1119).  Leaving 
the  surface  of  the  latter  along  this  ridge,  the  ependymal  layer  covers  the  under  side 
of  the  velum  interpositum,  as  well  as  the  double  row  of  vascular  villous  projections, 
which,  one  on  each  side  of  the  mid-line  of  the  roof,  constitute  the  choroid  plexus 
of  the  third  ventricle  (Fig.  974).  Although  similar  in  its  general  structure,  this 
vascular  fringe  is  much  smaller  and  less  conspicuous  than  that  within  the  lateral 
ventricle. 


It  is  evident  from  the  foregoing  description,  that  communication  between  the  third  and 
lateral  ventricles  is  completely  interrupted  by  the  attachment  of  the  ependymal  layer  and  that 
at  only  one  place,  the  foramen  of  Monroe  (page  1161),  does  such  communication  exist.  It  is 
of  interest  to  note  that  these  several  lines  of  ependymal  reflection — the  taenia  chorioidea,  the 
taenia  thalami  and  the  taenia  fornicis  and  its  prolongation,  the  taenia  fimbriae — form  a  contin- 
uous line  which  morphologically  marks  the  transition  of  the  thicker  nervous  part  of  the  wall  of 
the  hemisphere  into  the  thin  and  atrophic  area,  which  early  undergoes  an  invagination  leading 
to  the  production  of  voluminous  vascular  structures  later  seen  in  the  definite  choroid  plexuses 
of  the  lateral  and  third  ventricles.  Along  the  margin  of  the  choroidal  fissure,  at  which  such 
invagination  primarily  occurs,  the  white  matter  of  the  hemisphere  becomes  condensed  into  the 
tract  of  the  fornix  and  its  downward  prolongation,  the  fimbria.  These  structures,  together 
with  the  reflected  ependyma  and  the  septum  lucidum,  are  regarded,  therefore,  as  modified 
parts  of  the  mesial  surface  of  the  hemisphere. 

The  inferior  horn  (cornu  inferius),  also  called  the  descending  horn,  begins  above 
at  the  hind-end  of  the  body  of  the -ventricle,  thence  curves  backward  and  outward 
around  the  thalamus,  and  sweeps  downward  and  forward  and  a  little  inward  (Fig. 
1000)  into  the  temporal  lobe  well  towards  its  tip,  which,  however,  it  fails  to  reach  by 

about  2  cm.     Its  descent  is  not 

FIG.  1003.  on^y  verv  abrupt,   but  limited 

for  the  most  part  to  almost  a 
vertical  plane  ;  hence  this  part 
of  the  ventricle  does  not  diverge 
to  any  considerable  extent  be- 
yond the  plane  of  the  gyrus  hip- 
pocampi, just  to  the  outer  side 
'  of  which  the  lower  end  of  the 
inferior  horn  lies.  The  roof  of 
this  cornu  is  formed  chiefly  by 
the  tapetum  of  the  corpus  cal- 
losum,  and  within  it  descend  the 
recurved  attenuated  tail  of  the 
caudate  nucleus  and  the  fcenia 
semicircularis  to  join  a  rounded 
mass  of  gray  matter,  the  amyg- 
daloid nucleus  I  page  1172), 
which  lies  embedded  within  the 
temporal  lobe,  slightly  above 

and  in  front  of  the  lower  end  of  the  inferior  horn  (Fig.  967).  The  floor  of 
the  inferior  horn  begins  above  in  the  triangular  area,  the  trigonum  ventriculi, 
between  the  diverging  inferior  and  posterior  horns.  The  greater  part  of  this  field  is 
occupied  by  a  low  convexity,  the  collateral  protuberance  ( triuoiium  collateralc  >, 
which  is  continued  into  a  rounded  ridge,  the  collateral  eminence  (cmim-mia 


Taenia  chorioidea 


Taenia  thalam 


Tsenia  fornicis 


Choroid  plexus 
of  III  ventricle 


Diagram  showing  relation  of  pial  tissue  in  velum  interpositum  to 
ependyma  in  lateral  and  third  ventricle;  epenchma  is  represented  by 
red  line;  c,  c,  corpus  callosum;  /•",  fornix;  TV.  so-called  ventricle  of 
Verga  ;  C,  T,  caudate  nucleus  and  thalamus. 


THE   TELENCEPHALON. 


1165 


collateralis),  that  extends  for  a  variable  distance  along  the  outer  part  of  the  floor 
of  the  inferior  horn.  This  elevation  is  uncertain  as  to  prominence  and  length,  but 
even  when  well  developed  does  not  reach  the  lower  extremity  of  the  ventricle. 
It  results  from  the  invagination  of  the  wall  of  the  early  hemisphere  by  the  anterior 
part  of  the  collateral  fissure. 

A  second  longitudinal  elevation,  constant  and  much  more  conspicuous  than  the 
collateral  eminence  and  separated  from  the  latter  by  a  groove,  forms  the  inner  part  of 
the  floor  and  the  adjoining  mesial  wall  of  the  inferior  horn  of  the  lateral  ventricle. 
This  elevation,  known  as  the  hippocampus,  is  the  most  prominent  feature  of  the 
horn  and  curves  downward  and  inward  to  the  extreme  lower  limit  of  this  part  of  the 
ventricle.  It  is  due  to  the  early  invagination  of  the  hemisphere  by  the  hippocampal 
fissure.  The  lower  end  of  the  hippocampus  is  distinctly  broader  and  somewhat 
flattened  and  marked  by  a  number  of  oblique  shallow  furrows  and  intervening  low 
radiating  ridges  (digitationes  hippocampi).  These  confer  on  the  upper  surface  and 
especially  on  the  outer  rounded  border  of  the  elevation,  a  corrugated  and  notched 
appearance,  (Fig.  1004)  which  suggests  a  fancied  resemblance  to  a  paw,  the  lower 
end  of  the  projection  being- 
known  as  the  pes  hippo-  FIG.  1004. 
campi.  The  upper  surface 
and  the  anterior  and  lateral 
border  of  the  pes  are  free 
and  well  defined,  but  its 
deeper  surface  and  inner 
border,  to  a  large  extent,  are 
blended  with  the  surround- 
ing parts  of  the  hemisphere. 
The  intimate  structure  of  the 
hippocampus  is  described 
with  that  of  the  cerebral 
cortex  (page  1181). 

The  dorso-mesial  aspect 
of  the  hippocampus  is  over- 
laid by  a  white  flattened 
band,  the  fimbria  (timbria 
hippocampi),  which,  although 
bearing  a  special  name,  is 
the  direct  prolongation  of  the 
posterior  crus  of  the  fimbria, 
continued  from  the  lateral 
angle  of  the  corpus  fornicis 
into  the  inferior  horn.  Its 
concave  mesial  margin  is 
smooth,  rounded  and  free, 

whilst  its  sinuous  lateral  border  is  thin  and  sharp  and  gives  attachment  through- 
out its  entire  length  to  the  delicate  ependymal  layer  which  completes  the  mesial 
wall  and  thus  closes  in  the  descending  horn  (Fig.  1005).  Above  narrow  and  then 
broader,  on  reaching  the  pes  the  fimbria  becomes  abruptly  reduced  to  a  narrow 
strand,  which  may  be  followed  along  the  inner  margin  of  the  pes  to  the  uncus 
where  it  ends.  Traced  upward  the  fimbria  passes  without  interruption  into  the 
posterior  limb  of  the  fornix,  of  which,  as  already  noted,  it  is  the  direct  downward 
prolongation.  Beginning  in  the  uncus,  the  fimbria  continually  receives  accessions 
of  fibres  from  the  underlying  hippocampus,  with  which  it  is  closely  united  along 
its  deep  surface,  and  therefore  increases  in  bulk  as  it  ascends  towards  the  body 
of  the  fornix. 

When  the  structures  within  the  inferior  horn  of  the  lateral  ventricle  are  viewed 
in  their  undisturbed  relations  (Fig.  1004),  little  of  the  hippocampus  and  nothing  of 
the  fimbria  are  seen,  as  these  parts  are  hidden  by  the  overlying  mass  of  vascular  tissue 
constituting  the  choroid  plexus,  which  is  not  confined  to  the  body  of  the  ventricle, 
where  its  connections  have  been  already  described,  but  follows  the  descending 


Cyrus  hippocampi 
Fimbria 


Inferior  horn  of  left  lateral  ventricle,  viewed  from  above. 


u66 


HUMAN    ANATOMY. 


horn  to  its  lower  end.  On  turning  aside  the  vascular  fringe,  its  relations  to  this 
part  of  the  ventricle  will  be  found  to  be  identical  with  those  exhibited  in  the  body 
of  the  ventricle,  since  here,  as  there,  the  vascular  complex  is  everywhere  covered 
by  the  thin  layer  of  reflected  ependyma  and,  therefore,  excluded  from  actual 
entrance  into  the  ventricular  space.  Tracing  the  line  of  attachment  of  the  reflected 
ependyma,  which  alone  represents  the  true  ventricular  wall  closing  the  crescentic 
choroidal  fissure  along  the  dorso-mesial  aspect  of  the  inferior  horn,  it  will  be 
found  to  be  continuous  with  the  thin  lateral  edge  of  the  fimbria  throughout  the 
entire  length  of  this  attenuated  margin,  just  as  it  is  connected  with  the  fimbria 
within  the  body  of  the  ventricle.  Passing  from  this  line  of  attachment  (taenia 
fimbriae)  over  all  the  villous  projections  of  the  choroid  plexus,  the  reflected 
ependyma  returns  to  the  thicker  ventricular  wall,  which  it  joins  along  the  mesial 
border  of  the  roof.  Thence  the  ependyma  remains  in  close  contact  with  the 
remaining  parts  of  the  walls  of  the  inferior  horn,  all  the  surfaces  of  which,  including 
those  formed  by  the  hippocampus  and  the  collateral  eminence,  it  covers.  From 
these  relations  (Fig.  1005)  it  follows  that  the  fimbria  in  large  part  is  excluded, 
as  are  some  other  parts  of  the  fornix,  from  the  ventricle,  only  that  portion  of  its 
surface  which  extends  from  its  sharp  lateral  border  to  the  underlying  hippocampus 
forming,  strictly  regarded,  a  part  of  the  ventricular  wall.  The  rounded  mesial 
border  and  the  dorsal  surface  of  the  fimbria  belong  to  the  free  mesial  surface  of 
the  hemisphere. 

The  dentate  gyrus  (fascia  dentata)  is  part  of  an  atrophic  convolution  belong- 
ing to  the  rhinencephalon  (page  1151),  and  as  such  belongs  systematically  to  that 

division  of  the  hemisphere. 
FIG.  1005. 

Choroid  plexus 

Caudate  nucleus,  tail 

/     Tienia  semicircularis 


Ependyma 

Cavity  of  inferior 
horn  of  lateral 
ventricle 


Since,  however,  it  is  closely 
associated  with  the  struc- 
tures found  within  the  inferior 
horn  of  the  lateral  ventricle, 
its  description  has  been  de- 
ferred until  this  place.  The 
dentate  gyrus  lies  on  the 
mesial  surface  of  the  hemi- 
sphere, but  is  so  hidden  be- 
hind the  hippocampal  gyrus 
that  it  is  satisfactorily  dis- 
played only  after  the  over- 
hanging parts  of  the  thala- 
mus  and  cerebral  crura  are 
removed.  On  cutting  away 
these  structures  and  drawing 
downward  the  hippocampal 
gyrus,  a  narrow  band  of  gray 
matter,  notched  and  corru- 
gated by  numerous  minute  transverse  furrows,  is  seen  protruding  between  the  free 
rounded  mesial  border  of  the  fimbria  above  and  the  hippocampal  fissure  below  (  ML;. 
992).  This  band  is  the  gyrus  dentatus.  On  examining  frontal  sections  passing 
through  the  inferior  horn  of  the  lateral  ventricle  (Fig.  1005),  the  relations  of  the 
dentate  gyrus  will  be  appreciated.  In  such  preparations  the  gyrus  appears  as  the 
free,  somewhat  thinned  off  edge  of  cortical  gray  matter,  which  is  pushed  to  the 
surface  just  below  the  choroidal  fissure  through  which  the  pial  tissue  invaginates  the 
ventricular  wall  to  gain  a  seeming  entrance  to  the  inferior  horn.  Between  the  fimbria, 
which  lies  immediately  above  and  parallel  with  it,  and  the  gyrus  a  shallow  groove, 
the  sulcus  fimbrio-dentatus,  intervenes,  whilst  below  it  is  bounded  by  the  remains  of 
the  hippocampal  or  dentate  fissure.  The  latter  is  no  longer  an  evident  furrow,  as  it 
was  when  producing  the  hippocampus,  since  it  has  become  closed  and  almost  com- 
pletely obliterated  by  the  apposition  of  the  bordering  cortex. 

Traced  forward,  the  gyrus  dentatus  gradually  leaves  the  fimbria  and  passes  deeply 
along  the  inner  side  of  the  uncus  in  connection  with  which  it  ends.  The  terminal 
part  of  the  gyrus,  somewhat  reduced  in  size,  at  first  bends  sharply  medially  along 


Entrance  to 
choroidal  fissure 


Fimbria 

Fimbrio-dentate 
fissure 
Gyrus  dentatus 


\  Hippocampal  fissure 
Alveus 

\  Hippocampus 
Gyrus  hippocampi 
Collateral  fissure 

Frontal  section  of  part  of  left  hemisphere  passing  through  lower  end  of 
inferior  horn  of  lateral  ventricle.     X  2. 


THE   TELENCEPHALON.  1167 

the  under  surface  of  the  uncus  and  then  winds  over  the  inner  aspect  of  the  latter,  from 
within  outwards,  as  a  narrow  grayish  band,  the  frenulum  of  Giacomini,  which, 
continuing  upon  the  upper  surface  of  the  uncus,  for  a  short  distance  passes  slightly 
backward  and  disappears  (Fig.  1006), 

Followed  backward,  the  gyrus  dentatus  accompanies  the  fimbria  towards  the 
splenium,  at  the  lower  border  of  which  the  two  structures  part  company,  the  fimbria 
passing  to  the  under  side  of  the  corpus  callosum,  whilst  the  gyrus  dentatus,  losing  its 
corrugations  and  becoming  a  smooth  band,  known  as  the  fasciola  cinerea,  bends 
backward  and  curves  around  the  splenium  (Fig.  992)  to  spread  out  over  the  upper 
surface  of  the  corpus  callosum  as  the  thin  atrophic  sheet  of  gray  matter,  the 
induseum  griseum  in  which  are  embedded  the  fibre-strands  of  the  longitudinal 
striae  (page  1156).  The  structure  of  the  gyrus  dentatus  is  described  with  that  of 
other  parts  of  the  cerebral  cortex  (page  1182). 

FIG.  1006. 

•Splenium  of  corpus  callosum 


Frenulum  of  Giacomini 


\  3        , 

Fasciola  cinerea        Gyrus  hippocampi         \  Collateral  fissure 

Gyrus  dentatus 

Part  of  left  gyrus  hippocampi  has  been  cut  away  to  expose  gyrus  dentatus,  which  is  seen  continuing  as 

frenulum  of  Giacomini  over  uncus. 

The  fornix  is  to  be  regarded  as  the  chief  fibre-tract  connecting  the  olfactory  cortex,  situated 
within  the  uncus  and  the  hippocampus,  with  the  thalamus.  An  explanation  of  its  remarkable 
course  as  seen  in  the  adult  brain,  is  found  in  the  changes  which  affect  the  position  of  the  hippo- 
campus during  development.  Reference  to  Figs.  1030,  1032,  will  recall  the  origin  of  the  hemi- 
sphere (pallium)  as  an  outgrowth  from  the  end-brain,  and,  further,  that  the  hemisphere  in  man 
early  covers  in  the  thalamus  and  other  parts  of  the  diencephalon  and  the  mid-brain.  For  a  time 
the  thalamus  is  connected  with  the  hemisphere  by  means  of  only  the  thin  recurved  under  and 
inner  wall  of  the  pallium,  the  bulky  tracts  of  white  matter  in  which  it  is  later  embedded  being 
for  a  time  wanting.  This  same  independence  is  retained  by  the  thalamus,  even  in  the  adult 
condition,  on  its  upper  and  posterior  aspects,  where  the  excessively  thinned  out  ventricular  wall 
alone  forms  the  partition  between  the  ventricle  and  the  exterior,  and  where  the  thalamus  is  over- 
laid by,  but  not  in  contact  with,  the  hemisphere.  On  breaking  through  this  partition,  as  after 
removal  of  the  velum  interpositum,  the  thalamus  may  be  directly  reached  by  passing  beneath 
the  splenium.  When  a  definite  mesial  surface  of  the  hemisphere  becomes  developed,  an  area 
along  the  inferior  margin  of  this  aspect  becomes  marked  off  by  two  primary  grooves,  which  are 
the  early  choroidal  fissure  below  and  the  hippocampal  fissure  above.  The  area  so  defined  is 
the  primary  gyrus  dentatus.  This  tract  of  gray  matter  is  connected  with  the  thalamus  by  the 
fornix,  which  reaches  the  thalamus  around  the  front  end  of  the  choroidal  fissure.  In  many 
animals,  as  in  the  rabbit,  a  similar  relation  is  permanently  retained,  the  dentate  gyrus,  or  its 
equivalent,  the  hippocampus,  being  united  with  the  thalamus  by  a  fornix-tract  which  sweeps  from 
the  lower  and  posterior  part  of  the  pallium  (hippocampus)  over  the  roof  of  the  third  ventricle 
forward  and  downward  to  the  basal  surface  of  the  brain  (mammillary  body)  and  thence  by 
the  bundle  of  Vicq  d' Azyr  to  the  thalamus.  These  primary  relations  are  changed  by  the  future 
expansion  of  the  hemisphere,  which  grows  not  only  upward  and  backward,  but  also  downward 
to  form  the  temporal  lobe,  in  consequence  of  which  the  dentate  gyrus  and  the  fornix,  and  likewise 
the  choroid  plexus  and  its  fissure,  are  carried  backward,  downward  and  forward  around  the 
thalamus  into  the  temporal  lobe,  where  they  lie  on  the  mesial  wall  of  the  descending  horn  of  the 
lateral  ventricle  which  has  coincidently  been  formed.  Whilst  in  this  manner  the  chief  mass  of  the 
primary  gyrus  dentatus  is  carried  into  the  temporal  lobe,  where  it  becomes  the  hippocampus  and 


n68 


HUMAN    ANATOMY. 


the  definite  dentate  gyrus,  a  part  of  it,  greatly  attenuated  and  reduced,  retains  its  connection  with 
the  anterior  basal  surface  of  the  brain  (later  the  anterior  perforated  substance)  and  follows  the 
upper  surface  of  the  corpus  callosum,  which  likewise  has  extended  backward,  into  the  descend- 
ing horn  of  the  lateral  ventricle.  These  parts — the  gyrus  subcallosus,  the  longitudinal  stria-, 
the  fasciola  cinerea  and  the  gyrus  clentatus  of  the  adult  brain — constitute  the  supracallosal  gyrus, 
whose  gray  matter  is  an  atrophic  outlying  part  of  the  primary  gyrus  dentatus  and  whose  con- 
nections with  the  basal  olfactory  centres  are  retained  by  the  fibres  of  the  longitudinal  stria;. 
The  fornix  shares  the  displacement  of  its  cortical  area,  the  hippocampus,  and  is  consequently 
carried  with  the  latter  into  the  descending  horn  of  the  lateral  ventricle.  In  this  manner  parts 
which  at  first  lay  in  proximity  and  were  connected  by  short  paths,  become  widely  separated, 
with  corresponding  lengthening  of  the  fibre-tracts  uniting  them,  as  illustrated  in  the  long 
course  of  the  fornix  in  the  adult  brain.  Further,  since  the  path  of  migration  of  the  fornix 
and  associated  structures  of  the  inferior  horn  of  the  lateral  ventricle  describes  a  curve, 
it  follows  that  the  relations  of  these  parts  become  reversed,  those  originally  King 
above,  in  regard  to  adjacent  structures,  within  the  descending  horn  being  below  and 
vice  versa. 

The  posterior  horn  of  the  lateral  ventricle  (cornu  posterius),  much  smaller 
than  either  of  the  others,  is  an  elongated  diverticulum  which  curves  backward  from 


Superior  frontal  gyni> 

Middle  frontal  gyrus 


Longitudinal  6ssure- 


Genii  of  corpus 

callosura- 


Lateral  ventricle, 

anterior  horn- 


Inferior  frontal  gyrus 


Caudate  nucleus,  head 


""Orbital  gyri 
Frontal  section  of  brain  passing  through  genu  of  corpus  callosum. 


the  body  of  the  ventricle  into  the  occipital  lobe.  In  frontal  sections  (Fig.  1034)  its 
form  is  irregularly  crescentic,  the  convexity  of  its  outline  including  the  roof  and  the 
lateral  wall  and  the  concavity  corresponding  with  the  mesial  wall  and  narrow  floor. 
Above  and  to  the  outer  side,  the  horn  is  bounded  by  the  arching  fibres  of  the  tape- 
turn  of  the  corpus  callosum,  lateral  to  which  lies  the  important  thalamo-occipital  or 
optic  radiation  (page  1123).  The  lower  part  of  the  mesial  wall  is  modelled  (  Fig. 
1000)  by  a  narrow  but  well  marked  crescentic  elevation,  the  calcar  avis,  also 
called  the  hippocampus  minor,  which  is  produced  by  the  early  imagination  of  the 
wall  of  the  hemisphere  by  the  anterior  part  of  the  calcarine  fissure.  On  the  same 
wall  and  just  above  the  calcar  avis,  a  second  and  broader,  but  less  sharply 
defined,  elevation  ( bulbus  cornu  postcrioris  >,  marks  the  course  of  the  fibres  of  the 
forceps  posterior  as  they  encircle  the  parieto-occipital  fissure  in  their  journey  to  the 
occipital  lobe. 


THE   TELENCEPHALON.  1169 

THE  INTERNAL  NUCLEI  OF  THE  HEMISPHERE. 

Embedded  within  the  white  matter  of  each  hemisphere  and,  for  the  most  part, 
completely  separated  from  the  cerebral  cortex,  lie  certain  masses  of  gray  matter  to 
which  the  name  basal  ganglia  is  often  applied.  These  include:  (i)  the  caudate 
nucleus,  (2)  the  lenticular  nucleus,  (3  )  the  claustrum  and  (4)  the  amygdaloid  nucleus. 
The  first  two,  the  caudate  and  lenticular  nuclei,  are  parts  of  the  corpus  striatum, 
one  of  the  three  fundamental  divisions  of  the  end-brain  or  telencephalon.  Although 
almost  completely  separated  by  the  intervening  tract  of  white  matter,  the  internal 
capsule,  the  caudate  and  lenticular  nuclei  are  continuous  for  a  limited  distance  below 
and  in  front  (Fig.  1008),  and  together  constitute  a  large  mass  composed  chiefly  of 
gray  matter,  that  extends  from  the  lateral  ventricle  almost  to  the  cortex  of  the 
insula.  Between  the  latter  and  the  lenticular  nucleus  lies  a  thin  tract  of  gray 
matter,  the  claustrum,  whilst  within  the  temporal  lobe,  above  and  in  front  of  the 
anterior  extremity  of  the  inferior  horn  of  the  lateral  ventricle,  is  situated  the 
amygdaloid  nucleus. 

The  Caudate  Nucleus. — This  mass  (nucleus  caudatus),  the  inner  division  of 
the  corpus  striatum,  is  well  seen  from  the  lateral  ventricle,  where  it  appears  as  the 
large  and  conspicuous  elevation  which  contributes  the  infero-lateral  wall  of  the  anterior 
horn,  and  the  outer  part  of  the  floor  of  the  body  of  the  ventricle.  The  caudate 
nucleus  is  an  elongated  pyriform  or  comet-shaped  mass  of  gray  matter,  whose  bulky 
rounded  anterior  end  or  head  (caput  nuclei  caudati)  rapidly  diminishes  into  the 
attenuated  and  recurved  tail  (cauda  nuclei  caudati),  which  sweeps  backward  and  then 
downward  and  forward  within  the  roof  of  the  inferior  horn  to  the  tip  of  the  temporal 
lobe,  where  it  ends  in  relation  with  the  lower  part  of  the  amygdaloid  nucleus. 

The  relations  of  its  two  chief  surfaces,  the  mesial  and  lateral,  are  best  seen  in 
frontal  sections.  When  sectioned  through  its  head  near  the  anterior  pole  (Fig.  1007), 
the  caudate  nucleus  appears  as  an  ovoid  area  of  gray  matter  which  mesially  bulges 
strongly  into  the  lateral  ventricle,  but  from  which  it  is  separated  by  the  ependyma, 
and  laterally  is  embedded  within  the  white  matter  of  the  hemisphere.  In  sections 
passing  a  few  millimeters  farther  back  (Fig.  1009),  the  form  of  the  nucleus  has 
become  somewhat  changed,  its  inner  convex  surface  being  more  extensive  and  its 
outer  one,  now  somewhat  concave,  being  serrated  by  the  invasion  of  obliquely  hori- 
zontal stripes  of  white  matter  due  to  the  appearance  of  the  anterior  strands  of  the 
internal  capsule.  In  the  plane,  under  consideration,  these  strands  are  not  continuous 
but  interspersed  with  stripes  of  gray  matter,  which  below  still  connect  the  caudate 
with  the  laterally  situated  lenticular  nucleus  and  produce  the  coarse  striation  from 
which  the  entire  mass,  the  corpus  striatum,  derives  its  name. 

In  sections  passing  through  the  body  of  the  ventricle  (Figs.  1010,  1025),  from 
the  plane  of  the  foramina  of  Monroe  backward,  the  caudate  nucleus  is  much  reduced 
in  size,  whilst,  on  the  contrary,  the  lenticular  nucleus,  as  well  as  the  thalamus,  become 
more  conspicuous.  The  internal  capsule,  being  now  well  established,  appears  as  a 
large  oblique  tract  of  white  matter,  which  completely  separates  the  two  parts  of  the 
corpus  striatum  and  lies  to  the  outer  side  of  the  thalamus  (Fig.  1008).  By  reason 
of  the  recurved  course  of  its  attenuated  tail,  in  horizontal  sections,  as  well  as  in  frontal 
ones  passing  in  front  of  the  splenium,  the  caudate  nucleus  is  twice  cut,  one  cross- 
section  of  the  nucleus  appearing  above  in  the  lateral  wall  of  the  body  of  the  ventricle 
and  the  other  in  the  roof  of  the  inferior  horn  (Fig.  967). 

The  Lenticular  Nucleus. — This  division  of  the  corpus  striatum  (nucleus  len- 
tiformis)  is  a  wedge-shaped  mass  of  gray  matter,  broken  by  laminae  of  white,  that  lies 
bordered  by  the  internal  capsule  mesially,  and  laterally  is  separated  from  the  cortex 
of  the  insula  by  a  narrow  tract  of  white  matter  containing  a  thin  stratum  of  gray  sub- 
stance, the  claustrum.  The  lenticular  nucleus  reaches  neither  as  far  forward  nor  as 
high  as  the  caudate  nucleus,  and  lies  lateral  to  both  the  latter  and  the  thalamus, 
separated  from  them  respectively  by  the  anterior  and  posterior  limbs  of  the  internal 
capsule.  Its  dorso-mesial  surface,  when  seen  in  frontal  sections,  is  directed  from 
above  downward  and  inward  ;  in  transverse  sections  (Fig.  ion)  this  surface  is 
replaced  by  an  antero-mesial  and  a  postero-mesial  face  in  correspondence  with  the 
limbs  of  the  internal  capsule.  Its  slightly  convex  lateral  surface  is  approximally 

74 


I  I/O 


HIM  AX    ANATOMY. 


FIG.  1008. 


Caudate  nuclei 


vertical  and  in  immediate  contact  with  a  thin  sheet  of  white  matter,  the  external 
capsule,  which  separates  the  nucleus  from  the  claustrum.  Its  ventral  surface-  is  hori- 
zontal and  only  feebly  curved  and  is  continuous  in  front  with  the  caudate  nucleus 

and  farther  backward,  about  its  middle,  with 
the  anterior  perforated  substance  on  the 
basal  surface  of  the  brain.  The  lenticular 
nucleus  is  unequally  subdivided  by  two  thin 
concentric  sheets  of  white  matter,  the  ex- 
ternal and  internal  medullary  laminae, 
into  three  segments.  The  outer  of  these,  the 
putamen,  is  much  the  largest  and  occupies 
the  base  of  the  nucleus,  being  bounded  by 
the  external  capsule  laterally  and  by  the 
external  medullary  laminae  mesially.  Of  its 
two  somewhat  rounded  ends,  the  anterior 
is  the  broader  and  extends  farther  forward 
and  alone  joins  the  caudate  nucleus  of  which 
it  morphologically  is  a  part  (page  1169). 
The  putamen  is  the  most  conspicuous  part  of 
the  lenticular  nucleus,  not  only  on  account  of 
its  size  but  also  by  reason  of  its  darker  color, 
in  which  respect  it  corresponds  with  the  caudate  nucleus.  This  contrast  depends 
less  upon  the  actual  pigmentation  of  the  cells  of  the  putamen  than  upon  the 
lighter  color  of  the  other  zones  of  the  nucleus.  In  consequence  of  the  small 
number  of  fibres  entering  the  external  capsule  from  the  putamen,  the  attachment 
between  the  latter  and  the  capsule  is  relatively  loose  and  the  two  structures  may  be 


Tail  of  caudate  nucleus 


Lenticular 
nucleus 

Reconstruction  of  corpus  striatum  and  thala- 
mus  ;  lateral  aspect ;  probe  lies  in  space  occupied 
by  internal  capsule.  Drawn  from  Steger  model. 


FIG.  1009. 


Superior  frontal  gyrus 


Corpus 


Septum  lucidum 


Right    lateral    ventricle, 
anterior  horn 


\ 
Internal  orbital  gyrus 


Middle  frontal  gyms 


[-Inferior  frontal  gyni.< 

—  i  'audate  niH-li'iis 

Internal  capsule 
Lenticular  nucleus 

Temporal  1<>K 
Continuity  of  caudate  and  lenticular  nuclei 


Frontal  section  of  brain  passing  through  anterior  end  of  corpus  striatum  whore  caudate  and  lenticular  nuclei  are 

continuous  below. 

readily  separated.  This  condition  influences  the  course  taken  by  extravasations  of 
blood,  \\hich  are  frequent  in  this  locality  and  may  occupy  a  lari^e  part  of  the  lateral 
surface  of  the  putamen.  The  remaining  divisions  of  the  lenticular  nucleus  are  much 
lighter  in  tint  and  together  constitute  the  globus  pallidus.  They  are  subdivided 


THE   TELENCEPHALON. 


1171 


by  the  internal  medullary  laminae  and  from  the  edge  of  the  wedge,  lying  in  contact 
with  the  internal  capsule.  Although  composed  chiefly  of  gray  matter,  all  these 
segments  of  the  nucleus,  but  particulary  the  inner  two,  are  traversed  by  numerous 
strands  of  nerve-fibres  which  break  the  continuity  of  the  gray  substance  and  produce 
an  appearance  of  radial  striation. 

The  structure  of  the  corpus  striatum  varies  in  its  several  parts,  that  of  the 
caudate  nucleus  and  the  putamen  being  almost  identical,  whilst  that  of  the  globus 
pallidus,  although  similar  in  both  zones,  differs  from  the  histological  make  up  of  the 
other  parts.  The  close  resemblance  of  the  caudate  nucleus  and  the  putamen  corre- 
sponds to  their  early  common  origin,  since  at  first  they  constitute  a  single  mass  and 
become  partially  separated  by  the  ingrowth  of  the  fibres  forming  the  anterior  part  of 
the  internal  capsule. 

The  caudate  nucleus  is  invested  throughout  the  greater  part  of  its  periphery 
by  a  dense  layer  of  fibres,  the  stratum  zonale,  which  includes  fibres  passing  both  to 

FIG.  ioio. 


Corpus  callosum 
Choroid  plexus 

Fortiix 

Thalamus, 
mesial  nucleus 

Thalamus, 
lateral  nucleus 

Mammillo- 
thalamic  tract 

Third  ventricle  — 

Anterior  pillar 

of  fornix 

Optic  tract 


Caudate  nucleus 

Internal  capsule 

Lenticular 
nucleus,  putamen 

Insula 

Globus  pallidus 

Claustrum 
Amygdaloid  nucleus 


Pituitary  body  Optic  nerve 

Frontal  section  of  brain  passing  through  caudate  and  lenticular  nuclei  and  thalamus,  showing  relation  of  internal 

capsule  to  internal  nuclei. 

and  from  the  nucleus.  The  nerve-cells  are,  for  the  most  part,  rather  small  in  size 
and  stellate  or  fusiform  in  shape  and  provided  with  numerous  dendrites  beset  with 
minute  irregularities.  They  are  chiefly  cells  of  type  I,  although  many  of  the  second 
type  are  encountered,  whose  axones  are  limited  to  the  gray  matter  and  are  not 
prolonged  as  nerve-fibres  (Kolliker). 

The  putamen  is  invested  on  its  two  sides,  particularly  on  the  mesial  one,  with  a 
fibre-layer  derived  from  the  external  medullary  lamina  and  the  external  capsule,  the 
fibres  being  chiefly  such  as  enter  the  nucleus  from  other  centres  by  way  of  the  med- 
ullary layer.  In  addition  to  nerve-cells  of  round  or  stellate  form,  Kolliker  describes 
those  of  distinctive  appearance  possessing  a  slender  fusiform  body  and  dendrites  few 
in  number  but  of  unusual  length. 

The  globus  pallidus  owes  its  characteristic  color  to  the  light  yellowish  tint  of 
the  pigment  within  its  cells  and  to  the  large  number  of  medullated  nerve-fibres  which 
traverse  its  substance,  especially  its  inner  zone.  The  nerve-cells  are  mostly  small 
and  stellate,  possessing  numerous  short  but  richly  branched  dendrites. 


1 1 72  HUMAN   ANATOMY. 

The  Connections  of  the  Corpus  Gtriatum. — Much  uncertainty  prevails  as  to  the  details  of 
the  connections  of  the  several  parts  of  the  corpus  striatum  and  little  is  known  regarding  the 
function  of  these  nuclei,  notwithstanding  their  size  ;  certain  general  principles,  however,  may  be 
accepted.as  established.  The  comparative  studies  of  Gehuchten,  Sala  and  others,  and  especially 
of  Edinger,  emphasize  that  the  corpus  striatum  is  to  be  considered  as  supplemental  to  the 
cortical  substance,  in  the  lower  vertebrates  in  which  the  cortex  of  the  cerebral  mantle  is  feebly 
developed  constituting  the  chief  mass  of  cortical  gray  matter,  and  in  the  mammals  and  man 
being  subservient  to  the  overshadowing  cortex  of  the  hemisphere.  Such  being  the  warranted 
presumption,  it  is  to  be  anticipated  that  the  striate  body  both  receives  fibres  conveying  sensory 
impulses  and  gives  off  fibres  (perhaps  motor  in  function)  originating  from  its  cells,  these  latter 
tracts  constituting  the  strio-thalamic  radiation. 

The  centripetal  or  afferent  paths  probably  include  :  (i)  the  tegmcnto-striate  fibres,  which 
are  continued  chiefly  from  the  mesial  fillet,  and  perhaps  also  from  the  red  nucleus  and  subthal- 
amic  region,  by  way  of  the  internal  capsule,  to  end  around  the  cells  of  the  putamen  and  head  of 
the  caudate  nucleus  ;  (2)  the  thalatno- striate  fibres,  already  mentioned  in  connection  with  the 
thalamus  (page  1 123),  which  pass  from  the  thalamus  either  by  way  of  the  internal  capsule  directly 
to  the  caudate  nucleus,  or  by  way  of  the  ansa  lenticularis  to  the  putamen  or,  traversing 
the  medullary  laminae,  to  the  caudate  nucleus.  No  doubt  many  of  the  fibres  which  enter  the 
lenticular  nucleus  do  not  end  within  the  latter,  but  traverse  its  substance  as  part  of  their  path  to 
the  cerebral  cortex. 

The  centrifugal,  or  efferent  fibres,  which  arise  from  the  cells  of  the  corpus  striatum  include  : 
(i)  the  strio-thalamic  fibres,  passing  from  the  major  divisions  of  the  striate  body,  which 
comprise  (a)  those  from  the  caudate  nucleus  to  the  thalamus  direct ;  (6)  those  which  traverse 
the  internal  capsule  and  the  medullary  laminae  and,  joining  fibres  from  the  putamen,  pass  by- 
way of  the  ansa  lenticularis  to  the  thalamus  ;  (c )  those  from  the  putamen  which  reach  the 
thalamus  by  passing  partly  by  way  of  the  globus  pallidus  and  partly,  in  greater  numbers,  by 
means  of  the  ansa  lenticularis.  (2)  Strio-peduncnlar  fibres,  well  represented  in  the  brains 
of  the  lower  animals  as  the  continuation  of  the  basal  tract  of  the  fore-brain  (Edinger),  which 
pass  from  the  caudate  nucleus,  and  probably  from  the  lenticular  nucleus  also,  into  the 
sub-thalamic  region  and  the  cerebral  peduncle,  within  the  latter  forming  the  stratum  inter- 
medium closely  related  to  the  substantia  nigra.  Whether  cortico-striate  fibres,  extending 
from  the  cerebral  cortex  to  the  corpus  striatum,  exist  in  man  is  uncertain,  Dejerine  denying 
their  presence,  whilst  Edinger  regards  the  presence  of  a  meagre  number  of  such  bundles 
as  established. 

The  Claustrum. — The  claustrum  is  a  thin  lamina  of  gray  substance  embedded 
within  the  white  matter  intervening  between  the  lateral  surface  of  the  putamen  and 
the  cortex  of  the  island  of  Reil.  Its  mesial  surface  is  smooth  and  parallel  with  the 
outer  aspect  of  the  putamen,  from  which  it  is  separated  by  the  thin  tract  of  white 
matter  constituting  the  external  capsule.  Its  lateral  surface  presents  a  series  of 
elevations  and  depressions  which  in  a  general  way  repeat  the  contour  of  the  gray 
cortical  lamina  of  the  insula,  the  intervening  layer  of  white  matter  being  sometimes 
called  the  capsula  extrema.  Seen  in  horizontal  sections  (Fig.  ion),  the  claustrum 
fades  away  both  in  front  and  behind  ;  in  frontal  sections  (Fig.  1010),  however,  whilst 
it  gradually  disappears  above,  below  the  claustrum  materially  thickens  and  mesially 
becomes  continuous  with  the  anterior  perforated  substance.  Upon  comparative  and 
developmental  grounds,  the  claustrum  must  be  regarded  as  a  separated  portion  of 
the  corpus  striatum.  Its  nerve-cells  are,  for  the  most  part,  small  and  either  stellate 
or  fusiform  in  outline.  Nothing  is  known  with  certainty  as  to  the  course  or  connection 
of  its  fibres. 

The  Amygdaloid  Nucleus.  —This  structure  (nucleus  amygdalae)  comprises 
a  considerable  rounded  mass  of  gray  substance  (Fig.  1010)  which  occupies  the 
fore-part  of  the  temporal  lobe  and  lies  in  close  proximity  with  the  uncus,  overlying 
the  extremity  of  the  inferior  horn  of  the  lateral  ventricle.  Anteriorly  it  is  continuous 
with  the  cortical  gray  matter  of  the  temporal  lobe  as  a  thickened  portion  of  which 
it  may  be  regarded.  Its  lower  part  receives  the  tail  of  the  caudate  nucleus  and 
close  to  this,  the  taenia  semicircularis  (page  116),  which  accompanies  the  recurved 
nuclear  tail  in  its  descent  within  the  roof  of  the  inferior  horn.  The  nucleus 
approaches,  if  indeed  it  does  not  touch,  the  anterior  perforated  substance,  and  above 
corner  into  intimate  relations  with  the  lenticular  nucleus.  It  is  highly  probable  that 
the  nucleus  amygdala.-  forms,  along  with  the  uncus  and  the  hippocampus,  a  part 
of  the  olfactory  cortex  (Dejerine). 


THE   TELENCEPHALON. 


"73 


The  Internal  Capsule. — Repeated  mention  has  been  made  of  the  important 
tract  of  white  matter  bearing  the  name  of  internal  capsule  (capsula  interim);  its 
description,  therefore,  may  be  appropriately  undertaken  at  this  place.  It  is  a  broad, 
compact  band  of  nerve-fibres  which  passes  between  the  three  large  basal  ganglia, 
namely,  the  caudate  and  the  lenticular  nuclei  and  the  thalamus.  Although  the  details 
of  the  internal  capsule  vary  with  differences  both  of  direction  and  of  position  of  the 


FIG.  ion. 


Spleniun 
of  corpu: 
callosum 


Calcarine  fissure 


horn  of 

lateral 

ventricle 


Horizontal  sections  of  brain,  A  at  higher  level  than  B.  which  passes  through  lower  part  of  corpus  striatum  where 
caudate  and  lenticular  nuclei  are  continuous;  relations  of  limbs  of  internal  capsule  to  internal  nuclei  seen  on  right  side. 

planes  of  section,  its  general  relation  to  these  three  masses  of  gray  matter  is  con- 
stant, the  caudate  nucleus  and  the  thalamus  always  lying  to  its  inner  side  and  the 
lenticular  nucleus  to  its  outer  aspect.  When  exposed  by  frontal  sections  passing 
through  the  anterior  part  of  the  lateral  ventricles  (Fig.  1010),  the  internal  capsule 
appears  as  a  broad,  oblique  stripe,  extending  from  above  downward  and  inward, 
bounded  by  the  large  caudate  nucleus  mesially,  the  lenticular  nucleus  laterally, 
and  below  by  the  gray  substance  establishing  continuity  between  the  two  nuclei. 


H74 


III  MAN    ANATOMY. 


FIG.  1012. 


Seen  in  frontal  sections  passing  some  distance  behind  the  preceding  section, 
whilst  the  capsule  is  limited  laterally  by  the  lenticular  nucleus,  its  mesial  boundary 
now  includes  the  caudate  nucleus,  the  taenia  semicircularis  and  the  thalamus.  Still 
farther  back  (Fig.  968),  the  internal  capsule  is  bounded  internally  in  addition  by 
the  subthalamic  structures  and  becomes  continuous  below  with  the  crusta  of  the  cere- 
bral peduncle.  An  upper  and  a  lower  part  of  the  capsule  are  therefore  recognized, 
the  former — between  the  lenticular  nucleus  on  the  one  side,  and  the  caudate  nucleus 
on  the  other — is  known  as  the  thalamic  region  (rcgio  thalamica  capsulac  internae), 
whilst  that  between  the  lenticular  nucleus  and  the  subthalamic  structures  is  termed 
the  subthalamic  region  (regio  subthalamica). 

Viewed  in  horizontal  sections  (Fig.  ion,  A),  the  capsule  appears  not  only 
much  more  extensive,  but  is  seen  to  consist  of  two  mesially  converging  parts,  a 
shorter  anterior  limb  (pars  frontalis)  and  a  longer  posterior  limb  (pars  occipitalis). 
The  two  limbs  form  an  angle  which  opens  outward  and  encloses  on  two  sides  the 
gray  triangle  of  the  lenticular  nucleus.  The  junction  of  the  two  mesially  converging 
limbs  forms  the  knee,  or  genu,  of  the  internal  capsule  which  points  inward  and  lies 
opposite  the  taenia  semicircularis,  between  the  caudate  nucleus  and  the  thalamus. 
At  deeper  planes  (Fig.  ion,  j9),  passing  through  the  level  of  the  continuity 
between  the  two  parts  of  the  corpus  striatum,  the  anterior  limb  is  greatly  reduced 
in  length  or  entirely  disappears,  the  posterior  one  being  prolonged  into  the  cerebral 
peduncle. 

The  importance  of  the  internal  capsule  will  be  appreciated  when  its  function  as 
the  great  pathway  connecting  the  cerebral  cortex  with  the  lower  lying  centres  is 
recalled.  Its  fibres,  both  corticipetal  and  corticifugal,  after  passing  beyond,  or  before 

coming  under  the  restraint  of  the  boundaries  of  the 
capsule,  as  the  case  may  be,  radiate  to  and  from  all 
parts  of  the  hemisphere,  and  in  this  manner  form  the 
striking  fan-shaped  fibre-mass  known  as  the  corona 
radiata,  which  continues  the  internal  capsule  upward 
to  the  cerebral  cortex.  The  radiating  strands  of  this 
great  tract  interlace  with  the  radiation  of  the  corpus 
callosum  and  thereby  contribute  a  large  part  of  the 
fibres  composing  the  oval  centre  of  white  matter  within 
the  hemisphere. 

The  anterior  limb  of  the  internal  capsule  (pars  lenticulocau- 
data)  includes  the  front  third  of  the  tract  and  extends  from  the 
genu  forward  and  outward.  It  contains  fibres  passing  both 
toward  and  away  from  the  cortex.  Its  corticipetal  fibres  are  : 

(1)  the  thalamo-frontal,  which  pass  from  the  thalamus  by  way 
of  its  frontal  stalk  through  the  anterior  limb  of  the  internal  cap- 
sule and  the  .corona  radiata  to  the  cortex  of  the  frontal  lobe  ; 

(2)  the  thalamo-sfriatc,  which  also  pass  from  the  thalamus  into 
the  internal  capsule  and  proceed  to  the  caudate  and  lenticular 
nuclei.     The  corticifugal  fibres  include  :  (i )  \hefronto-ponf i>tt\ 
which  arise  in  the  cortex  of  the  frontal  lobe  and  descend  by 
way  of  the  corona  radiata,  the  anterior  limb  of  the  internal 
capsule,  the  crusta  of  the   cerebral  peduncle  and  the  ventral 
tracts  of  the  ponsto  end  around  the  cells  of  the  pontine  nucleus 
as  links  in  the  connection  between  the  cerebral  and  the  cere- 
bellar  cortex    (page    1094)  ;     (2)    the  frotito-ffiti/ainic,    which 
extend  from  the  cortex  of  the  frontal   lobe  to  the  thalamus  ; 
and  (3)  the  strio-thalamii ,  which  proceed  from  the  caudate  and 
lenticular  nuclei  to  the  thalamus. 

The  posterior  limb  of  the  internal  capsule  (pars  lenticulo- 
thalamica)  extends  backward,  outward  and  downward  from 
the  genu,  and  includes  the  remaining  two-thirds  of  tin-  tiact.  Its  hind  part  extends  beyond 
the  posterior  limit  of  the  lenticular  nucleus,  hence  the  posterior  limb  is  subdivided  into  a 
Icntii  nlar  and  a  retrolcnticular  portion.  As  does  the  anterior  limb,  so  also  does  the  posterior 
limb  of  the  capsule  contain  both  corticipetal  and  corticifugal  fibres. 

The  lenticular  portion  includes  corticipetal  fibres:  (  i  )  the  thalawo-cortical,  which  issue  from 
the  lateral  and  lower  aspect  oi"  the  thalamus,  traverse-  the  internal  capsule  and  to  a  considerable 


Diagram  showing  relative  posi- 
tions of  chief  tracts  in  internal  cap- 
sule (A)  and  in  crusta  of  cerebral 
peduncle  (H)\  F-T,  fronto-tlmlu- 
mic;  F-P,  f  ronto-pontine ;  T-O-P, 
temporo-occipito- pon  tine;  C-Ji,cor- 
tico-bulbar;  C-S,  cortioo-spmal  ;  .V, 
teg[tnental  sensory ;  OK,  optic  rad- 
iation. 


THE   TELENCEPHALON.  1175 

number,  the  lenticular  nucleus  and  the  external  capsule  and  proceed  to  the  cortex  of  the  'hind 
part  of  the  frontal  and  of  the  parietal  lobe;  and  (2)  probably  some  thalamo-lenticular  fibres 
which  pass  from  the  thalamus  to  the  lenticular  and,'  perhaps,  the  caudate  nucleus. 
The  corticifugal  fibres  include  :  ( i )  the  important  motor  cortico-bulbar  and  cortico- spinal 
tracts,  collectively  often  called  the  pyramidal  tracts,  which  descend  from  the  precentral 
(Rolandic)  cortical  region  through  the  corona  radiata  and  the  fore-part  of  the  posterior  limb  of 
the  internal  capsule  into  the  crusta  of  the  cerebral  peduncle  and  thence  to  the  appro- 
priate levels  of  the  brain-stem  or  of  the  spinal  cord.  A  tract  supplementary  to  the  pyramidal 
motor  paths,  the  cortico-rnbral  fibres,  must  be  mentioned.  These  arise  from  the  cortex 
(perhaps  of  the  parietal  lobe)  and  descend  through  the  lenticular  portion  of  the  posterior 
limb  to  the  mid-brain  where  they  end  in  relation  with  the  red  nucleus.  (2)  The  cortico- 
thalatnic  fibres,  which  converge  from  the  cerebral  cortex  to  the  thalamus.  The  retro- 
lenticular  portion  of  the  posterior  limb  is  traversed  by  important  corticipetal  fibres  con- 
cerned in  conveying  impressions  of  special  sense,  as  ( i )  those  of  the  optic  radiation, 
which,  issuing  as  the  occipital  stalk,  connect  the  thalamus  and  the  lateral  geniculate  and 
the  superior  quadrigeminal  body  with  the  occipital  cortex  ;  and  (2)  those  of  the  auditory 
radiation,  which  link  together  the  mesial  geniculate  and  the  inferior  quadrigeminal  body 
with  the  auditory  cortical  area  in  the  temporal  lobe.  The  corticifugal  fibres  are  represented 
by  (i)  the  temporo-occipito-pontine  tracts,  which  pass  from  the  cerebral  cortex  through  the 
retrolenticular  portion  of  the  capsule  into  the  crusta  of  the  cerebral  peduncle  and  thence 
to  the  pontine  nucleus  within  the  ventral  part  of  the  pons  ;  and  (2)  cortico-thalamic  fibres, 
which  course  in  reverse  order  through  the  optic  radiation  to  end  within  the  thalamus  and 
lateral  geniculate  body. 

The  relative  positions  of  the  longer  tracts  composing  the  internal  capsule,  as  seen  in  hori- 
zontal sections,  are,  in  a  general  way,  indicated  schematically  in  Fig.  1012.  The  anterior  limb 
is  shared,  from  before  backward,  by  the  fronto-thalamic  and  the  fronto-pontine  tracts  in  the 
order  named.  The  genu  is  appropriated  by  the  cortico-bulbar  tracts,  the  facial  fibres  lying 
immediately  in  advance  of  the  hypoglossal.  The  succeeding  part  of  the  posterior  limb, 
approximately  one-third,  affords  passage  to  the  cortico-spinal  or  pyramidal  tracts.  Next  follows 
a  narrow  segment  devoted  to  the  tegmental  sensory  tracts,  behind  which  the  occipito-temporo- 
pontine  tract  occupies  a  small  area,  the  last  part  of  the  retrolenticular  field  being  taken  up  by 
the  optic  radiation. 

STRUCTURE  OF  THE  CEREBRAL  CORTEX. 

The  surface  of  the  hemispheres  is  everywhere  clothed  with  a  thin  continuous 
stratum  of  cortical  gray  matter;  which  encloses  the  white  medullary  substance  com- 
posed of  the  interlacing  tracts  of  nerve-fibres.  This  cortical  sheet  varies  in  thick- 
ness not  only  in  the  same  area,  being 

thicker  over  the  summit  than  at  the  sides  IG-  IOI3- 

of  the  convolutions  or  at  the  bottom  of  stratum  zonaie- 

the  bounding  fissures,    but   in   different     Externaigray  stratum- 

r  M.I.      t.         •       i  T.U  Outer  stripe  of 

regions  of  the  hemisphere.  Its  average 
thickness  is  about  3  mm. ,  but  where  it 
borders  the  upper  end  of  the  Rolandic 
fissure,  particularly  in  the  paracentral 
lobule,  this  increases  to  over  5  mm. , 
whilst  over  the  frontal  and  occipital  poles 
the  thickness  of  the  cortex  is  reduced  to 
almost  2  mm.  The  entire  superficial 
extent  of  the  cortex  of  the  two  hemi- 
spheres  has  been  estimated  to  be  about 
2000  sq.  cm.,  of  which  scarcely  one- 
third  is  exposed  surface,  the  remainder  Caicarine  fissure 

Frontal  section  of  hemisphere   including-  cortex  sur- 

On  examining  sections  of  the  fresh  rounding  calcarine  fissure;  stripe  of  Gennari  (outer  stripe 
...  °  of  Baillarger)  is  here  unusually  distinct.  X  3- 

brain,     the     cortex     does     not     appear 

uniformly  tinted,  but  exhibits,  even  to  the  unaided  eye,  an  indistinct  division 
into  alternate  light  and  dark  layers.  From  without  in  these  are  :  (i)  a  thin 
peripheral  layer  of  whitish  color,  the  stratum  zonale ;  (2)  a  thicker  layer  of 
grayish  hue,  the  external  gray  stratum  ;  (3)  a  thin  lighter  band,  the  outer  stripe 
of  Baillarger ;  and  (4)  a  somewhat  broader,  yellowish-red  zone,  the  internal  gray 


1176 


HI  MAN   ANATOMY. 


stratum — four  layers  being  more  or  less  clearly  recognizable.  In  certain  localities, 
as  in  the  precentral  convolution,  the  inner  gray  lamina  is  subdivided  by  an 
additional  white  line,  the  inner  stripe  of  Baillargcr.  In  the  vicinity  of  the 
calcarine  fissure,  particularly  in  the  adjacent  part  of  the  cuneus,  the  outer  stripe  of 
Baillarger,  whilst  narrow,  is  unusually  distinct  and  confers,  therefore,  a  character- 
istic appearance  upon  the  cortex  of  this  region  (Fig.  1013).  The  band  in  this 
location  receives  the  name  of  the  stripe  of  Gennari,  or  the  stripe  of  Vicq  cT  A'.yr. 
In  recognition  of  the  priority  of  description,  Gennari's  name  is  sometimes  applied 
to  the  external  stripe  of  Baillarger  wherever  found.  The  significance  of  these 
light  colored  strata  will  be  pointed  out  in  connection  with  the  intimate  structure 
of  the  cortex,  suffice  it  here  to  note  that  the  stripes  of  Baillarger  correspond  to 
zones  in  which  the  felt-work  of  horizontal  cell-processes  is  unusually  dense,  the 
stratum  zonale  corresponding  to  a  compact  layer  of  fibres  running  parallel  with 
the  surface.  Occasionally  a  condensation  of  tangential  fibres  immediately  beneath 
the  stratum  zonale  produces  the  appearance  of  an  additional  light  line,  which  in 
honor  of  its  discoverer,  is  known  as  the  stripe  of  Bechterew. 

The  essential  histological  elements  of  the  cerebral  cortex  are  the  nerve-cells  and 
the  nerve-fibres.       The  importance  of  the  former  is  evident  when  their  three-fold 

activity  is  recalled — (i)  as  receptors  of 

FIG.  1014.  corticipetal  impulses,  (2)  as  distributors 

of  the  impressions  so  received  to  other 
parts  of  the  brain,  and  (3)  as  originators 
of  corticifugal  impulses  which  control 
the  nuclei  from  which  immediately  arise 
the  motor  nerves.  No  single  method 
of  preparation  suffices  to  display  satis- 
factorily both  groups  of  structural 
elements,  for  when  stains  are  employed 
which  best  bring  out  the  cells,  the 
fibres  are  inadequately  shown  ;  and, 
conversely,  when  methods  adapted  for 
the  demonstration  of  the  fibres  are 
followed,  the  cells  are  but  imperfectly 
displayed.  It  is  advantageous,  there- 
fore, to  study  the  histological  details 
of  the  brain  by  more  than  a  single 
method,  combining  the  results  ob- 
tained by  the  use  of  cellular  stains 
with  those  yielded  by  procedures  ex- 
hibiting the  fibres.  Among  the  latter, 
the  well  known  method  of  Weigert,  or 
its  modifications,  has  been  of  great 
service  in  extending  our  knowledge 
concerning  the  various  fibre-tracts. 
The  methods  of  silver  impregnation 
introduced  by  Golgi,  although  not 
producing  true  staining  but  only  in- 
crustations on  the  cell  and  its  pro- 
cesses, have  materially  advanced  our 
knowledge  concerning  the-  form  of  the 
cell-bodies  and  the-  number  and  c-xtent 
of  the  processes  of  the  neurones. 

\Yhilst  varying  as  to  details  in 
different  regions,  the  cerebral  cortex 
presents  a  -en. -ral  plan  of  Mnuture  which  may  be  considered:  (0)  in  relation  to 
the  nerve-cells  and  (  /> )  in  relation  to  the  nerve-fibres. 

The  Nerve-Cells  of  the  Cortex.— When  sections  cut  perpendicular  t 
surface  of   the  convolution  arc  staint-d  with  basic    stains   (Fig-    y\S)   <"'  prj-pan-t 
after  silver   impregnation    (Fig.    1016),    the    cerebral   cortex    exhibits    tour    layers. 


Subpial  layer 
Tangential  fibres 

Stratum  zonale 


Layer  of  small 
pyramidal  cells 


Outer  stripe  of 
Baillarger 

Layer  of  large 
pyramidal  cells 


Layer  of  poly- 
morphic cells 


Medullary  fibres 


Diagram  showing  constituents  of  cerebral  cortex ; 
cells  in  tin-  right  halt,  1'ihrcs  in  left  half  of  figure;  A,  /?, 
large  and  small  pyramidal  cells;  C.  polymorphic  cells; 
D,  cell  of  Martinotti;  K.  cell  of  type  II;  F;  association 
d-ll;  /,  /,  corticipetal  fibres;  2,  2,  corticifugal  fibres 
•  a  \Min-s  of  pyramidal  cells) ;  JV,  N,  neuroglia  cells. 


THE   TELENCEPHALON. 


FIG.  1015. 


BBSiPia 


Stratum 
zonale 


I  Small  pyra- 
"midal  cells 


which,  from  without  inward,  are:  (i)  the  stratum  zonale,  (2)  the  layer  of  small 
pyramidal  cells,  (3)  the  layer  of  large  pyramidal  cells,  and  (4)  the  layer  of  poly- 
morphic cells.  Although  each  presents  characteristics  which  are  distinctive,  with 
the  exception  of  the  junction  between  the  first  and  second  layers  where  the  change 
is  well  defined,  no  sharp  demarcation  separates  the  strata,  each  passing  insensibly 
into  the  adjoining  layer.  Neither  are  the  modifications  which  distinguish  the 
cortex  of  certain  regions  abruptly  assumed,  one  type  of  cortical  structure  being 
gradually  replaced  by  another  without  sudden  transition. 

The  stratum  zonale,  also  known  as  the  molecular  stratum,  underlies  the  pia 
and  measures  about  .25  mm.  in  thickness.  The  layer  contains  few  nerve-cells  and 
appears  subdivided  into  (a)  a  narrow  peripheral  zone,  from  .010 — .030  mm.  in  width, 
composed  of  a  subpial  condensation  of  neuroglia 
and  ($)  a  deeper  zone  characterized  by  numer- 
ous fibres  or  processes,  which  course  parallel  to 
the  surface,  and  a  meagre  number  of  nerve-cells 
whose  most  distinctive  representatives  are  small 
fusiform  elements  (Co/at's  cells^)  provided  with 
long  tangentially  directed  processes.  The  latter 
give  off  short  collaterals,  which  ascend  towards 
the  surface,  and  intermingle  with  the  number- 
less terminal  filaments  derived  from  the  periph- 
erally coursing  processes  of  the  pyramidal  and 
outer  cells  lying  at  deeper  levels  and  from  the 
corticipetal  fibres  which  continue  from  the 
white  core  of  the  gyrus  into  the  outermost 
layer  of  the  cortex. 

The  layer  of  small  pyramidal  cells  is 
marked  off  from  the  stratum  zonale,  which  it 
about  equals  in  thickness,  with  some  distinctness 
since,  in  contrast  to  the  last-mentioned  zone, 
it  contains  very  many  cells.  These,  as  indicated 
by  the  name  of  the  stratum,  are  of  small  size 
(.007 — .010  mm.)  and  pyramidal  form,  at 
least  in  the  deepest  part  of  the  layer.  In  the 
superficial  part  the  cells  are  rounded  or  irregu- 
larly triangular,  but  they  assume  the  distinctive 
pyramidal  outline  as  they  approach  the  sub- 
jacent layer,  whose  elements  they  resemble  in 
possessing  apical  and  lateral  processes. 

The  layer  of  large  pyramidal  cells  con- 
tains the  most  distinctive  neurones  of  the  cere- 
bral cortex.  It  measures  usually  about  1.25 
mm.  in  thickness,  but  in  some  localities  much 
more,  and  blends  with  the  adjoining  layers 
without  sharp  boundaries.  The  cells  in- 
crease in  size  but  diminish  in  numbers  as 
they  are  traced  from  the  second  layer  inward, 
the  largest  (from  .020 — .040  mm.  in  width)  and 
most  characteristic  lying  in  the  deepest  part 
of  the  stratum.  The  typical  pyramidal  cell 
possesses  a  conical  body,  triangular  in  section, 
the  apex  of  which  is  continued  into  a  long 
tapering  dendrite,  the  apical  process,  which 
extends  toward  the  periphery  for  a  variable  but  usually  considerable  distance, 
depending  upon  the  position  of  the  cell.  Upon  gaining  the  stratum  zonale,  towards 
which  the  apical  dendrite  is  always  directed,  the  process  breaks  up  into  a 
number  of  end-branches  that  run  parallel  with  the  surface  and  contribute  to  the 
fibre-complex  of  the  outer  layer.  During  its  journey  to  the  surface,  the  apical 
dendrite  gives  off  an  uncertain  number  of  branches  that  continue  horizontally  and, 


m 


y  Large  pyra- 
''  midal  cells 


rc£  Polymorphic 
cells 


Section  of  cerebral  cortex.     X  90. 


1178 


HUMAN   ANATOMY. 


Small  pyra- 
~1  tnidal  cells 


with  the  collaterals  and  similarly  directed  processes  from  other  cells,  take  part 
in  producing  the  felt-work  giving  rise  to  the  outer  stripe  of  Baillarger.  From 
the  deeper  or  basal  surface  of  the  cell  arises  the  delicate  centrally  directed  a.votic, 
which,  penetrating  the  intervening  fourth  layer,  acquires  a  medullary  coat  and 
enters  the  white  core  of  the  convolution  as  one  of  the  component  nerve-fibres. 
The  axone  gives  off  one  or  more  collaterals  which,  after  a  shorter  or  longer 
course,  establish  relations  with  other  and  often  remote  cells.  In  addition  to  the 
two  chief  processes,  the  peripherally  directed  apical  dendrite  and  the  centrally 
coursing  axones,  a  variable  number — from  four  to  twelve — of  secondary  lateral 

~  dendrites   spring    from    the    basal 

FIG.  1016.  ,  .  F      °    —. 

angles  01  the  cell.     1  hese  processes 

usually  divided  ichotomously,  each 
succeeding  pair  of  branches  in  turn 
splitting  into  twigs,  until  the  den- 
drite is  resolved  into  an  end-brush 
of  fibrillae  which  aid  in  producing 
an  intricate  felt-work  of  finest 
threads.  Each  pyramidal  cell  con- 
tains a  conspicuous  spherical  or 
ellipsoidal  nucleus,  within  which  a 
distinct  nucleus  is  usually  distin- 
guishable. The  cytoplasm  exhibits 
a  striation  and,  in  addition  to  the 
masses  of  tigroid  substance,  the 
Nissl  bodies,  a  mass  of  brownish 
pigment  granules.  The  larger 
pyramidal  cells  are  surrounded 
by  an  evident  pericellular  lymph- 
space. 

The  layer  of  polymorphic 
cells  includes  a  large  number  of 
small  nerve-cells,  from  .008 — .010 
mm.  in  diameter,  whose  forms 
vary  greatly,  irregular,  spherical, 
triangular,  stellate  and  fusiform 
elements  being  present.  Small 
pyramidal  cells  are  also  often  seen 
within  this  layer.  In  contrast  to 
dendrites  of  the  typical  pyramidal 
cells,  those  of  the  polymorphic 
elements,  although  peripherally 
directed,  do  not  reach  the  stratum 
zonale  but  end  before  gaining  the 
outermost  layer.  Their  axones 
pass  into  the  subjacent  fibre- 
layer.  The  radial  disposition 
of  the  groups  of  fibres  within 
the  deepest  stratum  of  the 
cortical  substance,  limit  the 
polymorphic  cells  chiefly  to  the 
consequently  appear  arranged  in  a 


Nerve- cells    of 
pregnation.    X  90. 
T.  G.  Lee. 


cerebral 
Drawn 


--t 


<oit<-\    as    so-n    after  silver    im- 
from    preparation   made    by    Pro- 


interfascicular   areas,    within    which    the    cells 
somewhat  columnar  order. 

Within  the  deeper  layers  of  the  cortex,  therefore  among  the  polymorphic 
and  the  pyramidal  elements,  two  additional  varieties  of  nerve-cells  arc  encountered. 
These  are  the  cells  of  Martinotti  and  the  cells  of  Golgi. 

The  cells  of  Martinotti  arc-  of  small  si/e  and  triangular  or  spindle-form  in 
out-line  and  particularly  distinguished  by  the  unusual  direction  of  their  axoiu-s. 
These  processes  pass  towards  the  surface  and  within  the  stratum  /onale  divide 
into  branches,  which  are  continued  horizontally  in  the  felt-work  of  tangential  tibre>.  A~> 


THE   TELENCEPHALON. 


1179 


FIG.  1017. 

•:•"-  '••• 


Tangential 
fibre-layer 


Supraradial 
felt-work 


Outer  stripe 
of  Baillarger 


in  other  parts  of  the  central  nervous  system,  so  too  in  the  cerebral  cortex  there  is 
found  a  sprinkling  of  Golgi'  s  cells  of  type  II.  Although  both  dendrites  and 
axones  of  these  cells  undergo  elaborate  arborization,  the  axone  is  confined  to  a 
limited  territory  in  the  vicinity  of  the  cell  and,  therefore,  never  reaches  the 
stratum  zonale. 

Neuroglia  cells  are  present  in  all  parts  of  the  cerebral  cortex  and,  whilst  in 
a  general  way  they  send  fibrils  in  all  directions  between  the  nervous  elements, 
which  they  then  support,  the  arrangement  of  the  fibrillae  is  fairly  definite  in  certain 
strata.  Thus  within  the  subpial  condensation  of  the  neuroglia,  the  glia  cells  send 
most  of  their  processes  as  inwardly  directed  brushes.  The  cells  within  the  deeper 
part  of  the  cortex  give  off  their  processes  in  two  chief  groups,  one  extending 
towards  the  periphery  and  the  other  towards  the  white  core. 

The  Nerve-Fibres  of  the  Cortex. — When  viewed  in  suitably  stained  sections 
cut  parallel  with  their  general  course,  the  cortical  nerve-fibres  do  not  appear  as  a  uni- 
form layer,  but  as  radially  disposed  bundles  which  gradually  become  less  distinct  as 
they  traverse  the  cortex  and  finally  disappear 
at  about  the  level  of  the  outer  border  of  the 
layer  of  large  pyramidal  cells.  The  radial 
fibres  are  partly  afferent  and  partly  efferent. 
The  corticifugal  components,  which  predomi- 
nate, are  largely  the  centrally  directed  axones 
of  the  pyramidal  and  the  polymorphic  cells 
which  are  continued  as  the  axis-cylinders  ol 
the  fibres  composing  the  subcortical  white 
matter.  The  peripherally  coursing  axones  of 
the  cells  of  Martinotti  also  contribute  to  the 
production  of  the  fibre-radii.  The  coiticipetal 
constituents  of  these  tracts  include  the  nerve- 
fibres  which  are  derived  from  cells  situated 
more  or  less  remote  from  the  convolution  in 
which  the  fibres  (their  axones)  end.  Such, 
for  example,  are  the  thalamo-cortical  and  the 
tegmento-cortical  fibres,  as  well  as  the  many 
commissural  fibres  that  arise  in  the  opposite 
hemisphere  and  cross  by  way  of  the  corpus 
callosum.  Although  for  the  most  part  the 
corticipetal  fibres  end  at  various  levels  in 
arborizations  around  the  pyramidal  cells,  some 
are  continued  into  the  stratum  zonale  where, 
breaking  up  into  horizontal  fibrillae,  they  assist 
in  producing  the  tangential  zone. 

The  spaces  between  these  radial  bundles 
are  occupied  by  a  delicate  interlacement,  the 
interradial  felt- work,  which  is  composed 
in  large  part  of  the  lateral  and  collateral 
processes  of  the  cells.  Within  the  third 
layer,  the  horizontally  coursing  collaterals 
and  processes  of  the  large  pyramidal  cells 
form  a  complex  of  unusual  intricacy,  which 
condensation  gives  rise  to  the  outer  stripe 
of  Baillarger.  Beyond  the  outer  ends  of  the  radial  fibre-bundles,  the  intercel- 
lular ground-work  is  occupied  by  a  second  delicate  interlacement  of  processes 
and  collaterals,  the  supraradial  felt-work  of  Edinger  ;  whilst  immediately 
beneath  the  narrow  subpial  neurogliar  zone  innumerable  delicate  terminal  fibrillae 
course  horizontally  and  parallel  with  the  surface  and  constitute  the  tangential 
fibre-layer.  The  components  of  this  layer  are  the  terminal  branches  of  the 
dendrites  of  the  pyramidal  and  polymorphic  cells  and  the  axones  of  the  cells  of 
Martinotti,  as  well  as  the  main  and  secondary  processes  of  the  fusiform  elements 
of  the  stratum  zonale. 


Interradial 
felt-work 


Radial  fibres 


Section  of  cerebral  cortex  stained  to  show  fibres. 
X  21. 


n8o 


HUMAN   ANATOMY. 


FIG.  1018. 


Choroid  plexus __ 

Lateral 
ventricle 


Alveus  covering 
hippocampus 


Fimbria 


The  evident  purpose  of  the  horizontally  directed  processes  and  collaterals  being  to  bring 
into  relation  different  cortical  cells,  such  association  tracts  become  evident  only  after  the  neces- 
sity for  the  exercise  of  the  corresponding  psychic  functions  has  arisen.  Hence  in  the  cortex  of 
young  children  the  strata  of  horizontal  fibres  are  very  feebly  developed.  With  the  progressive 
advance  of  intellectual  capacity,  the  association  paths  become  correspondingly  more  marked, 
according  to  the  suggestive  observations  of  Kaes,  the  increase  continuing  beyond  even  middle 
life.  Whether  this  augmentation  is  due  to  actual  increase  in  the  number  of  association  fibres, 
or,  as  suggested  by  Edinger,  is  dependent  upon  the  further  growth  and  myelination  of  collaterals 
already  present  in  an  immature  condition,  is  uncertain. 

Local  Variations  in  the  Cerebral  Cortex. — It  has  been  pointed  out,  in 
prefacing  the  foregoing  description  of  the  structure  of  the  cerebral  cortex,  that, 
whilst  in  the  main  certain  features  are  common  to  the  cortex  wherever  well  devel- 
oped, more  or  less  evident  variations  occur  in  different  localities.  Such  variations 
are,  for  the  most  part,  slight  and  depend  upon  the  size  and  number  of  the  nerve-cells 
and  the  richness  and  direction  of  the  nerve-fibres — changes  which  produce  alterations 
in  the  relative  proportions  of  the  strata.  The  width  of  the  stratum  zonale  is  almost 
constant  and  subject  to  little  modification,  being  usually  well  defined  from  the  layer 
of  small  pyramidal  cells.  The  layer  of  the  large  pyramidal  cells,  on  the  contrary, 
exhibits  considerable  variation,  either  in  increased  thickness,  as  in  the  precentral 

gyrus,  or  in  diminished 
breadth,  as  in  the  occipital 
lobe.  The  layer  of  poly- 
morphic cells  is  fairly 
uniform,  but  within  the 
precentral  convolutions 
is  reduced  almost  to 
disappearance,  although 
Gyrus  dentatus  the  pyramidal  cells  of 
the  superimposed  (third) 
layer  are  here  of  unusual 
size.  Such  variations  in 
the  histological  features 

^^^^^^^^  of   the   cortex  are  prob- 

"^-W.,'  ably   correlated  with  dif- 

Frontal  section  across  left  hippocampus  and  gyrus  dentatus.     X  2%. 

of    its    various    regions, 

although  the  exact  relations  between  such  differences  are  in  many  cases  still  obscure. 
Disregarding  the  cortical  regions  which  are  profoundly  modified  by  their  rudi- 
mentary character,  such  as  the  olfactory  lobe  (page  1152),  apart  from  minor  varia- 
tions in  details,  the  cortex  of  the  greater  part  of  the  frontal,  parietal,  occipital,  temporal 
and  limbic  lobes  and  of  the  insula  closely  corresponds  in  its  structure.  That  of  the 
motor  (Rolandic)  region,  of  the  calcarine  (visual)  area  of  the  occipital  lobe,  and 
of  the  hippocampus,  dentate  gyrus  and  adjacent  part  of  the  hippocampal  gyrus, 
however,  presents  modifications  which  call  for  brief  description. 

The  Rolandic  cortex  of  the  precentral  gyrus,  particularly  towards  the  upper  margin  of  the 
hemisphere,  of  the  paracentral  lobule  and  of  the  adjoining  part  of  the  postcentral  gyrus — the 
great  cortical  motor  area  of  the  hemisphere — is  distinguished  by  the  great  breadth  of  the  layer 
of  large  pyramidal  cells,  the  unusual  size  of  the  last-named  elements  and  the  feeble  development 
of  the  layer  of  polymorphic  cells.  The  pyramidal  cells  collectively  tend  to  larger  size  as  the 
upper  end  of  the  precentral  convolution  is  approached  and,  in  addition,  cells  of  extraordinary 
dimensions  appear.  These  elements,  known  as  the  giant  pyramidal  cells  of  Betz,  reach  their 
maximum  size  within  the  paracentral  lobule,  where  some  attain  a  breadth  of  .065  mm.  or  almost 
double  that  of  the  pyramidal  elements  in  other  regions.  The  giant  cells  are  further  distinguished 
by  their  robust  and  rounded  form,  their  distribution  in  small  groups  of  from  three  to  five  in  the 
deeper  layers  of  the  cortex,  and  the  exceptional  thickness  of  their  axones. 

The  occipital  cortex  in  the  vicinity  of  the  calcarine  lissure  i  Fig.  1013)  is  distinguished  even 
macroscopically  by  the  clearness  of  the  outer  stripe  of  Baillarger,  here  called  the  .s/;v/V  of 
(,'finntri  or  of  }'icq  d}  Azyr.  The  stratum  /onale  is  somewhat  smaller  than  usual,  but  is 
exceptionally  rich  in  tangential  fibres  and  fusiform  eel's.  The  more  superficially  placed 
elements  of  the  second  stratum  are  spindle  form  rather  than  pyramidal  and  give  off  two 


THE  TELENCEPHALON. 


1181 


dendritic  processes,  one  passing  outward  and  the  other  toward  the  subjacent  third  layer,  on 
entering  which  it  divides  and  gives  off  the  axone.  At  about  the  junction  between  the  layer  of 
small  and  large  pyramidal  cells,  the  stripe  of  Gennari  is  produced  by  a  close  felt-work  of 
medullated  fibres,  beneath  which  the  pyramidal  cells  very  gradually  increase  in  size.  In  the 
deepest  part  of  the  third  and  adjacent  part  of  the  fourth  layer,  pyramidal  cells  of  unusually 
large  dimensions  occur  singly  or  in  small  groups.  The  layer  of  polymorphic  cells  is  well 
represented. 

The  cortex  of  the  hippocampus  and  of  the  gyrus  dentatus  is  a  prolongation  of  that  of  the 
gyrus  hippocampi,  modified  by  the  peculiar  folding  which  here  occurs.  Reference  to  Fig.  992 
will  recall  the  relations  of  these  gyri  as  seen  on  the  mesial  surface,  namely,  that  at  the  bottom 
of  the  deep  groove  (the  hippocampal  fissure)  above  the  hippocampal  convolution  lies  the  corru- 
gated free  surface  of  the  dentate  gyrus  and  above  this  the  rounded  mesial  border  of  the  hippo- 
campus. Viewed  in  cross-section  (Fig.  1018),  the  cortex  of  the  hippocampal  convolution  is  seen 
to  bend  laterally  and  pass  into  that  of  the  hippocampus,  which  arches  upward,  mesially  and 

FIG.    1019. 


^f    '  --V-V  .!.-.<.-',    ->,-        "•-"    VV~-:->'- 


Fimbria 


glj}  Hil>« 


•-:-./'     -          '       ; 

Part  of  frontal  section  across  left  hippocampus  and  gyrus  dentatus,  showing  arrangement  of  cell-layers. 

then,  turning  sharply  laterally,  blends  with  the  dentate  gyrus,  which  recurves  mesially  to  reach 
the  free  surface  of  the  hemisphere  and  fill  the  recess  between  the  hippocampal  gyrus  and  the 
under  surface  of  the  hippocampus.  The  cortex  of  the  hippocampus,  therefore,  is  folded  upon 
itself  somewhat  like  the  curve  of  an  interrogation  mark.  On  approaching  its  upper  convexity, 
the  cortex  of  the  hippocampal  convolution,  here  called  the  subiculum,  becomes  modified  by 
the  excessive  but  unequal  thickening  of  the  tangential  fibre-layer  of  its  stratum  zonale  and  the 
irregularity  of  its  layer  of  small  pyramidal  cells,  the  large  pyramidal  cells  at  the  same  time 
becoming  the  sole  representatives  of  the  third  stratum.  The  layer  of  tangential  fibres,  some- 
what thinned,  passes  onto  the  hippocampus  which  it  follows  throughout  and  comes,  therefore, 
into  apposition  with  the  corresponding  tangential  zone  of  the  dentate  gyms.  The  two  fibre- 
layers  are  so  blended  that  a  differentiation  between  the  two  is  impracticable.  Beneath  (i)  the 
layer  of  tangential  fibres  lies  a  second  stratum  of  medullated  fibres,  (2)  the  lamina  medullaris 
circumvoluta,  which  is  probably  an  intracortical  association  tract  limited  to  the  hippocampus. 
The  zone  succeeding  the  medullary  lamina  is  penetrated  by  innumerable  long  dendritic  pro- 
cesses of  the  large  pyramidal  cells  and  in  consequence  presents  a  radial  striation,  the  layer 


1182 


HUMAN  ANATOMY. 


being  appropriately  termed  (3)  the  stratum  radiatum.  Following  this  comes  (4)  the  layer 
of  pyramidal  cells.  These  are  uniformly  of  large  size  and  closely  packed  within  a  clear 
ground-work  which  confers  a  light  appearance  upon  the  winding  lamella,  which  is  therefore 
sometimes  known  as  the  stratum  liicidiim.  Beneath  the  pyramidal  cells  lies  a  layer  of  fibres, 

(5)  the   stratum  oriens,    which  pass  to  and  from  the    hippocampus  ;  among  these  fibres  are 
embedded  spindle  cells,  as  well  as  peculiar  association  cells  (Cajalj  possessing  richly  branched 
axones  which  ramify  among  the  pyramidal  cells  which  they  probably  serve  to  link  together. 
The  axones  of  the  pyramidal  cells  are  directed  chiefly  towards  the  centre  of  the  gyrus  where, 
next  the  descending  horn  of  the  lateral  ventricle,  they  form  a  conspicuous  layer  of  fibres  called 

(6)  the  alveus.     It  is  -this  sheet,  covered  by  (7)  the  ventricular  cficndyma,  in  connection  with  the 
stratum  oriens,  which  confers  the  white  color  to  the  hippocampus,  as  seen  within  the  ventricle. 
On  reaching  the  recurved  end  of  the  hippocampus,  the  layer  of  pyramidal  cells  of  the  latter 
is  not  continuous  with  that  of  the  dentate  gyrus,   but  ends  irregularly  and  is  enclosed  by  the 
arched  dentate  cell-layer. 

The  cortex  of  the  gyrus  dentatus  is  highly  modified  and  Jess  in  accord  with  the  typical 
structure  of  the  cortical  substance  than  that  of  the  hippocampus.  The  outer  surface  where 
buried  in  the  concavity  of  the  hippocampal  arch  lies  in  contact  with  the  similar  surface  of  the  hip- 
pocampus, hence  the  peripheral  layers  of  the  two  gyri  are  opposed.  Within  the  gyrus  dentatus 
may  be  recognized  ( i )  the  stratum  zonale,  relatively  narrow  and  meagre  in  fibres.  The  surface 
of  the  gyrus  is  paralleled  by  a  narrow  layer  of  small  and  densely  packed  cells,  (2)  the  stratum 
granulosum.  These  almost,  but  not  quite  completely,  surround  the  gyrus  and,  therefore,  leave 
an  interval,  the  hilum,  through  which  the  fibres  gain  and  leave  the  deeper  parts  of  the  convolu- 
tion. Within  the  area  so  circumscribed,  known  as  (3)  the  nucleus  of  the  gyrus,  are  found, 
irregularly  disposed  elements,  the  representatives  of  the  layer  of  large  pyramidal  cells.  They 
are  for  the  most  part  small  in  size  and  atypical  in  form.  Their  axones,  together  with  the 
continuation  of  the  stratum  oriens,  pass  through  the  hilum,  the  dentate  gyrus  thereby  forming 
connections  with  other  parts,  either  of  the  hippocampus  or  of  the  fimbria. 


THE  WHITE  CENTRE  OF  THE  HEMISPHERE. 

The  extensive  medullary  substance  enclosed   by  the  cerebral   cortex  appears, 
above  the  level  of  the  corpus  callosum,  as  a  grayish  white  tract  (centrum  semiovale}  of 

seemingly    homogeneous   structure, 

FIG.  1020.  its  uniform  character   being  broken 

^^^^^  ^^^^^  at    most   by    minute    blood-vessels. 

At  lower  levels,  where  the  intercor- 
tical  area  is  encroached  upon  by 
the  large  collections  of  gray  sub- 
stance composing  the  corpus  stria- 
turn  and  the  thalamus,  the  white 
matter  is  most  conspicuous  immedi- 
ately subjacent  to  the  cortex.  When 
examined  with  the  microscope  after 
suitable  preparation,  the  apparently 
homogeneous  subcortical  tissue  is 
resolved  into  an  intricate  maze  of 
medullated  nerve-fibres,  supported 
by  neuroglia,  which  run  in  various 
directions  and  are,  therefore,  cut  in 
different  planes.  When  analyzed 
as  to  their  relations  with  the  cortex, 
the  components  of  the  medullary  sub- 
stance of  the  hemisphere  fall  into 
three  general  groups:  (  i )  the  associ- 
ation fibres,  (2)  tin-  conunissural 
fibres,  and  i  3)  the  projection  fibres. 
The  Association  Fibres.— The  association  fibres  link  together  different  por- 
tions of  the  same  hemisphere,  many  uniting  adjacent  areas  whilst  others  connect  parts 
widely  separated.  They  are  grouped,  therefore,  as  long  and  short  association  bundles. 
With  the  exception  of  a  narrow  zone  in  the  immediate  vicinity  of  the  upper  end  of  the 
Rolandic  fissure,  the  cerebral  cortex  at  birth  is  unprovided  with  association  fibres 
which  have  acquired  their  medullary  coat  and,  therefore,  are  capable  of  functioning. 


Frontal  section  of  brain  passing  through  hemispheres  in 
front  of  corpus  callosum;  core  of  white  matter  is  everywhere 
enclosed  by  cortical  gray  matter. 


THE  TELENCEPHALON. 


.183 


FIG.   1021. 


Diagram  showing;  association  fibres,  lateral  surface ; 
part  of  left  hemisphere  removed  to  expose  short  fibres ; 
long  fibres  are  supposed  to  show  through  transparent 
hemisphere ;  SLF,  superior  longitudinal  fasciculus ;  UF, 
uncinate  fasciculus. 


Within  the  early  months  after  birth,  however,  the  myelination  of  these,  as  well  as 
of  other  tracts,  progresses  rapidly,  although  this  process  is  not  even  moderately  com- 
pleted until  after  the  lapse  of  several  years.  Indeed,  there  is  sufficient  evidence  to 
believe  that  myelination  of  additional 
fibres  continues  so  long  as  intellectual 
effort  is  progressive,  the  demands  made 
by  education  and  special  mental 
exercise  being  met  by  a  corresponding 
completion  of  additional  association 
fibres. 

The  short  association  fibres 
pass  in  great  numbers  from  one  convo- 
lution to  the  next,  bending  in  U-like 
strands  around  the  intervening  fissure. 
Some  of  these  loops  are  confined  to  the 
deeper  layers  of  the  gray  matter  and 
constitute  the  intracortical  association 
fibres,  whilst  others  occupy  the  adjacent 
white  matter.  These  latter  are  known 
as  the  subcortical  association  fibres.  In 
addition  to  the  innumerable  fibres  which 
unite  the  adjoining  convolutions  {fibres  proprice)  and  occupy  the  white  matter 
immediately  below  the  cortex,  many  connect  gyri  somewhat  more  widely  separated, 
those  limited  to  the  convolutions  of  the  same  lobe  constituting  the  intralobar  fibres 
and  lying  at  somewhat  deeper  levels  within  the  medullary  substance. 

The  long  association  fibres  connect  more  or  less  remote  portions  of  the 
cortex  of  the  hemisphere,  and,  therefore,  vary  in  length,  but  are  sometimes  of  con- 
siderable extent.  Numerous  as  such  intcrlobar  bundles  undoubtedly  are,  only  a  few 
can  be  demonstrated  with  certainty.  Among  the  most  definite  of  these  are  :  (i)  the 
uncinate  fasciculus,  (2)  \htcingulum,  (3)  the  superior  longitudinal  fasciculus,  and 
(4)  the  inferior  longitudinal  fasciculus. 

The  uncinate  fasciculus  arises  from  the  convolutions  of  the  orbital  surface  of 

the  frontal  lobe,   arches  over  the  stem  of  the  Sylvian  fissure,   close  to  the  ventral 

border  of  the  insula,  and  ends  in  the  cortex  of  the  anterior  part  of  the  temporal  lobe. 

The  cingulum  is  a  long  arched  tract  lying  within  the  limbic  lobe.      It  begins  in 

front  in  the  vicinity  of  the  anterior  perforated  space,  arches  around  the  anterior  end 

of  the  corpus  callosum,  follows  the  up- 

FIG.  1022.  per   surface   of  this  structure,    lodged 

within  the  callosal  gyrus,  and,  curving 
around  the  splenium,  descends  within 
the  hippocampal  gyrus  to  end  in  the 
fore-part  of  the  temporal  lobe  and  per- 
haps also  in  the  uncus.  The  cingulum 
is  not  composed  of  fibres  which  extend 
its  entire  length,  but  is  made  up  of  a 
number  of  shorter  tracts,  as  shown  by 
its  incomplete  degeneration  after  section 
of  the  fasciculus. 

The  superior  longitudinal  fas- 
ciculus, also  called  the  fasciculus 
arcuatus,  passes  from  the  frontal  and 
parietal  opercula,  over  the  region  of 
the  insula,  to  the  inferior  parietal  con- 
volution, the  occipital  lobe  and  the  superior  and  middle  temporal  convolutions.  It 
is  composed  of  a  number  of  short  bundles  which  proceed  from  the  frontal  lobe  partly 
in  the  sagittal  direction  towards  the  occipital  lobe,  and  partly  in  curves  into  the 
temporal  lobe. 

The  inferior  longitudinal  fasciculus  is  a  well-marked  bundle  which  extends 
from  the  tip  of  the  occipital  lobe  and  the  cuneus,  along  the  outer  side  of  the  optic 


Diagram  showing  association  fibres,  mesial  surface;  fibres 
are  supposed  to  show  through  transparent  hemisphere. 


1184 


HUMAN  ANATOMY. 


FIG.  1023. 


radiation  and  the  posterior  and  inferior  horns  of  the  lateral  ventricle  to  the  fore-part 
of  the  temporal  lobe.  It  is  probably  an  important  path  by  which  visual  impressions 
are  transmitted  to  other  parts  of  the  cortex  (Dejerine). 

Among  the  additional  association  tracts  which  have  been  described  may  be  mentioned  : 

The  fasciculus  occipitalis  perpcndicularis,  which  extends  from  the  upper  part  of  the 
occipital  lobe  and  the  upper  part  of  the  inferior  parietal  convolution  to  the  occipito-temporal 
convolution. 

The  fasciculus  fronto-occipitalis,  which  courses  sagittally  and  lies  in  intimate  relation  with 
the  lateral  ventricle  and  the  caudate  nucleus,  and  to  the  mesial  side  of  the  corona  radiata. 

The  fasciculus  temporo-parietalis,  which  unites  the  temporal  convolutions  with  the  cortex 
of  the  parietal  region. 

The  fasciculus  fronto-parietalis,  which  runs  between  the  base  of  the  lenticular  nucleus  and 
the  claustrum  and  connects  the  frontal  and  parietal  cortex. 

The  fasciculus  lobi  lingualis,  which  is  a  bundle  passing  from  the  ventral  boundary  of  the 
calcarine  fissure  to  the  occipital  cortex  of  the  lateral  surface  of  the  hemisphere. 

The  Commissural  Fibres. — Under  this  heading  are  included  the  fibres 
which  cross  the  mid-line  and  connect  the  cortex  of  one  hemisphere  with  that  of  the 
other,  the  regions  so  united  being  by  no  means  necessarily  identical  on  the  two  sides. 

Such  discrepancy  is  accounted  for,  at 
least  in  part,  by  the  frequent  introduction 
of  an  association  neurone  in  the  com- 
missural  circuit,  the  impulse  carried  from 
one  hemisphere  to  the  other  being  thus 
transferred  to  another  region  of  the  cor- 
tex, from  which  there  arises  the  return 
commissural  fibre.  Preparatory  to  cross- 
ing the  median  plane,  the  fibres  are  col- 
lected into  compact  masses  which  form 
three  definite  bridges  or  commissures  : 
( i )  the  corpus  callosum,  (2)  the  anterior 
commissure  and  (3)  the  hippocampal 
commissure. 

The  fibre-system  of  the  corpus 
callosum,  the  chief  commissure  of  the 
pallium,  is  so  extensive  that  it  includes 
connecting  strands  from  all  parts  of  the 
cortex  of  the  hemispheres  with  the  ex- 
ception of  the  front  and  under  part  of  the  temporal  lobes  and  the  two  rhinencephala, 
which,  on  account  of  their  isolated  position,  are  provided  with  special  bonds  of  union. 
The  callosal  fibres  .  stream  out  in  all  directions,  constituting  the  radiation  of  the 
corpus  callosum  (radiatio  corporis  callosi),  of  which  an  anterior,  a  middle  and  a  pos- 
terior portion  are  recognized.  The  anterior  division,  the  pars  frontalis,  comprises 
the  fibres  which  cross  in  the  genu  and,  as  the  forceps  minor,  pass  to  the  frontal  pole. 
The  fibres  constituting  the  middle  portion,  the  pars  parietalis,  traverse  the  body 
of  the  corpus  callosum  and  continue  outward  to  the  hind-part  of  the  frontal  and  the 
parietal  and  temporal  lobes.  The  posterior  portion  includes  the  fibres  which  form 
the  splenium  and  the  adjoining  segment  of  the  body  of  the  corpus  callosum. 
These  course  outward,  downward  and  backward  and  as  the  pars  tcwporalis  and  the 
pars  occipitalis  reach  respectively  the  hind-part  of  the  temporal  and  the  occipital 
lobes.  The  fibres  destined  for  the  latter  region  lie  within  the  splenium,  from 
which,  as  a  condensed  bundle,  the  forceps  major,  they  arch  backward  along  the 
inner  wall  of  the  posterior  horn  of  the  lateral  ventricle  (page  1158)  into  the  occipital 
cortex. 

The  fibres  composing  the  corpus  callosum  probably  all  terminate  in  arborizations  within  tin- 
cortex  of  one  or  the  other  of  the  hemispheres.  Their  source  in  tin-  opposite  hemisphere,  how- 
ever, is  bv  no  means  always  the  same,  since  they  may  arise:  (  i }  as  the-  axones  of  the  pyramidal  or 
of  the  polymorphic  cells ;'( 2)  as  the  collaterals  of  association  fibres;  or  (3)  as  collaterals  of  projec- 
tion fibres,  in  the  last  two  cases  being,  therefore,  of  the  nature  of  association-fibres  rather  than  of 


Diagram  showing-  commissural  fibres  passing  between 
cerebral  hemispheres  by  way  of  corpus  callosum  (CC)  an- 
terior commissure  (AC),  and  hippocampal  commissure 
(HC). 


THE   TELENCEPHALON. 


1185 


strictly  commissural  ones.  Indeed,  with  the  more  exact  and  extended  study  of  the  corpus 
callosum,  it  becomes  more  and  more  evident  that  the  composition  and  relations  of  this  great 
bridge  are  very  intricate  and  complex,  and  that  it  receives  contributions  from  a  much  larger 
number  of  and  more  diverse  sources  than  was  formerly  recognized. 

The  observations  of  E.  A.  Spitzka  upon  the  size  and  sagittal  area  of  the  corpus  callosum 
have  conferred  additional 
interest  upon  this  struc- 
ture as  a  possible  index 
as  to  intellectual  develop- 
ment. The  examination 
of  a  series  of  brains 
which  included  some  from 
men  of  acknowledged 
intellectual  superiority, 
demonstrated  a  corpus 
callosum  of  unusual  area 
as  a  constant  feature  in  the 
brains  of  the  more  highly 
endowed  individuals. 
And,  further,  that  the 
size  of  the  corpus  callo- 
sum bore  a  direct  •  rela- 
tion to  the  character  of 
intellectual  superiority 
which  the  individual 
was  known  to  possess, 
the  largest  commissure 
being  found  in  the  brain 
of  a  man  whose  intel- 
lectual greatness  implied 
the  exercise  of  associa- 
tion paths  to  an  unusual 
degree.  The  later  con- 
clusions of  Bean,  however, 


Tapetum 


Choroid  plexus 


Hippocampus, 
cut  obliquely 


Fasc.  long,  inferior 


Frontal  section  of  right  hemisphere,  passing  just  behind  splenium  of  corpus  cal- 
losum ;    inferior  horn  of  lateral  ventricle  is  cut  obliquely. 


seriously  question  (consult  page  1197)  the  constancy  of  the  relations  above  suggested. 

The  anterior  commissure  consists  of  a  compact  cord-like  strand,  slightly 
compressed  from  before  backward  and-  therefore  oval  in  section  (Fig.  996), 
which  connects  the  anterior  ends  of  the  temporal  lobes,  as  well  as  the  olfactory 
bulbs.  As  it  crosses  the  mid-line,  the  commissure  is  placed  immediately  in  front 
of  the  downward  arching  anterior  pillars  of  the  fornix,  in  the  interval  between 
which  it  appears  as  a  white  transverse  ridge  on  the  narrow  anterior  wall  of  the 
third  ventricle  (Fig.  979).  Its  posterior  surface  is  covered  with  the  ventricular 
ependyma,  whilst  in  front  it  is  in  intimate  relation  with  the  lamina  cinerea 
(page  1130).  Laterally  it  arches  backward  and  downward,  the  entire  commissure 
forming  a  Il-shaped  tract,  with  the  convexity  presenting  forward,  whose  ends 
broaden  as  they  sweep  backward  into  the  temporal  lobes  (Fig.  968).  In 
addition  to  uniting  the  fore-parts  of  the  last-named  lobes,  the  anterior  commis- 
sure connects  the  olfactory  bulbs  and  consists,  therefore,  of  a  temporal  and  an 
olfactory  part. 

The  olfactory  part  is  much  the  smaller  and  appears  as  a  delicate  fasciculus  which 
curves  downward  and  forward  to  enter  the  olfactory  tract.  Its  fibres  include  :  ( i ) 
those  which  arise  in  one  olfactory  lobe  and  pass  to  that  of  the  opposite  side  ;  (2) 
those  which  connect  the  olfactory  lobe  of  one  side  with  the  cortex  of  the  hippocampal 
convolution  ;  (3)  those  which  extend  from  the  olfactory  lobe  through  the  commis- 
sure and,  joining  the  tsenia  semicircularis,  proceed  with  this  strand  along  the  roof 
of  the  inferior  horn  of  the  lateral  ventricle  to  end  in  the  amygdaloid  nucleus 
(page  1172). 

The  temporal  part  includes  the  greater  portion  of  the  commissure.  After  pass- 
ing almost  horizontally  outward  beneath  the  lenticular  nucleus  (Fig.  1025)  as  far 
as  the  mesial  borders  of  the  putamen,  it  turns  backward  and  continues  its  course 
beneath  the  lenticular  nucleus,  where  it  appears  in  frontal  sections  as  a  transversely 

75 


ii86 


HUMAN  ANATOMY. 


cut  oval  bundle  until,  farther  backward,  it  bends  abruptly  downward  to  disappear 
in  the  white  matter  of  the  temporal  lobe,  to  the  outer  side  of  the  inferior  horn  of 
the  lateral  ventricle,  preparatory  to  ending  in  the  cortex. 

The  fundamental  and  archaic  character  of  the  rhinencephalon,  this  division  of  the  hemi- 
sphere appearing  in  animals  in  which  the  pallium  is  only  feebly  developed,  early  led  to  the 
establishment  of  a  special  connection  between  the  olfactory  lobes  of  the  two  sides.  When  to 
this  necessity  was  added  that  of  linking  together  the  fore-parts  of  the  temporal  lobes,  which  are 
to  a  considerable  degree  isolated,  the  establishment  of  a  commissure  supplementary  to  the 
corpus  callosum  was  effected. 

FJG.  1025. 


Corpus  callosum 


Lateral  ventricle 
Septum  lucidum 

Anterior  end  of 
fomix,  cut 

Foramen  of  Monroe 

Anterior  pillars  of 

fornix 


Caudate  nucleus 

Striate  or  terminal 
vein 

Internal  capsule 

Thalamus,  anterior 
nucleus 

Lenticular  nucleus, 
putaman 

Claustrum 
Globus  pallidus 


Anterior  commissure  Olfactory  strands 

Frontal  section  of  brain  passing  through  anterior  commissure. 

The  hippocampal  commissure  connects  the  two  hippocampi  by  means  of 
fibres  which  cross  in  the  psalterium  (page  1158),  in  addition,  some  fibres  thus  under- 
going decussation  join  the  longitudinal  strands  of  the  fornix  and  proceed  towards  the 
thalamus. 

The  Projection  Fibres. — These  fibres  connect  the  cortex  of  the  cerebral 
hemisphere  with  the  lower  lying  parts  of  the  brain  —  the  thalamus,  the  corpus 
striatum,  the  tegmental  region,  the  pons  and  the  medulla  —  and  the  spinal  cord. 
Proceeding,  as  they  do,  from  all  parts  of  the  extended  cortical  area  towards  nuclei 
grouped  within  the  compass  of  a  relatively  small  space,  the  fibres,  for  the  most  part, 
at  first  curve  toward  their  objective  points  and  collectively  form  the  extensive  con- 
verging tract  known  as  the  corona  radiata.  The  greater  number  of  the  components 
of  the  latter  pursue  a  direct  path  to  the  lower  levels  and  take  part,  therefore,  in  the 
formation  of  the  compact  internal  capsule.  The  projection  fibres  are  by  no  means 
uniformly  numerous  in  all  parts  of  the  cortex,  relatively  few  issuing  from  the  frontal, 
parietal  and  latero-inferior  part  of  the  temporal  regions — areas  which,  according  to 
Flechsig,  are  particularly  significant  as  association  centres.  Furthermore,  the  olfac- 
tory cortex  does  not  contribute  to  the  corona  radiata,  its  own  special  projection  fibres 
being  represented  by  the  cortico-mammillary  tract  within  the  fornix  (page  1158). 
The  projection  fibres  are  not  cxelusively  corticifu^al  tracts,  since  the  connections  of 
the  thalamus  are  of  a  double  nature,  numerous  corticipetal  paths  passing  from  this 
great  sensory  nucleus  to  the  cortex  of  the  hemisphere.  The  projection  fibres  may 


THE  TELENCEPHALON. 


1187 


FIG.  1026. 


be  conveniently  considered  under  two  groups,  the  short  and  the  long  tracts,  accord- 
ing to  the  position  of  the  nuclei  with  which  they  are  associated. 

The  short  projection  tracts  include  the  following  :  i.  The  cortico-thalamic 
tracts,  the  fibres  of  which  pass  from  all  parts  of  the  cortex  of  the  hemisphere  to  the 
thalamus.  The  components  of  these  tracts  are  :  (a)  fibres  passing  from  the  cortex 
of  the  frontal  lobe  to  the  anterior  extremity  of  the  thalamus  ;  (<5)  fibres  passing  from 
the  cortex  of  the  Rolandic  region  and  the  adjoining  part  of  the  parietal  lobe  to  the 
lateral  and  mesial  nuclei  of  the  thalamus  ;  (V)  fibres  passing  from  the  occipito-tem- 
poral  lobe  to  the  medio- ventral  part  of  the  thalamus  ;  and  (a?)  fibres  passing  from  the 
posterior  part  of  the  parietal  and  from  the  occipital  lobe  to  the  pulvinar. 

Associated  with  the  foregoing 
corticifugal  paths  are  the  thalamo- 
cortical  tracts  which,  coursing  in  the 
opposite  direction  (corticipetally), 
proceed  by  way  of  the  stalks  or 
peduncles  of  the  thalamus  (page 
1 1 22)  to  all  parts  of  the  cortical 
sheet  of  gray  matter  investing  the 
cerebral  hemisphere.  The  thalamo- 
cortical  tracts  (Fig.  966),  are  the 
continuations  (by  means  of  the  thala- 
mic  neurones)  of  the  sensory  paths 
conveying  impulses  from  the  spinal 
cord  and  the  brain-stem  and  from 
the  cerebellum  to  the  great  sensory 
internode,  the  thalamus.  These 
include,  on  the  one  hand,  chiefly 
the  median  fillet,  the  spino-tha- 
lamic  tract  and,  probably,  a  part  of 
Goiuers1  tract,  by  which  paths  the 
sensory  impulses  collected  by  the 
spinal  and  the  cranial  nerves  are 
transmitted  to  the  thalamus  ;  and, 
on  the  other  hand,  the  cerebello- 
rubro-thalamic  tracts,  by  which  the 
cerebellum  is  linked  with  the  thal- 
amus by  way  of  the  superior  cerebel- 
lar  peduncle.  The  visual  impulses 
carried  by  the  fibres  of  the  optic 
tract  to  the  pulvinar  are,  in  a  similar 
manner,  conveyed  to  the  occipital 
cortex,  along  with  those  interrupted 
in  the  lateral  geniculate  and  the 
superior  quadrigeminal  body,  by  the 
optic  radiation  of  which  the  occipital 
stalk  of  the  thalmus  is  a  part. 

2.  The    cortico-genicidate    and 

the  cortico-qnadrigeminal  tracts  are  important  constituents  of  the  optic  radiation. 
Their  fibres  extend  from  the  occipital  cortex  to  the  primary  optic  centres  and,  as 
in  the  case  of  those  going  to  the  pulvinar,  are  accompanied  within  the  radiation 
by  corticipetal  fibres  passing  from  the  quadrigeminal  and  geniculate  bodies  and 
the  pulvinar. 

3.  The  auditory  radiation  comprises  both   corticipetal    and    corticifugal  fibres 
which,  in  proceeding  outward,  pass  from  the  inferior  quadrigeminal  and  the  median 
geniculate    body    through    the    retrolenticular    portion    of   the    posterior   limit    of 
the   internal  corpuscle  and   beneath  the  lenticular  nucleus  to    the   auditory  centre 
within    the    temporal  lobe.      This  cortical    centre    includes    the   middle    portion  «of 
the    superior    temporal    convolution    and,    probably,    the    adjoining    part    of    the 
temporal  operculum. 


Lateral 
pyramidal 


Direct  pyramidal 


Diagram  of  long  projective  fibres ;  nuclei  of  cranial  nerves  are 
indicated  by  Roman  numerals;  J?,  red  nucleus. 


u88  HUMAN   ANATOMY. 

4.  The  cortico-rubral  trad  constitutes  a  supplemental  motor  path.  The  exact 
location  of  its  cortical  origin  is  uncertain,  but  may  be  assumed,  at  least  provisionally, 
to  lie  within  the  parietal  lobe. 

The  long  projection  tracts  embrace  two  important  groups,  the  cortico-pontine 
and  the  motor  tracts,  the  former  contributing  the  first  link  in  the  chain  connecting 
the  cerebral  and  the  cerebellar  cortex,  and  the  latter  constituting  the  bond  between 
the  cortical  gray  matter  of  the  hemisphere  and  the  motor  nuclei  of  the  cranial  and 
of  the  spinal  nerves.  The  long  projection  fibres  are  important  constituents  of  the 
internal  capsule  which  they  all  traverse. 

1.  The    cortico-pontine     tracts    include     two     chief    subgroups,    the    fronto- 
pontine  and  the  temporo-occipito-pontine,  which  below  end  around  the  cells  of   the 
pontine   nucleus,    whence  the  impulses  are  transmitted  to  the  cerebellum  by   the 
ponto-cerebellar  strands  of  the  same  and  opposite  sides. 

a.  The  fronto-pontine  tract  arises  from  the   cortex  of  the  frontal  lobe   and, 
passing  by  way  of   the  corona  radiata,   enters  the  hind-part  of  the  anterior  limb 
of  the  internal  capsule.      Descending  into  the  crusta  of  the  cerebral   peduncle,   in 
which  it  occupies  the  mesial  fifth,   the    tract   ends   within  the    ventral  part  of  the 
pons  around  the  nerve-cells  constituting  the  pontine  nucleus. 

b.  The  temporo-occipito-pontine  tract  proceeds  from  the  cortex  of  the  temporal 
and  the  occipital  lobes  through  the  hindermost  segment  of  the  posterior  limb  of 
the    internal    capsule.     On   reaching    the    cerebral    peduncle,    its    position    corre- 
sponds approximately  with  the  lateral  fifth  of  the  crusta.      It  ends  within  the  pons 
around  the  cells  of  the   pontine   nucleus    in    the   same   manner   as    does  the    last- 
described  tract. 

2.  The  motor  tracts  are  composed  of  fibres  which  connect  the  cells  within  the 
cortical  areas  of  the  Rolandic  region  with  the  nuclei  from  which  arise  the  root-fibres 
of  the  motor  nerves.     Since  the  latter  take  origin  within  the  brain-stem  as  well  as 
within  the  spinal  cord,  the  motor  tracts  comprise  two  groups — the  cortico-bulbar  and 
the  cortico- spinal  tracts.     The  exact  locations  of  the  cortical  areas  controlling  the  vari- 
ous cell-groups  giving  origin  to  motor  nerves  are  still   far   from   being  accurately 
known.      Clinical  and  experimental  studies  have  indicated  \vith  considerable  certainty, 
however,  that  the  cerebral  cortex  in  the  immediate  vicinity  of  the  Rolandic  fissure, 
chiefly  in  the  precentral  convolution  and  paracentral  lobule,  and  probably  also  in  the 
adjacent  parts  of  the  superior  and  middle  frontal  gyri,  is  the  most  important  seat  of 
such  motor  centres.      In  a  general  way,  the  areas  controlling  the  muscles  of  the  lower 
limb  lie  highest  and  are  situated  in  advance  of  and  around  the  upper  part  of  the 
Rolandic  fissure.     The  conspicuous  backward  projection  of  the  precentral   gyrus 
(Fig.    984)    corresponds   to   the   arm-area,    whilst   the   lower    part    of    the    same 
convolution  contains  the  centres  for  the  neck  and  face.      (Consult  also  page  1212.) 

a.  The  cortico-bulbar  tract  includes  the  fibres  ending  around  the  nuclei  from 
which  proceed  the  motor  fibres  of  the  cranial  nerves.     The  fibres,  therefore,  arise 
from  the  pyramidal  cells  of  the  cortex  of  the  lower  part  of  the  precentral  gyrus  and, 
for  the  eye  muscles,  of  the  adjoining  portion  of  the  middle  frontal  convolution  (Mills). 
Proceeding  by  way  of  the  corona   radiata,    the  cortico-bulbar  path  occupies  the 
segment  of  the  internal  capsule  which  forms  the  genu,  being  bounded  in  front  by  the 
fibres  of  the  fronto-pontine  tract  and  behind  by  those  of  the  cortico-spinal  tract.     The 
exact  location  of  the  strands  destined  for  the  several  nerves  is  known  only  for  the  facial 
and  the  hypoglossal,  those  for  the  last-named  nerve  occupying  the  most  posterior 
part  of  the  genu,  whilst  those  for  the  facial  lie  just  in  advance  of  the  fibres  for  the 
twelfth.      Within    the    cerebral    peduncle    (Fig.    1012),   the   cortico-bulbar  strand 
occupies  the  lateral  part  of  the  inner  third  of  the  crusta,  the  fibres  destined  for  the 
third  and  fourth  nerves  soon  turning  dorsally  and  crossing  the-  raphe  to  end,  for  the 
most  part,   in  relation  with  the  nuclei  of  the  opposite  side.     The  fibres  for  the  lower 
lying  nuclei  continue  through  the  crusta  and  enter  the  ventral  part  of  the  pons  ;  they 
then  assume  a  medium  position  and  at  appropriate  levels  bend  dorsally  and  cross  the 
mid-line  to  end  in  relation  with  the  cells  of  their  objective  motor  nuclei,  some  feu 
fibres  probably  ending  in  the  nuclei  of  the  same  side. 

b.  The  cortico-s'piual  or  the  pyramidal  tracts    include    the    longest    of  all    the 
projection  fibres,  which,  as  in   the  case  of  those  passing  to  the  nuclei  oi  the  sacral 


THE   TELENCEPHALON. 


1189 


1027. 


Diencephalon 

Thalaniencephalon 


Tegmentuni 


Mid-brain 


III  nerve 


Mammillary 
^      body 


nerves,  may  traverse  the  entire  thickness  of  the  brain  and  the  length  of  the  spinal 
cord.  They  arise  from  the  pyramidal  cells  of  the  Rolandic  cortex,  follow  the  corona 
radiata  into  the  internal  capsule,  within  which  they  occupy  approximately  the  front 
half  of  the  posterior  limb,  those  destined  for  the  cervical  nerves  lying  in  advance  of 
those  for  the  trunk  and  leg  nerves.  Within  the  peduncle,  the  cortico-spinal  tract 
appropriates  approximately  the  middle  third  of  the  crusta,  having  the  sensory  paths 
to  its  outer  side.  The  further  course  of  these  fibres  leads  through  the  ventral  part 
of  the  pons  and  of  the  medulla,  until  near  the  lower  limit  of  the  last-named  division 
of  the  brain-stem,  the  greater  part  of  the  pyramidal  strands  take  part  in  the  motor 
decussation  and  thence  descend  within  the  lateral  pyramidal  tract  to  their  appropriate 
levels  where  they  end  in  relation  with  the  radicular  cells  of  the  anterior  horn  (page 
1043).  The  fibres  which  do  not  cross  in  the  pyramidal  decussation  exchange  their 
lateral  position  for  a  median  one  and  continue  within  the  cord  as  the  direct  pyramidal 
tract  at  the  side  of  the  median  longitudinal  fissure.  Before  gaining  their  final  levels 
within  the  cord,  these  fibres  also  cross,  by  way  of  the  anterior  white  commissure,  to 
end  around  the  root-cells  of  the  opposite  side. 

DEVELOPMENT  OF  THE  PARTS  DERIVED  FROM  THE  FORE-BRAIN. 

It  has  been  pointed  out  in  the  general  sketch  of  the  development  of  the  brain  (page  1060), 
that  the  fore-brain  very  early  undergoes  subdivision  into  two  secondary  cerebral  vesicles,  the 
anterior  of  which  is  the  ielencephalon,  or  end-brain,  and  the  posterior  the  diencephalon.  Each 
of  these  secondary  vesicles 

gives  rise  on  each  side  to  FIG. 

two  general  regions,  an 
upper  and  a  lower,  which 
in  the  telencephalon  are 
the  hemisphcerium  and  the 
pars  optica  hypothalami 
and  in  the  diencephalon 
are  respectively  the  thala- 
mencephalon  and  the  pars 
tnamillaris  hypothalami. 
These  two  parts  of  the 
hypothalatnic  region  to- 
gether constitute  the  hypo- 
thalamus,  which  includes 
the  portion  of  the  lateral 
wall  of  the  fore-brain  lying 
below  the  level  of  the  fo- 
ramen of  Monroe  and  cor- 
responds to  the  ventral  or 
basal  lamina  of  the  neural- 
tube  (Fig.  914).  This  tract 
gives  rise  to  the  structures 
situated  along  the  floor  of 
the  third  ventricle  —  the 
mammillary  bodies,  the 
tuber  cinereum,  the  in- 

fundibulum  and  the  posterior  lobe  of  the  pituitary  body,  the  optic  chiasm  and  the  optic  tracts. 
The  anterior  wall  and  the  roof  of  the  fore-brain  always  remain  thin.  This  is  especially  true 
of  the  roof,  which,  with  the  exception  of  its  hindmost  part  where  the  posterior  commissure 
is  formed,  does  not  lead  to  the  development  of  nervous  tissue  but  remains  thin,  being 
later  represented  by  the  attenuated  epithelial  layer  which  constitutes  the  morphological  roof 
of.  the  third  ventricle.  The  anterior  wall  of  the  fore-brain  is  the  thin  median  partition 
known  as  the  lamina  terminalis,  which,  whilst  giving  rise  to  the  rudimentary  sheets  of  gray 
matter  found  within  the  lamina  cinerea  and  the  septum  lucidum,  is  to  a  large  extent  concerned 
in  the  production  of  the  great  commissure,  the  corpus  callosum. 

The  hemisphccrium,  one  on  each  side,  comprises  by  far  the  greater  portion  of  the  end-brain 
and  represents  an  enormous  expansion  of  the  dorsal  or  alar  lamina  of  the  neural  tube.  Very  early  it 
exhibits  a  differentiation  into  :  (a)  \hv  pallium,  (b]  the  rhincnccphalon  and  (c)  the  corpus  striatmn. 

The  Pallium. — Of  the  three  parts  of  the  hemisphaerium,  in  man  the  pallium  soon  becomes  the 
most  conspicuous,  since  from  the  walls  of  this  rapidly  expanding  hemispherical  pouch  is  derived 
the  great  sheet  of  cortical  gray  substance  which  invests  the  cerebral  hemisphere.  For  a  time 
enclosing  a  large  caviiy  with  thin  walls,  the  pallium  later  becomes  consolidated  by  the 


Hypothalamus 
Future  lateral 
1    ventricle 


Pallium 

Posterior  limit 
of  telenceph- 
alon 

Rhinenceph- 

alon 

Corpus  striaturri 

Optic  recess 
Infundibular  recess' 

Tuber  cinereutil 
Geniculate  ganglion  of  facial" 

Vestibular  gangli.ni- 
Membranous  labyrinth 


Reconstruction  of  brain  of  human  embryo  of  four  and  one-half  weeks  (10.2 
mm.),  inner  surface  of  the  fore-brain  and  mid-brain  exposed  by  mesial  section. 
(Exterior  of  same  brain  shown  in  Fig.  1141).  X  12.  Drawn  from  His  model. 


1 1  go 


HUMAN   ANATOMY. 


intergrowth  of  the  fibre-tracts  (later  the  white  matter),  which  arise  partly  from  the  young 
nerve-cells  within  its  walls  and  partly  from  neuroblasts  situated  in  other  segments.  An  ad- 
ditional factor  of  moment  in  the  production  of  the  bulky  cerebral  hemisphere  is  the  special 
mass  of  gray  matter,  the  corpus  striatum,  which,  with  the  increasing  fibre-tracts,  leads  to 
the  reduction  and  conversion  of  the  cavity  of  the  pallium  to  the  irregular  lateral  ventricle.  Its 
once  wide  communication  (Fig.  1030)  with  the  cavity  of  the  fore-brain  is  retained  as  the 
proportionately  narrow  foramen  of  Monroe.  The  pallium  expands  in  all  directions  save 
directly  downward,  where  increase  concerns  chiefly  the  rhinencephalon,  but  the  lines  of  its 
growth  are  particularly  backward  and  downward,  in  consequence  of  which,  in  addition  to 
the  production  of  a  temporal  and  the  distinctive  occipital  lobe,  the  other  brain-segments 
become  gradually  covered  over  and  deposed  from  their  original  superior  position  toward  the 
basal  surface  of  the  brain.  This  process  is  already  marked  during  the  third  month  (Fig.  1031), 
by  the  end  of  which  period  the  pallium  covers  the  diencephalon.  By  the  beginning  of  the  fifth 
month  the  mid-brain  is  completely  overlaid,  and  by  the  eighth  month  the  entire  upper  surface 
of  the  cerebellum  is  covered. 

Development  of  the  Sulci  and  Gyri. — The  modelling  of  the  surface  of  the  cerebral  hemi- 
sphere begins  towards  the  end  of  the  fifth  month  of  foetal  life,  by  which  time  the  occipital  lobe 
is  well  formed  and  the  brain-case  is  separated  from  the  cerebral  surface  by  an  intervening  layer 

FIG.   1028. 


Pallium 


Lateral  ventricle 


Roof-plate  of  III 
ventricle,  with' 
choroid  plexus 


Corpus  striatum 


Thalamu 


Choroid  plexus 


Hippocampus 


Choroidal  fissures 


Frontal  section  of  brain  of  rabbit  embryo  showing  imagination  of  mesial  wall  of  hemisphere  along  hippocampal  and 
choroidal  fissures  ;  thin  roof-plate  of  third  ventricle  stretches  between  thalann.     X  13. 

of  yielding  arachnoid  tissue,  which  offers  little  opposition  to  the  production  of  the  convolutions 
which  now  follows.  Preceding  this  period,  the  outer  surface  of  the  young  hemisphere  is  quite 
smooth,  with  the  exception  of  the  crescentic  Sylvian  fossa  (Fig.  982)  which  marks  the  position 
of  the  later  insula.  This  depression  has  been  described  (page  1137)  in  connection  with  the  pro- 
duction of  the  Sylvian  fissure.  The  uncertain  creases,  the  so-called  "  transitory  fissures,"  some- 
times seen  on  brains  of  a  much  earlier  period  are  without  morphological  significance  and  are 
now  usually  regarded  as  artefacts  ( Ziehen,  Hochstetter) . 

Long  antedating  the  appearance  of  the  fissures  on  the  outer  aspect  of  the  pallium,  the 
mesial  surface  of  the  latter  is  early  marked  by  two  grooves,  tin-  choroidal  and  tin.-  kifpocamfftl 
fissures.  The  first  of  these  (Fig.  1031)  appears  by  the  end  of  the  fifth  week  as  an  invagination 
of  the  mesial  wall  of  the  pallium  just  above  the  position  of  the  foramen  of  Monroe.  At  first 
small,  the  groove  is  carried  backward  and  downward  by  the  expansion  of  the  pallium  until, 
finally,  it  is  traceable  along  tin-  inner  wall  of  the  inferior  horn  of  the  lateral  ventricle  as  far  as 
its  lower  limit.  Knterini;  by  means  of  this  invagination,  the  mesoblastic  tissue  forces  before 
it  the  attenuated  cerebral  wall  and  expands  into  a  voluminous  mass,  the  choroid  <Wr,  which 
on  becoming  supplied  with  blood-vessels,  forms  a  vascular  complex  that  for  a  time  almost 
completely  fills  the-  early  lateral  ventricle.  With  the  subsequent  growth  of  the  pallium 
backward  and  downward,  the  <  horoidal  fissure  and  the  contained  vascular  fringe  are  carried 
from  the  foramen  of  Monroe  over  and  around  the  thalamus  into  the  inferior  horn  of  the  lateral 


THE   TELENCEPHALON, 


1191 


ventricle,  where  its  remains  are  seen  as  the  definite  choroid  plexus.  The  second  furrow,  the 
hippocampal  fissure,  appears  shortly  after  and  above  the  choroidal  on  the  mesial  surface  of  the 
pallium.  Its  primary  position  is  marked  by  an  invagination  affecting  the  entire  thickness  of 
the  cerebral  wall  (Fig.  1028),  which,  therefore,  appears  on  the  inner  aspect  of  the  wall  of  the 
pallium  as  an  arched  longitudinal  ridge,  the  later  hippocampus.  At  first  open  on  the  mesial 
surface,  the  fissure  subsequently  becomes  almost  entirely  filled  by  the  dentate  gyrus  and  in  the 
fully  developed  brain  is  scarcely  seen. 

The  central  sulctts  or  the  fissure  of  Rolando  is  usually  the  first  of  the  permanent  furrows 
to  appear  on  the  outer  surface  of  the  hemisphere.  As  a  rule,  it  is  recognizable  during  the  last 
week  of  the  fifth  month,  although  its  appearance  may  be  delayed  until  a  month  later  (Cunning- 
ham). When  laid  down  as  two  separate  furrows,  as  it  not  infrequently  is,  the  lateral  one  is  the 
longer  and  usually  the  deeper.  Subsequently  the  two  parts  become  united  into  a  continuous 
sulcus,  although  very  rarely  the  primary  condition  may  persist  and  the  Rolandic  fissure  be 
interrupted  by  a  superficial  gyrus.  During  the  fifth  month,  on  the  mesial  surface  of  the  hemi- 
sphere, also  appear  the  calcarine  and  the  parieto-occipital  fissure.  The  first  of  these  is  often 
mapped  out  by  two  or  even  three  separate  parts,  of  which  the  front  one  is  complete  and,  as  the 
anterior  limb  of  the  calcarine  fissure,  produces  the  elevation  known  as  the  calcar  avis.  The 


FIG.    1029. 

Superior  collicnius         Pineal  body 


III  nerve 


Inferior  colliculus 


IV  nerve  — - 


Mammillary  body 


Cerebellum 


Rhombic  lip 


Median  geniculate  body 
'Lateral  geniculate  body 
Occipital  lobe 

Parietal  lobe 


Pallium 


-  Optic  stalk 

V        \         \v     Infundibulum 
\          Pituitary  body 
V  nerve 


Pons 


VIII  nerve 


|H— Frontal  lobe 
•Temporal  lobe 


Sylvian  fossa 
Rhinencephalon 


"^^^~          Spinal  cord 

Reconstruction  of  brain  of  human  embryo  of  five  weeks  (13.6  mm.);  external  lateral  aspect.     X  n. 

Drawn  from  His  model. 

other  parts  subsequently  unite  to  form  the  posterior  limb  of  the  calcarine  fissure.  When  first 
formed  the  parieto-occipital  fissure  is  usually  distinct  from  the  calcarine,  with  which,  however, 
it  soon  becomes  confluent.  Towards  the  end  of  the  fifth  month  the  collateral  fissure  appears 
on  the  inferior  surface  of  the  hemisphere.  The  inferior  and  the  superior  precenlral  sulcus  may 
usually  be  distinguished,  the  lower  slightly  in  advance  of  the  upper,  during  the  early  weeks  of 
the  sixth  month,  and  about  the  same  time  the  superior  temporal  and  the  olfactory  sulcus.  The 
middle  of  the  sixth  month  marks  the  appearance  of  the  postcentral  and  occipital  limbs  of  the 
interparietal  sulcus  and  the  first  suggestion  of  the  orbital  furrows  and  the  calloso-marginal 
sulcus,  as  well  as  the  junction  of  the  inferior  frontal  with  the  lower  precentral  sulcus.  Towards 
the  close  of  the  same  month  are  added  the  superior  frontal,  the  inferior  temporal  and  the 
occipital  sulci.  The  seventh  month  witnesses  the  extension  and  deepening  of  the  fissures  already 
formed  and  the  union  into  continuous  sulci  of  parts  which  before  were  separate.  During  the 
succeeding  month,  the  surface  of  the  hemisphere  and  the  brain-case  once  more  come  into  inti- 
mate relation,  from  which  it  follows  that  the  rounded  elevations  marking  the  convolutions  can 
no  longer  unrestrictedly  expand,  but  from  now  on  must  accommodate  themselves  in  their  growth 
to  the  inner  surface  of  the  cranium.  In  consequence  of  this  limitation,  the  convolutions  become 
less  rounded  and  more  closely  packed,  and  the  free  surface  of  the  hemisphere  conforms  with  the 
interior  of  the  cranium.  Increased  complexity  in  the  details  of  the  convolutions  arises  from  the 


1192 


HI  MAN  ANATOMY. 


development  of  secondary  gyri  and  sulci,  although  the  definite  brain-pattern  is  not  completed 
until  long  after  birth. 

Histogenesis  of  the  Cerebral  Cortex. — The  changes  in  the  walls  of  the  brain-vesicles 
incident  to  the  development  of  the  nervous  elements  of  the  cerebral  cortex  correspond 
essentially  with  those  occurring  in  the  cord-segment  of  the  neural  tube  (page  1049).  The  wall 
of  the  pallium  early  differentiates  into  three  zones  :  an  inner  layer,  at  first  crowded  with 
closely  packed  and  radially  disposed  proliferating  cells  ;  an  intermediate  or  mantle  /aver, 
composed  of  more  loosely  and  less  regularly  arranged  cells  ;  and  a  narrow  marginal  layer,  in 
which  nuclei  are  absent.  The  cells  of  the  intermediate  layer  very  soon  are  differentiated  into 
two  kinds,  which,  in  recognition  of  their  fate,  are  known  as  the  neuroblasts  and  the  spongio- 
blasts. Although  both  varieties  are  derived  from  the  indifferent  primary  elements  composing 
the  walls  of  the  brain-tube,  the  spongioblasts  are  concerned  in  producing  the  sustentacular 
tissue,  the  neuroglia,  whilst  the  neuroblasts  give  rise  to  the  neurones.  The  derivatives  of  the 
spongioblasts  become  elongated  into  nucleated  radial  fibres,  which  by  their  numerous  pro- 
cesses form  a  supporting  syncytium  that  at  the  inner  and  outer  borders  of  the  brain-wall 
is  condensed  into  the  internal  and  the  external  limiting  membrane  respectively.  The  neuro- 
blasts are  soon  distinguished  by  the  outgrowth  of  a  single  and  centrally  directed  process, 

FIG.   1030. 

Subthalamic  region  Pineal  body  Tegmcntum 


Foramen  of  Monro 
Chorokl  plexus  ^ 


Pallium 


Lamina  terniinalis 


Rhinencephalou 


Geniculate  recess 
Thalamu 


Mid-brain 


Mi'.nimillary  body 


Isthmus 


Cerebellum 


Corpus  striatum 


Optic  recess 
Optic  chiasm 

Pituitary  body 
Infundibular  recess 
Tuber  cinereui 


Cervical  flexure 


Spinal  cord 
Mesial  surface  of  preceding  reconstruction.    Drawn  from  His  model. 

which  later  is  continued  as  the  axis-cylinder  of  a  nerve-fibre.  They  are  further  distinguished 
by  their  peculiar  affinity  for  stains,  which  deeply  tinge  the  pointed  ends  of  the  cells  from 
which  the  axones  are  prolonged.  A  second  process  later  grows  from  the  young  neurone  in 
the  opposite  direction,  that  is,  towards  the  exterior  of  the  brain,  and  becomes  the  peripherally 
directed  apical  dendrite.  The  latter  stains  slightly  and  gradually  invades  the  marginal  layer. 
After  the  appearance  of  the  apical  processes,  the  conversion  of  the  neuroblasts  into  the 
characteristic  pyramidal  cortical  cells  follows,  so  that  by  the  end  of  the  eighth  week  these 
distinctive  elements  are  recognixed.  The  production  of  additional  pyramidal  cells  is  con- 
tinued by  the  migration  of  neuroblasts  from  the  nuclear  layer.  Tin-  subsequent  formation 
of  the  subcortical  white  matter  follows  the  invasion  of  the  inner  part  of  the  intermediate  layer 
by  not  only  the  axones  of  the  pyramidal  cells  but  by  those  of  cells  lying  in  more  remote 
parts  of  the  brain,  ingrowth  of  fibres  taking  place  particularly  from  the  tlialainus.  The  young 
nerve-fibres  for  a  time  are  unprovided  with  medullary  coats,  the  period  at  which  myelinat ion 
occurs  marking  the  completion  of  the  fibre  as  a  path  of  conduction.  The  time  at  which 
the  fibres  composing  the  various  tracts  within  the  brain  acquire  a  medullary  coat  varies  greatly. 
In  a  general  way,  according  to  Flechsig.  those  constituting  the  corticipetal  sensory  paths  first 
myelinate  ;  then  the  projection-fibres  from  the  sense-areas,  and  last  of  all  the  association  strands, 
which  link  together  the  sensc-an  as  and  the  association  fields. 


THE   TELENCEPHALON.  1193 

The  Rhinencephalon. — The  rhinencephalon,  using  the  term  as  including  the  various  parts 
of  the  hemisphere  concerned  with  receiving  and  distributing  the  impulses  of  smell,  comprises  an 
anterior  division,  the  olfactory  lobe,  and  the  posterior  or  cortical  division.  The  olfactory  lobe 
is  suggested  in  embryos  of  the  sixth  week  (Fig.  1029)  by  an  elongated  oval  area,  imperfectly 
defined  from  the  under  surface  ot  the  pallium  by  the  rhinal  furrow,  and  partially  subdivided 
by  a  faint  transverse  groove  into  a  fore  and  a  hind  part.  From  the  anterior  division  are 
developed  the  olfactory  bulb,  tract,  tubercle  and  striae  and  the  parolfactory  area;  from  the 
posterior,  the  anterior  perforated  space  and  the  subcallosal  gyrus.  Although  always  relatively 
rudimentary  in  man,  the  olfactory  lobe  at  first  contains  a  cavity  prolonged  from  the  lateral 
ventricle,  and  in  this  respect  resembles  the  corresponding  but  much  larger  olfactory  lobe  of 
the  osmatic  animals  which  remains  hollow.  In  the  human  brain,  however,  this  cavity,  the 
olfactory  ventricle,  is  only  transient  and  later  entirely  disappears,  its  former  position  being 
indicated  in  the  adult  structure  by  the  central  area  of  modified  neurogliar  tissue  (page  1152). 

The  posterior  or  cortical  division  includes  the  uncus,  the  hippocampus,  the  gyrus  dentatus 
with  the  associated  supracallosal  gray  matter  and  nerve-strands.  The  original  position  of  the 
olfactory  cortical  area  in  the  early  human  hemisphere  corresponds  with  the  permanent  location 
of  the  similar  region  in  animals  in  which  the  expansion  of  the  pallium  never  leads  to  the 
formation  of  a  well-marked  occipito-temporal  lobe.  The  early  appearance  of  the  primary 
hippocampal  and  choroidal  fissures  defines  an  intervening  tract  upon  the  mesial  surface  of  the 
pallium.  This  is  the  primary  gyrus  dentatus  and,  with  the  hippocampal  invagination,  repre- 
sents the  earliest  differentiation  of  the  olfactory  cortical  area.  Connection  between  the  latter 
and  the  region  of  the  mammillary  body  is  subsequently  established  by  the  advent  of  the 
cortico-mammillary  strand,  later  the  chief  part  of  the  anterior  column  of  the  fornix.  In 
consequence  of  the  migration  of  the  hippocampus  and  the  dentate  gyrus  incident  to  the  for- 
mation of  the  occipito-temporal  regions  of  the  hemisphere,  the  chief  parts  of  the  olfactory  cortex 
are  carried  downward  and  forward  into  the  inferior  horn  of  the  lateral  ventricle.  Along  with 
the  displaced  cortical  area  necessarily  follows  the  strand  connecting  it  with  the  mammillary 
region,  hence  the  prolongation  of  the  fornix,  by  means  of  its  posterior  pillar  and  the  fimbria, 
into  the  descending  horn  of  the  lateral  ventricle.  Although  the  major  part  of  the  olfactory 
cortex  thus  comes  to  occupy  the  infero-mesial  temporal  region,  a  small  portion  retains  its 
superior  connection  and  later,  when  the  corpus  callosum  appears,  becomes  the  greatly 
attenuated  sheet  of  gray  matter  which,  with  its  reduced  fibre-strands,  overlies  the  upper 
surface  of  the  bridge  as  the  atrophic  supracallosal  gyrus. 

The  Corpus  Striatum. — The  anlage  of  the  corpus  striatum,  the  fundamental  ganglion  of 
the  end-brain,  is  recognizable  very  early,  and  in  brains  of  the  fourth  week  appears  as  a  triangu- 
lar elevation  between  the  cavity  of  the  pallium  and  the  optic  recess  (Fig.  912,  B}.  Somewhat 
later  (Fig.  1030),  this  elevation,  produced  by  a  local  thickening  of  the  brain-wall,  is  seen  pro- 
jecting from  the  infero-lateral  wall  of  the  pallium  just  in  advance  of  the  large  foramen  of  Monroe. 
On  the  external  surface  of  the  pallium  this  thickening  corresponds  with  the  floor  of  the  Sylvian 
fossa  (Fig.  982),  and  it  is  this  close  association  between  the  corpus  striatum  and  this  area, 
which  fails  to  keep  pace  in  its  growth  with  the  surrounding  parts  of  the  hemisphere,  that  leads 
to  its  envelopment  by  the  opercula  and  the  permanent  covering  of  the  insula.  The  subsequent 
partial  separation  of  the  corpus  striatum  into  its  two  segments,  the  caudate  and  the  lenticular 
nucleus,  as  well  as  the  isolation  of  a  thin  peripheral  cortical  plate,  the  claustrum,  is  effected 
by  the  subsequent  ingrowth  of  the  strands  of  fibres  which  later  become  the  internal  and 
external  capsule. 

The  Diencephalon. — The  posterior  division  of  the  fore-brain,  the  diencephalon,  very  early 
( Fig.  1027)  exhibits  differentiation  into  an  upper  and  a  lower  part.  The  former  is  the  thalamen- 
cephalon  and  the  latter  the  pars  maminillaris  hypothalami,  which  correspond  to  expansions  from 
the  dorsal  and  ventral  laminae  of  the  brain-tube  respectively.  The  thalamencephalon  is  much 
the  larger  and  gives  rise  to  the  bulky  mass  of  the  thalamus  from  its  anterior  two-thirds  and  to 
the  epithalamus  and  the  metathalamus  from  its  posterior  third.  The  epitha/auius  is  prolonged 
backward  and  from  its  upper  surface  an  evagination  occurs,  the  walls  of  which  later  thicken  and 
become  the  pineal  body.  Subsequent  ingrowth  of  fibres  across  the  bottom  of  a  transverse 
groove  behind  and  below  the  pineal  evagination  leads  to  the  establishment  of  the  posterior 
commissure,  whilst  thickening  of  the  part  of  the  epithalamus  lying  in  front  of  the  pineal  recess 
gives  rise  to  the  habenular  region.  The  mciathalamus  appears  at  first  as  a  triangular  area  lying 
behind  and  to  the  outer  side  of  the  thalamus,  with  which  it  is  closely  connected.  It  early  pre- 
sents two  slight  external  elevations  which  become  the  lateral  and  median  geniculate  bodies. 
The  diencephalic  division  of  the  hypothalamus  early  shows  a  differentiation  into  a  series  of  eleva- 
tions and  furrows,  the  thickened  areas  becoming  the  mammillary  body  and  the  subthalamic 
region. 

The  roof  of  the  diencephalon  is  thin  from  the  first  and  remains  so.  In  front  it  is  directly 
continuous  with  the  correspondingly  attenuated  plate  which  connects  the  hemispheres  and, 
arching  over  the  foramen  of  Monroe,  joins  the  lamina  terminalis  that  closes  the  cavity  of  the 


1 194 


HUMAN  ANATOMY. 


fore-brain,  the  later  third  ventricle,  and  contributes  the  anterior  wall  of  this  space.  Attention 
has  been  called  to  the  invagination  of  the  mesial  pallial  wall  along  the  primary  choroidal  fissure 
immediately  above  the  line  of  attachment  of  the  roof-plate  to  the  hemisphere  (Fig.  1031).  The 
latter  is  connected  with  its  fellow  of  the  opposite  side  by  means  of  this  thin  lamina,  upon 
whose  upper  surface  the  mesoblastic  sheet  of  the  young  pia  is  spread.  On  each  side  the 
same  sheet  is  prolonged  through  the  choroidal  fissure  into  the  cavity  within  the  pallium, 
where  it  forms  an  extensive  vascular  mass,  the  choroid  body,  which,  for  a  time,  fills  the 
greater  part  of  the  hemispherical  space,  but  from  actual  entrance  into  which  it  is  now,  as  well  as 
subsequently,  separated  by  the  attenuated  invaginated  wall  of  the  pallium.  This  displaced 
wall,  with  the  enclosed  pial  tissue,  afterward  becomes  the  choroid  plexus  of  the  lateral 
ventricle  and  is  carried  downward  along  the  mesial  surface  of  the  inferior  horn  with  the  for- 
mation of  the  temporal  lobe.  Where  the  mesoblastic  sheet  overlies  the  roof  of  the  fore-brain 
it  becomes  the  velum  interpositum,  which,  it  is  evident,  is  continuous  on  each  side  with  the 
choroid  plexus.  Since'the  choroidal  fissure  begins  in  front  at  a  point  which  later  overlies  the 
foramen  of  Monroe  and,  further,  since  the  choroid  plexuses  of  the  two  sides  are  connected  by 


FIG.  1031. 


Choroidal  fissur 


Choroidal  artery 


Pallium 


Roof  of  third  ventricle 
Habemila 


.Mid-brain 


Lamina  terminalis 

Corpus  striatum 
Hypothalamic  region 


avity  of  mid-brain 
Isthmus 


erebellum 


Rhinencephalon1 

Optic  recess 

Optic  chiasm' 
Infundibular  re- 

Mammillary  body 

Pontine  flexure 


Pons 

Floor  of  IV  ventricle 
Medulla 


Cervical  flexure 


Reconstruction  of  brain  of  human  foetus  of  3  months  (50  mm.)  ;  mesial  surface.     X  41A-     Drawn  from  His  model. 

the  intervening  velum  interpositum,  it  follows  that  the  plexuses  converge  towards  and  meet 
over  the  foramina — a  relation  which  they  retain  in  the  adult  brain.  The  backward  expansion 
of  the  hemispheres  is  accompanied  by  a  corresponding  backward  prolongation  of  the  young 
pia  mater  covering  the  roof  of  the  diencephalon,  later  the  third  ventricle.  After  the  corpus 
callosum  and  the  fornix  have  been  superimposed,  the  impression  is  given  from  the  relation  of 
the  structures,  as  seen  in  the  completed  brain,  that  the  pia  has  gained  its  position  over  the 
roof  of  the  third  ventricle  by  growing  forward  beneath  the  splenium  and  fornix.  That  such, 
however,  is  not  the  case  is  evident  from  the  developmental  history  of  the  velum  interposi- 
tum. The  secondary  invagination  of  the  brain-roof  on  each  side  along  the  median  line  by 
the  vascular  tissue  of  the  pia  accounts  for  the  production  of  the  choroid  plexus  of  the  third 
ventricle. 

The  Cerebral  Commissures. — The  primary  simplicity  of  the  connections  between  the 
hemispheres  is  disturbed  by  the  formation  of  the  commissures,  which  become  necessary  in 
order  to  link  together  the  increasing  sheets  of  cortical  gray  matter.  The  development  of 
these  commissures,  the  corpus  callosum  and  the  anterior  commissure,  as  well  as  of  the 
septum  lucidum,  are  intimately  associated  with  changes  which  affect  the  lamina  terminalis. 


MEASUREMENTS  OF  THE  BRAIN. 


H95 


About  the  fourth  month,  the  last-named  structure,  which  until  this  time  is  of  uniform  width, 
exhibits  a  local  thickening  in  its  upper  part  just  in  front  of  the  foramen  of  Monroe  and  in 
advance  of  the  front-end  of  the  choroid  fissure.  This  thickening  of  the  lamina  terminalis, 
at  first  oval  in  section,  soon  becomes  pear-shaped  with  the  point  directed  downward  (Fig. 
1032).  The  point  enlarges  and,  after  its  later  invasion  by  an  ingrowth  of  transverse  fibres, 
forms  the  anterior  commissure.  The  upper  part  of  the  thickened  area  expands  in  the 
sagittal  direction  and  is  traversed  by  fibres  which  pass  from  one  hemisphere  to  the  other. 
It  thus  becomes  the  corpus  callosum.  This  structure  soon  assumes  an  elongated  and 
slightly  arched  form,  but  does  not  appropriate  the  entire  enlarged  upper  part  of  the  origi- 
nally pyriform  area.  The  antero-inferior  portion,  covered  above  by  the  corpus  callosum, 
remains  thin  and  is  converted  into  the  septum  lucidum.  With  the  later  growth  of  the  cal- 
losum forward  and  downward,  and  the  establishment  of  the  anterior  pillar  of  the  fornix  by 
fibres  which  pass  from  the  gyrus  dentatus  and  the  hippocampus  to  the  basal  surface  of  the 
brain,  the  septum  lucidum  becomes  enclosed  on  all  sides.  At  first  it  is  solid  although  thin  ; 
subsequently  it  is  partially  separated  into  two  lamellae  by  a  narrow  cleft,  the  so-called  fifth  ven- 
tricle, which  is  completely  closed,  is  devoid  of  an  ependymal  lining,  and,  therefore,  is  no  part  of 


FIG.  1032. 


Choroidal  fissure 
Primary  gyrus  dental 


Roof-plate  of  III  ventricle 
(tsenia  thalami) 


Thalamtis 
Posterior  commissure 

Quadrigeminal  plate 

Mid-braiti  cavity 

Cerebral  peduncle 

Cerebellum 

IV  ventricle 


Pitt 


Corpus  callosum 
Rostrum 

Septum  lucidum 

Anterior  commissure 

III  ventricle 
Olfactory  lobe 

lina  terminalis 
ic  chiasm 
litary  body 


Medulla 


Mesial  surface  of  left  half  of  human  foetus  of  fourth  month.     X  2.  (Marchand.) 

the  system  of  true  ventricular  spaces.  Concerning  the  manner  and  reason  of  its  formation 
opinions  differ.  The  older  view,  that  the  space  represents  an  isolated  portion  of  the  longitudi- 
nal fissure  cut  off  during  the  development  of  the  corpus  callosum,  is  sustained  neither  by  its 
history  nor  by  the  adult  condition  of  the  septum  lucidum  in  many  animals  in  which  the  partition 
is  solid  and  no  space  exits.  Goldstein,1  however,  accepts  this  view,  while  Marchand,2  His  and 
others,  regard  the  splitting  as  secondary.  In  consequence  of  the  growth,  increasing  bulk  and 
backward  extension  of  the  corpus  callosum  and  the  fusion  of  the  fornix  along  its  under  surface, 
the  primary  upper  part  of  the  hippocampus,  which  extends  well  forward  along  the  mesial  surface 
of  the  hemisphere,  entirely  disappears,  its  furrow,  the  hippocampal  fissure,  being  later  repre- 
sented by  the  callosal  sulcus,  whilst  the  corresponding  portion  of  the  gyrus  dentatus  is  reduced 
to  the  atrophic  sheet  of  gray  matter  and  the  longitudinal  striae  found  upon  the  upper  surface  of 
the  corpus  callosum. 

MEASUREMENTS    OF    THE    BRAIN. 

The  brain  fits  within  the  cranial  case  so  accurately  that  its  form  is  modified  by 
the  general  shape  of  the  skull,  being  relatively  long  and  ellipsoidal  in  dolichocephalic 
subjects  and  shorter  and  more  spherical  in  brachycephalic  ones.  The  usual  length 
of  the  brain,  measured  from  the  frontal  to  the  occipital  pole,  is  from  160-170  mm. 
(6^4  in.)  in  male  subjects  and  from  150—160  mm.  (6  in.)  in  female.  Its  greatest 
transverse  diameter  is  about  140  mm.  (5^  in.)  for  both  sexes  and  its  greatest  verti- 


1  Archiv  f.  Anatom.  u.  Entwickelung.,  1903. 

2  Archiv  f.  mikros.  Anatom.,  Bd.  xxxvii.,  1891. 


n96  HUMAN  ANATOMY. 

cal  dimension  through  the  hemisphere  is  about  125  mm.  (5  in.).  The  female  brain 
is  commonly  somewhat  shorter  than  that  of  the  male,  and,  therefore,  relatively 
broader  and  deeper. 

The  weight  of  the  brain  has  been  the  subject  of  repeated  investigation  with 
results  that  fairly  agree.  The  conclusions  of  Handmann1,  based  on  recent  examina- 
tions of  1014  brains  (546  male  and  468  female)  from  persons  ranging  in  age  from 
fifteen  to  eighty-nine  years,  are  of  interest  since  they  confirm  in  the  main  the  results 
obtained  from  previous  observations.  The  average  weight  of  the  adult  brain  (from 
15-49  years),  without  the  dura  but  surrounded  by  the  arachnoid  and  pia,  is  1370 
grams  (48.6  oz. )  for  men  and  1250  grams  (44.4  oz. )  for  women.  The  weight  of 
these  membranes,  including  the  enclosed  arachnoid  fluid,  has  been  estimated  at  56 
gm.  and  49  gm.  in  male  and  female  brains  respectively  (Broca).  The  brain  usually 
attains  its  maximum  weight  about  the  eighteenth  year,  perhaps  somewhat  earlier 
in  women,  no  increase  taking  place  after  the  twentieth  year.  Subsequent  to  the 
sixtieth  year  in  both  sexes  a  progressive  diminution  occurs,  by  the  age  of  eighty  the 
brain  having  lost  approximately  one-fifteenth  of  its  entire  weight  (Boyd).  Including 
the  brains  of  individuals  between  fifty  and  eighty-nine  years  in  his  series,  Handmann 
found  the  average  weight  to  be  1355  gm.  (47.8  oz. )  for  men  and  1223  gm.  (40.3  oz. ) 
for  women.  Approximately  81.5  percent,  of  adult  male  brains  have  a  weight  be- 
tween i2Ooand  1500  gm. ;  8.8  per  cent,  one  of  from  950-1200  gm. ;  whilst  20.3 
per  cent,  possess  a  weight  over  1450  gm.  Correspondingly,  about  84  per  cent,  of 
female  brains  weigh  between  1100-1400  gm. ;  44  per  cent,  between  1200-1350  gm. ; 
and  46  per  cent,  below  1 200  gm.  The  average  weight  of  the  brain  of  the  new-born 
male  child  is  400  gm.  (14  oz. )  and  that  of  the  female  one  is  380  gm.  (13.4  oz. ). 
During  the  early  years  of  childhood  the  brain  rapidly  becomes  heavier,  its  weight 
being  doubled  by  the  end  of  the  first  year  and  trebled  by  the  completion  of  the  sixth 
year.  At  first  the  increase  affects  the  brain  equally  in  both  sexes  ;  later  the  young 
female  brain  fails  to  keep  pace  in  its  growth  with  the  male  one,  the  differences 
becoming  progressively  more  marked. 

Whilst  the  brain-weight  and  stature  stand  in  direct  ratio  in  the  new-born  and  in 
children  up  to  75  cm.  in  length,  irrespective  of  age  and  sex,  after  attaining  such  stat- 
ure the  relation  is  irregular  and  uncertain.  Likewise  in  the  adult,  Handmann  found 
no  constant  ratio  between  the  stature  and  the  brain-weight,  although  in  general  a 
lower  average  weight  of  the  brain  is  found  in  short  individuals  than  in  those  of  mod- 
erate and  of  large  height.  The  relative  brain-weight,  as  expressed  in  the  ratio 
between  each  centimeter  of  height  and  the  brain-mass,  Handmann  found  to  be  8. 3 
gm.  for  each  centimeter  of  height  in  men  and  7.9  gm.  in  women,  a  slightly  higher 
proportion  in  favor  of  the  male  subject  being  thus  observed.  The  average  ratio  of 
the  weight  of  the  adult  brain  to  that  of  the  entire  body  is  approximately  i  :5O  (Ober- 
steiner).  In  the  new-born  child  this  ratio  is  much  greater,  being,  as  determined  by 
Mies,  i  :5-9.  Of  the  entire  weight  of  the  brain,  the  hemispheres  contribute  78.5  per 
cent.,  the  brain-stem  ir  per  cent.,  and  the  cerebellum  10.5  percent.,  no  material 
difference  being  observed  in  the  two  sexes  (Meynert). 

The  extent  of  the  superficial  surface  of  the  cortex  has  been  determined,  at  least 
approximately,  by  Wagner,  who  by  completely  covering  the  convolutions  with  gold 
leaf  concluded  that  the  large  brain  of  the  mathematician  Gauss  ( 1492  gm. )  presented 
an  aggregate  area  of  221,000  sq.  mm.,  or  not  quite  one-half  square  meter.  Of  this 
entire  area  about  twice  as  much  lay  along  the  sides  and  bottoms  of  the  fissures, 
therefore  sunken,  as  upon  the  exposed  surface.  The  estimate  of  the  same  observer 
concerning  the  brain  of  a  workman  placed  the  area  at  187,672  sq.  mm. 

The  significance  of  brain-weight  as  an  index  of  intellectual  capacity  has  long  excited  inter- 
est. Accumulating  data  prove  beyond  question  that,  as  applied  to  individuals,  the  weight  of 
the  brain  is  an  untrustworthy  index  of  relative  intelligence.  For  whilst  in  a  number  of  conspic- 
uous examples  the  weight  of  the  brains  of  men  of  acknowledged  intellectual  superiority  has  been 
markedly  above  the  average,  it  is  equally  true  that  some  of  the  heaviest  brains  recorded  have 
been  those  of  persons  of  ordinary,  and  indeed  in  some  cases  of  even  decidedly  inferior,  intelli- 
gence. Further,  the  brains  of  not  a  few  men  of  remarkable  achievement  in  the  fields  of  Science, 

'.\rchivf.  Anat.  u.  Kntwickelung.,  u>o6. 


THE  MEMBRANES  OF  THE  BRAIN.  1197 

of  Letters  and  of  Art  have  possessed  a  weight  little  above,  or  sometimes  even  below,  the  aver- 
age. In  this  connection  it  must  be  remembered  that  it  is  not  improbable  that  the  cortical  cells 
of  different  brains  vary  in  their  capacity  for  activity  and  in  their  power  of  retaining  impressions; 
that,  in  short,  differences  of  quality  exist.  Further,  that  notwithstanding  the  possible  low  gen- 
eral weight  of  a  brain,  the  amount  of  the  cortical  gray  matter,  especially  of  certain  regions  con- 
cerned in  some  particular  phase  of  mental  activity,  may  exist  in  unusual  abundance.  Moreover, 
it  is  probable,  from  the  investigations  of  Kaes ',  that  actual  increase  of  the  functioning  associa- 
tion fibres  takes  place  in  response  to  the  stimulus  induced  by  excessive  exercise  of  certain  parts 
of  the  cortex.  It  is  evident,  therefore,  that  as  applied  to  the  individual,  brain-weight  alone 
affords  little  dependable  information  as  to  intellectual  power,  and  that  brains  which,  judged 
from  their  weight,  apparently  have  been  ordinary,  may  have  been  exceptional  in  the  amount  of 
cortical  gray  matter  and,  perhaps,  in  the  unusual  capacity  of  their  neurones. 

Considered,  however,  in  relation  to  great  groups,  as  to  peoples  or  to  races,  brain-weight  has 
been  found  to  correspond  to  the  general  plane  of  intelligence  and  culture.  In  this  connection 
the  observations  of  Bean2  are  suggestive.  He  found  the  average  brain-weight  of  the  male  negro 
to  be  1292  gm.,  with  extremes  of  1010  gm.  and  1560  gm.  ;  that  of  the  male  Caucasian  1341  gm., 
with  extremes  of  1040  gm.  and  1555  gm.  Notwithstanding  the  relatively  low  class  of  the 
white  subjects  examined,  the  average  weight  of  their  brains  was  greater  than  that  of  the 
high-class  negroes.  Bean  concludes  that  the  smaller  size  of  the  negro  brain  is  primarily  in  the 
frontal  lobe,  and,  therefore,  that  the  anterior  association  centre  is  relatively  and  absolutely  smaller. 

The  observations  of  E.  A.  Spitzka3  concerning  the  area  of  the  corpus  callosum  in  median 
sagittal  section,  call  attention  to  the  unusual  size  of  this  commissure  in  the  brains  of  men  of  con- 
spicuous intellectual  power.  Moreover,  in  the  particular  group  of  brains  thus  examined  varia- 
tions in  the  details  of  the  callosa  strikingly  suggested  well-known  differences  in  the  mental  traits 
of  the  persons  during  life.  The  validity  of  the  area  of  the  callosum  as  a  trustworthy  index  as  to 
intellectual  capacity  has  been  seriously  affected  by  the  fact,  illustrated  by  Retzius  and  by  Bean, 
that  callosa  of  uncommon  size  usually  belong  to  brains  of  high  weight,  and  that  not  infrequently 
such  brains  are  from  individuals  of  ordinary  or  even  of  low  intelligence,  as  exemplified  by  the 
cases  of  Bean,  among  which  a  number  of  callosa  of  very  large  area  were  from  low-class  whites 
and  even  from  negroes. 

THE  MEMBRANES  OF  THE  BRAIN. 

Like  the  spinal  cord,  the  brain  is  enveloped  by  three  membranes,  or  meninges, 
which,  from  without  inward,  are:  (i)  the  dtira  mater,  (2)  the  arachnoid  and  (3) 
the  pia  mater.  The  first  of  these  is  closely  applied  to  the  inner  surface  of  the  cra- 
nium, of  which  it  constitutes  the  periosteum,  and,  in  addition,  by  means  of  its  processes 
serves  to  support  and  guard  from  undue  pressure  the  enclosed  mass  of  nervous  tissue. 
The  pia  mater  is  the  vascular  tunic  carrying  the  blood-vessels  for  the  nutrition  of  the 
brain  and,  therefore,  lies  in  contact  with  all  parts  of  the  external  surface  of  the  organ  ; 
whilst  the  arachnoid,  the  thinnest  and  most  delicate  of  the  three  coats,  is  free  frpm 
blood-vessels  but  is  intimately  related  with  the  intracranial  lymph-paths.  Although 
the  dura  and  the  pia  are  closely  attached  to  the  skull  and  the  brain  respectively,  they 
are  separated  by  an  interval  which,  in  turn,  is  subdivided  into  two  compartments  by  the 
arachnoid.  The  outer  of  these  clefts  lies  between  the  dura  and  the  arachnoid  and  is 
called  the  subdural  space ;  the  other,  between  the  arachnoid  and  the  pia,  is  the 
subarachnoid  space.  The  first  of  these  spaces  is  usually  a  mere  capillary  cleft,  the 
arachnoid  lying  against  the  dura,  and  contains  a  small  amount  of  a  clear  light  straw- 
colored  fluid  of  the  nature  of  lymph.  The  second  one,  although  much  more  capa- 
cious than  the  subdural,  is  crossed  by  so  many  trabeculae  of  arachnoid  tissue  that 
in  many  places  it  acquires  the  character  of  a  sponge-like  tissue,  rather  than  of  an 
unbroken  channel.  Whilst  anatomically  the  subdural  and  the  subarachnoid  spaces 
are  distinct  and  nowhere  communicate,  as  demonstrated  by  careful  artificial  injections 
into  the  subdural  cleft,  it  is  probable  that  during  life  the  cerebro-spinal  fluid  finds  its 
way  through  the  thin  partition  of  arachnoid  tissue  and  enters  the  subdural  space. 
The  interstices  of  the  arachnoid  are  filled  with  the  cerebro-spinal  fluid,  a  modified 
lymph,  which  is  produced  by  the  choroid  plexuses  within  the  ventricles.  After  dis- 
tending these  cavities,  the  fluid  gains  the  subarachnoid  space  .by  way  of  the  foramen 
of  Majendie  and  trie  foramina  of  Luschka  situated  in  the  attenuated  roof  of  the  fourth 

1  Die  Grosshirnrinde  des  Menschen,  1907 

2  Amer.  Journal  of  Anat.,  vol.  v.,  1906. 

3  Amer.  Journal  of  Anat.,  vol.  iv.,  1905. 


1 198 


HUMAN  ANATOMY. 


ventricle  (page  uoo).  The  paths  by  which  the  fluids  collected  within  the  brain- 
membrane  are  carried  off,  thereby  insuring  under  normal  conditions  the  prevention 
of  excessive  intracranial  tension,  will  be  considered  with  the  description  of  the  dura 
and  arachnoid,  suffice  it  here  to  mention  the  sheaths  contributed  by  these  envelopes 
along  the  nerve-trunks  as  they  leave  the  cranium  and  the  Pacchionian  bodies  as  the 
most  important. 

The  Dura  Mater. — This  structure  (dura  mater  encephali)  is  a  dense  and  inelas- 
tic fibrous  membrane,  which  lines  the  inner  surface  of  the  cranial  cavity  and  sends 
partitions  between  the  divisions  of  the  brain.  In  contrast  to  its  relation  within  the 
vertebral  canal,  where  it  is  separated  from  the  bony  wall  by  a  considerable  space 
(page  1022),  within  the  brain-case  the  dura  everywhere  lies  closely  applied  to  the 
bone — a  relation  essential  in  fulfilling  its  function  as  a  blood-carrying  organ  for  the 
nutrition  of  the  cranium.  Around  the  margins  of  the  larger  foramina,  over  the  pro- 
jecting inequalities  of  the  fossae  and  along  the  lines  of  the  more  important  sutures,  the 
attachment  of  the  dura  to  the  skull  is  particularly  close,  and  at  some  of  these  points 

FIG.   1033. 


•Falx  cerebri 


Junction  of  fal: 
and  tentorium 


Tentorium  cerebelli 

Opening  for  brain-stem 


/  Diaphragrna  sellae 

Free  margins  of  tentorium 


Portion  of  skull  removed,  showing?  partitions  of  dura  in  place. 

— the  foramina  and  the  ununited  sutures — the  dura  is  continuous  with  the  periosteum 
covering  the  exterior  of  the  skull.  On  separating  the  dura  from  the  bom-,  as  may  be 
readily  done  beneath  the  calvaria,  except  along  the  line  of  the  sagittal  suture,  its 
outer  surface  is  marked  with  the  conspicuous  ridges  produced  by  the  meningeal 
blood-vessels,  which  lie  much  nearer  the  outer  than  the  inner  surface  of  the  mem- 
brane and  hence  give  rise  to  the  corresponding  furrows  seen  on  the  inner  aspect 
of  the  skull.  In  addition,  the  roughened  surface  of  separation  is  beset  with  fine 
fibrous  processes,  the  larger  of  which  contain  minute  blood-vessels,  that  have 
been  drawn  out  of  the  canals  affording  passage  for  the  nutrient  twigs.  The  inner 
aspect  of  the  dura,  on  the  contrary,  is  smooth  and  shinny  and  clothed  with  a  layer 
of  endothelium  which  lines  the  outer  wall  of  the  subdural  space.  As  the  nerves  enter 
the  foramina  in  their  exit  from  the  cranium,  they  receive  a  tubular  prolongation  of 
the  dura  which  accompanies  the  nerve-trunk  for  a  short  distance  as  the  dural  sheath, 
separated  from  the  nerve  by  the  underlying  snbdural  cleft,  and  finally  becomes  con- 
tinuous with  the  epineurinm,  whilst  the  snbdural  space  communicates  with  the 
lymph-clefts  within  the  connective  tissue  envelopes  of  the  nerves.  The  dural  sheath 


THE  MEMBRANES  OF  THE  BRAIN.  1199 

surrounding   the  optic  nerve   through   its   entire   length  is  noteworthy  on  account 
of  its  unusual  thickness  and  completeness  (page  1223). 

The  two  layers  of  which  the  dura  is  composed  are,  for  the  most  part,  so  closely 
united  that  only  a  single  membrane  is  demonstrable.  The  division  into  two  layers, 
however,  is  evident  in  certain  localities,  particularly  in  the  middle  fossa  at  the  base  of 
the  skull.  Here,  on  each  side  of  the  body  of  the  sphenoid  bone,  the  layers  separate 
to  form  the  cavernous  sinus  and,  within  the  sella  turcica,  enclose  the  pituitary  body. 
Over  the  apex  of  the  petrous  portion  of  the  temporal  bone  they  include  between 
them  a  space,  the  cavum  Meckelii,  which  lodges  the  Gasserian  ganglion,  whilst  over 
the  aqueductus  vestibuli  the  dilated  end  of  the  endolymphatic  duct,  the  saccus 
endolymphaticus,  continued  from  the  membranous  labyrinth,  lies  between  the  two 
layers  of  the  dura.  Further,  along  the  lines  of  its  attachment  to  the  skull  beneath 
the  sagittal  suture,  to  the  crucial  ridges  on  the  occipital  bone  and  to  the  ridges  of 
the  petrous  bones,  the  inner  layer  of  the  dura  separates  from  the  outer  and  forms 
partitions,  which  project  inward  and  imperfectly  subdivide  the  cranial  cavity  into 
compartments  occupied  by  the  larger  divisions  of  the  brain,  as  well  as  enclose  the 
blood-spaces,  known  as  the  dural  sinuses.  These  spaces  have  been  described  with 
the  veins  (page  867)  and  will  be  here  only  incidentally  mentioned  in  connection  with 
the  partitions  in  which  they  lie.  On  either  side  of  the  superior  longitudinal  sinus,  the 
layers  of  the  dura  exhibit  local  areas  of  separation,  which  prolong  laterally  the  lumen 
of  the  venous  channel.  These  parasinoidal  spaces,  the  lacuna  venostz  laterales,  are 
of  consequence  as  receiving  many  of  the  cerebral  veins  and  as  affording  additional 
localities  in  which  the  Pacchionian  bodies  may  come  into  relation  with  the  blood- 
stream. The  septa  thus  formed  by  duplicatures  of  the  inner  dural  layer  are  :  ( i )  the 
falx  cerebri,  (2)  the  tcntorium  cerebelli,  (3)  the  falx  cerebelli,  and  (4)  the  dia- 
phragma  sellce. 

The  falx  cerebri  is  a  sickle-shaped  partition  which  occupies  the  greater  part  of 
the  longitudinal  fissure  separating  the  cerebral  hemispheres.  Its  upper  and  longer 
border  is  attached  in  the  mid-line  and  extends  from  the  cristi  galli  of  the  ethmoid 
bone  in  front  to  the  internal  occipital  protuberance  behind  and  encloses  the  superior 
longitudinal  sinus.  The  latter  channel  appears  triangular  in  cross-section  (Fig. 
1034),  the  upward  placed  base  being  the  outer  or  parietal  layer  of  the  dura  and  the 
sides  the  separated  lamellae  of  the  falx.  The  lower  and  shorter  border  of  the  falx  is 
free  and  more  sharply  arched  than  is  the  upper,  and  extends  from  the  hind  part  of 
the  cristi  galli  to  the  highest  point  of  the  tentorium.  Within  its  posterior  half  it 
encloses  the  inferior  longitudinal  sinus.  The  base  of  the  falx  is  oblique,  approxi- 
mately at  45°  with  the  horizontal  plane,  and  attached  to  the  upper  surface  of  the 
tentorium  in  the  sagittal  plane.  Along  this  junction  lies  the  straight  sinus.  The 
narrow  forepart  of  the  falx  is  the  thinnest  portion  of  the  partition  and  is  often,  more 
especially  during  the  latter  half  of  life,  the  seat  of  perforations,  which  may  be  so 
numerous  as  to  reduce  this  part  of  the  septum  to  a  fenestrated  membrane.  Occasional 
deposits  of  true  bone  are  found  within  the  falx,  which  may  be  without  pathological 
significance  and  represent  the  constant  ossification  of  this  partition  seen  in  some 
aquatic  mammals. 

The  tentorium  cerebelli  is  the  large  tent-like  partition  that  roofs  in  the  pos- 
terior fossa  of  the  skull  and  separates  the  cerebellum  from  the  overlying  posterior 
parts  of  the  cerebral  hemispheres.  In  its  general  form  it  is  crescentic,  the  longer 
convex  border  lying  behind  and  attached  to  the  posterior  and  lateral  margins  of  the 
posterior  cranial  fossa,  and  the  shorter  concave  anterior  border  curving  backward 
and  upward  from  the  anterior  clinoid  processes.  The  upper  surface  of  the  tentorium 
is  attached  by  its  entire  width  to  the  falx  cerebri  along  the  mesial  plane,  and  in  this 
manner  the  partition  is  maintained  in  a  tensed  condition.  The  sides  of  the  tent-like 
fold  are,  however,  not  simply  flat,  but  present  a  slight  downwardly  directed  convexity 
in  both  the  sagittal  and  frontal  planes.  The  peculiar  curvature  of  the  under  surface  of 
the  tentorium  is  reproduced,  in  reversed  relief,  by  the  upper  aspect  of  the  cerebellum 
which  is  accurately  applied  to  the  partition. 

The  posterior  border  of  the  tentorium  is  attached  to  the  horizontal  ridge  crossing 
the  occipital  bone  ;  farther  outward,  on  each  side,  it  is  fixed  to  the  postero-inferior 
angle  of  the  parietal  bone  and,  continuing  forward  and  inward,  to  the  upper  border 


I2OO 


HUMAN  ANATOMY. 


of  the- petrous  portion  of  the  temporal  bone,  and  thence  to  thev- posterior  clinoid  pro- 
cess. From  the  internal  occipital  protuberance  as  far  as  the  parietal  bone,  this  line  of 
attachment  corresponds  with  the  course  of  the  enclosed  lateral  sinus  (page  867) ;  but 
beyond,  the  venous  channel  leaves  the  tentorium  in  its  descent  to  the  jugular  fora- 
men, the  farther  attachment  of  the  tentorium  enclosing  the  superior  petrosal  sinus. 
Since  the  anterior  border  of  the  tentorium  springs,  on  each  side,  from  the  anterior 
clinoid  process,  it  follows  that  the  two  margins  of  the  crescentic  septum  intersect  in 
advance  of  the  apex  of  the  petrous  bone,  the  posterior  border  turning  inward  to  the 
posterior  clinoid  process,  whilst  the  anterior  margin  is  connected  with  the  anterior 
process.  The  free  tentorial  border,  in  conjunction  with  the  dorsum  sellae,  defines  an 
arched  opening,  the  incisura  tcntorii,  through  which  the  mesencephalic  portion  of 
the  brain-stem  is  continued  into  the  cerebral  hemispheres,  the  highest  point  of  this 
aperture  lying  just  behind  the  splenium  of  the  corpus  callosum. 


FIG.  1034. 


-Skin 


Superior  longitudinal  sinus 


Falx  cerebri 


Cerebral 
hemisphere 


Posterior  horn  of 
lateral  ventricle 


Tentorium — 
Left  lateral  sinus 


Superior  worm 


Fibro-aponeurotic  layers  of  scalp 


Parietal  layer  of  du'ra 


Bone 


Inferior  longitudi- 
nal sinus,  cut 
obliquely 


Posterior  horn  of 
lateral  ventricle 


Tentorium 

Right  lateral  sinus 

erebellum 
Inferior  worm 


Occipital  sinus 


Frontal  section  of  head,  viewed    from    behind,  showing  relations  of  dura  mater  to  cerebral    hemispheres  and 

cerebellum  and  position  of  sinuses. 

The  falx  cerebelli  is  a  small  sickel-shaped  dural  fold  which  descends  in  the 
mid-line  from  the  under  surface  of  the  tentorium,  with  which  its  broader  upper  end 
is  attached,  towards  the  foramen  magnum.  In  the  vicinity  of  this  opening  its  apex 
bifurcates  into  smaller  folds  that  fade  away  on  either  side  of  the  foramen.  Its  poste- 
rior border,  attached  to  the  vertical  internal  occipital  crest,  contains  the  small  occipital 
sinuses,  or  sinus  when  these  channels  are  fused.  The  narrow  crescent  projects  into 
the  posterior  cerebellar  notch  and  thus  intervenes  between  the  hemispheres  of  the 
cerebellum. 

The  diaphragma  sellae  is  an  oval  septum  of  dura,  which  roofs  in  the  pituitary 
fossa  and  is  continuous  on  cither  side  with  the  visceral  or  inner  layer  of  the  wall  of 
the  cavernous  sinus.  The  diaphragm  contains  a  small  aperture,  the  foramen  dia- 
phragmatis,  through  which  the  infumlibulum  connects  the  enclosed  pituitary  body 
with  the  brain. 

The  structure  of  the  duni  presents  the  histological  features  of  dense  hbro- 
elastic  tissue,  in  which  the  elastic  constituents,  however,  are  greatly  overshadowed 
by  the  white  fibrous  bundles.  The  inner  surface  of  the  dura  is  covered  with  endo- 


THE  MEMBRANES  OF  THE  BRAIN. 


I2OI 


thelial  plates  which  constitute  the  immediate  outer  wall  of  the  subdural  lymph-space. 
Patches  of  endothelium  sometimes  seen  on  the  external  aspect  of  the  membrane  are 
regarded  as  indications  of  uncertain  epidural  lymph-spaces.  The  outer  or  periosteal 
lamella  is  less  compact  and  richer  in  cells  than  the  inner  layer  and  contains  a  wide- 
meshed  net-work  of  capillary  blood-vessels.  The  larger  bundles  of  fibrous  tissue  are 
disposed  with  some  order  so  that  a  definite  radiation  from  the  two  ends  of  the  falx 
cerebri  may  often  be  recognized.  Within  the  last-named  fold,  from  the  point  where 
the  free  border  of  the  falx  and  that  of  the  tentorium  meet,  the  fibres  radiate  towards 
the  convex  attached  margin,  some,  therefore,  arching  far  forward.  From  the  same 
point  the  fibres  within  the  tentorium  pass  laterally. 

Minute  calcareous  concretions,  also  known  as  brain-sand  or  acervulus,  are 
not  infrequently  found  in  the  otherwise  normal  dura,  especially  in  subjects  of 
advanced  years.  They  consist  of  aggregations  of  particles  of  calcium  carbonate  and 
phosphate  arranged  in  concentric  layers  and  surrounded  by  a  capsule  of  fibrous 
tissue.  They  seldom  exceed  a  diameter  of  .070— .080  mm.,  but  may  be  so  numer- 
ous that  a  distinctly  gritty  feel  is  imparted  to  the  inner  surface  of  the  dura. 

The  blood-vessels  within  the  dura  are  the  branches  of  the  meningeal  arteries, 
and  their  accompanying  veins,  derived  from  various  sources — from  the  ophthalmic, 

FIG.  1035. 

Medullary  branch 


Larger  pial  artery 


White  matter 


Pia  within  fissure- 
Portion  of  injected  cerebral  cortex,  showing  capillary  supply  of  gray  and  white  matter.     X  18. 

internal  maxillary,  vertebral,  ascending  pharyngeal  and  occipital  arteries.  They  are 
destined,  for  the  most  part,  for  the  nutrition  of  the  skull,  which  they  enter  as  minute 
twigs  through  innumerable  openings  in  the  bone.  Some  few  perforating  arteries 
traverse  the  bone  and  communicate  with  the  pericranial  vessels,  whilst  others  are 
distributed  to  the  tissue  of  the  dura  itself. 

Definite  lymphatics  have  not  been  demonstrated  within  the  dura,  the  system 
of  absorbent  vessels  being  represented  within  this  membrane  by  numerous  lymph- 
spaces  within  the  connective  tissue  stroma.  These  communicate  indirectly  with  the 
subdural  lymph-space,  the  contained  fluid  escaping  at  the  foramina  chiefly  into  the 
lymph-paths  surrounding  the  cranial  nerves,  but  to  some  extent  also  directly  into 
the  venous  sinuses  around  the  Pacchionian  bodies. 

The  nerves  of  the  dura  include  principally  sympathetic  filaments,  distributed 
to  the  blood-vessels  and  to  the  bone,  and  sensory  fibres.  The  immediate  sources 
are  the  meningeal  twigs  contributed  by  the  trigeminus,  the  vagus  and  the  hypo- 
glossal  nerves.  Those  from  the  last  source,  apparently  from  the  twelfth,  are  really 
sensory  fibres  from  the  upper  cervical  spinal  nerves  and  sympathetic  filaments  from 
the  cervical  sympathetic  cord  ;  in  the  other  cases,  the  sensory  fibres  are  probably 
accompanied  by  sympathetic  filaments,  which  secure  this  companionship  by  means  of 

76 


1202 


III  MAN  ANATOMY. 


Gray  matter 


White  matter 


the  communications  which  these  cranial  nerves  have  with  the  plexuses  surrounding 
the  arteries  or  with  the  superior  cervical  ganglion.  The  sensory  nerves  of  the  dura 
form  a  rich  net-work  of  delicate  twigs  from  which  filaments  have  been  traced  to  the 
inner  surface  in  relation  to  which  some  end  in  bulbous  expansions. 

The  Pia  Mater. — This  membrane  (pia  mater  encephali)  lies  next  the  nervous 
substance  and,  being  the  vascular  tunic  supporting  the  blood-vessels  for  the  nutrition 
of  the  brain,  follows  accurately  all  the  inequalities  of  its  exterior.  It  not  only  closely 
invests  the  exposed  surface  of  the  cerebrum  and  cerebellum,  but  penetrates  along  the 
sides  and  to  the  bottom  of  all  the  fissures  as  well,  although  within  the  small  shallow 
fissures  of  the  cerebellum  a  distinct  process  of  pia  mater  can  not  be  demonstrated. 
Additionally,  in  certain  places  where  the  wall  of  the  brain-tube  is  very  thin,  the  pia 
pushes  before  it  the  attenuated  layer  and  seemingly  gains  entrance  into  the  ventricles. 
Examples  of  such  invagination  are  afforded  in  the  relations  of  the  velum  interpositum 
and  the  choroid  plexuses  to  the  lateral  and  third  ventricles  (page  1162)  and  of  the 

similar  plexuses    in    the    roof   of   the 

FIG.  1036.  fourth  ventricle  (page  1 100).     The  pia 

also  contributes  a  sheath  to  each  nerve, 
or  to  its  larger  component  bundles,  as 
the  nerve  leaves  the  brain  at  its  super- 
ficial origin,  which  sheath  surrounds 
the  nerve  during  its  intracranial  course 
and  for  a  variable  distance  beyond  its 
emergence  from  the  dural  sac. 

The  pia  is  so  thin  that  the  larger 
vessels,  especially  at  the  base  of  the 
brain,  lie  within  the  subarachnoid 
space,  although  in  most  cases  they  are 
enclosed  within  a  delicate  investment 
of  pial  tissue.  The  smaller  vessels, 
however,  ramify  within  the  pia  and  in 
this  situation  divide  into  the  twigs 
which  directly  enter  the  subjacent 
nervous  tissue.  As  they  penetrate  the 
latter  they  are  accompanied  by  a 
sheath  of  pia,  which  thus  gains  the 
nervous  substance  within  which  it  fol- 
lows the  subdivisions  of  the  arteriole, 
even  their  smallest  ramifications. 

Whilst  within  the  pia  the  larger 
arteries  form  frequent  anastomoses, 
the  smaller  twigs  remain  isolated  and, 
being  ' '  end-arteries, ' '  on  entering  the 
subjacent  gray  matter  break  up  into 
terminal  ramifications  which  furnish  the  only  supply  for  a  particular  district.  The 
capillary  net-work  within  the  cortical  gray  matter  is  much  closer  than  that  within  the 
subjacent  white  matter  (Fig.  1035),  in  which  the  vessels  are  comparatively  meagre. 
Here  and  there  larger  medullary  branches  are  seen  traversing  the  cortex,  to  which 
they  contribute  but  few  twigs,  to  gain  the  white  matter  within  which  they  find  their 
distribution.  The  contrast  in  richness  between  the  supply  of  the  gray  substance  and 
that  of  the  adjoining  white  matter  is  not  limited  to  the  cerebral  cortex,  but  is  also 
well  shown  when  the  internal  nuclei  are  examined  (Fig.  1036).  The  veins  emerge 
from  the  surface  of  the  brain,  but  do  not  retain  a  definite  relation  to  the  arteries,  since, 
instead  of  following  the  latter  to  their  points  of  entrance,  they  for  the  most  part  seek 
the  dural  sinuses  into  which  they  empty. 

The  special  invaginating  layers  of  pia  mater,  the  velum  interpositum  (page  1 162) 
and  the  choroid  plexuses  of  the  lateral  and  third  ventricles,  and  the  choroid  plexus  of 
the  fourth  ventricle  (page  noo)  have  been  described  in  connection  with  the  appro- 
priate parts  of  the  brain.  Attention  may  be  again  called  to  the  manner  in  which  the 
velum  interpositum  and  the  associated  plexuses  are  formed  (page  1194),  and  to  the 


Portion  of  injected  dentate  nucleus  of  cerebellum,  show- 
ing capillary  supply  of  internal  nucleus.     X  20. 


THE    MEMBRANES    OF   THE    BRAIN. 


1203 


Vascular  tuft 


fact  that  the  apparent  ingrowth  of  the  pia  beneath  the  spleniurn  and  the  fornix  to 
reach  its  final  position  over  the  third  and  within  the  lateral  ventricles  never  occurs, 
the  growth  actually  taking  place  in  the  opposite  direction,  that  is,  from  before 
backward  (page  1194). 

The  structure  of  the  pia  mater  presents  little  for  special  mention.  The 
membrane  consists  essentially  of  a  delicate  connective  tissue  envelope  in  which  inter- 
lacing bundles  of  white  fibrous  tissue,  intermingled  with  elastic  fibres  and  containing 
numerous  nuclei,  are  the  chief  features.  As  the  arteries  leave  the  pia  to  enter 
the  brain,  they  receive  sheaths  of  pial  tissue  within  which  are  prolonged  the  lymph- 
spaces  enclosed  between  the  trabeculae  of  the  pial  membrane.  Along  the  basal  surface 
of  the  brain,  especially  on  the  ventral  aspect  of  the  medulla,  the  pia  frequently  contains 
deeply  pigmented  branched  connective  tissue  cells.  These  may  be  so  numerous, 
particularly  in  aged  subjects,  that  the  membrane  appears  of  a  distinct  brownish  hue. 

The  numerous  nerves  encountered  within  the  pia  mater  are  chiefly  sympathetic 
filaments  destined  for  the  walls  of  the  blood-vessels  and  derived  from  the  plexuses 
surrounding  the  internal  carotid  and  the  vertebral  arteries.  Additional  nerve- 
fibres,  probably  sensory  in  function,  occur 

in    small    numbers.      The   mode   of   their  FIG.  1037. 

ending  is  uncertain,  although  terminal  bul-  r^ 

bus  expansions  and  tactile  corpuscles  have  ^      fij . 

been  observed. 

The  Arachnoid. — This  covering 
(arachnoidea  encephali),  the  intermediate 
membrane  of  the  brain,  is  a  delicate  con- 
nective tissue  envelope  that  intervenes 
between  the  dura  externally  and  the  pia 
internally.  In  contrast  to  the  last-named 
membrane,  which  follows  closely  all  the 
irregularities  of  the  sunken  as  well  as  of  the 
free  surface  of  the  cerebrum,  the  arachnoid 
is  intimately  related  to  the  convolutions 
only  along  their  convexities,  and  on  arriving 
at  the  margins  of  the  intervening  fissures 
stretches  across  these  furrows  to  the  con- 
volutions beyond.  From  this  arrangement 
it  follows  that  intervals,  more  or  less  tri- 
angular on  section,  are  left  over  the  lines 
of  the  fissures  between  the  arachnoid  and 
the  fold  of  pia  which  dips  into  the  sulcus. 
These  clefts  form  a  system  of  intercom- 
municating channels  which  are  parts  of  the 

general  subarachnoid  space.  Over  the  summits  of  the  convolutions,  the  arachnoid 
and  pia  are  so  intimately  united  that  they  constitute  practically  a  single  membrane, 
whilst,  where  parted  by  the  subarachnoid  space,  they  are  connected  only  by  the 
trabeculae  of  arachnoid  tissue.  In  many  places,  however,  where  the  intervening  cleft 
is  not  wide,  these  trabeculae  are  so  numerous  that  the  space  is  occupied  by  a  delicate 
reticulum  and  becomes  converted  into  a  layer  of  loose  subarachnoid  tissue.  Where, 
on  the  other  hand,  the  arachnoid  encloses  spaces  of  considerable  size,  as  it  does  on 
the  basal  surface  of  the  brain,  the  trabeculae  are  reduced  in  number  to  relatively  few 
long,  cobweb-like  threads  that  extend  from  the  arachnoid  to  the  pia  mater.  Over 
the  upper  and  outer  aspects  of  the  cerebrum  and  cerebellum  the  arachnoid  follows, 
in  a  general  way,  the  contour  of  the  brain.  On  the  ventral  surface,  however,  it 
bridges  from  the  median  elevation  presented  by  the  brain-stem  to  the  adjacent  promi- 
nences offered  by  the  cerebellum  and  the  cerebral  hemispheres.  The  irregular  spaces 
thus  enclosed  contain  considerable  quantities  of  cerebro-spinal  fluid  and  are  known 
as  the  cisternae  subarachnoidales,  of  which  several  subdivisions  are  recognized 
according  to  locality. 

The  cisterna  magna  (cisterna  cerebellomedullaris),  the  largest  of  these  spaces, 
overlies  the  dorsal  surface  of  the  brain-stem  and  is  continuous  through  the  foramen 


Velum  inter- 

positum 


Small  portion  of  injected  choroid  plexus  of  lateral 
ventricle ;  surface  view. 


1204 


HUMAN  ANATOMY. 


magnum  with  the  posterior  part  of  the  subarachnoid  space  of  the  cord.  The  arach- 
noid passes  from  the  back  part  of  the  under  aspect  of  the  cerebellum  to  the  posterior 
surface  of  the  medulla  and  thus  encloses  a  considerable  space  which  at  the  sides  of 
the  medulla  is  continuous  with  the  upward  prolongation  of  the  anterior  subdural 
space  of  the  cord.  The  lower  part  of  the  brain-stem  is  thus  completely  surrounded 
by  the  subarachnoid  cavity.  The  ventral  surface  of  the  pons  is  enveloped  by  the 
upward  extension  of  the  anterior  part  of  the  spinal  arachnoid,  the  cleft  so  enclosed 
constituting  the  cisterna  pontis,  of  which  a  median  and  two  lateral  subdivisions 
may  be  recognized.  From  the  upper  ventral  border  of  the  pons  the  arachnoid 
passes  forward  to  the  orbital  surface  of  the  frontal  lobes,  covering  the  corpora  mam- 
millaria,  the  infundibulum  and  the  optic  chiasm,  and  laterally  to  the  adjacent  project- 
ing temporal  lobes  and  thence,  covering  in  the  transverse  stem  of  the  Sylvian  fissures, 

FIG.  1038. 


Olfactory  tract 


.Optic  chiasm 

Internal  carotid 
artery 


Basilar  artery 


Extension  along 
'longitudinal  fissure 


_Extension  along 
Sylvian  fissure 


-Cisterna  basalis 


-Cisterna  pontis 


Vertebral  arteries  • 


•Cisterna  magna 


Inferior  aspect  of  brain  covered  with  pia  and  arachnoid,  showing  large  subarachnoid  spaces. 

to  the  frontal  lobes.  This  large  space,  which  includes  the  deep  depression  on  the 
basal  surface  of  the  brain,  is  the  cisterna  basalis.  It  is  imperfectly  subdivided  by 
incomplete  septa  of  arachnoid  tissue  into  secondary  compartments,  one  of  which  lies 
between  the  peduncles  (cisterna  interpeduncularis),  another  behind  the  optic  commis- 
sure (cisterna  chinsmatis)  and  a  third  above  and  in  front  of  the  chiasm  (cisterna 
laminae  terminalis).  Anteriorly  the  cisterna  basalis  is  continued  over  the  convex 
dorsal  surface  of  the  corpus  callosum  (cisterna  corporis  callosi),  and  on  cither  side 
along  the  stem  of  the  Sylvian  fissure  (cisterna  tissurae  lateralis  ).  Within  the  median 
region  of  the  cisterna  basalis  lie  the  large  arterial  trunks  forming  the  circle-  of  XYillis. 
These  vessels  are  invested  with  delicate  sheaths  of  arachnoid,  which  accompany  the 
smaller  branches  until  they  enter  the  vascular  membrane  to  become  pial  vessels. 

The  arachnoid  also  contributes  sheaths  to  the  cranial  nerves  as  they  pass  from 
their  superficial  origins  to  the  points  where  they  pierce  the  dura,  these  sheaths  over- 
lie those  derived  from  the  pia  and,  as  do  the  latter,  accompany  the  nerve-trunks  for  a 


1205 


variable  but  usually  short  distance  beyond  their  emergence  from  the  dural  sac.  The 
arachnoid  sheath  is  especially  well  marked  along  the  optic  nerve,  which  it  follows  as 
far  as  the  eyeball,  and  completely  subdivides  the  space  between  the  pial  and  dural 


FIG.  1039. 


Pacchionian  body 
Dura,  reflected  medially 

Cerebral  vein 


Cerebral  vein 

Pacchionian  body 


Portion  of  superior  surface  of  right  hemisphere  covered  by  pia  and  arachnoid  ;  dura  has  been  partly  separated 
and  reflected  towards  mid-line  to  expose  Pacchionian  bodies  and  cerebral  veins,  which  are  seen  entering  superior 
longitudinal  sinus. 

sheaths  into  a  subdural  and  a  subarachnoid  perineural  compartment,  directly  contin- 
uous with  the  corresponding  intracranial  spaces. 

As  previously  noted,  the  cerebro-spinal  fluid  secreted  within  the  ventricles 
escapes  through  the  openings  in  the  roof  of  the  fourth  ventricle — foramen  of  Majendie 
and  the  foramina  of  Luschka  (page  uoo) — into  the  subarachnoid  space.  After 
filling  the  cisterna  magna  and  the  other  large  spaces  on  the  basal  surface  of  the  brain 
and  surrounding  the  spinal  cord,  the  fluid  finds  its  way  into  the  smaller  spaces  on 
the  exterior  of  the  cerebrum.  In  this  manner  the  entire  mass  of  nervous  tissue  is 
enveloped  by  a  more  or  less  extensive  cushion  of  fluid  which,  particularly  at  the  base 
of  the  brain,  is  well  adapted  to  protect  the  enclosed  delicate  structures  from  undue 
concussion.  Since  the  cerebro-spinal  fluid  is  being  continuously  secreted,  it  is  evi- 
dent that  some  adequate  means  of  escape  must  be  provided  to  insure,  under  normal 
conditions,  the  maintenance  of  intra- 
cranial and  intracerebral  pressure 
within  due  limits.  The  paths  by  which 
this  is  accomplished  include  :  ( i )  the 
extension  of  the  subarachnoid  space 
along  the  nerve-trunks,  and  (2)  the 
villous  projections  of  arachnoid  tissue, 
the  Pacchionian  bodies,  along  the 
course  of  the  dural  blood-sinuses. 

The  Pacchionian  bodies  (gran- 
ulationes  arachnoidales)  are  numerous 
cauliflower-like  excrescences  of  the 
arachnoid,  for  the  most  part  small  but 
occasionally  reaching  a  diameter  of 
5  mm.  or  over,  which  lie  on  the  outer 
surface  of  the  membrane  along  the 
course  of  the  dural  venous  sinuses. 
Their  favorite  site  is  on  either  side  of 


FIG.  1040. 


Diagram  showing  relations  of  Pacchionian  bodies  to 
blood-spaces  and  dura;  B,  bone,  S,  longitudinal  sinus; 
/.,  lacunas ;  P,  Pacchionian  bodies ;  V,  cerebral  vein 
emptying  into  lacuna;  S£>,  subdural  space;  dura  is  blue 
and  pia  is  red,  intervening  tissue  is  arachnoid  ;  A. 


the  superior  longitudinal  sinus,  where 

they  occur  in  groups,  although  they  occur  in  smaller  number  and  size  in  connec- 
tion with  other  sinuses,  as  the  lateral,  cavernous  and  straight.  They  consist 
entirely  of  arachnoid  tissue  and  contain  no  blood-vessels.  Although  lying  mostly 
at  the  side  of  the  longitudinal  sinus  with  which  they  are  then  indirectly  related 
through  the  lateral  diverticula,  the  lacuna  laterales  or  blood-lakes,  in  some  instances 


1206  HUMAN   ANATOMY. 

they  encroach  upon  the  lumen  of  the  main  channel  itself,  within  which  they  appear 
as  irregularly  rounded  projections  on  its  lateral  walls.  Whatever  their  relation, 
whether  with  the  sinus  or  the  lateral  diverticula,  the  Pacchionian  bodies  never  lie 
free  within  the  blood-space,  but  are  always  separated  from  the  latter  by  the  dural 
wall.  Over  the  summit  of  the  elevation  the  dura  becomes  greatly  attenuated,  but 
never  entirely  disappears,  so  that  only  a  thin  membrane  and  the  subdural  cleft, 
theoretically  present  but  practically  more  or  less  obliterated,  intervene  between  the 
subarachnoid  spaces  and  the  blood-stream.  This  partition  offers  little  obstruction 
to  the  passage  of  the  cerebro-spinal  fluid,  which,  unless  the  pressure  within  the 
venous  channel  is  higher  than  that  within  the  subarachnoid  space,  passes  from  the 
latter  into  the  sinus  and  thus  relieves  the  intracranial  tension.  When  well  developed, 
as  they  often  are  after  adolescence  but  never  during  childhood  when  they  are 
small  and  rudimentary,  the  Pacchionian  bodies  are  frequently  lodged  in  depressions 
within  the  calvaria,  whose  inner  surface  is  sometimes  so  deeply  pitted  that  the  bom- 
in  places  is  translucent. 

THE    BLOOD-VESSELS    OF    THE    BRAIN. 

The  course  and  distribution  of  the  individual  blood-vessels  supplying  and  drain- 
ing the  nervous  tissue  of  the  brain  have  been  described  in  the  sections  on  the  Arteries 
(page  746)  and  the  Veins  (page  861).  It  remains,  therefore,  only  to  consider  at 
this  place  the  more  general  relations  concerning  these  vessels. 

The  arteries  supplying  the  brain  are  derived  from  two  chief  sources — the  inter- 
nal carotid  and  the  vertebral  arteries.  After  entering  the  cranium  these  vessels  and 
their  branches  form  the  remarkable  anastomotic  circuit  known  as  the  circle  of  Willis 
(page  760).  The  latter  gives  off,  in  a  general  way,  two  sets  of  branches,  the  gang- 
lionic — for  the  most  part  short  vessels  which  soon  plunge  into  the  nervous  mass  to 
supply  eventually  the  overlying  internal  nuclei,  the  corpora  striata  and  the  optic 
thalami — and  the  cortical,  which  pursue  a  superficial  course  and  are  carried  by  the 
pia  mater  to  all  parts  of  the  extensive  sheet  of  cortical  gray  substance,  as  well  as  to 
the  subjacent  tracts  of  medullary  white  matter. 

The  medulla  oblongata  and  the  pons  are  supplied  by  branches  from  the  anterior  spinal,  the 
vertebral,  the  basilar  and  the  posterior  cerebral  arteries.  These  branches  gain  the  nervous 
substance  as  two  sets,  the  radicular  and  the  median.  The  radicular  branches  follow  the  nerve- 
roots  and,  just  before  reaching  the  superficial  origins  of  the  nerves,  divide  into  peripheral  and 
central  twigs,  the  former  being  distributed  superficially  and  the  latter  following  the  root-fibres 
to  their  nuclei.  The  median  branches  are  numerous  minute  vessels  which  ascend  within  tin- 
median  raphe  towards  the  floor  of  the  fourth  ventricle  and  assist  the  centrally  directed  twigs  of 
the  radicular  branches  in  supplying  the  nuclei  of  the  nerves  situated  within  that  region.  Those 
supplying  the  nuclei  of  the  hypoglossal  and  the  bulbar  portion  of  the  spinal  accessory  nerves 
are  derivations  from  the  anterior  spinal  arteries ;  those  to  the  nuclei  of  the  vagus,  the  glosso- 
pharyngeal  and  the  auditory  are  from  the  vertebral  as  they  join  to  form  the  basilar ;  whilst 
those  to  the  nuclei  of  the  facial,  the  abducent  and  the  trigeminal  are  from  the  basilar.  The 
choroid  plexus  of  the  fourth  ventricle  is  provided  with  branches  from  the  posterior  cerelnll.it 
arteries. 

The  cerebellum  receives  its  supply  from  three  arteries,  the  anterior  and  posterior  in- 
ferior and  the  superior,  cerebellar.  The  general  course  of  these  vessels  is  approximately  at 
right  angles  to  the  direction  of  the  fissures  and  folia  of  the  hemispheres.  In  the  mid-brain  the 
interpcduncular  spaced  provided  with  branches  from  the  basilar  and  the  posterior  cerebral  arter- 
ies ;  the  cerebral  peduncles  with  those  from  the  posterior  communicating  and  the  terminal  part 
of  the  basilar;  and  the  corpora  qnadrigcmina  with  those  from  the  posterior  cerebral,  additional 
twigs  passing  from  the  superior  cerebellar  to  the  inferior  colliculi. 

The  thalamus  is  supplied  by  branches,  all  end-arteries,  from  different  sources,  those  for  its 
antero-median  portion  being  from  the  posterior  communicating,  those  for  its  antero-lateral  por- 
tion from  the  middle  cerebral,  whilst  those  for  its  remaining  parts,  as  well  as  for  the  pineal  and 
the  geniculate  bodies,  are  from  the  posterior  cerebral.  The  last  vessel  also  supplies  the  velum 
interpositnm  and  the  choroid  plexus  of  the  third  ventricle. 

The  structures  on  the  base  of  the  brain,  such  as  the  corpora  mammillaria,  the  tuber  cine- 
reum,  the  infundibulum  and  the  pituitary  body,  receive  twigs  from  the  posterior  communicating 
arteries.  The  optic  chiasm  and  tract  are  supplied  with  branches  from  the  anterior  cerebral,  tin- 
anterior  communicating,  the  internal  carotid,  the  posterior  communicating  and  the  anterior 
choroidal  .arteries. 


PRACTICAL  CONSIDERATIONS:  THE  BRAIN.  1207 

The  corpus  striatum,  both  the  caudate  and  lenticular  nuclei,  are  supplied  chiefly  by  branches 
from  the  middle  cerebral  artery,  which  pierce  the  anterior  perforated  space  and,  as  the  lenticular, 
lenticulo-striate  and  lenticulo-thalamic  vessels,  all  end-arteries,  traverse  the  lenticular  nucleus 
and  the  internal  capsule  and  terminate  in  the  caudate  nucleus  and  the  thalamus.  One  of  the 
lenticulo-striate  arteries,  which  pierces  the  outer  part  of  the  putamen,  was  named  by  Charcot 
the  "artery  of  cerebral  hemorrhage"  since  it  is  frequently  ruptured. 

The  choroid  plexus  of  the  lateral  ventricle  receives  its  blood-supply  from  the  anterior  and 
posterior  choroidal  arteries.  The  first  of  these,  given  off  by  the  internal  carotid  artery,  enters 
the  anterior  and  lower  part  of  the  choroidal  fissure  and  takes  part  in  forming  the  most  depend- 
ent portion  of  the  vascular  complex  which  overlies  the  hippocampus.  The  posterior  choroidal 
artery,  usually  represented  by  a  number  of  small  twigs,  is  derived  from  the  posterior  cerebral 
and  enters  the  upper  part  of  the  fissure.  After  supplying  the  velum  interpositum,  it  completes 
the  choroid  plexus  in  the  descending  horn  and  in  the  body  of  the  lateral  ventricle. 

The  cerebral  hemispheres  are  supplied  by  the  cortical  branches  of  the  anterior,  middle  and 
posterior  cerebral  arteries.  Of  these  the  middle  one  is  the  largest  and  is  distributed  to  the 
most  extensive  area,  which  embraces  the  greater  part  but  not  all  of  the  external  surface  of  the 
hemisphere.  This  vessel  also  supplies  the  outer  half  or  more  of  the  orbital  surface  and  the 
anterior  part  of  the  temporal  lobe.  The  anterior  cerebral  is  essentially  the  artery  of  the  mesial 
surface,  the  anterior  two-thirds  of  which,  in  conjunction  with  an  adjoining  zone  on  the  external 
and  on  the  orbital  surface,  it  supplies.  The  distribution  of  the  posterior  cerebral  is  chiefly  on 
the  mesial  and  tentorial  surface  of  the  occipito-temporal  region,  and  in  addition  an  adjoining 
strip  along  the  postero-inferior  margin  of  the  hemisphere.  It  follows,  therefore,  that,  with  the 
exception  of  the  occipital  lobe,  which  is  entirely  supplied  by  the  posterior  cerebral  artery,  all  of 
the  conventional  divisions  of  the  hemisphere  receive  their  arterial  supply  from  more  than  a  single 
source. 

The  frontal  lobe  is  supplied  by  the  anterior  cerebral  artery  : — over  its  entire  mesial  surface  ; 
over  the  superior  and  the  anterior  two-thirds  of  the  middle  frontal  convolutions  and  the  upper 
end  of  the  precentral  convolution  ;  and  over  the  orbital  surface  internal  to  the  orbital  sulcus. 
Over  all  the  remaining  parts,  the  frontal  lobe  receives  the  branches  of  the  middle  cerebral 
artery. 

The  parietal  lobe  is  supplied  by  the  middle  cerebral  artery  on  the  external  surface,  with  the 
exception  of  a  narrow  strip  along  the  upper  border  ;  this  zone,  together  with  the  mesial  surface 
of  the  lobe,  is  supplied  by  the  anterior  cerebral  artery.  The  occipital  lobe  is  supplied  exclusively 
by  the  posterior  cerebral  artery.  The  temporal  lobe  is  supplied  by  the  middle  cerebral  artery 
over  its  superior  and  the  upper  half  of  the  middle  temporal  convolution  with  the  tip  of  the  lobe  ; 
the  remainder  of  the  lobe  receives  the  branches  of  the  posterior  cerebral. 

The  limbic  lobe  shares  in  the  distribution  of  the  anterior  and  posterior  cerebral  arteries,  the 
district  of  the  former  including  the  gyrus  callosum  to  the  vicinity  of  the  isthmus,  whilst  that 
of  the  posterior  cerebral  includes  the  remainder  of  the  lobe. 

The  veins  returning  the  blood  from  the  brain  are  all  tributaries  of  the  dural 
sinuses,  and  they  therefore  only  to  a  limited  degree  follow  the  course  of  the  cerebral 
arteries.  They  are  further  distinguished  by  the  absence  of  valves.  The  superior 
cerebral  veins,  after  emerging  from  the  surface  of  the  brain,  course  within  the  pia 
over  the  convex  aspect  of  the  hemisphere  and  proceed,  for  the  most  part,  towards 
the  superior  longitudinal  sinus  into  which  they  open,  either  directly  or  through  the 
lacume  laterales,  by  from  12-15  trunks.  The  veins  draining  the  structures  situated 
around  the  lateral  and  third  ventricles  are  tributary  to  the  paired  lesser  veins  of  Galen, 
which  run  backward  within  the  velum  interpositum  and,  emerging  below  the  splenium, 
unite  to  form  the  great  vein  of  Galen.  This  vessel  joins  with  the  inferior  longitudinal 
sinus  to  form  the  straight  sinus,  which  is  lodged  in  the  line  of  juncture  between  the 
falx  cerebri  and  the  tentorium  cerebelli. 

PRACTICAL   CONSIDERATIONS  :   THE    BRAIN   AND    ITS 

MEMBRANES. 

Congenital  Errors  of  Development. — Various  defects  of  development  of  the 
brain  and  its  membranes  are  not  uncommon.  The  brain  may  be  absent  (anen- 
cephalus),  it  may  escape  from  the  skull  (exencephalus) ,  the  brain,  membranes  and 
vessels  may  be  only  rudimentary  (pseudencephalus},  or  there  may  be  arrest  of 
development  in  any  limited  portion  ( porencephalus — a  name  more  suitably  applied 
when  there  is  a  marked  depression  in  the  surface  of  the  brain).  The  brain  as  a  whole 
may  be  defective  (microcephalus} ,  or  it  may  be  abnormally  large  (macroccphahis}. 


I2o8  HUMAN  ANATOMY. 

The  most  common  enlargement  of  the  head,  hydroccphalus,  is  due  to  a  retention 
of  cerebro-spinal  fluid  within  the  cranium,  ordinarily  within  the  ventricles,  but  some- 
times in  the  subarachnoid  space.  It  is  usually  a  congenital  condition  ;  its  cause 
is  not  clearly  known.  It  is  believed  by  many  that  it  is  due  to  a  prenatal  inflam- 
mation of  the  ventricular  ependyma,  and  by  others  to  a  disarrangement  of  the  orifices 
of  communication  between  the  ventricles  (Luschka,  Monroe,  and  Neurath).  The 
aqueduct  of  Sylvius  has  been  found  obliterated,  and  inflammatory  processes  have 
been  seen  about  the  foramen  of  Monroe. 

Congenital  defective  ossification  of  the  skull  may  result  in  a  gap  through  which 
may  protrude  a  portion  of  the  meninges  with  or  without  brain  substance.  If  such  a 
protrusion  consists  of  a  meningeal  sac  containing  only  fluid,  it  is  called  a  meningocele. 
If  it  contains  a  portion  of  the  brain  also,  it  is  an  cnccphalocclc,  and  if  the  protruded 
portion  of  the  brain  encloses  a  portion  of  a  ventricle,  a  hydrenccphalocelc.  Such 
tumors  may  be  concealed  from  view  at  the  base  of  the  skull,  or  in  the  pharynx,  or 
may  protrude  into  the  nose  or  orbit.  They  are  usually  in  the  median  line  and  most 
frequently  in  the  occipital  region.  Next  in  frequency  they  occur  at  the  fronto-nasal 
suture,  and  more  rarely  in  other  parts  of  the  skull.  Pressure  on  the  tumor  will  often 
reduce  it  partly  or  completely  within  the  cranium,  but  in  the  latter  case  symptoms  of 
pressure  on  the  brain  will  arise.  Violent  expiratory  efforts,  as  in  crying  or  coughing, 
which  increase  the  cerebral  congestion,  render  the  tumor  more  tense. 

The  Meninges. — Diseases  of  the  meninges  are  relatively  more  common  than 
those  of  the  brain  proper,  and  many  conditions  often  spoken  of  as  brain  diseases  are 
affections  of  the  meninges,  the  pia  being  closely  adherent  to  the  brain  and  extending 
into  the  fissures.  Inflammation  of  the  dura  is  called  pachymeningitis ,  of  the  pia  and 
arachnoid  together  lepto-meningitis. 

External  pachymeningitis  is  usually  secondary  to  disease  of  the  cranial  bones, 
traumatism,  infection,  or  tumors.  It  is  most  frequently  the  result  of  ear  disease,  and 
is  therefore  generally  of  surgical  interest. 

Internal  pachymeningilis  is  apt  to  be  associated  with  effusions  of  blood  into  the 
subdural  space  ;  they  may  cover  a  considerable  area  without  producing  marked  symp- 
toms, or  they  may  be  encapsulated  (hsematomata  of  the  dura  mater),  and  may  reach 
the  size  of  a  man's  fist,  causing  compression  of  the  brain.  Occasionally  they  become 
purulent.  The  blood  or  pus  may  gravitate  to  the  base  of  the  brain  in  the  region  of 
the  cerebellum,  pons,  and  medulla,  when  the  pressure  symptoms  will  be  more  serious  ; 
or  it  may  find  its  way  into  the  spinal  canal. 

The  dura  is  especially  adherent  at  the  base  of  the  skull  and,  to  some  degree,  at 
the  sutures  of  the  vault.  In  the  rest  of  the  vault  it  is  loosely  attached,  and  accord- 
ing to  Tillaux,  particularly  so  in  the  temporal  region.  Collections  of  blood  may 
accumulate  between  the  dura  and  the  bone  (extradural  hemorrhage}.  This  variety 
of  intracranial  hemorrhage  is  commonly  the  result  of  rupture  of  one  of  the  branches 
of  the  middle  meningeal  artery  in  the  temporal  region,  the  effused  blood  separating 
the  loosely  attached  dura.  If  the  blood  is  poured  out  rapidly,  compression 
symptoms  will  soon  appear,  but  if  the  hemorrhage  is  slow,  the  escape  of  cerebro-spinal 
fluid  into  the  spinal  canal  permits  of  more  delay  in  the  appearance  of  those  symptoms. 
The  patient  has  often  time  to  recover,  at  least  partially,  from  the  unconsciousness 
of  concussion  before  that  of  compression  appears  ;  and  it  is  this  recovery  of  intelligence 
which  is  most  characteristic  of  the  condition.  There  will  often  be  localizing  symptoms 
indicating  the  part  of  the  brain  cortex  which  is  irritated  or  compressed. 

Subdural  hemorrhage  may  follow  the  rupture  of  a  number  of  small  vessels,  either 
of  the  pia  or  dura  under  a  depressed  fracture  ;  or  it  may  come  from  a  large  vessel, 
particularly  the  middle  cerebral.  The  symptoms  and  treatment  are  very  much  the 
same  as  in  the  extradural  variety. 

In  children  extradural  hemorrhage  is  very  rare,  because  of  the  relatively  firmer 
attachment  of  the  dura  during  the  period  of  growth.  The  blood  may  escape  under 
the  scalp  through  a  line-  of  fracture  in  the  skull ;  or,  what  is  more  likely,  it  may  pass 
through  a  tear  in  the  dura  into  the  subdural  space.  In  fractures  of"  the  base  of  the 
skull,  at  any  age,  owing  to  the  adhesion  of  the  dura,  the  latter  is  likely  to  be  torn  ; 
cerebro-spinal  fluid  mav  escape  into  the  adjacent  air  cavities,  as  into  the  nose,  pharynx 
or  middle  ear.  A  close  adhesion  of  the  dura  to  the  bone,  as  sometimes  found  at 


PRACTICAL   CONSIDERATIONS  :  THE  BRAIN.  1209 

operation,  indicates  a  previous  inflammation,  as  does  any  tendency  of  the  arachnoid 
to  adhere  to  the  dura,  since  these  two  are  normally  not  adherent.  The  arachnoid, 
however,  is  normally  closely  attached  to  the  pia,  and  for  practical  purposes  they 
are  usually  considered  as  one  layer,  the  lepto-meninx. 

Inflammation  of  this  layer — lepto-meningitis — may  attack  the  convexity  or  the 
base  of  the  brain,  and  may  be  primary  or  may  be  secondary  to  other  diseases,  usually 
purulent  infections.  It  is  asserted  that  the  primary  disease  attacks,  as  a  rule,  the 
base,  the  secondary,  the  convexity  of  the  brain  ;  but  this  is  not  beyond  dispute. 

Tuberculous  meningitis  is  frequently  found  at  the  base,  but  miliary  tubercles  are 
not  uncommon  on  the  convexity  of  the  brain.  The  exudate  which  is  deposited  at 
the  base  frequently  leads  to  irritation  or  paralysis  from  pressure  on  the  cranial  nerves 
in  close  relation  to  the  under  surface  of  the  brain.  Tumors  growing  at  the  base  of 
the  brain  produce  localizing  symptoms  early  by  pressing  on  the  adjacent  cranial 
nerves.  A  single  nerve  may  be  involved,  but  more  commonly  a  combined  paralysis 
from  involvement  of  several  nerves  results. 

The  cerebro-spinal  flidd  is  found  in  the  subdural  and  subarachnoid  spaces,  and 
in  the  ventricles.  Over  the  vault  it  is  comparatively  scanty  in  both  spaces.  At  the 
base,  however,  in  the  subarachnoid  space  of  the  middle  and  posterior  fossae,  it  is 
abundant,  forming  an  excellent  support  and  protection  to  the  most  delicate  part  of 
the  brain,  that  containing  the  vital  centres.  The  frontal  lobes,  of  much  less  impor- 
tance as  to  vital  function,  rest  directly  on  the  bone  in  the  anterior  fossa ;  and  are  there- 
fore more  subject  to  direct  traumatic  influences.  The  fact  that  the  subarachnoid 
space  is  continuous  with  the  ventricles  through  the  foramina  of  Magendie  and  of 
Luschka,  and  communicates  freely  at  the  foramen  magnum  with  the  subarachnoid 
space  of  the  cord,  explains  how  excess  of  pressure  within  the  cranium  at  one  part 
may  be  relieved  by  escape  of  fluid  to  other  parts.  It  explains  also  why  pressure 
on  a  spina  bifida  will  sometimes  produce  symptoms  of  cerebral  compression  ;  and 
vice  versa,  why  the  increased  congestion  of  the  cerebral  vessels  from  expiratory 
efforts,  as  in  coughing,  will  increase  the  tension  in  the  spinal  tumor. 

Occlusion  of  the  foramen  of  Magendie,  by  the  products  of  inflammation,  may 
cause  increase  of  fluid  from  retention  in  the  ventricles,  with  the  development  of 
hydrocephalus,  and  it  is  in  this  way  that  internal  hydrocephalus  occasionally  follows 
meningitis.  For  the  purpose  of  determining  the  cause  of  this  condition,  subarach- 
noid fluid  is  sometimes  withdrawn  through  a  hollow  needle. 

The  lateral  ventricles  can  be  tapped  through  a  trephine  opening  3  cm.  (i^ 
in.)  behind  the  external  auditory  meatus,  and  the  same  distance  above  Reid's  base 
line — drawn  from  the  lower  margin  of  the  orbit  through  the  middle  of  the  external 
auditory  meatus.  The  needle  is  passed  towards  a  point  on  the  opposite  side  of  the 
skull,  6.5-7.5  cm-  (2/^-3  m-)  vertically  above  the  external  auditory  meatus.  Under 
normal  circumstances  the  ventricle  is  from  5-5.6  cm.  (2—2*^  in.)  from  the  surface, 
but  if  the  ventricle  is  distended  the  distance  is  shorter. 

By  a  trephine  opening  in  the  occipital  bone  in  the  subcerebellar  region,  the 
subarachnoid  fluid  has  been  reached  at  the  base  of  the  brain  where  it  is  most 
abundant. 

Lumbar  puncture  for  withdrawing  cerebro-spinal  fluid  for  diagnostic  and  thera- 
peutic purposes  is  sometimes  employed.  The  needle  should  be  introduced  between 
the  third  and  fourth,  or  between  the  fourth  and  fifth  lumbar  vertebrae,  at  the  level 
of  the  lower  border  of  the  spinous  process,  or  opposite  its  lower  third,  and  about 
I  cm.  from  the  median  line.  It  should  be  passed  somewhat  upward  between  the 
sloping  laminae,  and  should  be  continued  inward  toward  the  canal  until,  by  the 
diminished  resistance,  it  is  recognized  that  the  point  of  the  needle  has  entered  the 
subarachnoid  space. 

The  Brain. — Of  all  the  affections  of  the  brain,  hemorrhage  is  the  most  frequent 
and  most  important,  whilst  in  the  spinal  cord  it  is  comparatively  rare  unless  as  a 
result  of  trauma.  Hemorrhage  from  the  meningeal  vessels  is  most  commonly  due  to 
trauma,  but  within  the  brain  substance  the  usual  cause  is  atheroma,  sometimes  with 
the  production  of  miliary  aneurisms.  A  sudden  strain  increases  the  intravascular 
tension  and  ruptures  one  of  these  diseased  vessels,  giving  rise  to  pressure  symptoms, 
depending  on  the  seat  and  extent  of  the  hemorrhage. 


i2io  HUMAN  ANATOMY. 

The  cortex  is  supplied  by  pial  vessels  distinct  from  those  supplying  the  basal 
ganglia  and  adjoining  regions.  The  latter  come  directly  from  the  branches  of  the 
circle  of  Willis  at  the  base.  The  cortical  vessels  anastomose  ;  those  in  the  region 
of  the  basal  ganglia  do  not.  The  latter  are  ' '  end  arteries, ' '  so  that  when  one  is 
plugged  by  an  embolus  the  part  supplied  is  deprived  of  blood  and  undergoes 
necrosis  (softening  of  the  brain).  In  such  a  case  the  cortical  supply  would  not  be 
permanently  interfered  with.  When  a  cortical  arteriole  is  blocked,  the  anastomosis 
may  furnish  a  sufficient  collateral  circulation  to  prevent  necrosis  in  the  affected 
part,  but  cortical  softening  is  exceedingly  common.  When  one  of  the  arteries  forming 
the  circle  of  Willis  is  occluded,  as  an  internal  carotid  by  ligation  of  the  common 
carotid,  the  anastomosis  in  the  circle  is  so  free  that,  in  most  cases,  no  marked 
effect  is  apparent.  Cerebral  disturbances,  as  delirium  or  convulsions,  do  occur  in 
some  cases,  and  in  some  are  fatal.  Even  when  both  carotids  are  ligated,  with  an  in- 
terval of  some  days  or  weeks,  the  operation  is  not  more  frequently  followed  by  cere- 
bral disturbances  than  when  only  one  is  tied  (Pilz).  A  case  in  which  the  patient 
lived  after  one  carotid  and  one  vertebral  had  been  obliterated  by  disease,  and  the 
other  carotid  ligatured,  has  been  reported  (Rossi).  In  another  case,  although  both 
carotids  and  both  vertebrals  had  been  occluded,  the  patient  lived  a  considerable  time 
afterward,  the  cerebral  circulation  being  maintained  through  the  medium  of  anas- 
tomosis of  the  inferior  with  the  superior  thyroids,  and  the  deep  cervical  with  the 
occipital  artery  (Davy).  Occasionally  ligation  of  the  carotid  has  been  followed  by 
hemiplegia. 

The  most  common  seat  of  intracerebral  hemorrhage  is  near  the  basal  ganglia  in 
the  region  of  the  internal  capsule.  The  artery  most  frequently  at  fault  is  a  branch  of 
the  middle  cerebral,  the  lenticulo-striate,  or  artery  of  Charcot  (page  1207).  Hemor- 
rhages occur  with  less  frequency  in  other  portions  of  the  cerebrum,  and  much  more 
rarely  in  the  pons,  medulla  oblongata,  and  cerebellum.  The  symptoms  produced  by 
the  hemorrhage  are  the  result  of  destruction  of  tissue  and  of  pressure  upon  adjacent 
parts,  and  will  vary  according  to  the  seat  of  the  lesion.  Tumors  or  inflammatory 
products  will  produce  essentially  the  same  symptoms. 

Cerebral  Localization. — In  order  to  understand  the  nature  of  the  symptoms 
produced  by  brain  lesions  it  will  be  necessary  to  study  at  least  some  of  the  functional 
areas  of  the  cortex  and  their  paths  of  conduction  through  the  brain  substance. 

Taylor  has  summarized  as  follows  the  researches  of  His  and  of  Flechsig,  which 
are  of  comparatively  recent  date  and  have  thrown  new  and  valuable  light  upon  the 
functions  possessed  by  the  cortical  regions  of  the  brain,  by  the  study' of  their  mode  of 
development.  Flechsig  succeeded  in  following  the  various  tracts  through  their 
myelination.  The  tracts  which  are  functional  earliest  receive  their  myelin  before  the 
others.  He  has  shown  that  the  fibres  in  the  spinal  cord,  medulla,  pons  and  corpora 
quadrigemina  are  almost  entirely  medullated  when  the  higher  parts  show  little  or  no 
myelin.  In  the  new-born  child  the  cerebrum  is  almost  entirely  immature,  and 
proportionately  few  of  its  fibres  are  medullated. 

According  to  Flechsig,  the  sensory  paths  in  the  brain  first  become  medullau  d, 
and  may  be  observed  developing  one  after  another,  beginning  with  that  of  smell  and 
ending  with  that  for  auditory  impulses  from  the  periphery  to  the  cortex.  In  this 
way  it  has  been  ascertained  that  the  individual  sensory  paths  terminate  in  tolerably 
sharply  circumscribed  cortical  regions,  for  the  most  part  widely  removed  from  one 
another,  being  separated  by  masses  of  cortical  substance  which  remain  for  a  consid- 
erable period  immature  or  undeveloped.  The  cortical  sense  areas  thus  mapped  out 
correspond  entirely  to  those  regions  of  the  surface  of  the  brain  which  pathological 
observation  has  shown  to  stand  in  relation  to  the  different  qualities  of  sensation. 
Olfactory  fibres  are  found  to  end  mainly  in  the  uncinate  gyrus.  Visual  fibres  have 
been  traced  to  the  occipital  lobe  in  the  neighborhood  of  the  calcarine  fissure,  and 
auditory  fibre*  to  the  temporal  lobe.  Flechsig  has  further  observed  that  new  paths 
begin  to  develop  from  the  points  where  certain  of  the  sense  fibres  terminate  and  pur- 
sue a  downward  course.  They  can  be  followed  from  the  cortex  to  the  medulla  and 
to  the  motor  nuclei  of  the  cord.  These  drsrcnding  paths  are  mainly  those  known  as 
the  pyramidal  or  motor  tracts,  and  the  area  from  which  they  proceed,  commonly 
called  the  Rolandic  region,  is,  according  to  Flechsig,  concerned  also  in  the  si -nsation 


PRACTICAL   CONSIDERATIONS  :  THE  BRAIN. 


I2II 


of  touch  ;  he  calls  it  the  someesthetic  area.  It  includes  the  precentral  and  postcentral 
convolutions,  the  paracentral  lobule.  The  sensory  fibres  passing  from  the  periph- 
ery to  this  area  would  appear  to  excite  sensations  of  touch,  pain,  temperature, 
muscle-  and  tendon-sense,  equilibrium,  etc.  This  cortical  region  probably  repre- 
sents a  complex  mass  of  sense  centres  rather  than  a  single  sensory  area,  and  in 
addition  to  being  a  sensory  field,  the  somaesthetic  area  is  the  great  motor  region 
of  the  brain. 

When  this  sensory-motor  area  and  the  various  sensory  areas  are  fully  taken  into 
account,  there  still  remain  about  two-thirds  of  the  cortex  which  appear  to  have  noth- 
ing to  do  with  the  periphery.  Flechsig  calls  these  regions  of  the  cortex  ' '  associa- 
tion centres,'"  as  he  believes  they  furnish  arrangements  for  uniting  the  various  central 
sense  areas. 

The  best  known  cortical  areas  are  the  motor,  speech,  visual,  and  auditory,  al- 
though new  contributions  to  our  knowledge  are  being  made  from  time  to  time.  Re- 
cently Griinbaum  and  Sherrington  have  demonstrated  in  the  cortex  of  the  higher 
apes,  including  the  orang  and  several  species  of  the  chimpanzee  and  gorilla,  that  the 
motor  area  was  found  in  the  whole  length  of  the  precentral  convolution  and  the  en- 

FIG.  1041. 


Left  cerebral  cortex  illustrating  diagrammatically  motor  zone  and  its  subdivisions.     (Mills.) 

tire  length  of  the  central  fissure.  It  did  not  at  any  point  extend  behind  the  central 
fissure.  They  demonstrated  other  important  facts  in  connection  with  this  and,  other 
areas.  These  results  have  been  in  part  at  least  confirmed  by  recent  histological  re- 
searches, and  by  faradization  of  the  human  brain  during  operation  for  the  purpose 
of  more  accurately  identifying  the  relations  of  the  opening  to  the  area  to  be  exposed. 

The  most  important,  because  the  best  known,  area  of  the  cortex,  is  that  asso- 
ciated with  the  fissure  of  Rolando  and  the  fissure  of  Sylvius. 

Before  the  publication  of  the  experiments  and  observations  just  alluded  to,  the 
motor  zone  was  regarded  as  extending  over  both  central  convolutions  which  lie  one 
anterior  and  the  other  posterior  to  the  central  fissure  or  fissure  of  Rolando,  also  over 
the  paracentral  lobule  on  the  median  aspect  of  the  hemisphere,  and  to  some  extent 
into  the  posterior  extremities  of  the  first  and  second  convolutions.  The  trend  of 
opinion  is  now  in  favor  of  the  view  that  the  motor  region  is  entirely  or  almost  en- 
tirely in  front  of  the  central  fissure  (Monakow,  Mills).  This  is,  of  course,  a  matter 
of  considerable  importance  in  trephining  for  a  tumor  or  hemorrhage  supposed  to  be 
situated  in  this  area,  as  instead  of  making  the  opening  directly  astride  of  the  fissure 
of  Rolando  it  would  be  better,  if  these  views  are  correct,  to  operate  with  the  idea  of 
exposing  a  region  two-thirds  or  three-fourths  in  front  and  one-third  or  one-fourth 
behind  the  central  fissure. 


1212 


HUMAN  ANATOMY. 


In  the  lower  one-third  or  fourth  of  the  motor  zone  are  found  the  motor  centres 
for  \h&face  and  tongue,  that  is,  for  the  facial  and  hypoglossal  nerves.  In  the  middle 
third  or  half  are  the  arm  centres.  In  the  upper  part  of  the  region  and  paracentral 
lobe,  are  the  centres  for  the  lower  extremity.  Localized  lesions  of  the  motor  zone 
may  therefore  produce  a  paralysis  limited  to  one  part  controlled  by  the  affected  por- 
tion of  the  cortex,  as  of  the  face,  arm  or  leg  (monoplegia).  The  lesion  is  much 
more  likely  to  involve  two  adjacent  areas,  as  of  the  face  and  arm,  or  of  the  arm 
and  leg,  giving  rise  to  a  combined  paralysis  ;  but  no  single  lesion,  unless  it  were 
crescentic  in  form,  could  involve  at  the  same  time  the  leg  and  face  areas  without 
including  the  intervening  arm  area. 

Within  each  of  the  larger  areas  a  more  specialized  differentiation  is  possible, 
although  none  of  them  can  be  sharply  defined,  not  even  the  larger.  That  the  facial 
centre  lies  in  the  lower  part  of  the  anterior  central  convolution  is  certain,  and  it  is 
believed  that  the  upper  and  lower  muscles  of  the  face  are  each  represented  by  a  sepa- 
rate centre.  In  the  upper  and  forward  part  of  the  face-area  are  represented  the 
movements  of  the  cheek  and  eye-lids  ;  in  the  posterior  part  the  movements  of  the 
pharynx,  platysma  and  jaws. 

FIG.  1042. 


Diagram  illustrating  probable  relations  of  physiological  areas  and  centres  of  lateral  aspect  of  left  cerebral 

hemisphere.    ( Mills.) 

In  the  arm-area  it  is  considered  as  certain  that  the  centre  for  the  movements  of 
the  thumb  and  index  finger  is  below;  above  is  that  for  the  finger  and  hands;  and 
in  th«  highest  part  is  that  for  the  shoulder.  In  the  posterior  parts  of  the  second 
frontal  convolution  and  in  a  portion  of  the  third  frontal  convolution  are  the  centres 
for  the  associated  lateral  movements  of  the  eyes  and  lateral  movement  of  the  head 
(Beevor  and  Horsley). 

Our  knowledge  of  the  more  special  localization  within  the  leg  centre  is  not  at  all 
exact,  and  the  many  views  held  are  very  contradictory.  It  is  believed  that  the 
centres  for  the  movements  of  the  thigh,  knee,  foot,  and  toes,  are  arranged  in  the 
order  named,  from  before  backward  on  the  lateral  border  of  the  hemisphere  and  in 
the  paracentral  lobe. 

A  narrow  zone  for  the  movements  of  the  trunk,  as  shown  by  Griinbaum  and 
Sherrington,  is  located  between  the  upper  border  of  the  arm-area  and  the  lower 
border  of  the  leg-area.  It  is  now  considered  probable,  however,  that  the  cutaneous 
sensory  centres  are  posterior  to  and  in  close  contact  with  the  motor  centres  in 
the  postcentral  convolution,  while  other  centres  for  stereognostic  perception  and  the 
muscular  sense  are  located  in  the  superior  and  inferior  parietal  convolutions. 

The  speech  centres  are  in  the  posterior  part  of  the  third  left  frontal  convolution 
(Broca's  convolution),  in  right-handed  people  in  the  first  left  temporal  convolution, 
and  perhaps  in  the  left  angular  gyrus. 


PRACTICAL   CONSIDERATIONS  :  THE  BRAIN. 


1213 


In  Broca's  convolution  is  probably  the  centre  for  motor  speech,  and  a  lesion 
here  gives  motor  aphasia,  an  inability  to  transform  concepts  into  words,  although 
the  patient  is  conscious  and  the  tongue  can  be  moved.  A  minor  part  in  speech  is 
played  by  the  posterior  part  of  the  right  third  frontal  convolution,  but  in  the  left- 
handed  it  is  probably  the  chief  centre. 

In  the  first  left  temporal  convolution  is  the  auditory  centre  for  speech,  a  lesion 
of  which  leads  to  a  loss  of  memory  for  word-sounds,  though  the  hearing  may  be 
undisturbed. 

The  centre  for  memory  of  printed  words  is  probably  in  the  left  angular  gyrus  ; 
and  a  lesion  there  probably  causes  a  loss  of  the  ability  to  read  or  to  understand 
written  language,  though  ordinary  sight  is  undisturbed.  The  existence  of  a  motor 
writing  centre  is  doubtful  (Oppenheim).  If  it  exists,  it  is  probably  located  in  the 
posterior  portion  of  the  left  second  frontal  convolution. 

We  have  no  definite  knowledge  of  the  location  of  centres  for  smell  and  taste. 
That  for  smell  is  thought  to  lie  in  the  uncinate  gyrus.  The  centre  for  taste  has  been 
supposed  to  be  in  the  anterior  portion  of  the  gyrus  fornicatus,  but  it  is  not  decided, 
although  it  is  probably  near  the  centre  for  smell. 

FIG.  1043. 


Diagram  illustrating  probable  relations  of  physiological  areas  and  centres  of  mesial  aspect  of  left  cerebral 

hemisphere.     (Mills.} 

The  auditory  centre,  as  indicated,,  is  in  the  upper  temporal  convolution.  It  is 
very  likely  that  the  centre  of  each  side  is  connected  with  both  auditory  nerves,  so 
that  a  paralysis  of  one  side  by  a  unilateral  lesion  of  one  side  may  be  compensated  for 
by  the  centre  of  the  opposite  side. 

It  is  probable  that  no  part  of  the  cerebral  cortex  is  absolutely  without  function, 
although  the  functions  of  some  areas  are  very  little  known.  Unilateral  disease  of  the 
anterior  portion  of  the  frontal  lobe  may  be  extensive  without  notable  symptoms  of"  any 
kind.  The  atrophy  is  often  most  marked  here  in  general  paralysis  of  the  insane, 
and  in  other  forms  of  dementia.  It  is  generally  agreed  that  the  seat  of  "  the  higher 
psychical  functions ' '  is  located  in  the  prefrontal  lobes,  the  left  side  being  perhaps 
more  active  than  in  the  right. 

Reference  has  already  been  made  to  the  relation  of  the  occipital  cortex  to  sight, 
and  of  the  temporal  to  hearing.  The  cuneus  and  calcarine  fissure  together  constitute 
a  primary  or  lower  cortical  or  visuo-sensory  centre,  while  the  lateral  aspect  of  the 
occipital  lobe  is  a  visuo-psychic  area,  containing  sub-areas  or  centres  concerned  with 
higher  visual  processes.  Mind  blindness,  for  instance,  results  from  destructive  lesion 
of  the  lateral  occipital  lobe,  particularly  if  the  lesion  is  a  large  one,  in  the  left  hemi- 
sphere, or  if  lesions  of  both  occipital  lobes  are  present.  A  lesion  of  the  cuneo- 
calcarine  cortex  causes  lateral  homonymous  hemianopsia.  This  may  be  produced 


I2i4  HUMAN  ANATOMY. 

also  by  a  lesion  in  the  lateral  portion  of  the  occipital  lobe,  if  it  extends  inwards 
sufficiently  to  interrupt  the  optic  radiations. 

In  spite  of  extensive  researches  the  functions  of  the  central  ganglia  are  very 
little  known. 

Lesions  of  the  cerebellar  hemispheres  may  not  produce  distinct  phenomena 
until  the  median  lobe  or  vermiform  process  is  involved,  when  two  especially  charac- 
teristic symptoms  .will  almost  certainly  develop.  These  are  a  peculiar  disturbance  of 
equilibrium  with  a  staggering  gait  (cerebellar  ataxia),  and  a  troublesome  vertigo. 
Although  the  patient  can  scarcely  stand  alone  he  may  possibly  be  able  to  perform 
the  most  delicate  movements  with  his  upper  extremities.  The  vertigo  occurs  only 
in  standing  or  walking,  and  is  then  almost  always  present.  Nystagmus  is  also  a 
frequent  symptom.  Vomiting  is  very  often  present,  but  is  not  characteristic,  since 
it  is  equally  frequent  in  other  brain  diseases. 

Extending  along  the  floor  of  the  aqueduct  of  Sylvius  and  of  the  fourth  ventricle, 
that  is,  along  the  cerebral  peduncles,  pons  and  medulla,  we  find  the  nuclei  of  origin 
of  the  motor  fibres  of  the  cranial  nerves.  It  should  be  borne  in  mind  that  the  con- 
trolling centres  of  these  nerves  are  in  the  cerebral  cortex.  Many  automatic  centres, 
as  of  circulation,  respiration,  sweating,  and  regulation  of  heat,  as  well  as  the  motor 
and  sensory  tracts  are  found  in  the  medulla. 

Cranio-Cerebral  Topography. — In  order  that  the  surgeon  may  expose  and 
recognize  certain  areas  of  the  cortex,  it  becomes  very  important  that  the  relations 
between  these  areas  and  the  corresponding  external  surface  be  well  understood.  For 
this  purpose  advantage  is  taken  of  the  landmarks  of  the  skull  (page  241).  From 
these  bony  points,  ridges  and  depressions,  by  means  of  lines  and  measurements,  the 
known  cortical  areas  may  be  accurately  mapped  out. 

The  upper  limit  of  each  cerebral  hemisphere  is  indicated,  approximately,  by  the 
median  line  at  the  top  of  the  skull  from  the  glabella  to  the  external  occipital  protu- 
berance, due  allowance  being  made  for  the  superior  longitudinal  sinus,  which  lies 
under  the  skull,  in  the  longitudinal  fissure,  between  the  two  hemispheres. 

The  lower  limit  is  represented  by  a  transverse  line,  in  front,  just  above  the  upper 
margin  of  the  orbit.  At  the  side  of  the  skull  the  line  passes  from  about  a  half  inch 
above  the  external  angular  process  of  the  frontal  bone  to  just  above  the  external 
auditory  meatus.  From  here  it  passes  to  the  external  occipital  protuberance  ;  this 
part  of  the  line  corresponding,  approximately,  to  the  lateral  sinus.  The  cerebellum 
lies  immediately  below  this  line. 

Of  the  brain  fissures,  those  of  greatest  importance  in  cerebral  localization  are 
the  Rolandic  and  Sylvian,  since  by  means  of  these  all  the  best  known  cortical  centres 
can  be  located.  Of  the  two,  the  fissure  of  Rolando  is  much  the  more  important, 
because  the  motor,  the  most  definitely  known  cortical  area,  is  associated  with  it.  Its 
upper  limit  is  at  a  point  about  12  mm.  (one-half  inch)  behind  the  mid-point  between 
the  glabella  and  the  inion,  and  about  one-half  inch  from  the  median  line.  It  passes 
outward,  downward,  and  forward,  approximately,  at  an  angle  of  71°  with  the  median 
sagittal  line  of  the  skull.  It  is  8.5  cm.  (3^  in.)  long  (Thane),  and  ends  below  just 
above  the  fissure  of  Sylvius.  Near  its  fower  end  it  turns  rather  suddenly  downward, 
so  that,  in  this  part,  it  is  not  in  the  line  of  the  angle  of  71°. 

Many  methods  have  been  devised  for  the  purpose  of  making  the  line  of  the 
fissure  on  the  scalp. 

Chiene1  s  method  consists  of  folding  an  ordinary  square  sheet  of  paper  on  the 
diagonal  line,  thus  dividing  an  angle  of  90°  in  half,  making  two  of  45°.  One  of  these 
angles  of  45°  is  again  halved  in  a  similar  manner,  making  two  new  angles  each  of 
22^°.  The  paper  is  then  so  unfolded  that  one  of  the  angles  of  22^°  is  added  to  that 
of  45°,  making  a  new  angle  of  67^°  ;  this  will  be  sufficiently  near  that  of  the  fissure 
of  Rolando  for  all  practical  purposes. 

Hors/fv  s  crrtoiiiticr  consists  of  two  strips,  either  of  thin,  flexible  metai  or  of 
parchment  paper,  each  graduated  in  inches.  The  lateral  arm  is  placed  at  an  angle 
of  67°  with  tin-  long  arm,  the  apex  of  the  angle  being  at  a  point  12  mm.  or  one-half 
inch  behind  the  mid-point  of  the  long  arm. 

Le  Fort  simply  drew  a  line  from  the  beginning  of  the  fissure,  above,  to  the  mid- 
dle of  the  zygoma,  below,  and  marked  off  on  this  line  the  proper  length  of  the  fissure. 


PRACTICAL   CONSIDERATIONS  :  THE  BRAIN. 


1215 


Anderson  and  Mackins  suggest  :  ( i )  a  median  sagittal  line  from  the  glabella  1,0 
the  inion  ;  (2)  a  frontal  line  from  the  mid-sagittal  point  to  the  depression  just  in  front 
of  the  ear  at  the  level  of  the  upper  border  of  the  meatus  ;  (3)  a  squamosal  line  from 
the  most  external  point  of  the  external  angular  process,  at  the  level  of  the  superior 
border  of  the  orbit  to  the  junction  of  the  middle  and  lower  thirds  of  the  frontal  line, 
and  prolonged  for  about  3. 7  cm.  ( i  yz  in. )  behind  the  frontal  line.  The  upper  ex- 
tremity of  the  central  fissure  was  found  by  them  to  lie  between  the  mid-sagittal  point 
and  a  point  18  mm.  (3/£  in.)  behind  it,  and  the  lower  extremity  of  this  fissure  they 
located  near  the  squamosal  line,  about  18  mm.  (^  in.)  in  front  of  its  junction  with 
the  frontal  line.  The  commencement  of  the  lateral  portion  of  the  Sylvian  fissure  is 
not  at  a  definite  fixed  point,  but  will  usually  be  hit  at  a  point  from  3.7-5  cm.  (1^-2 
in. )  behind  the  angular  process,  the  course  of  the  horizontal  portion  of  this 
fissure  corresponding  closely  to  the  squamosal  line  (Mills). 


Fissure  of  Rolando 


FIG.  1044. 

Bregma 


Line  for  Rolandic  fissure 


Pos 


Interparietal  fissure- 


External  parieto- 
occipital  fissure 


Parietal  eminence 


Inion 


Lateral  sinus 


isteripr  limb 
of  Sylvian  fissure 


ne  for 
Sylvian  fissure 


Vertical  limb 

of  Sylvian  fissure 

Horizontal  limb 
of  Sylvian  fissure 
Glabella 

Nasion 


Semidiagrammatic  view  of  head,  showing  relation  of  Rolandic  and  Sylvian  fissures  and  lines. 

The  fissure  of  Sylvius  begins  anteriorly,  approximately,  at  a  point  3  cm.  (i/^ 
in. )  behind  the  external  angular  process  of  the  frontal  bone  ;  and  ends  posteriorly  at 
a  point  18  mm.  (^  in.)  below  the  parietal  eminence.  A  straight  line  between  these 
two  points  will  represent  the  fissure,  which  is  about  10  cm.  (4  in.)  long.  The  an- 
terior 1 8  mm.  (24  in-)  of  this  line  will  correspond  to  the  main  portion  of  the  fissure 
and  the  remainder  to  the  horizontal  limb.  The  vertical  limb  ascends  for  about 
2.5  cm.  (i  in.)  from  the  posterior  end  of  the  main  fissure.  Around  the  posterior 
end  of  the  horizontal  limb,  and  approximately  under  the  parietal  eminence  lies  the 
supramarginal  convolution.  It  is  continuous  in  front  with  the  ascending  parietal 
convolution,  and  behind  with  the  angular  gyrus. 

The  parieto-occipital  fissure  is  most  marked  on  the  mesial  surface  of  the  brain. 
The  external  limb  passes  outwards,  almost  at  right  angles  to  the  longitudinal  fissure 
on  the  external  surface  for  about  2.5  cm.  and  lies  from  2-3  mm.  in  front  of  the  lambda. 

The  frontal  lobe  is  divided  into  three  main  convolutions  by  the  superior  and  in- 
ferior frontal  sulci.  The  line  for  the  superior  frontal  sulcus  passes  directly  backward 


I2l6 


HUMAN  ANATOMY. 


from  the  supraorbital  notch,  and  parallel  to  the  longitudinal  fissure  to  within  18 
mm.  (^  in.)  of  the  fissure  of  Rolando.  The  inferior  frontal  sulcus  is  represented, 
approximately,  by  the  anterior  end  of  the  temporal  ridge. 

In  the  parietal  lode  the  most  important  sulcus  is  the  intraparietal.  It  begins 
near  the  horizontal  limb  of  the  fissure  of  Sylvius,  and  passes  upward  and  backward 
about  midway  between  the  fissure  of  Rolando  and  the  parietal  eminence.  It  then 
turns  backward,  running  about  midway  to  the  longitudinal  fissure  and  the  centre 
of  the  parietal  eminence.  Above  the  sulcus,  in  front,  lies  the  ascending  parietal 
convolution,  just  posterior  to  the  fissure  of  Rolando  and  behind  the  superior  pari- 
etal lobule.  Below  the  sulcus,  anteriorly,  is  the  supramarginal  convolution,  and 
posteriorly,  the  angular  gyrus. 

FIG.  1045. 

Eregma 


Lateral  ventricle 


Middle  meningeal 

rtery,  anterior 
branch 


Posterior  horn  "f 
lateral  ventricle 


(I)  Iniou 


Lateral  sinus 


Middle  meningeal  artery,  posterior 
branch ;  inferior  horn  of  lateral, 
ventricle  seen  beneath 


/ 

Semidiagrammatic  view  of  head,  showing  position  of  ventricles,  lateral  sinus  and  middle  meuiugeal  arteries 

as  projected  on  skull. 


The  temporal  lobe  lies  below  the  fissure  of  Sylvius  and  extends  forward  as  far  as 
the  edge  of  the  malar  bone.  The  first  temporal  sulcus  lies  about  one  inch  below  and 
parallel  with  the  fissure  of  Sylvius,  and  the  second  about  18  mm.  (3/£  in.)  lower. 

The  occipital  lobe  lies  posterior  to  the  parieto-occipital  fissure  and  the  tem- 
poral lobe. 

The  motor  tracts  are  made  up  of  the  fibres  passing  from  the  motor  portion  of 
the  cortex  in  the  Rolandic  region  to  the  motor  nuclei  from  which  arise  the  nerves 
supplying  the  muscles  which  the  cortical  areas  control.  After  leaving  the  cortex  the 
fibres  pass  downward  in  the  corona  radiata,  and  converge  to  the  posterior  limb  of  the 
internal  capsule.  The  motor  fibres  of  the  cortico-bulbur  and  cortico-spinal  tracts, 
occupy  the  genu  and  adjacent  third  of  the  internal  capsule  (page  1188),  although 
Dejerinc  holds  that  the  whole  posterior  limb  is  motor.  They  continue  their  course 
downward  through  the  crura  cerebri,  pons,  and  medulla  ;  in  the  lower  part  of  the 
latter  the  givatrr  number  cross  to  the  opposite  side  and  pass  down  in  the  cord  as  the 
lateral  or  crossed  pyramidal  tract.  A  small  number,  sometimes  absent,  pass  down 


PRACTICAL  CONSIDERATIONS:   THE  BRAIN.  1217 

on  the  same  side.  We  have  already  seen  that  lesions  of  the  cortex  produce  mono- 
plegia, unless  large  enough  to  involve  the  whole  motor  zone,  but  cortical  hemiplegia 
is  much  more  common  than  cortical  monoplegia.  In  the  internal  capsule  the  motor 
fibres  are  gathered  together  so  compactly  that  a  small  lesion,  as  an  apoplectic  hemor- 
rhage, will  frequently  interrupt  the  whole  tract  and  give  a  hemiplegia  of  the  opposite 
side  of  the  body. 

In  the  medulla  and  cord  the  tracts  of  both  sides  are  so  close  together  that  a 
lesion  may  easily  paralyze  both  sides  (paraplegia)  ;  indeed,  diseases  of  the  cord  fre- 
quently involve  the  whole  transverse  section,  paralyzing  sensation  as  well  as  motion. 

Hemiplegia  is,  therefore,  the  common  form  of  cerebral  paralysis  ;  paraplegia  the 
common  form  of  spinal  paralysis  ;  while  monoplegia  occasionally  results  from  lesions 
of  the  brain  cortex,  but  more  commonly  from  lesions  of  peripheral  nerves. 

The  sides  and  convexity  of  the  brain  can  be  exposed  for  operation,  so  that  lesions 
of  the  cortex  can  be  attacked  and  often  removed  ;  but  the  region  of  the  internal 
capsule,  which  is  near  the  basal  ganglia,  cannot  be  reached. 

The  soft  brain  may  be  injured  by  contact  with  its  bony  walls  when  the  head  is 
violently  shaken,  the  spaces  surrounding  the  brain  and  filled  with  fluid  permitting 
considerable  movement  of  the  brain.  The  injury  in  cerebral  contusion  occurs  more 
frequently  on  the  under  surface,  both  as  regards  the  cerebrum  and  cerebellum,  than 
on  any  other  part  (Prescott  Hewett).  That  portion,  however,  which  includes  the 
medulla,  pons,  and  interpeduncular  space,  rests  on  a  large  collection  of  cerebro- 
spinal  fluid,  and  is  least  frequently  injured. 


77 


THE  PERIPHERAL  NERVOUS  SYSTEM. 


IN  a  broad  sense  and  as  contrasted  with  the  cerebro-spinal  axis,  the  peripheral 
nervous  system  includes  all  the  nerve-paths  by  which  the  various  parts  of  the  body 
are  brought  into  relation  with  the  brain  and  spinal  cord.  These  paths  embrace,  in 
a  general  way,  two  groups.  One  group,  the  somatic  nerves,  includes  the  nerves 

FIG.  1046. 


Olfactory  bulb 


Orbital  surface 
of  frontal  lobe 


Temporal  lobe 

Anterior 
perforated  space 

Mammillary 
bodies 

Cerebral 
peduncle 


Pon 


Cerebellum 


Ante  rior  roots  of  spinal  nerves 


Olfactory  tract 
Optic  nerve,  cut 


_  Optic 
commissure 

"Optic  tract 


Oculomotor 

nerve 
—Trochlear  nerve 

_Trigeminal 
'"nerve 

• — Abducent  nerve 
—-Facial  nerve 

Auditory  nerve  ' 
Glosso-pharyn- 

feal  nerve 
neumogastric 
nerve 
Spinal 

accessory  nerve, 
spinal  portion 

Pyramidal 
decussation 


Spinal  part  of 
XI.  nerve 


Occipital  lobe 


Spinal  cord 


Inferior  aspect  of  brain,  denuded  of  its  membranes,  showing  superficial  origins  of  cranial  nerves  ;  origin  of  trochlear 
nerve  is  on  dorsal  surface  and  therefore  not  seen. 

supplying  the  voluntary  muscles,  integument  and  organs  of  special  sense  ;  the  sec- 
ond group,  the  visceral  nerves,  includes  those  supplying  the  involuntary  muscle 
throughout  the  body  and  the  thoracic  and  abdominal  viscera.  The  somatic  nerves 
are  subdivided  into  (a)  the  cranial  nerves,  which  are  attached  to  the  brain  and  pass 
through  foramina  in  the  skull,  and  (b)  the  spinal  ttrrz'cs,  which  are  attached  to  the 
spinal  cord  and  traverse  the  intervertebral  foramina.  The  visceral,  or  splanchnic 

I2lS 


THE   CRANIAL   NERVES.  1219 

nerves,  although  directly  or  indirectly  connected  with  the  cerebro-spinal  axis,  pre- 
sent peculiarities  and,  as  the  system  of  sympathetic  nerves,  are  accorded,  at  least  for 
convenience  of  description,  a  certain  degree  of  independence.  While  by  no  means 
all  of  the  spinal  nerves  contribute  splanchnic  branches — such  branches  being  given 
off  especially  by  the  thoracic  and  upper  lumbar  nerves — they  all  receive  sympathetic 
filaments,  which  form,  therefore,  integral  parts  of  the  somatic  nerves.  From  the 
sympathetic  neurones  of  the  gangliated  cords  axones  pass,  by  way  of  the  gray  rami 
communicantes  (page  1357),  to  the  trunks  of  the  spinal  nerves  and  thence  by  these 
are  carried  to  all  parts  of  the  body  for  the  supply  of  the  involuntary  muscle  occur- 
ring within  the  blood-vessels  and  the  integument  and  for  the  cutaneous  glands.  Fur- 
thermore, it  must  be  remembered,  that  although  the  predominating  constituents  of 
a  spinal  nerve  may  be  axones  derived  from  anterior  horn  root-cells  and  destined  for 
voluntary  muscle,  such  trunk  also  contains  a  number  of  afferent  fibres  which  convey 
impulses  received  from  the  neuromuscular  and  neurotendinous  sensory  endings,  the 
nerve-trunks  reckoned  as  ' '  motor ' '  in  all  cases,  when  analyzed,  being  found  to  con- 
tain sensory  and  sympathetic  fibres  as  well  as  efferent  ones. 

THE  CRANIAL  NERVES. 

The  cranial  nerves  (nervi  cerebrates)  include  twelve  pairs  of  symmetrically 
arranged  nerve-trunks,  which  are  attached  to  the  brain  and,  traced  peripherally, 
escape  from  the  skull  by  passing  through  various  foramina  at  its  base  to  be  distrib- 
uted for  the  most  part  to  the  structures  of  the  head. 

The  point  at  which  a  cranial  nerve  is  attached  to  the  surface  of  the  brain  is 
designated  its  superficial  origin  ;  the  group  of  more  or  less  deeply  situated  nerve- 
cells  with  which  its  fibres  are  directly  related  is  often  spoken  of  as  its  deep  origin. 
From  what  has  been  said  (page  1278)  concerning  the  position  of  the  cell-bodies  of 
motor  and  sensory  neurones,  it  is  evident  that  only  the  motor  fibres  of  the  cranial 
nerves  spring  from  nerve-cells  within  the  cerebro-spinal  axis,  while  the  fibres  con- 
ducting sensory  impulses  arise  from  nerve-cells  situated  within  ganglia  lying  outside 
the  central  nervous  axis  and  somewhere  along  the  course  of  the  nerve-trunks.  It 
follows,  therefore,  that  the  term  "deep  origin,"  as  applied  to  the  cell-groups  within 
the  brain,  can  properly  relate  only  to  the  origin  of  motor  fibres  ;  the  cell-groups  with 
which  the  sensory  fibres  come  into  relation  after  entering  the  brain-substance  are  in 
reality  nuclei  of  reception,  or  of  termination,  and  not  of  origin.  The  sensory 
impulses  so  received  are  transmitted  to  various  parts  of  the  brain  by  the  more  or  less 
complex  paths  afforded  by  the  neurones  of  the  second,  third,  or  even  higher  order. 
In  addition  to  their  relation  to  the  deep  nuclei,  whether  of  origin  or  of  reception,  the 
fibres  of  every  cerebro-spinal  nerve  are  directly  or  indirectly  influenced  by  neurones 
situated  within  the  shell  of  gray  matter  that  covers  the  cerebrum.  The  position  of 
these  higher  cortical  centers,  as  they  are  termed,  is  known  with  considerable 
accuracy  for  many  groups  of  nerves,  but  regarding  others  more  definite  data  con- 
cerning cerebral  localization  must  be  awaited. 

Bearing  in  mind  the  foregoing  distinctions,  for  convenience  we  may  follow  the 
conventional  description  in  which  all  the  nerves  are  regarded  as  passing  away  from 
the  brain,  the  direction  in  which  they  convey  impulses,  centripetally  or  centrifugally, 
being  for  the  time  disregarded. 

On  leaving  the  surface  of  the  brain  at  its  superficial  origin,  each  cranial  nerve, 
invested  by  a  sheath  of  pia  mater,  traverses  for  a  longer  or  shorter  distance  the  sub- 
arachnoid  space,  pierces  the  arachnoid  and  from  the  latter  acquires  an  additional, 
but  usually  not  extensive,  sheath.  It  then  enters  a  canal  in  the  dura  mater  that 
leads  to  the  foramen  in  the  skull,  through  which  the  nerve  escapes  from  the  cranium, 
invested  by  a  sheath  prolonged  from  the  dura  which  is  continuous  with  the  epi- 
neurium  covering  the  nerve-trunk.  The  position  of  the  dural  aperture  and  that  of  the 
foramen  by  no  means  always  correspond,  some  of  the  nerves,  notably  the  fourth  and 
sixth,  pursuing  an  intradural  course  of  some  length  before  gaining  their  osseous  exit. 

According  to  the  order  in  which  they  pass  through  the  dura  lining  the  cranium, 
ihe  pairs  of  cranial  nerves  are  designated  numerically  from  the  first  to  the  twelfth. 
They  are  further  distinguished  by  names  based  upon  their  distribution  or  functions. 


I22O 


HUMAN   ANATOMY. 


Certain  of  the  cranial  nerves  are  entirely  motor  ;  some  convey  the  impulses  of  special 
sense  ;  while  others  transmit  impulses  of  both  common  sensation  and  motion.  A 
general  comparison  of  these  relations,  as  now  usually  accepted,  is  afforded  by  the 
following  summary  : 

THE  CRANIAL  NERVES. 


Number. 

I. 

II. 
III. 

IV. 
V. 

VI. 

VII. 


VIII. 
IX. 

X. 


XI. 
XII. 


Name. 

OLFACTORY  : 
OPTIC  : 
OCULOMOTOR  : 

TROCHLEAR : 
TRIGEMINAL  : 

ABDUCENT  : 
FACIAL  : 


AUDITORY, 

(a)  Cochlear  division  : 
(d)  Vestibular  division 

GLOSSO-PHARYNGEAL  : 


PNKUMOGASTRIC  OR  v.\<;rs 


SPINAL  ACCESSORY  : 
HYPOGLOSSAL  : 


Function. 

Special  sense  of  smell. 
Special  sense  of  sight. 
Motor  to  eye-muscles  and  levator  pal- 

pebrse  superioris. 
Motor  to  superior  oblique  muscle. 
Common  sensation  to  structures  of  head. 
Motor  to  muscles  of  mastication. 
Motor  to  external  rectus  muscle. 
Motor  to  muscles    of   head  (scalp   and 

face)  and  neck  (platysma). 
Probably  secretory  to  submaxillary  and 

sublingual  "lands. 
Sensory  (taste)  to  anterior  two-thirds  of 

tongue. 

Hearing. 

Equilibration. 

Special  sense  of  taste. 

Common   sensation   to   part  of  tongue 

and  to  pharynx  and  middle  ear. 
Motor  to  some  muscles  of  pharynx. 
Common  sensation  to  part  of  tongue, 

pharynx,  oesophagus,  stomach  and 

respiratory  organs. 
Motor  (in  conjunction  with  bulhar  part 

of   spinal  accessory)  to   muscles  of 

pharynx,  oesophagus,  stomach  and 

intestine,  and    respiratory  organs  ; 

inhibitory  impulses  to  heart. 
Spinal   Part:    Motor   to    sterno-mastoid 

and  trapezius  muscles. 
Motor  to  muscles  of  tongue-. 


Practical  Considerations. — Lesions  may  affect  a  cranial  nerve  within  the 
brain  or  .in  its  peripheral  portion.  A  central  lesion  clinically  is  one  above  the  nucleus 
of  the  nerve,  and  may  be  cortical  or  may  encroach  upon  its  intracerebral  connections. 
It  may  merely  irritate  the  nerve  or  may  paralyze  it.  By  a  peripheral  lesion  is  meant 
one  involving  the  nucleus  or  the  fibres  of  the  nerve  below  the  nucleus. 


THE  OLFACTORY  NERVE. 

The  olfactory  nerve  (n.  olfactorius),  the  first  in  the  series  of  cranial  nerves, 
presents  some  confusion  in  consequence  of  the  name,  as  formerly  employed,  being 
applied  to  the  olfactory  bulb  and  tract  as  well  as  to  the  olfactory  filaments — struc- 
tures of  widely  diverse  morphological  values.  As  already  pointed  out  (page  1151), 
the  olfactory  bulb  and  tract  (Fig.  993),  with  its  roots,  represent,  as  rudimentary 
structures,  the  olfactory  lobe  possessed  by  animals  in  which  the  sense  of  smell  is 
highly  developed.  It  is  evident  that  these  structures,  formerly  regarded  as  parts  of 
the  first  cranial  nerve,  are  not  morphological  equivalents  of  simple  paths  of  rondiu-- 
tion.  On  the  other  hand  such  paths  are  represented  by  a  series  of  minute  filaments, 
the  true  olfactory  nerves,  that  connect  the  perceptive  elements  within  the  nasal 
mucous  membrane  with  the  rudimentary  olfactory  lobe. 

The  olfactory  nerves  proper,  some  twenty  in  number,  are  the  axones  of  tile- 
peripherally  situated  neurones,  the  olfactory  cells  (page  1414),  which  lie  within  the 
limited  olfactory  area.  The  latter  embraees  in  extent  on  the  outer  nasal  wall  less 


THE   OLFACTORY    NERVE. 


1221 


than  the  mesial  surface  of  the  superior  turbinate  bone  and  a  somewhat  larger  field 
on  the  adjacent  upper  part  of  the  nasal  septum.      The  olfactory  nerves  (Fig.  1048), 

FIG.  1047. 


Exit  ext.  br.  nasal  nerve 


y  Olfactory  bulb 

^Olfactory  nerve-fibres 

An  upper  ant.  nasal  br. 
'Meckel's  ganglion 

I'pper  post,  nasal  brs. 
Meckel's  ganglion 

Naso-palatine  nerve 


Sup.  ant.  nasal  br.  of 
Meckel's  gangl.  and 
inf.  ant.  nasal  br.  of 
ant.  descending 
t  palatine  nerve 
A  posterior  nasal  br. 
Meckel's  ganglion 


Ant.  descending  palatine  nerve,  the  middle  palatine  appearing  posteriorly 


Right  nasal  fossa  showing  distribution  of  olfactory  and  nasal  nerves  on  lateral  wall;   mucous  membrane  has 

been  partly  removed  to  expose  nerves. 

whose  fibres  are  nonmedullated,  exhibit  a  plexiform  arrangement  within  the  deeper 
part  of  the  nasal  mucous  membrane,  pass  upward  through  the  cribriform  plate  of 


FIG.  1048. 


Crista  galli 


Int.  (septal)  br.  of  nasal  nerve 
,  Olfactory  bulb 


Ext.  br.  nasal  n 


Naso-palatine  nerve 


Olfactory  nerve-fibres 
,-Sphenoidal  sinus 

n  upper  ant.  nasal  br.  of 
eckel's  ganglion 
Naso-palatine  nerve 

An  upper  ant.  nasal  br. 
of  Meckel's  ganglion 


fiustachian  orifice 


•Vomer,  posterior  border 


Soft  palate,  cut  mesially 


Right  nasal  fossa  showing  distribution  of  olfactory  and  nasal  nerves  on  septal  wall ;  mucous  membrane  has 

been  partly  removed  to  expose  nerves. 

the  ethmoid  bone  and  enter  the  under  surface  of  the  olfactory  bulb.  Within  the 
latter  the  nerve-fibres  end  in  terminal  arborizations  in  relation  with  the  dendritic 
processes  of  the  mitral  cells  (Fig.  995),  sharing  in  the  production  of  the  peculiar 
o/ factory  glomcrnli. 


1222 


HUMAN   ANATOMY. 


Central  and  Cortical  Connections. — The  impulses  conveyed  by  the  olfactory  nerves  and 
received  by  the  mitral  cells  of  the  olfactory  bulb,  which  cells  may  be  regarded  as  constituting 
the  end-station  or  reception-nucleus  of  the  peripheral  path,  are  carried  to  neurones  situated  either 
within  the  gray  matter  of  the  olfactory  tract,  the  anterior  perforated  space  or  the  adjacent  part 
of  the  septum  lucidum  (Fig.  1049).  Fibres  connecting  the  olfactory  centres  of  the  two  sides  pro- 
ceed from  the  cortex  of  the  tract  by  way  of  the  anterior  commissure,  forming  the  pars  olfactoria 
of  the  latter,  to  end  in  relation  with  the  cells  within  the  opposite  tract  or  bulb.  From  these 
primary  centres  the  impulses  are  transmitted  by  different  paths  to  the  secondary  or  cortical 
centres  situated  in  the  anterior  part  of  the  hippocampal  convolution  in  the  vicinity  of  its  uncus, 
including  the  hippocampus  major  and  the  nucleus  amygdalae. 

i.  The  most  direct  path  is  by  way  of  the  lateral  root  of  the  olfactory  tract  (page  1046),  by 
which  fibres  from  cells  within  the  trigonum  olfactorium  pass,  skirting  the  Sylvian  fissure,  to  the 
anterior  part  of  the  gyrus  hippocampi  to  terminate  in  relation  with  the  cortical  cells  of  that 
convolution. 

FIG.   1049. 


Diagram  showing  most  important  connections  of  olfactory  tracts  ;  LC  lamina  cribrosa  ;  B,  olfactory  bulbs  :  TV, 
olfactory  tract ;  Tjf,  olfactory  trigone ;  Ls,  Ms,  lateral  and .mesial  striae  ;  A,  anterior  commissure  ;  CC,  corpus  callo- 
sum ;  SL,  septum  lucidum;  /•!*•,  anterior  pillar  of  fornix;  M,  mammillary  body;  m-t,  mammillo-thalamic  tract ; 
AP,  anterior  perforated  space;  Tsemj.\.xn\&  semicircularis  ;  T,  thalamus;  Fm,  fimbria  descending  on  hippocampus; 
U,  uncus;  AN,  amygdaloid  nucleus;  TL,  temporal  lobe. 


2.  Fibres  from  the  cells  within  the  olfactory  trigone  (page  1153)  and  the  anterior  perfo- 
rated space  (page  1 153)  pass  into  the  septum  lucidum  and,  reinforced  by  others  from  cells  of  the 
septum,  enter  the  fornix  ;  thence  continuing  backward  and  downward  by  way  of  the  fimbria 
they  reach  the  hippocampus  major. 

3.  Fibres  from  cells  within  the  olfactory  trigone  turn  inward  and  by  way  of  the  medial  root 
of  the  olfactory  tract  gain  the  gyrus  subcallosus  ;  thence  they  pass  along  the  upper  surface  of  the 
corpus  callosum  within  its  longitudinal  striae  and  descend  by  way  of  the  dentate  gyrus  to  reach 
the  anterior  end  of  the  hippocampus  major. 

4.  Fibres  from  cells  within  the  anterior  perforated  space  and  septum  lucidum,  joined  by 
accessions  from  the  opposite  olfactory  tract  by  way  of  the  anterior  commissure,  converge  to  the 
tacnia  semicircularis  (page  1162)  and,  passing  along  the  floor  of  the  lateral  ventricle,  descnul 
within  the  roof  of  the  descending  horn  to  end  in  the  amygdaloid  nucleus  (Dejerine).     During 
their  ascent  from  the  anterior  perforated  space,  some  fibres  diverge  almost  at  right  anglrs  and 
pass  backward  directly  to  the  optic  thalamus.     The  connections  between  the  cortical  centres  of 
olfartion  and  the  optic  thalamus,  as  well  as  those  between  the  olfactory  centres  of  the  two 
sides,  by  way  of  the  fornix,  are  described  on  page  1 167. 

Practical  Considerations. — Lesions  of  the  uncinate  gyrus  may  cause  loss 
of  the  sense  of  swell  on  one  or  both  sides.  Paralysis  of  the  olfactory  nerve  with  loss 
of  smell  may  also  occur  in  fractures  of  the  base  of  the  skull  in  the  anterior  fossa, 
involving  the  cribriform  plate. 


THE   OPTIC    NERVE.  1223 


THE  OPTIC  NERVE. 

The  optic  nerve  (n.  opticus)  is,  as  conventionally  described,  part  of  the  pathway 
which  includes  additionally  the  optic  commissure  and  the  optic  tract  and  transmits 
the  visual  impulses  received  by  the  retina  to  the  primary  centres  within  the  pulvinar 
of  the  optic  thalamus  and  the  external  geniculate  and  superior  quadrigeminal  bodies. 
The  retina,  the  nervous  tunic  of  the  eye  (page  1462),  comprises  three  fundamental 
layers — (a)  the  percipient  visual  cells,  (b~)  the  receptive  ganglion  retina  and  (c)  the 
cerebral  layer.  The  latter  contains  the  neurones,  the  axones  of  which  constitute  the 
nerve-fibres  that  converge  towards  the  optic  disc  and,  piercing  the  vascular  and 
fibrous  coats,  form  the  greater  part  of  the  optic  nerve,  commissure  and  tract. 

In  addition  to  the  fibres  of  retinal  origin,  which  alone  carry  visual  impulses,  the  optic 
nerve  contains  a  considerable  number  of  supplementary  fibres,  which  are  only  indirectly  con- 
cerned in  sight.  Some  of  these  fibres,  distinguished  by  their  small  diameter,  pass  towards  the 
retina,  originating  within  the  brain  from  the  cells  of  the  primary  visual  centres  or  from  sympa- 
thetic neurones,  and  probably  transmit  vasomotor  impulses  controlling  the  retinal  blood- 
vessels. Other  supplementary  fibres,  perhaps  by  way  of  a  centre  situated  within  the  medulla, 
pass  from  the  retina  and  are  regarded  as  conveying  indirectly  to  the  oculomotor  nucleus  the 
impulses  resulting  in  reflex  pupillary  movements. 

The  optic  nerve  (Fig.  1198)  extends  from  the  eyeball,  which  it  leaves  about 
3  mm.  to  the  medial  side  of  the  posterior  pole,  to  the  optic  commissure.  Leaving 
the  eyeball,  the  nerve  pursues  a  slightly  sinuous  course  backward,  inward  and  up- 
ward towards  the  apex  of  the  orbit,  where,  surrounded  by  the  origins  of  the  recti 
muscles,  it  traverses  the  optic  foramen  in  the  sphenoid  bone  in  company  with  the 
ophthalmic  artery,  which  lies  to  its  outer  and  lower  side.  On  gaining  the  interior 
of  the  cranium,  it  converges  towards  the  nerve  of  the  opposite  side  with  which  it 
joins  to  form  the  major  part  of  the  optic  commissure  in  the  vicinity  of  the  olivary 
eminence,  medial  to  the  internal  carotid  artery.  The  entire  length  of  the  optic  nerve 
is  from  30-40  mm.,  of  which  the  intraorbital  part  includes  from  20-30  mm.,  thus 
allowing  for  changes  in  ihe  position  of  the  eyeball  without  undue  stretching  of  the 
nerve.  Its  diameter  is  from  3-4  mm.  Within  the  orbit  the  nerve  is  embedded  in  the 
orbital  fat  and  surrounded  by  the  ocular  muscles  and,  near  the  eyeball,  by  the  ciliary 
vessels  and  nerves.  It  is  crossed  above  and  from  without  inward  by  the  ophthalmic 
artery  and  the  nasal  nerve,  and,  about  10  mm.  from  the  eyeball,  is  penetrated  by  the 
central  artery  of  the  retina,  which,  with  its  companion  vein,  continues  its  intra- 
neural  course  as  far  as  the  optic  disc.  In  addition  to  a  sheath  from  the  pia  mater 
and  a  delicate  one  from  the  arachnoid,  the  optic  nerve  receives  a  robust  tubular  pro- 
longation from  the  dura  at  the  optic  foramen.  These  sheaths,  with  the  intervening 
subarachnoidal  and  subdural  lymph-spaces,  are  continued  on  the  nerve  as  far  as  the 
eyeball,  where  they  blend  with  the  sclerotic  coat. 

The  optic  commissure  (Fig.  1046),  formed  by  the  meeting  of  the  converging 
optic  nerves  in  front  and  the  diverging  optic  tracts  behind,  is  somewhat  flattened  and 
transversely  oblong  and  measures  about  12  mm.  where  broadest.  It  rests  upon  the 
olivary  eminence,  is  embraced  at  the  sides  by  the  internal  carotid  arteries,  and  lies 
beneath  the  floor  of  the  third  ventricle  in  advance  of  the  tuber  cinereum  in  close  rela- 
tion with  the  inferior  surface  of  the  brain.  It  divides  posteriorly  into  the  two  optic 
tracts.  On  reaching  the  commissure,  or  chiasm,  as  it  is  sometimes  called,  the  optic 
fibres,  estimated  at  upwards  of  half  a  million  (Salzer),  undergo  partial  decussation, 
those  from  the  nasal  or  inner  half  of  each  retina  crossing  to  the  mesial  part  of  the 
opposite  optic  tract,  while  those  from  the  temporal  or  outer  half  continue  into  the 
lateral  part  of  the  tract  of  the  same  side.  The  existence  of  a  commissural  loop  con- 
necting the  two  optic  nerves  has  not  been  established,  although  formerly  accepted. 

Occasional  instances  have  been  encountered  in  which  the  decussation  of  the 
optic  fibres  was  complete,  thus  repeating  in  man  the  condition  that  normally  obtains 
in  all  nonmammalian  vertebrates,  as  well  as  in  a  few  rodents  (mouse,  guinea-pig). 
Rarely  the  optic  commissure  has  been  absent,  the  optic  fibres  passing  directly  into 
the  tract  of  the  same  side. 


1224 


HUMAN   ANATOMY. 


The  entire  commissure,  however,  is  not  composed  of  optic  fibres,  ^ince  its  posterior  part 
is  formed  by  a  bundle,  known  as  Gudden's  commissure  (commissura  inferior)  (page  mo),  which 
passes  forward  along  the  mesial  side  of  the  optic  tract,  1<  >ops  around  the  posterior  angle  of  the 
commissure  and  enters  the  opposite  tract.  These  fibres  have  no  connection  with  the  path  of 
sight-impulses,  but  are  probably  chiefly  related  with  the  median  or  internal  geniculate  bodies 
and  the  inferior  corpora  quadrigemina  (page  mo). 

The  optic  commissure  also  contains  fibre-strands  that  arch  around  its  posterior  angle,  par- 
allel with,  but  separated  by,  a  thin  layer  of  gray  matter  from  Gudden's  tract.  Concerning  the 
origin  and  destination  of  these  fibres,  termed  Meynert's  commissure  (commissura  superior),  little 
is  known.  By  some  they  are  regarded  as  continuations  of  the  mesial  fillet  that,  after  decussa- 


FIG.  ioso. 


RayqffLight 


Diagram  showing  course  of  retinal  fibres  fn  optic  pathway  and  their  connection  with  basal  ganglia  and  primary 
cortical  centres ;  smaller  figure  illustrates  path  of  light-ray  and  resulting  impulse  through  retina  :  R,  retina  :  ON,  OC, 
OT,  OR,  optic  nerve,  chiasm,  tract  and  radiation  ,  /*,  pulvinar  ;  Eg,  SQ,  lateral  geiiiculate  and  superior  quadrigem- 
inal  bodies;  Oc  Or,  occipital  cortex;  ///,  IV,  VI,  nuclei  of  eye-muscle  nerves. 

tion,  pass  to  the  globus  pallidus  of  the  lenticular  nucleus  of  the  opposite  side.  Others  deny 
such  relations,  while  Kolliker  describes  them  as  bending  upward,  traversing  the  ventral  part 
of  the  cerebral  peduncle,  to  end  within  the  corpus  subthalamicum  (page  iias  i. 

Additional  commissural  fibres  (commissura  ansata)  descend  from  the  floor  of  the  third 
ventricle  and  from  the  peduncle  of  the  septum  lucidum,  by  way  of  the  lamina  terminalis,  to  the 
front  and  upper  part  of  the  optic  chiasm  ;  other  fibres  pass  from  the  ventricular  floor  to  the  back 
of  the  chiasm.  For  the  most  part  these  fibres  cross  to  the  opposite  sick-  to  be  lost  in  the  sub- 
stance of  the  optic  commissure.  Although  regarded  as  in  a  way  constituting  a  ventral  <>f>tit 
roof,  their  connections  and  significance  are  not  understood. 

The  optic  tract  (Fig.  993)  is  the  continuation  of  the  optic  nerve,  its  chief 
constituents  being  the  crossed  and  uncrossed  retinal  and  the  supplementary  fibres. 
On  leaving  the  commissure,  the  tract  diverges  in  front  of  the  interpeduncular  space, 
mesial  to  the  anterior  perforated  space  and  tin-  termination  of  the-  internal  carotid 
artery,  and  sweeps  outward  and  backward  from  the  base  of  the  brain  around  and 
close  to  the  cerebral  peduncle,  becoming  flatter  and  broader  as  it  proceeds.  Near 


THE   OCULOMOTOR    NERVE.  1225 

its  posterior  end  the  tract  exhibits  a  furrow  that  indicates  a  subdivision  into  a  mesial 
and  a  lateral  root  (Fig.  915).  The  latter,  the  visual  portion  of  the  optic  tract,  is 
traceable  into  the  prominent  overhanging  pulvinar  of  the  optic  thalamus,  the  ill- 
defined  lateral  geniculate  body  and,  by  means  of  the  superior  brachium,  into  the  supe- 
rior quadrigeminal  body.  The  mesial  root,  on  the  other  hand,  contains  the  fibres 
forming  Gudden's  commissure  (page  mo)  and  is  related  to  the  distinct  median 
geniculate  body  and,  by  the  inferior  brachium,  to  the  inferior  quadrigeminal  body. 

Central  and  Cortical  Connections. — Arising  as  axones  of  the  retinal  neurones,  the  optic 
nerve-fibres  are  continued  backward  through  the  commissure  and  tract  and  end  in  relation  with 
the  neurones  of  the  primary  centres  situated  in  the  pulvinar,  the  lateral  geniculate  and  the 
superior  quadrigeminal  body.  .  It  is,  however,  within  the  lateral  geniculate  body  that  the  greater 
number  (80  per  cent,  according  to  Monakow)  of  the  visual  fibres  terminate,  relatively  few  pass- 
ing to  the  pulvinar  and  the  superior  quadrigeminal  body  (Spiller).  The  cortical  connections  are 
established  by  fibres  which  pass  from  the  cells  of  these  primary  centres  and,  as  the  optic  radia- 
tion (page  1123),  sweep  outward  and  backward  into  the  occipital  lobe  to  end  in  the  cortex  of  the 
cuneus  in  the  vicinity  of  the  calcarine  fissure.  It  is  probable  that  a  limited  number  of  retinal 
fibres  pass  directly  to  the  cerebral  cortex  without  interruption  in  the  primary  centres.  In  addi- 
tion to  the  centripetal  paths  just  mentioned,  fibres  arise  from  the  cortical  cells  of  the  cuneus 
and,  sharing  the  optic  radiation,  pass  as  efferent  tracts  which  not  only  terminate  in  the  lateral 
geniculate  and  quadrigeminal  bodies,  but  also  establish  indirect  relations  with  the  nucleus  of  the 
oculomotor  nerve.  The  ultimate  distribution  and  influence  of  the  impressions  of  sight  are  very 
complex  and  far  reaching,  such  impressions  being  capable  of  affecting  numerous  motor  and 
sensory  centres. 

The  exact  path  by  which  pupillary  impulses  reach  the  oculomotor  nucleus  is  uncertain  and 
perhaps  two-fold.  It  may  be  assumed,  however,  that  if  they  proceed  by  way  of  the  superior 
quadrigeminal  body,  the  optic  fibres  are  not  directly  continued  to  the  nucleus  of  the  third  nerve, 
but  end  within  the  superior  colliculus,  from  whose  neurones  the  immediate  connecting  links  pro- 
ceed to  the  oculomotor  nucleus.  Accumulating  evidence  points  to  the  existence  of  a  more 
remote  special  centre  for  pupillary  reflexes  within  the  lower  part  of  the  medulla  ;  in  such  case  the 
oculomotor  nucleus  is,  perhaps,  influenced  by  impulses  which  pass  from  the  medullary  centre 
upward  by  way  of  the  posterior  longitudinal  fasciculus  (Bach). 

Practical  Considerations. — The  cranial  nerves  of  the  eye  will  be  discussed 
in  connection  with  that  organ. 

THE  OCULOMOTOR  NERVE. 

The  third  or  oculomotor  nerve  (n.  oculomotorius),  the  chief  motor  nerve  of  the 
intrinsic  and  extrinsic  muscles  of  the  eyeball,  supplies  branches  to  all  the  extraocular 
muscles,  with  the  exception  of  the  external  rectus  and  superior  oblique,  as  well  as 
fibres  to  the  sphincter  pupillae  and  the  ciliary  muscle  within  the  eyeball. 

Its  deep  origin  is  from  the  oculomotor  nucleus  situated  medially  and  deeply 
within  the  gray  matter  of  the  floor  of  the  Sylvian  aqueduct,  in  close  relation  with  the 
dorsal  surface  of  the  posterior  longitudinal  fasciculus  (Fig.  963). 

The  nucleus  is  from  6-8  mm.  in  length  and  extends  from  opposite  the  upper  end  to  the 
caudal  pole  of  the  superior  quadrigeminal  bodies.  Below,  its  posterior  end  comes  almost  into 
contact  with  the  nucleus  of  the  fourth  nerve,  but  is  separated  from  it  by  a  narrow  interval.  In 
its  entirety  the  oculomotor  nucleus  includes  a  number  of  more  or  less  distinct  cell-groups, 
which  vary  in  importance  as  well  as  in  their  individual  prominence.  Of  these  the  most  impor- 
tant and  constant  are  two  long  columns  of  cells,  the  chief  nuclei,  that  extend,  one  on  each  side, 
along  the  dorsal  surface  of  the  posterior  longitudinal  fasciculi.  Each  nucleus  tapers  slightly 
towards  either  end  and  consists  of  two  fairly  distinct  subdivisions  which,  from  their  relative 
positions,  are  termed  the  dorsal and  the  ventral  cell-group.  The  component  nerve-cells  include 
those  of  large,  medium  and  small  size,  the  large  multipolar  ones  (from  .040-. 045  mm.  in  diam- 
eter) probably  being  the  elements  from  which  the  root-fibres  of  the  third  nerve  arise.  Dislo- 
cated portions  of  the  chief  nucleus  are  seen  as  small  groups  of  nerve-cells  that  lie  scattered 
among  or  even  beneath  the  fibres  of  the  posterior  longitudinal  bundle. 

Dorsal  to  the  chief  nucleus  and  partially  overlying  its  postero-median  surface  is  the  taper- 
ing column  of  small  nerve-cells  known  as  the  Edinger-Westphal  nucleus.  This  tract,  much 
more  bulky  above  than  below  (Tsuchida),  exhibits  a  subdivision  into  a  dorso-lateral  and  a 
ventro-median  portion,  which,  however,  are  fused  in  the  superior  pole  of  the  nucleus.  The 


1226 


HUMAN    ANATOMY. 


exact  relations  of  the  Edinger-Westphal  nucleus  to  the  fibres  of  the  third  nerve  are  still  unde- 
termined, and,  indeed,  even  its  close  association  with  these  has  been  questioned.  The  assumed 
importance  of  the  nucleus  as  a  centre  for  pupillary  reflexes  (Bernheimer)  has  been  seriously 
shaken  by  the  recent  observations  of  Tsuchida.1  This  investigator  also  denies  the  existence 
of  a  well  marked  and  constant  unpaired  median  nucleus  as  described  by  Perlia,  but  admits  the 
presence  of  broken  groups  of  medially  placed  cells,  especially  in  the  upper  and  lower  thirds  of 
the  nucleus.  The  lateral  group  of  cells,  beginning  in  the  floor  of  the  third  ventricle  and  extend- 
ing caudally  as  far  as  the  upper  third  of  the  chief  nucleus,  constitutes  the  nucleus  of  Darksche- 
witsch.  Notwithstanding  its  proximity  to  the  origin  of  the  third  nerve,  this  nucleus  is  now 
regarded  as  having  no  direct  relation  with  that  of  the  oculomotor,  but  as  standing  in  intimate  asso- 
ciation with  the  posterior  longitudinal  bundle,  among  whose  fibres  the  cells  to  a  large  extent 
lie  ;  it  is,  therefore,  now  often  referred  to  as  the  nucleus  fasciculi  longitudinalis  posterioris. 


FIG.  1051. 


<i 

* 

c 

C5 

•j 

.5 

s 

5 

0 

s 

.2 

0 

Oj" 

s 

_s 

? 

-^ 

B 

3 

"s 

A 

~ 

2 

£ 

o 

^ 

'2 
]> 

3. 

a 
£ 

o 

^ 

— 
\ 

~\ 

•5 

0 
• 

K 

11 
u, 

t;  3 

b  s 

li  _  *S 

B  2    O 


Lachrymal 
gland 

Xevator  palpe- 
brae  superioris 
Superior 
rectus  muscle 


External  rectus, 
insertion 


Inferior  oblique 
-muscle 


Cut  surface  of  malar 
bone 


Dissection  of  right  orbit,  showing  oculomotor  and  abducent  nerves. 

Although  it  may  be  assumed  with  much  probability  that  the  fibres  destined  for  the  different 
eye-muscles  originate  from  definite  groups  of  nerve-cells,  all  attempts  to  locate  with  accuracy 
the  position  of  such  centres  within  the  oculomotor  nucleus  have  met  with  only  partial  sue \ vss. 
Tsuchida's  conclusions,  based  upon  histological,  embryological,  comparative  and  clinical  data, 
point  to  an  unexpected  diffuseness  in  the  origin  of  the  oculomotor  fibres  with  only  a  limited 
relation  to  distinct  groups. 

Concerning  the  mooted  question  as  to  the  extent  of  decussation  of  the  oculomotor  librt-s 
it  seems  probable  that  such  crossing  occurs  principally  within  the  caudal  portion  of  the 
chief  nuclei,  although,  according  to  Tsuchida  and  others,  some  decussating  fibres  are  found 
throughout  the  greater  part  of  the  nuclei. 

The  fibres  of  the  third  nerve  originate  principally  as  the  axones  of  the  cells  on 
the  same  side,  although  a  small  number  are  derived  from  the  neurones  lying  on  the 
opposite  side  of  the  mid-line.  Some  of  these  decussating  fibres  supply  the  internal 
rectus  and  are  related  with  the  nucleus  of  the  sixth  nerve,  which  sends  fibres  by  way 
of  the  posterior  longitudinal  bundle  into  the  oculomotor  nucleus.  Whether  these 

1  Arbeiten  a.  d.  Hirnanatom.  Institut  in  Zurich,  Heft  ii.,  1906. 


THE   OCULOMOTOR   NERVE. 


1227 


fibres  end  within  the  latter  nucleus  around  the  cells  from  which  the  decussating  fibres 
proceed,  or  are  actually  prolonged  as  certain  of  the  decussating  fibres  is  uncertain  ; 
their  purpose  is  to  bring  into  coordinated  action  the  internal  rectus  of  one  side  with 
the  opposite  external  rectus  when  the  two  eyes  are  directed  laterally,  as  in  conjugate 
deviation. 

Cortical  and  Central  Connections. — As  in  the  case  of  all  other  motor  cranial  nerves, 
the  nucleus  of  the  third  nerve  stands  in  direct  relation  to  the  cerebral  cortex.  Fibres 
from  the  cells  of  the  cortical  centre — axones  from  the  neurones  within  the  posterior  part 

FIG.  1052. 

Branch  of  supraorbital  nerve 

Supratrochlear  branch  of  frontal 
Supraorbital  branch  of  frontal 
Lachrymal  gland 


Olfactory  bulbs 

Olfactory  tract 
Optic  nerve 

Optic  chiasm 
Optic  tracf"^ 

III.  nerve 

VII.  nerve 

VIII.  nerve- 

IX.  nerve 

X.  nerve 

XI.  nerve 

XI.  nerve 

spinal  portion 

Part  o 

XII.  nerve 

Superior 

medullary 

velum 


Lachrymal  nerve 
Ophthalmic  division  of 
V.  nerve — its   division 
into  frontal,  lachrymal 

III.  nerve    [and  nasal 
Maxillary  division 

of  V.  nerve 

IV.  nerve,  to  inner  side 
of  which  is  VI.  nerve 
Mandibular  division  of 

V.  nerve 

Gasserian  ganglion 

Sensory  root  of  V. 

VII.  nerve          [nerve 

VIII.  nerve 
Middle  cerebellar 
peduncle 

IX.  nerve 

X.  nerve, 

XII.  nerve 


IV.  ventricle 


Medulla,  closed  part 


Base  of  skull,  viewed  from  above,  showing  cranial  nerves  passing  through  dura;  roof  of  right  orbit  has  been  removed 

to  expose  the  ophthalmic  nerve. 


of  the  inferior  frontal  convolution,  slightly  in  front  of  the  precentral  fissure  (Mills) — proceed 
by  way  of  the  corona  radiata,  the  internal  capsule  and  the  cerebral  peduncle  to  the  oculo- 
motor nucleus,  around  whose  cells,  chiefly  but  not  exclusively  ,on  the  opposite  side,  they 
end.  Other  connections  of  the  nucleus  of  the  third  nerve  include  :  (i)  indirectly  with  the  cor- 
tical visual  area  by  fibres  that  pass  from  the  occipital  cortex  through  the  optic  radiation  and 
superior  brachium  to  the  superior  corpora  quadrigemina  ;  (2)  indirectly  with  the  visual  centres 
by  fibres  that  descend  from  the  cells  within  the  superior  corpora  quadrigemina  ;  (3)  by  means 
of  the  posterior  longitudinal  bundle  with  the  nuclei  of  the  other  ocular  nerves  (the  fourth  and 
the  sixth)  and  also  with  the  vestibular  (Deiters')  nucleus  of  the  eighth;  (4)  with  the  facial 
nucleus  by  fibres  that  descend  from  the  oculomotor  nucleus  along  the  posterior  longitudinal 
bundle  to  the  cells  from  which  proceed  .the  fibres  supplying  the  orbicularis  palpebrarum  and  the 
corrugator  supercilii  muscles,  which  are  thus  brought  into  coordinated  action  with  the  levator 
palpebrarum. 


1228  HUMAN   ANATOMY. 

Intracranial  Course. — Leaving  their  deep  origin  as  the  axones  of  the  nuclear 
cells,  the  oculomotor  fibres  sweep  in  ventrally  directed  curves  (Fig.  963)  through 
the  posterior  longitudinal  bundle,  tegmentum,  red  nucleus  and  inner  margin  of  the 
substantia  nigra  and,  collected  into  about  a  dozen  root-bundles,  have  their  super- 
ficial origin  along  a  shallow  groove,  the  oculomotor  siilcus  (Fig.  974),  on  the 
medial  surface  of  the  cerebral  peduncle,  just  in  front  of  the  pons  and  at  the  side  of 
the  interpeduncular  space. 

Beyond  this  superficial  origin,  the  linear  group  of  root-fibres  soon  becomes 
consolidated  into  the  large  and  conspicuous  trunk  of  the  third  nerve,  although  not 
infrequently  one  root-bundle  emerges  more  laterally  from  the  ventral  surface  of  the 
cerebral  peduncle  and  for  a  short  distance  remains  separated  from  the  other  constit- 
uents. The  nerve  courses  forward  and  outward  from  the  posterior  perforated  space, 
between  the  posterior  cerebral  and  superior  cerebellar  arteries,  to  the  outer  side 
of  the  posterior  clinoicl  process,  where,  in  the  triangular  interval  between  the  free 
and  attached  borders  of  the  tentorium,  it  enters  the  dura  (Fig.  1033).  Embedded 
within  this  membrane,  the  nerve  follows  the  upper  portion  of  the  outer  wall  of  the 
cavernous  sinus  and  leaves  the  cranium  by  entering  the  orbit  through  the  sphenoidal 
fissure.  On  gaining  the  median  end  of  the  fissure  the  nerve  divides  into  a  superior 
and  an  inferior  branch,  which  enter  the  orbit  by  passing  between  the  two  heads  of 
the  external  rectus  muscle,  in  company  with,  but  separated  by,  the  nasal  branch  of 
the  trigeminal  nerve,  the  sixth  nerve  lying  below. 

Branches  and  Distribution. — The  superior  branch  framus  superior)  (Fig. 
1051),  the  smaller  of  the  two,  passes  upward,  over  the  optic  nerve,  to  the  superior 
rectus  muscle,  which,  together  with  the  levator  palpebrae  superioris,  it  supplies.  In 
both  cases  the  nerve  enters  the  ocular  surface  of  the  muscle. 

The  inferior  branch  (ramus  inferior)  (Fig.  1051)  is  directed  forward  and, 
after  giving  off  twigs  to  the  ocular  surface  of  the  internal  and  inferior  recti,  is 
continued  below  the  eyeball,  between  the  inferior  and  external  straight  muscles,  to 
supply  the  inferior  oblique,  whose  posterior  border  it  enters.  This,  the  longest 
branch  of  the  oculomotor  nerve,  in  addition  to  sending  one  or  two  fine  twigs  to  the 
inferior  rectus,  contributes  a  short  thick  ganglionic  branch  (Fig.  1051),  which  joins 
the  postero-inferior  part  of  the  ciliary  ganglion  (page  1236)  as  its  short  or  motor 
root  and  conveys  fibres  destined  for  the  sphincter  pupillae  and  ciliary  muscles. 
Sensory  fibres  from  the  ophthalmic  division  of  the  fifth  nerve  are  distributed  to  the 
muscles  along  with  the  fibres  of  the  third,  having  joined  the  latter  before  it  entered 
the  orbit.  Similarly  in  the  wall  of  the  cavernous  sinus,  the  nerve  is  joined  by 
sympathetic  fibres  from  the  cavernous  plexus  on  the  internal  carotid  artery. 

Variations. — These  consist,  for  the  most  part,  of  unusual  branches  which  at  times  seemingly 
replace  one  of  the  other  motor  orbital  nerves.  Thus,  the  third  nerve  may  give  a  branch  to  the 
external  rectus,  either  in  addition  to,  or  to  the  exclusion  of  the  sixth,  which  may  be  absent ;  or 
it  may  give  a  filament  to  the  superior  oblique.  Minor  deviations  in  the  course  of  its  branches, 
such  as  piercing  the  inferior  rectus  or  the  ciliary  ganglion,  have  also  been  recorded. 

THE  TROCHLEAR  NERVE. 

The  fourth  or  trochlear  nerve  (n.  trochlearis),  also  called  the  pathetic,  is  the 
smallest  of  the  cranial  series  and  supplies  the  superior  oblique  muscle  of  the  eyeball. 
The  deep  origin  of  the  nerve  is  from  the  trochlear  nucleus,  a  small  oval  collection 
of  cells  situated  in  the  ventral  part  of  the  gray  matter  surrounding  the  Sylvian  aque- 
duct, that  extends  from  opposite  the  upper  part  of  the  inferior  quadrigeminal  body 
to  the  lower  pole  of  the  superior  colliculus.  This  nucleus,  about  2  mm.  in  length, 
lies  near  the  mid-line  and  immediately  below  (caudal  to)  that  of  the  third  nerve, 
from  which,  however,  it  is  distinct,  being  separated  by  a  narrow  interval  from  the 
ventral  part  of  the  oculomotor  nucleus.  It  lies  in  intimate  relation  with  the  pos- 
terior longitudinal  fasciculus  in  a  distinct  depression  on  the  dorsal  surface  of  that 
bundle  (Fig.  960).  In  structure  the  trochlear  nucleus  resembles  that  of  the  oculo- 
motor, its  nerve-cells  including  those  of  large,  medium  and  small  size. 

Arising  from  the  nucleus,  the  root-fibres  of  the  fourth  nerve  pursue  a  course 
of  considerable  length  within  the  mid-brain  before  gaining  their  superficial  origin. 


THE   TROCHLEAR   NERVE. 


1229 


Leaving  the  upper  and  lateral  part  of  the  nucleus  as  axones  of  the  trochlear  neurones, 
the  strands  of  fibres  pass  outward  and  backward  within  the  gray  matter  of  the  floor 
of  the  aqueduct  until  they  near  the  inner  concave  surface  of  the  mesencephalic  root 
of  the  fifth  nerve,  which,  after  being  condensed  into  one  or  two  bundles,  they  follow 
downward  as  far  as  the  superior  extremity  of  the  fourth  ventricle.  Then  bending 
sharply  medially,  the  fourth  nerve,  so  far  as  the  great  majority  of  its  fibres  are 
concerned,  enters  the  superior  medullary  velum,  in  which  it  decussates  with  its  fellow 
of  the  opposite  side  and  crosses  the  mid-line  to  emerge  at  its  superficial  origin  on 
the  dorsal  surface  of  the  brain-stem  (Fig.  957)  just  below,  the  inferior  corpora  quad- 
rigemina,  between  the  frenum  of  the  velum  and  the  mesial  border  of  the  superior 
cerebellar  peduncle. 

Cortical  and  Central  Connections. — The  trochlear  nucleus  is  directly  connected  with  the 
cerebral  cortex  by  fibres  which  descend  from  the  inferior  frontal  convolution  through  the  corona 
radiata,  the  internal  capsule  and  the  cerebral  peduncle  and  cross  to  the  nucleus  of  the  opposite 


FIG.  1053. 


Olfactory  tracts 
Optic  chiasm 
Gasserian  ganglion 
Int.  carotid  artery 
II  I. nerve 


Mid. lie  peduncle 
of  cerebellum 


Medulla 
oblongata 


XI.  nerve         \        \  , 

X.  nerve       \         \          \ 
IX.  nerve         \  \ 


Frontal  nerve 


Supratrochlear 


Supraorbital 


Levator  pal- 
pebrae  superioris 

Rectus  superior 


Lachrymal  nerve 

Rectus  extern  us 
lir.  of  communi- 
cation bet.  lachry- 
mal and  temporo- 
n.alar  br.  maxil- 
lary nerve 
-  Malar  br.  tempo- 
ro-malar  nerve 
Temporal  br. 
temporo-malar 
nerve 


^  Ophthalmic  div.  V.  nerve 

Maxillary  div.  V.  nerve 
.  v  Mandibular  div.  V.  nerve 

\  Geniculate  ganglion  of  VII.  nerve  fa  part  of  great 

4  4          VII.  nerve       superficial  petrosal  nerve  is  seen  passing  beneath 

VIII.  nerve    Temporal  bone,  cut       Gasserian  ganglion) 


Dissection  showing  right  trochlear  nerve  throughout  its  length,  also  oculomotor  and  frontal  and  lachrymal  branches 
of  trigemiual  nerve  ;  roof  and  outer  wall  of  orbit  have  been  removed. 

side.  By  means  of  the  posterior  longitudinal  bundle  it  is  brought  into  relation  with  the  nucleus 
of  the  third  and  of  the  sixth  nerve,  thus  insuring  harmonious  action  of  the  eye  muscles;  further, 
by  means  of  the  same  path,  it  is  probably  connected  with  the  cochlear  nucleus  by  way  of  the 
superior  olive  and  its  peduncle. 


Course  and  Distribution. — Emerging  at  its  superficial  origin,  the  nerve  is 
directed  outward  over  the  superior  cerebellar  peduncle,  then  winds  forward  around 
the  outer  surface  of  the  cerebral  peduncle,  parallel  to  and  between  the  posterior 
cerebral  and  superior  cerebellar  arteries,  and  appears  at  the  base  of  the  brain  (Fig. 
1053).  Proceeding  forward  to  the  floor  of  the  cranium,  the  nerve  enters  the  dura 
immediately  beneath  the  free  border  of  the  tentorium,  slightly  behind  and  external 
to  the  posterior  clinoid  process  and  the  third  nerve,  and  continues  in  the  outer  wall 
of  the  cavernous  sinus,  at  first  having  the  third  nerve  above  it  and  the  ophthalmic 
division  of  the  fifth  below,  and  then  crossing  above  the  third  from  below  inward,  to 
gain  the  medial  end  of  the  sphenoidal  fissure.  It  enters  the  orbit  above  the  heads,  of 


1230  HUMAN   ANATOMY. 

the  external  rectus  muscle  and,  directed  medially,  crosses  above  the  levator  palpebrse 
superioris  and  superior  rectus  and  reaches  the  superior  oblique,  which  it  enters  on 
the  upper  surface  close  to  the  external  border  (Fig.  1056). 

The  communications  of  the  trochlear  nerve,  as  it  courses  in  the  wall  of  the 
cavernous  sinus  are:  (i)  filaments  from  the  carotid  sympathetic  plexus;  (2)  fibres 
of  common  sensation  from  the  ophthalmic  division  of  the  fifth. 

Variations. — The  course  of  the  trochlear  nerve  is  sometimes  through  instead  of  over  the 
levator  palpebrse  superioris.  Unusual  branches  to  sensory  nerves,  as  the  frontal,  supratroch- 
lear,  the  infratrochlear  and  the  nasal,  are  probably  due  to  the  aberrant  course  of  sensory  fibres 
from  the  trifacial.  The  fourth  nerve  occasionally  sends  a  branch  to  the  orbicularis  palpebrarum. 

THE  TRIGEMINAL  NERVE. 

The  fifth,  trigeminal  or  trifacial  nerve  (n.  trigeminus),  the  largest  of  the  cranial 
series,  is  a  mixed  nerve  and  consists  of  a  large  sensory  part  (portio  major)  and  a 
much  smaller  motor  portion  (portio  minor).  The  former  supplies  fibres  of  common 
sensation  to  the  front  part  of  the  head,  the  face,  a  portion  of  the  external  ear,  the 
eye,  the  nose,  the  palate,  the  naso-pharynx  in  part,  the  tonsil,  the  mouth  and  the 
tongue.  The  motor  portion  is  distributed  to  the  muscles  of  mastication,  the  mylo- 
hyoid  and  the  anterior  belly  of  the  digastric.  The  relation  of  the  fibres  composing 
these  two  parts  to  the  cells  within  the  brain-stem  is,  therefore,  very  different,  in  the 
case  of  the  motor  fibres  the  cells  being  a  nucleus  of  origin  and  in  that  of  the  sensory 
fibres  one  of  reception. 

The  Sensory  Part. — The  fibres  comprising  the  sensory  part  of  the  trigeminal 
nerve,  which  convey  sensory  impulses  from  the  various  head-structures,  are  the  pro- 
cesses of  cells  lying  outside  the  central  axis  in  the  Gasserian  ganglion  on  the  sensory 
root.  The  portions  of  the  fibres  between  the  periphery  and  the  ganglion  correspond 
to  elongated  dendrites,  while  the  much  shorter  centrally  directed  constituents  of  the 
sensory  root,  connecting  the  ganglion  with  the  brain-stem,  are  the  axones  of  the 
Gasserian  neurones.  The  general  resemblance  between  the  fifth  cranial  nerve  and  a 
typical  spinal  nerve  is  striking,  in  each  case  the  sensory  root  bearing  a  ganglion  and 
the  motor  root  proceeding  from  cells  within  the  central  nervous  axis. 

Proceeding  brainward  as  axones  of  the  Gasserian  cells,  the  sensory  fibres  of  the 
trigeminal  nerve  become  consolidated  into  the  large  sensory  root,  which  passes 
through  an  opening  in  the  dura  mater  (Fig.  1033)  situated  beneath  the  attachment 
of  the  tentorium  cerebelli  to  the  posterior  clinoid  process.  Coursing  backward 
through  the  posterior  fossa  of  the  cranium  it  enters  the  brain-stem  on  the  lateral  sur- 
face of  the  pons,  slightly  behind  the  superior  border,  as  the  conspicuous  group  of 
robust  bundles  that  mark  the  superficial  origin  of  the  nerve  (Fig.  1046).  Just  above 
it  is  the  superficial  origin  of  the  motor  root,  from  which  it  is  separated  by  a  small 
bundle  of  pontine  fibres  which  belong  to  the  middle  cerebellar  peduncle.  Below  and 
in  line  with  it  are  the  superficial  origins  of  the  facial  and  auditory  nerves. 

Entering  the  tegmental  portion  of  the  pons,  close  to  the  overlying  superior  cerebellar 
peduncle,  the  sensory  fibres  soon  come  into  relation  with  the  extensive  trigeminal  reception- 
nucleus,  a  columnar  mass  of  gray  matter  within  the  lateral  part  of  the  tegmentum  (Fig.  935). 
This  nucleus  extends  from  the  middle  of  the  pons  through  the  entire  length  of  the  medulla  and 
into  the  spinal  cord  as  far  down  as  the  level  of  the  second  cervical  segment,  where  it  becomes 
continuous  with  the  substantia  gelatinosa  of  the  cord.  The  rounded  and  enlarged  upper  end 
of  this  tapering  column  is  described  as  the  sensory  nucleus  of  the  fifth  nerve,  although  it  com- 
prises only  a  small  part  of  the  reception-nucleus.  The  latter,  in  turn,  is  the  upward  prolongation 
of  the  substantia  gelatinosa  Rolandi,  conspicuous  in  all  cross-sections  of  the  lower  pons  and 
medulla  as  an  oval  field  of  gray  matter  (Fig.  930). 

On  nearing  this  column  the  sensory  fibres  divide  into  ascending  and  descending  brandies, 
much  in  the  same  way  as  the  posterior  root-fibres  bifurcate  within  the  posterior  columns  of  the 
cord.  The  ascending  fibres,  distinctly  finer  than  the  descending,  soon  penetrate  the  sensory 
nucleus  and  the  substantia  gelatinosa  and  end  in  arbori/ations  around  the  neurones  of  the 
reception  nucleus.  The  coarser  descending  fibres  become  collected  into  a  compact  bundle,  the 
descending  or  spinal  root  (tractus  spinalis  n.  irim-mini),  whose  medially  directed  concavity  closely 
embraces  the  lateral  surface  of  the  column  of  gray  substance.  Beginning  with  its  descent,  the 


THE   TRIGEMINAL   NERVE. 


1231 


spinal  root  gives  off  collaterals  and  fibres  that  bend  medially,  enter  the  adjacent  substantia  gel- 
atinosa  and  end  in  arborizations  around  the  reception  cells  of  that  nucleus.  Since  the  number  of 
fibres  is  thus  progressively  reduced  during  the  descent  of  the  spinal  root,  the  tract  is  tapering, 
becoming  smaller  and  smaller  as  it  approaches  the  spinal  cord  until  within  the  upper  part  of  the 
latter,  at  about  the  level  of  the  second  cervical  nerve,  it  finally  disappears.  In  its  descent  through 
the  brain-stem  the  spinal  tract  becomes  more  and  more  superficially  placed,  in  the  lower  part  of 
the  pons  lying  to  the  inner  side  of  the  restiform  body,  separated  from  it  by  the  vestibular  division 
of  the  auditory  nerve,  and  lower,  in  the  lateral  area  of  the  medulla,  occupying  a  position  close 
to  the  surface  as  it  rests  upon  the  expanded  gelatinous  substance  of  the  tuberculum  Rolandi. 

The  central  connections  of  the  sensory  part  of  the  trigeminus  (Fig.  1054),  by  way  either  of 
the  collaterals  of  the  fibres  of  the  spinal  root  or  of  the  axones  and  collaterals  of  the  axones  of 
the  reception  neurones,  are  undoubtedly  very  extensive,  since  the  impulses  collected  by  this 
important  nerve  are  widely  dispersed.  The  most  important  paths  for  such  distributions  are  : 

1.  By  axones  that  pass,  as  arcuate  fibres,  from  the  cells  of  the  reception-nucleus  across  the 
raphe  to  join  the  opposite  mesial  fillet 

and  ascend  to  the  optic  thalamus  and  FIG.  1054. 

thence,  after  interruption  in  the  cells  of 
the  latter,  by  axones  of  thalamic  neu- 
rones to  the  cerebral  cortex.  It  is  prob- 
able that  some  of  the  arcuate  fibres  do 
not  cross  the  mid-line,  but  ascend  within 
the  mesial  fillet  of  the  same  side.  It  is 
also  probable  that  collaterals  of  the 
arcuate  fibres  pass  to  the  trigeminal, 
facial  and  glosso-pharyngeo-vagal  motor 
nuclei. 

2.  By  axones  from  the  cells  of  the 
reception   nucleus  that  enter  the   infe- 
rior cerebellar  peduncle  of  the  same  side 
and  pass  to  the  cerebellar  cortex  as  con- 
stituents of  the  nucleo-cerebellar  tract. 

3.  By  collaterals  that  are  distrib- 
uted to  the  nuclei  of  origin  of  the  hypo- 
glossal  and  of  the  motor  part  of  the  tri- 
geminus   and    facial    nerves,    whereby 
these     important     motor     nerves     are 
brought  directly  under  the  influence  of 
the  sensory  part  of  the  fifth. 

The  Motor  Part. — In  con- 
trast to  the  median  position  of  the 
nuclei  of  origin  of  the  oculomotor, 
trochlear,  abducent  and  hypoglos- 
sal  nerves,  the  deep  origin  of  the 

f       .  .  .  .  Diaeram  showing  relations  of  tngeininal  root-fibres  to  nuclei 

motor    part     OI     the     tngemmUS    in-  within  brain-stem ;    GC,  Gasserian  ganglion  with  divisions  (/, 

rlnHpc    o-rminc    r>f    rv>11c     rhaf    lip    at  II,  HI)  of  sensory  part  of  nerve  ;   SR,  MR,  sensory  and  motor 

6    al  roots  :  S,  sensory  nucleus  ;  SG,  substantia  gelatinosa  :  Sp.K,  spi- 

some  distance  from  the  raphe  and  nal  or  descending  root ;  /s  mesial  fillet ;  Cb  nucleo-cerebellar 
f  ,.  .  -ill  11  fibre:  M,  motor  nucleus;  Ms/t,  mesencepnalic  root;  S/,  sub- 
fall  mtO  Series  With  the  laterally  stantia  ferruginea ;  CB,  cortico-bulbar  fibres. 

placed  nuclei  of  the  motor  parts  of 

the  other  mixed  cranial  nerves — the  facial,   the  glosso-pharyngeal  and  the  vagus. 


1.  The  largest  contingent  of  the  motor  fibres  of  the  trifacial  nerve  arise  as  axones  from  the 
neurones  within  the  chief  motor  nucleus  (nucleus  masticatorius)  (Fig.  935).     This  nucleus  con- 
sists of  a  short  columnar  collection  of  gray  matter,  oval  on  cross-section,  which  lies  in  the  upper 
part  of  the  pons,  close  to  the  median  side  of  the  sensory  nucleus.     It  is  composed  of  large  stel- 
late cells  from  which,  as  their  axones,  the  motor  fibres  proceed  outward  through  the  tegmentum 
to  their  superficial  origin  on  the  pons.     A  small  number  of  fibres,  from  the  more  medially  situ- 
ated cells  of  the  nucleus,  pursue  a  dorsally  convex  course  toward  the  raphe,  which  they  cross 
close  beneath  the  floor  of  the  fourth  ventricle  to  join  the  motor  nucleus  of  the  opposite  side  and 
become  incorporated  in  the  opposite  trigeminal  motor  root. 

2.  A  second  and  smaller  constituent  of  the  motor  root,  the  descending  mesencephalic  root 
(radix  descendens  n.  trigemini)  includes  fibres  that  arise  from  cells  lying  within  the  lateral  part 
of  the  gray  matter  surrounding  the  Sylvian  aqueduct.     In  cross-sections  (Fig.  936)  this  root 
appears  as  a  delicate  crescentic  bundle  that  descends  from  the  mid-brain  to  join  the  larger  tract 


1232 


III  MAN    ANATOMY. 


of  fibres  from  the  chief  motor  nucleus.  In  its  downward  course  the  mesencephalic  root  is 
joined  by  numerous  fibres  which  have  their  origin  in  the  pigmented  cells  of  the  substantia  ferru- 
ginea  (page  1081)  of  the  same  and,  possibly,  of  the  opposite  side. 

The  fibres  from  these  various  sources  —  the  mesencephalic  nucleus,  the  substan- 
tia ferruginea  and  the  motor  nucleus  —  become  consolidated  into  the  motor  root  of 
the  trigeminal  nerve,  whose  superficial  origin  (Fig.  1046)  is  just  above  that  of  the 
sensory  root,  from  which  it  is  separated  by  some  of  the  superficial  transverse  fibres 
of  the  pons.  Leaving  the  side  of  the  pons,  the  motor  root  follows  the  same  course 
to  and  through  the  dura  mater  as  does  the  sensory,  to  the  inner  side  of  which  it  lies. 
It  eventually  passes  beneath  the  Gasserian  ganglion  to  become  exclusively  an 
integral  portion  of  the  mandibular  division  of  the  trigeminal. 

The  cortical  connections  of  the  motor  root  are  established  by  fibres  that  arise  from  cells 
within  the  cortical  gray  matter  of  the  lower  third  of  the  precentral  convolution.  Thence,  as 
constituents  of  the  pyramidal  tracts,  they  descend  through  the  corona  radiata,  the  internal  cap- 
sule and  the  cerebral  peduncle  into  the  pons,  where,  for  the  most  part  after  decussation,  they 
terminate  in  end-arborizations  around  the  radicular  cells  of  the  motor  trigeminal  nuclei. 

The  Gasserian  Ganglion.  —  The  Gasserian  ganglion  (ganglion  semilunare 
[Gasseri])  (Fig.  1055)  is  an  important  complex  of  nerve-fibres  and  cells,  which  lies 

in  a  slight  depression   on   the 

FIG.  1055.  apex  of  the  petrous  portion  of 

the  temporal  bone.  In  shape 
it  is  a  flattened  crescent  with  its 
convexity  forward,  measuring 
from  1.5-2  cm.  in  width  and 
about  i  cm.  in  length.  The  sur- 
face of  the  ganglion  presents  an 
irregular  longitudinal  or  reticu- 
lar  striation.  From  the  anterior 
expanded  convex  border  of  the 
ganglion  arise  the  ophthalmic 
and  maxillary  nerves  and  the 
sensory  portion  of  the  mandib- 
ular nerve,  while  its  narrow 
concave  posterior  margin  is  con- 
tinued into  the  sensory  root  of 
the  fifth  nerve.  The  ganglion 
lies  in  McckcC  s  space  (cavuni 
Meckclii),  a  cleft  produced  by  a 
delamination  of  the  dura  mater, 
and  comes  in  relation  internally 
with  the  cavernous  sinus  and 
the  internal  carotid  artery.  Be- 
neath, but  unconnected  with  it, 
are  the  motor  root  of  the  trifacial  and  the  great  superficial  petrosal  nerve.  In  struc- 
ture it  resembles  a  spinal  ganglion,  being  composed  of  the  characteristically  modified 
neurones,  from  whose  single  processes  proceed  the  peripherally  directed  dendrite> 
and  the  centrally  coursing  axones. 

In  addition  to  the  three  large  trunks  given  off  from  the  anterior  margin,  the 
branches  of  the  Gasserian  ganglion  include  some  fine  meningeal  filaments 
which  arise  from  the  posterior  end  of  the  ganglion  and  are  distributed  to  the  adja- 
cent dura  mater. 


Optic 
nerve 

Internal 
carotid 
artery 


( '.asset-fan 
ganglion 


Gasserian   ganglion  of    left  side  viewed  from    above;     sensory  and 
motor  roots  and  three  divisions  of  trigeminal  nerve  are  seen. 


Communications.  —  At  its  inner  side  the  <  '.asserian   ganglion    receives   filaments   from   tin- 
adjacent  carotid  plexus  of  the  sympathetic,  which  end  in  relation  with  the  cells  of  the  ganglion. 

Divisions  of  the  Trigeminal  Nerve.  —  These  are  three  in  number,  the  o/>/i- 
f/itifinic,   the:   nta.  \illarv  and    the   iinuulihidar  nerves.        They  arise-  from  the  anterior 


THE   TRIGEMINAL   NERVE. 


I233 


margin  of  the  Gasserian  ganglion,  the  formation  of  the  mandibular  nerve  being  com- 
pleted by  the  accession  of  the  motor  root  of  the  trigeminal. 

I.  The  Ophthalmic  Nerve. — The  ophthalmic  nerve  (n.  ophthalmicus)  (Fig. 
1056),  the  smallest  of  the  three  divisions,  is  purely  sensory  and  supplies  the  upper 
eyelid,  the  conjunctiva,  the  eyeball,  the  lachrymal  gland,  caruncle  and  sac,  the  fore- 
head and  anterior  part  of  the  scalp,  the  frontal  sinus  and  the  root  and  anterior  por- 
tion of  the  nose.  It  arises  from  the  anterior  margin  of  the  Gasserian  ganglion  and 
passes  upward  and  forward  for  about  25  mm.  in  the  external  wall  of  the  cavernous 
sinus,  lying  below  the  fourth  nerve.  Reaching  the  sphenoidal  fissure  it  breaks  up 
intb  its  terminal  branches,  which  pass  through  the  fissure  into  the  orbit. 

Branches  and  Distribution. — The  branches  of  the  ophthalmic  nerve  are: 
(i)  the  recurrent,  (2)  the  communicating,  (3)  the  lachrymal,  (4)  the  fro ntal,  and 
(5)  the  nasal,  of  which  the  last  three  are  terminal  branches. 


FIG.  1056. 


Supratochlear  nerve 
Nasal  nerve 

Olfactory  bulbs 

Superior  oblique  muscle 
IV.  nerve 

Cut  edge  of  bone 
Optic  nerve 

Optic  chiasm 
Internal  carotid  artery 

Optic  tract 
VI.  nerve 

III.  nerves 
Cerebral  peduncles 


Supraorbital  nerve 
Lachrymal  gland 

Levator  palpebrse  superioris 
Superior  rectus 

Frontal  nerve 
External  rectus 


Lachrymal  nerve 

Ophthalmic  division  of  V.  nerve 
Maxillary  division  of  V.  nerve 
Mandibular  division  of  V.  nerve 

Gasserian  ganglion 

Meatus  auditorius  internus 

VII.  nerve,  motor  part 
Pars  intermedia 

VIII.  nerve 


Roof  of  right  orbit  has  been  removed  to  expose  branches  of  ophthalmic  division  of  trigeminal  nerve;  Gasserian 
ganglion,  and  third,  fourth,  sixth,  seventh  and  eighth  nerves  also  seen. 

1.  The  recurrent  branch  (n.  tentorii)  arises  shortly  after  the  nerve  leaves  the 
ganglion.     It  passes  across  and  is  adherent  to  the  trochlear  nerve  and  is  distributed 
between  the  layers  of  the  tentorium  cerebelli. 

2.  The  communicating  branches  are  three  slender  filaments  which  are  given 
off  before  the  nerve  breaks  up  into  its  terminal  branches  ;  they  join  the  trunks  of  the 
third,  fourth  and  sixth  nerves,  to  whose  muscles  they  supply  sensory  fibres.      During 
its  passage  through  the  cavernous  sinus,  the  ophthalmic  nerve  receives  some  tiny 
filaments  from  the  cavernous  sympathetic  plexus. 

3.  The  lachrymal  nerve   (n.  lacrimalis)    (Fig.  1053)  is  the  smallest  of  the 
terminal  branches.      It  lies  to  the  outer  side  of  the  frontal  nerve  and  traverses  the 
outer  angle  of  the  sphenoidal  fissure  in  its  own  sheath  of  dura  mater.      It  passes 
above  the  origin  of  the  orbital  muscles  and  courses  along  the  lateral  wall  of  the  orbit, 
above  the  external  rectus,  to  the  upper  outer  angle  of  trie  orbit,  where  it  pierces  the 
palpebral  fascia  near  the  external  canthus  to  terminate  in  the  upper  eyelid.      It  sup- 
plies the  lachrymal  gland,  the  upper  eyelid  and  the  skin  around  the  external  canthus. 

78 


1234  HUMAN   ANATOMY. 

Within  the  orbit  the  lachrymal  nerve  communicates  with  the  temporal  branch 
of  the  temporo-malar  nerve  and  on  the  face  with  the  temporal  branch  of  the  facial. 
The  latter  is  one  of  the  numerous  sensory-motor  communications  between  the 
terminal  fibres  of  the  fifth  and  seventh  nerves. 

Variations. — Occasionally  the  lachrymal  nerve  seems  to  be  partly  derived  from  the  troch- 
lear ;  the  true  source  of  such  fibres,  however,  is  probably  the  ophthalmic  nerve,  by  way  of  its 
communicating  branch  to  the  fourth.  Considerable  variation  is  found  in  connection  with  the 
temporal  branch  of  the  temporo-malar  nerve.  The  lachrymal  nerve  or  the  temporal  branch  of 
the  temporo-malar  may  be  absent,  the  place  of  either  being  taken  by  the  other,  or  the  lachrymal 
may  be  small  at  its  origin  and  later  increased  to  normal  size  by  accessions  from  the  temporal 
branch  of  the  tem'poro-malar. 

4.  The  frontal  nerve  (n.  frontalis)  (Fig.  1053)  is  the  largest  branch  of  the 
ophthalmic.      It  enters  the  orbit,  invested  by  its  own  dural  sheath,    through  the 
sphenoidal  fissure  and  above  the  orbital  muscles  and  passes  directly  forward  between 
the  periosteum  and  the  levator  palpebrae  superioris.     At  a  variable  point,  usually 
about  the  middle  of  the  orbit,  it  divides  into  its  terminal  branches,  the  (a)  supra- 
trochlear  and  (6)  the  supraorbital. 

a.  The   supratrochlear  nerve    (n.   supratrochlearis)    is  the  smaller  of  the  two  terminal 
branches.     It  passes  inward  and  forward  over  the  pulley  of  the  superior  oblique  and  thence 
between  the  orbicularis  palpebrarum  and  the  frontal  bone,  leaving  the  orbit  at  its  upper  inner 
angle.     Near  the  pulley  it  gives  off  a  branch  which  joins  the  infratrochlear  (Fig.  1057)  and  at 
the  edge  of  the  orbit  supplies  filaments  (nn.  palpebrales  superiores)  to  the  skin  and  conjunctiva  of 
the  upper  eyelid.     It  then  turns  upward  and  subdivides  into  a  number  of  small  branches  which 
pierce  the  substance  of  the  frontalis  and  orbicularis  palpebrarum  muscles  to  supply  the  inner 
and  lower  part  of  the  forehead. 

b.  The  supraorbital  nerve  (n.  supraorbitalis)  (Fig.   1056)  continues  directly  the  course  of 
the  frontal  nerve.     It  lies  close  to  the  periosteum  throughout  its  entire  orbital  course  and  leaves 
the  orbit  through  the  supraorbital  notch  or  foramen.     In  this  situation  it  sends  a  small  filament 
to  the  frontal  sinus  to  supply  its  diploe  and  mucous  membrane.     As  it  leaves  the  orbit  it  sup- 
plies some  fine  twigs  to  the  upper  eyelid  and  then  divides  into  a  larger  outer  and  smaller  inner 
branch.     These  pass  upward  on  the  forehead  beneath  the  frontalis  muscle,  occasionally  occupy- 
ing quite  deep  grooves  in  the  frontal  bone,  and  terminate  by  being  distributed  to  the  scalp  and 
pericranium.    The  outer  branch  extends  back  nearly  to  the  occipital  bone,  while  the  inner 
passes  only  a  short  distance  posterior  to  the  coronal  suture. 

Both  branches  of  the  frontal,  the  supratrochlear  and  the  supraorbital,  communicate  with 
branches  of  the  facial  nerve  and  thereby  supply  sensory  filaments  to  muscles  supplied  by  the 
seventh. 

Variations. — The  nerve  may  divide  before  leaving  the  orbit  and  in  that  event  only  the  outer 
branch  passes  through  the  normal  osseous  channel.  The  inner  sometimes  has  a  special  groove, 
named  by  Henle  ^n&  frontal  notch. 

5.  The   nasal    nerve    (n.  nasociliaris)    (Fig.    1057)   is   intermediate   in   size 
between  the  lachrymal  and  the  frontal.      It  enters  the  orbit,  clothed  in  dura  mater, 
through  the  sphenoidal  fissure,  between  the  heads  of  the  external  rectus  and  between 
the  superior  and  inferior  divisions  of  the  oculomotor  nerve.     Turning  obliquely  in- 
ward, it  crosses  the  optic  nerve  and  passes  beneath  the  superior  oblique  and  superior 
rectus  muscles  and  above  the  internal  rectus.     Thence  it  traverses  the  anterior  eth- 
moidal  foramen  to  enter  the  cranial  cavity,  where  it  passes  forward  in  a  groove  in 
the  lateral  part  of  the  cribriform  plate  of  the  ethmoid  bone.      Leaving  the  cranium 
through  the  nasal  fissure,  the  nerve  enters  the  nasal  fossa,  where  it  breaks  up  into 
its  three  terminal  branches. 

Branches. — These  are  :  (a)  tib&gangliomc,  (6)  the  long  ciliary,  (c)  tin-  infra- 
trochlear, (d)  the  internal  nasal,  (c)  the  external  nasal  and  (/)  the  anterior  nasal,  of 
which  the  last  three  are  terminal  branches. 

a.  The  gang/ionic  branch  (radix  longa)  (Fig.  1057)  usually  leaves  the  nerve  between  the 
heads  of  the  external  rectus  and  passes  forward  along  the  outer  side  of  the  optic  nerve  to  enter 
the  upper  posterior  portion  of  the  ciliary  ganglion,  of  which  it  forms  the  sensory  or  long  root. 

b.  The  long  ciliary  branches  (nn.  dliares  lonyi)  (Fig.  1058)  are  two  in  number.     They  pass 
forward  along  the  inner  side  of  the  optic  in-rve  and,  after  joining  one  or  motv  of  the  short  ciliary 
nerves,  pierce  the  sclerotic  coat  of  the  eye  to  be  distributed  to  the  iris,  ciliary  muscle  and  form  -A. 


THE   TRIGEMINAL   NERVE. 


1235 


c.  The  infratrochlear  nerve  (n.  infratrochlearis)  (Fig.  1058)  runs  forward  along  the  inner 
orbital  wall  and  beneath  the  superior  oblique  muscle  and  its  pulley  to  the  inner  end  of  the  pal- 
pebral  fissure,  where  it  terminates.     Near  the  pulley  it  receives  a  filament  (the  supratrochlear) 
from  the  nasal  nerve.     It  supplies  the  skin  of  the  upper  eyelid  and  root  of  the  nose,  as  well  as 
the  conjunctiva  and  the  lachrymal  caruncle  and  sac. 

d.  The  internal  nasal  or  septal  branch  (rr.  mediates)  (Fig.  1048)  supplies  the  mucous  mem- 
brane of  the  anterior  portion  of  the  septum. 

e .  The  external  nasal  branch  (rr.  laterales)  (Fig.  1047)  supplies  the  front  part  of  the  middle 
and  inferior  turbinate  bones  and  outer  wall  of  the  nasal  fossa. 

f.  The  anterior  nasal  branch    (r.   nasalis  extremus)    passes  downward   in   a  groove  in 
the  under  side  of  the  nasal  bone  and  then  between  the  lower  end  of  the  nasal  bone  and  the 

FIG.  1057. 


Superior  oblique  musclex. 

\ 
Internal  rectus  muscle>xNj1 


Infratrochlear  br.  of  nasal 
Nasal  nerve 

Olfactory  bulb' 

Levator  palpebrse  superi- 
oris, inverted 

III.  nerve,  superior, 

division 

Frontal  nerv 

Optic  nerve 
Internal  carotid  artery 
III.  nerv 

FOILS,  displaced  backward 


Levator  palpebrre  superioris 
Superior  rectus 


Lachrymal  gland 
Nerve  to  inferior  oblique 
External  rectus  muscle 

iliary  ganglion 


Nasal  nerve 
Lachrymal  nerve 


Maxillary  division  of  V. 
Ophthalmic  division  of  V. 
Mandibular  division  of  V 
Gasserian  ganglion 

VI.  nerve 
IV.  nerve 


Cerebral  peduncl 


Deeper  dissection  of  right  orbit,  viewed  from  above  ;  branches  of  nasal  nerve  shown. 

upper  lateral  cartilage  of  the  nose,  finally  emerging  from  under  cover  of  the  compressor  naris 
muscle.     It  supplies  the  skin  of  the  fore-part  and  tip  of  the  nose. 

Variations. — The  nasal  nerve  may  send  branches  to  the  superior  and  internal  recti  and 
levator  palpebrse  superioris  muscles.  In  one  case  a  small  ganglion  connected  with  the  nasal 
nerve  sent  fibres  to  the  third  and  sixth  nerves.  Instances  are  recorded  of  absence  of  the 
infratrochlear  branch,  the  deficiency  being  supplied  by  the  supratrochlear.  Branches  to  the 
frontal  and  ethmoidal  sinuses  are  described  as  being  given  off  in  the  anterior  ethmoidal  fora- 
men, and  a  branch  has  been  found  which  passes  through  the  posterior  ethmoidal  foramen  to 
supply  the  sphenoidal  and  posterior  ethmoidal  sinuses.  The  latter  has  been  called  by  Luschka 
the  spheno-ethmoidal  and  by  Krause  the  posterior  ethmoidal  branch. 

The  Ganglia  associated  with  the  Trigeminal  Nerve. — Four  small  ganglia 
are  connected  with  the  extracranial  portion  of  the  fifth  nerve.  They  are  the  ciliary,  the 
spheno-palatine,  the  otic  and  the  submaxillary.  The  ciliary  ganglion  is  associated 


1236 


HUMAN   ANATOMY. 


with  the  ophthalmic  nerve,  the  spheno-palatme  with  the  maxillary  and  the  otic  and 
submaxillary  with  the  mandibular.  Each  is  the  recipient  of  three  roots — a  motor,  a 
sensory  and  a  sympathetic — and  from  each  ganglion  branches  are  given  off  to  more  or 
less  contiguous  structures. 

The  significance  of  these  bodies — whether  of  the  nature  of  spinal  or  sympathetic 
ganglia — has  long  been  a  subject  of  discussion.  The  close  resemblance  of  their 
nerve-cells  to  the  stellate  neurones  of  undoubted  sympathetic  ganglia,  as  shown  by  the 
investigations  of  Retzius,  Kolliker  and  others,  as  well  as  the  results  of  experimental 
studies  (Apolant),  justifies  the  conclusion  that  these  ganglia  are  properly  regarded 
as  belonging  to  the  sympathetic  group.  They  are,  therefore,  probably  stations 
in  which  certain  motor  and  secretory  fibres  contributed  by  various  nerves  end  in 
arborizations  around  sympathetic  neurones,  from  which  axones  pass  for  the  immedi- 
ate supply  of  involuntary  muscle  and  glandular  tissue.  The  fact  that  these  small 
ganglia  are  derivations  of  the  early  Gasserian  ganglion  is  in  accord  with  the  mode 
of  origin  of  the  sympathetic  ganglia  elsewhere  (page  1013). 

FIG.  1058. 


Internal  carotid  artery 

IV.  nerve 
Cerebral   peduncle 


s  "  * 

>       ».fc'C>-E  "  X'o 

£8  i    S£.2 1,  |  Ifl 

5:2  °    2S.5  Rs  5  ««! 

II  >    jlll^  ^  |l i 


Middle  cerebella. 
peduncle 


Levator  palpebrae  superioris 

Superior  oblique  muscle 
Lachrymal  gland 

uperior  rectus  muscle 
Long  ciliary  branches  of  nasal  nerve 


Ext.  rectus,  insertion 
•Inferior  oblique  muscle 


Gasserian  ganglion 

^Ext.  rectus  muscle 

VI.  nerve 
Ganglionic  branch  of  nasal 

Ciliary  ganglion 


Branch  to  Inf.  oblique 
Inferior  rectus  muscle 


Short  ciliary  nerves  ..... .„.„  ...^.^ 

Dissection  of  right  orbit  after  removal  of  its  lateral  wall ;  external  and  superior  eye-muscles  have  been  cut  and 
displaced  to  expose  ciliary  ganglion  and  nerves. 

The  Ciliary  Ganglion. — The  ciliary,  ophthalmic  or  Icnticulat  ganglion 
(g.  ciliare)  (Fig.  1058),  as  it  is  varyingly  called,  is  a  small  reddish  mass,  about 
2  mm.  long  in  the  antero-posterior  direction,  and  approximately  quadrilateral  in  out- 
line. It  is  compressed  laterally  and  to  each  angle  is  attached  one  or  more  bundles  of 
nerve-fibres.  It  lies  near  the  apex  of  the  orbit  on  the  outer  side  of  the  optic  nerve, 
between  the  latter  and  the  external  rectus  muscle  and  anterior  to  the  ophthalmic  artery. 

The  nerve-cells  within  the  ganglion  are  chiefly  multipolar  elements,  which 
closely  resemble  sympathetic  neurones  (Retzius)  and  send  their  axones  towards  the 
eye  by  way  of  the  short  ciliary  nerves. 

Roots. — All  of  these  enter  the  posterior  margin  of  the  ganglion.  The  motor 
or  short  root  (radix  brcvis),  the  thickest  of  the  roots  and  sometimes  double,  is  an  off- 
shoot from  the  branch  of  the  oculomotor  nerve  which  supplies  the  inferior  oblique 
muscle.  It  is  short  and  comparatively  robust  and  joins  the  postero-inferior  portion 
of  the  ganglion.  The  sensory  or  long  root  (radix  lonsja)  arises  from  the  nasal  branch 
of  the  ophthalmic,  leaving  the  latter  between  the  heads  of  the  external  reetns.  It  is 
long  and  slender  and  passes  forward  to  enter  the-  upper  posterior  angle  of  the  gang- 
lion, occasionally  being  fused  with  the  sympathetic  root.  The  sympathetic  root  (radix 


THE   TRIGEMINAL   NERVE  1237 

media)  is  a  tiny  filament  which  arises  from  the  cavernous  plexus  and  runs  forward  to 
enter,  either  alone  or  with  the  sensory  root,  the  upper  posterior  angle  of  the  ganglion. 
Branches. — These  are  the  short  ciliary  nerves  (nn.  ciliares  breves).  They 
number  from  four  to  six  and  by  division  are  increased  to  twelve  or  twenty  before 
reaching  the  eyeball  (Fig.  1058).  They  arise  as  two  fasciculi  from  the  upper  and 
lower  anterior  angles  of  the  ganglion  and  pass  forward  above  and  below  the  optic 
nerve.  The  lower  set  is  the  more  numerous  and  on  its  way  forward  is  joined  by  the 
long  ciliary  nerves  from  the  nasal,  with  which  one  or  more  of  its  constituent  branches 
usually  fuse.  After  piercing  the  sclerotic  coat  in  two  groups,  one  below  and  the 
other  above  the  entrance  of  the  optic  nerve,  they  pass  forward  in  grooves  on  the 
inner  surface  of  the  sclerotic  to  supply  the  choroid,  iris,  ciliary  muscle  and  cornea. 

The  short  ciliary  nerves  include  three  sets  of  fibres  :  ( i )  Sympathetic  fibres  destined  for 
the  walls  of  the  blood-vessels  and  the  radial  (dilator)  muscle  of  the  iris  ;  these  are  links  in  the 
chain  made  up  of  (a)  white  rami  communicantes  from  the  upper  thoracic  spinal  nerves  to  the 
cervical  gangliated  cord,  and  (b)  the  axones  of  neurones  within  the  sympathetic  ganglia.  (2) 
Fibres  supplying  the  ciliary  muscle  and  the  circular  (sphincter)  muscle  of  the  iris,  which,  while 
in  a  sense  the  continuations  of  the  oculomotor  nerves,  are  immediately  the  axones  of  the  stellate 
sympathetic  neurones  within  the  ciliary  ganglion.  (3)  Trigeminal  fibres  which  transmit  sensory 
impulses  from  the  interior  of  the  eyeball,  in  conjunction  with  the  long  ciliary  nerves. 

Variations. — The  motor  root  occasionally  bifurcates  before  it  reaches  the  ganglion.  As 
noted  above,  the  sensory  and  sympathetic  roots  frequently  form  a  common  trunk  of  entrance 
into  the  ganglion.  Occasionally  the  ganglion  is  very  small,  due  possibly  to  the  scattering  of  its 
constituent  neurones  among  the  nerves  connected  with  it  (Quain).  Additional  roots  have  been 
described  as  coming  from  the  superior  division  of  the  oculomotor,  from  the  trochlear,  from  the 
lachrymal,  from  the  abducent  and  from  the  spheno-palatine  ganglion.  Absence  of  the  sensory 
root  has  been  noted,  the  deficiency  possibly  being  corrected  by  the  long  ciliary  nerves  convey- 
ing sensory  fibres  directly  from  the  nasal  to  their  destination,  instead  of  these  fibres  passing 
through  the  ganglion.  The  sympathetic  root  may  be  multiple,  a  condition  held  by  some  to  be 
normal,  some  of  the  fibres  accompanying  the  oculomotor  nerve. 

II.  The  Maxillary  Nerve  or  superior  maxillary  nerve  (n.  maxillaris)  is  purely 
sensory  and  is  intermediate  in  size  between  the  ophthalmic  and  mandibular  divisions 
of  the  trigeminus.  It  supplies  the  cheek,  the  anterior  portion  of  the  temporal  region, 
the  lower  eyelid,  the  side  of  the  nose,  the  upper  lip,  the  upper  teeth,  and  the  mucous 
membra'ne  of  the  nose,  naso-pharynx,  maxillary  antrum,  posterior  ethmoidal  cells, 
soft  palate,  tonsil  and  roof  of  the  mouth.  Arising  from  the  middle  of  the  anterior 
convex  border  of  the  Gasserian  ganglion,  it  passes  forward  beneath  the  dura  mater  in 
the  middle  cranial  fossa,  lying  below  the  cavernous  sinus  (Fig.  1053).  The  nerve 
leaves  the  cranium  through  the  foramen  rotundum,  traverses  the  spneno-maxillary 
fossa  and  enters  the  orbital  cavity  by  means  of  the  spheno-maxillary  fissure.  It 
occupies  and  then  parallels  the  floor  of  the  orbit  in  the  infraorbital  groove  and  canal, 
finally  emerging  on  the  face  by  passing  through  the  infraorbital  foramen.  Here  it 
breaks  up  fanlike  into  three  terminal  groups  of  branches  (Fig.  1060). 

Branches  and  Distribution. — Branches  are  given  off  from  the  maxillary 
nerve  in  the  cranium,  in  the  spheno-maxillary  fossa,  in  the  infraorbital  canal  and 
on  the  face.  These  are  :  within  the  cranium,  (  i )  the  recurrent ;  within  the 
spheno-maxillary  fossa,  (2)  the  spheno-palatine,  (3)  the  posterior  superior 
dental  and  (4)  the  temporo- malar ;  in  the  infraorbital  canal,  (5)  the  middle 
superior  dental  and  ( 6 )  the  anterior  superior  denial ;  on  the  face  ( 7 )  the 
inferior  palpcbral,  (  8 )  the  lateral  nasal  and  (  9 )  the  superior  labial.  The  last 
three  are  terminal  branches. 

1.  The  recurrent  branch  (n.  meningeus)  is  given  off  before  the  maxillary  nerve 
passes  through  the  foramen  rotundum.      It  supplies  the  dura  mater  in  the  middle 
cranial  fossa. 

2.  The  two  or  three  spheno-palatine  branches  (nn.  sphenopalatini)    (Fig. 
1061)  arise  in  the  spheno-maxillary  fossa.     They  are  short  and  thick  and  pass  directly 
downward  to  the  upper  margin  of  the  spheno-palatine  ganglion,  whose  sensory  root 
they  supply.      Only  a  small  part  of  their  fibres  actually  traverse  the  ganglion,   the 
much  larger  part  passing  lateral  to  or  in  front  of   the  ganglion,    to  be  continued 


1238 


HUMAN    ANATOMY. 


into  the  orbital,  posterior  nasal  and  palatine  branches.  While  in  neither  case  are  the 
trigeminal  fibres  interrupted  in  the  ganglion,  in  both  instances  they  receive  sympa- 
thetic fibres  from  the  ganglion,  which  accompany  the  trigeminal  ones. 

3.  The  posterior  superior  dental   nerve    (r.  alveolaris   superior   posterior) 
(Fig.  1060)  is  frequently  double.      It  passes  downward  and  forward  with  the  posterior 
dental  artery  through  the  pterygo-maxillary  fissure  to  reach  the  zygomatic  surface  of 
the  maxilla.      It  supplies  tiny  filaments  to  the  gum  and  adjacent  mucous  membrane  of 
the  cheek  and  enters  the  posterior  dental  canals  to  supply  the  molar  teeth.      It  forms 
a  fine  plexus  (plexus  dentalis  superior)  (Fig.    1059)    with   the  middle  and  anterior 
superior  dental  nerves. 

Variation. — In  the  absence  of  the  buccal  branch  of  the  fifth,  the  posterior  superior  dental 
has  been  observed  to  be  of  large  size  and  to  assume  the  distribution  of  the  buccal. 

4.  The  temporo-malar  or  orbital  nerve  (n.  zygomaticus)  (Fig.  1053)  after 
arising  from  the  maxillary  passes  from  the  spheno-maxillary  fossa  into  the  orbit 


FIG.  1059. 


Diagram  showing  plan  and  connections  of  second  and  third  divisions  of  trigeminus  and  their  ganglia. 


through  the  spheno-maxillary  fissure.  It  courses  along  the  external  orbital  wall  and 
divides  into  a  temporal  and  a  malar  branch.  The  temporal  branch  (n.  zygomaticotem- 
poralis)  after  inosculating  with  the  lachrymal  nerve  passes  through  the  spheno-malar 
foramen  to  enter  the  temporal  fossa.  It  then  runs  between  the  bone  and  the  temporal 
muscle  and  pierces  the  temporal  fascia  to  be  distributed  to  the  skin  of  the  anterior 
temporal  region.  It  communicates  with  the  tc'inporal  branch  of  the  facial  nerve. 
The  malar  branch  (n.  zygomaticofacialis)  traverses  the  malar  foramen  to  supply  the 
skin  of  the  malar  region.  It  joins  with  filaments  from  the  malar  branch  of  the 
seventh. 

Variations. — The  nerve  may  pass  through  the  malar  bone  before  it  divides,  both  branches 
may  pass  separately  through  canals  confined  to  the  malar  bone,  or  the  temporal  branch  may  pass 


THE   TRIGEMINAL   NERVE. 


1239 


through  the  spheno-maxillary  fissure.  Either  branch  may  be  absent  or  smaller  than  normal,  the 
other  branch  supplying  the  deficiency.  The  malar  may  be  replaced  in  its  distribution  by  the 
infraorbital  and  the  temporal  may  be  substituted  or  augmented  by  the  lachrymal. 

5.  The  middle  superior  dental  nerve  (r.  alveolaris  superior  medius)  leaves 
the  maxillary  in  the  posterior  part  of  the  infraorbital  canal.      It  occasionally  arises 
from  the  anterior  superior  dental.      It  passes  down  in  a  canal  in  the  outer  wall  of  the 
maxillary  antrum  and  after  forming  a  plexus  with  the  other  two  dental  nerves  supplies 
the  premolar  teeth. 

6.  The  anterior  superior  dental  nerve  (r.  alveolaris  superior  anterior)  is  the 
largest  of  the  three  superior  dental  nerves.      It  arises  from  the  maxillary  just  before 
the  exit  of   the  latter  at  the  infraorbital  foramen  and   descends  in  a  canal   in  the 
anterior  wall  of   the  antrum.      It  gives  off  a  nasal  branch,  which  enters  the  nose 

FIG.  1060. 


Middle  superior  dental  nerve 

Maxillary 

Posterior  superior  dental 

Buccal 

Sensory  division  of  mandibular 

Middle  meningeal  ar 
Auriculo-temporal  ne 


Ext.  pterygoid  muscle— — 

Lingual  n< 
Inferior  dental  nerve 

Superficial  temporal  artery 

Internal  maxillary  artery 

Int.  pterygoid  muscle 

Part  of  mandible 

I 

Ext.  carotid  artery __ 

Parotid  gland 


Mylo-hyoid  branch  of  inferior  dental 
Submaxillary  ganglion 


Submaxillary  gland 


Inferior  palpebral 


Lateral  nasal  and 
superior  labial 
branches  of 
infraorbital  nerve 
Anterior  superior 
dental  nerve 
Nasal  branch  of 
anterior  superior 
dental 


Sectional  surface  of 
mandible 


,Digastric  muscle,  anterior 
belly 


Myo-hyloid  muscle,  cut  to  shov 
lingual  nerve 


Dissection  showing  maxillary  and  mandibular  nerves  and  their  branches;  outer  wall  of  orbit,  part  of  facial  wall  of 
maxillary  sinus  and  part  of  mandible  have  been  removed. 


through  a  tiny  canal  in  the  outer  wall  of  the  inferior  meatus  of  the  nose  and 
supplies  the  mucous  membrane  of  the  anterior  part  of  the  inferior  nasal  meatus  and 
floor  of  the  nose.  After  helping  to  form  the  superior  dental  plexus,  the  anterior 
superior  dental  supplies  the  canine  and  incisor  teeth. 

Two  thickenings  are  sometimes  found  in  the  superior  dental  plexus.  One  of  these,  known 
as  the  ganglion  of  Valentin,  lies  above  the  tip  of  the  root  of  the  second  premolar  tooth,  at  the 
junction  of  the  middle  and  posterior  superior  dental  nerves;  and  the  other,  sometimes  called 
the  ganglion  of  Bochdalek,  is  situated  more  anteriorly,  at  the  junction  of  the  middle  and 
anterior  dental  nerves.  Neither  of  these  enlargements  is  a  true  ganglion,  being  without  nerve- 
cells  and  consisting  of  interlacing  bundles  of  nerve-fibres. 


1240  HUMAN   ANATOMY. 

7.  The  inferior  palpebral  branches  (rr.   palpebrales  inferiores)  (Fig.  1060) 
usually  two  in  number,  are  the  smallest  of  the  terminal  branches.      They  pass  upward 
from  the  infraorbital  foramen,  pierce  the  origin  of  the  levator  labii  superioris,  pass 
around  the  lower  margin  of  the  orbicularis  palpebrarum  and  supply  the  conjunctiva 
and  skin  of  the  lower  eyelid. 

8.  The  lateral  nasal  branches  (rr.  nasales  externi)  (Fig.  1060),  from  two  to 
four  in  number,  pass  inward  under  the  levator  labii  superioris  alaeque  nasi  and  supply 
the  skin  of  the  side  of  the  nose. 

9.  The  superior  labial  branches  (rr.  labiales  superiores)  (Fig.  1060),  two  to 
four  in  number,   are  the  largest  of  the  terminal  branches.     They  pass    downward 
under  the  levator  labii  superioris  and,  after  supplying  the  anterior  portion  of  the 
skin  of  the  cheek,  terminate  in  the  mucous  membrane  and  skin  of  the  upper  lip. 

The  last  three  branches  inosculate  freely  under  the  levator  labii  superioris  with 
the  infraorbital  branch  of  the  facial,  forming  the  infraorbital  plexus  (Fig.  1068). 

The  Spheno-Palatine  Ganglion. — The  spheno-palatine  ganglion  (g.  spheno- 
palatinum),  also  known  as  Meeker 's,  the  spheno-maxillary  or  the  nasal  ganglion,  is  a 
small  triangular  reddish-gray  body,  with  the  apex  directed  posteriorly,  situated  in 
the  upper  portion  of  the  spheno-maxillary  fossa.  It  is  flat  on  its  mesial  surface, 
and  convex  on  its  lateral,  and  measures  about  5  mm.  in  length.  It  lies  in  close 
proximity  to  the  spheno-palatine  foramen  and  just  beneath  the  maxillary  branch  of 
the  trigeminal  nerve  (Fig.  1061).  The  ganglion  is  regarded  as  belonging  to  the 
series  of  sympathetic  nodes,  and  consists  of  an  interlacement  of  nerve-fibres  in  which 
are  embedded  numerous  stellate  sympathetic  neurones. 

Roots. — The  sensory  root  consists  of  two,  sometimes  three,  short  stout 
filaments,  the  spheno-palatine  nerves  (nn.  sphenopalatini),  which  pass  directly 
downward  from  the  lower  margin  of  the  maxillary  nerve  to  the  upper  border  of  the 
ganglion.  While  some  few  of  the  fibres  of  this  root  are  axones  of  the  sympathetic 
ganglion-cells,  the  great  majority  are  dendrites  of  the-  cells  of  the  Gasserian  ganglion 
which  pass  to  a  limited  extent  through,  but  mostly  around,  the  spheno-palatine 
ganglion  independently  of  its  cellular  elements.  They  are  continued  entirely  into  the 
various  trunks  that  are  usually  described  as  branches  of  distribution  of  the  ganglion 
(see  below). 

The  motor  root  is  the  great  superficial  petrosal  nerve  (n.  petrosus  superficialis 
major)  which,  in  all  probability,  carries  sensory  as  well  as  motor  fibres.  It  arises  from 
the  facial  nerve  in  the  facial  canal,  passes  through  the  hiatus  Fallopii  and  a  groove  in 
the  petrous  portion  of  the  temporal  bone  and  then  under  the  Gasserian  ganglion  to- 
reach  the  cartilage  occupying  the  middle  lacerated  foramen.  Here  the  great  super- 
ficial petrosal  nerve  is  joined  by  the  sympathetic  root,  the  great  deep  petrosal, 
(n.  petrosus  profundus),  which  is  a  branch  from  the  carotid  plexus.  The  two  givut 
petrosal  nerves  fuse  over  the  cartilage  at  the  middle  lacerated  foramen  to  form  the 
Vidian  nerve  (n.  canalis  pterygoidei  [Vidii]  )  (Fig.  1061),  which  traverses  the  canal  of 
the  same  name  and  enters  the  spheno-maxillary  fossa  to  join  the  spheno-palatine 
ganglion.  In  its  course  through  the  canal  the  Vidian  nerve  gives  off  a  few  tiny 
nasal  branches,  which,  composed  of  trigeminal  and  sympathetic  fibres,  supply  the 
pharyngeal  ostium  of  the  Eustachian  tube  and  the  posterior  part  of  the  roof  of 
the  nose  and  the  nasal  septum.  While  in  the  canal,  the  Vidian  nerve  receives  a 
filament  from  the  otic  ganglion. 

In  addition  to  supplying  (according  to  many  anatomists)  motor  fibres  to  the  levator  palati 
and  azygos  uvulae  muscles,  some  of  the  facial  fibres  are  especially  destined  for  glandular  struc- 
tures. Such  fibres  are  probably  interrupted  around  UK-  stellate  cells  of  the  spheno-palatine 
ganglion,  the  axones  of  which  then  complete  the  paths  for  the  secretory  impulses.  The  sensory 
constituents  of  the  great  superficial  petrosal  nerve  are,  perhaps,  of  two  kinds:  (a)  fibres  from 
the  cells  of  the  geniculate  "ganglion  of  the  facial  to  the  palatine  taste-buds,  and  (b}  recurrent 
trigeminal  fibres,  that,  byway  of  tin.-  maxillary,  spheno-patetfatt  and  great  superficial  petrosal 
nerves,  are  distributed  with  the  peripheral  branches  of  the  Vidian  or  of  tin-  facial  m-rvr. 

The  great  deep  petrosal  nerve  represents  tin-  association  cord  between  the  superior  cervical 
sympathetic  and  the  spheno-palatine  ganglion.  Many  of  its  fibres  end  in  arbori/ations  around 
the  stellate  spheno-palatine  cells,  from  which,  in  turn,  axones  pass  to  blood-vessels  and  glands 
by  way  of  the  ganglionic  branches  of  distribution. 


THE   TRIGEMINAL    NERVE. 


1241 


Branches. — The  branches  of  distribution  of  the  spheno-palatine  ganglion  are 
conveniently  grouped  into  four  sets  :  (i)  the  ascending,  (2)  the  descending,  (3)  the 
internal  and  (4)  ^\^  posterior. 

1.  The  ascending  or  orbital  branches  (IT.  orbitales)  (Fig.  1059)  are  two  or 
three  tiny  filaments,  which  pass  into  the  orbit  through  the  spheno-maxillary  fissure  and, 
after  traversing  the  posterior  ethmoidal  canal  or  a  small  special  aperture,  are  distrib- 
uted to  the  sphenoidal  and  posterior  ethmoidal  air-cells  and  the  periosteum  of  the  orbit. 

2.  The  descending  branches  (nn.  palatial)  (Fig.  1059)  are  three  :   (a)  the 
large  posterior  palatine,  {b)  the  small  posterior  palatine,  and  (<:)  the  accessory  pos- 
terior palatine  nerves. 

a-  The  large  posterior  palatine  nerve  (n.  palatinus  anterior)  leaves  the  spheno-maxillary  fossa 
by  means  of  the  large  posterior  palatine  canal,  through  which  it  descends  to  the  inferior  surface 
of  the  hard  palate.  While  in  the  canal  it  gives  off  one  or  two  posterior  inferior  nasal  branches. 

FIG.  1061. 


Cavernous  plexus  and 
t.  carotid  artery 


, Great  superficial 

^'petrosal  nerve 

Great  deep  petrosat 
nerve  from  carotid 
plexus 


Post.  inf.  nasal 

brs.  of  large 

posterior  palatine 


Large,  small  am 

accessory  poste 

rior  palatine 

nerves 


Naso-palatine 

nerve, 

termination 


Otic  ganglion,  cut 
Cartilage  of  Eustachian 
tube,  cut 

Int.  br.  of  ascending 
ram  us  sup.  cerv.  gangL 
Ext.  br.  of  ascending 

ramus  of  sup.  cerv. 

ganglion 


Sup.  cerv.  ganglion 
of  sympathetic 


Int.  carotid  artery 


Uvula 


:onstrictor 
tor  palati 

Tensor  palati,  cut  above 


Dissection  showing  spheno-palatine  and  otic  ganglia  viewed  from  within. 

(rr.  nasales  posteriores  inferiores) ,  which,  escaping  through  small  apertures  in  the  perpendicular 
plate  of  the  palate  bone,  enter  the  nasal  fossa  and  supply  the  mucous  membrane  of  all  but  the 
anterior  portion  of  the  inferior  turbinate  bone  and  the  adjoining  portions  of  the  middle  and  infe- 
rior nasal  meatuses.  Emerging  from  its  canal  the  main  nerve  passes  forward  in  a  groove  on  the 
inferior  aspect  of  the  hard  palate  and  inosculates  with  the  terminal  filaments  of  the  naso-palatine 
nerve.  It  supplies  the  hard  palate  and  its  mucous  membrane,  as  well  as  the  inner  side  of  the  gum. 

b.  The  small  posterior  palatine  nerve  (n.  palatinus   posterior)  descends  in  the  small  pos- 
terior palatine  canal.     It  supplies  sensory  filaments  to  the  mucous  membrane  of  the  soft  palate 
and  the  tonsil  and  motor  ones  to  the  levator  palati  and  azygos  uvulae  muscles. 

c.  The  accessory  posterior  palatine  nerves  (nn.  palatinus  medius)  are   one  or  more  small 
filaments  which  pass  through  the  accessory  posterior  palatine  canals  and  supply  the  mucous 
membrane  of  the  soft  palate  and  tonsil. 

3.  The  internal  branches  (rr.  nasales  posteriores  superiores)  (Fig.  1059)  pass 
from  the  spheno-maxillary  into  the  nasal  fossa  through  the  spheno-palatine  foramen. 
They  are  :  (a)  the  posterior  superior  nasal  and  (b)  the  naso-palatine  nerve. 


i242  HUMAN   ANATOMY. 

a.  The  posterior  superior  nasal  nerve  (rr.  laterales)  supplies  the  mucous  membrane  of  the 
posterior  superior  portion  of  the  outer  wall  of  the  nasal  fossa. 

b.  The  naso-palatine  nerve    (n.  nasopalatinus)    (Fig.  1059)  crosses  the  roof  of  the  nasal 
chamber  and  passes  downward  and  forward  in  a  groove  in  the  vomer  and  septal  cartilage  to 
reach  the  anterior  palatine  canal.     It  then  passes  through  the  foramen  of  Scarpa,  the  left  nerve 
through  the  anterior  and  the  right  one  through  the  posterior  canal,  the  two  nerves  forming  in 
this  situation  a  fine  plexus.     Having  reached  the  inferior  surface  of  the  hard  palate,  the  naso- 
palatine  inosculates  with  the  large  posterior  palatine  nerve.     It  supplies  the  roof  and  septum  of 
the  nose  and  that  portion  of  the  hard  palate  which  lies  posterior  to  the  incisor  teeth. 

4.  The  posterior  branch  (Fig.  1059)  also  known  as  the  pharyngeal  or 
pterygo-palatine,  leaves  the  spheno-maxillary  fossa  through  the  pterygo-palatine 
canal  and  supplies  the  mucous  membrane  of  the  naso-pharynx  in  the  region  of  the 
fossa  of  Rosenmiiller. 

Variations. — Branches  of  the  ganglion  have  been  described  as  passing  to  the  abducent 
nerve,  to  the  ciliary  ganglion  and  to  the  optic  nerve  or  its  sheath.  The  accessory  posterior 
palatine  nerve  is  sometimes  absent.  Quite  frequently  the  left  naso-palatine  nerve  passes 
through  the  posterior  foramen  of  Scarpa  and  the  right  nerve  through  the  anterior. 

III.  The  Mandibular  Nerve. — The  mandibular  or  inferior  maxillary  branch 
(n.  mandibularis)  of  the  trigeminal  nerve  is  the  largest  of  its  three  divisions  and,  being  a 
mixed  nerve,  consists  of  two  portions,  one  sensory  and  the  other  motor.  The  sensory 
part  is  the  larger  and  arises  from  the  lower  anterior  portion  of  the  Gasserian  ganglion. 
The  smaller  motor  part  is  the  motor  root  of  the  trigeminal  nerve,  which  contributes 
exclusively  to  this  division  of  the  fifth  nerve.  Although  these  two  portions  are  inti- 
mately associated  in  their  passage  through  the  foramen  ovale,  the  motor  bundle 
lying  to  the  median  side  of  the  sensory,  it  is  not  until  they  emerge  from  the  skull 
that  they  unite,  immediately  below  the  lower  margin  of  the  foramen  ovale,  to  form 
the  mandibular  nerve.  The  sensory  portion  supplies  the  skin  of  the  side  of  the 
head,  the  auricle  of  the  ear,  the  external  auditory  meatus,  the  lower  portion  of  the 
face  and  the  lower  lip,  the  mucous  membrane  of  the  mouth,  tongue  and  mastoid 
cells,  and  the  lower  teeth  and  gums,  the  salivary  glands,  the  temporo-mandibular 
articulation,  the  dura  mater  and  the  skull.  The  motor  portion  supplies  the  muscles 
of  mastication  (the  temporal,  the  masseter  and  the  external  and  internal  pterygoids), 
the  anterior  belly  of  the  digastric,  the  mylo-hyoid,  the  tensor  palati  and  the  tensor 
tympani  muscles.  By  union  of  the  two  constituents,  a  thick  common  trunk  is  formed, 
which,  after  a  course  of  from  2-3  mm. ,  separates  under  cover  of  the  external  ptery- 
goid  muscle  into  an  anterior  and  a  posterior  division  (Fig.  1063). 

Branches  and  Distribution. — The  branches  from  the  main  trunk  of  the 
mandibular  nerve  are :  (i)  the  recurrent  branch  and  (2)  the  internal  pterygoid  nerve. 

1.  The  recurrent  branch  (n.  spinosus)  arises  just  beneath  the  foramen  ovale 
and  accompanies  the  middle  meningeal  artery  into  the  cranium  through  the  foramen 
spinosum.      It  then  divides  into  two  branches,  the  anterior  of  which  supplies  the  greater 
wing  of  the  sphenoid  and  the  adjacent  dura  mater,  while  the  posterior  passes  through 
the  petro-squamous  suture  and   supplies  the   mucous    membrane   of   the   mastoid 
air-cells. 

2.  The   internal    pterygoid   nerve    (n.  pterygoideus   interims)   (Fig.    1059) 
passes  downward  on  the  mesial  side  of  its  muscle  and,  in  addition  to  supplying  the 
pterygoid  muscle,  gives  off  the  motor  root  of  the  otic  ganglion  and  filaments  to  the 
tensor  tympani  and  tensor  palati  muscles. 

The  Anterior  Division  of  the  mandibular  nerve  (n.  masticatorius)  is  motor, 
with  the  exception  of  its  buccal  branch,  and  receives  almost  the  entire  motor  constit- 
uent of  the  trigeminal.  It  passes  downward  and  forward  for  a  short  distance  under 
the  external  pterygoid  muscle  and  then  breaks  up  into  its  branches. 

Branches. — These  are:  (i)  the  masscleric ,  (2)  the  external  pterygoid ,  (3) 
the  deep  temporal  and  (4)  the  buccal  nerve. 

i.  The  masseteric  nerve  (n.  massctericus)  (Fig.  1063)  passes  over  the 
upper  border  of  the  external  pterygoid  and  behind  the  posterior  margin  of  the 
temporal  muscle.  It  takes  a  course  horizontally  outward  and  traverses  the  sigmoiil 


THE   TRIGEMINAL   NERVE. 


1243 


notch  of  the  mandible  to  enter  the  posterior  portion  of  the  mesial  surface  of  the 
masseter.      It  supplies  one  or  two  filaments  to  the  temporo-mandibular  articulation. 

2.  The  external  pterygoid  nerve   (n.  pterygoideus  externus)    (Fig.    1063), 
usually  takes  its  origin  as  a  common  trunk  with  the  buccal  nerve.      It  enters  the 
deep  surface  of  the  external  pterygoid. 

3.  The  deep  temporal  nerves  (nn.  temporales  profundi  anterior  et  posterior) 
(Fig.    1063),   are   usually    three   or   two    in    number.     The   anterior  accompanies 
the  buccal  nerve  between  the  heads  of  the  external  pterygoid,  after  which  it  passes 
upward  to  supply  the  anterior  portion  of  the  temporal  muscle.     The  middle  passes 
outward  across  the  upper  margin  of  the  external  pterygoid  and  then  upward  close 
to  the  bone  to  enter  the  deep  surface  of  the  temporal  muscle.      It  often  fuses  with 
either  the  anterior  or  posterior  deep  temporal,  thus  reducing  the  number  of  temporal 


FIG.  1062. 


Gasserian  ganglion 
V.  nerve,  sensory  root 


Maxillary  division  V.  nerve 


'Spheno-palatine 
nerves 


division  V.  nerve 

Auriculo- 
temporal  ner 
Mandib.  div.  V. 
nerve,  partly  cut 

Chorda  tympan 

Otic  ganglion ;  it! 

br.  to  tensor  tym 

pani  is  seen  above 

the  leader 

Mlddli 

•neningeal  artery 


Part  ol 
parotid  gland 

Br.  from  otic  ganglion 
to  auriculo-temp.  nerve' 

/ 

Br.  from  otic  gang,  to  chorda  tympani 

Int.  pterygoid  nerv 

Int.  pterygoid  muscl 

Inferior  dental  nerve 
Lingual  br.  V 


Buccinator 
muscle 


Dissection  showing  lateral  view  of  spheno-palatine  and  otic  ganglia. 

nerves  to  two.  The  posterior  frequently  accompanies  the  nerve  to  the  masseter  for 
a  variable  distance,  after  which  it  turns  upward  along  the  bone  to  enter  the  deep 
surface  of  the  posterior  portion  of  the  muscle. 

4.  The  buccal  nerve  (n.  buccinatorius)  (Fig.  1063)  is  purely  sensory.  It 
arises  in  common  with  the  external  pterygoid  and  anterior  deep  temporal  nerves 
and  is  accompanied  by  the  latter  between  the  heads  of  the  external  pterygoid. 
Passing  downward  on  the  inner  side  of  the  temporal  muscle  it  reaches  the  outer 
surface  of  the  buccinator,  where  it  breaks  up  into  several  branches  which  form  a 
plexus  around  the  facial  vein,  with  the  buccal  branch  of  the  facial  nerve.  Some  of 
its  branches  pierce  the  buccinator  muscle  to  supply  the  mucous  membrane  of  the 
cheek  as  far  forward  as  the  angle  of  the  mouth,  while  the  others  supply  the  skin  of 
the  cheek. 


Variations. — Instead  of  lying  to  the  inner  side,  the  nerve  may  pierce  the  temporal  muscle. 
It  may  be  derived  from  the  posterior  superior  dental  nerve  or  from  the  inferior  dental,  in  the 
latter  instance  emerging  from  the  inferior  dental  canal  by  a  small  foramen  in  the  alveolar  border 


1244  HUMAN   ANATOMY. 

of  the  mandible,  just  anterior  to  the  ramus.  It  has  been  seen  in  one  case  to  arise  directly  from 
the  Gasserian  ganglion  and  emerge  from  the  cranium  through  a  special  foramen  situated  bt-tu  een 
the  foramina  rotundum  and  ovale. 

% 

The  Posterior  Division  of  the  niandibular  nerve  is  sensory,  with  the  exception 
of  the  mylo-hyoid  nerve.  It  passes  downward  beneath  the  external  pterygoid  and, 
after  giving  off  the  two  roots  of  the  auriculo-temporal  nerve,  terminates  by  dividing 
into  the  lingual  and  the  inferior  dental  nerve. 

Branches. — These  are  :  (i)  the  auriculo- temporal,  (2)  the  lingual  and  (3) 
the  inferior  dental. 

1.  The  auriculo-temporal  nerve  (n.  aunculotemporalis)  (Fig.  1063)  arises  just 
below  the  foramen  ovale  by  two  roots  which  enclose  between  them  the  middle  meningeal 
artery.      It  passes  backward  beneath  the  external  pterygoid  muscle  and  between  the 
spheno-mandibular  ligament  and  the  neck  of  the  mandible,  and  then  turns  upward 
through  the  parotid  gland  between  the  temporo-mandibular  articulation  and  the  external 
ear.      Emerging  from  the  upper  margin  of  the  gland,  the  nerve  passes  over  the  root  of 
the  zygoma  and  ascends  to  the  temporal  region  behind  and  in  company  with  the 
superficial  temporal  artery. 

Branches. — These  are  :  (a)  the  articular,  (b)  the  parotid,  (c~)  the  mealal,  (d*) 
the  anterior  auricular  and  (e)  the  superficial  temporal.  The  last  three  are 
terminal  branches. 

a.  The  articular  branches  (rr.  articulates)  are  one  or  two  delicate  filaments  which  enter 
the  posterior  portion  of  the  tempor-mandibular  articulation. 

b.  The  parotid  branches  (rr.  parotidei)  pass  to  the  gland;  they  arise  either  from   the 
auriculo-temporal  or  from  its  communicating  filaments  with  the  facial  nerve. 

c.  The  meatal  branches  (nn.  meatus  auditorii  externi)  are  two  in  number,  an  upper  and  a 
lower.     They  enter  the  external  auditory  canal  between  the  bone  and  the  cartilage  and  supply 
the  skin  covering  the  corresponding  parts  of  the  meatus,  the  upper  branch  in  addition  sending  a 
twig  (r.  membranae  tympani)  to  the  tympanic  membrane. 

d.  The  anterior  auricular  nerves  (nn.  auriculares  anteriores) ,  usually  two  in  number,  supply 
skin  of  the  tragus  and  of  the  upper  anterior  portion  of  the  auricle. 

e.  The  superficial  temporal  nerve   (rr.  temporales  superficiales)  (Fig.  1068)  breaks  up  into 
a  number  of  fine  twigs  which  supply  the  skin  of  the  temporal  region  and  of  the  scalp  almost  to 
the  sagittal  suture. 

The  auriculo-temporal  communicates  by  its  roots,  close  to  their  origin,  with  branches  from 
the  otic  ganglion,  and  by  its  parotid  and  superficial  temporal  branches  with  the  facial  nerve. 
By  the  first  of  these  communications  secretory  fibres  of  the  glosso-pharyngeal  and  sympathetic 
fibres  are  carried  to  the  parotid  gland  ;  by  means  of  the  second  junction  sensory  trigeminal 
fibres  accompany  the  peripheral  motor  filaments  of  the  facial. 

Variations.— In  a  specimen  found  in  the  anatomical  laboratory  of  the  University  of  Pennsyl- 
vania, the  middle  meningeal  artery,  instead  of  passing  between  the  two  roots  of  the  nerve, 
pierced  the  anterior  one. 

2.  The    lingual    nerve    (n.    lingualis)   (Fig.     1079)  is   the    smaller  of    the 
terminal  branches  of   the  mandibular  nerve.        Lying  internal  and  anterior  to  the 
inferior  dental  nerve,  it  passes  downward  beneath  the  external  pterygoid  as  far  as  the 
lower  border  of  that  muscle.    It  is  usually  connected  with  the  inferior  dental  nerve  by 
an   oblique  strand  of  fibres,  which  occasionally  crosses  the  internal  maxillary  artery 
and,  close  to  its  origin,  it  is  additionally  joined  at  an  acute  angle   by  the  chorda 
tympani   nerve.    After  emerging  from  undercover  of  the  external  pterygoid,  it  passes 
between  the  internal  pterygoid  and  the  ramus  of  the  mandible.      It  then  turns  inward, 
forward  and  downward  under  the  mucous  membrane  of  the  floor  of  the  mouth,  cross- 
in-  over  the  superior  border  of  the  superior  constrictor  of  the  pharynx  and  the  deep 
portion  of  the  submaxillary  gland,  and  passes  under  the  submaxillary  duct  between 
tlie  mylo-hyoid  and  hyo-glossus  muscles.     Reaching  the  side  of  the  tongue  tin-  nerve 
continues  forward  to  the  apex,  lying  just  beneath   the  mucous  membrane. 

Branches. — The  lingual  nerve  supplies  small  filaments  to  the  sublingual  gland, 
the  floor  and  side  of  the  month,  the  side-  of  the  tongue  and  the  lower  gum.  It 
gives  off  the  sensory  root  of  the  submaxillary  ganglion  and  its  terminal  filaments 
(rr.  linnuak's)  pass  upward  through  the  muscles  of  the  tongue  to  supply  the  mucous 


THE   TRIGEMINAL   NERVE. 


1245 


membrane  of  the  anterior  two-thirds  of  the  dorsum.  Its  fibres  have  their  main 
termination  in  the  filiform  and  fungiform  papillae. 

The  lingual  nerve  communicates  with  the  chorda  tympani  and  the  inferior 
dental  and  in  its  anterior  portion  forms  loops  with  the  hypoglossal. 

3.  The  inferior  dental  nerve  (n.  alveolaris  inferior)  (Fig.  1063)  is  the  larger 
of  the  terminal  branches  of  the  mandibular.  Lying  posterior  and  external  to  the 
lingual,  to  which  it  is  connected  by  a  small  nerve  strand,  it  passes  downward  and 
forward  under  cover  of  the  external  pterygoid.  Leaving  the  lower  margin  of  that 
muscle,  it  runs  between  the  ramus  of  the  mandible  and  the  spheno-mandibular 
ligament  and  enters  the  inferior  dental  canal,  along  which  it  courses  in  company 

FIG.   1063. 


Motor  division  of  mandibular  nervi 
Deep  temporal  branches 


Sensory  division  of 

Internal  pi 

Chorda  tym 

Middle  meningea 


Auriculo- 
temporal  nerve 

Superficial 
temporal  artery 

Mylo-hyoid  nerve 


Inte 


maxillary  artery 

auriculo-temporal 

and  facial  nerves 

Facial  nerve 


Inferior  dental  nerve 
Part  of  mandible 

Parotid  gland 

External 

carotid  artery 

Mylo-hyoid  nerve 


Zygomatic  process 
ot  malar  bone 


Hxt.  pterygoid 
muscle,  cut,  and 
its  nerve 


Masseteric  branch 
giving  off  a  temporal 
branch 


Cut  edge  ot 
buccinator 


Int.  pterygoid  muscle 
Lingual  nerve 


Mylo-hyoid  muscle, 
cut  to  show 
lingual  nerve 

ibmaxillary  ganglion 
Digastric  muscle, 
anterior  belly 


Submaxillary  gland 


Dissection  showing  mandibular  nerve  and  its  branches;  mandible  has  been  partially  removed,  exposing    inferior 

dental  nerve  in  its  canal. 

with  the  inferior  dental  artery,  and  supplies  filaments  to  the  teeth,  as  far  as  the  mental 
foramen.  Here  the  nerve  breaks  up  into  its  terminal  branches,  one  of  which,  the 
incisor,  continues  within  the  mandible  to  the  mid-line,  while  the  other  and  larger,  the 
mental,  emerges  at  the  mental  foramen. 

Branches.  —  These  are  :   (a)  the  mylo-hyoid,    (t>)  the  dental,    (c)  the  incisor 
and  (d)  the  mental,  of  which  the  last  two  are  terminal  branches. 


a.  The  mylo-hyoid  nerve  (n.  mylohyoideus)   (Fig.  1063)  is  the  only  motor  strand  in  the 
posterior  division  of  the   mandibular    nerve.      It  arises  from  the  inferior  dental  nerve,  just 
before  the  latter  enters  its  bony  canal,  and  passes  downward  and  forward  in  the  mylo-hyoid 
groove,  sometimes  a    canal  for  part  of  the  way,  in  the  mandible.     The  nerve  descends  into 
the  digastric  triangle  and  reaches  the  inferior  surface  of  the  mylo-hyoid  muscle,  in  this  situation 
being  overlain  by  the  submaxillary  gland  and  the  facial  artery  and  vein.     It  here  breaks  up  into 
filaments  which  supply  the  mylo-hyoid  muscle  and  the  anterior  belly  of  the  digastric. 

b.  The  dental  branches  (rr.  dentales  inferiores)  are  given  off  as  the  nerve  traverses  the 
inferior  dental   canal.     They  combine  and  unite  to  form   the  inferior  dental  plextis    (plexus 


1246 


HUMAN   ANATOMY. 


dentalis  inferior)  which  supplies  filaments  to  the  molar  and  premolar  teeth,  one  filament  to  each 
fang,  and  the  adjacent  portion  of  the  gum. 

c.  The  incisor  branch  (n.  alveolaris  inferior  anterior)  is  the  smaller  of  the  terminal  divisions 
and  continues  forward  within  the  mandible  the  course  of  the  inferior  dental  nerve  from  the 
mental  foramen  to  the  mid-line.     It  supplies  the  canine  and  incisor  teeth. 

d.  The  mental  nerve   (n.   mentalis)   (Fig.  1063)   is  much  the  larger  terminal 
branch  of  the  inferior  dental.     Emerging  from  the  mental  foramen,  it  breaks  up  under 
cover  of  the  depressor  anguli  oris  muscle  into  a  number  of  filaments  which  supply  the 
skin  of  the  chin  and  the  integument  and  mucous  membrane  of  the  lower  lip.     It  forms 
a  free  communication  with  the  supramandibular  branch  of  the  facial  nerve. 

The  Otic  Ganglion. — The  otic  or  Arnold' s ganglion  (g.  oticum)  (Fig.  1064)  is 
one  of  the  two  ganglia  associated  with  the  mandibular  nerve.      It  is  a  small  flattened 

FIG.  1064. 

Ophthalmic  division.V.  nerve 
Maxillary  division,  V.  nerve 

Gasserian  ganglion,  inf.  surface 

V.  nerve,  sensory  root 
:rve,  motor  root 
Mandibular  division,  V.  nerve 

Tensor  tympani,  cut       (tensor  tympani 
Br.  from  otic  ganglion  to 
Cartilaginous  portion  of 
'Eustach.  tube,  cut 

Petrosa  of  temporal 

bone 

Small  superf. 

petrosal  nerve 

Br.  from  ganglion  to 

chorda  tympani 

Middle  meningeal 
artery  and  plexus 
Carotid  canal  outer, 
Auriculo-tem-         [wall 
poral  nerve 
Lingual  nerve 

Inf.  dental  nerve 
Int.  maxillary  artery 
Temporal  artery 


Otic  ganglion 

~^^fc 
Br.  to  auriculo-temp.  nerve-^— 

Int.  pterygoid  nerve 
Br.  to  tensor  palati 

Tensor  palati,  cut 


Hamulus  of  int 
pterygoid  plate 


Ext.  carotid  artery 
'Styloid  process 


Otic  ganglion  and  branches  seen  from  mesial  aspect,  section  of  skull  being  not  sagittal,  but  approaching 

plane  of  long  axis  of  petrosa. 

body,  of  irregularly  oval  or  stellate  outline  and  reddish-gray  color,  and  measures 
about  4  mm.  in  its  longest  or  antero-posterior  dimension.  It  lies  just  below  the 
foramen  ovale  on  the  mesial  side  of  the  mandibular  nerve  and  covers  or  even  encloses 
the  origin  of  the  internal  pterygoid  nerve.  Internally  the  ganglion  is  in  relation  with 
the  tensor  palati  muscle  and  the  cartilaginous  portion  of  the  Eustachian  tube  and 
posteriorly  with  the  middle  meningeal  artery.  It  is  a  sympathetic  ganglion  and  con- 
tains numerous  stellate  neurones  which  are  characteristic  of  such  structures. 

Roots. — Of  the  communications  that  the  otic  ganglion  receives  from  several 
sources,  some  are  regarded  as  its  roots,  of  which  the  sensory  root  is  contributed  by 
small  superficial  petrosal  nerves  (n.  petrosus  superficialis  minor).  The  latter 
establish  connection  between  the  otic  ganglion  and  the  petrous  ganglion  of  the  glosso- 
pharyngeal  nerve  by  way  of  its  tympanic  branch  (page  1075)  on  the  one  hand  and, 
by  means  of  communicating  filaments,  between  the  otic  and  the-  geniculute  ganglion 
of  the  facial  nerve  on  the  other.  As  the  continuation  of  the  tympanic  nervr,  afu-r 
union  with  the  filaments  from  the  geniculate  ganglion,  the  small  superficial  petrosal 
leaves  the  upper  and  fore  part  of  the  tympanic  cavity,  traverses  a  small  canal  in  the 
temporal  bone,  and  emerges  on  the  upper  surface  of  the  latter,  to  the  outer  side  of 
the  hiatus  Fallopii.  It  then  turns  downward,  passes  through  the  petro-sphenoidal 
fissure  or  through  a  special  canal  in  the  sphenoid  bone,  and  joins  the  otic  ganglion. 


THE   TRIGEMINAL   NERVE. 


1247 


By  means  of  these  connections  and  the  branches  of  distribution  from  the  otic  gang- 
lion, secretory  fibres  are  carried  along  with  those  of  the  auriculo-temporal  (page 
1244)  to  the  parotid  gland.  The  small  superficial  petrosal  nerve  also  contains  taste- 
fibres,  which  pass  either  to  the  petrous  ganglion  of  the  ninth  or  to  the  geniculate 
ganglion  of  the  seventh,  and  thence  centralward  to  the  reception-nuclei  in  the 
medulla. 

The  motor  root  is  a  branch  from  the  internal  pterygoid  nerve.  The  sympathetic 
root  is  represented  by  one  or  two  nerve-filaments  from  the  plexus  on  the  middle 
meningeal  artery.  The  ganglion  also  receives  the  sphenoidal  branch  from  the  Vidian 
nerve. 

Branches. — A  number  of  delicate  strands  pass  from  the  otic  ganglion  to  adja- 
cent nerves.  These  so-called  branches  of  distribution  include  :  (#)  two  or  more  fila- 
ments which  join  the  roots  of  the  auriculo-temporal  nerve  and  so  convey  secretory 
fibres  from  the  glosso-pharyngeal  to  the  parotid  gland,  (£)  a  communicating  branch 


FIG.  1065. 


Ophthalmic 


Ophthalmic 


Maxillary 


Diagrams  showing  distribution  of  cutaneous  branches  of  trigeminal  and  cervical  spinal  nerves. 


to  the  chorda  tympani  and  (c~)  another  to  the  buccal  nerve,  (</)  a  branch  to  the 
internal  pterygoid  nerve,  and  (>)  and  (/")  branches  to  the  nerves  supplying  the 
tensor  palati  and  tensor  tympani  muscles. 

The  Submaxillary  Ganglion. — The  submaxillary  ganglion  (g.  submaxillare) 
(Fig.  1063)  is  a  reddish  triangular  or  fusiform  body,  measuring  from  2-3  mm.  in 
its  greatest  length,  and  is  the  smallest  of  the  sympathetic  ganglia  connected  with 
the  fifth  nerve.  It  is  situated  above  the  deep  portion  of  the  submaxillary  gland  and 
upon  the  hyo-glossus  muscle  and  lies  between  the  submaxillary  duct  and  the  lingual 
nerve,  apparently  suspended  from  the  latter  by  two  short  slender-  filaments.  The 
anterior  of  these  transmits  chiefly  sympathetic  fibres  that  pass  from  the  ganglion 
to  the  lingual  nerve,  the  posterior  fibres  going  from  the  lingual  to  the  ganglion  as  its 
sensory  and  motor  roots. 

Roots. — The  sensory  root  is  contributed  by  the  lingual  nerve  ;  the  motor  root 
proceeds  from  the  facial  by  way  of  the  chorda  tympani  and  contains  secretory  fibres  ; 
and  the  sympathetic  root  is  derived  from  the  adjoining  plexus  on  the  facial  artery. 

Branches. — The  branches  of  distribution  include:  (a)  a  number  of  fibres  which 
pass  to  the  submaxillary  gland,  (<£)  others  which  are  distributed  to  the  submaxillary 
duct  and  the  mucous  membrane  of  the  floor  of  the  mouth  and  (^)  filaments  which  join 


1248  HUMAN   ANATOMY. 

the  lingual  nerve  and,  after  accompanying  it  for  a  short  distance,  are  distributed  to 
the  sublingual  gland.  The  sensory  fibres,  processes  of  the  Gasserian  neurones,  tra- 
verse the  submaxillary  ganglion  without  interruption  ;  the  secretory  fibres  from  the 
facial  end,  at  least  in  part,  around  the  stellate  sympathetic  neurones  of  the  ganglion, 
from  which  cells  axones  pass  to  the  alveoli  of  the  submaxillary  and  sublingual 
glands  ;  while  other  sympathetic  filaments  proceed,  as  the  axones  of  stellate  cells 
either  within  the  submaxillary  or  a  more  remote  sympathetic  ganglion,  to  supply  the 
glandular  tissue  and  ducts,  as  well  as  to  accompany  the  peripheral  branches  of  the 
lingual  nerve. 

Practical  Considerations. — The  fifth  cranial  nerve  is  the  sensory  nerve  of 
the  face  and  the  motor  nerve  to  the  muscles  of  mastication.  It  is  more  frequently 
the  seat  of  excessively  painful  neuralgia  than  any  other  nerve  in  the  body.  Extra- 
cranial  lesions  are  much  more  commonly  the  cause  of  such  neuralgia  than  intracra- 
nial.  The  neuralgia  is  rarely  bilateral,  and  usually  does  not  involve  all  three  divisions 
of  the  nerve.  It  rather  attacks  one  or  two  divisions,  or  only  a  branch  of  one,  the 
first  and  second  divisions  being  most  frequently  involved.  Certain  tender  regions  can 
almost  always  be  found,  as  over  the  points  of  emergence  of  the  nerve  on  the  face,  at 
the  supraorbital,  infraorbital  and  mental  foramina,  where  in  an  interval  from  pain 
pressure  may  produce  a  paroxysm. 

The  supraorbital  notch  or  foramen  can  usually  be  felt  at  the  junction  of  the  inner 
and  middle  thirds  of.  the  supraorbital  margin.  The  mental  foramen  is  in  the  lower 
jaw,  below  and  between  the  two  bicuspid  teeth,  while  the  infraorbital  foramen  lies 
just  below  the  lower  margin  of  the  orbit  in  a  straight  line  between  the  supraorbital 
and  mental  foramina. 

When  the  first  division  is  the  seat  of  neuralgia,  the  disease  is  almost  always  con- 
fined to  the  supraorbital  branch.  Excision  of  this  branch  will  usually  give  relief  for 
about  two  years,  sometimes  permanently.  The  same  may  be  said  of  the  infraorbital 
nerve  when  the  disease  is  confined  to  the  second  division.  The  infraorbital  may  be 
excised  at  the  foramen,  through  the  mucous  membrane  of  the  mouth  or  by  an  in- 
cision in  the  skin  along  the  lower  margin  of  the  orbit.  Through  the  latter  the  orbital 
tissues  may  be  raised  and  the  nerve  reached  farther  back  in  its  canal,  which  in  its 
anterior  part  has  a  thin  bony  covering.  By  going  through  the  antrum  of  Highmore 
from  the  cheek,  just  below  the  infraorbital  foramen,  the  second  division,  with 
Meckel's  ganglion  attached  to  it  may  be  excised  at  its  emergence  from  the  skull. 
The  anterior  wall  of  the  antrum  is  opened  by  a  trephine  or  chisel  and  the  floor  of 
the  infraorbital  canal  in  the  roof  of  the  antrum  is  gouged  away  so  that  the  nerve  is  ex- 
posed and  followed  to  the  posterior  wall  of  the  antrum.  This  wall  is  then  opened, 
the  spheno-maxillary  fossa  exposed  and  the  nerve  is  divided  at  the  foramen 
rotundum  and  removed  with  the  ganglion.  The  bleeding  will  be  severe,  since 
large  and  numerous  branches  of  the  internal  maxillary  artery  surround  the  ganglion 
and  are  divided. 

When  the  neuralgia  is  confined  to  the  inferior  dental  nerve  the  mental  branch 
may  be  excised  at  its  foramen  through  the  mucous  membrane  of  the  mouth.  The 
inferior  dental  itself  is  more  frequently  attacked  through  a  trephine  opening  in  the 
ascending  ramus  of  the  lower  jaw.  It  may  with  greater  difficulty  be  reached  through 
the  mouth,  the  incision  being  made  along  the  anterior  margin  of  the  descending 
ramus,  and  the  soft  tissues  separated  from  the  inner  surface  of  the  ramus  until  the 
xiental  spine  marking  the  dental  foramen  is  exposed;  the  inferior  dental  nerve  and 
artery  will  be  found  entering  the  canal.  The  nerve  may  then  be  exposed  and  ex- 
cised with  due  regard  for  the  accompanying  vessels  and  the*  internal  maxillary  artrry, 
from  which  the  inferior  dental  branch  has  just  been  given  off. 

The  buccal  nerve  is  sometimes  the  seat  of  neuralgia,  and  may  be  reached  by  an 
incision  through  the  cheek  in  front  of  the  coronoid  process  and  the  insertion  of  the 
tendon  of  the  temporal  muscle.  The  nerve  can  be  reached  from  the  mouth  in  the 
same  situation. 

When  the  peripheral  operations  for  trigeminal  neuralgia  (tic  douloureux)  have 
failed  to  effect  a  curt-,  or  when  the  neuralgia  piimarily  shifts  from  one  branch  to  an- 
other, indicating  an  extensive  central  involvement,  tin-  (rasst'r/'tut  ga>ig/i<ni  must  be 


THE   ABDUCENT   NERVE.  1249 

removed  or  the  sensory  root  resected.  The  skull  is  opened  in  the  temporal  region 
and  the  unopened  dura  (unless  unavoidably  torn)  is  separated  inward  from  the  floor 
of  the  skull  until  the  ganglion,  lying  on  the  apex  of  the  petrous  portion  of  the 
temporal  bone  between  the  two  layers  of  the  dura,  is  exposed  and  removed.  The 
middle  meningeal  artery  is  especially  exposed  to  rupture  as  it  comes  through  the 
foramen  spinosum.  A  possible  source  of  even  more  dangerous  hemorrhage,  how- 
ever, is  the  cavernous  sinus,  with  which  the  ganglion  is  intimately  associated. 
Trophic  changes  in  the  eye  are  liable  to  occur  from  damage  to  the  first  division  of 
the  nerve. 

The  lingual  nerve  is  sometimes  divided  in  painful  conditions  of  the  tongue,  as 
in  cancer.  It  is  easily  reached  in  the  floor  of  the  mouth  as  it  is  passing  forward  to 
the  tongue,  just  under  the  mucous  membrane.  The  incision  is  made  about  midway 
between  the  tongue  and  the  alveolus  of  the  lower  jaw. 

Paralysis  of  the  sensory  branches  of  the  fifth  nerve,  nontraumatic  in  origin,  is  rare, 
and  when  it  does  occur  involves  usually  only  individual  branches,  and  these  often 
only  in  a  part  of  their  distribution.  When  implicating  all  the  divisions  of  the  fifth 
nerve  and  associated  with  pain,  it  should  suggest  a  tumor  of  the  Gasserian  ganglion. 

A  paroxysmal  cough  may  occur  in  some  patients  in  whom  the  respiratory 
organs  are  perfectly  normal,  from  irritation  of  the  terminal  branches  of  the  trigeminal 
nerve  in  the  nose,  pharynx  and  external  auditory  meatus. 

THE  ABDUCENT  NERVE. 

The  sixth  or  abducent  nerve  (n.  abducens)  is  exclusively  motor  and  supplies  the 
external  rectus  muscle  of  the  eyeball.  Its  deep  origin  is  from  the  abdticent  nucleus 
(nucleus  n.  abducentis)  (Fig.  933),  a  rounded  cluster  of  multipolar  neurones  which 
lies  in  the  dorsal  part  of  the  tegmentum  of  the  pons  and  under  the  gray  matter  of  the 
floor  of  the  fourth  ventricle.  It  is  situated  anterior  to  the  striae  acusticae,  beneath  the 
eminentia  teres  and  ventral  to  and  within  the  loop  formed  by  the  fibres  of  the  facial 
nerve.  Leaving  the  nucleus  on  its  inner  aspect,  the  root-fibres  form  several  fasciculi 
which  pass  backward  and  ventro-laterally,  lying  to  the  inner  side  of  the  superior 
olive.  Arriving  at  the  ventral  portion  of  the  pons,  the  major  portion  of  the  fibres 
passes  to  the  outer  side  of  the  pyramidal  group,  a  few  fasciculi  traversing  them  to 
reach  the  surface.  The  superficial  origin  (Fig.  1046)  lies  in  the  sulcus  which 
demarcates  the  lower  edge  of  the  pons  from  the  medulla,  a  little  lateral  to  the 
pyramid. 

Central  and  Cortical  Connections. — As  in  the  case  of  the  third  and  fourth  nerves,  the 
nucleus  of  the  sixth  receives,  by  way  of  the  posterior  longitudinal  fasciculus,  some  of  the 
fibres  of  the  pedicle  of  the  superior,  olive,  thus  completing  the  establishment  of  a  reflex-path 
between  the  auditory  apparatus  and  the  centres  for  the  nerves  controlling  the  eye-muscles.  A 
second  connection  is  effected  by  means  of  the  posterior  longitudinal  fasciculus  with  the  oculo- 
motor nucleus  of  the  opposite  side.  Finally,  the  abducent  nucleus  is  brought  into  relation  with 
the  motor  area  of  the  cortex  by  way  of  the  pyramidal  tract  of  the  opposite  side. 

Course  and  Distribution. — After  leaving  the  surface  of  the  brain-stem,  the 
nerve,  which  at  its  superficial  origin  is  flat  and  often  represented  by  several  strands, 
becomes  consolidated  and  rounded,  and  bends  forward  to  follow  for  about  15  mm., 
the  lower  surface  of  the  pons.  It  then  pierces  the  dura  mater  over  the  sphenoid  bone 
at  a  point  medial  and  slightly  posterior  to  the  opening  for  the  fifth  nerve  (Fig  1052). 
Thence  it  runs  forward  through  a  notch  beneath  the  posterior  clinoid  process  and 
passes  to  the  outer  side  of  the  inferior  petrosal  sinus  and  over  the  apex  of  the  petrous 
portion  of  the  temporal  bone  to  enter  the  cavernous  sinus.  Here  it  lies  somewhat 
below  and  to  the  outer  side  of  the  internal  carotid  artery  and,  eventually  reaching  the 
outer  wall  of  the  anterior  portion  of  the  sinus,  enters  the  orbit  through  the  sphenoidal 
fissure,  lying  above  the  ophthalmic  vein  and  below  the  third,  fourth  and  ophthalmic 
nerves.  Leaving  the  fissure,  it  passes  between  the  heads  of  the  external  rectus 
muscle,  which,  after  entering  its  ocular  surface,  it  supplies. 

The  communications  of  the  sixth  nerve  are  :  (i)  as  it  traverses  the  cavernous 
sinus,  filaments  from  the  carotid  plexus  of  the  sympathetic  and  (2)  as  it  enters  the 
orbit,  a  small  sensory  filament  from  the  ophthalmic  nerve. 

79 


1250 


HUMAN   ANATOMY. 


Variations. — The  nerve  may  be  absent  on  one  side,  the  external  rectus  being  supplied  by 
a  branch  from  the  oculomotor.  It  may  have  its  superficial  origin  by  several  widely  separated 
strands,  the  accessory  fasciculi  emerging  from  between  the  fibres  of  the  pyramid  or  through 
the  lower  border  of  the  pons. 

THE  FACIAL  NERVE. 

The  seventh  or  facial  nerve  (n.  facialis)  is  a  mixed  nerve  and  consists  of  two 
parts,  a  larger  motor  and  a  smaller  sensory.  The  former  supplies  with  motor  fibres 
the  muscles  of  expression,  the  extrinsic  and  intrinsic  muscles  of  the  external  ear, 
the  stylo-hyoid,  the  posterior  belly  of  the  digastric,  the  platysma  myoides  and  per- 
haps also  the  levator  palati  and  the  azygos  uvulae.  Certain  of  the  motor  fibres  are 
peculiar  and  as  secretory  fibres  are  destined  for  the  supply  of  the  submaxillary  and 
sublingual  glands.  The  sensory  part  of  the  facial  conveys  gustatory  fibres  to  the 
anterior  two-thirds  of  the  tongue. 

The  sensory  part  is  commonly  known  as  the  pars  intermedia  of  Wrisbcrg  (n. 
intermedius)  which,  instead  of  being  a  distinct  nerve,  may  with  propriety  be  regarded 
as  the  sensory  portion  of  the  seventh — a  view  strongly  supported  upon  morphologi- 
cal grounds.  The  sensory  fibres  are  processes  of  the  cells  situated  within  the 


FIG.  1066. 


Brain-stem  with  nuclei  of  cranial  nerves  shown  diagrammatically ;  motor  nuclei  and  fibres  are  hlue:  sensory 
nuclei  and  fibres  are  red.  a,  oculomotor  nerve;  b,  trochlear  nerve;  c,  motor  part  of  trigeminal  nerve;  rf,  sensory- 
part  of  trigeminal  nerve ;  e,  spinal  root  of  sensory  part  of  trigeminal  nerve ;  f,  facial  nerve;  g,  abducens  nerve;  A, 
vestibular  portion  of  auditory  nerve;  »,  cochlear  portion  of  auditory  nerve;  j,  glosso-pharyngeal  nerve;  &,  vagus 
nerve,  snowing  also  the  nucleus  ambiguus  in  black;  /,  hypoglossal  nerve;  m,  vagus  portion  of  spinal  accessory 
nerve.  (Posey  and  Spiller.) 

enlargement  on  the  facial  nerve  known  as  the  geniculate  ganglion,  which  is  situated 
within  the  facial  canal  at  the  so-called  knee.  Passing  through  the  proximal  part 
of  the  facial  canal,  the  axones  of  the  geniculate  ganglion  cells  enter  the  cranium 
through  the  internal  auditory  meatus,  lying  above  the  auditory  nerve  and  below 
the  motor  root  of  the  seventh,  with  both  of  which  they  communicate.  Leaving  the 
meatus,  they  pass  inward  and  enter  the  brain-stem  at  the  superficial  origin, 
(Fig.  1046),  which  is  located  at  the  lower  border  of  the  pons,  between  the  motor 
root  of  the  seventh  and  the  auditory  nerve. 

Entering  the  substance  of  the  medulla,  the  sensory  fibres  pass  either  through  or  dorsally  to 
the  spinal  root  of  the  trigeminal  nerve  to  reach  the  superior  part  of  the  HHC/CHS  of  reception, 
which  it  shares  with  the  glosso-pharyngea]  and  vagus  nerves  (page  1262).  On  gaining  this 
nucleus,  the  sensory  fibres  divide  into  short  ascending  and  much  longer  descending  branches, 
thus  behaving  in  a  manner  identical  with  that  of  the  corresponding  fibres  of  the  trigeminus  and 
other  mixed  cranial  nerves.  The  termination  of  the  sensory  fibres  is  around  the  neurones 
of  the  reception-nucleus,  from  which  axones  pass  to  the  mesial  fillet  of  the  opposite  side,  and 
i-vt-ntually.  to  tin-  cerebral  cortex. 


THE   FACIAL   NERVE.  1251 

The  motor  part  is  by  far  the  larger  of  the  two  and  constitutes  both  anatom- 
ically and  functionally  the  more  important  portion  of  the  nerve.  The  deep  origin 
of  the  motor  root  is  from  the  facial  nucleus  (Fig.  933),  an  oval  collection  of  some 
half  dozen  groups  of  large  multipolar  neurones,  which  measures  about  5  mm.  in 
length,  and  is  situated  in  the  posterior  portion  of  the  tegmentum  of  the  pons.  It 
lies  within  the  formatio  reticularis  medial  to  the  spinal  root  of  the  trigeminal  nerve 
and,  in  its  lower  part,  close  to  the  fibres  of  the  corpus  trapezoides  ;  higher  up  it  is 
tilted  dorsally  and  separated  from  these  fibres  by  the  superior  olive,  to  the  upper 
and  outer  side  of  which  it  lies.  Although  the  facial  nucleus  is  situated  close  to  the 
superficial  origin  of  the  seventh  nerve,  the  root-fibres  instead  of  taking  a  direct 
route  to  the  ventral  surface  of  the  brain- stem  follow  a  devious  course.  The  intra- 
cerebral  part  of  the  nerve  has  been  divided  for  convenience  of  description  into  a 
radicular,  an  ascending  and  an  emergent  portion. 

The  radicular  portion  consists  of  numerous  loose  fasciculi  of  root-fibres  which  arise  from 
the  dorso-lateral  aspect  of  the  nucleus  of  origin  and  pass  backward  and  slightly  inward.  The 
upper  fibres  stream  over  the  dorso-lateral  surface  of  the  nucleus  of  the  abducent  nerve  and  then, 
with  the  other  fibres  of  the  motor  root,  bend  mesially  along  the  floor  of  the  fourth  ventricle. 
As  they  near  the  mid-line  they  turn  sharply  upward  and  assemble  to  form  a  solid  strand,  the 
ascending  portion  of  the  seventh  nerve.  This  upward  course  continues  for  about  5  mm.  and  in 
this  situation  the  nerve  is  separated  from  the  floor  of  the  fourth  ventricle,  beneath  which  it  runs 
within  the  funiculus  teres,  only  by  the  lining  ependyma  and  lies  immediately  dorsal  to  the  pos- 
terior longitudinal  bundle  and  mesial  to  the  abducent  nucleus.  The  nerve  now  bends  abruptly 
outward  at  a  right  angle  and  enters  upon  the  emergent  portion  of  its  course,  during  which  it 
crosses  the  dorsal  aspect  of  the  abducent  nucleus  and  passes  backward  and  ventro-laterally,  be- 
tween its  own  nucleus  of  origin  and  the  spinal  root  of  the  trigeminal  nerve,  to  gain  the  exterior 
of  the  brain-stem  (Fig.  1066). 

The  central  and  cortical  connections  of  the  motor  part  of  the  facial  nerve  include  paths 
whereby  the  nucleus  is  brought  under  the  influence  of  the  reflex  and  the  cortical  centres. 
(a)  While  not  beyond  dispute,  it  is  probable  that  a  limited  number  of  root-fibres  are  connected 
with  the  facial  nucleus  of  the  opposite  side.  (6)  The  evidence  adduced  from  clinical  observa- 
tions and  pathological  findings  points  to  the  "existence  of  a  special  group  of  cells  from  which 
arise  the  fibres  supplying  the  orbicularis  palpebrarum  and  frontalis  muscles.  These  fibres, 
sometimes  called  the  superior  facial  nerve,  may  retain  their  functional  integrity  notwithstanding 
the  occurrence  of  paralysis  of  the  other  muscles  supplied  by  the  seventh  nerve,  (c)  The  latter, 
morever,  is  brought  into  association  with  the  visual  and  auditory  centres  by  paths,  probably 
within  the  posterior  longitudinal  fasciculus,  by  which  the  facial  cells  respond  to  the  impulses  of 
sight  and  hearing,  as  shown  by  the  automatic  closure  of  the  eyelids,  (d )  Connection  with  the 
hypoglossal  nerve  has  been  assumed  in  explanation  of  the  coordinated  action  of  the  muscles  of 
the  lips  with  those  of  the  tongue,  (e]  The  motor  facial  nucleus  is  brought  under  the  influence  of 
the  cortical  area  by  the  cortico-bulbar  fibres  which  proceed  as  axones  from  the  motor  neurones 
lying  within  the  lower  part  of  the  precentral  convolution.  These  fibres  descend  in  company 
with  the  cortico-spinal  tracts  to  appropriate  levels  and  end  around  the  radicular  cells  of  the 
facial  nucleus  of  the  opposite  side,  a  few  fibres,  however,  probably  terminating  in  the  nucleus 
of  the  same  side. 

The  superficial  origin  of  the  motor  root  is  at  the  lower  border  of  the  pons,  to 
which  it  may  be  adherent,  in  a  groove  between  the  inferior  olive  and  the  inferior 
cerebellar  peduncle  (Fig.  1046).  Just  above  the  facial  as  it  escapes,  often  as  several 
strands  of  root-fibres,  lies  the  fifth  nerve  and  to  its  outer  side  is  the  auditory,  from 
which  it  is  separated  by  the  sensory  root  of  the  seventh. 

Emerging  from  the  surface  of  the  brain-stem,  the  nerve  passes  outward,  its 
motor  and  sensory  roots  ununited,  to  the  internal  auditory  meatus,  through  which 
it  passes  above  and  anterior  to  the  auditory.  At  the  bottom  of  the  meatus  the 
seventh  and  eighth  nerves  part  company,  the  facial  entering  the  facial  canal,  whose 
course  it  follows  throughout.  At  first  the  canal  is  directed  horizontally  outward, 
between  the  cochlea  and  the  vestibule,  until  it  reaches  the  mesial  tympanic  wall.  It 
then  bends  abruptly  backward,  passes  above  the  fenestra  ovalis  and  turns  down- 
ward, behind  the  pyramid,  in  the  posterior  wall  of  the  tympanic  cavity,  to  end  at  the 
stylo-mastoid  foramen.  The  point  where  the  canal  turns  backward  marks  a  corre- 
sponding bend,  the  genu,  of  the  facial  nerve.  In  this  situation  is  found  the  genie ulate 
ganglion  and  here  the  two  roots  fuse  to  form  a  single  trunk.  After  emerging  from 


1252 


HUMAN    ANATOMY. 


the  stylo-mastoid  foramen  the  nerve  passes  downward,  outward  and  forward  through 
the  parotid  gland,  and  divides,  just  posterior  to  the  ramus  of  the  mandible,  into 
its  terminal  branches,  the  temporo-facial  and  the  cervico -facial.  The  filaments  of 
these  branches  freely  join  with  one  another  and  form  the  fan-like  parotid  plexus 
(plexus  parotideus),  also  called  pes  anserinus. 

The  geniculate  ganglion  (g.  geniculi)  is  a  small  oval  or  fusiform  thickening  on 
the  facial  nerve,  at  the  point  where  it  turns  backward  (gcniculum  n.  facialis),  and 
contains  unipolar  neurones,  whose  axones  form  the  sensory  root  of  the  facial  nerve 
and  whose  dendrites  form  the  sensory  fibres  of  distribution  of  the  seventh. 

The  so-called  branches  of  the  geniculate  ganglion — the  great  and  external 
superficial  petrosal  nerves  and  the  branches  to  the  tympanic  plexus — are  only  in  part 
composed  of  fibres  connected  with  the  ganglion  cells  ;  they  are,  therefore,  more 
appropriately  regarded  as  branches  of  the  facial  nerve. 

Branches  and  Distribution. — Within  the  facial  canal,  the  facial  nerve  gives 
off:  (i)  the  great  superficial  petrosal,  (2)  the  branch  to  the  tympanic  plexus,  (3) 
the  external  superficial  petrosal,  (4)  the  stapcdial,  (5)  the  chorda  tympani  and 


FIG.  1067. 


Diagram  showing  branches  and  connections  of  facial  nerve  within  facial  canal. 


(6)  the  communicating  branch  to  the  vagus.  The  first  three  are  closely  connected 
with  the  geniculate  ganglion.  Outside  the  facial  canal  arise:  (7)  the  posterior  auric- 
ular, (8)  the  digastric,  (9)  the  stylo-hyoid,  (10)  the  temporo-facial  and  (n)  the 
cervico-facial  nerve.  The  last  two  nerves  arise  in  an  uncertain  manner  from  that 
irregular  plexiform  expansion,  known  as  the  pes  anserinus,  into  which  the  facial 
broadens  within  the  substance  of  the  parotid  gland  after  emerging  from  the  stylo- 
mastoid  foramen. 

1.  The  great  superficial  petrosal  nerve  (n.  petrosus  supcrficialis  major)  (Fig. 
1062),  while  issuing  directly  from  the  ganglion,  contains  motor  fibres  in  addition  to  the 
sensory.    It  leaves  the  facial  canal  through  the  hiatus  Fallopii,  enters  the  middle  cranial 
fossa  and  passes  forward  under  the  Gasserian  ganglion  and  over  the  cartilage  of  the 
middle  lacerated  foramen.     The  nerve  then  crosses  the  outer  side  of  the  internal 
carotid  artery  to  reach  the  posterior  opening  of  the  Vidian  canal,  where  it  is  joined 
by  the  great  deep  petrosal  nerve  (page  1360)  from  the  carotid  sympathetic  plexus, 
with  which  it  unites  to  form  the    \  'idiaii   m-rrr.     The  latter  traverses  the  Vidian 
canal  to  the  spheno-maxillary  fossa  and  there   enters  the    posterior   aspect  of  the 
spheno-palatinc  ganglion,  whose  motor  and  sympathetic  roots  it  contributes.     The 
prol  »able  relations  and  destination  of  these  fibres  have  been  considered  in  connection 
with  the  spheno-palatine  ganglion  (page  1240). 

2.  The  communicating  branch  to  the  tympanic  plexus  (r.  anastomoticus 
cum  plexu  tympanico)  traverses    a   tiny    canal    in    the   temporal    bone    to    reach    the 
tympanic  cavity,  where  it  joins  the  main  continuation  of  the  tympanic  plexus  of  the 


THE   FACIAL   NERVE. 


1253 


glosso-pharyngeal  to  form  the  small  superficial  petrosal  and  proceeds  to  the  otic 
ganglion,  which  it  enters  as  the  sensory  root  (page  1246).  The  fibres  from  the  tym- 
panic plexus,  probably  secretory  in  function,  are  distributed  from  the  otic  ganglion  to 
the  parotid  gland. 

3.  The  external  superficial  petrosal  nerve  is  very  small  and  is  not  always 
present.      It  joins  the  sympathetic  plexus  on  the  middle  meningeal  artery. 

4.  The  stapedial  nerve  (n.  stapedius),  for  the  supply  of  the  stapedius  muscle, 
is  given  off  as  the  facial  passes  downward  behind  the  pyramid  in  the  posterior  wall  of 
the  tympanic  cavity,  the  nerve  gaining  access  to  the  muscle  by  passing  through  a 
minute  orifice  in  the  base  of  the  pyramid. 

IMG.   iu6S. 


Temporal  branch  .  if 

temj  H 

Mastoid  branch  of 
great  auricula! 


Auriculo-temporal 

Malar  branch  of  facial 

lemporal  branch 

of  facial 

Infraorbital  branch 
of  facial 

;..]  nerve 

Great  occipital  nerve 


Buccal  branch  of  facial 
Supramandibular  branch  of  facial 
Infraniandibular  branch  of  facial 

Small  occipital  nerve 

Cutaneous  branch  of  III.  cervical 

Great  auricular  nerve 


'Supraorbital  nerve 
•Supratrochlear  nerve 


Infratrochlear  nerve 
k  .  Malar  branch  of 


temporo-nialar 
X^lnfraorbital  nerve 
Internal  branch  of 


Mental  nerve 
Parotid  duct 


» Superficial  cer 


al  nerve 


Superficial  uissection  of  head  and  neck,  showing  terminal  branches  of  trigeminal,  facial  and  great  occipital  nerves, 
as  well  as  associated  branches  of  cervical  plexus. 

5.  The  chorda  tympani  nerve  (n.  chorda  tympani),  while  conveying  both 
motor  and  sensory  impulses,  consists  mainly  of  sensory  fibres  derived  from  the  cells 
of  the  geniculate  ganglion.  It  arises  from  the  facial  a  short  distance  above  the  stylo- 
mastoid  foramen  and  courses  upward  and  forward  through  the  iter  chordae  posterius 
to  enter  the  tympanic  cavity  (Fig.  1067).  Passing  between  the  fibrous  and  mucous 
layers  of  the  membrana  tympani,  over  the  tendon  of  the  tensor  tympani  and  between 
the  long  processes  of  the  incus  and  malleus,  it  arrives  at  the  anterior  edge  of  the 
membrane.  It  then  traverses  the  iter  chordae  anterius  to  reach  the  pterygo-maxillary 
region,  and,  after  receiving  a  filament  from  the  otic  ganglion,  takes  a  course  down- 
ward and  forward,  after  which,  under  cover  of  the  external  pterygoid  muscle,  it  unites 
and  becomes  incorporated  with  the  lingual  branch  of  the  mandibular  nerve.  As  the 
latter  passes  above  the  submaxillary  ganglion,  the  motor  fibres  of  the  chorda 
tympani  (facial)  descend  to  the  ganglion  as  its  motor  root  and  probably  eventually 
end  as  secretory  fibres  to  the  submaxillary  and  sublingual  glands.  The  sensory 


1254  HUMAN   ANATOMV. 

fibres  of  the  chorda  tympani,  on  the  other  hand,  are  distributed  to  the  mucous 
membrane  covering  the  anterior  two-thirds  of  the  side  and  dorsum  of  the  tongue, 
and  are  probably  concerned  in  transmitting  taste-impulses. 

6.  The  communicating  branch  to  the  auricular  branch  of  the  vagus 
(r.  anastomoticus  c.  rarao  auricular!  n.  vagi)  is  given  off  just  above  the  stylo-mastoid 
foramen  and  joins  the  auricular  at  the  point  where  the  latter  crosses  the  facial  canal. 

7.  The  posterior  auricular  nerve  (n.  auricularis  posterior)  arises  just  outside 
the  stylo-mastoid  foramen.      It  passes  backward  and  upward  between  the  external 
ear  and  the  mastoid  process  and  divides  into  (a)  an  occipital  branch,  which  supplies 
the  occipitalis  muscle  and  (b)  an  auricular  branch,  which  supplies  the  posterior  auric- 
ular muscle,  often  partially  the  superior,   and  the  transversus,  the  obliquus  and  the 
antitragicus  of  the  intrinsic  muscles  of  the  auricle. 

The  posterior  auricular  nerve  communicates  with  the  auricular  branch  of  the 
vagus,  the  small  occipital  and  the  great  auricular  nerve. 

8.  The  digastric  branch  (r.  digastricus)  arises  from  the  facial  below  the  pos- 
terior auricular  nerve  and  breaks  up  into  several  filaments  which  enter  the  posterior 
belly  of  the  digastric.      One  of  these  filaments,  after  passing  through  or  above  the 
digastric,  may  join  the  glosso-pharyngeal  nerve. 

9.  The  stylo-hyoid  branch  (r.  stylohyoideus)  is  a  small  twig  which  arises  in 
common  with  the  digastric  branch  and  passes  forward  to  enter  the  posterior  portion 
of  the  stylo-hyoid  muscle. 

10.  The    temporo-facial    division    (r.  temporofacialis)   (Fig.   1087)   is    the 
larger  of  the  two  terminal  branches.      It  traverses  the  upper  portion  of  the  parotid 
gland  in  a  forward  and  upward  direction,  lying  superficial  to  the  external  carotid 
artery  and  the  temporo-maxillary  vein.     By  repeated  branchings  and  unions  the 
nerve  forms  an  intricate  looped  plexus  which  breaks  up  into  three  more  or  less  defi- 
nite groups. 

Branches. — These  are :  (a)  the  temporal^  (b~)  the  malar  and  (c)  the  infraorbital. 

a.  The  temporal  branches  ( rr.  temporales )  pass  upward  and  forward  over  the  zygomatic 
arch  and  supply  the  frontalis,  the  corrugator  supercilii,  the  upper  part  of  the  orbicularis  palpe- 
brarum,  the  auricularis  superior  and  the  auricularis  anterior. 

The  temporal  branches  of  the  facial  communicate  with  the  following  branches  of  the 
trigeminal :  the  auriculo-temporal,  the  supraorbital,  the  lachrymal  and  the  temporal  branch  of 
the  temporo-malar. 

b.  The  malar  branches  (rr.  zygomatici)  are  rather  small.     They  extend  forward  over  the 
malar  bone  and  are  sometimes  incorporated  with  the  temporal  or  infraorbital  branches.     They 
supply  the  lateral  part  of  the  orbicularis  palpebrarum  and  sometimes  the  zygomatici   major 
et  minor. 

The  malar  branches  communicate  with  the  malar  branch  of  the  temporo-malar. 

c.  The  infraorbital  branches  (rr.  buccales  superiores)  are  comparatively  large.     They  course 
horizontally  forward  across  the  masseter  muscle  in  company  with  the  parotid  duct  and  supply 
the  lower  part  of  the  orbicularis  palpebrarum,  a  portion  of  the  buccinator,  the  zygomatici  major 
et  minor  and  the  muscles  of  the  nose  and  upper  lip. 

The  most  important  of  the  communications  is  the  one  between  the 'infraorbital  and  the 
terminal  branches  of  the  maxillary  division  of  the  trigeminal.  This  is  a  sensory-motor  plexus 
which  lies  below  the  infraorbital  foramen  and  under  the  levator  labii  sii|HTioris  and  is  called  the 
infraorbital  plexus  (Fig.  1068).  The  nasal  and  infratrochlear  nerves  communicate  with  the 
infraorbital  at  the  side  of  the  nose. 

n.  The  cervico-facial  division  (r.  cervicofacialis)  (Fig.  1087)  is  the  smaller 
of  the  terminal  branches  of  the  facial  and  resembles  in  its  general  arrangement  the 
temporo-facial.  It  passes  downward,  outward  and  forward  through  the  parotid 
gland  and  finally  breaks  up  into  three  branches. 

Branches. — These  are  :  (a)  the  buccal,  {b)  the  supramandibular  and  (c)  the 
inf ram  an  tiibiilar, 

a.  The  buccal  branch  ( rr.  Imccales)  may  be  single  or  multiple.  It  crosses  the  masseter 
and  supplies  the  buccinator  and  orbicularis  oris  muscles. 

It  communicates  on  the  outer  surface  of  the  buccinator  muscle  with  the  sensory  buccal 
branch  of  the  niandibular  division  of  the  trigeminal  nerve. 


THE   FACIAL   NERVE. 


1255 


b.  The  supramandibular  branch  (r.   marginalis  mandibularis)   passes  forward  between  the 
lower  lip  and  the  chin  and  supplies  the  muscles  of  the  lower  lip. 

Its  filaments  communicate  with  those  from  the  mental  branch  of  the  inferior  dental. 

c.  The  iiifraniandibular  branch  (r.  colli)  emerges  from  the  lower  margin  of  the  parotid 
gland  and  takes  a  downward  course  behind  the  angle  of  the  jaw.     Piercing  the  deep  cervical 
fascia,  it  passes  forward  in  the  neck  and  forms  a  series  of  loops  beneath  the  platysma  myoides 
as  far  down  as  the  hyoid  bone.     It  supplies  the  platysma  myoides. 

The  nerve  communicates  with  the  superficial  cervical  branch  of  the  cervical  plexus. 


Transverse  facial  artery 

Branches  of  the  facial  nerve 

Superficial 
temporal  artery 


Practical  Considerations. — The  facial  nerve  may  be  the  seat  of  spasm  (tic 
convulsif)  or  of  paralysis.  The  lesion  may  be  central  or  peripheral,  the  latter  being 
more  common.  When  the  spasm  is  confined  to  certain  branches  it  usually  involves 
the  muscles  about  the  eyes.  If  only  the  orbicularis  is  involved  it  is  called  blepharo- 
spasm  ;  if  the  adjacent  muscles  also  are  involved,  spasmus  nictitans.  The  facial  nerve 
is  more  frequently  associated  with  spasm  than  any  other  in  the  body,  except  the 
spinal  accessory. 

Facial  paralysis  is  relatively  common.  If  the  central  lesion — as  a  tumor,  abscess 
or  hemorrhage — is  limited  to  the  facial  centre  in  the  cortex,  a  monoplegia  of  the  facial 
nerve  will  result,  and  the 

paralysis  will  usually  be  ^IG-  Io69- 

confined  to  the  lower 
branches  of  the  nerve  in 
the  face  and  neck,  the 
upper  branches  escaping 
probably  because  of  bi- 
lateral innervation  of  the 
upper  muscles  of  the 
face.  A  cortical  isolated 
paralysis  of  this  type  is 
exceedingly  uncommon. 
If  the  lesion,  as  an  apo- 
plectic hemorrhage,  is  in 
the  internal  capsule,  a 
hemiplegia  on  the  same 
side  as  the  facial  paral- 
ysis will  be  associated 
with  it,  and  this  also 
usually  occurs  when 
the  lesion  is  cortical.  A 
lesion  in  the  upper  part 
of  the  pons  will  give  rise 
to  a  similar  condition, 
but  if  it  is  in  the  middle  or  lower  part  of  the  pons  the  facial  nerve  will  be  paralyzed 
on  the  side  of  the  lesion,  the  hemiplegia  being  on  the  opposite  side  (crossed  paral- 
ysis). This  is  explained  by  the  fact  that  the  facial  fibres  cross  to  the  opposite  side 
in  the  pons,  while  the  motor  fibres  to  the  extremities  and  trunk  cross  in  the  medulla. 
A  lesion  in  the  middle  or  lower  part  of  the  pons  on  one  side,  therefore,  will  involve 
the  facial  fibres  after  they  have  crossed,  and  the  motor  fibres  to  the  extremities  before 
they  have  crossed.  Thus  the  facial  nerve  will  be  paralyzed  on  the  side  of  the  lesion, 
and  there  will  be  a  hemiplegia  of  the  opposite  side. 

The  peripheral  portion  of  the  facial  extends  from  its  exit  at  the  pons  to  its 
terminal  filaments  on  the  face,  but  a  lesion  of  the  facial  nucleus  in  the  pons  gives  rise 
to  much  the  same  symptoms  as  one  of  the  nerve  at  its  exit  from  the  pons.  Its  intra- 
cranial  portion  may  be  involved  by  tuberculous  deposits,  tumors,  etc.  In  its  long 
course  through  the  Fallopian  canal  it  may  be  affected  by  swelling  of  the  soft  tissues, 
by  middle  ear  disease,  or  by  fractures  of  the  base  of  the  skull  in  the  middle  fossa. 
After  it  leaves  the  stylo-mastoid  foramen  it  is  in  greatest  danger,  as  from  exposure  to 
atmospheric  influences,  and  to  accidental  and  operative  wounds.  It  is  especially  apt 
to  be  wounded  in  that  portion  which  lies  within  the  parotid  gland. 


Parotid  gland 
Parotid  duct 


Masseter  muscle 


Dissection  showing  relations  of  facial  nerve  branches  as 
they  cross  masseter  muscle. 


I256  HUMAN   ANATOMY. 

When  all  branches  of  the  facial  are  paralyzed  the  symptoms  are  characteristic. 
Only  one  side  of  the  forehead  wrinkles  ;  the  tears  fail  to  enter  the  canaliculi,  and 
flow  over  the  cheek  ;  the  eye  cannot  be  closed  ;  foreign  bodies  on  its  surface  are  not 
removed  by  the  lid,  and  conjunctivitis  from  irritation  results.  The  affected  half  of 
the  face  is  expressionless,  and  the  corner  of  the  mouth  on  that  side  remains  partly 
open  and  hangs  down,  so  that  the  saliva  tends  to  run  out.  The  mouth  is  drawn  to 
the  opposite  side  ;  the  upper  lid  cannot  be  elevated,  and  whistling  is  impossible 
because  the  orbicularis  cannot  now  pucker  the  lips  ;  food  lodges  in  the  affected  side 
of  the  mouth,  because  the  buccinator  muscle  is  paralyzed,  and,  for  the  same  reason, 
the  mucous  membrane  often  gets  caught  between  the  teeth. 

In  those  cases  of  facial  paralysis  in  which  the  lesion  of  the  nerve  is  posterior 
to  the  stylo-mastoid  foramen,  attempts  have  been  made  recently  to  restore  function 
to  the  peripheral  portion  by  dividing  the  trunk  posterior  to  the  parotid  gland, 
and  anastomosing  the  peripheral  end  to  a  neighboring  cranial  nerve,  as  the  spinal 
accessory  or  the  hypoglossal.  The  results  have  not  been  entirely  satisfactory. 

The  line  of  the  main  trunk  of  the  nerve  is  from  the  slight  depression  between  the 
back  of  the  ear  and  the  mastoid  process,  forward  and  slightly  downward.  It  passes 
through  the  deeper  portion  of  the  parotid  gland. 

THE  AUDITORY  NERVE. 

The  eighth  or  auditory  nerve  (n.  acusticus)  is  not  only,  as  its  name  implies,  the 
nerve  by  which  sound  impulses  are  transmitted  to  the  brain,  but  also  the  nerve  of 
equilibration.  It  consists  of  two  portions,  the  cochlear,  the  true  nerve  of  hearing,  and 
the  vestibular,  which  is  concerned  with  equilibration. 

Traced  from  the  brain  toward  the  ear,  the  auditory  nerve  arises  at  its  super- 
ficial origin  by  two  roots,  a  mesial  (radix  vestibularis)  and  a  lateral  (radix  coch- 
learis),  which  embrace  the  inferior  cerebellar  peduncle,  the  mesial  passing  to  the 
inner  and  the  lateral  to  the  outer  side  of  the  peduncle.  The  nerve  thus  formed  by 
the  union  of  these  two  roots,  leaves  the  surface  of  the  brain-stem  at  the  posterior 
border  of  the  pons,  where  it  is  adherent  to  the  middle  cerebellar  peduncle.  To  its 
inner  side  and  closely  associated  with  it  are  the  motor  and  sensory  roots  of  the  facial 
nerve  (Fig.  1046),  which  lie  within  a  groove  on  the  mesial  surface  of  the  auditory 
and  with  it  enter  and  traverse  the  internal  auditory  canal.  Within  the  latter,  the 
auditory  nerve  separates  into  two  divisions,  of  which  the  superior  and  larger  is  the 
vestibular  nerve  (n.  vestibuli)  and  the  inferior  and  smaller  is  the  cochlear 
nerve  (n.  cochleae).  Although  in  a  general  way  these  divisions  continue  the 
corresponding  roots,  this  agreement,  as  to  the  source  of  their  fibres,  is  not  complete, 
since,  as  will  be  more  fully  noted,  strands  of  vestibular  fibres  are  incorporated  with 
the  cochlear  nerve. 

On  reaching  the  bottom  of  the  internal  auditory  canal,  the  facial  nerve  leaves 
the  meatus  and  enters  the  facial  canal,  while  the  fibres  of  the  auditory  nerve  dis- 
appear through  apertures  in  the  lamina  cribrosa  (Fig.  201)  to  gain  the  several 
parts  of  the  membranous  labyrinth  of  the  internal  ear.  During  their  journey  through 
the  meatus,  the  vestibular  and  facial  trunks  are  connected  (tila  anastomica)  by  a 
branch  which  passes  from  the  pars  intermedia  to  the  vestibular  nerve,  and  by  one 
from  the  latter  to  the  geniculate  ganglion.  These  apparent  communications  between 
the  seventh  and  eighth  nerves  are,  in  fact,  only  aberrant  strands  of  facial  fibres  that 
return  to  the  seventh  after  temporary  association  with  the  auditory. 

The  vestibular  nerve  divides  into  three  terminal  branches  which  pass  through 
apertures  in  the  cribriform  plate  above  the  falciform  crest  and  supply:  ( i  )  the  utricle, 
(2)  the  superior  and  (3)  tin-  external  semicircular  canal.  Not  all  the  fibres  of  the 
vestibular  root,  however,  are  included  in  these  branches,  since  of  the  three  given  off 
by  the  cochlear  nerve  two,  (4)  those  to  the  saecnle  and  (5)  to  the  posterior  semicir- 
cular canal,  are  incorporated  with  the  eochlear  fibres  and  seemingly  are  derived  from 
the  eorhlr.ir  nerve.  The  remaining  branch  of  the  cochlear  nerve  contains  the 
cochlear  fibres  proper,  which  traverse  the  numerous  foramina  of  the  tractus  spiralis 
foraminosus  and  the  central  canal  of  the  modiolus  to  supply  the  organ  of  Corti 
within  the  membranous  cochlea. 


THE   AUDITORY    NERVE. 


1257 


Although  the  auditory  nerve  as  a  whole  may  be  conveniently  followed  from  the 
brain  to  the  ear,    as  has  been  done  in  the  preceding  sketch,  it  is  evident  since  its 
fibres  are  sensory  and  therefore  afferent,   that  they  are  the  processes  (axones)  of 
nerve-cells  situated  somewhere  along  the  course 
of  the  nerve.      It  is  necessary,  consequently,  to 
seek  the  real  origin  of  these  fibres  in  the  ganglia 
occurring   on    the    divisions    of   the   nerve.      In 
recognition  of  the  functional  differences  of   the 
two  roots  of  the  eighth  nerve,  it  is  desirable  to 
trace    separately  the    pathway  followed    by  the 
impulses  conveyed  by  each  of  these  components. 

Peripheral,  Central  and  Cortical  Connections  of 
the  Cochlear  Nerve. — The  true  cochlear  fibres  arise 
within  the  internal  ear  (cochlea)  as  axones  of  the 
cells  of  the  spiral  ganglion  or  ganglion  of.  Corti  (g. 
spirale)  (Fig.  1071).  This  structure  consists  of  a 
series  of  bipolar  neurones  which  occupies  the  spiral 
canal  in  the  base  of  the  lamina  spiralis.  The  dendritic 
processes  of  these  cells  begin  as  fine  fibrils  which  lie 
in  close  relation  with  the  neuroepithelial  cells  compris- 
ing the  inner  and  outer  hair-cells  of  the  organ  of  Corti. 
Leaving  the  hair-cells  as  nonmedullated  fibres,  they 
traverse  the  foramina  nervosa  of  the  labium  tympani- 
cum,  at  which  point  they  become  medullated.  They 
then  interlace  to  form  an  elaborate  flat  felt-work  that 
lies  between  the  layers  of  the  lamina  spiralis  and  soon 
assembles  to  form  bundles  which  pass  to  the  cells  of 
the  ganglion  spirale,  each  fibre  probably  joining  its 
individual  cell.  Leaving  the  ganglion,  the  axones  of 
its  cells  enter  the  bony  canals  within  the  modiolus, 
from  which  they  emerge  at  the  tractus  spiralis  forami- 
nosus  and  are  collected  into  a  single  bundle,  the  coch- 
lear nerve  proper.  The  latter,  however,  soon  receives 
two  accessions,  one  of  which  consists  of  fibres  from 
the  saccule  and  the  other  from  the  posterior  semi- 
circular canal.  From  what  has  been  said,  it  is  evident 
that  these  accessions  are  parts  of  the  vestibular  nerve 
and,  beyond  their  temporary  companionship,  have  nothing  to  do  with  the  cochlear  root. 

On  reaching  the  medulla,  the  cochlear  fibres  come  into  relation  with  their  nucleus  of  recep- 
tion, which  includes  two  superficial  aggregations  of  nerve-cells  that  collectively  constitute  the 
acoustic  nucleus  (nucleus  acusticus).  The  latter  consists  of  two  parts  (Fig.  932)  of  which  one, 
the  ventral  cochlear  nucleus,  also  called  the  accessory  acoustic  nucleus  (nucleus  accessorius),  lies 
ventral  to  the  inferior  cerebellar  peduncle,  and  the  other,  the  lateral  cochlear  nucleus,  or  tuber- 
culum  acusticum,  rests  upon  the  dorso-lateral  surface  of  the  peduncle  and  occupies  the  extreme 
outer  part  of  the  triangular  acoustic  area  seen  in  the  lateral  angle  of  the  floor  of  the  fourth  ven- 
tricle (page  1097).  The  greater  number  of  cochlear  fibres  end  in  arborizations  around  the  stel- 
late cells  of  the  ventral  ganglion,  while  others  terminate  in  relation  with  the  more  elongated, 
fusiform  cells  of  the  lateral  nucleus.  From  the  neurones  of  these  subdivisions  of  the  reception 
nucleus,  the  auditory  pathway  is  continued  as  two  chief  tracts,  the  axones  of  the  cells  of  the 
ventral  nucleus  passing  for  the  most  part  ventral  to  the  restiform  body  and  the  spinal  root  of  the 
trigeminus  to  form  the  corpus  irapezoides,  while  those  from  the  lateral  nucleus  sweep  around  the 
outer  surface  of  the  restiform  body  and  then  medially  beneath  the  ependyma  of  the  floor  of  the 
fourth  ventricle,  where  they  show  with  varying  degrees  of  distinctness  as  the  acoustic  strics 
(Fig.  918). 

The  corpus  trapezoides,  the  conspicuous  transverse  tract  that  separates  the  tegmental  from 
the  ventral  region  of  the  pons  in  its  superior  part,  is  formed  chiefly  by  the  axones  of  the  cells 
within  the  ventral  cochlear  nucleus,  supplemented  by  a  limited  number  of  fibres  that  spring 
from  the -lateral  nucleus.  In  addition  it  contains  axones  from  the  large  cells  found  within  the 
trapezoid  body,  on  each  side  of  the  mid-line,  that  constitute  the  nucleus  trapezoideus.  In  close 
relation  with  the  dorsal  surface  of  the  corpus  trapezoides,  within  the  superior  olive  and  on 
either  side  of  the  median  raphe,  lies  the  superior  olivary  nucleus  (nucleus  olivaris  superior),  a 
collection  of  nerve-cells  around  which  many  of  the  cochlear  fibres,  chiefly  from  the  opposite 
but  also  from  the  same  side,  end  and  from  which  the  tract  of  the  lateral  fillet  principally  takes 


Reconstruction  of  left  membranous  laby- 
rinth of  human  embryo  of  ten  weeks  (30  mm.), 
lateral  aspect ;  vestibular  nerve  and  ganglion 
are  red ;  cochlear  nerve  is  blue ;  vestibular 
rami  are  seen  passing  to  ampullae  of  semi- 
circular canals  and  to  maculae  of  utricle  and 
saccule.  X  20.  (Streeter.) 


I258 


HUMAN   ANATOMY. 


origin  (Fig.  1079).  Not  all  of  the  fibres  arising  from  the  superior  olivary  nucleus,  however, 
enter  the  lateral  fillet.  A  considerable  number  leave  the  dorsal  surface  of  the  nucleus  and,  as 
its  peduncle,  pass  to  the  abducent  nucleus  and,  by  way  of  the  posterior  longitudinal  fasciculus, 
to  the  nuclei  of  the  other  eye-muscle  nerves.  In  this  manner  reflex  paths  are  established  by 
which  the  motor  nerves,  including  probably  the  facial,  are  brought  under  the  influence  of  audi- 
tory impulses.  Within  the  tract  of  the  fillet  and  a  short  distance  beyond  the  superior  olive,  is 
encountered  a  group  of  nerve-cells,  the  nucleus  of  the  lateral  fillet  (nucleus  lemnisci  lateralis). 
While  numerous  additions  to  the  fillet  are  received  from  these  cells,  their  relation  to  thecochlear 
fibres  is  uncertain.  The  characteristics,  course  and  destination  of  the  lateral  fillet  have  been 
elsewhere  described  (page  1082).  Suffice  it  here  to  recall  that,  so  far  as  the  auditory  fibres  are 
concerned,  the  tract  terminates  chiefly  in  the  inferior  colliculus  of  the  quadrigemina  .and  the 
median  geniculate  body. 

In  addition  to  its  constituents  through  the  corpus  trapezoides,  the  lateral  fillet  receives  con- 
siderable accessions  of  cochlear  fibres  by  way  of  "the  striae  acusticae.  These  strands  consist  of 
the  axones,  for  the  most  part,  of  the  cells  lying  within  the  tuberculum  acusticum,  but  to  a  limited 

FIG.  1071. 


S'C 


Diagram  showing  connections  of  auditory  nerve  ;  cochlear  fibres  and  connections  are  in  black,  vestibular  in  red  ; 
C,  cochlea  ;  GS,  ganglion  spirale ;  I  AC,  internal  auditory  canal  ;  VC,  DC,  ventral  and  dorsal  cochlear  nuclei ;  RR, 
restiform  body  ;  SO,  superior  olive  ;  TV?,  trapezoid  body ;  AcSt,  acoustic  striae ;  Nlf,  nucleus  of  lateral  fillet  (LF)  ; 
AfF,  median  fillet;  IQ,  inferior  quadrigeminal  body;  MG,  median  geniculate  body ;  AR,  auditory  radiation  ;  TC, 
temporal  cortex;  7',  thalamus;  SC,  semicircular  canal;  F,  vestibule ;  VG,  vestibular  ganglion;  MV,  median 
vestibular  nucleus  ;  DN,  lateral  (Deiters')  vestibular  nucleus;  Vsp,  vestibulo-spinal  fibre;  C*, cerebellum. 

extent  also  of  the  axones  of  the  ventral  cochlear  nucleus,  which  wind  over  the  latero-dorsal 
surface  of  the  inferior  cerebellar  peduncle,  pass  medially  beneath  the  ependyma  of  the  floor  of 
the  fourth  ventricle  as  far  as  the  median  groove,  and,  crossing  to  the  opposite  side,  then  sweep 
ventrally  through  the  dorsal  region  of  the  medulla  or  pons  to  join  the  tract  of  the  lateral  fillet, 
and  so  proceed  in  company  with  the  other  cochlear  fibres  to  the  higher  levels.  By  no  means 
all  of  the  component  fibres  of  the  acoustic  striae  follow  the  lateral  fillet,  since  some  after  decussa- 
tion  turn  brainward,  possibly  joining  the  mesial  fillet,  whilst  others  may  enter  the  posterior 
longitudinal  fasciculus  to  assist  in  establishing  reflex  paths  influencing  the  motor  nerves. 

The  auditory  path,  by  which  the  impulses  gathered  from  the  organ  of  Corti  by  the  cochlear 
fibres  are  conducted  to  the  cerebral  cortex,  includes  the  following  components  (  Fig.  1071)  : 

1.  Peripheral  neurones  of  the  ganglion  spiral. •,  whose  axones  (the  cochlear  fibres)  pass  to 
the  reception-nucleus  (ventral  and  lateral  cochlear  nuclei). 

2.  Neurones  of  the  cochlear  nuclei,  which  send  their  axones  :    (a)  by  way  of  the  corpus 
trapezoides  to  the  superior  olivary  nucleus,  chiefly  to  that  of  the  opposite  side  but  also  to  that 
of  the  same  side,  or  to  the  lateral  fillet  or  its  nucleus  without  interruption  in  the  olive  ;  (6)  by 
way  of  tlie  stria-  ;irustic;e  through  the  tegmentum  to  join  the  trapezoidal  fibres. 

3.  Neurones  of  the  superior  olivary  nucleus  or  of  the  fillet-nucleus,  whose  axones  pass  by 
way  of  the  lateral  fillet    ,H   to  the  cells  within  the  inferior  colliculus,  or  (/>)  without  interruption 
through  the  inferior  brachium  to  the  cells  within  the  median  geuiculate  body. 


THE   AUDITORY    NERVE. 


1259 


FIG.   1072. 

Floor  of  IV.  ventricle 


Superior  cerebellar 
peduncle 


Inferior  cerebellar 
peduncle 


Lateral  vestibular 
(Deiters')  nucleus 
Median  vestibular 
nucleus 
Cochlear  fibres 


Dorsal  cochlear  nucleus 

Descending  vestibular 
root 


4.  Neurones  of  the  inferior  colliculus  and  of  the  median  geniculate  body,  whose  axones 
pass,  as  the  auditorv  radiation,  to  the  auditory  cortical  area  within  the  temporal  lobe  of  the 
cerebrum.  Although  the  exact  extent  of  the  auditory  area  is  still  uncertain,  the  most  important 
part  of  this  centre  includes  the  superior  temporal  and  the  subjacent  part  of  the  middle  temporal 
convolution. 

The  cochlear  fibres  that  do  not  undergo  decussation  ascend  through  the  lateral  fillet  of  the 
same  side  and  eventually  establish  cortical  relations  with  the  corresponding  hemisphere  ;  from 
the  preceding  account,  however,  it  is  manifest  that  the  auditory  area  is  connected  chiefly  with 
the  cochlea  of  the  opposite  side. 

Peripheral,  Central  and  Cortical  Connections  of  the  Vestibular  Nerve. — The  fibres  of  the 
vestibular  portion  of  the  auditory  nerve  are  the  axones  of  the  bipolar  nerve-cells  situated  within 
the  small  vestibular  ganglion  (g.  vestibulare)  or  ScarpcC s  ganglion,  which  lies  at  the  bottom 
of  the  internal  auditory  canal.  The  dendrites  of  these  cells  constitute  the  five  branches  of  dis- 
tribution of  the  vestibular  nerve  and  pass  through  the  various  openings  in  the  inner  wall  of  the 
bony  labyrinth,  in  the  manner  above 
described  (page  1256),  to  reach  the 
specialized  areas,  the  maculcf  acustica', 
within  the  saccule,  the  utricle  and  the 
ampullae  of  the  semicircular  canals,  where 
the  nerve-filaments  end,  really  begin, 
in  intimate  relation  with  the  neuro- 
epithelium.  While  the  centrally  directed 
axones  of  the  neurones  supplying  the 
utricle  and  the  superior  and  external 
semicircular  canals  become  consolidated 
to  form  the  vestibular  nerve  of  descriptive 
anatomy,  those  from  the  saccule  and  the 
posterior  semicircular  canal  join  the  coch- 
lear fibres  and  with  these  course  within 
the  cochlear  nerve  until  the  latter  and 
the  vestibular  nerve  unite  to  form  the 
common  auditoiy  trunk.  Where  the 
common  trunk  separates  into  the  two 
roots,  the  vestibular  fibres  leave  the 
cochlear  and  permanently  assume  their 
natural  companionship  with  the  remain- 
ing fibres  of  the  vestibular  root. 

The  vestibular  fibres  enter  the 
brain-stem  at  a  slightly  higher  level  than 
does  the  cochlear  root,  lying  mesial  to  the 
latter  and  the  ventral  cochlear  nucleus, 
and  pass  dorsally  within  the  pons  between 
the  inferior  cerebellar  peduncle  and  the 

spinal  trigeminal  root.  On  reaching  a  level  dorsal  to  the  latter,  the  vestibular  fibres  divide 
into  short  upward  and  longer  downward  coursing  branches,  which,  after  condensing  into  an 
ascending  and  a  descending  root  respectively,  end  in  arborizations  around  the  cells  of  the 
vestibular  nucleus  of  reception.  The  exact  extent  and  constitution  of  this  nucleus,  which  under- 
lies the  area  acustica  in  the  floor  of  the  fourth  ventricle  (page  1097),  are  uncertain,  since  the 
neurones  directly  related  to  the  vestibular  fibres  contribute  only  a  part  of  those  contained  within 
a  large  diffuse  complex  of  cells  and  fibres,  many  of  whose  constituents  probably  have  only  an 
indirect  connection  with  the  vestibular  nerve.  When  reconstructed,  as  has  been  successfully 
done  by  Sabin,  this  complex  has  the  form  shown  in  Fig.  1072  and  comprises  two  general  parts, 
(a)  an  extended  irregularly  triangular  mass  of  cells  lying  for  the  most  part  mesial  to  the  tract 
formed  by  the  ascending  and  descending  branches  of  the  vestibular  fibres,  and  (b)  a  smaller 
mass  of  cells  which  lies  above  the  larger  one  and  partly  to  the  inner  and  partly  to  the  outer  side 
of  the  tract  of  the  vestibular  fibres.  The  apex  of  the  large  triangular  mass  approaches  the 
mid-line  and  its  superior  and  inferior  basal  angles  are  prolonged  upward  and  downward  along 
the  vestibular  tract. 

When  examined  microscopically  the  large  mass  is  found  to  include  three  subdivisions  :  (a) 
a  tapering  caudally  directed  nucleus  which  continues  the  inferior  angle  along  the  descending 
vestibular  root,  (b)  an  extended  triangular  nucleus  that  includes  the  greater  part  of  the  large 
mass  and  (c)  an  irregular  pyramidal  nucleus  that  prolongs  upward  the  superior  angle.  The  first 
of  these  subdivisions  (a]  is  known  as  the  spinal  vestibular  nucleus  (nuc.  spinalis  n.  vestibularis), 
the  second  (b')  as  the  median  vestibular  nucleus  (nuc.  mediali.s  n.  vestibularis),  also  as  the  chief 
nucleus  or  the  triangular  nucleus  and  the  third  (r)  as  the  superior  vestibular  nucleus  or  the 


Nucleus  cuneatus 


Closed  part  of  medulla 


Vestibular  nuclei  as  shown  in  reconstruction  by  Dr.  Florence 
R.  Sabin. 


i26o  HUM  AX    ANATOMY. 

nucleus  of  Bechterew.  The  small  mass  corresponds  with  the  lateral  vestibular  nucleus  (nuc. 
lateralis  n.  vestibularis)  or  nucleus  of  Deiters.  The  fibres  of  the  descending  root  end  around  the 
neurones  within  the  spinal  nucleus  in  a  manner  similar  to  that  in  which  the  constituents  of  the 
spinal  root  of  the  trigeminus  terminate  in  relation  with  the  neurones  within  the  substantia 
gelatinosa,  whilst  those  of  the  ascending  vestibular  root  end  around  the  cells  within  the  remain- 
ing vestibular  nuclei. 

Although  much  uncertainty  and  conflict  of  opinion  exist  as  to  the  details  of  the  secondary 
paths  by  which  the  impulses  carried  by  the  vestibular  fibres  are  distributed,  it  may  be  accepted 
as  established  that  fibres  pass  from  the  nuclei  of  reception  :  (a)  to  the  cerebellum  (chiefly  to  the 
roof  nucleus  of  the  opposite  side  and,  possibly,  also  to  the  nuclei  globosus  and  emboliformis ) 
as  constituents  of  the  nucleo-cerebellar  tract,  by  which  the  impulses  of  equilibration  are  carried 
to  the  great  coordinating  centres,  (b)  as  arcuate  fibres  ventro-medially  into  the  tegmentum  of  the 
pons,  cross  the  mid-line  and  bend  upward  or  downward  to  pass  to  other  levels,  some  fibres, 
however,  remaining  on  the  same  side.  From  the  character  of  the  impulses  it  is  probable  that 
only  relatively  few  vestibular  fibres  join  the  median  fillet  to  ascend  to  the  optic  thalamus.  Other 
connections  of  the  nuclei  include  :  (c)  commissural  fibres  between  Bechterew's  nucleus  of  the 
two  sides,  (d )  fibres  to  the  abducent  nucleus,  (e)  crossed  and  uncrossed  fibres  from  Deiters' 
nucleus  to  the  posterior  longitudinal  fasciculus  and  (f)  fibres  from  the  same  nucleus  to  the 
spinal  cord. 

It  must  be  understood  that  by  no  means  all  of  the  neurones  of  Deiters'  nucleus  are  con- 
cerned in  transmitting  afferent  impulses  to  the  cerebellum,  for,  as  a  matter  of  fact,  many  are 
links  in  the  path  by  which  the  cerebellar  cells  exercise  coordinating  influences  over  the  root- 
cells  of  the  spinal  nerves.  Starting  in  the  cerebellum,  such  efferent  impulses  are  carried  by 
efferent  fibres  which  descend  through  the  median  part  of  the  inferior  cerebellar  peduncle  and 
probably  end  around  certain  of  the  cells  within  Deiters'  nucleus.  From  these  cells,  in  turn, 
originate  the  fibres  of  the  vestibulo-spinal  tract,  which,  after  traversing  the  medulla,  enter  the 
antero-lateral  column  of  the  cord  and  end  in  relation  with  the  motor  root-cells.  A  shorter  and 
more  direct  path  for  vestibular  reflexes  is  probably  formed  by  the  collaterals  of  the  vestibular 
fibres  that  end  around  the  spinal  neurones  of  Deiters'  nucleus.  It  must  not  be  forgotten  that 
Deiters'  nucleus  is  the  origin  for  important  contributions  to  the  posterior  longitudinal  fasciculus 
(page  1117),  by  which  the  vestibular  impulses  impress  the  nuclei  of  the  motor  and,  perhaps  to  a 
limited  degree,  also  those  of  the  sensory  nerves. 

Practical  Considerations. — The  auditory  nerve  is  rarely  the  seat  of  primary 
disease.  It  is  most  frequently  affected  consecutively  to  disease  of  the  middle  and  in- 
ternal ears.  It  is  sometimes,  though  seldom,  paralyzed  in  fractures  of  the  base  of  the 
skull.  Operations  on  this  nerve  have  been  performed  for  relief  from  persistent 
and  annoying  tinnitus. 

• 

THE   GLOSSO-PHARYNGEAL    NERVE. 

The  ninth  or  glosso-pharyngeal  nerve  (n.  glossopharyngeus)  is  a  mixed  nerve, 
containing  motor  and  sensory  fibres,  the  latter  including  those  transmitting  the 
impulses  of  the  special  sense  of  taste.  The  motor  element  is  quite  small  and  sup- 
plies only  the  stylo-pharyngeus  muscle  and  secretory  fibres  to  the  parotid  gland, 
while  the  sensory  fibres  are  distributed  to  the  mucous  membrane  of  the  middle  ear, 
fauces,  tongue  and  pharynx. 

The  Nuclei  of  the  Glosso-Pharyngeal,  Vagus  and  Accessory  Nerves.— 
In  the  description  of  the  medulla  (page  1073)  attention  was  called  to  the  presence  of 
nuclei  common  to  a  greater  or  less  extent  to  the  series  of  lower  lateral  nerves  including 
the  seventh,  ninth,  tenth  and  vagal  part  of  the  eleventh,  which,  with  tin-  exception  of 
the  last  named,  are  mixed  nerves.  The  motor  fibres  of  these  nerves  differ  from  those 
of  the  series  of  median  motor  nerves — the  third,  fourth,  sixth  and  twelfth — ( a  )  in  the 
more  lateral  situation  and  less  compact  grouping  of  their  cells  of  origin  and  (/?)  in 
the  less  direct  course  they  follow  to  reach  the  surface  of  the  brain.  To  avoid  repeti- 
tion, the  general  arrangement  and  characteristics  of  the  nuclei  related  to  the  glosso- 
pharyngeal,  vagus,  and  accessory  part  of  the  eleventh  nerve  will  be  here  described. 

The  Motor  Nuclei. — These  include  the  root-cells  within  the  dorsal  HHC/CI/S 
and  those  constituting  the  nuc/ciis  <i»il>ignns.  The  dorsal  nucleus  (nucleus  <loi satis ), 
a  nucleus  both  of  origin  and  of  reception  for  the  fibres  of  the  ninth  and  tenth  nerves, 
is  a  narrow  e-loni;atc<l  tract  (lf  nerve-cells,  whose-  upper  three-fourths  underlies  the 
floor  of  the  fourth  ventricle-,  stretching  from  the  stria-  acustie-a-  above  to  the-  tip 
of  the  ventricle  In-low,  ami  \vhose  lower  fourth  extends  into  the  closed  part  of  the 


THE    GLOSSO-PHARYNGEAL    NERVE. 


1261 


FIG.  1073. 


medulla  to  the  level  of  the  nucleus  gracilis.  It  lies  immediately  lateral  to  the  lower 
part  of  the  median  vestibular  nucleus  and  the  upper  part  of  the  hypoglossal  nucleus, 
its  upper  third  being  covered  by  the  spinal  vestibular  nucleus  and  its  lower  third 
overlying  the  hypoglossal  nucleus.  Its  middle  third  corresponds  to  \\\efovea  vagi 
(Fig.  949)  and  comes  into  intimate  relation  with  the  ventricular  floor.  When 
examined  in  cross-sections  (Fig.  928)  the  nucleus  appears  prismatic  in  outline  and 
is  seen  to  consist  of  subgroups  of  cells,  of  which  the  median  contains  the  larger  and 
more  conspicuous  elements  and  corresponds  to  the  dorsal  motor  nucleus.  The 
remaining  groups,  the  dorsal  sensory  nucleus,  are  composed  for  the  most  part  of 
small  irregular  and  often  spindle  cells,  that  receive  end  arborizations  of  afferent  fibres. 

The  nucleus  ambiguus  (nucleus  ventralis)  consists  of  an  ill-defined  slender 
column  of  large  multipolar  cells,  which  extends  from  the  level  of  the  entrance  of  the 
cochlear  nerve  at  the  upper  border  of  the  medulla  to  about  the  level  of  the  beginning 
of  the  pyramidal  decussation,  and 
is  best  developed  in  its  upper  part. 
In  transverse  sections  of  the 
medulla  (Fig.  927),  the  tract  is 
distinguishable  within  the  formatio 
reticularis  grisea,  midway  between 
the  dorsal  accessory  olivary 
nucleus  and  the  substantia  gelati- 
nosa,  as  a  small  and  inconspicuous 
group  of  cells.  Arising  as  axones 
of  the  latter,  the  loosely  grouped 
motor  fibres  at  first  pass  dorsally 
to  the  vicinity  of  the  ventricular 
floor,  then  bend  sharply  outward, 
and,  as  in  the  case  of  the  vagus, 
join  with  the  similar  fibres  preced- 
ing from  the  dorsal  motor  nucleus 
to  form  the  emergent  root  strands. 

The  Sensory  Nuclei. — 
The  nuclei  receiving  the  afferent 
fibres  of  the  lateral  mixed  nerves 
in  question  include  the  sensory 


part  of  the  dorsal  nucleus  (nu- 
cleus alae  cinereae),  above  de- 
scribed, and  a  tapering  column  of 
gray  matter,  the  spinal  nucleus 
(nucleus  tractus  solitarii),  which 
resembles  the  corresponding 
nucleus  of  the  trigeminus.  The 
spinal  nucleus  is  closely  associated 
with  a  conspicuous  longitudinal 
tract  of  caudally  directed  fibres, 
the  fasciculus  solitarius 


Diagram  showing  connections  of  root-fibres  of  glosso-pharyngeal 
and  pneumogastric  nerves  and  of  sensory  fibres  of  facial ;  sensory 
fibres  are  black,  motor  ones  red;  K/7,  geniculate  ganglion;  IX, 
A',  ganglia  of  ninth  and  tenth  nerves;  DN,  dorsal  nucleus;  FS, 
fasciculus  solitarius,  accompanied  by  column  of  gray  matter;  NA, 
nucleus  ambiguus;  AcV,  accessory  vagus  (bulbar  portion  of  AT); 
AfF,  median  fillet. 


(tractus  solitarius),  so  called  on  account  of  the  apparent  isolation  of  the  bundle  when 
viewed  in  transverse  sections  (Fig.  927).  That  such,  however,  is  not  the  case  is 
evident  when  the  fact  is  recalled  that  the  fibres  which  turn  downward  to  form  the  tract 
are  accompanied  by  the  spinal  nucleus  of  reception,  around  whose  cells  they  end.  The 
fasciculus  solitarius  extends  from  the  upper  border  of  the  medulla  to  the  level  of  the 
lower  limit  of  the  decussation  of  the  fillet  and  is  related  to  the  sensory  fibres  of  three 
nerves.  The  first  of  these,  'the  facial,  contributes  only  a  limited  number  of  fibres  that 
occupy  the  uppermost  part  of  the  bundle  ;  the  second,  the  glosso-pharyngeal,  forms  by 
far  the  largest  constituent  of  the  fasciculus  ;  whilst  the  third,  the  vagus,  adds  fibres 
that  course  within  the  lowest  segment  of  the  tract. 


Central  and  Cortical  Connections  of  the  Motor  Part  of  the  Glosso-Pharyngeal  Nerve. — 
The  motor  fibres  of  the  glosso-pharyngeal  nerve  are  the  axones  of  the  motor  neurones  situated 


1262 


HUMAN    ANATOMY. 


within  the  dorsal  nucleus  and  the  nucleus  ambiguus.  The  ninth  nerve  shares  these  motor 
nuclei  to  only  a  limited  extent,  such  of  its  fibres  as  are  efferent  arising  from  the  uppermost  part 
of- the  cell-columns.  Those  taking  origin  from  the  nucleus  ambiguus  pass  at  first  toward  the 
floor  of  the  fourth  ventricle  ;  they  then  abruptly  change  their  direction  by  bending  outward  and, 
joining  the  fibres  arising  from  the  dorsal  motor  nucleus,  proceed  ventro-laterally  through  the 
gray  reticular  formation,  just  ventral  to  or  across  the  spinal  root  of  the  trigeminus,  to  emerge 
at  their  superficial  origin  along  the  bottom  of  the  postolivary  sulcus,  incorporated  with  the 
afferent  fibres  in  the  five  or  six  root-fasciculi  forming  the  entire  ninth  nerve.  The  cortical  con- 
nections of  the  motor  fibres  are  established  by  cortico-bulbar  fibres  that  arise  from  cells  situated 
within  the  gray  matter  of  probably  the  lower  part  of  the  precentral  gyms.  After  traversing 
the  motor  path  through  the  corona  radiata,  internal  capsule,  cerebral  peduncle  and  pons,  the 
cortical  fibres  end,  on  reaching  the  upper  level  of  the  medulla,  in  arborizations  around  the  motor 
root-cells  chiefly  of  the  opposite  side. 


FIG.  1074. 


Olfactory  bulbs 


Optic  nerve 
Internal  carotid  artery 


Optic  chiasni 


V.  nerve,  sensory 
root 


Cerebral  peduncle 


Middle  peduncle  of 
cerebellum 


!X.,X.andXI. 
nerves 


Branch  of  supraorhital  nerve 
Supraorbital  nerve 

Lachrymal  gland 
Supratrochlear  nerve 

Superior  rectus  muscle 

Levator  palpebrae  superioris 

'  Lachrymal  nerve 

IV.  nerve 


phthalmic  nerve  at 
jint  of  division 


VII.  nerve,  motor  part 
Pars  intermedia 

VIII.  nerve 

Superior  peduncle  of 
cerebellum,  cut 

IX. ,X.  and  XI.  nerves 
Floor  of  IV.  ventricle 
ipinal  portions  of  XI.  nerves 


Interior  aspect  of  base  of  skull,  viewed  from  above  and  behind,    showing  particularly  posterior  group  of  cran 
nerves  passing  from  brain-stem  to  points  of  emergence  through  dura  ;  posterior  part  of  skull  has  been  removed. 

Central  Connections  of  the  Sensory  Part  of  the  Glosso-Pharyngeal  Nerve. — The  afferent 
or  sensory  fibres  of  the  glosso-pharyngeal  nerve  are  the  axones  of  cells  within  the  jugular  and 
petrous  ganglia  situated  along  the  upper  part  of  the  nerve-trunk.  Entering  the  skull  through 
the  jugular  foramen,  the  sensory  fibres  approach  the  brain-stem  in  the  five  or  six  delicate  root- 
bundles  that  reach  the  medulla  along  the  groove  between  the  olivary  eminence  and  the  inierior 
cerebellar  peduncle.  Passing  to  the  ventral  side  of  the  spinal  root  of  the  trigeminus,  or 
traversing  this  field,  in  company  with  the  motor  fibres,  the  afferent  fibres  continue  dorso- 
mesially  through  the  formatio  reticularis  grisea  towards  the  dorsal  nucleus.  Just  before  reach- 
ing the  latter,  however,  the  sensory  fibres  separate  into  two  groups,  a  tiicifiaf  and  a  lateral.  The 
fust  and  smaller  of  these  continues  its  course  to  the  dorsal  sensory  nucleus,  around  the  cells 
of  which  its  fibres  end.  It  is  probable  that  the  cells  constituting  the  upper  groups  of  the  dorsal 
sensory  nucleus  are  particularly  concerned  in  receiving  the  impulses  giving  rise  to  gustatory 
impressions,  since  the  glosso-pharyngeal  is  recognized  as  the  nerve  of  taste.  Considering  tin- 
fact  that  the  afferent  fibres  of  the  facial  nerve,  which  constitute  the  pars  intermedia  of  Wrisberg, 
are  distributed  peripherally  chiefly  by  the  chorda  tympani,  are  also  concerned  in  convex  ing 
taste-impulses  and  end,  in  part  at  least,  in  the  same  nucleus  as  does  the  ninth,  the  sensory 
portion  of  the  seventh  nerve  may  be  regarded,  at  least  functionally,  if  not  from  a  morphological 
standpoint,  as  an  aberrant  strand  of  the  glosso-pharyngra]. 


THE   GLOSSO-PHARYNGEAL   NERVE. 


1263 


The  second  and  much  larger  group  turns  outward  and  abruptly  downward  to  form  the 
chief  constituent  of  the  spinal  tract,  the  fasciculus  solitarius.  In  transverse  sections  (Fig.  927) 
the  latter  appears  as  a  conspicuous,  compact,  rounded  bundle,  that  lies  lateral  to  the  dorsal 
nucleus  and  behind  the  strands  of  root-fibres.  The  solitary  fasciculus  is  accompanied  through- 
out its  course  by  a  slender  column  of  gray  matter,  which  lies  partly  on  the  surface  of  the  bundle 
and  partly  amongst  its  fibres  and  contains  numerous  nerve-cells  of  small  size  which  constitute 
the  reception-station  for  the  greater  number  of  the  afferent  fibres  of  the  ninth  nerve.  Since  these 
fibres  are  continually  ending  at  different  levels  in  their  descent,  it  follows  that  both  the  fascic- 
ulus and  its  nucleus  gradually  diminish  in  size,  until,  at  about  the  level  of  the  sensory  decussa- 
tion,  they  are  no  longer  distinguishable. 

Course  and  Distribution. — Leaving  the  superficial  origin  along  the  groove 
separating  the  olivary  eminence  from  the  inferior  cerebellar  peduncle,  the  isolated 
root-fasciculi,  about  half  a  dozen  in  number  and  in  series  with  those  of  the  vagus, 
assemble  to  form  a  single  trunk,  which  passes  outward  in  front  of  the  flocculus  of  the 
cerebellum  to  the  jugular  foramen.  As  it  traverses  this  foramen,  the  glosso-pharyn- 

FIG.  1075. 


Diagram  showing  tympanic  plexus  and  connections  of  glosso-pharyngeal  nerve. 

geal  lies  external  and  anterior  to  the  tenth  and  eleventh  nerves  and  in  its  own 
separate  dural  sheath.  It  occupies  a  groove,  or  sometimes  a  bony  canal,  in  the  fora- 
men and  in  this  situation  presents  two  thickenings,  the  jugular  and  petrous  ganglia. 
Emerging  from  the  foramen,  the  nerve  passes  between  the  internal  carotid  artery 
and  the  internal  jugular  vein  and,  dipping  beneath  the  styloid  process,  follows  a 
downward  course  along  the  posterior  border  of  the  stylo-pharyngeus  muscle,  with 
which  it  passes  between  the  internal  and  external  carotid  arteries.  Turning  gradually 
forward,  it  reaches  the  outer  side  of  the  stylo-pharyngeus  muscle  and  stylo-hyoid 
ligament  and  disappears  beneath  the  hyo-glossus  muscle  to  break  up  into  its  terminal 
branches  to  the  tongue  (Fig.  1079). 

Ganglia  of  the  Glosso-Pharyngeal  Nerve. — In  the  course  of  the  nerve 
two  ganglia  are  found,  the  jiigular  and  the  petrous.  They  contain  aggregations  of 
neurones  whose  dendrites  constitute  the  peripheral  sensory  fibres  and  whose  centrally 
directed  axones  form  the  sensory  root-fibres  of  the  nerve. 

The  jugular  ganglion  (g.  superius)  which  may  be  regarded  as  a  detached 
portion  of  the  petrous  ganglion,  lies  in  the  upper  part  of  the  groove  occupied 
by  the  glosso-pharyngeal  nerve  in  its  transit  through  the  jugular  foramen.  It  is 
variable  in  size  and  not  always  present  and  measures  only  from  1-2  mm.  in  length. 
The  ganglion  does  not  include  the  entire  thickness  of  the  nerve  but  only  the 
inferior  portion,  the  fibres  of  the  superior  portion  passing  uninterruptedly  over  it. 


1264  HUMAN    ANATOMY. 

The  petrous  ganglion  (g.  pctrosum)  is  larger  than  the  jugular  and  involves 
the  entire  nerve.  It  is  oval  or  fusiform  in  shape,  measures  from  4-5  mm.  in  length, 
and  is  lodged  within  a  slight  depression  in  the  lower  part  of  the  groove  for  the 
nerve  in  the  jugular  foramen. 

The  communications  of  the  petrous  ganglion  include  filaments  (a')  from 
the  superior  cervical  ganglion  of  the  sympathetic,  (/>)  to  the  auricular  branch  of  the 
vagus  and  sometimes  (c)  to  the  ganglion  of  the  root  of  the  vagus. 

Branches. — The  branches  of  the  giosso-pharyngeal  nerve  are:  (i)  the  tym- 
panic, (2)  the  pharyngeal,  (3)  the  muscular,  (4)  the  tonsillar  and  (5)  the  lingual. 

1.  The  tympanic  nerve   (n.  tympanicus)    or  Jacobsoris    )icrrc,  arises  from 
the  petrous  ganglion  as  its  most  important  branch  and  traverses  a  tiny  canal  in  the 
osseous  bridge  between  the  jugular  fossa  and  the  carotid  canal.      Entering  the  tym- 
panic cavity  and  receiving  fibres  from  the  carotid  plexus  of  the  sympathetic  by  way 
of  the  small  deep  petrosal  (n.  caroticotympanicus),  the    tympanic   nerve    passes 
upward  and  forward  in  a  groove  on  the  promontory  and  breaks  up  in  this  situation 
to  form  the  tympanic  plexus  (plexus  tympanicus  [Jacobsoni]  ).    After  distributing 
filaments  to  the  mucous  membrane  lining  the  tympanic  cavity  and  the  associated 
air-spaces  (mastoid  cells  and  Eustachian  tube),  its  fibres  reassemble  and  join  with  a 
filament  from  the  geniculate  ganglion  to  continue  as  the  small  superficial  petrosal 
nerve  to  the  otic  ganglion  (Fig.  1075). 

Branches. — These  are  :  (a)  the  small  superficial  petrosal  ncrrc,  (6)  the  branch 
to  the  fenestra  ovalis,  {c}  the  branch  to  the  fcncstra  rotunda,  (d)  the  branch  to  the 
Eustachian  tube,  (<*)  the  branch  to  the  mastoid  cells  and  (/")  the  branch  to  the  great 
superficial  petrosal  nerve. 

a.  The  small  superficial  pelrosal  nerve  (n.  petrosus  superficial  is  minor)  (Fig.  1075)  is  the 
continuation  of  the  tympanic  nerve,  formed  by  a  reassembling  of  the  fibres  of  the  plexus,  sup- 
plemented by  a  filament  from  the  geniculate  ganglion  of  the  facial.     It  traverses  a  canal  which 
begins  at  the  anterior  superior  portion  of  the  tympanic  cavity,  passes  beneath  the  upper  end  of 
the  canal  for  the  tensor  tympani  and  appears  on  the  superior  surface  of  the  petrous  portion  of 
the  temporal  bone,  to  the  outer  side  of  the  cranial  opening  of  the  hiatus  Fallopii.     While  in  the 
canal  it  sometimes  receives  a  communicating  branch  from  the  great  superficial  petrosal  nerve. 
It  leaves  the  cranium  through  a  canal  in  the  greater  wing  of  the  sphenoid,  or  through  the  fissure 
between  the  greater  wing  and  the  petrous  portion  of  the  temporal  bone,  and  on  reaching  the 
base  of  the  skull,  joins  the  otic  ganglion  as  its  sensory  root  (  Fig.  1075). 

b.  The  branch  to  the  fenestra  ovalis  supplies  the  mucous  membrane  in  the  neighborhood 
of  the  oval  window. 

c.  The  branch  to  the  fenestra  rotunda  is  distributed  to  the  mucous  membrane  over  and 
around  the  fenestra. 

d.  The  branch  to  the  Eustachian  tube  supplies  the  mucous  membrane  lining  the  osseous 
portion  of  that  canal. 

e.  The  branch  to  the  mastoid  cells  supplies  the  mucous  lining  of  these  cells. 

f.  The  branch  to  the  great  superficial  petrosal  nerve  joins  the  latter  in  the  hiatus  Fallopii. 

2.  The  pharyngeal  branches  (rr.  pharyngei)  number  two  or  more,  of  which 
the  largest  descends  along  the  course  of  the  internal  carotid  artery  and  joins  the 
pharyngeal  branches  of  the  vagus  and  sympathetic  to  form  the  pharyngeal  plexiis, 
which  supplies  the  mucous  membrane  and  muscles  of  the  pharynx.     The  smaller 
pharyngeal  branches  pierce  the   superior   constrictor   and   are   distributed    to   the 
mucous  membrane  lining  the  upper  portion  of  the  pharynx. 

3.  The  muscular  branch   (r.  stylopharyngetis)  enters  the  stylo-pharynegus, 
and,  after  giving  off  fibres  for  the  supply  of  that  muscle,  passes  through  it  to  be 
distributed  to  the  mucous  membrane  of  the  pharynx. 

4.  The  tonsillar  branches   (IT.  tonsillarcs)   are    given  off   near  the  base  of 
the  tongue.     They  are  slender  filaments  which  form  a  pk-.xiform  ramification,  the 
circulus  tonsillaris,  around  tin-  tonsil.      From  this  plexus  filaments  are  distributed  to 
the  tonsil,  the  soft  palate  and  the  faudal  pillars. 

5.  The  lingual  branches  (rr.  linguales )  are  the  two  terminal  filaments  of  the 
nerve.      The  larger  posterior  branch  passes  upward  and  separates  into  a  number  of 
filaments  which  supply  the  rircumvallate  papilla-  and  the  mucous  membrane  covering 


THE   VAGUS  NERVE. 


1265 


the  posterior  part  of  the  dorsum  of  the  tongue,  the  glosso-epiglottic  and  pharyngo- 
epiglottic  folds  and  the  lingual  surface  of  the  epiglottis.  The  smaller  anterior  branch 
supplies  the  mucous  membrane  of  the  side  of  the  tongue  half  way  to  the  tip. 

FIG.  1076. 


Thyro-hyoid  br.  XII.  nerve 
'Superior  laryngeal  nerve 


I.  cervical  n 
Spinal  accessory  n 


Occipitalis  minor  nerve  

1 1.  cervical  m 
Hypoglossal  (XII.)  n. 


Sup.  cerv.  gangl.  of  sympathetic 

Br.  from  II.  cerv.  nerve 

to  sp.  access. 


III.  cervical  ne 
Communicans  hypoglossi 
Great  auric,  and  superf.  cerv.ne 
IV.  cervical  n 


Descendens  hypoglossi 
Pneumogastric  nerve 


V.  cervical  nerve 
Br.  to  rhomboidei 


Omo-hyoid,  part  of  ant.  belly 


Communicating 

br.  to  sp.  accessory 

A  cutaneous  br. 


External 
pterygoid 
Ling.  br.  V.  nerve 

)  Chorda 

j  tympani  nerve 

Int.  pterygoid 
Edge  of  oral  mu- 
cous  membrane 

Glosso-pharyngeal 

nerve 

Mental  nerve 
•Jnf.  dental  nerve, 
distal  portion 
"ublingual  gland 

llary  gangl. 
Stylo-pharyngeus 


Middle  cervical  ganglion  of  sympathetic 

(the  cord  connecting  it  with  superior  gangl.  Is  also  seenj 


ubclavian  artery 


Deep  dissection  of  neck  showing  ninth,  tenth,  eleventh  and  twelfth  cranial  nerves  and  their  branches. 

Variation. — Instances  are  recorded  in  which  the  mylo-hyoid  nerve  was  absent  and  a 
branch  of  the  glosso-pharyngeal  supplied  the  mylo-hyoid  muscle  and  the  anterior  belly  of  the 
digastric,  the  innervating  fibres  being,  probably,  aberrant  filaments  of  the  trigeminus. 

THE   VAGUS   NERVE. 

The  tenth,  vagus  or  pneumogastric  nerve  (n.  vagus)  is  the  longest  and  most 
widely  distributed  of  the  cranial  series.  Starting  in  the  cranium,  it  passes  through 
the  neck,  thorax  and  upper  part  of  the  abdomen  before  breaking  up  into  its  terminal 
branches.  In  addition  to  certain  filaments  concerned  with  special  functions,  distrib- 
uted to  the  heart  and  abdominal  viscera,  it  contains  both  motor  and  sensory  fibres. 
Some  of  the  motor  constituents  of  the  nerve  arise  from  its  own  origin,  but  the  major- 
ity perhaps  are  contributions  of  the  accessorius  vagi,  the  so-called  accessory  part  of 
the  spinal  accessory  nerve.  The  vagus  supplies  motor  fibres  to  the  muscles  of  the 
.  soft  palate  (with  the  exception  of  the  tensor  palati  and,  probably,  partly  the  levator 
palati  and  azygos  uvulae),  pharynx,  oesophagus,  stomach,  and  intestine  (with  the 
exception  of  the  rectum),  and  to  those  of  the  larynx,  trachea,  and  bronchi  and  their 
subdivisions.  It  distributes  sensory  fibres  to  the  dura  mater,  external  ear,  pharynx, 
oesophagus,  stomach,  larynx,  trachea,  bronchi  and  subdivisions  and  pericardium. 

80 


1266  HUMAN    ANATOMY. 

Special  fibres  are  furnished  to  the  heart,  liver,   spleen,  pancreas,  kidneys,  suprarenal 
bodies  and  intestinal  blood-vessels. 

It  is  generally  admitted  that  the  bulbar  or  accessory  portion  of  the  eleventh  nerve  forms  air 
integral  part  of  the  motor  division  of  the  vagus,  and,  hence,  should  he  included  with  the  efferent 
fibres  of  the  tenth.  As  to  the  ultimate  distribution  of  these  accessory  fibres,  and  conversely  of 
the  vagus  motor  fibres  proper,  much  discussion  and  many  conflicting  views  have  existed  and, 
even  at  present,  a  consensus  of  opinion  can  scarcely  be  said  to  have  been  reached.  After 
reviewing  the  evidence,  both  anatomical  and  experimental,  Van  Gehuchten  '  concludes  that  the 
accessory  fibres  are  distributed  chiefly,  if  not  indeed  exclusively,  to  the  larynx  through  the  infe- 
rior laryngeal  branch  of  the  vagus,  and  are  continued  neither  to  the  heart  nor  to  the  stomach. 
The  efferent  vagus  fibres  proceeding  to  the  heart  are  inhibitory  in  function  ;  whether  they  directly 
reach  the  cardiac  muscle  is  doubtful,  since,  reasoning  from  analogy,  it  is  probable  that  the  vagus 
fibres  end  around  sympathetic  neurones  whose  axones  are  the  filaments  coming  into  immediate 
relations  with  the  muscle-fibres.  Of  the  efferent  -fibres  of  the  vagus  distributed  to  the  stomach 
and  other  parts  of  the  digestive  tract,  some  are  secretory,  while  others,  possibly,  influence  the 
caliber  of  the  blood-vessels,  in  both  cases  being  interrupted  in  sympathetic  ganglia  before  gain- 
ing their  destination. 

Deep  Origin  of  the  Motor  Portion.  —  As  stated  above,  the  efferent  fibres  of 
the  vagus  consist  of  two  sets,  vagus  fibres  proper  and  those  derived  from  the  acces- 
sory portion  of  the  spinal  accessory.  The  former  have  their  deep  origin  in  the  nu- 
cleus ambiguus  and  the  dorsal  motor  nucleus,  in  series  with  the  motor  fibres  of  the 
ninth  nerve  ;  the  accessory  fibres  arise  from  the  nucleus  ambiguus  only.  The 
detailed  description  of  these  nuclei  has  been  given  (page  1260).  The  fibres  arising 
from  the  nucleus  ambiguus  at  first  pass  backward  toward  the  floor  of  the  fourth 
ventricle,  then  bend  sharply  outward  and,  condensed  into  compact  strands  that 
receive  the  fibres  originating  from  the  motor  cells  of  the  dorsal  nucleus,  proceed, 
ventro-laterally  in  company  with  the  sensory  fibres,  to  their  superficial  origin  alont^ 
the  postero-lateral  groove  behind  the  olivary  eminence. 

Central  Connections  of  the  Sensory  Portion.  —  The  afferent  root-fibres  of 
the  vagus  are  the  axones  of  the  neurones  lying  within  the  ganglia  of  the  root  and 
of  the  trunk  situated  on  the  upper  part  of  the  nerve.  The  centrally  directed  processes 
pass  into  the  medulla,  in  company  with  the  motor  strands,  and  divide  into  two  sets. 
Those  forming  the  larger  of  these  end  in  arborizations  around  the  cells  within  the 
lower  portion  of  the  dorsal  sensory  nucleus  ;  those  of  the  smaller  set  bend  downward 
and  enter  the  fasciculus  solitarius  to  terminate  in  arborizations  around  the  cells  of 
the  spinal  nucleus  of  reception.  (For  details  of  these  nuclei  see  page  1260).  As  in 
the  case  of  the  other  mixed  nerves  —  the  fifth,  seventh  and  ninth  —  the  secondary- 
paths  distributing  the  sensory  impulses  include  (#)  fibres  that  pass  from  the  recep- 
tion-nuclei to  the  tract  of  the  mesial  fillet,  and  so  on  to  the  great  brain,  and 
(b)  those  that  pass  to  the  cerebellum. 

Course  and  Distribution.  —  The  vagus,  disregarding  its  accessory  fibres 
which  at  first  are  incorporated  in  a  common  trunk  with  the  eleventh  nerve,  arises 
from  its  superficial  origin  by  a  row  of  twelve  or  fifteen  filaments  which  emerge 
from  the  surface  of  the  medulla  along  the  postero-lateral  sulcus  between  the  olivary 
eminence  and  the  inferior  cerebellar  peduncle.  These  fasciculi  lie  in  series  with 
those  of  the  ninth  nerve  above  and  of  the  eleventh  below  (Fig.  1046). 

After  leaving  the  surface  of  the  brain-stem,  the  converging  rootlets  of  the  vagus 
fuse  to  form  a  single  flattened  trunk,  which  passes  outward  beneath  the  flocculus  of 
the  cerebellum  to  the  jugular  foramen  (Fig.  1074).  The  trunk  leaves  the  cranium 
through  the  rear  division  of  the  middle  compartment  of  this  foramen,  invested  by  a 
dural  sheath  shared  by  the  spinal  accessory  nerve.  In  this  situation  it  presents  a 
ganglionic  enlargement  called  the  gang/ion  of  the  root.  Emerging  from  the  jugular 
foramen,  the  vagus  bears  a  second  thickening,  \hzgangK0n  of  the  trnnk\  and  enters 
the  carotid  sheath,  through  which  it  passes  downward  tin-  entire  length  of  the  neck. 
Within  the  carotid  sheath  the  nerve  lies  at  first  between  the  internal  carotid  artery 
and  the  internal  jugular  vein,  and  then  between  the  common  carotid  artery  and  the 
vein,  occupying  the  posterior  ^mnve  between  these  vessels.  At  the  root  of  the 


1  Anatomii-  dn  System*-  Nervrux,  1906. 


THE   VAGUS    NERVE. 


1267 


neck  it  leaves  the  carotid  sheath  and  becomes  an  occupant  of  the  thorax.  Entering 
the  thoracic  cavity  the  nerve  traverses  first  the  superior  and  then  the  posterior 
mediastinum,  its  course  differing  widely  on  the  two  sides. 

The  right  vagus  (Fig.  1090),  after  passing  in  front  of  the  first  portion  of  the 
subclavian  artery  and  behind  the  right  innominate  vein  and  the  superior  vena  cava, 
descends  along  the  right  side  of  the  trachea  to  reach  the  posterior  aspect  of  the  root 
of  the  lung.  Here  the  entire  nerve  breaks  up  to  form  the  posterior  pulmonary 
plexus,  which  assembles  at  its  lower  border  to  form  two  cords.  These  pass  inward 
across  the  vena  azygos  to  the  oesophagus  and  again  break  up  to  unite  with  a 
similar  contribution  from  the  left  side  to  form  the  cesophageal  plexus  (Fig.  1081). 
On  approaching  the  cesophageal  opening  in  the  diaphragm,  the  fibres  of  the  plexus 
become  reunited  to  form  the  continuation  of  the  trunks  of  the  two  vagus  nerves. 
The  right  vagus,  somewhat  larger  than  the  left,  follows  the  posterior  aspect  of  the 
oesophagus  and,  after  entering  the  abdomen  through  the  cesophageal  opening,  is 

FIG.  1077. 


2C 


Diagram  showing  connections  between  the  superior  cervical  sympathetic  ganglion  and  the  glosso-pharyngeal,  vagus 

and  hypoglossal  nerves. 

distributed  to  the  posterior  surface  of  the  stomach  and  to  the  solar  plexus,  and 
indirectly  to  the  spleen,  pancreas,  intestine,  kidney  and  suprarenal  body. 

The  left  vagus,  after  passing  between  the  left  common  carotid  and  subclavian 
arteries  and  behind  the  left  innominate  vein,  crosses  the  anterior  surface  of  the  aorta 
and  then  bends  backward  to  reach  the  posterior  surface  of  the  root  of  the  lung.  In 
a  manner  similar  to  the  right,  it  forms  the  posterior  pulmonary  plexus  and  reassem- 
bles into  two  cords.  These  pass  inward  anteriorly  to  the  thoracic  aorta  and 
enter  the  icsophageal  plexus,  at  the  lower  end  of  which  the  fibres  of  the  left  nerve 
gather  on  the  anterior  surface  of  the  oesophagus,  traverse  as  a  single  solid  trunk 
the  cesophageal  opening  and  are  distributed  to  the  anterior  surface  of  the  stomach 
and  to  the  liver. 

Ganglia  of  the  Vagus  Nerve. — Two  ganglia  are  found  in  the  course  of  the 
nerve,  the  ganglion  of  the  root  and  the  ganglion  of  the  trunk.  They  are  collections 
of  neurones  whose  axones  form  the  sensory  root-fibres  of  the  vagus,  the  greater 
number,  however,  being  connected  with  the  cells  of  the  ganglion  of  the  root. 

The  ganglion  of  the  root  (g.  jugularc)  or  upper  ganglion  (Fig.  1077)  is 
a  grayish  spherical  mass  of  nerve-cells,  about  4  mm.  in  length,  situated  in  the  upper 
part  of  the  jugular  foramen. 


1268 


HUMAN   ANATOMY. 


The  communications  of  this  ganglion  include  filaments  which  pass  between  the  ganglion 
and  (a)  the  facial  and  (o)  spinal  accessory  nerves,  (c )  the  superior  cervical  ganglion  of  the 
sympathetic  nerve  and  (d)  the  petrous  ganglion  of  the  glosso-pharyngeal. 

The  ganglion  of  the  trunk  (g.  nodosum)  or  lower  ganglion  (Fig.  1077) 
is  a  reddish,  flattened,  fusiform  group  of  nerve-cells.  It  lies  beneath  the  jugular 
foramen,  about  i  cm.  below  the  ganglion  of  the  root,  and  measures  from  1.5-2  cm. 
in  length  and  about  4  mm.  in  diameter.  The  accessory  part  of  the  spinal  accessory 
nerve  passes  over  the  ganglion  on  its  way  to  fuse  with  the  vagus,  which  it  does 
usually  immediately  beyond  the  ganglion. 

The  communications  of  this  ganglion  include  filaments  which  pass  between  the  ganglion 
and  (a)  the  hypoglossal  and  (d)  spinal  accessory  nerves,  (c)  the  loop  between  the  first  and 
second  cervical  nerves  and  (d)  the  superior  cervical  ganglion  of  the  sympathetic. 

Branches. — The  vagus  nerve  gives  off  the  following  branches:  from  the 
ganglion  of  the  root,  (i)  the  meningeal  and  (2)  the  auricular ;  from  the  ganglion 

FIG.  1078. 


ICERVN 


HCERV. 


Diagram  of  upper  part  of  right  vagus  nerve,  showing  its  pharyngeal  and  laryngeal  branches  with  connections. 


of  the  trunk,  (3)  \hapharyngeal  and  (4)  the  superior  laryngeal ;  in  the  neck,  (5) 
the  superior  cervical  cardiac,  and  (6)  the  inferior  cervical  cardiac ;  in  the  thorax, 
(7)  the  inferior  laryngeal,  (8)  the  thoracic  cardiac,  (9)  the  anterior  pulmonary, 
(10)  the  posterior  pulmonary,  (n)  the  cesophageal  and  (12)  the  pericardia/ ;  and 
in  the  abdomen,  (13)  the  abdominal. 

1.  The    meningeal  branch  (r.  tncniiigcus)  arises  from  the  ganglion    of   the 
root  and  follows  a  recurrent  course  upward  through  tin-  jugular  foramen  to  supply 
the  dura  mater  of  the  posterior  fossa  of  the  cranium,  especially  in  the  vicinity  «>f  tin- 
lateral  and  occipital  sinuses. 

2.  The    auricular    branch    (r.    atiriculaiis  i   is   ^ivm   off   from    tlu>   ganglion 
of   the  root.      It  receives  a  filament   of  communication   from  tin-  petrous  ganglion 
of  the    ninth   nerve  and  follows    tin-   outer   margin    of   the  jugular   foramen    to  an 
opening  between  the  stylo-mastoid  and  jugular  foramina.      Kim-ring  this  foramen   it 
traverses  a  canal  in  tin-  temporal  bone  which  crosses  the  inner  side  of  the  facial  canal 
and   terminates   between    the  mastoid   process    and  the  external    auditory    im-atus. 


THE   VAGUS   NERVE. 


1269 


Leaving  the  canal  the  nerve  supplies  the  skin  of  the  posterior  part  of  the  auricle  and 
of  the  posterior  inferior  portion  of  the  external  auditory  meatus. 

While  traversing  the  temporal  bone  the  auricular  nerve  communicates  with  the  facial  and, 
after  reaching  its  area  of  distribution,  with  the  posterior  auricular  nerve. 

Variations. — The  auricular  nerve  may  be  absent  or  may  fuse  with  the  main  trunk  of  the 
facial,  its  fibres  under  these  circumstances  probably  reaching  their  destination  through  the  pos- 
terior auricular  nerve.  Its  branch  of  communication  with  the  facial  may  be  absent. 

3.  The  pharyngeal  branches  (rr.  pharyngei),  usually  an  upper  and  a  lower 
but  sometimes  more  or  only  one,  are  given  off  from  the  upper  portion  of  the  gang- 

FIG.  1079. 


Pneumogastric  ner 

Inferior  dental  ner 

Spinal  accessory  ner 

Part  of  facial  nerv< 

Hypoglossal  nerv< 

Stylo-pharyngeus  muscle 

Glosso-pharyngeal  nerve 

I.  cervical  nerve 

Pneumogastric  nerve 

Superior  cervical  ganglion  of 

sympathetic 

Superior  laryngeal  nerve 

Descendens  hypoglossi 

1 1 .  cervical  nerve 


III. 


IV.  cer- 

Association  cord  of 
sympathetic 


Middle  cervical  gangl 


Inferior  cervical 
gangl 


Phrenic  nerve 

Branches  from  inf. 
cervical  ganglion 


Lingual  nerve 
External  laryngeal  branch 


iuperior  cervical  cardiac  of 
sympathetic 


Middle  cervical  cardiac  of  sympathetic 
-Recurrent  laryngeal  nerve 


Middle  cervical  cardiac  of 

Common  [pneumogastric 

carotid  artery 
Inferior  cervical  cardiac  of 

pneumogastric 


Inferior  cervical  cardir 

of  sympathetic 

Recurrent  laryngeal 

nerve 
Internal  mammary  artery 

Cartilage  of  I.  rib 

Clavicular  facet  of  st 

Deep  dissection  of  right  side  of  head  and  neck,  showing  lingual,  glosso-pharyngeal,  pneumogastic,  hypoglossal 

and  sympathetic  nerves. 

lion  of  the  trunk  and  include  to  a  considerable  extent  fibres  brought  to  the  vagus  by 
its  accessory  portion.  They  pass  downward  and  inward,  between  the  external  and 
internal  carotid  arteries,  and  join  the  pharyngeal  branches  from  the  glosso-pharyn- 
geal nerve  and  from  the  superior  cervical  ganglion  of  the  sympathetic  to  form  the 
pharyngeal  plexus  (plexus  pharyngeus)  (Fig.  1078).  This  plexus  contains  one  or 


1270 


HUMAN   ANATOMY. 


more  minute  sympathetic  ganglia  and  ramifies  over  the  middle  constrictor  of  the 
pharynx.  It  supplies  motor  fibres  to  the  muscles  of  the  pharynx  and  of  the  soft 
palate,  with  the  exception  of  the  stylo-pharyngeus  and  the  tensor  palati.  From  the 
plexus  proceed  sensory  filaments  to  the  mucous  membrane  of  the  pharynx.  A 
filament  from  this  plexus,  the  lingual  branch  of  the  vagus  (r.  lingualis  vagi),  com- 
posed of  fibres  from  both  the  ninth  and  tenth  nerves,  joins  the  hypoglossal  as  it 
hooks  around  the  occipital  artery. 

Variation. — A  slender  branch,  the  middle  laryngeal  nerve,  is  described  as  arising  from  the 
pharyngeal  plexus  and  supplying  the  crico-thyroid  muscle,  after  which  it  pierces  the  crico- 
thyroid  membrane  and  supplies  the  mucous  membrane  of  the  lower  part  of  the  larynx. 

4.  The  superior  laryngeal  nerve  (n.  laryngeus  superior)  (Fig.  1079)  arises 
from  the  middle  of  the  ganglion  of  the  trunk  and  takes  a  downward  and  inward 
course  beneath  the  external  and  internal  carotid  arteries  toward  the  superior  cornu 
of  the  thyroid  cartilage.     It  divides  terminally  into  (a)  the  external  and  (£)  internal 
laryngeal  branches. 

Communications. — Before  dividing,  the  superior  laryngeal  nerve  receives  filaments  from 
the  superior  cervical  sympathetic  cardiac  and  from  the  pharyngeal  plexus. 

The  cardiac  twig  given  off  by  the  external  laryngeal  nerve  joins  with  the  superior  cervical 
cardiac  branch  of  the  sympathetic.  In  the  lower  part  of  the  larynx  the  external  laryngeal  nerve 
inosculates  with  the  terminal  fibres  of  the  internal  laryngeal. 

At  the  inferior  portion  of  the  larynx,  the  internal  laryngeal  nerve  communicates  with  the 
terminal  filaments  of  the  external  laryngeal,  and  in  this  way  supplies  sensory  fibres  to  the 
mucous  membrane  lining  the  lower  part  of  the  larynx  and  to  the  muscles. 

Variation. — Instead  of  passing  to  the  inner  side  of  the  internal  carotid  artery  the  nerve  may 
lie  external  to  it. 

a.  The  external  laryngeal  branch  (r.  externus),  much  smaller  than  the  in- 
ternal, passes  downward  upon  the  inferior  constrictor  of  the  pharynx  and  beneath  the 
infrahyoid  muscles  to  the  crico-thyroid  muscle,  which  it  supplies.      It  sends  filaments 
also  to  the  inferior  pharyngeal  constrictor  and  gives  off  a  cardiac  twig  which  joins  the 
superior  cervical  cardiac  branch  of  the  sympathetic. 

Variations. — The  external  laryngeal  has  been  seen  to  send  filaments  to  the  thyroid  gland, 
the  pharyngeal  plexus,  the  sterno-hyoid,  sterno-thyroid.  thyro-hyoid  and  crico-arytenoideus  lat- 
erahs  muscles  and  to  the  mucous  membrane  of  the  vocal  cord  and  lower  portion  of  the  larynx. 

b.  The  internal  laryngeal  branch    (r.  interims),  larger  than  the  external, 
passes  downward  and  inward  between  the  middle  and  inferior  constrictors  of  the 
pharynx  and  enters  the  larynx  by  piercing  the  thyro-hyoid  membrane.      By  means 
of  its  epiglottic,  pharyngeal,  descending  and  communicating  branches,  it  supplies  the 
mucous  membrane  covering  the  internal  and  pharyngeal  surfaces  of  the  larynx  and 
the  mucous  membrane  of  the  base  of  the  tongue. 

Variation. — Instead  of  piercing  the  thyro-hyoid  membrane  the  nerve  may  obtain  entrance 
to  the  larynx  through  a  small  foramen  in  the  thyroid  cartilage. 

5.  The  superior  cervical  cardiac  branch  (IT.  canliaci  superiorcs — both  cervi- 
cal cardiacs)  arises  from  the  vagus  in  the  upper  part  of  the  neck.      It  either  joins 
a  cardiac  branch  of  the  vagus  or  passes  independently  down  the  neck  and  along  (In- 
side of  the  trachea  to  end  in  the  deep  cardiac  plexus  (Fig.  1132). 

6.  The  inferior  cervical  cardiac  branch  leaves  the  vagus  at  the  root  of  the 
neck.     On  the  right  side  it  courses  along  the  side  of  the  innominate  artery  and  either 
independently,  <>r  after  joining  one  of  the  other  cardiac  nerves,  enters  the  deep  car- 
diac plexus.      The  left  passes  in  front  of  the  arch  of  the  aorta  and  joins  the  superior 
cervical  cardiac  branch  of  the  left  sympathetic  to  form  the  superficial  cardiac  plexu-. 
(Fig.  1132). 

7.  The  inferior  or  recurrent  laryngeal   nerve   (n.  recurrens)  (Fig.   mSo) 
differs  on  the  two  sides  in  the  early  part  of  its  course.     The  right  n<-rrr  is  given  otf  at 

: 


THE   VAGUS   NERVE. 


1271 


the  root  of  the  neck  as  the  vagus  crosses  the  anterior  surface  of  the  subclavian  artery, 
from  which  point  it  passes  under  and  behind  the  artery  and  ascends.  The  left  nerve 
takes  its  origin  as  the  vagus  crosses  the  anterior  aspect  of  the  aortic  arch,  and  after 
passing  below  and  behind  the  arch,  lateral  to  the  obliterated  ductus  arteriosus,  ascends 
in  the  superior  mediastinum  to  enter  the  neck.  After  entering  the  neck  the  further 
course  of  the  nerve  is  the  same  on  both  sides.  It  passes  upward  posterior  to  the 
carotid  sheath,  either  anterior  or  posterior  to  the  inferior  thyroid  artery,  occupies  the 

FIG.  1080. 


Superior  cervical  cardiac  branch  of  sympathetic 


Middle  cervical  ganglion 

Inferior  cervical  ganglion 

Superior  cervical  cardiac  of  vagus 


Middle  and  inf.  cervical  cardiac 
branches  of  sympathetic 

Recurrent  laryngeal  nerve 


Pulmonary  branch  of  vagi 
Vena  azygos  major 
Phrenic  nerve 

Right  pulmonary  artery 

Pulmonary  • 

Aorta 

Right  auricular  appendix 
Pericardium 


Superior  cervical  cardiac  branch 

of  sympathetic 

Superior  cervical  cardiac  branch  of  vagus 
Middle  cervical  ganglion 
Middle  cervical  cardiac  branch 

of  sympathetic 


[of  sympathetic 
I  nf.  cervical  cardiac  branch 
inf.  cervical  ganglion 


Middle  cervical  cardi; 

branch  of  vagus 
Inf.  cervical  cardiac 

branch  of  vagus 
Phrenic  nerve 


Left  vagus  nerve 
Recurrent  laryngeal  net 

—  Left  pulmonary  artery 
'Pulmonary  veins 

Pulmonary  orifice 

Mesial  surface  of  lung 
Pericardium 


Dissection  showing  cardiac  branches  of  pneumogastric  nerves  and  of  sympathetic  cords  ;  aortic  arch  and  branches 
and  pulmonary  artery  partially  removed  ;  pericardium  laid  open. 

groove,  between  the  cesophagus  and  the  trachea,  and,  dipping  beneath  the  lower 
edge  of  the  inferior  constrictor  of  the  pharynx,  enters  the  larynx  at  the  inferior 
margin  of  the  cricoid  cartilage. 

The  asymmetry  observed  in  the  first  part  of  the  course  of  the  nerves  of  the  two  sides  is 
secondary  and  referable  to  the  changes  incident  to  the  development  of  the  large  arterial  trunks. 
In  the  fcetus  both  nerves  hook  around  the  fourth  aortic  arch  of  the  corresponding  sides  and 
are,  therefore,  for  a  time  symmetrically  disposed.  Since,  however,  on  the  left  side  this  arch 
becomes  the  arch  of  the  aorta,  and  on  the  right  the  innominate  and  subclavian  arteries  (page 
726),  it  is  evident  that  the  vagi,  although  retaining  their  primary  associations,  later  alter  their 
actual  position  and  relations  in  consequence  of  the  unequal  growth  and  downward  displacement 
which  these  blood-vessels  undergo. 

Branches. — During  its  course  the  inferior  laryngeal  nerve  gives  off  :  (a)  the 
cardiac,  (<£)  the  trachcal,  (c)  the  cesophageal,  (d}  the  rmiscular  and  (V)  the  terminal 
branches. 


I2J2  HUMAN    ANATOMY. 

a.  The  cardiac  branches  (rr.  cardiac!  inferiores)  are  given  off  in  the  superior  mediastinum 
and  enter  the  deep  cardiac  plexus. 

b  and  c.  Tracheal  and  oesophageal  branches  ( rr.  tracheales  et  oesophagei)  are  given  off  as 
the  nerve  ascends  in  the  neck  between  the  trachea  and  cesophagus. 

d.  Muscular  branches  enter  the  inferior  constrictor  of  the  pharynx. 

e.  The  terminal  branches  (n.  laryngeus  inferior)  are  formed  at  the  point  where  the  nerve 
breaks  up  on  the  inner  side  of  the  thyroid  cartilage.     They  supply  the  intrinsic  muscles  of  the 
larynx,  with  the  exception  of  the  crico-thyroid. 

As  it  turns  to  ascend,  the  inferior  laryngeal  nerve  communicates  with  the  inferior  cervical 
ganglion  of  the  sympathetic,  its  terminal  filaments  joining  with  those  of  the  internal  laryngeal. 

Variations. — The  inferior  laryngeal  nerve  has  been  seen  to  supply  twigs  to  the  crico-thyroid 
muscle.  In  cases  in  which  the  subclavian  artery  arises  dorsally,  the  right  recurrent 
laryngeal  passes  directly  downward  and  inward  from  the  vagus  to  the  larynx. 

8.  The  thoracic  cardiac  nerves  (rr.  cardiaci  inferiores)  of  the  right  side  are 
derived  both  from  the  vagus  as  it  lies  beside  the  trachea  and  from  the  inferior  laryn- 
geal.    Those  of  the  left  side  arise  exclusively  from  the  inferior  laryngeal.     They 
help  to  form  the  deep  cardiac  plexus. 

9.  The    anterior    pulmonary  branches  (rr.  bronchiales  anteriores)  are   two 
or  three  small  filaments  which,  on  the  right  side,  receive  communicating  fibres  from 
the  deep  cardiac  plexus  and,  on  the  left  side,  are  joined  by  filaments  from  both  car- 
diac plexuses.     These  unite  to  form  the  anterior  pulmonary  plexuses  (plexus 
pulmonales  anteriores)  (Fig.  1080),  which  communicate  with  each  other  and  with  the 
posterior  plexuses,  and  ramify  over  and  supply  the  anterior  aspect  of  the  bronchus 
and  root  of  the  lung. 

10.  The    posterior    pulmonary  branches    (rr.    bronchiales    posteriores)    are 
several  large  twigs  which  join  with  filaments  from  the  second,  third  and  fourth  tho- 
racic ganglia  of  the  sympathetic  to  form  the  posterior  pulmonary  plexus  (plexus 
pulmonalis  posterior).     Fibres  from  this  plexus  communicate  with  the  corresponding 
structure  of  the  opposite  side  and  with  the  anterior  pulmonary  plexuses,  in  this  way  each 
vagus  sending  fibres  to  both  lungs.      Branches  from  the  plexus,  bearing  tiny  ganglia, 
follow  the  subdivisions  of  the  bronchi  to  supply  the  ultimate  units  of  the  lung. 

11.  The  cesophageal  branches  (rr.  oesophagei)  are  given  off  in  two  situa- 
tions :    in  the  superior  mediastinum,   where  the  right  vagus   and  the   left   inferior 
laryngeal  distribute  cesophageal  branches,  and  in  the  posterior  mediastinum,  where 
the  cesophagus  is  surrounded  by  branches  from  the  cesophageal  plexus  or  pic. \  us 
gula  (Fig.    1081).     This  plexus  is  composed  of  the  two  vagus  nerves,  after  they 
leave  the   posterior  aspect  of  the  bronchi,  in  conjunction  with  filaments  from   the 
great  splanchnic  nerves  and  from  some  of  the  lower  thoracic  ganglia.      Both  the 
muscular  and  mucous  coats  of  the  cesophagus  are  innervated  from  this  source. 

12.  The    pericardial  branches  (rr.   pericardiaci)  are  given  off  to  the  upper 
anterior  portion  of  that  membrane  by  either  vagus  and  to  the  posterior  portion  by 
the  oesophageal  and  frequently  the  posterior  pulmonary  plexuses. 

13.  The  abdominal  branches  come  from  both  nerves.      On  gaining  the  pos- 
terior surface  of  the  stomach  after  following  the  corresponding  aspect  of  the  cesopha- 
gus, the  right  vagus  forms  the  posterior  gastric  ple.vus  along  the  lesser  curvature, 
from  which  gastric   branches   supply  the   posterior   surface   of   the   stomach  ;    the 
remaining  and  larger   part  of   the   plexus  is  continued  as  the  ccrliac  branches  to 
the  plexus  of  the  same  name  and,  thence,  in  company  with  the  sympathetic  strands, 
to  the  subsidiary  plexuses   supplying  the  spleen,   the   pancreas,   the  intestine,   the 
suprarenal  bodies  and  the  kidneys.      In  a  similar  manner,  along  the  lesser  curvature 
the  left   vagus   forms  the  anterior  gastric  plexus,   from  which  numerous  gastric- 
branches  are  distributed  to  the  anterior  surface  of  the  stomach,  the  continuation  of 
the  plexus  being  hepatic  branches,  which  join  the  sympathetic  filaments  accompany- 
ing the  hepatic  artery  to  supply  the  liver. 

Practical  Considerations. — The  pneumogastric  nerve  may  be  compressed 
or  displaced  by  tumors  in  the  neck,  or  it  may  be  injured  in  accidental  or  operative 
wounds,  »>r  by  fracture  of  the  base  of  the  skull.  Its  division  is  not  always  fatal  ;  in 


THE   VAGUS   NERVE. 


1273 


fact,  a  portion  of  it  has  been  deliberately  removed  with  success.  In  those  cases  in 
which  the  nerve  was  divided,  difficulty  in  breathing  and  swallowing,  slowing  of 
the  respiration,  laryngismus,  changes  in  the  voice,  diminished  inspiratory  murmur, 
asthma  and  pneumonia  were  noticed  (Park).  In  cases  of  pressure  by  tumors  on 
the  pneumogastrics  of  both  sides,  lung  disturbances,  dyspnoea,  weakening  of  the 
pulse,  and  a  ravenous  appetite  were  observed. 

FIG.   1081. 


Superior  cervical  cardiac 
branch  of  sympathetic 

Vagus  nerve 

Middle  cervical  ganglion 
of  sympathetic 


Clavicle 

Recurrent  laryngeal 
nerve,  displaced  outward 
Inferior  cervical  cardiac  of  sympa- 
thetic,joining  superior  branch 
Recurrent  laryngeal    • 

nerve1 

Inferior  cervical  cardiac 

branch  of  vagus 

Innominate  artery 

Aorta 

Combined  sympathetic 

and  vagal  inferior 

cervical  cardiac  nerves 

Right  bronchus 


Pulmonary  artery" 
Right  vagus' 

Thoracic  duct 
Vena  azygos 


Vena  cava  inferior, s_ 

sectional  surface 


Liver,  under  surface 


Branches  to  liver 
and  gall  bladder' 


Vagus  nerve 

Superior  cervical  cardiac  branch 
Subclavian  artery      I°f  vagus 
Inferior  cervical  cardiac  branch 
Clavicle  [of  vagus 


I.  rib 

Inferior  cervical 
cardiac  branch  of 
sympathetic 
Recurrent  laryn- 
geal nerve 

Inferior  cervical 
cardiac  branch 
of  sympathetic 

Left  bronchus 
Pulmonary  artery 
Lung,  mesial  surface 

CEsophagus 
Part  of  left  vagus 
about  to  aid  in 
formation  of 
plexus  guise 


Part  of  right  vagus 
about  to  pass 
through  diaphragm 


Left  vagus 


Dissection  showing  lower  part  of  pneumogastric  nerves  and  their  branches. 

Lesions  of  the  recurrent  laryngeal  branch  of  the  pneumogastric,  from  tumors, 
abscesses,  etc.,  are  comparatively  common.  Injury  to  this  nerve  is  the  chief  danger 
to  be  feared  in  the  removal  of  the  thyroid  gland,  passing  as  it  does  so  close  to  the 
gland  and  to  the  inferior  thyroid  artery  where  the  latter  is  usually  ligated  preliminary 
to  or  during  the  excision  of  the  gland.  As  it  is  the  main  motor  nerve  of  the  larynx, 


HUMAN   ANATOMY. 

its  irritation  causes  spasm  of  the  laryngeal  muscles,  with  brassy  cough  and  stridulous 
breathing.  The  tendency  to  closure  of  the  glottis  is  sometimes  so  threatening 
as  to  demand  immediate  tracheotomy  or  intubation.  Paralysis  causes  hoarseness 
or  loss  of  voice  (aphonia).  In  a  bilateral  paralysis  both  cords  fall  into  the  cadaveric 
position.  Loss  of  voice  results  and  marked  inspiratory  dyspnoea,  which  may  demand 
tracheotomy  or  intubation. 

THE    SPINAL   ACCESSORY    NERVE. 

The  eleventh  or  spinal  accessory  nerve  (n.  accessorius)  is  purely  motor.  It  con- 
sists of  two  portions,  a  spinal  and  an  accessory,  which  differ  widely  in  origin,  course 
and  distribution.  The  spinal  portion  or  accessorius  spinalis  (r.  externus)  is  so  termed 
because  it  arises  from  the  spinal  cord  and  the  accessory  portion  or  accessorius  vagi 
(r.  interims)  receives  its  name  in  recognition  of  the  fact  that  it  is  accessory  to  the 
vagus.  As  emphasized  in  connection  with  the  last-named  nerve  (page  1266),  the 
so-called  accessory  portion  of  the  eleventh  is,  in  reality,  an  integral  part  of  the  vagus 
and  the  description  of  its  deep  origin  and  distribution  has  been  included  with  those 
of  the  vagus.  There  remains,  therefore,  only  the  spinal  portion  of  the  nerve  to  be 
considered.  The  spinal  part — the  eleventh  nerve  proper — supplies  the  sterno- 
mastoid  and  trapezius  muscles. 

Deep  Origin. — The  fibres  constituting  the  spinal  part  of  the  nerve  arise  as  the 
axones  of  a  column  of  large  multipolar  neurones  which  is  situated  in  the  anterior 
horn  of  the  spinal  gray  matter  and  extends  from  the  lower  end  of  the  medulla  to 
the  fifth  or  sixth  cervical  segment  of  the  spinal  cord.  The  cells  of  this  column, 
known  as  the  accessory  nucleus,  occupy  a  dorso-lateral  position  in  the  horn,  lying 
posterior  to  the  cells  from  which  arise  the  fibres  of  the  anterior  roots  of  the  cervical 
nerves.  Leaving  these  cells,  the  fibres  pass  dorsally  within  the  gray  matter  to  the 
vicinity  of  the  bay  between  the  anterior  and  posterior  horns,  where,  while  some  at 
once  curve  outward  and  traverse  the  white  matter  to  gain  the  lateral  surface  of  the 
cord,  the  majority  bend  abruptly  brainward  and  pursue  a  short  ascending  path  before 
turning  outward. 

Course  and  Distribution. — The  superficial  origin  of  the  accessory  nerve 
is  marked  by  the  emergence  of  a  series  of  fasciculi  along  the  lateral  surface  of  the 
spinal  cord  between  the  anterior  and  posterior  roots  of  the  cervical  spinal  nerves,  the 
fasciculi  progressively  nearing  the  posterior  roots  as  they  issue  at  higher  levels. 
Consecutively  joining  shortly  after  they  escape  from  the  cord,  the  fasciculi  unite  to 
form  a  common  trunk,  which  gradually  increases  in  size  by  accessions  of  fibres  at 
each  succeeding  segment.  The  nerve-trunk  thus  formed  passes  upward  in  the  sub- 
dural  space,  between  the  ligamentum  denticulatum  and  the  posterior  nerve-roots 
(Fig.  879),  to  the  foramen  magnum,  through  which  it  enters  the  cranium.  Upon 
reaching  the  side  of  the  medulla,  the  spinal  accessory  nerve  turns  outward  to  enter 
the  middle  compartment  of  the  jugular  foramen  and  to  unite  temporarily  with  the 
accessory  vagus.  It  occupies  the  posterior  part  of  the  middle  compartment  of  the 
jugular  foramen,  lying  within  a  dural  sheath  which  contains  also  the  vagus.  On 
reaching  the  lower  margin  of  the  foramen,  the  fibres  accessory  to  the  vagus  perma- 
nently leave  the  eleventh  nerve.  The  latter,  often  described  as  the  spinal  part, 
courses  downward  for  a  short  distance  in  the  interval  between  the  internal  carotid 
artery  and  the  internal  jugular  vein  and  then  passes  backward,  either  anterior  or  pos- 
terior to  the  vein,  until  it  reaches  the  deep  surface  of  the  sterno-mastoid  muscle, 
which  it  usually  enters.  While  within  the  substance  of  the  muscle,  the  spinal 
accessory  gives  off  filaments  which  unite  with  a  branch  from  the  second  cervical 
nerve  to  form  the  stcrno-wattoid  plf\ns  (Fig.  1082)  for  the  supply  of  that  muscle. 
Emerging  from  beneath  the  posterior  edge  of  the  sterno-mastoid,  the  eleventh 
nerve  crosses  the  occipital  triangle  and  dips  under  the  anterior  margin  of  the 
trape/ius  along  the  deep  surface  of  which  it  descends  almost  to  the  lower  margin 
of  the  muscle.  Under  the  trapezius  the  nerve  forms  a  plexus  of  varying  degrees 
of  intricacy  with  the  third  and  fourth  cervical  nerves.  This  is  called  the 
siihtmfH'-icil  plt-.vus  (Fig.  1082 ),  its  fibres  of  distribution  supplying  solely  the 
Ti]>e/ins  muscle. 


THE    HYPOGLOSSAL    NERVE.  1275 

Variations. — Considerable  deviation  from  the  normal  has  been  described  with  regard  to 
the  spinal  portion.  The  lower  limit  of  its  origin  has  been  observed  as  high  as  the  third  cervical 
nerve  and  from  that  level  as  far  down  as  the  first  thoracic.  In  one  instance  the  nerve  left 
the  subdural  space  below  the  first  cervical  nerve  and  re-entered  at  a  higher  level.  Quite  fre- 
quently it  fails  to  pierce  the  sterno-mastoid  muscle.  In  one  reported  case  the  nerve  ended  in 
the  sterno-mastoid,  the  trapezius  being  supplied  only  by  the  third  and  fourth  cervical  nerves. 
Two  similar  cases  have  been  observed  in  the  dissecting  room  of  the  University  of  Pennsylvania. 
Rarely  it  gives  off  a  filament  which  joins  the  n.  descendens  cervicalis. 

Practical  Considerations. — The  spinal  accessory  nerve  supplies  the  sterno- 
cleido-mastoid  and  trapezius  muscles.  A  few  fibres  of  the  second  and  third  cervical 
nerves  enter  into  the  supply  of  the  sterno-mastoid,  but  the  muscle  is  almost  com- 
pletely under  the  control  of  the  spinal  accessory.  The  cervical  nerves  take  a  greater 
part  in  the  supply  of  the  trapezius,  so  that  paralysis  of  the  spinal  accessory  does  not 
always  paralyze  this  muscle. 

Spasm  of  the  trapezius  will  draw  the  head  backward  and  toward  the  affected 
side  and  will  pull  the  scapula  toward  the  spine.  In  spasm  of  the  sterno-mastoid,  as 
in  "wry  neck,"  the  chin  will  be  turned  to  the  opposite  side  and  elevated,  while  the 
ear  will  look  forward.  If  both  sterno-mastoids  are  in  contraction  the  chin  will  be  in 
the  median  line  and  will  be  drawn  toward  the  sternum.  Paralysis  of  one  muscle  will 
produce  a  condition  somewhat  similar  to  that  produced  by  a  spasm  of  the  opposite 
one. 

The  spinal  accessory  nerve  enters  the  under  surface  of  the  sterno-mastoid  muscle 
near  the  junction  of  its  upper  and  middle  thirds,  where  it  may  be  reached  by  an 
incision  along  the  anterior  border  of  the  muscle.  The  nerve  emerges  from  the 
muscle  near  the  middle  of  its  posterior  border. 

THE   HYPOGLOSSAL    NERVE. 

The  twelfth  or  hypoglossal  nerve  (n.  hypoglossus)  is  a  purely  motor  nerve  and 
supplies  the  musculature  of  the  tongue,  intrinsic  as  well  as  extrinsic,  with  the  excep- 
tion of  the  palato-glossus. 

Central  and  Cortical  Connections. — The  hypoglossal  nerve  takes  its  deep  origin  from 
several  associated  groups  of  neurones  called  the  hypoglossal  nucleus  (nucleus  n.  hypoglossi) 
(Fig.  949),  which  underlies  the  floor  of  the  fourth  ventricle.  This  nucleus  is  a  narrow 
elongated  collection  of  large  multipolar  cells,  measuring  about  18  mm.  in  length  by  2  mm. 
in  width,  that  partly  corresponds  in  position  to  the  trigonum  hypoglossi  in  the  floor  of  the 
fourth  ventricle.  The  entire  nucleus,  however,  is  more  extensive  than  the  trigonum  and 
extends  from  the  level  of  the  striae  acusticae  above  into  the  closed  part  of  the  medulla  as  far 
down  as  the  decussation  of  the  pyramids  (Fig.  927).  It  lies  ventral  and  very  slightly  lateral 
to  the  central  canal  of  the  medulla  and  the  median  groove  in  the  floor  of  the  fourth  ventricle, 
close  to  the  mid-line  and  its  fellow  of  the  opposite  side.  The  large  size  and  branched  form 
of  the  nerve-cells  composing  the  nucleus,  as  well  as  their  ventral  position  in  relation  to 
the  central  canal,  emphasize  the  close  correspondence  of  these  elements  with  the  cells  of 
the  motor  roots  of  the  spinal  nerves.  Indeed,  as  has  been  noted  (page  1380),  the  gray  matter 
enclosing  the  hypoglossal  nucleus  is  the  morphological  equivalent  of  the  bases  of  the  anterior 
cornua.  Immediately  after  arising  and  before  leaving  the  nucleus,  the  axones  converge 
into  a  number  of  fasciculi  which,  emerging  from  the  ventral  aspect  of  the  nucleus,  take  a 
ventro-lateral  course  and  traverse  the  interval  between  the  gray  and  white  reticular  formations. 
From  this  situation  the  hypoglossal  fibres  continue  their  course  to  the  anterior  surface  of  the 
medulla  by  passing,  for  the  most  part,  between  the  nucleus  of  the  inferior  olive  and  the  mesial 
accessory  olivary  nucleus,  although  quite  a  number  of  the  strands  penetrate  the  ventral  portion 
of  the  olivary  nucleus  (Fig.  927). 

The  central  connections  of  the  hypoglossal  nucleus  include:  (a]  crossed  fibres  from  the 
nucleus  of  the  opposite  side  ;  (b)  fibres  from,  and  probably  also  to,  the  posterior  longitudinal 
fasciculus,  by  means  of  which  the  nucleus  of  the  twelfth  is  brought  into  relation  with  the  nuclei 
of  other  cranial  nerves;  and  (<*}  fibres  which  join  the  dorsal  bundle  of  Schiitz,  a  system  of 
longitudinal  fibres  underlying  the  floor  of  the  fourth  ventricle  and  traceable  upward  beneath 
the  Sylvian  aqueduct,  but  concerning  whose  destination  and  connections  little  is  known. 

The  cortical  centre  of  the  hypoglossal  nerve  probably  lies  within  the  lower  or  opercular 
extremity  of  the  precentral  convolution.  The  fibres  arising  as  the  axones  of  the  cells  within 
this  area  pass  over  the  upper  border  of  the  lenticular  nucleus  and  through  the  internal  capsule 
and  descend  in  the  brain-stem  within  the  median  part  of  the  pyramidal  tract  as  far  as  the 


1276 


HUMAN    ANATOMY. 


medulla.  The  cortico-nuclear  fibres  then  bend  dorso-medially  and,  for  the  most  part  but 
not  entirely,  cross  the  raphe  to  enter  the  ventro-lateral  surface  of  the  hypoglossal  nucleus  of 
the  opposite  side  and  end  in  arborizations  around  the  root-cells. 

Course  and  Distribution. — The  hypoglossal  takes  its  superficial  origin 
from  the  surface  of  the  brain-stem  in  the  form  of  from  ten  to  fifteen  slender  fasciculi, 
which  emerge  from  the  ventral  surface  of  the  medulla  in  the  groove  between  the 
olivary  eminence  and  the  pyramid  (Fig.  1046). 

FIG.  1082. 


I  >igastric  muscle,  cut 

I.  cervical  nerve — 
Spinal  accessory  nerve — 
Small  occipital  nerve 

1 1.  cervical 
Hypoglossal  ner 
Superior  cervical  ganglion 
anch  of  1 1 .  cervical  to  spinal  accessory 
III.  cervical  nerve 
Communicans  hypoglossi 
nps  of  great  auricular  and  superficial 
ical  nerves]  Iv  cervical  nerve 

V.  cervical  nerve 
Branch  to  rhomboidei 


scle 


xternal  pterygoifl 
ingual  branch  of  V.  ner 


,  _  ^Chorda  tympani  nerve 
E  -  Internal  pterygoid  muscle 
E  -  Edge  of  oral  mucous  membrane 
^___  —  •  Glosso-pharyngeal  nerve 
-  Mental  nerve 
I  -  Inferior  dental  nerve,  cut 
I  Sublingual  gland 

1  --  •Submaxillary  ganglion 
---  Stylo-hyoid  muscle 

Thyro-hyoid  branch  of  XII.  nerve 

Superior  laryngeal  nerve 

Descendens  hypoglossi  ;  sympathetic 

cord  is  to  its  outer  side 

Vagus  nerve 

External  laryngeal  nerve 


VI.  cervical  ner 
ranch  of  communication  to 
spinal  accessory 
Cutaneous  branch 
VII.  cervical  nerve 
Nerve  to  subclavius 
VIII.  cervical  nerve 
Posterior  thoracic 
nerve 
Suprascapular 


I.  thoracic  nerve  ' 


Omo-hyoid  muscle,  cut 

Phrenic  nerve 

Middle  cervical  ganglion  of  sympathetic 

Scalenusantlcus  muscle 

Subclavian  artery 


Deep  dissection  of  neck  showing  branches  of  vagus,  spinal  accessory  and  hypoglossal  nerves. 

These  root-bundles  pass  outward,  dorsal  to  the  vertebral  artery,  and  assemble 
into  two  groups,  which  pierce  the  dura  mater  separately  at  a  point  opposite  the 
anterior  condyloid  foramen.  Either  within  this  canal  or  as  they  leave  the 
cranium  through  its  external  opening  they  unite  into  a  single  trunk.  Arriving  at 
the  inferior  aspect  of  the  base  of  the  skull,  the  deeply  placed  hypoglossal  nerve 
descends  and  hooks  around  the  ganglion  of  the  trunk  of  the  vagus,  to  which  it  is 
closely  attached  by  connective  tissue.  It  then  takes  a  downward  and  forward 
course  between  the  internal  carotid  artery  and  the  internal  jugular  vein.  Arriving 
at  the  inferior  margin  of  the  posterior  belly  of  the  digastric,  the  nerve  winds  around 
the  occipital  artery  and  courses  downward  and  forward  to  the  outer  side  of  the 
external  and  internal  carotid  arteries.  It  then  continues  forward  above  the  hyoid 
bone  to  the  under  surface  of  the  tongue,  passing  beneath  the  tendon  of  the  digastric, 


THE    HYPOGLOSSAL    NERVE.  1277 

under  the  stylo-hyoid  and  mylo-hyoid  muscles  and  over  the  hyo-glossus  (Fig.  1082). 
It  terminates  by  piercing  the  genio-hyo-glossus  and  breaking  up  into  a  number  of 
fibres  for  the  supply  of  the  lingual  muscles. 

Communications. — Immediately  after  emerging  from  the  anterior  condyloid  foramen,  (a) 
a  tiny  branch  connects  with  the  superior  cervical  ganglion  of  the  sympathetic,  ( b )  one  or  two 
filaments  pass  to  the  loop  between  the  first  and  second  cervical  nerves  and  (c)  several  fibres 
associate  the  nerve  with  the  ganglion  of  the  trunk  of  the  vagus.  At  the  point  where  the  hypo- 
glossal  nerve  and  the  occipital  artery  cross,  (d)  the  lingual  branch  of  the  vagus  joins  the  twelfth  ; 
and  as  the  nerve  lies  beneath  the  mylo-hyoid  and  upon  the  hyo-glossus  muscle,  it  communi- 
cates with  (e)  the  lingual  branch  of  the  mandibular  nerve. 

Branches. — The  branches  of  the  hypoglossal  nerve  are  :  (i)  the  meningeal, 
(2)  the  descending,  (3)  the  thyro-hyoid  and  (4)  the  lingual. 

1.  The  meningeal  branch    (r.  meningeus)    consists  of  one  or   two    minute 
filaments  which  supply  the  dura  mater  of  the  posterior  cranial  fossa  and  the-diploe 
of  the  occipital  bone.      As  the  hypoglossal  is  motor  in  function,  it  is  likely  that  these 
twigs  are  contributed  to  the  nerve  by  the  loop  between  the  first  and  second  cervical 
nerves. 

2.  The  descending  branch   (r.  descendens),   or  r.  descendens  hypoglossi,   is 
in  reality  only  to  a  limited  extent  a  branch  of  the  twelfth,  since  the  greater  number 
of    its  fibres  are  accessions  to  the  hypoglossal    from  the  first  and  second  cervical 
nerves.     There  is  reason,  however,  to  believe  that  these  cervical  nerves  are  not  the 
exclusive  source  of  the  fibres  of  the  descendens  hypoglossi,  but  that  some  arise  from 
the  cells  of  the  hypoglossal  nucleus.      The  descending  branch  arises  near  the  point 
where  the  hypoglossal  nerve  hooks  around  the  occipital  artery  and  runs  downward 
and  inward  in  front  of  or  within  the  carotid  sheath.      It  gives  off  a  branch  to  the  an- 
terior belly  of  the  omo-hyoid  and,  about  the  middle  of  the  neck,  joins  the  descend- 
ing cervical  nerve,   or  n.   communicans   hypoglossi,   from   the  second  and   third 
cervical  nerves.      A  loop  or  plexus,  termed  the  ansa  hypoglossi,  is  thus  formed  and 
from  it  filaments  are  supplied  to  the  sterno-hyoid  and  sterno-thyroid  muscles  and  to 
the  posterior  belly  of  the  omo-hyoid  (Fig.  1082). 

3.  The    thyro-hyoid  nerve    (r.  thyreohyoideus)     is   also    only    an    apparent 
branch    of    the    hypoglossal,    as    its    fibres    can   be    traced   back    to    the    cervical 
plexus.      It  is  given  off  before  the  nerve  dips  beneath  the  stylo-hyoid  muscle  and 
passes  down  behind  the  greater  cornu  of  the  hyoid  bone  to  reach  its  distribution  to 
the  thyro-hyoid  muscle. 

4.  The  lingual  branches    (rr.   linguales)   with  one  exception,    comprise  the 
real    distribution    of    the  hypoglossal.      As  the  nerve  lies  beneath  the  mylo-hyoid 
muscle    filaments    are   given    off    to    the    hyo-glossus,    the   stylo-glossus   and    the 
genio-hyoideus.      The  fibres  going  to  the  genio-hyoid  are   in  all  probability  de- 
rived from  the  cervical  plexus  and  are  not  of  true  hypoglossal  origin.     After  giving 
off  the  above-named  branches,  the  hypoglossal  nerve  breaks  up  into  the  terminal 
filaments  which  pierce  the  genio-hyo-glossus  to  supply  it  and  the  lingualis  muscle. 

Variations. — Occasionally  the  hypoglossal  has  been  found  to  possess  a  posterior  root  bear- 
ing a  ganglion.  This  condition  is  to  be  regarded  as  a  persistence  of  the  temporary  embryonal 
stage  during  which  the  nerve  is  provided  with  a  posterior  root  and  a  ganglion  of  Froriep 
(page  1380).  In  one  case  the  superficial  origin  was  located  at  the  posterior  aspect  of  the  me- 
dulla. Quite  frequently  the  vertebral  artery  passes  between  the  rootlets  of  origin  and  in  rare 
instances  behind  them.  Sometimes  a  cross  filament,  situated  either  between  the  genio-hyo- 
glossus  and  genio-hyoid  muscles  or  in  the  substance  of  the  latter  connects  the  two  hypoglossal 
nerves.  Rarely  the  hypoglossal  has  been  seen  to  send  a  filament  to  the  mylo-hyoid,  the  digas- 
tric or  the  stylo-hyoid  muscle.  Occasionally  the  r.  descendens  hypoglossi  seems  to  be  derived, 
either  entirely  or  in  part,  from  the  vagus,  but  in  these  instances  the  fibres  can  be  traced  back  to 
their  true  origin  from  the  cervical  nerves.  A  filament  from  the  descending  nerve  sometimes 
passes  into  the  thorax,  where  it  joins  the  vagus  or  the  sympathetic  ;  in  such  cases  the  aberrant 
branch  is  probably  derived  originally  from  either  the  sympathetic  or  the  vagus.  The  r.  descen- 
dens hypoglossi  may  send  a  branch  to  the  sterno-mastoid  muscle. 

Practical  Considerations. — Involvement  of  the  hypoglossal  nerve,  usually 
together  with  other  cranial  nerves  is  frequent  in  bulbar  disease.  The  most  character- 
istic symptom  is  a  deviation  of  the  tongue,  when  protruded  to  the  affected  side,  caused 


1278  HUMAN    ANATOMY. 

by  the  unopposed  action  of  the  muscles  of  the  opposite  side.  The  nerve  may  be 
injured  by  operative  or  other  wounds  in  the  submaxillary  region  or  in  the  mouth,  as 
in  gun-shot  wounds.  It  can  be  easily  reached  in  the  submaxillary  region  by  the 
same  incision  as  that  used  for  ligating  the  lingual  artery  (page  736).  It  passes  for- 
ward to  the  tongue,  just  above  the  hyoid  bone,  and  forms  the  upper  boundary  of  the 
small  "lingual  triangle,"  which  is  exposed  when  the  submaxillary  gland  is  elevated. 

THE   SPINAL   NERVES. 

The  cranial  division  of  the  somatic  nerves  having  been  considered,  the  spinal 
group  next  claims  attention,  the  visceral  or  splanchnic  (sympathetic)  nerves  being 
reserved  for  a  final  and  separate  description. 

The  spinal  nerves  (nn.  spinales)  include  a  series  of  usually  thirty-one  pairs  of 
symmetrically  disposed  trunks  which  pass  laterally  from  the  spinal  cord  and  emerge 
from  the  vertebral  canal  through  the  intervertebral  foramina  ( Fig.  880).  Each 
nerve  arises  from  the  cord  by  a  dorsal  sensory  and  a  ventral  motor  root,  which  sepa- 
rately traverse  the  subarachnoid  and  subdural  spaces  and  evaginate  or  pierce  the  pia 
mater,  arachnoid  and  dura  mater.  Within  the  intervertebral  foramina  the  roots  unite  to 
form  a  common  trunk,  which  carries  with  it  a  sheath  composed  of  the  three  membranes, 
the  contribution  of  the  arachnoid  and  pia,  however,  soon  ending,  whilst  the  dural 
covering  is  prolonged  to  become  continuous  with  the  epineural  sheath  of  the  nerve. 

Nomenclature. — The  spinal  nerves  are  designated  not  relative  to  the  position 
at  which  they  arise  from  the  cord,  but  according  to' their  point  of  emergence  from  the 
vertebral  canal.  They  are  divided,  therefore,  into  the  cervical,  thoracic,  lumbar, 
sacral  and  coccygcal  groups.  With  the  exception  of  those  in  the  cervical  region, 
the  individual  nerves  are  named  according  to  the  vertebra  below  which  they  emerge 
from  the  vertebral  canal.  On  account  of  the  disproportion  between  the  eight  cervi- 
cal nerves  and  the  seven  cervical  vertebrae,  this  arrangement  necessarily  can  not 
prevail  in  the  neck.  The  first  cervical  nerve,  often  called  the  suboccipital  nerve, 
emerges  between  the  occipital  bone  and  the  atlas  ;  the  second  emerges  below  the  first 
vertebra,  the  third  below  the  second  and  so  on  down  to  the  eighth,  which  traverses 
the  foramen  between  the  seventh  cervical  and  first  thoracic  vertebral  segments. 

Constitution. — Every  spinal  nerve  arises  by  two  roots,  a  posterior  sensory 
and  an  anterior  motor,  the  latter  being  composed  of  the  axones  proceeding  from  the 
motor  neurones  situated  within  the  gray  matter  of  the  anterior  cornu  of  the  spinal  cord, 
whilst  the  fibres  composing  the  posterior  or  sensory  root  are  the  axones  of  the  neurones 
within  the  ganglia  which  are  invariably  present  on  these  roots.  The  formation  of  the 
common  trunk,  by  the  union  of  the  two  roots,  affords  opportunity  for  the  two  varie- 
ties of  fibres  to  intermingle,  so  that  the  anterior  and  posterior  primary  divisions  into 
which  the  common  trunk  divides  contain  both  sensory  and  motor  fibres.  In  addition 
to  these  fibres,  which  are  destined  for  the  somatic  muscles  and  the  integument,  others 
are  added  from  the  sympathetic  neurones  for  the  supply  of  the  outlying  involuntary 
muscle  and  glandular  tissue  occurring  in  the  regions  to  which  the  spinal  nerves  are 
distributed.  It  is  evident,  therefore,  that  the  terms  "motor"  and  "sensory,"  as 
applied  to  the  somatic  branches  of  the  spinal  nerves,  are  relative  and  not  absolute, 
since  in  all  cases  the  nerves  passing  to  the  muscles  contain  sensory  and  sympathetic 
fibres  in  addition  to  those  ending  as  motor  filaments  in  relation  with  the  striated 
muscle  fibres.  Likewise,  in  the  case  of  the  sensory  branches  distributed  to  the  integ- 
ument, sympathetic  filaments  (motor  to  the  involuntary  muscle  of  the  blood-vessels 
and  secretory  to  the  glands)  accompany  those  concerned  in  collecting  sensory 
impulses.  On  the  other  hand,  where  they  retain  their  typical  plan,  as  in  the  case  of 
the  thoracic  nerves,  the  spinal  nerves  contribute  motor  fibres  which  end  around  the 
sympathetic  neurones  to  supply  motor  impulses  either  to  the  involuntary  muscle 
of  the  organs,  by  way  of  the  splanchnic  efferents,  or  to  the  outlying  involuntary 
muscle  along  the  somatic  nerves  in  the  manner  above  described. 

The  sensory,  posterior  or  dorsal  roots  (radices  posteriores)  of  the  spinal 
nerves  are  usually  larger  than  the  motor,  a  condition  due  to  the  increased  number 
of  their  filaments  and  the  greater  size  of  those  filaments  ( fila  ladicularia  ).  The  fas- 
ciculi which  form  the  sensory  root  are  attached  to  the  cord  along  the  postero-lateral 


POSTERIOR    PRIMARY  DIVISIONS  OF    SPINAL    NERVES.      1279 

groove  as  a  continuous  series,  called  the  posterior  root  zone  (Fig.  884).  These 
rootlets  are  sometimes  so  numerous  and  so  crowded,  that  those  of  adjacent  nerves 
overlap  and  adhere  to  one  another.  Where  more  typically  disposed,  as  in  the 
thoracic  region,  the  cord-segments  (page  1024)  are  distinct.  The  fasciculi  for  any 
one  nerve  usually  collect  into  two  bundles  which  pass  to  the  proximal  aspect  of  the 
spinal  ganglion. 

The  spinal  ganglia  (<w.  spinalia)  are  aggregations  of  nerve-cells  found  on  the 
posterior  roots  of  all  the  spinal  nerves  (Fig.  852).  They  are  usually  ovoid  in  shape, 
from  4-6  mm.  in  length,  and  are  occasionally  bifid  at  their  proximal  ends.  They 
consist  of  a  cluster  of  unipolar  neurones,  whose  centrally  directed  axones  form  the 
sensory  root  of  the  spinal  nerve  and  whose  dendrites  extend  peripherally  as  the 
sensory  distribution.  The  ganglia  are  usually  situated  in  the  intervertebral  foramina, 
but  exceptions  to  this  rule  are  presented  by  the  ganglia  of  the  first  and  second  cervi- 
cal nerves,  which  lie  upon  the  neural  arches  of  the  atlas  and  axis  respectively,  and 
by  those  of  the  sacral  and  coccygeal  nerves,  which  are  lodged  within  the  vertebral 
canal.  Although  situated  beyond  the  dural  sheath  of  the  cord,  with  the  exception 
of  the  ganglion  of  the  coccygeal  nerve,  they  are  invested  by  a  prolongation  of  it. 

Variations. — The  first  cervical  nerve  may  either  have  no  posterior  root  or  may  derive  it'from 
or  share  it  with  the  eleventh  cranial  nerve.  Its  ganglion  may  be  very  rudimentary  or  entirely 
absent.  Considerable  variation  is  found  in  the  thoracic  region,  where  either  the  anterior  or  pos- 
terior or  both  roots  of  one  of  the  nerves  may  seemingly  be  absent.  In  the  lumbar  and  upper 
sacral  nerves  the  ganglion  may  be  double,  each  bundle  of  the  posterior  root  having  its  own. 

Ganglia  aberrantia  are  small  detached  portions  of  the  spinal  ganglia  occasionally  found 
along  the  posterior  roots  of  the  upper  cervical,  the  lumbar  and  the  sacral  nerves. 

The  motor,  anterior  or  ventral  roots  (radices  anteriores)  are  smaller  than 
the  posterior  and  have  no  ganglia.  They  emerge  from  the  anterior  surface  of  the 
cord  in  a  series  of  fasciculi  (fila  radicularia),  the  anterior  root-zone,  with  a  tendency 
to  form  two  groups  which  unite  in  the  completed  root  (Fig.  878).  As  in  the  pos- 
terior roots,  the  fasciculi  of  origin  may  overlap  one  another  or  fuse  with  those  of 
adjoining  nerves. 

Number. — As  usually  found  the  thirty-one  pairs  are  grouped  as  follows:  — eight 
cervical,  twelve  thoracic,  five  lumbar,  four  sacral  and  one  coccygeal. 

Variations. — Should  there  be  any  anomaly  in  the  number  or  arrangement  of  the  vertebrae, 
there  is  a  corresponding  modification  of  the  nerves.  The  greatest  variation  occurs  in  the 
coccygeal  region.  There  may  be  none  at  all  in  this  situation,  or  one  or  two  additional  ones  may 
be  found.  Traces  of  two  extra  ones,  which  are  rudimentary  caudal  nerves,  may  be  found  in  the 
tiltim  terminale. 

Size. — The  largest  spinal  nerves  are  those  which  are  concerned  in  the  forma- 
tion of  the  limb  plexuses — brachial,  lumbar  and  sacral — and  are,  therefore,  the  lower 
cervical,  the  first  thoracic,  the  lower  lumbar  and  the  upper  sacral.  The  largest  nerves 
in  the  entire  series  are  the  lower  lumbar  and  upper  sacral.  The  smallest  are  the  lower 
sacral  and  the  coccygeal.  Those  of  the  upper  cervical  region  are  smaller  than  those 
of  the  lower,  the  sixth  being  the  largest  of  those  in  the  neck.  With  the  exception  of 
the  first,  the  thoracic  nerves  are  comparatively  small. 

Divisions. — The  common  trunk  formed  by  the  union  of  the  two  roots  emerges 
from  its  intervertebral  foramen  and  almost  immediately  gives  off  a  meningeal  or 
recurrent  branch  (r.  meningeus).  This  tiny  nerve  is  joined  by  a  filament  from  a 
gray  ramus  communicans  and  enters  the  vertebral  canal  through  the  foramen  to  be 
distributed  to  the  vertebrae  and  their  ligaments,  and  to  the  blood-vessels  of  the 
vertebral  canal  and  of  the  spinal  cord  and  its  membranes.  After  giving  off  the 
recurrent  twig,  each  trunk  soon  splits  into  two  branches,  called  the  anterior  and 
posterior  primary  divisions  (rr.  anterior  et  posterior),  each  of  which  is  composed 
of  fibres  from  both  roots  (Fig.  1085),  as  well  as  of  sympathetic  filaments. 

THE  POSTERIOR  PRIMARY  DIVISIONS  OF  THE  SPINAL  NERVES. 

The  posterior  primary  divisions  (rr.  posteriores)  of  the  spinal  nerves  are  as  a 
rule  smaller  than  the  anterior  (rr.  anteriores).  They  arise  either  as  a  single  cord 
from  the  trunk  formed  by  the  union  of  the  two  roots,  or  as  two  separate  strands 


1280 


HUMAN   ANATOMY. 


from  the  roots  themselves.     They  turn  dorsally  almost  immediately  and  divide  into 
an  internal  (r.  raedialis)  and  an   external  branch  (r.    lateralis),   which  supply  the 

FIG.  1083. 


Third  occipital  nerve 

Cutaneous  hrs.  of  III. 
cervical,  dorsal  div. 


Cutaneous  brs.  of  IV.  and  V 
cervical,  dorsal  division 

VII.  cervical  spinous  process 

Cutaneous  brs.  of  dorsal 
divisions  of  : — 
I.  thoracic 


Occipitalis  major  nerve 


III.,  IV.,  V.,  VI.,  VII.. 
VIII.,  IX.,  X.  and  XI. 
thoracic  nerves,  lateral 
cutaneous  branches 


X.  thoracic 

Spinous    process 

of  XII.  thoracic 

vertebra 


Cutaneous  brs.  of  dorsal 
divisions  of  :  — 

XI.  thoracic 


I.,  II.  and  III.  lumbar  f 

nerves,  ext.  brs.  of  J. 

dorsal  divisions  I 


Cutaneous  brs.  of  dorsal 

divisions  of  sacral 

nerves 


XII.  thoracic,  lateral  cu- 

'ta neons  hr. 

Iliac  br.  ilio-hypogastric 


XII.  thoracic,  lateral  cu- 
taneous hr. 


Superficial  dissection,  showing  cutaneous  branches  of  posterior  divisions  and  lateral  cutaiK-ous  branches  of 

anterior  divisions  of  spinal  nerves. 

dorsal  muscles  and   internment.       At  the.-   two  extremities  of  the  spinal   series  the 
division  into  internal   and  external   branches    does   not   prevail,    the   nrst   cervical, 


THE   CERVICAL   NERVES.  1281 

the  fourth  and  fifth  sacral  and  the  coccygeal  nerve  failing  in  this  respect.  Down  to 
and  including  the  sixth  thoracic  nerve,  the  internal  branches  are  mainly  cutaneous  and 
the  external  entirely  muscular.  From  the  seventh  thoracic  down,  the  reverse  con- 
dition exists.  In  the  former  region  the  internal  branches  become  cutaneous  near  the 
spine,  whilst  in  the  latter  the  sensory  filaments  pass  laterally  for  some  distance  through 
the  muscles  before  reaching  their  cutaneous  distribution. 

THE  CERVICAL  NERVES. 

The  first  cervical  nerve  (n.  suboccipitalis),  the  first  of  the  spinal  series,  is 
atypical  in  several  respects.  Its  posterior  root  is  either  insignificant  or  entirely  absent, 
and  its  posterior  division,  which  does  not  divide  into  internal  and  external  branches,  is 
larger  than  the  anterior  and  usually  does  not  send  off  any  direct  cutaneous  branch. 
The  nerve  passes  dorsally  between  the  occipital  bone  and  the  posterior  arch  of  the 
atlas  and  traverses  the  suboccipital  triangle,  occupying  a  position  below  and  posterior 
to  the  vertebral  artery.  Superficial  to  it  is  the  complexus  muscle. 

Branches. — These  are  :  (i)  the  muscular,  (2)  the  communicating  and  (3)  the 
cutaneous. 

1.  The  muscular  branches  supply  the  superior  and  inferior  oblique,  the  com- 
plexus and  the  rectus  capitis  posticus  major  and  minor  muscles. 

2.  The  communicating  branch  forms  a  loop  with  the  second  cervical  nerve.      It 
usually  arises   in   common   with  the  twig  to  the  inferior  oblique  muscle,    through 
or  over  which  muscle  it    passes  to    reach  its  destination.       It  may  arise  with  the 
nerve  to   the  complexus,  after  piercing  which  muscle  it  communicates  with  the  great 
occipital  nerve. 

In  the  neck  and  close  to  the  vertebrae  is  a  series  of  loops  between  the  posterior 
divisions  of  the  first,  second,  third  and  sometimes  the  fourth  cervical  nerves.  This  is 
called  the  posterio r  cervical  plexus  and  from  it  filaments  are  distributed  to  the  neigh- 
boring muscles. 

3.  The  cutaneous  branch  is  not  always  present.      It  accompanies  the  occipital 
artery,  inosculates  with  the  small  and  great  occipital  nerves  and  supplies  the  occipital 
region. 

The  second  cervical  nerve  is  distinguished  by  the  size  of  its  posterior  division, 
(r.  posterior)  which  is  larger  than  the  anterior  (r.  anterior).  It's  posterior  division 
takes  a  dorsal  course  between  the  atlas  and  the  axis,  and  then  between  the  inferior 
oblique  and  semispinalis  colli  muscles.  Reaching  the  deep  surface  of  the  complexus 
it  breaks  up  into  its  external  portion  (r.  lateralis),  which  supplies  the  complexus, 
obliquus  inferior,  semispinalis  colli  and  multifidus  spinae  muscles,  and  its  internal 
portion  (r.  medialis).  The  latter  is  called  the  great  occipital  nerve  (n.  occipitalis 
major).  This  nerve  (Fig.  1087)  passes  upward  over  the  inferior  oblique,  pierces 
the  complexus  and  trapezius,  and  accompanies  the  occipital  artery  to  the  scalp, 
to  the  posterior  half  of  which  it  is  the  main  sensory  nerve.  It  becomes  superficial 
at  the  superior  nuchal  line,  at  a  point  from  2-3  cm.  lateral  to  the  external  oc- 
cipital protuberance,  and  spreads  out  into  numerous  branches  which  supply  the 
scalp  as  far  forward  as  the  vertex. 

The  great  occipital  nerve  communicates  \vith  the  small  and  least  occipital  and  the  posterior 
and  great  auricular  nerves. 

Variations. — An  approximate  balance  is  maintained  between  the  great  and  small  occipital 
nerves,  any  deficiency  in  the  distribution  of  either  usually  being  equalized  by  a  compensatory 
enlargement  of  the  other.  Sometimes  the  great  occipital  sends  a  branch  to  the  auricle.  The 
external  branch  may  give  off  a  cutaneous  filament  or  may  furnish  a  twig  to  the  superior  oblique. 

The  third  cervical  nerve  has  a  smaller  posterior  division  than  has  the  second. 
Passing  backward,  the  former  helps  to  form  the  posterior  cervical  plexus  and  divides 
into  external  and  internal  branches.  The  external  branch  (r.  lateralis)  supplies 
adjacent  muscles  and  the  internal  branch  (r.  medialis),  known  as  the  least  or  third 
occipital  nerve  (n.  occipitalis  tertius),  pierces  the  complexus,  splenius  and  trapezius  to 
supply  the  skin  of  the  occipital  and  posterior  cervical  regions  (Fig.  1083). 

Si 


12.32 


HUMAN   ANATOMY. 


In  addition  to  assisting  in  the  formation  of  the  posterior  cervical  plexus  it  communicates 
with  the  great  occipital  nerve. 

The  fourth,  fifth,  sixth,  seventh  and  eighth  cervical  nerves  have  quite 
small  posterior  primary  divisions  (rr.  posteriores).  The  fourth,  fifth  and  sixth 
divide  into  the  usual  external  and  internal  branches  (  IT.  latcralcs  ct  mediates),  which 
supply  respectively  the  adjacent  muscles  and  the  dorsal  integument.  The  seventh 
and  eighth  usually  have  no  cutaneous  branches  and  are  distributed  solely  to  the 
deeper  muscles  of  the  back. 

A  communicating  filament  from  the  fourth  may  aid  in  the  formation  of  the  posterior 
cervical  plexus. 

Variations. — The  cutaneous  branches  of  the  fifth  and  sixth  may  he  very  small  or  absent 
entirely. 

THE  THORACIC  NERVES. 

The  posterior  primary  divisions  (rr.  posteriores)  of  the  thoracic  or  dorsal  nerves 
(nn.  thoracales)  follow  the  general  arrangement  of  dividing  into  external  and  internal 
branches.  Of  these  the  internal  branches  of  the  upper  six  are  mainly  cutaneous 
and  the  external  entirely  muscular.  In  the  lower  six,  on  the  contrary,  the  external 
branches  are  principally  cutaneous  and  the  internal  entirely  muscular. 

The  external  branches  (rr.  latcrales)  gradually  increase  in  size  from  above 
downward.  They  pierce  or  pass  under  the  longissimus  dorsi  to  reach  the  interval 
between  that  muscle  and  the  ilio-costalis,  eventually  reaching  and  supplying  the 
erector  spinse.  Those  from  the  lower  half  of  the  thoracic  nerves  distribute  sensory 
fibres  for  the  supply  of  the  skin  overlying  the  angles  of  the  ribs  (Fig.  1083). 

The  internal  branches  (rr.  mediates)  of  the  upper  six  or  seven  pass  dorsally 
between  the  multifidus  spinae  and  semispinalis  muscles.  After  innervating  the  trans- 
verso-spinales  they  become  superficial  close  to  the  median  dorsal  line  and  supply  the 
skin  of  the  back,  sometimes  extending  laterally  beyond  the  vertebral  border  of  the 
scapula.  The  internal  branches  of  the  lower  nerves  traverse  the  interval  between 
the  longissimus  dorsi  and  the  multifidus  spinae  and  supply  the  latter  muscle. 

Variations. — The  sixth,  seventh  and  eighth  thoracic  nerves  may  give  off  cutaneous  twigs 
from  both  external  and  internal  branches.  The  first  thoracic  nerve  may  have  no  cutaneous 
branch. 

THE  LUMBAR  NERVES. 

The  posterior  primary  divisions  (rr.  posteriores)  of  the  lumbar  nerves  (nn.  lum- 
bales)  divide  into  the  usual  external  and  internal  branches. 

The  external  branches  (rr.  laterales)  of  all  five  lumbar  nerves  enter  and  sup- 
ply the  erector  spinae,  those  of  the  lower  two  terminating  there.  From  the  external 
branches  of  'the  first,  second  and  third  arise  cutaneous  offshoots  (nn.  chin  him  supe- 
riores)  of  considerable  size  (Fig.  1083).  These  pierce  the  ilio-costalis  and  the 
aponeurosis  of  the  latissimus  dorsi  above  the  crest  of  the  ilium  and  supply  the  skin 
of  the  gluteal  region  as  far  forward  as  the  great  trochanter.  From  the  fifth  a  branch 
passes  downward  to  inosculate  with  a  similar  branch  of  the  first  sacral  nerve  to  aid  in 
the  formation  of  the  posterior  sacral  plexus. 

The  internal  branches  (rr.  mediates)  turn  directly  backward  and  supply  the 
multifidus  spinae  muscle. 

THE  SACRAL  NERVES. 

The  posterior  primary  divisions  (rr.  posteriores)  of  the  sarral  nerves  (nn. 
sacrales),  with  the  exception  of  that  of  the  fifth,  emerge  from  the  vertebral  canal 
through  the  posterior  sacral  foramina.  The  first,  second  and  third  pass  outward 
under  cover  of  the  multifidus  spinae  and  divide  into  external  and  internal  branches. 

The  external  branches  (  IT.  latcralcs  )  of  the  first,  second  and  third  sacral  nerves 
unite  over  the  upper  part  of  the  sacrum  with  a  similar  branch  of  the  fifth  lumbar  and 
with  the  fourth  sacral  nerve  to  form  a  series  of  loops,  the  posterior  sacral  plexus 


THE   SACRAL    NERVES. 


1283 


(Fig.  1084).  From  this  structure  branches  pass  laterally  till  they  reach  the  inter- 
val between  the  great  sacro-sciatic  ligament,  which  they  pierce,  and  the  deep  surface 
of  the  glutens  maximus,  where  they  form  a  second  series  of  loops.  From  the  pri- 
mary loops  branches  are  supplied  to  the  multifidus  spinae  and  from  the  secondary 
loops  proceed  two  or  more  filaments,  usually  two  (nn.  clunium  mcdii),  which  pierce 
the  gluteus  maximus  on  a  line  connecting  the  posterior  superior  spine  of  the  ilium 


FIG.  1084. 


Loops  of 

communication 

between  V.  lumbar, 

and  I.,  II.  and  III. 

posterior  sacral 

nerves 

Cutaneous  branches  from 
last  lumbar  and  first 
three  sacral  ne 
post,  divii 
From  XII. 
thoracic  nerve 


Part  of  multifidus  spinse  muscle 

V.  lumbar  nerve,  posterior  division 
I.  sacral  nerve,  posterior  division 
II.  sacral  nerve,  posterior  division 
\_^-III.  sacral  nerve,  posterior  division 
IV.  sacral  nerve,  posterior 
division 

Coccygeal  nerve,  anterior  division 

V. sacral  nerve, posterior  division 
Coccygeal  nerve,  posterior 
division 

IV.  sacral  nerve,  anterior 
.division,  the  coccygeus 
muscle  being  partly  cut  away 
V.  sacral  nerve,  anterior 
division 


luscle, 


Coccygeus 
part  of  its 
'coccygeal 
attachment  cut 

Cutaneous  branch 
of  IV.  anterior 
sacral  nerve,  giving  off 
here  also  muscular 
branches  to 
levator  ani 


Dissection  showing  left  posterior  sacral  plexus. 

and  the  tip  of  the  coccyx.  One  is  usually  situated  near  the  lower  portion  of  the 
sacrum  and  the  other  at  the  side  of  the  coccyx.  They  pass  laterally  and  supply  the 
skin  of  the  buttock  (Fig.  1083). 

The  internal  branches  (rr.  mediales)  of  the  first,  second  and  third  sacral 
nerves  are  small  in  size  and  are  distributed  to  the  multifidus  spinae. 

The  posterior  primary  divisions  of  the  fourth  and  fifth  sacral  nerves  are  of  small 
size.  They  pass  below  the  multifidus  spinae  and  continue  as  single  trunks,  not 
breaking  up  as  do  the  others,  into  two  branches.  They  are  connected  with  each 
other  and  with  the  coccygeal  nerve  by  loops  which  form  the  posterior  sacro- 
coccygeal  nerve.  From  this  structure  fibres  which  pierce  the  great  sacro-sciatic 
ligament  are  given  off  to  be  distributed  to  the  integument  in  the  coccygeal  region 
(Fig.  1084). 


1284 


HI/MAX    ANATOMY. 


THE  COCCYGEAL  NERYK. 

The  posterior  primary  division  (  r.  posterior)  of  the  coccygeal  nerve  (n.  coccy- 
geus)  does  not  divide  into  internal  and  external  branches.  It  unites  with  the  fourth 
and  fifth  sacral  to  form  the  posterior  sacro-coccygeal  nerve,  whose  course  and  distri- 
bution are  described  above. 

THE  ANTERIOR  PRIMARY  DIYISIONS  OF  THE  SPINAL  NERYKS. 

The  anterior  primary  divisions  (rr.  anteriores)  of  the  spinal  nerves,  like  the 
posterior  (rr.  posteriores ) ,  contain  fibres  from  both  the  anterior  and  posterior  roots 
and,  with  the  exception  of  those  of  the  first  and  second  cervical  nerves,  are  larger 
than  the  posterior.  After  liberation  from  the  main  trunk  at  the  intervertebral 
foramina,  they  pass  ventrally  and  supply  the  lateral  and  anterior  portions  of  the  neck 
and  trunk,  as  well  as  the  limbs. 

Shortly  after  leaving  its  foramen,  each  anterior  division  is  joined  by  a  slender 
fasciculus  from  the  gangliated  cord  of  the  sympathetic,  called  the  gray  rann/s 
communicans  (page  1357).  Branches  to  the  sympathetic  system  are  given  off  from 

some  of  the  thoracic,  lum- 
bar and  sacral  nerves,  in  the 
shape  of  small  fasciculi  of 
medullated  fibres,  called  the 
ichitc  raini  communicantes. 
These  are  destined  for  the 
various  structures  of  the 
splanchnic  area  and  consti- 
tute the  visceral  or  splanch- 
nic distribution  of  the  spinal 
nerves.  The  remainder  of 
the  fibres  are  supplied  to 
the  body  wall  and  ex- 
tremities and  constitute  the 
somatic  distribution  of  the 
nerves. 

In  the  case  of  the 
cervical,  first  and  some- 
times second  thoracic,  lum- 
bar, sacral  and  coccygeal 


Diagram  illustrating  constitution  and  division  of  typical  spinal  nerve; 
SC,  spinal  cord ;  AR,  PR,  anterior  and  posterior  roots ;  SG,  spinal  gang- 
lion; CT,  common  trunk;  AD,  PD,  anterior  and  posterior  primary  divis- 
ions; PC,  LC,  AC,  posterior,  lateral  and  anterior  cutaneous  branches; 
RC,  ramus  communicans ;  Sy,  sympathetic  ganglion  and  cord. 


nerves,  plexuses  of  a  greater 
or  less  degree  of  intricacy 
are  interposed  between  the 
origin  and  distribution  of 
the  nerves.  This  renders  the  tracing  of  any  set  of  fibres  a  matter  of  extreme  difficulty, 
but  in  the  greater  portion  of  the  thoracic  region  the  original  segmental  and  less 
complex  arrangement  persists. 

A  typical  spinal  nerve  (Fig.  1085),  such  as  one  of  those  in  the  mid-thoracic 
region,  is  arranged  as  follows.  The  constitution  of  the  main  trunk  (page  u-S)  and 
the  distribution  of  its  posterior  branch  (page  1279)  have  already  been  described. 
The  anterior  primary  division  <  r.  anterior)  leaves  the  intervertebral  foramen  and 
almost  immediately  is  connected  with  the  gangliated  cord  by  gray  and  white  raini 
communicantes.  It  then  enters  an  intercostal  spare  through  which  it  courses 
between  the  external  and  internal  intercostal  muscles,  both  of  which  it  supplies.  At 
the  side  of  the  chest  it  gives  off  a  lateral  cutaneous  branch  ( r.  cutauciis  lateral^), 
which  distributes  a  few  tiny  motor  t \\igs  and  then  pierces  the  external  intercostal 
muscle  to  supply  the  skin  over  the  lateral  portion  of  the  trunk.  On  reaching 
the  superficial  fascia  it  usually  breaks  up  into  two  branches,  a  larger  anterior  (  r. 
anterior)  and  a  smaller  -posterior  \  r.  posterior).  Having  given  off  the  lateral 
cutaneous  branch,  the  main  anterior  primary  division  continues  its  forward  conr>e 
nearly  to  the  mid-line,  where  it  pierces  the  muscle  and  becomes  superficial  as  the 
anterior  terminal  cutaneous  branch  (  r.  cutanens  anterior). 


THE   CERVICAL   PLEXUS. 


1285 


FIG.  1086. 


1C. 


The  integument  is  therefore  supplied,  from  dorsal  to  ventral  mid- line,  by  the 
posterior  primary  division,  the  posterior  and  anterior  divisions  of  the  lateral 
cutaneous  branch  and  the  anterior  cutaneous  branch  of  the  anterior  primary 
division.  The  muscles  derive  their  nerve-supply  from  both  the  anterior  and  the 
posterior  primary  divisions. 

THE   CERVICAL   NERVES. 

The  anterior  primary  divisions  (IT.  anteriores)  of  the  eight  cervical  nerves  (nn. 
ccrvicales),  assisted  by  the  first  and  second  thoracic,  supply  the  head,  neck,  upper 
extremity,  thoracic  integument  and  diaphragm.  The  first,  second,  third  and 
fourth  communicate  freely  and  form  the  cervical  plexus  for  the  supply  of  the  head 
and  neck  and  the  skin  of  the  upper  pectoral  and  shoulder  regions,  whilst  the  fifth, 
sixth,  seventh,  and  eighth,  aided  by  the  first  and  sometimes  by  the  second  thoracic, 
form  the  brachial  plexus,  which  supplies  the  upper  extremity  and  the  lateral 
thoracic  wall. 

THE  CERVICAL  PLEXUS. 

The  cervical  plexus  (plexus  cervicalis  )  is  formed  by  the  union  of  the  anterior 
primary  divisions  (rr.  anteriores)  of  the  upper  four  cervical  nerves  (Fig.  1086). 
After  traversing  the 
intervertebral  foramina, 
they  pass  behind  the 
vertebral  artery  and 
emerge,  the  first  be- 
tween the  rectus  capitis 
lateralis  and  the  rectus 
capitis  anticus  minor 
muscles,  and  the  others 
first  between  the  inter- 
transversales  muscles 
and  then  between  the 
rectus  capitis  anticus 
major  and  scalenus  me- 
dius  muscles.  Each  is 
joined  by  a  gray  ram  us 
communicans,  derived 
either  from  the  superior 
cervical  ganglion  of  the 
sympathetic  or  from 
the  association  cord  be- 
tween the  superior  and 
middle  cervical  ganglia. 
Under  cover  of  the 
sterno-mastoid  the  four 
nerves  are  connected  to 
form  the  cervical  plexus. 
The  second,  third  and 
fourth  each  divide  into 
an  ascending  and  a 
descending  branch  ;  the 
first  does  not  divide. 
These  branches  are  connected  in  an  irregular  series  of  loops  that  constitute  the 
cervical  plexus,  which  lies  opposite  the  first  four  cervical  vertebrae  and  upon  the  sca- 
lenus medius  and  levator  anguli  scapula;  muscles,  and  is  covered  by  the  sterno-mastoid. 

Branches. — The  branches  of  the  plexus  may  be  divided  into  a  superficial  and  a 
deep  set.  The  former  reach  the  under  surface  of  the  deep  fascia  at  about  the  middle 
of  the  posterior  margin  of  the  sterno-mastoid  and  are  distributed  to  the  integument 
of  the  head,  neck,  shoulder  and  upper  pectoral  region.  The  latter  are  divided  into 
an  internal  and  an  external  group,  some  of  which  supply  the  muscles  of  the  neck 


Diagram  illustrating  plan  of  cervical  plexus. 


1286  HUMAN   ANATOMY. 

and  the  diaphragm,  whilst  others  communicate  with  the  ninth,  eleventh  and  twelfth 
cranial  and  the  sympathetic  nerves. 

THE  CERVICAL  PLEXUS. 

I.     Superficial  Branches.  II.     Deep  Branches. 

A.  Ascending-  branches  :  D.      External  branches  : 

1.  Small  occipital  7.      Muscular 

2.  Great  auricular  8.     Communicating 

B.  Transverse  branch  :  E.      Internal  branches  : 

3.  Superficial  cervical  9.      Muscular 

C.  Descending  branches  :  10.    Phrenic 

4.  Suprasternal  n.   Communicating 

5.  Supraclavicular 

6.  Supraacromial 

i.  The  superficial  branches  are  purely  sensory.  They  become  superficial 
at  the  posterior  border  of  the  sterno-mastoid,  slightly  above  its  middle,  and  from  that 
point  radiate  in  all  directions  to  reach  their  cutaneous  destinations  (Fig.  1087). 

1.  The  small  occipital  nerve  (n.  occipitalis  minor)  (Fig.  1087)  may  be  either 
single  or  double.      It  originates  from  the  second  and  third  cervical  nerves,  or  from 
the  second  only,  and  passes  backward  and  upward  beneath  the  deep  fascia  along  or 
overlapping  the  posterior  border  of  the  sterno-mastoid  muscle,  where  it  gives  off  (a) 
the  cervical  branches.      It  pierces  the  deep  fascia  at  the  upper  angle  of  the  occipital 
triangle  and  breaks  up  into  its  terminal  branches  :   (^)  the  auricular,  (c)  the  mastoid 
and  (d)  the  occipital. 

a^  The  cervical  branches  are  tiny  twigs  which  supply  the  skin  over  the  upper  part  of  the 
occipital  triangle. 

b.  The  auricular  branch  supplies  the  integument  over  the  cranial  aspect  of  the  posterior 
part  of  the  pinna. 

c.  The  mastoid  branch  supplies  the  scalp  overlying  and  above  the  mastoid  process. 

d.  The  occipital  branch  is  distributed  to  the  area  of  scalp  of  the  occiput  lying  between  the 
mastoid  process  and  the  distribution  of  the  great  occipital  nerve. 

The  small  occipital  communicates  with  the  posterior  and  great  auricular  nerves  and  with 
the  great  occipital. 

Variations. — The  small  occipital  varies  in  size  and  may  be  so  small  as  to  be  distributed 
only  to  the  integument  in  the  neck.  In  such  an  event,  and  usually  in  case  of  any  deficiency, 
the  unsupplied  area  receives  fibres  from  the  great  occipital.  It  sometimes  passes  backward 
instead  of  upward  and  pierces  the  trapezius  near  the  upper  border  before  reaching  the  scalp. 

2.  The  great  auricular  nerve  (n.  auricularis  magnus)  (Fig.  1087)  is  the  larg- 
est of  the  superficial  set  and  arises,  usually  with  the  superficial  cervical  nerve,  from 
the  second  and  third,  from  the  third  alone,  or  from  the  third  and  fourth  cervical 
nerves.     Turning  over  the  posterior  margin  of  the  sterno-mastoid  it  ascends  toward 
the  ear  between  the  platysma  and  the  deep  fascia.      Below  the  ear  it  gives  off  a  few 
(a}  facial  twigs  and  then  terminates  by  dividing  into  (£)  auricular  and  {c}  mastoid 
branches. 

a.  The  facial  twigs  pass  through  the  parotid  gland  and  over  the  angle  of  the  mandible, 
supplying  the  integument  over  the  parotid  gland  and  masseter  muscle  and  communicating  with 
the  cervico-facial  division  of  the  seventh  cranial  nerve. 

b.  The  auricular  branches  (r.  ••interior)  supply  mainly  the  cranial  surface  of  the  posterior 
part  of  the  pinna.     One  filament  passes  through  the  cartilage  by  means  of  a  cleft  between  the 
concha  and  the  antihelix  and  supplies  the  outer  surface,  while  a  few  twigs  are  distributed  to  the 
outer  surface  of  the  lobule.    The  auricular  branches  inosculate  with  the  small  occipital  and  pos- 
terior auricular  nerves.  • 

c.  The  mastoid  branch  (  r.  posterior)  is  distributed  to  the  skin  overlying  the  mastoid  process 
and  the  upper  part  of  the  sterno-mastoid  muscle.     It  inosculates  as  does  the  auricular  branch. 

Variation. — The  mastoid  branch  may  arise  independently  from  the  plexus  and  pass  upward 
to  its  destination  between  the  small  occipital  and  great  auricular  nerves. 


THE   CERVICAL    PLEXUS. 


1287 


<*  The  superficial  cervical  nerve  (n.  cutancus  colli)  usually  arises  m  com- 
mon  with  the  great  auricular  from  the  second  and  third,  the  third  only,  or  from  the 
third  and  fourth  cervical  nerves  (Fig.  1087).  From  the  posterior  margin  of  the  sterno- 
mastoid  it  passes  almost  directly  forward  over  the  middle  of  that  muscle  and 

FIG.  1087. 


Temporal  branch  of  facial 


Occipital  branch  of 
great  auricular 


Great  occipital  nerv 

Posterior  auricular  nerve 
Small  occipital  nerve 

Branch  of  communication  with  facial 

Cutaneous  branch  of  III.  cervical 

Great  auricular  nerve 


Communication  between 
spinal  accessory 


Supraacromial  branch 
Supraclavicular  branch 


Spinal  accessory  nerve 


Supraorbital  nerve 

Supratrochlear 
nerve 

Malar  branch  of 
facial  nerve 


Infraorbital 
nerve 


—  Infraorbital 

branch  of  facial 


Buccal  branch 

of  facial 
Communication  with 

buccal  branch  of 

mandibular 
Supramandibular 

branch  of  facial 


Inframandibular  branch 
of  facial 


perficial  cervical  nerve 


Superficial  descending  branch 
Suprasternal  branch 


Dissection  showing  superficial  branches  of  cervical  plexus,  as  well  as  parts  of  trigeminal,  facial,  spinal 
accessory  and  great  occipital  nerves  ;  ear  has  been  drawn  lorwara. 

the  platysma  myoides  and  the  external  jugular  vein.  It  perforates  the  deep  cervical 
fascia  near  the  anterior  border  of  the  sterno-mastoid  and  divides  into  O)  an  upper 
and  (£)  a  lower  set  of  branches. 

a.  The  upper  branches  (rr.  superiores)  form  an  extensive  inosculation  with  the  inframandib- 
ular  branch  of  the  facial  nerve,  after  which  they  pierce  the  platysma  and  supply  the  integument 
of  the  neck  as  far  forward  as  the  median  line  and  as  far  up  as  the  inferior  margin  of  the  mandit 

b.  The  lower  branches  ( rr.  inferiores )  after  piercing  the  platysma  are  distributed  to  the  skm 
of  the  lower  part  of  the  neck  to  the  mid-line  as  far  down  as  the  sternum. 


1288 


HUMAN    ANATOMY. 


Variation. — The  superficial  cervical,  instead  of  a  single  nerve,  may  arise  as  two  or  more 
filaments  from  the  cervical  plexus. 

The  descending  branches  (  nn.  stipraclavicularcs)  (Fig.  1089)  arise  from  the 
third  and  fourth  cervical  nerves  and  pass  downward  in  the  anterior  margin  of  the 
occipital  triangle  along  the  posterior  edge  of  the  sterno-mastoid.  On  nearing  the 
clavicle  they  break  up  into  three  distinct  sets  :  (4)  the  suprasternal,  (5)  the  supra- 
clavicular  and  (6)  the  snpraacromial. 

FK;.   1088. 


Third  occipital  nerve 


Great  occipital  nerve — i 


Branch  from  III.  cervical, 
dorsal  division 


Branches  trom  IV 
vical,  dorsal  divi 


Inosculation  between  facial  nerve  and 
small  occipital  and  great  auricular 
ni-rvcs 


Sterno-cleido-mastoid  muscle 

Great  auricular  nerve 

Small  occipital  nerve 

Superficial  cervical  nerve 


perficial  descending  branch  of  cervical  plexus; 
"  leader  crosses  the  suprasternal  branch 

nal  accessory  nerve 

scular  branch  to  trapezius 

araclavicular  branches 

Supraacroinial  branches 


Dissection  showing  superficial  branches  of  cervical  plexus  and  posterior  cutaneous  branches. 

4.  The   suprasternal    branches    (rr.   supraclaviculares    anteriores)   are    the 
smallest.     They  pass  over  the  lower  end  of  the  sterno-mastoid  and  the  inner  end  of 
the  clavicle  and  supply  the  skin  of  the  chest  as  far  down  as  the  angulus  Ludovici. 
One  or  two  filaments  terminate  in  the  sterno-clavicular  articulation. 

5.  The  supraclavicular  branches  (rr.  supraclaviculares  mcdii)    pass  across 
the  middle  of  the  clavicle  and  supply  the  integument  of  the  chest  as  far  down  as  the 
third  or  fourth  rib,  inosculating  with  twigs  from  the  anterior  cutaneous  branches  of 
the  upper  thoracic  nerves. 


Variation. — A  twig  may  perforate  the  clavicle. 


THE   CERVICAL    PLEXUS. 


1289 


6.  The  supraacromial  branches  ( rr.  supraclaviculares  posterities)  cross  the 
clavicular  insertion  of  the  trapezius  and  are  distributed  to  the  skin  over  the  anterior, 
external  and  posterior  aspects  of  the  shoulder  as  far  down  as  the  lower  portion  of  the 
deltoid. 

II.  The  deep  branches  are  divided  into  two  sets,  an  external  and  an  internal. 
Both  arising  beneath  the  sterno-mastoid,  the  former  pass  away  from  and  the  latter 
toward  the  median  line  of  the  neck. 

7.  The  external  muscular  branches  are  distributed  as  follows:— 

a.  The  sterno-mastoid  receives  a  branch  from  the  second  cervical  which  enters  the  deep 
surface  of  the  muscle  and  interlaces  with  a  branch  of  the  spinal  accessory  nerve  to  form  the 
sterno-mastoid  plexus. 

FIG.  1089. 


V.  cervical  nerve,  dorsal  division 
Ext.  brs.  dorsal  division  VI.  cervical  n 

VI.  cervical  nerve,  dorsal  division 


Small  occipit 
Complexi 

Muscular  brs.  to   complexus  and 
biventer  from  occip.  major 

Third  occipital  nerve 

Fascial  septum  from  ligamentum  nucha; 

Great  occipital  nerve 

Rectus  capitis  posticus  majc. 

Branch  toobliquusinferinr 
Spine  of  II.  cervical  vertebra 
Cutaneous  br.  from  III.  cervical- 
Part  of  complexus  and  biventer— 
Third  occipital  ner— -~ 

Branch  to  complexus  from  II.  cervi 

Branch  to  complexus  from  III.  cervical 
Part  of  splenius 


Cutaneous  brs.  from  IV.  cerv 
"Internal  br.  dorsal  division  of  VI.  cervical  ne 

VII.  cervical,  dorsal  division 
VIII.  cervical,  dorsal  division- 
Internal  branch  of  post.  div.  of  V.  cervical  ner 

Spinous  process  of  VII.  cervical  vertebra 


Obliquus  superior 
Transverse  process  of  atlas 
Ant.  division  I.  cervical,  cutaneous 
"br.  of  dorsal  div.  passing  backward 
"Obliquus  inferior 
'II.  cervical  nerve,  dorsal  division 

Levator  anguli  scapulae 

~ : — : - —  ...  .  . Branch  to  tr.:c!ielo-mastoid 

III.  cervical  nerve,  dorsal  division 

Communication  between  II.  and  I II.  dorsal  divisions 

External  brs.  oflll.  cervical,  dorsal  division 

'IV.  cervical  nerve,  dorsal  division 

Ext.  branch  of  dorsal  division  V.  cervical  nerve 


Transverse  process  I .  thoracic  vetebra 

Transverse  process  II.  thoracic  vertebra 

Levator  anguli  scapula; 

Trapezius 


Dissection  of  right  side  of  neck,  showing  deeper  relations  of  cervical  nerves. 


f>.  The  trapezius  receives  fibres  from  the  third  and  fourth  cervical  nerves  which  arise  with 
and  accompany  the  descending  branches  of  the  superficial  set  through  the  occipital  triangle. 
They  dip  under  the  anterior  margin  of  the  trapezius,  before  and  after  which  they  form  a  more 
or  less  complex  inosculation  with  the  spinal  accessory,  called  the  subtrapezial  plexus,  from 
which  filaments  are  distributed  to  the  trapezius  muscle  (Fig.  1088). 

c.  The  levator  anguli  scapulae  receives  two  branches  which  take  their  origin  from  the  third 
and  fourth  nerves. 

d.  The  scalenus  medius  and  (e)  scalenus  posticus  also  receive  fibres  from  the  third  and 
fourth. 

8.  The  communicating  branches  form  points  of  contact  and  union  with 
the  spinal  accessory  nerve  (#)  under  the  sterno-mastoid  and  (£)  in  the  occipital 
triangle  and  under  the  trapezius.  By  means  of  these  inosculations  are  formed  the 
sterno-mastoid  and  subtrapezial  plexuses. 


1290  HUMAN   ANATOMY. 

9.  The  muscular  branches  are  distributed  to  (a)  certain  prevertebral  muscles 
and  to  (<5)  the  genio-hyoid  and  the  infrahyoid  muscles. 

a.  The  rectus  capitis  anticus  major  and  minor  and  the  rectus  capitis  lateralis  are  supplied 
by  a  filament  arising  from  the  loop  between  the  first  and  second  cervical  nerves.    The  intertrans- 
versales,  the  longus  colli  and  a  portion  of  the  rectus  capitis  anticus  major  receive  their  supply 
from  the  second,  third  and  fourth,  and  the  upper  part  of  the  scalenus  anticus  receives  a  twig 
from  the  fourth  cervical  nerve. 

b.  The  genio-hyoid  and  the  four  muscles  of  the  infrahyoid  group  are  innervated  by  the 
cervical  plexus  in  a  rather  roundabout  manner.     From  the  first  and  second  cervical  nerves  are 
given  off  one  or  more  branches  which  join  the  hypoglossal  nerve  shortly  after  its  appearance  in 
the  neck.     These  fibres  for  a  time  form  an  integral  portion  of  the  hypoglossal  and  eventually 
escape  from  it  as  the  nerve  to  the  genio-hyoid,  the  nerve  to  the  thyro-hyoid  and  the  n.  descen- 
dens    hypoglossi  (Fig.   1082).     The  last-mentioned  nerve  leaves  the  hypoglossal  at  the  point 
where  the  latter  crosses  the  internal  carotid  artery  and  then  descends  in  the  anterior  cervical 
triangle.     In  front  of,  or  sometimes  within,  the  carotid  sheath  it  forms  a  loop  of  communication, 
called  the  hypoglossal   loop   or   ansa   cervicalis    (ansa   hypoglossi)    by   inosculation   with   the 
descending  cervical  nerve  (n.  descendens  cervicalis)  (Fig.  1082).     This  descending  cervical  nerve 
is  derived  from  the  second  and  third  cervical  nerves  and  at  first  consists  of  two  twigs  which  later 
unite  in  front  of  the  internal  jugular  vein.     From  this  point  it  passes  downward  and  inward  as  a 
single  trunk  to  reach  its  point  of  entrance  into  the  ansa  hypoglossi.     The  ansa  may  be  either  a 
simple  loop  or  a  plexus  and  is  situated  anterior  to  the  carotid  sheath  at  a  variable  point  in  the 
neck.     From  it  branches  are  given  off  to  the  sterno-hyoid,  the  sterno-thyroid  and  the  posterior 
belly  of  the  omo-hyoid  (Fig.  1076). 

10.  The  phrenic  nerve  (n.  phrenicus),  although  an  internal  muscular  branch 
of  the  cervical  plexus,   is   of  such   importance  as  to  merit  a  separate  description. 
Whilst  mainly  the  motor  nerve  to  the  diaphragm,  it  contains  some  sensory  fibres  ;  in 
this  connection  it  may  be  pointed  out  that  the  phrenic  is  not  the  only  motor  nerve 
to  the  diaphragm,  the  lower  thoracic  nerves  aiding  in  its  innervation.     The  phrenic 
arises  mainly  from  the  fourth  cervical  nerve  but  receives  additional  fibres  from  the 
third  and  fifth  (Fig.  1090).     It  passes  down  the  neck  on  the  scalenus  anticus,  which 
it  crosses  from  without  inward,  and  at  the  base  of  the  neck  accompanies  that  muscle 
between  the  subclavian  artery  and  vein.     At  the  entrance  to  the  thorax  it  passes 
over  the  root  of  the  internal  mammary  artery  from  without  inward  and  backward^ 
occupying  a  position  behind  the  sterno-clavicular  articulation  and  the  point  of  junc- 
tion of  the  subclavian  and  internal  jugular  veins.      It  then  follows  a  course  almost 
vertically  downward,   over  the  apex  of  the  pleura  and  through  the  superior  and 
middle  mediastina,  to  the  upper  surface  of  the  diaphragm. 

The  right  phrenic  (Fig.  1090)  is  shorter  than  the  left  on  account  of  its 
more  direct  downward  course  and  the  greater  elevation  of  the  diaphragm  on 
that  side.  It  crosses  the  second  part  of  the  subclavian  artery  and  accompanies 
the  right  innominate  vein  and  the  superior  vena  cava  on  their  lateral  aspect. 
It  then  passes  in  front  of  the  root  of  the  lung  and  finishes  its  course  by  de- 
scending between  the  lateral  aspect  of  the  pericardium  and  the  mrdiastinal  pleura. 
Nearing  the  diaphragm  it  breaks  up  at  the  antero-lateral  aspect  of  the  quadrate 
foramen  into  its  terminal  branches,  a  few  of  which  enter  the  abdomen  through 
this  opening. 

The  left  phrenic  (Fig.  1090),  having  to  wind  around  the  left  side  of  the 
heart  and  reach  the  more  inferior  half  of  the  diaphragm,  is  longer  than  its  fellow, 
about  one-seventh  longer  (Luschka).  Entering  the  thorax  between  the  subclavian 
artery  and  the  left  innominate  vein  it  crosses  the  anterior  face  of  the  left  vagus  nerve 
and  continues  its  downward  course  by  passing  over  the  left  side  of  the  aortic  arch. 
Reaching  the  middle  mediastinum  it  courses  in  front  of  the  root  of  the  lung,  behind 
the  lower  left  angle  of  the  pericardium,  and  descends  to  the  diaphragm  between  the 
pericardium  and  the  mcdiastinal  pleura.  It  breaks  up  into  its  terminal  branches 
before  arriving  at  the  thoracic  surface  of  the  diaphragm,  which  it  enters  at  a  point 
further  from  the  median  line  and  more  anterior  than  dors  the  right. 

Branches  of  the  phrenic  nerve  are  :  (a)  the  pleural,(b}  the  pcricardiac  and 
(f)  the  terminal. 


H 


THE   CERVICAL    PLEXUS. 


1291 


a.  The  pleural  branches,  two  in  number,  are  almost  microscopic  in  size,  and  are  given 
off  as  the  nerve  crosses  the  apex  of  the  pleura.     One  supplies  the  costal  pleura  and  the  other, 
which  sometimes  accompanies  the  internal  mammary    artery,   is  distributed  to  the   medias- 
tinal  pleura. 

b.  The  pericardiac  branch   (r.  pericardiacus)   is  a  tiny  filament  which  is  usually  given  off 
opposite  the  lower  margin  of  the  third  costal  cartilage.     It  is  sometimes  absent  on  the  left  side. 

c.  The  terminal  branches  arise  under  cover  of  the  pleura  and  differ  to  some  extent  on 
the  two  sides. 

The  right  phrenic  divides  antero-lateral  to  the  opening  for  the  inferior  vena  cava  into  (aa) 
an  anterior  and  (bb)  a  posterior  branch. 

aa.  The  anterior  branch  breaks  up  under  the  pleura  into  five  or  six  fine  twigs,  which  spread 
out  antero-laterally  in  the  sternal  portion  and  the  anterior  part  of  the  right  costal  portion  of  the 

FIG.   1090. 


Scaletius  medius  muscle 
Vagus  nerve 
V.  cervical  nerve 
Scaletius  atiticus  muscle 
Upper  trunk  of  brachial  plexus 
VII.  cervical  nerve 
Superior  intercostal  arte 
VIII.  cervical  nerve 
I.  thoracic  nerve 
Clavicle 

Phrenic  nerve 

Internal  mam- 
mary artery 


Innominate  veins 

Vena  cava  superior 

I.ung,  mesial  surface 


Pericardium 


Sterno-cleido-mastoid 
Vagus  nerve 
Internal  jugular  vein 
Subclavian  artery 
Omo-hyoid  muscle 
Subclavian  vein 
Clavicle 

Subclavius  r 


Lung,  mesial  surface. 
Showing  hiluin 


IV.  rib 


Diaphragm,  up- 
per surface 

VII.  rib 


Dissection  showing  phrenic  nerves ;  parts  of  sternum  and  ribs  have  been  removed  ;  lungs  are  pulled  aside ; 

pericardium  is  undisturbed. 

diaphragmatic  musculature.  Tiny  filaments  traverse  the  interval  between  the  sternal  and  costal 
portions  and  enter  the  abdomen,  where  they  are  distributed  to  the  peritoneal  covering  of  the 
diaphragm  and  to  the  falciform  ligament  of  the  liver  in  the  direction  of  the  umbilicus. 

bb.  The  posterior  branch  pierces  the  central  tendon  at  the  outer  margin  of  the  quadrate 
opening  and  divides  into  a  muscular  branch  and  the  right/// rt 'iiico-abdoin inal  branch  (r.  phrenico- 
abdominalis  dexter).  The  former  supplies  the  lumbar  portion  of  the  musculature  of  the  diaphragm. 
The  latter  traverses  the  quadrate  foramen  and  first  gives  off  a  recurrent  branch  which  accompanies 
the  inferior  vena  cava  back  to  the  right  auricle.  After  giving  off  this  branch,  under  cover  of  the 
peritoneum  some  of  its  fibres  enter  the  diaphragmatic  ganglion  and  others  unite  with  filaments 
from  the  cceliac  plexus  to  form  at  the  inferior  surface  of  the  diaghragm  the  diaphragmatic 
plexus,  which  is  joined  by  twigs  from  the  diaphragmatic  ganglion.  From  this  plexus  fibres 
are  distributed  to  the  coronary  ligament  and  peritoneum  of  the  liver  and  to  the  right  supra- 
renal body. 

The  left  phrenic  pursues  a  general  antero-lateral  course  and  pierces  the  diaphragm  at  the 
junction  between  the  musculature  and  the  central  tendon.  Under  cover  of  the  peritoneum  it 
splits  up  into  an  anterior,  a  lateral  and  a  posterior  branch.  The  anterior  branch  supplies  the 
muscle  of  the  left  sternal  portion  and  the  antero-lateral  part  of  the  left  costal  portion.  The 


i292  HUMAN   ANATOMY. 

lateral  branch  supplies  the  corresponding  part  of  the  left  costal  portion.  The  posterior  branch 
(r.  phrenicoabdominalis  sinister)  is  distributed  to  the  left  lumbar  portion  of  the  muscle  of  the 
diaphragm  and  usually  either  a  filament  passes  to  the  left  semilunar  ganglion  or  several  small 
threads  to  the  ca-liac  plexus,  one  of  which  can  be  traced  to  the  left  suprarenal  budy. 

The  phrenic  nerve  communicates  in  the  lower  part  of  the  neck  with  the  middle  or  inferior 
cervical  ganglion  of  the  sympathetic.  At  the  inferior  aspect  of  the  diaphragm  it  communicates, 
on  the  right  side,  with  the  diaphragmatic  plexus  of  the  sympathetic  and,  on  the  left  side,  with 
the  semilunar  ganglion  or  the  cceliac  plexus. 

Variations. — The  phrenic  may  receive  additional  roots  from  the  nerve  to  the  subclavius, 
the  nerve  to  the  sterno-hyoid,  the  second  or  the  sixth  cervical  nerve,  the  n.  descendens  cervi- 
calis  or  the  ansa  hypoglossi.  It  may  arise  exclusively  from  the  nerve  to  the  subclavius  or,  aris- 
ing normally,  may  give  a  branch  to  that  muscle.  It  sometimes  passes  along  the  lateral  border 
of  or  pierces  the  scalenus  anticus  muscle.  Instead  of  descending  behind  the  subclavian  vein  it 
may  pass  anterior  to  it  or  even  through  a  foramen  in  it. 

The  accessory  phrenic  nerve  arises  either  from  the  fifth  alone  or  from  the  fifth  and  sixth 
cervical  nerves  and,  entering  the  thorax  either  anterior  or  posterior  to  the  subclavian  vein, 
joins  the  phrenic  at  the  base  of  the  neck  or  in  the  thorax. 

II.  The  communicating  branches  of  the  internal  set  effect  unions  with  (a)  the  sympathetic, 
(6)  the  vagus  and  (c )  the  hypoglossal. 

a.  The  superior  cervical  ganglion  of  the  sympathetic  or  the  association  cord  connecting 
the  superior  and  middle  ganglia  sends  gray  rami  communicates  to  the  first,  second,  third  and 
fourth  cervical  nerves. 

b.  The  ganglion  of  the  trunk  of  the  vagus  is  sometimes  connected  by  means  of  a  tiny 
nerve  with  the  loop  between  the  first  and  second  cervical  nerves 

c.  The  hypoglossal  nerve  receives,  just  below  the  anterior  condyloid  foramen,  a  good 
sized  branch  from  the  loop  between  the  first  and  second  cervical  nerves.     This  communication 
furnishes  sensory  fibres  to  the  hypoglossal  nerve  which  subsequently  leaves  the  latter  as  its  men- 
ingeal  branch  ;  other  spinal  fibres  leave  the  twelfth  as  the  n. descendens  hypoglossi  and  as  the 
nerves  to  the  genio-hyoid  and  thyro-hyoid  muscles. 

Practical  Considerations. — Of  the  motor  ncrrcs  of  the  cervical  plexus  the 
phrenic  is  most  commonly  the  seat  of  trouble  and  this  may  result  in  or  be  associated 
with  spasm  or  paralysis  of  the  diaphragm.  The  involvement  of  the  diaphragm  may 
be  part  of  a  progressive  muscular  paralysis,  as  from  lead  poisoning,  or  from  injuries 
or  diseases  of  the  spine.  The  nerve  may  be  compressed  by  tumors  or  abscesses  of 
the  neck,  or  be  injured  in  wounds  of  the  neck.  It  passes  downward  under  the  sterno- 
mastoid  muscle  and  on  the  scalenus  anticus,  from  about  the  level  of  the  hyoid  bone. 
It  is  covered  and  somewhat  fixed  by  the  layer  of  deep  fascia  covering  the  scalenus 
anticus  muscle.  The  clonic  variety  of  spasm,  singultus  or  hiccough,  is  very  common, 
and  is  occasionally  though  rarely  dangerous  by  preventing  rest  and  sleep  ;  it  may 
complicate  apoplexy,  peritonitis  or  chronic  gastric  catarrh. 

If  only  one  phrenic  is  paralyzed  the  disturbance  of  function  is  slight  and  not 
easily  recognized.  In  a  bilateral  paralysis,  as  from  alcoholic  neuritis,  respiration 
depends  almost  entirely  on  the  intercostal  muscles,  since  the  diaphragm  is  completely 
paralyzed.  Dyspnoea,  therefore,  occurs  on  slight  exertion.  The  epigastrium  is 
depressed  rather  than  prominent  and  the  lower  border  of  the  liver  is  drawn  upward. 

The  superficial  branches  of  the  cervical  plexus  emerge  together  through  the  deep 
fascia  near  the  middle  of  the  posterior  border  of  the  sterno-mastoid  muscle,  and  from 
this  point  pass  in  various  directions.  The  auricularis  magnus  passes  upward  and 
forward  over  the  sterno-mastoid  to  the  ear  and  parotid  gland,  the  occipitalis  minor 
along  the  posterior  margin  of  the  same  muscle  to  the  scalp,  and  the  superficial 
cervical  branch  obliquely  forward  and  upward  to  the  submaxillary  region.  The 
descending  branches  are  three  in  number  and  puss  respectively  in  the  direction  of 
the  sternum,  clavicle  and  acromion.  They  give  rise  to  little  or  no  disturbance 
when  wounded. 

THE  BRACHIAL  PLEXUS. 

The  brachial  plexus  (plexus  brachialis)  is  a  somewhat  intricate  interlacement  of 
the  anterior  primary  divisions  of  usually  the  lower  four  cervical  and  first  thoracic- 
nerves.  To  these  are  sometimes  added  a  branch  from  the  fourth  cervical,  a  branch 
from  the  second  thoracic,  or  branches  from  both  of  these  nerves.  The  fasciculi  form- 


THE   BRACHIAL   PLEXUS. 


1293 


ing  tliis  plexus  emerge  in  the  interval  between  the  scalenus  anticus  and  medius  and 
from  the  side  of  the  neck  pass  beneath  the  clavicle  and  into  the  axilla  through  its  apex. 
The  plexus  is  divided,  therefore,  into  two  portions,  a  cervical  or  supraclavicular  part 
(pars  supraclavicularis)  and  an  axillary  or  infraclai'icular\)Wi\.  (pars  infraclavicularis). 
In  the  posterior  cervical  triangle  the  plexus  lies  first  above  and  then  to  the  outer  side 
of  the  subclavian  artery  and  vein,  is  crossed  by  the  posterior  belly  of  the  omo-hyoid 
muscle  and  is  frequently  threaded  by  the  transverse  cervical  or  the  posterior  scapu- 
lar artery.  After  entering  the  axilla  its  component  parts,  while  lying  mainly  to  the 
outer  side,  form  a  close  fasces  around  the  axillary  artery,  whose  sheath  they  occupy. 
In  the  upper  part  of  the  axilla  the  plexus  is  overlain  by  the  subclavius  and  pectoralis 
major  muscles  and  before  dividing  into  its  terminal  branches  it  lies  enclosed  between 
the  pectoralis  minor  and  subscapularis  muscles. 

Constitution  and  Plan. — In  the  various  weavings  of  the  component  elements 
of  the  plexus  five  stages  can  be  recognized  :  («)  anterior  primary  divisions  of 
the  spinal  nerves,  (/>)  trunks,  (r)  divisions,  (a)  cords  and  (>)  terminal  branches 
(Fig.  1091). 

!•'!(.;.   1091. 


Diagram  illustrating  plan  of  brachial  plexus. 

Emerging  from  the  interval  between  the  anterior  and  middle  scalene  muscles, 
the  fifth  and  sixth  cervical  nerves  unite  to  form  the  outer  or  upper  trunk,  the 
seventh  alone  is  continued  into  the  middle  trunk,  whilst  the  eighth  cervical  and  first 
thoracic  fuse  to  form  the  inner  or  lower  trunk.  These  trunks  continue  undivided 
until  slightly  beyond  the  lateral  margin  of  the  scalenus  anticus,  each  one  then  sepa- 
rating into  an  anterior  and  a  posterior  division.  These  are  of  about  equal  size, 
with  the  exception  of  the  posterior  division  of  the  inner  trunk,  which  is  much  smaller 
than  the  others  because  the  first  thoracic  nerve  sends  few  if  any  fibres  to  the  posterior 
division.  The  six  divisions,  three  anterior  and  three  posterior,  unite  differently  to 
form  three  cords.  The  outer  cord  (fasciculus  lateralis)  is  the  bundle  formed  by  the 
union  of  the  anterior  divisions  of  the  outer  and  middle  trunks.  The  posterior  cord 
(fasciculus  posterior)  is  the  result  of  the  fusion  of  the  posterior  divisions  of  all  of  the 
trunks  and  the  inner  cord  (fasciculus  medialis)  is  the  continuation  of  only  the 
anterior  division  of  the  inner  trunk.  The  trunks  are  named  in  correspondence  with 


1294 

their  position  as  regards  one  another,  while  the  cords  are  denominated  according  to 
their  relation  to  the  axillary  artery,  the  outer  lying  lateral  to,  the  inner  mesial  to,  and 
the  posterior  behind,  the  artery. 

Variations. — Considerable  variety  exists  as  regards  the  length  of  the  component  nerve- 
bundles  in  their  several  portions,  division  and  union  caking  place  at  different  levels  in  different 
individuals.  The  fifth  cervical  nerve  may  pass  in  front  of  or  through  the  scalenus  anticus.  The 
sixth,  though  not  so  frequently  as  the  fifth,  may  traverse  the  scalenus  anticus.  The  seventh 
cervical  nerve,  as  the  middle  trunk,  may  break  up  into  three  branches,  one  going  to  each  of 
the  three  cords.  The  fibres  of  the  posterior  cord  may  arise  from  only  the  seventh  and  eighth, 
or  the  sixth,  seventh  and  eighth  cervical  nerves.  Plexuses  have  been  seen  in  which  only  two 
cords,  a  smaller  and  a  larger,  were  present,  the  latter  taking  the  place  of  either  the  inner  and 
outer  or  the  inner  and  posterior  cords. 

Communications. — The  five  nerves  comprising  the  source  of  the  plexus  are 
connected  to  the  sympathetic  system  by  gray  rami  communicantes  and  there  is 
possibly  a  white  ramus  communicans  passing  from  the  first  thoracic  nerve  to  the 
first  thoracic  ganglion  of  the  sympathetic. 


FIG.   1092. 


I.  cervical  nerv-- 
II.  cervical  nerve 

III.  cervical  nerve  — 

IV.  cervical  nerve 


Scalenus  inedius  m  iscle 


Median  nerve 
Ulna 


External  anterior  thoracic  j 

Su|>raca|>ularnerve 
Upper  subscapular  nerve 

Outer  cord  of  plexus 
Posterior  cord  of  plexus 
Circumflex  n 
Deltoid  muscle 


Musculo-cutaneoiis  nerve 


Musculo-spiral  nerve 
Internal  cutaneous  nerve       , 
Lesser  internal  cutaneous  nerve 


Internal  anterior 
thoracic  nerve 
Insertion  of 
soak-mis  anticus 
Posterior 
thoracic  nerve 

I.  rib 


Serratus  magnus, 
first  serration 


II.  rib 
Inner  cord  of  plexus 

'Middle  subscapular  nerve 
I.owi-r  Mibsoupular  nerve 


Deep  dissection  of  neck,  showing  constitution  of   right  brachial  plexus. 

Practical    Considerations. — Sensory   disturbances    are   rather    rare   in    the 
distribution  of  the  brachial  plexus  of  nerves,  but  motor  troubles  are  comparatively 
common,  and  are  sometimes  associated  with  disturbances  of  sensation, 
plexus,  or  only  an  individual  branch,  may  be  involved.     The  most  common  cause 
is  injury,  such  as  dislocation  of  tin-  head  of  the  humerus,  a  fracture  of  the  clavicle, 
or   a   forced    apposition    of    the    clavicle   to   the   first   rib.     Other   causes   are   the 
pressure    of   tumors    or   the   constitutional    effects  of   poisons  and   infections, 
plexus   is   so  superficial  above  the  clavicle   that  it   can  be   felt    or  even    seen    in 
thin  people. 

Branches.— These    fall   naturally   into   two   groups,    those   -iven   off    from   the 
sH/>nicf<t~'icnlar  and  those  from  the  infnularicitlar  portion  of  the  plexus. 


THE    BRACHIAL    PLEXUS.  1295 

I.  Supraclavicular  Branches 

1.  Suprascapular  4.      Muscular 

2.  Posterior  scapular  5.      Communicating  to  the  phrenic 

3.  Posterior  thoracic  nerve 

II.  Infraclavicular  Branches 

A.    From  Outer  Cord :  B.   From  Inner  Cord  : 

6.  External  anterior  thoracic  9.      Internal  anterior  thoracic 

7.  Musculo-cutaneous  10.    Lesser  internal  cutaneous 

8.  Median  (outer  head)  n.   Internal  cutaneous 

12.  Ulnar 

13.  Median  (inner  head) 

C.   From  Posterior  Cord  : 

14.  Subscapular 

15.  Circumflex 

1 6.  Musculo-spiral 

I.  The  Supraclavicular  Branches. — These  are  given  off  at  various  levels 
while  the  plexus  is  still  in  the  neck. 

1.  The  suprascapular  nerve   (n.  suprascapularis)    (Fig.    1092)   arises   from 
the  posterior  surface  of  the  outer  trunk,    most  of  its  fibres  coming  from  the  fifth 
cervical  nerve  and  the  remainder  from  the  sixth.      It  traverses  the  posterior  cervical 
triangle  above  the  upper  border  of  the  plexus  and  under  cover  of  the  omo-hyoid  and 
trapezius  muscles.      Reaching  the  superior  margin  of  the  scapula,  it  passes  through 
the  suprascapular  notch,  under  the  suprascapular  ligament,  and  enters  the  supra- 
spinous  fossa.     After  giving  off  a  branch  for  the  supply  of  the  supraspinatus  muscle 
and   a   tiny    filament   to   the   posterior   portion    of    the   capsular   ligament   of    the 
shoulder,   it  passes  through  the  great  scapular  notch  in  company  with  the  supra- 
scapular  artery  and  vein.      Having  become  an  occupant  of  the  infraspinous  fossa,  the 
nerve   supplies    the    infraspinatus    muscle   and    often   gives    off   a    branch    to    the 
shoulder  joint. 

Variations. — It  may  receive  additional  fibres  from  the  fourth  cervical  nerve  or  may  arise 
entirely  from  the  fifth.  A  rare  anomaly  is  the  giving  off  of  a  branch  to  the  teres  minor  or  to  the 
upper  part  of  the  subscapularis.  Twigs  to  the  scapula  and  its  periosteum  and  to  the  acromio- 
clavicular  articulation  have  been  described.  Division  into  two  parts  may  occur,  the  upper  part 
passing  through  the  notch  and  the  lower  through  a  bony  foramen  below  the  notch. 

2.  The    posterior    scapular    nerve    or   the   branch    to    the    rhomboid 
muscles  (n.  dorsalis  scapulae)   (Fig.   1082)  arises,  in  common  with  a  root  to  the 
posterior  thoracic  nerve,  from  the  dorsal  aspect  of  the  fifth  cervical  nerve.      After 
traversing  the  substance  of.  the  scalenus  medius,  it  passes  downward  and  backward 
toward  the  vertebral  border  of  the  scapula,  lying  upon   the   deep  surface  of  the 
levator  anguli  scapulae  and  the  rhomboidei.     It  supplies  a  filament  to  the  levator 
anguli  scapulae  and  occasionally  one  to  the  upper  digitation  of  the  serratus  posticus 
superior,  and  terminates  by  entering  the  substance  of  the  rhomboideus  major  and 
minor  muscles. 

Variation. — It  may  pierce  the  levator  anguli  scapulae. 

3.  The    posterior    thoracic    (n.    thoracalis    longus),    also    called    the    long 
thoracic  or  external  respiratory  nerve  of  Bell  arises  from  the  fifth,  sixth  and 
seventh  cervical  nerves,  the  largest  contribution  coming  from  the  sixth  (Fig.   1092). 
The  roots  from  the  fifth  and  sixth  nerves  pass  through  the  scalenus  medius  and  unite 
either  in  the  substance  of  that  muscle  or  as  they  reach  its  surface.     The  root  from  the 
seventh  nerve  passes  anterior  to  the  middle  scalene  muscle  and  unites  with  the  main 
trunk  at  about  the  level  of  the  first  rib.      Entering  the  axilla  the  nerve  descends  on 


1296 


HUMAN    ANATOMY. 


the  inner  wall,  lying  posterior  to  the  brachial  plexus  and  the  axillary  vessels,  and  upon 
the  lateral  aspect  of  the  serratus  magnus.  It  gives  off  successive  twigs  to  the  digita- 
tions  of  the  last-named  muscle,  which  alone  it  supplies.  The  fibres  derived  from  the 
fifth  cervical  nerve  supply  the  upper  part,  those  from  the  sixth  the  middle  and  those 
from  the  seventh  the  lower  part  of  the  muscle. 

Variations. — The  contribution  from  the  fifth  nerve  sometimes  fails  to  join  the  main  nerve 
and  goes  directly  to  its  distribution  to  the  upper  digitations.  The  root  from  the  seventh  nerve 
may  be  absent.  An  additional  root  may  be  contributed  by  the  eighth  cervical  nerve. 

Practical  Considerations. — The  posterior  thoracic  nerve  may  be  paralyzed 
by  an  injury  in  the  suprascapular  region  or  in  the  axilla,  by  carrying  heavy 
weights  upon  the  shoulder,  or  as  a  result  of  infectious  disease,  cold  or  rheu- 
matism. The  most  noticeable  sign  is  a  prominence  of  the  scapula  (winged  scapula), 
from  the  failure  of  the  paralyzed  serratus  magnus  muscle  to  hold  the  vertebral  border 
of  the  scapula  close  to  the  thorax.  That  border  and  the  inferior  angle  project  and 


FIG.   1093. 


Axillary  artery 
Int.  cutaneous  ner 


Pectoralis  minor,  stump 

Outer  cord  of  plexus 
Coraco-brachialis  ^     ;>^ 
Musculo-cutaneous  nerve  \^Xy 

Median  nerve -^    jX'jip 


Acromial  thoracic  artery 
Deltoid 


Cephalic  vein 


f)t,    '    —  Sterno-cleido-mastoid 

«!~    r.xt.  anterior  thoracic  nerve 

^—" Clavicle 

Axillary  vein 

lOsA     ~~~">-  Internal  anterior 
thoracic  nerve 


Less 

cuta 

Long  thoracic  artery 
Intercosto-humeral  nvs: 
Subscapular  artery 

Latissimus  dorsi 
Long  Subscapular  nerve 
Teres 

Posterior  thoracic  nerve 


Serratus  magnus 
Dissection  of  right  axilla,  showing  relations  of  brachial  plexus  to  blood-\ 


become  prominent.  When  the  arm  is  in  front  of  the  chest  the  deformity  is  most 
marked  and  the  lower  angle  approaches  the  mid-line  of  the  back.  The  patient  can- 
not lift  anything  heavy  with  the  affected  arm.  Since  the  incision  to  open  an  axillary 
abscess  is  made  vertically  in  the  middle  of  the  thoracic  wall  of  the  axillary  space,  to 
avoid  the  vessels  at  its  borders,  this  nerve  is  in  some  danger  as  it  passes  to  the 
serratus  magnus  muscle. 

4.  The  muscular  branches  supply  the  l<>ngus  colli,  the  sraleni  anticus, 
medius  and  posticus  and  the  subclavius. 

a.  The  longus  colli  and  scalenus  anticus  are  supplied  by  small  twigs  which  arise  from 
the  anterior  surface  of  the  lower  four  cervical  nerves  as  they  leave  the  vertebral  column. 

b.  The  scaleni  medius  and  posticus  receive  fibres  given  off  from  the  posterior  aspect  of 
the  lower  four  cervical  nerves  as  they  pass  through  the  intervertebral  foramina. 

r.  The  nerve  to  the  subclavius  (n.  snhckiviiis)  takes  its  origin  from  the  outer  trunk  of  the 
plexus,  its  fibres  coming  mainly  from  the  fifth  cervical  nerve.  It  passes  through  the  subclavian 
triangle,  over  the  third  portion  of  the  subclavian  artery  and  behind  the  clavicle,  to  enter  the 
deep  surface  of  the  subclavius  muscle. 


\r\ct- 


THE   BRACHIAL   PLEXUS. 


1297 


Variations. — The  phrenic  nerve  may  give  off  a  branch  to  the  subclavius  or  may  receive  a  fila- 
ment from  the  nerve  to  the  subclavius.  A  branch  of  communication  with  the  external  anterior 
thoracic  and  a  branch  to  the  clavicular  head  of  the  sterno-cleido-mastoid  have  been  noted. 

5.  The  communicating  branch  to  the  phrenic  nerve  (Fig.  1090)  arises 
usually  from  the  fifth  cervical  nerve,  sometimes  from  the  fifth  and  sixth.  Originating 
at  the  outer  margin  of  the  scalenus  anticus  it  passes  inward  and  joins  the  phrenic.  If 
.this  nerve  is  not  present  the  nerve  to  the  subclavius  usually  supplies  the  deficiency. 
II.  The  Infraclavicular  Branches. — These  branches  comprise  those  given 
off  by  the  three  cords  of  the  plexus  after  the  latter  has  passed  beneath  the  clavicle 
into  the  axilla. 

6.  THE  EXTERNAL  ANTERIOR  THORACIC  NERVE. 

The  external  anterior  thoracic  nerve  (n.  thoracalis  anterior  lateralis)  (Fig.  1093) 
receives  its  fibres  from  the  fifth,  sixth  and  seventh  cervical  nerves.  Leaving  the  outer 
cord  beneath  the  clavicle,  it  passes  mesially  over  the  axillary  artery  and,  after  giving 

FIG.  1094. 


a          ^ 
I          1 


Common 
carotid  artery 


Phrenic  nerve 


Scalenus 
'anticus  muscle 


Lesser  internal  cutaneous 

nerve 
Internal  cutaneous  nerve 


Duociavian  artery          Subclavian  vein 

Dissection  of  right  axilla,  showing  relation  of  brachial  plexus  to  subclavian  and  axillary  vessels 

with  arm  abducted. 

off  a  filament  which  unites  with  a  similar  structure  from  the  internal  anterior  thoracic 
nerve,  divides  into  two  branches  which  pierce  the  costo-coracoid  membrane  and  enter 
the  deep  surface  of  the  pectoralis  major.  The  upper  branch  supplies  the  clavicular 
portion  of  the  muscle  and  the  lower  branch  the  upper  part  of  the  sternal  portion. 

The  loop  between  the  anterior  thoracic  nerves  gives  off  a  filament  which  pierces 
the  pectoralis  minor  and  ends  in  the  sternal  part  of  the  pectoralis  major,  to  both  of 
which  muscles  it  is  distributed. 

Variations. — This  nerve  may  supply  fibres  to  the  clavicular  portion  of  the  deltoid  and  to  the 
acromio-clavicular  articulation. 

82 


1298  HUMAN   ANATOMY. 


7.    THE  MUSCULO-CUTANEOUS  NERVE. 

The  musculo-cutaneous  nerve  (n.  musculocutaneus)  (Fig.  1098)  derives  its  fibres 
from  the  fifth  and  sixth,  and  sometimes  the  seventh,  cervical  nerves  and  is  a  branch 
of  the  outer  cord.  The  nerve  to  the  coraco-brachialis  muscle,  derived  from  the  seventh 
or  sixth  and  seventh  nerves,  is  usually  found  as  an  integral  part  of  it.  Leaving  the 
outer  cord  under  cover  of  the  pectoralis  minor  it  pierces  the  coraco-brachialis  and 
passes  obliquely  downward  and  outward  between  the  biceps  and  brachialis  anticus 
muscles.  Reaching  the  outer  margin  of  the  biceps  a  short  distance  above  the  elbow, 
the  nerve  pierces  the  deep  fascia  and  passes  under  the  median-cephalic  vein.  It  then 
becomes  superficial  (n.  cutaneus  antebrachii  lateralis)  and  divides  into  its  terminal 
cutaneous  branches. 

Branches. — These  are  :  (a)  the  muscular,  (b)  the  humeral,  (c)  the  articular  and  (d)  the 
terminal. 

a.  The  muscular  branches  supply  the  coraco-brachialis,  the  biceps  and  the  brachialis  anticus. 
The  nerve  to  the  coraco-brachialis,  which  commonly  has  an  independent  origin,  is  usually  double, 
one  filament  going  to  each  portion  of  the  muscle.  The  nerves  to  the  biceps  and  brachialis  anticus 
are  given  off  while  the  musculo-cutaneous  is  in  transit  between  those  muscles. 

b.  The  humeral  branch  accompanies  the  nutrient  branch  of  the  brachial  artery  into  the 
humerus. 

c.  The  articular  branch  aids  in  the  supply  of  the  elbow  joint. 

d.  The  terminal  part  (n.  cutaneus  antebrachii  lateralis)  (Fig.  1103)  of  the  musculo-cutaneous 
divides  into  two  branches,  (aa)  an  anterior  and  (66)  a  posterior. 

aa.  The  anterior  branch  descends  in  the  antero-lateral  portion  of  the  superficial  fascia  of  the 
forearm  (Fig.  1104).  It  inosculates  above  the  wrist  with  the  radial  nerve  and  supplies  the  in- 
tegument of  the  antero-lateral  part  of  the  forearm.  It  also  distributes  fibres  to  the  skin  over  the 
thenar  eminence,  to  the  wrist  joint  and  to  the  radial  artery. 

bb.  The  posterior  branch  passes  downward  and  backward  and  supplies  the  skin  of  the 
postero-lateral  portion  of  the  forearm  down  to  or  slightly  beyond  the  wrist  joint  (Fig.  1102 ).  It 
inosculates  with  the  radial  nerve  and  with  the  inferior  external  cutaneous  branch  of  the  musculo- 
spiral. 

Variations. — Instead  of  piercing  the  coraco-brachialis  the  nerve  may  adhere  to  the  median 
or  its  outer  head  for  some  distance  down  the  arm,  and  then  either  as  a  single  trunk  or  as  several 
branches  pass  between  the  biceps  and  brachialis  anticus  muscles.  Sometimes  only  a  part  of  the 
nerve  follows  this  course,  joining  the  main  trunk  after  the  latter' s  transit  through  the  muscle. 
The  muscular  part  only  or  the  cutaneous  part  only  may  pierce  the  muscle.  The  nerve  may  be 
accompanied  through  the  muscle  by  fibres  of  the  median  which  rejoin  the  latter  below  the 
coraco-brachialis.  The  nerve  may  remain  independent  and  fail  to  pierce  the  coraco-brachialis, 
either  passing  behind  it  or  between  it  and  the  associated  head  of  the  biceps.  It  may  perforate 
not  only  the  coraco-brachialis  but  also  the  brachialis  anticus  or  the  short  head  of  the  biceps. 
Rarely  the  entire  outer  cord,  after  giving  off  the  external  anterior  thoracic,  may  traverse  the 
coraco-brachialis.  Anomalies  in  distribution  include  a  branch  to  the  pronator  radii  teres,  the 
supply  of  the  skin  of  the  dorsum  of  the  hand  over  and  adjacent  to  the  first  metacarpal  bone, 
a  branch  to  the  dorsum  of  the  thumb  in  the  absence  of  the  radial  nerve  and  the  giving  off  of 
dorsal  digital  nerves  to  both  sides  of  the  ring  finger  and  the  adjacent  side  of  the  little  finger. 

8.     THE  MEDIAN  NERVE. 

The  median  nerve  (n.  mcdianus)  (Fig.  1098)  consists  of  fibres  which  can  be 
traced  to  the  sixth,  seventh  and  eighth  cervical  and  first  thoracic  nerves.  It  arises 
by  two  heads,  an  outer  and  an  inner,  which  are  derived  respectively  from  the  outer 
and  inner  cords  of  the  plexus,  the  former  containing  fibres  from  the  sixth  and 
seventh  cervical  and  the  latter  fibres  from  the  eighth  cervical  and  first  thoracic 
nerves.  The  two  heads,  the  inner  of  which  usually  crosses  the  main  artery  of 
the  upper  extremity  at  about  the  point  where  the  axillary  becomes  brachial, 
unite  either  in  front  of  or  to  the  outer  side  of  the  artery.  From  the  point  of  fusion 
of  the  two  heads  the  nerve  passes  down  the  arm  in  close  relation  with  the  brachial 
artery,  usually  lying  lateral  or  antero-lateral  to  the  artery  in  the  upper  part  of  the 
arm,  and  as  the  elbow  is  neared,  gradually  attaining  the  inner  side  by  crossing 
obliquely  the  anterior  surface  of  the  artery  (Fig.  1098).  It  passes  through  the 
cubital  fossa  beneath  the  median-basilic  vein  and  the  bicipital  fascia,  and  enters  the 
forearm  between  the  heads  of  the  pronator  radii  teres  muscle,  the  deep  head  of 


THE   BRACHIAL   PLEXUS. 


1299 


which  separates  the  nerve  from  the  ulnar  artery.      It  follows  a  straight  course  down 
the  forearm,  accompanied  by  the  median  artery,  lying  upon  the  flexor  profundus 

FIG.  1095. 


Deltoid  • 


Sup.  ext.  cutaneous  br.  musculo-spiral 
Inf.  ext.  cutaneous  br.  musculo-spiral 


Musculo-cutaneous  nerve,  ant.  and 
post.  brs. 

Musculo-spiral  nerve  - 
Posterior  interosseous  nerve . 

Radial  nerve . 
Supinator  brevis 

Pronator  radii  teres. 

Extensor  carpi  rad.  longior 

Extensor  carpi  rad.  brevior  - 

Radial  artery . 

Brachio- radialis  _ 
Flexor  subl.  digitorum 
radial  head " 

Flexor  carpi  radialis  • 


Median  nerve 
Palmar  cutaneous  br.  of  median 

Abductor  pollicis 
Digital  brs.  of  median  nerve 


•Median  nerve 
"  Brachial  artery 

-Edge  of  triceps 


—Ulnar  nerve 

"Inferior  profunda  artery 


Brachialis  anticus 


Biceps  tendon 

Pronator  radii  teres,  humeral  head 
Articular  branches  of  median  nerve 


Flexor  caroi  radialis 


•  Flexor  sublimis  digitorum 

•  Ulnar  nerve 

•  Ulnar  artery 

-Flexor  profundus  digitorum 

•Flexor  carpi  ulnaris 

•Palmar  cutaneous  br.  of  ulnar 

-Dorsal  br.  of  ulnar  nerve 
-Flexor  sublimis  digitorum 

-Pisiform  bone 
-Deep  br.  of  ulnar  nerve 
-Palmaris  brevis,  reflected 
-Abductor  minimi  digiti 

-Flexor  brevis  minimi  digiti 
.•Digital  brs.  of  ulnar  nerve 


Dissection  of  right  upp<T  extremity,   showing  nerves   of  anterior   surface;   anterior  annular   ligament   has   been 
cut  away  to  show  median  nerve  and  flexor  tendons. 

digitorum    and    covered    by    the    flexor   sublimis    digitorum.      Near   the    wrist  the 
median  becomes  more  superficial,  with  the  tendons  of  the  flexor  sublimis  digitorum 


1300 


HUMAN   ANATOMY. 


and  palmaris  longus  lying  mesial  and  that  of  the  flexor  carpi  radialis  lateral  to  it 
(Fig.  1095).  It  passes  into  the  hand  beneath  the  anterior  annular  ligament,  at  the 
lower  margin  of  which  it  spreads  out  into  a  reddish  gangliform  swelling,  which  lies 
upon  the  flexor  tendons.  Below  this  point  it  breaks  up  into  its  terminal  branches. 

Branches. — The  median,  as  is  the  case  with  the  ulnar,  gives  off  no  branches 
in  the  arm.  In  the  forearm  the  branches  are  :  (a)  the  articular,  (£)  the  muscular, 
(c)  the  anterior  intcrosseous  and  (d)  the  palmar  cutaneous,  and  in  the  hand  :  (e}  the 
muscular  and  (_/")  the  digital. 

a.  The  articular  branch  consists  of  one  or  two  tiny  twigs  which  supply  the  anterior  portion 
of  the  elbow  joint. 


FIG.  1096. 

Brachial  artery 


Median  nerve 

Hrachial  vein 


Musculo-spiral  nerve 

Cephalic  vein 

Posterior  interosseous  nerve 

Brachio-radialis  muscle 
Radial  nerve 

Radial  recurrent  artery 

Communications  between 

deep  and  superficial 

veins 


Cutaneous  branch  of  musculo- 
cutaneous  nerve 


Radial  vein 


Radial  artery 


Tendon  of  biceps 


Internal  cutaneous  nerve 

Bicipital  fascia 
•Median  nerve 

Pronator  radii  teres 


Superficial  dissection  of  right  arm,  showing;  relations  of  nerves  to  blood-vessels  on  front  of  elbow. 

b.  The  muscular  branches  (rr.  musculares)  (Fig.  1095)  consist  of  a  fasces  of  nerve-bundles 
which  arise  from  the  median  a  short  distance  below  the  elbow.     They  are  distributed  to  the 
pronator  radii  teres,  the  flexor  carpi  radialis,  the  palmaris  longus  and  that  portion  of  the  flexor 
sublimis  digitorum  which  arises  from  the  inner  condyle  and  from  the  ulna.     Two  additional 
filaments  from  the  median  supply  the  ^exor  sublimis,  one  entering  the  radial  head  and  the 
other  that  portion  which  flexes  the  index  finger. 

c.  The  anterior  interosseous  nerve    (n.  interosseus  antcbrncliii  volaris)   (Fig.  1098)  arises 
from  the  posterior  aspect  of  the  median  a  short  distance  below  the  elbow.     It  passes  down 
the  forearm,  accompanied  by  the  anterior  interosseous  artery,  on  the  anterior  surface  of  the 
interosseous  membrane  between  the  flexor  longus  pollicis  and  the  flexor  profundus  digitorum. 
At  the  upper  margin  of  the  pronator  quadratus  muscle  it  dips  under  that  muscle  and  continues 
down  for  some  distance,  finally  entering  the  deep  surface  of  the  pronator  quadratus. 


THE   BRACHIAL    PLEXUS.  1301 

It  supplies  the  flexor  longus  pollicis,  the  radial  half  of  the  flexor  profundus  digitorum 
and  the  pronator  quadratus.  It  distributes  filaments  to  the  interosseous  membrane,  the  anterior 
interosseous  vessels,  the  shafts  of  the  radius  and  ulna  (the  twigs  to  these  bones  entering 
them  with  the  nutrient  arteries) ,  the  periosteum  of  the  radius  and  ulna  and  the  radio-carpal 
articulation. 

d.  The  palmar  cutaneous  branch  (r.  cutaneus  palmaris)  (Fig.  1097)  leaves  the  median 
at  a  varying  distance  above  the  wrist.  It  becomes  superficial  near  the  upper  margin  of  the 
anterior  annular  ligament  by  piercing  the  deep  fascia  between  the  flexor  carpi  radialis  and  the 
palmaris  longus.  It  supplies  the  skin  of  the  palm  and  inosculates  with  the  palmar  cutaneous 
branch  of  the  ulnar  and  with  filaments  of  the  radial  and  musculo-cutaneous  nerves. 

<?.  The  muscular  branch  in  the  hand  (r.  muscularis)  (Fig.  1097)  is  a  short  nerve  which 
arises  below  the  anterior  annular  ligament  and  curves  outward  toward  the  base  of  the  thumb. 
It  breaks  up  into  filaments  which  supply  the  abductor  pollicis,  the  opponens  pollicis  and  the 
superficial  head  of  the  flexor  brevis  pollicis. 

f.  The  digital  branches  (Fig.  1097)  are  five  in  number  and,  with  the  exception  of 
the  twigs  supplying  the  two  outer  lumbricales,  are  purely  sensory.  They  arise  from  the 
median  a  short  distance  below  the  anterior  annular  ligament  of  the  wrist  ( nn.  digitales  volares 
communes)  and  pass  c'istally  beneath  the  superficial  palmar  arch  and  over  the  flexor  tendons. 
As  they  approach  the  interdigital  clefts  they  pass  between  the  primary  divisions  of  the  median 
portion  of  the  palmar  fascia  and  become  more  superficial  as  they  continue  along  the  borders  of 
the  fingers  (nn.  digitales  volares  proprii). 

The  first  lies  along  the  radial  side  of  the  thumb  and  inosculates  around  its  radial  aspect 
with  the  radial  nerve. 

The  second  occupies  the  ulnar  side  of  the  thumb. 

The  third  gives  off  a  branch  to  the  first  lumbricalis  and  supplies  the  radial  side  of  the  index 
finger. 

The  fourth  supplies  the  second  lumbricalis  and  then  di-vides  into  two  branches  which  are 
distributed  to  the  adjacent  sides  of  the  index  and  middle  fingers. 

The  fifth,  after  being  connected  with  the  ulnar  nerve  by  a  stout  filament  (r.  anastomot- 
icus  cum  n.  ulnare),  divides  for  the  supply  of  the  adjoining  aspects  of  the  middle  and  ring 
fingers. 

In  the  fingers  these  nerves  lie  anterior  to  the  vessels  and  in  their  course  toward  the  tip 
of  the  finger  they  give  off  anterior  and  posterior  branches,  the  latter  supplying  the  skin  over  the 
middle  and  distal  phalanges  of  the  index,  middle  and  ring  fingers  and  over  the  distal  phalanx  of 
the  thumb.  Twigs  are  supplied  to  the  interphalangeal  articulations  and  near  the  end  of  the  finger 
each  of  the  five  breaks  up  into  two  terminal  branches,  one  of  which  is  destined  for  the  sensitive 
skin  over  the  anterior  portion  of  the  distal  phalanx  and  the  other  for  the  matrix  of  the  nail. 

Variations. — Some  of  these  are  described  on  page  1298.  The  fibres  usually  contributed  to 
the  median  nerve  by  the  first  thoracic  may  be  wanting.  Either  the  outer  or  the  inner  head  may 
consist  of  two  nerve-bundles.  The  point  at  which  the  heads  unite  is  a  very  variable  one  and 
has  been  found  as  far  down  as  the  elbow.  The  heads  may  enclose  the  axillary  vein  instead  of 
the  artery.  In  those  instances,  many  of  which  have  been  found  in  the  anatomical  rooms  of  the 
University  of  Pennsylvania,  in  which  a  single  large  branch  of  the  axillary  artery  gives  off  the 
two  circumflex  arteries,  the  subscapular  and  the  two  profunda  arteries,  this  trunk,  instead  of  the 
axillary  artery,  is  embraced  by  the  heads  of  the  median  nerve.  The  inner  head,  the  outer  head 
or  the  median  itself  may  pass  behind  the  axillary  artery  instead  of  in  front.  The  outer  head  has 
been  seen  to  arise  in  the  middle  of  the  arm  and  pass  behind  the  artery  to  join  the  inner  head. 
One  instance  has  been  reported  in  which  the  median  entered  the  forearm  over  the  pronator  radii 
teres  instead  of  between  the  heads  of  that  muscle.  It  has  been  seen  lying  on  the  superficial 
surface  of  the  flexor  sublimis  digitorum.  The  median  may  be  cleft  for  a  short  distance  in  the 
forearm,  giving  passage  to  the  ulnar  artery  or  one  of  its  branches,  to  the  superficial  long  head 
of  the  flexor  longus  pollicis  or  to  an  extra  palmaris  longus  muscle.  A  communication  in  the 
arm  between  the  median  and  ulnar  nerves  has  been  noted  in  one  instance.  A  similar  connection 
in  the  forearm,  occurring  in  numerous  ways,  is  found  in  from  20-25  Per  cent,  of  cases  examined. 
A  connection  with  the  ulnar  in  the  hand  may  pass  either  from  the  ulnar  to  the  median  or  from 
the  median  to  the  ulnar.  The  anterior  interosseous  has  been  seen  to  receive  a  filament  from 
the  musculo-spiral  through  the  interosseous  membrane,  and  inosculation  between  the  two 
interosseous  nerves  has  been  noted  at  the  lower  part  of  the  forearm  ;  according  to  Rauber, 
this  is  the  normal  arrangement.  One  case  has  been  described  in  which  the  abductor  indicis 
was  supplied  by  the  median.  During  the  exchange  of  position  between  the  digital  branches 
of  the  median  nerve  and  the  digital  arteries  the  former  are  often  pierced  by  the  latter.  The 
fifth  digital  branch  may  arise  in  the  forearm  and  enter  the  hand  independently. 

Practical  Considerations. — A  pure  paralysis  of  the  median  nerve  is  rare,  and 
is  almost  always  traumatic,  in  origin.  The  paralysis  is  more  commonly  a  part  of  a 
more  extended  involvement  of  the  brachial  plexus.  When  this  nerve  is  paralyzed 
above  there  is  inability  to  pronate  the  forearm  or  flex  the  wrisf  properly,  since  the 


1302 


HUMAN    ANATOMY. 


pronators  and  all  the  flexors  except  the  flexor  carpi  ulnaris  and  the  ulnar  half  of  the 
flexor  profundus  digitorum  are  supplied  by  -it.  The  second  phalanges  of  the  middle 
and  index  fingers  cannot  be  flexed,  although  the  first  phalanges  can  be  flexed  and 
the  second  and  third  extended  in  all  the  fingers  through  the  interossei  muscles  ; 
flexion  of  the  third  phalanges  of  the  little  and  ring  fingers  can  be  accomplished  by 
the  ulnar  half  of  the  flexor  profundus,  which  is  supplied  by  the  ulnar  nerve.  The 


FIG.  1097. 


Brachio-radialis  tendon 
Branch  of  radial  nerve 


Palmar  cutaneous  br.  of 
median  nerve 


Median  nerve 
Flexor  carpi  radialis  tendon 


Abductor  pollicis 
Opponens  pollicis 

Abductor  pollicis 

Digital  brs.  of 

median  nerve 

Adductor 

transversus  pollicis 


Flexor  sublimis  digitorum 

Flexor  carpi  ulnaris 
Palmar  cutaneous  br.  of  ulnar 
nerve,  lying  upon  ulnar 
artery 
Ulnar  nerve 


Pisiform  bone 

Deep  branch  of  ulnar  nerve 
Abductor  minimi  digiti 
Palmaris  brevis,  reflected 

Digital  brs.  of  ulnar  nerve 

Opponens  minimi  digiti 
Flex,  brevis  minimi  digiti 


Superficial  dissection  of  right  palm,   showing  branches  of  median   and   ulnar  nerves;   part  of   anterior 
annular  ligament  has  been  removed  to  expose  median  nerve. 

thumb  cannot  be  flexed  or  abducted,  although  it  may  be  adducted.  One  of  the 
most  characteristic  features  of  the  hand  is  lost — that  is,  the  ability  to  appose  the 
thumb  to  any  one  of  the  fingers,  as  in  picking  up  small  objects. 

In  wounds  of  the  axilla  the  median  is  the  nerve  most  frequently  injured,  the 
musculo-spiral  least  frequently,  as  the  median  lies  more  superficially  and  the  musculo- 
spiral  behind  the  vessels.  In  the  arm  the  median  can  be  easily  found  to  the  inner 
side  of  the  biceps  and  coraco-bruchialis  muscles,  win-re  it  lies  on  the  brachial  vessels. 
At  the  elbow  it  is  found  to  the  inner  side  of  the  brachial  artery,  the  guide  to 
which  is  the  biceps  tendon  which  in  turn  lies  just  to  the  outer  side  of  the  artery. 
At  about  the  midd4e  of  the  wrist  the  nerve  lies  under  the  palmaris  longus  tendon. 


THE   BRACHIAL    PLEXUS.  1303 

9.  THE  INTERNAL  ANTERIOR  THORACIC  NERVE. 

The  internal  anterior  thoracic  nerve  (n.  thoracalis  anterior  medialis)  (Fig. 
1093)  arises  from  the  inner  cord  and  consists  of  fibres  derived  from  the  eighth 
cervical  and  first  thoracic  nerves.  It  passes  forward  between  the  axillary  artery  and 
vein  and,  after  giving  off  a  branch  which  forms  a  loop  with  a  similar  branch  from  the 
external  anterior  thoracic,  pierces  the  pectoralis  minor,  in  which  some  of  its  fibres 
terminate.  The  remainder  enter  the  deep  surface,  of  the  pectoralis  major  to  supply 
the  lower  part  of  the  sternal  portion  of  that  muscle. 

Variations. — The  fibres  which  supply  the  pectoralis  major  may  wind  around  the  lower 
border  of  the  pectoralis  minor.  Filaments  from  both  of  the  anterior  thoracic  nerves  may  supply 
the  integument  of  the  axillary  and  mammary  regions. 

10.  THE  LESSER  INTERNAL  CUTANEOUS  NERVE. 

The  lesser  internal  cutaneous  nerve  (n.  cutaneus  brachii  medialis)  (Fig.  1093), 
also  called  the  nerve  of  Wrisberg,  can  be  traced  to  the  first  thoracic  nerve.  It 
arises  from  the  inner  cord  usually  in  common  with  the  internal  cutaneous.  After 
leaving  its  point  of  origin,  it  descends  in  the  arm  along  the  inner  side  of  the  axillary 
and  basilic  veins,  pierces  the  deep  fascia  about  the  middle  of  the  arm  and  supplies 
the  integument  of  the  inner  aspect  of  the  upper  extremity  as  far  down  as  the  elbow. 
At  a  variable  point  it  forms  a  loop  with  the  intercosto-humeral  nerve. 

Variations. — The  lesser  internal  cutaneous  nerve  may  be  absent.  It  may  receive  fibres 
from  the  eighth  cervical  or  the  second  thoracic  nerve.  There  may  be  present  a  communication 
between  the  lesser  internal  cutaneous  nerve  and  the  lateral  cutaneous  branch  of  the  third  tho- 
racic. The  inosculation  with  the  intercosto-humeral  may  be  either  simple  or  plexiform  and 
either  nerve  may  be  deficient,  the  other  usually  recompensing  for  the  deficiency. 

ii.   THE  INTERNAL  CUTANEOUS  NERVE. 

The  internal  cutaneous  nerve  (n.  cutaneus  antebrachii  medialis)  (Fig.  1094) 
comprises  fibres  from  the  eighth  cervical  and  first  thoracic  nerves.  It  has  its  origin 
from  the  inner  cord  of  the  plexus  usually  as  a  common  trunk  with  the  lesser  internal 
cutaneous  nerve.  After  distributing  some  small  filaments  to  the  integument  of  the 
upper  arm  below  the  axilla,  it  runs  down  the  arm  between  the  brachial  artery  and 
the  basilic  vein  and  at  about  the  middle  of  the  upper  arm  breaks  up  into  its  terminal 
branches,  (a)  the  anterio r  and  (b}  \\\&  posterior. 

a.  The   anterior  branch   (r.  volaris)    passes   over,    sometimes  under,   the   median-basilic 
vein  and  supplies  the  skin  of  the  ulnar  half  of  the  forearm  as  far  down  as  the  wrist  (Fig.  1104). 
It  inosculates  with  the  superficial  branch  of  the  ulnar  nerve. 

b.  The  posterior  branch   (r.  ulnaris)  turns  obliquely  around  the  inner  side  of  the  upper 
part  of  the  forearm  and  supplies  the  integument  as  far  around  as  the  ulna  down  to  the  lower 
third  or  fourth  of  the  forearm.     It  unites  above  the  elbow  with  the  lesser  internal  cutaneous 
nerve  and  in  the  forearm  with  the  anterior  branch  of  the  internal  cutaneous  and  sometimes  with 
the  dorsal  ramus  of  the  ulnar. 

12.  THE  ULNAR  NERVE. 

The  ulnar  nerve  (n.  ulnaris)  (Fig.  1092)  is  the  largest  branch  of  the  inner 
cord.  Its  fibres  can  be  traced  to  the  eighth  cervical  and  first  thoracic  nerves  and 
sometimes,  by  a  root  from  the  outer  cord,  to  the  seventh  cervical.  Arising  from 
the  inner  cord  between  the  axillary  artery  and  vein  and  posterior  to  the  internal 
cutaneous  nerve  it  pursues  a  downward  course  in  front  of  the  triceps  and  to  the 
inner  side  of  the  axillary  and  brachial  arteries.  Reaching  the  middle  of  the  arm  it 
follows  an  inward  and  backward  direction,  in  which  it  is  accompanied  by  the  inferior 
profunda  artery,  and  passing  either  over  the  inner  margin  of  or  through  the  internal 
intermuscular  septum  and  in  front  of  the  inner  head  of  the  triceps,  attains  the  interval 
between  the  internal  condyle  of  the  humerus  and  the  olecranon  (Fig.  1095).  It 
becomes  an  occupant  of  the  forearm  by  passing  between  the  heads  of  the  flexor  carpi 
ulnaris  muscle,  a  situation  the  nerve  shares  with  the  inferior  profunda  and  posterior 


1304 


HUMAN   ANATOMY. 


ulnar  recurrent  arteries.      From  this  point  the  nerve  follows  a  straight  course  to  the 
wrist,  lying  in  the  forearm  upon  the  flexor  profundus  digitorum  and  covered  by  the 

FIG.  1098. 


Musculo-cutaneous  nerve 

Outer  head  of  median  nerve 

Inner  head  of  median  nervt 

Long  head  of  biceps 

Short  head  of  biceps,  everted 
Coraco-brach  ial  is 


Musculo-cutaneous  nerve 


Branchialis  anticus 

Musculo-spira!  nerve 
Cutaneous  branches  of  musculo-cutaneou 


Brachio-  radialis 

Posterior  interosseous  nerve 

Biceps  tendon 

Radial  artery 

Supinator  brevis 

Ext.  carpi  radialis  longior 

Ext.  carpi  radialis  brevier 

Radial  nerve 


Pronator  radii  teres,  cut 


Palmar  cutaneous  branch  of  median 


Pectoralis  minor 


Internal  cutaneous  nerve 


Ulnar  nerve 


Internal  cutaneous  branch  of 
musculo-spiral  nerve 


•Inferior  profunda  artery 


Muscular  branch  of  musculo-cutaneous 


Articular  branches  of  median  nerve 


Articular  branches  of  ulnar  nerve 
Flexor  carpi  ulnaris 
Ulnar  artery 


•Anterior  interosseous  nerve 
•Anterior  interosseous  artery 

Ulnar  nerve 

Flexor  profundus  digitorum 

Palmar  cutaneous  branch 
Pronator  quadratus 

Dorsal  branch  of  ulnar  nerve 


Deep  branch  of  ulnar  nerve 

Abductor  minimi  digiti 
•Opponens  minimi  di^iti 

Flexor  brevis  minimi  digiti 

3rd  and  4th  flexor  tendons  with  3rd  and  4th 
lumbricales,  turned  forward 


Dissection  of  right  upper  extremity,  showing  deeper  branches  of  nerves  of  anterior  surface. 

flexor  carpi  ulnaris.      At  about  the  middle  of  its  course  through  the  lower  arm  it 
approximates  the  ulnar  vessels,  close   to    the  inner   side  of  which  it  lies.     At  the 


THE   BRACHIAL    PLEXUS.  1305 

wrist,  accompanied  by  the  ulnar  artery,  it  pierces  the  deep  fascia  just  above  the 
annular  ligament,  to  the  outer  side  of  the  pisiform  bone,  and  enters  the  hand  by 
passing  superficial  to  the  anterior  annular  ligament  (Fig.  1097).  After  crossing 
the  ligament  it  divides  into  its  terminal  branches,  the  superficial  and  the  deep. 

Branches. — None  are  given  off  in  the  arm.  In  the  forearm  they  are  :  (#) 
the  articular,  (b~)  the  muscular,  (c)  the  cutaneous  and  (d*)  the  dorsal  branch  to  the 
hand.  The  terminal  branches  in  the  hand  are  :  (e~)  the  superficial  and  (  /")  the  deep. 

a.  The  articular  branch  consists  of  one  or  two  filaments  which  leave  the  ulnar  as  it  lies  in 
the  interval  between  the  olecranon  and  the  internal  condyle.     They  pierce  the  internal  part  of 
the  capsular  ligament  and  supply  the  elbow  joint. 

b.  The  muscular  branches  arise  from  the  ulnar  in  the  immediate  neighborhood  of  the 
elbow  and  supply  the  flexor  carpi  ulnaris  in  toto  and  the  ulnar  half  of  the  flexor  profundus 
digitorum.    They  consist  of  several  fine  twigs  which  leave  the  ulnar  nerve  as  it  lies  between  the 
heads  of  the  flexor  carpi  ulnaris. 

c.  The  cutaneous  branches  are  two  small  filaments  which  arise  by  a  common  trunk  at 
about  the  middle  of  the  forearm.     One,  which  is  inconstant,  after  piercing  the  deep  fascia,  runs 
downward  to  inosculate  with  a  twig  from  the   internal   cutaneous.     The  other,  the  palmar 
cutaneous  branch  (r.  cutaneus  palmaris)   (Fig.  1097  ),  lies  superficial  to  the  ulnar  artery,  which 
it  accompanies  to  the  hand  almost  as  far  as  the  superficial  palmar  arch.     It  sends  filaments  to 
the  ulnar  artery  and  breaks  up  into  a  number  of  tiny  threads  which  supply  the  integument  of  the 
hypothenar  region  and  inosculate  with  other  cutaneous  twigs  of  the  ulnar,  with  the  internal 
cutaneous  and  with  the  palmar  cutaneous  branch  of  the  median. 

d.  The   dorsal   branch   to   the   hand    (r.    dorsalis   manus)   is   a   good  sized  trunk   which 
leaves  the  ulnar  in  the  upper  part  of  the  lower  half  of  the  forearm.     To  reach  the  dorsum  of  the 
hand  it  passes  downward  and  backward  between  the  tendinous  portion  of  the  flexor  carpi 
ulnaris  and  the  shaft  of  the  ulna,  giving  off  a  branch  over  the  dorsum  of  the  wrist  to  supply 
that  region  and  inosculate  with  a  twig  from  the  radial  nerve.     Opposite  the  head  of  the  ulna  it 
splits  into  three  branches  (nn.  digitales  dorsales)  for  the  supply  of  the  fingers.     The  ulnar  or 
inner  branch  courses  along  the  inner  side  of  the  little  finger  to  ramify  in  its  integument  as  far  as 
the  base  of  the  nail.     The  middle  branch  follows  the  fourth  metatarsal  interval  and  divides  into 
two  filaments,  one  extending  along  the  radial  side  of  the  little  finger  as  far  as  the  base  of  the 
nail  and  the  other  along  the  ulnar  side  of  the  ring  finger  as  far  as  the  proximal  side  of  the 
ungual  phalanx.     The  radial  or  outer  branch  passes  toward  the  base  of  the  space  between  the 
ring  and  middle  fingers  and  inosculates  with  the  branch  from  the  radial  nerve  for  the  same  cleft. 
It  divides  into  two  sub-branches  and  in  connection  with  the  radial  supplies  the  adjacent  sides  of 
the  ring  and  middle  fingers  (Fig.  1102).     At  the  lateral  aspect  of  the  fingers  all  of  these  branches 
inosculate  with  the  palmar  digital  cutaneous  nerves. 

e.  The    superficial   terminal    branch    (r.    superfidalis    n.    ulnaris)    (Fig.     1097)    furnishes 
small  twigs  to  the  palmaris  brevis  muscle,  to  the  integument  of  the  ball  of  the  little  finger  and 
sometimes  to  the  fourth  lumbricalis.      It  then  divides,  one  of  its  subdivisions  supplying  the 
ulnar  side  of  the  little  finger  while  the  other  breaks  up  into  two  portions  which  course  along 
the  adjoining  sides  of  the  little  and  ring  fingers.     The  ultimate  distribution  of  these  filaments  is 
similar  to  that  of  the  digital  branches  of  the  median  nerve  (page  1301). 

A  twig  of  communication  passes  between  the  branch  for  the  little  and  ring  fingers  and  that 
from  the  median  for  the  ring  and  middle  fingers.  From  the  latter  tiny  threads  are  supplied  to 
the  integument  and  vessels  of  the  palm. 

f.  The  deep  terminal  branch  (r.  profundus  n.  ulnaris)  (Fig.  1099)  accompanies  the  deep 
branch  of  the  ulnar  artery  and  sinks  deeply  into  the  palm  between  the  abductor  and  flexor 
minimi  digiti  muscles.  It  passes  internal  to  and  below  the  uncus  of  the  unciform  bone,  in  which 
a  groove  for  the  nerve  is  sometimes  found,  crosses  the  palm  with  the  deep  palmar  arch  under 
the  deep  flexor  tendons  and  breaks  up  into  terminal  twigs  on  its  arrival  at  the  adductor  trans- 
versus  pollicis  (Fig.  1199).  Muscular  branches  (rr.  musculares)  are  furnished  1o  the  abductor, 
opponens  and  flexor  minimi  digiti,  the  third  and  fourth  lumbricales,  the  palmar  and  dorsal 
interossei,  the  adductores  obliquus  and  transversus  pollicis  and  the  deep  head  of  the  flexor  bre- 
vis pollicis.  Articular  branches  are  supplied  to  the  intercarpal  and  metacarpo-phalangeal  artic- 
ulations and  tiny  perforating  branches  accompany  the  posterior  perforating  arteries  between 
the  heads  of  the  second,  third  and  fourth  dorsal  interosseous  muscles  and  inosculate  with  the 
terminal  twigs  of  the  posterior  interosseous  nerve  (Rauber). 

Communications. — The  ulnar  communicates  freely  and  in  many  different  situations  with 
the  median  and  this  close  interlacing  is  paralleled  by  their  similarity  in  distribution.  Both  give 
off  no  branches  above  the  elbow,  both  supply  the  elbow  joint,  between  them  they  supply  all  the 
muscles  of  the  flexor  surface  of  the  forearm,  both  5;end  filaments  to  the  wrist  joint  and  the  integ- 
ument of  the  palm  and  between  them  all  the  muscles  of  the  hand,  the  palmar  aspect  of  all  the 
digits  and  the  interphalangeal  articulations  are  innervated. 


i3o6  HUMAN   ANATOMY. 

Further  description  of  the  communications  of  the  ulnar  nerve,  in  addition  to  those  just 
mentioned,  will  be  found  in  connection  with  the  median  nerve  (page  1301). 

Variations. — The  ulnar  may  have  a  root  from  the  seventh  cervical  nerve  by  way  of  the  outer 
cord,  or  may  be  derived  from  the  eighth  cervical  only  or  from  the  seventh  and  eighth.  It  may 
pass  in  front  of  the  internal  condyle  or  lie  behind  the  condyle  and  slip  forward  during  flexion  of 
the  elbow.  Connecting  twigs  have  been  seen  passing  from  the  ulnar  to  the  internal  cutaneous, 
to  the  median  in  the  upper  arm  and  to  the  musculo-spiral.  Frequently  there  is  an  associating 
branch  in  the  forearm  between  the  median  and  the  ulnar.  Muscular  twigs  have  been  noted  as 
passing  to  the  inner  head  of  the  triceps,  the  flexor  sublimis  digitorum,  the  first  and  second 
lumbricales  and  the  superficial  head  of  the  flexor  brevis  pollicis.  Deficiencies  in  the  branch  to 
the  dorsum  of  the  hand  have  been  observed  to  be  compensated  for  by  the  radial,  the  inferior 
external  cutaneous  branch  of  the  musculo-spiral  or  the  internal  cutaneous.  In  a  specimen  with 
absence  of  the  radial  nerve  all  four  fingers  were  supplied  by  the  ulnar.  The  dorsal  terminal 
filaments  of  the  ulnar  tend  to  encroach  on  the  radial  side  of  the  hand  and  in  one  case  reached 
the  dorsum  of  the  first  phalanx  of  the  thumb. 

Practical  Considerations. — In  paralysis  of  the  ulnar  nerve,  flexion  of  the  wrist 
is  impaired,  and  also  (on  account  of  the  flexor  carpi  ulnaris  paralysis)  lateral  motion 
toward  the  ulnar  side  (adduction).  There  is  difficulty  in  spreading  the  fingers,  as 
all  the  interossei  are  supplied  by  this  nerve.  The  hand  will  be  ' '  clawed' '  from  the 
paralysis  of  the  interossei,  which  now  fail  to  resist  the  action  of  the  extensors  on 
the  proximal  phalanges,  and  of  the  flexors  on  the  distal  and  medial,  except  in  the 
middle  and  ring  fingers  where  the  flexor  profundus — its  ulnar  half  being  paralyzed — 
has  only  a  slight  influence  on  the  distal  phalanges.  Besides  the  flexor  carpi  ulnaris, 
the  ulnar  half  of  the  flexor  profundus  and  the  interossei,  the  ulnar  nerve  supplies 
all  the  hypothenar  muscles,  the  adductor  pollicis,  the  inner  half  of  the  flexor  brevis 
pollicis  and  the  two  ulnar  lumbricales  ;  consequently  the  hypothenar  eminence  dis- 
appears and  the  thenar  eminence  shows  atrophy  in  ulnar  paralysis.  This  nerve  is 
involved  particularly  in  those  whose  occupations  require  them  to  press  their  elbows 
against  hard  objects  or  to  strike  blows  frequently  with  the  ulnar  border  of  the  hand. 
It  may  be  injured  in  fractures  of  the  elbow,  particularly  of  the  internal  condyle.  In 
the  forearm  and  wrist  it  is  the  nerve  most  frequently  injured.  It  is  found  on  the  inner 
side  of  the  brachial  artery  in  the  upper  half  of  the  arm,  but  in  the  lower  half  it  passes 
posteriorly  to  the  bony  interval  between  the  internal  condyle  and  the  olecranon, 
where  it  is  readily  located  by  pressure,  which  causes  a  tingling  sensation  down  the 
forearm.  The  same  sensation  is  often  produced  by  blows  on  the  elbow,  the  nerve 
being  compressed  between  the  internal  condyle  and  the  olecranon.  It  is  the  structure 
most  frequently  damaged  in  excisions  of  the  elbow.  In  the  lower  two-thirds  of  the 
forearm  it  lies  to  the  radial  side  of  the  flexor  carpi  ulnaris  muscle  and  to  the  ulnar 
side  of  the  ulnar  artery.  At  the  wrist  it  passes  over  the  anterior  annular  ligament  in 
the  same  relation  to  the  artery  and  to  the  radial  side  of  the  pisiform  bone. 

14.     THE  SUBSCAPULAR  NERVES. 

The  subscapular  nerves  (nn.  subscapulares)  (Fig.  1092)  arise  from  the  posterior 
cord  and  are  usually  three  in  number.  Together  they  supply  the  three  muscles  which 
form  the  posterior  boundary  of  the  axillary  space. 

The  upper  or  short  subscapular  nerve  is  composed  of  fibres  which  are 
prolonged  from  the  fifth  and  sixth  cervical  nerves.  It  often  is  either  double  in  origin 
or  divides  into  two  branches  shortly  after  leaving  the  posterior  cord.  It  arises 
behind  the  circumflex  nerve  and  after  a  short  course  enters  the  inner  surface  of  the 
subscapularis  near  the  upper  margin  of  that  muscle. 

The  middle  or  long  subscapular  nerve  (n.  thoracodorsalis),  the  largest  of  the 
three,  arises  from  the  rear  aspect  of  the  posterior  cord,  behind  the  origin  of  the 
musculo-spiral  nerve.  Its  fibres  are  derived  from  the  sixth,  seventh  and  eighth 
cervical  nerves,  the  majority  of  them  coming  from  the  seventh.  It  takes  a  course 
downward  and  outward  on  the  posterior  axillary  wall  behind  the  axillary  artery,  and 
accompanies  the  subscapular  artery  to  the  deep  surface  of  the  latissimus  dorsi,  before 
entering  which  it  breaks  up  into  a  number  of  strands. 

The  lower  subscapular  nerve  obtains  its  fibres  from  the  fifth  and  sixth  cer- 
vical nerves.  It  arises  from  the  posterior  cord  behind  the  origin  of  the  circumflex 


THE   BRACHIAL    PLEXUS. 


1307 


and  passes  downward  and  outward  beneath  the  axillary  artery  and  the  circumflex 
and  musculo-spiral  nerves.  It  sends  fibres  to  the  inferior  portion  of  the  subscap- 
ularis  muscle  and  terminates  in  the  substance  of  the  teres  major. 

Variations. — As  regards  origin  the  upper  may  arise  from  either  the  fifth  or  the  sixth  cervi- 
cal nerve,  the  middle  from  the  seventh  alone  or  from  the  seventh  and  eighth  or  rarely  by  an 
additional  filament  from  the  fifth,  and  the  lower  from  the  fifth,  sixth  and  seventh  or  from  the 
fifth  or  sixth  alone.  As  regards  distribution,  the  nerves  to  the  tower  part  of  the  subscapularis 
and  to  the  teres  major  may  proceed  separately  from  the  brachial  plexus  or  the  latter  nerve 
may  be  a  branch  of  the  circumflex. 

15.     THE  CIRCUMFLEX  NERVE. 

The  circumflex  or  axillary  nerve  (n.  axillaris)  (Fig-.  1092)  is  one  of  the  terminal 
branches  of  the  posterior  cord  and  contains  fibres  which  are  derivatives  of  the  fifth 

FIG.  1099. 


Median  nerve 
Flexor  longus  pollicis 

Palmar  cutaneous  br.  of  median  nerve 


Opponetis  pollicis 


Adductor  obliquus  pollicis 


Flex.  brev.  poll., 
inner  head 

Flex.  brev.  poll., 
outer  head 

Adductor  pollicis 

Adductor  transversus 
poll. 


An  articular  branch 


Flex.  prof,  digitorum, 
in  part 

Ulnar  nerve 
Flex,  carpi  ulnaris 


Pisiform  bone 
Deep  br.  of  ulnar  nerve 
Articular  br.  of  ulnar 
Unciform  bone         t  nerve 
Articular  brs.  of  ulnar 
nerve  [everted 

Abductor  minimi  digiti, 
Opponens  minimi  digiti 
Second  palmar  inter- 
osseous 

Third  dorsal  interosseous 
Third  palmar  inter- 
Fourth  dorsal        [osseous 
interosseous 
Flex,  brevis  minimi 
digiti 


V., 


Dissection  of  right  palm,  showing  distribution  of  deep  branch  of  ulnar;  flexor  tendons   of   third   and   fourth 
fingers,  with  corresponding  lumbricales,  divided  and  turned  down. 

and  sixth  cervical  nerves.  It  arises  near  the  lower  margin  of  the  subscapularis  and 
posterior  to  the  axillary  artery.  Accompanied  by  the  posterior  circumflex  artery  it 
takes  a  backward  course  through  the  quadrilateral  space,  bounded  above  by  the 
subscapularis  and  the  teres  minor,  below  by  the  teres  major,  internally  by  the 


1 3o8  HUMAN   ANATOMY. 

humeral  head  of  the  triceps  and  externally  by  the  humerus.  Having  traversed 
this  space  it  winds  around  the  surgical  neck  of  the  humerus  and  reaches  the  outer 
aspect  of  the  shoulder. 

Branches. — These  are  :  (a)  the  articular,  (£>}  the  cutaneous  and  (r)  the 
muscular. 

a.  The  articular  branches  are  usually  two  in  number.     The  upper  arises  near  the  origin  of 
the  circumflex  and  the  lower  during  the  passage  of  the  nerve  through  the  quadrilateral  space. 
They  supply  the  anterior  inferior  portion  of  the  capsular  ligament  of  the  shoulder.     A  third 
articular  branch  is  described  as  passing  up  the  bicipital  groove,  supplying  a  twig  to  the  upper 
end  of  the  humerus  and  one  to  the  neighboring  portion  of  the  capsular  ligament  of  the  shoulder. 

b.  The  cutaneous  branch  (a.  cutaneus  brachii  lateralis)  arises  as  a  common  trunk  with  the 
nerve  to  the  teres  minor.     It  becomes  superficial  between  the  long  head  of  the  triceps  and  the 
posterior  border  of  the  lower  third  of  the  deltoid  and  is  distributed  to  the  integument  over  the 
posterior  half  of  the  deltoid  and  the  posterior  surface  of  the  upper  half  of  the  arm. 

One  or  two  cutaneous  filaments  are  derived  from  the  muscular  branches  to  the  deltoid. 
They  pierce  the  deltoid  and  are  distributed  to  the  skin  over  the  lower  portion  of  that  muscle. 

c.  The  muscular  branches  (rr.  musculares)  innervate  (aa)  the  teres  minor  and   (bb}  the 
deltoid. 

aa.  The  nerve  to  the  teres  minor  arises  from  the  circumflex  at  the  posterior  margin  of  the 
quadrilateral  space  and  enters  the  middle  of  the  posterior  inferior  border  of  the  muscle  which  it 
supplies. 

bb.  The  deltoid  branches  comprise  the  largest  portion  of  the  nerve  and  consist  of  its  termi- 
nal fibres.  The  terminal  portion  of  the  circumflex  forms  a  bow,  with  its  convexity  in  contact 
with  the  deep  surface  of  the  deltoid,  extending  around  the  upper  part  of  the  humerus  almost  as 
far  forward  as  the  anterior  margin  of  the  deltoid  muscle.  It  gradually  diminishes  in  size  as  the 
result  of  the  departure  of  a  series  of  twigs  which  enter  and  supply  the  fasciculi  of  the  deltoid. 

Variations. — The  circumflex  may  receive  very  few  or  no  fibres  from  the  sixth  cervical  nerve. 
It  may  pierce  the  subscapularis  and  may  supply  that  muscle.  It  may  give  origin  to  the  nerve  to 
the  teres  major  and  has  been  observed  to  furnish  filaments  to  the  long  head  of  the  triceps  and 
to  the  infraspinatus. 

Practical  Considerations. — The  circumflex  nerve  is  frequently  paralyzed 
from  injuries  to  the  shoulder,  as  in  birth  palsies  when  pressure  is  made  in  the  axilla. 
It  undergoes  special  strain  in  dislocations  of  the  shoulder,  the  nerve  being  stretched 
over  the  head  of  the  humerus  and  often  lacerated.  Other  branches  of  the  brachial 
plexus  may  be  injured  in  this  dislocation.  Since  the  circumflex  passes  around 
the  humerus  at  about  the  level  of  the  surgical  neck  it  is  sometimes  damaged 
in  fractures  in  that  situation.  The  most  prominent  symptom  in  paralysis  of  this 
nerve  is  loss  of  the  rotundity  of  the  shoulder  from  atrophy  of  the  deltoid  muscle. 
As  the  circumflex  winds  around  the  posterior  surface  of  the  humerus  and  reaches 
the  anterior  part  of  the  deltoid  muscle  from  behind,  incisions  for  reaching  the 
shoulder  joint,  as  in  excisions,  should  be  made  anteriorly,  since  only  the  terminal 
branches  of  the  circumflex  will  then  be  divided  ;  paralysis  of  the  deltoid  is  thus 
prevented. 

1 6.    THE   MUSCULO-SPIRAL   NERVE. 

The  musculo-spiral  nerve  (n.  radialis)  (Fig.  noo),  the  larger  terminal  branch  of 
the  posterior  cord,  is  in  fact  the  continuation  of  the  latter.  Its  component  fibres  are 
derivatives  of  the  sixth,  seventh  and  eighth,  and  sometimes  of  the  fifth,  cervical 
nerves  and  it  is  distributed  to  the  muscles  and  integument  of  the  extensor  surface  of 
the  arm,  forearm  and  hand.  After  separating  from  the  circumflex,  it  passes  down- 
ward behind  the  axillary  artery  and  over  the  surface  of  the  latissimus  dorsi  and  teres 
major  muscles.  Accompanied  by  the  superior  profunda  artery,  it  turns  backward  on 
the  inner  aspect  of  the  arm  and,  entering  the  musculo-spiral  groove  and  traversing 
the  interval  between  the  internal  and  long  and  the  external  head  of  the  triceps, 
reaches  the  lateral  aspect  of  the  arm.  It  then  takes  a  forward  course  through  the 
external  intermuscular  septum  and  becomes  an  occupant  of  the  cleft  between  the 
brachioradialia  and  the  bntchialis  anticus.  Continuing  in  this  space  as  far  as  the  level 
of  the  external  condyle  of  the  humerus  the  nerve  divides  into  its  terminal  branches, 
i&bit  posterior  intcrosseous  and  the  radial  (Fig.  1095). 


THE   BRACHIAL    PLEXUS. 


1309 


Branches.  —  These  are  :  (<z)  the  cutaneous, 
the  articular  and  (e)  the  terminal. 

FIG.   i  i  oo. 


the  muscular,  (V)  the  humeral, 


Scapular  head  of  triceps 

Superior  profunda  artery 

Portion  of  external  head  of  triceps,  everted 

Muscular  branch 


Olecranon 

Anconeus 
Extensor  carpi  ulnaris 


Extensor  longus  pollicis 


Extensor  in 


-Musculo-spiral  nerve 


Upper  external  cutaneous  nerve 
External  head  of  triceps 


Brachialis  anticus 

Lower  external  cutaneous  nerve 


External  condyle 


Extensor  carpi  radialis  longior 


Extensor  carpi  radialis  brevior 

Supinator  brevis 

Posterior  iutei  osseous  nerve 


Extensor  communis  digitorum 
Extensor  minimi  digiti 


Extensor  ossis  metacarpi  pollicis 
Extensor  brevis  pollicis 


Extensor  longus  pollicis 


or  \  i,, Gangliform  enlargement  on 

V\\        posterior  interosseous  nerve 


Deep  dissection  of  extensor  surface  of  right  upper  extremity,  showing  course  and 
branches  of  musculo-spiral  nerve. 

a.     The  cutaneous  branches  are  three  in  number,  an  internal  and  two  external. 

The  internal  cutaneous  branch  frequently  arises  from  the  musculo-spiral  in  common  with 


1310 


HUMAN   ANATOMY. 


the  branches  to  the  long  and  inner  heads  of  the  triceps.  It  passes  backward,  posterior  to  the 
intercosto-humeral  nerve,  and  after  piercing  the  deep  fascia,  spreads  out  to  be  distributed  to  the 
integument  over  the  inner  head  of  the  triceps  to  within  a  short  distance  of  the  elbow  (Fig.  noi). 
It  is  accompanied  by  a  small  artery. 

The  superior  external  cutaneous  branch  (n.  cutaneus  brachii  posterior)  (Fig.  noi)  arises 
from  the  musculo-spiral  posterior  to  the  external  intermuscular  septum  and  pierces  the  deep 
fascia  below  the  middle  of  the  arm,  between  the  external  head  of  the  triceps  and  the  brachialis 
anticus.  It  passes  down  with  the  cephalic  vein  and  is  distributed  to  the  integument  of  the 
external  anterior  portion  of  the  arm  down  to  or  slightly  below  the  elbow. 

The  inferior  external  cutaneous  branch  (n.  cutaneus  antebrachii  dorsalis)  (Fig.  1102)  arises 
and  becomes  superficial  similarly  to  and  in  common  with  the  superior.  After  passing  down  the 

FIG.  noi. 


Cutaneous  branches  of  circumflex  nerve 


Branch  of  intercosto- 
humeral  nerve 

Int.  cutaneous  branch  of  mus- 
culo-spiral nerve 
Lesser  internal  cutaneous, 
joined  below  the  leader  by 
branch  of  intercosto-hu- 
meral  nerve 


Sup.  ext.  cutaneous  branch  of  mus- 
culo-spiral  nerve 


Inf.  ext.  cutaneous  branch  of  mus- 
culo-spiral  nerve 


Post,  cutaneous 
branch  of  musculo- 
cutaneous  nerve 


From  post,  branch  of  internal  cutaneous  nerve 


Superficial  dissection  of  right  arm,  showing  cutaneous  nerves  of  posterior  surface. 

arm  it  enters  the  forearm  by  crossing  the  dense  fascia  stretched  between  the  olecranon  and  the 
internal  condyle  of  the  humerus.  From  this  point  it  continues  its  downward  course  along  the 
posterior  aspect  of  the  forearm  as  far  down  as  the  wrist  or  even  onto  the  dorsum  of  the  hand. 
It  is  distributed  to  the  skin  of  the  posterior  portion  of  the  arm  between  the  areas  supplied  by 
the  other  cutaneous  branches  of  the  musculo-spiral  and  to  that  part  of  the  posterior  aspect  of 
the  forearm  between  the  portions  supplied  by  the  posterior  branch  of  the  internal  cutaneous 
and  the  posterior  branch  of  the  musculo-cutaneous.  In  the  neighborhood  of  the  wrist  it  inos- 
culates with  the  musculo-cutaneous  and  sometimes  with  the  branch  to  the  dorsum  of  the  hand 
from  the  ulnar. 

b.  The  muscular  branches  (rr.  musculares)  are  given  off  (aa)  before  the  musculo-spiral 
enters  the  musculo-spiral  groove  and  (f>b)  after  leaving  the  groove. 

aa.  Before  entering  the  groove  branches  arise  for  the  supply  of  the  three  heads  of  the 
triceps  and  the  anconeus. 


THE   BRACHIAL    PLEXUS. 


1311 


Int.  cutaneous 

branch  of  nius- 

culospiral  nerve 


Lesser  int.  cu- 
taneous nerve 


Inf.  ext.  cutaneous 
branch  of  musculo 
spiral  nerve 


Int.  cutaneous 

nerve,  post 

branch 


Post,  cutaneous 
br.  of  niusculo- 
cutaneous  nerve 


The  branch  for  the  long  head  of  the  triceps,  before  its  entrance  into  the  muscle,  breaks  up 
into  four  or  five  filaments. 

The  nerve  supply  of  the  inner  head  of  the  triceps  is  usually  effected  by  two  branches,  an 
upper  and  a  lower.  The  upper  is  short  and  enters  the  muscle  soon  after  leaving  the  musculo- 
spiral.  The  lower,  called  the  collateral  ulnar  branch,  is  longer  and  extends  for  a  considerable 
distance  along  the  inner  surface  of  the  triceps  in  close  association  with  the  ulnar  nerve. 
Posterior  to  the  internal  intermuscular 

septum   it  enters    its    muscle.      Tiny  FIG.   1102. 

filaments  accompany  the  collateral 
ulnar  artery  to  the  capsular  ligament 
of  the  elbow. 

The  nerves  to  the  outer  head  of  the 
triceps  and  to  the  anconeus  take  their 
origin  as  a  single  trunk.  The  former 
passes  directly  to  the  inner  surface  of 
the  outer  head,  while  the  latter  leaves 
the  musculo-spiral  groove  and  tra- 
verses the  outer  portion  of  the  internal 
head  of  the  triceps  until  the  anconeus 
is  reached. 

bb.  After  leaving  the  groove  and 
while  lying  in  the  cleft  between  the 
brachialis  anticus  and  the  brachio- 
radialis,  twigs  are  given  off  for  the 
supply  of  the  brachio-radialis,  the 
extensor  carpi  radialis  longior  and  the 
brachialis  anticus. 

The  nerve  to  the  brachio-radialis 
enters  the  mesial  surface  of  that  muscle 
and  usually  supplies  a  filament  to  the 
capsule  of  the  elbow. 

The  nerve  to  the  extensor  carpi 
radialis  longior  may  arise  either  from 
the  posterior  interosseous  or  directly 
from  the  musculo-spiral. 

The  nerve  to  the  brachialis  anti- 
cus, while  usually  present,  is  not  con- 
stant. It  enters  and  supplies  the  lateral 
portion  of  that  muscle. 

c.  The   humeral   branches  com- 
prise  one   which  is   supplied   to  the 
periosteum  of  the  extensor  surface  of 
the  humerus  and  one  which  enters  the 
shaft  of  the  humerus  with  the  nutrient 
artery,   when    the    latter   arises  as  a 
branch  of  the  superior  profunda. 

d.  The  articular  branches  are  des- 
tined for  the  elbow.     They  arise  from 
the  musculo-spiral  as  it  lies  between 
the  brachialis  anticus  and  the  brachio- 
radialis,  from  the  ulnar  collateral  nerve 
and  from  the  nerve  to  the  anconeus. 

e.  The  terminal  branches  of  the 
musculo-spiral  arises  at  about  the  level 
of  the  external  condyle  and  in  the  fis- 
sure  between    the   brachialis   anticus 
and  the  brachio-radialis.     They  com- 
prise (aa)   the  posterior  interosseous 
and  (bb)  the  radial. 


Radial  nerve 


Inf.  txt.  cutaneous 
branch  musculo-spiral" 

Dorsal  branch 
of  ulnar  nerve 


From  ulnar  nerve 


Superficial  dissection  of  right  forearm,  showing  cutaneous  nerves 
of  posterior  surface. 


aa.  The  posterior  interosseous  nerve  (r.  profundus  n.  radialis)  (  Fig. 
noo)  is  the  larger  of  the  terminal  branches  and  is  mainly  motor  in  function.  Its 
fibres  can  be  traced  back  to  the  sixth,  seventh  and  sometimes  the  eighth  cervical 
nerve.  Shortly  after  its  origin  it  approaches  the  supinator  brevis,  through  a  fissure 
in  whose  substance  it  makes  its  way  to  the  lateral  side  of  the  radius,  in  this  way  reach- 


1312 


HUMAN   ANATOMY. 


Supraacromial  brs.  cervical  plexus 


ing  the  posterior  aspect  of  the  forearm.  Here  it  takes  a  position  between  the  two 
layers  of  the  extensor  muscles  and  rapidly  decreases  in  size  by  giving  off  in  quick 
succession  branches  to  the  neighboring  muscles.  As  a  much  attenuated  nerve  it 
reaches  the  posterior  surface  of  the  interosseous  membrane  at  the  junction  of  the 
middle  and  lower  thirds  of  the  forearm.  From  the  interval  between  the  extensores 

longus  and  brevis  pol- 

FIG.  1103.  licis  it  courses  along 

the  membrane,  cov- 
ered in  turn  by  the  ex- 
tensor longus  pollicis, 
the  extensor  indicis 
and  the  tendons  of 
the  extensor  longus 
digitorum,  finally 
reaching  the  dorsum 
of  the  wrist,  where 
it  presents  a  small 
gangliform  swelling. 
In  the  lower  fourth  of 
its  course  it  is  some- 
times called  the  e.v- 
t  e  r  n  a  I  interosseous 
nerve. 

B  ranches  of 

Lesser  internal     the  posterior   interos- 
cutaiieous  nerve    SCOUS  nerve  Comprise 

two  sets:  those  given 
off  before  and  after 
traversing  the  supina- 
tor  brevis. 


Cutaneous  brs. . 
circumflex  nerve 


Sup.  ext.  cutaneous 

br.  of  musculo- 

spiral  nerve 


Inf.  ext.  cutaneous 
br.  of  rnusculo-i 
spiral  nerve 

M  uscu  lo-cuta  neous 
nerve,  post,  cutaneo 

branch 

Muscuio-cutaneous 

nerve,  ant. 

cutaneous  brancb 

Muscuio-cutaneous, 

post,  cutaneous  br. 


Internal 
cutaneous  nerve 


Those  arising  be- 
fore the  nerve  enters 
the  muscle  comprise  the 
nerves  for  the  extensor 
carpi  radialis  brerior 
and  the  supinator  brevis. 
The  latter  receives  two 
filaments,  which  supply 
the  two  strata  of  muscle 
consequent  upon  the  de- 
lamination  of  the  supin- 
ator brevis  by  the  pos- 
terior interosseous 
nerve.  Quite  frequently 
the  nerve  to  the  exten- 
sor carpi  radialis  long- 
ior  arises  from  this  por- 
tion of  the  posterior 
interosseous. 

The  branches  giv- 
en off  after  leaving  the 
muscle  include  the  sup- 
ply of  the  extensor  car- 
pi H/itaris,  the  extensor 
communis  dig  if  or  urn , 
the  extensor  minimi  digiti,  the  three  extensors  of  the  thumb  and  the  extensor  indicis. 

The  first  three  of  these  muscles  are  supplied  by  a  branch  which  leaves  the  posterior  inter- 
osseous soon  after  its  emergence  from  the  supinator  brevis.  This  nerve  divides  into  two 
branches,  one  of  which  is  distributed  to  the  extensor  carpi  iilnaris  and  the  other  to  the  remain- 
ing two  muscles.  The  extensor  communis  digitorum  receives  additional  innervation  from  a  tu  is; 
which  arises  from  the  posterior  interosseous  further  down  the  forearm. 


Superficial  dissection  of  right  arm,  showing  cutaneous  nerves  of 
anterior  surface;  cephalic  vein  is  seen  passing  up  to  di-lto-pectoral 
interval;  basilic  vein  pierces  deep  fascia  at  lower  inner  aspect  of  arm. 


THE   BRACHIAL    PLEXUS. 


1313 


Inf.  ext.  cutaneous 

br.  of  niusculo-' 

spiral  nerves 


Musculo-cuta- 
neous  nerve,  ant- 
cutaneous  br. 


Musculo-cuta- 

neous  nerve,  post. 

cutaneous  br. 


Lesser  internal 
cutaneous  nerve 


Internal  cutaneous 
nerve 


The  extensor  ossis  metacarf>i  pollicis  and  the  extensor  brevis  pollicis  are  innervated  by  a 
branch  arising  below  the  preceding,  which  breaks  up  into  two  decurrent  twigs,  one  of  which 
goes  to  each  muscle. 

The  extensor  longus  pollicis  is  the  recipient  of  a  small  filament,  which  arises  from  the 
posterior  interosseous  a  short  distance  below  the  preceding  nerve. 

The  extensor  indicis  is  sup- 

plied  b  y   the   lowermost  motor  FIG.   1  104. 

filament  arising  from  the  poste- 
rior interosseous. 

Terminal  twigs  are  distrib- 
uted to  the  dorsal  portion  of  the 
wrist  joint,  the  intercarpal  and 
carpo-metacarpal  joints,  the  peri- 
osteum of  the  radius  and  ulna 
and  the  interosseous  membrane. 
One  of  the  filaments  supplying 
the  last-mentioned  structure  fre- 
quently inosculates  with  a  branch 
from  the  anterior  interosseous. 

The  filaments  to  the  carpus 
are  continued  through  the  meta- 
carpal  spaces  and  are  joined  by 
twigs  from  the  deep  branch  of 
the  ulnar  (page  1305).  The  joint 
nerves  thus  formed  break  up  into 
two  branches  which  accompany 
adjoining  metacarpal  bones  to 
the  metacarpo-phalangeal  articu- 
lations. The  branch  to  the  first 
metacarpal  space  breaks  up  into 
seven  branches  (Rauber). 


Ant.  br.  internal 
cutaneous  nerve 


Brs.  of  ant .  br.  of 
musculo-cutaneous 


Palmar  cuta- 
neous br.  of  ul- 
nar nerve 

Palmar  cutane- 
ous br.  of  me- 
dian nerve 


Digital  brs.  of 
ulnar  nerve 

Digital  brs.  of 
median  nerve 


bb.  The  radial  nerve 
(r.  superficialis  n.  radialis) 
(Fig.  1095)  is  smaller  than 
the  posterior  interosseous 
and  is  purely  sensory  in  its 
function.  Its  fibres  originate 
from  the  sixth  cervical  nerve 
and  sometimes  from  the  fifth 
or  seventh.  From  the  end  of 
the  musculo-spiral  it  passes 
down  the  radial  side  of  the 
forearm  under  cover  of  the 
brachio-radialis  and  anterior 
to  the  supinator  brevis,  the 
pronator  radii  teres  and  the 
radial  head  of  the  flexor 
sublimis  digitorum.  It 
accompanies,  for  the  greater 
part  of  its  course,  the  radial 
artery,  to  the  radial  side  of 
which  the  nerve  lies.  At  the 
junction  of  the  middle  and 
lower  thirds  of  the  forearm 
it  begins  to  turn  gradually 
backward  over  the  radius  and  under  the  tendon  of  the  brachio-radialis  (Fig.  1095). 
Reaching  the  extensor  surface  of  the  forearm  just  above  the  wrist  it  divides  into 
two  diverging  branches,  which  supply  the  back  of  the  hand  and  the  three  outer 
digits  (Fig.  1102). 

Branches.  —  The  radial  nerve  divides  into  two  terminal  branches,  an  external 
and  an  internal. 

S3 


Superficial  dissection  of  rierht  forearm  and  hand,  showing  cutaneous 
nerves  of  anterior  and  palmar  surface. 


1 3i4  HUMAN   ANATOMY. 

The  external  or  radial  branch  inosculates  with  the  musculo-cutaneous  nerve  and  dis- 
tributes filaments  to  the  integument  of  the  thenar  eminence  and  the  radial  side  of  the  thumb  as 
far  out  as  the  base  of  the  nail. 

The  internal  or  ulnar  branch  splits  into  two  parts.  The  inner  of  these  likewise  under- 
goes dichotomous  division  and  supplies  the  dorsal  aspect  of  the  adjacent  surfaces  of  the  thumb 
and  the  index  finger.  The  outer  divides  similarly  to  the  inner  and  is  distributed  to  the  adjoining 
sides  of  the  index  and  middle  fingers.  It  gives  off  a  branch  which  inosculates  with  the  adjacent 
filament  from  the  dorsal  branch  of  the  ulnar  nerve,  so  that  the  contiguous  surfaces  of  the  middle 
and  ring  fingers  are  the  recipients  of  fibres  from  both  the  radial  and  ulnar  nerves. 

As  the  ulnar  side  of  the  hand  is  approximated  the  digital  area  of  distribution  of  the  radial 
nerve  gradually  recedes  toward  the  wrist.  On  the  thumb  the  radial  extends  as  far  out  as  the 
base  of  the  nail,  on  the  index  finger  as  far  as  the  middle  of  the  second  phalanx  and  on  the 
middle  finger  only  over  the  proximal  portion  of  the  first  phalanx.  The  deficiency  in  these 
instances  is  supplied  by  twigs  from  the  digital  branches  of  the  median  nerve. 

Variations. — The  musculo-spiral  may  accompany  the  circumflex  nerve  through  the  quad- 
rilateral space.  It  may  communicate  with  the  ulnar  nerve  in  the  upper  arm.  Cases  are 
recorded  in  which  the  dorsal  digital  nerves  to  the  little  and  the  ulnar  side  of  the  ring  finger 
were  furnished  by  the  musculo-spiral  instead  of  by  the  ulnar  and  in  which  the  inferior  external 
cutaneous  branch  extended  to  the  first  phalanx  of  the  ring  finger  and  the  second  phalanx  of 
the  little  finger.  The  radial  nerve  may  supply  the  entire  dorsum  of  the  hand  and  the  dorsal 
aspect  of  all  the  fingers,  or  it  may  be  absent,  the  musculo-cutaneous  going  to  the  thumb  and 
the  ulnar  to  the  remainder  of  the  digits.  The  external  division  may  send  a  branch  to  the 
palm.  The  posterior  interosseous  may  pass  over  the  surface  of  the  supinator  brevis  and  may 
furnish  a  branch  to  the  anconeus  muscle.  Two  instances  are  reported  in  which  the  posterior 
interosseous  supplied  the  opposed  surfaces  of  the  middle  and  index  fingers. 

Practical  Considerations. — The  musculo-spiral  is  more  frequently  paralyzed 
than  any  of  the  other  branches  of  the  brachial  plexus.  Its  axillary  portion  often 
suffers  from  crutch  pressure  ;  and  the  nerve  is  also  particularly  exposed  to  com- 
pression where  it  passes  between  the  triceps  muscle  and  the  humerus,  as  when  the  arm, 
during  sleep,  is  used  for  a  pillow.  It  has  been  injured  by  violent  contraction  of  the 
triceps  muscle,  as  in  the  act  of  throwing.  It  is  frequently  lacerated  by  the  fragments 
in  fractures  of  the  middle  of  the  shaft  of  the  humerus  When  the  lesion  is  in  the  axilla 
the  triceps  will  be  included  in  the  paralysis.  If  the  portion  in  the  arm  is  affected  the  tri- 
ceps and  anconeus  will  escape,  but  the  following  muscles  will  be  paralyzed  :  the  supina- 
tors,  the  extensors  of  the  hand,  the  extensor  communis  digitorum,  together  with  the 
extensor  indicis,  the  extensor  minimi  digiti  and  the  extensors  of  the  thumb.  The 
characteristic  symptom  is  the  inability  to  extend  the  hand  at  the  wrist  (wrist  drop), 
and  this  is  the  most  common  form  of  musculo-spiral  paralysis. 

THE  THORACIC   NERVES. 

The  thoracic  nerves  (nn.  thoracales)  (Fig.  1105)  consist  of  twelve  pairs  of  sym- 
metrical nerve-cords,  the  upper  eleven  of  which,  because  of  their  position  in  the 
intercostal  spaces,  are  called  intercostal  nerves,  and  the  twelfth,  which  lies  below  the 
twelfth  rib  and  is  an  occupant  of  the  abdominal  wall,  the  subcostal.  Since  only  seven 
ribs  reach  the  sternum,  the  upper  six  thoracic  nerves  alone  are  continued  throughout 
their  entire  course  in  intercostal  spaces.  The  lower  six,  with  the  exception  of  the 
twelfth,  after  traversing  their  respective  intercostal  spaces  proceed  within  the  abdom- 
inal wall,  through  which  they  course  to  within  a  short  distance  of  the  median  line. 
In  accordance  with  the  direction  of  the  ribs,  the  upper  nerves  lie  more  horizontally 
than  the  lower,  the  latter  becoming  more  and  more  oblique  as  the  lower  part  of  the 
abdominal  wall  is  reached.  As  they  advance  from  the  spine,  they  distribute  motor 
filaments  to  the  external  and  internal  intercostals,  the  subcostals,  the  levatores 
costarum,  the  serrati  postici  superior  et  inferior,  the  triangularis  sterni,  the  external 
oblique,  the  internal  oblique,  the  transversalis,  the  rectus,  the  pyramidalis  and  a  por- 
tion of  the  diaphragm.  Their  cutaneous  distribution  comprises  the  integument 
of  the  chest  and  abdomen  anterior  to  the  area  supplied  by  the  posterior  primary 
divisions  of  the  thoracic  nerves.  On  account  of  the  presence  of  the  shoulder  girdle, 
the  usual  nerve  distribution  is  modified  in  the  upper  thoracic  region  and  the  supra- 
clavicular  branches  of  the  cervical  plexus  assume  a  function  belonging  to  the  thoracic 
nerves.  At  the  lower  portion  of  the  trunk  the  usual  arrangement  is  likewise  altered, 


THE   THORACIC    NERVES.  1315 

the  area  immediately  above  Poupart's  ligament  and  the  pubes  being  innervated,  not 
by  the  thoracic,  but  by  the  lumbar  nerves  (Fig.  1105).  The  supply  of  the  cutane- 
ous area  is  provided  by  two  rows  of  sensory  twigs,  which  become  superficial  by 
piercing  the  musculature  and  deep  fascia  of  the  trunk.  Each  of  the  thoracic  nerves, 
with  the  exception  of  the  first,  sends  out  a  lateral  cutaneous  branch  and,  with  no 
exceptions,  an  anterior  cutaneous  branch.  The  upper  thoracic  nerves  deviate 
variously  from  this  typical  arrangement,  the  first  having  no  lateral  and  sometimes  no 
anterior  cutaneous  branch,  and  a  portion  of  the  lateral  cutaneous  branch  of  the 
second,  called  the  intercosto-humeral  nerve,  leaving  the  thorax  to  be  distributed 
in  the  upper  extremity.  The  third  nerve  of  the  series  is  the  first  to  present 
a  typical  arrangement,  although  it,  indeed,  sometimes  forms  a  loop  with  the 
lesser  internal  cutaneous  nerve  of  the  arm.  The  anterior  cutaneous  branches  are 
the  terminal  portions  of  the  thoracic  nerves  and  are  constant  in  their  arrangement 
and  distribution,  with  the  exception  of  the  first,  which  is  either  very  small  or  absent 
and  a  filament  from  the  last,  which  passes  over  the  crest  of  the  ilium  to  the 
gluteal  integument. 

After  separating  from  the  posterior  primary  divisions,  the  anterior  primary 
divisions  of  the  thoracic  nerves,  with  the  exception  of  the  twelfth,  enter  the  inter- 
costal spaces  by  passing  between  the  anterior  costo-transverse  ligaments  and  the 
external  intercostal  muscles.  From  this  situation  to  the  angles  of  the  ribs  they  lie 
between  the  posterior  intercostal  membrane  and  the  external  intercostal  muscles. 
Anterior  to  this  point,  they  are  situated  between  the  two  sets  of  intercostal  muscles, 
as  far  forward  as  the  termination  of  the  external  set  of  muscles  at  the  costo-chondral 
articulations,  from  which  point  forward  their  superficial  covering  is  the  anterior  inter- 
costal membrane  and  the  deep  the  internal  intercostal  muscles.  At  first  they  lie  within 
the  upper  part  of  the  intercostal  space,  but  as  they  advance  they  show  a  tendency 
to  occupy  the  middle  of  the  space.  While  accompanying  the  intercostal  vessels,  they 
lie  below  the  latter  and  at  a  greater  distance  from  the  rib  next  above.  The  upper 
two  nerves  extend  for  a  portion  of  their  course  along  the  inner  surface  of  the  corre- 
sponding ribs;  the  twelfth  passes  in  front  of  the  quadratus  lumborum. 

The  upper  thoracic  nerves,  as  they  approach  the  margin  of  the  sternum,  tra- 
verse the  substance  of  the  internal  intercostal  muscles  and  hold  a  position  anterior 
to  the  internal  mammary  artery  and  the  lateral  portion  of  the  triangularis  sterni 
muscle.  They  terminate  by  piercing  the  anterior  intercostal  membrane  and  the  pec- 
toralis  major,  and  ramify  in  the  pectoral  integument  as  the  anterior  cutaneoiis  nerves 
of  the  thorax  (Fig.  1105). 

The  lower  thoracic  nerves  pass  forward  and  at  the  anterior  ends  of  the  ribs 
take  up  a  deeper  position  in  the  trunk  wall  by  piercing  the  substance  of  the  internal 
intercostal  muscles.  They  then  traverse  the  intervals  between  the  digitations  of 
the  diaphragm  and  enter  the  abdominal  wall,  the  seventh,  eighth  and  ninth  nerves 
lying  behind  the  cartilages  of  the  eighth,  ninth  and  tenth  ribs  respectively.  From 
this  point  their  course  is  ventral,  between  the  internal  oblique  and  the  transversalis, 
as  far  as  the  lateral  edge  of  the  rectus  sheath,  which  they  enter  by  piercing  its  pos- 
terior lamella.  They  ultimately  turn  forward  and  become  superficial  by  traversing 
the  rectus  and  its  anterior  aponeurotic  covering,  terminating  as  the  anterior  cutaneous 
nerves  of  the  abdomen  (Fig.  1105). 

Communications. — Each  thoracic  nerve  is  connected  with  the  sympathetic 
gangliated  cord  by  one  or  two  rami  communicantes  (Fig.  1130).  Ordinarily  there 
is  no  intercommunication  between  the  upper  intercostal  nerves,  but  in  rare  instances 
a  twig  passes  from  one  nerve  over  the  inner  surface  of  the  rib  .next  below  to  the  sub- 
jacent nerve.  The  lower  three  or  four  thoracic  nerves,  while  lying  between  the  broad 
abdominal  muscles  are  occasionally  united  to  one  another,  sometimes  to  the  extent 
of  forming  a  small  plexus. 

Peculiar  thoracic  nerves. — The  first,  second,  twelfth,  and  sometimes  the 
third,  thoracic  nerves  present  peculiarities  which  differentiate  them  from  the  others. 

The  first  thoracic  nerve  sends  a  large  portion  of  its  fibres  to  the  brach- 
ial  plexus,  thus  suffering  great  reduction  in  its  size.  Although  occasionally  a  very 
small  branch  to  the  axilla  is  found,  a  lateral  cutaneous  branch  is  rare,  it  being 
generally  held  that  the  contribution  of  this  nerve  to  the  brachial  plexus  is  the 


1310 


HUMAN   ANATOMY. 


Supraacromial 

branches  of  cer- 

Pectoralis  minor  muscle      vical  plexus 

Pectoralis  major  muscle 
Lesser  internal 
cutaneous 
nerve 


FIG.  1105. 


Descending  branch  of 

superficiahs  colli 

Suprasternal  and  supra- 
clavicular  branches  of 
cervical  plexus 


\ 


Lateral  cutaneous 

branches  of  III., 

IV.,  V.  and  VI. 

thoracic 

nerves 


VII.,  VIII.,  IX.  and 

X.  thoracic 

nerves 


Lateral  cutaneous  branch  of 
XI.  thoracic  nerve 

XI.  thoracic  nerve 

Lateral  cutaneous  branch  of 
XII.  thoracic  nerve 

External  oblique  muscle, 

cut  and  everted 

Internal  oblique  muscle,  cut 

Transversalis  muscle 


Ilio-hypogastric  nerve 

Ilio-hypo-jhyPh 
^stricnerve  I  iliac  bran 

Internal  oblique  muscle       /'.) 
I li' >  in-uin.il  nerve 


Poupart's  ligament 


Anterior 
cutaneous  brs. 
of  II.,  III.,  IV., 
V.  and  VI.  tho- 
racic   nerve-. 


Anterior  brs. 
of  IX.  thoracic 
nerve,  the 
lowest  one  be- 
longing to 
the  X. 


Umbilicus 


Rectusabdom- 
^  inis,  cut 
jfl               Anterior 

V 

branch  of  X. 
thoracic  nerve 

Anterior 
j^B              branch  of 

XI.  thoracic 

Anterior 
•#—          branch  nfXTI 

thoracic  nerve 

Hypogastric 
portion  of  ilio- 

nerve 

of  external 
oblii|ue  mus- 
cle, cut  edge 

Ilio-inguinal  nerve 
Dissection  showing  thoracic,  ilio-hypogastric  and  ilio-inguinai  nerves. 

equivalent  of  a  lateral  cutaneous  branch.  In  addition  to  the  lateral  cutaneous,  the 
anterior  cutaneous  branch  may  also  be  wanting,  the-  area  typically  supplied  by 
the  absent  branch  beiii^  served  by  the  descending  branches  of  the  cervical  plexus. 


THE   THORACIC   NERVES.  1317 

The  second  thoracic  nerve  sometimes  contributes  fibres  to  the  brachial  plexus. 
The  posterior  ramus  of  its  lateral  cutaneous  branch  is  called  the  inter costo- humeral  nerve. 

The  intercosto-humeral  nerve  (n.  intercostobrachialis)  (Fig.  1105)  is  quite 
large  and  pierces  the  inner  axillary  wall  between  the  second  and  third  ribs.  Enter- 
ing the  axilla,  it  crosses  that  space  toward  the  arm  and  communicates  with  the  lesser 
internal  cutaneous  nerve  from  the  brachial  plexus.  After  piercing  the  deep  fascia, 
the  intercosto-humeral  nerve  supplies  the  internal  and  posterior  portion  of  the  integ- 
ument of  the  upper  half  of  the  arm,  a  few  of  its  fibres  extending  slightly  beyond  the 
margin  of  the  scapula. 

The  third  thoracic  nerve  may  form  an  inosculation  with  the  lesser  internal 
cutaneous  nerve. 

The  twelfth  thoracic  or  the  subcostal  nerve  lies  below  the  last  rib  and 
therefore  does  not  occupy  an  intercostal  space,  but  passes  outward  below  the 
external  arcuate  ligament  and  anterior  to  the  quadratus  lumborum  muscle.  It 
contributes  a  twig  to  the  lumbar  plexus  which  passes  down  to  join  the  first  lumbar 
nerve.  Its  lateral  cutaneous  branch  is  not  confined  in  its  distribution  to  the 
abdominal  wall,  since,  after  piercing  the  internal  oblique  and  sending  a  filament 
to  the  lower  digitation  of  the  external  oblique,  it  penetrates  the  substance  of  the 
latter  muscle  at  a  point  from  2-10  cm.  above  the  crest  of  the  ilium  and  supplies  the 
integument  of  the  gluteal  region  as  far  down  as  the  upper  margin  of  the  great 
trochanter  (Fig.  1083). 

Branches  of  the  thoracic  nerves  are  :  (i)  the  muscular  and  (2)  the  cutaneous. 

I.  The  muscular  branches  (rr.  musculares)  may  be  divided  into  two  groups:  (a)  the  thoracic 
and  (b)  the  abdominal. 

a.  The  thoracic  muscular  branches  arise  from  the  first  to  the  seventh  inclusive  and  supply 
the  external   and   internal   intercostals,    the  subcostals,  the  levatores  costarum,  the  serratus 
posticus  superior,  the  triangularis  sterni  and  the  rectus  abdominis. 

The  branches  to  the  intercostal  and  subcostal  muscles  are  distributed  throughout  the  course 
~>f  each  nerve.  The  first  to  be  given  off  is  the  largest  and  courses  forward  for  some  distance 
along  the  lower  part  of  the  intercostal  space.  The  others  vary  greatly  in  number  and  size. 

The  branches  to  the  levatores  costarum  consist  of  fine  threads,  one  arising  from  each  nerve 
beyond  the  anterior  costo-transverse  ligament.  They  pierce  the  external  intercostal  muscles 
and  enter  the  deep  surface  of  the  muscles  which  they  supply. 

THe  branches  to  the  serratus  posticus  superior  arise  from  the  upper  four  nerves.  After 
piercing  the  external  intercostal  muscles  they  pass  along  the  outer  margin  of  the  ilio-costalis  and 
supply  the  four  digitations  of  their  muscle. 

The  branches  to  the  triangularis  sterni  are  terminal  continuations  of  the  third  to  the  seventh 
intercostal  nerves.  After  piercing  the  internal  intercostal  muscles  they  pass  forward  between 
the  triangularis  sterni  and  the  internal  intercostals  or,  in  the  case  of  the  seventh,  anterior  to  the 
transversalis  muscle.  In  addition  to  supplying  the  triangularis  sterni  the  seventh  sends  fibres  to 
the  first  digitation  of  the  transversalis. 

The  branches  to  the  rectus  arise  from  the  fifth,  sixth  and  seventh  and  enter  the  deep 
surface  of  the  muscle. 

b.  The  abdominal  muscular  branches  arise  from  the  eighth  to  the  twelfth  inclusive  and  are 
distributed  to  the  intercostals,  the  subcostals,  the  levatores  costarum,  the  serratus  posticus  inferior, 
the  external  obique,  the  internal  oblique,  the  transversalis,  the  rectus,  the  pyramidalis  and  the 
diaphragm. 

The  branches  to  the  intercostal,  subcostal  and  levatores  costarum  muscles,  with  the  excep- 
tion of  arising  from  the  lower  thoracic  nerves,  resemble  in  origin,  course  and  distribution  those 
arising  from  the  upper  nerves. 

The  branches  to  the  serratus  posticus  inferior  are  larger  than  those  to  the  serratus  posticus 
superior.  They  arise  from  the  ninth,  tenth  and  eleventh  nerves  and  pass  around  the  lateral 
margin  of  the  ilio-costalis  to  reach  their  destination. 

The  branches  to  the  external  oblique,  the  internal  oblique  and  the  transversalis  comprise 
numerous  fine  twigs  which  supply  those  muscles  and  arise  from  the  lower  five  thoracic  nerves  as 
they  course  forward  between  the  transversalis  and  the  internal  oblique. 

The  branches  to  the  rectus  arise  from  the  eighth  to  the  twelfth  nerves  inclusive  after  they 
have  entered  the  sheath  and  as  they  pierce  the  rectus  on  their  way  to  the  surface. 

The  branches  to  the  pyramidalis  are  derived  from  the  twelfth  thoracic  and  first  lumbar 
nerves. 

The  branches  to  the  diaphragm  are  supplied  to  its  costal  portion  and  consist  of  fine 
filaments  which  are  given  off  by  the  lower  six  thoracic  nerves  (Luschka). 


I3i8  HUMAN   ANATOMY. 

2.  The  cutaneous  branches  are  larger  than  the  muscular  and  consist  of  two 
sets  :  (a)  the  lateral  cutaneous  and  (6)  the  anterior  cutaneous. 

a.  The  lateral  cutaneous  branches  (rr.  cutanei  laterales)  consist  of  two  series,  an  upper 
and  a  lower,  the  former  originating  from  the  first  to  the  sixth  and  the  latter  from  the  sixth  to  the 
twelfth  thoracic  nerves.     Those  of  the  upper  series  pierce  the  external  intercostal  muscles  and 
those  of  the  lower  the  external  oblique  in  a  line  situated  midway  between  the  mammary  and 
mid-axillary  lines.     The  upper  seven  pass  between  the  dictations  of  the  serratus  magnus  and  the 
lower  between  the  digitations  of  the  latissimus  dorsi  and  the  external  oblique.     The  one  arising 
from  the  twelfth  pierces  the  musculature  of  the  external  oblique.     Each  lateral  cutaneous  nerve 
divides  into  (aa)  an  anterior  and  (bb}  a  posterior  branch  (Fig.  1083). 

aa.  The  posterior  branches  (rr.  posteriores)  are  smaller  than  the  anterior.  They  wind 
around  the  edge  of  the  latissimus  dorsi  and  supply  the  integument  of  the  lateral  area  of  the 
trunk  as  far  back  as  the  anterior  margin  of  the  region  supplied  by  the  posterior  primary  divi- 
sions of  the  thoracic  nerves.  The  branches  from  the  third  to  the  sixth  inclusive  have  fibres 
which  are  distributed  over  the  lateral  portion  of  the  scapula. 

bb.  The  anterior  branches  ( rr.  anteriores  [pectorales  et  abdominales] )  are  of  considerably 
greater  size  than  the  posterior.  Those  from  the  second  to  the  seventh  pass  toward  the  lateral 
margin  of  the  pectoralis  major  and  supply  the  integument  of  this  region  as  far  forward  as  the 
nipple.  Branches  (rr.  mammarii  laterales)  from  the  fourth,  fifth,  and  sixth  send  filaments  to 
the  skin  and  substance  of  the  mammary  gland.  Those  from  the  seventh  to  the  eleventh  supply 
the  integument  of  the  abdomen  as  far  anterior  as  the  lateral  margin  of  the  rectus.  The  anterior 
branch  from  the  twelfth  has  a  filament  which  passes  over  the  iliac  crest  to  the  integument  of  the 
gluteal  region,  usually  sending  a  branch  as  far  as  the  great  trochanter.  It  maintains  a  more  or 
less  even  balance  with  the  corresponding  branch  of  the  first  lumbar  nerve,  each  supplying  any 
deficiency  in  the  other. 

b.  The  anterior  cutaneous  branches  (rr.  cutanei  anteriores)  are  the  terminal  fibres  of  the 
thoracic  nerves.    Those  from  the  upper  six  (rr.  cutanei  pectorales  anteriores)  pierce  the  pectoralis 
major  near  the  lateral  margin  of  the  sternum  and  supply  the  adjacent  integument  of  the  thorax. 
Filaments  (rr.  mammarii  mediales)  are  distributed  to  the  skin  of  the  mesial  portion  of  the  mam- 
mary gland.     The  anterior  cutaneous  branches  from  the  lower  six  (rr.  cutanei  al>dominales  ante- 
riores) vary  in  position.      They  consist  of  the  terminal  filaments  which  perforate  the  anterior 
portion  of  the  rectus  sheath  at  a  situation  anywhere  between  the  lineae  alba  and  semilunaris. 
Those  from  the  seventh  become  superficial  near  the  ensiform  cartilage,  those  from  the  tenth 
supply  the  region  of  the  umbilicus  and  those  from  the  twelfth  are  distributed  to  the  area  located 
midway  between  the  umbilicus  and  the  pubic  crest  (Fig.  1105). 

# 

Practical  Considerations. — Of  the  branches  of  the  thoracic  spinal  nerves, 
the  anterior  or  intercostals  suffer  most  frequently  from  sensory  disturbances,  and 
the  posterior  from  motor  disturbances.  Intercostal  neuralgia  may  result  from 
pressure,  as  from  aneurism  or  spinal  disease,  or  it  may  be  due  to  injury.  The  lower 
intercostals  enter  into  the  supply  of  both  the  thoracic  and  the  anterior  abdominal 
walls,  the  pleura  also  being  supplied  by  them.  Pain  referred  to  the  abdominal  wall 
and  rigidity  of  the  abdominal  muscles  may  therefore  be  due  to  diseases  within  the 
chest,  as  pleurisy.  Such  diseases  in  the  upper  part  of  the  chest  may  cause  pain  to 
extend  down  the  arm  along  the  intercosto-humeral  nerve,  which  is  the  lateral  cuta- 
neous branch  of  the  second  intercostal  nerve,  or  sometimes  of  the  second  and  third 
intercostals.  The  pain  of  intercostal  neuralgias  often  becomes  intense,  especially 
after  violent  expiratory  efforts,  as  in  coughing  and  sneezing  ;  not  infrequently  after 
the  pain  ceases,  herpes  zoster  appears  in  the  line  of  the  nerve  affected.  This  may  be 
a  trophic  disturbance  or  an  extension  of  the  inflammation  along  the  nerve  endings 
to  the  skin.  Mastodynia,  or  the  so-called  "irritable  breast  of  Cooper,"  is  due  to 
intercostal  neuralgia,  and  occurs  in  the  female  during  the  child-bearing  period. 

The  lower  intercostal  nerves,  with  the  ilio-hypogastric  and  ilio-inguinal,  supply 
the  muscles  of  the  abdominal  wall,  and  are  frequently  injured  by  the  incisions  mack' 
in  abdominal  operations,  thus  leading  to  more  or  less  impairment  of  the  muscles  sup- 
plied and  favoring  the  later  development  of  hernia.  The  incision  should  therefore, 
so  far  as  possible,  be  made  in  the  line  of  the  fibres  of  the  muscles  (page  535)- 

The  intercostal  nerves  continue  their  oblique  line  through  the  abdominal  mus- 
cles. The  pain  from  Pott's  disease'  is  often  transferred  along  the  nerves  coining  from 
the  affected  segment  of  the  cord.  In  this  way  pain  in  the  abdominal  region  may 


THE   LUMBAR    PLEXUS. 


13*9 


result  from  this  disease,  and  an  abdominal  lesion  may  be  suspected ;  this  has 
occurred  more  particularly  in  children.  A  feeling  of  tightness  is  sometimes  observed 
about  the  abdomen,  corresponding  to  the  course  of  one  or  more  pairs  of  these 
nerves,  and  may  be  due  to  impaired  sensation  in  them.  Since  the  abdominal 
muscles  are  supplied  chiefly  by  the  seven  lower  intercostal  nerves,  they  are 
concerned  in  respiration.  When  they  are  contracted  as  in  general  peritonitis,  the 
lower  ribs  become  immobile,  and  breathing  takes  place  chiefly  in  the  upper  portion 
of  the  chest. 


FIG.  1106. 


THE   LUMBAR    PLEXUS. 

The  lumbar  plexus  (plexus  lumbalis)  lies  in  the  substance  of  the  psoas  magnus 
muscle,  anterior  to  the  transverse  processes  of  the  lumbar  vertebrae,  and  consists  of 
a  series  of  loops  formed  by  the  anterior  primary  divisions  of  the  first,  second  and 
third  lumbar  nerves,  the  smaller  subdivision  of  the  fourth  lumbar  and  sometimes  a 
branch  from  the  twelfth  thoracic  nerve.  The  remainder  and  major  portion  of  the 
fourth  lumbar  nerve  unites  with  the  entire  anterior  primary  division  of  the  fifth  to 
form  a  conjoint  trunk,  the  lumbo-sacral  cord  (truncus  lumbosacralis),  which 
passes  into  the  pelvis  to  become  a  constituent  of  the  sacral  plexus  (Fig.  1106). 
The  lumbar  nerves  increase  in  thickness  from  above  downward,  the  first  being  only 
2.5  mm.,  while  the  fifth  attains  a  diameter  of  7  mm.  The  length  of  the  nerves  from 
their  exit  at  the  intervertebral  foramina  to  their  point  of  division  varies  considerably, 
in  the  case  of  the  first  being  i  mm.  or  less,  of  the  second  10  mm.  'and  of  the  third 
from  20-25  mm- 

Constitution  and  Plan. — In  forming  the  plexus  (Fig.  1106),  the  first  lumbar 
nerve  divides  almost  immediately  after  its  exit  from  the  vertebral  column  into  an 
upper  and  a  lower  branch.  The  upper, 
which  may  receive  a  contribution  from 
the  twelfth  thoracic  nerve,  becomes  the 
ilio-hypogastrica.nd  ilio-inguinal  nerves. 
The  lower  branch,  near  the  body  of  the 
second  lumbar  vertebra  joins  the  upper 
part  of  the  second  lumbar  nerve,  which, 
like  the  first,  divides  into  an  upper  and 
a  lower  branch.  The  union  of  the  lower 
branch  of  the  first  and  the  upper  branch 
of  the  second  results  in  the  formation  of 
the  genito-crural  nerve.  Sometimes 
fibres  from  the  first  aid  in  the  formation 
of  the  anterior  crural  and  obturator 
nerves.  The  lower  branch  of  the  second, 
all  of  the  third  and  that  part  of  the 
fourth  which  enters  the  lumbar  plexus 
divide  into  smaller  anterior  and  larger 
posterior  trunks.  From  the  union  of 
the  anterior  branches  of  these  three  the 
.obturator  nerve  is  formed,  and  from  the 
union  of  the  posterior  results  the  an- 
terior crural  nerve.  The  posterior  por- 
tions of  the  second  and  third  nerves 
give  off  from  their  dorsal  aspect  small 
branches  which  unite  into  the  external 
cutaneous  nerve.  The  accessory  obturator 
nerve,  when  it  exists,  arises  from  the  third  and  fourth  lumbar  between  the  roots  of 
the  anterior  crural  and  obturator  nerves. 

Communications. — All  of  the  lumbar  nerves  receive  gray  rami  communicantes 
from  the  gangliated  cord  of  the  sympathetic  ;  and  from  the  first  and  second,  and 
possibly  the  third  and  fourth,  white  rami  communicantes  pass  to  the  lumbar  portion 
of  the  gangliated  cord. 


Diagram  illustrating  plan  of  lumbar  plexus. 


1320  HUMAN   ANATOMY. 

Variations. — That  portion  of  the  fourth  lumbar  nerve,  or  n.  f urea/is,  which  joins  the  lumbo- 
sacral  cord,  is  usually  less  than  half  of  the  parent  trunk,  but  varies  from  one-twentieth  to 
nine-tenths.  When  large,  it  may  be  joined  by  a  branch  from  the  third  lumbar,  and  when 
small  the  fifth  lumbar  may  contribute  to  the  lumbar  plexus,  the  fibres  going  to  the  ante- 
rior crural  alone  or  to  the  anterior  crural  and  obturator  nerves.  The  branch  to  the  lumbo- 
sacral  cord  from  the  fourth  lumbar  may  be  absent  and  in  such  an  event  the  fifth  is  the  only 
furcal  nerve  sending  fibres  to  both  the  lumbar  and  the  sacral  plexus.  It  is  thus  possible  to 
have  as  furcal  nerves  the  third  and  fourth,  the  fourth  alone,  the  fourth  and  fifth  or  the  fifth 
alone,  and  according  to  the  high  or  low  position  of  these  there  is  found  a  corresponding  origin 
of  the  branches  of  the  lumbar  plexus.  In  this  manner  are  accounted  for  the  high  and  low,  or 
prefixed  and  postfixed  types  of  plexus. 

Branches  of  the  lumbar  plexus  are  : 

1.  The  Muscular  5.   The  External  Cutaneous 

2.  The  Ilio-Hypogastric  6.   The  Obturator 

3.  The  Ilio-Inguinal  7.   The  Accessory  Obturator 

4.  The  Genito-Crural  8.   The  Anterior  Crural 

i.     THE  MUSCULAR  BRANCHES. 

The  muscular  branches  (rr.  musculares)  supply  the  quadratus  lumborum,  the 
psoas  magnus  and  the  psoas  parvus. 

The  branches  to  the  quadratus  lumborum  arise  from  the  upper  three  or  four 
lumbar  nerves,  and  sometimes  from  the  last  thoracic,  and  pass  directly  into  the 
quadratus. 

The  branches  to  thefisoas  mag-mts  arise  mainly  from  the  second  and  third  lumbar 
nerves,  there  sometimes  being  additional  ones  from  the  first  and  fourth.  They  pass 
directly  into  the  muscle. 

The  branches  to  the  psoas  parvus  consist  of  filaments  from  the  first  or  second 
lumbar  nerve  which  reach  the  muscle  by  piercing  the  underlying  psoas  magnus. 

2.     THE  ILIO-HYPOGASTRIC  NERVE. 

The  ilio-hypogastric  nerve  (n.  iliohypogastricus)  (Fig.  1107)  is  the  uppermost 
branch  of  the  plexus  and  is  somewhat  larger  than  its  associate,  the  ilio-inguinal.  Whilst 
it  derives  the  major  portion  and  sometimes  all  of  its  fibres  from  the  first  lumbar  nerve, 
it  usually  receives  others  from  the  twelfth  and  occasionally  the  eleventh  thoracic.  It 
emerges  from  the  lateral  margin  of  the  upper  portion  of  the  psoas  magnus  and  runs, 
below  and  parallel  with  the  twelfth  thoracic  nerve,  outward  and  downward,  posterior 
to  the  kidney  and  anterior  to  the  quadratus  lumborum.  Reaching  the  crest  of  the 
ilium,  it  pierces  the  transversalis  muscle  and  occupies  the  intermuscular  space  between 
the  internal  oblique  and  the  transversalis.  After  coursing  along  this  interval  as  far 
as  the  middle  of  the  iliac  crest,  it  divides  into  its  terminal  branches,  (a}  the  iliac  and 
(£)  the  hypogastric,  which  correspond  morphologically  with  the  lateral  and  anterior 
cutaneous  branches  of  the  thoracic  nerves.  There  are  also  some  (c~)  muscular 
branches. 

a.  The  iliac  branch  (r.  cutaneus  lateralis)  pierces  the  internal  and  external  obliques  about 
the  middle  of  the  iliac  crest  and  is  distributed  to  the  integument  of  the  anterior  gluteal  region 
which   covers  the  gluteus  medius   and   the  tensor  fasciae  femoris  (Fig.   1083).     It  forms  an 
inosculation  with  the  lateral  cutaneous  branch  of  the  twelfth  thoracic  nerve  and  maintains  an 
even  balance1  with  it,  deficiency  in  the  development  of  either  being  recompensed  for  by  a  com- 
pensating increase  in  size  of  the  other. 

b.  The   hypogastric    branch  (r.   cutaneus   anterior)   continues   the   direction  and  course 
of  the  main  trunk  between  the  transversalis  and  the  internal  oblique  almost  to  the  linea  alba. 
Near  the  anterior  superior  spine  of  the  ilium  it  forms  an  inosculation  with  the   ilio-inguinal 
nerve.     As  it  approaches  the  region  of  the  internal  abdominal  ring  it  begins  to  push  its  way 
gradually  through  the  internal  oblique  and  gain  the  interval  between  the  internal  and  the  exter- 
nal oblique  (Fig.  1105).     A  short  distance  superior  and  internal  to  the  external  abdominal  ring 
it  traverses  a  tiny  foramen  in  the  aponeurosis  of  the  external  oblique  and  breaks  up  into  fibres 
of  termination  which  supply  the  integument  of  the  suprapubic  region. 

c.  Muscular  branches  (rr.  musculares)  arise  from  the  hypogastric  branch  in  its  course 
through  the  abdominal  wall  and  supply  the  transversalis,  the  internal  oblique  and  the  external 
oblique. 


THE   LUMBAR    PLEXUS. 


1321 


Variations. — The  iliac  branch  may  be  absent,  its  place  being  taken  by  the  lateral  cutaneous 
branch  of  the  twelfth  thoracic  nerve.  The  hypogastric  branch  may  inosculate  with  the  twelfth 
thoracic  and  may  supply  the  pyramidalis  muscle. 

3.     THE  ILIO-INGUINAL  NERVE. 

The  ilio-inguinal  nerve  (n.  ilioinguinalis)  (Fig.  1107)  is  the  second  branch  of 
the  lumbar  plexus  and  is  somewhat  smaller  than  the  ilio-hypogastric.  Its  fibres 
usually  arise  from  the  first  lumbar  nerve,  with  accessions  from  the  twelfth  thoracic. 

FIG.  1107. 


XII.  rib 
XII.  thoracic  nerve 


Quadratus  lumborum 
Psoas  magnus 


External  oblique 

Lateral  cutaneous  branch 

of  XII.  dorsal  nerve 

Internal  oblique 

Transversalis 

Ilio-hypogastric  nerve 

Ilio-inguinal  nerve 

Iliac  branch  of 
ilio-hypogastric 


Lateral  cutaneous  branch 
of  XII.  dorsal  nerve 


External  cutaneous  nerve 

Anterior  crural  nerve 
Genital  branch  of 
genito-crural  nerve 


Crural  branch  of 

genito-crural  nerve 


Branches  of  middle 

cutaneous  nerve 


I.  lumbar  ganglion 


Rami  communicantes 


Aorta 

IV.  lumbar  nerve 

lumbar  ganglion 

lumbar  nerve 

rt  of  V.  lumbar  ganglion 


nito-crural  nerve 
sacral  ganglion 

sacral  nerve 


II.  sacral  nerve 


sacral  ganglion 

urator  nerve 

:essory  obturator  nerve 

)  Hypogastric  branches 
j  of  ilio-hypogastric  nerve 

Ilio-inguinal  nerve 


Branch  of  internal 
cutaneous  nerve 


Deep  dissection,  showing  nerves  arising  from  lumbar  plexus  and  lower  part 
of  sympathetic  gangliated  cord. 

Sometimes  it  arises  entirely  from  the  twelfth  thoracic  or  from  the  second  lumbar  or 
from  the  loop  between  the  first  and  second  lumbar  nerves.  It  occasionally  forms  a 
common  trunk  of  considerable  length  with  the  ilio-hypogastric.  In  the  early  part 


1322  HUMAN    ANATOMY. 

of  its  course  it  parallels  the  ilio-hypogastric,  appearing  at  the  edge  of  the  psoas 
magnus,  crossing  the  quadratus  lumborum  behind  the  kidney  and  piercing  the  trans- 
versalis  to  reach  the  intermuscular  cleft  between  the  transversalis  and  the  internal 
oblique  (Fig.  1105).  While  in  the  last  situation  it  inosculates  with  the  ilio-hypo- 
gastric and  continues  forward  to  enter  the  inguinal  canal,  from  which  it  emerges 
either  through  the  external  abdominal  ring  or  through  the  external  pillar  of  the 
ring,  infero-lateral  to  the  spermatic  cord. 

Some  of  the  branches  of  the  ilio-inguinal  supply  the  integument  of  the  upper  inner  portion 
of  the  thigh.  Others  (nn.  scrotales  anteriores)  are  distributed  to  the  pubic  region  and  the  base 
of  the  penis  and  scrotum  or,  in  the  female  ( nn.  labiates  anteriores ),  the  mons  Veneris  and  labia 
majora.  Tiny  motor  filaments  (rr.  musculares)  are  given  off  in  the  course  of  the  nerve  to  the 
transversalis,  the  internal  oblique  and  the  external  oblique. 

Variations. — The  ilio-inguinal  may  be  small  and  terminate  near  the  iliac  crest  by  joining 
the  ilio-hypogastric,  which  then  sends  off  an  inguinal  branch  with  the  course  and  distribution  of 
the  absent  portion  of  the  ilio-inguinal.  The  nerve  may  be  absent  entirely  and  replaced  by  either 
branch,  usually  the  genital,  of  the  genito-crural.  It  may  give  off  a  lateral  cutaneous  or  iliac 
branch  for  the  supply  of  the  integument  in  the  region  of  the  anterior  superior  spine  of  the  ilium. 
The  ilio-inguinal  may  partially  replace  the  genital  branch  of  the  genito-crural  or,  in  rare  in- 
stances, the  external  cutaneous. 

4.    THE   GENITO-CRURAL   NERVE. 

The  genito-crural  nerve  (n.  genitofemoralis)  is  formed  by  two  roots,  one  of  which 
arises  from  the  loop  between  the  first  and  second  lumbar  nerves  and  the  other 
directly  from  the  second  lumbar  nerve,  its  fibres  being  derivatives  of  the  first  and 
second  lumbar.  The  nerve  passes  obliquely  forward  through  the  musculature  of  the 
psoas  magnus,  near  the  inner  border  of  whose  anterior  surface  it  emerges  opposite 
the  body  of  the  third  lumbar  vertebra,  where  division  into  the  two  terminal 
branches,  (a)  the  genital  and  (t>~)  the  crural,  takes  place  (Fig.  1107).  Occa- 
sionally division  occurs  earlier  in  the  course  of  the  nerve,  in  the  substance  of  the 
psoas,  and  under  these  circumstances  the  two  branches  emerge  separately  from  the 
muscle.  In  addition  to  the  terminal  branches  there  are  some  (r)  muscular  twigs. 

a.  The  genital  branch  (n.  spermaticus  externus)  obtains   its  fibres   from   the  first   lumbar 
nerve.     Passing  downward  on  the  inner  margin  of  the  psoas  magnus,  it  crosses  the  external 
iliac  artery  and  bends  forward  toward  the  posterior  wall  of  the  inguinal  canal.     It  then  enters 
the  canal  either  by  piercing  the  infundibuliform  or  the  transversalis  fascia  and,  lying  internal  to 
and  below  the  spermatic  cord,  traverses  the  canal  and  enters  the  scrotum  (Fig.  1108).     It  sends 
a  filament  to  the  external  iliac  artery  and  supplies  the  cremaster  muscle,  the  skin  of  the  scrotum 
and  the  integument  of  the  thigh  immediately  adjacent  to  the  scrotum.     In  the  female  it  is 
smaller  and  accompanies  the  round  ligament  of  the  uterus  to  the  labium  majus,  to  whose  in- 
tegument it  is  distributed.      It  communicates  with  the  ilio-inguinal  nerve  and  with  the  spermatic 
plexus  of  the  sympathetic. 

b.  The  crural  branch  (n.  lumboinguinalis)  consists  of  fibres  from  the  second  lumbar  nerve. 
It  courses  down  on  the  anterior  surface  of  the  psoas  magnus,  lateral  to  the  genital  branch  and 
to  the  external  iliac  vessels,  and  enters  the  thigh  by  passing  beneath  Poupart's  ligament.     One 
of  its  filaments  traverses  the  saphenous  opening,  while  the  remainder  of  the  nerve  pierces  the 
fascia  lata  to  the  outer  side  of  the  opening  (Fig.  1107).     Its  branches  vary  considerably  in  size 
and  length  and  are  distributed  to  the  cutaneous  area  of  the  upper  anterior  part  of  the  thigh 
between  the  regions  supplied  by  the  external  cutaneous  and   ilio-inguinal  nerves,  sometimes 
extending  downward  as  far  as  the  middle  of  the  thigh.     It  furnishes  a  minute  branch  to  the 
femoral  artery  and  inosculates  with  the  middle  cutaneous  nerve. 

c.  Muscular  branches  to  the  internal  oblique  and  transversalis  are  frequently  given  off  by 
the  genital  branch. 

Variations.— The  genital  and  crural  branches  may  arise  as  separate  offshoots  of  the  lumbar 
plexus  and  either  of  them  may  be  derived  entirely  from  the-  first  or  the  second  lumbar  nerve. 
The  genital  branch  sometimes  contains  fibres  from  the  twelfth  thoracic.  Absence  of  the  genito- 
crural  or  of  either  branch  may  occur,  the  fibres  of  the  genital  branch  being  contained  in  the  ilio- 
inguinal  and  those  of  the  crural  in  the  external  cutaneous  or  the  anterior  crural.  The  genital 
branch  may  replace  or  reinforce  the  ilio-inguinal  nerve;  the  crural  branch  may  act  similarly 
toward  the 'external  or  the  middle  cutaneous  nerve.  A  specimen  found  in  the  anatomical  labo- 
ratory of  the  I  niv.  rsity  of  Pennsylvania  showed  unusually  extensive  distribution  of  the  crural 


THE   LUMBAR    PLEXUS. 


1323 


branch.     It  was  larger  than  normal,  its  size  being  that  of  the  normal  external  cutaneous,  and  it 
emerged  from  the  deep  fascia  below  Poupart's  ligament  directly  anterior  to  the  femoral  vein.    It 

FIG.   1108. 


Psoas  parvus 

Genito-crural  nerv.e 
Psoas  magnus 

Anterior  crural  nerve 

External  cutaneous  nerve 

Genital  branch  of  genito-crural 

Sartorius,  stump 

Branch  to  pectineus 

Branch  to  rectus  femoris 
Branch  to  vastus  externus 


Rectus  femoris 
Middle  cutaneous  nerve 


Rectus  femoris 


-Accessory  obturator 

Crural  branch  of 

genito-crural 
Ilio-inguinal  nerve 

Pectineus 
Adductor  longus 

Internal  saphenous 

nerve 
Internal  cutaneous 

nerve 


Muscular  branch  of 
superficial  division 
of  obturator  nerve 


Branch  from  internal  saptienous 
to  subsartorial  plexus 


Branch  to  vastus  interims 


Anterior  branch  of  internal  cutaneous 

Cutaneous  branch  of  superficial  division 
of  obturator  nerve 


Posterior  branch  of  internal  cutaneous 


From  posterior  branch  of  internal  cutaneous- 


Articular  branch  from  nerve  to  vastus 
internus 


—  Cutaneous  patellar  branch  of  internal 
saphenous  nerve 

— -Internal  saphenous  nerve 


Dissection  of  right  thigh,  showing  branches  of  anterior  crural  nerve. 

divided  into  a  smaller  mesial  and  larger  lateral  branch  and  was  distributed  to  the  integument  of 
the  thigh  as  far  down  as  the  junction  of  the  middle  and  lower  thirds. 


i324  HUMAN   ANATOMY. 

5.     THE  EXTERNAL  CUTANEOUS  NERVE. 

The  external  cutaneous  nerve  (n.  cutaneus  femoris  lateralis)  (Fig.  1109)  arises  at 
the  posterior  aspect  of  the  lumbar  plexus  from  the  second  and,  to  a  less  extent,  the 
third  lumbar  nerve.  It  may  arise  from  the  first  and  second,  from  the  second  alone 
or  may  derive  a  majority  of  its  constituent  fibres  from  the  third.  It  passes  obliquely 
downward  and  outward  beneath  the  lateral  margin  of  the  psoas  magnus  and  over  the 
iliacus  muscle,  through  the  iliac  fossa,  covered  by  the  iliac  fascia.  After  crossing  the 
deep  circumflex  iliac  artery  it  enters  the  thigh  beneath  Poupart's  ligament,  mesial 
to  the  anterior  superior  spine  of  the  ilium,  and  passes  over,  sometimes  through  or 
under,  the  pointed  tendinous  origin  of  the  sartorius.  The  nerve  then  descends  in 
the  thigh  beneath  the  fascia  lata  and  soon  divides  into  (a)  an  anterior  and  (£)  a 
posterior  terminal  branch  (Fig.  moj. 

a.  The  anterior  branch  (r.  anterior)  follows  a  downward  course  in  the  thigh  in  a  tubular 
canal  in  the  fascia  lata,  from  which  it  emerges  at  a  point  10-15  cm.  below  the  anterior  superior 
iliac  spine.     It  continues  downward  anterior  to  the  vastus  externus  muscle  and  is  distributed  to 
the  integument  of  the  antero-lateral  aspect  of  the  thigh  as  far  as  the  knee.     Numerous  collateral 
branches  are  given  off,  the  majority  of  which  arise  from  its  lateral  edge  and  supply  the  skin  over 
the  ilio-tibial  band.     The  main  trunk  may  extend  quite  to  the  knee  and  become  a  participant  in 
the  formation  of  the  patellar  plexus. 

b.  The  posterior  branch  (r.  posterior)  passes  obliquely  backward  through  the  fascia  lata 
and  breaks  up  into  several  branches  which  are  distributed  to  the  integument  over  the  tensor 
fasciae  femoris  and  the  lower  portion  of  the  gluteal  region.     The  uppermost  filaments  are  crossed 
by  twigs  from  the  lateral  cutaneous  branch  of  the  twelfth  thoracic  nerve. 

Variations. — The  external  cutaneous  may  be  associated  with  the  anterior  crural  until  after 
Poupart's  ligament  has  been  passed.  A  branch  of  the  genito-crural  may  replace  the  posterior 
branch.  In  one  case  a  branch  of  the  ilio-inguinal  took  the  place  of  the  external  cutaneous. 

Three  specimens  found  in  the  anatomical  rooms  of  the  University  of  Pennsylvania  showed 
decided  anomalies.  In  one  the  nerve  passed  beneath  Poupart's  ligament  at  a  point  midway 
between  the  anterior  superior  spine  of  the  ilium  and  the  femoral  artery.  In  another  the  nerve 
of  the  right  side  resembled  in  position  the  one  just  mentioned,  while  the  left  was  apparently 
absent,  its  place  being  taken  by  a  branch  of  the  anterior  crural.  In  the  third  the  posterior 
branch  emerged  from  beneath  Poupart's  ligament  5  cm.  to  the  inner  side  of  the  anterior  superior 
iliac  spine.  The  anterior  branch  formed  a  common  trunk  with  the  external  branch  of  the  mid- 
dle cutaneous  nerve.  From  the  joint  trunk  a  small  branch  passed  to  join  the  internal  branch  of 
the  middle  cutaneous  after  the  latter  had  pierced  the  sartorius  muscle. 

6.     THE  OBTURATOR  NERVE. 

The  obturator  nerve  (n.  obturatorius)  (Fig.  1109)  is  composed  of  fibres  which 
arise  from  the  second,  third  and  fourth  lumbar  nerves,  the  fourth  supplying  the 
largest  and  the  second  the  smallest  contribution,  the  latter  sometimes  being  absent 
entirely.  Occasionally  additional  roots  are  derived  from  the  first  and  fifth  lumbar 
nerves,  and  sometimes  the  nerve  arises,  in  the  high  form  of  plexus,  from  the  first, 
second  and  third  lumbar  nerves. 

The  three  roots  having  united  in  the  substance  of  the  psoas  magnus,  the  nerve 
passes  vertically  downward  and  emerges,  the  only  constant  branch  of  the  plexus  to 
do  so,  from  the  mesial  margin  of  the  psoas  muscle  opposite  the  brim  of  the  true 
pelvis.  Lying  posterior  to. the  common  and  lateral  to  the  internal  iliac  vessels,  the 
obturator  nerve  courses  along  the  antero-lateral  wall  of  the  pelvis  below  the  ilio- 
pectineal  line,  above  the  obturator  vessels  and  upon  the  inner  surface  of  the  pelvic 
fascia.  It  escapes  from  the  pelvis  through  the  obturator  canal  in  the  obturator  mem- 
brane and  divides  into  its  terminal  branches,  either  while  still  within  the  foramen  or 
shortly  after  emerging  from  it.  These  branches  are  separated  from  each  other  first 
by  the  anterior  fibres  of  the  obturator  externus  muscle  and  later  by  the  adductor 
brevis  muscle.  They  supply  the  adductor  muscles,  the  hip  and  knee  joints  and  the 
integument  of  the  mesial  aspect  of  the  thigh. 

Branches. — The  obturator  gives  off:  (a)  a  branch  to  the  obturator  c.\-fcnms 
muscle  and  then  divides  into  its  terminal  branches,  (b)  the  anterior  and  (c)  the 
posterior. 


THE   LUMBAR    PLEXUS. 


1325 


a.  The  branch  to  the  obturator  externus  arises  within  the  pelvis  from  the  inner  surface  of 
the  obturator  nerve.     It  accompanies  the  parent  trunk  through  the  foramen,  immediately  after 

FIG.   i 109. 


Ext.  cutaneous  nerve 

Ant.  sup.  spine  of  ilium 

Ant.  crural  nerve 

Br.  to  rectus 

Sartorius 

Artie,  br.  of  accessory  obturator 
Iliacus 

Br.  to  vastus  ext.  and  crureus 
Rectus 

Middle  cutaneous  nerve 

Int.  cutaneous,  ant.  branch 

Femoral  artery 

Int.  cutaneous,  post,  branch 

Int.  saphenous  nerve 
Nerve  to  vastus  interims 

Rectus 


Artie,  br.  from  nerve 
.     to  vastus  int. 


Ext.  iliac  artery 

Int.  iliac  artery 

Accessory  obturator  nerve 


Obturator  nerve 

Pectineus 

Obturator  nerve,  ant.  division 

Adductor  longus,  cut 
Obturator  nerve,  post  division 
Articular  br.  to  hip-joint 
Adductor  brevis 


Pectineus 
Adductor  magnus 


ictor  brevis 

ilis 

ictor  longus 

nal  br.  ant.  division  obturator  nerve 

neous  branch 

an  int.  cutaneous  to  subsartorial  plexus 

:.  br.  to  knee-joint  from  obturator 
o  subsartorial  plexus  and  femoral 


Cutaneous  br.  to  inner  surface 
of  thigh  and  knee 


Internal  saphenous  nerve 

Cutaneous  patellar  br.  int.  saphenous 

Sartorius,  insertion 

Post.  br.  int.  cutaneous 
Internal  saphenous 


Dissection  of  right  thigh,  showing  branches  of  anterior  crural  and  obturator  nerves. 

escaping  from  which  it  dips  down  in  the  interval  between  the  obturator  membrane  and  the  obtur- 
ator externus  muscle.  From  this  situation  its  fibres  pass  through  the  deep  surface  into  the 
substance  of  the  muscle. 


1326  HUMAN   ANATOMY. 

b.  The  anterior  branch  (r.  anterior),  the  more  superficial,  descends  in  front  of  the  obturator 
externus  and  adductor  brevis  muscles  and  between  the  pectineus  and  the  adductor  longus. 
Having  reached  the  interval  between  the  adductores  brevis  and  longus  it  separates  into  its 
terminal  branches. 

Branches  of  the  anterior  division  are  :  (aa)  the  articular,  (bb)  the  muscular,  (cc)  the 
cutaneous,  (dd)  the  communicating  and  (ee)  the  vascular. 

aa.  The  articular  branch  leaves  the  obturator  at  the  inferior  margin  of  the  obturator 
foramen  and  passes  through  the  cotyloid  notch  to  supply  the  hip  joint. 

bb.  TJie  muscular  branches  supply  the  adductores  brevis  and  longus  and  the  gracilis. 

The  branch  to  the  adductor  brevis  enters  the  muscle  near  the  upper  margin  of  the  anterior 
surface. 

The  branch  to  the  adductor  longus  enters  the  posterior  surface  of  the  muscle  and  some- 
times gives  off  the  cutaneous  branch  of  the  obturator  (see  below). 

The  branch  to  the  gracilis  passes  inward  behind  the  adductor  longus  and  enters  the  deep 
surface  of  its  muscle. 

cc.  The  cutaneous  branch  (r.  cutaneus)  (Fig.  mo)  is  variable  in  size  and  maintains  an 
approximately  even  balance  with  the  internal  cutaneous  branch  of  the  anterior  crural.  Some- 
times arising  from  the  nerve  to  the  adductor  longus,  it  becomes  superficial  in  the  middle  of  the 
thigh  by  passing  between  the  adductor  longus  and  the  gracilis.  It  supplies  the  integument  of 
the  lower  inner  portion  of  the  thigh  and  beneath  the  sartorius  forms  an  inosculation  with 
branches  of  the  internal  cutaneous  and  internal  saphenous  nerves,  called  the  subsartorial  or 
obturator  plexus. 

dd.  The  communicating  branches  consist  of  twigs  which  unite  in  the  pelvis  with  the  accessory 
obturator  nerve  and  in  the  thigh  anterior  to  the  capsular  ligament  of  the  hip  joint  with  the 
anterior  crural. 

ee.  The  vascular  branch  enters  Hunter's  canal  along  the  mesial  edge  of  the  adductor  longus 
and  spreads  out  over  the  lower  portion  of  the  superficial  femoral  artery. 

c.  The  posterior  branch   (r.   posterior),   the  deeper,    pierces  the  anterior  fibres  of   the 
obturator  externus  muscle  and  descends  in  the  cleft  between  the  adductores  brevis  and  magnus, 
and  in  the  latter  situation  splits  into  its  terminal  twigs. 

Branches  of  the  posterior  division  are  :  (aa)  the  muscular  and  (bb)  the  articular. 

aa.  The  muscular  branches  supply  the  obturator  externus,  the  adductor  magnus  and  the 
adductor  brevis. 

The  branch  to  the  obturator  externus  is  additional  to  the  twig  from  the  main  trunk  of  the 
obturator  which  supplies  that  muscle.  It  arises  from  the  posterior  surface  of  the  posterior 
division  and  enters  the  superficial  surface  of  the  muscle. 

The  branch  to  the  adductor  magnus  is  associated  with  the  branch  to  the  knee  and  leaves 
the  latter  as  the  conjoint  nerve  passes  through  the  substance  of  the  adductor  magnus. 

The  branch  to  the  adductor  brevis  enters  the  posterior  surface  of  the  muscle  and  is 
present  only  when  the  usual  branch  from  the  anterior  division  is  absent. 

bb.  The  articular  branches  are  destined  for  the  supply  of  the  hip  and  knee  joints. 

The  branch  to  the  hip  joint  consists  of  one  or  two  fine  twigs  which  pass  beneath  the 
pectineus  to  be  distributed  to  the  antero-median  portion  of  the  capsular  ligament. 

The  branch  to  the  knee  joint  or  the  geniculate  branch  continues  the  course  of  the  posterior 
division.  Associated  with  the  nerve  to  the  adductor  magnus,  it  courses  down  the  anterior  sur- 
face to  the  adductor  magnus,  which  it  pierces  at  the  lower  portion  of  the  thigh.  Here  its  muscu- 
lar fibres  terminate  in  the  adductor  magnus  while  the  articular  portion  enters  the  popliteal  space. 
The  nerve  continues  downward  on  the  popliteal  artery,  to  which  it  distributes  filaments,  and 
finally  terminates  by  entering  the  knee  joint  through  the  posterior  ligament. 

Variations. — In  rare  instances  the  root  from  the  second  lumbar  nerve  is  absent.  Branches 
are  sometimes  given  off  to  the  obturator  internus  and  to  the  pectineus.  Tiny  branches  have 
been  found  going  to  the  obturator  artery  and  to  the  periosteum  of  the  pelvic  surface  of  the  os 
pubis.  In  a  cadaver  dissected  in  the  anatomical  laboratory  of  the  University  of  Pennsyl- 
vania the  obturator  of  the  right  side  divided  into  the  usual  anterior  and  posterior  branches,  but 
both  of  them  passed  posterior  to  the  adductor  brevis.  On  the  left  side  the  normal  arrangement 
was  present.  In  another  specimen  in  the  same  laboratory  the  branch  from  the-  main  trunk  to 
the  obturator  externus  muscle  lay  to  the  outer  instead  of  the  inner  side  of  the  obturator  nerve. 

7.     THE  ACCESSORY  OBTURATOR  NERVK. 

The  accessory  obturator  nerve  is  an  inconstant  branch  of  the  lumbar  plexus, 
being  found  in  29  per  cent,  of  the  cadavers  examined  (Eisler).  Its  fibres  arise  from 
the  third  and  fourth  lumbar  nerves,  with  an  occasional  root  from  the  fifth  ;  it  may  be 
derived  from  the  third  alone.  The  roots  of  origin  are  sittiated  between  those  of  the 
anterior  crural  and  the  obturator,  and  the  nerve  may  be  intimately  associated  with 
either  of  these  two,  usually  the  former. 


THE   LUMBAR    PLEXUS.  1327 

The  accessory  obturator  courses  downward  mesial  to  the  psoas  magnus  and 
beneath  the  iliac  fascia,  and  leaves  the  pelvis  by  passing  over  the  horizontal  ramus  of 
the  pubes  and  under  the  pectineus.  In  the  latter  situation  it  breaks  up  into  its 
branches,  one  of  which  («)  supplies  the  pectineus,  another  (<5)  the  hip  joint,  while 
the  third  (V)  inosculates  with  the  anterior  division  of  the  obturator  nerve.  Some- 
times it  is  very  small  and  its  fibres  pass  only  to  the  hip  joint.  By  means  of  its  in- 
osculation with  the  obturator  some  of  its  fibres  may  reach  the  adductores  longus  and 
brevis  and  gracilis  muscles,  as  well  as  the  integument  of  the  inner  region  of  the  thigh. 

8.  THE  ANTERIOR  CRURAL  NERVE. 

The  anterior  crural  or  femoral  nerve  (n.  femoralis)  (Fig.  noS),  the  largest 
branch  of  the  lumbar  plexus,  arises  from  the  first,  second,  third  and  fourth  lumbar 
nerves.  It  passes  obliquely  downward  and  outward,  posterior  to  the  psoas  magnus, 
and  emerges  from  beneath  the  middle  of  the  lateral  margin  of  that  muscle.  Thence 
it  continues  its  course  between  the  outer  edge  of  the  psoas  and  the  mesial  edge  of  the 
iliacus,  covered  by  the  iliac  fascia,  as  far  as  Poupart's  ligament,  under  which  it  passes 
to  become  an  occupant  of  the  anterior  portion  of  the  thigh.  The  nerve  lies  to  the 
outer  side  of  the  external  iliac  and  femoral  vessels,  in  the  abdomen  being  separated 
from  them  by  the  psoas  magnus,  but,  as  the  thigh  is  reached,  gradually  nearing  them 
until  in  Scarpa's  triangle  the  nerve  lies  in  apposition  to  the  femoral  sheath.  '  In 
the  immediate  neighborhood  of  Poupart's  ligament,  the  anterior  crural  nerve  rapidly 
splits  up  into  a  number  of 

Branches,  which  may  be  grouped  into  (/>)  a  superficial  division,  principally 
sensory,  and  (c)  a  deep  division,  mainly  motor.  In  addition  there  are  (a)  branches 
arising  from  the  main  trunk. 

a.  The  branches  from  the  main  trunk  consist  of  (aa)  the  muscular  branches  and  (bb)  the 
nerve  to  the  femoral  artery. 

aa.  The  muscular  branches  supply  the  iliacus,  the  psoas  magnus  and  the  pectineus. 

The  branches  to  the  iliacus  consist  of  two  to  four  filaments  which  arise  in  the  abdomen, 
pass  outward  and  enter  the  inner  margin  of  the  iliacus  muscle. 

The  branch  to  the  fisoas  magmis  arises  in  the  lower  part  of  the  iliac  fossa  and  supplies  the 
inferior  portion  of  that  muscle.  It  may  originate  in  common  with  the  nerve  to  the  femoral 
artery. 

The  branch  to  the  pectineus  leaves  the  anterior  crural  beneath  Poupart's  ligament,  passes 
inward  posterior  to  the  femoral  vessels  and  enters  the  anterior  surface  of  its  muscle. 

bb.  The  nerve  to  the  femoral  artery  usually  takes  origin  in  the  iliac  fossa,  but  frequently 
arises  higher,  sometimes  as  a  distinct  branch  from  the  third  lumbar  nerve.  It  accompanies  the 
anterior  crural  as  far  as  Poupart's  ligament,  leaving  the  parent  trunk  at  the  lateral  margin  of 
the  femoral  sheath.  At  the  ligament  it  gives  off  fine  twigs  which  ramify  over  the  posterior  part 
of  the  femoral  vessels,  and  from  them  tiny  filaments  pass  to  the  middle  of  the  thigh.  Other 
twigs  are  distributed  to  the  deep  femoral  artery  and  from  this  group  a  fine  terminal  thread 
traverses  the  nutrient  foramen  of  the  femur,  after  supplying  branches  to  the  periosteum. 

b.  The  anterior  or  superficial  division  is  mainly  cutaneous   in   distribution.     It  supplies 
sensory  twigs  to  the  anterior  and  mesial  surfaces  of  the  thigh  and  motor  twigs  to  the  sartorius. 

Branches  of  this  division  are  :     (aa}  the  middle  cutaneous  and  (bb)  the  internal  cutaneous. 

aa.  The  middle  cutaneous  nerve  (rr.  cutaneianteriores)  (Fig.  mo)  consists  of  two  branches, 
an  external  and  an  internal,  both  of  which  contain  motor  as  well  as  sensory  fibres. 

The  external  branch  passes  downward  under  the  sartorius,  to  whose  posterior  surface  are 
given  off  a  row  of  fine  twigs  which  enter  the  upper  portion  of  the  muscle.  The  continuation  of 
the  nerve  pierces  the  sartorius  at  the  junction  of  the  upper  and  middle  thirds,  then  pushes  its 
way  through  the  fascia  lata  and  splits  into  fine  filaments  which  supply  the  integument  over  the 
rectus  femoris  as  far  as  the  knee. 

The  internal  branch  is  sometimes  united  in  the  upper  part  of  its  course  with  the  external. 
It  supplies  twigs  to  the  sartorius  but  seldom  pierces  that  muscle,  usually  passing  internal  and 
anterior.  This  branch,  like  the  external,  is  distributed  to  the  anterior  integument  of  the  thigh 
as  far  down  as  the  knee  and  frequently  inosculates  with  the  crural  branch  of  the  genito-crural. 

Variations. — Sometimes  the  middle  cutaneous  arises  from  the  beginning  of  the  anterior 
crural  or  from  the  lumbar  plexus  and  replaces  in  toto  or  in  part  the  crural  branch  of  the 
genito-crural. 


1328 


HUMAN   ANATOMY. 


FIG.  1  1  10. 


From  ext. 

cutaneous 

nerve 

Communication  be- 
tween ext.  cutaneous 
and  middle  cutaneous 

Crural  br.  of 
genito-c  rural 


From  ext 
neous 


Middle  cuta- 
neous nerve 


Ilio-inguinal 
nerve 
(emerging 
through  ext. 
abd.  ring). 


bb.  The  internal  cutaneous  nerve  (rr.  cutanei  mediates)  leaves  the  anterior  crural  in  the 
neighborhood  of  Poupart's  ligament  and  descends  in  Scarpa's  triangle,  at  the  apex  of  which  it 
crosses  obliquely  the  femoral  vessels  to  attain  their  mesial  side.  It  passes  superficial  to  or 
through  the  sartorius  muscle  and  divides,  either  anterior  or  internal  to  the  superficial  femoral 
artery,  into  its  terminal  branches,  the  anterior  and  the  posterior  (  Fig.  mo). 

Two  or  three  branches  are  given  off  by  the  main  trunk.  One  of  these  pierces  the  fascia 
lata  immediately  below  the  saphenous  opening  and  accompanies  the  internal  saphenous  vein 
down  to  the  middle  of  the  thigh,  supplying  the  integument  in  its  immediate  vicinity.  Another 

branch  pierces  the  fascia  lata 
at  about  the  middle  of  the  thigh 
and  supplies  the  skin  of  the 
antero-median  aspect  as  far 
down  as  the  knee.  These 
branches  sometimes  arise  di- 
rectly from  the  anterior  crural, 
and  not  infrequently  the  nerve 
to  the  pectineus  gives  off  a 
branch  which  forms  a  loop  at 
the  linner  side  of  the  femoral 
artery  with  a  nerve  which  passes 
anterior  to  that  vessel. 

The  anterior  branch 
pierces  the  fascia  lata  in  the 
lower  third  of  the  thigh,  de- 
scends in  the  neighborhood  of 
the  tendon  of  the  adductor 
magnus  and  eventually  passes 
across  the  patella  to  reach  the 
lateral  region  of  the  knee.  It 
supplies  the  skin  in  the  vicinity 
of  the  adductor  magnus  tendon 
and  inosculates  at  the  knee 
with  a  branch  of  the  internal 
saphenous  nerve. 

"The  posterior  branch  con- 
tinues down  beneath  the  pos- 
terior edge  of  the  sartorius 
and  becomes  superficial  by 
perforating  the  fascia  lata  at 
the  mesial  aspect  of  the  knee. 
Its  ultimate  filaments  supply 
the  integument  of  the  lower 
part  of  the  inner  side  of  the 
thigh  and  the  upper  portion  of 
the  leg.  Before  becoming  su- 
perficial it  inosculates  below 
the  middle  of  the  thigh  with 
the  obturator  and  internal 
saphenous  nerves  to  form  the 
subsartorial  or  obturator  plexus 
(Fig.  1109).  At  the  knee  anil 
in  the  upper  part  of  the  leg 
it  again  forms  connections 
with  the  internal  saphenous 
nerve. 

c.  The  posterior  or  deep 
division  of  the  anterior  crural 
nerve  consists  of  a  fasces  of 
nerve-bundles  which  furnishes 


•  br.  of  int.  cutaneous 
(or  twigs  from 
ior  branch) 


Cutaneous  br.  of 
obturator  nerve 
Internal  saphenous 
vein 


Anterior  br.  of  int. 
cutaneous  nerve 


|  From  lower  (posterior) 
j  br.  int.  cutaneous  nerve 


Lower  (posterior)  br. 
int.  cutaneous  nerve 

Cutaneous  patellar  br. 
int.  saphenous  nerve 


nt.  saphenous  nerve 


Int.  saphenous  vein 


Superficial  dissection  of  right  thigh,  showing  ciit:itii-ous  IUTVCS  of  inner 
anterior  aspect ;  long  saphenous  vein  is  seen  disappearing  through  saphe- 
nous opening. 


innervation  to  those  muscles  which  comprise  the  quadriceps  extensor  femoris  and  terminates 
as  the  internal  saphenous  nerve. 

Branches  of  this  division  are:  (aa)  the  niuscu/ar,  (bb}  the  articular  and  (cc}  the 
internal  saphenous. 

aa.  The  muscular  branches  (  rr.  iniiscularcs  )  supply  the  rectus  femoris,  the  vastus  externus, 
the  crureus,  the  subcrureus  and  the  vastus  interims. 


THE    LUMBAR   PLEXUS. 


1329 


The  branch  to  the  rectus  femoris  usually  splits  into  three  twigs,  which  separately  enter  the 
posterior  surface  of  their  muscle.  It  furnishes  fine  twigs  to  the  antero-lateral  portion  of  the 
capsule  of  the  hip  joint. 

The  branch  to  the  vastus  externus  passes  over  the  rectus  and,  in  company  with  the 
descending  branch  of  the  external  circumflex  artery,  reaches  the  vastus  externus,  whose 
anterior  margin  it  enters  in  a  series  of  twigs.  It  sends  a  branch  down  to  the  knee  joint. 

The  nerves  to  the  crureus  number  usually  either  two  or  three.  The  upper  branch  is  usually 
the  shortest  and  passes  directly  to  the  anterior  surface  of  the  crureus,  where  it  penetrates  the  sub- 
stance and  supplies  the  upper 

portion  of  the  muscle.     A  sec-  pIG    ^lll 

and  branch  pierces  the  vastus 
internus  and  passes  down- 
ward under  the  anterior  bor- 
der of  that  muscle.  It  sup- 
plies the  lower  portion  of  the 
crureus,  the  subcrureus,  the 
periosteum  of  the  lower  an- 
terior part  of  the  femur  and 
the  capsular  ligament  of  the 
knee  joint.  A  third  branch  is 
distributed  to  the  lateral  por- 
tion of  the  crureus  and  by 
means  of  its  terminal  filaments 
aids  in  the  innervation  of  the 
knee  joint. 

The  branch  to  the  vastus 
internus  accompanies  the  in- 
ternal saphenous  nerve  along 
the  inner  side  of  the  vastus 
internus,  under  cover  of  the 
strong  aponeurosis  which 
forms  the  roof  of  Hunter's 
canal.  It  sends  filaments  to 
the  upper  part  of  the  vastus 
internus  and  then  enters  that 
muscle  about  the  middle  of 
the  thigh.  Its  continuation 
accompanies  the  deep  branch 
of  the  anastomotica  magna 
artery  and  supplies  the  cap- 
sule of  the  knee  joint. 

b  b .  The  articular 
branches  (rr.  articulares) 
supply  the  hip  and  knee 
joints.  Those  filaments  which 
are  destined  for  the  hip  are 
derivatives  of  the  branch  to 
the  rectus  femoris.  Those 
which  aid  in  the  innervation 
of  the  knee  arise  from  the  in- 
ternal saphenous  and  from 
the  nerves  to  the  vasti  exter- 
nus and  internus  and  the 
crureus. 

cc.  The  internal  or  long 
saphenous  nerve  ( n.  saphenus ) 
(Fig.  1109)  is  the  continuation 
of  the  posterior  division  of 
the  anterior  crural  nerve.     It 
courses    down    the    thigh 
first   lateral  to  and   then  an- 
terior to    the  superficial  femoral  artery  under  cover  of  the  sartorius  muscle.      At  the  apex 
of  Scarpa's  triangle  it  enters  Hunter's  canal  and  accompanies  the  vessels  therein  contained  as 
far  as  the  opening  in  the  adductor  magnus.     Departing  from  the  vessels  at  this  point,  the  nerve 
piercing  the  anterior  wall  of  Hunter's  canal,  continues  a  downward  course  between  the  vastus 


iliactti 

Anterior  crural  nerve, 
Rectus  femoris. 
Femoral  \ 

Nerve  to  pectineus' 
Femoral  artery 
Articular  branch 
Nerve  to  rectu 

Ext.  circumflex  artery. 

Middle  cutaneous, 

nerve 
Rectus  femoris,  cut 

A   descending   branch 
of  ext.  circumflex  art. 

Nerve  to  vastus 
interim: 


Nerve  to  crureus 
Crureu 


Pubic  bone 
Pectineus 

Adductor 
longus 
Adductor 
magnus 


Int.  saphenous 

nerve 
— Tost.  div.  int. 

cutaneous 

nerve 


Aponeurotic 
roof  of  Hunt- 
er's canal 


A  br.  of  int.  sa- 
phenous nerve 
A  muscular  hr. 
of  femoral 
artery 

Vastus 

internus 

Internal  saphenous  nerve 
Superficial  br.  anasto- 
motica magna  art. 

Tendon  of  adductor 
magnus 


Dissection  of  right  thigh,  showinj 
to  blood-vessels  an< 


;  relation  of  anterior  crural  nerve 
to  Hunter's  canal. 


84 


1330  HUMAN   ANATOMY. 

interims  and  the  adductor  magnus.  At  the  inner  side  of  the  knee  it  becomes  superficial  by 
passing  between  the  tendons  of  the  sartorius  and  gracilis  and  by  piercing  the  deep  fascia  in  this 
situation.  Thence  it  descends  in  the  leg  in  association  with  the  internal  saphenous  vein,  at  the 
ankle  passing  anterior  to  the  internal  malleolus  and  reaching  the  inner  aspect  of  the  foot,  on 
which  it  extends  only  as  far  as  the  metacarpo-phalangeal  articulation  of  the  great  toe  (Fig.  1118). 

Branches  of  the  internal  saphenous  are  :  the  communicating,  the  infrapatcllar,  the  articu- 
lar and  the  terminal. 

The  communicating  branch  arises  beneath  the  sartorius  at  about  the  middle  of  the  thigh 
and  inosculates  with  filaments  from  the  obturator  and  internal  cutaneous  nerves  to  form  the 
subsartorial  or  obturator  plexus. 

The  infrapatellar  branch  (r.  infrapatellaris)  (Fig.  1117)  arises  at  the  lower  part  of  the 
thigh.  It  perforates  the  sartorius  and  the  fascia  lata  and  spreads  out  beneath  the  integument 
of  the  knee,  where  it  inosculates  with  terminal  filaments  of  the  internal,  the  middle  and  some- 
times the  external  cutaneous  nerve  to  form  \\\o.  patellar  plexus  (Fig.  m?). 

The  articular  branch  (r.  articularis)  is  an  inconstant  twig  which  supplies  the  inner  portion 
of  the  capsule  of  the  knee  joint. 

The  terminal  branches  are  distributed  to  the  integument  of  the  anterior  internal  portion 
of  the  leg  and  the  posterior  half  of  the  dorsum  and  mesial  side  of  the  foot. 

Practical  Considerations. — All  the  branches  of  the  lumbar  plexus  have  motor 
and  sensory  fibres,  both  of  which  are  affected  in  paralysis.  The  lesion  is  usually 
central,  involving  the  spinal  cord,  as  in  tabes  dorsalis,  fracture  of  the  spine  or  Pott's 
disease,  and  involves  several  nerves,  or  all  of  them  below  the  seat  of  the  lesion  ;  the 
individual  branches  are  not  often  affected. 

The  ilio-hypogastric  may  be  divided  by  the  incision  in  kidney  operations  or 
may  be  included  in  the  sutures.  This  nerve  and  the  ilio-inguinal  are  sometimes 
involved  in  operations  in  the  inguinal  region. 

The  genito-crural  sends  one  branch  through  the  inguinal  canal  to  the  cremaster 
muscle,  and  another  under  Poupart's  ligament  to  the  skin  of  the  inner  side  of  the 
thigh,  just  below  the  ligament.  Gentle  irritation  of  the  skin  here  will  cause  retraction 
of  the  testicle  (cremaster  reflex),  especially  in  children. 

The  anterior  crural  has  been  paralyzed  by  the  pressure  of  tumors  in  the  pelvis, 
has  been  involved  in  a  psoas  abscess,  and  has  been  injured  in  fracture  of  the  pubic 
ramus  and — rarely — in  fractures  of  the  femur.  If  the  lesion  involving  the  nerve  is 
within  the  pelvis  the  paralysis  would  affect  the  ilio-psoas,  quadriceps  extensor  femoris, 
sartorius  and  pectineus.  If  the  lesion  is  outside  the  abdomen  the  ilio-psoas  will 
escape.  A  complete  paralysis  would  prevent  flexion  of  the  hip,  or  extension  of  the 
knee.  The  patient  is  then  compelled  to  avoid  flexion  of  the  knee  in  walking.  There 
will  be  anesthesia  in  the  parts  supplied  by  the  middle  and  internal  cutaneous,  and 
long  saphenous  nerves,  that  is,  in  the  thigh  along  the  anterior  and  inner  surface 
(middle  and  internal  cutaneous),  except  in  the  upper  third  (crural  branch  of  the 
genito-crural),  and  along  the  inner  surface  of  the  leg  and  inner  border  of  the  foot  to 
the  ball  of  the  big  toe  (long  saphenous).  The  long  saphenous  vein  and  nerve  lie 
close  together,  about  a  finger's  breadth  behind  the  inner  border  of  the  tibia.  In  the 
thigh,  while  they  have  the  same  general  direction,  the  vein  lies  in  the  superficial 
fascia,  the  nerve  under  the  deep  fascia.  The  nerve  in  the  thigh  is,  therefore,  not  so 
liable  to  injury  as  is  the  vein. 

Since  the  anterior  crural  breaks  up  into  numerous  branches  just  below  Poupart's 
ligament,  its  trunk  in  the  thigh  is  very  short.  It  lies  slightly  external  to  the  femoral 
artery  and  can  be  exposed  by  an  incision  extending  downward  from  the  middle  of 
Poupart's  ligament. 

Paralysis  of  the  obturator  nerve  would  interfere  with  adduction  of  the  thigh  as 
well  as  with  internal  and  external  rotation.  It  may  be  caused  by  pressure  within  the 
pelvis,  as  by  the  child's  head  in  difficult  labor,  by  a  tumor  or  by  an  obturator  hernia. 
Paralysis  of  the  obturator  is  usually  found  in  conjunction  with  paralysis  of  the  anterior 
crural.  The  nerve  may  be  irritated  in  coxalgia.  in  sacro-iliac  disease,  and  on  the  left 
side  in  carcinoma  or  fa cal  impaction  in  tin-  sigmoid  flexure.  On  account  of  its  ter- 
minal distribution  pain  in  the  knee  is  usually  complained  of  whenever  this  nerve  or 
one  of  its  brandies  is  involved. 


THE   SACRAL   PLEXUS. 


FIG.  ii 12. 


THE   SACRAL    PLEXUS. 

The  sacral  or  sciatic  plexus  (plexus  sacralis)  (Fig.  1112)  is  formed  by  a  portion 
of  the  fourth  lumbar  nerve,  all  of  the  fifth  lumbar,  the  entire  first  sacral  and  parts  of 
the  second  and  third  sacral  nerves.  As  previously  stated  (page  1320)  the  fourth 
lumbar  nerve  or  n.  furcalis  splits  into  two  portions,  a  larger  upper  and  a  smaller 
lower,  the  former  contributing  to  the  lumbar  plexus  and  the  latter  uniting  with  the 
fifth  lumbar  nerve.  The  lower  portion  of  the  fourth  lumbar  having  passed  downward 
behind  the  internal  iliac  vessels,  divides  into  anterior  and  posterior  branches,  which 
fuse  respectively  with  similar 
branches  of  the  fifth  lumbar,  the 
two  trunks  thus  formed  compris- 
ing the  lumbo-sacral  cord 
(truncus  lumbosacralis).  This 
double  structure  emerges  from 
the  mesial  margin  of  the  psoas 
magnus,  passes  down  over  the 
brim  of  the  pelvis  and  constitutes 
the  lumbar  contribution  to  the 
sacral  plexus.  The  first  and 
second  sacral  nerves  leave  their 
foramina,  pass  laterally,  anterior 
to  the  pyriformis,  and  split  into 
anterior  and  posterior  branches. 
The  third  sacral  nerve  or  n.  bi- 
geminus  divides,  not  into  ante- 
rior and  posterior  branches,  but 
into  upper  and  lower,  the  upper 
becoming  a  constituent  of  the 
sacral  and  the  lower  a  portion 
of  the  pudendal  plexus.  Con- 
verging toward  the  lower  por- 
tion of  the  great  sacro-sciatic 
foramen,  the  posterior  portion 
of  the  lumbo-sacral  cord  and  the 
posterior  branches  of  the  first 
and  second  sacral  nerves  fuse 
and  form  the  external  popliteal 
or  pcroneal  and  some  minor  pos- 
terior nerves.  The  anterior  por- 
tion of  the  lumbo-sacral  cord. 


3S 


•GREAT  SCIATIC 


Diagram  illustrating  plan  of  sacral  plexus. 


the    anterior    branches    of 
first    and  second    sacral 


the 


nerves  and  the  upper  part  of  the  third  sacral  unite  in 
the  internal  popliteal  or  tibial  nerve  and  some  small  anterior  branches  (Fig.  1112). 
The  resulting  composite  structure,  the  sacral  plexus,  is  a  broad  triangular  felt-work 
of  nerve-strands,  whose  base  points  toward  the  sacrum  and  whose  apex  presents  at 
the  great  sacro-sciatic  foramen.  The  plexus  is  an  occupant  of  the  pelvis,  on  whose 
posterior  wall  it  is  situated,  lying  upon  the  pyriformis  muscle  and  under  cover 
of  the  parietal  portion  of  the  pelvic  fascia.  In  relation  with  it  anteriorly  are  the 
ureter,  the  pelvic  colon  and  the  internal  iliac  artery  and  vein.  The  ilio-lumbar  vessels 
pass  above  the  lumbo-sacral  cord  and  between  the  cord  and  the  first  sacral  nerve  are 
found  the  superior  gluteal  vessels.  The  interval  between  the  second  and  third  sacral 
nerves  is  occupied  by  the  sciatic  artery  and  vein. 

In  size  the  roots  of  the  sacral  plexus  vary  considerably,  the  largest,  the  fifth 
lumbar  nerve,  measuring  about  7  mm.  in  diameter  and  the  smallest,  the  third  sacral, 
3.5  mm.  As  regards  length,  the  contribution  from  the  fourth  lumbar  has  the  long- 
est course  and  that  from  the  third  sacral  the  shortest. 

Branches. — The  branches  of  the  sacral  plexus  and  their  classification  centre 
around  the  great  sciatic  nerve  and  its  distribution.  This  nerve  comprises  two 


1332 


HUMAN   ANATOMY. 


essential  and  frequently  independent  elements,  the  internal  popliteal  or  tibial  and  the 
external  popliteal  or  peroneal.  Typically  the  sciatic  divides  into  these  two  nerves 
in  the  lower  part  of  the  thigh  ;  very  often,  however,  they  are  distinct  from  the  outset, 
arising  independently  from  the  plexus,  being  separated  in  the  great  sacro-sciatic  fora- 
men by  the  inferior  fibres  of  the  pyriformis  muscle  and  passing  through  the  thigh 
as  contiguous  but  ununited  structures.  Moreover,  even  when  the  sciatic  appears  to 
be  a  single  cord,  dissection  will  reveal  its  duality  in  origin  and  course.  The  branches 
of  the  sacral  plexus  may  be  grouped  as  follows  : — 


I.  Collateral  Branches. 

A.  Anterior  branches  : 

1.  Muscular 

2.  Articular 

B.  Posterior  branches  : 

3.  Muscular 

4.  Articular 


II.  Terminal  Branches. 

A.  Anterior  branch: 

5.  External  popliteal 

B.  Posterior  branch: 

6.  Internal  popliteal 


COLLATERAL   BRANCHES. 

The  collateral   branches   comprise  two  sets,    designated  according   to   the 
portion  of  the  plexus  from  which  they  arise  as  the  anterior  and  the  posterior. 

The  anterior  collateral  branches  include:    (i)  the  muscular  branches  and 
(2)  the  articular  branches. 

FIG.  1113. 


Superior  gluteal  nerve,  giving  abr.  to  pyriformis 


Psoas  magnus,  cut 
Ext.  iliac  artery 

Obturator  nerve 

Pubic  bone. 

mesial  surface 

Obturator  interims 

"  White  line"  of 

pelvic  fascia 


Left  corpus 

cavernosum,  cut 

Hr.  to  quadratus 

fern.,  ^emellus  inf. 

and  hip  Joint 

Inf.  gluteal 
nerve 


Urethra  - 


Levator  ani 


•' 


Coccygeus' 
Br.  to  levator  ani 


Nerve  to  obturator  internus  andgemellus  superior 

Anterior 
crural  nerve 


.  lumbar 
vertebra 

•""V.  lumbar  nerve 

I.  sacral 
ganglion 


—I.  sacral  nerve 


Dissection    of    right  half  of    pelvis, 


Brs.  to 

pyriformis 

If.  sacnil 

ganglion 

II.  sacral  nerve 

Visceral  br.  of 

II.  sacral  nerve 


III.  sacral 

ganglion 

IV.  sacral  ganglion 
(V.  ganglion  is  seen  l>elow) 


isceral  brs.  of  III.  and  IV. sacral  nerves 
.  sacral  nerve  (ventral  division) 

'Coccygeal  nerve  (ventral  division) 


Pudic  nerve  ;  the  small  sciatic  nerve  is  just  in  front 
Br.  to  sphincter  ani,  piercing  levator  am 

showing   sacral   and    pudenda!    plexuses;   section   is    not   mesial, 

but   to  left  ot   mill-line. 


i.   The  muscular  branches  supply  (a)  the  quadratus  femoris,  (£)  the  obtura- 
tor internus,  the  ^emelli  and  i  c  }  the  hamstring  muscles  and  the  adductor  magnus. 


a.  The  nerve  to  the  quadratus  femoris  arises  from  tlu-  anti-riot  surface  of  tin-  upper  portion 
of  the  plexus,  its  fibres  coming  from  the  fourth  and  fifth  lumbar  and  first  sacral  nerves.  It  is 
ire(|uently  united  in  the  first  part  of  its  course  with  the  nerve  to  tin-  obturator  interims.  Ha\  in- 
traversed  the  great  sacro-sciatic  foramen  it  courses  downward  anterior  to  the  s^teat  sciatic  nerve, 


COLLATERAL    BRANCHES.  1333 

the  obturator  internus  and  the  gemelli  and  posterior  to  the  capsular  ligament  of  the  hip. 
Reaching  the  upper  margin  of  the  quadratus  femoris  it  passes  anterior  to  that  muscle  and 
terminates  in  fibres  which  enter  the  anterior  surface  of  the  muscle  for  which  it  is  destined.  In 
addition  to  supplying  the  quadratus  femoris  it  sends  twigs  to  the  gemellus  inferior  and  to  the 
hip  joint. 

Variations. — The  nerve  to  the  quadratus  femoris  may  supply  the  upper  portion  of  the 
adductor  magnus  and  may  send  filaments  to  the  superior  gemellus,  either  as  an  additional  or 
as  a  sole  supply. 

b.  The  nerve  to  the  obturator  internus  has  an  origin  one  step   lower  than  that  of  the 
preceding  nerve,  with  which  it  is  frequently  associated  for  a  short  distance.     It  arises  from  the 
anterior  aspect  of  the  fifth  lumbar  and  first  and  second  sacral  nerves  and  leaves  the  pelvis  through 
the  great  sacro-sciatic  foramen,  below  the  pyriformis  and  the  great  sciatic  nerve  and  lateral  to 
the  pudic  nerve  and  vessels  (Fig.  1114).     Crossing  the  spine  of  the  ischium  it  courses  anteriorly 
through  the  lesser  sacro-sciatic  foramen  and  enters  the  ischio-rectal  fossa,  where  it  terminates  by 
splitting  into  filaments  which  enter  the  posterior  surface  of  the  obturator  internus.     A  small 
branch  of  this  nerve  supplies  the  gemellus  superior. 

c.  The  nerve  to  the  hamstring  muscles  consists  of  a  bundle  of  fibres  which  forms  the 
mesial  edge  of  the  gluteal  portion  of  the  sciatic  nerve.     Arising  from  the  anterior  aspect  of  the 
plexus  and  deriving  its  fibres  from  the  fourth  and  fifth  lumbar  and  first,  second  and  third  sacral 
nerves,  it  descends  in  close  connection  with  the  sciatic,  lying  first  anterior  to  the  latter  and  then 
to  the  inner  side  (Fig.   1115).     In  the  thigh  the  nerve  breaks  up  into  two  sets  of  fibres,  an 
upper  and  a  lower.     The  upper  set  leaves  the  sciatic  below  the  tuber  ischii  and  sends  fibres  to 
the  upper  portion  of  the  semitendinosus  and  the  long  head  of  the  biceps  femoris.     The  lower 
set  arises  further  down  in  the  thigh  and  funishes  twigs  to  the  semimembranosus,  the  adductor 
magnus  and  the  lower  part  of  the  semitendinosus. 

2.  The  articular  branches   are   derived   from  the  nerve  to   the  quadratus 
femoris  and  sometimes  from  the  anterior  aspect  of  the  sciatic.     After   descending 
between  the  capsule  of  the  hip  and  the  gemelli  they  supply  the  posterior  portion  of 
the  capsular  ligament  of  the  hip  joint. 

The  posterior  collateral  branches  comprise,  like  the  anterior,  (3)  the 
musctilar  and  (4)  the  articular  branches. 

3.  The  muscular  branches  include  (a)  the  nerve  to  the  pyriformis,  (b*)  the 
superior  and  (c)  the  inferior  gluteal  nerves  and   (rf)  the  nerve  to  the  short  head 
of  the  biceps. 

a.  The  nerve  to  the  pyriformis  may  be. either  single  or  double.     It  arises  from  the  dorsal 
aspect  of  the  second  or  first  and  second  sacral  nerves  and  enters  the  anterior  surface  of  its 
muscle.     There  may  be  an  additional  filament  from  the  root  to  the  superior  gluteal  nerve  con- 
tributed by  the  first  sacral  nerve. 

b.  The  superior  gluteal  nerve  (n.  glutaeus  superior)  (Fig.  1114)  arises  by  three  roots  from 
the  dorsal  surface  of  the  posterior  portion  of  the  lumbo-sacral  cord  and  the  first  sacral  nerve, 
its  fibres  being  derivatives  of  the  fourth  and  fifth  lumbar  and  first  sacral  nerves.     After  passing 
above  the  pyriformis  muscle  in  company  with  the  superior  gluteal  artery  and  vein,  it  leaves  the 
pelvis  through  the  great  sacro-sciatic  foramen  and  divides  into  (aa)  a  superior  and   (bb)  an 
inferior  branch. 

aa.  The  superior  branch  (Fig.  1114)  is  the  smaller  of  the  two,  and  after  passing  beneath 
the  gluteus  medius  and  along  the  upper  margin  of  the  gluteus  minimus  reaches  and  enters  the 
middle  of  the  inner  surface  of  the  former  muscle,  of  which  it  is  only  the  partial  nerve  supply. 

bb.  The  inferior  branch,  larger  than  the  superior,  is  the  continuation  of  the  main  trunk. 
After  a  forward  course  between  the  glutei  medius  and  minimus  in  company  with  the  lower 
branch  of  the  deep  portion  of  the  superior  gluteal  artery,  it  reaches  the  under  surface  of  the 
tensor  fasciae  femoris  (Fig.  1114).  It  supplies  the  glutei  medius  and  minimus  and  its  terminal 
fibres  constitute  the  supply  of  the  tensor  fasciae  femoris. 

c.  The  inferior  gluteal  nerve  (n.  glutaeus  inferior)  (Fig.  1114)  is  formed  by  twigs  which  arise 
from  the  dorsal  surface  of  the  posterior  part  of  the  lumbo-sacral  cord  and  the  first,  and  some- 
times the  second,  sacral  nerve.     It  is  frequently  fused  in  the  early  part  of  its  course  with  the 
small  sciatic  nerve  and  not  infrequently  with  the  nerve  to  the  short  head  of  the  biceps.     It 
usually  sends  a  small  branch  down  to  join  the  small  sciatic  nerve.     Passing  beneath  the  pyriformis 
it  emerges  from  the  pelvis  into  the  gluteal  region  through  the  great  sacro-sciatic  foramen,  super- 
ficial to  the  great  sciatic  nerve.     Immediately  upon  entering  the  buttock  it  breaks  up  fan-wise 
into  a  number  of  twigs  which  enter  the  deep  surface  of  the  gluteus  maximus  about  midway 
between  the  origin  and  insertion. 


1334 


HUMAN   ANATOMY. 


d.  The  nerve  to  the  short  head  of  the  biceps  (Fig.  1115)  apparently  arises  from  the  lateral 
margin  of  the  upper  part  of  the  great  sciatic  nerve.  The  fibres  comprising  it  can  be  traced  back 
to  the  fifth  lumbar  and  first  and  second  sacral  nerves,  sometimes  in  combination  with  the  roots 
of  the  inferior  gluteal  nerve.  Leaving  the  great  sciatic  in  the  middle  of  the  thigh,  often  as  a 
common  trunk  with  the  articular  branch,  it  enters  the  substance  of  the  short  head  of  the  biceps. 


Gluteus 
maximus 

Br.  from  V. 
lumbar  nerve 
I.  sacral  nerve, 
posterior  division 
Cutaneous  br. 
from  loop  of 
posterior  sacrals 
II.  sacral  nerve, 
posterior  division 

III.  sacral  nerve. 
Interior  division 


IV.  sacral  nerve 
posterior  division 

Cutaneous  br. 
from  loop  ol  pos- 


Great  sacro- 
sciatic  ligament 

Nerve  to  obtu- 
rator internus 
Cutaneous  and 
muscular  branch 
of  IV.  ant.  sacral 

Small  sciatic 
tierve 


Tuberosity 
of  ischium 


Inferior  pu- 
dendal  nerve 


Gluteus 
medius 


Tensor  fascia;  lata; 
Superior  gluteal 

nerve 
.Gluteus  minimus 


— Pyriformis 


Trochanter    major 
Nerve  to  quadratus 

femoris 

Tendon  of  obturator  ii 
ith  gemellussuperic 
.Gemellus  intt-rior 

Branch  to  hipjoint 

Inferior  gluteal 

nerve 
Quadratus  femoris 

Great  sciatic 
nerve 


Deep  dissection  of  right  buttock,  showing  emergence  of  great  sciatic  nerve  below  pyriformis  muscle;  also 
muscular  branches  and  posterior  divisions  of  sacral  nerves. 

4.  Thf:  articular  branches  supply  the  knee  and  are  usually  two  in  number. 
The  upper  arises  either  in  common  with  the  nerve  to  the  short  head  of  the  biceps  or 
independently  from  the  lateral  portion  of  the  great  sciatic.  Descending  on  the  pos- 
terior surface  of  the  femoral  head  of  the  biceps  it  passes  between  the  external  condyle 
of  the  femur  and  the  tendon  of  the  biceps  and  supplies  the  lateral  portion  of  the 
capsular  ligament  of  the  knee.  The  lower  arises  from  the  external  popliteal  nerve 
in  the  upper  portion  of  the  popliteal  space  and  divides  into  two  portions  which 
supply  the  lateral  and  posterior  portions  of  the  capsular  ligament  of  the  knee.  From 
the  branch  to  the  posterior  part  of  the  capsule  is  given  off  a  tiny  thread  to  the 
superior  tibio-fibular  articulation. 

TERMINAL   BRANCHES. 

The  terminal  branches  of  the  sacral  plexus  are  the  c.\t,»ial  and  the  internal 
popliteal,  and  these  are  usually  fused  in  the  upper  part  of  their  course  into  the  great 
sciatic  nerve. 


TERMINAL   BRANCHES. 


1335 


THE   GREAT   SCIATIC  NERVE. 

The  great  sciatic  nerve  (n.  ischiadicus) ,  the  largest  nerve  of  the  entire  human  body, 
is  a  thick  bundle  of  nerve-fibres  derived  from  both  the  anterior  and  posterior  portions  of 

FIG.  1115. 


Glutens  maximus 
Great  sciatic  nerve 

Great  sacro-sciatic  ligament 
Small  sciatic  nerve 

Tuber  ischii 
Great  sciatic  nerve 

Brs.  to  semitendinosus 

Adductor  magnus 
Biceps,  long  head 

Semitendinosus 
Semimembranosus 

Br.  to  adductor  magnus 
Br.  to  semimembranosus 
Semimembranosus  . 


Popliteal  artery 
Articular  branch 

Popliteal  vein 
Communicans  tibialis 


Gluteus  medius 
Pyriformis 
Gemellus  superior 

'-  Obturator  internus 
Gemellus  inferior 
Obturator  externus 
Trochanter  major 

Quadratus  femoris 


Gluteus  maximus 
Br.  to  .biceps 


Biceps,  short  head 
Int.  popliteal  nerve 

External  popliteal  nerve 
Articular  branch 
Azygos  articular  branch 
Femur,  popliteal  surface 


>  Muscu 


lar  branches 


Gastrocnemius 


Communicans  fibularis 


Deep  dissection  of  posterior  surface  of  right  thigh,  showing  great  sciatic  nerve  dividing 
into  external  popliteal  (peroneal)  and  internal  popliteal  (tibial)  nerves. 

the  sacral  plexus  (Fig.  1112).      Properly  it  consists  of  two  elements  only,  the  ex- 
ternal and  internal  popliteal  nerves,  the  former  from  the  posterior  and  the  latter 


1336  HUMAN   ANATOMY. 

from  the  anterior  portion  of  the  plexus,  its  constituent  fibres  being  derivatives  of 
all  of  the  spinal  nerves  contributing  to  the  sacral  plexus.  Bound  up  with  it  and 
apparently  integral  portions  of  it,  are  the  nerve  to  the  hamstring  muscles  and  the 
nerve  to  the  short  head  of  the  biceps.  From  within  outward,  the  four  components 
are  arranged  in  the  following  order:  the  nerve  to  the  hamstrings,  the  internal  popli- 
teal nerve,  the  external  popliteal  nerve  and  the  nerve  to  the  short  head  of  the  biceps. 
Arising  from  the  apex  of  the  sacral  plexus  and  proceeding  as  its  direct  continua- 
tion, the  great  sciatic  leaves  the  pelvis  through  the  greater  sacro-sciatic  foramen 
below  the  pyriformis  muscle  and  above  the  gemellus  superior.  In  the  form  of  a  thick 
flat  trunk,  about  1.5  cm.  wide,  it  turns  downward  and  lies  anterior  to  the  gluteus 
maximus  and  posterior  to  successively  the  gemellus  superior,  the  tendon  of  the 
obturator  internus,  the  gemellus  inferior,  the  quadratus  femoris  and  the  upper  portion 
of  the  adductor  magnus,  being  accompanied  in  the  upper  part  of  its  course  by  the 
sciatic  artery  and  the  arteria  comes  nervi  ischiadici.  Lying  external  to  the  nerve  is 
the  great  trochanter  and  internal  to  it  is  the  tuberosity  of  the  ischium  (Fig.  1115). 
Entering  the  thigh  by  emerging  from  beneath  the  gluteus  maximus,  the  nerve  lies  under 
cover  of  the  hamstrings  and  at  a  varying  position  in  the  thigh  it  splits  into  its  terminal 
divisions:  (5)  the  external popliteal  and  (6)  the  internal  popliteal.  As  previously 
stated  (page  1332),  these  nerves  may  be  separate  from  their  origin. 

5.  THE  EXTERNAL  POPLITEAL  NERVE. 

The  external  popliteal  or  peroneal  nerve  (n.  peronaeus  communis)  (Fig.  1115) 
is  homologous  with  the  musculo-spiral  of  the  upper  extremity.  It  comprises  fibres 
derived  from  the  posterior  portions  of  the  fourth  and  fifth  sacral  and  first  and  second 
lumbar  nerves.  As  a  part  of  the  great  sciatic,  it  follows  the  course  in  the  thigh  just 
described  and  after  the  bifurcation  of  the  sciatic  enters  the  popliteal  space  as  an  inde- 
pendent nerve.  In  the  upper  part  of  the  popliteal  space  it  lies  beneath  the  biceps  and 
later  inclines  gradually  outward  between  the  tendon  of  the  biceps  and  the  outer  head 
of  the  gastrocnemius.  Passing  over  the  latter,  it  reaches  the  under  surface  of  the 
deep  fascia  posterior  to  the  head  of  the  fibula,  2-3  cm.  below  which  it  divides  into  its 
terminal  branches. 

Branches  of  the  external  popliteal  nerve  are  :  the  cutaneous  and  the  terminal. 

The  cutaneous  branches  are:  (a)  the  sural  and  (£)  the  peroneal  communi- 
cating. 

a.  The  sural  branch    (n.  cutaneus  surae  lateralis)    (Fig.   1119)   consists  of  one  or  more, 
usually  two,  filaments  which  arise  in  the  popliteal  space,  frequently  in  common  with  the  peroneal 
communicating  nerve.     Becoming  superficial  by  piercing  the  deep  fascia  overlying  the  outer 
head  of  the  gastrocnemius,  it  is  distributed  to  the  integument  of  the  upper  two  thirds  of  the 
lateral  aspect  of  the  leg.    Its  degree  of  development  is  in  inverse  ratio  to  that  of  the  small  sciatic 
and  short  saphenous  nerves. 

b.  The    peroneal    communicating   nerve    (r.    anastomoticus    peronaeus)    (Fig.    1119),   also 
called  the  n.  communicant  fibularis,  is  larger  than  the  preceding.     Leaving  the  peroneal  in  the 
popliteal  space,  often  in  combination  with  the  sural  nerve  or  nerves,  it  descends  beneath  the 
deep  fascia  and  over  the  lateral  head  of  the  gastrocnemius  to  the  middle  of  the  leg.     Here  it  is 
usually  joined  by  the  tibial  communicating  branch  from  the  internal  popliteal  and  the  joint  trunk 
so  formed  (Fig.  1125)  is  called  the  external  or  short  saphenous  nerve  (page  1342). 

The  terminal  branches  comprise:  (a)  the  recurrent  articular,  (£)  the 
anterior  tibial  and  (r)  the  musculo-cidancous. 

a.  The  recurrent  articular  or  recurrent  tibial  branch  (  Fig.  1 1 1 6 )  is  the  smallest  of  the  three. 
Given  off  a  short  distance  below  the  head  of  the  fibula  it  passes  forward  under  the  peroneus 
longus  and  the  extensor  longus  digitorum,  courses  upward  in  the  musculature  of  the  tibialis 
anticus  and  divides  into  filaments  which  supply  the  upper  fibres  of  the  tibialis  anticus,  the 
anterior  portion  of  the  knee  joint,  the  superior  tibio-fibular  articulation  and  the  periosteum  of  the 
external  tuberosity  of  the  tibia. 

b.  THE  ANTERIOR  TIBIAL  NERVE. 

The  anterior  tibial  nerve  (n.  peronaeus  profundus)  originates  below  the  head  of 
the  fibula  in  the  interval  bi-t uvm  the  peroneus  longus  and  the  fibula.  After  winding 


TERMINAL   BRANCHES. 


1337 


externally  around  the  head  of  the  fibula  beneath  the  peroneus  longus,  the  extensor 
proprius  hallucis  and  the  extensor  longus  digitorum  it  reaches  the  anterior  aspect  of 

FIG.  1116. 


Extensor  longus  digitorum 

Anterior  tibial  artery' 

Anterior  tibial  nerve- 

Musculo-cutaneous  nerve  • 

Peroneus  longus,  laid  open 

Tibialis  anticus- 
Extensor  longus  digitorum . 


Anterior  tibial  nerve 
Articular  branch 
External  branch 


Head  of  fibula 

Peroneal  nerve 

Recurrent  tibial  branch 

Branch  to  extensor  longus  digitorum 


Muscular  branch  to  peronei 


Peroneus  brevis 


Internal  branch  of  musculo-cutaneous 


External  branch  of  musculo-cutaneous 


Peroneus  longus  tendon 
Peroneus  brevis  tendon 


Origin  of  extensor  brevis  digitorum 
External  saphenous  nerve 


Dissection  of  antero-lateral  surface  of  left  leg  and  of  dorsum  of  foot,  showing  anterior 
tibial  and  musculo-cutaneous  nerves. 

the  leg.      Lying  on  the  anterior  surface  of  the  interosseous  membrane  it  joins  the 
anterior   tibial    vessels    8—12   "cm.    below  its    origin  and  accompanies  these  vessels 


1338  HUMAN   ANATOMY. 

down  the  front  of  the  leg  as  far  as  the  ankle,  lying  first  to  their  outer  side,  then 
anterior  to  them  and  at  the  ankle  to  the  outer  side  again  (Fig.  1116). 

Branches  of  the  anterior  tibial  nerve  are  :  (aa)  the  muscular,  (66)  the  articular, 
(«•)  the  external  and  (dd)  internal  terminal. 

aa.  The  muscular  branches  are  distributed  to  the  tibialis  anticus,  the  extensor  longus 
digitorum,  the  extensor  proprius  hallucis  and  the  peroneus  tertius. 

The  nerves  to  the  tibialis  anticus  consist  of  two  twigs,  an  upper  and  a  lower.  The  upper 
arises  at  the  origin  of  the  anterior  tibial,  passes  beneath  the  peroneus  longus  and  the  extensor 
longus  digitorum  and  enters  the  upper  portion  of  the  muscle.  The  lower  arises  in  the  interval 
between  the  tibialis  anticus  and  the  extensor  longus  digitorum  and  passes  obliquely  downward 
into  the  substance  of  the  tibialis  anticus. 

The  nerve  to  the  extensor  longus  digitorum  arises  immediately  below  the  preceding  and 
enters  the  inner  surface  of  the  muscle  which  it  supplies. 

The  nerves  to  the  extensor  proprius  hallucis,  usually  two  in  number,  arise  in  the  middle  of 
the  leg  and  enter  the  substance  of  their  muscle. 

The  nerve  to  the  peroneus  tertius  is  usually  derived  from  the  nerve  to  the  extensor 
longus  digitorum. 

bb.  The  articular  branch  leaves  the  anterior  tibial  above  the  anterior  annular  ligament  and 
is  distributed  to  the  forepart  of  the  ankle-joint. 

cc.  The  internal  terminal  branch  (Fig.  1117)  courses  forward  in  the  foot  under  the  inner 
tendon  of  the  extensor  brevis  digitorum  and  lateral  to  the  dorsalis  pedis  artery,  and  reaches 
the  base  of  the  first  digital  cleft.  Here  it  splits  into  two  branches  (nn.  digitales  dorsales  hallucis 
lateralis  et  digiti  secundi  medialis),  which  supply  the  contiguous  sides  of  the  great  and  second 
toes  and  ino'sculate  with  branches  of  the  musculo-cutaneous  nerve.  In  the  region  of  the  tarsus 
it  sends  off  the  first  dorsal  interosseous  nerve,  which  supplies  the  first  dorsal  interosseous  muscle, 
the  mesial  metacarpal  articulations  and  the  first  and  second  metacarpo-phalangeal  joints.  Like 
the  other  interosseous  nerves,  it  sends  a  filament  between  the  heads  of  its  dorsal  interosseous 
muscle  for  the  supply  of  the  adjacent  articulations  (Ruge). 

dd.  The  external  terminal  branch  (Fig.  1118)  passes  laterally  over  the  tarsus  undercover 
of  the  extensor  brevis  digitorum,  to  which  muscle  it  sends  branches.  From  it  are  given  off  two 
to  four,  usually  three,  dorsal  interosseous  branches,  which  decrease  in  size  from  within  outward, 
the  fourth  often  being  lacking  and  the  third  quite  rudimentary.  These  interosseous  nerves  are 
distributed  to  the  adjacent  articulations  and  sometimes  to  the  second  and  third  dorsal  inter- 
osseous muscles.  The  fibres  from  the  anterior  tibial  to  the  dorsal  interosseous  muscles  are 
usually  not  their  sole  supply,  the  external  plantar  supplying  constant  branches  for  their  innerva- 
tion.  From  the  latter  are  probably  derived  the  motor  innervation  and  from  the  occasional  ante- 
rior tibial  branches  some  extra  sensory  filaments.  This  branch  usually  ends  in  a  gangliform 
enlargement,  from  which  its  branches  are  distributed. 

Variations. — The  anterior  tibial  sometimes  supplies  the  mesial  side  of  the  great  toe  or  the 
adjacent  sides  of  the  second  and  third  toes.  In  one  case  the  anterior  tibial  supplied  the  outer 
three  and  one-half  toes,  the  inner  toe  and  one-half  being  innervated  by  the  musculo-cutaneous 
nerve.  Rarely  the  anterior  tibial  has  no  digital  distribution  whatsoever. 

c.     THE  MUSCULO-CUTANEOUS  NERVE. 

The  musculo-cutaneous  nerve  (n.  peronaeus  superflcialis)  (Fig.  1116)  continues 
the  course  and  direction  of  the  external  popliteal.  Descending  through  the  leg  in  a 
fascial  tube  in  the  septum  between  the  peroneal  muscles  and  the  extensor  longus 
digitorum  it  becomes  superficial  by  piercing  the  deep  fascia  anterior  to  the  fibula  in 
the  lower  third  of  the  leg.  It  may  make  its  superficial  appearance  as  a  single  nerve 
or  as  two  branches. 

Branches  of  the  musculo-cutaneous  are:  (aa)  the  muscular,  (bb}  the  internal 
and  (cc}  the  external  terminal. 

aa.  The  muscular  branches  (rr.  musculares)  are  destined  for  the  peronei  longus  and 
brevis. 

The  nerves  to  the  peroneus  longus  are  two  in  number,  an  upper  and  a  lower.  They  are 
given  off  at  the  upper  and  lower  portions  respectively  of  the  fascial  canal  occupied  by  the  parent 
nerve  and  enter  the  mesial  surface  of  their  muscle. 

The  nerve  to  the  peroneus  brevis  arises  with  the  lower  branch  to  the  peroneus  longus  and 
enters  the  musculature  of  the  peroneus  brevis. 


TERMINAL    BRANCHES. 


1339 


bb.  The  internal  terminal  branch  (n.  cutaneus  dorsalis  medialis)  (Fig.  1117),  larger  than  the 
external,  passes  obliquely  inward  in  front  of  the  ankle  and  then  forward  over  the  dorsum  of  the 
foot.  Cutaneous  twigs  are  distributed 

FIG.   1117. 

From  internal 
.  cutaneous 
nerve 


to  the  anterior  aspect  of  the  lower  third 
of  the  leg  and  the  dorsum  of  the  foot. 
Just  below  the  anterior  annular  ligament 
the  nerve  breaks  up  into  an  inner,  a 
middle  and  an  outer  branch. 

The  inner  branch  inosculates  with 
the  internal  saphenous  nerve,  from  which 
it  receives  an  accession  of  fibres,  and 
passes  forward  to  supply  the  integument 
of  the  mesial  aspect  of  the  foot  and  great 
toe.  The  middle  branch  follows  the  first 
metatarsal  space  and  inosculates  with  the 
inner  branch  of  the  anterior  tibial  nerve. 
The  outer  branch  courses  down  the 
second  metatarsal  space  and  divides  into 
the  two  dorsal  digital  nerves  (nn.  digitales 
dorsales  pedis)  which  supply  the  contig- 
uous sides  of  the  second  and  third  toes. 
This  branch  is  sometimes  derived  from 
the  external  terminal  part  of  the  musculo- 
cutaneous. 

ct.  The  external  terminal  branch 
(n.  cutaneus  dorsalis  intermedius)  (Fig. 
1117)  courses  down  the  leg  anterior  to  the 
ankle  and  lateral  to  the  inner  branch, 
giving  off  twigs  to  the  antero-lateral  por- 
tion of  the  integument  of  the  lower  part 
of  the  leg  and  dorsum  of  the  foot.  Having 
reached  the  foot  it  breaks  up  into  inner 
and  outer  branches. 

The  inner  branch  divides  into 
dorsal  digital  branches  for  the  supply  of 
the  adjacent  sides  of  the  third  and  fourth 
toes,  and  the  outer  branch,  after  receiving 
an  accession  of  fibres  through  inoscula- 
tion with  the  external  saphenous,  divides 
similarly  into  twigs  for  the  contiguous 
sides  of  the  fourth  and  fifth  toes.  The 
dorso-lateral  aspects  of  the  terminal 
phalanges  and  the  nails  receive  addi- 
tional filaments  from  the  plantar  nerves. 

Variations. — Deficiencies  in  the  in- 
ternal branch  are  usually  supplied  by 
the  anterior  tibial  nerve  and  in  the  ex- 
ternal by  the  short  saphenous.  In  case 
the  external  branch  ends  at  the  dorsum 
of  the  foot,  the  external  saphenous,  which 
would  fill  the  vacancy  at  the  digits,  has 
its  root  from  the  external  popliteal  more 
strongly  developed  than  usual,  and  thus 
the  toes  are  supplied  in  an  unusual 
manner  but  still  by  fibres  from  the  ex- 
ternal popliteal  nerve. 


6. 


From  middle 
cutaneous — 
nerve 


From 
peroneal  nerve 


Sural  brs., 
peroneal  nerve 


Musculo-cuta- 
ueous  nerve 


Ext.  saphenous  ( 
nerve  ] 


Kxt.  terminal 

br.  musculo- 

cutaneous 

nerve 


From   internal 

cutaneous 

nerve 


Cutaneous 
patellar  br.  int. 
saphenous 
nerve 


Int.  saphenous 
nerve 


Crest  of  tibia 

Int.  saphenous 
nerve 


Int.  saphenous 
vein 


Int.  terminal 
br.  musculo- 
cutaiieous 
nerve 

Int.  terminal 
br.  ant.  tibial 
nerve 


THE  INTERNAL  POPLITEAL 
NERVE. 

The  internal  popliteal  or  tib- 
ial nerve  (n.  tibialis)  (Fig.  1115) 
is  of  greater  size  than  the  external 
and  corresponds  in  its  distribution 
to  the  combined  median  and  ulnar  nerves  of  the  arm.  Arising  from  the  anterior 
portion  of  the  sacral  plexus,  it  includes  fibres  derived  from  the  fourth  and  fifth  lumbar 


Superficial  dissection  of  right  leg  and  foot,  showing  cutaneous 
nerves  of  anterior  surface. 


1340 


HUMAN   ANATOMY. 


and  first,  second  and  third  sacral  nerves.  Leaving  the  pelvis  through  the  greater 
sacro-sciatic  foramen  below  the  pyriformis,  and  passing  through  the  gluteal  region 
and  upper  part  of  the  thigh  as  the  inner  portion  of  the  great  sciatic  nerve,  it  becomes 
an  independent  trunk  at  the  point  of  bifurcation  of  the  sciatic.  Emerging  from 
beneath  the  hamstring  muscles  and  descending  vertically  through  the  middle  of  the 

FIG.  1118. 


Musculo-cutaneous  nerve 


Fibula 


Extensor  longus 
digitorum  tendon 

Peroneus  tertius  tendon 

Anterior  tibial  nerve 
Articular  branches  to  ankle  joint 

Peroneus longus  tendon 

External  saphenous  nerve 

Musculo  cutaneous  nerve — 

external  division 

External  division  of  anterior 

tibial  nerve 

Extensor  brevis  digitorum 


Metatarsal  branches  of  external 
division  of  anterior  tibial  nerve 


External  saphenous  nerve 

Digital  branches  of  external 

division  of  musculo- 

cutaneous  nerve 


Extensor  proprius 
hallucis  tendon 


Internal  saphenous  nerve 


Tibialis  anticus  tendon 


Extensor  brevis  digitorum 


Internal  division 
of  musculo- 
cutaneous  nerve 
Anterior  tibial 
nerve — internal 
branch 


Dissection  of  dorsum  of  right  foot,  showing  distribution  of  anterior  tibial,  musculo-cutaneous,  and  internal  and 

external  saphenous  nerves. 

popliteal  space,  it  gradually  attains  the  inner  side  of  the  popliteal  vessels,  crossing 
them  superficially  from  without  inward.  In  the  lower  part  of  the  space  the  nerve 
lies  posterior  to  the  popliteus  muscle  and  anterior  to  the  plantaris  and  the  gastroc- 
nemius.  At  the  lower  border  of  the  popliteus  muscle  the  internal  popliteal  becomes 
the  posterior  tibial  nerve  (Fig.  1119). 


TERMINAL    BRANCHES. 


Branches  of  the  internal  popliteal  are  :   (#)  the  articular, 
(<•)  the  cutaneous  and  (//)  the  posterior  tibia/. 

FIG.  1119. 


Gracilis 

Semitendinosus 
Semimembranosus 

•  Superior  internal  articular  nerve 

Inner  head  of  gastrocnemius 

Inferior  internal  articular  nerve 


Tihial  (internal  popliteal)  nerve 
Peroneal  (external  popliteal)  nerve 


Superior  external  articular  nerve 
Biceps  tendon 


Ext.  head  of  gastrocnemius 
Tibial  communicating 


—  Inferior  external  articular  branch 


Muscular  branch         \fl'Af\<P     I 
\    'it      i\v  .t    i 


—  Peroneal  communicating 


Flexor  longus  digitorum 


Posterior  tibial  nerve — L 


Posterior  tibial  artery 


Peroneus  longus 
Peroneus  brevis 
Internal  calcanean  branch 


Tihialis  posticus  tendon 
Inner  malleolus 

Abductor  hall 
External  plantar  n< 

Internal  plantar  nerve  — 
Abductor  hallucis  and  fascia 


Flexor  brevis  digitorum, 


Dissection  of  the  posterior  surface  of  right  leg,  showing  posterior  tibial  nerve  and  its 
branches  and  part  of  peroneal  nerve. 

a.  The    articular    branches    (rr.    articulares)     supply    the    hip    and    knee    joints.       The 
one  destined  for  the  hip  has  been  described  0:1  page  1333.     The  branches  to  the  knee  are  of 


1342  HUMAN   ANATOMY. 

small  size  and  of  varying  number.  There  are  usually  two,  an  upper  and  a  lower,  and  these 
break  up  into  small  filaments  which  inosculate  with  the  lower  articular  fibres  of  the  external 
popliteal,  forming  the  popliteal  plexus  of  Riidinger.  The  upper  or  azygos  branch  usually 
pierces  the  posterior  ligament  of  the  joint,  while  the  lower  accompanies  the  inferior  internal 
articular  artery.  When  a  third  is  present  it  accompanies  the  superior  internal  articular  artery. 
From  the  popliteal  plexus  a  number  of  fine  filaments  are  furnished  to  the  posterior  portion  of 
the  knee  joint  and  an  occasional  twig  enters  the  popliteus  muscle  by  piercing  its  posterior 
surface. 

b.  The  muscular  branches  (rr.  musculares)  comprise  two  sets,  those  given  off  from  the 
part  above  the  division  of  the  sciatic  nerve  and  those  given  off  behow.     The  former  have  been 
described    on  page   1333.     The  latter  consist  of  a  series  of   five  twigs  which   innervate  the 
gastrocnemius,  the  soleus,  the  plantaris  and  the  popliteus. 

The  nerves  to  the  gastrocnemius^  soleus  and  plantaris  consist  of  two  stout  nerve  trunks, 
an  ttpper  and  a  lower.  The  tipper  arises  in  the  middle  of  the  popliteal  space  and  enters  the 
lateral  aspect  of  the  inner  head  of  the  gastrocnemius.  The  lower  arises  a  short  distance  below 
the  upper  and,  frequently  combined  with  the  nerve  to  the  plantaris,  divides  into  two  branches, 
a  shorter  for  the  outer  head  of  the  gastrocnemius,  and  a  longer,  which  enters  the  superior  bor- 
der of  the  soleus,  the  upper  part  of  which  muscle  it  supplies.  From  the  nerve  to  the  plantaris 
is  furnished  a  filament  to  the  knee  joint. 

The  nerve  to  the  popliteus  is  a  complex  structure,  with  a  distribution  much  wider 
than  is  implied  in  its  name.  After  reaching  the  lower  margin  of  the  popliteus  muscle  the 
nerve  turns  forward,  ascends  between  the  anterior  aspect  of  the  muscle  and  the  tibia,  and 
enters  the  anterior  surface  of  the  popliteus.  A  branch  supplies  the  periosteum  of  the  tibia  and 
then  enters  the  nutrient  foramen  of  that  bone.  Another,  the  interosscous  branch  (n.  interosseus 
cruris)  courses  first  posterior  to  and  then  between  the  layers  of  the  interosseous  membrane 
almost  to  its  lower  margin.  Terminal  fibres  are  distributed  to  the  periosteum  of  the  tibia  and 
to  the  inferior  tibio-fibular  articulation.  Other  filaments  reach  the  tibialis  posticus  muscle  and 
the  superior  tibio-fibular  articulation. 

c.  The  cutaneous  branch  is  the  tibial  communicating  nerve. 

The  tibial  communicating  nerve  or  n.  tibialis  cominunicans  (n.  cutaneus  surae  medialis) 
(Fig.  1119)  arises  in  the  upper  portion  of  the  popliteal  space,  through  which  it  passes,  posterior 
to  the  internal  popliteal  nerve,  to  the  fissure  between  the  heads  of  the  gastrocnemius.  In 
company  with  the  external  saphenous  vein,  the  nerve  descends  in  this  interval  to  the  tendo 
Achillis  and,  after  piercing  the  deep  fascia  at  about  the  middle  of  the  leg,  is  joined  by  the 
peroneal  communicating  nerve,  the  fusion  resulting  in  the  external  or  short  saphenous  nerve 
(n.  suralis).  This  joint  nerve  (Fig.  1119)  courses  down  the  postero-lateral  aspect  of  the  lower 
part  of  the  leg,  passes  posterior  to  and  beneath  the  external  malleolus  in  company  with  the 
external  saphenous  vein  and  follows  a  course  obliquely  downward  and  forward  along  the 
lateral  margin  of  the  foot  to  the  dorsal  aspect  of  the  outer  side  of  the  fifth  toe,  at  the  far  end 
of  whose  distal  phalanx  the  nerve  terminates.  In  its  course  through  the  leg  and  foot  it  supplies 
sensory  twigs  to  the  postero-lateral  part  of  the  lower  third  of  the  leg,  the  region  over  the 
external  malleolus,  the  lateral  portion  of  the  heel  (rr.  calcanei  laterales),  the  dorso-lateral 
portion  of  the  foot  (n.  cutaneus  dorsalis  lateralis)  and  the  outer  half  of  the  dorsum  of  the  fifth 
toe.  Twigs  are  furnished  to  the  ankle,  and  to  the  astragalo-calcanean  and  possibly  other  inter- 
tarsal  articulations.  In  the  foot  it  communicates  with  the  anterior  tibial  nerve. 

Variations. — The  point  of  union  of  the  two  tributaries  of  the  external  saphenous  is  subject 
to  wide  variations,  sometimes  being  high  in  the  popliteal  space  and  sometimes  there  being  no 
union  at  all,  in  the  latter  instance  the  nerve  which  readies  and  supplies  the  foot  usually  being 
the  n.  cominunicans  tibialis.  In  one  specimen  found  in  the  anatomical  rooms  of  the  I'uiversity 
of  Pennsylvania  the  great  sciatic  nerve  divided  just  below  the  margin  of  the  glutens  maximus. 
The  n.  communicans  fibularis  arose  in  the  middle  of  the  thigh  and  the  n.  communicans  tibialis 
in  the  popliteal  space.  Union  took  place  3  cm.  below  the  origin  of  the  n.  communicans  tibialis, 
then,  communicans  fibularis  sending  a  few  fibres  across  to  the  internal  popliteal  nerve  before 
entering  the  external  saphenous.  In  another  cadaver  in  the  same  laboratory  the  t\vo  tributa- 
ries arose  3  cm.  apart  from  each  other  about  10  cm.  above  the  knee,  the  n.  communicans  tib- 
ialis arising  the  higher  and  piercing  the  inner  head  ;>f  the  -astrocneinins  be-fore  joining  then. 
communicans  fibularis.  Variations  in  distribution  may  occur,  the  nerve  sometimes  supplying 
the  dorsal  aspect  of  two  and  one-half  digits,  under  such  circumstances  the  n.  communicans 
fibularis  usually  being  of  increased  si/e.  The  in  r\e  may  terminate  in  the  foot  and  not  have  any 
digital  distribution. 

d.   Tin-:  POSTERIOR  TIBIAL  NEKYI. 

The  posterior  tibial  nerve  (n.  tihialis  )  (  Fi^.  1 1 10. )  is  the  direct  continuation 
of  the-  internal  popliteal  and  begins  at  the  lower  Imrder  <  >t  tin-  popliteus  muscle.  It 
extends  downward,  in  a  sheath  shared  by  the  posterior  tibial  vessels,  between  the 
superficial  and  deep  muscles  of  the  posterior  portion  <>f  the  lei;.  Anterior  to  it  are 


TERMINAL   BRANCHES. 


1343 


the  tibia  and  the  deep  leg  muscles  and  posteriorly  lie  the  soleus  and  gastrocnemius 
in  the  tipper  part  of  the  leg.  Above  the  ankle  ihe  nerve  becomes  superficial,  and  is 
covered  only  by  integument  and  the  fasciae.  Owing  to  the  inward  inclination  of  the 
posterior  tibial  vessels  the  nerve,  while  pursuing  a  straight  course,  changes  its  rela- 
tive position  to  the  vessels,  in  the  upper  part  of  the  leg  lying  to  the  inner  side,  lower 
down  behind  and  above  the  ankle  attaining  the  outer  aspect  of  the  vessels  (Fig. 
1121).  Passing  posterior  to  and  then  below  the  internal  malleolus,  the  posterior 
tibial  nerve  divides,  under  cover  of  the  internal  annular  ligament,  into  its  terminal 
branches,  the  internal  and  the  external  plantar. 

FIG    i i 20. 


Internal  calcanean  branch 
of  posterior  tibial  nerve 


Digital  branches  of 
internal  plantar  nerve 


External  saphenous  nerve 


jf\ External  saphenous  nerve 


Digital  branches  of  external  plantar 
nerve 


Superficial  dissection  of  right  foot,  showing  cutaneous  nerves  on  plantar  surface. 

Branches  of  the  posterior  tibial  nerve  are  :  (aa}  the  muscular,  (bb}  the  infernal 
calcanean,  (cc)  the  articular,  (dd)  tint  internal  plantar  and  (cc)  the  external  plantar. 

aa.  The  muscular  branches  (rr.  musculares)  supply  the  tibialis  posticus,  the  soleus,  the 
flexor  longus  hallucis  and  the  flexor  longus  digitorum. 

The  nerve  to  the  tibialis  posticus  supplies  that  muscle  and  sends  a  branch  to  the  flexor 
longus  digitorum  and  one  to  the  lower  part  of  the  soleus.  At  the  posterior  aspect  of  the  tibialis 
posticus  it  gives  off  a  long  slender  branch  which  accompanies  the  peroneal  artery  nearly  to  the 
ankle,  supplying  tu-igs  to  the  artery,  to  the  periosteum  of  the  fibula  and  a  branch  which  enters 
the  nutrient  canal  of  the  fibula. 

The  nerves  to  \\\e  fle.rores  longus  hallucis  and  longus  digitorum  leave  the  posterior  tibial 
about  the  middle  of  the  leg  and  pass  directly  to  their  muscles. 


1344 


HUMAN   ANATOMY. 


bb.  The  internal  calcanean  nerve  (rr.  calcanei  mediates)  arises  from  the  posterior  tibial  at 
the  lower  part  of  the  leg  and  becomes  superficial  by  traversing  an  opening  in  the  internal 
annular  ligament.  Dividing  into  two  sets  of  twigs,  internal  calcanean  and  calcaneo-plantar,  it  is 
distributed  to  the  integument  of  the  internal  aspect  of  the  heel  and  posterior  portion  of  the  sole. 

cc.  The  articular  branches  are  two  tiny  twigs,  given  off  beneath  the  internal  annular 
ligament,  which  supply  the  ankle  joint. 

dd.  The  internal  plantar  nerve  (n.  plantaris  medial  is)  (Fig.  1121),  larger  than  the  external, 
resembles  in  its  distribution  the  median  nerve  in  the  hand.  From  the  point  of  division  of  the 
posterior  tibial  nerve  it  courses  forward  in  the  foot  in  company  with  the  internal  plantar  artery, 
lying  first  above  the  internal  annular  ligament  and  the  calcanean  head  of  the  abductor  hallucis 
and  then  between  the  abductor  hallucis  and  the  flexor  brevis  digitorum.  Passing  thence  for- 
ward between  the  flexor  brevis  hallucis  and  the  flexor  brevis  digitorum  it  divides  into  two  ter- 

FlG.   TT2I. 


Calcaneo-plantar 
cutaneous  br.  of  tibial  nerve 

Articular  br.  (usually  a  br. 
of  tibial  nerve) 

Br.  to  abductor  hallucis 


Int.  plantar  nerve 
Brs.  to  flex,  brevis  digitorum 


I.  and  Il.lumbricales 


Digital  brs.  of  int.  plantar  nerve 


Flexor  brevis  digitorum 
Ext.  plantar  nerve 

Br.  to  abductor  minimi  digit! 

Abductor  minimi  digiti 

Flexor  accessorius 

Br.  to  flex,  accessorius 

Superficial  br.  ext.  plantar  nerve 

Brs.  to  flex.  brev.  minimi  digiti 

Deep  br.  ext.  plantar  nerve 
Digital  branch 

Brs.  to  interossei  of  fourth  space 
Digital  branch 


III.  and  IV.  lumbricales 


Dissection  of  right  foot,  showing  internal  aud  external  plantar  nerves  and  their  branches. 

minal  branches,  an  inner  and  an  outer.  In  addition  to  the  terminal  branches  it  gives  off  certain 
collateral  twigs. 

The  collateral  branches  are  muscular,  cutaneous  and  articular  in  distribution.  The 
muscular  supply  the  abductor  hallucis  and  the  flexor  brevis  digitorum.  The  cutaneous  pass 
between  the  muscles  just  mentioned  to  be  distributed  to  the  integument  of  the  inner  portion  of 
the  sole.  The  articular  furnish  innervation  to  the  inner  tarsal  and  tarso-metatarsal  joints. 

The  terminal  branches  are  an  inner  or  mesial  and  an  outer  or  lateral. 

The  inner  or  mesial  terminal  branch  (Fig.  1121)  courses  forward  upon  the  under  surface  of 
the  abductor  hallucis,  pit-revs  tin:  plantar  fascia  posterior  to  tin-  tarsi )-nu-tatarsal  articulation  of 
the  great  toe  and  terminates  by  extruding  along  tin-  im-sial  side  of  that  toe  as  its  inner  plantar 
digital  nerve.  In  its  course  it  furnishes  filaments  to  the  inner  surface  of  the  foot  and  a  twig  to 
the  mesial  head  of  the  flexor  brevis  hallucis. 


THE   PUDENDAL    PLEXUS.  1345 

The  outer  or  lateral  terminal  branch  (Fig.  1121)  is  larger  than  the  inner  and  is  situated 
below  the  distal  portion  of  the  flexor  brevis  digitorum  and  above  the  deep  plantar  fascia.  After 
a  short  forward  course  it  splits  into  two  branches,  the  lateral  of  which  soon  divides  into  two. 
There  are  thus  formed  three  plantar  digital  nerves  (nn.  digitales  plantares  communes),  each  of 
which  at  the  distal  end  of  its  metatarsal  space  divides  into  two  digital  nerves  (nn.  digitales 
plantares  proprii),  the  inner  supplying  the  contiguous  sides  of  the  great  and  second  toes,  and  the 
middle  and  outer  being  distributed  similarly  to  respectively  the  second  and  third  and  third  and 
fourth  toes.  The  inner  of  the  three  sends  a  filament  to  the  first  lumbricalis,  the  middle  some- 
times to  the  second  lumbricalis,  while  the  outer  forms  an  inosculation  with  the  external  plantar 
nerve.  In  addition  to  innervating  the  muscles  enumerated  and  the  integument  of  the  plantar  sur- 
face of  the  mesial  three  and  one-half  toes,  each  of  the  digital  nerves  sends  tiny  filaments  toward 
the  dorsum  for  the  supply  of  the  nails  and  the  tips  of  the  toes. 

ee.  The  external  plantar  nerve  (n.  plantaris  lateralis)  ( Fig.  1121 )  is  a  smaller  nerve  than  the 
internal  and  corresponds  in  its  arrangement  and  distribution  with  the  palmar  branch  of  the  ulnar 
nerve.  After  separating  from  the  internal  plantar  beneath  the  internal  annular  ligament,  it 
follows  a  course  in  company  with  the  external  plantar  artery  obliquely  forward  and  outward 
above  the  flexor  brevis  digitorum  and  below  the  flexor  accessorius.  Reaching  the  interval 
between  the  abductor  minimi  digiti  and  the  flexor  brevis  digitorum  it  divides  near  the  head  of 
the  fifth  metatarsal  bone  into  superficial  and  deep  terminal  branches. 

Branches  of  the  external  plantar,  like  those  of  the  internal,  include  :  collateral  and  terminal 
branches. 

The  collateral  branches  comprise  muscular  and  cutaneous  twigs.  The  muscular  branches 
are  given  off  soon  after  the  origin  of  the  parent  nerve  and  supply  the  flexor  accessorius  and  the 
abductor  minimi  digiti.  The  cutaneous  branches  are  a  series  of  small  twigs  which  follow  the 
septum  between  the  flexor  brevis  digitorum  and  the  abductor  minimi  digiti  and  become  super- 
ficial by  piercing  the  deep  plantar  fascia.  They  supply  the  integument  of  the  lateral  portion  of 
the  sole. 

The  terminal  branches  are  :  the  superficial  and  the  deep. 

The  superficial  or  cutaneous  branch  (r.  superficialis)  inosculates  with  a  branch  of  the 
internal  plantar  and  continues  forward  in  the  interval  between  the  flexor  brevis  digitorum  and 
the  abductor  minimi  digiti,  eventually  splitting  into  an  external  and  an  internal  branch. 

The  external  branch  (Fig.  1121)  sends  filaments  to  the  flexor  minimi  digiti  and  the  inter- 
ossei  muscles  of  the  fourth  metatarsal  space,  after  which  it  becomes  cutaneous  near  the  fifth 
metatarso-phalangeal  articulation  and  continues  forward  as  the  plantar  digital  nerve  for  the 
lateral  aspect  of  the  fifth  toe. 

The  internal  branch  (Fig.  1121)  courses  forward  in  the  fourth  metatarsal  space,  at  whose 
distal  end  it  separates  into  two  filaments  which  supply  the  opposed  surfaces  of  the  fourth  and 
fifth  toes.  The  digital  branches  send  filaments  dorsally  for  the  nails  and  the  tips  of  the  toes. 

The  deep  or  muscular  branch  (r.  profundus)  accompanies  the  external  plantar  artery 
in  an  obliquely  forward  and  outward  course  above  the  adductor  obliquus  hallucis  and  the  flexor 
accessorius  and  below  the  interossei  muscles.  It  forms  an  arch  (Fig.  1121)  whose  convexity  is 
directed  forward  and  outward,  and  terminates  in  the  region  of  the  base  of  the  great  toe.  From 
the  convex  aspect  of  the  arch  are  given  off  the  filaments  which  innervate  the  interossei  muscles 
of  the  first,  second,  third  and  sometimes  the  fourth  interosseous  space.  Other  muscular  twigs 
supply  the  adductores  obliquus  and  transversus  hallucis  and  the  outer  three  lumbricales,  the 
branch  to  the  second  lumbricalis  first  passing  beneath  the  adductor  transversus  hallucis.  The 
branches  to  all  of  these  muscles  enter  their  deep  surface.  In  addition  to  the  muscular  distribu- 
tion, articular  twigs  are  furnished  to  the  tarsal  and  tarso-metatarsal  articulations. 

THE   PUDENDAL  PLEXUS. 

The  pudendal  plexus  (plexus  pudendus)  is  the  downward  continuation  of  the 
sacral  plexus,  and,  whilst  each  retains  more  or  less  its  individuality  as  a  distinct 
structure,  there  is  no  sharp  line  of  demarcation  between  the  two.  Considerable 
interlacing  and  overlapping  is  the  rule,  so  that  often  some  of  the  important  branches 
of  the  pudendal  plexus  are  derivatives  to  a  large  extent  from  the  elements  giving  rise 
to  the  sacral  plexus. 

The  pudendal  plexus  (Fig.  1122)  is  situated  on  the  posterior  wall  of  the  pelvis 
and  is  formed  by  contributions  from  the  anterior  primary  divisions  of  the  first,  second 
and  third  sacral  nerves,  from  the  entire  anterior  primary  divisions  of  the  fourth  and 
fifth  sacral  and  from  the  coccygeal  nerve. 

Communications. — The  nerves  helping  to  form  the  plexus  receive  gray  rami 
communicantes  from  the  gangliated  cord  of  the  sympathetic,  which  join  them  shortly 
after  the  nerves  emerge  from  their  intervertebral  foramina. 

85 


1346 


HUMAN    ANATOMY. 


FIG.  i 122. 


Branches. — The  branches  of  the  pudendal  plexus  are  :   (i)  the  visceral,  (2) 

the  muscular,  (3)  the  perforating  cu- 
taneous, (4)  the  small  sciatic,  (5)  the 
pudic  and  (6)  the  sacro-coccygeal. 

1.  The    visceral     branches    are 
really  white  rami  communicantes.     They 
are  derived  from  the  second  and  third  or 
third  and  fourth  sacral  nerves  and  are 
distributed  to  the  pelvic  viscera  by  way 
of  the  pelvic  plexus  of  the  sympathetic. 
The    details   of  these  nerves    are    des- 
cribed   with    the    pelvic   plexus    of    the 
sympathetic  (page  1374). 

2.  The    muscular    branches 
furnish  innervation   to    the   levator  ani, 
the  coccygeus  and  the  external  sphinc- 
ter ani.      They   arise  from    a    loop-like 
interlacement  of  nerve-fibres,  formed  by 
the  third  and  fourth  sacral  nerves,  with 
sometimes  the  addition  of  fibres  from  the 
second.      The    nerve    to    the    external 
sphincter  pierces  the  great  sacro-sciatic 
ligament   and    the    coccygeus    muscle, 
sending  filaments  to  the  latter,  and  enters 
the  ischio-rectal  fossa,  lying  between  the 
edge  of  the  gluteus  maximus  and  the 
sphincter  ani  externus.      It  supplies  the 


Diagram  illustrating  plan  of  pudendal  and  coccygeal 
plexuses. 


FIG.  1123. 


From  II.  lumbar  nerve 

From  I.  lumbar  nerve 


From  III.  lumbar 
nerve 


Cutaneous  brs.  post . 
divisions  of 
sacral  nerves 


Coccygeal  nerves, 
posterior  divisions 

Coccygeal  nerve, 
anterior  division 


From  ant.  V.  sacral 
From  ant.  IV.  sacral 
Inferior  hemor-  _ 
rhoidal  nerves     \ 


1  Iliac  brs.  of  ilio- 
(  hypogastric 


Glutcal  brs.  of 
small  sciatic  nerve 


Inferior  pudenda! 
nerve 


Superficial  dissection  of  right  buttock  and  adjacent  regions,  showing  cutaneous  IK  i  \  H. 


THE    PUDENDAL    PLEXUS. 


1347 


posterior  portion  of  the  external  sphincter   and   distributes    sensory    fibres  to  the 

integument    over  the 

base    of    the    ischio-  FIG.  1124. 

rectal  fossa  and  the  tip 

of  the  coccyx. 


Variation.  —  This 
nerve,  instead  of  pierc- 
ing the  coccygeus,  may 
pass  between  that  mus- 
cle and  the  levator  ani. 

The  nerve  to  the 
levator  ani  is  derived 
usually  from  the  third 
and  fourth,  sometimes 
the  second  and  third, 
sacral  nerves  and  en- 
ters the  muscle  by 
piercing  its  mesial 
surface. 

3.  The  perfo- 
rating cutaneous 
nerve  (Fig.  1126)  is 
an  inconstant  branch, 
being  found  in  about 
two  thirds  of  the 
bodies  examined.  It 
springs  from  the  dor- 
sal aspect  of  the 
second  and  third  sac- 
ral nerves  and  at  its 
point  of  origin  may 
be  associated  with  the 
pudic  or  the  small 
sciatic.  Passing 
downward  and  back- 
ward it  pierces  the 
great  sacro-s  ci  at  i  c 
ligament  in  company 
with  the  coccygeal 
branch  of  the  sciatic 
artery  and  winds 
around  the  lower  bor- 
der of,  or  in  rare  in- 
stances pierces,  the 
gluteus  m  a  x  i  m  u  s  . 
Perforating  the  deep 
fascia  slightly  lateral 
to  the  coccyx,  it  be- 
comes superficial  and 
is  distributed  to  the 
integument  over  the 
inner  and  lower  por- 
tion of  the  gluteus 
maximus. 

Variations.  —  I  n  - 


Inf.  piidendal 
nerve,   and   a   glu- 
teal  cutaneous  br. 
of  small  sciatic 

Small  sciatic  nerve 


From  lateral  cutane- 
ous br.  of  XI  I.  thoracic 
From  I.  lumbar 
nerve 


A    gluteal    cuta- 
neous br.  of  small 
sciatic  nerve 
From  lateral  cuta- 
neous br.  of  XII.     . 
thoracic 


jr~From  ext.  cutaneous 
nerve 


An  ext.  femoral  br. 
of  small  sciatic 


From  ext.  cuta- 
neous nerve 


Superficial   dissection   of   right   buttock    and    thigh,  showing   cutaneous 
nerves  of  posterior  surface. 


stead    of    piercing    the 

ligament  it  may  accompany  the  pudic  nerve  or  pass  between  the  ligament  and  the  gluteus 

maximus.     It  may  be  replaced  by  a  branch  of  the  small  sciatic  or  by  a  nerve,  called  by  Eisler 


1348 


HUMAN  ANATOMY. 


the   n.  per/orans  coccygens  major,    \\-hich   arises    from   the  third  and  fourth   or   fourth   and 
fifth   sacral    and   pierces   the   coccygeus  muscle. 

FIG.   1125. 


From  small  sciatic  nerve 


From  obturator  nerve  — ^m> 
From  internal  cutaneous 


Internal  saphenous  nerve 


Inner  malleolus 


External  calcanean  branches 


Small  sciatic  nerve 


Sural  from  peroneal  nerve 
Peroneal  communicating 


Part  of  sural  branch 


Tibial  communicating 


External  saphenous  nerve 


branch  of  musculo-cutaneous 


-Anterior  branch  of  ext.  saphenous 


Cutaneous  nerves  of  posterior  surface  of  right  leg. 

4.  THE   SMALL   SCIATIC   NERVE. 

The  small  sciatic  nerve  (n.  cutanciis  fcinoris  posterior)  (Fig.  1114)  is  a  purely 
sensory  structure.      It  originates  from  the  back  of  the  first,   second  and  third,   or 


THE    PUDENDAL    PLEXUS.  1349 

from  only  the  second  and  third,  sacral  nerves,  the  upper  root  usually  being  associ- 
ated with  one  of  the  roots  of  the  inferior  gluteal  nerve,  and  the  lower  root  with  the 
perforating  cutaneous  or  the  pudic  nerve.  Leaving  the  pelvis  through  the  great 
sacro-sciatic  foramen  below  the  pyriformis,  it  descends  in  the  gluteal  region  between 
the  tuber  ischii  and  the  great  trochanter,  posterior  to  the  great  sciatic  nerve  and 
anterior  to  the  gluteus  maximus,  accompanied  by  the  inferior  gluteal  nerve  and  the 
sciatic  artery.  Emerging  into  the  thigh  at  the  lower  border  of  the  gluteus  maximus 
it  continues  downward  beneath  the  deep  fascia  and  superficial  to  the  hamstring 
muscles  to  a  short  distance  above  the  knee,  where  it  pierces  the  deep,  and  becomes 
an  occupant  of  the  superficial,  fascia.  Thence  it  passes  downward  through  the  roof 
of  the  popliteal  space  and  through  the  upper  part  of  the  calf,  in  the  latter  situation 
accompanying  the  external  saphenous  vein  and  inosculating  with  the  external 
saphenous  nerve.  It  rarely  extends  beyond  the  middle  of  the  calf,  tapering  off  into 
tiny  threads  which  are  distributed  to  the  skin  of  the  posterior  surface  of  the  upper 
half  or  two  thirds  of  the  leg  (Fig.  1125.) 

Branches  of  the  small  sciatic  nerve  are  :  (a}  the  inferior  pudendal,  (b)  the 
ghiteal,  (r)  \.\\Q  femoral  and  (d)  the  sural. 

a.  The  inferior  pudendal  or  perineal  branch  (rr.  perineales)  (Fig.  1126)  leaves  the  parent 
nerve  at  the  lower  margin  of  the  gluteus  maximus,  curves  mesially  below  the  tuberosity  of  the 
ischium  and  over  the  origin  of  the  hamstrings  and  courses  through  the  groove  between  the 
thigh  and  the  perineum.     Piercing  the  deep  fascia  lateral  to  the  pubic  ramus,  it  enters  the 
perineum  and  supplies  the  integument  of  the  scrotum  and  base  of  the  penis,  or  of  the  labium 
majus  and  clitoris.     Branches  are  distributed  to  the  skin  of  the  upper  mesial  portion  of  the 
thigh  and  to  the  perineal  body  and  anus.     This  nerve  communicates   with   the   ilio-inguinal 
nerve  and  with  the  perineal  and  inferior  hemorrhoidal  branches  of  the  pudic  nerve.     It  may 
pierce  the  great  sacro-sciatic  ligament. 

b.  The  gluteal   cutaneous  branches   (rr.   clunium  inferiores)    (Fig.    1124)  consist  of  two, 
three  or  more  stout  filaments  which  arise  from  the  small  sciatic  a  short  distance  above  the 
inferior  margin  of  the  gluteus  maximus,  around  which  they  wind.      Piercing  the  fascia  lata 
individually  they  turn  upward  over  the  lower  portion  of  the  gluteus  maximus   and  are   dis- 
tributed to  the  skin  of  the  inferior  gluteal  region,  as  far  externally  as  the  great  trochanter  and 
internally  almost  to  the  coccyx.     The  outer  branches  overlap  the  terminal  twigs  of  the  posterior 
branch  of  the  external  cutaneous  nerve  and  the  posterior  primary  divisions  of  the  first,  second 
and  third  lumbar  nerves.     The  inner  branches  sometimes  pierce  the  great  sacro-sciatic  liga- 
ment ;  they  reinforce  or  may  replace  the  perforating  cutaneous  nerve. 

c.  The  femoral  branches  (Fig.   1124)  consist  of   two  series  of  twigs,  an  internal  and  an 
external,  which  pierce  the  fascia  lata  of  the  posterior  aspect  of  the  thigh  and  supply  the  integu- 
ment of  that  region. 

d.  The  sural  branches   (Fig.  1125)   are  usually  two  terminal  twigs  which  innervate  to 
a  varying  extent  the  integument  of  the  back  of  the  leg,  sometimes  not  extending  beyond 
the  confines  of  the  popliteal  space  and  sometimes  continuing  all  the  way  to  the  ankle.     They 
inosculate  with  the  external  saphenous  nerve,  and  when  they  are  lacking  their  place  is  taken  by 
the  external  saphenous. 

Variations. — In  those  cases  in  which  the  internal  and  external  popliteal  nerves  are  separate 
from  their  incipiency,  the  small  sciatic  also  is  double.  The  ventral  portion  accompanies 
the  internal  popliteal  and  gives  off  the  inferior  pudendal  and  internal  femoral  branches,  while 
the  dorsal  portion  accompanies  the  external  popliteal  and  gives  off  the  gluteal  and  external 
femoral  branches.  Sometimes  the  small  sciatic  is  joined  in  the  thigh  by  a  branch  from  the  great 
sciatic. 

5.     THE  PUDIC  NERVE. 

The  pudic  nerve  (n.  pudendus)  arises  from  the  front  of  the  second,  third  and 
fourth  sacral  nerves,  its  main  root  coming  from  the  third  and  there  being  a  doubtful 
root  from  the  first.  Leaving  the  pelvis  by  way  of  the  great  sacro-sciatic  foramen 
between  the  pyriformis  and  the  coccygeus  and  below  the  great  sciatic  nerve,  it  passes 
forward,  with  the  internal  pudic  artery  and  the  nerve  to  the  obturator  internus,  over 
the  base  of  the  lesser  sacro-sciatic  ligament  to  the  spine  of  the  ischium  (Fig.  1126). 
Reaching  the  small  sacro-sciatic  foramen  internal  to  the  internal  pudic  artery, 
the  nerve  traverses  this  opening  and  enters  the  ischio-rectal  fossa,  where  it  gives  off 
the  inferior  hemorrhoidal  nerve.  The  main  trunk  courses  forward  in  a  canal 
(Alcock's)  in  the  obturator  fascia  on  the  outer  wall  of  the  ischio-rectal  fossa 


135° 


HUMAN    ANATOMY. 


(Fig.  1126),  at  whose  anterior  portion  the  nerve  approaches  the  base  of  the  tri- 
angular ligament  and  divides  into  its  terminal  branches,  the  perineal  and  the  dorsal 
nerve  of  the  penis  or  clitoris. 

Branches  of  the  pudic  nerve  are  :  (a)  the  inferior  hemorrhoidal  nerve,  (b)  the 
perineal  nerve  and  (c)  the  dorsal  nerve  of  the  penis  or  clitoris. 

a.  The  inferior  hemorrhoidal  nerve  (nn.  hemorrhoidales  inferiores)  (Fig.  1127)  is  usually 
given  off  by  the  pudic  upon  entering  the  ischio-rectal  fossa,  hut  it  may  be  derived  directly  from 
the  plexus,  its  fibres  being  offshoots  of  the  third  and  fourth  sacral  nerves.  In  company  with  the 
inferior  hemorrhoidal  vessels  it  passes  mesially  across  the  base  of  the  ischio-rectal  fossa  toward 


FIG.   1126. 


Coccygeal  nerves,  posterior  divisions 


Coccyx 


anterior  division 


.Cutaneous  branches  from  loops  of  V.  luniUir 
and  I.  II.  and  III.  sacral  nerves,  posterior 
divisions 


Branch  of  IV.  sacral  nerve, 
(perforating  cutaneous) 

Levator  ani  and  anal 
fascia 


Pudic  nerve 

Cut  edge  of  obturator 

fascia 


Inferior  hemor- 
rhoidal nerve 
Internal  pudic 
artery 

Perineal  division  of 

pudic  nerve 
Dorsal  nerve  ot 
clitoris 


Inferior 
pudenda! 


Vulva 


Superficial  dissection  of  right  side  of  female  perineum  and  adjacent  region,  showing  cutaneous  nerves  ;  obturator 
fascia  has  been  partly  removed  to  expose  pudic  nerve  and  accompanying  blood-vessels  in  canal  on  outer  wall  of 
ischio-rectal  fossa. 

the  anus,  on  approximating  which  it  splits  into  a  number  of  filaments,  which  supply  the  external 
sphincter  and  the  integument  of  the  anal  region,  and  inosculate  with  the  small  sciatic, 
pudic  and  fourth  sacral  nerves. 

b.  The  perineal  nerve  (n.  perinei)  (Fig.  1126)  is  one  of  the  terminal  branches  of  the  pudic 
and  arises  at  the  bifurcation  of  that  nerve  near  the  posterior  margin  of  the  triangular  ligament. 
Soon  after  its  origin  it  splits  into  :  (aa  i  a  superficial  and  (bb)  a  deep  branch. 

aa.  The  superficial  branch  is  entirely  sensory  and  consists  of  two  parts,  a  lateral  or 
posterior  and  a  mesial  or  anterior.  These  pass  forward  toward  the  base  of  the  scrotum 
in  company  with  the  superficial  perineal  vessels. 

The  lateral,  c  vt,-»ial  or  posterior  branch  courses  along  the  lateral  margin  of  the  perineum, 
distributing  twigs  in  this  region  and  sometimes  sending  branches  to  the  inner  aspect  of  the  thigh 
and  a  filament  to  the  origin  of  the  ischio-cavernosns  muscle  (  Scluvalbe). 

The  mesial,  internal  or  anterior  branch  is  larger  than  the  lateral  and  is  more  deeply- 
placed.  It  pierces  the  posterior  margin  of  the  triangular  ligament  and  runs  forward  either 
beneath  or  through  the  transversus  perinei  muscle.  It  splits  into  two  or  more  branches 
(nn.  scrotales  vet  lal.iales  posteriores )  which  inosculate  freely  with  each  other  and  supply  the 
integument  of  th«-  scrotum  or  labinm  majus.  They  communicate  with  the  pudendal  branch  of 
the  small  sciatic  nerve  and  with  the  inferior  hemorrhoidal. 


THE   PUDENDAL    PLEXUS. 


56.  The  deep  branch  of  the  perineal  nerve  is  mainly  muscular  and  consists  of  a  single 
trunk  which  breaks  up  into  several  branches,  whose  main  destination  is  the  muscles  of 
the  perineum.  Passing  forward  from  the  ischio-rectal  fossa  it  enters  the  deep  perineal 
interspace  and  sends  filaments  to  the  external  sphincter  ani,  the  levator  ani,  the  transversus 
perinei,  the  ischio-cavernosus,  the  bulbo-cavernosus  or  sphincter  vaginae  and  the  compressor 
urethras.  One  branch,  the  nerve  to  the  bulb,  accompanied  by  the  artery  of  the  same  name, 
enters  the  bulb,  supplying  its  tissue  and  that  of  the  corpus  spongiosum,  and  innervating  the 
urethra  as  far  forward  as  the  glans  penis. 

c.  The  dorsal  nerve  of  the  penis  (n.  dorsalis  penis)  (Fig.  1127)  a  terminal  branch  and  the 
most  deeply  situated  of  all  the  branches  of  the  pudic,  accompanies  the  dorsal  artery  of  the  penis 
through  the  deep  perineal  interspace.  It  lies  beneath  the  crus  penis,  the  ischio-cavernosus 
muscle  and  the  inferior  layer  of  the  triangular  ligament  and  over  the  compressor  urethra: 

FIG.  1127. 


Dorsal  nerve 
of  penis 

Crus  penis, 
detached 

Ischio-cavernosus. 
detached 


Nerve  to  ischio- 
cavernosus 

Nerve  to  bulbo- 

cavernosus 
Nerve  to  bulb 

Nerve  to  trans- 
versus perinei 

Muscular  br.  of  perineal 

division  of  pudic  nerve 

Dorsal  nerve 

of  penis 

Cutaneous  br.  of  perineal 
division  of  pudic  nerve 

Pudic  nerve 

Inferior  hemor- 

rhoidal  nerve 


Sphincter  anij 
exterrius 


Colics'  fascia, 
reflected 


Crus  penis  and 
ischio-cavernosus 

Anterior  (internal) 
superficial 
perineal  nerve 
Inferior  pudendal 
nerve 

Transyersus 
perinei 

Posterior  superfi- 
cial perineal  nerve 
Dorsal  nerve  of  penis 
Perineal  division 
of  pudic  nerve, 
muscular  portion 
Pudic  nerve 


Inferior  hetnor- 
rhoidal  nerve 


Gluteus  maximus 

From  IV.  sacral 

nerve 
Perforating  cutaneous  nerve  and  a  branch  of  IV.  sacral  nerve 

Dissection  of   male  perineum,  showing;  distribution   of   pudic  nerve;   on  left  side  of   body  Colics'  fascia  has  been 
reflected  to  expose  superficial  perineal  interspace ;  dorsal  nerve  of  penis  is  seen  in  deep  interspace  on  right  side. 

muscle.  Piercing  the  inferior  layer  of  the  triangular  ligament  and  the  suspensory  ligament  of 
the  penis  it  reaches  the  dorsum  of  the  penis,  along  which  it  courses  as  far  as  the  glans.  It 
gives  off  the  nerve  to  the  corpus  cavernosuin,  which  pierces  the  triangular  ligament  and  supplies 
the  erectile  tissue  of  the  crus  penis  and  corpus  cavernosum.  The  main  nerve  innervates  the 
anterior  two  thirds  of  the  penis,  including  the  glans,  and  sends  off  ventral  branches  which  pass 
around  to  the  under  surface  of  the  organ. 

The  dorsal  nerve  of  the  clitoris  (n.  dorsalis  clitoridis)(Fig.  1128),  while  much  smaller  than 
the  dorsal  nerve  of  the  penis,  has  a  corresponding  course  and  distribution. 

The  dorsal  nerve  of  the  penis  or  clitoris  communicates  with  the  inferior  pudendal  branch 
of  the  small  sciatic. 


Variations.— The  pudic  may  receive  a  root  from  the  fifth  lumbar,  in  the  high  form  of  plexus. 
A  root  from  the  fifth  sacral  is  described  by  Henle.  The  inferior  hemorrhoiclal  may  pierce  either 
the  greater  the  small  sacro-sciatic  ligament,  and  the  former  of  these  ligaments  maybe  perforated 
by  the  lateral  superficial  perineal  nerve. 


1352 


HUMAN    ANATOMY. 


THE  COCCYGEAL  PLEXUS. 

6.  The  sacro-coccygeal  nerves  (nn.  anococcygei)  are  derived  from  a  small 
nerve  inosculation  called  the  coccygeal  plexus  (plexus  coccygeus),  a  structure  formed 
by  the  fifth  sacral  and  the  coccygeal  nerve,  with  a  contribution  from  the  fourth  sacral 
which  descends  over  or  through  the  great  sacro-sciatic  ligament.  The  fifth  sacral, 
having  been  joined  by  this  twig  from  the  fourth,  descends  along  the  margin  of  the 
coccyx  and  is  joined  by  the  coccygeal  nerve,  the  resulting  nerve-bundle  constituting 
the  coccygeal  plexus.  From  it  arise  minute  filaments  which  pierce  the  great  sacro- 
sciatic  ligament  and  are  distributed  to  the  integument  in  the  immediate  neighbor- 
hood of  the  coccyx  (Fig.  1084). 

Practical  Considerations. — Of  the  branches  of  the  sacral  plexus,  the  great 
sciatic  nerve  is  the  most  important,  owing  to  its  size,  its  extensive  distribution  and 
its  exposed  position.  The  greater  part  of  the  sacral  plexus  is  continued  into  the 

FIG.  1128. 


Bulbo-cavernosus 


Ischio-cavernosus 


Inferior  pudenda!  nerve 

Posterior  superficial 
perineal  nerve 

Anterior  superficial 
perineal  nerve 

Transversus  perinei 
superficialis 

1'erineal  division  of 
pudic  nerve 

Inferior  hemorrhoidal 
nerve 

Sphincter  ani 
Anal  fascia 


I  >eep  fascia  of  buttock 


Glansclitoridis 


Deep  layer  of 
triangular  ligament 


Superficial  perineal 
nerves 


Dorsal  i 
ofclitor 


Perineal  dhision 
of  pudic  nerve 
Levatorani 

(",reat  scacro-siatic 
ligament 


Inferior 
hemorrhoidal  nerve 

Perforating 
Uluteustnavimus 


From  IV.  sacral  nerve  Coco 

Dissection  of  female  perineum,  showing  nerves;  anal  fascia  in  position  on  right  side  of  body,  removed  on 
left ;  Colics'  fascia  removed  on  right  side,  exposing  superficial  perineal  interspace;  superior  layer  of  triangular 
ligament,  denuded  of  muscular  tissue,  seen  on  left  side. 

nerve.  Except  in  complete  lesions  of  the  spinal  cord  this  nerve  is  rarely  paralyzed 
in  all  its  branches.  The  paralysis  may  result  from  fractures  of  the  lumbar  vertebra, 
of  the  sacrum  or  of  the  innominate  bone,  from  pressure  of  tumors  in  the  pelvis  or  of 
the  child's  head  in  labor  or  from  the  use  of  forceps.  It  is  the  structure  in  greatest 
danger  in  dislocation  of  the  hip,  since  the  head  of  the  femur  in  the  most  frequent 
varieties  sweeps  backward  against  this  nerve.  In  the  reduction  of  these  posterior 
dislocations  the  nerve  lias  been  hooked  up  by  the  head  and  made  to  pass  across  the 
front  of  the  neck  of  the  bone.  From  its  close  relation  to  the  head  and  neck,  it 
may  be  injured  in  violent  movements  of  the  hip  joint  without  dislocation. 

It  passes  out  of  the  pelvis  through  the  greater  sacro-sciatic  foramen,  below  the 
pyriformis  muscle,  and  after  curving  outward  and  downward  under  the  glutens  maxi- 
nius  muscle  it  continues  its  course,  approximately,  in  a  line  from  a  point  midway 


THE  SYMPATHETIC   SYSTEM    OF   NERVES.  1353 

between  the  greater  trochanter  and  the  tuberosity  of  the  ischium  above  to  the  middle  of 
the  popliteal  space  below.  At  about  the  junction  of  the  middle  and  lower  thirds  of 
the  thigh  it  divides  into  the  internal  and  external  popliteal  nerves.  Below  the  gluteus 
maximus  muscle  it  is  comparatively  superficial,  so  that  tenderness  of  the  nerve,  as 
from  sciatica,  is  easily  elicited  by  pressure.  At  the  point  where  it  emerges  from 
under  the  gluteus  maximus  it  is  readily  reached  for  operation.  After  a  vertical  in- 
cision through  the  skin  and  fascia  at  this  level,  the  biceps  muscle  is  exposed.  The 
lower  margin  of  the  gluteus  maximus  is  raised  and  the  biceps  drawn  inward,  when 
the  nerve  can  be  easily  hooked  up  with  the  finger.  Because  of  the  great  importance 
of  this  nerve  to  the  lower  extremity  it  is  not  advisable  to  excise  or  divide  it  as  this 
would  paralyze  its  whole  area  below.  Stretching  is  the  only  justifiable  operation, 
although  the  results  obtained  are  often  disappointing,  and  the  operation  may  cause 
acute  neuritis.  According  to  Trombetta,  it  will  require  a  tension  equal  to  the  weight 
of  183  Ibs.  to  break  it,  and  it  is  more  likely  to  yield  at  its  attachment  to  the  spinal 
cord  than  elsewhere.  It  should,  therefore,  tolerate  a  stretching  force  of  from  100  to 
1 60  Ibs.  (Treves).  A  safe  working  rule  is  to  use  a  force  sufficient  to  raise  the 
affected  limb  from  the  table,  the  patient  lying  in  the  prone  position. 

It  has  been  observed  that  when  the  paralysis  is  due  to  some  pressure  upon  the 
nerves  of  the  sacral  plexus  within  the  pelvis  it  is  'often  confined  to  the  peroneal  or  ex- 
ternal popliteal  nerve,  or  is  most  marked  in  it.  This  has  been  explained  by  the  fact 
that  the  fibres  for  the  peroneal  nerve  lie  close  together  directly  on  the  pelvic  bones, 
and  are,  therefore,  particularly  exposed  to  pressure.  They  arise  for  the  most  part 
from  the  lumbo-sacral  cord,  formed  by  the  fourth  and  fifth  lumbar  and  first  sacral 
nerves,  which  lie  directly  on  the  innominate  crest,  the  rest  of  the  plexus  lying  on  the 
pyriformis  muscle. 

In  paralysis  of  the  external  popliteal  or  peroneal  nerve  the  extensors  of  the  foot 
and  toes,  the  tibialis  anticus  and  the  peronei  muscles  are  involved.  The  foot  hangs 
down  from  its  own  weight  (foot  drop),  and  turns  in  from  paralysis  of  the  peronei. 
In  some  cases  the  anterior  tibial  muscle  escapes.  In  walking  the  knee  must  be  un- 
duly flexed  to  prevent  the  toes  from  dragging  on  the  ground  and  the  arch  of  the  foot 
is  flattened  from  the  loss  of  the  support  given  to  the  arch  by  the  peroneus  longus. 
If  sensation  is  disturbed  it  will  be  only  to  a  slight  extent  over  the  anterior  part  of  the 
leg  about  the  shin,  and  outward  from  this  on  the  dorsum  of  the  foot  and  toes,  but  not 
at  the  sides  of  the  foot.  The  percmeal  nerve  may  be  divided  accidentally  in  a  sub- 
cutaneous tenotomy  of  the  biceps  tendon  for  contraction  at  the  knee,  the  nerve  lying 
close  to  the  inner  border  of  the  tendon.  It  may  be  injured  by  external  violence,  as 
it  passes  around  the  head  and  neck  of  the  fibula,  where  if  necessary,  an  incision  will 
easily  expose  it ;  or  it  may  be  injured  by  pressure,  as  in  prolonged  kneeling. 

In  paralysis  of  the  internal  popliteal  nerve  all  the  other  muscles  of  the  leg,  in- 
cluding the  superficial  and  deep  flexors,  the  tibialis  posticus,  the  plantar  muscles  and 
interossei  are  affected.  The  patient  cannot  extend  the  ankle  and  therefore  cannot 
stand  on  his  toes.  The  toes  cannot  be  flexed  or  moved  sideways.  Sensation  is  dis- 
turbed on  the  inner  and  posterior  surface  of  the  leg,  the  outer  border  of  the  foot,  the 
sole  and  the  plantar  surface  of  the  toes. 

In  paralysis  of  the  entire  sciatic  nerve  the  flexors  of  the  knee  also  are  involved, 
so  that  the  patient  cannot  bring  the  heel  toward  the  buttock.  If  only  one  sciatic  is 
involved  he  can  still  walk  by  fixing  the  knee  in  extension,  the  whole  limb  being 
brought  forward  by  the  quadriceps  extensor,  which  is  supplied  by  the  anterior  crural 
nerve. 

THE  SYMPATHETIC  SYSTEM  OF  NERVES. 

The  sympathetic  portion  (systema  nervorum  sympatheticum)  of  the  peripheral 
nervous  system  differs  from  that  already  described — the  spinal  and  the  cranial  nerves 
— in  being  particularly  concerned  in  carrying  efferent  and  afferent  impulses  to  and 
from  the  thoracic  and  abdominal  organs  (collectively  termed  the  splanchnic  area), 
in  contrast  to  the  great  somatic  ("skeletal)  masses  of  voluntary  muscle.  Whilst  the 
paths  for  the  afferent  or  sensory  impulses  conducted  from  the  splanchnic  area  differ 
in  no  important  respect  from  those  formed  by  the  cerebro-spinal  nerves,  the  efferent 
or  motor  paths  are  peculiar  («)  in  supplying  the  involuntary  and  cardiac  muscle  and 


1354 


HUMAN   ANATOMY. 


FIG.  1129. 


SoE 


the  glandular  tissue  and  (6~)  in  consisting  of  at  least  two,  often  of  several,  links  between 
the  source  of  the  impulse  (the  spinal  cord)  and  the  structure  upon  which  it  is 
expended.  It  is  these  interposed  links  that  constitute  the  sympathetic  elements 
proper — the  sympathetic  neurones.  The  cell-bodies  of  these  neurones  exhibit  a 
marked  disposition  to  become  aggregated  into  larger  or  smaller  collections,  which 
constitute  the  innumerable  ganglia  that  form  a  conspicuous  feature  of  the  sympathetic 
system,  whilst  their  axones  serve  to  connect  the  ganglia  with  the  terminal  structures 
(muscles  or  glands)  or  with  other  neurones.  It  is  evident,  therefore,  that  the 

sympathetic  system  consists  of 
a  complex  of  spinal  and  sym- 
pathetic fibres  intermingled 
with  groups  of  ganglion-cells. 
The  latter  are,  for  the  most 
part,  stellate  in  form  and  pro- 
vided with  axones  which,  while 
often  pursuing  a  long  course 
as  splanchnic  efferenis,  acquire 
only  partially  or  not  at  all  a 
medullary  coat  and  hence  may 
be  classified  usually  as  non- 
medullated  fibres.  Since  the 
spinal  fibres  are  provided  with 
this  covering,  the  bundles  of 
such  fibres  present  the  whitish 
color  distinguishing  medullated 
strands,  in  contrast  to  the  gray- 
ish tint  of  the  strands  of  the 
nonmedullated  sympathetic  fila- 
ments. It  is  upon  this  histolog- 
ical  variation  of  their  predomi- 
nating fibres  that  the  difference 
recognized  in  the  white  and 
gray  rami  communicantes,  pres- 
ently to  be  described,  depends. 
Although  the  supply  of  the 
thoracic,  abdominal  and  pelvic 
organs  constitutes  an  important 
part  of  the  duty  of  the  sympa- 
thetic nerves,  it  is  by  no  means 
their  entire  concern,  the  inner- 
vation  of  the  involuntary  muscle 
of  the  vessels  and  of  the  skin 
and  the  glands  throughout  the 
body  being  likewise  their  task. 
In  order  to  meet  their  obliga- 
tions to  the  structures  within 
the  body  cavities,  the  sympa- 
thetic nerves  naturally  follow 
the  course  of  the  blood-vessels, 
with  the  result  that  every  artery 
of  consequence  within  these  re- 
gions is  surrounded  by  a  more  or  less  elaborate  net-work,  these  plexuses  in  most 
cases  bearing  the  names  of  the  arteries  which  they  accompany.  In  order  to  pn>\i<le 
for  the  outlying  tracts  of  involuntary  muscle  contained  within  the  blood-vessels  outside 
the  body-cavities  and  within  the  skin,  as  well  as  for  the  glands,  the  sympathetic  fibres 
join,  by  way  of  the  gray  rami  communicantes,  the  somatic  spinal  nerves,  whirh 
they  accompany  to  all  parts  of  the  body.  For  this  reason  the  peripheral  somatic 
nerve-trunks  contain  three  varieties  of  fibres — afferent  and  efferent  spinal  and  efferent 
sympathetic. 


Diagram  showing  constitution  of  sympathetic  system ;  spinal 
efferents  are  black  ;  sympathetic  efferents  are  red;  sympathetic  (vis- 
ceral) efferents  are  blue;  SC,  spinal  cord;  AK,  PR,  anterior  and 
posterior  root  of  spinal  nerve  ;  SG,  spinal  ganglion  ;  AD,  PD, anterior 
and  posterior  primary  divisions;  WR,  GK,  white  and  gray  rami 
communicantes.  (>'C,  gangliated  cord;  SyG,  sympathetic  ganglia; 
CG,  cervical  sympathetic  ganglion  ;  PvG,  'SubG,  TrG,  prevertebral, 
subsidiary  and  terminal  ganglia;  SpKf,  splanchnic  efferents;  SoEf, 
somatic  efferents;  V,  vessels  of  the  spinal  meninges;  /,  intestine. 


THE   SYMPATHETIC   SYSTEM    OF   NERVES. 


1355 


Constitution  and  General  Arrangement. — The  sympathetic  system  serves 
to  receive,  rearrange  and  distribute  the  visceral  filaments  of  the  cerebro-spinal  nerves, 

FIG.  1130. 


Common  carotid  artery 
Vagus  nerve 


Superior  cervical  cardiac 

branch  of  vagus 


Middle  cardiac  br.  of  vagus 

Scalenus  anticus 
Cray  ramus  cominunicans  to 

VIII.  cervical  nerve 

VIII.  cervical  nerve 

I.  thoracic  nerve 

I.  rib 


1 1 1.  thoracic  nerve 


IV.  thoracic  ganglion 


Raini  communicantes 


XII.  thoracic  ganglion 
Branch  to  I.  lumbar 
ganglion 


Hyoid  bone 


Interganglionic  cord  of  sympathetic 

Thyroid  cartilage  [sympathetic 

Superior  cervical   cardiac  branch  of 
Middle  cervical  ganglion 

>-thyroid  muscle 


Inferior  cervical  ganglion 

I.  thoracic  ganglion 

Right  recurrent  laryngeal  nerve 

Combined  cervical  cardiac  branches 
Right  vagus  [of  sympathetic 

1  nferior  cervical  cardiac 

branch  of  vagus 
Left  middle  and  inferior  cervical 

cardiacs  of  sympathetic 

Trachea 


Right  bronchus 
(Esophagus 


Vena  azygos 


Great  splanchnic  nerve 
Aorta 


*A— Left  vagus  nerve 


—  Small  splanchnic  nerve 
- —  Least  splanchnic  nerve 


**  Diaphragm 


Dissection  showing  right  gangliated  cord  of  sympathetic  and  its  branches. 

and  to  complete,  by  the  interposition  of  one  or  more  of   its  especial  neurones,  the 
path  for  the  impulses  brought  by  such  fibres  to  the  objective  organs.      It  comprises 


1356  HUMAN    ANATOMY. 

two   principal   parts,   the  gangliated  cords  and  the  plexuses,  with  their  associated 
ganglia. 

The  gangliated  cord  (truncus  sympatheticus),  one  of  a  symmetrically  placed 
pair  of  gangliated  trunks  situated  anterior  or  lateral  to  the  bodies  of  the  vertebra 
(Fig.  1133),  begins  in  the  head  and  extends  through  the  neck,  thorax  and  abdo- 
men to  the  lower  portion  of  the  pelvis.  In  the  head  it  consists  of  a  plexus  of 
fibres  continued  up  from  the  neck  in  an  intricate  interlacement  which  follows  the 
internal  carotid  artery  ;  and  in  the  pelvis  it  terminates  by  the  two  cords  forming  a 
loop  or  fine  inosculation,  situated  anterior  to  the  coccyx  and  containing  the  coccygcal 
ganglion  or  ganglion  impar. 

The  plexuses  (plexus  sympathetic!)  are  a  series  of  more  or  less  distinct  col- 
lections of  groups  of  nerve-cells  (ganglia)  and  fibres,  situated  mainly  in  the  axial  line 
and  giving  off  and  receiving  fibres  connected  with  the  various  viscera  of  the  trunk. 
The  component  elements  of  the  plexuses  and,  indeed,  of  the  entire  sympathetic 
system,  are  the  ganglia  and  the  nerve-fibres. 

The  ganglia,  whilst  following  a  general  plan  of  arrangement  as  to  number,  size 
and  position,  are  subject  to  wide  individual  variations  and,  moreover,  where  they 
approach  a  segmental  type,  as  in  the  gangliated  cord,  there  is  considerable  deviation 
from  the  arrangement  presented  by  the  cerebro-spinal  system.  A  ganglion  may  or 
may  not  be  connected  with  a  spinal  nerve,  but  it  is  always  linked  by  association 
cords  with  other  ganglia.  According  to  their  position,  three  varieties  of  ganglia 
are  recognized.  One  group  includes  the  prevertebral  ganglia  (g.  trunci  sym- 
pathetici),  those  found  as  nodes  in  the  gangliated  cord  ;  a  second  variety  comprises 
the  collateral  or  intermediate  ganglia  (g.  plexuum  sympatheticorum),  which 
lie  either  on  the  peripheral  branches  of  the  gangliated  cord  or  in  a  prevertebral 
plexus  ;  whilst  to  the  third  set  belong  the  innumerable  minute  terminal  ganglia, 
composed  of  nerve-cells  which  lie  at  or  near  the  visceral  distributions  of  the  sympa- 
thetic fibres. 

Each  ganglion  consists  of  an  indefinite  number  of  multipolar  neurones,  which 
possess  one  axone  and  a  number  of  dendrites,  the  whole  cluster  of  cells  being 
enclosed  in  an  envelope  of  fibrous  tissue.  The  axone  is  often  medullated  in  the 
immediate  vicinity  of  its  cell,  but  usually  loses  this  sheath  as  it  gets  farther  and 
farther  away  from  its  origin.  The  course  taken  by  the  axone  of  a  prevertebral  gang- 
lion-cell may  be  one  of  three  :  (i)  it  may  pass  by  means  of  an  association  cord  into 
an  adjoining  prevertebral  ganglion,  (2)  it  may  proceed  as  a  constituent  of  a  gray 
ramus  communicans  to  join  a  spinal  nerve  or  (3)  it  may  follow  a  splanchnic  efferent 
toward  a  viscus. 

The  nerve-fibres  encountered  within  the  sympathetic  system  include  two  sets  : 
(a)  those  derived  from  the  cerebro-spinal  system,  which  are  usually  medullated,  and 
(£)  the  sympathetic  fibres  proper,  for  the  most  part  nonmedullated,  although  as 
stated  above,  many  of  the  axones  possess  a  medullary  sheath  for  a  short  distance 
beyond  their  origin  from  the  nerve-cell.  This  distinction  between  medullated  and 
nonmedullated  fibres  is,  however,  somewhat  indefinite,  since  the  medullated  spinal 
fibres  often  become  nonmedullated  before  terminating,  whilst  the  sympathetic  fibres 
occasionally  are  medullated  throughout  their  course. 

Rami  Communicantes. — Where  the  typical  segmental  arrangement  prevails, 
as  in  the  thoracic  region,  each  spinal  nerve  is  connected  with  the  adjacent  gangliated 
cord  by  a  pair  of  short  nerve-trunks,  known  as  the  raini  comnntnicantfs  (Fig.  1 129). 
These  are  divided  into  two  groups,  the  white  rami  and  \\\G.  gray  rami,  a  distinction 
depending  primarily  upon  the  difference  in  the  appearance  of  the  strands  when  seen 
in  the  fresh  condition  ;  this  distinction,  moreover,  corresponds  with  the  histological 
difference  above  noted — white  rami  appearing  so  in  consequence  of  the  prepon- 
derance of  opaque  medullated  fibres,  and  the  gray  rami  possessing  the  darker  tint 
on  account  of  the  absence  of  the  refracting  myelin  coat.  The  rami  communicantes 
pass  directly  between  the  spinal  nerves  and  the  gangliated  cord,  in  relation  to  the 
latter  joining  either  a  ganglion  or  an  association  cord  between  nodes. 

The  white  rami  communicantes  are  composed  almost  exclusively  of  the 
visceral  branches  of  certain  of  the  spinal  nerves  which  use  tin-  sympathetic  systrm 
as  the  pathway  by  which  they  arrive  at  their  destination.  They  consist  of  fasciculi  of 


THE   SYMPATHETIC   SYSTEM    OF    NERVES.  1357 

medullated  nerve-fibres  derived  from  both  the  anterior  and  the  posterior  roots  of 
the  spinal  nerves.  The  fibres  arising  from  the  anterior  root  are  called  the  splanch- 
nic efferent  fibres  and  those  from  the  posterior  root  the  splanchnic  afferent.  Not  all 
of  the  spinal  nerves,  however,  give  off  white  rami,  these  strands  of  communication 
forming  a  thoraco-lumbar  group,  from  the  first  or  second  thoracic  to  the  second 
or  third  lumbar  nerve  inclusive,  and  a  sacral  group,  derived  from  the  second  and 
third,  or  third  and  fourth  sacral  nerves.  The  cervical  nerves  do  not  give  off 
white  rami. 

The  splanchnic  efferent  fibres  are  the  axones  of  cells  located  within  the 
lateral  horn  of  the  gray  matter  of  the  spinal  cord.  They  furnish  motor  impulses  to 
the  unstriped  muscle  of  the  vessels  and  viscera,  and  secretory  ones  to  the  glands  of 
the  splanchnic  area  ;  they  also  convey  motor  impulses  to  the  heart.  Leaving  the 
spinal  cord  by  way  of  the  anterior  root,  they  pass  peripherally,  enter  a  white  ramus 
communicans  and  reach  the  gangliated  cord.  One  of  three  courses  is  then  pursued 
by  these  fibres  :  ( I )  they  may  end  at  once  by  forming  arborizations  around  cells  in 
the  ganglion  which  they  first  enter,  (2)  they  may  pass  through  this  ganglion,  thence 
up  or  down  through  an  association  cord  to  end  around  the  cells  of  a  node  of  the 
gangliated  cord  above  or  below  the  level  of  entrance  or  (3)  they  may  course  through 
the  gangliated  cord  and  one  of  its  visceral  branches,  and  terminate  in  arborizations 
around  the  cells  of  a  prevertebral  or  of  a  collateral  ganglion.  It  is  possible  that  in 
some  cases  the  spinal  efferents  may  continue  without  interruption  through  the  several 
divisions  of  its  path  as  far  as  the  terminal  ganglia.  In  any  event,  whether  ending 
in  the  gangliated  cord,  the  prevertebral,  the  collateral  or  the  terminal  ganglia,  the 
cerebro-spinal  fibre  as  such  probably  never  actually  gains  the  tissue  of  the  organ,  the 
last  link  in  the  path  of  conduction  being  supplied  by  a  sympathetic  neurone. 

The  splanchnic  afferent  fibres  are  the  sensory  fibres  of  the  splanchnic  area 
and  consist  of  the  dendrites  of  cells  situated  within  the  intervertebral  ganglia  on  the  pos- 
terior roots  of  the  spinal  nerves.  Whilst  the  greater  number  of  these  fibres  are  found 
in  the  white  rami,  a  few  are  thought  to  be  constituents  of  the  gray  rami.  Beginning 
in  the  viscera,  they  run  centrally,  without  interruption,  through  the  terminal  and 
collateral  ganglia,  through  the  gangliated  cord  and  the  white  (or  gray)  rami  to  the 
spinal  nerve,  and  thence  after  coming  into  relation  with  the  cells  of  the  ganglion  of 
the  posterior  root,  they  pass  by  way  of  the  posterior  roots  into  the  spinal  cord. 

The  gray  rami  communicantes  are  bundles  of  axones  of  sympathetic  neu- 
rones which  pass  from  the  gangliated  cord  to  each  one  of  the  entire  series  of  spinal 
nerves.  The  reason  of  this  generous  provision  will  be  evident  when  the  purpose  of 
the  communications  effected  by  the  gray  rami  is  recalled,  namely,  to  provide  sympa- 
thetic filaments  to  the  outlying  muscles  and  glands  by  way  of  the  convenient  path 
afforded  by  the  distribution  of  the  somatic  nerves.  Mingled  with  the  gray  fibres, 
a  few  of  the  medullated  variety  are  often  encountered  ;  these  are  probably  partly 
splanchnic  afferent  fibres  and  partly  medullated  sympathetic  fibres.  Variation  in  the 
origin  of  the  gray  rami  from  the  gangliated  cord  is  not  uncommon  ;  they  may 
arise  either  from  a  ganglion  or  from  the  association  cord  between  two  ganglia  ; 
after  leaving  the  gangliated  cord,  a  single  ramus  may  divide  and  supply  two  spinal 
nerves  ;  or  the  reverse  may  happen,  two  or  more  rami  arising  independent!)'  and 
either  separately  or  after  fusing,  joining  a  single  spinal  nerve. 

The  further  course  of  the  sympathetic  fibres,  after  having  joined  the  spinal  nerves 
by  way  of  the  gray  rami,  is  as  follows  :  ( i )  they  may  course  peripherally  along  with 
the  anterior  or  posterior  primary  divisions  of  the  spinal  nerve  and  convey  vasomotor, 
pilomotor  or  secretory  impulses  to  the  involuntary  muscle  and  glands  of  the  somatic 
area;  or  (2)  they  may  enter  the  spinal  canal  byway  of  the  anterior  or  posterior 
nerve-roots  and  be  distributed  to  the  spinal  meninges,  but  not  to  the  nervous  column. 
According  to  Dogiel,  it  is  probable  that  a  small  number  of  axones  of  sympathetic 
neurones  enter  the  root-ganglia  of  the  spinal  nerves  to  end  in  arborizations  around 
cells  of  type  II  (page  1008). 

The  association  cords  (Fig.  1130)  are  the  longitudinally  disposed  bundles  of 
fibres  comprising  the  interganglionic  portion  of  the  gangliated  cord  ;  they  contain  both 
white  and  gray  fibres.  The  gray  ones  are  the  axones  of  sympathetic  neurones  which 
are  either  passing  between  adjacent  or  more  remote  ganglia,  or  taking  an  upward  or 


1358 


HUMAN   ANATOMY. 


downward  course  before  passing  distally  to  their  ultimate  splanchnic  distribution. 
The  white  fibres  are  either  spinal  splanchnic  efferent  or  afferent  fibres. 

The  branches  of  distribution  from  the  gangliated  cord  include  the  somatic 
and  the  visceral.  The  somatic  branches  are  the  rami  communicantes  ;  the  vis- 
ceral branches  comprise  the  splanchnic  efferents,  which  consist  of  both  white  and 
gray  efferent  fibres,  as  well  as  the  white  splanchnic  afferents. 

THE  CERVICO-CEPHALIC  PORTION  OF  THE  GANGLIATED  CORD. 

The  cervico-cephalic  portion  of  the  gangliated  cord  (pars  cephalica  et  cervicalis 
systematis  sympathetici)  consists  of  a  series  of  ganglia,  usually  three,  but  often  only 
two,  connected  by  composite  association  cords  (Fig.  1131).  It  lies  posterior  to  the 

FIG.  1131. 

Lower  head  of  external  pterygoid  muscle 
Internal  pterygoid  muscle  \ 

\ 

Auriculo-temporal  nervi 
Internal  carotid  arterr 


Pneumogastric  nerve- 
Inferior  dental  nerve- 
Spinal  accessory  nerve- 
Part  of  facial  m 
Hypoglossal  nerv 
Stylo-pharyngeus  muscl 
Glosso-pharyngeal  ner 
I.  cervical  ner 
Pneumogastric  nerv 
Superior  cervical  ganglion  of 

sympathetic 

Superior  laryngeal  nerve 

Descendens  hypoglossi 

1 1 .  cervical  nerve 

III.  cervical  nerv 


IV.  cervical  nerve 


Interganglionic  association 
cord  of  sympathetic 


Middle  cervical  ganglion 

A 


Inferior  cervical 

ganglio 


Branch  to,  I .  thoracic 

ganglion 


Inferior  cervical  cardiac 
of  sympathetic 


Recurrent  laryngeal 

nerve 
Internal  mammary  artery 

Cartilage  of  I.  rib 

Clavicular  facet  of  sternum  ' 


Lingual  nerve 
External  laryngeal  branch 


uperior  cervical  cardiac  of 
sympathetic 


Middle  cervical  cardiac  of  sympathetic 
Recurrent  laryngeal  nerve 


Middle  cervical  cardiac  of 

C,.iiMi.,,n  [pneumogastric 

carotid  artery 
Inferior  cervical  cardiac  of 

pneumogastric 


Deep  dissection  of  neck,  showing  cervical  portion  of  sympathetic  gangliated  cord  and  its  connections. 


carotid  sheath  and  anterior  to  the  prevertebral  fascia  and  the  rectus  capitis  anticus 
major  and  scalenus  anticus  muscles.  Inferiorly  it  is  continued  into  the  thoracic 
portion  of  the  gangliated  cord,  and  superiorly,  at  the  base  of  the  skull,  it  forms  an 
intricate  plexus  around  the  internal  carotid  artery,  in  whose  company  it  enters  the 


THE   SYMPATHETIC   SYSTEM    OF   NERVES.  1359 

cranium.  The  small  ganglia  connected  with  the  trigeminal  nerve — the  ciliary,  the 
spheno-palatine,  the  otic  and  the  submaxillary — are  regarded  as  outlying  nodes  be- 
longing to  the  cephalic  continuation  of  the  gangliated  cord. 

The  dominant  characteristic  of  this  portion  is  the  absence  of  white  rami,  the 
spinal  fibres  present  reaching  the  cervical  region  from  the  upper  thoracic  nerves  by 
way  of  the  association  cord  between  the  highest  thoracic  and  lowest  cervical  gang- 
lion, around  whose  cells,  as  well  as  those  of  the  higher  cervical  ganglia,  the  processes 
of  the  spinal  neurones  end. 

The  distribution  of  the  cervical  portion  of  the  cord  includes  pupillo-dilator 
fibres,  cardio-accelerator  fibres,  vasomotor  fibres  to  the  arteries  of  the  head,  neck  and 
upper  extremities,  pilomotor  fibres  to  the  integument  of  the  head  and  neck,  motor 
fibres  to  the  involuntary  muscles  of  the  orbit  and  eyelids  and  secretory  fibres  to  the 
glands.  The  branches  consist,  as  elsewhere,  of  two  groups,  somatic  and  visceral,  the 
former  reaching  their  area  of  distribution  by  way  of  certain  cranial  and  spinal  nerves, 
and  the  latter,  either  alone  or  in  conjunction  with  other  nerves,  forming  plexuses 
which  accompany  blood-vessels  and  supply  various  viscera  and  vessels  of  the  head, 
neck  and  thorax. 

The  ganglia  of  the  cervical  portion  include  a  superior,  a  middle  and  an  inferior. 

The  Superior  Cervical  Ganglion. — The  superior  cervical  ganglion  (g.  cervi' 
calc  superius)  (Fig.  1077)  is  the  largest  of  the  entire  sympathetic  series,  measuring 
2-3  cm.  in  length  and  4—6  mm.  in  width.  It  rests  posteriorly  on  the  rectus  capitis 
anticus  major  muscle  opposite  the  second  and  third  cervical  vertebrae,  with  the 
internal  carotid  artery  anterior  to  it  and  the  vagus  nerve  to  its  lateral  aspect.  With 
the  typical  reddish-gray  hue  of  the  sympathetic  ganglia,  it  is  fusiform  in  outline, 
although  it  may  present  constrictions,  usually  three,  which  indicate  its  composition  of 
four  fused  ganglia. 

The  somatic  branches  consist  of  (i)  rami  communicantes  and  (2)  communi- 
cating branches  to  the  cranial  nerves. 

1.  The  rami  communicantes  consist  of  four  gray  rami  which  join  the  anterior 
primary  divisions  of  the  first  four  cervical  nerves. 

2.  The  communicating  branches  to  the  cranial  nerves  are  given  off  from  the 
upper  portion  of  the  ganglion,    (i)  one  joining  the  petrous  ganglion  of  the  glosso- 
pharyngeal,  (2)  others  entering  the  ganglia  of  the  root  and  trunk  of  the  vagus  and 
(3)  another  joining  the  hypoglossal  nerve.      In  addition  to  these  there  is  frequently 
given  off  from  the  lower  portion  of  the  ganglion  (4)  a  branch  which  joins  the  exter- 
nal laryngeal  nerve. 

The  visceral  branches  comprise  :  (i)  the pharyngeal ,  (2)  the  superior  cervi- 
cal cardiac ,  (3)  the  vascular  and  (4)  the  vertebral. 

1.  The  pharyngeal   branch   or  branches  (rr.  laryngopharyngei)   arises  from 
the  antero-mesial  aspect  of  the  ganglion  and  courses  obliquely  inward  and  downward 
posterior  to  the  carotid  sheath  to  reach  the  surface  of  the  middle  constrictor  of  the 
pharynx.      Here  it  unites  with  the  pharyngeal  branches  of  the  glosso-pharyngeal  and 
vagus  nerves  to  form  the  pharyngeal  plexus  (page  1269),  from  which  fibres  are 
distributed  to  the  muscles  and  mucous  membrane  of  the  pharynx,  a  few  filaments 
joining  the  superior  and  external  laryngeal  nerves. 

2.  The  superior  cervical  cardiac  nerve  (n.  cardiacus  superior)  (Fig.  1131) 
arises  as  two  or  three  twigs  from  the  ganglion,  with  sometimes  an  additional  filament 
from  the  association  cord  between  the  superior  and  middle  ganglia.     It  courses  down- 
ward anterior  to  the  longus  colli  muscle  in  the  posterior  part  of  the  carotid  sheath, 
crosses  the  anterior  or  the  posterior  surface  of  the  inferior  thyroid  artery,  and  then 
descends  in  front  of  the  inferior  laryngeal  nerve.     At  the  base  of  the  neck  the  course 
of  the  nerve  begins  to  differ  on  the  two  sides. 

The  right  nerve  enters  the  thorax  either  anterior  or  posterior  to  the  subclavian 
artery  and  accompanies  the  innominate  artery  to  the  aorta,  where  it  enters  the  deep 
cardiac  plexus,  a  few  fibres  passing  to  the  anterior  surface  of  the  aorta.  On  the  way 
down  a  few  twigs  join  the  inferior  thyroid  artery  and  with  it  enter  and  supply  the 
substance  of  the  thyroid  body. 

The  left  nerve  upon  entering  the  thorax  joins  the  common  carotid  artery,  along 
whose  lateral  and  anterior  surfaces  it  courses  to  the  aorta,  upon  reaching  which  it 


1360  HUMAN    ANATOMY. 

joins  the  superficial  cardiac  plexus.  In  some  instances  the  nerve  remains  behind  the 
carotid  artery  and  joins  the  deep  cardiac  plexus. 

A  pretracheal  branch,  derived  from  the  loop  between  the  superior  cervical 
cardiac  nerve  and  the  inferior  laryngeal,  descends  anterior  to  the  trachea  and  is  dis- 
tributed to  the  pericardium  and  the  anterior  pulmonary  plexus  (Drobnik. ) 

The  superior  cervical  cardiac  nerve  communicates  freely  in  the  neck  with  the 
middle  cardiac  and  other  branches  of  the  sympathetic,  and  with  the  external  laryngeal 
and  superior  cervical  cardiac  branches  of  the  vagus.  In  the  thorax  it  inosculates 
with  the  inferior  laryngeal  nerve. 

Variations. — The  superior,  as  well  as  the  other  cardiac  nerves,  presents  a  considerable 
degree  of  variation,  sometimes  to  so  grea:  an  extent  as  to  show  no  resemblance  to  the  accepted 
typical  plan  of  arrangement.  It  is  sometimes  absent,  especially  on  the  right  side,  and  in  such 
event  appears  to  be  replaced  by  a  branch  from  the  vagus  or  from  the  external  laryngeal  nerve. 
It  may  have  no  independent  course,  but  join  one  of  the  other  sympathetic  cardiac  nerves  and 
reach  its  destination  as  a  part  of  the  latter. 

3.  The  vascular  branches  comprise  plexiform  nerve-structures  which  accom- 
pany the  terminal  divisions  of  the  common  carotid  artery.  They  consist  of :  (a)  the 
external  carotid  branch  and  (£)  the  internal  carotid  branch. 

a.  The  external   carotid  branch   (n.  caroticus  externus)   (Fig.    1061)    joins 
the  external  carotid  artery  and  furnishes  subsidiary  plexuses  which  accompany  the 
branches  of  that  vessel.       In  addition  to  supplying  vasomotor  fibres  to  the  external 
carotid  tree,  sympathetic  filaments  are  furnished  to  two  of  the  ganglia  of  the  trigem- 
inal  nerve.      A  branch  (radix  g.  submaxillaris)  from  the  plexus  on  the  facial  artery 
(plexus    maxillaris    externus)   joins   the  submaxillary   ganglion   as    its   sympathetic 
root,  and  one  or  more,  the  smallest  deep  petrosal  nerve,  from  the  plexus  on 
the  middle  meningeal  artery  (plexus  meningeus),  forms  the  sympathetic  root  of  the 
otic  ganglion. 

Ganglia  of  microscopic  size  have  been  described  on  these  vascular  plexuses. 
The  most  important  of  these,  the  temporal  ganglion,  is  situated  on  the  external 
carotid  at  the  point  of  origin  of  the  posterior  auricular  artery  and  is  said  to  receive 
a  filament  of  communication  from  the  stylo-hyoid  branch  of  the  facial  nerve. 

b.  The    internal    carotid    branch    (n.  caroticus   internus)    is  apparently    an 
upward,  cranial  extension  of  the  superior  ganglion  (Fig.  1061).     Ascending  beneath 
the  internal  carotid  artery,  it  accompanies  that  vessel  into  the  carotid  canal,  where  it 
divides  into  two  plexuses,  the  carotid  and  the  cavernous,  the  former  ramifying  on  the 
lateral  and  the  latter  on  the  mesial  aspect  of  the  artery.     While  the  individuality  of 
these  two  is  distinct,  there  are  numerous  fine  fibres  connecting  them  as  they  pass 
upward  into  the  cranium. 

The  carotid  plexus  (plexus  caroticus  internus)  is  located  on  the  lateral  or  outer 
surface  of  the  internal  carotid  artery  at  its  second  bend.  In  addition  to  supplying 
fine  plexuses  which  accompany  the  branches  of  the  artery  to  their  ultimate  ramifica- 
tions, the  following  arise  from  the  carotid  plexus  :  (aa)  the  carotid  branches,  (bb) 
the  communicating  branch  to  the  abducent  nerve,  (cc}  the  communicating  branches 
to  the  Gasserian  ganglion,  (dd  )  the  great  deep  petrosal  nerve  and  (ee )  the  small 
deep  petrosal  nerve, 

aa.  The  carotid  branches  consist  of  numerous  fine  twigs  which  are  supplied  to  the  internal 
carotid  artery. 

bb.  The  communicating  branch  to  the  abducent  nerve  consists  of  one  or  two  twigs  which 
join  the  nerve  as  it  lies  in  the  wall  of  the  cavernous  sinus  in  close  proximity  to  the  internal 
carotid  artery. 

cc.  The  communicating  branches  to  the  Gasserian  ganglion  comprise  several  small  fila- 
ments which  pass  to  the  ganglion  ;  they  usually  arise  from  the  carotid  but  sometimes  are  derived 
from  the  cavernous  plexus. 

dd.  The  great  deep  petrosal  nerve  courses  forward  to  the  posterior  end  of  the  Vidian  canal, 
where  it  joins  the  great  superficial  petrosal  to  form  the  I'idian  nerve  (page  1059),  finally  en- 
tering Meckel's  ganglion  as  its  sympathetic  root. 

ee.  The  small  deep  petrosal  nerve  or  ;/.  carolicn-tymt>amcns  joins  the- tympanic  plexus 
(page  1075),  a  structure  formed  by  the  tympanic  branch  of  the  glosso-pharyngeal,  a  filament 
from  the  geniculate  ganglion  of  the  facial  nerve  and  the  small  deep  petrosal  nerve.  In  addition 


THE   SYMPATHETIC   SYSTEM    OF   NERVES. 


1361 


to  furnishing  twigs  to  the  mucous  membrane  of  the  middle  ear  and  vicinity,  this  plexus  con- 
tributes a  large  part  of  the  small  superficial  petrosal  nerve,  which  joins  the  otic  ganglion  as  its 
sensory  root  (page  1246). 

The  cavernous  plexus  (plexus  cavernosus)  lies  inferior  and  internal  to  the 
internal  carotid  artery  and  in  intimate  relation  with  the  cavernous  sinus.  Its 
branches  are:  (aa)  the  carotid  branches,  (bb}  the  communicating  branch  to  the  oculo- 
motor nerve,  (cc)  the  communicating  branch  to  the  trochlear  nerve,  (dd}  the  com- 
municating branch  to  the  ophthalmic  division  of  the  trigeminus  nerve,  (ee~)  a  branch 
to  the  ciliary  ganglion  and  Q/)  branches  to  the  pituitary  body. 

FIG.  1132. 


Superior  cervical  cardiac  branch  ot  sympathetic 


Sympathetic  association  cord 
Right  vagus  ne: 


Middle  cervical  ganglion 


Middle  and  inf.  cervical  card 
branches  of  sympathetic 

Recurrent  laryngeal  n 


Pulmonary  branch  of  vagus 

Vena  azygos  major 

Phrenic  nerve 


Right  pulmonary  artery 


Right  auricular  appendix 
Pericardium 


Superior  cervical  cardiac  branch 

of  sympathetic 

Superior  cervical  cardiac  branch  of  vagus 
Middle  cervical  ganglion 
Middle  cervical  cardiac  branch 

of  sympathetic 


[of  sympathetic 
cal  cardiac  branch 
cal  ganglion 


Middle  cervical  cardia 

branch  of  vagus 
Inf.  cervical  cardiac 

branch  of  vagus 
Phrenic  nerve 


Left  vagus  nerve 
Recurrent  laryngeal  nerve 

Left  pulmonary  artery 
Pulmonary  veins 

Pulmonary  orifice 

Mesial  surface  of  lung 
Pericardium 


Dissection  showing  cardiac  branches  of  pneumogastric  nerves  and  of  sympathetic  cords ;  aortic  arch  and 
branches  and  pulmonary  artery  partially  removed  ;  pericardium  laid  open. 

aa.  The  carotid  branches  are  distributed  to  the  internal  carotid  artery. 

bb.  The  communicating  branch  to  the  oculomotor  nerve  joins  the  latter  about  at  the  point 
where  it  breaks  up  into  its  superior  and  inferior  divisions. 

cc.  The  communicating  branch  to  the  trochlear  nerve,  sometimes  derived  from  the 
carotid  plexus,  joins  the  trochlear  in  the  wall  of  the  cavernous  sinus. 

dd.  The  communicating  branch  to  the  ophthalmic  division  of  the  trigeminus  nerve  joins 
the  mesial  surface  of  that  nerve. 

ee.  The  branch  to  the  ciliary  ganglion  (radices  sj  mpatheticae  g.  ciliaris)  arises  in  the 
cranium  and  enters  the  orbit  through  the  sphenoidal  fissure,  either  as  an  independent  structure 
or  jointly  with  the  nasal  or  with  the  oculomotor  nerve.  As  the  sympathetic  root  (radix  media), 
it  enters  the  upper  posterior  angle  of  the  ciliary  ganglion  (Fig.  1058),  either  alone  or  as  a 
common  trunk  with  the  sensory  root. 

86 


1362  HUMAN   ANATOMY. 

ff.  The  branches  to  the  pituitary  body  consist  of  several  tiny  filaments  which  enter  the 
substance  of  that  body. 

4.  T4ie  vertebral  branches  consist  of  two  or  three  filaments  which  pass 
backward,  pierce  the  prevertebral  muscles  and  are  distributed  to  the  bony  and  liga- 
mentous  structures  of  the  upper  portion  of  the  vertebral  column. 

The  Middle  Cervical  Ganglion. — The  middle  cervical  ganglion  (g.  cervicale 
medium),  a  structure  not  infrequently  absent,  consists  of  one  or  two  collections 
of  nerve-cells  situated  posterior  to  the  carotid  sheath  in  the  neighborhood  of 
the  inferior  thyroid  artery  (Fig.  1131).  It  lies  about  the  level  of  the  sixth  cervical 
vertebra  and  represents  the  fusion  of  two  primitive  cervical  ganglia. 

The  somatic  branches  are  :  (i)  the  gray  rami  communicantes  and  (2)  the 
subclavian  loop. 

1.  The  gray  rami  communicantes  arise  either  from  the  ganglion  or  from  its 
upper  or  lower  association  cord.      They  consist  of  two  trunks  which  pass  backward 
and  join  the  anterior  primary  divisions  of  the  fifth  and  sixth  cervical  nerves. 

2.  The  subclavian  loop   (ansa  subclavia  [Vieussenii] )  is  a  nerve,   frequently 
double,  which  passes  over  the  subclavian  artery  and  joins  the  inferior  cervical  gang- 
lion sending  twigs  (plexus  subclavius)  to  the  subclavian  artery  and  its  branches  and 
to  the  phrenic  nerve. 

The  visceral  branches  are:  (i)  the  thyroid  plexus  and  (2)  the  middle 
cervical  cardiac  nerve.  In  case  of  absence  of  the  middle  cervical  ganglion,  these 
branches  arise  from  the  interganglionic  association  cord  between  the  superior  and 
inferior  ganglia. 

1.  The   thyroid  plexus    (plexus  thyreoideus  inferior)   consists  of  several  fine 
inosculating  twigs  which  accompany  the  inferior  thyroid  artery  into  the  substance 
of  the  thyroid  body. 

2.  The  middle  cervical  cardiac  nerve   (n.  cardiacus  medius)  (Fig.  1131) 
differs  in  its  course  on  the  two  sides  of  the  body.      Descending  in  the  neck,  where 
it  inosculates  with  the  superior  cervical  cardiac  and  inferior  laryngeal   nerves,   it 
passes,  on  the  right  side,  either  anterior  or  posterior  to  the  subclavian  artery,  to 
the  front  of  the  trachea  where  it  receives  filaments  of  inosculation  from  the  inferior 
laryngeal   nerve.      On  the  left  side  it  enters  the  thorax  between  the  common  carotid 
and  subclavian  arteries.     On  both  right  and  left  sides  it  terminates  posterior  to  the 
arch  of  the  aorta  by  entering  corresponding  sides  of  the  deep  cardiac  plexus. 

Variations. — The  gangliated  cord,  in  the  region  of  the  middle  ganglion,  may  lie  posterior 
to  the  inferior  thyroid  artery  or  may  be  bifurcated,  the  artery  lying  between  the  two  portions. 

The  Inferior  Cervical  Ganglion. — The  inferior  cervical  ganglion  (g.  cervicale 
infenus)  (Fig.  1079)  is  situated  at  the  root  of  the  neck,  over  the  first  costo-central 
articulation,  between  the  neck  of  the  first  rib  and  the  transverse  process  of  the 
seventh  cervical  vertebra.  In  shape  it  is  irregular,  being  flat,  round  or  cres- 
centic,  and  it  is  often  fused  with  or  only  partially  separated  from  the  first  thoracic 
ganglion.  Situated  in  the  external  angle  between  the  subclavian  and  vertebral 
arteries  it  is  usually  connected  above  with  the  middle  ganglion  by  an  association  cord 
and  by  the  subclavian  loop,  the  former,  passing  posterior  to  the  vertebral  artery, 
but  sometimes,  especially  on  the  left  side,  forming  a  nervous  ring  around  that  vessel. 

The  somatic  branches  consist  of:  (i)  the  grav  rami  communicantes^  (2)  the 
subclavian  loop  and  (3)  a  communicating  branch  to  the  inferior  laryngeal  ncrrc. 

1.  The  gray  rami  communicantes  consist   of  two   nonmedullated    trunks 
which  join  the  anterior  primary  divisions  of  the  seventh  and  eighth  cervical  nerves. 

2.  The  subclavian  loop  (ansa    subclavia    [Vieussenii]  )   has  already  been  dt  - 
scribed,  as  a  branch  of  the  middle  cervical  ganglion. 

3.  The  communicating  branch  to  the  inferior  laryngeal  nerve  frequently 
accompanies  the  inferior  cervical  cardiac  nerve  ;  it  joins  the  inferior  laryngeal  pos- 
terior to  the  subclavian  artery. 

The  visceral  branches  comprise  :  (i)  the  vertebral  plexus  9sv&  (  2  )  tin-  inferior 
cervical  cardiac 


THE   SYMPATHETIC    SYSTEM    OF   NERVES. 


1363 


i.  The  vertebral  plexus  ( plexus  vertebralis)  is  a  closely  woven  net-work  of 
fibres  which  follows  the  course  and  distribution  of  the  vertebral  artery  in  the  neck 
and 'cranium. 

FIG.  1133. 


I.  rib 

II.  thoracic  nerve 
Intercostal  artery 
III.  thoracic  nerve 


Intercostal  artery 
V.  thoracic  nerve 


XI.  thoracic  ganglion  ;  immedi- 
ately below  it  is  the  XII. 


XII.  rib 

Diaphragm 

I.  lumbar  ganglion 

Ilio-hypogastric^ 

nerve 
II.  and  III.  lumbar 

ganglia,  fused 
Ilio-inguinal  nerve 

IV.  lumbar 

ganglion 

IV.  lumbar  nerve 

V.  lumbar  ganglion 

Interganglionic 

association  cord 

I.  sacral  ganglion 1 

Anterior  crural  nerve 

II.  sacral  ganglion  — — 

III.  sacral  nerve 
IV.  sacral  ganglion 


I.  thoracic  ganglion  partially 

blended  with  inferior 
cervical  ganglion 

II.  thoracic  ganglion 


Aorta 

Great  splanchnic  nerve 

Small  splanchnic  nerve 
Least  splanchnic  nerve 

Semilunar  ganglion  and 
solar  plexus 


Dissection  showing  thoracic,  lumbar  and  sacral  portions  of  right  gangliated  cord  and  their  branches. 

2.   The  inferior  cervical  cardiac  nerve  (n.  cardiacus  inferior)  (Fig.   1132), 
sometimes  arising  from  the  first  thoracic  ganglion,  descends  in  the  thorax  posterior  to 


1364  HUMAN   ANATOMY. 

the  subclavain  artery,  inosculates  with  the  middle  cervical  cardiac  and  inferior  laryngeal 
nerves  and  terminates  in  the  deep  cardiac  plexus. 

THE  THORACIC  PORTION  OF  THE  GANGLIATED  CORD. 

The  thoracic  portion  of  the  gangliated  cord  (pars  thoracalis  systematis  sympa- 
thetic!) consists  of  a  series  of  eleven,  twelve,  ten  or  even  fewer  irregularly  triangular, 
fusiform  or  oval  ganglia  (gg.  thoracalia),  situated  lateral  to  the  bodies  of  the  thoracic 
vertebrae,  covered  by  parietal  pleura  and  interconnected  by  association  cords  which 
lie  anterior  to  the  intercostal  blood-vessels  (Fig.  1133).  The  largest  of  the  ganglia 
is  the  first,  which  is  situated  at  the  mesial  end  of  the  first  intercostal  space  and  is 
not  infrequently  fused  with  the  inferior  cervical  ganglion.  The  location  of  the 
thoracic  ganglia  corresponds  usually  to  the  heads  of  the  ribs,  the  lowest  being  placed 
anterior  to  the  head  of  the  twelfth  rib  and  at  the  upper  margin  of  the  twelfth  thoracic 
vertebra. 

A  characteristic  of  the  thoracic  ganglia  is  the  almost  unvarying  presence  of  white 
rami  communicantes,  all  of  the  series,  with  the  possible  exception  of  the  first,  receiving 
these  rami  from  the  thoracic  spinal  nerves.  They  consist  of  an  upper  and  a  loti  'cr 
series,  the  former  coming  from  the  upper  five  nerves  and  coursing  head-ward  to  enter 
and  be  distributed  mainly  by  way  of  the  cervico-cephalic  portion  of  the  gangliated 
cord  ;  and  the  lower  arising  from  the  lower  seven  and  being  distributed  to  certain 
thoracic  and  abdominal  structures.  As  elsewhere,  so  here  from  each  of  the  ganglia 
is  given  off  a  gray  ramus  communicans  to  a  thoracic  spinal  nerve. 

The  somatic  branches  of  the  thoracic  portion  of  the  gangliated  cord  are 
chiefly  the  gray  rami  communicantes.  These  arise  from  each  of  the  thoracic  ganglia 
and,  in  close  proximity  to  the  white  rami,  pass  backward  and  join  the  anterior  pri- 
mary divisions  of  all  the  thoracic  spinal  nerves. 

The  visceral  branches  arise  from  the  ganglia  and  their  association  cords  and 
consist  of  gray  splanchnic  efferent  and  white  splanchnic  efferent  and  afferent  fibres. 

The  splanchnic  afferent  fibres  have  no  sympathetic  connections,  and  consist 
merely  of  tracts  which  carry  impulses  from  the  splanchnic  area  through  the  thoracic 
and  spinal  ganglia  to  the  posterior  roots  of  the  spinal  thoracic  nerves. 

The  splanchnic  efferent  fibres,  after  passing  through  the  gangliated  cord  or 
its  peripheral  branches,  form  links  with  the  cells  of  the  collateral  or  terminal  ganglia, 
from  which  nonmedullated  axones  are  derived  for  the  supply  of  various  visceral  or 
vascular  structures.  Those  of  the  upper  series  are  distributed  mainly  as  branches  of 
the  cervical  ganglia;  while  those  of  the  lower  series,  from  the  sixth  to  the  twelfth  thoracic 
nerves  inclusive,  in  the  thorax  supply  the  aorta  and  lungs  with  vasomotor  fibres. 
Below  the  thorax  their  distribution  is  quite  extensive,  including,  in  conjunction  with 
the  vagus,  viscero-inhibitory  fibres  for  the  stomach  and  intestine,  motor  fibres  for  a 
portion  of  the  circular  muscle  of  the  rectum,  vasomotor  fibres  for  the  abdominal  aorta 
and  its  branches  and  secretory  and  sensory  fibres  for  the  abdominal  viscera.  The 
thoracic  gangliated  cord  is  peculiar  in  containing,  along  with  the  visceral  fibres  dis- 
tributed by  its  splanchnic  efferents,  many  efferents  proceeding  from  the  spinal  cord 
destined  for  regions  supplied  by  way  of  the  limb  nerves  arising  from  the  cervical  and 
lumbo-sacral  segments  of  the  spinal  cord.  In  order  to  provide  gray  rami  at  appro- 
priate levels  to  join  the  spinal  nerves  the  spinal  efferents  course  both  up  and  down 
in  the  gangliated  cord  beyond  the  thoracic  region.  In  this  manner  the  thoracic 
nerves,  in  addition  to  giving  off  the  splanchnic  efferents,  provide  vasomotor,  pilo- 
motor  and  secretory  filaments  for  the  greater  part  of  the  lower  half  of  the  body. 

The  visceral  branches  comprise  :  (i)  the  pulmonary  branches,  (2)  the  aortic 
branches  and  (3)  the  splanchnic  nerves. 

1.  The  pulmonary  branches  (IT.  pulmonales)  are  derived  from  the  second, 
third  and  fourth  ganglia  and  proceed  forward  to  join  the  posterior  pulmonary  plexus. 

2.  The  aortic  branches  arise  from  the  upper  four  or  five  ganglia  and,   after 
furnishing  a  few  fine  twigs  to  the  vertebrae  and  their  ligaments,   inosculate  around 
the  thoracic  aorta  in  the  form  of  a  fine  plexus  (plexus  aorticus  thoracalis). 

3.  The  splanchnic  nerves   inn.  splanchnic!  >  (Fig.    1133^   are  three  trunks 
which  arise  from  the  lower  part  of  the  thoraeir  cord  and  are  distributed  to  structures 
situated  in  the  abdominal  cavity. 


THE   SYMPATHETIC   SYSTEM    OF    NERVES. 


1365 


The  great  splanchnic  nerve  (n.  splanchnicus  major)  arises  by  a  series  of  roots 
from  the  gang-Hated  cord  from  the  fifth  to  the  ninth  ganglia  inclusive.  Descending 
along  the  antero-lateral  aspect  of  the  vertebral  column,  this  nerve  pierces  the  crus  of 


- 


the  diaphragm  and  enters  the  upper  end  of  the  semilunar  ganglion,  some  of  its 
fibres  being  traceable  to  the  suprarenal  body  and  the  renal  plexus.  In  the  thoracic 
portion  of  its  course  is  developed  the  great  splanchnic  ganglion  (g.  splanchnicum)  from 


1366  HUMAN   ANATOMY. 

which,  as  well  as  from  the  nerve  itself,  are  given  off  filaments  for  the  supply  of  the 
oesophagus,  the  thoracic  aorta  and  the  vertebrae.  Sometimes  in  the  thorax  it  is 
divided  and  forms  a  plexus  with  the  small  splanchnic  and  in  this  event  several  small 
ganglia  are  present.  This  nerve  consists  mainly  (four-fifths,  according  to  Riidinger) 
of  medullated  fibres,  which  are  direct  continuations  of  white  rami  from  as  far  up  as 
the  third  thoracic  aerve  or  even  higher. 

The  small  splanchnic  nerve  (n.  splanchnicus  minor)  arises  from  the  ninth  and 
tenth,  or  tenth  and  eleventh  ganglia  or  from  adjacent  portions  of  interganglionic  cords. 
Entering  the  abdomen  by  piercing  the  crus  of  the  diaphragm  either  in  association  with 
or  in  close  proximity  to  the  great  splanchnic,  it  terminates  in  that  portion  of  the  semi- 
lunar  ganglion  called  the  aortico-rcnal ganglion. 

The  least  splanchnic  nerve  (n.  splanchnicus  imus)  arises  from  the  lowest  of 
the  thoracic  ganglia  and  may  receive  a  filament  from  the  small  splanchnic,  from  which 
it  occasionally  takes  origin.  Piercing  the  diaphragm  in  company  with  the  gangli- 
ated  cord  it  terminates  in  the  renal  plexus. 

A  fourth  splanchnic  nerve  is  rarely  present.  It  is  described  by  Wrisberg  as 
having  been  found  in  eight  cadavers  out  of  a  large  number  examined.  It  is  formed 
by  filaments  from  the  cardiac  nerves,  aided  by  twigs  from  the  lower  cervical  and 
upper  thoracic  ganglia. 

THE  LUMBAR  PORTION  OF  THE  GANGLIATED  CORD. 

The  lumbar  portion  of  the  gangliated  cord  (pars  abdominalis  systeniatis  sympa- 
thetici)  (Fig.  1 134)  consists  usually  of  four  small  oval  ganglia  connected  by  association 
cords.  There  may  be  a  decided  increase  in  the  number  of  the  ganglia,  as  many  as 
eight  having  been  found,  and,  on  the  other  hand,  occasionally  there  are  fewer  than 
four,  there  being  under  these  circumstances  a  compensatory  increase  in  the  size  of  the 
ganglia  present.  The  lumbar  portion  of  the  sympathetic  lies  nearer  the  median  line 
than  does  the  thoracic,  the  cords  being  placed  anterior  to  the  bodies  of  the  lumbar 
vertebrae  and  the  lumbar  vessels,  along  the  mesial  border  of  the  psoas  magnus,  on 
the  left  side  being  partially  concealed  by  the  aorta  and  on  the  right  by  the  inferior 
vena  cava.  It  is  connected  with  the  thoracic  portion  by  a  small  association  cord, 
which  passes  either  through  or  posterior  to  the  diaphragm,  and  with  the  sacral  portion 
by  a  cord  which  descends  behind  the  common  iliac  artery.  White  rami  communi- 
cantes  are  received  from  the  first,  the  second  and  sometimes  the  third  lumbar  nerve, 
additional  white  fibres  being  derived  from  the  lower  thoracic  nerves  by  way  of  the 
gangliated  cord. 

The  somatic  branches  comprise:  (i)  the  white  and  (2)  the  gray  rami 
communicantes.  These  are  the  longest  to  be  found  in  the  body,  on  account  of  the 
distance  between  the  ganglia  and  the  inttirvertebral  foramina.  They  accompany  the 
lumbar  vessels  and  pass  beneath  the  fibrous  arches  from  which  the  psoas  magnus 
takes  origin. 

1.  The    white    rami    communicantes    are  derived  from  the  upper  two  or 
three  lumbar  nerves  and  join  the  upper  ganglia  or  the  adjacent  portion  of  the  inter- 
ganglionic  cord.     They  contain  splanchnic  efferent  and  afferent  fibres,  which  continue 
downward  the  distribution  of  the  thoracic  portion  of  the  gangliated  cord,   including 
vasomotor  and  secretory  fibres  for  the  lower  extremities,    pilomotor  fibres,   vaso- 
motor  fibres  for  the  abdominal  vessels,   motor  fibres  for  the  circular  musculature 
of  the  rectum  and  inhibitory  fibres  for  the  longitudinal  muscle  of  the  rectum.     Fibres 
peculiar  to  the  lumbar  region  include  vasomotor  nerves  of  the  penis  and  motor  fibres 
for  the  bladder  and  uterus,  those  to  the  bladder  supplying  the  sphincter  as  well 
as  the   circular  and  longitudinal  muscle-fibres,    those  to   the  last-mentioned  group 
being  inhibitory. 

2.  The  gray  rami  communicantes  are  irregular  in   number  and  arrange- 
ment, sometimes  a  single  one  dividing  and  joining  two  lumbar  nerves  and  sometimes 
two  to  five-  passing  to  a  single  spinal  nerve. 

The  visceral  branches  vary  considerably  in  their  distribution,  some  joining 
the  hypogastric  plexus  (plexus  hypouastricus  ),  others  the  aortic  plexus  (  plexus  aorticus 
abdominalis)  and  still  others  supplying  the  vertebrae  and  their  ligaments. 


THE  SYMPATHETIC   SYSTEM    OF   NERVES.  1367 

THE  SACRAL  PORTION  OF  THE  GANGLIATED  CORD. 

The  sacral  portion  of  the  gangliated  cord  (pars  pelvina  systematis  sympathetic!) 
consists  of  four  ganglia  interconnected  by  association  cords,  there  being  a  consider- 
able degree  of  variation  in  both  the  number  and  the  size  of  the  ganglia  (Fig.  1133). 
Lying  anterior  to  the  sacrum  and  internal  to  the  anterior  sacral  foramina,  it  is  con- 
nected above  with  the  lumbar  portion  by  a  single  or  double  association  cord  which 
lies  posterior  to  the  common  iliac  artery,  and  below  it  gradually  approaches  the 
median  line  and  is  united  in  front  of  the  coccyx  with  its  fellow  of  the  opposite  side  by 
a  loop  or  fine  plexus  in  which  is  situated  the  single  coccygeal  ganglion  or  gang- 
lion impar. 

While  this  portion  of  the  gangliated  cord  receives  no  white  rami  communicantes, 
in  the  sense  of  trunks  passing  from  the  sacral  spinal  nerves  to  the  sacral  ganglia,  the 
visceral  branches  of  the  pudendal  plexus  pass  directly  to  the  pelvic  plexus  without 
traversing  ganglia,  and  are  considered  as  being  homologous  with  white  rami.  In 
addition  to  these,  white  fibres  reach  the  sacral  from  the  lumbar  portion  of  the 
gangliated  cord. 

The  somatic  branches  are  the  gray  rami  communicantes.  They  arise  from 
the  sacral  ganglia  and  pass  dorsally  to  join  the  anterior  primary  divisions  of  the  sacral 
and  coccygeal  spinal  nerves. 

The  visceral  branches  are  distributed  through  the  medium  of  the  pelvic 
plexus  (page  1374)  and  furnish  motor  fibres  to  the  longitudinal  and  inhibitory 
fibres  to  the  circular  musculature  of  the  rectum,  the  chief  motor  fibres  to  the  bladder 
(probably  to  the  longitudinal  muscular  fibres),  motor  fibres  to  the  uterus,  the  nervi 
erigentes  or  vaso-dilators  of  the  penis  and  secretory  fibres  to  the  prostate  gland. 

Additional  strands,  the  parietal  branches  unite  and  ramify,  anterior  to  the 
sacrum,  with  similar  twigs  from  the  opposite  side  and  furnish  filaments  to  the  sacrum 
and  coccyx  and  their  ligaments,  and  to  the  coccygeal  body. 

THE   PLEXUSES   OF   THE   SYMPATHETIC   NERVES. 

The  tendency  of  the  sympathetic  nerves  to  form  intricate  and  elaborate  plexuses 
(plexus  sympathetici)  is  a  marked  feature  of  this  portion  of  the  nervous  system. 
They  lie,  in  the  main,  anterior  to  the  plane  of  the  gangliated  cord  and  consist  of 
fibres  alone  or  of  fibres  and  ganglia,  from  which  smaller  plexuses  or  branches  pass 
to  the  viscera.  Some  of  them  are  of  sufficient  importance,  size  and  individuality 
to  merit  separate  descriptions  ;  such  are  the  cardiac,  the  pulmonary,  the  cesophageal, 
the  solar  and  the  pelvic.  The  pulmonary  and  cesophageal  plexuses  have  been 
described  in  connection  with  the  vagus  nerve  (page  1272). 

THE  CARDIAC  PLEXUS. 

The  cardiac  plexus  (plexus  cardiacus)  consists  of  an  interlacement  of  nerve-fibres, 
containing  one  well-marked  ganglion,  to  which  accessions  are  brought  by  the  vagus 
and  sympathetic  nerves  and  from  which  fibres  are  furnished  to  the  heart  and,  to  a 
slight  degree,  the  lungs.  It  comprises  two  portions:  (i)  the  superficial  cardiac 
plexus  and  (2)  the  deep  cardiac  plexus. 

1.  The  superficial  cardiac  plexus  (Fig.  1135)  is  much  the  smaller  of  the 
two  and  consists  of  a  fine  inosculation  of  nerve-fibres  in  the  meshes  of  which  is  con- 
tained a  small  ganglion,    the  ganglion   of    Wrisberg    (g.    cardiacum    [Wrisbergi] ). 
It  is  situated  in  the  concavity  of  the  arch  of  the  aorta,  between  the  obliterated  ductus 
arteriosus  and  the  right  pulmonary  artery.      Tributary  to  it  are  the  superior  cervical 
cardiac  branch  of  the  left  gangliated  cord  and  the  inferior  cervical  cardiac  branch 
of  the  left  vagus,  whilst  its  fibres  of  distribution  contribute  to  (a)  the  right  coronary 
plexus,   (£)  the  left  half  of  the  deep  cardiac  plexus  and,  along  the  left  pulmonary 
artery,    (r)   the  left  anterior  pulmonary  plexus. 

2.  The  deep  cardiac  plexus   (Fig.   1135),   considerably  larger  than  the  su- 
perficial, is  located  above  the  bifurcation  of  the  pulmonary  artery,  posterior  to  the 
arch  of  the  aorta  and  anterior  to  the  lower  end  of  the  trachea.      It  comprises  two 


1 368 


HUMAN   ANATOMY. 


distinct  portions,  a  right  and  a  left,  united  by  numerous  fibres  around  the  lower  end 
of  the  trachea.  The  right  portion  receives  as  tributaries  all  of  the  cardiac  branches 
of  the  sympathetic,  vagus  and  inferior  laryngeal  nerves  of  the  right  side.  The  left 
portion  receives  all  of  the  cardiac  branches  of  the  left  vagus  and  sympathetic  nerves, 
except  the  two  which  enter  the  superficial  plexus  (the  superior  cervical  cardiac  branch 
of  the  left  gangliated  cord  and  the  inferior  cervical  branch  of  the  left  vagus),  with  the 
addition  of  filaments  from  the  left  inferior  laryngeal  nerve  and  from  the  superficial 
cardiac  plexus. 

FIG.  1135. 


Thyroid  body 

Superior  cervical  cardiac 
branch  of  sympathetic 


Clavicle 

Combined  cervical 

cardiac   brs.  of 

right  sympathetic 

I.  rib 

Phrenic  nerve- 


Pericardium, 

cut  edge 


Right 

coronary 

artery 


Superior  cervical  cardiac  branch  of 

sympathetic 

Sympathetic  nerve 

Vagus  nerve 

Superior  cervical  cardiac  branch  of  vagus 

Middle  cervical  ganglion 

Scalenns  anticus 

Middle  cervical  cardiac  of  sympathetic 

Brachial  plexus 

Inferior  cervical  ganglion 
Inf.  cervical  cardiac  l>r.  of  sympathetic,  cross- 
Phrenic  nerve  I     ing  vertebral  artery 
Subclavian  artery  to  join  middle  br. 
Inf.  cervical  cardiac  branch  of  vagus 
Recurrent  laryngeal  nerve 

Phrenic  nerve 


Recurrent  laryngeal  nerve 

1  i  ardiac  plexus,  showing  ganglion 
of  Wrisberg 

Pulmonary  artery 
Left  coronary  artery 


Dissection  showing  constituents  of  superficial  cardiac  plexus,  other  cardiac  nerves  and  right 

coronary  plexus. 

From  the  right  portion  of  the  plexus  arises  the  right  or  anterior  corona 
plexus  (plexus  coronarius  cordis  anterior),  to  which  fibres  are  sent  from  the  supert'u-ial 
plexus.  This  plexus  reaches  the  heart  by  coursing  along  the  ascending  aorta  and 
then  follows  the  right  coronary  artery,  in  whose  course  it  distributes  fibres  to  adjacent 
portions  of  the  heart.  Other  branches  from  the  right  portion  join  the  superficial 
cardiac  plexus  and  the  right  anterior  pulmonary  plexus. 

From  the  left  portion  originates  the  left  or  posterior  coronary  plexus  (plexus 
coronarius  cordis  posterior)  which,  reinforced  by  fibres  from  the  superficial  plexus, 
follows  the  course  and  distribution  of  the  corresponding  artery.  The  left  portion 
contributes  filaments  to  the  superficial  cardiac  and  left  anterior  pulmonary  plexuses. 

THE  SOLAR  PLEXUS. 

The  abdominal  and  pelvic  cavities  are  innervated  by  the  solar,  hypogastric  and 
pelvic  plexuses,  composed  of  the  visceral  branches  of  the  lower  thoracic,  lumbar  and 
upper  sacral  portions  of  the  gangliated  cord,  in  conjunction  with  the  central  nervous 


THE   SYMPATHETIC   SYSTEM    OF   NERVES. 


1369 


axis  by  means  of  the  rami  communicantes  of  the  lower  thoracic  and  upper  lumbar 
nerves  and  the  visceral  branches  of  the  pudendal  plexus. 

The  solar  or  epigastric  plexus  (Fig.  1136),  the  largest  of  the  series,  is  situated 
in  the  upper  abdominal  region,  posterior  to  the  stomach,  anterior  to  the  aorta  and 
the  crura  of  the  diaphragm,  superior  to  the  pancreas,  between  the  suprarenal  bodies 
and  around  the  origins  of  the  cceliac  axis  and  the  superior  mesenteric  artery.  It  is 
continuous  above  with  the  diaphragmatic  plexus,  laterally  with  the  suprarenal  and 

FIG.  1136. 


Phrenic  nerve 


Diaphragmatic  gangli- 

Great  splanchnic  nerve 
Right  semilunar  ganglion 

Spermatic  artery 

III.  lumbar  ganglion 

Aortic  plexus  ~ 


Hypogastric  plexus 


Disc  between  V.  lumbar 

vertebra  and  sacrum 


I.  sacral  ganglio: 


Left  common  iliac  vein 


Left  pelvic  plexus 


Dissection  of  abdominal  sympathetic  nerves,  showing  solar,  hypogastric  and  secondary  plexuses. 


renal  plexuses,  below  with  the  superior  mesenteric  and  aortic  plexuses  and,  by 
means  of  the  aortic  and  hypogastric  plexuses,  with  the  two  pelvic  plexuses.  Con- 
tributory to  it  are  the  right  vagus  and  the  great  and  small  splanchnic  nerves.  The 
fully  formed  plexus  consists  of  two  portions:  (i)  the  semilunar  ganglia  and  (2) 
the  cceliac  plexus. 

i.  The  semilunar  ganglia  (gg.  coeliaca)  (Fig.  1136),  the  largest  of  the 
ganglionic  elements  in  the  solar  plexus,  are  situated  upon  the  crura  of  the  diaphragm 
at  the  superior  and  lateral  portions  of  the  plexus,  partly  overlapped  by  the  suprarenal 
bodies  and  separated  from  each  other  by  the  cceliac  axis  and  the  superior  mesenteric 
artery  ;  the  right  one  is  partially  covered  by  the  superior  vena  cava  and  the  two  are 


HUMAN   ANATOMY. 


connected  by  cords  which  pass  transversely  above  and  below  the  root  of  the  cceliac 
axis.  The  upper  end  of  each  is  expanded  and  receives  the  termination  of  the  great 
splanchnic  nerve,  while  the  lower  portion,  the  aortico-renal  ganglion,  is  partially 
detached  and  receives  the  small  splanchnic  nerve.  A  third  portion,  located  below 
and  to  the  right  of  the  root  of  the  superior  mesenteric  artery,  is  called  the  superior 
mesenteric  ganglion  (g.  mcsentericum  superius).  From  each  semilunar  ganglion 
branches  emerge  in  all  directions  to  join  those  plexuses  which  are  continuous  with 
the  solar. 

2.  The  cceliac  plexus  (plexus  coeliacus)  embraces  the  cceliac  axis  and  consists 
of  a  dense  felt-work  of  nerve-fibres,  in  which  are  embedded  numerous  small  ganglia, 
and  which  is  joined  by  branches  from  both  semilunar  ganglia  and  from  the  right 

FIG.  1137. 


Kiisiform  cartilage 


-Liver,  Spigelian 

lobe 
"CEsophagus 

-  Left  vagus  nerve 
-Right  vagus  nerve 

-Aorta 

-  Gastric  artery  and 

plexus" 

Splenic  artery  and 
plexus 

-Hepatic  artery  and 
plexus 

"Left  gastro-epi- 
ploic  artery 

-Branches  of  left 
vagus 


Gall-bladde 

Hepatic  artery. 

and  plexus 


Right  gastro-epi- 
ploic  artery  and 
plexus 


Dissection  showing  gastric  and  hepatic  plexuses. 

vagus.  Inferiorly  it  is  continued  into  the  superior  mesenteric  and  aortic  plexuses 
and  from  it  arise  the  coronary,  hepatic  and  splenic  plexuses. 

The  gastric  plexus  (plexus  gastricus  superior)  accompanies  the  gastric  artery 
along  the  lesser  curvature  of  the  stomach,  inosculates  with  both  vagus  nerves  and 
distributes  branches  which  run  for  a  short  distance  beneath  the  peritoneum  and  then 
enter  and  supply  the  deeper  coats  of  the  stomach. 

The  hepatic  plexus  (plexus  hepaticus  )  traverses  the  lesser  omentum  in  company 
with  the  bile  duct,  the  hepatic  artery  and  the  portal  vein  and,  after  inosculating  with 
fibres  of  the  left  vagus,  enters  the  liver,  in  which  it  ramifies.  In  addition  to  its 
terminal  distribution  it  contributes  filaments  to  the  right  suprarenal  plexus  and 
furnishes  offshoots  which  follow  the  collateral  branches  of  the  hepatic  artery,  sup- 
plying the  areas  to  which  these  arteries  are  distributed. 

The  splenic  plexus  (plexus  licnalis),  which  surrounds  the  splenic  artery, 
receives  accessions  from  the  left  semilunar  ganglion  and  the  right  vagus  and  enters 
the  spleen.  Branches  of  the  plexus  accompany  the  branches  of  the  splenic  artery 
and  are  distributed  similarly. 


THE   SYMPATHETIC   SYSTEM   OF    NERVES.  1371 

The  diaphragmatic  or  phrenic  plexus  (plexus  phrenicus)  is  derived  from  the 
upper  portion  of  the  semilunar  ganglion  and  accompanies  the  phrenic  branch  of  the 
abdominal  aorta  to  the  diaphragm,  the  right  being  larger  than  the  left.  After 
supplying  some  filaments  to  the  suprarenal  body,  it  enters  the  musculature  of  the 
diaphragm  and  there  unites  with  the  phrenic  nerve  from  the  cervical  spinal  plexus. 
At  the  point  of  inosculation,  on  the  right  side  only,  near  the  suprarenal  body  and  on 
the  under  surface  of  the  diaphragm,  is  a  small  ganglion  called  the  phrenic  ganglion 
(g.  phrenicum).  From  it  are  given  off  branches  to  the  suprarenal  body,  the  inferior 
vena  cava  and  the  hepatic  plexus. 

The  suprarenal  plexus  (plexus  suprarenalis)  arises  from  the  lateral  aspect  of 
the  semilunar  ganglion  and  is  joined  by  filaments  from  the  diaphragmatic  and  renal 

FIG.  1138. 


Liver,  inferior  surface 

Gastrq-epiploica 
dextra  with  plexus 

Pylqric  artery 
with  plexus 

Castro-duodenal  artery 
with  plexus 

Hepatic  artery  with  plexus 

Inf.  pancreatico-duodenal  artery 

Sup.  pancreatico-duodenal  artery 

Pancreas,  cut 

Superior  mesenteric 

artery  with  plexus 

Duodenum 


Stomach, 
turned  up 


Gastro-epiploica 
sinistra  with  plexus 

— Right  vagus  nerve 

Gastric  artery 

with  plexus 

.Splenic  artery 

with  plexus 


Spleen 


\ 


Dissection  showing  gastric,  hepatic  and  splenic  plexuses;  stomach  has  been  turned  up  and  part  of  pancreas  removed. 

plexuses.  It  consists  mainly  of  medullated  fibres  and,  while  very  short,  is  made  up 
of  a  number  of  filaments  and  is  of  considerable  size.  Numerous  tiny  ganglia  are 
scattered  throughout  the  meshes  of  this  plexus. 

The  renal  plexus  (plexus  renalis)  is  derived  mainly  from  the  aortico-renal 
ganglion,  additional  fibres  being  contributed  by  the  smallest  splanchnic  nerve,  some- 
times by  the  small  splanchnic,  and  by  the  aortic  and  suprarenal  plexuses  ;  there  is 
occasionally  present  a  twig  from  the  first  lumbar  ganglion.  Entering  the  hilum  of 
the  kidney  with  the  renal  artery,  the  plexus  splits  up  and  ramifies  in  the  renal  sub- 
stance. In  its  course  along  the  artery  a  number  of  ganglia  of  varying  size,  called 
the  renal  ganglia,  are  found.  In  addition  to  supplying  the  kidney,  filaments  are 
furnished  to  the  spermatic  plexus  and  to  the  ureter,  and  on  the  right  side  to  the 
inferior  vena  cava. 


1372 


HUMAN   ANATOMY. 


The  spermatic  plexus  (plexus  spermaticus)  follows  the  course  of  the  spermatic 
artery  through  the  abdomen,  inguinal  canal  and  scrotum,  inosculating  with  filaments 
which  arise  in  the  pelvis  and  accompany  the  vas  deferens  and  its  artery  to  the 
scrotum.  It  is  derived  from  the  renal  and  aortic  plexuses,  a  small  spermatic  gang- 
lion being  situated  at  the  point  of  origin  of  the  fibres  contributed  by  the  aortic  plexus. 

The  ovarian  plexus  (plexus  ovaricus),  arising  similarly  to  the  spermatic, 
accompanies  the  ovarian  artery  and  is  distributed  to  the  ovary,  the  oviduct,  the 
broad  ligament  and  the  uterus.  In  the  broad  ligament  it  inosculates  with  those 
pelvic  fibres  which  constitute  the  uterine  plexus. 


FIG.  1139. 


Hepatic 
artery  and 
plexus 


Transverse  colon 

Splenic  artery 

Jejunum 

Duodenum 

Superior  mesen- 
teric  artery  and 
plexus 


Superior 
mesenteric 
artery 

Termination 
of  ileum 


Caecum 


Dissection  showing  hepatic  and  superior  mesenteric  plexuses  ;  transverse  colon  has  hi-en  turned  up. 

The  superior  mesenteric  plexus  (plexus  meseiitcricus  superior)  (Fig.  1139"), 
firm  in  texture  and  containing  a  large  admixture  of  mcdullated  fibres,  is  continuous 
with  the  coeliac  plexus  above  and  with  the  aortic  below.  Its  fibres  are  derived  from 
the  semilunar  ganglia,  the  cceliac  plexus  and  the  right  vagus.  Situated  in  the  root 
of  the  plexus  and  lying  below  and  to  the  right  of  the  origin  of  the  superior  mesen- 
teric artery  is  the  superior  mesenteric  ganglion  (j».  mcsciitericum  supcrius), 
from  which  a  number  of  the  fibres  of  the  plexus  arise.  Accompanying  the  superior 
mesenteric  artery,  the  plexus  gives  off  subdivisions  which  correspond  to  and  follow 
the  course  of  the  branches  of  that  artery,  supplying  filaments  to  the  small  intestine, 
the  ccecum,  the  vermiform  appendix  and  the  ascending  and  transverse  colons.  As 


THE   SYMPATHETIC   SYSTEM    OF   NERVES. 


1373 


the  fibres  approach  the  distal  edge  of  the  mesentery  some  of  them  leave  the  vessels 
and  form  minute  independent  plexuses  from  which  filaments  pass  to  the  gut. 

The  aortic  plexus  (plexus  aorticus  abdominalis)  (Fig.  1136)  is  the  direct 
downward  extension  of  the  solar.  Embracing  the  aorta,  it  extends  from  the  origin 
of  the  superior  mesenteric  artery  above  to  that  of  the  inferior  mesenteric  below,  and 
is  connected  with  the  semilunar  ganglia  and  with  the  renal  and  superior  mesenteric 
plexuses  superiorly  and  with  the  hypogastric  inferiorly.  It  consists  of  a  pair  of 

FIG.  1140. 

Aorta       Renal  ganglion 

/  /     Ureter      ^Ovarian  artery 


Nerve  from  aortic  plexus 

Ovarian  vein 

Ovarian  artery 


Ureter 

Branches 

from  renal 

plexus 

Vena  cava 
inferior 


Ovarian  vein 


Part  of  inferior  mesenteric  plexus 

Inferior  mesenteric 
artery 


.  .  .£..  Left  common 
iliac  vein 


Ilium,  sec- 
tional surface 


-  Pelvic  plexus 


Branches  of  right 

pelvic  plexus  to. 

rectum 


Right  ovary 

Fallopian  tube 

Ligament  of 
ovary 


Dissection  showing  hypogastric  and  pelvic  plexuses. 

symmetrically  placed  nerve  trunks  situated  at  the  sides  of  the  aorta  and  connected 
with  each  other  by  several  branches  which  lie  anterior  to  that  vessel  ;  filaments  from 
the  lumbar  ganglia  join  the  main  cords  of  the  plexus.  It  gives  off  the  inferior  mes- 
enteric plexus,  sends  contributions  to  the  suprarenal,  renal  and  spermatic  or  ovarian, 
supplies  filaments  to  the  aorta  and  inferior  vena  cava  and  terminates  in  the  hypo- 
gastric  plexus. 

The  inferior  mesenteric  plexus  (plexus  mesentericus  inferior)  is  derived 
from  the  left  portion  of  the  aortic  plexus  and  follows  the  course  and  distribution 
of  the  artery  for  which  it  is  named.  Situated  a  short  distance  beyond  its  origin 
is  the  small  inferior  mesenteric  ganglion.  From  this  plexus  branches  are 


1374  HUMAN   ANATOMY. 

distributed  to  the  descending  and  sigmoid  colons  and  to  the  upper  portion  of  the 
rectum. 

The  hypogastric  plexus  (plexus  hypogastricus)  (Fig.  1140),  the  continuation 
of  the  aortic,  lies  on  the  posterior  wall  of  the  pelvis  in  the  angle  between  the 
common  iliac  arteries,  and  enclosed  in  a  firm  investment  of  fibrous  tissue.  In 
addition  to  the  fibres  derived  from  the  aortic  plexus,  others  are  contributed  by 
the  lumbar  ganglia,  and  the  resulting,  intricate  interlacement,  in  which  there  are 
no  ganglia,  constitutes  the  hypogastric  plexus.  It  supplies  the  pelvic  contents 
and  at  its  lower  end  divides  into  the  two  pelvic  plexuses. 

The  pelvic  plexuses  (plexus  hypogastrici  inferiores),  (Fig.  1140)  the  terminal 
divisions  of  the  hypogastric,  are  situated  lateral  to  the  rectum  and  to  the  vagina 
in  the  female.  They  comprise  fibres  derived  from  the  hypogastric  plexus  and  from 
the  upper  part  of  the  sacral  portion  of  the  gangliated  cord,  aided  by  the  visceral 
branches  of  the pudendal.  plexus,  all  of  these  forming  an  elaborate  net-work,  in  which 
are  dotted  numerous  small  ganglia.  The  completed  structure  follows  the  course 
of  the  internal  iliac  artery,  around  whose  branches  it  sends  derivatives  for  the 
supply  of  the  pelvic  contents. 

The  hemorrhoidal  plexus  (plexus  hemorrhoidalis  medius)  arises  from  the 
upper  portion  of  the  pelvic  plexus  and  after  inosculating  with  the  superior 
hemorrhoidal  branches  (nn.  hemorrhoidales  superiores)  of  the  inferior  mesenteric 
plexus,  are  distributed  to  the  rectum. 

The  vesical  plexus  (plexus  vesicalis)  consists  of  branches  of  the  pelvic  which 
accompany  the  vesical  arteries  to  the  lateral  and  inferior  portions  of  the  bladder, 
after  reaching  which  they  leave  the  vessels  and  split  into  small  twigs  for  the  supply 
of  the  bladder,  some  filaments  going  to  the  ureter,  the  vas  deferens  and  the  seminal 
vesicle. 

The  prostatic  plexus  (plexus  prostaticus)  comprises  a  number  of  nerves  of  con- 
siderable size  and  is  situated  between  the  lateral  aspect  of  the  prostate  gland  and 
the  mesial  surface  of  the  levator  ani  muscle.  After  furnishing  twigs  to  the  prostatic 
urethra,  the  neck  of  the  bladder  and  the  seminal  vesicle,  it  continues  forward  as  the 
cavernous  plexus. 

The  cavernous  plexus  (plexus  cavernosus  penis)  extends  forward  through  the 
triangular  ligament  and  the  compressor  urethrae  muscle  to  the  dorsum  of  the  base  of 
the  penis,  where  it  receives  some  communicating  filaments  from  the  pudic  nerve. 
After  supplying  branches  to  the  apex  of  the  prostate  gland  and  the  membranous 
urethra,  the  plexus  terminates  by  breaking  up  into  (i)  the  small  and  (2)  large 
cavernous  nerves  of  the  penis. 

1.  The  small  cavernous  nerves  (nn.    cavernosi    penis   minores)  pierce  the 
fibrous  envelope  of  the  crus  penis  and  end  in  filaments  which  supply  the  erectile 
tissue  of  the  corpus  cavernosum. 

2.  The  large  cavernous  nerve  (n.  cavernosus  penis  major),  consisting  mainly 
of  medullated  fibres,  passes  directly  along  the  dorsum  of  the  penis,  giving  off  fila- 
ments which  enter  the  substance  of  the  corpus  cavernosum.     At  about  the  middle  of 
the  body  of  the  penis  it  inosculates  with  the  dorsal  nerve  of  the  penis,  both  of  these 
nerves  sending  twigs  to  the  corpus  spongiosum. 

The  utero-vaginal  plexus  (plexus  uterovaginalis)  corresponds  to  the  prostatic 
plexus  of  the  male  and  consists  of  two  portions  :  (i)  the  uterine  plexus  and  (2)  the 
vaginal  plexus. 

1.  The  uterine  plexus  (plexus  uterinus)  is  derived  from  the  pelvic  plexus  and  is 
supplemented  in  its  distribution  by  the  visceral  branches  from  the  pudendal  pk-xus. 
These  fibres  accompany  the  uterine  vessels  along  the  side  of  the  uterus,  most  of  them 
entering  the  cervix  and  the  lower  portion  of  the  body  of  the  uterus.     They  inoscu- 
late with  fibres  from  the  ovarian  plexus  and  in  their  meshes  arc  found  many  small 
ganglia,  a  collection  of  which  is  located  near  the  cervix  uteri  and  is  called  the  gang- 
lion cervicale. 

2.  The  vaginal   plexus    (plexus  va^iualis)   arises  from   tin-  lower  part  of  the 
pelvic  and  comprises  mainly  fibres  derived  from  the  viseeral  branches  of  the  puden- 
da! plexus.      It  supplies  the-  vagina  and  the  urethra  and  continues  forward  as  the 
cavernous  plexus  of  the  clitoris  (plexus  cavernosus  clitoridis  ). 


DEVELOPMENT   OF    PERIPHERAL    NERVES.  1375 

Practical  Considerations. — The  cervical  sympathetic  may  be  injured  by  deep 
wounds  of  the  neck,  or  may  be  compressed  by  tumors,  abscesses  or  aneurisms.  It 
supplies  motor  fibres  to  the  involuntary  muscles  of  the  orbit  and  eyelids,  vasomotor 
fibres  to  the  face,  neck  and  head,  dilator  fibres  to  the  pupil,  accelerator  fibres  to  the 
heart  and  secretory  fibres  to  the  salivary  glands.  If  it  is  irritated,  some  or  all  of  the 
following  symptoms  will  be  present :  the  palpebral  fissure  will  open  wider,  the  eyes 
will  be  protruded,  the  skin  of  the  face  and  neck  will  be  pale  and  cold,  the  pupils 
dilated,  and  the  sweat,  nasal  secretion  and  saliva  diminished.  Section  or  destruction 
of  the  cervical  sympathetic  will  give  the  opposite  symptoms. 

The  cervical  sympathetic  has  been  removed  for  epilepsy,  glaucoma  and  exoph- 
thalmic goitre.  The  greatest  success  has  been  obtained  in  the  last  condition,  espe- 
cially by  Jonnesco,  who  advises  this  procedure  in  hysteria,  chorea,  and  tumors  of  the 
brain,  as  well  as  in  the  above-mentioned  conditions.  It  may  be  excised  through  an 
incision  anterior  to  the  sterno-mastoid,  as  it  lies  posterior  to  the  carotid  sheath 
on  the  prevertebral  fascia.  The  superior  cervical  ganglion  is  the  largest  and  lies 
opposite  the  transverse  processes  of  the  second  and  third  vertebrae.  Branches  of  it 
go  upward  along  the  external  and  internal  carotid  arteries,  the  ascending  branch 
passing  along  the  internal  carotid  artery  through  its  bony  canal  in  the  base  of  the 
skull  to  form  the  carotid  and  cavernous  plexuses,  both  of  which  are  really  parts  of 
one  plexus  arranged  around  this  artery.  Other  branches  communicate  with  the 
cranial  nerves,  the  pharyngeal  nerves  and  the  superficial  cervical  cardiac  nerve. 
The  middle  cervical  ganglion  is  the  smallest,  lies  on  the  inferior  thyroid  artery  oppo- 
site the  sixth  cervical  vertebra  and  is  in  danger  in  the  ligation  of  that  artery.  The 
inferior  ganglion,  intermediate  in  size  between  the  other  two,  lies  in  a  depression 
between  the  neck  of  the  first  rib  and  the  transverse  process  of  the  seventh  cervical 
vertebra. 

The  branches  of  the  upper  four  or  five  thoracic  ganglia  of  the  sympathetic  enter 
into  the  supply  of  the  thoracic  viscera,  but  the  branches  of  the  lower  seven  or  eight 
form  the  splanchnic  nerves  and  go  to  the  supply  of  the  abdominal  viscera  through  the 
solar  plexus  and  its  extensions  into  other  sympathetic  plexuses  of  the  abdomen.  It 
is  of  interest  and  importance  to  observe  that  those  intercostal  nerves  corresponding  in 
their  origin  from  the  spinal  cord  with  the  ganglia  giving  off  the  splanchnics,  together 
with  the  first  two  lumbar  nerves,  the  ilio-hypogastric  and  ilio-inguinal,  supply  the 
abdominal  wall  with  motor  and  sensory  branches.  In  this  way  the  same  segments 
of  the  spinal  cord  supply  the  abdominal  viscera  as  well  as  the  skin  and  muscles  over 
them.  A  similar  arrangement  of  the  nerves  is  seen  in  the  joints,  where  the  same 
nerves  supply  the  skin  covering  the  joint,  the  muscles  which  move  it,  and  the  joint 
structures.  As  a  result  of  this,  when  necessary,  all  parts  of  the  joint  act  in  sympa- 
thy. In  an  inflammation  of  the  joint  the  skin  becomes  sensitive,  tending  to  ward  off 
interference,  and  the  muscles  become  rigid,  preventing  motion  and  favoring  rest.  In 
a  similar  manner  the  abdominal  muscles  become  rigid  to  protect  inflamed  viscera 
underneath,  the  muscles  of  one  side  only  if  the  inflammation  is  localized  to  one  side, 
but  the  muscles  of  both  sides  if  a  general  peritonitis  is  present. 

DEVELOPMENT    OF    THE    PERIPHERAL     NERVES. 

The  manner  in  which  the  nerve-fibres  composing  the  peripheral  nervous  system  develop 
from  the  primary  cells,  the  neuroblasts,  has  been  indicated  in  the  previous  sketch  of  their 
histogencsis  given  on  page  ion.  It  remains,  therefore,  to  describe  briefly  at  this  place  the  more 
important  features  of  their  morphogenesis.  The  fundamental  fact  has  been  repeatedly  empha- 
sized, that  efferent  or  motor  fibres  are  outgrowths  from  neurones  situated  within  the  cerebro- 
spinal  axis,  whilst  all  afferent  or  sensory  fibres  arise  from  cells  placed  outside  this  axis  and 
within  the  ganglia  located  along  the  course  of  the  nerves.  It  is  evident,  furthermore,  that  the 
efferent  constituents  of  the  peripheral  nerves  have  their  nuclei  of  origin  within  the  spinal  cord 
or  brain  and  grow  outward,  as  axones,  to  their  destinations.  The  afferent  fibres,  on  the  other 
hand,  proceed  in  both  directions,  the  axones  early  growing  centrally  to  join  the  nervous  axis, 
hence,  having  usually  a  short  course,  being  represented  by  the  entering  sensory  roots.  The 
dendrites  grow  in  the  opposite  direction  and  contribute  the  sensory  fibres  that  extend  often  to 
remote  parts  of  the  body.  Whilst  in  the  lowest  vertebrates,  the  amphioxus  and  the  cyclos- 
tomes,  the  ventral  and  dorsal  roots  of  the  spinal  nerves  remain  distinct,  in  the  higher  types 
they  join  to  form  the  mixed  nerve,  which  typically  divides  into  the  anterior,  posterior  and 


1376  HUMAN   ANATOMY. 

visceral  divisions.  Such  typical  division,  however,  is  displayed  only  by  those  spinal  nerves  dis- 
tributed to  that  part  of  the  trunk  in  which  the  primary  segmentation  is  retained,  namely,  the 
thoracic  region,  where  the  skeletal  muscular,  and  vascular  segments,  as  well  as  the  nerves, 
retain  their  identity.  In  the  other  parts  of  the  spinal  series,  the  cervical  and  the  lumbo-sacral, 
where  provision  is  made  for  the  supply  of  the  highly  differentiated  musculature  of  the  ex- 
tremities from  a  number  of  cord-segments,  the  nerves  early  unite  to  form  plexuses  from  \vhich 
the  limb-trunks  grow  out,  an  arrangement  well  adapted  for  the  distribution  of  fibres  from 
different  sources  without  undue  multiplication  of  nervous  paths.  Concerning  the  factors  which 
guide  the  young  nerve  to  its  destination  with  such  remarkable  constancy,  nothing  is  known, 
but  it  may  be  assumed  that  these  are  probably  influences  of  a  physical  character,  the  developing 
nerve  taking  the  path  offering  least  resistance.  The  visceral  division  of  the  spinal  nerve,  to 
which  reference  has  been  made,  corresponds  to  the  white  ramus  communicans  given  off  by 
certain  of  the  thoracic  and  lumbo-sacral  nerves.  These  splanchnic  fibres  differ  from  the 
somatic  efferent  ones  in  taking  their  origin  from  cells  which  occupy  a  more  lateral  position 
within  the  gray  matter  of  the  spinal  cord  than  do  the  root-cells  giving  rise  to  the  motor  fibres 
destined  for  the  skeletal  muscles.  Whilst  the  great  majority  of  the  splanchnic  fibres  reach  the 
ramus  of  communication  by  way  of  the  anterior  root,  some  few  probably  traverse  the  posterior 
or  sensory  root  and  its  ganglion  before  continuing  their  course  to  the  sympathetic.  The  sensory 
fibres  described  within  the  anterior  roots  of  the  spinal  nerves  are  not  actual  constituents  of  these 
roots,  which  are  exclusively  motor,  but  recurrent  meningeal  twigs  destined  for  the  membranes 
of  the  cord. 

The  Cranial  Nerves. — From  the  preceding  account  of  these  nerves,  it  is  evident  that  the 
optic  nerve  differs  morphologically  widely  from  an  ordinary  nerve,  since  it  may  be  regarded  as 
a  modified  outlying  portion  of  the  brain.  Its  development  may  be  omitted,  therefore,  from 
this  series  and  appropriately  considered  in  connection  with  the  development  of  the  eye  (page 
1482).  There  is  sufficient  reason,  as  will  appear  later,  for  regarding  the  hypoglossal  nerve  as  a 
cranially  displaced  member  of  the  spinal  series.  Of  the  remaining  nerves,  only  the  olfactory 
and  auditory  are  purely  sensory  ;  the  third,  fourth,  sixth  and  eleventh  are  exclusively  motor ; 
and  the  fifth,  seventh,  ninth  and  tenth  are  mixed,  the  motor  strands  taking  origin  from  the  neu- 
rones within  the  brain-stem,  while  the  sensory  ones  are  derivations  from  the  neurones  lying 
within  the  ganglia  connected  with  the  afferent  fibres.  Although  at  first  sight  the  trigeminus 
closely  corresponds  to  a  spinal  nerve  in  the  possession  of  a  gangliated  sensory  and  a 
motor  root,  critical  examination  of  the  origin  of  its  motor  fibres  discloses  an  important  differ- 
ence, namely  that  they  arise  from  the  lateral  nuclei  and  not  from  the  mesial,  which  correspond 
to  collections  of  ventral  root-cells.  A  similar  difference  also  appears  between  the  efferent 
trigeminal  fibres  and  those  of  the  eye-muscle  nerves,  the  latter  arising  from  groups  of  root-cells 
occupying  a  position  close  to  the  mid-line.  In  order  to  appreciate  the  significance  of  this  differ- 
ence, reference  must  be  made  to  the  primary  division  of  the  musculature  of  the  head  already 
referred  to  in  connection  with  the  grouping  of  the  muscles  (page  472  ).  It  was  there  pointed 
out  that  it  may  be  assumed  that  the  segmented  condition  of  the  trunk  musculature,  as  expressed 
by  the  metameres,  is  continued  into  the  cephalic  region  but  with  subsequent  suppression  of  the 
middle  members  of  the  possible  nine  or  ten  segments  which  constituted  the  original  quota  of 
head-metameres.  Of  those  persisting  two  groups  are  recognized — one  including  the  first  three 
metameres,  giving  rise  to  the  ocular  muscles  and  being  supplied  by  the  third,  fourth  and  sixth 
nerves  ;  the  other  including  the  last  three  or  four,  producing  the  tongue-muscles,  and  being  sup- 
plied by  the  twelfth  nerve.  To  these  groups  of  cephalic  metameres  is  added  a  third,  the 
branchiomeres,  which  are  regarded  as  representing  a  supplementary  series  connected  with  the 
branchial  arches  and  not  present  in  the  trunk.  The  branchiomeres  receive  the  mixed  cranial 
nerves,  whose  motor  filaments  supply  muscular  masses  surrounding  the  visceral  tubes  ( digestive 
and  respiratory),  and  arise  from  the  lateral  motor  nuclei.  It  follows  that  none  of  the  cranial 
nerves  contain  fibres  from  all  these  sources,  in  the  case  of  the  fifth,  seventh,  ninth  and  tenth,  the 
fibres  being  derived  from  the  lateral  motor  and  the  sensory  nuclei,  and  in  the  case  of  the  third, 
fourth  and  sixth,  from  the  mesial  (ventral)  nuclei  alone.  From  the  primary  conditions,  as 
revealed  by  studies  on  the  lower  vertebrates,  it  is  probable  that  the  dorsal  fibres  also  are  by  no 
means  of  similar  morphological  value,  since  some  represent  a  somatic  sensory  system,  as  those 
distributed  to  the  integument,  and  others  belong  to  a  visceral  sensory  one,  as  those  distributed 
to  the  walls  of  the  mouth,  pharynx  and  larynx.  Following  the  principle  already  emphasized, 
the  motor  fibres  of  the  cranial  nerves  grow  from  the  brain  outward,  while  the  sensory  ones  extend 
centrally  from  the  ganglia  of  the  nerves  associated  with  the  brain.  The  cranial  and  spinal  nerves 
appear  on  the  surface  of  the  neural  tube  at  a  very  early  period,  their  presence  being  conspicuous 
by  the  end  of  the  fourth  week  (Fig.  901 ). 

The  olfactory  nerve  is  developed  in  connection  with  the  epithelial  lining  of  the  primary 
olfactory  pit  (page  1429).  As  early  as  the  end  of  the  first  fiL-tal  month,  in  the  human  embryo, 
cells  corresponding  to  neuroblasts  appear  in  the  anlage  of  the  olfactory  organ.  From  these 
elements  processes  soon  grow  brainwanl,  nucleated  tracts  indicating  the  formation  of  the  later 
olfactory  fibres.  The  cell-bodies  of  the  young  neurone  mi-rate  so  that  for  a  time  their  position 


DEVELOPMENT  OF  PERIPHERAL  NERVES. 


1377 


is  no  longer  within  the  primary  epithelium,  but  deeper  and  within  a  cell  aggregation  known 
as  the  olfactory  ganglion.  The  neurones,  however,  retain  connection  with  the  olfactory  epithe- 
lium by  means  of  their  peripherally  directed  processes,  which  correspond  to  dendrites,  and  with 
the  brain  by  means  of  their  axones.  With  the  thickening  of  the  olfactory  epithelium  which  sub- 
sequently occurs,  the  peripheral  fibres  and  their  nuclei  comes  to  lie  entirely  within  the  epithelial 
stratum  and  persist  as  the  olfactory  cells,  whose  centrally  directed  processes  form  the  olfactory 
filaments  that  end  as  arborizations  within  the  characteristic  olfactory  glomeruli.  The  first 
cranial  nerve  is  peculiar  in  the  superficial  position  of  its  cell-bodies  and  in  the  extreme  shortness 
of  its  dendrites,  which  are  represented  by  the  rod-like  fibres  of  microscopic  length  extending 
from  the  cell-bodies  toward  the  free  surface  of  the  olfactory  mucous  membrane.  This  superficial 
position  of  the  olfactory  neurones  is  regarded  as  an  unusual  persistence  of  the  primary  condition 
of  all  sensory  elements  and  as  evidence  of  the  archaic  nature  of  the  olfactory  nerves. 


FIG.  1141. 


Superior  colliculus 
Mid-brain 


ineal  body 

Diencephalon 

Median  geniculate  body 
Pallium 


Inferior  colliculus 

Oculomotor  nerve 

Trochlear  nerve 


Cerebellum 
Trigeminal  nerve 
Auditory  nerve 

Glosso-pharyngeal  nerve 
Vagus  nerve 


Spinal  accessory  nerve 


Rhinencephalon 

Optic  stalk 

nferior  part  of  III.  ventricle 
Facial  nerve 
Abducent  nerve 


Hypoglossal  nerve 


Reconstruction  of  brain  of  human  embryo  of  four  and  one  half  weeks  (10.2  mm.);  outer  surface,  showing 
developing  nerves.    X  12.    Drawn  from  His  model. 

The  optic  nerve  is  so  inherently  a  derivative  of  the  cerebral  and  optic  vesicle,  that  its  develop- 
ment is  appropriately  considered  with  that  of  the  eye  (page  1482) ;  moreover,  its  morphological 
significance  being  so  at  variance  with  that  of  the  other  nerves,  it  may  be  omitted  from  further 
discussion  in  the  series  now  being  described. 

The  oculomotor  nerve  being  strictly  a  motor  nerve  has  much  in  common  in  its  mode  of 
formation  with  the  ventral  root  of  a  spinal  nerve,  with  which  it  is  homologous.  The  nerve 
originates  as  an  outgrowth  from  a  group  of  neuroblasts,  which  occupies  the  ventral  zone  about 
the  middle  of  the  mesencephalon.  From  these  neurones,  visible  in  the  fourth  week  in  the 
human  embryo,  the  axones  proceed  as  a  converging  group  of  fibres  which,  piercing  the  wall  of 
the  brain-tube  close  to  the  mid-line,  appear  on  the  ventral  surface  of  the  brain-stem  as  the  fibres 
of  the  third  nerve.  Although  by  some  regarded  as  possessing  a  transient  rudimentary  dorsal 
root  that  early  entirely  disappears,  thus  bringing  the  nerve  of  a  cranial  myomere  into  close 
correspondence  with  those  of  the  spinal  series,  it  is  doubtful  whether  such  structure  is  usually 
present,  the  suppression  of  the  dorsal  portion  of  the  nerve  being  complete.  Soon  after  its  for- 
mation, the  main  trunk  undergoes  division  into  a  smaller  upper  and  a  larger  posterior  limb, 
which  foreshadow  the  superior  and  inferior  divisions  of  the  mature  nerve. 

The  trochlear  nerve,  although  springing  from  a  central  group  of  neuroblasts  in  close 
proximity  with  those  giving  rise  to  the  third,  is  peculiar  in  the  course  of  its  axones.  Instead 
of  maintaining  a  ventral  course,  these  proceed  dorsally  and  become  superficial  on  the  upper 
(dorsal)  aspect  of  the  hind-brain,  piercing  the  plate  which  later  becomes  the  superior  medul- 

8? 


1378 


HUMAN   ANATOMY. 


lary  velum.  As  in  the  case  of  the  third,  so  for  the  trochlear  an  abortive  transient  dorsal 
ganglion  and  root  have  been  described  (Martin).  If  present  these  must  be  regarded  as  ex- 
ceptional and  not  constant  features. 

The  trigeminal  nerve  is  a  mixed  nerve  and  therefore  takes  its  origin  differently  for  its 
two  roots.  The  motor  one  is  developed  from  a  series  of  neuroblasts,  which  lie  at  some  distance 
from  the  mid-line  within  the  wall  of  the  neural  tube,  at  a  position  corresponding  to  the  junction 
of  the  dorsal  and  ventral  zones  of  the  mid-brain  and  metencephalon.  The  axones  of  these 
neuroblasts  grow  forward  and  converge  to  the  surface  of  the  later  pons  at  a  position  close  to 
where  the  ingrowing  sensory  fibres  join  the  neural  tube.  The  sensory  fibres  are  the  axones  of 
neurones  located  within  the  Gasserian  ganglion.  The  latter  is  derived  as  a  ventrally  directed 
outgrowth  from  the  ectoblast  of  the  roof  of  the  hind-brain,  with  which  it  remains  attached  for  a 
short  time,  but  later  becomes  entirely  separated.  The  neuroblasts  acquire  a  bipolar  form,  one 
set  of  processes,  the  axones,  growing  centrally  to  establish  secondary  connections  with  the 
hind-brain  as  the  large  sensory  root,  while  the  others,  the  dendrites,  extend  peripherally  into 
the  substance  of  the  fronto-nasal  and  maxillary  processes  to  form  the  ophthalmic  and  maxillary 
nerves  and  into  the  mandibular  process  to  form,  in  conjunction  with  the  smaller  motor  root, 

FIG.  1142. 


Reconstruction  of  brain  and  cranial  nerves  of  pig  embryo;  cranial  nerves  indicated  by  figures ;  ci-C3,  cervical 
spinal  nerves;  in  connection  with  seventh  nerve., l.s.p, large  superficial  petrosal ;  ch.ty.,  chorda  tympani ;  fa.,  facial ; 
j.,  «.,  vagus  ganglia  of  root  and  trunk  ;  com.,  comtnissuraF  extension  of  ganglion  of  root ;  f,  Froriep's  hypoglossal 
ganglion,  (f.  T.Lewis.) 

the  mandibular  division  of  the  trigeminus  from  the  ganglion  ridge.  Provision  for  the  ciliary 
ganglion  is  made  early  by  the  migration  of  cells  from  the  major  ganglion  along  the  de- 
veloping ophthalmic  division.  Similar  migrations  along  the  other  divisions  give  rise  to  the 
spheno-palatine,  the  otic  and  the  submaxillary  ganglia.  The  later  histological  characteristics 
of  these  cells,  as  well  as  their  mode  of  origin,  warrant  the  view  that  the  ciliary  ganglion,  as  well 
as  the  others  connected  with  the  trigeminus,  belong  to  the  sympathetic  system.  On  entering 
the  wall  of  the  brain-tube,  the  bulk  of  the  sensory  trigeminal  fibres  assume  a  longitudinal  course 
and  early  establish  the  tract  of  the  spinal  cord. 

The  abducent  nerve  developes,  in  a  manner  identical  with  the  third  and  fourth,  from  a 
median  group  of  cells  occupying  the  ventral  zone  of  the  upper  part  of  the  hind-brain.  In  the 
human  embryo  of  about  four  and  a  half  weeks  (Fig.  1141),  the  nerve  appears  at  its  super- 
ficial origin  mesial  to  the  Gasserian  ganglion.  The  root-fibres  early  consolidate  into  a  compart 
strand. 

The  facial  nerve  being  a  mixed  one  also  arises  from  a  double  source,  its  motor  fibres 
taking  origin  from  efferent  neuroblasts  situated  in  the  ventro-lateral  wall  of  the  metencephalon. 
In  contrast  to  the  direct  ventral  course  of  the  axones  of  the  mesial  motor  nerves,  those  of  t lie- 
facial  pursue  a  path  to  the  surface  of  the  brain-stem  even  more  indirect  than  that  taken  by  the 
lateral  motor  fibres  of  the  other  mixed  nerves.  Proceeding  as  the  axones  of  neuroblasts  lying 
within  the  lateral  part  of  the  ventral  zone  of  the  wall  of  the  hind-brain,  they  are  directed  dor- 
sally,  then  grow  forward,  turn  outward  and,  finally,  ventrally  to  gain  emergence  from  the  brain. 
The  sensory  portion  of  the  facial  is  topographically  closely  connected  during  its  development 
with  the  auditory,  the  nuclei  of  the  two  nerves  often  being  designated  the  facial-acoustic  com- 
plex. The  three  components  of  this  aggregation — the  geniculatc,  the  cochlear  and  the  vestibu- 
lar  ganglia — are  primarily  derived  from  an  ectoblastic  cell-mass  in  tin-  vicinity  of  the  otic  vesicle. 


DEVELOPMENT   OF   PERIPHERAL   NERVES. 


1379 


FIG.  1143. 

Vagus  root  gang. 


Accessory  root  gang. 


The  neuroblasts  of  the  facial  constituent,  the  geniculate  ganglion,  send  their  centrally  directed 
processes  to  the  brain-stem  as  the  pars  intermedia,  whilst  their  peripherally  growing  dendrites 
contribute  the  sensory  fibres,  passing  by  way  of  the  chorda  tympani  and  the  greater  and  lesser 
superficial  petrosal  nerves.  The  geniculate  ganglion  and  the  pars  intermedia  correspond, 
therefore,  to  a  dorsal  root. 

The  auditory  nerve,  although  for  a  time  closely  related  in  position  (Fig.  1103)  with  the 
facial  (geniculate)  ganglion,  developes  entirely  independently  and  at  no  time  has  more  than  an 
incidental  relation.  The  primary  auditory  nucleus  is  defined  in  human  embryos  by  the  begin- 
ning of  the  fourth  week  as  an  elongated  ellipsoidal  mass  in  contact  with  the  anterior  wall  of  the 
otic  vesicle.  According  to  Streeter 1,  the  nucleus  very  shortly  exhibits  a  differentiation  into 
a  superior  and  an  inferior  part,  from  the  latter  of  which  soon  appears  a  third  portion.  This 
third  portion,  the  later  ganglion  spirale,  early  manifests  a  tendency  to  coil  in  consequence  of 
its  close  relations  with  the 
d  u  c  t  u  s  cochlearis.  The 
major  part  of  the  primary 
acoustic  complex,  including 
the  superior  and  most  of 
the  inferior  part,  becomes 
the  vestibular  ganglion, 
from  the  neuroblasts  of  which 
centrally  directed  a  x  o  n  e  s 
pass  to  the  young  brain- 
stem  as  the  vestibular  nerve, 
while  the  dendrites  become 
connected  at  certain  places 
with  the  semicircular  canals, 
the  utricle  and  the  saccule. 
The  grouping  of  the  vestibular 
rami  seen  in  the  adult  is  early 
foreshadowed  in  the  develop- 
ing nerve,  since  from  the 
upper  part  of  the  vestibular 
ganglion  grows  out  the  su- 
perior division  of  the  vestib- 
ular nerve  which,  supplies 
the  utricle  and  the  ampullae 
of  the  superior  and  external 
semicircular  canals  (Fig. 
1070) .  The  lower  part  of  the 
ganglion,  in  addition  to  fur- 
nishing the  anlage  for  the 
cochlear  nerve,  gives  off  the 
inferior  division  of  the  vestib- 
ular nerve,  by  which  the 


IX.  root  gang. 


N.  tymp. 
Gang,  petros. 

IX. 

Gang,  nodos. 
N.  iaryg.  sup. 


XI I.  with  r.  descend. 


Froriep 


Sympathetic 


Vagus 


Reconstruction  of  peripheral  nerves  of  human  embryo  of  five  weeks 
(14  mm.)  X  13-     (Streeter.) 


saccule     and    the    posterior 
canal  are  supplied.     During 
the  subsequent  growth  of  the 
structures,    the    neurones   of 
the  spiral  ganglion  send  ax- 
ones  towards  the  brain  which  become  the  cochlear  nerve,  whilst  their  dendrites-grow  peripherally 
into  the  ductus  cochlearis   and   are  represented  by  the  minute  filaments  extending  from  the 
cells  of  the  spiral  ganglion  to  the  auditory  cells  of  Corti's  organ. 

The  glosso-pharyngeal  nerve  is  a  mixed  nerve  and  has,  therefore,  a  double  origin.  Its 
motor  fibres  arise  from  neuroblasts  situated  in  the  dorsal  part  of  the  ventral  zone  of  the  wall  of 
the  hind-brain  just  posterior  to  the  otic  vesicle.  The  sensory  part  of  the  nerve,  along  with 
that  of  the  vagus,  offers  greater  complexity,  since  it  is  developed,  as  shown  by  Streeter2,  from 
two  sources.  The  ganglion  of  the  root  (g.  stiperius  or  jugular  ganglion)  arises  very  early  as 
a  small  mass  of  cells  derived  from  the  ganglion-crest  of  the  hind-brain.  It  varies  in  size  and 
soon  ceases  to  grow,  which  behavior,  in  connection  with  the  preponderating  ingrowth  of  the 
motor  fibres,  accounts  for  the  well-known  inconstancy  of  the  structure.  The  ganglion  of 
the  trunk  (g.  petrosum)  arises,  according  to  Streeter,  not  from  the  neural  crest,  but  in 
relation  with  the  ectoblast  of  the  second  visceral  furrow.  At  first  ununited  with  the  smaller 
ganglion  superius,  the  ganglion  of  the  root  subsequently  becomes  joined  to  it,  the  two  nodes 

1  Amer.  Jour,  of  Anatomy,  vol.  yi.,  1907. 
2Amer.  Jour,  of  Anatomy,  vol.  iv.,  1904. 


1380  HUMAN   ANATOMY. 

being  later  closely  related,  both  as  to  position  and  fibres.  An  outgrowth  of  distally  directed 
fibres  establishes  the  main  trunk  of  the  nerve,  while  a  forwardly  growing  strand  represents  the 
later  tympanic  branch. 

The  vagus  and  spinal  accessory  nerves  are  so  inseparably  related  in  their  development 
that  their  origin  must  be  regarded  as  proceeding  from  a  common  vagus  complex.  The  latter 
comprises  three  elements  :  (a]  a  series  of  motor  roots,  which  arise  from  the  ventral  zone  of 
the  hind-brain  and  extend  from  near  the  glosso-pharyngeal  anlage  in  front  as  far  as  the  third  or 
fourth  spinal  segment  below ;  (£)  a  partially  subdivided,  but  at  first  continuous,  ganglionic 
mass,  which  arises  from  the  ganglion-crest  of  the  hind-brain  and  represents  the  root-ganglia  ; 
(c)  a  secondary  ventral  cell-mass,  the  primitive  ganglion  of  the  trunk,  which,  as  in  the  case  of 
the  glosso-pharyngeal  nerve,  is  developed  in  close  relation  with  the  ectoblast  of  the  posterior 
branchial  furrows.  Whilst  the  motor  rootlets  persist  and  become  the  efferent  root-fibres  of  the 
later  vagus  and  accessory  nerves,  the  dorsal  or  crest-ganglia  soon  exhibit  differences  in  their 
growth,  the  one  situated  farthest  forward  outstripping  the  others  and  becoming  the  vagal  gang- 
lion of  the  root,  and  the  remaining  ones  becoming  the  accessory  root-ganglia.  These  latter 
constitute  a  chain  which  below  meets  with  the  spinal  dorsal  ganglia.  Primarily,  therefore,  the 
entire  length  of  the  vagus  complex  is  occupied  by  a  series  of  mixed  nerve  strands  possessing 
both  motor  and  sensory  elements.  The  head-end  of  the  series  later  becomes  predominatingly 
sensory,  while  in  the  tail-end  of  the  same  the  motor  character  prevails.  The  ventral  vagus 
nucleus  is  attached  secondarily  to  the  dorsal  nucleus  by  centrally  growing  fibres,  while  from  its 
distal  end  extend  the  dendritic  processes  which  constitute  the  trunk  of  the  vagus  and  its 
branches.  In  consequence  of  the  intergrowth  of  these  afferent  and  efferent  fibres,  the  definite 
tenth  nerve  in  the  usual  sense,  with  its  two  ganglia,  becomes  established.  Although  for  a  short 
period  the  accessory  part  of  the  complex  is  provided  with  both  motor  and  sensory  parts,  the 
latter  are  subsequently  overpowered  by  the  efferent  fibres,  so  that  the  presence  of  the  rudimen- 
tary ganglionic  elements  within  the  accessorius  can  be  demonstrated  only  by  microscopic  exam- 
ination (Streeter) .  From  the  preceding  facts  it  is  evident  that  the  estimate  of  the  eleventh  nerve 
as  an  integral  part  of  the  vagus  is  well  founded. 

The  hypoglossal  nerve  appears  in  the  human  embryo,  towards  the  close  of  the  third  week, 
as  several  strands  which  grow  from  the  ventral  zone  of  the  wall  of  the  hind-brain  and  are  in 
series  with  the  ventral  root-fibres  of  the  upper  cervical  spinal  nerves.  Soon  the  separate  root- 
lets converge  and  consolidate  into  a  common  trunk,  from  which,  by  the  end  of  the  fifth  week, 
the  chief  branches  of  distribution  arise.  The  production  of  the  wide-meshed  net-work  which 
distinguishes  the  communications  between  the  upper  cervical  and  hypoglossal  nerves  results 
from  the  separation  of  fibres  which  are  at  first  closely  adjacent,  the  subsequent  migration  of  the 
growing  tongue-muscles  drawing  the  hypoglossal  fibres  away  from  the  spinal  nerves,  except  at 
such  points  where  they  have  become  enclosed  in  a  common  sheath.  There  is  good  reason  for 
regarding  the  hypoglossal  nerve  as  representing  the  ventral  roots  of  trunk-nerves,  which  have 
been  cephalicly  displaced  and  drawn  within  the  cranium.  Moreover,  the  observations  of 
Froriep  and  others  upon  adult  mammals  and  of  His  upon  the  human  embryo  have  shown  the 
presence  of  a  rudimentary  dorsal  ganglion  and  abortive  dorsal  root-fibres.  The  occasional 
presence  of  a  rudimentary  ganglionic  mass,  known  as  Froriep's  ganglion,  attached  to  the 
fibres  of  the  adult  hypoglossal  nerve  in  man  is  to  be  interpreted  as  the  persistent  dorsal 
element  which  ordinarily  disappears. 

From  the  preceding  sketch  it  is  evident  that  in  no  instance,  as  observed  in  the  usual  adult 
condition  in  man,  is  there  complete  correspondence  between  the  members  of  the  cephalic 
series  and  those  of  the  trunk.  The  group  of  purely  sensory  nerves — the  olfactory,  optic  and 
auditory — includes  one,  the  optic,  which  is  so  exceptional  in  its  fundamental  relations  as  to  lie 
without  the  pale  of  peripheral  nerves  in  their  strict  sense.  The  remaining  two  sensory  nerves 
are  held  to  be  primarily  the  equivalents  of  constituents  of  a  peculiar  system  of  sensory 
organs,  best  developed  in  fibres,  known  as  the  organs  of  the  lateral  line.  The  third,  fourth, 
sixth  and  twelfth,  the  ventral  motor  nerves,  are  undoubtedly  associated  with  head-somites, 
although  the  exact  number  and  nerve  relations  of  such  mesoblastic  segments  are  uncertain ; 
in  fundamental  significance,  therefore,  these  nerves  agree  with  those  of  the  trunk-series, 
although  modified  by  the  suppression  of  their  dorsal  or  sensory  constituents.  The  mixed 
nerves— the  fifth,  seventh,  ninth  and  tenth  (the  eleventh  being  reckoned  as  part  of  the  vagus)— 
are  unrepresented  in  the  spinal  series  and  belong  to  the  branchiomere  represented  by  the 
visceral  arches.  Of  these  nerves,  the  trigeminus  most  nearly  accords  in  constitution  with  a  typical 
spinal  nerve,  since,  with  the  exception  of  ventral  motor  constituents  which  are  wanting,  it  pos- 
sesses as  does  the  typical  spinal  nerve,  both  somatic  (general  cutaneous)  sensory  and  visceral 
sensory  fibres.  A  further  rest -mblance  is  found  in  the  character  of  the  gray  matter  constituting 
the  reception-nucleus  for  the  sensory  fibres  of  the  trigeminus,  since  this  column  is  composed  of 
substantia  gelatinosa  continuous  with  the  Rolandic  substance  capping  the  posterior  cornu  of  Un- 
cord. A  similar,  although  less  intimate,  arrangement  is  seen  in  the  column  of  gray  matter  accom- 
panying the  descending  root  (funiculus  solitarius)of  the  facial,  glosso-pharyngeal  and  vagus  nerves. 


THE  ORGANS  OF  SENSE. 

THE  cells  directly  receiving  the  stimuli  producing  the  sensory  impressions  of 
touch,  smell,  taste,  sight  and  hearing  are  all  derivations  of  the  ectoblast — the  great 
primary  sensory  layer  from  which  the  essential  parts  of  the  organs  of  special  sense 
are  differentiations.  The  olfactory  cells — nervous  elements  that  correspond  to 
ganglion  cells  —  retain  their  primary  relation,  since  they  remain  embedded  within 
the  invaginated  peripheral  epithelium  lining  the  nasal  fossae,  sending  their  dendrites 
towards  the  free  surface  and  their  axones  into  the  brain.  Usually,  however,  the 
nerve  cells  connected  with  the  special  sense  organs  abandon  their  superficial  position 
and  lie  at  some  distance  from  the  periphery,  receiving  the  stimuli  not  directly,  but 
from  the  epithelial  receptors  by  way  of  their  dendrites.  In  the  case  of  the  most 
highly  specialized  sense  organs,  the  eye  and  the  ear,  the  percipient  cells  lie  enclosed 
within  capsules  of  mesoblastic  origin,  the  stimuli  reaching  them  by  way  of  an 
elaborate  path  of  conduction. 

THE  SKIN. 

Since  the  extensive  integumentary  sheet  that  clothes  the  exterior  of  the  entire 
body  not  only  serves  as  a  protective  investment,  an  efficient  regulator  of  body 
temperature  and  an  important  excretory  structure,  but  also  contains  the  special  end- 
organs  and  the  peripheral  terminations  of  the  sensory  nerves  that  receive  and  convey 
the  stimuli  producing  tactile  impressions,  the  skin  may  be  appropriately  considered 
along  with  the  other  sense-organs  of  which  it  may  be  regarded  as  the  primary  and 
least  specialized.  On  the  other  hand,  the  correspondence  of  its  structure  with  that 
of  the  mucous  membranes,  with  which  it  is  directly  continuous  at  the  orifices  on  the 
exterior  of  the  body,  emphasizes  the  close  relation  of  the  skin  to  the  alimentary  and 
other  mucous  tracts. 

This  general  investment,  the  tegmentum  commune,  includes  the  skin  proper  > 
with  the  specialized  tactile  corpuscles,  and  its  appendages — the  hairs,  the  nails  and 
the  cutaneous  glands.  Its  average  superficial  area  is  approximately  one  and  a  half 
square  meters. 

The  skin  (cutis),  using  the  term  in  a  more  restricted  sense  as  applied  to  the 
covering  proper  without  its  appendages,  everywhere  consists  of  two  distinct  portions 
— a  superficial  epithelial  and  a  deeper  connective  tissue  stratum.  The  former,  the  epi- 
dermis, is  devoid  of  blood-vessels,  the  capillary  loops  of  which  never  reach  farther  than 
the  subjacent  corium,  as  the  outermost  layer  of  the  connective  tissue  stratum  is  called. 

The  thickness  of  the  skin,  from  .5-4  mm.,  varies  greatly  in  different  parts  of 
the  body,  being  least  on  the  eyelids,  penis  and  nymphae,  and  greatest  on  the  palms 
of  the  hands  and  soles  of  the  feet  and  on  the  shoulders  and  back  of  the  neck.  In 
general,  with  the  exception  of  the  hands  and  feet,  the  skin  is  thicker  on  the  extensor 
and  dorsal  surfaces  than  on  the  opposite  aspects  of  the  body.  Of  the  entire  thick- 
ness, the  proportion  contributed  by  the  epidermis  is  variable,  but  in  most  localities 
it  is  about  .  i  mm.  Where  exposed  to  unusual  pressure,  as  on  the  palms  of  laborers 
or  on  habitually  unshod  soles,  the  epidermis  may  attain  a  thickness  of  4  mm. 

As  seen  during  life,  the  color  of  the  skin  results  from  the  blending  of  the  in- 
herent tint  of  the  tissues  with  that  of  the  blood  within  the  superficial  vessels.  When 
the  latter  are  empty,  as  after  death,  the  skin  assumes  the  characteristic  pallor  and 
ashen  hue.  Where  the  capillaries  are  numerous  and  the  overlying  strata  thin,  the 
skin  exhibits  the  pronounced  rosy  color  of  the  lips,  cheeks,  ears  and  hands.  Where, 
on  the  contrary,  the  contents  of  fewer  vessels  shimmer  through  the  epidermis,  the 
paler  tint  of  the  limbs  and  trunk  is  produced. 

In  certain  localities — especially  over  the  mammary  areolae  after  pregnancy,  the 
axillae,  the  external  genital  organs  and  around  the  anus — the  skin  presents  a  more  or 
less  pronounced  brownish  color  owing  to  the  unusual  quantity  of  pigment  within  the 

1381 


I382 


HUMAN   ANATOMY. 


epidermis. 


The  amount  of  skin-pigment  not  only  differs  permanently  among  races 

(white,  yellow  and  black)  and  indi- 


FIG.  1144. 


Imprint  of  dorsal  surface  of  left  hand  near  ulnar  border; 
radiating  lines  are  produced  by  creases  connecting  points  at 
which  hairs  emerge. 


viduals  (blond  and  brunette),  but 
also  varies  in  the  same  person  with 
age  and  exposure,  as  contrasted  by 
the  rosy  tint  of  the  infant  and  the 
bronzed  tan  of  the  weather  beaten 
mariner. 

Unless  bound  down  to  the 
underlying  tissues,  as  it  is  over  the 
scalp,  external  ear,  palms  and  soles, 
the  skin  is  freely  movable.  Its 
physical  properties  include  con- 
siderable extensibility  and  marked 
elasticity.  By  virtue  of  the  latter  the 
temporary  displacement  and  stretch- 
ing produced  by  movements  of  the 
joints  and  muscles  is  overcome  and 
the  smoothness  of  the  skin,  so  con- 
spicuous in  early  life,  is  maintained. 
With  advancing  age  the  elasticity 
becomes  impaired  and  folds  are'  no 
longer  effaced,  resulting  in  the  perma- 
nent wrinkles  seen  in  the  skin  of  old 


FIG.  1145. 


people.  Certain  folds  and  furrows,  however,  are  not  only  permanent  and  ineffaceable, 
appearing  in  the  foetus,  but  are  fairly  constant  in  position  and  form.  One  group, 
produced  by  flexion  of  the  joints,  includes  the  conspicu- 
ous creases  on  the  flexor  surface  of  the  wrist,  palm  and 
fingers,  and  the  similar  markings  on  the  soles  of  the  feet. 
The  other  group,  more  extensive  but  less  striking, 
includes  the  fine  grooves  that  connect  the  points  of 
^emergence  of  the  hairs  and  cover  the  trunk  and  extensor 
surface  of  the  limbs  with  a  delicate  tracery  (Fig.  1144)- 

The  surface  modelling  of  the  skin  covering  the 
palms,  soles  and  flexor  aspects  of  the  digits  is  due  to 
the  disposition  of  numerous  minute  ridges  (cristae  cutis) 
and  furrows  (sulci  cutis).  The  cutaneous  ridges,  about 
.  2  mm.  in  width,  correspond  to  double  rows  of  papillae 
which  they  cover,  the  sweat  glands  opening  along  the 
summit  of  the  crests.  The  patterns  formed  by  the 
cutaneous  ridges  (Fig.  1145)  remain  throughout  life 
unchanged  and  are  so  distinctive  for  each  individual 
that  they  afford  a  reliable  and  practical  means  of  identi- 
fication. In  addition  to  the  various  longitudinal,  trans- 
verse and  oblique  ranges  of  ridges  that  cover  the  greater 
part  of  the  hand,  groups  of  concentrically  arranged 
ridges  occupy  the  volar  surface  over  the  distal  phalanges, 
the  pads  between  the  metacarpo-phalangeal  joints  and 
the  middle  of  the  hypothenar  eminence.  These  highly 
characteristic  areas,  the  so-called  tactile  pads  (toruli 
tactiles)  are  most  strikingly  developed  over  the  bulbs 
of  the  fingers,  where  the  ridges  are  often  disposed  in 
whorls  rather  than  in  regular  ovals.  The  markings  of 
corresponding  areas  of  the  two  hands  are  symmetrical 
and  sometimes  identical. 

Structure. — The  two  parts  of  which  the  skin  is 
everywhere  composed — the  epidermis  and  the  connec- 
tivr  tissue  stratum — are  derivatives  of  the  ectoblast  and 
of  the  mesoblast  respectively.  The  connective  tissde  portion  includes  two  layers, 


Imprint  of  palmar  MM  laic  of  left 
middle  finger,  showing  arrangement 
of  cutaneous  ridges ;  transverse  in- 
ti-rniptions  arc  produced  by  flexion 
creases  over  joints. 


THE    SKIN. 


1383 


the  corium  and  the  tela  subcutanea,  which,  however,  are  so  blended  with  each  other 
as  to  be  without  sharp  demarcation. 

The  corium  or  derma,  the  more  superficial  and  compact  of  the  connective 
tissue  strata,  lies  immediately  beneath  the  epidermis  from  which  it  is  always  well 
defined.  With  the  exception  of  within  a  few  localities,  as  over  the  forehead,  external 
ear  and  perineal  raphe,  the  outer  surface  of  the  corium  is  not  even  but  beset  with 
elevations,  ridges,  or  papillae,  which  produce  corresponding  modelling  of  the  opposed 
under  surface  of  the  overlying  epidermis.  The  pattern  resulting  from  these  eleva- 
tions varies  in  different  regions,  being  a  net-work  with  elongated  meshes  over  the 
back  and  front  of  the  trunk,  with  more  regularly  polygonal  fields  over  the  extremi- 


FIG.  1147. 


Portion  of  corium  from  palmar 
surface  of  hand  after  removal  of  epi- 
dermis ;  each  range  includes  a  double 
row  of  papillae,  which  underlie  the 
superficial  cutaneous  ridges  and  en- 
close openings  of  sweat  glands ;  latter 
appear  as  dark  points  along  ranges 
of  papillae.  X  5- 


Small  portion  of  preceding  specimen, 
showing  papillae  under  higher  magnifica- 
tion ;  orifices  of  torn  sweat  glands  are  seen 
between  papillae.  X  24. 


ties  and  with  small  irregular  meshes  on  the  face  (Blaschko).  The  best  developed 
papillae  are  on  the  flexor  surfaces  of  the  hands  and  feet,  where  they  attain  a  height 
of  .2  mm.  or  more  and  are  disposed  in  the  closely  set  double  rows  that  underlie  the 
cutaneous  ridges  on  the  palms  and  soles  above  noted.  The  papillae  afford  favorable 
positions  for  the  lodgement  of  the  terminal  capillary  loops  and  the  special  organs  of 
touch  and  are  accordingly  grouped  as  vascular  and  tactile. 

In  recognition  of  the  elevations,  which  in  vertical  sections  of  the  skin  appear 
as  isolated  projections,  the  corium  is  subdivided  into  an  outer  papillary  stratum 
(corpus  papillare),  containing  the  papillae,  and  a  deeper  reticular  stratum  (tunica 
propria),  composed  of  the  closely  interlacing  bundles  of  fibrous  and  elastic  tissue 
that  are  continued  into  the  more  robust  and  loosely  arranged  trabeculae  of  the  tela 
subcutanea.  These  two  strata  of  the  corium,  however,  are  so  blended  that  they 
pass  insensibly  and  without  definite  boundary  into  each  other.  Although  composed 
of  the  same  histological  factors — bundles  of  fibrous  tissue,  elastic  fibres  and  con- 
nective tissue  cells — the  disposition  of  these  constituents  is  much  more  compact  in 
the  dense  reticular  stratum  than  in  the  papillary  layer,  in  which  the  connective 
tissue  bundles  are  less  closely  interwoven.  While  the  general  course  of  the  fibrous 
bundles  within  the  corium  is  parallel  or  oblique  to  the  surface,  some  strands, 
continued  upward  from  the  underlying  subcutaneous  sheet,  are  vertical  and 
traverse  the  stratum  reticulare  either  to  bend  over  and  join  the  horizontal  bundles 
or  to  break  up  and  disappear  within  the  papillary  stratum.  The  elastic  tissue, 


HUMAN   ANATOMY. 


which  constitutes  a  considerable  part  of  the  corium,  occurs  as  fibres  and  net-works, 
which  within  the  reticular  stratum  form  robust  tracts  corresponding  in  their 
disposition  with  the  general  arrangement  of  the  fibrous  bundles.  Towards  the 
surface  of  the  corium,  the  elastic  fibres  become  finer  and  more  branched  and  beneath 
the  epidermis  anastomose  to  form  the  delicate  but  close  subcpithelial  elastic  net-work 
that  is  present  over  the  entire  surface  of  the  body  with  the  exception,  possibly,  of 
the  eyelids  (Behrens). 

The  tela  subcutanea,  the  deeper  layer  of  the  connective  tissue  portion  of  the 
skin,  varies  in  its  thickness,  and  in  the  density  and  arrangement  of  its  component 
bundles  of  fibro-elastic  tissue,  with  the  amount  of  fat  and  the  number  of  hair-follicles 
and  glands  lodged  within  its  meshes. 

The  latter  are  irregularly  round  and  enclosed  by  tracts  of  fibrous  tissue,  some 
of  which,  known  as  the  retinacula  cutis,  are  prolonged  from  the  corium  to  the  deepest 
parts  of  the  subcutaneous  stratum.  Here  they  often  blend  into  a  thin  but  definite 
sheet,  the  fascia  subcutanea,  which  forms  the  innermost  boundary  of  the  skin  and  is 


FIG.  1148. 


Epidermis 
Papillary  stratum 

Reticular  stratum 


Hair  follicle 


Retinaculum 


Fat 


Section  of  skin,  showing  its  chief  layers— epidermis,  corium  and  tela  subcutanea.    X  17. 

connected  with  the  subjacent  structures  by  strands  of  areolar  tissue.  Where  such 
loose  connection  is  wanting,  as  on  the  scalp,  face,  abdomen  (linea  alba),  palms  and 
soles,  the  skin  is  intimately  bound  to  the  underlying  muscles  or  fasciae  and  lacks  the 
independent  mobility  that  it  elsewhere  enjoys.  The  integument  covering  the  eye- 
lids and  penis  is  peculiar  in  retaining  to  a  conspicuous  degree  its  mobility  although 
devoid  of  fat.  Where  the  latter  is  present  in  large  quantity,  the  term  panniculiis 
adiposus  is  often  applied  to  the  tela  subcutanea. 

In  places  in  which  the  skin  glides  over  unyielding  structures,  the  interfascicular 
lymph-spaces  of  the  tela  subcutanea  may  undergo  enlargement  and  fusion,  resulting 
in  the  production  of  the  subcutaneous  mucous  bursce.  These  are  found  in  many 
localities,  among  the  most  constant  bursae  being  those  over  the  olecranon.  the  patella 
and  the  metatarso-phalangeal  joints  of  the  little  and  the  great  toe.  The  bursae  in 
the  latter  situation,  when  abnormally  enlarged,  are  familiar  as  bunions. 

In  addition  to  the  strands  of  inroluntayy  II/HSC/C  associated  with  the  hairs  as  the 
arrectores  pilorum,  unstriped  muscular  tissue  is  incorporated  with  the  skin  in  the 
mammary  areolae  and  over  the  scrotum  and  penis  (tunica  dartos).  The  facial 
muscles  having  largely  cutaneous  insertions,  the  skin  covering  the  face  is  invaded 
by  tracts  of  striated  muscular  tissue  that  penetrate  as  far  as  the  corium. 


THE    SKIN. 


1385 


The  epidermis  or  cuticle,  the  outer  portion  of  the  skin,  consists  entirely  of 
epithelium  and,  being  partly  horny,  affords  protection  to  the  underlying  corium  with 
its  vessels  and  nerves.  The  thickness  of  this  layer  varies  in  different  parts  of  the 
body.  Usually  from  .08— .10  mm.,  it  is  greatest  on  the  flexor  surfaces  of  the  hands 
and  feet,  where  it  reaches  from  .5-.  9  mm.  and  from  1.1-1.3  mm.  respectively 
(Drosdoff). 

The  cuticle  consists  of  two  chief  layers,  the  deeper  stratum  germinativum,  con- 
taining the  more  active  elements,  and  the  stratum  corneum,  the  cells  of  which  undergo 
cornification.  Between  these  layers  lies  a  third,  the  stratum  intermedium,  that  is 

FIG.  1149. 


Stratum  corneum 


....  , 

Portion  of  section  of  skin  from  sole  of  foot,  showing  layers  of  epidermis.    X  70. 


ordinarily  represented  by  only  a  single  row  of  cells  to  which  the  name,  stratum 
granulosum,  is  usually  applied.  This  layer  marks  the  level  at  which  the  conversion 
of  the  epithelial  elements  into  horny  plates  begins  and  also  that  at  which  the 
separation  effected  by  blistering  usually  occurs. 

On  the  palms  and  soles,  where  the  epidermis  attains  not  only  great  thickness 
but  also  higher  differentiation,  four  distinct  layers  may  be  recognized  in  vertical  sec- 
tions of  the  cuticle.  From  the  corium  outward,  these  are:  (i)  the  stratum  germina- 
tivum,  (2)  the  stratum  granulosum,  (3)  the  stratum  lucidum  and  (4)  the  stratum 
corneum.  The  first  two  represent  the  portion  of  the  epidermis  endowed  with  the 
greatest  vitality  and  powers  of  repair  and  the  last  two  the  horny  and  harder  part. 

The  stratum  germinativum,  or  stratum  Malpighi,  rests  upon  the  outer  sur- 
face of  the  corium,  by  the  papillae  of  which  it  is  impressed  and,  hence,  when 
viewed  from  beneath  after  being  separated,  commonly  presents  a  more  or  less 
evident  net-work  of  ridges  and  enclosed  pits,  the  elevations  corresponding  to  the 


386 


HUMAN   ANATOMY. 


Stratum  corneum 


Stratum  lucidum 


_    Stratum 

granulosum 


Stratum 

germinativum 


Deepest  cells 

of  epidermis 

Corium 


Portion  of  preceding  preparation,  showing  in  more  detail  layers  of  epidermis 
only  deeper  part  of  stratum  corneum  is  represented.     X  200. 


interpapillary  furrows  and  the  depressions  to  the  papillae.  In  recognition  of  this 
reticulation  the  name,  rete  Malpighi,  is  sometimes  applied  to  the  deepest  layer  of 
the  epidermis.  As  in  other  epithelia  of  the  stratified  squamous  type,  the  deepest  cells 

are  columnar  and  lie  with 

FIG.  1150.  their  long  axes  perpen- 

dicular to  the  supporting 
connective  tissue.  The 
basal  ends  of  the  colum- 
nar cells  are  often  slight- 
ly serrated  and  fit  into 
corresponding  indenta- 
tions on  the  corium. 
Their  outer  ends  are 
rounded  and  received 
between  the  super- 
imposed cells.  Succeed- 
ing the  single  row  of 
columnar  elements,  the 
cells  of  the  stratum 
germinativum  assume  a 
pronounced  polygonal 
form,  but  become  some- 
what flatter  as  they 
approach  the  stratum 
granulosum.  The  num- 
ber of  layers  included 
in  the  germinal  stratum 
is  not  only  uncertain, 
but  varies  with  the  rela- 
tion to  the  papillae,  being  greater  between  than  over  these  projections.  The  finely 
granular  cytoplasm  of  the  cells  of  the  stratum  germinativum  contains  delicate  but 
distinct  fibrilla:,  which,  longitudinally  disposed  in  the  deep  columnar  cells,  in  the 
polygonal  elements  (Fig.  1151),  radiate  from  the  nucleus  towards  the  periphery 
(Kromayer).  The  fibrillae  are  not  confined  to  the  cells,  but  extend  beyond  and  pass 
across  the  intercellular  lymph-clefts  as  delicate  protoplasmic  bridges  that  connect 
the  units  of  the  various  layers  of  the  stratum  and  confer  upon  them  the  character- 
istics of  the  so-called  ' '  prickle  cells. 

The  stratum  granulosum  is  exceptionally  well  marked  on  the  palms  and  soles 
and   in  these  localities  includes  from 

two  to  four  rows  of  polygonal  cells,  FIG-  "Si- 

somewhat  horizontally  compressed, 
that  stand  out  conspicuously  in  stained 
sections  by  reason  of  the  intensely 
colored  particleswithin  theircytoplasm. 
The  nature  of  the  peculiar  substance, 
deposited  within  the  body  of  the  cells 
as  particles  of  irregular  form  and  size, 
is  still  uncertain.  To  it  Ranvier  gave 
the  name  of  eleidin  and  Waldeyer  that 
of  keratohyalin.  Since  the  nuclei  of 
the  cells  in  which  the  deposits  occur 
always  exhibit  evidences  of  degenera- 
tion, it  is  probable  that  keratohyalin 
is  in  some  way  derived  from  disintegra- 
tion of  the  nucleus  (Mertsching)  and 
represents  a  transition  stage  in  the 

process  ending   in  cornification   of   the  succeeding  layers  of  the  cuticle   (Brunn). 

The  stratum  lucidum,  usually  wanting  in  other  localities,   in  the  palm  and 

sole  appears  as  a  thin,  almost  homogeneous  layer,  separating  the  corneous  from  the 


Fibrillae 


Portion  of  horizontal  section  of  skin,  showing  intracellular 
fibrillie  within  cells  of  stratum  germinativum.     X  800. 


THE    SKIN. 


1387 


Pigmental 
epidermis 


Duct  of 
sweat  gland 


granular  layer.  With  the  latter  it  constitutes  the  stratum  intermedium.  As  indicated 
by  its  name,  the  stratum  lucidum  appears  clear  and  without  distinct  cell  boundaries, 
although  suggestions  of  these,  as  well  as  of  the  nuclei  of  the  component  elements,  are 
usually  distinguishable.  The  cells  of  the  stratum  lucidum  are  uniformly  cornified 
and  differ,  therefore,  from  those  of  the  overlying  layers  in  which  the  process  is  often 
confined  to  a  mantle  zone. 

The  stratum  corneum  includes  the  remainder  of  the  epidermis  and  consists 
of  many  layers  of  horny  epithelial  cells  that  form  the  exterior  of  the  skin.  Where 
no  stratum  lucidum  exists,  as  is  usually  the  case,  the  corneous  layer  rests  upon  the 
stratum  granulosum,  from  which  its  horny  elements  are  being  continually  recruited. 
During  their  migration  towards  the  free  surface,  the  cells  lose  their  vitality  and 
become  more  flattened  until  the  most  superficial  ones  are  converted  into  the  dead 
horny  scales  that  are  being  constantly  displaced  by  abrasion. 

The  pigmentation  of  the  skin,  which  even  in  white  races  is  conspicuous  in 
certain  regions  (page  1381),  depends  upon  the  presence  of  colored  particles  chiefly 
within  the  epidermis,  although,  when  the  dark  hue  is  pronounced,  a  few  small 
branched  pigmental  connective 

.  .  T? 

tissue   cells  may  appear  within  1G-  i:52- 

the  subjacent  corium.  The  dis- 
tribution of  the  pigment  particles 
varies  with  the  intensity  of  color, 
in  skins  of  lighter  tints  being 
principally,  and  sometimes  en- 
tirely, limited  to  the  columnar 
cells  next  the  corium.  With 
increasing  color  the  pigment 
particles  invade  the  neighboring 
layers  of  epithelium  until,  in  the 
dark  skin  of  the  negro,  they 
are  found  within  the  cells  of  the 
stratum  corneum  but  always 
in  diminishing  numbers  towards 
the  free  surface.  Even  when 
the  cells  are  dark  and  densely 
packed,  the  colored  particles 
never  encroach  upon  the  nuclei, 
which,  therefore,  appear  as  con- 
spicuous pigment  free  areas. 
The  source  of  the  pigment  within  the  epidermis  is  uncertain,  by  some  being  found 
in  an  assumed  transference  of  the  colored  particles  from  the  corium,  by  means 
of  wandering  cells  or  of  the  processes  of  pigmented  connective  tissue  cells  that 
penetrate  the  cuticle,  and  by  others  ascribed  to  an  independent  origin  in  situ 
within  the  epithelial  elements.  While  it  may  be  accepted  as  established  that  at 
times  the  connective  tissue  cells  are  capable  of  modifying  pigmentation  (Karg),  it 
is  equally  certain  that  the  earliest,  and  probably  also  later,  intracellular  pigmenta- 
tion of  the  epidermis  appears  without  the  assistance  of  the  connective  tissue  or 
migratory  cells. 

The  blood-vessels  of  the  skin  are  confined  to  the  connective  tissue  portion 
and  never  enter  the  cuticle.  The  arteries  are  derived  either  from  the  trunks  of  the 
subjacent  layer  as  special  cutaneous  branches  destined  for  the  integument,  or  indi- 
rectly from  muscular  vessels.  When  the  blood  supply  is  generous,  as  in  the  palms 
and  soles  and  other  regions  subjected  to  unusual  pressure  or  exposure,  the  arteries 
ascend  through  the  subdermal  layer  to  the  deeper  surface  of  the  corium  where, 
having  subdivided,  they  anastomose  to  form  the  siibcutaneoiis  plexus  (rete  arteriosum 
cutaneura).  From  the  latter  some  twigs  sink  into  the  subdermal  layer  and  contribute 
the  capillary  net-works  that  supply  the  adipose  tissue  and  the  sebaceous  glands. 

Other  twigs,  more  or  less  numerous,  pass  outward  through  the  deeper  part  of 
the  corium  and  within  the  more  superficial  stratum  unite  into  a  second,  subpapillary 
plexus  (rete  arteriosum  subpapillare),  that  extends  parallel  to  the  free  surface  and 


Section  of  skin,  surrounding;  anus,  showing  pigmentation  of  deeper 
layer  of  epidermis.    X  50. 


I388 


HUMAN   ANATOMY. 


Papillary 
loops 


beneath  the  bases  of  the  papillae.  The  latter  are  supplied  by  the  terminal  twigs  which 
ascend  vertically  from  the  subpapillary  net-work  and  break  up  into  capillary  loops 
that  occupy  the  papillse  and  lie  close  beneath  the  epidermis  (Fig.  1153).  With  the 
exception  of  the  loops  entering  the  hair-papillae,  the  capillaries  enclosing  the  hair- 
follicles  arise  from  the  subpapillary  plexus. 

The  arrangement  of  the  cutaneous  veins,  more  complex  than  that  of  the  arteries, 
includes  four  plexuses  (retes  venosum)  lying  at  different  levels  within  the  corium  and 

extending  parallel  to  the 

FIG.  1153.  surfaces.     The   first   and 

most    superficial    one    is 

"  '^-..  formed    by  the    union  of 

^-^    ^^  the  radicles  returning  the 

blood   from   the  papilla?. 
w  The  component  veins  lie 

below  and  parallel  to  the 
rows  of  papillae  and  im- 
mediately beneath  the 
bases  of  the  latter.  At 
a  slightly  lower  level,  in 
the  deeper  part  of  the 
stratum  papillare,  the  ve- 
nous channels  proceeding 
from  the  subpapillary  net- 
work join  to  form  a  second 
plexus  with  polygonal 
meshes.  A  third  occurs 
about  the  middle  of  the 
corium,  while  the  fourth 
shares  the  position  of 
the  subcutaneous  arterial 
plexus  at  the  junction  of 
the  corium  and  subdermal 
strata.  The  deepest  plexus 
receives  many  of  the 
radicles  returning  the 
blood  from  the  fat  and 
the  sweat  glands,  the  re- 
mainder being  tributary 
to  the  veins  accompany- 
ing the  larger  arteries 
as  they  traverse  the  tela 
subcutanea. 

The  lymphatics  of 
the  skin  are  well  repre- 
sented by  a  close  super- 
ficial plexus  within  the 
papillary  stratum  of  the 
corium  into  which  the 
terminal  lymph-radicles  of 
the  papillae  empty.  The 
relation  of  these  channels  to  the  interfascicular  connective  tissue  spaces  is  one  only 
of  indirect  communication,  since  the  lymphatics  are  provided  with  fairly  complete 
endothelial  walls.  It  is  probable  that  the  lymph-paths  within  the  papillae  are  closely 
related  to  the  intercellular  clefts  of  the  epidermis,  according  to  Unna,  indeed,  direct 
communications  existing.  Migratory  leucocytes  often  find  their  way  into  the  cuticle 
where  they  then  appear  as  the  irregularly  stellate  cells  of  I.ungerhans  seen  between 
the  epithelial  elements.  A  wide-meshed  deep  plexus  of  lymphatics  is  formed  within 
the  subdermal  layer,  from  which  the  larger  lymph -trunks  pass  along  with  the 
subcutaneous  blood-vessels. 


Section  of  injected  skin,  showing  general  arrangement  of  blood-vessels.    X  4<>- 


THE   HAIRS.  1389 

The  numerous  nerves  within  the  highly  sensitive  integument  are  chiefly  the 
peripheral  processess  of  sensory  neurones  which  terminate  in  free  arborizations  between 
the  ephithelial  elements  of  the  cuticle,  or  in  relation  with  special  endings  located,  for 
the  most  part,  within  the  corium  or  subdermal  connective  tissue.  Some  sympathetic 
fibres,  however,  are  present  to  supply  the  tracts  of  involuntary  muscle  that  occur  within 
the  walls  of  the  blood-vessels  or  in  association  with  the  hairs  and  the  sweat  glands. 

On  entering  the  skin  the  medullated  nerves  traverse  the  subdermal  layer,  to 
which  they  give  off  twigs  in  their  ascent,  and,  passing  into  the  corium,  within  the 
papillary  stratum  divide  into  a  number  of  branches.  Those  destined  for  the  epidermis 
beneath  the  latter  break  up  into  many  fibres  which,  losing  their  medullary  substance, 
enter  the  cuticle  and  end  in  arborizations  that  ramify  between  the  epithelial  cells  as  far 
as  the  outer  limits  of  the  stratum  germinativum.  The  ultimate  endings  of  the  fibrillee, 
whether  tapering  or  slightly  knobbed,  always  occupy  the  intercellular  channels  and  are 
never  directly  connected  with  the  substance  of  the  epithelial  elements.  According  to 
Merkel,  special  tactile  cells,  (Fig.  1016)  occur  in  the  human  epidermis,  particularly 
over  the  abdomen  and  the  thighs.  These  cells,  spherical  or  pyriform  in  shape  and 
composed  of  clear  cytoplasm,  occupy  the  deeper  layers  of  the  cuticle  and,  on  the  side 
directed  towards  the  corium,  are  in  contact  with  the  end-plate  or  meniscus  of  the  nerve. 

The  nerve-fibres  particularly  concerned  with  the  sense  of  touch  terminate  within 
the  connective  tissue  portion  of  the  skin,  either  within  the  corium  in  special  end-organs 
— the  tactile  bodies  of  Meissner,  the  end-bulbs  of  Krause,  the  genital  corpuscles  and 
the  end-organs  of  Ruffini,  or  within  the  subdermal  layer  in  the  Vater-Pacinian  cor- 
puscles, or  their  modifications,  the  Golgi-Mazzoni  corpuscles.  The  structure  of  these 
special  end-organs  is  elsewhere  described  (pages  1018,  1019),  their  chief  locations 
being  here  noted. 

Meissner's  corpuscles  (Fig.  1017)  are  especially  numerous  in  the  tactile 
cushions  on  the  flexor  surface  of  the  hands  and  feet.  While  much  more  plentiful  in 
all  the  tactile  pads  than  in  the  intervening  areas,  the  touch  corpuscles  are  most 
abundant  in  those  on  the  volar  surface  of  the  distal  phalanges,  where  they  approxi- 
mate twenty  to  the  square  millimeter  (Meissner).  Their  favorite  situation  is  the 
apex  of  the  papillae,  where  they  appear  as  elongated  elliptical  bodies,  sometimes  in 
pairs,  whose  outer  pole  lies  immediately  below  the  epidermis.  These  corpuscles  are 
additionally,  although  sparingly,  distributed  on  the  dorsum  of  the  hand,  the  flexor 
surface  of  the  forearm,  the  lips,  the  eyelids,  the  nipple  and  the  external  genital  organs. 

The  Vater-Pacinian  corpuscles  (Fig.  1018)  are  well  represented  in  the  hands 
and  feet  and  usually  occupy  the  subdermal  tissue,  although  sometimes  found  within  the 
corium.  Their  distribution  corresponds  closely  to  that  of  Meissner's  corpuscles,  they 
being  most  numerous  beneath  the  tactile  cushions  in  the  order  above  described. 

The  Golgi-Mazzoni  corpuscles  are  modifications  of  the  Pacinian  bodies  and, 
like  the  latter,  are  found  within  the  subdermal  tissue. 

The  end-bulbs  of  Krause  (Fig.  1016)  occur  within  the  corium,  either  slightly 
below  or  within  the  papillae,  on  the  lips  and  external  genital  organs,  as  well  as 
probably  in  other  regions. 

The  genital  corpuscles  (Fig.  1017)  lie  within  the  corium  of  the  modified  skin 
covering  the  glans  penis  and  the  prepuce  and  the  clitoris  and  surrounding  parts  of 
the  nymphae. 

The  end-organs  of  Ruffini  resemble  the  sensory  terminations  in  tendons 
(page  1017)  and  lie  within  the  deeper  parts  of  the  corium,  often  associated  with  the 
Pacinian  bodies. 

The  mode  of  ending  of  the  nerves  supplying  the  hairs  and  sweat  glands  will  be 
described  in  connection  with  those  structures  (pages  1394,  1400). 

THE  HAIRS. 

The  appendages  of  the  skin — the  hairs,  nails  and  cutaneous  glands — are  all 
specializations  of  the  epidermis  and  are.  therefore,  exclusively  of  ectoblastic  origin. 

The  hairs  (pili)  are  present  over  almost  the  entire  body,  the  few  localities  in 
which  they  are  absent  being  the  flexor  surface  of  the  hands  and  feet,  the  extensor 
aspect  of  the  terminal  segment  of  the  fingers  and  toes,  the  inner  surface  of  the 


1390 


HUMAN   ANATOMY. 


prepuce  and  of  the  nymphae  and  the  glans  penis  and  clitoridis.  With  the  exception  of 
those  regions  in  which  the  growth  is  sufficiently  long  to  constitute  a  complete  cover- 
ing— the  scalp,  Bearded  parts  of  the  face  in  the  male,  axillae  and  mons  pubis — the 
hairs  are  for  the  most  part  short  and  scattered,  although  subject  to  great  individual 
variation  and  sometimes  to  remarkable  redundance. 

The  hairs  in  various  locations  are  known  by  special  names  ;  those  of  the  scalp 
being  capilli ;  of  the  eyebrows,  superdlia ;  of  the  eyelashes,  cilia;  of  the  nostrils, 
vibrissa ;  of  the  external  ear,  tragi ;  of  the  beard,  barba ;  of  the  axillae,  hi  ret  ;  of 
the  pubes,  pubes  ;  while  the  fine  downy  hairs  that  cover  other  parts  of  the  body  are 
designated  lanugo. 

The  closest  set  hairs  are  on  the  scalp,  where  according  to  Brunn,  in  the  vertex 
they  number  from  30x3-320,  and  in  the  occipital  and  frontal  regions  from  200-240 
per  square  centimeter.  On  the  chin  44  were  counted,  on  the  mons  pubis  30-35, 


Epidermis 


Erector  muscle 


Sweat  gland 


Hair-papilla 


Inner  root-sheath 

Outer  root-sheath 
Bulb 

Papilla 


Paniculus 
adiposus 


Section  of  scalp,  showing  longitudinally  cut  hair-follicles.    X  14- 

on  the  extensor  surface  of  the  forearm  24  and  on  the  back  of  the  hand  1 8  for  like 
areas.  Even  where  their  distribution  is  seemingly  uniform,  close  inspection  shows 
the  hairs  to  be  arranged  in  groups  of  from  two  to  five. 

The  length  of  the  hairs  includes  the  extremes  presented  by  the  lanugo,  only  a 
few  millimeters  long,  on  the  one  hand,  and  by  the  scalp-growth,  sometimes  measur- 
ing 150  cm.  (108  in.)  or  more,  on  the  other.  Their  thickness,  likewise,  shows 
much  variation,  not  only  in  different  races,  individuals  and  regions,  but  also  in  the 
same  person  and  part  of  the  body,  as  on  the  scalp  where  fine  and  coarse  hairs  may 
lie  side  by  side.  The  thickest  scalp-hairs  have  a  diameter  of  .162  mm.  and  the 
finest  one  of  .on  mm.,  with  all  intermediate  sizes.  The  hairs  of  the  beard  vary 
from  .101-. 203  mm.  and  those  on  the  pubes  from  .054-.  135111111.  (Falck).  In  a 
general  way  hairs  of  light  color  are  finer  than  dark  ones,  the  respective  diameters  of 
blond,  brown  and  black  hairs  being  .047,  .054  and  .067  mm.  (Wilson).  On 
attaining  their  full  growth  without  mutilation,  hairs  do  not  possess  a  uniform  thick- 
ness throughout  their  length,  since  they  diminish  not  only  towards  the  tip,  when  the 
>haft  ends  in  a  point,  but  also  towards  the  root.  This  feature  is  most  evident  in 
short  hairs,  as  in  those  of  the  eyebrows. 

The  color  of  the  hair,  which  varies  from  the  lightest  straw  to  raven  black,  is 
closely  associated  with  racial  and  individual  characteristics,  being  usually,  but  by  no 


THE   HAIRS.  1391 

means  always,  in  harmony  with  the  degree  of  general  pigmentation.  The  latter  is 
commonly  uniform  throughout  the  length  of  the  hair,  but  in  rare  cases  it  may  be  so 
variable  that  the  shaft  presents  a  succession  of  alternating  light  and  dark  zones 
(Brunn).  The  straight  and  curly  varieties  of  hair  depend  chiefly  upon  differences  in 
the  curvature  of  the  follicle  1  and  the  form  of  the  hair.  In  the  case  of  straight  hairs 
the  follicle  is  unbent  and  the  shaft  is  cylindrical,  and  therefore  circular  in  cross- 
section  ;  hairs  that  are  wavy  or  curly  spring  from  follicles  more  or  less  bent  and  are 
flattened  or  grooved,  with  corresponding  oval,  reniform,  irregularly  triangular  or 
indented  outlines  when  transversely  cut. 

Arrangement  of  the  Hairs. — Since  the  buried  part  of  the  hair,  the  root,  is 
never  vertical  but  always  oblique  to  the  surface  of  the  skin,  it  follows  that  the  free 
part,  the  shaft,  is  also  inclined.  The  direction  in  which  the  hairs  point,  however,  is 
by  no  means  the  same  all  over  the  body,  but  varies  in  different  regions  although 
constant  for  any  given  area.  This  disposition  depends  upon  the  peculiar  placing 
of  the  hair-roots  which  in  certain  localities  incline  towards  one  another  along 
definite  lines,  an  arrangement  that  results  in  setting  the  shafts  in  opposite  directions. 
As  these  root-lines  are  not  straight  but  spiral,  on  emerging  from  the  skin  the  hairs 
diverge  in  whorls  (vortices  pilorum),  the  position  and  number  of  which  are  fairly 
definite. 

Such  centres  include  :  (i )  the  conspicuous  vertex  whorl  on  the  head,  usually  single  but 
sometimes  double;  (2)  the  facial  whorls  surrounding  the  openings  of  the  eyelids;  (3)  the 
auricular  whorls  at  the  external  auditory  meatus  ;  (4)  the  axillary  whorls  in  the  armpits  ;  and 
(5)  the  inguinal  whorls,  just  below  the  groin  ;  additional  (6)  but  less  constant  lateral  whorls 
may  be  located,  one  on  each  side,  about  midway  between  the  axilla  and  the  iliac  crest  and 
somewhat  beyond  the  outer  border  of  the  rectus  muscle. 

These  whorls,  all  paired  except  the  first,  apportion  the  entire  surface  of  the  body  into 
certain  districts,  each  covered  by  the  hairs  proceeding ,  from  the  corresponding  vortex.  The 
whorl-districts,  moreover,  are  irregularly  subdivided  into  secondary  areas  by  lines,  the  hair- 
ranges  (flumina  pilorum),  along  which  the  hairs  diverge  in  opposite  directions.  Additional  lines, 
the  converging  hair-ranges,  mark  the  meeting  of  tracts  pointing  in  different  directions  and  in 
places  also  assume  a  spiral  course.  In  consequence  of  these  peculiarities  the  body  is  covered 
with  an  elaborate  and  intricate  hair-pattern,  that  is  most  evident  on  the  foetus  towards  the  close 
of  gestation  ;  later  in  life  the  details  of  the  pattern  are  uncertain  owing  to  its  partial  effacement 
by  the  constant  rubbing  of  clothing. 

Structure.  —  Each  hair  consists  of  two  parts,  the  shaft,  which  projects  beyond 
the  surface,  and  the  root,  which  lies  embedded  obliquely  within  the  skin,  the  deepest 
part  of  the  root  expanding  into  a  club-shaped  thickening  known  as  the  bulb.  The 
root  is  covered  with  a  double  investment  of  epithelial  cells,  the  inner  and  outer  root- 
sheaths,  which,  in  turn,  are  surrounded  by  a  connective  tissue  envelope,  the  theca. 
The  entire  sac-like  structure,  consisting  of  the  hair-root  and  its  coverings,  constitutes 
the  hair-follicle  (folliculus  pili).  At  the  bottom  of  the  latter,  immediately  beneath 
the  bulb,  the  wall  of  the  follicle  is  pushed  upward  to  give  place  to  a  projection  of 
connective  tissue,  the  hair-papilla,  which  carries  the  capillary  loops  into  close  relation 
with  the  cells  most  active  in  the  production  of  the  hair.  Save  in  the  case  of  the 
finest  hairs  (lanugo),  which  are  limited  to  the  corium,  the  hair-follicles  traverse  the 
latter  and  end  at  varying  levels  within  the  fat-laden  subdermal  layer  (panniculus 
adiposus ).  In  a  general  way  the  follicle  may  be  regarded  as  a  narrow  tubular  invagi- 
nation  of  the  epidermis,  at  the  bottom  of  which  the  hair  is  implanted  and  from  the 
entrance  of  which  the  shaft  projects.  The  most  contracted  part  of  the  follicle,  the 
neck,  lies  at  the  deeper  end  of  the  relatively  wide  funnel-shaped  entrance  to  the  sac. 
Closely  associated  with  the  hair-follicle,  which  they  often  surround,  are  the  sebaceous 
glands  that  pour  their  oily  secretion  at  the  upper  third  of  the  follicle  into  the  space 
between  the  shaft  and  the  wall  of  the  sac. 

The  Hair-Shaft. — In  many  thick  hairs,  but  by  no  means  in  all,  three  parts 
can  be  distinguished — the  cuticle,  the  cortex  and  the  mediilla.  The  latter,  however, 
is  usually  wanting  in  hairs  of  ordinary  diameter,  being  often  also  absent  in  those  of 
large  size. 

1  Frederic  :  Zeitschr.  f.  Morph.  u.  Anthropol.,  Bd.  ix.,  1906. 


1392 


HI  MAN    ANATOMY. 


FIG.  1155. 


Portion  of  shaft  of  hair;  //,  shaft 
covered  with  cuticle ;  s,  cuticle  re- 
moved to  expose  cortical  substance; 
*»,  medulla  X  125.  a,  b,  isolated  cells 
of  cuticle  and  of  co 
respectively.  X  240. 


jrtical    substance 


The  cuticle  of  the  hair  appears  as  a  transparent  outermost  layer  marked  by  a  net-work  of 
fine  sinuous  lines,  the  irregular  meshes  of  which  have  their  longest  diameter  placed  obliquely 
transverse.  These  lines  correspond  to  the  free  borders  of  extremely  thin  glassy  cuticle-plates 

that  overlie  the  hair  as  tiles  on  a  roof,  the  imbrication  involv- 
ing from  four  to  six  layers.  Seen  in  profile  (Fig.  1155),  the 
contour  of  the  hair-shaft,  therefore,  is  not  smooth  but  serrated, 
the  minute  teeth  formed  by  the  free  margins  of  the  scales 
being  directed  towards  the  tip  of  the  hair.  After  isolation  by 
suitable  reagents,  the  cuticular  elements  appear  as  transparent 
structureless  cells,  quadrilateral  in  outline  and  curved  to  con- 
form to  the  hair-shaft  which  they  cover. 

The  cortical  substance,  often  indeed  constituting  practi- 
cally the  entire  shaft,  consists  of  elongated  fusiform  cells  so 
compactly  arranged  that  the  individual  elements  are  only  dis- 
tinguishable after  the  action  of  disassociating  reagents.  In 
addition  to  the  remains  of  the  shrunken  nuclei  the  hair- 
spindles,  as  these  modified  epithelial  cells  are  called,  possess 
fibrillse  that  pass  between  adjacent  cells  similar  to  the  inter- 
cellular bridges  in  the  epidermis.  A  variable  amount  of 
pigment,  present  either  as  a  diffuse  tint  of  the  spindles,  or  as 
granules  within  or  between  the  same,  is  a  constant  constituent 
of  the  cortical  substance.  In  blond  hair  the  color  is  chiefly 
diffuse,  the  pigment  granules  being  often  entirely  wanting  ;  in 
hair  of  darker  shades,  the  granules  predominate  and  increase  in  intensity  of  color  as  well  as 
in  quantity.  As  the  hair  grows  outward  from  the  bulb,  it  loses  much  of  its  moisture,  and  in 
consequence  later  contains  minute  air-vesicles  that  replace  the  fluid  previously  occupying  the 
clefts  between  the  hair-spindles.  Even  when  conspicuous,  the  medulla  does  not  extend  the 
entire  length  of  the  hair,  often  being  interrupted  and  always  disappearing  before  reaching  the  tip. 
The  medulla,  when  well  represented,  is  seen  as  an  axial  stripe,  somewhat  uneven  in  outline, 
that  varies  with  illumination,  with  transmitted  light  appearing  as  a  dark  band  and  with  reflected 
light  as  a  light  one.  This  peculiarity  depends  upon  the  presence  of  air  imprisoned  between  the 
shrunken  and  irregular  medullary  cells— -dried  and  cornified  epithelial  elements  which  are  con- 
nected by  branching  processes  into  a  net-work  incompletely  filling  the  medulla.  The  air  within 
the  shaft  is  a  factor  modifying  the  color  of  the  hair,  since  the  resulting  reflex  tends  to  lessen  the 
intensity  of  the  tint  directly 

referable  to  the  pigment ;  FIG.  1156. 

this  diminution  affects  par- 
ticulary  the  lighter  shades,  °*er  root-sheath  Hair  surrounded  by 

as  in  dark  hairs  the  large  /f/^Tb  ,/  l^  in"er  root"sheath 

amount  of  pigment  masks 
the  reflex. 

f<'.'**^-  ,<9t0q£^.;    .'/- 

The  Hair-Folli- 
cle.— This  structure 
consists  essentially  of 
( i )  a  connective  tissue 
sheath,  the  theca,  con- 
tributed by  the  corium ; 
(2) an  epithelial  lining, 
the  outer  root- sheath, 
continued  from  the 
deepest  layer  of  the 
epidermis;  and  (3)  the 
inner  root-sheath,  an 
epithelial  investment 
probably  differentiated 
within  the  follicle,  and 
not  a  direct  prolonga- 
tion from  the  cuticle. 

The  theca  folliculi  includes  three  strata  :  an  outer,  composed  of  loosely  dis- 
posed longitudinal  bundles  of  fibrous  tissue  with  few  cells  and  elastic  fibres  ;  a  middle 
one,  madi-  up  of  closely  placed  circular  bundles;  and  a  very  thin,  homogeneous 
inner  coat,  the  glassy  membrane,  which  represents  an  unusually  well  developed 


s  Adipose 


Fibrous  tissue 


Horizontal  section  of  scalp,  showing  group  of  transversely  cut 
hair-follicles.     X  65. 


THE   HAIRS. 


1393 


basement  membrane  separating  corium  from  cuticle.  Greatly  attenuated,  it  is 
prolonged  over  the  hair-papilla,  which,  as  a  special  vascularized  thickening  of  the 
connective  tissue  of  the  follicle,  carries  nutrition  to  the  bulb  of  the  growing  hair. 

The  outer  root-sheath  is  the  continuation  of  the  stratum  germinativum  alone, 
the  other  layers  of  the  epidermis  thinning  out  and  disappearing  before  reaching  the 
neck  of  the  follicle.  Its  cells  present  the  characteristics  of  those  of  the  germinating 
layer,  with  exceptionally  well  marked  fibrillae.  On  approaching  the  level  of  the 
papilla,  the  outer  root-sheath,  which  farther  above  consists  of  numerous  layers, 
rapidly  diminishes  in  thickness  until,  on  the  sides  of  the  papilla,  it  is  reduced  to  a 
single  row  of  low  columnar  cells. 

The  inner  root-sheath,  which  is  best  developed  over  the  middle  third  of  the 
hair-root  and  fades  away  on  reaching  the  upper  third,  includes  three  layers.  The 
outer,  known  as  Henle1  s  layer,  consists  of  a  single  row  of  flat  polygonal  cells,  often 
partially  separated  by  oval  spaces.  Their  nuclei  are  very  indistinct  or  invisible 


FIG.  1157. 


Theca  folliculi 


Middle  layer 


Henle's  layer 

of  inner  root-sheath 


Hf*    Outer  root-sheath 

gkr~. 


Transverse  section  of  hair-follicle,  showing  hair  surrounded  by  internal  and  external  root-sheaths.    X  285. 

within  the  cornified  cytoplasm.  The  middle  or  Huxley' s  layer,  also  horny  in 
nature,  often  comprises  only  one  stratum  of  nucleated  cuboidal  cells,  but  in  the 
thicker  hairs  two  or  even  three  rows  of  irregularly  interlocked  cells  may  be  present. 
The  third  layer,  known  as  the  sheath  cuticle,  resembles  the  external  coat  of  the  hair, 
against  which  it  lies,  in  being  extremely  thin  and  composed  of  flat  horny  plates. 
The  latter,  however,  are  always  nucleated  and  so  disposed  that  they  are  opposed  to 
the  serrations  of  the  thicker  hair-cuticle. 

Traced  towards  the  bottom  of  the  follicle,  the  root-sheaths  and  the  hair,  which  above  are 
sharply  defined  from  one  another,  become  more  and  more  alike  until,  in  the  immediate  vicinity 
of  the  hair-papilla,  they  blend  into  a  still  imperfectly  differentiated  mass  of  cells.  The  deepest 
elements  of  this  complex,  however,  are  cuboidal  or  low  columnar  and  form  an  uninterrupted 
tract  over  the  papilla,  continuous  with  the  outermost  cells  of  the  outer  root-sheath.  It  is  from 
the  proliferation  of  these  deepest  cells  that  the  formative  material,  or  matrix,  is  provided 
to  meet  the  requirements  of  growth  and  replacement  of  the  hairs.  Without  anticipating  the 
account  of  the  detailed  changes  described  in  connection  with  the  development  of  the  hair 
(page  1401),  it  may  be  here  noted  that  of  the  three  parts  of  the  hair,  the  medulla  is  produced  by 

88 


1394 


HUMAN   ANATOMY. 


FIG.  1158, 


the  cells  overlying  the  summit  of  the  papilla,  while  those  converted  into  the  cortical  substance, 
cuticle  and  inner  root-sheath  occupy  the  sides  of  the  papilla  and  deepest  part  of  the  follicle. 

With  few  exceptions,  the  hair  follicles  are  associated  with  two  or  more 
sebaceous  glands,  rarely  with  only  one,  the  ducts  of  which  open  into  the 
sac  in  the  vicinity  of  the  neck.  The  glands  usually  lie  on  the  side  towards  which 
the  hair  inclines,  but  sometimes,  especially  in  the  case  of  the  smaller  hairs,  they  may 
completely  surround  the  follicle.  Since  these  glands  are  outgrowths  from  the  same 
tissue  that  lines  the  follicles,  their  ducts  pierce  the  outer  root-sheath,  bringing  their 
oily  secretion  into  direct  relation  with  the  hairs. 

The  structure  of  the  sebaceous  glands  is  described  with  the  cutaneous  glands 
(page  1397). 

Most  of  the  larger  hair-follicles,  particularly  those  of  the  scalp,  are  provided  with 
ribbon-like  bundles  of  involuntary  muscle,  called  the  arrectores  pilorum  in  recog- 
nition of  their  effect  on  the  hairs.  They  arise  from  the  superficial  part  of  the  corium, 

passobliquely  downward  to  be  inserted 
into  the  sheath  of  the  hair-follicle  near 
the  junction  of  corium  and  subdermal 
tissue  and  on  the  side  corresponding 
with  the  inclination  of  the  hair  and 
the  situation  of  the  sebaceous  glands. 
Since  the  latter  are  closely  embraced 
by  the  muscular  bands,  contraction  of 
the  muscles  exerts  pressure  upon  the 
glands  and  facilitates  the  discharge  of 
their  secretion  {sebum} — hence  these 
muscles  are  sometimes  also  designated 
expressores  sebi.  The  effect  of  con- 
traction of  the  arrectores  pilorum  is 
oftenconspicuouslyseen  on  the  surface 
in  the  condition  known  as  "goose- 
flesh"  (Vw/'/.ytfw.f^TzVm),  where  the  hairs 
and  surrounding  tissue  appear  to  be 
unusually  elevated  owing  to  the 
upward  pull  on  the  hair-follicles  and 
the  consequent  erection  of  the  hairs 
in  the  opposite  direction. 

The  blood-vessels  supplying 
the  hair-follicle,  which  in  a  sense  con- 
stitute a  special  system  for  each  sac,  include  the  capillary  loops  ascending  within  the 
hair-papilla  and  the  net-work  of  capillaries  surrounding  the  follicle  immediately  outside 
the  glassy  membrane.  The  first  are  derived  from  a  small  special  twig  that  ascends 
to  the  follicle,  and  the  second  from  the  subpapillary  net-work  of  the  corium.  With 
the  exception  of  those  draining  the  papilla,  which  are  tributary  to  the  deeper  stc-ms, 
the  veins  join  the  subpapillary  plexus. 

The  nerves  distributed  to  the  follicles  follow  a  fairly  definite  arrangement.  As 
shown  by  Retzius,  usually  each  hair-sac  is  supplied  by  a  single  fibre,  sometimes  by 
two  or  more,  which  approaches  the  follicle  immediately  below  the  level  of  the  mouth 
of  the  sebaceous  glands.  After  penetrating  the  fibrous  sheath  as  far  as  the  glassy 
membrane,  the  nerve-fibre  separates  into  two  divisions  that  encircle  more  or  less 
completely  the  follicle  and  on  the  opposite  side  break  up  into  numerous  fibrillre 
constituting  a  terminal  arborization.  The  nerve-endings  usually  lie  on  the  outer 
surface  of  the  glassy  membrane  within  the  middle  third  of  the  follicle  and  only 
exceptionally  are  found  within  the  outer  root-sheath  or  the  hair-papilla. 

THE  NAILS. 

The-  nails  (unties),  the  horny  plates  overlying  the  ends  of  the  dorsal  surfaces  of 
the  fingers  and  toes,  correspond  to  the  (-laws  and  hoofs  of  other  animals  and,  like 
them,  are  composed  exclusively  of  epithelial  tissue.  They  are  specializations  of  the 


Papillary 


Portion  of  section  of  injected  scalp,  showing  capillary 
net-works  surrounding  hair-follicles  and  twigs  entering 
papillae.  X  20. 


THE    NAILS. 


1395 


epidermis  and,  therefore,  may  be  removed  without  mutilation  when  the  cuticle  is 
taken  off  after  maceration. 

The  entire  nail-plate  is  divided  into  the  body  (corpus  unguis),  which  includes 
the  exposed  portion,  and  the  root  (radix  unguis),  which  is  embedded  beneath  the 
skin  in  a  pocket-like  recess,  the  nail-groove  (sulcus  unguis).  The  modified  skin 
supporting  the  nail-plate,  both  the  body  and  the  root,  constitutes  the  nail-bed 
(solum  unguis),  the  cutaneous  fold  overlying  the  root  being  the  nail-wall  (vallum 
unguis). 

The  sides  of  the  quadrilateral  nail-plate  are  straight  and  parallel  and  at  their 
distal  ends  connected  by  the  convex  free  margin  (margo  liber)  that  projects  for  a 
variable  distance  beyond  the  skin.  The  proximal  buried  border  (margo  occultus)  is 
straight  or  slightly  concave,  more  rarely  somewhat  convex,  and  often  beset  with 
minute  serrations  (Brunn).  Both  surfaces  of  the  transversely  arched  nail  are  smooth 
and  even,  with  the  exception  of  the  longitudinal  parallel  ridges  that  often  mark  the 
upper  aspect.  Inspection  of  the  latter  during  life  shows  color-zones,  the  translu- 
cent whitish  crescent  formed  by  the  projecting  portion  of  the  nail  being  immediately 
followed  by  a  very  narrow  yellow  band  that  corresponds  to  the  line  along  which  the 
stratum  corneum  of  the  underlying  skin  meets  the  under  surface  of  the  plate.  The 

FIG.  1159. 
ABC 


Distal  portions  of  fingers,  showing  relations  of  nail ;  A  was  drawn  from  living  subject ;  B  atid  C  are  lateral  and 
under  veiws  respectively  of  inner  surface  of  cuticle  with  nail ;  nothing  but  the  epidermal  structures  are  present,  the 
cuticle  and  nail  having  been  removed  together,  a,  i>,  distal  and  proximal  borders  of  nail ;  c,  under  surface  of  nail ; 
d,  nail  in  section  ;  e,  line  of  deflection  of  cuticle  to  under  surface  of  nail ;  f,  lunula ;  g,  nail-wall ;  A,  cuticle  in  section. 

succeeding  and  larger  part  of  the  nail  is  occupied  by  the  broad  pink  zone  which  owes 
its  rosy  tint  to  the  blending  of  the  color  of  the  blood  in  the  underlying  capillaries 
with  that  of  the  horny  substance.  On  the  thumb  constantly,  but  on  the  fingers  often 
only  after  retraction  of  the  cuticle,  is  seen  a  transversely  oval  white  area,  the 
so-called  lunula,  which  marks  the  position  of  the  underlying  matrix.  Additional 
white  spots,  irregular  in  position,  form  and  size,  are  sometimes  seen  as  temporary 
markings. 

The  thickness  of  the  nail-plate — greatest  on  the  thumb  and  large  toe  and  least 
on  the  last  digits — diminishes  towards  the  sides,  but  in  the  longitudinal  direction, 
between  the  lunula  and  the  free  margin  of  the  nail,  is  fairly  uniform  ;  beneath  the 
white  area,  however,  the  under  surface  of  the  nail  shelves  off  towards  the  buried 
border,  where  it  ends  in  a  sharp  edge. 

Structure. — The  substance  of  the  nail-plate  (stratum  corneum  unguis)  consists 
entirely  of  flattened  horny  epithelial  cells,  very  firmly  united  and  containing  the 
remains  of  their  shrunken  nuclei.  These  cornified  scales  are  disposed  in  lamellae, 
which,  in  transverse  section,  pursue  a  course  in  general  parallel  with  the  dorsal  sur- 
face. In  nails  which  possess  the  longitudinal  ridges,  however,  the  latter  coincide 
with  an  upward  arching  of  the  lamellae  dependent  upon  the  conformation  of  the 
nail  matrix  (Brunn).  In  longitudinal  section  the  lamellation  is  oblique,  extending 


1396 


HUMAN   ANATOMY. 


from  above  downward  and  forward,  parallel  to  the  shelving  under  surface  beneath  the 
white  area  that  rests  upon  the  matrix.  Minute  air-vesicles,  imprisoned  between  the 
horny  scales,  are  constant  constituents  of  the  nail-substance.  When  these  occur  in 
unusual  quantities,  they  give  rise  to  the  white  spots  in  the  nail  above  mentioned. 

Corresponding  respectively  to  the  colored  zones — the  white,  rosy  and  yellow — 
seen  on  the  dorsal  surface  of  the  nail,  the  nail-bed  is  divided  into  a  proximal, 

FIG.  1160. 


Subcutaneous 


Stratum  ger 
Stratu 


Corium  ^^VY';     ; 
of  nail-bed       /' ..--^ './'.-''; 


•V>*s  Transformation 
-'•'.,     zone 


•Matrix 


*•.•'•/•*  ••:• 

Longitudinal  section  of  proximal  part  of  nail  lying  within  the  nail  groove.    X  30. 


a  middle  and  a  distal  region,  each  of  which  exhibits  structural  differences.  The 
most  important  of  these  regions  is  the  proximal,  known  as  the  matrix,  which  lies 
beneath  the  white  area  and  alone  is  concerned  in  the  production  of  the  nail. 

The  corium  of  the  nail-bed  varies  in  the  different  regions  in  the  arrangement  and  size  Of  its 
elevations.  Within  the  proximal  third  of  the  matrix,  these  elevations  occur  in  the  form  of  low 
papillae,  which  decrease  in  height  and  number  until  they  disappear,  a  smooth  field  occupying 
the  middle  of  the  matrix.  This  even  field  is  succeeded  by  one  possessing  closely  set,  low, 
narrow  longitudinal  ridges,. that  at  the  distal  margin  of  the  lunula  suddenly  give  place  to  more 
pronounced,  but  less  numerous  broader,  linear  elevations.  These  continue  as  far  as  the  distal 
end  of  the  nail-bed  and  are  then  replaced  by  papillae.  Owing  to  the  strong  fibrous  bands  and 
the  absence  of  the  usual  layer  of  fatty  subdermal  tissue,  the  corium  of  the  nail-bed  is  closely 
attached  to  the  bone.  The  fibrous  reticulum  formed  by  the  interlacing  of  the  longitudinal  with 
the  vertical  bundles  contains  few  elastic  fibres,  since  these  are  entirely  wanting  beneath  the  body 
of  the  nail  and  only  present  in  meagre  numbers  within  the  matrix. 

In  view  of  its  genetic  activity,  the  relations  of  the  epidermis  underlying  the  nail  are  of 
especial  interest.  While  the  stratum  germinativum  of  the  skin  covering  the  finger  tip  passes 
directly  and  insensibly  onto  the  nail-bed,  the  entire  extent  of  which  it  invests  (stratum  Kermina- 
tivum  im^uis),  the  stratum  corneum  ends  on  reaching  the  under  surface  of  the  nail-plate,  the  line 
of  apposition  corresponding  to  the  narrow  yellow  zone  which  defines  the  distal  boundary  ot  the 
rosy  area.  Beneath  the  latter,  therefore,  the  epidermis  of  the  nail-bed  consists  of  the  stratum 
germinativum  alone,  which,  without  cornification  of  any  of  its  cells,  rests  against  the  under  sur- 
face of  the  nail.  Beneath  the  white  zone,  that  is,  within  the  matrix,  the  epidermis  includes  a  half 
dozen  or  more  layers  of  the  usual  elements  of  the  stratum  germinativum,  surmounted  by  a  like 
number  of  strata  of  cells  distinguished  by  a  peculiar  brownish  color.  On  reaching  tin-  nail  these 
modified  epithelial  elements,  which  appear  white  by  rellected  light,  are  not  circumscribed,  but 
pass  over  into  the  substance  of  the  nail,  into  the  constituent  cells  of  which  they  are  directly  con- 
verted. Their  cytoplasm  presents  a  marked  fibrillation  to  which,  according  to  Brunn,  the  light 
appearance  of  the  cells  is  referable  as  an  interference  phenomenon  and  not  as  a  true  pigmenta- 
tion. This  peculiarity  of  the  cells,  coupled  with  the  relatively  small  si/e  of  subjacent  capillaries, 


THE   CUTANEOUS    GLANDS. 


1397 


probably  accounts  for  the  tint  distinguishing  the  white  area.  Since  the  transformation  of  the 
cells  of  the  stratum  germinativum  into  those  of  the  nail-plate  is  confined  to  the  matrix,  it  is  evi- 
dent that  the  continuous 

FIG.  1161. 

Nail-plate 


Nail-bed 


growth  of  the  nail  takes 
place  along  the  floor  and 
bottom  of  the  nail-groove, 
the  last  formed  increment 
of  nail-substance  pushing 
forward  the  previously  dif- 
ferentiated material  and 
thus  forcing  the  nail  to- 
wards the  end  of  the  digit. 
The  relation  of  the  epi- 
dermis of  the  nail-wall  to 
the  substance  of  the  plate 
is  one  of  apposition  only, 
production  of  the  nail  oc- 
curring in  no  part  of  the 
fold.  Over  the  greater 
extent  of  the  latter  all  the 
typical  constituents  of  the 
cuticle  are  represented,  but 
within  the  most  proximal 
portion  the  stratum  germi- 
nativum alone  is  present, 
the  stratum  corneum  fad- 
ing away.  Where  the 
horny  layer  exists,  it  rests 
directly  upon  the  nail,  but 
is  differentiated  from  the 
latter  by  being  less  dense 
and  by  its  response  to 

stains.  As  the  nail  leaves  the  groove,  a  part  of  the  stratum  germinativum  of  the  nail-wall  is 
prolonged  distally  for  a  variable  distance  over  the  dorsal  surface  of  the  nail-plate  as  a  delicate 
membranous  sheet,  the  eponychium,  which  usually  ends  in  a  ragged  abraded  border. 


Stratum  corneum 
and 

Stratum 

germinativum 

of  nail-wall 


Eponychium 
Margin  of  nail 


Corium 


Transverse  section  of  nail- wall  and  adjacent  part  of  nail-plate  and  nail-bed.     X  90. 


THE  CUTANEOUS  GLANDS. 

These  structures  include  two  chief  varieties,  the  sebaceous  and  the  sweat 
glands,  together  with  certain  modifications,  as  the  ceruminous  glands  within  the 
external  auditory  canal,  the  circumanal  glands,  the  tarsal  and  ciliary  glands 
within  the  eyelid  and  the  mammary  glands.  In  all  the  epithelial  tissues — the 
secreting  elements  and  the  lining  of  the  ducts — are  derivatives  of  the  ectoblast 
and,  therefore,  genetically  related  to  the  epidermis. 

THE  SEBACEOUS  GLANDS. 

Although  these  structures  (glandulae  sebacae)  are  chiefly  associated  with  the 
hair-follicles,  in  which  relation  they  have  been  considered  (page  1394),  sebaceous 
glands  also  occur,  if  less  frequently,  independently  and  in  those  parts  of  the  skin  in 
which  the  hairs  are  wanting,  as  on  the  lips,  angles  of  the  mouth,  prepuce  and  labia 
minora.  The  size  of  these  glands  bears  no  relation  to  that  of  the  hairs,  since  among 
the  smallest  (.2-.4  mm.)  are  those  on  the  scalp.  The  largest,  from  .5-2.0  mm., 
are  found  on  the  mons  pubis,  scrotum,  external  ear  and  nose.  Conspicuous  aggre- 
gations, modified  in  form,  occur  in  the  eyelid  as  the  Meibomian  glands. 

Depending  upon  the  size  of  the  glands  their  form  varies.  The  smallest  ones  are 
each  little  more  than  a  tubular  diverticulum,  dilated  at  its  closed  end.  In  those  of 
larger  size  the  relatively  short  duct  subdivides  into  several  expanded  compartments, 
which,  in  the  largest  glands,  may  be  replaced  by  groups  of  irregular  alveoli,  with 
uncertain  ducts  that  converge  into  a  short  but  wide  common  excretory  passage. 

Structure. — The  structural  components  of  these  glands  include  a  fibrous 
envelope,  a  membrana  propria  and  the  epithelium,  the  first  two  being  continuous 
with  the  corresponding  coverings  of  the  hair-follicle.  The  epithelium  continued 


1398 


HUMAN   ANATOMY. 


.  Mouth 
of  gland 


Alveoli 


Corium 


Sebaceous  glands  from  skin  covering  nose. 


into  the  ducts  and  alveoli  of  the  sebaceous  glands  is  directly  prolonged  from  the 
outer  root-sheath  of  the  epidermis,  where  associated  with  the  hair-follicles,  or  from 

the  epidermis  where  the  hairs 

FIG.  1162.  are  wanting.      The    periphery 

of  the  alveolus  is  occupied  by  a 
single,  or  incompletely  double, 
layer  of  flattened  and  imper- 
fectly defined  basal  cells,  that 
rest  immediately  upon  the  mem- 
brana  propria  and  are  distin- 
Duct  guished  by  their  dark  cytoplasm 

•?**e^»a  •••••  ««•,-•  and  outwardly  displaced  oval 

nuclei.      Passing    towards    the 

centre  of  the  alveolus,  the  next 

.... .     ./. ,  I  cejjs  contain  a  number  of  small 

" r~  '.'\  >  »^'  oil  drops  which,  with  each  suc- 

cessive row  of  cells,  become 
larger  and  appropriate  more 
and  more  space  at  the  expense 
of  the  protoplasmic  reticulum 
in  which  they  are  lodged.  In 
consequence,  the  cells  occupy- 
ing the  axis  of  the  alveoli,  which 
are  completely  filled  and  with- 
out a  lumen,  contain  little  more 
than  fat.  As  the  cells  are 
escaping  from  the  glands  they 
x  60.  lose  their  nuclei  and  individual 

outlines  and,  finally,  are  merged 

as  debris  into  the  secretion,  or  sebum,  with  which  the  hairs  and  skin  are  anointed. 

The  necessity  for  new  cells,  created  by  the  continual  destruction  of  the  glandular 

elements  that  attends  the  activity  of  the  sebaceous 

glands,  is  met  by  the  elements  recruited  from   the  FIG.  1163. 

proliferating  basal  cells,  which  in  turn  pass  towards 

the    centre    of    the    alveolus    and    so    displace    the 

accumulating  secretion. 

THE  SWEAT  GLANDS. 

These  structures  (glandulae  stidoriferae),  also 
called  the  sudoriparous  glands,  are  the  most  important 
representatives  of  the  coiled  glands  (glandulae  glomi- 
formes)  often  regarded  as  constituting  one  of  the  two 
groups  (the  sebaceous  glands  being  the  other)  into 
which  the  cutaneous  glands  are  divided.  They 
occur  within  the  integument  of  all  parts  of  the  body, 
with  the  exception  of  that  covering  the  red  margins  of 
the  lips,  the  inner  surface  of  the  prepuce  and  the  glans 
penis.  They  are  especially  numerous  in  the  palms  and  soles,  in  the  former  locality 
numbering  more  than  noo  to  the  square  centimetre  (Horschelmann),  and  fewest  on 
the  back  and  buttocks,  where  their  number  is  reduced  to  about  60  to  the  square 
centimetre  ;  their  usual  quota  for  the  same  area  is  between  two  and  three  hundred. 

Modified  simple  tubular  in  type,  each  gland  consists  of  two  chief  divisions,  the 
body  (corpus)  or  gland-coil,  the  tortuously  wound  tube  in  which  secretion  takes 
place,  and  the  c.vcrrtorv  duct  (ductus  sudoriferus')  which  opens  on  the  surface  of  the 
skin,  exceptionally  into  a  hair-follicle,  by  a  minute  orifice,  the  sweat  pore  (porus 
sudoriferus),  often  distinguishable  with  the  unaided  eye. 

The  body  of  the  gland,  irregularly  spherical  or  flattened  in  form  and  yellowish 
red  in  color,  consists  of  the  windings  of  a  single,  or  rarely  branched,  tube  and  com- 
monly occupies  the  deeper  part  of  the  corium,  but  sometimes,  as  in  the  palm  and 


I'mm  ahvoli  of  sebaceous glan 
showing    irtiou'aU'il    protoplasm  due   to 
presence  of  oil  droplets,    x  700. 


THE   CUTANEOUS    GLANDS. 


1399 


Stratum 
"corneum 


S.  lucidum 
S.  granulosum 

-S.germinativum 


Duct  of 
sweat-gland 

Corium 


scrotum,  lies  within  the  subdermal  connective  tissue.  The  coiled  portion  of  the 
gland  is  not  entirely  formed  by  the  secretory  segment,  since,  as  shown  by  the  recon- 
structions of  Huber,  about  one  fourth  is  contributed  by  the  convolutions  of  the  first 
part  of  the  duct. 

On  leaving  the  gland-coil,  in  close  proximity  to  the  blind  end  of  the  gland,  the 
duct  ascends  through  the  corium  with  a  fairly  straight  or  slightly  wavy  course  as 
far  as  the  epidermis.  On  entering  the  latter  its  further  path  is  marked  by  conspicu- 
ous cork-screw-like  windings,  which,  where  the  cuticle  is  thick  as  on  the  palm,  are 
close  and  number  a  dozen  or  more  and  terminate  on  the  surface  by  a  trumpet-shaped 
orifice,  the  sweat-pore. 

In  its  course  through  FlG-  Il64- 

the  corium  the  duct 
never  traverses  a 
papilla  or  ridge,  but 
always  enters  the  cuti- 
cle between  these  ele- 
vations. On  the  palms 
and  soles,  where  the 
pores  occupy  the  sum- 
mit of  the  cutaneous 
ridges,  the  ducts  enter 
the  cuticle  between  the 
double  rows  of  papillae. 
Structure. — The 
secreting  portion  of 
the  gland-coil,  called 
the  ampulla  on  account 
of  its  greater  diameter, 
possesses  a  wall  of 
remarkable  structure. 
The  thin  external 
sheath,  composed  of  a 
layer  of  dense  fibrous 
tissue  and  elastic  fibres, 
supports  a  well  defined 
membrana  propria. 
Immediately  within  the 
latter  lies  a  thin  but 
compact  layer  of  invol- 
iintary  muscle  whose 
longitudinally  disposed 
spindle  -  shaped  ele- 
ments in  cross-section 
appear  as  a  zone  of 
irregularly  nucleated 
cells  that  encircle  the  secreting  epithelium  and  displace  it  from  its  customary  position 
against  the  basement  membrane.  This  muscular  tissue  enjoys  the  distinction,  sharing 
.it  with  the  muscle  of  the  iris,  of  being  developed  from  the  ectoblast.  The  secreting 
cells  constitute  a  single  row  of  low  columnar  epithelial  elements,  that  lie  internal  to 
the  muscle  and  surround  the  relatively  large  lumen.  Their  finely  granular  cytoplasm 
contains  a  spherical  nucleus,  situated  near  the  base  of  the  cell,  and  in  certain  of  the 
larger  glands,  as  the  axillary,  includes  fat  droplets  and  pigment  granules.  These 
are  liberated  with  the  secretion  of  the  gland  and  when  present  in  unusual  quantity 
account  for  the  discoloration  produced  by  the  perspiration  of  certain  individuals.  In 
the  case  of  the  ceruminous  glands,  the  amount  of  oil  and  pigment  is  constantly  great 
and  confers  the  distinguishing  characteristics  on  the  ear-wax. 

The  sudden  and  conspicuous  reduction  in  the  size  of  the  tube  which  marks  the 
termination  of  the  secreting  segment  and  the  beginning  of  the  duct,  is  accompanied 
by  changes  in  the  structure  of  its  wall.  In  addition  to  a  reduction  of  its  diameter  to 


f-S?''' .,-  Fat-cells 


Coiled  part  of 
sweat-gland 


Section  of  skin  from  palm,  showing  different  parts  of  sweat-glands  extending  from 
surface  into  tela  subcutanea.     X  65. 


1400 


HUMAN   ANATOMY. 


Muscle-cell 
Secreting-cells 

Parts  of  duct 


one-half  or  less  of  that  of  the  ampulla,  the  duct  loses  the  layer  of  muscle  and 
becomes  flattened,  with  corresponding  changes  in  the  form  of  its  lumen.  The  single 
row  of  secreting  elements  is  replaced  by  an  irregular  double  or  triple  layer  of 
cuboidal  cells,  which  exhibit  an  homogeneous  zone,  sometimes  described  as  a 
cuticle,  next  the  lumen.  On  entering  the  epidermis,  the  duct  not  only  loses  its 
fibrous  sheath  and  membrana  propria,  but  the  epithelial  constituents  of  its  wall  are 
soon  lost  among  the  cells  of  the  stratum  gerfninativum,  so  that  its  lumen  is  continued 
to  the  surface  as  a  spiral  cleft  bounded  only  by  the  cornified  cells  of  the  cuticle. 

Apart  from  mere  variations  in  size,  certain  glands — the  circumanal,  the  ciliarv 
and  the  ceruminous — depart  sufficiently  from  the  typical  form  of  the  coiled  glands  to 
entitle  them  to  brief  notice.  The  circumanal  glands,  lodged  chiefly  within  a 
zone  from  12-15  mm-  wide  and  about  the  same  distance  from  the  anus,  are  not 

all  the  same,  but  include, 
according  to  Huber,  four 
varieties.  In  addition  to  ( i ) 
the  usual  sweat  glands  and 
(2)  some  (Gay's)  of  excep- 
tional size,  (3)  others  have 
relatively  straight  ducts  that 
end  in  expanded  saccules, 
from  which'  secondary  alveoli 
arise  ;  finally  (4)  branched 
glands  of  the  tubo-alveolar 
type  are  present.  The  cili- 
ary glands  (Moll's )  of  the 
eyelid  are  not  typical  coiled 
structures,  but  belong  to 
the  branched  tubo-alveolar 
groups.  The  ceruminous 
glands,  distinguished  by 
the  large  amount  of  oil  and 
pigment  mingled  with  their 
secretion,  are  likewise  refer- 
able to  the  branched  tubo- 
alveolar  type. 

The  blood-vessels  of 
the  sweat  glands  include 
arterial  twigs  given  off  from 
the  cutaneous  rete,  a  capillary 
net-work  outside  the  mem- 
brana propria,  best  developed 
within  the  coiled  portion  of  the  tube,  and  the  veins  that  join  the  deeper  plexus 
within  the  corium. 

The  nerves  are  especially  numerous  and  consist  of  nonmedullated  sympathetic 
fibres  that  traverse  the  fibrous  sheath  and  form  a  close  plexus  on  the  outer  surface 
of  the  membrana  propria.  From  this  net-work  fibrillae  penetrate  the  basement 
membrane  and  end  in  close  apposition  with  the  gland-cells  and  muscle-elements. 
Their  termination  on  the  secreting  cells  is,  according  to  Arnstein,  in  the  form  of 
peculiar  endings  consisting  of  groups  and  clusters  of  minute  terminal  knobs  with 
which  the  nerve  fibrillae,  without  or  after  division,  are  beset. 

THE  DEVELOPMENT  OF  THE  SKIN  AND  ITS  APPENDAGES. 

The  Skin.— The  integument  consists  of  two  genetically  distinct  parts — the 
t-fiillu'/inni  (epidermis)  developed  from  the  ectoblast,  and  the  connective  tissue 
(corium  and  tela  subcutanea)  from  the  mesoblast.  During  the  earliest  stages  of 
development  the  ectoblast  is  represented  by  a  single  layer  of  cells,  which,  by  the  end 
of  the  first  month,  is  in  places  reinforced  by  an  external  second  layer,  that  by  the 
seventh  week  has  appeared  over  the  entire  surface.  This  double  layer  now  consists 


Parts  of  coiled 

secreting 

segment 


Muscle-cells 


T 


Section  of  deeper  coiled  portion  of  sweat-gland.     X  325. 


DEVELOPMENT   OF   SKIN    AND   APPENDAGES. 


1401 


FJG.   1166. 


Sections  of  developing 
skin,  showing  earliest  stages 
in  formation  of  hair-follicles; 
in  D  epithelial  cylinder  is 
invading  mesoblast.  X  90. 


of  a  deeper  row  of  cuboid  or  low  columnar  cells,  covered  by  a  superficial  sheet, 

known  as  the  epitrichium,  composed  of  flattened  elements  often  lacking  in  definition, 

and  nuclei.      During  the  succeeding  weeks  the  epitrichial  cells  become  swollen  and 

vesicular  and   differentiated   from   the   underlying  elements,   which   meanwhile  are 

engaged    in    producing    the    epidermis.      The    epitrichium 

persists  until  the  sixth  month,  when  it  becomes  loosened  and 

is  cast  off.      During  the  third  and  fourth  months  the  ectoblastic 

cells   have   so   multiplied,   that   from   four  to  five  layers  are 

present,  those  next  the  mesoblast  being  columnar  and  rich  in 

protoplasm,    while    the   more    superficial    are    irregular   and 

clearer.      By  the  middle  of   the   fifth   month,   by  which  time 

the  layers  have  increased  to  almost  a  dozen,  the  outer  cells 

become   horny  and  assume   the   characteristics  of  a  stratum 

corneum,  while  the  deepest  ones  represent  the  stratum  germi- 

nativum,  with  an  intervening  transitional  zone.      About  the 

sixth  month  desquamation   of   the   surface   cells   begins,   the 

discarded  epitrichial  and  other  scales  mingling  with  the  secre- 
tion from  the  sebaceous  glands,  which  meanwhile  have  been 

developed,  as  constituents  of  the  white  unctuous  coating,  the 

vernix  caseosa  (smegraa  embryonum),  that  covers  the  surface 

of  the  fcetus,   especially  in   the  folds  and   creases.      During 

the  last  weeks  of  gestation  the  epidermis  acquires  considerable 

thickness  and  a  sharper  differentiation  of  its  component  strata. 
The  connective  tissue  part  of  the  skin  is  developed  as 

a  superficial  condensation  of  the  mesoblast,  that  during  the 

first  month  consists  of  closely  placed  spindle  cells.      Coinci- 

dently  with  the  appearance   of    the   fibrous    fibrillae,    in   the 

third  month,  differentiation  takes  place  within  the  condensed 

mesoblastic  tissue,  which  so  far  exists  as  a  uniform  zone,  into 

a  superficial   and    more    compact   layer   and    a    deeper   and 

looser  one  ;    the  former   becomes   the  corium  and  the  latter  the   tela  subcutanea. 

Within  the  last  layer  soon  appear  larger  or  smaller  groups  of  round  cells  in  which 

oil  drops,  at  first  minute  and  then  of  increasing  diameter,  indicate  the  beginning 

of  their  conversion  into  adipose  tissue.      By  the  sixth  month  the  panniculus  adiposus 

is  established.      About   the  fifth   month   the  line   marking  the   junction   of   cuticle 

and   corium   becomes  uneven   in   consequence  of  the   development  of  the  papillae 

and  ridges  of  the  corium  and  the  attendant  invasion  of  the  epidermis.      Certain  of 

the  mesoblastic  cells  are  transformed  into  the  component  elements  of  the  involuntary 

muscle  that  occurs  either  associated  with  the  hair  follicles  as  the  arrectores  pilorum, 

or  as  the  more  extended  tracts  of  the  dartos. 
The  Hairs. — The  primary  development 
of  the  hair  begins  about  the  end  of  the  third 
month  of  fcetal  life  as  localized  proliferations 
of  the  epidermis.  In  section  these  appear  as 
lenticular  thickenings  and  on  the  surface  as 
slight  projections.  Very  soon  solid  epithelial 
cylinders  sprout  from  the  deeper  surface  of 
these  areas  and  invade  the  subjacent  corium 
to  form  the  anlages  of  the  hair-follicles.  The 
original  uniform  outline  of  these  processes  is 
early  replaced  by  a  flask-shaped  contour  in 
consequence  of  the  enlargement  of  their  ends 
which  in  their  growth  surround  connective 
tissue  processes  to  form  the  hair-papilla. 

The  embryonal  connective  tissue  immediately  surrounding  the  epidermal  ingrowth 

differentiates  into  the  fibrous  sheath  and  the  glassy  membrane. 

Meanwhile  and  even  before  the  formation  of  the  papilla  the  epithelial  contents  of 

the  young  follicles  differentiate  into  an  axial  strand  of  spindle  cells  that  later  undergo 

keratinization    and    become    the    hair-shaft   that    grows    by    subsequent    additions 


FIG.  1167. 


-follicle 


Papilla 


Developing  skin,  showing  later  stages  of  forma- 
tion of  hair-follicles;  surrounding  mesoblast  is 
forming  hair-papilla  and  fibrous  sheath  of  follicle. 
X  90. 


1402 


HUMAN   ANATOMY. 


FIG.  1168. 


from  the  matrix  surmounting  the  papilla.  In  addition  to  forming  the  outer  root- 
sheath  the  peripheral  elements  contribute  the  matrix-cells  that  occupy  the  fundus  of 
the  follicle  and  surround  the  papilla.  The  cells  covering  the  summit  and  adjacent 
sides  of  the  papilla  are  converted  into  elongated  spindles  that  later  gradually  become 
horny  and  assume  the  characteristics  of  the  cortical  substance  of  the  hair.  When 
present,  the  medulla  is  developed  by  the  transformation  of  the  cells  occupying  the 
summit  of  the  papilla,  which  enlarge,  become  less  granular  and  grow  upward  as  an 
axial  strand  that  invades  the  chief  substance  of  the  hair  and  accumulates  kerato- 
hyalin  within  its  cells.  At  first  present  as  minute  drops,  this  substance  increases 
in  quantity  until  it  occupies  the  cells  in  the  form  of  large  vesicles.  The  subsequent 
disappearance  of  these,  followed  by  shrinkage  of  the  cells  and  the  introduction  of 
air,  completes  the  differentiation  of  the  medulla.  The  pigment  particles,  which 
appear  later,  are  first  evident  in  the  hair-bulb  and  probably  arise  within  the  epithelial 
tissue.  The  elements  of  the  hair-cuticle  and  of  the  inner  root-sheath  are  differentiated 
from  the  matrix-cells  at  the  sides  of  the  papilla.  The  tall  columnar  elements  become 
elongated  and  converted  into  the  cornified  plates  of  the  cuticle  both  of  the  hair  and 

of  the  inner  root-sheath.  The  layers 
of  Huxley  and  of  Henle  are  derived 
from  cells  that  soon  exhibit  granules  of 
keratohyalin,  so  that  on  reaching  the 
level  of  the  summit  of  the  papilla  the 
process  of  cornification  has  been  estab- 
lished. This  is  especially  marked  in 
the  elements  of  Henle' s  layer,  in  which 
the  deposit  takes  the  form  of  a  longi- 
tudinal fibrillation. 

The  growth  of  the  hair  takes 
place  exclusively  at  the  lower  end  of 
its  bulb,  where,  so  long  as  the  hair 
grows,  the  conversion  of  the  matrix- 
cells  into  the  substance  of  the  hair  is 
continuously  progressing.  By  this  pro- 
cess the  substance  already  differentiated 
is  pushed  upward  by  the  cells  under- 
going transformation  and  these  in 
turn  are  displaced  by  the  succeeding 
elements.  In  this  way,  by  the  addition 
of  new  increments  in  its  bulb,  the  hair  is  forced  onward  and,  in  the  case  of  those 
first  formed,  through  the  epidermis  that  still  blocks  the  mouth  of  the  follicle.  This 
eruption  begins  on  the  scalp  and  regions  of  the  eyebrows  about  the  fifth  foetal  month 
and  on  the  extremities  about  a  month  later. 


Sebaceous  gland 


Root-sheath— 


Bulb 


Papilla- 


Developing  skin,  showin 
is  now 


ing  later  stage  of  hair-follicle;  hair 
differentiated. 


X  80- 


The  hairs  covering  the  foetus  are  soon  shed,  during  the  last  weeks  of  gestation  and  immedi- 
ately following  birth,  and  are  replaced  by  the  stronger  hairs  of  childhood.  These  latter,  too,  are 
continually  falling  out  and  being  renewed  until  puberty,  when  in  many  localities,  as  on  the  scalp, 
face,  axilla  and  external  genital  organs,  they  are  gradually  replaced  by  the-  much  longer  ami 
thicker  hairs  that  mark  the  advent  of  sexual  maturity.  Even  after  attaining  tlu-ir  mature  growth, 
the  individual  life  of  the  hairs  is  limited,  those  on  the  scalp  probably  retaining  their  vitality  for 
from  two  to  four  years  and  the  eyelashes  for  only  a  few  months  (Pincus). 

During  the  years  of  greatest  vitality  not  only  are  the  discarded  hairs  replaced  by  new  ones, 
but  the  actual  number  of  hairs  may  increase  in  consequence  of  the  development  of  additional 
follicles  from  the  epidermis  after  the  manner  of  the  primary  formation.  When  from  age  or  other 
cans,  the  hair-follicles  loose  their  productive  activity  and,  therefore,  are  no  longer  capable  of 
replacing  the  atrophic  hairs,  more  or  less  conspicuous  loss  of  hair  results,  whether  only  tem- 
porary or  permanent  evidently  depending  upon  the  recuperative  powers  of  the  follicles. 

The  change  of  hair  that  is  continually  and  insensibly  occurring  in  man,  in  contrast  to  the 
conspicuous  periodic  shedding  of  the  coat  seen  in  other  animals,  includes  the  atrophy  of  the  old 
hair  on  the  one  hand,  and  the  development  of  the  new  on  the  other. 

The  earliest  manifestations  of  this  atrophy,  as  seen  in  longitudinal  sections  of  the  hair- 
follicle,  are  reduction  in  the  sixe  and  differentiation  of  the  mass  of  matrix-cells  at  the  bottom  of 
the  follicle  and  the  diminution  of  the  hair-papilla.  The  progressive  reduction  of  the  matrix  is 


DEVELOPMENT  OF  SKIN  AND  APPENDAGES. 


1403 


FIG.  1169. 


accompanied  by  the  production  of  a  club-shaped  enlargement  of  the  hair,  between  which  and 

the  shrunken  matrix  a  strand  of  atrophic  epithelial  cells  for  a  time  remains.    With  the  continued 

progress  of  these  changes,  the  root  of  the  club-hair,  as  the  degenerating  hair  is  termed,  shortens 

so  that  the  bulbus  enlargement  recedes  from  the  bottom  of  the 

hair-sac,  until  it  lies  just  below  the  narrow  neck  of  the  follicle, 

where  it  remains  for  a  longer  or  shorter  period  until  the  hair 

is  dislodged  and  finally  discarded.     A   hair  that  has  fallen  out 

in  consequence  of  these  atrophic  changes  presents  well-marked 

differences  in   the  appearance  and   structure  of  its  root  from  a 

growing  hair  removed  by  force.     In  the  discarded  hair  the  root 

possesses  the  characteristic  club  shape,  with  contours  broken  by 

irregular  processes  composed  of  the  splintered  cortical  substance, 

which  alone  forms  the  terminal  bulb  that  is  always  solid  and  has 

neither  cuticle  nor  medulla. 

While  the  old  hair  is  still  lodged  in  the  upper  part  of  the 
follicle,  the  first  steps  towards  its  replacement  are  initiated  by  the 
stratum  germinativum  of  the  old  hair-sac.  Whether  surrounding 
a  new  papilla,  as  held  by  many,  or  capping  the  revived  original 
one  (Brunn),  the  deepest  follicle-cells  contribute  by  proliferation 
the  material  from  which  the  new  hair  is  developed  in  a  manner 
agreeing  essentially  with  that  in  which  its  predecessor  was  evolved. 


pilla 


Section  of  foetal  skin,  show- 
ing sebaceous  gland  developing 
from  hair-follicle.  X  90. 


FIG.  1170. 


The  Nails.— The  first  appearance  of  a  definite  nail- 
area  on  the  dorsum  of  the  distal  phalanx  is  seen  towards  the 
end  of  the  third  foetal  month  (Kolliker),  although  Zander 
has  described  a  local  thickening  of  the  epidermis  covering 
the  tip  of  the  digit  at  the  ninth  week.  By  the  fourth  month  the  nail-area  shows 
as  a  slightly  depressed  field  that  is  defined  proximally  and  laterally  by  a  curved 
swelling,  the  earliest  suggestion  of  the  nail-wall.  Distally  the  field  is  limited  by  a 
transverse  elevation.  Shortly  after  the  nail-area  has  been  thus  defined,  the  outer 
cells  of  its  stratum  germinativum  exhibit  deposits  of  keratohyalin  which,  by  the  end 
of  the  fourth  month,  lead  to  the  formation  of  a  thin  overlying  layer  of  nail-substance. 
For  a  time  this  gains  in  thickness  by  additions  to  its  under  surface  alone,  the  primary 
nail  being  produced  by  the  progressive  conversion  of  the  cells  of  the  stratum  granu- 
losum,  which  is  present  throughout  the  nail-area. 

At  this  stage  the  young  nail  lies  completely  buried  within  the  epidermis,  lying 
between  the  most  superficial  elements  of  the  epidermis  and  the  epitrichial  cells  above, 
and  the  deeper  layers  of  the  cuticle  below.  The  overlying  epithelial  mass,  composed 
of  the  epidermal  and  epitrichial  elements,  constitutes  the  eponychium,  the  remains 

of  which,  after  the  disappearance  of  its  middle  and 
distal  parts,  are  subsequently  seen  as  a  thin  mem- 
brane covering  the  proximal  part  of  the  nail-plate. 
As  yet  the  young  nail-plate  has  not  come  into 
relation  with  the  epidermis  of  the  nail-groove,  since 
it  is  still  confined  to  the  primitive  area.  But  during 
the  fifth  month  the  proximally  growing  root  invades 
more  and  more  the  sulcus  until  it  attains  its  definite 
relations  with  the  nail-wall.  Meanwhile  the  nail-bed 
beneath  the  developing  root  undergoes  thickening 
and  becomes  the  matrix,  while  the  cells  containing 
keratohyalin  gradually  disappear  from,  the  distal 
region  of  the  nail-area  in  consequence  of  their  com- 
pleted conversion  into  the  nail-substance.  Subse- 
quently these  cells  are  limited  to  the  proximal 
nail-producing  zone  of  the  matrix  from  which,  after 
the  initial  formation  of  the  primary  nail-substance, 
the  nail  alone  receives  the  additions  necessary  for  its 
continued  growth.  In  consequence  of  the  resulting 
forward  growth  the  nail  pushes  its  way  through  the  elevated  distal  boundary  of  the 
nail-field,  the  epithelium  lying  above  the  nail-plate  being  lost,  while  that  below  remains 
as  the  representative  of  the  sole-plates  that  are  well  marked  in  many  other  animals. 


Section  of  foetal  skin,  showing  develop- 
ing sweat-glands  ;  a,  is  less  advanced  than 
b  and  c.  X  100. 


1404  HUMAN   ANATOMY. 

The  Sweat  Glands. — The  development  of  these,  the  most  important  members 
of  the  group  of  coiled  glands,  begins  during  the  fifth  foetal  month  as  solid  epithelial 
sprouts  from  the  under  surface  of  the  epidermis.  At  first  cylindrical  in  form, 
these  processes  soon  acquire  a  club-shaped  lower  end  and  for  a  time  resemble 
developing  hair-follicles.  The  terminal  segment  of  the  gland-anlage  enlarges  in 
diameter  and  thus  early  differentiates  the  later  ampulla.  With  subsequent  increase 
in  length,  the  characteristic  coils  soon  appear,  after  which  a  lumen  makes  its 
appearance  in  the  ampullary  segment  and  gradually  extends  to  the  surface. 

Practical  considerations  of  the  skin  find  mention  in  connection  with  the 
various  regions,  to  which  the  reader  is  referred. 

THE  NOSE. 

Although  only  a  small  part  of  the  nasal  chambers  is  occupied  by  the 
peripheral  olfactory  organ  in  man,  the  greater  part  forming  the  beginning  of  the 
respiratory  tract,  comparative  anatomy  and  embryology  establish  the  primary 
significance  of  the  nasal  groove  and  its  derivations  as  the  organ  of  smell,  the 
relation  of  the  nose  to  respiration  being  entirely  secondary.  The  nose,  therefore, 
is  appropriately  grooped  with  the  organs  of  special  sense,  notwithstanding  its  relation 
to  the  proper  production  of  voice  and  to  taste  and  the  role  that  it  plays  in  varying 
facial  expression. 

The  nose  consists  of  two  portions,  the  outer  nose  (nasus  externus)  and  the  inner 
chamber  (cavum  nasi),  which  is  divided  by  the  median  partition  into  the  right  and 
left  nasal  fossa? 

The  outer  nose  forms  the  prominent  triangular  pyramid  that  projects  from  the 
glabella  forward  and  downward,  supported  by  a  bony  and  cartilaginous  framework 
and  covered  by  muscles  and  integument.  Its  upper  end  or  root  (radix  nasi)  springs 
from  below  the  glabella  from  the  frontal  bone,  with  which  it  usually  forms  an  angle 
and  from  which,  in  consequence,  it  is  separated  by  a  groove.  When  the  latter  is 
wanting  and  the  rounded  median  ridge,  or  dorsum,  of  the  nose  continues  the  plane 
of  the  forehead,  the  nose  is  said  to  be  of  the  Grecian  type.  The  dorsum  ends  below 
in  a  free  angle  or  point  (apex  nasi),  the  upper  or  bony  part  of  the  dorsum,  often 
termed  the  bridge,  in  the  aquiline  type  of  nose  forming  a  more  or  less  conspicuous 
angle  with  the  cartilaginous  part. 

The  sides  of  the  nose  (partes  laterales  nasi)  descend  from  the  root  with  increas- 
ing'Obliquity  until  they  reach  the  broadest  part  of  the  nasal  pyramid,  or  base,  which 
is  pierced  by  the  openings  of  the  nostrils  or  anterior  nares  (nares).  Just  before 
meeting  the  base,  each  lateral  surface  expands -into  the  mobile  and  rounded  wing  (ala 
nasi)  that  forms  the  outer  wall  of  the  nostril  and  is  limited  above  by  a  shallow- 
groove,  the  alar  sulcus.  Under  the  influence  of  the  attached  muscles,  the  alae  are 
subject  to  dilitation,  compression,  elevation  and  depression  and  thereby  participate 
in  modifying  facial  expression. 

In  addition  to  the  endless  minor  variations  of  form  that  the  outer  nose  presents, 
which,  apart  from  individual  distinction,  have  little  significance,  the  relation  of  its 
greatest  breadth  across  the  ala;  to  its  total  length,  from  root  to  tip,  is  of  sufficient 
anthropological  importance  to  receive  attention  in  the  classification  of  the  races  of 

/greatest  breadth    X  ioo\ 

mankind.     This  relation,  the  cephalometnc  nasal  index  I  — = -r— 

\         greatest  length         / 

varies  with  different  races,  according  to  Topinard  the  index  of  the  white  races  being 
below  70  (leptorhines} ,  that  of  the  yellow  and  red  races  between  70  and  85 
(mesorhines),  and  that  of  the  black  races  above  85  (platyrkmes). 

THE  CARTILAGES  OF  THE  NOSE. 

The  cordiform  nasal  opening  (.-iportura  pyrifonnis)  of  the  facial  skeleton,  bounded 
by  the  free  margins  of  the  nasal  and  superior  maxillary  bones,  is  enclosed  and 
continued  to  the  anterior  nares  by  the  nasal  cartilages  and  contiguous  fibrous  tissue. 
These  cartilages  arc-  usually  considered  as  including  five  chief  plates,  the  unpaired 
sef>a/-am\  the  paired  nf>f>er  and  lower  lateral,  and  a  variable  number  of  smaller 


THE   CARTILAGES   OF   THE    NOSE.  1405 

supplemental  pieces  (cartilagines  minores).  The  conventional  division  of  the  first 
three,  however,  is  unwarranted,  since  embryologically  and  morphologically  they 
constitute  one  piece  (cartilage  mediana  nasi),  which  even  in  the  adult  is  represented 
by  the  connected  septal  and  upper  lateral  plates. 

The  cartilage  of  the  septum  (cartilage  septi  nasi)  (Fig.  1171)  completes  the 
median  partition  that  divides  the  right  and  left  nasal  fossae  from  each  other  and 
represents  the  anterior  extremity  of  the  primordial  cartilaginous  cranum.  It  is 
irregularly  rhomboidal  in  form  and  so  placed  that  its  superior  angle  lies  above, 
received  between  the  nasal  bones  and  the  median  plate  of  the  ethmoid,  and  its 
inferior  angle  below,  resting  upon  the  incisor  crest  of  the  maxillae.  The  anterior 
angle  is  directed  forward  and  the  posterior,  much  the  more  pointed,  is  prolonged 
as  the  sphenoidal  process  (processus  sphenoidalis  septi  cartilaginei)  for  a  variable 
distance  between  the  mesethmoid  and  the  vomer  towards  the  body  of  the  sphenoid, 
which  exceptionally  it  may  reach.  The  antero-superior  margin  of  the  septal  carti- 
lage, thickest  above,  is  attached  to  the  under  surface  of  the  internasal  suture  for  a 

FIG.  1171. 


Perpendicular  plate  of  ethmoid 
Frontal  sinus 


Septal  cartilage 

^.  '  I 

Sphenoidal  sinus 


Mesial  crus  of  left 

lower  lateral  cartilage 


Sphenoidal  process  Vomer 

Nasal  septum  viewed  from  left  side  ;  mucous  membrane  has  been  partially  removed. 

distance  of  from  12-15  mm-  Below  the  nasal  bones,  the  margin  of  the  septal 
cartilage  is  continuous  with  the  upper  lateral  cartilages  which  form  ring-like  expan- 
sions (alae)  of  the  median  plate.  Still  lower,  the  free-margin  of  the  latter  extends 
between  the  lower  lateral  cartilages  to  within  about  a  half  inch  from  the  tip  of  the 
nose  which,  however,  it  does  not  reach,  the  medial  crura  of  the  lower  lateral  plates 
intervening.  The  postero-superior  margin,  the  thickest  part  of  the  cartilage,  is 
attached  to  the  free  margin  of  the  perpendicular  plate  of  the  ethmoid  bone.  The 
postero-inferior  margin  rests  upon  the  anterior  part  of  the  upper  margin  of  the 
vomer  and  the  incisive  crest  as  far  as  the  anterior  nasal  spine,  where  the  border 
passes  into  the  rounded  antero-  inferior  margin  that  joins  the  nasal  spine  with  the 
anterior  angle.  This  border  is  always  convex  and  does  not  reach  the  lowest  part  of 
the  partition  between  the  nostrils,  which  being  devoid  of  septal  cartilage,  is  freely 
movable  and  constitutes  the  septum  -mobile. 

The  upper  lateral  cartilages  (cartilagines  nasi  laterales)  (Fig.  1172)  are  two 
triangular  plates,  one  on  either  side,  that  by  their  median  and  longest  border  are 
attached  to  the  septal  cartilage,  with  which  in  their  upper  part  they  are  directly 
continuous.  The  upper  margin  of  each  is  joined  to  the  free  border  of  the  nasal  bone, 
which  it  slightly  underlies,  and,  exceptionally,  the  adjacent  edge  of  the  maxilla.  The 
lower  margin  is  embedded  in  fibrous  tissue  which  connects  it  with  the  adjoining  plates. 
The  median  parts  of  the  cartilages  are  markedly  convex  and  separated  by  a  slight 
groove  that  is,  for  the  most  part,  obliterated  by  fibrous  tissue. 


1406 


HUMAN    ANATOMY. 


Upper  lateral 
cartilage 


Nasal  bone 


Septal 
cartilage 


Cartilage 
at  tip 


Bony  and  cartilaginous  framework  of  nose,  front  aspect. 


The  lower  lateral  cartilages  (cartilagines  alares  majores)  (Fig.  1172)  area 
pair  of  thin  curved  plates  that  encircle  the  apertures  of  the  nostrils  anteriorly  and 
constitute  the  framework  of  the  tip  of  the  nose.  Each  cartilage  consists  of  an  inner 

P/ate(crus  mediate),  from  6—7  mm. 

FIG.  1172.  broad,  which,  with   its  fellow  of 

the  opposite  side,  embraces  the 
lower  and  anterior  part  of  the 
septal  cartilage  and  aids  in  com- 
pleting the  partition  separating 
the  nares.  In  front  it  narrows, 
bends  sharply  outward,  and  passes 
more  or  less  abruptly  into  a 
broader  outer  plate  ( crus  laterale), 
which  is  of  very  uncertain  form 
and  size,  although  of  a  general 
elongated  oval  shape  and  some 
12  mm.  broad.  The  triangular 
space  between  the  varyingly 
prolonged  posterior  end  of  the 
lateral  plate,  the  maxilla  and  the 
upper  lateral  cartilage  is  filled 
out  by  fibrous  tissue  in  which 
are  embedded  two,  three  or 
more  small  cartilaginous  pieces 
(cartilagines  alares  minores).  These  vary  greatly  in  size  and  form,  but  in  a  general 
way  tend  to  complete  the  ring  of  cartilage  surrounding  the  lateral  wall  of  the 
nares.  They  do  not,  however,  reach  the  lower  border  of  the  nasal  ring,  which, 
as  well  as  the  remaining  part  of  the  lower  boundary  of  the  aperture  of  the  nostril, 
is  devoid  of  cartilage  and  composed  of  integument  and  fatty  connective  tissue. 
The  rounded  anterior  angles  of  the  lower  lateral  cartilages  occupy  the  tip  of  the 
nose,  close  together  when  this  is  pointed,  but  separated  by  a  space  that  shows 
externally  as  a  more  or  less  evident  groove  when  the  tip  of  the  nose  is  blunt 
and  broad.  The  median  plates  approach  the  septal  cartilage  closer  in  front  than 
behind,  where  they  curve  outward  to  end  in  a  rounded  and  upward  curving  hook. 
The  fibrous  tissue  uniting  the  median  borders  of  the  lower  lateral  plates  with  the 
anterior  edge  of  the  septal  cartilage  usually  contains  two  small  sesamoid  cartilages 
(cartilagines  sesamoideae  nasi)  that  partly  fill  the  triangular  intervals  on  either  side  of 
the  median  line. 

The  vomerine  cartilages  (cartilagines  vomeronasales)  are  two  narrow  strips, 
from  1-2  mm.  wide  and  from  10-15  mm.  long,  that  lie,  one  on  either  side,  along  the 
lower  border  of  the  septal  cartilage 
in  the  vicinity  of  the  nasal  crest. 
They  are  attached  to  the  carti- 
lage and  bone  by  fibrous  tissue 
and  situated  beneath  the  mucous 
membrane  lining  the  nasal  fossae. 
Their  chief  interest  is  their  rela- 
tion to  the  rudimentary  organ 
of  Jacobson  (page  1417)  below 
which  they  lie.  In  animals  in 
which  the  organs  are  well  devel- 
oped these  cartilages  form  protect- 
ing and  supporting  scrolls  ;  in 
man,  however,  both  organ  and 
cartilage  are  so  feebly  developed 
that  they  loose  their  close  relation. 

The  integument  covering  the  outer  nose  is  in  general  thin  and  closely  bounc 
down  to  the  underlying  fibrous  tissue,  being  particularly  unyielding  over  the  Up  ami 
al;c.  With  the  exception  of  within  the  al;i-  and  lateral  borders  of  the  nostrils,  the 


FIG.  1173 


Lower  lateral 
cartilage 

Upper  lateral 
cartilage 

Small  alar 
cartilage 


Cartilage  of  tip 
Lateral  crus 
Mesial  crus 


canilage 


Nasal  aperture 
Septal  cartilage 


Cartilages  of  nos>-.   \  if\\ 


PRACTICAL    CONSIDERATIONS:   THE    EXTERNAL    NOSE.     1407 

fatty  tissue  is  very  meagre.  The  sebaceous  glands,  on  the  other  hand,  are  well 
developed  and  open  in  many  instances  in  conjunction  with  the  follicles  of  the  delicate 
hairs  that  cover  all  parts  of  the  surface.  On  the  alae  the  closely  placed  glands  are  of 
exceptional  size  and  open  by  ducts  readily  seen  as  minute  depressions. 

Vessels. — In  order  to  compensate  for  the  exposed  position,  the  external  nose 
is  generously  supplied  with  arteries,  derived  chiefly  from  the  facial  and  ophthalmic, 
which  are  united  by  numerous  anastomoses  with  each  other  as  well  as  with  branches 
from  the  infraorbital.  The  veins  are  all  tributary  to  the  angular  vein,  which  begins 
at  the  inner  canthus  and  descends  along  the  side  of  the  nose  to  the  facial  trunk, 
receiving  in  its  course  the  dorsal,  lateral,  and  alar  branches.  The  angular  vein 
communicates  with  the  ophthalmic  and  the  veins  of  the  nasal  fossa. 

The  lymphatics  are  arranged  in  three  sets  (Kiittner).  The  first,  beginning  at 
the  root  of  the  nose,  passes  above  the  upper  eye-lid  and  along  the  supraorbital  ridge 
to  the  parotid  nodes.  The  second  group,  formed  by  the  superficial  and  deep  lym- 
phatics at  the  nasal  root,  skirts  the  lower  margin  of  the  orbit  and  ends  in  the  lower 
parotid  nodes.  The  third  and  most  important  set  includes  from  6  to  10  trunks  that 
follow  the  blood-vessels  and  end  in  the  submaxillary  nodes. 

The  nerves  supplying  the  outer  nose  include  the  motor  branches  of  the  facial 
.  to  the  muscles  and  the  sensory  twigs  from  the  trifacial  to  the  skin,  distributed  by  the 
infratrochlear  and  nasal  branches  of  the  ophthalmic  and  by  the  infraorbital  of  the 
superior  maxillary. 

PRACTICAL  CONSIDERATIONS  :  THE  EXTERNAL  NOSE. 

The  Nose  may  be  congenitally  absent,  or  bifid,  or  imperfect,  as  from  absence 
of  the  septum  or  of  one  nostril,  or — very  rarely — of  both  nostrils.  As  to  its  external 
aspect  it  may  be  of  various  types,  e.g.:  Grecian,  when  the  dorsum  is  on  a  practi- 
cally continuous  straight  line  with  the  forehead,  with  no  marked  naso-frontal  groove ; 
aquiline,  with  the  dorsum  slightly  arched  ;  rounded,  with  the  arch  much  more 
pronounced;  foetal — "pug" — with  the  bridge  depressed  and  the  nostrils  directed 
somewhat  forward. 

The  foetal  type  is  simulated  in  the  new  born  by  the  subjects  of  inherited 
syphilis  in  whom  the  bridge  of  the  nose  is  often  much  depressed  as  a  result 
either  of  (a)  imperfect  development  following  the  severe  specific  coryza  that 
affects  the  nasal  mucosa  and,  through  the  close  apposition  of  the  latter  to  the 
periosteum  of  the  fragile  nasal  bones,  interferes  with  their  nutrition  ;  or  (£)  by 
actual  caries  or  necrosis  of  those  bones  or  of  the  septum  favored  by  the  same 
conditions.  In  acquired  syphilis  the  similar  nasal  deformity  is  practically  always 
the  result  of  the  destruction  of  the  septum,  or,  less  frequently,  of  the  nasal  bones,  by 
late  (tertiary)  lesions. 

As  a  consequence  of  faulty  development  in  the  anterior  mid-portion  of  the 
frontal  bone  the  membranes  of  the  brain  may  protrude,  forming  a  meningocele, 
which  is  more  common  at  the  naso-frontal  junction  than  elsewhere.  Occasionally 
the  defect  permitting  the  protrusion  exists  in  the  cribriform  plate  of  the  ethmoid, 
and  the  meningocele  occupies  the  nasal  fossa,  having  under  these  circumstances 
been  mistaken  for  a  nasal  polyp  and  removed,  death  resulting  from  subsequent  septic 
meningitis. 

The  cosmetic  importance  of  the  nose  is  so  great,  the  diseases  producing 
deformity  so  frequent,  and  the  susceptibility  of  the  organ  to  injury  so  marked,  that 
much  ingenuity  has  been  expended  upon  devices  to  restore  it  when  lost,  or  to 
improve  its  appearance.  In  the  Tagliacotian  operation  a  cutaneous  flap  is  taken 
from  the  arm  which  is  held  close  to  the  nose  by  a  complicated  dressing  until  the  flap 
is  firmly  united  in  its  new  position,  when  its  pedicle  is  detached  from  the  arm.  The 
Indian  method  is  more  particularly  anatomical,  since  the  flap  taken  from  the  fore- 
head is  so  fashioned  that  it  receives  intact  the  blood  from  the  frontal  branch  of  the 
ophthalmic  artery  from  the  internal  carotid,  "the  ophthalmic  receiving  at  the  origin 
of  the  frontal  an  important  anastomosis  from  the  angular  branch  of  the  facial  artery, 
which  is  given  off  from  the  external  carotid  artery.  For  partial  deformities  flaps 
may  be  taken  from  the  sides  according  to  the  size  and  situation  of  the  deficiency. 


I4o8  HUMAN    ANATOMY. 

As  upon  other  parts  of  the  face,  plastic  operations  are  very  successful  owing  to 
the  free  blood  supply.  Acne  rosacea  is  common  on  account  of  the  ready  response 
in  vascularity  of  the  nose  to  external  irritating  influences,  and  to  internal  disturbances 
of  the  circulation,  as  from  heart  and  lung  disease,  chronic  gastritis,  and  alcoholism. 
Furuncles  and  superficial  infections  are  frequent  because  of  the  number  of  sebaceous 
and  sweat  glands  present.  Lupus  and — in  the  alar  sulcus — rodent  ulcers  are  com- 
mon because  of  the  constant  exposure  of  the  nose  to  external  irritation  and  to 
lowering  of  temperature,  depressing  its  vital  resistance.  Frost-bite  of  the  nose  is 
also  common,  especially  about  the  tip,  because  of  its  exposed  position  and  the  lack 
of  protection  to  the  delicate  vessels  from  overlying  tissues. 

The  nerve  supply  to  the  nose  is  likewise  very  free,  as  is  shown  in  a  practical 
manner  by  the  pain  which  accompanies  inflammatory  conditions,  especially  those 
involving  the  lower  cartilaginous  portion  where  the  skin  and  subcutaneous  tissues 
are  very  adherent.  The  resulting  exudate  is  therefore  much  confined,  pressing 
upon  the  nerves  ;  this  accounts  also  for  the  frequency  with  which  gangrene  occurs 
under  these  circumstances. 

Watering  of  the  eyes  from  irritation  of  the  skin  or  mucous  membrane  of  the 
nose  is  due  to  the  free  nerve  supply,  and  to  the  fact  that  the  same  nerve,  the  tri- 
geminal,  supplies  the  nose  and  the  lachrymal  apparatus  ;  as  a  portion  of  the  nasal 
chamber  is  supplied  by  a  branch  of  the  ophthalmic  nerve,  raising  the  eyes  to  the  sun 
will  often  give  the  added  irritation  necessary  to  precipitate  a  sneeze  when  the  nasal 
stimulus  suggests  one,  but  is  not  quite  strong  enough  unaided.  Cough  and  bronchial 
asthma  have  resulted  from  nasal  affections  due  to  the  indirect  relations  between 
the  fifth  cranial  nerve  and  the  pneumogastric.  As  the  olfactory  portion  of  the 
nasal  fossa  is  in  the  upper  portion  of  the  cavity,  an  earnest  effort  to  recognize 
an  odor  or  to  enjoy  one  to  the  utmost,  is  accompanied  by  a  deep  inspiration 
through  the  nose  with  dilatation  of  the  nostril.  In  paralysis  of  the  facial  nerve, 
the  involvement  of  the  dilatores  naris  has  been  thought  to  explain  the  lessening  of 
the  olfactory  sense  sometimes  seen  in  this  condition.  Paralysis  of  the  levatores 
alae  nasi  muscles  has  permitted  the  nostrils  to  close  during  inspiration,  causing  stridor 
and  mouth-breathing.  The  loss  of  the  sense  of  smell  is  a  not  uncommon  result 
of  severe  blows,  especially  on  the  forehead,  and  may  be  due  to  (a)  concussion  of 
the  olfactory  bulbs  ;  (£)  fracture  of  the  cribriform  plate  of  the  ethmoid  ;  (c)  injury 
to  the  olfactory  roots  where  they  cross  the  lesser  wing  of  the  sphenoid  ;  or  (d) 
lesion  of  the  olfactory  nerves  where  they  traverse  the  cribriform  foramina.  Sneezing 
from  irritation  of  the  nose  is  probably  due  to  the  indirect  relationship  between  the 
fifth  pair  and  the  vagus  and  may  be  so  violent  that  serious  injury  may  result,  as  in 
cases  in  which  a  subcoracoid  luxation  of  the  shoulder,  a  fracture  of  the  ninth  rib, 
and  the  rupture  of  all  the  coverings  of  a  large  femoral  hernia  were  produced  by 
this  act  (Treves). 

The  abundant  sweat  and  sebaceous  glands  in  the  skin  of  the  nose  account  for 
the  frequency  with  which  acne  vulgaris  attacks  it.  The  alse,  the  only  movable  por- 
tions, take  part  in  the  movements  of  expression,  as  in  contempt  and  scorn. 

Fractures  of  the  nose  are  common  because  of  its  exposed  position,  and  of  the 
frequency  of  blows  and  other  forms  of  violence  applied  to  the  face.  Their  chief 
importance  depends  upon  the  prominence  of  the  nose  as  a  feature  of  the  face,  any 
change  in  its  shape  attracting  general  attention.  The  fracture  occurs  most  com- 
monly in  the  lower  part,  because  of  the  greater  weakness  of  the  bones  and  their  greater 
prominence  at  that  level.  In  its  upper  part,  the  relative  depression  of  the  dorsum, 
the  greater  thickness  of  the  bones,  and  their  more  firm  support,  make  fracture  less 
common.  On  the  other  hand,  the  higher  fractures  arc  mere  dangerous  because  of 
their  possible  relation  with  the  cribriform  plate  and  sinuses  of  the  ethmoid  bone,  the 
frontal  sinuses  and  the  nasal  duct.  Involvement  of  the  cribriform  plate  is  in  effect  a 
compound  fracture  of  the  base  of  the  skull,  exposing  the  meninges  to  the  danger  of 
infection.  Fractures  of  the  nose  are  almost  always  compound,  because  of  the 
intimate  adhesion  of  the  mucous  membrane  to  the  bone,  with  little  intervening 
tissue,  so  th:it  when  the  hone  breaks  the  overlying  adherent  tissue  is  torn  through. 
This  accounts  for  the  practically  uniform  occurrence  of  epistaxis,  on  account  of  which 
it  is  often  difficult  to  detect  the  presence  of  escaping  cerebro-spinal  fluid  when  the 


THE   NASAL    FOSS.E.  1409 

cribriform  plate  is  also  fractured.  On  the  other  hand,  the  rich  glandular  supply  of 
the  mucous  membrane,  which  makes  the  usual  mucous  secretion  exceptionally  free, 
may,  in  a  post-traumatic  coryza,  result  in  a  watery  discharge  of  such  quantity  as  to 
suggest  the  escape  of  the  cerebro-spinal  fluid.  Emphysema  within  the  orbit  and 
under  the  skin  may  result  from  the  communication  of  the  nose  with  the  ethmoidal  or 
frontal  sinuses.  In  the  effort  to  keep  the  nose  clear  of  blood  by  blowing,  the  air  is 
forced  into  the  subcutaneous  tissues. 

In  fractures  at  the  lower  part,  the  deformity  is  frequently  lateral,  because  of 
the  greater  exposure  to  side  blows,  and  the  tendency  of  the  cartilaginous  alae  and 
septum  to  avoid  crushing.  In  the  upper  part  depression  is  more  likely,  because  of 
the  tendency  to  escape  any  but  forces  from  in  front,  the  greater  force  necessary  to 
produce  the  fracture,  and  the  presence  of  a  bony  septum  underneath,  which  crushes 
rather  than  bends. 

When  the  deformity  has  been  replaced  there  are  no  strong  muscles  to  repro- 
duce it,  so  that  little  or  no  effort  is  necessary  to  maintain  the  fragments  in  position. 
The  deformity  must  be  reduced  early  and  the  reduction  maintained,  because  owing 
to  the  free  blood  supply,  union  is  usually  rapid,  sometimes  occurring  in  a  week. 
One  must  bear  in  mind  in  reducing  the  deformity  that  the  roof  of  each  nasal  fossa  is 
not  more  than  2-3  mm.  wide,  and  that,  therefore,  a  narrow  rigid  instrument  is 
necessary  to  press  the  fragments  upward  into  their  normal  positions. 

THE  NASAL  FOSSAE. 

The  cavity  of  the  nose  is  divided  by  the  median  septum  into  two  nasal  fossae 
which  extend  from  the  anterior  to  the  posterior  nares,  or  choance,  through  which 
they  open  into  the  naso-pharynx.  They  communicate  more  or  less  freely  with  the 
accessory  air-spaces  within  the  frontal,  ethmoid,  sphenoid  and  maxillary  bones,  into 
which,  as  a  lining,  the  mucous  membrane  of  the  nasal  fossae  is  directly  continued. 

Seen  in  frontal  section  (Fig.  1176),  each  fossa  is  triangular  in  its  general  outline, 
the  apex  being  above  at  the  narrow  roof  and  the  base  below  on  the  floor.  The 
smooth  median  wall  is  approximately  vertical  and  meets  the  floor  at  almost  a  right 
angle,  while  the  sloping  lateral  wall  is  modelled  by  the  projecting  scrolls  of  the  three 
turbinates,  which  overhang  the  corresponding  meatuses.  In  sagittal  sections 
(Fig.  1 174)  the  contour  of  the  fossa  resembles  an  irregular  parallelogram  from  which 
the  upper  front  corner  has  been  cut  off,  so  that  in  front  the  upper  border  slopes 
downward  to  correspond  with  the  profile  of  the  outer  nose.  The  greatest  length  of 
the  fossa,  measured  along  the  floor,  is  from  7-7.5  cm.  (2^-3  in.)  and  its  greatest 
height  from  4-4.5  cm.  The  width  is  least  at  the  roof,  where  it  is  less  than  3  mm., 
and  greatest  in  the  inferior  meatus  a  short  distance  above  the  floor,  where  it  expands 
to  from  15-18  mm. 

The  Vestibule. — The  anterior  part  of  the  fossa,  immediately  above  the  open- 
ing of  the  nostril  and  embraced  by  the  outer  and  inner  plates  of  the  lower  lateral   • 
cartilage  and  adjoining  portion  of  the  septum,  is  somewhat  expanded  and  constitutes   ] 
the  vestibule  (vestibulutn  nasi),  a  pocket-like  recess  prolonged  towards  the  tip  being    ; 
the  ventricle  (recessus  apicis).      These  spaces  are  lined  by  delicate  skin,  directly  con- 
tinuous with  the  external  integument  and  tightly  adherent  to  the  underlying  cartilage, 
and,  in  the  lower  half  of  the  vestibule,  containing  numerous  sebaceous  glands  and 
hairs.      In  the  vicinity  of  the  nostril  the  hairs,  known  as  vibrissce,    are  coarse  and 
long  and   curved  downward  to  afford  protection  to  the  nasal  entrance.      Over  the 
upper  part  of  the  vestibule,  the  skin   is  smooth  and  closely  attached  to  the  lower 
lateral  cartilage,  the  upper  margin  of  the  outer  plate  projecting  as  a  slightly  arching 
ridge,  the  limen  vestibuli,  which  forms  the  superior  and  lateral  boundary  of  the  vesti- 
bule and  marks  the  line  of  transition  of  the  skin  into  the  mucous  membrane  that  lines  • 
the  remaining  parts  of  the  nasal  fossa. 

Above  and  beyond  the  vestibule,  the  nasal  fossa  rapidly  expands  into  a 
triangular  space,  the  atrium  nasi,  that  lies  in  advance  of  the  entrance  into  the  middle 
nasal  meatus.  Above  and  in  front  the  atrium  is  bounded  by  a  low  and  variable 
ridge,  the  agger  nasi,  that  represents  a  rudimentary  naso-turbinate,  which  in  many 
mammals  attains  a  large  size.  The  space  lying  in  front  of  the  agger,  extending 

89 


1410 


HUMAN   ANATOMY. 


from  the  limen  to  the  cribriform  plate  of  the  ethmoid  and  roofed  in  by  the  forepart 
of  the  arched  upper  boundary  of  the  fossa,  is  long  and  narrow  in  consequence  of 
the  approximation  of  the  median  and  lateral  walls.  It  leads  from  the  nasal  aperture 
to  the  summit  of  the  nasal  fossa  and  to  it  Merkel  applied  the  name  carina  nasi. 

The  Nasal  Septum. — The  median  wall  consists  of  the  partition  formed  chiefly 
by  the  perpendicular  plate  of  the  ethmoid,  the  vomer  and  the  septal  cartilage,  cov- 
ered on  both  sides  by  mucous  membrane.  The  extreme  lower  and  anterior  part  of 
the  septum,  consisting  of  the  alar  cartilage  and  the  integument,  is  flexible,  and  there- 
fore called  the  membranous  portion,  or  septum  mobile  ;  the  terms  bony  and  cartilagi- 
nous portions  are  applied  to  the  remaining  parts  of  the  septum  supported  by  bone 
and  cartilage  respectively. 

While  during  early  childhood  its  position  is  median,  in  the  great  majority  of 
adults  the  septum  presents  more  or  less  asymmetry  and  lateral  deflection,  most  often 

FIG.  1174. 


Frontal  sinus 


Nasal  bone 


Superior  turbinate 

Spheno-ethmoidal  recess 

Opening  of  sphenoidal  sinus 

Superior  meatus 


Agger  nasi 


Opening  of 
Eustachian  tube 


rm\ltl*  \  \      \  \         Posterior  limit  of  nasal  fossa 

Middle  meatus 
Middle  turbinate 
Inferior  meatus 
Right  nasal  fossa,  lateral  wall ;  and  naso-pharynx. 

to  the  right.  This  deviation  may  affect  the  septal  cartilage  alone,  may  be  limited  to 
the  bones  (in  53  per  cent,  according  to  Zuckerkandl),  or  may  be  shared  by  both. 
The  most  common  seat  of  the  deflection  is  the  junction  of  the  ethmoid  and  vomer,  in 
the  vicinity  of  the  spheno-ethmoidal  process,  or  along  the  union  of  the  vomer  and 
the  septal  cartilage.  The  asymmetry  may  involve  the  entire  septum,  which  then  is 
oblique  ;  or  it  may  take  the  form  of  a  simple  bulging  towards  one  side,  a  double  or 
sigmoid  projection  ;  or  be  an  angular  deflection  resembling  a  fold,  crest  or  spur  that 
projects  into  one,  sometimes  both,  of  the  fossae  (Heymann). 

Although  the  mucous  membrane  covering  the  nasal  septum  is  generally  smooth 
and  of  fairly  constant  thickness,  its  surface  is  marked  by  inequalities  caused  chiefly 
by  variations  in  the  amount  and  development  of  the  glandular  and  vascular  tissue. 
One  such  accumulation,  the  tubcrcidnm  scpti,  is  relatively  constant  and  on  the  septum 
about  opposite  the  anterior  end  of  the  middle  turbinate.  During  early  life  a  series 
of  from  four  to  six  or  more  oblique  ridges,  plica  scpti,  often  model  the  lower  and 
posterior  part  of  the  septum,  extending  from  below  upward  and  forward.  Slightly 
above  the  anterior  nasal  spine,  the  septal  mucosa  presents  the  minute  openings  lead- 
ing  into  the  rudimentary  organ  of  Jacobson.  Behind,  the  margin  of  the  bony  septum 
is  covered  by  mucous  membrane  of  unusual  thickness  which,  therefore,  forms  the 
immediate  free  edge  of  the  partition  separating  the  posterior  nares. 

The  Lateral  Wall. — The  lateral  wall  of  the  nasal  fossae  is  characteristically 
modelled  by  the  projecting  scrolls  (conchac  nasi)  of  the  three  turbinates.  The  latter 
partly  subdivide  each  fossa  into  three  lateral  recesses,  the  superior,  middle,  and 


THE   NASAL 


1411 


inferior  meatuses.  These  are  overhung  by  the  corresponding  bony  concha,  the 
superior  meatus  being  roofed  in  by  the  upper  turbinate  and  the  inferior  lying  between 
the  lower  turbinate  and  the  floor  of  the  fossa.  That  part  of  the  nasal  fossa  between 
the  conchae  and  the  septum,  into  which  the  recesses  open  medially,  is  sometimes  called 
the  meatus  nasi  communis.  The  details  of  the  nasal  fossa  as  seen  within  the  macerated 
skull  have  been  described  in  connection  with  the  skeleton  (page  223).  In  the  recent 
condition,  when  the  soft  parts  are  in  place,  while  their  general  contour  is  preserved, 
the  compartments  of  the  fossae  are  materially  reduced  in  size  by  the  thickness  of  the 
mucous  membrane  and  the  erectile  tissue  that  cover  the  bony  framework. 

The  Superior  Meatus. — Corresponding  to  the  small  size  of  the  upper  turbinate, 
the  superior  meatus  (meatus  nasi  superior),  or  ethmoidal  fissure,  is  narrow  and 
groove-like  and  little  more  than  half  the  length  of  the  middle  one.  It  is  directed 
downward  and  backward  and  is  floored  by  the  convex  upper  surface  of  the  middle 
concha.  When  the  upper  turbinate  is  replaced  by  two  scrolls  (conchae  superior 
et  suprema) — a  condition  that  Zuckerkandl  regards  as  very  frequent,  if  indeed,  not 
the  more  usual — the  meatus  is  accordingly  doubled.  Into  the  upper  and  front  part 
of  the  superior  meatus  the  posterior  ethmoidal  air-cells  open  by  one  or  more  orifices 

FIG.  1175. 


Frontal  sinus 
Probe  in  infundibulum 


Middle  turbinate,  partly 
removed 


Hiatus  semilunaris 
Ethmoidal  bulla 

Openings          Agger  nas: 

of  maxillary  sinus 

into  infundibulum 

Ventricle 

Li  men  nasi 
Vestibul 


Probe  in  naso-lachrymai 
duct 


Opening  of  middle  ethmoidal  cells 

Superior  turbinate,  partly  removed 

ening  into  spheno-ethmoidal  recess 


Ope 


Sphenoidal  sinus 


Opening  of  posterior 
ethmoid  cells  into 
superior  meatus 

Naso-pharynx 


Opening  of  Eustach- 
ian  tube 


Inferior  meatus 


Inferior  turbinate, 
partly  removed 


Middle  meatus 


Lateral  wall  of  nasal  fossa ;  portions  of  turbinate  bones  have  been  removed  to  expose 
openings  into  air  spaces. 

of  variable  size.  Above  and  behind  the  upper  turbinate  and  in  front  of  the  body  of 
the  sphenoid  bone  lies  a  diverticulum,  the  spheno-ethmoidal  recess,  into  the  posterior 
part  of  which  opens  the  sphenoidal  sinus. 

The  Middle  Meatus. — The  recess  beneath  the  middle  turbinate  (meatus  nasi 
medius)  is  spacious  and  arched  to  conform  with  the  contour  of  the  middle  and 
inferior  conchae  which  constitute  its  roof  and  floor  respectively.  On  elevating, 
or  still  better  removing  close  to  its  attachment,  the  lower  turbinate  bone/ a  deep 
crescentic  groove,  the  infundibulum,  is  seen  on  the  outer  wall  of  the  fossa  overhung 
by  the  anterior  half  of  the  concha.  The  crescentic  cleft  leading  from  the  middle 
meatus  into  the  infundibulum  is  the  hiatus  semilunaris?  which  extends  from  above 
downward  and  backward,  with  its  convexity  directed  forward.  Its  anterior  boundary 
is  a  sharp  crescentic  ridge  due  to  the  uncinate  process  of  the  ethmoid  covered 
with  thin  mucous  membrane,  while  behind  it  is  limited  by  a  conspicuous  elevation 
produced  by  the  corresponding  underlying  bony  projection  of  the  ethmoidal  bulla. 

1  Some  confusion  exists  in  the  use  of  this  term,  since  it  is  often  applied  to  the  entire  groove  and 
not  merely  to  the  cleft  which  leads  from  the  meatus  into  the  groove.  The  name  is  here  employed 
as  indicating  the  lunate  cleft  and  not  the  groove  (which  is  the  infundibulum),  as  originally  used 
by  Zuckerkandl,  who  introduced  it.  See  Antomie  der  Nasenhohle,  Wien,  1882,  page  39. 


1412 


HUMAN   ANATOMY. 


When  the  infundibulum  does  not  end  blindly  above,  which  it  often  does  (page 
194),  its  upper  extremity,  usually  somewhat  expanded,  receives  the  opening  of  the 
frontal  sinus,  ostium  frontale.  The  sinus  is,  however,  not  dependent  upon  the 
infundibulum  for  its  communication  with  the  middle  meatus,  since,  as  pointed  out 
by  Zuckerkandl,  between  the  front  of  the  attachment  of  the  middle  turbinate  bone 
and  the  uncinate  process  of  the  ethmoid  there  exists  a  passage  which  leads  to  the 
ostium  frontale.  Into  the  upper  part  of  the  infundibulum  usually  open  some  of  the 
anterior  ethmoidal  air-cells  ;  lower  in  the  groove  lies  the  oval  or  slit-like  ostium 
tnaxillare,  the  chief  communication  of  the  antrum  of  Highmore.  When  the  latter 
is  provided  with  an  additional  orifice,  as  it  is  in  10  per  cent.  (Kallius),  the  smaller 
accessory  communication  opens  into  the  infundibulum  a  few  millimeters  behind 
the  principal  aperture.  Above  the  hiatus  semilunaris,  either  on  or  above  the 
bulla,  is  usually  seen  the  slit-like  opening  through  which  the  middle  ethmoidal  cells 
communicate  with  the  meatus. 

The  Inferior  Mealus. — This  passage  (meatus  nasi  inferior),  the  largest  of  the 
three,  measures  from  4. 5-5. 5  cm.  in  length,  its  anterior  end  lying  from  2.5-3.5  cm- 
behind  the  tip  of  the  nose.  At  first  relatively  contracted,  it  abruptly  expands,  not 


FIG.  1176. 


Scalp 


Cerebral  hemisphe 


Superior  longitudinal  sinus 
Bone 

•Falx  cerebri 


Ethmoidal  cells 

Lower  end  of  probe 

lying  in  hiatus 

semilunaris 


Middle  turbinate_ 


Probe  passing  from 

antrum  into 

infundibulum 


Inferior  turbinate 


Nasal  septum/ 


Right  eyeball 

Hiatus  semilunaris 
Middle  meatus 

-—Maxillary  sinus 

— 'Inferior  meatus 
Floor  of  nasal  fossa 

mucous  membrane 


Tongue 


Frontal  section  of  head,  viewed  from  behind,  showing  nasal  fossic  and  communications 
with  frontal  and  maxillary  sinuses. 

only  in  height,  in  correspondence  with  the  arched  attached  border  of  the  lower 
turbinate,  but  also  in  width.  Farther  backward,  it  gradually  diminishes  and  is  again 
reduced  at  its  choanal  end.  On  the  lateral  wall  of  the  inferior  meatus,  usually  from 
3-3.5  cm.  behind  the  posterior  margin  of  the  nostril,  after  removal  of  the  lower 
turbinate,  may  be  seen  the  opening  of  the  naso-lurhrymal  duct.  The  position  and 
form  of  the  orifice  are  subject  to  much  variation.  When  close  to  the  arching  attached 
border  of  the  concha,  the  aperture  is  usually  oval  or  even  round  ;  when  its  position 
is  lower,  it  is  narrow  and  slit-like,  obliquely  vertical,  and  often  guarded  by  a  fold  of 
mucous  membrane,  the  so-called  rakr  of  rfasner. 

The   arched    roof  of  the    nasal    fossa    is    divisible    into  a  naso-frontal,   an 
ethmoidal  and   a  sphenoidal    part   in   accordance  with   the  bones  over  which   the 


THE  NASAL  MUCOUS  MEMBRANE.  1413 

mucous  membrane  stretches.  The  lower  part  of  the  naso-frontal  division,  below  the 
nasal  bone,  is  cutaneous  and  cartilaginous.  Anteriorly  the  roof  is  reduced  to  little 
more  than  a  groove  on  account  of  the  approximation  of  the  lateral  and  median 
walls,  but  posteriorly  broadens  towards  the  choana.  The  median  part  of  the  roof, 
formed  by  the  cribriform  plate  of  the  ethmoid,  is  very  thin  and  makes  a  sharp  angle 
with  the  steeply  descending  sphenoidal  division.  Between  the  latter  and  the  superior 
turbinate  bone  lies  the  spheno-ethmoidal  recess. 

The  floor  of  the  nasal  fossa,  much  broader  than  the  roof  and  supported  by 
the  palatal  process  of  the  maxilla  and  the  horizontal  plate  of  the  palate  bone,  from 
before  backward  is  approximately  horizontal,  but  from  side  to  side  is  distinctly  con- 
cave. Anteriorly  this  wall  is  robust,  but  rapidly  diminishes  in  thickness  as  it  passes 
backward.  About  2  cm.  behind  the  posterior  margin  of  the  nostril  and  close  to  the 
septum,  the  floor  of  each  nasal  fossa  presents  a  slight  depression,  sometimes  narrow 
and  funnel-shaped,  that  leads  into  a  small  canal  lined  with  a  prolongation  of  mucous 
membrane.  This  canal  converges  towards  the  septum  with  its  fellow  of  the  opposite 
fossa,  descends  almost  vertically,  and  passes  through  the  incisive  foramen  in  the  hard 
palate  to  end  on  the  roof  of  the  mouth  as  a  minute  slit  at  the  side  of  the  incisive  pad 
or  papilla  palatina.  Although  the  two  tubes  of  mucous  membrane  may  join  to  form 
a  single  incisive  canal,  they  usually  retain  their  independence  (Leboucq,  Merkel). 
They  are  often  closed  and  impervious  ;  sometimes,  however,  even  in  the  adult 
communication  is  retained  between  the  nasal  and  oral  cavities. 

The  posterior  nares  or  choanae,  the  apertures  through  which  the  nasal  fossae 
communicate  with  the  naso-pharynx,  one  on  either  side  of  the  septum,  resemble  in  form 
somewhat  a  Gothic  arch  (Fig.  1354).  They  are  relatively  much  lower  in  the  new- 
born child  than  in  the  adult,  in  which  they  measure  about  3  cm.  in  height  and 
1.5  cm.  in  breadth  (Zuckerkandl),  although  individual  variation  is  considerable. 
Each  opening  is  bounded  below  by  the  horizontal  plate  of  the  palate  bone  ;  laterally 
by  the  inner  surface  of  the  internal  pterygoid  plate  of  the  sphenoid  ;  above  by  the 
vaginal  process  of  the  sphenoid  and  the  ala  of  the  vomer  ;  and  mesially  by  the 
vertical  posterior  borders  of  the  vomer.  Over  this  bony  arch  the  nasal  mucous 
membrane  is  continuous  with  that  lining  the  pharynx.  Laterally  the  posterior 
limit  of  the  nasal  fossa  in  the  recent  condition  is  indicated  by  a  furrow  (sulcus  nasalis 
posterior)  that  extends  from  the  under  surface  of  the  sphenoid  downward  to  about 
the  junction  of  the  hard  and  soft  palates.  Behind  this  furrow,  about  on  a  level  with 
the  lower  border  of  the  inferior  turbinate,  lies  the  opening  of  the  Eustachian  tube 
(Fig.  1174).  Since  the  turbinates  end  approximately  12  mm.  in  advance  of  the 
choanae,  the  outlines  of  these  openings  are  unbroken  by  the  scrolls  that  model  the 
lateral  wall  of  the  nasal  fossae,  all  three  conchae,  however,  being  visible  through  the 
posterior  nares. 

THE  NASAL  MUCOUS  MEMBRANE. 

Beyond  the  limen  that  marks  the  limit  of  the  integument  clothing  the  vestibule 
(page  1409),  the  nasal  fossa  is  lined  by  mucous  membrane  continuous  with  that  of  the 
naso-pharynx  through  the  choanae.  Since  in  addition  to  lining  the  tract  over  which 
the  respired  air  passes  the  nasal  mucous  membrane  contains  the  cells  receiving  the 
impressions  giving  rise  to  the  sense  of  smell,  it  is  appropriately  divided  into  a  respir- 
atory and  an  olfactory  part. 

The  Olfactory  Region. — The  highly  specialized  regio  olfactoria  is  quite 
limited  in  extent  and  embraces  an  area  situated  over  the  middle  of  the  upper  tur- 
binate and  the  corresponding  part  of  the  septum.  According  to  Brunn,  x  whose 
conclusions  are  here  presented,  the  olfactory  area  of  each  fossa  includes  only  about 
250  sq.  mm. ,  the  septum  contributing  something  more  than  one-half  of  the  entire  surface. 
Accordingly  the  specialized  field  is  by  no  means  coextensive  with  the  upper  turbinate 
bone,  as  it  reaches  neither  its  lower  nor  posterior  border  (Fig.  1177).  The  anterior 
margin  of  the  area,  which  lies  about  i  cm.  behind  the  front  wall  of  the  nasal  fossa,  is 
irregular  in  outline  owing  to  the  invasion  of  the  specialized  region  by  the  adjacent 

1  Archiv  f.  mikros.  Anat,  Bd.  39,  1892.      * 


HUMAN   ANATOMY. 


FIG.  1177. 


respiratory  mucous  membrane,  tongues  or  even  islands  of  the  latter  projecting  into 
or  being  surrounded  by  the  former.  Upon  the  evidence  derived  from  careful  dissection 
of  the  olfactory  mucous  membrane,  however,  it  is  difficult  to  avoid  the  conclusion 

that  Brunn's  areas  are  too  limited,  as  nerve-fila- 
ments clearly  attached  to  the  olfactory  bulb  are 
usually  traceable  onto  the  upper  part  of  the  middle 
turbinate  bone.  In  fresh  preparations  the  olfactory 
area  usually,  but  not  always,  can  be  approximately 
mapped  out  by  the  yellowish  hue,  lighter  or 
darker,  that  distinguishes  it  from  the  respiratory 
region  in  which  the  mucous  membrane  exhibits 
a  rosy  tint. 

The  epithelium  contains  two  chief  con- 
stituents— the  supporting  and  the  olfactory  cells. 
The  supporting  cells  are  tall  cylindrical  elements, 
about  .06  mm.  in  height,  that  extend  the  entire 
thickness  of  the  epithelium.  Their  outer  and 
broader  ends  are  of  uniform  width  and  contain 
the  oval  nuclei  which,  lying  approximately  at 
the  same  line  and  staining  readily,  form  a 
deeply  colored  and  conspicuous  nuclear  stra- 
tum at  some  distance  beneath  the  free  margin. 
Between  the  latter  and  the  row  of  nuclei,  the 

Right  nasal   fossa,  septum  (s)   has    been  .  . ' 

partially  separated  and  turned  upward ;  dark  epithelium     presents     a  Clear     ZOttC     devoid     OI 

field  shows  olfactory  area  on  lateral  and  mesial  nllr|«:  Trip  innpr  rvjrt  r«f  rhp  ciinnnrrino-  rf>11c 
walls  of  fossa,  as  mapped  out  by  Brutin..  1C*. 

is  thinner  and    irregular  in   contour  and  often 

terminates  by  splitting  into  two  or  more  basal  processes  that  rest  upon  the  tunica 
propria.  Between  these  ends  lie  smaller  pyramidal  elements,  the  basal  cells,  that 


FIG.  1178. 


Outer  zone 
Nuclear  layer  of 
supporting  cells 

Olfactory  cells 


Blood-vessel 
Glands 


Bundle  of 

olfactory  nerves 


^fetl^ffe 

-^<^«^«i»s^^^«^v<V1Ra      \'i     \fJ5> 
-  •  V>  « *"*.•«£?&•  A*& -•^fiSL^X'v— ^ v M 

*"*5Ss*«^**^--^><;1*"-^'  -  "      -:      "v-\\ 


Section    of    olfactory   mucous    membrane;    epithelium   displays  outer  nuclei-free   and   nuclear   layers   formed    by 
supporting  cells  and  broad  stratum  containing  nuclei  of  olfactory  ci-lls.      <  300. 

probably   represent  younger  and  supplementary  forms  of  the   sustentacular  cells. 
The  granular  protoplasm  of  the  basal  processes  often  contains  pigment  particles. 

The  olfactory  cells,  the  perceptive  elements  receiving  the-  smell-stimuli,  con- 
sist of  a  fusiform  body,  lodging  a  spherical  nucleus  enclosed  by  a  thin  envelope  of 
cytoplasm,  and  two  attenuated  processes,  a  peripheral  and  a  central.  The  olfactory 
cells  are  in  fact  sensory  neurones  that  have  retained  their  primitive  position  within 
the  surface  epitheliinfl,  as  in  many  invertebrates,  instead  of  receding,  as  is  usual  ii» 


THE  NASAL  MUCOUS  MEMBRANE. 


the  higher  animals,  to  situations  more  remote  from  the  exterior.  The  slender 
peripheral  process  of  the  olfactory  cell,  which  corresponds  to  the  dendrite  of  the 
neurone,  is  of  uniform  thickness  and  ends  at  the  surface  in  a  small  hemispherical 
knob  that  projects  slightly  beyond  the  general  level  of  the  epithelium  and  bears  from 
6-8  minute  stiff  cilia,  the  olfactory  hairs.  The  length  of  the  peripheral  processes, 
being  dependent  upon  the  position  of  the  nuclei,  varies,  since  the  latter  occupy 
different  levels  within  the  epithelium  in  order  to  accommodate  their  greater  number — 
about  60  per  cent,  in  excess  of  those  of  the  supporting  cells  (Brunn).  The  central 


FIG.  1180. 


FIG.  1179. 


Olfactory  cell 
Supporting  cell 


Nerve-fibre 


Section  of  numan  olfactory  mucous 
membrane,  silver  preparation ;  two 
olfactory  cells  are  seen,  one  of  which 
sends  nerve-fibre  towards  brain.  X  335. 
(Brunn.) 


Isolated  elements  of  epithelium  of  olfactory 
mucous  membrane ;  a,  olfactory  cells  ;  &,  sup- 
porting cells.  X  1000.  (Brunn.) 


processes  of  the  olfactory  cells,  much  more  delicate  than  the  peripheral,  are  directly 
continued,  as  the  axis-cylinders,  into  the  subjacent  nonmedullated  nerve-fibres  within 
the  tunica  propria,  from  which  they  pass  through  the  cribriform  plate  to  enter  the 
brain  and  end  in  the  arborizations  within  the  olfactory  glomeruli  of  the  bulbus 
olfactorius  (page  1152). 

The  tunica  propria  is  differentiated  into  a  superficial  and  a  deep  layer  by 
the  adenoid  character  of  the  stratum  immediately  beneath  the  epithelium.  The 
superficial  layer,  from  .01 5 -.020  mm.  thick,  consists  of  closely  packed  irregularly 
round  cells,  resembling  lymphocytes,  and  meagre  bundles  of  delicate  connective 
tissue.  The  deep  layer,  on  the  other  hand,  contains  robust  bundles  of  fibro-elastic 
tissue  and  relatively  few  cells.  A  distinct  membrana  propria  is  wanting  within  the 
olfactory  region. 

The  glands  of  Bowman  (glandulae  olfactoriae)  are  characteristic  of  the  olfactory 
region  and  probably  elaborate  a  specific  secretion  (Brunn).  They  open  onto  the 
free  surface  by  very  narrow  ducts  that  lead  into  saccular  fusiform  dilatations,  into 
which  the  tubular  alveoli  open.  The  ducts  possess  an  independent  lining  of  flattened 
cells  that  extend  as  far  as  the  surface  and  lie  between  the  surrounding  epithelial  ele- 
ments. The  dilatations  are  clothed  with  flattened  or  low  cuboidal  cells,  which  are 
replaced  by  those  of  irregular  columnar  or  pyramidal  form  within  the  tubular 
alveolar.  From  the  character  of  their  secretion  the  glands  of  Bowman  are  probably 
to  be  reckoned  as  serous  and  not  mucous  (Brunn,  Dogiel). 

The  Respiratory  Region. — The  mucous  membrane  lining  of  the  respiratory 
region  differs  greatly  in  thickness  in  various  parts  of  the  nasal  fossa.  In  situations 
where  the  contained  cavernous  tissue  is  well  represented,  as  over  the  inferior  turbinate, 
it  may  reach  a  thickness  of  several  millimeters,  while  when  such  tissue  is  wanting,  as 
on  the  lateral  wall,  it  is  reduced  to  less  than  a  millimeter. 


1416 


HUMAN   ANANOMY. 


The  epithelium  is  stratified  ciliated  columnar  in  type,  from  .050-. 070  mm. 
thick,  and  includes  the  tall  surface  cells,  bearing  the  cilia,  between  the  inner  ends  of 
which  lie  the  irregularly  columnar  basal  cells.  Numerous  elements  exhibit  various 
stages  of  conversion  into  mucous  containing  goblet  cells.  The  current  produced  by 
the  cilia  is  toward  the  posterior  nares. 

Beneath  the  epithelium  stretches  the  membrana  propria  or  basement  membrane, 
that  varies  greatly  in  thickness  ;  although  in  certain  localities  feebly  developed,  it  is 
usually  well  marked  and  measures  from  .010-. 020  mm.  in  thickness  (Brunn) 


Duct  of  glands 


Blood-vessel 


/^^^^^ap^jv^v^gi 
I      "'fcilSf^li^^^S 


Glands 


•'•[•••:•••••-•'•  ••••'•• 

Section  of  respiratory  mucous  membrane  covering  nasal  septum.     X  75- 

Under  pathological  conditions  its  thickness  may  increase  fourfold  or  more.  In  many 
places  the  membrana  propria  is  pierced  by  minute  vertical  channels,  the  basal  canals, 
in  which  connective-tissue  cells  and  leucocyctes  are  found,  but  never  blood-capillaries 
(Schiefferdecker). 

The  tunica  propria  consists  of  interlacing  bundles  of  fibro-elastic  tissue  which 
are  most  compactly  disposed  towards  the  subjacent  periosteum.  The  looser  super- 
ficial stratum  is  rich  in  cells  and  here  and  there  contains  aggregations  of  lymphocytes 
that  may  be  regarded  as  masses  of  adenoid  tissue  (Zuckerkandl).  In  certain  parts 
of  the  nasal  fossa  the  stroma  of  the  mucous  membrane  contains  vascular  areas  com- 
posed of  numerous  intercommunicating  blood-spaces  that  confer  the  character  of  a 
true  cavernous  tissue.  These  specialized  areas,  the  corpora  cavernosa,  as  they  are 
called,  are  especially  well  developed  over  the  inferior  and  the  lower  margin  and 
posterior  extremity  of  the  middle  conchae,  and  less  so  over  the  posterior  end  of 
the  upper  turbinate  and  the  tuberculum  septi.  When  typical,  they  occupy  practically 
the  entire  thickness  of  the  mucous  membrane  from  periosteum  to  epithelium,  tin- 
interlacunar  trabeculae  containing  the  glands  and  blood-vessels  destined  for  the  sub- 
epithelial  stroma.  The  blood-sinuses,  tin  general  disposition  of  which  is  vertical 
to  the  bone  (Zuckerkandl),  include  a  superficial  reticular  zone  of  smaller  spaces 
and  a  deeper  one  of  larger  lacuna?.  The  engorgement  and  emptying  of  the  cavernous 
tissue  is  controlled  by  nervous  reflexes  and  probably  has  warming  of  the  inspired  air 
as  its  chief  purpose  (Kallius  ). 

The  glands  of  the  respiratory  region  are  very  numerous,  although  varying  in 
size,  tubo-alveolar  in  form  and,  for  the  most  part,  mixed  mucous  in  type.  The 
chief  ducts  open  on  the  free  surface  by  minute  orifices  barely  distinguishable  with  the 
unaided  eye.  Their  deeper  ends  branch  irregularly  into  tubes  that  bear  the  ovoid 
terminal  alveoli.  The  latter  are  lined  with  mucous-secreting  cells,  between  which  lie 


PRACTICAL   CONSIDERATIONS:    THE   NASAL  CAVITIES.      1417 


FIG.  1182. 


the  crescentic   groups  of   serous   cells   that   stamp   the   glands  as   mixed   (Stohr). 
Exceptionally  exclusively  serous  glands  are  also  encountered  (Kallius). 

Jacobson's  Organ.— Mention  has  been  made  of  the  rudimentary  structure 
(organon  vomeronasale)  found  in  man,  almost  constantly  in  the  new-born  child  and 
frequently  in  the  adult,  as  a  representative  of  the  organ  of  Jacobson  that  is  present> 
in  varying  degrees  of  perfection,  in 
all  amniotic  vertebrates  (Peter).  In 
many  animals  possessing  in  high 
degree  the  sense  of  smell  (macros- 
matic),  the  organ  is  well  developed 
and  functions,  serving  possibly  as  an 
accessory  and  outlying  surface  by 
which  the  first  olfactory  impressions 
are  received  (Seydel). 

In  man  the  organ  is  represented 
by  a  laterally  compressed  tubular 
diverticulum,  from  1.5-6  mm.  in 
length,  that  passes  backward  and 
slightly  upward  to  end  blindly  be- 
neath the  mucous  membrane  on  each 
side  of  the  septum.  The  entrance 
to  the  tube  is  a  minute  aperture 
situated  near  the  lower  border  of 
the  septum,  above  the  anterior  nasal 
spine  and  the  rudimentary  vomerine 
cartilage.  The  median  wall  of  the 
diverticulum  is  clothed  with  epithe- 
lium composed  of  tall  columnar  cells 
resembling  those  of  the  olfactory 
region,  but  the  characteristic  olfac-  HIHUWIHW 

£orv  rgUs  are  wanting?"       The  eoithe-       Portion  of  frontal  section  through  nasal  fossae  of  kitten,  showing 
p"      .  organ  of  Jacobson.     X  20. 

hum    covering   of   the    lateral    wall 

corresponds  to  that  of  the  respiratory  region.      In  macrosmatic  animals  branches  of 

the  olfactory  nerve  are  traceable  to  Jacobson's  organ  in  which  are  found  olfactory  cells. 


PRACTICAL  CONSIDERATIONS  :  THE  NASAL  CAVITIES. 

The  nasal  cavities  have  certain  important  clinical  relationships  which  may  be 
classified  as  (i)  physiological — (a)  respiratory,  phonatory  and  olfactory  ;  ($)  sexual  ; 
(2)  topographical — (a)  the  nasal  chamber  and  the  vestibule  ;  (£)  the  premaxillary, 
maxillary,  and  palatal  portions  ;  (c)  the  septum,  and  the  turbinate  bones. 

i.  (a)  The  air  passing  out  from  the  pharynx,  being  confined  to  the  plane  of 
the  posterior  nares,  is  not  carried  up  to  the  olfactory  region,  so  that  the  odors  on  the 
expired  breath  are  not  appreciated.  When  the  communication  between  the  respira- 
tory and  olfactory  portions  is  cut  off,  as  by  swell  of  the  mucous  membrane  at  the 
region  of  union  of  these  portions,  loss  of  smelling  supervenes.  Discharge  which  may 
accumulate  about  the  middle  turbinate  bone  or  in  the  upper  portion  of  the  vestibule 
cannot  be  removed  by  the  act  of  blowing  the  nose,  for  the  reason  above  assigned  that 
the  air  of  expiration  cannot  pass  within  the  olfactory  portion.  The  act  of  blowing 
the  nose,  or  the  process  of  washing  out  the  nose  by  a  current  thrown  in  from  the 
naso-pharynx,  will  wash  out  the  inferior  meatus  with  ease,  provided  the  discharge  is 
not  inspissated,  and  the  parts  of  the  floor  of  the  nose  are  normal  (Allen).  An 
abnormal  width  or  patency  of  the  respiratory  portion  of  the  fossa — especially  of  the 
inferior  meatus — due  to  imperfect  development  of  the  inferior  turbinates,  has 
been  thought  (Lack),  by  diminishing  the  vis  a  tcrgo  in  blowing  the  nose  and  thus 
favoring  the  retention  and  decomposition  of  the  nasal  mucus,  to  contribute  to  the 
occurrence  of  atrophic  rhinitis  (ozaena).  The  value  of  the  nose  as  an  accessory 
organ  of  phonation  consists  in  its  action  as  a  resonating  cavity  which  adds  quality, 
color  and  individuality  to  the  voice.  This  function  of  the  nose  becomes  strikingly 


I4i8  HUMAN   ANATOMY. 

apparent  when,  as  during  an  acute  coryza,  the  fossae  are  more  or  less  completely 
obstructed  and  the  voice  becomes  flat  and  entirely  without  resonance. 

(£)  The  relations  between  the  nasal  chambers  and  the  sexual  apparatus  are  of 
practical  importance  and  have  as  an  anatomical  basis  the  analogy  between  the  mucosa 
covering  much  of  the  turbinates  and  part  of  the  septum,  and  the  erectile  tissue  of  the 
penis,  and  the  sympathy  between  the  erectile  portions  of  the  generative  tract  and 
erectile  structures — e.  g. ,  the  nipple — in  other  parts  of  the  body. 

2.  (a)  The  distinction  between  the  nasal  chamber  and  the  vestibule  is,  in  the 
main,  based  upon  the  difference  in  their  lining  membrane,  that  of  the  vestibule 
being  simply  a  continuation  inward  of  the  external  integument  to  the  line  (timen 
nasi}  at  which  the  nasal  fossa  proper  begins.  The  vestibular  cavity  is  provided  with 
rigid  hairs  (to  aid  in  arresting  foreign  particles  carried  in  with  the  air  current),  and 
sebaceous  glands,  and  is  especially  susceptible  to  eczematous  or  furuncular  affections. 
Diseases  of  the  vestibule  may,  therefore,  be  dealt  with  as  though  they  were  affections 
of  the  skin  ;  while  diseases  of  the  mucosa  of  the  nasal  chambers  are  to  be  treated  on 
the  same  principles  as  those  of  the  mucous  membranes  generally,  with  special  refer- 
ence to  its  erectile  character  and  to  its  close  relation  to  the  underlying  periosteum 
.and  bone. 

(<£)  The  sutural  lines  of  the  premaxilla,  of  the  maxilla,  and  of  the  palatal  bones 
aid  in  determining  the  boundaries  of  the  subdivisions  of  the  nasal  chamber,  which 
are  indicated  to  some  degree  by  the  production  of  the  planes  of  the  sutures  of  the 
roof  of  th^  mouth,  vertically  upward  through  the  nasal  chambers. 

(c')  The  morphological  significance  of  the  septum,  placed  as  it  is  in  the  median 
line  of  the  face  of  the  embryo,  with  the  turbinate  bones  lodged  to  its  right  and  left 
sides,  remains  the  same  in  the  skull  of  the  adult,  notwithstanding  the  fact  that,  with 
cultivated  races  at  least,  the  septum  is  usually  deflected  through  the  greater  part  of 
its  course  from  the  median  line.  This  deflection  has  been  said  to  be  due  to  the 
persistent  growth  of  the  septal  bones  in  a  vertical  plane  after  their  edges  have 
united — the  apex  of  the  deflection  being  often  found  at  the  junction  of  the  ethmoid 
and  vomer  ;  any  preponderance  in  strength  of  one  of  these  bones  will  cause  bending 
of  the  weaker — usually  the  perpendicular  plate  of  the  ethmoid.  The  usual  direction 
of  the  deflection  is  to  the  left,  and  this  has  been  thought  to  be  due  to  the  habit  of 
using  the  right  hand  in  blowing  the  nose.  Asymmetry  of  the  nasal  chambers  is  a 
result  of  the  deflection.  One  of  these  chambers,  commonly  the  left,  is  much  smaller 
than  its  fellow  of  the  opposite  side,  and  may  be  occluded,  when  the  right  chamber 
will  be  larger  than  normal  and  possess  both  osseous  and  erectile  structures  which 
have  undergone  physiological  hypertrophy.  Care  should  be  taken  to  distinguish 
between  such  hypertrophy  and  the  effects  of  diseased  action  (Allen). 

The  anterior  nares  are  directed  downward  and  are  on  a  lower  plane  than  the 
floor  of  the  nose.  To  examine  the  interior  of  the  nose  the  movable  nostril  must 
therefore  be  elevated  and  the  head  thrown  backward.  The  speculum  shaped  for  the 
purpose  should  not  be  passed  beyond  the  dilatable  cartilaginous  portion.  With  good 

«  •  .  r     .  1  "ill.  !•.!-_  1        _  *.. _f 

light  one  may  see  the  anter 

the  inferior  turbinate,  the  b« 

inferior  meatus,  the  septum 

duct  cannot  be  seen,  although  it  is  only  about  an  inch  from  the  orifice  of  the  nostril, 

and  three-fourths  of  an  inch  above  the  floor  of  the  nose.     This  is  due  to  the  fac' 

that  it  is  concealed  behind  the  attached  and  depressed  anterior  end  of  the  inferio 

turbinate. 

To  expose  better  the  structures  in  the  external  wall  of  the  narrow  and  rigi 
nasal  fossa,  various  procedures  have  been  adopted.  Rouge  made  an  opening  into 
the  anterior  nares  from  the  mouth,  by  incising  in  the  angle  between  the  upper  lip  and 
the  gum.  By  separating  the  alar  cartilages  from  the  bones  and  dividing  the  cartilag- 
inous septum  the  movable  anterior  portion  of  the  nose  can  be  turned  upward,  giving 
a  full  exposure  of  the  nasal  fossae,  without  leaving  an  unsightly  scar. 

To  permit  a  freer  exploration  with  the  linger,  Kocher  divided  the  septum  as  far 
back  as  possible  with  scissors.  He  also  divided  the  roof  of  the  nose  near  the  septum, 
turning  the  divided  parts  aside.  An  osteoplastir  flap  may  be  made  by  extending  this 
incision  upward,  dividing  the  bone  in  this  line  and  making  a  second  incision  around 


PRACTICAL   CONSIDERATIONS:   THE  NASAL  CAVITIES.      1419 

the  alae  and  along  the  side  of  the  nose,  again  dividing  the  bone.  The  flap  thus 
formed  can  be  turned  upward,  after  breaking  the  bridge  of  bone  between  the  upper 
ends  of  the  two  incisions,  exposing  the  nasal  fossa. 

The  finger  can  be  passed  backward  through  the  nostril  far  enough  to  meet  the 
finger  of  the  other  hand  passed  to  the  posterior  nares  through  the  mouth. 

The  posterior  nares  can  be  examined  by  the  rhinoscopic  mirror  or  by  the  finger 
introduced  through  the  mouth.  Posterior  rhinoscopy,  like  laryngoscopy,  is  carried 
out  with  difficulty,  because  the  region  of  the  naso-pharynx  is  sensitive  and  is  intol- 
erant of  intrusion.  In  the  act  of  swallowing,  the  epiglottis  protects  the  larynx  by 
closing  the  laryngeal  opening,  and  the  soft  palate  rises  against  the  posterior  wall  of 
the  pharynx,  preventing  regurgitation  into  the  nose.  When  the  rhinoscopic  mirror 
is  used  the  same  thing  occurs,  so  that  the  view  of  the  larynx  and  naso-pharynx  is 
shut  off.  Considerable  difficulty  is  sometimes  experienced  in  training  the  patient  to 
•overcome  this  tendency.  The  employment  of  the  nasal  douche  is  based  upon  the 
same  mechanism.  When  the  stream  of  fluid  passed  through  one  nostril  reaches  the 
posterior  part  of  the  nose,  its  progress  toward  the  mouth  is  obstructed  by  the  elevated 
soft  palate,  and  it  therefore  passes  around  the  posterior  edge  of  the  septum  and  back 
through  the  opposite  nasal  fossa. 

With  the  rhinoscopic  mirror  in  good  position,  and  the  soft  palate  quiet,  one 
may  see  the  posterior  nares  divided  by  the  septum,  the  turbinated  bones,  and  the 
meati  (especially  the  middle  turbinate  and  the  middle  meatus),  the  roof  of  the  naso- 
pharynx and  "the  orifices  of  the  Eustachian  tubes.  The  finger  introduced  through 
the  mouth  can  feel  the  same  structures,  and  can  recognize  naso-pharyngeal  adenoids, 
tumors,  or  abscesses. 

The  mucous  membrane  over  the  turbinates,  owing  to  the  presence  of  a  rich 
venous  plexus,  is  one  of  the  most  vascular  in  the  body,  and  resembles  erectile  tissue 
(page  1968).  This  and  the  general  vascularity  of  the  nose  partly  explain  the  great 
frequency  of  epistaxis.  The  excessive  supply  of  blood  to  the  mucosa  may  be  (a)  for 
the  purpose  of  enabling  it  to  raise  the  temperature  and  add  to  the  moisture  of  the 
inspired  air  ;  ($)  to  favor  the  activity  of  the  numerous  mucous  glands,  the  free  secre- 
tion of  which  together  with  the  action  of  the  cilia  of  the  epithelial  cells  is  required  to 
remove  the  dust  and  the  micro-organisms  that  are  filtered  from  the  air  during  inspi- 
ration by  the  vibrissse  and  the  cilia  themselves  ;  (c)  to  endow  it  with  sufficient  vitality 
to  resist  the  pathogenic  action  of  such  micro-organisms.  In  spite  of  this  defensive 
quality,  the  constant  exposure  to  atmospheric  irritants  often  leads  to  congestions  and 
coryzas,  which  if  long  continued  and  frequently  repeated  result  in  hypertrophy  of 
the  mucous  membrane.  This  may  require  removal  by  cauterization  or  excision  to 
relieve  the  consequent  obstruction.  The  mucous  membrane  is  somewhat  less  closely 
attached  to  the  septum  than  to  the  neighboring  parts,  and  hence  haematomata  of  the 
septal  submucosa  are  not  infrequent  after  an  injury  to  the  nose.  Such  haematomata 
are  almost  invariably  infected  and  proceed  to  suppuration  forming  septal  abscesses, 
the  constitutional  symptoms  (toxaemia)  of  which  may  give  rise  to  anxiety  if  their 
local  cause  is  overlooked. 

Epistaxis  is  common  not  only  because  of  (a)  this  vascularity  of  the  mucosa,  but 
also  by  reason  of  (£)  the  frequency  of  trauma  to  the  nose  ;  the  relation  of  its  veins 
(c~)  to  the  general  venous  current  so  that  they  may  be  congested  in  cardiac  or  in  pul- 
monary disease,  or  in  straining,  or  in  paroxysms  of  coughing,  as  in  whooping  cough  ; 
and  (d)  to  the  intracranial  sinuses,  so  that  nose-bleed  may  be  a  symptom  of  cerebral 
congestion  or  tumor  ;  (<?)  the  bleeding  may  be  vicarious,  as  in  cases  of  suppressed 
menstruation  (an  illustration  of  the  sexual  relations  of  the  nasal  apparatus);  (/) 
it  not  uncommonly  follows  ulceration — simple,  tuberculous  or  syphilitic — and  in 
obstinate  cases  such  ulcers  should  always  be  sought  for. 

The  source  of  hemorrhage  from  the  nose  is  most  frequently  in  the  anterior  part, 
particularly  on  the  septum,  and  is  then  ordinarily  controlled  with  ease.  Usually  the 
patient  should  be  kept  upright,  with  the  head  back,  (not  in  the  usual  position  lean- 
ing over  a  basin,  increasing  the  tension  of  the  vessels  of  the  neck  and  head)  and 
should  be  made  to  take  deep  breaths  with  the  arms  raised,  thus  fully  expanding  the 
thorax  and  depleting  the  cervical  veins  and,  indirectly,  the  facial  and  ophthalmic  into 
which  the  veins  of  the  nose  empty.  If  ordinary  means  fail,  and  this  is  more  likely 


i42o  HUMAN   ANATOMY. 

if  the  bleeding  point  is  posterior,  the  posterior  nares  may  be  plugged.  For  this 
purpose  a  long  silk  ligature  is  passed  through  the  nose  to  the  pharynx  and  out 
through  the  mouth,  by  means  of  a  Bellocq's  cannula  or  a  soft  catheter.  To  me 
middle  of  the  ligature  is  attached  a  plug  of  gauze  slightly  larger  than  the  posterior 
nares,  which  is  then  drawn  by  the  anterior  end  of  the  ligature  into  the  nasal  fossa, 
which  it  should  tightly  fill. 

Postnasal  adenoids  originate  in  the  normally  excessive  lymphoid  tissue — pharyn- 
geal  tonsil — of  the  postnasal  space,  of  which  tissue  they  are  a  simple  hypertrophy. 
The  growth  forms  a  mass  in  the  vault  of  the  naso-pharynx  and  often  extends  down- 
ward and  forward,  rilling  up  Rosenmiiller's  fossae  and  involving  the  orifices  of  the 
Eustachian  tubes.  The  tonsils  are  commonly  also  enlarged. 

The  symptoms  produced  are  :  (a)  obstructed  nasal  respiration,  more  marked 
during  sleep,  when  the  mouth  is  closed  by  the  approximation  of  the  tongue  to  the 
palate  ;  (£)  as  a  result  of  this,  broken  rest  and  "  night  terrors"  ;  and  (c)  as  a  further 
consequence  (and  also  from  deficient  oxygenation),  deterioration  of  the  general 
health,  delayed  or  arrested  growth,  and  anaemia  ;  (d)  intermittent  partial  deafness 
and  recurrent  attacks  of  catarrhal  or  suppurative  otitis  media  ;  (e)  pigeon-breast  from 
inequality  of  intra-  and  extra-thoracic  atmospheric  pressure. 

The  early  removal  of  adenoids  that  produce  any  or  all  of  these  symptoms  is 
usually  indicated,  and  is  facilitated  by  their  friability  and  by  the  toughness  and  den- 
sity of  the  submucosa  on  which  they  lie,  circumstances  which  permit  of  their  usually 
easy  enucleation  either  with  the  fingers  or  with  the  adenoid  forceps  and  curette. 

Naso-pharyngeal  growths  may  be  either  simple  fibromata  or  ribro-sarcomata. 
They  are  usually  dense,  and  contain  large  venous  channels,  which  have  no  definite 
sheath  and  thus  do  not  retract  when  severed.  Incision  into  them  may  therefore  be 
followed  by  severe  hemorrhage  with  no  tendency  to  spontaneous  arrest.  Ulceration 
or  abrasion  of  the  surface  of  these  growths  is  not  infrequent,  and  is  also  attended  by 
repeated  and  often  dangerous  loss  of  blood. 

The  nasal  fossae,  already  very  narrow,  are  frequently  further  obstructed  by  path- 
ological conditions,  such  as  deviations  of  the  septum,  hypertrophy  of  the  mucous 
membrane  covering  the  turbinates,  spurs  on  the  septum,  polypi  and  tumors.  The 
septum  is  rarely  straight  after  the  seventh  year,  in  about  seventy-five  per  cent,  of 
cases  being  turned  to  one  or  the  other  side,  most  frequently  the  left  (vide  supra). 
Both  the  bony  and  cartilaginous  portions,  more  especially  the  anterior  cartilaginous, 
are  involved.  The  deflection  is  sometimes  due  to  a  fracture  from  blows  or  falls.  The 
whole  nose  usually  deviates  more  or  less  to  one  side.  Spurs  on  the  septum  com- 
monly occur  at  the  junction  of  the  bony  and  cartilaginous  portions.  A  deviation  of 
the  septum  does  not  necessarily  mean  that  the  narrowed  nasal  fossa  is  seriously 
obstructed.  It  frequently,  however,  comes  in  contact  with  the  surface  of  the  turbin- 
ates, and  may  result  in  an  adhesion  or  synechia  from  the  irritative  inflammation  which 
is  set  up.  Operations  are  often  necessary  to  correct  the  difficulties  arising  from 
deviation  of  the  septum.  The  concavity  on  the  opposite  side  will  differentiate  it  from 
a  tumor. 

Hypertrophy  of  the  ethmoidal  labyrinth,  or  bulla  ethmoiclalis,  is  sometimes  sa 
far  advanced  as  to  obstruct  the  nasal  fossa  on  that  side.  The  middle  turbinate  over- 
lies and  yields  before  this  expanded  cell,  and  may  even  press  against  the  septum 
to  such  an  extent  as  to  make  it  bend  and  obstruct  the  opposite  nasal  fossa  to 
a  greater  or  lesser  degree.  The  removal  of  the  middle  turbinate  is  sometimes 
practiced  in  these  cases  (Taylor),  or  the  bulla  itself  may  be  obliterated  by  means  of 
the  cutting  forceps  or  curette.  Over-development  of  the  bulla  ethmoidalis  may  at 
times  be  so  great  as  to  occasion  obstruction  of  the  upper  portion  of  the  corresponding 
nasal  fossa. 

The  floor  of  the  nose  is  the  widest  part,  and  slopes  gradually  backward  and 
downward  in  the  upright  position,  so  that  collecting  mucus  tends  to  run  backward 
and  drop  into  the  throat.  Rhinoliths,  which  arc  incrustations  usually  about  a  foreign 
body,  are  most  frequently  found  in  the  inferior  im-atus,  which  is  the  largest.  The 
posterior  nares  are  below  the  level  of  the  respiratory  portion,  so  that  any  discharge 
above  the  middle  turbinate  cannot  be  blown  from  the  nose.  The  anterior  portion  of 
the  inferior  turbinate  slopes  downward  and  forward,  and  its  anterior  end  is  attached 


THE   ACCESSORY   AIR-SPACES. 


1421 


-so  near  the  floor  of  the  nose  that  the  roomiest  portion  of  the  inferior  meatus  is 
posterior.  Therefore,  the  entrance  of  air  into  the  lower  part  of  the  nasal  fossa  is 
obstructed,  and  is  favored  toward  the  upper — "respiratory" — portion,  especially 
through  the  wide  anterior  opening  of  the  middle  meatus,  which  reaches  as  high  as 
the  tendo-oculi.  This  anatomical  arrangement  is  the  explanation  of  the  fact  already 
mentioned,  that  odors  on  expired  air  are  not  recognized. 

The  relations  of  the  nasal  chambers  explain  why  a  coryza  may  cause  (a)  lach- 
rymation,  by  affecting  the  tear  duct,  lachrymal  sac,  and  conjunctiva  ;  (^)  dysphagia, 
by  extending  to  the  pharynx  by  way  of  the  posterior  nares  ;  (c)  hoarseness  or  cough, 
by  further  extension  to  the  respiratory  tract  ;  (d)  frontal  headache,  by  involving  the 
frontal  sinuses  ;  (e)  "face  ache,"  by  implicating  the  antrum  ;  (/)  grave  intraorbital 
or  intracranial  disease,  by  way  of  either  the  ethmoidal  cells  or  the  sphenoidal  sinuses  ; 
basal  meningitis  by  extending  along  the  perineural  or  perivascular  sheaths,  or  by 
way  of  the  lymphatics  through  the  cribriform  foramina  to  the  floor  of  the  anterior 
cranial  fossa  ;  (£•)  extension  to  the  retropharyngeal  lymph  node  (page  955),  into 
which  certain  of  the  nasal  lymphatics  empty,  may  result  in  a  retropharyngeal  ab- 
scess ;  or  (A)  infection  (pyogenic  or  tuberculous)  of  the  submaxillary,  preauricular, 
or  deep  cervical  nodes  may  follow  nose  diseases.  The  graver  of  these  complications 
are,  of  course,  associated  with  the  severer  infective  forms  of  rhinitis.  Malignant 
growths — commonly  sarcomatous — may  begin  in  the  nasal  chambers  and  may  extend 
in  any  of  the  directions  above  mentioned. 

THE  ACCESSORY  AIR-SPACES. 

The  nasal  fossae  communicate  with  a  number  of  remarkable  cavities,  hollowed 
out  within  the  surrounding  bones,  which  are  filled  with  air  and  lined  by  mucous 
membrane  directly  continuous  with  that  of  the  meatuses.  These  pneumatic  spaces 
include  the  maxillary,  the  frontal,  the  sphenoidal  and  the  palatal  sinuses  and  the 


FIG.  1183. 


Roof  of  inferior  meatus 


Right  maxillary  sinus 


Lower  lateral  cartilage 
Septum 


Masscter  muscle- 


Roof  of  inferior  meatus 


Inferior  turbinate 


Roof  of 
naso-pharynx 
Temporal  muscle 
Masseter  muscle 

Internal 
pterygoid  muscle 

Eustachian  tube 

Condyle  of 
mandible 


Internal  carotid  artery 


Pharyngeal  tonsil 


\  External  pterygoid  muscle 

Fosa  of  Rosenmiiller 


Portion  of  transverse  section  of  head  passing  through  nasal  fossae  just  below  middle  turbinates;  the  inferior  surface 
of  the  section  has  been  drawn  and  the  nasal  fossae  and  other  spaces  are  viewed  from  below. 

ethmoidal  air-cells,  all  paired  and  within  the  corresponding  bones.  Since  the 
mucous  membrane  is  thin  and  intimately  adherent  to  the  bones,  the  form  of  the  cavi- 
ties as  observed  in  the  recent  condition  corresponds  closely  to  that  seen  in  the 
macerated  skull.  The  size  and  extent  of  the  spaces  vary  not  only  at  different  periods 


1422 


HUMAN    ANATOMY. 


of  life,  but  also  often  on  the  two  sides  of  the  same  individual  ;  their  communications 
with  the  nasal  fossae,  however,  are  fairly  constant. 

The  Maxillary  Sinus. — This  space,  (sinus  maxillaris),  or  the  ant  rum  of 
Highmore,  the  largest  of  the  pneumatic  cavities,  lies  to  the  outer  side  of  the  nasal 
fossa  and  resembles  in  its  general  form  a  three-sided  pyramid  (Fig.  1184).  It 
occupies  the  greater  part  of  the  superior  maxillary  bone,  so  that  its  walls,  with  the 
exception  of  the  postero-inferior  one,  are  very  thin  and  often  in  places  of  papery 
delicacy  (Fig.  256).  The  median  wall,  or  base,  is  directed  toward  the  nasal  fossa,  from 
which  it  is  separated  by  a  thin  osseous  partition  in  the  formation  of  which  the  vertical 
plate  of  the  palate  bone,  the  uncinate  process  of  the  ethmoid,  the  maxillary  process 
of  the  inferior  turbinate  and  a  small  part  of  the  lachrymal  bone  assist.  The  apc.v  lies 
at  the  zygomatic  process  of  the  maxilla.  The  upper  or  orbital  wall  is  thin  and  often 

FIG.  1184. 


Vestibule 


Anterior  ethmoidal  cells 


Left  maxillary  sinus 


Left  sphenoidal  cell 


Inferior  in  cat  us 
Place  where  frontal  sinus  was  attached 


Anterior  ethmoidal  cells 


Maxillary  sinus 
Posterior  ethmoidal  cells 


r Right  sphenoidal  cell 


Naso-pharynx 


Cast  of  nasal  fossae  and  accessory  air-spaces,  viewed  from  above;   casts  of  frontal  sinuses  have  been  removed; 

natural  size.    (Kallius.) 

modelled  by  the  ridge  containing  the  infraorbital  canal.  The  anterior  wall  presents 
towards  the  face  and  is  varyingly  impressed  by  the  canine  fossa.  The  postero- 
inferior  wall  is  normally  the  thickest,  but  is  sometimes  reduced  by  extension  of  the 
sinus  into  the  adjacent  alveolar  border.  The  sinuses  are  often  so  modified  by  local 
enlargements  that  the  typical  pyramidal  form  is  lost  and  their  dimensions  materially 
influenced.  As  an  indication  of  the  size  of  the  average  sinus,  a  sagittal  diameter  of 
35  mm.  (1^6  in.),  and  a  vertical  and  frontal  one  of  27  mm.  (about  i  in.),  each 
(Kallius)  may  be  taken  as  approximate  measurements.  Not  infrequently,  however, 
considerable  asymmetry  exists  even  to  the  extent  of  one  antrum  being  almost  twice  as 
large  as  the  other.  The  usual  capacity  of  the  antrum  is  between  12-18  cc.  (3/^-^ 
-4  fl.  dr.  ),  with  an  average  of  approximately  15  cc. ,  or  4  fl.  dr.  (Braune  and  Clasen). 
The  antrum  communicates  indirectly  with  the  middle  meatus  by  means  of  an 
ajx  itiiK  (  ostiuni  imtxillare)  that  pierces  the  upper  and  anterior  part  of  the  base  to 
open  into  the  infundibtilum,  and  thence  by  way  of  the  hiatus  semilunaris,  into  the 


THE    ACCESSORY   AIR-SPACES. 

meatus.  The  ostium,  which  is  usually  in  the  lateral  wall  of  the  infundibulum, 
about  one  centimeter  from  the  upper  end  of  the  hiatus,  is  an  oval  or  elliptical  cleft 
of  variable  size,  with  extremes  of  length  from  3—19  mm.  (Zuckerkandl),  and  from 
2-5  mm.  in  width.  An  additional  communication  (ostium  accessorium),  present 
in  about  10  per  cent.,  likewise  opens  into  the  infundibulum,  lying  behind  the  chief 
aperture.  It  is  ordinarily  small,  its  diameter  being  only  a  few  millimeters.  The 
mucous  membrane  lining  the  maxillary  sinus  is  directly  continuous  with  that 
covering  the  lateral  wall  of  the  nasal  fossa.  With  the  exception  of  being  thinner,  it 
corresponds  in  structure  with  the  mucous  membrane  of  the  respiratory  region,  being 
invested  with  ciliated  columnar  epithelium  and  possessing  numerous,  although  small 
and  scattered,  tubo-alveolar  glands. 

Variations. — The  investigations  of  Zuckerkandl  (Kallius)  have  shown  tnat  enlargement  of 
the  maxillary  sinus  may  be  produced  by:  (i)  hollowing  out  of  the  alveolar  process  (alveolar 
recess)  ;  (2)  excavation  of  the  floor  of  the  nasal  fossa  by  extension  of  the  alveolar  recess 
between  the  plates  of  the  hard  palate  (palatal  recess);  (3)  encroachment  of  the  sinus  into  the 
frontal  process  of  the  maxilla  ;  (4)  hollowing  out  of  the  zygomatic  process  of  the  malar  bone 
(malar  recess) ;  (5)  extension  to  and  appropriation  of  a,n  air-cell  within  the  orbital  process  of 
the  palate  bone  (palatal  recess).  Contraction  of  the  maxillary  sinus,  on  the  other  hand,  may 
follow  :  ( i )  imperfect  absorption  of  the  cancellated  bone  on  the  floor  of  the  sinus,  or  secondary 
thickening  of  its  walls  ;  (2)  encroachment  due  to  approximation  of  the  facial  and  nasal  walls, 
unusual  depression  of  the  canine  fossa,  excessive  bulging  of  the  lateral  nasal  wall,  or  imperfectly 
erupted  teeth. 

The  crescentic  projections  which  quite  commonly  are  seen  protruding  from  the  walls  into 
the  interior,  occasionally  are  replaced  by  septa  that  completely  divide  the  sinus  into  two  cavities, 
each  having  its  independent  opening  into  the  nasal  fossa,  but  not  being  in  communication  with  each 
other.  These  partitions  vary  in  position  and  direction,  sometimes  subdividing  the  antrum  into  an 
anterior  and  a  posterior  compartment,  and  at  others,  into  an  upper  and  a  lower  chamber.  In 
the  last  case  the  lower  space  may  communicate  with  the  inferior  meatus  (Zuckerkandl,  Briihl). 


Right  frontal  sinus 


Left  frontal  sinus 


Passage  leading  into 
infundibulum  and 
middle  meatus 


Nasal  septum 


Portion  of  frontal  section  exposing  frontal  sinuses  which  are  asymmetrical. 

The  Frontal  Sinus. — The  air-spaces  between  the  outer  and  inner  tables  of 
the  frontal  bones  (sinus  frontales)  are  very  variable  in  extent  and  form.  The  relative 
development  and  general  position  of  these  cavities  are  usually  indicated  by  the 
degree  of  prominence  of  the  superciliary  ridges,  but  by  no  means  invariably,  since 
numerous  exceptions  to  this  correspondence  occur.  The  sinuses  are  frequently 
quite  asymmetrical  (Fig.  1185),  one  cavity  being  enlarged,  sometimes  at  the  expense 
of  the  other,  with  accompanying  displacement  of  the  intervening  septum.  The 
latter,  usually  approximately  median  in  position,  is  often  very  thin,  but  only  rarely 


H24 


HUMAN   ANATOMY. 


incomplete,  so  that  the  spaces  very  seldom  communicate.  Numerous  instances  have 
been  observed  in  which  one  sinus  was  entirely  wanting.  The  average  dimensions  of 
the  frontal  sinus,  as  given  by  A.  L.  Turner,  include  a  height  of  31  mm.  (i ^  in.),  a 
width  of  30  mm.,  and  a  depth  of  17  mm.  The  capacity  varies  from  3-8  cc.  (Bruhl). 
These  spaces  are  not  recognizable  in  the  new-born  child,  first  appearing  about  the 
seventh  year,  after  the  absorption  of  the  cancellated  bone.  It  is  not  until  after 
puberty,  however,  that  they  attain  their  full  size.  They  are  usually  larger  in  the 
male  than  in  the  female. 

The  typical  pyramidal  form  of  the  space  is  often  modified  by  the  enlargement 
of  the  sinus  beyond  its  usual  limits,  since  when  exceptionally  developed  it  may 
extend  into  the  orbital  plate  of  the  frontal  bone,  at  times  reaching  as  far  as  the 
lesser  wing  of  the  sphenoid,  or  into  the  median  orbital  wall,  or  laterally  into  the 
external  angular  process,  or,  exceptionally,  into  the  nasal  spine  beneath  the  root  of 
the  nose.  On  the  other  hand,  the  frontal  sinus  may  be  encroached  upon  by 
projecting  ethmoidal  cells. 

The  frontal  sinus  communicates  with  the  middle  nasal  meatus  through  either  the 
infundibulum,  or  a  passage  between  the  anterior  attachment  of  the  middle  turbinate 
and  the  uncinate  process,  or  both.  Its  aperture  (ostium  frontalis)  lies  from  2-10 
mm.  from  the  upper  end  of  the  hiatus  semilunaris.  The  frontal  sinus  is  lined  by  a 
prolongation  of  the  respiratory  nasal  mucous  membrane,  diminished  in  thickness  but 
otherwise  of  its  usual  structure. 

FIG.  1186. 


Sphenoidal  sinus 


Frontal  sinus 


Superior  meatus 

Middle  meatus 
Naso-pharynx 


Infundibulum 


Entrance  to 
middle  meatus 


Inferior  meatus 

Vestibule  and 
Choana  (posterior  naris)  /  |C  J     nasal  aperture 

Maxillary  sinus 
Cast  of  nasal  fossae  and  accessory  air-spaces,  viewed  from  ri^ht  side  ;  natural  size.     (A'af/ius.) 

The  Ethmoidal  Air-Cells. — These  spaces  (cellulae  cthmoidales)  include  a 
series  of  pneumatic  cavities,  very  variable  in  number  and  size,  that  from  birth  lie 
between  the  upper  part  of  the  nasal  fossae  and  the  orbits,  from  which  they  are  separated 
by  osseous  plates  of  papery  thinness.  They  are  all  lined  with  mucous  membrane 
which  covers  the  thin  bony  partitions  that  separate  the  spaces'  from  one  another. 
When  these  partitions  are  deficient,  as  they  often  are  in  old  subjects,  the  intervening 
septa  are  entirely  membranous.  The  ethmoidal  air-spaces,  completed  by  the  articu- 
lation of  the  ethmoid  with  the  frontal,  maxillary,  lachrymal,  sphenoid  and  palate 
bones,  usually  form  three  groups,  the  anterior,  the  middle  and  tin-  posterior  cells. 
Every  space  communicates  with  the  nasal  fossa,  either  directly  by  means  of  an 
independent  aperture,  or  indirectly  through  one  or  more  cells  of  tin-  same  group. 
Sometimes  the  cells  are  so  fused  that  two  general  cavities,  an  anterior  and  a  poste- 
rior, replace  the  corresponding  groups.  When  typically  arranged,  the  anterior  cells 
communicate  with  the  middle  meatus  by  means  of  apertures  that  open  into  the 
upper  part  of  the  infundibulum.  The  middle  cells  also  open  into  the  middle  meatus, 


THE   ACCESSORY   AIR-SPACES. 


1425 


usually  by  a  crescentric  cleft  upon  or  above  the  ethmoidal  bulla,  but  sometimes  into 
the  infundibulum.  The  posterior  cells  communicate  with  the  superior  meatus  by  one 
or  more  openings  overhung  by  the  upper  concha.  Very  exceptionally  the  ethmoidal 
cells  may  communicate  with  the  sphenoidal  or  the  maxillary  sinuses,  or  may  extend 
into  the  substance  of  the  middle  turbinate  bone.  The  mucous  membrane  clothing 
the  ethmoidal  cells  is  exceedingly  thin,  but  corresponds  in  its  general  structure, 
even  in  possessing  glands,  with  that  lining  the  respiratory  region  of  the  adjacent 
nasal  fossae. 

The  Sphenoidal  Sinus. — The  paired  air-spaces  (sinus  sphenoidales)  produced 
by  the  absorption  of  the  cancellated  tissue  within  the  body  of  the  sphenoid  bone  are 
separated  by  an  osseous  partition  and  seldom  communicate.  They  are  very  variable 
in  size  and  often  asymmetrical,  with  corresponding  displacement  of  the  septum.  A 
length  of  22  mm.,  a  width  of  15  mm.,  and  a  height  of  12  mm.,  are  the  approximate 
dimensions  of  the  average  sinus.  The  capacity  of  the  latter,  as  determined  by  Briihl, 
is  from  1-4  cc.  When  large,  the  spaces  may  appropriate  not  only  a  large  part  of 
the  sphenoid,  extending  into  both  wings,  the  pterygoid  processes  and  the  rostrum, 
but  also  include  the  basilar  process  of  the  occipital  bone.  Not  infrequently  one  or 


FIG.  1187. 


Anterior  ethmoidal  cells 


Probe  passes  to  middle  meatus 


Sphenoidal  sinuses 


Pituitary  body 


Openings  of  sphenoidal  sinus 
and  posterior  ethmoidal  cells 

Internal  carotid  artery 


Portion  of  section  of  frozen  formalin-hardened  head,  exposing  ethmoidal  and  sphenoidal  air-spaces; 

viewed   from  above. 

more  of  the  posterior  ethmoidal  air-cells  projects  or  opens  into  the  sphenoidal  sinuses. 
Very  exceptionally  these  spaces  may  come  into  close  relations  with  or  even  open  into 
the  maxillary  antrum  (Zuckerkandl) — a  condition  normally  found  in  some  apes. 
The  sphenoidal  sinus  of  each  side  communicates  with  the  nasal  fossa  by  means  of 
the  spheno-ethmoidal  recess,  above  the  superior  turbinate  and  close  to  the  roof  of 
the  fossa,  by  an  aperture  that  pierces  the  upper  part  of  the  anterior  wall  of  the  sinus. 
Through  this  opening,  reduced  in  the  recent  condition,  the  respiratory  mucous 
membrane  is  prolonged  into  the  sinus  which  it  lines. 

The  palatal  sinus,  the  small  air-space  within  the  orbital  process  of  the  palate 
bone,  communicates  indirectly  with  the  nasal  fossa  by  either  the  posterior  ethmoidal 
cells  or  the  sphenoidal  sinus  into  which  it  opens. 

Vessels. — Of  the  arteries  supplying  the  nasal  fossa  the  spheno-palatine  branch 
of  the  internal  maxillary  is  the  largest  and  most  important.  Entering  the  nose 
through  the  spheno-palatine  foramen,  it  divides  into  external  (posterior  nasal)  and 
internal  (naso-palatine)  branches,  which  supply  an  extended  tract  reaching  from  the 
posterior  to  the  anterior  nares.  The  external  branches  are  distributed  to  the  turbinate 

90 


1426  HUMAN   ANATOMY. 

bones  and  the  mucous  membrane  of  the  meatuses,  including  the  lower  part  of  the 
olfactory  region,  and  in  addition  send  twigs  to  the  ethmoidal  cells  and  the  frontal 
and  maxillary  sinuses.  The  naso-palatine  artery  supplies  the  septum  and  upper  part 
of  the  olfactory  region.  Numerous  smaller,  and  for  the  most  part  collateral,  twigs 
derived  from  the  anterior  and  posterior  ethmoidal  branches  of  the  ophthalmic  pass  to 
the  upper  part  of  the  fossa;  from  the  descending  palatine,  branches  are  distributed 
to  the  posterior  part;  and  from  the  lateral  nasal  and  septal,  branches  from  the  facial 
twigs  supply  the  nostril.  In  addition  to  those  from  the  posterior  nasal,  the  antrum 
receives  branches  from  the  infraorbital.  The  sphenoidal  sinus  is  supplied  chiefly 
by  the  pterygo-palatine  artery.  The  ultimate  distribution  is  effected  by  capillary 
net-works  which  supply  the  periosteum,  the  glands  and  the  tunica  propria. 

The  veins  returning  the  blood  from  the  rich  venous  plexuses  and  the  cavernous 
tissue  within  the  nasal  mucous  membrane  follow  three  chief  paths  passing  (a)  forward 
to  the  facial  vein,  (^)  backward  to  the  spheno-palatine,  and  (c)  upward  into  the 
ethmoidal  veins.  The  latter  communicate  with  the  ophthalmic  vein  and  the  veins 
and  superior  sagittal  sinus  within  the  dura  mater.  A  communication  of  greater 
importance,  however,  is  established  by  a  vein  that  accompanies  the  anterior  ethmoidal 
artery  through  the  cribriform  plate  into  the  anterior  central  fossa  and  empties  either 
into  the  venous  plexus  of  the  olfactory  tract  or  into  one  of  the  larger  veins  on  the 
orbital  surface  of  the  frontal  lobe  (Zuckerkandl). 

The  lymphatics  within  the  mucous  membrane  are  represented  by  an  irregular 
plexus  of  lymph-vessels  in  addition  to  perineural  lymph-sheaths  surrounding  the 
olfactory  nerve-bundles.  Both  sets  may  be  filled  by  injection  from  the  subarachnoid 
space.  The  larger  lymphatics  pass  backward  toward  the  posterior  nares  and  join 
two  trunks,  one  of  which  is  continued  to  the  prevertebral  node  and  the  other  to  the 
hyoid  nodes.  According  to  Schiefferdecker,  the  basal  canals  (page  951)  communi- 
cate with  the  lymphatics  and  probably  facilitate  the  escape  of  fluid  which  aids  the 
glands  in  keeping  moist  the  epithelium  lining  the  nasal  fossae. 

The  nerves  include  the  special  olfactory  fibres  concerned  in  the  sense  of  smell, 
and  those  of  common  sensation  derived  from  the  ophthalmic  and  superior  maxillary 
divisions  of  the  trigeminal  nerve.  The  lateral  wall  of  the  nasal  fossa  is  supplied  from 
several  sources,  including  the  upper  posterior  nasal  branches  from  Meckel's  ganglion 
and  the  lower  posterior  nasal  branches  from  the  larger  palatine  nerve  behind,  and, 
in  front,  the  external  division  of  the  nasal  nerve  and  the  nasal  branch  of  the  anterior 
superior  dental,  which  also  distributes  twigs  to  the  floor  of  the  fossa.  The  septum 
receives  its  chief  supply  from  the  naso-palatine  nerve,  supplemented  by  branches 
from  Meckel's  ganglion  behind  and  by  the  internal  division  of  the  nasal  nerve 
in  front.  The  mucous  membrane  lining  the  antrum  receives  filaments  from  the 
infraorbital  nerve  by  means  of  its  superior  dental  branches.  The  frontal  sinus  is 
supplied  by  twigs  from  the  supraorbital  and  the  nasal  nerves  ;  the  ethmoidal  air-cells 
by  minute  branches  from  the  nasal,  and  the  sphenoidal  sinus  by  filaments  from  the 
pheno-palatine  ganglion. 


PRACTICAL  CONSIDERATIONS  :  THE  ACCESSORY  AIR-SPACES. 

Trauma  of  the  accessory  sinuses — with  the  exception  of  the  maxillary  antrum, 
which  may  be  involved  in  extensive  (crushing)  fractures  of  the  face — usually  takes 
the  form  of  perforating  wounds,  commonly  from  falls  on  sharp  objects.  The 
thinness  of  their  walls,  and  the  ease  with  which  they  may  be  traversed  by  such  a 
vulnerating  body,  are  well  illustrated  by  a  case  in  which  a  fall  forward  on  to  the  tip 
of  an  umbrella  resulted  in  a  wound  which  began  on  the  face  above  the  bicuspid 
teeth,  passed  through  the  maxillary  sinus,  the  sphenoidal  sinus,  and  entered  the 
cranium,  the  ferrule  of  the  umbrella  being  found  embedded  in  the  pons  (Treves). 
Inflammation  of  the  accessory  sinuses  is  not  infrequent,  on  account  of  the  con- 
stant exposure  of  the  nasal  mucosa  to  atmospheric  sources  of  infection.  It  has  a 
tendency  to  become  chronic  because  (a)  the  openings  of  the  sinuses  are  small  and— 
with  the  exception  of  the  frontal — are  badly  placed  for  drainage- ;  (£)  the  ciliated 
epithelium,  on  the  activity  of  which  the  removal  of  the  sinus  contents  depends,  is  apt 
to  be  so  damaged  by  the  primary  inflammation  that  retention  of  secretion  occurs  ; 
(c)  the  mucosa  around  the  different  ostia  is  so  loosely  attached  that  it  readily 


PRACTICAL   CONSIDERATIONS  :    ACCESSORY   AIR-SPACES.  1427 

becomes  oedematous  and  is  thrown  into  folds  which  later  are  obstructive  ;  (d)  foreign 
bodies  (as  a  carious  tooth,  in  the  case  of  the  antrum)  have  little  chance  for  escape, 
and  mucous  cysts,  polyps,  and  lesions  of  the  sinus,  walls  (pyogenic,  syphilitic  or 
tuberculous  caries  or  necrosis)  are  not  uncommon  ;  (e)  one  cavity  may  be  infected 
from  another,  pus  from  the  frontal  sinus  entering  the  ethmoidal  cells,  or  pus  from 
either  of  these  entering  the  antrum  through  its  normal  opening,  or  through  a 
perforation  of  its  wall  in  the  vicinity  of  the  infundibulum  (Lack). 

In  the  greater  number  of  cases,  the  chief — often  the  only — symptom  of  chronic 
suppuration  of  the  accessory  sinuses,  is  a  purulent  nasal  discharge.  Spontaneous 
recovery  is  practically  impossible,  and  in  the  great  majority  of  cases,  operation — for 
disinfection  and  drainage — becomes  necessary.  The  cavities  (as  one  may  act  as  a 
reservoir  of  pus  coming  from  another)  may  have  to  be  attacked  in  a  definite  order. 
Ordinarily  it  is  possible  to  determine  whether  the  pus  comes  from  the  sinuses  that  open 
into  the  same  passage  within  the  middle  meatus — the  anterior  group — or  from  those 
which  open  more  posteriorly,  above  the  middle  turbinate  bone — the  posterior 
group.  If  no  definite  evidence  can  be  obtained  as  to  which  of  the  anterior  group  is 
involved,  it  would  be  well  to  attack  first  the  antrum,  then  the  ethmoidal  cells,  and 
then  the  frontal  sinus.  If  the  posterior  group  is  affected  it  is  usually  proper  to 
remove  the  posterior  portion  of  the  middle  turbinate  and  open  the  posterior  ethmoidal 
cells,  later,  if  necessary,  opening  the  sphenoidal  sinus.  Occasionally,  as  in  ozaena 
(on  account  of  the  width  of  the  inferior  meatus  and  the  atrophy  of  the  inferior  and 
middle  turbinates),  the  opening  of  the  sphenoidal  sinus  can  be  seen  from  the  front, 
and  then  this  sinus  may  be  explored  first  (Lack). 

The  frontal  sinuses  do  not  appear  as  distinct  spaces  until  about  the  seventh 
year,  and  are  developed  by  a  separation  of  the  two  tables  of  the  skull,  with  more 
or  less  resulting  prominence  above  the  superciliary  ridges.  There  may  be  a 
greater  relative  bulging  toward  the  interior  of  the  cranium,  so  that  the  prominence 
of  the  superciliary  ridges  is  no  indication  of  the  size  of  the  cavities  of  the  sinuses. 
They  are  often  very  irregular  in  size,  one  being  larger  at  the  expense  of  the  other, 
the  septum  deviating  to  one  or  the  other  side  accordingly.  It  is  therefore,  difficult, 
at  times,  to  decide  which  side  is  involved  by  disease. 

Fracture  of  the  skull  over  a  frontal  sinus  does  not  imply  that  the  cranial  cavity  is 
opened,  even  when  depression  exists.  The  frequent  presence  in  these  fractures  of  em- 
physema within  the  orbit  and  in  the  subcutaneous  tissue,  results  from  the  entrance  of  air 
through  the  communication  with  the  nose,  when  the  latter  is  blown.  The  dependent 
position  of  its  opening  into  the  middle  meatus  or  the  infundibulum,  provides  better 
drainage  for  discharges  than  is  the  case  in  the  other  sinuses,  and  probably  accounts  for 
the  relative  infrequency  of  empyema  of  this  sinus,  although  this  advantage  is  partly  off- 
set by  the  length,  narrowness,  and  tortuosity  of  the  canal,  which  render  it  easily  liable 
to  obstruction.  Swelling  of  the  mucous  lining  of  the  outlet  of  the  frontal  sinus  may 
thus  occlude  the  canal,  and  result  in  abscess  (empyema).  If  this  remains  undrained  the 
pus  would  tend  to  burrow  through  the  weakest  point  of  the  wall,  which  usually  leads  it 
through  the  floor  of  the  cavity  into  the  orbit,  giving  rise  to  an  orbital  cellulitis,  and  to 
displacement  of  the  eyeball.  It  later  tends  to  escape  through  the  inner  portion  of  the 
upper  eyelid.  In  some  cases  it  extends  through  the  posterior  wall  of  the  sinus  into 
the  cranial  cavity,  clausing  a  septic  meningitis,  or  an  extradural  or  brain  abscess. 

Extensive  necrosis  of  the  frontal  bone  may  follow  sinus  disease,  as  the  frontal 
diploic  vein,  which  empties  into  the  frontal  vein  at  the  supraorbital  notch,  receives 
blood  from  the  sinus. 

If  free  drainage  is  maintained  these  complications  are  very  rare,  but  if  drainage 
is  defective  it  is  imperative  to  open  the  sinus  early.  This  may  be  done  externally, 
the  anterior  wall  being  removed  by  a  chisel  or  trephine.  The  incision  may  be  verti- 
cal or  along  the  superciliary  ridge  from  the  inner  end  to  the  supraorbital  notch, 
sometimes  dividing  the  supraorbital  vessels.  The  thinness  of  the  nasal  portion  of 
the  floor  of  the  sinus  is  marked — as  well  as  that  of  the  orbital  portion — and  therefore 
frontal  sinus  suppuration  is,  as  a  rule,  associated  with  infection  of  some  of  the  anterior 
ethmoidal  cells,  which- surgically — may  perhaps  be  considered  as  forming  a  part 
of  that  sinus  (Lack),  although  Kiimmel  notes  that  he  has  seen  the  ethmoidal  cells 
perfectly  intact  in  a  series  of  cases  of  frontal  sinusitis. 


1428  HUMAN    ANATOMY. 

Attempts  have  been  made  to  pass  a  probe  into  the  ostium  frontale  from  the  nose, 
but  this  is  exceedingly  difficult  because  of  the  concealed  position  of  its  orifice  behind 
the  anterior  end  of  the  middle  turbinate  bone,  and  sometimes  because  of  its  tortuous 
course.  Efforts  to  reach  the  sinus  through  the  nose  are  usually  made  by  removing 
the  anterior  end  of  the  middle  turbinate  bone,  at  the  same  time  opening  the 
anterior  ethmoidal  cells  which  are  frequently  involved  by  the  same  inflammatory 
process.  By  this  method  an  aperture  is  left  for  the  permanent  discharge  of  the 
sinus  into  the  nose,  whereas  by  the  external  method  the  opening  into  the  nose  may 
remain  closed. 

The  maxillary  sinus,  or  antrum  of  Highmore,  is  the  largest  and  most 
important  of  the  accessory  sinuses  of  the  nose.  It  is  most  frequently  the  seat  of 
pathological  processes,  as  infections  and  tumors. 

Infection  may  reach  it  from  the  nose  through  the  opening  in  the  middle  meatus, 
when  it  may  be  secondary  to  disease  of  the  frontal  and  anterior  ethmoidal  sinuses, 
the  openings  into  all  three  being  closely  associated  ;  or  it  may  be  caused  by  caries  of 
the  teeth,  especially  of  the  first  and  second  molars,  the  roots  of  which  frequently 
produce  prominences  in  the  floor  of  the  antrum,  or  may  very  exceptionally  extend 
into  its  cavity.  Occlusion  of  the  small  orifice  with  retention  of  the  pus  frequently 
causes  great  pain  from  pressure  on  the  infraorbital  nerve  in  the  roof  of  the  antrum. 
The  pus  may  burrow  into  the  nose,  the  ethmoidal  cells,  or  the  orbit. 

The  normal  orifice  is  too  high  on  the  internal  wall  for  drainage,  and  is  too  small 
for  effective  irrigation,  which  may  be  provided  for  (a),  if  the  cause  is  a  carious  tooth, 
by  removing  a  tooth  and  making  an  opening  through  the  roof  of  the  socket  into  the 
antrum  ;  this  affords  dependent  drainage,  but  permits  the  entrance  of  food  from  the 
mouth  ;  (£)  by  perforating  the  bony  wall  between  the  antrum  and  the  inferior  meatus 
with  or  without  removing  the  anterior  end  of  the  inferior  turbinate  ;  or  (c)  by 
making  an  opening  through  the  thin  anterior  wall,  above  the  roof  of  the  second 
bicuspid  tooth,  at  the  level  of  the  canine  fossa. 

A  tumor  of  the  maxillary  sinus  may  be  either  benign  or  malignant.  Its  growth 
will  lead  to  enlargement  of  the  cavity,  and  to  the  following  symptoms,  one  or  more 
of  which  will  predominate,  according  to  the  direction  it  takes  :  (a)  inward,  through 
the  thin  inner  wall  of  the  sinus,  causing  epistaxis,  obstructed  respiration,  epiphora 
from  pressure  on  the  nasal  duct  }  (b~)  inward  and  backward,  involving  the  naso- 
pharynx and  interfering  v/ith  both  respiration  and  deglutition  ;  (c)  forward,  pushing 
the  anterior  wall — also  thin — before  it  and  obliterating  the  inframalar  depression  in 
the  cheek;  (a?)  upward,  causing  infraorbital  neuralgia  (as  the  infraorbital  nerve 
runs  in  the  roof  of  the  sinus),  toothache  from  compression  of  its  middle  and  anterior 
superior  dental  branches,  face  ache  from  involvement  of  the  other  branches  of  the 
superior  maxillary,  and  later  exophthalmos  and  diplopia  ;  (>)  downward,  pushing 
down  the  arch  of  the  hard  palate  so  that  the  roof  of  the  mouth  on  the  affected  side 
becomes  convex,  and,  by  pressure  on  the  superior  dental  nerves,  causing  severe 
odontalgia  in  the  upper  teeth,  which  later  become  loosened.  Benign  growths  ma 
be  removed  through  an  opening  made  by  cutting  away  the  anterior  wall.  Malignan 
growths  necessitate  excision  of  the  superior  maxilla. 

In  diseases  of  the  sphenoidal  sinuses  their  intimate  relation  with  the  brain 
above,  the  optic  nerve  and  ophthalmic  artery  above  and  to  the  oirter  side,  and,  along 
the  outer  wall,  with  the  internal  carotid  artery,  the  cavernous  sinus  and  the  nerv 
passing  through  the  sphenoidal  fissure,  should  be  borne  in    mind.     Such   diseas< 
may  lead  to   (0)  optic  neuritis  and  blindness,  if  the  optic  nerve   is  involved  ;   (I) 
tc.  general  Ophthalmoplegia  if  the  third,  fourth,  the  ophthalmic  division  of  the  fifth, 
the  sixth,  and   the  sympathetic  filaments  from   the  cavernous  plexus  (all  transmitted 
through  the  sphenoidal  fissure)  are  implicated  ;  (r)  to  cavernous  sinus  thrombosis 
if  the  ophthalmic  vein — passing  through  the  same  fissure — is  infected. 

Tumors  of  the  pituitary  body — resting  in  the  pituitary  fossa  in  the  sella  turcica 
and  just  above  the  roof  of  the  sinus — may  penetrate  its  cavity.  The  opening  of  each 
sinus  is  in  the  upper  part  of  the  anterior  wall,  a  very  unsuitable  position  for  drainage, 
in  the  presence  of  infection.  Encroachment  on  any  of  the  surrounding  structures 
might  lead  to  serious  results.  The  anterior  wall  may  be  exposed  and  attacked  by  the 
surgeon,  but  only  with  considerable  difficulty,  because  of  its  deep  situation  and  its 


1 


DEVELOPMENT   OF   THE   NOSE.  1429 

restricted  avenue  of  approach  through  the  nasal  fossa.  The  chief  obstacle  is  the 
middle  turbinate  bone,  which  must  be  removed  before  the  orifice  can  be  seen  or  the 
anterior  wall  removed.  Any  efforts  at  cleaning  pathological  tissue  from  the  sinus 
must  be  made  with  due  regard  for  the  important  structures  just  outside  and  the  thin 
intervening  bone. 

Inflammation  of  the  ethmoidal  cells  is  most  frequently  associated  with  the 
presence  of  myxomatous  polypi  within  the  nose.  Infection  may  extend  (#)  upward 
to  the  cranial  cavity,  either  directly  or  by  way  of  the  ethmoidal  veins,  or  into  the 
cavernous  sinus  via  the  ophthalmic  vein,  or  to  the  longitudinal  sinus — especially  in 
children — by  the  small  vein  traversing  the  foramen  caecum  ;  (£)  outward  to  the 
orbit,  causing  an  orbital  cellulitis  ;  (c)  to  the  lachrymal  sac  (on  account  of  the 
contiguity  of  the  lachrymal  bone)  causing  dacryo-cystitis. 

A  valuable,  but  not  always  reliable,  sign  of  involvement  of  the  ethmoidal  cells, 
is  localized  pain  at  the  inner  canthus  of  the  eye  (Kiimmel),  and  swelling  of  the 
mucous  membrane  around  the  middle  turbinate  may  in  this — as  in  infection  of  the 
other  sinuses — be  considered  an  important  symptom.  In  order  to  evacuate  the 
diseased  cells,  the  middle  turbinate  (as  in  the  case  of  the  sphenoidal  sinus)  must  be 
removed  before  the  ethmoidal  cells  can  be  exposed.  As,  in  the  large  majority  of 
cases  at  least,  the  condition  is  coincident  with  similar  infection  of  the  frontal  sinus, 
the  anterior  cells  may  be  easily  reached  from  the  floor  of  the  latter  after  it  has  been 
opened.  The  optic  nerve,  the  trochlear  nerve,  the  superior  oblique  ocular  muscle 
and  the  anterior  and  posterior  ethmoidal  arteries,  are  the  most  important  structures 
endangered  during  this  operation. 

DEVELOPMENT  OF  THE  NOSE. 

The  earliest  trace  of  the  nasal  anlage  appears  about  the  beginning  of  the  third 
week  of  foetal  life  as  a  thickening  of  the  ectoblast  to  form  the  nasal  area  at  each 
side  of  the  anterior  portion  of  the  head.  About  one  week  later  the  convexly  cres- 
centic  outline  of  this  area  gives  place  to  a  slight  depression  that  deepens  into  the 
olfactory  pit  or  fossa  in  consequence  of  the  increased  thickness  of  the  surrounding 
mesoblast.  The  encircling  ridge  thus  produced  is  best  marked  on  the  mesial  and 
lateral  boundaries  of  the  fossa  (Kallius),  where  the  resulting  elevations  foreshadow 
the  development  of  the  inner  and  outer  nasal  processes.  With  the  forward  growth 
and  union  of  the  maxillary  process  of  the  first  visceral  arch  with  the  median  nasal 
process,  or  processus  globularis,  to  complete  the  upper  boundary  of  the  primitive 
oral  cleft  (page  62),  the  margin  of  the  entrance  of  the  nasal  pit  becomes  closed  in 
below.  Subsequently,  however,  the  lateral  nasal  process  extends  medially  above 
the  maxillary  process  until  it  meets  the  median  nasal  process  and  thus  becomes  the 
immediate  lower  and  lateral  boundary  of  the  opening  of  the  fossa.  The  latter  grows 
and  deepens  chiefly  upward,  towards  the  brain,  and  backward  and  in  consequence 
the  olfactory  organ  for  a  time  consists  of  two  blind  pouches,  separated  by  the  frontal 
process,  lying  above  the  primitive  oral  cavity.  These  pouches  invade  the  mesoblast 
until  their  blind  posterior  ends  reach  the  primitive  oral  cavity  between  which  and  the 
olfactory  diverticula  a  thin  partition,  composed  of  the  two  abutting  layers  of  epithe- 
lium, alone  intervenes.  This  septum,  bucco-nasal  membrane  of  Hochstetter,  becomes 
attenuated  and  finally  ruptures,  the  resulting  openings,  the  primitive  choancs,  estab- 
lishing communication  between  the  nasal  fossae  and  the  primitive  oral  cavity.  That 
part  of  the  roof  of  the  latter  which  extends  from  the  choanae  to  the  nasal  apertures 
constitutes  the  primitive  palate,  and  contributes  not  only  the  anterior  portion  of  the 
definite  palate,  but  also  the  tissue  forming  the  lips  (Hochstetter).  The  primitive 
palate  includes  contributions  from  different  sources,  its  middle  portion  being  from  the 
median  nasal  process  and  its  lateral  portions  being  derived  from  the  lateral  nasal 
process  in  front  and  from  the  maxillary  process  behind  (Peter). 

Subsequent  to  the  formation  of  the  primitive  palate,  about  the  fifth  week,  the 
primitive  nasal  fossae  increase  in  size,  sink  deeper  into  the  head  between  the  median 
plane  and  the  eye,  and  come  into  closer  relation  with  the  brain.  The  nasal  fossae, 
however,  in  acquiring  their  definite  expansion  additionally  appropriate  a  considerable 
portion  of  the  primitive  oral  cavity  which  becomes  separated  from  the  remainder  of 
that  space  by  the  formation  of  the  dejinite  palate. 


1430 


HUMAN   ANATOMY. 


Nasal  area 


Fore-brain 


Nasal  area 


The  first  step  in  the  production  of  the  latter  is  the  appearance,  about  the  ninth 
week,  of  the  palatal  ridges,  wedge-shaped  elevations  that  grow  downward  and  in- 
ward from  the  maxillary  processes.  In  front  these  ridges  begin  at  the  primitive 
choanae,  where  they  are  continuous  with  the  primitive  palate,  and  extend  backward 
as  far  as  the  tympanic  pouches.  At  first  almost  sagittal  in  their  plane,  the  palatal 
ridges  become  gradually  converted  into  horizontal  plates  that  come  into  contact 

and    finally    unite    along    their 

FIG.  1188.  opposed  median  edges  to  com- 

Fore-brain  plete  the  roof  of  the  mouth  and 

the  floor  of  the  nasal  fossae  and 
the  definite  or  secondary  choantc, 
this  fusion  being  accomplished 
by  the  end  of  the  third  month. 
Coincidently  with  these 
changes  the  primitive  choanae 
elongate  and  come  to  lie  on 
either  side  of  the  posterior  por- 
tion of  the  nasal  septum  to 
which  the  frontal  process  has 
now  become  reduced.  The 
union  of  a  pair  of  outgrowths 
from  the  palatal  plates,  beyond 
their  point  of  fusion  beneath 
the  choanae,  produces  the  uvula, 
while  the  remaining  ununitecl 
portions  of  the  ridges  give  rise 
to  the  palato-pharyngeal  arches. 
For  a  time  the  nasal  sep- 
tum is  still  incomplete,  since  it 
has  not  yet  reached  the  palate, 
and  the  nasal  fossae  communi- 
cate by  means  of  a  cleft  between 
the  septum  and  the  palate. 
With  the  downward  growth  of 
the  partition  this  communica- 
tion is  obliterated,  the  septum 
joining  the  palate  along  the  line 
of  the  median  suture. 

The  formation  of  the  ante- 
rior part  of  the  floor  of  the  nasal 
fossae  is  more  complex  since, 
according  to  Peter,1  in  this 
region  the  palatal  processes  do 
not  come  in  contact  with  each 
other  owing  to  the  interposi- 
tion of  a  portion  of  the  partition 
that  separates  the  primitive 
choanae.  The  palatal  plates, 
however,  fuse  with  this  wedge 
of  tissue  along  the  line  of  appo- 
sition except  at  one  point  on 

each  side,  where  the  epithelium  persists  as  a  solid  strand  leading  downward  and  inward 
from  the  fore  part  of  the  floor  of  the  nasal  fossa  to  the  roof  of  the  oral  cavity.  These 
strands  acquire  a  lumen  and  become  the  incisive  canals  (page  1413  )  that  may  persist 
throughout  life  and  establish  communication  between  the  nasal  and  oral  chambers. 

The  further  differentiation  of  the  nasal  fossae  of  man  follows  the  same  funda- 
mental plan  that  applies  to  other  mammals,  but  is  modified  by  the  reduction  that 


Fore-brain 


Lateral  nasal 
process 


mil 


Nasal  fossa 


Fore-brain 


Nasal  fossa 


Naso-frontal  process      Processus  globularis 


Frontal  sections  of  fore-brain  of  rabbit  embryos,  illustrating  early 
stages  in  development  of  nose ;  in  A.  nasal  area  shows  as  thickening 
of  ectoblast ;  in  B,  nasal  area  is  slightly  depressed  ;  in  C  and  I),  nasal 
fossae  are  forming.  X  30. 


Anatom. 


r,  I'.il.  xx.,  1902. 


DEVELOPMENT   OF   THE   NOSE. 


occurs  in  the  production  of  the  relatively  feebly  developed  human  olfactory  apparatus. 
With    this    differentiation    is   associated    the    formation    of    the   turbinates  and  the 
intervening    clefts    (the 
meatuses)  and  of  the  acces- 

an  i  Cartilaginous  capsule 

sory  air-spaces.    1  he  stud-  Ethmo-turbinai 

iesof  Zuckerkandl,  Killian, 
Schoenemann,  Peter1  and 
others  have  shown  that 
the  typical  development  of 
the  conchae  proceeds  from 
three  primary  outgrowths 
from  the  lateral  nasal  wall  in 
regions  later  correspond- 
ing to  the  maxilla,  ethmoid 
and  nasal  bones.  These 
elevations,  appropriately 
known  as  the  maxillo-tur- 
binal, the  ethmo-turbinal 
and  the  naso-tur&inal,  un- 
dergo differentiation  that 
leads  to  the  simple  or  com- 
plex definite  arrangement 
of  the  conchae  found  in 
various  animals. 


Maxillo-turbinal 

Nasal  fossa 
Jacobson's  organ 


Palatal  process 
Oral  cavity 


Tongue 


Frontal  section  through  developing  nasal  fossae  and  oral  cavity  which 
communicate ;  palatal  processes  are  forming.    X  15. 


In  man  the  maxillo-turbinal,  later  the  inferior  turbinate,  first  appears  and  pre- 
cedes the  ethmo-turbinal  plate  that  later  is  supplemented  by  a  second  scroll,  thus 
producing  the  middle  and  superior  turbinates  respectively.  The  naso-turbinal, 
always  rudimentary  in  man,  is  represented  by  a  small  ridge  that  appears  in  front  of 
the  ethmo-turbinal  and  above  the  maxillo-turbinal  plates  and  persists  as  the  agger 
nasi.  The  ethmo-turbinal  is  most  intimately  related  to  the  true  olfactory  area  and 
undergoes,  even  in  man,  conspicuous  subdivision.  Although  finally  reduced  to  two 
(the  upper  and  middle  turbinates),  in  the  human  fcetus,  just  before  birth,  five  ethmo- 
turbinal  plates  defined  by  six  grooves  are  present  (Killian).  Persistence  in  excess 
of  the  usual  complement  accounts  for  the  presence  of  the  supernumerary  ethmoidal 
turbinates  so  often  observed. 

As  interpreted  by  Killian,  the  subsequent  modifications  of  the  ethmo-turbinals 
and  the  intervening  furrows,  either  by  further  expansion  or  by  fusion,  are  not  only 
intimately  concerned  in  producing  details  modelling  the  lateral  wall  of  the  nasal  fossa, 
as  the  uncinate  process,  ethmoidal  bulla,  hiatus  semilunaris  and  infundibulum,  but 
also  associated  with  the  first  appearance  of  the  accessory  air-spaces.  The  earliest 

establishment  of  these  spaces  pre- 

FIG.  1190.  cedes  the  appearance  of  the  carti- 

lage that  later  encloses  them,  their 
relations  to  the  skeleton  being, 
therefore,  secondary  (Kallius). 
The  ethmoidal  air-cells  and  the 
sphenoidal  sinus  are  primarily  con- 
Maxiiiary  process  strictions  from  thenasal  fossae,  while 

the  maxillary  and  frontal  sinuses 
are  more  or  less  direct  extensions 
from  the  same  cavities. 

The  maxillary  sinus  ap- 
pears about  the  middle  of  the  third 
fcetal  month  as  a  minute  epithe- 
lium-lined sac  within  the  mesoblast  at  the  side  of  the  nasal  fossa,  from  which  it 
has  been  evaginated  ;  by  the  sixth  month  it  measures  some  5  mm. ,  and  at  birth 
has  acquired  the  size  of  a  pea.  Until  the  eruption  of  the  milk  teeth  provides  the 


Fore-brain 


Nasal  aperture 
Lateral  nasal  process 


Primitive  choana 


Palatal  process 


Part  of  head  of  fcctus  15  mm.  in  length,  showing  primitive  choanas 
and  palate.     X  8.     (Peter.) 


1  In  Hertwig's  Handbuch  d.  Entwikelungslehre,  Lief.  4  and  5,  1902. 


1432 


HUMAN   ANATOMY. 


FIG.  1191. 

Fore-brain 

Infranasal  area 

Nasal  fossa 

Lateral  nasal  process 
Median  nasal  process 

Processus  globularis 
Maxillary  process 

Mandibular  process 

Anterior  end  of  head  of  foetus  10.5  mm.  in  length, 
showing  early  development  of  external  nose.  X  8. 
(Peter.) 


necessary  room  for  expansion,  its  growth  is  retarded.  After  the  sixth  year,  when 
the  eruption  of  the  permanent  teeth  begins,  the  antrum  loses  its  general  spherical 
outline  and  gradually  acquires  the  definite  pyramidal  form. 

The  frontal  sinus  formed  as  an  extension  of  the  nasal  fossa  during  the  third 
foetal  month,  is  for  a  time  so  small  that  it  is  usually  regarded  as  absent  at  birth. 
Although  indistinctly  seen  during  the  third  year,  not  until  about  the  seventh  is  the 

sinus  a  definite  space ;  it  remains  small,  how- 
ever, until  puberty,  after  which  its  adult 
proportions  are  gained. 

The  sphenoidal  sinus, primarily  arises 
by  the  constriction  and  partial  isolation  of  a 
part  of  the  primitive  nasal  fossa.  Although 
its  development  begins  during  the  third 
fcetal  month,  the  space  remains  so  rudimen- 
tary that  not  until  the  seventh  year  has 
absorption  of  the  cancellous  bone  progressed 
sufficiently  to  make  the  sinus  apparent. 

Notwithstanding  its  rudimentary  condi- 
tion in  man,  the  organ  of  Jacobson  devel- 
ops at  a  very  early  period,  beginning  as  a 
groove-like  depression  on  the  median  wall  of  the  nasal  pit.  This  groove  is  converted 
into  a  tubular  pouch  that  soon  becomes  laterally  compressed  and,  by  the  middle  of 
the  third  month,  measures  about  .5  mm.  in  length  and  receives  twigs  from  the  olfac- 
tory nerve  (Kallius).  After  the  fifth  fcetal  month  the  organ  suffers  regression  and 
becomes  rudimentary  and  variable  in  comparison  with  the  perfection  it  attains  in 
animals  possessing  olfactory  sense  in  a  high  degree. 

The  development  of  the  outer  nose  is  closely  associated  with  the  changes 
affecting  the  median  and  lateral  nasal  processes — prominences  considered  in  connection 
with  the  formation  of  the  upper  boundary  of  the  primitive  oral  cleft  (page  62). 

Reference  to  Fig.  1 192  shows  the  median  nasal  processus,  separated  by  a  distinct 
furrow  that  soon   becomes   filled  and  partially  obliterated  by  ingrowth  of  young 
connective  tissue,  as  does  likewise 
the  groove  between  the  globular  and 
maxillary  processes.     At  first  sepa- 
rated by  a  relatively  wide  interval, 
the  infranasal  nasal  area  of  His,  the 
nasal  apertures  are  brought  nearer 
together  by  the  rapid  narrowing  of 
the  interposed  portion  of  the  frontal 
process.      Eventually  the  tissue  be- 
tween the  globular  processes  becomes 
the  philtrum  of  the  upper  lip  and 
that   between    the    nasal    openings 
persists  as  the  partition  between  the 
nostrils.      By  the  end  of  the  second 
month  the  external  nose  is  defined, 
but  is  very  broad  and  flat  and  lim- 
ited above  by  an  arched  furrow  that 
separates  the  convex  nasal  margin 
(His)  from  the  forehead.    The  nos- 
trils, originally  placed  high  and  for 
a  long  time  directed  forward,  grad- 
ually  descend  and  assume  a  hori- 
zontal plane  as  the  middle  of  the  arched  nasal  margin  grows  downward  and  forward 
to  become  the  point  of  the  nose.     These  changes,  however,  are  not  accomplished 
until  near  the  end  of  gestation  and  at  birth  the  bridge  of  the  nose  is  still  small  and 
flat  which,   in  connection  with    the  general  breadth  of  the  organ,   imparts  to  the 
infantile  nose  its  peculiar  stumpy  appearance.    Not  until  long  after  birth,  and,  indeed, 
not  until  after  puberty,  does  the  outer  nose  acquire  its  definite  individual  form  in 


FIG.   1192. 


Fore-brain 


Infranasal  area 

Nasal  aperture 
Lateral  nasal  process 
Medial  nasal  process 
Processus  globularis 

Mandibular  process 


Head  of  foetus  of  about   20  days,  showing  developing  nose. 
X  13-    (Rabl.) 


THE  ORGAN  OF  TASTE. 


H33 


which  family  and  racial  characteristics  are  often  so  strikingly  reproduced.  From  the 
second  until  the  sixth  month  the  nostrils  are  occluded  by  epithelial  plugs  which 
subsequently  undergo  gradual  resolution,  so  that  before  birth  the  nasal  apertures  are 
unobstructed.  The  cartilages  of  the  outer  nose  are  derived  from  the  common  carti- 
laginous capsule  that  constitutes  the  primary  nasal  skeleton.  Subdivision  into  the 
individual  plates  is  probably  effected  by  ingrowth  of  the  surrounding  connective 
tissue  (Mihalkovics,  Kallius). 

THE  ORGAN  OF  TASTE. 

In  the  description  of  the  tongue  and  its  papillae  (page  1575),  reference  is  made 
to  the  presence  of  specialized  epithelial  structures,  the  taste-buds,  that  serve  for  the 
reception  of  gustatory  stimuli.  These  bodies  collectively  constitute  the  peripheral 
sense-organ  of  taste  and  as  such  will  be  here  considered. 

As  implied  by  their  name,  the  taste-buds  (calyculi  gustatorii)  are  irregular  ellip- 
soidal or  conical  bodies,  sometimes  broadly  oval  but  more  often  slender  in  outline, 
and  in  the  adult  measure  from  .070-.  080  mm.  in  length  and  about  half  as  much  or 

FIG.  1193. 


Lymphoid  nodules 
—  Foramen  caecum 


Circumvallate 
papillae 


Anterior  palatine 
arch 

Folia  linguae 


Fungiform  papilla 


Part  of  dorsum  of  tongue,  showing  papillae. 

less  in  breadth.  Since  they  lie  entirely  within  the  epithelium  clothing  the  mucous 
membrane,  the  necessary  access  to  the  interior  of  the  buds  is  afforded  by  minute 
pore-canals,  each  of  which,  beginning  on  the  free  surface  at  the  outer  taste-pore,  leads 
through  the  intervening  layer  of  epithelium  to  the  inner  pore  that  caps  the  subjacent 
pole  of  the  bud.  By  means  of  these  canals  the  sapid  substances  dissolved  in  the 
fluids  of  the  mouth  reach  and  impress  the  gustatory  cells  within  the  taste-buds. 
Pore-canals  are  not,  however,  invariably  present,  since,  as  pointed  out  by  Graberg, 
certain  taste-buds  remain  immature  and  retain  their  embryonal  form  and  relations, 
being  broad  and  conical  and  in  contact  with  the  free  surface.  In  such  buds  the 
gustatory  cells  are  few,  only  two  or  three,  and  so  superficially  placed  that  a  dis- 
tinct canal  is  absent.  Occasionally  double  buds  are  encountered  in  which  two 
gustatory  bodies  are  implanted  by  a  common  base,  but  partly  retain  their  inde- 
pendence in  having  separate  distal  poles,  each  provided  with  its  separate  taste-pore 
and  canal. 

The  chief  position  of  the  taste-buds  is  within  the  epithelium  lining  the  sides  of 
the  annular  groove  on  the  circumvallate  papillae,  the  buds  being  more  numerous  and 
closely  placed  on  the  median  than  on  the  lateral  wall  of  the  furrow.  Their  number 


H34 


HUMAN   ANATOMY. 


has  been  variously  estimated,  but  it  is  probable  that  from  100  to  150  represents  the 
maximum   for  a  single  papilla,  in  many  cases  the  quota  being  less  than  one  half 

FIG.  1194. 


Epithelium 


Section  of  circumvallate  papilla  from  tongue  of  child.     X  70. 


FIG.  1195. 


of  these  figures  (Graberg).  The  locality  of  next  importance  numerically  is  the 
papillae  foliatae  on  the  sides  of  the  tongue  in  the  furrows  of  which,  even  in  man, 
the  taste-buds  are  plentiful. 

Additional  situations,  in  which,  however,  the  taste-buds  are  very  sparingly  and 
uncertainly  distributed,  include  the  fungiform  papillae,  the  soft  palate,  the  posterior 
surface  of  the  epiglottis  and  the  mesial  surface  of  the  arytenoid  cartilages.  Within 

the  fungiform  papillae  a  few  buds  may  be  found  on 
the  free  surface,  where  the  epithelium  is  thinnest. 
Over  the  soft  palate  their  distribution  is  irregular 
and  uncertain,  while  in  the  larynx  the  buds  are  lim- 
ited to  the  areas  covered  by  squamous  epithelium. 
According  to  Davis,  between  fifty  and  sixty  taste- 
buds  of  varying  size  may  be  counted  on  the 
epiglottis  within  an  area  3  mm.  in  diameter. 

Structure. — Wherever  found,  the  taste-buds 
consist  exclusively  of  epithelial  tissue  and,  in  cor- 
respondence with  other  sense  organs,  include  two 
chief  varieties  of  elements — the  supporting  cells 
and  the  more  highly  specialized  neuro-epithelium, 
the  gustatory  cells,  among  which  lie  the  terminal 
fibrillae  of  the  nerve  of  taste. 

The  supporting  cells  are  represented  prin- 
cipally by  elongated  epithelial  elements  that  occupy 
both  the  superficial  and  deeper  parts  of  the  taste- 
buds  of  which  they  contribute  the  chief  bulk.  They 
vary  in  their  individual  contour,  being  lanceolate, 
wedge-shaped  or  columnar,  according  to  the  model- 
lint;  to  which  they  are  subjected  by  the  neighboring 
cells.  They  possess  large,  clear,  vesicular  nuclei 
that  contain  little  cliroinatin  and,  therefore,  stain 
faintly.  The  position  of  the  nucleus  is  inconstant,  in  some  cells  being  near  the 
base  and  in  others  in  the  middle  or  nearer  the  apex.  The  peripheral  ends  of  the 


Taste-hud 


Taste-pore 


Epithelium 


Taste-bud 


Taste-buds  in  section  ;  upper  one  shows 
gustatory  hairs  projecting  into  pore-canal. 
X440. 


THE   ORGAN    OF   TASTE. 


H35 


FIG.  1196. 

Outer  taste-pore 


supporting  cells,  somewhat  blunted  and  flattened  and  beset  with  a  narrow  cuticular 
zone,  are  closely  grouped  to  bound  the  annular  opening  of  the  inner  taste-pore, 
through  which  project  the  stiff  hair-processes  of  the  gustatory  cells.  Their  deeper 
or  central  ends  are  prolonged  into  one  or  more  protoplasmic  processes  which  unite 
with  similar  extensions  of  the  basal  cells,  as  the  peculiar  supporting  cells  at  the  base 
of  the  bud  are  called. 

The  basal  cells  are  modified  sustentacular  elements,  probably  epithelial  in  nature, 
which  occupy  the  lower  fourth  of  the  buds,  resting  upon  the  subjacent  epithelium 
and,  in  turn,  affording  support  for  the  elongated  cells.  Although  differing  in  size 
and  details  of  form,  the  basal  cells  are  provided  with  oval  nuclei  and  are  generally 
more  or  less  branched.  By  means  of  their  protoplasmic  processes  they  are  united 
with  the  central  ends  of  the  longitudinally  disposed  supporting  and  gustatory  cells, 
with  one  another  and  with  the  surrounding  epithelial  cells.  The  number  of  basal 
cells  in  each  bud  is  small,  often  only  two  or  three  and  seldom  more  than  half  a 
dozen  being  present  (Graberg1,  Kallius2). 

The  percipient  elements,  the  gustatory  cells,  are  irregularly  arranged  between 
the  more  deeply  placed  supporting  cells  and  enclosed  within  a  shell  formed  by  the 
more  superficial  ones.  They  are  long  and  fusiform,  reaching  from  the  base  of  the 
bud  to  the  inner  taste-pore,  through  which 
the  stiff  hair-like  processes  that  cap  their 
outer  ends  project.  Their  slender  nuclei, 
rich  in  chromatin  and  deeply  staining, 
occupy  the  thickest  parts  of  the  cells, 
which  beyond  the  nucleus  are  continued 
in  either  direction  as  thin  processes.  The 
peripheral  ones,  as  noted,  extend  not  only 
as  far  as  the  inner  taste-pore,  but  through 
the  latter  and  into  the  canal  by  means  of 
the  gustatory  hairs  into  which  the  taste 
cells  are  prolonged.  The  centrally  directed 
ends  are  usually  much  the  shorter  and 
join  the  processes  of  the  basal  cells.  The 
number  of  gustatory  cells  within  a  single 
taste-bud  varies,  in  exceptional  cases  only 
two  or  three  being  present,  but  more 
often  they  are  almost  as  numerous  as  the 
supporting  cells  (Graberg). 

The  capillary  clefts  observed  within 
and  around  the  taste-buds — the  intra-  sub-  and  peri-bulbar  juice-spaces  described 
by  Graberg — are  regarded  by  some  as  existing  during  life  and,  therefore,  not  as 
artefacts.  To  these  intercellular  clefts  the  last-named  authority  attributes  the  func- 
tion of  insuring  and  facilitating  an  active  lymph-circulation  within  and  around 
the  taste-buds,  whereby  is  effected  the  prompt  removal  of  foreign  substances  that 
might  prove  deleterious  if  too  long  retained  in  close  relation  with  the  delicate 
sensory  elements. 

Hermann  has  shown  that  the  taste-buds  are  the  seat  of  continual  degeneration 
and  repair,  sometimes,  indeed,  entire  buds  undergoing  regression.  Whether  such 
destructive  processes  are  to  be  ascribed  directly  to  the  invasion  of  leucocytes,  al- 
though the  latter  are  normally  found  in  insignificant  numbers  within  the  buds,  is  still 
a  subject  of  discussion. 

The  nerves  distributed  to  the  gustatory  bodies  are  the  fibres  of  the  glosso- 
pharyngeal,  the  nerve  of  taste.  From  the  rich  subepithelial  plexus  numerous  twigs 
ascend  into  the  epithelium,  one  set  going  directly  into  the  taste-buds  and  the  other 
ending  within  the  surrounding  tracts  of  epithelium.  Since  the  last  set — the  inter- 
•bulbar  fibres — probably  have  no  concern  with  the  impressions  of  taste  and  serve  to 
convey  sensory  stimuli  of  other  value,  it  suffices  to  note  that  after  repeated  division 


Peripheral 
supporting  cell 


Gustatory  cell 
Central 
supporting  cell 


Lymph-space 


Basal  cell 


Diagrammatic  sectioti    illustrating   architecture   of 
taste-bud.     (Graberg.} 


1  Anatomische  Hefte,  Bd.  xii.,  Hf.  2,  1899. 

2  Bardeleben's  Handbuch  d.  Anatomic  des  Menschen,  Lief.  13,  1905. 


1436  HUMAN    ANATOMY. 

the  ultimate  fibrillae  terminate  in  minute  bead-like  endings  that  lie  free  between  the 
epithelial  cells,  either  near  the  free  surface  or  at  a  deeper  level. 

The  nerves  distributed  to  the  taste-buds — the  intrabulbar  fibres — enter  at  the 
basal  pole.  Usually  numbering  from  two  to  five  for  each  bud,  on  gaining  the 
interior  of  the  latter  they  undergo  rapid  division  and  become  numerous.  A  majority 

of  the  resulting    fibrillae    ascend  in  tortuous   windings 
FIG.  1197.  towards  the  apex  of  the  bud  in  the  vicinity  of  which 

some  end,  while  others  recurve  and  end  at  lower  levels. 
The  fibrillae  terminate  in  free,  usually  minute  knob-like 
endings,  that  lie  between  and  often  in  close  contact  with 
the  supporting  and  gustatory  cells.  It  is  probable  that 
in  no  instance  do  the  nerve-fibrillae  actually  unite  with 
the  gustatory  cells,  the  relation  being  one  of  apposition 
and  not  of  continuity. 
Partially  separated  ceils  of  taste-  Development. — The  earliest  evidences  of  the 

^^^"x^^M^       taste-buds '  appear,  about  the  third  foetal  month,  within 

the  deepest  stratum  of  the  immature  epithelium  as  groups 

of  ectoblastic  cells  that  are  distinguished  by  their  large  size  and  elongated  form  from 
the  surrounding  epithelial  elements.  The  anlage  tends  to  become  conical,  the  apex 
gradually  reaching  the  free  surface  and  the  base  resting  or  slightly  encroaching  upon 
the  subjacent  connective  tissue,  from  which  it  is  only  indistinctly  defined.  The 
primary  slender  form  of  the  developing  bud  is  later  replaced  by  one  of  broad  conical 
proportions  in  which  the  wide  base  is  supported  directly  by  the  connective  tissue 
without  the  interposition  of  epithelium. 

For  a  time  the  height  of  the  young  taste-bud  equals  the  entire  thickness  of  the 
epithelium,  the  position  of  its  apex  being  marked  by  a  slight  depression  on  the  free 
surface.  In  consequence  of  the  rapid  increase  of  the  surrounding  epithelium,  this 
depression  gradually  deepens  until  the  bud,  which  meanwhile  has  grown  but  slightly, 
lies  at  the  bottom  of  a  narrow  funnel-shaped  passage,  the  pore-canal  (Graberg). 
Previous  to  the  fifth  month,  the  constituents  of  the  taste-bud  are  apparently  of 
the  same  character  and  not  until  towards  the  end  of  gestation  is  the  differentiation 
between  the  supporting  and  gustatory  cells  clearly  established.  The  definition  of 
the  taste-buds  from  the  surrounding  tissue  is  sharpened  by  the  appearance  of  the 
so-called  extrabtdbar  cells,  flattened  protecting  epithelial  elements  in  which  partial 
cornification  probably  takes  place  (Kallius).  Coincidently  many  of  the  conical 
embryonal  buds  gradually  assume  their  more  slender  and  ovoid  mature  form.  Before 
birth  the  taste-buds  are  present  not  only  on  the  sides  but  also  over  the  summit  of 
the  circumvallate  papillae.  While  exceptionally  some  of  those  in  the  latter  situation 
may  remain,  as  a  rule  they  disappear  and,  hence,  in  the  adult  the  gustatory  bodies 
are  usually  confined  to  the  sides  of  the  papillae.  Likewise  the  complement  of  taste- 
buds  on  the  fungiform  papillae  is  much  larger  at  birth  than  later  (Stahr2),  giving  to 
these  papillae  an  importance  during  early  childhood  that  subsequently  is  lost. 

THE   EYE. 

Although  the  organ  of  sight  (organon  visus),  strictly  regarded,  consists  only  of 
the  eyeball  or  globe  of  the  eye,  it  is  closely  associated  with  other  structures,  as  the 
eyelids,  the  lachrymal  apparatus,  the  orbital  fascia  and  fat  and  the  ocular  muscles, 
which  serve  for  its  protection,  support  and  change  of  axis.  The  description  of  some, 
at  least,  of  these  accessory  structures  therefore  appropriately  here  finds  place. 

THE  ORBIT  AND   ITS   FASCIAE. 

The  walls  of  the  orbit  have  been  described  in  connection  with  the  skull  (page 
222) ;  suffice  it  here  to  point  out  that  in  its  general  form  the  orbital  cavity  resembles 
a  pyramid,  so  modified  by  the  rounding  of  its  angles  that  it  approximates  an  irregu- 
lar cone.  The  base  corresponds  with  the  orbital  opening  on  the  face  and  the  apex 

'Graberg  :  Srhwalbe's  Morpholog.  Arheiten,  Bd.  viii.,  1898. 
-A'itsihr.  f.  Morphol.  u.  Anthropol.,  Bd.  4,  1901. 


THE   ORBIT   AND    ITS   FASCIA. 


H37 


with  the  optic  foramen.  The  median  walls  of  the  two  orbits  are  slightly  divergent 
behind,  but  almost  parallel  with  the  sagittal  plane  and  with  each  other  ;  the  lateral 
walls  are  obliquely  placed  and  with  the  sagittal  plane  form  an  angle  of  about  48° 
and,  therefore,  with  each  other  one  of  something  more  than  a  right  angle.  The  axis 
of  the  orbit  is  directed  inward  and  upward,  forming  an  angle  of  from  i5°-2o°  with 
the  horizontal  plane,  and  one  of  about  45°  with  the  orbital  axis  of  the  opposite  side, 
which  it  intersects  in  the  vicinity  of  the  sella  turcica.  The  width  of  the  orbital  en- 
trance is  about  4  cm.  and  the  height  about  5  mm.  less,  while  the  depth  of  the  orbit  is 
approximately  4  cm.  The  space,  therefore,  is  much  more  capacious  than  necessary 
to  accomodate  the  eyeball  and  the  associated  muscles,  blood-vessels  and  nerves. 
The  interspaces  thus  left  are  occupied  by  the  orbital  fat  (corpus  adiposum  orbitae),  sup- 
ported by  a  framework  of  connective  tissue  lamellae  prolonged  from  the  orbital  fascia 
which,  in  turn,  is  continuous  with  the  periosteum  lining  the  orbit.  The  latter,  also 
known  as  the  periorbita,  is  thin  but  resistent  and  at  the  various  openings  in  the  walls  of 
the  orbit  continuous  with  the  periosteum  covering  the  adjacent  surfaces  of  the  skull. 

FIG.  1198. 


Eyelid 


Nasal  fossa 
Anterior  ethmoidal  cells 

Mesial  orbital  wall 

Internal  rectus  muscle 
Posterior  ethmoidal  cells 


Conjunctival  sac 
Anterior  chamber 
Cornea 
Lens 

Vitreous  chamber 

Check  ligament 
Orbital  wall 


External  rectus  muscle 
Solera 


Orbital  fat 
,  Optic  nerve 
Horizontal  section  of  right  orbit  showing  eye  in  position. 

The  eyeball  does  not  rest  directly  in  contact  with  the  fatty  cushion  forming  the 
walls  of  the  cup-shaped  recess  in  which  it  lies,  but  is  separated  from  the  surrounding 
adipose  tissue  by  a  fascial  investment,  the  capsule  of  Tenon  (page  504).  This 
sheet  covers  the  posterior  three-fourths  of  the  eyeball  and  encloses,  between  it  and 
the  eye,  the  space  of  Tenon.  The  latter  in  front  begins  beneath  the  conjuctival 
sac,  close  to  the  corneal  margin,  and  behind  ends  in  the  vicinity  of  the  optic  nerve. 
It  does  not,  however,  quite  reach  the  latter,  but  terminates  where  the  eyeball  is 
pierced  by  the  posterior  ciliary  vessels  and  nerves,  thus  leaving  an  irregular  oval  area 
uncovered  (Merkel).  Farther  backward  the  space  of  Tenon  communicates  with  the 
subdural  lymph-channel  prolonged  along  the  optic  nerve  and  thus  establishes  relations 
with  the  intercranial  lymph-paths  (page  949). 

The  eye  muscles,  which  together  with  the  elevator  of  the  upper  lid  have  been 
described  (page  502),  are  inserted  by  fascial  sheaths  prolonged  from  the  orbital 
periosteum.  These  sheaths  increase  in  thickness  as  they  approach  the  eyeball  until, 
at  the  points  where  the  tendons  of  the  ocular  muscles  meet  the  fascial  sheet  investing 
the  posterior  part  of  the  eye — the  capsule  of  Tenon — the  muscle  sheaths  blend  with 
this  capsule  on  the  one  hand,  and,  on  the  other,  are  attached  at  certain  points  to  the 
orbital  wall  as  robust  pointed  processes  of  considerable  strength.  One  such  process, 


1438  HUMAN   ANATOMY. 

attached  to  the  upper  lateral  wall,  is  formed  by  the  fusion  of  the  fascial  lamellae  con- 
tributed by  the  sheaths  of  the  levator  palpebrae  superioris  and  of  the  superior  and 
external  straight  muscles.  Another  and  broader  process,  inserted  along  the  median 
wall,  includes  the  blended  extensions  from  the  investments  of  the  internal  rectus  and 
superior  oblique  ;  whilst  a  third  process,  formed  by  the  union  of  prolongations  from 
the  fasciae  covering  the  inferior  and  internal  recti  and  the  inferior  oblique,  is  attached 
to  the  lower  and  median  orbital  wall.  These  fascial  extensions,  passing  as  they  do 
from  the  tendons  of  the  eye-muscles  to  the  orbital  wall,  restrain  excessive  muscular 
action  and  hence  the  name,  check  ligaments,  has  been  applied,  especially  to  those 
limiting  the  action  of  the  internal  and  external  recti.  The  processes  also  materially 
assist  in  maintaining  the  position  of  the  eyeball  within  the  orbit.  This  function  is 
particularly  exercised  by  the  robust  fascial  expansion  which  stretches  across  the  orbit 
below  the  eyeball  and  as  the  suspensory  ligament  of  Lockwood  serves  to  support  the 
bulbus  oculi. 

The  orbital  fat  is  prevented  from  projecting  forward  beyond  a  certain  limit  and, 
therefore,  from  encroaching  unduly  upon  the  eyelid,  by  a  sheet  of  fibrous  tissue,  the 

FIG.  1199. 

Upper  tarsal  plate  Palpebral  fascia 


„  ^.  Lachrymal  sac 

Lachrymal  gland. 


Palpebral  fascia,  cut 

Lateral  palpebral  ligament ft ^~  ^fSftf^^"  ^  ~T^^f Median  palpebral  ligament 

Lachrymal  punctum  and 
canaliculus 

Nasal  duct 


Lower  tarsal  plate 


__  Opening  of  nasal  duct  in 
inferior  nasal   meatus 


Maxillary  sinus 
Dissection  of  orbit  and  adjacent  structures,  showing  palpebral  fascia,  lachrymal  sac  and  nasal  duct. 

palpebral  fascia  or  septum  orbitale  (Henle),  which  stretches  across  the  orbital 
entrance  and  materially  strengthens-  and  aids  the  eyelid  in  closing  this  aperture. 
Above,  the  septum  is  attached  to  the  border  of  the  orbit,  just  behind  the  margin, 
from  which  it  extends  downward  to  become  firmly  united  with  the  common  fascial 
investment  of  the  levator  palpebrae  superioris  and  superior  rectus  and,  still  lower, 
with  the  upper  convex  border  of  the  superior  tarsal  plate.  On  each  side  the  septum 
blends  with  the  corresponding  palpebral  ligament,  while  below  it  passes  from  the 
orbital  margin  to  the  inferior  tarsal  plate,  after  becoming  united  with  the  sheath 
of  the  inferior  rectus.  The  septum  orbital  is  not  of  uniform  thickness,  but  is 
strongest  above,  especially  towards  the  sides,  and  weakest  beneath  the  lower  eyelid  ; 
further,  in  a  general  way,  the  sheet  is  more  robust  near  its  peripheral  bony  attach- 
ment than  where  it  joins  the  tarsal  plates.  In  conjunction  with  the  palpebral  liga- 
ments, it  is  so  strong  behind  the  angles  of  the  eye  that  in  these  localities,  particularly 
medially,  it  is  very  unyielding  and  capable  of  resisting  forward  displacement.  The 
internal  union  of  the  levator  palpebrae  superioris  with  the  septum  orbitale  enables 
this  muscle  when  it  contracts  to  tense  the  fascial  diaphragm. 

Practical  Considerations. — The  orbital  cavity  is  somewhat  pyramidal  in 
shape  and  its  anterior  or  basal  portion  is  occupied  chiefly  by  the  eyeball,  which  lies 
slightly  nearer  the  roof  and  the  outer  walls  than  the  lower  and  inner  walls.  Its  diameter 


PRACTICAL   CONSIDERATIONS:    ORBIT   AND    FASCIA.       1439 

is  greatest  just  back  of  its  anterior  margin,  which  is  thickened  and  offers  the  best 
protection  to  the  eye  from  injury.  The  upper  margin  is  most  marked  and  with  the 
eyebrow  offers  a  good  protection  to  the  eye  in  that  direction.  The  inner  margin  is 
not  prominent,  but  is  well  reinforced  by  the  bridge  of  the  nose.  The  outer  edge  is 
least  prominent,  and  on  that  side  palpation  is  possible  as  far  back  as  the  equator  of 
the  globe.  For  this  reason,  and  because  the  outer  walls  converge  backward  while 
the  inner  walls  are  parallel,  incisions  for  reaching  the  interior  of  the  orbit  are  best 
made  on  the  outer  side.  The  walls  are  thin  and  easily  fractured  by  direct  violence, 
as  from  canes  and  similar  objects,  which  sometimes  enter  the  adjacent  cavities,  as 
the  ethmoidal.  Tumors  may  encroach  upon  the  orbital  space  either  by  causing  the 
absorption  of  the  thin  intervening  bone,  or  by  growing  through  one  or  more  of  the 
openings  in  its  wall,  as  through  the  optic  foramen  and  sphenoidal  fissure  from  the 
cranial  cavity,  the  nasal  duct  from  the  nose,  or  the  temporo-maxillary  fissure  from 
the  temporal  or  zygomatic  fossae. 

The  eyeball  occupies  about  one-fifth  of  the  orbital  cavity,  the  remaining  space 
being  filled  by  nerves,  vessels,  muscles,  the  lachrymal  gland,  fat,  and  a  system  of 
fasciae.  In  the  ordinary  case  a  straight  edge  placed  against  the  upper  and  lower 
margins  of  the  orbit  will  just  touch  the  closed  lids  covering  the  apex  of  the  cornea, 
but  will  not  compress  the  eye.  A  straight  line  between  the  two  lateral  margins 
would  pass  back  of  the  cornea,  on  the  outer  side  posterior  to  the  ora  serrata  and  on 
the  inner  side  at  the  junction  of  the  ciliary  body  and  iris. 

An  exophthalmos  is  a  protrusion  forward  of  the  ball,  and  is  usually  due  to- 
pressure  from  behind,  more  rarely  to  paralysis  of  the  recti  muscles.  Some  of  the 
more  common  causes  of  retrobulbar  pressure  are  orbital  cellulitis  or  abscess,  tumors, 
distension  of  the  orbital  vessels,  and  excess  of  fat. 

Enophthalmos,  due  to  exhausting  disease,  is  more  apparent  than  real,  but  a  true 
sinking  of  the  globe  may  be  due  to  paralysis  of  Miiller's  muscle  due  to  lesion  of  the 
sympathetic,  to  atrophy  of  the  retro-bulbar  cellular  tissue  caused  by  trophic  dis- 
turbance, to  fracture  and  depression  of  the  orbital  bones  with  cicatricial  adhesion 
and  contraction,  and  to  injury  of  Tenon's  capsule  and  the  check  ligaments. 

Inflammation  of  the  capsule,  or  Tenonitis,  may  be  due  to  constitutional  poison 
or  to  infection  following  operations  involving  it,  as  in  tenotomy  of  the  ocular 
muscles.  It  may  be  an  extension  from  an  inflammation  of  the  eyeball.  The  inflam- 
matory exudate  in  the  capsule  and  adjacent  tissues  will  sometimes  cause  a  slight 
exophthalmos,  and  the  eye  will  be  immobile.  All  the  extrinsic  muscles  of  the  eye 
pierce  the  capsule  about  the  equator  of  the  globe  to  reach  their  insertions  in  it. 
Each  muscle  receives  a  tubular  investment  from  the  capsule,  which  fuses  with  the 
proper  sheath  of  the  muscle  and  leaves  a  small  bursa  on  the  anterior  surface  of 
each.  To  open  the  capsule  for  a  tenotomy,  the  incision  is  made  just  back  of  the 
cornea,  and  goes  through  only  the  conjunctiva  and  outer  layer  of  the  capsule.  The 
desired  tendon  is  easily  found  and  brought  out  with  a  hook  when  it  is  divided.  The 
capsular  prolongation  about  the  tendon  prevents  retraction  of  the  stump  after  the 
division,  and  so  preserves  the  function  of  the  muscle.  This  is  aided  by  expansions 
of  the  capsule  passing  to  the  margins  of  the  orbit  and  continuous  with  the  perios- 
teum. Those  passing  from  the  internal  and  external  recti  are  stronger  than  the 
others  and  are  called  the  internal  and  external  check  ligaments.  They  are  united 
by  a  layer  of  fascia  (suspensory  ligament  of  the  eyeball)  passing  under  the  eyeball 
so  that  the  eye  is  supported  after  the  bony  floor  of  the  orbit  has  been  removed,  as 
after  excision  of  the  superior  maxillary  bone.  If  the  outer  layer  of  the  globe  is  left 
after  enucleation  of  the  eye,  the  muscles  will  still  have  an  attachment  and  be  capable 
of  moving  an  artificial  eye  fitted  to  the  stump. 

While  the  movements  of  the  eyeball  are  free  in  all  directions,  as  in  a  ball  and 
socket  joint,  no  change  in  position  of  the  eyeball,  as  a  whole,  takes  place,  as  the 
centre  of  rotation  is  about  in  the  centre  of  the  globe.  By  these  movements  the 
image  of  the  object  to  be  especially  seen  is  fixed  upon  the  most  sensitive  part  of  the 
retina. 

The  internal  rectus  draws  the  ball  directly  inward  and  the  external  rectus 
directly  outward.  The  other  four  muscles,  the  superior  and  inferior  recti  and  the 
two  oblique,  have  a  complicated  action.  The  upward  and  downward  movements 


1440  HUMAN   ANATOMY. 

are  controlled  chiefly  by  the  superior  and  inferior  recti  respectively,  but  each  has  a 
slight  adducting  and  a  slight  rotating  movement — i.e.,  the  superior  rectus  will  move 
the  upper  extremity  of  the  vertical  meridian  slightly  inward  (intorsion),  and  the 
inferior  rectus  will  move  the  same  part  slightly  outward  (extorsion).  The  superior 
oblique  is  attached  to  the  globe  behind  the  equator,  and  lower  than  its  pulley,  so  that 
in  addition  to  its  chief  or  internal  rotating  action  upon  the  upper  limit  of  the  ball  it 
has  also  an  elevating  effect  upon  the  posterior  portion,  the  cornea  moving  down- 
ward. Since  its  pull  is  inward,  the  cornea  also  moves  outward.  The  chief  move- 
ment of  the  inferior  oblique  is  rotary  in  the  opposite  direction  (extorsion  of  the  upper 
part).  It  is  likewise  inserted  into  the  posterior  half  of  the  globe,  which  is  depressed 
by  it,  and  the  cornea  is  raised  and  moved  outward.  In  elevation  of  the  cornea  by 
the  superior  rectus  the  internal  rotation  of  this  muscle  is  counteracted  by  the  inferior 
oblique,  and  in  a  similar  manner  when  the  cornea  is  moved  downward  by  the  inferior 
rectus,  its  external  rotation  is  opposed  by  the  superior  oblique.  The  upward  and 
outward  movement  is  produced  chiefly  by  the  superior  and  external  recti,  the  infe- 
rior oblique  opposing  the  intorsion  of  the  superior  rectus.  Motion  downward  and 
outward  is  due  to  the  external  and  inferior  recti,  the  superior  oblique  opposing  the 
outward  wheel  action  of  the  inferior  rectus.  The  downward  and  inward  motion  is 
due  to  the  internal  and  inferior  recti,  the  superior  oblique  opposing  the  inferior 
rectus. 

When  one  muscle  is  weaker  or  larger  than  its  opposing  muscle,  the  eye  is  turned 
to  the  side  of  the  stronger,  producing  strabismus  or  squint.  It  is  usually  turned 
laterally,  most  frequently  to  the  inner  side  producing  internal  or  convergent  strabis- 
mus. All  the  recti  except  the  external  are  supplied  by  the  oculomotor  nerve.  If 
that  nerve  is  paralyzed  only  the  external  rectus  can  act,  and  an  external  squint  will 
result.  If  the  sixth  cranial  nerve  (abducens)  which  supplies  the  external  rectus  is 
paralyzed,  the  eye  will  turn  inward,  the  superior  and  inferior  recti  opposing  each 
other. 

Paralyses  of  one  or  more  muscles  may  occur.  If  a  single  muscle  is  involved  it 
is  usually  the  superior  oblique  or  external  rectus,  as  each  of  these  is  supplied  by  a 
separate  cranial  nerve,  the  fourth  and  sixth  respectively. 

Although  the  third  or  oculomotor  has  a  much  wider  distribution  than  these,  sup- 
plying all  the  other  extrinsic  muscles,  as  well  as  the  ciliary  muscle  and  sphincter  of 
the  iris,  when  it  is  completely  paralyzed  the  clinical  picture  is  definite.  Ptosis  is 
present  and  is  due  to  paralysis  of  the  levator  palpebrae.  External  strabismus  and 
slight  depression  of  the  eye  are  produced  by  the  unopposed  action  of  the  external 
rectus  and  superior  oblique,  while  the  eye  is  otherwise  motionless.  The  pupil  is 
dilated  from  paralysis  of  the  sphincter  of  the  iris,  and  accommodation  for  near  objects 
is  lost  from  paralysis  of  the  ciliary  muscle.  Slight  exophthalmos  appears  from  paral- 
ysis of  all  but  one  of  the  recti  muscles. 

The  fourth  nerve  alone  is  rarely  paralyzed.  There  will  be  little  disturbance 
of  function,  since  the  motion  of  the  superior  oblique  is  performed  partly  by  the 
other  muscles.  The  eye  will  turn  inward  when  the  object  looked  at  is  lowered, 
and  upward  only  when  the  object  is  turned  far  toward  the  healthy  side.  One  eye 
must  be  closed  to  prevent  double  vision  or  diplopia. 

Of  the  single  paralyses,  that  of  the  sixth  nerve  is  most  frequent  on  account  of 
its  extended  course  from  its  origin  in  the  brain  to  its  peripheral  termination  in  the 
external  rectus,  rendering  it  liable  to  involvement  by  adjacent  pathological  processes, 
as  meningitis,  tumors,  or  hemorrhages.  Such  lesions  may  involve  it  alone,  or 
together  with  a  series  of  cerebral  nerves,  paralyzed  one  after  another  from  a  progress- 
ing pathological  condition,  which  would  then  probably  be  at  their  central  origin,  or 
in  the  wall  of  the  cavernous  sinus,  where  they  are  close  together.  The  sixth  nerve 
may  be  paralyzed  by  a  fracture  of  the  base  of  the  cranium  in  the  middle  fossa. 

When  the  ophthalmic  division  of  the  fifth  ncrrc  is  paraly/ed.  there  follows 
anesthesia  of  the  conjunctiva  of  the  globe  and  upper  lid,  and  of  the  other  parts  supplied 
by  this  nerve.  The  lids  do  not  respond  reflexly,  as  usual,  for  protection  of  the 
cornea,  which  is  liable  then  to  troublesome  ulceration. 

The  cen<ical  sympathetic  *\\\)\)\\v*  the  dilatator  muscle  of  the  iris,  and  reaches  the 
cranium  along  the  internal  carotid  artery.  When  the  cervical  sympathetic  is  paralyzed 


THE   EYELIDS   AND   CONJUNCTIVA.  1441 

the  pupil  contracts.  There  will  be  some  drooping  of  the  upper  lid  due  to  paralysis 
of  the  superior  palpebral  muscle  of  Miiller  which  passes  from  the  under  surface  of  the 
levator  palpebrae  muscle  to  the  upper  margin  of  the  upper  tarsal  cartilage,  and  is 
supplied  by  the  cervical  sympathetic.  There  will  be  slight  enophthalmos  from  paral- 
ysis of  a  thin  layer  of  unstriped  muscle  passing  across  the  spheno-maxillary  fissure 
(orbitalis  muscle  of  Miiller). 

The  normal  pupil  will  contract  for  accommodation  and  convergence  to  near 
objects  and  from  stimulation  by  a  bright  light.  An  Argyll- Robertson  pupil  is  one 
which  does  not  react,  either  directly  or  indirectly  (consensually)  to  the  influence  of 
light,  but  contracts  promptly  on  convergence  of  the  visual  axes.  The  exact  situation 
of  the  lesion  is  uncertain  ;  it  may  involve  the  fibres  which  pass  from  the  proximal 
end  of  the  optic  nerve  to  the  oculomotor  nuclei  ;  it  may  be  nuclear  in  its  position  ; 
or  it  may  be  in  the  spinal  end  of  the  floor  of  the  fourth  ventricle. 

Owing  to  the  relatively  large  amount  of  fat  and  loose  connective  tissue  in  the 
orbit,  infection  may  lead  to  an  extensive  orbital  abscess,  so  that  an  early  opening  is 
imperative  to  prevent  disturbance  or  loss  of  sight.  The  muscles  may  be  impaired 
by  the  process,  leading  to  the  lessened  mobility  of  the  eye.  The  optic  nerve  may 
be  inflamed  with  resulting  atrophy  and  permanent  impairment  of  sight,  and  the  other 
ocular  nerves  may  also  be  paralyzed.  From  the  exophthalmos  the  optic  nerve  may 
be  stretched,  although  the  degree  of  stretching  permitted  without  disturbing  sight  is 
often  remarkable.  Pus  may  enter  the  cranial  cavity  through  the  optic  foramen,  and 
set  up  a  meningitis  or  a  brain  abscess. 

Injuries  of  the  orbital  tissues  are  usually  the  result  of  penetration  by  foreign 
bodies.  The  eye  has  been  pried  out  by  the  ringer,  or  thumb,  on  the  outer  side  by 
insane  people,  or  in  fights,  the  finger  being  readily  forced  back  of  the  equator  of 
the  globe.  There  are  cases  in  which  the  eye  has  been  replaced  and  vision  regained 
after  such  accidents,  although  it  is  usually  lost. 

Fracture  of  the  bony  wall  of  the  orbit  ordinarily  leads  to  hemorrhage  into  the 
soft  tissues,  showing  later  under  the  conjunctiva  of  the  ball  (subconjunctival  ecchy- 
mosis).  If  the  neighboring  air  cavities,  as  the  ethmoidal  and  sphenoidal  sinuses,  are 
involved,  emphysema  of  the  orbit  may  result.  The  exophthalmos  from  air  behind 
the  eye,  can  be  reduced  by  backward  pressure,  the  air  being  forced  back  into  the  air 
sinuses.  A  collection  of  blood  would  not  disappear  by  such  pressure.  In  cases  of 
emphysema  the  patient  should  be  instructed  not  to  blow  the  nose,  as  by  that  act 
additional  air  is  forced  into  the  orbit. 

Tumors  of  the  orbit  are  comparatively  common.  They  may  begin  in  the  adja- 
cent cavities  and  invade  the  orbit  secondarily.  The  most  important  symptom  in  all 
cases  is  exophthalmos.  Pain  and  paralysis  from  pressure  on  the  nerves,  and  con- 
gestion and  edema  of  the  lids  from  pressure  on  the  veins  frequently  occur. 

THE    EYELIDS    AND    CONJUNCTIVA. 

The  eyelids  (palpebrae)  are  two  movable  folds  of  integument — an  upper 
and  a  lower — strengthened  along  their  free  margins  by  a  lamina  of  dense  fibrous 
tissue,  the  tarsal  plate,  and  modified  on  their  deeper  aspect  so  that  this  surface 
resembles  a  mucous  membrane,  the  conjunctiva.  When  in  apposition  or  closed  they 
completely  cover  the  orbital  entrance  and  the  eyeball  ;  at  other  times,  when  open, 
they  cover  the  periphery  of  the  orbit  but  allow  a  variable  portion  of  the  anterior  part 
of  the  eye  to  remain  exposed. 

The  palpebral  fissure  (riraa  palpebrarum)  is  bounded,  above  and  below,  by 
the  free  margins  of  the  lids  and  at  the  ends,  where  the  lids  join,  by  two  fibrous 
bands,  the  median  and  lateral  palpebral  ligaments.  Of  these  the  inner  and 
stouter  springs  from  the  nasal  process  of  the  superior  maxillary  bone  and  the  narrow 
outer  one  is  attached  to  the  malar  bone.  The  palpebral  fissure  is  an  oval  cleft  of 
not  quite  symmetrical  form,  since  the  curvature  of  its  upper  boundary  is  somewhat 
greater  than  that  of  the  lower  ;  further,  the  points  marking  the  summit  of  the 
two  curves  neither  correspond  to  the  middle  of  the  arches  nor  lie  opposite  each 
other,  that  of  the  upper  arch  lying  nearer  the  mid-line  and  that  of  the  lower  nearer 
the  lateral  wall.  Neither  is  the  palpebral  fissure  strictly  horizontal,  since  the  inner 


1442 


HUMAN    ANATOMY. 


Fi<;.    1 200. 


of  its  ends,  the  angles  or  canihi,  lies  slightly  (from  4-6  mm. )  lower  than  the  other  one. 
The  free  borders  of  the  lids  meet  at  the  outer  canthus  without  change  of  curvature, 
but  on  approaching  the  inner  canthus  they  alter  their  direction  and  extend  medially 
for  several  millimeters  before  meeting.  In  this  manner  immediately  external  to 

the  inner  canthus  the  lids  bound  a  shallow 
D-shaped  recess,  about  5  mm.  long,  known 
as  the  lachrymal  lake  (lacus  lacrimalis). 
The  palpebral  fissure,  which  possesses  an 
average  length  of  30  mm.  and  a  height  of  from 
12—14  mm. ,  is  subject  to  considerable  individ- 
ual variation  in  size,  thereby  exposing  a  vari- 
able amount  of  the  eyeball.  In  consequence, 
the  appearance  of  a  larger  or  smaller  eye 
is  produced,  an  impression,  however,  that 
depends  upon  the  size  of  the  opening  between 
the  lids  and  not  upon  differences  in  the  eyeball 
itself,  the  diameters  of  which,  under  normal 
conditions,  are  practically  constant.  The 
height  of  the  palpebral  fissure  in  young 
children  is  relatively  greater  than  in  the  adult, 
a  peculiarity  that  confers  the  characteristic 
wide-eyed  appearance  in  early  life. 

The  upper  lid  is  not  only  much  the 
broader,  its  height  being  about  double  that 
of  the  lower  one,  but  also  the  more  movable 
and  the  chief  agent  in  closing  the  palpebral 
opening.  When  the  latter  is  closed  the  free 
edges  of  the  two  lids  are  in  contact  through- 
out their  length,  the  anterior  margin  of  the 
upper  one  overlapping  slightly  the  corre- 
sponding edge  of  the  lower.  The  line  of 
apposition  is  somewhat  arched,  with  the 
convexity  directed  downward,  and  falls  below 
a  horizontal  line  passing  through  the  inner 
canthus.  When  the  eyelids  are  separated 
to  the  usual  extent,  the  free  edge  of  the 
upper  lid  lies  just  below  the  upper  margin 
of  the  cornea,  a  narrow  crescentic  area  of 
which  it  masks,  while  the  corresponding 
border  of  the  lower  lid  falls  slightly  below 
the  inferior  corneal  margin.  Tin-  position 
of  the  pupil  is  about  midway  between  the 
two  canthi.  When  the  eyelids  are  closed, 
the  upper  fold  covers  the  entire  cornea,  its 
lower  border  lying  opposite  the  correspond- 
ing margin  of  the  cornea. 

Viewed  in  sagittal  section  (  Fig.  1 20 1  ) 
the  free  border  of  the  lid  presents  a  wcl" 
defined  posterior  margin,  along  which  open 
the  minute  ducts  of  the  tarsal  glands. 
whilst  the  anterior  margin  is  rounded  and  passes  insensibly  into  the  adjoining 
external  skin-surface  and  is  beset  with  the  eyelashes.  The  latter,  the  cilia,  arc-  stiff 
outwardly  curving  hairs,  which  number  from  100-150  in  the  upper  lid  and  about  half 
as  many  in  the  lower.  With  the  exception  of  about  5  mm.  next  the  inner  angle, 
when-  the  lids  border  the  lachrymal  lake  and  the  eyelashes  are  absent,  the  cilia  are 
arranged  in  a  double  or  triple  row,  with  the  longest  (  S-i2  mm.  )  in  the  centre  of  tin- 
upper  series,  Although  their  follicles  occupy  a  /one  of  from  1-2  mm.  in  width,  the 
free  ends  of  the  cilia  lie  practically  in  a  single  row,  the  longer  and  more  closely  set 
upper  lashes  either  crossing  or  overlying  the  shorter  ones  of  the  lower  lid. 


Conjunct!' 


Three  views  of  living  eye,  showing  relations  of 
eyeball  to  palpebral  fissure  and  details  of  inner 
canthus. 


THE   EYELIDS   AND   CONJUNCTIVA. 


H43 


The  palpebral  fissure  leads  into  the  conjunctival  sac,  which,  when  the  lids  are 
in  contact,  is  a  closed  capillary  space  between  the  lids  and  the  anterior  surface  of  the 
eyeball.  When  the  cleft  is  open,  the  conjunctival  space  becomes  an  annular  groove 
of  unequal  depth,  its  height  being  from  22-25  mm.  behind  the  upper  lid  and  only 
about  half  as  much  behind  the  lower,  and  being  shallowest  at  the  inner  angle. 
That  part  of  the  sac  which  covers  the  posterior  surface  of  the  lids  constitutes  the 
palpebral  conjunctiva  and  that  reflected  onto  the  eye  ball  is  the  bulbar  con- 
junctiva, while  the  bottom  of  the  groove,  where  these  two  portions  are  continuous, 
is  known  as  the  fornix  conjunctivas,  the  superior  and  inferior  being  distinguished. 

The  lachrymal  lake  (lacus  lacriraalis)  is  the  shallow  bay  into  which  the  con- 
junctival sac  is  prolonged  for  about  5  mm.  between  the  medial  ends  of  the  eyelids.  It 
contains  an  irregularly  oval  or  comet-shaped  elevation,  the  lachrymal  caruncle. 
The  latter  (caruncula  lac- 

FIG.  1201. 

Skin 

Subcutaneous  tissue 

Orbicularis  palpebrarum 


Tarsal  muscle 

Levator  palpebrse 

superioris 


Blood-vessel 


Heiile's  gland 


rimalis)  consists  of  an  is- 
let of  modified  skin  from 
which  project  usually 
about  a  dozen  minute 
and  scarcely  visible  hairs, 
provided  with  large  seba- 
ceous and  smaller  sweat 
glands  and  embedded  in 
a  cushion  of  fatty  tissue. 
Just  to  the  outer  side  of 
the  caruncle,  a  vertical 
crescentic  fold,  the  plica 
semilunaris,  indicates 
the  limit  of  the  bulbar 
conjunctiva.  The  fold  is 
of  interest  as  probably 
representing  in  a  very 
rudimentary  way  the 
nictitating  membrane,  or 
third  eyelid,  of  the  lower 
animals.  The  semilunar 
fold  frequently  contains 
a  minute  plate  of  hyaline 
cartilage  as  the  vestige  of 
the  stronger  bar  in  the 
nictitating  membrane. 
Likewise  the  small  group 
of  alveoli  sometimes 
found  within  the  base  of 
the  fold  is  regarded  as 
the  homologue  of  the 
Harderian  gland  of  the 
lower  types.  The  points 
at  which  the  slightly 
curved  boundaries  of  the 
lachrymal  lake  pass  into 
the  more  arched  edges  of  the  eyelids  are  emphasized  by  little  elevations,  the  lach- 
rymal papillae,  each  of  which  is  pierced  by  a  minute  aperature,  the  punctum 
lacrimalis,  that  marks  the  beginning  of  the  canals  by  which  the  tears  are  normally 
carried  off  from  the  conjunctival  sac. 

Structure  of  the  Eyelids. — The  eyelid  comprises  five  layers  which,  from 
without  inward,  are:  (i)  the  ^m,  (2)  the  subcutaneous  tissue,  (3)  the  muscular 
layer,  (4)  the  tarso-fasdal  layer  and  (5)  the  conjunctiva. 

The  skin  covering  the  outer  surface  of  the  eyelids  is  distinguished  by  its  unusual 
delicacy,  being  thin  and  beset  with  very  fine  downy  and  widely  scattered  hairs,  pro- 
vided with  sebaceous  follicles  ;  small  sweat  glands  also  occur.  It  presents  numerous 


Artery  of  tarsal  arch 


Meibomian  duct 


Glands  of  Moll 


Cilia 


Ciliary  muscle 
Vertical  section  of  upper  eyelid  of  child. 


1444  HUMAN   ANATOMY. 

ineffaceable  transverse  creases  which,  with  advancing  years,  are  supplemented  by 
vertical  furrows.  Towards  the  inner  canthus,  particularly  in  the  lower  lid,  pigment 
exists  in  variable  quantity,  often  in  amount  sufficient  to  confer  a  distinct  brownish 
hue  to  the  interment. 

The  subcutaneous  tissue  is  distinguished  by  the  entire  absence  of  fat,  its  loose 
texture  and  great  extensibility  and  elasticity.  In  consequence  of  these  properties,  it 
sometimes  becomes  the  seat  of  extensive  swelling  after  edema  or  hemorrhage.. 

The  muscular  layer,  for  the  most  part  consisting  of  the  annular  bundles  of  the 
orbicular  is  palpebrarum,  is  in  fact  so  blended  with  the  subcutaneous  tissue  as  to  be 
practically  embedded  within  the  latter.  Reference  to  the  description  of  the  orbicu- 
laris  palpebrarum  (page  484)  will  recall  the  general  division  of  the  muscle  into 
an  orbital  and  a  palpebral  portion,  and  the  relations  of  the  deeper  or  lachrymal  slip 
( tensor  tarsi)  to  the  tear-sac  and  the  tarsal  plate.  In  vertical  sections  of  the  eyelid 
(Fig.  1201)  the  circularly  arranged  bundles  of  the  palpebral  portion  show  as 
transversely  cut  groups  of  muscle-fibres  enclosed  by  condensations  of  the  surround- 
ing areolar  tissue.  A  distinct  annular  tract,  known  as  the  ciliary  bundle  ( in.  ciliaris 
Riolani)  lies  close  to  the  free  border  of  the  lid,  chiefly  between  the  tarsal  plate  and 
the  hair  follicles,  but  in  part  often  also  between  the  conjunctiva  and  the  tarsus.  In 
the  upper  lid,  in  addition  to  the  circular  bundles  of  the  orbicularis  palpebrarum,  the 
terminal  strands  of  the  longitudinal  fibres  from  the  levator  palpebrae  superioris 
descend  along  the  deeper  surface  of  the  first-named  muscle.  Some  of  these 
penetrate  between  the  circular  bundles  and  end  in  the  deeper  layer  of  the  skin  ; 
others  descend  more  vertically  to  find  their  insertion  in  the  upper  border  of  the 
tarsal  plate. 

Under  the  name,  tarsal  muscles  or  muscles  of  Midler,  are  described  the  un- 
certain bundles  of  involuntary  muscle  that  are  found  in  the  vicinity  of  the  convex 
border  of  the  tarsi.  Those  within  the  upper  lid  arise  from  the  tendon  and  inter- 
mingle with  the  fibres  of  the  levator  palpebrarum,  with  the  course  of  which  they 
agree,  and  end  either  by  insertion  into  the  upper  border  of  the  tarsal  plate,  or  into 
the  adjacent  fibrous  tissue.  In  the  lower  lid,  they  are  less  numerous  and  regular, 
and  extend  from  the  fornix  conjunctivas  to  the  adjacent  border  of  the  tarsus.  The 
tarso-fascial  layer  is  represented  next  the  margins  of  the  lids  by  the  tarsal  plates  and 
beyond  the  latter  by  the  septum  orbitale. 

The  tarsal  plates  (tarsi)  are  two  lamellae  of  dense  fibrous  tissue,  one  in  each 
lid,  that  occupy  the  margins  of  the  eyelids,  to  the  maintenance  of  whose  form  they 
largely  contribute.  They  are  crescentic  in  outline,  the  borders  next  the  lid-cleft 
being  only  slightly  curved  and  almost  straight  and  the  thinner  distal  borders  mark- 
edly convex.  Their  ends  are  joined  to  the  palpebral  ligaments  which  branch  into 
upper  and  lower  limbs  for  the  attachment  of  the  tarsal  plates.  The  upper  tarsus  is 
the  more  arched  and  broader,  measuring  about  10  mm.  or. about  double  the  lower 
plate,  in  both  cases  the  median  ends  of  the  crescents  being  blunted  and  less  pointed 
than  the  lateral.  The  plates  are  approximately  i  mm.  in  thickness  and  consist  of 
densely  felted  fibrous  tissue,  and  are  blended  in  front  and  below  with  the  subcu- 
taneous tissue,  above  with  the  septum  orbitale  and  the  insertion  of  the  lid-muscles, 
and  behind  with  the  conjunctiva. 

In  addition  to  preserving  the  curvature  of  the  lids,  the  tarsal  plates  lodge  the 
linear  series  of  the  Meibomian  or  tarsal  glands  (glandulae  tarsales).  These  struc- 
tures, between  thirty  and  forty  in  number  in  the  upper  lid  and  about  one-third  less 
in  the  lower  one,  consist  of  a  chief  tubular  duct,  placed  vertically  and  lined  by  stratified 
squamous  epithelium,  which  is  beset  with  numerous  simple  or  branched,  irregular, 
flask-shaped  alveoli.  The  latter  contain  cuboidal  epithelial  elements  that  resemble 
in  appearance  and  condition  those  found  in  sebaceous  follicles,  to  which  class,  in  fact, 
the  tarsal  glands  belong.  They  secrete  an  oily  substance,  sebum  palpebrarum,  which 
is  discharged  through  the  minute  punctiform  orifices  of  the  ducts  that,  on  evert inu 
the  edges  of  the  lids,  are  seen  as  a  row  of  dark  points  just  external  to  the  sharp  con 
junctival  border  of  the  eyelid.  In  this  manner  the  latter  is  kept  lubricated,  and  thus, 
under  usual  conditions,  maintains  an  effective  barrier  against  the  overflow  of  the 
tears  from  the  conjunctival  sac.  Within  the  free  edge-  of  the  eyelids,  just  in  advance 
of  the  tarsal  plates,  lie  the  glands  of  Moll,  and  the  glands  of  Zeiss.  The  former 


THE    EYELIDS    AND    CONJUNCTIVA.  1445 

are  coiled  tubules,  resembling-  modified  sweat  glands,  the  latter  sebaceous  glands, 
the  ducts  of  which  usually  open  close  to  or  into  the  mouths  of  the  follicles  of  the 
eye-lashes. 

The  palpebral  conjunctiva  lines  the  ocular  surface  of  the  eyelids.  Since  the 
latter  are  developed  as  integumentary  folds,  at  first  the  conjunctiva  resembles  the 
skin,  but  after  the  temporary  closure  of  the  lids,  from  the  middle  of  the  third  month 
until  shortly  before  birth,  it  loses  its  original  character,  and  later,  bathed  continu- 
ously with  the  secretion  of  the  tear-gland,  assumes  the  translucently  rosy  tint  and 
general  appearance  of  a  mucous  membrane,  as  which  the  conjunctiva  is  often 
regarded.  Over  the  tarsi  the  palpebral  conjunctiva  is  so  tightly  adherent  to  the 
underlying  fibrous  plate,  that  the  tunica  propria  is  reduced  to  an  insignificant  layer 
and  the  Meibomian  glands  shimmer  through  the  smooth  translucent  conjunctiva  and 
appear  as  parallel  yellowish  stripes.  On  gaining  the  rctrotarsal  fossa,  along  the 
convex  border  of  the  tarsal  plates,  the  conjunctiva  becomes  loose  and  movable  and 
marked  by  circular  folds  since  the  tunica  propria,  which  here  connects  the  epithelium 
with  the  underlying  fascial  tissue,  is  plentiful.  The  small  tubular  glands  of  Henle 
often  occupy  the  subepithelial  tissue  of  this  part  of  the  conjunctiva.  In  the  fornix 
and  its  vicinity  minute  lymph-nodules  occur  normally,  either  discrete  or  in  small 
groups.  In  the  same  locality  and  at  the  convex  borders  of  the  tarsi,  small  nests  of 
serous  alveoli,  known  as  accessory  tear-glands,  or  glands  of  Krause,  are  found,  being 
much  more  numerous  in  the  upper  than  in  the  lower  lid. 

The  bulbar  conjunctiva  passes  from  the  fornix  onto  the  anterior  part  of  the 
eyeball,  over  which  it  extends,  unwrinkled  but  gradually  thinning,  as  far  as  the 
corneal  margin,  at  which  point  (limbus  corner}  the  tunica  propria  ends  and  the 
epithelium  alone  continues  uninterruptedly  over  the  cornea.  During  its  passage  from 
the  free  edge  of  the  eyelid  to  the  cornea,  the  character  of  the  conjunctival  epithelium 
varies  in  different  parts  of  the  sac.  Thus,  at  the  border  of  the  lids  and  for  a  few 
millimeters  over  the  tarsi,  it  resembles  the  epidermis  in  being  stratified  squamous. 
Towards  the  convex  border  of  the  tarsal  plates  the  squamous  type  gives  way  to  the 
cylindrical  ;  in  the  retrotarsal  fossa,  throughout  the  fornix  and  for  a  short  distance 
(.5—1  mm.)  over  the  eyeball,  the  epithelium  is  exclusively  columnar,  varying  in 
thickness  and  in  the  number  of  its  layers  ;  whilst  over  the  cornea  and  adjacent  parts 
of  the  sclera,  the  epithelium  is  again  stratified  squamous. 

Vessels  of  the  Eyelids. — The  arteries  chiefly  supplying  the  eyelids  are  the 
superior  and  inferior  palpebral  branches  from  the  ophthalmic  and  from  the  lachrymal 
arteries.  These  form  the  first  source,  the  internal  palpebral,  which  arise  either  sepa- 
rately, or  by  a  short  common  stem,  pierce  the  septum  orbitale  a  short  distance  above 
or  immediately  below  the  internal  palpebral  ligament,  and,  in  addition  to  sending 
twigs  to  the  lachrymal  caruncle,  canals  and  sac,  pursue  a  tortuous  course  near  the 
free  margin  of  the  lids  towards  the  external  canthus.  On  nearing  the  latter  the 
superior  and  inferior  internal  branches  join  the  corresponding  branches  from  the 
external  palpebral  and  from  the  lachrymal,  as  well  as  anatomosing  with  twigs  from  the 
superficial  temporal  and  transverse  facial  arteries.  In  this  manner  a  tarsal  arch  is 
formed  in  each  lid  along  the  base  of  each  tarsus,  between  the  latter  and  the  orbicu- 
laris  muscle,  from  which  perforating  twigs  penetrate  the  tarsal  plates  for  the  supply  of 
the  Meibomian  glands  and  the  adjacent  conjunctiva.  In  the  upper  lid  a  less  regular 
secondary  tarsal  arch  is  formed  along  the  convex  border  of  the  tarsus  by  the  anasto- 
mosis of  the  palpebrals  and  the  frontal  and  supraorbital  branches.  A  similar,  but  less 
constant  and  complete,  arch  occurs  in  the  lower  lid. 

In  consequence  of  the  double  path  of  escape  of  the  blood  from  the  orbit — through 
the  ophthalmic  and  the  facial  veins — the  veins  of  the  eyelids  are  tributaries  of  two 
systems.  Those  from  the  deeper  structures  (conjunctiva,  Meibomian  glands),  the 
retrotarsal  veins,  empty  into  the  branches  of  the  ophthalmic,  while  those  draining  the 
more  superficial  parts  of  the  eyelid,  pretarsal  veins,  are  tributary  to  the  frontal  and  facial 
veins  medially  and  to  the  supraorbital  and  superficial  temporal  laterally.  Since  not 
only  the  supraorbital,  but  also  the  frontal  veins  communicate  with  the  ophthalmic 
system,  the  blood  is  carried  off  by  way  both  of  the  orbital  and  facial  channels. 

The  lymphatics  of  the  eyelids  are  arranged  in  two  sets,  a  pretarsal  and  a  post- 
tarsal,  the  net- works  of  which  are  connected  by  vessels  which  pierce  the  tarsi.  The 


1446  HUMAN    ANATOMY. 

former  receives  lymph  from  the  skin  and  muscles,  the  latter  from  the  Meibomian 
glands  and  the  conjunctiva.  The  larger  vessels  on  the  outer  side  pass  to  the  pre- 
auricular  and  parotid  lymph-nodes,  and  those  on  the  inner  or  mesial  side  follow  the 
tributaries  of  the  facial  vein  and  enter  the  submaxillary  lymph-nodes. 

Nerves  of  the  Eyelids. — The  sensory  nerves  are  branches  of  the  ophthalmic 
and  superior  maxillary  divisions  of  the  trigeminal.  The  upper  lid  is  supplied  mainly  by 
the  frontal  and  supraorbital  nerves,  the  lower  lid  by  the  infraorbital  nerve.  On  the 
nasal  side  these  nerves  are  supplemented  by  twigs  from  the  supra-  and  infratrochlear 
branches  of  the  ophthalmic,  and  on  the  outer  side  by  terminal  filaments  from  the 
lachrymal  nerve.  The  main  branches  lie  between  the  tarsi  and  the  orbicularis 
muscle,  sending  branches  forward  to  the  skin  and  backward  through  the  tarsi  to  the 
conjunctiva  and  Meibomian  glands.  In  addition  a  marginal  plexus  is  formed  near 
the  edge  of  each  lid,  which  supplies  the  adjacent  parts  and  the  follicles  of  the  cilia. 

The  motor  nerve  to  the  levator  palpebrae  is  a  branch  of  the  superior  division  of 
the  oculomotor  nerve  ;  the  orbicularis  palpebrarum  is  supplied  by  the  facial,  and  the 
involuntary  muscle  of  the  lids  by  fibres  from  the  sympathetic. 

Practical  Considerations. —  The  Eyebrows. — The  hair  of  the  eyebrows  may 
be  absent,  dark  brows  may  show  white  patches  (piebald  eyes),  or  they  may  be 
entirely  white,  as  in  albinos.  Incisions  in  this  area,  as  for  neurectomy  in  supra- 
orbital  neuralgia,  should  be  made  in  the  line  of  the  brow  and  within  the  limits  of  the 
hair,  so  that  the  scar  which  results  may  be  hidden. 

Dcrmoid  cysts  occur  in  the  line  of  the  orbito-nasal  fissure  of  the  foetus,  and  are 
most  frequent  near  the  outer  end  of  the  brow,  under  the  orbicularis  palpebrarum, 
next  to  the  periosteum.  Usually  they  are  no  larger  than  a  cherry,  and  in  some 
instances  lie  deep  in  the  orbit,  when  they  would  be  difficult  of  diagnosis.  More 
rarely  they  occur  at  the  inner  angle  of  the  orbit,  when  they  may  be  connected  with 
the  dura.  In  such  cases  they  would  1)e  difficult  of  removal  and  might  be  confused 
with  meningoceles. 

Epicanthus  is  a  crescentic  fold  of  skin  lying  over  the  inner  canthus  and  the 
inner  end  of  the  palpebral  fissure.  It  may  be  associated  with  a  congenital  defect  in 
the  bridge  of  the  nose.  In  many  children  a  slight  tendency  to  it  is  seen  before  the 
bridge  of  the  nose  has  reached  its  full  development,  while  in  those  races  which  have 
little  or  no  bridges  to  their  noses,  a  slight  epicanthus  is  normal.  Until  this  condition 
is  suspected,  these  children  are  often  thought  to  have  convergent  squint,  because 
the  cornea  is  nearer  to  the  skin  than  in  a  normal  eye. 

Very  rarely  the  lids  may  fail  to  develop  (ablepharia)  ;  less  rarely  a  cleft  in  the 
margin  of  the  lid  is  seen,  usually  to  the  median  side  of  the  centre  of  the  lid  (colo- 
boma),  and  most  frequently  in  the  upper  lid.  Sometimes  the  eye  has  a  uniform 
covering  of  skin  which  replaces  the  lids,  no  palpebral  fissure  being  present.  This 
is  probably  due  to  a  persistence  of  the  early  foetal  condition,  in  which  the  t\v<>  lids 
are  adherent.  It  is  called  ankylo-blcpharon. 

Lagophthahnus  is  an  incomplete  closure  of  the  lids,  and  is  sometimes  congenital, 
sometimes  the  result  of  paralysis  of  the  facial  nerve  which  supplies  the  orbicularis 
muscle.  Voluntary  contraction  of  this  muscle  will  usually  close  the  lids  in  the  lesser 
degrees  of  the  congenital  variety,  but  in  sleep  they  are  not  closed.  Since  the  eye 
turns  up  as  the  lids  are  brought  together,  the  cornea  is  concealed. 

Ptosis  is  a  drooping  of  the  upper  lid,  and  when  congenital  is  usually  associated 
with  epicanthus,  and  is  bilateral.  The  forehead  is  often  wrinkled  from  the  effort  of 
the  occipito-frontalis  muscle  to  aid  the  orbicularis  in  lifting  the  lid.  The  head  is 
usually  thrown  back  and  the  eyes  depressed  to  bring  the  sensitive  part  of  the  retina 
and  pupil  in  line  with  the  object  to  be  seen. 

Blfpharospasm  is  an  irritable  spasm  of  the  orbicularis  closing  the  lids,  and  is 
usually  due  to  disease  of  other  parts  of  the  eye. 

The  skin  of  the  lids  is  the  thinnest  in  the  body  and  is  very  loosely  applied, 
through  the  loose  areolar  subcutaneous  tissue.  It  therefore  wrinkles  easily,  is  readily 
deformed  by  scars,  and  is  a  favorable  field  for  plastic  operations.  If  cicatricial  con- 
traction everts  the  lower  lid,  as  it  often  does,  the  condition  is  known  as  cctropiou. 
More  rarely  contraction  of  the  conjunctiva  after  ulceration  or  injury  inverts  a  lid, 


THE    EYEBALL.  1447 

producing  cntropion.  The  eyelids  become  cedematous  or  ecchymotic  from  slight 
causes,  and  in  erysipelas  are  markedly  swollen,  closing  the  lids,  or  in  severe  cases 
may  become  gangrenous,  the  exudate  interfering  with  the  blood-supply. 

Herpes  zoster  is  sometimes  seen  along  the  cutaneous  distribution  of  the  frontal 
and  nasal  branches  of  the  trigeminal  nerve.  It  is  found  on  the  forehead,  lids,  nose, 
and  even  the  cornea.  The  iris,  ciliary  body,  or  choroid  may  be  involved,  since- 
through  the  lenticular  ganglion,  the  nasal  nerve  supplies  these  structures.  The 
cause  is  an  inflammation  of  the  trunk  of  the  trigeminal  nerve,  the  Gasserian  ganglion, 
or  the  lenticular  ganglion. 

Hordeolum  or  stye  is  a  suppuration  of  one  of  the  sebaceous  glands  (Zeiss's 
glands)  associated  with  the  follicles  of  the  eyelashes.  A  chalazion  is  an  affection  of 
one  of  the  Meibomian  glands,  with  occlusion  of  the  duct  and  retention  of  the  secre- 
tion. There  is  often  no  inflammation  present.  For  this  reason,  and  because  of 
its  situation  on  the  under  surface  of  the  tarsal  cartilage,  it  is  often  not  noticed 
until  it  reaches  considerable  size  and  shows  through  the  lid.  Normally  the  cilia  or 
eyelashes  curve  away  from  the  surface  of  the  eyeball.  Sometimes  from  inflammation, 
most  commonly  in  trachoma  or  granular  lids,  they  take  the  opposite  direction  and 
irritate  the  cornea  (trichiasis  or  wild  hairs). 

The  Conjunctiva. — Congenital  fatty  growths  occur  rarely  in  the  outer  part  of 
the  upper  conjunctival  sac.  Dermoids  and  nsevi  have  also  been  seen  in  the  con- 
junctiva. This  membrane  covers  the  anterior  third  of  the  eyeball,  and  where  it  passes 
to  the  lids  forms  the  fornices.  Because  the  upper  fornix  is  deeper  than  the  lower, 
being  therefore  turned  less  easily,  foreign  bodies  are  removed  from  the  upper  sac 
with  greater  difficulty.  These  particles  strike  first  on  the  surface  of  the  globe,  and 
are  usually  brushed  down  into  the  lower  sac  by  the  upper  lid.  They  frequently, 
however,  catch  in  the  conjunctiva  of  the  ball  or  of  the  upper  lid,  and  are  held  in  the 
conjunctival  sac  only  when  they  get  above  the  upper  retro-tarsal  fold,  where,  if  not 
removed,  they  may  set  up  a  chronic  inflammation,  or  remain  unnoticed.  They 
have  been  found  there  months  or  even  years  afterward,  entirely  embedded  in  the 
outgrowths  of  the  inflamed  conjunctiva  (Fuchs). 

A  pterygium  is  an  elevated  layer  of  conjunctiva  and  subconjunctival  tissue, 
triangular  in  shape  with  its  apex  near  the  edge  of  the  cornea,  and  its  base  usually 
towards  the  inner  canthus.  It  tends  to  progress  towards  the  pupil,  but  may  stop 
anywhere  short  of  it. 

A  pinguccula  is  a  yellowish  elevation  of  conjunctiva,  to  the  inner  side  of  the 
cornea,  sometimes  to  the  outer  side.  It  corresponds  to  the  part  of  the  conjunctiva 
constantly  exposed  in  the  interpalpebral  fissure,  which  therefore  undergoes  a  change 
in  structure.  That  at  the  inner  side  is  most  marked  and  may  become  a  pterygium  later. 

The  scleral  portion  of  the  conjunctiva  is  loosely  applied  to  permit  of  free  motion 
of  the  ball.  Near  the  margin  of  the  cornea  it  becomes  more  fixed,  and  should  be 
caught  there  by  the  forceps  in  the  effort  to  fix  the  eye  when  operating  upon  it.  The 
palpebral  portion  is  more  firmly  attached,  especially  at  the  back  of  the  tarsal  plates 
where  it  is  more  vascular,  and  where  paleness  is  taken  to  indicate  a  general  anaemia. 

In  fractures  of  the  base  of  the  skull  involving  the  roof  of  the  orbit  the  hemor- 
rhage into  the  orbital  tissues  shows  first  under  the  conjunctiva  of  the  globe  (subcon- 
junctival ecchymosis).  It  finds  its  way  under  the  conjunctiva  of  the  lids  later  because 
that  is  more  firmly  attached,  and  unless  the  lid  is  lifted,  it  will  first  be  noticed  at  the 
margin  of  the  lid,  after  which  it  may  grow  upward  under  the  skin.  This  is  due  to 
the  fact  that  the  orbito-tarsal  or  palpebral  ligament  passes  between  the  margin  of  the 
orbit  and  the  upper  edge  of  the  tarsal  plate  like  a  curtain  and  prevents  the  progress 
of  the  blood  forward  to  the  skin  until  it  has  first  passed  down  behind  the  tarsal  plate 
and  under  its  lower  margin.  Owing  to  the  thinness  of  the  conjunctiva,  oxygen  per- 
meates it  more  readily  than  it  does  the  skin,  so  that  blood  under  it  retains  its  redness 
instead  of  becoming  dark,  as  under  the  skin  of  the  lid  in  ordinary  "  black  eye." 

THE    EYEBALL. 

The  eyeball  is  situated  in  the  anterior  part  of  the  orbit,  about  2  mm.  nearer 
the  lateral  than  the  nasal  wall,  and  slightly  nearer  the  superior  than  the  inferior 
wall.  A  line  drawn  from  the  superior  margin  of  the  orbit  to  the  inferior  is  tangent  to 


HUMAN    ANATOMY. 


the  surface  of  the  cornea.  The  axes  of  the  eyeballs  are  practically  parallel,  when 
fixed  on  a  distant  object,  but  the  optic  nerves  converge  considerably,  so  that  they 
enter  the  eyeball  from  2-3  mm.  to  the  nasal  side  of  the  posterior  pole  of  the  eye. 
The  general  form  of  the  eyeball  is  that  of  a  sphere,  but  in  sagittal  section  it  is  found 
to  be  composed  of  the  segments  of  two  spheres,  an  anterior  smaller  segment,  corre- 
sponding to  the  transparent  cornea,  which  has  a  radius  of  from  7-8  mm.  and  a  pos- 
terior opaque  segment,  corresponding  to  the  sclera,  with  a  radium  of  12  mm.  The 
junction  between  the  two  segments  is  marked  externally  by  a  broad,  shallow  groove. 
the  snlcns  sclera:,.  which  is  filled  by  the  scleral  conjunctiva. 

The  diameters  of  the  eyeball  measure  approximately  as  follows  :  the  antero-pos- 
terior,  24.2  mm.  ;  the  vertical,  23.2  mm.  ;  and  the  transverse,  23.6  mm.  Its  shape 
is,  therefore,  that  of  a  spheroid  somewhat  flattened  from  above  downward,  and  from 


FIG.  1202. 


Lens 


Suspensory  ligament  of  lens 
Canal  of  Schlemm 
Ciliary  process 

Conjunctiva 


Cornea 

Anterior  chamber 
Iris 

Posterior  chamber 

Sclerocorneal  juncture 


Tendon  of  in- 
ternal rectus— 
muscle 

Vena  vorticosa 


Tendon  of 
external  rectus 
muscle 


Sclera 


Ciliary  nerve-' 


Posterior  ciliary  vessel 


Hyaloid  canal 

Optic  nerve 

Central  retinal  vessels 


roid 


Retina 
Fovea  centra lis 


Optic  papilla 


Diagrammatic  horizontal  section  of  right  eye.     X  3%. 

side  to  side.  The  diameters  are  slightly  greater  in  the  male  than  in  the  female,  am 
vary  according  to  the  refractive  power,  being  longer  in  nearsighted  or  myopic,  am 
shorter  in  oversighted  or  hyperopic  eyes. 

The  eyeball  consists  of  three  concentric  coats  or  tunics  :  ( i )  the  external 
fibrous  tunic,  composed  of  the  sclerotic  and  the  cornea  ;  (2)  the  middle  or  rasculat 
tunic,  which  is  pigmented  and  partly  muscular,  and  is  composed,  from  behind  for 
ward,  of  the  choroid,  the  eiliarv  body,  and  the  iris  ;  and  (3)  the  inno  -or  nerroi 
tunic,   the  retina,  an  expansion  of  the  brain,  which  contains  beside  the  nerve-cell 
and  the  nerve-fibres  the  specialized  neuroepithelium  for  the  reception  of  visual  stimuli 

Within  these  tunics  are  enclosed  the  refracting  media,  the  crystalline  lens,  tl 
at/neons  /minor  and  the  rifrcons  body. 

Practical  Considerations. — Congenital  anomalies  may  affect  the  whole  eyt 
the  appendages,  or  the  individual  structures  of  the  eye. 

The  eye  may  be  congcnitafly  absent,  on  one  or  both  sides  ( anophthalmos ).      Ii 
cases  of  apparent  absence  the  eyeball  has  been  found  to  be  exceedingly  sin; 


THE   FIBROUS   TUNIC. 


1449 


( microphthalmos)  and  situated  deep  in  the  orbit  near  the  optic  foramen.  The  patient 
may  otherwise  be  entirely  normal  ;  or  other  developmental  errors,  as  hare-lip  or 
cleft-palate  may  be  present.  In  some  instances  where  no  eyeball  was  found,  the 
optic  nerve  had  not  entered  the  orbit,  and  in  others  the  chiasm  had  not  formed,  the 
primary  optic  vesicle  having  failed  to  develop. 

Multiple  eyes  occur  in  some  monsters.  As  digits  sometimes  bifurcate  to  form 
supernumerary  digits,  so  the  cephalic  end  of  the  embryo  may  divide,  giving  rise  to 
two  heads.  These  may  fuse,  when,  according  to  the  extent  of  fusion,  there  will  be 
four,  three,  or  two  eyes  ;  or  if  both  the  orbits  and  the  eyes  fuse  there  may  be 
only  one  eye  (cyclopia). 

The  actual  size  of  the  eye  in  man  varies  little,  the  apparent  size  depending 
chiefly  upon  the  projection  from  the  orbit  and  the  part  exposed  between  the  lids. 
The  variation  in  different  animals  depends  rather  upon  the  necessity  for  acuteness  of 
vision  than  upon  the  size  of  the  animal.  The  larger  the  globe  the  farther  the  cornea 

and  lens  from  the  retina,  and 

FIG.  1203. 

-Fibre  layer 

.    .:•.*•••'•         .  I  ,an  orlir»n    r-<^ 


Ganglion  cells 
Bipolar  cells 
Visual  cells 

Pigment  layer 

Stroma 
Large  vein 


Lamina  fusca 


Fibrous  tissue 
of  sclera 


therefore  the  larger  and 
more  distinct  the  image  on 
the  retina  of  the  object  seen. 
The  more  active  the  animal 
the  greater  is  the  necessity 
for  acuteness  of  vision,  and 
therefore  the  larger  the  eye. 
The  eyes  of  birds  are  pro- 
portionally larger  than  those 
of  other  animals.  Nocturnal 
animals,  such  as  the  owl, 
have  large  eyes.  The  large 
retinal  image  probably  com- 
pensates for  the  scarcity  of 
light,  to  which  they  are 
accustomed. 

THE  FIBROUS  TUNIC. 
The    Sclera.— The 

sclera,  or  sclerotic  coat,  is 
a  firm,  dense  fibrous  coat 
which  forms  the  posterior 
four-fifths  of  the  outer  coat 
of  the  eye,  being  closely  con- 
nected with  the  sheaths  of 
the  optic  nerve  posteriorly, 
and  joining  in  front  with 
the  cornea.  In  the  neigh- 
borhood of  the  optic  nerve  it  measures  i  mm.  in  thickness,  and  gradually  becomes 
thinner  toward  the  equator,  until,  just  posterior  to  the  attachment  of  the  tendons 
of  the  ocular  muscles,  it  measures  only  .4  mm.  After  receiving  the  expansions 
of  these  tendons  it  again  becomes  thicker  and  reaches  a  thickness  of  .6  mm.  In 
children  and  in  individuals  who  have  thin  sclerae  and  deeply  pigmented  eyes, 
the  sclera  possesses  a  bluish  white  color,  while  in  old  age  it  assumes  a  yellowish 
tinge.  The  optic  nerve  passes  through  this  tunic  at  a  position  i  mm.  below  and 
from  3-4  mm.  to  the  inner  side  of  the  posterior  pole  of  the  eye  ;  the  canal  is 
partially  bridged  over  by  interlacing  fibrous  bundles,  the  lamina  cribrosa,  which 
are  intimately  associated  with  the  supporting  tissue  of  the  nerve.  Grouped  around 
the  nerve  entrance  are  small  openings  for  the  ciliary  nerves  and  posterior  ciliary 
arteries,  and  toward  the  equator  four  or  five  for  the  vencz  vorticose  which  emerge 
from  the  choroid. 

Structure  of  the  Sclera. — The  sclera  is  composed  of  interlacing  bundles  of 
white  fibrous  tissue,  which  on  the  outer  and  inner  surface  have  chiefly  a  meridional 
direction,  while  the  central  bundles  form  a  fairly  regular  alternation  of  circular  and 


Episcleral 
endothelium 
Space  of  Tenon 
between  sclera 
and  capsule 
of  Tenon 


Section  of  three  coats  of  eyeball,  about  five  millimeters  from  optic  papilla » 
capsule  of  Tenon  seen  below  sclera.    X  40. 


HUMAN    ANATOMY. 


Epithelium 

-  Anterior 
limiting 
membrane 


?r-     Cortical  cell 


meridional  lamellae.  The  tissue  yields  gelatine  on  boiling.  With  the  fibrous  bundles 
is  associated  a  rich  net-work  of  fine  elastic  fibers.  The  clefts  between  the  lamella- 
contain  irregularly  stellate  connective  tissue  cells — the  scleral  corpuscles.  On  the 
inner  surface  of  the  sclera  many  of  these  cells  are  pigmented  and  give  it  a  brownish 
color.  This  layer — the  lamina  fusca- — forms  with  the  underlying  choroid  a  narrow 
lymph-space,  the  suprachoroidal  lymph-space,  both  walls  of  which,  together  with  the 
fine  connective  tissue  trabeculae  which  cross  it,  are  lined  with  endothelial  cells.  The 
outer  surface  of  the  sclera,  from  the  optic  nerve  entrance  to  the  attachment  of  the 
ocular  muscles,  is  similarly  covered  with  endothelial  plates,  and  forms  part  of  the  lining 
of  Tenon's  lymph-space.  Anterior  to  the  muscle-insertions  it  is  covered  with  a 
loosely  meshed  connective  tissue,  the  episderal  tissue,  which  is  richly  supplied  with 

blood-vessels,  nerves  and  lymph- 
vessels,  and  is  continuous  with 
the  subconjunctival  tissue  of  the 
conjunctiva  scler&. 

The  blood-vessels  of  the  sclera 
arise  from  the  arteries  which  per- 
forate it  to  supply  the  vascular  coat 
of  the  eye,  viz  :  the  anterior  and 
posterior  ciliary  arteries.  They 
form  a  wide  meshed  net-work  on 

SroSrfatia  t^ie  sur^ace  °f  tne  sclera,  which 
sends  anastomosing  vessels  to  a 
deeper  lying  set  in  the  substance  of 
the  membrane.  In  the  neighbor- 
hood of  the  optic  nerve  entrance 
the  branches  of  the  short  posterior 
ciliary  arteries  form  an  arterial 
circle,  the  circulus  Zinni,  which 
sends  branches  to  the  optic  nerve 
and  choroid,  and  is  therefore  of 
great  importance  in  establishing 
an  anastomosis  between  the  cho- 
roidal  circulation  and  the  artcria 
centra/is  retina;  which  supplies  tin 
retina. 

The  veins  of  the  sclera  empty 
into  the  anterior  and  posterior 
ciliary  veins,  and  into  the  vemr 
vorticosce.  At  the  junction  of  the 
cornea  and  sclera  is  an  important  circular  venous  channel,  the  canal  of  Schlcnun, 
which  will  be  described  later.  The  lymphatics  of  the  sclera  are  represented  by 
the  intercommunicating  cell-spaces,  which  communicate  with  the  suprachoroidal 
and  suprascleral  lymph-spaces,  and  anteriorly  with  the  spaces  of  Fontana,  at  the 
corneo-scleral  angle. 

The  nerves  of  the  sclera  are  derived  from  the  ciliary  nerves  during  their  course 

between  the  sclera  and  the  choroid,  their  terminal  filaments  being  distributed  to  the 

vessels,  and  also  as  a  fine  tortuous  net-work  between  the  bundles  of  the  scleral  tissue 

The  relations  of  the  sclera  to  the  optic  nerve  sheaths  will  be  considered  in  tl 

description  of  the  optic  nerve  entrance  (page  1470). 

The  Cornea. — The  cornea  forms  the  anterior  one-fifth  of  the  fibrous  tunic 
the  eyeball,  and,  although  composed,  like  the  sclera,  of  bundles  of  connective  tissue, 
is  transparent  and  allows  rays  of  light  to  enter  the  eyeball.  Its  anterior  surface 
is  nearly  but  not  quite  circular,  measuring  ii.<)  nun.  in  its  greatest  transverse 
diameter,  and  n  mm.  in  its  vertical  diameter.  The  posterior  surface  is  circular  and 
measures  13  nun.  in  diameter.  The  sclera  therefore  encroaches  more  upon  the  cornea 
anteriorly  than  posteriorly,  so  that  the  cornea  fits  into  a  groove  in  tin-  sclera.  The 
radius  of  curvature  of  the  anterior  corneal  surface  is  about  7.7  mm.,  that  of  the  hori- 
zontal meridian  being  slightly  greater  (7. S  nun.)  than  that  of  the  vertical.  The 


Section  of  human  cornea.     X  85. 


THE  FIBROUS  TUNIC. 


H5I 


radius  of  curvature  of  the  posterior  surface  is  only  6  mm. ;  the  cornea  is  consequently 

thicker  in  the  periphery  than  at  the  center,  in  the  proportion  of.  i.i  mm.  to  .8  mm. 

The  degree  of  curvature  varies  in  different  individuals  and  at  different  periods  of  life, 

being  greater  in  youth  than  in 

old  age.    As  the  radius  of  curva-  FIG.   1205. 

ture  of  the  sclera,  with  which  its 

bundles  are   continuous,    is    12 

mm. ,  the  cornea  rests  upon  the 

sclera  as  a  watch-glass  upon  a 

watch.      At  the  junction  of  the 

two  membranes,   on  the  outer 

surface,  is  the  shallow  groove, 

the  snh'i/s  sclcra'. 

Structure  of  the  Cor- 
nea.— The  cornea  is  composed 
of  five  distinct  layers,  which 
from  without  in  are:  (i)  the 
anterior  epithelium,  (2)  the  an- 
terior limiting  membrane,  (3) 
the  substantia  propria,  (4) 
the  posterior  limiting  mem- 
brane, and  (5)  the  posterior 
endothelium. 

The  anterior  epithelium 

of     the      Cornea      is       Continuous  Corneal  corpuscles  (connective  tissue  cells),  surface  view.    X  350. 

with  that  covering  the  surface 

of  the  adjacent  conjunctiva  sclerae.  It  is  of  the  stratified  squamous  variety,  usually 
five  cells  deep  in  man,  and  measures  .045  mm.  in  thickness  at  the  center,  and 
.080  mm.  at  the  periphery.  The  deepest  cells  are  columnar  in  form,  with  broad 
basal  plates  resting  upon  the  anterior  limiting  membrane,  to  which  they  are  firmly 
attached  by  means  of  minute  projections  which  roughen  the  anterior  surface  of 

the  latter.  The  outer  parts  of  the  basal 
cells  contain  the  nucleus  and  fit  into  corre- 
sponding depressions  in  the  cells  of  the 
superimposed  layers.  The  middle  layers  are 
composed  of  irregular  polyhedral  cells, 
which  usually  present  fine  protoplasmic 
denticulations,  and  resemble  prickle  cells. 
The  superficial  layers  consist  of  flattened 
cells  which  lie  parallel  to  the  free  surface 
and  contain  well-staining  nuclei. 

The  anterior  limiting  membrane,  <>r 
Bowmari  s  membrane,  is  situated  immedi- 
ately below  the  epithelium,  and  appears  as  a 
homogeneous  band,  about  .02  mm.  in  thick- 
ness at  the  center  and  thinner  at  the  periph- 
ery, where  it  terminates  without  extending 
into  the  conjunctiva  of  the  sclera.  The  mem- 
brane may  be  split  into  fine  fibrillae  by 
the  use  of  suitable  reagents,  is  connected 
firmly  with  the  cornea  proper  by  delicate 
filaments,  and  is  to  be  considered  a  special  condensation  of  the  latter.  It  contains 
no  elastic  tissue. 

The  substantia  propria  constitutes  the  main  portion  of  the  cornea,  and  is 
made  up  of  interlacing  bundles  of  connective  tissue,  which  are  directly  continuous 
with  those  of  the  adjacent  sclera.  The  bundles  are  composed  of  fine  fibrillae,  have 
a  flattened  form,  and  are  so  disposed  as  to  produce  regular  lamellae,  about  sixty 
in  number,  running  parallel  with  the  surface.  The  alternating  lamellae  have  a  direction 
approximately  at  right  angles  to  each  other  and  are  frequently  joined  together  by 


FIG.   1206. 


Corneal  spaces,  after  action  of  argentic  nitrate  ; 
surface  view.      <  350. 


1452 


HIM  AX    ANATOMY. 


FIG.  1207. 

Canal  of  Schlemm 


hands,  which  are  especially  numerous  in  the  anterior  lamelke,  to  which  the  name 
fibres  arcuatcc  has  been  given.  The  fibril  ke  and  bundles  are  held  together  by  an 
amorphous  cement  substance,  and  embedded  in  it  are  the  cellular  elements,  the 
corneal  corpuscles.  These  are  flattened  connective  tissue  cells,  with  faintly  granular 
protoplasm,  the  nuclei  of  which  in  the  adult  are  irregular  and  show  nucleoli.  The 
cells  are  provided  with  branching  processes  which  anastomose  with  those  of  other 
cells  both  on  the  same  level  and  with  those  between  adjacent  lamellae,  and  so  con- 
stitute a  continuous  net-work  of  protoplasm,  upon  which  the  nutrition  of  the  cornea 
largely  depends.  They  have  been  described  as  occupying  part  of  a  regular  system 
of  cell-spaces  and  canaliculi,  but  most  recent  investigations  seem  to  indicate  that 
during  life  they  fill  out  the  spaces  completely,  and  leave  no  gaps  through  which 
fluid  can  pass.  Occasionally  leucocytes  or  wandering  cells  are  found  between  the 
fibrous  elements. 

The  posterior  limiting  membrane,  also  known  as  Deseemet  \v  membrane,  the 
Membrane  of  Demours,  or  the  posterior  elastic  membrane,  is  a  practically  homo- 
geneous band,  which  varies  in  thickness  from  .006 — .012  mm.  at  the  center  and 
at  the  periphery  respectively.  It  is  less  firmly  united  to  the  substantia  propria  than 
is  the  anterior  limiting  membrane,  and  is  less  easily  affected  by  acids,  alkalies,  boiling 

water  and  other  regents.  It  resembles 
elastic  tissue  and  is  very  firm  and  resist- 
ant to  injury  or  perforation  from  inflam- 
mation. At  the  periphery,  Descemct'> 
membrane  splits  up  into  bundles  of  fine 
fibres,  which  are  gradually  strengthened 
and  form  a  series  of  firm  connective 
tissue  trabecuke,  some  of  which  form 
the  point  of  attachment  of  the  ciliary 
muscle  ;  others  run  into  the  iris,  and  still 
others  constitute  the  outer  wall  of  a 
circularly  disposed  venous  channel,  tin- 
sinus  circulars  iridis,  or  canal  of 
Schlemm.  These  fibres  are  known  as 
the  ligamentum  pectinatum  iridis 
and  form  the  outer  boundary  of  the  angle 
of  the  anterior  chamber.  They  are 
incompletely  covered  with  endothelial 
cells  and  enclose  between  their  loose  meshes  the  spaces  of  Fontana.  These, 
better  developed  in  lower  animals  than  in  man,  directly  communicate  with  the  aqueous 
chamber,  and  thus  form  an  important  point  for  filtration  of  fluid  from  the  interior  of 
the  eye,  by  way  of  the  canal  of  Schlemm,  into  the  anterior  ciliary  veins. 

The  posterior  endothelium  covers  the  inner  surface  of  Descemet's  membrane. 
It  is  composed  of  a  single  layer  of  flattened  polygonal  cells,  the  nuclei  of  which  often 
extend  above  the  level  of  the  cell  body.  The  cells  are  connected  together  by  deli- 
cate protoplasmic  processes  and  are  continuous  with  the  cells  lining  the  spaces  of 
Fontana  and  the  anterior  surface  of  the  iris.  With  Descemet's  membrane  they  con- 
stitute a  barrier  to  the  filtration  of  fluid  from  the  anterior  chamber  into  the  cornea. 
although  its  passage  by  diffusion  is  possible; 

The  blood-vessels  of  the  normal  cornea  are  limited  to  a  peripheral  /one, 
from  1-2  mm.  in  width,  where  the  terminal  twigs  of  the  episcleral  brandies  of 
the  anterior  ciliary  arteries  end  in  loops  (F"ig.  1215),  from  which  the  blood  is 
carried  to  the  anterior  ciliary  veins.  The  remainder  of  the  cornea  is  free  from 

blood-channels. 

The  ncri'i's  of  the  cornea  are  exceedingly  numerous.  They  are  branches  ot 
the  long  and  short  ciliary  nerve-,  from  40  to  45  in  number,  and  form  a  plexus  which 
surrounds  the  margin  of  the  cornea  (plexus  annularis).  Those  which  supply  the 
anterior  part  of  the  cornea  anastomose  first  with  the  conjum  Ural  nerves.  Entering 
the  cornea,  they  are  accompanied  for  a  distance  of  I  mm.  by  a  perineiiral  lymph- 
sheath,  and  then  losing  this  and  their  medullary  sheath,  they  form  within  the  corneal 
stroma  a  number  of  plexuses  at  various  depths.  A  few  of  the  fibres  pass  backward 


Trabeculae  of 

pectinate 

ligament 


Bundles  of  ciliary  muscle 

Meridional  section  through  angle  of  anterior  chamber 
showing  spaces  of  Fontana  between  relaxed  fibres  of 
pectinate  ligament  and  canal  of  Schlemm.  X  65. 


PRACTICAL    CONSIDERATIONS:     THE    FIBROUS   TUNIC.      1453 

and  supply  the  posterior  layers.  Fully  two-thirds,  however,  after  forming  a  funda- 
mental plexus,  push  forward  and  send  perforating  branches  through  Bowman's  mem- 
brane and  form  on  its  surface  a  subepithclial  plexus,  the  minute  fibres  of  which  pass 
in  a  radial  manner  toward  the  center  of  the  cornea.  From  this  plexus  fine  fibrils 
ascend  between  the  epithelial  cells,  and  end  either  as  varicose  fibrils,  or  in  connection 
with  special  end-bulbs  (the  intracpithelial plexus).  In  the  substantia  propria  the 
branches  from  the  fundamental  plexus,  after  forming  complex  secondary  plexuses, 
end  as  naked  fibrilke  between  the  lamellae,  probably  in  close  connection  with  the 
corneal  corpuscles. 

Practical  Considerations. — The  external  or  fibrous  covering  of  the  eyeball 
consists  of  the  sclera  and  cornea,  and  is  the  protective  covering.  The  posterior  five- 
sixths  is  made  up  of  sclera,  which  in  some  animals  becomes  cartilaginous  or  even 
bony.  In  the  human  eye  the  average  normal  tension  within  the  globe  is  equivalent 
to  a  column  of  mercury  26  mm.  high.  Excessive  intraocular  tension  occurs  under 
pathological  conditions  (glaucoma)  and  may  reach  70  mm.  or  more.  The  more 
delicate  structures  then  suffer  severely  and  unless  the  pressure  is  relieved  they  are 
functionally  destroyed.  The  sclera  is  thickest  and  strongest  posteriorly  and  grad- 
ually grows  thinner  as  it  passes  forward.  Immediately  behind  the  insertions  of  the 
recti  muscles  it  is  thinnest  (.4  mm.).  Here  bulging  is  most  likely  to  occur  from 
internal  pressure  (anterior  scleral  or  ciliary  staphyloma),  or  pus  within  to  burrow 
through.  In  front  of  this  zone  it  is  reinforced  by  expansions  from  the  insertions  of 
the  muscles,  and  would  seem  therefore  to  be  stronger,  although  it  is  in  this  region, 
just  back  of  the  margin  of  the  cornea,  that  ruptures  are  most  likely  to  occur  from 
external  violence. 

Ruptures  of  the  sclera  occur  close  to — within  3  mm.  of — the  corneal  margin  and 
concentric  with  it,  because  in  most  cases,  as  Fuchs  points  out,  the  application  of  the 
force  does  not  lie  in  the  centre  of  the  cornea,  but  in  the  sclera  below  and  to  the  outer 
side  of  the  cornea.  The  greatest  expansion  of  the  sclera  takes  place  in  its  upper  half 
near  the  margin  of  the  cornea,  at  which  place,  therefore,  the  sclera  ruptures. 

This  region  is  the  so-called  dangerous  zone  of  the  eyeball,  because  the  iris  and 
ciliary  body  correspond  to  it,  and  in  wounds  involving  these  structures,  sympathetic 
ophthalmia  frequently  results,  often  leading  to  destruction  of  both  eyes.  Besides  the 
anterior  staphyhmata  of  the  sclera,  \ve  may  have  the  eqiiatorial  and  the  posterior. 
The  equatorial  develops  at  the  spots  where  the  venae  vorticosae  penetrate  and  thus 
weaken  the  sclera  about  the  equator  of  the  globe. 

The  posterior  is  assumed  to  be  the  result  of  a  congenital  weakness  of  the  sclera. 
The  anterior  or  equatorial  can  be  seen  or  palpated,  while  the  posterior  is  recognized 
only  by  demonstrating  the  existence  of  a  high  degree  of  short-sightedness,  which  is 
due  to  an  increase  of  the  sagittal  axis  of  the  eyeball. 

Rupture  of  the  sclera  is  usually  the  result  of  a  blow  on  the  eye.  The  ciliary  body 
and  anterior  portion  of  the  choroid  are  frequently  forced  into  the  wound,  the  vitreous 
and  aqueous  chambers  contain  blood,  while  the  lens  may  find  its  way  through  the 
rent  and  lie  under  the  conjunctiva,  which  may  or  may  not  be  torn.  Rarely  the  rup- 
ture will  be  in  the  posterior  portion  of  the  globe. 

Congenital  opacities  of  the  cornea  may  occur  and  may  be  complete  or  partial. 
In  some  of  the  cases  reported  of  the  complete  variety  the  anterior  elastic  lamina 
was  absent,  and  the  anterior  layers  of  the  stroma  were  not  laminated  as  usual,  but 
crossed  each  other,  and  among  them  were  found  blood-vessels.  The  partial 
varieties  may  consist  of  a  dense  white  opaque  ring  at  the  margin  of  the  cornea, 
as  though  the  sclera  had  extended  into  the  cornea,  or  they  may  resemble  an  arcus 
senilis  in  which  a  perfectly  clear  strip  of  cornea  divides  the  opaque  line  from  the 
margin  of  the  sclera. 

The  cornea  in  health  is  transparent,  and  almost  all  pathological  lesions  render  it 
opaque.  It  is  the  most  exposed  and  therefore  the  most  frequently  injured  part  of  the 
eye.  Wounds  of  the  cornea  heal  readily  under  favorable  circumstances,  showing  that 
its  nutrition  is  good,  although  there  are  no  vessels  in  it,  except  within  1-2  mm.  of 
its  margin.  When  the  cornea  is  inflamed,  however,  new  vessels  may  form  from 
those  at  the  margin  and  extend  a  variable  distance  inward.  Under  the  influence  of 


1454 


HUMAN    ANATOMY. 


irritating  conditions  a  superficial  inflammation  may  develop,  covering  the  cornea  with 
a  new  vascular  tissue  (pannus),  the  deeper  layers  still  being  bloodless.  Owing  to  a 
very  free  nerve-supply  the  cornea  is  very  sensitive. 

As  in  the  sclera,  weakness  of  the  cornea  leads  to  bulging,  from  internal  pressure. 
The  causes  of  weakness  may  be  congenital  and  acquired.  Congenital  conical  cornea 
or  kerataconus  may  occur,  and  it  is  believed  that  some  congenital  defect  predisposes 
to  the  same  condition  that  occurs  in  the  adult.  It  is  not  due  to  weakening  from  pre- 
vious ulceration  or  injury  of  the  cornea,  and  the  exact  cause  is  not  known. 

A  staphyloma  of  the  cornea  is  a  similar  condition  in  which  the  protuberance  is 
due  to  the  distention  of  a  cicatrix,  to  the  posterior  surface  of  which  the  iris  may  be 
attached  (anterior  synechiae  of  the  iris).  The  cicatrix  involves  all  the  layers  of  the 
cornea,  and  is  the  result  of  a  perforating  ulcer.  If  the  ulcer  had  been  a  non-per- 
forating one,  and  the  iris  did  not  adhere  to  its  posterior  surface,  the  protrusion  of  the 
cornea  would  then  be  called  a  keratedasia. 

If  all  the  layers  of  the  cornea  to  the  posterior  elastic  lamina  had  been  destroyed 
by  the  ulcer,  and  this  layer  had  bulged  through  the  weakened  spot  like  a  hernial 
pouch  it  would  be  called  a  keratocele. 

Arcus  sent/is  is  usually  a  sign  of  old  age.  Modern  investigation  indicates  that  it 
is  due  to  a  fatty  degeneration  of  the  substantia  propria,  the  exact  nature  of  the  fatty 
material  being  unknown.  It  first  appears  as  a  crescent  above,  then  below,  and  finally 
a  complete  circle  is  formed.  It  never  interferes  with  sight.  It  is  occasionally  seen 
in  children. 

THE  VASCULAR  TUNIC. 

The  middle  or  vascular  coat  of  the  eye  (tunica  vasculosa  oculi),  or  uveal  tract, 
consists  of  a  vascular  connective  tissue  sheath,  which  lies  internal  to  the  outer  fibrous 

FIG.  1208. 


Anterior  chamber 

Pupil 

Circulus  arteriosus  minor 

Artery  joining  ring — ._ 


Vena  vorticosa 


Short  post,  ciliary 
artery 


Cornea 

Iris 

Circulus  arteriosus  major 

Anterior  ciliary  artery 
Ciliary  nerves 


•Venous  whorl 


Ciliary  nerve  •']] 
}}f  posterior  ciliary  artery' 


\ 
Sclera 


ptic  nerve 


Injected  eyeball,  showing  arrangement  of  ciliarv  aiu-ne>  ami  «\  choroidal  veins,     v  3.     Drawn  from 

ptrparation  made  l>v  1'iotessoi  Kciller. 

tunic.      It   cMrnds  from  tin-  entrance  of  the  optic  nerve  to  the  pupil  and  include 
three   portions,  which  from   behind  forward  arc-  the  choroid,  the  ciliary  body  and   the 
iris.      The  choroid  and  ciliary  body  arc  in  contact  with  tin-  sclcra,  but  the  iris  bends 


THE   VASCULAR  TUNIC. 


H55 


sharply  inward  and  floats  in  the  aqueous  humor,  incompletely  dividing  the  space 
anterior  to  the  crystalline  lens  into  a  posterior  and  an  anterior  chamber. 

The  Choroid. — The  choroid  (tunica  chorioidea)  forms  the  posterior  two-thirds 
of  the  vascular  coat.      It  lies  between  the  sclera  and  the  retina  and  extends  from  the 


FIG.  1209. 


»-•,-*"    ~ 


optic  nerve  entrance  to 
the  anterior  limit  of  the 
visual  part  of  the  retina 
at  the  ora  serrata,  its 
main  function  being  to 
supply  nutrition  to  the 
nervous  tunic.  It  is 
a  delicate  coat,  which 
has  a  thickness  of  .  i 
mm.  near  the  nerve  and 
gradually  diminishes  in 
thickness  towards  the 
ora  serrata,  where  it 
measures  only  .06  mm. 
The  outer  surface  is 
roughened  by  the  tra- 
beculae  of  connective 
tissue  which  cross  the 
suprachoroidal  lymph- 
space  and  connect  the  choroid  with  the  overlying  sclera.  The  connection  is  main- 
tained partly  also  by  the  larger  vessels  and  nerves,  which  lie  within  this  space 
during  their  course  forward  and  send  branches  to  supply  the  choroid.  The  inner 


Membrana 
vitrea 

Chorio- 
capillaris 


Large  vein— 


Choroiclal 
stroina 
Lamina  su- 
prachorioidea 
Suprachoroi- 
dal space  — 
Lamina  fusca 
of  sclera^ 


Section  of  choroid. 


275- 


Large  vein 


Artery 


Surface  view  of  injected  human  choroid,  showing  venous  radicles  converging  to  form  larger  veins.      •    is. 

surface  of  the  choroid  is  smooth  and  covered  by  the  pigmented  cells  of  the  retina, 
which  are  so  closely  attached  that  they  frequently  adhere  to  the  choroid  when  the 
membranes  are  separated.  Posteriorly,  the  choroid  helps  to  form  the  lamina  crib- 
rosa,  the  fenestrated  membrane  through  which  the  optic  nerve-fibres  pass  ;  anteriorly 
it  is  continuous  with  the  ciliary  body. 


HTM  AN   ANATOMY. 


FIG.  121 i. 


Portion    of    injected    choriocapillaris   layer 
human  choroicl.     X  130. 


Structure  of  the  Choroid. — The  choroid  consists  of  four  layers,  which  from 
without  inward,  are  :  (i)  the  lamina  sitprachorioidea,  (2)  the  choroid  proper,  which 
contains  the  larger  vessels,  (3)  the  choriocapillaris,  or  layer  of  fine  capillaries,  and 
(4)  the  membrana  vitcra. 

The  lamina  suprachorioidea  forms  the  outer  boundary  of  the  choroid  and 
connects  it  with  the  sclera.  It  is  composed  of  interlacing  bundles  of  fibrous  connec- 
tive tissue,  which  are  strengthened  by  a  rich  net- 
work of  elastic  fibres.  The  cellular  elements 
consist  of  (a)  flattened  endothelial  plates,  which 
line  the  lymph-clefts  and  cover  the  connective 
tissue  trabeculae  connecting  the  choroid  and  the 
sclera  by  traversing  the  suprachoroidal  lymph- 
space  ;  and  (£)  large,  irregularly  branched  con- 
nective tissue  cells,  the  chromatophorcs,  which 
are  conspicuous  on  account  of  their  deeply 
pigmented  protoplasm.  The  lamellae  of  the 
suprachoroid  continue,  without  definite  boun- 
dary, into  the  subjacent  choroidal  stroma. 

The  choroid  proper,  as  the  choroidal 
stroma  is  called,  has  the  same  general  structure 
as  the  suprachoroidal  layer,  but  the  connective 
tissue  elements  are  denser  and  support  a  large 
number  of  blood-vessels,  between  which  are 
placed  the  stellate  chromatophores.  The  largest 
vessels  occupy  the  outer  part  of  the  coat,  and 
are  chiefly  venous.  They  are  surrounded  with 
perivascular  lymph-sheaths,  and  converge  in  peculiar  whorls  to  form  four  or  five 
large  trunks,  the  vence  vorticosa,  which  pierce  the  sclera  in  the  equatorial  region  and, 
running  obliquely  backward,  drain  not  only  the  choroid,  but  partly  also  the  ciliary 
body  and  iris.  The  arteries  are  derived  from  the  short  ciliary  vessels,  which  pass 
through  the  sclera  near  the  optic  nerve. 
They  lie  internal  to  the  veins  and  their 
walls  contain  longitudinally  disposed  muscu- 
lar fibres  in  addition  to  the  customary  cir- 
cular ones. 

The  choriocapillaris,  or  membrane  of 
Ruysch,  is  composed  of  the  fine  capillaries 
of  the  choroidal  vessels,  which  form  an 
extremely  fine  mesh-work  embedded  within 
a  homogeneous,  nonpigmented  matrix. 
Between  the  choriocapillaris  and  the  layer  of 
larger  vessels  is  a  narrow  boundary  zone  of 
closely  woven  fibro-elastic  strands,  which  is 
nearly  free  from  pigment.  In  some  animals 
this  layer  possesses  a  peculiar  metallic  reflex 
and  is  known  as  the  tapetum  fibrosum  ;  in 
carnivora  its  iridescent  appearance  is  due  to 
the  presence  of  cells  containing  minute  crys- 
tals (tapetion  cellnlosnm'}. 

The  membrana  vitrea,  or  membrane 
of  Bruch,  the  innermost  layer  of  the  choroid, 
measures  only  .002  mm.  in  thickness.  It 
separates  the  choriocapillaris  from  the 
retina  and  is  composed  of  two  strata,  an 
inner  homogeneous  one,  probably  an  exu- 
dation product  of  the  retinal  pigment  cells,  and  an  outer  highly  elastic  portion. 
The  lymphatics  of  the  choroid  are  represented  (i)  by  vessels  which  begin  in  the 
lymph-spaces  between  large  blood-vessels,  and  are  in  communication  with  the  space> 
between  the  suprachoroidal  lamellae,  and  (2)  by  the  perivascular  lymph-spaces  of 


FIG.  1 212. 


Sclera 


Cornea 


Anterior  part 
showing  nis,  cili 
serrata.  X  3. 


of 


sectioned    eye-ball, 
processes   and   ring   and   ora 


THE   VASCULAR   TUNIC. 


H57 


the  veins,  which  begin  between  the  meshes  of  the  choriocapillaris,  the  two  systems 
being  separate. 

The  nerves  of  the  choroid  arise  from  the  long  and  short  ciliary  nerves  during 
their  course  on  the  inner  surface  of  the  sclera.  They  form  a  plexus  within  the 
lamina  suprachorioidea,  which  contains  groups  of  ganglion  cells,  and  sends  numerous 
nonmedullated  fibres  chiefly  to  the  muscular  coats  of  the  arteries.  A  few  ganglion 
cells  are  found  along  the  blood-vessels.  The  choroid  contains  no  sensory  nerve-fibres. 

FIG.  1213. 


Choroidal  strom 
Pigmented  cells- 
Clear  cells 
Blood-vessels 


Clear  cells 


Sections  of  ciliary  processes;  A,trom  anterior;  B,  from  posterior  part ;  two  epithelial  layers,  pigmented  and  clear, 
of  pars  ciliaris  retinae  cover  choroidal  stroma.     X  80. 

The  Ciliary  Body. — The  ciliary  body  (corpus  ciliare),  the  middle  portion  of 
the  vascular  tunic,  extends  from  the  ora  serrata  to  the  sclero-corneal  junction. 
Sections  through  the  eyeball  in  a  meridional  direction  (Fig.  1214)  show  that  it  has 
a  triangular  form.  The  outer  side  is  in  apposition  to  the  sclera,  the  inner  is  covered 
by  the  pigmented  extension  of  the  retina,  and  the  short  anterior  side,  at  right  angles 
to  the  outer,  extends  inward  from  the  pectinate  ligament  toward  the  lens. 

The  ciliary  body  presents  three  subdivisions  ;  the  ciliary  ring,  the  ciliary  pro- 
cesses and  the  ciliary  muscle. 


Cornea 


FIG.  1214. 

Canal  of  Schlemm 


.  Pectinate  ligament 


-  Ciliary  muscle  (radial  fibres) 

:vJv*!=>_^'Sclera 

K^    ^  Meridional  fibres 


Ciliary  processes  Circular  fibres  Choroid  Pars  ciliaris  retinae 

Meridional  section  of  ciliary  region,  showing  ciliary  body  with  its  muscle  and  processes.     X  40. 

The  ciliary  ring,  or  orbictihis  ciliaris,  consists  of  a  smooth  band  of  tissue,  4 
mm.  in  width,  in  advance  of  the  ora  serrata.  It  differs  in  structure  from  the  choroid 
in  the  absence  of  the  choriocapillaris,  its  vessels  running  in  a  longitudinal  direction 
and  returning  the  blood  from  the  iris  and  ciliary  body  to  the  venae  vorticosae.  On 
its  inner  surface,  delicate  meridionally  placed  folds  make  their  appearance,  by  the 
union  of  which  the  ciliary  processes  are  formed. 

The  ciliary  processes  constitute  the  remainder  of  the  inner  portion  of  the 
ciliary  body.  They  form  an  annular  series  of  folds,  about  seventy  in  number,  which 
surround  the  lens  and  act  as  points  of  attachment  to  its  suspensory  ligament. 

92 


H58 


HUMAN   ANATOMY. 


Commencing  by  the  union  of  several  plications  of  the  orbiculus  ciliaris,  they  rapidly 
increase  in  height  and  breadth,  until  they  reach  an  elevation  of  from  .8-1  mm.,  and 
then  fall  suddenly  to  the  iris  level.  They  consist  of  a  rich  net-work  of  vessels  em- 
bedded in  a  pigmented  connective  tissue  stroma,  like  that  of  the  choroid.  The  inner 
surface  is  covered  with  a  homogeneous  membrane,  which  is  continuous  with  the 
membrana  vitrea  of  the  choroid,  on  the  inner  surface  of  which  is  placed  the  double 
layer  of  cells  representing  the  ciliary  portion  of  the  retina  (pars  ciliaris  retina^. 
Each  ciliary  process  is  composed  of  a  number  of  irregularly  projecting  folds  which 
increase  in  height  as  the  iris  is  approached. 


Cornea 


Greater  arterial  ring 
Iris 

Lesser  arterial  ring 
Ciliary  process 


FIG.  1215. 

Canal  of  Schlemm 

jrneal  loop 


Perforating  branch 

'onjunctival  vessels 


Recurrent  cho- 
roidal  artery 
Long  posterior 
ciliary  artery 

Choroidal  vein 


Anterior  ciliary  vessels 


Sclera 
Episcleral  vessels 


Communication  between  Retinal  vessels 

choroidal  and  optic  vessels 
Central  retinal  vessels 


Vena  vorticosa 

Supplying  choroid 

Short  posterior  ciliary  artery 

Long  posterior  ciliary  artery 
Communicating  twig 
Inner  sheath  vessels 
Outer  sheath  vessels 


Communication  between  optic 
and  sheath  vessels 


Diagram  illustrating  circulation  of  eyeball.     (Leber.) 


The  ciliary  muscle  occupies  the  outer  portion  of  the  ciliary  body,  lying 
between  the  sclera  and  the  ciliary  processes.  It  forms  an  annular  prismatic  band 
of  involuntary  muscle,  which  in  meridional  sections  has  the  form  of  a  right-angled 
triangle,  the  hypothenusc  being  the  outer  side,  next  to  the  sclera,  and  the  right 
angle  facing  the  lens.  Its  main  fibres  arise  from  the  sclera  and  pectinate  ligament, 
at  the  corneo-sclera  junction  internal  to  the  canal  of  Schlemm,  and  run  in  a 
nn •>  hiioual  direction  backward  along  the  sclera  to  be  inserted  into  the  choroidal 
stroma  (hence  their  name,  tensor  chorioidc<r}.  The  inner  angle  of  the  triangle,  at 
the  base  of  the  iris,  is  occupied  by  a  band  of  circularly  disposed  fibres,  which  consti- 
tute the  circular  ciliary  muscle  of  Miillcr.  Between  the  circular  and  meridional 
portions,  the  fibres  assume  a  radial  direction  and  an-  separated  by  considerable 
connective  tissue,  which  in  the  deeply  pigmented  races  may  contain  many  branched 


PRACTICAL  CONSIDERATIONS:  THE"  VASCULAR  TUNIC.      1459 

pigmented  cells,  but  in  the  white  races  is  free  from  pigment.  In  hyperopic  eyes  the 
circular  bundles  are  usually  better  developed  than  in  myopic  ones. 

The  blood-vessels  of  the  ciliary  body  arise  from  the  anterior  and  the  long  ciliary 
arteries.  They  form  a  ring  around  the  root  of  the  iris,  the  circulus  arteriosus  iridis 
major,  from  which  vessels  are  sent  inward  to  supply  the  iris,  ciliary  muscle  and 
ciliary  processes.  The  veins  from  the  ciliary  muscle  empty  chiefly  into  the  anterior 
ciliary  veins;  those  from  the  ciliary  processes,  and  a  few  from  the  ciliary  muscle  pass 
backward  and  become  tributary  to  the  vena;  vorticosa;. 

The  nerves  of  the  ciliary  body  are  derived  from  the  anterior  branches  of  the  long 
and  short  ciliary  nerves,  which  form  an  annular  plexus  within  the  ciliary  muscle. 
Four  sets  of  fibres  probably  exist  :  ( i )  sensory  fibres,  largely  subscleral  in  distribu- 
tion ;  (2)  vasomotor  fibres  running  to  the  blood-vessel  walls  ;  (3)  motor  fibres  sup- 
plying the  muscle  bundles  ;  (4)  fibres  terminating  within  the  interfascicular  tissue  of 
the  ciliary  muscle. 

Practical  Considerations. — Congenital  coloboma  of  the  choroid,  as  of  the 
iris,  usually  occurs  in  the  lower  part,  along  the  line  of  the  foetal  ocular  cleft.  In  the 
defect  the  sclera  shows  pearly  white  through  the  ophthalmoscope,  writh  here  and 
there  a  little  pigment  and  a  few  ciliary  vessels.  The  retina  is  frequently  absent,  but 
its  occasional  presence  explains  why  this  area  is  not  always  blind. 

In  acute  exudative  inflammation  of  the  choroid,  foci  of  inflammation  are  seen 
scattered  over  the  fundus,  and  are  characteristic.  They  form  yellowish  spots  between 
the  choroid  and  retina,  and  are  later  converted  into  connective  tissue,  binding  the 
choroid  and  retina  together.  The  two  layers  become  atrophic  finally,  the  layers  of 
rods  and  cones  disappearing.  The  exudate  may  extend  into  the  retina  and  even  into 
the  vitreous,  producing  opacities. 

Sarcoma  is  the  common  tumor  of  the  choroid  and  is  usually  pigmented. 

Carcinoma  of  the  choroid  is  always  a  metastatic  growth,  usually  a  metastasis  from 
a  carcinoma  of  the  breast.  Adenoma,  angioma,  and  enchondroma  of  the  choroid 
have  been  described. 

The  Iris. — The  iris  forms  the  anterior  segment  of  the  vascular  tunic  and  is 
visible  through  the  cornea.      Slightly  to  the   inner  side  of  its  centre  is  placed  an 
approximately    circular 
opening,  the  pupil.    The  FlG-  I216- 

periphery     Of      the     iris,     Or         Pupillary  margin        Anterior  endotheliun 

ciliary  border,  is  attached 
to  the  ciliary  body  behind 
and  receives  fibres  from 
the  pectinate  ligament  an- 
teriorly. The  free  border, 
which  forms  the  margin 
of  the  pupil,  rests  upon 
the  anterior  surface  of  the 

lenS.          1  he     iriS       meaSUreS  Sphincter  muscle  Pigmented  pars  iridica  retina; 

1 1    mm.  in  diameter  and  Section  of  pupillary  end  of  iris,    x  210. 

about  .4  mm.  in  thick- 
ness. The  pupil  varies  from  i— 8  mm.  in  diameter.  The  color  of  the  iris,  viewed 
from  in  front,  varies  in  different  individuals  and  gives  the  color  to  the  eyeball.  It  is 
dependent  partly  upon  the  amount  of  pigment  within  the  iris  stroma,  and  partly 
upon  the  density  of  the  pigmentation  of  the  cells  on  its  posterior  surface.  In  light 
blue  eyes,  the  stroma  contains  very  little  pigment  and  the  posterior  pigment  layer, 
seen  through  it,  gives  it  a  bluish  tint ;  whereas  in  brown  eyes  the  stroma  contains  so 
much  pigment  that  the  posterior  pigment  layer  is  totally  obscured  and  the  iris  appears 
brown.  The  anterior  surface  is  marked  by  a  number  of  fine,  radiating  lines,  or  ridges, 
which  indicate  the  position  of  the  blood-vessels.  Concentric  to  the  pupillary  margin, 
at  a  distance  of  from  i— 2  mm.,  is  an  irregular  ridge,  the  circulus  arteriosus  iridis 
minor,  which  divides  the  iris  into  a  pupil larv  and  a  ciliary  zone  which  are  often  differ- 
ently colored.  The  pupil  is  surrounded  by  a  narrow  black  border.  The  posterior 


1460 


HUMAN   ANATOMY. 


FIG.  1217. 


Pupillary  border  of  iris- 


Lesser  arterial  circle" 


Ciliary  artery 


Vascular  plexus  i 
ciliary  process- 


surface  of  the  iris  presents  a  series  of  delicate  converging  folds,  which  are  intersected 
by  concentric  lines. 

Structure  of  the  Iris. — Radial  sections  of  the  iris  show  the  stroma  to  be  com- 
posed of  numerous  thick-walled  blood-vessels,  running  in  a  radiating  manner  from  the 
ciliary  border  toward  the  pupil.  They  are  supported  by  a  delicate  connective  tissue 
framework,  which  contains  irregularly  shaped,  branching  pigmented  cells,  many 
nerves  and  lymph-spaces.  The  anterior  surface  is  covered  with  a  single  layer  of  polyg- 
onal endothelial  cells,  continuous  with  those  lining  Descemet's  membrane.  Beneath 
these  cells  is  a  condensation  of  the  connective  tissue  stroma — the  anterior  boundary 
layer,  in  which  the  cells  are  closely  placed.  Minute  clefts  in  the  tissue  form  a  direct 
communication  between  the  anterior  chamber  and  the  interfascicular  lymph-clefts. 
In  very  dark  irides  pigment  is  found  not  only  within  the  branched  cells,  but  heaped 
in  irregular  masses  within  the  stroma.  The  muscular  tissue  of  the  iris  consists 

of  two  distinct  masses,  the 
sphincter pupilla  and  the  dila- 
tator pnpi  I  Ice. 

The  sphincter  muscle,  is 
a  band  of  involuntary  muscle 
measuring  about  .7  mm.  in 
width,  which  surrounds  the 
pupil  and  is  situated  in  the 
vascular  stroma,  back  of  the 
blood-vessels,  and  separated 
from  the  pupil  edge  by  the 
narrow  border  constituted  by 
the  posteriorpigmented  layer. 
The  dilatator  muscle  is 
formed  by  a  sheet  of  smooth 
muscle-fibres  in  the  position 
formerly  described  as  the 
posterior  limiting  lamella,  or 
membrane  of  Bruch.  The 
investigations  of  Grynfeltt 
and  Heerfordt  have  settled 
definitely  the  question  of  its 
existence,  and  shown  that  its 
fibres  arise  from  the  outer  cells 
of  the  retinal  pigment  layer, 
on  the  posterior  surface  of  the 
iris.  They  do  not  reach  quite 
to  the  pupillary  border. 

The  posterior  surface  of 
the  iris  is  covered  by  the  pig- 
mented layer  ^  which  morphologically  represents  the  anterior  segment  of  the  atrophic 
nervous  tunic,  or  pars  iridica  retina.  This  is  continuous  with  the  pigmentary  layer 
covering  the  ciliary  processes,  but  the  cells,  disposed  as  a  double  layer,  are  so  deeply 
pigmented  as  to  be  indistinguishable  without  bleaching  the  tissue.  The  dilatator 
muscle  is  developed  from  the  outer  layer  of  fusiform  cells,  so  that  it  represents  an 
epithelial  (ectoblastic)  muscle.  The  inner  cells  are  larger  polygonal  elements,  which 
gradually  lose  their  pigment  as  they  approach  tin- ciliary  processes.  Over  the  latter 
they  contain  no  pigment,  whereas  the  outer  cells  remain  pigmented. 

The  blood-vessels  of  the  iris  pass  radially  inward  from  the  circu/us  (irlerivsits  iridis 
major  at  the  periphery.  Near  the  pupillary  border,  they  form  a  second  ring,  the  r/V- 
CH/US  arteriosns  iridis  minor,  branches  from  which  supply  the  sphincter  muscle  and  the 
pupillary  /one.  The  venous  radicles  unite  to  form  trunks  which  accompany  those 
from  the  ciliary  processes  to. empty  into  the  reinr  rorticos<r. 

The  lymphatics  are  represented  by  the  intcrfaseicular  clefts  which  communicate 
with  the  anterior  chamber,   with   tin-  spaces  within   the  ciliary   body,  and  with  the 
I  of    l-'ontana. 


Veins  draining 
ciliary  processes 


Choroidal  v 


Injected  ciliary  processes  and  iris;  vessels  are  seen  from  the 
posterior  surface.     X  30. 


PRACTICAL  CONSIDERATIONS  :     THE    IRIS.  1461 

The  nerves  of  the  iris  are  branches  of  the  ciliary  nerves.  They  follow  the  course 
of  the  blood-vessels  and,  branching,  form  a  plexus  of  communicating  nonmedullated 
fibres,  which  supply  sensory,  motor  and  vasomotor  impulses.  The  human  iris  prob- 
ably contains  no  ganglion  cells. 

Practical  Considerations. — The  iris  may  be  partially  or  completely  absent, 
when  by  bringing  down  the  eyebrows  and  partially  closing  the  lids,  the  patient 
will  make  an  effort  to  shut  off  the  excess  of  light,  as  in  albinism,  and  the  eye  will 
frequently  be  nystagmic. 

A  congenital  coloboma  or  deficiency  in  the  iris  is  usually  in  the  lower  part,  and 
may  be  associated  with  a  corresponding  defect  in  the  ciliary  body  and  choroid.  The 
pupil  may  be  eccentric  in  position  (corectopia),  unusually  small  (microcoria), 
irregular  in  shape  (discoria),  or  it  may  be  represented  by  several  pupils  (polycoria). 
The  pupillary  membrane  of  the  foetus,  covering  the  pupil,  not  infrequently  persists 
for  a  short  time  after  birth.  A  portion  of  it  persisting  permanently  is  one  of  the 
commonest  congenital  anomalies  of  the  eye. 

The  color  of  the  ins  varies  according  to  the  amount  and  location  of  the  pigment 
in  it.  When  the  coloring  matter  is  absent  from  the  stroma,  and  present  only  in  the 
posterior  layer  of  epithelium,  the  eye  is  blue.  If  such  an  iris  is  thicker  than  usual 
the  opacity  will  be  greater  and  the  eye  will  tend  to  be  grayish.  When  there  is  pig- 
ment only  in  slight  amount  in  the  stroma,  the  eye  is  greenish,  and  when  in  marked 
quantity  in  the  stroma,  the  eye  is  brown  or  even  black,  as  in  negroes.  The  deepest 
tints  of  brown  are  usually  called  black. 

In  albinism  there  is  an  absence  of  pigment  in  the  iris,  and  in  the  other  parts  of 
the  body  where  pigment  is  usually  found.  The  eyes  are  pinkish  in  color,  because 
the  light  enters  through  the  tunics  and  is  not  absorbed  by  the  choroid  and  retina, 
owing  to  the  absence  of  pigment  in  it.  The  retina  is  therefore  intolerant  of  light, 
so  that  the  patient  tries  to  shut  it  out  by  screwing  up  the  eyebrows  and  lids,  and  by 
contraction  of  the  iris.  He  will  frequently  show  nystagmus  or  oscillation  of  the 
eyeball,  and  amblyopia,  or  subacuteness  of  vision. 

The  two  eyes  are  not  always  of  the  same  color,  and  even  in  the  same  eye,  one 
part  of  the  iris  may  be  blue  and  another  brown  (piebald  iris).  One  eye  may  have 
its  color  permanently  changed  as  the  result  of  inflammation,  so  that  the  difference  in 
color  may  be  an  important  diagnostic  sign  of  previous  disease. 

The  iris  acts  as  a  colored  curtain  to  shut  off  excess  of  light,  as  more  or  less 
light  is  necessary  for  the  definition  of  images.  Too  much  light  impairs  the  defini- 
tion and  injures  the  retina.  The  pupils  are  usually  of  equal  size  in  health,  and  any 
marked  inequality  has  a  pathological  significance.  The  iris  does  not  hang  in  a  verti- 
cal plane,  but  is  pushed  slightly  forward  and  supported  at  its  pupillary  margin  by  the 
lens.  If  the  lens  is  absent  or  dislocated,  the  pupillary  margin  of  the  iris  may  be 
seen  to  quiver  with  the  movement  of  the  eyes.  The  iris  in  spite  of  its  great  vascu- 
larity  may  not  bleed  much  when  wounded,  probably  because  of  the  contraction  of 
its  abundant  muscular  fibres.  The  iris  is  continuous  with  the  ciliary  .body,  and 
through  the  latter  with  the  choroid,  the  three  taken  together  making  up  the  uveal 
tract,  or  middle  tunic  of  the  eye.  Any  inflammation  of  the  one  may  easily  spread 
to  the  others.  This  usually  occurs,  but  as  the  inflammation  is  predominant  in 
one,  we  speak  of  an  iritis,  a  cyclitis,  or  a  choroiditis,  and  not  of  the  whole  pro- 
cess as  a  uveitis.  In  an  iritis  the  exudation  which  affects  the  stroma  as  well  as 
the  anterior  and  posterior  aqueous  chambers  can  be  studied  by  inspection.  It 
thickens  and  discolors  the  iris,  renders  the  aqueous  fluid  turbid,  and  leaves  a 
deposit  on  the  contiguous  surfaces  of  the  cornea  and  lens.  Since  the  pupillary 
margin  of  the  iris  is  in  contact  with  the  lens  on  the  posterior  surface  the  exudate 
causes  adhesions  of  this  margin  to  the  lens  (posterior  synechiae).  Since  the  pupil 
is  contracted  in  inflammation,  when  these  adhesions  form,  dilatation  of  the  pupil 
normally  or  under  the  influence  of  atropine,  gives  rise  to  a  very  irregular  pupil, 
the  unattached  portion  dilating,  the  attached  portions  not.  Sight  need  not  be 
affected  if  the  pupil  is  large  enough.  If  the  whole  margin  of  the  pupil  is  attached 
to  the  lens,  or  the  pupil  is  occluded  by  exudate,  the  normal  flow  of  fluid  from 
the  posterior  to  the  anterior  chamber  cannot  take  place,  and  glaucoma  (vide  supra), 


HUMAN   ANATOMY. 


a  disease  due  to  increased  intraocular  tension  from  retention  results.  It  is  neces- 
sary, therefore,  in  iritis  to  keep  the  pupil  dilated,  so  as  to  prevent  such  adhesions 
as  far  as  possible. 

THE  NERVOUS  TUNIC. 

The  Retina. — The  retina,  the  light  perceiving  portion  of  the  eye,  with  its  con- 
tinuation, the  optic  nerve,  in  contrast  to  the  other  sense  organs  represents  a  portion 
of  the  brain  itself,  and  develops  in  close  connection  with  it.  It  is  a  delicate  mem- 
brain,  which  extends  from  the  optic  nerve  entrance  to  the  pupillary  border.  The 
functionating  portion,  or  pars  optica  retina,  reaches  as  far  forward  as  the  ora  serrata, 
where  it  terminates  as  an  irregular,  wavy  line  ;  anterior  to  this  the  retina  is  repre- 
sented by  an  atrophic  portion,  consisting  of  the  double  layer  of  cells  covering  the 


Fibre  layer 
Ganglion  cells 


Cerebral  layer 


Sustentacular  cell 


Neuroepithelial  layer 


Pigmented  layer 


Inner  plexiform  layer 


Inner  nuclear  layer 
(bipolar  nerve-cells) 


r-        Outer  plexiform  layer 


Outer  nuclear  layer 
(bodies  of  visual  cells) 


Rods  and  cones 


Pigmented  layer 


Choroid 
Diagram  illustrating  structure  of  retina  and  relations  of  three  fundamental  layers.     (Greeff.) 

ciliary  body  and  the  iris,  already  referred  to  in  the  description  of  these  structures, 
and  known  respectively  as  the  pars  ciliaris  retina,  and /tors  iridica  retina-. 

The  pars  optica  retinae  is  closely  applied  to  the  inner  surface  of  the  ebon  ml 
and  is  in  contact  with  the  hyaloid  membrane  investing  the  vitreous  body.  It  grad- 
ually diminishes  in  thickness  from  .4  mm.  at  the  posterior  pole  to  .1  mm.  near  the 
ora  serrata.  -During  life  the  membrane  is  transparent  and  possesses  a  purplish  ivd 
color,  owing  to  the  presence  in  its  outer  layers  of  the  so-called  visual  purple ;  after 
death  the  retina  rapidly  becomes  opaque  and  has  the  appearance  of  a  grayish  veil. 
The  inner  surface  is  smooth  and  presents  at  the  posterior  pole  of  the  eye,  a  small 
circular  or  transversely  oval  yellow  spot,  the  macula  littca,  from  1-2  mm.  in  diam- 
eter. At  the  centre  of  the  macula  is  a  small  depression,  the/o:vw  ccntralis,  from 
.2-.4  mm.  in  diameter,  in  which  position  the  retina  is  reduced  in  thickness  to  .  I  mm. 

The  entrance  of  the  optic  nerve  forms  a  conspicuous  spot  of  light  color,  situated 
3  mm.  to  the  nasal  side  of  the  macula  lutea.  This  area,  called  the  optic  papilla  or 
poms  opticHs,  is  in  form  of  a  vertical  oval,  about  1.5  mm.  in  its  horizontal  and 


THE  NERVOUS  TUNIC. 


1463 


1.7  mm.  in  its  vertical  diameter.  At  its  centre  is  often  seen  a  well-marked  excava- 
tion, the  optic  cup,  from  the  bottom  of  which  emerge  the  blood-vessels  which  supply 
the  retina. 

Structure  of  the  Retina. — The  retina  is  composed  of  nervous  elements  which 
are  supported  by  a  specialized  sustentacular  tissue  or  neuroglia.  Morphologically  it 
must  be  considered  as  composed  of  two  lamellae,  which  correspond  to  the  outer  and 
inner  walls  of  the  optic  vesicle  (page  1482)  from  which  it  is  developed.  These  fun- 
damental divisions  of  the  retina  are  :  ( i )  the  external  lamella,  the  pigmented  layer 
on  the  outer  surface  ;  and  (2)  the  internal  lamella,  which  includes  the  remaining  layers 
of  the  retina.  The  inner  lamella  may  be  subdivided  further  into  the  neuroepithelial 
and  the  cerebral  layers.  Sections  of  the  retina,  made  perpendicularly  to  its  surface 
(Fig.  1220),  show  under  the  microscope  from  without  inward  the  following  layers  : — 


I.  OUTER  LAYER  OF  OPTIC 

VESICLE 


II.    INNER  LAYER    OF    OPTIC 
VESICLE 


j  i. 

(^ 


LAYERS  OF  THE  RETINA. 

Pigmented  layer 


>•  Pigmented  layer 


2.  Layer  of  rods  and  cones  ")  Neuro- 

3.  Layer  of  bodies  of  visual  cells  or  outer  nuclear  j-  epithelial 

layer 

4.  Outer  plexiform  layer 

5.  Layer  of  bipolar  cells,  or  inner  nuclear  layer 

6.  Inner  plexiform  layer 

7.  Layer  of  ganglion  cells 

8.  Layer  of  nerve-fibres 


J  layer 

Cerebral 
layer 


FIG.  1219. 


To  these  nervous  layers  must  be  added  two  delicate  membranes,  ( i )  the  membrana 
limitans  interna,  which  bounds  the  inner  surface  of  the  retina,  and  (2)  the  membrana 
limitans  externa,  which  lies  between  the  outer  nuclear  layer  and  the  layer  of  rods 
and  cones.  These  membranes  represent  the  terminal  portions  of  the  supporting  neu- 
rogliar  fibres,  or  fibres  of  Miiller. 

The  pigmented  layer,  formed  of  deeply  pigmented  cells,  constitutes  the  most 
external  layer  of  the  retina  and  represents  the  outer  wall  of  the  fcetal  optic  vesicle. 
It  is  composed  of  hexagonal  cells,  from  .oi2-.oi8  mm. 
in  diameter,  the  protoplasm  of  which  is  loaded  with  fine, 
needle-shaped  crystals  of  pigment  (fuscin).  The  outer 
portion  of  the  cells  is  almost  free  from  pigment  and  con- 
tains the  nucleus.  From  the  inner  border  fine  proto- 
plasmic processes  extend  inward  between  the  rods  and 
cones  of  the  neuroepithelial  layer.  Under  the  influence 
of  light,  the  pigment  particles  wander  into  these  processes 
and,  under  such  conditions,  the  pigmented  cells  may 
remain  attached  to  the  retina  when  the  latter  is  separated 
from  the  choroid.  Ordinarily,  the  pigmented  layer  ad- 
heres to  the  choroid  and,  hence,  was  formerly  considered 
to  be  a  part  of  that  membrane.  The  pigmented  cells  are 
separated  by  a  distinct  intercellular  cement  substance  and  in  some  of  the  lower 
animals  contain  colored  oil  droplets  and  particles  of  a  highly  refracting  myelin-like 
substance  (myefoid granules  of  Kiihne). 

The  layer  of  rods  and  cones,  although  usually  described  as  a  distinct  stratum, 
is  only  the  highly  specialized  outer  zone  of  the  layer  of  visual  cells  and,  therefore, 
constitutes  the  outer  portion  of  the  neuroepithelial  division  of  the  retina.  It  is  com- 
posed, as  its  name  indicates,  of  two  elements,  the  rods  and  the  cones,  which  are  the 
outer  ends  of  the  rod  and  cone  visual  cells.  They  are  closely  set,  with  their  long 
axes  perpendicular  to  the  surface  of  the  retina.  The  rods  far  outnumber  the  cones, 
except  in  the  fovea  centralis,  in  which  location  cones  alone  are  found.  In  the  macula 
each  cone  is  surrounded  by  a  layer  of  rods  ;  elsewhere  the  cones  are  separated  by 
intervals  occupied  by  three  or  four  cones. 

The  rods  of  the  human  retina  (Fig.  1221)  have  an  elongated,  cylindrical  form, 
and  measure  approximately  .060  mm.  in  length  and  .020  mm.  in  diameter.  Each  rod 


Pigmented  cells  from  outer  layer  of 
retina ;  surface  view.    X  250. 


1464 


HUMAN   ANATOMY. 


is  composed  of  an  outer  and  an  inner  segment,  of  about  equal  length.  The  outer 
segment  possesses  a  uniform  diameter,  is  doubly  refracting,  and  readily  breaks  up  into 
minute  disks.  It  is  invested  with  a  delicate  covering  of  neurokeratin,  contains 
myeloid  (Kuhne)  and  is  the  situation  of  the  visual  purple  or  rhodopsin.  The  inner 
rod  segment  is  somewhat  thicker  and  has  an  ellipsoidal  form.  It  is  singly  refracting, 
homogeneous  in  structure  (rapidly  becoming  granular  after  death)  and  from  its  inner 
extremity  sends  the  delicate  rod-fibre  through  the  external  limiting  membrane  into 
the  outer  nuclear  layer  where  the  nucleus  of  the  rod  visual  cell  is  found. 

The  cone  visual  cell  is  composed  of  the  same  general  divisions  as  the  rod-cell, 
including  the  specialized  outer  part,  the  cone,  and  the  body  within  the  external  nu- 
clear layer.  The  cones  are  shorter  than  the  rods,  and,  except  in  the  fovea,  have  a 
length  of  .035  mm.  Each  one  (Fig.  1221)  is  composed  of  an  outer  narrow  cone- 
shaped  segment,  and  an  inner  broader  segment,  which  is  distinctly  ellipsoidal  in 
form,  with  a  diameter  of  .060  mm.  The  inner  segment  is  double  the  length  of  the 

outer,  and  is  continue'd  inward  as 

FIG.  1220.  the  cone-fibre  with  its   nucleus  in 

the  outer  nuclear  layer.  In  the 
fovea,  where  the  cones  alone  are 
found,  they  are  of  approximately 
the  same  length  as  the  rods,  and 
possess  about  one  half  the  usual 
diameter. 

The  outer  nuclear  layer, 
the  inner  portion  of  the  neuroepi- 
theleal  layer,  is  composed  of  the 
bodies  of  the  rod  and  cone  visual 
cells,  which  show  chiefly  as  the 
nuclei,  the  so-called  rod-  and  cone- 
granules.  The  rod-granules  oc- 
cupy an  elliptical  enlargement  of 
the  attenuated  rod-fibres.  They 
exhibit  a  transverse  striation  and 
are  placed  at  varying  levels  within 
the  layer.  The  rod-fibres  are  con- 
tinued as  a  thin  protoplasmic  pro- 
cess into  the  outer  reticular  layer, 
where  they  form  small  end-knobs 
which  are  associated  with  the  outer 
terminals  of  the  small  nerve-cells, 
the  rod-bipolars.  The  cone-gran- 
nies are  less  numerous  than  those 
of  the  rods,  display  no  transverse 


Internal  limiting 
membrane 


Ganglion  cell 


Fibre  of  Miiller 


Bipolar  nerve- 
cells 


Blood-vessel  — H 


Layer  of  visual 
cells 


Nucleus  of  cone- 
cell" 


Cone  - 
Rod- 


Pigment  layer 
Section  of  human  retina  from  near  posterior  pole.    X  230. 


markings,  and  are  found  only  in  the 
outer  portion  of  the  nuclear  layer, 
near  the  external  limiting  mem- 
brane. The  cone-fibres,  the  attenuated  bodies  of  the  cone  visual  cells,  are  broader 
than  the  corresponding  parts  of  the  rods  and  are  continued  through  the  outer  nuclear 
layer  as  far  as  the  outer  portion  of  the  external  plexiform  layer,  where  they  end  with 
a  broad  base,  from  which  delicate  processes  extend  inward  to  interlace  with  the 
terminal  arborizations  of  the  cone-bipolars.  The  outer  nuclear  layer  is  about  .05 
nun.  in  thickness. 

The  outer  plexiform  layer  is  a  narrow  granular  looking  stratum,  between  the 
outer  and  the  inner  nuclear  layer,  and  constitutes  the  first  of  the  cerebral  layers 
of  the  retina.  It  is  composed  of  the  dendritic  arborizations  of  the  bipolar  nerve-cells 
of  the-  succeeding  layer,  which  lie  in  close  relation  with  the  centrally  directed  proces- 
ses from  the  foot-plates  of  the  cone-cells  and  with  the  end-knobs  of  the  rod-fibre's. 
In  addition  to  these  constituents  of  the  plexiform  layer,  numerous  fibres  arising  from 
the  protoplasmic  processes  of  the  horizontal  cells  of  the  inner  nuclear  layer  also  take 
part  in  its  formation. 


THE  NERVOUS  TUNIC. 


1465 


FIG.  1221. 


The  inner  nuclear  layer,  the  most  complicated  of  the  retinal  strata,  measures 
.035  mm.  in  thickness  near  the  optic  disc.  It  contains  nervous  elements  of  three 
main  types — the  horizontal  cells,  the  bipolar  cells,  and  the  amacrine  cells — and, 
associated  with  these,  the  nuclei  of  the  sustentacular  cells. 

The  horizontal  cells  form  the  external  layer,  and  were  formerly  included  in  the 
outer  plexiform  layer.  They  have  flattened  cell-bodies  and  send  out  from  five  to 
seven  dendrites,  which  divide  into  innumerable  branches-  and,  passing  into  the  outer 
plexiform  layer,  terminate  in  close  association  with  the  bases  of  the  rod  and  cone 
visual  cells.  Each  horizontal  cell  possesses  also  an  axone,  which  is  directed  outward 
through  the  outer  plexiform  layer,  and  ends  in  a  richly  branched  arborization  about 
the  visual  cells.  A  second  type  of  large  horizontal  cells 
is  also  described,  some  of  which  send  axis-cylinder  pro- 
cesses through  the  inner  nuclear  layer  to  form  terminal 
arborizations  in  the  inner  plexiform  layer.  The  function  of 
the  horizontal  cells  is  not  well  understood,  but  they  prob- 
ably serve  as  association  fibres  between  the  visual  cells. 

The  bipolar  cells,  the  ganglion  cells  of  this  layer, 
are  of  two  chief  varieties,  the  rod-bipolars  and  the  cone- 
bipolars.  They  are  oval  cells,  each  sending  an  axone 
inward  toward  the  inner  plexiform  layer,  which  ends  in 
communication  with  the  large  nerve-cells  of  the  ganglion 
cell  layer,  and  a  dendrite  outward  which  is  associated  with 
the  end  terminals  of  the  visual  cells  and  with  the  arboriza- 
tions of  the  horizontal  cells.  The  dendrites  of  the  rod- 
bipolars  form  an  arborescence  of  vertical  fibrils,  which 
enclose  from  three  to  twenty  end  knobs  of  the  rod-fibres, 
whilst  their  axis-cylinders  pass  entirely  through  the  inner 
plexiform  layer  and  usually  embrace  the  cell-body  of  one 
of  the  large  ganglion  cells.  The  dendrites  of  the  cone- 
bipolars,  on  the  other  hand,  bear  horizontal  arborizations 
which  interlace  with  the  fibrils  from  the  foot-plates  of  the 
cone-cells.  Their  axones  penetrate  less  deeply  into  the 
inner  plexiform  layer  than  do  those  of  the  rod-bipolars, 
coming  in  contact  at  various  levels  with  the  peripherally 
directed  dendrites  of  the  ganglion  cells. 

The  amacrine  cells  are  placed  in  the  inner  portion  of 
the  nuclear  layer.  Formerly  considered  as  sustentacu- 
lar elements,  they  are  now  recognized  as  nerve-cells, 
although,  as  their  name  indicates,  no  distinct  axone  can 
be  demonstrated.  They  possess,  however,  richly  branched 
dendritic  processes,  which  ramify  in  the  inner  plexiform 
layer  and  end  either  as  the  brush-like  arborizations  of  the 
diffuse  amacrines,  or  as  the  horizontally  branching  arborizations  of  the  stratiform 
amacrines.  A  third  type,  known  as  association  amacrines,  is  also  described.  They 
connect  widely  separated  amacrine  cells  of  the  same  layer  (Cajal). 

The  nuclei  of  the  sustentacular  cells,  the  fibres  of  Miiller,  will  be  described  later 
(page  1466). 

The  inner  plexiform  layer,  .04  mm.  in  thickness,  appears  granular,  similar 
to  the  corresponding  outer  zone,  and  is  composed  of  the  interlacing  axones  of  the 
bipolar,  amacrine  and  horizontal  cells  from  the  inner  nuclear  layer  and  the  dendrites 
of  the  large  ganglion  cells  in  the  subjacent  retinal  layer.  Intermingled  with  them 
are  also  the  fibres  of  Miiller,  which  form  conspicuous  vertical  striae,  with  lateral 
offshoots  within  the  stratum. 

The  layer  of  ganglion  cells,  consists,  throughout  the  greater  part  of  the 
retina,  of  a  single  row  of  large  multipolar  neurones,  each  with  a  cell-body  containing  a 
vesicular  nucleus  and  nucleolus  and  showing,  like  many  other  ganglion  cells  of  The 
central  nervous  system,  typical  Nissl  bodies  and  a  fibrillar  structure.  Near  the 
macular  region,  the  ganglion  cells  are  smaller  but  more  numerous  and  arranged  as 
several  superimposed  layers;  toward  the  ora  serrata,  on  the  contrary,  the  individual 


Visual  cells  from  human  ret- 
ina, A,  cone-cell;  B,  rod-cell;  a, 
b,  outer  and  inner  segments;  c, 
attenuated  bodies  (fibres),  with 
nucleus  (d)  and  central  ends  (<?); 
em,  position  of  external  limiting 
membrane.  X  750.  (Greeff.) 


1466 


HUMAN   ANATOMY. 


FIG.  1222. 


cells  are  separated  by  considerable  intervals.  Their  axones,  or  axis-cylinder  pro- 
cesses, pass  inward  and  become  the  nerve-fibres  of  the  fibre  foyer.  Converging  toward 
the  optic  entrance,  they  become  consolidated  into  the  optic  nerve  and  pass  to  the 
brain.  The  dendrites  of  the  ganglion  cells,  one  to  three  in  number,  run  outward  into 

the  inner  plexiform  layer  and  end  as  richly  branched 
arborizations.  These,  like  those  of  the  amacrine  cells, 
terminate  either  diffusely,  or  in  horizontal  ramifica- 
tions limited  to  definite  strata,  in  connection  with  the 
centrally  directed  processes  from  the  bipolar  cells. 

The  nerve-fibre  layer  is  composed  almost 
entirely,  but  not  exclusively,  of  the  axones  of  the 
ganglion  cells  of  the  preceding  layer.  The  individual 
fibres,  from  .005-. 05  mm.  in  diameter,  are  collected 
into  bundles  of  varying  size,  which  take  a  horizontal 
course  and  converge  toward  the  optic  disc.  They  are 
normally  devoid  of  medullary  sheaths,  but  acquire 
them  after  passing  through  the  lamina  cribrosa  of  the 
sclera.  A  few  of  the  fibres  are  centrifugal,  arising 
from  ganglion  cells  within  the  brain,  and  terminate 
apparently  in  connection  with  the  association  amacrines 
of  the  inner  nuclear  layer. 

In  the  macular  region,  the  nerve-fibres  are  prac- 
tically absent,  those  from  the  retinal  area  lying  directly 
to  the  temporal  side  of  the  macula  arching  above 
and  below  the  yellow  spot.  From  the  macula  itself, 
a  special  strand,  known  as  the  maculo-papillary  bundle 
and  composed  of  about  twenty-five  fasciculi,  pas><  - 
directly  to  the  nerve-disc. 

The  sustentacular  tissue,  the  neuroglia  of  the 
retina,  exists  in  two  forms — as  faz  fibres  of  Mutter  and 
as  the  spider  cells. 

The  fibres  of  Miiller  are  modified  neuroglia 
fibres  which  pass  vertically  from  the  inner  surface  of 
the  retina  through  the  succeeding  layers  as  far  as  tin- 
bases  of  the  rods  and  cones  (Fig.  -1222).  The  inner 
extremities  of  the  fibres  possess  conical  expansions, 
which  are  in  apposition  and  form  an  incomplete  sheet. 
known  as  the  membrana  limitans  interna.  As  the  fibres  traverse  the  retinal  layers, 
they  give  off  delicate  lateral  offshoots,  which  break  up  into  a  fine  supporting  retieu- 
lum.  Within  the  inner  nuclear  layer  each  fibre  presents  a  broad  expansion,  in  which 
is  situated  the  oval  nucleus  of  the  sustentacular  cell,  the  fibre  of  Miiller.  After 
traversing  the  outer  nuclear  layer  their  broadened  peripheral  ends  come  into  contact 
and  form  a  continuous  sheet,  the  membrana  limitans  externa.  From  the  latter  deli- 
cate offshoots  continue  outward  and  embrace  the  bases  of  the  individual  rods  and 
cones.  In  addition  to  the  robust  fibres  of  Miiller,  neuroglia  cells,  in  the  form  of 
spider  cells,  are  found  in  the  nerve-fibre  and  ganglion  cell  layers.  These  cells  send 
out  long  delicate  processes  which  extend  between  the  processes  and  cells  and  thus 
help  to  support  them. 

The  Macula  Lutea. — The  structure  of  the  retina  undergoes  important  modifi- 
cations in  two  areas,  at  the  macula  lutea  and  at  the  ora  serrata.  In  the  former  the 
ganglion  cells  increase  rapidly  in  number  as  the  macula  is  reached,  so  that  instead 
of  forming  a  single  layer  they  are  distributed  in  from  eight  to  ten  strata.  The  inner 
nuclear  layer  is  also  increased  in  thickness.  Within  the  fovea  centralis,  however, 
in  order  to  reduce  to  a  minimum  the  layers  traversed  by  the  light-rays,  the  cerebral 
layers  are  almost  entirely  displaced,  only  the  absolutely  essential  retinal  strata — the 
pigment  cells  and  the  visual  cells  with  their  necessary  connections — being  retained 
within  the  area  of  sharpest  vision  (Fig.  1223).  On  approaching  the  fovea,  the 
ganglion  cells  rapidly  de-crease  in  number,  until  at  the  centre  of  the  depression,  they 
are  entirely  absent  and  the  nerve-fibre  layer,  therefore,  disappears.  The  bipolar 


Supporting  fibres  of  Miiller  from 
retina  of  ox;  Golgi  preparation. 
(Cajal.) 


THE   NERVOUS  TUNIC. 


1467 


cells  are  present  as  an  irregular  layer  within  the  fused  remains  of  the  two  plexiform 
layers.  The  most  conspicuous  elements  are  the  visual  cells,  which  in  this  position  are 
represented  solely  by  the  cones,  which  have  about  twice  their  usual  length  and 
thickness,  the  increase  in  length  being  contributed  by  the  outer  segments.  The 
cone-cell  nuclei  become  removed  from  the  external  limiting  membrane;  the  cone- 
fibres  are  therefore  lengthened,  pursue  a  radial  direction,  and  constitute  the  so-called 

FIG.  1223. 

Internal  limiting 

membrane          Inner  plexiform  layer 

Ganglion  cells  Fovea  centralis 


^&& 


Bipolar  cells         Outer        Pigmented    Cone         Cones 
plexiform  layer      layer      visual  cells 

Section  of  human  retina  through  fovea  centralis.     X  80. 

fibre-layer  of  Henle.  Opposite  the  centre  of  the  fovea,  the  choroid  is  thickened  by 
an  increase  in  the  choriocapillaris.  The  yellow  color  of  the  macula  is  due  to  a 
diffuse  coloration  of  the  inner  retinal  layers. 

The  Ora  Serrata. — The  visual  part  of  the  retina  ends  anteriorly  in  an  irregu- 
lar line,  the  ora  serrata.  Within  a  zone  of  about  i  mm.  in  width,  the  retina  dimin- 
ishes in  thickness  from  .50  to  .15  mm.,  in  consequence  of  the  abrupt  disappearance 
of  its  nervous  elements.  The  rods  disappear  first ;  then  the  cones  become  rudimen- 
tary, and  finally  cease  ;  the  ganglion  cells,  nerve-fibre  layer  and  inner  plexiform  layer 
fuse,  and  the  two  nuclear  layers  unite  and  lose  their  characteristics,  most  of  the 
nuclei  present  being  those  of  the  supporting  fibres  of  Muller,  which  are  here  highly 
developed.  These  elements 
continue  beyond  the  ora 
serrata  (Fig.  1224)  as  the 
transparent  cylindrical  cells 
composing  the  inner  layer  of 
the  pars  ciliaris  retince,  the 
densely  pigmented  cells  of 
the  outer  layer  being  a  direct 


FIG.  1224. 


.PiKm 
layer 


Inner  cells 
Pigmented  cells 


^PlffipPj  £- Bipolar  cells 


9    Ganglion 
=~  cells 


Section  of  human  retina  through  ora  serrata,  showing  transition  of  pars 
optica  into  pars  ciliaris.     X  165 


continuation  of  the  retinal 
pigmented  cells.  These  two 
strata  of  cells  are  prolonged 
over  the  ciliary  body  and  the 
iris  as  far  as  the  pupillary  margin,  over  the  iris  constituting  the  pars  iridica  retina. 
As  the  columnar  cells  pass  forward,  they  gradually  decrease  in  height,  and  at  the 
junction  of  the  ciliary  body  and  the  iris  the  cells  of  both  layers  become  deeply  pig- 
mented, with  consequent  masking  of  the  boundaries  of  the  individual  elements. 
The  cells  of  the  anterior  layer  are  of  additional  interest  as  giving  rise  to  the  dilatator 
muscle  of  the  iris. 

The  aggregation  incident  to  the  convergence  of  the  nerve-fibres  from  all  parts  of 
the  retina  produces  a  marked  thickening  of  the  fibre-layer  around  the  optic  disc, 
and  as  the  fibres  turn  outward  to  form  the  optic  nerve  the  other  layers  of  the  retina, 
together  with  those  of  the  choroid,  suddenly  cease.  On  the  temporal  side  a 
narrow  meshwork  of  intermediate  tissue  separates  the  nerve-fibres  from  the  other 
retinal  strata,  but  at  the  nasal  side  this  tissue  is  absent.  The  ganglion  cells  dis- 
appear first,  whilst  the  pigmented  cells,  with  the  lamina  vitrea  of  the  choroid, 
extend  furthest  inward. 

The  blood-vessels  of  the  retina  are  derived  from  a  single  artery,  the  arteria 
centralis  retinas,  which  enters  the  optic  nerve  at  a  point  from  15-20  mm.  behind 
the  eyeball,  and,  with  its  accompanying  vein,  runs  in  the  axis  of  the  nerve  and 


1468 


HUMAN   ANATOMY. 


emerges  slightly  to  the  nasal  side  of  the  centre  of  the  optic  disc.  Here  the  artery 
divides  into  two  main  stems  (Fig.  1225),  the  superior -and  inferior  papillary  branches, 
each  of  which  subdivides  at  or  near  the  disc-margin  into  superior  and  inferior 
nasal  and  temporal  branches  which  run  respectively  mesially  and  laterally,  dividing 
dichotomously  as  end  arteries,  no  anastomosis  existing.  The  macular  region  is 
supplied  by  special  macular  branches,  the  center  of  the  fovea,  however,  being  free 
from  blood-vessels.  The  larger  branches  from  the  central  artery  course  within  the 
nerve-fibre  layer,  and  send  fine  twigs  peripherally  inward  to  form  an  inner  and  an 
outer  plexus,  the  former  on  the  outer  surface  of  the  inner  plexiform  layer,  and  the 
latter  within  the  inner  nuclear  layer.  Beyond  the  outer  plexiform  layer  the  vessels 
do  not  penetrate,  the  visual  cells  being  dependent  for  their  nourishment  upon  the 
choriocapillaris  of  the  choroid.  At  the  nerve  entrance  an  indirect  communication 
exists  between  the  arteria  centralis  and  the  posterior  ciliary  arteries,  through  the 
medium  of  the  small  branches  which  constitute  the  circulus  arteriosus  Zinni. 

FIG.  1225. 


Temporal 


Nasal 


Normal  fundus  of  right  eye  as  seen  with  ophthalmoscope ;  central  retinal  vessels  seen  emerging  from  optic 
nerve;  arteries  are  lighter,  veins  darker  vessels;  fovea  centralis  shows  as  light  point  in  macular  region,  which 
lies  in  temporal  field  and  is  devoid  of  large  vessels. 

The  lymphatics  of  the  retina  are  represented  chiefly  by  the  perivascular  lym- 
phatic spaces  which  surround  all  the  veins  and  capillary  blood-vessels.  These  spares 
may  be  injected  from  the  subpial  lymph-space  of  the  optic  nerve,  and  by  the  same 
method  communications  may  be  demonstrated  between  (i)  this  space  and  the 
interstices  between  the  nerve  bundles  which  converge  toward  the  optic  papilla, 
(2)  a  space  between  the  membrana  limitans  interna  and  the  hyaloid  membrane  of 
the  vitreous,  and  (3)  a  narrow  cleft  between  the  pigmented  cells  and  the  layer  of 
rods  and  cones. 

Practical  Considerations. — All  pathological  conditions  of  the  retina  ap- 
pear as  opacities,  and  thus  interfere  with  sight.  The  medullary  sheaths  of  tin-  optic 
nerve-fibres  end  at  the  lamina  cribrosa.  Rarely  the  sheaths  around  these  may 
extend  some  distance  into  the  retina,  showing  as  a  white  striated  margin  around 
the  optic  disc  and  continuous  with  it.  Sometimes  the  blood-vessels  of  the  retina 
may  enter  at  the  margins  of  the  optic  disc,  instead  of  at  its  centre,  as  usual,  which 
is  then  free  of  vessels  and  very  pale.  At  the  entrance  of  the  optic  nerve,  the 
transparency  of  the  retina  is  lessened  by  the  thickening  of  its  fibre-layer 


PRACTICAL   CONSIDERATIONS  :    THE    RETINA. 


1469 


The  integrity  of  the  central  artery  of  the  retina  is  necessary  to  the  preservation 
of  sight.  The  branches  of  this  vessel  are  distributed  to  the  retina  only,  and  have 
no  communication  with  those  of  the  other  coats,  nor  do  they  anastomose  with  one 
another.  If  the  main  artery  or  one  of  its  branches  is  plugged  with  an  embolus,  the 
area  supplied  by  the  blocked  vessel  is  then  deprived  of  sight. 

The  retina  may  undergo  inflammatory  change  in  nephritis,  syphilis,  diabetes, 
and  other  constitutional  diseases.  Of  all  these  inflammations  of  the  retina,  that  due 
to  kidney  disease  (albuminuric  retinitis)  is  the  most  characteristic.  Besides  the 
signs  of  general  inflammation,  as  haziness  of  the  retina,  choked  disc,  distended 
retinal  arteries,  or  hemorrhages  into  the  retina,  pure  white  or  even  silvery  patches 
often  occur  ;  they  are  due  to  fatty  degeneration.  Retinitis  without  these  charac- 
teristic changes  may  occur  from  albuminuria,  so  that  the  urine  should  be  examined  in 
all  cases  of  retinitis. 

The  retina  between  the  optic  nerve  and  the  ora  serrata  is  held  in  apposition  to 
the  choroid  only  by  the  support  afforded  by  the  vitreous  body.  It  may  be  readily 
detached  from  the  choroid  by  such  causes  as  injury,  extravasation  of  blood  or 
serum  between  the  two  layers,  or  by  tumors  of  the  choroid. 

In  contusions  of  the  eye  the  retina  is  sometimes  torn  alone,  although  this  is 
rare.  The  retina  does  not  tear  as  easily  as  the  choroid,  as  is  shown  by  the  fact  that 
in  ruptures  of  the  choroid  the  retina  is  generally  not  lacerated. 

Glioma  is  the  only  tumor  found  in  the  retina,  and  occurs  exclusively  in  children, 
usually  under  three  years  of  age. 

A  rare  tumor  arising  from  the  pars  ciliaris  retinae  has  been  described,  to  which 
the  name  terato-neuroma  has  been  applied  by  Verhoeff. 

The  Optic  Nerve. — The  extraocular  portion  of  the  optic  nerve  has  been  de- 
scribed elsewhere  (page  1 223).  Likewise,  the  three  sheaths — the  dural,  the  arachnoid 

FIG.  1226. 

Physiological  excavation  Lamina  cribrosa 


Fibre-layer 

Visual  cells— tjg 
Choroid--^ 


Sclera  — 


JL — Subarachnoid  space 

rr  V5 

\  L__ '31 —  Subdural  space 


Pial  sheath 


/ 
Central  retinal  vessels  within  optic  nerve 

Section  of  eyeball  through  entrance  of  optic  nerve.     X  20. 

and  the  pial — which,  with  the  subdural  and  the  subarachnoid  lymph-spaces,  are  con- 
tinued over  the  nerve  as  prolongations  of  the  corresponding  brain-membranes  ( page 
949).  On  reaching  the  eyeball,  the  dural  sheath  bends  directly  outward,  its  fibres 
commingling  with  those  of  the  outer  third  of  the  sclera  (Fig.  1226)  ;  the  arachnoid 
ends  abruptly  on  the  inner  wall  of  the  intervaginal  space  ;  whilst  the  pia  arches 
outward  to  form  part  of  the  inner  third  of  the  sclera,  but  sends  longitudinal  fibres  as 
far  as  the  choroid.  As  the  nerve-fibres  enter  the  eyeball,  for  convenience  assuming 
that  they  are  passing  from  the  brain  toward  the  retina,  they  traverse  a  fenestrated 


1470 


HUMAN   ANATOMY. 


Blood-vessel 


Bundles  of . 
nerve-fibres 


Interfascicular 
connective  tissue 


membrane,  the  lamina  cribrosa,  which  is  formed  by  interlacing  bundles  from  the 
inner  third  of  the  sclera  and  from  the  pial  sheath.  As  they  penetrate  the  lamina 
cribrosa  they  lose  their  medullary  sheaths  ;  in  consequence  the  optic  nerve  is 
reduced  one  third  in  diameter.  The  intervaginal  lymph-space  ends  abruptly,  being 

separated  from  the  choroid 

FlG-   I227-  by  the  fibres  of  the  pia  which 

arch  outward  to  join  the 
sclera.  The  nerve  projects 
slightly  into  the  eyeball  on 
account  of  the  thickness  of 
the  layer  of  arching  nerve- 
fibres  and  forms,  therefore, 
a  circular  elevation,  known 
as  the  optic  papilla  or 
optic  disc,  about  1.5  mm. 
in  diameter,  the  center  of 
which  is  occupied  by  a  fun- 
nel-shaped depression,  the 
so-called  physiological  exca- 
vation. The  axis  of  the  nerve 
is  occupied  by  the  central 
artery  of  the  retina,  which 
gives  off  minute  branches  for 

Transverse  section  of  part  of  optic  nerve,  showing  several  fasciculi  of       the    nutrition    of    the    nerve 
nerve-fibres.     X  125.  .  .         ,    ' 

that    anastomose   with    the 

pial  vessels,  and,  through  the  circulus  arteriosus  Zinni,  with  branches  of  the  posterior 
ciliary  arteries.  When  seen  in  transverse  sections  (Fig.  1227),  the  optic  nerve 
appears  as  a  mosaic  of  irregular  polygonal  areas,  composed  of  bundles  of  medullated 
nerve-fibres  surrounded  by  connective  tissue  envelopes.  Although  provided  with 
medullary  sheaths,  the  optic  fibres  are  devoid  of  a  neurilemma,  in  this  respect 
agreeing  with  the  nerve-fibres  composing  the  central  nervous  system.  The  entire 
nerve  corresponds  to  a  huge  funiculus,  the  perineurium  being  represented  by  the 
pial  sheath,  and  the  endoneurium  by  the  interfascicular  septa  of  connective  tissue 
prolonged  from  the  pia  between  the  bundles  of  fibres.  Numerous  connective 
tissue  cells  occur  along  the  strands  of  fibrous  tissue. 

Practical  Considerations.  Any  disturbance  of  the  optic  nerve-fibres  passing 
from  the  retina  to  the  cortex  of  the  brain  (page  1225)  will  cause  disturbance  of 
vision,  and  within  certain  limits  the  lesion  may  be  localized  by  the  character  of 
the  symptoms  produced. 

The  most  characteristic  symptom  from  a  lesion  on  one  side  behind  the  chiasm 
is  a  homonymous  lateral  hemianopsia, — that  is,  the  right  or  the  left  half  of  each  eye  will 
be  blind.  This  is  explained  by  the  fact  that  the  optic  tracts  are  made  up  of  tibn-s 
coming  from  the  corresponding  lateral  halves  of  both  retinae, — i.e.,  the  fibres  from 
the  right  half  of  each  retina  pass  to  and  make  up  the  right  optic  tract,  and  puss 
therefore  to  the  right  half  of  the  brain.  It  will  thus  be  seen  that  anything  com- 
pressing the  optic  fibres  of  the  right  side  behind  the  chiasm,  for  instance  a  hemorrhage, 
would  produce  a  blindness — more  or  less  complete  according  to  the  extent  of  tin- 
fibres  involved — of  the  right  half  of  each  eye. 

Since  most  of  the  optic  fibres  enter  the  lateral  geniculate  bodies,  a  lesion  there 
always  causes  hemianopsia,  or  half-eye  blindness.  Lesions  of  the  optic  thalamus, 
or  of  the  superior  quadrigeminal  body,  may  also  by  compression  of  the  adjacent 
optic  tract  produce  hemianopsia. 

In  the  optic  radiation  are  other  than  optic  fibres,  so  that  hemianopsia  may  or 
may  not  follow  lesions  in  that  tract,  according  to  whether  optic  fibres  arc-  involved 
or  not.  The  exact  course  of  the  visual  fibres  in  the  optic  radiation  is  uncertain. 
If  the  visual  area  of  the  brain  cortex  is  involved  by  the  lesions,  no  other  symptoms 
will  be  present,  but  the  hemianopsia  will  be  complete  and  homonymous — that  is,  tin- 
corresponding  halves  of  the  two  eyes  will  be  blind. 


THE  CRYSTALLINE  LENS. 


1471 


FIG.  1228. 


If  the  lesion  affect  the  chiasm,  as  from  tumors  of  the  pituitary  body,  periostitis 
of  the  body  of  the  sphenoid  bone,  tuberculous  or  syphilitic  exudate,  causing  pressure 
on  the  mesial  portion  of  the  chiasm  involving  the  decussating  fibres,  the  nasal  half 
of  each  eye  supplied  by  these  fibres  will  be  blind  (heteronymous  hemianopsia). 
Since  the  nasal  half  of  each  eye  perceives  the  temporal  half  of  the  visual  field,  this 
variety  of  half-blindness  is  called  bitemporal hemianopsia. 

If  the  optic  fibres  of  one  side  in  front  of  the  chiasm  are  involved,  the  disturbance 
of  vision  will  affect  one  eye  only,  so  that  the  occurrence  of  absolute  blindness  of  one 
eye,  without  other  known  cause,  with  good  sight  in  the  other,  would  suggest  a  lesion 
in  front  of  the  chiasm. 

Inflammation  of  the  intraocular  end  of  the  optic  nerve — that  is,  of  the  optic  disc, 
or  papilla — gives  rise  to  the  condition  to  which  the  name  optic  neuritis,  or  papillitis, 
is  applied,  which  is  then  recognizable  with  the  ophthalmoscope.  If  in  addition  to 
or  independently  of  the  signs  of  inflammation  there  are  marked  engorgement,  oedema, 
and  the  evidence  of  mechanical  compression,  so  that  the  swollen  nerve-head  protrudes 
into  the  vitreous  beyond  ^  to  ^  mm.,  the  phenomena  of  "choked  disc"  are  pre- 
sent. This  variety  of  papillitis,  as  well  as  more  moderate  grades  of  optic  neuritis, 
constitutes  one  of  the  important  symptoms  of  brain  tumor,  occurring  in  fully  80  per 
cent,  of  the  cases.  The  development  of  the  papillitis  does  not  necessarily  depend 
upon  the  size  of  the  growth,  nor  upon  its  situation,  except  that  tumors  of  the 
medulla  are  less  apt  to  originate  optic  neuritis  than  those  in  other  parts  of  the  brain. 
Usually  a  bilateral  condition,  it  is  sometimes  unilateral,  and  under  such  circum- 
stances it  suggests  that  the  cerebrum  is  the  seat  of  the  growth,  and  is,  on  the  whole, 
in  favor  of  the  tumor  being  on  the  same  side  as  the  neuritis.  With  this  exception, 
however,  optic  neuritis,  although  an  important  symptom  of  brain  tumor,  has  no 
localizing  significance.  Other  intracranial  causes  of  optic  neuritis  are  the  various 
types  of  meningitis  (when  the  ophthalmoscopic  picture  often  appears  in  the  form  of 
the  so-called  "descending  neuritis"),  abscess  and  soft- 
ening of  the  brain,  cerebritis,  hydrocephalus  and  aneu- 
rism. In  addition  to  the  intracranial  causes  of  papillitis, 
this  phenomenon  may  arise  from  a  general  infection—- 
for example,  influenza,  syphilis,  rheumatism,  small-pox, 
etc. — and  is  then  known  as  infectious  optic  neuritis. 
It  is  also  caused  by  various  toxic  agents,  by  anaemia,  by 
menstrual  disturbances,  nephritis,  and  other  constitu- 
tional disorders  (de  Schweinitz). 

Injuries  of  the  optic  nerve  are  most  frequently  the 
result  of  fractures  of  the  base  of  the  skull  at  the  optic 
foramen,  the  nerve  being  injured  by  the  fragments. 
It  may  be  wounded  by  foreign  bodies  entering  the  orbit, 
with  or  without  injury  of  the  eyeball. 


THE  CRYSTALLINE  LENS. 


The  lens,  the  most  important  part  of  the  refractive 
apparatus  of  the  eye,  is  a  biconvex  body  situated  on  a 
level  with  the  anterior  plane  of  the  ciliary  body,  from 
which  it  is  suspended  by  the  suspensory  ligament,  or 
zonulc  of  Zinn.  Its  anterior  surface  supports  the  pu- 
pillary margin  of  the  iris,  and  its  posterior  surface  rests 
in  a  depression,  the  patellar  fossa,  on  the  anterior  sur- 
face of  the  vitreous  body.  It  is  completely  transparent  and  enclosed  in  a  transparent 
elastic  membrane,  the  lens  capsule.  Together  with  the  capsule,  the  lens  measures 
from  9-10  mm.  in  its  transverse  diameter,  and  about  4  mm.  in  thickness  from  pole 
to  pole.  The  convexity  of  its  two  surfaces  is  not  the  same,  that  of  the  posterior 
being  greater  than  that  of  the  anterior.  Neither  are  these  convexities  constant,  since 
they  are  continually  changing  with  the  variations  in  lens-power  incident  to  viewing 
distant  or  near  objects.  The  radius  of  curvature  of  the  anterior  surface  is  approxi- 
mately 9  mm.  and  that  of  the  posterior  surface  6  mm.  when  the  eye  is  accommodated 


Meridional  section  of  human  lens 
and  its  capsule  ;  anterior  epithelium 
and  transitional  zone  are  seen.  X  7- 
(Babuchin.) 


1472 


HI. MAN   ANATOMY. 


FIG.  1229. 


P 


6(1 


Fragments  of  isolated  lens-fibres;  A,  from 
superficial  layers;  B,  from  deeper  layers;  C, 
young  fibres  with  nuclei.  X  275. 


for  distant  objects  ;  these  radii  are  reduced  to  about  6  and  5  mm.  respectively  in 
accommodation  for  near  objects.  The  anterior  surface  is  therefore  more  affected  in 
the  act  of  accommodation,  the  lens  becomes  more  convex  and  its  antero-posterior 
diameter  increases  from  4  to  4.4  mm.  The  superficial  portion  of  the  lens  beneath 
the  capsule  is  composed  of  soft  compressible  material,  the  substantia  corticalis ;  the 
consistency  gradually  increases  toward  the  centre,  especially  in  later  life,  so  that  the 
central  portion,  the  nucleus  lentis,  is  much  firmer  and  dryer. 

The  structure  of  the  lens  includes  the  capsule  and  its  epithelium  and  the  lens 
substance.  The  capsule,  which  entirely  surrounds  the  lens,  is  a  transparent,  struc- 
tureless, highly  elastic  membrane,  which,  while 
resistent  to  chemical  reagents,  cuts  easily  and 
then  rolls  outward.  It  is  thickest  on  the  anterior 
surface,  where  it  measures  from  .oio-.oi5  mm., 
and  thinnest  at  the  posterior  pole  (.005-. 007 
mm.).  In  the  adult  the  lens  is  devoid  of  blood- 
vessels, but  during  a  part  of  foetal  life  it  is 
surrounded  by  a  vascular  net-work,  the  tunica 
vasculosa  lentis,  which  is  supplied  chiefly  by  the 
hyaloid  artery.  This  temporary  vessel  is  the 
terminal  branch  of  the  central  artery  of  the  retina 
and  passes  from  the  optic  disc  forward  through 
the  hyaloid  canal  or  canal  of  Cloquct  in  the  vit- 
reous to  the  posterior  surface  of  the  lens.  The 
vascular  lens  tunic  and  the  hyaloid  artery  are 
temporary  structures  and  usually  disappear  be- 
fore birth.  Exceptionally  they  may  persist, 
the  tunic  being  represented  by  the  pupillary 
membrane  and  the  artery  by  a  fibrous  strand  within  the  vitreous,  stretching  from 
the  optic  disc  towards  the  lens.  The  capsule  probably  represents  an  exudation 
product  of  the  cuticular  elements  from  which  the  lens- 
substance  is  developed. 

The  anterior  portion  of  the  capsule  is  lined  by  a  sin- 
gle layer  of  flat  polygonal  cells,  the  epithelium  of  the  lens 
capsule,  which  represents  morphologically  the  anterior 
wall  of  the  original  lens-vesicle  (page  1480).  On  ap- 
proaching the  equator  of  the  lens,  these  cells  become 
elongated,  and  gradually  converted  into  the  young  lens- 
fibres,  the  nuclei  of  which  form  a  curved  line,  with  its 
convexity  forward,  in  the  superficial  part  of  the  lens. 

The  lens-substance  is  composed  of  long  flattened  fibres,  the  cross-sections  of 
which  have  a  compressed  hexagonal  outline,  from  .005— .01 1   mm.   broad  and  from 

.002— .004    mm.   thick,   held 

FIG.  1231.  together  by  an  interfibrillar 

cement  substance.  These 
fibres  are  modified  epithelial 
elements,  which  develop  by 
the  elongation  of  the  original 
ectoblastic  cells  of  the  poste- 
rior layer  of  the  lens-vesicle. 
The  subsequent  growth  of 
the  lens  depends  upon  a 
similar  modification  of  the 
anterior  capsule-cells,  the  re- 
gion where  this  transforma- 
tion occurs  being  known  as 
the  transitional  rifttf.  The  individual  lens-libres  vary  greatly  in  length,  those  form- 
ing the  outer  layers  being  longer  and  thicker  than  those  which  constitute  the  nucleus 
of  the  lens.  The  edges  of  the  fibres  are  finely  serrated,  and,  as  the  points  of  the 
Serrations  «>f  adjacent  fibres  are  in  contact,  tine  intercellular  channels  are  left  for  tl 


FIG.  1230. 


Lens-fibres  seen  in  transverse  section. 
X  280. 


Adult  crystalline  lens,  showing  lens-stars;  A,  anterior;  />'. 
sun. n  .  ;  r.uliating  lines  of  juncture  meet  at  central  area.     X  4-    (Arnold.) 


THE  VITREOUS  BODY.  1473 

passage  of  nutritive  fluid.  The  fibres  are  so  arranged  that  their  ends  terminate  along 
definite  radiating  striae,  or  lens-stars,  which  in  the  young  lens  are  three  in  number 
on  each  surface.  In  the  adult  lens  additional  rays  increase  the  number  to  from  six  to 
nine,  the  striae  being  less  distinct  but  distinguishable  with  the  ophthalmoscope.  The 
lens-fibres  which  come  from  the  pole  of  one  surface  of  the  lens  terminate  at  the  end  of 
one  of  the  radial  striae  in  the  other,  and  conversely ;  the  intervening  fibres  take  up 
intermediate  positions.  In  adult  life  the  lens-fibres  become  more  coridensed,  the  lens 
loses  its  clear  appearance,  and  assumes  a  yellowish  tint.  This  change  affects  the 
nucleus  first  and  the  periphery  later,  coincidently  the  lens  becoming  less  elastic  as 
the  result  of  its  loss  of  water. 

Practical  Considerations. — The  lens  may  be  congenitally  absent  (aphakiaj, 
or  it  may  be  abnormal  in  size,  shape,  position,  or  transparency.  Its  anterior  or 
posterior  surface  may  be  abnormally  convex  (lenticonus).  Congenital  anomalies  of 
position  (ectopia  lentis)  occur  rarely.  The  lens  may  remain  in  its  fcetal  position  in 
the  vitreous  chamber,  or  it  may  be  displaced  in  an  equatorial  direction  from  faulty 
development  and  weakness  of  some  part  of  the  suspensory  ligament.  This  weakness 
usually  occurs  below  so  that  the  lens  moves  upward.  The  ligament  may  be  absent  in 
its  whole  circumference,  when  the  lens  may  be  protruded  into  the  anterior  chamber. 

Coloboma  or  partial  deficiency  of  the  lens  is  very  rare.  It  is  with  comparative 
frequency  associated  with  a  similar  defect  in  the  iris,  ciliary  body  and  choroid,  and, 
like  it,  is  usually  in  the  lower  portion.  A  defect  of  the  corresponding  part  of  the 
suspensory  ligament  is  occasionally  present. 

Traumatic  luxation  of  the  lens  may  take  place  into  the  vitreous  or  aqueous 
chamber.  It  may  occur  laterally  through  the  coats  of  the  eyeball  into  the  capsule 
of  Tenon  or  under  the  conjunctiva.  That  into  the  vitreous  is  most  frequent. 

The  capsule  of  the  lens  is  strong  and  elastic.  It  is  at  the  same  time  brittle, 
breaking  like  thin  glass  when  torn  as  by  a  sharp  instrument.  For  this  reason  it  is 
sometimes  called  the  vitreous  membrane.  The  anterior  layer  of  the  capsule  is  con- 
siderably thicker  than  the  posterior,  and  is  more  liable  to  pathological  changes,  pro- 
ducing opacities.  Wounds  of  the  capsule  permit  the  aqueous  fluid  to  reach  the  lens 
fibres,  which  then  become  swollen,  opaque,  and  finally  disappear  from  the  dissolving 
action  of  the  aqueous.  Advantage  of  this  is  taken  in  the  needling  operation  (dis- 
cission )  for  the  removal  of  a  cataract. 

In  children  the  lens  substance  is  of  nearly  equal  consistency  throughout,  but  as 
age  advances  the  central  portion  becomes  gradually  more  condensed,  and  is  called 
the  nucleus.  A  well-marked  nucleus,  however,  does  not  exist  until  adult  life.  In 
old  age  the  lens  loses  its  elasticity  so  that  the  changes  necessary  for  accommodation 
are  interfered  with,  and  sight  is  disturbed.  The  hardened  nucleus  permits  a  greater 
reflection  of  light  than  the  outer  portion,  so  that  the  lens  is  more  readily  seen  in 
older  people,  and  the  pupil  loses  more  or  less  its  blackness. 

A  cataract  is  an  opacity  of  the  lens,  or  its  capsule,  but  that  of  the  lens  is  so 
much  more  common  than  that  of  the  capsule,  that  by  the  word  cataract  the  lenticular  is 
usually  meant,  unless  the  word  is  otherwise  qualified.  All  cataracts  are  at  sometime 
partial,  and  they  are  called  according  to  their  location,  anterior  polar  or  capsular, 
posterior  polar  or  capsular,  central  or  nuclear,  lamellar,  perinuclear  and  cortical. 
Cataract  occurs  sometimes  in  the  young,  and  is  then  soft ;  that  is,  the  lens  has  no 
nucleus. 

THE  VITREOUS  BODY. 

The  vitreous  body  (corpus  vitreum)  fills  the  space  between  the  lens  and  the 
retina,  being  in  close  contact  with  the  retina  and  acting  as  a  support  to  it  as  far 
forward  as  the  ora  serrata.  Here  it  becomes  separated  from  the  retina  and  passes  to 
the  posterior  surface  of  the  lens,  presenting  a  shallow  depression,  the  fossa  hya- 
loidea  or  patellar  fossa,  on  its  anterior  surface  for  the  reception  of  the  lens.  The 
fresh  vitreous  is  a  semifluid,  perfectly  transparent  mass  which  consists  of  about  98.5 
per  cent,  of  water. 

The  structure  of  the  vitreous  has  been  a  subject  of  protracted  dispute,  but 
recent  investigations  have  established  beyond  question  that  it  possesses  a  framework, 

93 


M74 


HUMAN   ANATOMY. 


FIG.  1232. 


Portion  of  adult  vitreous  body,  showing;  felt-work  of  fibres 
and  atrophic  traces  of  cells.     X  450.    (Retzius.) 


composed  of  delicate,  apparently  unbranched  fibrils,  which  pass  in  all  directions 
through  the  vitreous  space  and  form  the  meshes  in  which  the  fluid  constituents  of 
the  mass  are  held.  The  surface  of  the  vitreous  is  enclosed  by  a  delicate  boundary 
layer,  called  the  hyaloid  membrane,  formed  by  condensations  of  the  fibrils, 
which  are  here  arranged  parallel  to  the  surface,  and  closely  felted.  It  is,  however, 

not  a  true  membrane,  but  only  a  con- 
densation of  the  vitreous  fibres.  The 
vitreous  is  attached  firmly  to  the  retina 
at  the  nerve  entrance  and  at  the  ora 
serrata,  between  these  points  the  hya- 
loid being  indistinct.  As  the  vitreous 
leaves  the  retina,  the  boundary  layer 
becomes  thicker,  in  some  cases  to  be- 
come thin  again  or  absent  in  the  region 
of  the  patellar  fossa. 

The  central  part  of  the  vitreous  is 
occupied  by  a  channel,  the  hyaloid 
canal,  also  known  as  the  canal  of  Stil- 
ling or  the  canal  of  Cloqud,  which  is 
about  one  millimeter  wide  and  extends 
from  the  optic  entrance  toward  the  pos- 
terior pole  of  the  lens.  During  total 
life  this  canal  lodges  the  arteria  hya- 
loidea,  the  continuation  of  the  central 
artery  of  the  retina,  which  passes  to 
the  lens  and  assists  in  forming  the  embryonal  vascular  envelope  surrounding  the  lens. 
Usually  the  embryonal  connective  tissue,  together  with  the  blood-vessel,  disappears  ; 
occasionally,  however,  delicate  remnants  of  this  tissue  can  be  detected. 

The  normal  adult  vitreous  ordinarily  contains  no  cells,  but  some  are  occasionally 
seen  near  the  surface,  beneath  or  on  the  hyaloid  membrane.  They  are  amoeboid, 
often  contain  vacuoles  and  are  to  be  considered  as  modified  leucocytes.  In  addition 
a  few  branched  connective-tissue  cells  may  be  present. 

Practical  Considerations. — Congential  abnormalities  of  the  vitreous  are  due 
either  to  a  persistence  of  some  part  of  its  foetal  vascular  apparatus  or  to  an  atypical 
development  of  the  tissue  from  which  it  is  formed.  The  remains  of  these  structures 
may  occasionally  be  seen  as  a  filamentous  band,  free  at  one  end,  which  floats  in  the 
vitreous,  the  other  end  being  attached  to  the  optic  disc  behind,  or  the  posterior  sur- 
face of  the  lens  in  front.  The  strand  may  be  attached  at  both  ends,  with  or  without 
a  patent  artery.  Small  rounded  gray  bodies,  apparently  cystic  and  attached  to  the 
disc,  are  occasionally  seen.  They  are  in  some  way  the  remains  of  the  fcetal  vascular 
apparatus.  The  congenital  opacities  sometimes  seen  at  the  posterior  pole  of  the  lens 
are  probably  derived  from  the  posterior  fibre-vascular  sheath  of  the  lens.  Materials 
from  the  blood  are  readily  absorbed  by  the  vitreous,  as  the  bile  in  jaundice. 

Muses  volitantes  are  the  flocculi,  seen  by  the  patient  as  black  spots  be- 
fore the  eyes,  and  are  sometimes  made  up  of  inflammatory  exudate  from  inflam- 
mation of  the  internal  or  middle  coat  of  the  eye.  They  may  be  due  to  blood  from 
traumatic  or  spontaneous  hemorrhage  into  the  vitreous.  Muscae  volitanU  s  arc  often 
seen  independently  of  any  vitreous  disease  and  are  due  to  the  shadows  thrown  upon 
the  retina  by  naturally  formed  elements  in  the  vitreous  body,  perhaps  the  remains 
of  embryonic  tissue.  Some  of  the  vitreous  may  be  lost  and  rapidly  replaced  with- 
out seriously  disturbing  sight.  In  the  removal  of  cataract,  the  suspensory  ligament 
may  be  divided  and  an  embarrassing  loss  of  vitreous  may  result. 

A  foreign  body  in  the  vitreous  chamber  generally  gives  rise  to  a  serious  inflam- 
mation, which  may  destroy  the  eye.  If  loose,  it  tends  by  gravity  to  settle  in  the 
lower  portion,  and  usually  rests  on  the  posterior  part  of  the  ciliary  body  ( T.  Collins). 
Rarely,  in  the  absence  of  infection,  it  has  remained  for  years  without  setting  up 
inflammation.  The  rule  is,  however,  to  remove  them,  when  recent,  as  early  as 
possible,  as  inflammation  may  set  in  at  any  time.  In  most  cases  the  foreign  body 


SUSPENSORY  APPARATUS  OF  THE  LENS. 


H75 


can  be  exactly  localized  by  the  X-ray,  and  if  of  iron  or  steel,  may  often  be  removed 
by  a  magnet.  The  accident  is  always  serious  and  may  be  followed  by  a  virulent 
inflammation,  demanding  an  excision  of  the  globe  to  prevent  a  sympathetic  involve- 
ment of  the  other  eye.  Because  of  the  risk  of  infection  and  loss  of  fluid,  operative 
interference  in  the  vitreous  chamber  is  usually  to  be  avoided. 

Sv»ipathctic  ophthahnitis,  or  more  accurately,  infective  irido-cyclitis,  or  uveitis, 
is  an  inflammation  of  one  eye,  usually  called  the  "sympathizer,'"  owing  to  injury  or 
disease  of  the  fellow  eye,  usually  called  the  ' '  exciter. ' '  Traumatisms  of  the  ciliary 
region  (danger  zone)  which  have  set  up  an  irido-cyclitis  or  uveitis  are  responsible 
for  fully  80  per  cent,  of  the  cases  of  so-called  sympathetic  inflammation.  This 
disease  was  formerly  supposed  to  be  due  to  reflex  action  through  the  ciliary  nerves, 
and  this  theory  in  a  modified  form  is  still  maintained  by  a  few  clinicians.  The  "  mi- 
gration theory"  propounded  by  Leber  and  Deutschmann  that  the  inflammation  is  a 
progressive  process  in  the  continuity  of  the  tissue  of  one  eye  to  the  other  by  way 
of  the  optic  nerve  apparatus  and  is  of  bacterial  origin,  has  not  been  proved.  It  is 
believed  by  some  investigators  that  the  bacteria  which  enter  the  primarily  affected 
eye  produce  a  toxin  which  causes  the  disease,  and  by  others  that  it  represents  an 
endogenous  infection  produced  by  invisible  bacteria,  that  is,  that  it  is  a  metastasis 
(de  Schweinitz). 

THE  SUSPENSORY  APPARATUS  OF  THE  LENS. 

The  lens  is  held  in  position  by  a  series  of  delicate  bands,  which  pass  from  the 
vicinity  of  the  ora  serrata  over  the  ciliary  processes  to  be  attached  to  the  periphery 
of  the  lens.  These 

fibres  collectively  con-  FIG.  1233. 

stitute  the  suspen- 
sory ligament,  or 
zonula  of  Zinn,  a 
structure  of  impor- 
tance not  only  for  the 
support  of  the  lens 
but  also  in  assisting 
the  ciliary  muscle  in 
effecting  the  changes 
in  the  curvature  of 
the  lens  incident  to 
accommodation.  The 
zonula  is  not,  as  for- 
merly believed,  a  con- 
tinuous membrane, 
but  is  composed  of  a 
complicated  system 
of  fibres.  The  latter, 
varying  in  thickness 
from  .005-. 022  mm., 
arise  chiefly  from  the 


Cornea 
Canal  of  Schlemm 


Sclera 


Meridional  section  of  ciliary  region,  showing  ciliary  processes  and  suspensory 
ligament  of  lens.     X  20. 


cuticular  membrane 
covering  the  pars  ciliaris  retinse  in  the  vicinity  of  the  ora  serrata.  The  investigations 
of  Retzius,  Salzmann  and  others  indicate  that  some  fibres  arise  also  from  the  mein- 
brana  limitans  interna  of  the  pars  optica  retina-,  whilst  others  pass  into  and  end 
within  the  vitreous  body.  The  greater  number  of  the  fibres  pass  forward  chiefly  in 
the  depressions  between  the  ciliary  processes,  and  along  the  sides  of  the  latter,  closely 
applied  to  the  surface  ;  they  then  proceed  outward  across  the  circumlental  space  to 
be  attached  to  the  capsule  of  the  lens.  Some  of  the  fibres  are  inserted  anterior  to 
the  equator,  others  posterior  to  the  equator,  and  some  directly  into  the  lens  margin. 
Those  inserted  anteriorly  arise  behind  and  chiefly  from  the  valleys  between  the  ciliary 
processes,  whilst  those  inserted  back  of  the  equator  come  from  the  ciliary  processes 
in  front.  As  they  diverge  to  gain  their  insertion  in  the  lens-capsule,  the  crossing- 
fibres  enclose  an  annular  space,  triangular  in  section,  whose  base  is  directed  toward 


1476  HUMAN    ANATOMY. 

the  lens  equator.  The  fibres  are  so  closely  interlaced  that  it  is  possible  to  inject  air 
between  them  and  so  produce  a  beaded  ring  surrounding  the  lens.  This  appearance 
was  long  interpreted  as  demonstrating  the  presence  of  a  delicate  channel,  the  canal 
of  Petit,  encircling  the  lens.  The  existence  of  a  definite  channel,  however,  is  no 
longer  accepted,  the  space  capable  of  inflation  being  part  of  the  larger  circumlental 
space,  which  is  filled  with  fluid  and  communicates,  by  means  of  fine  clefts,  with  the 
posterior  chamber. 

In  addition  to  the  chief  zonular  fibres,  accessory  bands  occur,  some  of  which 
pass  from  the  ciliary  processes  to  the  long  zonular  fibres,  whilst  others  extend  from 
point  to  point  on  the  ciliary  processes. 

The  origin  of  the  vitreous  body  and  of  the  suspensory  ligament  has  long  been  and  still  is  a 
matter  of  dispute.  The  fact  that  these  structures  are  very  closely  connected,  that  fibres  from  the 
suspensory  ligament  pass  through  the  vitreous,  and,  in  some  cases  at  least,  end  in  that  body, 
renders  it  probable  that  the  two  structures  have  a  common  genesis.  Anatomists  are  divided, 
however,  in  their  views,  some  believing  the  structures  in  question  to  be  derived  from  the 
mesoblast  which  enters  the  choroidal  cleft  with  the  blood-vessels,  whilst  others  assign  to  them 
an  ectoblastic  origin,  either  from  the  lens-vesicle,  or  from  the  retina  ( inner  wall  of  the  second- 
ary optic  vesicle).  In  many  of  the  lower  animals  the  vitreous  contains  no  blood-vessels,  and, 
further,  since  the  vitreous  is  formed  without  the  presence  of  embryonal  connective  tissue, 
the  presumption  is  strong  that  the  vitreous  arises  from  the  retina.  That  the  ectoblast  in  mam- 
mals, however,  is  the  sole  source  of  the  vitreous  has  not  been  proven  ;  moreover,  the  close 
histological  resemblance  of  the  vitreous  to  embryonal  connective  tissue  suggests  with  much  force 
the  probability  that  the  mesoblast  has  at  least  some  share  in  the  formation  of  the  vitreous  body. 

THE  AQUEOUS  HUMOR  AND  ITS  CHAMBER. 

The  aqueous  humor  is  the  transparent  fluid  which  fills  the  space  between  the 
anterior  surface  of  the  vitreous  body  and  the  posterior  surface  of  the  cornea.  In 
chemical  composition  it  closely  resembles  water,  containing  only  traces  of  albumin 
and  extractives,  and  differing  from  lymph  in  its  low  percentage  of  albumin.  It  is 
produced  chiefly  by  the  blood-vessels  of  the  ciliary  processes,  the  iris  taking  probably 
little  or  no  part  in  the  process.  The  albumin  of  the  blood  is  separated  by  the  action 
of  the  double  layer  of  cells  covering  the  pars  ciliaris  retinae,  which  act  either  as  a  filter- 
ing medium  (Leber),  or  as  a  secreting  epithelium  (Treacher  Collins).  The  aque- 
ous humor  is  constantly  being  produced  and  is  carried  off  through  the  spaces  of 
Fontana  into  the  canal  of  Schlemm,  and  also  through  the  lymph-spaces  in  the  iris, 
its  quantity  being  an  important  factor  in  determining  intraocular  tension.  With  the 
exception  of  a  few  migratory  leucocytes,  the  aqueous  humor  is  devoid  of  morpho- 
logical elements. 

The  space  occupied  by  the  aqueous  humor  is  incompletely  subdivided  by  the 
iris  into  two  compartments,  the  anterior  and  posterior  chambers.  The  anterior 
chamber  (camera  oculi  anterior)  is  bounded  in  front  by  the  cornea,  and  behind  by 
the  ids  and  lens,  and  has  a  depth  at  its  centre  of  from  7.5-8.5  mm.  The  posterior 
chamber  (camera  oculi  posterior)  is  the  small  annular  space,  triangular  in  cross-st •<•- 
tion,  which  has  for  its  anterior  boundary  the  iris,  and  is  limited  laterally  by  the  ciliary 
processes,  and  medially  and  posteriorly  by  the  lens  and  the  vitreous  body.  Tin- 
spaces  between  the  fibres  of  the  suspensory  ligament  communicate  with  the  poste- 
rior chamber,  are  filled  with  aqueous  humor,  and  are,  therefore,  only  a  part  of  the 
posterior  chamber. 

Practical  Considerations. — When  the  cornea  is  perforated  as  by  a  wound 
or  by  ulceration,  the  aqueous  is  forced  through  the  opening  so  rapidly  that  the  iris 
is  swept  along  by  it,  and  unless  great  rare  is  observed  it  will  become  adherent  to  tin- 
margin  of  the  corneal  opening  (anterior  synechia). 

The  aqueous  humor  is  of  importance  in  the  removal  of  foreign  matter.  Blood 
will  often  be  removed  in  a  few  days.  Suppuration  of  the  adjacent  tissue  may  lead 
to  the  collection  of  pus  in  the  anterior  chamber  (hypopion).  Hyphaemia  is  a  collec- 
tion of  blood  in  this  chamber,  and  of  itself  is  not  a  grave  condition,  although  it  may 
be  a  sign  of  a  more  serious  disease. 


LACHRYMAL    APPARATUS.  H77 

Glaucoma  is  a  disease  due  to  excessive  intraocular  tension  which,  unless  re- 
lieved, progressively  increases  until  the  eye  is  destroyed,  and  which  almost  always 
involves  the  other  eye.  The  abnormal  tension  is  the  result  of  disturbance  in  the 
outflow  of  the  intraocular  fluid.  This  fluid  is  an  exudation  from  the  blood-vessels  of 
the  ciliary  body.  From  the  posterior  chamber  the  fluid  passes  through  the  pupil  to 
the  anterior  chamber.  It  then  escapes' in  the  angle  formed  by  the  iris  and  cornea 
by  passing  through  the  lymph-spaces  in  the  ligamentum  pectinatum  and  by  diffusion 
reaches  the  canal  of  Schlemm.  Thence  it  passes  out  by  the  anterior  ciliary 
veins.  Obstruction  in  the  path  of  this  current  occurs  usually  either  in  the  lymph- 
channels  of  this  region,  or  at  the  pupil  from  adhesion  of  the  whole  pupillary  margin 
to  the  lens,  or  from  occlusion  of  the  pupil  by  inflammatory  exudate,  in  iritis. 

Iridectomy  frequently  gives  relief  in  both  varieties  ;  in  the  former  by  opening 
up  the  lymph-spaces  near  the  corneal  angle  of  the  anterior  chamber,  the  incisions 
being  carried  well  into  this  angle  ;  in  the  latter  by  making  a  new  opening  for  the 
current  between  the  posterior  and  anterior  chambers. 

The  symptoms,  like  the  cause,  may  be  explained  largely  upon  an  anatomical 
basis.  The  venae  vorticosae  pass  obliquely  through  the  sclerotic  and  are  therefore 
compressed  and  obstructed  by  the  distension.  Their  blood  is  then  compelled  to 
escape  through  the  anterior  ciliary  veins,  which  penetrate  the  sclerotic  more  at  a 
right  angle,  and  are  consequently  distended.  CEdema  of  the  cornea  results  causing 
a  superficial  haziness.  The  cornea  is  insensitive  from  paralysis  of  the  anterior  ciliary 
nerves.  Usually  the  anterior  chamber  is  shallow  because  the  lens  and  iris  are  pushed 
forward  by  the  obstructed  fluid  behind,  and  the  ciliary  nerves  being  paralyzed  the 
pupil  is  dilated  and  immobile,  giving  a  staring  expression.  The  optic  disc  is  at  first 
hyperaemic,  and  is  consequently  markedly  depressed  from  the  intraocular  tension, 
giving  rise  to  one  of  the  most  important  symptoms,  pathological  cupping  of  the  disc, 
or  the  glaucomatous  cup.  The  great  pain  in  glaucoma  is  due  to  compression  of  the 
sensory  nerves  of  the  ciliary  body  and  iris  against  the  unyielding  sclera.  The 
distended  retinal  veins  can  be  seen  through  the  ophthalmoscope. 

A  condition  analogous  to  glaucoma,  hydrophthalmos,  occurs  in  children,  and  is 
either  congenital  or  acquired  very  early  in  life.  Unless  relieved  it  almost  always 
produces  blindness. 

THE    LACHRYMAL    APPARATUS. 

The  lachrymal  apparatus  consists  of  the  gland  secreting  the  tears,  situated  in  the 
anterior  and  outer  portion  of  the  orbital  cavity,  and  the  system  of  canals  by  which 
the  tears  are  conveyed  from  the  mesial  portion  of  the  conjunctival  sac  to  the  inferior 
nasal  meatus. 

The  lachrymal  gland  (glandule  lacrimalis),  resembling  in  shape  and  si/e  a 
small  almond,  consists  of  two  fairly  distinct  parts — the  superior  orbital  portion  and  the 
inferior  palpcbral  or  accessory  portion.  The  former  occupies  the  fossa  lacrimalis  in 
the  frontal  bone  and  is  the  larger  portion.  It  measures  20  mm.  in  length,  12  mm. 
in  breadth  and  reaches  from  the  edge  of  the  superior  palpebral  muscle,  along  the 
upper  margin  of  the  orbit  to  the  suture  between  the  frontal  and  malar  bones.  The 
upper  convex  border  is  attached  to  the  periosteum  of  the  fossa  by  means  of  a  number 
of  bundles  of  connective  tissue,  which  are  inserted  into  its  capsule.  Below,  it  rests 
upon  a  fascial  arch,  which  runs  from  the  trochlea  to  the  fronto-malar  suture. 

The  lower  or  palpcbral  portion  of  the  gland,  glandula  lacrimalis  inferior,  is 
somewhat  smaller  than  the  upper  and  separated  from  the  latter  by  the  fascial 
expansion  already  mentioned.  Its  lower  concave  surface  rests  upon  the  lornix  of 
the  conjunctiva,  extending  laterally  almost  to  the  outer  canthus. 

The  ducts  from  both  portions  of  the  gland  are  exceedingly  fine,  those  from  the 
upper  portion,  from  three  to  six  in  number,  passing  downward  through  the  inferior 
portion.  Some  of  the  ducts  from  the  lower  gland  join  those  coming  from  above  ; 
others  run  independently,  in  all  about  a  dozen  ducts  opening  into  the  conjunctival 
sac  along  a  line  just  in  front  of  the  fornix.  In  structure  the  glands  correspond  to 
the  tubo-alveolar  type,  and  resemble  the  serous  glands  in  their  general  character. 
The  acini  of  the  lower  portion  are  separated  by  robust  septa  of  connective  tissue, 
which  contain  considerable  lymphoid  tissue. 


1478 


HUMAN    ANATOMY. 


The  arteries  of  the  gland  are  derived  from  the  lachrymal,  and  the  veins  empty 
into  the  ophthalmic  vein.  The  nerves  include  sensory  fibres  from  the  lachrymal 
branch  of  the  ophthalmic,  as  well  as  secretory  fibres  from  the  sympathetic. 

Accessory  lachrymal  glands  ott  found  in  both  the  upper  and  lower  fornices,  from 
eight  to  thirty  being  present  in  the  upper  lid  and  from  two  to  four  in  the  lower. 
They  are  very  small  and  situated  chiefly  near  the  outer  angle  of  the  palpebral  fissure. 

FIG.  1234. 


Alveoli 


?& Ducts 


FIG.  1235. 


Beginning  of  dm  t 


'Fat-cells 
Section  of  lachrymal  gland,  under  low  magnification,  showing  general  arrangement  of  alveoli.    X  20. 

The  lachrymal  passages  (Fig.  1236)  begin  by  minute  openings,  the  lachrymal 
puncta,  which  are  usually  placed  at  the  summit  of  the  conical  lachrymal  papillae. 
The  latter  occupy  the  margins  of  the  eyelids,  near  the  mesial  extremity,  at  a  point 

where  the  arched  palpebral  borders  passes  over  into  the 
approximately  horizontal  boundaries  of  the  lachrymal 
lake.  The  upper  punctum  is  situated  6  mm.  from  tin- 
inner  canthus  ;  the  lower  one  is  slightly  larger  and  a 
trifle  farther  removed  from  the  canthus. 

The  puncta  open  into  the  lachrymal  canaliculi, 
which  at  first  are  vertically  directed,  then  bend  abruptly 
mesially  and,  taking  a  nearly  horizontal  course  parallel 
with  the  borders  of  the  lachrymal  lake,  run  as  far  as  the 
inner  canthus,  where  they  empty  usually  by  a  common 
canal  into  the  lateral  and  slightly  posterior  wall  of  the 
lachrymal  sac.  Occasionally  the  two  canaliculi  do  not 
unite  but  open  separately  into  a  diverticulum  of  the  sac, 
known  as  the  sinus  of  Maier.  Each  canaliculus  is  from 
8-10  mm.  in  length.  The-  I  ton  en  of  the  canal  measures 
only  .1  mm.  in  diameter  at  the  punctum,  presents  a  diverticulum  i  mm.  in  diameter 
at  the  bend,  and  continues  with  an  approximately  uniform  calibre  of  .5  mm.  in  its 
horizontal  portion. 

The  structure  of  the  canaliculi  includes  a  lining  of  stratified  squamous 
epithelium,  which  rests  upon  a  delicate  tunica  propria  rich  in  elastic  fibres,  muscular 
fibres  from  the  orbicularis  palpebrarum  affording  additional  support.  The  muscle 
bundles  run  parallel  to  the  horizontal  portion  of  the  canaliculi,  but  are  arranged  as  a 
circular  sphincter  about  the  vertical  portion. 

The  lachrymal  sac  (saccus  lacrimalis)  may  be  regarded  as  the  upper  dilated 
portion  of  the  naso-lachrymal  duct,  the  lower  part  of  which  passes  through  a  bony 
canal  and  opens  into  the  inferior  nasal  meatus  beneath  the  lower  turbinate  bone, 


Alveoli  of  lachrymal  gland  more 
highly  magnified.     X  235. 


PRACTICAL  CONSIDERATIONS  :    LACHRYMAL  APPARATUS.  1479 

The  sac  is  about  15  mm.  long,  and  5-6  mm.  in  diameter  when  distended.  It  is 
situated  near  the  inner  canthus  and  lies  within  the  deep  lachrymal  groove  between 
the  superior  maxillary  and  the  lachrymal  bone.  Its  closed  upper  end,  or  fundns, 
extends  beneath  the  internal  tarsal  ligament  and  some  of  the  fibres  of  the  orbicularis 
palpebrarum,  whilst  its  orbital  surface  is  covered  by  the  fibres  of  the  latter  muscle, 
which  spring  from  the  lachrymal  bone  and  are  known  as  the  tensor  tarsi  or  Horncr  \v 
iwiscle.  The  lower  end  of  the  sac  narrows  where  it  passes  into  the  nasal  duct.  The 
wall  is  lined  with  a  double  layer  of  columnar  epithelial  cells,  which  in  part  are 
provided  with  cilia.  It  is  composed  of  fibro-elastic  tissue  and  is  loosely  connected  with 
the  periosteum. 

The  nasal  or  naso-lachrymal  duct,  the  lower  portion  of  the  tear-passage,  is 
situated  within  the  bony  canal  formed  by  the  superior  maxillary,  lachrymal  and  infe- 
rior turbinate  bones.      It  varies  in  length  from  12—24  mm-.  according  to  the  position 
of  the  lower  opening,  and  is  from  3—4  mm.  in  diameter.    Its 
direction  is  also  subject  to  individual  variation,  but  is  slightly  FIG.   1236. 

backward,  as  well  as  downward,  and  is  usually  indicated  by 
a  line  drawn  from  the  inner  canthus  to  the  anterior  edge  of 
the  first  upper  molar  tooth.  The  duct  opens  into  the  lower 
nasal  meatus,  at  a  point  from  30-35  mm.  behind  the  poste- 
rior margin  of  the  anterior  nares.  The  aperture  may  be 
imperfectly  closed  by  a  fold  of  mucous  membrane,  the  so- 
called  valve  of  Hasner  (plica  lacrimalis).  The  structure 
of  the  duct  includes  a  lining  of  mucous  membrane  which  is 
clothed  with  columnar  epithelium  and  may  contain  glandular 
tissue  in  the  lower  portion.  The  mucous  membrane  is  sep- 
arated from  the  periosteum  by  areolar  tissue  and  a  venous- 
plexus  ;  it  may  present  additional  folds,  resembling  valves, 

i         1  i        i       r        i  •    1     •        •  i  i         •  •'  c      1  icdr-passages ,    c, 

the  best  marked  of  which  is  situated  at  the  junction  or  the     canaiiculi;  s,  lachrymal  sac; 

I.,,  D,   naso-lachrvmal   duct ;   nat- 

SaC  and   the  dtlCt.  uralsize.     (Divight.} 

The  arteries  supplying  the  lachrymal  duct  are  from  the 

nasal  and  the  inferior  palpebral.  The  large  and  numerous  veins  mostly  join  the 
nasal  plexus  and  empty  into  the  ophthalmic  and  facial.  The  nerves  are  derived  from 
the  infratrochlear  division  of  the  nasal  branch  of  the  ophthalmic. 

Practical  Considerations. — The  most  frequent  congenital  error  of  develop- 
ment in  the  lachrymal  apparatus  is  found  in  connection  with  the  canaliculus.  It 
may  be  entirely  absent,  or,  what  is  more  common,  may  appear  only  as  a  groove, 
the  edges  having  failed  to  unite.  This  union  of  the  edges  may  occur  only  in  part, 
so  that  the  canaliculus  may  have  two  or  more  openings. 

The  lachrymal  gland  is  rarely  the  seat  of  inflammation.  Hypertrophy  or 
enlargement  may  be  congenital  or  syphilitic.  Prolapse  or  dislocation  forward  may 
occur  so  that  the  gland  can  be  seen  or  felt  below  the  upper  outer  margin  of  the  orbit  ; 
it  has  been  excised  in  extreme  cases.  Cysts  are  due  to  occlusion  of  one  or  more  ducts. 

The  ducts  of  the  gland  open  into  the  outer  third  of  the  upper  conjunctival 
fornix,  and  the  tears  sweep  over  the  front  of  the  eye  towards  the  puncta  under  the 
influence  of  gravity  and  the  contractions  of  the  orbicularis  muscle.  The  lower 
punctum  is  frequently  everted  so  that  it  no  longer  dips  into  the  lacus  lacrimalis,  arjd 
the  tears,  instead  of  finding  their  way  into  the  normal  passage,  flow  over  the  lower 
lid  on  to  the  cheek  (epiphora).  This  is  usually  the  first  step  in  the  development  of 
ectropion  or  turning  out  of  the  lid  (vide  supra).  When  the  eversion  cannot  be  cor- 
rected, the  canaliculus  is  usually  slit  up  on  its  posterior  side  so  as  to  form  a  groove 
dipping  into  the  lacus,  from  which  the  tears  may  again  be  taken  up  by  the  natural 
passages.  The  most  common  cause  of  epiphora  is  obstruction  of  the  lachrymal 
passages.  This  occurs  most  frequently  at  the  junction  of  the  lachrymal  sac  and 
nasal  duct,  which  is  the  narrowest  part  of  the  duct.  The  method  of  correcting  such 
an  obstruction  is  by  the  use  of  sounds,  which  are  passed  from  the  punctum  with  or 
without  first  slitting  the  canaliculus.  The  rule  is  to  slit  the  canaliculus  when  the  sound- 
ing is  to  be  kept  up  for  any  length  of  time,  but  if  it  is  performed  for  diagnosis  only, 
the  slitting  is  not  done.  The  upper  canaliculus  is  shorter  but  narrower  than  the  lower, 


1480 


HUMAN    ANATOMY. 


which  is  usually  selected,  as  there  is  less  danger  of  laceration  of  the  lining  mucous 
membrane  leading  to  narrowing  or  occlusion  of  the  canaliculus  by  scar  tissue. 

Congenital  fistula  sometimes  result  from  non-closure  of  the  groove  from  which 
the  sac  and  nasal  duct  are  formed.  The  lachrymal  sac  is  situated  at  the  inner  side 
of  the  inner  canthus,  behind  the  inner  palpebral  ligament,  which  is  the  best  guide  to 
it,  and  crosses  about  the  junction  of  the  upper  and  middle  thirds  of  the  sac. 

A  collection  of  mucus  or  pus  in  the  lachrymal  passage  is  usually  in  the  sac,  and 
when  not  otherwise  relieved,  it  tends  to  discharge  itself  through  the  skin  below 
the  tendo-oculi,  and  frequently  lower  than  the  level  of  the  sac.  The  abscess  is 
therefore  opened  below  the  tendon  and  external  to  the  inner  edge  of  the  lachrymal 
groove. 

The  line  of  the  sac  and  duct,  taken  together,  is  approximately  from  the  inner 
canthus  to  the  space  between  the  second  premolar  and  first  molar  teeth.  It  opens 
below  into  the  inferior  meatus  of  the  nose,  just  below  and  behind  the  anterior  end  of 
the  inferior  turbinate  bone,  which  conceals  it  from  view  at  the  anterior  naris.  The 
sac  and  duct  form  a  slightly  curved  line  with  its  convexity  backward,  and  its  course 
downward,  backward  and  slightly  outward.  To  pass  a  probe  along  the  lachrymal 
passage,  the  lower  lid  is  everted  by  the  thumb  so  that  the  punctum  may  be  seen. 
The  probe  should  be  entered  into  the  punctum  vertically.  It  should  then  be  turned 
horizontally  and  passed  through  the  canaliculus  to  the  inner  wall  of  the  lachrymal 
sac.  It  is  then  made  vertical  and  passed  along  the  duct — i.e. ,  downward,  slightly 
backward,  and  outward  to  the  nose. 


DEVELOPMENT  OF  THE   EYE. 

The  development  of  the  eye  begins  as  a  lateral  diverticulum  which  very  early  appears  on 
either  side  of  the  fore-brain  (Fig.  911).  These  outgrowths,  the  primary  optic  vesicles,  are 
hollow  and  directly  communicate  with  the  general  cavity  of  the  primitive  brain  by  means  of 
the  optic  stalks,  which  are  at  first  broad,  but  later  become  narrowed.  As  the  development 
proceeds,  the  transversely  placed  optic  stalks  gradually  assume  a  more  oblique  axis,  and,  after 
the  differentiation  of  the  fore-brain  into  its  two  subdivisions,  open  into  the  diencephalon  or 
inter-brain.  The  primary  optic  vesicle  expands  until  it  comes  into  contact  with  the  surface 
ectoblast.  The  next  important  step  is  a  thickening  of  the  wall  of  the  vesicle  where  it  is  in  con- 
tact with  the  ectoblast  (Fig.  1238).  In  consequence  of  the  rapid  multiplication  of  its  cells, 
this  portion  of  the  wall  becomes  invaginated  and,  as  a  result,  the  cavity  of  the  primary  optic 

vesicle  is   gradually  obliterated,  the    application  of 

FIG.   1237.  the  invaginated  portion  of  the  wall  to  the  inner  sur- 

face of  the  uninvaginated  part  of  the  vesicle  bringing 
about  the  formation  of  a  cup-shaped  structure  pro- 
vided with  a  double  wall.  This  cup  is  called  the 
secondary  optic  vesicle  and  from  it  the  retina  is 
developed,  which  must  be  considered,  therefore,  as 
modified  portion  of  the  brain  itself. 

Coincidentally  with  the  invagination  of  the  optic 
vesicle,  the  overlying  ectoblast  undergoes  active 
proliferation  and  pushes  into  the  space  vacated 
the  receding  invaginated  wall,  thus  producing 
depression  known  as  the  lens-pit.  The  lens-pit  (Fig. 
1238)  deepens  and  becomes  cup-shaped  ;  the  edges 
of  its  anterior  walls  approach  each  other  and  then 
fuse,  and  in  this  manner  form  a  closed  sac,  the  lens- 
vesicle.  This  remains  for  a  time  connected  with  the 
surface  ectoblast,  but  later  becomes  separated  from 
it  and  forms  an  isolated  sac  of  epidermal  tissue,  which, 

by  the  proliferation  of  its  cells,  becomes  converted  into  a  solid  structure  and  constitutes  the 
crystalline  lens.  At  first  the  lens-vesicle  fills  the  cavity  of  the  optic  cup  completely,  but  with 
the  deepening  of  the  latter,  a  space  appears  between  its  anterior  wall  and  the  lens-vesicle, 
which  gradually  widens  and  forms  the  vitreous  cavity.  The  space  between  the  lens-vesicle 
and  the  ectoblast  is  invaded  by  a  process  from  the  surrounding  mesoblast,  which  pushes  in 
from  the  side.  From  this  ingrowth  is  developed  the  cornea,  with  the  exception  of  the  surface 
epithelium,  and  the  stroma  of  the  iris. 

Almost  from  the  first  appearance  of  the  invagination  of  the  primary  optic  vesicle,  the 
invaginated  portion  of  the  wall  exhibits  a  marked  tendency  to  proliferation  of  its  cells.  The 


Part  of  frontal  section  of  head  of  early  rabbit 
embryo,  showing  optic  vesicles  evaginated  from 
brain-vesicle.  X  30. 


DEVELOPMENT   OF   THE    EYE. 


1481 


FIG.   i2;rs. 


Brain-vesicle 


Uninvaginated 

wall 

Invaginated  wall 
Optic  stalk 

Optic  vesicle 
-Lens-pit 


Lens-pit  shows  as  depressed  area  of  thickened 
ectoblast ;  anterior  wall  of  optic  vesicle  beginning 
to  be  invaginated  ;  optic  stalk  narrowing.  X  30. 


uninvaginated  portion  of  the  wall,  on  the  contrary,  gradually  becomes  thinner,  until  it  is  repre- 
sented by  a  single  layer  of  cubical  cells.  These  soon  assume  a  dark  color  in  consequence 
of  the  appearance  within  their  protoplasm  of  fine  pigment  particles.  From  this  wall,  there- 
fore, the  layer  of  pigmented  cells  composing  the  outermost  stratum  of  the  retina  is  developed, 
whilst  from  the  rapidly  augmenting  layers  of  the  inner  wall,  the  essential  nervous  elements 
of  the  retina,  together  with  the  supporting  neurogliar  tissue,  are  formed. 

The  invagination  of  the  optic  vesicle  is  not  confined  to  its  outer  wall,  but  also  affects  its 
lower  wall,  in  consequence  of  which  a  groove,  the  fcttal  ocular  cleft,  appears  in  this  position 
(Fig.  1240).  This  is  continued  backward  to  and  along  the  under  surface  of  the  optic  stalk,  in 
the  form  of  a  furrow.  By  means  of  this  slit  a  com- 
munication is  established  between  the  cavity  of  the 
secondary  optic  vesicle  and  the  centre  of  the  optic 
stalk,  and  through  it  blood-vessels  from  the  sur- 
rounding mesoblast  gain  entrance  to  the  interior  of 
the  nerve  and  the  eyeball.  The  walls  of  this  fcetal 
cleft  gradually  approximate  and  become  fused.  The 
imprisoned  vessel,  the  hyaloid  artery,  later  gives 
rise  to  the  arteria  centralis  retinae.  The  vitreous 
body  has  been  usually  considered  as  a  derivative 
exclusively  of  mesoblastic  tissue  which  entered  the 
eye  in  company  with  the  blood-vessels.  According 
to  the  recent  investigations  of  Schon,  Kolliker  and 
others,  however,  this  view  is  inadequate,  since  at 
least  the  anterior  or  ciliary  portion  of  the  vitreous 
is  a  product  of  the  cells  of  the  inner  wall  of  the 
secondary  optic  vesicle.  The  choroid  and  the 
sclera  are  differentiated  from  the  mesoblast,  which 
surrounds  the  eyeball. 

Development  of  the  Lens. — Soon  after  the  iso- 
lation of  the  primitive  lens-vesicle  from  the  surface  ectoblast,  the  cells  in  the  posterior  wall 
begin  to  proliferate  actively,  while  those  on  the  anterior  wall  are  reduced  to  a  single  layer. 
The  latter  persists  as  the  lining  epithelium  of  the  adult  lens-capsule.  By  the  growth  of  the 
cells  of  the  posterior  wall  and  their  elongation  into  lens-fibres,  the  hollow  vesicle  is  gradually 
converted  into  a  solid  mass  of  lens-substance,  the  fibres  extending  forward  until  they  come  in 
contact  with  the  anterior  wall.  Subsequently  the  growth  of  the  lens  proceeds  by  the  application 
of  additional  layers  of  fibres  to  the  surface  of  the  primary  nucleus,  the  new  fibres  developing 

from  the  cells  lining  the  anterior  capsule.  Their  con- 
version takes  place  at  the  equator  of  the  lens,  where 
the  nuclei  of  the  elongating  lens-fibre  are  arranged  in 
a  convex  line  known  as  the  nuclear  zone  (Fig.  1228). 
The  capsule  of  the  lens  appears  very  early, 
even  before  the  closure  of  the  lens-vesicle,  and  long 
before  the  appearance  of  blood-vessels  around  the 
lens.  It  forms  a  sharp  boundary  line,  at  first  along 
the  posterior  border,  which  gradually  thickens  and 
finally  surrounds  the  entire  lens.  The  capsule  is  to 
be  considered  as  a  secretion  product  of  ihe  lens-cells. 
The  rapid  early  growth  of  the  young  lens 
requires  an  adequate  blood  supply.  This  is  insured 
by  the  development  of  a  vascular  net-work,  the 
tunica  vasculosa  lentis,  which  completely  surrounds 
the  lens  from  the  second  month  until  the  close  of 
foetal  life,  when  this  temporary  membrane  is  ab- 
sorbed. The  chief  supply  of  this  vascular  net-work 
is  derived  from  the  vessels  of  the  vitreous,  which, 
as  already  noted,  enter  the  eye  through  the  cleft  in 
the  optic  nerve.  Passing  forward  through  the  canal  of  Cloquet  in  the  centre  of  the  vitreous 
cavity,  the  chief  vessel,  the  hyaloid  artery,  reaches  the  posterior  pole  of  the  lens,  when  it  divides 
into  numerous  branches.  These  branches  pass  around  the  equator  of  the  lens  onto  the  anterior 
surface,  where,  joined  by  vessels  from  the  mesoblastic  tissue  which  is  to  constitute  the  future 
iris  and  ciliary  body,  they  proceed  to  the  centre  of  the  pupil  and  break  up  into  their  terminal 
loops.  The  portion  of  the  net-work  covering  the  pupillary  area  is  called  the  membrana  pupil- 
laris,  whilst  the  remainder  is  known  as  the  membrana  capsularis.  This  vascular  sheet  is  usually 
entirely  absorbed  before  birth,  but  occasionally  portions  of  it  may  be  seen  persisting  in  the 
form  of  fine  threads  in  the  pupillary  space,  or  on  the  posterior  pole  of  the  lens.  The  retention 
of  such  strands  is  sometimes  associated  with  the  persistence  of  portions  of  the  hyaloid  artery. 


FIG. 


1239- 


Ectoblast 

Outer  layer 
Lip  of  optic  cup 

_  Inner  layer 

Anterior  wall 
-  Optic  stalk 

Posterior  wall 
of  lens-sac 


Lens-sac  closed  ;  outer  and  inner  layers  of  sec- 
ondary optic  vesicle  now  almost  in  contact. 


HUMAN   ANATOMY. 


FIG.  1240. 


Outer  layer 
Inner  layer 

I'osh Tior  wall 
of  lens-sac 

Mesohlast 
Lip  of  optic  cup 


Foetal  cleft 

Sagittal  section  of  developing  eye  at  same 
stage  as  preceding  specimen,  showing  invagi- 
nation  of  optic  vesicle  along  foetal  cleft.  X  30. 


Development  of  the  Retina. — As  already  pointed  out,  the  retina  develops  from  the  walls  of 
the  optic  vesicle,  the  pigmented  layer  being  derived  from  the  uninvaginated  outer  wall,  the  pig- 
ment appearing  early  and  first  near  the  anterior  margin  of  the  optic  cup;  the  remainder  of  the 
retina  comes  from  the  rapidly  growing  cells  of  the  inner  wall.  The  first  cells  to  be  differentiated 
in  the  nervous  portion  of  the  retina  are  the  spongioblasts  which  develop  into  the  supporting 

neurogliar  fibres,  the  fibres  of  Wilier.  These  are 
strengthened  by  the  addition  of  mesoblastic  elements, 
which  enter  the  inner  layers  along  with  the  blood- 
vessels. The  neuroblasts  develop  from  cells  which 
correspond  in  position  to  those  of  the  external  nu- 
clear layer.  As  they  divide,  the  cells  are  displaced 
inward,  so  that  the  ganglion-cells  represent  the  oldest 
descendents.  When  seven  or  eight  layers  have  been 
differentiated,  the  ganglion-cells  send  out  axones, 
which  form  the  fibre-layer  and  converge  toward  the 
optic  nerve.  The  visual  cells  are  the  last  to  appear, 
the  layer  of  rods  and  cones  developing  as  cuticular 
outgrowths  from  the  cells  of  the  external  nuclear  layer. 
Anteriorly  the  walls  of  the  secondary  optic  vesicle 
are  reduced  to  a  double  layer  of  cells.  For  a  certain 
distance,  corresponding  to  the  position  of  the  future 
ciliary  body  (pars  ciliaris  retinae),  the  outer  cells  are  pigmented,  whilst  the  inner  ones  are  trans- 
parent. Still  farther  forward,  the  rudimentary  portion  of  the  nervous  tunic  is  continued  over 
the  posterior  surface  of  the  iris  (pars  iridica  retinae)  as  a  double  layer  of  deeply  pigmented 
cells  which  extends  as  far  as  the  pupillary  margin  which  thus  corresponds  to  the  anterior  lip  of 
the  secondary  optic  vesicle. 

The  optic  nerve  is  developed  secondarily  and  in  close  association  with  the  early  optic  stalk, 
which  is  at  first  hollow,  and  later  becomes  grooved  along  its  inferior  surface.  The  walls  of 
this  foetal  cleft  become  approximated  and,  after  the  entrance  of  the  blood-vessels,  the  lips 
of  the  cleft  fuse,  the  vessels  being  thus  enclosed.  Since  the  fibres  of  the  optic  nerve  are  for 
the  most  part  axones  of  the  ganglion-cells  of  the  retina,  it  is  evident  that  they  are  not  developed 
within  the  nerve,  but  invade  the  latter  as  outgrowths  of  fibres  from  the  retina,  pushing  along 
the  optic  nerve  and  tract  to  reach  their  cerebral  connections.  In  addition  to  these  centripetal 
fibres,  a  certain  number  of  centrifugal  ones  appear  later  as  outgrowths  from  cells  within  the 
brain.  The  supporting  tissue  is  developed  by 
proliferation  of  the  cells  of  the  optic  stalks 
and  their  differentiation  into  neurogliar  ele- 
ments, assisted  by  the  mesoblastic  elements 
from  the  surrounding  pia  and  the  portion 
which  enters  the  cleft  with  the  blood-vessels. 
The  nerve-fibres  are  at  first  naked  axis-cylin- 
ders, which  later  acquire  medullary  sheaths. 
Development  of  the  Fibrous  and  Vascular 
Tunics. — With  the  separation  of  the  lens- 
vesicle  from  the  overlying  ectoblast,  the  meso- 
blast  insinuates  itself  between  these  structures, 
in  addition  to  surrounding  the  entire  ecto- 
blastic  optic  vesicle.  The  portion  surrounding 
the  optic  vesicle  posteriorly  thickens  rapidly 
and  becomes  differentiated  into  the  vascular 
tunic,  or  choroid,  whilst  the  outer  layer  be- 
comes the  fibrous  tunic,  or  sclera.  The  choroid 
appears  first,  the  pigmentation  of  its  cells  being 


FIG.  1241. 


Upper  eyelid 
outer  pigmented 
retinal  layer 
Inner  retinal 
layer 
Mesoblast 

Lens,  now  solid 
Optic  nerve 

Vascular  vitreous 

tissue 

Ectoblast 

Lip  of  retinal  coa 


Mesoblast 
Lower  eyelid 


Much  later  stage,  showing  lens  now  solid;  layti-.  »i 
optic  vesicle  converted  into  retinal  coat ;  vascular  vi'treous 
tissue;  condensation  and  invasion  of  mesoblast.  -'<>. 


evident  by  the  seventh  month.  The  meso- 
blastic process  between  the  lens  and  the  ecto- 
blast is  very  thin  at  first,  but  subsequently 
splits  into  two  layers.  The  anterior  of  these 
becomes  the  substantia  propria  of  the  cornea  and  its  lining  endothelium.  The  latter  produces 
the  membrane  of  Descemet.  The  posterior  mesoblastic  layi-r  carries  blood-vessels  which  help 
to  form  the  capillary  net-work  surrounding  the  lens.  The  space  between  the  two  mesoblastic 
layers  represents  the  future  anterior  chamber  of  the  eye.  About  the  fourth  fu-tal  month  the  an- 
terior lip  of  the  optic  vesicle  pushes  forward  in  advance  of  the  lens  and  carries  with  it  additional 
mesoblastic  tissue.  From  this  the  iris  is  developed,  the  stroma  being  formed  by  the  mesoblast, 
whilst  the  posterior  pigmented  portion  represents  the  anterior  part  of  the  optic  vesicle,  from 
which  the  dilatator  muscle  (and,  according  to  some  authorities,  also  the  sphincter  pupillae)  is 
derived.  The  ciliary  processes  are  produced  by  the  rapid  lateral  expansion  of  the  walls  of  the 


THE    EAR. 


1483 


optic  vesicle,  about  the  fourth  or  fifth  month,  in  consequence  of  which  folds  in  the  membrane 
arise,  into  which  blood-vessels  and  other  mesodermic  elements  extend.  The  corneal  stroma 
becomes  blended  with  the  sclera,  thenceforth  the  two  forming  a  continuous  tunic. 

Development  of  the  Vitreous  Body. — As  already  stated,  the  vitreous  body  is  at  present  re- 
garded as  developing  chiefly  by  proliferation  of  the  cells  of  the  inner  wall  of  the  optic  vesicle, 
especially  from  its  anterior  or  ciliary  portion.  The  suspensory  ligament  of  the  lens  is  derived 
from  the  same  source.  The  cells  develop  into  the  fibres  which  form  the  fine  net-work  of  the 
vitreous  body;  at  the  periphery  these  become  condensed  and  form  the  boundary  layer  or 
hyaloid  membrane.  The  vitreous  is  supplied  with  blood  by  branches  of  the  hyaloid  artery, 
which  springs  from  the  head  of  the  optic  nerve.  An  especially  complete  net-work  is  found  at 
the  periphery  of  the  vitreous  and  these  vessels  pass  forward  to  the  equator  of  the  lens  and 
assist  in  forming  the  tunica  vasculosa  lentis.  The  retinal  vessels  are  formed  later  as  branches  of 
the  central  artery,  the  vitreous  vessels  usually  undergoing  complete  absorption  before  birth. 

The  development  of  the  eyelids  begins  with  the  production  of  folds  of  integument,  which 
appear  above  and  below  the  cornea  during  the  second  foetal  month.  The  folds  approach  each 
other  and  the  epidermal  cells  fuse  about  the  third  month,  the  eyelids  remaining  united  until 
shortly  before  birth.  The  Meibomian  and  other  glands  of  the  lids  are  produced  by  ingrowths 
of  the  surface  ectoblast.  The  lachrymal  gland  arises  during  the  third  month  as  a  solid  ingrowth 
from  the  conjunctiva!  epithelium  close  to  the  upper  lid.  The  lachrymal  canal  begins  as  a  solid 
process  of  epithelial  cells  from  the  lid,  which  dips  inward  along  the  lachrymal  furrow,  between 
the  superior  maxillary  and  nasal  processes.  This  cord  of  cells  becomes  isolated  from  the  sur- 
face, and  later  acquires  a  lumen,  connecting  by  means  of  the  canaliculi  with  the  conjunctival  sac 
.above.  The  duct  establishes  communication  with  the  nasal  fossa  just  before  birth. 


THE   EAR. 

The  ear  (organon  audittis)  may  be  conveniently  studied  under  its  three  natural 
subdivisions,  which  are  conventionally  described  as  the  external,  middle  and  the 
internal  ear — structures  lodged  entirely  or  in  part  within  the  temporal  bone.  The 


FIG.  1242. 


Bone 
Malleus 
Incus 


Stapes 


Inner  ear 

Semicircular  canal 


Internal  auditory  canal 
Auditory  nerve 


Endolymphatic  sac 


Cartilage 


Diagram  showing  relations  of  three  subdivisions  of  ear.     (Modified  from  Schwalbe.) 


external  ear  includes  the  auricle  and  the  external  auditory  canal ;  the  middle  ear 
the  tympanum,  the  Eustachian  tube  and  the  mastoid  cells  ;  and  the  internal  ear 
the  labyrinth,  with  the  peripheral  ramifications  of  the  auditory  nerve. 

Such  division,  moreover,  is  justified  by  the  developmental  history  of  the  organ, 
since  the  internal  ear  is  developed  essentially  from  the  highly  differentiated  otic  vesicle 
which  gives  rise  to  the  complicated  membranous  labyrinth  ;  the  middle  ear  largely 
from  the  first  pharyngeal  pouch  ;  whilst  the  external  ear  represents  the  deepened 
and  modified  boundaries  of  the  first  external  visceral  furrow. 


1484 


HUMAN    ANATOMY. 


Fossa  helici 


THE  EXTERNAL   EAR. 

The  external  ear,  the  outermost  subdivision  of  the  auditor)-  organ,  includes 
( i )  the  auricle,  the  funnel-shaped  appendage  attached  to  the  side  of  the  head  for  the 
collection  of  the  sound-waves,  and  (2)  the  external  auditory  catial,  which  conveys 
these  stimuli  to  the  tympanic  membrane,  the  flexible  partition  closing  the  canal  and 
separating  it  from  the  middle  portion  of  the  ear. 

THE  AURICLE. 

The  auricle  (auricula),  also  called  the  pinna,  is  attached  to  the  side  of  the  head 
around  the  opening  of  the  external  auditory  canal,  midway  between  the  forehead  and 
the  occiput.  It  presents  two  surfaces,  an  external  and  an  internal.  The  angle  which 
its  internal  surface  forms  with  the  head,  the  cephalo-auriailar  angle,  is  usually  about 
30°,  but  varies  from  20-45°.  The  circumference  of  the  auricle  is  somewhat  pyriform 
in  outline,  with  the  broadest  part  of  the  figure  above.  The  external  surface  of  the 
auricle  is  irregularly  concave  and  presents  for  examination  several  well-marked 
depressions  and  elevations,  which  depend,  for  the  most  part,  upon  the  corresponding 
modelling  of  the  underlying  cartilage.  The  concha,  the  largest  and  deepest  of  the 
concavities,  surrounds  the  entrance  or  meatus  to  the  external  auditory  canal.  This 
funnel-like  fossa  is  subdivided  by  an  obliquely  transverse  ridge,  the  crus  helicis, 
continuous  with  the  helix,  into  the  upper  and  smaller  part,  the  cymba  con- 
chae,  and  a  lower  and  larger  part,  the  concha  proper  or  cavum  conchae.  The 

tragus    is     an     irregular 

FIG.  1243.  eminence  in  front  of,  and 

slightly  overlapping,  the 
meatus.  At  the  upper 
extremity  of  the  tragus, 
just  below  a  notch,  the 
incisura  anterior,  that 
separates  the  tragus  from 
the  upper  part  of  the 
auricle,  is  sometimes  seen 
a  small  elevation,  the 
— Trasus  tuberculum  supratrag- 

icum.  The  antitragus 
is  an  eminence  behind  the 
tragus  and  separated  from 
it  by  a  deep  notch,  the 
incisura  intertragica. 
The  lobule  contributes 
the  rounded  lower  ex- 
tremity of  the  auricle.  In 
contrast  to  other  parts  of  the  pinna,  it  possesses  no  framework  of  cartilage  and,  hence, 
is  soft  and  inelastic.  The  helix  forms  the  scroll-like  margin  of  the  ear,  sweeping  from 
the  upper  part  of  the  tragus  in  front  to  the  lobule  behind.  It  is  more  or  less  rolled 
upon  itself  so  that  its  margin  looks  forward.  On  the  anterior  edge  of  the  helix,  near 
the  junction  of  its  upper  and  middle  thirds,  is  sometimes  found  a  small  triangular  ele- 
vation, the  car-point  or  tubercle  of '  fhvicin,  which  is  of  interest  as  representing,  ac- 
cording to  the  last-named  authority,  the  erect  pointed  extremity  in  the  expanded  ears 
of  certain  quadrupeds.  It  is  said  to  be  constant  in  the  fcetus  of  about  the  sixth  month 
and  to  be  more  common  in  the-  male  than  in  the  female.  In  front  of  and  parallel  to 
the  helix,  is  a  curved  ridge,  tin-  antihelix  which  begins  at  the  antitragus  below, 
forms  the  concave  posterior  boundary  of  the  concha,  and  divides  above  it  into  a 
superior  and  an  inferior  crus  between  which  lies  the  fossa  of  the  antihelix  or  the 
fossa  triangularis.  A  narrow  groove  between  the  helix  and  the  antihelix  marks 
the  fossa  of  the  helix  or  the  scaphoid  fossa. 

The  elevations  on   the  external  surface  of   the  auricle  are  represented  by 
depressions  on  the  cranial  surface,  and  conversely  tin-  depressions  on  the  external 


Cavum  concha: 


Fossa  triangularis 


Crura  antihelicis 

Cymba  conchse 
Crus  helicis 
Incisura  anterior 


Incisura 
intc-rtragica 


Lohulii> 


Right  auricle,  outer  aspect. 


THE   EXTERNAL   EAR. 


surface  are  represented  by  eminences.  Thus,  the  concavity  of  the  concha  is 
represented  on  the  cranial  surface  by  the  eminentia  conchae  ;  the  antihelix  by 
the  fossa  antihelicis  ;  the  fossa  triangularis  by  the  eminentia  fossae  triangu- 
laris ;  the  scaphoid  fossa,  by  the  eminentia  scaphae.  The  other  elevations  and 
depressions  corresponding-  to  those  of  the  outer  surface  are  not  seen  on  the  cranial 
surface,  except  in  the  dissected  cartilage  denuded  of  the  integument. 

Structure  of  the  Auricle. — The  auricle  consists  of  integument  and  an  enclosed 
plate  of  yellow  elastic  cartilage  continuous  with  that  of  the  meatus.  It  is  also  provided 
with  several  unimportant  ligaments  and  muscles.  The  lobule,  however,  contains  no 
cartilage,  but  only  fibrous  tissue  and  fat  enclosed  within  the  integumentary  fold. 

The  skin  of  the  auricle  is  thin  and  closely  adherent  to  the  cartilage,  especially 
on  the  outer  surface.  In  certain  parts  it  contains  fine  hairs  and  sebaceous  and  sweat 
glands.  The  hair  follicles  are  especially  abundant  over  the  tragus,  antitragus  and 
the  notch  lying  between  them,  the  hairs  guarding  the  entrance  into  the  external 
auditory  canal,  known  as  tragi,  being  exceptionally  long.  The  sebaceous  glands 
are  especially  well  developed  in  the  cavity  of  the  concha. 

Cartilage  of  the  Auricle.— The  cartilage  of  the  auricle  may  be  divided  into 
two  parts  :  (a~)  the  scroll-like  plate  forming  the  tragus  and  external  auditory  canal, 
and  (£)  the  large  irregular  plate  forming  the  main  cartilage.  These  two  divisions 


FIG.  1244. 


Insertion  of  auricularis  superior 


Ohliquus 


Helicis  major 


Tragicus 


Plate  of  tragus 

and  external 

auditory  canal 


Cartilaginous  framework  of  right  auricle,  with  intrinsic  auricular  muscles;  A,  outer,  B,  inner  surface. 

are  connected  by  a  cartilaginous  isthmus  lying  between  the  incisura  intertragica  on 
its  outer  side  and  the  deep  fissure,  (incisura  terminalis  auris),  which  in  the  isolated 
cartilage  is  seen  between  the  posterior  wall  of  the  outer  meatus  and  the  anterior 
border  of  the  lower  part  of  the  concha,  on  its  inner  side.  Two  smaller  clefts,  the 
fissures  of  Santorini,  are  found  between  the  three  plates  which  form  the  carti- 
laginous scroll  supporting  the  tragus  and  outer  end  of  the  external  auditory  canal. 
The  cartilage  of  the  tragus  is  an  irregular  plate  and  subject  to  considerable  variation. 

The  depressions  and  elevations  of  the  cartilage  proper  correspond  in  general  to 
the  surface  modelling  of  the  auricle,  but  are  sharply  marked,  especially  on  the  cranial 
aspect.  A  deep  notch,  the  fissura  antitragohelicina,  separates  the  lower  part  of 
the  helix  from  the  antitragus,  thus  defining  the  caudal  process  (cauda  helicis),  as 
the  lower  extremity  of  the  cartilage  forming  the  helix  is  called. 

The  spin  a  helicis  is  a  small  conical  projection,  directed  forward  and  down- 
ward, opposite  the  first  bend  of  the  helix.  This  serves  for  the  attachment  of  the 
anterior  ligament.  The  upper  end  of  the  tragus-plate  fits  into  an  angle  formed  by 
the  junction  of  the  beginning  of  the  helix  and  the  upper  end  of  the  anterior  border  of 
the  concha.  In  addition  to  the  elevations  and  depressions  already  referred  to,  on 
the  mesial  surface  is  found  a  ridge,  the  ponticulus,  which  extends  downward 
and  forward  over  the  eminence  of  the  concha  and  serves  for  the  attachment  of  the 
posterior  auricular  muscle  (Fig.  1244,  B}. 


1486 


HUMAN    ANATOMY. 


Ligaments  of  the  Auricle. — The  extrinsic  ligaments  of  the  auricle,  those 
which  attach  the  auricle  to  the  temporal  bone,  form  a  more  or  less  continuous  mass 
of  fibres.  These  are  separated  somewhat  arbitrarily  and  described  as  the  anterior 
and  posterior  ligaments.  The  anterior  ligament  extends  from  the  helix  and  the 
tragus  to  the  root  of  the  zygoma.  The  posterior  ligament  extends  from  the  emi- 
nence of  the  concha  and  ponticulus  to  the  anterior  part  of  the  mastoid  process.  A 
number  of  bands  of  fibrous  tissue,  the  instrinsic  ligaments,  bind  the  parts  of  the 
cartilage  together. 

The  Muscles  of  the  Auricle. — These  include  the  extrinsic  and  the  intrinsic 
muscles. 

The  extrinsic  muscles  of  the  auricle,  those  which  extend  from  the  head  to  the 
auricle  and  move  it  as  a  whole,  have  been  described  under  the  muscular  system 
(page  483).  They  are  the  anterior,  superior  and  posterior  auricular  muscles. 

The  intrinsic  muscles,  six  in  number,  consist  of  small  strands  of  muscle-fibres 
attached  to  the  skin,  which  extend  from  one  part  of  the  auricle  to  another  and  are 

confined  to  the  auricle  itself.  Of  these, 


FIG.  1245. 


four  are  on  the  external  surface  of  the 
auricle  and  two  on  the  cranial. 


Plate  of  trains 


Cartilaginous 
canal 


1.  The   smaller   muscle   of    the   helix 
(m.  lie/ids  minor}  lies  upon  the  crus  helicis 
and  the   beginning  of  the  helix,  its  fibres 
running  obliquely  upward  and  forward. 

2.  The   greater   muscle    of    the    helix 
(in.  helicis  major')  arises  from  the  spine  of 
the   helix   and   extends   upward    along   the 
anterior  border  of  the  helix  and  is  inserted 
into  the  eminence  of  the  triangular  fossa. 

3.  The  muscle  of  the  tragus  (in.  tragi- 
cus)  is  a  flat  muscle  on  the  outer  surface  of 
the  tragus  ;  usually  only  its   vertical   fibres 
are  distinguishable.    Occasionally  a  separate 
bundle  of  muscular  fibres  (///.  pyrainidalis] 
extends  from  the  tragus  to  the  spine  of  the 
helix.     Likewise  another  band,  the   in.  in- 
cisurce    Sanforhii,     sometimes    called    the 
dilatator    concha?,     bridges  •  the     incisura 
terminalis.     Both  of  these,  however,  belong 
to  the  system  of  the  tragus  muscle. 

4.  The  muscle  of  the   antitragus    i  in. 
antitragicus)'\s  attached  to  the  outer  surface 
of  the  antitragus.     Its  fibres  run   obliquely 
from  the  antitragus  upward  and  backward 
and  are  inserted  into  the  caudate  process  of 

the  helix.     On  the  cranial  surface  of  the  auricle  are  the  transverse  and  the  oblique  muscles. 

5.  The  transverse  muscle  (///.  traiisi'crsus)  bridges  over  the  fossa  antihelicis  and  extends 
from  the  eminence  of  the  scaphoid  fossa  to  the  eminence  of  the  concha. 

6.  The  oblique  muscle  (/;/.  ob/iquits),  considered  by  Gegenbauer  as  a  part  of  the  trans- 
verse muscle,  extends  from  the  back  of  the  concha  to  the  eminence  of  the  triangular  fossa. 

Actions. —  Duchenne  and  Ziemssen  found  that  by  stimulating  the  muscles  of  tin-  tragus  and 
antitragus  the  external  auditory  canal  was  narrowed.  Duchenne  further  demonstrated  that  the 
greater  and  lesser  muscles  of  the  heli,\  were  antagonistic  to  those  of  the  tragus.  The  transverse 
muscle  and  the  oblique  muscle  by  their  contraction  are  said  to  cause  a  slight  flattening  of  the 
auricle. 


Bony  canal 


Dissection  showing  bony  and  cartilaginous  rx>rtions  of 
right  external  auditory  canal  ;  seen  from  in  front. 


Vessels  of  the  Auricle. — Arteries. — The  auricle  receives  its  blood  supply 
from  branches  of  the  superficial  temporal  artery  and  the  posterior  auricular  artery, 
and  thus  indirectly  from  the  external  carotid.  The  superficial  temporal  sends  three 
brandies  to  the-  outer  surface  of  the  auricle:  (a)  the  artery  of  the  hc/i.v  to  the 
ascending  part  of  the  helix,  fossa  triangularis  and  the  superior  crus  of  the  anti- 
helix;  </>)  the  artery  of  the  cms  helicis  to  the  region  of  the  crus  helicis;  (<•)  the 
artery  of  Hie  trains  to  the  region  of  the  tragus  and  lobule,  the  lobule  receiving 


THE  EXTERNAL  EAR. 


1487 


a  branch,  the  anterior  artery  of  the  lobule,  from  the  artery  of  the  tragus.  The  pos- 
terior auricular  artery  supplies  a  variable  number  of  branches  to  the  auricle.  Usually 
two  of  these  are  given  off  below  and  one  above  the  posterior  auricular  muscle.  These 
branches  are  larger  and  longer  than  those  from  the  superficial  temporal.  After  rami- 
fying over  the  cranial  surface  of  the  auricle,  they  reach  its  outer  surface  by  piercing 
the  auricle  or  by  passing  over  its  free  margin.  They  supply  the  posterior  part  of 
the  outer  surface  and  anastomose  with  the  branches  of  the  superficial  temporal. 

The  veins  of  the  auricle  accompany  the  arteries  and  include  :  (a)  the  anterior 
auricular,  which  empties  into  the  superficial  temporal  ;  (b)  the  posterior  auricular, 
three  or  four  in  number,  which  join  a  plexus  behind  the  ear  which  empties  principally 
into  the  external  jugular  vein,  but  also  unites  with  the  posterior  facial  vein.  Com- 
munications with  the  mastoid  emissary  vein  of  the  lateral  sinus  also  frequently  exist. 

The  Lymphatics. — The  lymphatics  of  the  auricle  form  a  close  net- work  within  the 
deeper  layers  of  the  integument,  from  which  lymphatic  stems  pass  in  three  general 
groups.  Those  from  the  outer  surface  are  afferents  chiefly  of  the  anterior  auricular 
nodes,  which  are  placed  immediately  in  front  of  the  tragus  and  beneath  the  parotid 
fascia  ;  a  few,  however,  bend  backward  over  the  helix  to  end  in  the  posterior  auricu- 


FIG.  1246. 


A.  perforans 
fossae  triangularis 

A.  helicis 


A.  auricularis 
post.  sup. 


A.  temporalis  ,  Posterior 

auricular  muscle 

A.  cruris 
helicis 


A.  perforans 
cymba: 


A.  caudae  helicis 


A,  tragi 


A.  auricular^ 
post.  inf. 


A.  auricularis 
posterior 


Parotid  branch 
Arteries  of  right  auricle,  A,  lateral  surface;  B,  postero-mesial  surface.    (Schivalbe.) 

lar  nodes  that  overlie  the  insertion  of  the  sterno-mastoid  muscle.  Those  from  the 
upper  part  of  the  cranial  surface  pass  mainly  to  the  posterior  auricular  nodes,  some 
being  tributary  to  the  external  jugular  nodes.  A  number  of  stems  from  the  lower 
part  of  the  auricle  and  from  the  lobule  terminate  in  the  parotid  nodes. 

Nerves  of  the  Auricle. — The  motor  nerves  supplying  the  intrinsic  muscles 
of  the  auricle  are  from  the  temporal  and  posterior  auricular  branches  of  the  facial 
nerve,  the  former  being  distributed  to  the  muscles  of  the  helix,  tragus  and  antitragus, 
whilst  the  posterior  auricular  supplies  the  tranverse  and  "oblique  muscles.  The  sen- 
sory nerves  include  branches  from  :  (a)  the  great  auricular  nerve,  which  supplies  the 
integument  of  the  lower  three-quarters  of  the  inner  surface  of  the  auricle,  with  the 
exception  of  a  small  portion  near  the  meatus,  and  sends  filaments  to  the  outer  surface 
of  the  lobule  and  adjacent  area  ;  ($)  the  small  occipital  nerve,  which  supplies  the 
upper  one-quarter  of  the  inner  surface  ;  (c~)  the  auricular  branch  of  the  vagus,  which 
supplies  the  small  muscles  on  the  back  of  the  concha  and  a  limited  cutaneous  area 
near  the  meatus  ;  and  ('</)  the  auriculo-temporal  nerve,  which  divides  at  the  level  of 
the  tragus,  and  sends  filaments  from  its  auricular  branches  to  the  outer  surface  of  the 
auricle. 

THE  EXTERNAL  AUDITORY  CANAL. 

The  external  auditory  canal  (meatus  acusticus)  leads  from  the  cavity  of  the 
concha  to  the  tympanic  membrane,  which  closes  its  inner  extremity.  Although  the 
adult  meatus  varies  considerably  in  size  and  direction,  it  is  usually  tortuous. 

In  a  general  way,  in  its  external  portion  the  canal  extends  somewhat  forward 
and  inward,  perhaps  slightly  upward  ;  then,  in  its  middle  portion,  almost  directly 


1488 


HUMAN   ANATOMY. 


FIG.  1247. 


Internal  auditory 
canal 


inward,  possibly  slightly  backward  ;  and  finally,  in  its  internal  portion,  forward. 
downward  and  inward.  Its  supero-posterior  wall  measures  about  25  mm.  ( i  in. )  in 

length,  and  the  anterior 
wall  about  35  mm.  (i|/g 
in.),  the  greater  length 
of  the  anterior  wall  be- 
ing due  to  the  obliquity 
of  the  drum-head  and 
the  outward  protrusion 
of  the  tragus.  The 
canal  is  almost  as  long 
in  the  infant  as  in  the 
adult. 

Structure. — The 
external  auditory  canal 
is  composed  of  an  outer 
cartilagino-membranous 
(cartilaginous)  and  of  an 
inner  bony  portion,  both 
of  which,  as  well  as  the 
external  surface  of  the 
tympanic  membrane,  are 
lined  by  skin.  The  car- 
tilagino-  membranous 

part  contributes  something  more  than  one-third  of  the  entire  length  of  the  canal, 
and  is  a  continuation  of  the  cartilage  of  the  auricle.  The  cartilage  of  the  canal, 
histologically  of  the  elastic  type,  does  not  form  a  complete  tube,  but  is  deficient  at 
its  upper  back  part,  where  it  is  filled  in  by  fibrous  tissue.  On  approaching  the 
bony  portion,  this  deficiency  in  the  cartilage  is  more  marked  and  the  fibrous  tissue 
correspondingly  increased. 

Two  or  more  slit-like  apertures,  the  fissures  of  Santorini  (incisurae  cartilag- 
inis  mcatus  acustici  externi)  are  usually  found  traversing  the  cartilagino-membranous 

FIG.  1248. 


Lateral  sinus 


Frontal  section  passing  through  right  ear,  showing  external,  middle, 
and  internal  divisions;  section  is  seen  from  in  front. 


Condyle  of  jaw 


Cartilaginous  canal 


Tympanic  membrane 


External  auditory  canal 


Mastoid  cells 


Bony  canal 


Eustachian  tuhe 

Internal  carotid  artery 
Tympanic  cavity 


Lateral  sinus 


Horizontal   section  passing  through  right  car,  viewed  from  below. 

canal  nearly  at  right  angles  (Fig.    1245);  as  they  are    filled    with   fibrous    tissue, 
they  permit  the  anastomosis  between  the  vessels  of  the  anterior  and  posterior  surfaces 


THE   EXTERNAL    EAR. 


1489 


Sebaceous  gland 


Cartilage 


of  the  ear.  At  its  inner  end  the  cartilagino-membranous  meatus  is  attached 
to  the  inferior  and  lateral  edges  of  the  osseous  meatus,  the  fibrous  part  being 
continuous  superiorly  and  posteriorly  with  the  periosteum  lining  of  the  osseous 
canal.  The  osseous  portion  of  the  tube,  about  14  mm.  in  length,  is  longer 
and  narrower  than  the  cartilagino-membranous  part.  At  its  inner  end  it  presents 
a  narrow  groove,  the  sulcus  tympanicus,  for  the  insertion  of  the  tympanic 
membrane.  The  sulcus  extends  around  the  sides  and  floor  of  the  canal,  but  is 
deficient  above. 

The  skin  lining  the  external  auditory  canal  is  closely  attached  to  the  underlying 
cartilaginous  portion  of  the  tube,  the  skin  measures  about  1.5  mm.  in  thick- 
ness, but  is  much  thinner  within  the  bony  canal,  except  along  the  roof,  where  it 
remains  relatively  thick.  Over  the  outer  surface  of  the  tympanic  membrane  the 
skin  is  reduced  to 

a  very  delicate  and  FlG-  I249- 

smooth  investment, 
covered  by  a  corre- 
spondingly attenu- 
ated epidermis,  and 
a  suggestion  of  sub- 
cutaneous tissue. 
Numerous  fine  hairs 
and  large  sebace- 
ous glands  occur 
in  the  cartilaginous 
portion,  but  dimin- 
ish in  size  and  fre- 
quency towards  the 
bony  canal,  in  which 
they  are  entirely 
wanting.  Within  the 
cartilaginous  meatus 
and  along  the  roof 
of  the  bony  tube,  the 
skin  is  closely  be- 
set with  the  large 
coiled  ceruminous 
glands,  which  re- 
semble in  structure 
modified  sweat 
glands.  Like  the 
latter,  the  cerumin- 
ous glands  consist  of 
a  deeper  and  wider 
coiled  portion,  the 

secretory  segment,  and  a  long  narrow  excretory  duct,  which  ends  in  most  cases  inde- 
pendently on  the  free  surface  of  the  skin,  but  sometimes,  particularly  in  the  very 
young  child,  may  open  into  the  duct  of  a  sebaceous  gland.  The  cuboidal  secreting 
cells  contain  yellowish  brown  pigment  particles  and  granules  resembling  fat.  The 
ear-wax  or  cerumen  is,  as  usually  found,  the  more  or  less  dried  mixture  of  the 
secretions  derived  from  both  varieties  of  glands,  together  with  discarded  squamous 
epidermal  cells. 

Vessels. — The  arteries  distributed  to  the  external  auditory  canal  are  from  three 
sources :  (a)  anterior  branches  of  the  superficial  temporal  supply  the  external  por- 
tion of  the  meatus  ;  (b}  the  deep  auricular  artery,  a  branch  of  the  internal  maxillary, 
passes  to  the  deeper  portions  ;  whilst  (c~)  the  posterior  auricular  provides  branches 
for  the  posterior  and  superior  surfaces.  The  arteries  destined  for  the  interior  of  the 
canal  pierce  the  membranous  roof  of  the  cartilaginous  meatus,  the  fissures  of  Santo- 
rini  and  the  fibrous  tissue  connecting  the  cartilaginous  with  the  bony  portion  of  the 
tube.  They  form  capillary  net-works  within  the  perichondrium  and  periosteum  and, 

94 


Sis 


Ceruminous 
gland 


Cartilage 


Hair-follicle 


Coriura 


Transverse  section  of  skin  lining  cartilaginous  portion   of   external 
auditory  canal.    X  30. 


1490 


HUMAN   ANATOMY. 


External  a 
Merabrana  fl 
Depression  f< 
malleus 


Umfao 

Tympanic  membrane 


within  the  skin,  around  the  glands  and  the  hair  follicles,  some  extending  on  to 
the  upper  part  of  the  membrana  tympani.  The  deeper  veins  of  the  meatus, 
which  drain  the  bony  and  a  small  part  of  the  cartilaginous  meatus,  empty  into  the 
venous  plexus  behind  the  articulation  of  the  lower  jaw,  those  from  the  upper 
wall  of  the  meatus  extending  upward  to  join  the  venous  plexus  which  spreads  out 
over  the  skull. 

The  lymphatics  of  the  external  auditory  canal  arise  from  a  cutaneous  net-w<  >rk 
from  which  trunks  pass  in  three  general  groups,  as  do  those  of  the  auricle,  (i) 
The  trunks  of  the  posterior  group  arise  in  the  posterior  wall  of  the  external  meatus 

and  empty,  for  the  most  part,  into 

FIG.  1250-  the    posterior   auricular    (mastoid) 

nodes.  Some,  however,  avoid  this 
first  station  and  join  the  efferent 
vessels  of  the  upper  nodes  of  the 
superior  deep  cervical  chain.  (2) 
The  inferior  group  includes  a  vari- 
able number  of  trunks  coming  from 
the  lower  wall  of  the  external  audi- 
tory meatus,  some  of  which  pass  to 
the  nodes  placed  along  the  course 
of  the  external  jugular  vein  at  its 
exit  from  the  parotid,  whilst  others 
end  in  the  mastoid'  nodes.  (3) 
The  anterior  group  is  from  the 
concha  and  the  anterior  wall  of  the 
meatus.  These  vessels  are  tribu- 
tary to  the  parotid  nodes,  more 
particularly  to  the  anterior  auricular 
nodes  situated  immediately  in  front 
of  the  tragus. 

Nerves. — The  sensory  nerves 

supplied  to  the  external  auditory  canal  are  derived  from  the  auriculo-temporal 
branch  of  the  trigeminus  and  from  the  auricular  branch  of  the  pneumogastric.  The 
latter,  also  known  as  Arnold's  nerve,  perforates  the  wall  of  the  meatus  and  supplies 
its  lining  membrane. 

Practical  Considerations  :  The  Auricle. — The  auditory  mechanism  may 
be  said  to  consist  of  two  portions — that  which  conducts  the  sound  and  that  which 
receives  it.  The  former  is  represented  by  the  external  and  the  middle  ear  ;  the 
latter,  by  the  internal  ear.  The  function  of  the  auricle  is  to  collect  and  intensify 
the  sound-waves  and  to  direct  them  into  the  external  auditory  canal.  That  it 
does  not  play  a  very  important  part  in  hearing  is  shown  by  the  fact  that  its 
removal  has  been  followed  by  comparatively  little  loss  in  the  acuteness  of  hearing 
(Treves).  Complete  .absence  of  the  auricle  is  exceedingly  rare  ;  partial  defect 
(microtia}  is  more  frequent  ;  while  congenital  fisluhe  are  comparatively  common. 
These  fistulce  are  considered  to  be  due  to  a  defective  closure  of  the  first  branchial 
cleft.  According  to  His,  however,  they  are  due  to  deficient  union  of  the  crus  helicis 
and  the  crus  supratragicus.  If  a  fistula  closes  at  its  orifices,  a  retention  cyst, 
sometimes  dermoid,  may  result.  The  ear  may  be  abnormally  laryr  (  )nacrotid),  or, 
as  a  result  of  defective  union  of  the  rudimentary  tubercles  from  which  the  auricle 
is  developed,  auricular  appendages  (polyotia)  may  be  met  with.  A  supernumerary 
auricle  may  very  rarely  be  found  on  the  side  of  the  neck  at  the  orifice  of  one  of 
the  lower  branchial  clefts. 

Owing  to  the  rich  blood-supply  of  the  auricle,  wounds  heal  rapidly.  When, 
however,  they  occur  near  the  external  auditory  meatus  and  are  large,  cicatricial 
closure  of  the  canal  must  be  guarded  against. 

I' n>st-bite  is  frequent  because  of  the  exposure  to  cold  and  the  lack  of  protec- 
tion to  the  blood-vessels  from  overlying  tissues,  since  little  more  than  skin  covers 
tin -m.  An  intense  reactive  congestion  follows,  and  frequently  leads  to  gangrene. 


Cast  of  right  external  auditory  canal,  seen  from  be- 
hind ;  natural  size.  Drawn  from  cast  made  by  Professor 
Randall. 


PRACTICAL   CONSIDERATIONS  :     THE   EXTERNAL    EAR.      1491 

The  skin  is  closely  adherent  to  the  underlying  tissues,  especially  on  the  anterior 
surface,  so  that  the  exudate  is  under  much  tension,  interfering  with  the  blood- 
supply.  The  nerves  are  also  compressed,  accounting  for  the  great  pain. 

Hesmatomata  of  the  auricle  are  due  to  effusions  of  blood  between  the  cartilage 
and  its  perichondrium.  They  occur  usually  on  the  concavity  of  the  auricle  from  a 
blow,  as  in  boxers,  or  foot-ball  players.  They  may  occur  rarely,  without  traumatism, 
as  in  the  insane,  although  some  believe  that  injury  is  the  exciting  cause  in  these 
cases  ;  or  even,  in  very  exceptional  instances,  may  appear  without  precedent  trauma 
or  mental  disease.  In  those  cases  in  which  there  is  great  tension,  it  may  be  neces- 
sary to  incise  and  drain  to  prevent  necrosis. 

Of  the  tumors,  keloid,  following  punctures  for  ear-rings,  is  common  in  the 
negro  ;  capillary  naevi  are  frequent,  whilst  cirsoid  aneurism  may  occur.  Cysts  in 
connection  with  the  first  branchial  cleft  have  already  been  mentioned. 

The  External  Auditory  Canal. —  Congenital  atresia  is  rare  and  is  often 
associated  with  malformations  of  the  auricle,  the  middle  and  the  internal  ear,  so 
that  correction  of  the  external  condition  will  usually  fail  to  restore  the  hearing. 

The  length  of  the  external  meatus  is  about  i^  inches,  about  ^  inch  of  which 
is  bony  and  about  ^  inch  cartilaginous.  In  the  new-born  it  consists  of  skin  and 
cartilage  only,  and  its  lumen  is  very  small.  Owing  to  the  obliquity  of  the  tympanic 
membrane,  that  structure,  in  the  new-born,  is  in  close  contact  with  the  floor  of  the 
canal,  so  that  the  latter  must  be  drawn  away  from  the  membrane  to  expose  it.  For 
this  purpose  the  auricle  should  be  drawn  downward  and  backward.  The  skin  of 
the  cartilaginous  portion  is  supplied  with  hair,  sebaceous  and  ceruminous  glands. 
Furuncles  are  frequent,  the  infection  passing  along  the  hair-follicles  to  the  asso- 
ciated sebaceous  glands.  In  some  persons,  one  boil  follows  another  from  successive 
glandular  infection.  The  skin  of  the  bony  portion  is  thinner  than  that  of  the  car- 
tilaginous, except  in  the  posterior  part  of  the  roof,  where  a  thicker  wedge-shaped 
piece  containing  glands  extends  as  far  as  the  drum-head. 

Ceruminous  masses  often  collect,  and  frequently  contain  pathogenic  bacteria. 
They  may  press  upon  the  tympanic  membrane,  and  through  intralabyrinthine  pres- 
sure may  produce  vertigo,  or  may  lead  to  vomiting  or  convulsions.  Interference 
by  the  mass,  with  air  conduction,  may  result  in  loss  of  hearing. 

A  diffuse  infection  of  the  meatus  may  be  primary,  but  it  is  more  apt  to  be  a 
secondary  result  of  otitis  media.  In  severe  cases  the  pus  may  extend  to  the  bone 
separating  the  periosteum.  It  may  then  pass  to  the  parotid  region  through  the 
anterior  bony  wall,  but  it  is  more  likely  to  do  so  through  the  fissures  in  the  cartilag- 
inous portion.  Abscesses  in  the  parotid  region  more  frequently  extend  by  the  same 
route  in  the  reverse  direction. 

The  general  direction  of  the  canal  is  from  without  inward,  downward,  and 
slightly  forward.  The  auricle  and  cartilaginous  meatus  are  suspended  from  the 
margin  of  the  bony  portion  so  that  an  angle  is  formed  opening  downward.  For 
a  short  distance  from  the  external  orifice  the  meatus  inclines  forward.  In  the  remain- 
ing cartilaginous  portion  it  turns  backward,  while  in  the  bony  portion  it  is  again 
deflected  forward.  Therefore,  to  examine  the  tympanic  membrane  the  cartilaginous 
meatus  must  be  drawn  upward  to  correct  the  vertical  curve,  and  backward  to 
straighten  the  antero-posterior  curve. 

The  diameter  of  the  canal  is  greater  at  the  two  extremities  than  in  the  centre. 
The  smallest  diameter  in  the  bony  portion  is  at  the  inner  third,  where  foreign  bodies 
most  frequently  lodge,  which  have  been  known  to  remain  in  the  canal  for  years 
without  much  discomfiture,  or  even,  in  some  cases,  without  their  presence  being 
known.  Care  is  necessary  in  their  removal  lest  the  tympanic  membrane  be  injured. 

The  anterior  wall  of  the  meatus  is  in  relation  with  the  temporo-maxillary  articu- 
lation, and  its  bony  portion  has  been  fractured  from  blows  upon  the  lower  jaw.  The 
parotid  gland  is  in  relation  with  this  wall  as  well  as  with  the  floor,  so  that  tumors  of 
the  gland  may  narrow  or  occlude  the  canal  by  pressure.  Parotid  abscesses  opening 
into  the  canal  are  likely  to  pass  through  the  deficiencies  in  the  cartilage  (fissures  of 
Santorini).  Since  the  lower  jaw  is  in  relation  with  the  cartilaginous  as  well  as  with 
the  bony  portion  of  the  meatus,  the  former  is  drawn  forward  when  the  mouth  is 
opened.  Hence  the  mouth  is  usually  opened  when  one  listens  intently. 


1492  HUMAN   ANATOMY. 

The  posterior  wall  is  separated  from  the  mastoid  process  by  the  tympano-mas- 
toid  fissure.  The  auricular  branch  of  the  pneumogastric  (Arnold's  nerve)  passes 
through  this  fissure  to  the  posterior  wall  of  the  canal.  The  coughing,  sneezing,  or 
vomiting  that  sometimes  follows  irritation  of  the  canal,  as  from  cleaning  the  ear,  or  ex- 
amining it  with  instruments,  is  said  to  be  due  to  a  reflex  effect  upon  the  pneumogastric 
through  this  branch.  The  auriculo-temporal  branch  of  the  trigeminal  nerve  enters 
into  its  supply,  and  may  explain  the  earache  in  cancer  of  the  tongue  or  disease  of  the 
lower  teeth.  Between  the  posterior  wall  of  the  meatus  and  the  mastoid  cells  is  a 
thin  plate  of  bone  one  or  two  millimeters  in  thickness.  The  sigmoid  portion  of  the 
lateral  sinus  is  usually  about  12  mm.  back  of  this  wall,  and  the  mastoid  antrum 
about  5  mm.  posterior  to  its  deeper  portion. 

The  superior  wall,  which  is  from  4-5  mm.  in  thickness,  often  contains  air- 
cells  between  two  plates  of  compact  bone.  Pus  may  burrow  through  it  from  the 
canal  to  the  interior  of  the  cranium.  At  the  posterior  superior  angle  .of  the  canal  are 
a  number  of  small  openings  for  blood-vessels  and  some  connective  tissue  fibres, 
through  or  along  which  pus  may  find  its  way  from  the  mastoid  antrum  to  the  under 
surface  of  the  periosteum  in  the  meatus. 

THE   MIDDLE   EAR. 

The  middle  ear  includes  three  subdivisions  :  the  tympanic  cavity ,  the  Eustachian 
tube,  and  the  mastoid  cells. 

It  is  an  irregular  air-chamber,  beginning  on  the  lateral  wall  of  the  naso-pharynx 
with  the  Eustachian  tube,  which  leads  upward,  backward  and  outward,  for  about 
one  inch  and  a  half  into  the  temporal  bone.  Opposite  the  external  auditory  canal, 
it  widens  into  the  tympanic  cavity  and  continues  backward  into  the  mastoid  cells. 

THE  TYMPANIC  CAVITY. 

The  tympanic  cavity  (cavum  tympani),  also  called  the  tympanum,  is  an  irregu- 
lar space  within  the  temporal  bone,  lying  between  the  internal  ear  and  the  external 

FIG.  1251. 

Superior  ligament  Articular  surface  for  incus 

Head  of  malleus     \  __Z 

Tendon  of  tensor  tympani         \      V/"/ZI^ -     _   -/"  EP11-™1!*"110  sPace 
Posterior  semicircular  canal' 

Facial  nerve.  ^X~^-^f/^  V    -?£*         ^"Lateral  ligament 


—Handle  of  malleus 

External  auditory  canal 
•** Tympanic  membrane,  cut 


Vestibule 


Internal  auditory  canal 
Cochlea 


Promontory 
Probe  in  Eustachian  tube  Tympanic  cavity 

Frontal  section  through  right  ear,  viewed  from  behind.     X  2^. 

auditory  canal.  It  is  lined  with  mucous  membrane  and  contains,  in  addition  to  the 
air  which  enters  by  way  of  the  Eustachian  tube,  the  chain  of  ear  ossicles.  Its  short- 
est diameter,  that  between  the  middle  of  the  tympanic  membrane  and  the  wall  of  the 
labyrinth,  is  alxmt  2  mm.  The  antero-posterior  diameter  is  about  12  mm.,  whilst 
the  distance  from  the  roof  (tegmen  tympani)  to  the  floor,  the  supero-inferior  diam- 
eter, is  about  15  mm. 


THE   MIDDLE    EAR. 


H93 


The  cavity  of  the  tympanum  is  subdivided  into  three  parts  :  ( i )  the  atrium  or 
tympanic  cavity  proper;  (2)  the  cavnm  epitympanicum,  the  upper  part  of  the  space 
which  overlies  the  atrium  ;  and  (3)  the  antrum,  which  leads  into  the  mastoid  cells. 

The  atrium  (Fig.  1251)  resembles  in  shape  a  short  cylinder  with  concave 
ends,  the  outer  end  being  formed  by  the  tympanic  membrane  and  its  bony  margin, 
whilst  the  inner  end  is  formed  by  the  outer  wall  of  the  labyrinth. 

The  cavurn  epitympanicum  or  attic  occupies  the  space  between  the  atrium 
and  the  roof  and  constitutes  approximately  one-third  (about  5  mm. )  of  the  supero- 
inferior  diameter.  It  contains  the  head  of  the  malleus  and  the  body  of  the  incus 
(Fig.  1252).  It  extends  considerably  over  the  external  auditory  canal  and  is 
bounded  laterally  by  a  wedge-shaped  portion  of  the  temporal  bone,  called  the  scutum. 

The  antrum  tympanicum  is  an  irregularly  pyramidal  space  communicating 
with  the  upper  back  part  of  the  tympanicum  by  a  triangular  orifice.  Its  dimensions 
vary,  but  its  average  length  is  about  12  mm.,  its  height  8.5  mm.,  and  its  width  6.7 
mm.  It  is  larger  in  the  infant  than  in  the  adult,  and  its  lumen  is  frequently  lessened 
by  bands  of  mucous  membrane  which  stretch  across  it  and  thus  encroach  upon  the 
space.  Its  roof  is  formed  by  the  tegmen  tympani  sometimes  called  the  tegmen 
antri  in  this  location.  Its  external  wall  is  formed  by  the  squamous  portion  of  the 


FIG.  1252. 


Superior  ligament 
Superior  ligament 
Head  of  malleus 


Chorda  tympani  nerve 


Tensor  tympani 
Processus  cochleariformis 

Eustachian  tube 


•Epitympanic  space 


Process  for  stapes 


Handle  of  malleus 


Tympanic  membrane 


Inner  aspect  of  outer  wall  of   right   tympanic   cavity,  showing  incus  and   malleus  and  tympanic 

membrane  in  position.   X  2%. 

temporal  bone,  and  on  its  internal  one  is  seen  the  outer  wall  of  the  horizontal  semicir- 
cular canal.  The  thin  mucous  membrane  of  the  antrum  is  closely  united  with  the 
periosteum  and  possesses  a  layer  of  low  nonciliated  squamous  epithelium. 

The  walls  of  the  tympanic  cavity  present  many  irregularities  and  depres- 
sions and  the  boundaries  are  not  sharply  defined.  As  the  direction  of  the  supero- 
inferior  axis  of  the  cavity  is  not  perpendicular  but  oblique,  it  follows  that  the  outer 
wall,  composed  of  the  tymparric  membrane  and  its  bony  margin,  is,  accurately 
speaking,  the  infero-lateral  wall,  whilst  that  formed  by  the  labyrinth  is  the  dorso- 
mesial  wall.  For  convenience  of  description,  however,  there  may  be  recognized 
with  advantage  an  external  and  an  internal,  a  superior  and  an  inferior,  and  an 
anterior  and  a  posterior  wall. 

The  outer  wall  (paries  membranacea)  of  the  tympanic  cavity  proper  (the 
atrium)  is  formed  by  the  drum-head  and  the  margin  of  bone  into  which  it  is  inserted, 
whilst  the  outer  wall  of  the  epitympanic  space  is  formed  by  the  scutum.  In  the  infant 
the  bony  external  auditory  canal  consists  of  a  ring  of  bone,  the  annulus  tympani- 
cus.  This  ring,  incomplete  at  its  upper  anterior  part  at  the  notch  of  Rivinus, 
possesses  a  well-marked  groove,  the  sulcus  tympanicus,  for  the  reception  of  the 
tympanic  membrane.  At  the  notch  of  Rivinus,  the  tympanic  membrane  is  attached 
to  the  bony  margo  tympanicus  and  the  external  lateral  ligament  of  the  malleus,  and 
is  continuous  with  the  skin  lining  the  bony  auditory  canal. 


1494  HUMAN   ANATOMY. 

The  Membrana  Tympani. — The  tympanic  membrane  or  drum-head  is  a 
delicate  transparent  disc,  irregularly  oval  or  ellipsoidal  in  outline  and  concave  on  its 
outer  surface.  It  is  placed  obliquely  with  the  horizontal  plane,  forming  an  angle  of 
about  55°,  opening  outward.  As  the  middle  portion  of  the  membrane  is  drawn 
inward,  the  inclination  of  its  different  parts  varies.  The  obliquity  of  the  membrane 
is  about  the  same  in  the  infant  as  in  the  adult.  With  the  upper  back  wall  of 
the  external  auditory  canal  the  drum-head  forms  a  very  obtuse  angle,  whilst  with 
the  antero-inferior  wall  it  encloses  an  angle  of  about  27°.  The  longest  diameter  of 
the  membrane  is  directed  from  above  and  behind,  forward  and  downward,  and 
measures  from  9.5-10  mm.  ;  the  shortest  is  from  8.5-9  mm-  The  membrane  is 
about .  10  mm.  thick,  except  at  the  periphery,  where  it  is  thickened.  Like  the  rest  of 
the  tympanum  and  the  labyrinth,  it  is  practically  as  large  in  the  infant  as  in  the  adult. 

Embedded  in  the  tympanic  membrane  is  the  handle  of  the  malleus  (Fig.  1252), 
which  extends  from  a  point  near  its  middle,  upward  and  forward  toward  its 
periphery,  and  ends  at  the  short  process.  At  its  lower  end,  the  handle  of  the 
malleus  is  flattened  laterally  and  broadened  at  the  umbo,  which  corresponds  to  the 
deepest  part  of  the  concavity  of  the  membrane.  The  short  process  of  the  malleus 
forms  a  conspicuous  rounded  projection  at  the  antero-superior  part  of  the  drum- 
head. Extending  from  the  short  process  of  the  malleus  to  the  anterior  and 
posterior  ends  of  the  tympanic  ring  are  two  straight  striae.  The  part  of  the 
drum-head  included  between  these  striae  and  the  Riviniah  notch  is  known  as  the 
membrana  flaccida  (pars  flaccida)  or  Shrapnell's  membrane.  It  is  thinner 
and  less  tense  than  the  remaining  larger  part  of  the  drum-head  which  is  called  the 
membrana  tensa  (pars  tensa). 

The  inner  aspect  of  the  drum-head  presents  two  folds  of  mucous  membrane  which 
stretch  horizontally  backward  and  forward  to  the  annulus  and  form  an  anterior  and  a 
posterior  inverted  pocket.  The  anterior  pocket  contains  in  its  wall,  in  addition  to  the 
mucous  membrane,  the  long  process  of  the  malleus,  the  chorda  tympani  nerve  and 
the  inferior  tympanic  artery,  the  nerve  also  running  along  the  lower  border  of  the 
posterior  fold. 

The  structure  of  the  tympanic  membrane  includes  three  main  layers :  ( i )  the  middle 
fibrous  stratum,  or  membrana  propria  ;  ( 2 )  the  external  cutaneous  layer,  the  prolongation  of 
the  skin  lining  the  external  auditory  canal ;  and  ( 3 )  the  internal  mucous  membrane,  a  continua- 
tion of  the  mucous  membrane  clothing  other  parts  of  the  tympanic  cavity. 

The  fibrous  layer  or  membrana  propria  represents  the  mesoblastic  portion  of  the  drum-head 
and  consists  of  an  outer  stratum  of  radially  disposed  fibres  which  diverge  from  the  malleus 
towards  the  periphery  of  the  membrane,  and  an  inner  stratum  of  circular  fibres,  concentrically 
arranged  and  best  developed  near  the  periphery  of  the  membrane  but  absent  at  the  umbo.  The 
radiating  fibres,  on  the  contrary,  become  more  dense  at  the  umbo,  partly  through  accumulation 
and  partly  through  splitting  (Gerlach).  Between  the  fibres  of  the  two  layers  are  seen  connect- 
ive tissue  corpuscles  which  are  spindle-shaped  in  longitudinal  and  stellate  in  cross-section. 

The  membrana  propria  is  absent  within  the  pars  flaccida  or  Shrapnell's  membrane.  At  the 
periphery  of  the  membrana  propria,  the  fibres,  especially  those  of  the  radial  stratum,  are  con- 
nected with  those  of  a  ring  of  thick  connective  tissue,  the  annulus  fibrosus  which  occupies  the 
sulcus  tympanicus.  The  fibres  of  the  annulus  fibrosus  run  in  various  directions,  but  for  the 
most  part  radially,  that  is,  toward  the  tympanic  membrane  proper  (Fig.  1253) .  Round  cells  are 
found  between  these  fibres. 

The  cutaneous  layer  consists  of  a  thin  epidermal  stratum,  composed  of  two  or  three  rows 
of  cells  and  a  delicate  sheet  of  connective  tissue,  but  neither  a  definite  corium  nor  papillae  are 
present.  A  thickened  band  of  subepithelial  connective  tissue  extends  across  Shrapnell's  mem- 
brane and  along  the  handle  of  the  malleus  and  contains  the  large  vessels  and  nerves  which  pass 
from  the  meatus  to  the  membrana  tympani. 

The  mucous  membrane  cove-ring  the  inner  surface  of  the  drum-head  consists  of  a  scanty 
layer  of  connective  tissue,  invested  with  a  sheet  of  large  low  nonciliated  epithelial  cells. 

The  vessels  of  the  tympanic  membrane  include  arteries  which  are  arranged  as  an  outer  and 
inner  set,  separated  by  the  membrana  propria.  The  former  set  is  derived  from  the  deep  auricu- 
lar branch  of  the  internal  maxillary  artery  ;  the  latter  from  the  tympanic  branch  of  the  internal 
maxillary  and  from  the  stylo-mustoid  branch  of  the  posterior  auricular.  Each  of  these  sets 
forms  a  plexus  of  vessels  with  a  large  branch  extending  downward  along  the  malleus  handle, 
and  another  around  the  periphery  of  the  membrane,  these  two  branches  being  connected  by 
numerous  radiating  twigs.  Perforating  vessels  connect  the  two  sets  of  arteries,  especially  along 


THE  MIDDLE  EAR. 


H95 


the  malleus  handle  and  at  the  periphery  of  the  membrane.  The  veins  are  most  numerous  at  the 
handle  of  the  malleus  and  periphery  of  the  membrane  and  communicate  with  those  of  the  exter- 
nal meatus  and  tympanic  cavity. 

The  lymphatics  are  arranged  similarly  to  the  blood-vessels  in  two  sets,  one  under  the  skin 
and  the  other  under  the  mucous  membrane.  They  communicate  freely  with  each  other  and 
probably  empty  partly  into  the  lymph-nodes  situated  over  the  mastoid  process  and  in  the 
region  of  the  tragus,  and  partly  into  the  lymph-tracts  of  the  Eustachian  tube  and  thence  event- 
ually into  the  retropharyngeal  and  deep  cervical  nodes. 

FIG.  1253. 


Epithelium  of  tympanic 
surface 


Circular  fibres 
Radial  fibres 


Mucous  membrane 


Blood-vessels 


Epidermis  of  drum-head 
Subepidermal  layer 
External  auditory  canal 

Epidermis  of  canal 


Corium  of  skin  lining 
canal 

'_ Epidermis  passing  onto 

drum-head 


Bone 


Radial  fibres  of  annulus 
fibrosus 


Section  through  attached  margin  of  tympanic   membrane,  showing  continuation  of   skin  and  mucous  membrane 
over  its  outer  and  inner  surfaces  respectively.     X  75-     Drawn  from  preparation  made  by  Dr.  Ralph  Butler. 

The  nerves  supplying  the  tympanic  membrane  are  derived  chiefly  from  the  auriculo-tem- 
poral  branch  of  the  trigemlnus,  supplemented  by  twigs  from  the  tympanic  plexus  and  by  the 
auricular  branch  of  the  vagus.  They  accompany,  for  the  most  part,  the  blood-vessels  and,  in 
addition  to  supplying  the  latter,  form  both  a  subcutaneous  and  a  submucous  plexus. 

The  inner  wall  (paries  labyrinthica)  of  the  tympanic  cavity  separates  it  from 
the  internal  ear.  It  presents  for  examination  a  number  of  conspicuous  features. 

The  promontory  appears  as  a  well-marked  bulging  of  the  inner  wall  near  its 
middle  (Fig.  1254)  and  corresponds  to  the  first  turn  of  the  cochlea.  The  branches 
of  the  tympanic  plexus  are  found  in  the  mucous  membrane  covering  it.  At  the 
bottom  of  a  niche,  whose  anterior  border  is  formed  by  the  lower  posterior  margin 
of  the  promontory,  lies  the  round  window  (fenestra  cochlea).  It  is  closed  by 
the  secondary  tympanic  membrane  (membrana  tympani  secundaria),  which 
separates  the  tympanic  cavity  from  the  scala  tympani  of  the  cochlea  (Fig.  1259). 
The  membrane  is  attached  in  an  obliquely  placed  groove,  is  slightly  concave 
toward  the  tympanum,  and  measures  from  1.5—3  mm-  m  diameter.  The  oval 
window  (fenestra  vestibuli)  lies  at  the  bottom  of  a  depression,  the  fossula 
vestibuli,  in  the  upper  back  part  of  the  inner  wall,  above  the  round  window,  and 
leads  into  the  vestibule.  It  is  somewhat  kidney-shaped,  its  upper  border  being 
concave,  its  lower  slightly  convex.  In  the  recent  state  the  oval  window  is  closed 
by  the  foot-plate  of  the  stapes  and  the  ligament  which  connects  the  ossicle  with 
the  sides  of  the  window  (Fig.  1260).  The  longest  diameter  of  the  latter  is 
about  3  mm.  and  its  shortest  1.5  mm.  Abov~  the  oval  window  a  well-marked 


1496 


HUMAN   ANATOMY. 


ridge  indicates  the  position  of  the  facial  canal  or  aqueductus  Fallopii.  This 
ridge  is  bordered  posteriorly  and  superiorly  by  the  elevation  which  corresponds  to 
the  wall  of  the  horizontal  semicircular  canal  ( prominentia  canalis  semicircularis  later- 
alis).  The  sinus  tympani,  a  well-marked  depression,  is  behind  the  promontory, 
between  the  niche  of  the  round  window  and  the  pyramid,  below  and  behind  the 
oval  window.  It  is  separated  from  the  fossulae  of  the  two  windows  by  bony  ridges. 
It  varies  in  depth  from  2-5  mm. ,  with  a  vertical  diameter  of  from  2-6  mm. 

The  superior  wall  (paries  tegmentalis)  is  formed  by  a  plate  of  bone,  the  teg- 
men  tympani,  which  is  a  part  of  the  upper  and  anterior  surface  of  the  petrous 
portion  of  the  temporal  bone.  Posteriorly  it  forms  the  roof  of  the  antrum  tympani- 
cum,  and  anteriorly  contributes  the  roof  of  the  canal  for  the  tensor  tympani  muscle 
and  of  the  adjoining  part  of  the  Eustachian  tube.  It  varies  in  thickness  and  may  be 
defective  to  a  large  extent  from  atrophy  or  arrested  development. 

The  inferior  wall  (paries  jugularis),  narrower  than  the  superior,  separates  the 
typanum  from  the  jugular  fossa.  Its  bony  plate  may  be  incomplete  and  may  lie 
considerably  below  the  level  of  the  membrana  tympani. 

The  anterior  wall  (paries  carotica)  separates  the  tympanum  from  the  carotid 
artery  and  at  times  presents  a  fissure.  At  its  upper  part  is  the  irregular  trian- 
gular opening  of  the  Eustachian  tube  and  above  this  opening  lies  the  small  canal  for  the 


Outer  end  of  horizontal 
part  of  facial  canal 


Stapes  lying  in 

oval  window 

Stapedius  muscle 

Round  window 


Facial  canal 


FIG.  1254. 


Promontory 

Tensor  tympani 


Eustachian  tube 


Outer  aspect  of  inner  wall  of  right  tympanic  cavity ;  stapes  lies  within  oval  window.    X  zj^. 

tensor  tympani  muscle.  The  canaliculus  caroticus  tympanicus  perforates  the  anterior 
wall  just  below  the  mouth  of  the  Eustachian  tube,  and  transmits  the  tympanic  branch 
of  the  internal  carotid  artery  and  carotico-tympanic  nerves. 

The  posterior  wall  (paries  mastoidea)  of  the  tympanum  at  its  upper  part  is 
occupied  by  the  antrum  tympanicum,  which  leads  into  numerous  irregular  cavities, 
the  mastoid  cells.  At  the  lower  border  of  the  antrum  is  a  saddle-shaped  notch,  the 
fossa  incudis,  which  lodges  the  short  process  of  the  incus.  Extending  forward 
from  the  posterior  wall,  on  a  level  with  the  lower  border  of  the  oval  window,  projects 
the  small  bony  elevation,  the  pyramid  (eminentia  pyramidalis),  which  encloses  the 
stapedius  muscle  (Fig.  1254).  Its  apex  is  pierced  by  a  small  round  opening  for 
the  exit  of  the  stapedius  tendon.  The  canal  within  this  eminence  communicates 
posteriorly  with  the  facial  canal.  On  a  level  with  the  eminentia  pyramidalis,  close 
to  the  posterior  margin  of  the  drum-membrane,  lies  the  apcrtura  tympanica  canaliculi 
chordae  tympani,  the  opening  through  which  the  chorda  tympani  nerve  enters  the 
middle  ear. 

THE  CONTENTS  OF  THE  TYMPANUM. 

The  Auditory  Ossicles. — Three  small  bones  (ossicula  auditus)  form  a  chain 
extending  across  the  upper  part  of  the  tympanum  from  the  tympanic  membrane  to 
the  labyrinth.  The  outermost  of  these,  the  malleus  (hammer),  is  attached  to  the 
tympanic  membrane  ;  the  innermost,  the-  .v/W/V.v  (stirrup),  is  fixed  in  the  oval  window, 
and  between  these  two  bones  and  connected  with  both  of  them,  lies  the  third  link  in 
the  chain,  the  incus  (anvil). 


THE   MIDDLE   EAR. 


1497 


The  malleus  (hammer)  is  about  8  mm.  long  and  consists  of  a  head,  a  neck  and  three 
processes.  The  head  is  the  upper  club-shaped  portion,  lying  in  the  epitympanic  space  ;  the 
constricted  portion  just  below  the  head  is  the  neck,  and  below  this  is  a  prominence  to  which 
the  three  processes  are  attached  The  posterior  surface  of  the  head  bears,  for  the  articulation 
with  the  incus,  an  oblong  depressed  surface  with  prominent  margins  extending  in  a  spiral 
manner  downward  and  inward  to  the  neck.  This  articular  surface  consists  of  two  principal 
facets  separated  by  an  oblique  ridge,  the  upper  facet  looking  backward,  the  lower,  inward. 
The  axis  of  the  head  forms  with  that  of  the  handle  an  angle  of  about  140°,  opening  upward 
and  inward. 


FIG.   1255. 


Read 
/  Articular 


Head 


Point  of  insertion  of 
lateral  ligament 


Manubrium 


"Processus  gracilis 


Manubrium 


Right  malleus  \A,  seen  from  behind;  B,  seen  from  in  front.  X 


The  manubritiin  (handle),  a  tapering  process  extending  downward  backward  and  inward, 
is  embedded  in  the  substance  of  the  tympanic  membrane  (Fig.  1255).  Near  the  upper  part 
of  the  inner  anterior  surface  of  the  handle  is  sometimes  found  a  slight  projection  for  the 
insertion  of  the  tensor  tympani  muscle.  The  lower  end  of  the  manubrium  is  spatula  shaped, 
flattened  transversely.  The  long  process  is  directed  toward  the  Glaserian  fissure,  whilst  the 
short  process  looks  toward  the  external  meatus. 

The  processus  brevis  (short  process)  is  a  small  conical  elevation  situated  at  the  upper  end 
of  the  handle,  below  the  neck  of  the  malleus.  Like  the  handle  it  is  attached  to  the  tympanic 
membrane  and  covered  by  a  layer  of  cartilage,  notably  on  its  external  surface. 

The  processus  gracilis  (long  process)  arises  from  the  anterior  angle  of  the  internal  surface 
of  the  neck,  close  to  the  base  of  the  short  process,  and  extends  downward  and  forward  to  the 
Glaserian  fissure.  It  is  well  developed  in  the  foetus  and  in  young  children,  but  is  often  rudi- 
mentary in  the  adult. 

FIG.  1256. 


Body 


Upper  facet — 
Lower  facet 

I'rocessus  longiis 


Right  incus;  A,  lateral;  />,  anterior  aspect.  "X  41A. 


_Processus 
brevis 


Processus 
orbicularis 


The  incus  (anvil)  resembles  a  molar  tooth  with  two  widely  separated  fangs,  rather  than  an 
anvil.  It  consists  of  a  body,  a  long  process  and  a  short  process.  The  body  of  the  incus  has 
two  main  facets  on  its  anterior  and  antero-external  surfaces,  which  correspond  to  those  on  the 
head  of  the  malleus  and  articulate  with  them.  The  processus  brevis  (short  process)  is  conical 
in  shape,  flattened  laterally  and  projects  nearly  horizontally  backward  to  a  depression  in  the 
posterior  wall  of  the  tympanum  at  the  entrance  of  the  antrum,  where  its  apex  is  attached.  The 
processus  longus  (long  process)  runs  downward  and  backward,  behind  and  nearly  parallel  with 
the  handle  of  the  malleus,  and  forms  nearly  a  right  angle  with  the  short  process.  At  its  lower 
end  it  is  bent  inward  and  narrowed,  or  constricted,  into  a  neck,  which  terminates  in  a  rounded 
tubercle,  the  processus  orbicularis,  that  articulates  with  the  head  of  the  stapes.  In  the  fu-tus 
this  process  is  separated  from  the  rest  of  the  long  process. 


1498 


HUMAN   ANATOMY. 


The  stapes  (stirrup),  as  its  name  implies,  is  stirrup-shaped  and  consists  of  a  head,  neck, 
two  crura  and  a  base  or  foot-plate.  The  external  surface  of  the  small  rounded  head  is  hollowed 
out  for  articulation  with  the  orbicular  process  of  the  incus.  Just  below  this  is  the  constricted 
neck,  from  which  the  two  crura  diverge  to  become  attached  to  the  foot-plate  near  its  lower 


FIG.   1257. 


Upper  edge 


Posterior 
Lower  edge 


Foot-plate 
Right  stapes,  A,  seen  from  above;  B,  mesial  surface  of  foot-plate.  X  4^. 

margin.  The  anterior  crus  is  shorter  and  straighter  than  the  posterior,  both  being  slightly 
curved.  The  fool-plate  consists  of  a  lamina  of  bone  and  corresponds  to  the  bean-shape  of  the 
oval  window,  into  which  it  neatly  fits.  The  upper  edge  of  the  foot-plate  is  convex  ;  its  lower 
edge  is  almost  straight,  being  si ightly.  hollowed  out  near  its  middle. 

Articulations  of  the  Ossicles. — In  the  malleo-incudal  joint,  both  articular  surfaces  are 
covered  with  a  thin  layer  of  hyaline  cartilage.  The  fairly  well-developed  capsular  ligament, 
reinforced  mesially,  is  fastened  to  the  depressed  margins  of  the  articular  surfaces.  A  wedge- 
shaped  meniscus  of  fibre-cartilage  projects  from  the  superior  wall  of  the  capsule  between  the 


FIG.  1258. 


layers  of  hyaline  cartilage.  "When  the 
manubrium  handle  moves  inward,  its 
lower  cog  catches  the  corresponding  cog 
of  the  incus  and  the  long  process  of  the 
latter  must  follow.  If  the  handle  moves 
outward,  the  lower  cog  moves  away 
from  the  incus  and  the  latter  moves  but 
little"  (Politzer). 

The  articulation  of  the  incus  and 
stapes  is  a  very  delicate  but  true  joint. 
Both  the  slightly  convex  surface  of  the 
lenticular  process  of  the  incus  and  the 
slightly  concave  surface  of  the  head  of 
the  stapes  are  covered  with  hyaline  car- 
tilage and  united  by  a  capsular  ligament 
made  up  largely  of  elastic  fibres  and 
thickened  on  the  posterior  surface. 
Sometimes  a  meniscus  of  fibro-cartilage 
separates  the  two  articular  surfaces. 

The  articulation  of  the  stapes  and 
oval  window  is  effected  by  the  margins 
of  the  window  and  the  foot-plate  of  the 
stapes.  These  surfaces,  as  well  as  the 
vestibular  aspect  of  the  stapes,  are  cov- 
ered with  a  layer  of  hyaline  cartilage. 
The  cartilage  of  the  foot-plate  and  that 
of  the  window  are  connected  by  a  liga- 
ment of  elastic  fibres,  forming  a  syn- 
chondrosis. 

In  addition  to  the  ligaments  con- 
cerned in  the  foregoing  articulations, 
four  bands  attach  ossicles  to  the  tym- 
panic walls  and  prevent  their  excessive 

Frontal  section  passing  through  malleus  and  tympanic  membrane,      movement;  of  these,  three   Connect   the 
60.     Drawn  from  preparation  made  by  Dr.  Ralph  Butler.  m;lneus  and  one  the  incus. 

1.  The  superior  ligament  of  the  malleus  extends  from  the  legmen  tympani  to  the  head  of 
the  malleus. 

2.  The  anterior  ligament  of  the  malleus  is  a  strong,  broad,  fibrous  band  arising  from  the 
anterior  part  of  tin.-  head  and  neck  of  the  malleus.     Some  of  its  fibres  are  attached  to  the  ante- 
rior end  of  the  annulus  tympanicus  (spina  tympana  -a  major }  and  other  fibres  pass  through  the 
<  ilaserian  fissure  to  become  attached  to  the  spine  of  the  sphenoid.     These  fibres  correspond  to  the 
remains  of  the  embryonic  process  of  Meckel  of  the  malleus  and  envelop  the  processus  gnu  ills. 


Sup.  ligament 

Head 

External  ligament 

Mem.  flaccida  or 

Schrapnell's  membrane 

Prussak's  space 

Neck 

Short  process 

Chorda  tympanum 

Tendon  of  tensor 
tympani 

Handle 

Cartilage 

Epithelium  of  epidermis 

Mcmhrana  propria 

-Mucous  membrane 
Membrana  tensa 


Annulus  tendinosus 


THE   MIDDLE    EAR. 


1499 


3.  The  lateral  ligament  of  the  malleus  is  somewhat  fan-shaped  and  extends  between  the 
roughened  neck  of  the  malleus  and  the  external  wall  of  the  tympanum  above  the  Rivinian  notch. 
The  posterior  fibres  of  this  ligament  are  called  the  posterior  ligament  of  the  malleus  ( Helmholtz) , 
and,  together  with  the  fibres  of  the  anterior  ligament  lying  in  the  same  plane,  form  the  "  axis- 
ligameiit  of  the  malleus,"  since  the  axis  on  which  the  malleus  turns  passes  through  the  attach- 
ment of  these  two  fibrous  structures. 

4.  The  posterior  ligament  of  the  incus  extends  from  the  apex  of  the  short  process  of  the 
incus  to  the  tympanic  wall  at  the  lower  part  of  the  mouth  of  the  antrum.     It  is  fan-shaped,  the 
incudal  attachment  being  less  extensive  than  that  of  the  tympanic.     The  end  of  the  short 
process  is  covered  with  hyaline  cartilage. 

The  Intratympanic  Muscles. — The  muscles  within  the  tympanum  connected  with  the 
ossicles  (musculi  ossiculorum  auditus)  are  :  (i )  the  tensor  tympani  and  (2)  the  stapedins. 

The  tensor  tympani  is  a  diminutive  spindle-shaped  muscle,  about  1.25  cm.  long,  lying  in  the 
bony  canal  directly  above  the  osseous  part  of  the  Eustachian  tube,  from  which  it  is  partly 

FIG.  1259. 


Facial  nerve 


Ramus  utriculus 
ampulla  ris 


Utricle  — 


Foot  of  stapes 


Cisternaperi-      >/ 
lymphatica 

Lowest  part  of 
spiral  lamina 

Beginning  of 
posterior 
ampulla 


Secondary  tym- 
panic membrane 


Stapedius 
muscle 


External 


ii     auditory  canal 

• 

3*1  \<    Handle  of 
malleus 

jj —  Promontory 


Drum-head  or 

tympanic 

membrane 


Tympanic  cavity 


Vertical  section  through  human  middle  and  internal  ear. 


Drawn  from  preparation  made  by  Dr.  Ralph  Butler. 


separated  by  the  bony  scroll,  the  processiis  cochleariformis.  The  posterior  fibres  arise  from 
the  top  of  the  cartilage  of  the  Eustachian  tube  and  the  adjoining  part  of  the  great  wing  of  the 
sphenoid.  Some  of  the  fibres  are  connected  with  the  tensor  palati  muscle  and  others  arise 
from  the  wall  of  the  canal  which  the  muscle  occupies.  The  fibres  converge  in  a  feather-like 
manner  to  the  tendon,  which  begins  within  the  muscle  about  the  middle  of  the  canal,  and,  pass- 
ing through  the  tympanic  opening  of  the  canal,  turns  at  nearly  a  right  angle  over  the  end  or 
rostrum  of  the  processus  cochleariformis  to  be  inserted  into  the  anterior  part  of  the  inner 
margin  of  the  malleus-handle  just  below  the  short  process.  The  tendon  is  almost  per- 
pendicular to  the  plane  of  the  tympanic  membrane,  is  oblique  to  the  long  axis  of  the  manu- 
brium  and  is  enveloped,  along  with  the  muscle-belly,  in  a  fibrous  sheath.  The  tensor  tympani 
and  tensor  palati  muscles  receive  their  nerve  supply  from  the  same  source,  namely,  the  trigem- 
inus,  through  the  otic  ganglion. 

The  stapedius  muscle  lies  within  the  triangular  canal  of  the  eminentia  pyramidalis,  arising 
from  its  floor  and  sides.  Its  fibres  converge  to  the  tendon,  which,  passing  through  the  opening 
at  the  apex  of  the  canal,  extends  forward,  slightly  upward,  and  outward,  to  be  inserted  into  the 
lower  posterior  part  of  the  head  of  the  stapes.  Some  of  the  fibres  of  the  tendon  also  pass  to  the 


1500 


HUMAN   ANATOMY. 


lenticular  process  and  the  capsular  ligament.  The  tendon  is  frequently  enveloped  in  a  fold  of 
mucous  membrane.  A  branch  of  the  facial  nerve  passes  through  a  small  orifice  between  the 
Fallopian  canal  and  the  canal  for  the  stapedius  to  supply  this  muscle. 

Movements  of  the  Ossicles. — When  the  tympanic  membrane  and  malleus-handle  are  moved 
inward,  the  long  process  of  the  incus  is  also  moved  inward  and  pushes  the  head  of  the  stapes 
inward,  and  slightly  upward.  This  causes  pressure  upon  the  liquid  within  the  labyrinth,  and, 
since  the  bony  walls  of  the  labyrinth  are  inelastic,  the  membrane  of  the  round  window  is  bulged 
outward.  As  the  tympanic  membrane  regains  its  normal  position,  these  movements  are  re- 
versed. When  on  the  other  hand  the  tympanic  membrane  is  moved  outward,  the  movement  of 
the  long  process  of  the  incus  is  very  slight  because  of  the  unlocking  of  the  malleo-incudal  articu- 
lation. Contraction  of  the  tensor  tympani  muscle  draws  the  centre  of  the  tympanic  membrane 
inward  and  in  this  way  increases  the  tension  of  the  membrane  and  of  the  posterior  part  of 
the  axial  ligaments  of  the  malleus,  especially  of  its  external  ligament.  Contraction  of  the 
stapedius  muscle  pulls  the  head  of  the  stapes  backward,  thus  tilting  the  anterior  end  of  the 
foot-plate  outward,  the  posterior  end  acting  as  a  fulcrum. 

The  Mucous  Membrane  of  the  Tympanum. — The  tympanic  cavity  is 
lined  by  a  thin  transparent  mucous  membrane,  closely  adherent  to  the  periosteum 
and  continuous  with  that  of  the  Eustachian  tube  and  naso-pharynx  anteriorly,  and, 

FIG.  1260. 


Posterior  crus  of       •'£? 
stapes 


Lower  end  of 
incus 


Malleus  handle 


Cochlear  nerve 


Basal  turn  of 
cochlea 


Tympanic  cavity 


Horizontal  section  through  human  middle  and  internal  ear;  stapes  occludes  oval  window.     X  51A.     Drawn  from 

preparation  made  by  Dr.  Ralph  Butler. 


with  that  of  the  mastoid  cells  posteriorly.  It  covers  the  ossicles  and  their  ligaments, 
the  muscles,  the  tendons  and  the  chorda  tympani  nerve,  and  forms  a  number  of  folds 
extending  across  the  cavity.  These  folds  vary  in  location,  direction  and  number, 
and  form  pouches  within  the  tympanum. 

The  attic  is  divided  into  an  external  and  an  internal  compartment  by  the  incus, 
the  head  of  the  malleus,  the  superior  ligament  of  the  malleus  and  the  superior  mallco- 
tncudal  fold  of  mucous  membrane.  The  external  compartment  is  bounded  on  the 
outer  side  by  the  external  tympanic  wall,  and  is  itself  subdivided  into  a  superior  and 
an  inferior  space  by  the  external  ligament  of  the  malleus.  The  inferior  division  is 
called  Prussak's  space  and  is  hounded  externally  by  Shrapnell's  membrane,  inter- 
nally by  the  neck  of  the  malleus,  interiorly  by  the  short  process  of  the  hammer,  and 
superiorly  by  the  external  ligament  of  the  malleus  (Fig.  1258).  A  number  of 


THE   MIDDLE   EAR.  1501 

inconstant  folds  of  mucous  membrane,  extend  from  the  wall  of  the  tympanum  to 
the  malleus  and  the  incus.  The  most  constant  of  these  is  the  outer  malleo-incudal 
plica,  which  stretches  backward  to  the  posterior  ligament  of  the  incus.  Additional 
folds  frequently  extend  between  the  cura  of  the  stapes  and  from  them  to  the  wall 
of  the  tympanum. 

The  epithelium  of  the  tympanic  mucosa  varies  in  different  parts  of  the  cavity. 
Over  the  promontory,  the  ossicles  and  the  tympanic  membrane,  it  consists  of  a  single 
layer  of  low  cuboidal  nonciliated  cells,  whilst  over  the  other  parts  the  cells  are  ciliated 
columnar  in  type.  Small  tubular  glands  occur  within  the  lining  of  the  anterior  part 
of  the  cavity.  The  subepithelial  connective  tissue,  which  supports  the  vessels  and 
nerves,  comprises  two  layers,  the  outer  forming  the  periosteum  of  the  bony  wall. 

The  secondary  tympanic  membrane  closing  the  fenestra  cochleae,  bulges 
somewhat  toward  the  cochlea  and  is  attached  to  the  bony  crest  or  ridge  of  the  win- 
dow by  its  widened  rim.  It  consists  of  three  layers,  of  which  the  middle  one  is  a 
middle  fibrous  lamina  propria,  which  is  covered  on  the  tympanic  surface  by  mucous 
membrane,  and  on  the  other  side  by  an  extension  of  the  lining  of  the  perilymphatic 
space.  The  lamina  propria  is  composed  of  radially  disposed  bundles  of  fibrous 
tissue.  The  outer  mucous  stratum  is  formed  of  a  thin  fibrous  tunica  propria, 
invested  by  a  single  layer  of  flattened  nonciliated  epithelial  cells,  similar  to  those 
covering  the  neighboring  promontory.  The  innermost  stratum  of  the  membrane 
includes  a  thin  layer  of  subendothelial  fibrous  tissue,  over  which  stretches  a  layer  of 
endothelial  plates. 

Vessels  and  Nerves  of  the  Tympanum. — The  arteries  supplying  the 
tympanic  cavity  are  from  five  sources. 

1.  The  stylo-mastoid  branch  of  the  posterior  auricular  artery  passes  through  the 
stylo-mastoid  foramen  and  the  Fallopian  aqueduct,  and  sends  a  branch  to  the  sta- 
pedius  muscle  and  three  branches  to  the  posterior  part  of  the  tympanic  cavity.     One 
of  these  passes  to  the  floor,  one  through  the  canal  for  the  chorda  tympani  nerve,  and 
one  to  the  posterior  part  of  the  oval  window. 

2.  The  tympanic  branch  of  the  internal  maxillary  artery  enters  the  tympanic 
cavity  through  the  Glaserian  fissure  and  supplies  the  anterior  part  of  the  cavity, 
including  the  anterior  ligament  of  the  malleus,  the  processus  gracilis  and  the  tympanic 
membrane. 

3.  The  middle  meningeal  branch  of  the  internal  maxillary  artery  sends  a  branch 
through  the  hiatus  Fallopii  to  anastomose  with  the  stylo-mastoid  artery,  a  branch 
through  the  canaliculus  tympanicus  to  the  promontory,  and  a  branch  to  the  tensor 
tympani  muscle. 

4.  The  ascending  pharyngeal  sends  branches  to  the  floor  and  the  promontory, 
one  of  them  accompanying  Jacobson's  nerve. 

5.  The  internal  carotid  artery  in  its  passage  through  the  carotid  canal  gives  off 
branches  to  the  anterior  wall  of  the  tympanic  cavity. 

The  veins  follow,  in  a  general  way,  the  course  of  the  arteries.  They  are  tribu- 
tary to  the  middle  meningeal,  the  pharyngeal  plexus  and  the  jugulars. 

The  lymphatics  arise  from  a  net- work  within  the  mucous  membrane  and  end 
chiefly  in  the  retropharyngeal  and  the  parotid  nodes. 

The  nerves  supplying  the  mucous  membrane  of  the  tympanum  are  branches 
from  the  tympanic  plexus  formed  by  the  tympanic  branch  of  the  glosso-pharyngeal 
nerve,  in  conjunction  with  sympathetic  filaments  from  the  net-work  accompanying  the 
carotid  artery.  The  tensor  tympani  muscle  receives  its  supply  from  the  trigeminus; 
the  stapedius  muscle  from  the  facial.  Although  the  chorda  tympani  nerve  has  an 
intimate  topographical  relation  to  the  space,  which  it  traverses  close  to  the  outer 
wall,  it  gives  no  filaments  to  the  structures  within  the  tympanum. 

THE  EUSTACHIAN  TUBE. 

The  Eustachian  tube  (tuba  auditivaj  is  a  canal,  partly  bony  and  partly  cartilagi- 
nous, extending  from  the  lateral  wall  of  the  naso-pharynx  backward,  upward  and  out- 
ward to  the  anterior  part  of  the  tympanum.  In  the  adult  it  measures  about  37  mm. 
(il/2  in.y  in  length,  of  which  approximately  the  upper  third  (tympanic  portion^ 


1502 


HUMAN   ANATOMY. 


belongs  to  the  bony  division,  whilst  the  remainder  is  contributed  by  the  cartilaginous 
division  of  the  tube.  With  the  sagittal  plane  it  forms  an  angle  of  45°,  and  with  the 
horizontal  plane  one  of  about  33°.  With  the  long  axis  of  the  external  auditory 
canal  it  forms  an  angle  of  from  i35°-i45°,  opening  outward.  The  cartilaginous  and 
bony  divisions  of  the  tube  do  not  lie  exactly  in  the  same  plane,  but  join  at  a  very 
obtuse  angle  opening  outward.  The  tube  has  somewhat  the  shape  of  an  hour  glass, 
being  wider  at  the  ends  and  narrowed  at  the  junction  of  the  cartilaginous  and  bony 
portions  into  the  isthmus,  where  its  height  is  about  3  mm.  and  its  breadth  about  half 
as  much. 

The  osseous  or  tympanic  portion  (pars  ossea)  about  12  mm.  long,  is  bounded 
above  by  the  tegmen  tympani  and  the  canal  for  the  tensor  tympani  muscle,  from 
which  it  is  incompletely  separated  by  the  processus  cochleariformis.  Below  and 
internal  to  it  lies  the  canal  for  the  carotid  artery.  Its  lumen  is  irregularly  triangular 
in  cross-section. 


FIG.  1261. 


Tympanic  membrane 
Tympanic  cavity 

Ant  ram 
Condyle  of  jaw 


Basilar  process 


External  audi- 
tory canal 

Parotid  gland 

Fossa  of  Kosen- 

muller 

Cartilage  of. 

EuStachian  tube 

1  list. i<  hi, in  tube 


Levator  palati 
Tensor  palati 
Hamular  process 

Palatal  raphe 
Palatal  rugae 


Internal  auditory  canal 

Right  internal  carotid  artery 


Incisor  canal 

Incisi%'e  pad 


-Tympanic  membrane 
External  auditory 
meatus 

Parotid  gland 
External 
pterj'goid  muscle 

Ramus  of  jaw 
Internal  pterygoid 
muscle 
•Soft  palate 

Masseter  muscle 


.Vestibule 


Buccinator  muscle 


Anterior  part  of  section  through  hend  at  plane  shown  in  small  outline  figure,  viewed  from  below ;    left 
Eustachian  tube  exposed  throughout  its  length.     Drawn  from  preparation  made  by  Professor  Dwight. 

The  cartilaginous  or  pharyngeal  portion  (pars  cartilaginea)  is  about  25 
mm.  (i  In.)  in  length  and  attached  to  the  rough  oblique  margin  of  the  anterior 
end  of  the  osseous,  portion  of  the  tube. 

Its  posterior  wall  is  formed  by  a  plate  of  cartilage  Ccartilago  tubac  auditivae),  the 
upper  margin  of  which  is  curled  outward  upon  itself  to  form  a  guttrr,  which  appears 
as  a  hook  on  transverse  section,  whose  inner  and  outer  plates  are  known  as  the 
mesial  and  lateral  lamina  respectively.  The  interval  between  the  margins  of  this 
cartilagjnous  groove  presents  outward  and  forward  and  is  rilled  up  with  a  strong 
fibrous  membrane,  thus  completing  tin-  canal.  Therefore  part  of  the  anterior  wall 
and  the  posterior  superior  wall  of  the  tube  are  formed  by  this  cartilage  and  the  rest 
of  the  anterior  wall  and  all  of  the  inferior  by  fibrous  tissue.  The  cartilage  is  attached 
to  the  base  of  the  skull  and  frequently  is  deficient  in  places,  sometimes  being 
divided  into  several  pieces.  At  birth  the  cartilage  is  entirely  of  the  hyaline  variety, 
but  later,  particularly  in  the  pharyngeal  division,  this  is  more  or  less  extensively 
replaced  by  fibrocartilage,  except  in  the  upper  part  where  the  hyaline  cartilage 


THE    MIDDLE   EAR.  1503 

persists.  It  is  this  cartilage,  covered  by  the  cushion  of  mucous  membrane,  that 
confers  the  characteristic  Gothic  arch  contour  to  the  lower  opening,  the  osteum 
pharyngeum,  of  the  tube. 

The  Mucous  Membrane  of  the  Eustachian  Tube. — The  Eustachian 
tube  is  lined  throughout  its  length  with  mucous  membrane,  which  differs  some- 
what in  the  cartilaginous  and  osseous  portions.  That  in  the  former  resembles  the 
mucous  membrane  of  the  naso-pharynx,  with  which  it  is  directly  continuous,  whilst 
that  of  the  osseous  division  resembles,  to  some  extent,  the  mucous  membrane  of  the 
tympanic  cavity.  The  epithelium  of  both  divisions  consists  of  the  ciliated  stratified 
columnar  type,  with  some  goblet  cells,  but  the  cells  in  the  pharyngeal  division, 
especially  in  the  lower  part,  are  taller  than  those  of  the  tympanic  portion,  which  are 
low  cuboidal. 

In  the  tympanic  portion  the  mucous  membrane  is  closely  united  with  the  perios- 
teum and  contains  very  few  mucous  glands  and  little  or  no  adenoid  tissue.  In  the 
cartilaginous  division,  on  the  contrary,  the  epithelium  overlies  a  layer  of  adenoid 

FIG.  1262. 


Lateral  lamina — ^4* 


Oblique  musclc-fibres- 


_Mesial  lamina  of  cartilage 
of  tube 


Lumen  of  iube- 


•fc  J  l*< >'. i  -.--Glands 

Tensor  palati  dilator  tuba: 

i^SsSji^ 

Levator  palati  — " 
Transverse  section  of  cartilaginous  Eustachian  tube.    X  7. 

tissue,  often  called  the  tubal  tonsil.  This  tissue  is  especially  abundant  in  children, 
and  beneath  it  are  found  numerous  mucous  glands  which  open  on  the  free  surface  of 
the  tube.  These  glands  extend  nearly  to  the  perichondrium  and  sometimes  can  be 
traced  even  through  the  fissures  in  the  cartilage  into  the  surrounding  connective  tissue. 
A  considerable  amount  of  adipose  tissue  often  occupies  the  submucosa  of  the  lower 
and  lateral  walls.  The  submucous  layer  is  well  developed  in  the  cartilaginous 
division  of  the  tube,  particularly  in  the  outer  membranous  wall.  It  consists  of 
loosely  arranged  fibro-elastic  tissue,  which  supports  the  mucous  glands  and  the 
larger  vessels  and  nerves. 

The  muscles  of  the  Eustachian  tube  are  the  levator  and  the  tensor  palati, 
which  when  they  contract  not  only  affect  the  palate,  but  also  produce  changes  in  the 
position  of  the  floor  and  in  the  lumen  of  the  tube.  These  muscles  are  described  in 
connection  with  the  palate  fpage  1593),  suffice  it  here  to  note  their  close  relations  to 
the  Eustachian  tube,  beneath  and  to  the  inner  side  of  which  the  levator  lies,  and  to  the 
outer  side  of  which  the  tensor  extends.  By  reason  of  the  intimate  attachment  which 
both  muscles  have  to  the  cartilage  of  the  tube,  since  both  take  partial  origin  from  this 
structure,  contraction  of  their  fibres  tend  to  draw  apart  the  walls  of  the  canal  and  they 
thus  serve  as  dilators.  Such  action  is  particularly  true  of  the  tensor  palati,  many  of 


1504  HUMAN   ANATOMY. 

whose  fibres  are  inserted  into  fibrous  tissue  completing  the  lateral  wall  of  the  tube 
(Fig.  1262),  this  part  of  the  muscle  being  designated  the  dilator  tnbfc.  In  addition 
to  opening  the  tube,  the  levator  palati  causes  elevation  of  its  floor. 

The  blood-vessels  of  the  Eustachian  tube  include  the  arteries,  which  arise  from 
the  ascending  pharyngeal  and  from  the  middle  meningeal  and  the  Vidian  branches  of 
the  internal  maxillary;  and  the  veins,  which  communicate  with  those  of  the  tym- 
panum and  of  the  pharynx  and  also  form  a  plexus  connecting  with  the  cavernous 
sinus. 

The  nerves  are  supplied  from  the  tympanic  plexus  and  from  the  pharyngeal 
branches  from  the  spheno-palatine  ganglion. 

THE  MASTOID  CELLS. 

The  antrum  tympanicum  communicates  posteriorly  with  a  variable  number  of 
irregular  pneumatic  cavities,  the  mastoid  cells  (cellulae  mastoideae),  so  called  because 
the  majority  of  these  spaces  occupy  the  mastoid  process.  Unlike  the  antrum,  these 
cells  are  not  developed  at  birth.  As  the  mastoid  process  develops,  the  original 
diploetic  structure  is  usually  more  or  less  replaced  by  larger  cavities  forming  the 
pneumatic  type.  In  a  study  of  one  thousand  bones,  Randall  found  that  scarcely  two 
per  cent,  of  mastoids  could  be  classed  as  diploetic,  and  only  some  ten  per  cent,  as 
combining  a  notable  amount  of  diploe  with  pneumatic  spaces  ;  further,  that  no  mastoid 
is  absolutely  pneumatic,  although  some  senile  bones  show  a  single  thin-walled  cell 
occupying  the  greater  part  of  the  process.  The  pneumatic  cells  of  this  region  may 
extend  to  the  sigmoid  portion  of  the  lateral  sinus  ;  into  the  occipital  bone  ;  into  the 
squamous  portion  of  the  temporal  bone  and  above  the  external  auditory  canal  ;  into 
the  root  of  the  zygomatic  process  ;  into  the  floor  of  the  Eustachian  tube  close  to  the 
carotid  canal,  and  occasionally  as  far  as  the  apex  of  the  petrous  portion  of  temporal 
bone.  These  spaces  are  lined  by  a  very  thin  mucous  membrane,  which  is  continu- 
ous with  that  of  the  antrum  and  of  the  tympanic  cavity.  It  is  closely  united  with 
the  periosteum  and  possesses  a  layer  of  low  nonciliated  squamous  epithelium. 

The  blood-vessels  supplying  the  mastoid  cells  are  the  arteries  derived  from 
the  stylo-mastoid  and  the  middle  meningeal,  and  the  veins,  which  communicate  with 
those  of  the  tympanum  and  the  external  wall  of  the  mastoid  process.  Some  of  the 
veins  are  tributary  to  the  mastoid  emissary  and  the  lateral  sinus,  whilst  others  pass 
beneath  the  superior  simicircular  canal  through  the  cranial  wall  to  join  the  dural  veins. 

The  nerves  are  the  mastoid  ramifications  of  the  tympanic  plexus. 

Practical  Considerations  :  The  Tympanum. — This  cavity  is  continuous 
anteriorly  with  the  nasopharynx  by  way  of  the  Eustachian  tube,  and  posteriorly 
with  the  mastoid  antrum  and  air  cells  by  way  of  the  attic,  so  that  infection,  which 
is  very  common  in  the  pharynx,  may  extend  throughout  this  whole  tract.  The 
tympanic  cavity  extends  above  the  limits  of  the  membrane  about  5-6  mm.  as  th 
attic,  and  about  2-3  mm.  below  as  the  ' '  cellar ' '  or  hypotympanic  recess.  Secre 
tions  on  the  floor,  therefore,  may  not  be  seen  through  the  membrane.  The  defective 
drainage  which  results  from  the  lower  level  of  the  floor  of  the  tympanum,  as  com- 
pared with  that  of  the  external  meatus,  is  one  of  the  causes  of  the  frequency  o 
chronic  otitis  media  with  purulent  discharge,  even  after  the  early  evacuation  o 
the  products  of  inflammation  in  the  acute  stage. 

On  the  internal  wall  the  facial  nerve  passes  in  a  curve  over  the  vestibule  in  the 
angle  between  the  roof  and  inner  wall  of  the  tympanum,  then  downward  in  the 
slightly  projecting  Fallopian  canal  with  a  concave  turn  above  and  behind  the  oval 
window,  continuing  its  course  downward  at  the  junction  of  the  posterior  and  inner 
wall  to  emerge  below  from  the  skull  at  the  stylo-mastoid  foramen.  This  canal 
offers  considerable  resistance  to  caries  in  its  immediate  neighborhood,  although  the 
disease  not  infrequently  communicates  itself  to  the  nerve.  Such  involvement  of 
the  nerve  is  often  the  prodromal  symptom  of  a  fatal  cerebral  affection  (Politzer). 
At  birth  this  portion  of  the  Fallopian  canal  is  very  thin  and  translucent,  and  is 
deficient  as  it  arches  over  the  oval  window,  so  that  involvement  of  the  nerve  is 
much  more  common  in  children  than  in  adults. 


PRACTICAL   CONSIDERATIONS  :    THE    MIDDLE    EAR.         1505 

Roofing  in  the  antrum  and  the  passage  leading  into  it  from  the  attic  is  a  thin 
layer  of  bone  (tegmen  antri),  which  is  particularly  thin  over  the  antrum  and 
separates  these  spaces  from  the  middle  fossa  of  the  skull.  Not  infrequently  there 
are  membranous  defects  in  the  tegmen,  upon  which  the  dura  rests  (Macewen). 
Pus  frequently  passes  through  this  bony  plate,  or  its  deficiencies,  to  the  temporo- 
sphenoidal  region  of  the  brain,  which  is  the  most  frequent  seat  of  brain  abscess. 

Fractures  of  the  base  of  the  skull  in  the  middle  fossa  may  pass  through  the 
tegmen,  rupturing  the  adherent  dura,  and  permitting  cerebro-spinal  fluid  to  pass  into 
the  tympanum.  If  there  is  coincident  rupture  of  the  tympanic  membrane,  the  fluid 
will  likely  appear  at  the  external  auditory  meatus,  or  if  the  membrane  remains  intact, 
the  fluid  may  pass  to  the  pharynx  through  the  Eustachian  tube. 

Often  the  hearing  in  chronic  plastic  otitis  media  is  better  during  a  great  noise 
than  when  the  surroundings  are  more  quiet,  because  the  stiffened  ossicles  transmit 
additional  ordinary  sounds  more  readily  after  they  have  been  loosened  by  the  more 
violent  vibrations;  or  it  may  be  because  the  auditory  nerve,  owing  to  the  greater 
irritation,  becomes  more  sensitive  (Urbantschitsch). 

The  various  relationships  of  the  tympanum  as  involved  in  infectious  disease 
should  be  understood  from  the  standpoint  of  etiology  and  from  that  of  sequelae  or 
complications. 

Infection  may  reach  the  tympanum  from  («)  the  naso-pharynx  through  the 
Eustachian  tube  (scarlatina,  diphtheria,  pharyngitis,  tonsillitis,  rhinitis);  or  (<£)  the 
mastoid  antrum  and  cells  posteriorly.  It  may  extend  from  the  tympanum  (#) 
upward,  by  perforation  of  the  tegmen,  often  deficient  at  places,  leading  to  external 
pachymeningitis,  or  to  subdural  abscess  ;  the  dura,  arachnoid,  and  pia  mater  at 
this  level  are  fused,  so  that  when  the  dura  is  ulcerated  through,  a  diffuse  meningeal 
infection  does  not  ensue,  but  the  process  tends  rather  to  spread  into  the  brain  along 
the  perivascular  lymphatic  sheaths  of  the  pial  vessels,  resulting  in  an  abscess  in 
the  temporal  lobe  (Taylor);  (£)  to  the  internal  jugular  vein  through  venules  that 
penetrate  the  fundus  tympani  to  empty  into  the  jugular  bulb,  and  thence  to  the 
lateral  sinus  ;  (^r)  to  the  superior  petrosal  sinus  and  the  dura  mater  of  the  middle 
fossa  of  the  skull  by  the  structures  (veins  and  areolar  tissue)  passing  through  the 
petro-squamous  suture  ;  (<af)  to  the  facial  canal  either  through  congenital  defects  in 
its  walls,  or  through  carious  openings,  or  along  the  course  of  the  stylo-mastoid 
artery  ;  facial  paralysis  may  follow,  or  infection  may  travel  along  the  internal  auditory 
meatus  and  give  rise  to  a  diffuse  leptomeningitis  in  the  cerebellar  fossa  (Taylor) ; 
(e)  to  the  labyrinth  by  way  of  the  fenestra  ovalis,  or  through  the  membrana 
tympani  secondaria,  which  closes  the  fenestra  rotunda  opening  into  the  scala 
tympani  ;  permanent  deafness  may  result  from  destruction  of  the  labyrinth,  and  the 
infection  may  pass  along  the  cochlear  branch  of  the  auditory  nerve  and  the  nerve 
itself  to  the  cerebellar  fossa  ;  (_/")  to  the  ossicles  causing  caries  and  deafness  ;  (g^) 
to  the  mastoid  antrum  (_q.v. ). 

The  Tympanic  Membrane. — The  tympanic  membrane  is  oblique  in  its 
lateral  as  well  as  in  its  vertical  direction,  so  that  the  inferior  wall  of  the  auditory 
canal  is  longer  than  the  superior,  and  the  anterior  wall  longer  than  the  posterior. 
The  firm  attachment  of  the  handle  of  the  malleus  to  the  membrane  causes  it  to 
assume  the  shape  of  a  hollow  cone  with  its  convexity  pointing  internally.  The 
innermost  point  of  the  cone  is  at  the  lower  end  of  the  handle  of  the  malleus  and 
is  called  the  umbo.  The  distance  between  it  and  the  promontory  on  the  internal 
wall  of  the  tympanic  cavity  is  only  about  2  mm. 

Retention  of  the  products  of  inflammation  within  the  tympanum  may  decrease 
the  inward  bulging  of  the  membrane  or  even  cause  it  to  protrude  outward.  When 
the  Eustachian  tube  is  obstructed,  the  air  then  confined  within  the  middle  ear,  may 
become  partly  absorbed,  allowing  the  external  atmospheric  pressure  to  increase  the 
inward  bulging, .  and  to  press  the  base  of  the  stapes  more  firmly  into  the  fenestra 
ovalis,  giving  rise  to  a  ringing  in  the  ears. 

If  an  imaginary  line  in  the  axis  of  the  handle  of  the  malleus  is  continued  to  the 
lower  margin  of  the  membrane,  and  a  second  at  right  angles  to  this  is  carried  through 
the  itmbo,  the  membrane  will  be  divided  by  the  vertical  line  into  a  lesser  anterior  and 
a  greater  posterior  portion,  and  by  the  horizontal  line  into  a  greater  upper  and  a  lesser 

95 


1506 


H  I'M  AN    ANATOMY. 


FJG.  1263. 


lower  portion,  the  umbo  being  slightly  below  the  middle  of  the  membrane.  By  the 
two  lines  the  membrane  is  divided  into  unequal  quadrants.  This  arrangement  into 
quadrants  is  a  very  important  one  since  the  pathological  appearances  occurring  in 
each  differ  greatly. 

The  antero- superior  quadrant  corresponds  to  the  tympanic  opening  of  the  tube,  the 
canal  for  the  tensor  tympani  muscle,  and  the  anterior  pouch  of  the  drum-head.  The 
antero-inferior  quadrant  corresponds  to  the  carotid  canal.  The  postero-superior  quad- 
rant contains  the  long  process  of  the  incus,  the  stapes,  and  the  articulations  of  these 
bones,  the  oval  window,  the  pyramid,  and  stapedius  muscle,  the  posterior  pouch  of 
the  drum-head,  the  chorda  tympani,  and  the  posterior  fold  (pathologic).  ^\\z postero- 
inferior  quadrant  contains  the  round  window,  the  tympanic  cells  in  the  floor  of  the 
tympanic  cavity  and  the  bulb  of  the  jugular  vein.  The  flaccid  portion  or  Shrapnell's 
membrane  corresponds  to  the  neck  of  the  malleus  and  Prussak's  space  (Briihl-Politzer). 
The  bulb  of  the  jugular  vein  may  be  larger  than  usual  in  which  case  it  may 
encroach  upon  the  posterior  half  of  the  membrane.  Moreover,  it  may  have  an 
imperfect  bony  covering  when  it  will  be  in  danger  during  paracentesis  tympani, 
the  place  of  election  of  which  is  in  this  portion  of  the  membrane.  For  the  same 
reason,  pus  in  the  middle  ear  may  more  readily  encroach  upon  the  vein.  The 

posterior  inferior  quadrant  is 
selected  for  openings  to  evac- 
uate effusions  in  the  tympanum, 
because  it  is  less  sensitive  and 
vascular  than  the  rest  of  the 
membrane  and  corresponds  to 
less  important  structures.  The 
opening  also  gives  better  drain- 
age than  through  any  other 
portion.  It  should  be  borne 
in  mind  that  the  floor  of  the 
tympanum  is  2-3  mm.  below 
the  inferior  margin  of  the  drum 
head,  so  that  in  the  upright 
position  perfect  drainage  can- 
not be  obtained.  The  tym- 
panic membrane  has  an  internal 
mucous  lining,  an  external 
cutaneous  and  an  intervening 
fibrous  layer.  It,  therefore,  has 
little  elasticity,  so  that,  while 
small  openings  often  heal  rap- 
A  permanent  opening,  however. 


Troltsch'sfold  - 


idon  of 
stapes 


Round 
window 


1'romontory 


Posterior 

pensory  ligament 
Membrana 
flaccida 
Anterior 

ispensory 
ligament 
Short  process 

f  malleus 
Anterior  fold 

4  -Malleus 
;    handle 


-r-Umba 


Light  reflex 


Normal  drum-head  of  right  side  as  seen  with  mirror.     X  4. 


idly,  large  openings  close  slowly,  or  not  at  all. 
does  not  of  necessity  produce  deafness. 

With  an  aural  speculum  and  good  light,  one  may  locate  the  various  structures 
as  follows  :  Above  and  in  front  is  seen  the  short  process  of  the  malleus  as  an  appar- 
ently prominent  point.  From  this  point  two  streaks  pass  to  the  periphery,  showing 
the  division  between  the  tense  portion  of  the  membrane  and  its  flaccid  portion 
(Shrapnell's  membrane),  seen  only  in  a  roomy  meatus.  Extending  backward  and 
downward  from  this  point  is  seen  a  whitish  streak  ending  at  the  umbo.  This  is  the 
long  process  or  handle  of  the  malleus.  Directed  downward  and  forward  from  the 
umbo  is  a  cone  of  light  with  its  apex  at  the  umbo  and  its  base  near  the  periphery  of 
the  membrane.  It  is  triangular  in  shape  and  is  due  to  the  funnel  shape  of  the 
membrane  and  the  resulting  light-reflex.  Above  and  in  front  of  the  short  process  of 
the  incus  is  the  membrane  of  Shrapnell.  Through  the  grayish  translucent  tympanic 
membrane  the  contents  of  the  tympanum  may  sometimes  be  seen,,  changing  appar- 
ently the  color  of  the  membrane.  Its  conical  shape  has  been  proven  by  trial  and 
mathematically  to  be  the  most  favorable  for  the  reception  of  sound  waves.  The 
vibrations  are  transmitted  through  the  ossicles  to  the  labyrinth  by  way  of  the  oval 
window.  The  malleus  rests  on  the  membrane,  the  stapes  is  in  the  oval  window 
and  the  incus  lies  between  and  articulates  with  the  two. 


PRACTICAL    CONSIDERATIONS:    THE   MIDDLE   EAR.         1507 

The  Eustachian  Tube. — The  superior  orifice  of  the  Eustachian  tube  is  in 
the  upper  part  of  the  anterior  wall  of  the  tympanum,  and  is  therefore,  not  well 
adapted  for  drainage  of  that  cavity.  The  tube  is  directed  downward,  forward,  and 
inward  to  the  side  of  the  naso-pharynx,  where  it  is  on  a  level  with  the  posterior  end 
of  the  inferior  turbinate  bone.  In  children  it  is  wider,  shorter,  and  more  horizontal, 
so  that  in  infection  of  the  middle  ear  drainage  in  them  is  better,  but,  for  the  same 
anatomical  reasons,  otitis  media  is  more  likely  to  follow  pharyngeal  and  tonsillar 
infections.  The  pharyngeal  orifice  is  bounded  above  and  at  the  inner  side  by  the 
prominent  cartilaginous  arch  which  encloses  a  funnel-shaped  opening.  The  mucous 
membrane  over  this  projection  is  thickened  by  a  cushion  of  adenoid  tissue,  hyper- 
trophy of  which  is  frequently  associated  with  pharyngeal  adenoids  and  enlarged 
tonsils,  and  may  occlude  the  tube,  ultimately  causing  deafness.  The  upper  border 
of  the  pharyngeal  opening  of  the  tube  is  a  half  inch  above  the  soft  palate,  and  the 
same  distance  below  the  basilar  process,  below  the  hinder  end  of  the  inferior  turbi- 
nate bone  and  in  front  of  the  posterior  pharyngeal  wall  (Tillaux).  Immediately 
behind  this  orifice  is  the  well-marked  depression  called  Rosenmiiller's  fossa,  the 
depth  of  which  is  increased  in  cases  of  enlargement  of  the  pharyngeal  tonsil  and 
which  may  then  lead  to  difficulty  in  the  passage  of  a  catheter  into  the  Eustachian 
tube.  It  may  also,  when  recognized,  serve  as  a  useful  guide  to  the  orifice  of  the 
tube.  Injury  to  the  orifice  of  the  tube  during  operations  in  the  naso-pharynx, 
or  at  the  posterior  ends  of  the  turbinates,  may  lead  to  cicatricial  contraction  and 
occlusion,  thus  causing  defective  hearing.  Ulcerations  in  the  naso-pharynx  may 
produce  a  like  effect.  The  length  of  the  tube  is  about  37  mm.  (\%  in.)  and  its 
pharyngeal  opening  is  about  25  mm.  (i  in.  )  lower  than  the  tympanic.  Its  upper 
third  (12  mm.)  is  bony,  and  its  lower  two-thirds  (25  mm.)  cartilaginous.  The 
narrowest  part,  the  isthmus,  is  at  the  junction  of  these  two  portions.  The  lumen 
of  the  cartilaginous  portion  forms  a  somewhat  S-shaped  slit,  the  walls  being  in 
actual  contact,  except  during  the  acfr  of  swallowing,  when  the  slit  opens  so  that 
air  may  reach  the  tympanum  and  equalize  the  atmospheric  pressure  on  the  two 
sides  of  the  tympanic  membrane.  In  the  bony  portion,  though  the  lumen  is 
smaller,  it  is  open.  In  cases  of  obstruction  of  the  tube  at  its  pharyngeal  end — : 
as  by  pressure  from  a  growth,  or  from  a  thickened  mucosa — the  outside  pres- 
sure predominates,  the  tympanic  membrane  is  pushed  inward,  and  buzzing  or 
' '  singing  in  the  ears' '  results.  Whenever  the  palate  is  raised  or  deglutition 
takes  place,  the  tensor  palati  and  palato-pharyngeus  contract,  and  in  so  doing 
open  the  Eustachian  tube  by  traction  on  the  fibrous  tissue  which  unites  the  outer 
borders  of  the  triangular  fibro-cartilage  of  which  the  tube  is  composed.  Con- 
cussion of  the  tympanic  membrane  from  loud  reports,  as  from  the  firing  of 
great  guns,  is  minimi/eel  by  breathing  with  the  mouth  open,  thus  elevating  the 
soft  palate,  opening  the  Eustachian  tube,  and  equalizing  the  pressure  on  the  two 
sides  of  the  membrane. 

Inflation  of  the  tympanum  is  accomplished  through  the  Eustachian  tube,  and  is 
employed  for  diagnostic,  prognostic,  and  therapeutic  purposes.  Several  methods 
are  in  use.  Valsalva's  consists  of  a  vigorous  expiratory  effort  while  the  nose  and 
mouth  are  kept  closed.  Politzer  inflates  the  tympanum  through  one  nostril  by  a 
vigorous  compression  of  a  rubber  air-bag,  while  the  patient  is  in  the  act  of  swallow- 
ing. The  opposite  nostril  and  mouth  are  closed.  The  most  satisfactory  method  in 
difficult  cases  is  by  means  of  the  Eustachian  catheter.  The  instrument  is  passed  tip 
downward  along  the  floor  of  the  nose  until  it  drops  into  the  post  nasal  space  and 
the  posterior  wall  of  the  pharynx  is  reached.  The  tip  is  then  turned  gently  outward 
and  withdrawn  about  i  cm.  when  the  slight  resistance  of  the  cartilaginous  rim  is 
felt.  After  gliding  forward  over  this  prominence,  it  will  engage  in  the  orifice  of  the 
tube.  The  ring  at  the  proximal  end  of  the  catheter — which  is  in  the  plane  of  the 
the  curve  of  the  beak  and  thus  shows  the  position  of  the  latter — is  then  directed 
toward  the  external  meatus  of  the  same  side  (Bonnafont).  The  catheter  may  be 
withdrawn,  and  the  tip  at  the  same  time  be  turned  to  the  opposite  side  from  the 
one  to  be  catheterized,  so  that  the  beak  of  the  instrument  catches  on  the  edge  of 
the  vomer.  It  is  then  turned  upward  through  180°,  and  thus  enters  the  tubal 
opening  (Frank,  Lowenberg). 


1508  HUMAN   ANATOMY. 

Foreign  bodies  may  lodge  in  the  tube  during  vomiting,  or  a  broken  piece  of  the 
bougie  may  be  left  in.  They  will  usually  escape-  during  vomiting  or  hawking,  or 
they  may  be  removed  by  an  instrument  if  visible. 

If  the  tube  is  normal,  a  bougie  i  ^  mm.  in  diameter  will  easily  pass  the  isthmus, 
the  narrowest  part.  Strictures  may  be  dilated  or  applications  made  by  bougies. 
Narrowing  of  the  lumen  may  occur  near  the  isthmus  from  chronic  inflammation  or, 
at  the  pharyngeal  orifice,  from  the  pressure  of  pharyngeal  adenoids,  tumors,  or  polypi. 

Mastoid  Process  and  Cells. — The  mastoid  process  which  is  formed  by  the 
posterior  extremity  of  the  petrous  bone,  is  relatively  small  at  birth  and  contains  no 
air  cells  except  the  antrum.  The  antrum  is  almost  constant,  although  its  size  varies. 
In  the  infant  it  will  hold  a  small  pea,  while  in  the  adult  its  average  length  is  from  12- 
15  mm.  (one-half  inch  or  slightly  more),  its  height  8-10  mm.,  and  its  width  about 
7  mm.  (Briihl).  It  is  the  means  of  communication  between  the  tympanum  and  the 
mastoid  cells,  so  that  infection  finds  an  easy  passage  from  the  former  to  the  latter. 
Its  distance  from  the  external  surface  of  the  mastoid  process  will  depend  upon  the 
size  of  its  cavity.  This  is  usually  from  12-14  mm-  Anteriorly  the  antrum  opens 
into  the  attic  portion  of  the  tympanum,  and  is  in  almost  a  direct  line  through  that 
cavity  with  the  Eustachian  tube.  A  probe  passed  up  the  tube  from  the  pharynx 
would  pass  through  the  attic  into  the  antrum  and  would  strike  the  joint  between  the 
incus  and  the  stapes.  The  axis  of  the  external  canal  would  strike  the  line  at  an  angle 
of  about  thirty  degrees. 

The  floor  of  the  antrum  is  below  the  level  of  the  entrance  into  the  attic,  so  that 
pus  in  the  antrum  tends  rather  to  enter  the  mastoid  cells.  Sometimes  nearly  all  the 
mastoid  cells  are  pneumatic  ;  more  frequently  they  are  diploetic  at  the  tip  of  the 
mastoid  process,  and  pneumatic  above  (page  148).  Pus  in  the  air  spaces  may 
reach  the  diploetic  region  by  breaking  down  the  thin  intervening  septa.  Those 
cases  in  which  there  are  no  mastoid  spaces  are  probably  sclerotic  from  pathological 
causes.  Thus  a  chronic  inflammation  of  the  mastoid  may  give  rise  to  new  bone 
formation,  filling  the  diploe  and  causing  eburnation.  This  would  tend  to  prevent 
the  outward  progress  of  pus  and  would  favor  its  extension  toward  the  interior  of 
the  cranium. 

The  suprameatal  spine  is  about  10—12  mm.  above  the  floor  of  the  antrum, 
which  corresponds  to  a  point  about  half  way  up  the  posterior  wall  of  the  bony  meatus, 
and  lies  about  5  mm.  posterior  to  the  inner  end.  Thus  bulging  of  the  posterior  wall 
of  the  meatus  may  result  from  disease  in  the  antrum.  The  squamo-mastoid  suture  is 
frequently  seen  on  the  surface  of  the  mastoid  process  in  children,  and  may  give  pas- 
sage to  pus  from  the  antrum  to  the  surface.  Through  deficiencies  in  the  mastoid 
process  near  its  tip  pus  may  find  its  way  into  the  sheath  of  the  sterno-cleido-mastoid 
muscle,  or  along  the  large  blood-vessels  into  the  neck. 

The  bony  wall  between  the  antrum  and  posterior  fossa  of  the  skull  is  thin  and 
cancellous,  and  may  show  deficiencies  through  which  pus  may  reach  the  posterior 
fossa.  In  the  fossa  on  the  posterior  surface  of  the  mastoid  process  is  the  groove 
for  the  sigmoid  sinus,  which  is  frequently  infected  from  disease  of  the  antrum.  Such 
infection  may  extend  from  the  antrum  to  the  posterior  or  cerebellar  fossa  of  the  skull, 
causing  meningitis,  septic  thrombus  of  the  lateral  sinus,  or  a  subdural  or  cerebellar 
abscess. 

The  possible  lines  of  extension  of  mastoid  inflammation  may  be  summarized  as 
follows  (after  Taylor)  :  ( i )  Upward,  from  absorption  of  the  thin  tegmen  antri,  or 
through  the  veins  passing  up  through  foramina  in  tin-  tegmen  (  causing  external 
pachymeningitis  in  the  floor  of  the  middle  cranial  fossa  ),  or  through  the  remains  of 
the  petro-squamous  suture  (causing  thrombosis  of  the  superior  prtrosal  sinus).  (2) 
Downward,  by  emissary  veins,  or  through  a  sinus  at  the  lower  part  of  tin-  mastoid  in 
the  digastric  fossa  (causing  cellulitis  beneath  the  sterno-mastoid,  or  travelling  along 
the  stylo-glossus,  si ylo-pharyngi-us  and  stylo-hyoid  to  the  retro-pharyngeal  region). 
(3)  Forward,  through  the  thin  bony  layer  separating  the  external  auditory  meatus 
from  the  antrum  and  the  mastoid  cells  C causing  discharge  from  the  meatus  if  the 
perforation  is  complete,  or  if  it  remains  subperiosteal,  directing  the  pus  outward  to 
a  point  just  back  of  the  pinna).  (4)  Outward—  especially  in  children — through  the 
thin  post-auditory  process  of  the  squainous  bone,  or  through  the  open  masto- 


PRACTICAL   CONSIDERATIONS  :    THE   MIDDLE    EAR.         1509 

squamous  antrum  (causing  a  fluctuating  adenomatous  postauricular  swelling,  pushing 
the  pinna  forward  and  making  it  unduly  prominent).  (5)  Imvard,  either  through 
venules  passing  to  the  sigmoid  sinus,  or  through  caries  of  the  wall  of  the  sigmoid 
groove  (causing  external  pachy meningitis,  or  subdural  abscess,  or  suppurative  basal 
meningitis,  or  ccrebellar  abscess — by  way  of  the  cerebellar  veins  emptying  into  the 
lateral  sinus — or,  most  frequently,  sigmoid  sinus  thrombosis). 

The  sigmoid  sinus  is  usually  about  i  cm.  behind  the  suprameatal  spine,  but  is 
occasionally  so  far  forward  as  to  lie  just  beneath  the  external  surface  of  the  mastoid 
process,  and  immediately  behind  the  bony  wall  of  the  meatus. 

Owing  to  its  close  relation  to  the  mastoid  antrum  and  cells,  no  other  cranial 
sinus  is  so  frequently  the  seat  of  infective  inflammation.  In  infants,  however,  it  is 
seldom  seen,  owing  to  the  following  facts  :  First,  the  mastoid  cells  are  not  developed 
in  them,  though  the  antrum  exists  ;  secondly,  the  squamous  covering  of  the  antrum 
is  not  yet  soldered  to  the  mastoid,  and  therefore,  purulent  matter  finds  a  ready  exit, 
not  being  enclosed  in  a  complete  bony  casing  ;  thirdly,  more  numerous  exits  for 
the  venous  blood  exist  in  infants  than  in  adults  ;  and  fourthly,  the  sigmoid  sinus 
rests  on  a  flatter  osseous  surface  than  in  adults,  the  bony  gutter  which  imbeds  the 
adult  sinus  being  not  yet  fully  formed.  In  infants  the  internal  ear  is  more  exposed 
than  in  adults  to  pathological  encroachments  from  the  middle  ear,  hence  in  them 
leptomeningitis  is  apt  to  ensue,  which  frequently  ends  fatally,  and  that  so  rapidly  as 
to  prevent  the  formation  of  sigmoid  sinus  thrombosis  (Macewen). 

When  the  sigmoid  sinus  is  infected,  extension  may  occur  to  the  venous  channels 
associated  with  it,  especially  to  the  internal  jugular,  anterior  condylar,  and  deep  veins 
of  the  neck  into  which  the  anterior  condylar  empty  themselves.  Evidence  of  involve- 
ment of  these  may  be  found  in  two  areas, — along  the  internal  jugular,  and  in  the  upper 
third  of  the  posterior  cervical  triangle.  Pain  on  pressure  over  the  inflamed  veins  may 
be  elicited  even  when  the  patient  is  deeply  somnolent  or  semi-conscious.  Thrombosis 
of  the  internal  jugular  when  marked,  is  very  easy  of  detection,  as  it  lies  so  super- 
ficially. The  finger  perceives  a  cord-like  formation  to  the  inner  side  of  the  sterno- 
mastoid  on  the  outer  side  of  the  artery,  though  the  latter  is  sometimes  overlapped  by 
it.  This  may  extend  the  whole  length  of  the  internal  jugular,  but  it  is  frequently 
confined  to  the  upper  third.  The  entire  thrombus  may  be  disintegrated  and  its  par- 
ticles carried  by  the  current  to  the  lung,  where  they  may  set  up  infective  infarction. 
They  may  be  carried  to  the  lungs  by  the  veins  passing  into  the  posterior  cervical 
triangle  which  flow  through  the  vertebral  and  other  channels  to  the  subclavian 
(Macewen). 

The  complication  most  to  be  feared  in  middle  ear  disease  is  the  spread  of  the 
infection  to  the  interior  of  the  cranium.  This  may  occur  by  direct  extension  of 
the  carious  process  through  the  bone  ;  more  rarely  through  the  labyrinth  and  internal 
auditory  canal  or  the  aqueducts  ;  or,  still  more  rarely  along  the  small  blood-vessels 
or  connective  tissue  fibres  which  pass  through  the  bone  between  the  middle  ear  and 
the  dura.  Very  exceptionally  the  pus  may  find  its  way  through  the  thin  anterior 
wall  into  the  carotid  canal  and  along  this  to  the  cranial  cavity. 

Although  otitis  media  appears  to  occur  on  both  sides  with  equal  frequency,  the 
right  side  of  the  head  has  been  said  to  be  more  frequently  affected  by  intracranial 
sequelae.  If  so,  this  is  probably  due  to  the  greater  size  of  the  lateral  sinus  and  the 
sigmoid  sinus  on  the  right  side.  Consequently  the  right  sigmoid  sinus  encroaches 
more  upon  the  petrous  and  the  mastoid  portions  of  the  temporal  bone,  especially  at 
the  sigmoid  knee,  and  the  distance  between  the  lower  border  of  the  tympanum  and 
the  antrum  on  the  one  hand  and  the  sigmoid  sinus  on  the  other,  is  less  than  between 
the  corresponding  points  on  the  left  side  (Macewen). 

Involvement  of  the  internal  ear  from  otitis  media  is  comparatively  rare.  This 
portion  of  the  ear  is  developed  independently  of  the  rest,  and,  after  necrosis,  may  be 
extruded  in  sequestrae,  in  which  may  be  recognized  the  structure  of  the  labyrinth. 
If  the  pus  associated  fails  to  escape  externally,  there  is  danger  of  its  passing  through 
the  internal  auditory  meatus  and  aqua^ductus  vestibuli  to  the  brain.  Affections  of  the 
semi-circular  canals  produce  disturbances  of  equilibrium. 

The  sinus  is  in  danger  in  operations  on  the  antrum,  the  external  opening  for 
which  should  be  immediately  behind  the  meatus,  and  the  centre  of  the  opening  2—3 


1 5 io  HUMAN   ANATOMY. 

mm.  below  the  level  of  its  upper  wall.  If  the  sinus  is  in  an  abnormally  anterior  posi- 
tion, the  posterior  wall  of  tin-  meatus  must  be  removed  to  permit  more  room. 

The  facial  nerve  is  also  in  great  danger  in  these  operations,  and  has  frequently 
been  injured.  It  lies  in  the  inner  wall  of  the  mouth  of  the  antrum,  and  is  therefore, 
in  front  of  it.  The  antrum  is  approximately  about  12  mm.  (one-half  inch)  in  a  direc- 
tion very  slightly  inward,  forward,  and  upward  from  a  point  on  the  external  surface, 
5  mm.  posterior  to  the  suprameatal  spine.  The  anterior  edge  of  the  opening  made 
to  reach  the  antrum,  should  be  at  this  point,  and  its  upper  edge  3  mm.  below  the 
spine.  It  should  never  be  carried  deeper  than  i '/j  cm.  ( J/g  in. )  from  the  anterior 
edge  of  the  external  opening,  for  fear  of  injuring  the  facial  nerve  or  external  semi- 
circular canal. 

As  the  situation  of  the  mastoicl  antrum  is  the  key  to  the  position  in  all  operations 
upon  either  the  antrum  itself  or  the  mastoid  cells,  Macewen  has  noted  three  points  in 
the  anatomy  of  the  mastoid  that  may  govern  the  surgeon  in  reaching  the  antrum 
without  (a)  opening  the  sigmoid  groove  and  injuring  its  enclosed  sinus;  ( /> ) 
encroaching  upon  the  Fallopian  canal  and  destroying  the  facial  nerve  ;  (r)  invading 
the  middle  cerebral  fossa  ;  (</)  injuring  the  semicircular  canals. 

1.  The   suprameatal  triangle — the  lower  border  of  which  corresponds  with 
the  level  of  the  roof  of  the  antrum,  and  is,  therefore,  a  few  lines  below  the  level  of  the 
base  of  the  temporo-sphenoidal  lobe — is  bounded  above  by  the  posterior  root  of  the 
zygoma,  below  by  the  postero-superior  segment  of  the  bony  external  meatus,  and 
behind  by  a  line  uniting  these  two  and  drawn  vertically  from  the  posterior  border  of 
the  meatus  to  the  zygomatic  root.      The  opening  is  made  within  this  triangle  and 
close  to  the  last  line — the  base  of  the  triangle. 

2.  The  excavation  of  the  bone  is  carried  inward  and  a  little  forward,  in  the  direc- 
tion of  the  posterior  wall  of  the  bony  meatus,  as  shown  by  a  probe  passed  into  it  from 
behind  between  the  skin  and  the  osseous  wall.      The  more  oblique  the  direction  of 
this  wall  from  behind  forward,  the  more  anterior  the  situation  of  the  antrum. 

3.  The  depth  of  the  inner  wall  of  the  tympanic  cavity  from  the  level  of  the 
skull  at  the  bony  external  meatus  should  be  determined  by   introducing  a  probe 
through    the  external  ear   (and  through   the   tympanic   membrane   previously   per- 
forated by  pathological  processes)  until  it  touches  the  inner  wall  of  the  tympanum. 
If  this   cavity  lies  deeply,  the  more  superficial  mastoid  antrum  will  be  relatively 
deep  also. 

Of  forty  brain  abscesses,  the  bone  was  diseased  directly  to  the  dura  in  thirty-seven 
(92  per  cent.),  the  bone  was  diseased,  but  not  the  dura,  in  one  (2.5  per  cent.  ),  and 
the  bone  was  healthy  in  two  (5  per  cent.)  (Korner). 

It  follows  from  this  list  of  cases,  that  after  a  thorough  exposure  of  the  antrum  and 
the  ear  cavities,  the  carious  process  should  be  followed  inward  to  the  dura  or  brain. 
In  case  an  abscess  in  the  temporo-sphenoidal  lobe  cannot  be  reached  in  this  way  the 
skull  may  be  opened  by  a  trephine,  or  by  an  osteo-plastic  resection  immediately  al><  >\  e 
the  ear.  A  cerebellar  abscess  might  be  reached  by  an  opening  one  and  one-half 
inches  behind  the  centre  of  the  bony  meatus  and  one  inch  below  Reid's  base  line. 

Till:  INTERNAL  EAR. 

The  internal  ear  consists  essentially  of  a  highly  complex  membranous  sac,  con- 
nected with  the  peripheral  ramifications  of  the  auditory  nerve,  and  a  bony  capsule, 
which  encloses  all  parts  of  the  membranous  structure  and  is  embedded  within  the 
substance  of  the  petrous  portion  of  the  temporal  bone.  These  two  parts,  known 
respectively  as  the'  membranous  and  the  bony  labvrhitli,  are  not  everywhere  in  close 
apposition,  but  in  most  places  are  separated  by  an  intervening  space  filled  with  a 
tluid,  the  f)«-ri/yin/>/i,  the  inner  sac  lying  within  the  osseous  capsule  like  a  shrunken 
cast  within  a  mould.  The  membranous  labyrinth  is  hollow  and  everywhere  filled 
with  a  fluid,  called  the  ciidolyinfih,  which  nowhere  gains  access  to  the  cavity 
occupied  by  tin-  perilymph.  The  internal  ear  is  closely  related  with  the  bottom  of 
the  internal  auditory  canal,  which  its  inner  wall  contributes,  on  the  one  side,  and 
with  the  inner  wall  of  the  tympanic  cavity  on  the  other.  Its  entire  length  is  about 
20  mm.,  and  its  long  axis  corresponds  closely  with  that  of  the  pyramidal  or  petrous 


THE    INTERNAL    EAR. 


portion  of  the  temporal  bone.  The  position  of  approximately  its  posterior  third 
is  indicated  by  the  transverse  ridge  that  crosses  the  upper  surface  of  the  temporal 
bone  a  short  distance  behind  the  internal  auditory  meatus.  The  irregular  cavity  of 
the  bony  labyrinth,  hollowed  out  in  the  temporal  bone,  comprises  three  subdivis- 

FIG.  1264. 


'"T 

Tympanic  cavity 
Facial  canal 

Cochlea 


Semicircular  canals 


Internal  auditory  canal 


Right  temporal  bone,  upper  part  of  petrous  portion  has  been  removed  to  show  bony 
labyrinth  lying  in  position. 

ions  : — a  middle  one,  the  vestibule,  an  anterior  one,  the  cochlea,  and  a  posterior  one, 
the  semicircular  canals.  Both  the  front  and  hind  divisions  communicate  freely  with 
the  vestibule,  but  neither  communicates  with  the  membranous  labyrinth  nor,  in  the 
recent  condition,  with  the  tympanic  cavity.  Although  corresponding  in  its  general 
form  with  the  bony  compartments  of  the  cochlea  and  semicircular  canals,  the 
membranous  labyrinth  less  accurately  agrees  in  its  contour  with  the  bony  vestibule, 
since,  instead  of  presenting  a  single  cavity,  it  is  subdivided  into  two  unequal 
compartments,  known  as  the  saccule  and  the  utricle,  which  are  lodged  within  the 
bony  vestibule.  The  divisions  of  the  membranous  labyrinth  are,  therefore,  four, 
which  from  before  backward  are  :  the  membranous  cochlea,  the  saccule,  the  utricle 
and  the  membranous  semicircular  canals. 

THE  OSSEOUS  LABYRINTH. 

The  Vestibule. — The  vestibule  (vestibulum),  the  middle  division  of  the  bony 
labyrinth  lies  between  the  cochlea  in  front  and  the  semicircular  canals  behind  and 
communicates  freely  with  both.  It  is  an  irregularly  elliptical  cavity,  measuring  about 
5  mm.  from  before  back- 
ward, the  same  from  above  FIG-  1265. 
downward, and  from  3-4  mm. 
from  without  inward.  The 
lateral  (outer)  wall  separates 
it  from  the  tympanic  cavity, 
and  contains  the  oval  window 
with  the  foot-plate  of  the 
stapes.  The  medial  (inner) 
wall,  directed  toward  the 
bottom  of  the  internal  audi- 
tory canal,  presents  two 
depressions  separated  by  a 
ridge,  the  crista  vestibuli, 
the  upper  pointed  end  of  which  forms  the  pyramidalis  vestibuli.  The  anterior  and 
smaller  of  these  depressions  is  the  spherical  recess  (rcccssus  sphaericus)  and  lodges 
the  saccule.  In  the  lower  part  of  this  fossa,  about  a  dozen  minute  perforations  mark 
the  position  of  the  macula  cribrosa  media  for  the  passage  of  branches  of  the  vestibu- 
lar  nerve  from  the  bottom  of  the  internal  auditory  canal  to  the  saccule.  The  posterior 
and  larger  depression  is  the  elliptical  recess  (recessus  ellipticus).  Behind  the  lower 


Superior  ampulla 


Common  cms 


Lodges  utricle 
Lodges  saccule 


Cochlea 


Superior  canal 


External  canal 


Posterior  canal 


Posterior  ampulla 
Cast  of  right  bony  labyrinth,  mesial  aspect.     X  2. 


1512 


HI  MAN    ANATOMY. 


part  of  the  spherical  recess,  the  crista  vestibuli  divides  into  two  limbs  between  which 
is  the  recessus  cochlearis,  which  lodges  the  beginning  of  the  ductus  cochlearis  and 
is  pierced  by  a  number  of  small  openings  for  the  passage  of  nerve  filaments  to  this 
duct.  The  numerous  minute  holes  piercing  the  crista  (pyramid)  and  the  elliptical 

recess     collectively     form 

FIG    1266.  the    macula    cribrosa 

superior  (Fig.  1266)  and 
transmit  branches  of  the 
vestibular  nerve  to  the 
utricle  and  to  the  ampullae 
of  the  superior  and  hori- 
zontal semicircular  canals. 
Below  and  behind  the  re- 
cessus ellipticus  lies  a 
groove,  the  fossula  sul- 
ciformis,  which  deepens 
posteriorly  into  a  very 
small  canal,  the  aqueduct 
of  the  vestibule  (aquae- 
ductus  vestibuli)  which  runs 
in  a  slightly  curved  course 
to  the  posterior  surface  of 
the  petrous  portion  of  the 
temporal  bone,  where  it 
ends  in  a  slit-like  opening, 
the  apertura  externa  aquaeductus  vestibuli,  situated  between  the  internal 
opening  of  the  internal  auditory  canal  and  the  groove  for  the  lateral  sinus.  The 
canal  transmits  the  ductus  endolymphaticus  and  a  small  vein.  The  anterior  wall  of 
the  vestibule  is  pierced  by  the  large  opening  leading  into  the  scala  vestibuli  of  the 
cochlea.  Near  this  aperture  is  seen  the  beginning  of  the  lamina  spiralis  ossea  which 
lies  on  the  floor  of  the  vestibule  below  the  oval  window.  Posteriorly  the  vestibule 
directly  communicates  with  the  semicircular  canals  by  five  round  openings. 

The  Semicircular  Canals. — The  three  bony  semicircular  canals — the  superior, 
the  posterior  and  the  horizontal — lie  behind  the  vestibule  and  are  perpendicular  to 
one  another  (Fig.  1265).  Their  disposition  is  such  that  the  planes  of  the  three  canals 


Crus  commune 


Aquaeductus 
vestibuli 

Recessus 

ellipticus 

Macula  inferior 

Crista  vestibuli 

Recessuss  pfcaeri- 

cus  with  macula 

media 


Lamina  spiralis 


Section  of  right  bony  labyrinth  passing  through  plane  of  superior  semi- 
circular canal ;  anterior  wall  of  vestibule  is  seen  from  behind.    X  4- 


FIG.  1267. 


Small  end  of 
posterior  canal 


Crus  commune 


correspond  with  the 
sides  of  the  corner  of  a 
cube,  suggestively  re- 
calling the  relations  of 
the  three  cardinal 
planes  of  the  body — 
the  sagittal,  frontal  and 
transverse.  Each  canal 
possesses  at  one  end  a 
dilatation,  called  the 
osseus  ampulla.  The 
superior  canal  (ca- 
nalis  superior)  lies  farth- 
est front  and  in  a  nearly 
vertical  plane  at  right 
angles  to  the  long  axis 
of  the  petrous  portion 
of  the  temporal  bone, 
whilst  the  plane  of  the 
longest  canal,  the  pos- 
terior (canalis  posterior)  is  approximately  parallel  to  it.  The  external  portion  of 
the  horizontal  semicircular  canal  forms  a  prominence  on  the  inner  wall  of  the  middle 
ear  behind  the  facial  canal,  while  the  upper  part  of  the  superior  semicircular  canal 
produces  the  conspicuous  elevation,  the  eminentia  arouata,  si-en  on  the  superior 


Ampulla  of 
superior  canal 

Ampulla  of 
external  canal 


Facial  canal 

oval  ( vestibulnr) 

wi  in  low 

Lamina  spiralis 


Round  (cochlear)  windo\\ 


Section  of  right  bony  labyrinth  passing  through  plain-  of  superior  semicircular 
canal;    posterior  wall  of  vestibule  is  seen  from  before.     X  4. 


Small  end  of 
external  canal 


Ampulla  of 
posterior  canal 


THE   INTERNAL    EAR. 


1513 


surface  of  the  petrous  bone.  The  semicircular  canals  open  into  the  posterior  part  of 
the  vestibule  by  five  apertures  (Fig.  1267),  the  unciilated  ends  of  the  superior  and 
posterior  canals  joining  to  form  a  common  limb  (crus  commune).  The  horizontal 
canal  (canalis  lateralis)  alone  communicates  with  the  vestibule  by  two  distinct  open- 
ings. Its  ampulla  is  at  its  outer  end  and  lies  at  the  upper  part  of  the  vestibule  above 
the  oval  window,  from  which  it  is  separated  by  a  groove  corresponding  to  the  facial 
canal.  Lying  above  and  close  to  this  opening  is  placed  the  ampullary  end  of  the 
superior  canal.  The  ampullary  end  of  the  posterior  canal  lies  on  the  floor  of  the 
vestibule,  near  the  opening  of  the  non-dilated  end  of  the  horizontal  canal  and  of  the 
canalis  communis.  In  the  wall  of  the  ampulla  of  the  posterior  canal,  a  number  of 
small  openings  (macula  cribrosa  inferior)  provide  for  the  entrance  of  the  special 
branch  of  the  vestibular  nerve  destined  for  this  tube. 

The  Cochlea. — The  bony  cochlea  constitutes  the  anterior  part  of  the  labyrinth 
and  appears  as  a  short  blunt  cone,  about  5  mm.  in  height,  whose  base  forms  the  an- 
terior wall  of  the  inner  end  of  the  internal  auditory  meatus.  Its  apex  is  directed  hori- 


FlG.     T268. 


Scala  vestibuli 


Sea  la  tynipani 


Modiolus 
Area  cochlearis 

Area  vestibularis  inferior. 


Internal  auditory  can 

Foramen  singulare 


Hamulus,  overlying 
helicotrema 


Lamina  spiralis  ossea 

Canalis  spiralis  iiiodioli 

Facial  canal 
Crista  falciformis 


Area  vestibularis 
superior 


Cochlea  and  bottom  of  internal  auditory  canal  exposed  by  vertical  section  passing  parallel  with  zygoma ;  prepara- 
tion has  been  turned  so  that  cochlea  rests  with  its  base  downward  and  apex  pointing  upward.     X  5. 

zontally  outward,  somewhat  forward  and  downward,  and  reaches  almost  to  the  Eusta- 
chian  tube.  Its  large  lower  turn  bulges  into  the  tympanic  cavity  and  produces  the 
conspicuous  elevation  of  the  promontory  seen  on  the  inner  wall  of  the  middle  ear 
(Fig.  1269).  The  bony  cochlea  consists  essentially  of  a  tapering  central  column, 
the  modiolus,  around  which  the  bony  canal,  about  30  mm.  long,  makes  something 
more  than  two  and  a  half  spiral  turns,  the  basal,  middle  and  apical.  The  conical 
modiolus  has  a  broad  concave  base  which  forms  part  of  the  base  of  the  cochlea  (basis 
cochlea),  and  a  small  apex  which  extends  nearly  to  the  apex  of  the  cochlea,  or 
cupola  (cupula).  It  is  much  thicker  within  the  lowest  turn  of  the  canal  than  above, 
and  is  pierced  by  many  small  canals  for  the  nerves  and  vessels  to  the  spiral  lamina 
(Fig.  1268).  The  axis  of  the  modiolus,  from  base  to  apex,  is  traversed  by  the 
central  canal,  whilst  a  more  peripherally  situated  channel,  the  canalis  spiralis, 
encircles  the  modiolus  and  contains  the  spiral  ganglion  and  a  spiral  vein.  Project- 
ing at  a  right  angle  from  the  modiolus  into  the  canal  of  the  bony  cochlea  is  a  thin 
shelf  of  bone,  the  lamina  spiralis  ossea,  which  is  made  up  of  two  delicate  bony 
plates  between  which  are  fine  canals  containing  the  branches  of  the  cochlear  nerve. 
The  spiral  lamina  begins  between  the  round  window  and  the  lower  wall  of  the 


1514  HUMAN   ANATOMY. 

vestibule  (Fig.  1269),  and  after  winding  spirally  around  the  modiolus  to  the 
apex  of  the  cochlea,  ends  in  a  hook-like  process,  the  hamulus,  which  forms  part 
of  the  the  boundary  of  the  helicotrema  (Fig.  1269).  The  partial  division  of  the 
canal  of  the  bony  cochlea  effected  by  the  osseous  spiral  lamina  is  completed  by  the 
membranous  spiral  lamina,  which  stretches  from  the  free  edge  of  the  osseous 
lamina,  to  which  it  is  attached,  to  the  outer  wall  of  the  canal  (Fig.  1271).  The 
upper  division  of  the  canal  is  called  the  scala  vestibuli  and  communicates  with 
the  vestibule,  whilst  the  lower  division,  the  scala  tympani,  would  open  into  the 
tympanic  cavity,  were  it  not  separated  from  that  space  by  the  secondary  tympanic 
membrane.  These  scalae  communicate  with  each  other  through  an  opening,  the 
helicotrema,  at  the  apex  of  the  cochlea.  Close  to  the  beginning  of  the  scala  tym- 
pani at  the  round  window  is  the  inner  orifice  of  the  aquaeductus  cochleae  (ductus 
peril}  mphaticus),  its  outer  opening  being  in  a  depression  on  the  lower  surface  of 
the  pyramid  near  its  posterior  edge.  It  transmits  a  small  vein  and  establishes  a 
communication  between  the  subarachnoid  space  and  the  scala  tympani. 

The  internal  auditory  canal  communicates  with  the  cranial  cavity  by  an  oval 
opening  on  the  posterior  surface  of  the  pyramidal  portion  of  the  temporal  bone,  from 
which  it  extends  outward  to  the  internal  ear.  Its  outer  or  lateral  end,  the  fundus. 
is  divided  into  a  smaller  superior  and  a  larger  inferior  fossa  by  a  transverse  ridge,  the 
crista  falciformis.  In  the  anterior  part  of  the  superior  fossa  (area  fascialis )  is 
the  opening  of  the  facial  canal  (aquaeductus  Fallopii)  for  the  transmission  of  the  facial 
nerve.  In  its  posterior  part  are  the  openings  (area  vestihularis  superior)  for  the 
branches  of  the  vestibular  nerves  which  supply  the  utricle  and  the  ampullae  of  the 
superior  and  horizontal  semicircular  canals.  These  openings  appear  in  the  macula 
cribrosa  superior  on  the  inner  surface  of  the  bony  labyrinth  (page  1512 ).  The  ante- 
rior part  of  the  inferior  fossa  is  called  the  area  cochlearis  and  is  perforated  about  its 
middle  by  the  opening  of  the  central  canal  of  the  modiolus.  Surrounding  this  are 
the  numerous  small  apertures  of  the  tractus  spiralis  foraminosus  for  the  trans- 
mission of  branches  of  the  cochlear  nerve  to  the  two  lower  turns  of  the  cochlea. 
Behind  the  area  cochleae  and  separated  from  it  by  a  ridge,  lies  the  inferior  area  of 
the  vestibule  (area  vestihularis  inferior)  with  its  small  openings  for  the  passage  of 
nerves  to  the  saccule.  The  macula  cribrosa  media,  described  above,  is  formed  by 
these  openings.  Behind  the  fossula  inferior  is  a  large  opening,  the  foramen  singu- 
lare,  which  leads  into  a  canal  at  the  other  end  of  which  are  the  small  openings 
of  the  macula  cribrosa  inferior.  It  transmits  the  branch  of  the  vestibular  nerve  di->- 
tined  for  the  ampulla  of  the  posterior  semicircular  canal. 

THK  MEMBRANOUS  LABYRINTH. 

The  membranous  labyrinth  (labyrinthus  membranaceus )  lies  within  the  bony 
labyrinth,  which  it  resembles  in  general  form.  This  agreement  is  least  marked 
within  the  vestibule,  since  here  the  single  division  of  the  bony  capsule  is  occupied 
by  two  compartments  of  the  membranous  sac,  the  utricle  and  the  saccule.  The 
membranous  labyrinth  comprises:  (i)  the  utricle  and  the  saccule,  which,  with  the 
ductus  endolympkaticuS)  lie  within  the  vestibule;  (2)  the  three  membranous  semi- 
circular canals  lodged  within  the  bony  semicircular  canals;  and  (3)  the  mem- 
branous cochlea  enclosed  within  the  bony  cochlea.  The  membranous  labyrinth 
is  attached,  especially  in  certain  places,  by  connective  tissue  to  the  inner  wall  of 
the  bony  capsule.  The  interval  between  the  membranous  and  bony  labyrinths,  larg- 
est in  the  scahe  tympani  and  vestibuli  of  the  cochlea  and  in  the  vestibule,  constitutes 
the  perilymphatic  space  (spatium  peiilymphaticnm)  and  contains  a  modified  lym- 
phatic fluid,  the  perilymph.  The  fluid  within  tin-  membranous  labyrinth,  appro- 
priately (ailed  the  endolymph,  can  puss  from  one  part  of  the  labyrinth  to 
another,  although  the  saccule  and  utricule  are  only  indirectly  connected  through  a 
narrow  channel,  the  ductus  endolymphaticus. 

The  Utricle. — The  utricle  (utricafae)  occupies  the  recessus  ellipticus  in  the 
upper  back  part  of  the  vestibule.  It  is  larger  than  the  saccule  and  communicates 
with  the  three  membranous  semicircular  canals.  Attached  to  the  upper  and  inner 
walls  of  the  vestibule  by  connective  tissue,  it  extends  from  the  roof  of  the  vestibule 


THE    INTERNAL    EAR.  1515 

backward  and  downward  to  the  opening  of  the  posterior  ampulla,  a  distance  of  from 
5.5-6  mm.  The  utricle  is  made  up  of  three  subdivisions,  the  uppermost  of  which  is 
respresented  by  a  blind  sac,  from  3-3.5  mm.  in  length  and  breadth,  called  the 
recessus  utriculi,  whilst  the  two  lower  divisions  together  form  the  utriculus  pro- 
prius,  which  measures  3  mm.  by  from  1.5-2  mm.  The  lower  part  of  the  utricle 
proper  is  prolonged  into  the  tube-shaped  sinus  posterior,  which  connects  the  am- 
pulla of  the  posterior  semicircular  canal  with  the  utricle. 

The  openings  of  the  semicircular  canals  into  the  utricle  are  disposed  as 
follows:  into  the  recessus  utriculi  open  (i)  the  ampulla  of  the  superior  semicircular 
canal  and  (2)  that  of  the  horizontal  canal.  Into  the  utriculns  propriris  open  (3) 
the  sinus  superior,  which  lies  within  the  crus  commune  and  receives  in  turn  the 
nonampullated  ends  of  the  superior  and  posterior  semicircular  canals;  (4)  the  non- 
ampullated  end  of  the  horizontal  semicircular  canal  ;  and  (5)  the  ampulla  of  the 
posterior  semicircular  canal  through  the  sinus  posterior.  On  the  antero-lateral  wall 
of  the  recessus  utriculi  is  placed  the  macula  acustica  of  the  utricle,  whilst  from  its 

FIG.  1269. 

Hamulus  Helicotrema 


Facial  canal 
Vest  i  bii  la  r  i  oval)  window 


Pyramxl 


Tympanic  cavity/  \          IliliMF  ^Scala  tympani 

\        "       \  \-  '        \ 

/  \  ~V —  "\  Scala  vestibuli 

Promontory  \  \  \Lamina  spiralis  ossea 

Probe  passes  through  cochlear  (round)  window  Lamina  spiralis  secundaria 

Right  bony  cochlea  partially  exposed  by  section  passing  through  outer  wall  of  apex  and  of  first  turn. 

antero-mesial  wall  springs  the  canalis  utriculo-saccularis,  the  small  canal  from  the 
utricle  that  joins  even  a  smaller  passage  from  the  saccule  to  form  the  ductus 
endolymphaticus. 

The  Saccule. — The  saccule  (sacculus)  is  an  irregularly  oval  compartment,  about 
3  by  2  mm.  in  size,  which  occupies  the  recessus  sphericus  in  the  lower  and  anterior 
part  of  the  vestibule,  to  which  it  is  attached  by  connective  tissue.  It  is  somewhat 
flattened  laterally  and  at  its  lower  end  gradually  narrows  into  a  passage,  the  canalis 
reuniens,  which  connects  the  saccule  with  the  ductus  cochlearis.  Its  upper  end 
bulges  backward  forming  the  sinus  utricularis,  whose  wall  comes  in  contact  with 
that  of  the  utricle.  The  small  canal,  already  mentioned  as  helping  to  form 
the  ductus  endolymphaticus,  arises  from  the  posterior  wall  of  the  saccule.  The 
ductus  endolymphaticus  passes  through  the  aquaeductus  vestibuli  to  end  in  a 
blind  dilated  extremity,  the  saccus  endolymphaticus,  lying  between  the  layers 
of  the  dura  mater  below  the  opening  of  the  aqueduct.  Through  the  openings  in 
the  recessus  sphericus  branches  of  the  vestibular  nerve  enter  and  pass  to  the 
macula  acustica  sacculi  on  the  anterior  wall  of  the  saccule.  The  canalis  reuniens 
is  the  very  small  tube  passing  from  the  lower  part  of  the  saccule  into  the  upper 
wall  of  the  cochlear  duct  near  the  caecum  vestibulare,  as  its  blind  vestibular  end 
is  called. 

The  Membranous  Semicircular  Canals. — These  tubes  (ductus  semicircu- 
lares)  occupy  about  one  third  of  the  diameter  of  the  osseous  canals  and  correspond 


1516 


HUMAN   ANATOMY. 


FIG.  1270. 


Trabeculae 


Membranous 
canal 


to  them  in  number,  name  and  form.      They  are  closely  united  along-  their  convex 
margins  with  the  bony  tube  (Fig.  1270),  whilst  their  opposite  wall  lies  free  in  the 

perilymphatic  space, 
being  attached  only  by 
irregular  vascular  con- 
nective tissue  bundles, 
ligamenta  labyrin- 
thi  canaliculorum, 
which  stretch  across 
this  space.  Like  the 
bony  canals,  each  of 
the  membranous  tubes 
possesses  an  ampulla, 
which  in  the  latter  is 
relatively  much  larger 
than  in  the  former, 
being  about  three  times 
the  size  of  the  rest  of 
the  tube.  The  part  of 
the  ampulla  corre- 
sponding to  the  con- 
vexity of  the  semicir- 
Bony  waii  cular  canal  is  grooved 

on  the  outer  surface  at 
the  entrance  of  the 
ampullary  nerves.  On 
the  corresponding  in- 
ternal surface  is  a  pro- 
jection, the  septum 
transversum,  which  partially  divides  this  space  into  two  parts  and  is  surmounted 
by  the  crista  acustica,  which  contains  the  endings  of  the  vestibular  nerves.  The 
crescent-shaped  thickening  beyond  each  end  of  the  crista  is  called  the  planum 
semilunatum. 


Trabecnhe 


Perilymphatic. 
space 


Transverse  section  of  superior  semicircular  canal,  showing  relations  of 
membranes  to  bony  tube.     X  35. 


Structure  of  the  Utricle,  Saccule  and  Semicircular  Canals. — The  vestibule  and  the  bony 
semicircular  canals  are  lined  by  a  very  thin  periosteum  composed  of  a  felt-work  of  resistant 
fibrous  tissue,  containing  pigmented  connective  tissue  cells.  Endothelium  everywhere  lines  the 
perilymphatic  space  between  the  membranous  and  osseous  canals,  covering  the  free  inner  sur- 
face of  the  periosteum,  the  fibrous  trabeculae,  and  the  outer  or  perilymphatic  surface  of  this 
part  of  the  membranous  labyrinth. 

The  walls  of  the  utricle,  saccule  and  membranous  semicircular  canals  are  made  up  of  (a) 
an  outer  fibrous  connective  tissue  lamella  and  (b}  an  inner  epithelial  lining,  the  latter  consisting 
throughout  the  greater  part  of  its  extent  of  a  single  layer  of  thin  flattened  polyhedral  cells.  Be- 
neath the  epithelium,  especially  in  the  region  of  the  maculae,  is  (r)  a  thin,  almost  homogeneous 
hyaline  membrane,  with  few  cells.  This  middle  layer  presents  in  places  on  its  inner  surface 
small  papillary  elevations  covered  by  epithelium.  On  the  concave  side  of  each  of  the 
semicircular  canals  is  a  strip,  the  raphe,  of  thickened  epithelium  in  which  the  cells  become  low 
cylindrical  in  type.  In  the  plana  semilunata  they  are  cylindrical  in  type.  Over  the  regions 
receiving  the  nerve-fibres,  the  maculae  acusticae  and  the  crista;  acusticae,  the  epithelium 
undergoes  a  marked  alteration,  changing  from  the  indifferent  covering  cells  into  the  highly 
specialized  neuroepithelium. 

The  maculae  acusticae  are  about  3  mm.  long  by  2  nun.  broad,  the  macula  of  the  saccul' 
being  a  little  narrower  (1.5-1.6  mm. )  than  that  of  the  utricle  (2  mm. ).  At  the  margin  of  these 
areas  the  cells  are  at  first  cuboidal,  next  low  columnar,  and  thru  abruptly  increase  in  length,  until 
they  measure  from  .030-. 035  mm.,  in  contrast  with  their  usual  height  of  from  .oo3-.cx>4  mm.  The 
acoustic  area  includes  two  kinds  of  elements,  the  sustentacular  or  fibre-cells  and  the  hair-cells. 
The  sustenfacufar  ce//s  are  long,  rather  narrow,  irregularly  cylindrical  dements  and  extend  the 
entire  thickness  of  the  epithelial  layer,  resting  upon  a  well-developed  basement-membrane  by 
their  expanded  or  divided  basal  processes.  At  a  variable  distance  from  the  base,  they  present  a 
swelling  enclosing  an  oval  nucleus  and  terminate  at  the  surface  in  a  cuticular  zone.  The  cylin- 
drical hair-cell  a  are  broader  but  shorter  than  the  sustentacular  cells,  and  reach  from  the  free 
surface  only  as  far  as  the  middle  of  the  epithelial  layer,  where  each  cell  terminates  usually  in  a 


THE    INTERNAL    EAR. 


1517 


rounded  or  somewhat  swollen  end  containing  a  spherical  nucleus.  The  central  end,  next  to  the 
free  surface,  exhibits  a  differentiation  into  a  cuticular  zone,  similar  to  that  covering  the  inner 
ends  of  the  sustentacular  elements.  From  the  free  border  of  each  hair-cell,  a  stiff  robust  hair 
(.O2O-.O25  mm.  long)  projects  into  the  endolymph.  This  conical  process,  however,  is  resolv- 
able into  a  number  of  agglutinated  finer  hairs  or  rods. 

The  free  surface  of  the  neuroepithelium  within  the  saccule  and  the  utricle  is  covered  by  a 
remarkable  structure,  the  so-called  otolith  membrane.  This  consists  of  a  gelatinous  membrane 
in  which  are  embedded  numberless  small  crystalline  bodies,  the  otoliths  or  ear-stones.  Between 
it  and  the  cuticular  zone  is  a  space,  about  .020  mm.  in  width  and  filled  with  endolymph,  through 
which  the  hair-cells  pass  to  the  otolith  membrane.  The  otoliths  (otoconia)  are  minute  crystals, 
usually  hexagonal  in  form,  with  slightly  rounded  angles,  and  from  .oog-.on  mm.  in  length. 
They  are  composed  of  calcium  carbonate  with  an  organic  basis. 

On  reaching  the  macula  the  nerve-fibres  form  a  subepithelial  plexus,  from  which  fine 
bundles  of  fibres  pass  toward  the  free  surface.  The  fibres  usually  lose  their  medullary  substance 
in  passing  through  the  basement  membrane  and  enter  the  epithelium  as  naked  axis-cylinders. 
Passing  between  the  sustentacular  cells  to  about  the  middle  of  the  epithelium,  they  break  up 
into  fine  fibrillae,  which  embrace  the  deeper  ends  of  the  hair-cells  and  give  off  fine  threads  that 
pass  as  free  axis-cylinders  between  the  cells  to  higher  levels. 

The  crista  acustica  and  the  planum  semilunatum  are  covered  with  neuroepithelium  similar 
to  that  of  the  maculae.  The  hairs  of  the  hair-cells,  however,  are  longer  and  converge  to  and  are 
embedded  within  a  peculiar  dome-like  structure,  known  as  the  cupola,  which  probably  does  not 
exist  during  life,  but  is  an  artefact  formed  by  coagulation  of  the  fluid  in  which  the  ends  of  the 
hairs  are  bathed.  Otoliths  probably  do  not  exist  in  the  cristae  acusticae. 

The  Cochlear  Duct. — The  membranous  cochlea  (ductus  cochlearis)  lies 
within  the  bony  cochlea,  and  like  it  includes  from  two  and  one-half  to  two  and  three- 
quarter  turns,  named  respectively  the  basal,  middle  and  apical,  the  latter  being 


FIG.  1271. 


Organ  of  Corti 


Corti's  membrane 


Ganglion  spirale 


Ligamen- 
tum  spirale 


f    «^~-.*,**- 
,    •- .     "-— :- 
Basilar  membrane 

Ganglion  spirale 


Scala  vestibuli 


Ductus 
'cochlearis 


_  Scala 
"tympani 


/  \  \  Cochlear  nerve  in  inters 


Modiolus  auditory  canal 

Section  of  human  cochlea  passing  through  axis  of  modiolus.     X  12. 

three-fourths  of  a  turn  at  the  apex  of  the  cochlea.  The  tapering  tube  of  the  bony 
cochlea,  winding  spirally  around  the  modiolus,  is  subdivided  into  three  compart- 
ments by  the  osseous  spiral  lamina  and  two  membranes,  namely,  the  membranous 
spiral  lamina  and  Reissner's  membrane.  The  membranous  spiral  lamina 
(lamina  basilaris)  or  basilar  membrane  extends  from  the  free  border  of  the  lamina 
spiralis  ossea  to  the  outer  wall  of  the  cochlea,  where  it  is  connected  to  an  inward 
bulging  of  the  periosteum  and  subperiosteal  tissue,  called  the  spiral  ligament. 
The  lower  of  the  two  tubes  thus  formed  is  the  scala  tympani  and  communicates,  in 
the  macerated  skull,  with  the  tympanum  through  the  round  window.  The  upper 
tube  is  subdivided  into  two  compartments  by  an  exceedingly  delicate,  partition, 
known  as  Reissner's  membrane  (membrana  vestibularis)  which  extends  from  the 
upper  surface  of  the  osseous  lamina  near  its  outer  end,  obliquely  upward  and  outward, 
to  the  external  wall  of  the  cochlea.  The  compartment  above  this  membrane  is  the 


1 5i 8  HUMAN    ANATOMY. 

scala  vestibuli  and  communicates  with  the  perilymphatic  space  of  the  vestibule.  The 
scalae  tympani  and  vestibuli  communicate  only  at  the  apex  of  the  cochlea  through 
the  helicotrema.  They  contain  perilymph  and  are  brought  into  relation  with  the 
subarachnoid  space  through  the  aquaeductus  cochleae.  They  are  lined  by  a  delicate 
fibrous  periosteum,  usually  covered  on  the  surface  which  is  in  co'ntact  with 
the  enclosed  perilymph,  by  a  single  layer  of  endothelial  plates.  In  some  localities, 
however,  as  on  the  tympanic  surface  of  the  basilar  membrane,  the  lining  cells 
retain  their  primitive  mesoblastic  character  and  never  become  fully  differentiated  into 
endothelium. 

The  third  compartment,  the  ductus  cochlearis,  is  triangular  on  cross-section 
(Fig.  1271),  except  at  its  ends,  and  bounded  by  Reissner's  membrane  above,  by 
the  basilar  membrane  and  a  part  of  the  osseous  spiral  lamina  below,  and  by  the 
outer  wall  of  the  bony  cochlea  externally.  Save  for  the  narrow  channel,  the 
canalis  reuniens,  by  which  it  communicates  with  the  saccule,  the  cochlear  cluct  is 
a  closed  tube  and  contains  endolymph.  It  begins  below  as  a  blind  extremity,  the 
caecum  vestibulare,  lodged  within  the  recessus  cochlearis  of  the  vestibule  and, 
after  making  two  and  three-quarter  turns  through  the  cochlea,  ends  above  at  the 
cupola  of  the  cochlea  in  a  second  blind  extremity,  the  caecum  cupulare,  or 
lagena,  which  is  attached  to  the  cupola  and  forms  a  part  of  the  boundary  of  the 
helicotrema. 

Architecture  and  Structure  of  the  Cochlear  Duct. — Reissner's  membrane  (membrana  vestib- 
ularis),  the  delicate  partition  separating  the  cochlear  duct  from  the  scala  vestibuli,  begins  on 
the  upper  surface  of  the  lamina  spiralis,  about  .2mm.  medial  to  the  free  edge  of  the  bony 
shelf,  and  extends  at  an  angle  of  from  40-45°  with  the  lamina  spiralis  ossea  to  the  outer  wall  of 
the  cochlea,  where  it  is  attached  to  the  periosteum.  Notwithstanding  its  excessive  thinness 
(.003  mm.),  it  consists  of  three  layers  :  (a)  a  very  delicate  middle  stratum  of  connective  tissue, 
(b)  the  endothelium  covering  the  vestibular  side,  and  (c )  the  epithelium  derived  from  the  coch- 
lear duct,  and  contains  sparingly  distributed  capillary  blood-vessels. 

The  outer  wall  of  the  cochlear  duct  (Fig.  1272)  is  bounded  by  a  part  of  a  thickened  cres- 
centic  cushion  of  connective  tissue,  whose  convex  surface  is  closely  united  with  the  bony  wall 
and  whose  generally  concave  surface  looks  toward  the  cochlear  duct.  This  structure,  the  liga- 
mentum  spirale,  extends  slightly  above  the  attachment  of  Reissner's  membrane  and  to  a  greater 
distance  below  the  attachment  of  the  basilar  membrane,  thus  forming  part  of  the  outer  walls 
of  the  scalae  vestibuli  and  tympani.  At  its  junction  with  the  basilar  membrane  it  presents  a 
marked  projection,  the  crista  basilaris,  whilst  a  very  slight  elevation  marks  the  point  of  attach- 
ment of  the  membrane  of  Reissner.  The  part  of  this  ligament  lying  between  these  projections 
corresponds  to  the  outer  wall  of  the  cochlear  duct.  Its  concave  free  inner  surface  is  broken  In 
a  third  elevation,  the  prominentia  spiralis,  or  accessory  spiral  ligament,  distinguished  usually  by 
the  presence  of  one  large  (vas  prominent]  or  several  small  blood-vessels.  The  lower  and 
smaller  of  these  two  divisions  of  the  outer  wall  is  called  the  sulcus  spiralis  externus  and  is  lined 
by  cuboidal  epithelium,  whilst  the  larger  upper  division  is  occupied  by  a  peculiar  vascular 
structure,  the  striae  vascularis,  which  contains  capillary  blood-vessels  within  an  epithelial  struc- 
ture. Its  surface  is  covered  with  pigmented  irregular  polygonal  epithelial  cells,  and  its  deeper 
strata  consist  of  cells  which,  especially  in  the  superficial  layers,  resemble  the  surface  epithelium, 
but  in  the  deeper  layers  assume  more  and  more  the  character  of  connective  tissue.  Over  the 
prominentia  spiralis  the  cells  become  flat  and  polyhedral. 

The  ligamentum  spirale  is  composed  of  a  peculiar  connective  tissue,  rich  in  cells  and  blood- 
vessels. Its  thin  outer  layer  forms  the  periosteum  and  is  denser  than  the  adjacent  loose  con- 
nective tissue.  The  latter  is  broadest  opposite  the  scala  tympani,  where  its  fibres  converge 
towards  the  crista  basilaris.  Opposite  the  outer  wall  of  the  cochlear  duct  it  again  becomes 
more  compact  and  is  rich  in  cells  and  blood-vessels.  An  internal  layer  extending  from  near  UK- 
prominentia  spiralis  to  the  basilar  membrane  consists  of  a  hyaline,  noncellular  tissue.  Some 
authors  claim  to  have  found  smooth  muscle-fibres  in  the  ligamentum  spirale. 

The  tympanic  wall  or  floor  of  the  cochlear  duct  (Fig.  1272)  comprises  the  fmsi/ar  mcm- 
hnuii\  extending  from  the  basilar  crest  to  the  outer  end  of  the  bony  spiral  lamina,  and  the-  limbus 
lamiiKt-  spini/is,  which  includes  this  wall  from  the  attachment  of  Reissner's  membrane  to  the  end 
of  the  bony  lamina.  The  limbus  (criM.i  spir.-ilis'i  is  a  thick  mass  of  connective  tissue  upon  the 
upper  surface  of  the  outer  end  of  the  osseous  lamina  spiralis.  Its  outer  extremity  is  deeply 
grooved  to  form  a  gutter,  the  sulcus  spiralis  internus,  the  projections  of  the  limbus  above  and 
below  the  sulcus  forming  lespi-ctively  its  superior  (vestibular)  and  inferior  (tympanic)  labia. 
The  upper  surface  of  the  limlnis  is  marked  by  clefts  and  furrows  which  are  most  conspicuous 
near  the  outer  margin  of  the  upper  lip  ( l.iliium  vestiluilare),  where  the  irregular  projections  between 


THK    INTERNAL    EAR. 


1519 


the  furrows  form  the  so-called  auditory  teeth,  because  of  their  fancied  resemblance  to  incisor 
teeth.  The  lower  lip  (labium  tympanicum )  is  continuous  externally  with  the  basilar  membrane 
and  is  perforated  near  its  outer  end  by  some  4000  apertures  (foramina  nervosa)  transmitting 
minute  branches  of  the  cochlear  nerve.  The  epithelium  covering  the  elevated  portions  of  the 
limbus,  including  the  auditory  teeth,  is  of  the  flat  polyhedral  variety,  the  intervening  furrows  and 
clefts  being  lined  by  columnar  cells.  The  epithelium  of  the  sulcus  spiralis  consists  of  a  single- 
layer  of  low  cuboidal  or  flattened  cells,  continuous  with  the  epithelium  of  the  auditory  teeth 
above  and  with  the  highly  specialized  elements  of  Corti's  organ  below. 

The  basilar  membrane  consists  of  a  median  (inner)  and  a  lateral  (outer)  part.  The  former, 
known  as  the  zona  arcuata,  is  thin  and  supports  the  modified  neuroepithelium  constituting  the 
organ  of  Corti;  the  outer  part,  named  the  zona  pectinata,  is  the  thicker  division  and  lies  external 
to  the  foot-plates  of  the  outer  rods  of  Corti.  The  basilar  membrane  is  made  up  of  three  distinct 
layers,  the  epithelium,  the  substanlia  propria  and  the  tympanic  lamella.  The  snbstantia  propria 
is  formed  of  an  almost  homogeneous  connective  tissue  with  a  few  nuclei  and  fine  fibres,  which 
radiate  toward  the  outer  edge  of  the  spiral  lamina.  The  fibres  of  the  zona  arcuata  are  very  fine 
and  interwoven,  appearing  to  be  an  extension  of  those  of  the  lower  lip  of  the  limbus,  whilst 
straight  and  more  distinct  fibres  stretch  from  the  outer  rods  of  Corti  to  the  spiral  ligament  and 
constitute  the  so-called  auditory  strings.  According  to  the  estimate  of  Retzius,  there  are  24,000 

FIG.   1272. 


Stria  vascularis 


issuer's  membrane 


otninentia  spiralis 
Membrana  tectoria 


V 

Spiral  ligament — \ 


Nerve-fibres 


Crista  basilaris 


Basilar,-  '  Vas  spiralis  Bone 

membrane 

Cross-section  of  ductus  cochlearis  from  human  cochlea.     X  W-      Drawn  from  preparation  made  by  Dr.  Ralph  Butler. 

of  these  special  fibres.  Their  length  increases  from  the  base  toward  the  apex  of  the  cochlea,  in 
agreement  with  the  corresponding  increase  in  breadth  of  the  basilar  membrane.  The  tympanic 
lamella  contains  numbers  of  fusiform  cells  of  immature  character  interspersed  with  fibres.  In 
this  location  the  differentiation  of  the  mesoblastic  cells  lining  the  tympanic  canal  has  never 
advanced  to  the  production  of  typical  endothelial  plates,  the  free  surface  of  the  lamella  being 
invested  by  the  short  fusiform  cells  alone.  The  inner  zone  of  this  layer  contains  capillaries 
which  empty  into  one,  or  sometimes  two,  veins,  frequently  seen  under  the  tunnel  of  Corti  and 
known  as  the  vas  spimle.  The  epithelium  covering  the  inner  zone  of  the  basilar  membrane 
forms  the  organ  of  Corti,  the  highest  example  of  specialization  of  neuro-epithelium. 

The  Organ  of  Corti. — The  organ  of  Corti  (organon  spiralej  consists  in  a  general  way  of  a 
series  of  epithelial  arches  formed  by  the  interlocking  of  the  upper  ends  of  converging  and  greatly 
modified  epithelial  cells,  the  pillars  or  rods  of  Corti,  upon  the  inner  and  outer  sides  of  which  rest 
groups  of  neuroepithelial  elements — the  auditory  and  the  sustentacular  cells.  The  triangular- 
space  included  between  the  converging  pillars  of  Corti  above  and  the  basilar  membrane  below 
constitutes  the  tunnel  of  Corti,  which  is,  therefore,  only  an  intercellular  space  of  unusual  size.  It 
contains  probably  a  soft  semifluid  intercellular  substance  serving  to  support  the  nerve-fibrils 
traversing  the  space  (Fig.  1273).  The  pillars  or  rods  of  Corti,  examinee!  in  detail,  prove  to  be 
composed  of  two  parts,  the  denser  substance  of  the  pillar  proper,  and  a  thin,  imperfect  proto- 
plasmic envelope,  which  presents  a  triangular  thickening  at  the  base  directed  toward  the  cavity  of 
the  tunnel.  Each  pillar  possesses  a  slender  slightly  sigmoid,  longitudinally  striated  body,  whose 


1520 


HUMAN    ANATOMY. 


upper  end  terminates  in  a  triangular  head,  and  whose  lower  extremity  expands  into  the  fool 
resting  upon  the  basilar  membrane.  The  inner  pillar  is  shorter,  more  perpendicular  and  less 
curved  than  the  outer  ;  its  head  exhibits  a  single  or  double  concave  articular  facet  for  the  recep- 
tion of  the  corresponding  convex  surface  of  the  head  of  the  outer  rod.  The  cuticular  substance 
of  both  pillars  adjoining  the  articular  surfaces  is  distinguished  by  a  circumscribed,  seemingly 
homogeneous  oval  area  of  different  nature.  The  upper  straight  border  of  the  head  of  both  pil- 
lars is  prolonged  outwardly  into  a  thin  process  or  head-plate,  that  of  the  inner  lying  uppermost 
and  covering  over  the  head  and  inner  part  of  the  plate  of  the  outer  pillar.  The  head-plate  of  the 
latter  is  longer  and  projects  beyond  the  termination  of  the  plate  of  the  inner  rod  as  the  phalan- 
geal  process,  which  unites  with  the  adjacent  phalanges  of  the  cells  of  Deiters  to  form  the  mcm- 
brana  reticularis.  The  inner  pillars  of  Corti  are  more  numerous,  but  narrower  than  the  outer 
elements,  from  which  arrangement  it  follows  that  the  broader  outer  rods  articulate  with  two  and 
sometimes  three  of  the  inner  pillars,  the  number  of  the  latter  in  man  being  estimated  by  Retzius 
at  5600,  as  against  3850  of  the  outer  rods. 

Immediately  medial  to  the  arch  of  Corti,  resting  upon  the  inner  rods,  a  single  row  of  spe- 
cialized epithelial  elements  extends  as  the  inner  auditory  or  hair-cells.  These  elements,  little 
more  than  half  the  thickness  of  the  epithelial  layer  in  length,  possess  a  columnar  body  contain- 
ing an  oval  nucleus.  The  outer  somewhat  constricted  end  of  each  hair-cell  is  limited  by  a 


FIG.  1273. 

Nnel's  space  Inner  hair-cells 


Inner  hair 
cells 
Hensen's  cells . 


Cells  of  Deiters 


Membrane  tectoria 


Sulcus 
spiralis 


Section  showing  details  of  Corti's  organ  from  human  cochlea ;  owing  to  slight  obliquity  of  section,  width   some- 
what exaggerated.    X  375.    Drawn  from  preparation  made  by  Dr.  Ralph  Butler. 


sharply  denned  cuticular  zone,  from  the  free  surface  of  which  project,  in  man,  some  twenty-five 
rods  or  hairs.  The  inner  hair-cells  are  less  numerous  (according  to  Retzius  about  3500),  as  well 
as  shorter  and  broader,  than  the  corresponding  outer  elements.  Their  relation  to  the  inner  rods 
of  Corti  is  such,  that  to  every  three  rods  two  hair-cells  are  applied.  The  inner  sustentacular 
cells  extend  throughout  the  thickness  of  the  epithelial  layer  and  exhibit  a  slightly  imbricated 
arrangement  as  they  pass  over  the  sides  of  Corti's  organ  to  become  continuous  with  the  lower 
cells  of  the  sulcus  spiralis. 

The  cells  covering  the  basilar  membrane  from  the  outer  pillar  to  the  basilar  crest  comprise 
three  groups:  (a)  those  composing  the  outer  part  of  Corti's  organ,  including  the  outer  hair- 
cells  and  cells  of  Deiters  ;  {b}  the  outer  supporting  cells,  or  cells  of  llcnscn  ;  (r)  and  the  "low 
cuboidal  elements,  the  cells  of  Claudius,  investing  the  outermost  part  of  the  basilar  membrane. 

The  outer  auditory  or  hair-cells  are  about  five  times  more  numerous  (approximately  18,000 
according  to  Waldeyer)  than  the  corresponding  inner  elements,  and  in  man  and  apes  are  dis- 
posed in  three  or  four  rows.  They  alternate  with  the  peculiar  end-plates  or  "phalanges"'  of 
Deiters'  cells,  which  separate  the  ends  of  the  hair-cells  and  join  to  form  a  cuticnlar  mesh-work,  the 
nicinhnuni  rt-liculuris,  through  the  openings  of  which  the  Iviir-cells  reach  the  free  surface.  The 
inner  row  of  these  cells  lies  directly  upon  the  outer  rods  of  ("orti,  so  placed  that  each  cell,  as  a 
rule,  rests  upon  two  rods.  The  cells  of  the  second  row,  however,  are  so  disposed  that  each  cell 
lies  opposite  a  single  rod,  whilst  the  third  layer  repeats  the  arrangement  of  the  first.  In  conse- 
quence of  this  grouping,  these  elements,  in  conjunction  with  the"  phalanges,"  appear  in  surface 
views  like  a  checker-board  mosaic,  in  which  the  oval  free  ends  of  the  auditory  cells  are  included 
between  the  peculiar  compressed  and  indented  octagonal  areas  of  the  end-plates  of  I  )eiters'  cells 


THE    INTERNAL    EAR. 


1521 


FIG.  1274. 


Cells  of  Hensen 


!-  Deiters'  cells 


Outer  hair-cells 


Plate-like  processes  of 
hair-cell 


|£j Outer  pillar  cells 

Inner  hair-cells 


(Fig.  1274).  The  outer  hair-cells  are  cylindrical  in  their  general  form,  terminating  about  the  mid- 
dle of  the  epithelial  layer  in  slightly  expanded  rounded  ends,  near  which  the  spherical  nuclei  are 
situated.  The  outer  sharply  defined  ends  of  the  cells  are  distinguished  by  a  cuticular  border  sup- 
porting about  twenty-five  rigid  auditory  rods  or  hairs  which  project  beyond  the  level  of  the  mem- 
brana reticularis.  The  deeper  end  of  each  outer  hair-cell  contains  a  dense  yellowish  enclosure, 
known  as  the  body  of  Retzius,  which  is  triangular  when  seen  in  profile.  The  bodies  are  absent 
in  the  inner  hair-cells. 

The  cells  of  Deiters  have  much  in  common  with  the  rods  of  Corti,  like  these  being  special- 
ized sustentacular  epithelial  cells  which  extend  the  entire  thickness  of  the  epithelial  stratum  to 
terminate  in  the  peculiar  end-plates  or  phalanges.  It  follows,  that  whilst  the  free  surface  of  Corti's 
organ  is  composed  of  both  auditory  and  sustentacular  cells,  the  elements  resting  upon  the  basi- 
lar membrane  are  of  one  kind  alone — the  cells  of  Deiters.  The  bodies  of  the  latter  consist  of 
two  parts,  the  elongated  cylindri- 
cal chief  portion  of  the  cell,  con- 
taining the  spherical  nucleus  and 
resting  upon  the  basilar  mem- 
brane, and  the  greatly  attenuated 
pyramidal  phalangeal  process. 
A  system  of  communicating  in- 
tercellular clefts,  the  spaces  of 
Nuel,  lie  between  the  auditory 
and  supporting  cells ;  like  the 
tunnel  of  Corti,  these  spaces  are 
occupied  by  a  semifluid  intercel- 
lular substance.  The  cells  of 
Deiters  are  arranged,  as  a  rule, 
in  three  rows,  although  in  places 
within  the  upper  turns  four  or 
even  five  alternating  rows  are 
sometimes  found.  Each  cell 
contains  a  fine  filament,  \h&  fibre 
of  Retzius,  which  begins  near  the 


12: 

middle  of  the  base  with  a  conical 
expansion,  and  extends  through 
the  cell-body  to  the  apex  of 
the  phalangeal  process,  where, 
according  to  Spee,  it  splits  into  seven  or  more  fine  end-fibrils,  that  extend  into  the  cuticular 
superficial  layer  under  and  about  the  phalanges. 

The  membrana  tectoria  or  Corti's  membrane  stretches  laterally  from  the  upper  lip  of  the 
limbus,  above  the  sulcus  spiralis  and  Corti's  organ,  as  far  as  the  last  row  of  outer  hair-cells. 
The  membrane  is  a  cuticular  production,  formed  originally  by  the  cells  covering  the  region  of 
the  auditory  teeth  and  the  spiral  sulcus.  Medially  it  rests  upon  the  epithelial  cells,  but  farther 
outward  it  becomes  separated  from  the  free  edge  of  the  auditory  teeth  and  assumes  its  conspic- 
uous position  over  the  organ  of  Corti.  The  membrane  seems  to  be  composed  of  fine  resistant 
fibres,  held  together  by  an  interfibrillar  substance.  During  life  the  membrane  is  probably  soft 
and  gelatinous,  and  much  less  rigid  than  its  appearance  indicates  after  the  effect  of  reagents. 
The  lower  surface  of  the  free  portion  of  the  membrane,  opposite  the  inner  hair-cells,  is  mod- 
elled by  a  shallow  furrow,  which  indicates  the  position  of  a  spirally  arranged  band  known  as  the 
stripe  of  Hensen.  Like  the  basilar  membrane,  the  membrana  tectoria  increases  in  width  from 
the  base  towards  the  apex  of  the  cochlea. 

The  outer  sustentacular  cells  or  cells  of  Hensen  form  an  outer  zone  immediately  external  to 
the  last  Deiters'  cells.  These  elements  resemble  the  inner  sustentacular  cells,  but  differ  somewhat 
in  form  and  arrangement.  In  consequence  of  their  oblique  position,  the  bodies  are  not  only 
greatly  elongated,  but  also  imbricated.  They  do  not  contain  the  fibres  of  Retzius.  The  cells  of 
Claudius  are  the  direct  continuations  of  Hensen's  cells,  and  laterally  pass  uninterruptedly  into 
the  low  columnar  elements  covering  the  remaining  part  of  the  basilar  membrane.  They  consist  of 
a  simple  row  of  cuboidal  cells  possessing  clear,  faintly  granular  protoplasm  and  spherical  nuclei. 

The  Nerves  of  the  Cochlea. — The  branches  of  the  cochlear  division  of  the 
auditory  nerve  enter  the  base  of  the  cochlea  through  the  tractus  spiralis  foraminosus 
(page  1514),  those  destined  for  the  apical  turn  traversing  the  central  canal  of  the 
modiolus.  From  the  modiolus  a  series  of  stout  lateral  branches  diverge  at  quite 
regular  intervals  through  canals  which  communicate  with  the  peripheral  spiral  canal 
within  the  base  of  the  bony  spiral  lamina.  Within  the  peripheral  canal  the  nerve- 
fibres  join  numerous  aggregations  of  bipolar  nerve-cells,  which  continue  along  the 

96 


Corti's  organ  viewed  from  above,  showing  mosaic  formed  by  pillars 
and  Deiters'  cells  ;  outer  ends  of  auditory  cells  occupy  meshes  of  cuticular 
net-work.  (Retzius). 


1522 


HUMAN   ANATOMY. 


spiral  canal  and  collectively  constitute  the  ganglion  spirale.  From  these  cells 
numerous  dendrites  are  given  off,  which  pass  along  the  canals  within  the  spiral 
lamina  towards  its  margin,  the  twigs  meanwhile  subdividing  to  form  an  extensive 
plexus  contained  within  corresponding  channels  in  the  bone.  At  the  edge  of  the 
spiral  lamina  bundles  of  fine  fibres  are  given  off,  which  escape  at  the  foramina  nervina 
of  the  labium  tympanicum  and  enter  the  epithelial  layer  close  to  the  inner  rod  of  Corti. 
During  or  before  their  passage  through  the  foramina,  the  nerve-fibres  lose  their  med- 
ullary substance  and  proceed  to  their  destination  as  fine  naked  axis-cylinders.  The 
radiating  bundles  pass  within  the  epithelium  to  the  mesial  side  of  the  base  of  the  inner 
pillar  ;  here  they  divide  into  two  sets  of  fibrillae,  one,  the  mesial  spiral  fasciculus, 
going  to  the  inner  hair-cells  and  the  other,  the  lateral  spiral  fasciculus,  passing 
between  the  inner  pillars  to  reach  the  tunnel  of  Corti.  Within  this  space  fibrillae  are 
given  off  which,  after  crossing  the  tunnel,  escape  between  the  outer  rods  into  the 
epithelium  lying  on  the  lateral  side  of  the  arch.  The  further  course  of  the  fibrilke 
seems  to  be  such  that  some  extend  between  the  outer  pillar  of  Corti  and  the  first  n  >ws 
of  hair-cells,  whilst  succeeding  groups  of  fibrillae  course  between  the  rows  of  Deiters' 

FIG.  1275. 


iperior  canal 


Ductus  endolymphaticus 


External  canal 


Ligamentum 

spirale 


Branches  of  cochlear  nervr  to 

Corti's  organ  Membranous  cochlea 

Canalis  reuniehs  opening  into  cochlear  duct 


Posterior  canal 
Blind  sac  of  ductus  coclilcaris 
Branch  of  vestibular  nerve  to  posterior  canals 


Membranous  labyrinth  of  five  months  foetus,  postero-mesial  aspect ;  u,  utricle;  ss,  sp,  superior  and  posterior  utric- 
ular  sinus;  s,  saccule ;  us,  utriculo-saccular  canal ;  cr,  canalis  reuniens;  pa,  posterior  ampulla.  X  6.  (Rftzius). 

cells  to  reach  the  remaining  hair-cells.  The  relation  between  the  nerve-fibrils  and 
the  auditory  cells  is  in  all  cases  probably  close  contact  and  not  actual  junction  with 
the  percipient  elements.  The  paths  by  which  the  impulses  collected  from  the  audi- 
tory cells  are  conveyed  to  the  cochlear  nucleus,  and  thence  to  the  higher  centres,  are 
described  in  connection  with  the  Auditory  Nerve  (page  1258). 

Blood-Vessels  of  the  Membranous  Labyrinth. — The  arteries  supplying 
the  internal  ear  arise  from  the  internal  auditory  artery,  supplemented  to  a  limited 
extent  by  branches  from  the  stylo-mastoid.  The  auditory  artery,  a  branch  of  the 
basilar,  after  entering  the  internal  auditory  meatus  divides,  according  to  Siebenmann, 
into  three  branches  : — (i)  the  anterior  vestibular,  (2)  the  cochlear  proper,  and  (3) 
the  vestibulo-cochlcar  arterv. 

1.  The  vestibular  artery  accompanies  the  utriculo-ampullary  nerve  and  sup- 
plies the  upper  part  of  the  vestibule,  including  the  posterior  part  of  the  utricle  with 
its  macula,  the  saccule  and  the  cristae  of  the  upper  and  outer  ampullae  of  the  corre- 
sponding semicircular  canals. 

2.  The  cochlear  artery  pursues  a  spiral  course.      It  gives  off  three  branch*  s, 
two  of  which  are  distributed  to  the  lower  turn  of  the  cochlea,  whilst  the  third  sup- 
plies the  middle  and  apical  turns. 

3.  The  vestibulo-cochlear  artery  arises  either  from  the  cochlear  artery  or 
independently  and  divides,  within  the;  spiral  lamina,  into  a  cochlear  and  a  vestibular 


DEVELOPMENT   OF   THE   EAR. 


1523 


branch.  The  cochlcar  branch  is  distributed  to  the  lower  turn  of  the  cochlea  and 
anastomoses  with  the  cochlear  artery  proper.  The  vestibular  branch  is  distributed 
to  the  lower  part  of  the  vestibule,  including  the  lower  part  of  the  saccule  and  utricle, 
to  the  cms  commune  and  part  of  the  semicircular  canals,  and  to  the  lower  end  of  the 
cochlea.  According  to  Siebenmann,  the  macula  of  the  saccule  receives  its  arterial 
supply  from  a  blood-vessel  which  usually  arises  from  the  common  stem  of  the  vestib- 
ulo-cochlear  artery,  or,  more  rarely,  runs  independently  through  the  whole  internal 
meatus.  A  similar  origin  applies  to  the  artery  supplying  the  nerve  of  the  posterior 
ampulla.  In  the  base  of  tl^e  spiral  lamina  the  arteries  are  connected  by  capillary 
loops  especially  in  the  lower  turn  of  the  cochlea.  As  mentioned  above,  one  or  more 
spiral  vessels  are  often  seen  under  the  tunnel  of  Corti  within  the  tympanic  covering 
of  the  basilar  membrane.  The  region  of  the  stria  vascularis  and  prominentia  spiralis 
are  especially  well  supplied  with  blood-vessels.  Those  seen  in  the  scala  tympani  are 
principally  veins,  while  a  larger  number  of  arteries  are  found  in  the  scala  vestibuli. 
The  blood-supply  of  the  lower  turn  of  the  cochlea  is  much  more  generous  than  that 
of  the  others. 

The  veins  by  which  the  blood  escapes  from  the  cochlea  include  :  ( i )  the  vein 
of  the  vestibular  aqueduct,  which  empties  into  the  superior  petrosal  sinus  ;  (2)  the 
vein  of  the  cochlear  aqueduct,  which  empties  into  the  internal  jugular  and  (3)  the 
venous  plexus  of  the  inner  auditory  canal,  which  empties  either  into  the  transverse  or 
inferior  petrosal  sinus.  The  first  of  these  channels  collects  the  blood  from  the  semi- 
circular canals;  the  second  from  the  whole  cochlear  canal  through  the  anterior,  pos- 
terior and  middle  spiral  veins  and  from  most  of  the  vestibule  through  the  anterior 
and  posterior  vestibular  veins.  The  veins  of  the  internal  auditory  canal  form  collat- 
erals to  the  other  veins  of  the  labyrinth  and  receive  the  large  central  cochlear  vein 
(Siebenmann),  which  leaves  the  cochlea  near  the  border  of  the  central  foramen  of  the 
modiolus,  as  well  as  tributaries  corresponding  to  the  branches  of  the  acoustic  nerve. 


FIG.  1276. 

Hind-brain 


Otic  pit 


THE    DEVELOPMENT  OF  THE"  EAR. 

The  development  of  the  ear  includes  the  formation  of  two  morphologically  distinct  divis- 
ions, the  membranous  labyrinth,  the  essential  auditory  structure,  and  the  accessory  parts,  com- 
prising the  middle  ear,  with  its  ossicles  and  associated  cavities,  and  the  external  auditory  canal 
and  the  auricle.  The  developmental  history 
of  the  organ  of  hearing  proper  in  its  early 
stages  is  largely  an  account  of  the  growth  and 
differentiation  of  the  ectoblastic  otic  vesicle, 
since  from  this  is  produced  the  important 
membranous  tube,  the  enveloping  fibrous 
and  osseous  structures  being  comparatively 
late  contributions  from  the  mesoblast. 

Development  of  the  Labyrinth. — The 
internal  ear  appears  as  a  thickening  and 
soon  after  depression  of  the  ectoblast  within 
a  small  area  on  either  side  of  the  cephalic 
end  of  the  neural  tube,  at  a  level  correspond- 
ing to  about  the  middle  of  the  hind-brain 
(Fig.  1276). 

This  depression,  the  auditory  pit,  is 
widely  open  for  a  considerable  time  and 
distinguished  by  the  greater  thickness  of 
its  depressed  wall,  which  contrasts  strongly 
with  the  adjacent  ectoblast.  After  a  time 
the  lips  of  the  pit  approximate  until,  by 
their  final  union,  the  cup-like  depression  is  converted  into  a  closed  sac,  the  otic  vesicle. 

This  sac,  after  severing  all  connection  with  the  ectoblast,  gradually  recedes  from  the  sur- 
face in  consequence  of  the  growth  of  the  intervening  mesoblastic  layer  ;  it  next  loses  its  sphe- 
roidal form  and  becomes  somewhat  pear-shaped,  with  the  smaller  end  directed  dorsally.  The 
smaller  end  rapidly  elongates  into  a  club-shaped  diverticulum,  the  recessus  endolymphaticus, 
which  later  becomes  the  ductus  and  the  saccus  endolymphaticus.  The  remainder  of  the  otic 
sac  soon  exhibits  a  subdivision  into  a  larger  dilatation,  the  vestibular  pouch,  and  a  smaller 
ventral  one,  the  cochlcar  pouch  (Fig.  1297). 


77\ Dorsal  aorta 


—  Oropharynx 

—  r  visceral  furrow 


I  visceral  arch 


Frontal  section  of  early  rabbit  embryo,  showing 
otic  pits.    X  40. 


1524 


HUMAN   ANATOMY. 


FIG.  1277. 


Hind-brain 


Otic  sac 


The  semicircular  canals  differentiate  from  three  folds  which  grow  from  the  vestibulat 
pouch  opposite  the  attachment  of  the  ductus  endolymphaticus.  The  central  parts  of  the  two 
walls  of  each  fold  unite  and  undergo  absorption,  while  the  peripheral  part  of  each  fold  remains 
open,  thus  forming  a  semicircular  tube,  one  end  of  which  becomes  enlarged  to  form  the 
ampulla.  The  superior  vertical  canal  appears  first,  and  the  horizontal  or  external  last.  The 
growth  of  the  epithelial  diverticula  is  later  accompanied  by  a  condensation  of  the  surrounding 
mesoblast,  which  differentiates  into  an  external  layer,  the  future  cartilaginous  and  later  bony 
capsule  ;  a  layer  internal  to  this  becomes  the  perichondrium  and  later  periosteum.  A  second 
mesoblastic  layer  is  formed  from  the  cells  immediately  surrounding  the  otic  vesicle,  whilst  the 
space  between  these  fibrous  layers  is  filled  by  a  semi-gelatinous  substance  which  later  gives 
place  to  the  perilymph  occupying  the  perilymphatic  space.  Within  the  ampullae,  which  early 
develop,  the  epithelial  lining  undergoes  specialization,  accompanied  by  thickening  of  the  meso- 
blastic wall  within  circumscribed  areas,  to  form  the  cristae  acusticae. 

Coincidently  with  the  development  of  the  semicircular  canals,  a  diverticulum,  the  cochlear 
canal,  appears  at  the  lower  anterior  end  of  the  membranous  sac.  This  tube,  oval  in  section, 

grows  forward,  downward,  and  inward,  and  represents 
the  future  cochlear  duct.  After  attaining  considerable 
length,  further  elongation  is  accompanied  by  coiling 
and  the  assumption  of  the  permanent  disposition  of 
the  tube.  The  epithelium  of  the  cochlear  tube  early 
exhibits  a  distinction,  the  cells  of  the  upper  surface 
of  the  somewhat  flattened  canal  becoming  attenuated, 
whilst  those  on  the  lower  wall  undergo  thickening  and 
further  differentiation.  The  flattened  cells  form  the 
epithelial  covering  of  Reissner's  membrane  and  of  the 
outer  wall,  and  the  taller  elements  are  converted  into  the 
complicated  structures  of  the  tympanic  wall  of  the  ductus 
cochlearis,  including  the  crista,  the  sulcus,  and  the 
organ  of  Corti. 

The  development  of  these  structures  includes  the 
differentiation  of  two  epithelial  ridges  ;  from  the  inner 
and  larger  of  these  is  derived  the  lining  of  the  sulcus 
spiralis  and  the  overhanging  membrana  tectoria.  The 
outer  ridge  is  made  up  of  six  rows  of  cells,  the  inner 
row  becoming  the  inner  hair-cells,  the  outer  three 
rows  becoming  the  outer  hair-cells,  whilst  the  two 
rows  between  these  two  groups  form  the  rods  of 
Corti.  The  crista  appears  between  the  sulcal  cells  and 
the  cochlear  axis  as  a  thickening  of  the  spiral  lamina. 

The  cochlear  outgrowth  of  the  primary  otic  vesicle  forms  the  membranous  cochlea,  or 
scala  media,  alone,  the  walls  of  the  adjacent  divisions,  the  scala  vestibuli  and  scala  tympani, 
resulting  from  the  changes  within  the  surrounding  mesoblast.  The  latter  differentiates  into  two 
zones,  an  outer,  which  becomes  the  cartilaginous,  and  finally  osseous,  capsule,  and  an  inner, 
lying  immediately  around  the  membranous  canal,  which  for  a  time  constitutes  a  stratum  of  deli- 
cate connective  tissue  between  the  denser  capsule  and  the  ectoblastic  canal.  Within  this  layer 
clefts  appear,  which  gradually  extend  until  two  large  spaces  bound  the  membranous  cochlea 
above  and  below. 

These  spaces,  the  scala  vestibuli  and  the  scala  tympani,  are  separated  for  a  time  from  the 
scala  media  by  a  robust  septum  consisting  of  a  mesoblastic  layer  of  considerable  thickness  and 
the  wall  of  the  ectoblastic  tube.  With  the  further  increase  in  the  dimensions  of  the  lymph- 
spaces,  the  partitions  separating  them  from  the  cochlear  duct  are  correspondingly  reduced, 
until,  finally,  the  once  broad  layers  are  represented  by  frail  and  attenuated  structures,  the 
membrane  of  Reissner  and  the  basilar  membrane,  which  consequently  include  an  ectoblastic 
stratum,  the  epithelial  layer,  strengthened  by  a  mesoblastic  lamina,  represented  by  the  sub- 
stantia  propria  and  its  endothelioid  covering. 

The  main  sac  of  the  otic  vesicle  from  which  the  foregoing  diverticula  arise  constitutes  the 
primitive  membranous  vestibule,  and  later  subdivides  into  the  sarcule  and  utricle.  This  separa- 
tion begins  as  an  annular  constriction  of  the  primitive  vestibule,  incompletely  dividing  the  vesicle 
into  two  compartments.  The  still  relatively  large  ductus  endolymphaticus,  the  direct  successor 
of  the  recessus  endolymphaticus,  unites  with  tlu-  narrow  canal  connecting  these  vesicles  in  such 
a  manner  that  each  space  receives  one  of  a  pair  of  converging  limbs,  an  arrangement  foreshad- 
owing the  permanent  relations  of  the  parts. 

Even  before  tin-  subdivision  of  the  primitive  vestibule  is  established,  the  vestibular  end 
of  the  cochlear  canal  becomes  constricted,  so  that  communication  between  this  tube  and  the 
future  saccule  is  maintained  by  only  a  narrow  passage,  later  the  canalis  reunions.  The  devel- 
opment of  the  macula;  acusticae  of  the  saccule  and  utricle  depends  upon  the  specialization  ot 


Part  of  frontal  section  of  head  of  rabbit 
embryo ;  otic  sac  is  separated  from  ectoblast 
and  beginning  to  elongate.  X  40. 


! 


DEVELOPMENT   OF   THE   EAR. 


1525 


Wall  of 
braiii-vesicle- 


Endolymphatic 
recess 


Vestibular 
pouch 


-Cochlear 
pouch 


Otic  vesicle  shows  differentiation  into  three  subdivisions,  endo- 
,  lymphatic,  vestibular  and  cochlear.     X  40. 


the  epithelium  within  certain  areas  associated  with  the  distribution  of  the  auditory  nerves. 

The  nerve-fibres  form  their  ultimate  relations  with  the  sensory  areas  by  secondary  growth  into 

the  epithelial  structures. 

Development  of  the  Auditory  Nerves. — The  vestibular  and  cochlear  nerves,  according  to 

Streeter1,  develop  from  a  ganglion-mass  first  seen  at  the  anterior  edge  of  the  otic  vesicle.     This 

consists  of  an  upper  and  lower  part 

from  the  dorsal  and  ventral  portion  pIG    1278. 

of  which  peripheral  nerve  branches 

are  developed,  whilst  a  single  stem 

connects  it  with  the  brain. 

The    nerves    destined  for  the 

utricle  and  the  superior  and  external 

ampullae    develop  from    the    upper 

part  of  the  ganglionic  mass,  while 

the  nerves  which  supply  the  saccule 

and  posterior  ampulla  develop  from 

the  lower  part  of  this  mass.    The 

stem  extending   centrally  from  the 

ganglion  toward  the  brain  becomes 

the  vestibular  nerve. 

The  spiral  ganglion  begins  its 

development  at   the  ventral  border 

of  the  lower  part  of  this  mass,  the 

cochlear  nerve  growing  toward  the 

brain  while  the  peripheral  division 

containing  the  ganglion  extends  into 

the    membranous    cochlea.      From 

the  foregoing   sketch,   it  is  evident 

that  the   membranous   labyrinth   is 

genetically  the  oldest  part  of  the  internal  ear,  and  that  it  is,  in  fact,  only  the  greatly  modified 

and  specialized  closed  otic  vesicle  surrounded  by  secondary  mesoblastic  tissues  and  spaces. 

Development    of    the 

FIG.   1279.  Middle  Ear.— The  tympanic 

cavity  and  the  Eustachian 
tube  are  formed  essentially 
by  the  backward  prolonga- 
tion and  secondary  expansion 
of  the  inner  entoblastic  por- 
tion of  the  first  branchial  fur- 
row, the  pharyngeal  pouch. 
The  dorsal  part  of  the  latter, 
in  conjunction  with  the  adja- 
cent part  of  the  primitive 
pharynx,  gives  rise  to  the  sec- 
ondary htbo-tympanic  space 
(Fuchs);  the  posterior  end 
of  this  becomes  dilated  to 
form  the  tympanic  cavity, 
while  the  segment  interven- 
ing between  the  tympanic 
diverticulum  and  the  pharynx 
is  converted  into  the  Eusta- 
chian tube.  The  first  and 
second  branchial  arches  con- 
tribute the  roof  of  the  tym- 
panic cavity. 

The  ear  ossicles  are  de- 
veloped in  connection  with 
the  primitive  skeleton  of  the 
visceral  arches.  The  malleus 


Endolymphatic  duct 


Wall  of  brain- 
vesicle 


Canalicular 

recess 


Utriculo- 
saccular  pouch 


t — Surface 


Cochlear  duct 


Further  differentiation    of    otic    vesicle    into    endolymphatic    duct,  utriculo- 
saccular  pouch  and  cochlear  duct. 


and  incus  represent  specialized  parts  of  the  cartilaginous  rod  of  the  first  arch,  the  tensor  tym- 
pani  being  developed  from  the  muscular  tissue  of  the  same  arch.     The  stapes  is  developed  from 
the  second  arch.     The  mesoblast  which  surrounds  the  structures  of  the  tympanic  cavity  during 
their  development  becomes  spongy  and  finally  degenerates  toward  the  end  of  fcetal  life. 
1  Amer.  Jour,  of  Anatomy,  Vol.  VI.,  1907. 


1526 


HUMAN   ANATOMY. 


The  air-cells  of  the  temporal  bone,  including  those  of  the  mastoid  process,  are  formed 
later  by  a  process  of  absorption. 

The  tympanic  membrane  results  principally  from  changes  which  take  place  in  the  first 
branchial  arch  ;  it  is  originally  thick  and  consists  of  a  mesoblastic  middle  stratum,  covered  on  its 
outer  surface  by  the  ectoblast  and  on  its  inner  surface  by  the  entoblast. 

Development  of  the  External  Ear. — The  median  portion  of  the  ectoblastic  groove  of  the 
first  branchial  furrow  becomes  deepened  to  form  the  outer  part  of  the  external  auditory  canal, 

Fie.   1280. 


sac.rnaolyfriph.   ^ 


10  vwEEKS   f . 


Diagram  illustrating  development  of  human  membranous  cochlea ;  primary  otic  vesicle  subdivides  into  vestibular 
and  cochlear  pouches  and  endolymphatic  appendage;  cochlear  pouch  becomes  duct  us  cochlearis ;  from  vestibular 
pouch  are  derived  utricle,  saccule  and  semicircular  canals ;  whilst  endolymphatic  appendage  gives  rise  to  endo- 
lymphatic sac  and  duct.  (Streeter. ) 

while  the  surrounding  parts  of  the  first  and  second  arches  develop  into  the  auricle.  About  the 
fourth  week  of  foetal  life,  the  thickened  posterior  margin  of  the  first  arch  is  broken  up  into  three 
tubercles  "by  two  transverse  furrows.  Similarly  on  the  adjoining  margin  of  the  second  arch,  a 
second  vertical  row  of  three  tubercles  is  formed  and,  in  addition,  behind  these  a  longitudinal 
groove  appears  marking  off  a  posterior  ridge.  From  these  six  tubercles  and  the  ridge  are  differ- 
entiated the  various  parts  of  the  auricle,  the  lowest  nodule  of  the  first  arch  becoming  the  tragns, 
the  remaining  ones  with  the  ridge  giving  rise  to  the  helix,  whilst  from  the  three  ventricles 
of  the  second  arch  are  developed,  from  above  downward,  the  antihelix,  the  antilragiis 
and  the  lobule. 


THE  GASTRO-PULMONARY 

SYSTEM. 

GENERAL    CONSIDERATIONS. 

THE  food-stuffs  required  to  compensate  the  continual  loss  occasioned  by  the 
tissue-changes  within  the  body  are  temporarily  stored  within  the  digestive  tube. 
During  this  sojourn  the  food  is  subjected  to  the  digestive  processes  whereby  the  sub- 
stances suitable  for  the  nutritive  needs  of  the  animal  are  separated  by  absorption  from 
the  superfluous  materials  which,  sooner  or  later,  are  cast  out  as  excreta.  Closely 
associated  with  digestion,  and  in  a  sense  complementary  to  it,  is  the  respiratory  func- 
tion by  which  the  supply  of  oxygen  is  assured.  In  the  lowest  vertebrates  these  two 
life-needs,  food  and  oxygen,  are  obtained  from  the  water  in  which  the  animal  lives, 
this  medium  containing  both  nutritive  materials  and  the  air  required  for  the  perform- 
ance of  the  respiratory  interchange  of  gases  (oxygen  and  carbon  dioxide). 


FIG.   1281. 

Wolffian  body 

Spleen          /         Notochord 
Neural  canal 

^  J 


^ 


Oral  cavity     Pharyngeal    /  I  *  ^  Cloacal  orifice 

pouches      Heart     Luilgsc  U 

Stomach       Pancreas 

Hind-gut 
Sagittal  section  of  schematic  vertebrate      (Modified  from  Fleischntann.) 

Since,  therefore,  in  these  animals  both  food  and  oxygen  are  secured  from  the 
same  source,  the  water,  the  digestive  and  respiratory  organs  form  parts  of  a  single 
gastro-pulmonary  apparatus.  This  close  relation  is  seen  in  the  lower  vertebrates 
(fishes),  in  which  the  anterior  segment  of  the  digestive  tube  is  connected  on  either 
side  with  a  series  of  pouches  and  apertures,  the  branchial  clefts,  bordered  by  the 
vascular  gill-fringes  by  means  of  which  the  blood-stream  is  brought  into  intimate 
relation  with  the  air-containing  water. 

When  the  latter  element  is  forsaken  as  a  permanent  habitat  and  the  animal 
becomes  terrestrial,  a  more  highly  specialized  apparatus,  suited  for  aerial  respiration, 
becomes  necessary.  This  need  results  in  the  development  of  the  lungs.  The  latter, 
however,  retain  the  intimate  primary  relation  to  the  digestive  tract,  and  are  formed 
as  direct  ventral  outgrowths  from  the  gut-tube. 

The  vertebrate  digestive  tract  early  becomes  differentiated  into  three  divisions  : 
fore-gut,  mid-grit,  and  hind-gut.  The  first  includes  the  mouth,  pharynx,  cesopha- 
gus,  and  stomach,  and  serves  for  the  mechanical  and  chemical  preparation  of  the  food 
materials.  The  second  comprises  the  longer  or  shorter,  more  or  less  convoluted 
small  intestine,  and  forms  the  segment  in  which  absorption  of  the  nutritive  materials 
chiefly  takes  place.  The  third  embraces  the  large  intestine,  and  contains  the  super- 
fluous remains  of  the  ingested  materials  which  are  discarded  from  the  body  at  the 

1527 


I528 


HUMAN   ANATOMY. 


anal  opening.  Associated  with  the  mid-gut  are  two  important  glands,  the  liver  and 
the  pancreas.  Greater  complexity  in  the  character  of  the  food  and  in  the  manner  of 
securing  it  necessitates  increased  specialization  in  the  first  segment  of  the  digestive 
tube  ;  hence  the  addition  of  accessory  organs,  as  the  lips,  oral  glands,  tongue,  and 
teeth,  the  latter  often  serving  as  prehensile  as  well  as  masticatory  organs. 

Reference  to  the  early  relations  of  the  embryo  to  the  vitelline  sac  (page  32) 
recalls  the  important  fact  that  the  greater  part  of  the  gut-tract  is  formed  by  the  con- 
striction and  separation  of  a  portion  of  the  yolk-sac  by  the  approximation  and  closure 
of  two  ventral  folds,  the  splanchnopleura.  Since  the  latter  consists  of  two  layers,  the 
entoblast  and  the  visceral  lamina  of  the  mesoblast,  the  tube  resulting  from  the  union 
of  the  splanchnopleuric  folds  possesses  a  lining  directly  derived  from  the  inner  germ- 
layer,  supplemented  externally  by  mesoblast.  The  latter  contributes  the  connective 
tissue,  muscular  and  vascular  constituents  of  the  digestive  tube,  while  the  epithelium 
and  the  associated  glandular  elements  are  the  products  of  the  entoblast. 


MUCOUS    MEMBRANES. 

The  apertures  of  the  digestive,  respiratory,  and  genito-urinary  tracts  mark  loca- 
tions at  which  the  integument  becomes  continuous  with  the  walls  of  cavities  and 
passages  communicating  with  the  exterior.  The  linings  of  such  spaces  constitute 

FIG.  1282. 


S_Epithelium 


^_Papilla  of  tunica 
propria  occu- 
pied by  blood- 
vessels 


pConnective- 
t  issue  stroma 


Section  of  oral  mucous  membrane.    X  350. 

mucous  membranes.  The  latter,  however,  not  only  form  the  free  surface  of  th 
chief  tracts,  but  also  that  of  the  ducts  and  tubes  continued  into  the  glands  which  ar 
developed  as  outgrowths  from  the  mucous  membranes. 

Temporarily  in  the  higher  types  and  permanently  in  such  of  the  lower  animals 
as  possess  a  common  cloacal  space,  all  the  mucous  membranes  of  the  body  are  con- 
tinuous. After  acquiring  the  definitive  arrangement  whereby  the  uro-genital  tract 
becomes  separated  from  the  digestive  tube,  these  membranes  in  man  and  mammals 
(except  monotremata)  form  two  great  tracts,  the  gastro-pulmonary  and  the  genito- 
urinary. 

The  free  surfaces  of  the  mucous  membranes  are  kept  continually  moist  by  a 
viscid,  somewhat  tenacious  secretion,  the  mucus,  derived  from  the  glands  ;  they  are 
thus  protected  from  the  drying  and  irritating  influences  of  the  air,  foreign  substances, 
and  secreted  or  excreted  matters  with  which  they  are  brought  into  contact. 

Structure. — Every  mucous  membrane  comprises  two  distinct  parts  :  the  epi- 
thelium, which  forms  the  immediate  free  surface  and  furnishes  protection  for  the  more 
delicate  tissues  beneath  ;  and  the  tunica  propria,  a  connective-tissue  layer  which 
constitutes  the  stroma  and  gives  place  and  support  to  the  terminal  branches  of  the 


MUCOUS   MEMBRANES. 


1529 


FIG.   1283. 


-Epithelium 


nerves  and  the  blood-vessels  and  the  beginnings  of  the  lymph-radicles.  Thus  it  will 
be  seen  that  the  general  structure  of  a  mucous  membrane  corresponds  closely  with 
that  of  the  integument,  the  protecting  epidermis  of  the  latter  being  represented  by 
the  epithelium  of  the  former,  while  both  the  corium  and  the  tunica  propria  include 
the  connective-tissue  basis  over  which  the  epithelial  layer  stretches.  A  stratum  of 
sub  mucous  tissue,  corresponding  with  the  subcutaneous  layer  in  the  skin,  connects 
the  mucous  membrane  with  the  surrounding  structures. 

The  epithelium  may  be  squamous  or  columnar,  simple  or  stratified.  Its  char- 
acter is  usually  determined  by  the  conditions  to  which  it  is  subjected  ;  thus,  where 
covering  surfaces  exposed  to  mechanical  influences  of  foreign  bodies,  it  is  commonly 
stratified  squamous,  as  in  the  upper  part  of  the  digestive  tract.  Where,  on  the  other 
hand,  the  mucous  membrane  is  concerned  in  facilitating  absorption,  as  in  the  intestinal 
tube,  the  epithelium  is  simple  columnar  in  type.  In  localities  in  which  the  existence 
of  a  current  favors  the  function  of  an  organ,  either  as  a  means  of  freeing  the  surface 
from  secretion  or  particles  of  foreign  matter,  as  in  the  respiratory  tract,  or  of  propul- 
sion through  a  tube,  as  in  the  epididymis  or  the  oviduct,  the  epithelium  is  of  the 
ciliated  columnar  variety.  Modifications  of  the  epithelial  cells,  due  to  the  presence 
of  pigment  or  of  secretion,  distinguish  certain  mucous  membranes,  as  those  clothing 
the  olfactory  region  and  the  large  intestine  respectively. 

The  tunica  propria  or  stroma  consists  of  interlacing  bundles  of  fibre-elastic  tissue 
which  support  spindle  or  stellate  connective-tissue  cells.  The  latter  usually  lie  within 
the  uncertain  clefts  between  the 
stroma  bundles,  which  may  be  re- 
garded as  lymph-spaces.  In  many 
localities  the  surface  of  the  tunica 
propria  is  beset  with  numerous  ele- 
vations or  papilla:,  over  which  the 
epithelium  extends.  Such  irregu- 
larities, when  slight,  may  not  modify 
the  free  surface  of  the  mucous  mem- 
brane, since  the  epithelial  layer  com- 
pletely fills  the  depressions  between 
the  elevations  ;  when  more  pro- 
nounced, the  papillae  or  folds  of  the 
connective  tissue  produce  the  con- 
spicuous modelling  of  the  surface 
seen  in  the  papillae  of  the  tongue 
or  the  rugae  of  the  vagina.  The 
papillae  contain  the  terminal  loops 
of  the  blood-vessels  and  the  nerves 
supplying  the  mucous  membrane. 
Where  especially  concerned  in  ab- 
sorption, the  mucous  membranes  often  gain  increase  of  surface  by  cylindrical  eleva- 
tions, or  villi,  as  conspicuously  seen  in  the  small  intestine.  These  projections, 
consisting  of  the  stroma  covered  by  epithelium,  contain  the  absorbent  vessels,  or 
lacteals,  in  addition  to  the  blood-capillaries. 

A  more  or  less  well-defined  line  separates  the  epithelium  from  the  subjacent 
tunica  propria.  This  demarcation  is  the  basement  membrane,  or  membrana  propria, 
a  detail  which  has  been  variously  interpreted.  Usually  the  basement  membrane 
appears  as  a  mere  line  beneath  the  epithelium,  and  is  then,  probably,  formed  by  the 
apposition  of  the  basal  processes  of  the  epithelial  cells.  When  surrounding  glandular 
tissue  it  is  better  developed,  presenting  a  distinct  and  much  more  robust  structure.  In 
these  positions  the  basement  membrane  is  probably  a  product  of  the  tunica  propria  and 
occurs  in  two  types,  sometimes  being  homogeneous,  at  other  times  reticular  (Flint1). 

In  many  localities  the  deepest  part  of  the  mucous  membrane,  next  the  submu- 
cous tissue,  is  occupied  by  a  narrow  layer  of  involuntary  muscle,  the  muscularis 
mucosce.  While  not  everywhere  present,  it  is  especially  well  developed  in  the  intes- 
tinal tract  from  the  gullet  to  the  anus,  and  in  places  consists  of  two  distinct  layers, 

1  American  Journal  of  Anatomy,  vol.  ii.,  No.  i,  1902. 


Section  of  mucous  membrane  of  oesophagus.     X  55. 


1530 


HUMAN   ANATOMY. 


a  circular  and  a  longitudinal.  The  inner  surface  of  the  stratum  is  often  broken  by 
processes  of  muscular  tissue  which  penetrate  the  tunica  propria  well  towards  the 
epithelium.  The  muscularis  mucosae  belongs  to  the  mucous  membrane,  and  there- 
fore must  be  distinguished  from  the  muscular  coat  proper,  which  is  frequently  a 
conspicuous  additional  layer  in  the  digestive  tract. 

Mucous  membranes  are  attached  to  the  surrounding  structures  by  a  submucous 
layer  of  areolar  tissue.  The  latter  varies  in  thickness  and  density,  consequently  the 
firmness  of  the  union  between  the  mucous  and  submucous  strata  differs  greatly  in 
various  localities.  Usually  the  attachment  is  loose,  and  readily  permits  changes  in 
position  and  tension  of  the  mucosa,  which,  in  the  relaxed  condition,  is  often  thrown 
into  temporary  folds  or  rug&,  as  in  the  oesophagus  and  stomach.  In  other  places 
the  folds  are  permanent  and  not  effaced  by  distention  of  the  organ  ;  a  conspicuous 
example  of  such  arrangement  is  seen  in  the  valvulae  conniventes  of  the  small  intestine, 
in  which  the  submucous  tissue  forms  the  basis  of  the  elevation. 

The  blood-vessels  supplying  mucous  membranes  reach  the  latter  by  way  of  the 
submucous  tissue,  in  which  the  larger  branches  divide  into  the  twigs  which  pass  into 

FIG.  1284. 


gmHMK''' ' ' rr>s :' "T"', •*? ' '    *"-£-'-        -\on-vascularepithelium 

•        :&*• 


—Terminal  capillary  loops 


_Tunica  propria 


Larger  branches  within 
suhmucosa 


Section  of  injected  oral  mucous  membrane.     X  60. 


the  mucosa.  Within  the  deeper  parts  of  the  tunica  propria  the,  smaller  arterial 
branches  break  up  into  the  capillaries  forming  the  subepithelial  and  papillary  net- 
works, the  vascular  loops  being  limited  to  the  connective  tissue  stroma  and  never 
entering  the  epithelium.  The  venous  stems  usually  follow  the  arteries  in  their  gen- 
eral course.  When  glands  are  present,  the  capillaries  surround  the  tubules  or  alveoli 
with  rich  net- works  in  close  relation  to  the  basement  membrane. 

The  lymphatics  within  mucous  membranes  are  seldom  present  as  definite  chan- 
nels, since  they  begin  as  the  uncertain  interfascicular  clefts  between  the  bundles  of 
stroma-tissue.  Towards  the  deeper  parts  of  the  mucosa  the  lymph -paths  become 
more  definite,  and  exist  as  delicately  walled  varicose  passages  which  converge  towards 
the  submucous  tissue.  Within  the  latter  the  lymph-vessels  form  net-works  richly 
provided  with  valves  and  the  accompanying  dilatations. 

The  nerves  distributed  to  mucous  membranes  include  cerebral  or  spinal  and 
sympathetic  branches,  the  latter  supplying  especially  the  involuntary  muscle  of  the 


GLANDS. 

stroma  and  of  the  blood-vessels.  Surfaces  highly  endowed  with  general  and  tactile 
sensibility  are  provided  with  a  generous  supply  of  twigs  containing  medullated  fibres. 
As  the  latter  pass  towards  their  ultimate  destination  (for  convenience  assuming  that 
all  are  peripherally  directed)  they  lose  their  medullated  character  and,  as  naked  axis- 
cylinders,  form  the  siibepithelial plexuses,  from  which  delicate  filaments  pass  into  the 
papillae,  where  they  terminate  either  as  free  club-shaped  or  special  sensory  endings. 
It  is  probable  that  in  places  the  nerves  penetrate  between  the  epithelial  cells  forming 
the  layers  next  the  basement  epithelium  and  terminate  in  varicose  free  endings. 

GLANDS. 

Certain  of  the  epithelial  cells  lining  the  mucous  membranes  of  the  body  become 
modified  to  assume  the  role  of  secretion-forming  organs  or  glands,  the  products  of 
which  are  poured  out  upon  the  free  surface  and  keep  the  latter  moist.  The  latter 
purpose  is  secondary  in  the  case  of  many  important  glands,  as  the  parotid,  pancreas/ 

FIG.  1285. 


Diagram  showing  types  of  glands,    a-e,  tubular;  f-i,  alveolar  or  saccular.     a,  simple;  6,  coiled;  c-d,  increasingly 
complex  compound  tubular;  e,  tubo-alveolar  ;  f,  simple ;  g-h-i,  progressively  complex  compound  alveolar. 

or  liver,  since  these  organs  supply  special  secretions  for  particular  ends.  Aggrega- 
tions of  the  secreting  elements  vary  greatly  in  size,  form,  and  arrangement,  as  well 
as  in  the  character  of  their  products. 

The  simplest  type  is  the  unicellular  gland  found  in  the  lower  forms;  in  principle 
this  is  represented  in  man  and  the  higher  animals  by  the  goblet-cells  seen  in  pro- 
fusion in  mucous  membranes  covered  with  columnar  epithelium.  The  secretion 
poured  out  by  these  goblet-cells  serves  to  protect  and  lubricate  the  surface  of  the 
mucous  membranes  in  which  they  occur.  The  term  "gland,"  however,  usually 
implies  a  more  highly  developed  organ  composed  of  a  collection  of  secreting  epithe- 
lial elements. 

Glands  are  classified  according  to  their  form  into  two  chief  groups,  the  tubular 
and  the  alveolar,  each  of  which  occurs  as  simple  or  compound.  It  should  be  empha- 
sized that  in  many  instances  no  sharp  distinction  between  these  conventional  groups 


1532 


HUMAN   ANATOMY. 


FIG.  1286. 


Opening  on 
mucous  membrane 


Excretory  duct 


exists,  some  important  glands,  as  the  salivary,  being  in 'fact  a  blending  of  the  two 
types  ;  such  glands  are,  therefore,  appropriately  termed  tubo-alveolar. 

In  the  least  complex  type,  the  simple  tubular,  the  gland  consists  of  a  cylindrical 
depression  lined  by  epithelium  directly  continuous  with  that  covering  the  adjacent  sur- 
face of  the  mucous  membrane,  as  an  outgrowth  of  which  the  gland  originally  devel- 
oped. In  such  simple  gland  the  two  fundamental  parts,  \hafundus  and  the  duct,  are 
seen  in  their  primary  type.  The  fundus  includes  the  deeper  portion  of  the  gland  in 
which  the  epithelium  has  assumed  the  secretory  function,  the  cells  becoming  larger  and 
more  spherical  in  form,  while  in  structure  the  distinction  between  the  spongioplasm  and 
hyaloplasm  is  usually  marked  in  consequence  of  the  particles  of  secretion  stored  up 
within  the  meshes  of  the  spongioplastic  net-work,  which  is  often  sharply  displayed. 
The  duct  connects  the  fundus  with  the  free  surface  and  carries  off  the  products  elabo- 
rated within  the  gland.  It  is  lined  with  cells  which  take  no  part  in  secretion  and 
hence  retain  for  some  distance  the  character  of  the  adjacent  surface  epithelium. 
Dilatation  of  the  fundus  of  the  primitive  type  produces  the  simple  alveolar  or  saccular 

gland  ;  division  of  the  fundus  and  part  of 
the  duct  gives  rise  to  the  compound  tubu- 
lar variety  ;  repeated  cleavage  and  subdivi- 
sion of  the  duct,  with  moderate  expansion 
of  the  associated  terminal  tracts,  lead  to 
the  production  of  the  tubo-alveolar  type. 
Simple  tubular  glands  may  be 
minute  cylindrical  depressions  of  practi- 
cally uniform  diameter,  as  the  crypts  of 
Lieberkuhn  in  the  intestine,  or  they  may 
be  somewhat  wavy  and  slightly  expanded 
at  the  fundus,  as  often  seen  in  the  gastric 
glands  towards  the  cardiac  end  of  the 
stomach.  When  the  torsion  becomes 
very  pronounced,  as  in  the  sweat-glands, 
the  coiled  variety  results. 

Compound  tubular  glands  pre- 
sent all  degrees  of  complexity,  from  a 
simple  bifurcation  of  the  fundus  and  ad- 
jacent part  of  the  duct,  as  in  the  pyloric 
or  uterine  glands,  to  the  elaborate  duct- 
system  ending  in  terminal  divisions  either 
of  a  tubular  form,  as  in  the  kidney  and  tes- 
ticle, or  of  a  modified,  somewhat  dilated, 
alveolar  form,  the  tubo-alveolar  type,  as 
in  the  salivary  glands. 

Tubo-alveolar  glands,  modified 
compound  tubular,  constitute  a  verv  im- 

Diagram  showing  relations  of  various  portions  of  duct-  •  ,_,  • 

system  in  glands  of  tubo-alveolar  type.  portant  group,  since  they  embrace  many 

of  the  chief  secretory  organs  of  the  body. 

They  are  made  up  by  repetition  of  similar  structural  units,  differences  in  the  size  of 
the  organ  depending  upon  the  number  of  those  associated  to  compose  the  gland. 
These  units  correspond  to  the  groups  of  terminal  compartments,  or  alveoli,  con- 
nected with  a  single  ultimate  division  of  the  duct-system.  The  alveoli  or  acini  contain 
the  secreting  cells,  and  are  limited  externally  by  a  basement  membrane,  often  well 
developed,  which  supports  the  glandular  epithelium  and  separates  the  latter  from  the 
blood-  and  lymph-vessels  that  surround  the  acinus. 

The  alveoli  belonging  to  the  same  excretory  duct,  held  together  by  delicate 
connective  tissue,  constitute  a  pyramidal  mass  of  glandular  tissue,  \ht  primary  lobules. 
The  latter  are  assembled  into  larger  groups,  or  secondary  lobules,  which  in  turn  are 
united  by  interlobular  connective  tissue  into  the  lobes  composing  the  entire  gland. 
The  lobes  are  held  together  more  or  less  firmly  by  the  interlobar  areolar  tissue 
continuous  with  the  general  fibrous  envelope,  which  forms  a  capsule  for  the  entire 
organ  and  separates  it  from  the  surrounding  structures. 


Beginning  of 
uct  in  alveoli 

'erminal 
alveolus 


GLANDS. 


1533 


The  interlobar  tissue  and  its  interlobular  continuations  contain  the  blood-vessels, 
lymphatics,  and  nerves  supplying  the  gland  and,  in  addition,  the  major  portion  of 
the  excretory  ducts.  In  the  larger  glands  the  latter  form  an  elaborate  system  of  pas- 
sages arranged  after  the  general  plan  shown  in  -the  accompanying  diagram  (Fig. 
1285).  Traced  from  the  terminal  compartments,  or  alveoli,  of  the  gland,  the  duct- 
system  begins  as  a  narrow  canal,  the  intermediate  dud,  lined  by  low  cuboidal  or  flat- 
tened cells  directly  continuous  with  the  glandular  epithelium  of  the  alveoli.  After  a 
short  course  the  tube  increases  in  diameter  and  becomes  the  intralobular  duct,  which 
is  often  conspicuous  on  account  of  its  tall  and  sometimes  striated  or  rod-epithelium. 
The  further  path  of  the  excretory  tubules  lies  within  the  connective  tissue  separating 
the  divisions  of  the  glandular  substance,  and  embraces  the  interlobular  and  the  inter- 
lobar ducts,  the  latter  joining  to  form  a  single  main  excretory  duct  which  opens  upon 
the  free  surface  of  the  mucous  membrane.  The  last-named  passage  is  lined  for  some 
distance  by  cells  resembling  those  covering  the  adjacent  mucous  membrane  ;  where 
these  are  stratified  squamous  in  type,  this  character  is  maintained  for  only  a  limited 

FIG.  1287. 


•i  &  -;ii %    v'' :      •  ' 
"  /  '.       - 


Wl,,;r    :-'-,. 


^w/-    • 

J^i'i^     ; 


/         "^  '^si''    >i  I     /•  :<i^'!-'' 

'  '•          vA  V/;5^-  i    ••'•      ;  £+*  -i^-rfvife;  *"  „<*-;--  :A    . 

Mucous  alveoli  X  /'  '•-    , .  f  *  ^,,  •;-^-'-:'^^,>,-    \ 

•   ;•'"  '  .-V1^.^'':':"    "•  '.    \ 
_:    •  --»:£/     .  v  • ..  -•.•'      \ 

v    lfit$'';'^''~    ''J^''  Serous  alveoli 

Section  of  posterior  part  of  tongue,  showing  alveoli  of  serous  and  mucous  types  of  glands.    X  60. 

extent,  before  the  interlobar  ducts  are  reached  gradually  giving  place  to  a  simple, 
sometimes  at  first  double,  layer  of  columnar  epithelium  which  extends  as  far  as  the 
intralobular  tubules.  The  walls  of  the  larger  ducts  consist  of  a  fibro-elastic  coat,  lined 
by  epithelium,  and  sometimes,  in  the  case  of  the  large  glands,  as  the  parotid,  liver, 
pancreas,  or  testicle,  are  strengthened  externally  by  a  layer  of  involuntary  muscle. 
In  the  case  of  the  large  ducts  the  latter  is  usually  disposed  as  a  transverse  and  longi-' 
tudinal  layer,  to  which,  as  in  the  hepatic  duct  (Hendrickson),  a  third  oblique  one 
may  be  added.  Differential  stains  show  the  presence  of  a  large  amount  of  elastica. 

The  glandular  epithelium  lining  the  alveoli  rests  upon  the  limiting  basement 
membrane  as  a  single  layer  of  irregularly  spherical  or  polygonal  secreting  cells  ;  these 
do  not  completely  fill  the  alveolus,  but  leave  an  intercellular  cleft  into  which  the 
product  of  the  cells  is  poured  and  in  which  the  system  of  excretory  ducts  begins. 
Depending  upon  the  peculiarities  of  the  cells  and  the  character  of  their  secretion, 
glands  are  divided  into  serous  and  mucous. 


1534 


HUMAN   ANATOMY. 


FIG.   1288. 


The  serous  glands  are  distinguished  by  cells  which  are  distinctly  granular, 
generally  pyramidal  in  form,  with  nuclei  situated  in  the  vicinity  of  the  centre.  The 
secretion  elaborated  by  such  glands  is  thin  and  watery.  The  general  appearance-  <  >f 
the  cells  depends  upon  the  number  and  size  of  the  granules  stored  within  their  cyto- 
plasm, and  changes  markedly  with  the  variations  of  functional  activity  of  the  gland. 
When  a  serous  gland  is  in  a  condition  of  rest,  the  cells  are  loaded  with  secretion, 
and  appear,  therefore,  larger  and  coarsely  granular.  After  active  secretion,  on  the 
contrary,  the  cells  are  exhausted  and  smaller  and  contain  little  of  their  product,  often 
exhibiting  differentiation  into  a  clear  outer  zone,  free  from  granules,  and  a  darker 
inner  zone,  next  the  lumen,  in  which  the  granules  still  remain. 

The  mucous  glands  elaborate  a  clear,  viscid,  homogeneous  secretion,  which, 
when  present  in  considerable  quantity,  as  during  rest,  distends  the  cells,  crowding 
the  nuclei  to  the  periphery  against  the  basement  membrane,  and  gives  to  the  glandu- 
lar epithelium  a  clear  and 
transparent  appearance  in 
marked  contrast  to  the 
granular  character  of  the 
elements  of  a  serous  gland. 
During  rest,  when  loaded 
and  distended  with  mucoid 
secretion,  the  transparent 
cells  possess  well-defined 
outlines,  and  present  a  nar- 
row peripheral  zone  con- 
taining the  displaced  nuclei 
and  granular  protoplasm. 
After  prolonged  activity  the 
exhausted  cells  contain  rela- 
tively little  mucoid  secre- 
tion, and  hence  the  threads 
of  spongioplasm  are  no 
longer  widely  separated,  but 
lie  closely  ;  in  consequence 
of  these  changes  the  cells 
lose  their  former  transpar- 
ency and  resemble  the 
elements  of  serous  glands, 
becoming  smaller,  darker, 
and  more  granular  than 
the  cells  of  the  quiescent 
mucous  gland 

The  alveoli  of  mucous 
glands  often  contain  small 
crescentic  groups  of  small 
granular  cells  lying  between 
the  usual  larger  clear  ele- 
ments and  the  basement 
membrane  ;  these  are  the 
crescents  of  Gianurjzi,  or  demilunes  of  fJcidenhain,  the  interpretation  of  which  has 
caused  much  discussion.  The  older  view  regarded  the  crescents  as  groups  of  cells 
differing  from  the  surrounding  ones  only  in  their  stage  of  activity  and  not  in  their 
essential  characters,  all  the  cells  within  the  alveolus  being  of  the  same  nature.  Tin- 
opposite  view,  advanced  by  Ebner  over  a  quarter  of  a  century  ago,  has  received  sup- 
port from  more  recent  critical  studies  by  Kuchenmeister,  Solger,  Oppel,  R.  Krause, 
and  others,  who  have  shown  that  the  cells  composing  the  crescents  differ  from  the 
mucus-containing  elements,  elaborate  a  special  secretion,  and  are  similar  to,  if  not 
identical  with,  those  tilling  the  alveoli  of  serous  glands.  According  to  these  observers, 
the  crescents  are  groups  of  serous  cells  compressed  and  displaced  by  the  predomi- 
nating mucous  elements,  but  not  excluded  from  the  lumen  of  the  alveolus,  as  was 


Demilune  of 
serous  cells 


Duct 


Mucous  cells 


V 


Demilune 


Section  of  human  sublingual  gland,  showing  serous  cells  arranged  as  demi- 
lunes.   X  300. 


GLANDS.  1535 

formerly  thought  to  be  the  case,  since  extensions  of  the  lumen  pass  between  the 
mucous  cells  to  reach  the  demilunes. 

In  addition  to  the  main  alveolar  lumina,  always  narrow  in  serous  and  wider  in 
mucous  acini,  the  existence  of  intercellular  passages,  or  secretion-capillaries,  has  been 
established  for  many  glands,  especially  by  the  employment  of  the  Golgi  and  other 
special  methods.  These  clefts  penetrate  laterally  be- 
tween the  glandular  epithelium  from  the  axial  lumen  1289. 
towards  the  basement  membrane,  partially  enclosing 
the  secreting  cells  with  a  branching  system  of  minute 
canals.  Alveoli  containing  exclusively  mucous  cells 
do  not  possess  these  intercellular  canaliculi,  the  axial 
lumen  alone  being  present.  In  acini  of  the  serous 
type  the  accessory  channels  are  represented  by  minute 
branching  passages  which  penetrate  between  the  cells, 
but  seldom  reach  the  basement  membrane.  The  most 
conspicuous  of  the  secretion-capillaries  occur  in  alve- 
oli containing  the  demilunes,  the  product  of  the 
serous  cells  escaping  into  the  main  lumen  by  means 
of  the  lateral  intercellular  canals  which  pass  between 
the  mucous  elements  to  reach  the  peripheral  group  of  Section  of  several  alveoli  of  submax- 
serous  cells  composing  the  crescent.  The  view  that  |j£g  f^mi^Zriipsbfg 
the  secretion -capillaries  normally  extend  into  the  cyto-  t«  crescentic  (stippled)  groups  of  serous 

,     ,  111  -11-  i  r  cells-     x  5°o-     (Retzms.) 

plasm  of  the  glandular  epithelium,  and  are,  therefore, 

also  intracellular,  must  be  regarded  as  doubtful  and  still  undecided,  although  sup- 
ported by  many  able  histologists. 

Depending  upon  the  distribution  of  the  two  varieties  of  alveoli,  the  tubo- 
alveolar  glands  may  be  divided  into  four  groups  (Ebner): 

1.  Pure  serous  glands,  in  which  only  serous  alveoli  occur,  as  the  parotid. 

2.  Mixed  serous  glands,  in  which  a  few  mucous  alveoli  are  intermingled  with  the 
serous,  as  the  submaxillary. 

3.  Mixed  mucous  glands,  in  which  the  serous  cells  occur  as  crescentic  groups  or 
demilunes,  as  the  sublingual  and  buccal. 

4.  Pure  mztcous  glands,  without  serous  alveoli  or  demilunes,  as  the  palatal. 
Simple  alveolar  or  saccular  glands  in  their  typical  flask-like  form,  as  seen 

in  the  skin  of  amphibians,  are  not  found  in  man.  The  dilated  spherical  fundus  is  lined 
with  clear  and  distended  secreting  cells,  in  which  the  nuclei  are  displaced  towards  the 
periphery  by  the  mucus  elaborated  within  the  epithelial  elements.  In  the  higher 
animals  this  type  of  gland  is  represented,  somewhat  modified,  by  the  simple  sebaceous 
follicles. 

Compound  alveolar  or  saccular  glands  constitute  a  group  much  less  exten- 
sive than  formerly  supposed,  since  careful  study  of  the  form  and  arrangement  of  many 
organs,  as  the  salivary  glands,  pancreas,  etc. ,  has  shown  that  these  are  more  appro- 
priately regarded  as  tubo-alveolar  than  as  branched  saccular  glands.  The  latter, 
however,  still  have  representatives  in  the  larger  sebaceous  and  Meibomian  glands. 
The  most  conspicuous  example  of  the  compound  saccular  or  racemose  type  is  the 
lung,  which  in  its  development  and  the  arrangement  of  the  air-tubes  and  the  sac-like 
terminal  compartments  corresponds  to  this  variety. 

The  blood-vessels  distributed  to  glands  are  always  numerous,  since  secretory 
activity  implies  a  generous  blood-supply.  In  the  case  of  the  smaller  and  simpler 
glands,  the  capillaries  within  the  mucosa  form  a  mesh-work  outside  the  basement 
membrane  enclosing  the  glandular  epithelium.  The  large  compound  glands  are  pro- 
vided with  a  vascular  system  which  usually  corresponds  in  its  general  arrangement 
to  that  of  the  excretory  ducts,  following  the  tracts  of  the  interlobar  and  interlobular 
areolar  tissue  and  its  extensions  between  the  groups  of  the  alveoli.  On  reaching  the 
individual  acini,  the  capillaries  form  net-works  which  surround  the  basement  mem- 
brane enclosing  the  alveoli,  thus  bringing  the  blood-current  into  close,  but  not  direct, 
relation  with  the  secreting  cells,  an  arrangement  favoring  the  selection  by  the  proto- 
plasm of  the  particular  substances  required  for  the  function  of  the  gland.  When  the 
relation  between  the  glandular  epithelium  and  the  capillaries  is  unusually  intimate, 


1536 


HUMAN   ANATOMY. 


as  in  the  case  of  the  liver,  a  distinct  basement  membrane  is  sometimes  wanting,  a 
delicate  supporting  reticulum  alone  intervening  between  the  blood-stream  and  the 
protoplasm  of  the  cells.  Although  subject  to  local  deviations,  conspicuously  excep- 
tional in  the  liver,  the  veins  follow  in  general  the  course  of  the  arterial  branches,  the 
larger  blood-vessels,  together  with  the  main  excretory  ducts,  the  lymphatics,  and  the 
nerves,  occupying  the  principal  extension  of  the  connective  tissue  into  the  glandular 
mass. 

The  lymphatics  are  represented  by  the  larger  trunks  which  follow  the  excretory 
ducts  and  freely  anastomose  within  the  interlobular  areolar  tissue.  After  the  intra- 
lobular  portion  of  the  vessel  is  reached,  its  definite  character  is  gradually  lost  until  the 
lymphatic  channels  are  to  be  recognized  only  as  the  clefts  between  the  bundles  of 
connective  tissue  separating  the  alveoli. 


FIG.  1290. 


FIG.  1291. 


Injected  gastric  mucous  mem- 
brane, showing  capillary  net-work 
surrounding  tubular  glands.  X  55- 


Section  of  submaxillary  gland  of  rabbit ;  upper 
half  of  figure  shows  distribution  of  nerve-fibres 
to  alveoli ;  lower  half  shows  terminal  ducts  and 
secretion-capillaries.  X  290.  (Jfftsinx.t 


The  nerves  supplying  the  larger  glands  include  fibres  from  two  sources,  the 
cranial  or  spinal  nerves  and  the  sympathetic.  They  follow  the  interlobular  excretory 
ducts,  around  which  plexuges  are  formed,  ganglion-cells  being  frequent  at  the  points 
of  junction.  The  stronger  twigs  contain  a  preponderating  proportion  of  thick 
medullated  fibres,  which  become  progressively  less  in  size  and  number  in  their  course 
towards  the  alveoli.  Upon  reaching  the  latter  the  nerves  consist  almost  entirely  of 
nonmedullated  fibres,  and  in  the  end-plexuses  around  the  alveoli  such  fibres  alone 
are  present.  The  terminal  distribution,  as  demonstrated  by  the  Golgi  and  methylene- 
blue  methods,  includes  cfiilctnniar  and  hypolcmmar  fibriUa:,  the  former  lying  upon 
and  the  latter  beneath  the  basement  membrane.  The  hypolemmar  fibrillae  pass  into 
the  acini  from  the  extra  alveolar  plexus  formed  by  the  filaments  surrounding  the  base- 
ment membrane.  The  ultimate  relation  between  the  terminal  fibrillce  and  the  glandu- 
lar epithelium  is  still  uncertain,  but  it  may  be  regarded  as  established  that  the  nerves 
extend  between  and  around  the  cells  ;  an  intracellular  termination,  on  the  contrary, 
is  doubtful.  Retxius,  Ebner,  and  others  agree  in  picturing  the  delicate  perialveolar 
plexus  as  consisting  of  tortuous  and  convoluted  filaments  which  end  in  occasional 


GLANDS. 


1537 


FIG.  1292. 


delicate  varicosities.  Arnstein  l  has  described  a  special  minute  plate-like  end-organ 
as  a  widely  occurring  mode  of  nerve-ending  in  glands.  W.  Krause 2  has  noted  in 
certain  glands  a  form  of  end-capsule  resembling  a  simplified  Pacinian  corpuscle.  The 
sympathetic  fibres  are  distributed  especially  to  the  involuntary  muscle  of  the  blood- 
vessels and  the  ducts,  the  peristaltic  wave  within  the  muscular  coat  of  the  latter  facili- 
tating emptying  of  the  secretion. 

Development. — Since  glands  are  only  extensions  of  the  mucous  membrane  or 
integument  upon  which  they  open,  their  development  begins  as  an  outgrowth  or 
budding  from  the  epithelium  covering  such  surfaces.  In 
the  simple  tubular  glands  the  minute  cylinders  are  closely 
placed  and  composed  of  densely  packed  cells.  In  the 
case  of  the  larger  compound  glands,  as  the  salivary  or 
pancreas,  the  first  anlage  consists  of  a  solid  cylindrical 
plug  which,  penetrating  into  the  mesoblast,  soon  begins 
to  branch.  The  ends  of  the  terminal  divisions  enlarge 
and  eventually  become  the  alveoli.  Meanwhile  the  sur- 
rounding mesoblast  undergoes  condensation  and  forms 
the  interlobular  and  other  septa,  as  well  as  the  general 
envelope,  or  capsule,  thereby  giving  definite  form  to  the 
general  glandular  aggregation.  The  vascular  and  other 
structures  usually  found  within  the  interparenchymatous 
tissue  are  secondary  and  later  formations.  The  develop- 
ment of  the  gland  involves  a  double  process  of  active 
growth, — not  only  the  extension  of  the  epithelial  pro- 
cesses, but  also  a  coincident  invasion  and  subdivision  of 
the  latter  by  the  mesoblast  to  form  the  constituent  units 
of  the  organ.  The  lumen  of  the  gland  appears  first  in 
the  main  excretory  duct,  from  which  it  extends  into  the 
secondary  tubes  and,  finally,  into  the  alveoli.  Growth, 
separation,  and  more  regular  arrangement  of  the  cells 
composing  the  epithelial  cylinders  are  the  chief  factors  in  producing  the  lumen.  In 
the  early  condition  of  the  glands,  before  the  assumption  of  functional  activity,  the 
cells  later  constituting  alveoli  of  the  serous  or  mucous  type  are  similar  and  without 
histological  distinction.  Upon  the  establishment  of  their  different  roles,  however, 
the  characteristics  distinguishing  the  varieties  of  glands  appear,  the  differences  de- 
pending upon  physiological  rather  than  upon  inherent  anatomical  variation. 

1  Anatom.  Anzeiger,  Bd.  x.,  1895.  • 

2  Zeitschrift  f.  rational.  Med.,  Bd.  xxiii.,  1865. 


Section  of  foetal  oral  mucous 
membrane,  showing  developing 
tubo-alveolar  gland.  X  50. 


97 


THE  ALIMENTARY  CANAL 

THIS  is  a  long  and  complicated  tube  extending  from  the  mouth  to  the  anus. 
Excepting  the  two  ends,  each  of  which  is  at  first  a  pouch  from  the  ectoblast,  it  is 
developed  from  the  entoblast  with  a  mesoblastic  envelope.  It  consists  of  the  month, 
pharynx,  and  oesophagus  above  the  diaphragm,  and  of  the  stomach  and  small  and 
large  intestines  below  it.  There  are  many  accessory  organs  connected  with  it  whose 
primary  function  is  to  assist  in  the  process  of  nutrition.  The  chief  ones  above  the 
diaphragm  are  the  teeth,  the  tongue,  and  the  salivary  glands ;  those  below  it  are 
glands  of  various  kinds,  mostly  so  small  as  to  be  contained  in  the  mucous  membrane. 
But  two  distinct  organs,  the  liver  and  the  pancreas,  belong  to  this  class,  both  being 
originally  outgrowths  from  the  gut.  The  trachea  and  lungs  have  a  similar  origin, 
but  their  physiological  function  is  so  different  that  they  are  treated  of  under  a  separate 
heading. 

The  general  structural  plan  of  the  digestive  tube,  presenting  in  places  great  mod- 
ifications, is  :  (i)  a  lining  of  mucous  membrane  ;  (2)  a  submucous  layer  of  areolar 
tissue,  into  which  glands  may  penetrate  from  the  former  ;  (3)  a  double  layer  of  non- 
striped  muscular  fibres,  of  which,  as  a  rule,  the  inner  is  circular  and  the  outer  longi- 
tudinal ;  (4)  below  the  diaphragm,  a  serous  covering  from  the  peritoneum,  which, 
although  originally  complete,  is  in  the  adult  wanting  in  certain  parts. 

The  length  of  the  alimentary  canal  is,  on  the  average,  not  far  from  9  m.  (ap- 
proximately 30  ft.),  of  which  not  more  than  45  cm.  (about  18  in.)  is  above  the 
diaphragm.  A  preliminary  sketch  of  the  divisions  above  the  diaphragm  may  be  con- 
venient. The  vestibule  of  the  mouth  is  the  space  between  the  lips  and  cheeks  exter- 
nally and  the  jaws  and  teeth  internally.  The  (potential)  cavity  of  the  mouth  is  within 
the  arches  of  the  gums  and  teeth.  It  is  bounded  above  by  the  hard  palate  and  its 
backward  continuation  the  soft  palate.  The  greater  part  of  the  floor  is  occupied  by 
the  tongue.  There  is  a  free  horseshoe-shaped  space  beneath  the  tongue  within  the 
lower  jaw,  called  the  alveolar-lingual  groove  or,  better,  the  sublingual  space.  The 
pharynx  joins  the  mouth  at  the  anterior  pillar  of  the  fauces,  a  fold  passing  outward 
and  downward  to  the  tongue  from  the  soft  palate.  The  pharynx  extends  from  the 
base  of  the  skull  to  the  lower  border  of  the  larynx.  The  upper  part,  the  naso- 
pharynx, is  behind  the  nasal  chambers  which  open  into  it,  the  oro-pharynx  is  behind 
the  mouth,  and  the  laryngo- pharynx  behind  the  larynx.  At  the  lower  border  of  the 
larynx  it  is  followed  by  the  oesophagus,  a  long  tube  which,  piercing  the  diaphragm, 
opens  into  the  stomach. 

THE   MOUTH. 

The  framework  of  the  mouth  is  made  by  the  hard  palate  and  the  alveolar 
processes  of  the  upper  jaw,  by  the  greater  part  of  the  body  (including  the  alveolar 
processes)  of  the  lower  jaw  and  part  of  the  ramus,  and  by  the  hyoid  bone,  to  which 
may  be  added  the  mylo-hyoid  muscle  forming  the  floor. 

When  the  lips  are  opened  and  the  lower  jaw  dropped,  the  mouth  is  a  true  cavity 
extending  to  the  pharynx  ;  when  these  parts  are  closed,  the  tongue  fills  practically  the 
whole  space.  It  is  convenient,  however,  to  speak  of  the  cavity  of  the  mouth.  This 
space  is  subdivided  into  the  vestibule  or  preoral  cavity  and  that  of  the  oral  cavity  or 
mouth  proper.  The  former  is  the  region  between  the  closed  lips  and  cheeks  in  front 
and  the  closed  jaws  and  teeth  behind.  When  the  lips  are  closed,  it  communicates  with 
the  mouth  proper  only  by  a  small  passage  behind  the  wisdom-teeth,  in  front  of  the 
ramus  of  the  jaw. 

THE   LIPS,   CHEEKS,  AND   VESTIBULE. 

The  orifice  of  the  mouth  (rima  oris)  is  a  transverse  slit  of  variable  length, 
bounded  by  projecting  folds, — the  lips.  These,  like  the  checks,  with  which  they  arc 
continuous,  are  composed  of  complicated  layers  of  muscle,  covered  externally  by 
skin  ami  internally  by  mucous  membrane. 

1538 


THE  LIPS,  CHEEKS,  AND   VESTIBULE. 


1539 


Fat  is  found  irregularly  disposed  among  the  muscles  of  the  cheeks  in  varying 
quantity,  but  in  the  depression  in  front  of  the  masseter  and  superficial  to  the  buccinator 
there  is  a  distinct  ball  of  fat  enclosed  by  a  capsule,  which  is  the  remnant  of  the  so- 

FIG.  1293. 


Frontal  sinu 


Orbicularis  oris 


•Sphenoidal  sinus 
Sphenoid 

Pharyngeal  tonsil 

.Orifice  of  Eustachian 
tube 

Soft  palate 
Atlas 


Genio-glossus 


Genio-hyoid 


Epiglottis 


Mylo-hyoi 

Hyoid  bone 


Sagittal  section  of  head  of  young  adult,  three-fourths  natural  size. 

called  "  button"  of  infancy, — a  collection  which  gives  resistance  to  the  cheek  and  pre- 
vents it  from  being  flattened  by  atmospheric  pressure  during  nursing.  The  mucous 
membrane  is  reflected  from  the  cheeks  onto  the  jaws,  where  it  covers  the  gums. 
This  line  of  reflection  at  the  middle  of  the  lower  jaw  is  7  or  8  mm.  from  the  alveolar 


154° 


HUMAN   ANATOMY. 


border  and  about  twice  as  far  from  it  in  the  upper.  In  both  jaws,  but  especially  in 
the  lower,  the  line  approaches  the  teeth  as  it  passes  backward.  There  is  a  distinct 
fold  or  frenum  of  mucous  membrane  passing  from  the  anterior  nasal  spine  to  the 
middle  of  the  upper  lip.  The  free  edge  is  often  irregular,  and  may  have  a  nodular 
enlargement.  A  much  smaller  fold  is  often  found  on  each  side  in  the  region  of 
the  bicuspids.  A  median  fold  to  the  lower  lip  is  small  and  inconstant.  Externally 
the  lips  present  a  red  region  of  modified  mucous  membrane,  intermediate  between 
the  skin  of  the  face  and  the  mucous  membrane  of  the  mouth.  A  sagittal  section 
through  either  lip  shows  these  three  parts.  In  the  new-born  the  intermediate '  part 
is  subdivided  into  two,  of  which  the  inner — rather  the  broader — more  closely  resem- 
bles true  mucous  membrane  than  the  latter.  After  death  in  the  young  child  it 
assumes  a  brownish  color,  which  has  been  mistaken  for  the  effect  of  acid.  In  the 
adult  these  two  subdivisions  lose  their  distinctness.  The  lower  lip  is  the  larger  and 

FIG.  1294. 


^^f  Ul.lf,  UMl 

"    .    /    /    Sublingual  glan 


Facial  artery  _i_ 
Mandible — V — 


Mylo-hyoid 
Platysma 


Anterior  belly  of  digastric 


Genio-hyoid 


Genio-glossus 

Frontal  section,  showing  oral  cavity  and  lower  part  of  nasal  fossae  ;  plane  of  section  passes  through  anterior  end  of 

zygoma.    Three-fourths  natural  size. 

1 


fuller,  showing  more  red  except  towards  the  angles  of  the  mouth,  where  it  disap- 
pears. Its  lower  border  is  slightly  indented  in  the  middle.  The  upper  lip  shows  a 
more  marked  indentation  below  a  little  gutter,  the  philtrum,  running  down  from  the 
nasal  septum.  A  slight  median  prominence  of  the  lower  edge  of  the  upper  lip  is  the 
tubercle,  which  interrupts  the  straightness  of  the  cleft  when  the  lips  are  closed,  making 
the  line  resemble  a  Cupid's  bow. 

The  muscles  of  the  lips  are  a  complicated  interlacement  from  many  sources. 
The  orbicularis  oris,  formerly  supposed  to  form  a  sphincter,  has  no  separate  exist- 
ence. The  general  plan  is  as  follows.  The  upper  fibres  of  the  buccinator  enter  the 
lower  lip  and  pass  out  at  the  opposite  angle  to  ascend  into  the  upper  part  of  the  other 
buccinator.  Those  of  the  lower  part  traverse  the  upper  lip  in  a  similar  manner. 
The  layer  formed  by  the  buccinator  lies  under  the  mucous  membrane  near  the  border 
of  the  lips,  and  bends  forward  so  that  its  edge  is  nearest  the  skin  at  about  its  junction 

1  Otto  Neustatter  :  Ueber  den  Lippensaum,  etc.,  Inaug.  Dissert.,  Munich,  1894. 


THE  LIPS,  CHEEKS,  AND   VESTIBULE. 


FIG.   1295. 


with  the  free  red  surface.      In  the  lower  lip  the  quadratics  (depressor  labii  inferioris) 
runs  upward  under  the  skin  to.  break  up  into  fibres  ending  in  the  lips.      The  tri- 

angularis  (depressor  anguli  oris)  passes 
at  the  angle  of  the  mouth  into  the  upper 
lip  and  ends  as  a  series  of  separate  fibres 
inserted  into  the  mucous  membrane,  many 
of  them  crossing  the  middle  line.  This 
muscle,  before  it  breaks  up,  is  in  the  same 
plane  as  the  buccinator,  but  farther  from 
the  edge  of  the  lips.  Some  German  au- 
thors, by  grouping  together  the  various 
muscles  of  the  upper  lip,  have  made  a 
siiperior  quadratics  and  triangularis 
which  are  disposed  in  a  similar  manner 
.to  the  lower  ones.  Besides  these  there 
are  two  muscles,  the  zygomaticus,  de- 
scending, and  the  risorius,  ascending, 
which  meet  at  the  oral  angles  and  end 
-there  in  the  skin  or  mucous  membrane, 
or  in  both.  There  are  also  numerous 
fibres,  seen  only  with  the  microscope  in 
sagittal  sections,  passing  from  the  skin 
to  the  mucous  membrane  ;  these  consti- 
tute the  rectus.1 


Philtrum       — 


Tubercle 


Labial  region,  from  life,  reduced  one-fifth. 


FlG.    1296. 

-  ,  |w( 
Hi 


Labial  glands 


Fibres  of  orbicularis-iiiti 
V^ 


Transition  into  true 

mucous  membrane 


Modified  mucous  membrane 


Integument 


Sebaceous  gland 


Transition  into 
modified  skin 


Sagittal  section  of  lip  of  young  child.     X  20. 


The   mucous    membrane,    which    is    smooth,   is  so  closely  attached   to  the 
muscles  that  it  follows  the  movements  of  the  latter.      Mucous  glands  are  lodged  in  its 
1  Aeby  :  Archiv  f.  mikro.  Anat. ,  Bd.  xvi.,  1879. 


1542  HUMAN   ANATOMY. 

deeper  parts  and  in  the  scanty  submucous  tissue.  They  are  named  labial,  buccal, 
and  molar,  according  to  their  situation.  The  labial  glands  are  gathered  into  a  series 
of  groups  near  the  inner  border  of  the  lips,  the  buccal  glands  are  smaller  and  scattered, 
and  the  molar  glands  are  well-defined  groups  opposite  the  molar  teeth.  The  duct 
of  the  parotid  gland  (y.v.)  opens  into  the  vestibule,  the  space  between  the  lips  and 
cheeks  externally,  and  the  teeth  and  alveolar  processes  internally.  Separating  the 
vestibular  space  from  that  of  the  mouth  proper  behind  the  alveolar  processes  is  a 
prominent  fold  of  mucous  membrane  over  the  pterygo-maxillary  ligament.  This  fold 
appears  at  the  inner  side  of  the  last  upper  molar  and  runs  downward  and  outward  to 
that  of  the  lower.  The  space  behind  the  teeth  when  the  mouth  is  closed  is  small, 
but  a  tube  some  5  mm.  in  diameter  can  be  passed  through  it. 

Vessels. — The  arteries  supplying  the  lips,  which  are  very  vascular,  are  chiefly 
the  coronary  branches  of  the  facial  arteries,  each  of  which  forms  an  arch  meeting  its 
fellow  in  each  lip.  The  vessel  lies  between  the  muscles  and  the  glands  of  the  mucous 
membrane,  nearly  opposite  the  line  of  junction  of  the  latter  and  the  intermediate  por- 
tion. The  pulsation  is  easily  felt  through  the  mucous  membrane.  The  veins,  less 
regular,  lie  on  the  outer  side  of  the  muscles.  The  lymphatics  empty  into  the  glands 
at  the  angle  of  the  jaw,  excepting  those  near  the  median  line  of  the  lower  lip,  which 
run  into  the  suprahyoid  glands. 

Nerves. — The  mucous  membrane  of  the  cheek  is  supplied  by  the  buccal  branch 
of  the  inferior  maxillary  division  of  the  fifth  cranial  nerve,  the  lips  by  the  terminal 
branches  of  its  second  and  third  divisions. 

THE   TEETH. 

In  form  the  teeth  present  three  parts, — the  body  or  crown,  coated  with  enamel  ;  a 
somewhat  constricted  part,  the  neck,  covered  by  the  gums  ;  and  the  root  or  fang, 
which,  covered  by  the  cementum,  is  fixed  in  the  socket.  The  greater  part  of  the 
tooth  is  composed  of  the  dentine  and  surrounds  the  pulp-cavity,  to  which  minute 
openings  in  the  root  or  roots  transmit  vessels  and  nerves. 

The  shape  of  the  crowns  is  the  basis  of  classification.  Thus,  in  the  front  teeth 
the  crown  is  flattened  so  as  to  have  a  chisel-like  shape,  adapted  to  cutting,  hence 
these  are  termed  incisors  ;  the  canine  teeth  have  the  crown  forming  a  single  point  or 
cusp  ;  the  bicuspids  have  two,  and  the  multicuspids,  or  molars,  several  cusps.  The 
crowns  of  all  the  teeth  may  be  considered  •  as  modifications  of  a  simple  cone,  or  as 
combinations  of  several  cones.1 

In  man  the  teeth  come  in  two  sets,  the  temporary  or  milk  and  the  permanent 
teeth  ;  the  total  number  of  the  former  is  twenty,  that  of  the  latter  thirty-two.  The 
number  and  arrangement  of  the  teeth  of  any  animal  is  expressed  in  its  dental  formula  ; 
this  for  man,  for  the  left  half  of  the  mouth,  may 'be  written  as  follows  : 

Temporary  Teeth  :  i 2  c  z  »i  2  (=  5  X  2  =  2oY 

a    i  2  V     5  ) 

Permanent  Teeth  :   /  2  c  I  tn  ~  m  3  (—  -  X  2  =  32^. 
2      i       2       3  \      8  / 

It  will  thus  be  seen  that  in  the  milk-teeth  there  are  no  bicuspids  and  one  molar  less. 

Since  the  typical  mammalian  dental  formula  is  i-  C-  bi-  wv  ,  it  may  be  assum 

3^43 

that  in  man  three  pairs  have  been  suppressed.     These  suppressed  teeth  are  occasion 
ally  represented  by  supernumerary  ones  ;  from  the  position  of  the  latter  it  is  probable 
that  the  missing  teeth  are  the  second  incisors  and  the  first  and  fourth  bicuspids. 

To  avoid  confusion  in  the  nomenclature  of  the  teeth  from  the  curve  of  the  jaws, 
it  is  customary  to  speak  of  the  Ar/>/V?/ and  //;/;>  ual  surfaces  of  the  incisors  and  canines, 
ami  of  the  facial,  or  bnccal,  and  lingual  surfaces  of  the  bicuspids  and  molars.  The 
sides  against  the  other  teeth  are  often  called  tin-  median  and  distal,  supposing  the 
teeth  to  be  implanted  in  a  straight  transverse  line.  This  is  not  satisfactory  in  all 

'See  Homologies,  page  1566. 


THE   TEETH. 


1543 


cases.  We  shall  speak  instead  of  the  inner  and  outer  sides  of  the  incisors  and 
canines  and  of  the  anterior  and  posterior  sides  of  the  bicuspids  and  molars.  If  the 
position  of  the  tooth  in  the  jaw  be  remembered,  no  confusion  is  possible. 

The  Incisors. — The  crowns  are  characterized  by  slightly  convex  quadrilateral 
labial  surfaces,  rather  broader  than  the  lingual  ones,  and  ending  in  straight  cutting 
edges,  slightly  concave  lingual  surfaces  slanting  forward  and  bevelled  at  the  edge, 
triangular  lateral  surfaces,  and  single  roots.  The  labial  and  lingual  surfaces  of  the 
crowns  are  bounded  at  the  root  by  curved  lines,  the  convexity  being  towards  the 
gums.  At  the  sides  these  borders  are  continued  as  straight  lines  towards  the  free 

FIG.   1297. 


Partly  developed  fangs  of  last  molar, 


Crown  of  last  molar 


Permanent  teeth,  showing  their  forms  and  relations;  outer  surface  of  jaws  partly  removed.     Last  molars  are  only 

partially  formed. 

edge,  and  meet  at  an  acute  angle.  The  enamel  is  continued  farther  on  the  lingual 
surface,  especially  in  the  lateral  incisors  of  both  jaws.  The  cutting  edge  shows  three 
small  scallops  on  its  first  appearance,  but  they  speedily  wear  away  (Fig.  1298). 

The  superior  median  incisors  are  much  the  largest.  The  labial  surface  of 
the  crown  is  nearly  square.  The  inner  half  of  this  surface  is  more  strongly  convex 
than  the  lateral.  Traces  of  three  swellings  are  often  found  on  the  labial  side  of  the 
lower  half  of  the  crown  extending  to  the  three  primitive  scallops  on  the  edge.  The 
free  edge  meets  the  internal  border  at  nearly  a  right  angle,  but  the  outer  angle  is 
rounded.  The  lingual  surface,  narrower  than  the  labial,  is  a  little  concave.  Some- 
times the  edges  are  raised  so  as  to  leave  a  distinct  V-shaped  depression,  in  the 
middle  of  which  runs  a  vertical  ridge,  the  cingulum,  which  ends  below  in  a  tubercle. 


1544 


HUMAN   ANATOMY. 


Often  the  cingulum  of  the  incisors  is  represented  merely  by  the  tubercle.  There  are 
all  kinds  of  intermediate  stages  between  this  and  a  nearly  plane  surface.  Sometimes 
the  tubercle  is  triple.  The  fang  is  nearly  conical,  and  usually  has  an  outward  slant. 
The  superior  lateral  incisors  are  more  cusp-shaped,  the  angles,  especially  the  outer, 
tending  to  be  rounded.  The  lingual  surface  is  less  plane  than  in  the  median  incisors 
and  the  cingulum  larger.  Sometimes  it  is  almost  a  distinct  cusp.  The  fang  is  also 
conical,  with  an  outward  inclination. 

The  inferior  incisors  are  smaller  than  the  superior,  and  the  median  ones  the 
smallest  of  all.  The  croivns  broaden  from  the  neck  to  the  edge.  This  feature  is 
more  marked  in  the  lower  races,  and  still  more  in  apes.  The  labial  surface  is  more 
nearly  plane  than  in  the  upper  ones  ;  the  lingual  surface  is  more  even.  The 
cingulum  is  small,  often  not  very  evident.  The  angles  of  the  free  edge  are  sharper 
than  those  of  the  upper  jaw,  excepting  the  outer  one  of  the  lateral  tooth,  which  is 
generally  rounded.  The  fangs  are  compressed  from  side  to  side  and  their  tips  turn 
a  little  away  from  the  median  line.  This  is  particularly  true  of  the  lateral  one,  but 


FIG.  1298. 


Unworn  surfaces  of  upper 
and  lower  permanent  incisor 
teeth,  lingual  aspect.  X  2. 


Median  incisor  teeth 
of  left  side,  labial  (A) 
and  lateral  (B)  aspects. 
(Letdy.) 


Temporary  incisor 
teeth  of  left  side.  A, 
median ;  B,  lateral  in- 
cisors. (Leidy.) 


The 


is  a  constant  feature  of  neither.     The  sides  of  the  fangs  are  often  grooved, 
external  groove  is  the  deeper,  and  when  only  one  is  present  it  is  on  that  side. 

The  pulp-cavity  is  relatively  large  in  the  superior  median  incisors,  in  which  it 
presents  three  expansions  towards  the  free  edge.  It  is  smaller  in  the  others,  and  has 
usually  but  two  distinct  diverticula.  The  canal  of  the  lower  teeth,  especially  when 
the  roots  are  deeply  grooved,  often  divides  below  the  pulp-cavity  into  an  anterior 
and  a  posterior  branch,  which  usually  reunite  before  reaching  the  tip  of  the  fang. ' 

The  upper  incisors  occupy  in  all  more  space  than  the  lower,  which  is  due  chirfly 
to  the  great  size  of  the  upper  median  ones.  In  the  lower  jaw  the  median  incisors 
are  the  smaller,  but  there  is  no  great  difference  between  them  and  the  laterals.  The 
superior  laterals  are  but  slightly  larger  than  those  below  them. 

The  temporary  incisors  differ  only  slightly,  save  in  size,  from  the  permanent 
ones.  The  edges,  however,  are  originally  straight,  except  those  of  the  inferior  median 
ones,  which  show  the  irregularities.1' 

The  Canines. — These,  called  by  the  Germans  the  "corner  teeth"  as  marking 
the  point  where  the  alveolar  arch  changes  direction  most  suddenly,  are  characterized 
by  a  crown  with  a  single  cusp,  a  long  conical  root  somewhat  compressed  laterally  and 
marked  by  a  groove  on  each  side.  The  crown,  convex  on  the  labial  side,  expands 

1  Miihlreiter  :  Anatomic  des  Menschlichen  drbisses,  I.Hp/ig,  1891. 

1  Zuckerkandl  :   Anatomic  der  Mundhohle,  mit  besondere  Beriicksichtigung  der  Zaline 
Wien,  1891. 


THE  TEETH. 


1545 


FIG. 


Canine  teeth  of  left  side, 
labial  (A)  and  lateral  (ft)  as- 

fects.     C,  temporary  canines. 
Leidy.) 


from  the  root  and  suggests  that  of  an  incisor  with  the  angles  taken  off.  The  lingual 
side  of  the  crown  of  the  upper  tooth  tends  to  be  convex,  often  having  a  ridge  running 
down  to  the  small  tubercle  at  the  base.  In  the  lower  tooth  this  side  is  plane  or  con- 
cave, with  a  distinct  tubercle,  which  exceptionally  is  enlarged 
so  as  to  hint  at  a  secondary  cusp.  The  sides  of  the  crown 
are  triangular.  The  borders  of  the  enamel  are  convex  to 
the  gum  on  the  labial  side,  less  so  on  the  lingual,  and  slightly 
concave  laterally.  The  _/#«£•  of  the  upper  tooth  is  the  longer 
and  the  less  compressed  ;  it  very  rarely  ends  in  a  bifurcation, 
but  this  is  less  uncommon  in  the  lower.  The  direction  of  the 
end  of  the  fang  is  uncertain.  The  whole  tooth  is  broader 
on  the  labial  than  on  the  lingual  side.  The  pulp-cavity  is 
most  marked  in  antero-posterior  sections,  which  show  an  en- 
largement of  its  continuation  at  the  beginning  of  the  root, 
just  beyond  the  neck. 

The  milk  canines  are  much  like  the  second  ones, 
only  smaller.  The  labial  surface  of  the  upper  tends  to  divide 
into  an  outer  and  an  inner  facet.  The  root  is  approximately 
triangular  on  section,  with  rounded  edges. 

The  Bicuspids  or  Premolars. — These  teeth,  of  which 
the  second  is  the  larger  in  both  jaws,  are  characterized  by 
crowns  with  two  cusps,  one  on  the  buccal  and  one  on  the 
lingual  side.  The  upper  ones,  being  very  much  the  more 
typical,  will  be  used  for  the  general  description.  Both  the 
labial  and  the  lingual  aspects  of  the  crowns  are  convex  ;  they 
expand  laterally  from  the  neck,  and  each  ends  in  a  pointed 
cusp  of  which  the  anterior  border  is  the  shorter.  This  is 
used  in  determining  the  side,  but  we  agree  with  Testut  that 
the  guide  is  often  useless.  The  buccal  cusp  is  the  larger.  The  cusps  are  separated 
by  a  furrow  from  which  small  ramifications  often  run  onto  the  buccal  one.  The  lin- 
gual cusp  has  an  unbroken  surface.  The  buccal  cusp  of  the  first  bicuspid  is  more 
prominent  than  the  lingual,  but  in  the  second  they  reach  the  same  plane.  The  bor- 
der of  the  enamel  is  convex  towards  the  root  on  both  the  buccal  and  lingual  aspects, 
the  ends  of  these  curves  meeting  on  the  other  sides.  The  fang  is  compressed  with 
a  groove  on  the  sides  next  its  neighbors.  That  of  the  second  is 
often  bifid  just  at  the  tip,  but  that  of  the  first  is  very  often,  per- 
haps usually,  divided  into  two  throughout,  having  a  buccal  and 
a  lingual  root.  Sometimes  the  former  is  subdivided,  so  that  it 
has  three  like  a  molar.  The  root  has  in  general  a  backward 
slant. 

The  lower  bicuspids  have  smaller  grinding  surfaces  on 
the  crowns  than  the  upper,  but  the  roots  are  longer,  and  the 
crowns,  seen  from  the  side,  are  at  least  as  large.  The  first  has 
a  well-developed  buccal  cusp,  curving  in  from  the  buccal  surface, 
and  a  very  small  lingual  one  connected  to  the  former  by  a  ridge 
interrupting  the  fissure  between  them,  which  gives  the  tooth 
something  of  the  effect  of  a  small  canine.  The  second,  like  that 
of  the  upper  jaw,  has  the  two  cusps  in  one  plane  ;  the  lingual 
one  is  sometimes  double,  and  the  plane  is  often  obscure.  The 
flattened  fang  is  but  faintly  grooved,  if  at  all,  and  is  rarely 
bifid. 

The  pulp-cavity  of  the  bicuspids  ends  in  an  expansion  below 
each  cusp,  that  under  the  buccal  being  the  larger.  In  the  upper 
teeth  the  cavity  is  much  compressed  from  side  to  side  in  the 
root.  In  the  first  upper  bicuspid  there  are  usually  two  pro- 
longations to  the  point  of  the  fang,  even  when  the  root  is  not 
split.  In  the  second  the  cavity  generally  agrees  with  the  conformation  of  the  root. 
In  the  lower  teeth  the  cavity  is  less  compressed  and  is  tolerably  roomy  as  it  enters 
the  root.  It. is  usually  single,  but  may  split. 


FIG. 


First  premolar  teeth 
of  left  side,  labial  (A) 
and  lateral  (£)  aspects. 
(Leidy.) 


1546 


HUMAN   ANATOMY. 


The  Molars. — These  teeth — three  on  each  side — are  distinguished  by  the  large 
crown,  into  which  the  neck  expands,  the  number  of  cusps  on  the  surface,  and  the 
greater  subdivision  of  the  root.  Those  of  the  lower  jaw  are  the  larger  ;  and  in  both 
jaws  the  first  is  the  largest  and  the  last  (called  from  its  late  appearance  the  tcisdom- 
tooth}  the  smallest.  The  croivns  are  convex  on  both  the  buccal  and  lingual  sides, 
but  nearly  plane  on  the  others.  The  enamel  ends  in  a  nearly  straight  line  all  the  way 
round.  The  grinding  surfaces  are  four-sided  ;  those  of  the  upper  are  somewhat  dia- 
mond-shaped, the  buccal  anterior  angle  being  rather  in  front  ;  those  of  the  lower  are 
nearly  parallelograms,  the  long  diameter  being  antero-posterior.  Typical  upper 
molars  have  four  cusps  at  the  angles  ;  typical  lower  ones  have  an  additional  cusp  at 
the  posterior  border  ;  but  in  the  upper  jaw  the  first  is  the  only  one  that  can  be  called 
typical. 

In  the  upper  molars  the  largest  cusp  is  the  anterior  lingual,  which  is  connected 
by  a  ridge  (the  cingulum)  to  the  posterior  buccal.  The  posterior  lingual  cusp  is  the 
smallest.  A  minute  rudimentary  cusp  is  found  on  the  lingual  surface  of  the  anterior 
lingual  cusp,  usually  too  small  to  reach  the  grinding  surface,  and  often  hard  to  recog- 
nize. Not  counting  this,  the  first  upper  molar  has  four  cusps  in  more  than  90 
per  cent.  Owing  to  the  cingulum,  the  grooves  on  the  grinding  surface  are  best 
described  as  two  oblique  ones,  the  first  from  the  anterior  border  to  the  middle  of  the 


FIG.  1303. 
A  B 


FIG.   1304. 

Upper  molars 


First 


Another  first 
Lower  molars 


Second 


First 


Another  first 


Second 


Second  molar  teeth  of  left 
side,  labial  (A)  and  lateral 
(/?)  aspects.  (Leiity.) 


Triturating  surfaces  of  molar  teeth  of  right 
side.  The  upper  margin  of  the  figures  corresponds 
to  the  labial  surface.  (  Leidy.  ) 


buccal,  the  second  from  the  lingual  border  to  the  middle  of  the  buccal.  They  are 
deepest  at  the  middle.  They  appear  on  the  buccal  and  lingual  sides,  deeper  on  the 
former,  but  rarely  reach  the  gum.  They  may  end  in  a  pit,  a  favorite  seat  of  caries 
(Tomes).  The  crown  of  the  second  upper  molar  presents  three  chief  forms  (Miihl- 
reiter).  It  may  have  four  cusps  and  differ  but  slightly  from  the  first  molar.  The 
lingual  surface  is  relatively  narrower  and  the  posterior  lingual  cusp  smaller.  In  the 
second  form  the  last-mentioned  cusp  is  wanting.  The  cingulum  persists  and  the 
grinding  surface  is  approximately  triangular.  The  third  form  is  compressed  from 
side  to  side  into  a  very  narrow  diamond,  with  the  anterior  buccal  cusp  in  front  and 
the  posterior  lingual  behind.  Three  and  four  cusps  are  about  equally  common  in  this 
tooth  in  Caucasians,  but  the  lower  races  have  more  often  four.  The  crown  of  the 
upper  wisdom-tooth  presents  many  remarkable  variations.  The  posterior  lingual 
cusp  is  wanting  in  about  two-thirds  of  the  cases.  The  crown  may  be  strongly  com- 
pressed, as  has  been  described  for  the  second  molar,  but  with  greater  variation.  In 
size  the  wisdom-tooth  may  be  very  large  or  very  small. 

The  crowns  of  the  lower  molars  are  divided  oy  a  crucial  fissure,  the  main  line 
running  antero  posteriorly.  The  hind  part  of  this  splits  so  as  to  enclose  the  fifth 
cusp,  which  is  near  or  actually  at  the  buccal  side.  The  effect  of  this  is  to  form  a 
cavity  at  the  crossing  of  the  lines  in  the  middle  of  the  crown.  The  lines  on  the  sides 


THE   TEETH. 


1547 


of  the  crowns  are  less  deep  than  in  the. upper  jaw.  Sometimes  the  fifth  cusp  is  wanting, 
in  which  case  the  posterior  part  of  the  furrow  does  not  divide  and  the  arrangement  is 
remarkably  symmetrical.  Very  rarely  the  first  molar  has  a  sixth  cusp  on  the  lingual 
side.  The  first  molar  has  five  cusps  in  more  than  90  per  cent. ;  the  second  four  only 
in  more  than  80  per  cent. ;  the  third  four  rather  more  often  than  five.  The  buccal 
cusps  of  the  lower  molars  are  worn  down  earlier  than  the  lingual  ones. 

The  following  tables  from  the  independent  researches  of  Rose l  and  of  Zuckerkandl  show 
the  percentage  of  frequency  of  different  groupings  of  cusps.  Although  there  is  some  discrepancy 
in  the  percentages,  both  agree  as  to  the  most  and  least  common  arrangement  in  both  jaws. 
These  statistics,  like  those  of  the  separate  teeth,  apply  to  Europeans.  (It  is  to  be  remembered 
that  a  certain  percentage  of  teeth  cannot  be  included.) 


Cusps  .  . 
Cusps  .  . 
Cusps  .  . 


UPPER  JAW. 
Molars. 


•444 
•443 
•433 


Per  Cent. 
Rose.          Zuck. 


LOWER  JAW. 
Molars. 
123  Per  Cent. 


Rose. 


Zuck. 


19.9 
28.9 
37-9 


9.6 
28.7 
60. 1 


Cusps 
Cusps 
Cusps 


•555  I9-8  u-5 
•545  30-4  30-5 
.544  40.4  50.0 


FIG.   1305. 


The  fangs  of  the  first  and  second  upper  molars  are  two  buccal  and  one  lingual, 
which  latter  is  much  the  largest.  It  is  often,  especially  in  the  first  molar,  grooved 
on  the  lingual  side.  It  is  conical  and  strongly  divergent.  It  often  shows  a  tendency 
to  subdivision,  which  may  actually  occur,  although  rarely.  The  two  buccal  ones  are 
compressed  antero-posteriorly  and  nearly  vertical.  The  front  one  is  the  broader,  and  is 
grooved  before  and  behind.  This  is  often  the  case  with  the  other.  The  roots  of  the 
upper  wisdom-tooth  are  smaller  ;  the  lingual  is  less  divergent,  and  may  be  connected 
by  a  plate  with  one  of  the  buccal  ones.  All  may  be  fused  more  or  less  completely  into 
one.  The  roots  of  the  inferior  molars  are  two  :  an  anterior  and  a  posterior,  of  which 
the  former  is  rather  the  larger,  both  compressed  from  before 
backward  and,  especially  the  first,  deeply  grooved,  suggesting 
the  fusion  of  two.  Sometimes,  again  especially  in  the  first, 
each  root  is  bifid.  Those  of  the  wisdom-tooth  are  usually 
nearer  together,  and  are  frequently  fused  into  a  common  coni- 
cal root.  Apart  from  their  position  in  the  jaws,  the  roots  of 
the  molars,  excepting  the  upper  wisdom-tooth,  have  a  back- 
ward slant  of  varying  degree.  Their  twists  and  curves  are 
remarkably  uncertain.  Sometimes  they  converge  and  some- 
times diverge  unduly,  hooking  in  either  case  under  bone,  so 
as  to  make  extraction  difficult  or  impossible.  The  pulp- 
cavity  of  the  molars  is  large,  especially  at  the  level  of  the 
neck.  In  the  upper  teeth  it  is  distinctly  wider  transversely 
than  from  before  backward.  It  has  as  many  prolongations 
towards  the  surface  as  there  are  cusps.  There  is  a  canal  in 
each  root  of  the  upper  teeth.  Those  in  the  buccal  fangs  are 
compressed,  that-  in  the  lingual  cylindrical.  The  anterior 
fang  of  the  lower  molars  has  two  canals  which  develop  from 
a  single  one.  The  posterior  fang  has  but  one. 

The  milk  molars  are  two  in  number.  Like  the  perma- 
nent ones,  the  lower  are  the  larger  ;  but,  unlike  them,  the 
second  tooth  is  larger  than  the  first  in  both  jaws.  The  crown 
of  both  first  molars  presents  a  prominence  on  the  buccal  sur- 
face near  the  root.  The  crown  of  the  first  upper  molar  is 

rather  suggestive  of  a  bicuspid,  although  there  are  two  buccal  cusps  and  one  lingual. 
The  first  inferior  molar  is  relatively  narrow  and  long  from  before  backward.  The 
length  of  the  buccal  side  is  greater  than  that  of  the  second  permanent  one.  The 
second  molars  resemble  very  closly  the  first  permanent  ones.  The  upper  has  four 
cusps  and  a  cingulum,  the  lower  five  cusps.  The  hollow  in  the  crown  of  the  tem- 
porary molars  is  relatively  deeper  than  that  of  the  permanent  ones,  but  smaller  and 
more  divergent.  .  They  straddle  the  crowns  of  the  developing  bicuspids. 

1  Anatom.  Anzeiger,  Bd.  vii.,  1892. 


Temporary  molar  teeth 
(A,  first;  B,  second)  of  left 
side.  Triturating  surfaces  of 
crowns  also  shown.  (Leidy.) 


1548 


HUMAN   ANATOMY. 


TOOTH-STRUCTURE. 

In  principle,  and  among  the  lower  vertebrates,  in  fact,  as  well,  teeth  may  be 
regarded  as  hardened  papillae  of  the  oral  mucous  membrane  ;  they  consist,  therefore, 
of  two  chief  parts, — the  connective-tissue  core  and  the  epithelial  capping.  Of  the 
three  constituents  present  in  typical  mammalian  teeth,  the  enamel  is  the  derivative  of 
the  ectoblastic  epithelium,  the  dentine,  with  the  pulp,  and  the  cementum  being  con- 
tributions of  the  embryonal  connective  tissue. 

The  Enamel. — This,  the  hardest  tissue  of  the  body,  covers  the  crown,  being 
thickest  on  the  cutting  edge  or  grinding  surface  of  the  tooth.  It  gradually  thins  away 

FIG.   1306. 


Contour  lines 
Schreger's  lines 

Neck 


Stripes  of  Retzius  (longitudinal) 


Prism-stripes  of  Schreger  (light  and 
dark) 


Gum 

Pulp-tissue 
IJfJL- Dentine     . 

Cementum 
Alveolar  periosteum 

Osseous  tissue  of  jaw 
Root-canal 


Sagittal  section  of  canine  tooth  in  situ.    Semi-diagrammatic. 

towards  the  neck,  around  which  its  terminal  border  appears  as  a  more  or  less  distinct 
and  often  serrated  edge.  The  external  surface  of  the  enamel,  especially  in  young 
teeth,  often  exhibits  a  tine  striation  composed  of  horizontally  disposed  lines.  Under 
a  hand-glass  these  lines  are  seen  to  be  minute  elevations,  the  enamel-ridges,  which 
encircle  the  crown.  The  remarkable  hardness  of  this  tissue  is  due  to  the  large-  amount 
(97  per  cent.)  of  earthy  material  and  the  small  proportion  of  organic  matter,  which 
latter  in  adult  enamel  averages  only  about  3  per  cent. ;  in  infantile  enamel  the  amount 
of  animal  material  is  from  five  to  six  times  greater  (Hoppe-Seyler). 


STRUCTURE   OF   THE   TEETH.  1549 

The  enamel — the  product  of  epithelial  cells,  the  ameloblasts — consists  of  an  aggre- 
gation of  five-  or  six-sided  columnar  elements,  the  enamel-prisms,  which  measure 
from  .0035-.  0045  mm.  in  diameter  and  from  3-5  mm.  in  length.  Their  general 
disposition  is  at  right  angles  to  the  surface  of  the  dentine  upon  which  they  rest,  on 
the  one  hand,  and  to  the  exterior  of  the  crown  on  the 

other.      They  usually  extend  the  entire  thickness  of  the  FIG.  1307. 

enamel,  and  are  of  slightly  larger  diameter  at  the  surface 
of  the  tooth  than  next  the  dentine,  in  this  manner  com- 
pensating for  the  increase  in  the  external  circumference 
of  the  crown.  The  assumption  that  additional  prisms 
are  intercalated  at  the  periphery  is  not  supported  by  the 
manner  of  the  production  of  the  enamel-columns.  The 
latter  run  for  a  short  distance  almost  at  right  angles  to 
the  surface  of  the  dentine,  then  bend  laterally  for  a 
considerable  part  of  their  course,  but  assume  a  vertical 
disposition  on  approaching  the  external  surface.  In 
addition  to  these  general  curves,  the  ranges  of  enamel- 
columns  possess  a  spiral  arrangement,  in  consequence 
of  which  the  parallelism  of  the  prisms,  as  seen  in  ground- 
sections,  is  disturbed  and  their  bundles  are  apparently 
interwoven. 

T         ,  .  ,  .  ,  Ground-section  of  enamel,  showing 

In  thin  accurately  transverse  sections  enamel  pre-       ranges  of  enamel-prisms,   x  500. 
sents  a  mosaic  in  which  the  hexagonal  areas  represent 

the  ends  of  the  individual  prisms.  Critically  examined,  the  areas  consist  of  a  darker 
central  portion  surrounded  by  a  narrow  lighter  peripheral  zone.  The  interpreta- 
tion of  the  latter  has  been  various,  many  observers  regarding  such  lines  as  cement- 
substance  holding  together  the  prisms.  According  to  Walkhoff,1  however,  what  is 
usually  regarded  as  cement-substance  is  a  cortical,  apparently  homogeneous  layer  of 
less  thoroughly  calcified  material  which  encloses  the  denser  central  portion  of  the 
prism  and  acts  as  a  cushion,  thereby  reducing  the  effect  of  pressure.  After  the 
decalcifying  action  of  acids,  the  prisms  may  be  outlined  by  stains  which  color  the 
very  meagre  amount  of  true  cement-substance  which  exists  between  the  enamel- 
columns  and  appears  as  delicate  lines  defining  the  prisms. 

Under  favorable  conditions,  especially,  but  not  only,  after  the  action  of  acids,  the 
enamel-prisms  exhibit  alternate  light  and  dark  transverse  markings.  The  true  rela- 
tions of  these  bands  are  to  be  appreciated  only  by  accurate  focusing  in  thin  sections 
passing  exactly  parallel  to  the  axes  of  the  prisms  ;  otherwise  the  obliquity  of  section 
produces  the  optical  distortions  often  represented  in  the  assumed  wavy  contour  of  the 
enamel-rods.  The  varicose  appearances  commonly  seen  depend  upon  the  beaded 
form  and  consequently  scalloped  border  of  the  denser  central  portion  of  the  prisms, 
which  give  a  corresponding  arrangement  to  the  lighter  cortical  substance  whreh  fills 
the  minute  inequalities  of  that  portion  ;  the  true  outline  of  the  enamel-prism,  how- 
ever, is  smooth  and  straight,  and  not  varicose,  as  the  optical  impressions  lead  one 
to  believe  and  as  usually  pictured.  According  to  Williams,  the  apparent  varicosities 
depend  upon  the  spherical  form  of  the  enamel -globules  of  which  the  prisms  are  built  up. 

When  an  axial  longitudinal  section  of  a  tooth  is  examined  by  reflected  light,  the 
enamel  displays  a  series  of  alternate  dark  and  light  bands, — the  prism-stripes  of 
Schreger.  These  markings  extend  generally  vertical  to  the  surface  of  the  enamel, 
and  depend  upon  the  relation  of  the  ranges  of  the  enamel-prisms  to  the  axes  of  the 
light-rays.  Rotation  of  the  illuminating  pencil  through  180°  effects  the  change  of 
the  dark  stripes  to  light  ones  and  vice  versa.  Each  stripe  includes  from  ten  to  twenty 
enamel-prisms,  and  is  invisible  by  transmitted  light. 

In  addition  to  the  foregoing  markings,  the  enamel  often  presents,  in  radial  longi- 
tudinal sections,  brownish  parallel  lines,  the  stripes  of  Retzius,  which  run  in  the 
general  direction  of  the  contour  of  the  tooth,  but  at  an  angle  of  from  15°  to  30°  with 
the  free  surface.  Seen  in  sections  cut  at  right  angles  to  the  tooth-axis,  these  stripes 
appear  as  a  series  of  concentric  lines  encircling  the  crown  parallel  to  and  near  the 
surface ;  in  the  middle  and  deeper  parts  of  the  enamel  they  are  less  evident  or  entirely 

1  Normale  Histologie  mensch.  Zahne,  1901. 


1550 


HUMAN   ANATOMY. 


FIG.   1308. 


Longitudinal  ground-section  of 
enamel,  treated  with  acid,  showing 
disposition  of  ranges  of  enamel-prisms 
(p,p')  in  stripes  of  Schreger.  Left 
third  of  figure  shows  alternate  light 

's  as  seen  " 
X  200.     (Ebner.) 


(s)  and  dark  (s')  bands  as  seen  by  re- 
flected light 


absent.  The  interpretation  of  the  stripes  of  Retzius  is  still  a  subject  of  dispute.  The 
brown  appearance  of  the  stripes  by  transmitted  light  only,  by  reflected  light  appear- 
ing bluish  white,  disproves  the  assumption  that  they  depend  upon  the  presence  of 
pigment  within  the  enamel.  The  widely  accepted  view  of  -Ebner,  that  the  stripes  are 
due  to  air  contained  in  the  interfascicular  clefts,  has  been  modified  by  Walkhoft,  who 

regards  the  markings  as  due  to  local  diminution  in  the 
calcification  of  the  enamel-prisms  during  certain  periods 
in  the  growth  of  the  tissue  when  the  central  as  well  as 
the  cortical  substance  of  a  great  number  of  columns 
fails  to  take  up  sufficient  lime  salts. 

The  enamel- cuticle,  or  membrane  of  Nasmyth, 
forms  a  continuous  investment  of  the  crown  of  the 
newly  erupted  tooth.  In  the  course  of  time  it  dis- 
appears from  the  areas  exposed  to  wear,  but  over  the 
protected  surfaces  it  may  persist  during  life.  The 
membrane  (.oog-.oiS  mm.  in  thickness)  is  transparent 
and  remarkably  resistant  to  the  action  of  acids,  less 
so  to  alkalies,  affording  admirable  protection  to  the 
underlying  enamel.  After  separation  from  the  latter 
by  acids  it  appears  structureless,  or  at  most  granular. 
The  inner  surface  of  the  membrane  presents  markings 
and  slight  irregularities  which  correspond  to  the  free 
ends  of  the  subjacent  enamel-prisms. 

The  origin  of  the  enamel-cuticle  has  been  much 
discussed,  and  even  now  is  not  without  some  uncer- 
tainty. It  may  be  regarded  as  established  that  it  rep- 
resents the  remains  of  part  of  the  tissue  once  concerned 
in  the  production  of  the  enamel.  The  latter  is  formed, 
as  more  fully  described  on  page  1561,  through  the 
agency  of  the  epithelial  cells  constituting  the  inner 

layer  of  the  enamel-organ.  With  the  completion  of  their  task  as  enamel  builders, 
these  cells  produce  a  continuous  cuticular  envelope  which  persists  as  Nasmyth' s 
membrane,  the  epithelial  elements  of  the  enamel-organ,  so  far  as  they  are  concerned 
in  forming  enamel,  subsequently  degenerating.  The  enamel-cuticle  is  continuous 
with  the  cortical  substance  of  the  prisms,  with  which  it  agrees  in  optical  and  chemical 
properties, — a  relation  which  confirms  the  identity  of  origin  of  Nasmyth' s  membrane 
and  the  enamel-columns. 

The  Dentine. — The  dentine  or  ivory  resembles  bone  both  in  its  genesis  and 
chemical  composition,  being  a  connective  tissue  modified  by  the  impregnation  of  lime 
salts.  Dentine  exceeds  bone  in  hardness,  containing  a  larger  proportion  (72  per 
cent.)  of  earthy  matter  and  a  smaller  amount  (28  per  cent.)  of  organic  substance. 
When  decalcified  by  acids,  the  remaining  animal  material  retains  the  previous  form 
of  the  dentine  and  yields  gelatin  on  prolonged  boiling.  Dentine,  like  bone,  is  formed 
through  the  agency  of  specialized  connective-tissue  cells,  the  odontoblasts ,  but  differs 
from  osseous  tissue  in  the  small  number  of  these  cells  which  become  imprisoned  in 
the  intercellular  matrix.  When  this  occurs,  as  it  exceptionally  does  in  normal  human 
dentine  and  more  frequently  in  pathological  conditions  or  in  the  lower  animals,  the 
dentine-cells  correspond  to  the  bone-corpuscles,  both  being  connective-tissue  elements 
lying  within  lymph-spaces  in  the  calcified  intercellular  substance. 

Examined  in  dried  sections  under  low  magnification,  the  dentine  presents  a  radial 
striation  composed  of  fine  dark  lines  which  extend  from  the  pulp-cavity  internally  to 
the  enamel  or  the  cementum  externally.  These  dark  lines  are  the  dentinal  tubules, 
filled  with  air,  which  are  homologous  with  the  lacunae  and  canaliculi  of  bone,  and 
contain  the  processes  of  the  odontoblasts.  In  the  crown,  as  seen  in  longitudinal 
sections,  the  course  of  the  dentinal  tubules  is  radial  to  the  pulp-cavity  ;  in  the  root 
their  disposition  is  horizontal  and  almost  parallel.  The  canals,  however,  are  not 
straight,  but  sigmoid,  the  first  convexity  being  directed  towards  the  root,  the  second 
towards  the  crown.  In  addition  to  these  primary  curves,  which  are  especially  marked 
in  the  crown,  the  dentinal  tubules  present  numerous  shorter  secondary  curves  which 


STRUCTURE  OF  THE  TEETH. 


impart  to  the  individual  canaliculi  a  spiral  course.  The  cause  of  the  latter  Kollmann 
refers  to  the  more  rapid  growth  of  the  dentinal  fibres  than  of  the  slowly  forming 
dentinal  matrix.  In  consequence  of  the  correspondence  of  the  curvature  of  the  den- 
tinal tubules,  the  tooth-ivor-y  exhibits  a  series  of  linear  markings,  Schreger'  s  lines, 
which  run  parallel  to  the  inner  surface  of  the  dentine.  These  markings  must  not  be 
confounded  with  the  contour  lines  of  Owen  (page  1552),  also  within  the  dentine,  or 
with  Schreger' s  prism-stripes  within  the  enamel  (Fig.  1306). 

The  dentinal  tubules  are  minute  canals,  from  .001 3-.  002  mm.  in  diameter,  which 
begin  at  the  pulp-cavity  with  the  largest  lumen  and  extend  to  the  outer  surface  of 
the  dentine,  to  end  beneath  the  enamel  or  cementum.  Each  spirally  coursing  canal 
undergoes  branching  of  two  kinds,  a  dichotomous  division  at  an  acute  angle  in  the 
vicinity  of  the  pulp-cavity,  resulting  in  two  canaliculi  of  equal  diameter,  and  a  lateral 
branching  during  the  outer  third  of  their  course  whereby  numerous  twigs  are  given  off 
with  a  corresponding  dimi- 
nution in  the  size  of  the  cana-  FIG.  1309. 
liculi  ;  the  terminal  tubes, 
often  reduced  in  diameter  to 
mere  lines,  frequently  anas- 
tomose with  one  another  or 
form  loops.  The  dentinal 
tubules  are  occupied  by  the 
delicate  dentinal  fibres,  the 
processes  of  the  odonto- 
blasts,  which  in  the  young 
tooth  constitute  a  net-work  of 
protoplastic  threads  through- 
out the  dentine  of  importance 
for  the  nutrition  of  the  tis- 
sue. The  relation  of  the  den- 
tinal tubules  on  the  external 
surface  of  the  dentine  varies 
on  the  crown  and  root.  In 
the  former  situation  the  free 
surface  of  the  dentine  pre- 
sents crescentic  depressions, 
filled  by  the  enamel,  in  which 
the  tubules  appear  as  ab- 
ruptly terminating  or  cut  off  ; 
on  the  root,  on  the  contrary, 
where  the  dentinal  surface  is 
smooth,  the  tubules  stop  in 
curved  ends  or  loops  beneath 
the  cementum,  only  in  very 
exceptional  cases  communi- 
cating with  the  canaliculi  of 
the  latter. 

The  immediate  wall  of  the  dentinal  tubules  is  formed  by  a  delicate  membrane, 
the  sheath  of  Neumann,  which  in  appropriate  transverse  sections  appears  as  a  con- 
centric ring.  On  softening  the  decalcified  dentine  by  acids  or  alkalies,  the  sheaths 
may  be  isolated,  since  they  resist  the  action  of  the  reagents  which  attack  the  sur- 
rounding intertubular  substance.  The  sheaths  of  Neumann  are  formed  through  the 
agency  and  at  the  expense  of  the  dentinal  fibres,  the  latter  being  smaller  in  old  than 
in  young  dentine.  The  sheaths,  therefore,  may  be  regarded  as  specialized  parts  of 
the  intertubular  matrix,  distinguished  by  less  complete  calcification  and  greater 
density. 

The  intertubular  ground- sub  stance  of  dentine  resembles  that  of  bone  in  being 
composed  of  bundles  of  extremely  delicate  fibrillae  of  fibrous  connective  tissue.  The 
latter,  best  seen  in  decalcified  tissue,  swell  on  treatment  with  water  containing  acids 
or  alkalies,  and  yield  gelatin  after  prolonged  boiling.  The  disposition  of  the  bundles 


Ground-section  of  dried   tooth  including  adjacent  enamel   and  dentine. 

X  300. 


1552 


HUMAN   ANATOMY. 


of  fibrillae — more  regular  in  dentine  than  in  bone — is  longitudinal  and  parallel  to  the 
primary  surfaces  of  the  dentine.  In  addition  to  the  fibres  which  extend  lengthwise, 
others  run  obliquely  crosswise  in  the  layers  of  dentine.  The  bundles  of  fibrillae 
measure  from  .002-.  003  mm.  in  diameter,  and  appear  in  transverse  sections  as  small 
punctated  fields.  The  fibrillae  are  knit  together  by  the  calcified  organic  matrix,  in 
which  the  lime  salts  are  deposited  in  the  form  of  spherules,  the  interstices  between 
which  are  later  filled  and  calcification  thus  completed.  When,  as  often  happens,  the 
latter  process  is  imperfect,  irregular  clefts,  the  interglobular  spaces,  remain,  the  con- 
tours of  which  are  formed  by  the  spheres  or  dcntinal  globules  of  calcareous  material. 
The  interglobular  spaces  are  of  irregular  form  and  uncertain  extent,  being  usually 
largest  in  the  crown.  At  the  border  between  the  dentine  and  the  cementum  there 
exists  normally  a  distinct  zone,  the  granular  layer  of  Tomes  (Fig.  131 1),  composed  of 


FIG.   1310. 


Alveolar  periosteum — -^w|^B 


Transverse  section  of  root  of  lower  canine  tooth.    X  30. 

closely  placed  interglobular  spaces  of  small  size  ;  under  low  magnification  in  ground- 
sections  the  spaces  appear  as  dark  granules,  hence  the  designation  of  the  zone.  Since 
the  existence  of  these  spaces  depends  upon  imperfect  calcification  of  the  intertubular 
ground-substance,  the  dentinal  tubules  are  unaffected  and  pass  through  the  spaces  on 
their  course  to  the  surface  of  the  dentine,  several  of  the  canals  traversing  the  larger 
spaces.  The  contour  lines  of  Owen,  or  the  incremental  lines  of  Salter,  appear  as 
linear  markings,  which  usually  run  obliquely  to  the  surface  of  the  dentine  (Fig.  1306). 
They  probably  depend  upon  variations  in  calcification  incident  to  the  growth  of  the 
dentine,  and  resemble  the  interglobular  spaces  in  their  origin.  The  contour  lines 
are  best  marked  in  the  crown  and  are  only  exceptionally  seen  in  the  fang.  As 
pointed  out  by  Walkhoff,  the  lines  of  Owen  and  those  of  Retxius  in  the  enamel  are 
usually  present  at  the  same  time,  since  both  are  expressions  of  imperfect  calcification. 
The  Cementum. — The  cement,  or  crusta  fr-trosa  of  the  older  writers,  forms 
an  investment  of  slightly  modified  osseous  tissue  from  the  neck  of  the  tooth  to  its 


STRUCTURE   OF   THE   TEETH. 


1553 


FIG. 


1311. 


apex.  Beginning  where  the  enamel  ceases,  or  overlapping  the  latter  to  a  small 
extent,  as  a  layer  only  .02— .03  mm.  thick,  the  cement  gradually  increases  in  thick- 
ness until  over  the  root,  especially  between  the  fangs  of  the  molars,  its  depth  reaches 
several  millimetres.  When  well  developed  the  cement  usually  presents  two  layers, — 
an  inner,  almost  homogeneous  stratum  next  the  dentine,  in  which  the  cement-cells  are 
absent,  and  an  outer  supplemental  layer  which  exhibits  the  appearance  of  true  bone- 
tissue.  The  ground-substance  of  cemen- 
tum  differs  from  that  of  ordinary  bone 
in  containing,  according  to  Bibra,  slightly 
less  organic  matter  and  a  great  number 
of  fibre-bundles  that  extend  vertically  to 
the  lamellae,  corresponding  to  Sharpey's 
fibres.  The  lacunae  are  larger  than  those 
of  bone  and  vary  greatly  in  their  number 
and  form  ;  their  processes,  the  canaliculi, 
are  unusually  long  and  elaborate.  As  in 
bone,  so  these  lymph-spaces  contain  con- 
nective-tissue cells,  the  cement- corpuscles. 
The  lamellae  are  so  disposed  that  the 
lacunae  lie  generally  parallel  with  the  long 
axis  of  the  tooth,  their  processes  extend- 
ing vertically  to  the  free  surface.  While 
connecting  with  one  another  by  means 
of  the  canaliculi,  the  lacunae  very  rarely 
communicate  with  the  dentinal  tubules, 
the  latter  terminating  in  blind  endings. 
The  union  between  the  outer  surface  of 
the  cement  and  the  pericementum  is  in- 
timate, since  the  latter  is  in  fact  the  alve- 
olar periosteum  from  which  the  cement 
was  derived  ;  this  close  relation  is  indi- 
cated by  the  roughness  which  the  outer 
surface  of  the  cement  presents  when 
macerated.  Although  at  times  feebly 

developed  under  normal  conditions,  typical  Haversian  canals  are  found  only  in  con- 
ditions  of  hypertrophy. 

The  Alveolar  Periosteum. — The  periosteum  investing  the  jaws  likewise  lines 
the  sockets  receiving  the  roots  of  the  teeth,  which  are  by  this  means  securely  held 
in  place.  The  name  pericementum  is  often  applied  to  this  special  part  of  the  peri- 
osteum, which  clothes  the  alveoli  on  the  one  hand  and  covers  the  cement  on  the 
other,  thereby  fulfilling  the  double  role  of  periosteum  and  root-membrane.  The 
latter  consists  of  tough  bundles  of  fibrous  tissue,  elastic  tissue  being  almost  want- 
ing, which  are  prolonged  into  the  penetrating  fibres  characterizing  the  cementum 
on  one  side  and  into  the  fibres  of  Sharpey  of  the  alveolar  wall  on  the  other.  The 
fibrous  bundles  run  almost  horizontally  in  the  upper  part  of  the  root,  but  become 
more  oblique  towards  the  apex  of  the  fang.  In  the  latter  situation  the  pericemen- 
tum loses  its  dense  character  and  becomes  a  loose  connective  tissue  through  which 
the  blood-vessels  and  nerves  pass  to  reach  the  tooth.  The  less  dense  portions 
of  the  root-membrane  between  the  penetrating  bundles  of  fibrous  tissue  contain, 
in  addition  to  the  vessels  and  nerves,  irregular  groups  of  epithelial  cells  which 
appear  as  cords  or  net-works  within  the  connective-tissue  stroma.  These  groups 
are  the  remains  of  the  epithelial  sheath  which  surrounded  the  young  tooth  during 
its  early  development.  They  have  sometimes  been  described  as  glands,  lymphatics, 
and  other  structures,  their  true  nature  being  unrecognized.  At  the  alveolar  mar- 
gin the  pericementum  is  directly  continuous  with  the  tissue  composing  the  gum, 
the  fibrous  bundles  being  so  disposed  immediately  beneath  the  enamel-border  that 
they  form  an  encircling  band  of  dense  fibrous  tissue,  the  ligamenttim  circulare 
dentis  of  Kolliker,  which  aids  in  maintaining  firmer  union  between  the  tooth  and 

the  alveolar  wall. 

98 


Granular  layer 
of  Tomes 


Cementum 


-Lacuna 


Ground-section  of  root  of  dried  tooth  including  adjacent 
dentine  and  cementum.     X  300. 


1554 


Fir  MAN   ANATOMY. 


FIG 


Dentine 


The  Pulp. — The  contents  of  the  pulp-cavity  is  the  modified  tissue  of  the 
mesoblastic  dental  papilla  remaining  after  the  completed  formation  of  the  dentine. 
The  major  part  of  the  adult  pulp  consists  of  a  soft,  very  vascular  connective  tissue 
containing  few  or  no  elastic  elements,  but  numerous  irregularly  distributed  cells  of 
uncertain  form.  The  general  type  of  the  tissue  resembles  the  embryonal,  both  in  the 
character  of  the  fibrous  tissue  and  of  the  cells,  which  are  round,  oval,  or  stellate  with 
long  processes.  The  fibrous  bundles  and  the  more  elongated  cells  are  most  regu- 
larly disposed  around  the  blood-vessels  and  nerves,  which  they  invest  in  delicate 
fibrous  sheaths. 

The  peripheral  zone  of  the  pulp,  next  the  dentine,  presents  the  greatest  special- 
ization, since  in  this  situation  lie  the  direct  descendants  of  the  dentine-producing 
cells,  the  odontoblasts.  In  this  locality  the  pulp,  especially  in  older  teeth,  presents 

three  layers.  The  outer  (.04— .08  mm.  thick) 
consists  of  several  rows  of  large  cylindrical 
elements,  of  which  the  most  superficial  are 
arranged  vertically  to  the  free  surface  of 
the  pulp,  after  the  manner  of  an  epithelium. 
These  are  the  odontoblasts,  now  no  longer 
active,  about  .025  mm.  in  length  and  .005 
mm.  broad,  which  send  out  long,  delicate 
processes  (the  dentinal fibres)  into  the  den- 
tal tubules  externally,  and  shorter  ones 
towards  the  pulp-tissue.  When  very  young 
they  probably  possess  also  lateral  processes. 
The  deeper  cells  of  the  odontoblastic  layer 
are  less  regularly  disposed  and  less  cylindri- 
cal in  form.  The  second,  or  H'eit's  layer, 
best  seen  in  older  teeth,  is  characterized 
by  absence  of  cells,  the  fibrous  tissue  and 
the  cell-processes  forming  a  clear,  cell-free 

i.   »fW6  IfcT^nsif  ^W  "SSV^  zone  wmch  separates   the  striking  layer  of 

ll  $^|»^4§O  §£4v-%rBlood-       odontoblasts  from  the  subjacent  third  or  in- 
*  -»$•  a> — A»  WMffifflk  Tft  termediate  layer.     The  latter  consists  of  nu- 

merous small  round  or  spindle-cells,  closely 
placed,  but  irregularly  disposed,  which  grad- 
ually blend  with  the  ordinary  pulp-tissue. 
The  blood-vessels  supplying  the  pulp  are  from  three  to  ten  small  arteries  which 
soon  after  entering  the  pulp-cavity  break  up  into  very  numerous  branches  from  which 
a  rich  capillary  net- work  is  derived.  In  human  teeth  the  capillaries  usually  do  not 
invade  the  layer  of  odontoblasts,  although  at  times  the  vascular  loops  may  extend 
between  these  cells.  The  venous  radicles  form  larger  veins  which  follow  the  course 
of  the  arteries.  Distinct  lymphatics  have  not  been  demonstrated  within  the  pulp. 

The  nerves  are  numerous,  each  fang  receiving  a  main  stem  and  several  additional 
smaller  twigs,  which  in  a  general  way  accompany  the  blood-vc-ssrls  in  their  coarser 
distribution.  On  reaching  the  crown-pulp  the  larger  twigs  are  replaced  by  tiiu-r 
branches,  which  divide  into  innumerable  interwoven  fibres.  The  latter,  on  reaching 
the  margin  of  the  pulp,  form  a  peripheral  plexus  beneath  the  layer  of  odontoblasts, 
from  which  terminal  non-medullated  fibrillae  are  given  off.  Some  of  these  rnd 
beneath  the  odontoblasts  in  minute  knot-like  swellings  ;  others  penetrate  the  odonto- 
blastic layer  to  terminate  in  pointed  free  endings.  There  is  no  trustworthy  evidence 
supporting  the  view  that  the  nerves  directly  communicate  with  the  odontoblasts  or 
enter  the  dentine. 


Pulp- 
tissue 


Section  of  periphery  of  pulp-tissue  of  young  tooth. 
X  175- 


IMPLANTATION   AND   RELATIONS   OF   THE   TEETH. 

The  Permanent  Teeth. — Each  fang  is  implanted  in  a  socket  corresponding 
to  it  in  shape,  so  that  the  pressure  is  transmitted  from  the  surface  of  the  conical  fang 
throughout,  except  at  the  very  tip,  which  has  a  hole  for  the  vessels  and  nerves.  A 
corresponding  hole  in  the  socket  communicates  with  the  dental  canals.  The  human 


IMPLANTATION   AND    RELATIONS    OF   THE   TEETH.          1555 

teeth  are  all  in  contact  with  their  neighbors,  there  being  no  break  or  diastcma  in  the 
upper  jaw  between  the  incisors  and  canines  for  the  points  of  the  canines  of  the  lower 
jaw.  The  canines  project  very  little  beyond  the  line  of  the  free  edges.  The  crowns 
increase  in  size  from  the  incisors  to  the  first  molars  and  then  decrease.  The  ver- 
tical distance  from  the  gum  to  the  free  edge  regularly  diminishes  from  the  median 
incisors  backward,  with  the  exception  of  the  canines.  The  lines  of  the  teeth  above 
and  below  are  practically  of  the  same  length.  When  the  mouth  is  closed  the  superior 

canines  lie  to  the  outer  side  of  the 

FIG.  1313.  inferior  ones,  opposite  the  ends  of 

the  lips  ;  thus  the  median  upper 
incisors  impinge  on  both  the  lower 
ones  of  the  same  side,  and  the 
upper  lateral  incisors  strike  both 
the  lower  lateral  and  the  canine. 
In  the  same  way  the  point  of  the 
cusp  of  the  upper  first  bicuspid 
rests  between  the  points  of  both 
the  inferior  ones,  and  that  of  the 
second  on  both  the  second  lower 
and  the  first  molar.  The  first 
upper  molar  has,  perhaps,  a  quar- 
ter of  its  grinding  surface  on  that 
of  the  inferior  second  molar,  but  a 
smaller  part  of  the  second  upper 
molar  rests  on  the  lower  wisdom- 
tooth.  The  smaller  size  of  the 

upper  wisdom-tooth  brings  its  posterior  border  into  line  with  that  of  the  lower.  This 
arrangement  causes  the  opposed  crowns  to  interlock  to  a  certain  extent,  but  not  so 
closely  that  grinding  movements  cannot  occur  between  them.  The  advantage  of  each 
tooth  coming  in  contact  with  two  is  evident  after  the  loss  of  a  tooth,  as  the  one  cor- 
responding to  it  is  not  rendered  useless.  In  the  upper  jaw  the  incisors  have  a  marked 

FIG. 


Dental  arches  seen  from  before.  Letters  in  this  and  subsequent 
cuts  indicate  the  groups  of  teeth:  i,  incisors;  c,  canines;  b,  bicus- 
pids ;  m,  molars. 


Dental  arches  seen  from  behind. 


forward  inclination,  and  overlap  the  lower,  concealing  nearly  a  third  of  their  crowns,  the 
mouth  being  closed.  The  crowns  of  the  upper  bicuspids  look  pretty  nearly  downward 
and  those  of  the  molars  slant  outward.  This  is  very  marked  in  the  wisdom-tooth  and 
may  be  very  slight  in  the  first  molars.  The  lower  incisors  have  the  front  surfaces  nearly 
vertical  ;  the  molars  have  an  inward  slant,  so  as  to  bring  their  axes  into  the  same  line 


1556 


HUMAN   ANATOMY. 


FIG.  1315. 


Dental  arches  seen  from  the  side,  showing  relations 
of  upper  and  lower  teeth. 


as  those  of  the  upper  ones  ;  hence  it  follows  that  the  alveolar  arches  of  the  upper  and 
lower  teeth  are  in  different  curves,  the  latter  having  a  great  transverse  distance 
between  the  necks  of  the  wisdom-teeth. 

The  right  half  of  •  the  jaw  is  usually  the  stronger  and  the  teeth  form  a  smaller 
curve.  It  has  been  pointed  out  in  the  section  on  the  motions  of  the  lower  jaw  that 
the  line  between  the  molars,  and  probably  the  bicuspids,  is  a  part  of  the  circumference 
of  a  circle  the  centre  of  which  is  near  the  top  of  the  lachrymal  bone  ;  it  may  now  be 
added  that  the  line  of  the  cutting  edges  of  the  lower  incisors  is  a  part  of  a  transverse 
curve  with  the  convexity  upward.  There  is  no  corresponding  concavity  in  the  line 
of  the  edges  of  the  upper  incisors,  for  the  lower  do  not  naturally  meet  them  ;  but  the 
convexity  plays  along  the  lingual  surfaces  of  the  upper  ones.  The  position  and  shape 
of  the  superior  incisors  make  their  inner  surface  a  part  of  a  vault.  A  transverse 
section  of  this  is  necessarily  a  curve  with  an  upward  convexity.  The  wearing  of  the 
outer  corners  of  the  lateral  incisors  is  evidence  of  this  action.  The  fact  that  there  is 

no  purely  lateral  motion,  but  an  oblique 
one,  modifies,  without  invalidating,  this  con- 
ception. 

The  relations  of  the  roots  of  the  su- 
perior teeth  to  the  antrum  are  very  impor- 
tant. The  incisors  have  no  relation  with  it 
whatever.  The  long  fang  of  the  canine  is 
opposite  the  wall  between  the  antrum  and 
nose,  and  separated  by  diploe  from  the 
former.  The  first  bicuspid  is  usually  sepa- 
rated in  the  same  manner.  The  second  is 
very  close  to  its  front  wall  and  may  indent 
the  floor.  The  first  and  second  molars 
always  do  this.  The  wisdom-tooth  also  in- 
dents it  at  the  junction  of  the  floor  with  the 
posterior  wall.  Its  relation,  owing  in  part 

to  its  varying  development,  is  less  certain.  Exceptionally  the  first  bicuspid  and 
even  the  canine  may  be  in  contact  with  the  antrum.  Thus  caries  of  the  roots  of 
any  of  the  molars,  but  especially  of  the  first  and  second,  sometimes  of  the  second 
bicuspid  and  exceptionally  of  the  first,  or  even  of  the  canine,  may  lead  to  inflamma- 
tion of  the  antrum.  In  certain  cases  pus  may  pass  directly  into  it  from  the  root. 

The  Temporary  Teeth. — In  the  first  dentition  the  dental  arches  differ  from 
the  permanent  ones  in  showing  a  broader  curve,  more  nearly  approaching  half  a  circle, 
symmetrical  on  both  sides,  in  having  the  upper  incisors  less  slanting,  and  the  molars 
of  each  row  more  nearly  vertical.  This  implies  less  difference  in  curve  between  the 
jaws.  The  line  of  meeting  of  the  teeth  is  more  horizontal.  The  crowns  increase  in 
size  from  the  incisors  backward.  In  the  young  child  the  antrum  is  but  a  small  pouch, 
and  the  roots  of  the  first  teeth  and  the  sacs  of  the  second  lie  in  diploetic  tissue.  The 
first  permanent  molar,  as  its  fangs  grow,  is  nearest  the  antrum,  having  extended  above 
it  by  the  end  of  the  second  year.  In  its  early  stages  the  first  bicuspid  is  too  far  forward 
to  have  any  relation  to  the  antrum,  and  the  second  reaches  only  its  extreme  anterior 
border.  The  second  permanent  molar  is  at  first  behind  rather  than  below  it,  and  the 
third  is  still  higher.  As  these  descend  they  swing  around  the  antrum.  Thus  the  roots 
of  only  the  first  permanent  molar  are  in  approximately  the  same  relation  to  the  antru 
throughout. 

DEVELOPMENT   OF   THE   TEETH. 

About  the  beginning  of  the  seventh  week  of  foetal  life  the  ectoblastic  epithelium 
presents  a  thickening  along  the  margins  of  the  oral  cavity.  The  ridge-like  epithelial 
proliferation,  or  labio-dcnUU  strand,  so  formed  grows  into  the  surrounding  mrsoblast 
and  divides  into  two  plates  which,  while  still  continuous  at  the  surface,  diverge  almost 
at  right  angles  at  the  deeper  plane.  The  lateral  or  outer  plate  is  vertical,  and  cor- 
responds to  the  plane  of  separation  which  soon  occurs  in  the  differentiation  of  the 
borders  of  the  lips  and  jaw.  The  median  or  inner  plate  grows  more  hori/ontally  into 
the  mesoblast,  and  is  the  one  intimately  concerned  in  the  tooth  development  ;  for  this 


DEVELOPMENT   OF   THE   TEETH. 


1557 


reason  it  is  termed  the  dental  ledge.  It  will  be  seen  that  the  formerly  described  pri- 
mary stage  of  the  dental  groove  is  unfounded,  since  the  furrow  that  does  exist  is 
secondary  and  not  directly  related  to  the  formation  of  the  teeth,  but  to  the  differ- 
entiation of  the  lips.  During  the  third  foetal  month  the  anlages  for  the  entire  set  of 
milk-teeth  become  evident  along  the  dental  bar,  coincidently,  by  the  eleventh  week, 
the  completion  of  the  labial  furrow  separating  the  lip  from  the  original  epithelial 
strand  with  which  the  dental  ledge  alone  for  a  time  remains  attached. 

The  anlages  of  the  milk-teeth  are  indicated  by  club-shaped  epithelial  outgrowths 
which  grow  down  from  the  deeper  surface  of  the  dental  ledge  to  form  the  enamel- 

FIG.   1316. 


—Id 


Reconstructions  of  oral  ectoblast  of  human  embryos;  only  epithelium  of  lips,  mouth,  and  enamel-organs  shown. 
A,  embryo  of  2.5  cm.  length;  m,  oral  opening;  e,  labial  epithelium;  Id,  reverse  of  labio-dental  groove;  ds,  dental 
ledge.  B,  embryo  of  4  cm. ;  /«,  projection  caused  by  labio-dental  groove ;  ds,  dental'  ledge.  C,  embryo  of  11.5  cm., 
or  of  about  fourteen  weeks;  ml,  enamel-organ  of  first  molar  tooth.  £),  embryo  of  18  cm.,  or  of  about  seventeen 
weeks  ;  /'-  »i  >,  enamel-organs  of  second  incisor  and  of  first  molar  teeth.  (Drawnfrom  Rosens  models.) 

organs  and  to  meet,  and  later  cap,  the  mesoblastic  elevations  or  denial  papilla.  With 
the  rapid  growth  and  expansion  of  the  extremity  of  the  epithelial  plug,  a  differentia- 
tion of  the  latter  into  the  typical  three-layered  enamel-organ  takes  place,  the  pro- 
jecting dental  papilla  apparently  invaginating  the  overlying  epithelial  structure.  At 
first  connected  by  a  broad  band  of  cells,  the  attachment  of  the  enamel-organ  with  the 


HUMAN   ANATOMY. 


dental  ledge  becomes  more  and  more  attenuated  until  finally  it  is  broken  ;  its  remains 
appear  for  some  time  as  nests  or  islands  of  epithelial  cells  embedded  within  the  young 
connective  tissue  of  the  alveolar  border. 

The  Dental  Papilla. — This  structure  first  appears  shortly  after  the  beginning 
expansion  of  the  club-shaped  developing  enamel-organ  as  a  condensation  of  the  meso- 


FIG.  1317. 


Dental  ledge 


Thickened 
oral  epithelium 


Labiodental 
strand 


• 

\ 

Dental  ledge] 


'^•imrnm^m" 

,r  J../'.  '.'.''    .    •   ','S;'i '•••:'•:•:•.•.•    •  '  .'"    •    '    .' .' J& 


Inner  layer 
of  enamel- 
organ 


Dental 
papilla 


Frontal  sections,  showing  four  early  stages  of  tooth-development 


blast  beneath  the  epithelial  ingrowth.  The  papilla  consists  for  a  time  of  a  close 
aggregation  of  small,  round,  proliferating  cells  ;  with  the  differentiation  of  the  lavcrs 
of  the  enamel-organ,  the  elements  occupying  the  periphery  of  the  dental  papilla 
become  elongated  and  arranged  as  a  continuous  row  of  cylindrical  cells  over  the  api- 
cal portion  of  the  papilla  beneath  the  capping  enamel-organ.  These  cylindrical  nieso- 
blastic  cells  are  the  odontoblasts,  the  active  agents  in  the  formation  of  the  dentine. 


DEVELOPMENT   OF   THE   TEETH. 


1559 


FIG.  1318. 


When  engaged  in  the  latter  process  the  cells  measure  from  .035-.  050  mm.  in  length 
and  from  .005— .010  mm.  in  breadth,  but  over  the  sides  of  the  papilla  they  gradually 
become  lower  until  towards  the  base  they  blend  with  and  become  indistinguishable 
from  the  deeper  cells  of  the  mesoblastic  elevation.  So  long  as  the  tooth  grows, 
division  proceeds  and  odontoblasts  are  differentiated  in  the  vicinity  of  the  last-formed 
parts  of  the  root  ;  after,  however,  the  odontoblasts  are  engaged  in  forming  dentine, 
mitosis  is  no  longer  to  be  observed  in  these  elements. 

The  formation  of  the  dentine  is  accomplished  through  the  agency  of  the 
odontoblasts  much  in  the  same  manner  that  the  osteoblasts  produce  the  matrix  of 
bone.  The  earliest  trace  of  the  dentine  appears  as  a  thin  homogeneous  stratum,  the 
membrana  prceformaliva,  overlying  the  coincidently  forming  layer  of  odontoblasts. 
Although  separable  by  certain  reagents  as  a  cuticular  structure,  the  membrane  is  only 
a  part  of  the  general  dentinal  ground-substance  with  which  it  blends  ;  later  it  is  prob- 
ably absorbed  when  brought  into  contact  with  the  enamel.  The  dentinal  matrix, 
deposited  through  the  influence  of  the  odontoblasts,  is  for  a  time  without  fibrous 
structure  and  uncalcified,  the  deposition  of  the  lime  salts  occurring  first  near  the  apex 
of  the  papilla  and  next  the  enamel,  a  zone  of  uncalcified  matrix  around  the  pulp- 
cavity  marking  the  youngest  dentine.  The  calcareous  material  is  first  deposited  in 
the  form  of  globules,  the  dentinal  spheres,  the  calcification  being  completed  by  the 
subsequent  invasion  of  the  interstices  between  the  spherical  masses.  When  for  any 
reason  calcification  is  incomplete  these  clefts  remain 
lime  free,  a  condition  seen  in  the  interglobular  spaces 
already  described.  The  spherical  form  of  the  calca- 
reous deposits  is  indicated  by  the  uneven  condition  of 
the  inner  surface  of  the  dentine  in  macerated  teeth,  the 
wall  of  the  pulp-cavity  presenting  numerous  minute 
hemispherical  projections  which  correspond  to  the 
globular  masses  of  lime  salts.  The  scalloped  border 
and  pitted  outer  surface  of  the  dentine,  together  with 
the  extension  of  the  dentinal  tubules  as  far  as  or  into 
the  enamel,  point  to  the  absorption  of  the  primary 
dentine  constituting  the  preformed  membrane,  proba- 
bly through  the  influence  of  the  enamel.  As  empha- 
sized by  Ebner,1  the  formation  of  the  fibrillae  of  the 
ground-substance  takes  place  independently  of  the 
direct  influence  of  the  dentine-cells,  since  the  general 
disposition  of  the  earliest  fibrillae  is  at  right  angles  to 
that  of  the  odontoblasts  and  their  processes.  The 
dentinal  matrix  differs  from  that  of  bone  in  being  the 
production  of  a  single  set  of  cells,  while  the  osseous 
tissue  is  the  collective  work  of  different  elements, 
many  of  which,  after  contributing  their  increment,  be- 
come surrounded  by  the  ground-substance  to  form 
the  bone-corpuscles  within  the. lacunae.  In  human 
dentine,  on  the  contrary,  the  odontoblasts  are  only 
rarely,  under  normal  conditions,  imprisoned  within  the 
ground-substance  which  they  have  formed.  The  de- 
mands made  upon  the  odontoblasts  during  their  active  r61e  as  dentine  producers  are 
met  by  the  nutrition  supplied  by  the  rich  vascular  supply  of  the  dentinal  papilla,  so 
that  for  a  time  the  cells  are  enabled  not  only  to  increase  the  dentinal  matrix,  but  also 
to  extend  their  processes,  which  they  send  into  the  tubules  of  the  dentine  as  the  den- 
tinal fibres,  without  diminution  in  size.  With  the  completion  of  dentine  production, 
and  the  consequent  decrease  in  the  area  upon  which  they  rest,  the  odontoblasts 
become  narrower  and  smaller  (Walkhoff)  ;  later  they  exhibit  evidences  of  impaired 
vitality  and  degeneration,  their  dentinal  processes  likewise  growing  thinner  and  less 
flexible  and  assuming  the  characteristics  of  the  fibres  of  Tomes  of  the  adult  tissue. 
According  to  Walkhoff,  the  dentinal  fibres  suffer  in  size  as  the  result  of  their  activity 
in  the  production  of  the  sheath  of  the  tubules. 

1  In  Kolliker's  Gewebelehre  des  Menschen,  6te  Auf.,  1899. 


Isolated  odontoblasts  from  incisor 
tooth  of  new-born  child,  a,  b,  from 
upper  part  of  crown  ;  c,  d,  e,  from  lat- 
eral region.  X  400.  (Ebner.) 


1560 


HUMAN   ANATOMY. 


After  the  entire  dentine  has  been  formed,  the  odontoblasts  remain  as  the  periph- 
erally situated  pulp-cells,  retaining  their  connection  with  the  dentine  by  means  of  the 
dentinal  fibres.  The  other  portions  of  the  dental  papilla  become  converted  into  the 
pulp-tissue,  which  retains  the  embryonal  type  throughout  life  and  later  receives  the 
larger  vascular  and  nervous  trunks. 

The  Enamel-Organ. — The  extremity  of  the  cylinder  of  ectoblastic  epithelium 
which  early  marks  the  position  of  the  future  tooth  by  its  ingrowth  from  the  dental 
ledge  soon  broadens  out  and  becomes  invaginated  to  form  the  young  enamel-organ 
overlying  the  apex  of  the  mesodermic  dental  papilla.  In  contrast  to  the  latter,  which 
as  the  pulp-tissue  remains  as  a  permanent  structure,  the  enamel-organ  is  but  embry- 
onal and  transient,  and  later  entirely  disappears.  When  fully  developed,  the  enamel- 
organ  consists  of  three  principal  parts, — the  outer,  middle,  and  inner  layers.  Since 
the  organ,  originally  pyriform,  is  converted  into  a  cap  by  the  invagination  of  its 
broader  and  deeper  surface,  it  follows  that  the  external  and  internal  layers  are 
directly  continuous  at  the  margin  of  the  inverted  area. 


FIG.  1319. 


Sublingual  space 


Fibres  of 
genio-glossus 


d£.'   Oral  epithelium 


Developing 

gland 
Dental  papilla 


Muscular  fibres 


Skin 


Sagittal  section  through  mandible  and  surrounding  structures  of  eighteen-weeks  foetus.    X  30. 

The  outer  layer  consists  of  larger  and  smaller  epithelial  cells  of  flattened  form 
and  about  .010  mm.  average  diameter  ;  these  cells  send  numerous  processes  into  the 
surrounding  vascular  connective  tissue  forming  the  tooth-sac  which  invests  the  dental 
germ,  whereby,  in  conjunction  with  the  vascular  tufts,  the  sac  and  the  enamel-organ 
are  intimately  united. 

The  middle  layer  of  the  enamel-organ  consists  apparently  of  mucoid  tissue, 
since  it  presents  a  net-work  of  stellate  cells  separated  by  large  clear  spares.  Critical 
examination,  however,  shows  that  this  tissue  consists  of  epithelial  elements  which 
have  become  modified  in  consequence  of  an  enormous  distention  <>f  tin-  intercellular 
spaces  by  fluid  and  a  corresponding  elongation  of  the  intercellular  bridges,  the  ep»- 
thelial  plates  in  this  manner  being  reduced  to  stellate  cells  connected  by  long,  delicate 
processes.  The  inner  border  of  tin-  highly  characteristic  middle  layer  forms  a  transi- 
tion zone,  known  as  the  intt-rnifdiatc  layer, .in  which  gradations  from  the  modified  to 
the  ordinary  type  of  stratified  epithelium  are  seen.  The  intermediate  layer  is  best 
marked  over  the  upper  part  of  the  crown,  at  the  sides  thinning  out  and  entirely  dis- 


DEVELOPMENT   OF   THE   TEETH.  1561 

appearing  at  the  margin  of  the  enamel-organ,  where  the  outer  and  inner  layers  of  the 
latter  are  continuous.  The  modified  epithelial  tissue  of  the  middle  layer,  sometimes 
called  the  enamel-pulp,  is  greatest  in  amount  just  prior  to,  or  during  the  beginning 
of,  active  tooth-formation,  about  the  fifth  or  sixth  foetal  month. 

The  inner  layer  of  the  enamel-organ  comprises  a  single  row  of  closely  set,  tall, 
cylindrical  elements,  the  enamel-cells,  adamantoblasts,  or  ameloblasts,  through  the 
active  agency  of  which  the  enamel  is  produced.  The  ameloblasts  are  best  developed 
where  they  cover  the  apex  of  the  dental  papilla,  the  location  of  the  earliest  formed  den- 
tine ;  in  this  situation  the  cells  measure  from  .025-. 040  mm.  in  length  and  from 
.004— .007  mm.  in  breadth.  They  possess  an  oval  nucleus  about  .010  mm.  long, 
which  usually  lies  close  to  the  outer  end  of  the  cell,  embedded  in  cytoplasm  exhibit- 
ing a  reticulum  and  often  minute  granules.  The  ameloblasts  are  united  with  one 
another  by  a  small  amount  of  cement-substance,  and  are  denned  from  the  interme- 
diate layer  by  a  fairly  distinct  border.  Opposite  the  sides  of  the  dental  papilla,  cor- 
responding to  the  limits  of  the  future  crown,  the  ameloblasts  gradually  diminish  in 
height  until  they  are  replaced  by  low  cubical  cells  which,  at  the  margin  of  the  enamel- 
organ,  are  continuous  with  the  epithelium  of  the  outer  layer.  Preparatory  to  the  for- 
mation of  the  dentine  of  the  tooth-root,  this  margin  grows  downward  towards  the 
base  of  the  elongating  dental  papilla,  which  is  thus  embraced  by  the  extension  of  the 


Dental  groove 
Oral  epithelium v 


Atrophic  epithelial  net-work __i^^{fj 

Enamel^ 
Dentine 


Epithelial  sheath  —  Position  of  mesoblastic  dental  papilla 


Reconstruction  of  developing  lower  incisor  tooth  from  embryo  of  30  cm.  length,  about  twenty-four  weeks. 

(Drawn  from  Rose' s  model.) 

enamel-organ.  The  investment  thus  formed  constitutes  the  epithelial  sheath  (Fig. 
1320),  a  structure  of  importance  in  determining  the  form  of  the  tooth,  since  it  serves 
as  a  mould  in  which  the  young  dentine  is  subsequently  deposited  ;  there  is,  however, 
insufficient  evidence  to  regard  the  epithelial  sheath  as  an  active  or  necessary  factor  in 
the  production  of  the  dentine. 

The  formation  of  the  enamel,  in  contrast  to  that  of  the  dentine,  results  from 
the  activity  of  ectoblastic  epithelium,  and  may  be  regarded  as  a  cuticular  development 
carried  on  by  the  ameloblasts.  The  earliest  stage  in  the  production  of  enamel  is 
the  appearance  of  a  delicate  cuticular  zone  at  the  inner  end  of  the  ameloblast  ;  this 
fuses  with  similar  structures  tipping  the  adjoining  cells  to  form  a  continuous  homo- 
geneous mass.  The  latter  soon  exhibits  differentiation  into  rod-like  segments,  the 
enamel-processes,  or  processes  of  Tomes,  which  are  extensions  from  the  ameloblasts 
and  are  the  anlages  of  the  enamel-prisms,  and  the  interprismatic  substance.  The 
latter  becomes  greatly  reduced  in  amount  as  the  development  of  the  enamel-columns 
progresses  ;  the  major  part,  becoming  incorporated  with  the  processes  of  Tomes, 
forms  the  cortical  portion  of  the  enamel-prisms,  while  the  remainder  persists  as  the 
cement-substance  which  exists  in  meagre  quantity  between  the  mature  prisms.  The 
enamel -processes  are  for  a  time  uncalcified,  but  with  the  more  advanced  formation  of  the 
enamel-prisms  the  calcareous  material,  which  is  deposited  as  granules  and  spherules, 
appears  first  in  the  axis  of  the  prism,  later  invading  the  periphery  (Ebner).  The 


1562 


HUMAN   ANATOMY. 


enamel  increases  in  thickness  by  the  addition  of  the  last-formed  increments  at  the 
inner  ends  of  the  ameloblasts,  the  same  cells  sufficing  for  the  deposit  of  the  entire 
Owing  to  the  expansion  of  the  external  surface  of  the  crown,  the  diameter  of 


mass. 


FIG.  1321. 


Section  of  developing  tooth  throu 


Intermediate  layer  of 
enamel-organ 


Ameloblasts 


Young  enamel  with 
Tomes 's  processes 


Dentine 


Last-formed  dentine 
Odontoblasts 

Embryonal  pulp-tissue 
nction  of  enamel  and  dentine.    X  400. 


FIG. 


1322. 


the  enamel-prisms  augments  towards  their  outer  ends  to  compensate  for  the  increased 
area  which  they  must  fill,  since  no  additional  prisms  are  formed. 

The  complex  curvature  of  the  enamel-prisms  and  the  oppositely  directed  ranges 
of  the  latter,  producing  the  appearance  of  Schreger's  stripes,  result  from  changes  in 
the  position  of  the  enamel-cells  incident  to  the  growth  of  the  crown,  since  the  axes 
of  the  newly  formed  prisms  correspond  with  those  of  the  ameloblasts,  variations  in  the 
direction  of  which  affect  the  disposition  of  the  enamel-columns. 

The  earliest  formed  enamel  lies  in  close  apposition  with  the  oldest  dentine  con- 
stituting the  membrana  praeformativa  ;  the  last  devel- 
oped immediately  beneath  the  ameloblasts.  The  enamel, 
therefore,  is  deposited  from  within  outward,  or  in  the 
reversed  direction  followed  by  the  growth  of  the  dentine. 
The  oldest  strata  of  both  substances  lie  in  contact  ;  the 
youngest  on  the  extreme  outer  and  inner  surfaces  of  the 
tooth. 

After  the  requisite  amount  of  enamel  has  been  pro- 
duced, differentiation  into  prisms  ceases,  in  consequence 
of  which  the  last-formed  enamel  remains  as  a  continu- 
ous homogeneous  layer  investing  the  free  surface  of  the 
crown,  known  as  the  membrane  of  Nasmyth. 

The  Tooth-Sac.  —  Coincidently  with  the  develop- 
ment of  the  enamel-organ  and  the  growth  of  the  dental 
papilla,  the  surrounding  mesoblast  undergoes  differen- 
tiation into  a  connective-tissue  envelope  known  as  the 
dental  or  tooth-sac.  The  latter  not  only  closely  invests  the  enamel-organ,  but  is 
intimately  related  to  the  base  of  the  dental  papilla,  with  which  it  is  continuous.  In 
contrast  to  the  epithelial  enamel-organ,  which  is  entirely  without  blood-vessels,  the 


Isolated  ameloblasts  from  in- 
cisor of  new-born  child,  a,  basal 
plate;  />,  cuticular  border;  c,  pro- 
of Tomes;  <i,  homogeneous 
mass  still  covering  process.  X  400. 
l  //»„•>:) 


DEVELOPMENT   OF   THE   TEETH. 


1563 


inner  part  of  the  tooth-sac  is  richly  provided  with  capillaries,  and  therefore  is  an 
important  source  of  nutrition  to  the  developing  dental  germ.  The  part  of  the  sac 
opposite  the  root  of  the  young  tooth  is  at  first  prevented  from  coming  into  direct 
contact  with  the  dentine  by  the  double  layer  interposed  by  the  epithelial  sheath. 
This  relation  is  maintained  until  the  development  of  the  cement  begins,  when  the 
vascular  tissue  of  the  dental  sac  breaks  through  the  epithelial  sheath  to  reach  the 
surface  of  the  dentine,  upon  which  the  cementum  is  deposited  by  the  mesoblast.  In 
consequence  of  this  invasion,  the  epithelial  sheath  is  disrupted  into  small  groups  or 
nests  of  cells  which  persist  for  a  long  time  as  epithelial  islands  within  the  fibrous 
tissue  of  the  alveolar  periosteum  into  which  the  dental  sac  is  later  converted. 

The  formation   of  the  cementum   takes  place  through  the  agency  of  the 
mesoblastic  tissue  in  a  manner  almost  identical  with  the  development  of  subperiosteal 

FIG.  1323. 


Jaws  of  child  of  six  years,  showing  all  temporary  teeth  in  place  with  permanent  teeth  in  various  stages  of 

development. 

bone,  the  active  cement-producing  cells,  or  cementoblasts,  corresponding  to  the  osteo- 
blasts  which  deposit  the  osseous  matrix  upon  the  osteogenetic  fibres  of  the  periosteum. 
A  conspicuous  feature  of  cementum  is  the  unusual  number  of  transversely  disposed 
bundles  of  fibrillae,  or  Sharpey's  fibres,  among  which  many  are  imperfectly  calcified. 
The  cementum  appears  first  in  the  vicinity  of  the  neck  of  the  tooth,  and  progresses 
towards  the  apex  of  the  root  as  the  dentine  of  the  fang  is  deposited.  After  the  tooth 
is  fully  formed,  the  layer  of  cement  continues  to  grow  until  thickest  at  the  apex,  which 
it  completely  invests,  with  the  exception  of  the  canal  leading  to  the  entrance  of  the 
pulp-cavity.  The  cement  being  deposited  directly  upon  the  homogeneous  layer  con- 
stituting the  external  surface  of  the  dentine,  the  firm  connection  between  the  two 
portions  of  the  teeth  is  one  of  adhesion  rather  than  of  union.  Later  secondary 
changes  may  exceptionally  bring  the  canaliculi  of  the  cement  into  communication 
with  the  terminations  of  the  dentinal  tubules.  During  the  changes  incident  to  the 


1564  HUMAN   ANATOMY. 

completed  tooth-development  the  tissue  of  the  dental  sac  becomes  denser,  the  part 
opposite  the  root  persisting  as  the  pericementum  which  intimately  connects  the 
cementum  with  the  alveolar  wall,  while  the  more  superficial  part  blends  with  the 
tissue  forming  the  gum. 

The  development  of  the  permanent  teeth  is  early  provided  for  by  the  dif- 
ferentiation of  the  anlages  of  the  secondary  dental  germs  during  the  growth  of  the 
first.  This  provision  includes  the  thickening  and  outgrowth  of  the  dental  bar  to  form 
the  enamel-organ  of  second  dentition,  and  later  the  appearance  of  a  new  dental  pa- 
pilla beneath  the  epithelial  cap.  The  enamel-organ  for  the  first  permanent  molar 
appears  about  the  seventeenth  week  of  foetal  life,  followed  soon  by  the  corresponding 
dental  papilla.  The  germs  of  the  permanent  incisors  and  canines,  including  the 
papillae,  are  formed  about  the  twenty-fourth  week  ;  those  for  the  first  bicuspids  are 
seen  at  about  the  twenty-ninth  week,  and  those  for  the  second  bicuspids  about  one 
month  later.  The  interval  between  the  formation  of  the  enamel-organ  and  the  asso- 
ciated dental  papilla  increases  in  the  case  of  the  last  two  permanent  molars.  While 
the  enamel-germ  of  the  second  molar  appears  about  four  months  after  birth  and  the 
corresponding  papilla  two  months  later,  the  enamel-organ  for  the  third  molar,  or 
wisdom-tooth,  which  is  visible  about  the  third  year,  precedes  its  papilla  by  almost 
two  years. 

The  First  and  Second  Dentition  and  Subsequent  Changes. — At  birth 
the  jaws  contain  the  twenty  crowns  of  the  milk-teeth,  the  still  separate  cusps  of  the 
first  permanent  molars,  one  of  which  has  begun  to  calcify,  and  the  uncalcified  rudi- 
ments of  the  permanent  incisors  and  canines  behind  and  above  the  corresponding 
milk-teeth  of  the  upper  jaw,  behind  and  below  those  of  the  lower.  At  birth  the  bony 
plate  above  the  alveoli  of  the  upper  jaw  is  separated  by  a  little  diploe  from  the  floor 
of  the  orbit.  The  milk-teeth  come  through  the  gum  in  five  groups  at  what  are  called 
dental  periods,  separated  by  intervals  of  rest.  The  grouping  is  more  regular  than  the 
time  of  eruption.  The  teeth  of  the  lower  jaw  have  a  tendency  to  precede  their  fellows 
of  the  upper. 

TABLE  OF  ERUPTION   OF  MILK-TEETH.1 

Dental  Periods.  Groups  of  Teeth. 

I.     Six  to  eight  months.  Two  middle  lower  incisors. 

II.     Eight  to  ten  months.  Four  upper  incisors. 

III.  Twelve  to  fourteen  months.  Two  lateral  lower  incisors  and  four  first  molars. 

IV.  Eighteen  to  twenty  months.  Four  canines. 

V.     Twenty-eight  to  thirty-two  months.     Four  second  molars. 

The  interval  between  the  first  and  second  periods  is  practically  nothing.  It  is 
very  common  to  have  the  first  two  groups  appear  together.  After  this  every  interval 
is  longer  than  the  preceding  one.  In  the  matter  of  time  no  part  of  development  is 
more  irregular  than  that  of  the  teeth.  The  first  incisors  occasionally  appear  early  in 
the  fifth  month  and  sometimes  not  till  the  tenth,  or  even  later.  The  first  dentition  is 
sometimes  complete  at  or  shortly  after  the  close  of  the  second  year.  The  roots  arc- 
not  fully  formed  when  the  crowns  pierce  the  gums.  The  first  set  of  teeth  is  in  its 
most  perfect  condition  between  four  and  six  years. 

Calcification  of  the  second  set  begins  in  the  first  molar  before  birth,  in  the  incisors 
and  canines  at  about  six  months,  the  bicuspids  and  the  second  upper  molar  in  the  third 
year,  the  second  lower  molar  at  about  six,  and  the  wisdom-tooth  at  about  twelve. 

The  first  permanent  molars  come  into  line  with  the-  milk-teeth,  piercing  the  gums 
before  any  of  the  latter  are  lost.  Before  eruption  the  upper  first  molars  lie  nearer  tin- 
median  line  and  farther  forward  than  the  lower.  The  roots  of  the  incisors  arc-  absorbed 
and  the  crowns  fall  out  to  make  way  for  their  successors.  The  molars  do  the  same 
for  the  bicuspids  which  grow  between  their  roots.  The  permanent  superior  canines 
are  developed  above  the  interval  between  the  lateral  permanent  incisors  and  the  first 
bicuspid,  which  are  almost  in  contact.  An  expansion  of  the  jaw  is  necessary  for  them 
to  come  into  place.  The  inferior  ones  have  more  room.  Both  are  somewhat  external 
to  their  predecessors.  The  second  upper  molar  comes  down  from  above  and  behind, 

1  From  Hotch's  JVdiatrirs. 


DEVELOPMENT   OF   THE   TEETH. 


1565 


and  so  does  the  wisdom-tooth  much  later.  The  inferior  second  molar  is  formed 
almost  in  the  angle  between  the  body  and  ramus.  The  inferior  wisdom-tooth,  before 
it  cuts  the  gum,  faces  forward,  inward,  and  slightly  upward.  To  the  table  from 

FIG.   1324. 


Permanent  molars 


Permanent  molar 


Permanent  canine 
Bicuspids 

Permanent  incisors 

Temporary  canine 
Temporary  molars 

Permanent  incisors 
Temporary  canine 

Permanent  canine 
Bicuspids 


Jaws  of  child  of  ten  years,  showing  partially  erupted  permanent  teeth  with  temporary  canines  and  molars  still  in 

place. 

Rotch  we  add  one  from  Livy,1  who  made  observations  on  several  thousand  children 
of  English  and  Irish  operatives. 


TABLE  OF  ERUPTION  OF  PERMANENT  TEETH.2 


Years.  Groups. 

6  Four  first  molars. 

7  Four  middle  incisors. 

8  Four  lateral  incisors. 

9  Four  first  bicuspids. 


Years.  Groups. 

10  Four  second  bicuspids. 

11  Four  canines. 

12  Four  second  molars. 
17  to  25  Four  wisdom-teeth. 


TABLES   SHOWING   TIME   OF   ERUPTION   OF   PERMANENT   TEETH.3 

BOYS. 


Ages.  9 

Lateral  incisors     ....       2        42 
First  bicuspids      ....       i 

Second  bicuspids 

Canines 

Second  molars 


76        12 


4 
I 

59        36  5 

18         28         25 

5 


16        Total. 

•  •  59 

90 

.  .  loi 
79 


British  Medical  Journal,  1885. 


42        67        275        184        78        12        663 
2  From  Rotch.  3  From  Livy. 


1566  HUMAN   ANATOMY. 

GIRLS. 

Ages.                                       9  10  ii  12  13  14            15           16  Total. 

Lateral  incisors 24  8  4  .    .  .    .        .    .        .    .  36 

First  bicuspids 56  13  2  i  i        .    .        .    .  73 

Second  bicuspids 51  16  2  2         71 

Canines 30  34  12  5  .    .           i        .    .  82 

Second  molars 5  44  80  288  249        66        14  746 

( It  seems  possible  from  the  method  employed  that,  especially  in  the  case  of  the  second  molars, 
the  tables  may  err  on  the  side  of  overstating  the  age.)  Livy's  researches  sho\v  that  in  the 
first  dentition  the  first  molars,  incisors,  and  canines  conn-  through  first  in  the  lower  jaw.  In 
most  cases  the  bicuspids  come  first  in  the  upper.  The  second  molars  come  first  in  the  lower  jaw, 
unless  their  appearance  is  delayed,  in  which  case  the  order  is  uncertain.  The  date  of  the  appear- 
ance, of  the  second  molar  can  be  only  an  approximate  guide  to  the  age.  When  it  is  present  the 
child  is  unlikely  to  be  under  twelve.  The  change  in  the  shape  of  the  jaw — namely,  the  lengthening 
necessary  for  a  longer  row  of  larger  teeth,  as  well  as  the  widening  required  to  make  room  for  the 
canines — begins  in  the  course  of  the  second  dentition  and  continues  after  its  close,  as  the  second 
molar  does  not  at  once  assume  its  permanent  position  in  regular  line  with  the  rest.  It  was 
pointed  out  in  the  section  on  the  growth  of  the  face  that  the  greatest  activity  of  growth  takes 
place  at  the  pauses  of  dentition.  The  roots  of  the  permanent  teeth  are  by  no  means  fully 
developed  at  their  eruption.  With  their  perfection  the  sockets  are  formed  around  them  by  the 
harmonious  moulding  of  the  parts  involved. 

Homologies. — There  are  two  chief  evolutionary  theories  of  the  origin  of  the  mammalian 
teeth  :  one,  the  concrescence  theory,  is  that  they  are  formed  by  the  growing  together  of  originally 
separate  cones,  the  primitive  reptilian  teeth.  This  view  is  supported  by  Rose l  and  Kiikenthal,2 
at  least  for  the  bicuspids  and  molars.  Cope,*  whom  Osborn*  has  followed,  advanced  the 
differentiation  theory,  according  to  which  the  many  cusps  of  the  molars  have  arisen  as  outgrowths 
from  a  primitive  cone.  This  is  based  on  comparative  anatomy  and  paleontology.  According  to 
this,  there  was  first  the  cone,  in  the  upper  jaw  called  the  protocone  and  in  the  lower  the/ro/o- 
conid.  Two  secondary  cusps  next  appeared  respectively  before  and  behind  it :  the  paracone 
and  metacone  of  the  upper  teeth  and  the  paraconid  and  mctaconid  of  the  lower.  The  next 
change  is  for  these  to  move  to  the  labial  side  in  the  upper  jaw  and  to  the  lingual  in  the  lower. 
Thus  the  primitive  cone  and  these  two  secondary  ones  form  the  points  of  a  triangle  with  the  base 
outward  in  the  upper  jaw  and  inward  in  the  lower.  A  prolongation,  the  talon  or  heel,  is  next 
developed  on  the  posterior  end  of  the  tooth,  and  rises  into  a  single  cusp,  the  hvpocone  in  the 
upper  jaw  and  the  hypoconid  in  the  lower.  The  last,  however,  has  two  secondary  cusps  spring 
from  it,  the  entoconid  and  the  hypoconid.  According  to  this  theory,  the  paraconid  of  the  lower 
teeth  has  disappeared  in  the  human  molars  owing  to  want  of  room  consequent  on  the  develop- 
ment of  the  talon  of  the  upper  teeth.  The  following  table  shows  the  homologies  of  the  cusps 
of  the  human  molars  according  to  Osborn. 

UPPER  MOLARS. 

Anterior  lingual Protocone. ") 

Anterior  buccal "...  Paracone.    \  Forming  the  triangle. 

Posterior  buccal Metacone.  ) 

Posterior  lingual Hypocone.     The  talon. 

LOWER  MOLARS. 

Anterior  buccal Protoconid.     )  D 

Anterior  lingual Metaconid.       (R 

Posterior  buccal Hypoconid. 

Posterior  lingual  .* Entoconid.       J-  The  talon. 

Posterior        Hypoconulid. 

Rose  has  advanced,  in  support  of  his  theory  of  concrescence,  that  calcification  begins  sepa- 
rately for  each  cusp.  Osborn  points  out  that  Rose  has  shown  that  they  ossify  very  nearly  in 
the  order  of  their  alleged  evolution.  Schwalbe5  professes  himself  unable  to  decide  on  "the 
relative  merits  of  the  two  theories. 

Variations.  -Variations  of  the  cusps  and  of  the  fangs  have  been  described  with  the  teeth. 
Those  of  number  affect  chiefly  the  incisors  and  molars.  An  additional  incisor  may  occur  on 
one  or  both  sides  in  either  dentition,  not  very  rarely  in  the  upper  jaw,  but  extremely  so  in  the 
lower,  the  condition  in  the  latter  being  more  stable.  Extra  upper  incisors  are  often  more  or  less 
displaced  to  the  rear  and  implanted  obliquely.  They  are  particularly  common  in  rases  of  cleft 
palate  ;  not  impossibly  the  presence  of  additional  teeth  predisposes  to  the  non-union  of  the 

1  Anatom.  Anzeiger.  Hd.  \ii.,  1892. 

2  Jenaiselie  Xeitschrift,  Hd.  xxviii.,  1893. 
s  Journal  of  Morphology,  iSSS,  iss(). 

4  American  Naturalist,  iSSS,  and  International  Dental  Journal,  1895. 

5  Anatom.  An/ei^er,  Hd.  ix.,  iS<»4. 


THE   GUMS.  1567 

premaxillary  and  the  maxillary  bones,  or  to  the  non-union  of  two  parts  of  the  former,  supposing 
that  two  such  parts  really  exist.  The  extra  incisor  may  apparently  appear  on  the  median  side 
of  the  first,  between  the  first  and  second,  or  between  the  latter  and  the  canine.  To  account  for 
this  Rosenberg1  asserts  that  the  typical  number  is  five,  as  in  the  opossum,  of  which  the  second 
and  fourth  are  the  two  persistent  ones,  and  that  either  the  first,  third,  or  fifth  may  occasionally 
present  itself.  Th.  Kolliker 2  records  a  case  of  right  cleft  palate  in  which,  besides  the  four  regular 
incisors,  three  were  found  between  the  cleft  and  the  right  canine.  As  cases  of  excess  of  incisors 
are  much  more  common  than  of  deficiency,  the  disappearance  of  the  upper  lateral  one  does  not 
seem  imminent  ;  still,  there  are  signs  of  degeneratiqn.  The  crown  is  less  square  than  that  of  the 
central,  it  is  occasionally  pointed,  often  unusually  small,  sometimes  not  reaching  the  line  of  the 
other  crowns.  It  may  be  absent,  and  then  a  series  of  cases  can  be  made  ranging  from  those  in 
which  the  remaining  incisor  is  separated  both  from  its  fellow  of  the  other  side  and  from  the 
canine  beside  it  by  large  gaps  to  those  in  which  the  teeth  are  regular  and  continuous.  Very 
rarely  one  of  the  lower  incisors  is  wanting,  and,  according  to  Rosenberg,  either  may  fail. 

A  fourth  molar  is  very  uncommon  ;  but  not  at  all  rarely  the  wisdom-tooth  is  late  in  coming 
through  the  gum,  and  occasionally  it  never  does.  It  seems  sometimes  to  be  wanting  and  often 
is  rudimentary.  It  has  been  seen  represented  by  three  detached  cusps,  an  apparent  confirmation 
of  Rose's  views  of  the  homology  of  the  teeth. 

The  entire  dental  series  may  be  unusually  large  or  small.  In  the  former  case  the  face  is 
prognathous,  probably  as  a  result  of  the  increase  of  space  required  for  the  teeth.  The  upper 
central  incisors  are  occasionally  very  large  without  increase  in  size  of  the  other  teeth.  The  same 
is  true  of  the  molars  ;  in  which  case  the  number  of  cusps  is  generally  greater,  but  the  converse 
does  not  occur  when  the  molars  are  unusually  small.3 

The  points  of  the  canines  may  project  beyond  the  line  of  the  other  teeth  and  the  molars  may 
increase  in  size  from  the  first  to  the  third. 

Teeth  are  sometimes  remarkably  displaced.  The  superior  canines,  owing  to  their  high  origin 
in  the  second  dentition,  are  particularly  subject  to  it.  They  may  appear  on  the  front  of  the  jaw, 
in  the  antrum,  the  nose,  or  the  back  of  the  mouth.  The  molars,  and  especially  the  wisdom-teeth, 
are  also  erratic. 

THE   GUMS. 

This  term  is  used  rather  vaguely  to  indicate  the  mucous  membrane  and  sub- 
mucous  tissue  covering  the  alveolar  processes  and  closely  attached  to  the  necks  of 
the  teeth.  Whether  the  neck  is  entirely  surrounded  by  it  varies  in  different  indi- 
viduals as  the  teeth  are  not  in  all  equally  close  ;  as  a  rule,  owing  to  the  ordinary 
expansion  of  the  crown  from  the  neck,  at  least  a  little  of  the  gum  is  found  between 
the  teeth.  It  is  some  3  mm.  thick,  dense,  firmly  fastened  to  the  bone,  and  is  neither 
very  vascular  nor  very  sensitive. 

In  structure  the  gums  resemble  other  parts  of  the  oral  mucous  membrane,  con- 
sisting of  the  epithelium  and  the  connective-tissue  layer.  The  latter,  directly  con- 
tinuous with  the  periosteum  of  the  alveolar  border  and  the  pericementum,  is  composed 
of  closely  fitted  bundles  of  fibrous  tissue  and  beset  with  numerous  papillae.  On 
young  teeth  the  epithelium  is  prolonged  for  from  .5-1  mm.  over  the  enamel  and  often 
for  a  short  additional  distance  over  the  cement,  ending  in  an  abrupt  margin.  In  the 
immediate  vicinity  of  the  tooth  the  papillae  sometimes  exhibit  infiltrations  of  lym- 
phoid  cells.  The  gums  are  without  glands.  The  structures  sometimes  described  as 
such,  as  the  "glands  of  Serres,"  consist  of  nests  of  epithelial  cells  derived  from  the 
remains  of  the  atrophic  embryonal  epithelial  sheath  (page  1563). 

THE   PALATE. 

The  Hard  Palate. — The  shape  and  proportions  of  the  hard  palate  have  been 
discussed  with  the  bones  (page  228),  so  we  have  here  to  do  only  with  its  mucous 
covering.  This  is  very  firmly  fastened  to  the  rough  surface  of  the  bones  by  dense 
connective  tissue  which  is  particularly  thick  at  the  sides,  doing  much  to  fill  up  the 
angle  between  the  roof  and  the  alveolar  process.  On  either  side  near  the  front, 
extending  onto  the  inner  surface  of  the  alveolar  processes,  is  a  series  of  raised  ridges 
(Fig.  1325),  in  the  main  transverse,  although  slightly  convex  anteriorly,  the  analogues 
of  the  palatal  riigce  of  most  mammals.  They  never  extend  behind  the  first  molar 
tooth,  are  numerous  and  prominent  in  childhood,  but  much  reduced  in  middle  age, 
and  occasionally  wholly  lost. 

1  Morphol.  Jahrbuch,  Bd.  xxii.,  1895. 

2  Nova  Acte  des  Leopold.  Carol.  Akad.  der  Naturforscher,  Bd.  xliii.,  1882. 

3  Magitot  :  Traite"  des  Anomalies  du  Systeme  Dentaire,  1887. 


i568 


HUMAN    ANATOMY. 


Just  behind  the  incisors,  at  or  before  the  iiicisor  canal,  there  is  a  small  raised 
pad  or  fold  of  mucous  membrane,  on  either  side  of  which  the  orifice  of  the  incisor 
canal  is  often  found.  When  pervious,  it  is  very  minute,  admitting  merely  a  bristle. 
Behind  this  the  palate  presents  a  median  raphc  of  paler  color  than  the  rest,  which  may 

FIG.   1325. 


Orifices  of  palatine  glands 


Incisor  pad  with  orifice  of  incisor 

canal 


Raphe 


Mucous  membrane  removed  to 
show  layer  of  glands 


Soft  palate 


Superior  dental  arch  and  palate  ;  palatal  rugae  occupy  anterior  part.    Soft  palate  partially  cut  away. 

run  to  the  root  of  the  uvula  or  may  stop  short  of  it,  being  often  deflected  to  the  left. 
A  little  behind  the  pad  this  line  may  be  interrupted  by  a  pale  oval  elevation  or  more 
often  a  depression.  The  membrane  of  the  roof  of  the  mouth  is  nowhere  bright  red  ; 
that  of  the  hard  palate,  however,  is  paler  than  the  rest.  There  are  no  glands  in  the 
oval  white  space,  but  there  is  a  continuous  layer  on  either  side  of  it.  The  orifices  of 
the  glands  are  easily  seen  with  a  lens,  sometimes  with  the  naked  eye.  A  little  in 

FIG.   1326. 


Muscular  fibres  of  tongue 


Dorsal  surface  of  tongue 


Anterior  pillar  of  fauces 

Plica  triangularii 


Tonsil 


Soft  palate 


upratonsillar  fossa 
Uvula 

Posterior  pillar  of  fauces 


Epiglottis 


Sagittal  section  through  palate,  uvula,  and  tongue,  showing   il^ht  l.iu-nil  wallot   i.uuvs;    tongue  has  bri-n  pulled 

downward  by  hook. 

front  of  the  origin  of  the  soft  palate  the  mucous  membrane  becomes  deeper  colored. 
These  differences  in  color  are  more  striking  in  children. 

The  Soft  Palate. — This  structure  consists  of  a  fold  of  mucous  membrane,  con- 
tinuous with  the  hard  palate,  enveloping  several  layers  of  interlacing  muscular  fibres, 
at  least  i  cm.  in  thickness  at  its  origin.  Its  lower  border  is  the  edge  of  the  fold. 


THE  PALATE.  1569 

This  is  concave  on  each  side,  and  presents  a  median  elongation,  the  uvula,  which 
varies  from  a  short  prominence  to  a  cord  2  cm.  in  length.  Thus  the  palate  has' 
a  lower  surface  looking  downward  and  forward  and  an  upper  one  looking  upward 
and  backward.  When  the  mouth  is  closed  the  palate  and  uvula  rest  against  the 
tongue  ;  when  open  they  hang  free,  but  the  muscles  inside  can  modify  their  shape 
and  position.  Median  sections  show  the  tip  of  the  uvula  often  reaching  within  half 

FIG.   1327. 

Pharvngeal  mucous  membrane        Azygos  luAulf        Tendon  °f  ^*™.  Pajati 

v       Artery    /     Levator  palati      Palato-pharyngeus 


Masses  of  glands  Oral  mucous  membrane 

Transverse  section  of  soft  palate  near  its  anterior  attachment.    X  4. 

an  inch  of  the  tip  of  the  epiglottis.  Possibly  muscular  relaxation  allows  it  to  descend 
somewhat  farther  than  in  life,  but  it  is  certain  that  no  very  great  elongation  is  neces- 
sary for  it  to  touch  that  organ  and  give  rise  to  great  discomfort.  The  soft  palate  can 
be  raised  so  as  to  touch  the  back  of  the  pharynx  and  close  all  communication  between 
the  nose  and  the  mouth.  Two  folds,  the  pillars  of  the  fauces,  each  the  reflection  of 
the  mucous  membrane  over  a  muscular  bundle,  start  from  the  palate  on  either  side. 
The  anterior  pillar,  enclosing  the  palato-glossus  muscle,  arises  from  the  front  of  the 
palate  near  the  uvula,  some  distance  anterior  to  the  edge,  and,  curving  downward, 
runs  to  the  tongue  at  the  junction  of  the  middle  and  posterior  thirds,  separating  the 
mouth  from  the  pharynx  and  forming  the  posterior  border  of  the  sublingual  space. 
The  posterior  pillar  starts  from  the  lower  border  of  the  palate  on  either  side  of  the 
uvula,  covering  \hzpalato-pharyngeus,  and  runs  down  the  throat  to  the  superior  cornu 
of  the  thyroid  cartilage,  the  lower  part  being  indistinct.  Some  of  the  muscular  fibres 
within  it  go  to  the  upper  border  of  the  thyroid  cartilage  in  front  of  the  horn,  but  the 
fold  is  not  often  found  so  low,  except  in  frozen  sections,  in  which  it  appears  at  the 
sides  of  the  back  of  the  pharynx. 

A  deep  triangular  recess  on  either  side,  between  the  anterior  and  posterior 
pillars,  contains  the  tonsil.  This  region  is  often  vaguely  described  as  the  isthmus  of 
the  fauces,  one  being  left  in  doubt  whether  it  belongs  to  the  pharynx  or  to  the  mouth. 
In  the  preceding  pages  the  pharynx  is  described  as  beginning  at  the  anterior  pillar. 

The  reasons  for  this  divi- 
FIG.  1328.  sion   are  developmental, 

Fibres  of  azygos  uvulae  Pharyngeal  mucous  membrane       morphological,  and  phys- 

\rvvrv~'* "'••:••'«•. '.x-.,^  iological.      The    part    of 

the    tongue    anterior    to 

pa.ato^yn.cus  fi/^«^  thjs  io^  *  <?f  mandibular 

V(buccal)  origin,  while  the 
jM  ^S-^(  ;,an(is  part  behind  it  comes  from 

^J^W-^  J~-"  the  pharynx.      The  sur- 

Masses  of  glands  Oral  mucous  membrane  face  of  the   former  IS    SUp- 

Transverse  section  of  soft  palate  near  base  of  uvula.     X  4.  plied    by   the    mandlbular 

nerve,  the  third  division 

of  the  fifth,  and  the  latter  by  the  glosso-pharyngeal.  The  mucous  membrane  of  the 
posterior  third  does  not  bear  papillse  (except  the  circumvallate  papillae  near  the  junc- 
tion of  the  two  regions),  but  is  rich  in  adenoid  tissue  and  glands,  differing  in  both 
respects  from  the  part  in  front  of  it.  The  arrangement  of  the  transverse  fibres  of  the 
glosso-palati  muscles  in  the  substance  of  the  tongue  suggests  a  sphincter  at  the 
entrance  of  the  pharynx.  Finally,  in  deglutition  it  is  in  passing  this  line  that  the 
bolus  ceases  to  be  under  the  control  of  the  will. 

99 


157° 


HUMAN   ANATOMY. 


The  following  layers  compose  the  soft  palate  from  above  downward  :  ( i )  The 
pharyngeal  mucous  membrane.  (2)  A  fibre-muscular  layer.  The  fibrous  portion 
is  the  expansion  of  the  tendons  of  the  tensor  palati  muscles.  It  is  strong  and  tense 
near  the  hard  palate,  gradually  dwindles  lower  down,  and  joins  the  pharyngeal 
aponeurosis  at  the  sides.  Below  this  is  the  complex  of  the  muscles.  (3)  A  glan- 
dular layer  opening  into  the  mouth.  This  is  some  5  mm.  thick  at  its  origin  and 
practically  continuous  throughout  most  of  the  palate.  It  is  interrupted  at  the  median 
line  near  the  hard  palate  by  a  septum  of  muscular  and  fibrous  tissue,  is  wanting  near 
the  free  edge  of  the  palate  a  little  on  either  side  of  the  root  of  the  uvula,  and  is  con- 
tinued down  the  uvula  as  a  cylindrical  string  of  glands  nearly  to  the  tip,  through  and 
about  which  run  the  fibres  of  the  azygos  uvulae  muscle.  Irregular  glandular  collections 
are  found  near  the  latter,  especially  at  the  base  of  the  uvula.  (4)  A  lower  layer  of 
mucous  membrane. 

The  mucous  membrane  of  the  soft  palate  is  red  on  the  pharyngeal  and  pale  on 
the  buccal  surface  ;  on  both  sides  it  presents  papillae,  those  on  the  upper  surface 

FIG.   1329. 


Glands 


Glands 


Aponeurotic  tissue 


Oral  mucous  membrane 


Sagitto-lateral  section  of  soft  palate.    X  15. 

especially  being  near  the  base.  The  most  common  form,  slender  and  elongated,  is 
scattered  over  the  entire  buccal  surface  and  the  front  of  the  uvula  ( Rudinger  >. 
Thicker  short  papillae  are  also  found  near  the  beginning  of  tin-  pharyngeal  surface. 
Small  adenoid  collections  occur  on  the  upper  surface,  as  well  as  small  glands  situated 
in  the  depth  of  the  mucous  membrane.  The  orifices  of  the  chief  glandular  layer 
pierce  the  inferior  palatal  surface. 

The  Muscles  of  the  Soft  Palate. — Some  of  the  muscles  arise  in  the  soft 
palate  ;  others  run  into  it.  Isolation  of  the  individual  sets  of  fibres  is  not  always 
possible. 

The  tensor  palati  (dilatator tube)  (Fig.  1330)  arises  from  the  scaphoid  fossa  at 
the  root  of  the  internal  pterygoid  plate,  from  the  spine  of  the  sphenoid,  and  from  the 
outer  membranous  part  of  the  Eustachian  tube.  It  descends,  vertically  along  the 
internal  pterygoid  plate  as  a  round,  red,  and  distinct  muscle,  which  become  s  tendinous 
as  it  turns  inward  under  the  hamular  process  at  right  angles  to  its  previous  course, 
after  which  it  broadens  into  the  fibrous  expansion  in  the  soft  palate  already  described, 
above  the  other  muscles.  A  bursa  lies  between  the  tendon  and  the  hamular  process. 


THE  PALATE. 

The  levator  palati  (Fig.  1330)  arises  from  the  base  of  the  skull  at  the  apex 
of  the  petrous  portion  of  the  temporal  bone  and  from  the  cartilaginous  part  of  the 
Eustachian  tube  beside  it.  At  first  thick,  it  passes  downward,  forward,  and  inward 
with  the  tube,  and,  leaving  it,  expands  into  a  layer  which  spreads  out  through  the 
soft  palate.  Some  of  the  anterior  fibres  from  the  tube  go  to  the  back  of  the  hard 
pajate,  constituting  the  salpingo-palatinus,  while  others,  descending  in  the  lateral 
wall  of  the  pharynx,  form  the  salpingo-pharyngcus,  beneath  the  fold  of  corresponding 
name.  The  great  body  of  the  fibres  crosses  the  middle  line  in  the  front  part  of  the 
soft  palate.  Most  of  them  descend  in  the  opposite  side.  Some  seem  to  form  loops 
with  an  upward  concavity  with  fibres  from  the  fellow-muscle.  Near  the  hard  palate 
this  decussation  completely  divides  the  glandular  layer  (Fig.  1327). 

The  azygos  uvulae  (Fig.  1331),  although  probably  a  double  muscle  originally, 
soon  (even  at  birth)  becomes  practically  a  single  one.  Arising  from  the  tendinous 
fibres  of  the  tensor  palati  just  behind  the  posterior  nasal  spine,  it  soon  becomes  mus- 
cular and  increases  in  size.  Its  course  is  downward  into  the  uvula,  but  on  reaching 
*he  base  it  is  already  broken  up  into  separate  bundles  which  pass  about  and  through 

FIG.  1330. 

Hard  palate 


Hamular  process 

Tensor  palati 
Levator  palati 


Soft  palate  (cut) 

External  pterygoid  plate 

Posterior  nares 

Opening  oi  Eustachian  tube 


Cut  edge  of  pharynx 
Mass  of  adenoid  tissue 


Fossa  of  Rosenmuller 
(opened) 

Styloid  process 


Occipital  condyle 
Inferior  surface  of  skull  with  upper  part  of  opened  pharynx  and  palatal  muscles  attached  ;  viewed  from  behind. 

the  glandular  core  of  the  uvula.  The  belly  of  the  muscle  lies  near  the  dorsal  surface, 
between  the  fibrous  expansion  of  the  tensor  palati  and  the  levator  palati,  which  decus- 
sates on  its  oral  surface. 

The  palato-pharyngeus  (Fig.  1331)  has  a  complicated  origin  in  more  than 
one  layer  from  the  border  of  the  hard  palate,  from  the  lower  surface  of  the  apo- 
neurosis,  and  perhaps  from  fibres  of  the  levator  palati.  Certain  fibres,  either  arising 
in  the  middle  line  or  coming  from  the  other  side,  pass  downward  and  outward 
over  the  azygos  uvulae  ;  others  lie  beneath  the  glandular  layer.  Some  of  the  fibres 
seem  to  continue  the  course  of  the  salpingo-pharyngeus  of  the  opposite  side,  with- 
out being  directly  continuous.  The  muscle  passes  down  near  the  edge  of  the  soft 
palate  and  then  in  the  posterior  pillar  into  the  side  of  the  pharynx,  where  it  min- 
gles with  the  stylo-pharyngeus.  A  part  is  inserted  into  the  upper  border  of  the 
thyroid  cartilage,  and  sometimes  into  the  superior  horn.  It  also  expands,  together 
with  the  stylo-pharyngeus,  into  a  thin  layer  just  beneath  the  mucous  membrane 
of  the  back  of  the  pharynx,  which  meets  its  fellow  in  the  median  line  where  it  is 
inserted  into  the  pharyngeal  aponeurosis.  Its  lower  limit  is  a  curved  line  with  the 
concavity  looking  upward  and  outward,  behind  the  larynx  (Fig.  1361).  (This  part 


1572 


HUMAN  ANATOMY. 


of  the  muscle  must  be  dissected  from  behind,  after  removing  the  constrictors  of 
the  pharynx.  ) 

The  palato-glossus  (Fig.  1339)  is  a  small  bundle  arising  from  near  the  middle 
line  of  the  oral  side  of  the  lower  part  of  the  soft  palate,  forming  by  its  projection  the 
anterior  pillar  of  the  fauces,  in  which  it  runs  to  the  tongue,  where  it  joins  the  trans- 
verse fibres.  The  pair  of  muscles  act  as  a  sphincter  tending  to  close  the  passage  from 
the  mouth  to  the  pharynx.  A  thin  expansion  from  this  muscle  passes  over  the  tonsil. 

Vessels.— The  arteries  of  the  palate  (both  hard  and  soft)  come  chiefly  from 
the  descending  palatine,  which,  emerging  from  the  posterior  palatine  canal,  runs  for- 
ward along  the  inner  side  of  the  base  of  the  alveolar  process.  It  sends  a  few  branches 


FIG.  1331. 


Salpingo- 
pharyngeus 


Levator  palati 


Palato-pharyngeus 


Nasal  septum  Eustachian  tube 


^ — External 

\         pterygoid 

Levator  palati 

I — Tensor  palati 

Internal 

pterygoid 
f- — Hamular  process 

Tensor  palati 
ygos  uvula- 


Palato-pharyngeus 
Stylo-pharyngeus 


Posterior  surface  of  tongue 


.Superior  orifice  of  larynx 


Posterior  crico-arytenoid 


(Esophagus 


Muscles  of  palate  and  pharynx,  seen  from  behind  ;  pharynx  laid  open. 

inward  and  backward  to  the  front  of  the  soft  palate,  which  is  supplied  on  the  side  by 
a  branch  either  from  the  facial  or  from  the  ascending  pharyngeal.  It  is  to  be  noted 
that  no  vessel  is  likely  to  interfere  with  the  division  of  the  tensor  palati  at  the  inner 
side  of  the  hamular  process. 

The  veins  of  the  hard  palate  follow  in  the  main  the  arteries.  Those  of  the  upper 
side  of  the  soft  palate  join  the  plexus  of  the  zygomatic  fossa.  The  larger  ones  of  the 
under  side  connect  with  the  veins  of  the  tonsil  and  tin-  root  of  the  tongue. 

The  lymphatics  of  the  hard  palate  and  of  the  under  side  of  the  soft  palate  form 
a  rich  plexus.  Those  on  the  upper  side  of  the  latter  are  small.  The  chief  current  is 
to  the  deep  glands  of  the  neck. 


THE  TONGUE. 


1573 


Nerves. — The  tensor  palati  is  supplied  by  the  mandibular  division  of  the  fifth 
pair,  the  other  muscles  by  the  pharyngeal  plexus.  The  mucous  membrane  of  the 
hard  palate  is  supplied  by  the  anterior  palatine  nerve  and  terminal  branches  of  the 
naso-palatine.  That  of  the  soft  palate  is  supplied  by  the  other  palatine  nerves 
and  by  branches  from  the  glosso-pharyngeal. 


THE   TONGUE. 

The  tongue  is  a  median  muscular  organ  attached  to  the  floor  of  the  mouth, 
the  symphysis  of  the  jaw,  and  the  body  and  both  horns  of  the  hyoid,  covered  with 
mucous  membrane,  which  when  the  mouth  is  closed  it  practically  fills  (Fig.  1339). 
The  root  is  the  attached  portion,  extending  from  the  hyoid  to  the  symphysis,  com- 
posed of  the  genio-glossi  and  the  hyo-glossi  muscles.  The  tip  is  the  free  anterior 
end,  flat  both  above  and  below  when  extended,  and  surrounded  by  mucous  mem- 
brane. Behind  this  the  tongue  is  a  solid  mass.  The  dorsum  in  its  anterior  two- 
thirds  is  convex  from  side  to  side,  and  rests  against  the  hard  and  soft  palates  ;  the 
posterior  third,  nearly  vertical,  looks  backward,  forming  the  front  wall  of  the  pharynx 
when  the  mouth  is  closed.  There  is  a  median  groove  in  the  upper  part  of  this  pos- 
terior third,  continued  for  a  little  distance  onto  the  top,  in  which  the  uvula  rests. 
This  hind  portion  is  so  broad  that  the  edges  of  the  tongue  reach  quite  to  the  sides 

FIG.  1332. 


Anterior  tongue  anlage 


II  arch 


III  arch 


Larynx 

Reconstruction  of  floor  of  primitive  oro-pharynx  of  embryo 
12.5  mm.  in  length.     X  16.     (His.) 


Under  surface  of  tongue  of  new-born  child. 
(Gegenbaur,) 


of  the  pharynx.  In  the  anterior  two-thirds  the  edges  of  the  tongue  are  prominent, 
overhanging  the  sides. 

Development  shows  that  the  tongue  has  a  double  origin,  the  posterior  third 
arising  from  the  sides  of  the  pharynx  and  overlapping  on  each  side  the  anterior  two- 
thirds,  which  comes  from  a  median  mass,  the  tuberculum  impar,  of  buccal  origin  ( Fig. 
1332).  The  thyro-glossal  duct  comes  to  the  surface  at  the  junction  of  these  parts, 
which  in  the  infant  are  separated  by  the  snlcus  terminalis.  As  will  later  be  evident, 
the  manner  of  development  is  of  much  significance. 

The  mucous  membrane  of  the  lateral  and  inferior  surface  is  thin  and  smooth 
with  small  papillae  at  the  tip.  In  the  middle  it  forms  a  fold,  \\\<t  frenum,  running 
from  near  the  tip  to  the  floor  of  the  mouth.  In  infancy  this  is  occasionally  so 
shcrt  as  to  restrain  the  tip  of  the  tongue  from  the  motions  necessary  for  nursing. 
Often  it  is  hardly  visible.  The  plica  jftrnbriata  and  the  plica  sublingu&lis  are  two 
folds  on  either  side  of  the  front  part  of  the  under  surface,  of  which  the  former  with 
ragged  edges  is  the  outer,  the  longer,  and  the  larger.  Both  are  distinct  in  the  infant 
and  (especially  the  latter)  lost  or  poorly  marked  later.  The  plicae  fimbriata:'  bound 
a  triangular  space  which  Gegenbaur  considers  a  rudiment  of  the  under-tongue  of  some 
mammals.  The  mucous  membrane  of  the  dorsum  is  divisible  into  two  wholly  differ- 
ent regions  :  the  one  comprising  the  anterior  two-thirds,  the  other  the  posterior  ver- 
tical third.  The  line  of  separation,  or  sulcns  terminalis,  is,  however,  not  transverse, 
but,  starting  at  the  side  from  the  anterior  pillar  of  the  fauces,  runs  backward  and 
inward  to  meet  its  fellow.  This  is  not  usually  visible  in  the  adult  ;  but  its  place  is 


HUMAN   ANATOMY. 


easily  recognized,  as  just  before  it  is  a  V-shaped  arrangement  of  circumvallate  papillae, 
the  median  apex  being  at  or  near  a  small  depression,  the  foramen  ceecum,  which 
marks  the  termination  of  the  foetal  duct  through  the  tongue  from  the  thyroid.  In 
the  adult  this  may  be  a  short  tunnel  or  a  depression,  into  which  the  ducts  of  several 
glands  open.  According  to  Munch,1  it  is  always  behind  the  hindmost  circumvallate 


FIG.   1334. 


ihenoidal 
sinus 


Cut  zygoma 

Pterygoid 

plates 
Eustachian 
tube 


Cut  and  reflectei 
soft  palat 


Spine  of 
sphenoid 
Zygoma 

Fossa  of 
Rosenmuller 


Soft  palate  cut  and  turned 
aside 


Half  of  uvula 
Anterior  pillar  of  fauces 

Posterior  pillar  of  fauces 


Lymph-nodules  constituting 
lingual  tonsil 


Anterior  portion  of  head  has  been  removed  by  frontal  section  |ia-.Mii.n  through  plane  of  posterior  nares;  the  soft  palate 
cut  in  mid-line  and  turned  asiik-.  exposing  posterior  wall  ol  phar>nx  ;  tongue  drawn  forward  and  downward. 


papilla.  The  mucous  membrane  covering  the  dorsum  of  the  tongue  is  closely  beset 
with  elevations,  or  pafiillte,  of  which  there  are  three  varieties,  the  filiform,  fungifonn, 
and  circumvallate.  In  general  they  consist  of  a  core  of  connective-tissue  stroma  cov- 
ered with  stratified  squamous  epithelium  ;  the  projection  formed  by  the  connective 
tissue  bears  minute  secondary  papilla-,  which,  however,  do  not  model  the  free  sur- 

Arbeilcn,  Mil.  vi.,  1896. 


THE   TONGUE. 


1575 


face  of  the  mucous  membrane.  The  anterior  two-thirds  of  this  surface  are  rough 
with  fungiform  and  filiform  papilla;  ;  the  former,  less  numerous,  appear  as  red 
points  chiefly  near  the  edges,  while  the  filiform  are  everywhere,  but  arranged  in  par- 
allel rows  continuing  forward  the  lines  of  the  circumvallate  papillae.  At  the  edges  of 
the  tongue,  just  in  front  of  the  end  of  the  anterior  pillar  of  the  fauces,  close  inspec- 
tion, especially  with  a  lens,  will  generally  show  a  small  series  of  minute  transverse 
parallel  ridges,  corresponding  to  the  papilla  foliata  of  rodents  in  a  rudimentary  con- 
dition. The  papilla  circumvallata:  are  fungoid  papillae  surrounded  by  a  depression 
bounded  externally  by  a  low  annular  wall.  The  usual  number  of  these  papillae  is 
from  nine  to  ten,  ranging  from  six  to  sixteen  (Miinch).  The  sides  of  the  V  in  which 
they  are  disposed  are  not  very  symmetrical.  Usually  there  is  at  least  one  median 
papilla  behind  the  apex,  and  very  rarely  one  or  two  before  it.  The  circumvallate 
papillae  are  of  especial  interest  as  being  the  most  important  seat  of  the  gustatory  end- 


1335 


Filiform  papilla 


Surface  epithelium  covering 
fungiform  papilla 

Projections   of    tunica    pro- 
pria  constituting  basis  of 


Muscular  tissue  of 
tongue 


Section  of  lingual  mucous  membrane,  showing  filiform  and  fungiform  papillae.     X  75- 


organs,  or  taste-buds,  which  lie  embedded  within  the  epithelium  lining  the  groove 
encircling  the  central  elevation.  A  detailed  description  of  the  taste-buds  is  given 
with  the  organs  of  special  sense  (page  1433). 

The  surface  of  the  vertical  posterior  third  of  the  tongue  is  smooth,  in  the  sense 
that  there  are  no  papillae  nor  roughnesses,  but  it  is  studded  with  masses  of  lymphoid 
tissue,  sometimes  called  the  lingual  tonsil  ( Fig.  1334),  which  make  numerous  eleva- 
tions on  its  surface.  The  mucous  membrane  of  the  back  of  the  tongue  is  continued 
in  a  thinner  layer  onto  the  front  of  the  epiglottis.  It  presents  the  median  glosso- 
epiglottic  fold,  containing  fibro-elastic  tissue  and  muscular  fibres  of  the  genio-glossi, 
which  separate  two  little  depressions,  the  glosso-epiglottic  fossa.  These  may  be  with- 
out any  definite  lateral  boundary,  or  may  be  embraced  by  the  small  lateral  glosso- 
epiglottic  folds,  the  internal  borders  of  which  are  concave.  The  mucous  membrane 
is  firmly  attached  to  the  subjacent  muscles  in  the  anterior  two-thirds  of  the  tongue, 
but  less  firmly  behind. 

Glands  of  the  Tongue. — The  lingual  glands  include  both  serous  and  mucous 
varieties,  which  are  distributed  as  three  groups  :  (i)  serous  glands,  (2)  posterior 
mucous  glands  and  (3)  anterior  mucous  glands. 


'576 


HIM  AN    ANATOMY. 


The  tubo-alveolar  glands  surrounding  the  circumvallate  and  the  foliate  papillae 
are  the  only  ones  of  a  purely  serous  type  ;  their  thin,  watery  secretion  is  no  doubt  an 
important  medium  in  conveying  sapid  substances  to  the  taste-buds  situated  in  this 


FIG.    1336. 


/ 


Epithelium  covering 
filiform  papillae 


Capillary  loops  within 
connective-tissue  basis 
of  papillae 


Mucous  membrane 


Muscular  tissue 


I 
Injected  mucous  membrane  and  subjacent  areolar  and  muscular  tissue  from  upper  surface  of  tongue.     X  60. 


FIG.   1337 


Efc\ 

-.'  ,"v  :lx       \m-  •    ••••'••:••  ':*? 


Taste-bud       Annu]ar  wal, 


Central/  ^\"vv' 

portion  (it  |  >a-  -    »*-  ' 

pilla— con-  ., 

nective  tissue  •.,".'•) 

;sue  *     .*  *  * 

I'allate  papilla  from  child's  tongue,  showing  central  portion  ami  cnnirlin.i;  lold.     X  75- 


s>~$£yi  \£&^\  *' 

Miisi-ular  tissue  *      *  *  * 

Si-,  tidii  at  ran  fin-umvallatf  papilla  from  child's  tongue,  showing  central  porti 


vicinity.  The  glands  encircling  the  circumvallate  papillae  constitute  an  annular  group 
some  4  nun.  wide.-  and  alxuit  t \\icc  as  deep.  Those  alxnit  the  pajtilhr  foliata  foKin  an 
elongated  group,  about  3.5  mm.  in  width,  which  extends  from,  8—15  mm.  in  front  of 


THE  TONGUE. 


1577 


the  base  of  the  palato-glossal  fold.  Anteriorly  towards  the  dorsum  the  serous  glands 
remain  isolated  ;  posteriorly  they  come  into  contact  with  the  mucous  glands,  so  that 
alveoli  of  both  varieties  may  be  included  within  a  single  microscopical  field  (  Fig.  1 287  ). 

The  posterior  third  of  the  dorsum,  from  the  circumvallate  papillae  backward, 
possesses  a  rich,  almost  continuous  layer  of  mucous  glands,  5  mm.  or  more  in  thick- 
ness, which  lie  beneath  the  mucous  membrane  and  mingle  with  the  lymphoid  tissue. 
Since  the  alveoli  lie  among  the  muscles  at  some  depth,  the  excretory  ducts  often 
attain  a  length  of  from  10-15  nim. ,  and  open  on  the  free  surface  in  close  association 
with  the  lymph-follicles. 

The  anterior  mucous  glands  (Fig.  1287)  are  disposed  principally  as  two  elon- 
gated groups,  glandules  linguales  anteriores,  or  glands  of  Nuhn,  or  of  Blandin 
(from  15-20  mm.  in  length,  7-9  mm.  in  width,  and  somewhat  less  in  thickness), 
which  lie  on  either  side  of  the  mid-line,  near  the  tip  of  the  tongue,  among  the  mus- 
cular bundles.  They  meet  in  front,  but  diverge  behind,  where  they  may  be  con- 

• 
FIG.   1338. 


Glands 


Interlacing  fibrous  and 
muscular  bundles 


Glands 


Section  from  posterior  third  of  child's  tongue,  showing  lymph-nodes  constituting  a  part  of  lingual  tonsil.     X  30. 


tinned  backward  by  additional  collections  of  mucous  glands  akmg  the  edges  of  the 
tongue.  The  ducts — five  or  six  in  number — open  on  the  folds  occupying  the  under 
surface  of  the  tongue  near  the  frenulum. 

Muscles  of  the  Tongue. — These  include  two  groups,  the  extrinsic  and  the 
intrinsic  muscles.  The  former  pass  from  the  skull  or  hyoid  bone  to  the  tongue  ;  the 
latter  comprise  the  particular  muscles  forming  the  principal  mass  of  the  organ.  Their 
general  arrangement  is  as  follows.  Under  the  mucous  membrane  is  a  dense  sheath 
of  longitudinal  fibres,  surrounding  the  others  completely  near  the  apex,  and  farther 
back  wanting  at  the  middle  of  the  under  surface  where  the  fibres  of  the  genio-glossi 
and  hyo-glossi  enter  the  organ.  This  outer  layer  is  the  cortex.  The  inner  part  is 
divided  into  two  by  a  vertical  median  septum  of  areolar  tissue,  which  is  quite  dense 
in  its  upper  part.  It  is  sickle-shaped,  with  the  point  in  front  and  not  reaching  the 
apex.  The  inner  portion,  or  medulla,  is  composed  of  transverse  muscle-fibres  inter- 
posed between  layers  of  those  called  vertical,  which  in  fact  present  many  degrees  of 
obliquity. 

The  extrinsic  muscles  are  the genio-^ glossus,  the  hyo-glossus,  the  stylo-glossus, 
and  the  palato-glossus,  to  which  may  be  added,  from  its  position,  the  genio-hyoid. 
All  of  these  are  in  pairs  and  symmetrical. 


1578 


HUMAN  ANATOMY. 


The  genio-hyoid  (Fig.  1339)  is  a  collection  of  fleshy  fibres  extending  close  to 
the  median  line,  from  the  inferior  genial  tubercle  to  the  anterior  surface  of  the  body 
of  the  hyoid  bone.  It  is  a  thick  band,  four-sided  on  transverse  section,  with  rounded 
angles,  and  expands  laterally  on  approaching  its  insertion.  A  layer  of  areolar  tissue 
separates  it  from  its  fellow. 

Nerve. — The  nerve-supply  is  from  the  hypoglossal,  but  probably  consists  of 
fibres  derived  from  the  cervical  nerves. 

Action. — To  draw  the  hyoid  forward  and  upward  ;  or,  when  fixed  below,  to 
depress  the  mandible. 

The  genio-glossus  (Fig.  1339)  arises  just  above  the  preceding  by  short  ten- 
dinous fibres  from  the  superior  genial  tubercle.  Its  inferior  fibres  run  horizontally 
backward  to  the  base  of  the  tongue,  passing  over  the  hyoid  bone  to  the  base  of  the 
epiglottis  ;  the  fibres  above  these,  inserted  successively  into  the  mucous  membrane  of 

FIG.   1339. 


Stump  of  masseter 


Tensor     . 
palati  _  » 

palati  ^B/ 

Hamula 

process    styd  process 

Superior  constrictor 

Pterygo-mandibular  ligament 

Stylo-glossus 

Stylo-pharyngeus 
Stylo-hyoid  (cut) 

Middle  constrictor 


Genio-hyoid        Hyo-glossus 


Inferior  constrictor 


Pharyngeal  and  extrinsic  lingual  muscles 

the  dorsum  of  the  tongue  near  the  middle  line,  are  at  first  oblique,  then  vertical,  and 
finally  concave  anteriorly  as  they  approach  the  apex,  so  that  the  muscle  is  fan-shaped 
when  seen  from  the  side.  Each  muscle  is  separated  from  its  fellow  by  the  median 
septum. 

Nerve. — The  hypoglossal. 

Action. — The  complex  action  of  this  muscle  includes  retraction  of  the  tongue  by 
the  anterior  fibres,  drawing  forward  and  protrusion  by  the  posterior  fibres,  and  depres- 
sion, with  increased  concavity,  of  the  dorsum  by  its  middle  part. 

The  hyo-glossus  (Fig.  1339),  external  to  the  preceding,  from  which  it  is  sepa- 
rated by  areolar  tissue,  arises  from  the  side  of  the  body  of  the  hyoid,  the  whole  of  the 
greater  horn,  and  the  lesser  horn.  The  last  portion,  rather  distinct  from  the  rest,  is 
deseribed  sometimes  separately  as  the  chondro-glossus.  The  whole  muscle, 
applied  to  the  side  of  the  tongue,  forms  a  layer  of  fibres  directed  upward  and  for- 


THE   TONGUE.  1579 

ward  ;  towards  the  front  its  fibres  are  almost  longitudinal.  The  fibres  from  the  lesser 
horn  run  on  the  dorsum  beneath  the  mucous  membrane,  forming  a  part  of  the  super- 
ficial longitudinal  system. 

Nerve. — The  hypoglossal. 

Action. — To  depress  the  sides  of  the  tongue,  thereby  increasing  the  transverse 
convexity  of  the  dorsum  ;  the  muscle  also  retracts  the  protruded  tongue. 

The  stylo-glossus  (Fig.  1339)  arises  from  the  tip  of  the  styloid  process  and 
from  the  beginning  of  the  styio-maxillary  ligament.  It  is  a  small  ribbon-like  muscle 
with  an  anterior  and  a  posterior  surface,  but  as  it  descends  it  twists  so  as  to  lie  along 
the  outer  side  of  the  tongue,  which  it  reaches  in  the  region  of  the  circumvallate 
papillae.  On  joining  the  tongue  the  fibres  divide  into  an  upper  and  a  lower  bundle, 
both  of  which  are  chiefly  longitudinal,  although  some  fibres  blend  with  the  transverse 
series.  It  is  soon  lost  in  the  sheath  of  longitudinal  fibres. 

Nerve. — The  hypoglossal. 

Action. — To  retract  the  tongue  and  to  elevate  the  sides,  thus  aiding  in  pro- 
ducing transverse  concavity  of  the  dorsum. 

The  palato-glossus  (Fig.  1339)  arises  from  the  anterior  or  buccal  aspect  of 
the  palate,  and  descends  within  the  fold  forming  the  anterior  pillar  of  the  fauces  to 
the  tongue,  where  it  joins  the  transverse  fibres,  passing  between  the  two  parts  of  the 
stylo-glossus. 

Nerve. — From  the  pharyngeal  plexus,  the  motor  fibres  coming  probably  from 
the  spinal  accessory  nerve. 

Action. — To  elevate  the  tongue,  to  depress  the  soft  palate,  and,  with  its  fellow 
by  approximating  the  anterior  pillars,  to  close  the  fauces. 

FIG.   1340. 

Longitudinal  fibres  Longitudinal 

,  .>^:  <..*.i*MtitftattClft}MafeMna»«M.  /     fibres 


.Transverse  fibres 


\ 
\ 

Plica  fimbriata  Glands  Vertical  fibres 

Transverse  section  of  tongue  of  child,  near  tip.    X  3. 

The  intrinsic  muscles  are  the  lingualis,  the  transversus,  and  the perpendicu- 
laris  (Fig.  1340). 

The  lingualis,  sometimes  divided  into  a  superior  and  an  inferior,  comprises  the 
greater  number  of  the  longitudinal  fibres, — all,  in  fact,  that  do  not  come  from  the 
extrinsic  muscles.  The  thickness  of  this  layer  is  some  5  mm. 

The  transversus  furnishes  nearly  all  the  transverse  fibres,  the  most  important 
extrinsic  contribution  being  from  the  palato-glossus.  It  arises  from  the  septum  and 
runs  outward  to  the  mucous  membrane  ;  as  it  approaches  the  cortex  the  fibres  break 
up  into  bundles,  among  which  pass  groups  of  the  fibres  of  the  lingualis.  The  trans- 
versus is  arranged  in  a  series  of  vertical  layers,  between  which  pass  layers  of  the 
vertical  set.  Thus  a  horizontal  section  has  the  effect  of  a  series  of  transverse  fibres 
like  the  bars  of  a  gridiron  with  the  cut  ends  of  the  vertical  fibres  between  them  and 
the  longitudinal  fibres  of  the  lingualis  at  either  side.  Near  the  apex  fibres  of  this 
system  run  directly  from  the  mucous  membrane  of  one  side  to  that  of  the  other. 

The  perpendicularis  is  the  name  given  to  the  few  vertical  fibres  that  do  not 
come  from  the  extrinsic  muscles.  They  occur  chiefly  at  the  tip  and  sides,  passing 
from  the  lower  to  the  upper  mucous  membrane. 

Nerve. — All  the  intrinsic  muscles  are  supplied  by  the  hypoglossal. 

Action. — The  tongue  is  protruded  chiefly  by  the  action  of  the  posterior  fibres  of 
the  genio-glossus,  drawing  the  posterior  part  of  the  tongue  forward,  assisted,  perhaps, 
by  the  contraction  of  the  transversus.  It  is  withdrawn  by  its  own  weight.  The 


HUMAN    ANATOMY. 


longitudinal  system,  the  various  parts  of  which  can  act  separately,  turns  the  tip  in 
any  direction.  The  stylo-glossus  and  palato-glossus  raise  the  posterior  portion, 
particularly  at  the  edges,  but  the  latter  probably  acts  more  on  the  palate  than  on  the 
tongue. 

Vessels. — The  principal  arteries  supplying  the  tongue  are  branches  of  the 
lingual,  elsewhere  described  (page  735).  Although  there  may  be  a  trifling  anasto- 
mosis at  the  tip  between  the  vessels  of  the  opposite  sides,  there  is  no  communication 
sufficient  to  re-establish  the  circulation  at  once,  so  that  ligation  of  either  artery 
will  render  that  half  of  the  tongue  bloodless  for  an  operation.  The  -veins  consist  of 
four  sets  on  each  side,  communicating  freely  with  one  another.  They  are  ( i )  the 
dorsal  veins  forming  a  submucous  plexus  on  the  back  of  the  tongue  above  the  larynx 
and  joining  those  of  the  tonsil  and  pharynx,  (2)  two  veins  accompanying  the  artery 
and  sometimes  forming  a  plexus  about  it,  (3)  two  with  the  lingual  nerve,  (4)  two 
with  the  hypoglossal  nerve.  Of  these  latter,  the  one  below  the  nerve  is  the  larger 
and  is  the  ranine  vein,  running  on  the  under  surface  of  the  tongue  on  either  side  of 
the  frenum.  The  lymphatics  present  a  rich  net-work  on  the  anterior  two-thirds  of 
the  dorsum.  The  multitude  of  spaces  throughout  the  organ  communicate  with  lym- 


FIG.  1341. 


Longitudinal  fibres 


Glands 


Portion  of  sublingual  gland 


Vertical  fibres 
Transverse  fibres 


Septum        Genio-glossus      Hyo-glossus 


Transverse  section  of  tongue  of  child,  through  middle  third.    X  3. 

phatics.  Some  from  the  median  part  empty  into  the  suprahyoid  glands,  but  most 
go  to  the  submaxillary  and  to  the  deep  cervical  glands. 

Nerves. — The  motor  fibres  are  supplied  by  the  hypoglossal,  aided  probably  by 
the  facial  through  the  chorda  tympani.  Those  of  common  sensation  are  from  the 
lingual  branch  of  the  fifth  for  the  anterior  two-thirds  and  from  the  gkeso-pharvngeal 
for  the  remainder,  excepting  the  region  just  in  front  of  the  epiglottis,  which  is 
supplied  by  the  superior  laryngeal  from  the  vagus.  The  glosso-pharyngeal  a-rca 
somewhat  overlaps  the  posterior  third,  as  it  supplies  the  circumvallate  and  foliate 
papillae.  The  chief  fibres  of  special  sense  are  derived  from  the  glosso-pharyngeal, 
their  principal  distribution  being  to  the  taste-buds  on  the  circumvallate  papillae.  Re- 
garding the  source  of  the  taste-fibres  to  the  anterior  parts  of  the  tongue  opinions 
still  differ.  According  to  many  anatomists,  these  fibres  reach  their  destination 
through  the  chorda  tympani,  since  the  latter  nerve  is  supposed  to  receive  taste- 
til  >res  from  the  ninth  by  way  of  the  pars  intermedia  of  \VrisU-rg,  which  accompanies 
the  facial.  According  to  Zander,1  Dixon,2  Spiller,8  and  others,  however,  the  view 
attributing  fibres  of  special  sense  for  the  anterior  part  of  the  tongue  partly  to  the 
fifth  nerve  is  eorrect. 

Growth  and  Changes. — At  birth  the  tongue  is  remarkable  chiefly  for  its  want 
of  depth,  as  shown  in  a  median  section,  which  depends  on  th'e  undeveloped  condition 
of  the  jaws.  This  is  gradually  corrected  coincidently  with  the  growth  of  the  face. 

1  Anatomischer  Anzeigef ,  Hd.  \i\.,  1897. 

-  Kdinbur<rh  Medical  Journal,   iSg;. 

3  University  of   Pennsylvania  Medi  al  Mnlletin,  March,  1903. 


THE   SUBLINGUAL    SPACE. 


1581 


The  circumvallate  papillae l  are  imperfectly  developed  for  some  time  after  birth,  so 
much  so  that  it  is  not  easy  to  recognize  them.  The  foliate  papillae  are  also  relatively 
undeveloped.  On  the  other  hand,  the  fungiform  papillae  are  proportionately  both 
larger  and  more  numerous  than  in  the  adult.  The  development  of  the  adenoid  tissue 
at  the  back  of  the  tongue  occurs  during  the  last  two  months  of  fcetal  life.  In  places 
the  connective  tissue  surrounding  the  ducts  of  the  mucous  glands  becomes  infiltrated 
with  leucocytes  and  is  transformed  into  lymphoid  tissue  (Stohr). 

THE    SUBLINGUAL    SPACE. 

This  space  is  between  the  lower  jaw  and  the  tongue,  above  the  mylo-hyoid,  and 
bounded  behind  by  the  fold  of  the  anterior  pillar  of  the  fauces  passing  to  the  tongue. 
It  is  lined  with  thin,  smooth  mucous  membrane  reflected  from  the  mandible  to  the 
tongue  and  attached  lightly  to  the  parts  beneath.  With  the  mouth  closed,  this 
space  is  filled  by  the  tongue.  In  the  living  subject  it  is  best  examined  when  the 
mouth  is  open  and  the  tip  of  the  tongue  applied  to  the  upper  incisors.  Thefreiutw, 


FIG. 


1342. 


Plica  fimbriata 


Frenum 


Sublingual  ridge 
.Orifices  of  submaxillary  and 
sublingnal  ducts 


Sublingual  space,  tongue  pulled  up. 

if  well  developed,  passes  in  the  middle  line  from  the  tongue  to  end  over  the  floor  of 
the  mouth.  Close  to  its  termination  on  either  side  is  a  smooth  elevation  caused  by 
the  sublingual  gland,  which  in  the  present  position  is  drawn  upward  under  the 
tongue.  A  varying  number  of  gland-ducts  perforate  the  mucous  membrane  with 
orifices  hardly  visible  to  the  naked  eye.  Internal  to  these  swellings  at  the  lower  end 
of  the  frenum  is  a  small  enlargement  on  each  side  of  the  median  line,  so  closely 
blended,  however,  as  to  seem  but  one  ;  these  elevations,  the  carunculcc  salivares, 
mark  the  point  at  which  the  duct  of  the  submaxillary  gland  opens  on  each  side. 
This  duct  runs  along  the  floor  of  the  sublingual  space  between  the  mylo-hyoid 
muscle  and  the  mucous  membrane,  a  small  part  of  the  gland  usually  accompanying 
the  duct  a  short  distance  over  the  muscle,  forming  a  prominence,  the  sublingual 
ridge  (plica  sublingualis).  A  constant  group  of  glands  is  found  in  the  mucous 
membrane  below  the  incisors.2 

1  Stahr  :  Zeitschrift  fiir  Morph.  and  Anthrop.,  Bd.  iv.,  Heft  2,  1902. 

2  The  sublingual  bursa  alleged  to  exist  on  either  side  of  the  frenum  has  not  been  described, 
since  it  is  at  most  extremely  uncommon. 


I582 


HUMAN   ANATOMY. 


THE   SALIVARY   GLANDS. 

These,  besides  the  mucous  follicles  of  the  mouth,  are  the  parotid,  the  submax- 
illary,  and  the  sublingual  glands  of  the  two  sides.  They  are  all  reddish  gray  in 
color  and  of  about  the  same  firmness,  excepting  the  parotid,  which  is  denser. 

The  Parotid  Gland. — The  parotid  is  the  largest  of  the  salivary  glands,  weigh- 
ing from  20-30  gm. ,  with  a  considerable  range  beyond  these  limits.  It  is  situated 
behind  the  upper  part  of  the  ramus  of  the  lower  jaw,  which  it  overlaps  both  within 
and  without.  Its  limits  in  both  directions  are  very  variable.  The  prolongation  for- 
ward over  the  masseter  muscle  may  become  nearly  distinct  from  the  rest  of  the  gland, 


FIG.   1343. 


Parotid  gland 


Buccal  branch 
facial  nerve 


Infratnandibular. 
branch  of  facial 
nerve 

External  jugular. 
vein 


— Zygomatictu 

major 
-Parotid  duct 


— Buccinator 
— Masseter 


.Facial  arterv 


Mylo-hyoid 
^Digastric,  anterior  belly 

^Submaxillary  gland 


Superficial  dissection,  showing  parotid  and  submaxillary  glands  undisturbed. 

and  is  then  known  as  the  soda  parotidis.  The  sheath  of  the  parotid  is  a  strong  fibrous 
envelope  continuous  with  the  cervical  fascia  in  front  of  the  sterno-mastoid,  closely 
applied  to  the  glandular  substance  and  continuous  with  the  partitions  that  pass 
through  the  organ,  so  that  it  can  be  dissected  off  from  the  gland  only  with  difficulty. 
The  parotid  is  divided  into  many  small  compartments  or  lobules  by  these  resisting 
septa  of  fibrous  tissue,  the  quantity  of  which  gives  it  toughness.  The  shape  of  the 
parotid,  as  well  as  its  size,  is  variable,  since  it  grows  where  it  can  among  more  or  less 
resisting  structures.  Its  shape  and  relations,  therefore,  may  be  considered  together. 
Relations. — The  parotid  occupies  a  cavity  bounded  in  front  by  the  ramus  of 
the  jaw,  covered  by  the  masseter  and  internal  pterygoid  muscles  ;  behind  by  tin- 


THE   SALIVARY    GLANDS.  1583 

external  auditory  meatus,  the  tympanic  plate,  the  base  of  the  styloid  process,  and  the 
front  of  the  atlas.  These  two  walls  meet  above  at  the  Glaserian  fissure.  The  pos- 
terior wall  is  prolonged  laterally  by  the  posterior  belly  of  the  digastric,  the  stylo- 
hyoid,  and  more  externally  by  the  sterno-mastoid  muscles.  The  styloid  process  as 
it  descends  becomes  internal,  and  the  stylo-glossus  and  stylo-pharyngeus,  together 
with  the  fascia  known  as  the  stylo-maxillary  ligament,  bound  the  posterior  part  of 
the  gland  internally.  In  front  of  the  styloid  process  there  is  no  wall  to  the  space 
occupied  by  the  parotid,  the  gland  resting  against  the  areolar  tissue  mixed  with  fat 
that  lies  on  the  outer  wall  of  the  pharynx.  The  widest  part  of  this  cavity  is  at  the 
surface,  where  the  fascia  is  connected  with  the  capsule  of  the  gland.  The  largest 
expanse  of  the  parotid  is,  therefore,  external.  It  overlaps  the  jaw  and  may  reach 
down  to  the  angle  and  be  separated  merely  by  fibrous  tissue  from  the  submaxillary 
gland.  A  constant,  but  very  variable,  prolongation  on  the  face  below  the  zygoma 
accompanies  the  duct.  The  parotid  gland  reaches  upward  between  the  joint  of  the 
jaw  and  the  external  auditory  meatus  and  tympanic  plate.  Internally  it  lies  against  the 
structures  above  described,  always  resting  on  the  inner  side  of  the  internal  pterygoid 
muscle  and  extending  to  the  great  vessels  and  nerves  which  separate  it  from  the 
side  of  the  pharynx.  There  may  or  may  not  be  a  higher  prolongation  inward 
through  the  space  in  front  of  the  styloid  process.  The  internal  carotid  artery,  inter- 
nal jugular  vein,  and  pneumogastric  nerve  are  close  against  the  lower  part  of  the  inner 
surface  of  the  gland.  The  external  carotid  artery  enters  the  gland  from  the  inner 
side  and  divides  into  its  temporal  and  internal  maxillary  branches,  besides  giving  off 
the  posterior  auricular,  and  sometimes  the  occipital  arteries,  within  its  substance. 
The  external  jugular  vein  is  formed  within  the  gland  and  emerges  from  its  lower  side. 
Near  the  skull  the  great  vessels  and  nerves  are  separated  from  the  gland  by  the  styloid 
process.  The  facial  nerve  enters  the  gland  on  its  posterior  side  and  passes  through 
it  obliquely  so  as  to  become  more  superficial  as  it  travels  forward,  lying  external  to  the 
external  carotid  artery  and  jugular  vein.  Before  emerging  from  the  gland  the  facial 
nerve  breaks  up  into  its  two  great  divisions,  the  branches  of  which  begin  to  subdivide 
within  the  glandular  mass.  The  auriculo-temporal  nerve  also  passes  through  the 
upper  part  of  the  gland,  emerging  on  its  outer  aspect.  A  varying  number  of  lym- 
phatic glands  lie  in  the  substance  of  the  parotid,  mostly  in  the  more  superficial  part. 
They  are  small  and  not  easy  to  find.  A  larger  one,  said  by  Sappey  to  be  constant, 
is  in  the  gland  just  in  front  of  the  ear. 

The  parotid  or  Stenson's  duct  is  formed  by  two  chief  tributaries,  and  emerges 
from  the  front  of  the  gland,  above  its  middle,  running  forward  and  a  little  down- 
ward across  the  masseter  muscle  to  turn  in  sharply  at  its  anterior  border.  It  then 
crosses  a  collection  of  fat  and  runs  obliquely  through  the  buccinator  muscle  and 
the  oral  mucous  membrane  to  empty  into  the  vestibule  of  the  mouth  opposite  the 
second,  often  the  first,  superior  molar  tooth.  The  length  is  some  40  mm.  and  the 
diameter  3  mm.  The  termination  is  a  mere  slit.  Its  walls  are  firm  and  resistant. 
The  general  direction  of  the  duct  is  that  of  a  line  from  the  lower  side  of  the  concha 
of  the  ear  to  midway  between  the  border  of  the  nostril  and  the  red  edge  of  the  lip. 
The  transverse  facial  artery  lies  above  it,  on  leaving  the  gland,  and  a  plexus  of  veins 
surrounds  it. 

Vessels. — The  arteries  of  the  parotid  gland  are  derived  from  several  sources  ; 
although  numerous,  none  of  them  is  large.  Besides  several  small  branches  from 
the  external  carotid  itself  while  in  the  gland-substance,  there  are  twigs  from  the 
temporal,  especially  from  its  transverse  facial  branch,  from  the  posterior  auricular, 
the  internal  maxillary,  and  probably  from  an  occasional  branch  that  may  pass  through 
the  gland.  The  veins  form  quite  a  plexus  through  the  gland  and  open  into  the  sys- 
tem of  the  temporo-maxillary  and  of  the  external  jugular.  Of  the  lymphatics  much 
remains  to  be  learned,  but  they  probably  empty  into  both  the  deep  and  the  super- 
ficial cervical  nodes. 

Nerves  are  from  the  facial,  auriculo-temporal,  and  great  auricular,  besides  sym- 
pathetic fibres  from  the  carotid  plexus. 

The  Submaxillary  Gland. — This  gland,  weighing  from  7-10  gm.,  lies 
largely  under  cover  of  the  lower  jaw,  just  before  the  angle,  in  a  fossa  on  the  inner 
side  of  the  bone.  As,  however,  the  skin  is  carried  inward  under  the  jaw  at  this 


HUMAN   ANATOMY. 


point,  the  gland  appears  on  the  surface.  It  projects  but  little,  if  at  all,  on  the  outer 
side  of  the  jaw,  but  curls  around  the  posterior  border  of  the  mylo-hyoid  muscle 
and  extends  for  some  distance  in  the  floor  of  the  mouth,  under  the  mucous  mem- 
brane, in  the  angle  between  the  mylo-hyoid  and  the  hyo-glossus,  sometimes  reach- 
ing the  sublingual  gland  (Fig.  1344).  It  lies  in  a  capsule  derived  from  the  cervical 
fascia,  which  is  so  loosely  attached  that  the  gland  can  easily  be  isolated.  The 
anterior  end  of  the  posterior  belly  of  the  digastric  and  of  the  stylo-hyoid  pass  behind 
and  beneath  it.  The  hypoglossal  nerve  and  the  lingual  vein  lie  beneath  it,  as  does 
the  first  part  of  the  lingual  artery,  until  the  latter  passes  under  the  hyo-glossus. 
Its  sublingual  branch  runs  along  the  inner  side  of  the  prolongation  of  the  gland, 

FIG. 


Accessory  parotid  gland 

~~v  Parotid  duct 

^  j.  Masseter 


Buccinator 


Js  Lingual 
r        nerve 

Facial  artery 

Oral  mucous 
membrane 

Deeper  portion  of  sub- 
Cut  inaudible 
Submaxillary  du.-t 
Sublingual  gland 


Genio-glossus 
'    '       '  '  (cut) 


Parotid  gland 


Internal  pterygoid 

(cut) 

Superior  constrictor 

Digastric 

Stylo-hyoid 

Stylo-glossus 

Stylo-pharyngeus 

Occipital  artery 

Internal  carotid 

Middle  constrictor 

Facial  artery 

External  carotid 

Lingual  artery 


Superior  thyroid_ 
artery 

Inferior  constrictor— 

Stump  of  digastric,  anterior  belly 
\  'Submental  artery 

,  J^W  Submaxillary  gland,  superficial  part 

v       A 

\      Great  cornu  of  hyoid  bone 
Hyo-glossus 
Yhyro-hyoid 
Deeper  dissection,  showing  relations  of  salivary  glands. 

to  which  it  sends  vessels.     The  facial  artery  lies  beneath  the  gland  before  reaching 
the  border  of  the  jaw.     The  facial  vein  is  superficial  to  it.      The  lingual  nerve  li 
above  the  prolongation. 

The  Submaxillary  or  Wharton's  duct  runs  from  the  front  of  the  main  body 
of  the  gland  along  the  floor  of  the  mouth  under  the  mucous  membrane,  often  accom- 
panied externally  by  the  prolongation  of  the  gland.  It  is  from  4-5  cm.  long,  with  a 
diameter  of  3  mm.  Its  walls  are  decidedly  thinner  than  those  of  the  parotid  duct. 
Anteriorly  it  rises  to  open  into  the  mouth  by  a  little  papilla  on  the  side  of  the  frenum 
linguae,  the  last  few  millimetres  running  in  a  fold  of  mucous  membrane.  The  lingual 
nerve  passes  under  the  duet  from  without  inward  soon  after  it  leaves  the  gland. 
The  sublingual  artery  is  beside  it  and  a  plexus  of  veins  around  it. 


STRUCTURE   OF   THE    SALIVARY    GLANDS. 


1585 


Vessels. — The  arteries  of  the  sublingual  gland  are  derived  from  the  facial  and 
the  sublingual  branch  of  the  lingual.  The  veins  are  from  the  corresponding  ones. 
The  lymphatics  go  to  the  submaxillary  glands. 

Nerves. — The  gland  receives  filaments  from  the  sympathetic  plexus  accompa- 
nying the  facial  artery,  from  the  lingual  nerve,  and  from  the  submaxillary  ganglion. 

The  Sublingual  Gland. — This  differs  from  the  two  preceding  glands  in  having 
no  capsule.  It  lies  in  loose  areolar  tissues  on  the  mylo-hyoid  muscle,  at  the  front 
part  of  the  sublingual  space.  Its  weight  is  3  or  4  gm.  Each  gland  rests  internally 
against  the  genio-glossus,  and  anteriorly  they  touch  one  another.  They  are  more 
readily  separated  into  lobes  than  the  others.  Testut  regards  them  as  aggregations  of 
separate  glands.  The  sublingual  glands  are  covered  by  the  mucous  membrane  of  the 
floor  of  the  mouth,  which  they  press  upward  into  rounded  swellings  on  either  side 

FIG.   1345. 


Opening  of  anterior, 
lingual  glands 

Frenum 


Tongue,  pulled  upward 


Caruncle  and  opening  of 
submaxillary  duct 


Genio-glossus 


Sublingual 
gland 


Genio-hyoid 
Mylo-hyoid 


Cut  fibres  of  digastric 


Section  across  anterior  part  of  floor  of  mouth,  showing  relations  of  sublingual  glands  to  mucous  membrane  and 

muscles. 

of  the  beginning  of  the  frenum.  The  lingual  nerve  and  the  submaxillary  duct  are 
on  the  inner  side.  The  sublingual  or  Rivini's  ducts  vary  in  number  from  four 
to  twenty  or  more.  They  open  for  the  most  part  in  the  floor  of  the  mouth,  but 
some  may  join  Wharton's  duct.  Bartholiri  s  duct  is  an  inconstant  one,  larger 
than  the  others,  that  usually  opens  close  to  the  outer  side  of  Wharton's  duct,  which 
it  follows. 

Vessels. — The  arteries  are  from  the  sublingual  branch  of  the  lingual  and  the 
submental  branch  of  the  facial,  which  latter  sends  minute  twigs  through  the  mylo-hyoid 
muscle.  The  blood  escapes  into  the  ranine  vein.  The  lymphatics  run  to  the  sub- 
maxillary nodes. 

Nerves  are  from  the  sympathetic,  the  lingual,  the  submaxillary  ganglion,  and, 
according  to  some,  from  the  chorda  tympani. 


STRUCTURE   OF   THE   SALIVARY   GLANDS. 

The  three  chief  salivary  glands  possess  in  common  the  tubo-alveolar  type  of 
structure;  depending  upon  the  character  of  their  secreting  cells  and  products,  the  func- 
tionating organs  represent  both  the  serous  and  mucous  varieties.  The  parotid  is  a 
pure  serous  gland  ;  the  submaxillary  is  a  mixed  one,  the  alveoli  containing  serous  cells 
predominating  ;  the  sublingual,  also  a  mixed  gland,  consists  chiefly  of  mucous  alveoli, 
the  serous  cells  being  limited  to  the  marginal  groups  constituting  the  demilunes  of 
Heidenhain. 


I586 


HUMAN   ANATOMY. 


The  parotid  gland  consists  entirely  of  serous  alveoli,  although  mucus-pro- 
ducing acini  may  occur  in  the  accessory  lobules  situated  along  the  duct  of  Stenson. 
The  primary  lobules  are  made  up  of  alveoli,  from  .015  to  .020  mm.  in  diameter,  lined 
with  epithelial  cells,  which  are  somewhat  pyramidal  in  form,  since  they  are  broader 
next  the  basement  membrane  and  narrower  towards  the  cleft-like  lumen.  The  rest- 
ing cells,  fresh  and  examined  without  the  addition  of  reagents,  appear  filled  with 
numerous  minute,  glistening  granules  which  lie  embedded  within  a  less  strongly 
refracting  substance.  The  granules,  however,  are  readily  affected  by  reagents,  often 
undergoing  partial  or  complete  solution;  hence  the  reticulated  appearance  of  the  pro- 
toplasm frequently  observed  in  glandular  epithelium  after  fixation.  The  nuclei  of 
the  serous  cells  are  usually  of  spherical  form  and  contain  distinct  nucleoli  and  delicate. 

FIG.   1346. 


Interlobular  duct 


Artery 


Small 

Intralobular 
duct 


Interlobular  septum 


Duct 


Section  of  small  lobule  of  parotid  gland.     X  So. 

chromatin  net-works.  The  system  of  excretory  canals  begins  at  the  alveoli  as  the 
intermediate  tubules,  which  in  the  parotid  are  relatively  long,  about  .010  mm.  in 
diameter,  and  lined  with  low,  flattened  cells,  directly  continuous  with  the  taller  alveolar 
epithelium,  on  the  one  hand,  and  with  that  of  the  intralobular  ducts  on  the  other. 
The  latter,  or  saliva  rv  tubules  of  Pfliiger,  of  larger  diameter  (about  .035  mm.)  than 
that  of  the  immediately  preceding  or  succeeding  segments  of  the  canal,  are  clothed 
with  a  single  layer  of  columnar  cells,  some  .014  mm.  in  height,  which  present  a 
peculiar  differentiation  into  an  inner  and  an  outer  zone.  The  former,  next  the 
lumen  of  the  tube  and  containing  the  nucleus,  appears  finely  granular  or  almost 
homogeneous,  while  the  outer  or  basal  /one  exhibits  a  longitudinal  striation  composed 
of  rows  of  minute  granules.  After  treatment  with  certain  reagents,  the  striated  zone 


STRUCTURE   OF   THE   SALIVARY    GLANDS. 


1587 


breaks  up  into  delicate  rod-like  processes,  in  recognition  of  which  the  cells  lining  the 
intralobular  tubules  are  often  designated  rod-epithelium.  An  active  secretory  role 
has  been  ascribed  to  these  cells,  R.  Krause '  having  succeeded  in  demonstrating  an 
excretory  function  by  means  of  sodium  sulphindigotate.  The  interlobular  and  inter- 
lobar  ducts  gradually  increase  in  size  and  possess  a  lining  of  columnar  cells  which  are 
usually  arranged  as  a  single  layer.  In  the  larger  canals,  however,  the  epithelium 
consists  of  two  imperfect  rows,  since  smaller  cells  lie  next  the  basement  membrane, 
wedged  in  between  the  larger  typical  elements.  The  columnar  cells  continue  until 
near  the  termination  of  the  main  excretory  duct,  where  they  give  place  to  the  stratified 
squamous  epithelium  prolonged  from  the  oral  mucous  membrane. 

FIG.   1347. 

Intermediate  duct 


Tubular  alveolus 


i_Alveolar  lumen 


Interlobular  duct 


Connective  tissue 


Section  of  parotid  gland,  showing  serous  alveoli.    X  270. 

The  submaxillary  gland  differs  in  structure  from  the  parotid  in  possessing 
both  serous  and  mucous  alveoli,  the  latter  forming  approximately  one-fifth  of  the 
entire  organ.  The  alveoli  containing  serous  cells  correspond  closely  with  those  of 
the  parotid,  being  from  .020  to  .030  mm.  in  diameter  and  filled  with  elements  loaded 
with  minute  granules.  Not  infrequently  the  cells  exhibit  differentiation  into  an  inner 
granular  and  an  outer  almost  granule-free  zone.  The  mucous  alveoli  are  often  some- 
what larger  than  the  serous,  reaching  a  diameter  of  .040  mm.  or  more.  The  mucus- 
producing  cells  present  the  usual  appearance  and  share  the  acinus  with  typical  demi- 
lunes consisting  of  cells  identical  with  those  lining  the  serous  alveoli.  The  mucous 
acini  are  directly  connected  with  those  of  the  serous  type. 

Intermediate  tubules  connect  alveoli  of  both  kinds  with  the  intralobular  canals; 
those  beginning  in  mucous  acini  are  shorter  (.035-. 060  mm. )  and  less  richly  branched 
than  the  tubules  originating  in  serous  alveoli.  The  latter  measure  from  .060-.  140 
mm.  in  length,  and  repeatedly  divide  ;  they  are  lined  with  low  cubical  cells  which  are 
gradually  transformed  from  the  alveolar  epithelium  in  contrast  to  the  abrupt  transition 
seen  in  the  tubules  connected  with  mucous  acini.  The  cells  lining  the  intralobular 
tubules  of  the  submaxillary  gland  exhibit  the  characteristic  rod-like  striation  seen  in 
the  parotid,  the  rod-epithelium  sometimes  containing  yellowish  pigment  granules. 
The  interlobular  and  interlobar  ducts  resemble  those  of  the  parotid  gland.  The 
chief  excretory  duct  possesses,  in  addition  to  a  subepithelial  elastic  layer,  a  weakly 
developed  stratum  of  longitudinally  disposed  involuntary  muscle.  Goblet-cells  appear 
between  the  columnar  elements  lining  the  duct. 

The  sublingual  gland,  being  of  the  mixed  mucous  type,  resembles  in  structure 
the  labial  and  buccal  glands,  and  consists  of  a  series  of  individual  lobules,  opening  by 
half  a  dozen  or  more  separate  ducts,  rather  than  a  compact  single  organ.  In  com- 

1  Archiv  f.  mikro.  Anat.,  Bd.  xlix.,  1897. 


I588 


HUMAN    ANATOMY. 


mon  with  other  mucous  glands,  the  sublingual  lobules  do  not  possess  intralobular 
tubules  lined  with  the  characteristic  rod-epithelium.  The  interlobular  ducts  subdi- 
vide into  smaller  canals  which  extend  within  the  primary  lobules  and  give  off  wider 
passages  lined  with  cubical  epithelium.  Towards  the  end  of  these  terminal  canals 


FIG.   1348. 


.S&&&& 


•-,  u;v£, «,;     ;     -  Y't  '    • 

I » 


Duct 


.Mucous  alveoli 


Serous  alveoli 
Section  of  submaxillary  gland,  showing  serous  and  mucous  alveoli.     X  270. 

the  mucous  cells  appear,  at  first  isolated  or  in  groups,  increasing  in  numbers  until 
they  form  the  entire  lining  of  the  passage  and  become  the  secreting  elements  occupy- 
ing the  tubular  alveoli  of  the  gland.  The  latter  vary  from  .030— .060  mm.  in  diam- 
eter, and  are  clothed  with  cells  averaging  .015  mm.  high.  The  condition  of  the 

FIG.  1349. 


Duct 


Crescents  of  serous  cells 


Section  of  suhlingual  gland,  showing  serous  rolls  grouped  as  crescents.     X  270. 


alveoli  as  regards  the  mucus-bearing  cells  varies  greatly  even  in  the-  same  lobule.  At 
times  an  entire  primary  lobule  is  composed  of  acini  filled  with  mucous  cells  ;  at  others 
empty  and  gorged  alveoli  alternate,  or  the  depleted  acini  may  predominate.  Uncer- 
tainty as  to  the  presence  of  the  demilunes  also  exists,  since  these  may  be  absent  in 


PRACTICAL    CONSIDERATIONS:     THE    MOUTH.          .      1589 

certain  well-developed  alveoli  filled  with  large  mucous  cells,  or  they  may  be  present 
in  considerable  numbers.  Mucous  cells  are  much  less  numerous  in  the  sublingual 
glands  of  young  infants  than  in  the  adult  organ.  The  relatively  wide  lumen  of  the 
alveoli  and  the  more  reticulated  appearance  of  their  epithelium  serve  to  distinguish 
the  exhausted  sublingual  gland  from  the  parotid  of  similar  condition. 

The  normal  secretions  of  the  oral  glands,  mucous  as  well  as  serous,  contain  no 
formed  elements  ;  occasionally  accidental  granules  or  cell  remains  are  present.  The 
characteristic  spherical  so-called  salivary  corpuscles  which  occur  in  varying  numbers 
in  the  mixed  oral  secretion  have  no  relation  to  the  salivary  glands,  since  they  are 
only  modified  leucocytes  escaped  from  the  lymphoid  tissue  of  the  faucial  and  lingual 
tonsils.  On  gaining  the  oral  cavity,  these  cells  are  affected  by  the  saliva  and  become 
greatly  swollen,  the  granular  remains  of  their  cytoplasm  exhibiting  molecular  motion 
in  a  marked  degree. 

Development  of  the  Oral  Glands. — The  earliest  traces  of  the  salivary 
glands  are  seen  during  the  second  foetal  month.  The  anlage  for  the  submaxillary 
gland  first  appears  about  the  sixth  week  ;  next  that  for  the  parotid  about  the 
eighth  week  ;  a  little  later  that  for  the  sublingual.  The  parotid  anlage  develops 
from  the  oral  ectoblast  along  the  lateral  groove  separating  the  upper  and  lower  jaws. 
The  submaxillary  and  sublingual  glands  arise  from  a  ridge-like  anlage  of  the  buccal 
epithelium  occupying  the  furrow  marking  the  angle  between  the  tongue  and  the  floor 
of  the  mouth,  the  anlage  for  the  sublingual  lying  nearer  the  tip  of  the  tongue.  At 
first  the  parotid  and  submaxillary  lie  about  equally  removed  from  the  oral  opening, 
but  later  migration  occurs,  the  former  passing  backward  and  the  latter  forward. 

The  development  of  the  gland  in  each  case  begins  as  a  solid  cylindrical  out- 
growth from  the  deeper  layer  of  the  oral  epithelium,  which  presents  a  local  thicken- 
ing. The  cylinder  rapidly  lengthens  and  branches,  so  that  by  the  eighth  or  tenth 
week  the  submaxillary  and  parotid  glands  respectively  consist  of  a  main  stalk  and 
terminal  buds.  The  anlage  of  the  sublingual  gland  gives  off  epithelial  buds  on 
acquiring  a  length  of  about  i  mm.  The  primary  sprouts  of  the  anlage  subdivide  and 
eventually  become  the  smaller  ducts  and  the  glandular  tissue.  Meanwhile  the  imme- 
diately surrounding  mesoblast  undergoes  condensation,  and  contributes  the  connective- 
tissue  envelope  with  its  prolongations  between  the  lobules  and  acini  supporting  the 
blood-vessels  and  nerves.  Towards  the  close  of  the  third  month,  while  the  gland- 
tubules  are  still  solid,  the  lumen  of  the  future  main  excretory  duct  appears  in  the 
epithelial  cylinder,  extending  from  the  free  surface  towards  the  alveoli.  The  latter 
acquire  their  lumen  during  the  fifth  month. 

The  smaller  oral  glands,  including  those  of  the  lips,  cheeks,  tongue,  and  palate, 
develop  much  later  than  the  larger  salivary,  since  their  anlages  appear  during  the 
fourth  month.  The  details  of  their  development  correspond  in  general  with  those 
attending  the  formation  of  the  larger  oral  glands. 

PRACTICAL   CONSIDERATIONS  :   THE  MOUTH. 

The  chief  congenital  deformities  of  the  mouth  are  harelip  and  cleft  palate. 
Harelip  results  from  a  failure  of  the  developmental  procedures  concerned  in  forming 
and  differentiating  the  nasal  and  buccal  cavities.  These  processes  have  already  been 
described  in  connection  with  the  formation  of  the  face  (page  59).  Upon  the  down- 
growth  of  the  fronto-nasal  process  depends  the  formation  of  the  vomer,  the  perpen- 
dicular plate  of  the  ethmoid  and  the  external  nose,  and  of  the  intermaxillary  bone 
and  that  portion  of  the  upper  lip  corresponding  to  the  four  incisors.  The  partition 
separating  the  nasal  from  the  oral  cavity,  later  the  hard  and  soft  palates,  is  formed 
by  the  union  of  the  horizontal  palatal  plates  from  the  buccal  aspect  of  the  two  maxillary 
processes  (Fig.  76).  When  the  frontal  and  maxillary  processes  fail  to  unite  on  one 
side,  single  harelip  results,  the  cleft  in  one  side  of  the  lip  lying  opposite  the  space 
between  the  upper  canine  and  lateral  incisor,  or  between  the  latter  and  the  central 
canine.  When  union  between  the  maxillary  and  the  frontal  processes  fails  on  both 
sides,  double  harelip  follows,  the  lateral  incisors  often  being  absent  and  the  inter- 
maxillary bone  with  the  central  incisors  and  the  median  portion  of  the  lip  occupying 
a  position  beneath  the  nasal  septum. 


I59Q  HUMAN   ANATOMY. 

Cleft  palate  is  caused  by  faulty  union  between  the  palatal  processes  of  the  maxillary 
arches.  The  cleft  is  always  in  the  middle  line,  and  may  involve  only  the  uvula  and 
soft  palate,  may  extend  to  the  posterior  margin  of  the  intermaxillary  bone,  or  may 
diverge  from  that  point  on  one  or  both  sides  and  run  forward  through  the  alveolus, 

being  then  associated  with  single  or  double  hare- 
lip, the  cleft  or  clefts  in  the  alveolus  corresponding 
in  position  to  the  deficiencies  in  the  lip  (page  63). 

The  Lips. — The  mucous  membrane  of  the 
lips  and  the  adjacent  skin  are  often  affected  by 
herpes  labialis,  which  may  be.  associated  with 
gastro-intestinal  disturbance,  or  may  be  purely 
neurotic  in  its  origin,  following  mental  depression 
or  anxiety.  It  is  found  in  the  distribution  of  the 
second  and  third  divisions  of  the  fifth  pair  which 
supply  sensation  to  the  upper  and  lower  lips  re- 
;.  •«*fp  spectively.  The  vascularity  of  the  lips,  while  it 

leads  to  excessive  exudate  and  large  swelling  after 
contused  or  lacerated  wounds,  favors  rapid  heal- 
ing and  the  avoidance  of  infection  after  surgical 
wounds.  In  few  places  equally  exposed  to  con- 
New-born  child  with  double  harelip.  tact  with  infectious  organisms  was  healing  by  ' '  first 

intention"  so  common  before  the  introduction  of 

antisepsis.  The  coronary  arteries  run  between  the  mucous  membrane  and  the  orbicu- 
laris  oris.  They  are  therefore  more  often  severed  by  wounds  extending  from  within 
outward — usually  made  by  the  teeth — than  by  those  beginning  externally.  The  coro- 
naries  anastomose  very  freely.  In  arresting  hemorrhage  from  them  by  direct  ligature 
both  ends  should  be  tied.  If  a  wound  of  the  lips  is  united  by  pins  and  figure-of- 
eight  sutures,  the  pins  should  be  passed  close  to  the  inner  edges  of  the  wound  so  that 
the  coronaries  may  be  compressed  between  the  pins  and  the  sutures.  The  vascu- 
larity of  the  lips  renders  chancres  of  that  region,  like  those  of  the  face,  exceptionally 
large  both  in  depth  and  in  superficial  area.  It  also  adds  greatly  to  the  extent  of 
furuncular  or  carbuncular  infection  in  this  region,  the  occurrence  of  which  is  favored 
by  the  large  number  of  hair  and  sebaceous  follicles  present.  The  danger  of  infective 
sinus  thrombosis  (intracranial)  as  a  result  of  such  infection  here  or  elswhere  on  the 
face  is  much  increased  by  the  free  anastomosis  between  the  valveless  facial  vein  and 
its  tributaries  and  the  ophthalmic  vein,  which  is  also  without  valves.  As  might  be 
expected,  nsevi  are  frequent  in  the  lips.  In  the  male  the  lower  lip  is  the  favorite  seat 
of  epithelioma.  Either  infection  or  diminished  tissue  resistance  from  minor  trauma- 
tisms,  or  from  tobacco-irritation  in  smokers,  is  supposed  to  explain  this  clinical  fact. 
The  mucous  glands  of  the  lip  are  not  rarely  the  seat  of  retention-cysts  from  obstruc- 
tion of  their  ducts. 

The  Gums. — The  mucous  membrane  of  the  lips  is  continuous  with  that  cover- 
ing the  fibrous  tissue  of  the  gums,  but  the  latter  is  slightly  less  vascular  and  much  less 
sensitive.  The  gums  are  sometimes  congenitally  hypertrophied  ;  the  condition  is 
usually  associated  with  defective  or  aberrant  developmental  processes  often  affecting 
the  mentality.  They  are  also  often  found  hypertrophied  in  edentulous  old  persons  or 
in  persons  with  badly  fitting  artificial  dentures.  They  are  the  frequent  seat  of  inflam- 
mation from  various  causes,  the  most  common  of  which  are  the  decomposition  of 
food  and  the  deposition  of  calcium  salts — tartar — about  the  necks  of  the  teeth.  Infec- 
tion frequently  follows  the  hypeni'inia  produced  by  these  forms  of  irritation.  When 
it  is  confined  to  the  space  between  the  mucous  membrane  and  the  fibrous  tissue,  it 
causes  a  limited  superficial  abscess, — "gum-boil;"  if  it  gains  access  to  the  sub- 
periosteal  space,  it  may  cause  a  form  of  alveolar  abscess,  the  usual  variety  of  which 
is,  however,  due  to  infection  secondary  to  dental  caries,  and  is  situated  about  the  root 
of  a  tooth  (  ride  in/m  |. 

Tartar  is  found  most  abundantly  near  the  openings  of  the  submaxillary  and  sub- 
lingual  ducts, — i.e. ,  near  the  inner  sin  faces  of  the  lower  incisor  teeth.  Mercury  and 
lead  cause  gingivitis  probably  by  the  actual  presence  of  their  salts  in  quantity  suffi- 
cient to  act  as  irritants,  their  deposition  from  terminal  capillaries  being  favored  by  the 


PRACTICAL    CONSIDERATIONS  :    THE   MOUTH.  1591 

frequent  hyperaemia  due  to  the  vascularity  and  the  warmth  and  moisture  of  the  region, 
together  with  slight  but  repeated  trauma  during  mastication.  The  gingivitis  of 
scurvy  or  of  purpura  is  merely  a  local  evidence  of  a  constitutional  condition,  and  is 
hemorrhagic  rather  than  inflammatory. 

During  dentition  the  resistance  of  the  gums  may  cause  backward  pressure  upon 
the  nervous  and  vascular  supply  of  the  pulp  of  the  tooth,  giving  rise  to  some  pain  and 
sometimes  to  grave  reflex  disturbances,  especially  in  infants.  The  insensitive  gum 
then  becomes  exceedingly  tender  and  is  swollen  and  cedematous.  The  wide-spread 
relations  of  the  fifth  nerve  render  long-continued  irritation  of  its  dental  branches  dan- 
gerous. '  '  Lancing'  '  the  gums  is  the  obvious  remedy.  It  is  especially  apt  to  be 
needed  over  the  molars  and  cuspids,  and  the  lines  of  incision  should  be  planned  so  as 
to  release  fully  the  presenting  "surfaces  of  those  teeth. 

The  Teeth.  —  Alveolar  Abscess.  —  The  line  of  penetration  in  dental  caries  is 
often  in  the  direction  of  the  pulp,  through  which  infection  extends  to  the  "apical 
space'  '  between  the  root  of  the  tooth  and  its  socket,  containing  the  vessels  and  nerves 
and  some  loose  connective  tissue.  This  space  soon  becomes  filled  with  pus,  the  cavity 
enlarges,  and  reaches  the  compact  bone  on  the  surface  of  the  alveolus  (the  density 
of  which  impedes  the  process  somewhat)  ;  but  finally  the  bone  is  perforated,  usually 
through  the  thinner  external  or  buccal  wall  of  the  alveolus.  The  periosteum  usually 
yields  opposite  the  gum  immediately  over  the  apex  of  the  tooth,  where  it  is  reinforced 
by  mucous  membrane  only.  If  the  root  of  the  tooth  is  a  long  one  or  the  abscess 
has  gone  deeply  into  the  bone,  the  pus  may  reach  the  periosteum  at  a  point  where  it 
is  supported  by  the  muscular  and  fibrous  tissues  of  the  cheek.  The  pus  may  then 
strip  the  periosteum  from  the  bone  so  as  to  cause  extensive  necrosis.  This  is  less 
likely  to  occur  in  the  alveolus  of  the  upper  jaw  or  in  the  hard  palate,  on  account  of 
their  free  blood-supply  derived  from  several  sources.  In  cases  of  this  type  in  either 
jaw,  a  sinus  followed  by  a  depressed,  adherent,  and  disfiguring  cicatrix  is  liable  to 
result  (Roughton).  Alveolar  abscess  is  also  influenced  in  its  course  by  the  situation 
of  the  particular  tooth  involved.  In  the  maxilla,  abscesses  connected  with  the  canines 
or  incisors  may  point  into  the  nasal  cavity  or  on 

the  under  surface  of  the  hard  palate.     The  pus  FIG-  I35I- 

is  more  likely,  however,  to  descend  by  gravity 
alongside  of  the  root  to  the  edge  of  the  gum,  or 
to  follow  the  canal  of  the  root  into  the  pulp-cavity. 

Abscesses  connected  with  the  upper  molars,  es-  "^1^   <$N 

pecially  the  first,  or,  more  rarely,  those  in  relation  ''^/^J^Stt^^ 

to  the  cuspids,  may  point  in  the  antrum.  They 
occasionally  open  on  the  face  in  front  of  the  an- 
terior border  of  the  masseter.  The  relation  of 
the  apex  of  the  root  to  the  mucous  membrane  of 
the  gum  often  determines  the  point  of  opening. 
If  the  apex  in  the  case  of  the  lower  teeth  is  above,  — 


or  in  that  of  the  upper  teeth  is  below  the  line  of 
reflection  of  the  mucous  membrane  from  the 
cheek  to  the  gum,  the  abscess  tends  to  point  in 
the  mouth.  If  the  contrary  is  the  case,  pointing 
on  the  face  or  neck  may  result. 

In  syphilis  the  first  teeth  exhibit  malforma-     A< 

tions  characteristic  of    perversions  of    nutrition  or  notched  ;  lateral  incisors  show  no  defect  ;  right 

r  •     n                ._•            t  -u                           cc.    •       *.1  canine  has  deep  notch;   exposed  dentine  has 

Of  inflammation  Of  the  gums  Sufficiently  Severe  tO  become  discolored.    #,  upper  incisors  only  re- 

p   hlnnH-mmnl  v   tr>    the    font  h  -^a  r<^        Trip  cently  erupted  ;  central  notch  marked  out  but 

not  yet  cleared  out  by  breaking  away  of  unpro- 

may    be    deficient,    Opaque  Or  Chalky,    the  tected  dentine;  four  lower  incisors  present  pe>j- 

,                        ef          r   •    11        .1               -u  •               i          •          •  'ike  excrescences  due  to  loss  of    enamel  and 

dentine  soft  or  friable,  the  teeth  irregular  in  size    exposure  of  dentine.    (Hutchison.) 
and  uneven  in  position. 

The  permanent  teeth  may  show  the  same  general  aberrations  as  to  growth  and 
nutrition  that  are  produced  by  stomatitis  from  digestive  derangements  or  from  local 
irritation.  After  mercurial  stomatitis,  for  example,  the  teeth  are  irregularly  outlined, 
horizontaHy  seamed,  scraggy,  malformed,  deficient  in  enamel,  separated  too  widely, 
and  dirty  yellow  in  color. 


1592  HUMAN   ANATOMY. 

The  typical  (and  pathognomonic)  syphilitic  teeth — "  Hutchinson's  teeth" — are 
the  upper  permanent  central  incisors.  The  type  is  observed  in  its  perfection  soon 
after  the  extrusion  of  these  teeth.  The  essential  characteristic  is  a  crescentic  notch 
(Fig-  iSS.1!-^)  in  tne  free  edge  of  the  tooth,  the  anterior  border  of  the  notch  being 
bevelled  from  above  downward  and  from  before  backward, — i.e. ,  at  the  expense  of 
the  anterior  surface  and  border  of  the  tooth.  Typical  Hutchinson's  teeth  are,  fur- 
thermore, reduced  in  length  and  narrowed, — "stunted  ;"  their  angles  are  rounded 
off,  the  lateral  and  inferior  borders  merging  in  a  curved  line  ;  they  deviate  from  nor- 
mality in  direction,  their  axes  being  obliquely  convergent,  or  more  rarely  divergent, 
instead  of  parallel. 

The  other  surgical  relations  of  the  teeth  and  of  the  dental  tissues  which  are  of 
chief  importance  are  concerned  with  the  new  growths  originating  in  dental  elements. 
The  odontomata  are  divided  by  Sutton  as  follows,  and  the  classification  should  be 
remembered  in  studying  the  anatomical  development  of  the  teeth  : 

(i)  Persistent  portions  of  the  epithelial  sheath  (page  1561),  taking  on  over- 
growth, may  give  rise  to  an  epithelial  odontome  (multilocular  cystic  tumor).  (2 ) 
Expansion  of  the  tooth-follicle  with  retention  of  the  crown  or  root  of  an  imperfectly 
developed  tooth  results  in  a  follicular  odontome  (dentigerous  cyst).  (3)  Hyper- 
trophy of  the  fibrous  tooth-sac  causes  a  fibrous  odontome,  especially  frequent  in 
rickets,  which  usually  affects  the  osteogenetic  fibrous  membranes.  (4)  If  the  fore- 
going hypertrophy  occurs  and  the  thickened  capsule  ossifies,  a  ceviciitome  results.  (  5  ) 
If  this  takes  place  irregularly,  small  malformed  teeth — "denticles" — may  form  in 
large  numbers  and  occupy  the  centre  of  the  tumor  (compound follicular  odontome}. 
(6)  Tumors  of  the  root,  after  the  full  formation  of  the  crown,  are  of  necessity  com- 
posed of  dentine  and  cementum  only,  enamel  not  entering  into  them  (radicu/ar 
odontomata}.  (7)  Tumors  composed  of  irregular  conglomerations  of  enamel,  den- 
tine, and  cementum,  and  often  made  up  of  two  or  more  tooth-germs  fused  together, 
constitute  composite  odontomata.  All  these  growths  can  be  understood  only  by 
careful  study  of  the  normal  development  of  the  teeth.  They  are  rarely  diagnosed 
before  operation,  which  is  therefore  in  some  cases  needlessly  severe.  Sutton  says 
very  truly,  "  In  the  case  of  a  tumor  of  the  jaw  the  nature  of  which  is  doubtful,  par- 
ticularly in  a  young  adult,  it  is  incumbent  on  the  surgeon  to  satisfy  himself,  before 
proceeding  to  excise  a  portion  of  the  mandible  or  maxilla,  that  the  tumor  is  not 
an  odontome,  for  this  kind  of  tumor  only  requires  enucleation.  In  the  case  of  a 
follicular  odontome  it  is  usually  sufficient  to  excise  a  portion  of  its  wall,  scrape  out  the 
cavity,  remove  the  tooth  if  one  be  present,  stuff  the  sac,  and  allow  it  to  close  by  the 
process  of  granulation. ' ' 

The  Roof  of  the  Mouth  and  the  Palate. — The  mucous  membrane  cov- 
ering the  hard  palate  is  so  fused  with  the  periosteum  as  practically  to  be  inseparable 
from  it.  It  is  dense,  resistant,  and  comparatively  insensitive.  A  vertical  trans- 
verse section  of  the  roof  of  the  mouth  (Fig.  1294)  shows  the  mucous  membrane  to 
be  thickest  laterally  and  thinner  in  the  median  line. 

Cleft  palate  (page  1590)  results  from  imperfect  fusion  between  the  horizontal 
palatal  plates  of  the  maxillary  processes  of  the  first  visceral  arch.  It  is  always  in  the 
middle  line.  It  may  involve  the  soft  palate  and  uvula.  If  it  extends  forward  as  far 
as  the  alveolus,  it  follows  the  line  between  the  maxilla  and  the  premaxillary  bone, 
usually  terminating  in  a  harelip  (page  1589)  opposite  the  interval  between  the  lateral 
incisor  and  canine  teeth.  If  it  separates  the  maxillae  on  both  sides  from  the  pre- 
maxillary bone,  it  is  almost  always  associated  with  double  harelip. 

The  toughness  of  the  muco-periosteum  of  the  hard  palate  facilitates  the  forma- 
tion of  flaps  in  operations  for  the  closure  of  such  a  cleft.  In  dissecting  up  the  flaps 
it  is  well  to  keep  close  to  the  bone  and  to  avoid  the  descending  or  posterior  pala- 
tine branches  of  the  internal  maxillary  artery.  These  vessels,  on  which  the  nutri- 
tion of  the  flaps  as  well  as  of  the  bone  depends,  emerge  from  the  posterior  palatine 
canal  at  a  point  on  the  line  of  junction  of  the  hard  and  soft  palates  8  mm.  (y$  in.) 
anterior  to  the  hamular  process  and  a  little  to  the  inner  side  of  the  last  molar  tooth. 
They  run  forward  in  a  shallow  groove  just  internal  to  the  outer  border  of  the  hard 
palate.  They  are  nearer  to  the  bone  than  to  the  mucous  surface,  but  their  pulsa- 
tions can  often  be  felt  by  the  finger.  For  these  reasons  incisions  in  uranoplasty 


PRACTICAL  CONSIDERATIONS:  THE  MOUTH. 


1593 


FIG.  1352. 


Anterior  lingual 

gland 


should  be  made  close  to  the  alveolus  and  the  bone  should  be  hugged  as  the  flaps 
are  raised.  In  troublesome  bleeding  from  these  arteries  the  posterior  palatine  canal 
may  be  plugged  by  a  sharpened  stick,  which  should  previously  be  sterilized. 

When  the  clelt  involves  only  the  soft  palate,  staphylorrhaphy  is  required. 
The  muscles  that  tend  to  pull  the  edges  apart  are  the  tensor  palati  and  levator 
palati.  The  former  turns  around  the  hamular  process  and  passes  almost  horizon- 
tally towards  the  median  line,  the  latter  lies  close  to  the  posterior  surface  of  the 
soft  palate  and  runs  obliquely  from  above  downward  and  inward.  These  muscles 
may  be  divided  by  various  incisions,  the  simplest  being  a  section  of  the  velum  near 
its  lateral  border  and  parallel  with  the  cleft. 

The  hamular  process  may  be  felt  behind  and  a  little  internal  to  the  last  molar 
tooth.  The  pterygo-mandibular  ligament  may  be  felt  passing  from  the  hamular 
process  to  the  posterior  end  of  the  mylo-hyoid  ridge  of  the  lower  jaw  just  behind  the 
last  molar  tooth.  The  fold  of  mucous  membrane  covering  it  may  be  seen  when  the 
jaws  are  separated  widely.  The 
lingual  branch  of  the  fifth  nerve 
may  be  felt  between  the  mucous 
membrane  and  the  bone  anterior  to 
the  base  of  the  pterygo-mandibular 
ligament  and  below  the  last  molar. 
With  a  finger  passed  behind  the 
last  molar,  the  swell  of  the  alveolar 
ridge  can  be  recognized  as  it  nar- 
rows to  pass  into  the  ramus.  The 
nerve  is  below  and  parallel  with 
that  ridge.  It  is  sometimes  divided 
for  the  relief  of  the  unbearable  pain 
of  carcinoma  of  the  tongue.  This 
may  be  done  by  entering  the  point 
of  a  curved  bistoury  a  little  less 
than  three-quarters  of  an  inch  be- 
hind and  below  the  last  molar  and 
cutting  on  the  bone  towards  the 
tooth. 

The  Floor  of  the  Mouth. 
— The  mylo-hyoid  muscle,  extend- 
ing from  the  symphysis  to  the  last 
molar  tooth,  separates  the  buccal 
cavity  from  the  neck.  Infections 
or  neoplasms  beginning  above  this 
muscle  are  first  recognized  through 
the  mouth  ;  those  below  it  in  the 

neck.          The    SublingfUal     Sfland      for  Dissection  of  under  sunace  of  tongue  and  sublingual  space; 

,          ,.  .         mucous  membrane  removed  and  tongue  drawn  upward  and  for- 

example,    lies    altogether   above  it     ward  from  mouth. 
and   directly   beneath    the    mucous 

membrane  of  the  floor  of  the  mouth  ;  the  duct  of  the  submaxillary  gland  occupies 
a  similar  position.  Affections  of  these  structures,  therefore,  manifest  themselves 
in  the  mouth.  The  submaxillary  gland,  however,  lies  partly  beneath  the  poste- 
rior border  of  the  mylo-hyoid.  Accordingly,  disease  of  this  gland  is  apt  to  show 
most  markedly  beneath  the  jaw  (Fig.  267,  page  247).  "  Ludwig's  angina"  (page 
553)  may  spread  to  the  loose  connective  tissue  between  the  mylo-hyoid  muscle 
and  the  mucous  membrane  of  the  floor  of  the  mouth.  That  membrane  is  reflected 
from  the  under  surface  of  the  tongue  to  the  alveoli  and  is  divided  anteriorly  by 
the  frenum  linguae.  On  either  side  of  this  may  be  seen  the  ridges  indicating  the 
situation  of  the  sublingual  glands,  and  close  to  the  frenum  at  the  inner  end. of  the 
ridge  the  papillae  at  the  opening  of  Wharton's  ducts,  into  which  a  fine  probe  may 
be  passed  (Fig.  1352).  The  inelastic  character  of  the  walls  of  the  latter  should  be 
remembered  as  explaining  in  part  the  intense  pain  caused  by  an  impacted  submax- 
illary calculus.  This  is  also  in  part  due  to  the  close  relation  of  the  duct  to  the 


-    — Cut  surface  of 

mucous  membrane 


jjr — Lingual  vein 

\ 

il — Lingual  artery 

Submaxillary  duct 
— Sublingual  gland 


1594  HUMAN   ANATOMY. 

lingual  nerve.       The  relation  of  that   nerve  to  the  floor  of  the  mouth  posteriorly 
has  already  been  described  (page  1249). 

The  fold  of  mucous  membrane  constituting  the  frenum  may  be  abnormally 
short  and  prevent  the  free  movements  of  the  tongue,  interfering  with  sucking  during 
infancy  and  with  articulation  later.  When  its  division  is  necessary,  it  should  be  cut 
through  close  to  the  jaw,  and  with  blunt-pointed  scissors  directed  away  from  the 
tongue  so  as  to  avoid  the  ranine  veins  which  may  be  seen  close  to  it  on  the  under 
surface  of  the  tongue. 

The  ranine  arteries  lie  farther  out  and  are  more  deeply  situated,  being  placed 
beneath  two  converging  raised  fringed  lines  of  mucous  membrane,  the  plica 
fimbriattz. 

A  sublingual  bursa  is  described  by  Tillaux  as  a  triangular  space  situated  between 
the  genio-hyo-glossus  and  the  mucous  membrane,  its  tip  being  at  the  frenum,  its 
base  at  the  sublingual  gland.  Its  existence,  by  no  means  constant,  is  said  by  Tillaux 
to  explain  the  occurrence  of  the  acute  cystic  tumor  (grenmtillette) ,  "acute  ranula,'' 
which  is  occasionally  met  with  in  this  region. 

Ranulae — ordinary  retention  cysts — are  common  in  the  floor  of  the  mouth,  and 
.branchiogenic  cysts,  due  to  the  incomplete  closure  of  the  first  branchial  cleft,  are 
sometimes  found  there. 

The  Cheeks. — The  buccal  limits  of  the  cheeks  are  accurately  indicated  by  the 
reflections  of  mucous  membrane  lining  them.  By  making  outward  traction  on  the 
angle  of  the  mouth  that  membrane  can  be  seen  and  palpated,  and  ulceration,  as 
from  a  jagged  tooth  or  beginning  epithelioma,  or  mucous  patches,  or  abscess,  or  new 
growths,  can  easily  be  detected. 

The  papilla  indicating  the  opening  of  the  parotid  duct  may  be  seen  or  felt 
opposite  the  upper  second  molar  tooth.  A  fine  probe  may  be  made  to  enter 
the  duct  for  a  short  distance,  the  normal  curves  then  interfering  with  its  passage 
(Fig.  1343). 

Lipoma  originating  in  the  "  boule  de  Bichat"  (page  493)  can  be  recognized. 

As  the  jaws  are  separated  and  closed  the  anterior  border  of  the  masseter  may 
be  seen  and  felt.  The  important  structures  of  the  cheek — the  facial  vein  and  artery 
and  the  parotid  duct — are  all  anterior  to  this  line  (Fig.  691). 

The  Tongue. — Congenital  deformity  of  the  tongue  is  rare.  Forked  tongue 
— normal  in  some  birds  and  reptiles  and  in  seals — is  rare  ;  it  is  usually  in  asso- 
ciation with  other  developmental  defects,  as  cleft  palate.  Congenital  absence  has 
been  noted  (de  Jussieu). 

Macroglossia  {lymphangioma  cavernosum,  Virchow)  is  a  congenital  affection 
in  which  the  lymph-channels  and  lymph-spaces  are  dilated  and  the  lymphoid  tissue 
throughout  the  tongue,  but  especially  at  the  base,  greatly  increased.  The  tongue 
may  attain  an  enormous  size,  and  has  even,  by  pressure,  caused  deformities  of  the 
teeth  and  alveolar  arches  and  luxation  of  the  mandible.  The  foramen  caecum,  indi- 
cating the  junction  of  the  pharyngeal  and  buccal  parts  of  the  tongue,  is  the  superior 
termination  of  the  foetal  thyro-glossal  duct.  "  Ducts  lined  with  epithelium  have  been 
found  leading  from  the  foramen  caecum  to  accessory  glands  about  the  hyoid  bone. 
It  is  probably  from  these  glandular  and  epithelial  collections  about  the  hyoid  bone 
that  certain  deep-seated  forms  of  cancer  of  the  neck  are  developed.  Some  of  these 
take  the  form  of  malignant  cysts"  (Treves). 

The  upper  surface  of  the  tongue  has  for  centuries  been  the  object  of  especial 
observation  in  disease.  The  practical  value  of  these  observations  is  not  univer- 
sally conceded,  and  too  much  weight  has  been  placed  upon  them  ;  but  there  can 
be  no  doubt  that  some  help  in  prognosis  and  even  in  diagnosis  in  digestive  <K 
range-meats,  in  fevers,  and  in  various  toxaemias  may  be  obtained  by  inspection  of 
the  tongue. 

The  "fur,"  so  carefully  studied,  consists  of  a  mixture  of  desquamated  epithelial 
cells,  food  particles,  and  micro-organisms  of  various  kinds  overlying  living  epithelium 
which  may  be  abnormally  proliferating. 

The  surface  between  the  circumvallatc  papillae  is  apt  to  be  the  most  heavily 
coated,  either  in  Ix-alth  or  disease,  because  it  is  the  least  mobile  part  of  the  tongue 
and  is  not  .kept  clean  by  friction,  as  are  the  sides  and  tip.  The  appearance  of 


PRACTICAL  CONSIDERATIONS:  THE  MOUTH.  1595 

the  coating  and  of  the  tongue  itself  varies  greatly,  but  it  may  be  said  that  dry- 
ness  not  due  to  mouth-breathing,  but  from  deficient  secretion,  as  in  fevers  ;  dark- 
ness, from  decomposition  and  desiccation  of  the  coating,  or  from  imperfect  oxy- 
genation  of  the  blood  ;  roughness,  from  papillary  overgrowth  with  marked  epithelial 
proliferation  and  desquamation  ;  redness,  from  epithelial  denudation  ;  and  stiff- 
ness, slowness,  or  tremulousness  in  protrusion,  from  either  thick,  inflexible  coating, 
muscular  weakness,  or  mental  hebetude,  are  uniformly  regarded  as  unfavorable 
conditions. 

Unilateral  furring  of  the  tongue  has  been  observed  in  cases  of  dental  caries,  of 
fractured  skull,  and  of  intracranial  disease,  in  all  three  instances  the  furring  being  on 
the  side  on  which  there  was  irritation  of  the  branches  of  the  fifth  pair  of  nerves.  In 
some  of  them  it  was  confined  to  the  anterior  two-thirds  of  the  upper  surface, — i.e. , 
to  the  distribution  of  the  lingual  branch  of  the  fifth  (Hilton). 

In   tonsillitis  the  tongue  will   often  be   furred   over  its  posterior  part  only  - 
i.e. ,  the  portion  which,   like  the  tonsil,  receives  its  nerve-supply  from  the  glosso- 
pharyngeal  (Jacobson).     Unilateral  furring  in  the  presence  of  toothache  may  be  due 
partly  to  the  instinctive  immobilizing  of  that  side  of  the  tongue  nearest  the  painful 
tooth  (Hutchinson). 

In  chronic  superficial  glossitis  the  epithelium  thickens  at  places  into  rounded, 
whitish  patches,  which  are  difficult  to  heal  on  account  of  the  constant  exposure 
to  warmth,  moisture,  infection,  and  minor  traumatisms,  and  the  impossibility  of 
securing  rest.  This  condition  (Jeukoplakia)  may  precede  the  development  of 
epithelioma. 

In  rare  cases  the  epidermis  covering  the  filiform  papillae  undergoes  hypertrophy, 
producing  the  so-called  "  hairy  tongue." 

The  lymphoid  tissue  behind  the  circumvallate  papillae,  from  overgrowth,  forms 
an  irregular  rounded  mass  just  beneath  the  mucous  membrane, — the  lingual  tonsil, 
— which  from  its  proximity  to  and  interference  with  the  epiglottis  may  require 
removal. 

The  connective  tissue  of  the  tongue  is  scanty,  but  is  abundant  enough  to  permit 
of  great  swelling  in  cases  of  acute  glossitis,  and  this  is  favored  by  the  vascularity  of 
the  organ.  The  cause  is  always  infection  through  a  surface  solution  of  continuity 
either  traumatic  or  during  some  disease  attended  by  drying  and  fissuring  of  the 
tongue.  On  account  of  the  vascularity,  naevoid  growths  are  frequent. 

Carcinoma  of  the  tongue  is  exceedingly  common,  and  Treves  calls  attention  to 
the  fact  that  it  usually  affects  the  anterior  two-thirds  or  that  portion  which  is  derived 
from  the  mandibular  arch,  as  is  the  lower  lip,  which  is  also  one  of  the  commonest 
sites  of  epithelioma.  Cancer  of  the  fore  part  of  the  tongue  may  follow  the  lym- 
phatics of  that  region  into  the  submaxillary  glands,  or  pass  by  the  main  lymphatic 
channels  into  the  deep  cervical  glands.  Those  first  demonstrably  enlarged,  what- 
ever the  site  of  the  cancer,  are  apt  to  be  in  the  group  beneath  and  behind  the  angle 
of  the  jaw. 

The  pain  in  cancer  of  the  tongue  is  almost  always  associated  with  what  are 
described  as  "earache,"  "toothache,"  "faceache, "  and  sometimes  with  spasm  of 
the  muscles  of  mastication.  These  symptoms  are  due  to  the  connection  of  the 
lingual  branch  of  the  fifth  pair  with  other  branches  of  the  third  division  of  the  fifth, 
especially  the  auriculo-temporal  and  inferior  dental,  with  the  tympanic  branch  of  the 
glosso-pharyngeal,  and  with  the  chorda  tympani  from  the  facial. 

Pressure  upon,  or  disease  of,  the  hypoglossal  nerve  may  cause  unilateral  atrophy 
of  the  tongue.  The  various  paralyses  should  be  studied  in  connection  with  tjie 
nervous  supply  of  the  tongue. 

As  the  tongue  depends  upon  muscular  and  not  ligamentous  attachments  for  the 
preservation  of  its  position  in  the  mouth,  its  tendency  to  drop  backward  by  gravity 
during  complete  anaesthesia  or  some  other  forms  of  profound  unconsciousness  in 
which  muscular  relaxation  or  paralysis  occurs  should  not  be  forgotten.  If  it  is 
allowed  to  fall  back,  the  pressure  on  the  epiglottis  may  close  the  opening  into  the 
larynx.  During  anaesthetization  it  is  well  to  press  the  lower  jaw  well  forward,  carry- 
ing the  tongue  with  it  through  the  attachments  of  the  genio-glossi,  and  to  elevate  the 
chin,  which  still  farther  advances  the  tongue  and  removes  it  from  close  proximity  to 


1596  HUMAN   ANATOMY. 

the  epiglottis.  Often  this  does  not  suffice,  and  direct  traction  on  the  tongue  itself 
is  required. 

Excision  of  the  entire  tongue  necessitates  division  of  the  muscles  of  the  tongue, 
its  connections  by  mucous  membrane  with  the  soft  palate,  the  alveoli,  and  the 
epiglottis,  the  lingual  arteries  and  veins,  and  the  glosso-pharyngeal,  lingual,  and 
hypoglossal  nerves. 

In  opening  abscesses  of  the  tongue  the  position  of  the  lingual  arteries — much 
nearer  the  lower  than  the  upper  surface — should  be  remembered. 

Hemorrhage  from  wounds  or  during  operation  may  temporarily  be  controlled  by 
pressure  from  behind  forward  on  the  base  of  the  tongue  by  two  fingers  thrust  well 
below  and  behind  it  in  the  pharynx.  By  this  procedure,  or  by  forcing  up  the  soft 
tissues  between  the  inferior  maxilla  and  the  hyoid  bone  with  the  finger  or  thumb, 
the  cut  surface  during  partial  excision  may  be  brought  well  into  view  and  the 
hemorrhage  controlled  while  the  vessels  are  sought  and  secured. 

THE    PHARYNX. 

The  pharynx  is  a  bag,  open  in  front,  with  musculo-membranous  walls,  lined  with 
mucous  membrane,  extending  from  the  base  of  the  skull  to  the  lower  border  of  the 
larynx,  near  the  level  of  the  top  of  the  seventh  cervical  vertebra.  Thus  it  is  bounded 
behind  by  the  spine,  covered  by  the  prevertebral  muscles  and  fascia,  and  by  the  basilar 
process  of  the  occipital  bone,  which,  especially  in  the  median  line,  is  separated  by 
much  areolar  tissue,  as  well  as  by  muscles  from  the  posterior  wall.  The  steep  rise 
of  the  basilar  process,  together  with  the  downward  growth  of  the  face,  forms  the 
deep  recess  known  as  the  naso-pharynx.  The  roof  is  formed  by  a  little  of  the  front 
of  the  basilar  process  and  by  the  back  part  of  the  basi-sphenoid.  The  anterior  wall  is 
formed  by  the  back  of  the  framework  of  the  face,  the  soft  palate,  the  back  of  the 
tongue,  the  hyoid  bone,  and  the  larynx.  The  pharynx  communicates  in  front  with 
the  nasal  chambers  and  the  mouth  ;  the  Eustachian  tubes  open  into  it  on  either  side 
near  the  top  ;  and  below  it  contains  the  opening  of  the  larynx,  behind  which  it  passes 
into  the  oesophagus.  The  framework  consists  of  the  pharyngeal  aponeurosis,  a  dis- 
tinct fibrous  membrane  above,  placed  between  the  mucous  membrane  and  the  mus- 
cular layer,  which  grows  weaker  below  and  is  continued  into  the  gullet.  This  is 
attached  above  to  the  pharyngeal  tubercle  and  to  the  occipital  bone  on  either  side 
of  it,  to  the  cartilage  between  the  petrous  portion  of  the  temporal  and  the  basilar 
process,  to  the  Eustachian  tube  which  passes  over  it,  and  to  the  base  of  the  internal 
pterygoid  plate.  This  fascia  is  wanting  in  front.  The  parts  forming  most  of  the 
anterior  wall — the  soft  palate  and  the  back  of  the  tongue — are  capable  of  changing 
their  relations.  The  pharynx  is  enclosed  by  a  layer  of  fascia,  the  bucco-pharyngeal 
(not  to  be  confounded  with  the  pharyngeal  aponeurosis),  the  front  part  of  which  is 
connected  with  the  pterygo-mandibular  ligament  and  covers  the  buccinator  muscle. 
This  fascia  lies  beneath  the  parotid  gland  and  mingles  with  the  cobweb-like  tissue  of 
the  carotid  sheath  to  make  a  large  amount  of  rather  dense  areolar  tissue  on  either  side. 
At  the  back  it  is  very  lax,  allowing  the  pharynx  to  move  on  the  smooth  prevertebral 
fascia.  The  condition  there  approaches  that  of  a  serous  bursa. 

The  pharynx  is  divided  into  the  naso-,  oro-,  and  laryngo-pharynx  by  folds  on 
the  anterior  and  lateral  walls.  The  uninterrupted  posterior  wall  is  covered  with 
smooth  mucous  membrane,  which,  behind  the  larynx,  tends  to  be  puckered  into 
longitudinal  folds.  The  naso-pharynx  is  that  part  above  the  free  edge  of  the  soft 
palate.  The  oro-pharynx  communicates  at  the  anterior  pillar  of  the  fauces  with  the 
mouth.  The  isf/inins,  a  niche  between  the  faucial  pillars  containing  the  tonsils,  is  its 
anterior  part.  It  is  separated  from  the  laryngo-pharynx  by  \ht  phvryngo-epiglottic 
fold,  which  extends  from  the  epiglottis  to  tin-  side  of  the  pharynx,  as  more  particu- 
larly described  later.  The  length  of  the  male  pharynx  is  about  13  cm.  (about  5  in.), 
which  is  rarely  much  exceeded.  The  greatest  breadth  (4-5  mi.  )  is  near  the  top  of 
the  laryngo-pharynx,  rather  below  the  greater  horns  of  the  hyoid  bone.  The  greatest 
breadth  in  the  naso-pharynx,  between  the  deepest  points  of  the  fossa  of  Rosenmiiller, 
is  3.5  cm.,  or  perhaps  a  little  more.  Behind  the  upper  margin  of  the  rricoid  curtilage 
the  breadth  is  not  over  3  cm.,  below  which  it  abruptly  diminishes.  The  antero- 


THE  PHARYNX. 


1597 


posterior  diameter  in  the  median  line  is  greatest  in  the  naso-pharynx, — about  2  cm. 
The  back  of  the  lower  part  of  the  soft  palate  is  less  than  half   that  distance  from  the 

FIG-    1353- 


Frontal  sinus 


*& 


««SSte:>- 

*f* 


Li  men-/ — 
vestibuli    I 


Pterygo-mandibular  fold 1 

Anterior  pillar  of  fauces— j£ 


Ventricle  of  larynx V \ 

Thyroid  cartilage ', 


Sella  turcica 


ffc   V Naso-pharyngeal 

fold 

Fossa  of  Rosenmiiller 
Eustachian  tube 
_L-J>haryngeal  tonsil 
;— X-Salpingo-palatine  fold 

_  ,lpingo- 
'     pharyngeal  fold 


Faucial  tonsil 

c — Posterior  wall  of 
pharynx 

Palato-pharyngeal 
fold 


Pharyngo-epiglottic 
fold 


Epiglottis 

Cuneiform  tubercle 
Tubercle  of  Santorini 


1 Cricoid  cartilage 


t (Esophagus 


Tracheal  cartilag 


Sagittal  section  of  head,  slightly  to  right  of  median  plane ;  tongue  has  been  pulled  down. 

posterior  pharyngeal  wall.     The  greatest  depth  in  this  direction  (3-4  cm.)  is  at  the 
side,  from  the  anterior  pillar  to  the  posterior  wall.      Behind  the  cricoid  cartilage  the 


1598  HUMAN   ANATOMY. 

front  and  back  walls  are  probably  in  contact.  In  the  female  several  of  these  distances 
are  smaller.  Thus  the  pharynx  is  in  horizontal  sections  at  most  levels  a  transverse 
cleft. 

The  naso-pharynx,  broad  from  side  to  side  and  short  from  before  backward, 
passes  insensibly  into  the  oro-pharynx  when  the  soft  palate  is  not  raised  so  as  to  cut 
off  communication.  Anteriorly  are  the  nasal  openings,  described  with  the  nose. 
The  separation  of  the  two  regions  on  the  lateral  waH  is  determined  by  the  naso- 
pharyngcal fold  which  runs  from  the  base  of  the  skull  to  the  beginning  of  the  soft 
palate.  This  fold  is  very  irregular  in  course  and  development.  It  occasionally  is 
grooved  so  as  to  present  a  furrow.  Sometimes  the  furrow  takes  the  place  of  the  fold 
and  at  other  times  the  fold  joins  that  in  front  of  the  opening  of  the  Eustachian  tube. 
This  orifice  is  on  a  level  with  the  end  of  the  inferior  turbinate  bone  and  less  than 
I  cm.  behind  it.  It  is  usually  a  triangular  opening  without  a  distinct  border  below, 
although  it  may  be  oval  or  even  round.  The  longest  diameter  is  about  i  cm.  The 
end  of  the  cartilage  of  the  tube  curves  over  the  top  of  the  opening  from  the  front 
and  descends  along  its  posterior  border,  producing  a  strong  fold  of  the  mucous  mem- 
brane, the  salpingo-pharyngeal,  which  descends  to  be  lost  in  the  lateral  wall  of  the 
oro-pharynx,  or  even  sooner.  The  salpingo-palatine  fold  in  front  of  the  opening  of 
the  Eustachian  tube  is,  as  a  rule,  less  prominent  and  very  variable.  It  is  formed 
above  by  the  bent  end  of  the  cartilage,  and  below  by  a  small  band  of  fibrous  tissue, 
the  salpingo-palatine  ligament,  running  from  the  cartilage  into  the  soft  palate.  The 
fossa  of  Rosenmuller  is  a  deep  pocket  at  the  angle  of  the  pharynx  between  the 
posterior  wall  and  the  back  of  the  projection  of  the  cartilage  of  the  tube.  Its  anterior 
and  posterior  walls  are  almost  in  contact  and  are  often  connected  by  accidental 
adhesions.  This  is  the  broadest  part  of  the  naso-pharynx.  Adenoid  collections — the 
tubal  tonsils — are  found  in  varying  degree  about  the  orifice  of  the  tube,  especially 
over  the  fold  behind  it.  The  belly  of  the  levator  palati  muscle  makes  a  prominence 
in  the  lateral  wall  below  the  tubal  orifice. 

The  oro-pharynx  opens  into  the  mouth  at  the  anterior  pillar  of  the  fauces. 
The  posterior  pillar,  covering  the  palato-pharyngeus  muscle,  runs  down  the  side  of 
the  pharynx  as  the  palato-pharyngeal  fold.  It  may  be  traced  to  the  base  of  the 
superior  horn  of  the  thyroid  cartilage,  or,  as  is  most  common,  it  is  lost  on  the  lateral 
wall  a  little  higher.  The  pharyngo-epiglottic  fold  above  mentioned  arises  from  the 
front  of  the  epiglottis  near  the  lateral  edge  and  runs  upward  and  backward  across 
the  pharynx.  It  may  end  soon,  or  it  may  reach  the  palato-pharyngeal  fold,  or, 
crossing  this,  may  extend  even  as  far  as  the  salpingo-pharyngeal  one.  It  contains 
muscular  or  tendinous  fibres  from  the  stylo-pharyngeus.  If  well  marked,  it  may 
bound  below  the  niche  containing  the  tonsil.  The  anterior  wall  of  the  oro-pharynx 
is  formed,  the  mouth  being  closed,  by  the  posterior  vertical  part  of  the  tongue.  The 
respiratory  tract,  passing  through  the  nose,  and  the  digestive,  passing  through  the 
mouth,  cross  each  other  in  the  oro-pharynx,  so  that  the  former  is  the  anterior  below 
this  point. 

The  laryngo-pharynx,  the  lowest  part  of  the  pharynx,  is,  roughly  speaking, 
the  part  below  the  level  of  the  hyoid  bone.  It  is  separated  from  the  oro-pharynx 
by  the  pharyngo-epiglottic  fold.  In  the  middle  of  it  is  the  opening  of  the  larynx 
behind  the  epiglottis  and  enclosed  by  the  aryteno-epiglottic  and  interarytenoid  folds. 
The  sinus  pyriformis  is  a  depression  on  either  side  of  the  entrance  of  the  larynx 
between  the  aryteno-epiglottic  fold  and  the  arytenoid  cartilage  internally  and  a  part 
of  the  great  wing,  of  the-  thyroid  cartilage  and  the  thyro-hyoid  membrane  externally. 
It  is  open  behind.  The  thin  mucous  membrane  lining  the  sinus  has  a  transverse 
fold,  formed  by  the  superior  laryngeal  nerve,  in  front  between  the  hyoid  bone  and 
the  thyroid  cartilage.  The  lower  part  of  the  palato-pharyngeal  fold  is  seen  in  frozen 
sections  near  the  superior  horn  of  the  thyroid  cartilage  at  the  lateral  aspect  of  the 
cleft,  which  is  all  that  appears  of  the  pharynx.  The  anterior  wall  behind  the  aryte- 
noid cartilages  and  the  structures  between  them  slants  backward  as  it  descends. 
Behind  the  cricoid  cartilage  it  is  vertical.  Here  the  pharynx  narrows  to  join  the 
oesophagus. 

The  mucous  membrane  of  the  pharynx  is  smooth,  except  for  the  elevations 
caused  by  collections  of  lymphoid  follicles.  It  is  more  loosely  attached  and  more 


THE  PHARYNX. 


1599 


disposed  to  be  thrown  into  folds  in  the  lower  part.  Mucous  glands,  on  the  other 
hand,  are  numerous  in  the  upper  part,  scarce  below  ;  they  lie  partly  within  the 
mucosa  and  partly  in  the  submucous  tissue  and  between  the  muscular  bundles.  The 
character  of  the  pharyngeal  epithelium  varies  in  different  localities.  In  the  nasal 
pharynx  the  stratified  ciliated  columnar  cells  of  the  nasal  fossa  are  continued  as  the 
covering  of  the  pharyngeal  mucous  membrane,  while  the  oro-pharynx  is  clothed  with 
stratified  squamous  epithelium  continued  from  the  mouth.  The  last-named  type 
of  epithelium  likewise  covers  the  greater  part  of  the  laryngeal  portion.  The 
exact  distribution  of  the  two  varieties  of  cells  is  subject  to  considerable  individual 
variation.  The  ciliated  columnar  type  extends  laterally  to  include  the  openings 
of  the  Eustachian  tubes,  but  lower  down  gives  place  to  the  squamous.  By  no 


Base  of  skull 
I 


FIG.   1354. 

Nasal  septum 


N'aso-pharyngeal  fold 

Lymphoid  tissue 

Posterior  pillar  of  fauces.. 
Faucial  tonsil  - 


Pharyngo-epiglottic  fold- 


• 

'      - 
•  ' 


jSl-Uvula 


—  Dorsum  of  tongue 


'    "N,     /ytiStyf*'.1  Glosso-epiglottic  fossa 

djjrjjjp-ff Median  glosso-epiglottic  fold 

^Epiglottis.  turned  back 


Cut  edge  of  pharynx 


Posterior  surface  of  larynx 


Pharynx  opened  from  behind  ;  epiglottis  turned  back. 

means  the  entire  posterior  surface  of  the  soft  palate  is  clothed  with  ciliated  colum- 
nar cells,  since  the  entire  uvula  and  the  edges  of  the  palato-pharyngeal  folds  are 
invested  with  stratified  squamous  epithelium.  The  latter  also  covers  the  posterior 
wall  of  the  pharynx  and  extends  above  as  far  as  the  vault.  When  covered  with 
ciliated  epithelium,  the  mucous  membrane  is  redder,  thicker,  and  contains  more 
glands,  but  fewer  papillae,  than  in  those  parts  in  which  the  squamous  cells  prevail. 
While  containing  much  lymphoid  tissue,  fat  is  limited  to  a  few  deeply  seated  lobules 
of  adipose  tissue. 

Lymphoid  Structures. — The  upper  .part  of  the  pharynx  contains  many 
lymphoid  collections  which  make  the  surface  uneven.  They  are  much  less  frequent 
below.  The  larger  and  more  constant  masses  are  called  ' '  tonsils. ' '  These  include 
tin&faucial  tonsi/s  in  the  oro-pharynx,  between  the  pillars  of  the  fauces,  the  pharyn- 


i6oo 


HUMAN   ANATOMY. 


FIG. 


X355- 


geal  tonsil  in  the  upper  part  of  the  pharynx,  the  tubal  tonsils  at  the  openings  of 
the  Eustachian  tubes,  especially  on  the  posterior  fold,  and  the  lingual  tonsil,  con- 
sisting of  the  scattered  adenoid  collections 
over  the  posterior  third  of  the  tongue.  Many- 
additional  lymph-nodules  are  scattered  over 
the  sides  and  roof,  so  connected  as  to  form 
a  lymphoid  ring  at  the  upper  part  of  the 
pharynx. 

The  faucial  tonsils  (Figs.  1326,  1353) 
are  theoretically  two  almond-shaped  masses 
of  adenoid  tissue,  placed  one  on  each  side  of 
the  oro-pharynx,  between  the  pillars  of  the 
fauces.  The  long  diameter  is  vertical,  and 
they  have  an  outer  and  an  inner  surface  and 
an  anterior  and  a  posterior  border.  The 
length  is  conventionally  put  at  from  20-25 
mm.,  the  breadth  at  15  mm.,  and  the  thick- 
ness at  10  mm.  Practically,  however,  there 
is  no  definite  shape  nor  size.  In  childhood 
the  tonsil  generally  projects  as  a  globular 
mass.  If  it  extends  more  than  slightly  be- 
yond the  level  of  the  faucial  pillars,  it  is  said 
to  be  enlarged.  After  middle  life  it  rises  usu- 
ally but  little  from  the  floor  of  the  niche. 
The  shape  of  the  free  surface  gives  no  clue 
to  the  size  of  the  deep  surface.  In  structure 
the  tonsil  is  a  mass  of  adenoid  tissue  en- 
closed in  a  fibrous  capsule  which  is  crossed 
on  both  the  deep  and  free  surfaces  by  a  thin 
layer  of  muscular  fibres.  The  superficial  layer 
belongs  to  the  palato-glossus  ;  the  deep  or 
external  layer  arises  from  the  superior  con- 
strictor and  passes  to  the  tongue.  Beyond 

this  externally  are  fat  and  areolar  tissue.     The  closely  adherent  mucous  membrane 
covers  the  free  surface,  which  is  full  of  pits  from   i   or  2  mm.  to  i  cm.  in  depth. 


Section  through  faucial  tonsil,  showing  general  dis- 
position of  lymphoid  tissue.     X  20. 


FIG.   1356. 


Lymphocytes, 
invading 

Epithelium 


Blood-vessel 


The  larger  ones  often  expand  be- 
low the  orifice,  so  that  they  may 
collect  and  retain  secretions.  A 
small  free  space,  the  supratonsillar 
fossa,  lies  above  the  tonsil  at  the 
apex  of  the  niche  containing  it  ;  at 
the  front  of  this  there  is  very  often 
a  series  of  crypts  with  detached 
adenoid  tissue  about  them,  bur- 
rowing under  the  anterior  pillar 
from  behind  and  making  a  pouch 
beneath  a  fold,  the  plica  trian- 
gularis.  The  adenoid  tissue  is 
continuous  below  with  that  of  the 
tongue.  The  mucous  membrane 
of  the  oro-pharynx  shows  many 
scattered  lymphoid  follicles  in  its 
walls,  especially  on  the  sides  at 
and  above  the  level  of  the  tonsils. 
Vessels. — The  arteries  sup- 
plying the  faucial  tonsil  are  de- 
rived from  several  sources,  and  the  arrangement  of  the  vessels  is  extremely  irregular  ; 
the  branch  from  the  ascending  pharyngral  and  that  from  the  facial  artery — one  or 
both — enter  its  base,  while  twigs  from  the  lingual  and  descending  palatine  arteries, 


Portion  of  faucial  tonsil,  showing  epithelial  lining  of  crypt  invaded 
by  escaping  lymphocytes.     X  325. 


THE  PHARYNX. 


1601 


and  perhaps  others,  reach  it  beneath  the  mucous  membrane.  Under  ordinary  cir- 
cumstances the  tonsil  is  not  very  vascular,  but  receives  a  large  quantity  of  blood 
when  inflamed.  There  is  a  -venous  plexus  communicating  with  the  veins  of  the 
pharynx.  The  lymphatics  probably  communicate  both  with  those  of  the  dorsum 
of  the  tongue  and  with  the  glands  near  the  angle  of  the  jaw. 

Nerves.  — The  nervous  supply  is  from  the  fifth  and  the  glosso-pharyngeal. 
(The  relations  of  the  tonsils  are  given  with  those  of  the  pharynx,  page  1602.) 
The  pharyngeal  tonsil  (Fig.    1353),  sometimes  called  the  third  tonsil,  is  a 
median  mass  of  adenoid  tissue  in  the  postero-superior  wall  of  the  pharynx,  which 
reaches  its  greatest  development  in  early  childhood,   generally  dwindling  after  the 
twelfth  year.     When  well  developed,  it  lies  below  the  occipital  and  the  basi-sphenoid, 
nearly  filling  the  space  from  the  nasal  septum  to  the  back  of  the  pharynx  and  almost 
touching  on  either  side  the  folds  made  by  the  tubal  cartilages.      Its  thickness  in  the 
median  line  is  nearly  i  cm.     Thus  without  being  hypertrophied  it  nearly  fills  the  naso- 
pharynx.    The  pharyngeal  tonsil  is  a  lobulated  organ,  the  swellings  being  often  regu- 


Foramen  caecum 


FIG.   1357. 

Crista  galli 


Cartilage  of  septum 
Vomer 


Permanent  incisor 


Tongue 


Frenum  of  tongue 


Pituitary  body 

Cranio-pharyngeal  canal 


Pharyngeal  tonsil 
Occipital  bone 
Pharyngeal  tonsil 

V     Anterior  arch  of  atlas 


Genio-hyoid 

Mylo-hyoid 

Hyoid  bone 
Thyroid  cartilage 


Third  cervical  vertebra 


Ventricle  of  larynx 


Cricoid  cartilage 

Reduced  one-fourth. 


"    LUWIS&— — (j..  ijjj- *-/r't-:i.v.i» 
Anterior  portion  of  mesial  sagittal  section  of  child's  head,  probably  of  about  three  years. 


larly  arranged  around  a  central  depression  ;  consequently  it  presents  many  pockets. 
The  central  one,  which  varies  widely,  is  often  improperly  called  the  bursa  pharyngea. 
It  has  absolutely  nothing  to  do  with  the  canal  from  the  mouth  to  the  sella  turcica, 
through  which  a  process  of  the  oral  tissue  passes  in  early  foetal  life  to  the  pituitary 
body  (Fig.  1357),  being  decidedly  behind  that  passage.  Neither  is  it  the  true  bursa 
pharyngea,  since  this  term  is  more  properly  applied  to  a  structure  of  uncommon 
occurrence, — namely,  a  still  more  posterior  pocket  in  the  mucous  membrane  leading 
from  the  roof  of  the  pharynx,  just  behind  its  tonsil,  into  a  small  recess  not  over  1.5 
cm.  in  length,  on  the  under  side  of  the  basilar  process. 

Relations  of  the  Pharynx. — The  structures  behind  the  posterior  wall  have 
been  mentioned  (page  1596).  The  tip  of  the  normal  uvula  hangs  on  a  level  near  the 
lower  part  of  the  axis  or  the  top  of  the  third  cervical  vertebra.  The  tip  of  the  epi- 
glottis is  usually  opposite  the  lower  part  of  the  third.  The  second  and  third  cervical 
vertebrae  are  those  behind  that  part  of  the  pharynx  seen  through  the  open  mouth. 
The  pharynx  ends  at  about  the  top  of  the  seventh  cervical  vertebra.  The  lateral  wall 
of  the  pharynx  is  very  narrow,  except  in  the  region  of  the  tonsils,  where  it  reaches  for- 
ward to  the  anterior  pillar  of  the  fauces.  From  the  top  of  the  thyroid  downward  it 


TOT 


1602 


HUMAN   ANATOMY. 


Pharyni 


isil  of   child   one  year 
(Schwabach. ) 


Lymph-nodule 


is  nothing  more  than  the  fold  around  the  end  of  a  transverse  linear  cleft.     The  whole 

lateral   aspect   is   covered   by  a  thick  layer  of  areolar  tissue,  continuous   with   that 

of  the  carotid  sheath.      It 'is  most  convenient  to  give  the  relations  of  the  lateral  wall 

from  below  upward,  excepting  the  nerves.     The  upper 

part  of  the  lobes  of  the  thyroid  gland  comes  very  close  FIG.   1358. 

to  the  lower  part  of  the  pharynx,  and  may  even  touch 

it   without    undue    enlargement.      They  separate    the 

common  carotid  from   the  pharynx.     A  little   higher 

this  vessel  is  on  the  outer  side  of  the  great  wing  of 

the  thyroid  cartilage,   but  if   the  head   be  turned  to 

one  side  the  vessel  of  the  other  side  will  rest  on  the 

pharynx.      The  common  carotid  artery  is  very  close 

to  the  pharynx  just  before  its  division.      The  inter-  "  "  old. 

nal  carotid  lies  against  it  until  it  reaches  the  skull. 

The  beginning  of  the  external  carotid  with   its  lingual  and  facial   branches  is  also 

against  it.      The  ascending  pharyngeal  artery  runs  along  it,  the  middle  meningeal 

lying  against  its  upper  part.     The  internal  jugular  vein  is,   probably,  nowhere  in 

direct  contact  with   the  pharynx   unless  just  below   the  skull.       The  submaxillary 

gland  touches  it  at  the  angle  of  the  jaw. 

The  sympathetic  nerve  comes  in  contact  with  the  back  or  side  of  the  pharynx. 
The  vagus  lies  against  the  pharynx  behind  the  internal  carotid  ;   on  reaching  the 

common     carotid,     however, 

FIG.  1359.  it    is   in    less   direct    contact. 

Its  superior  laryngeal  branch 
crosses  the  pharynx  to  reach 
the  thyro-hyoid  membrane. 
The  spinal  accessory  and  the 
glosso-pharyngeal  nerves  lie 
against  the  upper  part  of  the 
pharynx. 

The  faucial  tonsil  lies 
about  2. 5  cm.  above 'the  angle 
and  opposite  a  vertical  line  di- 
viding the  ramus  of  the  jaw 
into  a  front  and  a  back  half.  It 
lies  between  the  pillars  of  the 
fauces,  and  is  separated  from 
the  mucous  membrane  by  a 
thin  layer  of  muscular  fibres. 
The  lower  end  reaches  the 
tongue,  the  adenoid  tissue 
being  at  times  continuous 
between  them.  The  tonsil 
covered  by  the  superior  co 
stricter.  External  to  this  is 
yielding  mass  of  areolar  t 
sue,  continuous  with  that  o 
the  carotid  sheath,  into  which 
the  tonsil  may  force  its  way 
if  enlarged.  This  areolar  tis- 
sue is  bounded  in  front  by 
the  internal  pterygoid  muscle, 
and  is  pierced  by  the  stylo- 
tylossus  and  the  stylo-pha- 
ryngeus,  which  subdivide  it, 
leaving  a  small  part  of  it  be- 
tween them  and  the  tonsil.  At  this  level  both  carotids  are  at  a  considerable  dis- 
tance from  the  tonsil.  The  internal  is  posterior  and  external,  about  2  cm.  distant. 
According  to  Zuckerkandl,  a  transverse  line  through  the  posterior  pillar  will  pass 


tSar*  Bundles  of 

muscular  tis- 
_siu  ul  constric- 
tors 


-Pharynjjeal 

apom-uroMs 


ffl 


Surface 

epithelium 


Sagittal  section  of  posterior  wall  of  pharynx  ol  child,  showing  part  of 
pharytiKcal  tonsil. 


THE  PHARYNX.  1603 

2  cm.  in  front  of  the  vessel.  The  external  carotid  is  placed  more  directly  outward  and 
is  rather  the  nearer  of  the  two.  The  parotid  inland,  according  to  Tillaux,  sends  a 
process  in  front  of  the  styloid  process,  which  reaches  the  lateral  wall.  This  extension, 
however,  does  not  seem  to  be  by  any  means  constant. 

Development  and  Growth  of  the  Pharynx. — An  account  of  the  formation 
of  the  primitive  pharynx  is  included  in  the  Development  of  the  Alimentary  Tract 
(page  1694),  the  later  changes  being  here  noted.  In  the  section  on  the  bones  it  was 
shown  that  the  chief  peculiarities  of  the  infant  skeleton  in  this  region  are  due  to  the 
small  size  of  the  face  and  the  more  horizontal  base  of  the  skull.  The  naso-pharynx 
has  very  little  height,  while,  owing  to  the  peculiar  disposition  of  the  parts,  it  has  nearly 
the  same  antero-posterior  diameter  as  in  the  adult.  It  is  relatively  broad  and  long, 
but  very  shallow.  The  tongue,  in  proportion,  is  much  less  thick  at  the  base  than 
later.  The  larynx  is  small,  and,  moreover,  is  placed  higher  in  relation  to  the  vertebral 
column,  so  that  the  termination  of  the  pharynx  is  also  higher.  The  position  of  the 
larynx  at  different  ages  is  considered  with  that  organ  (page  1571 ).  The  soft  palate  is 
in  the  main  horizontal  at  birth  and  about  on  a  level  with  the  top  of  the  atlas.  The 
uvula  is  rudimentary.  In  a  child  of  probably  not  over  three  years  we  have  found 
the  tip  of  the  uvula  rather  below  the  middle  of  the  body  of  the  axis.  In  Symington's 
section  of  a  girl  of  thirteen  it  is  pretty  nearly  in  the  adult  position.  In  infancy  the 
soft  palate  probably  closes  the  passage  into  the  naso-pharynx  from  below  less  perfectly 
than  later. 

The  opening  of  the  Eustachian  tube,  although  necessarily  in  the  naso-pharynx, 
is  in  the  foetus  below  the  level  of  the  hard  palate.  At  birth  it  is  at  about  that  level, 
but  rather  below  than  above  it.  According  to  Disse,  there  is  but  little  change  for 
nine  months,  after  which  the  opening  is  on  the  level  of  the  inferior  meatus.  Proba- 
bly the  adult  position  is  generally  reached  after  puberty.  The  opening  is  small 
in  the  infant  and  young  child,  and,  owing  to  want  of  development  of  the  cartilage, 
there  is  but  a  slight  elevation  about  it  and  consequently  but  a  small  fossa  of  Rosen- 
miiller.  The  entire  adenoid  system  of  this  region  l  has  made  but  little  progress 
before  birth. 

At  birth  the  pharyngeal  tonsil  is  a  very  small  collection  of  adenoid  tissue  at  the 
back  of  the  roof,  covered  by  more  or  less  converging  folds  of  the  mucous  membrane. 
It  is  not  necessarily  present.  During  the  first  year  it  grows  rapidly,  and  particularly 
forward,  so  that  by  the  end  of  that  time  it  extends  to  the  back  of  the  upper  margin  of 
the  choanae.  Under  normal  conditions  the  pharyngeal  tonsil  retains  its  relative  size 
to  the  cavity  of  the  pharynx  up  to  twelve  years  ;  but  during  this  time  the  total  amount 
of  adenoid  tissue  has  decidedly  increased,  owing  to  the  development  of  the  tubal 
tonsils. 

The  faucial  tonsils  are  developed  in  a  recess  of  the  primitive  pharynx  between 
the  second  and  third  visceral  arches.  By  the  fourth  fcetal  month  the  tonsillar  anlage 
presents  a  number  of  slit-like  depressions,  lined  with  entoblastic  epithelium,  from 
which  secondary  epithelial  sprouts  invade  the  neighboring  mesoblast.  This  process 
continues  after  birth  during  the  first  year.  The  young  connective  tissue  surrounding 
the  epithelial  sprouts — the  latter  being  at  first  solid,  but  later  possessing  a  lumen — 
becomes  infiltrated  by  accumulating  leucocytes  and  gradually  assumes  the  character 
of  adenoid  tissue,  the  differentiation  into  distinct  lymph-nodes,  however,  being  delayed 
until  after  birth.  The  source  of  the  lymphoid  cells  is  a  matter  of  dispute.  Accord- 
ing to  some,  these  elements,  are  leucocytes  from  the  circulation  caught  within  the 
young  connective  tissue  ;  others  maintain  that  they  are  derived  from  the  transforma- 
tion of  the  epithelium,  the  lymphoid  tissue  resulting  from  the  mutual  invasion  and  in- 
tergrowth  between  the  ento-  and  mesoblastic  elements.  According  to  Hammar,*  who 
has  carefully  studied  the  development  of  the  tonsils,  the  lymphoid  cells  are  derived 
chiefly  from  the  fixed  connective-tissue  elements.  At  birth  the  tonsils  are  insignifi- 
cant, but  grow  rapidly  during  the  first  year.  At  from  the  twelfth  year  to  puberty 
the  entire  adenoid  system  of  the  pharynx  enters  .upon  a  stage  of  retrogression.  In 
the  adult  the  pharyngeal  and  tubal  tonsils  are  much  smaller  ;  after  middle  age  they 
undergo  atrophy. 

1  Escat :  Evolution  de  la  Cavit6  Naso-Pharyngienne,  1894. 

2  Archiv  f.  mikro.  Anat.,  Bd.  xli.,  1902. 


1604 


HUMAN    ANATOMY. 


THE   MUSCLES   OF  THE   PHARYNX. 

The  arrangement  of  the  muscular  tissue  differs  from  the  ordinary  one  of  the 
digestive  tract,  inasmuch  as  the  outer  layer  is  approximately  circular  and  the  longi- 
tudinal fibres  are  largely  internal.  The  chief  elements  are  the  three  constrictors, 
which  overlap  one  another  from  below  upward,  the  stylo-pharyngeiis,  the  palato- 
pharyngeus,  and  certain  accessory  and  rather  irregular  bundles  of  muscular  fibres. 


Internal  carotid  artery 
Internal  jugular  vein 


Central  attachment  of  pharynx 


,  Pharvn- 
/  seal  ' 
aponeu- 
rosis 


Styloid  process 

Digastric, 

posterior  belly 

Stylo- 

pharyngeus 
Stylo-glossus 


Stylo-hyoid 

Stylo-hyoid< 
ligament 


Tip  of  great  cornu  of 
hyoid  bone 

Thyro-hyoid  ligament 
Superior  cornu  of  thyroid 
cartilage 


Middle 
constrictor 


Mandible 


Raphe 


Inferior  constrictor 


Longitudinal  muscle  of  oesophagus 


Muscles  of  pharynx  from  In-hind  ;  portion  of  interior  constrictor  has  been  removed. 

The  superior  constrictor  (  Figs.  1339,  1360)  arises  from  the  lower  part  of  the 
internal  pterygoid  plate,  from  the  Kamular  process,  the  pterygo-mamlibular  ligament 
which  is  stretched  from  it  to  the  lingula  of  the  lower  jaw,  from  the  neighboring  end 
of  the  mylo-hyoid  ridge,  and  from  the  side  of  the  tongue.  From  this  origin  the  fibres 
pass  backward  to  meet  their  fellows  in  a  median  raphe,  which  extends  almost  the 


THE    PHARYNX. 


1605 


entire  length  of  the  posterior  wall  of  the  pharynx,  being  attached  above  to  the 
pharyngeal  tubercle  on  the  under  side  of  the  basilar  process.  The  upper  edge  of 
the  muscle  is  concave  on  either  side,  not  reaching  the  base  of  the  skull  and  passing 
under  the  Eustachian  tube,  the  vacant  space  being  filled  by  the  pharyngeal  aponeu- 
rosis.  The  lower  fibres  pass  somewhat  downward  as  well  as  backward.  The  pterygo- 
mandibular  ligament  separates  the  superior  constrictor  from  the  buccinator,  with 
which  it  would  otherwise  be  continuous,  forming  a  circle  around  the  alimentary  canal. 


FIG.  1361. 


Anterior  margin  of  foramen  magnum 


Styloid  process 
Pharyngeal  aponeurosis 

Stylo-hyoid  ligament 

r'lo-glossus 
Stylo-hyoid 

Deep  fibres  of  superior 
constrictor 

Palato-pharyngeus 
Great  cornu  of  hyoid  bone 


* Stylo-pharyngeus 


_J._Thyroid  cartilage 


Pharyngeal  aponeurosis 


— i (Esophagus 


Pharyngeal  aponeurosis  and  longitudinal  musculature,  seen  from  behind. 

The  middle  constrictor  (Figs.  1339,  1360)  arises  from  the  lower  end  of  the 
stylo-hyoid  ligament,  from  the  lesser  horn  of  the  hyoid  bone,  and  from  the  upper 
border  of  the  greater  horn.  The  fibres  diverge  from  this  narrow  origin,  the  upper 
reaching  the  pharyngeal  tubercle,  the  lower  going  to  nearly  the  lower  end  of  the 
pharynx,  and  all  meeting  their  fellows  in  the  median  raphe.  It  conceals  a  consider- 
able part  of  the  preceding  muscle. 


1606  HUMAN   ANATOMY. 

The  inferior  constrictor  (Figs.  1339,  1360),  the  thickest  of  the  three,  arises 
from  the  posterior  part  of  the  outer  aspect  of  the  cricoid  cartilage,  from  the  oblique 
line  and  the  triangular  surface  below  and  behind  it  on  the  thyroid  cartilage,  including 
the  inferior  horn.  It  overlaps  the  preceding  muscle,  its  upper  fibres  reaching  to  some 
3  cm.  below  the  base  of  the  skull  and  the  lower  ones  being  nearly  horizontal.  The 
median  raphe,  which  receives  almost  all  the  fibres,  is  wanting  below.  The  lowest 
fibres  are  circular  and  continuous  with  the  circular  fibres  of  the  gullet. 

The  stylo-pharyngeus  (Fig.  1361)  arises  from  the  inner  side  of  the  styloid 
process  near  its  root  and  descends  to  the  interval  between  the  superior  and  middle 
constrictors  near  the  hyoid  bone,  where  it  passes  under  the  latter  and  ends  by  expand- 
ing in  the  side  of  the  pharynx,  some  of  its  fibres  going  to  the  posterior  border  of  the 
thyroid  cartilage  and  others  joining  the  expansion  of  the  palato-pharyngeus.  A 
bundle  from  the  thyroid  division  passes  to  the  side  of  the  epiglottis,  forming  on  the 
wall  of  the  pharynx  the  fold  known  as  the  plica  pharyngo-epiglottica.  The  fibres 
of  the  superior  constrictor  may  be  inseparable  from  the  upper  part  of  this  layer. 

The  salpingo-pharyngeus  has  been  described  in  connection  with  the  levator 
palati  (page  1571). 

Variations. — Additional  muscles  are  very  common,  being  chiefly  longitudinal  bundles  due 
to  splitting  of  one  of  the  normal  muscles,  especially  the  stylo-pharyngeus,  or  to  new  bundles  of 
fibres  arising  from  the  base  of  the  skull  in  the  vicinity  of  the  upper  insertion  of  the  pharyngeal 
fascia.  There  may  be  a  pair  of  occipito-pharyngeal  muscles,  arising  from  the  occipital  bone  on 
either  side  of  the  median  line  and  descending  to  be  lost  in  the  posterior  pharyngeal  wall  ;  or 
there  may  be  an  azygos  muscle  instead .  Bands  may  arise  at  the  side  from  the  petrous  portion 
of  the  temporal  bone  or  the  spine  of  the  sphenoid. 

Actions. — The  general  action  of  the  pharyngeal  muscles  is  sufficiently  evident ; 
the  constrictors  decrease  the  size  of  the  pharynx,  probably  drawing  the  larynx  upward 
and  backward  at  the  same  time.  The  longitudinal  muscles  raise  the  larynx  and 
pharynx,  acting  chiefly  on  the  latter. 

Vessels. — The  arteries  of  the  pharynx  are  from  many  sources  and  are  irregu- 
lar. The  chief  is  the  ascending  pharyngeal,  which  runs  up  near  the  posterior  lateral 
angle.  Occasionally,  when  enlarged,  it  is  seen  pulsating  on  the  posterior  wall. 
Branches  from  the  facial  play  an  uncertain  part.  The  veins  form  the  pharyngeal 
plexus  situated  outside  of  the  constrictors  and  communicating  in  all  directions.  The 
chief  outlets  are  by  a  pair  of  veins  on  each  side,  one  going  up  to  the  internal  jugular 
near  the  base  of  the  skull  and  the  other  down  to  the  external  jugular  or  some  of  its 
tributaries  (Luschka).  A  submucous  plexus  is  particularly  developed  in  the  lower 
posterior  wall,  which  opens  into  the  pharyngeal  plexus  by  several  branches  piercing 
the  inferior  constrictor.  The  following  are  nearly  constant  :  a  superior  and  posterior 
one  near  the  middle  line,  one  running  outward  on  each  side  near  the  back  of 
the  thyroid  cartilage,  forming  a  part  of  the  origin  of  the  pharyngeal  vein,  and  one 
passing  forward  to  the  superior  thyroid  vein.1  The  lymphatics,  which  are  numerous, 
run  in  the  upper  part  to  the  prevertebral  nodes  and  to  the  deep  cervical  system,  as 
do  the  lower  ones  at  another  level.  The  presence  of  lymphatic  nodes  behind  the 
naso-pharynx  is  of  practical  importance,  as  they  are  sometimes  inflamed  and  may 
suppurate.  They  lie  near  the  fossae  of  Rosenmiiller. 

Nerves. — The  constrictors  are  supplied  by  the  pharyngeal  plexus,  the  lower 
receiving  fibres  also  from  the  recurrent  laryngral.  The  stylo-pharyngeus  is  supplied 
by  the  glosso-pharyngeal.  The  nerves  of  the  mucous  membrane  are  from  the  glosso- 
pharyngeal,  the  pneumogastric,  and  the  sympathetic,  to  a  great  extent  in  a  plexiform 
arrangement. 

PRACTICAL  CONSIDERATIONS  :   THE    PHARYNX. 

The  pharynx  may  be  said  to  present  only  three  sides  for  consideration,  but  its 
continuity  above  with  the  nares,  anteriorly  with  the  mouth,  and  below  with  the  ori- 
fices of  the  larynx  and  oesophagus  associates  it  intimately  with  the  diseases  of  those 
iv- ions.  The  naso-pharynx  and  the  laryngeal  relations  will  be  considered  with  the 
Respiratory  Passages  (page  1829). 

1  Bimar  et  I.apeyre  :    Comptes  rendus  de  1'Acacl.  drs  Srirmvs,  Tan's,  tome  cv.,  1887. 


PRACTICAL   CONSIDERATIONS:   THE    PHARYNX.  1607 

The  posterior  -wall  of  the  pharynx  is  separated  from  the  anterior  surfaces  of  the 
bodies  of  the  first  five  cervical  vertebrae  only  by  some  loose  connective  tissue  and  by 
the  prevertebral  fascia  and  muscles.  Through  it,  by  pushing  the  finger  up  above 
the  soft  palate,  the  basilar  process  of  the  occipital  bone  may  be  felt,  and  below  the 
bodies  of  the  upper  four  cervical  vertebrae — in  children  the  upper  six — may  be  pal- 
pated. The  hard  palate,  or  the  lower  margin  of  the  posterior  nares,  and  the  anterior 
arch  of  the  atlas  are  on  the  same  level. 

In  disease  of  the  body  of  the  sphenoid,  in  fracture  of  the  base  of  the  skull 
involving  the  basilar  process,  or  in  fracture  or  dislocation  of  the  cervical  vertebrae 
the  information  gained  by  this  examination  will  often  be  of  great  value. 

The  retropharyngeal  alveolar  tissue — which  is  necessarily  loose  to  permit  of 
the  movements  of  the  pharynx  during  deglutition  and  of  its  distensibility — is  some- 
times the  seat  of  infection  which  may  have  gained  access  through  the  pharynx  itself, 
or  through  the  lymphatics  which  spring  from  the  posterior  nares,  the  summit  of  the 
pharynx  and  the  prevertebral  muscles,  and  which  empty  into  a  lymph-gland  situ- 
ated between  the  prevertebral  fascia  and  the  pharyngeal  wall.  Abscess  in  this 
situation  may  by  gravity  descend  by  the  side  of  the  oesophagus  into  the  mediasti- 
num and  has  been  known  to  reach  the  base  of  the  thorax  (page  553,  Fig.  546). 
During  its  descent  it  may  cause  much  dyspnoea  by  setting  up  oedema  in  the  region 
of  the  glottis.  Usually  it  first  pushes  forward  the  posterior  wall  of  the  pharynx, 
and  can  be  recognized  as  a  fluctuating  swelling  and  opened  by  direct  incision. 

Collections  of  fluid  resulting  from  tuberculous  disease  of  the  cervical  vertebrae 
may  occupy  the  same  space  after  perforating  the  thin  prevertebral  fascia  and  may 
take  the  same  course,  or  they  may  be  guided  by  the  lateral  expansions  of  that 
fascia  to  the  posterior  and  lateral  portions  of  the  root  of  the  neck  or  to  the  axilla 
(page  552,  Fig.  545).  As  in  these  cases  the  avoidance  of  mixed  infection  is  very 
important,  such  tuberculous  collections,  when  they  require  opening,  should  be 
approached  through  the  neck  by  an  incision  along  the  posterior  border  of  the 
sterno-mastoid. 

Retropharyngeal  abscess  of  any  type  should  never  be  allowed  to  open  spon- 
taneously on  account  of  the  danger  of  immediate  suffocation  from  flooding  of  the 
larynx  with  pus. 

In  cases  of  fracture  of  the  posterior  fossa  of  the  base  of  the  skull,  with  hemor- 
rhage into  the  pharynx  (fracture  of  the  basilar  process),  or  of  the  middle  fossa, 
with  hemorrhage  reaching  the  pharynx  through  the  Eustachian  tube  (fracture  of 
the  petrous  portion  of  the  temporal),  the  need  for  frequent  and  persistent  attempts 
to  make  and  keep  the  pharynx  as  nearly  aseptic  as  possible  should  never  be 
forgotten. 

The  adenoid  tissue  of  the  posterior  wall — the  pharyngeal  tonsil — may  undergo 
hypertrophy,  cause  deafness  or  respiratory  obstruction,  and  require  removal. 

The  lateral  walls  of  the  pharynx  are  in  such  close  relation  with  the  internal 
carotid  artery  that  in  aneurism  of  that  vessel  the  pulsations  may  most  easily  be  felt 
and  seen  through  the  pharynx.  In  many  instances  the  vessel  has  been  opened  in 
penetrating  wounds  of  the  pharyngeal  wall  by  foreign  bodies.  The  internal  jugular 
vein  is  not  so  exposed  to  injury  and  is  more  rarely  wounded.  In  one  instance  of 
pulsating  tumor  of  the  pharynx,  pressure  on  the  external  carotid  arrested  the  pulsa- 
tions (Barnes). 

The  styloid  process  and  a  rigid  or  ossified  stylo-hyoid  ligament  can  be  felt 
through  the  lateral  wall.  Attempts  have  been  made  (in  cases  of  hysterical  persist- 
ence of  pharyngeal  symptoms  after  the  supposed  swallowing  of  a  foreign  body)  to 
remove  these  structures  or  a  cornu  of  the  hyoid  bone,  under  the  impression  that 
they  were  the  offending  substances. 

The  pharynx  is  very  distensible,  and  foreign  bodies,  if  not  of  great  size,  are 
apt  to  pass  through  it  as  far  as  the  level  of  the  cricoid  cartilage,  where  its  diameter 
is  only  18  mm.  (^  in.).  In  an  adult  this  point  is  beyond  the  reach  of  an  average 
finger,  as  it  is  about  the  entrance  of  the  oesophagus,  which  is  about  six  inches  from 
the  incisor  teeth. 

For  the  removal  of  impacted  foreign  bodies,  or  for  operation  on  malignant  dis- 
ease, the  pharynx  may  be  reached,  after  a  preliminary  tracheotomy,  by  an  incision 


i6o8  HUMAN   ANATOMY. 

through  the  neck  from  a  point  midway  between  the  symphysis  and  the  angle  of  the 
jaw  to  the  cricoid  cartilage,  dividing  the  platysma  and  the  omo-hyoid  and  sepa- 
rating the  posterior  belly  of  the  digastric  and  the  stylo-hyoid  from  the  hyoid  bone  ; 
or  a  subhyoid  pharyngotomy  will  give  access  to  the  lower  walls  of  the  pharynx  by 
division  of  the  superficial  fascia,  the  sterno-hyoid  and  thyroid  muscles,  the  thyro- 
hyoid  ligament  and  membrane,  and  the  mucous  membrane  of  the  pharynx  at  the 
level  of  the  lower  margin  of  the  hyoid  bone.  These  operations  are  more  interest- 
ing anatomically  than  surgically. 

The  tonsils,  as  seen  from  the  mouth,  are  situated  between  the  arches  of  the 
palate  and  the  base  of  the  tongue.  They  may  be  almost  concealed  in  these  re- 
cesses or  may  project  into  the  pharynx,  and  when  hypertrophied  may  actually  meet 
in  the  middle  line.  They  rest  on  the  superior  constrictor  muscles  and  move  with 
those  muscles  during  the  act  of  deglutition.  They  are  somewhat  elevated  and  with- 
drawn from  the  pharynx  by  the  coincident  contraction  of  the  stylo-pharyngei. 
Swallowing  is  therefore  apt  to  be  painful  in  all  forms  of  tonsillitis.  If  not  enlarged, 
they  are  often  almost  hidden  in  persons  who  have  large  palato-glossi  muscles,  and 
therefore  prominent  anterior  palatal  arches.  Externally  they  are  separated  by  the 
pharyngeal  aponeurosis  and  the  superior  constrictor  muscle  from .  the  pharyngo- 
maxillary  space.  This  space  is  bounded  by  these  fibro-muscular  structures 
internally,  the  internal  pterygoid  muscle  externally,  and  the  antero-lateral  aspects  of 
the  bodies  of  the  second  and  third  cervical  vertebrae.  It  is  occupied  by  some  con- 
nective tissue  and  fat.  According  to  Zuckerkandl,  the  stylo-pharyngeus  and  stylo- 
glossus  muscles  divide  the  space  into  an  anterior  portion  in  relation  to  the  tonsil 
and  a  posterior  in  relation  to  the  internal  carotid  artery  and  internal  jugular  vein. 

Tonsillitis  in  the  lacunar  or  follicular  form  does  not  usually  involve  the  stroma 
of  the  gland,  the  infection  and  the  exudate  being  limited  to  the  tonsillar  crypts  and 
to  the  surface.  In  the  suppurative  form  the  infection  is  deeper,  the  stroma  is 
affected,  and  the  resulting  abscess  may  in  rare  cases  become  peritonsillar,  extend  to 
the  cellular  tissue  of  the  pharyngo-maxillary  space,  and  open  the  internal  carotid 
artery.  Usually,  as  the  infection  progresses,  even  if  this  space  is  invaded,  the  out- 
ward extension  is  limited  by  the  internal  pterygoid  muscle,  and  the  swelling  and  the 
ulceration  or  necrosis  take  the  line  of  least  resistance, — i.e. ,  towards  the  pharynx, 
where  tonsillar  abscesses  often  open  spontaneously. 

During  an  acute  tonsillitis  the  palato-glossus  and  its  covering  of  mucous  mem- 
brane, with  the  soft  palate  on  the  affected  side,  are  tense,  thinned,  and  spread  out 
over  the  surface  of  the  tonsil.  Abscesses  may  be  evacuated  by  incision  directly 
through  these  structures  and  from  above  downward  in  a  direction  parallel  with  the 
anterior  pillar, — that  is,  with  the  fibres  of  the  palato-glossus. 

The  vascular  relations  of  the  tonsil  should  be  remembered  in  this  operation  or 
in  tonsillotomy  for  hypertrophy.  The  internal  carotid  is  nearly  2.5  cm.  (i  in.) 
behind  and  to  the  outer  side  of  the  tonsil.  The  external  carotid  is  still  farther  re- 
moved, as  it  lies  outside  of  the  stylo-glossus  and  stylo-pharyngeus  muscles.  Its 
ascending  pharyngeal  branch  is  nearer  the  tonsil  than  either  of  the  main  trunks,  and 
in  a  case  of  accidental  wounding  by  a  foreign  body  has  been  the  source  of  fatal 
hemorrhage.  Wounding  of  the  tonsillar  branch  of  the  facial  artery  has  likewise 
proved  fatal  after  tonsillotomy,  and  either  this  vessel  or  the  facial  itself,  especially  if 
it  is  tortuous  where  it  passes  between  the  stylo-glossus  and  digastric  muscles,  is  prob- 
ably involved  in  cases  of  grave  hemorrhage  after  this  operation.  The  plexus  of 
lymphatics  surrounding  the  follicles  of  the  tonsils  communicates  directly  with  the 
deep  cervical  lymph-glands  behind  and  beneath  the  angle  of  the  jaw.  These  glands 
are  therefore  commonly  enlarged  in  affections  of  the  tonsils,  and  when  tender  and 
palpable  are  sometimes  mistaken  for  the  tonsils  themselves.  The  latter  cannot, 
however,  be  palpated  externally,  except  in  cases  of  new  growth,  as  the  resistance 
offered  by  the  constrictor,  the  internal  pterygoid,  and  other  structures  intervening 
between  the  tonsils  and  the  skin  causes  them  to  project  towards  the  pharynx.  This 
projection  may  be  a  cause  of  various  forms  of  ill  health  associated  with  deficient 
oxygenation,  of  chronic  pharyngitis  from  mouth-breathing,  of  thickened  articula- 
tion, and  even  of  alterations  in  the  facies  or  in  the  skeleton, — e.g. ,  "pigeon- 
breast"  (page  167). 


THE  (ESOPHAGUS.  1609 

The  deafness  often  associated  with  hypertrophied  tonsils  is  the  result  of  adenoid 
growth  in  and  about  the  Eustachian  tube.  The  intervention  of  the  soft  palate  pre- 
vents direct  pressure  by  the  enlarged  tonsil  upon  that  canal.  Reflex  spasmodic 
cough  may  follow  irritation  of  the  glosso-pharyngeal  filaments  by  inspissated  secre- 
tion within  the  follicles' ;  fetid  breath  often  results  from  the  decomposition  of  such 
secretion  ;  epithelial  necrosis  and  denudation  render  such  tonsils  a  common  seat  of 
entrance  of  various  infections,  as  the  tuberculous — emphasized  by  the  frequency 
with  which  the  cervical  glands  just  mentioned  are  the  first  to  enlarge  in  tuberculous 
adenitis  of  the  neck — or  those  streptococcic  or  staphylococcic  varieties  in  which 
acute  arthritis  (including  many  cases  of  so-called  "inflammatory  rheumatism")  or 
endocarditis  may  follow  a  trifling  "sore  throat." 

THE   (ESOPHAGUS. 

The  oesophagus  or  gullet  is  a  musculo-membranous  tube,  about  25  cm.  (10  in.) 
in  length,  connecting  the  pharynx  and  the  stomach.  It  begins  at  the  lower  border  of 
the  cricoid  cartilage  near  the  disk  between  the  sixth  and  seventh  cervical  vertebrae, 
about  15  cm.  from  the  incisor  teeth,  and  ends  below  the  diaphragm,  opposite  the  tenth 
(sometimes  the  eleventh)  thoracic  vertebra.  The  entrance  into  the  stomach  is  marked 
by  a  groove  on  the  left  of  the  gullet,  best  seen  when  the  organs  are  inflated.  There 
is  no  line  of  separation  on  the  right  when  the  parts  are  unopened.  The  form  and 
calibre  of  the  oesophagus  are  very  variable  and  uncertain.  Longitudinal  folds  are 
sometimes  found,  especially  in  the  upper  part,  which  give  the  cavity  a  star-shaped 
appearance  on  transverse  section.  Often  the  front  wall  lies  in  contact  with  the  back 
one  ;  at  the  lower  part,  however,  there  may  be  a  permanent  cavity.  Constrictions 
have  been  described  very  variously.  Probably  the  most  marked  occurs  at  the  very 
beginning,  with  a  diameter  of  perhaps  only  14  mm.  There  is  usually  one  at  the 
passage  through  the  diaphragm,  often  one  at  the  point  where  the  arch  of  the  aorta 
crosses  the  gullet,  and  another  where  the  latter  goes  behind  the  origin  of  the  left 
bronchus.  Mehnert l  has  described  thirteen  places,  at  any  one  of  which  there  may  be 
a  constriction.  They  correspond  to  the  points  of  entrance  of  the  arteries,  and,  accord- 
ing to  him,  have  a  metameric  significance.  Occasionally  the  oesophagus  is  much 
dilated,  the  diameter  exceeding  3  cm.  It  is  probably  constricted  in  life.  After 
passing  through  the  diaphragm  it  presents  a  funnel-like  expansion. 

Course  and  Relations. — Throughout  its  course  the  gullet  is  surrounded  by 
much  areolar  tissue  and  frequently  sends  fibres  from  its  muscular  coat  to  neighbor- 
ing parts.  While  following  the  general  direction  of  the  vertebral  column,  although 
not  closely,  below  the  bifurcation  of  the  trachea  the  gullet  lies  i  or  2  cm.  in  front 
of  the  spine.  Directly  after  its  beginning  it  inclines  to  the  left,  so  that  soon  it  pro- 
jects by  one-half  beyond  the  left  border  of-  the  trachea.  We  have  seen,  in  a  child, 
the  two  tubes  lie  side  by  side.  Just  above  the  bifurcation  of  the  trachea  the  oesophagus 
meets  the  arch  of  the  aorta,  which,  so  to  speak,  pushes  it  to  the  right  ;  it  lies,  how- 
ever, always  behind  the  beginning  of  the  left  bronchus,  while  to  a  less  degree,  or  even 
not  at  all,  it  is  in  relation  to  the  right  one.  Owing  to  the  influence  of  the  aorta,  the 
gullet  passes  farther  to  the  right;  but,  leaving  the  spine,  it  lies  behind  the  pericardium 
in  a  plane  somewhat  anterior  to  that  of  the  aorta,  and  near  the  diaphragm  sweeps  in 
front  of  the  aorta  to  the  left  of  the  median  line,  passes  into  the  abdomen  near  the 
lower  border  of  the  tenth  thoracic  vertebra,  and,  running  very  obliquely,  presently 
ends  in  the  stomach.  Hardly  more  than  i  cm. ,  which  lies  behind  the  left  lobe  of  the 
liver  and  in  front  of  the  left  pillar  of  the  diaphragm,  can  be  said  to  be  subdiaphrag- 
matic,  when  examined  from  without.  The  line  of  separation  between  the  oesophagus 
and  the  stomach,  however,  is  very  clear  on  the  inner  surface,  owing  to  the  sudden 
change  in  the  nature  of  the  epithelial  lining.  There  is  often  a  fold  on  the  left  of  the 
end  of  the  gullet,  usually  at  the  upper  and  back  part,  from  2-5  mm.  broad,2  which, 
perhaps,  acts  as  a  valve  against  regurgitation.  The  subdiaphragmatic  part  is  about 
3  cm.  long.  Sometimes  the  longitudinal  folds  of  the  gullet  seem  to  project  into  the 
stomach,  but  usually  it  ends  in  a  gradual  expansion. 

1  Verhandlung.  der  Anat.  Gesellschaft,  1898. 

J  Berry  and  Crawford  :  Journal  of  Anatomy  and  Physiology,  vol.  xxxiv.,  1900. 


i6io 


HUMAN   ANATOMY. 


At  first  the  oesophagus  lies  behind  the  trachea  on  the  prevertebral  fascia,  the 
lobes  of  the  thyroid  gland  touching  it  on  either  side.  As  it  descends  to  the  left,  the 
trachea  is  partly  on  the  right.  The  left  recurrent  laryngeal  nerve  runs  on  the  front. 
The  right  one  is  in  relation  with  only  the  very  beginning  of  the  gullet.  The  right 
inferior  thyroid  artery  is  against  it.  On  the  right  also  a  chain  of  lymphatics  in  the 
areolar  tissue  lies  very  close  to  it.  The  left  carotid  and  subclavian  arteries  are  very 
near  it,  if  not  in  actual  contact.  As  may  be  inferred,  the  gullet  and  the  aorta  are 

FIG.   1362. 


Superior  cornu  of  thyroid  cartilage 


Thyroid  body 

Left  common  carotid — 
Left  subclavian  artery- — 


Arch  of  aorta, 
Left  pulmonary  artery 

Left  bronchus 


Thyroid  body 

Right  common  carotid 

Right  subclavian  artery 


Innominate  artery 

— Trachea 

— Superior  vena  cava 


Right  bronchus 


Left  pulmonary  vein 


CEsophagus —  


Diaphragm — 

Cardiac  end  of  stomach 

Abdominal  aorta — 
Spleei 


Right  pulmonary  veins 


— Azygos  major  vein 


Diaphragm 
Inferior  vena  cava 

Posterior  surface  of 
liver 


Right  suprarenal  body 

.Right  kidney 


CEsophagus  and  related  structures,  seen  from  behind.    Lungs  have  been  pulled  aside  and  posterior  part  of  diaphragm 

removed. 

spirally  entwined.  The  thoracic  duct  and  the  vena  a/ygos  major  are  in  contact  with 
ii  from  the  diaphragm  to  above  the  roots  of  the  lungs,  the  former  lying  between  it 
and  the  aorta  as  far  as  the  level  of  the  aortic  arch,  the  latter,  at  first  more  posterior 
than  the  duct,  passing  as  it  rises  behind  the  oesophagus  and  finally  arching  forward 
close  to  its  right  side.  The  left  vena  azygos,  such  left  intercostal  veins  as  open  into 
the  azygos  major,  and  the  right  intercostal  arteries  pass  behind  the  gullet.  The  pneu- 
mogastrics  reach  it  in  thr  thorax  :  the  right  after  crossing  the  subclavian  artery  and 


THE  (ESOPHAGUS. 


1611 


the  left  after  crossing  the  aorta.  The  nerves  then  break  up  into  plexuses,  from  which 
they  emerge  near  the  diaphragm,  the  left  in  front,  the  right  behind  the  food-tube. 
On  entering  the  thorax,  the  oesophagus  is  in  contact  with  the  left  pleura,  and  con- 
tinues to  be  until  separated  from  it  by  the  aorta.  Behind  the  pericardium  it  is  in 
contact  with  the  right  pleura,  and  just  before  passing  through  the  diaphragm  it  is  in 
contact  with  both. 

Muscular  fibres  bind  the  oesophagus  to  various  neighboring  structures.  A  toler- 
ably constant  band  attaches  it  to  the  left  bronchus,  and  others  may  go  obliquely  to 
the  right  bronchus.  Several  irregular  bands,  mostly  muscular,  pass  from  it  to  various 
parts  of  the  pleurae  and  pericardium. 

Structure. — The  wall  of   the  oesophagus  (3.5-4  mm.  thick)  consists  of  four 


FIG.   1363. 


Epithelium 


Tunica  propria  of 
mucous  membrane 


:|V  •  ^^mi} 

^>,%l     V  4  '  >*%^;?SP  tf  t     Gland-ducts. 
>/§&>•'  •  <tnf*yi<'          -1^$5Sii«J'       obliquely  cut 

'»&•  s9S^  ••  >  •  -  -.%^t?kK  ^ 
^••A;^V  - ,„-.  v;>^, 

:^;;^  ,:.-, 
• 

^S  ••%;•      .Glands 


•'•^' 

•' 


.-* 


'*-*>.,      s^Submucous  coat 


^.Circular  bundles 
of  non-striated 
muscle 


Striated  fibres 


Longitudinal 
bundles  of  non- 
striated  muscle 


Bundles  of  striated  fibres 
Transverse  section  of  oesophagus,  junction  of  middle  with  upper  third.     X  25. 


layers,  which,  from  within  outward,  are  the  mucous,  the  submucous,  the  muscular, 
and  the  fibrous  coats. 

The  mticous  coat,  usually  thrown  into  longitudinal  folds,  is  composed  of  a  tunica 
propria  formed  of  fibrous  connective  tissue  and  delicate  elastica  and  covered  with 
stratified  squamous  epithelium.  Beneath  the  latter  the  surface  of  the  stroma-layer 
presents  longitudinal  ridges  and  papillae,  between  which  pass  the  ducts  of  the  glands  in 
their  course  to  the  free  surface.  The  deeper  part  of  this  layer  is  occupied  by  a  mus- 
cularis  mucostz,  the  involuntary  muscle  of  which  begins  at  the  cricoid  cartilage,  first 


l6l2 


HUMAN    ANATOMY. 


FIG.   1364. 


Lymph 

ide  in 


no 
mucosa 


appearing  in  the  continuation  of  the  elastic  lamina  of  the  pharynx.  At  the  upper  end 
only  slightly  developed,  the  muscularis  mucosae  becomes  more  robust  until  in  the 
lower  portion  of  the  oesophagus  it  is  conspicuous. 

The  submucous  coat,  between  the  mucous  and  muscular  layers,  although  consid- 
erable, is  not  dense,  and  therefore  allows  free  motion  of  the  former  upon  the  latter, 
as  well  as  the  formation  and  effacement  of  folds.  It  is  continuous  with  the  pharyn- 
geal  fascia  above. 

The  cesophageal  glands  are  of  two  kinds, — the  ordinary  mucous,  situated  within 
the  submucous  coat  and  scattered  throughout  the  length  of  the  tube,  and  special 
glands  within  the  tunica  propria  limited  to  the  two  ends  of  the  oesophagus.  The 
last  mentioned  correspond  in  structure  to  those  found  at  the  cardiac  orifice  of  the 
stomach  ;  they  are  therefore  known  as  the  upper  and  lower  cardiac  acsophageal  glands 
(J.  Schaffer). 

The  usual  secretory  structures  are  small  tubo-alveolar  mucous  glands  in  which 
mucus-producing  cells  are  alone  present,  crescents  of  serous  elements  being  absent. 
The  ducts  are  commonly  somewhat  tortuous,  and  often  present  dilatations  or  ampullae; 

the  smaller  tubes  are  clothed  with  simple 
columnar  epithelium.  In  the  larger  the 
epithelium  may  be  stratified,  and  near  the 
free  surface  assume  a  squamous  character. 
The  cardiac  glands  at  the  lower  end 
of  the  oesophagus  are  continuations  of 
those  situated  about  the  entrance  of  the 
gullet  into  the  stomach,  in  connection  with 
which  organ  they  are  more  fully  described 
(page  1624).  They  form  oval  or  pyrami- 
dal groups  of  branched  tubular  glands,  the 
bases  of  which  lie  against  the  muscularis 
mucosae,  the  narrow  parts  being  directed 
towards  the  free  surface  onto  which  their 
wavy  or  tortuous  ducts  open.  The  upper 
cardiac  glands  form,  according  to  Schaf- 
fer,1 a  constant,  though  variable,  group 
around  the  superior  end  of  the  oesophagus. 
Lymphatic  tissue  occurs  within  the 
mucosa  of  the  oesophagus  as  more  or  less 
distinct  aggregations.  Sometimes  these 
are  in  the  form  of  small  diffuse  areas  of 
infiltration  around  the  ducts  of  the  mucous  glands  ;  in  other  places,  especially  towards 
the  lower  end,  distinct  lymph-nodules  are  present  (Fig.  1364). 

The  muscular  coat  consists  of  an  inner  circular  and  an  outer  longitudinal  layer, 
although  the  disposition  of  the  individual  bundles  is  often  irregular  and  oblique,  and 
above  somewhat  intermingled.  In  the  upper  third  of  the  tube  the  muscular  tissue 
consists  entirely  of  striped  fibres,  the  circular  ones  being  continuous  with  the  simi- 
larly disposed  fibres  of  the  inferior  constrictor  of  the  pharynx.  The  longitudinal 
fibres  arise  from  a  tendon  attached  to  the  median  ridge  of  the  cricoid  cartilage  and 
to  the  fascia  covering  the  posterior  crico-arytenoid  muscles,  whence  they  descend 
to  embrace  the  gullet.  They  are  few  at  the  top  behind,  but  lower  down  the  circular 
and  longitudinal  layers  are  distinct  and  symmetrically  disposed.  Towards  the  middle 
of  the  oesophagus  the  muscular  coat  includes  both  the  striated  and  non-striated  form 
of  tissue,  the  involuntary  variety  gradually  predominating  until  in  the  lower  third  it 
alone  is  present. 

The  fibrous  coat  is  poorly  developed  above  the  diaphragm,  consisting  of  the 
areolar  tissue  which  connects  the  gullet  to  the  surrounding  structures.  After  piercing 
the  diaphragm,  the  peritoneal  investment  contributes  a  limited  serous  tunic  which  from 
this  point  on  is  well  represented. 

Vessels. — The  arfcn'cs  are  links  in  the  chain  running  the  whole  length  of  the 
alimentary  canal.     The  highest  are  from  the  inferior  thyroids,  succeeded  by  those 
1  Beitrage  zur  Histologie  mensch.  Organe,  Bd.  vi. 


Musculai 
tissue 


Section  of   mucous  membrane  of  oesophagus,  showing 
lymph-node.     X  55. 


PRACTICAL  CONSIDERATIONS:  THE  CESOPHAGUS.  1613 

from  the  thoracic  aorta  and  the  gastric.  The  veins  are  interesting  only  inasmuch 
as  the  upper  ones  open  into  the  azygos  system  and  that  of  the  inferior  thyroid  above 
and  the  gastric  system  below  ;  they  thus  form  a  communication  between  the  general 
and  the  portal  venous  systems.  The  lymphatics — not  numerous — go  to  the  nodes 
of  the  deeper  part  of  the  neck  and  of  the  posterior  mediastinum. 

Nerves  are  from  the  oesophageal  plexus. 

The  mechanism  of  the  closure  of  the  cardiac  end  of  the  stomach  is  most  properly 
considered  with  the  oesophagus,  depending  as  it  does  partly  on  the  direction  of  that 
tube,  partly  on  the  relation  of  the  diaphragm  to  it,  and  partly  on  the  folds  of  mucous 
membrane  at  its  orifice.  Frozen  sections  (Fig.  1372),  both  horizontal  and  frontal 
(Giibaroff1),  show  that  the  termination  is  almost  horizontal.  Dissections  of  the  dia- 
phragm from  above  demonstrate  that  the  arrangement  of  the  muscular  fibres  is  that  of 
a  sphincter,  although  a  weak  one.  The  projection  of  the  folds  into  the  stomach  is  a 
further  protection.  It  has  been  shown  that  the  cardia  will  resist  moderate  pressure 
from  below  upward,  but  will  yield  to  considerable  force.  The  action  of  the  longi- 
tudinal fibres  from  both  the  cricoid  cartilage  and  the  diaphragm  is  to  dilate  the  tube. 

PRACTICAL   CONSIDERATIONS  :    THE   CESOPHAGUS. 

Congenital  malformations  are  rare,  as  yet  unexplained  embryologically,  and  usu- 
ally fatal.  The  oesophagus  may  be  double,  deficient,  or  absent.  Most  commonly 
there  are  an  upper  cul-de-sac  and  a  lower  segment  opening  into  the  stomach,  some- 
times communicating  with  the  respiratory  passage.  Cases  in  which  there  has  been 
an  cesophago-pleuro-cutaneous  fistula  are  possibly  associated  with  this  malformation 
(MacLachlan,  Osier).  Congenital  diverticula  are  found,  and  Francis  suggests  three 
theories  for  their  occurrence  :  first,  that  they  might  be  analogous  to  the  diverticula 
which  were  found  in  some  of  the  Sauropsida  and  in  ruminant  animals,  forming  the 
first  two  compartments  of  the  stomach  ;  secondly,  that  they  were  fcetal  varieties 
analogous  to  the  oesophageal  diverticulum  from  which  the  larynx,  trachea,  and  lungs 
are  formed  ;  and  thirdly,  that  they  resulted  from  a  failure  in  the  internal  closure  of 
a  branchial  cleft  (May lard). 

The  curves,  distensibility,  and  constrictions  of  the  normal  oesophagus  and  its 
relations  to  surrounding  structures  are  of  importance  with  reference  to  foreign 
bodies,  to  stricture,  to  disease  of  the  gullet  with  possible  extension  to  neighboring 
organs,  or  to  extrinsic  disease  involving  the  oesophagus  either  by  mechanical  pressure 
or  traction  or  by  extension  to  its  walls. 

Foreign  bodies,  if  moderately  smooth  or  regular  in  shape,  are  apt  to  be  arrested 
at  one  of  the  three  relatively  constricted  portions, — i.e.  (i),  and  most  commonly, 
at  the  commencement,  15  cm.  (6  in.)  from  the  incisor  teeth,  which  (with  the  head 
midway  between  flexion  and  extension)  is  opposite  the  lower  edge  of  the  cricoid 
cartilage  and  the  sixth  cervical  vertebra.  At  this  point  its  average  diameter  is  14 
mm.  (approximately  ^  in. )  ;  foreign  bodies  arrested  here  are  really  in  the  lower 
pharynx.  (2)  At  the  point,  about  10  cm.  (4  in.)  lower,  where  the  left  bronchus 
crosses  the  oesophagus  and  where  the  lumen  is  again  lessened  by  pressure  (the  dis- 
tance occupied  by  the  left  bronchus  in  crossing  the  oesophagus  is  about  2.5  cm.). 
(3)  At  the  diaphragmatic  opening,  where  the  diameter  is  once  more  reduced  to 
14  mm.  by  the  constriction  of  the  muscular  and  tendinous  fibres  surrounding  the 
opening.  This  point  is  about  12.5  cm.  (5  in.)  below  the  level  of  the  left  bronchus, 
and  therefore,  approximately,  38  cm.  (15  in.)  from  the  incisor  teeth.  The  majority 
of  foreign  bodies  that  pass  completely  from  the  pharynx  and  are  arrested  in  the 
oesophagus  are  stopped  at'  or  about  the  level  of  the  left  bronchus.  Many  of  them 
can  be  extracted  through  the  mouth  by  suitable  instruments  ;  others  require  an 
cesophagotomy,  which  may  be  done  through  an  incision  along  the  anterior  border 
of  the  left  sterno-mastoid  muscle  from  the  cricoid  cartilage  to  the  sternum.  The 
longitudinal  fibres  of  the  oesophagus  will  be  recognized  a  little  to  the  left  of  the 
trachea,  at  the  bottom  of  the  space  between  the  sterno-thyroid  muscle  and  the 
common  carotid  artery.  An  oesophageal  bougie  passed  through  the  mouth  will  aid 
in  the  recognition  of  the  tube. 

1  Arch,  fur  Anat.  und  Phys.,  Anat.  Abtheil.,  1885. 


i6i4  HUMAN   ANATOMY. 

The  recurrent  laryngeal  nerve  lying  in  the  groove  between  the  trachea  and 
oesophagus  should  be  avoided,  as  should  the  superior  and  inferior  thyroid  arteries 
which  run  across  the  deeper  part  of  the  wound. 

With  the  additional  help  of  a  gastrotomy,  digital  exploration  (with  perhaps  the 
disengagement  of  impacted  foreign  bodies)  is  possible  throughout  at  least  the  lower 
two-thirds  of  the  gullet.  If  the  impaction  is  near  the  cardiac  end,  gastrotomy  alone 
may  suffice. 

Mediastinal  or  posterior  cesophagotomy  has  been  done  on  both  the  left  and 
right  sides  by  resection  of  three  or  four  ribs  (third  to  eighth),  pushing  the  parietal 
pleura  to  One  side.  The  pleura  on  the  left  side  is  more  easily  displaced  than  that  on 
the  right,  which  extends  across  the  median  line  as  far  as  to  the  right  of  the  thoracic 
aorta. 

Strictures  from  escharotics  or  from  trauma  of  foreign  bodies  may  occur  at  any 
point,  but  are,  for  obvious  reasons,  most  often  found  at  the  upper  end.  Compression 
of  the  oesophagus,  giving  rise  to  the  clinical  phenomena  of  stricture,  may  be  sec- 
ondary'to  enlargement  of  the  thyroid  body  or  of  the  bronchial  lymph-glands,  to 
tumors  of  the  mediastinum,  to  disease  of  the  lower  cervical  or  upper  dorsal  verte- 
brae, or  to  aortic  aneurism.  The  measurement  from  the  incisor  teeth  to  the  seat  of 
the  narrowing,  and  comparison  with  the  cesophageal  relations  at  that  point,  may  be 
of  great  service  in  diagnosis. 

Carcinoma  is  the  chief  disease  by  which  the  gullet  is  attacked.  It  is  found 
most  often  at  either  the  upper  or  lower  end  of  the  tube  in  accordance  with  its  predi- 
lection for  sites  where  epithelium  changes  in  character,  as  at  the  various  muco- 
cutaneous  outlets  of  the  body.  It  is  also  not  infrequent  at  the  region  where  the 
left  bronchus  crosses.  It  may  extend  by  continuity  to  the  pharynx  or  stomach  or 
to  any  of  the  structures  with  which  the  oesophagus  is  in  close  contact,  or  it  may 
spread  to  the  bronchial  or  mediastinal  lymph-glands. 

Extrinsic  disease  may  not  only  (as  in  the  case  of  tumors  or  of  aneurism)  affect 
the  oesophagus  by  causing  compression  of  its  walls  (vide  supra},  but  may  open  it  by 
pressure-necrosis  or  ulceration,  or  may  involve  it  in  the  extension  of  the  disease,  as 
in  cases  of  tracheal,  bronchial,  or  pulmonary  suppuration  or  gangrene,  or  of  verte- 
bral caries. 

Disease  extending  from  the  left  lung  or  pleura  to  the  oesophagus,  or  in  the 
reverse  direction,  is  more  apt  to  affect  the  upper  portion  of  the  gullet  on  account  of 
its  closer  relation  to  the  pleural  sac  on  the  left  side.  Below  it  is  in  more  intimate 
relation  to  the  right  pleura. 

Diverticula  of  the  oesophagus,  when  acquired,  may  be  due  to  (a)  pressure 
from  within,  as  in  the  region  just  above  a  stricture,  or  oftener  on  the  posterior  wall 
at  the  pharyngo-oesophageal  junction.  At  this  point  the  inferior  constrictor  and  the 
circular  fibres  of  the  oesophagus — both  horizontal  in  direction — fuse  ;  it  is  a  point  of 
marked  constriction  ;  the  cricoid  cartilage  in  front  is  movable  and  non-resistant. 
In  whatever  situation  found  they  are  apt  to  be  in  effect  a  hernia  of  the  mucous  and 
submucous  tissues  through  the  thinned  and  weakened  muscular  fibres  of  the  oesoph- 
agus or  of  the  inferior  constrictor  ;  or  they  may  be  due  to  (b')  traction  from  without. 
as  in  cases  of  bronchial  lymphadenitis,  in  which  adhesions  and  subsequent  ricatridal 
contraction  have  dragged  the  wall  out  into  a  pouch.  It  is  apparent  that  tin-  aim rior 
wall  in  the  neighborhood  of  the  bifurcation  of  the  trachea  and  of  the  left  bronchus 
is  most  likely  to  be  thus  affected. 

The  recorded  cases  in  which  hemorrhage  into  the  oesophagus  has  taken  place 
from  the  ascending  portion  of  the  aorta,  the  innominate  artery,  and  the  superior  vena 
cava  will  readily  be  understood.  The  relation  of  the  oesophagus  just  below  the 
aortic  arch  to  the  pericardium  and  left  auricle  explains  the  dysphagia  soim •tinu-s 
seen  in  pcricardial  dropsy  or  in  cardiac  enlargement  when  the  patient  is  supine,  as 
well  as  the  cases  in  which  foreign  bodies  impacted  in  the  oesophagus  have  wounded 
the  heart. 

In  a  general  way  it  may  be  said  that  the  upper  or  tracheal  curve  'or  segment 
of  the  oesophagus  is  most  liable  to  invasion  by  diseased  conditions  from  without  and 
to  obstruction  from  within,  and  the  lower  or  aortic  curve  is  relatively  free  from 
liability  to  external  pressure  or  intrinsic  occlusion  (Allen). 


THE  ABDOMINAL  CAVITY.  1615 

In  the  use  of  cesophageal  instruments  the  normal  curves,  measurements,  and 
constrictions  should  be  remembered,  as  should  the  possible  relation  of  abnormal 
narrowing  to  abscess,  aneurism,  or  thoracic  disease.  The  curve  made  by  the  roof 
of  the  mouth,  the  pharynx,  and  the  beginning  of  the  oesophagus  should  be  some- 
what straightened  out  by  throwing  the  patient's  head  slightly  back  ;  the  tongue  and 
anterior  pharyngeal  wall  should  be  pulled  forward  or  pushed  in  that  direction  by  a 
ringer  in  the  pharynx.  The  point  of  the  instrument  should  be  guided  past  the 
epiglottis  and  brought  in  contact  with  the  posterior  wall  of  the  pharynx  before  it  is 
pushed  downward.  This  wall — like  the  upper  wall  of  the  urethra — is  the  more 
fixed  and  should  guide  the  instrument  safely  into  the  gullet,  except  in  cases  of 
pressure  of  diverticula.  The  beginning  of  the  procedure  may  be  facilitated  by 
voluntary  deglutition  on  the  part  of  a  non-anaesthetized  patient. 

In  some  cases,  especially  in  children,  it  is  preferable  to  pass  the  instrument 
through  the  nose  to  avoid  the  struggle  to  keep  the  mouth  open. 

THE   ABDOMINAL   CAVITY. 

The  general  shape  of  the  abdominal  cavity  is  best  understood  by  dividing  it  into 
three  imaginary  zones,  one  above  the  lumbar  region  of  the  spine,  one  opposite  to  it, 
and  one  below  it.  The  anterior  wall  is  but  slightly  convex.  The  upper  zone, 
excepting  a  small  part  in  front,  is  within  the  cage  of  the  thorax,  from  which  it  is 
separated  by  the  dome  of  the  diaphragm,  the  lower  part  of  which  is  nearly  vertical 
and  posterior  to  the  abdominal  viscera.  This  zone  is  very  capacious.  The  second 
zone,  bounded  behind  by  the  convexity  of  the  lumbar  spine,  which  is  broadened  on 
each  side  by  the  psoas  muscle,  is  very  shallow  in  the  middle,  the  antero-posterior 
diameter  not  being  more  than  5  cm.  (2  in.).  At  the  sides  it  is  deep,  extending  into 
the  hollow  of  the  lower  ribs.  Thus  it  presents  two  deep  lateral  recesses  connected  by 
a  shallow  median  portion.  The  lowest  zone,  below  the  promontory  of  the  sacrum, 
consists  in  the  middle  of  both  abdominal  cavity  proper  and  of  the  cavity  of  the  true 
pelvis  ;  for,  owing  to  the  inclination  of  the  pelvis,  the  promontory  is  near  the  level 
of  the  anterior  superior  spines  of  the  ilia.  On  each  side  of  this  deep  median  portion 
the  lower  zone  is  bounded  behind  by  the  shallow  iliac  fossae,  rendered  yet  more  so 
by  the  ilio-psoas  muscles.  The  deep  lateral  divisions  of  the  middle  zone  pass  with- 
out interruption  into  these  shallow  ones. 

It  has  been  so  long  the  custom  to  divide  the  abdomen  into  nine  regions  by 
drawing  two  vertical  and  two  transverse  lines  on  the  anterior  wall,  that  the  names 
applied  to  these  conventional  regions  must  be  retained  for  general  and  vague  use, 
although  the  method  is'  worthless  for  accurate  description.1  Hardly  two  authorities 
agree  as  to  the  location  of  the  lines,  but  for  general  purposes  the  following  suffices. 
Draw  a  vertical  line  upward  from  the  middle  of  Poupart's  ligament  on  each  side. 
Let  the  upper  transverse  line  cross  these  at  their  points  of  contact  with  the  lower 
borders  of  the  costal  cartilages  ;  let  the  lower  line  connect  the  anterior  superior  spines 
of  the  ilia.  The  three  middle  regions  thus  mapped  out  are  named,  from  above  down- 
ward, epigastric,  umbilical,  and  hypogastric ;  the  lateral  ones,  the  right  and  left 
hypochondriac,  lumbar,  and  iliac.  The  advantage  of  this  method  is  that  the  vertical 
lines  approximately  represent  the  borders  of  the  median  divisions  of  the  two  lower 
zones,  and  the  lower  cross-line  is  near  the  level  of  the  sacral  promontory. 

The  abdominal  cavity  is  lined  by  a  serous  membrane,  the  peritoneum,  which,  in 
addition  to  covering  the  walls  of  the  space,  forms  a  more  or  less  extensive  investment 
for  the  abdominal  organs.  The  latter,  however,  all  lie  really  without  the  cavity  of 
the  peritoneal  sac,  the  serous  membrane  being  pushed  in  by  the  viscera.  When  the 
latter  remain  attached  to  the  body-wall,  as  the  kidneys,  the  peritoneal  reflection  is 
limited  ;  if,  on  the  contrary,  the  organ  becomes  otherwise  free,  as  the  small  intestine, 
the  serous  covering  forms  practically  a  complete  investment.  The  latter  is,  however, 
never  absolutely  complete,  since  there  is  always  an  uncovered  area  through  which 
the  blood-vessels,  lymphatics,  and  nerves  reach  the  organs.  The  detailed  description 
of  the  complex  relations  of  the  peritoneum  will  be  given  later  (page  1740)  ;  suffice  it 

1  The  information  conveyed  by  this  method  is  of  the  same  nature  as  that  given  by  saying 
that  Boston  is  north  of  Washington  and  Chicago  west  of  it. 


i6i6 


HUMAN    ANATOMY. 


now,  in  anticipation  of  the  references  to  peritoneal  relations  which  necessarily  follow 
in  the  consideration  of  the  organs,  to  point  out  that  the  parietal  and  visceral  portions 
of  the  serous  membrane  are  continuous,  the  former  investing  the  abdominal  walls, 
the  latter  the  organs.  The  peritoneal  folds  passing  from  a  viscus  to  the  body-wall 
have  received  in  many  cases  the  name  ligaments,  although  often  such  bands  con- 
tribute little  support.  The  intestinal  canal  was  originally  attached  to  the  abdominal 
wall  by  a  fold  covering  vessels  and  nerves  named  the  mesentery,  parts  of  which  per- 

FIG.  1365. 


Infraclavicular  fossa 
Coracoid  process 


Groove  between  deltoid — -j 
and  pectoralis  major 


X-rib  cartilage 
Duodenum 


Linea 

semilunaris 
Ascending 
colon 


Anterior  superior  iliac  spine 
Line  of  Poupart's  ligament 


Suprasternal  notch 

^Clavicle 
Sternum 

Aeromion 


Deltoid 

Left  lung 


Ensifortn  cartilage 

Infrasternal 
depression 

Spleen 


Stomach 


Vermiform 


Spermatic  cord  emerging 
at  external   abdomi 
ring 


Anterior  surface  of  body,  drawn  from  photograph.    General  relations  of  thoracic  and  abdominal  organs  to  body-wall 

are  shown  by  colored  outline. 


sist  as  free  folds,  while  others  fuse  with  the  abdominal  walls.  The  term  incscntcn'  is 
vaguely  applied  to  that  portion  going  to  the  jejuno-ileum,  while  other  parts  are  distin- 
guished by  tin-  name  of  the  part  of  the  intestine  to  which  they  are  attached,  as  HICSD- 
colon.  The  term  onicntuin  is  applied  to  folds  attached  to  the  stomach,  as  the  gastro- 
hepatic  cnio/fiiin.  The  peritoneal  sac  is  entirely  closed,  except  in  the  female  at  the 
upper  end  of  the  oviduct,  where  the  mucous  membrane  of  the  tube  and  the  serous 
lining  are  directly  continuous.  The  opposed  smooth  walls  of  the  peritoneal  sac  are 


THE  STOMACH.  1617 

in  contact  and  lubricated  with  a  thin  layer  of  serous  fluid,  secreted  by  the  membrane, 
by  which  friction  between  the  organs  and  movable  surfaces  is  reduced  to  a  minimum. 

The  serous  membrane,  consisting  of  the  endothelium  and  the  fibro-elastic  tunica 
propria,  is  attached  to  the  subjacent  fasciae  of  the  abdominal  wall  and  the  organs  by 
a  layer  of  subperitoneal  tissue,  an  areolar  stratum  forming  a  more  or  less  intimate 
connection  between  the  serous  coat  and  the  structures  which  it  covers. 

The  relations  and  attachments  of  the  peritoneum  observed  in  the  adult  are  in 
some  places  entirely  different  from  those  existing  in  early  life  ;  hence  the  history  of 
the  changes  occurring  during  development  is  essential  for  understanding  the  complex 
relations  found  at  later  periods. 

PLAN   OF   THE   DIGESTIVE   TRACT   BELOW   THE   DIAPHRAGM. 

The  subcliaphragmatic  digestive  tube  is  divided  into  the  stomach,  the  small  intes- 
tine, and  the  large  intestine.  The  small  intestine  is  subdivided  into  the  duodemim  and 
the  jejuno-ileum.  The  former  of  these  is  an  imperfect  ring  or  horseshoe-shaped 
portion  from  25—30  cm.  (10-12  in.)  long,  all  of  which,  except  the  first  inch  or  two, 
lies  on  the  posterior  abdominal  wall  behind  the  peritoneum  in  the  adult  ;  then  comes 
something  over  6  m.  (usually  about  21.5  ft. )  of  intestine  thrown  into  folds  by  its 
attachment  to  the  free  edge  of  the  mesentery.  The  upper  two-fifths  of  this  is  called 
the  jejunum  and  the  rest  the  ileum ;  but,  as  the  division  is  absurd,  it  is  better  to 
speak  of  this  portion  of  the  small  intestine  as  the  jejuno-ileum,  sometimes  alluding 
to  the  upper  part  as  jejunum  and  to  the  lower  as  ileum.  It  ends  at  the  right  iliac 
fossa  by  joining  the  large  intestine,  a  little  over  1.5  m.  (usually  about  5.5  ft.)  long, 
which  is  subdivided  into  the  c&cum,  a  blind  pouch,  and  the  colon,  which  is  ascend- 
ing in  the  right  flank,  transverse  across  the  middle  of  the  abdomen,  and  descending 
on  the  left.  This  is  followed  at  the  crest  of  the  ileum  by  the  sigmoid  flexure,  a  free 
fold  attached  to  the  left  of  the  pelvis,  usually  reckoned  as  a  part  of  the  colon,  which, 
after  crossing  the  left  sacro-iliac  joint,  descends  in  the  hollow  of  the  sacrum,  to 
become  the  rectum  at  the  third  sacral  vertebra.  The  termination  of  the  gut,  passing 
through  the  thickness  of  the  floor  of  the  pelvis,  is  the  anal  canal.  Two  large  glands 
— the  liver  and  the  pancreas — pour  their  secretions  into  the  second  part  of  the  duo- 
denum, from  which  they  originally  sprouted. 

The  liver,  the  stomach,  and  the  spleen  occupy  nearly  all  the  space  in  the  dome- 
like upper  zone  of  the  abdomen  ;  the  right  kidney,  caecum,  and  ascending  colon 
on  the  right,  the  left  kidney  and  the  descending  colon  on  the  left,  occupy  the  lower 
lateral  recesses,  leaving  the  middle  space — shallow  in  the  umbilical  region  and  deep 
below  it — for  all  the  rest  of  the  intestines,  except  such  parts  as  can  be  squeezed  into 
the  preceding  regions,  and  for  the  greater  part  of  the  pancreas. 

THE   STOMACH. 

The  stomach,  the  most  dilated  part  of  the  digestive  tube,  follows  the  oesopha- 
gus, lying  in  the  upper  part  of  the  abdomen  below  the  diaphragm  on  the  left,  and 
passing  downward  and  inward  across  the  median  line.  In  the  early  embryo  it  is  a 
tubular  dilatation,  but  it  becomes  flattened  from  side  to  side  and  the  posterior 
border  develops  excessively,  so  that  it  rises  above  the  upper  opening  and  descends 
below  the  lower  one.  The  stomach  also  swings -on  its  long  axis,  so  that  its  posterior 
border  is  carried  to  the  left  and  the  original  left  side  to  the  front.  The  lesser  curva- 
ture is  that  part  of  the  right  border  of  the  stomach  between  the  two  orifices.  It  is 
straight  or  nearly  so,  and  runs  downward  and  forward  to  near  its  end,  when  it  rises 
and  passes  to  the  right.  The  lesser  omentum,  originally  the  anterior  mesentery,  is 
attached .  to  it.  The  greater  curvature  is  more  difficult  to  define.  It  is  usually 
erroneously  described  as  identical  with  the  line  of  attachment  of  the  greater  omentum. 
It  is  more  accurate  to  define  it  as  the  line  from  one  orifice  to  the  other  which  passes 
along  the  left  side  of  the  stomach  and  separates  the  anterior  from  the  posterior 
aspect.  The  greater  omentum — the  original  posterior  mesentery — is  attached  to  the 
greater  curvature  all  along  except  at  the  upper  part,  where  it  passes  onto  the  pos- 
terior surface. 


i6i8 


HT.MAX    ANATOMY. 


FIG.  1366. 


Gastro-phrcnic 
ligament 

Oesophagus 


Gastro-hepatic 

omentuni  — 


Fundus 


Pylorus 


The  shape  of  the  stomach  may  be  compared  to  that  of  a  pear,  somewhat  flat- 
tened, with  the  large  end  up  and  the  point  bent  to  the  right.  The  fundus  is  the 
highest  part  of  the  stomach  which  projects  upward  above  the  level  of  the  end  of  the 
oesophagus.  The  greatest  breadth  of  the  stomach  is  at  about  the  level  of  the  oeso- 
phageal  or  cardiac  orifice,  and  exceeds  the  antcro-posterior  diameter.  The  fundus 
generally  contains  air,  if  nothing 
else,  and  is  somewhat  distended, 
although  thrown  into  uncertain 
contours  by  the  partial  contraction 
of  its  walls.  Towards  the  lower 
or  pyloric  end  the  stomach  gradu- 
ally becomes  more  tubular,  but 
the  termination  is  often  dilated 
into  a  cavity  known  as  the  antrum 
Pylori.  The  constriction  on  its 
left  may  be  very  slight,  so  that 
the  antrum  is  hardly  to  be  seen, 
or  it  may  be  so  deep  as  to  be 
mistaken  for  the  pylorus.  The 
antrum  may  be  double  or  even 
triple.  Sometimes,  on  the  other 

hand,     the     terminal    part    of     the  Anterior  aspect  of  stomach,  moderately  distended. 

stomach  is  tubular  and  to  be  dis- 
tinguished from  the  intestine  only  by  its  thick  walls.  Fig.  1368  shows  such  a  case 
which  seems  to  extend  beyond  the  usual  limits  of  the  stomach.  The  superior  or 
cardiac  orifice  faces  upward  and  to  the  right,  being  much  nearer  the  front  than  the 
back  of  the  stomach.  Its  diameter  is  at  least  2  cm.  and  may  be  much  more.  When 
the  stomach  is  distended  a  well-defined  grpove  appears  between  the  fundus  and 
the  left  of  the  oesophagus.  Further  details  have  been  given  with  the  gullet  (page 
1609).  The  position  of  the  lower  orifice  or  pylorus  may  not  be  recognizable  on  the 
outer  surface,  or  it  may  be  marked  by  a  groove.  Internally,  it  presents  a  distinct 
ring  caused  by  the  thickening  of  the  layer  of  circular  muscular  fibres,  improperly 
called  the  valve  of  the  pylorus,  which  raises  the  mucous  membrane.  This  can 
always  be  felt  through  the  walls.  It  is  only  by  touch  that  the  position  of  the  pylorus 

can  be  certainly  recognized   when  the 
FIG.   1367. 

Greater 
omentum  (cut) 

— 


Antrum 


Gastro-splenic 
omentum 


Fundus 


parts  are  unopened.  The  gastric  cavity 
gradually  narrows  towards  the  pylorus 
on  the  stomach  side,  but  from  the  duo- 
denum there  seems  to  be  a  perforated 
partition  across  the  tube  like  an  optical 
diaphragm.  The  opening,  although 
nearly  always  elliptical,  is  sometimes 
almost  circular.  Some  of  the  larger 
openings  in  a  series  of  thirty  casts ' 
show  a  long  diameter  of  from  17-18  mm. 
and  a  short  one  of  from  13-15  mm. 
Some  of  the  smaller  openings  measure 
6x7  mm.  and  8x8  mm.  We  have 
observed  more  extreme  figures  at  both 
ends  of  the  series  than  those  quoted. 
It  is  difficult  to  say  whether  some  of 
the  smaller  ones  would  admit  of  greater 
dilatation.  Probably  13x15  mm.  is 
not  far  from  the  average  size.  The 
position  of  the  longer  axis  of  the  orifice  is  uncertain,  although  it  usually  runs  down- 
ward and  backward.2 

Owing  to  the  difference  in  size  of  the  two  ends  of  the  organ,  the  axis  of  the 

1  I  hviirht  :  Journal  of  Anatomy  and  Physiology,  vol.  xxxi.,  1897. 
Berry  ana  Crawford  :  Ibid.,  vol.  xxxvi.,  1902. 


Gastro-phrenic 

ligament >f 

Uncovered — - 

area 
CEsophagus « 


Posterior 
surface 

Gastro-ln-]i:itif 
omentum 


Pylorus 


Superior  aspect 


Antrum 


rh,  moderately  distended. 


THE  STOMACH. 


1619 


FIG.   1368. 


Pyloru; 


Outline  of  stomach  with 
constricted  and  greatly  elon- 
gated pylorus. 


stomach  is  necessarily  oblique,  although  the  lesser  curvature  is  vertical  until  near  its 
end.  The  axis  slants  downward  and  to  the  right  as  well  as  forward,  the  pyloric 
portion  being  disregarded.  The  stomach  is  sometimes  comparatively  tubular,  the 
fundus  being  but  little  developed,  although  the  cardiac  opening  is  always  on  the 
right  side.  This  is  a  continuation  of  the  fcetal  form,  and  is  more  often  seen  in 
women.  There  is  often  (possibly  normally)  a  hint  of  a  con- 
striction about  the  middle. 

The  above  description,  which  is  essentially  the  conven- 
tional one,  is  that  of  a  distended  stomach.  The  constrictions 
marking  off  a  single,  double,  or  even  triple  antrum  pyloris 
are  due  to  the  contraction — which  generally  persists  for  some 
hours  after  death — of  bundles  of  the  circular  fibres.  Such 
constrictions  sometimes  become  fixed.  The  true  shape  of 
the  stomach  in  life  when  non-distended  is  very  different,  but 
not  yet  thoroughly  known.  It  is  rather  tubular,  owing  to 
the  contraction  of  the  muscles  in  its  walls.  The  fundus  is 
puckered  and  more  or  less  constricted  off  from  the  rest,  as  is 'shown  by  the  study 
of  hardened  bodies  (Fig.  1369). 

Weight  and  Dimensions. — Not  only  is  the  normal  development  of  the 
stomach  very  variable,  but  it  is  impossible  to  define  the  limits  between  the  normal 
and  the  pathological  ;  naturally,  therefore,  statements  differ  widely  and  are  of  little 
value.  According  to  Glendinning,  the  weight  is  127  gm.  (4^  oz. )  for  man  and  a 
little  less  for  woman.  The  greatest  length,  directed  nearly  vertically,  is  some  25  cm. 
(10  in.  ),  the  greatest  breadth  from  10-12  cm.  (4-5  in.  ),  and  its  diameter  from  before 
backward  from  7.5-10  cm.  (3-4  in.).  The  average  adult  capacity  is  said  to  range 
from  600-2000  cc.  (1.25-4.25  pints),  with  an  average  of  1200  cc.  (2.50  pints). 

Peritoneal  Relations. — The  greater  omentum,  the  original  posterior  mesen- 
tery, passes  to  the  back  of  the  stomach  just  to  the  left  of  the  oesophagus,  where  its 
layers  diverge  so  as  to  leave  a  small  triangular  part  behind  it  attached  to  the  dia- 
phragm without  peritoneal  covering.  The  lower  of  the  diverging  lines  runs  to  the 
lesser  omentum.  The  line  of  attachment  then  passes  across  the  posterior  surface  of 
the  fundus  near  the  top,  but  posterior  to  the  greater  curvature.  At  the  left  of  the 
stomach  the  line  of  insertion  is  at 

the  greater  curvature,  and  continues  FIG. 

so  till  it  reaches  the  pylorus.  The 
fold  passing  to  the  diaphragm  at 
the  beginning  is  the  gastro-phrenic 
ligament.  This  is  joined  by  the 
gastro-pancreatic  fold  on  the  pos- 
terior abdominal  wall  which  con- 
veys the  coronary  artery  to  the 
right  of  the  cardiac  opening.  This 
last  fold  is  important  in  relation  to 
the  topography  of  the  peritoneum, 
but  not  to  the  stomach.  The  lesser 
omentum  is  attached  along  the 
whole  of  the  lesser  curvature,  ex- 
cept that  its  posterior  layer  may 
leave  it  below  the  cardia  to  join  on 
the  back  of  the  stomach  the  layer 
of  the  greater  omentum  which  forms 
the  inferior  border  of  the  non-serous 
triangle.  With  the  exception  of  this  triangle,  and  of  the  trifling  interval  between 
the  lines  of  attachment  of  the  omenta,  the  whole  organ  is  invested  by  peritoneum. 

Position  and  Relations. — The  cardiac  opening  is  opposite  the  tenth  thoracic 
vertebra  and  not  far  from  the  level  of,  but  from  8-10  cm.  (3-4  in.)  behind,  the  sixth 
left  costal  cartilage,  about  12  mm.  (*/>  in.)  to  the  left  of  the  median  line.  The 
lesser  curvature  descends  vertically  in  an  antero-posterior  plane,  parallel  to  the  left 
border  of  the  ensiform,  but  slanting  strongly  forward,  until  it  suddenly  turns  to  the 


Fundus 


Pylorus 


Stomach  with  puckered  fundus,  seen  from  behind  and  somewhat 
from  left  ;  hardened  by  formalin. 


i62o  HUMAN   ANATOMY. 

right,  rises,  and  ends  opposite  the  space  between  the  ensiform  and  the  end  of  the 
eighth  or  ninth  right  costal  cartilage,  on  a  level  with  the  first  lumbar  vertebra  or  the 
disk  below  it,  about  1.2  cm.  (^  in.)  from  the  median  line.  The  pyloric  orifice  is 
affected  to  such  an  extent  by  changes  incident  to  variations  in  distention  that  it 
is  manifestly  impossible  definitely  to  fix  the  position  of  the  lower  end  of  the  stomach. 
The  pylorus  is  usually  separated  from  the  anterior  abdominal  wall  by  the  over- 
lapping liver,  when  the  stomach  is  empty  lying  near  the  mid-line.  According  to 
Addison,  a  point  12  mm.  (^  inch)  to  the  right  of  the  median  plane  midway  between 
the  top  of  the  sternum  and  the  pubic  crest  will  ordinarily  correspond  to  the  position 
of  the  pylorus.  The  fundus  is  at  the  top  of  the  left  side  of  the  abdomen  un'der  the 
diaphragm,  reaching  the  level  of  the  sternal  end  of  the  fifth  costal  cartilage.  The 
anterior  surface,  looking  upward  as  well  as  forward,  is  covered  by  the  left  and  quad- 
rate lobes  of  the  liver.  A  varying  part  of  it  touches  the  diaphragm  in  front  of  the 
former.  The  extent  of  this  must  depend  on  the  size  of  both  organs.  The  liver  may 
separate  it  entirely  from  that  part  of  the  diaphragm  below  the  pericardium,  or  the 
stomach  may  be  against  the  diaphragm  in  the  anterior  part  of  this  region.  A  small 
triangular  part  of  the  stomach,  normally  in  contact  with  the  front  wall  of  the  abdo- 
men, bounded  below  by  the  greater  curvature,  is  seen,  on  opening  the  abdomen, 
between  the  liver  and  the  line  of  the  left  costal  cartilages.  This  appearance  gave 
rise  to  the  old  error  that  the  stomach  is  placed  transversely.  According  to  Tillaux, 

the   stomach    in    its    most  con- 

FIG.  1370.  tracted  state  always  descends  to 

a  line  between  the  ends  of  the 
ninth  costal  cartilages.  The  pos- 
Non-peritoneal  area  terior  surface,  forming  a  part  of 
the  anterior  wall  of  the  lesser 
peritoneal  cavity,  rests  against 
the  transverse  mesocolon,  which 
lies  on  the  organs  at  the  back  of 

-Lesser  omentum 

that  space,  so-  as  to  make  a  part 
of  the  concavity  for  it  which  Bir- 
mingham1  has   well    called    the 
-pylorus  stomach-bed  (Fig.  1371).     This 

hollow  is  made  by  the  diaphragm 
on  the  left  of  the  aorta,  by  the 

left  Suprarenal   capsule,   the  gas- 
Posterior  aspect  of  stomach  at  birth,  showing  peritoneal  relations,        trie    surface   of    the    spleen,    t 

antero-superior    surface   of    the 

pancreas,  and  usually  by  the  upper  part  of  the  left  kidney,  although  exceptionally 
this  may  be  shut  off  from  the  stomach  by  the  spleen  and  pancreas.  The  left  crus 
of  the  diaphragm  makes  a  deep  indentation  in  the  stomach  to  the  left  of  the  car- 
dia.  The  cceliac  axis  and  the  semilunar  ganglia  are  rather  to  the  right  of  the  lesser 
curvature.  The  transverse  mesocolon  continues  the  lower  part  of  the  stomach-bed 
forward  to  the  transverse  colon,  which  lies  below  the  stomach,  following  its  curve 
when  the  stomach  is  distended.  The  splenic  flexure  of  the  colon  is  close  against 
it.  When  free  from  solid  contents,  the  stomach  is  usually  found  in  dissecting-room 
subjects  hanging  more  or  less  vertically  in  longitudinal  folds  containing  more  or  less 
air  and  fluid  ;  but  during  life,  as  already  stated,  it  is  in  a  contracted  and  puckered 
condition,  the  long  axis  running  strongly  forward  as  well  as  downward.  With  dis- 
tention the  stomach  enlarges  at  first  upward,  backward,  and  to  the  left,  then  forward 
against  the  abdominal  walls.  The  upper  part  enlarges  chiefly  backward,  the  lower 
forward.  This  does  not  imply  a  forward  swing  of  the  greater  curvature  such  as 
has  been  described.  The  pyloric  end  is  moved  to  the  right,  it  may  be  as  far  as 
the  gall-bladder.  The  antrum  may  thus,  according  to  Birmingham,  be  carried  to 
the  right  of  the  pylorus.  The  latter  rarely  moves  more  than  5  cm.  to  the  right  of 
the  median  line.  Except  in  its  last  part,  the  lesser  curvature  continues  essentially 
vertical,  as  seen  from  before.  The  transverse  colon  is  driven  downward  unless  it  be 
so  much  distended  as  to  offer  effectual  resistance. 

1  Journal  of  Anatomy  and  Physiology,  vols.  xxxi.,  xxxv.,  1897,  1901. 


THE  STOMACH. 


1621 


Structure. — The  walls  of  the  stomach,  thickest  and  most  resistant  near  the 
pylorus,  consist  of  four  coats, — the  mucous,  the  submucous  or  areolar,  the  muscu- 
lar, and  the  serous. 

The  mucous  coat  or  mucosa  is  soft  and  velvety,  easily  movable  on  the  lax 
subjacent  areolar  tissue,  thickest  near  the  pylorus,  and  presents  many  folds  or  ruga, 
which  during  distention  are  more  or  less  completely  effaced.  The  folds  are  in  the 

FIG.   1371. 


Falciform  ligament 


Ascending  colon  - 


Ca?cum 


Ileui 


Left  lobe  of  liver 


Transverse  mesocolon 


Transverse  colon 


Descending  colon 


Ileum 


Sigmoid 


Abdominal  organs  of  formalin  subject ;  stomach  has  been  removed  to  show  that  part  of  its  "bed  "  formed  by  trans- 
verse mesocolon  and  colon. 

main  longitudinal,  especially  at  the  pyloric  end,  but  many  smaller  ones  run  in  all 
directions. 

The  epithelium  covering  the  free  surface  of  the  mucous  membrane  consists  of  a 
simple  layer  of  tall  columnar  elements,  from  .020-. 030  mm.  in  height,  many  of  which 
are  goblet-cells  engaged  in  producing  the  mucus  lubricating  the  gastric  surface.  At 
the  passage  of  the  oesophagus  into  the  stomach,  some  2-3  cm.  below  the  diaphragm, 
the  opaque  stratified  squamous  epithelium  of  the  gullet  abruptly  changes  into  the 


1622 


III  MAN   ANATOMY. 


transparent  columnar  cells  clothing  the  stomach.  The  line  of  transition  is  zigzag 
and  well  defined,  the  cesophageal  surface  being  paler  than  the  highly  vascular  red 
gastric  mucosa.  At  the  pylorus  the  mucous  membrane  -is  raised  into  a  ring,  chiefly 

FIG.   1372. 

Ensiform  cartilage  VI  rib-cartilage 

VIII  rib-cartilage        VII  rib-cartilage    ]    VII  rib-cartilage    /        Falciform  ligament 

Transverse  mesocolon  ^_  ^      r  ,,-^--^, 

VI  rib-cartilage 

Pyloric  antrum  of 
stomach 
Diaphragm 


Hepatic 

artery 

A  ^Gall-bladder 
Pyloric 

sphincter 
Cystic  duct 
Pleura! 

cavity 
Duodenum 


Hepatic 
duct 


Right  supra- 
renal body 


Pancreatic 
duct 
Splenic 
vein 
Xrib 

Left  supra-1 
renal  body 


XI  rib 


XII  rib          XII  vertebra    XII  rib 
Frozen  section  across  body  at  level  of  twelfth  thoracic  vertebra. 


in  consequence  of  the  local  thickening  of  the  circular  fibres  of  the  muscular  coat,  but 
also  in  part  on  account  of  the  increased  thickness  of  the  mucosa  itself,  which  in  this 
part  of  the  stomach  may  measure  over  2  mm.  At  the  cardia  it  is  thinnest, — .5  mm. 
or  less, — while  in  the  intermediate  region  it  is  about  i  mm.  The  increased  thick- 
ness at  the  pyloric  end  is  due  to  the  considerable  depth  of  the  depressions,  or 

FIG.   1374- 


FIG.  1373. 


Surface  view  of  mucous  membrane  from  pyloric  end 
of  stomach.     Natural  size. 


Surface  view  of  gastric  mucous  membrane,  show- 
ing reticular  appearance  due  to  orifices  of  group--  ol 
gastric  glands.  X  30. 


gastric  crypts,  into  which  open  the  gastric  glands.  Beyond  the  summit  of  the 
pyloric  ring  the  mucous  membrane  assumes  the  characteristics  of  the  intestine.  In 
addition  to  the  larger  rugae,  the  gastric  surface  exhibits  a  mammillated  condition 


THE  STOMACH. 


1623 


consisting-  of  small  polygonal  areas  pitted  by  the  crypts  which  receive  the  orifices  of 
the  glands. 

The  gastric  glands  constitute  two  principal  groups,  the /undies  and  \\\z  pyloric 
glands  ;  the  former  occupy  the  major  part  of  the  stomach,  including  the  fundus,  the 
anterior  and  posterior  walls,  and  the  curvatures  ;  the  latter  occur  in  the  pyloric  fifth 
of  the  organ.  An  additional  fundus  variety — the  cardiac  glands — is  represented  by 
a  narrow  zonular  group  in  the  immediate  vicinity  of  the  cesophageal  opening. 

The  fundus  or  peptic  glands — the  gastric  glands  proper — consist  of  numerous 
closely  set  tubules,  usually  somewhat  wavy  and  from  .4—2  mm.  long,  which  extend 
the  entire  thickness  of  the  mucosa  and  abut  against  the  muscularis  mucosae.  Each 
gastric  crypt,  corresponding  to  the  excretory  duct,  usually  receives  a  group  of  sev- 
eral of  the  smaller  tubules,  which  include  the  body  and  fundus  of  the  gland,  the 
constricted  commencement  of  the  tubule  constituting  the  neck.  At  the  latter  position 

FIG.  1375. 


r,astric  glands 


ML 

— ; 

*-  •*-"• -* — ^-^*V   -  •  * 

-r     —  •  -      "~*  '.--"-i'V'-* -••."«"»»•. i-v_-,  •<• 

--'.;•     t^.,/^  .-     -.  .  •-•'.:•*,•,•  .*w'     •-.    •--'•'^Tv- 


Blood-vessel 


Submucosa 


Muscularis 


Serosa 


->%.        -r*^  ^»     ,  f-^-   '.x       -T      -      V      •-          --  *"-.  *         •- — re     ^«1^  ^-i^*^- 

^  "  ' 

'•**£  ^  •  -  >''''<^.       ' 


Obliquely  cut 
bundles    of 
circular 
muscle 


— >;> 


. 
Transverse  section  of  stomach  (left  end),  showing  general  arrangement  of  coats.  •  X  20. 

the  columnar  epithelium  prolonged  into  the  crypts  from  the  free  surface  becomes 
lower  and  modified  into  the  secreting  elements. 

The  cells  lining  the  gastric  tubules  are  of  two  kinds,  the  chief  and  the  parietal. 

The  chief,  central  or  adelomorphous  cells  correspond  to  ordinary  glandular  epi- 
thelium, being  low  columnar  or  pyramidal,  and  surrounding  a  circular  lumen  from 
.002  to  .007  mm.  in  diameter.  During  certain  stages  of  digestion  they  contain 
numerous  granules,  which  are  probably  concerned  in  producing  pepsin. 

The  parietal  cells,  known  also  as  acid,  oxyntic,  or  delomorphous,  although  rela- 
tively few,  are  conspicuous  elements  which  occupy  the  periphery  of  the  gland-tubes. 
Their  position  is  indicated  by  protrusions  of  the  profile  of  the  gastric  tubules  caused 
by  the  cells  lying  immediately  beneath  the  basement  membrane.  The  parietal  cells, 
although  arranged  with  little  regularity,  are  most  numerous  in  the  vicinity  of  the 
neck,  where  they  may  equal  or  even  outnumber  the  central  cells  ;  in  the  body  of  the 


1624 


1 1 T. MAX    ANATOMY. 


FIG.    1376. 


gland  they  decrease  in  number  towards  the  fundus,  in  which  locality  they  may  be 
almost  absent.  Their  protoplasm  is  finely  granular  and  lighter  than  that  of  the  chief 
cells.  The  parietal  cells,  although  apparently  excluded  by  the  central  ones,  are  con- 
nected with  the  gland-lumen  by  means  of  lateral  intercellular  secretion-capillaries  ; 
the  latter  extend  from  the  axial  space  to  the  peripherally  situated  elements,  over 
which  they  form  characteristic  basket-like  net-works. 

The  pyloric  glands,  branched  tubular  in  type,  differ  from  the  fundus  glands 
in  the  excessive  width  and  depth  of  their  excretory  ducts,  into  which  a  group  of 
relatively  short  but  very  tortuous  gland-tubules  opens,  and  in  the  simple  character  of 

their  lining.  The  latter  consists  of 
a  single  layer  of  low  columnar  or 
pyramidal  elements,  which  corre- 
spond to  and  resemble  the  chief 
cells  of  the  fundus  glands.  Their 
secretion  often  reacts  as  mucus 
(Bensley).  Owing  to  the  tortuous 
course  of  the  pyloric  tubules,  the 
deeper  parts  of  the  glands  are  cut 
in  all  planes,  portions  of  the  same 
tubule  often  appearing  as  isolated 
transverse,  oblique,  or  longitudinal 
sections.  The  transitional  or  in- 
termediate zone  connecting  the  py- 
loric and  adjoining  portions  of  the 
stomach  contains  both  forms  of 
glands,  those  of  the  fundus  variety 
with  parietal  cells  being  intermin- 
gled with  the  pyloric  type.  Towards 
the  intestine  the  change  of  the  py- 
loric glands  into  those  of  the  duo- 
denum is  gradual,  the  gastric  tubules 
sinking  deeper  until,  as  the  glands 
of  Brunner,  they  occupy  the  sub- 
mucous  coat  of  the  intestine. 

The  cardiac  glands  form  a 
narrow  annular  group,  some  5  mm. 
broad,  surrounding  the  orifice  of 
the  gullet,  into  which  they  are  con- 
tinued for  a  short  distance  (page 
1612).  These  glands,  which  in  some 
animals  constitute  a  much  wider 
zone  (in  the  hog  almost  a  third  of 
the  entire  stomach),  are  to  be  re- 
garded as  modified  fundus  glands 


Chief  cell 


Parietal  cell 


(Oppel),  since  they  possess  similar 
epithelium,  including  usually  a  few 

:ts 


Deeper  portion  of  gastric  glands  from  fundus,  showing  two 
varieties  of  lining  cells  and  secretion-capillaries  connecting  pari- 
etal cells  with  lumen.  X  423. 


parietal  cells.  Their  excretory  due 
or  crypts,  lined  with  the  gastric 
epithelium,  often  exhibit  ampulla- 
like  dilatations.  Among  the  typi- 
cal tubules  area  few  shorter  ones 
which  recall  the  glands  of  Lieber- 
kiihn  of  the  intestine,  since  they  contain  goblet-cells  and  exhibit  a  cuticular  bord' 
(J.  Schaffer). 

The  stroma  or  tunica  propria  of  the  gastric  mucous  membrane  consists  of  a 
loose  fibro-elastic  connective  tissue  containing  numerous  cells  and  resembling  lym- 
phoid  tissue,  which  fills  the  interstices  between  the  glands  and,  in  conjunction 
with  the  extensions  of  the  muscularis  mucosa?,  forms  envelopes  and  partitions  for 
the  groups  of  tubules  constituting  the  deeper  parts  of  the  gastric  glands.  In 


THE  STOMACH. 


1625 


the  vicinity  of  the  pylorus,  and  sometimes  also  at  the  cardia,  a  number  of  small 
lymphatic  nodes — the  so-called  lenticular  glands — normally  occupy  the  deeper 
parts  of  the  mucosa  ;  occasionally  they  are  of  sufficient  size  to  almost  reach  the 
free  surface. 

The  muscularis  mucosce,  as  in  other  parts  of  the  intestinal  tube,  consists  of  a 
well-marked  collection  of  involuntary  muscle,  deeply  situated  next  the  submucous 
coat.  Two  layers  are  usually  distinguishable,  an  inner  circular  and  an  outer  longi- 

FIG.   1377. 


Mucous  coat 


Wide  orifice  of 
glands 


Pyloric 
glands 


Submucous  coat 


^    — Circular  muscle 


Longitudinal  muscle 


Serous  coat 


Transverse  section  of  stomach,  pyloric  end  ;  ruga  is  cut  across,  showing  mucosa  supported  by  core  of  submucous 

tissue.    X  20. 


tudinal.  Towards  the  mucosa  numerous  bundles  of  muscle-cells  extend  between  the 
glands  and  in  places  penetrate  almost  as  far  as  the  epithelium. 

The  submucous  coat  consists  of  lax  connective  tissue,  allowing  the  mucous 
membrane  to  move  freely  on  the  muscular  layer.  It  contains  blood-vessels  of  con- 
siderable size,  a  mesh-work  of  lymphatics,  and  the  nerve-plexus  of  Meissner. 

The  muscular  coat  comprises  three  layers, — an  outer  longitudinal,  a  middle 
circular,  and  an  imperfect  inner  oblique, — of  which  the  middle  one  is  the  most 


1626 


HUMAN    ANATOMY. 


important.  This  layer  is  composed  of  circular  fibres,  which  are  thickest  and  most 
simply  arranged  near  the  pylorus.  Owing  to  the  enlargement  of  the  upper  end  of 
the  stomach,  and  the  fact  that  the  cardiac  opening  is  not  at  the  end  but  at  the  side, 
the  arrangement  becomes  complicated.  The  fibres  surround  the  cardia,  but  become 
oblique  at  a  short  distance  from  it.  At  the  top  of  the  fundus  they  are  arranged  in  a 
whorl  mingling  with  those  of  the  internal  layer.  Still  lower,  although  in  the  main 
circular,  their  course  is  uncertain.  Towards  the  pylorus  they  thicken  considerably, 
being  particularly  well  developed  in  stomachs  of  which  the  pyloric  part  is  tubular. 
At  the  opening  they  are  collected  into  a  ring — \\\z  pyloric  sphincter — capable  of  closing 
the  orifice.  The  longitudinal  layer  is  outside  of  the  circular  one  and  continuous 

FIG.   1378. 


Mouth  of  gla 


Pyloric  gla 


' 


liteiiil 


IP^I^^^ 


x"  ."  »•     VV-V  •;.'  ,«      •    aSIJ.VWS^ 

Lymph-node — vS3*i_  '•y't^Vf'^r^'R'^'- 


Fundus  of  gland. 


Muscularis  mucosae- 

:tion  of  pyloric  end  of  stomach,  showing  glands  and  part  of  lymph-node.      •    too. 


Section  < 


with  the  longitudinal  fibres  of  the  oesophagus.  Along  the  lesser  curvature,  and  to 
less  extent  along  the  greater,  these  fibres  are  collected  into  bands  ;  over  the  front 
and  the  back  of  the  stomach  they  are  oblique.  At  the  antrum  pylori,  although  the 
layer  is  continuous  all  around,  it  presents  an  anterior  and  a  posterior  band, — the 
Pyloric  ligaments, — that  pass  over  folds  of  all  the  layers  internal  to  them,  thus 
forming  the  duplicature  at  the  beginning  of  the  antrum.  At  the  pylorus  itself  the 
longitudinal  layer,  which  has  become  thicker,  sends  a  series  of  fibres  through  the 
circular  fibres,  subdividing  them  into  n, any  groups,  (Fig.  1392).  The  innermost 
muscular  layer  consists  of  oblique  fibre*  spreading  out  from  tin-  cardia  over  the 
front  and  back  of  the  stomach.  They  are  continuations  of  the  circular  fibres  of 


THE  STOMACH. 


1627 


the  gullet  and  diverge  to  either  side,  showing  a  well-marked  border  near  the  lesser 
curvature.  Their  posterior  expansion  is  the  stronger.  The  diverging  fibres  are  lost 
near  the  pylorus,  while  in  the  vicinity  of  the  fundus  they  mingle  with  the  circular 
ones  that  form  the  whorl.  The  latter,  according  to  Birmingham,  is  formed  by  this 
layer  alone. 

The  serous  coat  corresponds  in  structure  with  other  portions  of  the  perito- 
neum,  consisting  of  the  endothelium  of  the  free  surface,   beneath  which  lies  the 
fibre-elastic  stroma  attached 
to  the  muscular  tunic. 

Blood-Vessels. —  The 
arteries  of  the  stomach,  de- 
rived from  the  coeliac  axis,  are 
arranged  in  two  arches  along 
the  lines  of  attachment  of  the 
omenta  ;  hence  that  which  is 
attached  to  the  greater  cur- 
vature below  passes  behind  it 
on  the  fundus.  The  arch 
along  the  lesser  curvature  is 
formed  by  the  coronary  ar- 
tery, which  sends  an  cesopha- 
geal  branch  upward  to  meet 
the  lowest  of  the  cesophageal 
arteries,  and  joins  the  py- 
loric  branch  of  the  hepatic 
artery  below.  The  arteries 
of  the  greater  omentum  are 
the  right  and  left  gastro-epi- 
ploic,  reinforced  behind  the 
fundus  by  the  vasa  brevia 
of  the  splenic  artery.  The 
gastro-epiploicadextra  passes 
down  on  the  right  of  the  first 
part  of  the  duodenum  close 
to  the  pylorus  ;  branches 
arising  on  the  front  at  that 
region  may  nearly  or  quite 
make  an  arterial  ring  around 
the  organ.  The  coronary 
artery  supplies  the  longer 
branches  to  the  walls,  there 
being  a  richer  arterial  distri- 
bution on  the  back  than  on 
the  front  and  at  the  cardiac 
than  at  the  pyloric  end.  The 
general  plan  is  as  follows  :  on 
the  anterior  surface  several 
arteries,  of  which  some  four 
are  large  ones,  run  from  the 
lesser  curvature  across  the 
stomach,  sending  out  successive  lateral  branches  to  inosculate  with  those  from  their 
fellows  ;  finally,  the  main  vessel  breaks  up  into  branches  that  meet  those  from  the 
greater  curvature.  On  the  posterior  surface  the  chief  trunks  divide  with  less  regu- 
larity. At  first  the  arteries  are  just  beneath  the  peritoneum,  between  the  folds  of 
which  they  gain  the  stomach  ;  presently  they  enter  and  pierce  the  muscular  coat,  the 
outer  parts  of  which  are  supplied  during  their  passage.  On  reaching  the  submucous 
coat  the  arteries,  now  reduced,  but  still  of  considerable  size,  divide  into  smaller 
branches,  some  of  which  pass  to  the  muscular  tunic,  while  the  majority  enter  the 
mucous  coat.  The  latter  soon  break  up  into  capillaries  which  surround  the  gland- 


Oblique  section  of  mucous  membrane  from  pyloric  end  of  stomach,  show- 
ing glands  cut  at  various  levels.     X  100. 


1 628 


Iir.MAX    ANATOMY. 


Pyloric  ring 


Stomach  turned  ir 


of  oblique  and 


tubules  with  a  close  mesh-work.  Somewhat  larger  capillaries  constitute  a  superficial 
plexus  beneath  the  epithelium  encircling  the  orifices  of  the  gastric  crypts.  The 
veins,  relatively  wide,  begin  in  the  subepithelial  capillary  net-work  and  traverse  the 
gland-layer,  between  which  and 

the  muscularis  mucosae  they  form  FIG.  1380. 

a  plexus  ;  from  the  latter  radicles 
pass  into  the  submucous  coat,  in 
which  the  venous  trunks  run  paral- 
lel with  the  arteries,  but  lie  nearer 
the  mucosa  (Mall).  The  emerging 
tributaries  are  often  provided  with 
valves  at  their  junction  with  the 
larger  gastric  veins. 

The  lymphatics  originate 
within  the  mucous  membrane,  be- 
neath the  epithelium,  as  wide,  ir- 
regular capillary  channels  which 
freely  communicate  with  one  an- 
other and  pass  between  the  glands 

as  far  as  the  muscularis  mucosae  ;  at  this  level  they  form  a  plexus  from  which  vessels 
descend  into  the  areolar  coat  to  join  the  wide-meshed  submucous  plexus.  Larger 
lymphatics  pierce  the  muscular  tunic  and  unite  to  form  the  chief  channels  which 
escape  from  the  walls  of  the  stomach  along  both  curvatures  to  empty  into  the  lymph- 
nodes  which  occur  in  these  situations. 

The   nerves    supplying   the   stomach    are   from    the   pneumogastric   and    the 
sympathetic,    and    contain   both    medullated  and  nonmedullated    fibres,    the  latter 

predominating.          On 

FIG.  1381.  reaching  the  organ,  the 

stems  pierce  the  exter- 
nal longitudinal  muscu- 
lar layer,  between  which 
and  the  circular  layer 
they  form  the  plexus  of 
Aiterbach.  The  points 
of  juncture  in  this  net- 
work are  marked  by  mi- 
croscopic sympathetic 
ganglia,  from  which 
non-medullated  fibres 
supply  the  involuntary 
muscle.  Leaving  the 
intramuscular  plexus, 
twigs  pass  obliquely 
through  the  circular 
muscular  tunic,  and  on 
gaining  the  subnuicous 
coat  form  a  second  net- 
work, the  f>le.\ns  of 
Me  issuer.  Numerous 
non-medullated  fibres 
leave  the  latter  to  enter 
the  mucous  coat,  in 
which  some  end  in  deli- 
cate plexuses  supply- 
ing the  gastric  glands 
(  Kytmanow  >,  as  well  as 

in  special  endings  in  the  muscularis  mucosae  (Berkley).  Large  medullated  fibres,  the 
dendrits  of  sensory  neurones,  are  also  present  within  the  mucosa,  where'  they  form 
a  subepithelial  plexus  after  losing  their  medullary  substance.  The  ultimate  termi- 


MUCO! 


Submucos:;  =s? 


Muscular 


Seros;< 


•  -  _  _. 


Transverse  section  of  injected  stomach.     X  50. 


PRACTICAL  CONSIDERATIONS:  THE  STOMACH.  1629 

nations  of  the  nerve-fibres  within  the  mucosa,  especially  their  relations  with  the 
gland-cells,  are  still  uncertain. 

Growth. — At  birth  the  capacity  of  the  stomach  is  25  cc.  The  organ,  although 
sometimes  rather  tubular,  does  not  differ  very  much  in  shape  from  that  of  the  adult. 
The  oesophagus  enters  it  less  obliquely  than  later,  so  that  regurgitation  occurs  more 
readily.  The  sphincter  of  the  pylorus  is  already  developed.  We  do  not  remem- 
ber ever  to  have  seen  at  birth  a  well-marked  antrum  pylori.  An  important  pecu- 
liarity of  the  growth  of  the  stomach  is  the  unequal  development  of  the  two  sides  at 
the  fundus.  At  an  early  period  the  top  of  the  original  left  side,  which  becomes  the 
anterior  one,  grows 

upward,    so    that    the  FIG.  1382. 

line  of  attachment  of 
the  greater  omentum  3v-i 
is  along  the  posterior 
surface.  This  unequal 
growth  is  quite  analo- 
gous to  that  of  the 
caecum.  According  to 
Keith  and  Jones,  this 
asymmetry  is  most 
marked  in  the  third 
and  fourth  months  of 
fcetal  life.  We  have 
examined  no  younger 
foetuses  than  these, 
and  cannot  state  how 
earlv  the  process  be- 

i       t7>  u  J        Surface  view  of  fragment  of  muscular  coat  of  stomach,  showing  groups  of  gau- 

glllS.          r  rom    the  end  ^lion-cells  and  nerve-fibres  of  plexus  of  Auerbach.     >    70. 

of  the  first  week  after 

birth  the  growth  of  the  stomach  is  very  rapid  during  the  first  three  months.  It  is 
slow  in  the  fourth  month,  and  in  the  two  months  following  it  is  almost  quiescent.2 
We  have  seen  it  at  a  few  weeks  relatively  broader  than  in  the  adult.  While  it  is 
probable  that  individual  variations  show  themselves  early,  the  shape  and  size  of  the 
stomach  depend,  beyond  question,  to  a  great  extent  on  the  nature  and  quantity  of 
the  food.  With  advancing  years  the  stomach  often  becomes  dilated,  and,  apart 
from  dilatation,  is  likely  to  descend  lower  in  the  abdomen.  The  female  stomach, 
except  for  its  greater  tendency  to  subdivision,  differs  less  than  the  male  from  the 
fcetal  form. 

Variations. — Apart  from  those  of  size  and  shape,  already  alluded  to,  the  important  ones 
are  those  of  subdivision.  There  may  be  a  constriction  at  the  middle  dividing  the  organ  into 
two  chambers  connected  by  a  narrow  passage  :  the  "  hour-glass  stomach."  There  may  also  be 
a  reduplication  of  the  antrum,  or,  indeed,  there  may  be  three,  or,  on  the  other  hand,  the  place  of 
the  antrum  may  be  taken  by  a  tube  with  thick  walls.  It  is  probable  that  these  changes  are 
sometimes  caused  by  a  local  contraction  becoming  fixed. 

PRACTICAL   CONSIDERATIONS  :    THE  STOMACH. 

Congenital  malformations  are  rare.  Perhaps  the  most  common  is  a  constriction 
dividing  it  into  two  unequal  compartments,  —  "  hour-glass  constriction," — a  condi- 
tion somewhat  similar  to  that  found  normally  in  the  kangaroo. 

The  position  of  the  stomach  varies  with  its  degree  of  distention.  When  it  is 
empty  the  pyloric  end  descends  and  the  long  axis  of  the  stomach  is  oblique  from 
left  to  right,  approximating  the  vertical  (i.e.,  the  fcetal)  position  or  that  which  pre- 
ceded functional  use.  This  falling  of  the  pyloric  end  is  due  to  gravity,  the  nearest 
firmly  fixed  point  of  the  alimentary  canal  below  being  the  lower  portion  of  the  duo- 

1  Priority  of  publication  of  this  peculiarity  of  development  belongs  to  Mr.  Arthur  Keith  and 
to  Mr.  F.  Wood  Jones  :     Proceedings  of  the  Anatomical  Society  of  Great  Britain  and  Ireland. 
Journal  of  Anatomy  and  Physiology,  vol.  xxxvi.,  1902. 

2  Rotch's  Pediatrics. 


!63o  HUMAN   ANATOMY. 

denum  (the  fixation  being  due  to  the  relation  of  the  superior  mesenteric  artery  and 
to  the  root  of  the  mesocolon  in  front),  while  above  the  cardiac  end  is  suspended 
from  the  oesophagus  and  held  in  place  by  the  gastro-phrenic  and  gastro-splenic  liga- 
ments. The  transverse  colon  may  then  lie  in  front  of  the  stomach  and  may,  if  dis- 
tended, be  taken  for  it.  The  empty  stomach  lies  upon  the  posterior  abdominal 
wall.  If  the  emptiness  is  habitual,  the  pylorus  will  resemble  the  first  portion  of 
the  duodenum  and  regurgitation  of  duodenal  contents  is  exceptionally  easy.  The 
"gnawing  pains"  of  hunger  or  starvation  (distinct  from  the  sensation  of  hunger 
itself)  are  at  least  partly  due  to  the  traction  on  the  nerve-plexuses  and  filaments 
resulting  from  this  altered  position,  and  can,  therefore,  in  many  cases  be  relieved 
temporarily  and  partially  by  tightening  the  clothing  about  the  waist  and  abdomen, 
giving  support  to  the  viscera. 

When  the  stomach  is  distended  the  enlargement,  which  occurs  at  first  upward 
and  backward  and  towards  the  left  side,  raises  the  arch  of  the  diaphragm  in  that 
region  and  with  it  the  heart  and  pericardium.  The  gastric  plexuses  derived  from 
the  two  pneumogastrics  and  the  associated  sympathetic  fibres,  together  with  the 
coronary  plexus  from  the  sympathetic,  are  all  in  close  relation  with  the  lesser 
curvature,  especially  its  cardiac  end.  It  is  not,  therefore,  difficult  to  understand 
how  this  change  in  the  position  of  the  stomach  aids  in  producing  the  flushed 
face,  embarrassed  respiration,  and  irregular  heart  action  often  seen  in  various  forms 
of  dyspepsia  or  after  overeating.  If  distention  continues,  the  right  lobe  of  the 
liver  is  also  pushed  upward,  the  pylorus  moves  to  the  right,  and  the  transverse 
colon  downward  ;  the  stomach  comes  in  close  contact  with  the  anterior  wall  of  the 
abdomen,  the  "  scrobiculus  cordis"  (page  171)  is  obliterated,  and  a  tympanitic 
note  replaces  the  normal  resonance. 

Conversely,  cardiac  disease  may  cause  vascular  congestion  of  the  stomach, 
catarrh,  dyspepsia,  or  even  hsematemesis.  The  "  black  vomit"  of  moribund  per- 
sons is  due  to  a  similarly  produced  distention  and  rupture  of  the  stomach  capillaries. 

The  position  of  the  stomach  varies  with  the  respiratory  movements.  In  forced 
inspiration  the  cardiac  opening  descends  about  one  inch  with  the  crura  of  the  dia- 
phragm ;  the  pylorus  reaches  about  the  level  of  the  umbilicus. 

Eructation  of  stomach  contents  in  its  typical  form  is  accomplished  by  con- 
traction of  the  muscular  walls  of  the  stomach  ;  vomiting  by  compression  of  the 
stomach  against  the  under  surfaces  of  the  liver  and  diaphragm  through  contrac- 
tion of  the  abdominal  muscles.  This  is  associated  with  contraction  of  the  circular 
pyloric  fibres  and  relaxation  of  the  oblique  fibres  at  the  cardia,  and  is  probably 
aided  by  contraction  of  the  stomach  walls  themselves. 

It  is  obvious  that  a  full  stomach  is  more  easily  and  directly  compressed  in  this 
way,  and  therefore  the  ingestion  of  large  quantities  of  fluids  favors  emesis. 

Vomiting  is  a  clinical  symptom  often  of  the  greatest  significance,  and  should 
be  studied  in  relation  to  the  pneumogastric  and  sympathetic  distribution  to  the 
stomach,  lungs,  and  abdominal  viscera  ;  and  its  various  causes — central,  reflex,  and 
direct — should  be  worked  out  systematically. 

Injuries  of  the  Stomach. — The  changes  in  position  and  the  degree  of  distention 
are  of  the  utmost  importance  in  trauma  expended  upon  the  stomach,  which,  if  quite 
empty,  almost  certainly  escapes  contusion  and  rupture.  It  is,  at  any  rate,  much  less 
frequently  ruptured  than  the  intestines  on  account  of  its  thicker  walls  and  of  the 
protection  afforded  it  by  the  overhanging  ribs  and  the  interposed  liver.  The 
"stomach-bed  "  (page  1620)  supplies  an  elastic  and  movable  base  of  support,  which 
also  favors  its  escape  from  injury. 

In  penetrating  or  gunshot  wounds  its  condition  as  to  emptiness  or  the  reverse 
is  even  more  important.  When  either  wall  is  opened  by  rupture  or  wound,  eversion 
of  the  mucous  membrane,  which  is  favored  by  its  thickness  and  by  the  laxity  of  the 
submucous  connective  tissue,  may  temporarily  plug  the  opening,  and  through  the 
formation  of  adhesions  permit  of  spontaneous  cure.  The  different  directions  of 
the  muscular  fibres  in  the  three  layers  of  that  coat  ordinarily  prevent  wide  separa- 
tion of  the  margins  of  the  wound,  and  thus  also  favor  its  closure  by  natural  processes. 
In  escape  of  storuach  contents  through  tilccration,  wound,  or  rupture,  if  the  poste- 
rior wall  is  involved,  the  lesser  onu-ntal  cavity  is  infected,  and  a  localized — sub- 


PRACTICAL  CONSIDERATIONS:     THE  STOMACH.  1631 

phrenic — abscess  may  follow  ;  if  the  anterior  wall  is  opened,  infection  of  the  general 
peritoneal  cavity  and  septic  peritonitis  are  more  likely  to  result.  On  account  of  the 
course  of  the  blood-vessels  (page  1627),  wounds  parallel  with  the  axes  of  the  curva- 
tures are  attended  by  free  bleeding,  especially  if  near  those  borders  of  the  stomach. 
Wounds  running  more  or  less  at  right  angles  to  the  curvatures  and  removed  from 
them  are  much  less  likely  to  open  large  vessels.  The  vessels  just  beneath  the  sur- 
face of  the  mucous  membrane  are  numerous  but  smaller.  Bleeding  from  them  may 
be  controlled  by  separate  suture  of  the  mucosa,  which  is  facilitated  by  its  thickness 
and  by  the  looseness  of  the  submucous  cellular  tissue. 

Ulcers  of  the  stomach  are  found  most  often  on  the  posterior  wall  at  the  pyloric 
end  and  along  the  lesser  curvature.  It  has  been  suggested  that  they  originate  in  a 
bacterial  necrosis  of  the  epithelium,  which  is  favored  by  the  absence  of  the  fundus 
or  peptic  glands  (page  1623)  at  this  region,  and  is  followed  by  "digestion"  of  the 
subjacent  tissues.  Allen  thinks  that  the  immense  preponderance  of  pyloric  ulcers  is 
an  illustration  of  the  "law  of  localization  of  diseased  action," — viz.,  that  parts 
enjoying  the  most  rest  are  least  liable  to  involvement  by  structural  disease.  When 
they  cause  hemorrhage,  it  is  apt  to  be  from  the  branches  of  the  coronary  artery.  Per- 
foration occurs  with  much  greater  frequency  in  ulcers  situated  on  the  anterior  wall, 
which  is  the  one  with  the  greatest  range  of  motion  in  varying  stages  of  digestion 
and  degrees  of  distention,  and  also  during  the  movements  of  respiration.  Perfora- 
tion from  such  ulcers  with  spontaneous  cure  may  result  in  adhesions  between  the 
stomach  and  pancreas,  colon,  duodenum,  or  gall-bladder,  and  may  be  followed  by 
fistulas  communicating  with  those  viscera.  They  may  perforate  the  diaphragm  and 
cause  empyema.  They  have  opened  into  the  pericardium  and  into  a  ventricle  of 
the  heart.  An  ulcer  may  be  so  surrounded  by  adhesions  that,  even  when  on  the 
anterior  wall,  perforation  does  not  cause  a  general  peritonitis,  but  a  localized  abscess. 
If  this  is,  for  example,  in  the  splenic  region,  it  will  be  observed  that  there  is  immo- 
bility of  the  upper  left  quadrant  of  the  abdomen  with  restriction  of  the  respiratory 
movements  of  the  left  thorax,  both  occasioned  by  the  connection  between  the 
splanchnic  and  the  intercostal  nerves  through  the  sympathetic  ganglia.  The  local- 
ization of  such  collections  of  pus  after  perforation  of  the  anterior  wall  near  the 
cardia  is  favored  by  the  "  costo-colic"  fold  of  peritoneum  extending  from  the  dia- 
phragm opposite  the  tenth  and  eleventh  ribs  to  the  splenic  flexure  of  the  colon 
and  forming  part  of  the  left  portion  of  the  "stomach-bed."  This  fold,  especially 
with  the  patient  supine,  forms  a  ' '  natural  well, ' '  containing  the  spleen  and  a  part 
of  the  stomach,  into  which  any  fluid  exudate  or  stomach  contents  may  gravitate 
(Box). 

Cancer  of  the  stomach  occupies  by  preference  the  pyloric  region.  When  the 
growth  becomes  palpable,  but  before  it  is  tied  down  by  adhesions  to  neighboring 
organs,  it  often  illustrates  the  mobility  of  the  pyloric  end  of  the  stomach  ( vide 
snpra),  as  it  can  be  pushed  even  across  the  mid-line  of  the  body  into  the  splenic 
region. 

Carcinoma,  according  to  its  situation,  may  extend  in  the  course  of  the  lym- 
phatic vessels  running  along  the  lesser  curvature  in  the  gastro-hepatic  omentum  and 
emptying  into  the  lymph- nodes  near  the  cceliac  axis  and  hepatic  blood-vessels,  or 
along  the  greater  curvature  and  the  cardia  to  the  retro-cesophageal  glands.  The 
retro-pyloric  lymph-nodes  may  be  invaded  in  cancer  of  the  pylorus.  Its  early  recog- 
nition as  a  tumor  obviously  depends  upon  its  anatomical  site.  If  it  occupies  the 
fundus,  the  cardia,  the  lesser  curvature,  or  the  upper  and  outlying  portions  of  the 
anterior  wall,  the  ribs  and  the  liver  intervene  and  prevent  palpation  of  the  growth  ; 
and  if  on  the  posteridr  wall,  the  depth  at  which  the  tumor  lies  renders  its  palpation 
difficult  and  unsatisfactory. 

Dilatation  of  the  stomach  (gastrectasis}  may  be  due  to  simple  hypertrophy  of 
the  pyloric  muscle,  may  follow  stricture  of  the  pylorus  or  duodenum  from  cicatriza- 
tion of  an  ulcer,  or  may  result  .from  pyloric  occlusion,  as  from  carcinomatous  growth 
invading  the  pylorus  itself,  or  from  pressure  of  an  extrinsic  tumor,  or  a  displaced 
liver  or  right  kidney.  The  distention  is  often  extreme,  and  in  some  instances  the 
outline  of  the  distended  stomach  can  plainly  be  seen,  the  lesser  curvature  a  couple 
of  inches  below  the  ensiform  cartilage  and  the  greater  curvature  passing  obliquely, 


1632  HUMAN  ANATOMY. 

from  the  tip  of  the  tenth  rib  on  the  left  side,  towards  the  pubes,  and  then  curving 
upward  to  the  right  costal  margin  (Osier).  The  dilatation  may  be  of  any  degree, 
the  lower  border  of  the  stomach  sometimes  reaching  to  the  level  of  the  pubes. 

Displacement  of  the  stomach  {gastroptosis)  is  attended  by  great  stretching  of 
the  gastro-hepatic,  gastro-splenic,  and  gastro-phrenic  folds.  It  is  sometimes  a  dila- 
tation with  the  stomach  vertical  instead  of  oblique  rather  than  a  true  descent  of  the 
whole  organ. 

Three  forms  are  described  :  ( i )  a  slight  descent  of  the  pylorus,  and  with  it  of 
the  lesser  curvature,  so  that  the  latter  comes  from  beneath  the  liver  ;  (2)  "  vertical 
stomach,"  already  alluded  to  ;  (3)  a  descent  of  the  lesser  curvature,  the  pylorus 
remaining  fixed,  making  a  U-shaped  stomach  (Riegel).  The  last  is  very  rare.  All 
forms  are  favored  by  the  use  of  corsets  or  clothing  constricting  the  lower  thorax, 
especially  in  women  with  flaccid  abdominal  walls.  The  displacement  may  be  con- 
genital, or  may  be  due  to  primary  elongation  or  relaxation  of  the  peritoneal  folds 
which  act  as  ligaments,  or  to  malposition  or  displacement  of  other  abdominal 
viscera. 

Hernia  of  the  stomach  is  usually  diaphragmatic  and  often  congenital.  The 
viscus  may  enter  the  thorax  through  a  stab  wound  or  rupture,  or  through  weakened 
or  enlarged  spaces  at  (<z)  the  central  tendon,  (b)  the  posterior  inferior  muscular  area, 
(V)  the  interval  between  the  sternal  and  costal  fibres,  (d)  the  oesophageal  foramen, 
(<?)  the  fissure  between  the  lumbar  and  costal  portions,  or  (_/)  the  point  of  passage 
of  the  sympathetic  trunk  (Sultan).  These  possible  locations  have  been  mentioned 
in  the  order  of  frequency. 

The  hernia  may  carry  the  peritoneum  with  it  (true  hernia),  as  in  cases  of 
partial  rupture  or  non-penetrating  wound  of  the  diaphragm,  or  may  avoid  or  pass 
through  the  peritoneum  (false  hernia).  The  latter  are  more  common.  All  forms 
are  found  most  frequently  on  the  left  side  in  consequence  of  the  presence  of  the 
liver  on  the  right  side. 

Operations  on  the  Stomach. — The  stomach  is  most  accessible  for  operation 
through  a  triangular  space,  apex  upward,  bounded  on  the  left  by  the  eighth  and 
ninth  costal  cartilages,  on  the  right  by  the  free  edge  of  the  liver,  and  below  by  a 
horizontal  line  joining  the  tips  of  the  tenth  costal  cartilages  and  corresponding 
approximately  to  the  line  of  the  transverse  colon.  The  tenth  cartilage  has  a  dis- 
tinct tip  and  plays  over  the  ninth  cartilage,  producing  a  peculiar  crepitus  (Labb£). 

If  the  incision  is  median,  it  passes  between  the  recti  muscles  ;  if  lateral  and 
vertical,  it  is  made  through  the  rectus  or  along  its  outer  edge  ;  if  oblique,  through 
the  rectus  and  the  external  and  internal  oblique  and  transversalis.  The  terminal 
branches  of  either  the  superior  or  deep  epigastric  artery  may  be  divided,  or  the  latter 
vessel  itself  if  the  vertical  incision  is  prolonged  downward.  As  the  blood-supply 
of  the  stomach  comes  from  three  distinct  sources — the  gastric,  hepatic,  and  splenic 
arteries — and  the  anastomoses  are  very  numerous,  the  nutrition  of  the  flaps,  even 
after  extensive  resection,  is  usually  maintained,  in  the  absence  of  infection  or  of 
cardio-vascular  disease.  On  the  contrary,  in  operations  on  the  intestines  the  greatest 
care  must  be  exercised  in  dealing  with  the  mesentery  to  preserve  the  vitality  of 
the  gut. 

Upon  exposing  the  stomach,  it  is  well  to  bear  in  mind  its  oblique  position  and 
the  facts  that  the  pylorus  is  the  only  part  that  is  really  transverse,  that  three- 
fourths  of  the  stomach  are  to  the  left  of  the  middle  line,  that  the  upper  part  of  the 
cardia  is  an  inch  above  the  level  of  the  lower  end  of  the  oesophagus,  and  that  the 
larger  part  of  the  greater  curvature  is  directed  to  the  left  and  of  the  lesser  curvature 
to  the  right.  According  to  Meinert,  the  pylorus  lies  behind'  the  intersection  of  a 
transverse  horizontal  line  drawn  through  the  tip  of  the  xiphoid  cartilage  with  the 
right  costal  border  ;  while  the  lower  curvature,  beginning  at  the  latter  point,  crosses 
tin-  mid-line  and  ascends,  describing  a  half-circle  around  an  antero-posterior  hori- 
zontal line  drawn  through  the  xiphoid  tip. 

The  relations  of  the  stomach  in  general  have  been  described  (page  1619).  The 
transverse  colon — especially  in  cases  of  cesophageal  strict mv  in  which  the  stomach  is 
contracted  and  rests  far  back  and  well  up  under  tin-  diaphragm — may  present  itself, 
and  has  been  mistaken  for  the  stomach.  The  gut,  however,  is  thinner,  not  so 


THE  SMALL  INTESTINE.  1633 

pinkish,  and  the  longitudinal  band,  the  sacculations,  and  the  epiploic  appendages 
on  its  lower  aspect  may  be  seen.  If  any  doubt  exists,  the  under  surface  of  the  left 
lobe  of  the  liver  should  be  followed  up  by  the  finger  to  the  transverse  fissure  and 
then  down  on  the  gastro-hepatic  omentum  to  the  lesser  curvature  of  the  stomach. 
The  dependent  greater  omentum  and  the  gastro-epiploic  artery  on  the  greater  cur- 
vature aid  in  the  recognition  of  the  stomach. 

In  gastrotomy — as  for  foreign  body,  for  exploration,  or  for  retrograde  dilatation 
of  the  oesophagus — the  incision  may  be  vertical  and  midway  between  the  two  curva- 
tures to  minimize  the  hemorrhage  (vide  supra). 

In  gastrostomy — the  establishment,  for  purposes  of  feeding,  of  a  direct  com- 
munication between  the  surface  of  the  body  and  the  stomach  cavity — the  abdominal 
incision  may  be  oblique,  parallel  to  the  left  costal  cartilages,  and  2.5  cm.  (i  in.) 
from  them,  or  vertical  down  to  the  left  rectus,  the  fibres  of  which  may  be  separated 
without  division.  In  either  case  a  part  of  the  anterior  wall  of  the  stomach,  made 
conical  by  traction,  is  brought  out,  carried  upward  beneath  a  bridge  of  skin,  and 
fixed  to  the  margins  of  a  second  opening  over  the  costal  cartilages.  Various  mod- 
ifications are  employed,  all  with  the  idea  of  securing  a  valvular  or  sphincteric  con- 
dition in  or  about  the  orifice  so  as  to  prevent  leakage  of  the  stomach  contents. 

\npyloroplasty — applicable  to  simple  hypertrophic  stenosis  or  cicatricial  stric- 
ture—an incision  is  made  from  the  stomach  to  the  duodenum  through  the  pylorus 
and  parallel  to  the  long  axis  of  the  tract  at  that  point.  Its  borders  are  then 
separated  as  widely  as  possible  so  that  their  mid-points  become  the  ends  of  the 
opening,  the  edges  of  which  are  then  sutured  together  in  this  position,  materially 
widening  the  lumen  of  the  canal. 

In  pylorectomy  or  gastrectomy  large  portions  of  the  stomach,  or  the  whole  organ, 
are  excised  for  malignant  disease  ;  in  the  former  the  omental  connections  of  the 
pylorus  must  be  severed  and  the  right  gastro-epiploic,  the  pyloric,  and  the  gastro- 
duodenal  arteries  divided  ;  in  the  latter,  in  addition,  the  pneumogastric  nerves 
below  the  diaphragm  and  many  more  vascular  trunks. 

Partial  gastrectomies,  as  for  the  excision  of  a  nodular  carcinoma  or  of  a  gastric 
ulcer,  are  much  less  serious.  Division  of  the  gastro-hepatic  omentum,  which  holds 
the  stomach  up  under  the  costal  margins,  will  facilitate  the  freeing  of  the  pylorus  and 
lesser  curvature  and  permit  of  ready  access  to  the  lesser  peritoneal  cavity.  The 
gastro-colic  omentum  attached  to  the  region  of  disease  can  then  be  made  tense  by 
the  fingers  passed  behind  and  beneath  the  pylorus  and  can  be  ligated  and  divided 
(Mayo). 

In  gastro-enterostomy — as  a  palliative  in  cancerous  pyloric  stenosis  or  for  the 
treatment  of  gastric  ulcer — the  intestinal  canal  (usually  that  of  the  jejunum,  as 
the  highest  movable  portion  of  the  small  intestine)  is  made  directly  continuous  with 
the  stomach  cavity  by  the  establishment  of  a  permanent  fistula  between  the  two.  The 
posterior  wall  of  the  stomach  is  now  usually  selected  because  of  its  nearness  to  the 
jejunum.  It  may  be  reached  through  the  transverse  mesocolon,  the  greater  omentum 
with  the  transverse  colon  having  been  turned  upward  ;  or  the  gastro-colic  omentum 
may  be  torn  through  or  divided. 

Gastroplasty  (analogous  to  pyloroplasty)  has  been  done  in  cases  of  -hour-glass 
stomach  following  cicatricial  contraction  after  gastric  ulcer.  Occasionally  in  these 
cases  the  constricting  band  has  been  mistaken  for  a  thickened,  contracted  pylorus. 
Adhesions  sometimes  connect  the  constrictions  with  neighboring  parts,  as  with  the 
right  rectus  muscle  (Elder)  or  the  liver  (Childe). 

THE   SMALL    INTESTINE. 

The  stomach  is  followed  by  the  long  and  complicated  tube  of  the  small  intestine, 
divided  into  the  duodenum  and  the  jejimo-ileum.  According  to  Treves,  the  average 
length  in  the  male  is  6.8  m.  (22  ft.  6  in.)  and  in  the  female  nearly  15  cm.  (6  in.) 
more.  This  excess,  however,  would  probably  not  be  confirmed  by  a  larger  series. 
In  the  male  the  extremes  were  9.7  m.  (31  ft.  10  in.)  and  4.7  m.  (15  ft.  6  in.),  in 
the  female  8.9  m.  (29  ft.  4  in.)  and  5.7  m.  (18  ft.  10  in.).  The  outer  wall  of  the 
tube  is  regular,  without  sharp  folds  or  sacculations,  beyond  the  duodenum.  The 

103 


1 634 


HUMAN  ANATOMY. 


circumference  is  greatest  in  the  duodenum  (not  always  at  the  same  point),  beyond 
which  it  gradually  decreases,  the  diameter  of  the  gut  at  its  lower  end  being  nearly 
one-third  smaller  than  at  the  beginning.  Since  certain  structural  features  are  com- 
mon to  the  entire  small  intestine,  it  will  be  convenient  to  consider  these  in  this  place, 
further  details  being  given  with  the  descriptions  of  the  special  parts. 

FIG.   1383. 


Liver 


Gall-bladder 


Transverse  colon 


Ascending 
colon 


lie-mil 


Falciform  ligament 


-Stomach 


Greater  omentum  (cut 
surface) 


Coils  of  jejunum 


-32> Descending  colon 


Sigmoid  flexure 


• 


Abdominal  organs  of  formalin  subject.     Stomach  was  unusually  large,  giving  an  exaggerated  impression  of  it 

transverse  jxjsition. 

Structure. — The  small  intestine,  as  other  parts  of  the  alimentary  tube  below 
the  diaphragm,  consists  of  four  coats,  the  witcon.f,  tin-  submit  cons,  the  muscular,  and 
the  serous. 

The  mucous  coat,  in  addition  to  the  glandular  structures,  possesses  folds  and 
villi  that  not  only  greatly  increase  its  surface,  hut  also  contribute  peculiarities  which 
aid  in  differentiating  between  typical  portions  taken  from  various  regions.  The 


THE  SMALL  INTESTINE. 


1635 


epithelium  covering  the  free  surface  consists  of  a  single  layer  of  cylindrical  cells  which 
exhibit  a  striated  cuticular  border  next  the  intestinal  lumen.  This  border  lacks 
stability,  and  is  resolvable  into  minute  prismatic  rods,  placed  vertically  and  probably 
continuous  with  the  spongioplastic  threads  within  the  body  of  the  cell.  In  many 
places,  especially  over  the  villi,  mucus-producing  goblet-cells  share  the  free  surface 
with  the  ordinary  epithelial  elements.  Between  the  latter  migratory  leucocytes  are 
always  to  be  seen.  The  stroma  or  tunica  propria  of  the  mucous  coat  resembles 
lymphoicl  tissue,  being  composed  of  a  connective-tissue  reticulum  containing  numerous 
small  round  cells  similar  to  lymphocytes.  This  stroma  fills  the  spaces  between  the 
glands  and  forms  the  core  of  the  villi  over  which  the  epithelium  stretches.  The  deep- 

FIG.  1384. 


Villus 


Duct  of  Brunner's  glands— V^ij 


Muscularis  mucosae 


Brunner's  gla 


Orifice  of  gland  of  Lieberkiihn 


—  Brunner's  glands 


". 

•-^-5- 

^v-i^sagwsifcwss:'1**^ 


•  ..'  , 


Serous  coat 


ire/1  - 

••H-S--V      Circular  muscle 


Longitudinal  muscle 


Transverse  section  of  small  intestine  (lower  part  of  duodenum),  showing  general  arrangement  of  coats.     X  90. 

est  part  of  the  mucous  coat  is  occupied  by  a  well-marked  muscularis  mucosce,  in 
which  an  inner  circular  and  an  outer  longitudinal  layer  are  distinguishable. 

The  villi  are  minute  projections  of  the  mucous  surface,  barely  visible  to  the  un- 
aided eye,  the  presence  of  which  imparts  the  characteristic  velvety  appearance  to  the 
inner  surface  of  the  small  intestine.  Although  found  throughout  the  latter,  from  the 
pylorus  to  the  ileo-colic  valve,  they  are  most  numerous  (from  20-40  to  the  sq.  mm.  ) 
in  the  duodenum  and  jejunum  and  less  frequent  (from  15-30  to  the  sq.  mm.)  in  the 
ileum.  In  the  duodenum  they  appear  immediately  beyond  the  pylorus,  but  reach 
their  best  development  in  the  second  part,  where  they  measure  from  .  2-.  5  mm.  in 
height  and  from  .3-1  mm.  in  breadth  ;  they  are,  therefore,  here  low  and  broad.  In 
the  jejunum  the  villi  are  conical  and  somewhat  laterally  compressed,  while  in  the 
ileum  their  shape  is  cylindrical,  filiform,  or  wedge-like,  their  length  and  breadth 
being  from  .5-1  mm.  and  from  .2-.  4  mm.  respectively.  The  villi  are  projections  of 


i636 


HI. MAN  ANATOMY. 


FIG     1385. 

v   /• 
t       V./, 


the  mucous  coat  alone,  and  consist  of  a  framework  of  the  lymphoid  stroma-tissue, 
covered  by  columnar  epithelium,  which  supports  the  absorbent  vessel  and  the  blood- 
vessels, together  with  involuntary  muscle.  The  reticular  tissue  constituting  the  villus 
is  condensed  at  the  periphery,  the  existence  of  a  definite  limiting  membrane  being 
assumed  by  some  (J.  Schaffer,  Spalteholz,  Ebner).  Each  villus  is  supplied  by  from 
one  to  three  small  arteries,  derived  from  the  vessels  of  the  submucosa,  which  break 
up  into  a  capillary  net-work  lying  beneath  the  peripheral  layer  of  the  stroma.  The 
blood  is  returned  usually  by  a  single  vein  which,  beginning  at  the  summit  by  the 
confluence  of  capillaries,  traverses  the  central  parts  of  the  villus  and  becomes  trib- 
utary to  the  larger  venous  stems  within  the  submucous  coat. 

The  absorbent,  chyle-vessel,  or  lacteal,  as  the  lymph-vessel  occupying  the  villus 
is  variously  termed,  lies  near  the  centre  of  the  projection,  surrounded  by  the  mus- 
cular tissue  and  the  blood-capillaries.  While  the  slender  cylindrical  villi  contain 
only  a  single  lymphatic,  from  .025-. 035  mm.  in  diameter,  those  of  broader  form  often 
contain  two,  three,  or  even  more  such  vessels,  which  may  communicate  by  cross- 
channels.  Their  walls  consist  of  a  single  layer  of  endothelial  plates.  The  muscular 
tissue  within  the  villus,  prolonged  from  the  muscularis  mucosse,  forms  a  delicate 
layer  of  slender  fibre-cells,  longitudinally  disposed,  which  surround  the  central  chyle- 
vessel.  Contractions  of  this  tissue 
shorten  the  villus  and  aid  in  propel- 
ling the  emulsified  contents  of  the 
lymphatic. 

The  presence  of  numerous  oil- 
droplets  of  considerable  size  within 
the  epithelial  cells,  as  well  as  stroma, 
of  the  villi  during  certain  stages  of 
digestion  has  caused  much  specula- 
tion as  to  their  mode  of  entrance. 
On  histological  grounds  there  is 
good  reason  for  assuming  that  a  large 
part  of  the  fat  particles  seen  within 
the  tissues  gains  access  in  a  condition 
either  of  solubility,  saponification, 
or  exceedingly  fine  molecular  sub- 
division, the  accumulations  observed 
within  the  tissues  being  due  to  sec- 
ondary change  (Ebner). 

The  valvulae  conniventes 
(plicae  circulates),  within  the  duo- 
denum and  jejunum,  additionally 

model  the  mucous  coat  and  greatly  increase  its  secreting  and  absorbent  surface  ; 
they  also  retard  the  passage  of  the  intestinal  contents,  thereby  facilitating  the 
digestive  processes.  These  transverse  folds  begin  in  the  second  part  of  the  duo- 
denum and  consist  of  duplicatures  which  involve  not  only  the  entire  thickness  of 
the  mucosa,  but  contain  a  central  supporting  projection  of  the  submucous  coat  ; 
hence,  while  they  may  fall  on  their  sides,  they  cannot,  as  a  rule,  be  effaced  by  dis- 
tention.  The  height  of  the  folds,  where  well  developed,  rarely  much  exceeds  i  cm., 
and  towards  the  lower  part  of  the  jejunum  is  much  less.  The  majority  of  the  valves 
do  not  extend  more  than  two-thirds  or  three-fourths  of  the  circumference  of  the 
gut  ;  exceptionally,  however,  circular  and  spiral  ones  describe  two  or  three  com- 
plete turns.  Their  ends,  usually  simple,  may  be  bifurcated.  Smaller  folds,  more  or 
less  effaceable,  run  obliquely  as  offshoots  from  the  larger  ones.  The  valves  are  much 
larger  on  the  attached  side  of  the  gut  than  on  the  free  one  ;  in  the  latter  position 
they  may  be  entirely  absent  in  localities  in  which  the  folds  are  feebly  developed. 
Succeeding  the  first  part  of  the  duodenum,  the  yalvuhe  conniventes  are  very  numer- 
ous and  large,  and  so  near  together  that  in  falling  over  any  fold  would  come  in  con- 
tact with  the  next  one.  Descending  the  small  intestine,  they  gradually  become 
smaller  and  farther  apart,  so  that  the 'distance  between  them  considerably  exceeds 
their  height.  They  also  become  more  effaceable,  and  finally  very  much  so.  In 


Gland 


Villus 


Surface   view  of  mucous  membrane  of  jejunum,  showing  villi 
and  orifices  of  glands.     X  35. 


THE  SMALL  INTESTINE. 


1637 


this  respect  much  variation  exists,  which  partially  accounts  for  the  differences  found 
at  the  lower  part  of  the  small  intestine,  where  often  the  valves  are  absent,  while  at 
other  times  they  are  well  marked.  Sernoff '  found  in  subjects  treated  with  chromic 
acid  injections  that  the  valves  were  as  frequent  in  one  part  of  the  small  intestine 
as  another,  but  less  regularly  transverse  in  the  lower.  He  observed  places  without 
valves,  usually  at  the  convexity  of  folds,  in  all  parts  of  the  gut,  and  regards  them  as 
largely  dependent  upon  the  condition  of  the  muscular  coat.  It  is  certain,  however, 
that  the  valves  of  the  upper  part  of  the  intestine  are  independent  of  this  influence  ; 
those  in  the  lower  portion,  perhaps,  may  be  produced  in  such  manner. 

Glands. — The  structures  within  the  alimentary  tube  to  which  the  term  "  glands" 
has  been  applied  include  two  entirely  different  groups,  the  true  and  \hefalse  glands. 

FIG.    1386. 


Stroma  of  tunica  p 


Circular  m 
Tra 


'irrnln-  mi:m-lp  _•      "2^- ;"  -^    ^V*  —     -,  -     "    -•   "_«^.~i*- 

Transverse  section  of  small  intestine  (jejunum),  showing  villi  cut  lengthwise 


X  150. 


The  former  are  really  secreting  organs,— the  glands  of  Lieberkiihn  and  of  Brunner  ; 
the  latter  are  more  or  less  extensive  accumulations  of  adenoid  tissue,  and  are  appro- 
priately spoken  of  as  lymphatic  nodules  or  follicles. 

The  glands  of  Lieberkiihn  are  simple  tubular  depressions  which  are  found  not 
only  throughout  the  entire  small  intestine,  but  in  the  large  as  well.  They  are  very 
closely  set,  narrow,  and  extend  the  thickness  of  the  mucous  coat  as  far  as  its  mus- 
cular layer.  In  length  they  vary  from  .3-.  4  mm.  and  in  diameter  from  .060-. 080  mm. 
The  fundus  of  the  glands  is  slightly  expanded  and  in  exceptional  cases  divided.  The 
lining  of  the  crypts  rests  upon  a  delicate  basement  membrane,  and  consists  of  a  single 
1  Internal.  Monatsschrift  f.  Anat.  u.  Physiol.,  Bd.  xi.,  1894. 


i638 


HUMAN  ANATOMY. 


layer  of  columnar  cells  directly  continuous  with  those  covering  the  villi.  They  differ 
from  the  latter  in  being  only  about  half  so  high  (.018  mm.  )  and  in  not  presenting  the 
characteristic  cuticular  border.  This  last  gradually  disappears  as  the  cells  dip  into 

FIG.  1387. 


-Goblet-cell 


Capillary 

Cuticular  border 
r~~of  epithelium 


Lacteal 


Transverse  section  of  single  intestinal  villus,  showing  relation  of 
epithelium,  stroma,  and  vessels.     X  350. 


Surface  view  of  mucous  membrane  from 
end  of  jejunum  showing  valvulae  conni- 
ventes.  Stippled  appearance  is  clue  to  villi 
covering  folds.  Natural  size. 


the  follicles  to  become  the  lining  of  the  glands.  Under  low  magnification  the  sur- 
face of  the  small  intestine  presents  numerous  pits,  the  orifices  of  the  glands,  which 
almost  entirely  fill  the  spaces  between  the  bases  of  the  villi  ;  with  the  exception  of 

FIG.  1389. 

Subtnucous  coat  Villi 


Mucosa 


Submucosa 


Longitudinal  section  of  duodenum  ;  valvuhr  i-onnivontes  cut  across,  showing  relation  of  these  folds  to  villi.    X  15. 


the  areas  immediately  over  the  lymph-nodules,  where  they  are  partially  pushed  aside, 
ihcsc  glands  are  present  in  all  parts  of  the  intestine.  They,  however,  take  no  part  in 
.absorption,  never  containing  fatty  particles  during  periods  in  which  such  substances 


THE  SMALL  INTESTINE. 


1639 


arc  seen  within  the  epithelium  of  the  villi.  It  is  worthy  of  note  that  even  in  the  adult 
mitotic  figures  are  frequently  observed  within  the  cells  lining  Lieberkuhn's  glands, 
although  such  evidences  of  cell-division  are  rare  among  the  elements  covering  the 


Lymph- 
node 


Circular      '•.'.;•'•_'      '•'.';:  .- 
muscle  "' '  -  ;    /.'TT 


Gland  of  Lieberkiihn 


Longitudinal, 
muscle 


Serous  coat . 


Longitudinal  section  of  duodenum,  showing  Brunner's  and  Lieberkuhn's  glands,  villi,  and  lymph-node.    X  too. 

villi.  Bizzozero  therefore  regards  the  lining  of  these  glands  as  an  active  source  for 
the  regeneration  of  the  intestinal  epithelium  by  the  production  of  new  cells.  As  on 
the  villi,  so  also  in  these  glands  goblet-cells  lie  among  the  usual  epithelial  elements  ; 
likewise  migratory  leucocytes  are  present  between  the  gland-cells. 

FIG.  1391. 

Pyloric  glands 


sss!  '•  •  •.•:••'-••;-••--•;-•  •  -  -    - 


Longi- 
tudinal 
muscle 


Stomach 


Duodenum 


Longitudinal  section  through  junction  of  stomach  and  duodenum,  showing  transition  of  pyloric  into  duodenal  glands  ; 
also  thickening  of  circular  muscle  to  form  sphincter  pylori.     X  23. 

The  glands  of  Brunner,  also  often  appropriately  termed  the  dtwdenal glands, 
are  limited  to  the  first  division  of  the  small  intestine.  Beginning  at  the  pylorus, 
where  they  are  most  numerous  and  extensive,  they  gradually  decrease  in  number  and 


1640 


HUMAN   ANATOMY. 


size,  being  sparingly  present  beyond  the  opening  of  the  bile-duct  and  entirely  want- 
ing at  the  lower  end  of  the  duodenum.  These  glands  are  direct  continuations  of 
the  pyloric  glands  of  the  stomach,  with  which  they  agree  in  all  essential  details. 
While,  however,  their  gastric  representatives  are  confined  to  the  mucous  coat, 

FIG.   1392. 


Solitary 


Fold 


nodules 


jff  *>".  /'," 


r393- 


Surface  views  of  mucous  membrane  from  upper  (A)  and  lower  (B)  part  of  ileum,  showing  folds  and  solitary  lymph- 
nodules.    The  velvety  appearance  is  due  to  the  villi.     Natural  size. 

Brunner's  glands  chiefly  occupy  the  submucosa,  the  migration  taking  place  at  the 
pyloric  ring  (Fig.  1392).  The  duodenum,  therefore,  possesses  a  double  layer  of  true 
glands, — those  of  Lieberkiihn  within  the  mucous  coat,  beneath  which,  in  the  submu- 
cosa, lie  those  of  Brunner.  The  individual  glands,  tubo-alveolar  in  type,  form  some- 
what flattened  spherical  or  polygonal  masses,  measuring  from  .5-1  mm.,  which  con- 
sist of  richly  branched  tubules,  ending  in  dilatations.  Their  excretory  ducts  pierce 
the  mucous  coat  and  open  either  directly  on  the  free  surface  or  into  the  crypts  of 
Lieberkiihn.  While  narrower  than  the  flask-shaped  alveoli,  the  epithelium  of  the 
ducts  is  the  same  as  that  found  in 

the  deeper  parts  of   the   tubules.  FIG. 

The  clear,  low  columnar  cells  lining 

the   duodenal   glands   are   proba-  n'-^ffgiP'^M 

bly  identical  in  nature  with  those 
of  the  pyloric  glands,  the  varia- 
tions in  size  and  granularity  some- 
times observed  depending  upon 
differences  in  .functional  condition. 
Brunner's  glands  correspond  to 
the  pure  mucous  type  (Bensley). 

Lymph  -  Nodules.  -  -  The 
lymphatic  tissue  within  the  intesti- 
nal tube  occurs  in  the  form  of  cir- 
cumscribed nodules,  which  may 
remain  isolated,  as  the  solilarv  nod- 
ules, or  be  collected  into  consider- 
able masses,  as  Pcycr  s  patches. 

The  solitary  nodules  vary 
greatly  in  number  and  size,  some- 
times being  present  in  profusion  in  all  parts  of  the  small  intestine,  at  other  times 
almost  wanting  ;  they  are  usually  scanty  in  the  upper  anil  more  numerous  in  the 
middle  and  lower  parts.  They  appear  as  small  whitish  elevations,  spherical  or  pyri- 
form  in  shape,  and  In. in  .2-2  or  even  3  mm.  in  diameter,  at  the  bottom  of  small  pits. 


Surface  view  of  mncout  membrane  of  ik-um.    x  30. 


THE  SMALL  INTESTINE. 


1641 


The  walls  of  the  latter,  however,  are  so  closely  applied  to  the  nodules  that  the  exist- 
ence of  the  pit  is  not  at  first  evident.  Villi  are  wanting  over  the  prominence  of  the 
nodules  ;  likewise  the  glands  of  Lieberkiihn,  the  orifices  of  which  are  arranged  as  a 

wreath  around  the  nodules.  The 
latter  are  found  as  much  on  one 
side  of  the  intestinal  tube  as  on 
the  other. 

In  structure  the  solitary  nod- 
ules correspond  to  similar  lymph- 
nodes  in  other  localities,  con- 
sisting of  a  capsule  of  denser 
tissue  enclosing  the  delicate  ade- 
noid reticulum  which  supports 
the  characteristic  lymphocytes 
within  its  meshes.  Within  the 
larger  nodules  germ-centres, 
spherical  or  ellipsoidal  in  form, 
occupy  the  middle  of  the  nodules; 
the  germ-centres  are,  however, 
not  constant,  being  present,  as  a 
rule,  in  young  subjects,  but  often 
absent  in  old  individuals.  A 

Surface  view  of  portion  of  mucous  membrane  of   ileum,   showing       rrr>nam,ic     K1<~./~v/-l   cnr.i-.Kr      i'c      nm 
Peyer's  patch  and  solitary  lymph-nodules.     Natural  size. 

vided    by   the  rich    net-work   of 

small  vessels  which  surrounds  the  nodules  ;  fine  capillaries  penetrate  into  their  interior, 
but  usually  do  not  reach  the  centre  of  the  nodes.  Definite  lymph-paths  have  not 
been  demonstrated  within  the  nodules,  although  a  plexus  of  lymphatics  surrounds 
their  exterior  (Teichmann). 

Peyer's  patches  (noduli  lymphatic!  aggregati)  are  collections  of  solitary 
lymph-nodules,  the  individual  follicles  being  blended  by  intervening  adenoid  tissue. 
They  are  seen  in  the  lower  half  of  the  small  intestine,  especially  near  the  lower  end 
(ileum)  ;  exceptionally  they  are  found  in  the  upper  part  of  the  jejunum  in  the 
vicinity  of  the  duodenum.  The  patches  appear  as  slightly  raised,  elongated  ovals, 

FIG.  1395. 

Submucous  fold  supporting  mucosa  with  villi 


Transverse  section  of  ileum,  showing  Peyer's  patch  cut  across.     X  10. 

always  on  the  side  of  the  intestine  opposite  to  the  attachment  of  the  mesentery. 
Their  usual  number  is  about  thirty,  although  as  few  as  eighteen  and  as  many  as 
eighty-one  have  been  counted  (Sappey).  In  length  they  ordinarily  measure  from 


1642 


HUMAN  ANATOMY. 


Mucous  coat 


1-4  cm.  and  in  breadth  from  6-16  mm. ;  exceptionally  their  length  may  reach  10  cm. 
or  more.  In  general  the  size  of  the  patches  increases  as  the  termination  of  the  ileum 
is  approached.  Each  patch  contains  usually  from  twenty  to  thirty  lymph-nodules, 
although  as  many  as  sixty  or  less  than  ten  may  be  present.  The  individual  nodules 
are  commonly  somewhat  pear-shaped,  and  when  well  developed  occupy  both  the 
mucous  and  submucous  coats,  their  smaller  end  almost  reaching  the  epithelium  and 
their  base  the  muscular  tunic.  The  free  surface  of  the  patches  is  modelled  by  minute 
pits,  from  .4-2  mm.  in  diameter,  and  low  intervening  ridges  ;  the  former  mark  the 
positions  of  the  component  nodules,  the  latter  that  of  the  blending  internodular 
tissue.  The  villi  and  the  crypts  of  Lieberkiihn  are  present  over  the  areas  between 
the  pits,  although  less  developed  than  beyond  the  patch.  In  their  minute  structure 
the  lymph-nodes  composing  the  patch  closely  correspond  to  the  solitary  nodules,  the 

aggregated  nodules  be- 

FIG.   1396.  ing  blended  into  a  con- 

tinuous mass  by  the  less 
dense  adenoid  tissue 
which  fills  the  spaces 
between  the  individual 
follicles.  The  entire 
patch  is  defined  from 
the  surrounding  struc- 
tures by  an  imperfect 
capsule. 

The  submucous 
coat  is  lax,  but  not 
enough  so  to  allow  the 
displacement  of  the  val- 
vuhr  conniventes,  ex- 
cept at  the  lower  part. 
As  in  other  segments 
of  the  intestinal  tube, 
the  submucosa  contains 
blood-  and  lymph-ves- 
sels of  considerable  size 
and  the  nerve-plexus  of 
Meissner. 

The  muscular 
coat,  about  .4  mm. 
thick,  consists  of  an 
outer  longitudinal  and 
an  inner  circular  layer. 
The  latter  is  some  two 
or  three  times  as  thick  as 
the  former  and  is  pretty 
regularly  arranged.  Th< 
thin  longitudinal  laye: 
thickest  at  the  free  bor- 
der, is  often  imperfect,  especially  at  the  attachment  of  the  mesentery.  The  entire 
muscular  coat  diminishes  in  thickness  from  above  downward. 

The  serous  coat,  with  the  exception  of  that  of  the  duodenum,  completely  su 
rounds  the  gut  except  at  the  line  of  attachment  of  the  mesentery,  where  the  two  layers 
of  peritoneum  diverge,  leaving  an  uncovered  space  between  them  just  large  enough 
for  the  passage  of  the  vessels  and  nerves.  Its  structure  resembles  that  of  the  serous 
coat  of  the  stomach  (page  1627),  and  includes  the  fibro-elastic  stroma  covered  with 
the  endothelinm. 

The  blood-vessels  supplying  the  small  intestine  are  distributed  to  the  walls  of 
the  tube  in  a  manner  closely  agreeing  with  the  arrangement  found  in  the  stomach 
(page  1627);  the  same  general  plan  applies  also  to  the  large  intestine.  The  tutfn't*, 
which  pass  to  the  intestine  between  the  peritoneal  folds  constituting  the  mesentery, 


Muscular 
coat 


Transverse  section  of  injected  small  intestine,  showing  general  distribution.    X  55- 


THE  SMALL  INTESTINE. 


after  supplying  the  serous  coat,  penetrate  the  muscular  tunic  to  reach  the  submucosa. 
Within  the  latter  branches  arise  which,  in  conjunction  with  those  directly  given  off 
during  the  passage  through  the  muscular  coat,  supply  the  muscular  tissue.  The  more 
important  and  larger  arterial  twigs  from  the  vessels  of  the  submucosa  enter  the 
mucous  coat,  in  which  some  break  up  into  capillaries  forming  net-works  surrounding 
the  gland-tubules  and  supplying  the  muscular  and  stroma  tissue  ;  others  pass  directly 
towards  the  villi,  which  they  enter  and  supply  by  capillary  net-works  occupying  the 
periphery  of  the  projections.  The  veins  of  the  intestinal  walls  commence  within  the 
mucosa  beneath  the  epithelium  and,  gradually  enlarging  as  they  descend,  become 
tributary  to  the  larger  veins  within  the  submucosa.  The  latter  follow  the  arteries  ,in 
their  passage  through  the  muscular  tunic,  uniting  to  form  the  larger  emergent  venous 
channels  which  accompany  the  arterial  trunks  between  the  peritoneal  folds. 

The  lymphatics  of  the  small  intestine,  long  known  as  the  lacteals  from  their 
conspicuous  milky  appearance  when  filled  with  emulsified  fat  during  certain  stages  of 
digestion,  begin  as  the  absorbent  or  chyle-vessels  within  the  villi.  In  addition  to 
these,  radicles  commence  within  the  stroma-tissue  of  the  mucosa,  in  which  the  lym- 


Branch  of  mesenteric  artery 
Mesenteric  vein 


Lymph-node 


Lymphatics 


Cut  edge  of  removed 
peritoneum 


Nerves 


Portion  of  small  intestine  and  mesentery,  showing  arteries,  nerves,  and  lymphatics;  latter  have  been  injected  with 

quicksilver.     Anterior  layer  of  mesentery  has  been  removed. 

phatics  form  a  plexus  in  the  plane  of  the  muscularis  mucosae.  From  the  latter  tribu- 
taries descend  to  the  larger  plexus  within  the  submucosa,  which  is  characterized  by 
channels  of  irregular  form  and  calibre  containing  numerous  valves.  The  emergent 
lymphatics  form  larger  vessels  within  the  serous  coat,  which  pass  to  the  lymph- 
nodes  situated  between  the  peritoneal  layers  ;  from  these  smaller  lymphatic  masses 
efferent  vessels  converge  to  the  larger  mesenteric  lymph-glands  at  the  root  of  the 
mesentery. 

The  nerves  supplying  the  small  intestine,  derived  from  the  solar  plexus  and 
consisting  of  both  medullated  and  non-medullated  fibres  from  the  cerebro-spinal  and 
sympathetic  systems,  closely  follow  the  disposition  observed  in  the  stomach  (page 
1 628).  After  piercing  the  other  longitudinal  layer  they  form  the  intramuscular  plexus 
of  Auerbach,  consisting  of  both  varieties  of  fibres  and  microscopic  sympathetic  gan- 
glia. The  nerves  continue  obliquely  through  the  circular  muscular  layer  and  form 
within  the  submucous  coat  the  plexu s  of  Meissncr.  From  this  plexus  non-medullated 
fibres  enter  the  mucous  coat  and  are  distributed  as  periglandular  and  subepithelial 
net-works,  as  well  as  supplying  the  muscular  tissue,  in  which,  according  to  Berkley, 
additional  special  end-organs  exist.  Within  the  villi  a  rich  plexus  of  non-medullated 


1 644  HUMAN  ANATOMY. 

fibres  has  been  demonstrated  from  which  terminal  fibrillae  are  distributed  to  the  mus- 
cular tissue  and  vessels,  as  well  as  beneath  the  epithelium. 

THE   DUODENIM. 

The  duodenum  at  an  early  stage  is  a  loop  with  a  forward  convexity  passing  from 
the  pylorus  back  to  the  spine.  It  enlarges  into  nearly  a  circle  and  turns  onto  its 
right  side,  its  termination  remaining  attached  below  the  cceliac  axis  to  the  top  of  the 
second  lumbar  vertebra.  The  part  immediately  following  the  stomach  remains  free, 
but  a  little  farther  back  it  is  suspended  from  the  liver  by  the  duodeno- hepatic  ligament, 

which   is  the  free  border  of  the  lesser 

FIG.  1398.  omentum,   containing    the   portal  vein, 

the  hepatic  artery,  and  the  bile-duct 
with  the  connective  tissue  about  them. 
This  structure  is  strong  enough  to  de- 
serve to  be  called  a  ligament.  The 
duodenum  is  therefore  nearly  a  ring  sus- 
pended at  two  points,  one  near  the 
beginning  and  the  other  (to  be  de- 
scribed later)  at  the  end.  In  the  adult 
f ,  ,-  the  shape  is  more  or  less  a  modification 

of  this  imperfect  ring.     When  relaxed 

Casts  of  duodenum,  showing  u- and  v-forms.  and  empty  it  often   nearly  retains  this 

shape.      When    distended   by   inflation 

or  injection  it  usually  shows  four  parts.  The  first,  some  5  cm.  (2  in.)  long,  runs 
backward  from  the  pylorus,  slightly  upward  and  to  the  right.  The  beginning  of 
this  portion  is  movable  ;  later  the  part  is  fixed  by  the  structures  just  mentioned. 
The  other  divisions  of  the  duodenum  are  disposed  so  as  to  form  a  U.  The  second 
part  descends  along  the  right  of  the  spine  to  the  fourth  lumbar  vertebra.  The  third 
runs  forward  and  to  the  left,  with  a  slight  rise.  The  fourth  ascends  on  the  spine  to 
the  upper  part  of  the  second  lumbar  vertebra,  where,  after  a  sharp  bend, — the 
duodeno-jejunal  flexure, — it  becomes  the  jejunum. 

The  next  most  common  form  is  the  V-shaped,  of  which  there  are  two  varieties.  In  the 
more  usual  one  the  second  part  descends,  as  in  the  preceding  form,  and  the  third  and  fourth 
are  represented  by  one  which  ascends  obliquely  to  the  termination.  The  less  frequent  variety 
has  the  second  part  inclining  forward  and  to  the  left  as  it  descends,  so  that  the  V  is  more  sym- 
metrical. A  modification  of  the  U-form,  which  we  have  called  the  C-shaped,  is  characterized  by 
a  very  short  second  part,  so  that  the  first  and  third  parts  are  almost  in  contact.  From  seventy 
observations1  on  adults  (including  one  girl  of  fourteen),  mostly  by  means  of  casts,  we  find  the 

following  forms  : 

Male.         Female.    Sex  not  noted. 

U-shaped 10  3  9 

V-shaped ....9.  9  3 

Ring-shaped 2  2 

Indeterminate 7  3  * 

C-shaped ....     5 

Not  to  be  classified 5  _^ 

3«  '7  '5 

By  "indeterminate"  is  understood  those  that  might  be  placed  in  any  two  of  the  U,  V,  or  C 
types,  according  to  the  classifier.  Those  marked  "  not  to  be  classified"  are  absolutely  irregular. 
The  V-shape  is  particularly  common  in  women  and  the  irregular  forms  in  men.  It  slit  mid  be 
noted  that  a  very  large  part  of  the  duodenum  lies  in  an  essentially  antero-posterior  plane,— 
namely,  the  first,  second,  and  a  considerable  portion  of  the  third  part,  the  organ  being  moulded 
on  the  spinal  column.  The  length  of  the  whole  duodenum  and  of  its  parts  is  so  variable  that  a 
statement  can  be  only  general.  The  first  part  is,  according  to  Testnt,  5  cm.,  the  second  S  cm.,  the 
third  6  cm.,  and  the  fourth  7  cm.,  the  total  length  of  the  duodenum  being  2h  cm.,  or  about 
10  in.  The  circumference  varies  greatly  in  different  bodies.  The  fourth  part  is  the  smallest. 
The  second  increases  in  si/e  as  it  descends,  and  the  largest  point  is  in  either  the  second  or  third. 
The  two  largest  circumferences  that  we  have  measured  \vere  in  the  second  part.  _  \Ye  are  sat- 
isfied that  the  si/.- of  some  immense  duodena  is  in  no  way  due  to  artificial  distention  ;  to  what 
extent  it  is  pathological  is  uncertain. 

1  Journal  of  Anatomy  and  Physiology,  vol.  xxxi.,  1X97. 


THE   DUODENUM.  1645 

The  first  part  is  often  egg-shaped,  narrowing  at  the  ends.  Its  main  direction 
is  backward,  slightly  upward  and  to  the  right,  to  reach  the  first  lumbar  vertebra  ;  but, 
as  it  is  movable,  its  direction  is  somewhat  variable.  The  gut  rests  above  against  the 
quadrate  lobe  of  the  liver  and  the  neck  of  the  gall-bladder,  behind  which  it  is  free, 
forming  the  lower  border  of  the  foramen  of  Winslow.  The  left  side  looks  into  the 
lesser  peritoneal  cavity,  and  is  crossed  near  the  back  by  the  common  bile-duct.  The 
right  side  is  chiefly  against  the  liver  and  gall-bladder  ;  otherwise  it  is  in  contact,  as 
is  the  lower  side,  with  coils  of  the  small  intestine.  The  lower  side,  moreover,  rests 
on  the  head  of  the  pancreas. 

The  second  part  descends  vertically,  forming  an  acute  angle  with  the  first. 
It  is  bent  so  sharply  that  a  fold  of  the  entire  thickness  often  projects  into  the  gut.  It 
lies  on  the  right  side  of  the  vertebral  bodies  beside  the  vena  cava,  and  behind  rests  on 
the  right  suprarenal  capsule  and  kidney,  being  in  contact  also  with  the  pelvis  of  the 
latter,  the  renal  vein,  and  the  beginning  of  the  ureter.  The  precise  relations  with 
the  right  kidney  are  uncertain,  owing  to  the  variations  both  of  that  organ  and  of  the 
duodenum.  It  lies  on  the  right  against  the  ascending  colon  and  on  the  left  against 
the  head  of  the  pancreas,  which  may  overlap  it  in  front.  The  bile-duct  runs  along  the 
left  side  and  passes  obliquely  through  the  intestinal  wall,  to  empty,  in  conjunction  with 
the  pancreatic  duct,  some  10  cm.  from  the  pylorus. 

From  observations  on  fifty-four  adult  duodena  (thirty-eight  male,  sixteen  female)  we  have 
found  that  in  the  great  majority  of  duodena  of  both  sexes  the  lowest  point  is  opposite  the  fourth 
lumbar  vertebra  or  the  disk  above  or  below  it.  In  about  one-quarter  of  the  cases  it  is  opposite 
the  third,  and  only  some  half  dozen  times  opposite  the  fifth,  of  which  cases  some  were  probably 
pathological.  The  mean  of  the  female  duodenum,  in  which  sex  the  V-shape  is  most  frequent, 
is  a  little  lower  than  that  of  the  male,  but  not  strikingly  so.  The  angle  between  the  second 
and  the  third  parts  in  the  U-form  is  rather  less  sharp  than  that  between  the  first  and  the  second. 

The  third  part  curls  around  the  spinal  column,  passing  forward  to  its  front  and 
then  to  the  left  with  a  slight  ascent  till  it  reaches  the  aorta.  It  crosses  the  vena 
cava  and  has  the  pancreas  above  it,  which,  with  the  first  and  second  parts,  it  tends  to 
enclose.  The  head  of  the  pancreas  may,  however,  more  or  less  overlap  the  third  part 
as  it  does  the  second,  and  also  insinuate  itself  behind  it.  In  less  than  one-quarter  of 
the  cases  the  third  part  crosses  the  aorta,  its  course  being  more  transverse  than  the 
one  just  described.  It  may  be  connected  to  the  aorta  by  areolar  tissue  or,  especially 
if  it  run  only  just  beyond  the  aorta,  a  fold  of  peritoneum  may  intervene. 

The  fourth  part  usually  begins  at  an  obtuse  angle  with  the  third,  and  ascends 
on  the  front  of  the  spine  to  the  top  of  the  second  lumbar  vertebra.  In  this  course 
it  overlaps  the  aorta  and  usually  ends  either  directly  over  it  or  just  at  its  left.  In 
fifty-four  observations  the  duodenum  was  on  the  right  of  the  aorta  until  just  before 
its  final  flexure  twenty-six  times.  It  was  wholly  on  the  right  of  the  aorta  six  times. 
The  fourth  part  lay  in  front  of  the  aorta  eleven  times  and  the  third  part  actually 
crossed  it  eleven  times.  It  is  clear  from  the  above  that  it  is  exceptional  for  the  duo- 
denum to  reach  the  left  kidney  and  ureter,  but  it  may  do  so  when  it  really  crosses 
the  aorta.  The  tail  of  the  pancreas  is  behind  it,  as  is  usually  a  part  of  the  left  supra- 
renal capsule.  The  head  of  the  pancreas  may  be  so  developed  as  to  overlap  it,  but 
this  is  rare.  The  mesentery  of  the  small  intestine  usually  rises  above  on  its  front  sur- 
face and  gradually  crosses  it  to  the  right.  It  may  be  very  nearly  surrounded  by 
peritoneum,  or  the  posterior  surface  may  be  without  it.  Sometimes,  although  rarely, 
the  last  part  stops  short  of  the  second  lumbar.  In  the  V-shaped  duodenum  the  third 
and  fourth  parts  are  in  one.  This  form  evidently  is  wholly  to  the  right  of  the  aorta, 
except,  perhaps,  the  very  end.  It  sometimes  ascends  along  the  right  side  of  the  right 
iliac  artery,  and  then  on  the  right  or  front  of  the  aorta.  The  duodenum  ends  in  a 
sharp  turn,  the  duodeno-jejunal  flexure.  The  very  top  of  the  gut  at  the  bend  is 
suspended  from  the  left  cms  of  the  diaphragm  and  from  the  areolar  tissue  about  the 
cceliac  axis  by  the  duodenal  suspensory  muscle  of  Treitz,  a  small  triangular  band  of 
muscular  and  fibrous  tissue,  which  reaches  the  gut  where  it  is  uncovered  by  perito- 
neum, and  is  said  to  join  the  layer  of  longitudinal  muscular  fibres.  This  band  and 
the  duodcno- hepatic  ligament  hold  all  the  duodenum  after  the  very  beginning  sus- 
pended and  fixed  so  that  only  the  beginning  is  movable.  It  is  further  secured  by 


1646 


Hl'MAN   ANATOMY. 


the  retro-peritoneal  connective  tissue  and  by  the  peritoneal  reflections.  The  shape 
allows  the  food  from  the  stomach  as  well  as  the  fluid  poured  into  it  from  the  liver 
and  pancreas  to  accumulate  and  thus  to  act  as  an  S-trap  to  prevent  the  passage  of 
gases  from  the  intestine  into  the  stomach.  At  the  same  time  the  great  development 
of  the  valves  tends  to  retard  the  passage  of  the  food. 

Peritoneal  Relations. — The  peritoneum  of  the  front  and  back  of  the  stomach 
is  continued  along  the  right  and  left  sides  of  the  first  part  of  the  duodenum  respec- 

FIG.  1399. 


Right  lunj. 


Cut  diaphragm 


Hepatic  veins- 

Vena  cava_B 

Right  suprarenal  body 

Castro-hepatic  omerttum 
Probe  in  foramen  ot 
Winslow 

Right  kidney 

Beginning  of 

duodenum 

Beginning  of 

transverse  colon JL 

Head  of  pancreas • 

Duodenum — 


Right  mesocolon 
Ascending  colon 


nd  of  ileum 

V    \ 


Appendix 
Rectum 
Bladder 


Left  lung 


-Pericardium 

Cayal  opening  in 
diaphragm 

_CEsophagus 

_Spleen 
Left  suprarenal 
body 

Left  kidney 
Splenic  flexure 
Tail  of  pancreas 

Left  end  of  cut 
transverse  colon 
Jejunum 
Superior  mesen- 

teric  artery- 


Left  mesocolon 


Cut  root  of 
mesentery 


igmoid  flexure 


Abdomen  of  formalin  subject ;  peritoneum  partially  dissected  off,  exposing  organs  in  situ  on  posterior  wall  ;  transverse 
colon,  mesocolon,  mesentery,  and  jejuno-ileum  removed. 


lively.  These  layers  meet  above  along  the  greater  portion  of  the  first  part  to  form 
the  lesser  omen  turn,  which  ends  posteriorly,  as  already  stated,  by  forming  the  hepatico- 
duodenal  ligament,  consisting  of  the  vessels  entering  the  portal  fissure  of  the  liver 
with  their  enveloping  connective  tissue.  The  free  edge  where  the  peritoneum  passes 
behind  the  ligament  is  on  the  inner  side  rather  than  above  the  gut.  Just  back  of  this 


THE  DUODENUM. 


1647 


fold  the  upper  surface  of  the  first  part  of  the  duodenum  is  covered  by  peritoneum 
and  forms  the  floor  of  the  foramen  of  Winslow.  The  attachment  of  the  greater 
omentum,  which  is  continued  from  the  greater  curvature  of  the  stomach  onto  the 
under  side  of  the  duodenum,  passes  along  its  inferior  surface  to  the  second  part, 
where  in  the  adult  it  has  fused  with  the  mesentery  of  the  transverse  colon.  The  peri- 
toneum of  the  right  side  of  the  first  part  of  the  duodenum  looks  into  the  general 
peritoneal  cavity  and  that  of  the  left  side  into  the  lesser  cavity. 

The  relations  of  the  remainder  of  the  duodeuum  necessarily  vary  with  the  dis- 
tention  of  the  intestine  ;  but  it  is  correct  to  say  that  it  lies  behind  the  peritoneum, 
owing  to  the  change  into  connective  tissue  subsequent  to  the  fusion  of  the  serous 
membrane  of  the  right  side  of  the  duodenum  and  that  of  the  posterior  abdominal 
wall.  Very  often  when  the  fourth  part  lies  in  front  of  the  aorta  a  fold  of  peritoneum 
passes  some  distance  in  between  them  from  the  left  ;  but  this  pocket  disappears  when 
the  gut  is  distended.  The  pancreas,  when  it  overlaps  the  second,  third,  or  even  the 
fourth  part,  more  or  less  displaces  the  peritoneum.  The  duodenum  is  crossed  by 
the  attachment  of  the  mesentery  of  the  jejuno-ileum  and  by  that  of  the  transverse 
mesocolon.  The  series  of  changes  by  which  this  has  occurred  is  dealt  with  under 

FIG.  1400. 

Transverse  mesocolon 
Jejunum  Duodenum 


Superior 
duodenal  fossa 
Branch  of  left 

colic  artery 


Inferior  duodenal 

'M    f°ssa 

Descending  colon 


.'  •'.-&- ~-!$L — Mesentery  of  small 

/  .'?  '"'•'          intestine 

v 

f 

Duodeno-jejunal  junction,  showing  duodenal  fossae  ;  jejunum  turned  to  the  right. 

Peritoneum  (page  1742),  the  adult  condition  alone  being  here  considered.  The  line 
of  attachment  of  the.  transverse  mesocolon  crosses  the  second  part  of  the  duodenum 
a  little  below  the  deep  flexure  which  on  the  front  separates  it  from  the  first.  The 
position  of  the  line  of  attachment  of  the  mesentery  of  the  jejuno-ileum  varies  with 
the  shape  and  position  of  the  duodenum.  Should  the  latter  have  its  third  part 
crossing  the  aorta,  the  attachment  of  the  mesentery  will  cross  the  third  part  only, 
passing  somewhat  obliquely  downward  to  the  right.  In  the  more  usual  arrangement, 
in  which  the  fourth  part  of  the  duodenum  either  ends  on  the  front  of  the  aorta  or 
crosses  it  only  just  before  its  termination,  the  line  of  attachment  starts  on  the  front 
of  the  fourth  part  or  somewhat  on  the  right  of  it  and  descends  on  more  or  less, 
sometimes  on  the  whole  length  of  this  portion,  or  else  lies  just  to  the  right  of  it  and 
then  crosses  the  third  part.  In  the  case  of  the  V-shaped  duodenum  the  mesentery 
runs  down  on  or  along  the  right  of  the  oblique  portion. 

Duodeno-jejunal  Fossae. — Several  pockets  formed  by  folds  of  peritoneum 
are  found  near  the  end  of  the  duodenum  in  the  greater  cavity  of  the  peritoneum. 
Some  are  vascular, — that  is,  containing  a  vessel  at  or  near  the  edge  of  the.fold, — while 
others  are  not.  We  have  adopted  the  classification  of  Jonnesco,  who  describes  five 
forms. 


HUMAN   ANATOMY. 


The  inferior  duodenal  fossa  (Fig.  1400)  is  the  most  common  form,  occurring, 
according  to  Jonnesco,  in  75  per  cent.,  and  to  Treves  in  40  per  cent.  It  is  non- 
vascular,  formed  by  a  fold  of  peritoneum  passing  from  the  left  of  the  fourth  part  of 
the  duodenum  to  the  posterior  wall,  with  a  free  concave  edge  looking  upward.  The 
pocket  extends  down  behind  this  fold  for  a  variable  distance.  It  may  reach  the 
fourth  lumbar  vertebra. 

The  superior  duodenal  fossa  occurs  in  50  per  cent.  This  corresponds  to  the 
preceding,  only  it  runs  upward  behind  a  fold,  with  a  concave  free  edge  looking 
downward,  passing  from  the  duodeno-jejunal  flexure  to  the  posterior  wall  on  the 
left.  The  pocket  is  less  deep  than  the  preceding.  It  is  usually  vascular,  the  in- 
ferior mesenteric  vein  running  in  the  fold,  sometimes  near  its  edge.  These  two 
fossae  frequently  coexist,  and  the  left  ends  of  the  folds  may  be  continuous,  so  as  to 
form  a  large  C-shaped  fold,  open  to  the  right,  with  a  pocket  under  both  the  upper 
and  the  lower  limbs.  In  this  case  the  vein  may  be  in  the  vertical  part  of  the  fold. 
An  arterial  arch,  formed  either  by  the  ascending  branch  of  the  left  colic  artery  or 
by  the  left  branch  of  the  middle  colic,  is  often  very  close  to  the  vein.  Such  a 
pouch  may  extend  deeply  under  the  fourth  part  of  the  duodenum. 

The  mesocolic  fossa,1  found  in  20  per  cent.,  and  always  alone,  is  a  little  pocket 
on  the  top  of  the  duodeno-jejunal  flexure  under  a  fold  from  the  posterior  layer  of  the 
transverse  mesocolon.  When  th  s  membrane  is  reflected  so  as  to  show  it,  the  fossa 

appears  to  run  upward.  The  in- 
ferior mesenteric  vein  may  be  in 
the  fold. 

The  paraduodenal  fossa  is  in 
the  peritoneum  of  the  posterior 
abdominal  wall,  less  intimately 
connected  with  the  gut  than  the 
others.  It  is  a  pocket  formed  by 
'  the  superior  branch  of  the  left  colic 
artery  raising  a  fold  of  the  perito- 
neum. The  mouth  of  the  pouch 
is  to  the  right.  It  is  not  uncom- 
mon in  the  infant,  rare  in  the  adult. 
The  retrodnodcnal fossa  is  an 
uncommon  pouch  under  the  third 
and  fourth  parts  of  the  duodenum, 
extending  upward  with  the  mouth 
below. 

Interiorof  the  Duodenum. 


FIG.  1401. 


Surface  view  of  mucous  membrane  of  duodenum  ;  entrance  of       The  I11UCOUS    COat    is    smooth    ill 

bile  and  pancreatic  ducts  shown  by  probe,  which  lies  in  bile-duct. 

Papilla  is  surrounded  by  hood-like  fold.     Natural  size.  the     first     part     and      OVerllCS      the 

glands   of    Brunner   (page    1639), 

which  lie  chiefly  within  the  submucosa  and  form  a  continuous  layer  for  some  4  or 
5  cm. ;  beyond  they  are  scattered  for  some  distance  farther.  The  villi  are  small  at 
the  beginning,  but  soon  attain  their  complete  size.  The  valvulae  conniventes  are  at 
first  absent  for  about  4.5  cm.,  appearing  at  the  end  of  the  first  part,  and  are  almost 
at  once  large,  near  together,  and  non-effaceable.  A  very  large  one  is  formed  by  the 
folding  in  of  the  wall  at  the  junction  of  the  first  and  second  parts  ;  beyond  this  tin- 
valves  at  once  reach  their  greatest  development.  In  the  second  part  tin-  bile-papilla 
is  seen  in  the  back  part  of  the  left  or  inner  wall,  from  8.  5-10  cm.  (about  3^-4  in.) 
beyond  the  pylorus,  or  rather  below  the  middle,  through  which  the  common  bile-duct 
and  the  duct  of  the  pancreas  pass  to  open  by  a  common  orifice.  The  papilla  is  almost 
always  overhung  by  a  valvular  fold  (Fig.  1401 ),  and  when  non-distended  is  only  some 
5  mm.  long.  The  accessory  duct  of  the  pancreas  often  opens  2  or  3  cm.  above 
the  main  one  through  a  much  smaller  and  inconstant  papilla.  The  submucous  coat 
holds  the  mucous  membrane  pretty  firmly  in  place,  so  that  the  folds  are  permanent. 

'Jonnesco  calls  this  also  the  fossette  duodcno-jcjnnale ;  but.  although  following  him  other- 
wise we  !..iv.  retained  duodeno-jejunal  as  the  generic  name.  We  have  applied  the  named  fossa 
duodenO'jejunalis  in  Fig.  1418  to  what  is  probably  an  accidental  and  quite  irregular  fossa. 


THE  JEJUNO-ILEUM.  1649 

Blood-Vessels. — Arteries. — The  duodenum,  like  the  stomach,  is  attached  to 
that  part  of  the  original  mesentery  through  which  the  branches  of  the  cceliac  axis 
run.  The  stomach  is  supplied  chiefly  by  the  coronary  and  the  splenic  arteries,  the 
duodenum  by  the  hepatic  with  the  help  of  a  recurrent  branch  from  the  superior 
mesenteric.  The  hepatic  artery  gives  off  the  pyloric,  which  sends  some  insignificant 
twigs  to  the  beginning  of  the  duodenum,  and  the  gastro-duodenal, 
which  runs  on  the  left  of  the  first  part  and  sends  off  the  superior  FIG.  1402. 
pancreatico-duodenal,  which  passes  downward  and  to  the  left  in  the 
concavity  of  the  duodenum  between  it  and  the  pancreas,  lying 
rather  on  the  front  of  the  duodenum,  of  which  it  is  the  chief  artery. 
The  superior  is  met  by  the  inferior  pancreatico-duodenal  artery, 
which  arises  from  the  right  side  of  the  superior  mesenteric  and 
descends  along  the  right  of  the  fourth  part  of  the  duodenum.  The 
superior  mesenteric  distributes  one  or  two  small  twigs  to  the  very 
end  of  the  duodenum.  

Veins. — The  pyloric  vein, — larger  than  the  artery  of  the  same          Abnormal  form 
name, — in    conjunction    with    the    superior    pancreatico-duodenal,     and  course  of  duo- 

,      .  .  ,      .         ,         ,  ^L  clenum.    (Schicffet- 

drams  the  greater  part  of  the  duodenum.      Ihey  may  open  in  com-    decker.) 

mon  or  separately  into  the  portal  vein,  and  are  in  direct  connection 

with  the  inferior  pancreatico-duodenal,   which   opens  into  the  superior  mesenteric 

vein. 

The  lymphatics  pass  to  the  pre-aortic  lymph-nodes. 

The  nerves  of  the  duodenum,  as  are  those  supplying  other  parts  of  the  small 
intestine,  are  from  the  solar  plexus. 

Variations. — As  already  shown  (page  1644),  much  variation  exists  in  the  shape  of  the 
duodenum  ;  moreover,  very  extraordinary  duodena  sometimes  occur.  It  is  probable  that  these 
are  generally  due  to  an  over-long  duodenum,  which,  after  having  completed  the  usual  course, 
describes  one  or  more  additional  curves  before  reaching  the  duodeno-jejunal  flexure.  We 
have  seen  a  case  in  which  the  end  of  the  V  almost  touched  the  pylorus  and  then,  mounting  still 
higher,  described  a  ioop  to  the  left  behind  the  peritoneum.  This  occurred  in  a  man  with  the 
sigmoid  flexure  and  rectum  on  the  right.  These  cases  usually  are  associated  with  other  errors 
of  intestinal  or  peritoneal  development.  In  the  remarkable  case  of  Schiefferdecker1  (Fig.  1402) 
there  was  a  mesenterium  commune. 

THE  JEJUNO-ILEUM. 

The  jejuno-ileum  includes  the  remainder  of  the  small  intestine,  which,  disposed 
in  folds  attached  on  one  side  to  the  mesentery,  extends  from  the  duodeno-jejunal  fold 
to  the  caecum,  its  length  being,  therefore,  approximately  6.75  m.  (nearly  22  ft.),  of 
which  the  first  two-fifths  are  conventionally  credited  to  the  jejunum  and  the  remain- 
ing three-fifths  to  the  ileum.  It  is  a  cylindrical  tube  continually  decreasing  in  size. 
The  diameters  are  variously  stated,  Testut  giving  the  mean  diameter  of  the  upper 
part  as  from  25-30  mm.  and  that  of  the  lower  as  from  20—25  mm.  These  latter  figures 
our  own  measurements  confirm,  since  on  thirty-seven  inflated  specimens  of  the  lower 
end  the  average  diameter  was  24  mm.,  the  extremes  being  17  and  37  mm.  Chaput 
and  Lenoble2  assert  that  the  inferior  circumference  is  reduced  internally  to  32  mm. 
(on  inflated  specimens  to  50  mm.)  by  a  valve  near  the  caecum.  This  valve,  which 
we  have  found  in  about  one-third  of  the  cases,  is  remarkable  in  being  always  situ- 
ated on  the  posterior  aspect  of  the  gut,  generally  at  a  sharp  bend  ;  it  often  contains 
a  small  artery,  and  is  probably  formed  by  the  folding  in  of  the  muscular  coat.  Its 
position  is  frequently  near  the  point  at  which  the  ileum  begins  to  lie  against  the 
wall  of  the  caecum,  but  it  may  be  2.5  cm.  or  more  higher.  The  valve  is  sometimes 
double,  and  varies  in  height  from  2  mm.  to  i  cm.  We  have  not  found,  however, 
that  this  fold  is  necessarily  the  narrowest  point  of  this  part  of  the  gut.  A  piece  of 
the  intestine  from  the  upper  part  of  the  jejunum  weighs  more  than  one  of  equal  area 
from  the  lower  part  of  the  ileum,  owing  to  the  greater  thickness  of  the  walls  of  the 
former  and  to  the  greater  development  of  the  valves  in  that  part.  The  structure 
of  this  part  of  the  small  intestine  has  already  been  described  (page  1634). 

1  Arch,  fiir  Anat.  und  Entwicklng.,  1887. 

2  Bull.  Soc.  Anat.  de  Paris,  1894. 

104 


1650 


HUMAN   ANATOMY. 


The  Mesentery  and  Topography  of  the  Jejuno-Ileum. — Since  consid- 
eration of  the  mesentery  is  indispensable  for  the  study  of  the  disposition  of  the  folds 
and  relations  of  the  small  intestine,  this  structure  next  claims  attention.  The  serous 
covering  of  the  gut  itself  requires  no  further  description  than  to  note  that  it  com- 
pletely surrounds  the  bowel,  except  at  the  double  line  of  its  attachment,  where  there 
is  left  space  just  large  enough  for  the  passage  of  the  vessels  and  nerves.  The  attached 
border  of  the  mesentery  (Fig.  1399)  extends  from  the  left  of  the  front  of  the  first 


FIG.   1 103. 


.    -      ,-.    v; • 


Right  lung 


Diaphragm  (cut) 


Hepatic  vein 

Behind  Spigelian 
lobe 

Right 

suprarenal  body. 
Probe  in  foramen 
of  Winslow 

Right  kidney. 

Beginning 

of  duodenum 

Left  end  of, 

transverse  colon 

Duodenum 


Jejunum- 


Ascending  colon — L& 


Ileun 


Left  lung 


H — CEsophagus 


Spleen 

•Left  suprarenal  body 

Left  kidney 


Left  end  of  colon 
•Duodeno-jejunal 


Formalin  subject;  liver,  stomach,  transverse  mesocolon,  and  colon  have  been  removed,  leaving  other  abdominal 
organs  in  situ  ;  attachment  of  cut  peritoneum  Indicated  by  white  line. 

or  second  lumbar  vertebra,  immediately  below  the  end  of  the  duodenum,  where  the 
superior  mesenteric  artery  enters  it,  to  the  right  sacro- iliac  joint,  a  distance  of  about 
15  cm.  (6  in.).  The  relations  of  the  upper  part  of  the  fold  are'determined  by  the 
shape  and  position  of  the  duodenum.  Probably  the  usual  course  of  the  mesenteric 
attachment  is  from  the  front  of  the  aorta  downward  on  the  fourth  part  of  the  duo- 
denum, across  the  vena  cava  to  the  right  sacro-iliac  joint.  With  a  V-shaped  duo- 


THE  JEJUNO-ILEUM. 


1651 


denum  the  line  of  the  mesentery  is  usually  on  the  right  of  the  gut  ;  with  a  duodenum 
that  crosses  the  aorta  the  line  is  across  the  third  part.  The  lower  end  of  the  mesen- 
tery is  determined  by  the  degree  of  adhesion  of  the  right  mesocolon  to  the  abdomi- 
nal wall.  It  rarely  stops  short  of  the  sacro-iliac  joint,  but  it  may  be  continued 
farther  into  the  right  iliac  fossa. 

The  free  or  intestinal  border  of  the  mesentery  is  some  6  m.  or  about  20  ft.  long. 
In  the  middle  the  distance  between  the  borders  is  from  20-22.5  cm-  (8-9  in.). 
Near  its  origin,  in  the  first  six  inches  of  the  intestine,  the  mesentery  has  reached  a 
breadth  of  from  12-15  cm-  (5~6  in.).  At  the  lower  end  its  breadth  is  more  uncer- 
tain, being  usually  slight,  only  from  2.5-5  cm-  f°r  tne  last  six  inches.  It  increases 
with  age,  presumably  concurrently  with  the  increase  of  girth.  The  mesentery  con- 
tains vessels  and  nerves  as  well  as  lymphatic  glands  between  its  folds  ;  these  struc- 
tures may  lie  in  a  considerable  mass  of  fat,  adding  to  the  thickness,  which  is  much 
greater,  on  account  of  the  size  and  number  of  the  vessels,  in  the  upper  part  than  in 
the  lower.  The  larger  lymph-nodes 

and  the  fat  accumulate  chiefly  near  the  FIG.  1404. 

spinal  border,  where  the  mesentery 
may  be  very  thick  and  heavy,  while 
the  part  near  the  intestine,  except  in 

the   case  of  excessive  fatty   accumula-  __... 

tion,   is  always  thin  and  yielding.     It  -.^Si  •amr***'    •*-*'* '          ;  « 

is  evident  that  the  mesentery  with  an 
attached  border  of  only  15  cm.  (6  in.) 
and  a  free  one  of  6  m.  (20  ft. )  must  be 
very  much  folded  ;  and  further,  that 
while  the  intestinal  border  must  pre- 
sent a  vast  number  of  totally  irregular 
and  transitory  folds,  changing  with 
the  movements  of  the  gut,  the  heavier 
and  more  fixed  part  of  the  mesentery 
near  the  root  must  present  certain  chief 
folds  the  position  of  which  is  tolerably 
stable. 

Henke l  has  shown  that  if  the  hand 
be  introduced  among  the  coils  of  intes- 
tines in  the  line  of  the  left  psoas  muscle 
and  carried  upward,  it  enters  the  con- 
cavity of  a  horseshoe-shaped  fold  of  the 
mesentery,  and  that  the  intestines  easily 
fall  apart  to  either  side.  The  coils  on 
the  left  are  in  the  main  transverse  and 
those  to  the  right  chiefly  vertical.  This 
plan,  although  sometimes  obscure,  is  often  beautifully  clear,  especially  in  infants. 
Weinberg,2  from  studies  on  the  new-born  infant,  has  carried  the  plan  into  further 
details.  He  finds  that  the  upper  two-fifths  of  the  intestine  are  arranged  in  trans- 
verse folds  in  the  upper  left  part  of  the  abdomen  ;  the  middle  fifth  lies  in  the  left 
iliac  region  without  definite  arrangement  ;  the  last  two-fifths  are  in  the  median 
part  and  in  the  right  iliac  region,  disposed  in  the  main  vertically.  Still,  cases 
occur  at  all  ages  in  which  the  plan  is  obscure.  Mall s  has  traced  the  plan  of  the 
intestines  throughout  development,  and  incidentally  confirms  Weinberg' s  state- 
ments. The  following  account  of  the  normal  arrangement  in  the  adult  is  essentially 
according  to  his  researches.  The  gut  is  to  be  conceived  as  arranged  in  spiral  coils 
travelling  from  the  left  hypochondriac  region  to  the  right  iliac  fossa,  successive  coils 
being  in  the  main  parallel.  Starting  from  the  duodenum,  there  are  two  transverse 
folds  in  the  left  hypochondrium,  followed  by  a  long  fold  that  goes  across  the  body 
and  back.  Some  less  distinctly  transverse  folds  occupy  the  left  iliac  fossa.  The 

1  Arch,  fur  Anat.  und  Entwicklng.,  1891. 

3  Internal.  Monatsschrift  fur  Anat.  und  Phys.,  Bd.  xiii.,  1896. 

3  Arch,  fiir  Anat.  und  Entwicklng.,  1897.     Supplement  Bd. 


Typical  disposition  of  folds  of  mesentery  shown  after 
removal  of  jejuno-ileum.  i,  end  of  duodenum  ;  2,  3,  4,  jeju- 
num ;  =;,  ileum  ;  6,  termination  of  ileum  into  large  intestine. 

(Mall.) 


1652  HUMAN   ANATOMY. 

remainder  is  disposed  vertically,  occupying  the  lower  part  of  the  umbilical  region 
and  the  pelvis,  and  extending  on  the  right  as  far  as  the  large  intestine  will  allow. 
The  vertical  arrangement  of  this  portion  is  generally  less  striking  than  the  trans- 
verse disposition  of  the  preceding.  The  end  of  the  ileum  rises  from  the  pelvis  into 
the  right  iliac  fossa.  There  are,  of  course,  frequent  deviations  from  the  above  plan 
of  arrangement  of  the  folds.  It  is  easy  to  see  that  the  appearance  at  the  surface  of 
some  that  are  usually  deep  would  obscure  the  plan.  It  is  worth  noting  that  adjacent 
folds  should  never  be  assumed  to  be  continuous. 

Blood-Vessels. — The  arteries  of  the  jejuno-ileum  are  branches  of  the 
superior  mesenteric,  which  enters  the  mesentery  below  the  pancreas.  The  vessels 
for  the  gut  are  straight  ones  arising  from  the  arterial  arches.  In  the  upper  part 
they  are  from  4-5  cm.  long,  3  cm.  in  the  middle,  and  very  small  at  the  end  of  the 
ileum.  They  run  without  anastomoses  to  the  edge  of  the  gut,  where  they  break  up 
into  bunches  of  slightly  diverging  branches.  All  of  these  usually  go  to  one  side  of 
the  gut,  each  alternate  vessel  taking  a  different  side,  although  sometimes  a  vessel 
may  send  branches  to  both  sides.  Anastomoses  in  the  walls  of  the  gut  between 
the  branches  of  neighboring  arteries  are  not  numerous,  and  occur  only  between 
very  fine  vessels,  except  opposite  the  mesentery,  where  vessels  of  the  different  sides 
meet.  The  distribution  of  the  veins  is  essentially  the  same. 

The  lymphatics,  large  and  numerous,  empty  into  the  mesenteric  nodes, 
which  they  connect.  These  lymph-nodes  vary  in  number  from  one  to  two  hundred, 
the  largest  lying  near  the  root  of  the  mesentery,  from  which  position  they  grow 
smaller  as  they  approach  the  free  edge.  There  are  no  nodes,  however,  between  the  gut 
and  the  last  vascular  arch,  unless,  perhaps,  near  the  very  end  of  the  small  intestine. 

The  nerves  of  the  entire  small  intestine  are  from  the  solar  plexus.  They 
receive  many  cerebro-spinal  fibres  through  the  splanchnics. 

Meckel's  Diverticulum. — This  is  an  outgrowth  from  the  ileum,  shaped  like 
the  finger  of  a  glove,  and  found  in  some  2  per  cent.  It  is  the  remnant  of  the  vitel- 
line  duct,  which  at  an  early  stage  connects  the  gut  with  the  yolk-sac.  It  springs 
most  frequently  from  the  free  border  of  the  bowel,  sometimes,  however,  from  the 
side,  and,  as  a  rule,  but  not  invariably,  is  composed  of  all  the  intestinal  coats.  Its 
usual  position  is  within  i  m.  (on  an  average,  82  cm. )  of  the  caecum.  Diverticula 
said  to  have  been  found  in  the  upper  part  of  the  small  intestine  are  regarded  with 
suspicion.  The  diameter  of  the  diverticulum  is  usually  that  of  the  gut,  but  it  may 
be  less  and  associated  with  a  conical  form.  The  length  varies  from  2.5  cm.  or  less 
to  17.5  cm. (7  in.),  although  ordinarily  between  2.5  and  7.5  cm.  (i  and  3  in.). 
As  a  rule,  its  end  is  free,  but  often  a  delicate  band  extends  from  its  apex  to  the 
umbilicus  or  to  some  of  the  contents  of  the  abdomen,  generally  the  mesentery. ' 

PRACTICAL   CONSIDERATIONS  :   THE   SMALL  INTESTINE. 

i.  The  Peritoneal  Coat. — This  is  complete  below  the  duodenum  except  at  the 
mesenteric  aspect,  where  the  two  layers  of  peritoneum  diverge  for  about  8  mm.  ( */3  in. ). 
The  jejuno-ileum  is  therefore  practically  an  intraperitoneal,  and  not  merely  an  intra-ab- 
dominal,  viscus,  although,  of  course,  really  outside  the  peritoneal  sac.  Inflammation 
of  this  portion  of  the  general  peritoneum  is  more  apt  to  be  acute,  to  spread  rapidly, 
and  to  be  attended  by  serious  or  fatal  results  than  is  that  of  any  other  portion.  Such 
infection  is  frequent  on  account  of  the  great  length  of  the  small  intestine,  its  exposure 
to  trauma,  the  thinness  of  its  muscular  walls,  the  variety  and  number  of  the  lesions 
of  its  mucosa,  its  close  relation  to  all  the  intra-abdominal  viscera,  and  its  consequent 
participation  in  their  injuries  and  diseases.  Direct  transmission  of  infection  from 
within  outward  is  favored  by  the  relatively  intimate  relation  between  the  peritoneal 
and  muscular  coats,  the  subserous  areolar  tissue  being  much  scantier  and  containing 
much  less  fat  than  that  intervening  between  the  parietal  peritoneum  and  the  fascia' 
and  muscles  of  the  abdominal  wall.  The  extent  and  fatality  of  peritoneal  inflam- 
mation result  from  the  facility  with  which  it  spreads  by  both  continuity  and  contiguity, 
and  from  the  fact  that,  ctrtcrh  f>aribus,  its  toxic  products  are  proportionate  in  amount 
to  the  area  involved.  The  association  of  the  spinal  and  sympathetic  nerves  in  the 
1  Lamb  :  American  Journal  of  the  Medical  Sciences,  1893. 


PRACTICAL  CONSIDERATIONS  :  THE  SMALL  INTESTINE.     1653 

intramuscular  plexus  of  Auerbach  and  the  submucous  plexus  of  Meissner,  and  their 
connection  with  the  lower  seven  intercostal  nerves  distributed  to  the  skin  and  muscles 
of  the  abdomen,  explain  (a)  the  abdominal  rigidity  and  tenderness  which  often  pre- 
cede an  extension  of  disease  from  the  visceral  to  the  parietal  peritoneum  ;  (^)  the 
paresis  or  paralysis  of  the  intestines  which  is  so  common  as  a  symptom  of  peritonitis, 
and  which  favors  stasis  of  intestinal  contents,  putrefaction,  and  distention  ;  (c)  the 
vasomotor  disturbance  which  is  an  important,  if  not  the  chief,  factor  in  the  production 
of  meteorism  ;  (d)  the  vomiting,  first  reflex  and  then  from  irregular  muscular  con- 
traction (reversed  peristalsis)  ;  and  (e)  the  reference  of  the  early  pains,  no  matter 
what  the  seat  of  the  peritonitis,  to  the  epigastrium  or  umbilicus, — i.e. ,  to  the  solar 
and  superior  mesenteric  plexuses. 

The  usual  cause  of  peritonitis  of  the  small  intestine,  by  infection  from  within,  is 
penetration  of  its  walls  by  the  colon  bacillus,  following  epithelial  necrosis  or  ulceration 
due  to  catarrh  or  to  various  forms  of  infection,  or  secondary  to  diseases  which  pro- 
duce engorgement  of  the  terminal  vessels  of  the  portal  system.  It  is  sometimes,  in  a 
less  acute  form,  a  final  phenomenon  in  fatal  cases  of  renal  or  cardiac  disease.  It  may 
follow  tuberculosis  or  typhoid  ulceration  of  the  solitary  or  agminated  lymph- nodules. 

In  all  cases  of  enterorrhaphy — as  after  resection  or  anastomosis — especial  atten- 
tion should  be  paid  to  the  non-peritoneal  area  included  between  the  two  mesenteric 
layers.  The  success  of  these  operations  depends  primarily  upon  the  rapid  union  of 
apposed  peritoneal  surfaces  ;  hence  the  serous  coat,  including  the  two  layers  of  the 
mesentery,  should  be  brought  together  through  the  complete  circumference  of  the 
bowel  and ''accurately  sutured. 

2.  The  Muscular  Coat. — Irregular  or  spasmodic  contraction  of  the  muscular  wall 
of  the  small  intestine  produces  typical  ' '  colic, ' '  the  pain  being  analogous  to  that  felt 
in  a   "cramp"  of  one  of  the  voluntary  muscles.      Intestinal  colic  is  not  associated 
with  tenderness  of  the  surface  of  the  abdomen,  or  with  rigidity  of  the  abdominal 
muscles,  and  is  usually  relieved  by  firm  pressure, — supporting  and  controlling  the 
affected  segment  of  gut.      The  abdominal  wall  may  be  moved  freely  over  the  under- 
lying viscera.      It  may  thus  be  distinguished  from  the  early  pain  of  peritonitis. 

The  greater  thickness  of  the  inner — circular — coat  causes  longitudinal  wounds  to 
gape  more  than  transverse  ones.  The  latter  are  more  apt  to  gape  if  they  are  at  the 
free  border  of  the  gut,  where  the  longitudinal  fibres  are  most  numerous.  As  the 
muscular  coat  in  its  entirety  lessens  in  thickness  from  above  downward,  wounds  of 
the  jejunum  gape  more  than  those  of  the  ileum.  Intestinal  punctures  usually,  and 
very  small  wounds  not  infrequently,  are  closed  by  muscular  action,  so  that  healing 
takes  place  without  extravasation  of  intestinal  contents.  Slightly  larger  wounds 
may  be  stopped  by  a  plug  of  mucous  membrane.  This  is  favored  in  the  upper 
portion  of  the  tube  by  the  presence  of  the  valvulae  conniventes  and  in  the  lower  part 
by  the  laxity  of  the  submucosa.  This  eversion  of  the  mucous  membrane,  caused  by 
muscular  contraction,  must  always  be  overcome  in  the  suture  of  intestinal  wounds, 
since  the  mucous  surfaces  will  not  unite  with  each  other. 

3.  The  mucous  and  submucous  coats  and  their  contained  glandular  and  vascu- 
lar structures  are  subject  to  many  varieties  of  disease.      If  catarrhal  inflammation 
affects  the  mucosa  of  the  small  intestine,  it  is  apt,  if  localized  in  the  duodenum,  to 
be  associated  with  gastritis  and  to  extend  into  the  bile-ducts,  causing  jaundice.      If 
in  the  jejuno-ileum,  it  may  be  mistaken  for  colitis  ;  usually,  if  in  the  small  intestine, 
the  diarrhoea  is  less  marked,  the  colicky  pains  are  greater,  borborygmi  are  fewer, 
less  mucus  is  found  in  the  stools,  and  tenesmus  is  absent.      Neither  duodenitis,  jeju- 
nitis,  nor  ileitis  can,  however,  positively  be  diagnosticated  from  one  another  or  from 
general  intestinal  catarrh  (Osier). 

Ulcers  of  the  duodenum  are  in  the  vast  majority  of  cases  (242  out  of  262,  Col- 
lin,  quoted  by  Weir)  situated  within  5  cm.  (2  in.)  of  the  pylorus  (the  most  movable 
portion  of  the  duodenum)  and  are  most  often  on  the  anterior  wall,  especially  its 
right  side.  The  peritoneum  of  the  right  side  of  the  first  part  of  the  duodenum  looks 
into  the  general  peritoneal  cavity,  and  of  the  left  side  into  the  lesser  cavity  (page 
1645).  When  perforation  follows,  the  general  peritoneal  cavity  is  therefore  likely  to 
be  infected,  and  the  death  of  one-half  of  the  subjects  of  perforating  duodenal  ulcer 
from  general  peritonitis  is  thus  accounted  for.  The  second  part  of  the  duodenum  is 


1654  HUMAN    ANATOMY. 

in  close  relation  on  the  lower  part  of  the  right  aspect  with  the  liver  and  gall-bladder, 
on  the  upper  part  of  the  left  aspect  with  the  head  of  the  pancreas  and  foramen  of 
Winslow,  and  posteriorly  is  partly  uncovered  by  peritoneum  and  rests  on  areolar 
tissue  and  the  common  bile-duct. 

The  general  relations  of  the  duodenum  (page  1645)  explain  the  remaining 
lesions  following  duodenal  ulcer, — e-g-,  perforations  into  the  gall-bladder,  liver,  or 
colon  ;  opening  of  the  hepatic  artery  or  the  aorta,  or  of  the  superior  mesenteric  or 
portal  vein  ;  or  the  development  of  subphrenic  abscess. 

As  compared  with  the  symptoms  of  gastric  ulcer,  pain  is  apt  to  be  less  on 
account  of  the  relative  immobility  of  the  duodenum  ;  vomiting  after  feeding  is 
later  ;  hemorrhage  is  often  greater  on  account  of  the  larger  vessels  that  may  be 
involved  ;  bloody  stools  are  more  common,  as  is  jaundice  from  the  involvement  of 
the  bile-duct. 

In  exposure  of  this  part  of  the  duodenum  it  is  well  to  remember  the  suggestions 
of  Pagenstecher  (quoted  by  Weir), — viz.,  that  the  fundus  of  the  gall-bladder  when 
distended  lies  in  front  of  the  duodenum  ;  that  by  raising  and  drawing  forward  the 
transverse  colon,  which  lies  in  front  of  and  below  the  horizontal  portion  of  the  duo- 
denum, the  first  portion  is  revealed  ;  and  that  by  pushing  the  stomach  and  pylorus 
to  the  left  and  elevating  the  liver,  access  to  the  region  of  perforation  may  be  gained. 
In  emaciated  patients  with  contracted  stomachs  the  duodenum  may  be  found  lying 
above  the  level  of  the  transverse  colon. 

Infection  through  the  mucous  coat  has  already  been  spoken  of.  If  of  the  tuber- 
culous variety,  it  affects  chiefly  the  lower  part  of  the  ileum,  and  tends,  as  is  charac- 
teristic of  that  disease,  to  follow  the  course  of  the  vessels  which  run  from  their 
entrance  at  the  mesenteric  attachment  transversely  around  the  gut.  If  such  ulcers 
cicatrize,  they  are  therefore  especially  prone  to  lead  to  stricture  of  the  intestine,  a  very 
rare  sequel  of  typhoid  ulceration,  which,  affecting  the  same  portion  of  the  small 
intestine,  extends  in  the  line  of  the  agminated  lymph-nodules, — i.e.,  longitudinally. 
The  tuberculous  ulcer  sometimes  produces  a  slow  general  peritonitis,  rarely  a  local- 
ized abscess,  much  more  rarely  an  acute  perforation  with  general  septic  peritonitis, 
as  the  process  is  so  slow  that  protective  adhesions  to  neighboring  coils  of  gut  or  to 
the  parietal  peritoneum  have  time  to  form. 

Typhoid  ulcers  cause  perforation  in  6.58  per  cent.  (Fitz)  of  all  cases.  The  large 
majority  of  perforations  occur  in  the  ileum,  most  of  them  within  60  cm.  (2  ft.)  of 
the  ileo-caecal  junction.  In  operation  this  should  therefore  be  sought  for  and  the 
ileum  followed  upward  from  that  point.  The  ulceration  may  so  thin  the  intestinal 
wall  as  to  permit  of  leakage  and  the  production  of  general  peritonitis  without  actual 
perforation  ;  or  it  may  be  accompanied  by  such  an  extensive  exudate  as  to  make  the 
ileum  palpable,  a  condition  which,  in  conjunction  with  localized  tenderness  and 
abdominal  rigidity  (vide  supra),  has  led  to  many  mistaken  diagnoses  of  appendicitis 
in  cases  of  typhoid  fever. 

Syphilitic  ulceration  of  the  small  intestine  is  rare,  but  is  said  to  be  most  frequent 
in  the  upper  portions  (Rieder). 

The  lymphatics  of  the  mucous  and  submucous  coats  empty  into  the  mesenteric 
lymph-nodules  (page  1643)  and  convey  to  them  various  forms  of  infection  or  disease, 
— typhoid,  carcinomatous,  tuberculous,  etc. 

The  veins  emptying  into  the  vena  porta  through  the  superior  mesenteric  are 
likewise  channels  of  infection,  ulceration  of  the  bowel  sometimes  resulting  in  abscess 
of  the  liver. 

Contusion  and  rupture  of  the  small  intestine  are  favored  by  its  exposure  to 
trauma  through  its  close  apposition  to  the  abdominal  wall,  which,  if  relaxed, 
offers  but  little  protection.  The  interposition  of  the  greater  omentum  with  its  con- 
tained fat  is  a  slight  safeguard,  but  the  movement  of  the  coils  of  gut  upon  one 
another  and  their  elasticity  are  of  much  more  value. 

Contusion  here,  as  elsewhere,  may  be  followed  later  by  infection  and  ulceration. 
Traumatic  rupture  is  much  more  frequent  in  the  jejunum  and  ileum  than  in  any 
other  portions  of  the  alimentary  canal  (of  219  cases,  79  per  cent,  were  in  the  small 
intestine,  11.5  per  cent,  in  the  colon,  and  9.5  per  cent,  in  the  stomach,  Petry). 
The  duodenum  suffers  very  infrequently  on  account  of  its  sheltered  position  ;  other- 


PRACTICAL  CONSIDERATIONS  :  THE  SMALL  INTESTINE.     1655 


FIG.   1405. 


Intussusceptum 


-Entering  layer 


.Returning 
layer 


wise  its  lower  portion — the  most  fixed  part  of  the  intestine — would  probably  be  more 
often  injured.  The  upper  portion  of  the  jejunum,  which  partakes  somewhat  of  this 
fixity,  is  more  commonly  ruptured  than  any  other  part.  So,  too,  the  most  fixed 
part  of  the  ileum — that  nearest  the  ileo-caecal  junction — is  most  often  the  site  of  rup- 
ture. An  incarcerated  or  irreducible  hernia  may  constitute  a  fixed  point  of  the  gut 
and  favor  its  rupture  elsewhere  from  trauma  to  the  surface  of  the  abdomen. 

Ruptures  of  the  intestine,  like  wounds  or  obstruction,  are  more  serious  the 
higher  they  are  situated.  The  nervous  disturbance  and  shock  are  greater,  possibly 
on  account  of  the  more  immediate  relation  of  the  lesion  and  of  the  resulting  patho- 
logical changes  to  the  great  nerve-plexuses  or  to  the  pericardial  portion  of  the  dia- 
phragm (Crile)  ;  vomiting  begins  earlier  and  is  more  severe  for  the  same  reason  ; 
peristalsis  is  more  vigorous  (as  the  muscular  coat  of  the  gut  is  better  developed) 
and  therefore  rapid  extravasation  of  intestinal  contents  is  more  likely  and  spontane- 
ous closure  of  a  wound  less  likely  to  occur  ;  and,  if  the  condition  is  at  all  chronic, 
nutrition  is  interfered  with  to  a  greater  extent.  Clinical  experience  shows  that  in 
such  injuries  the  anatomical  are  more  potent  than  the  purely  bacteriological  factors, 
which  would  tend  to  make  jejunal  wounds  less  dangerous  than  those  lower  in  the 
tract.  Investigation  has  shown  (Cush- 
ing  and  Livingood,  and  later  Lorrain 
Smith  and  Tennant)  that  the  bacterial 
flora  in  the  upper  portion  of  the  intestinal 
tract  is  more  scanty  than  in  the  lower 
portion  ;  and  it  is  true  that  peritonitis 
following  intestinal  wounds,  operative  or 
accidental,  is  dependent  for  its  charac- 
teristics upon  the  bacteria  at  the  site  of 
lesion,  and  that  the  prognosis  should  be 
favorable  in  proportion  to  the  scarcity 
and  innocuousness  of  the  micro-organ- 
isms present.  But  the  anatomical  con- 
ditions, by  adding  to  shock,  favoring 
intestinal  extravasation,  and  minimizing 
the  chance  of  a  reparative  peritonitis,  are 
more  than  sufficient  to  counterbalance 
the  relative  dearth  of  bacteria. 

It  should  be  remembered  that  the 
position  of  the  wound  or  contusion  on  the 
surface  of  the  abdomen  is  of  but  slight 
value  in  determining  the  area  of  gut  in- 
volved. Thus,  a  jejunal  fistula  following 
a  wound  was  situated  midway  between 

the  umbilicus  and  pubes,  but  measurements  made  by  attaching  ligature  silk  to  portions 
of  food  swallowed  and  extruded  at  the  fistula  showed  that  the  latter  was  but  119  cm. 
(3  ft.  ii  in.  )  from  the  incisor  teeth,  and  was  therefore  high  in  the  jejunum  (  Gushing.  ) 

It  may  be  noted  that  fistulae  so  situated  are  apt  to  be  complicated  by  excessive 
dermatitis,  supposed  to  be  due  to  the  presence  of  pancreatic  juice  in  the  discharge, 
as  gastric,  biliary,  and  colonic  fistulae  do  not  give  rise  to  this  trouble  in  any  such 
degree  of  severity. 

Obstruction  of  the  small  intestine  may  be  due  to  (<z)  foreign  bodies  (including 
intestinal  concretions  and  gall-stones  that  have  ulcerated  into  the  duodenum),  and 
is  then  most  apt  to  occur  at  the  ileo-csecal  junction  on  account  of  the  narrowing  of 
the  canal  at  that  point  ;  (b)  bands,  producing  constriction  of  a  coil  or  knuckle 
of  gut,  such  bands  arising  from  the  elongation  of  adhesions  due  to  previous  perito- 
nitis, from  inflammatory  attachment  of  the  free  end  of  Meckel's  diverticulum  (page 
1652),  of  adventitious  diverticula  (from  protrusion  of  the  mucous  membrane  through 
the  muscular  coat),  or  of  the  appendix.  Either  the  Fallopian  tubes,  the  appendices 
epiploicse,  the  omentum,  or  the  mesentery  may  in  like  manner  become  converted 
into  constricting  bands  ;  (c}  stricture,  as  from  tuberculous  ulcer  in  the  ileum  or 
syphilitic  ulcer  in  the  jejunum  ;  (d)  volvulus,  especially  in  the  lower  part  of  the 


InUissuscipieti': _ 


Ensheathing 
layer 


Longitudinal  section  of  tntussuscepted  gut,  showing 
layers. 


1656  HUMAN   ANATOMY. 

ileum  when  its  mesentery  has  been  elongated  by  prolonged  stretching,  as  in  the 
presence  of  an  old  hernia  (Maylard);  (e)  internal  hernice,  as  into  the  duodeno- 
jejunal,  pericaecal,  or  intersigmoid  fossae,  or  through  the  foramen  of  Winslovv,  or 
through  an  aperture  in  the  omentum  (page  1758),  which  may  be  traumatic  or  may 
be  .one  of  the  rounded  openings  due  to  congenital  atrophy  of  a  comparatively  vas- 
cular area  of  the  mesentery  of  the  terminal  portion  of  the  ileum  and  embraced 
within  the  ileo-colic  artery  and  the  lowest  vasse  intestini  tenuis  ;  (/")  hernia?  through 
the  usual  hernial  apertures  or  regions  of  the  parietes  (page  1762);  (g}  intussuscep- 
tion, one  form  of  which  is  due  to  irregular  contraction  of  the  circular  fibres  of  the 
muscular  coat,  so  that  as  the  peristaltic  wave  passes  downward  a  segment  of  gut, 
made  smaller  by  this  contraction,  is  forced  into  the  portion  immediately  beneath  it, 
which  is  of  larger  calibre  as  a  result  of  having  failed  to  contract  at  the  proper  time  ; 
(h)  pressure  from  without,  as  from  tumors,  which,  as  they  must  meet  with  counter- 
resistence  and  relative  fixity  of  the  gut  to  produce  constriction,  most  often  affect  the 
duodenal  (as  in  cancer  of  the  pancreas),  upper  jejunal,  or  ileo-caecal  segments  ; 
(z)  peritonitis,  the  relation  of  which  to  intestinal  obstruction  has  already  been 
explained  (page  1758);  (j)  tumors  of  the  intestines  themselves,  not  very  frequent  in 
the  small  intestine,  but  most  often  found  at  its  two  extremities. 

The  position  of  the  different  portions  of  the  small  intestine  varies  greatly.  The 
lower  end  of  the  duodenum,  the  upper  end  of  the  jejunum,  and  the  lower  end  of 
the  ileum  are  the  most  fixed  points.  A  description  of  the  normal  arrangement  of 
the  coils  of  the  jejuno-ileum  has  been  given  (page  1651). 

Of  the  duodenum  only  the  first  portion  has  been  found  involved  in  internal 
hernias.  The  more  or  less  vertical  coils  of  the  jejunum,  and  especially  those  of  the 
terminal  portion  of  the  ileum  which  occupy  the  pelvis  when  the  bladder,  rectum, 
and  sigmoid  are  not  distended,  are  those  most  likely,  for  a  priori  reasons,  to  be 
found  in  inguinal  or  femoral  enteroceles,  but  clinical  evidence  in  support  of  this  is 
not  conclusive.  In  umbilical  hernia  the  jejunum  is  apt  to  be  involved,  and  the 
gravity  of  this  form  of  hernia,  when  strangulated,  is  supposed  to  be  partly  due 
to  this  fact  as  well  as  to  the  effect  upon  the  circulation  of  the  constricted  coil 
produced  by  the  sharp  edge  of  the  cicatricial  tissue  which  surrounds  the  opening 
and  aggravated  by  the  downward  pull,  through  gravity,  of  the  remainder  of  the 
intestines. 

When  the  stomach  is  full  the  intestines  are  depressed  ;  when  it  is  empty  they 
rise,  so  that  in  the  left  hypochondriac  region  they  may  be  in  contact  with  the  dia- 
phragm. If  the  colon  is  distended,  the  small  intestine  can  Occupy  but  little  of  the 
lumbar,  epigastric,  or  hypochondriac  regions.  Conversely,  if  the  small  intestine  is 
distended,  it  may  so  fill  the  pelvis  and  compress  the  rectum  as  to  prevent  the 
passage  of  a  tube  or  bougie  into  the  sigmoid,  and  thus  give  rise  to  a  mistaken  diag- 
nosis of  obstruction  at  that  point.  If  the  spleen  is  enlarged,  they  are  carried  down- 
ward and  to  the  right  ;  if  the  liver,  downward  and  to  the  left  ;  if  the  bladder  or 
uterus,  upward. 

In  ascites  they  are  above  the  fluid,—  i.e.,  in  the  umbilical  region  in  the  supine 
and  the  epigastric  region  in  the  erect  position. 

Normally  the  coils  of  the  small  intestine  are  closely  applied  to  one  another,  and 
this  condition,  by  permitting  of  rapid  adhesion,  and  thus  of  isolation  of  an  infeeted 
focus,  has  saved  thousands  of  lives,  especially  in  cases  of  appendicitis  and  pyosal- 
pinx,  and  less  frequently  in  cholecystitis  and  other  forms  of  intra-abdominal  infection. 

Operations. — The  principles  which  should  govern  in  opening  the  small  intestine, 
in  avoiding  or  controlling  hemorrhage,  and  in  suturing  wounds  accidental  or  opera- 
tive have  been  sufficiently  explained  (page  1653). 

The  recognition  of  the  duodenum  is  not  difficult.  It  occupies  portions  of  the 
right  hypochondriac,  right  lumbar,  and  umbilical  regions.  The  spine  of  the  second 
lumbar  vertebra  is  just  above  it.  The  hepatic  flexure  of  the  colon  is  anterior  to  it 
at  a  point  just  below  the  ninth  nib  on  the  right  side.  The  mesentery  commences  at 
the  duodeno-jejunal  junction.  A  notch  which  can  be  felt  in  the  peritoneum  serves 
as  a  guide  to  this  particular  part  (Maylard). 

nnodniototuy  may  be  required,  either  as  an  aid  or  as  the  main  avenue  of  ap- 
proach, in  cases  of  impacted  calculus  in  the  common  bile-duct  (page  1732).  It  is 


THE  LARGE   INTESTINE.  1657 

rarely  needed  for  the  removal  of  foreign  bodies,  as  those  small  enough  to  pass  the 
pylorus  effect,  as  a  rule,  only  temporary  lodgment  in  the  duodenum  and  usually 
reach  the  ileo-caecal  region.  • 

The  jejunum  may  be  distinguished  from  the  ileum  by  its  greater  width  and 
thickness,  its  deeper  color,  and  by  the  presence  of  the  many  large  folds  of  the  val- 
vulae conniventes  which  can  be  seen  in  the  collapsed  and  tense  gut  by  transmitted 
light.  By  drawing  a  loop  of  intestine  out  of  the  abdomen  so  that,  with  the  loop 
parallel  with  the  long  axis  of  the  body,  its  mesentery  is  stretched  and  straightened, 
it  is  easy  to  determine  which  is  the  upper  end  of  the  loop,  and  so  to  follow  the  gut 
either  towards  the  duodenum  or  the  caecum,  as  may  be  desired.  The  finger  should 
be  passed  down  to  the  spine,  keeping  in  close  contact  with  the  mesentery  ;  if  it 
remains  on  one  side  until  the  posterior  attachment  is  reached,  it  is  evident  that 
there  is  no  twist  of  the  loop  and  that  its  upper  portion  is  normally  the  portion 
nearest  the  stomach.  As  loop  after  loop  is  examined,  if  the  intestine  leads  in  an 
upward  direction  the  color  becomes  paler,  and  the  walls  become  thicker  owing  to  the 
valvulae  conniventes  and  to  the  increase  in  the  submucous  and  muscular  coats. 

Other  methods  of  locating  with  accuracy  a  given  coil  of  bowel  are  (i )  by  means 
of  the  length  of  the  vasa  recta  (3—5  cm.  in  the  upper  and  i  cm.  or  less  in  the  lower 
portion)  ;  (2)  by  the  vascular  loops  from  which  the  vasa  recta  originate,  which  are 
primary  in  the  first  four  feet  of  the  mesentery.  Secondary  loops  appear  as  we  go 
farther  down,  until  in  the  lower  third  there  is  a  net-work  of  loops  ;  (3)  by  the  loops 
or  "lunettes"  at  the  intestinal  attachment  of  the  mesentery,  best  visible  by  trans- 
mitted light.  Below  the  first  eight  feet  these  lunettes  disappear  (Monks). 

Enterotomy — for  temporary  relief  of  obstruction  or  distention  or  for  the  removal 
of  a  foreign  body — is  done  at  as  low  a  point  as  circumstances  permit,  through  a 
transverse  incision  at  the  part  opposite  the  mesenteric  attachment. 

Enterostomy — the  establishment  of  a  permanent  fistula  for  the  purpose,  if  it  is  a 
jejunostomy,  of  feeding  the  patient  in  cases  of  obstruction  of  the  alimentary  tract 
above  the  opening  ;  or  if  it  is  an  ileostomv,  of  relieving  fecal  accumulation  in  cases 
of  obstruction  at  a  lower  point — is  done  by  suturing  the  selected  knuckle  of  gut  to 
the  parietal  peritoneum  by  a  double  line  of  sutures  and  opening  the  bowel  between 
them. 

Enterectomy  and  cntcro-anastomosis  (either  lateral  or  end-to-end)  require  for 
their  performance,  so  far  as  anatomy  goes,  application  of  the  facts  and  principles  to 
which  reference  has  already  been  made. 

THE   LARGE    INTESTINE. 

The  general  plan  ot  the  large  intestine  has  already  been  given  (page  1617).  It 
is  easily  distinguished  from  the  small  intestine,  not  so  much  by  its  greater  size  as  by 
being  sacculated,  excepting,  perhaps,  the  sigmoid  flexure. 

The  length  of  the  large  intestine  from  the  root  of  the  appendix  to  the  beginning 
of  the  rectum  is,  according  to  Treves,  about  1.4  m.  (4  ft.  8  in.)  in  man  and  5  cm. 
(2  in.)  less  in  woman.  The  extremes  were  2  m.  (6  ft.  6  in.  )  and  i  m.  (3  ft.  3  in.  ). 
Excluding  the  dilated  part  of  the  rectum,  the  capacity  decreases  from  above.  Owing 
both  to  variation  and  to  occasional  cases  of  extreme  contraction  as  well  as  of  dis- 
tention, the  diameter  is  very  uncertain.  It  may  vary  from  7  cm.  (2-5-  in. )  to  3.5  cm. 
(if  in.)  without  the  more  extreme  figures  implying  a  pathological  condition. 

Structure. — The  mucous  coat  of  the  large  intestine  agrees  in  its  essential 
structure  with  that  of  the  small  gut,  consisting  of  a  stroma  resembling  adenoid  tissue, 
covered  by  a  single  layer  of  columnar  epithelium  exhibiting  a  cuticular  border.  The 
chief  difference,  on  the  other  hand,  is  the  absence  of  villi,  in  consequence  of  which 
the  velvety  appearance  imparted  by  the  latter  is  not  seen  in  the  large  intestine. 
Valvulae  conniventes  are  also  wanting,  although  there  are  projections  into  the  large 
gut  involving  all  or  a  part  of  the  coats  internal  to  the  serous  tunic.  The  muscularis 
mucosae  is  less  regular  in  its  development,  being  feebly  represented  in  the  colon  and 
exceptionally  thick  in  the  rectum. 

The  glands  of  Lieberkuhn  in  general  resemble  those  of  the  small  intestine, 
but  are  larger  (about  .45  mm.  in  length),  and  form  a  more  regular  and  less  inter- 


HUMAN   ANATOMY. 


rupted  layer  of  parallel  tubules.  The  largest  ones  are  in  the  rectum,  where  they 
measure  7  mm.  (Verson).  The  lining  of  the  glands  is  conspicuous  on  account  of 
the  great  number  of  goblet-cells,  -which  in  the  middle  and  upper  parts  of  the  tubules 

FIG.  1406. 


XV 

, 
V. 

• 
^^^^^  iA-^v>^_ 


Surface  views  of  mucous  membrane  of  ascending  colon.    A,  natural  size  ;  B,  magnified  30  diameters,  showing  orifices 

of  Lieberkiihn's  glands. 

often  exist  in  such  profusion  that  the  ordinary  cells  are  almost  entirely  replaced  ; 
towards  the  deepest  part,  or  fundus,  of  the  glands  they  are  comparatively  infrequent. 
The  presence  of  goblet-cells  in  such  numbers  accounts  for  the  considerable  amount 
of  mucus  normally  poured  into  the  large  intestine. 


FIG.  1407. 


Lieberkiihn's  glands 


Solitary  lymph-nodule 


Mucous  coat 


• 

•••j£ri&^ 


Longitudinal 
muscle 
Serous  coat 

Longitudinal  section  of  ascending  colon,  showing  general  arrangement  of  coats  and  solitary  lymph-nodule.     X  30. 

The  lymphatic  tissue  in  definite  collections  occurs  as  solitary  nodules  only, 
Peyer's  patches  being  absent  within  the  large  intestine.  The  lymph-nodules,  which 
occupy  a  portion  of  the  submucous  coat  as  well  as  the  mucosa,  are  largest  and  most 


THE  LARGE  INTESTINE. 


1659 


numerous  in  the  caecum,  and  especially  in  the  vermiform  appendix,  in  which  the 
nodules  are  so  plentiful  that  they  form  in  places  almost  a  continuous  mass  of  lymphoid 

tissue.      The  solitary  follicles  are  less  fre- 

FIG.  1408.  quent  in  the  colon,  but  are  again  numer- 

ous in  the  rectum.  They  are  generally 
of  larger  size  than  in  the  small  intestine, 
measuring  from  1.5-3  mm.  in  diameter, 
and  are  situated  at  the  bottom  of  pit-like 
depressions  on  the  mucous  surface  into 
which  the  nodules  project. 

The  submucous  coat  closely  cor- 
responds with  the  similar  areolar  tunic  of 
the  small  intestine,  allowing  of  fairly  free 


: Peritoneal  coat 


ij Adipose  tissue 


_Vein 


—  Artery 


Portion  of  descending  colon,  somewhat  distended,  show- 
ing sacculations,  taenia,  and  epiploic  appendages. 


Longitudinal  section  of  epiploic  appendage.    X  23. 


play  of  the  mucosa.     In  addition  to  the  blood-vessels,  lymphatics,  and  nerve-plexus 
of  Meissner,  it  contains  the  deeper  and  more  expanded  parts  of  the  solitary  nodules. 


i66o 


HUMAN   ANATOMY. 


The  muscular  coat  consists  of  a  thicker  layer  of  internal  circular  fibres  and  of 
an  external  longitudinal  one,  the  fibres  of  which  are  in  most  places  collected  into 
three  bands.  Although  longitudinal  fibres  exist  between  these,  they  are  fe\v  and 
apparently  not  quite  universal.  Beginning  in  the  caecum,  at  the  base  of  the  vermi- 
form appendix,  the  three  bands,  or  tcenia;  coli,  continue  along  the  large  intestine  as  far 

as  the  sigmoid  flexure,  over  which 
1412. 


FIG. 


Mucous  coat 


•='    Serous  coat 


Transverse  section  of  injected  large  intestine,  showing  distribution 
of  arteries  to  coats.     X  30. 


and  the  rectum  the  bands 
only  two,  and  no  longer  sharply 
defined.  In  the  rectum  one  is 
on  the  front  and  the  other — the 
stronger — behind.  The  circular 
fibres  increase  very  much  towards 
the  end  of  the  rectum,  the  muscu- 
lar apparatus  of  which  will  receive 
special  description  (page  1675). 

The  serous  coat  which  once 
surrounded  the  gut,  in  certain 
places  disappears  during  develop- 
ment, and  in  others  its  arrange- 
ment becomes  modified  by  new 
relations  with  other  peritoneal 
layers.  These  features  will  be 
described  with  the  parts  con- 
cerned. In  structure  it  corre- 
sponds with  the  serous  coat  of 
other  parts  of  the  intestinal  tube. 
The  appendices  epiploicae 
are  little  fringes  or  bags  of  perito- 
neum containing  fat  hanging  from 
the  large  intestine.  They  may 
be  as  much  as  2.5  cm.  (i  in.)  in 
length,  and  are  very  prominent  in 
fat  subjects,  but  in  thin  ones  may 
be  overlooked.  They  are  found 
particularly  on  the  inner  aspects 
of  the  ascending  and  descending 
colon  and  on  the  lower  one  of 
the  transverse  colon.  It  is  often 
stated  that  they  occur  along  one 
of  the  bands,  but  this  relation  is 
at  least  not  constant,  although 
they  are  generally  arranged  in  a 
single  line.  They  are  found  also 
on  the  sigmoid  flexure.  It  is  usu- 
ally stated  that  they  are  not  pres- 
ent during  childhood.  Oddono,1 
however,  has  shown  that  they  ap- 
first  on  the  descending  colon  and  sigmoid 


pear  in  the  fifth    month  of    foetal    life, 
flexure.     We  have  seen  them  before  birth. 

The  blood-vessels,  lymphatics,  and  nerves  of  the  large  gut  in  general 
follow  the  arrangement  already  described  in  connection  with  the  small  intestine 
(luge-  1642). 

THE  CAECUM. 

The  caecum,  or  blind  gut,  the  first  part  of  the  large  intestine,  is  a  pouch  hanging 
downward  at  the  junction  of  the  ileum  and  colon,  from  which  the  vermiform  appendix 
arises.  The  ileum  opens  into  the  large  intestine  by  a  transverse  orifice  placed  in- 

1  Dal  Bollettino  della  Societa  Medico-Chirurgica  di  Pavia,  1889. 


THE  C^CUM. 


1661 


FIG.  1413. 


Anterior  band 


Ascending  colon 


ternally  and  somewhat  posteriorly.  From  the  top  of  the  ileum  a  deep  furrow  passes 
posteriorly  partly  around  the  gut,  and  a  less  marked  one  is  found  in  front. 
Although  starting  as  just  stated,  the  furrows  at  once  descend  a  little,  so  as  to  repre- 
sent truly  the  middle  of  the  orifice.  These  serve  as  an  external  boundary  between 
the  caecum  and  the  colon,  which  are  much  alike  in  general  characters.  The  average 
length  of  the  caecum  in  the  adult  is  between  6  and  7  cm.  (about  2^  in.),  and  its 
breadth  about  8  cm.  (3^5  in.).1  The  bands  of  the  colon  are  continued  onto  the 
caecum  of  the  adult,  and  terminate  at  the  origin  of  the  appendix.  One  band  is  in 
front  and  the  other  two  externally  and  internally  at  the  back.  The  parts  between 
the  bands  are  generally  expanded  pouches,  which  may  be  subdivided  by  horizontal 
constrictions.  There  are  two  chief  forms  of  caecum  with  several  minor  modifica- 
tions :  the  first  is  a  persistence  of 
the  fcetal  type,  in  which  the  caecum 
has  the  shape  of  a  cornucopia  bent 
towards  the  left,  with  the  tapering 
end  continued  as  the  vermiform 
appendix  ;  the  other,  which  is  the 
usual,  and  occurs  in  from  91-94 
per  cent,  of  adults,  is  due  to  the 
part  between  the  external  and  the 
anterior  band  growing  out  of  all 
proportion,  so  that  the  pouch  be- 
tween them  becomes  the  lowest 
part,  apparently  the  apex,  the  ap- 
pendix arising  from  the  internal 
posterior  side  near  the  ileum.  In 
extreme  cases  the  two  may  be  very 
close  together.  Very  rarely  the 
caecum  is  symmetrically  sacculated, 
with  the  appendix  at  the  lower  end. 
To  understand  the  interior 
of  the  caecum  it  must  be  remem- 
bered that  the  end  of  the  ileum  is 
thrust  in  at  the  angle  between  the 
colon  and  caecum  in  such  a  way 
that  originally  in  fcetal  life  all  the 
coats  were  involved.  The  serous 
coat  is  replaced  by  areolar  tissue 
where  two  layers  come  together 
and  new  longitudinal  muscular 
fibres  are  subsequently  developed 
which  do  not  enter  the  folds  ;  how- 
ever, the  original  longitudinal  mus- 

11  11  .1  •         i  Beginning  of  large  intestine,  somewhat  inflated ;  part  of  an- 

CUiar   layer,    as  Weil    as    me    Circular      terior  wall  removed  to  show  ileo-cascal  valve  and  orifice  of  vermi- 

one,  does  so.      The  latter  is  thick-     form  appendix. 
ened  inside  the  fold.      The  ileum, 

as  it  approaches  its  end,  lies  between  "the  surface  of  the  caecum  below  and  the  lower 
swelling  of  the  colon  above  ;  thus  the  upper  of  the  two  lips  of  the  elliptical  opening 
is  composed  of  colon  and  ileum,  the  lower  of  ileum  and  caecum.  They  form  promi- 
nent shelf-like  projections  into  the  large  gut,  opposite  the  external  furrows,  and 
constitute  the  ileo-caecal  valve  (valvula  coli).  The  folds  meet  at  the  ends  of 
the  opening,  forming  single  continuations  or  retinacula,  of  which  the  posterior  is 
much  the  larger.  It  often  extends  across  the  posterior  to  the  lateral  aspect  of  the 
gut.  The  two  segments  converge,  but  at  different  angles.  The  upper,  slanting 
somewhat  downward,  is  approximately  horizontal,  while  the  lower  is  more  nearly 
vertical.  The  orifice  of  the  ileum  between  these  folds  is  elongated  when  the  gut 
is  distended,  the  posterior  end  being  sharper  than  the  anterior.  The  diameter  of 
the  segments,  measured  from  the  origin  to  the  free  edge  on  35  inflated  and  dried 

1  Berry  :  The  Anatomy  of  the  Caecum,  Anat.  Anzeiger,  Bd.  x.,  1895. 


- —  Upper  fold 
—  Retinaculum 
.Ileo-caecal  valve 

'  j>      Lower 


Ileum 


Caecum 

Opening  of 
appendix 


1662 


HUMAN   ANATOMY. 


specimens,  is  as  follows:  average  of  upper  segment  25  mm.,  of  lower  33  mm. 
The  largest  pair  was  an  upper  of  37  mm.  and  a  lower  of  44  mm.  ;  the  smallest  of 
12  mm.  and  3  mm.  respectively.  The  last,  perhaps,  was  pathological  ;  the  next 
smallest  was  14  mm.  and  19  mm.  We  have  seen  a  caecum  with  the  upper  seg- 
ment entirely  wanting.  The  absence  of  both  has  been  observed.  The  average 
length  of  the  ileo-caecal  opening  on  30  similar  specimens  was  31  mm.,  the  extremes 
being  46  mm.  and  21  mm.  It  is  probable  that,  owing  to  the  shrinking  of  the  tissues, 
these  dimensions  of  the  opening  are  excessive.  Although  the  lower  fold  is  the 
larger,  the  upper  overlaps  it  almost  invariably,  so  that  when  the  valve  is  closed  the 
two  edges  do  not  come  in  contact,  the  orifice  being  closed  by  the  application  of  the 
lower  fold  to  the  under  surface  of  the  upper  one.  Inflated  specimens  show  that 
the  upper  fold  is  tense,  while  the  lower  remains  flaccid.  Much  difference  of 
opinion  exists  as  to  the  completeness  of  the  closure  of  the  ileo-caecal  valve,  and 
experiments  do  not  agree.  If  the  experiment  of  injecting  water  or  air  from  the 
colon  be  performed  in  situ,  the  closure  is  more  likely  to  be  perfect  than  if  the  parts 
have  been  removed.  These  experiments,  however,  do  not  represent  the  true  con- 


FIG.  1414. 


Ascending  color 


Anterior  band 


Caecum 


Ileo-caecal  artery 
Superior  ileo-caecal  fossa 

Mesentery 


Ileum 


Meso-appendix 
Vermiform  appendix/ 
Caecum  and  related  structures  seen  from'  the  left. 


Artery 


ditions  during  life,  since  the  tonicity  of  the  muscular  fibres  of  the  gut  is  lost, 

in  the  opened  abdomen,  the  pressure  of  the  viscera  on  the  end  of  the  ileum  is  less 

than  normal.      In  life  the  valve  probably  is  efficient. 

The  orifice  of  the  vermiform  appendix  is  very  variable.  In  sonic  cases 
the  caecum  narrows  to  it  so  gradually  that  it  is  hard  to  say  where  it  begins  ;  in 
others  it  begins  suddenly  with  an  oval  or  round  opening  measuring  from  5  mm.  or 
less  to  i  cm.  or  more.  The  valve  which  often  is  found  at  the  orifice  is  not  usually 
a  true  valve,  but  the  projection  made  by  the  wall  at  the  union  of  caecum  and  appen- 
dix in  the  entering  angle  when  it  arises  obliquely.  According  to  Struthers,  there  is 
no  valve  when  it  arises  at  right  angles.  Owing  to  its  usual  upward  course,  the  fold 
is  most  often  on  that  side  when  present.  We  have  seen  a  true  valve  as  a  small 
independent  fold  ;  usually,  however,  there  is  no  effective  guard  to  the  entrance  of 
the  appendix. 

Position. — The  caecum  is  situated  in  the  right  iliac  fossa,  resting ^ on  the  iliac 
fascia  covering  the  ilio-psoas  muscle,  above  the  outer  part  of  Poupart's  ligament, 


THE   C^CUM. 


1663 


about  half  below  and  half  above  the  level  of  the  anterior  superior  iliac  spine.  Some- 
times, owing  to  the  shortness  of  the  ascending  colon,  the  caecum  remains  in  the 
foetal  position  under  the  liver,  or  it  may  be  arrested  at  any  part  of  its  descent.  It 
not  rarely  hangs  down  into  the  pelvis,  and  when  the  lower  part  of  the  mesentery  is 
long,  particularly  if  the  lower  part  of  the  ascending  colon  be  not  attached  to  the 
posterior  wall,  it  may  be  very  freely  movable.  In  cases  of  mesenterium  commune 
there  seems  to  be  no  anatomical  reason  why  it  should  not  be  anywhere.  The 
caecum  is  sometimes  turned  up  over  the  lower  part  of  the  ascending  colon,  but  we 
cannot  agree  with  Curschmann's1  statement  that  this  is  not  rare.  In  these  cases  the 
appendix  rises  from  near  the  highest  point  of  the  caecum.  We  have  seen  the  caecum 
in  the  umbilical  region  with  two  vertical  coils  of  small  intestine  occupying  the  right 
flank. 

Structure. — The  description   of   the   structure  of  the  large  intestine  already 
given  (page  1657)  applies  in  general  to  the  caecum.      Its  mucous  membrane,   like 


Lymph-nodules 


..Lieberkiihn's  glands 


Mucous  coat 


Longitudinal  section  through  junction  of  appendix  with  caecum.     X  12. 

that  of  the  rest  of  the  large  intestine,  has  no  villi.  This  change  occurs  near  the 
margin  of  each  segment  of  the  ileo-caecal  valve,  the  villi  gradually  diminishing  and 
finally  disappearing  before  the  free  edge  of  the  folds  is  reached  (Langer).  The 
bands  of  longitudinal  muscular  fibres  always  end  at  the  base  of  the  appendix,  but 
the  precise  manner  of  their  termination  is  uncertain.  According  to  Struthers,2  each 
band  bifurcates  as  it  approaches  the  appendix,  and  the  divisions,  meeting  those  of 
the  others,  form  a  ring  around  a  weak  spot  close  about  it.  According  to  Toldt,3  the 
ring  is  formed  by  the  circular  layer.  The  arrangement  is  not  always  clear,  but  we 
incline  to  think  the  latter  the  more  common.  The  coats  of  the  caecum  are  all  found 
in  the  appendix.  The  lumen  of  the  latter  is  small,  except  near  the  entrance,  and 
the  walls  may  be  in  contact.  The  lymph-nodules  of  the  appendix  are  exceedingly 
numerous  and  large,  in  places  fusing  into  masses  of  considerable  size,  which  en- 

1  Deutsches  Archiv  fur  Klin.  Med.,  Bd.  liii.,  1894. 

2  Edinburgh  Medical  Journal,  1893. 

3  Sitzungsber.  Acad.  Wissen.,  Wien,  Bd.  ciii.,  1894. 


1664 


HUMAN  ANATOMY. 


croach  upon  the  mucosa  and  its  glands  to  reach  almost  the  free  surface.  The  layer 
of  circular  muscular  fibres  is  i  mm.  thick,  or  about  twice  the  thickness  of  the  lon- 
gitudinal one.  Both  layers  have  interruptions,  so  that  the  submucous  and  subperi- 
toneal  layers  are  in  places  continuous.  This  occurs  particularly  along  the  insertion 
of  the  fold  of  peritoneum  called  the  mesentery  of  the  appendix. 

The  vermiform  appendix  (processus  vcrraiformis)  is  a  long,  slender,  worm- 
like  outgrowth  from  the  caecum,  formed  of  all  the  coats  of  the  intestine.  Its  length 
varies  from  I  cm.  (^3  in.)  to  24  cm.  (9^  in.),  the  average  being  probably  about 
8.4  cm.1  (3^  in.).  Monks  and  Blake,"  from  the  records  of  641  autopsies  at  the 
Boston  City  Hospital,  give  the  average  length  as  7.9  cm.  (3  in..),  with  the  extremes 
as  above.  Berry  finds  that  the  appendix  is  on  the  average  about  i  cm.  longer  in 


FIG.  1416. 


Longitudinal  muscle 


.Circular  muscle 


Transverse  section  of  vermiform  appendix.    X 


the  male  ;  others  find  no  particular  difference.  The  diameter  at  the  base  is  6  mm. 
and  at  the  apex  5  mm.  Its  usual  origin  is  from  the  postero-median  aspect  of  the 
caecum.  According  to  Berry,  this  occurs  in  more  than  90  per  cent.,  the  point  of 
origin  being  1.7  cm.  distant  from  the  end  of  the  ileum.  This  is  very  important  as 
showing  a  relatively  fixed  point  of  origin,  as  the  general  direction  of  the  appendix  is 
very  uncertain.  That  of  the  distal  half  especially  is  largely  a  matter  of  chance. 
Moreover,  the  position  after  death  is,  except  in  certain  cases,  no  guide  to  that 
during  life.  The  appendix  is  attached  to  the  caecum  and  to  neighboring  structures 
by  a  peritoneal  fold  to  be  described  later.  If  this  fold  be  long  and  narrow,  the 
movements  of  the  appendix  are  much  restricted  ;  if  the  base  of  the  fold  be  short 
and  its  attachment  to  the  appendix  a  long  one,  the  appendix  is  thrown  into  coils. 

1  Fawcett  and  Blatchford  (for  the  average  length)  :  Proceedings  of  the  Anatomical  Society 
of  Great  Hritain  and  Ireland,  Journal  of  Anatomy  and  Physiology,  vol.  xxxiv.,  1900. 

2  Boston  Medical  and  Surgical  Journal,  November  27,  1902. 


THE  CAECUM.  1665 

This,  to  a  greater  or  less  extent,  is  the  normal  condition.  There  is  no  doubt  that  in 
the  great  majority  of  cases  the  appendix  is  wholly  behind  the  caecum,  mesial  to  it, 
or  below  it.  Monks  and  Blake  found  a  reference  to  this  point  in  the  records  of 
572  autopsies.  It  was  "down  and  in"  179  times,  "behind"  with  no  statement  of 
the  direction  104  times,  "down"  79  times,  and  "in"  62  times.  Thus  in  almost 
three-quarters  of  the  cases  it  was  in  one  of  these  positions.  It  ran  "  up"  52  times, 
"up  and  in"  39  times,  and  "up  and  out"  29  times.  In  9  cases  it  was  "out," 
"down  and  out"  in  5,  and  "in  pelvis"  in  14.  It  sometimes  is  attached  to  the  as- 
cending colon  by  its  peritoneal  fold,  and  runs  upward  with  probably  accidental  incli- 
nations to  one  side  or  the  other.  It  may  also  be  found  in  some  of  the  peritoneal  fossae 
of  the  region.  In  many  of  the  cases  marked  "down  and  in"  it  hung  over  the 
pelvic  brim.  Of  123  cases  in  which  the  appendix  was  covered  by  peritoneum,  and 
therefore  presumably  normal,  Ferguson1  found  it  hanging  downward  in  n,  placed 
mesially  in  18,  on  the  right  of  the  caecum  in  19,  and  behind  it  in  75.  Total  absence 
of  the  appendix  is  extremely  rare,  but  has  been  observed  by  ourselves  and  others. 

Obliteration  of  the  Cavity  of  the  Appendix. — The  adenoid  tissue  of  the  vermiform  ap- 
pendix is,  as  elsewhere,  most  developed  in  childhood  and  tends  to  atrophy  in  middle  life. 
Coincident  with  this  atrophy  is  a  tendency  (the  cause  of  which  is  not  clear)  in  the  walls  to 
adhere,  more  or  less  obliterating  the  cavity.  Ribbert a  found  in  400  specimens  more  or 
less  obliteration  in  25  per  cent.,  and,  putting  aside  those  under  twenty  years,  in  32  per  cent. 
After  fifty  it  occurred  in  more  than  50  per  cent.  He  found,  however,  the  obliteration  complete 
in  only  3^  per  cent.  In  approximately  one-half  of  the  cases  it  involved  only  about  one-half 
of  the  tube.  The  process  usually  begins  at  the  closed  end  of  the  tube,  and  is  much  more  fre- 
quent in  short  than  in  long  appendices.  Zuckerkandl 3  observed  more  or  less  obliteration  in 
23.7  per  cent,  of  232  specimens,  the  process  being  nearly  or  quite  complete  in  13.8  per  cent. 
Ribbert  saw  the  process  beginning  in  childhood,  but  never  under  five  years.  Fawcett  and 
Blatchford*  found  the  appendix  pervious  196  times  in  221  cases,  and  91  of  the  pervious  ones 
were  from  those  over  fifty  years.  We  agree  with  them  that  much  more  conclusive  evidence  is 
needed  to  establish  the  existence  of  a  special  atrophy  of  the  appendix  in  old  age  or  after 
middle  life. 

Peritoneal  Relations. — The  caecum,  being  originally  an  outgrowth  from  the 
convex  side  of  the  primitive  intestinal  loop,  is  completely  covered  by  peritoneum 
and  has  no  mesentery,  since  the  mesentery  of  the  ileum  passes  directly  to  the  colon. 
The  appendix,  being  the  original  end  of  the  caecal  pouch,  is  consequently  also  com- 
pletely invested  with  peritoneum.  When  the  ascending  colon  has  come  to  lie  in  the 
right  flank,  the  posterior  layer  of  its  mesentery  degenerates  into  areolar  tissue,  fusing 
with  that  resulting  from  the  degeneration  of  the  parietal  peritoneum  behind  it,  and 
by  the  same  process  the  back  of  the  colon  is  attached  by  areolar  tissue  to  the 
abdominal  wall  behind.  This  condition  almost  always  ends  a  short  distance  above 
the  caecum.  It  is  far  more  common  to  find  the  lower  third  of  the  ascending  colon 
with  peritoneum  on  its  posterior  surface  than  to  find  none  on  the  upper  posterior 
part  of  the  caecum.  This  condition,  indeed,  does  occur,  we  having  seen  it  at  birth  ; 
but  it  is  very  exceptional.  From  the  preceding  facts  it  follows  that  the  caecum 
and  the  appendix  can  have  no  mesentery  in  the  strict  sense  ;  nevertheless,  the 
term  mesentery  of  the  appendix,  or  meso-appendix  ( mesenteriolum  processus  vermi- 
formis),  is  applied  to  an  almost  constant  fold  of  peritoneum,  presumably  caused 
by  the  artery  of  the  appendix,  which  usually  is  attached  to  nearly  the  entire  length 
of  that  organ.  Authorities  differ  widely  as  to  how  far  the  line  of  attachment  ex- 
tends along  the  appendix.  Beyond  question  it  is  very  variable.  According  to 
Monks  and  Blake,  it  extends  nearly  or  quite  to  the  end  in  fully  one-half  of  the 
cases,  and  in  most  of  the  other  half  it  reaches  or  passes  the  middle  of  the  appendix. 
Its  general  appearance  is  triangular,  but,  according  to  both  Jonnesco5  and  Berry,6 
with  whom  we  agree,  it  is  more  properly  described  as  quadrilateral.  One  side  runs 

1  American  Journal   of  the  Medical   Sciences,  1891. 

2  Virchow's  Archiv,  Bd.  cxxxii.,  1893. 
5  Anat.  Hefte,  Bd.  iv.,  1894. 

*  Proceedings  of  the  Anatomical  Society  of  Great  Britain  and  Ireland,  Journal  of  Anat- 
omy and  Physiology,  vol.  xxxiv.,  1900. 

5  Hernies  internes  re'tro-pe'ritone'ales,  Paris,  1890. 

6  The  Csecal  Folds  and  Fossae  and  the  Topographical  Anatomy  of  the  Vermiform  Appendix, 
Edinburgh,  1897. 

105 


1 666 


HUMAN   ANATOMY. 


Ileum,  turned  up 


Inferior  ileo-caecal 
fold 


along  the  proximal  half  or  even  the  whole  length  of  the  appendix,  one  is  free,  and 
the  other  two  are  attached  to  the  left  side  of  the  mesentery  and  to  the  caecum 
respectively.  These  latter  are  not  readily  distinguished  from  each  other;  hence  the 
triangular  effect.  The  artery  of  the  appendix  enters  the  fold  on  the  back  of  the 
caecum,  and  runs  at  first  from  5  mm.  to  i  cm.  distant  from  its  free  edge,  which 
gradually  approaches  it.  Although  the  fold  may  terminate  before  reaching  the  end 
of  the  appendix,  it  does  not  follow  that  the  whole  of  the  latter  is  not  enclosed  in  peri- 
toneum, since  under  normal  circumstances  it  always  must  be.  The  course,  shape, 
and  size  of  the  meso-appendix  are  very  irregular.  It  is  almost  invariably  so  short 
that  the  proximal  half  of  the  appendix  is  thrown  into  coils.  We  have  seen  this  fold 
attached  to  the  right  side  of  the  mesentery,  as  well  as  not  attached  to  it  at  all. 
Sometimes  it  runs  upward  along  the  posterior  part  of  the  left  side  of  the  colon,  so 
that  the  appendix  is  vertical  ;  at  other  times  it  is  attached  to  the  floor  of  the  iliac 
fossa  ;  and  very  rarely  it  is  wanting.  In  the  female  adult  a  secondary  fold  can  very 
often,  but  by  no  means  always,  be  traced  from  the  meso-appe'ndix  to  the  broad 
ligament.  This  fold  is  probably  due  to  the  persistence  of  one  which  in  the  fcetus 
often  connects  the  appendix  or  caecum  with  the  early  ovary  and  the  oviduct.  The 
lymph-node  which  the  meso-appendix  is  said  to  contain  we  have  seldom  found. 

It  happens  frequently  that,  from 

FIG.  1417.  pathological  causes  by  which  ad- 

hesions have  changed  the  perito- 
neal relations,  the  appendix  lies 
behind  the  peritoneum.  Fergu- 
son found  it  so  77  times  in  200. 

Pericaecal  Fossae.  —  An 
indefinite  number  of  fossae  or 
pouches,  all  more  or  less  variable, 
are  to  be  found  about  the  caecum. 
The  two  following  are  usually 
demonstrable,  although  not  so 
constant  as  held  by  some  authors. 
The  superior  ileo-caecal 
fossa1  (Fig.  1414)  is  roofed  in 
by  a  peritoneal  duplicature,  the 
superior  ileo-ccecal  fold,  which, 
starting  from  the  right  surface  of 
the  mesentery,  curves  over  the 

end  of  the  ileum  from  behind  forward.  The  attached  border,  in  which  the  ileo-coljp 
artery  lies,  runs  along  the  colon  just  where  it  joins  the  ileum,  and  is  usually  con- 
tinued forward  down  onto  the  front  of  the  caecum  for  a  short  distance.  The  pouch 
between  this  fold  above  and  the  end  of  the  ileum  below  opens  to  the  left,  but  if  the 
ileum  be  distended,  the  free  edge  of  the  fold  is  so  closely  applied  to  it  that  the  fossa 
is  easily  overlooked.  The  depth  of  the  fossa  may  reach  3  cm.  It  is  most  distinct 
in  infants  and  frequently  obliterated  in  middle  life,  although  careful  examination  often 
reveals  a  small  fold  and  recess  that  may  be  overlooked.  Berry  found  this  fossa 
absent  in  12  of  100  cases,  all  of  the  12  being  over  forty  years. 

The  inferior  ileo-caecal  fossa2  (Fig.  1417)  is  less  constant  and  much  more 
complicated  than  the  preceding.  Its  practical  importance  is  greater,  since  it  may 
contain  the  appendix.  To  display  it  the  ileum  must  be  drawn  upward  and  the 
appendix  downward  and  to  the  right  ;  the  caecum  may  or  may  not  require  to  be 
displaced  to  the  right  or  inverted.  This  fossa  is  situated  in  the  entering  angle 
formed  by  the  end  of.  the  ileum  joining  the  caecum,  and  is  bounded  on  the  right  by 
the  first  part  of  the  appendix.  The  meso-appendix  shuts  it  in  behind,  and  in  front 
it  is  covered  by  the  inferior  ileo-ca'cal  fold?  The  latter,  which  usually  joins  the 

1  There  is  much  to  he  said  in  favor  of  the  term  ilco-colii\  since  the  pocket  lies  at  the  angle 
of  the  ileum  and  colon.    It,  however,  so  frequently  extends  downward  to  tin-  front  of  the  caecum 
that  the  more  usual  nomenclature  is  here  adopted. 

2  Known  also  as  the  ilro-folic  fossa,  the  ilco-appendicular  fossa,  etc. 

8  This  is  the  "  bloodless"  fold  of  Treves  or  the  ileo-appendicular  fold  of  Jonnesco. 


Meso-appendix 


Caecum  from  inner  side  and  below. 


THE  CAECUM.  1667 

meso-appendix,  is  in  its  conventional  form  described  as  having  four  sides  :  a  superior 
on  the  ileum,  a  right  one  on  the  caecum,  an  inferior  joining  the  appendix  or  the 
meso-appendix,  and  a  free  concave  one  looking  towards  the  left  and  overhanging 
the  entrance  to  the  fossa,  which  may  be  nearly  4  cm.  ( i  ^  in. )  in  depth.  The  fold 
usually  contains  only  small  vessels,  and  has  been  described  as  "bloodless."  It 
sometimes  contains  muscle-fibres  passing  between  the  ileum  and  caecum.  The  size 
as  well  as  the  formation  of  this  pocket  is  very  variable.  When  we  consider  the 
extreme  variability  of  the  meso-appendix  which  is  concerned  in  its  typical  forma- 
tion, it  is  manifest  that  such  must  be  the  case.  Sometimes  the  meso-appendix  is  in 
no  way  connected  with  it,  only  a  small  fold  of  peritoneum  passing  from  the  ileum  to 
the  caecum  at  the  side  most  removed  from  the  mesentery.  Berry  found  this  fossa  in 
74  per  cent. 

The  Retro-Colic  Fossa. — In  the  great  majority  of  cases  the  posterior  sur- 
face of  the  caecum  lies  free  in  the  abdominal  cavity,  covered  by  its  original  peri- 
toneum. At  a  variable  distance  from  it  the  back  of  the  colon  becomes  adherent  to 
the  posterior  abdominal  wall  and  to  the  front  of  the  right  kidney  ;  hence  there  is, 
or  may  be,  especially  if  the  colon  be  drawn  away  from  the  wall,  a  fold  on  either  side 
stretching  from  the  gut  to  the  wall.  These  are  the  ligaments  of  the  colon,  the  exter- 
nal and  the  internal.  The  former  runs  outward  and  downward  from  the  side  of  the 
colon  along  the  abdominal  wall,  or  perhaps  across  the  lower  end  of  the  kidney,  and 
presents  a  free  concave  border  overhanging  a  pouch  running  upward  and  outward. 
The  internal  or  mesian  fold  is  the  more  often  distinct,  and  is  formed  chiefly  by  the 
insertion  of  the  mesentery.  According  to  its  degree  of  development,  the  free  falci- 
form edge  overhangs  a  pouch,  looking  downward  and  more  or  less  to  the  right. 
The  fold  may  be  continued  downward  either  to  the  right  or  to  the  left.  In  the 
former  case  it  may  form  a  pocket,  of  which  the  lower  end  opens  upward.  It  is 
clear,  therefore,  that  with  both  these  folds  well  developed  a  retro-colic  fossa  exists, 
which  is  shown  when  the  caecum  is  turned  up.  Its  greatest  depth  is  in  the  middle 
behind  the  colon,  and  it  is  continued  downward  on  either  side  under  the  folds 
caused  by  these  ligaments.  Should  either  ligament  be  wanting,  there  can  be  no 
fold  on  that  side.  Some  authors  have  thought  it  best  to  describe  an  external  and 
an  internal  fossa  under  each  of  the  ligaments,  of  which  the  internal  is  the  more  fre- 
quent ;  it  is  more  simple,  however,  to  describe  only  one.  The  fossa  may  be  sub- 
divided by  a  median  fold.  Very  often  there  is  no  definite  fossa  at  all.  The  internal 
part  is  more  commonly  well  developed  than  the  external. 

The  subcaecal  fossa  is  an  uncommon  pouch,  sometimes  small  and  sometimes 
large,  situated  above  the  middle  of  the  iliac  fossa.  It  seems  to  be  due  to  an  irregu- 
lar development  of  the  iliac  fascia,  which  forms  a  pocket  in  itself,  with  the  mouth 
above,  guarded  in  front  by  a  semilunar  fold.  The  fossa  is  lined  by  the  parietal  peri- 
toneum. It  may  unite  with  the  inner  fold  of  the  retro-colic  fossa,  or  the  two  may 
exist  at  the  same  time.  It  may  contain  the  appendix,  even  a  part  of  the  caecum, 
or,  according  to  Jonnesco,  coils  of  the  small  intestine. 

Blood-Vessels. — The  artery  supplying  the  caecum  is  the  ileo-colic,  a  branch 
of  the  superior  mesenteric  artery,  which  sends  to  it  both  an  anterior  and  a  larger 
posterior  branch,  which  ramify  downward  over  the  front  and  back  of  the  caecum. 
A  large  branch  from  the  posterior  division  runs  between  the  folds  of  the  posterior 
retinaculum  ;  less  constantly  a  smaller  vessel  courses  in  the  anterior  one.  The 
segments  of  the  ileo-caecal  valve  are  very  vascular.  The  artery  of  the  vermiform 
appendix  arises  from  the  posterior  division  of  the  ileo-colic,  crosses  the  back  of  the 
ileum,  and  runs  in  the  fold  of  peritoneum  to  the  end  of  the  appendix.  The  veins 
of  the  caecum  are  arranged  on  much  the  same  plan  as  the  arteries.  That  of  the 
appendix  is  relatively  more  important,  receiving  tributaries  from  the  front  and  the 
back  of  the  caecum.  It  passes  behind  the  end  of  the  ileum  to  the  ileo-colic  vein. 

The  lymphatics  are  divided  into  a  posterior  and  an  anterior  set.  The  former 
empty  into  small  nodes  on  the  back  of  the  caecum  beneath  its  peritoneal  covering. 
The  anterior  ones  are  in  or  near  the  fold  between  the  caecum  and  colon.  The  appendix 
contains  a  large  lymph-sinus  at  the  base  of  the  follicles.  Lymphatics  pass  through 
the  interruptions  of  the  muscular  layer.  They  may  enter  a  node  in  the  peritoneal 
fold  in  the  angle  between  the  caecum  and  ileum.  There  are  several  possible  communi- 


1 668  HUMAN   ANATOMY. 

cations  :  one  with  nodes  in  the  mesentery  ;  one  with  nodes  on  the  left  of  the  as- 
cending colon  behind  the  peritoneum  ;  one  with  nodes  of  the  iliac  fossa  ;  and,  in 
the  female,  one  with  the  system  of  the  ovary.  There  is  a  constant  lymph-node  at 
the  angle  between  the  ileum  and  colon.1 

The  nerves  supplying  the  caecum  and  appendix  are  derived  from  the  superior 
mesenteric  plexus.  Their  mode  of  distribution  within  the  gut  has  already  been 
given  (page  1643). 

Development  and  Growth. — At  birth  and  for  some  years  after  the  caecum 
is  very  small  and  the  fcetal  or  cornucopia  shape  is  more  frequent  than  later.  The 
appendix  is  relatively  rather  long.  In  eleven  cases  below  ten  years  Berry  ~  found  the 
average  length  of  the  caecum  28  mm.  and  the  breadth  37  mm.  In  eighteen  cases 
he  found  the  average  length  of  the  appendix  74  mm.  (2^5  in.).  Ribbert  gives  the 
following  lengths  of  the  appendix  :  at  birth,  34  mm. ;  up  to  five  years,  76  mm. 
(3  in.);  from  five  to  ten  years,  90  mm.  (3^  in.). 

At  birth  the  caecum  is  usually  higher  than  in  the  adult,  since  it  has  not  de- 
scended to  its  permanent  position  and  the  adhesion  of  the  mesentery  of  the  ascend- 
ing colon  has  not  occurred  in  the  lower  part  of  the  flank.  It  is  often  rather  above 
the  anterior  superior  spine  of  the  ilium.  In  five  of  about  thirty-five  observations 
on  young  children,  mostly  newly-born,  it  was  so  free  from  fixed  attachment  that  it 
could  hardly  be  said  to  have  any  definite  position. 

THE   COLON. 

The  ascending  colon  extends  from  the  caecum  to  the  under  side  of  the  liver, 
where  it  makes  a  sudden  bend — the  hepatic  flexure  (flexura  coli  dextra) — and  be- 
comes the  transverse  colon,  which  crosses  the  abdomen  to  the  splenic  flexure  (flexura 
coli  sinistra)  at  the  spleen,  whence,  as  the  descending  colon,  it  passes  to  the  crest  of 
the  ilium.  From  that  point  to  the  middle  of  the  third  sacral  vertebra  it  is  known  as 
the  sigmoid flexure.  The  three  bands  of  the  colon,  or  t&nicz  coli,  formed  by  accu- 
mulations of  longitudinal  fibres,  are  each  about  i  cm.  broad.  Their  disposition  in 
the  walls  of  the  gut  is  difficult  to  follow  and  is  not  constant.  The  following  arrange- 
ment is  probably  the  most  usual.  In  the  ascending  colon  one  is  in  front  and  two 
behind,  one  of  the  latter  being  near  the  outer  and  the  other  near  the  inner  aspect. 
On  reaching  the  transverse  colon,  the  anterior  becomes  the  inferior,  while  the 
external  becomes  the  superior,  receiving  the  attachment  of  the  transverse  meso- 
colon.  The  internal  also  lies  on  the  upper  surface,  but  behind  the  preceding.  On 
the  descending  colon  they  resume  their  original  positions,  but  tend  to  grow  indis- 
tinct. They  are  still  more  so  in  the  sigmoid  flexure,  and  before  the  rectum  is 
reached  there  are  but  two  bands,  an  anterior  and  a  posterior,  of  which  the  latter  is 
the  stronger.  The  interior  of  the  colon  shows  the  sacculated  condition,  but  there 
are  no  folds  or  valvulae  conniventes  like  those  of  the  small  intestine.  The  solitary 
lymph-nodules  continue,  much  like  those  of  the  jejuno-ileum. 

Relations. — The  ascending  colon  is  in  the  right  flank  against  the  psoas  and 
quadratus  lumborum,  but  does  not  overlap  the  latter  unless  greatly  distended.  It 
lies  in  front  of  the  lower  end  of  the  right  kidney,  projecting  but  little  beyond  its 
outer  border,  with  the  second  part  of  the  duodenum  on  its  inner  side.  It  ends  with 
the  hepatic  flexure,  which  makes  a  large  impression  on  the  under  side  of  the  right 
lobe  of  the  liver  directly  anterior  to  the  kidney.  It  is  often  completely  covered  in 
front  by  the  small  intestine. 

The  transverse  colon  is  suspended  between  its  beginning,  the  hepatic 
flexure,  and  its  end,  the  splenic  flexure,  like  a  festoon,  forward  and  downward  ; 
for  the  ends  are  near  the  back  of  the  abdominal  cavity.  The  splenic  flexure,  in  front 
of  the  lower  part  of  the  spleen,  is  both  higher  and  more  posterior  than  the  hepatic 
one.  The  transverse  colon  is  covered  above  and  in  front  by  the  greater  omentum. 
It  runs  along  the  liver,  touching  the  gall-bladder  and  the  greater  curvature  of  the 
stomach,  around  which  it  ascends  to  the  spleen.  The  splenic  flexure  may  or  may 

1  Lockwood  :  Proceedings  of  tin-  Anatomical  Society  of  Great  Britain  and  Ireland,  Journal 
of  Anatomy  and  Physiology,  vol.  xxxiv.,  1900. 
*  Anat.  Anzeiger,  Bd.  x.,  1895. 


THE   COLON. 


1669 


not  rest  against  the  under  side  of  the  diaphragm,  according  to  its  distention  and 
that  of  the  stomach.  It  rests  behind  and  below  on  the  small  intestine.  It  may  or 
may  not  be  in  immediate  relation  to  the  tail  of  the  pancreas. 

The  descending  colon  descends  partly  in  front,  but  still  more  external  to  the 
kidney,  and  after  passing  the  kidney  rests  wholly  on  the  quadratus  lumborum. 
Although  more  externally  placed  than  the  ascending  colon,  it  does  not  usually  project 
beyond  that  muscle. 

The  sigmoid  flexure  (colon  sigmoideum),  the  continuation  of  the  large  intestine, 
begins  at  the  crest  of  the  ilium  as  a  loop  of  very  varying  length,  which  is  attached  by 

FIG.  1418. 


Left  side  of  abdomen;  small  intestine  turned  to  right,  exposing-  mesentery,  mesocolon  of  descending  colon,  and 

mesosigmokl. 

a  mesentery,  and  ends  at  the  middle  of  the  third  sacral  vertebra.  Its  usual  length  is 
from  25-56  cm.  ( 10-18  in. ),  but  is  occasionally  much  longer.  While  it  is  true  that  the 
gut  does  not  always  become  free  at  the  crest  of  the  ilium,  but  may  descend,  bound 
down  closely,  to  the  iliac  fossa  for  some  distance,  it  is  best  to  regard  the  sigmoid 
flexure  as  beginning  at  a  definite  although  arbitrary  point  rather  than  at  the  less 
certain  one  at  which  the  gut  really  has  a  mesentery.  Moreover,  there  is  no  great 
inaccuracy  in  the  statement  that  this  generally  occurs  at  the  crest  of  the  ilium  or 
just  below  it.  The  simplest  form  of  the  sigmoid  flexure  is  a  loop.  If  it  be  a  small 
one,  it  usually  is  made  of  the  last  part  of  this  section  of  the  gut  ;  very  often  the  first 
part  is  but  slightly  free  while  the  last  part  is  very  much  so.  Short  sigmoid  flexures, 


i6yo 


HUMAN   ANATOMY. 


especially  with  short  mesenteries,  can  hardly  vary  much  from  a  simple  loop  ;  under 
opposite  conditions,  however,  they  may  present  the  most  diverse  forms,  so  that  a 
definite  shape  can  hardly  be  assumed.  The  M-form  is  common.  We  have  seen 
the  sigmoid  disposed  in  three  parallel  vertical  folds  occupying  all  of  the  left  iliac 
fossa  and  overhanging  the  true  pelvis.  As  the  sigmoid  flexure  descends  along  the 
sacrum  it  usually  curves  to  the  right  and  crosses  the  median  line. 

Peritoneal  Relations. — The  lower  part  of  the  ascending  colon  is  very 
often,  for  one  or  two  inches,  completely  surrounded  by  serous  membrane.  The 
ligaments  of  the  colon  (described  with  the  retro-colic  fossa,  page  1667)  occur  more  or 
less  well  marked  at  the  line  where  the  peritoneum  leaves  the  posterior  wall.  Above 
this  the  colon  is  connected  by  areolar  tissue  to  the  kidney.  Occasionally  the  colon 
is  adherent  as  far  as  the  csecum.  The  non-peritoneal  portion  of  the  upper  part  of 
the  ascending  colon  equals  about  one-third  of  its  circumference. 

The  transverse  colon  is  attached  to  the  transverse  mesocolon  and  otherwise 
completely  surrounded  by  peritoneum.  The  transverse  mesocolon,  after  attaining 
its  permanent  condition,  arises  along  the  back  of  the  abdomen  from  one  kidney  to 

FIG.  1419. 


Sigmoid  flexure 
pulled  up 


Anterior  band 


Rectum 


Bladde 


Anterior  abdominal  wall  turned^ 
forward 


Mesentery  of 
sigmoid 


Anterior  superior 
spine  of  ilium 

Recto-vesical  fold 


Sigmoid  flexure  and  rectum  ;  sigmoid  has  been  displaced  upward  to  show  its  mesentery. 

the  other.  It  crosses  the  front  of  the  right  kidney,  the  second  part  of  the  duo- 
denum, and  passes  along  the  lower  border  of  the  pancreas  above  the  duodeno-jejunal 
flexure,  to  end  on  the  left  kidney.  Sometimes  in  the  left  part  of  its  course  its 
origin  rises  onto  the  superior  anterior  surface  of  the  pancreas.  Its  greatest  breadth 
— i.e.,  the  distance  from  its  origin  to  insertion — is  at  the  middle,  and  varies  from 
10-15  cm-  The  posterior  layer  of  the  greater  omentum  fuses  with  it.  The  phn-no- 
colic  ligament,  which  runs  inward,  shelf-like,  from  the  left  abdominal  wall  under  the 
spleen,  although  in  acquired  relation  with  the  mesentery  of  the  transverse  colon,  is 
really  a  part  of  the  greater  omentum.  The  latter  hangs  down  from  the  transverse 
colon  over  the  small  intestine,  but  its  relation  to  the  colon  is  not  the  same  through- 
out. On  the  right  it  is  fused  with  the  peritoneum  of  the  anterior  surface  of  the  gut 
and  lea'ves  it  at  the  lower  border.  On  the  left  it  leaves  the  upper  surface  of  the 
colon,  or  even  the  transverse  mesocolon,  before  the  latter  reaches  the  gut.  Thus 
the  line  at  which  it  leaves  the  intestine  rises  gradually  from  right  to  left. 

The  descending  colon  is  usually  uncovered  posteriorly  by  peritoneum. 
According  to  Lesshaft,1  whose  results  have  been  generally  accepted,  it  has  mon-  or 
less  of  a  mesentery  once  in  six  times.  According  to  Symington,1  the  mesenteries 

1  Reichert  and  Du  Bois-Reymond's  Archiv,  1870. 

2  Journal  of  Anatomy  and  Physiology,  vol.  xxvi.,  1892. 


THE   COLON.  1671 

thus  found  are  due  to  a  displacement  of  the  peritoneum,  which  is  but  loosely  attached. 
True  mesenteries  are  probably  less  frequent. 

At  the  sigmoid  flexure  the  peritoneum  usually  begins  to  surround  the  gut, 
although  the  point  at  which  this  commences  maybe  much  lower.  In  the  former 
case  the  line  of  origin  of  the  mesentery  descends  tolerably  straight  to  the  middle  of 
the  third  sacral  vertebra,  where  it  ends.  The  gut  may,  however,  be  pretty  closely 
bound  down  to  the  iliac  fossa  as  far  as  the  true  pelvis  over  the  posterior  border  of 
the  obturator  foramen,  in  which  case  the  line  of  attachment  runs  thence  backward 
along  the  border  of  the  true  pelvis  until  it  crosses  the  sacro- iliac  joint,  after  which 
it  descends  across  the  sacrum.  There  may,  of  course,  be  an  indefinite  number  of 
variations  between  these  extremes.  The  attachment  to  the  sacrum  is  usually  near 
the  median  line  over  the  second  and  third  vertebrae,  but  it  may  diverge  to  either 
side  of  it.  Variation  also  exists  as  to  the  point  at  which  the  mesentery  ends.  The 
greatest  breadth — i.e.,  from  origin  to  insertion — of  the  latter  is  usually  found  in  the 
part  which  springs  from  the  first  sacral  vertebra.  It  is,  on  the  average,  about  9  cm. , 
rarely  less  than  5,  not  more  than  16  ;  exceptionally  it  may  be  as  much  as  25  cm. 
With  a  long  loop  it  is,  of  course,  relatively  narrow  at  its  origin. 

The  intersigmoid  fossa  is  an  inconstant  small  peritoneal  pouch,  present 
about  three  times  out  of  four,  on  the  under  side  of  the  mesentery  of  the  sigmoid 
flexure,  which  is  shown  by  throwing  the  loop  upward  and  to  the  right.  It  is  ob- 
viously due  to  the  failure  of  the  sigmoid  mesentery  to  unite  completely  with  the 
peritoneum  of  the  posterior  wall,  and  consequently  is  under  the  edge  of  the  part  that 
fails  to  unite,  lying  usually  just  above  the  true  pelvis  near  the  common  iliac  artery. 
The  orifice  of  the  pocket  is  very  likely  to  be  circular,  with  a  diameter  of  from  1—3 
cm. ,  in  most  cases  nearer  the  lower  figure.  The  pouch  may  be  quite  rudimentary, 
or  may  extend  up  like  a  tunnel  between  the  layers  of  peritoneum  for  an  inch  or  two, 
or  exceptionally  for  a  greater  distance. 

Development  and  Growth. — The  length  of  the  intestines,  and  especially  of 
the  colon,  is,  according  to  Treves,  singularly  constant  at  birth.  He  found  the 
average  length  of  the  small  intestine  about  287  cm.  (9  ft.  5  in.)  and  that  of  the  large 
about  56  cm.  (  i  ft.  10  in.  ).  It  is  remarkable  that  while  during  the  first  two  months 
the  small  intestine  grows  at  the  rate  of  about  two  feet  a  month,  the  large  intestine 
remains  of  the  same  length  for  three  or  even  four  months.  This  is  due  to  the  fact 
that  during  this  period  the  large  intestine  grows  at  the  expense  of  the  sigmoid  flexure, 
which  at  birth  forms  nearly  one-half  of  the  whole,  while  at  four  months  it  has 
assumed  approximately  its  permanent  proportions  (Treves).  After  this  the  growth  of 
both  small  and  large  intestine  is  extremely  irregular,  as  shown  by  the  following  table  : 

Observer.                                            Age.  Small  Intestine.  Large  Intestine. 

Dwight.  10  months.  670  cm.  78  cm. 

Dwight.  10  months.  435  cm.  90  cm. 

Treves.                                  i  year.  ...  76  cm. 

Dwight.                                3  years.  490  cm.  84  cm. 

Treves.                                 6  years.  ...  91.5  cm. 

Treves.  13  years.  .    .    .  107  cm. 

As  the  sigmoid  flexure  is  relatively  large  in  the  infant  and  the  pelvis  very  small, 
the  convexity  of  the  loop  lies  in  the  right  side  of  the  abdomen. 

Variations. — The  mesentery  of  the  small  intestine  and  of  the  ascending  and  the  transverse 
colon  may  remain  attached  only  at  the  origin  of  the  superior  mesenteric  artery,  giving  the  con- 
dition known  as  mesenterium  commune.  The  ascending  colon  may,  on  the  other  hand,  be  so 
long  as  to  make  secondary  folds.  Curschmann '  has  seen  its  mesentery  long  enough  to  be 
twisted.  The  transverse  colon  may  be  short,  wanting  one  or  both  flexures.  In  the  latter  case 
the  ascending  and  the  descending  colon  are  almost  like  the  sides  of  an  inverted  V.  Probably 
much  more  often  the  transverse  portion  may  be  too  long  and  descend  in  the  middle  like  an  M, 
with  the  middle  point  at  the  pelvis.  A  fold  is  more  common  at  the  left  than  the  right.  A 
double  fold  of  the  transverse  colon  has  been  seen.  This  part  of  the  gut,  when  over  large,  may 
decidedly  diminish  the  area  of  the  liver  dulness.  The  descending  colon  may  also  present 
folds,  but  an  immense  sigmoid  flexure,  which  usually  is  accompanied  by  great  length  of  the 
large  intestine,  is  more  common.  The  convexity  of  this  fold  may  reach  to  the  transverse 
colon  or  to  the  caecum.  Sometimes  the  sigmoid  flexure  consists  of  two  successive  folds. 

1  Deutsches  Archiv  fur  Klin.  Med.,  Bd.  liii.,  1894. 


1672 


HUMAN   ANATOMY. 


Blood-Vessels. — The  arteries  of  the  colon  are  derived  from  the  superior  and 
the  inferior  mesenteric.  The  former  supplies  the  caecum,  the  ascending  and  the 
transverse  colon,  and  a  varying  amount  of  the  descending  colon.  The  supply  of  the 
latter  is  completed  by  the  inferior  mesenteric,  which  is  also  distributed  to  the  sigmoid 
flexure.  The  general  plan  includes  a  series  of  anastomoses  between  neighboring 
branches,  by  which  long  arterial  arches  run  near  the  border  of  the  gut,  to  which 
they  give  off  irregular  twigs.  There  is  no  system  of  straight  vessels  as  in  the  greater 
part  of  the  small  intestine.  In  the  sigmoid  flexure  there  is  a  recurrence  of  the 
superimposed  arches,  which  may  be  three  in  number.  The  superior  hemorrhoidal 
branch  of  the  inferior  mesenteric  artery  runs  in  the  last  part  of  the  mesentery  of  the 
sigmoid,  and  often  divides  in  it  into  two  branches,  which  run  side  by  side  on  the 
back  of  the  gut  towards  the  rectum.  The  veins  are  disposed  much  the  same  as 
the  arteries,  but  with  a  system  of  straight  vessels  from  the  intestine. 

The  lymphatics,  which  are  many,  empty  into  lymph-nodes  on  the  posterior 
wall  of  the  abdomen,  which  are  a  part  of  the  same  system  as  those  of  the  small 
intestine. 

The  nerves  are  from  the  superior  and  inferior  mesenteric  plexuses,  which  are 
derived  chiefly  from  the  solar  and  the  aortic  plexus  respectively. 

THE  RECTUM,  ANAL  CANAL,  AND  ANUS. 

The  Rectum. — The  rectum  begins  at  the  middle  of  the  third  sacral  vertebra, 
the  point  at  which  usually  the  mesentery  that  restrains  the  sigmoid  flexure  termi- 
nates. It  was  formerly  described  as  beginning  at  the  left  sacro-iliac  joint,  but 
this  division,  which  is  unwarranted,  is  falling  into  disuse.  The  rectum  descends 

FIG.  1420. 


Rectal  folds  I  — 


.^-Bladder 

\mi&^^. 

\\S&Es^i^''fc- •••:•-'-•    -----     — Seminal  vesicle 

jJQfe -*£\S$£:    sf       '  -^-.  :.',.,. Symphysis  pubis 

EAK^'-  -"  /:»( vx  /  •  •  •  • 


Sacro-coccygeal 
articulation 

Hemorrhoidal  vein 


Veins  of  mucosa  of  anal  canal  ( 

Fold  of  mucous  membrane 


l  sphincter 


Sagittal  section  of  pelvis  passing  through  rectum,  anal  canal,  bladder,  and  urethra. 

along  the  hollow  of  the  sacrum  and  coccyx,  passes  the  point  of  the  latter,  and  con- 
tinues until  it  reaches  the  lower  and  back  part  of  the  prostate  gland  in  the  male  or 
the  vagina  in  the  female.  Its  length  is  about  12.5  cm.  (approximately  5  in.).  The 
gut  is  then  continued  by  the  anal  canal,  sometimes  called  the  sphincteric  portion  of 


THE  RECTUM,  ANAL  CANAL,  AND  ANUS. 


1673 


the  rectum,  situated  in  the  thickness  of  the  pelvic  floor,  and  directed  downward 
and  backward,  making  a  sharp  angle  with  the  rectum  proper. 

The  rectum  proper,  having  passed  the  tip  of  the  coccyx,  rests  on  the  levator  ani 
muscle,  although  separated  from  it,  as  well  -as  from  the  sacrum  and  coccyx,  by  the 
dense  rectal  fascia.  The  rectum,  although  not  exhibiting  the  pouching  seen  in 
the  colon,  is  sacculated,  presenting,  when  distended,  usually  three  dilatations,  of 
which  the  lowest  and  largest,  called  the  ampulla,  may  measure  25  cm.  (9^3  in.),  or 
even  more,  in  circumference.  The  saccules  are  separated  by  deep  creases,  passing 
about  two-thirds  around  the  gut,  caused  by  a  folding  in  of  all  the  coats  internal  to  the 
two  bands  of  longitudinal  muscular  fibres.  The  folds  form  the  valves  of  the  rectum, 
to  be  described  with  its  interior.  In  the  male  the  ampulla  extends  against  the  back 
of  the  prostate  and  the  lower  part  of  the  seminal  vesicles  and  the  terminal  parts  of 
the  vasa  efferentia,  to  all  of  which  it  is  connected  by  areolar  tissue.  A  pocket  of 
peritoneum  intervenes  higher  up,  the  walls  of  which,  however,  come  in  contact  when 
the  hollow  organs  are  distended.  In  the  female  the  end  of  the  ampulla  lies  against 
the  posterior  wall  of  the  vagina  from  about  opposite  the  level  of  the  os  uteri  to  the 
junction  of  the  middle  and  lower  thirds.  There  is  above  this  a  fold  of  peritoneum 
corresponding  to  that  of  the  male. 

FIG.  1421. 


Glands  of  mucosa 


Levator  ani 


External  sphincter 


Levator  ani 


Internal  sphincter. 
Longitudinal  muscle 

External  sphincter 


Skin       Anal  glands      Anal  glands 
Frontal  section  through  anal  canal. 

The  Anal  Canal. — This  part  of  the  large  intestine  (pars  analis  recti)  is  situ- 
ated in  the  thickness  of  the  pelvic  floor  and  extends  downward  and  backward.  It 
differs  from  the  rest  of  the  intestinal  canal  in  having  no  lumen  under  ordinary  cir- 
cumstances, when  the  sphincters  surrounding  it  are  contracted.  The  anus  is  the 
very  vaguely  used  name  of  the  termination  of  the  anal  canal.  It  is  deeply  situated 
between  the  nates,  especially  in  the  female  ;  its  distance  from  the  tip  of  the  coccyx, 
variously  stated  by  different  observers,  may  be  said  to  be  about  5  cm.  (2  in.). 
Much  confusion  has  arisen  from  the  difficulty  of  defining  the  lower  end  of  the  anal 
canal,  since  the  skin,  which  is  puckered  up  by  the  external  sphincter  and  the  cor- 
rugator  cutis  ani,  somewhat  resembles  mucous  membrane,  so  that  the  canal  appears 
longer  than  it  really  is.  The  anatomical  boundary,  the  ano-rectal  groove,  the  so- 
called  white  line  of  Hilton,  is  a  slight  zigzag  furrow,  usually  to  be  seen  on  the  living 
and  not  on  the  dead.  It  lies  a  little  above  the  lower  limit  of  the  internal  sphincter, 
which,  covered  by  dilated  veins,  projects  towards  the  potential  lumen  above  the 
external  sphincter,  and  is  i  cm.  or  more  within  what,  on  a  superficial  examination, 
would  be  called  the  anus.  When  the  dissected  rectum  is  laid  open,  much  is  evidently 
a  part  of  the  skin  which  during  life  is  drawn  into  the  canal  by  the  contraction  of  the 
muscles  ;  hence  the  length  of  the  canal  is  very  variously  stated.  Seldom  does  it 


1 674 


HUMAN    ANATOMY. 


FIG.  1422. 


measure  as  much  as  15  mm.  from  its  upper  end  to  the  ano-rectal  groove  ;  probably 
this  distance  is  usually  about  i  cm.,  while  what  may  practically  be  called  the  canal  is 
twice  as  much,  or  even  more.  It  is  longer  in  men  than  in  women.  In  the  male  the 
beginning  of  the  anal  canal  is  near  the  lower  part  of  the  prostate  and  the  mem- 
branous urethra,  at  a  point  from  3.5-4  cm.  in  front  of  and  somewhat  lower  than  the 
tip  of  the  coccyx.  Lower  still,  the  bulb  of  the  urethra  is  separated  from  the  anal 
canal  by  the  pyramidal  mass  of  connective  tissue  constituting  the  perineal  body, 
The  latter  is  of  greater  importance  in  the  female,  and  separates  the  anal  canal  from 
the  lower  part  of  the  vagina  and  from  the  vulva.  The  moist  and  dark  skin  which 
is  puckered  up  to  form  the  continuation  of  the  anal  canal  is  at  first  very  thin,  but 
gradually  assumes  the  appearance  of  ordinary  integument.  The  so-called  anal  glands 
surrounding  the  anus  are  of  two  kinds,  both  of  which  have  their  orifices  in  this  skin. 
Those  nearest  to  the  boundary  line  are  sebaceous  follicles,  and  external  to  them  is  a 
zone  of  large  sweat-glands.  Just  at  the  termination  of  the  skin  apparently  forming  the 
end  of  the  canal  there  is,  especially  in  the  male,  a  considerable  development  of  hair. 
Structure  of  the  Rectum. — The  mucous  coat  is  thick  and  vascular,  and 
corresponds  in  its  general  histological  details  with  the  mucosa  of  other  parts  of  the 
large  intestine.  The  glands  of  Lieberkiihn,  however,  are  exceptionally  large,  at- 
taining a  length  of  .  7  mm.  The  muscularis 
mucosae  is  better  developed  than  in  the  colon. 
The  rectal  valves  (plicae  transversales  recti) 
are  two  or  three  folds,  exceptionally  four  or 
five,  projecting  like  transverse  shelves  into 
the  cavity  when  it  is  distended,  and  hanging 
loose  when  it  is  not.  They  are  semilunar 
in  shape,  with  the  greatest  breadth  from  the 
attached  border  to  the  free  edge,  ranging 
from  i  cm.  to  more  than  3  cm.  They  cor- 
respond to,  or  rather  are  the  causes  of,  the 
constrictions  between  the  saccules.  They 
contain  all  the  coats  of  the  gut,  except  that, 
chiefly  on  the  posterior  wall,  some  of  the 
longitudinal  muscle-fibres  pass  outside  of 
them,  thus  securing  the  fold.  In  large  folds 
there  is  an  accumulation  of  the  circular 
fibres.  These  folds  tend  to  be  effaced  in 
the  isolated  and  opened  rectum,  but  they 
are  unquestionable,  being  shown  by  casts 
and  frozen  sections,  and  in  both  the  living 
and  the  dead  body  when  placed  in  the 
knee-chest  position  with  the  rectum  cleared 
of  faeces  and  distended  with  air.  They  are  placed  laterally,  and  have  in  common 
that  their  points  cross  the  middle  line,  although  not  symmetrically,  extending  more 
onto  the  front  than  the  back.  According  to  the  usual  arrangement,  the  lowest, 
which  is  also  the  smallest,  projects  from  the  left  ;  the  second,  the  largest,  from  the 
right  ;  and  the  third  from  the  left.  The  first  is  about  2.5  cm.  (i  in.)  above  the 
anal  canal  and  the  second  about  as  much  higher.  If  the  first — as  often  happens — 
be  wanting,  the  second  is  not  necessarily  any  lower.  The  third  is  usually  at  about 
the  same  distance  above  the  second,  but  is  subject  to  greater  variations,  since  the 
two  may  be  very  near  together.1  The  columns  of  Morgagni  are  a  series  of  per- 
manent vertical  folds  of  mucous  membrane  passing  from  the  anal  canal  upward  into 
the  rectum.  The  number  of  these  folds  varies  from  five  to  considerably  more  than 
ten,  which  latter  number  is  perhaps  about  the  average.  The  length  of  the  folds  is 
in  most  cases  from  1-2  cm.,  but  some  are  considerably  longer.  They  are  broad 
and  highest  at  their  anal  end,  or  base,  from  which  they  diminish  to  the  upper  t-nd, 
a  transverse  cut  near  the  lower  end  showing  them  to  be  triangular  on  section.  The 
rn/rt's  of  Morgagni  arc  semilunar  folds  of  the  mucous  membrane  connecting  the 
bases  of  the  columns  of  the  same  name,  and  forming  with  them  a  number  of 

1  Otis  :  Anatomische  Untersuchungen  am  menschlichen  Rectum,  Leipzig, 


Folds  of  rectum  seen  after  dilatation.     (Otis.) 


THE  MUSCLES  AND  FASCIAE  OF  THE  RECTUM  AND  ANUS.    1675 

pouches  opening  upward.  They  are  situated  in  the  anal  canal  at  the  upper  part 
of  the  internal  sphincter.  The  mucous  membrane  of  the  rectum  is  thrown  into  a 
series  of  longitudinal  folds.  These  are  easily  effaceable,  although  some  are  continu- 
ous with  the  columns  of  Morgagni. 

The  submucous  coat  is  lax,  allowing  the  mucous  membrane  to  be  readily  dis- 
placed, but  at  the  lower  end  of  the  anal  canal  the  latter  is  firmly  attached  to  the 
muscles. 

The  muscular  coat  of  the  rectum  is  thicker  than  that  of  the  colon,  reaching  to 
2  mm.  The  thickening  is  greatest  in  the  layer  of  the  circular  fibres.  The  longitu- 
dinal ones,  although  forming  a  continuous  layer,  are  for  the  most  part  collected 
front  and  back  into  the  two  bands  already  mentioned,  of  which  the  posterior  is  the 
larger  and  the  more  concerned  in  bridging  over  the  folds.  The  internal  sphincter  is 
but  an  hypertrophy  of  the  circular  muscles,  while  the  external  sphincter  is  a  muscle 
of  the  perineum.  It  has  been  thought  advisable  to  here  describe  together  the 
muscles  and  some  of  the  fasciae  of  the.  rectum  and  anus,  including  some  that  are 
largely  extrinsic. 


THE   MUSCLES   AND    FASCIA   OF  THE   RECTUM    AND   ANUS. 

The  levator  ani  (Figs.  1423,  1424)  arises  from  the  back  of  the  body  of  the  pubes, 
about  midway  between  the  upper  and  lower  border,  very  close  to  the  middle  line, 
and  thence,  from  the  ' '  white  line' '  formed  by  the  splitting  of  the  pelvic  fascia,  as 
far  as  the  spine  of  the  ischium.  The  anterior  fibres  from  the  pubic  bone  pass  below 
the  prostate,  some  going  to  its  capsule,  as  a  strong  muscular  bundle  to  the  central 


Fro. 


1423. 


Bulbo-cavernosus  — 


Ischio-cavernosus  — 


Trans,  perinei  • 
superf. 


Obturator 
interims 

White  line 

Levator  ani . 
Coccygeus 


Triangular  lig- 
ament, inf.  layer 

Perineal  centre 


Tuberosity  of 
ischium 


Anus 
Obturator  fascia 


Gluteus 

maximus  (cut) 

Greater  sacro- 
sciatic  ligament 


Coccvx 


Muscles  of  pelvic  floor  and  perineum  from  below. 


point  of  the  perineum  and  the  front  and  sides  of  the  rectum,  in  which  some  of  them 
end.  The  remainder  of  this  set  passes  with  the  fibres  from  the  white  line  to  the 
side  of  the  coccyx  and  to  a  fibrous  band  (ligamentum  anococcygeum)  running  from  it 
to  the  anus.  This  latter  part  of  the  muscle  is  thinner  and  more  transversely  placed 
than  the  former.  In  the  female  the  pubic  portion  sends  some  fibres  to  the  vagina 
and  some  around  it  to  the  central  point  of  the  perineum.  The  fibres,  for  the  most 


i676 


HUMAN   ANATOMY. 


part  in  both  sexes,  pass  by  the  rectum  so  as  to  compress  it,  although  some  enter 
its  walls  and  mingle  with  those  of  the  sphincters. 

Nerve. — A  branch  from  the  sacral  plexus  (sometimes  there  are  more  than  one) 
runs  to  the  levator  ani  on  its  upper  surface.  The  fibres  come  from  the  third  and 
fourth  sacral  nerves.  According  to  some,  the  muscle  also  receives  fibres  from  the 
inferior  hemorrhoidal  branch  of  the  pudic  nerve. 

The  coccygeus  (Fig.  1424),  a  triangular  muscle  arising  from  the  spine  of  the 
ischium  and  inserted  into  the  border  of  the  coccyx,  is  in  the  same  plane  and  practi- 
cally continuous  with  the  levator  ani.  The  two  muscles  of  both  sides  have  been  well 
called  the  diaphragm  of  the  pelvis.  They  form  a  funnel-like  structure  with  the  walls 
converging  downward  to  the  anal  canal,  and  an  anterior  opening  for  the  prostate  in 
the  male  and  the  vagina  and  urethra  in  the  female. 

FIG.  1424. 


—  Sacrum  (cut) 


Pyriformis 


-    -Coccygeus 


Levator  ani 

•Recto-coccygeal  fibres 
evator  ani  (cut) 


Obturator  internus 


Ischial  spine 
Obturator  canal 


Cut  edge  of  pelvic    I 
fascia,  white  line 


Pubic  bone 


Triangular  ligament,  superior  layer    / 

Triangular  ligament,  inferior  layer  • 

Urethra    Bulb  of  penis,  covered  by  muscle 

Muscles  of  pelvic  floor  from  within  ;  sivtion  passed  to  left  of  mid-line. 

Nerve. — The  muscle  receives  branches  from  the  fourth  and  fifth  sacral  nerves 
and  perhaps  from  the  first  coccygeal. 

The  external  sphincter  ani  (Fig.  1423),  situated  beneath  the  skin  and  car- 
ried up  into  the  puckering  at  the  anus,  is  a  flat  oval  muscle  composed  of  striated 
fibres  surrounding  the  end  of  the  rectum.  It  arises  from  the  tip  of  the  coccyx, 
from  the  skin  over  it,  and  from  a  raphe  extending  from  it  to  the  anus.  The  fibres 
diverge  on  either  side  to  enclose  the  anus,  meeting  in  front  of  it  at  the  central 
point  of  the  perineum  (page  1917),  where  they  mingle  with  other  muscles  which 
meet  at  that  point.  Some  of  the  inner  fibres  completely  encircle  the  anus.  In 
the  female  some  fibres  decussate  with  those  of  the  sphincter  vaginae.  This  sphinc- 
ter is  "external  "  in  two  senses  :  it  is  nearer  the  outer  surface'  than  the  inner,  and 
also  surrounds  it. 

Nerve. — It  is  supplied  by  branches  of  the  fourth  sacral  and  of  the  inferior 
hemorrhoidal  nerve'. 


THE  MUSCLES  AND  FASCIAE  OF  THE  RECTUM  AND  ANUS.     1677 


The  internal  sphincter  ani  (Fig.  1421),  composed  of  involuntary  muscular 
fibres,  is  a  thickening  of  the  circular  layer  of  the  rectum,  which  becomes  marked  at 
the  beginning  of  the  anal  canal.  It  surrounds  the  latter  for  a  distance  of  from 
2.5-3  cm->  and  is  about  4  mm.  thick. 

Nerves  reach  the  internal  sphincter  through  the  sympathetic  system.  Very 
probably  some  of  them  come  directly  from  spinal  nerves. 

Accessory  Muscular  Bundles. — As  they  reach  the  anal  canal,  the  longi- 
tudinal fibres  of  the  rectum  send  bundles  to  the  skin,  which  gain  their  destination  by 
coursing  through  those  of  the  external  sphincter  ;  the  longitudinal  muscle-fibres  of 
the  mucous  coat,  becoming  enlarged,  pass  in  the  same  way  between  the  bundles  of 
the  internal  sphincter.  No  important  accessions  are  received  from  the  levator  ani. 
The  longitudinal  muscular  fibres  of  the  rectum,  moreover,  enter  into  connection  with 
the  areolar  tissue  of  the  pelvic  fascia  between  the  peritoneum  and  the  levator  ani,  and 
perhaps  with  the  latter  also.  Various  bundles  of  muscle-fibres,  apparently  arising 

FIG.    1425. 


External, 
iliac  vessels 


Pelvic 
fascia 


White  line. 

Recto-vesi-  - 

cal  fascia 

Obturator 

fascia 


Obturator 
membrane 

Cowper's_ 
gland 


Iliacus 

—  Iliac  fascia 
.Peritoneum 

Ilio-pecti- 
neal  line 


Obturator 
internus 

Ampulla 

Seminal 
vesicle 
_  Anterior  wall 

of  rectum 
Levator  ani 

_.Prostate  gland 

Obturator 
externus 

—Pubic  ramus 


Corpus  cavernosum 

Ischio-cavernosus 
Triangular  ligament,  inferior  layer 

Bulbo-cavernosus 


Colles's  fascia 

Triangular  ligament,  superior  layer 
Trans,  perinei  superf. 
Bulb  of  penis 


Frontal  section  or  pelvis  passing  just  behind  the  bladder,  posterior  surface. 

from  the  pelvis,  mingle  with  those  of  the  rectum.  The  recto-coccygeus  of  Treitz 
arises  from  the  anterior  surface  of  the  coccyx  above  the  pelvic  floor  and  mingles  with 
both  the  longitudinal  and  circular  fibres  at  the  back  of  the  rectum.  It  is  said  to  con- 
sist of  striated  fibres  at  its  origin.  Bundles  of  fibres  are  described  as  arising  from 
the  fascia  on  the  deep  surface  of  the  transversus  perinei  profundus  muscle  and  pass- 
ing to  the  front  of  the  gut. 

The  corrugator  cutis  ani  is  a  small  system  of  muscular  fibres  radiating  from  the 
submucous  tissue  at  the  anus  to  the  deep  side  of  the  skin,  which  it  tends  to  pucker. 

Actions. — The  function  of  the  sphincters  is  to  keep  the  anal  canal  closed. 
They  differ,  inasmuch  as  the  external,  although  mostly  acting  automatically,  is 
under  the  control  of  the  will  and  the  internal  is  not.  The  levator  ani  has  a  more 
complicated  and  in  part  an  apparently  inconsistent  action,  since  it  may  pull  the  anus 
upward  and  probably  dilate  it,  as  it  pulls  its  borders  apart  under  the  resistance  of 


1678 


HUMAN    ANATOMY. 


the  descending  faeces,  while  at  other  times,  by  its  antero-posterior  fibres,  it  may 
compress  the  sides  of  the  gut.  To  the  action  of  the  levator  is  probably  due  the 
control  of  the  heces  which  sometimes  persists  after  division  of  the  sphincter,  unless, 
indeed,  the  upper  part  of  the  latter  has  escaped. 

The  Ischio-Rectal  Fossa. — This  space  is  a  deep,  roughly  pyramidal  hollow, 
filled  chiefly  with  fat,  on  either  side  of  the  rectum.  The  base  is  at  the  skin  between 
the  tuberosity  of  the  ischium  and  the  anus,  bounded  in  front  by  the  line  of  reflection 
of  the  deep  perineal  fascia  and  behind  by  the  great  sacro-sciatic  ligament  and  the 
edge  of  the  glutens  maximus.  The  base  measures  some  5  cm.  (2  in.)  from  before 
backward  and  half  as  much  crosswise.  The  fossa  is  bounded  externally  by  the  tuber- 
osity of  the  ischium  and  above  the  latter  by  the  obturator  fascia,  internally  by  the 
external  sphincter  and  the  under  surface  of  the  levator  am'.  The  space  narrows 
above  to  a  line  at  the  splitting  of  the  pelvic  fascia  ;  hence  it  can  only  vaguely  be 
called  pyramidal.  The  depth  of  the  fossa  is  about  5  cm.  (2  in.). 


FIG.  1426. 

Venous  plexus  Anterior  wall  of  bladder 

Pelvic  fascia       j   Prostate  gland  |  Superior  pubic  ramus 


Obturator  internus 


Diaphragmatic  or 
recto-vesical  fascia 


Obturator  fascia 
Levator  ani 


Gluteus  maximus 
Ischio-rectal  fossa 


External  sphincter 

Internal  sphincter 
Oblique  transverse  section  through  pelvis  in  plane  shown  in  small  outline  figure. 


The  diaphragmatic  fascia,  the  inward  continuation  of  the  pelvic  fascia  which 
covers  the  upper  surface  of  the  levator  ani,  reaches  the  side  of  the  rectum  as  a  bed 
of  areolar  tissue  beneath  the  peritoneum,  and  is  more  or  less  closely  attached  to  the 
gut,  sometimes  by  muscular  bands,  as  already  stated.  The  systematic  deseriptio 
of  this  fascia  is  given  elsewhere  (page  559). 

The  rectal  fascia  is  a  dense  layer  of  areolar  tissue  surrounding  the  rectui 
below  the  reflection  of  the  peritoneum,  being  continuous  below  with  the  preceding 
fascia.  It  is  particularly  dense  behind  the  rectum,  which  it  separates  from  the 
sacrum  and  coccyx. 

The  anal  fascia  is  a  web-like  areolar  sheet  covering  the  under  side  of  the 
levator  ani. 

A  superficial  fascia  between  the  skin  and  the  base  of  the  ischio-rectal  fossa 
can  be  artificially  dissected,  but  is  of  little  importance. 


THE  MUSCLES  AND  FASCIA  OF  THE  RECTUM  AND  ANUS.    1679 


Peritoneal  Relations  of  the  Rectum. — The  posterior  surface  of  the  highest 
part  of  the  rectum  is  usually  coated  like  the  rest  with  peritoneum,  except  near  the 
median  line  ;  but  this  narrow  retroperitoneal  surface  enlarges  rapidly,  so  that  soon 
the  entire  posterior  surface  in  the  hollow  of  the  sacrum  and  coccyx  is  without  serous 
covering.  The  gut  rests  on  the  dense  rectal  fascia.  The  sides  and  front  of  the 
rectum  are  covered  with  peritoneum,  which  is  reflected  laterally,  first  onto  the  sides 
of  the  posterior  wall  of  the  pelvis,  then  onto  the  floor.  The  peritoneum  forms  a 
deep  pouch  in  front  of  the  rectum, — the  pouch  of  Douglas, — known  from  its  anterior 
wall  as  the  recto-vesical  in  the  male  and  the  recto-vaginal  in  the  female.  In  man 
this  pouch  separates  the  rectum  from  the  bladder  and  the  upper  part  of  the  seminal 
vesicles  and  in  woman  from  the  upper  part  of  the  vagina.  The  distance  of  the  line 
of  reflection  of  peritoneum — that  is  to  say,  the  bottom  of  the  pouch— from  the  ano- 
rectal  groove  may  be  as  little  as  5  cm.  (2  in.),  as  usually  given ;  if,  however,  by  the  word 
' '  anus' '  be  understood  what  is  practically  the  orifice  of  the  gut,  the  distance  is  nearly 
7  cm.  (2^  in.)  in  both  sexes.  If  both  bladder  and  rectum  be  distended,  the  pouch 
is  considerably  raised;  when  the  rectum  is  collapsed,  it  contains  loops  of  the  small  in- 
testine or  the  sigmoid  flexure.  The 
recto-vesical  folds  in  the  male,  although 
described  with  the  bladder  (page  1 905) , 
should  be  mentioned  here.  They  are 
reckoned  among  the  false  ligaments 
of  the  bladder,  and  bound  laterally 
the  pouch  just  described  ;  extending 
backward  from  the  bladder  around 
the  rectum  to  the  sides  of  the  sacrum, 
they  tend  to  divide  the  cavity  of  the 
pelvis  into  an  upper  and  a  lower  com- 
partment. Their  free  edges  are  semi- 
lunar  and  sharp,  and  curve  around 
the  rectum  above  the  ampulla,  which 
they  partially  roof  in.  These  liga- 


FIG.  1427. 


Internal  hemorrhoidal  vein 


Levato 


Middle 

hemorrhoida 

vein 


Groove 


lernal 

emorrhoidal 

ein 


Skin 


Frontal   section  of  wall  of  anal   canal,  showing  relations  of 
hemorrhoidal  veins.     (Otis.) 


ments  contain  more  or  less  fibrous 
tissue.  In  the  female  they  are  less 
developed,  although  important,  and, 
arising  from  the  uterus  instead  of  the 
bladder,  are  known  as  the  sacro-uterine 
folds. 

Blood-Vessels. — The  arteries 
supplying  the  rectum  are  derived 
chiefly  from  the  three  hemorrhoidals. 
The  superior  hemorrhoidal,  the  ter- 
mination of  the  inferior  mesenteric 
artery,  divides  opposite  the  sacrum, 

sometimes  near  the  beginning  of  the  rectum,  sometimes  higher,  and  even  above  the 
pelvis,  into  two  branches,  of  which  the  right  is  the  larger,  that  descend  on  either  side 
of  the  rectum  and  give  off  smaller  branches.  A  median  posterior  branch  usually 
arises  from  the  right  one.  The  mucous  membrane  is  supplied  by  these  above  the 
boundary  line.  Vessels  may  be  received  also  from  the  sacra  media.  The  middle 
hemorrhoidal  arteries,  of  uncertain  origin  and  distribution,  rarely  give  any  consider- 
able supply  to  the  gut.  The  inferior  hemorrhoidals — two  or  three  small  branches 
from  the  internal  pudic — supply  chiefly  the  external  sphincter,  but  also  form  a  num- 
ber of  fine  anastomoses  with  the  superior  hemorrhoidal  artery.  The  general  dis- 
tribution of  the  veins  is  not  very  different  from  that  of  the  arteries.  The  superior 
hemorrhoidal  veins,  tributaries  of  the  inferior  mesenteric,  drain  into  the  portal  system. 
They  form  a  very  rich  plexus  throughout  the  rectum,  particularly  in  the  upper  and 
middle  parts  of  the  anal  canal.  In  this  situation  they  present  a  series  of  dilatations 
encircling  the  gut  on  the  bases  of  the  columns  of  Morgagni,  just  above  the  boundary 
line  between  the  mucous  and  cutaneous  areas  ;  this  line  also  marks  the  parting  of 
the  ways  between  the  superior  and  external  hemorrhoidal  veins.  The  latter  form 


i68o  HUMAN   ANATOMY 

a  circle  of  smaller  dilatations  just  below  the  line  of  demarcation,  in  the  region  that 
is  reckoned  as  skin,  but  is  practically  puckered  into  the  anus.  There  are  communi- 
cations between  the  two  systems,  some  of  which  pierce  the  muscular  coat. 

Lymphatics. — The  principal  lymphatics  of  the  rectum,  after  joining  the 
lymph-nodes  situated  along  the  superior  hemorrhoidal  veins,  pass  to  the  sacral 
glands  on  the  front  of  the  sacrum.  In  the  lower  part  of  the  bowel  a  very  rich  plexus 
is  found  under  the  skin  around  the  anus,  which  drains  into  the  superior  internal 
inguinal  glands,  and  a  still  richer  one  inside,  which  at  the  lower  part  is  concentrated 
on  the  columns  of  the  rectum,  but  few  vessels  lying  in  the  pouches.  A  considerable 
system  of  lymphatics  exists  also  in  the  muscular  layer.  Most  of  those  of  the  inside 
of  the  anus  run  to  a  few  small  lymph-nodules  discovered  by  Gerota  I  on  the  back 
of  the  muscular  coat  of  the  rectum,  distributed  with  the  branches  of  the  superior 
hemorrhoidal  artery. 

Nerves. — The  nerve-supply  of  the  rectum  includes  both  sympathetic  and 
cerebro-spinal  fibres.  The  former  are  derived  chiefly  from  the  inferior  mesenteric 
and  the  pelvic  plexuses,  accompanying  the  superior  and  middle  hemorrhoidal 
arteries  respectively.  The  cerebro-spinal  fibres  are  contributed  by  the  second, 
third,  and  fourth  sacral  nerves.  The  skin  around  the  anal  orifice  is  supplied  by  the 
inferior  hemorrhoidal  branch  from  the  pudic  nerve. 

Growth. — At  birth  the  rectum  is  tubular  and  generally  relatively  small.  We 
do  not  remember  to  have  seen  a  well-marked  ampulla  at  that  period.  At  least 
frequently  the  anal  canal  is  very  long, — about  i  cm.  The  transverse  folds  of  the 
rectum  are  apparent  in  the  latter  months  of  pregnancy.  We  have  found  an  ampulla 
with  a  circumfejence  of  13  cm.  (5  in.  )  at  three  years.  In  the  same  specimen  the  valves 
were  well  developed,  and,  except  in  size,  it  resembled  the  rectum  of  the  adult. 
The  peculiarities  of  the  infantile  sacrum  have  their  effect  on  the  course  of  the  rec- 
tum, which  is  necessarily  straighter  than  in  the  adult  and  does  not  run  so  far  forward 
in  front  of  the  coccyx. 

PRACTICAL   CONSIDERATIONS  :    THE   LARGE    INTESTINE. 

The  Caecum. — This  part  of  the  large  intestine  may  remain  undescended  in  its 
foetal  position  in  the  left  hypochondrium,  at  a  point  above  and  to  the  left  of  the 
umbilicus,  the  ileum  opening  directly  into  it  in  this  locality  ;  or  it  may  be  found  in 
the  right  hypochondrium  just  below  the  liver,  or  at  any  level  between  that  and  its 
normal  situation.  The  caecum  is  rudimentary  in  man  and  other  meat-eating  animals, 
being  much  more  capacious  and  of  greater  functional  importance  in  the  herbivora. 

The  caecum  is  larger,  more  distensible,  and  more  superficial  than  any  other 
portion  of  the  large  intestine,  and  more  mobile  than  any  other  portion  except  the  sig- 
moid.  On  account  of  its  mobility  it  is  selected  for  the  operation  of  iliac  colostomy 
when  that  operation  is  done  on  the  right  side. 

As  a  result  of  the  inspissation  of  the  intestinal  contents,  which  first  occurs  here, 
it  is  a  common  seat  of  fecal  impaction,  or  of  distention  by  gases  arising  from  fermen- 
tation. The  increase  in  numbers  of  the  intra-intestinal  pathogenic  bacteria  due  to 
impaired  inhibiting  power,  which,  as  we  descend  the  gut,  first  becomes  marked  in 
the  lower  ileum,  continues  in  the  caecum.  As  in  the  former  situation,  where  it  prob- 
ably aids  in  determining  the  localization  of  typhoid  and  tuberculous  lesions,  so  in 
the  caecum,  in  conjunction  with  fecal  accumulation,  or  with  disturbance  of  circulation 
from  distention,  such  augmentation  adds  to  the  frequency  and  severity  of  catarrhal 
inflammations  and  of  stercoral  ulcers,  which  are  found  oftener  here  than  elsewhere. 

Fecal  concretions  (the  formation  of  which  is  favored  by  intestinal  catarrh  just 
as  is  that  of  renal  calculi  by  catarrhal  pyelitis)  are  often  found  in  the  co-aim,  and 
undoubtedly  by  mechanical  irritation  favor  here,  as  they  do  in  the  appendix,  epi- 
thelial necrosis  and  subsequent  infection. 

In  the  erect  position  gravity  aids  in  bringing  about  these  pathological  condi- 
tions, since  the  caecum,  having  no  mesentery  of  its  own,  and  yet  completely  covered 
by  peritoneum  (so  that  it  is  never  anchored  to  the  posterior  parietes  or  to  the  iliac- 
fossa  by  areolar  tissue),  depends  upon  its  attachments  to  the  colon  and  ileum  to  hold 
1  Arch,  fiir  Anat.  und  Entwicklng.,  1895. 


PRACTICAL  CONSIDERATIONS  :    THE  LARGE  INTESTINE.     1681 

it  in  position.      It  has  often  been  part  of  the  contents  of  right  inguinal  or  femoral 
hernia,  and  has  even  been  found  in  such  herniae  on  the  left  side. 

The  influence  of  gravity  in  retaining  fecal  masses  and  favoring  concretion  is 
illustrated  by  the  fact  that  foreign  bodies  small  enough  to  pass  through  the  ileo-caecai 
valve  are  prone  to  remain  in  the  caecum,  where  they  have  in  many  cases  given  rise 
to  ulceration  and  perforation,  followed  by  perityphlitis. 

With  varying  degrees  of  displacement  or  of  distention  of  the  caecum  come 
changes  in  the  tension  of  the  ileo-colic  vessels,  and  congestion — so  often  the  first 
stage  of  serious  pathological  processes — is  thereby  favored.  The  close  relation  of 
the  caecum,  if  distended  even  slightly,  to  the  anterior  abdominal  wall  and  to  the  ilio- 
psoas  muscle  exposes  it  to  frequent  trauma.  These  relations  explain  why  flexion  of 
the  thigh  on  the  abdomen  will  empty  a  moderately  distended  caecum. 

Enormous  distention  sometimes  occurs,  so  that  the  caecum  may  fill  the  larger 
part  of  the  abdomen,  and  in  nearly  all  cases  of  intestinal  obstruction  between  the  anus 
and  the  ascending  colon  the  caecum  shows  the  most  marked  evidence  of  the  backward 
pressure,  the  ileo-caecal  valve,  although  not  absolutely  complete,  resisting,  for  a  time 
at  least,  the  participation  of  the  ileum  even  in  distention  from  gases.  Manifestly,  in 
uncomplicated  cases  of  obstruction  of  the  small  intestine  the  caecum  will  be  found 
flaccid  or  collapsed. 

The  ileo-ccecal  valve  is  usually  competent  to  prevent  the  return  of  fecal  matter 
from  the  caecum  into  the  ileum.  Gas  injected  per  rectum  under  pressure  of  from 
.7-1.02  kilos  (1^2-2^  Ibs. )  (Senn)  may  be  made  to  enter  the  ileum,  and  has  been 
used  in  detecting  and  localizing  wounds  of  the  small  intestine  and  in  the  treatment 
of  intussusception.  Less  force  is  necessary  when  the  patient  is  anaesthetized,  proba- 
bly because  of  the  relaxation  of  both  the  abdominal  muscles  and  the  circular  fibres 
of  the  valve  itself.  Fluids  are  arrested  at  the  valve,  although  they  may  be  made  to 
pass  it  either  by  immediate  force  sufficient  to  lacerate  the  peritoneal  attachments  and 
covering  or  by  slow  increase  of  pressure  until  the  distention  of  the  caecum  gradually 
overcomes  the  weak  resistance  of  the  circular  muscular  fibres  in  the  segments  of  the 
valve  and  separates  their  margins.  Organic  or  spasmodic  narrowing  of  the  ileo-caecal 
valve  has  been  suggested  as  a  possible  cause  of  chronic  constipation,  and  two  cases 
have  been  operated  upon  by  making  a  longitudinal  incision  through  the  valve  and 
uniting  its  edges  transversely,  as  in  pyloroplasty  (page  1633)  (Mayo). 

Invagination  of  the  ileum  and  the  caecum  into  the  colon  is  the  most  common 
form  of  intussusception  (44  per  cent,  of  all  cases,  Leichtenstern  ;  89  cases  out  of 
103,  Wiggin),  and  occurs  most  commonly  (70  per  cent,  of  all  cases)  in  children. 
The  ileo-caecal  valve  forms  the  summit  or  apex  of  the  intussusceptum,  and  may  pass 
through  the  entire  colon  (the  intussuscipiens),  reaching  the  rectum  or  anus.  Ileo- 
colic  intussusception — in  which  the  ileum  passes  through  the  valve,  the  caecum  re- 
maining in  place — is  much  rarer  (8  per  cent,  of  all  cases). 

In  acute  cases,  here  as  elsewhere  in  the  intestinal  tract,  pressure  on  the  mesen- 
tery produces  consecutively  venous  congestion,  oedema,  swelling,  obstruction  or 
strangulation  of  the  mesenteric  vessels,  and  either  leakage  through  the  damaged  in- 
testinal walls  and  septic  peritonitis  or  actual  perforation,  rupture,  or  gangrene  of  the 
bowel.  In  chronic  cases  dense  adhesions  form  between  the  peritoneal  coats  of  the 
entering  and  returning  layers  of  gut  (Fig.  1405).  The  traction  upon  the  mesentery 
narrows  the  lumen  of  the  intussusceptum  so  as  to  prevent  the  passage  through  it  of 
the  contents  of  the  intestine. 

In  adults  the  situation  of  the  ileo-caecal  valve  corresponds  to  a  point  on  the  wall 
of  the  abdomen  from  3-5  cm.  (1-2  in.)  internal  to  and  above  the  anterior  superior 
spine  of  the  ilium. 

The  Vermiform  Appendix. — On  account  of  the  frequency  with  which  it  is 
the  seat  of  catarrhal  or  infectious  disease,  the  appendix  is  of  the  greatest  surgical 
interest.  In  addition  to  the  description  of  its  structure,  position,  and  peritoneal 
relations  already  given  (pages  1664,  1665),  various  important  anatomical  data 
relating  to  the  causes,  symptoms,  results  or  complications,  and  treatment  of 
appendiceal  inflammations  should  be  here  considered,  even  at  the  risk  of  repetition. 

Etiology  of  Appendicitis.  —  i.  The  appendix  is  an  apparently  functionless  organ, 
found  only  in  man,  in  certain  of  the  anthropoid  apes,  and  in  the  wombat.  An  analo- 

106 


1682  HUMAN   ANATOMY. 

gous  organ  exists  in  some  of  the  rodents  and  marsupials,  but  it  is  a  long,  tapering- 
caecum  rather  than  an  appendix  strictly  comparable  to  that  of  man.  The  appendix 
is  a  vestige  of  the  capacious  caecum  of  some  of  the  lower  animals,  or  may  be  regarded 
as  a  rudimentary  caecum  just  as  the  human  caecum  is  a  rudiment  of  that  found  in  the 
herbivora  or  the  rodents.  Like  other  vestigial  structures,  or  those  which  in  the  his- 
tory of  either  the  race  or  the  individual  have  outlived  their  usefulness,  it  appears  to 
be  of  low  resistant  power.  This  doubtless  explains  in  part  the  special  susceptibility 
of  the  appendix  to  disease,  as  it  does  that  of  the  uterus  and  the  female  breast 
during  the  post-sexual  period  of  life. 

2.  Its  mesentery — a  fold  made  by  the  passage  of  the  appendicular  artery  from 
the  ileo-colic  at  the  back  of  the  ileum  to  the  appendix  (page  1665) — is  scanty;  its 
free  border  is  shorter  than  the  border  applied  to  the  appendix,  and  sometimes  does 
not  extend  much  beyond  its  middle.     The  appendix,  like   the   small  intestine,   is 
therefore  thrown  into  irregular  curves  or  coils.      Another  peritoneal  duplicature — the 
ileo-caecal  fold — runs  from  that  part  of  the  ileum  most  remote  from  its  mesenteric 
attachment  and  is  united  with  the  mesentery  of  the  appendix.      It  carries  no  blood- 
vessels of  consequence,  and  is  regarded  by  Treves  as  the  remains  of  the  true  mesen- 
tery of  the  appendix.      It  is  interesting  to  note  the  fact  that  in  the  different  types  of 
the  human  caecum  those  which  involve  a  disproportionate  growth  of  the  caecum  show 
that  it  derives  its  peritoneal  covering  partly  at  the  expense  of  the  mesentery  of  the 
appendix,  which  becomes  more  scanty  and  more  vertical  in  direction  the  larger  the 
relative  size  of  the  caecum.     The  appendix  moves  directly  with  the  caecum,   but, 
through  the  attachments  of  the  meso-appendix  to  the  caecum  and  to  the  mesentery 
of  the  ileum,  distention  or  displacement  of  those  portions  of  the  intestine  makes  trac- 
tion upon  it  and  causes  increased  curving  or  angulation.      For  these  reasons,  and  on 
account  of  the  lessened  interference  with  the  blood-supply  (vide  infra),  appendices 
with  exceptionally  ample  mesenteries  extending  to  the  tip  of  the  organ  are  less  fre- 
quently the  seat  of  disease  and,  when  diseased,  are  less  often  found  in  a  condition  of 
complete  gangrene. 

3.  The  single  artery  supplying  the  appendix  and  running  in  the  folds  of  the  meso- 
appendix,  and  its  accompanying  veins,  are  subjected  to  pressure  by  such  traction, 
or  by  the  angulation  of  the  organ  itself,  and  various  degrees  of  vascular  obstruction  and 
congestion  may  result.     The  consequent  oedema  and  swelling  of  the  mucous  mem- 
brane aid  the  distortion  of  the  appendix  in  causing  interference  with  the  escape  of 
the  contents  of  the  appendix  into  the  caecum.     After  infection  has  started  the  vessels 
are  not  infrequently  occluded  by  septic  thrombi.     The  peritoneal  fold,  which  in  the 
female  is  often  found  running  from  the  appendix  to  the  broad  ligament  (page  1666), 
may  contain  a  second  artery  the  presence  of  which  has  been  offered  as  an  explana- 
tion of  the  relative  infrequency  of  appendicitis  in  women. 

4.  The  disproportion    between    the  length  and  the  lumen  of  the  appendix  (16 
to  i,  Finkelstein),  the  similar  disproportion  between  the  lumen  and  the  area  of  th 
secreting  surface,   its  removal  from  the  direct  intestinal  current,   the  feebleness  of  i 
muscular  walls,   its    dependent  position,   the  absence  or  inefficiency  of  any  valvula: 
arrangement  at  the  appendiculo-caecal  orifice,  and  the  ease  with  which  that  orince 
may  be  diminished  in  size  by  oedema  of  the  mucous  membrane  in  its  vicinity  readily 
explain  the  fact  that  under  most  circumstances  in  which  drainage  from  the  appendix 
into  the  intestine  would  be  desirable,  it  is  apt  to  be  lacking.      Even  a  hyperaemic 
catarrh  from  twists,  kinks,  or  traction  may  in  this  way  become  the  starting-point  of 
serious  trouble,  the  successive  steps  of  which  might  subsequently  be  retention  of 
mucus,   epithelium,  and   fecal     contents    (possibly    in   the   form   of   a   concretion), 
ulceration,  parietal  infection,  or  perforation  or  gangrene,  and  peritonitis,   localized 
or  general. 

5.  The   abundance    of  lymphoid  tissue  in  the  appendix,  as  in  the  tonsils,  favors 
rapid  swelling  and  infectious  inflammations  and  aids  in  obstructing  drainage.     It  may 
to  some  extent  account  for  these  pathological  conditions  showing  themselves  during 
the  periods  of  growth  and  activity  of  the  system   much  more  frequently  than  in  old 
aiM-,  when  the  lymph-nodules  in  the  walls  of  the  intestinal  canal  become  atrophied 
(Stnithers  ).     In  this  connection  it  may  be  noted  that  other  causes  contributing  to  the 
relative  frequency  of  appendicitis  in  early  life  are  (a)  the  susceptibility  of  children 


PRACTICAL  CONSIDERATIONS  :   THE  LARGE  INTESTINE.    1683 

to  catarrhal  enteritis,  favoring  the  formation  of  concretions,  or  at  least  impairing 
the  protective  power  of  the  intestinal  epithelium  ;  (6)  the  relatively 'greater  length 
of  the  appendix  in  young  persons  (in  infants  one-tenth  and  in  adults  one-twentieth 
the  length  of  the  large  intestine,  according  to  Ribbert)  increasing  the  difficulty  of 
drainage  ;  and  possibly  (c)  the  tendency  to  shrinkage  or  obliteration  after  middle 
life, — a  process  to  be  expected  in  a  rudimentary  organ. 

6.  It  must  not  be  forgotten,  in  interpreting  the  foregoing  anatomical  facts  as  to 
(a)  the  rudimentary  character  of  the  appendix,  (b)  the  scantiness  of  its  mesentery, 
(c)  its  dependence  for  its  blood-supply  upon  one  vessel,  (af')  its  imperfect  drainage, 
and  (<?)  the  profusion  of  its  lymphoid  tissue,  that  these  are  but  predisposing  causes 
in  most  cases  of  serious  appendix  disease,  and  that  the  congestion,  catarrh,  distention, 
or  ulceration  occasioned  by  them  occurs  invariably  in  the  presence  of  micro-organ- 
isms capable  of  great  virulence,  which  exist  in  increased  numbers  in  this  portion  of 
the  intestinal  tract  (page  1680),  and  which,  as  has  been  abundantly  proved,  'are 
ready  to  take  on  pathogenic  action  in  the  presence  of  either  mechanical  or  chemical 
irritation  of  the  intestinal  tissues,  especially  if  there  is  deficient  drainage  of  the  early 
products  of  such  irritation  or  of  the  resultant  inflammation.  The  proximity  of  the 
appendix  to  areas  of  abdominal  or  pelvic  infection,  as  in  typhoid  fever,  intestinal 
tuberculosis,  dysentery,  .or  salpingitis,  is  a  factor  of  minor  but  definite  importance. 

Anatomical  Points  relating  to  the  Symptoms  of  Appendicitis. — i.  Pain. — This  is 
at  first  general  and  diffused  because  the  superior  mesenteric  plexus  of  the  sympathetic, 
which  supplies  the  appendix,  also  largely  supplies  the  intestines,  and  because  irrita- 
tive nerve-pain  is  apt  to  be  referred  to  the  peripheral  extremities  of  nerves  ;  next  and 
within  a  very  short  time  felt  in  the  umbilical  region,  because  as  such  pain  increases 
in  intensity  it  is  often  referred  to  the  nearest  nerve-centre,  and  the  great  sympathetic 
ganglia  of  the  abdomen  are  situated  in  proximity  to  that  region. 

At  this  time  the  pain  is  often  colicky  in  nature,  and  a  discussion  has  arisen  as  to 
whether  or  not  the  circular  muscular  fibres  in  the  appendix  are  of  sufficient  strength 
to  cause  it.  The  question  seems  unimportant,  as  appendix  irritation  may  result  in 
colicky  spasm  of  neighboring  portions  of  either  small  or  large  intestine.  The  pain  of 
the  later  stages  of  appendicitis  may  be  partly  due  to  peritoneal  swelling  causing 
traction  upon  the  peritoneal  attachments. 

2.  Tenderness. — After   a   few    hours  the  pain    is    felt    in   the  right  iliac  fossa, 
because  it  has  then  become  a  neuritis  of  sufficient  grade  to  cause  tenderness  on  press- 
ure.     It  is  localized  tenderness  in  all  the  varieties  of  appendicitis,  because,  while  the 
appendix  itself  is  movable,   it  always  arises  from  the  same  part  of  the  caecum,  and 
the  mobility  of  the  latter  is  more  restricted.      The  point  of  pain  on  pressure  indicates, 
therefore,   with  moderate  accuracy,   the  base,   not  the  tip,   of  the  appendix,  and  is 
rarely  absent  even  in  gangrenous  cases,   because  that  portion  of   the  appendix    is 
usually   the   last  to  be  affected   by  interference  with  the  blood-supply.      This  point 
is  where  the  omphalo-spinous  line  (drawn  from  the  umbilicus  to  the  anterior  superior 
iliac  spine)  meets  the  outer  border  of  the  rectus,  or  a  point  on  that  line  from  5-7.5 
cm.  (2-3  in. )  from  the  iliac  spine  (McBurney's  point).     In  the  majority  of  instances 
the  base  of  the  appendix  lies  beneath  a  circle  two  inches    in  diameter,   having  this 
point  as  its  centre.      Its  situation  must  obviously  vary  with  that  of  the  caecum,  and 
undue  diagnostic  value  has  been  placed  upon  tenderness  at  this  precise  position. 
The  chief  tenderness  may  be  lumbar  if  the  appendix  is  post-caecal  in  position,  or  close 
to  Poupart's  ligament  or  to  the  median  line,  or  best  elicited  by  rectal  touch  if  the 
appendix  lies  in  the  pelvis. 

3.  Rigidity  of  the  right  rectus  muscle,  and  later  of  the  other  abdominal  muscles 
over  the  right  iliac  fossa,  is  often,  but  perhaps  not  necessarily,  due  to  peritonitis, 
and  in  any  event  arises  from  the  fact  that  those  muscles  receive  their  nerve-supply 
partially  from  the  six  lower  intercostals,  while  the  superior  mesenteric  plexus  gets 
its  contribution  from  the  spinal  system  through  the  splanchnics,  derived  from  some 
of  the  same  intercostals. 

4.  Vomiting  commonly  follows,  has  little  relation  to  gastric  conditions,  is  ordi- 
narily reflex  and  due  to  reversed  peristalsis,  and  is  apt  to  be  associated  with  moderate 
fever  and  slightly  increased  pulse-rate  due  to  autotoxaemia. 

Other  and  later  symptoms  are  mentioned  in  the  next  section. 


1 684  HUMAN   ANATOMY. 

Results  and  Complications  vf  Appendicitis. — A  cursory  review  of  the  anatomical 
relations  of  the  appendix,  considered  in  conjunction  with  the  pathological  varieties 
of  appendicitis,  will  explain  the  varying  results  of  this  disease.  The  appendix  is 
entirely  intraperitoneal  in  its  situation  and  becomes  primarily  the  focus  of  intraperito- 
neal  lesions,  although  in  certain  cases  (vide  infra),  from  pathological  changes,  it  and 
the  associated  exudate  or  abscess  may  be  either  practically  or  really  extraperitoneal. 
That  focus  may  be  isolated  by  adhesions  between  the  peritoneal  coverings  of  the 
neighboring  structures — the  coils  of  small  intestine,  the  caecum  or  colon,  the  parietes 
— or  may  become  the  starting-point  of  a  general  septic  peritonitis.  In  the  former  case 
the  usual  local  symptoms  of  inflammation  or  of  abscess  will  follow  according  to  the  be- 
havior of  the  exudate,  which  may  remain  plastic  or  may  liquefy  and  become  purulent. 
In  the  latter  case,  to  the  above-mentioned  symptoms — which  are  much  intensified,  as 
a  rule — are  added  general  rigidity  from  involvement  of  larger  areas  of  the  abdominal 
wall,  distention  and  tympanyfrom  paresis  of  the  small  intestine  (page  1756),  and  from 
the  same  cause  obstinate  vomiting  and  more  or  less  complete  intestinal  obstruction. 

The  acuteness  of  the  attack,  the  presence  or  absence  of  gross  perforation  or 
gangrene,  and  the  anatomical  position  of  the  individual  appendix  will  often  determine 
the  localization  or  diffusion  of  the  septic  infection. 

The  usual  anatomical  situations  of  appendix  abscess  may  be  summarized  as  fol- 
lows, (i)  Anterior,  the  caecum  forming  the  posterior  wall,  agglutinated  coils  of 
intestines  the  inner  wall,  and — after  the  abscess  has  attained  some  size — the  parietal 
peritoneum  the  anterior  wall.  (2)  Posterior,  the  hinder  surface  of  the  caecum 
forming  the  anterior  wall,  especially  if  the  appendix  is  post-caecal  in  position,  or  if  a 
septic  lymphangitis  has  extended  backward  between  the  layers  of  the  meso-appendix. 
Such  an  abscess  is  extraperitoneal,  and  may  originate  in  an  appendix  which,  it  is 
believed  by  some,  was  ab  initio  either  wholly  or  partly  extraperitoneal  (4  per  cent. , 
Bryant),  or,  as  seems  more  probable,  had  become  so  through  pathological  causes 
(38  per  cent.,  Ferguson,  page  1666).  The  abscess  is  limited  by  the  fascia  transver- 
salis  anteriorly  and  the  fascia  iliaca  posteriorly,  and  by  their  fusion  at  Poupart's  liga- 
ment inferiorly,  although  rarely  it  may  follow  the  femoral  vessels  downward  and 
appear  on  the  thigh,  or  may  perforate  the  parietes  above  the  outer  third  of  Poupart's 
ligament,  or  may  make  its  way  into  the  peritoneal  cavity,  or  into  the  pelvis,  escaping 
through  the  obturator  or  the  sacro-sciatic  foramen.  It  may  ascend  (following  some- 
times the  retro-colic  fossa,  page  1667)  to  the  perinephric  or  even  to  the  subphrenic 
region.  (3)  Inner,  the  inner  surface  of  the  colon  and  caecum  and  the  mesocolon 
bounding  it  postero-externally  and  adherent  coils  of  small  intestine  antero-internally. 
If  the  parietal  peritoneum  does  not  form  part  of  the  anterior  wall  of  such  an  ab- 
scess, the  general  peritoneal  cavity  must  be  traversed  in  reaching  and  evacuating 
it.  (4)  Inferior,  the  abscess  occupying  part  of  the  pelvic  cavity  with  agglutinated 
intestinal  coils  bounding  it  superiorly. 

All  these  abscesses  may  perforate  into  the  cavity  of  the  peritoneum,  but  sponta- 
neous opening  into  the  caecum,  colon,  rectum,  small  intestine,  bladder,  or  on  the  sur- 
face of  the  body  has  frequently  occurred  ( Finkelstein,  quoted  by  Mynter ) .  The  various 
symptoms  which  may  result  from  the  propinquity  of  the  abscess  to  other  structures 
should  be  worked  out  anatomically, — e.g. ,  (i)  oedema  of  the  abdominal  wall  over  the 
abscess  ;  (2)  flexion  of  the  thigh,  extension  of  which  is  painful  from  involvement 
of  the  ilio-psoas  ;  or  marked  lumbar  tenderness  (perinephric)  ;  or  immobility  of  the 
right  lower  thorax  (subphrenic)  ;  (3)  tympany  over  an  ill-defined  swelling,  from  in- 
terposition of  coils  of  small  intestine  between  the  abscess  and  the  parietes  (although 
this  may  be  simulated  by  the  escape  of  intestinal  gases  through  a  gross  perforation 
into  the  cavity  of  an  abscess  of  any  type)  ;  or  (4)  vcsical  or  rectal  irritation. 

Anatomical  Points  relating  to  the  Treatment  of  Appendicitis. — The  medical 
treatment  of  this  disease  is  of  anatomical  interest  only  in  its  relation  to  the  possibility 
of  removing  the  mechanical  causes  and  favoring  either  resolution  or  locali/ing  adhe- 
sions. Opium  for  the  purpose  of  lessening  peristalsis  and  thus  permitting  oinental 
and  intestinal  adhesions  to  wall  off  the  appendix  has  still  some  advocates,  especially 
when  combined  with  gastric  lavage  and  exclusive  rectal  alimentation  (Ochsm-n. 
But  the  received  views  as  to  etiology  (rit/c  supra')  and  clinical  experience  are  both 
overwhelmingly  in  favor  of  purgation  and  starvation  as  preventing  or  removing  the 


PRACTICAL  CONSIDERATIONS  :    THE  LARGE  INTESTINE.    1685 

constipation  which,  when  involving  the  caecum,  may,  by  causing  irritation  and  swell- 
ing of  mucous  membrane,  by  encouragement  of  bacterial  growth,  by  favoring  the  for- 
mation of  fecal  concretions,  by  producing  traction  on  the  meso-appendix,  or  by  direct 
pressure  upon  the  appendicular  vessels,  start  the  chain  of  pathological  phenomena 
which,  beginning  with  hyperaemia,  hypersecretion,  and  imperfect  drainage,  proceed 
to  distention,  ulceration,  perforation,  or  gangrene,  with  their  associated  degrees  of 
parietal  or  peritoneal  infection. 

Constipation  is  present  in  the  majority  of  cases  of  appendicitis  (58  out  of  69, 
McCosh),  and  not  only  acts  as  a  causative  factor,  but  has  a  prejudicial  effect  on  the 
result.  In  22  cases  of  peritonitis  from  appendix  disease  occurring  at  the  London 
Hospital  there  were  9  cases  of  constipation,  with  4  deaths,  and  13  cases  in  which 
the  bowels  were  loose  or  easily  moved,  with  2  deaths.  In  another  series  of  cases 
(Richardson)  there  was  8  per  cent,  of  constipation  among  those  that  recovered  and 
28  per  cent,  among  those  that  died  (White).  No  other  important  point  of  medical 
treatment  is  in  dispute  and  none  has  any  anatomical  bearing. 

Operation  for  appendicitis  will,  of  course,  vary  with  the  seat  and  character  of 
the  disease. 

1.  The  preferable  method  of  access  in  removal  of  an  appendix  very  early  in  an 
attack,  or  during  an  interval,  or  when  neither  abscess  nor  extensive  adhesions  are 
present,   is  as  follows.     The  incision  begins  one  inch  above  a  line  drawn  from  the 
anterior  superior  spine  to  the  umbilicus,  and  crosses  that  line  one  and  a  half  inches 
internal  to  the  iliac  spine.      It  should  pass  downward  and  inward  and  be  about  three 
inches  long.      The  skin  and  aponeurosis  of  the  external  oblique  are  divided  in  that 
direction  ;    the  internal  oblique  and  transversalis  fibres  are  separated  in  a  direction 
almost  at  right  angles  to  the  first  incision  ;  the  transversalis  fascia  and  peritoneum 
are  divided  on  the  same  line  with  the  internal  oblique. 

The  advantages  of  this  incision  are  thus  described  by  its  originator.  "  Muscu- 
lar and  tendinous  fibres  are  separated,  but  not  divided,  so  that  muscular  action  can- 
not tend  to  draw  the  edges  of  the  wound  apart,  but  rather  to  actively  approximate 
them.  Excepting  during  the  incision  of  the  skin,  almost  no  bleeding  occurs.  The 
fascia  transversalis  not  being  drawn  away  by  the  retraction  of  the  deepest  layer  of 
muscular  fibres,  this  fascia  is  easily  completely  sutured,  and  thus  greater  strength  of 
repair  is  assured"  (McBurney). 

More  room  may  be  obtained  and  the  transverse  severance  of  muscular  or 
fascial  fibres  still  minimized  by  stripping  the  external  oblique  aponeurosis  up  to  the 
median  line,  dividing  the  anterior  sheath  of  the  rectus  in  the  line  of  the  separation 
of  the  internal  oblique  and  transversalis  fibres,  lifting  up  and  retracting  the  rectus 
towards  the  median  line,  ligating  the  epigastric  vessels  (which  will  be  seen  lying  on 
the  thin  transversalis  fascia  over  the  peritoneum),  and  then  extending  the  original 
peritoneal  incision  as  far  inward  as  may  be  necessary  (Weir). 

2.  In  later  operations  it  is  best  to  be  guided  by  the  situation  of  the  tumor  or 
the  area  of  tenderness  or  dulness,  inclining  to  approach  it  from   without  inward. 
An  oblique  incision  well  out  towards  the  upper  third  of  Poupart's  ligament  will  be 
less  likely  to  open  the  general  peritoneal  cavity  unnecessarily  in  cases  of  abscess, 
and   less  likely   to   be  followed   by  ventral  hernia.      In    retroperitoneal    abscess   an 
incision  so  placed  will  not  infrequently  open  the  abscess  without  going  through  the 
peritoneum  at  all. 

3.  In  the  presence  of  general  purulent  peritonitis  a  vertical  incision  on  the 
outer  border  of  the  rectus  or  a  long  median  incision  will  best  enable  the  appendix  to 
be  dealt  with  and  at  the  same  time  permit  of  the  efficient  cleansing  and  irrigation  of 
the  peritoneal  cavity  and  the  introduction  of  drainage. 

4.  After  the  peritoneal  opening  is  made  the  appendix  can  often  easily  be  found 
and  brought  out  of  the  wound.      If  this  is  not  done  readily,  the  colon  should  be 
identified — the  first  portion  of  intestine  found  attached  to  the  posterior  wall  as  the 
finger  is  passed  along  that  wall  inward  from  the  incision — and  the  anterior  muscular 
band  traced  downward  to  the  base  of   the  appendix. 

The  Colon  and  Sigmoid  Flexure. — Like  the  other  main  subdivisions  of 
the  intestinal  tract,  the  colon  is  larger  at  its  commencement  than  at  its  termination, 
measuring  on  the  average  8  cm.  (3^  in.)  in  diameter  at  the  caecum  and  3.5  cm. 


i686  HUMAN   ANATOMY. 

(i^  in.)  at  the  lower  end  of  the  sigmoid  flexure.  Its  average  capacity  in  infants 
of  six  months  is  ^  litre  (i  pint);  in  children  two  years  old,  1.25  litres  (2.5  pints); 
and  in  adults,  4.5  litres  (9  pints). 

It  is  normally  palpable  through  most  of  its  extent,  the  more  deeply  placed 
hepatic  and  splenic  flexures  excepted,  the  former  being  beneath  the  liver,  the  latter 
behind  the  cardiac  end  of  the  stomach.  The  ascending  and  descending  portions  are 
usually  overlapped  in  front  by  the  more  mobile  small  intestine,  which,  if  not  dis- 
tended, can  be  displaced  towards  the  median  line.  The  thickened  and  sometimes 
tender  edge  of  a  chronically  congested  or  inflamed  caecum  can  often  be  rolled  under 
the  finger  against  the  floor  of  the  iliac  fossa,  and  has  been  mistaken  for  the  appendix. 
The  colon  is  susceptible  of  great  distention,  and  in  cases  of  obstruction  in  the 
sigmoid  flexure  or  rectum  it  may  occupy  most  of  the  abdomen,  push  up  the  dia- 
phragm, displace  the  heart,  and  occasion  dyspnoea  and  palpitation. 

Distention  either  from  gas  or  fecal  accumulation  renders  the  colon  visible,  as 
well  as  palpable,  except  at  the  flexures.  In  chronic  obstruction  in  the  rectum  or 
sigmoid  its  peristaltic  movements  may  be  seen  through  the  thinned  abdominal  walls. 
In  the  common  ileo-caecal  variety  of  intussusception  the  tumor  can  often  be  seen  as 
well  as  felt,  and  sometimes  the  progress  of  the  intussusceptum  along  the  colon  can 
be  traced  with  the  eye. 

Tumors  of  the  colon  or  upper  end  of  the  sigmoid  are  often  visible  in  thin  pa- 
tients, especially  when  they  have  contracted  anterior  parietal  attachments. 

Distention  of  the  colon  gives  rise  to  prominence  and  outward  curving  of  the 
flanks,  as  the  patient  lies  supine,  and  to  fulness  below  the  costal  arches  and  the 
margin  of  the  liver.  The  anterior  surface  of  the  belly— taking  the  umbilicus  as  a 
centre — is  relatively  flat.  In  distention  of  the  small  intestine  the  swelling  is  most 
marked  in  the  latter  region. 

Normally  the  colonic  percussion-note  is  of  somewhat  lower  pitch  than  that  of 
the  small  intestine,  but  of  higher  pitch  than  that  of  the  stomach,  the  variation  being 
due  to  the  difference  in  the  size  of  these  viscera  and  in  the  thickness  of  their  walls. 
In  general  gastro-intestinal  distention  the  same  variations  are  often  observable. 

A  large  quantity  of  fluid  faeces  in  the  colon  will  give  rise  to  percussion  dulness 
in  the  flanks,  which  may  disappear  when  the  patient  is  turned  on  his  side.  That 
sign  is  therefore  not  conclusive  evidence  of  the  presence  of  free  fluid  in  the  peri- 
toneal cavity,  unless  the  condition  of  the  colon  is  known. 

Rupture  from  distention — a  rare  occurrence — will  usually  be  incomplete,  the 
mucous  membrane  remaining  unbroken. 

Idiopathic  dilatation  of  the  colon  has  been  seen  in  young  children,  chiefly  among 
those  affected  with  rickets. 

Displacements. — The  caecum  and  ascending  colon  or  the  sigmoid  and  descend- 
ing colon  may  be  found  in  inguinal  or  femoral  herniae,  may  be  at  the  median  line  of 
the  body,  or  may  even  lie  in  the  iliac  fossa  of  the  opposite  side.  A  misplaeed, 
movable,  or  enlarged  kidney  may  cause  variation  in  the  position  of  the  colon. 
"When  the  left  kidney  occupies  the  iliac  fossa  or  is  situated  over  the  left  sacro-iliac 
synchondrosis  there  is  generally  no  sigmoid  flexure  in  the  left  iliac  fossa  ;  but  the 
descending  colon  passes  across  the  middle  line,  and  the  rectum  commences  on  the 
right  side  of  the  sacrum"  (Morris).  Paranephric  tumors,  by  pressure  on  the  colon, 
have  produced  such  marked  symptoms  of  intestinal  obstruction  as  to  be  mistaken 
for  intussusception  (Ibid.). 

The  transverse  colon,  as  the  most  movable  of  the  three  divisions  of  the  colon 
proper,  is  peculiarly  liable  to  assume  abnormal  positions,  usually  as  a  result  of 
habitual  constipation  or  secondary  to  obstruction  lower  in  the  gut.  It  can  readily 
be  understood  how  the  weight  of  fecal  masses  may  in  time  exaggerate  the  normal 
downward  curve  of  the  transverse  colon,  resting  only  on  the  easily  displaced  small 
intestine,  and  i-arry  it  towards  the  pubes,  which  it  sometimes  reaches.  The  normal 
level  of  the  middle  or  lower  portion  of  the  transverse  colon  is  at  the  upper  umbilical 
or  the  lower  epigastric  region,  or  on  the  line  separating  those  two  regions.  The 
position  of  the  transverse  colon  in  relation  to  the  stomach  varies  greatlv  within 
normal  limits.  If  the  stomach  is  empty,  it  is  behind  the  colon;  if  full  or  distended, 
it  will  push  the  latter  downward  and  overlap  it  from  in  front. 


PRACTICAL  CONSIDERATIONS  :     THE  LARGE  INTESTINE.    1687 

The  sigmoid  flexure,  the  most  movable  part  of  the  large  intestine,  normally  occu- 
pies the  pelvis  rather  than  the  iliac  fossa  (Fig.  1418),  into  which,  however,  it  rises  if  dis- 
placed by  pelvic  swellings  or  by  a  distended  bladder  or  rectum,  or  if  it  is  itself  distended. 

From  its  shape  and  position  and  the  relatively  great  length  of  its  mesentery  it  is 
very  liable  to  assume  unusual  positions.  It  may  be  found  on  the  right  side  of  the 
abdomen,  may  sink  low  in  the  pelvis  (especially  when  loaded  with  faeces),  and  in 
this  latter  position  may,  as  a  result  of  ulceration,  adhesion,  and  perforation,  open 
into  the  bladder,  the  vagina,  or  even  into  the  vas  deferens  (Allen),  producing  a 
fecal  fistula. 

Obstruction  of  the  large  intestine  may  be  due  to  (i)  fecal  impaction.  The 
presence  of  the  sacculi,  the  inspissation  of  intestinal  contents,  and  the  necessity  for 
overcoming  gravity  in  the  ascending  colon,  the  left  half  of  the  transverse  colon,  and 
the  lower  segment  of  the  sigmoid  curve  favor  the  production  of  this  condition. 

(2)  Stricture  is  more  common  in  the  large  intestine  than  in  the  small.     It  may  be 
(a)  cicatricial  and  follow  dysenteric  ulceration  in  the  rectum,  sigmoid,  or  descending 
colon  ;  tuberculous  or  stercoral  ulceration  in  the  ileo-caecal  region  ;  or  syphilitic  or 
tuberculous  ulceration  in  the  rectum  ;  or  (<5)  malignant,  most  common  as  we  ap- 
proach the  termination  of  the  intestinal  tract,  so  that  rectum,  sigmoid,  descending 
colon,  hepatic  flexure,  splenic  flexure,  transverse  colon,  caecum,  and  ascending  colon 
represent  the  clinical  order  of  frequency.      The  intimate  relation    of    the    hepatic 
flexure  to  the  gall-bladder  subjects  it  to  various  forms  of  irritation,  which  probably 
account  for  its  relative    susceptibility  to  malignant  disease  as  compared  with  the 
transverse  colon  ;  while  the  mechanical  conditions  present  in  the  caecum  (page  1680) 
apparently  have  a  similar  effect  upon  it,  making  it  more  frequently  the  seat  of  car- 
cinoma than  is  the  ascending  colon. 

Malignant  disease,  in  addition  to  producing  stricture  and  obstruction,  may  ex- 
tend into  and  involve  any  of  the  neighboring  viscera. 

(3)  Volvulus,  in  its  usual  form,  is  a  twist  of  a  portion  of  the  bowel  upon  an  axis 
passing  transversely  through  the  affected  segment  of  gut  and  its  mesentery.     In  more 
than  two-thirds  of  all  cases  of  volvulus  the  sigmoid  loop  is  the  part  involved.      The 
usual  cause  is  habitual  constipation.      The  gut,  becoming  paretic  from  continued  dis- 
tention,  hangs  over  into  the  pelvis  and  drags  upon  and  lengthens  the  mesosigmoid. 
Irregular  contraction  of  the  muscular  layer. of  the  gut  in  the  effort  to  rid  itself  of  the 
fecal  mass,  or  accumulation  of  faeces  in  one  segment  of  the  loop,  so  that  it  falls  over 
and  descends  below  the  other  and  less  distended  segment,  may  then  cause  the  twist. 
The   immediate  result  is  stoppage  of  the  fecal  current  from  the  pressure  of  the  two 
ends  of  the  loop  on  each  other,  and  intense  congestion  of  the  whole  loop  from  ob- 
struction of  the  mesenteric  vessels.      Meteorism  develops  early  and  becomes  exces- 
sive as  the  entire  intestinal  tract  is  sooner  or  later  involved  in  the  distention.      Vom- 
iting appears  late  and  is  not  very  marked.      The  difference  in  this  respect  between  a 
volvulus  of  the  sigmoid  and  an  acute  appendicitis  (in  which  vomiting  is  often  an  early 
and  significant  symptom)  may  be  due  to  the  fact  that  the  nerve-supply  of  the  former 
is  from  the  inferior  mesenteric  plexus,  communicating  directly  with  the  aortic  plexus 
and  only  indirectly  with  the  solar  plexus.      The  region  of  the  caecum  and  appendix, 
like  the  small  intestine,  is  supplied  by  the  superior  mesenteric  plexus,  having  rela- 
tion especially  and  directly  to  the  solar  plexus  and  to  the  right  pneumogastric.      In 
volvulus  of  the  small  intestine  vomiting  is  an  early  and  persistent  symptom.     As  well 
known,  for  mechanical  reasons  and  because  of  the  greater  fluidity  of  the  intestinal 
contents,  vomiting  is  more  apt  to  occur  early  and  to  be  marked  the  higher  the  site 
of  an  intestinal  obstruction. 

The  other  forms  of  obstruction  involving  the  large  intestine — foreign  bodies, 
bands,  peritonitis,  etc. — have  no  especial  anatomical  significance.  Intussusception 
has  already  been  mentioned.  Hernia  will  be  described  later. 

The  relations  of  the  large  intestine  should  be  carefully  studied  (Fig.  1383)  in 
order  to  understand  how  (a)  a  renal,  perinephric,  or  spinal  abscess,  or  malignant 
neoplasm  of  the  kidney  may  open  into,  obstruct,  or  involve  either  the  ascending  or  de- 
scending colon;  (6)  a  suppurating  gall-bladder  or  an  abscess  of  the  liver  may  evacuate 
into  the  beginning  of  the  transverse  colon;  (r)  a  gastro-colic  fistula  may  become  es- 
tablished in  cases  of  gastric  ulcer  involving  the  greater  curvature;  (d}  an  aneurism 


i688  HUMAN   ANATOMY. 

of  the  abdominal  aorta  may  burst  into  the  gut,  the  blood  passing  between  the  layers 
of  the  transverse  mesocolon  ;  (e)  an  iliac  abscess  may  discharge  into  the  caecum  or 
sigmoid  flexure  ;  (/")  the  latter  may  by  ulceration  communicate  with  the  bladder  or 
vagina  ;  (g)  or  may,  in  chronic  fecal  distention,  produce  left-sided  varicocele  (the 
more  frequent)  by  pressure  on  the  left  spermatic  vein. 

The  angulation  at  the  junction  of  the  lower  end  of  the  sigmoid  flexure  with  the 
first  part  of  the  rectum,  caused  by  the  greater  mobility  of  the  former  and  its  descent  by 
gravitation  to  a  lower  level,  often  constitutes  an  obstacle  to  the  passage  of  a  bougie  or 
tube,  or  sometimes  even  of  liquids,  into  the  sigmoid.  In  various  examinations  and  in 
washing  out  the  colon  it  is. therefore  frequently  desirable  to  put  the  patient  in  the  knee- 
chest  posture,  which  often,  by  gravity,  lessens  or  removes  this  cause  of  obstruction. 

Usually  a  tube  cannot  be  passed  completely  through  the  sigmoid  flexure,  but 
often  carries  the  latter  with  it  by  engaging  in  a  sacculus  or  a  fold  of  mucous  mem- 
brane. The  tip  of  the  instrument  may  be  felt  through  the  abdominal  wall  at  a  point 
at  or  beyond  the  mid-line,  which  may  lead  to  the  mistaken  belief  that  it  has  entered 
the  colon.  Exceptionally  it  is  possible  to  make  it  do  so,  the  passage  of  the  tube 
being  facilitated  by  the  injection  through  it,  as  it  advances,  of  an  oily  liquid  in  suf- 
ficient quantity  to  distend  as  well  as  lubricate  the  sigmoid  curve. 

Wounds  of  the  large  intestine  are  less  dangerous  than  those  of  any  other  portion 
of  the  intestinal  tract  because  (a)  the  lessened  fluidity  of  the  intestinal  contents  dimin- 
ishes the  risk  of  fecal  extravasation,  and  (o)  if  the  wound  passes  through  the  lumbar 
parietes  and  involves  only  the  posterior  wall  of  the  gut,  the  opening  may  be  entirely 
extraperitoneal.  According  to  Treves,  a  mesocolon  is  found  in  connection  with 
the  ascending  colon  approximately  once  in  four  times,  and  with  the  descending  colon 
once  in  three  and  one-half  times.  In  75  cases  out  of  100,  therefore,  such  a  wound 
of  the  colon  would  be  attended  by  a  minimum  of  danger. 

In  operations  on  the  large  intestine  it  may  be  identified  by  (a)  the  longitudinal 
bands,  especially  the  anterior  and  inner,  the  posterior  being  uncovered  by  peritoneum 
and  therefore  less  conspicuous,  and  being  placed  along  the  attached  border  of  the 
ascending  and  the  descending  colon  ;  (<£)  the  epiploic  appendages  found  more  abun- 
dantly along  the  inner  band  and  on  the  transverse  colon  ;  (V)  its  sacculi  which  may  be 
seen,  and  its  fecal  concretions  which  may  often  be  felt ;  and  in  addition,  as  compared 
with  the  small  intestine,  (</)  its  lesser  mobility,  greater  diameter,  and  the  absence 
of  the  palpable  transverse  ridges  of  the  valvulse  conniventes.  It  should  be  remem- 
bered that  when  it  is  greatly  distended  the  longitudinal  bands  and  sacculi  are  almost 
or  quite  obliterated,  and  that  the  epiploic  appendages — peritoneal  pouches  filled  with 
fat — are  absent  on  the  posterior  aspect  of  the  gut  and  in  the  rectum. 

Co/ostomy. — (a}  Lumbar. — If  the  descending  colon  is  opened  through  the  loin, 
it  should  be  through  an  incision  following  the  oblique  supra-iliac  crease.  The  course 
of  the  gut  corresponds  to  a  vertical  line  12  mm.  (  J^  in.)  external  to  the  centre  of 
the  crest  of  the  ilium.  The  incision  crosses  this  at  its  middle,  therefore  a  little  below 
the  kidney  or  on  a  level  with  its  lower  edge,  and  divides  the  posterior  fibres  of  the 
external  oblique,  the  anterior  ones  of  the  latissimus  dorsi  and  those  of  the  internal 
oblique,  the  lumbar  fascia,  the  posterior  fibres  of  the  transversalis  muscle,  and  the 
transversalis  fascia.  At  this  level  the  descending  colon  lies  in  the  angle  between  the 
psoas  and  quadratus  lumborum  muscles.  In  the  absence  of  a  mesocolon  (64  per 
cent.  )  the  operation  should  be  extraperitoneal. 

(£)  Inguinal. — An  incision  similar  to  that  often  employed  in  appendix  cases 
and  largely  intermuscular  may  be  made,  its  centre  being  4  cm.  (about  i^  in.)  from 
the  left  anterior  superior  spine  on  a  line  from  that  point  to  the  umbilicus.  The  sig- 
moid flexure,  the  portion  of  gut  to  be  opened,  may  be  recognized  by  the  tu'iihe,  the 
sacculi,  the  appendages,  etc. 

The  various  operations  to  effect  anastomosis  between  portions  of  intestine  above 
and  below  occluded,  diseased,  or  gangrenous  areas  depend  for  their  success  in  many 
instances  upon  the  mobility  of  the  intestine  and  therefore  upon  the  existence  and  the 
length  of  a  mesocolon. 

In  colectomy,  or  complete  resection  of  a  portion  of  the  large  intestine,  the  usual 
care  as  to  the  vascular  supply  of  the  retained  gut,  the  inversion  of  its  edges,  and  the 
approximation  of  serous  surfaces  must  be  exercised. 


PRACTICAL  CONSIDERATIONS:    THE  LARGE  INTESTINE.    1689 

The  Rectum  and  Anus. — In  relation  to  its  diseases  and  injuries,  the  rectum 
may  most  conveniently  be  divided  into  two  portions  :  ( i )  the  pelvic,  from  the  ter- 
mination of  the  sigmoid  flexure,  at  the  middle  of  the  third  sacral  vertebra,  to  the 
level  of  the  reflection  of  the  recto-vesical  fascia  from  the  upper  surface  of  the  levator 
ani  to  the  wall  of  the  rectum  ;  and  (2)  the  perineal, — the  "anal  canal," — which 
extends  from  this  level,  through  the  floor  of  the  pelvis,  to  the  anus. 

The  recto-vesical  fascia  (page  1678),  while  perforated  by  vessels,  constitutes  an 
efficient  barrier  to  the  progress  upward  of  infections  or  collections  of  pus  and  ren- 
ders the  surgical  relations  of  the  anal  canal  perineal  instead  of  pelvic.  The  distinc- 
tion between  these  portions  is  developmental  as  well  as  practical. 

The  pelvic  portion  is  the  termination  of  the  hind-gut,  which  has  a  blind  caudal 
end  ;  the  anal  portion  results  from  an  inflection  of  the  ectoblast.  Between  them 
lies  the  anal  membrane,  which  may  be  persistent  to  a  greater  or  less  extent,  causing 
various  degrees  of  constriction  or  resulting  in  imperforate  anus.  If  thin,  it  is  car- 
ried downward  by  the  meconium,  and  may  easily  be  felt  and  incised.  If  the  sep- 
tum is  thicker  and  includes  a  layer  of  fibre-muscular  tissue,  a  considerable  distance 
may  separate  the  lower  end  of  the  rectum  and  the  rudimentary  anal  canal.  Either 
portion  may  be  completely  absent. 

The  occasional  abnormal  opening  of  the  rectum  upon  the  surface  of  the  body 
has  been  observed  in  the  pubic,  gluteal,  lumbar,  or  sacral  region.  Its  more  fre- 
quent communication  with  the  vagina,  urethra,  or  bladder  is  explained  by  persist- 
ence of  the  early  association  of  the  gut-tube  with  the  genital  and  urinary  canals  in 
the  common  cloacal  space  (page  1696). 

In  early  childhood  the  pelvic  portion  of  the  rectum  is  straighter,  more  vertical, 
more  of  an  abdominal  organ,  and  more  movable  than  later  in  life.  The  support 
given  by  the  fascial  reflections  from  the  rectum  to  the  other  pelvic  organs  is  less,  on 
account  of  the  undeveloped  condition  of  the  prostate  and  uterus.  The  sacral  curve 
is  less  marked.  The  connective  tissue  between  the  mucous  and  muscular  coats  of 
the  rectum,  always  lax,  is  especially  so  in  children.  Prolapsus  ani  is  therefore  not 
infrequent  in  them,  especially  when  straining  has  been  caused  by  the  presence  of 
lumbricoids  or  by  other  sources  of  rectal  irritation.  It  occurs  in  adults,  chiefly  in 
old  age,  when  muscular  tonicity  has  been  weakened,  and  is  favored  by  chronic  vesi- 
cal  or  pulmonary  conditions  producing  frequent  straining  or  coughing.  Between 
the  normal  protrusion  from  the  anus  during  defecation  of  a  very  narrow  ring  of 
mucous  membrane,  which  returns  when  the  act  is  completed,  and  the  extrusion  of  a 
large  portion  of  the  rectum  {procidentia  recti},  including  all  its  coats,  every  degree 
of  prolapse  may  be  met  with.  The  anal  canal  is  so  firmly  held  by  the  levator  ani 
that  it  is  rarely  involved  in  prolapse. 

In  many  cases  of  prolapse  the  recto-vesical  or  recto-vaginal  pouch  is  dragged 
down  and  is  followed  by  coils  of  small  intestine  (which  the  pouch  normally  con- 
tains), so  that  it  constitutes  a  hernial  sac. 

Hemorrhoids. — The  anatomical  conditions  related  to  the  development  of  vari- 
cosities  or  dilatations  of  the  veins  of  the  hemorrhoidal  plexus  may  be  summarized  as 
follows  :  ( i )  The  absence  of  valves  and  of  any  muscular  or  fascial  support  between 
the  veins  and  the  mucous  membrane  and  the  looseness  of  the  submucous  connective 
tissue  rendering  the  effect  of  gravity  in  the  sitting  and  standing  postures  particu- 
larly harmful.  It  should  be  noted  in  this  connection  that  quadrupeds  are  almost 
free  from  this  disease.  (2)  The  passage  of  the  tributaries  of  the  superior  hemor- 
rhoidal vein  directly  through  the  muscular  wall  of  the  rectum,  about  three  inches 
above  the  anus,  causing' intermittent  constriction  of  the  veins  at  that  point.  (3)  The 
communication  of  the  superior  hemorrhoidal  vein — carrying  most  of  the  blood — 
with  the  inferior  mesenteric  vein,  and  thus  with  the  portal  system,  which  is  sub- 
ject to  periodic  physiological  congestions  (as  during  digestion)  and  to  frequent 
pathological  obstruction.  (4)  The  plexiform  anastomoses  just  within  the  anus,  be- 
tween the  inferior  and  middle  and  the  superior  hemorrhoidal  tributaries  (Fig.  767), 
so  that  the  former,  although  connected  with  the  systemic  circulation,  are  subject  to 
dilatation  as  a  result  of  portal  congestion.  (5)  The  relation  of  the  hemorrhoidal 
veins  and  of  the  terminal  branches  of  the  inferior  mesenteric  veins  to  the  fecal  con- 
tents of  the  sigmoid  and  rectum,  exposing  them  to  frequent  pressure. 


1690  IITMAX    ANATOMY. 

It  may  now  readily  be  understood  how,  in  the  presence  of  the  above  pre- 
disposing conditions,  hemorrhoids  may  result  from  (a)  direct  pressure  upon  the 
veins,  as  in  constipation,  pregnancy,  ovarian  or  prostatic  enlargements  ;  (b)  indirect 
pressure  through  the  column  of  blood,  as  in  hepatic  or  splenic  disease,  or  from 
the  contraction  of  the  diaphragm  and  abdominal  muscles,  as  in  coughing  or  lifting 
heavy  weights,  or  as  in  straining  clue  to  the  presence  of  stricture  or  vesical  cal- 
culus or  cystitis  ;  and  (c)  irritation  of  the  rectum  or  anus,  causing  congestion  of 
the  hemorrhoidal  veins. 

It  will  be  seen  that  chronic  constipation  is  a  possible  cause  of  hemorrhoids 
under  each  of  the  above  headings  :  the  fecal  masses  press  upon  the  veins,  irritate 
the  rectal  mucosa,  and  necessitate  straining  for  their  expulsion. 

Ulceration  of  the  rectum  and  anal  canal,  whether  from  inflammation  or  infec- 
tion following  trauma  (from  indurated  faeces  or  from  foreign  bodies),  or  caused  by 
dysentery,  tuberculosis,  syphilis,  or  cancer,  is  of  anatomical  interest  in  its  relation, 
first,  to  the  vascular  and  nervous  supply  of  the  parts,  and,  next,  to  the  surrounding 
regions. 

The  rectum  proper  is  characterized,  as  Hilton  long  ago  showed,  by  great 
distensibility  and  little  sensibility  ;  the  anal  canal  strongly  resists  distention  and  is 
extremely  sensitive. 

The  rectum  is  supplied  largely  from  the  sympathetic  system  through  the  infe- 
rior mesenteric  and  hypogastric  plexuses.  The  anal  nerve-supply  is  chiefly  from 
the  sacral  plexus,  especially  the  fourth  sacral  and  the  pudic  nerves,  the  filaments  of 
which  enter  the  gut  at  about  the  level  of  the  "white  line"  which  marks  the  junc- 
tion of  skin  and  mucous  membrane  and  also  the  demarcation  between  the  internal 
and  external  sphincters.  The  motor  and  sensory  supply  to  the  anal  canal  is  far  in 
excess  of  that  to  the  rectum.  Corresponding  differences  are  observed  in  the  vascu- 
lar supply.  Although  the  inferior  mesenteric  artery  brings  through  the  superior 
hemorrhoidal  a  relatively  large  amount  of  blood  to  the  rectum,  it  contributes  but 
little  to  the  anal  canal,  which  is  richly  vascularized  by  the  pudic  arteries. 

These  facts  explain  the  extraordinary  absence  of  subjective  symptoms  often 
observed  in  cases  of  large  fecal  accumulation,  malignant  growths,  or  extensive 
ulceration,  when  the  rectum  alone  is  involved.  They  likewise  explain  (through  the 
association  of  the  pudic,  the  fourth  sacral,  and  other  branches  of  the  sacral  plexus) 
the  great  pain  of  anal  ulceration  (Assure}  or  of  inflamed  and  protruding  hemor- 
rhoids and  the  associated  muscular  cramps  in  the  limbs,  the  vesical  irritation  or 
spasm  (often  causing  post-operative  retention  of  urine),  the  lumbar  and  iliac  pains, 
and  other  reflex  phenomena  so  common  in  anal  disease. 

The  great  power  conferred  upon  the  sphincters  by  their  unusually  rich  nerve- 
supply,  and  developed  by  the  resistance  they  must  frequently  and  necessarily  offer  to 
the  peristaltic  action  of  the  intestines  and  to  the  descent  by  gravity  of  feculent  matter, 
enables  these  muscles,  especially  the  external  sphincter,  through  their  obstinate  and 
almost  continuous  reflex  spasm,  to  become  not  only  a  cause  of  the  excessive  pain  of 
fissure,  but  also  an  obstacle  to  healing.  It  is  therefore  usually  requisite  in  the  treat- 
ment of  such  ulcers  to  paralyze  the  sphincters  by  overstretching,  often  supplemented 
by  either  partial  or  complete  section  of  the  external  sphincter.  The  higher  an  ulcer 
in  the  rectum  the  more  amenable  it  is  to  treatment  by  physiological  rest  (Hilton). 

Ulceration  in  the  rectum,  as  elsewhere  in  the  intestinal  tract,  may  result  in 
stricture,  or  in  fistulous  connection  with  neighboring  organs  or  tracts,  as  the  bladder 
or  vagina. 

Lymph  infection  proceeding  from  the  rectum  involves'  the  pelvic  and  lumbar 
glands,  especially  those  lying  on  the  front  of  the  sacrum  ;  if  from  the  anal  canal,  the 
'upper  and  inner  inguinal  glands  are  involved.  The  lymphatic  distribution,  like  that 
of  the  nerves  and  blood-vessels,  is  thus  seen  to  be  quite  different  for  the  rectum 
and  for  the  anal  canal. 

If  infection  spreads  by  vascular  rather  than  lymphatic  channels,  it  usually  travels 
by  way  of  the  portal  vessels  and  affects  organs  connected  with  the  digestive  system, 
•especially  the  liver.  Thus  a  not  uncommon  sequel  of  dysentery  is  hepatic  abscess. 
•On  the  other  hand,  emboli  from  external  hemorrhoids  have  been  known  to  enter  the 
general  venous  circulation  and  have  caused  death. 


PRACTICAL  CONSIDERATIONS  :   THE  LARGE  INTESTINE.    1691 

Subcutaneous  or  submucous  infection  involving  the  anal  canal  may  open  into 
the  canal  (^incomplete  internal  fistula  in  ano),  or  upon  the  cutaneous  surface  just 
without  the  margin  of  the  anus  (incomplete  external  fistula  in  ana),  or  in  both  direc- 
tions (complete  fistula  in  ano). 

It  may  begin  with  ulceration  within  the  canal  (most  often,  but  not  necessarily, 
tuberculous),  and  may  extend  into  the  ischio-rectal  fossa  ;  or  it  may  originate  in  that 
space,  and,  beginning  as  an  ischio-rectal  abscess,  cause  either  of  the  above  varieties  of 
fistula.  Such  abscesses  are  very  frequent  because  of  («)  the  proximity  of  the  rec- 
tum, the  frequency  of  rectal  ulceration,  and  the  invariably  septic  character  of  che 
rectal  contents  ;  (<£)  the  poorly  vascularized  fat  and  loose  connective  tissue  occupy- 
ing the  fossa  ;  (c)  the  effect  of  gravity  in  inducing  congestion  ;  (d)  the  absence  of 
muscles  competent  to  facilitate  the  return  of  venous  blood  ;  (e)  the  slight  but  often 
repeated  trauma  caused  by  coughing  or  straining,  the  effect  reaching  the  fossa 
through  the  impact  of  the  intestines  on  the  levator  ani,  its  roof  ;  (f)  the  exposure  of 
its  contents  to  frequent  slight  external  trauma,  as  in  sitting  on  irregular  surfaces,  and 
to  marked  changes  of  temperature. 

The  anal  fascia,  the  levator  ani,  and  the  strong  recto-vesical  fascia  offer  usually 
a  sufficient  barrier  to  the  progress  of  the  abscess  upward  ;  its  outward  extension  is 
limited  by  the  obturator  fascia,  the  obturator  internus,  and  the  tuberosity  of  the 
ischium  (Fig.  1426).  Internally,  below  the  level  of  the  levator  ani,  usually  about  12 
mm.  (%  in. )  above  the  anus,  it  finds  its  point  of  least  resistance,  and  accordingly, 
when  it  results  in  fistula,  the  internal  opening  will  usually  be  found  about  on  the  line 
between  the  sphincters,  its  higher  exit  from  the  fossa  being  prevented  by  the  blend- 
ing of  the  anal  and  recto-vesical  fasciae  and  the  levator  ani  muscle  with  the  bowel- 
wall.  If  it  reaches  the  surface  of  the  body,  it  will  do  so  inferiorly  in  the  space 
between  the  anus  and  the  tuberosity  of  the  ischium  and  the  edge  of  the  gluteus  maxi- 
mus  behind  and  the  reflection  of  the  deep  perineal  fascia  in  front  (Fig.  1423).  This 
external  opening  is  apt  to  be  just  beyond  the  outer  margin  of  the  external  sphincter. 

Such  abscesses  should  be  opened  early  on  account  of  the  suffering  caused  by 
pressure  on  the  twigs  of  the  small  sciatic,  the  fourth  sacral  (on  its  way  to  supply  the 
external  sphincter),  the  inferior  hemorrhoidal  and  superficial  perineal  nerves,  and 
also  to  avoid  the  formation  of  fistula,  and  to  forestall  any  possible  extension  upward 
and  a  resulting  pelvic  cellulitis  from  involvement  of  the  connective  tissue  between  the 
recto-vesical  and  pelvic  fasciae  and  the  peritoneum  (Fig.  1425).  They  should  be 
opened  widely  to  permit  of  perfect  drainage,  as  the  walls  cannot  definitely  be  ap- 
proximated; the  incision  should  be  on  a  line  radiating  from  the  anus,  so  as  to  avoid 
the  hemorrhoidal  vessels.  In  the  presence  of  fistula  following  such  an  abscess,  the 
incision  should  unite  the  external  and  internal  openings,  and  will  usually  divide  the 
external  sphincter  and  the  wall  of  the  rectum.  Incontinence  of  faeces  does  not  per- 
sist for  any  time,  unless  both  sphincters  are  divided.  The  levator  ani  may  aid  in 
preventing  it  (page  1692). 

In  women  free  anterior  division  of  the  external  sphincter  may  cause  permanent 
incontinence  on  account  of  the  laxness  of  its  anterior  connections,  the  interposition 
of  the  vagina  preventing  the  firmer  attachment  to  the  pubes  which  in  men  is  attained 
through  the  medium  of  the  triangular  ligament. 

Fistula  requires  operation  because  drainage  is  imperfect  and  the  region  is  acted 
upon  by  the  contractions  of  the  levator  ani,  the  muscular  coat  of  the  gut  itself,  and 
by  the  external  sphincter,  the  latter  muscle  being  especially  irritable  and  sometimes 
hypertrophied. 

Cancer  of  the  rectum  may  involve  any  portion,  but  is  apt  to  be  found  within 
two  or  three  inches  of  the  anus.  In  addition  to  the  symptoms  of  obstruction,  the  pain 
from  contact  of  faeces  with  an  ulcerated  surface,  and  the  blood  which  may  streak  the 
stools,  there  are  symptoms  due  to  its  anatomical  surroundings  which  should  be  care- 
fully studied.  If  it  extends  towards  the  hollow  of  the  sacrum,  it  will  press  upon  the 
sacral  plexus,  causing  pain  which  may  suggest  sciatica,  lumbago,  sacro-iliac  disease, 
or  coxalgia.  If  it  extends  anteriorly,  distressing  vesical  symptoms  in  the  male  may 
distract  attention  from  the  real  seat  of  the  disease  ;  while  in  the  female  menstrual 
derangement  and  suffering  may  have  the  same  effect.  Laterally  it  may  involve  the 
ischio-rectal  fossae,  producing  abscess  and,  later,  multiple  and  intractable  fistulae. 


i692  HUMAN   ANATOMY. 

If  it  spreads  to  distant  parts,  it  should  be  remembered  that,  if  it  is  high  and  fol- 
lows lymphatic  channels,  it  involves  first  the  sacral  glands  in  the  sacral  curve  and 
then  the  lumbar  glands  by  the  sides  of  the  lumbar  vertebrae.  The  former,  when 
much  enlarged,  may  be  felt  with  the  finger  in  the  rectum.  The  latter  are  palpable 
through  the  anterior  abdominal  wall.  If  the  carcinoma  is  at  or  near  the  anus,  the 
upper  inguinal  glands  are  apt  to  be  first  involved.  If  it  spreads  through  the  blood- 
vessels, it  may,  whatever  its  seat,  follow  the  superior  hemorrhoidal  veins  to  the  portal 
system  and  the  liver  or  the  internal  pudic  and  iliac  veins  to  the  vena  cava  and  to  the 
lungs  and  elsewhere. 

The  relations  of  the  rectum  are  of  much  practical  importance.  Those  with  the 
peritoneum  have  been  described  (page  1753).  The  fact  that  this  membrane  leaves 
the  rectum  uninvested  posteriorly  makes  it  possible  in  rectal  cancer  to  remove  safely 
more  of  the  posterior  than  of  the  other  walls.  Penetrating  ulcers  are  more  apt  to 
involve  the  peritoneal  cavity  if  on  the  anterior  wall. 

In  the  male  the  rectum  is  in  relation  anteriorly  to  the  prostate,  the  seminal  vesi- 
cles, and  the  base  of  the  bladder.  Dilatation  of  the  rectum  raises  the  recto-vesical  fold 
of  peritoneum  and  elevates  and  advances  the  bladder,  bringing  a  larger  non-peritoneal 
surface  in  closer  contact  with  the  abdominal  wall.  This  is  sometimes  made  use  of 
in  suprapubic  lithotomy  or  prostatectomy  (<?. v. ).  In  the  female  rectal  distention 
pushes  the  fundus  uteri  upward  and  towards  the  pubes. 

Injuries  to  the  rectum  are  dangerous,  aside  from  shock  and  hemorrhage,  on 
account  of  the  risks  of  septic  peritonitis  or  cellulitis.  The  height  of  the  wound  or 
rupture  or  perforation  and  its  relation  to  the  peritoneal  pouch  or  to  the  recto-vesical 
fascia  are  of  great  importance.  The  rectum  is  less  liable  to  direct  trauma  than  are 
other  portions  of  the  intestinal  tract,  on  account  of  the  protection  afforded  it  by  the 
bony  walls  of  the  pelvis. 

Enlargement  of  the  prostate  may  so  depress  the  anterior  wall  of  the  rectum  as 
greatly  to  diminish  its  lumen.  Occasionally  symptoms  of  rectal  obstruction  are 
produced  thereby.  Acute  prostatic  inflammation  and  prostatic  abscess  may  be 
recognized  by  rectal  touch,  as  may  similar  conditions  of  the  seminal  vesicles.  They 
are,  for  obvious  reasons,  apt  to  be  associated  with  rectal  irritation,  tenesmus,  and 
painful  defecation. 

In  operations  on  the  rectum,  as  for  excision  of  carcinoma,  it  may  be  approached 
(a)  from  below,  when  the  disease  is  near  the  anus,  by  isolating  the  lower  end  of  the 
gut.  If  the  anus  is  involved,  the  incision  may  be  made  outside  the  external  sphinc- 
ter ;  if  not,  the  incision  may  follow  the  li  white  line."  It  will  be  necessary  to  divide 
the  lateral  fascial  attachments,  the  levator  ani  on  each  side,  the  connective  tissue 
between  the  rectum  and  vagina  or  rectum  and  urethra  and  prostate,  and  numerous 
hemorrhoidal  branches.  (£)  It  may  be  approached  from  above,  when  the  growth  is 
high,  by  opening  the  peritoneal  cavity.  The  sigmoid  may  also  be  opened,  the  dis- 
eased segment  of  gut  invaginated  into  it  and  excised,  and  the  remainder  of  the 
rectum  and  sigmoid  united  (Maunsell).  (c)  It  may  be  reached  from  in  front 
through  a  median  incision  in  the  posterior  wall  of  the  vagina  ;  or  (d  )  from  bchi. 
by  removal  of  the  coccyx  ;  or,  if  more  room  is  required,  by  detachment  of  the  sac 
sciatic  ligaments  ;  or,  in  still  more  extensive  disease,  by  resection  (osteoplastic  o 
otherwise)  of  the  left  half  of  the  sacrum  up  to  the  level  of  the  lower  border  of  the 
third  sacral  foramen.  Paralysis  of  the  bladder  may  follow  interference  with  the  third 
sacral  nerve.  The  sacral  and  coccygeal  attachments  on  the  left  side  of  tin  U -\  aim- 
am,  the  cocrygeus,  and  the  sacro-sciatic  ligaments  must,  of  course,  be  divided,  as 
must  the  fourth  and  tilth  sacral  and  the  coccygeal  nerves.  The  lateral  and  median 
sacral  arti  rii  -,  and  their  accompanying  veins  are  raised,  with  the  fibrous  tissue  on 
which  they  lie,  from  tin-  anterior  surface  of  the  sacrum  by  a  blunt  elevator. 

/•. '\aniination  per  rectum  may  be  made  by  the  linger,  by  inspection,  by  bougies, 
or  by  the  introduction  of  the  whole  hand. 

(a)  With  the  finger  one  can  feel  the  involuntary  contraction  of  the  sphincters 
embracing  the  linger  for  the  space  of  about  an  inch.  If  th<'  patient  is  asked  to  con- 
tract the  sphincter  voluntarily,  the  levator  ani  will  participate,  as  both  muscles  are 
innervated  by  the  fourth  sacral  nerve.  As  a  result  of  this,  the  upper  margin  of  tin- 
contracted  portion — i.e..  of  the  anal  canal — will  then  be  felt  to  "end  abruptly  and 


PRACTICAL  CONSIDERATIONS  :   THE  LARGE  INTESTINE.    1693 

give  a  sensation  of  a  broad  muscular  band  around  the  bowel"  (Cripps).  This  is 
more  distinct  posteriorly  and  represents  the  posterior  edge  of  the  levator  ani.  It  is 
from  1^2-2  in.  from  the  anus.  A  patulous  condition  of  the  anus  or  a  cavernous  or 
"ballooned"  condition  of  the  rectum  should  suggest  stricture,  the  muscles  below 
which,  having  no  function  to  perform,  become  enlarged  and  yielding.  An  excep- 
tionally tight  grip  of  the  finger,  with  marked  tenderness,  should  suggest  fissure. 

If  the  patient  is  asked  to  strain,  a  slightly  increased  area  of  bowel  will  be  made 
accessible  to  examination  by  the  finger,  but,  except  anteriorly,  the  finger  cannot,  as 
a  rule,  reach  beyond  the  portions  uncovered  by  peritoneum.  The  upward  distance 
thus  made  palpable  is  on  the  average  from  3-4  in.  The  distance  from  the  anus  to 
the  recto-vesical  pouch,  when  the  bladder  and  rectum  are  empty,  is  about  2  y?  in. ; 
when  they  are  distended,  it  is  about  ^y2  in.  Growths  in  the  sigmoid  often  descend 
so  that  they  may  be  felt  through  the  rectal  wall  with  the  finger. 

Anteriorly,  from  1^2-2  in.  from  the  anus,  the  prostate  may  be  felt  in  the  male. 
Between  its  apex  and  the  anus  the  membranous  urethra  is  accessible  to  digital 
examination  and  can  be  distinctly  outlined  when  a  catheter  or  sound  occupies  it. 
Posterior  to  the  prostate  there  may  be  felt  the  triangular  area  of  the  base  of  the 
bladder,  which  is  closely  held  to  the  rectum  by  dense  connective  tissue,  and  the  sides 
of  which  are  formed  by  the  seminal  vesicles,  the  base  by  the  edge  of  the  recto- 
vesical  peritoneal  pouch.  It  is  through  this  triangle,  and  as  near  its  apex — i.e. ,  the 
prostate — as  possible,  that  the  bladder  is  tapped  per  rectum,  and  it  may  be  noted  in 
connection  with  what  has  already  been  said  as  to  the  lack  of  sensibility  in  the  upper 
rectum,  that  the  operation — now  rarely  performed — is  almost  painless.  The  seminal 
vesicles,  and  in  some  cases  a  portion  of  the  vas  deferens,  can  be  felt  above  the  pros- 
tate and  at  the  sides,  especially  if  diseased.  Their  relations  to  the  rectum  explain 
the  spurious  cases  of  spermatorrhoea  in  which,  during  defecation,  their  contents  are 
squeezed  into  the  urethra  by  the  descending  fecal  masses,  exciting  the  apprehension 
of  the  patient,  usually  a  young  neurasthenic. 

In  children  the  bladder  may  be  examined  to  its  bas-fond,  and,  even  if  not  dis- 
tended, may  be  felt  by  bimanual  palpation,  one  hand  being  above  the  pubes. 

The  back  of  the  pubic  bones  and  symphysis  and  the  obturator  foramina  may  also 
be  reached  anteriorly. 

In  females  the  recto- vaginal  walls  and  the  os  uteri  may  be  felt  anteriorly  and  the 
broad  ligaments  and  (in  some  cases  of  disease)  the  ovaries  laterally.  Laterally  also, 
in  both  sexes,  the  inner  aspect  of  the  ischial  tuberosities  and  part  of  the  rami  may  be 
felt,  as  well  as  the  inner  walls  of  the  ischio-rectal  fossae,  which  will  be  soft  and  yielding 
under  normal  conditions,  and  tense,  tender,  and  bulging  if  an  abscess  occupies  the 
ischio-rectal  space. 

The  pulsations  of  some  of  the  hemorrhoidal  arteries  may  often  be  felt,  and  one 
or  more  of  Houston's  folds  and  the  lower  portion  of  the  columns  of  Morgagni  and 
the  ' '  valves ' '  of  the  same  name  recognized.  Posteriorly  the  front  of  the  coccyx 
and  the  sacro-coccygeal  junction  can  be  reached. 

(6)  By  inspection,  with  the  aid  of  various  specula,  and  with  reflected  or  electric 
light,  ulcers,  polyps,  or  other  new  growths,  the  internal  openings  of  fistulous  tracts, 
hemorrhoids,  fissure,  and  other  pathological  conditions  may  be  seen.  By  placing 
the  patient  in  the  "  knee- chest  position"  the  intestines  gravitate  towards  the  dia- 
phragm, the  recto-vesical  and  recto-vaginal  pouches  are  emptied,  downward  pressure 
upon  the  sigmoid  and  rectum  is  removed,  the  latter  has  room  to  dilate  upon  the 
admission  of  air,  and  inspection  is  thus  facilitated. 

(c)  By  bougies  stricture  may  be  recognized,  but  care  must  be  taken  that  ob- 
struction due  to  contact  with  one  of  the  so-called  "valves" — Houston's  folds — is 
not  mistaken  for  a  contraction.  It  should  be  remembered,  too,  that  the  sigmoid  is 
quite  movable,  and  that  the  demonstration  by  touch  of  the  presence  of  the  end  of  the 
bougie  close  to  the  abdominal  wall,  even  if  it  is  also  near  the  median  line,  does  not 
proy,e  that  it  has  passed  into  the  colon.  It  may  have  carried  the  sigmoid  with  it. 

(d*)  By  the  whole  hand  introduced  into  the  bowel  there  may  be  felt  (in  addition 
to  the  structures  mentioned  in  a)  (i)  the  spines  of  the  ischium  ;  (2)  the  curve  and 
promontory  of  the  sacrum  ;  (3)  the  outlines  of  the  greater  and  lesser  sacro-ischiatic 
foramina  ;  (4)  the  external  iliac  artery  from  the  brim  of  the  pelvis  to  the  crural 


1694 


H-l'MAN    ANATOMY. 


arch  ;  (5)  the  internal  iliac  artery  through  most  of  its  course  ;  (6)  in  the  female  the 
uterus  and  the  ovaries.  If  the  hand  will  enter  the  sigmoid  flexure,  most  of  the  abdo- 
men may  be  explored. 

Examination  through  the  rectum  by  this  method  is  distinctly  dangerous  from 
the  risk  of  laceration  of  the  gut.      It  is  therefore  not  in  much  favor. 


DEVELOPMENT   OF   THE   ALIMENTARY   TRACT. 

Reference  to  the  cross-section  of  a  young  mammalian  embryo  (Fig.  1428)  shows 
the  early  relation  between  the  primitive  gut  and  the  yolk-sac,  of  which  latter  the 
former  is  evidently  a  part.  The  longitudinal  section  of  a  very  young  human  embryo 
(Fig.  46,  page  39)  emphasizes  the  wide  communication  between  the  two.  The 
differentiation  of  the  gut  from  the  yolk-sac  is  accomplished  by  the  approximation 
and  union  of  the  two  splanchnopleuric  folds  which  consist  of  the  entoblast  internally, 
continuous  with  that  of  the  yolk-sac,  and  the  visceral  layer  of  the  mesoblast  exter- 
nally. As  the  union  of  the  splanchnopleurse  proceeds,  the  gut-tube  becomes  closed 

FlG.    1428.  Neural  tube 

1^_ 


Myotome 


Amniotic  sac 


Amnio 


Notochord 
Primitive  aorta 


Body-cavity 


Vitelline  vein. 

&       ^^    I      l^m^m 

Open  gut-tube  Visceral  mesoblast 

Transverse  section  of  early  rabbit  embryo,  showing  differentiating  gut-tube  still  communicating  with  vitelline 

sac.     X  80.  • 

throughout  its  cephalic  and  caudal  segments,  between  which,  however,  it  remai 
open  and  connected  with  the  yolk-sac  by  a  communication  that  rapidly  narrows  an 
elongates  into  the  vitelline  or  umbilical  duct,  a  structure  that  for  a  considerable  time 
remains  as  a  canal  bearing  the  diminishing  yolk-sac  or  umbilical  vesicle  at  its  outer 
'end.  The  primitive  digestive  tract,  therefore,  is  closed  both  anteriorly  and  pos- 
teriorly, and  soon  may  be  divided  into  three  segments  :  the  fore-,  mid-,  and  hind-gut. 
Formation  of  the  Mouth. — The  cephalic  segment,  the  fore-gut,  is  somewhat 
dilated  at  its  anterior  extremity,  and  there  constitutes  the  prim  Hire  fiharvn.v,  which  at 
first  is  separated  from  a  bay-like  depression,  the  oral  recess  (stomodtmm)^  which 
meanwhile  has  been  formed  by  the  downward  flexure  of  the  anterior  cerebral  vesicle 
and  the  development  of  the  visceral  arches.  The  septum  between  the  fore-gut  and 
the  oral  recess,  the  />//</;  -yn gcal  membrane  (Fig.  1429),  consists  of  the  directly  apposed 
entoblast  lining  the  primitive  pharynx  and  the  ectoblast  continued  from  the  surface, 
no  mesoblast  intervening.  The  pharyngeal  membrane  very  early  (probably  about 
the  thirteenth  or  fourteenth  day  in  man)  becomes  broken  up  by  the  formation  of 
holes  and  soon  disappears,  the  primitive  oral  and  pharyngeal  spaces  thereafter  freely 
communicating, 


DEVELOPMENT  OF  THE  ALIMENTARY  TRACT. 


1695 


The  entrance  into  the  primary  oral  cavity  is  a  pentagonal  opening  bounded  by 
five  projections, — superiorly  by  the  unpaired  frontal  process,  extending  downward 
from  the  region  of  the  anterior  cerebral  vesicle,  laterally  by  the  maxillary  processes, 
and  inferiorly  by  the  fused  mci)idibular  processes  of  the  first  visceral  arches  (Fig.  74). 
The  further  changes  leading  to  the  formation  of  the  definitive  mouth  and  the  sepa- 
ration of  the  oral  and  nasal  cavities  are  described  in  connection  with  the  development 
of  body-form  (page  59). 

The  primitive  pharynx  bears  on  each  side  a  series  of  four  lateral  dilatations,  the 
pharyngeal  pouches  (Fig.  73),  corresponding  to  the  inner  half  of  the  visceral  clefts 
seen  in  water-breathing  animals.  In  the  mammals  true  fissures  are  not  formed,  the 
visceral  clefts  being  represented  by  the  external  and  internal  furrows  lying  between 
the  visceral  arches  and  separated  by  a  delicate  ecto-entoblastic  partition.  The  details 
of  the  development  and  metamorphosis  of  the  visceral  arches  and  furrows  have  been 
considered  (page  60). 


FIG.  1429. 


Posterior  cerebral  vesicle 
Primitive  pharynx 


Ventral  aorta 


Gut-tube 


Primitive  auricle 


Neural  tube 


Middle  cerebral  vesicle 


Anterior  cerebral  vesicle 


•^|#-?haryngeal  membrane 


Oral  recess  (stomodseum) 


Primitive  ventricle 


Vitelline  duct 


Caudal  pole  (obliquely  cut) 


Sagittal  section  of  early  rabbit  embryo,  showing  oral  recess  and  primitive  pharynx  still  separated.    X  12. 


Formation  of  the  Anus. — The  posterior  or  caudal  segment  of  the  primitive 
gut-tube  is  the  seat  of  the  changes  leading  to  the  formation  of  the  excretory  orifice. 
Formerly  the  development  of  the  anus  was  regarded  largely  as  the  repetition  of  a 
process  similar  to  that  leading  to  the  communication  between  the  oral  recess  and  the 
fore-gut,  an  external  depression  (proctodccum}  being  separated  from  the  hind-gut  by 
an  ecto-entoblastic  partition  which  later  was  broken  down  to  form  the  anus,  which  was 
considered  a  new  structure. 

The  studies  of  Gasser,  Kupffer,  Bonnet,  Hertwig,  and  others  have  emphasized 
the  close  relations  between  the  anus  and  the  blastopore.  According  to  these  investi- 
gations, the  blastopore  probably  gives  rise  to  two  openings,  an  anterior  and  a  posterior. 
The  former  is  the  transient  neurenteric  canal,  the  latter  the  anus.  When  the  primitive 
streak  is  regarded  as  the  fused  and  elongated  blastopore  (page  25),  it  follows  that 
the  anlage  for  the  anus  is  located  in  the  posterior  part  of  that  structure,  and,  further, 
that  the  primary  position  of  the  anal  anlage  is  on  the  dorsal  surface  of  the  embryo. 


1696 


H  I'M  AN   ANATOMY. 


Its  migration  to  the  ventral  surface  is  associated  with  the  growth  and  changes  affect- 
ing the  tract  situated  between  the  neurenteric  canal  and  the  anal  anlage  giving  rise 
to  the  tail-bud  (Hertwig)  from  which  the  caudal  appendage  arises.  In  conse- 
quence of  the  displacement  occasioned  by  these  changes,  the  anal  anlage  gradually 
assumes  a  ventral  position  immediately  beneath  the  tail. 

Coincident  with  this  migration  the  primitive  gut-tube  becomes  enlarged  in  the 
vicinity  of  the  allantois  to  form  a  common  space,  the  cloaca,  into  which  open  the  hind 
gut,  the  allantois,  the  Wolffian  ducts,  and  the  caudal  or  post-anal  gut,  a  temporary 
entension  of  the  gut-tract  toward  the  tail-bud.  The  ventral  wall  of  the  cloaca  shutting 
it  off  from  the  exterior  is  formed  by  a  delicate  partition,  the  anal  or  cloacal  >ne»i- 
brane  (Fig.  1644),  consisting  of  the  apposed  entoblast  and  ectoblast.  A  slight  de- 
pression, the  primitive  anal  groove,  indicates  the  position  at  which  the  membrane 
breaks  through  to  establish  the  cloacal  orifice  in  those  forms,  as  birds  and  mono- 


FIG.  1430. 


Optic  vesicl 
Fore-brain 


Hind-brain 


I  pharyng.  pouch 
Ventral  aorta._ 


i  aortic  bow 


Primitive  —pi- 
ventricle       SjU 
Sinus — -^ 
reuniens          ^^ 
Liver — mm 

Liver- 
diverticulum. 


Vitelline-1— 
duct      \ 


II  pharyng.  pouch 

III  pharyng.  pouch 
Gut-tube 

Duct  of  Cuvier 
Aorta 


Liver 


Vitelline 

duct 

Vitelline- 
Neural  tube  artery 


Gut-tube, 
lower  part 


Allantoic  duct 


Belly-stalk_ 


Reconstruction  of  sagittally  sectioned  human  embryo 
of  third  week,  showing  relations  of  digestive  tube.  X  26. 
(After  His  model.) 


1  pharyng.  pouch 

2  aortic  bow 

II  pharyng.  pouch 
3  aortic  bow 

III  pharyng.  pouch 
4  aortic  bow 

IV  pharyng. 
pouch 

Lung-anlage 


Allantoic  duct. 
Umbilical  artery- 


Reconstruction  of  digestive  tube  of  preceding 
bryo  ;  aortic  bows  and  trunk  also  shown.    X  26.    (Aft> 
His  model.) 


tremes,  in  which  the  cloaca  persists.  In  the  higher  mammals  the  cloacal  stage  is 
only  temporary,  the  cloaca  becoming  subdivided  into  two  compartments  by  the  for- 
mation of  a  septum,  which  grows  downward  to  meet  the  cloacal  membrane.  The 
anterior  compartment  becomes  the  uro-genital  sinus,  the  posterior  the  rectum. 
Later  the  remains  of  the  cloacal  membrane  disappear,  and  these  spaces  are  provided 
with  the  uro-genital  cleft  and  the  definitive  anus  respectively. 

Differentiation  of  the  simple  gut-tube  into  distinctive  segments  begins  with  the 
stomach,  which  appears  as  a  small  spindle-form  enlargement  at  some  little  distance 
below  the  primitive  pharynx,  the  portion  of  the  tube  between  the  two  correspond- 
ing to  the  early  oesophagus.  The  gut-tube  lies  close  to  the  posterior  wall  of  the 
body-cavity,  and  at  this  stage  (  corresponding  to  about  the  fourth  week  in  the  human 
embryo)  presents  five  divisions, — the  primitive  oral  cavity,  the  primitive  pharynx, 
the  oesophagus,  the  stomach,  and  the  intestinal  tube,  which  latter  freely  communi- 
cates with  the  yolk-sac  through  the  vitelline  duct. 


DEVELOPMENT  OF  THE  ALIMENTARY  TRACT. 


1697 


The  digestive  tube  is  at  first  closely  bound  to  the  posterior  body-wall  by  a  short, 
broad  mesoblastic  band.  This  attachment,  or  primitive  mesentery,  from  the  lower 
end  of  the  oesophagus  downward,  gradually  increases  in  its  sagittal  dimensions,  at 
the  expense  of  its  breadth,  in  consequence  of  the  gut-tube  leaving  the  dorsal  wall  and 
assuming  a  more  ventral  position,  the  entire  gastro-intestinal  tube  being  thus  attached 
by  a  mesentery.  That  portion  of  the  latter  connected  with  the  stomach  is  known  as  the 
mesogastriumt  that  with  the  intestinal  tube  as  the  mesenterium  commune  (Fig.  1478). 

The  elongation  of  the  stomach  soon  results  in  loss  of  the  primary  sagittal  direc- 
tion of  its  axis,  which  becomes  oblique,  the  lower  end  of  the  organ  passing  to  the 
right,  while  its  upper  end  is  displaced  towards  the  left  in  consequence  of  the  increasing 
volume  of  the  liver.  Embryos  of  the  sixth  week  exhibit  marked  change  in  the  form 
of  the  stomach,  since  the  dorsal  wall,  later  the  greater  curvature,  has  become  bulged 
spineward,  while  the  ventral  surface  presents  a  slight  concavity  foreshadowing  the  later 
smaller  curvature.  Somewhat  later  the  stomach  also  undergoes  rotation  about  its 
longitudinal  axis,  its  primary  left  surface  becoming  the  ventral  or  anterior,  and  its 
primary  ventral  border  the  lesser  or  upper  curvature.  The  primary  wall  of  the 


Allantoic  duct- 


External  surfa 


« Intestine 


Cloaca  — I 


Cloacal  membrane 


Tail-bud 


Part  of  caudal  end  of  sagittal  section  of  rabbit  embryo  of  twelve  days,  showing  cloacal  space  in  communication 
with  lower  end  of  gut-tube  and  allantoic  duct.     X  35- 


stomach  consists  of  the  entoblastic  lining  surrounded  by  the  splanchnopleuric  meso- 
blast.  The  differentiation  of  the  gastric  glands  begins  towards  the  close  of  the  third 
month  as  minute  epithelial  outgrowths  from  the  entoblastic  layer.  A  few  weeks  later 
the  glands  become  branched,  and  the  parietal  cells  appear  as  differentiations  from 
single  epithelial  elements  lining  the  peptic  follicles.  In  the  fifth  month  the  length  of 
the  glands  has  increased  to  about  .20  mm.,  and  during  the  succeeding  month  to 
from  .40—.  70  mm.  (Kolliker).  Differentiation  of  the  mesoblastic  tissue  into  the  inner 
circular  and  outer  muscular  layers  occurs  during  the  fourth  month. 

The  lower  funnel-shaped  pyloric  end  of  the  stomach  at  first  passes  insensibly 
into  the  relatively  wide  beginning  of  the  characteristic  U-shaped  intestinal  loop  which 
extends  from  the  stomach  ventrally,  its  closed  end  or  arch  being  attached  to  the 
vitelline  duct,  and  then  returns  to  the  posterior  body-wall  to  be  continuous  with  the 
terminal  segment,  which  maintains  its  sagittal  relations  in  close  attachment  with 
the  dorsal  boundary  of  the  body-cavity.  The  inferior  limb  of  the  loop  early  shows 
beginning  differentiation  into  large  intestine,  the  junction  of  the  latter  with  the  small 
intestine  being  indicated  by  the  slight  ca?cal  expansion.  Even  at  this  period  a  defi- 
nite vascular  relation  has  been  established  by  the  three  main  segments  of  the  gastro- 

107 


1698 


1 1 1. MAN    ANATOMY. 


intestinal  tube  and  its  mesentery.  Within  the  mesogastrium  course  the  three 
branches  of  the  cceliac  axis  ;  the  superior  mesenteric  artery  passes  within  the  mesen- 
tery between  the  limbs  of  the  intestinal  loop,  while  the  inferior  mesenteric  artery  is 
distributed  to  the  last  part  of  the  intestinal  tube. 

The  subsequent  changes  which  the  intestinal  tube  exhibits  during  its  growth  have 
been  carefully  studied  in  reconstructions  by  Mall,1  whose  conclusions  differ  materially 
from  the  prevailing  views.  According  to  this  investigator,  the  rapidly  augmenting 
liver-mass  occupies  so  large  a  portion  of  the  still  small  abdominal  cavity  that  there  is 
no  space  left  for  the  expansion  of  the  intestinal  tube.  In  consequence  of  this  con- 
dition the  greater  part  of  the  gut  is  early  displaced  from  the  abdominal  cavity  into 
the  ccelom  within  the  umbilical  cord,  the  upper  limb  of  the  U-loop  then  lying  to  the 
right  and  the  lower  to  the  left.  The  growth  of  the  small  intestine — more  rapid  than 
that  of  the  large — soon  results  in  the  production  of  six  primary  coils,  the  identity  of 
which  is  retained  not  only  throughout  development,  but  can  be  established  even  in 
the  adult  (Mall).  The  first  part  of  the  gut- tube,  continuous  with  the  stomach  and 
receiving  the  ducts  of  the  liver  and  the  pancreas,  increases  relatively  little  in  its 


FIG.  1432. 


Future  diaphragm 


Anterior  mesentery 
(falciform  ligament) 

Liver- 


Anterior  mesentery 
(gastro-hepatic  omentum) 


Connectioi 
vitelline  stalk 


Umbilical  veit 
Body-cavity___^pS 

Mt 
.  j 

ion  of__^ 


Stomach 

Spleen 

Mesogastrium 

CoL-liac  axis 

Pancreas 

Duodenum 

.Superior  mesen- 
teric artery 

Mesenterium 
commune 


Inferior  mesenteric  artery 

Allantoic  duct 

Clocca 


Beginning  of  large  intestine 
Diagram  showing  early  relations  of  anterior  and  posterior  mesentery.     (Based  on  figures  of  Mall  and  Toldl.) 

length,  and  therefore  does  not  become  secondarily  convoluted,  as  do  the  remaining 
coils  of  the  small  intestine.  This  part  is  later  represented  by  the  duodenum.  The 
outer  primary  coils  undergo  great  elongation,  and  consequently  present  secondary 
convolutions  of  increasing  complexity,  all  of  which  for  a  considerable  time  (until  the 
embryo  has  attained  a  length  of  about  30  mm.)  are  retained  within  the  umbilical 
ccelom.  About  this  period  the  lower  part  of  the  body  grows  rapidly,  resulting  in 
increased  space  within  the  peritoneal  cavity,  which  now  affords  room  for  the  tempo- 
rarily displaced  gut-coils.  In  consequence  of  these  changes  the  intestine  returns  to 
the  abdominal  cavity,  and  in  embryos  of  40  mm.  length  the  coils  no  longer  lie  within 
the  umbilical  cord.  Mall  has  shown  that  their  return  to  the  abdominal  cavity  occurs 
in  a  definite  order,  the  upper  part  of  the  small  intestine  being  first  withdrawn,  the 
l.ii-r  intestine  with  its  ca-cal  dilatation  last.  On  re-entering  the  abdomen  the  upper 
|..ut  of  the  small  iMit  passes  to  the  left  hypochondriac  region,  while  the  lower  segment 
of  the  small  intestine  with  the  ca rum  takes  up  a  position  towards  the  right  hypo- 
chondriac region.  Coincident  with  this  migration  the  large  intestine  is  differentiated 

1  Arch,  fiir  Anat.  n.  Physiol.,  Supplement  Bd.,  1897. 


DEVELOPMENT  OF  THE  ALIMENTARY  TRACT. 


1699 


FIG. 


M33- 


into  a  descending  and  a  transverse  colon,  the  former  being  the  upper  part  of  the  vertical 
limb  of  the  original  dorsal  flexure  lying  below  the  stomach.  This  flexure  indicates 
the  division  between  the  descending  and  transverse  colon,  since  the  latter  corresponds 
to  the  segment  in  front  of  the  bend.  Once  back  in  the  peritoneal  cavity,  the  loops, 

which  collectively  lay  in  the  sagittal 
plane  of  the  cord,  are  arranged  gen- 
erally at  right  angles  to  the  long  axis 
of  the  body,  and  the  antero-posterior 
colon  becomes  transverse  (  Mall ' ).  In 
consequence  of  these  changes  the  por- 
tion of  the  large  gut  that  lay  within  the 
cord  now  lies  obliquely  across  the  ab- 
domen in  front  of  the  duodenum,  the 
remaining  coils  of  the  small  intestine 
being  placed  below.  The  caecum, 
therefore,  occupies  a  position  beneath 
the  liver,  on  the  right  side,  as  a  slight 
dilatation  at  the  beginning  of  the 
transverse  colon.  The  caecum,  while 
gradually  increasing,  retains  this  gen- 
eral position  until  adjustment  in  the 
length  of  the  segments  of  the  large 
intestine  takes  place  shortly  after  birth. 
The  lower  part  of  the  large  gut  is 
thrown  into  a  loop  extending  across 

the  abdominal  cavity,  which  becomes  the  sigmoid  flexure,  the  latter  at  birth  including 
nearly  one-half  of  the  entire  length  of  the  colon.  After  the  fourth  month  after  birth, 
the  sigmoid  flexure  becomes  shorter  and  the  other  parts  of  the  colon  proportion- 
ately longer,  in  consequence  of  which  the  caecum  is  pushed  downward  towards  the 
right  iliac  fossa,  with  corresponding  lengthening  of  the  ascending  colon.  These  por- 
tions of  the  large  intestine,  however,  continue  to  grow  for  some  time  after  birth, 
and  it  is  not  until  the  third  year  that  they  acquire  their  definitive  relations. 

The  anomalous  arrangement  and  position  of  the  transverse  and  ascending  colon 
and  the  caecum,  not  infrequently  observed  in  the  adult,  are  usually  dependent  upon 
arrested  development,  the  large  intestine  failing  to  take  up  a  transverse  and  superior 
location,  and  hence  altering  its  relations  with  the  small  intestine. 


Reconstruction  of  intestinal  tube  and  part  of  liver  of 
human  embryo  of  17  mm.  vertex-breech  length.  (Same  em- 
bryo as  represented  in  Fig.  1436.)  77K,  hepatic  vein;  UV, 
umbilical  vein;  PV,  portal  vein;  GB,  gall-bladder;  FW, 
foramen  of  Winslow.  The  figures  in  this  and  in  the  two 
following  reconstructions  refer  to  corresponding  parts  of  the 
gut-tube,  i  being  gastro-duodenal  junction.  X  12.  (Mall.) 


FIG.   1434. 


FIG.  1435- 


Reconstruction  of  intestinal  coils  of  human  embryo 
of  28  mm.  vertex-breech  length.  Arrow  indicates  po- 
sition of  foramen  of  Winslow.  X  8.  (Mall.) 


Reconstruction  of  intestinal  coils  of  human  embryo  of 
80  mm.  vertex-breech  length.    X  2.     (Mall.) 


The  caecum,  which  first  appears  as  a  slight  lateral  diverticulum  from  the  larger 
inferior  limb  of  the  primary  U-loop  of  the  gut-tube  (Fig.  1432),  increases  in  size  until 
it  forms  a  conical  pouch,  joining  the  colon  where  the  latter  receives  the  small  in- 
testine. The  growth  of  all  parts  of  the  caecum,  however,  is  not  uniform,  since  its 

^natom.  Anzeiger,  Bd.  xvi.,  1899. 


T7oo  HUMAN   ANATOMY. 

dependent  terminal  portion  does  not  keep  pace  with  that  nearest  the  intestine.  The 
apical  segment  of  the  caecum  remains  proportionately  small,  and  persists  as  the  ver- 
miform appendix.  The  latter,  therefore,  corresponds  to  the  unexpanded  morpho- 
logical termination  of  the  caecum.  This  relation  is  evident  at  birth,  when  the  appendix 
forms  the  direct  continuation  of  the  funnel-shaped  caecum  ;  it  is  exceptionally  re- 
tained in  the  adult  as  the  foetal  type  of  caecum  occasionally  observed.  Usually  the 
caecum  continues  to  expand  with  the  colon,  the  demarcation  of  the  appendix  be- 
coming progressively  more  emphasized,  until  the  relative  size  of  the  two  tubes  com- 
monly seen  is  established.  The  usual  displacement  of  the  appendix,  so  that  it  arises 
from  the  left  and  posterior  wall  of  the  caecum,  results  from  the  later  unequal  expansion 
of  the  right  side  of  the  latter,  whereby  the  origin  of  the  appendix  is  pushed  to  the 
left. 

Differentiation  of  the  walls  of  the  intestinal  tube  begins  early  in  the  third  month 
by  the  formation  of  longitudinal  folds,  at  first  in  the  upper  part,  later  the  entire 
length  of  the  small  intestine.  These  folds  increase  in  number  and  size,  and  subse- 
quently break  up  transversely  into  areas  from  which  the  villi  are  formed.  The  latter 
first  appear  in  the  upper  part  of  the  small  intestine  in  embryos  of  about  30  mm. 
in  length  (Berry1),  and  gradually  extend  to  the  lower  segments,  the  villi  being- 
present  throughout  the  small  intestine  in  embryos  of  about  10  cm.  in  length.  Yilli 
also  exist  temporarily  in  the  large  intestine,  but  later  undergo  absorption,  so  that 
shortly  after  birth  they  have  completely  disappeared,  while  those  within  the  small 
intestine  have  greatly  increased  in  numbers  and  size.  Early  in  the  fourth  month  the 
intestinal  glands  appear  in  the  upper  part  of  the  tube  as  minute  diverticula  clothed 
with  extensions  of  the  entoblastic  lining  of  the  gut.  The  glands  of  Brunner  develop 
somewhat  later  during  the  same  month  as  outgrowths  of  the  entoblast.  During  the 
fourth  month  the  mesoblastic  stratum,  from  which  arise  all  parts  of  the  intestinal  wall 
except  the  epithelial  elements  of  the  mucosa  and  the  glands,  undergoes  differentia- 
tion into  the  muscular  and  areolar  layers  ;  by  the  close  of  the  fifth  month  all  coats 
of  the  intestine  are  well  defined. 

Differentiation  of  the  Body-Cavity. — Owing  to  the  precocious  develop- 
ment of  the  mammalian  heart,  the  latter  organ  is  formed  by  the  approximation  and 
fusion  of  two  lateral  anlages,  at  first  widely  separated,  in  consequence  of  which  union 
the  upper  part  of  the  ventral  body-wall  is  closed,  while  the  more  caudally  situated  is 
still  incomplete,  the  gut-tube  being  but  imperfectly  separated  from  the  yolk-sac. 
With  the  more  advanced  closure  of  the  ventral  body-wall  the  abdominal  cavity  is  de- 
fined. The  primary  ccelom,  according  to  His,  may  be  divided,  therefore,  into  an 
upper  and  a  lower  portion,  the  parietal  and  the  trunk-cavity  respectively.  These  spares 
communicate  on  either  side  by  an  extension  of  the  parietal  cavity,  \\\e  parietal  recess 
of  His.  The  ventral  portion  of  the  parietal  cavity,  which  from  its  earliest  appear- 
ance contains  the  heart,  becomes  the  pericardial  cavity,  and  is,  therefore,  appropri- 
ately named  the pericardial  ccelom  (Mall2).  The  upper  part  of  the  parietal  recess, 
since  it  later  contains  the  lung  and  forms  the  greater  portion  of  the  surrounding 
lung-sac,  may.  similarly  be  designated  the  pleural  ccelom.  For  a  time  the  separation 
between  the  pericardial  and  pleural  cceloms  is  imperfect,  owing  to  the  incompleteness 
of  the  postero-lateral  walls  of  the  heart-sac.  This  deficiency  is  corrected  by  tin- 
growth  and  differentiation  of  fat. pulmonary  ridge  (Mall),  a  structure  that  extends 
from  the  liver  along  the  dorsal  wall  of  the  duct  of  Cuvier  to  the  dorsal  attachment  of 
the  early  fold  suspending  the  he-art,  or  mesocardium.  Mall  has  shown  that  the  pul- 
monary ridge  grows  headward  as  the  plenro  pericardia!  membrane,  which  complet 
the  separation  between  the  heart-  and  lung-sacs,  and  later  tailward  to  form  \\\c  pleitro- 
peritoneal  membrane,  which  subsequently  aids  in  closing  the  communication  U-t \\een 
the  pleural  and  peritoneal  cavities. 

At  first,  immediately  below  the  young  heart  lies  the  wall, of  the  wide  yolk-stalk. 
embedded  within  the  mesoblastic  tissue  of  which  the  two  large  vitelline  veins  pass  in 
their  course  towards  the  lower  end  of  the  heart.  With  the  formation  of  the  body- 
wall  and  the  narrowing  of  the  yolk-stalk,  the  enlarged  vitelline  veins,  in  their  journey 
towards  the  heart,  produce  a  broad  fold  which  projects  horizontally  into  the  body- 

1  Anatom.  An/dger,   Hd.  xvii.,  1900. 

1  Johns  Hopkins  Hospital  Bulletin,  vol.  xii.,  1901  ;  Journal  of  Morphology,  vol.  xii.,  1897. 


DEVELOPMENT  OF  THE  ALIMENTARY  TRACT. 


1701 


cavity,  and  extends  from  the  ventral  wall  to  the  sinus  venosus,  its  median  part  be- 
neath the  heart  being  attached  dorsally  to  the  gut-tube,  while  its  lateral  expansions 
form  the  floor  of  the  pleural  ccelom.  This  imperfect  partition,  the  septum  trans- 
versum  of  His,  also  affords  passage  for  the  two  ducts  of  Cuvier,  formed  on  each  side 
by  the  union  of  the  primitive  jugular  and  cardinal  veins,  to  gain  the  sinus  venosus  ; 
the  septum  transversum  receives  the  hepatic  outgrowth  from  the  primitive  duodenum, 
which  soon  develops  a  conspicuous  liver-mass  within  the  substance  of  the  septum. 
The  rapid  increase  in  the  mass  of  the  developing  liver  is  attended  by  great  thicken- 
ing of  the  septum  transversum,  particularly  towards  its  dorsal  edge.  Coincidently 
with  this  augmentation,  the  septum  differentiates  into  a  thinner  upper  and  a  thicker 
lower  stratum,  the  former  constituting  the  floor  of  the  pericardial  cavity  and  sur- 
rounding the  ducts  of  Cuvier,  the  latter  enclosing  the  liver. 

FIG.   1436. 


Trachea 


Per 


Septum  transv 


Loop  of  small 

Intestine  extend- 
ing into  cord 
Vitelline  vessels"" 


Caecum 


(Esophagus 


Lung 


Communication 
between  pleural 
_£_  and  peritoneal  sacs 

_1.  Suprarenal  body 
_i  Aorta 


Wolffian  body 
Mesogastrium 

Duodenum 
Kidney 


Wolffian  duct 
Ureter 


Allantoic  duct 


Reconstruction  of  human  embryo  of  17  mm.  vertex-breech  length.    X   14-     (Mall.) 

The  subsequent  development  of  the  liver  is  attended  by  progressive,  although 
•only  partial,  separation  of  the  inferior  layer  from  the  superior  stratum  of  the  septum 
transversum,  the  latter  layer  remaining  as  the  primitive,  but  still  imperfect,  dia- 
phragm between  the  pleuro-pericardial  and  peritoneal  divisions  of  the  body-cavity. 
The  dorsal  attachment  of  the  septum  transversum,  at  first  high  in  the  cervical  region, 
gradually  recedes  tailward.  On  reaching  the  level  of  the  fourth  cervical  segment  the 
fourth  myotome  is  prolonged  into  the  upper  layer  of  the  septum  to  supply  muscular 
tissue  to  what  now  becomes  the  diaphragm.  The  latter,  however,  is  still  incomplete 
dorsally,  owing  to  the  existence  on  each  side  of  the  communication  between  the  pul- 
monary and  peritoneal  sacs.  This  opening  is  gradually  closed  by  the  backward 
growth  of  the  diaphragm  and  the  forward  and  downward  extension  of  the  pleuro- 
peritoneal  membrane  until  the  aperture  between  the  thoracic  and  abdominal  cavities 
is  effaced  and  the  diaphragm  is  complete. 


IJO2 


IIT.MAN   ANATOMY. 


Development  of  the  Peritoneum. — The  attachment  of  the  primitive  ali- 
mentary tube,  from  the  oesophagus  downward,  to  the  posterior  wall  of  the  body- 
cavity  by  means  of  a  sagittal  fold,  the  primary  mesentery,  has  already  been  noted 
(page  1697).  Likewise  the  conventional  division  of  this  duplicature  into  a  lower  part 
attached  to  the  intestines,  the  mcsenterium  commune,  and  an  upper  portion  passing  to 
the  dorsal  surface  of  the  stomach,  the  mesogastrium.  The  latter  differs  from  the 
common  mesentery  in  not  ending  at  the  ventral  border  of  the  digestive  tube,  but, 
after  enclosing  the  stomach  and  the  upper  part  of  the  duodenum,  in  continuing  for- 
ward, embracing  the  liver,  to  be  attached  to  the  ventral  body-wall.  The  portion  of 
the  duplicature  between  the  stomach  and  duodenum  and  parietes  is  known  as  the 
ventral  mesogastrium,  or  anterior  mesentery,  as  distinguished  from  the  dorsal  meso- 
gastrium behind  the  stomach.  The  ventral  mesentery  is  at  first  attached  above  to 
the  septum  transversum  and  in  front  to  the  body-wall  as  far  as  the  entrance  of  the 
umbilical  vein,  which  occupies  its  lower  free  border  as  far  as  the  liver.  As  already 

FIG.  1437. 


Vertebral  column 


Spinal  cord 


Truncus  arteriosus 


Ventricle 


Diaphragm 


Liver 


Stomach 


Omental  sac 
Greater  omentuni 


.Communication 

between   pleu-     ;  f'.iJ3| 
ral  and  perito- 
neal cavities 

Spleen 


Sexual  gland  _Lj 

Kidney  -1 

\ 

Atrophic  Wolffian  body 


Part  of  sagittal  section  of  pig  embryo  of  23  mm.,  showing  thoracic  and  abdominal  organs.     X  15. 

noted  incidentally,  the  latter  organ  during  its  development  is  almost  entirely  fre 
from  the  diaphragm  by  the  appearance  of  grooves  on  each  side  and  before  which 
cleave  the  septum  transversum  and  almost  completely  separate  the  lower  layer  con- 
taining the  liver,  the  lateral  expansion  of  which  organ  materially  aids  in  this  process 
of  delamination.  The  separation,  however,  is  not  complete,  since  the  recesses  over 
the  sides  and  top  of  the  liver  do  not  quite  meet  in  the  mid-line,  but  leave  a  sagittal 
fold  attached  above  to  the  diaphragm  and  below  to  the  supero-ventral  surface  of  the 
liver,  beyond  which  it  extends  along  the  body-wall  as  far  as  the  umbilicus.  It  is 
evident  that  this  primitive,  sickle-shaped  fold  foreshadows  the  persistent  falciform  or 
s/ts/y,  ns<nv  ligament  of  the  adult  organ,  the  lower  free  border  of  the  duplicature  en- 
closing the  umbilical  vein,  later  the  ligamentum  teres,  in  its  passage  to  the  under 
surface  of  the  liver.  The  portion  of  the  sagittal  fold  continued  from  the  liver  to  tin- 
digestive  tube  later  constitutes  the  gastro-hepuiic  or  lesser  amentum  and  contains  th 
bile-duct,  portal  vein,  and  hepatic  artery. 


DEVELOPMENT  OF  THE  ALIMENTARY  TRACT. 


1703 


In  general,  the  serous  membranes  lining  the  pleural  and  peritoneal  coeloms  rep- 
resent the  specialized  mesoblastic  layer  forming  the  immediate  boundary  of  these 
cavities.  The  peritoneum,  therefore,  covering  the  lower  surface  of  the  diaphragm 
and  certain  surfaces  of  the  liver  is  derived  from  those  portions  of  the  septum  trans- 
vt-rsum  that  constitute  the  upper  and  lower  walls  of  the  hepatic  recesses  which  are 
instrumental  in  freeing  the  liver  from  its  primary  position  within  the  septum.  The 
separation  of  the  liver  from  the  diaphragm  is  incomplete  not  only  above,  as  already 
noted,  but  also  behind  ;  consequently  the  greater  part  of  the  posterior  surface  of  the 
organ  remains  attached  to  the  posterior  body-wall  by  areolar  tissue  and  is  non-peri- 
toneal, the  remains  of  the  peripheral  portion  of  the  lower  layer  of  the  septum  trans- 
versum,  which  becomes  the  peritoneum  of  the  liver,  being  reflected  at  the  sides 
backward  as  the  coronary  ligaments. 

Coincidently  with  the  (development  of  the  liver  and  its  liberation  from  the  sep- 
tum transversum,  the  stomach  undergoes  change  in  its  axis,  which  becomes  less  vertical 
and  more  obliquely  transverse,  and  in  consequence  its  attachment  to  the  liver, 
the  primitive  gastro-hepatic  omentum,  is  drawn  towards  the  right  and  assumes  a 

FIG.  1438. 


Neural  tube 


Notochord 


Mvotome 


—Mesentery 


—Lower  limb-bud 


Umbilical  veins 
Umbilical  artery 

Body-wall  continuous  with  amr 
Transverse  section  of  rabbit  embryo  of  eleven  and  a  half  days,  showing  primitive  mesentery.     X  35. 


transverse  position  almost  at  right  angles  to  its  former  sagittal  plane.  These  altera- 
tions in  the  position  of  the  stomach  and  its  anterior  mesentery  affect  the  mesogas- 
trium,  which  becomes  elongated  and  twisted  towards  the  right  to  follow  the  stomach 
in  order  to  maintain  its  attachments  to  the  greater  curvature.  The  result  of  these 
changes  is  the  production  of  a  pocket  behind  the  stomach,  the  floor  and  left  wall  of 
which  are  the  mesogastrium,  the  roof  being  the  under  surface  of  the  liver.  This 
pocket,  the  lesser  sac  of  the  peritoneum,  communicates  with  the  remaining  part  of 
the  peritoneal  cavity  on  the  right  by  means  of  a  passage  behind  the  displaced  lesser 
or  gastro-hepatic  omentum,  the  free  border  of  the  latter  bounding  the  opening  lead- 
ing into  the  passage  or  vestibule  (page  1749).  The  opening,  at  first  large,  later 
diminishes  in  size  and  becomes  the  foramen  of  Winslow,  which  leads  from  the 
greater  peritoneal  sac  into  the  vestibule  of  the  lesser. 

Beneath  the  stomach  very  soon  appears  an  extension  of  the  pocket,  which 
pushes  out  between  the  stomach  above  and  the  transverse  colon  below.  This  protru- 
sion, the  omcntal  sac,  continues  to  grow  downward  and  forms  an  apron  which  later, 
as  the  greater  omentum,  covers  the  loops  of  the  small  intestine.  On  referring  to 
Fig.  1439,  it  is  evident  that  the  greater  omentum  at  first  comprises  a  duplicature  the 


1704  HUMAN   ANATOMY. 


anterior  and  the  posterior  fold  of  which  each  consists  of  two  serous  surfaces  enclosing 
a  thin  stratum  of  intervening  tissue  ;  there  are,  therefore,  four  serous  layers  included 
within  the  original  omental  curtain.  Tracing  the  posterior  fold  of  the  latter  upward, 
it  is  seen  to  pass  over  the  transverse  colon  and  the  mesocolon,  without  attachment, 
to  reach  the  posterior  body-wall.  On  gaining  the  latter,  the  anterior  or  inner  serous 
layer  may  be  followed  in  front  of  the  pancreas  as  the  posterior  wall  of  the  lesser' 
peritoneal  sac,  being  continued  over  the  under  surface  of  the  liver.  The  outer  or 
posterior  serous  layer  passes  behind  the  pancreas  to  reach  the  body- wall,  from  which 
it  is  reflected  to  become  continuous  with  the  upper  layer  of  the  transverse  meso- 
colon. For  a  time  these  original  foetal  relations  persist,  the  greater  omentum  being 
unattached  to  and  removable  from  the  transverse  colon  and  its  mesentery.  Later  this 
separation  is  no  longer  possible,  since  the  posterior  layer  of  the  greater  omentum  and 
the  transverse  mesocolon  and  colon  become  fused,  the  intervening  serous  surfaces  and 
space  being  obliterated  in  consequence.  Thereafter  the  peritoneal  layers  of  the 
greater  omentum  are  attached  to  and  apparently  enclose  the  large  gut,  one  passing 
as  the  upper,  the  other  as  the  lower  serous  layer  of  the  transverse  mesocolon.  In 
consequence  of  these  fusions  the  serous  surfaces  originally  behind  the  pancreas  also 
disappear,  and  the  gland  thenceforth  assumes  its  permanent,  although  secondary, 
retroperitoneal  relation.  Subsequently  the  originally  distinct  folds  constituting  the 
greater  omentum  fuse,  and  after  birth  usually  appear  as  a  single  sheet  attached  above 
to  the  greater  curvature  of  the  stomach  and  behind  and  below  to  the  transverse  colon. 

The  excessive  volume  of  the  right  half  of  the  liver  not  only  induces  the  ob- 
liquity and  rotation  of  the  stomach,  but  likewise  influences  the  disposition  of  the  in- 
testinal coils  on  their  return  from  the  umbilical  ccelom  into  the  peritoneal  cavity. 
The  duodenal  segment  necessarily  follows  the  migration  of  the  pylorus  ;  its  begin- 
ning, therefore,  lies  to  the  right,  while  the  lower  end  passes  to  the  left  with  the 
jejunum.  Since  the  most  available  space  within  the  abdomen,  to  the  left  and  below, 
is  appropriated  by  the  coils  of  the  small  intestine  which  first  return  to  the  peritoneal 
cavity,  the  most  movable  portion  of  the  elongating  large  intestine,  the  transverse 
colon,  is  displaced  upward  and  assumes  an  obliquely  transverse  position  beneath  the 
stomach  and  liver,  above  the  rapidly  increasing  volume  of  the  coils  of  the  small  gut. 
The  latter  tend  to  displace  the  descending,  later  also  the  ascending,  colon  later- 
ally and  backward.  In  consequence  of  these  influences  and  changes  the  transverse 
colon  crosses  and  lies  in  front  of  the  duodenum,  which  is  thus  pushed  against  the 
abdominal  wall.  The  serous  investment  of  the  duodenum  undergoes  obliteration 
where  such  contact  is  maintained,  and  later  occurs  chiefly  on  the  anterior  surface  of 
this  part  of  the  gut  (Fig.  1403). 

Reference  to  the  original  relation  of  the  primitive  mesentery  (Fig.  1432)  in- 
cluded between  the  limits  of  the  U-loop  shows,  the  principal  dorsal  attachment  of  the 
mesentery  to  be  the  comparatively  limited  area  along  the  body-wall  opposite  the  um- 
bilical loop.  The  intestinal  margin  of  the  mesentery,  on  the  contrary,  rapidly  expands 
to  keep  pace  with  the  increasing  length  of  the  gut-coils,  the  result  being  that  the 
mesentery  attached  to  the  upper — soon  right — limb  of  the  umbilical  loop  assumes 
more  and  more  the  form  of  a  ruffle,  towards  the  edge  of  which  ramify  the  branches 
of  the  superior  mesenteric  artery  supplying  the  small  intestine, — the  later  vasa  intes- 
tini  tenuis.  The  branches  distributed  to  the  left  or  colic  limb  of  the  U-loop  pass  to 
the  large  gut  through  a  mesentery  only  slightly  wavy.  When  the  arrangement  of 
the  intestinal  coils  takes  place,  the  small  gut  occupying  the  left  and  lower  parts 
of  the  peritoneal  cavity  and  the  large  intestine  being  reflected  upward  and  across  the 
duodenum,  twisting  or  "rotation"  takes  place  around  a  fixed  point  marking  the 
duodeno-jejunal  junction.  This  location  also  corresponds  in  general  to  the  early 
position  of  the  superior  mesenteric  artery,  the  relations  of  the  branches  of  which  are 
also  affected  by  the  rotation  of  the  mesentery,  since  thereafter  the  vessels  passing  t« 
the  coils  of  the  small  intestine  lie  on  the  left  and  those  to  the  large  gut  on  the 
right  side, — the  opposite  of  their  original  situation. 

On  assuming  its  position  in  front  of  the  duodenum,  the  attachment  of  the  trans- 
verse «"lon  is  at  first  a  limited  sagittal  one.  With  the  backward  displacement  of  the 
duodenum,  thr  mesentery  of  the  transverse  colon  also  comes  into  relation  with  the 
posterior  parietal  peritoneum  and  acquires  a  secondary  attachment  extending  cross- 


THE   LIVER. 


1705 


wise,  thus  forming  the  dorsal  connections  of  the  transverse  mesocolon  which  exist 
until  fusion  takes  place  between  this  duplicature  and  the  posterior  fold  of  the  omental 
sac.  Since  originally  all  parts  of  the  large  gut  possess  a  mesentery,,  the  descending 
colon  and  sigmoid  are  for  a  time  provided  with  a  free  mesocolon.  In  consequence 
of  the  increasing  bulk  of  the  small  intestine  the  descending  colon  is  pushed  not 
only  to  the  left,  but  also  against  the  body-wall.  The  intervening  serous  surfaces 
usually  disappear  behind  the  gut,  which  later,  therefore,  ordinarily  possesses  a  peri- 
toneal coat  only  in  front  and  at  the  sides.  In  a  considerable  number  of  cases,  how- 
ever, this  fusion  and  obliteration  do  not  take  place,  the  mesocolon,  although  displaced 
towards  the  left,  then  persisting  as  a  free  mesentery  for  this  segment  of  the  gut. 
The  fold  attached  to  the  sigmoid  for  a  time  allows  of  great  mobility  ;  subsequently 
this  is  reduced,  although  partly  retained  as  the  definite  mesosigmoid.  The  rectal 
segment  of  the  large  gut  retains  its  primary  sagittal  situation,  but  loses  the  greater 
part  of  its  peritoneal  coat,  becoming  attached  to  the  posterior  pelvic  wall  by  areolar 
tissue. 

The  ascending  colon  and  caecum,  in  their  downward  growth  towards  the  right  iliac 
fossa  from  the  hepatic  flexure,  carry  with  them  a  peritoneal  covering.     This  remains 

FIG.  1439. 

ABC 


Pgo 


Diagrams  illustrating  formation  of  greater  omentum  and  omental  sac.  A  shows  duodenum  and  pancreas  in 
mesogastrium  unattached;  in  B  these  organs  are  partly  against  posterior  abdominal  wall,  posterior  wall  of  lesser 
peritoneal  cavity  is  still  free;  in  C duodenum  and  pancreas  lie  against  posterior  abdominal  wall,  posterior  wall  of 
omental  sac  has  fused  with  transverse  mesocolon.  a,  aorta  ;  rf,  diaphragm;  /,  liver;/"/,  falciform  ligament;  uv,  um- 
bilical vein  ;  J,  stomach  ;  tc,  transverse  colon  attached  by  transverse  mesocolon  (true)  ;  si,  small  intestine  attached  by 
mesentery  (;«)  ;  />,  pancreas;  du,  duodenum;  Ips,  lesser  peritoneal  sac;  os,  omental  sac;  lo,  lesser  omentum;  go, 
greater  omentum  ;  ago  and  pgo,  its  anterior  and  posterior  layers ;  f,  fusion  between  posterior  wall  of  lesser  peri- 
toneal sac  and  transverse  mesocolon.  {After  Kollmann  and  Hertwig.} 

unattached  over  the  caecum  and  appendix,  but  forms  secondary  connections  where 
the  ascending  colon  comes  into  contact  writh  the  abdominal  wall  ;  hence  this  part  of 
the  colon  usually  possesses  a  serous  coat  only  anteriorly  and  laterally.  Sometimes, 
however,  obliteration  of  the  serous  covering  does  not  take  place,  the  ascending  colon 
being  attached  by  a  mesocolon. 

The  vermiform  appendix  being  primarily  an  outgrowth  from  the  large  gut,  since 
it  represents  the  morphological  apex  of  the  caecum,  is  completely  invested  with 
peritoneum  and  is  without  a  mesentery.  Later  the  appendicular  artery,  in  its  course 
from  the  ileo-colic  to  the  appendix,  produces  a  serous  fold  which  stretches  from  the 
left  layer  of  the  mesentery  of  the  ileum  to  the  caecum  and  appendix.  This  fold,  the 
meso-appendix,  is,  therefore,  functionally,  but  not  morphologically,  a  true  mesentery. 


THE  LIVER. 

The  liver  (hepar),  the  largest  gland  in  the  body,  is  formed  of  very  delicate  tissue 
disposed  around  the  ramifications  of  the  portal  vein.  It  is  developed  in  the  anterior 
mesentery,  its  mesoblastic  elements  having  a  common  origin  with  the  diaphragm, 


1706 


Hl'.MAX    ANATOMY. 


while  its  duct  and  glandular  elements  are  derived  from  a  sprout  from  the  duodenum  ; 
hence  the  liver,  as  are  other  glands  connected  with  the  digestive  tract,  is  an  out- 
growth and  appendage  of  the  alimentary  tube.  Its  peculiar  shape  is  chiefly  due  to 
the  pressure  of  surrounding  organs,  as  its  tissue  is  so  plastic  that  it  is  moulded  by 
them.  In  the  adult  it  becomes  firmer  from  the  increase  of  connective  tissue,  but 
under  normal  circumstances  it  is  always  very  soft,  and,  unless  hardening  agents  are 
used  before  its  removal,  collapses  into  a  flattened  cake-like  mass  affording  little 
information  as  to  its  true  form.  Indeed,  it  is  only  in  the  present  generation,  since 
the  introduction  of  adequate  methods  of  hardening  in  situ,  that  this  has  been 
learned.  The  liver  in  general  may  be  described  as  an  ovoid  mass  which  in  the  young 
foetus  nearly  fills  the  abdomen,  but  in  the  adult  has  the  appearance  of  having  had  at 
least  a  third  of  its  substance  scooped  out  from  below,  the  back  of  the  right  end  alone 
having  been  left  intact.  The  organ  is  therefore  a  thick  mass  in  the  right  hypochon- 
drium,  growing  thinner  to  the  left.  The  greatest  diameter  is  transverse  and  the 
next  vertical.  The  liver  is  usually  described  as  composed  of  five  lobes, — namely, 
the  right,  the  left,  the  lobe  of  Spigetius,  the  quadrate,  and  the  caudate.  More 
properly  it  consists  of  a  right  and  a  left  lobe,  separated  on  the  superior  surface  by 
the  falciform  ligament.  The  other  lobes  are  subdivisions  of  the  right  lobe,  the  lobe 


FIG.  1440. 


Left  layer  of  falciform 

ligament  continuous 

...with  lateral  ligament 


Union  of  right^ 
and  left  layers 
of  falciform 
ligament 


Right  lobe- 


irdiac 
impression 


-Left  lobe 


Obliterated  umbilical  vein  in  free  margin  of  falciform- 
ligament 

^Gall-blarfder 
Antero-superior  surface  of  liver  hardened  in  situ. 

of  Spigelius  being  at  the  back  and  the  other  two  below.  They  are  described  wit 
the  respective  surfaces.  The  size  varies  greatly  with  the  size  of  the  body  and  from 
many  other  causes.  The  transverse  diameter  usually  nearly  equals  that  of  the  cavity 
of  the  abdomen,  although  it  often  falls  an  inch  or  so  short  of  it.  It  may  be  given  at 
from  22-24  cm-  (8^-9^  in.).  The  greatest  vertical  dimension  or  depth  is  about 
i6cm.  (6J<£  in.);  the  antero-posterior  diameter  12—18.5  cm.  (4^4-7 Y\  in.).  On 
peculiar  form  of  liver  occasionally  met  with  shows  great  increase  of  the  right  lob 
particularly  in  the  vertical  direction,  with  a  want  of  development  of  the  left  lob 
which  is  thin  and  short  (Fig.  1456).  The  weight  is,  with  considerable  variations, 
generally  from  1450-1750  gm.,  or  approximately  from  3-3^  Ibs. ,  and  in  the  adult 
is  about  one-fortieth  of  the  body  weight.  The  specific  gravity  is  given  at  from 
1.05-1.06.  The  color  is  a  reddish  brown.  The  naked  eye  can  recognize  that  the 
surface  is  covered  with  the  outlines  of  polygons  from  1-2  mm.  in  diameter.  These 
are  the  lobules,  each  of  which  is  surrounded  by  vessels  and  ducts  in  connective  tissue, 
and  contains  in  the  middle  a  vessel,  the  beginning  of  the  system  of  the  hepatic  vein. 
Sometimes  the  centre  of  the  lobule  is  lighter  that!  the  periphery,  sometimes  the 
reverse,  depending  upon  whether  the  blood  has  stagnated  in  the  portal  or  hepatic 
system  respectively. 


THE    LIVER.  1707 

Surfaces. — In  its  natural  form,  as  shown  in  specimens  hardened  before  removal 
from  the  body,  the  liver  presents  five  surfaces.  The  superior  surface  is  in  the 
main  convex,  looking  upward  beneath  the  diaphragm.  The  anterior  surface,  directed 
forward,  is  continuous  with  the  former,  on  the  hardened  liver  a  fairly  distinct  line 
marking  the  change  of  direction  that  separates  them.  The  right  surface  faces 
towards  the  right  and  is  separated  in  a  similar  way  from  the  superior.  It  passes 
insensibly  into  the  anterior  surface.  In  a  flaccid  liver,  in  which  the  normal  form  has 
•been  lost,  these  three  surfaces  are  indistinguishable,  constituting  the  old  superior 
surface.  In  the  hardened  organ  the  three  represent  a  dome,  of  which  the  flattened 
upper  surface  is  slightly  separated  from  the  others.  The  posterior  surface  is  on  the 
back  of  the  right  lobe.  The  inferior  surface  is  moulded  over  the  organs  beneath  it. 

The  borders  are  best  described  from  the  posterior  surface  as  a  starting-point. 
The  upper  border  of  the  latter  separates  it  from  the  superior  and  right  surfaces  ;  the 
lower  border  from  the  inferior.  On  the  right  these  meet  at  a  mor°:  or  less  acute 
angle.  On  the  left  the  posterior  surface  narrows  to  a  border,  first  thick  and  then 
sharp,  which  runs  around  the  liver,  separating  first  the  upper  and  lower  surfaces  of  the 
left  lobe  and  later  the  lower  from  the  anterior  and  right  ones,  until  finally  it  reaches 
the  right  end  of  the  lower  border  of  the  posterior  surface.  Along  the  front  of  the 
liver  the  border  is  sharp  and  directed  downward,  overhanging  the  concave  lower 
surface.  A  conspicuous  incision,  the  umbilical  notch  (incisura  umbilicalis),  in  the 
anterior  border  marks  the  place  at  which  a  sickle-like  fold  of  peritoneum,  the  falci- 
form ligament,  conveying  the  obliterated  umbilical  vein,  now  the  round  ligament 
(ligamentum  teres  hepatis),  to  the  lower  surface,  reaches  the  liver.  The  falciform 
ligament  is  continued  back  between  the  top  of  the  liver  and  the  diaphragm,  and  marks 
off  on  the  anterior  and  superior  surfaces  a  large  right  lobe  and  a  small  left  one. 

The  superior  surface  (Fig.  1440)  includes  the  upper  part  of  both  lobes  and  is 
moulded  to  the  opposed  surface  of  the  diaphragm.  The  top  of  the  right  lobe  fills 
in  the  whole  of  the  space  below  the  corresponding  half  of  the  diaphragm,  but  the 
left  lobe  does  not  usually  reach  the  walls  of  the  abdomen,  unless  in  front.  It  may, 
however,  touch  the  left  wall.  Well-hardened  livers  show  a  slight  cardiac  depression 
on  the  left  lobe  beneath  the  heart.  The  posterior  border  of  the  superior  surface  is 
marked  on  the  right  lobe  by  the  reflection  of  the  peritoneum  onto  the  diaphragm 
above  the  triangular  posterior  surface,  and  on  the  left  by  the  rounded  posterior 
border  of  the  liver. 

The  right  and  anterior  surfaces  lie  against  the  diaphragm,  except  where 
the  anterior  rests  against  the  abdominal  wall  between  the  costal  arches,  and  offer 
little  for  description. 

The  posterior  surface  (Figs.  1441,  1456),  on  the  back  of  the  right  lobe,  con- 
sists of  a  triangular  non-peritoneal  area  and  of  the  lobe  of  Spigelius.  The  former, 
adherent  to  the  diaphragm,  extends  from  the  inferior  vena  cava  to  the  right,  where 
it  ends  in  the  point  formed  by  the  meeting  of  the  upper  and  lower  borders.  The 
greatest  vertical  dimension  of  the  non-peritoneal  area  is  not  over  7.5  cm.  (3  in.  ),  and 
the  transverse  not  over  12.5  cm.  (5  in.  ).  A  triangular  hollow  at  the  lower  border  of 
this  space,  just  to  the  right  of  the  vena  cava,  receives  the  right  suprarenal  capsiile, 
which  rests  also  on  the  lower  surface.  To  the  left  of  this  depression  is  a  deep  furrow 
for  the  inferior  vena  cava,  which  sometimes  at  the  top  is  converted  into  a  canal.  Still 
farther  to  the  left  is  the  lobe  of  Spigelius  (lobus  caudatus), — a  four-sided  prism  placed 
vertically  on  the  back  of  the  liver,  bounding  a  part  of  the  lesser  cavity  of  the  perito- 
neum. The  lower  end,  which  hangs  free,  is  continuous  on  the  right  with  the  caudate 
lobe  (processus  caudatus).  It  often  presents  on  the  left  of  the  lower  end  a  distinct 
tubercle,  the  tuber  papillare  (His),  which  is  by  no  means  constant.  The  Spigelian 
lobe  lies  between  the  fossa  of  the  vena  cava  on  the  right  and  the  fissure  of  the  duct  us 
venosus  on  the  left.  The  latter  joins  the  former  in  front  of  this  lobe,  just  below  the 
diaphragm,  so  that  the  lobe  ends  in  a  point  above.  It  more  or  less  encircles  the  vena 
cava,  sometimes  meeting  the  right  lobe  behind  it.  The  vena  cava  is  frequently  over- 
lapped by  a  projection  from  the  right  lobe,  and  sometimes  the  overlapping  is  done 
both  by  this  and  by  the  lobe  of  Spigelius.  The  prismatic  shape  of  the  latter  is  well 
shown  by  transverse  sections.  The  amount  of  attachment  to  the  rest  of  the  liver 
varies,  and  the  shape  of  the  lobe  with  it.  Sometimes  the  fissure  of  the  ductus 


1708 


HUMAN   ANATOMY. 


venosus  makes  but  a  small  angle  with  the  portal  fissure,  so  that  it  is  a  three-  instead 
of  a  four-sided  prism.  It  is  also  influenced  by  the  depth  of  the  fossa  for  the  vena 
cava,  at  times  being  attached  merely  by  a  line  of  tissue.  To  the  left  of  the  fissure 
of  the  ductus  venosus  the  posterior  surface  of  the  liver  is  continued  as  the  posterior 
border.  This  at  first  is  thick,  and  presents  a  rounded  cesophagcal  impression  for 
the  end  of  the  gullet  to  the  left  of  which  it  becomes  sharp. 

The  inferior  surface  (Fig.  1442)  of  the  liver  is  subdivided  by  a  system  of 
fissures  formerly  described  as  resembling  an  H.  This  description  must  be  modified 
by  recognizing  that  the  posterior  limbs  of  the  H  are  not  horizontal,  but  run  vertically 
on  the  hind  surface  of  the  liver,  and  that  the  cross-piece — the  portal  fissure — is  not 
in  the  middle,  but  very  near  the  posterior  border  of  the  inferior  surface.  The  old 
error  came  from  studying  distorted  livers  in  which  the  posterior  surface  had  flattened 
out  so  as  to  be  reckoned  a  part  of  the  inferior.  The  portal  or  transverse  fissure 
(porta  hepatis)  is  of  an  entirely  different  nature  from  the  others.  It  is  the  hilum  of 
the  organ  for  the  passage  of  the  vessels  and  ducts  ;  while  the  other  fissures  more 
properly  deserve  the  name,  being  due  to  the  pressure  of  the  gall-bladder  and  of 
vessels.  The  portal  fissure  is  from  4-5  cm.  (1^2-2  in.)  long.  It  transmits  the  por- 
tal vein,  the  hepatic  artery,  the  subdivisions  of  the  gall-duct,  the  lymphatics,  and 


Spigelian 


FlG.    1441. 
Falciform  ligament 


Fissure  for. 
ductus  venosus 


Vena  cava 


N'on-peritoneal 
surface 

Suprarenal 
vein 


Tuber  omentale 


Obliterated  umbilical  vein 

Quadrate  lobe 


Renal 
impression 


Right  lateral 

ligament 


Caudate  lobe         Gall-bladder 
Posterior  surface  of  same  liver ;  peritoneal  reflection  indicated  by  white  line. 

the  nerves,  all  enveloped  in  a  mass  of  areolar  tissue  known  as  Glissori 's  capsule. 
The  large  portal  vein  is  posterior.  The  hepatic  artery  lies  before  it  on  the  left  and 
the  hepatic  duct,  formed  by  two  chief  tributaries,  lies  before  it  on  the  right.  The 
lesser  omentum  is  attached  to  the  lips  of  the  fissure  outside  of  these  structures.  At 
its  left  end  the  portal  fissure  receives  the  umbilical  fissure,  which  runs  backward 
from  the  notch  in  the  anterior  border  and  contains  the  obliterated  umbilical  vein,  in 
the  adult  known  as  the  round  ligament.  This  fissure  is  very  often  bridged  over. 
Continuous  with  the  umbilical  fissure,  the  fissure  of  the  ductus  venosus  ascends  the 
posterior  surface,  only  a  small  part  of  it  being  on  the  inferior  aspect.  In  foetal  life  it 
contained  the  blood  channel  (ductus  rcnosus)  which  established  a  short  cut  between  the 
umbilical  vein  and  the  inferior  vena  cava  ;  after  birth  it  is  redm-ed  to  a  cord  of  fibrous 
tissue  ( ligamcntum  venosmn).  At  the  left  end  of  the  portal  fissure  the  falciform  liga- 
ment joins  the  lesser  omentum,  the  latter  being  continued  backward  in  the  fissure  of 
tin  ductus  venosus.  The  fossa  for  the  gall-bladder  (  fossa  vcsica>  fellcae)  is  a  depres- 
sion on  the  under  surface  of  the  right  lobe,  in  which  that  organ  rests.  It  may  or 
mav  not  indent  the  anterior  border.  Broad  in  front,  the  fossa  narrows  to  a  fissure 
behind  that  joins  the  right  end  of  the  portal  fissure.  The  quadrilateral  region  on  the 
under  surface  of  the  ri^ht  lobe,  bounded  by  the  portal  fissure  behind,  the  border  of 
the  liver  in  front,  the  gall-bladder  on  the  right,  and  the  umbilical  fissure  on  the  left, 


THE   LIVER.  1709 

is  the  quadrate  lobe  ( lobus  quadratus).  Behind  the  portal  fissure  the  lower  end  of  the 
lobe  of  Spigelius  appears  on  the  inferior  surface,  with  the  groove  for  the  vena  cava 
on  its  right  and  the  fissure  of  the  ductus  venosus  on  its  left.  The  caudate  lobe 
(  processus  caudatus)  is  a  rounded  ridge,  particularly  developed  in  early  life,  running 
from  the  under  side  of  the  right  lobe,  just  behind  the  right  part  of  the  portal  fissure 
and  in  front  of  the  vena  cava,  obliquely  backward  and  to  the  left  into  the  lower  end 
of  the  lobe  of  Spigelius.  A  groove  caused  by  the  hepatic  artery  separates  it  from  the 
tuber  papillare.  The  caudate  lobe  overhangs  the  foramen  of  Winslow.  In  the  adult 
it  is  sometimes  rounded,  sometimes  sharp,  and  not  always  to  be  distinguished.  The 
under  side  of  the  liver,  being  moulded  over  the  neighboring  organs,  presents  many 
irregularities  dependent  on  their  pressure.  The  posterior  part  of  the  under  side  of 
the  right  lobe  is  hollowed  into  the  renal  impression,  a  concavity  fitting  closely  over 
the  right  kidney.  The  suprarenal  capsule  rests  against  the  liver  to  the  left  of  this, 
at  the  beginning  of  the  caudate  lobe  on  the  under  surface  and  also  on  the  posterior 
surface.  The  first  part  of  the  duodenum  rests  against  and  moulds  the  under  side  of 
the  right  lobe  between  the  renal  impression  and  the  gall-bladder.  This  area  of  con- 

FIG.  1442. 

Vena  cava 
Spigelian  lobe         / 
CKsophageal  impression 


Fissure  for 
duct  us  venosus 


lateral  ligament 


Hepatic  arter 

|^P-x-     /  -pi          ,         •  _C,,lic  impression 

Common  bile-duct'  /          II 

Obliterated  umbilical  vein  /     j 

yuadrate  lobe    /  ^^^^ 

Cystic  duct 

Gall-bladder 

Inferior  and  posterior  surfaces  of  same  liver.     It  must  be  clearly  understood  that  the  Spigelian  lobe  and  vena  cava 
are  on  the  posterior  surface,  the  limit  of  the  inferior  surface  behind  being  the  transverse  fissure. 

tact  can  hardly  be  called  an  impression,  for  the  surface  here  is  slightly  convex.  In 
front  of  the  renal  impression  is  a  hollow  for  the  colon  of  very  varying  size.  It  may 
be  almost  wanting,  or  it  may  be  very  deep.  It  may  be  confined  to  the  right  part  of 
the  under  surface,  or  it  may  compress  the  front  of  the  gall-bladder  and  indent  the 
quadrate  lobe,  and  even  the  left  one.  The  under  side  of  the  right  lobe  presents 
also  one  or  more  occasional  fissures  which  seem  in  the  main  to  diverge  from  the 
right  end  of  the  portal  fissure  and  from  the  fossa  for  the  gall-bladder.  They  are 
more  common  in  the  foetus,  and  some  of  them  occur  more  or  less  frequently  in 
anthropoid  apes.1  The  under  side  of  the  left  lobe  is  in  general  concave,  resting 
against  the  fundus  and  anterior  wall  of  the  stomach.  Near  the  posterior  part  of 
the  umbilical  fissure  on  the  left  lobe  is  a  rounded  prominence, — tuber  omeniale, — due 
to  the  growth  of  the  liver  against  the  non-resisting  lesser  omentum. 

The  Blood-Vessels. — The  portal  vein,  some  15  mm.  or  more  in  diameter, 
divides  into  a  right  and  a  left  branch,  10  mm.  or  over  in  diameter,  of  which  the  right 
is  a  little  the  larger  and  shorter.     From  the  right  end  of  the  transverse  fissure  it  runs 
1  Thomson  :  Journal  of  Anatomy  and  Physiology,  vol.  xxxiii.,  1899. 


ryio 


HUMAN    ANATOMY. 


backward  in  a  curve  to  the  right  of  the  vena  cava,  keeping  in  the  lower  part  of  the 
liver  and  giving  off  successively  a  series  of  large  branches  to  the  front  and  right  of 
the  organ.  Smaller  branches  arise  from  the  sides  of  these.  The  right  primary 
division  soon  gives  off  a  large  superior  branch  almost  equal  to  itself,  which  describes 
a  similar  but  smaller  curve  at  a  higher  level.  The  general  course  of  the  left  subdi- 
vision is  towards  the  posterior  angle  of  the  organ,  giving  branches  chiefly  from  its 
anterior  side,  and  also  one  that  supplies  the  greater  part  of  the  quadrate  lobe.  The 
lobe  of  Spigelius  generally  receives  a  chief  branch  near  its  lower  end,  which  runs 
upward  within  it.  This  branch  is  most  often  from  the  left  subdivision,  but  it  may 
be  from  the  right,  or  from  the  vessel  directly  behind  the  end  of  the  portal  vein. 
There  are  several  systems  of  so-called  accessory  portal  veins  around  the  liver  in  the 
lesser  omentum  near  the  gall-bladder,  about  the  diaphragm,  and,  most  important, 
in  the  falciform  ligament,  where  the  par-umbilical  veins  communicate  with  veins  of 
the  integument  of  the  abdominal  walls.  These  accessory  vessels,  small  and  incon- 
spicuous under  normal  conditions,  may  become  enlarged  and  important  channels 


FIG.  1443- 


;\ 


Portions  of  inferior  and  posterior  surfaces  of  liver  have  been  removed  to  show  injected  blood-vessels  and  bile- 
ducts.  Vena  cava  is  somewhat  displaced  forward,  its  course  being  more  venical  when  supported  on  posterior  sur- 
face. Large  upper  branch  of  right  division  of  portal  vein  is  hidden  by  liver-substance.  Portal  vein  ami  branches 
are  purple ;  hepatic  artery,  red ;  hepatic  veins  and  vena  cava,  blue ;  bile-ducts,  yellow,  uv,  obliterated  umbilical  vein  ; 
vc,  inferior  vena  cava. 


for  the  return  of  the  blood  conveyed  by  the  portal  vein  when  the  hepatic  circula- 
tion is  obstructed.  Under  such  conditions  the  blood  finds  its  way  from  the  portal 
vein  into  the  accessory  veins  and  by  the  anastomoses  of  the  latter  into  the  general 
circulation. 

The  hepatic  veins  carrying  off  the  blood  from  the  liver  arise  as  the  intra- 
lobular  veins,  which  empty  into  the  siiblobular,  which  join  larger  vessels  conver^in^ 
towards  the  vena  cava.  At  first  the  general  direction  of  the  small  branches  is  paral- 
lel to  that  of  those  of  the  portal  system  of  the  same  size  ;  but  the  hepatic  branches 
always  travel  alone.  The  direction  of  the  large  branches  as  they  near  the  vena  cava 
is  at  right  angles  to  that  of  the  portal.  The  arrangement  of  the  hepatic  branches  is 
in  the  main  like  that  of  the  portal,  but  near  the  edge  of  the  liver  we  find  more 
instances  of  the  union  of  two  rather  small  trunks  meeting  symmetrically  like  the 
arms  of  a  Y.  The  main  trunks  of  the  right  lobe  run  between  the  upper  and  lower 
branches  of  the  portal.  The  upper  end  of  the  vena  cava  is  considerably  enlarged, 
and  immediately  below  the  diaphragm  receives  two  large  hepatic  veins,  a  right  and  a 
left  one,  from  15  to  20  mm.  in  diameter.  The  latter  is  formed  by  two  large  branches 
that  unite  just  before  its  end.  Many  small  veins  open  into  the  vena  cava  at  different 


THE   LIVER.  1711 

points  along  its  course  in  the  groove  on  the  posterior  surface  of  the  liver,  several 
coming  from  the  Spigelian  lobe.  Sometimes  quite  a  large  branch  from  the  right 
lobe  opens  at  a  low  level.  There  is  no  such  thing  as  an  hepatic  vein  in  the  adult 
considered  as  an  isolated  structure.  The  ramifications  of  the  portal  and  hepatic 
veins  are  inextricably  mingled  throughout,  but  in  the  main  the  branches  of  the  latter 
lie  above  those  of  the  former  (Fig.  1443). 

The  hepatic  artery,  the  nutritive  vessel  of  the  liver,  divides  into  two 
branches  which,  together  with  the  bile-duct,  accompany  the  portal  vein,  the  two  arte- 
ries generally  being  on  the  same  side  of  the  vein.  The  hepatic  artery  gives  off  so 
many  branches  in  its  course  as  to  be  almost  or  quite  of  capillary  size  when  it  reaches 
the  twigs  of  the  portal  vein  that  break  up  into  the  intralobular  net-work.  The  blood 
conveyed  by  the  hepatic  artery  is  distributed  by  three  sets  of  branches,  the  capsular, 
the  vascular,  and  the  lobular.  The  first  ramify  within  the  connective-tissue  envelope 
of  the  organ  and  anastomose  with  branches  from  the  internal  mammary,  phrenic,  cystic, 
suprarenal,  and  sometimes  right  renal.  The  second  supply  the  structures  between 
the  lobules,  especially  the  walls  of  the  ramifications  of  the  portal  vein  and  the  bile- 
ducts.  The  third  are  small  in  size,  and  accompany  the  intralobular  branches  of  the 
portal  vein  for  a  short  distance  within  the  lobule.  There  is  no  special  system  of 
veins  to  return  the  blood  carried  by  the  hepatic  artery  to  the  venous  trunks  outside 
the  organ,  the  minute  veins  collecting  the  blood  from  the  capsular  and  vascular  sets 
being  tributaries  usually  of  the  smaller  branches  of  the  portal  vein.  •  The  blood 
passing  through  the  lobular  arterioles  is  emptied  into  the  intralobular  capillary  net- 
work. 

The  lymphatics  of  the  liver  constitute  a  superficial  and  a  deep  set,  the  former 
lying  beneath  the  peritoneum,  the  latter  within  the  deeper  interlobular  connective 
tissue.  The  superficial  lymphatics  of  the  superior  surface  are  arranged  as  three 
groups,  posterior,  anterior,  and  superior.  The  posterior  group  forms  a  right  trunk 
which  passes  from  the  right  triangular  ligament  across  the  right  crus  of  the  dia- 
phragm to  the  cceliac  lymph-nodes.  Middle  trunks — from  five  to  seven  in  number — 
accompany  the  inferior  vena  cava  to  end  in  diaphragmatic  nodes  around  the  vein. 
Left  trunks  traverse  the  left  triangular  ligament  and  terminate  in  the  cesophageal 
nodes  surrounding  the  lower  end  of  the  gullet.  The  anterior  group  passes  in  the  op- 
posite direction  to  those  just  described  and,  crossing  the  anterior  border  of  the  liver, 
empties  into  the  hepatic  lymph-nodes  within  the  lesser  omentum.  The  superior 
group,  the  most  important  of  those  of  the  upper  surface,  ascends  within  the  falciform 
ligament.  A  number  of  anastomosing  vessels  form  a  posterior  trunk  which  crosses 
the  inferior  vena  cava  and  enters  the  thorax  with  the  latter,  to  end  in  the  lymph-nodes 
around  the  vena  cava.  An  anterior  trunk  accompanies  the  round  ligament  to  the  infe- 
rior surface  and  ends  in  the  hepatic  nodes  at  the  hilum.  Numerous  middle  trunks 
form  vessels  which  pierce  the  diaphragm,  to  end  in  the  anterior  mediastinal  nodes, 
becoming  tributaries  to  the  right  lymphatic  duct.  The  superficial  lymphatics  of  the 
inferior  surface  include,  on  the  right  lobe,  a  posterior  group,  accompanying  the  vena 
cava  into  the  thoracic  cavity,  to  end  in  nodes  around  that  vein,  a  middle  group  passing 
to  the  hepatic  nodes  around  the  cystic  duct,  and  an  anterior  group  terminating  in  the 
same  nodes  as  the  preceding.  On  the  left  lobe  the  vessels  pass  to  the  nodes  of  the 
hilum  and  about  the  hepatic  artery.  The  lymphatics  of  the  Spigelian  lobe  pass  partly 
to  the  hilum  nodes  and  partly  to  those  surrounding  the  thoracic  segment  of  the  infe- 
rior vena  cava.  Communications  exist  between  the  superficial  and  deep  lymphatics. 

The  deep  lymphatics  include  two  distinct  groups,  the  one  following  the  branches 
of  the  portal  vein,  the  other  accompanying  the  hepatic  veins.  The  first  descends 
within  the  capsule  of  Glisson  in  company  with  the  portal  vein  and  other  interlobular 
vessels.  On  emerging  at  the  hilum,  the  fifteen  to  eighteen  trunks,  arranged  as 
two  groups  at  the  ends  of  the  transverse  fissure,  join  the  hepatic  nodes.  The 
lymphatics  which  accompany  the  hepatic  veins  form  a  plexus  surrounding  the 
blood-vessels  and  proceed  towards  the  vena  cava,  with  which  they  pass  through 
the  diaphragm  to  enter  the  nodes  lying  immediately  above  the  caval  opening. 

The  nerves  are  chiefly  derived  from  the  solar  plexus  of  the  sympathetic  with 
some  fibres  from  the  left  pneumogastric  which  reach  the  liver  by  passing  from  the 
anterior  surface  of  the  stomach  between  the  layers  of  the  lesser  omentum.  The 


1712 


HUMAN    ANATOMY. 


sympathetic  fibres  accompany  the  hepatic  artery,  forming  the  hepatic  plexus,  to 
the  transverse  fissure,  where,  together  with  the  fibres  from  the  vagus,  they  pass  into 
the  liver  along  with  the  interlobular  vessels,  to  the  walls  of  which  they  are  chiefly 
distributed.  According  to  Berkley,  the  interlobular  plexuses  give  off  fine  intralob- 
ular  twigs  which  terminate  between  the  liver-cells. 

STRUCTURE    OF    THE    LIVER. 

In  its  fundamental  arrangement  the  liver  corresponds  to  a  modified  tubular 
gland,  the  system  of  excretory  ducts  of  which  is  an  outgrowth  from  the  primary 
gut-tube.  Early  in  foetal  life,  however,  the  terminal  divisions  of  the  tubules  unite 
to  form  net-works,  after  which  the  tubular  character  of  the  liver  becomes  progressively 

FIG.   1444. 


Portal  vein 
Blood-capillaries 


Central  vein 


Blood-capillaries 

Portal  vein 

Hepatic  artery 

Bile-vessel 


Bile-vessel 
Blood-capillary 

Hepatic  cords 
Bile-vessel 


Portal  vein 


Bile-capillaries 


Blood-capillaries 


Portal  vein 


Suhlobular  branch  of  hepatic  vein 


Diagram  of  hepMtic  lobule ;  portion-;  of  figure  represent  median  longitudinal  section  of  lobule  ;  parts  of  transv 
sections  also  shown.     Branches  of  portal  vein  :ue  purple  ;  of  hepatic  artery,  red ;  of  bile-ducts,  yellow.     Intralobular 
bile-capillaries  are  black. 

more  masked  by  the  intergrowth  of  the  cell-cords  and  the  large  veins.  Among 
some  of  the  lower  vertebrates,  as  in  certain  vermiform  fishes  or  cyclostomes 
(Afvxtne),  the  primary  tubular  arrangement  is  retained. 

The  glandular  tissue  composing  the  liver  is  subdivided  into  small  cylindrical 
masses,  the  lobules,    by  the  connective  tissue  which,  in  continuation  of  the  fibrous 


STRUCTURE   OF   THE   LIVER. 


1713 


envelope,  or  capsule,  investing  the  exterior,  at  the  transverse  fissure  enters  the 
organ  and  accompanies  the  interlobular  vessels  in  their  ramifications  as  the  capsule 
of  Glisson  (capsula  tibrosa).  The  distinctness  with  which  the  lobules  are  defined 
depends  upon  the  amount  of  this  interlobular  tissue.  In  certain  animals,  notably 
in  the  hog,  this  is  great,  the  lobules  being  completely  surrounded  and  plainly  dis- 
tinguishable as  sharply  marked  polygonal  areas.  In  the  human  liver,  on  the  con- 
trary, the  interlobular  connective  tissue  is  present  in  small  amount,  the  lobules,  in 
consequence,  being  poorly  defined  and  uncertain  in  outline. 

The  Lobular  Blood-Vessels. — Since  the  arrangement  of  the  blood-vessels 
is  the  salient  feature  in  the  architecture  of  the  fully  formed  lobule,  it  is  desirable  to 
study  the  vascular  distribution  before  considering  the  disposition  of  the  hepatic  cells. 
As  already  described,  the  branches  of  the  portal  vein,  the  functional  blood-vessel 
of  the  organ,  ramify  within  the  capsule  of  Glisson  and  encircle  the  periphery  of  the 
lobule  ;  inasmuch  as  these  vessels  supply  the  divisions  of  glandular  tissue  with 
blood  for  the  performance  of  their  secretory  role,  they  correspond  with  the  inter- 
lobular arterioles  of  ordinary  glands. 

Numerous  minute  branches  are  given  off  from  the  interlobular  ramifications  of 
the  portal  vein  which  enter  the  periphery  of  the  adjacent  lobules  and  break  up  into 


Central  vein 


"Hi 

Section  of  liver  injected  from  hepatic  vein,  showing  intralobular  capillary  net-work.     X  100. 

the  intralobular  capillary  net-work.  The  disposition  of  the  latter  is  in  general 
radial,  the  capillaries  converging  towards  the  middle  of  the  lobule,  where  they  join 
to  form  the  central  or  intralobular  vein,  the  beginning  of  the  system  of  the  hepatic 
veins  by  which  the  blood  passing  into  the  lobules  is  eventually  carried  into  the 
inferior  vena  cava.  The  general  course  of  the  central  vein  corresponds  to  the  long 
axis  of  the  lobule  (Fig.  1444),  and  hence  in  cross-sections  of  the  latter  the  vein 
appears  as  a  transversely  cut  canal  towards  which  the  capillary  vessels  converge 
(Fig.  1445). 

The  capillary  net-work  within  the  lobule  is  composed  of  channels  with  a 
diameter  usually  of  about  .010  mm.  ;  the  widest  capillaries — some  .020  mm.  in 
diameter — are  found  in  the  immediate  vicinity  of  the  afferent  and  efferent  veins, 
the  narrowest  occupying  the  intermediate  area.  The  meshes  of  the  vascular  net- 
work vary  from  .OI5-.O4O  mm.  in  their  greatest  dimension,  those  at  the  periph- 
ery being  broader  and  more  rounded,  while  those  near  the  centre  are  narrower 
and  more  elongated.  The  central  vein  occupies  the  long  axis  of  the  lobule  and 
increases  in  size  as  it  proceeds  towards  the  base  of  the  lobule,  as  the  side  of  the 
latter  through  which  the  vein  escapes  is  termed.  It  begins  usually  about  midway 

108 


I7H 


HUMAN    ANATOMY. 


between  the  base  and  the  opposite  side  of  the  lobule,  by  the  confluence  of  the  capil- 
laries, which,  after  the  central  vein  is  formed,  open  directly  into  the  latter  at 
lower  planes.  In  those  lobules  which  form  part  of  the  exterior  of  the  liver  the 
central  vein  ascends  almost  to  the  free  surface  ;  otherwise  its  commencement  is 
separated  from  the  periphery  by  about  one-half  the  thickness  of  the  lobule.  Im- 
mediately on  emerging  from  the  lobule  the  central  vessel  opens  into  the  sublobular 
vein,  which  runs  generally  at  right  angles  to  its  intralobular  tubularies  and  along  and 
beneath  the  bases  of  the  lobules,  the  outlines  of  which  are  often  seen  through  the 
walls  of  the  vein.  The  channels  for  the  sublobular  veins  are  thus  surrounded  by 
the  bases  of  the  lobules,  a  single  central  vein  returning  the  blood  from  each.  The 


Hepatic  artery 

Portal  vein 

Bile-duct 


Centra]  (intra- 
lobular) vein 


Interlobular 
connective 
tissue 


Section  of  uninjected  liver,  showing  Ki-iu-ral  arrangement  of  lobules,  interlolmlui  and  intralobular  vessels.     X  120. 

sublobular  veins  join  to  form  larger  vessels,  which   in  turn  unite  and  constitute  the 
branches  of  the  hepatic  veins. 

The  Liver-Cells. — The  meshes  of  the  interlobular  capillary  net-work  are  oc- 
cupied by  the  hepatic  cells,  the  bile-capillaries,  and  a  meagre  amount  of  connective 
tissue.  The  cells  are  arranged  as  cords  or  trabecuke  which  conform  in  their  general 
disposition  to  the  intercapillary  spaces,  which  they  completely  fill.  In  a  sense,  the 
entire  lobule  consists  of  a  solid  mass  of  hepatic  cells  elaborately  tunnelled  by  the 
radially  coursing  capillaries  and  their  short  anastomosing  branches,  the  proportion 
of  the  space  occupied  l>v  the'  vascular  channels  to  that  filled  by  the  cells  being  ap- 
proximately as  one  to  three.  When  isolated,  the  liver-cells  present  a  polygonal 


STRUCTURE   OF   THE   LIVER.  1715 

outline  and  measure  usually  from  .01  5-.  025  mm.  in  their  longest  dimension.  Each 
cell  comes  into  contact  with  from  six  to  nine  other  elements,  the  surfaces  of  contact 
being-  plane  from  mutual  pressure.  Always  one  side,  often  more  than  one,  exhibits 
a  shallow  depression  which  indicates  the  surface  of  former  contact  with  a  capillary 
and  emphasizes  the  intimate  relation  existing  between  the  blood-vessels  and  the  cells. 
The  latter  lie  against  at  least  one  capillary  and  sometimes  several,  this  relation  being 
dependent  upon  the  size  of  the  blood-channels.  The  larger  the  latter,  as  at  the 
periphery  and  near  the  centre  of  the  lobule,  the  greater  the  number  of  cells  with 
only  one  or  two  capillary  facets  ;  conversely,  where  the  capillaries  are  of  small 
diameter,  the  cells  come  into  contact  with  three  or  four.  The  liver-cell  consists  of 
finely  granular  protoplasm  which  sometimes  exhibits  a  differentiation  into  an  outer 
and  an  inner  zone.  It  is  without  a  cell-membrane,  although  the  peripheral  zone 
of  its  cytoplasm  is  condensed,  especially  when  it  forms  part  of  the  wall  of  the  bile- 
canaliculi.  The  nucleus,  of  vesicular  form  and  from  .006-.  008  mm.  in  diameter, 
contains  a  small  amount  of  chromatin  and  usually  a  nucleolus.  Occasional  cells 
are  conspicuous  on  account  of  their  large  size,  as  well  as  the  unusual  diameter  of 

FIG.   1447- 


-         . 


IS, 


Section  of  uninjected  liver,  showing  cords  of  hepatic  cells  between  capillary  blood-vesseis.     v  450. 

their  nucleus.  Such  cells,  according  to  Reinke,1  undergo  direct  division  and  pro- 
duce the  double  nucleated  elements  constantly  encountered  in  sections  of  normal 
liver.  Centrosomes  have  also  been  observed  in  resting  hepatic  cells.  Particles  of 
glycogen,  minute  oil  droplets,  and  granules  of  bile-pigment  are  more  or  less  constant 
constituents  of  these  elements.  The  fat-containing  cells  are  most  numerous  at  the 
periphery  of  the  lobule,  those  enclosing  pigment  particles  near  the  centre. 

The  Bile-Capillaries. — These  minute  canals,  representing  the  lumena  of 
ordinary  tubular  glands,  form  a  net-work  of  intercommunicating  channels  throughout 
the  lobule  closely  related  to  the  liver-cells.  Whereas  in  the  usual  arrangement  a 
single  surface  of  several  gland-cells  borders  the  lumen,  in  the  exceptional  case  of  the 
liver  the  excretory  channels  are  bounded  by  the  opposed  surfaces  of  only  two  cells, 
the  bile-capillary  occupying  but  a  small  part  of  the  surfaces,  on  each  of  which  it 
models  a  narrow,  centrally  situated  groove.  Moreover,  not  only  a  single  surface 
of  the  hepatic  cell  takes  part  in  bounding  the  canaliculi,  but  the  latter  are  found 
between  all  surfaces  where  two  liver-cells  are  directly  in  contact,  so  that  each  hepatic 
element  comes  into  direct  relation  with  a  number  of  bile-capillaries.  The  latter, 
1  Verhandlung  d.  Anatom.  Gesellschaft,  1898. 


HUMAN    ANATOMY. 


however,  never  lie  on  the  narrow  sides  of  the  liver-cells  opposed  to  the  blood- 
vessels, the  bile-canal  never  separating  the  blood-capillary  from  the  cell.  While  the 
predominating  direction  of  the  bile-capillaries  is  radial  and  corresponds  to  the 


Blood-capillary 


Bile-capillary 


Liver-cell 


FIG.  1449. 


Section  of  liver  in  which  both  blood-  and  bile-capillaries  have  been  injected  ;  the  latter  surround  the  individual  liver- 
cells.     X  3°°- 

similar  general  disposition  of  the  cylinders  or  leaflets  of  hepatic  tissue,  the  radial 
arrangement  is  converted  into  a  net-work  by  the  numerous  cross- branches.  The 
resulting  meshes  correspond  in  size  with  the  individual  liver-cells,  which,  in  appro- 
priate sections,  often  appear  almost  com- 
pletely surrounded  by  the  bile-capillaries. 
The  latter  possess  no  walls  other  than  the 
substance  of  the  liver-cells  between  which 
they  lie.  The  diameter  of  the  bile-capil- 
laries, from  .OOI-.OO2  mm.,  remains  prac- 
tically the  same  throughout  the  lobule  until 
the  canaliculi  reach  the  extreme  periphery. 
At  this  point  the  liver-cells  abruptly  dimin- 
ish in  height  and  are  transformed  into  the 
low  cuboidal  cells  lining  the  excretory  tubes 
that  pass  from  the  lobule  into  the  surround- 
ing connective  tissue  to  become  tributaries 
to  the  larger  interlobular  bile-ducts. 

The  ultimate  relations  between  the 
bile-capillaries  and  the  liver-cells  is  still  a 
subject  of  discussion.  Based  upon  the  evi- 
dence supplied  by  injections  and  silver 
impregnations,  it  is  believed  by  some 
(Kupffer,  R.  Krause,  and  others)  that  ex- 
tensionsof  the  bile- capillaries  normally  exist 
within  the  substance  of  the  cells,  thus  form- 
ing intracellular  secretion  catialiculi.  The  latter  are  sometimes  pictured  as  ending  in 
connection  with  minute  dilatations  or  accretion  vacuolcs.  It  is  by  no  means  certain 
that  such  appearances  are  not  artifacts,  or  at  least  due  to  changes  after  death  of 


Section  of   liver  treated  by  Goljji   silver   meth< 
showing  part  of   intralobular   m-t  \voik   of   bili-capil- 
l:u  U-s.     X  200. 


STRUCTURE    OF   THE    LIVER. 


1717 


FIG.   1450. 


the  cells.  The  secretion  vacuoles,  probably  due  to  the  coalescence  of  minute 
drops  of  bile,  exist  only  as  transient  details,  and  cannot  be  regarded  as  constant 
features  of  the  hepatic  cells.  Holmgren1  asserts  the  existence  of  "  juice-canaliculi" 

within  the  liver-cells  in  addition  to 
and  independent  of  the  intracellular 
secretion  channels.  Schiifer2  has 
described  nutritive  channels  within 
the  liver-cells  which  communicate 
with  the  blood-capillaries. 

The  intralobular  connec- 
tive tissue,  or  reticulum,  consists 
of  delicate  prolongations  of  the 
fibrous  tissue  of  Glisson's  capsule 
which  unite  the  blood-capillaries  and 
cords  of  liver-cells.  This  tissue,  in 
general  meagre  in  amount,  forms 
a  delicate  reticulum  extending  be- 
tween the  blood-channels  and  the 
glandular  elements  throughout  the 
lobule,  and  connects  the  peripheral 
fibrous  tissue  with  the  perivascular 
tissue  that  exists  around  the  central 
vein  in  considerable  quantity.  In 
addition  to  the  delicate  fibres  of  the 
intralobular  reticulum,  the  perivas- 
cular tissue  contains  lymph-spaces 
and  connective-tissue  elements,  the 

Artificially  digested  section  of  liver,  showing  supporting  inter-       Cells    Of     Knpjjer.          I  he     latter     are 

lobuiar  fibrous  tissue  and  intralobular  reticulum.    x  230.          small  spindle  or  stellate  and  lie  in 

close  relation  with  the  blood-vessels, 
their  processes  penetrating  for  a  limited  distance  between  the  adjacent  liver-cells. 

The  interlobular  bile-ducts,  which  receive  the  biliary  canals  that  pierce  the 
periphery  of  the  lobule  as  the  outlets  of  the  intralobular  net-work,   accompany  the 

FIG.  1451. 


Fibrous  tissue 


Reticulum 


Portal  vein 


Bile-duct 
Hepatic  artery 


Interlobular  connective 
tissue 


Hepatic  ceils 


Section  of  liver,  showing  interlobular  tissue  and  vessels.     X  160. 

branches   of   the  portal  vein  and  the  hepatic  artery  within  the  capsule  of  Glisson. 

These  ducts,  from  .030-.  050  mm.  in  diameter,  constitute  a  net-work  over  the  exterior 

1  Anatomischer  Anzeiger,  Bd.  xxii.,  No.  i,  1902.  2  Ibid.,  Bd.  xxi.,  No.  i,  1901. 


iyi8 


HUMAN   ANATOMY. 


surface  of  the  lobule.  They  consist  of  a  dense  fibre-elastic  coat  lined  with  cylindri- 
cal epithelium,  some  .020  mm.  thick,  which  latter  is  continued  into  the  low  cuboidal 
or  flattened  cells  that  form  the  lining  of  the  excretory  channels  connecting  the  intra- 
lobular  net-work  of  bile-capillaries  with  the  bile-ducts.  Beginning  as  the  small 
vessels  that  surround  the  lobules,  they  become  tributary  to  the  larger  bile-ducts, 
which  increase  in  diameter  as  they  approach  the  transverse  fissure.  In  the  vicinity 
of  the  latter  these  trunks  join  into  the  two  main  lobular  ducts  forming  the  hepatic 
duct.  The  largest  bile-vessels  possess  bundles  of  unstriped  muscle  which  in  the 
hepatic  duct  are  arranged  principally  as  a  longitudinal  layer,  supplemented  by  cir- 
cular and  oblique  bundles  (Hendrickson). 


Gall-bladder 


Hepatic  duct 
Cystic  duct 


THE   BILIARY   APPARATUS. 

In  addition  to  the  small  interlobular  bile-vessels  already  described,  the  system 
of  canals  receiving  and  conveying  the  secretion  of  the  liver  to  the  intestinal  tract 
consists  of  the  hepatic  duct,  the  excretory  tube  of  the  organ  ;  the  gall-bladder,  a  res- 
ervoir in  which  the  bile  ac- 

FIG.  1452.  cumulates    during    intervals 

of  digestion ;  the  cystic  duct, 
the  continuation  of  the  bile- 
sac  opening  into  the  side  of 
the  hepatic  duct ;  and  the 
common  bile-duct,  which,  al- 
though formed  by  the  union 
of  the  other  two,  is  in  struc- 
ture and  direction  really  the 
continuation  of  the  hepatic 
duct. 

The  hepatic  duct  (due- 
tus  hepaticus)  is  formed  be- 
low the  hilum  by  the  union 
of  its  two — a  right  and  a 
left — chief  tributaries.  The 
latter  issue  from  the  portal 
fissure,  one  on  each  side, 
and  generally  unite  with  the 
hepatic  duct  nearly  in  the 
shape  of  a  T,  the  last-named 
canal  forming  almost  a  right 
angle  with  each  of  its  tribu- 
taries. Tracing  the  chief 
ducts  into  the  liver,  the  left 
branch  runs  at  first  in  front 
of  the  left  division  of  the 
portal  vein,  while  the  right 
one  usually  crosses  it.  We 
have  seen  the  hepatic  duct 
issue  from  the  right  lobe 
and,  forming  a  loop  in  the 
fissure,  leave  it  with  the  K  ft 
division  of  the  portal  vein, 
receiving  branches  along  its 
convexity  from  the  various  parts  of  the  liver.  Sometimes  the  chief  ducts  are  longer 
than  usual,  and  meet  to  form  the  hepatic  duct  at  an  acute  angle  farther  from' tlu 
liver.  The  length  of  the  hepatic  duct,  therefore,  varies  with  these  details,  proba- 
bly being  usually  from  20-40  mm.  (^-i^  in.),  with  a  diameter  of  from  4-6  mm. 
It  lies  in  the  gastro-hepatic  omentum,  in  front  of  the  portal  vein  and  to  the  right 
of  the  hepatic  artery,  and  inclines  downward  to  the  inner  side  of  the  second  part 
of  the  duodenum,  resting  previously  on  the  top  of  the  first  part.  The  hepatic  duct 


Vena  cava 
Probe  in  foramen 
of  Winslow 


Portions  of  liver,  duodenum,  and  pancreas,  showing  biliary  and  pancreatic 
ducts;  head  of  pain n-as  turned  back. 


THE   BILIARY   APPARATUS. 


1719 


ends  at  the  point  at  which  the  cystic  duct  opens  into  it.  The  duct  is  lined  with 
mucous  membrane,  covered  with  simple  columnar  epithelium,  and  presents  many 
minute  pits,  into  which  open  the  orifices  of  numerous  small  tubular  glands.  Its 
walls  consist  of  fibro-elastic  connective  tissue  and  unstriped  muscular  fibres.  The 
latter,  neither  numerous  nor  separated  into  a  distinct  layer,  are  grouped  for  the 
most  part  into  longitudinal  bundles,  but  there  are  also  circular  and  oblique  ones.1 

The  gall-bladder  (vesica  fellea)  is  a  pear-shaped  receptacle  for  the  bile,  rest- 
ing in  its  fossa  on  the  under  side  of  the  liver,  with  the  large  end  forward.  The 
long  axis  runs  also  somewhat  inward.  The  length  is  from  8— 10  cm.  (3^—4  in.) 
and  the  capacity  some  50  c.c.  (about  i%  fl.  oz. ).  It  narrows  to  a  point  where 
it  usually  bends  to  the  left  and  ends  in  the  cystic  duct  without  definite  external 
demarcation.  The  bent  terminal  portion,  or  neck,  about  i  cm.  long,  is  more  or 
less  closely  bound  beneath  the  peritoneum  to  the  side  of  the  gall-bladder,  so  that 
before  this  is  separated  it  sometimes  looks  as  if  the  duct  arose  from  the  side  of 
the  latter. 

The  fundus  of  the  gall-bladder  lies  near  the  end  of  the  ninth  right  costal  carti- 
lage. The  neck  is  at  the  right  end  of  the  portal  fissure.  Anteriorly  the  bladder 
rests  on  the  transverse  colon,  behind  which  it  lies  first  to  the  right  of  and  then  above 
the  first  part  of  the  duodenum. 


FIG.  1453- 


ll-bladder 


Surface  view  of  portion  of  mucous  membrane  of  gall- 
bladder.   X  12. 


Portion  of  gall-bladder  and  biliary 
passages  laid  open,  showing  surface  of 
mucous  membrane.  Natural  size. 


The  wall  of  the  gall-bladder  is  very  resistant,  being  composed  of  a  mixture  of 
fibrous  tissue  and  of  unstriped  muscular  fibres.  Most  of  the  latter  are  disposed  circu- 
larly, but  oblique  and  longitudinal  ones  are  interwoven.  The  fibro-muscular  tunic  is 
lined  by  a  layer  of  mucous  membrane  which  is  very  adherent  to  it.  The  mucous 
membrane,  covered  with  simple  columnar  epithelium,  presents  slightly  raised  ridges 
marking  off  a  net-work  of  small  irregular  spaces  some  5  mm.  in  diameter.  The 
small  bifurcated  tubular  glands  are  few  and  may  be  wanting.  The  bent  portion,  or 
neck,  is  separated  from  the  bladder  by  a  strongly  raised  fold.  There  are,  or  may 
be,  one  or  two  smaller  folds  within  the  neck,  the  separation  of  which  from  the  duct 
is  usually  arbitrary. 

Vessels  of  the  Gall- Bladder. — Arteries. — The  chief  distribution  of  the 
cystic  artery,  a  branch  of  the  hepatic,  is  on  the  free  under  surface,  which  it  ap- 
proaches from  the  left,  running  on  the  cystic  duct.  There  is  a  smaller  branch 
which  lies  deeply  on  the  right  between  the  gall-bladder  and  the  liver-substance. 
Veins. — The  superficial  veins  join  the  cystic  artery  and  empty  into  the  right 
division  of  the  portal  vein.  According  to  Sappey,  a  number  of  small  veins  run 
directly  into  the  liver-tissue  joining  the  portal  system.  The  lymphatics,  for  the  most 

1  For  the  musculature  of  the  biliary  apparatus,  see  Hendrickson  :  Johns  Hopkins  Hospital 
Bulletin,  Nos.  90,  91,  1898. 


1720 


HUMAN   ANATOMY. 


FIG.   1455. 


part,  empty  into  the  nodes  in  the  portal  fissure.      Some  open  into  a  node  said  to 
lie  in  the  angle  at  the  bend  of  the  neck. 

The  nerves  are  from  the  solar  plexus  through  the  hepatic  plexus. 
The  peritoneal  relations  of  the  bladder  and  ducts  are  considered  with  those  of 
the  liver  (page  1721). 

The  cystic  duct  (ductus  cysticus),  3  or  4  cm.  in  length,  with  a  diameter  of 
from  2—3  mm.,  passes  in  a  fold  of  peritoneum  from  the  neck  of  the  gall-bladder  to 
the  gastro-hepatic  omentum,  where  it  joins  the  hepatic  duct  at  an  acute  angle  or, 
rather,  opens  into  its  side.  It  is  said  sometimes  to  present  an  enlargement  at  its 
end.  In  its  natural  condition  it  looks  externally  like  the  other  ducts,  but  if  distended 
and  dried  it  presents  a  series  of  irregular  folds  giving  the  impression  of  a  spiral  fold 
which,  in  the  adult  at  least,  a  closer  inspection  does  not  confirm. 

Structure. — In  structure  the  cystic  duct  presents  much  more  of  a  muscular 
layer  than  the  others.  This  is  thickest  at  the  upper  part,  and  consists  chiefly  of 
circular  fibres.  These  enter,  especially  near  the  beginning,  the  valvular  folds  of  the 
mucous  membrane,  which  is  clothed  with  simple  columnar  epithelium.  In  the  foetus 
there  is  a  fairly  distinct  spiral  valve,  most  developed  in  the  upper  part,  and,  in  fact, 
starting  in  the  neck  of  the  gall-bladder.  Later  the  continuous  spiral  ridge  (valvula 

spiralis  Heisteri)  usually  atro- 
phies and  is  broken  up  at  many 
places,  leaving  detached  folds 
with  a  semilunar  outline  and 
no  longer  distinctly  spirally  ar- 
ranged. Little  pockets  also  de- 
velop between  them.  Small 
tubular  glands  are  few  in  the 
upper  part,  but  plentiful  in  the 
lower. 

The  common  bile-duct 
(ductus  choledochus)  is  about 
7  cm.  (2^4  in. )  long.  Its  diam- 
eter is  from  6—7  mm.  at  the 
commencement  and  rather  less 
at  the  end.  Beginning  imme- 
diately below  the  transverse 
fissure,  although  conventionally 
regarded  as  formed  by  the  union 
of  the  cystic  and  the  hepatic 
ducts,  being,  in  fact,  the  direct 
continuation  of  the  latter,  the 
common  bile-duct  passes  down- 
ward between  the  layers  of 
the  gastro-hepatic  omentum,  in 
front  of  the  foramen  of  Winslow,  with  the  hepatic  artery  to  its  left  and  the  portal 
vein  behind.  It  descends  along  the  postero-inner  aspect  of  the  bend  joining  the 
first  and  second  parts  of  the  duodenum,  then  along  the  inner  side  of  the  second  part, 
where  it  is  more  or  less  surrounded  by  the  head  of  the  pancreas.  Near  its  termina- 
tion it  meets  the  pancreatic  duct  and,  in  company  with  the  latter,  pierces  the  duo- 
denal wall,  which  it  traverses  obliquely  for  the  distance  of  some  15  mm.,  to  empty 
into  the  duodenum  at  a  papilla  marking  the  common  orifice  of  the  two  ducts.  This 
papilla  is  situated  near  the  posterior  border  of  the  internal  aspect  of  the  descending 
part  of  the  duodenum,  from  9-10  cm.  (about  3^-4  in.)  from  the  pylorus.  In  the 
natural  condition  it  is  not  easy  to  find,  being  situated  beneath  a  transverse  fold  and 
not  being  prominent  in  the  shaggy  mucous  membrane.  Its  length  umlistended  is 
only  about  5  mm.  When  inflated  or  injected  it  is  a  prominent  object  more  than 
twice  as  large.  Moreover,  it  does  not  project  freely,  but  lies  on  its  side  pointing 
downward,  the  surface  next  to  the  wall  becoming  free  only  very  near  its  end.  The 
orifice  looks  downward.  It  may  be  oval  or  circular,  with  a  diameter  of  from  1-2  mm. 
A  slight  vertical  fold,  the  frenum,  often  runs  downward  from  the  opening  for  the 


Bile-du 


Ampulla 

Pancreatic 
duct 


A,  portion  of  duodenum,  with  anterior  wall  removed,  showing 
entrance  of  bile  and  pancreatic  ducts;  B,  papilla  laid  open,  showing 
floor  of  ampulla.  One-half  natural  size. 


THE   BILIARY    APPARATUS. 


1721 


distance  of  I  cm.  The  structure  of  the  common  duct  is  much  the  same  as  that 
of  the  hepatic,  containing  but  little  muscular  tissue  and  that  not  well  denned.  The 
papilla  contains  a  fusiform  dilatation,  the  ampulla  (of  Vater),  which  may  be  i  cm. 
broad  when  distended.  Into  this  the  bile-duct  and  the  duct  of  the  pancreas  usually 
open  by  a  common  orifice.  Be  these  orifices  common  or  distinct,  each  is  sur- 
rounded by  an  accumulation  of  the  circular  muscular  fibres  which  amounts  to  a 
sphincter.  The  glands,  which  are  found  throughout  the  common  duct,  are  particu- 
larly large  and  numerous  in  the  ampulla. 

Ligaments  and  Peritoneal  Relations. — The  term  "ligament,"  applied 
to  the  folds  of  serous  membrane,  is  entirely  inappropriate.  It  is  in  part  retained, 
but  the  enumeration  of  five  ligaments  as  separate  entities  is  antiquated.  The  round 
ligament  (ligamentum  teres  hepatis)  is  a  cord  of  fibrous  tissue,  the  remains  of  the 
obliterated  umbilical  vein,  running  from  the  umbilicus  to  the  left  end  of  the  portal 
fissure.  Its  continuation,  the  ductus  venosus,  is  represented  by  fibrous  tissue  (liga- 
mentum venosum )  in  the  fissure  of  that  name.  The  round  ligament  lies  against  the 
abdominal  wall  for  an  inch  or  more  above  the  navel  and  then  passes  backward  in  the 
free  edge  of  the  falciform  ligament,  a  fold  of  peritoneum  presumably  detached  from 
the  anterior  wall  and  from  the  diaphragm  by  the  development  of  this  vein.  The 


FIG.   1456. 

CEsophageal  impression  Vena  cava 

Left  coronary  ligament 


Fissure  of  ductus  venosus 

Spigelian  lobe 

Portal  vein 
Caudate  lobe,  left  end 


Right  coronary  ligament 


Posterior 
non-peritoneal 

surface 


Right 
triangular 
^/"-ligament 
— Suprarenal 
impression 


Renal 
impression 


Vena  cava  I 

Colic  impression 


Posterior  surface  of  liver,  showing  peritoneal  reflections. 

front  part  of  the  falciform  ligament  is  appropriately  described  as  sickle-shaped.  The 
point  is  in  front,  and  it  grows  broader  as  it  passes  backward  until  it  reaches  the  liver, 
where,  growing  narrower,  it  extends  above  the  liver  to  the  spine  at  about  the  median 
line.  It  contains  very  little  tissue  between  its  folds,  which  are  reflected  on  either 
side  over  the  superior  surface  of  the  liver.  At  the  notch  in  the  anterior  border  the 
round  ligament  passes  onto  the  inferior  surface  of  the  liver  in  the  umbilical  fissure. 
The  coronary  ligaments  are  differently  arranged  on  the  two  sides.  The  right  one  is 
made  by  the  two  reflections  onto  the  diaphragm  from  the.  upper  and  lower  borders 
of  the  part  of  the  posterior  surface  adherent  to  it.  These  come  together  at  the 
right  of  that  surface  and  are  continued  as  a  fold,  the  right  triangular  ligament,  on 
the  right  surface,  connecting  it  to  the  diaphragm  in  the  flank  by  a  line  of  attach- 
ment some  5  cm.  long.  On  the  top  of  the  left  lobe,  but  not  on  the  posterior  bor- 
der, there  is  a  small  area  without  peritoneal  covering,  enclosed  by  the  two  folds  of 
the  left  coronary  ligament,  of  which  the  anterior  is  analogous  to  the  right  one,  but 
the  posterior  begins  at  the  left  of  the  upper  end  of  the  fissure  of  the  ductus  venosus. 
They  soon  unite  to  form  the  left  triangular  ligament,  which  lies  between  the  dia- 
phragm and  the  top  of  the  left  lobe,  being  considerably  longer  than  the  right  one. 


1722 


HUMAN    ANATOMY. 


On  the  under  side  of  the  liver  the  end  of  the  round  ligament  lies  in  its  fissure  cov- 
ered by  a  slight  fold  of  peritoneum.  The  same  is  true  of  the  gall-bladder.  Some- 
times the  latter  is  more  or  less  surrounded,  and  it  may  be  almost  completely  so, 
hanging  from  the  fossa  by  a  fold.  The  lesser  or  gastro-hcpatic  amentum  is  a  fold 
enclosing  the  vessels  in  the  portal  fissure  and  passing  to  the  lesser  curvature  of  the 
stomach  and  the  first  part  of  the  duodenum.  A  secondary  fold  containing  the 
cystic  duct,  the  duodena-cystic  fold,  joins  it  on  the  right.  Near  this  it  presents  a 
free  border  forming  the  edge  of  the  foramen  of  Winslow.  On  the  left  it  runs  along 
the  fissure  of  the  ductus  venosus  to  the  notch  in  the  liver  made  by  the  passage  of 
the  oesophagus.  There  its  left  layer  is  reflected  as  the  under  one  of  the  left  coro- 
nary ligament,  while  the  right  layer  descends  along  the  left  of  the  vena  cava  to  join 
the  right  inferior  coronary  ligament.  The  posterior  surface  of  the  Spigelian  lobe  is 
covered  with  peritoneum  which  is  almost  surrounded  by  these  lines  of  attachment, 
but  is  continuous,  by  means  of  the  caudate  lobe,  with  the  serous  coat  of  the  under 
surface  of  the  right  lobe.  Thus  a  pocket  is  roofed  in  behind  the  lobe  of  Spigelius. 


FIG.  1457. 


Pericardial  fat 


IV  rib 


Cavity  of__ 
pericardium 


V  rib- 


Inferior  vena 
cava 


VI  rib 


VIII  rib 


Aorta 


IX  rib 

Major  azygos  vein 


X  thoracic  vertebra 


Transverse  section  at  level  of  tenth  thoracic  vertebra,  upper  surface  of  diaphragm  exposed,  showing  relation 
viscera  ;  outline  of  liver, ;  of  stomach, ;  of  colon,  o  o  o  o  o ;  of  spleen,  x  x  x  x  x. 

The  hepatic  duct  lies  within  the  lesser  omentum  to  the  right  and  in  front  of  th( 
portal  vein.  It  is  joined  by  the  cystic  duct  in  its  fold,  already  mentioned.  As  it 
leaves  the  gall-bladder,  the  duodeno-cystic  fold  is  a  distinct  duplicature  which  joins 
the  lesser  omentum  at  an  angle  ;  but  at  the  lower  part,  where  the  cystic  duct  opens 
into  the  hepatic,  the  folds  become  one.  The  common  bile-duct  may  be  in  the  very 
lowest  part  of  the  lesser  omentum,  where  it  is  attached  to  the  postero-inner  surface 
of  the  duodenum  where  the  first  part  bends  down  to  become  the  second  ;  but  the 
relations  are  variable,  and  the  common  duct  may  have  no  peritoneal  relation. 

Position  of  the  Liver. — The  relations  to  other  organs  have  been  treated  in 
the  account  of  the  surfaces.  The  relations  to  the  walls  of  the  abdomen  can  be 
given  only  in  general,  owing  to  the  variations  of  both  the  organ  and  the  thorax  in 
size  and  shape.  The  liver  lies  under  the  dome  of  the  diaphragm,  which  separates 
it  from  the  ribs.  Occasionally  it  extends  across  the  whole  breadth  of  the  abdomen, 
but  the  left  lobe  may  end  at  the  left  mammary  line.  The  highest  point  is  on  the 


THE    BILIARY    APPARATUS. 


1723 


right,  where,  after  death,  it  reaches  to  the  level  of  the  sternal  end  of  the  fifth  costal 
cartilage.  It  is  doubtful  whether  in  life  the  liver  is  ever  quite  so  high.  On  the  left 
it  is  about  i  cm.  lower,  and  in  the  middle  it  is  not  more  than  2  cm.  lower  still. 
The  relation  of  the  left  lobe  to  the  floor  of  the  thorax  varies  considerably.  If  large, 
the  organ  may  extend  to  the  left  wall,  but  this  is  rather  uncommon.  The  liver 
may  reach  the  front  wall  as  far  to  the  left  as  the  mammary  line,  in  which  case  it  will 
be  below  nearly  the  whole  of  the  floor  of  the  pericardium,  although  it  may  not  lie 
below  the  anterior  part.  It  always  passes  just  in  front  of  the  cesophageal  opening. 
The  inferior  border  rests  against  the  posterior  wall  on  the  right,  the  diaphragm  of 
course  intervening,  at  the  right  border  of  the  right  kidney  near  the  end  of  the  last 
rib,  on  about  the  level  of  the  second  lumbar  spine,  and  descends  to  the  right  along 
the  line  of  the  eleventh  rib.  At  the  mid-axillary  line  it  begins  to  rise,  following 
pretty  closely  the  border  of  the  thorax,  to  the  ninth  and  tenth  costal  cartilages, 


VI 


FIG.   1458 

VII  rib-cartilage  Transverse  fissure 

i-cartilage  \    Left  lobe       ' 


sc  iibbuie 

Falciform  ligament 


Quadrate  lobe 


VII  rib 


VIII  rib 


IX  ri 

Left  supra 
renal  body 

X  rib 


.Spigelian  lobe 


.Right  supra- 
renal body 


XI  rib      Diaphragm      XII  rib,  head        1  Diaphragm 

XII  thoracic  vertebra 

Frozen  section  across  body  at  level  of  twelfth  thoracic  vertebra. 

after  which  it  crosses  the  epigastrium  to  strike  the  left  costal  arch  at  the  eighth  car- 
tilage. The  notch  for  the  round  ligament  is  a  little  to  the  right  of  the  median  line 
and  the  fundus  of  the  gall-bladder  at  or  near  the  end  of  the  ninth  right  cartilage. 
It  is  usually  crossed  by  a  vertical  line  from  the  middle  of  the  clavicle.1  In  the  re- 
cumbent position  the  liver  gravitates  to  the  top  of  the  abdomen,  so  that  normally 
in  the  male  no  portion  is  left  below  the  costal  arch  except  near  the  middle.  The 
inferior  vena  cava  runs  in  a  groove  on  the  back  of  the  organ,  but  the  aorta,  passing 
the  diaphragm  at  a  lower  point,  has  the  latter  muscle  between  them.  The  vena  cava 
pierces  the  diaphragm  at  the  level  of  the  body  of  the  ninth  thoracic  vertebra.  The 
lungs,  especially  the  right,  overlap  the  liver  very  considerably. 

Development  and  Growth. — Very  early,  in  the  human  embryo  of  3.5  mm. 
in  length,   a  groove-like  evagination  appears  on  the  ventral  wall  of  the  gut-tube, 
immediately  above  the  widely  open  vitelline  duct.      This  evagination,  the  first  indi- 
cation of  the  hepatic  anlage,  extends  into  the  primitive  ventral  or  anterior  mesentery 
1  Carmichael  :  Journal  of  Anatomy  and  Physiology,  vol.  xxxvii.,  1902. 


1724 


HUMAN   ANATOMY. 


which  connects  the  stomach  and  the  duodenum  with  the  anterior  body-wall.  The 
hepatic  diverticulum  grows  forward  and  upward  into  the  anterior  mesentery  until  it 
comes  into  relation  with  the  imperfect  partition  which  partially  separates  the  thoracic 
and  abdominal  divisions  of  the  body-cavity.  This  partition,  the  septum  transversum, 
primarily  consists  of  lateral  folds,  projecting  at  right  angles  from  the  anterior  mesen- 
tery, caused  by  the  large  vitelline  veins  traversing  the  anterior  mesentery  on  their 
way  to  the  sinus  venosus  of  the  early  heart.  The  relation  of  these  structures  is 
more  fully  considered  in  connection  with  the  development  of  the  diaphragm  ( page 
1701);  for  the  present  purpose  it  is  sufficient  to  note  that  the  liver-anlage  early 
comes  into  relation  with  the  septum  transversum.  The  ventral  portion  of  the  pri- 
mary liver-evagination,  clothed  with  the  entoblastic  lining  of  the  gut-tube,  very  soon 
differentiates  into  two  diverticula  :  the  one  nearer  the  head,  or  hepatic  division,  pro- 
duces the  liver  proper ;  the  other,  or  cystic  division,  later  becomes  the  gall-bladder 
and  its  duct.  These  divisions  are  gradually  removed  from  the  primitive  duodenum 
by  the  growth  of  the  primary  diverticulum,  which  at  one  end  becomes  converted 
into  a  tube  connected  with  the  digestive  canal  and  at  the  other  bifurcates  into  the 
hepatic  and  cystic  channels.  This  tube,  evidently  later  the  common  bile-duct,  is  at 
first  short  and  wide,  but  later  rapidly  lengthens. 


FIG.  1459. 


Septum  transversum 


Hepatic  diverticulum 


Liver-anlage 
Cystic  diverticulum 

Cut-tube 


V  N  V»  •    vr '<  f        */'"'*••'•    .*•    . 

f  <| 

Portion  of  sagittal  section  of  early  rabbit  embryo,  showing  liver-anlage  and  ducts.     X  95. 

The  cells  lining  the  longer  hepatic  diverticulum  undergo  marked  proliferation 
and  produce  the  liver-mass  which  invades  the  septum  transversum  almost  as  far  as 
the  sinus  venosus  and  surrounds  the  vitelline  veins.  The  formation  of  the  liver-mass 
follows  at  first  the  type  of  development  seen  in  tubular  glands,  outgrowths  of  the 
hepatic  tube  branching  and  subdividing  to  form  solid  sprouts  and  buds  composed  of 
epithelial  cells.  In  some  of  the  lower  animals,  as  the  amphibians,  the  tubular  type 
is  retained  in  the  adult  organ;  but  in  the  higher  forms,  including  man,  the  tubular 
character  of  the  young  liver  is  soon  lost  and  replaced  by  the  reticular  arrangement 
produced  in  consequence  of  the  growing  together  and  union  of  the  terminal  divis- 
ions of  the  gland. 

Coincidently  with  the  formation  of  the  net-work  of  glandular  tissue  by  the 
junction  of  the  cylinders  of  hepatic  cells,  the  meshes  of  the  reticulum  become  occu- 
pied by  blood-vessels  derived  from  vitelline  veins.  These  are  now  represented  at 
the  hepatic  anlage  by  venous  stumps  from  which  numerous  afferent  branches  (vfn«- 
hepaticce  advchentes}  penetrate  the  liver-mass  to  become  the  portal  system.  The 
division,  subdivision,  and  union  of  these  blood-vessels  keep  pace  with  the  increasing 
complexity  of  the  net-work  of  hepatic  cords,  the  intergrowth  of  these  constituents 
eventually  leading  to  the  intimate  relations  between  the  hepatic  secreting  tissue  and 
the  intralobular  capillaries  seen  in  the  fully  developed  organ.  The  cell-trabeculae 
composing  the  primary  hepatic  net-work  are  partly  solid  and  partly  hollow  ;  the 


THE   BILIARY    APPARATUS. 


1725 


bile-duct 


latter,  with  a  portion  of  those  without  a  lumen,  are  converted  into  the  system  of 
bile-canals,  while  the  remaining  cylinders  give  off  additional  sprouts  which  reduce 
the  intervening  meshes  and  increase  the  solidity  of  the  organ.  The  solid  cylinders 
of  secreting  tissue  at  first  contain  no  bile-capillaries.  The  latter  are  hollowed  out 
between  two  adjacent  cells  as  extensions  of  the  meanwhile  differentiating  biliary 
ducts.  Differentiation  of  the  developing  liver  into  lobules  does  not  occur  until  the 
beginning  of  the  fourth  foetal  month,  by  which  time  the  larger  blood-vessels  and 
bile-ducts  become  surrounded  by  condensations  of  the  mesoderm  which  form  the 
capsule  of  Glisson. 

The  details  of  the  formation  of  the  hepatic  blood-vessels  are  considered  in  con- 
nection with  the  development  of  the  veins  (page  928).  It  may  be  here  men- 
tioned, however,  that  the  primary  circulation  of  the  liver,  including  the  portal  vein, 
the  intralobular  capillary  net-work,  and  the  hepatic  veins,  is  derived  from  the  modi- 
fication of  the  vitelline  veins,  in  conjunction  with  their  tubularies  from  the  digestive 
organs.  The  relations  of  the  placental  circulation  to  the  liver  are  secondary.  The 
left  umbilical  vein  for  a  time  pours  practically  all  the  blood  returned  from  the  placenta 
into  the  portal  vessel ;  when  the  latter  is  no  longer  capable  of  receiving  the  entire 
amount  of  the  placental 

blood,    the    development  FIG.  1460. 

of  the  ductus  venosus 
brings  relief  by  establish- 
ing a  short  cut  by  which 
the  excess  of  placental 
blood  passes  directly  into 
the  ascending  vena  cava. 

The  development  of 
the  gall-bladder  and  its 
duct  proceeds,  as  already 
indicated,  from  the  more 
caudally  placed  cystic  di- 
vision of  the  primary  he- 
patic diverticulum.  The 
subsequent  changes  in- 
clude the  growth  and  ex- 
pansion of  the  terminal 
portion  of  the  primitive 
cystic  canal  to  form  the 
bile-sac,  its  elongated 
stalk  becoming  the  cystic 
duct,  while  differentiation 
of  the  entoblastic  lining 

and  the  surrounding  mesoblast  produces  the  distinguishing  details  of  the  fully  formed 
organs. 

With  the  conversion  of  the  primary  liver-mass  into  the  more  definite  organ,  the 
relations  of  the  ventral  mesentery,  into  which  the  early  liver-anlage  grows,  become 
changed.  For  a  time  the  developing  liver  lies  within  the  septum  transversum,  but 
later,  with  the  formation  of  the  diaphragm,  it  separates  from  the  latter  and  projects 
into  the  body-cavity.  This  projection  results  in  a  differentiation  of  the  ventral 
mesentery  into  three  parts  :  (a)  the  middle  portion,  the  layers  of  which  become 
separated  by  the  growing  liver  to  form  its  serous  investment ;  (£)  the  anterior  portion, 
which  extends  from  the  front  surface  of  the  liver  to  the  umbilicus  and  becomes  the 
falciform  ligament  enclosing  the  umbilical  vein,  later  the  ligamentum  teres  ;  (c)  the 
posterior  portion,  which  stretches  between  the  digestive  tube  and  the  liver  and,  as 
the  gastro-hepatic,  or  lesser  omentum,  maintains  similar  relations  and  encloses  the 
biliary  ducts. 

In  the  foetus  the  liver  is  relatively  immense,  especially  at  an  early  period.  At 
the  fourth  fcetal  month  it  practically  fills  the  whole  of  the  top  of  the  abdomen. 
Although  it  increases  absolutely  after  this,  it  relatively  diminishes,  but  at  birth  is  still 
considerably  above  the  relative  size  of  the  adult  organ,  forming  approximately  one- 


Portion  of  sagittal  section  of  rabbit  embryo,  showing  developing  liver  and 
ducts.     X  95- 


1726  HUMAN   ANATOMY. 

eighteenth  of  the  entire  body  weight.  The  left  lobe  reaches  across  the  stomach  so 
as  to  be  in  contact  with  the  spleen.  The  tubercle  at  the  lower  extremity  of  the 
Spigelian  lobe  and  the  caudate  lobe  are  relatively  large.  In  the  infant  there  is  little 
connective  tissue  in  the  organ,  which  is  very  friable  and  also  easily  moulded  on  the 
surrounding  structures.  At  birth  the  weight  of  the  liver  is  about  150  gm.  (3  oz. ). 

PRACTICAL   CONSIDERATIONS:     THE    LIVER,   GALL-BLADDER, 
AND    BILIARY    PASSAGES. 

The  Liver. — Anomalies  in  the  position  of  the  liver  occasionally  occur,  as  in 
"  transposition,"  when  the  whole  organ  may  be  on  the  left  side  ;  in  such  cases  the 
spleen  and  other  asymmetrical  abdominal  viscera  (and  frequently,  but  not  neces- 
sarily, the  thoracic  organs)  will  also  be  found  to  be  transposed.  "  Accessory"  lobes 
are  not  uncommon  and  have  been  mistaken  for  new  growths. 

The  shape  of  the  liver  may  obviously  be  affected  by  compression  exerted 
through  the  parietes.  The  chief  type  of  the  so-called  "lacing"  or  "corset"  liver 
is  marked  by  a  transverse  groove  separating  the  main  body  of  the  organ  from  a  pro- 
longation downward  of  the  anterior  portion,  especially  of  the  right  lobe,  which  may 
reach  to  below  the  umbilical  level.  This  portion  has  been  mistaken  for  a  movable 
right  kidney.  Knuckles  of  intestine  may  lie  between  it  and  the  anterior  abdominal 
parietes  and  prevent  the  recognition  of  its  continuity  with  the  liver  by  either  palpa- 
tion or  percussion. 

Movable  liver  (hepatoptosis}  is  a  condition  in  which,  through  stretching  of  the 
tissues  and  structures  which  normally  retain  it  in  place  beneath  the  arch  of  the  dia- 
phragm, it  sinks  by  gravity  to  a  lower  level.  It  has  then  been  mistaken  for  various 
forms  of  abdominal  or  renal  tumor  and  for  movable  kidney.  Hepatoptosis  is  often 
associated  with  displacements  or  abnormal  mobility  of  other  abdominal  viscera. 
Traction  of  the  liver  on  the  suspensory  ligament  is  said  to  produce  a  fold  of  skin 
which  hides  the  lower  part  of  the  umbilicus  (Glenard). 

The  structures  most  potent  in  holding  it  in  its  proper  position  are,  in  the  order 
of  their  importance  :  (a)  the  attachment  of  the  hepatic  veins  to  the  inferior  vena 
cava,  (&y  the  coronary  ligaments  and  the  cellulo-vascular  bands  in  and  between  its 
layers,  (c}  the  fibrous  tissue  near  the  vena  cava  and  on  the  non-peritoneal  posterior 
surface  of  the  right  lobe,  (a?)  the  muscular  wall  of  the  abdomen  (keeping  the  in- 
testinal mass  pressed  upward  beneath  the  liver),  and  (e)  the  lateral  and  "suspen- 
sory" ligaments. 

Coincidently  with  the  descent  of  the  viscus  it  undergoes  a  rotation  or  tilting 
forward  so  that  its  diaphragmatic  surface  is  in  contact  with  the  abdominal  wall. 

Hepatopexy  consists  in  suturing  such  a  movable  liver  in  its  normal  position  by 
stitches  which  may  be  variously  placed,  but  the  most  useful  of  which  seem  to  be 
those  which  unite  the  round  ligament  and  liver-substance  with  the  anterior  abdominal 
wall  near  the  xiphoid  cartilage  (Francke,  Treves). 

The  normal  relations  of  the  liver  to  the  diaphragm  and  the  abdominal  parietes 
cause  it  to  be  much  influenced — especially  as  to  its  circulation — by  the  respiratory 
and  other  movements  associated  with  energetic  exercise  ;  hence  the  congestion  of 
the  organ  resulting  in  "biliousness,"  or  even  in  jaundice,  seen  in  cases  in  which, 
from  accident  or  disease,  persons  who  have  led  active  lives  are  confined  to  bed.  In 
walking,  and  more  markedly  in  horseback  riding,  the  compression  of  the  organ  be- 
tween the  diaphragm  and  the  upper — or  respiratory — segment  of  the  abdominal  wall 
which  takes  place  during  deep  inspiration  is  aided  by  its  downward  movement  from 
gravity.  It  has  been  suggested  ( Jacobson)  that  such  movement  must  slightly  open 
the  inferior  vena  cava,  which  is  then  immediately  compressed  by  the  following  up- 
ward movement, — during  expiration, — thus  directly  influencing  the  systemic  venous 
current  and  with  almost  equal  directness  that  in  the  hepatic  veins. 

In  deep  inspiration  the  anterior  edge  of  the  liver  descends  from  under  cover  of 
the  lower  ril>s,  and  in  very  thin  persons  may  be  palpated.  A  similar  descent  occurs 
when  a  reclining  is  exchanged  for  an  erect  position. 

The  direct  connection  between  the  gastrointestinal  and  the  portal  circulation 
causes  the  latter  to  be  markedly  affected  by  the  use  of  alcoholic  or  other  irritants  and 


PRACTICAL   CONSIDERATIONS  :   THE   LIVER.  1727 

by  the  amount  and  character  of  food  taken.  Drinking  and  overeating  thus  exaggerate 
the  periodic  physiological  congestions  of  the  liver  and  often  result  ultimately  in  organic 
changes.  Of  course,  passive  congestion  is  likely  to  follow  valvular  disease  of  the 
heart,  emphysema,  pulmonary  cirrhosis,  or  any  condition  in  which  the  right  heart  is 
engorged,  the  backward  pressure  through  the  vena  cava  reaching  the  hepatic  veins 
and  their  sublobular  tributaries.  The  thin  interlobular  and  perihepatic  connective 
tissue,  known  as  Glisson's  capsule,  which  closely  invests  the  ducts  and  vessels,  is 
commonly  affected  in  chronic  irritation  of  the  liver,  especially  that  form  due  to  al- 
coholic excess,  and  in  some  infectious  diseases,  notably  the  specific  fevers  and 
syphilis.  Its  anatomical  relations  explain  the  usual  sequence  of  phenomena.  Pro- 
liferation of  the  portions  surrounding  the  terminal  branches  of  the  portal  vein  causes 
obstruction  which,  either  alone  or  aided  by  the  concurrent  toxaemia,  results  in  con- 
gestion and  catarrh  of  the  stomach  and  intestines,  in  enlargement  of  the  spleen  and 
pancreas,  and  later  in  ascites. 

As  the  obstruction  increases,  a  collateral  circulation  is  often  established  to  re- 
lieve the  portal  congestion  by  means  of  communication  between  (#)  the  accessory 
portal  veins  (particularly  those  in  the  falciform  ligament)  and  the  diaphragmatic, 
para-umbilical,  and  epigastric  veins  ;  (b}  the  veins  of  Retzius  and  the  retroperitoneal 
veins  ;  (c^  the  hemorrhoidal  and  the  inferior  mesenteric  veins  ;  (d  )  the  gastric  and 
the  cesophageal  veins.  An  operation  has  been  employed  to  establish  a  better  and 
more  satisfactory  compensatory  circulation  in  cases  of  cirrhosis  by  effecting  adhesions 
between  the  surfaces  of  the  liver  and  the  spleen  and  the  diaphragmatic  peritoneum, 
on  the  one  hand,  and  the  parietal  peritoneum  and  omentum,  on  the  other. 

When  compression  of  the  liver  is  carried  beyond  physiological  limits,  as  from 
contusion  or  from  forced  flexion,  rupture  results.  This  is  more  frequent  in  the 
liver  than  in  the  other  abdominal  viscera  on  account  of  its  size,  its  friability,  its 
fixity,  its  close  diaphragmatic  and  parietal  relations,  and  its  great  vascularity.  A 
similar  disjunction  of  liver-substance  may  occur  from  a  fall  on  the  feet  from  a  height. 
It  is  grave  in  proportion  to  the  extent  of  the  rupture  and  to  its  involvement  or  non- 
involvement  of  the  peritoneal  covering.  Ruptures  confined  to  the  liver-substance, — 
i.e. ,  not  reaching  the  surface, — and  moderate  in  extent,  are  not  infrequently  recovered 
from.  The  commonest  seat  of  rupture  of  the  liver  is  near  the  falciform  and  coro- 
nary ligaments,  with  which  the  rupture  is  apt  to  be  parallel.  If  they  are  extensive 
enough  to  reach  the  surface  of  the  organ,  death  often  results  from  hemorrhage,  the 
intimate  association  of  the  hepatic  substance  with  the  thin-walled  vessels  preventing 
their  retraction  or  collapse.  Hemorrhage  is  also  favored  by  the  direct  connection 
of  the  valveless  hepatic  veins  with  the  vena  cava  and  by  the  absence  of  valves  in 
the  portal  veins.  According  to  the  situation  of  the  rupture,  the  blood  may  be  poured 
into  the  general  peritoneal  cavity  ;  into  that  portion  of  it  known  as  the  subhepatic 
space,  and  bounded  below  by  the  transverse  mesocolon  ;  or  into  the  retroperitoneal 
space  behind  the  liver  and  ascending  colon.  The  local  symptoms  will  vary  with  the 
situation  of  the  collected  blood. 

Wounds  of  the  liver  should  be  considered  with  reference  to  its  relations  to  the 
parietes,  especially  on  the  right  side,  where,  on  account  of  its  greater  bulk,  it  is 
more  often  injured.  Except  at  the  subcostal  angle,  where  a  small  part  of  the  anterior 
surface  lies  against  the  abdominal  wall  (the  lower  edge  being  on  a  line  between  the 
eighth  left  and  the  ninth  right  costal  cartilages),  the  lower  ribs  and  costal  cartilages 
surround  the  liver.  Thus  stab  wounds  must  pass  between  them,  while  fracture  of 
the  ribs  with  depression  may  penetrate  the  interposed  diaphragm  and  then  the  liver- 
substance.  Anteriorly,  a  little  internal  to  the  mammary  line,  the  liver  may  reach  to 
the  fourth  intercostal  space  or  even  quite  to  the  level  of  the  nipple,  and  may  be 
directly  wounded  throughout  that  area.  Laterally  it  is  not  usually  found  above  the 
sixth  interspace.  Posteriorly  a  stab  wound  through  the  sixth,  seventh,  or  eighth 
intercostal  space,  or  even  down  to  the  level  of  the  tenth  dorsal  spine,  would  pene- 
trate four  layers  of  pleura,  the  thin  concave  base  of  the  right  lung,  and  the  dia- 
phragm before  reaching  the  liver.  Still  lower,  the  base  of  the  lung  may  escape, 
but  a  wound  of  the  liver  may  involve  the  two  layers  of  pleura  of  the  costo-phrenic 
sinus  and  the  diaphragm.  Of  course,  the  alterations  in  position  of  the  liver  during 
inspiration  and  expiration,  and  according  to  the  position  of  the  body,  must  be 


i728  HUMAN   ANATOMY. 

remembered  in  obscure  cases  before  basing  a  diagnosis  upon  the  situation  of  the 
external  wound. 

In  bleeding  from  the  liver  after  either  rupture  or  stab  wound,  or  during  opera- 
tions, temporary  occlusion  of  the  portal  vein  and  hepatic  artery  may  be  secured  by 
pressing  them  between  the  finger  and  thumb,  the  former  being  placed  just  within 
the  foramen  of  Winslow  and  the  latter  externally  on  the  gastro-hepatic  omentum. 

Enlargement  of  the  liver,  if  uniform  (congestion,  multiple  abscess,  perihepatitis, 
fatty  degeneration,  hypertrophic  cirrhosis),  causes  a  bulging  of  the-  right  lower  ribs 
and  their  cartilages  and  an  increase  of  the  area  of  absolute  percussion  dulness.  The 
upper  limits  of  the  latter  should  normally  be  found  at  the  sterno-xiphoid  junction  in 
the  median  line,  the  sixth  intercostal  space  in  the  right  mammary  line,  the  seventh 
rib  in  the  axillary  line,  and  the  lower  border  of  the  ninth  rib  in  the  scapular  line. 
A  modified  dulness  is  obtained  posteriorly  over  the  area  where  the  lung  overlaps  the 
liver,  down  to  the  level  of  the  ninth  rib.  The  lower  level  of  the  dulness — and  thus 
of  the  liver  itself — is  in  the  mid-line,  half-way  between  the  sterno-xiphoid  junction 
and  the  umbilicus,  at  or  a  little  below  the  costal  margin  in  the  mammary  line,  on  a 
level  with  the  tenth  and  eleventh  ribs  laterally  and  opposite  the  eleventh  dorsal  ver- 
tebra posteriorly.  At  this  point  it  is  continuous  with  the  lumbar  dulness  due  to  the 
thickness  of  the  spinal  muscles,  the  quadratus  lumborum,  the  kidneys,  and  the 
perirenal  fat. 

In  localized  enlargements,  as  from  tumor,  abscess,  or  hydatids  occupying  the 
upper  surface  of  the  right  lobe,  the  diaphragm  is  pushed  upward  and  the  upper 
limit  of  the  percussion  dulness  raised,  the  lower  limit  remaining  temporarily  unaf- 
fected, the  area  of  dulness  being  thus  increased. 

In  emphysema  or  pneumothorax  both  limits  are  lowered  (as  they  are  also  in 
empyema,  although  in  that  condition  the  liver-dulness  merges  into  that  of  the  pleural 
abscess),  and  in  phthisis,  collapse  or  retraction  of  the  lung,  or  abdominal  meteor- 
ism  both  limits  are  raised,  the  total  area  of  dulness  remaining  unchanged  in  these 
cases.  Of  course,  in  atrophic  disease  the  area  is  diminished  and,  as  in  cases  in 
which  the  whole  liver  is  drawn  or  pushed  up,  or  there  is  free  gas  in  the  abdominal 
cavity,  there  may  be  tympany  over  the  right  lower  ribs. 

Abscess  of  the  liver  may  be  due  to  infection  through  the  portal  system,  as  from 
dysentery  or  hemorrhoids,  or  from  typhoid  fever,  colitis,  or  appendicitis  ;  or  through 
the  general  blood -supply,  as  from  osteomyelitis  or  cranial  trauma.  In  addition  to 
the  usual  symptoms  of  suppuration,  it,  like  many  other  liver  troubles,  is  sometimes 
characterized  by  pain  in  or  above  the  right  shoulder.  This  is  thought  to  be 
explained  by  the  facts  that  (a}  the  right  lobe  is  far  more  commonly  affected,  (6) 
the  phrenic  contributes  to  the  nerve-supply  to  the  liver  and  is  derived  partly  from 
the  fourth  cervical,  and  (c)  the  supra-acromial  nerve  is  a  branch  of  the  latter. 
Other  evidence  showing  relations  between  the  supra-acromial  and  phrenic  nerves, 
e.g. ,  hiccough  in  shoulder  arthritis,  makes  this  explanation  seem  reasonable. 

Hepatic  abscess  may  open  (a)  inferiorly  into  the  stomach,  colon,  duodenum,  or 
right  kidney,  or  into  some  portion  of  the  peritoneal  cavity, — either  the  subhepatic 
space,  the  general  cavity,  or  the  lesser  cavity  via  the  foramen  of  Winslow  ;  (£) 
superiorly  into  the  pleura,  lung,  or  bronchi,  or  into  the  pericardium  ;  (c)  posteri- 
orly into  the  retroperitoneal  space  and  the  loin  ;  (d}  anteriorly  on  the  surface  of 
the  body,  sometimes  following  the  remains  of  the  umbilical  vein  to  the  umbilicus. 

The  resistance  of  the  ribs,  intercostal  muscles,  and  diaphragm  makes  pointing 
in  other  directions  of  rare  occurrence.  Pus  may  invade  the  suprahepatic  (subdia- 
phragmatic)  space  or  the  liver  itself  from  above  the  diaphragm.  Many  empyemas 
have  taken  this  course.  Nephric  or  perinephric  abscess  on  the  right  side  may 
extend  to  the  liver. 

Hydatid  cysts  are  more  common  in  the  liver  than  elsewhere,  as  the  embryo  of 
the  egg  of  the  trenia  echinococcus,  freed  from  its  shell  by  digestion,  readily  pene- 
trates the  gastric  and  intestinal  vessels,  and  is  very  likely  to  enter  a  tributary  of  the 
portal  system  and  thus  be  carried  direct  to  the  liver,  where  it  multiplies  and 
develops  into  the  mature  hydatid.  Spontaneous  evacuation  of  the  cysts  may  occur 
in  any  of  the  directions  already  mentioned. 

In  opening  an  hepatic  abscess  or  hydatid  cyst  the  liver  must  be  reached,  as  in 


PRACTICAL    CONSIDERATIONS  :   THE    GALL-BLADDER.       1729 

other  operations,  by  traversing  either  the  peritoneal  or  the  pleural  cavity.  In 
doubtful  cases,  or  when  there  is  an  anterior  swelling,  a  vertical  incision  in  the  mid- 
line  through  the  right  rectus  or  at  its  outer  edge,  beginning  at  the  costal  margin 
and  prolonged  downward,  will  permit  of  exposure  of  the  liver  and  evacuation  of  the 
abscess  or  cyst,  the  peritoneal  cavity  being  walled  off  by  gauze  packing.  If  the 
liver  is  approached  above  the  lower  ribs  or  posteriorly,  it  will  be  necessary  to  resect 
a  portion  of  one  or  more  ribs,  suture  the  diaphragmatic  and  parietal  pleurae 
together  or  to  the  thoracic  wound,  and  then  incise  the  diaphragm.  If  the  liver  is  to 
be  reached  laterally, — i.e.,  in  the  right  axillary  line, — resection  of  the  tenth  rib  will 
disclose  the  diaphragm  with  no  intermediate  layer  of  pleura.  Penetration  of  the 
diaphragm  opens  the  peritoneal  cavity  and  permits  access  to  the  lower  and  outer 
portion  of  the  right  lobe. 

Cancer  of  the  liver  is  usually  secondary  (to  metastasis  through  the  portal 
system),  multiple,  and  diffuse.  When  primary  and  consisting*  of  a  single  nodule, 
excision  may  be  attempted.  In  controlling  hemorrhage,  the  friability  of  the  liver- 
substance  makes  ligation  of  separate  vessels  difficult,  and  it  may  be  necessary  to 
employ  an  elastic  tourniquet,  the  cautery,  gauze  pressure,  or  all  three. 

Lymphatic  involvement  secondary  to  hepatic  cancer  may  be  found  in  the 
cesophageal,  mediastinal,  lumbar,  or  omental  glands. 

The  relation  to  the  cesophageal  lymphatics  is  also  shown  by  a  case  in  which 
hepatic  abscess  followed  a  mediastinal  cesophagotomy. 

The  Gall-Bladder. — This  sac  may  be  absent,  as  is  normally  the  case  in  some 
of  the  lower  animals  ;  it  may  be  congenitally  of  hour-glass  shape  ;  it  may  be  bifid  ;  it 
may  communicate  directly  with  the  liver  by  a  "  hepato-cystic' '  duct  ;  it  may  be 
transposed  (in  conjunction  with  other  viscera),  and  in  one  such  case  cholecystostomy 
for  gall-stones  was  performed  on  a  gall-bladder  lying  on  the  left  side. 

Wounds  of  the  gall-bladder  are  rare. 

Rupture  of  the  gall-bladder  may  occur  from  traumatism  to  the  abdominal  pari- 
etes  ;  it  is  favored  by  distention  of  the  viscus  and  by  enlargement  of  the  liver,  both 
of  which  carry  the  gall-bladder  downward  to  a  less  protected  position  and  favor  the 
direct  transmission  of  the  force.  Extravasation  of  bile  into  the  general  peritoneal 
cavity  follows.  It  may  be  sterile,  and  may  then  act  merely  as  an  irritant,  causing  an 
extensive  plastic  exudate,  but  is  apt  to  be  fatal  by  setting  up  septic  peritonitis. 

If  operation  discloses  such  a  rupture,  it  may  be  remembered  (i)  that  the 
extravasated  bile  first  flows  into  the  large  peritoneal  pouch  bounded  above  by  the 
right  lobe  of  the  liver,  below  by  the  ascending  layer  of  the  transverse  mesocolon 
covering  the  duodenum  internally,  externally  by  the  peritoneum  lining  the  parietes 
down  to  the  crest  of  the  ilium,  posteriorly  by  the  ascending  mesocolon  covering 
the  kidney,  and  internally  by  the  peritoneum  covering  the  spine  ;  (2)  that  this 
pouch  can  be  easily  and  thoroughly  drained  through  a  lumbar  incision  ;  and  (3) 
that  it  is  capable  of  holding  nearly  a  pint  of  fluid  before  it  overflows  into  the 
general  peritoneal  cavity  through  the  foramen  of  Winslow  or  over  the  pelvic  brim 
(Morison).  • 

Distention  of  the  gall-bladder  is  ordinarily  due  to  ( i )  inflammatory  obstruction 
of  the  cystic  duct  (cholangitis)  ;  (2)  mechanical  obstruction  of  the  cystic  duct,  usu- 
ally from  the  impaction  of  gall-stones  ;  (3)  acute  cholecystitis,  (a)  catarrhal,  (b} 
suppurative  ;  or  (4)  obstruction  of  the  common  duct  from  tumor  or,  much  more 
rarely,  from  impaction  of  a  calculus  in  that  duct  before  the  gall-bladder  has  become 
inflamed,  contracted,  and  formed  adhesions.  The  gall-bladder  itself  may  be  the 
primary  seat  of  a  malignant  growth.  It  is  impossible  to  feel  the  normal  gall-bladder 
through  the  abdominal  wall. 

Enlargement  of  the  gall-bladder  from  any  cause  usually  takes  place  in  a  down- 
ward and  forward  direction  on  a  line  which,  beginning  a  little  below  the  ninth  costal 
cartilage,  crosses  the  linea  alba  just  below  the  umbilicus.  If  the  liver  is  of  normal 
size,  the  neck  of  the  gall-bladder  is  about  opposite  the  ninth  costal  cartilage.  If  the 
liver  is  enlarged,  the  gall-bladder  will  be  so  much  depressed  that  its  neck  may  be  on 
a  level  with,  or  even  lower  than,  the  umbilicus.  The  rounded,  pear-shaped,  or 
gourd-like  fundus  can  usually  be  felt,  movable  laterally,  and  sometimes  with  a  pal- 
pable groove  between  it  and  the  lower  edge  of  the  liver.  The  swelling  descends 

109 


1730 


Hl'MAN    ANATOMY. 


during  inspiration.  If  the  cause  of  the  enlargement  is  inflammatory  and  adhesive 
peritonitis  has  resulted,  the  tumor  may  be  fixed  so  that  it  does  not  move  with  res- 
piration ;  but  there  is  then,  especially  in  acute  cases,  apt  to  be  pain  and  tender- 
ness over  the  swelling  or  at  a  point  between  the  ninth  costal  cartilage  and  the 
umbilicus. 

It  may  be  mentioned  here  that  the  diagnosis  between  the  chronic  form  of  gall- 
bladder disease  and  movable  kidney  is  not  always  easy  ;  that  the  two  conditions  not 
infrequently  coexist  in  the  same  person  ;  and  that  the  possibility  of  error  is  increased 
by  the  fact  that  they  are  each  met  with  much  oftener  in  women  than  in  men,  and 
that  the  right  kidney  is  far  more  frequently  movable  than  the  left. 

The  anatomical  explanation  is  that  in  women  with  flabby  abdominal  walls 
either  tight  lacing  or  a  relatively  slight  jar  or  strain  tends  to  produce  displacement  of 
both  the  kidney  and  the  liver,  the  latter  resulting  in  tension  or  angulation  and  con- 
sequent obstruction'  of  the  bile-ducts.  The  two  conditions  also  act  reciprocally, 
descent  of  the  liver  causing  displacement  of  the  kidney,  which,  through  its  traction 
upon  the  duodenum,  tends  to  obstruct  the  bile-ducts. 

A  movable  kidney,  as  compared  with  an  enlarged  gall-bladder,  is  less  influenced 
by  respiration  ;  has  a  wider  range  of  motion,  especially  in  the  long  axis  of  the  body  ; 
is  more  influenced  by  position  ;  slips  backward  towards  the  loin  instead  of  upward 
beneath  the  liver  ;  is  less  often  visible  and  less  frequently  tender  on  pressure,  which 
is  apt  to  cause  a  sickening  sensation  analogous  to  testicular  nausea  (page  1951). 

Acute  cholecystitis  (phlegmonous)  is  due  to  infection.  The  colon  or  typhoid 
bacillus,  or  the  pneumococcus,  streptococcus,  or  staphylococcus,  may  reach  the  gall- 
bladder either  through  the  blood,  as  during  a  pneumonia,  by  lymphatic  and  vascular 
channels,  as  after  an  appendicitis,  or  through  the  intestine  and  bile-ducts,  as  in  some 
of  the  post-typhoidal  cases. 

The  symptoms  are  (#)  generalized  abdominal  pain,  due  to  the  association  of 
the  cystic  plexus,  through  the  coeliac,  with  the  superior  mesenteric  ;  (b)  pain  below 
the  right  costal  margin  passing  towards  the  epigastrium, — i.e. ,  referred  to  the  coeliac 
and  solar  plexuses, — and  towards  the  right  scapular  region,  from  the  association  of 
the  phrenic  and  the  supra-acromial  nerves  through  the  fourth  cervical  (page  1758) ;  (c) 
rigidity  over  the  right  hypochondrium,  due  to  the  connection  between  the  splanch- 
nics  and  the  intercostals  ;  (</)  nausea,  vomiting,  and  prostration,  due  at  first  to  the 
close  relation  of  the  cystic  plexus  with  the  cceliac  and  solar  plexuses,  later  to  toxaemia 
and  to  peritonitis  ;  (e)  localized  tenderness  at  the  junction  of  the  upper  and  middle 
thirds  of  a  line  drawn  from  the  ninth  rib  to  the  umbilicus, — i.e.,  over  the  fundus  of 
the  inflamed  gall-bladder;  (_/)  distention  and  paresis  of  the  intestines,  due  sometimes 
to  a  localized  peritonitis  affecting  the  hepatic  flexure  of  the  colon  and  simulating 
an  acute  intestinal  obstruction. 

Gangrene  has  occurred,  emphasizing  the  clinical  and  pathological  resemblance 
of  this  condition  to  appendicitis,  but  is  very  rare,  illustrating  the  importance  of  one 
anatomical  factor — the  scanty  blood-supply — in  causing  the  gangrene  which  is  so 
exceedingly  common  in*  that  disease  (page  1682).  Bacterial  infection  and  absence  of 
drainage  (and  therefore  tension)  are  two  conditions  predisposing  to  gangren 
present  in  both  cases  ;  but  the  third — thrombosis  of  the  nutrient  vessels — determines 
the  frequency  of  gangrene  in  the  appendix,  which  is  supplied  by  only  one  nutrient 
artery,  and  is  relatively  ineffective  in  the  case  of  the  gall-bladder,  which  has  a  rich 
blood-supply  through  the  large  cystic  artery  and  also  through  the  anastomoses  of  its 
branches  with  the  hepatic  vessels  where  the  gall-bladder  is  fixed  to  the  liver  (Ma 
Robson). 

l''.tnpyema  of  the  gall-bladder  (suppurative  cholecystitis),  due  usually  to  chole 
lithiasis,  obstructive  catarrh,  and  infection  through  the  ducts,  may  discharge  itself  i 
various  directions  determined  by  the  occurrence  of  inflammatory  adhesions.  The 
most  common  communication  is  with  the  cutaneous  surface,  the  pus  having  been 
evacuated  through  the  parietes  beneath  the  costal  margin  in  50  per  cent,  of  Cour- 
voisier's  184  cases,  and  in  the  umbilical  region,  where  it  was  conducted  by  the  sus- 
pensory ligament,  in  29  per  cent.  The  colon  or  duodenum  beneath,  the  subphrenic 
space  or  pleiinil  cavity  above-,  and  the  right  prenephric  peritoneal  pouch — walled 
off  by  adhesions — have  been  favorite  seats  for  the  spontaneous  evacuation  of  pus 


its 

I 


PRACTICAL    CONSIDERATIONS:    THK    BILK    DUCT.  1731 

and  gall-stones  in  old  cases  of  empyema  of  the  gall-bladder.    Its  anatomical  relations 
to  surrounding  structures  and  spaces  should  therefore  be  carefully  studied. 

Cholelithiasis. — As  the  normal  expulsive  efforts  of  the  muscular  walls  of  the 
gall-bladder  are  usually  aided  by  the  contraction  of  the  abdominal  muscles  during 
exercise,  gall-stones  are  more  commonly  found  in  persons  of  sedentary  habits,  in 
invalids,  and  in  females,  especially  in  multipara.  Tight  lacing,  by  depressing  both 
liver  and  gall-bladder,  as  well  as  kidney  (vide  supra),  is  also  a  distinct  predisposing 
cause.  Bacterial  infection  with  the  colon  or  typhoid  bacillus,  and  more  rarely  with 
other  organisms,  is,  however,  a  frequent  exciting  cause  of  the  hypersecretion  and 
epithelial  proliferation  which  lead  to  the  formation  of  gall-stones. 

The  presence  of  stones  in  the  gall-bladder  may  be  unaccompanied  by  symptoms, 
or  may  cause  the  development  of  such  phenomena  as  either  have  no  distinct  ana- 
tomical bearing  (biliary  fever  and  secondary  visceral  lesions)  or  as  have  already 
been  considered  (abscess  of  the  liver,  empyema  of  the  gall-bladder,  fistulae,  etc.). 
There  are  mechanical  accidents,  however,  connected  with  the  emigration  of  the 
stones  which  will  be  considered  from  the  anatomical  stand-point  in  relation  to  the 
biliary  ducts. 

The  Cystic  and  Common  Bile-Ducts. — The  cystic  duct  is  the  narrowest 
portion  of  the  biliary  passages.  Its  calibre  would  permit  the  passage  of  a  probe 
through  it  into  the  hepatic  duct,  but  the  irregular  folds  of  its  mucous  membrane 
(sometimes  regarded  as  constituting  a  "spiral  valve," — the  valve  of  Heister)  usu- 
ally effectually  prevent  satisfactory  probing.  Its  muscular  fibres  are  better  devel- 
oped than  are  those  of  the  other  biliary  ducts.  The  passage  of  a  stone  through  it 
is  attended  by  (i)  colicky  pains  of  the  sort  usually  associated  with  violent  mus- 
cular contraction  ;  ( 2 )  continuous  pain  resembling  that  due  to  an  acute  cholecystitis 
(the  two  conditions  being  often  mistaken  one  for  the  other),  and  due  (a)  to  the  slow 
progress  of  the  stone  in  the  cystic  duct,  in  which  it  takes  a  rotary  course  owing  to 
the  arrangement  of  the  mucous  folds  ;  (£)  to  the  acute  inflammation  which  usually 
accompanies  an  attack  ;  and  (c)  to  the  stretching  and  distention  of  the  gall-bladder  by 
retained  secretions  (Osier).  The  pain  may  be  even  more  intense,  and  is  apt  to  be 
accompanied  by  (3)  vomiting,  (4)  prof "use  sweating,  and  (5)  great  depression  of  the 
circulation,  all  due  to  reflex  irritation  of  the  sympathetic  plexuses  and  the  pneumo- 
gastric.  There  may  be  (6)  a  rigor,  either  purely  nervous  or  due  "to  retained  secre- 
tions and  a  concurrent  lithaemic  inflammation.  In  the  latter  case  there  will  be  (7) 
fever  from  the  accompanying  toxaemia. 

If  the  stone  passes  into  the  intestine,  all  the  symptoms  usually  disappear.  It 
may  cause  (8)  intestinal  obstruction,  and  is  a  far  more  common  factor  in  the  pro- 
duction of  this  condition  than  are  enteroliths.  Of  149  cases  of  this  type  of  obstruc- 
tion, 133  were  due  to  gall-stones  and  only  16  to  enteroliths,  and  10  of  these  had 
gall-stone  nuclei.  Although  a  stone  of  considerable  size  may  pass  through  the  duct, 
those  large  enough  to  bring  about  intestinal  obstruction  usually  enter  the  duodenum 
by  ulceration.  If  the  stone  becomes  impacted  in  the  cystic  duct,  (9)  dilatation  of 
the  gall-bladder  with  mucus  (hydrops)  occurs  ;  or  (10)  cholecystitis,  acute  or  chronic, 
may  follow  (vide  supra}.  Calcification  and  atrophy  of  the  gall-bladder  are  not 
uncommon  sequelae. 

The  stone  may  pass  into  and  obstruct  the  common  duct.  This  is  about  three 
times  the  diameter  of  the  cystic  duct,  and,  therefore,  many  stones  which  have  given 
rise  to  the  above  symptoms  pass  through  it  easily.  If  a  stone  permanently  occludes 
it,  there  will  usually  be  deep  and  persistent  jaundice,  clay-colored  stools,  vague  and 
dull  hepatic  and  shoulder  pain,  rarely  colicky  in  character,  and  absence  of  septic 
phenomena  and  of  enlarged  gall-bladder,  the  latter  symptom  occurring  in  not  more 
than  10  or  12  per  cent,  of  cases  of  calculous  common-duct  obstruction.  A  stone  may 
pass  as  far  as  the  ampulla  of  Vater  and  act  as  a  "  ball- valve, ' '  in  which  case  there 
will  be  variable  jaundice  and  ague-like  paroxysms  of  chills,  fever,  and  sweating, 
accompanied  by  hepatic  pains  and  gastric  disturbance  (Osier).  The  mechanical 
effect  of  a  stone  in  such  a  position,  plus  the  resulting  nerve  irritation  and  infective 
cholangitis,  sufficiently  explains  these  phenomena. 

Occlusion  of  the  common  ducts  may  occur  from  other  causes,  as  stricture  follow- 
ing ulceration  due  to  stone,  the  presence  of  lumbricoid  worms,  echinococci,  etc.,  or 


1732  HUMAN    ANATOMY. 

even  of  foreign  bodies  which  have  been  swallowed.  Pressure  from  extrinsic  causes  is 
far  more  frequent,  however,  as  a  cause  of  occlusion.  It  may  be  due  to  carcinoma  of 
the  lymph-nodes  in  the  transverse  fissure,  secondary  to  rectal  or  to  gastric  cancer  ; 
or  to  enlargement  of  the  head  of  the  pancreas  from  new  growth  or  from  inflammation  ; 
or  to  aneurism  of  branches  of  the  cceliac  axis. 

In  these  cases,  contrary  to  what  is  found  in  occlusion  from  gall-stones,  the  gall- 
bladder is  usually  enlarged. 

Congenital  obliteration  of  the  ducts  may  occur. 

Operations  on  the  Gall- Bladder  and  Biliary  Ducts. — A  vertical  incision,  at  least 
7.5-10  cm.  (3-4  in. )  in  length  from  the  costal  margin  downward,  made  over  the 
middle  of  the  right  rectus  muscle,  the  fibres  of  which  are  separated,  will  usually 
satisfactorily  expose  the  gall-bladder.  If  it  is  necessary  to  open  either  of  the  ducts, 
the  incision  may  be  prolonged  upward  in  the  interval  between  the  xiphoid  cartilage 
and  the  costal  cartilages.  If  the  liver  is  then  drawn  downward  from  beneath  the  ribs 
and  rotated  upward  and  outward  and  the  transverse  colon  is  drawn  downward,  the 
subhepatic  space  will  be  well  exposed,  bounded  by  the  under  surface  of  the  liver  above 
and  externally,  the  colon  and  transverse  mesocolon  below,  and  the  duodenum  and 
pyloric  end  of  the  stomach  internally.  In  this  position,  especially  if  a  sand-bag  has 
been  placed  beneath  the  back  opposite  the  liver,  so  as  to  push  the  spine  forward,  the 
cystic  and  common  ducts  are  brought  close  to  the  surface,  the  angle  between  them  is 
effaced,  the  region  of  entrance  into  the  duodenum  is  in  full  view,  and  incision  for  drain- 
age of  the  gall-bladder  (cholecystostomy),  or  for  the  extraction  of  a  calculus  either 
from  the  gall-bladder  (cholelithotomy)  or  a  duct  (choledochotomy),  or  for  the  re- 
moval of  the  gall-bladder  (cholecystectomy)  becomes  possible.  If  there  are  many  and 
troublesome  adhesions,  the  fundus  and  body  of  the  gall-bladder  being  buried  and  not 
recognizable,  it  is  well  first  to  locate  the  hepatico-duodenal  fold  of  peritoneum, — the 
right  border  of  the  lesser  omentum, — in  which  the  common  duct  may  be  traced  from 
its  duodenal  termination  upward,  the  portal  vein  lying  behind  it  and  the  hepatic 
artery  to  the  left.  The  cystic  and  hepatic  ducts  may  then  be  identified.  The  ducts 
may  often  best  be  examined  by  passing  the  forefinger  of  the  left  hand  through  the 
foramen  of  Winslow,  the  back  of  the  surgeon  being  turned  towards  the  patient. 
The  duct,  the  portal  vein,  and  the  hepatic  artery  may  thus  easily  be  grasped  between 
the  thumb  and  finger.  The  close  relation  of  the  lower  end  of  the  common  duct  to 
the  vena  cava  should  be  remembered  in  operations  upon  it.  This  portion  may  be 
reached,  if  necessary,  as  in  some  cases  of  stone  impacted  at  the  duodenal  papilla, 
by  opening  the  second  portion  of  the  duodenum  and  slitting  up  the  duct  as  it  lies  in 
the  inner  and  posterior  wall  of  the  intestine,  where  it  may  be  felt  as  a  cord. 

The  duct  may  be  reached  at  a  higher  point  by  an  incision  through  the  perito- 
neum to  the  right  of  the  duodenum,  the  latter  being  freed  posteriorly  and  drawn 
towards  the  median  line. 

In  cases  in  which  the  common  duct  is  permanently  obstructed  a  portion  of  the 
duodenum  or  jejunum  may  be  anastomosed  with  the  gall-bladder  (cholecystenteros- 
tomy)  by  direct  suture. 

THE   PANCREAS. 

The  pancreas,  the  "  abdominal  salivary  gland,"  lies  moulded  across  the  spinal 
column  with  its  head  on  the  right,  enclosed  in  the  loop  of  the  duodenum,  and  its 
tail  on  the  left,  in  contact  with  the  spleen.  It  is  of  a  light  straw  color  running  into 
red,  according  to  the  amount  of  blood  within  the  organ.  The  weight  ranges  from 
30-150  gm.  (1-5  oz.)  or  even  more.  The  specific  gravity  is  about  1045.  The 
length  in  situ  is  approximately  15  cm.  (about  6  in.).  It  consists  of  an  enlarged 
descending  part  on  the  right,  the  licad,  and  of  a  long  body  placed  transversely, 
which  is  needlessly  divided  into  neck,  body,  and  tail.  When  the  organ  is  removed 
from  the  body  and  straightened  it  somewhat  resembles  a  revolver  in  shape,  the  head 
being  the  handle.  The  gland,  however,  is  so  modelled  by  the  surrounding  parts 
that  its  true  form  is  sn-n  only  in  its  undisturbed  position,  or  after  hardening  in  situ 
before  removal  from  the  body. 

The  head  (caput  paiicreatis)  is  a  rounded  but  irregular  disk  packed  into  the 
space  between  the  first  and  third  parts  of  the  duodenum,  and  lying  close  against  the 


THE   PANCREAS. 


1733 


left  of  the  second  part.  It  overlaps  both  the  second  and  third  parts  anteriorly,  and 
tends  to  insinuate  itself  behind  them.  We  have  seen  it  overlapping  the  fourth  part 
also.  So  much  has  been  said  of  the  variations  of  the  duodenum  (page  1644)  that  it 
must  be  evident  that  the  head  of  the  pancreas  can  hardly  have  any  certain  size  or 
shape.  Its  diameter  from  above  downward  is  probably  rarely  less  than  7  cm.  and 
may  be  greater.  It  is  separated  from  the  neck  by  a  groove  on  the  front  of  the  gland 
for  the  gastro-duodenal  branch  of  the  hepatic  artery.  It  rests  behind  on  the  inferior 
vena  cava,  sometimes  on  the  right  renal  vein,  and  may  approach  the  right  suprarenal 
body.  It  is  opposite  the  first  and  second  lumbar  vertebne  and  often  a  part  of  the 
third  lumbar  vertebra. 

The  body  (corpus  pancreatis),  including  the  neck  and  tail,  is  prismatic,  having. 
a  posterior,  an  antero- superior,  and  a  narrow  inferior  surface.  It  is  so  tortuous  in 
its  natural  position  as  to  seem  shorter  than  it  is.  Starting  on  the  right  of  the  spine 
at  the  level  of  the  first  lumbar  vertebra,  it  passes  around  it  to  the  left  and  backward 
and  again  forward  to  the  spleen,  which  it  may  or  may  not  cross.  Towards  its  end 
it  also  turns  downward. 

FIG.  1461. 


Portal  vein       Hepatic  artery 


Left  suprarenal  body 
Left  kidney 


— \ Spleen 


Right  suprarenal 
body 

Vena  cava 

Common 
bile-duct- 


First  part  of 
duodenum 
Right  kidney— j 

Gastro 

duodenai 
artery 


Tail  of 
pancreas 


Splenic 
flexure  of 
colon 

Beginning 
of  jejunum 
Superior  mes- 
enteric  artery 
Superior  mes- 

enteric  vein 
Descending 

colon 


Aorta 


Vena  cav 


Anterior  aspect  of  pancreas  in  situ;  the  organ  is  exceptionally  broad,  and  covers  more  of  left  kidney  than  usual; 

peritoneum  has  been  removed. 

The  neck  is  the  part  (2-3  cm.  in  length)  which  crosses  the  portal  vein  with  a 
forward  convexity,  being  deeply  grooved  by  the  vein  on  its  posterior  surface.  The 
left  extremity  of  the  body  is  the  tail  (cattda  pancreatis),  the  end  of  which  is  very 
variable  in  form.  If  it  lies  in  front  of  the  spleen  it  is  more  or  less  pointed,  but  if  it 
ends  against  the  gastric  surface  of  that  organ  it  may  have  a  true  terminal  concave 
surface,  fitting  it  accurately  (Fig.  1461). 

The  posterior  surface  has  first  (from  the  neck  towards  the  left)  the  deep 
groove  for  the  portal  vein,  which  may  be  entirely  surrounded  by  glandular  tissue. 
Beyond  this  it  lies  on  the  vena  cava,  then  on  the  aorta  between  the  cceliac  axis  and 
the  superior  mesenteric  artery,  which  groove  it  above  and  below.  It  next  lies  on  the 
left  pillar  of  the  diaphragm,  the  left  suprarenal  capsule,  and  the  left  kidney.  The 
left  end  may  have  a  concave  surface  resting  on  the  gastric  surface  of  the  spleen,  or 


1734 


HUMAN   ANATOMY. 


it  may  extend  across  this  surface,  or  rest  on  the  basal  one.  There  are  two  horizon- 
tal grooves  on  the  posterior  surface.  The  lower,  which  is  the  longer  and  deeper,  is 
caused  by  the  splenic  vein.  It  extends  from  the  left  end  to  the  groove  for  the  portal 
vein,  inclining  to  the  lower  border  as  it  approaches  it.  A  smaller  groove  for  the 
splenic  artery  lies  above  the  former  from  the  left  to  near  the  aorta. 

The  antero-superior  surface,  the  largest  of  the  three,  slants  downward  and 
forward,  presenting  a  concavity  which  forms  a  part  of  the  stomach-bed.  It  is  on 
the  average  some  4  cm.  broad,  but  may  exceed  5  cm.  There  is  often  a  swelling — the 
omental  tuberosity  (tuber  omentale) — to  the  left  of  the  neck  opposite  the  aorta.  This 
is  behind  the  lower  end  of  the  vertical  part  of  the  lesser  curvature  of  the  stomach, 
and  is  in  contact  with  that  organ  rather  than  with  the  omentum. 

The  inferior  surface,  the  smallest,  rarely  as  much  as  2  cm.  in  breadth, 
rests  on  the  lower  layer  of  the  transverse  mesocolon.  It  is  rounded  and  irregular, 
except  where  it  lies  above  the  duodeno-jejunal  fold,  where  it  is  smooth  and  concave. 
To  the  right  of  this  it  is  grooved  by  the  superior  mesenteric  artery. 

The  borders  at  which  the  surfaces  meet  call  for  no  special  description  beyond 
that  both  the  inferior  ones  are  grooved  by  the  superior  mesenteric  artery  and  the 
upper  by  the  coeliac  axis. 

Structure. — While  agreeing  in  its  general  structure  with  other  serous  salivary 
glands,  as  the  parotid,  the  pancreas  differs  in  certain  particulars.  The  most  im- 

FIG.  1462. 


Section  of  pancreas  under  low  magnification,  showing  general  arrangement  of  lobules.     X  30. 

portant  of  these  are  the  tubular,  rather  than  saccular,  form  of  the  alveoli,  the  marked 
differentiation  of  a  granular  zone  in  the  protoplasm  of  the  secreting  cells,  the  abseno 
of  specialized  intralobular  ducts,  and  the  presence  of  the  islands  of  Langerhans. 

The  chief  pancreatic  duct  gives  off  numerous  lateral  interlobular  branches  which 
are  lined  with  a  single  layer  of  columnar  epithelium,  about  .006  mm.  in  height,  the 
direct  continuation  of  that  clothing  the  large  ducts,  in  which  the  cells  are  from  two 
to  three  times  as  tall.  The  canals  springing  from  the  interlobular  ducts  after  enter- 
ing the  lobules  possess  a  layer  of  flattened  epithelial  plates  some  .012  mm.  long  by 
.003  mm.  high,  and  correspond  to  the  intercalated  or  intermediate  ducts.  The  in- 
tralobular canals  being  wanting,  the  relatively  long  intermediate  ducts  pass  directly 
into  tin-  tubular  alveoli,  within  which  their  attenuated  epithelium  protrudes  as  the 
centro-acinal  cells.  The  relation  of  the  latter  to  the  usual  glandular  elements  lining 
the  alveolus  is  peculiar,  the  thinned-out  and  spindle  duct-cells  being  surrounded  ex- 
ternally by  the  secreting  cells. 

The  tubular  alveoli  of  the  gland,  often  tortuous  and  sometimes  divided,  possess 
a  well  defined  membrana  propria  against  which  lie  the  secreting  cells.  The  latter 


THE  PANCREAS. 


1735 


FIG.   1463. 


are  usually  of  a  blunted  pyramidal  shape,  although  many  aberrant  forms  are  seen, 
with  an  average  length  of  about  .010  mm.  During  functional  inactivity  their  cyto- 
plasm exhibits  two  well-differentiated  zones  :  an  inner  one,  next  the  lumen,  which  is 
highly  granular,  and  an  outer  one,  next  the  basement  membrane,  which  is  free  from 
granules  and  at  times  almost  homogeneous.  The  round  or  oval  nucleus  occupies 
the  external  area.  The  relative  breadth  of  these  two  zones  varies  with  the  func- 
tional activity  of  the  cells.  During  fasting,  when  the  latter  are  stored  with  zymogen 
particles,  the  granular  zone  is  very  broad  and  the  outer  homogeneous  one  corre- 
spondingly narrow.  With  beginning  discharge  of  the  pancreatic  secretion  during 
digestion,  the  granular  zone  diminishes  and  reaches  its  minimum,  almost  dis- 
appearing when  the  gland  is  exhausted.  The  return  of  the  latter  to  a  condition  of 
rest  is  accompanied  by  the  formation  and  gradual  accumulation  of  a  new  store  of 
zymogen  particles  until  the  granular  zone  is  again  restored  to  its  maximum.  Occa- 
sionally in  fixed  tissue  the  parietal  cells  exhibit  within  their  cytoplasm  a  body 
termed  the paranudeus  (Nebenkern).  The  latter  is  of  uncertain  form,  often  singu- 
larly round  and  indented,  and 
smaller  than  the  nucleus  in  the 
vicinity  of  which  it  usually  lies. 
The  nature  and  significance  of 
this  body  are  still  undeter- 
mined, some  observers  regard- 
ing it  as  an  artifact  (Ebner), 
others  that  its  presence  is  in 
some  way  connected  with 
changes  affecting  the  nucleus 
(Henneguy).  Intercellular  se- 
cretion-capillaries have  been 
demonstrated  in  the  alveoli  of 
the  pancreas.  They  extend 
between  the  cells  for  sonic  dis- 
tance, but  do  not  reach  the 
basement  membrane  surround- 
ing the  acini.  Intracellular 
secretion-vacuoles  are  also  de- 
monstrable at  times  by  means 
of  Golgi  stains,  but  are  tem- 
porary and  cannot  be  regarded 
as  constant  details  of  the  cells 
(Ebner). 

The  interalveolar  cell- 
areas,  or  islands  of  Langer- 
hans,  appear  as  small  collec- 
tions of  cells,  some  .3  mm.  in  diameter,  lying  between  the  tubular  acini,  from  which 
they  are  separated  by  a  delicate  envelope  of  connective  tissue.  These  cell-areas  are 
constant  features  of  the  pancreas,  not  only  of  man,  but  likewise  of  a  wide  range  of 
animals  representing  mammals,  birds,  reptiles,  and  amphibians.  Their  distribution 
within  the  pancreas  is  by  no  means  uniform,  since,  as  has  been  shown  by  Opie,'  while 
about  equally  numerous  in  the  head  and  adjacent  part  of  the  body  of  the  organ,  they 
may  be  almost  double  in  number  towards  the  tail.  The  cells  composing  these  masses, 
although  developed  from  the  same  tissue  which  gives  rise  to  the  usual  glandular 
elements  of  the  pancreas,  differ  from  the  latter  in  being  smaller,  polygonal  rather 
than  pyramidal  in  form,  less  granular,  and  undifferentiated  into  the  characteristic 
zones  usually  seen  in  the  pancreatic  cells.  They  are  arranged  as  a  net-work  con- 
sisting of  solid  cords  or  trabeculae,  the  meshes  of  which  are  occupied  by  blood- 
capillaries  of  large  size  ;  the  whole  recalling  the  arrangement  of  hepatic  tissue.  No 
extension  of  the  system  of  excretory  tubes  has  been  demonstrated  within  these 
cell-islands,  secretion-capillaries  being  therefore  wanting.  The  significance  of  the 
islands  of  Langerhans  has  long  been  a  subject  of  dispute,  but  in  view  of  their  isola- 
1  Johns  Hopkins  Hospital  Bulletin,  September,  1900. 


Section  of  pancreas,  showing  interlobular  connective  tissue  with  vessels 
and  duct  surrounded  by  tubular  alveoli.     X  200. 


1736 


HUMAN   ANATOMY. 


tion  from  the  surrounding  glandular  tissue  and  their  close  relation  with  the  blood- 
vessels, the  opinion  is  held  by  many  that  they  produce  some  substance  which  passes 
directly  into  the  blood  and  may  be  regarded,  at  least  provisionally,  as  concerned  in 
' '  internal  secretion. ' ' 

The  Pancreatic  Ducts. — The  gland  is  surrounded  by  a  fibrous  sheath  which 
sends  in  many  processes  dividing  it  into  small  lobules.  The  chief  excretory  canal  in 
the  adult  is  the  duct  of  Wirsung  (ductus  pancreaticus),  which,  beginning  near  the  end 
of  the  tail,  runs  through  the  middle  of  the  pancreas  towards  the  right,  and  bends 
downward  as  it  passes  through  the  head.  Branches  sprout  from  the  main  duct 
at  right  angles,  which  receive  bunches  of  smaller  ramifications.  The  diameter  of 
the  duct  near  its  end  is  about  5  mm.  It  descends  just  in  front  of  the  common  bile- 
duct  to  the  wall  of  the  duodenum  and  empties  in  common  with  it  at  the  papilla 
(Fig.  1455).  Its  termination  very  often  is  in  the  floor  of  the  ampulla  (diverticulum 
duodenale),  so  that  the  papilla  presents  but  one  opening.  The  tributary  ducts  of  the 
head  are  larger  than  the  others.  A  particularly  large  one — the  duct  of  Santorini 

(ductus  pancrcaticus  acces- 

FIG.  1464.  sorius) — is    in    the   early 

stage  of  development  the 
chief  duct  of  the  head, 
and  consequently  of  the 
gland.  In  the  adult  it 
usually  descends  from  the 
right  to  empty  into  the 
duct  of  Wirsung  as  the 
latter  turns  downward. 
In  about  half  the  cases, 
according  to  Schirmer,1  it 
opens  independently  into 
the  duodenum,  some  3 
cm.  above  the  papilla  and 
more  anteriorly.  The  or- 
ifice is  usually  surrounded 
by  a  small  raised  ring. 
Even  when  so  terminating 
it  retains  its  connection 
with  the  duct  of  Wir- 
sung. Thus  fluid  in  the 
body  of  the  pancreas  may 
in  such  cases  pass  into 
the  duodenum  by  either 
opening,  and  fluid  in  the 
duct  ot  Santorini  may  pass  either  directly  into  the  gut  or  through  the  duct  of  Wir- 
sung. The  canal  of  Santorini  may  be  no  more  than  an  insignificant  side  branch  of 
the  other,  or  it  may  be  the  chief,  or  sole,  excretory  duct. 

Relations  to  the  Peritoneum. — Although  developed  in  both  the  posterior 
and  the  anterior  mesenteries,  the  pancreas,  owing  to  the  changes  by  which  the  spleen 
on  the  left  and  the  descending  part  of  the  duodenum  on  the  right  have  come  to  lie 
against  the  posterior  abdominal  wall,  is  entirely  retroperitoneal.  The  posterior  sur- 
face, with  the  possible  exception  of  the  end  of  the  tail,  which  may  be  surrounded  by 
peritoneum,  is  attached  to  the  parts  behind  it  by  connective  tissue.  The  layers  of 
peritoneum  covering  the  antero-superior  and  the  inferior  surfaces  meet  to  form  the 
transverse  mesocolon,  which  is  attached  along  the  border  between  these  surfaces,  and 
is  continued  on  the  right  across  the  head,  and  may  sometimes  rise  towards  the  left 
onto  the  antero-superior  surface.  The  gastro- pancreatic  fold,  made  by  the  gastric 
artery,  crosses  the  gland  upward  from  a  point  a  varying  distance  below  the  coeliac 
axis. 

Vessels. — Tin*  arteries  are  many  small  branches  derived  from  the  splenic, 
hepatic,  and  superior  mesenteric.  As  the  splenic  runs  along  the  top  of  the  posterior 

1  Beitriige  ztir  Geschichte  uncl  Anatomic  des  Pancreas,  Basel,  1803. 


Connective- 
tissue  envelope 


Capillary 
blood-vessel 


Modified 
epithelial  cells 


Alveolus  with 
ordinary  cells 


Section  of  pancreas,  showing  island  of  Langerhans.     X  200. 


THE   PANCREAS. 


1737 


surface  it  sends  a  series  of  branches  into  the  upper  part  of  the  body  and  tail.  The 
hepatic  runs  along  the  top  of  the  front  of  the  head  and  neck,  doing  the  same.  In  the 
groove  between  head  and  neck  the  gastro-duodenal  sends  the  superior  pancreatico- 
duodenal  across  the  front  of  the  gland,  supplying  chiefly  the  head.  The  superior 
mesenteric  artery,  just  after  its  origin,  sends  from  its  right  the  inferior  pancreatico- 
duodenal.  This  vessel  gives  off  a  larger  branch  running  to  the  right  to  meet  the 
superior  pancreatico-duodenal  on  the  front  of  the  head,  and  sends  a  smaller  branch 
to  the  left  along  the  lower  surface.  Sometimes  the  two  branches  which  meet  across 
the  head  enclose  it  by  a  similar  anastomosis  behind.  The  veins  follow  in  the  main 
the  arteries.  They  are  all  tributaries  of  the  portal  system,  and  some  open  directly 
into  the  portal  vein.  The  lymphatics  are  many.  Most  of  them  run  to  the  cceliac 
and  splenic  plexuses.  A  small  group  of  lymph-nodes  is  situated  on  the  front  of  the 
head. 

The  nerves,  composed  chiefly  of   non-medullated  fibres,   are  from  the  solar 
plexus,  by  way  of  the  cceliac,  splenic,  and  superior  mesenteric  plexuses. 


FIG.   1465. 


1  .*>.-.' 


Section   of   injected   pancreas,  showing   intralobular   capillary   net-works;   also   convolutions  of   islands  of 

Langerhans.      •    50. 

Development. — The  human  pancreas  develops  from  two  separate  anlages,  a 
dorsal  and  a  ventral  one.  The  former,  which  appears  by  the  fourth  fcetal  week,  is 
a  direct  outgrowth  from  the  primitive  duodenum.  The  ventral  anlage,  slightly  later 
in  its  formation,  develops  as  two  outgrowths,  one  from  each  side  of  the  early  bile- 
duct,  and  is  therefore  not  strictly  a  direct  derivative  from  the  gut.  The  left  ventral 
outgrowth  soon  disappears,  leaving  the  right  one  connected  with  the  bile-canal. 
This  close  association  is  retained  throughout  life,  as  evidenced  by  the  intimate  rela- 
tions between  the  common  bile  and  pancreatic  ducts.  The  dorsal  pancreas  rapidly 
grows,  elongates,  and  soon  becomes  the  chief  part  of  the  organ,  opening  by  an  in- 
dependent canal — the  duct  of  Santorini — into  the  duodenum.  The  repeated  division 
of  the  duct  and  the  proliferation  and  extension  of  the  terminal  compartments  pro- 
duce the  system  of  excretory  passages  and  glandular  tissue  of  the  organ.  The  ven- 
tral pancreas,  which  has  meanwhile  increased  more  slowly,  and  in  consequence  of  the 
changes  in  the  gut  has  suffered  displacement  to  the  left  and  behind,  grows  towards 
the  dorsal  gland,  with  which  it  soon  inseparably  fuses.  The  head  of  the  fully  formed 


1738 


HUMAN   ANATOMY. 


organ  represents  the  primitive  ventral  pancreas,  the  body  and  tail  the  dorsal  seg- 
ment. The  duct  of  the  ventral  portion,  which  remains  as  the  duct  of  Wirsung,  forms 
a  communication  with  that  of  Santorini,  and  for  a  time  the  pancreas  possesses  t\vo 
outlets  into  the  duodenum.  Usually  the  duct  of  Santorini  loses  its  intestinal  con- 
nection and  becomes  tributary  to  the  duct  of  Wirsung.  Variations  from  this  ar- 
rangement are  often  encountered,  the  different  combinations  being  due  to  deviations 

FIG.   1466. 


h   d 


Diagrammatic  reconstructions,  showing  development  of  pancreas  and  relations  to  liver-ducts,  a,  common  bile- 
duct ;  *,  hepatic  and  c  cystic  ducts;  d,  right  and  e  left  ventral  pancreatic  anlages ;  /,  dorsal  pancreas  and  its 
duct  (g)  ;  h,  junctipn  of  common  bile  (a)  and  ventral  pancreatic  (d )  ducts.  After  fusion  of  ventral  and  dorsal  pan- 
creas, d  becomes  duct  of  Wirsung,^-  duct  of  Santorini,  and  /'  head  of  pancreas. 

from  the  ordinary  progress  of  development  as  to  the  fusion  of  the  two  parts  and  per- 
sistence of  their  canals.  The  areas  of  Langerhans  are  developed  from  the  same 
entoblastic  outgrowths  as  give  rise  to  the  ordinary  glandular  tissue  (Laguesse, 
Pearce1).  The  connective-tissue  septa  are  derived  from  the  ingrowing  mesoblast. 

Variations. — The  pancreas  has  been  seen  to  surround  the  descending  part  of  the  duodenum. 
Small  accessory  pancreases  have  been  found  in  the  walls  of  the  intestine.  Although  usually  in 
the  duodenum,  they  may  be  in  the  stomach  or  at  the  beginning  of  the  jejunum,  and  occasionally 
some  distance  from  it.  Presumably  they  are  parts  of  the  gland  which  became  separated  at  an 
early  stage  and  were  drawn  by  the  growth  of  the  intestine  away  from  their  original  position.2 


PRACTICAL  CONSIDERATIONS:  THE  PANCREAS. 

•  Certain  abnormalities  that  may  affect  surgical  procedures  or  may  of  themselves 
produce  symptoms  of  disease  should  be  mentioned.  Accessory  pancreases  are 
found  in  various  localities  and  may  be  mistaken  for  new  growths.  The  anterior  wall 
and  the  two  curvatures  of  the  stomach  and  the  walls  of  the  small  intestine,  especially 
the  duodenum,  are  the  situations  in  which  such  glands  are  most  frequently  foun 
They  have  ducts  opening  into  the  intestine. 

An  accessory  gland  has  been  found  to  the  right  of  the  duodenum  entirely  dis- 
tinct from  the  main  gland.  Perhaps  the  most  important  anomaly  is  one  in  which 
the  gland  completely  surrounds  the  second  part  of  the  duodenum,  constricting  it  and 
causing  dilatation  of  the  first  portion  and  of  the  stomach.  Several  cases  have  been 
reported.  The  common  bile-duct  may  also  be  contained  within  the  head  of  the  pan 
creas,  as  may  the  superior  mesenteric  vessels  within  its  body.  The  accessory  pan- 
creatic duct  may  be  absent,  or  there  may  be  three  ducts,  all  opening  into  the 
duodenum. 

Movable  Pancreas. — The  gland  may  fall  forward  or  downward  (when  it  may 
sometimes  be  felt  below  the  stomach),  or  it  may  be  a  part  of  the  contents  of  a  dia- 
phragmatic hernia,  or  may  even — but  with  great  rarity— be  contained  within  the  sac 
of  an  umbilical  hernia. 

Injuries. — The  situation  of  the  pancreas  behind  the  lesser  peritoneal  cavity  and 
the  stomach  and  between  the  spleen  and  the  duodenum,  the  partial  protection  it 
receives  from  the  costal  arch,  and  the  depth  at  which  it  lies  render  its  uncompli- 


1  American  journal  of  Anatomy,  \ol.  ii.,  1903. 

2  Zenkrr  :  Yirdiow's  Archiv,  Bd.  xxi.,  1861. 


PRACTICAL  CONSIDERATIONS  :   THE  PANCREAS.  1739 

cated  injury  of  very  rare  occurrence.  In  only  three  fatal  cases  in  which  all  other 
abdominal  viscera  escaped  has  it  been  found  to  be  ruptured. 

In  less  severe  cases  it  has  been  bruised  or  torn,  hemorrhage  has  occurred,  a 
rapidly  enlarging,  fluctuating  epigastric  tumor  has  formed,  and  the  patient  has  recov- 
ered after  a  laparotomy,  evacuation  of  the  blood-cyst,  and  drainage.  In  such  cases 
it  is  probable  that  the  traumatism  has  caused  a  laceration  of  the  posterior  layer  of  the 
lesser  sac  of  the  peritoneum  (with  which  the  pancreas  is  intimately  adherent)  and  of 
the  pancreas  itself.  Blood,  or  blood  with  pancreatic  secretion,  is  poured  into  the 
lesser  sac,  causing  adhesive  peritonitis  and  sealing  the  foramen  of  Winslow.  The 
lesser  cavity,  now  converted  into  a  closed  sac,  is  distended  with  serous  exudate, 
blood,  and  pancreatic  fluid.  After  evacuation  and  drainage,  the  pancreas  may  con- 
tinue to  pour  its  secretion  into  the  cyst-cavity  through  the  original  peritoneal  tear 
(Robson  and  Moynihan). 

Pancreatitis. — The  close  relation  of  its  duct  to  the  common  bile-duct,  which  it 
often  joins  at  the  ampulla  and  before  reaching  the  duodenum,  explains  the  frequent 
association  of  gall-stones  with  chronic  inflammation  of  the  pancreas.  A  small  ball- 
valve  calculus  in  the  ampulla  has  been  thought,  by  occluding  the  duodenal  orifice,  to 
convert  the  two  ducts  into  a  continuous  channel,  permitting,  if  the  gall-bladder  is 
functionally  active,  the  entrance  of  bile  into  the  pancreatic  duct  (duct  of  Wirsung) 
and  causing  pancreatitis.  A  larger  stone  might  occlude  also  the  orifices  of  both  the 
pancreatic  duct  and  the  bile-duct  and  produce  in  both  glands  the  troubles  associated 
with  retained  secretions.  In  the  pancreas  these  troubles  are  lessened  by  the  fact  that 
occlusion  of  the  main  pancreatic  duct  does  not  of  necessity  completely  obstruct  the 
egress  of  the  pancreatic  fluid  (Opie).  In  about  50  per  cent,  of  bodies  the  acces- 
sory duct  (duct  of  Santorini)  communicates  within  the  gland  with  the  main  duct 
and  opens  into  the  duodenum  by  a  separate  orifice  about  2.5-3.5  cm.  (1-1^6  in.) 
nearer  the  stomach  than  the  papilla  at  which  the  ampulla  of  Vater  opens  (Schirmer). 
Nevertheless,  just  as  jaundice  follows  occlusion  of  the  common  bile-duct  by  forcing 
the  secretion  of  the  liver  back  upon  that  gland,  whence  it  finds  its  way  into  the  inter- 
stitial tissue,  the  lymphatics,  the  thoracic  duct,  the  blood,  and  the  tissues  at  large, 
so  the  fat-splitting  ferment  of  the  pancreatic  juice,  in  cases  of  occlusion  of  the  pan- 
creatic duct,  finds  its  way  beyond  the  parenchyma  of  the  gland  and  causes  fat- 
necrosis,  first  in  the  vicinity  of  the  pancreas,  later  over  widespread  areas  (Opie). 

There  can,  at  any  rate,  be  no  question  of  the  etiological  association  of  gall- 
stones with  many  cases  of  pancreatitis  ;  but  it  is  probable  that  in  a  large  proportion, 
in  addition  to  mechanical  pressure  or  independently  erf  it,  bacterial  invasion  follow- 
ing inflammation  of  the  ducts  or  of  the  duodenum  is  an  important  factor. 

The  anatomical  symptoms  of  acute  pancreatitis  depend  upon  the  close  associa- 
tion of  the  gland  (#)  with  the  solar  plexus  through  the  cceliac,  superior  mesenteric, 
and  splenic  plexuses  ;  (<£)  with  the  duodenum  ;  (c )  with  the  bile-ducts  ;  (d  )  with 
the  great  blood-vessels  behind  it  ;  and  (<?)  upon  its  more  remote  relation  with  the 
epigastric  region,  directly  beneath  which,  but  at  a  considerable  depth,  it  lies.  These 
relations  explain  (a)  the  acute  and  agonizing  pain,  vomiting,  and  collapse  ;  (^) 
the  intestinal  paresis  and  distention,  often  simulating  intestinal  obstruction  ;  (c)  the 
slight  but  deepening  jaundice  sometimes  present;  (d')  the  cyanosis  of  the  face  and 
abdomen  so  commonly  seen,  and  probably  due  partly  to  reflex  cardiac  disturbance  ; 
and  (e)  the  circumscribed,  tender  epigastric  swelling  which  follows  closely  on  the 
above  symptoms.  In  differentiating  the  condition  from  acute  intestinal  obstruction, 
— for  which  it  is  most  likely  to  be  mistaken, — the  immediate  presence  of  localized 
epigastric  tenderness  and  the  usual  absence  of  both  conspicuous  general  tympany  and 
of  limited  distention  of  intestinal  coils  should  be  given  due  weight.  The  rarity  in 
the  epigastrium  of  an  obstructed  small  intestine  should  be  remembered,  and  the 
patency  and  capacity  of  the  large  intestine  should  be  determined  (Fitz). 

Chronic  obstruction  of  the  duct  may  cause  the  development  of  retention-cysts, 
of  chronic  interstitial  pancreatitis,  or  of  pancreatic  calculi.  The  latter  may  later 
become  themselves  the  chief  cause  of  continued  obstruction  and  of  further  cystic 
changes. 

In  chronic  pancreatitis,  especially  in  thin  patients  and  when  the  stomach  and 
colon  are  empty,  it  may  be  possible  to  feel  the  tender,  swollen  gland  through  the 


1740  HUMAN   ANATOMY. 

abdominal  wall.  In  gastroptosis  the  normal  pancreas  may  easily  be  felt  above  the 
stomach  and  might  readily  be  mistaken  for  a  new  growth.  Usually  the  swelling  is 
behind  the  stomach  and  above  or  behind  the  colon.  In  suppurative  pancreatitis  the 
collection  of  pus  may  push  the  stomach  forward,  or  may  become  superficial,  either 
above  or  below  it  ;  it  may,  starting  at  the  pillar  of  the  diaphragm,  and  guided  by  the 
psoas-sheath  or  the  iliac  fascia,  reach  the  iliac  region  ;  it  may  occupy  the  areolar 
tissue  of  the  loin,  becoming  a  perirenal  abscess  ;  it  may  open  into  either  the  stomach 
or  duodenum.  When  confined  to  the  pancreas,  it  will  usually  be  recognized  during 
an  exploratory  operation.  It  may  be  drained  posteriorly  by  an  incision  at  the  costo- 
vertebral  angle,  or  anteriorly  through  a  large  tube  surrounded  by  gauze  packing. 

Cancer  of  the  pancreas  usually  affects  the  head  of  the  gland,  which  accounts  for 
the  frequency  with  which  obstruction  of  the  common  bile-duct  and  of  the  duodenum 
occurs  in  such  cases. 

The  further  growth  of  the  tumor  may  cause  compression  of  the  pylorus,  of  the 
cardiac  end  of  the  stomach,  of  the  whole  stomach  by  forcing  it  against  the  anterior 
abdominal  wall,  of  the  colon,  the  ureter,  the  portal  vein,  the  vena  cava,  the  aorta, 
the  splenic  vessels,  and  the  superior  mesenteric  vein  (Robson  and  Moynihan). 

If  the  tumor  extends  to  the  right,  there  are  apt  to  be  jaundice  and  intestinal 
obstruction  ;  if  upward,  in  addition  to  these  symptoms,  pyloric  obstruction  and 
gastric  dilatation  ;  if  backward,  ascites  and  cedema  of  the  lower  limbs. 

The  pancreas  may  be  approached  for  operation  through  a  median  incision,  and 
reached,  above  the  stomach,  through  the  gastro-hepatic  omentum  ;  below  the  stom- 
ach, through  the  gastro-epiploic  omentum  or  the  transverse  mesocolon,  the  omentum 
having  been  turned  upward.  It  has  been  exposed  (in  a  case  of  hydatid  cyst) 
by  an  incision  beginning  at  the  tip  of  the  twelfth  rib  and  passing  forward  in  the 
direction  of  the  umbilicus.  Indirect  drainage  in  chronic  pancreatitis  by  means  of 
cholecystostomy  has  given  excellent  results  (Robson). 

In  cases  of  nephrectomy  the  relations  of  its  tail  to  the  left  kidney  and  renal 
vein  should  be  remembered.  The  relations  of  the  vena  porta,  the  vena  cava,  the 
aorta,  the  superior  mesenteric  artery,  and  the  coeliac  axis  are  so  close  that  when 
complicated  by  adhesions  or  infiltration,  as  in  chronic  inflammations  or  new 
growths,  operations  for  total  excision  of  the  pancreas  become  formidable  and  have 
rarely  been  undertaken.  The  close  relation  of  the  pylorus — especially  when  the 
stomach  is  depressed  by  a  new  growth — to  the  neck  of  the  pancreas  should  be 
remembered  in  pyloroplasty  or  pylorectomy,  as  should  the  proximity  of  the  spleen 
to  the  other  extremity  of  the  pancreas  in  cases  of  splenectomy. 


THE   PERITONEUM. 

lected 


The  peritoneum  is  the  serous  membrane  lining  the  abdominal  cavity  and  reflecte 
over  the  viscera.  Like  all  serous  membranes,  it  consists  of  a  free  mesothelial  sur- 
face and  a  deeper  layer  of  fibro-elastic  tissue,  the  tunica  propria.  Beneath  the  latter  a 
variable  amount  of  subperitoneal  tissue  connects  the  peritoneum  with  the  structures 
which  it  covers.  The  quantity  of  this  areolar  layer  differs  in  various  localities,  and 
it  is  at  times  difficult  to  decide  just  what  is  really  a  part  of  the  serous  membrane 
proper.  It  is  convenient  to  look  upon  the  peritoneum  as  having  a  right  side  and  a 
wrong  side  ;  the  former  is  the  free  mesothelial  surface,  the  latter  the  areolar  which 
is  attached  to  other  structures.  Thus  it  may  be  compared  to  a  wall-paper  of  a 
room  without  door  or  window,  of  which  the  right  side  is  always  free  and  the  wrong 
side  adherent  to  walls  or  to  projections  from  them.  Should  a  flue  traverse  the 
room,  it  is  easy  to  imagine  it  invested  by  a  continuation  of  the  paper  on  the  walls. 
It  passes  through  the  room,  but  is  not  within  the  closed  sac  formed  by  the  right 
side  of  the  paper.  While  it  is  true  that  during  development  the  mesothelial  covering 
grows  pari passu  with  the  tissue  beneath  it,  the  conception  that  projections  of  organs 
into  the  peritoneal  cavity  carry  the  serous  membrane  before  them  is  very  convenient 
and  justified.  The  peritoneum  of  the  female  is  the  only  serous  membrane  that  is 
not  a  closed  sac,  on  account  of  the  openings  of  the  Fallopian  tubes.  The  blood- 
vessels for  the  viscera,  around  which  the  peritoneum  is  thrown,  must  pass  on  its 
wrong  side.  To  return  to  the  simile  of  the  flue  in  the  chamber  ;  if  this  should  need 


THE    PERITONEUM. 


1741 


support,  we  can  imagine  it  suspended  in  the  middle  by  a  series  of  cords  which  might 
be  all  enclosed  in  one  fold  of  paper  from  the  ceiling.  This  would  be  a  mesentery  and 
the  cords  would  be  blood-vessels  going  to  the  gut.  The  cords,  of  course,  would  be 
on  the  wrong  side  of  the  paper  and  the  vessels  on  the  areolar  side  of  the  mem- 
brane. A  fold  of  peritoneum  may  contain  large  vessels  and  strong  bundles  of  fibres, 
and  at  other  places  be  no  more  than  a  duplicature  of  membrane.  The  former  are 
the  mesenteries  and  certain  bands  called  "ligaments,"  the  latter  plica  or  folds. 
The  complications  of  the 

peritoneum  are    reduced  FIG.  1467. 

as  much  as  possible  by 
studying  it  in  the  light  of 
development,  the  account 
of  which  has  been  already 
given  (page  1452).  Here 
only  some  of  the  chief 
points  and  general  prin- 
ciples are  recapitulated. 

In  the  early  foetus  the 
peritoneum  is  merely  the 
lining  of  the  abdomen, 
the  parietal  peritoneum, 
which  covers  the  Wolfnan 
bodies  and  the  beginning 
of  the  abdominal  walls, 
and  certain  median  folds 
called  mesenteries,  con- 
veying blood-vessels  to 
the  gut,  within  which  cer- 
tain accessory  organs  are 
developed.  There  is  a 
posterior  mesentery  ex- 
tending from  the  spine  to 
the  whole  length  of  the 
alimentary  canal  below 
the  diaphragm,  to  which 
it  carries  vessels  from  the 
aorta,  and  an  anterior 
mesentery  running  to  the 
upper  part  of  this  canal 
from  the  anterior  abdom- 
inal wall  (Fig.  1432). 
The  original  posterior 
mesentery  is  divided  into 
three  regions,  each  of 
which  conveys  a  particu- 
lar artery,  i.  The  mesen- 
tery of  the  stomach  and 
of  the  duodenum,  con- 
taining the  cceliac  axis. 
It  is  to  be  noted  that  this 
region  may  be  subdivided 

into  two  parts,  the  upper  formed  by  the  stomach  and  the  first  part  of  the  duodenum, 
the  lower  formed  by  the  remainder  of  the  duodenum.  The  latter  originally  arches 
forward,  both  ends  being  fixed  at  the  spine.  2.  The  mesentery  of  the  rest  of  the 
small  intestine  and  of  the  ascending  and  the  transverse  colon,  containing  the  superior 
mesenteric  artery.  3.  The  mesentery  of  the  remainder  of  the  large  intestine,  con- 
taining the  inferior  mesenteric  artery. 

The  anterior  mesentery,  in  which  the  liver  is  developed,  reaches  the  stomach 
and  the  upper  part  of  the  duodenum,  extending  on  the  anterior  wall  as  low  as  the 


Diagram  showing  general  arrangement  of  peritoneum,  which  is  represented 
by  the  black  line ;  arrow  passes  from  greater  into  lesser  sac  through  foramen 
of  Winslow.  /,,  liver;  S,  stomach;  P,  pancreas;  D,  duodenum;  TC,  trans- 
verse colon  ;  /,  small  intestine ;  R,  rectum  ;  B,  bladder ;  U,  uterus. 


1742  HUMAN   ANATOMY. 

umbilicus  (Fig.  1432).  The  umbilical  vein  runs  in  its  free  lower  border  to  the  por- 
tal fissure  of  the  liver,  whence  its  continuation,  the  ductus  venosus,  passes  to  the 
inferior  vena  cava.  The  anterior  mesentery,  containing  the  liver,  is  opposite  to  the 
mesogastrium,  or  mesentery  of  the  stomach,  which  contains  the  spleen.  The  pan- 
creas, although  developed  in  both  the  anterior  and  the  posterior  mesenteries,  lies 
chiefly  in  the  latter.  As  the  jejuno-ileum  enlarges  it  hangs  in  loops  from  the  spine, 
carrying  folds  of  mesentery  with  it  surrounding  the  vessels.  The  multiplication  of 
these  folds  gives  rise  to  the  complication  of  the  adult  arrangement. 

When  two  layers  of  a  serous  membrane  come  to  lie  permanently  and  practically 
immovably  upon  each  other,  there  is  a  tendency  to  fusion  between  them,  the  meso- 
thelium  covering  the  apposed  surfaces  disappearing  and  its  place  being  taken  by 
connective  tissue  (Fig.  1472).  Thus,  when  a  mesentery  lies  against  the  abdominal 
wall,  the  mesothelium  of  the  parietal  peritoneum  and  of  the  mesentery  apposed  to 
it  degenerates  into  connective  tissue,  and  the  peritoneum  on  the  free  surface  of  the 
mesentery  becomes  a  part  of  the  permanent  parietal  peritoneum.  Much  of  the 
originally  free  parietal  peritoneum  is  thus  replaced  by  fusion  with  what  once  belonged 
to  a  mesentery. 

The  stomach  undergoes  rotation,  so  that  the  original  left  side  becomes  the 
anterior  and  the  posterior  border  the  greater  curvature.  The  mesogastrium  grows 
out  of  all  proportion,  so  as  not  only  to  describe  a  curve  to  the  left,  but  to  hang 
downward  in  a  free  fold.  The  loop  of  the  duodenum  turns  to  the  right,  so  that  all 
of  it,  except  the  first  part,  lies  against  the  posterior  abdominal  wall.  The  head  of  the 
pancreas  is  carried  with  it.  The  serous  covering  of  the  back  of  the  duodenum  (in 
its  new  position),  that  of  its  mesentery,  and  that  of  the  back  of  the  head  of  the 
pancreas  disappear,  fusing  with  the  parietal  peritoneum  of  the  posterior  abdominal 
wall. 

The  mesentery  of  the  jejuno-ileum  and  that  of  most  of  the  large  intestine 
become  twisted  as  the  gut  returns  into  the  abdomen  from  the  umbilical  cord,  so 
that  the  caecum  is  thrown  upward  and  to  the  right  to  lie  under  the  liver,  whence  it 
descends  to  its  permanent  place  ;  hence  the  original  right  and  left  sides  of  the 
mesentery  change  places.  The  mesentery  of  the  ascending  colon  fuses  with  the 
posterior  covering  of  the  right  side  of  the  abdomen  ;  that  of  the  descending  colon 
to  the  sigmoid  flexure  does  the  same  on  the  left. 

The  sub-  or  retroperitoneal  tissue  is  very  important.  As  above  stated,  there 
is  a  thin  fibre-elastic  layer  supporting  the  mesothelial  cells,  which  is  a  part  of  the 
serous  membrane,  although  it  is  not  present  in  the  earlier  stages.  Beneath  this 
tunica  propria  there  may  be  a  continuous  mass  of  connective  tissue,  to  be  compared 
to  dense,  sponge-like  cobwebs,  which  serves  as  a  packing  between  different  organs 
and  around  vessels,  nerves,  and  ducts.  It  may  contain  a  large  amount  of  fat.  This 
is  particularly  developed  about  retroperitoneal  viscera  and  along  the  aorta.  The 
parietal  peritoneum  is  usually  thin  where  no  fusion  with  another  layer  nor  with 
fasciae  has  occurred. 

We  shall  describe  (i)  the  peritoneum  of  the  anterior  and  lateral  abdominal 
walls,  with  its  prolongations  onto  the  diaphragm  and  into  the  pelvis  ;  (2)  the  folds 
derived  from  the  anterior  mesentery  ;  (3)  those  from  the  posterior  mesentery  from 
above  downward.  Most  matters  of  dejtail  are  discussed  with  the  various  organs 
having  peritoneal  relations. 

The  Anterior  Parietal  Peritoneum. — Four  folds  diverge  from  the  umbili- 
cus, three  running  downward,  symmetrically  disposed, — namely,  a  median  fold  (plica 
umltilicalis  media),  expanding  to  the  top  of  the  bladder  covering  the  urachus,  a 
fibrous  cord  representing  the  atrophied  Ultra-embryonic  segment  of  the  allantoic 
duct,  and  two  lateral  folds  (plies  umbilicales  latcralcs)  containing  fibrous  cords,  the 
obliterated  hypogastric  arteries,  continuous  with  the  permanent  superior  vesical  arte- 
ries. If  the  bladder  be  distended,  they  can  be  traced  to  its  upper  lateral  aspects  ; 
otherwise  to  the  sides  of  the  pelvis.  The  fibrous  tissue  of  the  obliterated  arteries 
becomes  very  scanty  near  the  umbilicus.  The  suf» -aTcsical  fossa  (fovea  supravesi- 
calis)  or  depression  lies  on  each  side  above  the  pubes,  between  the  median  and 
lateral  folds.  On  the  outer  side  of  the  latter,  above  the  middle  of  Poupart's  ligament, 
is  the  internal  or  median  inguinal  fossa  (fovea  inguinalis  mcdialis),  which  is  very 


THE    PERITONEUM. 


1743 


distinct,  and  often  extends  inward  under  the  obliterated  hypogastric  artery.  Farther 
out  a  very  small  fold  (plica  epigastrica ) ,  caused  by  the  deep  epigastric  artery,  runs 
upward  and  inward  from  the  external  iliac  artery  just  as  the  latter  passes  under  Pou- 
part's ligament.  The  external  or  lateral  inguinal  fossa  (fovea  inguinalis  lateralis) 
is  theoretically  just  external  to  this  fold,  but  the  fold  is  barely  raised  and  a  fossa  not 
easily  made  out.  The  internal  abdominal  ring  (annulus  inguinalis  ulxlominalis)  is 
in  this  fossa,  about  i  cm.  above  the  middle  of  Poupart's  ligament.  A  slight  fold, 
caused  by  the  vas  deferens  or  the  round  ligament,  is  described  as  running  downward 
from  the  ring  into  the  pelvis  ;  the  fact  is,  however,  that  the  structure  can  be  only 
indistinctly  seen  through  the  peritoneum,  and  a  raised  fold  is  rare.  It  forms  the 
outer  border  of  the  slightly  marked  femoral  depression  (fovea  femoralis)  opposite  the 
femoral  ring  (annulus  cruralis),  between  the  pubes  and  Poupart's  ligament.  The 
peritoneum  is  continued  laterally  on  either  side  without  presenting  any  feature  that 
calls  for  description  until  it  reaches  the  ascending  or  the  descending  colon.  All 
the  serous  covering  anterior  to  these  structures  is  derived  from  the  parietal  perito- 
neum ;  that  posterior  to  them  is  derived  from  the  mesenteries  of  the  colons  which 


FIG.   1468. 


Umbilicus 


^-Umbilical  vein 


Rectus  muscle 


External  inguinal 
fossa 

Anterior 
•  crural  nerve 
Ext.  iliac  artery 
External  iliac  vein 


Internal  inguina' 
fossa 


Supravesical  fossa 


Summit  of  bladder 


Anterior  superior 
iliac  spine  (cut) 

Median  umbilical 
fold  (urachus) 
Lateral 
umbilical  fold 
Epigastric  fold 

Internal 
abdominal  ring 

Vas  deferens 


Peritoneum 


\  Bladder  (cut) 

Pubic  bone  (cut) 
Frontal  section  of  formalin  subject,  showing  posterior  aspect  of  abdominal  wall,  covered  with  peritoneum. 


have  fallen  over  onto  the  posterior  abdominal  walls.  It  will  be  considered  later. 
The  parietal  peritoneum  is  also  to  be  traced  onto  the  under  surface  of  the  dia- 
phragm until  far  back  it  meets  the  folds  derived  from  the  mesenteries.  On  either 
side  of  the  bundle  of  fibres  arising  from  the  ensiform  cartilage  there  is  an  inter- 
ruption in  the  muscle  of  the  diaphragm,  where  only  areolar  tissue  separates  the 
peritoneum  and  the  pleura  or  pericardium. 

The  parietal  peritoneum  is  continued  into  the  pelvis,  where  it  meets  the  mesen- 
tery of  the  colon  and  is  continued  over  the  bladder,  and  in  the  female  over  the 
uterus  and  Fallopian  tubes.  Nowhere  is  the  comparison  to  a  wall-paper  so  apt  as 
here,  where  the  peritoneum  can  be  traced  from  the  walls  over  the  inequalities 
formed  by  the  upper  surfaces  of  the  pelvic  organs.  The  depression  between  the 
bladder  and  the  rectum  in  the  male,  the  redo-vesical pouch  (excavatio  recto-vesicalis), 
in  the  female  is  subdivided  into  the  utcro-vesical pouch  (excavatio  utero-vesicalis)  and 
the  recto-uterine  pouch  (excavatio  recto-uterina).  The  latter  and  deeper,  also  known 
as  the  pouch  of  Douglas  (cavum  Douglas! ),  is  bounded  laterally  by  the  utero-sacral ^ 
folds  (plicae  recto-uterinae),  which  pass  from  the  lower  part  of  the  uterus  backward 


1744 


HUMAN   ANATOMY. 


and  outward  to  the  side  of  the  rectum  and  the  pelvic  wall.  The  peritoneal  fold 
investing  the  uterus  extends  laterally  on  either  side  as  the  broad  ligament  (ligamen- 
tum  latum)  to  blend  with  the  parietal  peritoneum  covering  the  sides  of  the  pelvis. 
Below,  the  broad  ligament  is  attached  to  the  pelvic  floor,  its  superior  margin  being 
the  free  edge  of  the  fold.  On  either  side  of  the  rectum,  between  the  gut  and  the 
wall  of  the  pelvis,  lies  the  pararectal  fossa,  the  size  of  which  varies  with  the  disten- 
tion  of  the  intestine.  The  special  features  of  the  peritoneum  are  described  with  the 
rectum  (page  1679)  and  with  the  uro-genital  system  (page  1905). 

The  arrangement  over  the  anterior  half  of  the  lateral  wall  of  the  true  pelvis  is 
different  according  to  sex,  since  in  the  female  there  is  the  line  of  attachment  of  the 
broad  ligament  of  the  uterus  and  the  fossa  for  the  ovary.  Otherwise  the  features 
are  about  the  same,  the  vas  deferens  of  the  male  and  the  round  ligament  of  the 
female  causing  similar  folds.  These  structures  run  backward  from  the  internal  ring 
along  the  wall  of  the  pelvis,  turn  down  to  the  side  of  the  bladder,  and  bound 
externally  and  posteriorly  the  paravesical  fossa  between  the  pelvic  wall  and  the 

FIG    1469. 


Bladdes 


Urachus 


Internal—  - 
abdominal  ring     \ 


Transverse  - 
vesical  fold 


Left  uret 
Sigmoid  flexure 


Vas  deferens 

, Spermatic  vessels 

Sup.  vesical  artery 

— Ext.  iliac  artery 

— I'reter 

_; Vas  deferens 

\  Recto-vesical    ' 
T~    fold 

I'reter 

Peritoneum 
(cut) 

Internal  iliac 
artery 


Left  common  iliac  artery 


Pelvic  peritoneum  from  above  and  behind,  showing  folds  and  fossae. 

bladder  when  the  latter  is  not  distended.  A  transverse  fold  of  peritoneum,  plica 
vesicalis  transversal  passes  laterally  from  the  upper  surface  of  the  empty  bladder 
and  subdivides  the  paravesical  fossa  into  an  anterior  and  a  posterior  compartment. 
The  vas  deferens,  or  round  ligament,  forms  (the  body  being  upright)  the  lower  side 
of  the  obturator  triangle,  which  is  completed  in  front  by  the  external  iliac  vein  and 
behind  by  the  ureter,  which  crosses  the  external  iliac  vein  at  the  apex.  The  obtu- 
rator vessels  and  nerve  lie  in  the  floor  of  this  triangle.  In  the  female  it  is  crossed 
by  the  lateral  attachment  of  the  broad  ligament  of  the  uterus,  behind  which  is  the 
fossa  for  the  ovary  (fossa  ovarica). 

The  Anterior  Mesentery. — This  originally  extended  from  the  anterior  abdom- 
inal wall  to  the  lesser  curvature  of  the  stomach  and  to  the  beginning  of  the  duo- 
denum. It  is  subdivided  into  two  portions  by  the  liver,  which  develops  within  it. 
The  anterior  part  is  the  falciform  ligament,  between  the  abdominal  wall  and  the 
liver  ;  the  posterior  part  is  the  gastro-hepatic  omentum,  between  the  liver  and  the 
^tomach. 

1  Waldeyer  :  Journal  of  Anatomy  and  Physiology,  vol.  xxxii.,  1898. 


THE   PERITONEUM. 


r745 


FIG. 


1470. 


The  falciform  ligament  (ligamentum  falciforme  hepatis)  makes  the  fourth  fold 
which  has  been  mentioned  as  leaving  the  umbilicus.  Seen  from  the  side,  it  is  a 
sickle-shaped  fold  attached  to  the  anterior  wall  above  the  umbilicus  and  later  to  the 
diaphragm  as  far  back  as  the  top  of  the  fissure  of  the  ductus  venosus  on  the  pos- 
terior surface  of  the  liver  (Fig.  1441).  In  its  free  inferior  border  runs  the  round 
ligament,  once  the  umbilical  vein,  from  the  umbilicus  to  the  notch  in  the  liver,  and 
thence  in  its  own  fissure  on  the  under  surface  until  it  reaches  the  portal  fissure, 
where  the  falciform  ligament  ends.  The  latter  divides  the  upper  part  of  the  dome 
of  the  abdomen  into  two  chambers,  one  on  either  side,  of  which  the  left  one  is  the 
larger.  There  is  but  little  areolar  tissue  in  the  folds  of  the  falciform  ligament. 
Small  veins  run  along  the  round  ligament,  connecting  the  hepatic  system  with  that 
of  the  abdominal  walls.  Although  in  the  embryo  the  fold  starts  from  the  navel,  in 
the  adult  it  does  not  leave  the  abdominal  wall  for  an  inch  or  more  above  it. 

The  superior  surface  of  the  liver  is  covered  with  peritoneum  from  either  side  of 
the  falciform  ligament,  which  at  the  top  of  the  posterior  surface  is  reflected  onto 
the  under  side  of  the  dia- 
phragm. At  the  edge  of 
the  right  lobe,  which  has  a 
considerable  posterior  sur- 
face uncovered  by  perito- 
neum and  attached  to  the 
diaphragm,  the  layers  cov- 
ering the  upper  and  lower 
surfaces  meet  to  form  the 
right  triangular  ligament, 
which  is  attached  for  a 
short  distance  beyond  the 
liver  to  the  diaphragm  and 
has  a  sharp,  free  edge. 
There  is  a  similar  arrange- 
ment on  the  upper  surface 
of  the  left  lobe,  but  the 
left  triangular  ligament  is 
longer,  and  passes  to  the 
diaphragm  on  the  left  of  the 
oesophageal  opening  and 

above  the  spleen.  Passing  around  the  border  of  the  right  lobe  of  the  liver,  the  peri- 
toneum spreads  over  the  inferior  surface  of  that  lobe  as  well  as  of  the  quadrate  cov- 
ering the  gall-bladder  which  lies  in  a  hollow  between  them.  Exceptionally  the  gall- 
bladder is  entirely  surrounded,  and  is  attached  to  the  liver  merely  by  a  narrow  fold. 
The  peritoneum  is  continued  over  the  cystic  duct  to  the  edge  of  the  lesser  omentum, 
to  be  presently  described.  The  entire  under  surface  of  the  left  lobe  is  also  covered 
by  peritoneum  continuous  with  the  preceding.  The  passage  of  the  finger  on  this 
surface  to  the  right  is  interrupted  at  the*  front  by  the  end  of  the  falciform  ligament 
between  it  and  the  quadrate  lobe.  At  the  back  farther  progress  to  the  right  is 
stopped  by  the  lesser  omentum  in  the  fissure  of  the  ductus  venosus.  All  the  peri- 
toneal covering  of  the  liver  has  thus  been  accounted  for,  excepting  that  of  the 
caudate  lobe  and  of  the  lobe  of  Spigelius. 

The  gastro- hepatic  or  lesser  omentum  (ligamentum  hepatogastrium,  omentum 
minus)  is  that  part  of  the  original  anterior  mesentery  connecting  the  stomach  and 
the  beginning  of  the  duodenum  with  the  liver.  It  must,  theoretically,  have  been 
originally  a  median  antero-posterior  fold,  but  it  is  now  so  twisted  in  consequence  of 
the  change  in  position  of  the  stomach  as  to  be  chiefly  nearly  transverse.  Its  line  of 
attachment  to  the  stomach  is  along  the  lesser  curvature  from  the  gullet  past  the 
pylorus,  continued  onto  the  first  part  of  the  duodenum,  where  it  crosses  from  the 
top  to  the  left  of  the  gut,  until  it  passes  the  common  bile-duct  (by  which  the  ducts 
of  the  liver  originally  grew  out  of  the  gut)  with  its  companions,  the  hepatic  artery 
and  the  portal  vein.  It  is  formed  by  the  union  of  the  peritoneal  layers  covering 
respectively  the  front  and  back  of  the  stomach  and  the  sides  of  the  duodenum  con- 


Uiagram  showing  early  arrangement  of  parietal  and  visceral  perito- 
neum. Blue,  parietal ;  yellow,  right  side,  red,  left  side  of  visceral.  L,  liver; 
St,  stomach  ;  5/>,  spleen  ;  P,  pancreas  ;  K,  kidney. 


1746 


HUMAN   ANATOMY. 


tinuous  with  them.  The  two  layers  join  at  the  bundle  of  vessels  just  mentioned. 
thus  forming  a  fold  which  is  the  termination  of  the  lesser  omentum  on  the  right, 
known  as  the  duodena-  hepatic  omentum  (ligamentum  hepatoduodenale).  The  lesser 
omentum  is  sometimes  described  as  prolonged  across  the  first  part,  of  the  duodenum 
to  the  transverse  colon,  fusing  with  the  greater  omentum.  This  is  only  an  acci- 
dental modification,  although  a  very  common  one.  An  accessory  fold,  the  duodeno- 
\cystic  ligament,  is  prolonged  to  the  right  from  the  front  of  the  lesser  omentum, 
around  the  cystic  duct  from  the  gall-bladder.  The  hepatic  attachment  of  the  lesser 
omentum  is  to  the  transverse  fissure  of  the  liver  and  from  its  left  end  to  the  fissure 
of  the  ductus  venosus.  From  the  point  at  which  the  latter  reaches  the  diaphragm 

the  two  layers  diverge,  the 
FIG.  147  1  .  j 


Diagram  showing  changed  relation  of  visceral  peritoneum  in  consequence 
of  twisting,  so  that  original  right  and  left  sides  of  mesentery  of  small  intes- 
tine and  of  part  of  colon  have  exchanged  places.  The  detached  portion 
which  is  twisted  is  supposed  to  be  attached  at  a  higher  level.  D,  duode- 
num ;  C,  C,  ascending  and  descending  colon  ;  /,  smallintestine  ;  K,  kidney  ; 
/?,  C,  Care  being  displaced  towards  posterior  wall. 


to  the  jou  -er 

side  of  the  left  lobe  and  the 
right  one  to  the  lobe  of 
Spigelius.  The  structure 
of  the  lesser  omentum  is 
dense  and  fibrous  at  the 
right.  It  is  very  delicate  in 
the  middle,  but  somewhat 
thicker  at  the  left  end.  The 
fold  around  the  vessels  at 
the  free  edge  (Fig.  1473) 
forms  the  anterior  border 
of  the  foramen  of  Winslow 
(foramen  epiploicum),  a  nar- 
row part  of  the  peritoneal 
cavity  by  which  the  general 
cavity  communicates  with 
that  behind  the  stomach 
which  has  been  formed  by 
the  rotation  of  that  organ 
and  the  inordinate  growth 
of  the  mesogastrium.  The 
foramen  is  circular,  with  a  diameter  of  from  2-3  cm.  Of  the  three  vessels  in 
the  fold  forming  its  anterior  border,  the  portal  vein  is  the  posterior  at  the  point 
of  entrance  into  the  liver,  with  the  hepatic  artery  in  front  on  the  left  and  the 
hepatic  duct  in  front  on  the  right.  The  cystic  duct  is  really  in  an  accessory  fold. 
The  hepatic  artery,  which  passes  along  the  left  side  of  the  duodenum  and  turns 
upward,  is  the  vessel  that  most  definitely  bounds  the  foramen  in  front.  The  duo- 
denum lies  below  the  foramen,  but  its  lower  border  is  often  formed,  not  by  the 
gut,  but  by  a  fold  of  serous  membrane  arising  from  it.  The  foramen  is  bounded 
behind  by  the  vena  cava  and  above  by  the  caudate  lobe  of  the  liver,  which  is  covered 
by  peritoneum. 

The  Posterior  Mesentery  :  Part  I.—  The  posterior  mesentery  arises  from  the 
spine,  with  the  aorta  between  its  folds.  The  first  part  is  the  mesogastrium,  in  which 
run  the  branches  of  the  cceliac  axis.  It  will  be  remembered  that,  except  at  the 
fundus,  this  is  attached  to  the  greater  curvature  of  the  stomach,  which  was  originally 
the  posterior  border,  but  which  has  turned  to  the  left.  The  spleen  and  most  of  the 
pancreas  are  developed  in  this  fold,  which  grows  inordinately.  We  must  trace  it  both 
in  a  horizontal  and  in  a  sagittal  plane.  To  understand  the  horizontal  arrangement, 
it  is  sufficient  to  remember  that  the  original  mesentery,  which  ran  straight  forward 
from  the  spine  to  the  stomach,  in  its  subsequent  excessive  growth  describes  a  loop 
to  the  left  (Fig.  1470),  so  that  the  original  left  side  of  the  mesentery  near  its  root  faces 
backward,  and  later,  after  the  bend  of  the  loop,  forward,  ultimately  covering  the  an- 
terior wall  of  the  stomach.  This  fold  forms  a  givat  pouch  behind  and  below  the 
stomach  called  the  lesser  cavity  of  the  peritoneum  (  Imrsa  onic-ntalis),  which,  of  course, 
is  continuous  with  the  general  cavity.  The  mesothelium  of  the  left  side  of  the  mes- 
entery nearly  to  the  spleen  fuses  with  that  of  the  posterior  wall  of  the  abdomen,  so 
that  the  splenic  vessels  and  the  pancreas  which  are  in  it  come  to  lie  behind  the  per- 


THE   PERITONEUM. 


1747 


Diagram  showing  later  stage  where  secondary  mesentery  is  formed  and 
duodenum  (D)  and  colons  (C,  C)  lie  against  posterior  body-wall.  The  ad- 
ditional colors  indicate  the  fusion  of  the  original  parietal  and  visceral  perito- 
neum, purple  from  the  blue  with  the  red,  green  from  the  blue  with  the  yellow. 


manent  serous  covering  of  the  posterior  abdominal  wall,  which  here  is  that  of  the 
original  right  side  of  the  mesogastrium.  The  spleen,  and  perhaps  the  tail  of  the 
pancreas,  lie  free,  surrounded  by  peritoneum.  If  the  hand  be  introduced  into  the 
left  hypochondrium,  it  slides  along  the  wall  behind  the  spleen  to  the  point  at  which 

the  splenic  vessels  leave  the 

FIG.  1472.  posterior  wall  and  pass  in 

a  fold,  the  lieno-renal  liga- 
ment, to  the  hilum  of  the 
spleen.  From  this  position 
the  hand  can  be  carried 
around  the  spleen  to  the 
front  of  the  vessels  at  the 
hilum  and  thence  to  the 
right  along  the  continua- 
tion of  the  mesogastrium  to 
the  greater  curvature  of  the 
stomach,  where  its  layers 
separate  to  coat  the  front 
and  back  of  that  organ. 
T,he  part  of  the  mesogas- 
trium between  the  stomach 
and  the  spleen  is  \hegastro- 
splenic  omentum.  The  right 
layer  of  peritoneum  of  the 
mesogastrium,  lining  first 
the  hind  wall  of  the  abdo- 
men and  then  the  back  of  the  stomach,  bounds  the  lesser  cavity  of  the  peritoneum. 
The  gastro-phrenic  ligament  is  a  small  vertical  fold,  usually  found  extending  from 
the  left  of  the  end  of  the  oesophagus  to  the  top  of  the  stomach.  Near  it  is  often 
another,  the  suspensory  ligament  of  the  spleen,  extending  from  the  diaphragm  to 
the  top  of  that  organ,  of  which  it  may  enclose  a  small  part.  It  marks  the  upper 
part  of  the  line  of  reflection  of  the  mesogastrium  from  the  posterior  abdominal  wall. 
The  phreno-colic  fold,  also  derived  from  the  mesogastrium,  is  a  horizontal  shelf 
with  a  free  anterior  semi- 
lunar  edge  forming  the  floor 
of  a  niche  for  the  spleen. 
It  extends  from  about  the 
eleventh  rib  inward  onto  the 
upper  surface  of  the  trans- 
verse colon.  That  this  liga- 
ment is  really  a  part  of  the 
mesogastrium,  and  not  a  lig- 
ament of  the  colon,  is  shown 
by  development,  as  well  by 
its  existence  (as  in  the  mon- 
key) when  the  descending 
colon  is  unattached  to  the 
wall. 

The  Greater  Omentum. 
—We  are  now  to  trace  the 
mesogastrium  in  a  sagittal 
plane  downward  from  the 
greater  curvature  of  the 
stomach.  On  opening  the 
abdomen  the  first  thing  that 
appears  below  the  stomach  is  the  greater  omentum  (omentum  majus),  which  is 
spread  like  an  apron  over  the  intestines.  It  is  that  part  of  the  mesogastrium 
which  is  situated  in  front.  The  terms  gastro-colic  and  g  astro -splenic  omenta 
are  but  names  for  different  parts  of  this  structure.  It  extends  from  the  greater 


FIG.  1473. 


Diagrammatic  section  passing  through  level  of  foramen  of  Winslow, 
showing  relations  of  parietal  and  visceral  peritoneum  within  lesser  sac 
(LS)  ;  GH,  cut  gastro-hepatic  omentum,  containing  portal  vein  (/"),  he- 
patic artery  (//),and  bile-duct  (B}\  Si,  stomach  ;  CrS,  gastro-splenic  omen- 
tum ;  LR,  lieno-renal  omentum  ;  VC,  A,  vena  cava  and  aorta. 


1748 


HUMAN   ANATOMY. 


curvature  of  the  stomach,  where  it  is  continuous  on  the  left  with  the  double  layer 
coming  from  the  spleen  and  on  the  right  with  that  coming  from  the  inferior  sur- 
face of  the  first  part  of  the  duodenum  ;  from  this  broad  origin  the  greater  omentum 
hangs  down  over  the  intestines  to  near  the  pubes,  where  it  turns  upon  itself  and 
ascends  posteriorly.  Often  it  does  not  descend  so  far,  but  may  be  folded  upon 
itself  to  almost  any  degree  and  in  almost  any  position.  For  purposes  of  description 
it  is  supposed  to  lie  spread  out  smoothly,  and  to  consist  of  an  anterior  and  a  pos- 

FIG.  1474. 


Ensiform  cartilage 


Liver 


Gall-bladder 


Ascending  colon 


Caecum 


Undisturbed  abdominal  viscera  of  formalin  subject;  liver  and  stomach  abnormally  large,  hence  the  exaggerated 

apparent  transverse  position  of  stomach.      • 

terior  fold  (Fig.  1467).  The  former  passes  down  over  the  transverse  colon,  but  with- 
out adhering  to  it.  The  peritoneum  on  its  anterior  surface  faces  forward  into  the 
greater  peritoneal  cavity,  while  that  on  its  posterior  surface  looks  into  the  lesser  one. 
On  turning  backward  upon  itself,  it  runs  up  to  the  transverse  colon.  If  this  were 
literally  true-,  it  is  evident  that  the  lesser  cavity  would  extend  from  behind  the  stomach 
over  the  colon  down  into  this  fold  (  reccssus  inferior  omcntalis)  of  the  greater  omen- 
tum, and  in  fact  this  is  actually  the  case  in  the  foetus  (Fig.  1439)  and  exceptionally 


THE   PERITONEUM.  1749 

in  the  adult  ;  but  generally,  except  just  below  the  colon,  the  two  layers  fuse  into  one. 
In  the  adult,  when  the  returning  fold  reaches  the  transverse  colon,  the  two  layers 
composing  it  seem  to  diverge  to  enclose  the  intestine,  and,  reuniting  above  it,  to  be 
continued  upward  as  the  transverse  mesocolon  to  a  line  running  across  the  back  of 
the  abdomen,  to  be  described  later.  This  is  an  extraordinary  and  apparently  con- 
tradictory arrangement  by  which  a  part  of  the  mesogastrium,  or  mesentery  of  the 
stomach,  has  become  also  the  mesentery  of  a  part  of  the  colon.  The  explanation 
is  furnished  by  embryology,  since  the  original  arrangement  is  very  different.  In 
the  fcetus  (Fig.  1439)  the  returning  fold  of  the  greater  omentum  passes  up  in  front 
of  the  colon  to  the  posterior  wall  along  the  lower  border  of  the  pancreas.  The  pos- 
terior layer  of  the  greater  omentum  is  in  fact  the  left  layer  of  the  original  mesogas- 
trium, which  we  should  be  able  to  follow  to  the  aorta,  had  it  not,  with  the  pancreas, 
become  adherent  to  the  posterior  wall.  It  has  no  connection  whatever  with  the 
transverse  mesocolon  ;  it  simply  lies  upon  it.  At  about  birth,  however,  the  two 
opposed  layers  begin  to  fuse.  The  acquired  line  of  attachment  to  the  transverse 
colon  is  low  on  the  right  and  high  on  the  left.  Sometimes  near  the  spleen  it  joins, 
not  the  colon,  but  the  mesocolon  above  it. 

The  Structure  of  the  Greater  Omentum. — There  is  hardly  any  framework  apart 
from  the  vessels  that  course  through  it,  save  a  most  delicate  layer  of  nbro-elastic 
tissue  which  supports  the  mesothelium.  In  the  adult  more  or  less  fat  is  found  about 
the  vessels,  and  in  some  cases  the  omentum  is  loaded  with  it.  The  two  layers  of 
serous  membrane  are  sometimes  beautifully  distinct  ;  in  other  cases  no  trace  of  a 
double  origin  can  be  recognized.  Sometimes  parts  of  the  omentum  atrophy  and 
disappear,  leaving  windows,  or  fenestw,  between  the  meshes  of  the  vessels.  The 
arteries  are  long  and  very  slender.  They  arise  from  the  gastro-epiploic  arteries  at 
the  greater  curvature  of  the  stomach  and  run  straight  downward  to  the  folded 
border  of  the  omentum,  and  then  up  again  in  the  posterior  fold,  to  anastomose 
with  the  arteries  of  the  colon.  In  their  course  they  send  off  small  side  branches 
which  meet  those  from  the  next  branch.  The  arrangement  of  the  veins  is  essen- 
tially the  same. 

The  Lesser  Cavity  of  the  Peritoneum. — The  mesogastrium,  starting  at  the  aorta, 
takes  a  great  turn  to  the  left,  and  its  first  part,  containing  the  pancreas,  fuses  with 
the  posterior  abdominal  wall.  This  fold  is  only  a  part  of  a  great  pouch  that  runs 
downward  also.  If  examined  before  it  has  become  adherent  to  the  transverse  meso- 
colon, its  continuation  from  below  the  pancreas  is  to  be  followed  down  over  the 
colon  as  the  posterior  layer  of  the  greater  omentum.  In  the  description  of  the  folds 
of  the  adult  in  a  sagittal  plane  it  was  necessary,  on  account  of  this  adhesion,  to 
reverse  the  normal  course  and  to  follow  it  from  its  insertion  into  the  stomach  back 
to  its  origin.  If  a  cut  be  made  through  the  greater  omentum  between  the  stomach 
and  the  transverse  colon,  the  lesser  sac  ( bursa  omentalis)  is  opened  so  that  its  pos- 
terior wall  can  be  examined  (Fig.  1475).  This  is  seen  covering  the  pancreas,  the 
splenic  vessels  and  the  posterior  abdominal  wall,  part  of  the  spleen,  part  of  the  left 
kidney,  and  the  left  suprarenal  capsule.  At  the  right  is  the  foramen  of  Winslow, 
which  is  generally,  but  inaccurately,  considered  the  communication  between  the 
greater  and  lesser  cavities.  It  cannot  be  the  true  entrance  into  the  lesser  cavity, 
because,  owing  to  the  median  arrangement  of  the  original  mesentery,  this  opening 
cannot  be  on  the  right  of  the  median  line.  The  real  communication  between  the 
two  cavities  is  somewhat  contracted  (isthmus  bursa'  omentalis)  and  indicated  by 
the  median  vertical  fold — plica  gastro-pancreatica — made  by  the  mesogastrium  over 
the  gastric  artery  of  the  stomach  as  it  arises  from  the  cceliac  axis  to  the  cardia.  On 
the  left  of  this  fold  is  the  lesser  cavity  proper  ;  on  the  right  of  it,  extending  to  the 
foramen  of  Winslow,  is  a  small  cavity, — the  vestibule  ( vestibulmn  bursa1  omentalis), 
— bounded  behind  by  the  original  parietal  peritoneum  of  the  right  abdominal  wall 
and  extending  upward  behind  the  lobe  of  Spigelius  (Fig.  1476).  The  sides  of  the 
pocket  behind  the  liver  (recessus  superior)  are  the  reflections  of  the  peritoneum  over 
the  left  of  the  inferior  vena  cava  and  the  right  of  the  ductus  venosus,  which  meet 
above,  roofing  it  in.  The  first  part  of  the  duodenum,  which  forms  the  lower  boundary 
of  the  foramen  of  Winslow,  passes  backward  and  upward,  so  that  the  loop  of  intes- 
tine, which  the  duodenum  originally  formed,  must  be  considered  as  having  fallen 


1750 


HUMAN   ANATOMY. 


over  onto  the  right  side  against  the  right  of  the  spinal  column,  to  the  peritoneal 
covering  of  which  it  has  grown  with  the  transformation  into  connective  tissue  of  the 
right  serous  covering  of  its  mesentery.  The  second  or  descending  portion  of  the 
duodenum  lies  against  the  right  of  the  column  under  the  permanent  parietal  peri- 
toneum, derived  from  the  mesocolon,  as  is  shown  later.  The  great  difficulty  of  un- 
derstanding the  lesser  cavity  is  that  in  man  the  duodenum  rises  to  so  near  the  liver 
that  the  entrance  to  the  vestibule  at  the  foramen  of  Winslow  is  very  small.  If,  as  in 
many  animals,  these  parts  were  more  distant,  it  would  be  evident  that  this  is  a  pouch- 


FIG.   1475. 

Hepatic  artery 


Gastro-hepatic  omentutn 


Accidental  peritoneal  fold 

Pylorus 
First  part  of 
duodenum 


Foramen  of  Winslow 

Gastro-pancreatic 
fold 


Stomach 


Peritoneum  lining  posterior 
wall  of  lesser  sac 


Transverse  colon 


Greater  omentum,  cut 


Spleen 


Pancreas 
Folds  of  greater  omcntum 

Gastro-splenic  omentum 


The  subject,  lying  on  its  back,  is  seen  from  the  left  side  ;  the  stomach,  except  fundus,  is  turned  ovi-r.  Tin-  greater 
omentum  has  been  cut  below  the  greater  curvature  of  the  stomach  so  as  to  open  the  lesser  sac  to  show  the-  toiaineti 
of  Winslow  from  the  left  side. 


like  formation,  the  mouth  of  which  is  behind  the  edge  of  the  lesser  omentum.  The 
relations  to  the  mesogastrium  of  three  branches  of  its  artery,  the  cceliac  axis,  are  as 
follows.  The  splenic  artery,  in  the  adult  condition,  lies  entirely  behind  the  perma- 
nent peritoneum  to  near  the  hilum  of  the  spleen,  where  the  mesogastrium  is  no 
longer  attached  to  the  wall.  It  then  sends  its  terminal  branches  to  the  spleen,  the 
gastro-epiploica  sinistra  to  the  greater  curvature  of  the  stomach,  and  the  vasa  brevia 
to  the  fundus.  The  gastric  artery,  originally  in  the  mesentery  of  the  duodenum, 
reaches  the  cardiac  end  of  the  stomach  through  the  /V/Vv  gastro-pctncreaticct^  and 
then  runs  between  the  layers  of  the  lesser  omentum  along  the  lesser  curvature. 


THE   PERITONEUM. 

The  hepatic  artery  reaches  the  duodenum  through  its  mesentery,  and  crosses  the 
left  side  of  the  gut,  to  which  it  gives  branches.  Thence  it  runs  in  or  near  the  edge 
of  the  lesser  omentum  at  the  foramen  of  Winslow  to  the  portal  fissure. 


FIG.  1476. 


Gastro-pancreatic  fold 


ieno-renal  fold 


Vestibule  of  lesser  sac 


Lesser  or  gastro-hepatic 
omentum. 


Gastro-splenic  omentum 


Greater  omentum 


Schematic  reconstruction,  showing  relations  of  peritone.il  layers  in  vicinity  of  lesser  sac.  Upper  surface  of  duo- 
denum (£))  at  floor  of  foramen  of  Winslow  lies  at  deeper  level  than  plane  of  section.  It  is  to  be  noted  that  only  that 
part  of  peritoneum  covering  posterior  wall  of  lesser  sac  is  derived  from  greater  omentum  which  lies  to  left  of  aorta, 
beginning  at  gastro-pancreatic  fold.  L,  liver;  .S*,  stomach  ;  Sp,  spleen  ;  P,  pancreas  ;  A',  kidney. 

The  Posterior  Mesentery  :  Part  II. — This  is  that  part  of  the  peritoneum 
derived  from  the  original  mesentery  of  the  jejuno-ileum,  the  caecum,  and  the  ascend- 
ing and  transverse  colon.  Its  artery  is  the  superior  mesenteric.  If  the  transverse 
colon  with  the  greater  omentum  be  turned  upward  and  the  small  intestine  to  the  right, 
the  left  side  of  the  mesentery  of  the  jejuno-ileum  is  seen  running  from  the  left  of  the 
top  of  the  body  of  the  second  lumbar  vertebra  to  the  right  sacro-iliac  joint.  At 
the  beginning  this  is  attached  to  the  lower  side  of  the  gut,  where  it  makes  a  sharp 
flexure  at  the  origin  of  the  jejunum  from  the  end  of  the  duodenum.  This  flexure 
lies  directly  in  front  of  the  aorta,  which  usually  lies  covered  with  peritoneum  at  the 
back  of  the  abdomen,  with  the  fourth  part  of  the  duodenum  to  the  right  of  it.  (This 
relation  is  more  fully  described  with  the  duodenum  (page  1647).  The  line  of  attach- 
ment of  the  mesentery  (Fig.  1477)  descends  over  the  fourth  part  of  the  duodenum, 
crossing  the  third  part  and  the  inferior  vena  cava.  The  greatest  breadth  of  the  mes- 
entery to  the  free  border  is  from  20-23  cm-  (8-9  in.).  It  reaches  its  full  breadth 
almost  at  once  after  its  origin.  Usually  it  becomes  very  narrow — perhaps  only  1 2  mm. 
— at  its  termination  ;  but  this  varies  much,  as  does  also  the  point  of  that  termina- 
tion. The  connective  tissue  between  the  layers  is  thickest  and  the  lymph-nodes  most 
numerous  near  the  attached  part.  Except  in  very  fat  subjects,  there  is  little  between 
the  layers  of  peritoneum  besides  the  vessels,  within  an  inch  or  so  of  the  gut.  The 
superior  mesenteric  artery  can  be  felt  at  the  top,  entering  it  from  under  the  lower 
border  of  the  pancreas.  The  peritoneum  can  be  followed  at  any  point  across  from 
the  left  to  the  right  side  of  the  mesentery.  From  the  latter  it  is  followed  along  the 
posterior  wall  to  the  kidney  and  the  ascending  colon,  lying  on  the  front  of  the 
latter,  where  they  are  in  contact.  The  membrane  crosses  the  ascending  colon, 
leaving  its  posterior  surface  without  covering  attached  to  the  parts  behind  it,  and 
completely  envelops  the  caecum,  passing  on  the  left  into  the  mesentery.  Very 
often  the  peritoneum  is  carried  for  an  inch  or  two  behind  the  lower  part  of  the 
ascending  colon.  It  then  passes  into  the  left  flank  and  the  pelvis  without  incident. 
Development  shows  that  this  is  a  departure  from  the  original  condition,  in  which  the 


1752 


HUMAN    ANATOMY. 


attachment  of  this  mesentery  was  exceedingly  short,  merely  broad  enough  to  contain 
the  superior  mesenteric  artery.  The  so-called  permanent  mesentery  is  caused  by  the 
falling  over  to  the  right  of  the  fold  of  mesentery  for  the  ascending  colon,  twisting  the 
membrane,  and  the  downward  growth  of  that  part  of  the  gut  which  brings  the 
caecum  down  from  under  the  liver  to  the  right  iliac  fossa.  The  twist  having  occurred, 
and  the  ascending  colon  having  fallen  against  the  abdominal  wall,  the  fold  bearing 
the  ascending  and  transverse  colon  becomes  fused  with  the  peritoneum  of  the  pos- 
terior right  abdominal  wall  on  the  right  of  a  line  from  the  beginning  of  the  jejunum 

FIG.  1477. 


Right  supra- 
renal body 


Vena  cava 
Portal  vein  I 


Duodenum 


Right  kidney 

Transverse 
mesocolon 
(cut) 


Beginning  of 
transverse 
colon 

Mesentery  of. 
jejuno-ileum 
(cut) 


Ascending  _ 

colon 

1  leu  in,  lower 
end 


Pancreas 

Splenic  flexure  of 
colon 


Jejunum 


Mesentery  of 
descending 
colon  ami  si.ij- 
moid  flexure 


Sigmoid 
flexure,  lower 
end 


Bladder 


Caecum 


Showing  relations  and  attachments  of  mesentery  of  small  and  large  intestines;  greater  part  of  transverse  colon, 
of  sigmoid  flexure  and  of  jejuno-ileum  has  been  removed,  the  latter  by  cutting  through  the  mesentery  near  its 
posterior  attachment. 


to  the  end  of  the  ileum,  the  part  bearing  the  small  intestine  remaining  free.  This 
oblique  line  of  attachment  becomes  the  permanent  mesentery.  The  peritoneum  to 
the  right  of  it,  as  far  as  the  ascending  colon,  forms  the  permanent  parietal  perito- 
neum, having  fused  with  the  original  parietal  layer  behind  it.  When  the  colon 
under  the  liver  becomes  the  transverse,  the  part  nearest  to  the  latter  continues  free 
and  lianas  down  as  a  transverse  fold,  on  which  the  greater  omcntum  lies,  and  sub- 
sequently fuses,  as  already  described.  The  transverse  colon  is  attached  by  the 
transverse  mesocolon  (also  a  secondary  adhesion)  to  the  front  of  the  right  kidney 
and  to  the  posterior  wall  across  the  second  part  of  the  duodenum  and  the  head  of 


THE    PERITONEUM. 


1753 


the  pancreas  along  the  lower  border  of  that  gland  to  the  left  kidney  (Fig.  1477).  Its 
greatest  breadth  is  some  five  or  six  inches.  (For  a  fuller  description,  see  peritoneal 
relations  of  the  colon,  page  1670.)  The  breadth  of  the  transverse  mesocolon  is  from 
12-15  cm-  (5~6  in.).  In  the  adult  it  is  fused  with  the  greater  omentum,  as  already 
described.  The  superior  mesenteric  artery  enters  this  mesentery  under  the  pancreas, 
and  gives  from  its  left  or  convex  side  the  branches  for  the  small  intestine.  From 
its  right,  just  after  its  origin,  it  gives  off  the  inferior  pancreatico-duodenal  and  the 
branches  for  the  caecum  and  the  ascending  and  transverse  colon.  In  the  adult  the 
right  colic  artery  runs  behind  the  permanent  posterior  parietal  peritoneum. 

The  Posterior  Mesentery  :  Part  III. — The  region  of  the  inferior  mesen- 
teric artery  is  very  simple.  Starting  at  the  left  of  the  permanent  mesentery  of  the 
small  intestine,  the  peritoneum  is  traced  over  the  posterior  abdominal  wall,  over 


Caecum 


FIG.   1478. 

Small  intestine 


Transverse  colon 


Ascending  colon 
Lower  end  of  ileum 

Mesentery 


Duodenum 

Descending  colon 
Mesentery 


Posterior  wall  of  abdom 


Bladder 


Mesenterium  commune  in  child  of  three  years  ;  the  usual  relations  would  be  restored  by  bringing  upper  dotted  line 

in  contact  with  lower. 

the  lower  part  of  the  left  kidney,  and  over  the  descending  colon,  which,  although 
touching  that  organ,  lies  chiefly  external  to  it.  The  posterior  surface  of  the  gut  is 
retroperitoneal.  The  descending  colon  has  fallen  over  to  the  left,  so  that  the  peri- 
toneum of  the  left  side  of  its  mesentery  has  fused  with  that  of  the  abdominal  wall, 
and  the  permanent  serous  covering  of  the  posterior  wall  is  derived  from  that  of  the 
right  side  of  the  original  mesentery.  This  fusion  ceases  at  the  crest  of  the  ilium,  and 
the  sigmoid  flexure  retains  at  least  a  part  of  the  original  mesentery  (Fig.  1478).  The 
line  of  its  attachment  runs  in  more  than  one  direction,  according  to  the  amount  of 
freedom  of  the  fold,  from  that  point  to  the  middle  of  the  third  sacral  vertebra.  (The 
chief  forms  are  described  on  page  1671.)  Beyond  the  latter  level  the  rectum  is 
partly  uncovered  behind,  where  the  mesentery  ceases,  and  its  gradually  diverging 


1754  HUMAN   ANATOMY. 

lines  pass  onto  its  sides,  leaving  the  termination  of  the  gut  without  any  peritoneal 
covering.  The  branches  of  the  inferior  mesenteric  artery  in  this  region  are  the  left 
colica  sinistra,  which  runs  behind  the  permanent  parietal  peritoneum  ;  the  sigmoid, 
which  does  the  same  until  it  reaches  the  part  of  the  mesentery  which  is  free  ;  and  the 
superior  hemorrhoidals,  which  descend  in  the  lower  part  of  the  original  mesentery 
until  they  reach  the  retroperitoneal  area  behind  the  rectum. 

PRACTICAL  CONSIDERATIONS  :     THE  PERITONEUM. 

The  development,  topography,  and  relations  of  the  peritoneum  have  already 
been  sufficiently  described.  It  remains  to  consider  its  diseased  conditions  and  those 
in  which  it  is  an  important  or  controlling  factor  in  the  production  of  disease  in  so  far 
as  they  are  influenced  by  anatomical  circumstances. 

Peritonitis  is  the  most  common  and  the  most  serious  of  peritoneal  diseases.  The 
separate  consideration  of  wounds  of  the  peritoneum  is  not  necessary,  as  traumatism, 
unassociated  with  infection,  produces  merely  hyperaemia  and  exudation.  The  pro- 
cess is  for  convenience  known  as  plastic  or  reparative  peritonitis,  a  term  also  applied 
to  those  forms  of  true  (infective)  peritonitis  in  which  the  bactericidal  and  absorptive 
powers  of  the  membrane  itself  and  of  its  serum  have  resulted  in  the  destruction  or 
the  isolation  of  the  invading  bacteria. 

The  anatomical  routes  by  which  bacteria  may  reach  the  peritoneum  are  : 

1.  From  without,  as  through  an  accidental  or  operative  wound. 

2.  From  within,  as  from  an  escape  of  the  micro-organisms  through  intestinal  walls 
leaky  as  a  result  of  strangulation  (as  in  intestinal  hernias  or  volvulus  or  intussuscep- 
tion) or  of  inflammation  (as  in   appendicitis)  ;  or  through  an  actual  perforation,  as 
in  gastric  ulcer,  typhoid  fever,  or  intestinal  cancer. 

3.  Through  the  blood-   or  lymph-channels,   as  in   many  cases  of  tuberculous 
peritonitis  and  possibly  in  so-called  rheumatic,  nephritic,  and  other  clinical  forms  of 
peritonitis,  in  some  of  which  the  infecting  organism  is  still  unknown. 

4.  Through  the  Fallopian  tubes. 

The  peritoneum  is  not  equally  susceptible  to  traumatism  or  to  infection  on 
both  its  surfaces  or  in  all  its  parts.  The  external,  areolar,  or  "wrong"  side  (page 
1740)  may  be  extensively  separated  from  the  subjacent  structures  (as  in  the  extraperi- 
toneal  approach  to  the  ureter  or  to  the  common  iliac  artery),  or  may  be  in  contact 
for  a  long  time  with  an  inflamed  or  a  suppurating  surface  (as  in  perirenal  or  other 
retroperitoneal  abscess)  without  damage  to  the  mesothelial  or  free  surface  of  the 
membrane,  and  with  but  little  risk  of  the  supervention  of  peritonitis. 

On  the  other  hand,  a  small  penetrating  wound  made  with  a  dirty  instrument  will 
probably  set  up  a  diffuse  and  perhaps  a  fatal  inflammation. 

The  difference  in  results  is  due  to  the  delicacy  and  vulnerability  of  the  mesothe- 
lial as  compared  with  the  fibrous  surface  ;  to  the  great  absorbent  power  of  the  former 
(vide  infra),  the  area  of  which  is  about  equal  to  that  of  the  cutaneous  surface  of  the 
body,  favoring  toxaemia  if  the  bacteria  and  their  toxins  are  not  destroyed  or  encap- 
sulated ;  to  the  excellent  culture  material  supplied  by  blood-clot  or  by  the  injured  or 
necrotic  epithelial  surface  ;  and  to  the  involvement  in  diffuse  or  spreading  cases  of  th 
peritoneal  covering  of  the  neighboring  viscera,  particularly  the  intestines. 

These  facts  determine  the  surgical  rule  that  in  doubtful  cases  of  bullet  and  stab 
wounds  of  the  abdominal   wall  it  is  well — under  aseptic  conditions — to  enlarge  the 
wound,  ascertain  the  presence  or  absence  of  penetration,  and  cleanse  or  drain  i 
necessary. 

Not  only  are  the  two  sides  of  the  peritoneum  thus  unlike  in  susceptibility  to  in- 
fection, but  a  similar  difference  exists  between  the  parietal  peritoneum  and  that  cover- 
ing the  viscera.  The  former,  applied  by  a  layer  of  fat-containing  connective  tissue  t 
the  relatively  immobile  muscular 'layer  of  the  abdominal  wall,  is  less  easily  inflamed, 
or  if  inflamed  develops  a  less  diffused  and  less  quickly  spreading  form  of  peritonitis 
than  docs  the  thinner,  more  sensitive,  and  more  vulnerable  visceral  peritoneum, 
especially  that  covering  the  most  mobile  of  the  abdominal  viscera,  the  small  intestine. 

So,  too,  peritonitis  originating  in  certain  regions  is,  l>y  reason  of  the  facility 
with  which  they  may  be  shut  off  by  adhesions,  less  threatening  in  its  course  and 


PRACTICAL    CONSIDERATIONS  :    THE   PERITONEUM.          1755 

more  amenable  to  surgical  treatment  than  that  beginning  elsewhere.  Pelvic  perito- 
nitis, para-appendical  and  paracolic  peritonitis,  subdiaphragmatic  and  subhepatic 
peritonitis,  and  peritonitis  limited  to  the  lesser  peritoneal  sac  (vide  infra)  are  all  va- 
rieties that  are  less  dangerous  than  is  peritonitis  beginning  among  the  shifting  coils 
of  small  intestine. 

The  anatomical  sources  of  peritoneal  infection  may  therefore  be  arranged  ap- 
proximately in  the  order  of  their  gravity,  as  follows  :  (a)  perforations  or  wounds  of 
the  small  intestine  ;  (£)  perforations  or  wounds  of  the  stomach  or  large  intestine  ; 
(c)  perforations  or  wounds  of  other  viscera,  including  kidneys,  ureters,  bladder,  pan- 
creas, and  bile-passages  ;  (d)  entrance  of  bacteria  by  continuous  growth  through 
inflamed  gastro- intestinal  walls  ;  (<?)  bacterial  migration  through  strangulated  intes- 
tine ;  (_/")  infection  through  the  Fallopian  tubes  ;  (£•)  wounds  of  the  abdominal 
wall  (Eowler). 

This  arrangement  is  based  upon  two  factors  :  the  number  and  virulence  of  the 
bacteria  which  are  likely  to  gain  entrance,  and,  the  opportunity  which  will  probably 
be  afforded  for  the  formation  of  limiting  adhesions.  The  latter  factor  should  be  con- 
sidered from  the  anatomical  stand-point,  as  the  variations  in  the  intensity  of  the  in- 
flammation due  to  varying  forms  and  doses  of  the  invading  bacteria  are  influenced  by 
the  site  of  a  wound  or  other  traumatism,  or  of  an  ulcerative  or  necrotic  process  in  the 
abdominal  viscera.  For  example,  and  for  reasons  already  indicated,  penetrating 
wounds  above  the  level  of  the  umbilicus  are  less  likely  to  produce  fatal  peritonitis 
than  are  those  in  the  lower  half  of  the  abdomen.  The  differences  in  this  respect  be- 
tween wounds  or  perforations  of  the  stomach,  of  the  different  portions  of  the  small 
intestine,  and  of  the  large  intestine  have  been  described  in  relation  to  the  anatomy  of 
those  portions  of  the  gastro-intestinal  tract. 

The  resistance  of  the  peritoneum  to  infection  is  usually  in  direct  proportion  to 
the  normality  of  its  mesothelial  coat,  which  is  lessened  by  all  forms  of  traumatism, 
including  handling  or  sponging,  or  irrigation  with  strong  antiseptics.  To  a  certain 
extent  the  sensitiveness  of  the  peritoneum  and  the  rapidity  with  which  it  responds  to 
irritation  is  a  conservative  process.  The  prompt  exudation  which  follows  either  injury 
or  infection  often  isolates  the  affected  area  and  prevents  a  fatal  diffusion  of  inflamma- 
tion. The  great  absorptive  power  of  the  peritoneum — which  should  be  studied  also  in 
connection  with  the  lymphatic  system — may  be  alluded  to  here,  as  it  aids  materially 
in  lessening  the  danger  from  infection.  It  has  been  demonstrated  experimentally 
that  from  3  to  8  per  cent,  of  the  body  weight  in  fluid  can  be  taken  up  by  the  peri- 
toneum from  within  its  cavity  in  one  hour,  which  is  equivalent  to  the  total  body 
weight  in  twenty-four  hours  (Wegner).  The  current  of  this  process  of  absorption  of 
peritoneal  serum  has  been  shown  to  set  normally  from  the  peritoneal  cavity  towards 
the  diaphragm,  and  to  be  much  hastened  by  elevation  of  the  pelvis  and  lower  abdo- 
men. Small  particles  (carmine,  bacteria,  etc. )  are  carried  through  the  intercellular 
spaces  in  the  diaphragmatic  peritoneum — "the  openings  made  by  the  retraction  of 
the  endothelium"  (Kelly) — into  the  lymph-spaces  beneath,  then  into  the  mediastinal 
lymph-spaces  and  glands,  and  then  into  the  blood-current  (Muscatello).  This  pro- 
cess goes  on  much  more  rapidly  in  this  direction — towards  the  diaphragm  and  medi- 
astinal glands — than  does  the  similar  process  beginning  in  the  visceral  (intestinal) 
peritoneum  and  associated  with  the  mesenteric  lymph-nodes, — an  additional  ana- 
tomical explanation  of  the  greater  fatality  of  visceral  peritonitis. 

The  close  relation  of  the  nerves  of  the  peritoneum  and  of  the  abdominal  viscera 
to  the  nerves  supplying  the  abdominal  and  the  lower  intercostal  muscles  has  been 
mentioned  in  relation  to  appendicitis  and  other  intra-abdominal  lesions  (pages,  528, 
1683),  and  is  of  the  highest  importance  in  connection  with  the  clinical  symptoms 
of  peritonitis.  Hilton  compares  the  peritoneum  and  the  muscles  of  the  abdomen  to 
the  synovial  membrane  and  the  muscles  moving  a  joint.  The  rigidity  that  follows 
inflammation  in  either  case  is  due  to  the  reflex  muscular  spasm  resulting  from  the 
correlation  of  the  nerve-supply.  Thus  the  six  lower  intercostals  supplying  the  corre- 
sponding intercostal  muscles  and  passing  through  the  diaphragm,  to  which  they  send 
twigs,  are  distributed  to  the  skin  over  most  of  the  abdomen,  and  to  the  rectus.  ex- 
ternal and  internal  oblique,  and  transversalis  muscles.  Through  the  splanchnics 
they  join  also  in  the  innervation  of  the  peritoneum  and  of  the  abdominal  viscera.  In 


1756  HUMAN   ANATOMY. 

a  case  of  injury  to  the  abdominal  wall,  therefore,  the  impression  is  barely  made  upon 
the  skin  before  the  muscles  contract  and  an  attempt  at  protection  is  made.  In  a  case 
of  visceral  lesion  or  of  beginning  peritonitis  the  rigid  contraction  of  the  muscles  in 
closest  nerve  relation  to  the  area  involved  will  constitute  a  valuable  diagnostic  symp- 
tom. In  general  peritonitis  the  board-like,  tender  abdomen,  the  fixed  diaphragm, 
and  the  thoracic  breathing  (to  lessen  movement  of  the  abdominal  viscera)  are  all 
phenomena  to  be  understood  only  by  recalling  the  correlation  of  the  nerves  involved. 
The  flexion  of  the  thighs  (to  remove  pressure  from  the  tender  surface  and  to  relax 
the  muscles  as  much  as  possible)  is  a  secondary  symptom  due  to  the  same  cause. 
The  condition  is  in  strong  contrast  with  that  seen  in  intestinal  spasm  (colic},  in 
which,  although  the  patient  may  be  doubled  up  with  pain,  pressure  gives  relief  and 
the  loose,  relaxed  abdominal  muscles  may  be  moved  easily  and  freely  over  the  un- 
derlying viscera.  The  intestinal  distention  and  paresis  of  peritonitis  are  due  partly 
to  the  involvement  of  the  nerve-plexuses  of  the  gut  and  partly  to  the  extension  of  in- 
flammation to  its  muscular  walls.  They  are  increased  by  later  vasomotor  paralysis 
and  by  fermentative  decomposition  of  intestinal  contents. 

Other  phenomena  common  to  many  abdominal  lesions,  but  especially  to  those 
affecting  the  peritoneum,  are  due  to  the  relation  of  the  nerves  of  the  latter  to  the 
great  abdominal  nerve- plexuses.  They  have  been  grouped  by  Giibler  under  the 
term  peritonism,  are  independent  of  toxaemia,  and  are  essentially  the  symptoms  of 
"  shock," — subnormal  temperature,  a  running  pulse,  pallor  or  lividity,  quick,  shallow 
breathing,  and  great  mental  and  physical  depression.  The  more  distinctive  peritoneal 
symptoms  are  vomiting  (although  that  is  not  uncommon  in  many  forms  of  shock  ) 
and  generalized  abdominal  pain  becoming  epigastric  or  umbilical,  and  later — if  peri- 
tonitis develops — associated  with  tenderness.  In  illustration  of  this  relation  of  nerves 
and  nerve-centres,  Treves  says,  very  truly,  that  almost  all  acute  troubles  within  the 
abdomen  begin  with  the  same  group  of  symptoms,  and  that  until  some  hours  have 
elapsed  it  is  often  impossible  to  say  whether  a  violent  abdominal  crisis  is  due  to  the 
perforation  of  an  appendix  or  other  portion  of  the  intestine,  the  bursting  of  a  pyo- 
salpinx,  the  strangulation  of  a  loop  of  gut,  the  passage  of  a  gall-stone,  the  rupture  of 
a  hydatid  cyst,  an  acute  infection  of  the  pancreas,  the  twisting  of  the  pedicle  of  an 
ovarian  tumor,  or  a  sudden  intraperitoneal  hemorrhage. 

The  later  symptoms  of  peritonitis — the  board-like  rigidity  of  the  abdominal  mus- 
cles, the  tenderness,  the  meteorism,  the  intestinal  paresis  or  paralysis,  and  the  ascitic 
dulness  in  the  flanks — require  no  further  anatomical  explanation.  The  factors  already 
described,  plus  the  existence  of  profound  toxaemia,  sufficiently  account  for  them. 

Chronic  peritonitis  of  the  proliferative  type  (said  to  be  found  frequently  in  the 
subjects  of  chronic  alcoholism)  is  attended  by  great  thickening  followed  by  fibroid 
contraction,  which,  in  accordance  with  the  locality  chiefly  involved,  may  cause  (a) 
constriction  of  the  gastro-hepatic  omentum  with  pressure  on  the  portal  vein  and  re- 
sulting serous  effusion  ;  (6)  diminution  in  the  volume  of  the  liver  from  perihepatitis  ; 
(c}  thickening  of  the  omentum,  which  forms  a  hardened  roll  lying  transversely 
between  the  colon  and  the  stomach  ;  (</)  shortening  of  the  mesentery  so  that  the 
intestines  are  drawn  into  a  rounded  mass,  situated  in  the  mid-line  and  feeling  like  a 
solid  tumor  ;  (e}  thickening  and  contraction  of  the  intestinal  walls,  the  mucous  mem- 
brane being  thrown  into  folds  like  the  valvulae  conniventes  ;  (_/")  the  formation  of 
cicatricial  bands  attached  at  their  ends  to  intestine  and  parietes  or  to  two  portions  of 
the  gut,  and  under  which  other  coils  of  intestine  may  pass  and  become  strangulated. 

'liberations  peritonitis  is  the  most  common  chronic  form  of  the  disease.  The 
infection — especially  in  children  and  males — usually  proceeds  from  the  digestive  tract 
through  the  retroperitoneal  lymphatics  ;  or  from  the-  lung  or  pleura  and  bronchial 
lymph-nodes  by  the  same  route  ;  or,  less  frequently,  directly  from  ulcers  within  the 
intestine  ;  in  women  it  often  enters  through  the  Fallopian  tubes.  It  may  be  con- 
veyed by  the  blood. 

Of  the  conditions  described  as  due  to  chronic  peritonitis,  the  omental  thickening 
and  the  retraction  and  thickening  of  intestinal  coils  are  frequently  present.  Agglu- 
tination of  these  coils  is  apt  to  occur  and  to  contribute  to  the  sense  ot  resistance  which 
may  be  erroneously  interpreted  as  indicating  the  presence  of  a  tumor.  In  addition 
there  are  apt  to  be  (a)  a  sacculated  exudation  in  which  the  effusion  is  limited  and 


PRACTICAL   CONSIDERATIONS:   THE    PERITONEUM.         1757 

confined  by  adhesions  between  the  coils  of  gut,  the  parietal  peritoneum,  the  mesen- 
tery, and  the  abdominal  or  pelvic  organs  (Osier)  ;  and  (6)  enlargement  of  the 
mesenteric  glands. 

The  existence  of  a  superficial  periumbilical  area  of  redness  and  thickening  is  said 
to  be  a  symptom  of  this  variety  of  peritonitis  (Fagge),  and  is  even  thought  to  be 
pathognomonic  (Henry).  It  may  follow  adhesion  of  intestine  to  the  inner  parietes, 
or,  more  probably,  is  due  to  extension  of  the  inflammation  of  the  parietal  peritoneum 
along  the  track  of  the  obliterated  umbilical  vessels. 

Localized  peritonitis  should  be  briefly  considered  from  the  topographical  stand- 
point. 

Pelvic  peritonitis,  usually  due  to  infection  by  way  of  the  uterus  and  Fallopian 
tubes,  is  of  relatively  lessened  danger  on  account  of  (a)  the  fact  that  the  source  of 
bacterial  supply  is  not  large,  the  endometrium  possessing  a  high  degree  of  vital  re- 
sistance and  its  secretion  rendering  its  cavity  in  most  instances  sterile  ( Warbasse) ; 
(b)  the  comparatively  low  virulence  of  the  bacteria  most  frequently  found  in  tubal 
infection,  the  gonococcus  and  bacillus  tuberculosis  ;  and  (e')  the  opportunity  usually 
afforded  (by  the  thickness  and  immobility  of  the  subperitoneal  tissues  involved)  for 
the  formation  of  competent  adhesive  barriers,  including  those  which  seal  the  opening 
of  the  tube  and  confine  the  infection  to  the  latter  and  its  vicinity  (Fowler). 

Puerperal  peritonitis  is  much  more  serious,  owing  to  the  anatomical  conditions 
associated  with  pregnancy — chiefly  the  vastly  greater  size  and  vascularity  of  the 
uterus  and  the  enlargement  of  its  lymph-channels — and  to  the  minor  traumatisms  to 
the  endometrium  which  occur  even  in  physiological  parturition.  These  offer  an 
opportunity  for  increased  dosage  of  bacteria  and  of  their  toxins.  The  danger  is 
increased  by  the  fact  that  the  invading  organism  is  apt  to  be  a  streptococcus  and  by 
the  usual  post-partum  diminution  of  vital  resistance. 

Subdiaphragmatic  peritonitis  may  be  confined  to  the  space  between  the  arch  of 
the  diaphragm  and  the  upper  surface  of  the  liver  to  the  right  or  left  of  the  suspen- 
sory ligament.  It  is  apt  to  assume  a  suppurative  form.  It  may  follow  (or  precede) 
a  pleural  or  pulmonary  infection.  It  is  commonly  mistaken  for  an  empyema.  The 
infection  is,  of  course,  at  its  onset  within  the  greater  cavity  of  the  peritoneum,  but  is 
often  soon  shut  off  by  adhesions.  When  it  has  followed  a  perforation  of  the  stomach 
or  duodenum,  the  abscess  usually  contains  air  (pyo-pneumothorax  subphrenicus), 
the  diaphragm  may  be  pushed  up  to  the  level  of  the  second  or  third  rib,  the  liver  is 
depressed,  there  is  bulging  of  the  right  thorax,  and  the  physical  signs  are  those  of 
pneumothorax  (Osier). 

The  variety  of  Subdiaphragmatic  peritonitis  which  involves  the  lesser  peritoneal 
cavity  may  originate  in  gastric,  duodenal,  or  colic  perforations,  in  pancreatic  disease, 
or  in  other  ways.  The  communication  with,  the  greater  peritoneum  is  soon  cut  off 
by  adhesive  inflammation  of  the  edges  of  the  gastro-hepatic  omentum  at  the  foramen 
of  Winslow. 

Distention  of  the  lesser  sac  with  serum  or  with  pus  follows  and  first  causes  an 
epigastric  swelling,  extending  by  gravity  to  the  umbilical  region  ;  on  account  of  the 
lesser  resistance  offered  by  its  left  boundary — the  lieno-renal  ligament — as  compared 
with  that  of  the  gastro-hepatic  omentum,  and  because  the  lesser  sac  extends  farther 
towards  that  side,  the  swelling  may  appear  later  in  the  left  hypochondriac  region. 
As  the  floor  of  the  space  is  formed  by  the  upper  layer  of  the  transverse  mesocolon, 
the  colon  is  depressed  and  never  lies  in  front  of  or  above  the  enlargement,  as  it  does 
in  cases  of  renal  tumor.  As  the  space  lies  below  and  behind  the  stomach,  distention 
of  the  latter,  if  with  liquid,  will  render  the  swelling  less  palpable,  but  may  apparently 
increase  its  area  of  dulness  ;  if  with  air,  will  convert  the  dulness  into  resonance  and 
prevent  recognition  of  the  swelling  by  touch. 

Spontaneous  evacuation  of  a  Subdiaphragmatic  abscess  may  take  place  into  any 
of  the  surrounding  viscera  or  into  the  general  peritoneal  cavity,  but  the  pus  usually 
enters  the  pleural  cavity  or  the  thorax  either  by  direct  ulceration  and  perforation  of 
the  diaphragm  or,  more  circuitously,  through  the  weakened  intervals  between  the 
sternal,  costal,  and  vertebral  portions  of  that  muscle. 

The  appendicular  and  subhepatic  varieties  of  localized  peritonitis  have  been  suffi- 
ciently described  in  connection  with  the  organs  involved. 


1758  HUMAN   ANATOMY. 

Cancer  of  the  peritoneum  is  occasionally  primary,  but  is  usually  due  to  exten- 
sion from  the  stomach,  uterus,  ovaries,  liver,  or  other  organs.  The  irregular  mass  of 
a  carcinomatous  omentum  cannot  be  distinguished  by  touch  from  the  similar  tumor 
due  to  chronic  peritonitis. 

The  peritoneal  cavity  as  a  whole — the  interval  between  adjacent  visceral  surfaces 
or  between  such  surfaces  and  the  parietes — may  be  scarcely  more  than  a  potential 
space,  containing  enough  serous  fluid  for  purposes  of  lubrication,  or  may  be  more  or 
less  distended  by  an  effusion  of  the  same  fluid, — ascites.  Such  effusion  may  result 
from  (a)  infection  followed  by  chronic  inflammation  ;  (&')  abdominal  tumors,  causing 
irritation  and  pressure  ;  (c)  obstruction  of  the  portal  circulation,  either  terminal,  as 
in  hepatic  cirrhosis,  or  by  pressure  on  the  vein  itself  in  the  gastro-hepatic  omen- 
tum, as  from  certain  pancreatic  or  duodenal  growths,  aneurism,  or  the  exudate  of 
a  chronic  peritonitis  (vide  supra};  or  (a?)  from  conditions  producing  a  general 
dropsy  (of  which  the  ascites  is  but  a  part),  such  as  cardiac  or  renal  disease,  chronic 
empyema,  or  pulmonary  sclerosis.  Ascites  is  recognized  by  (a)  a  flat  abdomen 
bulging  at  the  flanks,  with  prominent  umbilicus  ;  (6)  dulness  in  the  flanks  varying 
with  change  of  posture  ;  (c)  resonance  over  the  uppermost  part  of  the  abdomen 
in  either  dorsal  or  lateral  decubitus  (from  floating  upward  of  the  intestine)  ;  (d)  fluc- 
tuation. Sudden  withdrawal  of  ascitic  fluid  may  cause  syncope  in  persons  with 
pre-existing  cardiac  lesions  by  diminishing  intra-abdominal  pressure,  permitting  a 
dilatation  of  the  deep  circumflex  iliac,  the  deep  epigastric,  the  lumbar  and  other 
deep  abdominal  veins,  and  thus  suddenly  lessening  cardiac  blood-pressure. 

The  difference  between  the  peritoneal  cavity  and  the  abdominal  cavity  should 
not  be  overlooked  by  the  student.  A  number  of  the  abdominal  viscera  are  not  intra- 
peritoneal,  but  lie  more  or  less  completely  behind  that  membrane.  Thus  the  kidney 
and  pancreas  and  certain  aspects  of  the  ascending  and  descending  colon  and  duode- 
num may  be  wounded,  or  may  be  the  subject  of  infectious  disease,  without  involve- 
ment of  the  peritoneum,  while  similar  wounds  or  infections  of  the  liver,  spleen,  stom- 
ach, or  small  intestine  would  necessarily  include  it  to  some  extent. 

The  parietal  peritoneum,  the  least  sensitive  portion  of  the  membrane  (vide 
supra},  is  thickest  below  and  posteriorly,  and  is  there  connected  loosely  with  the 
abdominal  wall  by  relatively  abundant  subperitoneal  cellular  tissue  containing  fat. 
This  loose  connection  permits  it  to  be  stripped  forward,  as  in  some  operations  on 
the  kidneys  or  ureters  or  on  the  iliac  vessels.  About  the  umbilicus  and  along 
the  mid-line  of  the  abdomen  it  adheres  much  more  closely.  It  is  strong,  bearing 
a  weight  of  fifty  pounds  (Huschke)  ;  distensible,  as  shown  by  the  gradual  stretch- 
ing it  undergoes  in  ascites,  during  pregnancy,  or  in  a  hernial  sac  ;  and  elastic,  as  in 
such  cases  it  returns  to  its  normal  dimensions  when  the  distending  cause  is  removed. 
It  may  be  ruptured  by  sudden  force  without  injury  being  done  to  the  underlying 
viscera. 

From  its  superficial  position,  the  greater  o me ntu m  is  often  involved  in  penetrating 
wounds  of  the  abdominal  wall.  Wounds  of  the  omentum  are  not  in  themselves  seri- 
ous, except  from  hemorrhage.  The  rapid. adhesive  inflammation  which  follows  injury 
to  the  omentum,  as  to  other  parts  of  the  peritoneum,  may  act  beneficially  by  leading 
to  the  closure  of  an  intestinal  wound  or  perforation  before  extravasation  occurs,  or  by 
favoring  the  localization  of  an  area  of  infection.  It  is  sometimes  utilized  by  the  sur- 
geon to  reinforce  an  intestinal  suture  or  to  cover  intestinal  defects,  especially  in  the 
caecum  (E.  Senn)  ;  or  to  protect  the  general  peritoneal  cavity,  as  in  some  operations 
on  the  bile-ducts.  Through  inflammatory  adhesions,  portions  of  the  omentum  may- 
act  as  bands  beneath  which  a  loop  of  gut  may  be  strangulated,  or  such  a  loop  may- 
pass  through  an  aperture  in  the  omentum  itself  and  become  strangulated.  The 
omentum  is  constantly  found  in  sacs  of  ordinary  hernise  or  may  constitute  their  only 
contents  (epiplocele),  especially  in  umbilical  and  frequently  in  femoral  hernise.  It 
almost  always  contracts  adhesions  to  the  neck  or  other  portion  of  a  hernial  sac,  if  the 
hernia  is  not  kept  permanently  reduced.  It  then  prevents  reduction.  It  is  found 
oftener  in  left-sided  hernise,  because  it  was  developed  from  the  mesogastrium  and 
inclines  somewhat  towards  that  side.  It  is  very  vascular,  and  has — through  acci- 
dental adhesions — maintained  the  blood-supply  of  an  ovarian  tumor  the  pedicle  of 
which  has  been  twisted  so  as  to  occlude  its  vessels.  Its  vascularity  and  rapid  adhe- 


PRACTICAL  CONSIDERATIONS  :   ABDOMINAL    HERNIA.       1759 

sion  to  other  peritoneal  surfaces  have  been  utilized  in  an  operation  for  the  relief  of  the 
portal  congestion  in  certain  forms  of  hepatic  cirrhosis  (page  1727). 

The  Mesentery. — The  length  of  this  portion  of  the  peritoneum  is  of  importance 
in  its  relation  to  the  causation  and  the  forms  of  hernia,  in  connection  with  which  it 
will  be  referred  to.  From  its  oblique  attachment  it  results,  that  in  an  intraperitoneal 
right-sided  hemorrhage  the  blood  is  first  conducted  into  the  right  iliac  fossa  ;  if  the 
hemorrhage  takes  place  to  the  left  of  the  mesentery,  the  blood  descends  directly  into 
the  pelvis  (Treves).  Collections  of  blood  are  said  to  be  more  common  in  the  right 
than  in  the  left  iliac  fossa.  Treves  has  shown  that,  in  addition  to  certain  slit-like 
holes  due  to  injury,  there  are  others  which  are  congenital  defects  in  the  mesentery, 
and  has  called  attention  to  the  fact  that  the  latter  are  round  ;  are  in  the  lower  ileum  ; 
are  surrounded  by  an  anastomotic  arch  between  the  ileo-colic  branch  of  the  superior 
mesenteric  artery  and  the  last  of  the  intestinal  arteries  ;  that  the  area  is  often  the  seat 
of  atrophied  peritoneum  ;  and  that  fat,  visible  blood-vessels,  and  glands  are  absent. 
Herniae  of  knuckles  of  gut  through  this  cribriform  area  of  mesentery  could  occur 
with  comparative  ease. 

The  use  of  the  mesentery  as  a  means  of  recognition  of  a  particular  portion  of  gut 
during  operative  procedures  has  been  described  (page  1657). 

The  practical  relations  of  the  peritoneal  fosscE  and  folds  will  be  considered  in  the 
section  on  hernia  (page  1765). 

PRACTICAL  CONSIDERATIONS  :  ABDOMINAL  HERNIA. 

Abdominal  hernia  would  be  correctly  defined,  in  the  great  majority  of  cases,  as 
the  protrusion  of  any  abdominal  viscus  from  the  cavity  of  the  abdomen,  and  if  the 
term  were  limited  to  include  protrusion  of  only  portions  of  the  small  intestine  (jejunum 
and  ileum)  and  of  the  omentum,  it  would  still  embrace  by  far  the  larger  number  of 
herniae.  Intra-abdominal  herniae  occur,  however,  in  which  a  portion  of  the  intestine 
passes  from  the  general  into  the  lesser  peritoneal  cavity  or  into  one  of  the  various 
peritoneal  fossae  or  recesses.  The  resulting  evil  effects  in  both  cases  are  due  not  to 
the  protrusion  but  to  the  secondary  changes  that  follow  the  displacement  of  the  gut 
(incarceration,  strangulation).  It  is  well,  therefore,  to  subdivide  abdominal  herniae 
into  external  and  internal,  and  in  the  latter  variety  to  recognize  the  necessary  modifi- 
cation of  the  above  definition. 

External  Hernia. — The  general  conditions  that  predispose  to  or  actually  produce 
external  hernia  are  those  associated  with  ( i )  increased  intra-abdominal  pressure  and 
(2)  decreased  resistance  of  the  abdominal  wall. 

1.  Under  the  former  should  be  placed   (a)  occupations  that  necessitate  much 
muscular  effort,  particularly  if  it  is  in  the  direction  of  lifting  heavy  weights,  or  is  ex- 
erted while  the  person  is  in  a  stooping  posture  (vide  infra),  or  if,  at  the  same  time, 
increased  respiratory  effort  is  required,  so  that  during  forced  inspiration  the  diaphragm 
aids  in  augmenting  the  outward  pressure  of  the  abdominal  viscera  ;    (£)  diseases 
causing  vesical  or  rectal  tenesmus  ;    (r)  respiratory  diseases  producing   chronic  of 
violent  coughing,  or  inspiratory  obstruction. 

2.  Decreased  resistance  of  the  whole  abdominal  wall  may  be  due  to  (a)  debili- 
tating  illness,    (&')    old  age,    (r)    prolonged   distention   (ascites,    abdominal   tumor, 
repeated  pregnancies,  (d)  excessive  corpulence,  or  (e)  emaciation.     The  last  two 
causes  are  assumed  to  act  as  follows  :  with  the  occurrence  of  general  emaciation,  the 
fatty  tissue  filling  up  the  hernial  orifices  usually  disappears,  and  these  places,  which  are 
already  less  resistant,  become  more  yielding  and  relaxed  ;  with  the  rapid  appearance  of 
obesity  there  is  an  increase  in  the  amount  of  the  subperitoneal  areolar  tissue,  and  this 
consequently  results  in  a  greater  mobility  of  the  peritoneum.    The  traction  of  a  rapidly 
growing  subperitoneal  lipoma  upon  the  peritoneum,  to  which  it  is  tightly  adherent, 
is  also  a  factor  in  the  development  of  a  hernial  sac,  although  it  does  not  follow  that 
this  method  of  origin  is  frequent  or,  as  Roser  asserted,  the  usual  one  (Sultan). 

The  disappearance  of  fat  and  connective  tissue  in  emaciation  has  been  thought 
(Macready)  particularly  to  favor  the  occurrence  of  femoral  hernia. 

Other  predisposing  causes  are  as  follows  :  Age. — Hernia  is  very  common  during 
the  first  year  of  life.  Its  frequency  then  is  probably  due  to  (a)  the  existence  of 


1760 


HUMAN   ANATOMY. 
FIG.  1479. 


Superficial  fascia 
External  oblique  muscle 

Anterior  superior  spine  of  ilium 

Deep  layer  of  superficial  fascia,  cut  edge 

Superficial  circumflex  iliac  artery 

Outer  pillar  of  external  ring 

Fascia  lata 

Part  of  deep  layer  of  superficial  fascia 
Cribriform  fascia 

Middle  cutaneous  nerve 

External  cutaneous  nerve 

Superficial  fascia 
Superficial  fascia,  cut  edge 


Aponeurosis  of  external  oblique 
Linea  alba 

s 

Intercolumnar  fibres 

Intercolumnar  fascia,  artificially  distended 
-Inner  pillar  of  external  ring 

Dartos,  cut  edge 


Branch  of  internal  cutaneous  nerve 
Internal  saphenous  vein 


Superficial  dissection  of  inguinal  region ;  spermatic  cord  is  seen  issuing  from  external 
abdominal  ring;  intercolumnar  fascia  has  been  artificially  distended  by  injection  of  fluid; 
saphenous  opening  is  closed  by  cribriform  fascia. 

FlG.    1480. 


External  oblique,  cut  edge 


Internal  oblique  muscle 

Aponeurosis  of  external  oblique, 

cut  edge 


Anterior  superior  spine  of  ilium 


Ponpart's  ligament 

•Attachment  of  deep  layer  of  superficial 

fascia  of  abdomen  to  fascia  lata 

Transversalis  muscle 

Spermatic  cord 

Fascia  lata 

External  pillar  of  external  ring, 
tin  in  c  1  down 

Falciform  process  of  fascia  lata 

Femoral  sheath  seen  through 

saphenous  opening 

Middle  cutaneous  nerve 
Extern*!  cutaneous  nerve 


Internal  saphenous  vein 


Branch  of  Internal  cutaneous  nerve 


Conj  nined  tendon 
Triangular  f.is,  i.i 
Suspensory  ligament  of  penis 
Insertion  of  creniaster  muscle 
Pubic  portion  of  fascia  lata 


Creniaster  muscle 


Deeper  dissection  in  which  external  oblique  has  been  partially  removed,  exposing  spermatic 
cord  lying  in  inguinal  canal ;  cribriform  fascia  removed  to  show  saphenous  opening. 


PRACTICAL   CONSIDERATIONS:   ABDOMINAL    HERNIA. 

FIG.   1481. 


1761 


Internal  oblique  '    ma 


Transversalis  muscle — ^H 

Aponeurosis  of  transversalis  —-J^B 

Internal  oblique,  iliac  origin—, x!. 

External  oblique,  iliac  insertion^-^S 

Branch  of  deep  circumflex— !L_i 
iliac  artery  V 

Anterior  superior  spine  of  ilium f-% 

Internal  oblique,  cut  edge^^^jB 

Poupart's  ligament -JEI 
Spermatic  cord -fe — 
Transversalis  fascia     " 
Cremasteric  fascia,  cut  edge 
Conjoined  tendon 
Anterior  crural  nerve 
Falciform  process  of  fascia  lata 
Crural  branch  of  genito-crural  nerve 
Femoral  art.  within  femoral  sheath 
Femoral  canal.artificiallydistended 
Femoral  vein  within  femoral  sheath 

External  pillar  of  external  ring,  turned  d. 

Insertion  of  cremaster 


—  Aponeurosis  of  external  oblique, 
cut  edge 


ft>  Internal  oblique,  cut  edge 

i^ 

\^-  Transversalis  muscle 


Triangular  fascia 


Spermatic  blood-vessels 


Cremasteric  fascia,  reflected  from 
spermatic  cord 


-'2»» Cremaster  muscle 


Internal  oblique  muscle  has  been  partially  removed,  showing  fibres  of  transversalis  arch- 
ing over  spermatic  cord  to  reach  conjoined  tendon  ;  fascia  lata  has  been  opened  to  expose 
femoral  vessels  lying  within  sheath  ;  temoral  canal  has  been  artificially  distended. 


FlG.    1482. 


Aponeurosis  of  transversalis 

Internal  oblique,  cut  edge 

Transversalis  muscle 

Transversalis,  cut  edge 

Internal  oblique,  iliac  origin 

External  oblieme,  iliac  insertion 

Transversal 

Branch  of  deep  circumflex  iliac  artery 
Deep  epigastric  artery 

Internal  abdominal  rin 

Poupart's  ligament 
Infundibuliform  fascia,  artificially 
distended]  Anterior  crural  nerve 

Femoral  sheath^ 

Sartorius 
Fascia  lata 


Fascial  septum  betw 


irtery  and  vein 
Femoral  vein 


-  1 

«t 


Septum  between  vein  arid  femoral  canal 

Femoral  canal 
External  pillar  of  external  ring,  turned  down 

Cremasteric  fascia,  cut  edge 


Deep  epigastric  artery 

Posterior  wall  of  sheath  of  rectus 

Rectus  abdominis 

Anterior  wall  of  sheath  of  rectus 


Aponeurosis  of  external  oblique, 
cut  edge 


—Transversalis  fascia 
-  Conjoined  tendon 


-Triangular  fascia 
— Spermatic  cord 

.Cremasteric  fascia  reflected  from 
spermatic  cord 


Transversalis  muscle  has  been  partially  cut  away  to  expose  transversalis  fascia ;  sper- 
matic cord  is  seen  issuing  from  internal  abdominal  ring,  covered  by  infundibuliform  fascia, 
which  has  been  artificially  distended  ;  anterior  layer  of  femoral  sheath  has  been  removed; 
showing  femoral  vessels  and  canal ;  anterior  wall  of  sheath  of  rectus  has  been  opened  above 
upper  part  of  muscle  removed  atid  posterior  wall  of  sheath  exposed. 

Ill 


1 762  HUMAN   ANATOMY. 

developmental  defects  ;  (b)  the  presence  in  the  abdomen  of  portions  of  the  pelvic 
organs  increasing  intra-abdominal  pressure  ;  (c)  the  habitual  flexion  of  the  thighs  on 
the  abdomen  in  infants,  relaxing  the  tissues  about  the  hernial  orifices  ;  (d  )  the  ex- 
treme shortness  of  the  inguinal  canal,  the  internal  ring  then  lying  almost  directly 
behind  the  external  ring,  so  that  the  canal  is  about  equal  in  length  merely  to  the 
thickness  of  the  abdominal  wall.  The  diminution  in  frequency  during  childhood  is 
due  to  the  improvement  in  posture,  to  the  lessening  in  size  of  the  abdominal  rings 
and  to  the  shortening  of  the  tissues  about  them,  and  to  the  lengthening  of  the  interval 
between  the  rings  as  the  ilia  grow  and  incline  outward  and  the  internal  ring  follows 
them, — i.e.,  to  the  formation  of  the  inguinal  canal  with  its  valve-like  resistance  to  the 
protrusion  of  viscera.  The  increase  in  frequency  as  puberty  approaches  and  is 
passed  is  due  to  the  more  active'  habits  of  life  and  the  assumption  of  occupations 
often  laborious.  It  may  also  be  due  to  a  slight  extent  to  the  fact  that  until  the  pel- 
vis has  fully  developed  the  femoral  ring  and  canal  scarcely  exist,  and  that  therefore 
the  femoral  variety  of  hernia  is  rarely  found  before  that  time  of  life.  Later  in 
life  hernia  is  still  more  frequent,  although  it,  like  aneurism,  lessens  in  numbers  as 
old  age  draws  on.  This  is  due  to  the  fact  that  although  in  both  instances  the  pre- 
disposing cause — the  weakness  of  vessels  or  of  the  abdominal  wall — may  be  said 
usually  to  increase  when  the  active  period  of  life  is  passed,  the  exciting  causes  due 
to  occupation  and  muscular  effort  diminish  with  relatively  greater  rapidity. 

Sex. — Hernia  is  more  frequent  in  males  because  (a)  the  structures  connected 
with  the  male  genitalia  are  more  often  the  subject  of  developmental  defects  (ride 
infra),  and  (b)  the  inguinal  canal  in  the  female  is  narrower  (containing  only  the 
round  ligament)  and  longer  (the  distance  between  the  anterior  superior  iliac  and  the 
pubic  spines  being  greater),  and  for  both  these  reasons  offers  less  opportunity  for  the 
descent  of  viscera. 

The  descent  of  the  testicle  and  the  associated  changes,  which  are  often  imperfect, 
sufficiently  account  for  the  great  frequency  of  inguinal  (92-95  per  cent. )  as  compared 
with  all  other  forms  of  hernia  in  males. 

In  females  femoral  hernia  is  less  common  than  inguinal  hernia.  It,  is  however, 
relatively  more  common  than  in  males  because  (a)  in  females  Gimbernat's  ligament 
(q.v.)  is  narrower,  thus  increasing  the  area  of  the  femoral  ring  ;  and  (t>)  it  is  weaker 
and  less  firmly  attached,  and  accordingly  offers  less  resistance  to  visceral  protrusion. 
In  loo  ruptured  persons  the  percentages  as  to  inguinal  and  femoral  hernia  in  the 
two  sexes  are  as  follows  :  male  inguinal,  83.5  ;  female  inguinal,  8.5  ;  female  femoral, 
5.9;  male  femoral,  2.1  (Macready). 

The  extent  of  the  influence  of  a  certain  shape  of  the  abdomen — with  lateral 
bulgings  parallel  with  and  just  above  Poupart's  ligament  and  extending  above  the 
level  of  the  crest  of  the  ilium — is  doubtful,  but  it  certainly  indicates  a  laxity  of  the 
abdominal  wall,  and  just  as  certainly  is  often,  as  a  precedent  condition,  associated 
with  hernia. 

The  almost  invariable  preponderance  of  right-sided  hernia  in  all  varieties,  at  all 
ages,  and  in  both  sexes  has  been  variously  attributed  to  (a)  the  greater  bulk  and 
weight  of  the  liver  ;  (6)  to  right-sidedness  in  walking  and  lying,  and  to  the  greater 
strain  on  the  muscles  of  the  right  side  caused  by  "right-handedness  ;"  (c)  to  the 
inclination  from  left  to  right  of  the  mesentery  of  the  small  intestine  as  it  descends  ; 
(d)  to  the  greater  frequency  of  incomplete  descent  of  the  testis  and  of  a  patulnus 
funicular  process  on  the  right  side  ;  and  (e)  to  the  larger  capacity  and  circumference 
of  the  right  side  of  the  pelvis  (Knox,  Macready)  as  compared  with  the  left,  causing 
a  corresponding  increase  in  the  size  of  the  right  femoral  ring. 

External  hernia;  are  influenced  as  to  the  site  of  their  protrusion  by  anatomical 
conditions  causing  a  diminution  over  certain  localized  areas  in  the  resistance  of  the 
abdominal  wall  to  intra-abdominal  pressure.  These  conditions  depend  usually  upon 
the  necessity  for  the  passage  from  within  out  of  (a)  normal  structures  such  as  the 
spermatic  cord  ( oblique  M  external  inguinal  hernia)  or  the  round  ligament  (the 
labial  variety  of  oblique  hernia}  ;  or  (6)  such  as  tin  larger  vessels  Of  nerves  {umbilical, 
femoral,  obturator,  seiatie  hernia)  ;  or  (e)  upon  the  weakness  or  absence  at  givrn 
points  of  some  of  the  components  of  the  abdominal  wall,  as  at  the  internal  inguinal 
fossa  or  the  supravesical  fossa  {direct  or  internal  inguinal  hernia),  along  the  linea 


Mouth 


Peritoneum 

nsversalis  fasci 


Superficial  fascia  and  skin 


PRACTICAL  CONSIDERATIONS:    ABDOMINAL    HERNIA.       1763 

alba  or  the  linea  semilunaris  (ventral hernia) ,  through  the  pelvic  diaphragm, — the  coc- 
cygeus  and  levator  ani  {perineal  hernia)  ;  or  through  Petit's  triangle  (page  530)  or 
the  superior  lumbar  triangle  of  Grynfelt  and  Lesshaft  (page  1777),  or  ' '  Braun's  space" 
(page  1777)  {lumbar  hernia}.  Other  varieties  depend  upon  (d~)  congenital  defects, 
as  in  some  forms  of  inguinal,  umbilical,  ventral,  and  diaphragmatic  hernia  ;  or  in  the 

varieties  of  properitoneal  or  interstitial  hernia 

FIG.  1483.  that    accompany    misplaced    or    undeveloped 

testes  ;  or  (e)  pathological  changes,  as  in 
those  ventral  hernia  that  follow  abscesses  or 
wounds. 

This  classification,  although  not  exhaustive, 
will  serve  as  a  basis  for  the  later  and  more  de- 
tailed consideration  of  the  anatomical  factors 
concerned  in  the  production  of  special  external 
herniae  and  of  their  symptoms. 

The  component  parts  of  an  external  ab- 
dominal hernia  (Fig.  1483)  are  (i)  the  sac, 
consisting  of  distended  and  protruding  parietal 
peritoneum,  and  subdivided  into  (a)  the  mouth, 
the  aperture  corresponding  to  the  internal  her- 
nial  orifice  ;  (b)  the  body,  the  expanded  pro- 
truding portion,  the  lowest  portion  of  which  is 

called  the  fundus ;  and  (c )  the  neck,  the  constricted  portion  connecting  the  body 
and  mouth  ;  and  (2)  the  contents,  which  in  the  order  of  frequency  are  ileum,  omen- 
turn,  jejunum,  sigmoid,  caecum,  and  transverse  colon.  More  rarely  the  ascending 
and  descending  colon,  the  bladder,  the  ovary,  and  the  various  abdominal  viscera,  with 
the  exception  of  the  liver,  have  been  found  among  the  contents  of  herniae. 

Inguinal  hernia,    by   far   the    most   frequent   of   all    the  varieties  of  hernia, 
(95—97  per  cent,  in  males,  55—60  per  cent,  in  females),  may  best  be  studied  anatom- 

FIG.  1484. 


Body 


Fundus 


Diagram  showing-  general  components  of  external 
abdominal  hernia. 


Anterior  superior  iliac  spine— 


•Aponeurosis  of  external  oblique 


Poupart's  ligament — 

Falciform  process — 
Iliac  portion  of  fascia  lata. 

Femoral  ring. 
Femoral  artery. 
Femoral  vein 


Internal  saphenous  vein 


-Intercolumnar  fibres 

External  abdominal  ring 
External  pillar 
Internal  pillar 

.Gimbernat's  ligament 


Pubic  portion  of  fascia  lata 
permatic  cord 


—Scrotum 


Dissection  of  right  inguinal  region,  showing  external  abdominal  ring  and  saphenous  opening  in  fascia  lata. 

ically  by  considering  its  mode  of  production  when,  (a)  as  a  direct  result  of  some 
developmental  defect,  it  is  present  at  or  soon  after  birth  ;  (£)  the  hernial  sac  being 
present  congenitally,  the  hernia  follows  some  increase  of  intra-abdominal  pressure  ; 
or,  (c)  as  a  consequence  of  a  less  marked — or  less  complete — original  defect  or  of 


1764 


HUMAN   ANATOMY. 


an  acquired  defect  (vide  supra),  the  hernia  develops  in  the  presence  of  causative 
factors  (page  1759). 

Acquaintance  with  the  changes  in  the  abdominal  wall  and  peritoneum  involved 
in  the  descent  of  the  testis  is  necessary  to  an  understanding  of  the  anatomy  of  inguinal 
hernia.  Although  these  changes  are  described  with  the  development  of  the  testicle 
(page  2040),  the  chief  features  of  the  process  may  be  noted  here  with  advantage. 

By  the  end  of  the  second  foetal  month  the  developing  testicle  lies  behind  the 
peritoneum  at  the  side  of  the  upper  lumbar  vertebrae,  the  epididymis  and  later  the 
testicle  being  attached  to  a  fibro-muscular  band,  the  genito-inguinal  ligament,  which 
stretches  from  the  sexual  gland  to  the  lower  part  of  the  anterior  abdominal  wall. 
During  the  third  month,  guided  by  this  attachment,  the  testicle  migrates  from  its 
primary  location  to  a  position  which  later  corresponds  to  the  internal  abdominal  ring. 
About  this  time  the  muscular,  fascial,  and  peritoneal  layers  of  the  abdominal  wall 
show  a  protrusion  in  the  inguinal  region  which  results  in  the  production  of  a  sac, 
the  inguinal  bursa ;  this  deepens  and  extends  into  the  scrotal  fold,  which  meanwhile 
is  formed  independently  as  an  integumentary  fold.  The  genito-inguinal  ligament, 

FIG.  1485. 


Internal  oblique- 


Cremaster  muscle 


Aponeurosis  of  external 
oblique,  turned  outward 


Saphenous  opening 


Cut  edge  of  aponeurosis  of 
external  oblique 

Sheath  of  rectus 

Transversalis  fascia 
Conjoined  tendon 
Triangular  fascia 


^Spermatic  cord 


Dissection  of  right  inguinal  canal ;  aponeurosis  of  external  oblique  has  been  cut  and  turned  outward. 

being  attached  to  the  structures  undergoing  evagination,  extends  into  the  inguinal 
bursa.  The  muscular  tissue  within  the  wall  of  the  latter  is  derived  from  the  internal 
oblique  and  transversalis  and  constitutes  the  en-master.  The  lining  of  the  inguinal 
bursa  is  obviously  the  direct  continuation  of  the  general  serous  membrane  of  the 
abdominal  cavity  and  later  constitutes  the  processes  vaginulis  pcritonei.  Thicken- 
ing of  the  lower  end  of  the  genito-inguinal  ligament  produces  an  elevation  of  tin- 
floor  of  the  bursa  known  as  the  inguinal  conns,  a  structure,  however,  that  in  man  is 
very  feebly  developed  as  compared  with  that  found  in  some  lower  animals.  Subse- 
quently,  during  the  seventh  and  eighth  months,  the  inguinal  conns  and  the  attached 
testicle  are  drawn  downward  into  and  through  the  inguinal  canal  until,  shortly  before 
birth,  the  sexual  gland  gains  its  permanent  position  in  the  scrotum.  The  rudimentary 
conns  and  the  genito-inguinal  ligament,  which  together  correspond  to  the  structure 
usually  described  as  the  guba-nacnlunt  /fs//'s,  become  progressively  shorter  and 
smaller  as  the  testicle  descends,  their  remains  constituting  the  scrotal  ligament,  the 
subserous  band  which  permanently  attaches  the  tunica  vaginalis  and  the  testicle  to 
the  surrounding  tissue  of  the  walls  of  the  scrotum. 

The  original  retroperitoncal  position  of  the  testicle  is  always  retained,  this  organ 
•.ind    the   accompanying   constituents  of   tin-  spermatic  cord  descending  outside  the 


PRACTICAL  CONSIDERATIONS  :    ABDOMINAL    HERNIA.       1765 


peritoneal  pouch  which  extends  into  the  scrotum.  For  a  time  free  communication 
with  the  abdominal  cavity  is  maintained  by  the  now  tubular  processus  vaginalis  ; 
usually,  however,  by  the  time  of  birth,  or  shortly  after,  this  canal  is  obliterated,  the 
isolated  lower  end  of  the  peritoneal  pouch  persisting  as  the  sac  of  the  tunica  vaginalis 
which  almost  surrounds  the  testicle.  The  peritoneal  evagination  occurs  in  both 
sexes,  in  the  female  extending  into  the  labium  majus  as  the  diverticulum  of  Nuck  ; 
this  usually  early  disappears,  but,  as  a  great  rarity,  may  remain  as  an  open  peritoneal 
process  at  the  time  of  puberty  (Merkel). 

If  obliteration  of  the  processus  vaginalis  does  not  occur,  a  congenital  hernial  sac 
results  (Fig.  1488  ),  and  this  may  become  a  hernia,  either  at  birth  or  in  later  life,  by 
the  descent  of  some  of  the  abdominal  viscera.  During  their  descent  the  testicle  and 
spermatic  cord  obtain  more  or  less  extensive  investments  of  such  parts  of  the  abdomi- 
nal walls  as  have  taken  part  in  the  formation  of  the  original  bursa  ingualis.  From 
within  outward  these  would  be,  therefore,  ( i )  peritoneum,  after  obliteration  of  the 
stalk  of  the  peritoneal  pouch,  however,  coextensive  with  only  the  tunica  vaginalis  ; 
(2)  infundibuliform  fascia  (tunica  vaginalis  communis),  continued  from  the  trans- 

FIG.  1486. 


Internal  oblique,  cut  and- 
turned  outward 

Transversalis  muscle- 


Aponeurosis  of  external  - 
oblique 


External  abdominal  ring 


Saphenous  openin, 


Aponeurosis  of  external  oblique, 
cut  edge 


Aponeurosis  of  internal 
oblique,  cut  edge 

Internal  abdominal  ring; 
—cord  covered  by  infundib- 
uliform fascia 
Transversalis  fascia  (weak  spot) 
— -Conjoined  tendon 

—Triangular  fascia 


Dissection  of  right  inguinal  canal;  external  and  internal  oblique  cut  and  reflected,  exposing  transversalis  muscle. 

versalis  fascia  ;  (3)  cremaster  fibres,  from  the  transversalis  and  internal  oblique  mus- 
cles, blended  by  areolar  tissue  into  the  cremasteric  fascia  ;  (4)  inter  columnar  fascia, 
from  the  aponeurosis  of  the  external  oblique.  In  addition  to  these  coverings  from 
the  abdominal  wall,  the  envelopes  forming  the  scrotum  proper  contribute  (5)  the 
modified  superficial  fascia  or  tunica  dartos  and  (6)  the  skin.  Unusual  attachments 
of  the  gubernaculum  below  to  the  tuber  ischii  and  sphincter  ani  account  for  some  of 
the  forms  of  testicular  ectopia  (q.v.).  Attachments  above  to  the  peritoneum  of  the 
caecum  or  ileum,  or  of  the  sigmoid,  or  to  the  loosely  attached  peritoneum  lining  the 
iliac  fossa,  account  in  part  for  the  formation  of  the  sac  in  infantile  hernia  (vide  infra}. 

The  strength  of  the  attachments  of  the  gubernacula  to  the  testes  and  to  the  dartos 
is  shown  by  the  fact  that  in  cases  of  elephantiasis  scroti,  although  the  enormously 
thickened  skin  and  dartos  may  form  a  tumor  reaching  to  the  knee,  the  testicles  will 
usually  be  found  near  its  lower  extremity. 

The  next  step  in  the  anatomical  study  of  inguinal  hernia  should  consist  in  a 
survey  of  the  inner  surface  of  the  abdominal  cavity  in  the  inguinal,  iliac,  and  hypo- 
gastric  regions  (Fig.  1487  ).  This  will  show  that  the  space  between  the  lateral  wall 
of  the  abdomen  and  the  mid-line — marked  by  the  peritoneal  fold  over  the  urachus 


1766 


HUMAN   ANATOMY. 


(plica  urachi) — is  divided  on  each  side  into  two  shallow  depressions  by  a  slight  eleva- 
tion of  the  peritoneum  over  the  deep  epigastric  artery  (plica  epigastrica}  running 
from  a  little  internal  to  the  middle  of  Poupart's  ligament  to  a  point  on  the  outer 
edge  of  the  rectus  muscle  about  one-third  the  distance  between  the  level  of  the 
symphysis  pubis  and  that  of  the  umbilicus.  The  outer  of  these  depressions  is  called 
the  external  inguinal  fossa  (hernial  fossa).  The  inner  contains  a  triangular  space 
known  as  Hesselbach's  triangle,  bounded  by  the  plica  epigastrica,  the  outer  edge 
of  the  rectus,  and  Poupart's  ligament.  The  whole  inner  region — extended  to  the 
mid-line — is  further  subdivided  by  a  line  corresponding  to  the  peritoneal  fold  over 
the  obliterated  hypogastric  artery  (plica  hypogastrica)  into  two  other  fossae,  the 
internal  inguinal  and  the  supravesical,  which  are  of  use  as  aids  to  the  description 
of  hernia,  but,  viewed  as  mechanical  factors,  have  little  bearing  on  its  production. 

The  external  inguinal  fossa  is  deepened  just  to  the  outer  side  of  the  epigastric 
artery  into  a  slight  pouch  (Fig.  1487),  which  marks  the  point  of  exit  of  the  sper- 
matic cord  from  the  abdomen,  and  therefore  the  site  of  the  internal  abdominal  ring 
and  of  the  mouth  of  one  form  of  inguinal  hernia, — the  external,  oblique,  or  indirect. 
On  the  external  surface  of  the  abdomen  this  pouch  corresponds  to  an  area  about  three- 
quarters  of  an  inch  in  circumference,  situated  a  finger' s-breadth  above  the  middle  of 
Poupart's  ligament.  To  the  inner  side  of  the  epigastric  artery  are  two  other  and 

FIG.  1487. 


Peritoneal  surface  - 


Plica  epigastrica 

Hesselbach's  triangle 

Vas  deferens 

External  iliac  artery 
External  iliac  vein 

Plica  hypogastrica 


Median  umbilical  ligament 

Posterior  surface  of  anterior  abdominal  wall  of  formalin  subject. 


Outer  edge  of  rectus 
muscle 


-Supravesical  fossa 

Outer  inguinal  fossa 
Inner  inguinal  fossa 


Bladder,  somewhat 
distended 


still  slighter  depressions  corresponding  approximately  in  position  to  the  outer  part 
of  the  posterior  wall  of  the  canal  and  to  the  external  abdominal  ring  (page  1771)  and 
the  lower  fifth  of  the  inguinal  canal.  When  viscera  make  their  way  outward 
from  either  of  these  depressions  as  the  point  of  departure,  the  resulting  hernia 
is  known  as  direct  because  it  does  not  pass  through  the  entire  length  of  the  inguinal 
canal,  but  takes  a  shorter  route,  or  internal  because  it  lies  to  the  inner  side  of  the 
epigastric  artery.  A  further  examination  of  the  structures  (already  described  on 
pages  523,  524)  which  are  related  to  the  production  of  inguinal  hernia  will  serve  to  ex- 
plain its  occurrence  in  certain  localities  and  in  certain  forms  that  may  now  be  considered 
separately  in  their  simpler  varieties,  the  rarer  and  more  complicated  being  merely 
mentioned  or  altogether  omitted  as  unessential  to  the  anatomical  study  of  hernia. 

Obliqiie,  external,  or  indirect  inguinal  henna,  which  makes  its  exit  from  the  abdo- 
men at  the  internal  ring,  is  incomplete  if  it  remains  in  the  inguinal  canal,  complete  if  it 
emerges  at  the  external  ring,  and  scrota/  if  it  descends  into  the  scrotum.  In  frequency 
it  bears  about  the  same  relation  to  the  other  form  of  inguinal  hernia — the  direct — as 
inguinal  hernire  do  to  all  other  forms  of  hernia  in  males, — viz.,  from  95-97  per  cent. 
This  frequency  depends  upon  the  following  anatomical  conditions.  (a)  The  descent 
of  the  testicle  from  behind  the  peritoneum  (page  2040),  carrying  with  it  a  process 
i  vaginal  >  of  peritoneum,  a  portion  of  the  transversalis  fascia  (infundibuliform  fascia), 


PRACTICAL  CONSIDERATIONS  :    ABDOMINAL    HERNIA.       1767 

and  of  the  transversalis  and  internal  oblique  muscles  (cremaster  muscle),  makes  its 
region  of  exit  from  the  abdomen — i.e.,  of  its  entrance  into  the  inguinal  canal — the 
area  in  the  abdominal  wall  best  adapted  by  reason  of  its  weakness  and  its  shape  to 
favor  the  exit  of  viscera.  (6)  This  spot  is  situated  near  the  lowest  level  of  the 
inferior  zone  of  that  cavity, — i.e.,  at  a  level  at  which,  when  the  size  of  the  cavity  is 
either  temporarily  decreased  (as  during  coughing  or  straining),  or  relatively 
decreased  (as  when  the  upper  zone  is  compressed  by  tight  lacing),*  or  actually 
decreased  (as  by  intra-abdominal  fat,  or  by  a  tumor  or  ascites),  the  outward  thrust 
of  the  abdominal  viscera  is  added  to  by  their  superincumbent  weight,  (c}  The  peri- 
toneum over  the  lower  part  of  the  anterior  abdominal  wall  is  thin  and  loosely  attached, 
so  that  it  .is  unable  to  offer  much  effective  resistance  to  distention  by  pressure  from 
within.  Such  distention  is  favored  by  the  funnel-shaped  depression  at  this  point, 
and,  having  once  begun,  its  influence  in  localizing  a  hernia  is  obvious,  (d)  The 
union  of  the  iliac  fascia  with  the  transversalis  fascia,  which  is  strongest  in  the  imme- 
diate vicinity  of  Poupart's  ligament,  presents  an  insuperable  obstacle  to  the  descent 
of  hernia  external  to  the  internal  ring,  (e)  The  conjoined  tendon  of  the  trans- 
versalis and  internal  oblique  muscles  inserted  into  the  crest  of  the  pubes  and  the  ilio- 
pectineal  line  is  strong  internally,  but  has  an  ill-defined  outer  edge  ;  while  that  por- 
tion of  the  tendon  which  is  derived  from  the  internal  oblique  has  generally  a  less 
extensive  attachment  than  that  from  the  transversalis  muscle,  so  that  the  space 
between  the  border  of  the  rectus  and  the  internal  ring  is  closed  by  the  two  tendons 
conjoined  at  the  innermost  part,  farther  outward  by  the  transversalis  tendon  alone, 
while  near  the  entry  of  the  cord  there  may  be  a  space  unprotected  by  tendon  or 
muscle  (Macready).  The  thinnest  and  least  protected  portion  of  the  inner — posterior 
— wall  of  the  canal  is  therefore  that  adjacent  to  the  inner  edge  of  the  internal  abdominal 
ring  (Ibid.).  It  should  be  noted  that  Treves  is  inclined  to  consider  the  resistant 
power  of  the  normal  abdominal  wall  as  less  over  Hesselbach's  triangle  than  over  the 
external  inguinal  fossa  ;  but  even  if  this  is  true,  the  existence  of  the  internal  ring  and 
of  the  canal  more  than  compensates  for  it  in  favoring  hernia. 

These  facts  sufficiently  explain  the  frequency  of  oblique  inguinal  hernia  of  the 
acquired  form  (vide  infra), — i.e. ,  the  form  in  which  the  congenital  deficiencies  or 
definite  pathological  changes  next  to  be  mentioned  are  not  demonstrable,  although 
it  is  not  unlikely  that  some  original  or  acquired  defect  of  the  abdominal  wall  in  the 
neighborhood  of  the  hernial  orifices  is  present  in  the  great  majority  of  cases  of  hernia 
of  this  as  of  all  varieties.  (/)  The  not  infrequent  total  or  partial  patency  of  the 
vaginal  process  gives  rise  to  a  number  of  subvarieties  of  inguinal  hernia  {congenital, 
infantile,  funicular},  all  of  which  are  oblique, — i.e.,  enter  the  inguinal  canal  at  the 
internal  ring  and  to  the  outer  side  of  the  epigastric  artery.  These  herniae,  depend- 
ing on  anomalies  in  the  closure  of  the  processus  vaginalis,  have  been  variously  sub- 
divided and  defined,  often  with  unnecessary  complexity.  It  will  suffice  here  to  say 
that  congenital  hernia  (Fig.  1488)  is  due  to  complete  patency  of  the  vaginal  process, 
the  cavity  of  which  is  directly  continuous  with  the  cavity  of  the  abdomen,  the  sac 
of  the  hernia  enclosing  both  its  visceral  contents  and  the  testicle,  which  lie  in  con- 
tact. Although  the  condition  leading  to  the  formation  of  this  hernia  is  truly  con- 
genital, the  hernia  itself  is  very  rarely  in  existence  at  the  time  of  birth,  but  is  apt  to 
occur  in  early  life  when  intra-abdominal  pressure  is  either  habitually  or  suddenly 
increased.  It  should  be  remembered  that,  although  a  true  congenital  hernia  neces- 
sarily depends  upon  a  patent  processus  vaginalis,  patency  of  the  process  may  exist 
without  hernia.  A  fold  of  peritoneum  at  the  edge  of  the  infundibuliform  fascia 
partly  screening  the  abdominal  opening  of  such  a  process  has  been  described  and 
has  been  thought  to  aid  in  preventing  hernia  (Macready).  In  women  patency  of 
the  canal  of  Nuck  acts  similarly  as  a  predisposing  cause  of  congenital  hernia,  which 
is,  however,  of  great  rarity,  on  account  of  the  narrowness  of  the  canal  itself,  the  fact 
that  its  internal  orifice  is  still  smaller,  and — supposedly — by  reason  of  the  relatively 
larger  size  and  greater  distinctness  in  the  female  than  in  the  male  of  the  peritoneal 
and  fascial  fold  covering  the  entrance  to  the  canal. 

Infantile  hernia  (Fig.  1489)  results  from  occlusion  of  the  processus  vaginalis  at 
the  internal  ring  only,  the  visceral  pressure,  aided  by  the  attachments  of  the  guber- 
naculum  testis  above  described,  carrying  this  septum  and  the  neighboring  perito- 


1768 


HUMAN   ANATOMY. 


neum  downward  to  constitute  a  sac  that  descends  behind  the  tunica  vaginalis, 
especially  if  the  latter  is  capacious,  as  it  is  apt  to  be  when  its  upper  limit  is  at  the  in- 
ternal ring.  A  hernia  of  this  variety  has,  therefore,  between  the  skin  and  the  con- 
tents three  layers  of  serous  membrane,  two  of  the  tunica  vaginalis  and  one  of  peri- 
toneum (its  own  sac)  connected  with  one  another  at  the  neck.  Not  uncommonly, 
however, — as  might  be  expected  from  the  tendency  of  serous  membranes  to  adhesive 


FIG.  1488. 


FIG.   1489. 


Peritoneum 
Spermatic  cord 
in  and  fascia 


Peritoneum 
Spermatic  cord 
Skin  and  fascia 


Diagram  of  congenital  hernia,  showing  relation  of 
hernial  sac  to  peritoneum. 


Hernial  sac 


Tunica  vagina 


Diagram  of  infantile  hernia,  showing  relation  of 
hernial  sac  to  tunica  vaginalis. 


inflammation, — the  posterior  layer  of  the  tunica  vaginalis  is  intimately  blended  with 
the  front  wall  of  the  sac.  Infantile  hernia,  while  due,  like  the  congenital  variety,  to 
anomaly  in  development,  is  even  less  apt  to  exist  at  birth  and,  in  fact,  is  rarely  seen 
in  infancy.  A  variety  of  infantile  hernia  known  as  the  encysted  (Fig.  1490)  is  de- 
scribed, in  which  the  intestine  depresses  the  septum  at  the  internal  ring,  making  a 
sac  which  passes  into  instead  of  behind  the  processus  vaginalis,  so  that  the  hernia 
has  in  front  of  it  a  layer  of  tunica  vaginajis  and  a  layer  of  septum  (sac).  This 
hernia  is  very  properly  described  (Lockwood,  Macready)  as  "a  figment  of  the 
imagination."  When,  after  occlusion  of  the  process  at  the  internal  ring  only,  the 
septum  gives  way  suddenly  during  some  unusual  intra-abdominal  pressure,  the  intes- 
tine may  descend  at  once  into  instead  of  behind  the  tunica  vaginalis  and  lie  in  con- 
tact with  the  testicle, — a  form  of  "  congenital"  hernia  that  appears  in  adult  life. 


FIG.  1491. 


Peritoneum 
Spermatic  cord 
'.  Skin  and  fascia 


Peritoneum 
^_    Spermatic  cord 
—  Skin  and  fascia 


Hernial  sac 


Tunica  vagina 


Diagram  of  so-called  encysted  hernia,  showing  sup- 
posed relation  of  hernial  sac  tn  pel  itoneimi. 


Diagram  of  funicular  lu-inia.  showing  relation  of 
hernial  sac-  to  tunica  \;tgin:ilis. 


Funicular  hernia  (  Fig.  1491")  is  a  sequence  of  the  closure  of  tin-  vaginal  process 
at  the  upper  end  of  the  epididymis  only,  the  short  pouch  of  peritoneum  remaining 
in  communication  with  the  peritoneal  cavity.  Tin-  contents  of  such  a  hernia  are 
separated  from  the  testicle  by  the  septum  formed  at  the-  point  of  closure. 

Inlcrf>arictal  (  intraparietal,  interstitial  i  hernia  is  so  usually  a  variety  of  oblique 
inguinal  hernia,  and  is  so  commonly  associated  in  the  male  with  anomalies  of  the 


PRACTICAL  CONSIDERATIONS  :   ABDOMINAL   HERNIA.       1769 

testis,  that  it  may  be  described  here.  It  derives  its  name  from  the  protrusion  from 
the  sac  of  an  inguinal  hernia  (usually  of  the  incomplete  variety)  of  a  pouch  or 
diverticulum  which  insinuates  itself  into  or  between  the  separate  layers  of  the  ab- 
dominal wall,  as  (a)  between  the  peritoneum  and  transversalis  fascia  ( properitoneal 
hernia)  ;  (6)  between  that  fascia  and  the  transversalis  muscle,  or  among  the  fibres 
of  the  internal  oblique,  or  between  the  internal  and  external  oblique  muscles,  or 
sometimes — the  transversalis  and  internal  oblique  having  been  pushed  aside,  a's  in  the 
descent  of  an  ordinary  acquired  inguinal  hernia  (vide  infra) — between  the  transver- 
salis fascia  and  the  external  oblique  muscle  or  aponeurosis  (interstitial  hernia)  ;  (c) 
between  the  external  oblique  aponeurosis  and  the  skin  {superficial  inguinal  hernia) 
(Sultan). 

While  the  exact  mechanism  of  the  formation  of  these  herniae  is  still  unknown, 
and  the  various  conflicting  theories — although  of  great  anatomical  interest — cannot 
here  be  set  forth,  it  is  perhaps  safe  to  say  that  the  following  facts  have  a  direct  bear- 
ing upon  the  question  :  (a)  a  hernia,  like  other  swellings,  enlarges  in  the  direction 
of  least  resistance  ;  (b)  the  preponderance  of  the  association  of  these  interparietal 
herniae  with  incomplete  inguinal  herniae  and  with  retained  testis,  in  neither  of  which 
cases  have  the  external  ring  and  the  scrotum  undergone  dilatation,  may  be  due  to  a 
lesser  resistance  in  the  course  of  the  diverticulum  than  at  the  external  ring  ;  (c)  they 
are  also  often  associated  with  imperfections  of  the  abdominal  wall,  correlated  with 
the  anomalies  of  the  testicle,  because,  as  Macready  says,  when  that  organ  is  defective 
it  is  very  probable  that  the  parts  through  which  it  passes  and  with  which  it  is  so  in- 
timately associated  will  likewise  be  deficient. 

The  mechanism  of  formation  of  the  so-called  acqtiired  oblique  inguinal  hernia — 
the  most  frequent  and  therefore  the  most  important  of  all  forms  of  hernia — will  now 
readily  be  understood.  Because  of  the  anatomical  conditions  above  enumerated 
(page  1763),  and  in  the  presence  of  one  or  more  of  the  etiological  factors,  the  peri- 
toneum covering  the  internal  ring  yields  to  the  pressure  of  the  viscera  (usually  a 
portion  of  the  small  intestine)  and,  together  with  the  latter,  passes  through  the  in- 
ternal ring  above  the  cord,  the  component  structures  of  which,  with  the  artery  to  the 
vas  deferens,  the  cremasteric  artery,  the  genital  branch  of  the  genito-crural  nerve, 
and  the  inguinal  branch  of  the  ilio-inguinal  nerve,  are  close  to  the  lower  margin 
of  the  ring.  After  entering  the  canal  it  meets  with  less  resistance,  and,  aided  by 
gravity  and  sometimes  by  prolapse  of  the  mesentery, — a  loosening  or  slipping  down 
of  its  vertebral  attachment, — which  slightly  increases  the  weight  of  the  intestines 
that  must  be  borne  by  the  abdominal  wall,  descends  until  it  reaches  a  point  at  which 
the  resistance  is  greater  than  the  forces  that  are  carrying  it  downward.  Its  descent 
has  been  thought  to  be  aided  by  the  weight  of  masses  of  fat  (subserous  lipomata) 
sometimes  found  in  the  extraperitoneal  connective  tissue  that  precedes  the  sac  and 
forms  one  of  the  coverings  of  nearly  all  abdominal  herniae,  but  this  is  more  than 
doubtful.  The  most  frequent  point  of  arrest  is  at  the  lower  part  of  the  canal,  where 
the  rigid,  non-elastic  pillars  of  the  external  ring,  strengthened  by  the  intercolumnar 
fibres,  often  closely  embrace  the  cord,  and  where  the  course  of  the  hernia  changes 
slightly  in  direction.  Until  it  emerges  from  the  external  ring  it  is  known  as  an  in- 
complete hernia  (bubonocele).  It  is  obvious  that,  with  the  exception  of  a  few  con- 
genital herniae,  every  inguinal  hernia  must  at  some  time  have  been  incomplete.  After 
emerging  from  the  external  ring  it  is  known  as  a  complete  hernia  and  usually  enters 
the  scrotum.  It  then  meets  with  but  little  resistance  until  it  reaches  the  level  of  the 
upper  end  of  the  testicle,  where  it  may  be  again  arrested — often  permanently — by 
the  close  connection  of  the  coverings  of  the  cord  to  the  tunica  vaginalis,  or  it  may 
descend  quite  to  the  bottom  of  the  scrotum  (scrotal  hernia).  It  lies  throughout  its 
course  in  front  of  the  spermatic  cord. 

In  females  the  corresponding  hernia  follows  the  round  ligament  through  the 
inguinal  canal  and  appears  in  the  labium  majus  (labial  hernia). 

As  the  peritoneal  sac  and  its  contents  follow  this  course  from  the  abdominal 
cavity  downward,  they  are  covered  by  various  structures  that  represent  portions  of 
the  different  layers  of  the  abdominal  wall,  modified  in  character,  however,  at  the  time 
of  the  descent  of  the  testis  and  designated  by  new  names.  The  clinical  importance 
of  this  list  of  "coverings"  has  been  greatly  exaggerated,  but  they  have  a  certain 


1770 


HUMAN   ANATOMY. 


Peritoneum  and  suhserous  t  issue 
Infundibuliform  (transversalis  fascia) 
Internal  oblique 

External  oblique  (intercolumnar  fascia) 
Superficial  fascia  and  skin 


Deep  epigastric, 
artery 


usefulness  as  denoting  the  route  of  the  hernia,  and  are  occasionally  of  value  as  land- 
marks during  herniotomies  or  operations  for  the  radical  cure  of  hernia. 

The  sac  of  a  complete  oblique  inguinal  hernia  (Fig.  1492)  would  carry  with  it 
(i)  a  layer  of  extraperitoneal  connective  tissue  ;  (2)  that  portion  of  the  transversalis 
fascia  known  as  the  inf undibul if orm  fascia  ;  (3)  the  muscular  fibres  derived  from  the 
transversalis  and  internal  oblique  muscles,  and  called  the  cremaster  -muscle ;  (4)  the 
fibres  from  the  external  oblique  aponeurosis  that  aid  in  strengthening  the  external 
"ring,"  especially  the  upper  angle, — the  intercolumnar  fascia  ;  (5)  the  siiperficial 
fascia, — in  the  scrotum  the  dartos  layer  ;  (6)  the  skin. 

The  coverings  of  an  incomplete  oblique  inguinal  hernia  will  obviously  depend 
upon  the  point  of  its  arrest,  but  such  a  hernia  cannot  be  covered  by  either  inter- 
columnar fascia  or  dartos. 

The  sac  of  a  complete  oblique  inguinal  hernia,  if  followed  from  within  outward, 
would  show  first  a  puckered  or  pleated  appearance  at  the  mouth,  due  to  the  folds  of 

peritoneum     produced    by 

FIG.  1492.  constriction  ;  next  a  portion 

narrow  and  elongated  by 
the  pressure  of  the  walls 
of  the  canal, — the  neck, — 
which  in  such  a  hernia 
would  extend  from  the  in- 
ternal to  the  external  ring  ; 
and  finally  a  portion — the 
fundus  or  body — which,  re- 
lieved from  pressure,  is  usu- 
ally irregularly  ovoidal  in 
shape. 

The  anatomical  points 
at  which  strangulation  is 
likely  to  occur  are,  in  the 
order  of  frequency,  ( i )  the 
edge  of  the  internal  ring, 
(2)  the  edge  of  the  exter- 
nal ring,  and  (3)  in  the 
canal  (from  fibres  of  the 

transversalis  or  internal  oblique),  but  the  constriction  of  the  contents  is  not  infre- 
quently due  to  pathological  changes  in  the  neck  of  the  sac  itself.  In  operating  to 
relieve  constriction  at  the  internal  ring,  the  relation  of  the  epigastric  artery  should 
be  remembered.  The  incision  should  be  directly  upward. 

Taxis. — In  reducing — i.e. ,  returning  to  the  abdominal  cavity — an  oblique  in- 
guinal hernia,  the  shoulders  and  thorax  should  be  raised  to  relax  the  abdominal 
muscles  ;  the  thigh  flexed  and  adducted  to  relax  the  fascia  lata  and  external  oblique 
aponeurosis,  and  thus  the  margins  of  the  external  ring  and  the  anterior  wall — the  most 
unyielding — of  the  inguinal  canal  ;  and  the  pelvis  elevated  so  as  to  secure  by  the  aid 
of  gravity  a  backward  or  upward  pull  on  the  contents  of  the  hernia.  After  gentle 
downward  traction  in  the  line  of  the  canal  so  as  to  remove  folds  and  lessen  lateral 
bulging  of  the  sac  and  contents  over  the  pillars  of  the  external  ring,  and  while 
making  pressure  with  the  thurhb  and  fingers  of  one  hand  at  that  point  to  prevent  its 
recurrence,  the  other  hand  encircles  the  fundus  of  the  sac  and  with  as  evenly  dis- 
tributed force  as  possible  makes  pressure  at  first  upward,  then  upward  and  outward, — 
in  the  line  of  the  canal, — and  finally  backward. 

Direct  or  internal  inguinal  hernia  occurs  in  only  3—5  per  cent,  of  cases.  The 
reasons  for  its  relative  infrequency  have  been  given.  To  understand  it,  the  region 
internal  to  the  deep  epigastric  artery  should  1><  examined  (  Fig.  1487).  It  has  been 
mentioned  that  this  region  has  been  subdivided  by  a  fold  corresponding  to  the  plica 
hypogastrica  into  a  supravesical  and  an  internal  inguinal  fossa  (  Fig.  1487).  At  the 
inner  angle  of  the  former  we  find  the  abdominal  wall  strengthened  ( a)  by  the 
presence  of  the  rectus  muscle,  which  extends  outward  as  far  as  the  pubic  crest  ;  (6) 
by  Colics' s  ligament  {triangi</ar  ligament,  ligatncntunt  inguinalc  }r/l<:\'n»i),  consist- 


Diagram  showing  coverings  of  complete  left  indirect  inguinal  hernia. 


PRACTICAL   CONSIDERATIONS:    ABDOMINAL    HERNIA.      1771 


ing  of  the  inner  deeper  fibres  of  Poupart's  ligament,  which  turn  upward  and  inward 
from  the  crest  of  the  pubes  in  front  of  the  insertion  of  the  conjoined  tendon  and  pass 
behind  the  internal  pillar  of  the  external  ring  to  be  inserted  into  the  anterior  sheath 
of  the  rectus  and  into  the  linea  alba  (Fig.  1486);  these  fibres  protect  the  inner  and 
posterior  wall  of  the  canal  in  the  angle  between  the  pubes  and  the  rectus  muscle,  and 
as  far  outward  as  corresponds  to  the  inner  third  of  the  external  ring  in  males  and  the 
inner  half  in  females  (Malgaigne,  quoted  by  Macready)  ;  (V)  by  the  conjoined  tendon, 
which  becomes  thinner  and  weaker  as  it  leaves  the  mid-line. 

It  will  be  seen,  therefore,  that  there  is  a  space  between  the  outer  edge  of  the 
rectus  and  the  epigastric  artery  in  which  the  abdominal  wall  is  very  thin,  contains  no 
muscular  layer,  and  is  weakened  anteriorly  by  the  gap  in  the  external  oblique  apo- 
neurosis  at  the  external  ring,  especially  at  its  upper  and  outer  angle,  the  posterior 
wall  of  the  canal  at  this  point  not  being  reinforced  by  the  presence  of  the  conjoined 
tendon  or  Colics' s  ligament  (Fig.  1485).  This  "thin  spot,"  lying  thus  partly  behind 
the  external  ring,  is  bounded  internally  by  some  aponeurotic  fibres  of  the  trans- 
versalis  muscle  running  from  the  upper  surface  of  the  pubes  to  the  rectus  (falx  apo- 
ne^^,rotica  inguinalis}  and  externally  by  similar  fibres  running  down  from  the  same 
muscle,  encircling  the  inner  border  of  the  internal  ring  and  fusing  with  the  inner 
surface  of  Poupart's  ligament  (ligamentum  interfoveolare)  (Fig.  1493).  When 
these  two  structures  are  broad  the  thin  spot  is  narrow,  and  vice  versa  (Spalteholz). 

FIG.  1493- 


Rectus 


Deep  epigastric  artery 

Interfoveolar  or 
Hesselbach's  ligament 

Weak  an 
Conjoined  tendo: 
Muscular  fibres 
Lower  end  of  Poupart's  ligament 

Urachus 
Bladder 


Poupart's  ligament 
.Transversalis  muscle 
Spermatic  vessels 
External  iliac  artery 
External  iliac  vein 

Deep  epigastric  artery  (cut) 
.Vas  deferens 


oral  ring 
lat's  ligament 


Dissection  of  posterior  surface  of  anterior  abdominal  wall,  showing  relations  of  conjoined  tendon  and  its  expansions 

to  internal  abdominal  ring. 

It  is  perhaps  intrinsically  weaker  than  any  portion  of  the  external  hernial  fossa 
(Treves),  but  the  infundibuliform  depression  at  the  entrance  to  the  inguinal  canal, 
the  presence  of  the  canal  itself,  and  the  many  anomalies  associated  with  the  descent 
of  the  testis  far  outweigh  this  weakness  as  factors  in  the  production  of  hernia. 

A  direct  inguinal  hernia  may  escape  through  (a)  the  inner  inguinal  fossa,  be- 
tween the  plica  epigastrica  and  the  plica  hypogastrica,  which  corresponds  in  situation 
to  the  outer  part  of  the  posterior  wall  of  the  inguinal  canal, — i.e.,  to  that  part  formed 
by  the  transversalis  fascia  ;  it  would  go  around  the  outer  edge  of  the  conjoined 
tendon,  enter  the  inguinal  canal  a  little  below  the  internal  ring,  and  have  the  same 
coverings  as  the  oblique  hernia,  except  that  the  general  transversalis  fascia  would  re- 
place the  infundibuliform  fascia  ;  or  ($)  the  outer  part  of  the  supra vesical  fossa, 
between  the  plica  hypogastrica  and  the  plica  urachi, — the  outer  and  deepest  part  of 
which  corresponds  to  the  external  ring, — in  which  case  it  might  either  also  go  around 
the  outer  edge  of  the  conjoined  tendon  and  triangular  ligament,  or,  if  those  struc- 
tures are  thin  and  poorly  developed,  might  carry  them  with  it,  so  that  its  coverings 
would  be  (i)  extraperitoneal  connective  tissue,  (2)  transversalis  fascia,  (3)  con- 
joined tendon,  (4)  Colics' s  ligament,  (5)  intercolumnar  fascia,  (6)  superficial  fascia, 
(7)  skin.  The  spermatic  cord  usually  lies  on  the  outer  side  of  the  sac.  As  many 
such  herniae  practically  issue  through  the  lowest  part  of  the  linea  semilunaris,  it  has 
been  proposed  to  call  them  ventro-inguinal  hernia:.  They  have  no  such  essential 


1772 


HUMAN    ANATOMY. 


relation  to  the  inguinal  canal  as  have  oblique  herniae,  although  when  the  peritoneal 
pouch  first  forms,  and  before  the  resistance  of  the  aponeurosis  at  the  external  ring 
has  been  overcome,  they  usually  enter  the  lower  part  of  the  canal,  as  the  resistance 
that  direction  is  less  than  it  is  inward,  towards  the  rectus.  They  are  never  con- 


in 


FIG. 


1494- 


Peritoneum 
Transversalis  fascia 

Conjoined  tendon  (and  Colles's  ligament* 

Intercolumnar  fascia 

Fascia  and  skin 


Diagram  showing  coverings  of  complete  direct  inguinal  hernia 


genital  and  have  no  definite  pre- 
existing path.  They  are  there- 
fore herniae  of  slow  development, 
usually  seen  in  adult  life,  especially 
if  the  local  weakness  of  the  ab- 
dominal wall  is  emphasized  by 
its  laxity  from  general  muscular 
atrophy,  or  by  increased  intra- 
abdominal  pressure  from  accu- 
mulation of  fat.  They  are  usually 
small,  globular  in  shape  (by  rea- 
son of  the  shortness  of  the  neck), 
do  not,  as  a  rule,  descend  into  the  scrotum,  but  remain  above  the  crest  of  the 
pubes,  and  when  reduced  go  directly  backward  into  the  abdomen.  The  orifice  in 
the  abdominal  wall  is  easily  felt,  the  outer  edge  of  the  rectus  to  its  inner  side,  the 
crest  of  the  pubes  below.  The  epigastric  artery  is  to  the  outer  side  of  this  aperture, 
but  its  pulsation  can  rarely,  if  ever,  be  felt.  Macready  says  :  the  opening  in  the 
posterior  wall  of  the  inguinal  canal  through  which  a  direct  hernia  comes  is  much  more 
accessible  to  examination  in  the  living  than  the  internal  abdominal  ring,  so  that  it  is 
quite  possible,  in  the  majority  of  cases,  to  explore  the  conjoined  tendon  with  the 
finger  and  ascertain  the  shape  and  size  of  the  opening  as  well  as  the  extent  to  which 
the  posterior  wall  has  suffered.  When  a  hernia  is  oblique,  the  posterior  wall  of  the 
canal  is  felt  as  a  plane  surface  by  the  finger  passed  into  the  external  ring,  and  its 
attachment  along  the  pubes  can  be  traced.  The  finger  is  prevented  from  entering 
the  abdomen  till  it  reaches  the  internal  ring.  But  in  direct  hernia,  when  fully  devel- 
oped, the  finger  at  once  passes  into  the  belly  over  the  bare  pubes,  and  can  feel  the 
back  of  that  bone  and  of  the  rectus  muscle.  No  trace  of  the  posterior  wall  of  the 
canal  is  felt  nor  the  margin  of  an  opening  in  it.  All  that  remains  is  a  narrow  layer 
of  membrane  which  just  fills  the  angle  between  the  pubes  and  the  rectus  ;  it  seems 
as  if  the  triangular  ligament  had  alone  withstood  the  distending  force  of  the  hernia.  In 

these  cases,  in  which  the'pro- 


FIG.  1495. 


ica  hypogastrica 


lica  epigastrica 
Oblique  inguinal  hernia 

i  \l<  1  i:;il  lossa) 

inguinal  hernia 
rual 
oral  hernia 


Plica  urachi  Supravesical  fossa 


SemidiagmmtlMtic  \ir\v  m   posti-iim-  surface  of  anterior  abdominal  wall, 
•bowing  relative  positions  of  vaiious  forms  of  herniae.     (After  Mrrkfl.) 


trusion  has  done  its  worst, 
all  the  posterior  wall  of  the 
canal  between  the  rectus  and 
epigastric  artery  has  gone, 
and  the  large  opening  has  a 
triangular  figure  coinciding 
with  the  triangle  of  Hessel- 
bach. 

If  strangulation  occurs, 
it  is  apt  to  be  at  the  exter- 
nal ring,  and  the  incision 
for  relief  of  the  constriction 
should  be  upward  with  a 
slight  inclination  inward. 

Large  oblique  herniae 
(scrota!  \,  especially  when  of 
long  standing  and  in  old 
persons  with  relaxed  abdom- 
inal walls,  may  have  the  in- 


ternal  ring  displaced  so  far  towards  tin-  median  line  by  the  weight  of  tin-  hernia  that 
it  occupies  almost    exactly  tile  usual   site  of  exit  of  a  direct   hernia.      The  epigastric 
artery  will,  of  course,  still  lie  to  its  inner  side,  but  cannot  be  felt.      As  a  rule,  how 
ever,  a  sufficient  portion  of  the  posterior  wall  of  the  inguinal  canal  will  be  left  to  pre- 
serve some  obliquity  of  the  neck  (Macready),  by  which  the  hernia  may  be  recogni/ed. 


PRACTICAL   CONSIDERATIONS  :    ABDOMINAL  HERNIA.       1773 


FIG.   1496. 


Iliac  crest 


Anterior, 
superior  iliac 
spine 

Muscular  space. 


Femoral  hernia  is  more  common  in  females  than  in  males  for  reasons  already 
given  (page  1762).  It  is  always  acquired,  as  the  femoral  "canal"  is  even  less  an 
actual  passage  than  is  the  inguinal  canal.  Its  upper  orifice  (the  femoral  or  crural  ring  ) 
(Fig.  1493)  is  the  weakest  spot  in  that  portion  of  the  abdominal  parietes  represented 
by  the  inner  surface  of  the  inguino-femoral  region.  The  firm  union  of  the  trans- 
versalis  and  iliac  fasciae  to  the  outer  half  of  Poupart's  ligament  and  the  presence  of 
the  ilio-psoas  muscle  enclosed  in  its  osseo-fascial  space  {lacuna  musculorum]  by  the 
ilium  and  the  iliac  fascia  offer  practically  insuperable  obstacles  to  the  descent  of 
abdominal  contents  beneath  Poupart's  ligament  external  to  the  femoral  vessels  (Fig. 
1496).  Only  a  very  few  such  cases  have  been  reported.  At  the  extreme  inner  angle 
of  the  ilio-pubic  space,  bridged  over  by  Poupart's  ligament,  the  pectineus  muscle, 
covered  by  the  pectineal  fascia  and  Gimbernat's  ligament,  offers  a  similar  resistance. 
Between  these  two  muscular  compartments,  however,  lies  the  space  occupied  by  the 
great  vessels  of  the  lower  extremity  in  their  passage  between  their  retroperitoneal 
position  in  the  abdomen  and  the  thigh.  This  space — the  vascular  compartment 
{lacuna  vasorum} — is  only  partially  occupied  by  the  vessels.  Their  sheath  is  made 
up  by  the  lateral  union,  externally  and  internally,  of  the  transversalis  fascia  anteriorly 
and  the  iliac  fascia  pos- 
teriorly. This  sheath 
does  not  embrace  the 
vessels  closely  until  it 
descends  from  one-half 
to  three-quarters  of  an 
inch  below  the  rela- 
tively unyielding  Pou- 
part's ligament,  about 
opposite  the  upper 
margin  of  the  saphe- 
nous  opening,  — i.  e. , 
to  a  point  at  which,  in 
the  movements  of  flex- 
ion and  extension  of  the 
thigh  on  the  abdomen, 
the  vessels  are  less  lia- 
ble to  injurious  traction 
or  compression.  It  is 
therefore  infundibuli- 
form,  and  at  its  begin- 
ning there  is  a  space — 
the  femoral  ring  (annulus  femoralis} — between  the  innermost  side  of  the  femoral 
vein,  covered  by  a  layer  of  fibrous  tissue  connecting  the  anterior  and  posterior  walls 
of  the  sheath,  and  the  outer  curved  margin  of  Gimbernat's  ligament  (Fig.  1496). 
This  space  varies  in  size  with  the  degree  of  development  of  the  latter  structure,  which, 
as  has  been  said,  is  broader  and  stronger  in  males  than  in  females,  and  with  the  size 
of  the  pectineus  and  ilio-psoas  muscles.  Its  internal  aspect  and  relations  are  shown 
in  Fig.  1493.  The  ring  is  on  an  average  from  12-15  mm-  (/^~f  m- )  m  width  in  men 
and  from  18-25  mm.  (fy-i  in.)  wide  in  women.  The  femoral  canal  leading  down 
from  it  is  occupied  by  loose,  fatty  areolar  tissue  and  some  lympathic  vessels.  The  ring 
itself,  as  seen  from  within,  presents  on  its  surface,  covered  by  peritoneum,  a  very 
slight  depression.  Beneath  the  peritoneum  at  this  point  the  extraperitoneal  tissue  is 
exceptionally  abundant  and  is  frequently  the  site  of  subserous  lipomata  which  have 
been  thought  (Roser)  by  their  traction  to  cause  the  peritoneal  depression  just  spoken 
of,  and  even  to  account  for  the  development  of  hernia.  The  septum  crurale  ( sept  ion 
femoralc) — variously  described  as  a  condensation  of  the  subserous  tissue  and  as  a 
portion  of  the  transversalis  fascia — fills  in  the  ring  and  is  perforated  by  a  number  of 
lymphatic  vessels  passing  from  the  inguinal  to  the  pelvic  nodes.  A  small  lymph-node 
not  infrequently  lies  on  the  septum  beneath  the  peritoneum. 

The  boundaries  of  the  ring  should  be  carefully  studied  in  their  relation  to  the 
neck  of  a  femoral  hernia.      On  the  inner  side  is  Gimbernat's  ligament,  which  in  child- 


Poupart's 
ligament 


Iliac  fascia 


Pectineal  fascia 


Gimbernat's  ligament 
Deep  dissection  of  right  half  of  pelvis,  showing  attachments  of  iliac  fascia. 


HUMAN   ANATOMY. 

hood  is  relatively  undeveloped  ;  its  outer  edge  and  the  vein  may  then  almost  touch. 
It  is  strengthened  by  the  conjoined  tendon  and  Colics' s  ligament,  while  some  fibres 
of  the  iliac  portion  of  the  fascia  lata  and  of  the  deep  femoral  arch  (vide  infra) 
also  contribute  to  the  formation  of  the  inner  boundary.  On  the  outer  side  is  the 
femoral  vein.  Behind  lies  the  horizontal  ramus  of  the  pubes  covered  by  the  origin 
of  the  pectineus  muscle  and  its  fascia.  In  front  are  Poupart's  ligament  and  the 
strong  band  of  fibres  running  along  its  deep  surface  from  the  anterior  superior  iliac 
spine  to  the  pubic  spine,  and  known  as  the  deep  femoral  arch.  At  the  point  at  which 
the  sheath  of  the  vessels  closely  embraces  them — the  lowest  limit  of  the  femoral  canal 
— the  saphenous  opening  in  the  fascia  lata  (described  on  page  635)  has  somewhat 
the  same  relation  to  a  femoral  hernia  that  the  external  abdominal  ring  has  to  an  in- 
guinal hernia.  After  emerging  from  these  openings  neither  hernia  is  further  arrested 
in  its  progress  by  any  strong  aponeurotic  barrier,  and  they  are  both  therefore  more 

likely  to  increase  in  size  ;  but  in  femoral  hernia 

FIG.  1407.  the  change  in  direction  of  the  axis  of  the  fundus 

as  compared  with  that  of  the  neck  is  much 
more  marked. 

In  its  etiology  femoral  hernia  conforms 
to  the  general  laws  already  enumerated  (page 
1759).  As  the  knuckle  of  gut  involved  presses 
the  peritoneum  before  it  into  the  femoral  ring 
and  down  through  the  femoral  canal,  it  car- 
ries before  it  (i)  the  extrapcritoneal  tissue ; 

Femoral  artery  ,    ~ 

(2)  the  septum  crurale.  when  that  constitutes 

Femoral  vein  v    /     .          f 

a  distinct  layer  ;  (3)  \hefemoral  sheath,  some- 
times described  as  transversalis  fascia  because 

Hermal  sac  pro-        ,  .,  ,,         ,          i-j-jr 

truding  through     the  anterior  layer  of  the  sheath  is  derived  irom 
saphenous  open-     ^^   structure  .    (4)    tne   cribriform  fascia  ; 

(5)  the  superficial  fascia  ;   (6)  the  skin. 

As  the  transverse  axis  of  the  femoral  ring 
—parallel  with  that  of  Gimbernat's  ligament 
— is,  in  the  erect  posture,  nearly  horizontal,  a 

Superficial  dissection  of  left  femoral  hernia  pro-      ,  ,    ,  •       /-  j  j         i 

truding  through  saphenous  opening.  femoral  hernia  first  descends  almost  perpen- 

dicularly. After  it  reaches  the  point  of  close 

adhesion  of  the  sheath  to  the  femoral  vessels  it  takes  the  direction  of  least  resistance 
and  protrudes  through  the  saphenous  opening.  Its  neck  is,  of  course,  the  portion  of 
the  sac  between  the  femoral  ring  and  the  bottom  of  the  femoral  canal.  The  body  is 
apt  to  be  small  and  globular  or  hemispherical  in  shape. 

The  following  anatomical  relations  of  the  latter  will  be  found  of  great  importance 
in  distinguishing  between  femoral  and  incomplete  inguinal  hernia.  (#)  The  upper 
edge  of  a  femoral  hernia  does  not,  as  a  rule,  pass  above  the  inguinal  furrow  ( page 
670),  although  it  may  reach  it, — i.e.,  the  hernia  will  be  below  a  line  drawn  from  the 
anterior  superior  spine  of  the  ilium  to  the  spine  of  the  pubes.  This  may  usually  be 
determined  by  inspection.  Exceptionally,  on  account  of  the  stronger  attachment  of 
the  cribriform  fascia  to  the  lower  edge  of  the  saphenotis  opening,  the  hernia  finds  its 
direction  of  least  resistance  after  emergence  from  that  opening  to  be  upward,  when 
this  sign  will  be  fallacious.  (6)  The  neck  of  a  femoral  hernia  is  external  to  the  pubic 
spine,  that  of  an  inguinal  hernia  internal  to  it.  The  already  described  methods  for 
locating  that  process  (page  349)  may  fail  in  very  fat  persons,  especially  in  females. 
In  that  case  the  lower  crease  that  in  such  persons  crosses  the  abdomen  (page  551), 
and  which  in  the  mid-line  rests  upon  the  symphysis  pubis,  will  be  a  reliable  guide  to 
the  latter  point  ;  the  bone  may  thence  be  traced  outward  to  the  pubic  spine. 

In  the  reduction  of  a  femoral  hernia — apt  to  be  difficult  on  account  of  the  nar- 
rowness of  the  channel  of  exit — the  position  of  the  patient  should  be  that  already 
described  as  appropriate  when  the  hernia  is  inguinal.  The  thigh  should  be  in  a  posi- 
tion of  inward  rotation,  llexion,  ami  adduction,  to  relax  the  fascia  lata  and  relieve  ten- 
sion about  the  saphenous  opening.  After  the  hernia — the  axis  of  the  body  of  which 
is  nearly  at  right  angles  with  the  axis  of  the  neck — is  drawn  downward  so  that  the 
axes  correspond,  it  is  gradually  pushed  backward  and  then  upward. 


PRACTICAL   CONSIDERATIONS:    ABDOMINAL  HERNIA.      i?75 


It  should  be  noted  that  in  this  form  of  hernia  the  density  of  the  aponeuroses 
that  bound  the  femoral  ring  and  the  upper  edge  of  the  saphenous  opening  adds  to  the 
evil  effects  of  constriction  of  the  hernia,  which  are  also  intensified  by  the  congestion 
of  its  contents  due  to  the  sharp  angle  made  by  the  sac  as  it  presses  forward  upon  the 
thigh.  The  constriction  may  be  due  to  pressure  against  Hey's  ligament  (page  636  ), 
Poupart1  s  ligament,  or  Gimhernat'  s  ligament.  The  relations  of  the  neck  of  the  sac  to 
the  obturator  artery  (page  814  ),  which  once  in  three  and  a  half  cases  arises  from  the 
epigastric  and  in  two-fifths  of  such  cases  passes  across  the  femoral  ring  (Fig.  1498  ) 
or  close  to  its  inner  border,  should  be  recalled  in  performing  herniotomy.  About  a 
half-inch  above  and  to  the  outer  side  of  the  ring  lie  the  deep  epigastric  vessels  ;  the 
femoral  vein  lies  externally  ;  beneath  the  ring  the  pectineus  fibres  covering  the  bone 
are  often  so  thin  that  not  enough  room  can  be  obtained  by  incision,  which  is  therefore 
made  upward  and  a  little  inward,  and  preferably  with  a  blunted  knife  that  may  divide 
the  tense  aponeurosis  without  damage  to  the  vessels  which,  when  they  are  present, 
lie  in  loose  cellular  tissue  a  twelfth  to  a  sixth  of  an  inch  from  the  edge  of  the  ring. 


FIG.  1498. 


Anterior  superior  iliac  spine 

Iliacus  muscle 

Deep  circumflex  iliac  artery 


/  Artery. 
External  iliac -| 

^    Vein 

Obturator  nerv 

Round  ligament 

Obturator  canal 
Pubic  branch  of  obturator  artery 


Poupart's  ligament 
Transversalis  muscle 


Rectus  muscle 


Deep  epigastric  vessels 

emoral  ring 
imbernat's  ligament 


bturator  artery  from  deep 
epigastric 


.Symphysis 


Dissection  of  part  of  left  half  of  pelvis  and  adjacent  body-wall,  showing  obturator  artery  arising  from  deep 

epigastric  and  crossing  femoral  ring. 

Umbilical  hernia  is  most  conveniently  divided  from  either  a  clinical  or  an 
anatomical  stand-point  into  the  congenital  and  the  acquired  forms.  A  congenital  um- 
bilical hernia  (hernia  funiciili  umbilicalis}  is  the  result  of  a  defect  of  development, 
the  anterior  abdominal  wall  failing  to  close  in  the  region  of  the  navel.  Analogous 
malformations — harelip,  spina  bifida,  vesical  exstrophy — sometimes  coexist.  In  addi- 
tion to  intestine,  other  abdominal  viscera  may  be  found  in  the  hernial  contents  ;  and 
in  marked  cases  the  condition  resembles  an  eventration  (fissura  abdominalis)  rather 
than  a  hernia.  Indeed,  in  some  of  its  forms,  the  congenital  variety  is  not  a  true 
hernia,  for  ' '  we  are  not  concerned  with  viscera  escaped  from  a  cavity,  but  with  viscera 
which  have  never  entered  it"  (  Malgaigne ) . 

In  the  lesser  cases  the  gut — possibly  Meckel's  diverticulum  (_q.v.} — protrudes 
into  the  substance  of  the  cord,  separating  the  structures  (page  53)  and  covered  by 
a  layer  of  embryonic  tissue  (the  jelly  of  Wharton)  and  by  the  amniotic  tissue  con- 
tinuous with  the  skin.  A  thin  avascular  membrane  directly  continuous  with  the 
parietal  peritoneum  is  sometimes  present.  These  layers  are  rarely  separately  demon- 
strable, and  are  often  so  thin  as  to  be  transparent. 

In  the  cases  in  which  only  a  very  small  knuckle  of  gut  or  a  diverticulum  is 
involved  (hernia  at  the  root  of  the  cord)  there  may  be  merely  thickening  or  enlarge- 


1776  HUMAN   ANATOMY. 

ment  at  that  point.      If  this  is  overlooked  and  the  cord  is  tied  within  the  limits  of 
this  enlargement,  the  intestine,  if  not  previously  replaced,  may  be  included. 

Acquired  Umbilical  Hernia. — Usually,  although  the  cord  is  tied  at  a  short  dis- 
tance from  the  abdominal  wall,  the  stump  separates  on  a  level  with  the  latter  on 
account  of  the  contraction  of  the  elastic  fibrous  tissue  around  the  umbilicus.  This 
cuts  off  the  urachus  and  the  vessels  passing  through  the  ring, — the  two  allantoic 
or  hypogastric  arteries  and  the  umbilical  vein.  Viewed  from  within,  the  fibrous 
cords  representing  these  obliterated  vessels  would  be  seen  converging  to  the  puckered 
umbilical  scar,  the  vein  from  above,  the  urachus  and  the  arteries  from  below.  As 
the  usual  contraction  of  fibrous  tissue  takes  place,  and  as  the  abdomen  grows,  the 
traction  of  these  cords  depresses  the  umbilicus  so  that  anteriorly  it  lies  a  little  below 
the  surrounding  surface  of  the  abdomen.  The  larger  amount  of  tissue  represented 
by  the  urachus  and  the  two  arteries  and  their  close  attachment  to  the  lower  edge 
cause  that  portion  of  the  umbilicus  to  become  the  stronger,  the  umbilical  vein  being  less 
closely  connected  to  the  upper  edge  of  the  ring. 

In  infantile  umbilical  hernia  these  changes  are  not  complete,  but  when  a 
knuckle  of  gut  protrudes  through  the  umbilicus  during  infancy,  as  a  result  of 
increased  intra-abdominal  pressure,  it  usually  escapes  between  the  vein  and  the  upper 
margin  of  the  ring  on  account  of  their  loose  attachment.  The  coverings  are  peri- 
toneum, transversalis  fascia,  and  skin.  These  herniae  are  usually  small,  and  are  often 
cured  spontaneously  by  the  contraction  of  the  umbilical  and  periumbilical  scar  tissue. 
Their  occurrence  is  favored  by  tight  phimosis  or  by  constipation,  causing  straining, 
or  by  improper  feeding,  causing  flatulence.  After  infancy  umbilical  hernia  is  rare 
until  adult  life. 

The  umbilical  hernia  of  adults  is  far  more  common  in  women  than  in  men  (73 
per  cent.),  and  is  especially  favored  by  obesity — with  accumulation  of  fat  in  the 
omentum  and  mesentery — and  by  repeated  pregnancies.  The  coverings  of  such  a 
hernia  are  peritoneum,  transversalis  fascia,  superficial  fascia,  the  fibrous  tissue  of  the 
umbilical  scar  and  the  linea  alba,  and  skin. 

For  the  reasons  above  given,  it  appears  usually  at  the  upper  semicircumference 
of  the  umbilical  ring  and  often  involves  the  linea  alba  immediately  above  it, — a  form 
of  ventral  hernia.  Such  herniae  are  very  apt  to  contain  omentum — the  growth  of 
fat  in  which  often  makes  them  irreducible — and  portions  of  the  colon,  and,  on 
account  of  the  readiness  with  which  fecal  obstruction  may  be  caused  in  the  large 
intestine,  they  are  prone  to  incarceration. 

Ventral  herniae  protrude  through  the  abdominal  parietes  at  other- points  than 
the  umbilicus  or  groin,  or  than  those  weakened  by  the  passage  of  vessels  and  nerves 
from  within  outward. 

The  most  common  are  in  the  linea  alba,  between  the  umbilicus  and  a  point 
midway  between  it  and  the  ensiform  cartilage  (epigastric  hernia).  Above  that  they 
are  very  rare,  as  the  effect  of  gravity  is  lacking  and  the  contiguous  viscera  are  less 
mobile.  Immediately  below  the  umbilicus  they  are  not  uncommon,  as  the  linea  alba 
has  still  an  appreciable  width.  Lower,  where  it  has  become  a  mere  raphe,  they  art- 
very  rare.  They  are  often  associated  with  subserous  lipomata,  and  may  be  caus 
by  them.  The  protrusion  of  fat  from  the  subserous  tissue  is  thought  to  draw  the 
peritoneum  out  into  a  diverticulum  which  readily  becomes  a  hernial  pouch  wht-n 
intra-abdominal  pressure  is  great  enough. 

The  linea  semilunaris,  especially  below  the  level  of  the  umbilicus,  is  a  not 
uncommon  site  of  ventral  hernise.  It  has  been  suggested  that  their  position  is  de- 
termined by  the  fold  of  Douglas  (page  522), — the  semilunar  lower  margin  of  the 
posterior  layer  of  the  internal  oblique  aponeurosis,  which  fuses  with  the  tnmsvrrsali 
aponeurosis  to  form  the  posterior  sheath  of  the  rectus  niusrk-,  which  i-nds  about 
half-way  between  the  umbilicus  and  tin-  pubes.  Below  that  all  tin-  aponeuroses  pass 
in  front  of  the  reetus,  leaving  the  posterior  surface  of  the  inferior  portion  of  that 
muscle  separated  from  the  abdominal  contents  only  by  the  transversalis  fascia  and 
peritoneum. 

Ventral  hernia  of  the  linea  semilunaris  near  its  lowest  portion  and  direct  hernia 
issuing  through  the  internal  inguinal  fossa  (page  1770)  are  indistinguishable,  if  not 
practically  identical. 


PRACTICAL   CONSIDERATIONS:    ABDOMINAL   HERNIA      1777 


Lumbar  hernia  undoubtedly  occurs  most  frequently  in  the  space  known  as 
Petit' s  triangle  (Fig.  1499,  page  530),  although  its  protrusion  through  that  space 
has  not  been  demonstrated  by  exact  dissection. 

Above  Petit' s   triangle  is  another  triangular    space, — Grynfelt  and  Lesshaft's 


FlG.      T4QQ. 


Latissimus  dorsi,  cut  edgi 


XII  rib 


Fascial  triangle 
Quadrattis  lumborum — 

Internal  oblique 

(Petit's  triangle) 
Vertebral  aponeurosis 


Cut  digitation  of  latissimus  dorsi 


External  oblique 


Entrance  of  hernia 


Dissection  of  postero-lateral  abdominal  wall,  showing  fascial  (Grynfelt  and  Lesshaft's)  triangle;  posterior  boundary 

of  Petit's  triangle  has  been  cut  away. 

triangle, — bounded  posteriorly  by  thequadratus  lumborum,  anteriorly  by  the  internal 
oblique,  and  above  by  the  twelfth  rib.  When  the  latissimus  dorsi  is  turned  aside 
here  it  covers  only  the  aponeurotic  origin  of  the  transversalis  (Fig.  1499). 

Braun  has  found,  at  a  place  just  posterior  to  Petit's  triangle,  the  fibres  of  the 
aponeurosis  of  the  latissimus  dorsi  lacking  on  both  sides  in  a  case  in  which  a  lumbar 
hernia  existed  on  one  side. 

Obturator  hernia  escapes  through  the  obturator  canal,  which  runs  downward, 
forward,  and  inward  below  the  horizontal  ramus  of  the  pubes.  The  internal  hernial 

orifice  is  at  the  fissure  in  the  obturator 

FIG.  1500.  interims  muscle  which  permits  of  the  pas- 

sage of  the  vessels  and  nerve.  A  hernia 
starting  there  passes  through  the  opening 
between  the  upper  edge  of  the  obturator 
membrane  and  the  lower  surface  of  the 
pubic  ramus  (Fig.  1500),  and  usually 
descends  between  the  obturator  externus 
and  pectineus  muscles  to  lie  beneath  the 
latter  muscle  and  the  adductor  longus. 
It  is  therefore  to  be  looked  or  felt  for 
below  the  pubes  and  the  inner  end  of 
Poupart's  ligament,  but  at  a  point  both 
lower  and  more  internal  than  the  site  of 
femoral  hernia.  The  thigh  should  be 
flexed,  adducted,  and  rotated  outward  to 
relax  the  pectineus,  adductor  longus,  and 

obturator  externus.  As  this  hernia  occurs  most  frequently  in  elderly  females,  it  is 
well  to  note  that  the  inner  orifice  of  the  canal  may  be  felt  through  the  vagina.  The 
narrowness  of  the  canal  and  the  rigidity  of  the  thin  pectineus  and  obturator  externus 
muscles  make  the  nerve-pressure  symptoms  of  this  hernia  of  exceptional  diagnostic 


Hernia  seen  through  obturator  membrane 

Right  obturator  hernia,  seen  from  within 


1773  HUMAN   ANATOMY. 

value.  The  obturator  nerve,  which  is  in  close  relation  with  the  vessel  and  the  track 
of  the  hernia,  supplies  the  hip-  and  knee-joints  and  the  adductor  muscles  and  aids  in 
furnishing  sensation  to  the  inner  side  of  the  thigh  as  low  as  the  knee,  and  sometimes 
to  the  middle  of  the  leg.  Pain  in  these  joints  and  in  that  region  not  otherwise 
explicable,  and  especially  if  associated  with  intestinal  symptoms,  should  therefore 
suggest  a  careful  examination  of  the  obturator  region. 

Sciatic  herniae  include  all  the  herniae  that  emerge  from  the  pelvis  through  one 
or  other  of  the  sciatic  foramina, — that  is,  (i)  through  the  great  sacro-sciatic  foramen 
alongside  of  the  gluteal  artery  (above  the  pyriformis)  ;  (2)  through  the  same  fora- 
men alongside  of  the  sciatic  nerve  and  artery  (below  the  pyriformis)  ;  (3)  through 
the  lesser  sacro-sciatic  foramen  (Sultan).  They  are  all  very  rare.  The  pelvic 
fascia  forms  one  of  the  coverings  of  the  sac.  Within  the  pelvis  the  hernia  is  anterior 
to  the  pyriformis  muscle  and  sciatic  nerve.  On  entering  the  thigh  the  sac  crosses 
over  the  nerve  to  its  posterior  surface,  and  is  covered  by  the  gluteus  maximus.  As 
the  rupture  enlarges,  it  emerges  from  beneath  the  lower  border  of  the  gluteus  and 
descends  the  thigh,  or  may  pass  forward  above  the  trochanter  towards  the  groin. 

When  the  hernia  is  small  and  makes  no  obvious  swelling  in  the  buttock,  it  is 
found  at  the  spot  where  the  sciatic  artery  is  tied  just  outside  the  pelvis.  A  line  is 
drawn  from  the  posterior  superior  iliac  spine  to  the  trochanter  major  rotated  inward, 
and  about  half  an  inch  below  the  junction  of  the  upper  with  the  middle  third  of  this 
line  the  hernia  enters  the  buttock  (Macready). 

Perineal  herniae  include  those  which  pass  through  the  outlet  of  the  pelvis  and 
its  muscular  floor.  The  boundaries  of  the  former  are  the  glutei  maximi  and  coccyx 
posteriorly,  the  pubo-ischiatic  arch  anteriorly,  and  the  great  sacro-sciatic  ligaments  con- 
necting the  coccyx  and  the  tuberosities  of  the  ischium  (Fig.  1423).  The  coccygeus 
and  levator  ani  muscles  form  the  floor  of  this  space,  which  is  perforated  by  the  rectum 
and  urethra  and  vagina,  and  extends  from  the  outer  walls  of  these  structures  to  the 
inner  walls  of  the  pelvis  (Fig.  1424).  It  might  be  supposed  that  the  comparatively 
yielding  nature  of  the  parts  which  close  the  lower  opening  of  the  pelvis  would 
favor  the  production  of  herniae,  but,  as  Macready  has  shown,  hernia  through  muscular 
planes  is  everywhere  very  infrequent.  The  normal  oblique  inclination  of  the  pelvic  floor 
and  its  elasticity  are  doubtless  factors  in  preventing  the  occurrence  of  perineal 
herniae.  A  hernia  starting  at  the  upper  surface  of  the  pelvic  diaphragm  must  pass 
between  the  coccygeus  and  levator  ani  or  between  the  fibres  of  the  latter  muscle,  and 
will  descend  into  the  ischio-rectal  space  (Fig.  1423),  where  it  may  cause  a  protrusion 
of  the  skin  of  the  perineum,  or  may  advance  towards  the  rectum  (rectal  hernia], 
the  vagina  (vaginal  hernia),  or  the  posterior  portion  of  the  labium  majus  (pudcndal 
hernia}. 

The  development  of  perineal  hernia  is  believed  by  Ebner  to  depend  upon  an 
abnormally  low  descent  of  the  recto-uterine  peritoneal  fold  which  occupies  Douglas's 
pouch  in  the  female  or  of  the  recto-vesical  fold  in  the  male.  In  the  presence  of  such 
a  fold,  intra-abdominal  pressure  is  able  to  carry  a  peritoneal  pouch,  with  or  without 
included  intestinal  coils,  to  the  right  or  left  (its  progress  in  the  mid-line  being 
arrested  by  the  firm  septum  between  the  rectum  and  vagina  or  the  rectum  and 
urethra),  so  that  it  rests  on  the  levator  ani  muscle,  the  fibres  of  which  are  often 
separated  at  places  (Henle  describes  it  as  three  muscles).  Its  subsequent  downw 
progress  has  been  noted  (vide  supra}. 

A  form  of  perineal  hernia  known  as  inguino-pcrincat  has  been  described  (Coley) 
in  which  the  hernial  sac  accompanied — or  followed — the  misplaced  testicle  (ectopia 
perinaealis)  into  the  perineum. 

Diaphragmatic  herniae  are  usually  congenital  and  due  to  defective  develop- 
ment of  the  diaphragm.  A  review  of  the  anatomy  of  that  muscle,  with  special  refer- 
ence to  its  various  openings  and  to  the  fissures  between  its  sternal  and  costal  and 
costal  and  lumbar  portions  (Fig.  549),  will  explain  the  occurrence  of  hernial  orifices 
in  certain  situations,  already  detailed  in  connection  with  hernia  of  the  stomach 
(page  1362). 

The  symptoms  are  largely  those  due  to  gastric  disturbance  (when  the  stomach 
is  involved)  and  to  alteration  in  physical  signs  caused  by  compression  and  displace- 
ment of  the  heart  and  lun^s. 


PRACTICAL  CONSIDERATIONS  :   ABDOMINAL  HERNIA.        1779 


Internal  (intra-abdominal,  retroperitoneal)  herniae  are  those  which 
arise  within  the  abdominal  cavity,  whether  they  develop  in  normal  peritoneal  recesses 
or  in  abnormal  peritoneal  recesses  arising  in  a  physiological  manner  (Brosike). 
The  classification  adopted  by  Sultan  is  sufficiently  comprehensive  to  include  all 
herniae  coming  under  the  above  definition.  Five  varieties  can  be  defferentiated  : 
(i)  hernia  of  the  foramen  of  Winslow,  (2)  hernia  of  the  duodeno-jejunal  recess, 
(3)  hernia  of  the  retrocctcal  and  ileo-csecal  recesses,  (4)  hernia  of  the  intersigmoid 
recess,  (5)  retrovesical  hernia. 

1.  The  hernia  of  the  foramen  of  Winslow  (Fig.   1475) — into  the  lesser  peritoneal 
cavity,  which  may  be  regarded  as  a  pre-existing  hernial  sac — is  rare  on  account  of 
the  narrowness  of  the  opening  (page  1746),  and  Merkel  believes  that  either  an  abnor- 
mally long  mesentery  or  a  retardation  of  the  normal  process  of  fixation  of  the  colon 
must  exist  if  portions  of  the  intestine  are  present  in  the  lesser  peritoneal  cavity.     The 
part  of  the  bowel  involved  is  usually  the  colon. 

2.  The  duodeno-jejunal  fossa,  the  orifice  of  which  looks  upward  (Fig.    1501), 
is  formed  by  a  peritoneal  fold  and  is  usually  to  the  left  of  the  spine  at  the  duodeno- 
jejunal  junction.      It  may,  in  marked  cases,  receive  the  whole  of  the  small  intestine 

FIG.  1501. 

Transverse  mesocolon 
Jejunum  !  Duodenum 


Superior  duodeno-jejunal 
fossa 

Branch  of  left 
colic  artery 


Inferior  duodeno- 
jejunal  fossa 
Descending  colon 


Mesentery  of  small 

intestine 


Duodeno-jejunal  junction,  showing  duodenal  fossae;  )ejunum  turned  to  the  right. 

which  is  then  placed  behind  the  posterior  parietal  peritoneum.  The  duodenum  can 
be  seen  to  enter  the  sac  and  the  end  of  the  ileum  to  leave  it.  The  renal  artery  is 
behind  the  sac  and  the  inferior  mesenteric  artery  in  front  of  it  (Treves).  The  inferior 
mesenteric  vein  and  sometimes  the  colica  sinistra  artery  run  in  the  upper  margin  of 
the  orifice. 

3.  The  more  important  peritoneal  fossa?  about  the  caecum  are  shown  in  Fig.  1502. 
They  contain  herniae  with  great  rarity  ;  the  retrocaecal  pocket — extending  upward 
behind  the  caecum  and  ascending  colon — has  received  coils  of  the  lower  ileum. 

4.  By  raising  the  sigmoid  flexure  and  drawing  it  to  the  left,  the  intersigmoid 
fossa  may  be  seen  opening  towards  the  left  between  the  root  of  the  sigmoid  meso- 
colon and  the  parietal  peritoneum.      It  is  caused  by  the  sigmoid  artery,  and  is  about 
over  the   bifurcation   of  the  iliac  vessels.      It  has  been  occupied  by  coils  of 'small 
intestine. 

5.  The  plica  hypogastrica  (ligamcntum  umbilicalis  latcralis^)  (Fig.  1487)  may  be 
so  exceptionally  salient  as  to  form  a  deep  peritoneal  pocket  becoming  a  retrovesical 
hernial  pouch. 

All  these  internal  herniae  have  in  common  the  essentials  of  abdominal  herniae  of 
all   varieties, — viz.,    an   orifice   through  which,  by  intra-abdominal  pressure  or  by 


iy8o 


HUMAN  ANATOMY. 


gravity,  or  by  their  own  vermicular  movement,  intestines  may  be  forced  into  a  cavity 
or  space  cither  actually  or  potentially  pre-existing,  in  which,  under  lessened  pressure 
as  compared  with  that  at  the  orifice,  the  bulk  of  the  hernia  may  increase,  with  the 

FIG.  1502. 


Ileuin 


lleo-anpendiculsr 
fold 


Inferior  ileo-Ccecal 

fossa 

Meso-appendix 


Posterior  ciecal 
fold 

Posterior  layer  of 
mesentery 


Retrocax-al  fossa 


Peritoneal  fossa;  of  ileo-c£ecal  region,  caecum  being  drawn  forward  and  upward.     ( fonnesco}. 

constant  danger  of  incarceration  (stoppage  of  the  fecal  current)  or  strangulation 
(cutting  off  the  supply  of  blood).  The  symptoms  of  internal  hernias  are  therefore 
always  those  of  intestinal  disturbances  and  very  often  those  of  complete  intestinal 
obstruction. 


THE   SPLEEN. 


1781 


ACCESSORY   ORGANS   OF   NUTRITION. 

In  this  group  may  be  included  the  spleen,  the  thyroid  body,  the  parathyroids,  the 
thy mus  body,  the  suprarenal  capsules,  and  the  anterior  lobe  of  the  pitu itary  body. 

These  are  sometimes  called  the  ' '  ductless  glands, ' '  but,  as  several  of  them  are  cer- 
tainly not  glands,  the  name  is  unfortunate.  To  certain  members  of  the  above  group, 
as  the  thyroid  and  suprarenal  bodies,  the  designation  "organs  of  internal  secretion" 
may  appropriately  be  applied.  Considered  morphologically,  they  do  not  belong  to 
any  one  system  ;  but  on  the  whole  it  may  be  said  without  grave  error  that  they  are 
concerned  in  nutrition,  and  that  disease  of  several  of  them  manifests  itself  by  certain 
tolerably  well-defined  symptoms  indicating  a  serious  disturbance  of  nutrition,  differ- 
ing according  to  the  organ  involved. 


THE   SPLEEN. 

The  spleen  is  essentially  a  lymphatic  organ.  It  is  of  a  purplish  color  and  of 
very  friable  structure,  and  is  situated  in  the  left  hypochondrium  behind  the  stomach. 
The  weight  is  excessively  variable,  changing  with  the  state  of  digestion,  and  liable 
to  immense  increase  in  certain  diseases,  as  well  as  to  slighter  modifications  in  others. 
Sappey  gives  the  average  weight  in  ten  men  as  195  gm.  (approximately  7  oz. ). 
The  specific  gravity  is  variously  stated  between  1.037  and  1.060.  The  length,  ac- 
cording to  Sappey,  in  the  same  ten  men  was  12.3  cm.  (4^6  in.  J. 


FIG.  1503. 


Posterior  horde 


Intermediate  border 


Gastric  surface 


rior  border, 


Internal  basal  ar 


Cut  peritoneum 
surrounding  hilum 


Anterior  basal  :uij*le 


Posterior  basa 


Basal  surface 
Visceral  aspect  ol  spleen  hardened  in  situ. 


The  shape  of  this  delicate  organ  has  been  but  recently  understood,  through 
methods  of  hardening  in  situ.  It  depends  so  essentially  on  the  neighboring  viscera 
that  what  may  be  the  most  usual  arrangement  of  several  details  still  remains  to  be 
determined.  We  follow  Cunningham  in  describing  a  triangular  basal  surface  at  the 
lower  end,  although  it  is  by  no  means  always  to  be  recognized.  Besides  this  there  are 
three  distinct  surfaces, — the  phrenic,  the  renal,  and  the  gastric,— aft  ol  which  meet 
at  a  rounded  point  at  the  top  of  the  organ. 

The  phrenic  surface  is  convex.  It  is  Jthe  largest  and  gives  the  general  put- 
line  of  the  organ.  It  lies  against  the  diaphragm  in  the  left  hypochondrium.  The 


1782 


HUMAN   ANATOMY. 


Lun 


Diaphragm 

(cut) 

Spleen 


outline  of  this  surface  is  that  of  a  lozenge  enclosed  by  an  anterior  and  a  posterior 
border,  one  point  being  above  and  behind,  the  other  below  and  in  front.  Thus  in 
the  main  the  long  axis  corresponds  to  the  course  of  the  lower  ribs,  which  sometimes 
make  impressions  on  this  convex  surface.  The  anterior  border,  formerly  the  marqo 
crenatus,  separating  this  surface  from  the  gastric,  is  sharp,  especially  below.  It 
shows  one  or  more  notches  in  93  per  cent.1  of  the  cases.  They  are  most  com- 
mon in  the  lower  part  of  the  border,  which  is  sometimes  quite  scalloped.  The  pos- 
terior border,  formerly  the  margo  obtusus,  separating  the  phrenic  surface  from  the 
renal,  is  much  less  prominent.  Parsons  found  notches  in  it  in  32  per  cent. ;  but  the 
general  appearance  of  this  border  is  very  different  from  the  preceding,  being  in  the 
main  solid  and  uniform.  The  phrenic  surface  occasionally  (20  per  cent.)  presents  a 
sharp  fissure,  rarely  more  than  one.  It  usually  starts  from  a  notch  in  the  posterior 
border  and  runs  some  distance  across  this  surface,  forward  and  upward.  Less  fre- 
quently it  starts  from  the 

FIG.  1504-  anterior  border,  or  lies  en- 

tirely   in    the    convexity, 
reaching  neither  border. 

The  renal  surface, 
facing  inward,  does  not 
extend  so  high  as  the  pre- 
ceding. It  is  enclosed  by 
the  posterior  border,  the 
internal  or  intermediate 
border,  which  separates  it 
from  the  gastric  surface, 
and  by  one  side  of  the  ba- 
sal surface.  In  the  upper 
third  this  surface  is  nearly 
plane,  resting  against  the 
suprarenal  capsule,  and  in 
the  lower  two-thirds  dis- 
tinctly concave,  where  it  is 
moulded  over  the  upper 
part  of  the  left  kidney. 
The  end  of  the  pancreas, 
if  that  organ  be  short,  may 
rest  against  the  anterior 
part  of  this  surface. 

The  gastric  surface, 
considerably  larger  than 
the  preceding,  is  bounded 
by  the  intermediate  and 
anterior  borders  and,  be- 
low, by  another  side  of 
the  base.  It  is  concave, 
being  for  the  most  part  moulded  over  the  stomach.  It  contains  the  hilum,  a  fissure 
some  inch  and  a  half  long,  running  parallel  to  the  intermediate  border  and  about 
one-half  inch  distant  from  it,  which  receives  the  vessels.  The  part  of  this  surface 
which  is  not  against  the  stomach  is  at  the  lower  end,  and  rests  against  the  splenic 
flexure  of  the  colon.  In  some  cases,  when  the  stomach  is  contracted  and  the  colon 
distended,  the  relative  areas  of  the  two  may  be  reversed.  Moreover,  the  omentum 
may  reach  the  spleen  between  them.  The  tail  of  the  pancreas  may  touch  the  right 
part  of  this  surface  or,  if  long,  lie  against  the  spleen  just  above  the  colon. 

The  basal  surface  is  a  triangular  area,  much  smaller  than  the  other  surfaces. 
It  is  enclosed  by  the  lower  part  of  the  posterior  bonier  of  the  spleen  and  by  two  lines 
diverging  from  the  lower  end  of  the  intermediate  border.  One  of  these  separates 
the  basal  surface  from  the  gastric  and  the  other  from  the  renal  surface.  One  or  both 
of  these  lines  may  be  so  rudimentary  that  the  base  may  seem  a  part  of  either  the 

1  Parsons:  Journal  of  Anatomy  and  Physiology,  vol.  xxxv.,  1901. 


Left  kidney 


Parietal  peri 
toneuni,  pos- 
terior aspect 
Iliac  crest 


Postero-lateral  wall  of  formalin  subject  has  been  removed  to  show  relations  of 
spleen  hardened  in  situ. 


THE   SPLEEN.  1783 

gastric  or  renal  surface,  more  often  the  former,  or  it  may  appear  simply  as  a  knob  at 
the  inner  side  of  the  lower  end.  This  knob,  the  inferior  tubercle,  is  usually  more  or 
less  evident  at  the  termination  of  the  intermediate  border. 

Structure. — In  addition  to  the  serous  covering  contributed  by  the  peritoneum, 
the  spleen  is  completely  invested  by  a  distinct  capsule,  or  tunica  albuginca,  composed 
of  dense  bundles  of  fibrous  tissue,  numerous  elastic  fibres,  and,  in  its  deeper  layer, 
sparsely  distributed  bundles  of  involuntary  muscle.  At  the  hilum  the  tissue  of  the 
capsule  is  continued  into  the  organ,  supporting  the  blood-vessels  and  nerves.  The 
capsule  likewise  gives  off  numerous  trabeculae  which  pass  into  the  substance  of  the 
gland  and  break  up  into  innumerable  delicate  processes  which  unite  to  form  the  sup- 
porting framework. 

Mall  *  has  shown  that  this  framework  is  arranged  with  greater  regularity  than  was 
formerly  recognized,  since  the  trabeculae  subdivide  the  spleen  into  fairly  regular  com- 
partments, the  splenic  lobuJes,  measuring  about  i  mm.  in  diameter.  Each  of  these 
units  is  bounded  by  three  interlobular  trabeculce,  from  which  secondary  intralobular 
processes  penetrate  into  the  lobule,  whereby  the  latter  is  subdivided  into  about  ten 
primary  compartments.  These,  as  well  as  the  lobules  themselves,  are  not  isolated, 

FIG.   1505. 

Capsule — 


Interlobular 
trabecula  and 
vein 


--Splenic  pulp 


v- Interlobular 
trabecula 


;    '.  •   •  :' 

y^j;™ 

Section  of  spleen  under  very  low  magnification,  showing  general  arrangement  of  splenic  tissue.     X  10. 

but  freely  communicate,  since  the  intervening  trabeculae  form  only  incomplete  parti- 
tions. The  spaces  within  the  fibrous  framework  are  filled  with  the  highly  vascular 
lymphoid  tissue  constituting  the  splenic  pulp. 

The  relation  of  the  blood-vessels  to  the  lobules  of  the  spleen  is,  according  to 
Mall,  very  definite.  The  branches  of  the  splenic  artery,  after  entering  at  the  hilum 
and  running  for  some  distance  within  the  trabeculae,  break  up  into  smaller  vessels, 
each  of  which  enters  the  proximal  end  of  the  lobule,  through  the  middle  of  which  it 
passes,  giving  off  lateral  twigs,  one  for  each  primary  compartment  of  the  lobule. 
The  lymphoid  tissue  occupying  the  compartment  is  arranged  as  anastomosing  cylin- 
drical masses,  the  pulp-cords.  Within  the  latter  course  the  terminal  branches  of  the 
splenic  arteries,  while  outside  and  between  the  cords  lies  the  plexus  of  venous  spaces 
from  which  the  more  definite  channels,  the  intralobular  veins,  arise.  The  terminal 
arteries  within  the  pulp-cords  give  off  numerous  small  branches  which  terminate  in 
minute  expansions,  the  ampulla  of  Thorn  a.  The  latter  communicate  with  the  venous 
spaces  surrounding  the  pulp-cords,  so  that  finely  divided  substances,  such  as  metallic 

1  Johns  Hopkins  Hospital  Bulletin,  1898  ;  Zeitschrift  f.  Morphol.  u.  Anthropol.,  Bd.  ii.,  1900. 


I784 


HUMAN   ANATOMY. 


pigments,  when  injected  into  the  arteries,  pass  into  the  veins.  The  walls  of  the 
ampullae  are  very  thin  and,  towards  the  junction  with  the  venous  radicles,  imper- 
fect, being  here  composed  of  the  reticulum  of  the  surrounding  pulp-tissue.  The 
channels,  however,  are  sufficiently  definite  to  prevent  the  escape  of  the  blood-cells 
under  normal  conditions,  although  the  plasma  constantly  passes  into  the  intercellular 
spaces  of  the  pulp  (Mall).  The  walls  of  the  venous  spaces 'are  even  more  pervious 
than  those  of  the  ampullae,  and,  like  the  latter,  possess  only  an  incomplete  endothelial 
lining,  supported  externally  by  a  mesh  of  circularly  disposed  elastic  fibres.  The  endo- 
thelium  consists  of  narrow,  elongated  spindle-cells  instead  of  the  usual  plate-like  ele- 
ments which  line  the  larger  splenic  blood-vessels.  The  round  or  oval  nuclei  project 
into  the  lumen  of  the  venous  space  beyond  the  level  of  the  protoplasm  of  the  cell,  which 
often  presents  a  distinct  striation. 

The  venous  spaces  between  the  pulp-cords  are  the  beginnings  of  more  definite 
channels,  the  intralobular  veins,  which  pass  from  the  primary  compartments  towards 


FIG.  1506. 


Capsule 


Primary  compartment 


Interlobular  trabecula 


Intralobular  trabecula 


Interlobular  vein 


Malpighian  body 


ular  vein 


ic  artery 


v»-          //    / / 
Diagram  showing  architecture  of  splenic  unit ;  splenic  pulp  is  represented  in  only  one  compartment.     (After  Mall.} 


the  trabeculae  between  the  lobules  to  become  tributaries  of  the  larger  interhtndat 
veins  occupying  the  periphery  of  the  lobules  within  the  boundary  septa.  These  veins 
follow  the  larger  trabeculae  until,  finally,  they  emerge  at  the  hilum  to  form  the  splenic 


vein. 


In  their  journey  through  the  lobule,  shortly  after  leaving  the  trabeculae,  the 
branches  of  the  splenic  artery  present  marked  local  accumulations  of  lymphoid  tissue 
within  their  adventitia.  These  aggregations  constitute  the  Malpighian  bodies,  or 
splenic  nodules.  When  seen  in  transverse  section,  they  appear  as  conspicuous  oval 
an-as  of  dense  lymph-tissue  surrounding  the  artery,  which  usually  occupies  a  somewhat 
eccentric  position.  Longitudinally  sectioned,  the  splenic  nodules  appear  as  cylinders. 
They  correspond  in  structure  with  true  lymph-nodes,  possessing  germ-centres.  Sur- 
rounding the  Malpighian  bodies,  the  spleen-tissue  presents  the  usual  arrangement  of 
the  pulp-cords. 

The  splenic  pulp  consists  of  a  delicate  supporting  reticulum,  continuous  with 
the  terminal  ramifications  of  the  intralobular  trabecuhi-,  and  the  cells  contained  within 


THE   SPLEEN. 


1785 


FIG.   1507. 


Germ-ce 


and  supported  by  the  mesh-work.  The  pulp-cells  include  a  variety  of  elements,  the 
most  constant  of  which  are  :  ( a )  small  mononuclear  lymphocytes  ;  (b)  leucocytes  of 
the  mononuclear  and  polymorphonuclear  types  ;  (c)  red  blood-cells  ;  (d  )  nucleated 
red  blood-cells ;  (e)  large 
phagocytic  cells  containing 
disintegrating  red  blood-cells, 
or  pigment  particles  derived 
from  the  destruction  of  the 
same  ;  (/)  giant-cells  with 
large  composite  nuclei,  chiefly 
in  young  animals.  In  addi- 
tion a  variable  amount  of  free 
pigment  is  present,  probably 
from  the  broken-down  red 
blood-cells.  During  embry- 
onic life  and  later,  -in  response 
to  unusual  demands  for  addi- 
tional red  blood-cells,  as  after 
severe  hemorrhage,  the  spleen 


is  the  birthplace  of  new  red 
corpuscles  ;  these  are  at  first 
nucleated,  but  soon  lose  their 
nuclei. 

Peritoneal  Relations. — The  spleen  is  developed  in  the  posterior  mesogas- 
trium,  and  usually  retains  all,  or  nearly  all,  of  its  original  serous  covering,  which  is 
reflected  at  the  hilum  over  the  vessels.  The  splenic  artery  reaches  the  spleen 
through  the  peritoneal  duplicature  known  as  the  lieno-renal  or  licno-ph ren ic  fold, 
which  leaves  the  abdominal  wall  at  the  tail  of  the  pancreas.  The  vessels  for  the 
stomach  leave  the  artery  before  it  enters  the  spleen  by  the  fold  known  as  the  gastro- 


Transverse  section  of   Malpighian   body,  showing   its  relations  to  sur- 
rounding pulp-tissue. 


FIG.  1508. 


mm 


i  r& 

V«*f*?(S 

Arteriole-^ 

»»\w  >v>  ^  •  ( *l?"*'*   ;  ^^^ 

*?^?*?»c'    M^'^r    ;-       -v^:  ^:S 


X   ^ 


W 
-Jhr. 


&  •  T*  •&,•;„  ?'•,- ,  •-•  ty  'mm 

^ 

W:^':.  *V^V^*rT:iP¥ 

- «  - <L«f %«»,. .•' :..  \  J\'9  ,& "Jv ''; T"J ' 

\-e  ^"t 


^ulp-cords 


Venous  space 


Cell  containing 


Section  of  spleen,  showing  details  of  pulp-tissue.      •;  300. 


splenic  amentum,  which  extends  forward  to  the  greater  curvature  and  above  to  the 
back  of  the  fundus  of  the  stomach.  These  two  folds,  stretching  respectively  back- 
ward and  forward  from  the  hilum,  bound  a  part  of  the  lesser  cavity  of  the  peritoneum. 


1786 


HUMAN   ANATOMY. 


The  suspensory  ligament  of  the  spleen  is  an  inconstant  fold  belonging  to  the  lieno- 
phrenic  ligament,  extending  from  near  the  cesophageal  opening  in  the  diaphragm  to 
the  top  of  the  spleen.  It  contains  connective  tissue  between  its  layers,  which 
connects  a  triangular  retroperitoneal  area  of  the  spleen  with  the  diaphragm.  The 
phreno-colic  ligament  is  a  shelf-like  fold,  derived  from  the  greater  omentum,  stretched 
with  its  free  edge  forward  from  the  abdominal  wall  in  the  region  of  the  eleventh 
rib  to  the  transverse  colon  so  as  to  form  the  floor  of  a  niche  in  which  the  spleen 
rests. 

The  Vessels. —  The  Arteries. — The  splenic  artery  is  a  large,  tortuous  vessel, 
a  branch  of  the  cceliac  axis.  It  is  remarkable  not  only  for  its  large  size  in  propor- 
tion to  the  organ,  but  for  the  thickness  of  its  walls.  About  an  inch  from  the  spleen 
it  breaks  up  into  six  or  more  branches  which  enter  the  hilum  one  above  another,  in 

FIG.  1509. 

Ensiform  cartilage 


Diaphragm  - 


Left  lobe  of  liver 


OSsophagus 

Gastro-hepatic 
omentum 

Lobe  of  Spigelius 

Inferior 
vena  cava 

Vena 

azygos  major 
Aorta 

Vena 
azygos  minor 


Diaphragm  J 


.Lung 


Lung 


Gastro-spU-nu-  omentum 
Left  half  of  frozen  section  across  body  at  level  of  eleventh  thoracic  intervertebral  disk  ;  under  side  of  section 

the  main  anterior  to  the  veins,  with  which  they  travel  along  the  fibrous  walls  of  th 
interior.  No  arterial  branch  has  any  anastomosis  with  the  others.  Soon  after  its 
origin  the  splenic  artery  gives  off  a  branch  which  runs  above  the  main  trunk,  supplies 
some  twigs  to  the  stomach,  and,  breaking  up  into  smaller  branches,  enters  the  spleen 
near  the  top.1 

The  veins  ramify  in  the  spleen  in  company  with  the  arteries,  and  leave  it  in 
about  the  same  number  of  branches,  which  unite  to  form  the  splenic  vein  behind  and 
below  the  artery, 

The  lymphatics  are  chiefly  deep  ones  emerging  from  the  hilum,  but  there  are 

1  Haberer:  Archiv  fiir  Anat.  mid  Phys.,  Anat.  Abtheil.,  1902. 


PRACTICAL   CONSIDERATIONS:    THE   SPLEEN.  1787 

also  a  few  superficial  ones.  They  empty  into  a  little  group  of  lymph-nodes  at  the 
tail  of  the  pancreas. 

The  nerves,  from  the  solar  plexus,  enter  the  hilum  with  the  vessels. 

Development  and  Growth. — The  splenic  anlage  appears  about  the  fifth 
week  of  foetal  life  as  a  slight  condensation  of  the  mesoblastic  tissue  of  the  meso- 
gastrium,  associated  with  local  thickening  of  the  mesothelium  clothing  the  left  surface 
of  this  serous  fold.  According  to  Tonkoff,1  the  mesoblast  is  invaded  by  migrating 
cells  from  the  mesothelium,  which  play  an  important  role  in  the  production  of  the 
pulp-cords,  the  trabeculae  resulting  from  the  differentiation  of  the  vascular  mesoblastic 
tissue.  The  Malpighian  bodies  appear  relatively  late  as  accumulations  of  young 
lymphocytes. 

At  birth  the  spleen  weighs  from  10-15  gm->  and  is  said  to  be  relatively  rather 
large.  In  the  foetus  accessory  spleens  are  found  very  frequently  along  the  course  of 
the  splenic  vessels.  On  the  other  hand,  Parsons  seems  to  find  the  surface  of  the 
spleen  more  regular  than  in  later  life.  The  fissures  on  the  convex  surface  are  less 
frequent  and  less  deep.  The  great  size  of  the  liver  in  the  foetus  brings  the  left  lobe 
into  contact  with  the  spleen.  The  relatively  large  suprarenal  capsule  nearly  or  quite 
separates  it  from  the  left  kidney. 

Accessory  spleens2  are  common,  but  they  are  not  all  of  the  same  signifi- 
cance. Some  are  constricted  parts  of  the  spleen  which  have  become  separated, 
mostly  from  the  anterior  border,  and  are  connected  with  the  organ  only  by  fibrous 
tissue.  Others,  found  chiefly  in  the  greater  omentum  near  the  hilum,  are  apparently 
distinct  masses  of  splenic  tissue.  Many  of  them,  however,  have  no  Malpighian 
corpuscles,  are  intermediate  between  the  spleen  and  the  lymph-nodes,  and,  proba- 
bly, are  to  be  classed  as  haemolymph-glands.  They  are  said  to  be  found  some- 
times within  the  pancreas.  It  is  not  impossible  that  certain  irregular  nodules  occa- 
sionally found  on  the  spleen  near  the  hilum  are  due  to  the  fusion  of  such  accessory 
spleens.  Otto  has  seen  twenty-three  accessory  spleens  in  one  body.  They  are 
usually  of  the  size  of  a  pea. 

Surface  Anatomy. — The  relations  of  the  spleen  to  other  organs  have  been 
described,  but  it  should  be  stated  that  the  phrenic  surface  lies  beneath  the  ninth, 
tenth,  and  eleventh  ribs  (sometimes  the  eighth  also),  and  that  its  long  axis  is  that  of 
the  shafts  of  these  ribs.  It  is  important  to  note  that  the  spleen  is  situated  behind  the 
stomach  rather  than  to  the  left  of  it,  so  that  in  general  language  the  organ  is  more  in 
the  back  than  in  the  flank.  The  highest  level  of  the  spleen  is  opposite  the  body  of 
the  ninth  thoracic  vertebra,  and  its  lowest  opposite  that  of  the  first  or  second  lumbar. 
A  line  from  the  top  of  the  sternum  to  the  tip  of  the  eleventh  rib  should  be  entirely 
anterior  to  the  spleen. 

PRACTICAL   CONSIDERATIONS  :    THE   SPLEEN. 

The  spleen  may  be  congenitally  absent,  or  it  may  be  of  extremely  small  size, — 
no  larger  than  a  walnut  ;  or  there  may  be  supernumerary  spleens  connected  with  the 
main  gland  ;  or  there  may  be  nmltiple  spleens  entirely  separate  and  lying  in  the 
folds  of  the  greater  omentum,  the  gastro-splenic  omentum,  or  the  transverse  meso- 
colon.  It  is  conceivable  but  unlikely  that  these  anomalies  may  lead  to  mistaken 
diagnoses. 

The  outline  of  the  normal  spleen  is  difficult  of  accurate  determination  by  either 
palpation  or  percussion  because  (a)  it  is  covered  in  front  by  the  stomach,  the  cardiac 
end  of  which — if  the  stomach  is  distended — completely  overlaps  it  ;  (b~)  posteriorly 
it  is  covered  at  its  lower  portion  by  the  diaphragm  and  by  the  tenth  and  eleventh 
ribs  and  the  thick  muscles  overlying  them,  and  at  its  upper  portion  by  the  same 
muscles,  the  diaphragm,  the  ninth  rib,  the  pleura,  and  the  lung  ;  (r)  inferiorly  it  is 
in  contact  internally  with  the  upper  end  and  part  of  the  outer  edge  of  the  left  kidney, 
and  externally  with  the  splenic  flexure  of  the  colon  ;  (a?)  the  upper  part  of  the 
phrenic  surface  is  occasionally  in  contact  with  the  left  lobe  of  the  liver  (Quain)  ;  (>) 
it  is  the  most  variable  in  both  shape  and  size  of  all  the  abdominal  viscera  ;  (_/")  it 

1  Archiv  f.  mikro.  Anat.,  Bd.  Ivi.,  1900. 

2  Consult  articles  by  Parsons  and  by  Haberer,  just  noted. 


1788  HUMAN   ANATOMY. 

changes  in  position  with  the  movements  of  the  stomach,  having  its  longest  diameter 
vertical  when  the  latter  is  contracted  and  horizontal  when  it  is  distended. 

These  relations  sufficiently  explain  the  difficulty  not  only  in  determining  the 
size  of  the  normal  spleen,  but  also  in  distinguishing  by  percussion  its  abnormal 
enlargement  from  cases  of  colonic  fecal  impaction,  of  tumors  of  the  left  kidney, 
of  large  plastic  exudate  at  the  base  of  the  left  pleura  or  lung,  of  hypertrophic 
cirrhosis  involving  the  left  lobe  of  the  liver,  and  of  certain  growths  of  the  stomach 
or  omentum. 

In  cases  of  hypertrophy  or  of  swelling  of  the  spleen,  as  in  malaria  (  "  ague-cake"  ), 
palpation  is  often  of  more  value  than  percussion,  the  sharp  crenated  anterior  border 
being  recognizable  below  the  tenth  costal  cartilage.  Physiological  increase  in  size 
occurs  during  digestion,  but  pathological  enlargement  may  follow  portal  congestion, 
leukaemia,  malaria,  typhoid,  or  other  infectious  disease,  including  most  forms  of  general 
sepsis,  or  may  result  from  infection  of  the  splenic  substance.  It  may — as  in  some 
malarial  and  leuksemic  cases — so  enlarge  as  to  occupy  most  of  the  abdominal  cavity. 
It  is  then  closely  applied  to  the  parietes,  and  is  not,  like  renal  tumors,  covered  ante- 
riorly by  the  intestines. 

Enlargement  of  the  spleen  in  infants  is  often  due  to  inherited  syphilis,  and  if  it 
occurs  at  the  age  of  two  or  three  months  is  usually  of  that  character.  It  is  of  more 
diagnostic  value  than  enlargement  of  the  liver,  because  that  organ  is  normally  dispro- 
portionately large  in  infancy,  and  because  other  causes  than  congenital  syphilis  lead 
to  its  enlargement. 

In  all  forms  of  enlargement  of  the  spleen  in  children  there  is  said  to  be  more 
relative  encroachment  upon  the  thoracic  cavity  than  in  adults,  owing  to  the  firmer 
support  of  the  phreno-colic  ligament  in  young  persons  (Treves).  Whenever  it  is 
greatly  enlarged,  at  any  age,  it  is  apt  to  push  upward  the  diaphragm  and  compress 
injuriously  the  base  of  the  left  lung  and  the  heart.  In  splenic  tumors,  therefore, 
irregular  cardiac  action  and  dyspnoea  are  often  present  for  mechanical  reasons  as  well 
as  on  account  of  the  associated  anaemia. 

The  normal  movements  of  the  spleen  are  not  so  much  affected  by  respiration  as 
are  those  of  the  liver,  which  is  more  closely  and  extensively  connected  with  the  dia- 
phragm. It  rises  slightly  in  expiration  and  descends  during  inspiration.  It  is 
pushed  down  in  emphysema  and  in  left-sided  empyema,  haemothorax,  or  pneumo- 
thorax.  It  is  pushed  up  by  ascites  or  by  intra-abdominal  new  growths. 

Its  relations  explain  why  abscesses  of  the  spleen  (usually  due  to  septic  emboli,  as 
in  pyaemia  or  septicaemia,  typhoid  fever,  or  ulcerative  endocarditis)  open  spontaneously 
in  the  following  directions:  (i)  Into  the  general  peritoneal  cavity  (the  most  fre- 
quent). (2)  On  the  cutaneous  surface  below  the  costal  margin  anteriorly  or  poste- 
riorly. (3)  Into  the  large  intestine.  (4)  Into  the  left  pleural  cavity.  (5)  Into 
the  left  kidney. 

Movable  spleen  {dislocated,  floating,  wandering  spleen}  occurs  only  in  adults, 
and  is  especially  found  associated  with  some  degree  of  splenic  enlargement — in- 
creasing its  weight — in  persons  with  relaxed  or  flabby  abdominal  walls.  It  is,  there- 
fore, often  found  in  anaemic  multiparae,  as  it  is  held  in  position  normally  not  only  by 
the  phreno-splenic  and  phreno-colic  ligaments,  but  also  by  the  pressure  of  the  other 
abdominal  viscera  due  to  the  general  tonicity  of  the  abdominal  muscles. 

In  such  cases,  after  elongation  of  the  phreno-splenic  ligament,  the  spleen  falls 
forward,  lies  horizontally  with  the  hilum  directed  upward,  and  is  sustained  only  by  the 
gastro-splenic  attachments  and  the  vessels,  thus  drawing  the  stomach  downward  and 
causing  serious  gastro-intestinal  disturbance,  or  possibly,  if  the  vessels  are  twisted 
and  obliterated,  a  fatal  peritonitis  (Shattuck  >. 

In  exceptional  cases  a  movable  spleen  may  reach  the  pelvis. 

I'Yoin  a  movable  kidney  a  wandering  spleen  may  be  distinguished  l>y  the  super- 
ficial position  of  the  latter,  its  shape,  the  disappearance  of  the  spleen  from  its  normal 
position,  and  the  absence  of  urinary  symptoms. 

H'oHHctx  of  the  spleen,  if  posterior,  usually  involve  the  diaphragm  and  the  base 
of  the  left  pleiiral  cavity,  or,  if  higher,  the  lung  itself  :  if  anterior,  the  stomach  may 
In  penetrated.  Ill  gunshot  wounds  the  kidney,  colon,  or  pancreas  may  likewise  be 

involved. 


THE   THYROID    BODY.  1789 

In  fractures  of  the  ninth,  tenth,  or  eleventh  rib  the  fragments  may  lacerate  the 
spleen.  On  account  of  its  great  vasctllarity,  wounds  of  the  spleen  are  serious  and 
often  necessitate  operation,  but  occasionally,  after  small  stab  wounds  or  gunshot 
wounds  from  bullets  of  small  calibre,  spontaneous  recovery  takes  place,  and  has  been 
attributed  (Treves)  to  the  contractility  of  the  muscular  tissue  of  the  splenic  capsule, 
which  narrows  the  wound-track,  enables  it  to  retain  the  blood-clot,  and  thus  stops 
the  hemorrhage. 

The  blood  from  a  wound  of  the  spleen  is  usually  bright  red.  In  wounds  of 
the  liver  it  is  apt  to  be  dark,  if  the  lung  is  wounded  the  blood  is  commonly  frothy, 
and  if  the  stomach  has  been  penetrated  the  blood  is  mixed  with  the  acid  gastric 
contents. 

Rupture  of  the  normal  spleen  is  not  very  frequent,  in  spite  of  its  friability,  on 
account  of  the  way  in  which  it  is  suspended  from  the  diaphragm,  supported  beneath 
by  the  elastic  colon  and — indirectly — the  small  intestine,  and  partially  protected 
anteriorly  by  the  stomach  and  posteriorly  by  the  lung.  When  it  is  enlarged,  on  the 
contrary,  it  extends  beyond  the  region  of  safety,  becomes  more  closely  and  exten- 
sively applied  to  the  parietes,  and  may  be  ruptured  by  blows,  by  falls  from  a  height, 
or  even  by  muscular  violence.  Spontaneous  rupture  can  occur  only  in  cases  of  ad- 
vanced hypertrophy  with  softening  of  the  parenchyma.  The  latter  may  be  ruptured, 
but  the  elastic  capsule  escape.  In  all  these  cases  of  splenic  injury  the  symptoms  of 
localized  intra-abdominal  lesion,  pain,  often  at  first  general,  then  referred  to  the  epi- 
gastrium or  umbilicus,  then  more  marked  in  the  splenic  area,  sometimes  accompanied 
by  nausea  or  vomiting  and  followed  by  rigidity  of  the  left  upper  quadrant  of  the 
abdomen,  immobility  of  the  lower  thorax  on  that  side,  meteorism,  etc.,  plus  the 
symptoms  of  internal  hemorrhage,  will  be  present  to  a  greater  or  less  degree.  They 
have  been  sufficiently  explained  in  the  sections  on  the  intestine,  the  appendix,  and 
the  peritoneum. 

In  operations  on  the  spleen  it  may  be  approached  through  incision  either  at  the 
outer  edge  of  the  left  rectus  muscle  or  in  the  median  line. 

In  splenectomy  great  care  must  be  taken  to  avoid  premature  tearing  or  division 
of  the  large  vessels  contained  within  the  gastro-splenic  omentum  and  lieno-renal 
ligament,  particularly  the  splenic  vein.  The  "pedicle" — omentum  and  vessels — 
may  sometimes  best  be  reached  by  lifting  the  inner  border  of  the  spleen,  and  some- 
times (Warren)  by  pulling  the  spleen  down  from  beneath  the  diaphragm  and  turning 
it  completely  over. 

Next  to  hemorrhage,  the  chief  risk  is  that  arising  from  damage  to  adjoining 
viscera  during  the  separation  of  adhesions,  and  the  relations  of  the  stomach,  pan- 
creas, colon,  and  kidney  should  therefore  be  carefully  borne  in  mind. 

THE   THYROID    BODY. 

This  organ  is  situated  in  the  neck  in  front  and  at  the  sides  of  the  trachea.  It 
is  symmetrical  in  plan,  but  not  usually  in  the  details,  consisting  of  two  lateral  lobes 
connected  by  a  narrow  strip,  the  isthmus,  from  5  mm.  to  2  cm.  in  breadth.  The 
height  of  the  lateral  lobes  ranges  from  3  cm. ,  or  less,  to  twice  as  much  within  normal 
limits.  The  transverse  diameter  of  the  whole  organ  is  6  or  7  cm.  The  weight  is 
from  30—40  gm.  (i— i^j  oz. ),  with  wide  variations.  It  has  the  appearance  of  a 
lobulated  glandular  body,  reddish  yellow  in  color. 

Shape  and  Relations. — Each  lateral  lobe  is  an  irregular  body,  vaguely 
pyramidal  in  form,  which  can  be  properly  studied  only  in  situ.  There  is  an  antero- 
external  surface  which  meets  the  inner  at  a  sharp  border.  The,  inner  surface  is  con- 
cave, being  moulded  over  the  side  of  the  trachea  and  larynx.  These  surfaces  are 
connected  by  a  third,  the  posterior  surface  (usually  improperly  called  a  border),  which 
faces  backward  and  outward,  sometimes  nearly  backward.  The  surfaces  come  to- 
gether above  in  an  apex  over  the  posterior  part  of  the  body,  so  that  the  border  sepa- 
rating the  antero-external  and  the  internal  surfaces  rises  from  the  middle  of  the  body 
obliquely  backward.  The  lower  end  of  the  lateral  lobe  is  thick  and  rounded.  The 
isthmus,  connecting  the  lateral  lobes  below  the  middle,  usually  crosses  the  second  and 
third  rings  of  the  trachea.  Its  anterior  surface  passes  without  interruption  into  the 


1790 


HUMAN    ANATOMY. 


Epiglottis 


Superior  cornu  of 
thyroid  cartilage 


antero-external  surfaces  of  the  lateral  lobes.  The  isthmus  varies  much  in  size, 
and  is  often  more  or  less  incorporated  in  one  of  the  lobes.  In  10  per  cent,  it  is 
absent.1  An  upward  projection,  the  pyramidal  process,  rising  from  either  the  isthmus 
or  one  of  the  lateral  lobes,  and  usually  regarded  as  a  remnant  of  the  median  anlage 
ot  the  thyroid,  is  found  more  or  less  developed  in  probably  half  the  cases.  A  typical 
one  reaches  the  hyoid  bone,  to  the  body  of  which  the  process  is  generally  attached 
either  by  muscle  or  ligament.  It  is  rarely  quite  median,  being  more  frequently  found 
on  the  left.  Statements  as  to  its  frequency  vary  greatly.  Streckeisen  *  says  it  is 

wholly  wanting  in  only  about 

FIG.  1510.  20  per  cent. ;  but,  since  goitre 

is  common  in  Switzerland,  his 
sources  of  information  are  not 
of  the  best.  Ztickerkandl, 
however,  puts  the  occurrence 
of  the  process  at  74  per  cent. 
Gruber,  in  Russia,  found  it  in 
only  40  per  cent.,  and  Mar- 
shall, in  England,  in  43  per 
cent.  We  incline  to  believe 
that  these  latter  figures  rep- 
resent the  more  common  pro- 
portion. 

The  thyroid  lies  beneath 
the  group  of  infrahyoid  mus- 
cles, from  which  it  is  separated 
by  the  middle  layer  of  the 
cervical  fascia.  The  sterno- 
mastoid  muscle  crosses  the 
lower  part  of  the  lateral  lobes. 
The  inner  surface  lies  against 
the  trachea,  the  cricoid  carti- 
lage, and  the  lower  posterior 
part  of  the  wings  of  the  thy- 
roid cartilage.  It  reaches  back 
to  the  oesophagus,  which  it 
touches  on  the  left,  and  some- 
times on  the  right  also.  It 
may  touch  the  lower  part  of 
the  pharynx  on  both  sides. 
The  sheath  of  the  carotid  lies 
against  the  posterior  surface  at 
its  outer  border  and  is  in  part 
external  to  the  organ.  The 
common  carotid  is  usually  be- 
hind the  thyroid  and  the  inter- 
nal jugular  vein  beyond  it. 
This  explains  how  an  enlarged 
gland  insinuates  itself  between 
these  vessels.  Frozen  sections  show  that  often  the  carotid  is  external  rather  than 
posterior  to  the  organ,  but  still  in  close  relation  to  it.  Internal  to  the  carotid 
sheath,  it  rests  behind  against  the  prevertebral  fascia.  The  inferior  thyroid  arteries 
enter  the  lateral  lobes  from  the  inner  side  and  the  superior  thyroid  arteries  from  the 
antero-external.  The  middle  cervical  sympathetic  ganglion  is  behind.  The  inferior 
laryngeal  nerves  lie  at  its  inner  surface,  the  left  one  being  in  actual  contact  with  the 
thyroid  and  the  right  one  at  least  very  close  to  it.  The  sheath  connects  the  thyroid 
body  very  closely  to  neighboring  parts.  It  is  so  firmly  bound  to  the  trachea  as  to 
follow  its  movements.  Median  bands  to  the  cricoid  and  thyroid  cartilages  have  been 

1  Marshall  :  Journal  ot  Anatomy  and  Physiology,  vol.  xxix.,  1895. 
*  Virchow's  Archiv,  Bel.  dii. 


Lobule 


Trachea 


Thyroid  body  in  xitii ;  anterior  aspect. 


THE   THYROID    BODY. 


1791 


distinguished  as  suspensory  ligaments.  A  lateral  ligament  from  the  inner  side  of  the 
lateral  lobe  is  tolerably  well  defined.  It  passes  backward  and  upward  to  the  first  ring 
of  the  trachea,  to  the  cricoid,  and  perhaps  to  the  inferior  horn  of  the  thyroid.  The 
levator  glandule  thyroidea;  is  a  small  muscle  often  found  passing  down  from  the  hyoid 
bone  to  the  capsule.  It  may  or  may  not  be  connected  with  the  pyramidal  process. 


Sterno-thyroid  muscle 


FIG.   1511. 

Sterno-hyoid  muscle 


Left  internal  jugul 
Left  pneumogastr 
Left  com 


mon  caro 


Infer 


Right  internal 
jugular  vein 
Pneumogastric  nerve 
Right  common  carotid  artery 


Infer 


Prevertebral  fascia 


Tra 


Inferior  laryngeal  nerve 
chea 


CEsophagus 
Anterior  part  of  frozen  section  across  neck,  showing  relations  of  thyroid  body. 

Structure.  —  Although  in  principle  corresponding  in  its  development  with  other 
compound  alveolar  glands,  the  thyroid  body  possesses  no  excretory  ducts  and  pre- 
sents peculiarities  in  the  structure  of  its  terminal  compartments.  The  fibre-elastic 
capsule  investing  the  gland  gives  off  septa  which  subdivide  the  organ  into  the  chief 
lobules,  the  latter  being  composed  of  smaller  compartments  separated  by  thin  parti- 
tions of  connective  tissue.  These  subdivisions,  or  primary  lobules,  from  .  5-1  mm. 


FIG.  1512. 


•{      ,     •    '*,!""    <.-3T.  wj?     •>$"'         V> 


Interlobular 
connective-tis- 
sue septum 


"  "I*"'     - 

>^-h  'V,?  "•- 

•••(  >O.  a/'3  •  •'.  •#- 
•i&J '$.;'.   '/Baf...'.;'.'     Acinus  dis- 
:^;«"  V--,/^-::^        tended  with 
«  *  rtjjti  ,'bfjj&'^      colloid 


'' 


.Undistended 
acinus 


•r''^yy~ 
Section  of  thyroid  body,  showing  acini  in  various  degrees  of  distention.     X  100. 


Interactions 
connective 
tissue 


in  diameter,  contain  a  variable  and  usually  large  number  of  terminal  vesicles  or  folli- 
cles which  correspond  to  the  alveoli  or  acini  of  ordinary  glands.  The  delicate  and 
highly  vascular  framework  supporting  the  follicles  consists  essentially  of  fibrous  con- 
nective tissue,  elastic  fibres  being  few  or  entirely  absent. 

The  acini  vary  greatly  in  size  (.050— .200  mm.),  depending  upon  the  amount 


I792 


HUMAN    ANATOMY. 


of  secretion  and  the  distention  of  the  acini.  Their  lining  consists  of  a  single  layer  of 
fairly  regular  polygonal  cells,  about  .010  mm.  in  diameter,  the  height  of  the  cells 
varying  with  the  dilatation  of  the  follicle.  In  young  subjects,  in  whom  the  acini  are 
generally  less  completely  filled  than  in  older  ones,  the  epithelium  of  the  follicles 
approaches  the  columnar  type.  A  similar  condition  is  often  to  be  noted  in  certain 
acini,  even  in  thyroids  in  which  the  usual  distention  affects  the  majority  of  follicles. 
A  distinct  basement  membrane  is  wanting,  the  cells  resting  directly  upon  a  somewhat 
condensed  stratum  of  the  surrounding  connective  tissue.  Since  the  epithelial  lining 
is  the  source  of  the  peculiar  colloid  secretion  of  the  gland,  the  cells  ordinarily  con- 
tain a  variable  number  of  highly  refracting  granules,  particularly  in  the  zone  next 
the  sac.  The  peculiar  substance  or  colloid  commonly  found  within  the  follicles  of 
the  adult  organ  is  regarded  as  a  proteid,  although  its  exact  chemical  characteristics 
are  still  uncertain.  The  consistence  of  this  substance  varies,  being  more  fluid  in 
young  than  in  old  glands.  Its  varying  appearance  within  the  follicles,  as  vacuo- 
lated,  reticular,  or  shrunken,  is  referable  to  the  action  of  reagents,  in  its  natural 
condition  the  secretion  being  homogeneous  and  entirely  filling  the  follicle.  The 
differentiation  of  the  epithelial  lining  of  the  acini  into  chief  and  colloid  cells  (Lang- 
endorff),  as  representing  distinct  elements,  is  doubtful,  since  specific  differences 
probably  do  not  exist. 

Vessels. — The  blood-supply  is  very  generous,  coming  from  two  pairs  of  rela- 
tively large  arteries,  the  superior  thyroids  from   the  external  carotids,  and  the  in- 
ferior  thyroids   from    the 

FIG.   isn.  subclavians.    The  superior 

descend  to  the  top  of  the 
lateral  lobes  and  ramify 
over  the  front  of  the  organ, 
sending  branches  to  the 
interior,  and  sometimes 
meeting  on  the  isthmus. 
The  inferior  arteries  pass 
upward  behind  and  enter 
the  organ  on  its  inner  sur- 
face. Their  relations  to 
the  inferior  laryngeal  nerve 
are  of  practical  impor- 
tance. In  437  observa- 
tions '  the  artery  was  found 
in  front  of  the  nerve  on 
the  right  in  about  41  per 
cent,  and  on  the  left  in 
63  per  cent.  In  over  10 
per  cent,  of  the  cases  the 
branches  were  so  inter- 
laced that  the  relation  was 
uncertain.  It  is  evident 
that  in  enlargement  of  the 
thyroid  body,  with  conse- 
quent enlargement  of  the  arteries,  the  number  of  such  indefinite-  relations  would  be 
very  much  increased,  as  very  minute  branches  would  then  spring  into  importance. 
An  enlarged  tortuous  artery  tends  to  curl  around  the  nerve.  There  was  no  artery  on 
the  right  in  one  case  and  none  on  the  left  in  five  cases  of  this  series.  An  artcria 
tkyroidea  ima  springing  from  the  arch  of  the  aorta  and  ascending  in  the  median  line  is 
occasionally  seen.  From  the  rich  superficial  arterial  plexus  numerous  branches  pass 
along  the  interl. .bular  septa,  following  the  ramifications  of  the  latter  to  the  follicles, 
where  the  arterioles  break  up  into  capillaries.  These  surround  the  follicles  with  close- 
meshed  net -\vorks,  \\hich  are  often  common  to  the  adjacent  sacs,  resembling  the 
capillary  net-works  around  the  pulmonary  alveoli. 

The  veins  are  very  numerous.      Emerging  from  the  organ,  they  form  a  large 

1  Dui-lit:  Anatom.  An/ri-.-r,  Md.  \.,   i$95- 


Acinus  con- 
taining col- 
loid 


Section  of  injected  thyroid  body.    X  46. 


THE    THYROID    BODY.  1793 

plexus  beneath  the  capsule,  from  which  the  blood  escapes  by  three  chief  courses  on 
each  side.  The  superior  thyroid  veins  are  double,  and  follow  the  artery  to  open  either 
into  the  internal  jugular  directly  or  into  the  facial.  They  may  communicate  with 
the  linguals.  The  middle  thyroid  vein,  less  regular,  passes  from  the  side  of  the  lobe 
into  the  internal  jugular,  anastomosing,  as  a  rule,  with  the  pharyngeal  venous  plexus. 
The  interior  thyroid  veins,  generally  two  in  number,  some  5  mm.  in  diameter,  come 
from  the  deeper  part  of  the  organ  and  form  a  rich  plexus  in  front  of  the  trachea  under 
the  middle  layer  of  the  cervical  fascia,  draining,  for  the  most  part,  into  the  left  in- 
nominate ;  but  a  vein  may  end  at  the  angle  of  the  two  innominate  veins.  The  in- 
ferior thyroid  veins  can  be  injected  from  below. 

The  lymphatics  begin  within  the  organ  as  perifollicular  lymph-spaces  ;  from 
these  plexuses  follow  the  interlobular  septa  in  their  course  to  the  exterior,  where  they 
constitute  a  superficial  plexus  from  which  the  lymph  passes  in  all  directions.  Some 
runs  upward  from  the  isthmus  to  small  lymph-nodes  in  front  of  the  larynx,  some 
from  the  sides  to  the  deep  glands  about  the  internal  jugular,  and  some  from  the 
isthmus  and  adjacent  parts  downward  to  pretracheal  lymph-nodes. 

The  nerves  are  derived,  for  the  rnpst  part,  from  the  cervical  sympathetic.  It 
is  probable  that  filaments  are  contributed  by  sympathetic  fibres  running  in  company 
with  the  inferior  laryngeal  and  the  hypoglossal  nerves.  In  addition  to  the  fibres 
destined  for  the  walls  of  the  blood-vessels,  the  terminal  twigs  end  around  the  follicles 
in  close  relation  with  the  glandular  epithelium. 

Development. — The  thyroid  is  developed  from  three  anlages,  an  unpaired 
median  and  two  lateral.  The  median  an/age  (Fig.  1521)  appears  in  embryos  of  from 
3-4  mm.  as  an  epithelial  outgrowth  from  the  anterior  wall  of  the  primitive  pharynx 
in  the  region  of  the  second  visceral  arch,  and  therefore  in  close  relation  with  the 
posterior  part  of  the  tongue.  At  first  possessed  of  a  narrow  lumen,  the  evagination 
soon  loses  its  cavity  and  becomes  a  solid  pyriform  mass,  which  for  a  short  time  is 
connected  with  the  pharyngeal  wall  by  a  delicate  epithelial  strand.  Usually  the  latter 
soon  disappears  and  the  isolated  median  thyroid,  which  meanwhile  rapidly  increases 
as  a  bilobed  mass,  passes  to  the  lower  level  of  the  lateral  anlages.  The  position  of 
the  primary  outgrowth  is  later  indicated  by  the  depression  on  the  tongue,  the  fora- 
men ctzcum,  just  behind  the  apex  of  the  V-row  of  the  circumvallate  papilte.  Occa- 
sionally the  evagination  persists,  and  then  forms  the  thyro-glossal  duct,  a  narrow  tube 
extending  for  a  variable  distance  from  the  tongue  towards  the  thyroid  body.  The 
lateral  anlage  appears  on  each  side  as  an  epithelial  outgrowth  from  the  ventral  wall 
of  the  fourth  pharyngeal  furrow  (Fig.  1521),  the  minute  pocket  soon  becoming  trans- 
formed into  a  sac,  which  early  separates  from  the  pharynx.  The  three  primary  rudi- 
ments grow  ventrally,  and  later,  in  embryos  of  about  20  mm. ,  join  to  form  the  definitive 
thyroid  surrounding  the  larynx.  Of  the  three,  the  median  anlage  contributes  the 
most  important  part  of  the  thyroid  body.  Comparative  embryology  emphasizes  the 
significance  of  the  median  anlage  as  the  thyroid  proper  ;  indeed,  all  participation  of 
the  lateral  rudiments  in  forming  the  organ  in  certain  animals  is  denied  (Verdun). 
The  histogenesis  of  the  thyroid  includes  two  stages,  the  first  being  distinguished  by 
numerous  cylindrical  epithelial  cords  from  which  grow  out  lateral  branches.  The 
second  stage  witnesses  the  fusion  of  these  epithelial  cords  into  a  net-work  the  meshes 
of  which  are  occupied  by  vascular  mesoblastic  tissue.  During  the  third  fcetal  month 
the  epithelial  reticulum  breaks  up  into  masses  corresponding  to  the  follicles  of  the 
thyroid.  These  gradually  acquire  a  lumen  around  which  the  cells  become  arranged 
to  constitute  the  epithelial  lining  of  the  compartments  in  which  later  the  characteristic 
colloid  substance  is  secreted.  The  thyroid  agrees  with  the  parathyroids  and  the 
thymus  in  originating  from  the  walls  of  the  primitive  pharnyx  and,  likewise,  in  devi- 
ating in  its  later  development  from  its  primary  correspondence  to  a  typical  gland. 

Accessory  Thyroids. — Small  detached  bodies  of  the  same  structure  as  the 
thyroid  are  occasionally  found  about  the  hyoid  bone  in  the  median  line,  both  before 
and  behind  and  sometimes  below  it.  They  are  remnants  of  the  median  thyroid  diver- 
ticulum  from  the  primitive  pharynx,  sometimes  represented  by  the  thyro-glossal  duct. 
This  passed  originally  in  front  of  the  hyoid  bone,  thus  accounting  for  suprahyoid 
and  prehyoid  accessory  thyroids.  Those  behind  and  below  the  hyoid  are  probably 
the  result  of  an  upward  or  downward  growth  from  the  primary  diverticulum. 


1794  HUMAN   ANATOMY. 


PRACTICAL   CONSIDERATIONS:    THE   THYROID    BODY 

Congenital  absence  of  the  thyroid  body,  or  its  atrophy  with  loss  of  function, 
occurring  at  any  time  before  puberty,  is  apt  to  be  followed  by  the  interference  with  nu- 
trition and  with  normal  mental  and  physical  development  that  produces  the  condition 
known  as  cretinism.  Similar  atrophic  changes  occurring  later  in  life  cause  wr.iv/-- 
dema,  and  the  same  condition — also  known  as  cachexia  strumipriva — may  be  brought 
about  by  the  complete  excision  of  the  gland.  Calcification  of  the  gland  may  take 
place  in  old  age.  The  isthmus  may  be  congenitally  absent  and. two  separate  lobes  be 
present,  representing  the  originally  distinct  embryonic  lateral  anlages  of  the  organ. 

Accessory  thyroids  may  undergo  hypertrophy  and  form  large  masses  occupying 
the  pleural  or  the  mediastinal  cavity  (Osier- Packard)  ;  or  they  may  develop  at  the 
base  of  the  tongue, — lingual  goitre  ;  or,  on  account  of  their  embryonic  relation  to 
the  thyro-glossal  duct  (which  passes  behind  the  hyoid  bone),  they  may  be  found  in 
the  median  line  of  the  neck  below  or  behind  the  hyoid,  and  may  be  mistaken  for 
growths  of  a  different  character  (page  554): 

The  thyroid  gland  may  be  temporarily  enlarged  in  women  during  menstruation. 

Hypertrophy  of  the  thyroid  gland  (goitre)  may  be  (a)  parenchymatous  when 
it  results  from  a  general  hyperplasia  of  the  gland-tissue  ;  (3)  -vascular,  due  to  a 
great  increase  in  the  size  and  number  of  the  blood-vessels  ;  (c )  cystic,  characterized  by 
the  formation  of  walled-off  cavities  within  the  already  enlarged  gland  ;  (d  )  fibrinous, 
the  connective-tissue  elements  being  in  excess  ;  (^)  exophthalmic  ( Graves' s  disease), 
in  which  the  thyroid  enlargement  is  associated  with  exophthalmos  and  functional 
derangement  of  the  vascular  system  ;  (_/")  adenomatous,  the  hypertrophy  affecting 
one  or  more  lobules  or  the  isthmus.  This  last  form  appears  as  a  one-sided  or  asym- 
metrical swelling,  is  common,  and  is  often  classified  with  tumors  of  the  thyroid, 
rarer  forms  of  which  are  the  cancerous  and  sarcomatous.  It  may  be  noted  that  the 
gland  is  relatively  larger  in  females,  and  that  the  right  lobe  is  larger  than  the  left. 
This  has  been  thought  to  explain  the  greater  frequency  of  goitre  on  the  right  side, 
and  in  women. 

Inflammation  of  the  thyroid  is  rare,  and  usually  occurs  during  typhoid  or  other 
infections,  although  it  is  favored  by  previous  thyroid  disease  or  overgrowth.  The 
tumefaction  which  it  produces  may  cause  acutely  many  of  the  symptoms  brought  on 
more  slowly  by  the  chronic  forms  of  enlargement.  These  symptoms,  so  far  as  they 
have  any  anatomical  bearing,  are  :  (i)  The  swelling  rises  and  falls  with  the  larynx 
during  deglutition.  This  is  due  to  the  attachment  of  the  thyroid  gland  to  the  cricoid 
cartilage  by  the  upward  prolongations  of  its  capsule  known  as  the  suspensory  liga- 
ments and  to  the  subjacent  larynx  and  trachea  by  connective  tissue.  (2)  Dyspna-a. 
The  gland  is  covered  and  its  growth  anteriorly  resisted  by  the  sterno-hyoid  and 
sterno-thyroid  muscles  (Fig.  545),  and,  to  a  less  degree,  by  the  omo-hyoid  and  the 
anterior  border  of  the  sterno-mastoid.  Its  forward  progress  is  also  resisted  by  the 
pretracheal  layer  of  the  cervical  fascia.  Its  close  relation  to  the  trachea,  therefore, 
renders  the  latter  subject  to  direct  pressure,  especially  in  the  firmer  forms  of  bilateral 
enlargement,  or  in  those  adenomata  which  begin  in  the  isthmus  or  lie  between  the 
trachea  and  the  sternum.  In  the  unilateral  forms  the  trachea  may  be  displaced  to 
one  side.  (3)  Headache,  vertigo,  cyanosis,  and  cpistaxis.  The  relation  of  the 
outer  border  of  the  thyroid  to  the  carotid  sheath  explains  the  disturbance  of  the  cir- 
culation in  the  carotid  and  internal  jugular  (either  through  direct  pressure  or  by 
deflection  of  the  vessels  outward)  and  accounts  for  these  phenomena.  (4)  Hys- 
phagia  is  relatively  rare,  but  may  occur  as  the  result  of  pressure  upon  the  upper 
< MK!  of  the  gullet  or  the  lower  portion  of  the  pharynx.  It  is  more  common  in  left- 
sided  goitres,  owing  to  the  curvation  of  the  oesophagus  towards  the  left.  As  a  great 
rarity  the  isthmus  of  the  gland  is  found  between  the  trachea  and  oesophagus  (  Burns  ). 

(5)  Hysphonia,  or  aphonia,  due  to  pressure  upon  the  recurrent  laryngeal   nerves. 

(6)  Pulsation  or  bruit.      These  may  be  apparent,  and  caused  by  the  close  relation  of 
the  enlargement  to  the  common  carotid  artery,  or — much  more  rarely — real,  and 
due  to  the  relatively  enormous  bloed-supply  of  the  vascular  form  of  goitre,  the  thyroid 
with  its  four  constant  arteries  and  occasional  fifth  one  (the  thyroidea  inia, — 10  per 


THE   PARATHYROID   BODIES. 


1795 


cent,  of  cases)  being'  normally  one  of  the  most  vascular  structures  of  the  body. 
They  are  most  common  in  the  exophthalmic  form.  (7)  The  tremor,  tachycardia, 
and  protrusion  of  the  eyeballs  seen  in  Graves' s  disease  in  association  with  thyroid 
enlargement  have  no  satisfactory  anatomical  explanation,  although  the  close  relation 
of  the  sympathetic  nerve  and  middle  cervical  sympathetic  ganglion  to  the  inferior 
thyroid  artery,  the  distribution  of  their  vasomotor  fibres  to  the  thyroid  vessels,  and 
of  other  associated  fibres  to  the  ocular  apparatus,  and  their  possible  central  connec- 
tion— "  probably  in  the  medulla"  (Treves) — have  been  invoked  to  explain  the  phe- 
nomena of  this  form  of  goitre. 

Operations  on  thyroid  enlargements  vary  with  the  character  of  the  latter. 

In  the  adenomatous  and  cystic  varieties,  after  division  of  the  capsule  of  the 
gland,  the  tumor  or  the  cyst  may  generally  be  shelled  out  with  the  finger  or  by  blunt 
dissection  (enucl cation).  Under  these  circumstances  only  some  superficial  veins 
may  require  ligation,  although  free  bleeding  may  occur  from  the  intrinsic  vessels  of 
the  gland.  In  most  of  the  other  varieties  of  goitre  the  greater  part  of  the  growth 
should  be  removed  (excision,  thyroidectomy).  This  should  always  be  partial, — 
i.e.,  a  portion  of  the  gland  should  be  left  in  place  with  sufficient  vascular  connection 
to  insure  its  vitality. 

In  excision  the  skin  platysma  and  cervical  fascia  should  be  freely  divided  and 
the  sterno-hyoids  and  thyroids  retracted  or  divided  ;  after  its  anterior  surface  has 
been  well  exposed  the  growth  is  first  loosened  externally, — as  it  will  be  found  fixed 
above  by  the  superior  thyroid  vessels,  below  by  the  inferior  thyroids,  and  internally 
by  the  isthmus, — the  vessels  separately  ligated,  great  care  being  taken  to  avoid  the 
recurrent  laryngeal  nerve  when  the  ligature  is  applied  to  the  inferior  thyroid  artery, 
the  posterior  surface  dissected  from  the  larynx,  trachea,  and  other  underlying 
structures,  and  the  growth  removed. 


FIG.  1514. 


THE   PARATHYROID   BODIES. 

These  organs,  the  epithelial  bodies  of  many  authors,  are  small  elliptical  masses 
situated  near  the  thyroid,  which  formerly  were  mistaken  either  for  accessory  thy- 
roids or  for  lymphatic  nodules.  They  arise  from  the  posterior  wall  of  the  third  and 
fourth  pharyngeal  pouches,  and  thus  differ  from  the  thyroid  body  in  origin  as  well 
as  in  structure.  They  are  6  or  7  mm.  long,  3  or  4  mm. 
broad,  and  1.5  or  2  mm.  thick.  The  length  may  be  as  much 
as  15  mm.  "They  are  always  separated  from  the  thyroid  by 
the  capsule.  Most  frequently  the  parathyroids  exist  as  two 
pairs  on  each  side  ;  their  disposition,  however,  may  be 
asymmetrical,  in  some  cases  as  many  as  four,  in  others  none, 
lying  on  one  side.  The  position  of  the  siiperior pair  is  the 
more  constant.  According  to  Welsh,1  they  lie  on  the  pos- 
terior wall  of  the  oesophagus,  about  the  level  of  the  lower 
edge  of  the  cricoid  cartilage,  immediately  internal  to  the 
posterior  border  of  the  lateral  lobe  of  the  thyroid  and  in 
front  of  the  prevertebral  fascia.  They  are  always  behind 
the  lateral  thyroid  ligament,  unless,  as  sometimes  happens, 
they  are  placed  so  high  or  so  low  as  to  have  no  relation  with 
it.  The  inferior  pair  is  lower  and  more  anterior  than  the 
superior,  their  position  being  less  constant.  Sometimes 
they  lie  against  the  side  of  the  trachea  near  the  ends  of 
the  rings,  under  cover  of  the  lower  part  of  the  thyroid 
lobes  ;  sometimes  they  are  found  in  a  corresponding  rela- 
tion to  the  windpipe,  but  much  lower,  so  as  to  have  no 
relation  with  the  thyroid  ;  occasionally  they  lie  on  the  front 
of  the  trachea  below  the  thyroid.  The  lower  pair  are  always  below  the  inferior 
thyroid  arteries. 

Structure. — Each  organ  is  invested  by  a  thin  fibrous  capsule  and  subdivided 
into    ill-defined  lobules   by  a  few  delicate  septa  which  support  the  blood-vessels. 
1  Journal  of  Anatomy  and  Physiology,  vol.  xxxii.,  1898. 


Diagram  showing  more 
usual  positions  of  parathyroid 
bodies,  seen  from  behind,  sp, 
superior  pair,  lying  at  level  of 
cricoid  cartilage  (cc)  ;  ip,  in- 
ferior pair;  th,  lateral  lobe  of 
thyroid  body  ;  />k,  pharynx  ;  ce, 
oesophagus  ;  ita,  inferior  thy- 
roid artery.  (After  li'elsh.) 


1796  HUMAN   ANATOMY. 

The  gland-tissue  consists  of  closely  placed  polygonal  epithelial  cells,  about  .010  mm. 
in  diameter,  varyingly  disposed  as  continuous  masses  or  imperfectly  separated  cords 
and  alveoli.  The  cells  possess  round  nuclei  which  contain  chromatin  reticula.  The 
cells  are  surrounded  by  a  honey-comb  of  delicate  membranes,  fibrous  tissue  appear- 
ing only  in  the  immediate  vicinity  of  the  larger  blood-vessels  and  not  between  the 
epithelial  elements.  The  latter  lie  against  the  endothelial  lining  of  the  relatively 
wide  and  numerous  capillaries,  the  attenuated  membrane  of  the  intercellular  honey- 
comb alone  intervening.  While  admitting  the  independence  of  the  parathyroids  as 

FIG.  1515. 

/>•  c 


* . 

*   •       *"      ~   ••  ^•••^••••••••v 

Sections  of  human  parathyroid  bodies,  showing  different  types  of  structure.      .!,  ptmi-ipal  ix-lls  an 
uniform  continuous  masses;  B,  broken  up  into  lobules  by  vascular  septa  (v) ;  C,  disposed  as  acini,  some  of  whic 
contain  colloid  (c).     X  200.     (After  Welsh.) 

distinct  organs,  as  now  established  by  both  anatomical  and  physiological  investiga- 
tions,1 opinions  differ  as  to  their  histological  relations.  Schaper2  and  others  incline 
to  the  view  advanced  by  Sandstroem,  that  the  parathyroids  correspond  in  structure 
to  the  immature  and  undeveloped  thyroid.  Welsh,  on  the  contrary,  denies  this 
resemblance  and  points  out  the  close  similarity  to  the  anterior  lobe  of  the  pituitary 
body,  in  both  organs  colloid-containing  alveoli  being  occasionally  present. 

The  arteries  distributed  to  the  parathyroids  are  derived  from  the  branches  sup- 
plying the  thyroid  body.  Regarding  the  lymphatics  and  the  nerves  little  is  known  ; 
the  latter  are  chiefly  sympathetic  fibres  destined  for  the  walls  of  the  blood-vessels. 

THE   THYMUS   BODY. 

The  thymus  is  apparently  an  organ  of  service  to  the  nutrition — possibly  blood- 
formation —  of  the  foetus  and  infant,  since  it  usually  reaches  its  greatest  size  at  about 
the  end  of  the  second  year,  having  grown  since  birth  fairly  in  proportion  to  the 
body.  It  continues  for  some  years  to  enlarge  in  certain  directions  and  to  dwindle  in 
others  ;  coincidently  deposits  of  fat  appear  and  it  gradually  degenerates.  When  in 
its  prime  it  is  moderately  firm  and  of  a  pinkish  color  ;  later  it  becomes  very  friable 
and  resembles  fat  and  areolar  tissue. 

Shape  and  Relations. — The  appearance  of  the  thymus  is  that  of  a  glandular 
organ.  It  is  surrounded  by  a  fibrous  capsule  which  sends  prolongations  among  the 
lobules.  It  is  situated  beneath  the  upper  part  of  the  sternum,  rising,  when  largest, 
perhaps  2  cm.  into  the  neck,  descending  to  about  the  fourth  costal  cartilages,  excep- 
tionally as  far  as  the  diaphragm.  The  organ  is  thickest  above,  where  it  rests  on  the 
pericardium,  and  descends  in  front  of  the  latter  in  two  flattened  lobes,  more  or  less 
distinct,  which  grow  thinner  and  sometimes  diverge  below.  These  are  separated  by 
a  layer  of  fibrous  tissue  which  enters  obliquely  from  the  front  in  such  a  way  that 
above  the  left  lobe  overlaps  the  other.  The  lobes  are  generally  of  unequal  si/e,  the 
left  one  being  more  often  the  larger.  Sometimes  the  lobes  arc  fused,  and  there  may 
be  a  third  one  between  them,  such  variations  merely  implying  irregularities  of  the 
fibrous  septa.  The  thymus  lies  in  front  of  and  above  the  pericardium,  and  against 

1  A  critical   n-viru  <>t  tin-  relations  of  the  epithelial  organs  derived  from  the  pharyogeal 
pouches  is  given  by  Kohn  in  Merkel  and  Bonnet's  Krgebnisse,  lid.  i\.,  1X99. 
'Archiv  f.  mikro.  Anat.  u.  Kntwick.,  Bd.  xlvi.,  1X95. 


THE   THYMUS    BODY. 


1797 


the  aorta  and  the  pulmonary  artery  after  they  have  emerged  from  the  heart-sac.  It 
is  in  contact  with  a  large  part  of  the  arch  of  the  aorta,  and  is  grooved  on  the  posterior 
surface  by  the  innominate  veins  and  the  superior  vena  cava.  If  strongly  developed, 
its  highest  Pal"t  may  rest  on  the  trachea  and  even  on  the  oesophagus  where  this  tube 
appears  on  the  left  of  the  former.  It  extends  laterally  on  each  side  into  the  interval 
between  the  pericardium  and  the  pleura.  At  the  time  of  its  greatest  size,  a  hori- 
zontal section  in  this  region  shows  the  thymus  as  a  thick  crescent  (Fig.  1518),  which 
becomes  thinner  as  the  organ  atrophies.  Behind  the  very  top  of  the  sternum  its  out- 

FIG.  1516. 


Common  carotid  artery. 
Pneumogastric  nerve 

Internal  jugular 
vein 


I  rib 


Larynx 
Thyroid  body 


uspensory  ligament 

Trachea 


Left  lobe  of 
thymus 


Dissection  of  new-born  child,  showing  thyroid  and  thymus  bodies  in  situ. 

line  on  section  is  roughly  quadrilateral.  One  or  more  fibrous  bands  from  the  thyroid 
body  to  the  capsule  of  the  thymus  are  known  as  the  suspensory  ligaments.  The 
internal  mammary  vessels  run  in  front  of  it. 

Weight  and  Changes. — According  to  Friedleben,  the  average  weight  of  the 
thymus  at  birth  is  13. 75  gm. ;  the  statements  of  authors,  however,  vary  widely,  Sappey 
giving  3  gm.  and  Testut,  from  twenty  observations,  an  average  of  5  gm.  When  heavi- 
est, about  puberty  according  to  Hammar,  its  average  weight  is  37.52  gm.  Atrophy 
and  the  replacement  of  thymus  tissue  by  fat  set  in  while  growth  in  length  is  still  pro- 


1798 


HUMAN    ANATOMY. 


Groove  for 
left  innominate  vein 


gressing  ;  this  increase  is  said  to  continue  even  after  puberty,  the  organ,  how- 
ever, becoming  thinner  and  softer.  Although  later  almost  completely  replaced  by 
adipose  and  connective  tissue,  the  thymus  never  entirely  disappears,  remains  of  its 

tissue  being  present  even  in  extreme 

FIG.  1517.  old  age  (Waldeyer).        Cntil    about 

twenty  years  the  organ  is  usually 
readily  found.  In  ordinary  dissec- 
tions it  is  not  easily  recognized  in  mid- 
dle age,  although  still  clearly  shown 
in  frozen  sections.  Occasionally  a 
well-preserved  thymus  persists  in  the 
adult  ;  on  the  other  hand,  it  may 
suffer  atrophy  very  early  in  child- 
hood. 

Structure .  —  The  histological 
character  of  the  thymus  completely 
changes  during  its  development,  since 
it  begins  as  an  epithelial  outgrowth 
from  the  third  pharyngeal  pouch,  for 
a  time  attains  the  nature  of  a  tubo- 
alveolar  gland,  and  later  permanently 
assumes  the  type  of  a  lymphoid  organ. 
Externally  the  thymus  is  invested 
by  a  loose  fibro-elastic  capsule,  from 
which  septa,  rich  in  blood-vessels,  pass  towards  the  interior  and  subdivide  the  organ 
into  a  number  of  indefinite  lobes.  The  latter  are  broken  up  into  small,  almost  spheri- 
cal lobules,  which  correspond  to  lymph-nodules,  and  consist,  therefore,  of  a  denser 
cortical  and  looser  medullary  zone,  although  these  are  not  sharply  defined  from  each 
other. 

The  cortical  substance  presents  histological  characteristics  resembling  those  of 
dense  lymphoid  tissue, — closely  packed  lymphocytes  lying  within  the  narrow  meshes 
of  the  supporting  reticulum.  The  latter  consists' of  stellate  anastomosing  cells. 


Posterior  aspect  of  thymus  body  hardened  in  situ. 


II  rib-cartilage 


FIG.  1518. 

Sternum 


II  rib-cartilage 


Left  lung 


III  rib 


/          1 —  — v —  \ 

IV  rib        Head  of  IV  rib          Head  of  IV  rib  IV  lib 

Transverse  section  of  body  at  level  of  fourth  thoracic  vertebra  ;  from  child  of  about  one  year 

In  addition  to  the  usual  elements,  eosinophilic  cells  ;m-  t<>un<l  throughout  the 
cortex  particularly  in  the  neighborhood  of  the  capillaries.  According  to  J. 
Schaffer,  the  cortex  of  the  thymus  contains  nucleated  and  other  developmental 


THE  THYMUS  BODY. 


1799 


stages  of  red  blood-cells,  and  therefore  must  be'regarded,  at  least  exceptionally,  as  a 
blood-forming  organ.      This  function,  however,  is  denied  by  Hammar. 

The  medullary  substance,  although  varying  in  its  details  according  to  the  gen- 
eral condition  of  the  organ,  consists  of  a  supporting  framework,  composed  of 
brancing  cells,  within  the  meshes  of  which  lie  small  mononuclear  lymphocytes,  less 
frequently  polymorphonuclear  leucocytes.  Occasional  eosinophiles  are  seen  along 
the  blood-vessels,  as  well  as  multinuclear  giant  cells.  Islands  or  cords  of  flattened 
elements,  regarded  by  many  as  epithelial  in  nature  and  derivatives  of  the  primary 
entoblastic  anlage,  also  occur.  The  medulla  of  the  fully  developed  thymus,  or  of 
the  organ  just  entering  upon  its  retrogression,  contains  numerous  spherical  or  ellip- 
soidal masses  of  concentrically  disposed,  flattened  modified  cells.  These  bodies  are 
the  corpuscles  of  Hassall,  which  were  formerly  regarded  as  the  remains  of  the  epithe- 
lium of  which  for  a  time  the  thymus  was  composed.  Found  only  in  the  medulla, 
they  vary  greatly  in  form  and  size,  sometimes  being  simple  spherical  masses  (.012- 
.020  mm.  in  diameter),  at  others  composite  bodies  (.1  mm.  or  more  in  diameter) 
consisting  of  aggregations  of  small  groups.  The  centre  of  the  concentric  bodies 
often  consists  of  slightly  glistening,  homogeneous,  or  granular  substance  which  is 


FIG.  1519. 


Lobule 


Blood- 
vessels, 
injected 


Medulla 


Cortex 


Cortex 


Transverse  section  of  thymus  body  of  child,  showing  general  arrangement  of  lobules.    X  25. 


albuminous,  not  fatty,  in  nature.  According  to  Hammar,  the  corpuscles  of  Hassall 
arise  from  hypertrophied  reticulum  cells,  the  latter  being  directly  derived  from  the 
primary  epithelium. 

Vessels. — The  arteries  are  chiefly  from  the  internal  mammaries,  but  small 
branches  may  come  from  the  thyroid  as  well  as  from  the  pericardial  arteries.  The 
arteries  gain  the  interior  of  the  lobule,  and  break  up  into  capillaries  along  the  junc- 
tion of  the  cortical  and  medullary  zones.  The  cortex  is  provided  with  a  rich  capil- 
lary net-work,  the  medulla  being  relatively  poorly  supplied.  The  veins  between  the 
lobules,  which  chiefly  drain  the  capillaries,  unite  to  form  the  larger  trunks  carrying 
the  blood  from  the  organ.  These  run  in  many  directions,  the  most  important  being 
tributary  to  the  left  innominate.  The  lymphatics  are  large  and  numerous,  and  empty 
into  nodes  behind  the  sternum.  Traced  into  the  interior  of  the  organ,  the  lym- 
phatics follow  the  connective-tissue  septa  to  the  lobules,  around  which  they  form  a  rich 
plexus.  Although  it  is  probable  that  the  lymph-paths  come  into  close  relations  with 
the  thymus-tissue,  the  existence  of  intralobular  passages,  corresponding  to  lymph- 
sinuses,  has  not  been  established. 


i8oo 


HUMAN   ANATOMY. 


.Capsule 


Cortex 


The  nerves  are  small  and  come  from  the  sympathetic  and  the  vagus.  They 
are  traceable  along  the  arteries  and  connective-tissue  septa,  and  end  chiefly  in  the 
walls  of  the  blood-vessels.  Bovero  has  described  terminal  filaments  which  pass  from 

the  interlobular  plexuses  into 
FIG.  1520.  the  medulla. 

Development.  --  The 
thymus  proper  originates  from 
a  paired  anlage  (Fig.  1521) 
which  appears  as  an  epithelial 
outgrowth  from  the  ventral 
wall  of  the  third  pharyngeal 
pouch.  From  this  results  a 
long  cylindrical  mass  of  closely 
packed  epithelial  cells  which 
grows  downward  and  en- 
closes a  narrow  lumen.  The 
lower  end  of  this  mass  in- 
creases in  size  by  the  formation 
of  solid  acinous  outgrowths 
resembling  those  of  an  im- 
mature tubo-alveolar  gland. 
Coincident  with  the  downward 
extension  of  the  organ,  the 
upper  cylindrical  portion  grad- 
ually assumes  the  alveolar  con- 
dition until  the  entire  thymus 
acquires  a  lobulated  character. 
During  these  changes  histo- 
logical  alterations  take  place, 
the  epithelial  masses  becoming 
invaded  by  ingrowing  lym- 
phoid  tissue  and  blood-vessels 
and  broken  up  into  irregular  islands.  The  latter  become  smaller  and  less  conspicu- 
ous as  the  lymphoid  character  of  the  thymus  becomes  more  predominant.  The  cor- 
puscles of  Hassall  represent  derivatives  of  the  primary  epithelial  elements.  For  a 
time  the  two  originally  distinct  anlages  develop  independently  ;  later  they  come  into 
close  contact  in  the  mid-line,  and  form  the  single  irregular  organ  the  bilateral 


/'\^2#£V:-$  %Y.  •/.V/'*'  '*'  ' 


Hassall 
within  medulla 


Section  of  thymus  body,  showing  details  of  cortical  and  medullary 
substance.    X  200. 


FIG.  1521. 


^L^T^^  Jf~'-v 


I 


Reconstructions  of  developing  thyroid,  thvmus,  and  parathyroid  bodies  in  embryos  of  14  mm.  (.1 )  and  of  26  mm. 
(B).  nit.  median  thyroid;  //,  lateral  thyroid";  tv,  thymus;  t,  thyroid  ;  />',  p",  superior  and  inferior  parathyroids; 
vc,  vena  cava  superior  ;  a,  aorta.  (  Tournrux  and  l-'erdun.) 


derivation  of  which  is  indicated  by  the  connective  tissue  separating  the  right  and  left 
divisions.  The  upper  ends  of  the  latter  are  often  continued  as  far  as  the  thyroid 
as  lateral  processes.  Subsequent  to  the  second  year  regression  sets  in,  and  the 


THE    SUPRARENAL    BODIES. 


1 80 1 


Thymus 
tissue 


thymus  structure  is  largely  replaced  by  fibrous  and  adipose  tissue,  vestiges  of  the 
characteristic  tissue,  however,  persisting  (Fig.  1522). 

In  addition  to  the  chief  anlage  from  the  third  pharyngeal  pouch,  a  rudimentary 
outgrowth  occurs  from 

the  ventral  wall  of  the  FIG.  1522. 

fourth  one,  external  to 
the  origin  of  the  lateral 
thyroid.  According  to 
Groschuff,1  this  anlage 
may  persist  in  man  as 
\\~\eparathvmus,  a  small 
body  which  occurs  in 
close  association,  or 
even  encloses,  the  para- 
thyroid derived  from 
the  dorsal  wall  of  the 
fourth  pouch.  The  lat- 
ter, -therefore,  corre- 
sponds to  the  third 
pharyngeal  pouch  in 
giving  rise  to  both  a 
parathyroid  and  a  thy- 
mus ;  in  addition  it  pro- 
duces the  lateral  thy- 
roid anlage. 

According  to  Beard, 

~  °,  ,  Section  of  thymus  body  of  man  of  twenty-eight,  showing  invasion  and  replace- 

rreiiaut,       and      Others,  ment  of  thymus  tissue  by  fat.     X  20. 

the    transformation    of 

the  thymus  into  a  lymphoid  organ  occurs  as  the  direct  conversion  of  its  original 
epithelial  elements  into  lymphocytes  and  not  by  invasion  of  pre-existing  lymphoid 
cells.  While  accepting  such  origin  for  the  reticulum,  Hammar2  regards  the  lymph- 
ocytes as  entering  from  without. 


Fat  V 


Thymus  tissue 


THE    SUPRARENAL    BODIES. 

These  are  a  pair  of  cocked-hat-shaped  bodies  situated  at  the  back  of  the  abdo- 
men, on  the  inner  aspect  of  the  upper  ends  of  the  kidneys.  Each  has  a  base,  or 
renal  surface,  corresponding  to  the  bottom  of  the  hat,  and  an  anterior  and  a  posterior 
surface,  the  basal  borders  of  which  are  concave  and  look  outward  and  downward. 
There  are  an  upper  and  a  lower  angle  at  either  end  of  the  base.  The  inner  convex 
border  tends,  especially  in  the  right  capsule,  to  present  a  third  angle  rather  above 
the  middle.  Thus  the  right  one  is  more  triangular  and  the  left  more  crescentic. 
They  may  be  6  or  7  cm.  long  and  about  half  as  broad.  The  thickness  does  not 
probably  often  exceed  2  cm.  The  base  is  concave,  adapted  to  the  kidney,  of  which 
it  overhangs  the  anterior  surface.  The  lower  end  is  much  thicker  than  the  upper. 
The  concavity  deepens  above  into  almost  a  furrow  filled  by  areolar  tissue.  The  an- 
terior surface  bears  a  deep  fissure,  the  hilum,  in  the  main  parallel  with  the  base,  sub- 
dividing it  into  two  approximately  equal  regions.  The  posterior  surface  is  con- 
siderably smaller  than  the  anterior,  owing  to  the  projection  of  the  latter  over  the 
front  of  the  kidney.  It  also  presents  a  fissure  nearly  parallel  with  the  base-line,  but 
neither  extending  the  whole  length  of  the  organ  nor  so  deep  as  the  front  one. 

In  color  the  suprarenals  are  of  a  dirty  yellowish  brown  and  more  or  less  pig- 
mented.  They  weigh  6  or  7  gm.  The  left  one  is  usually  the  larger. 

Relations. —The  basal  surfaces  are  on  the  kidneys.  The  posterior  surfaces 
are  against  the  diaphragm.  The  anterior  surface  of  the  right  capsule  has  its  lower 
inner  part  behind  the  inferior  vena  cava.  The  part  of  the  lower  end  near  this  may  be 
behind  the  duodenum.  The  remainder  is  in  contact  with  the  liver.  The  highest 

1  Anatom.  Anzeiger,  Bd.  xvii.,  1900. 
1  Ibid.,  Bd.  xxvii.,  1905. 


1802 


HUMAN   ANATOMY. 


part  is  between  the  non-peritoneal  posterior  surface  of  the  liver  and  the  abdominal 
wall.  This,  of  course,  like  the  two  preceding  areas,  has  no  peritoneum.  The  rest 
lies  in  contact  with  the  lower  surface  of  the  liver,  and  is  coated  by  the  peritoneum  of 
the  posterior  abdominal  wall.  The  anterior  surface  of  the  left  capsule  is  nearly  or 
quite  peritoneal,  resting  against  the  stomach,  the  spleen,  and  the  tail  of  the  pancreas. 
Structure.  —  The  suprarenal  body  is  invested  by  a  thin,  but  fairly  strong, 
fibrous  capsule.  Section  across  the  thicker  parts  of  the  organ  displays  an  outer  zone, 
or  cortex  (.25-1.20  mm.  in  thickness),  which  surrounds  the  central  medulla.  Where 
thinnest,  as  towards  the  borders,  the  medulla  is  reduced  to  a  narrow  zone  and  may  be 
entirely  wanting  ;  where  best  developed,  as  in  the  middle  of  the  organ,  it  may  attain 
a  thickness  of  over  3  mm.  The  cortex  is  usually  of  a  dirty  yellow  color,  presenting 

FIG.  1523. 

Crura  of  diaphragm 


Capsular  vein  in  groove 
for  vena  cava 


Hepatic  surface 


Peritoneal  surface 
Inferior  vena  cava  _  j 

Right  kid 


Cceliac  artery 

L_  Superior  mesenteric  artery 


Capsular  vein 
emerging  from  hilum 


Left  renal  vein 


.Left  kidney 


Diaphragmatic  surfa 


Anterior  aspect  of  suprarenal  bodies  hardened  in  situ. 

FIG.  1524 


Renal  surface 


Diaphragmatic  surface 


Renal  surface 


Left  Right 

Posterior  aspect  of  suprarenal  bodies  shown  in  preceding  figure. 


next  the  medulla  a  narrow  darker  zone  of  varying  shades  of  brown.  The  medulla  is 
of  a  grayish  tint  and  generally  lighter  in  color  than  the  cortex.  Its  exact  tint,  how- 
ever, varies  with  the  amount  and  condition  of  the  contained  blood,  when  engorged 
with  venous  blood  appearing  dark.  In  consistence  the  medulla  is  less  resistant  and 
more  friable  than  the  cortex. 

The  cortical  substance  consists  of  a  delicate  framework  of  connective  tissue,  con- 
tinuous with  and  prolonged  imvanl  from  the  capsule,  in  the  meshes  of  which  lies  the 
glandular  epithelium.  The  arrangement  of  the  latter,  although  generally  columnar, 
varies  at  different  levels,  three  zones  being  distinguished  within  the  cortex.  The 
zomt  x/flnirnt/osti  lies  next  the  capsule,  and  consists  of  the  somewhat  tortuous  or 
coiled  groups  of  cells.  The  -:onn  faxciculata  forms  the  chief  part  of  the  cortex,  and 
maintains  the  radial  disposition  of  the  cell-columns.  The  zona  rcticularis,  next  the 


THE   SUPRARENAL   BODIES. 


1803 


w  Capsule 


Cortex 


medulla,  includes  the  net-works  of  epithelial  elements  formed  by  the  union  of  the  cyl- 
inders. The  cells  throughout  the  cortex  are  very  similar,  being  rounded  polygonal 
elements  .01 5-. 020  mm.  in  diameter,  and  very  often  contain  fat  granules.  Those 
composing  the  zona  fasciculata  are  largest,  while  those  within  the  reticular  zone  are 
more  or  less  pigmented  and  responsible  for  the  darker  tint  of  this  portion  of  the  cortex. 

The  medullary  substance  consists  chiefly  of  net-works  composed  of  anastomosing 
cords  of  epithelial  cells  from  .020— .036  mm.  in  diameter;  in  addition  there  are  numer- 
ous blood-vessels,  particularly  veins,  and  many  bundles  of  nerve-fibres  with  ganglion- 
cells.  The  protoplasm  of  the  medullary  cells  is  finely  granular  and  possesses  an 
especial  affinity  for  chromic  acid  and  its  salts,  staining  yellow  or  brown.  They 
vary  from  polyhedral  to  columnar  in  form,  and  often  border  large  blood-  and  lymph- 
spaces.  The  cells  of  the  medulla  are 

more  prone  to  undergo  post-mortem  FIG-  I525- 

change  than  those  of  the  cortex. 

Vessels. — The  chief  arteries 
supplying  the  organ-  are  the  three 
suprarenal  or  capsular  arteries, — the 
middle  from  the  aorta  and  the  su- 
perior and  inferior  from  the  phrenic 
and  renal  arteries  respectively.  They 
break  up  into  a  dozen  or  more  fine 
branches  before  reaching  the  organ, 
which  they  enter  at  various  points, 
some  penetrating  directly  into  the 
medulla,  others  terminating  in  the 
cortex.  The  latter  form  a  superficial 
capillary  net-work  within  the  cap- 
sule, from  which  continuations  pass 
between  the  cortical  cell-columns, 
around  which  they  constitute  capil- 
lary net-works.  The  medulla  is  di- 
rectly supplied  by  arteries  destined 
for  the  interior  of  the  organ.  These 
soon  break  up  into  capillaries  which 
surround  the  medullary  cords  and 
pass  over  into  an  unusually  rich 
plexus  of  veins.  The  latter  claim  as 
tributaries  the  venous  radicles  of  the 
zona  reticularis  and  impart  to  the 
medulla  in  general  a  spongy  charac- 
ter. The  veins  form  a  rich  plexus 
about  the  organ,  communicating 
freely  with  those  of  the  kidney.  The 
chief  vein  of  the  right  suprarenal 
passes  into  the  inferior  vena  cava  and  that  of  the  left  one  into  the  renal.  The  lym- 
phatics are  numerous,  the  chief  trunks  accompanying  the  arteries.  In  addition  to  the 
superficial  net-works  in  the  outer  part  of  the  cortex,  the  medulla  contains  many 
deeper  lymphatics  in  the  vicinity  of  the  larger  veins. 

Nerves. — The  very  rich  supply  is  derived  principally  from  the  solar  and  renal 
plexuses.  The  number  of  medullated  fibres  would  imply  that  many  come  through 
the  splanchnic  nerves.  Branches  probably  come  also  from  the  vagus  and  the  phrenic 
(Bergmann).  Within  the  capsule  lies  a  superficial  plexus  from  which  small  bundles 
of  nerve-fibres  enter  the  cortex,  between  the  cell-columns  of  which  they  form  plexuses, 
chiefly  for  the  walls  of  the  blood-vessels.  The  greater  number  of  the  nerves,  how- 
ever, pass  to  the  medulla,  where  they  unite  into  coarse  plexuses,  from  which  finer 
twigs  are  distributed  to  the  vessels  and  the  cords  of  medullary  cells  surrounding  the 
veins.  Dogiel  has  traced  the  terminal  filaments  between  the  epithelial  elements. 
Numerous  ganglion-cells  lie  within  the  medulla.  Sometimes  they  occur  in  groups 
along  the  larger  nerve-bundles  ;  at  other  times  they  are  encountered  as  isolated  ele- 


Capsule 

Section  of  suprarenal  body  including  entire  thickness  of  organ, 
showing  general  arrangement  of  cortex  and  medulla.     X  27. 


1804 


HUMAN    ANATOMY. 


FIG.  1526. 


sj--""  1  Capsule 


gp          Papillary 


Zona 
isciculata 


ments  ;  but  in  all  cases  they  exhibit  the  characteristics  of  sympathetic  cells.  Indeed, 
so  numerous  are  the  latter  that  the  suprarenal  is  regarded  by  some  anatomists  as  an 
organ  accessory  to  the  sympathetic  nervous  system. 

Development  and  Growth. — The  genesis  of  the  suprarenal  body  has  been 
the  subject  of  much  discussion  and  uncertainty,  especially  as  to  the  origin  of  the 
medulla.  Comparative  and  embryological  studies  clearly  indicate  that  the  mam- 
malian suprarenal  body  consists  of  two  separate  and  distinct  organs,  which,  although 
intimately  united  as  cortex  and  medulla,  possess  a  different  origin  and  function.1 

According  to  the  investigations  of 
Aichel,2  the  suprarenal  in  the  higher 
mammals  first  appears  in  close  rela- 
tion to  the  Wolffian  body,  the  anlage 
arising  from  the  proliferation  of  meso- 
blastic  cells  at  the  ends  of  imaginations 
of  the  mesothelium  lining  the  body- 
cavity.  The  individual  cell-groups 
thus  arising  with  the  several  in  vagi  na- 
tions fuse  into  the  general  anlage  of  the 
suprarenal.  The  primary  close  asso- 
ciation of  the  latter  with  the  Wolffian 
body  is  later  lost,  the  subsequent  mi- 
gration of  the  organ  bringing  it  into 
secondary  relation  with  the  permanent 
kidney. 

Regarding  the  origin  of  the  me- 
dulla two  views  obtain.  According 
to  the  one  now  widely  accepted,  the 
medullary  portions  are  developed  from 
cells  which  are  derived  from  the  ad- 
jacent embryonic  sympathetic  gan- 
glia, the  chief  support  of  this  opinion 
being  found  in  the  close  correspond- 
ence of  the  medullary  cells  with  the 
chromaffin  elements  of  sympathetic  ori- 
gin occurring  in  other  localities,  such 
cells  wherever  found  exhibiting  an 
especial  affinity  for  chromium  salts. 
When  fully  developed,  the  medullary 
cells  may  be  regarded  as  highly  special- 
ized cells  which  elaborate  a  powerful 
stimulant  that  passes  into  the  blood 
(Vincent).  The  other  view,  supported 
by  Janosik,  Valenti,  and  Aichel,  attri- 
butes the  origin  of  the  medullary  cells 
to  the  same  mesoblastic  anlage  that 
produces  the  cortical  cords  of  which 
Medulla  those  of  the  medulla  are  only  speciali- 
zations. The  differentiation  of  the  su- 
prarenal into  cortex  and  medulla  Occurs 
comparatively  late  and  long  after  the 
primitive  organ  has  become  sharply  de- 
fined from  the  surrounding  tissue.  For  a  time  the  entire  organ  consists  of  cells  which 
are  identical  in  appearance.  During  the  third  month  this  common  tissue  differenti- 
al es  into  cortex  and  medulla,  in  consequence  of  the  breaking  up  of  the  outer  zone  into 
columnar  masses  by  the  advent  of  connective-tissue  trabeculae  from  which  delicate 
tibrill.t  arise,  forming  the  inner  boundary  of  the  cortex.  Within  the  central  part  of 
the  organ  thus  defined  numerous  venous  capillaries  appear  and  break  up  the  tissue 

1  Vincent:  Journal  of  Anatomy  and  Physiology,  vol.  xxxviii.,  1903. 
a  Archiv  f.  mikro.  Anat.,  Bd.  Ivi.,  1900. 


Zqna 
isciculata 


K\ 


Capillary 


Section  of  suprarenal  body,  showing  details  of  superficial 
and  deep  portions  of  cortex.     X  225. 


THE   SUPRARENAL    BODIES. 


1805 


into  the  cords  of  medullary  cells  which  lie  directly  in  contact  with  the  endothelium  of  the 
veins.      The  subsequent  ingrowth  of  the  nervous  constituents  provides  the  unusually 
rich  supply  of  nerve-fibres  and   ganglion- 
cells  distinguishing  the    medulla.       These  FIG-  1528. 
organs    are    proportionally    very    large    in 
the    fcetus    (Fig.    1529).        At    birth    the 
antero-posterior  diameter  is  i  cm.  and  the 
greatest  transverse  diameter  at  the  base  is 


FIG.  1527. 


Section  of  suprarenal  body,  showing  portions  of  cortex 
and  medulla.    X  225. 


Section  of  injected  suprarenal  body ;  the 
vessels  in  lower  third  of  figure  are  chiefly  tribu- 
taries to  the  central  vein.  X  25. 


FIG.  1529. 


Suprarenal 


Kidney 

Ureter 

Fallopian  tube 

Round  ligament 

Bladder 


_  Suprarenal 


1.5  cm. ;  the  length  from  the  apex  to  the  anterior  end  of  the  base  is  3.5  cm.  and  to 
the  posterior  end  1.5  cm.  At  this  age  the  suprarenal  covers  most  of  the  upper  half 
of  the  kidney.  At  an  earlier  period  these  organs  are  markedly  lobulated  so  as  closely 
to  resemble  the  kidneys  ;  at  term,  however, 
the  lobulation  has  nearly  disappeared. 

Accessory  Suprarenals. — These  are 
mostly  very  small,  rarely  surpassing  a  pea 
in  size.  They  may  be  found  near  the  su- 
prarenal body,  in  the  kidney,  in  the  liver, 
in  the  solar  and  renal  plexuses,  or  beside 
the  testis  or  the  ovary.  The  accessory  su- 
prarenal situated  within  the  broad  ligament 
in  the  vicinity  of  the  ovary  is  regarded  by 
Marchand  and  others  as  a  normal  and 
.almost  constant  organ.  The  latter  under- 
goes compensatory  hypertrophy  after  re- 
moval of  the  chief  suprarenal.  The  in- 
vestigations of  Aichel  emphasize  that  the 
•organs  included  under  the  designation 
' '  accessory  suprarenals' '  comprise  two 
groups  of  structures  of  different  origin  and 
morphological  significance.  Those  asso- 
ciated in  position  with  the  chief  organ,  as  when  in  the  kidney  or  liver,  are  derived 
from  separated  and  isolated  portions  of  the  principal  anlage  of  the  suprarenal,  and, 


Dissection  of  three  months  female  foetus,  show- 
ing huge  suprarenals,  lobed  kidneys,  and  sexual 
glands. 


1806  HUMAN    ANATOMY. 

therefore,  are  supernumerary.  The  bodies,  on  the  contrary,  situated  within  the 
broad  ligament,  or  in  intimate  relations  with  the  epididymis,  are  probably  developed 
from  the  atrophic  tubules  of  the  Wolffian  body,  and  hence  must  be  regarded  as  inde- 
pendent structures.  It  is  said  that  the  suprarenal  bodies  are  sometimes  wanting. 

PRACTICAL  CONSIDERATIONS  :  THE  SUPRARENAL  BODY. 

Hemorrhage  into  the  suprarenal  body  in  new-born  infants  has  been  observed 
(pqst  mortem)  in  a  number  of  cases.  Various  opinions  as  to  its  cause  have  been 
expressed.  They  have  been  summed  up  (Hamill)  as  follows  :  (i)  weakness  of  the 
vessel-walls,  normal  or  abnormal  ;  (2)  traumatism,  especially  during  labor,  from 
pressure  of  the  hands  in  making  traction  in  delivery  by  the  lower  pole,  and  from 
the  frictions  and  flagellations  used  to  resuscitate  the  apparently  dead-born  ;  (3) 
asphyxia  from  delay  in  the  establishment  of  respiration  at  birth  ;  (4)  acute  fatty 
degeneration  of  the  vessel-walls  ;  (5)  fatty  degeneration  of  the  tissues  of  the  organ  ; 
(6)  firm  contraction  of  the  uterine  muscles,  the  resistance  of  the  parts  traversed, - 
and  consequent  compression  of  the  inferior  vena  cava  between  the  liver  and  the 
vertebral  column,  thereby  producing  congestion  and  hemorrhage  into  the  non- 
resistant  tissues  of  the  suprarenal  gland  ;  (7)  convulsions  ;  (8)  syphilis  ;  (9)  cen- 
tral vasomotor  influence  from  cerebral  lesions  ;  (10)  mechanical  squeezing  of  blood 
into  the  part  during  the  process  of  labor  ;  (n)  too  early  ligation  of  the  cord  ;  (12) 
arrest  of  the  circulation  through  the  umbilical  artery  from  compression  of  the  cord 
or  separation  of  the  placenta  ;  (13)  thrombosis  of  the  renal  vein  or  inferior  vena 
cava;  (14)  infection. 

Hamill  concludes  that  the  first  of  these  seems  to  be  the  fundamental  anatomical 
element  favoring  the  occurrence  of  hemorrhage,  that  in  still-born  children  prolonged 
and  difficult  labor  is  the  exciting  cause,  and  that  in  those  dying  later  some  form  of 
infection  is  responsible. 

In  cases  of  tumor  of  the  suprarenal  body  the  following  symptoms  have  been 
noted  (Mayo  Robson)  :  (a)  shoulder-tip  pain,  probably  explained  by  the  fact  that 
a  small  branch  of  the  phrenic  nerve  passes  to  the  semilunar  ganglia  ;  (£)  pain  radi- 
ating from  the  tumor  across  the  abdomen  and  to  the  back,  not  along  the  genito-crural 
nerve  ;  (c*)  marked  loss  of  flesh  ;  (</)  nervous  depression  with  loss  of  strength  ; 
(e)  digestive  disturbance,  flatulence  and  vomiting  ;  (/")  presence  of  a  tumor  beneath 
the  costal  margin,  right  or  left,  at  first  movable  with  respiration,  but  soon  becoming 
fixed  ;  it  can  be  carried  into  the  costo-vertebral  angle  posteriorly,  and  can  be  pushed 
forward  into  the  hollow  of  the  palpating  hand  in  front  of  the  abdomen. 

Bronzing  of  the  skin  is  not  usual  unless  both  suprarenals  are  affected. 

THE   ANTERIOR    LOBE   OF   THE   PITUITARY   BODY. 

The  pituitary  body  (hypophysis),  although  usually  described  in  connection  with 
the  brain,  to  the  base  of  which  it  is  attached  by  a  stalk  continued  from  the  infun- 
dibulum  (Fig.  976),  consists  of  two  entirely  distinct  parts  which  differ  both  in  their 
genesis  and  structure.  These  are  the  so-called  anterior  and  posterior  lobes.  The 
latter,  being  derived  from  the  diencephalon,  is  appropriately  described  with  the  brain 
(page  1130)  ;  the  former,  derived  as  an  outgrowth  from  the  roof  of  the  primitive  oral 
cavity,  in  view  of  its  probable  function  as  an  organ  of  internal  secretion,  may  be 
here  considered,  since  in  certain  respects  it  resembles  the  thyroid  body. 

The  anterior  lobe,  which  constitutes  the  major  part  of  the  entire  hypophysis,  is 
kidney-shaped  and  receives  the  infundibular  process  in  a  hilum-like  depression  on  its 
posterior  surface.  It  increases  in  size  until  about  the  thirtieth  year,  when  it  meas- 
ures in  the  transverse  direction  about  12  mm.,  in  the  sagittal  about  7  mm.,  and  in 
the  vertical  5  mm.  The  anterior  lobe  of  the  hypophysis  is  light  grayish  ml  in 
color,  the  posterior  appearing  grayish  white.  It  is  surrounded  by  a  well-marked 
fibrous  capsule  which  forms,  even  where  the  two  lobes  are  in  contact,  a  distinct 
investment.  In  the  anterior  part  of  the  lobe,  on  either  side  of  the  mid-line,  a  con- 
densation of  the  connective  tissue  marks  the  position  of  large  blood- vessels.  Fine 
processes  extend  from  the  capsule  inward  and  form  a  delicate  net-work,  rich  in  capil- 


THE   ANTERIOR    LOBE   OF   THE    PITUITARY    BODY.          1807 

laries,  the  meshes  of  which  are  occupied  by  spherical  or  cord-like  masses  of  cuboidal 
or  polygonal  epithelial  cells.  The  latter  are  apparently  of  two  kinds, — the  smaller 
and  slightly  staining  chief  cells,  from  .003-. 004  mm.  in  diameter,  and  the  larger  and 

FIG.  1530. 


Interlobar  septum 


Posterior  or  cerebral  lobe 


-Blood-vessel 


Connective-tissu 
trabecula 


. Anterior  or 

oral  lobe 


Transverse  section  of  pituitary  body, 


^^^^MB—— -Capsule 
and  posterior  (cerebral)  lobes.     X  7. 


deeply  staining  chromophilc  cells  (.005-. 008  mm.),  so  called  because  of  their  marked 
affinity  for  certain  dyes.  The  two  varieties  of  cells  seem  to  be  intermingled  without 
definite  arrangement,  and  are  regarded  by  some  as  the  expression  of  differences  de- 
pending upon  merely  functional  changes,  the  two  kinds  of  cells  being  essentially 
identical. 

The  aggregations  of  the  cells,  cord-like  or  spherical  in  form  and  usually  without 
distinct  lumen,   lie  in  very  close  relation   to   the  wide   capillary  blood-vessels  that 

FIG.  1531. 


Colloid 


_..  (    .. 

Chief  cells^      •-.<*;,•::::-      S&*J!p&*®i*.3r 


Chief  cells-»S    <  '•£   t  «,     \  Chromophile  cells 


Capillary 


Section  of  anterior  lobe  of  pituitary  body;  three  acini  contain  colloid  material.     X  250. 

ramify  between  them,  supported  by  the  delicate  connective-tissue  septa.  Here  and 
there,  however,  the  glandular  epithelium  surrounds  a  lumen  which  may  contain 
colloid  material,  thus  resembling  the  acini  of  the  thyroid  body.  The  colloid-contain- 


iSoS 


HUMAN    ANATOMY. 


ing  acini  lie  chiefly  against  the  posterior  lobe,  in  which  location  a  number  of  such 
spaces  (Fig.  1531),  of  moderate  size  and  lined  with  cuboidal  epithelium,  are  usually 
normally  present,  although  colloid  vesicles  may  be  absent  in  other  parts  of  the  ante- 
rior lobe  (Schoenemann). 

The  absence  of  excretory  ducts,  the  activity  of  the  epithelial  cells  as  excretory 
elements,  and  their  intimate  relation  to  the  blood-vessels  all  support  the  view  that 


Wall  of  rhombencephalon 


Pituitary  evagination  from  diencephalon 


Pituitary'  evagination  from  oral  cavity 


Communication  with  oral 
cavity 


Portion  of  sagittal  section  of  rabbit  embryo,  showing  early  stage  of  development  of  pituitary-  body.    X  80. 

the  anterior  pituitary  lobe  is  to  be  regarded  as  an  organ  engaged  in  internal  secre- 
tion. Its  assumed  function  as  directly  concerned  with  somatic  growth,  suggested  by 
the  enlargement  of  the  pituitary  body  observed  in  giants  and  in  cases  of  acromegaly, 
needs  further  confirmation,  since,  as  pointed  out  by  Thorn,1  such  changes  are  by  no 
means  constant. 

Development. — As  above  stated,  the  two  lobes  of  the  pituitary  body  are  de- 
veloped from  entirely  different  sources.      While   the  posterior  lobe  originates  as  a 

tubular  extension  of  the 

FIG.  1533.  cavity  of  the  interbrain 

(diencephalon),  the  an- 
terior lobe  is  derived 
from  an  ectoblastic 
outgrowth  from  the  pri- 
mary oral  cavity  which 
appears  during  the 
fourth  week.  The  cere- 
bral end  of  this  evagina- 
tion (J\at/ik\''s  poitcli 
soon  expands  into  tin 
hypophysial  pouch, 
which  remains  con- 
nected with  the  mouth 
for  a  considerable  time, 
until  the  formation  of 
the  base  of  the  primi- 
tive skull  leads  to  sev- 
erance of  the  tubular 
communication,  the  hy- 
pophysial anlage  then  lying  within  the  cranium  against  the  lower  surface  of  the 
interbrain.  In  very  exceptional  cases  a  canal  in  the  sphenoid  bone,  leading  from 
the  sella  turcica  to  the  base  of  the  skull,  contains  a  prolongation  of  the  hypophysis,  and 

1  Archiv  f.  mikro.  Anat.,  Bel.  Ivii.,  1901. 


Cerebral  evagination 


Wall  of  diencephalon 


Wall  of. 
rhombencephalon 


Oral  evaluation 


Portion  of  sagittal  section  of  rabbit  embryo,  showing  development  of 

pituitary  body.     X  80. 


FIG.  1534- 


THE   ANTERIOR   LOBE   OF   THE    PITUITARY    BODY.          1809 

thus  represents  the  condition  existing  in  some  animals,  in  which  the  pituitary  stalk 
persists  during  life,  passing  through  a  canal  in  the  base  of  the  skull  and  connecting 
with  the  oral  epithelium.  During  the  latter  half  of  the  second  month  the  hypo- 
physial  sac  sends  tubular  out- 
growths into  the  surrounding  vas- 
cular mesoblastic  tissue.  Later 
these  tubules  become  separated 
from  the  main  pouch,  until  the 
latter  finally  becomes  entirely  con- 
verted into  a  mass  of  small,  tor- 
tuous tubules  or  acini  which  in 
large  part  lose  their  narrow  lumen 
and  become  solid  masses  separated 
by  septa  of  vascular  connective 
tissue.  The  anterior  lobe  thus 
formed  becomes  pressed  against 
the  under  surface  of  the  brain-lobe 
with  which  it  is  closely  bound. 

The  posterior  pituitary  lobe 
is  developed  from  the  tubular 
outgrowth  from  the  diencephalon 
and  retains  its  connection  with  the 
brain  through  the  infundibulum. 
The  primary  lumen,  however,  be- 
comes obliterated  and  the  organ 
converted  into  a  solid  mass  com- 
posed of  tissue  which  resembles 
neuroglia  and  contains  few  or  no 
cells  that  can  be  identified  as  ner- 
vous elements.  Further  details  concerning  the  posterior  lobe  are  given  in  connection 
with  the  brain  (page  1130). 


.Wall  of  diencephalon 


Posterior  (cerebral)  lobe 


nterior  (oral)  lobe 


Developing 

acini 


i^~ Cartilage  of 
base  of  skull 


-Wall  of  oral  cavity 


Portion  of  sagittal  section  of  rabbit  embryo,  showing  later 
stage  of  developing  pituitary-  body.  Anterior  lobe  now  con- 
sists of  numerous  tubular  acini.  X  50. 


As  a  matter  of  convenience,  mention  may  be  made  at  this  place  of  three  organs 
— the  carotid  bodies,  the  coccygeal  body  and  the  temporary  aortic  bodies — concerning 
whose  function  little  or  nothing  is  known.  The  systematic  position  of  these  struc- 
tures is  at  present  uncertain,  but  from  their  histological  characteristics  the  carotid 
and  aortic  bodies  are  probably  to  be  regarded  as  closely  related  to  or,  in  a  sense, 
appendages  of  the  system  of  sympathetic  nerves,  whilst  the  coccygeal  body  may  be 
included,  with  seeming  propriety,  with  the  organs  of  internal  secretion.  Their 
grouping  and  description  here,  therefore,  must  be  understood  to  be  a  matter  of  con- 
venience and  expediency  and  not  an  attempt  to  define  their  true  relations. 

THE  CAROTID  BODY. 

This  organ  (glooms  caroticum),  also  known  as  the  carotid  gland  and  ganglion 
intercaroticum,  is  a  small  ovoid  body  measuring  usually  about  5  mm.  in  length,  from 
2.5-4  mm-  m  width  and  about  1.5  mm.  in  thickness.  It  may  attain  a  length  of  7  mm. 
and  exists  on  both  sides.  Its  most  frequent  position  is  on  the  median  and  deep  side 
of  the  upper  end  of  the  common  carotid  artery  in  close  relation  with  the  point  of 
division  of  the  latter  vessel  into  the  external  and  internal  carotids.  The  body 
usually  lies  not  within  the  bifurcation,  but  rather  on  the  inner  side  of  the  common 
carotid,  so  that  its  form  and  relations  are  best  displayed  by  dissection  from  within 
outward.  When  freed  from  the  surrounding  fat  and  connective  tissue,  the  carotid 
body  appears  of  a  grayish  or  brownish  red,  according  to  the  condition  of  the  capillary 
injection.  The  organ  consists  sometimes  of  two  unequal  divisions,  united  below. 

Its  structure  includes  a  thin  fibrous  capsule,  from  which  delicate  septa  pene- 
trate inward  and  divide  the  organ  into  a  small  and  uncertain  number  (5-15)  of 
spherical  masses  or  "lobules,"  from  .2— .5  mm.  in  diameter,  which  consist  of  a  com- 

114 


i8io 


HUMAN   ANATOMY. 


plex  of  blood-vessels,  nerve-fibres  and  peculiar  cells.  The  latter  are  irregularly, 
disposed  as  clumps  or  cell-balls  (Schaper1)  and  occupy  the  interspaces  within  the 
close  net-work  of  large  capillaries  which  ramify  among  the  cells.  The  characteristic 
elements  of  the  carotid  body  are  the  polygonal  cells,  about  .01  mm.  in  diameter, 
with  large  round  nuclei.  Their  protoplasm  is  finely  granular  and  is  especially  prone 
to  change,  being  best  preserved  in  solutions  of  chromic  acid  salts.  When  so  treated, 
they  take  on  the  peculiar  yellow  color  entitling  them  to  be  classed  as  chromajfinc 
cells.  The  large  number  of  nerve-fibres  within  the  carotid  body  is  remarkable.  They 
are  mostly  nonmedullated  and  are  derived  chiefly  from  the  neighboring  sympathetic 
plexus  surrounding  the  carotid  artery  and,  after  entering  at  different  places,  ramify 
within  the  organ  in  all  directions,  the  finest  filaments  being  lost  among  the  groups  of 
cells.  The  penetrating  nerve-trunks  usually  enclose  typical  ganglion -cells  and,  in  a 
sense,  the  chromaffine  cells  likewise,  since  the  nerve-fibres  surround  the  groups  of 

these  elements. 

FIG.  1535. 

Carotid  Body 


Blood-vessel 


.^or :  -Wv>>-<  -V; 

,.-v  £$&  ^i^^sgs 

;ff^:^:^ 

[HEBBIS^r^Ai^^ ''  '*'  s  *"  •  • 

T^s^^isiiii ;' 

fe?S$  'V- •&«•;•  f^Y£&3&t 


?stf 

'*•* 


-  -'•r 

^ 

£»$£' 

tC'-.N*^   \    » 


L  Capillaries 


^ 

^1^^    ^*»  k 
Section  of  adult  human  carotid  body  ;  one  entire  lobule  is  shown.    X  170. 

In  view  of  ( i )  the  identity  of  its  elements  with  other  chromaffine  cells,  which 
are  now  recognized  as  closely  associated  with  the  sympathetic  system  in  other  locali- 
ties, as  in  the  medulla  of  the  suprarenal  body,  (2)  its  extraordinary  richness  in  nerve- 
fibres,  (3)  its  general  resemblance  to  a  sympathetic  ganglion,  and  (4)  its  direct 
development  from  embryonal  sympathetic  ganglion  cells,  Kohn'2  concludes  that  simv 
the  carotid  body  is  neither  a  gland  nor  a  typical  ganglion  it  must  be  regarded  as  ace 
sory  to  the  sympathetic  system  and,  in  recognition  of  this  relation,  proposes  t 
name  paraganglion  caroticum  for  the  organ.  Concerning  its  function  nothing 
definitely  known. 

The  blood-vessels  supplying'  the  carotid  body  are  branches  which  pass  directl 
from  either  the  common  carotid  artery  or  its  terminal  branches. 

THE  COCCYGEAL  BODY. 

This  organ  (tjlonius  coccyneum),  also  often  called  the  coccygcal  gland, 
Liischka  s  gland  (  in  honor  of  the  anatomist  who  described  it  half  a  century  ago:i),  is 
a  small  reddish  yellow  ovoid  body  which  lies  embedded  in  fatty  areolar  tissue  usually 
immediately  in  front  of  the  tip  of  the  coccyx,  but  sometimes  just  below.  According 
to  Walker,4  the  surest  guide  to  the  body  is  the  middle  sacral  artery ,  to  whose  ante- 

1  Archiv  f.  mikros.  Anatomic,  Bd.  40,  1892. 

2  Archiv  f.  mikros.  Anatomie,  Bd.  56,  1900. 

;  Die  Hirnanhan^  uiul  die  Stdssdriise  cfes  Menschen.   Berlin,  1860. 
4  Archiv  f.  mikros.   Anatomic,  Bd.  64,  1904. 


THE   COCCYGEAL   BODY. 


1811 


rior  surface  the  little  organ  is  attached,  its  long  axis  lying  transverse  to  that  of  the 
blood-vessel.  Approached  from  the  posterior  surface,  the  body  is  found  just  beneath 
or  within  a  small  opening  in  the  tendinous  insertion  of  the  levator  ani  muscle  into  the 
last  coccygeal  segment,  covered  by  the  origin  of  the  external  sphincter  muscle 
(Luschka).  The  dimensions  of  the  organ  are  small,  its  transverse  and  greatest 
diameter  being  from  2. 5-3mm.  and  its  thickness  less  than  2  mm.  It  sometimes  is 
divided  into  two  or  even  more  tiny  lobes.  The  body  thus  described  is,  however, 
only  the  largest  of  a  series  of  nodules  which  includes  a  variable  number  of  structures, 
for  the  most  part  of  minute  size,  irregularly  grouped  around  the  chief  mass 
(Walker).  The  additional  nodules  are  in  many  cases  connected  with  the  principal 
body  by  means  of  delicate  pedicles,  in  others  entirely  free,  but  in  all  instances  they  are 
grouped  around  the  middle  sacral  artery  or  its  branches.  In  opposition  to  the  pre- 
vailing belief,  Walker  found  neither  an  unusually  rich  nerve-supply  nor  intimate 
connection  between  the  coccygeal  body  and  the  sympathetic. 

FIG.  1536. 

Coccygeal  gland 


Capillaries 


Connective  tissue  .'       **V*  ^ 

stromaV 


%&§j^\^«^  i  f^hl,  ^  '*E«?  - 


.  ,  -  -     yjE     .  '.-  -          I 

irr^B 

$Urc^*r£ 

•     \VJS9>/ 


Cells 
Blood-vessels 


Section  of  human  adult  coccygeal  body.    X  220. 

The  structure  of  the  body,  as  seen  in  transverse  sections  (Fig.  1536),  includes 
an  irregularly  oval  field  of  connective  tissue,  fairly  well  defined  from  the  surrounding 
fatty  areolar  tissue,  in  which  are  enclosed  numerous  aggregations  of  epithelial  cells 
and,  sometimes,  a  thick-walled  artery.  The  proportion  of  cell-masses  to  the  connec- 
tive tissue  stroma  varies,  in  some  cases  the  cellular  constituents  predominating,  but 
commonly  the  fibrous  stroma  being  the  more  bulky.  The  individual  cell -groups  are 
uncertainly  circumscribed  by  a  slight  condensation  of  the  surrounding  fibrous  stroma. 
Each  aggregation  of  cells  contains  a  central  blood-space,  limited  by  an  endothelial 
wall  similar  to  that  of  a  capillary.  Against  this  wall  the  epithelial  cells  lie  without 
the  intervention  of  connective  tissue ;  likewise  the  cells  themselves  are  closely  packed 
in  direct  apposition  with  one  another  and  in  consequence  present  a  polygonal  con- 
tour. They  are  disposed  around  the  central  vessel  in  from  two  to  five  layers,  the 
individual  cells  being  indistinctly  outlined  and  composed  of  clear  protoplasm  con- 
taining a  relatively  large  and  deeply  staining  nucleus.  Concerning  the  mooted  ques- 
tion as  to  the  presence  of  chromaffine  cells  within  the  coccygeal  body,  the  testimony 
of  Walker,  Schumacher  and  especially  of  Stoerk '  as  to  their  absence  seems  convin- 
cing. The  last-named  investigator  concludes  that  these  cells  at  no  period  exhibit  the 
chrome-reaction,  and,  further  and  in  opposition  to  Jakobsson,  that  they  have  no  his- 
togenetic  relation  to  the  sympathetic  system.  On  the  other  hand,  the  epithelial 
character  of  the  cells,  their  intimate  relation  to  the  blood-vessels,  and  the  absence  of 

1  Archiv  f.  mikros.  Anatomic,  Bd.  69,  1906. 


I8l2 


HUMAN   ANATOMY. 


Irv 


LAB 


RLE    " 


excretory  ducts,  seem  to  justify  the  inclusion  of  the  coccygeal  body,  at  least,  pro- 
visionally, among  the  organs  of  internal  secretion,  as  suggested  by  Walker. 

THE  AORTIC    BODIES. 

These  temporary  organs  were  described  by  Zuckerkandl '  a  few  years  ago  and 
are  also  known  as  the  bodies  of  Zuckerkandl.  According  to  their  discoverer,  as 
found  in  the  new-born  child,  they  are  a  pair  of  small  narrow  bodies  that  lie  upon  the 
anterior  surface  of  the  abdominal  aorta,  opposite  the  origin  of  the  inferior  mesenteric 
artery  (Fig.  1537),  in  close  relation  with  the  aortic  plexus  of  the  sympathetic  nerves. 
Although  usually  separated,  in  about  15  percent,  of  the  bodies  examined,  in  which 
they  were  invariably  present,  the  bodies  were  joined  by  an  isthmus  into  a  horseshoe- 
shaped  organ  of  varying  dimensions. 

FIG.  1537.  The  right  body  is  usually  the  larger, 

ic  a  with  an  average  vertical  length  of  1 1 . 6 

•  j  mm.  the  corresponding  dimension  of 

the  left  body  being  8. 8  mm.  The  ex- 
tremes of  length  for  the  right  body 
are  from  8-20  mm.,  and  of  the  left 
one  from  3-15  mm.  The  width  is 
about  one-fifth  of  the  length,  and  the 
thickness  something  less.  The  sur- 
face of  the  little  organ  is  smooth  and 
its  color  light  brown.  Whilst  its 
consistency  is  about  the  same  as  that 
of  the  neighboring  lymph-nodes,  the 
body  is  softer  than  the  adjacent  sym- 
pathetic ganglia.  The  aortic  bodies 
are  essentially  organs  of  foetal  life  or 
at  most  of  early  childhood,  and  in 
the  adult  they  are  represented  by 
mere  atrophic  remains  (Zucker- 
kandl). 

The  structure  of  the  aortic 
body  includes  a  fibrous  capsule,  which 
is  prolonged  into  the  interior  as  con- 
nective tissue  strands  that  accompany 
the  numerous  blood-vessels  entering 
the  organ.  The  arteries,  minute 
twigs  from  the  aorta,  the  inferior 
mesenteric  and  sometimes  the  sper- 
matic, break  up  into  a  rich  capillary 
net-work  whose  wide  meshes  are 
filled  with  closely  packed  cells  of 
varying  size.  These  are  polygonal, 
spherical  or  cuboidal  in  form  and  distinguished  in  many  cases  by  exhibiting 
the  peculiar  color  reaction,  after  treatment  with  the  chrome-salts,  entitling  tin  in 
to  be  classed  as  chromaffine  cells.  According  to  the  observations  of  Zucker- 
kandl, the  genetic  relations  of  the  sympathetic  ganglia,  the  medulla  of  the  supra- 
renals,  and  the  aortic  bodies  are  most  intimate,  since  these  various  structures  are 
derivatives  of  a  continuous  primary  cell-mass.  In  consideration  of  this  association 
and  the  constant  presence  of  the  distinctive  chromafifine  cells,  it  is  highly  probable 
that  the  aortic  bodies  are  to  be  regarded,  along  with  the  medullary  portion  of  tin- 
suprarenal  and  the  carotid  bodies,  as  appendages  or  paraganglia  of  the  sympathetic. 

1  Verhancllungen  der  Anatom.  Gesellschaft,  1901. 


Aortic  bodies  of  new-born  child  ;  RAB,  LAB,  right 
and  left  aortic  bodies  ;  a,  aorta  ;  I'M,  inferior  mesen- 
teric artery  ;  let,  left  common  iliac  ;  ic,  inferior  cava  ; 
Irv,  left  renal  vein  ;   ap,  aortic  sympathetic  pk.xu- 
w,  ureter.     X  2.     {Zuckerkandl.) 


THE  ORGANS  OF  RESPIRATION. 

THIS  tract  includes  the  organs  by  which  an  interchange  of  gases  takes  place 
between  the  blood  and  the  air.  It  consists  of  the  larynx,  the  trachea  or  windpipe, 
and  its  subdivisions — the  bronchi,  the  lungs,  and  the  serous  membranes,  the  pleitrce, 
which  surround  them.  Morphologically  this  tract  is  an  outgrowth  from  the  fore- 
gut.  The  larynx  is  a  specialized  apparatus  for  the  production  of  the  voice,  situated 
at  the  beginning  of  the  windpipe,  of  sufficient  importance  to  be  considered  by  itself. 

THE    LARYNX. 

The  larynx  consists  of  a  number  of  cartilages  which,  by  their  relative  changes 
of  position,  modify  the  approximation  and  tension  of  two  folds  of  mucous  mem- 
brane over  fibrous  tissue,  known  as  the  vocal  cords,  on  either  side  of  the  cleft  through 
which  the  air  enters  the  \vindpipe.  The  larynx  is  in  the  neck,  being  suspended  from 
the  hyoid  bone  and  leading  to  the  trachea.  It  is  practically  subcutaneous  in  front.  Its 
superior  orifice  is  behind  the  base  of  the  tongue,  and  can  be  seen  in  life  only  by  a  mirror. 
The  cartilages  are  connected  by  joints  and  ligaments,  moved  by  muscles,  and  covered 
by  mucous  membrane,  the  folds  of  which  form  important  morphological  parts  of  the 
larynx. 

THE  CARTILAGES,  JOINTS,  AND  LIGAMENTS. 

The  cartilages  which  form  the  framework  of  the  larynx  are  three  single  ones  :  the 
cricoid,  \hethyroid,  and  the  epiglottis;  and  three  pairs:  \\\Q  arytenoid  cartilages ,  the  cor- 
niculce  laryngis  or  cartilages  of  Santorini,  and  the  cuneiform  cartilages  or  those  of 
Wrisberg.  The  last  pair,  although  determining  well-defined  swellings  of  the  mucous 
membrane,  are  very  small  ;  indeed,  the  cartilage  is  not  always  to  be  found.  There  are 
other  minute  points  of  cartilage  to  be  mentioned  with  the  structures  in  which  they  occur. 

The  epiglottis,  the  upper  part  of  the  cartilages  of  Santorini,  those  of  Wrisberg,  and 
the  ends  of  the  vocal  and  apical  processes  of  the  arytenoids  consist  of  elastic. cartilage,  the 
others  being  of  hyaline  cartilage.  The  cricoid  and  arytenoid  cartilages  are  derivations 
from  the  trachea  and  represent  the  more  primitive  form  of  larynx.  The  thyroid  and  the 
epiglottis  appear  in  mammals.  In  monotremes  the  epiglottis  is  of  hyaline  cartilage. 

The  Cricoid  Cartilage. — This  is  the  foundation  of  the  larynx,  being  a  ring 
on  the  top  of  the  trachea.  It  is  nearly  circular,  the  diameter  in  the  male  being  19 
mm.  (Luschka).  It  is  narrow  in  front,  being  from  3-8  mm.,  usually  about  5  mm. 
broad,  and  some  four  or  five  times  as  much 

behind.     The  height  at  the  back  is  approxi-  FIG.  1538. 

mately  25  mm.  in  the  male  and  from  16-23 
mm.  in  the  female.    The  cricoid  is  3  or  4  mm.       Articu]ar  facet. 
thick  in  the  lower  part  and  in  the  upper  as         for  arytenoid 

i  .-  .-pi  cartilage 

much  as  5  or  6  mm.      1  he  posterior  aspect  is 
somewhat  quadrilateral,  the  upper  border  de- 

,•  i          .    ,1          -i  T     .  11  Articular  facet 

scending  very  steeply  at  the  sides.     Internally         for  thyroid 
the  cricoid   is   perfectly  smooth.      The  lower         cartilage 
border  presents  a  slight  median  descent  in  front  Cricoid  cartilage,  right  lateral  aspect, 

and  an  inconspicuous  notch  behind.  Never- 
theless, the  cricoid  is  so  placed  that  its  posterior  margin  is  a  trifle  the  lower.  A  small 
median  depression  occurs  in  the  superior  border  behind,  and  on  either  side  is  an 
articular  eminence  for  the  arytenoid  cartilage.  Being  situated  on  the  superior  border 
of  the  cricoid,  this  elongated  eminence  has  its  long  diameter  (8-10  mm.)  slanting 
outward,  downward,  and  somewhat  forward.  Its  free  edge  may  be  slightly  coin-ex 
or  concave  in  the  long  axis,  but  is  not  far  from  straight.  .  It  is  convex  transversely 
and  about  4  mm.  thick.  The  whole  elevation  is  inclined  slightly  away  from  the 
interior  of  the  larynx,  so  as  somewhat  to  overhang  its  posterior  surface,  and  is 

1813 


1814 


HUMAN    ANATOMY. 


J539- 


Cartilage  of  Santorini 


Posterior  surface  for    ,rL^t 
arytenoideus 

Posterior  crico-         /X 
arytenoid  ligament    . 

Muscular  process  *>^ 


Posterior  ridge  on  4- 
cricoid  cartilage  \ 

Depression  for 
crico-arytenoideus 
posticus 


Cricoid  and  arytenoid  cartilages  from  behind. 


extremely  variable  in  all  its  details.  A  median  ridge  divides  the  posterior  surface  of 
the  cricoid  cartilage  into  two  symmetrical  depressions  for  the  origin  of  the  posterior 
crico-arytenoid  muscles.  Each  lateral  surface  of  the  cricoid,  below  the  middle,  and 
nearer  the  back  than  the  front,  bears  an  oval  articular  facet  for  the  crico-thyroid 
joint,  its  long  diameter  extending  upward,  backward,  and  inward.  The  facet,  which 
is  nearly  plane,  faces  chiefly  outward,  but  also 

somewhat  upward  and  a  little  backward.      The  FIG. 

long  diameter  is  about  5  mm.  and  the  cross  one 
nearly  as  great.  A  ridge  connecting  it  with  the 
superior  articular  facet  bounds  the  posterior  sur- 
face of  the  cartilage.  The  anterior  surface  of 
the  cricoid  is  somewhat  convex  vertically,  so 
as  to  resemble  an  over-large  tracheal  ring. 

The  Thyroid  Cartilage.  —  This,  the 
shield-shaped  cartilage,  consists  of  two  quadri- 
lateral plates,  the  alee,  broader  than  high,  which 
meet  in  front  and  are  widely  apart  behind.  The 
posterior  border  of  each  is  prolonged  upward 
and  downward  into  two  horns,  or  cornua,  some- 
what flattened  from  side  to  side.  The  lower  pair 
rest  on  the  inferior  articular  facets  of  the  cricoid 
and  the  upper  are  attached  by  ligaments  to  the 

ends  of  the  greater  horns  of  the  hyoid  bone.  Being  thus  open  behind,  the  thyroid 
cartilage  is  complementary  to  the  cricoid  upon  which  it  rests.  The  thyroid  notch 
(incisura  thyroidea)  is  a  deep  median  depression  of  the  upper  border  in  front,  extend- 
ing nearly  or  quite^  half-way  down.  The  plates  are  strongly  everted  (especially  in 
the  male)  at  the  sides  of  the  notch,  thus  causing  most  of  the  prominence  known  as 
Adam's  apple  (protuberantia  laryngea).  The  resulting  median  ridge  ends  shortly 
below  the  notch,  and  at  the  lower  border  the  front  of  the  thyroid  is  smooth  and 
convex.  The  upper  border  is  slightly  convex  on  either  side,  and  usually  presents  a 
small  notch  just  in  front  of  the  root  of  each  superior  horn.  The  superior  tubercle  is 
a  little  prominence  on  the  outer  surface,  just  below  and  anterior  to  this  notch.  The 
lower  border  is  alternately  convex  and  concave.  There  is  a  moderate  median  con- 
vexity followed  by  a  hollow,  external  to  which  is  a  marked  prominence,  the  inferior 
tubercle,  between  which  and  the  inferior  horn  is  a  deep  notch.  The  posterior  border 

is  slightly  concave  in  the  middle. 

FIG.  1540.  The  oblique  line  is  a  ridge  running 

downward  and  forward  from  the 
upper  tubercle  to  the  lower.  It 
marks  the  interruption  of  the  mu 
cular  layer  out  of  which  the  sterno 
thyroid  and  the  thyro-hyoid  mus- 
cles arise.  The  inferior  constrictor 
of  the  pharynx  is  inserted  behind  it. 
The  superior  horns,  usually  longer 
and  more  flexible  than  the  inferior, 
run  upward,  backward,  and  inward. 
They  become  more  cylindrical  and 
have  blunt  rounded  ends.  The  in- 
ferior horns,  broader  than  thick, 
run  downward  and  slightly  inward, 
with  a  turn  forward  at  the  ends.  In- 
ternally each  presents  near  the  tip 
a  round  articular  surface  of  indefi- 
nite shape  for  the  inferior  articular  surface  of  the  cricoid.  The  dimensions  of  the  aloe 
vary  with  the  sex  :  in  man  the  height  is  30  mm.  and  the  breadth  ;VS  mm.;  in  woman, 
_'.}  and  2S  mm.  respectively.  The  prominence  and  sharpness  of  the  angle  are  male 
characteristics,  in  man  the  average  being  00°  and  in  woman  120°.  It  is  chiefly 
through  the  thyroid  cartilage  that  the  male  larynx  acquires  its  relatively  large  si/e. 


Epiglottis 


Oblique  line,  end- 
ing in  tubercles 
above  and  1»  \"\\ 


':<>]<•.  I  ion.  be- 
low notch, 
formitit;  pi> 
mum  Adami 


Inferior  cornu 
'I  liM'i.iil  OUtibgB,  with  i-pigluttis.  right  nntero-lateral  aspect. 


THE    LARYNX. 


1815 


Development  and  Growth. — The  thyroid,  probably  formed  from  the  fourth 
and  fifth  branchial  arches,  is  originally  rounded  in  front,  the  angle  becoming-  promi- 
nent at  puberty,  when  the  great  increase  in  size  in  the  male  and  the  greater  promi- 
nence occur.  A  slight  strip  of  cartilage,  separate  from  the  rest,  is  found  in  the  angle 
in  early  childhood  ;  subsequently  it  becomes  less  and  less  distinct. 

Variations. — It  is  not  rare  to  find  a  foramen  near  the  upper  outer  angle,  a  little  below  the 
superior  tubercle,  which  transmits  the  superior  laryngeal  artery  and  exceptionally  some  fibres 
of  the  external  branch  of  the  superior  laryngeal  nerve.  Assuming  that  the  thyroid'  is  developed 
as  above  stated,  the  foramen  represents  a  cleft  between  the  fourth  and  fifth  branchial  bars.  It  is 
common  for  one  of  the  superior  horns  to  be  shorter  than  the  other,  and  not  very  rare  for  one  to 
be  absent.  Our  experience  agrees  with  that  of  others  in  finding  the  absence  more  common  on 
the  left  side. 


Cartilage  triticea — 

r 

Thyro-hyoid 
membrane,  left 
half 

Cartilage 
of  Santorini 


Posterior 
crico-arytenoid 
ligament 


Joints  and  Ligaments  connecting  the  Thyroid  with  the  Cricoid  Car- 
tilage  and  with  the   Hyoid   Bone. — The  crico-thyroid  joints,  between  the 
lower  articular  facets  of  the  cricoid  and  the  inferior  horns  of  the  thyroid,  are  very 
indefinitely  shaped.     The  facet  of  the  thyroid  is  on  the  inner  side  of  the  inferior  horn, 
and  is  nearly  plane,  but  either  par- 
ticipant of  the  joint  may  be  the  FIG.   1541. 
contained   one.     The    capsule    is  Epiglottis 
lax,  although  somewhat  strength- 
ened by  two  by  no  means  con- 
stant ligamentous  bands.    An  an- 
terior one  extends  downward  and 
forward    from    the   front   of    the 
lower  horn  ;  a  posterior  one  ex- 
tends upward  and  backward  from 
the  back  of  the  same.    The  motion 
is  usually  described  as  rotation  on 
a  transverse  axis  passing  through 
both  joints,  but  in  fact  a  great  deal 
of  irregular  sliding  is  possible. 

The  crico-thyroid  mem- 
brane, although  connecting  the 
cartilages  in  front,  has  no  direct 
attachment  to  the  thyroid  at  the 
sides,  and  consists  of  a  central 
anterior  and  a  lateral  part.  The 
anterior  part,  also  known  as  the 
conoid  ligament,  is  triangular  in 
shape,  with  its  base  attached  to 
the  upper  edge  of  the  cricoid  car- 
tilage and  its  truncated  apex  to  • 
the  lower  border  of  the  thyroid.  This  is  the  strongest  part  of  the  membrane,  con- 
taining considerable  elastic  tissue,  and  closes  the  middle  of  the  space  between  the  two 
cartilages.  It  is  pierced  by  several  small  holes  for  blood-vessels,  and  is  crossed 
superficially  by  the  crico-thyroid  artery.  The  lateral  part  (Fig.  1544),  while  directly 
continuous  with  the  anterior  and  attached  below  to  the  upper  border  of  the  anterior 
arch  of  the  cricoid  cartilage,  is  thin  and  membranous,  and  on  each  side  extends 
upward  and  inward  beneath  the  lower  border  of  the  thyroid  alae  without  being  at- 
tached. The  upper  border  of  this  part  of  the  membrane  becomes  directly  blended 
and  continuous  with  the  inferior  thyro-arytenoid  ligament,  the  latter  being  practically 
the  thickened  and  free  superior  border  of  the  crico-thyoid  membrane,  which  in  this 
sense,  becomes  the  supporting  framework  for  the  true  vocal  cord.  The  lateral  crico- 
arytenoid  and  thyro-arytenoid  muscles  intervene  between  the  thyroid  ahe  and  the 
lateral  parts  of  the  membrane.  The  inner  surface  of  the  latter  is  covered  by  the 
laryngeal  mucous  membrane. 

The  thyro-hyoid  ligament  or  membrane  is  one  continuous  sheet  of  fibrous 
tissue,  the  posterior  borders  of  which  are  thickened  as  they  extend  between  the  supe- 


Posterior 
crico-thyroid 
ligament 


.  Trachea 


Cartilages  of  larynx  united  by  their  ligaments  ;  right  half  of  thyro- 
hyoid  membrane  has  been  removed  ;  poslero-lateral  aspect. 


i8i6 


HUMAN  ANATOMY. 


Crista  arcuata 


Fovea  oblongata,  for 
thyro-arytenoideus 
muscle 
Muscular  process 


FIG.  1542. 


'artilage    of    Santorini 
Apex 

ubercle  for  false  vocal 

•d 
Fovea  triangularis 

Anterior  border 
Vocal  process  - 


Postero- 
medial 
surface 


Articular  facet 


Articular  facet 


A,  antero- 


rior  horns  of  the  thyroid  and  the  tips  of  the  greater  horns  of  the  hyoid.  They 
may  be  artificially  dissected  to  resemble  cords  ( li^amenta  thy reohyo idea  lateralia), 
although  in  fact  they  are  continuous,  not  only  with  the  rest  of  the  membrane,  but 
with  its  expansion  which  mingles  with  the  fasciae  of  the  neck.  As  a  rule,  a  little 
nodule  {cartilago  triticea)  is  found  in  the  middle  of  this  lateral  thickening  (Fig. 
1541).  According  to  Gegenbaur,  it  is  the  remnant  of  a  closer  connection  between 
the  third  and  fourth  branchial  bars.  The  more  membranous  part  of  the  ligament 
extends  from  the  superior  border  and  the  inner  side  of  the  superior  horns  of  the 
thyroid  to  the  upper  border  of  the  body  of  the  hyoid  and  its  greater  horn.  A  bursa, 
extending  under  the  body  of  the  hyoid,  lies  on  the  anterior  surface  of  this  membrane, 
which  is  denser  beneath  it. 

The  Arytenoid  Cartilages. — These  are  a  pair  of  very  irregular  four-sided 
pyramids  (one  side  being  the  base)  perched  on  the  superior  articular  facets  of  the 
cricoid.  The  vocal  cords  extend  between  them  and  the  entering  angle  of  the  thyroid. 
Besides  the  base,  there  is  a  posterior,  an  internal,  and  an  antero- external  surface,  sep- 
arated by  tolerably  distinct  borders.  A  section  near  the  base  is  semilunar,  the  bound- 
ary between  the  posterior  and  internal  surfaces  being  effaced.  The  two  remaining 
angles  are  each  prolonged  (Fig.  1542).  The  anterior,  extending  forward  as  ihevoca/ 

process  for  the  attachment 
of  the  true  vocal  cord,  is 
long  and  slender  ;  the  ex- 
ternal or  muscular  process, 
short  and  thick,  projects  out- 
ward and  backward.  The 
base  is  chiefly  occupied  by 
an  oval  articular  cavity  rest- 
ing on  that  of  the  cricoid. 
The  long  axis  of  this  articu- 
lar facet,  which  does  not 
much  surpass  its  transverse 
one,  extends  in  the  main  for- 
ward, crossing  that  of  the  opposed  facet.  The  concavity  is  nearly  at  right  angles  to 
the  long  axis.  The  posterior  surface  is  well  defined  and  deeply  concave,  being  filled 
by  the  arytenoid  muscle.  The  internal  surface  is  nearly  plane,  offering  nothing  for 
description.  The  antero-external  surface  is  triangular.  A  ridge,  the  crista  arcnata, 
starts  from  the  vocal  process  and  runs  backward  and  upward,  ultimately  describing 
nearly  a  circle  around  a  hollow,  the  fovea  triangularis,  which  is  quite  as  often  oval. 
This  little  hollow  is  filled  by  a  mass  of  glands,  and  is  overlooked  unless  the  cartilage 
be  cleaned  very  carefully.  The  false  vocal  cord  is  attached  to  a  little  tubercle  on  this 
ridge  either  above  or  behind  the  fovea.  The  borders  meet  above  at  a  blunt  apex. 

The  Crico-Arytenoid  Joint. — From  the  foregoing  description  of  the  two 
opposed  articular  surfaces  it  is  evident  that  in  consequence  of  the  crossing  of  their 
long  axes  the  whole  of  one  is  not  in  contact  with  the  whole  of  the  other.  The  joint 
is  surrounded  by  a  lax  capsule,  strengthened  behind  by  straight  vertical  fibres,  which 
have  been  called  the  posterior  crico-arytenoid  ligament  ( Fig.  1541).  The  motions 
are  very  difficult  to  analyze.  The  arytenoid  may  tip  on  the  elongated  elevation  of 
the  cricoid  or  slide  along  it  ;  moreover,  it  may  rotate  upon  it  at  any  point  occupied. 
This  movement,  from  the  nature  of  the  surfaces,  is  a  screw  motion  rather  than  a  true 
rotation,  but  the  term  is  sufficiently  accurate. 

The  Epiglottis. — This  is  a  leaf-shaped  plate  of  elastic  cartilage  which,  inserted 
by  its  stalk  into  the  angle  of  the  thyroid,  rises  above  the  hyoid  bone  and  guards  the 
entrance  into  the  larynx.  The  length  is  some  3.5  cm.  The  epiglottis  expands  trans- 
versely and  curls  forward  over  the  root  of  the  tongue.  Its  posterior  surface  is 
entirely  free,  but  less  than  the  upper  half  of  the  anterior  surface  is  exposed.  Begin- 
ning at  the  free  border,  which  is  bent  forward  towards  the  tongue,  the  posterior 
surface  is  convex,  slightly  concave,  and  finally  convex  again,  owing  to  a  prominence, 
called  the  tubercle,  which  its  root  forms  in  the  larynx.  The  free  edge  is  rounded 
traiisvrrsrlv  and  the  posterior  surface  in  the  main  concave  across.  The  stalk,  when 
well  developed,  is  triangular  on  section,  fitting  into  the  angle  of  the  thyroid.  The 


Right  arytenoid  cartilage,  capped  by  cartilage  of  Santorini. 
lateral  aspect  ;  B,  postero-medial  aspect.    X  j}. 


THE   LARYNX. 


1817 


FIG.  1543- 


Depressions 
for  glands 


cartilaginous  stroma  is  full  of  pits,  or  even  perforations,  containing  glands.  The 
mucous  membrane  is  attached  to  it  very  closely,  so  that  in  dissecting  the  cartilage  it 
is  difficult  to  determine  its  true  outline. 

The  Ligaments  of  the  Epiglottis. — The  thyro-epiglottic  ligament  is  an  elastic 
band  continuing  the  stalk  of  the  epiglottis  into  the  angle  of  the  thyroid,  just  below 
the  notch.  Owing  to  the  ill-defined  structure  of  the  epiglottis,  it  is  often  hard  to  say 
what  is  ligament  and  what  is  stalk.  The  glosso-epiglottic  ligaments,  one  median  and 
two  lateral,  are  three  folds  of  mucous  membrane  with  more  or  less  elastic  tissue  within 
them,  extending  from  the  front  of  the  epiglottis  to  the  tongue,  with  which  they  have 
been  more  particularly  described  (page  1575).  The  hyo-cpiglottic  ligament1  is  de- 
scribed as  a  bundle  of  elastic  tissue  extending  between  the  middle  of  the  anterior 
surface  of  the  epiglottis  and  the  upper  border  of  the  hyoid.  Such  a  structure  may 
be  artificially  dissected  ;  but  the  important  point  is  the  presence  of  a  mass  of  very 
dense  areolar  tissue,  probably  largely  elastic,  and  with  fat  in  its  meshes,  which  forms 
a  firm  pad  between  the  front  of  the  epiglottis  below  the  line  of  reflection  of  the 
mucous  membrane  and  the  thyro-hyoid  membrane  which  is  attached  to  the  upper 
border  of  the  hyoid.  This  mass  gives  support  to  the  epiglottis,  and -probably  may 
be  made  to  press  it  backward  when  the  hyoid  is  carried 
in  that  direction.  It  is  continuous  with  the  septum  of  the 
tongue. 

The  Movements  of  the  Epiglottis. — The  old  idea  that 
the  epiglottis  turns  over  backward  like  a  lid  to  close  the 
larynx  in  swallowing  is  disproved.  That  it  could  ever  be 
so  bent  is  unlikely.  In  swallowing  it  is  carried  bodily 
backward,  probably  receiving  the  bolus  on  its  laterally 
concave  posterior  surface  and  transferring  it  to  the  grasp 
of  the  pharynx.  While  there  are  muscular  fibres  in  the 
aryepiglottic  fold,  they  are  scanty  and  irregular  and  hardly 
capable  of  exercising  any  great  influence  on  the  shape  of 
the  epiglottis. 

The  corniculae  laryngis,  or  cartilages  of  Santo- 
rini,  are  a  pair  of  small  horn-like  structures  of  elastic  car- 
tilage on  the  apices  of  the  arytenoids  (Fig.  1542).  As 

their  sheath  is  continuous  with  the  perichondrium  of  the  latter,  they  are  not  very 
easily  isolated.  They  are  4  or  5  mm.  long,  curve  backward  and  inward,  and  are 
attached  by  their  fibres  to  the  arytenoids. 

The  cuneiform  cartilages  (of  Wrisberg}  are  two  very  slender  rods  of  elastic 
cartilage  situated  a  little  in  front  of  the  corniculae  laryngis  in  the  aryepiglottic  folds 
(Fig.  1545).  They  are  some  5  mm.  or  more  long  and  i  mm.  thick.  While  the 
swellings  which  they  seem  to  produce  in  the  folds  are  constant,  the  same  cannot  be 
said  of  the  cartilages.  They  are  often  difficult  to  isolate. 

Minute  nodules  of  elastic  cartilage  are  occasionally  found  in  certain  parts  of  the 
larynx.  The  posterior  sesamoid  cartilages  are  on  the  lateral  sides  of  the  joints  be- 
tween the  arytenoids  and  the  corniculae.  The  anterior  sesamoid,  which  may  be  double, 
is  at  the  anterior  origin  of  the  true  vocal  cords.  An  occasional  interarytenoid  has 
been  described  under  the  mucous  membrane  of  the  pharynx  between  those  cartilages. 
It  is  regarded  as  representing  a  prccricoid  cartilage. 

The  elastic  sheath  of  the  larynx  is  a  layer  of  areolar  tissue,  rich  in  elastic 
fibres,  which  lines  the  inside  of  the  larynx,  and  is  prolonged  from  it  into  the  folds 
of  mucous  membrane  to  be  presently  described.  The  superior  and  inferior  thyro- 
arytenoid  ligaments  in  the  false  and  true  vocal  cords  repectively  and  thicking  of  this 
layer. 

The  superior  thyro-arytenoid  ligaments  (ligamcnta  ventricularia),  one  on 
each  side,  extend  between  the  angle  of  the  thyroid  above  its  middle  (the  point  of 
origin  will  be  described  accurately  with  the  vocal  cords)  and  the  tubercle  on  the  bor- 
der of  the  fovea  of  the  arytenoid.  They  are.  in  no  sense  ligaments,  but  at  most 
slight  thickenings  of  the  elastic  tissue  in  the  folds  of  the  mucous  membrane  forming 
the  false  vocal  cords,  and  can  be  demonstrated  only  by  an  artificial  dissection. 

1  Dieulafe  :  La  membrane  glosso-hyoidienne,  Bibliographic  Anatomique,  tome  xi.,  1901. 


.Stalk 


Epiglottic  cartilage  from  behind. 


i8l8 


HUMAN    ANATOMY. 


The  inferior  thyro-arytenoid  ligaments  ( li^amenta  vocalia)  are  a  pair  of 
bands  of  fibrous  tissue,  chiefly  elastic,  supporting  the  free  edges  of  the  true  vocal 
cords,  extending  from  the  angle  of  the  thyroid  a  little  below  the  false  ones  to  the 
vocal  processes  of  the  arytenoids.  These  ligaments  are  continuous  with  the  lateral 
parts  of  the  crico-thyroid  membrane,  as  the  thickened  and  modified  upper  borders 
of  which  they  may  be  regarded  (Fig.  1544)-  Each  band  is  triangular  on  section, 

having  the  free  edge  at  that  of  the 

FIG.  1544-  cord.      There  may  be   a    minute 

nodule  of  cartilage  in  the  ligament 
just  in  front  of  its  posterior  attach- 
ment. 


Superior  cornu 
of  thyroid  car- 
tilage 


Cartilage  of 

Santorini 


Arytenoid 
cartilage 


Articular  facet 
for  inferior  thyroid 
cornu 


Right  thyroid 
ala  (cut) 
eral     part    of 
crico-thyroid  mcm- 
rane    attached    to 
vocal  process 
Median  part  of  crico- 
thyroid  membrane 
Cricoid  cartilage 


Trachea 


Ossification  of  the  Larynx. — The 
process,  beginning  as  it  does  at  about 
twenty,  is  a  normal  change.  Chievitz ' 
found  some  ossification  in  every  male 
larynx  of  over  twenty  and  in  every  fe- 
male one  of  over  twenty-two.  It  ap- 
pears at  about  the  same  time  in  the 
cricoid  and  thyroid, — namely,  at  about 
the  beginning  of  the  twentieth  year, — 
and  in  the  arytenoid  at  about  the  mid- 
dle of  the  twenties  in  man  and  nearer 
the  thirties  in  woman. 

The  Cricoid. — The  first  nucleus 
appears  on  each  side  at  the  back  of 
the  facet  for  the  arytenoid,  and  almost 
at  the  same  time  another  appears  at 
its  front.  These  are  shortly  followed 
by  one  at  the  joint  for  the  thyroid. 
These  three  unite,  forming  a  lateral 
ossification  which  spreads  across  the 
back.  One  or  mpre  points  appear  in 
front  near  the  upper  border  of  the  arch,  which  is  thus  ossified  and  joins  with  the  sides.  After 
these  various  unions  the  entire  lower  border  of  the  cricoid  is  still  cartilaginous.  The  youngest 
man  observed  by  Chievitz  with  complete  ossification  was  forty-four  and  the  youngest  woman 
seventy-six. 

The  Thyroid. — The  process  begins  near  the  posterior  inferior  angle  and  invades  the  in- 
ferior horn.  It  appears  next  near  the  lower  part  of  the  anterior  angle,  and  these  tun  centres 
on  each  side  join  by  spreading  along  the  inferior  border.  The  superior  horn  then  ossifies  either 
by  a  separate  centre  or  by  extension  along  the  hind  border,  finally  a  tongue-like  process, 
starting  near  the  inferior  tubercle,  extends  upward  and  forward  across  the  ala  to  meet  the  ossi- 
fication which  has  spread  along  the  superior  border,  leaving  before  and  behind  it  places  which 
are  the  last  to  ossify.  This  tongue-like  process  is  peculiar  to  the  male  ;  in  the  female  ossifica- 
tion advances  chiefly  from  the  posterior  border.  The  youngest  man  with  complete  ossification 
of  the  thyroid  was  fifty  and  the  youngest  woman  seventy-six. 

The  Arytenoids. — The  process  begins  in  the  base.     In  man  the  starting-point  is  the  mus- 
cular process,  but  in  woman  it  is  less  certain.     The  youngest  man  in  whom  the  process  was 
complete  was  seventy-five  and  the  youngest  woman  eighty-five. 
The  cartilago  triticea,  when  present,  also  tends  to  ossify. 


Lateral  view  of  larynx  after  removal  of  greater  part  of  right 
thyroid  ala,  showing  attachment  of  crico-thyroid  membrane  to 
arytenoid  cartilage.  The  free  border  of  the  membrane  constitutes 
the  thyro-arytenoid  ligament  and  the  framework  of  the  vocal  cord. 


THE  FORM  OF  THE  LARYNX  AND  ITS  MUCOUS  MEMBRANE. 


The  shape  of  the  larynx  depends  not  only  on  the  cartilages,  but  also  on  folds  of 
mucous  membrane  stretched  over  bands  of  connective  tissue  and  over  muscles. 

The  cavity  of  the  larynx  is  subdivided  into  three  parts  :  the  supraglottic,  the 
glottic,  and  the  infraglottic. 

The  supraglottic  region  (vestilmlum  laryngis)  begins  with  the  entrance  to  tin- 
larynx,  an  oval  (or  rather  a  heart-shaped)  plane,  which,  owing  to  the  height  and 
the  position  of  the  larynx,  faces  nearly  backward.  It  is  bounded  by  the  free  border 
of  the  epiglottis  in  front  and  by  the  arvcf>iglottic  fold  which  passes  from  this  on 
either  side  back  over  the  top  of  the  arytenoid  cartilages.  It  is  interrupted  in  the 
median  line  behind  by  a  notch.  On  either  side  of  this  the  fold  presents  a  small 
swelling  ( tuhcmilum  corniculntuni ),  caused  by  the  cartilage  of  Santorini,  anterior  to 
which  is  a  larger  one  ( tubc-rculuin  cimeifoi  me)  containing  that  of  Wrisberg.  Between 

1  Archiv  f.  Anat.  und  Phys.,  Anat.  Abth.,  1882. 


THE    LARYNX. 


1819 


these  and  the  sides  of  the  epiglottis  the  fold  contains  only  the  general  fibrous  envel- 
ope and  some  stray  muscular  fibres.  Below  the  entrance  in  front  lies  the  posterior 
surface  of  the  epiglottis,  concave  from  side  to  sick',  and  presenting  in  the  median  line, 
from  above  downward,  first  a  convexity,  extending  so  far  back  as  to  overhang  much 
of  the  larynx,  then  a  hollow,  and  finally  a  prominence,  the  tubercle  or  cushion.  A 
deep  crease  descends  on  each  side,  bounding  the  lower  part  of  the  epiglottis,  and 
meeting  its  fellow  below  the  tubercle.  The  mucous  membrane  is  very  closely  attached 
to  the  epiglottis,  and  so  thin  that  the  straw  color  of  the  cartilage  is  seen  through  it, 
turning  into  red  at  the  lower  part.  The  pits  for  the  glands  in  its  substance  can  also 
be  made  out.  The  lateral  wall  of  this  region,  which  is  separated  from  the  front  by 


FIG.  1545- 


["ongue 


Cushion  of  epiglottis 

Cuneiform  tubercle 
Tubercle  of  Santorini 

Posterior  crico-arytenoid 
muscle 


Cricoid  cartilag 


Foramen  caecum 


Right  faucial  tonsil 


t— Median  )  „. 
T_ ;  Lateral   I  Gtose<*«PiSlottiC  fold 


Superior  hyoid  cornu 
Superior  thyroid  cornu 

Sinus  pyriformis 
Glottis 


Pharyngeal  wall 


.(Esophagus 


Pharynx  opened  from  behind,  showing  superior  laryngeal  aperture  and  mucous  pouches  embraced  by  wings  of 
thyroid  cartilage  ;  cricoid  cartilage  and  muscles  are  covered  with  mucous  membrane. 

the  crease,  inclines  inward,  and  becomes  the  fold  of  mucous  membrane  known  as  the 
false  vocal  cord.  Farther  back  a  shallow  groove,  the  philtrum,  runs  from  the  inter- 
val between  the  tubercles  of  Santorini  and  of  Wrisberg  to  the  ventricle. 

The  sinus  pyriformis  (Figs.  1545,  1354)  is  a  shallow  cavity  to  the  outer  side  of 
the  aryepiglottic  fold,  bounded  externally  by  the  greater  horn  of  the  hyoid,  the  upper 
part  of  the  ala  of  the  thyroid,  and  the  thyro-hyoid  membrane  between  them.  It  is 
bilateral  and  properly  a  part  of  the  pharynx  (page  1598).  Its  mucous  membrane, 
continuous  with  that  of  the  larynx,  is  smooth  and  thin,  and  but  loosely  attached  to 
the  areolar  tissue  below  it.  In  the  front  part  there  is  a  transverse  fold  caused  by  the 
internal  branch  of  the  superior  laryngeal  nerve  passing  from  the  thyro-hyoid  mem- 
brane, which  it  perforates,  to  the  larynx  proper. 


1 820 


HUMAN   ANATOMY. 


The  glottic  region  extends  from  the  free  edges  of  the  false  cords  above  to 
those  of  the  true  ones  below.  The  narrowest  part  of  the  larynx,  the  rima  glottidis  or 
chink  of  the  larynx,  is  the  interval  between  the  true  cords  in  front  and  the  arytenoid 


FIG.   1546. 

Cartilage  of  epiglottis 
Areolar  tissue 


Mucous  membrane  covering  epiglottis 
Fissure  between  cartilages 
of  Santorini 


Internal 
jugular  vein 


Cartilage  of  Santorini  tubercle 
Stern  o-hyoid 

Thyro-hyoid 

Sinus  pyriformis 


Prevertebral  muscles 

Fourth  cervical  vertebra 


Superior 
cornu  of  hyoid  (cut) 


Sterno-mastoid 


Aryteno-epiglottic  fold  (cut) 
Posterior  wall  of  pharynx 


Anterior  part  of  section  across  neck  at  level  of  fourth  cervical  vertebra,  passing  through  upper  part  of  superior 

aperture  of  larynx. 

cartilages  behind.  The  false  vocal  cords  (plicae  ventriculares)  are  folds  of  mucous 
membrane  continuous  with  the  sides  of  the  supraglottic  space.  They  are  attached  in 
front  to  the  inner  side  of  the  angle  of  the  thyroid,  above  its  middle,  and  behind  to 
the  antero- external  surface  of  the  arytenoids.  They  are  soft  folds  of  mucous  mem- 
brane containing  connective  tissue  (out  of  which  a  skilful  dissector  can  manufacture 


FIG.  1547. 


Superior  hyoid  cornu 
/lj. —  Thyro-hyoid  ligament 


Body  of  hyoid 
bone 


Thyro-hyoid — 
membrane 
Mass  of  fat. 


Ventricle 

Thyroid 
cartilage 


Crico-thyroid 

membrane 
Cricoid  cartilage, 
anterior  arch 


Trachea 


Median  sagittal  section  of  larynx  ;  ri^-lit  side  seen  from 
within. 


Superior  thyroid 
cornu 


Cuneiform  tubercle 

— Tubercle  of 
Santorini 

False  vocal  cord 
Vocal  cord 

Thyroid  cartilage 


>icoid  car-  Arytenoid 
tilage,  pos-  cartilage 
terior  arch 


FIG.  1548. 


Ventricle 


Larynx  has  been  parlK  rut  ;u  r»ss  at  level  between 
false  HIM  I  true  \u.  Ml  COrat;  Upper  half  of  figure  re]iiesents 
under  surface  of  upper  pieee,  which  is  turned  backward. 


a  superior  thyro-arytenoid  ligament),  many  glands,  and  some  fibres  from  the  thyro- 
arytenoid  muscle.  The  true  vocal  cords  (plicae  vocnles)  arise  a  little  below  the  false 
ones,  and  run  to  the  vocal  processes  of  the  arytenoid  cartilages.  They  arise  in  both 


THE    LARYNX. 


1821 


sexes^a  little  above  the  middle  of  a  line  from  the  bottom  of  the  thyroid  notch  to  the 
lower  border  of  the  thyroid.  Taguchi l  gives  the  average  distance  in  men  from  the 
notch  to  the  vocal  cord  as  8.5  mm.,  and  from  below  as  10.5  mm.  In  women  he 
finds  these  distances  6. 5  mm.  and  8  mm.  respectively.  The  cords  arise  either  di- 
rectly from  the  thyroid,  just  on  each  side  of  the  depth  of  the  angle,  or  from  a 


FIG.  1549. 

False  vocal  cord 
Vocal  cord 
Ventricle  of  larynx 

Arytenoid  cartilage 


Stern  o-hyoid 

Ventricle  of  larynx 
Bursa 


Thyroid  cartilage 


Thyro-hyoid 
Pharynx 
Omo-hyoid 


Sterno-mastoid 


Sterno-mastoid 


Internal 
jugular  vein 


Pneumogastric  nerve 
Carotid  artery 

Palato-pharyngeus 

Prevertebral  fascia 


\  Thyro-arytenoideus 

Inferior  pharyngeal  constrictor 
Arytenoideus 


Anterior  part  of  section  across  neck  at  level  of  false  vocal  cords ;  on  left  side  ventricle  of  larynx  is  exposed. 

median  cartilaginous  nodule,  or  from  one  for  each  cord,  the  distance  between  them 
being  1.5  mm.  in  both  sexes.  The  false  cords  arise  about  3.5  mm.  above  the  true 
ones,  and,  on  the  average,  4  mm.  apart  from  each  other.  The  true  cords  are  tri- 
angular on  section,  with  a  sharp  free  edge,  an  upper  surface  slanting  downward  and 
outward  from  it,  a  longer  internal  surface  which  slants  steeply  downward  and  out- 
ward, and  an  imaginary  attached  base  placed  laterally.  The  free  edge  is  composed 
of  the  whitish  ligament  which  shows  through  the  thin  and  closely  attached  mucous 
membrane.  The  substance  is  chiefly  muscular  tissue  from  the  thyro-arytenoid,  which 
forms  a  three-sided  prism,  giving  a  solidity  which  the  false  cord  has  not.  Behind 
the  cords  the  glottic  region  is  bounded  by  the  arytenoid  cartilages,  and,  as  the  true 

FIG.  1550. 


Base  of  tongue 


Epiglottis- 


Vocal  cord 

Aryteno-epig-lottic  fold 

Sinus  pyriformis 

Vocal  proces 

Cuneiform  tubercl 

Tubercle  of  Santorini 


HE-- — • Lateral  glosso- 

epiglottic  fold 

&L, Median  glosso- 

epiglottic  fold 
B* Epiglottis 


False  vocal  cord 
Ventricle  of  larynx 
Vocal  cord 

.Rima  glottidis 
.Cuneiform  tubercle 
•Vocal  process 

-Tubercle 

of  Santorini 


Interior  of  larynx  as  seen  with  laryngoscope.    A,  rima  glottidis  widely  open  ;  B,  rima  glottidis  closed. 

cords  end  at  the  vocal  processes,  a  considerable  part  of  the  chink  of  the  glottis  is 
bounded  by  these  cartilages.  The  posterior  part  between  them  is  called  the  respira- 
tory, and  the  anterior,  between  the  cords,  the  vocal  part.  According  to  Moura,2  the 
entire  length  of  the  chink  in  the  male  is  23  mm.,  of  which  the  vocal  part  is  15.5  mm. 

1  Archiv  f.  Anat.  u.  Phys.,  Anat.  Abth.,  1889. 

2  Bull,  de  1'Acad.  de  M£decine,  Paris,  1879. 


1822 


HUMAN    ANATOMY. 


and  the  respiratory  7.5  mm.  In  the  female  the  length  is  17  mm.,  and  the  respective 
parts  measure  11.5  mm.  and  5.5  mm.  The  elasticity  of  the  vocal  part,  however, 
allows  it  to  stretch.  The  shape  of  the  rima  glottidis  \  aries  with  the  position  of  the 
arytenoids,  and  the  theoretically  straight  lines  of  its  borders  may  both  be  approxi- 
mated and  drawn  asunder,  and,  moreover,  may  be  bent  at  the  junction  of  the  two 
parts. 

The  ventricle  or  laryngeal  sinus  (ventriculus  laryngis)  is  a  pouch,  lined  with 
mucous  membrane,  opening  into  the  larynx  between  the  true  and  false  cords  of  each 
side.  The  horizontal  elliptical  opening  has  a  breadth  (vertically)  of  from  3-6  mm. 
As  has  been  stated,  the  upper  surface  of  the  true  cord  slants  downward  and  outward  ; 
but  the  ventricle  is  partly  under  cover  of  the  false  cord,  around  which  it  ascends. 
The  ascent  may  be  due  to  an  appendix  of  the  ventricle  (Fig.  1551),  which  may  be  an 
almost  separate  cavity  connected  with  the  front  of  the  ventricle  by  a  slit  or  an  irregular 

FIG.  1551. 


Glands 


Epiglottis 


,Lymphoid  tissue 


.Glands 


.  \Vntricle 


-Point  at  which 
squatnous  epithe- 
lium ends 


..Lateral  crico- 

arytenoid  muscle 


False  vocal  cord 


Lymphoid  tissue 
Vocal  cord 


Thyro-aryten 
muscle 


Thyroid  cartilage 


Cricoid  cartilage 
Frontal  section  of  larynx,  about  middle  of  vocal  cords.     X  3. 

opening.  Not  rarely,  however,  it  is  without  separation  from  the  rest  of  the  ventricle. 
It  may  ascend  to  a  height  of  15  mm.  from  the  bottom  of  tin-  ventricle.  These  cavi- 
ties are  compressed  laterally,  and  situated  in  the  thickness  of  the  wall  of  tin-  larynx 
proper,  internal  to  the  fossa  pyriformis.  According  to  Riidinger,  the  ventricles  are 
relatively  much  larger  in  the  male.  Occasionally  cases  of  great  over-development  of 
the  ventricles  are  met  with.  They  may  even  perforate  the  thyro-hyoid  membrane. 
This  is  analogous  to  the  sacs  of  the  anthropoid  apes.  Brosike l  has  seen  a  median 
pouch  perforating  the  thyroid  in  the  region  of  the  vocal  cords.  A  similar  structure 
occurs  in  the  horse,  ass,  and  mule.  The  function  of  the  true  cords  is  to  change  the 
size  and  shape  of  the  glottis  both  during  respiration  and  phonation,  and  to  cause 
sound  by  their  vibrations,  which  depend  in  part  on  their  tension.  When  drawn  into 

1  Virchow's  Archiv,  Bel.  xcviii.,  1884. 


THE    LARYNX. 


1823 


contact,  they  close  the  glottis  and  prevent  the  entrance  of  air,  but  from  their  shape 
they  seem  unfitted  to  prevent  its  exit.  This,  according  to  the  general  teaching,  is 
accomplished  by  the  valvular  action  of  the  false  cords,  to  which  the  ventricles  con- 
tribute, but  it  is  not  clear  that  they  contain  the  musculature  necessary  for  such  action. 

The  infraglottic  region  (conus  elasticus)  expands  laterally  beneath  the  true 
cords  so  as  to  become  practically  circular  before  reaching  the  lower  border  of  the 
cricoid.  The  little  fossa  beneath  the  arytenoid  cartilages  is  the  upper  part  of  this 
region,  which  is  broadest  between  them. 

The  mucous  membrane  of  the  larynx  is  in  parts  thin  and  tightly  bound 
down  to  the  cartilages  beneath  it,  and  elsewhere  thick,  with  much  subjacent  areolar 
tissue.  It  is  very  intimately  connected  to  the  free  part  of  the  epiglottis  and  to  all  of 
its  intralaryngeal  surface,  but  less  so  to  the  anterior  part  near  the  tongue.  It  is  closely 
applied  to  the  arytenoids  and  also  to  the  lower  part  of  the  cricoid.  It  is  thin  and 
adheres  very  tightly  to  the  true  vocal  cords  along  the  ligament.  In  the  aryepiglottic 


FIG.  1552. 


Glands 


Vocal  cords 

Thyro-arytenoid 
muscle 

Ventricle - 


Fibres  of  thyro 
arytenoid  perhaps 
inserted  into  vocal 
process 

Lateral  crico- 
arytenoid  muscle 


Glands 

— „ False  vocal  cord 

i 


Ventricle 


Vocal  process  of 
arytenoid  cartilage 


Cricoid  cartilage 


Frontal  section  of  larynx  through  vocal  processes  of  arytenoid  cartilages.    X  3. 

folds  it  is  lax  and  redundant.  Beginning  at  the  base  of  the  epiglottis,  the  epithelium 
covering  the  mucous  membrane  is  of  the  stratified  ciliated  columnar  type  throughout 
the  larynx,  with  the  exception  of  that  over  the  vocal  cords,  false  as  well  as  true, 
which  abruptly  changes  to  stratified  squamous.  Mucus-secreting  goblet-cells  occur 
in  varying  profusion  among  the  columnar  elements.  The  superficial  layers  of  the 
fibro-elastic  stroma  of  the  mucous  membrane  contain  many  lymphocytes,  which  in 
places  are  so  numerous  that  the  tunica  propria  resembles  lymphoid  tissue. 

The  glands  are  very  general.  They  occupy  pits  in  the  epiglottis,  are  very  numer- 
ous and  large  in  the  false  cords,  and  plentiful  in  the  walls  of  the  ventricles.  They  do 
not  occur  on  the  upper  surface  of  the  true  cords  within  3  or  4  mm.  of  the  free  edges, 
but  in  the  infraglottic  region  form  nearly  a  continuous  shallow  layer  to  within  2  or  3 
mm.  of  the  free  edge  of  the  vocal  cord.  The  laryngeal  glands  are  tubulo-alveolar  in 
form  and  mixed  mucous  in  type,  in  addition  to  the  mucus-producing  cells  containing 
groups  of  serous  elements. 

Lymphoid  tissue,   as  distinct  nodules,   is  occasionally  observed  on  the  posterior 


HUMAN   ANATOMY. 


surface  of  the  epiglottis  and  the  side  and  back  walls  of  the  larynx,  its  most  usual 
position  being  the  ventricle  (Fig.  1551).  Within  the  laryngeal  pouch  the  lymphoid 
tissue  is  so  constant  and  plentiful  that  laryngeal  tonsz/has  been  suggested  (Fraenkel) 
as  an  appropriate  name  for  these  collections. 


Cartilage  triticea 


Thyro-hyoid 
membrane 


Aryepiglotticus 

Arytenoideus, 
oblique  portion 

Arytenoideus, 
transverse  por- 
tion 

Crico- 

arytenoideus 
posticus 


Epiglottis,  dorsal  surface 


Superior  cornu 
of  hyoid  bone 

Superior  thyroid 
cornu 


THE  MUSCLES  OF  THE  LARYNX. 

The  extrinsic  muscles  of  the  larynx  should  include  those  going  to  the  hyoid  bone, 
which  is  physiologically  a  part  of  this  apparatus.  These  have  been  described  in  the 
systematic  consideration  of  the  Muscular  System  (page  543).  The  intrinsic  muscles 
are  the  crico-thyroid,  \\\&  posterior  crico-arytenoid,  the  lateral  crico-arytenoid,  the  thyro- 
arytenoid,  and  the  arytenoid.  All  of  these,  except  the  last,  are  in  pairs.  From  a 
physiological  stand-point  these  muscles  may  be  divided  into  three  groups  :  the  con- 
strictors, including  both  the  adductors  of  the  cords  and  those  which  draw  together  the 
supraglottic  portion  of  the  larynx  ;  the  dilators,  which  abduct  the  cords  ;  and  those 
which  modify  the  tension  of  the  cords  without  necessarily  approaching  or  separating 
them.  The  constrictors  are  the  lateral  crico-arytenoids,  the  thyro-arytenoids,  and 
the  arytenoid.  The  dilators  are  the  posterior  crico-arytenoids.  Those  modifying 
the  tension  of  the  cords  are  the  crico-thyroids,  which  stretch  them,  and  a  part  of 

the  thyro-arytenoids,  which  relax 

FIG.  1553.  them.      Moreover,  many  of  these 

muscles,  even  antagonistic  ones, 
when  acting  together  may  be  con- 
sidered as  parts  of  a  sphincter. 
The  laryngeal  muscles  are  ex- 
tremely variable,  especially  the 
thyro-arytenoid,  detached  fibres 
of  which  have  been  described  as 
the  thyro-epiglottideus. 

The  crico-thyroid  muscle 
(Fig.  1510)  is  well  defined,  pass- 
ing upward  and  outward  from  the 
anterior  ring  of  the  cricoid  to 
the  under  border  and  the  inferior 
horns  of  the  thyroid.  The  origin 
is  from  the  whole  of  the  anterior 
surface  of  the  arch,  except  for  a 
slight  interval  between  the  mus- 
cles. The  internal  fibres  are  nearly 
vertical  and  the  lateral  ones  nearly 
horizontal.  The  insertion  is  into 
the  lower  border  of  the  thyroid 
cartilage  from  a  point  a  few  milli- 
metres in  front  of  the  inferior  tubercle  to  all  the  rest  of  the  lower  border  and  the  front 
of  the  inferior  horn.  It  often  extends  a  little  onto  the  posterior  surface  of  the  ala. 
The  muscle  is  frequently  divided  into  a  superficial  and  a  deep  part.  The  distinction 
may  be  very  striking,  and  also  not  to  be  seen.  The  superficial  is  the  more  internal 
vertical  part,  which  conceals  a  little  of  the  origin  of  the  deeper.  The  crico-thyroid 
may  be  continuous  by  some  fibres  with  the  inferior  constrictor  of  the  pharynx.  It 
may  descend  to  the  first  ring  of  the  trachea,  and  it  may  give  off  fibres  to  the  capsule 
of  the  thyroid  body.  Occasionally  the  muscles  of  the  two  sides  are  connected  at  the 
lower  border  of  the  cricoid.  In  extreme  cases  each  may  cross  the  median  line. 

Action. — This  muscle  is  a  tensor  of  the  vocal  cords  by  separating  their  points 
of  attachment  on  the  thyroid  cartilage  from  those  on  the  arytenoids.  Although  the 
conventional  names  of  origin  and  insertion  have  been  used,  the  more  movable  of  tin- 
two  cartilages  is  the  cricoid,  and  the  action  of  the  muscles  is  to  raise  its  anterior  arch, 
thereby  tipping  the  posterior  plate  with  the  arytenoids  backward,  and  so  stretching 
the  cords.  While  the  thyroid  can  be  held  fixed  by  many  muscles,  the  only  extrinsic 
one  attached  to  the  cricoid  is  a  part  of  the  inferior  constrictor  of  the  pharynx,  so  that 


Posterior  margin 
of  thyroid  car- 
tilage 


Inferior  thyroid 
cornu 

Cricoid  cartilage 


Trachea 


Muscles  of  larynx  from  behind. 


THE    LARYNX. 


1825 


upon  the  cricoid  cartilage  devolves  the  whole,  or  nearly  the  whole  of  the  movement. 
Although  the  movement  is  generally  described  as  rotation  on  a  transverse  axis  pass- 
ing through  the  two  crico-thyroid  joints,  the  articulation  is  of  so  vague  a  character 
that  a  great  deal  of  sliding  occurs. 

The  posterior  crico-arytenoid  muscle  (Fig.  1554)  is  very  distinct  and 
occupies  the  hollow  on  either  side  of  the  median  ridge  on  the  back  of  the  cricoid 
cartilage.  It  is  triangular,  with  rounded  angles  at  the  base,  which  is  at  the  ridge, 
and  the  third  sharp  angle  at  the  posterior  border  and  upper  aspect  of  the  muscular 
process  of  the  arytenoid.  The  origin  is  not  from  the  whole  of  the  fossa  on  the  cri- 
coid, but  chiefly  from  the  region  of  the  ridge  whence  it  springs  by  tendinous  fibres. 
It  arises  also  from  the  lower  part  of  the  cricoid,  but  not  from  the  part  near  the 
arytenoid.  It  passes  over  the  capsule  of  the  joint,  with  which  it  is  intimately  fused, 
and  is  inserted  as  above  stated,  some  of  its  fibres  becoming  tendinous. 

Action. — It  pulls  the  muscular  process  downward  and  inward,  thus  raising  and 
everting  the  vocal  process  and  consequently  enlarging  the  cleft  of  the  glottis. 

Two  occasional  small  muscles  in  the  neighborhood  of  the  inferior  horn  of  the  thyroid  are- 
probably  aberrant  bundles  of  the  posterior  crico-arytenoid.  One,  the  posterior  crico-thyroid, 
slightly  diverging  from  the  lower  external  fibres,  runs  from  the  back  of  the  cricoid  upward  and 
outward  to  the  internal  aspect  of  the  inferior  horn  of  the  thyroid.  The  other,  ti\e  posterior  thyro- 
arytenoid,  runs  from  the  lower  horn  upward  to  be  inserted  with  the  posterior  crico-arytenoid  into 
the  muscular  process. 


Epiglottis 


Superior  thyroid 
cornu 

Aryepiglotticus  — 


Arvtenoideus 


Crico-arytenoideus  - 
lateralis 

Crico-arytenoideus 
posticus 

Cricoid  cartilage 


Hyoid  bone 


Laryngeal  pouch 

Right  thyroid  ala 
(cut) 


The  lateral  crico-arytenoid  muscle  (Fig.  1554),  of  an  elongated  triangular 
form,  arises  from  the  upper  border  of  the  lateral  part  of  the  cricoid  and  from  the 
ascending  edge  of  the  plate  as  far  as  the  arytenoid  joint.  It  also  may  have  fibres 
springing  from  the  crico-thyroid 

membrane.      It  is  inserted  into  the  FIG.  1554. 

front  of  the  muscular  process.  This 
muscle  is  less  well  defined  than  the 
posterior  crico-thyroid,  and  may 
be  more  or  less  fused  with  the 
thyro-arytenoid,  on  the  one  hand, 
and  the  crico-thyroid,  on  the  other. 

Action. — It  pulls  the  muscular 
process  forward,  thereby  bringing 
the  vocal  cord  nearer  to  its  fellow. 

The  thyro-arytenoid  mus- 
cle (Fig.  1554)  arises  from  the 
inner  surface  of  the  thyroid,  just 
outside  the  entering  angle,  from 
the  level  of  the  true  cord  to  the 
lower  border.  At  the  side  it  arises 
from  a  part  of  the  crico-thyroid 
membrane,  and  may  there  be  con- 
tinuous with  the  lateral  crico-ary- 
tenoid. It  runs  backward  and  is 
inserted  into  the  upper  surface  of 
the  vocal  process  of  the  arytenoid 
and  into  the  antero-external  sur- 
face of  that  cartilage.  It  is  convenient  to  speak  of  an  internal  and  an  external  part, 
but  there  is  no  separation  between  them.  The  internal  portion  (m.  thyreoarytae- 
noideus  vocalis)  is  a  prismatic  mass,  triangular  on  section  (Fig.  1551),  forming  the 
bulk  of  the  true  cord,  with  one  of  its  angles  against  the  ligament  in  the  free  edge. 
Ludwig  taught  that  fibres  diverged  from  the  body  of  this  muscle  to  be  inserted  suc- 
cessively into  the  ligamentous  band  of  the  vocal  cord,  which  thus  resembled  the 
tendon  of  a  muscle  receiving  oblique  fibres  along  its  side.  These  were  supposed  to 
modify  its  tension  indefinitely  by  pulling  upon  it  at  various  points.  This  view  has 
been  denied  by  Luschka,  and  the  point  remains  undecided.  Jacobson l  found  on 
1  Archiv  f.  mikro.  Anat.,  Bd.  xxix.,  1887. 
US 


Thyro-arytenoideus 
externus 


' Crico-thyroideus 

(cut) 


Trachea 


Muscles  of  larynx,  lateral  view  after  partial  removal  of  right 
thyroid  ala. 


1826 


HUMAN    ANATOMY. 


FIG.    1555. 


Body  of  hyoid 
bone  (cut) 


microscopic  sections  that  fibres  were  often  inserted  obliquely  into  the  cord  and  into 
the  end  of  the  vocal  process.  There  was,  however,  much  variation,  and  in  some 
cases  no  such  fibres  were  found.  Our  own  observations  incline  us  to  look  upon  such 
fibres  as  possible,  but  probably  in  the  ordinary  larynx  they  are  few  and  far  between. 
The  external  portion  (Fig.  1554)  is  a  thin  membrane  on  the  outer  side  of  the  ven- 
tricle, with  its  fibres  spreading  upward  and  backward  towards  the  aryepiglottic  fold. 
Some  few  fibres  are,  or  may  be,  found  in  the  false  cord,  and  some  occasionally  arch 
over  the  ventricle.  The  external  portion  is  very  irregular  and  inclined  to  give  off 
aberrant  bundles.  The  superior  thyro-arytenoid  is  a  common  one.  It  arises  from 
the  inner  side  of  the  ala  of  the  thyroid,  near  the  top,  a  little  outside  of  the  notch,  and 
runs  downward  and  backward  to  the  top  and  anterior  aspect  of  the  vocal  process, 
resting  on  the  outer  side  of  the  external  part  of  the  thyro-arytenoid  and  crossing  it 
at  right  angles.  It  consists  of  long  parallel  fibres  and  varies  much  in  size.  The 
thyro-epiglottic  muscle  is  simply  fibres  of  the  system  of  the  thyro-arytenoid  that  pass 
upward  to  the  side  of  the  epiglottis.  We  incline  to  consider  the  aryepiglottic  muscle 

(F"ig.  1554) — a  little  bundle  ex- 
tending from  the  side  of  the 
arytenoid  to  the  epiglottis  in 
the  edge  of  the  fold — a  part 
of  this  same  system. 

Action. — That  of  the  in- 
ternal part  of  the  thyro-aryte- 
noid is  to  relax  the  vocal  cords 
by  approximating  their  ends  ; 
if,  however,  the  fibres  inserted 
into  the  cords  be  worth  consid- 
ering, this  action  must  be  modi- 
fied by  the  stretching  of  parts 
of  the  cords  while  others  are 
relaxed.  The  irregularity  of 
this  arrangement  is  quite  in  har- 
mony with  the  endless  variations 
of  the  human  voice.  The  shape 
of  the  walls  below  the  true  cords 
must  also  be  modified  by  the 
swelling  of  the  contracting  mus- 
cle. The  action  of  the  outer 
portion  of  this  muscle  must  be 
in  the  main  that  of  a  constrictor 

of  the  supraglottic  region.      It  is  possible  that  when  the  cords  are  abducted  some  of 
the  fibres  inserted  into  the  muscular  processes  may  act  as  adductors. 

The  arytenoid  muscle  (m.  interarytaenoideus)  is  a  mass  of  fibres  running  trans- 
versely between  the  hollows  on  the  posterior  surfaces  of  the  arytenoid  cartilages,  which 
it  fills  (Fig.  1553).  There  is  usually  a  superficial  oblique  part  of  this  muscle  which, 
when  well  developed,  is  formed  by  two  bands  crossing  each  other  like  the  arms  of  an 
X  placed  on  its  side.  Each  arm  starts  from  the  muscular  process  of  the  arytenoid  and 
crosses  to  the  summit  of  the  arytenoid  of  the  opposite  side.  Here  it  may  end  or  be 
continuous  with  the  fibres  of  the  aryepiglottic  muscle,  which  ascend  to  the  epiglottis. 
One  or  both  arms  may  be  wanting,  and  this  part  may  be  more  or  less  fused  with  the 
deeper  transverse  fibres. 

Action. — It  draws  the  arytenoid  cartilages  together,  and  is,  moreover,  an  im- 
portant part  of  the  sphincter-like  arrangement. 

Vessels. — The  arteries  are  the  superior  laryngeal  and  the  crico-thyroid  from 
the  superior  thyroid  artery  and  the  inferior  laryngeal  from  the  inferior  thyroid  artery. 
The  superior  laryngeal  pierces  the  thyro-hyoid  membrane  some  5  mm.  from  the 
superior  horn  of  the  thyroid  and  about  midway  between  the  top  and  the  bottom. 
After  giving  off  an  epiglottic  branch,  which  on  its  way  supplies  the  areolar  tissue 
anterior  to  the  epiglottis,  the  vessel  runs  downward  and  backward  under  cover  of  the 
ala  of  the  thyroid  to  its  distribution  in  the  upper  part  of  the  larynx.  The  crico- 


Epiglottis 


Mass  of  fat 


False  vocal  cord 

Thyroid  cartilage 

True  vocal  cord 

Thyro-arytenoideus, 

internus 

Crico-thyroideus 

Anterior  arch  of  cricoid 
cartilage 


Tracheal 
cartilages 


Greatei  hycid 
cornu 


Superior  thyroid 
cornu 


Ventricle  of  larynx 
Arytenoid  cartilage 

Crico-arytenoideus 

lateralis 
Posterior  arch  of 

cricoid  cartilage 
Line  of  cut  mucosa 


Trachea 


Sagittal  section  of  larynx  from  within  ;   mucous  membrane  has  been 
removed  from  vocal  cord  to  lower  level  of  cricoid  cartilage. 


THE  LARYNX. 


1827 


FIG.   1556. 


thyroid  branch  meets  its  fellow  so  as  to  form  an  arch  across  the  median  line  and 
sends  perforating  branches  into  the  larynx  through  the  crico-thyroid  membrane. 
The  inferior  laryngeal  from  the  inferior  thyroid  reaches  the  region  of  the  back  of  the 
larynx  from  the  side.  It  anastomoses  with  the  superior  laryngeal  and  sometimes 
sends  branches  through  or  into  the  arytenoid  muscle.  The  vocal  cords  possess 
relatively  few  blood-vessels. 

The  veins  correspond  in  the  main  to  the  arteries,  but,  owing  to  their  greater 
size  and  freer  anastomoses,  they  seem  in  more  immediate  relation  with  those  of  the 
thyroid  body.  Moreover,  they  tend  to  form  a  median  descending  vessel  in  the  front 
of  the  neck.  There  is  a  plexus  on  the  pharyngeal  side  of  the  back  of  the  larynx 
which  communicates  through  the  folds  at  the  sides  of  the  entrance  with  the  veins  of 
the  dorsum  of  the  tongue.  The  inferior  laryngeal  vein  empties  into  the  inferior 
thyroid  through  a  circular  plexus  around  the  entrance  of  the  trachea. 

The  lymphatics  of  each  side  empty  into  two  chief  vessels,  of  which  the  superior 
pierces  the  thyro-hyoid  membrane,  carrying  the  lymph  from  the  supraglottic  region 
to  the  nodes  under  or  near  the  sterno-mastoid.  The  inferior  vessel  descends  under 
the  mucous  membrane  outward  and  backward  to  the  nodes  along  the  posterior  sur- 
face of  the  trachea.  It  may,  however,  open  into  an  inconstant  node  in  front  of  the 
crico-thyroid  membrane.  This  node  occurs  in  44  per  cent, 
of  adults  and  in  57  per  cent,  of  children.  It  may  be 
double.1 

Nerves. — These  are  the  superior  and  the  inferior 
laryngeal  nerves,  both  from  the  vagus.  The  superior,  on 
reaching  the  thyro-hyoid  membrane,  divides  into  an  exter- 
nal and  an  internal  branch.  The  external  continues  down- 
ward and  forward  to  the  crico-thyroid  muscle,  which  it 
supplies.  It  is  in  relation  with  the  pharyngeal  plexus  and 
the  superior  sympathetic  ganglion.  The  internal  branch 
pierces  the  membrane  together  with  the  superior  laryngeal 
artery,  and  supplies  the  greater  part  of  the  mucous  mem- 
brane. Its  ramifications  are  in  two  groups  :  ascending 
ones  to  the  epiglottis,  the  region  just  before  it,  and  to  the 
aryepiglottic  folds  ;  others  passing  to  the  mucous  mem- 
brane within  the  larynx  and  to  that  of  the  posterior  surface 
looking  towards  the  pharynx.  The  inferior  laryngeal,  as- 
cending by  the  side  of  the  back  of  the  trachea,  divides  into 
two  branches.  The  branch  nearer  the  median  line  inner- 
vates the  posterior  crico-arytenoid  and  the  arytenoid  mus- 
cles. Its  fibres,  in  part  sensory,  enter  into  communication 
with  those  of  the  superior  laryngeal.  The  other  branch 
of  the  inferior  laryngeal  goes  to  the  other  intrinsic  muscles 
of  the  pharynx.  Thus  the  superior  laryngeal  divides  into 
a  motor  branch  that  ends  in  one  muscle,  and  a  sensory  division  which  plays  the 
greater  part  in  supplying  the  mucous  membrane.  The  inferior  laryngeal  is  also  a 
mixed  nerve,  but  chiefly  motor.  It  supplies  all  the  other  muscles  and  helps  to  sup- 
ply the  mucous  membrane.  A  remarkable  peculiarity  of  the  sensory  nerves  is  a 
tendency  to  cross  the  median  line,  so  that  certain  regions  are  reached  from  both 
sides. 

The  general  teaching  by  English  anatomists  has  been  that  the  superior  laryngeal 
is  as  above  stated  and  that  the  inferior  is  purely  motor.  Exner  *  made  observations, 
in  part  confirmed  and  in  part  disputed,  to  the  effect  that  both  nerves  are  mixed, 
supplying  both  muscles  and  mucous  membrane  (the  superior  supplying,  in  part  at 
least,  certain  muscles  within  the  larynx),  and  that  both  motor  and  sensory  fibres 
cross  the  median  line,  so  that  some  muscles  receive  the  corresponding  nerve  of  both 
sides.  Moreover,  he  found  in  some  animals  a  middle  laryngeal  nerve  from  the 
pharyngeal  branch  of  the  vagus,  of  which  the  analogue  exists  in  man,  in  whom  it 
goes,  together  with  the  superior  laryngeal,  to  the  crico-thyroid  muscle  of  both  sides. 

1  Nicolas  in  Poirier's  Trait£  d' Anatomic  Humaine. 

2  Vienna  Akad.  Sitzungsbericht,  1884. 


t—  Vestibule 


alse  vocal 
cord 


Ventricle 


Vocal  cord 


Trachea 


Cast  of  cavity  of  larynx  and 
adjacent  part  of  trachea  ;  anterior 
aspect. 


1828  HUMAN   ANATOMY. 

In  the  above  description  we  have  followed  Onodi,1  who  denies  entirely  the  existence 
of  the  middle  laryngeal  in  man. 

The  endings  of  the  numerous  sensory  nerves  in  the  mucous  membrane,  as 
described  by  Retzius,  Fusari,  Ploschko,  and  others,  include  free  terminations  between 
the  epithelial  cells  and  subepithelial  end-arborizations.  According  to  Ploschko, 
special  end-organs,  composed  of  columnar  cells  surrounded  by  delicate  nerve-fibrilke, 
exist  within  the  true  vocal  cords.  Taste-buds  occur  not  only  on  the  posterior  sur- 
face of  the  epiglottis,  but  also  within  the  laryngeal  mucous  membrane  in  the  vicinity 
of  the  arytenoid  cartilages. 

Position  and  Relations  of  the  Larynx. — The  larynx  forms  a  part  of  the 
anterior  wall  of  the  pharynx  and  rests,  therefore,  against  its  posterior  wall.  In  the 
adult  male  the  tip  of  the  epiglottis  is  opposite  the  lower  border  of  the  third  cervical 
vertebra  and  the  lower  end  of  the  cricoid  opposite  some  part  of  the  seventh  vertebra. 
Thus  in  man  it  covers  about  four  vertebral  bodies,  with  the  intervening  disks.  It  is 
small  in  the  female  and  rather  higher.  Mehnert  '2  believes  that  in  the  living  body  in 
the  upright  position  the  cricoid  is  about  one  vertebra  lower  than  it  is  after  death  in 
the  recumbent  position.  Individual  variation  is  marked,  as  is  shown  by  the  results 
compiled  from  the  researches  of  Taguki.3  Thus  in  thirty-five  men  the  lower  border 
of  the  cricoid  was  opposite  or  below  the  seventh  vertebra  twenty-nine  times,  but  in 
thirty-three  women  only  twenty-one  times.  It  was  above  it  six  times  in  men  and 
twelve  times  in  women  ;  in  one  case  (male)  it  was  as  high  as  the  fifth  vertebra. 

Anteriorly  the  larynx  lies  beneath  the  middle  layer  of  the  cervical  fascia.  The 
lobes  of  the  thyroid  rest  on  either  side  against  the  cricoid  and  thyroid.  The  larynx 
as  a  whole  can  be  raised  and  depressed  by  muscles,  and  changes  its  position  with  the 
movements  of  the  spine.  Thus,  when  the  neck  is  bent,  it  falls  i  cm. ,  and  rises  3  cm. 
when  the  neck  is  extended.  When  the  head  is  turned  to  one  side,  the  hyoid  is  twisted 
less  than  the  head,  but  more  than  the  larynx,  although  the  latter  and  the  trachea  may 
share  in  the  movement.  The  larynx  may  be  displaced  sideways  by  external  pressure. 

Changes  with  Age  and  Sexual  Differences. — At  birth  the  larynx  is  very 
small,  but  may  be  said  to  be  relatively  larger  than  later.  The  sharp  angle  of  the  thy- 
roid cartilage  is  entirely  wanting.  The  larynx  grows  gradually  up  to  puberty,  when  it 
takes  on  a  sudden  expansion,  which  occurs  in  both  sexes,  but  is  much  more  marked 
in  the  male.  According  to  Luschka,  it  doubles  in  man  and  increases  by  less  than 
half  in  woman.  The  most  marked  sexual  difference  is  the  size  and  prominence  of 
the  thyroid  cartilage  in  the  male.  The  duration  of  the  process  by  which  the  larynx 
of  a  child  changes  into  that  of  an  adult  may,  according  to  F.  Merkel,  be  as  much  as 
two  years,  and,  in  fact,  changes  may  occur  throughout  growth.  In  the  foetus  the 
position  of  the  larynx  is  very  high.  At  birth  the  lower  border  of  the  cricoid  is  oppo- 
site the  lower  border  of  the  fourth  vertebra.  Symington  found  it  at  six  years  at  the 
lower  border  of  the  fifth  and  at  thirteen  at  the  top  of  the  seventh.  Probably  it  reaches 
what  may  be  called  its  permanent  position  at  about  puberty.  Mehnert,  however,  finds 
from  his  observations  on  the  living  that  the  descent  continues  till  about  thirty,  when 
there  is  a  great  retardation,  or  even  a  suspension,  of  the  process  till  about  sixty,  when 
it  goes  on  again  with  renewed  activity.  According  to  him,  the  cricoid  may  ultimately 
reach  the  second  or  even  the  third  thoracic  vertebra.  It  is  to  be  noted  that,  while 
the  earlier  descent  is  a  physiological  process,  that  of  old  age  is  a  degenerative  one, 
depending  in  part  on  changes  in  the  spine  and  on  the  loss  of  elasticity  of  the  tissu 

PRACTICAL   CONSIDERATIONS:    THE   LARYNX. 

The  Air-Passages. — The  hyoid  bone  is  closely  contiguous  to  the  opening  of 
the  larynx,  and  as  its  injuries  derive  their  chief  surgical  importance  from  that  rela- 
tion, they  are  considered  here. 

Fracture  of  the  hyoid  results  from  compression  by  the  grasp  of  a  hand,  by  the 
rope  in  cases  of  hanging,  or  from  a  direct  blow.  It  usually  occurs  near  the  junction 
of  the  greater  cornu  with  the  body  of  the  bone.  Displacement  is  not  apt  to  be 

1  Die  Anatomic  und  Physiologic  der  Kehlkopfnerven,  Berlin,  1902. 

1  Ueber  topographische  Altersveriindertingen  des  Atmungsapparates,  1901. 

1  Archiv  f.  Anat.  u.  Phys.,  Anat.  Abth.,  1889. 


PRACTICAL   CONSIDERATIONS:   THE   LARYNX.  1829 

marked,  because  the  great  horn  is  held  above  by  the  digastric  aponeurosis  and  the 
hyo-glossus  muscle  and  below  by  the  thyro-hyoid  ligament  and  muscle.  Excep- 
tionally the  middle  constrictor  of  the  pharynx  may  draw  it  somewhat  backward  and 
inward.  The  attachments  to  the  hyoid  of  the  constrictor  and  of  the  hyo-glossus  and 
genio-hyo-glossus  invariably  make  deglutition  and  speech  painful  after  this  fracture, 
while  the  genio-hyoid  and  digastric,  by  their  contraction,  cause  pain  on  opening  the 
mouth.  The  associated  swelling  may  involve  the  epiglottic  mucous  membrane  and, 
spreading  thence,  give  rise  to  serious  dyspnoea. 

The  thyro-hyoid  membrane,  springing  from  the  posterior  upper  margin  of  the 
hyoid  bone  and  attached  to  the  upper  border  of  the  thyroid  cartilage,  has  interposed 
between  its  anterior  surface  and  the  posterior  face  of  the  body  of  the  hyoid  a  bursa 
which  descends  below  the  lower  border  of  that  bone,  and  when  enlarged  forms  a 
cystic  swelling  situated  in  the  median  line  of  the  neck,  just  beneath  the  hyoid. 
Thyro-lingual  cysts  are  sometimes  found  in  the  same  situation. 

A  similar  cystic  swelling,  lined  with  columnar  epithelium  and  occupying  the 
same  region,  is  referable  to  the  persistence  of  the  fcetal  thyro-lingual  duct.  At  the 
upper  end  of  that  duct  such  a  cyst  would  lie  in  the  mid-line  of  the  tongue  between 
the  two  genio-hyo-glossi  muscles.  At  the  lower  end  it  would  lie  over  the  thyroid  or 
the  cricoid  cartilage.  The  sinuses  formed  by  the  bursting  of  such  cysts,  or  originally 
by  the  persistence  of  portions  of  the  thyro-lingual  duct,  are  obstinate,  and,  on  account 
of  their  epithelial  lining,  must  be  dissected  out  completely  to  secure  healing. 

The  lower  portion  of  the  thyro-hyoid  membrane  is  covered  in  the  mid-line  by 
cervical  fascia  and  skin,  laterally  by  the  sterno-hyoid  and  thyro-hyoid  muscles. 

Cut-throat  wounds  of  the  neck,  especially  if  suicidal,  are  apt  to  pass  through 
this  membrane,  which  is  made  tense  when  the  head  is  thrown  backward,  and,  if  they 
are  deep,  will  divide  the  inferior  constrictor,  open  the  pharynx,  and  possibly  wound 
or  sever  the  epiglottis  near  its  base,  first  passing  through  the  cellulo-adipose  tissue 
that  intervenes.  If  the  wound  is  not  immediately  beneath  the  lower  border  of  the 
hyoid,  it  may  divide  the  internal  branches  of  the  superior  laryngeal  nerve,  leading 
ultimately  to  a  pneumonia  from  the  inspiration  of  foreign  matter.  In  infrahyoid 
pharyngotomy  such  a  transverse  wound,  hugging  the  lower  edge  of  the  hyoid,  gives 
access  to  the  base  of  the  pharynx  and  the  supraglottideal  region. 

Above  the  hyoid  a  cut-throat  wound  would  divide  the  tongue  muscles  and  enter 
the  mouth.  Below  the  thyroid  it  would  pass  through  the  crico-thyroid  membrane 
and  open  the  larynx.  Still  lower  the  trachea  would  be  incised  or  severed. 

The  great  vessels  often  escape  in  suicidal  wounds,  as  the  usual  position  of  the 
head  in  extreme  extension  increases  the  projection  of  the  laryngeal  apparatus  and 
therefore  the  depth  of  the  vessels  from  the  surface.  One  reason  for  their  escape 
when  the  air-passages  below  the  glottis  are  opened  may  be  that  the  sudden  rush 
of  air  from  the  lungs  and  consequent  collapse  of  the  chest-walls  deprive  the  muscles 
running  from  the  thorax  to  the  humerus  of  their  fixed  point  of  support,  and  that 
the  arm  necessarily  drops  (Hilton).  Death  may  be  caused,  however,  by  hemor- 
rhage from  the  superior  thyroid  or  the  lingual  artery,  or  even  from  the  crico-thyroid 
if  the  blood  enters  the  larynx  or  trachea  ;  or  may  result  from  suffocation  produced 
by  the  dropping  backward  of  the  tongue  after  division  of  the  genio-hyoid,  hyo- 
glossus,  and  genio-hyo-glossus  muscles,  or  by  the  occlusion  of  the  glottis  by  a  partly 
divided  epiglottis  or  arytenoid. 

Fracture  of  the  thyroid  or  cricoid  cartilage  may  occur  from  the  same  causes  that 
produce  fracture  of  the  hyoid  bone.  The  thyroid,  on  account  of  its  greater  prom- 
inence, suffers  more  frequently.  Fractures  of  the  thyroid  are  seen  oftener  in  males 
than  in  females,  because  («)  in  the  former  it  is  relatively  more  prominent  ;  (3)  the 
process  of  ossification — which,  in  common  with  other  hyaline  cartilages,  it  undergoes 
after  adult  life  has  been  reached — is  more  complete  in  them  ;  and  (<:)  males  are 
oftener  exposed  to  violence. 

The  symptoms  depend  for  their  gravity  chiefly  upon  the  degree  of  involvement  of 
the  laryngeal  mucous  membrane.  If  that  is  wounded,  bloody  expectoration,  aphonia, 
and  dyspnoea  are  present,  and  tracheotomy  may  be  urgently  indicated.  In  any  event, 
deglutition  is  painful.  The  voice  is  usually  altered,  and  there  is  apt  to  be  some  ex- 
ternal deformity.  Crepitus  may  be  present,  but  should  be  distinguished  from  the 


1830  HUMAN   ANATOMY. 

sound  produced  by  moving  the  normal  larynx  laterally,  and  caused  by  the  friction  be- 
tween the  somewhat  irregular  anterior  surface  of  the  vertebral  column  and  the  posterior 
border  of  the  thyroid,  the  corresponding  surface  of  the  cricoid,  and  the  lower  part  of 
the  pharynx,  which  move  together.  This  normal  crepitus  disappears  in  retropharyn- 
geal  abscess,  but  persists  in  retrolaryngeal  abscess  (Allen).  It  should  be  remembered 
that  the  superior  cornua  of  the  thyroid  are  sometimes  found  separate  from  the  body. 

The  cricoid  and,  much  more  rarely,  the  thyroid  and  arytenoid  cartilages  may 
be  the  subject  of  perichondritis  secondary  to  ulceration  (typhoidal,  cancerous,  syphi- 
litic, or  tuberculous)  of  the  interior  of  the  larynx.  In  the  case  of  the  cricoid  it  is 
asserted  that  the  condition  may  result  from  the  pressure  of  the  posterior  aspect  of 
the  cartilage  against  the  spine  in  very  debilitated  subjects,  or  from  the  traumatism 
caused  by  the  frequent  passage  of  an  cesophageal  bougie  (Pearce  Gould).  The 
origin  of  the  inferior  constrictor  from  the  cricoid  accounts  for  the  pharyngeal  spasm 
and  dysphagia  said  to  accompany  disease  of  this  cartilage  (Gibbs). 

Allen  says  that  the  cricoid  is  relatively  more  prominent  in  women  than  in  men, 
and  that  it  is  often  the  site  to  which  abno.rmal  sensations  originating  in  the  pharynx 
are  referred,  because  in  such  conditions  deglutition  is  painful,  and  since  the  cricoid  lies 
at  the  lower  part  of  the  pharynx,  its  motions  determine  a  greater  amount  of  distress 
than  do  the  corresponding  motions  at  any  other  part  of  the  throat. 

The  epiglottis  is  not  infrequently  affected  by  syphilis,  and  is  also,  although  more 
rarely,  the  seat  of  tuberculous  lesions,  and  may  be  extensively  ulcerated  or  may  become 
necrotic.  The  danger  of  such  cases  results  usually  from  the  accompanying  oedema 
(vide  infra),  but  in  rare  instances  a  sloughing  and  wholly  or  partially  separated  epi- 
glottis may  directly  occlude  the  laryngeal  aperture. 

Infection  originating  m  disease  of  the  epiglottis  may  involve  the  cellulo-adipose 
tissue  between  its  base  and  the  thyro-hyoid  membrane,  giving  rise  to  a  thyro-hyoid 
abscess  which  may  extend  towards  the  mouth  and  project  in  the  groove  between  the 
root  of  the  tongue  and  the  epiglottis.  Such  an  abscess  may  also  follow  primary 
infection  of  either  the  tongue  or  the  thyroid.  It  is  very  apt  to  cause  oedema  of  the 
glottis.  The  condition  known  by  this  name  may  occur  in  any  form  of  laryngitis,  or 
by  extension  of  inflammation  from  the  mouth,  tongue,  or  pharynx,  or  as  a  result 
of  trauma  or  of  wound,  scald,  or  the  application  of  local  irritants.  It  involves  the 
glottis  only  secondarily.  The  thin  mucous  membrane  covering  the  true  vocal  cords 
and  the  arytenoids  is  so  closely  applied  to  them,  and  the  subcutaneous  connective 
tissue  is  so  scanty,  that  there  is  no  opportunity  for  much  exudation.  But  in  the 
supraglottidean  region  the  mucosa  is  thick  and  the  submucosa  plentiful,  especially 
over  the  aryteno-epiglottidean  folds,  and  almost  equally  so  in  the  ventricles  and  over 
the  false  cords  and  the  posterior  surface  of  the  epiglottis.  Effusion  of  serum  and 
swelling  are  thus  favored  and,  according  to  their  degree,  will  produce  hoarseness, 
aphonia,  dyspnoea,  cyanosis,  or  positive  suffocation.  In  some  cases  of  oedematous 
laryngitis  the  swelling  affects  chiefly  the  region  below  the  glottis  {subglottic  a-dcma ) 
and  causes  the  same  symptoms.  This  is  rarer  and  is  attended  by  less  effusion  on 
account  of  the  relatively  closer  association  of  the  mucosa  and  the  cricoid  cartilage. 

The  mucous  glands  of  the  larynx  which  supply  the  moisture  needed  in  normal 
phonation  are  sometimes  inflamed  as  an  indirect  result  of  the  over-use  of  the  voice, 
— as  in  clergymen,  costermongers,  public  speakers,  etc.  The  increased  volume  of 
air  taken  in  through  the  mouth  dries  up  the  mucous  surface  of  the  larynx,  and  the 
effort  to  compensate  for  this  may  result  in  such  irritation  of  the  glands  and  mucosa 
as  to  cause  a  form  of  chronic  laryngitis, — "  clergyman's  sore  throat." 

The  rima  glottidis, — the  aperture  of  \he  glottis, — the  narrowest  portion  of  the 
air-passages,  measures  a  little  less  than  one  inch  antero-posteriorly  in  the  adult  male. 
Its  transverse  diameter  at  its  widest  portion  is  about  one-third  of  an  inch.  In  the 
male  before  puberty,  and  in  the  female,  these  measurements  are  about  one-fourth 
less.  They  are  important  in  reference  to  the  introduction  of  instruments  and  the 
arrest  of  foreign  bodies  (vide  infra). 

The  level  of  the  glottis — i.e. ,  of  the  true  vocal  cords — is  a  little  above  the 
middle  of  the  anterior  margin  of  the  thyroid  cartilage. 

The  shape  of  the  aperture  varies.  It  is  linear  when  a  high  note  is  produced  in 
speaking  or  singing,  triangular  (with  the  apex  forward,  equal  sides  and  a  narrow 


PRACTICAL   CONSIDERATIONS  :   THE   LARYNX.  1831 

base)  during  quiet  respiration,  and  diamond- shaped  (with  the  posterior  angle  cut 
off)  in  forced  breathing.  As  various  forms  of  ulceration  (tuberculous,  syphilitic, 
diphtheritic)  may  affect  the  mucous  membrane  covering  the  true  vocal  cords,  or  the 
cords  themselves,  or  the  structures  in  their  immediate  vicinity  (especially  the  aryteno- 
epiglottidean  and  interarytenoid  folds  and  the  ventricular  bands),  and  as  cicatrization 
with  subsequent  contraction  of  scar  tissue  may  follow,  diminution  of  the  calibre  of 
the  rima  glottidis  (stricture)  is  not  uncommon. 

Polyps,  warty  growths,  and  other  benign  tumors  are  found  in  the  vicinity  of  the 
vocal  cords,  and  if  they  cannot  be  removed  by  intralaryngeal  operation,  may  neces- 
sitate thyrotomy.  Subglottic  tumors  are  relatively  infrequent.  They  often  spring 
from  the  inferior  surface  of  the  vocal  cords,  intraglottic  growths  from  the  free 
border  of  the  anterior  part  of  the  vocal  cords,  and  supraglottic  growths  from  the 
epiglottis  and  the  aryteno-epiglottic  folds  (Delavan). 

Spasm  of  the  glottis  (laryngismus  stridulus)  may  occur,  especially  in  infancy, 
from  reflex  irritation,  and  may  cause  great  dyspnoea  or  may  even  result  fatally.  The 
irritation  is  conveyed  chiefly  to  the  inferior  laryngeal  nerves  through  the  pneumo- 
gastrics,  if  the  cause  is  undigested  food  ;  through  the  trifacial,  if  the  irritation  is  asso- 
ciated with  dentition  ;  or  through  the  spinal  accessory,  if  vertebral  disease  is  present. 

The  different  forms  of  laryngeal  paralysis  should  be  studied  in  connection  with 
the  physiology  of  phonation.  Some  of  the  chief  anatomical  considerations  may  be 
indicated  by  the  following  classification,  which  is,  however,  necessarily  incomplete, 
as  failing  to  include  the  central  causes  of  paralysis — as  in  bulbar  palsy — and  those 
due  to  toxaemia,  as  the  post-diphtheritic. 

1.  Those  due  to  direct  or  indirect  involvement  of  the  superior  laryngeal  nerves. 
(a)   Sensory  and  thyro-epiglottic — or  aryepiglottic — paralysis,  characterized  by  a 

tendency  of  food  or  liquids  to  enter  the  larynx,  by  dysphagia,  by  immobility  of  the 
epiglottis,  and  by  diminished  sensation  in  both  the  pharyngeal  and  laryngeal  mucous 
membranes,  would  suggest  especial  implication  of  the  internal  branch. 

(£)  Crico-thyroid  and  thyro-arytenoid  paralysis,  causing  loss  of  tension  in  the 
vocal  cords,  inability  to  regulate  and  control  the  voice,  and  with  evidence  of  the 
want  of  action  of  the  crico-thyroids  detected  by  the  finger  placed  on  either  side  of 
the  crico-thyroid  interval  externally  during  phonation  (Agnew),  may,  in  some  cases, 
be  referred  anatomically  to  the  external  branch. 

2.  Those  due  to  involvement  of  the  inferior  laryngeal  nerves. 

(#)  Lateral  crico-arytenoid  paralysis,  causing  separation  of  the  vocal  cords, 
with  more  or  less  complete  aphonia,  may  be  due  to  implication  of  the  external 
branch.  In  many  cases  there  will  be  evidence  of  the  existence  of  innominate  or 
aortic  aneurism,  thyroid  or  bronchial  glandular  enlargement,  carcinoma  of  the  cesoph- 
agus,  or  some  other  condition  competent  to  produce  pressure  on  the  nerve.  The 
paralysis  may  be  unilateral  and  attended  only  by  hoarseness  and  partial  loss  of  voice. 

(b'}  In  posterior  crico-arytenoid  paralysis  (abductor  paralysis)  the  loss  of  power 
in  the  abductors  permits  the  lateral  crico-arytenoid  muscles  to  narrow  the  glottis 
into  a  mere  fissure,  so  that  inspiration  becomes  stridulous  and  dyspnoea  is  marked  ; 
the  voice  is  not  materially  interfered  with.  The  condition  may  be  due  to  intra- 
or  extralaryngeal  growths,  or  to  inflammatory  conditions,  possibly  causing  pressure 
on  the  inner  branch.  It  may  be  unilateral  and  due  to  aneurism. 

It  should  be  understood  that  the  relation  of  these  paralyses  to  the  external  and 
internal  branches  of  the  superior  and  inferior  laryngeal  nerves  cannot  be  demonstrated 
clinically  with  definiteness.  Pressure  on  the  main  trunk  of  either  nerve,  tabes, 
hysteria,  toxaemia,  and  other  central  or  general  causes  may  produce  any  of  these 
forms  of  paralysis. 

In  intubation  of  the  larynx  (employed  in  some  forms  of  acute  stenosis,  as  in 
diphtheria  or  oedematous  laryngitis)  an  irregular  cylindrical  tube  with  a  fusiform 
enlargement  and  an  expanded  upper  extremity — so  that  it  may  rest  on  the  ven- 
tricular bands — is  carried  into  place  by  an  "  introducer1 '  and  is  guided  by  the  left 
forefinger  of  the  surgeon,  which  is  passed  over  the  dorsum  of  the  tongue  to  the 
epiglottis  and  made  to  recognize  the  laryngeal  opening. 

Thyrotomy  is  sometimes  done  for  the  removal  of  intralaryngeal  tumors.  The 
incision  extends  from  the  thyro-hyoid  space  to  the  top  of  the  cricoid  cartilage,  is 


I832 


HUMAN   ANATOMY. 


directly  in  the  median  line,  and  divides  skin,  superficial  and  deep  fascia,  the  junction 
of  the  alae  of  the  thyroid,  and  the  mucous  membrane  of  the  larynx. 

Laryngotomy  (through  the  crico-thyroid  membrane)  may  be  indicated  in  adults 
for  impending  suffocation  from  any  form  of  obstruction  of  the  glottis.  In  children 
the  space  is  too  small.  A  median  incision  beginning  over  the  thyroid  cartilage  is 
carried  to  half  an  inch  below  the  cricoid  cartilage.  The  skin  and  fasciae  having  been 
divided,  the  crico-thyroid  membrane  is  exposed  between  the  two  crico-thyroid  muscles, 
which  sometimes  require  separation.  The  crico-thyroid  arteries  may  be  exception- 
ally large,  and  in  any  event  should  usually  be  ligated,  although  in  cases  of  great 
emergency  that  step  may  be  postponed  until  the  membrane  has  been  divided.  This 
may  be  done  by  a  transverse  incision  to  minimize  the  risk  of  hemorrhage.  The 
nearness  of  the  vocal  cords  to  the  opening  renders  this  operation  unsuitable  to  cases 
in  which  a  tracheotomy  tube  must  be  worn  for  some  time. 

Excision  of  the  larynx,  occasionally  done  for  malignant  disease,  necessitates  the 
separation  of  the  larynx  from  the  sterno-thyroid  and  thyro-hyoid  muscles  laterally, 
from  the  inferior  constrictor  and  the  hyoid  bone  above,  from  the  trachea  below,  and 
from  the  pharynx  and  oesophagus  posteriorly.  The  superior  and  inferior  thyroid  arte- 
ries, or  their  branches,  and  the  superior  and  inferior  laryngeal  nerves  will  be  divided. 

For  landmarks  of  the  neck,  see  page  554. 

THE   SUBDIVISIONS   OF   THE  THORAX. 

As  the  entire  respiratory  apparatus,  with  the  exception  of  the  larynx  and  a  part 
of  the  trachea,  is  within  the  thorax,  it  is  advisable  to  describe  the  subdivisions  of  that 

FIG.  1557. 


(Esophagus — 

Innominate  art  pry 
Left  innominate  vein — 
Arch  of  aorta — 


Trachea 


1 — IV  thoracic  vertebra 


Right  pulmonary 

artery 


Sternum 
Ascending  aorta 

Right  ventricle 
Right  auricle_J. 

Diaphragm 


Inferior  vena  cava 


Spigelian  lobe 
Median  s:igittal  section  of  formalin  subject  ;  relative  position  of  mediastitial  spaces  outlined  in  red. 

cavity.     The  lungs,  enveloped  in  their  serous  coverings,  the  pleune,  fill  the  greater 
part  of  the  sides  of  the  chest  external  to  planes  passing  forward  from  the  sides  of  the 


PRACTICAL   CONSIDERATIONS  :   THE   MEDIASTINUM.        1833 

bodies  of  the  vertebrae  to  the  sides  of  the  sternum.  The  median  space  between  the 
pleurae  is  called  the  mediastinal  space,  and  is  subdivided  into  four  parts  called  medi- 
astina.  The  above  statement  of  the  lateral  boundaries  of  the  mediastinal  space  is 
only  a  general  one,  for  in  the  middle  the  mediastinal  space  expands  beyond  them 
and  in  front  is  restricted  by  the  advance  of  the  pleurae  beneath  the  sternum.  The 
superior  mediastinum  is  that  part  of  the  space  above  a  plane  passing  from  the  disk 
below  the  fourth  thoracic  vertebra  to  the  junction  of  the  first  and  second  pieces  of  the 
sternum.  This  is  occupied  by  the  upper  part  of  the  thymus,  the  arch  of  the  aorta 
and  the  vessels  rising  from  it,  the  innominate  veins,  and  the  superior  vena  cava.  It 
is  traversed  by  the  trachea  and  oesophagus,  the  thoracic  duct,  the  pneumogastric, 
the  phrenic,  and  the  sympathetic  nerves.  The  region  below  the  above-mentioned 
plane  is  subdivided  by  the  pericardial  sac  into  an  anterior,  middle,  and  posterior 
compartment.  The  middle  mediastinum  is  occupied  by  the  heart  within  the  peri- 
cardium. The  roots  of  the  lungs  are  partly  in  this  and  in  the  superior  mediastinum. 
The  shallow  anterior  mediastinum  is  between  the  middle  one  and  the  sternum.  It 
contains  the  lower  part  of  the  thymus,  a  few  lymph-nodes,  fat,  and  areolar  tissue. 
The  posterior  mediastinum,  between  the  spine  and  the  middle  mediastinum,  contains 
the  oesophagus,  the  aorta,  the  thoracic  duct,  the  azygos  veins,  the  pneumogastric  and 
sympathetic  nerves. 

PRACTICAL   CONSIDERATIONS:    THE   MEDIASTINUM. 

Wounds  penetrating  the  mediastinum,  even  when  they  do  not  involve  the  air- 
passages,  may,  in  consequence  of  air  being  drawn  into  the  space  by  respiratory 
movements,  be  followed  by  general  emphysema  or  by  mediastinal  emphysema.  This 
condition  is  not  infrequent  after  tracheotomy,  the  conditions  favoring  its  production 
being  free  division  of  the  deep  fascia,  continued  obstruction  of  the  air-passages,  and 
labored  inspiration. 

If  there  is  hemorrhage  into  the  mediastinal  space,  or  if  abscess  results  from  infec- 
tion of  a  clot,  or  from  extension  of  tuberculous  disease  of  the  bronchial  glands,  or  as 
a  sequel  of  typhoid  fever,  the  anatomical  symptoms  will  be  those  of  pressure  (vide 
infra).  In  the  presence  of  a  large  abscess,  pus  may  perforate  the  sternum  by  ero- 
sion or  may  find  its  way  out  through  the  little  circular  openings  sometimes  found  as  a 
result  of  developmental  failure  (page  168).  It  may  also  be  evacuated  through  an 
intercostal  space  or  into  the  trachea  or  oesophagus. 

Tumors  may  be  malignant  or  benign  (lymphomata,  dermoids,  hydatids,  fibro- 
mata), the  order  of  mention  being  that  of  their  relative  frequency.  The  chief  symp- 
toms are  those  due  to  intrathoracic  pressure,  which  is,  of  course,  not  uniform,  and 
varies  with  the  origin,  extent,  and  density  of  the  tumor,  but  in  its  effects  upon  the 
separate  structures  contained  within  the  mediastinum  affords  a  reasonably  accurate 
basis  for  an  anatomical  classification  of  the  clinical  phenomena  of  these  growths. 

1.  Compression  of  veins,      (a)  The  superior  vena  cava  :  cyanosis  or  lividity  of 
the  face  ;  dilatation  of  the  superficial  veins  of  the  neck,  face,  and  head  ;  oedema  of 
the  same  region  ;  epistaxis  ;  disturbances  of  vision  or  amaurosis  ;  tinnitus  aurium  or 
total  deafness  ;  cerebral  effusion  or  hemorrhage  ;  cedema  of  one  or  both  arms.      (^) 
The  greater  azygos  vein  :  dilatation  first  of  the  right  and  later  of  the  left  intercostal 
veins  ;  oedema  of  the  upper  part  of  the  chest-wall  ;    right-sided  hydrothorax  with 
secondary  or  later  effusion  into  the  left  pleura  (Stengel) ;  pericardial  effusion  ;  medi- 
astinal effusion.      (<:)   The  pulmonary  vein  :  cedema  of  the  lung  ;  haemoptysis. 

2.  Compression  of  arteries  (much  rarer  than   of  venous  channels),     (a)  The 
aorta  :   inequality  in   the  radial  pulses  ;   engorgement  of  the  left  side  of  the  heart  ; 
pulsation  of  the  growth,   if  it  is  visible  or  palpable  (as  the  suprasternal  notch  or 
over  the  sternal  ends  of  the  clavicles ');  pallor;  giddiness;  anginose  pains.    (6)  The 
pulmonary  artery  :    distention  of  the  right  heart  ;  dyspnoea  ;  ultimately — as  a  sec- 
ondary result  of  the  cardiac  condition — ascites  ;   cedema  of  the  lower  extremities  ; 
general  anasarca. 

3.  Compression  of   nerves,      (a)    The   pneumogastric  :    irregular  heart  action 
with  marked  rapidity  or  slowness  ;   syncope  ;  vomiting  ;   hiccough  ;  pharyngeal  or 
laryngeal  spasm  or  paralysis  ;  dysphagia  ;  spasmodic  cough.     (£)  The  inferior  laryn- 


HUMAN  ANATOMY. 


Thyroid  cartilage 


geal  nerve  :  posterior  crico-arytenoid  paralysis  with  stridor  and  inspiratory  dyspnoea 
(page  1273).     (c)  The  sympathetic  :  various  disturbances  of  vision  ;  irregular  pupils. 

4.  Compression   of    the  thoracic   duct.      Emaciation  ;    chylo-thorax  ;    chylous 
ascites  ;  mediastinal  effusion  of  chyle. 

5.  Compression   of    the  air-passages,      (a)   The  trachea  :     stridor  ;    dyspnoea. 
(£)  The  bronchi  :    feeble  breath-sounds  ;    dyspnoea  ;    recession  of  the  suprasternal 
and  supraclavicular  fossae  and  base  of  chest ;   cough.      (V)  The  lungs  and  pleura  : 
dyspnoea  ;   collapse  of  the  lungs  ;    pleural  effusion. 

6.  Compression  of  the  heart  and  pericardium.     Displacement  of  the  heart  ;  peri- 
cardial  effusion  ;  irregular  heart  action. 

7.  Compression  of  the  oesophagus.      Dysphagia. 

8.  Outward  pressure  upon  the  walls  of  the  mediastinal  space.    Widening  of  inter- 
costal spaces  ;  bulging  of  the  sternum  ;  increase  of  the  circumference  of  the  chest  on 

one  side  ;    weakness  or 

FIG.  1558.  absence  of  vocal  fremi- 

tus  ;  increased  area  of 
transmission  of  heart- 
sounds. 

Of  course,  all  of 
these  symptoms  are  not 
present  in  any  given  case 
of  mediastinal  growth, 
but  some  of  them  are 
sure  to  be  and  can  be 
more  readily  understood 
if  referred  to  their  ana- 
tomical causes. 

The  phenomena  ref- 
erable to  the  separate 
subdivisions  of  the  me- 
diastinum can  be  classi- 
fied only  in  a  very  gen- 
eral way.  It  may  be 
said,  however,  that :  ( i ) 
The  anterior  mediasti- 
num is  the  most  fre- 
quent seat  of  abscess  ; 
that  its  growths  usually 
begin  in  the  thymus  ; 
and  that  the  chief  symp- 
toms are  apt  to  be  those 
of  pressure  upon  the  su- 
perior vena  cava,  inva- 
sion of  the  suprasternal 
fossa,  involvement  of  the 

Trachea  and  bronchial  tree,  anterior  aspect.  R,  L,  right  and  left  bronchus;  Cervical  glands,  bulging 
A,  left  apical  bronchus  dividing  into  ventral  (a)  and  dorsal  (a')  branches;  fi,  or  erosion  of  the  Ster- 
continuation  of  main  bronchus;  *,  *',  ventral  and  dorsal  branches;  c,  cardiac  ,  ,  ,  <. 

bronchus.  num,  and  dyspnoea.  (2) 

Growths  of  the  poste- 
rior and  middle  mediastinum  are  apt  to  originate  in  the  lymph-nodes,  and  the  chief 
symptoms  are  those  of  pressure  upon  the  pneumogastric,  recurrent  laryngeal  or  sym- 
pathetic nerves,  the  greater  azygos  vein,  the  oesophagus,  and  the  air-passages.  The 
urgent  dyspnoea  and  troublesome  cough  are  out  of  all  proportion  to  the  physical 
signs  (Osier). 

THE   TRACHEA. 

The  trachea  or  windpipe  (Fig.  1558)  is  a  tube,  composed  of  cartilage  and  mem- 
brane, extending  from  the  cricoid  cartilage  to  a  point  opposite  the  disk  below  the 
fourth  thoracic  vertebra,  corresponding  to  the  level  of  the  junction  of  the  first  and 


THE   TRACHEA. 


1835 


Epithelium 


.Tunica  propria 


_Tracheal 
glands 


Pi 


_Submucous 
layer 


'          Cartilage 


second  pieces  of  the  sternum,  where  it  divides  into  the  two  bronchi.  The  point  of 
division  is  usually  on  the  right  of  the  median  line  :  sometimes  so  far  as  to  lie  behind 
the  right  edge  of  the  sternum.  The  trachea  is  a  cylindrical  tube,  flattened  behind. 
The  convexity  is  due  to  the  so-called  rings,  which  represent  only  about  three-quarters 
of  a  circle.  The  length  is  difficult  to  determine  with  accuracy  on  account  of  the  elas- 
ticity of  the  organ  as  well  as  of  its  variation.  It  may  be  said  to  be,  on  the  average, 
from  10.5-12  cm.  (4—4^  in.)  in  man  and  from  9-11  cm.  (3^-4 /^  in.)  in  woman. 
The  isolated  trachea  can  be  stretched  and  compressed  to  a  surprising  extent,  and 
even  in  life  the  changes  are  considerable.  The  antero-posterior  and  the  transverse 
diameters  are  not  very  different,  except  just  at  the  lower  end,  where  the  trachea 
enlarges  transversely.  It  is  very  plausibly  stated  by  Lejars l  that  in  life  the  windpipe 
is  more  or  less  constricted  by  the 

tonic  contraction  of  its  muscles.  FlG-  1559- 

According  to  him,  it  grows  con-  j?£~ 

tinually  smaller  from  above  down- 
ward. Braune  and  Stahel2  be- 
lieved that  after  death  it  is  largest 
in  the  middle.  We  have  no  doubt 
whatever  that,  as  a  rule,  the  dead 
trachea  is  enlarged  transversely 
at  the  lower  end.  Abey8  gives 
the  following  measurements  for 
the  upper  and  lower  ends  :  upper 
transverse  diameter  13.1  mm., 
sagittal  1 6  mm. ;  lower  transverse 
diameter  20.7  mm.,  sagittal  19.1 
mm.  The  framework  of  the 
trachea  is  so  light  that  its  shape 
may  be  influenced  by  neighbor- 
ing organs,  such  as  the  thyroid 
body  and  the  arch  of  the  aorta.  . 

Structure.  —  The     frame- 
work of  the  anterior  and  lateral 

walls  of  the  trachea  consists  of  i 

the  so-called  rings  of  hyaline  car-  ,-&£'' 

tilage,  which  form   some  three- 
quarters  of  a  circle.    In  the  great  1_Fibrous  tunic 
majority  of  cases  there  are  from                               W^H^ 
sixteen  to  nineteen  rings.      It  is                       '^jjf**^-' 
not  rare  to  find  twenty,  but  very 
rare  to  find  more.     The  rings  are 
from    2-5    mm.    broad,    usually 

measuring  3  Or  4  mm.    They  are        Transverse  section  of  trachea,  showing  general  arrangement 

plane  externally  and  convex  in-  of  its  wail,   x  80. 

ternally,  becoming  pointed  at  the 

ends.  They  are  very  irregular  in  many  respects.  Sometimes  one  end  bifurcates, 
the  rings  above  and  below  ending  prematurely.  Occasionally  bifurcation  of  the  oppo- 
site ends  of  alternate  rings  is  observed.  Rarely  both  ends  of  the  same  ring  may 
divide.  The  first  ring,  which  is  broader  than  the  others,  is  occasionally  fused  with 
the  cricoid  cartilage.  A  highly  elastic  fibrous  sheath,  continuous  with  the  peri- 
chondrium  of  the  rings,  envelops  them,  connects  their  posterior  ends,  and  completes 
the  tube.  The  distance  between  the  rings  is  less  than  their  breadth,  at  times  only 
half  as  much.  Involuntary  muscular  fibres  of  the  trachealis  muscle  lie  between  the 
fibrous  sheath  and  the  lining  mucous  membrane.  They  are  in  the  main  disposed 
transversely,  some  of  them  connecting  the  ends  of  the  rings  ;  some  bundles,  however, 
run  longitudinally. 

1  Revue  de  Chirurgie,  1891. 

2  Archivf.  Anat.  u.  Phys.,  Anat.  Abth.,  1886. 

3  Der  Bronchialbaum  der  Menschen,  u.  s.  w.,  1880. 


.Perichondrium 


i836 


HUMAN   ANATOMY. 


A  layer  of  connective  tissue,  representing  a  submucosa,  separates  the  cartilage 
and  muscle  from  the  mucous  lining  of  the  trachea.  The  submucosa  contains  small 
aggregations  of  fat-cells  and  the  trachea!  glands.  The  latter,  tubulo-alveolar 
mucous  in  type,  are  most  numerous  and  largest  between  the  rings  of  cartilage, 
especially  towards  the  lower  end  of  the  trachea.  Over  the  cartilages  they  are  small 
and  often  wanting.  Their  ducts  pierce  the  mucosa  to  gain  the  free  surface  of  the 
latter. 

The  mucous  membrane,  smooth  and  attached  with  considerable  firmness  to  the 
underlying  tissues,  is  clothed  with  stratified  ciliated  columnar  epithelium.  Many  of 
the  surface  cells  contain  mucus  and  are  of  the  goblet  variety.  The  stroma  of  the 
mucosa  is  rich  in  fine  elastic  fibres,  which,  in  the  lower  part  of  the  trachea,  are  con- 
densed into  a  distinct  elastic  lamella  separating  the  mucous  membrane  from  the  sub- 
mucosa. Lymphoid  cells  are  constantly  found  in  the  mucosa,  in  places,  particularly 
around  the  openings  of  the  ducts  of  the  tracheal  glands,  being  aggregated  into  small 
collections  which  suggest  lymph-nodules. 

Vessels. — The  arteries,  which  are  insignificant,  are  branches  of  the  inferior 
laryngeal  from  the  inferior  thyroid,  and  tend  to  form  a  series  of  horizontal  arches 
between  the  rings.  They  anastomose  below  with  the  bronchial  arteries  and  with 

the  internal  mammaries 

FIG.   1560.  through    the    anterior 

mediastinal  twigs.  The 
veins,  arranged  like  the 
arteries,  belong  to  the 
system  of  the  inferior 
laryngeals.  They  com- 
municate with  those  of 
the  oesophagus,  with 
the  thyroid  plexus,  and, 
according  to  Luschka, 
with  the  azygos.  The 
lymphatics,  which  are 
very  numerous,  are  also 
disposed  in  horizontal 
curves.  Leaving  the 
windpipe  at  the  sides 
of  the  membranous 
portion,  they  open  into 
small  tracheal  lymph- 
nodes  and  communi- 
cate with  the  bronchial 
nodes  also. 

The  nerves  are 
from  the  pneumogas- 
tric  and  sympathetic 
nerves.  Their  ultimate 

distribution,  in  addition  to  the  supply  for  the  muscular  tissue  and  the  walls  of  the 
blood-vessels,  includes  sensory  endings  within  the  mucous  membrane  which,  accord- 
ing to  Ploschko,  are  similar  to  those  of  the  larynx. 

The  Relations  of  the  Trachea.— The  oesophagus,  beginning  at  the  lower 
border  of  the  cricoid  cartilage,  lies  at  first  behind  the  trachea,  to  which  it  is  con- 
nected by  areolar  tissue  ;  but  almost  at  once  it  is,  relatively  to  the  trachea,  displaced 
to  the  left,  to  be  pushed  over  again  by  the  arch  of  the  aorta,  where  this  vessel  lies 
on  the  left  of  the  trachea.  The  gullet  always  lies  behind  the  origin  of  the  left  bron- 
chus. Behind  the  first  piece  of  the  sternum  the  arch  of  the  aorta  passes  in  front  of 
the  trachea,  which  is  placed  almost  symmetrically  in  the  fork  made  by  the  innomi- 
nate and  left  carotid  arteries.  The  isthmus  of  the  thyroid  crosses  usually  the  second 
and  third  rings,  its  lobes  resting  on  the  sides  of  the  trachea.  The  inferior  thyroid 
veins  constitute  a  vascular  layer  before  the  lower  part  of  the  cervical  portion  of  the 
trachea.  The  recurrent  laryngeal  nerves  run  up  at  the  back  of  either  side  of  the 


Longitudinal  muscle 
Submucous  layer 


Epithelium  of 
oesophagus 


Circular  muscle 


Cartilage 


Transverse  section  of  trachea  and  oesophagus  of  child,  seen  from  below.     X  15. 


THE   TRACHEA.  1837 

trachea,  the  left  one  being  the  first  to  reach  this  position.  The  inferior  laryngeal 
artery  and  veins  are  near  them.  The  relations  of  the  artery  and  nerve  are  given 
with  the  relations  of  the  thyroid.  The  remains  of  the  thymus  lie  in  front  of  the 
trachea  within  the  thorax.  Owing  to  the  forward  inclination  of  the  sternum,  the 
trachea  is  more  deeply  placed  as  it  descends.  A  lymph-node  or,  more  frequently,  a 
group  of  them  is  constantly  found  under  the  bifurcation.  Tillaux '  found  the  dis- 
tance of  the  cricoid  cartilage  above  the  sternum  (in  a  small  series)  to  range  in  the 
male  from  4.5-8.5  cm.,  with  an  average  of  6.5  cm.;  and  in  the  female  from  5-7.5 
cm.,  with  an  average  of  6.4  cm.  This  distance,  however,  may  be  modified  by  other 
factors  than  the  length  of  the  trachea. 

Growth  and  Subsequent  Changes. — In  the  infant  the  trachea  measures 
from  4-5  cm.  in  length,  begins  at  a  higher  point  in  the  neck,  as  has  been  shown  for 
the  larynx,  and  divides  at  a  higher  point  in  the  thorax.  The  level  of  this  division 
varies  very  much  in  the  foetus,  but  at  birth  is  generally  opposite  the  third  thoracic 
vertebra.  The  lowest  position  is  opposite  the  fourth  and  the  range  extends  over 
two  vertebrae. 

There  are  comparatively  few  records  of  the  changes  during  childhood.2  We  have  found 
it  opposite  the  lower  part  of  the  fourth  thoracic  vertebra  in  a  child  whose  age  was  estimated  at 
about  three.  Symington s  has  found  it  at  the  top  of  the  fifth  in  two  children  of  six  and  oppo- 
site the  fourth  in  one  of  thirteen.  In  the  young  adult  it  is  opposite  the  disk  between  the 
fourth  and  fifth  thoracic  vertebra;,  which  is  its  normal  position,  although  it  is  not  abnormal  for 
it  to  be  opposite  the  fifth.  Late  in  life  it  descends  to  the  lower  border  of  the  fifth  and  even  to 
the  seventh  vertebra.4  The  trachea  of  the  infant  appears  almost  round,  the  rings  forming  a 
relatively  larger  part,  perhaps  five-sixths  of  the  periphery.  According  to  several  authorities, 
the  transverse  diameter  much  exceeds  the  sagittal  ;  but,  although  we  have  seen  this  condition, 
we  are  not  inclined  to  agree  that  it  is  normal  in  the  infant,  unless,  perhaps,  at  the  lower  end. 
The  size  of  the  transverse  section  of  the  trachea  is,  for  many  reasons,  hard  to  determine. 
Merkel 5  thinks  we  may  accept  the  following  statement  of  the  diameter  of  the  upper  part  of  the 
trachea  without  fear  of  being  much  out  of  the  way  in  particular  instances  :  from  six  to  eighteen 
months,  5  mm. ;  from  two  to  three  years,  6  mm.  ;  from  four  to  five,  7  mm. ;  from  five  to  ten, 
8  mm.;  from  ten  to  fifteen,  10-11  mm.  Ossification  of  the  rings  begins  decidedly  later  than  in 
the  larynx.  The  earliest  appearances  of  it  observed  by  Chievitz  were  at  about  forty  in  man  and 
about  sixty  in  woman.  His  youngest  case  of  complete  ossification  was  at  fifty  in  man  and 
seventy-eight  in  woman.  The  deposit  is  first  seen  in  the  upper  rings,  but  not  in  the  first  one, 
the  points  being  irregularly  distributed  along  the  borders.  They  come  next  in  the  lower  rings, 
and  here  at  the  posterior  ends.  As  the  process  spreads,  there  is  left  a  median  unossified  tract 
along  the  trachea,  which  probably  is  usually  invaded  from  below. 


THE  BIFURCATION  OF  THE  TRACHEA  AND  THE  ROOTS  OF 

THE  LUNGS. 

The  carina  trachea?  (Fig.  1561)  is  a  prominent  semilunar  ridge  running  antero- 
posteriorly  across  the  bottom  of  the  trachea  between  the  origin  of  the  two  bronchi.  It 
usually  starts  from  a  larger  anterior  triangular  space  and  ends  at  a  smaller  pos- 
terior one.  Heller  and  v.  Schrotter6  found  the  framework  of  the  spur  cartilaginous 
in  56  per  cent.,  membranous  in  33  per  cent.,  and  mixed  in  n  per  cent.  The 
spur,  when  cartilaginous,  is  derived  in  various  ways  :  from  a  tracheal  ring,  from  the 
first  ring  of  either  bronchus,  or  from  a  combination  of  these  sources.  The  height 
of  this  ridge,  especially  when  membranous,  is  difficult  to  measure,  but  these  authors 
believe  that  it  may  reach  6  mm.  According  to  Luschka,  the  free  edge  of  the  spur 
is  15  mm.  from  the  apparent  lowest  point  of  the  windpipe,  seen  from  without.  This 
great  distance  should  in  part  be  accounted  for  by  the  interbronchial  ligament,  a  col- 
lection of  fibres  running  transversely  in  the  angle  between  the  bronchi.  This  band  is, 
however,  very  variable  in  development  and  not  constant,  so  that  Luschka' s  estimate 
of  the  distance  is  probably  excessive  for  most  cases.  Heller  and  v.  Schrotter  found 

1  Anatomic  Topographique,  3tne  e"dit.,  1882. 

2  Dwight :  Frozen  Sections  of  a  Child,  1881. 

3  Anatomy  of  the  Child,  1887. 

4  Mehnert :  Ueber  topographische  Altersveranderungen  des  Atmungsapparates,  1901. 

5  Handbuch  der  Topograph.  Anat.,  Bd.  ii.,  1899. 

6  Denkschrift  der  Acad.  Vienna,  1897. 


l838 


HUMAN    ANATOMY. 


FIG.  1561. 

Anterior  surface     Carina,  anterior  triangle 


Cartilage 


Left  bronchus 
Carina  tracheae         /         Origin  of  apical  bronchus 
Continuation  of  right  main  bronchus 

Bifurcation  of  trachea,  seen  from  above  after  section  of 
windpipe  just  above  carina. 


the  spur  on  the  left  of  the  middle  of  the  trachea  in  57  per  cent. ,  in  the  middle  in  42 
per  cent.,  and  on  the  right  of  it  in  the  remainder.1  Semon,  in  100  examinations  of 
the  living,  found  it  on  the  left  in  59,  at  the  middle  in  35,  and  on  the  right  in  6. 

The  roots  of  the  lungs  consist  of  the  bronchi  (the  right  one  giving  off  a  branch 
before  entering  the  lung),  the  pulmonary  artery  and  vein,  the  bronchial  arteries  and 
veins,   the   lymphatic   vessels   and  nodes, 
and  the  nerves. 

The  bronchi  (Fig  1562)  are  the 
two  tubes  into  which  the  windpipe  divides, 
one  running  downward  and  outward  to 
each  lung.  Until  they  enter  the  lungs, 
their  shape  and  structure  are  precisely 
those  of  the  trachea,  the  membranous  por- 
tion being  still  posterior.  This  applies  also 
to  the  branch  that  springs  from  the  right 
bronchus  before  it  enters  the  lung.  While 
treating  of  the  root  of  the  lung  we  shall 
consider  only  the  extrapulmonary  part  of 
the  bronchi.  According  to  modern  usage, 
the  term  ' '  bronchus' '  is  applied  to  the 

whole  of  the  chief  tube  that  runs  through  each  lung  ;  formerly  it  was  restricted  to 
the  part  from  the  trachea  to  the  first  branch.  As  the  left  bronchus  gives  off  no 
branch  before  entering  the  lung,  it  was  described  as  much  longer  than  the  right  one. 
The  length  of  the  left  bronchus  to  its  first  branch  is  about  5  cm.  (2  in. ) ,  that  of  the 
right  is  rarely  more,  and  often  less,  than  2  cm.  (^  in.).  There  are  some  eight  or 
ten  rings  in  the  left  bronchus  before  the  branch,  while  in  the  right  one  there  are  three, 
often  two,  and  sometimes  four.  The  right  bronchus,  which  is  the  more  direct  con- 
tinuation of  the  trachea,  is  the  larger.  The  diameter  of  the  bronchi  at  their  origin  is 
greater  from  above  downward  than  from  before  backward.  The  dimensions  are  very 
differently  given.  According  to  Aeby,  the  transverse  diameter  of  the  right  bronchus 

is  from  13.5-21  mm.  and  that  of  the  left 
from  12.5-17  mm.  Braune  and  Stahel 
found  that  the  calibre  of  the  right  pne  is 
to  that  of  the  left  as  100:77.9.  The 
extreme  ratios  of  the  series  were  100  :  7 1. 6 
and  loo  :  83.3.  We  have  deduced  from 
Heller  and  v.  Schrotter's  tables  that  in 
some  10  per  cent,  the  calibres  are  equal. 
It  was  formerly  taught  that  the  larger 
right  bronchus  is  more  nearly  horizontal 
than  the'left,  but  that  the  contrary  is  true 
is  easily  proved  by  a  glance  down  the 
trachea  in  a  frozen  section  (Fig.  1561). 
The  cause  of  the  error  is  that,  if  it  be  not 
recognized  that  after  the  apparent  splitting 
of  the  right  bronchus  the  lower  division  is 
the  main  trunk,  the  eye  is  apt  to  follow 
the  upper  border  of  the  primitive  bron- 
chus, which  carries  it  along  the  upper 
branch.  It  is  very  difficult  to  determine 
the  angles  at  the  origin  of  the  bronchi, 
for  the  parts  are  so  flexible  that  observa- 
tions on  non-hardened  subjects  are  of  little 

value,  and  it  is  not  easy  accurately  to  measure  even  good  preparations,  on  account  of 
the  irregularity  of  the  outline.  One  fact  which  adds  to  the  difficulty  of  taking  satisfac- 
tory measurements,  and  which  also  tends  to  make  the  right  bronchus  the  more  direct 
continuation  of  the  trachea,  is  the  inclination  of  the  latter  to  the  right  as  it  descends. 

1  They  state  that  this  remainder  consists  of  8  cases,  but  as  their  series  comprised  125,  it 
would  seem  that  there  must  be  a  misprint. 


FIG.    1562. 


Membranous 


Right  - 
apical 
bronchus 


Left  bronchus 


Bifurcation  of  trachea  laid  open  after  incision  along  an- 
terior wall  of  trachea  and  bronchi. 


THE   TRACHEA. 


1839 


We  have  made  measurements  on  two  casts  from  frozen  sections  of  the  adult,  and  one  from 
a  section  of  a  child  thought  to  be  of  about  three  years,  and  have  calculated  the  angles  between  the 
prolongation  of  the  axis  of  the  terminal  part  of  the  windpipe  and  that  of  each  bronchus.  An 
attempt  was  also  made  to  measure  the  angles  from  a  skiagraph  made  by  Blake 1  after  injecting 
fusible  metal  into  the  trachea  of  a  hardened  body.  Two  observations  on  adults  by  Kobler  and 
v.  Hovorka2  are  included  for  comparison. 

It  seems  that  the  subtracheal  angle,  that  of  divergence  of  the  bronchi,  is  about  70°.  We  have 
found  it  precisely  that  in  another  specimen.  Kobler  and  v.  Hovorka  measured  the  lateral 
angles  in  the  hardened  bodies  of  sixteen  new-born  infants.  The  average  was  right  25.6,  left 
48.9.  The  variations  ranged  on  the  right  from  10  to  35  and  on  the  left  from  30  to  65.  We 
found  their  average  angle  of  divergence  74.5.  This  shows  that,  contrary  to  the  general  im- 
pression, the  bronchi  are  not  more  nearly  vertical  in  the  infant  than  subsequently.  Aeby  gives 
the  angles  of  divergence  of  two  new-born  children  as  33  and  61  ;  Mettenheimer  *  as  50  and  63. 

Vessels. — The  pulmonary  artery  at  its  bifurcation  is  anterior  to  the  bronchi 
and  at  a  lower  plane.  Each  branch  of  the  artery  rises  over  the  bronchus  and  comes 
to  lie  more  or  less  external  to  it.  This  apparent  crossing  of  the  bronchus  by  the 
artery  occurs  on  the  right  just  after  the  origin  of  the  first  secondary  bronchus.  The 
usual  teaching,  following  Aeby,  that  the  artery  actually  arches  over  the  extrapul- 


FIG.  1563. 

Sternum 


Pulmonary  semilunar  valve 


Left  lung 


Aorta 
/  Superior  vena  cava 


Left  pulmonary 
veins 

Left  bronchus  — 


.Parietal  pleura 
.Visceral  pleura 

Reflection  of  visceral 
onto  mediastinal  pleura 


_III  rib 

-N  —  Right  bronchus 


-     Right  lung 


Thoracic  aorta 


Body  of  vertebra    (Esophagus 
Right  pulmonary  artery 
Transverse  section  of  thorax  at  level  of  fifth  thoracic  vertebra. 


Spine  of  scapula 
Superior  fissure 


monary  bronchus  and  lies  behind  it,  is  incorrect.  The  artery  divides  before  enter- 
ing the  lung,  one  branch  entering  through  the  upper  and  the  other  through  the 
lower  part  of  the  hilum. 

The  pulmonary  veins  are  usually  two  on  each  side.  The  superior  lie  in  front  of 
and  below  the  artery.  The  inferior  are  the  lowest  of  the  large  vessels  of  the  lung- 
root,  passing  from  behind  under  the  bronchus  into  the  heart. 

The  bronchial  arteries  follow  the  bronchi  along  their  posterior  surfaces.  The 
bronchial  veins  are  both  anterior  and  posterior.  On  the  right  side  both  open  into 
the  larger  azygos  vein.  The  left  posterior  ones  often  receive  the  anterior  and  open 
into  the  superior  hemiazygos.  There  may  be  various  anastomoses  with  mediastinal, 
pericardial,  and  tracheal  veins. 

The  lymphatics  run  for  the  most  part  behind  the  bronchi.  The  lymph-nodes 
are  for  the  most  part  on  the  posterior  and  inferior  aspects  of  .the  tubes,  the  group 
under  the  bifurcation  joining  others  at  the  sides.  Some  nodes  occur  on  the  front. 

The  nerves  from  the  sympathetic  and  vagus  form  plexuses  both  before  and 

behind. 

1  American  Journal  of  the  Medical  Sciences,  1899. 

2  Sitzbericht.  Acad.,  Vienna,  1893. 

3  Morpholog.  Arbeit.  Schwalbe,  1894. 


1840  HUMAN   ANATOMY. 

The  dimensions  of  the  lung-roots  are  difficult  to  determine.  They  are  nar- 
rower below  than  above  and  shorter  behind  than  in  front.  The  lower  posterior  bor- 
ders, which  are  formed  by  the  inferior  pulmonary  veins,  are  of  about  the  same  length 
(2  cm.  )  on  each  side  and  very  symmetrical.  We  may  put  the  right  root  in  front  and 
above  at  from  4-4. 5  cm.  and  the  left  at  about  i  cm.  longer.  They  are  thickest 
above,  and  expand  as  they  approach  the  hilum  of  the  lung,  where  the  diameter  is 
approximately  3.5  cm.,  the  left  one  being  rather  the  thicker.  The  height  at  the 
hilum  is  from  5-6  cm. ,  probably  sometimes  rather  more. 

The  Relations  of  the  Roots. — Below  lies  the  pericardium  covering  the  heart, 
chiefly  the  left  auricle.  The  great  azygos  vein  arches  over  the  right  root  from  be- 
hind, to  join  the  superior  vena  cava,  which  is  against  the  root  in  front.  The  arch  of 
the  aorta  crosses  the  left  root  from  before  backward,  being  less  closely  applied  to  it 
behind  than  elsewhere.  The  oesophagus  is  behind  the  very  beginning  of  the  left 
root.  The  pleura  is  reflected  over  each  root,  which  it  completely  envelops  as  it 
passes  from  the  parietal  into  the  visceral  layer.  The  broad  ligament  of  the  lungs  is  a 
fold  of  pleura  extending  downward  from  the  end  of  the  root.  The  phrenic  nerve 
of  each  side  passes  in  front  of  the  root,  between  the  pericardium  and  the  pleura. 

PRACTICAL  CONSIDERATIONS  :  THE  AIR-PASSAGES. 

The  Trachea  and  Bronchi. — The  elasticity  and  mobility  of  the  trachea,  the 
compressible  character  of  its  walls,  the  loose  cellular  tissue  in  which  it  lies,  and  the 
variety  of  the  structures  with  which  it  is  in  close  relation  should  all  be  remembered 
in  considering  its  injuries  and  diseases. 

Wounds  of  the  cervical  portion  of  the  trachea — as  in  cut  throat  below  the  cricoid 
— are  not  rare.  The  trachea  is  rendered  more  superficial  by  extreme  extension  of 
the  neck,  and  is  also  elongated.  A  deep  wound  may  therefore  sever  it  completely, 
in  which  case  the  lower  end  may  retract  below  the  level  of  the  superficial  wound, 
making  the  hurried  introduction  of  a  tracheotomy  tube  difficult. 

Rupture — "fracture" — of  the  cervical  trachea  has  resulted  from  contusion,  and 
in  the  presence  of  pre-existing  disease  has  followed  coughing.  The  depth  of  the 
thoracic  trachea  protects  it  from  all  but  penetrating  wounds,  and  these,  on  account 
of  the  important  structures  also  implicated,  are  usually  fatal. 

Disease  beginning  in  or  confined  to  the  trachea  is  rare,  but  it  may  be  involved 
in  the  extension  of  either  bronchial  or  laryngeal  morbid  processes.  The  normal 
tracheal  mucous  membrane  is  said  to  resist  cadaveric  disintegration  longer  than  any 
other  mucous  membrane  of  the  body  (Elsberg). 

Stenosis  of  the  trachea,  if  from  intrinsic  change,  is  usually  due  to  ulceration, 
either  syphilitic  or  tuberculous,  followed  by  cicatrization.  It  is,  however,  far  more 
commonly  due  to  extrinsic  causes,  the  mechanism  of  which  will  be  readily  under- 
stood if  the  relations  of  the  trachea  are  recalled  (page  1836).  From  above  down- 
ward it  is  evident  that  the  trachea  may  be  compressed  by  enlargements  of  the  thyroid 
gland,  by  retro-cesophageal  tumors  or  abscesses,  by  carotid,  innominate,  or  aortic 
aneurism,  or  by  lymphatic  swellings  in  the  neck  or  near  the  bifurcation.  As  the 
posterior  part  of  the  tracheal  wall  is  musculo-membranous  (partly  in  order  to  avoid 
undue  pressure  of  the  trachea  on  the  oesophagus),  the  impaction  of  a  foreign  body  in 
the  latter  tube  may  cause  tracheal  narrowing.  The  trachea  may  be  involved  in  dis- 
ease originating  elsewhere,  as  in  tuberculous  infecti6n  of  the  thoracic  lymphatic 
glands,  or  in  carcinoma  of  the  same  glands,  or  of  the  cervical  chain,  or  of  the  oesoph- 
agus. Abscesses  or  aneurisms  may  ulcerate  through  its  \valls  and  empty  into  its 
lumen,  suffocating  the  patient.  The  close  relation  of  the  trachea  to  the  aorta  makes 
it  possible  in  some  cases  of  aortic  aneurism  to  hear  a  systolic  bruit  either  in  the 
trachea  or  at  the  patient's  mouth  when  opened.  This  is  either  the  sound  conveyed 
from  the  sac  or  is  produced  by  the  air  as  it  is  driven  out  of  the  trachea  during  the 
systole  (Osier).  The  sign  known  as  "tracheal  tugging"  also  depends  upon  the 
same  close  relation.  With  the  patient  erect,  his  mouth  closed  and  his  chin  elevated, 
when  the  cricoid  is  grasped  between  the  finger  and  thumb  and  pressed  gently  and 
steadily  upward,  if  aortic  aneurism  or  dilatation  exists,  the  pulsation  of  the  aorta 
will  be  distinctly  transmitted  through  the  trachea  to  the  hand  (Oliver). 


PRACTICAL   CONSIDERATIONS:   THE   AIR- PASSAGES.       1841 

Tracheotomy  may  be  required  for  obstruction  in  the  larynx  or  above  it,  for  the 
removal  of  foreign  bodies,  or  as  a  preliminary  step  in  other  operations,  as  excision 
of  the  tongue. 

It  may  be  done  at  any  point  between  the  cricoid  cartilage  and  a  short  distance 
above  the  suprasternal  notch.  The  difficulties  of  the  operation  increase  with  the 
distance  from  the  cricoid  because  (a)  the  depth  of  the  trachea  from  the  surface  in- 
creases as  it  approaches  the  thorax  ;  (6)  it  is  more  movable  ;  (c)  it  is  more  com- 
pletely covered  in  by  the  sterno-hyoid  and  sterno- thyroid  muscles  ;  (d  )  it  is  more 
apt  to  be  overlapped  by  the  common  carotids  ;  or  (e)  crossed  by  the  left  common 
carotid  when  it  arises  from  the  innominate  artery  ;  or  by  (_/)  various  venous  trunks, 
as  the  transverse  branches  between  the  anterior  jugulars,  or  the  inferior  thyroids,  or 
even  by  the  left  innominate  vein,  which, — lying  as  it  does  in  front  of  the  trachea, — in 
the  presence  of  venous  congestion,  may  extend  above  the  level  of  the  top  of  the 
sternum.  Moreover,  in  children  under  two  years  of  age  the  upper  edge  of  the  vas- 
cular thymus  gland  may  lie  in  front  of  the  trachea  at  the  root  of  the  neck.  The  in- 
nominate artery  itself  or  the  thyroidea  ima  may  occupy  the  same  position. 

For  these  reasons  tracheotomy  is  done  with  comparative  rarity  below  the  level 
of  the  isthmus,  which  lies  in  front  of  the  second,  third,  and  fourth  tracheal  cartilages. 
The  incision  is  made  with  the  head  in  full  extension  so  as  to  lengthen  the  trachea, 
steady  it  by  increasing  its  tension,  and  bring  it  nearer  the  surface.  The  chin,  thyroid 
angle,  and  suprasternal  notch  should  be  in  the  same  line.  The  incision  should  be 
exactly  in  this  line,  extend  about  two  inches  downward  from  the  cricoid,  and  divide 
the  skin,  platysma,  and  fascia  and  expose  the  interval  between  the  sterno-hyoid  and 
sterno-thyroid  muscles,  which  may  be  separated  by  blunt  dissection.  The  pretracheal 
fascia  is  then  divided,  exposing  the  upper  ring  of  the  trachea  and  the  thyroid  isthmus. 
The  isthmus  may  be  depressed  to  give  more  room  for  the  tracheal  opening,  or  may, 
after  ligation  on  both  sides,  be  divided  in  the  mid-line,  where,  as  Treves  says,  it, 
like  other  median  raphes,  has  but  slight  vascularity.  A  large  communicating  branch 
between  the  superior  thyroid  veins  often  runs  along  the  upper  border  of  the  isthmus, 
and  over  its  anterior  surface  there  may  be  a  plexus  made  up  by  the  branches  of  the 
thyroid  veins  of  the  two  sides.  These  vessels,  if  present,  may  be  dealt  with  sepa- 
rately or  may  be  picked  up  with  the  two  sides  of  the  divided  isthmus  in  the  grasp 
of  heavy  haemostatic  forceps,  which  by  dropping  over  the  neck  raise  the  trachea 
into  the  wound  (Pearce  Gould). 

The  trachea  is  then  seen  and  felt,  steadied  and  made  still  more  superficial  by 
upward  traction  by  a  small,  sharp  hook  thrust  into  the  lower  edge  of  the  cricoid,  and 
opened  exactly  in  the  middle  line  by  a  bistoury  thrust  in  at  about  the  level  of  the 
third  or  fourth  ring  and  made  to  cut  upward  to  about  the  first. 

In  very  fat  or  very  muscular  persons  the  depth  of  the  trachea  is  increased. 

In  children  its  small  size,  its  shortness  (one  and  a  half  inches  in  the  neck  in  a 
child  of  from  three  to  four  years  of  age),  its  mobility,  its  depth  (on  account  of  the 
considerable  quantity  of  subcutaneous  fat  usually  present),  the  compressibility  of  its 
thin  cartilaginous  rings,  the  height  to  which  the  great  vessels  may  rise  in  front  of  it, 
the  venous  engorgement  usually  present,  and  the  occasional  interposition  of  the 
thymus  (vide  supra},  all  increase  the  difficulties  of  the  operation. 

Foreign  bodies  in  the  air-passages  are  most  likely  to  be  arrested  at  the  upper 
laryngeal  opening,  at  the  ventricle  or  the  glottis,  at  the  bifurcation  of  the  trachea, 
or  in  the  right  bronchus.  They  are  apt  to  enter  that  bronchus  instead  of  the  left 
because  (a)  the  right  lung  is  larger  (the  left  being  encroached  upon  by  the  heart) 
and  there  is  a  greater  intake  of  air  and  a  stronger  current  ;  (3)  the  right  bronchus 
has  the  larger  transverse  diameter  ;  (r)  it  is  less  horizontal  and  therefore  more 
directly  a  continuation  of  the  trachea  than  the  left  bronchus  (page  1838);  and  (</) 
the  carina  tracheae  is  situated  to  the  left  of  the  middle  line  in  the  majority  of  cases 
(page  1837).  If  small  enough,  they  may  be  drawn  into  some  of  the  lesser  bron- 
chioles by  the  inspiration — usually  sudden — which  has  caused  their  entrance  into  the 
air-passages.  The  immediate  symptoms  are  always  those  due  to  obstruction  of  the 
air-current,  either  mechanical — from  the  size  of  the  foreign  body — or  reflex,  as  when 
spasm  of  the  glottis  is  excited  by  the  irritation  of  the  superior  laryngeal  or  tracheal 

nerves. 

116 


1842  HUMAN   ANATOMY. 

The  symptoms  that  would  sug-gest  arrest  in  the  larynx  are  violent  cough,  alter- 
ation or  loss  of  voice,  frequent  spasm,  stridor,  and  rapidly  increasing  dyspnoea  (from 
swelling  and  oedema  of  the  mucosa).  In  the  trachea  a  foreign  body  is  apt  to  cause 
moderate  but  persistent  cough,  hurried  respiration,  occasional  reflex  spasm  of  the 
glottis,  and  slight  dyspnoea.  Arrest  in  a  division  or  subdivision  of  a  bronchus,  if 
the  body  is  large  enough  to  plug  it,  will  cause  absence  of  vocal  and  respiratory 
sounds  over  the  area  involved,  collapse  of  the  lung,  and  flattening  of  the  side  of  the 
thorax.  Later  symptoms  will  be  due  to  irritation  (hypereernia  and  catarrh),  fol- 
lowed by  infection  (inflammation  and  ulceration)  and,  in  cases  of  long  standing, 
possibly  by  the  involvement  of  neighboring  structures  or  organs  (the  lungs  or 
pleura,  the  aorta  or  vena  cava,  the  pericardium,  or  the  oesophagus).  The  relatively 
unyielding  walls  of  the  air-passages  render  this  termination  less  common  than  in 
cases  of  oesophageal  impaction  of  foreign  bodies.  Spontaneous  expulsion  during  a 
coughing  spell  may  take  place,  or  operation  may  be  needed.  (See  thyrotomy, 
laryngotomy,  tracheotomy,  bronchotomy. ) 

The  bronchi  begin  at  the  bifurcation  of  the  trachea,  about  opposite  the  space 
between  the  fourth  and  fifth  thoracic  vertebrae.  This  is  behind  the  lower  part  of  the 
arcli  of  the  aorta  and  on  a  horizontal  line  passing  through  the  sternal  angle  (angu- 
lus  Ludovici)  and  the  root  of  the  spine  of  the  scapula.  As  at  their  origin  they  are 
nearer  the  posterior  than  the  anterior  wall  of  the  thorax,  auscultatory  sounds  in  the 
primary  bronchi  can  best  be  heard  between  the  scapulae  and  about  the  level  of  the 
inner  ends  of  their  spines. 

The  most  frequent  as  well  as  the  most  serious  forms  of  compression  of  the  air- 
passages  are  found  within  the  thorax.  In  the  neck,  even  in  the  presence  of  large 
tumors  or  swellings,  the  feeble  resistance  of  the  skin  and  other  tissues  may  permit 
the  trachea  to  escape  ;  but  within  the  thorax,  between  the  spine  and  the  unyielding 
sternum,  even  small  growths  may  cause  serious  symptoms  of  obstruction. 

Thus  the  group  of  lymph-nodules  surrounding  the  bifurcation  may,  when  dis- 
eased, make  pressure  upon  either  the  trachea  or  bronchi,  as  may  aneurisms  of  the 
aorta  or  innominate,  or  tumors  of  the  posterior  mediastinum,  or  even  a  dilated  left 
auricle. 

In  chronic  interstitial  pneumonia  attended  by  great  increase  in  the  connective- 
tissue  elements  of  the  lung,  followed,  as  is  invariably  the  case,  by  contraction  of 
such  tissue,  the  atmospheric  pressure  retains  the  lung  in  contact  with  the  inner  sur- 
face of  the  chest  in  spite  of  the  pull  of  the  atrophying  fibrous  tissue.  The  force  is, 
therefore,  exerted  on  the  bronchi,  the  walls  of  which  are  dragged  apart,  forming 
great  cavities  (bronchiectasis}.  Such  cavities  may  also  be  due  to  dilatation  under 
increased  pressure  from  within,  as  when  a  foreign  body  or  an  aneurism  occludes  o 
bronchus  ;  or  to  chronic  disease  and  weakening  of  the  bronchial  walls. 

Asthma  of  the  spasmodic  type  may  be  due  to  reflex  pneumogastric  irritatio 
causing  contraction  of  the  muscular  tissue  in  the  walls  of  the  smaller  bronchi.  It 
should  be  noted  that  the  transverse  muscular  fibres  (trachealis  muscle)  connecting 
the  ends  of  the  tracheal  cartilages  have  in  the  bronchioles  become  converted  into  a 
complete  circular  muscular  coat,  and  are  found  even  in  divisions  so  small  that  the 
cartilage  has  disappeared. 

Bronchotomy. — The  relations  of  the  bronchi  (page  1857)  show  that  in  case  of 
impaction  of  a  foreign  body  jn  or  just  below  a  primary  bronchus  it  might  be  reached 
by  a  posterior  thoracotomy  done  at  the  level  of  the  fourth  to  the  sixth  or  seventh 
rib.  The  flap  of  soft  parts  is  three  inches  square,  its  base  being  about  over  the 
costo-vertebral  gutter  on  the  side  to  be  operated  upon.  The  underlying  i"ibs  arc-  sepa- 
rated from  the  pleura  and  divided.  The  proximity  of  the  great  a/ygos  vein  on  tin- 
right  side,  and  of  the  arch  of  the  aorta,  the  descending  aorta,  the  (esophagus,  and 
the  left  auricle  on  the  left,  must  be-  remembered.  It  is  more  difficult  to  retract  the 
pleura  on  the  right  side  so  as  to  expose'  the  bronchus.  Bryant  has  called  attention 
to  the  following  anatomical  (joints  bearing  upon  this  operation,  whether  it  is  under- 
taken for  the  removal  of  a  foreign  body  from  a  broiK  hus  or  the  oesophagus,  or  for 
posterior  mediastinal  tumors  or  abscess,  or  for  the  relief  of  pressure  from  enlarged 
bronchial  glands  :  the  lower  portion  of  the  fourth  dorsal  vertebra  is  the-  boundary 
line  bet \veen  the  posterior  mediastinum  and  the  lower  part  of  the  superior  medias- 


THK    l.r.XGS.  i*43 

tinuni  ;  the  spinous  process  of  any  dorsal  vertebra,  with  the  exception  of  the  first, 
eleventh,  and  twelfth,  denotes  the  situation  of  the  posterior  extremity  <>f  the  rib 
articulating  with  the  transverse  process  of  the  vertebra  immediately  below  ;  the  tips 
of  the  spinous  processes  of  the  first,  eleventh,  and  twelfth  dorsal  veru-bra-  are  above 
rather  than  opposite  the  transverse  processes  of  the  vertebne  immediately  below  ; 
the  space  between  the  ends  of  the  transverse  processes  and  the  angles  of  the  ribs 
varies*  from  one  to  two  and  a  half  inches,  according  to  the  numerical  position  of  the 
rib  ;  the  incomplete  rings  of  the  bronchi  render  those  tubes  easily  recognizable  by 
touch  ;  they  are  found  about  an  inch  and  a  half  anterior  to  the  opening  in  the 
thoracic  wall. 

THE    LUNGS. 

The  lungs  are  a  pair  of  conical  organs,  each  enveloped  in  a  serous  membrane, — 
the  pleura, — occupying  the  greater  part  of  the  cavity  of  the  thorax,  and  separated  from 
each  other  by  the  contents  of  the  mediastina.  Although  in  general  conical,  the  lung 
differs  in  many  respects  from  a  true  cone.  The  base  is  concave,  moulded  over  the  con- 
vexity of  the  diaphragm,  and  descending  farther  at  the  back  and  side  than  at  the  front 
and  internally.  The  apex  is  not  over  the  middle  of  the  base,  but  much  to  the  inner 
and  posterior  side  of  it,  so  that  the  back  and  inner  side  of  the  lung  descend  much 
more  directly  than  the  rest.  The  right  lung  is  the  larger  on  account  of  the  greater 
encroachment  of  the  heart  on  the  left. 

The  surfaces  of  the  lungs  are  the  base,  the  external  surface  (which  is  the 
mantle  of  the  cone  from  apex  to  base,  and  embraces  all  the  periphery  from  the  front  of 
the  mediastinal  space  around  the  wall  of  the  thorax  to  nearly  opposite  the  front  of  the 
vertebral  column),  and  the  internal  or  mediastinal  surface. 

The  borders  are  the  inferior,  which  surrounds  the  base,  and  the  anterior  and 
posterior,  which  bound  respectively  the  back  and  front  of  the  internal  surface. 

The  external  surface  (fades  costalis),  much  the  largest,  is  closely  applied  to 
the  portion  of  the  wall  of  the  pleural  cavity  formed  by  the  ribs  and  the  intercostal 
muscles.  The  region  of  the  apex  is  a  part  of  this  surface.  It  rises  slightly — possibly 
i  cm. — above  the  oblique  plane  of  the  first  rib,  which  indents  it  towards  the  front. 
The  apex  itself  is  in  the  internal  and  posterior  part  of  this  region.  It  rests  closely 
against  the  firm  fibrous  structures  that  roof  in  this  region,  and  is  grooved  trans- 
versely by  the  subclavian  artery,  more  anteriorly  on  the  right  lung  than  on  the  left. 
A  slight  groove  made  by  the  subclavian  vein  may  be  found  in  front  of  the  arterial 
one.  The  rest  of  the  external  surface  is  smooth,  except  where  it  may  be  slightly 
depressed  beneath  the  individual  ribs.  It  should  be  noted  that  a  part  of  what  is 
termed  the  external  surface  faces  inward  against  the  vertebral  column  and  the  first 
part  of  the  ribs  as  they  pass  backward.  The  external  surface  descends  lowest  at  the 
back  and  at  the  side. 

The  internal  surface  (fades  mcdiastinalis)  is  approximately  plane,  except  for 
the  cardiac  fossa,  which  is  much  deeper  oil  the  left  than  on  the  right,  and  extends  as 
far  as  the  lower  surface.  The  left  lung  presents  a  shelf-like  projection  from  behind 
under  this  fossa.  The  other  chief  feature  of  the  internal  surface  is  the  hilion  for  the 
entrance  of  the  structures  composing  the  root  of  the  lung.  It  is  situated  nearer  the 
back  than  the  front  and  below  the  middle,  being  behind  and  above  the  cardiac  fossa. 
The  outline  of  the  hilum  in  the  left  lung  is  approximately  oval,  with  the  lower  end 
sharpened  and  the  long  diameter  vertical.  It  is  more  triangular  in  the  left  lung,  as 
the  root  expands  forward  near  the  top.  The  position  of  the  bronchi  and  the  chief 
vessels  as  they  enter  the  lungs  differs  on  the  two  sides.  Rio  lit  IIDIO  .•  the  chief  bron- 
chus enters  at  the  middle  or  lower  part  and  its  first  branch  near  the  top,  both  being 
at  the  back  of  the  hilum  ;  the  pulmonary  artery,  generally  in  two  branches,  enters  one 
branch  in  front  of  the  main  bronchus  and  the  other  in  front  of  the  secondary  bronchus, 
but  at  a  higher  level  ;  the  superior  pulmonary  vein  is  high  and  in  front  of  the  higlu-r 
arterial  branch  ;  the  inferior,  often  subdivided,  is  near  the  lower  end  of  the  hilum  ;  one 
branch  may  be  in  front  of  the  bronchus  and  one  below  it.  Left  //on:  :  the  bronchus 
enters  the  back  of  the  hilum  rather  above  the  middle  ;  the  pulmonary  artery  is  at  the 
top,  sometimes  in  two  divisions  ;  the  superior  pulmonary  vein  is  high  up  in  front, 


HUMAN   ANATOMY. 


FIG.  1564. 

Apex 


Groove  for  subclavian 
artery 

Groove  for 
nnominate  vein 


Anterior 
border 


Middle 
lobe 


Inferior  lobe 
Right  lung,  hardened  in  situ  •  antero-lateral  aspect. 


causing  the  expansion  which  makes  the  outline  triangular,  the  inferior  vein  being  in  the 

lower  angle.     The  inner  surfaces  are  also  marked  by  certain  adjacent  structures  which 

require  a  separate  account  for  each  lung. 

The  right  lung  presents  a  vertical  groove 

above  and  in  front  for  the  superior  vena 

cava,  and  one  for  the  vena  azygos  major, 

which  is  distinct  behind  the  upper  part 

of   the   hilum   and   above  it  where   this 

vein  runs  forward  to  the  cava.    The  right 

subclavian  artery,  owing  to  its  high  origin 

from  the  innominate,  indents  but  little  of 

the    internal   surface.      A  more   or   less 

marked  vertical  groove  for  the  oesophagus 

is  seen  behind  the  hilum  and  below  that 

for  the  azygos.     There  is  also  a  groove 

below  on  the  inner  surface  where  the  in- 
ferior vena  cava  turns  forward  to  enter  the 

heart.     A  slight  impression  made  by  the 

trachea   may  also  be   present   near   the 

apex.     The  inner  surface  of  the  left  lung 

is  deeply  grooved  by  the  aorta  arching 

over  the  root  and  descending  behind  it, 

the  imprint  growing  faint  and  disappear- 
ing at  the  lower  end.     The  left  carotid 

and    subclavian    arteries    make  distinct 

impressions  at  the  upper  part  diverging 

from  the  aortic  groove. 

The  base  (facies  diaphragmatica)  is 

concave,    that   of    the   right   one   being 

rather  the  more  so.       Both   are  semilunar  in  outline,   owing  to  the  part  cut  out 

of   them  by  the  heart ;    since  this  encroachment  is  greater  on   the  left,  the  base 

of  that  lung  is  a  narrower 
FIG.  1565.  crescent. 

The  inferior  border 
surrounds  the  base.  The 
latter  forms  about  a  right 
angle  with  the  internal  sur- 
face, but  at  the  periphery, 
especially  at  the  back  and 
at  the  side,  a  sharp  edge 
of  lung  is  prolonged  down 
into  the  narrow  space  be- 
tween the  diaphragm  and 
the  thoracic  walls.  The 
anterior  border  is  sharp 
and  somewhat  irregular, 
often  presenting  a  series  of 
convexities.  Starting  near 
the  apex,  it  descends  on 
both  lungs  with  a  forward 
curve,  which  is  most  promi- 
nent in  the  upper  part,  so 
that  the  lungs  nearly  or 
quite  meet  behind  the  ma- 
nubrium.  The  anterior  b<  >r- 
der  of  the  right  lung  then 
inclines  downward  and  out- 
ward so  as  to  meet  the  inferior  border  in  a  gradual  curve.  On  the  left  this  ronvex- 

ity  is  changed  into  a  sharp  concavity  where  the  border  curves  outward  around  the 


Groove  for. 
innominate  artery 


Groove  for  right 
innominate  vein 

Groove  for 
vena  cava 
superior 

Secondary, 
bronchus 
Branches  of — 
pulmonary 
artery 

Cardiac 
impression 

Inferior  pul- 
monary vein 


Groove  for 
vena  a/ygos  major 


Main  bronchus 


^  _^  ^  Diaphragmatic  surface 

Preceding  lung  ;  median  aspect. 


THE    LUNGS. 


FIG. 


Groove  for 
subclavian  artery 

Groove  for  — - - 
innominate  vein 


Superior 
lobe 


Inferior  lobe 


Left  lung,  hardened  in  situ  ;  antero-lateral  aspect. 


heart.  As  this  concavity  ends  in  front,  the  anterior  and  inferior  borders  enclose  a 
prolongation  of  the  lung  towards  the  median  line,  known  as  the  lingula.  The  pos- 
terior border  is  variously  described. 
Often  the  term  is  applied  to  the  thick 
mass  of  lung  that  fills  the  region  of  the 
thorax  along  the  sides  of  the  vertebrae 
and  the  part  of  the  ribs  running  back- 
ward. Properly,  it  is  a  ridge  starting  on 
the  inner  side  of  the  apex,  growing  sharp 
as  it  descends,  but  becoming  vague  and 
effaced  at  the  lower  end.  The  position 
of  this  line  is  not  the  same  on  both  sides, 
nor  is  it  probably  always  dependent  on 
the  same  causes.  On  the  left  it  is  more 
regular,  beginning  as  the  posterior  bor- 
der of  the  groove  for  the  subclavian  ar- 
tery, and  continuing  as  that  of  the  aortic 
impression  until  it  is  lost  near  the  lower 
border  of  the  lung.  Sometimes  the  be- 
ginning has  no  relation  to  the  subclavian 
groove,  but  appears  posterior  to  it,  the 
lung-tissue  forming  a  ridge  which  enters 
a  little  into  the  space  between  the  front 
of  the  spine  and  the  oesophagus,  which 
is  here  deflected  to  the  left.  The  line 
behind  the  aortic  groove  lies  on  the  side 
of  the  vertebrae,  and  consequently  is  the 
farther  back  the  more  the  aorta  is  on  the 

side  of  the  column.  On  the  right  the  posterior  border  is  farther  forward,  being 
about  opposite  the  anterior  surface  of  the  spine.  It  may  begin  as  the  posterior  bor- 
der of  the  subclavian  groove,  or  more  posteriorly,  and  continues  as  a  ridge  tending 
to  insinuate  itself  between  the  spine  and  the  contents  of  the  posterior  mediastinum. 
From  just  above  the  root  of  the  lung  it  is  for  a  short  distance  continued  as  the  back 
of  the  groove  for  the  major 

azygos  vein,   below   which  FIG-  i567- 

it  tends  to  pass  between  the 
oesophagus  and  the  pericar- 
dium, and  finally  disappears 
a  little  above  the  lower 
border. 

The  Lobes  and  Fis- 
sures.— The  lungs  are  di- 
vided into  lobes  by  deep 
fissures.  The  chief  fissure 
starts  on  the  inner  aspect  of 
the  lung,  behind  the  upper 
part  of  the  hilum,  and  as- 
cends to  the  posterior  sur- 
face, which  it  may  reach 
at  the  same  level  on  both 
sides,  or,  as  is  perhaps  more 
frequent,  the  right  fissure 
may  be  one  intercostal 
space  lower.  The  fissure 
then  descends  obliquely 
along  the  outer  aspect  of 
the  lung,  and  reaches  the 
inferior  border,  where  it  ends  somewhat  sooner  on  the  right  side  than  on  the  left. 
In  the  right  lung  this  occurs  at  the  front  of  the  lateral  aspect,  while  it  is  likely  to 


-Groove  for  left  subclavian 
artery 


oove  for  left 
imon  carotid 


Superior  pulmo- 
nary vein 


Lingula 


Diaphragmatic 
surface 


Preceding 


T846  HUMAN   ANATOMY. 

encroach  somewhat  anteriorly  in  the  left,  terminating  below  the  lingula.  The  left 
lung  is  thus  divided  into  a  superior  and  an  inferior  lobe.  In  the  right  lung  a  middle 
lobe  is  cut  off  from  the  superior  by  a  secondary  fissure,  which  starts  from  the  main 
fissure  far  back  on  the  lateral  aspect  and  runs  forward,  either  straight  or  with  an 
upward  or  a  downward  inclination.  The  foregoing  description  applies  to  the  course 
of  these  fissures  as  seen  on  the  surface  ;  but  the  chief  fissure  is,  moreover,  very  deep, 
penetrating  to  the  main  bronchus,  and  completely  dividing  the  lung  into  a  part  above 
it  and  one  below  it.  The  depth  from  the  surface  of  an  inflated  lung  to  the  bronchus 
at  the  bottom  of  the  fissure  (taken  at  the  point  of  origin  of  the  secondary  fissure  on 
the  right  and  at  a  corresponding  point  on  the  left)  is  from  7-8  cm.  on  the  right  and 
about  i  cm.  less  on  the  left.  The  secondary  fissure  is  much  less  deep  and  may  end 
prematurely,  or  even  be  wanting,  so  that  the  middle  lobe  is  a  very  irregular  structure. 
The  left  superior  lobe  comprises  the  apex  and  the  entire  front  of  the  lung,  while 
the  inferior  takes  in  most  of  the  back  and  all  of  the  base,  unless  the  lingula  be  re- 
garded as  constituting  its  anterior  border.  In  the  right  lung  the  middle  lobe  forms 
a  varying  part  of  the  front  and  one-fourth  or  one-third  of  the  base.  The  volume  of 
the  upper  and  lower  lobes  of  the  left  lung  is  about  equal.  In  the  right  lung  that  of 
the  inferior  is  about  equal  to  that  of  the  other  two.  We  consider  the  middle  lobe 
simply  as  a  piece  cut  off  from  the  upper,  so  that  the  right  upper  and  middle  lobes 
correspond  to  the  left  upper  one. 

Variations  of  the  Lobes  and  Fissures. — Were  it  not  for  the  great  difficulty  in  properly 
examining  the  lungs,  their  marked  tendency  to  variation  would  doubtless  be  more  fully  appre- 
ciated. Schaffner *  has  shown  that  an  accessory  inferior  lobe  is  very  frequently  found  on  the 
under  surface,  extending  up  onto  the  inner  surface  in  front  of  the  broad  ligament.  This  lobe 
may  be  merely  indicated  by  shallow  fissures  or  sharply  cut  off  from  the  rest.  It  may  present 
a  tongue-like  projection  inward  or  may  comprise  the  entire  inner  portion  of  the  base.  It  usu- 
ally represents,  when  present,  from  one-fifth  to  one-third  of  the  base.  It  may  occur  on  either 
side  or  on  both,  but  is  larger  and  more  frequently  well  defined  on  the  right.  On  the  other  hand, 
it  is  present,  or  at  least  indicated,  rather  more  often  on  the  left.  Schaffner  found  it  in  47.  i  per 
cent,  of  210  lungs.  The  lobe  of  the  right  lung  represents  the  subcardiac  lobe  of  many  mam- 
mals, that  of  the  left  being  evidently  its  fellow.  The  irregularity  and  occasional  absence  of  the 
fissure  marking  off  the  middle  lobe  have  been  mentioned.  An  irregular  fissure  may  subdivide 
the  left  lung  into  three  lobes,  and  both  lungs  may  exceptionally  be  still  further  subdivided,  espe- 
cially the  right  one.  A  little  process  of  the  right  lung  just  above  the  base,  behind  the  termina- 
tion of  the  inferior  vena  cava,  may  very  rarely  become  more  or  less  isolated  as  the  lobus  carer. 
The  azygos  major  vein  may  be  displaced  outward,  so  that,  instead  of  curving  over  the  root 
of  the  lung,  it  may  make  a  deep  fissure  in  the  upper  part  of  the  right  lung,  marking  off  an 
extra  lobe. 

External  Appearance  and  Physical  Characteristics.— The  adult  lung 
is  bluish  gray,  more  or  less  mottled  with  black.  At  birth  the  lung-tissue  proper  is 
nearly  white,  but  the  blood  gives  it  a  pinkish  or  even  a  red  color.  It  grows  darker 
with  age,  partly,  perhaps  chiefly,  by  the  absorption  of  dirt,  but  also  by  the  greater 
quantity  of  pigment.  Before  middle  age  the  lungs  become  decidedly  dark  by  t he- 
presence  of  black  substance  (be  it  dirt  or  pigment),  arranged  so  as  to  bound 
irregular  polygons  from  1-2.5  cm-  m  diameter,  which  are  the  lobules.  At  first, 
while  the  black  is  scanty,  the  lines  seem  to  enclose  considerably  larger  spaces,  but 
when  more  of  the  lobules  appear,  owing  to  a  greater  deposit  of  the  pigment  in  the 
areolar  tissue  and  lymphatics  marking  them  off,  it  is  clear  that  their  diameter  rarely 
much  exceeds  1.5  cm.  Some,  however,  are  relatively  long  and  narrow.  It  is  re- 
markable that  the  deposit  of  pigment  is  much  greater  in  certain  places  than  in  others. 
Thus  the  rounded  posterior  parts  of  the  lungs  are  darker  than  the  anterior  portions. 
In  general  the  external  surface  is  much  darker  than  the  mediastinal  or  the  base,  while 
the  surface  within  the  fissures  is  the  lightest  of  all.  Moreover,  the  pigment  on  the 
external  surface,  before  the  coloration  has  become'  general,  is  often  in  stripes  corre- 
sponding to  the  intercostal  spaces,  as  if  there  were  more  pigment  in  the  places  most 
accessible  to  li.uht. 

The  lungs  being  filled  with  air,  after  respiration  has  begun,  arc  soft  and  crack- 
ling on  pressure.  They  are  extremely  elastic,  so  as  to  collapse  to  perhaps  a  third 
of  their  size  when  the  chest  is  opened. 

1  Yin-how's  Arrhiv,  Ikl.  clii.,  iSi,s. 


THE    LUNGS. 


1847 


FIG.   1568. 


External  surface  of  lung,  showing  polygonal  areas 
corresponding  to  lobules  mapped  out  by  deposits  of 
pigmented  particles  within  connective  tissue. 


The  weight  of  the  lung  is  difficult  to  determine,  owing  to  the  impossibility  of 
quite  excluding  fluids.  Sappey  puts  it  at  60  or  65  gm.  for  the  foetus  at  term,  and  at 
94  gm-  on  the  average  for  the  new-born  infant  that  has  breathed  (thus  show- 
ing convincingly  the  worthlessness  of  the 
method).  Krause  gives  the  adult  weight 
as  1300  gm.  in  the  male  and  1023  gm.  in 
the  female.  According  to  Braune  and 
Stahel,  the  weight  of  the  right  lung  is  to 
that  of  the  left  as  100  :  85. 

The  specific  gravity  of  the  lung  be- 
fore breathing  is  greater  than  that  of  water, 
so  that  the  lung  sinks  in  it.  Wilmart l  has 
recently  stated  it  as  1068,  which  is  the 
same  as  Sappey 's  statement  and  greater 
than  that  of  Krause  (1045-1056).  After 
breathing  it  may  be  as  little  as  .342,  but 
may  go  as  high  as  .  746.  Probably  figures 
like  the  latter  represent  either  diseased  or 
congested  lungs. 

The  dimensions  are  necessarily  of  lit- 
tle value.  According  to  Krause,  the  length 
in  man  is  27.1  cm.  on  the  right  and  29.8 
cm.  on  the  left.  In  woman  these  dimen- 
sions are  21.6  cm.  and  23  cm.  respectively. 
There  is  little  difference  in  length  between 
the  lungs,  but  such  as  there  may  be  is  in  favor  of  the  left.  The  other  dimensions 
are  probably  more  variable.  According  to  Sappey,  the  antero-posterior  diameter, 
which  increases  from  above  downward,  finally  reaches  16  or  17  cm.  Krause  gives 
the  transverse  diameter  at  the  base  in  man  as  13.5  cm.  on  the  right  and  12.9  cm.  on 
the  left,  and  in  woman  as  12.2  cm. 
and  10. 8  cm.  respectively. 

The  average  capacity  of  the 
lungs  of  a  powerful  man,  after  an 
ordinary  inspiration,  is  stated  at  from 
3400—3700  cc.  The  vital  capacity, 
which  is  the  greatest  amount  of  air 
that  can  be  expelled  in  life  after  a 
forced  inspiration,  is  from  3200-3700 
cc.  for  men  and  2500  cc.  for  women. 
The  Bronchial  Tree.— The 
plan  of  the  bronchi  of  the  human  lung 
(Fig.  1558)  is  as  follows.  The  two 
primary  bronchi,  resulting  from  the 
bifurcation  of  the  trachea,  run  down- 
ward and  outward  into  the  lowest 
lateral  part  of  the  lungs,  the  right 
one  descending  more  steeply.  Their 
course  has  been  variously  described. 
That  of  the  right  one  has  been  said 
to  resemble  a  C  with  the  concavity 
inward,  and  that  of  the  left  an  S  ; 
but  both  comparisons  are  very  forced. 
On  their  way  they  give  off  secondary 
bronchi,  which  are  divided  into  ven- 
tral and  dorsal  branches.  The  ven- 
tral might  more  properly  be  called  lateral,  since  they  spring  from  the  outer  aspect  of 
the  primary  bronchus.  They  are  much  the  larger,  and  supply  all  the  lung,  except  the 
apex  and  the  posterior  portion  lying  along  the  spine  ;  the  latter  is  supplied  by  the 

1  La  Clinique,  1897. 


FIG.   i  569. 


Relations  of  bronchial  tree  to  anterior  thoracic  wall,  as  shown 
by  X-rays.     (After  Blake.) 


1848 


HUMAN   ANATOMY. 


dorsal  branches,  which  are  small  and  irregular.  There  are  usually  four  large  and  well- 
marked  ventral  secondary  bronchi,  besides  one  or  two  insignificant  ones  the  nature 
of  which  is  not  easily  determined.  The  ventral  bronchi  describe  a  spiral  course 
through  the  lung,  curving  forward  and  inward  as  they  descend,  so  as  to  be  in  the 
main  parallel  with  the  chief  fissure.  The  dorsal  branches,  running  backward,  inward, 
and  downward,  are  not  more  than  four  in  number,  and  may  be  reduced  to  two.  There 
are  two  bronchial  tubes  besides  those  mentioned  above  :  one,  the  apical  bronchus, 
supplies  the  upper  part  of  the  lung,  on  the  right  springing  from  the  primary  bronchus 
2  cm.  or  less  from  its  origin.  It  is  a  large  branch,  about  10  mm.  in  diameter,  running 
upward  and  outward,  and  divides  into  three  branches,  orie  of  which  ascends  and  two 
of  which  run  downward  and  outward  on  the  front  and  back  respectively.  It  is  really 
the  first  dorsal  branch  of  the  right  primary  bronchus,  but  we  have  not  included  it  in 
the  dorsal  branches.  On  the  left  the  apical  bronchus,  which  closely  resembles  the 
right  one,  but  is  rather  smaller,  rises  from  the  first  ventral  bronchus,  of  which  it 
may  be  called  a  dorsal  branch.  The  other  secondary  bronchus,  not  included  in  the 
foregoing  scheme,  is  the  subcardiac  bronchus,  which  on  the  right  arises  usually  from 
the  main  trunk  between  the  first  and  second  ventral  bronchi,  or  from  the  second 

ventral  bronchus.     It 

FIG.  1570.  runs  downward  and 

inward  to  the  region 
in  front  of  the  hi- 
lum  and  above  the 
lower  border  of  the 
lung,  which  may  be 
marked  off  as  a  sep- 
arate lobe,  held  to 
represent  the  cardiac 
lobe  of  mammals. 
On  the  left  the  cor- 
responding bronchus 
arises  always  from 
the  second  ventral 
branch. 

Homologies  of  the 
Bronchi. — We  are  in- 
debted to  Aeby  *  for  the 
idea,  now  practically 
universally  accepted, 
that  there  is  a  mam  or 
primary  bronchus  ex- 
tending through  the 

lung  and  giving  off  both  ventral  and  dorsal  branches.  After  the  bifurcation  of  the  pulmonary 
artery,  each  of  its  subdivisions  reaches  the  front  of  the  primary  bronchus  of  each  lung,  and 
(according  to  Aeby)  crosses  over  it  so  as  to  lie  behind  it.  This  alleged  crossing  occurs  on  the 
right  just  after  the  origin  of  the  apical  bronchus,  which  is  said,  therefore,  to  be  above  the  cross- 
ing, and  is  called  by  Aeby  the  eparterial  bronchus.  Thus  on  the  right  all  but  one  of  the  branches, 
and  on  the  left  all,  without  exception,  are  given  off  below  the  crossing,  and  are  called  hyparterial 
bronchi.  Aeby  attached  so  much  importance  to  this  relation  that  he  considered  the  little  irregu- 
lar middle  lobe  of  the  right  lung,  because  it  is  supplied  by  the  first  hyparterial  bronchus,  the 
representative  of  the  left  upper  lobe,  the  right  upper  lobe  being  without  a  mate  and  the  t\vo 
lower  lobes  homologous.  It  is  difficult  to  understand  why  such  a  relation  should  be  of  so  great 
import.  Narath,*  in  refutation  of  Aeby,  pointed  out  that  during  fcetal  life  the  pulmonary  artery  is 
a  very  insignificant,  and  withal  variable  structure,  and,  moreover,  that  it  does  not  cross  fairly 
over  the  main  bronchus,  but  runs  on  its  outer  side,  the  crossing  occurring,  if  at  all,  deep  in  the 
lung.  Narath  showed  also  that  the  so-called  eparterial  apical  bronchus  of  the  right  lung  is 
present  in  the  left,  arising  from  the  first  ventral  instead  of  the  primary  bronchus.  It  is  a  ter- 
tiary bronchus  from  the 'first  ventral  which,  especially  on  the  right,  is  (among  mammals)  given 
to  wandering,  so  that  it  may  spring  from  the  main  bronchus  or  even  from  the  trachea. 
arterial  relation  he  considers  of  no  importance.  Huntington,3  after  much  work  on  human 
and  mammalian  lungs,  came  to  somewhat  similar  conclusions.  He  believes  that  the  primary 
type  among  mammals  is  one  with  a  hyparterial  bronchus  on  both  sides,  and  the  furthest 

1  Der  Bronchialbaum  der  Siiugethiere  und  des  Menschen,  1880. 

1  Verhandl.  d.  Anat.  Gesellschaft,  1892. 

3  Annals  of  the  New  York  Academy  of  Sciences,  1898. 


Relations  of  bronchial  tree  to  posterior  thoracic  wall,  as  shown  by  X-rays. 
(After  Slake.) 


THE   LUNGS.  1849 

departure  from  it  one  with  symmetrical  eparterial  bronchi.  The  type  found  in  man  is  the  most 
common  among  mammals.  Huntingdon  would  do  away  entirely  with  the  terms  "eparterial" 
and  "hyparterial,"  except  for  purposes  of  topography.  Certainly  there  is  no  need  of  them  in 
human  anatomy  as  a  special  study  ;  whether  or  not  the  arterial  relations  should,  as  Narath  main- 
tains, be  absolutely  discarded  in  comparative  anatomy,  we  must  leave  undetermined.1 

It  must  be  admitted  that  were  our  knowledge  derived  solely  from  the  human  lung  it  would 
be  impossible  to  make  out  this  plan.  We  shall  now  describe  what  is  actually  to  be  seen. 

Distribution  of  the  Bronchi. — In  the  right  lung  the  apical  bronchus,  with  a  diameter  of 
about  10  mm.,  arises  about  2  cm.  from  the  trachea  (often  nearer  and  rarely  farther),  and, 
entering  the  top  of  the  hilum,  divides  as  described  above.  The  diameter  of  the  main  trunk,  after 
giving  off  the  apical  branch,  is  12  mm.  The  first  right  ventral  branch  arises  from  its  outer  side, 
about  5  or  6  cm.  from  the  bifurcation  of  the  trachea,  and  runs  downward,  outward,  and  for- 
ward. It  is  about  8  mm.  in  diameter.  The  apical  branch  and  the  first  ventral  supply  the  supe- 
rior lobe,  of  which  the  middle  lobe  is  really  a  part.  Shortly  after  the  origin  of  the  first  ventral 
branch  the  chief  bronchus  seems  to  break  up  into  a  bundle  of  branches  running  mostly  in  the 
same  general  direction,  but  diverging.  It  is  usually  not  possible  to  determine  which  is  the 
main  trunk,  but  the  subcardiac  branch  may  sometimes  be  distinguished.  In  the  left  lung  the 
first  branch  is  the  first  ventral,  with  a  diameter  of  12  mm.,  arising  some  40  mm.  from  the  bifurca- 
tion. It  gives  off  the  apical,  7  or  8  mm.  in  diameter,  after  which  the  diameter  of  the  main 
branch  is  12  mm.  It  presently  breaks  up  like  the  right  one.  On  this  side  the  first  ventral  sup- 
plies the  upper  lobe.  A  branch  from  the  second  ventral  goes  to  the  accessory  lobe,  if  there 
be  one.  The  branches  of  the  left  bronchus  are  very  apt  to  give  the  appearance  of  being  divided 
into  an  upper  and  a  lower  set,  the  former,  consisting  of  the  first  ventral  branch,  bearing  the 
apical  and  supplying  the  superior  lobe,  while  the  lower  sheaf  of  branches  supplies  the  inferior. 

The  secondary  bronchi  give  off  branches  of  4  or  5  mm.  in  diameter,  which  diverge  at  acute 
angles  from  the  parent  trunk,  and  in  turn  give  off  smaller  branches  at  continually  greater  angles. 
The  branches  to  the  lobules  are  probably  the  fourth  or  fifth  branches.  They  are  about  i  mm. 
in  diameter  and  arise  by  the  subdivision  of  the  preceding  branch.  In  the  larger  tubes  the 
ramification  is  clearly  from  the  side,  but  in  the  smaller  ones  it  is  more  suggestive  of  a  splitting. 
His,2  Minot.3  and  more  recently  Justesen4  defend  the  theory  that  the  origin  of  the  bronchi  is 
throughout  by  bifurcation,  with  subsequent  unequal  growth  of  the  subdivisions  until  we  come  to 
the  smallest.  Aeby  gives  the  following  table  of  diameters  of  the  main  bronchus  above  the  origin 
of  the  chief  branches,  the  nomenclature  being  his. 

Right.  Left. 

Above  the  eparterial  branch 12.8  mm.  .    .    . 

Above  the  first  hyparterial  branch 9.6mm.  10. i  mm. 

Above  the  second  hyparterial  branch 7.2  mm.  7.7  mm. 

Above  the  third  hyparterial  branch 5.8  mm.  6.4  mm. 

Above  the  fourth  hyparterial  branch 4.6  mm.  5.3  mm. 

The  variations  of  the  bronchial  tree  are  very  numerous.  Very  rarely  indeed  the  right 
apical  branch  does  not  spring  from  the  primary  bronchus,  so  that  the  disposition  of  the  two 
sides  is  symmetrical.  The  origin  of  the  left  apical  from  the  primary  bronchus  has  been 
observed  in  two  or  three  cases  of  infants,  which  also  makes  the  arrangement  symmetrical. 
Chiari 5  has  seen  several  cases  in  which  the  right  apical  bronchus  is  double,  the  duplication 
being  apparently  due  to  the  springing  of  one  of  its  branches  from  the  main  bronchus.  The 
right  apical  bronchus  may  spring  from  the  trachea,  as  in  the  sheep  and  other  mammals.  \Ye 
have  such  an  instance  in  which  it  is  separated  from  the  chief  bronchus  by  the  azygos  vein. 
The  dorsal  secondary  bronchi  are  particularly  likely  to  be  reduced  in  number.  The  ventral 
ones  may  also  be  reduced  by  two  having  a  common  origin  or  by  one  becoming  merely  the 
branch  of  another.  The  number  may  be  apparently  increased  by  the  separate  origin  from  the 
parent  stem  of  what  are  normally  branches  of  branches. 

The  Lung  Lobule. — The  surface  of  the  lung  is  covered  with  lines  of  con- 
nective tissue  containing  blood-vessels  and  lymphatics,  with  pigment  either  within  the 
latter  or  free,  the  lines  marking  off  little  polygons  (Fig.  1568),  which  are  the  bases  of 
pyramidal  masses  of  pulmonary  tissue  known  as  the  lobules.  The  shape  of  the  latter 
within  the  depths  of  the  lungs  is  not  accurately  known  ;  those  at  the  sharp  borders 
are  modifications  of  the  typical  ones  at  the  surface.  The  bases  of  the  pyramids  at 
the  surface  are  bounded  by  four,  five,  or  six  sides,  the  larger  diameter  varying  from 
10-25  mm.  and  the  smaller  from  7-12  mm.  If  the  base  be  assumed  to  be  square, 
the  average  breadth  would  be  12.57  mm.6  The  average  height  is  13  mm.  The 
lobules  are  separated  from  one  another  by  a  layer  of  connective  tissue  containing 

1  The  latest  and  most  elaborate  work  on  this  subject  is  Narath's  Der  Bronchialbaum  der 
Siiugethiere  und  des  Menschen,  Stuttgart.  1901. 

2  Archiv  f.  Anat.  u.  Phys.,  Anat.  Abth.,  1887. 

3  Human  Embryology,  1892. 

4  Archiv  f.  mikro.  Anat.,  Bd.  Ivi.,  1900. 

5  Zeitschrift  fiir  Heilkunde,  Prag.,  Bd.  x.,  1890. 

6  Bibliographic  Anatomique,  1898. 


i85o 


HUMAN   ANATOMY. 


FIG.  1571. 


vessels.  Each  lobule  is  entered  by  an  iniralobular  bronchus  (.5-1  mm.  in  diam- 
eter), accompanied  by  its  artery, — not  quite  at  the  apex  of  the  pyramid,  but  slightly 
to  one  side  of  it.  The  bronchus  divides  into  two,  at  an  angle  of  from  9O°-ioo°,  a 
little  above  the  middle  of  the  lobule,  having  previously  given  off  two  or  three  col- 
lateral branches  to  its  upper  part.  In  the  third 
quarter  of  the  lobule  the  two  subdivisions  ( 2-3 
mm.  in  length)  again  split,  with  about  the  same 
degree  of  divergence  as  the  parent  stems,  but  in 
a  plane  at  right  angles  to  that  of  the  previous 
splitting.  This  is  repeated  in  three  or  four  suc- 
cessive bifurcations,  a  varying  number  of  col- 
lateral branches  being  given  off.  Thus  the  num- 
ber of  branches  in  the  third  quarter  is  much  in- 
creased ;  but  it  is  in  the  last  quarter  and  towards 
the  periphery  of  the  lobule  throughout  that  the 
tubes  break  up  into  the  great  number  of  truly 
ultimate  bronchi.  The  various  collaterals,  spread- 
ing and  even  reascending,  undergo  subdivision 
also.  Laguesse  and  d'  Hardiviller 1  estimate  the 
number  of  terminal  bronchi  (ductuli  alveolares) 
within  a  single  lobule  at  from  fifty  to  one  hun- 
dred or  even  more.  The  slightly  dilated  distal  ex- 
tremity of  the  terminal  bronchus  communicates 
with  from  three  to  six  spherical  cavities,  the  atria 
of  Miller2  (so  named  by  him  from  the  resemblance 
to  the  arrangement  of  an  ancient  Roman  house). 
The  atria,  in  turn,  communicate  with  a  group  of 
larger  and  irregular  cavities  or  air-sacs  (sacculi 

alveolares),  into  which  directly  open  the  ultimate  air-spaces,  the  alveoli  or  air-cells 

(alveoli  pulmonis).    The.  latter  open  not  only  into  the  air-sacs,  but  also  into  the  atria,  the 

dilated  distal  part  of  the  terminal  bronchus  being  likewise  beset  with  scattered  alveoli. 

Miller  holds  that  the  terminal  bronchus,  the  air-chambers  connected  with  it, 

together  with  the  vessels  and 
nerves,  is  the  true  lung-unit, 
and  calls  it  the  lobule.  We 
cordially  agree  that  this  is 
the  true  lung-unit,  and  pro- 
pose that  name  for  it,  retain- 
ing the  term  ' '  lobule' '  for 
the  above-described  more  or 
less  isolated  portion  of  the 
lung  which  is  surrounded  by 
connective  tissue-  and  vessels 
and  receives  a  single  intra- 
lobular  bronchus  and  artery. 
In  some  animals  the  lobules 
are  perfectly  distinct  ;  they 
may  be  isolated  in  the  infant, 
and  can  be  in  the  main  easily- 
made  out  in  the  adult.  The 
lung-unit,  on  the  other  hand, 
is  not  surrounded  by  areolar 
tissue,  and  its  limits  can  be 


Diagram  showing  relations  of  terminal  sub- 
divisions of  air-tubes.  £,  bronchiole  ending  in 
terminal  bronchi  (  7'£)  ;  latter  divide  into  atria 
(A),  each  of  which  communicates  with  several 
air-sacs  (s)  into  which  open  the  alveoli  (</i; 
PA,  branch  of  pulmonary  artery  follows  bron- 
chiole ;  PI/,  pulmonary  vein  at  periphery  of 
lung-unit.  {After  Miller.} 


Corrosion-preparation  of  lung,  showing   lung-units.     <;,  minute  bnmrlm> 
ending  in  terminal  bronchi  (/>,/»;  r,  atria  ;  ii,  air-sac  ;  /•,  alveoli.     X  8. 


determined    only    by    recon- 

struction from  microscopical  sections  ;  hence,  apart  from  its  minuteness,  it  is  practi- 
cally too  much  <>t  an  abstraction  to  deserve  the  name  almost  universally  applied  to 
something  tangible. 


apliie  Anntomiqne,  1898. 
'Journal  of  Morphology,  1X93.     Archiv  f.  Anat.  u.  1'lus.,  Anat.  Alith.,  1900. 


THE   LUNGS. 


1851 


Bronchiole 


Mucous 
membrane 


Cartilage 


The  intralobular  bronchus  is  accompanied  by  some  areolar  tissue,  and  certain 
fibrous  prolongations  extend  into  the  lobule  from  the  connective  tissue  disposed 
about  its  surface.  Although  superficially  these  appear  to  divide  the  lobule  into  from 

four  to  twelve  parts,  they 

FIG.  1573.  penetrate  but  a  short  dis- 

Bronchioie  tance.    They  are  not  real 

partitions,  and  the  sub- 
divisions they  suggest 
have  no  morphological 
significance. 

Structure. — As  far 
as  their  entrance  into  the 
lungs,  the  bronchi  pos- 
sess essentially  the  same 
structure  as  the  trachea. 
After  the  division  of 
the  bronchus  within  the 
lung,  the  cartilage-rings 
are  replaced  by  irregu- 
lar angular  plates,  which 
appear  at  longer  and 
longer  intervals  until 
they  finally  cease,  the  last 
nodules  usually  marking 
the  points  of  bifurcation 
Alveoli/  7li  .;r  of  the  bronchi.  Within 

Section  of  lung,  showing  small  air-tubes  and  branch  of  pulmonary  artery.     X  35-       the   Walls  of    bronchioles 

of  a  diameter  of  i  mm. 

or  less  cartilage  is  seldom  present.  As  the  cartilage  disappears  the  unstriped  muscle 
broadens  into  a  continuous  layer,  which,  however,  gradually  becomes  thinner  as  the 
air-tube  diminishes,  and  extends  only  as  far  as  the  terminal  bronchi.  Around  the 
circular  openings,  by  which  the  latter  communicate  with  the  atria,  the  muscle  is 
arranged  as  a  sphincter-like  band 
(Miller). 

The  walls  of  bronchi  of  medium 
size  consist  of  three  coats,  which 
from  without  in  are  :  ( i )  an  exter- 
nal fibro-elastic  tunic  which  encloses 
the  cartilage  and  blends  with  the 
surrounding  lung-tissue  ;  (2)  a  usu- 
ally incomplete  layer  of  involuntary 
muscle  composed  of  circularly  dis- 
posed elements  ;  (3)  the  mucosa, 
consisting  of  a  stratum  of  compact 
elastic  fibres  next  the  muscle,  the 
fibro-elastic  stroma  and  the  cili- 
ated columnar  epithelium.  Mucous 
glands,  similar  to  those  of  the 
trachea,  are  present,  decreasing  in 
number  and  size  until  the  bronchus 
approaches  i  mm.  in  diameter, 
when  they  disappear.  Their  chief 
location  is  outside  the  muscular 
layer,  which  is  pierced  by  the  ducts. 

In    addition    tO    diffused  Cells  within  Portion  of  wall  of  small  bronchus.     X  180. 

the  mucosa,   more   definite  aggre- 
gations of  lymphoid  tissue  occur  as  minute  lymph-nodules  along  the  bronchi,  the 
points  of  bifurcation  of  the  latter  being  their  favorite  seats. 

The  epithelium  lining  the  air-tubes  retains  the  ciliated  columnar  type,  with  many 


FIG. 


F.pithelium 

Goblet-cell 


Cartilage 


I852 


HUMAN   ANATOMY. 


goblet-cells,  as  far  as  the  smaller  bronchi.  Within  these  the  ciliated  cells  are  replaced 
by  simple  columnar  elements  which,  in  turn,  give  place  to  low  cuboidal  cells  within 
the  proximal  part  of  the  terminal  bronchi.  Towards  the  termination  of  the  latter, 
transition  into  a  simple  squamous  epithelium  takes  place. 

The  walls  of  the  air-spaces — the  atria,  the  air-sacs,  and  the  alveoli — have  es- 
sentially the  same  structure,  consisting  of  a  delicate  fibre-elastic  framework  which 
supports  the  blood-vessels  and  the  epithelium.  Within  the  adult  lung  the  latter  is 
simple  and  is  represented  b'y  two  varieties  of  cells,  the  large,  flat,  plate-like  elements 
(.020— .045  mm. )  and  the  small  nucleated  polygonal  cells  (.007-. 015  mm.)  occurring 
singly  or  in  limited  groups  between  the  plates.  Before  respiration  and  the  conse- 
quent expansion  of  the  air-spaces  take  place,  the  cells  lining  these  cavities  are  small 
and  probably  of  one  kind.  The  groups  of  the  smaller  cells  are  larger,  more  numer- 
ous, and  more  uniformly  distributed  in  young  animals  than  in  old  ones,  in  which 
they  are  often  represented  by  single  cells  irregularly  disposed. 

The  adjacent  alveoli  share  in  common  the  interposed  wall,  which  consists  of  the 
two  layers  of  delicate  elastic  membrane  beneath  the  epithelium  lining  the  alveoli  and 


Air-sacs 


Passage  from 
atrium  into  air-sa 


Alveolus— j 

Terminal  bronchus 

Pulmonary  artery 
Bronchiole 


Atrium 


Alveolus 


Air-sacs 


Section  of  lung,  showing  general  relations  of  divisions  of  air-tubes.     X  50. 


the  intervening  capillary  net-work,  supported  by  a  delicate  framework  of  elastic  fibn 
The  capillary  net-work  is  noteworthy  on  account  of  the  closeness  of  its  meshes,  which 
are  often  of  less  width  than  the  diameter  of  the  component  capillaries.  The  latter  are 
not  confined  to  a  single  plane,  but  pursue  a  sinuous  course,  projecting  first  into  one 
alveolus  and  then  into  the  one  on  the  opposite  side  of  the  interalveolar  septum.  The 
capillaries  are,  therefore,  excluded  from  the  interior  of  the  air-cells  by  practically 
only  the  attenuated  respiratory  epithelium,  the  large  plate-like  cells  lying  over  the 
blood-vessels  while  the  small  cells  cover  the  intercapillary  areas.  Distinct  intercellu- 
lar apertures  or  stomata,  formerly  described  as  affording  direct  entrance  from  the 
alveoli  into  definite  lymphatics,  probably  do  not  exist.  That,  however,  inspired 
foreign  particles  may  pass  between  the  epithelial  cells  into  lymph-spaces  within  the 
alveolar  wall  and  thence  into  lymphatics,  to  be  transported  to  more  or  less  dis- 
tant points,  is  shown  by  the  gradual  accumulation  of  carbonaceous  and  other  parti- 
cles within  the  interlobular  tissue  and  the  lymph-nodules  along  the  course  of  the 
lymphatic  vessels.  Such  accumulations  may  acquire  conspicuous  proportions,  the 
entire  interlobular  septum  appearing  almost  black.  In  view  of  the  very  frequent 
presence  of  pigment-loaded  leucocytes  within  the  alveoli,  as  well  as  outside  the  alve- 


•I 


THE   LUNGS. 


13.53 


FIG.  1576. 


Capillary- 
net-work 


Branch  of  pul 


Portion  of  injected  and  inflated  lung.     X  80. 


olar  walls,  it  is  highly  probable  that  such  cells  are  important  agents  in  transporting 
the  particles  of  inspired  carbon  through  the  walls  of  the  air-cells.  Additional  par- 
ticles, however,  usually  occupy  the  cement-substance  between  the  alveolar  epithelial 

cells,  sometimes  lying  appar- 
ently within  the  cytoplasm  of 
the  latter. 

Blood-Vessels  of  the 
Lung. — T\\e  pulmonary  artery, 
serving  not  for  the  nutrition  of 
the  lung  but  for  the  aeration  of 
the  blood,  is  very  large, — at 
first  larger  than  the  bronchus, 
which  it  follows  very  closely 
throughout  its  ramifications  to 
the  terminal  bronchi.  Situated 
at  first  anterior  to  the  bronchus, 
it  passes  onto  its  superior  and 
then  onto  its  outer  side,  and  in 
most  cases  twists  around  the 
bronchus,  so  as  finally,  when 
deep  in  the  lung,  to  reach  its 
dorsal  aspect.  This  is  very  dif- 
ferent from  Aeby's  alleged  cross- 
ing of  the  main  bronchus.  The 
arterial  branches  accompanying 
the  apical  bronchus  are  in  the 
main  anterior  to  the  tubes  in  the 
right  lung  and  behind  them  in  the  left.  According  to  Narath,  the  general  course 
of  the  artery  along  the  main  bronchus  is  between  the  ventral  and  dorsal  branches  ; 
but,  as  he  states,  this 

is  not  constant.      We  FIG. 

have  found  certain 
ventral  bronchi  in 
the  lower  part  of  the 
lung  with  the  artery 
before  them.  An  in- 
tralobular  branch  en- 
ters each  lobule  near 
the  apex  with  the 
bronchus,  and  follows 
its  ramifications  until 
the  ultimate  bronchi 
have  ended  in  the  air- 
chambers  of  the  lung- 
unit.  The  terminal 
arterioles  are  in  its 
interior  until  they 
break  up  into  capil- 
laries in  the  walls  of 
the  alveoli.  Side 
branches,  interlobu- 
lar  arteries,  run  in 
the  connective  tissue 
between  the  lobules. 
It  is  from  these,  ac- 
cording to  Miller,  that  the  subpleural  net- work  is  filled  ;  formerly  the  latter  was 
held  to  be  supplied  by  the  bronchial  arteries. 

The  pulmonary  veins,  which  return  the  aerated  blood  to  the  left  auricle,  are  also 
large  wrhen  they  leave  the  hilum, — two  on  each  side,  one  near  the  top  and  the  other 


Smaller  cells 
Larger  cells 


Epithelium 
lining  al- 


Section  of  lung,  showing  collections  of  particles  of  carbon  in  perivascular  connective 
tissue.    X  14°. 


1 854 


HUMAN    ANATOMY. 


FIG.  1578. 


Portion  of  injected  lung,  showing  relation  of  blood- 
vessels to  bronchi ;  pulmonary  arteries  (blue)  accompany- 
ing bronchi  (white) ;  pulmonary  veins  (red)  at  periphery 
of  lobule.  X  2 


near  the  bottom.  They  arise  from  the  capillaries  in  the  walls  of  the  air-chambers, 
running  first  on  the  outside,  of  the  lung-units,  unite  with  others,  and  ramify  in  the 
connective  tissue  about  the  lobules,  so  that,  first  in  the  lung-units  and  then  in  the 
lobules,  the  circulation  is  from  the  centre  towards  the  periphery.  As  they  ascend  to 
the  hilum  they  unite  with  others  and  form 
trunks  that  accompany  the  bronchi,  lying 
in  the  main  lower  and  to  the  inner  side 
of  the  latter.  Corrosion  preparations 
(Fig.  1578)  show  very  clearly  that  the 
small  arteries  travel  in  close  company 
with  the  bronchi,  while  the  veins  course 
by  themselves. 

The  bronchial  arteries  carry  the 
blood  for  the  nutrition  of  the' lungs,  es- 
pecially that  of  the  air-tubes,  the  lymph- 
nodes,  the  walls  of  the  blood-vessels, 
and  the  areolar  tissue  about  them  ;  hence 
they  follow  the  course  of  the  bronchi. 
They  are  in  communication  with  the 
interlobular  system  of  the  pulmonary 
arteries. 

The  bronchial  veins  are  very  irreg- 
ular. Both  anterior  and  posterior  are 
described.  The  former  carry  the  blood 
back  from  the  bronchi  and  the  tissues 
about  them,  becoming  perceptible  at  the 

bronchi  of  the  third  order  (i.e.,  the  branches  of  the  first  branches)  and  running 
to  the  hilum  anterior  to  the  bronchi,  two  with  each.  The  posterior  bronchial  veins 
appear  at  the  back  of  the  hilum  and,  without  any  close  connection  with  the  bronchi, 
anastomose  with  other  veins  at  the  back  of  the  roots  of  the  lungs. 

Anastomoses  betiveen  the 

FIG.  1579.  Pulmonary  and   the    Bron- 

pieura  chtal  Systems.  — Not  only  do 

the  capillaries  at  some  places 
drain  into  either  system  of 
veins,  but  important  com- 
munications occur  between 
both  the  arteries  and  the 
veins.  (a)  The  bronchial 
arteries  as  they  enter  the 
lungs  give  off  occasional 
branches  which,  running  tor 
some  distance  beneath  the 
pleura,  suddenly  plunge  into 
the  lung  to  anastomose  with 
an  interlobular  artery.  Such 
a  branch  may  arise  from  an 
cesophageal  artery.  There 
are  also  deep  connections 
between  the  arteries  of  the 
two  systems  on  or  ivar  the 
secondary  bronchi  and  their 
branches.  (£)  The  com- 
munications between  the  two 
systems  of  veins  are  very 
extensive.  Apparently  ail 
the  blood  from  the  smallest  branches  of  the  bronchial  arteries  returns  by  the  pul- 
monary veins  ;  and,  moreover,  the  bronchial  veins  about  the  larger  bronchi  have 
free  communication  with  those  of  the  pulmonary  system.  According  to  Zucker- 


Pnliiionarv  vein 


Lymph-vessel 

Section   of    injected    lung,     showing   Ivtnphalir   arrompanving   pi-riphi-ral 
In. iin  h  "I  pulmonary  vein,     •  «>.    i.i////v».) 


THE  LUNGS.  1855 

kandl,1  the  pulmonary  veins  anastomose  freely  with  those  of  the  organs  of  the  pos- 
terior mediastinum,  and  even  of  the  portal  system. 

The  lymphatics  of  the  lung-  are  very  numerous.  The  deeper  ones  probably 
begin  as  lymph-spaces  within  the  interalveolar  septa,  distal  to  the  terminal  bronchi, 
distinct  lymphatics  being  found  only  along  the  arteries  and  veins.  These  commu- 
nicate with  the  subpleural  lymphatic  plexus.  Surrounding  the  walls  of  the  terminal 
bronchi  Miller  found  usually  three  lymph-vessels.  The  latter  increase  in  size  and 
number  as  the  calibre  of  the  air-tubes  enlarges.  On  reaching  the  bronchi  the  lym- 
phatics form  plexuses  along  them  which  ultimately  open  into  the  lymphatic  nodes, 
which  are  numerous  in  the  hilum  and  in  the  roots  of  the  lungs.  According  to  Miller, 
where  cartilage-rings  are  present  a  double  net-work  exists,  one  on  each  side  of  the 
cartilage,  the  inner  lying  within  the  submucosa.  The  lymph-nodes  of  the  lungs  are 
deeply  pigmented,  owing  to  the  colored  particles  of  foreign  substances  inspired. 

Nerves. — The  nerves  of  the  lungs,  from  the  pneumogastrics  and  sympathetics, 
form  the  very  rich  anterior  and  posterior  pulmonary  plexuses  about  the  roots,  whence 
they  enter  the  lungs,  runni-ng  along  the  branches  of  the  bronchial  arteries  and  the 
bronchi  to  their  ultimate  distribution  in  the  septa  between  the  alveoli  (Retzius,  Berk- 
ley). The  nerves  are  destined  chiefly  for  the  walls  of  the  blood-vessels  and  of  the  air- 
tubes.  Berkley  describes  interepithelial  end.-arborizations  within  the  smaller  bronchi. 

THE  RELATIONS  OF  THE  LUNGS  TO  THE  THORACIC  WALLS. 

The  relations  of  the  median  and  diaphragmatic  surfaces  of  the  lungs  have  been 
given  (page  1844).  The  apex  rises  vertically  about  3  cm.  above  the  level  of  the  upper 
border  of  the  first  costal  cartilage  and  about  i  cm.  above  the  level  of  the  clavicle. 
These  distances  are  to  be  reckoned  on  a  vertical  plane,  not  on  the  slanting  surface  of 
the  root  of  the  neck.  They  vary  extremely,  depending,  as  they  do,  on  the  formation 
of  the  body.  Thus  a  sunken  chest,  which  means  a  very  oblique  first  rib,  would  have 
more  lung  above  the  cartilage  than  a  full  chest  with  a  more  nearly  horizontal  first  rib. 
In  extreme  cases  the  lung  may  rise  as  much  as  5  cm.,  or  as  little  as  i  cm.,  above  the 
first  cartilage.  The  plane  of  the  inlet  of  the  chest  is  made  by  the  oblique  first  ribs. 
The  fibrous  parts  enclosing  it  are  dome-like,  the  roof  of  the  cavity,  to  which  the  lung 
is  closely  applied,  swelling  upward  perhaps  i  cm.  above  this  oblique  plane  ;  the 
top  of  the  lung,  however,  is  never  above  the  level  of  the  neck  of  the  first  rib.  It 
was  formerly  taught  that  the  right  lung  rises  higher  than  the  left.  As  a  rule,  there  is 
no  appreciable  difference  between  the  two  sides.  The  most  that  can  be  said  for  the 
old  view  is  that,  if  there  be  some  trifling  difference,  it  is  probably  rather  more  often 
in  favor  of  the  right.  The  anterior  borders  of  the  lungs  descend  obliquely  behind 
the  sterno-clavicular  joints,  and  curve  forward  so  as  to  nearly,  or  quite,  meet  in  the 
median  line  on  the  level  of  the  junction  of  the  manubrium  and  body  of  the  sternum. 
Below  this  the  right  lung  extends  a  little  across  the  median  line  and  the  left  recedes 
slightly  from  it.  The  right  border  leaves  the  sternum  at  the  sixth  right  costal  carti- 
lage, to  which  it  has  gradually  curved,  runs  along  that  same  cartilage,  or  a  little  above 
it,  to  its  junction  with  the  sixth  rib,  then  crosses  the  ribs,  passing  the  eighth  at  about 
the  axillary  line,  and  reaches  the  spine  at  the  eleventh  rib  or  a  little  higher,  the 
guide  being  the  spine  of  the  tenth  thoracic  vertebra.  The  lowest  part  of  the  lung  is 
on  the  side  at  the  axillary  line  or  behind  it,  but  the  line  thence  along  the  back, 
although  rising  a  little,  is  very  nearly  horizontal.  The  course  of  the  border  of  the  left 
lung  is  essentially  the  same,  except  that,  leaving  the  sternum  at  the  fourth  cartilage, 
or  at  the  space  above  it,  the  border  describes  a  curve  with  an  outward  convexity, 
exposing  a  large  piece  of  the  pericardium,  and  turns  forward  to  end  as  the  lingula 
opposite  the  sixth  cartilage,  'some  distance  to  the  left  of  the  sternum.  As  this  point 
depends  on  the  development  of  the  lingula,  it  cannot  be  stated  accurately.  It  may 
be  said  in  general  to  be  3  or  4  cm.  to  the  left  of  the  median  line.  The  greatest  depth 
of  this  curve  is  in  the  fourth  intercostal  space,  about  5  cm.  from  the  median  line.  The 
course  of  the  inferior  border  along  the  side  and  back  is  practically  that  of  the  right 
one,  although,  perhaps,  the  left  lung  may  descend  a  trifle  lower  at  the  side.  At  the 
back  the  lower  borders  are  very  symmetrical. 

1  Sitzungsberichte  d.  Wiener  Akad.,  Bd.  Ixxxiv.,  1881. 


18^6 


HUMAN   ANATOMY. 


Apart  from  variations  in  the  lungs  themselves,  the  different  shapes  and  sizes  of 
the  chest,  with  the  consequent  differences  in  the  inclination  of  the  ribs,  make  these 
relations  very  uncertain,  especially  at  the  side.  In  forced  respiration  there  is  no 
change  in  the  relations  of  the  top  of  the  lungs  and  the  dome  of  the  pleura,  as  they 
are  always  in  close  apposition,  and  but  little  change  in  the  first  part  of  the  anterior 
borders.  The  latter,  however,  approach  one  another  behind  the  sternum  in  forced 
inspiration,  a  considerable  advance  of  the  left  lung  taking  place  at  the  cardiac  notch. 
We  agree  with  Hasse  that  during  inspiration  the  anterior  parts  of  the  lungs  rise 
just  about  as  much  as  the  thoracic  walls.  The  greatest  changes  of  relations  are  below 
and  at  the  side.  It  is  said  that  in  the  axillary  line  the  border  may  descend  as  much 
as  from  3-4  cm.,  and  at  the  back  as  much  as  3  cm.  According  to  Hasse,1  the 
lower  border  of  the  lung  in  the  axillary  line  never  descends  nearer  to  the  lower  edge 
of  the  thoracic  wall  than  7  cm.  on  the  right  and  5  cm.  on  the  left.  He  finds  that  in 

FIG.  1580. 


Semidiagrammatic  reconstruction,  showing  relations  of  pleural  sacs  (blue)  and  lungs  (red)  to  thoracic  wall; 

anterior  asprrt. 

extreme  expiration  the  lower  borders  of  the  lungs  rise  in  the  axillary  lines  to  13  cm. 
on  the  right  and  14  cm.  on  the  left  above  the  lower  border  of  the  chest.  He  states 
also  that  the  anterior  borders  may  withdraw  to  the  parasternal  lines  (vertical  lines 
dropped  from  the  inner  third  of  the  clavicles),  which  to  us  appears  excessive.  In 
our  opinion,  the  great  factor  in  the  expansion  of  the  lungs  is  the  increase  in  the  vari- 
ous diameters  of  the  chest  rather  than  the  changes  of  relation  of  the  borders  of  the 
lungs  to  the  walls. 

The  relations  of  the  fissures  to  the  surface  are  rather  variable.  The  chief  ones 
ascend  from  the  hila  and  reach  the  posterior  surface  at  the  sides  of  the  vertebral  col- 
umn, generally  at  different  levels,  the  right  being  the  lower.  We  must,  therefore, 

1  Die  Formen  des  menschlichen    Korpers   und  die    Kormanderungen   bei  der   Athmung, 
Jena,   1888  and  1890. 


THE   LUNGS. 


1857 


trace  the  course  of  each  fissure  separately.  The  fissure  of  the  right  lung  leaves  the 
vertebral  column  either  at  the  fifth  rib  or  at  the  interspace  above  or  below  it.  The 
fissure  tends  to  follow  the  fifth  rib,  being  in  the  axillary  line  still,  either  beneath  it  or 
beneath  an  adjacent  intercostal  space.  Towards  the  front  the  fissure  gets  relatively 
lower,  ending  in  most  cases  either  at  the  fifth  space  or  beneath  the  sixth  rib,  near 
the  junction  of  the  bone  and  cartilage,  from  5-10  cm.  from  the  median  line.  The 
secondary  fissure  of  the  right  lung  leaves  the  chief  one  somewhat  behind  the  axillary 
line,  and,  running  about  horizontally  forward,  ends  at  a  very  uncertain  point. 
Rochard,  in  his  small  series  of  twelve  observations,  found  it  at  the  third  intercostal 
space  seven  times.  Once  it  was  higher  and  four  times  lower.  The  fissure  of  the  left 
lung  leaves  the  side  of  the  spine  at  a  less  definite  point,  ranging  in  most  cases 
from  beneath  the  third  rib  to  the  upper  border  of  the  fifth,  and  being  sometimes  even 

FIG.   1581. 


Semidiagrammatic  reconstruction,  she 


// 


relations  oi  pleura!  sacs  (blue)  and  lungs  (red)  to  body-wall; 
posterior  aspect. 


lower.  At  the  axillary  line  it  is  at  the  fifth  rib  a  little  more  often  than  at  any  other 
particular  point,  but  it  is  almost  as  often  at  the  fourth  and  more  often  somewhere 
below  the  fifth.  Its  termination  is  more  constant  than  its  course,  being  beneath  the 
sixth  rib,  or  the  space  above  or  below  it,  usually  from  6-1 1  cm.  from  the  median 

line.1 

The  relations  of  the  bronchi  to  the  chest-wall  have  not  been  studied  on  a  suffi- 
cient number  of  bodies  for  satisfactory  conclusions.  Blake2  has  had  X-ray  photo, 
graphs  taken  of  an  adult  body  hardened  with  formalin,  the  bronchi  being  injected 
with  an  opaque  substance.  The  bifurcation  was  normally  placed.  We  attach  the 

1  Gazette  des  Hopitaux,   1892.     Our  description  is  almost  wholly  a  synopsis  of  Rochard's 

•American  Journal  of  the  Medical  Sciences,  1899. 

"7 


i858 


HUMAN   ANATOMY. 


most  importance  to  the  course  of  the  main  bronchus  :  ' '  On  the  posterior  wall  the 
course  of  the  left  bronchus  is  from  a  point  to  the  right  of  the  fourth  thoracic  spine  to 
a  point  on  the  eighth  rib  three  inches  to  the  left  of  the  spine.  The  course  of  the 
right  bronchus  is  from  the  same  point  above  to  a  point  on  the  eighth  rib  two  inches 
to  the  right  of  the  spine.  On  the  anterior  wall  the  course  of  the  left  bronchus  is  from 
the  lower  part  of  the  second  right  sterno-chondral  articulation  to  a  point  on  the  fifth 
rib  just  internal  to  the  mammillary,  and  of  the  right  bronchus  from  the  same  point 
above  to  the  intersection  of  the  fifth  rib  with  the  parasternal  line. ' '  The  hilum  is 
opposite  the  bodies  of  the  sixth  and  seventh  thoracic  vertebrae  and  a  part  of  the 
adjacent  ones. 

(The  changes  of  the  relations  of  the  lungs  during  growth  and  in  old  age  are 
considered  with  those  of  the  pleurae.  ) 


THE    PLEURAE. 

The  pleurae  are  a  pair  of  serous  membranes  disposed  one  over  each  lung  and  then 
reflected  so  as  to  line  the  walls  of  the  cavity  containing  it,  thus  forming  a  distinct 
closed  sac  about  each  lung  ;  hence  the  pleura  is  divided  into  a  viscera/ and  a.  parietal 
layer.  The  latter  is  subdivided  according  to  its  situation  into  a  mediastinal,  a  costal, 

a  cervical,  and  a  diaphragmatic  part. 

FIG.   1682.  The  visceral  layer  closely  invests  the 

lung,  following  the  surface  into  the 
depth  of  the  fissures.  It  leaves  the 
lung  at  the  borders  of  the  hilum  and 
invests  the  root  for  a  short  distance 
(1-2  cm.),  when  it  leaves  the  latter 
and  spreads  out  as  the  mediastinal 
pleura,  which  is  applied,  back  to 
back,  to  the  pericardium,  thus  form- 
ing on  each  side  a  vertical  antero- 
posterior  septum  between  the  lungs 
and  the  contents  of  the  mediastina. 
The  prolongation  over  the  root  is  not 
quite  tubular,  since  a  triangular  fron- 
tal fold  extends  from  beneath  the  n  ><  >t 
to  the  inner  side  of  the  lung,  growing 
narrower  as  it  descends,  to  end  at  or 
near  the  lower  borders.  This  is  the 
broad  ligament  of  the  htng  ( liuamen- 
tum  latum  pulmonis).  Its  line  of  at- 
tachment to  the  lung  often  slants 
backward.  The  mediastinal  pleura, 
besides  being  applied  to  the  side  of 
the  pericardium,  lies  also  against  s<  >me 
of  the  structures  of  the  other  medi- 
astina. Above  it  is  in  contact  with  the 
thymus  on  both  sides,  the  superior 
vena  cava  on  the  right  and  the  arch 
of  the  aorta  on  the  left.  The  phrenic 
nerve  descends  on  each  side  between 
it  and  the  pericardium  in  front  of  the 
root  of  the  lung.  In  the  posterior 
mediastinum  it  lies  against  the  left  side  of  the  descending  aorta  and  the  right  of  the 
upper  part  of  tin-  greater  a/ygos  vein.  It  is  in  contact  with  nearly  the  whole  of  the 
oesophagus  on  the  right,  and  just  before  the  latter  passes  through  the  diaphragm  on 
the  left  also.  It  covers  the  gangliated  cord  of  the  sympathetic  on  both  sides  as  it 
passes  into  the  costal  pleura,  and  is  here  stretched  so  tightly  across  the  terminations 
of  the  intercostal  veins  as  to  keep  their  walls  distended.  Anteriorly  it  crosses  the 
areolar  tissue  of  the  anterior  mediastinum  below  the  remnants  of  the  thymus.  It 


SemtdiafiTammatic    reconstruction,   showm)-    relations  of 

null!  plfiiral  sac  (blue)  and  lunjf  (reil)  to  tliorarii-  wall ;  lateral 
Mpect. 


THE    PLEURA. 

is  continued  outward,  both  before  and  behind,  to  become  the  costal  pleura,  and  is 
continuous  above  with  the  cervical  pleura  which  lines  the  dome  in  the  concavity  of 
the  first  rib.  It  passes  below  into' the  diaphragmatic  pleura  which  invests  the  upper 
surface  of  the  diaphragm.  Laterally,  and  still  more  behind,  it  follows  for  a  certain 
distance  the  vertical  fibres  of  the  diaphragm,  and  then  is  reflected  onto  the  thoracic 
wall  so  as  to  line  a  potential  cavity  between  the  two  layers  which,  except  for  some 
little  serous  fluid,  are  here  in  apposition.  Villous  projections  occur  along  the  borders 
of  the  lungs,  especially  at  the  inferior  border,  where  they  form  a  dense,  but  very 
minute  fringe,  not  over  i  mm.  broad. 

Relations  of  the  Pleurae  to  the  Surface.— In  some  places  the  lungs  and 
the  pleurae  are  always  in  the  same  relation  ;  in  others  the  pleurae  extend  a  certain 
distance  beyond  the  lungs,  which  fill  them  in  complete  inspiration  so  that  their  out- 
lines correspond  ;  in  other  places  the 

pleurae  extend  so  much  beyond  the  lungs  FlG-   J  5^3- 

that  even  in  the  most  extreme  inspira- 
tion the  latter  do  not  reach  the  limits  of 
the  former.  At  the  apices  the  relations 
of  the  lungs  and  pleurae  are  constantly 
the  same,  both  being  in  contact.  All 
that  has  been  said  of  the  relation  of  one 
to  the  body-walls  is  true  of  the  other. 
Behind  the  first  piece  of  the  sternum  the 
relations  are  nearly  the  same,  but  below 
this  level  a  space  exists  in  the  pleurae 
into  which  the  lungs  enter  during  deep 
inspiration.  This  is  notably  the  case  at 
the  left  half  of  the  body  of  the  sternum. 
The  pleurae  present  inferiorly  at  the  sides 
and  behind  a  merely  potential  cavity 
between  the  diaphragm  and  the  chest- 
walls,  to  the  bottom  of  which  (probably 
at  the  sides  and  certainly  behind)  the 
lungs  can  never  descend.  The  pleurae, 
however,  never  approach  closely  the 
lower  border  of  the  chest  at  the  sides, 
for  the  diaphragm  arising  from  the  inner 
surface  of  the  frame  of  the  thorax  takes 
up  a  certain  amount  of  space,  and  above 
it  the  connective  tissue  fills  the  cleft  so 
that  the  pleurae  do  not  descend  to  within 
3  cm.  of  the  lower  border.  In  the  sub- 
ject used  by  Hasse  the  space  in  the  ax- 
illary line  below  the  reflection  of  the 
pleurae  to  the  origin  of  the  diaphragm 
(the  lower  border  of  the  chest)  was  5.5  cm.  on  the  right  and  4  cm.  on  the  left. 

The  outlines  of  the  pleurae  are  as  follows.  Beginning  at  the  apex,  about  3 
cm.  vertically  above  the  cartilage  of  the  first  ribs,  the  anterior  borders  descend 
behind  the  sterno-clavicular  joints  to  meet  at  the  median  line  at  the  level  of  the 
second  cartilage.  They  then  descend  together,  or  nearly  so,  behind  the  left  half  of  the 
body  of  the  sternum.  Half-way  down  the  body  of  the  sternum  the  left  pleura  tends 
to  diverge  to  the  left,  passing  from  behind  the  sternum  usually  at  about  the  junction 
with  the  sixth  cartilage.  The  right  pleura  descends  more  nearly  in  a  straight  line  and 
turns  suddenly  outward  at  the  level  of  the  seventh  cartilage.  Laterally  the  pleurae  run 
pretty  close  to  the  cartilages  of  the  sixth  rib  on  the  left  and  the  seventh  on  the  right, 
but  both  cross  the  eighth  rib  at  or  near  the  junction  of  bone  and  cartilage.  In  the  axillary 
line,  or  a  little  behind  it,  the  pleura  crosses  the  tenth  rib  at  about  the  same  place  on 
both  sides,  and  usually  ends  posteriorly  opposite  the  lower  part  of  the  twelfth  thoracic 
vertebra,  the  right  one  being  often  the  lower  (Tanja).  While  such  is  the  general 
outline,  there  are  considerable  and  important  variations  both  anteriorly  and  pos- 


Semidiagrammatic  reconstruction,  showing  relations  of 
left  pleural  sac  (blue)  and  lung  (red)  to  thoracic  wall ; 
lateral  aspect. 


i860 


HUMAN   ANATOMY. 


FIG.  1 584. 


teriorly.  The  former  teaching,  according  to  which  the  left  pleura  describes  at  the 
front  a  curve  somewhat  similar  to  that  of  the  left  lung,  is  quite  wrong.  However,  the 
point  at  which  it  leaves  the  sternum,  the  extent  to  which  it  is  in  contact  with  the 
right  pleura,  and  the  distance  the  latter  advances  under  the  sternum  are  all  very 
uncertain.  The  most  important  point  is  the  extent  to  which  the  pleura  covers  the 
pericardium.  According  to  Side's1  observations  on  twenty-three  bodies  of  adults, 
the  reflection  of  the  left  pleura  at  the  fifth  cartilage  was  in  seventeen  either  behind 
the  sternum  or  just  at  its  border  ;  thus  it  left  the  sternum  at  a  higher  point  only  six 
times.  At  the  sixth  cartilage  the  pleura  was  ten  times  behind  the  sternum  and  less 
than  i  cm.  from  it  in  six.  At  the  seventh  cartilage  it  was  five  times  at  the  border  of 
the  sternum  or  behind  it  and  five  times  not  over  i  cm.  external  to  it.  It  left  the 
sternum  close  to  the  seventh  cartilage  five  times.  Tanja,  *  however,  found  the  left 
pleura  leaving  the  sternum  at  the  fourth  cartilage  in  four  of  fourteen  bodies  ranging 

from  eight  years  upward.  The  left  pleura  may  ex- 
ceptionally cross  the  median  line,  and,  it  is  said,  may 
not  extend  forward  as  far  as  the  sternum  ;  but  such 
a  condition  must  be  very  exceptional.  There  is  con- 
siderable variation  as  to  the  depth  of  the  descent 
posteriorly.  Tanja  never  found  the  lower  fold  at 
the  back  in  the  adult  higher  than  the  middle  of  the 
last  thoracic  vertebra.  It  may  descend  to  the  first 
lumbar  and  even  to  the  second. 

Structure. — The  pleura,  like  other  serous  mem- 
branes, consists  of  a  stroma-layer  composed  of  bun- 
dles of  fibrous  tissue  intermingled  with  numerous 
elastic  fibres.  The  general  disposition  of  the  con- 
nective-tissue bundles  is  parallel  to  the  free  surface, 
although  the  bundles  cross  one  another  in  various 
directions.  The  free  surface  of  the  pleura  is  covered 
with  a  single  layer  of  nucleated  endothelial  cells 
(from  .020— .045  mm.  in  diameter),  which  rest  upon 
a  delicate  elastic  limiting  membrane  differentiated 
from  the  stroma-layer.  The  existence  of  definite 
openings,  or  stomata,  between  the  endothelial  plates, 
leading  into  the  numerous  lymphatics  of  the  pleura, 
is  doubtful. 

The  subserous  layer  is  very  thin  over  the  lung 
where  it  is  continuous  with  the  elastic  interlobulur 
tissue.  In  the  mediastinum  it  has  a  firm  fibrous 
backing  so  as  to  make  a  strong  and  dense  membrane. 
The  cervical  pleura  is  extremely  thick  and  resistant,  being  strengthened  by  fibrous 
or  muscular  bands  from  the  system  of  the  scaleni  muscles  spreading  into  it  from 
behind,  as  well  as  by  expansions  from  the  areolar  tissue  about  the  trachea,  cesopha- 
gus,  and  subclavian  vessels.  The  costal  pleura  has  a  subserous  layer,  known  as  the 
fascia  endothoracica,  through  which  it  is  attached  to  the  thoracic  walls  less  closely 
than  elsewhere.  This  fascia  is  thickest  near  the  top.  The  ribs  show  clearly  through 
the  pleura  of  the  opened  thorax,  appearing  light  in  contrast  to  the  congested  inter- 
costal spaces.  The  subserous  layer  is  hardly  existent  beneath  the  diaphragmatic 
pleura,  but  at  the  sides  of  the  thorax  there  is  a  considerable  space  below  the  reflection 
of  the  pleura  from  the  diaphragm,  occupied  by  areolar  tissue  connecting  the  dia- 
phragm and  walls. 

Blood-Vessels. — The  arteries  of  the  visceral  pleura  have  been  shown  by 
Miller  to  come  from  the  system  of  the  pulmonary  arteries  instead  of  from  that  of 
the  bronchial,  as  previously  believed.  They  form  a  fine  net-work  over  the  lung. 
Those  of  the  parietal  pleurae  come  from  the  aortic  and  superior  intercostals,  the  in- 
ternal mammaries,  the  mediastinal,  the  cesophageal,  the  bronchial,  and  the  phrenic 
arteries. 

1  Archiv  f.  Anal.  u.  I'hys.,  Anat.  Abth.,  1885. 
s  Morphol.  Jahrbuch,  1891. 


—  I  literal  veolar 

wall 


-Endothelium 
or  free  surface 


Connective-tissue 

stronia  of  pleura 


Section  through  free  ed^e  of  lung,  show- 
ing visceral  pleura.     X  150. 


THE    PLEUR/E. 


1 86 1 


FIG.    1585. 


Injected  lymphatics  of  pleura,  seen  frotn  surface. 

X  75-     (Miller.) 


The  veins  of  the  visceral  pleurae  are  tributary  to  the  pulmonary  system  ;  those 
of  the  parietal  pleurae  open  into  the  veins  corresponding  to  the  arteries.  It  is 
important  to  note  that  the  intercostal  spaces  have  many  veins  and  that  the  pleura 
over  the  ribs  has  but  few,  these  chiefly  communicating  with  the  veins  above  and 

below  them.  Owing  to  the  arrangement  by 
which  the  intercostal  veins  are  kept  open,  the 
venous  circulation  of  the  parietal  pleurae  is 
under  the  influence  of  the  suction  power  both 
of  respiration  and  of  the  heart. 

The  lymphatics  are  numerous  over  the 
lungs  and  also  in  the  intercostal  spaces. 
Those  of  the  parietes  open  into  both  inter- 
costal and  substernal  lymph-nodes. 

Nerves. — The  nerves  of  the  visceral 
pleurae  are  from  the  pulmonary  plexuses,  con- 
taining both  pneumogastric  and  sympathetic 
fibres  ;  those  of  the  parietal  pleurae  are  from 
the  intercostal,  the  phrenic,  the  sympathetic, 
and  the  pneumogastric  nerves. 

Development  of  the  Respiratory 
Tract. — The  respiratory  tract  develops  as 
an  outgrowth  from  the  primitive  digestive 
tube.  Early  in  the  third  week,  in  embryos 
of  little  over  3  mm.  in  length,  a  longitudinal 

groove  appears  on  the  ventral  wall  of  the  fore-gut,  extending  from  the  primitive 
pharynx  above  well  towards  the  stomach  below.  This  groove  becomes  deeper, 
constricted,  and  finally  separated  from  the  fore-gut  as  a  distinct  tube,  the  differen- 
tiation resulting  in  the  production  of  two  canals, — the  respiratory  tube  in  front  and 
the  oesophagus  behind.  Separation  and  completion  of  the  former  proceeds  from 
the  lower  end  of  the  groove  upward  as  far  as  the  pharynx,  into  which  both  oesopha- 
gus and  air-tube  open.  The  cephalic  end  of  the  latter  becomes  enlarged  and  forms 
the  larynx,  the  adjoining  portion  correspond- 
ing to  the  trachea. 

The  Lungs. — The  distal  extremity  of 
the  primary  respiratory  tube  soon  enlarges 
and  becomes  bilobed,  pouching  out  on  each 
side  into  a  lateral  diverticulum  which  rep- 
resents the  primitive  bronchus  and  lung. 
These  pulmonary  diverticula  elongate  and 
subdivide,  the  right  one,  which  is  somewhat 
the  larger,  breaking  up  into  three  secondary 
divisions  and  the  left  into  two,  thus  early 
foreshadowing  the  later  asymmetry  of  the 
lung-lobes.  Since  the  primary  air-tube  lies 
medially  in  the  dorsal  attachment  of  the  sep- 
tum transversum,  the  pulmonary  buds  extend 
laterally  and  backward  into  the  dorsal  parie- 
tal recesses  (later  the  pleural  cavities),  carry- 
ing before  them  a  covering  of  mesoblast. 

The  primary  lobes  increase  in  size  and 
complexity  as  additional  outgrowths  arise  bv 
the  division  of  the  enlarged  terminal  part  of 
each  diverticulum.  The  resulting  divisions, 
or  new  bronchi,  are  at  first  equal,  but  soon 
grow  at  an  unequal  rate,  the  one  elongating 
most  rapidly  becoming  so  placed  as  to  continue  the  main  air-tube,  while  the  less 
rapidly  elongating  division  becomes  a  lateral  branch.  The  repeated  bifurcation  in 
this  manner  results  in  the  production  of  a  chief  bronchus,  traversing  the  entire 
length  of  the  lung,  into  which  open  numerous  lateral  tubes  or  secondary  bronchi. 


FIG.  1586. 


CEsophagu 


Lung-tub 


Part  of  sagittal  section  of  rabbit  embryo, 
ing  lung-tube  growing  downward  and  forward  f  n 
primitive  laryngo-pharynx.     X  40. 


1 862 


HUMAN    ANATOMY. 


FIG.  1587. 


The  latter,  from  their  relation  to  the  principal  stem  of  the  pulmonary  artery  which 
accompanies  the  chief  air-tube,  are  regarded  as  dorsal  and  ventral.  They  alternate 
with  one  another,  and  usually  number  four  in  each  series  ;  not  infrequently,  how- 
ever, the  third  dorsal  bronchus  fails  to  develop,  thereby  leading  to  a  corresponding 
reduction  and  asymmetry  in  the  series.  In  the  left  lung  the  first  dorsal  bronchus 
springs  from  the  corresponding  ventral  bronchus  instead  of  the  chief  tube,  as  on 
the  right  side.  This  arrangement  is  probably  associated  with  the  fusion  of  the 
upper  and  middle  lobes  in  the  left  lung. 

The  secondary  bronchi  elongate  and  give  origin  to  tertiary  bronchi,  and  these, 
in  turn,  to  air-tubes  of  lesser  calibre,  until  the  ramifications  end  as  terminal  bronchi 
and  the  associated  divisions — atria,  air-sacs,  and  alveoli — of  the  lung-unit.  Since 
the  fore-gut  is  clothed  with  entoblast,  it  is  evident  that  the  lining  of  the  respiratory 
tract  is  derived  from  the  same  germ-layer.  At  first  the  outpouchings  of  the  respira- 
tory tube  are  surrounded  by  relatively  thick  masses  of 
mesoblastic  tissue.  Since  the  growth  of  the  latter  fails 
to  keep  pace  with  the  increasing  mass  and  complexity 
of  the  bronchial  tree,  the  intervening  mesoblast  becomes 
greatly  reduced.  Coincidently  the  mesoblast  becomes 
vascular  and  rich  net-works  of  blood-vessels  appear 
between  the  terminal  divisions  of  the  epithelial  tubes, 
later  forming  the  chief  constituents  of  the  alveolar  walls. 
The  mesoblastic  tissue  remains  between  the  lobules  as 
the  interlobular  septa,  as  well  as  contributing  all  con- 
stituents of  the  walls  of  the  air-tubes  except  the  lining 
epithelial  and  its  glandular  derivatives,  which  are  ento- 
blastic.  By  the  close  of  the  fourth  month  of  foetal  life 
the  low  columnar  cells  lining  the  trachea  and  bronchi 
acquire  cilia.  The  peripheral  layer  of  the  mesoblast 
invaded  by  the  lungs  eventually  becomes  the  investing 
serous  membrane,  or  pulmonary  pleura,  all  parts  of 
which  are  of  mesoblastic  origin.  Before  inflation  occurs 
at  birth,  the  lung-tissue  is  comparatively  solid  and  re- 
sembles in  many  ways  a  racemose  gland.  With  the 
expansion  following  the  establishment  of  respiration,  the 
epithelial  cells  lining  the  ultimate  air-spaces  undergo 
stretching,  a  majority  of  the  small  polygonal  elements 
becoming  converted  into  the  flat  plate-like  cells  seen 
in  the  functionating  lung. 

The  Larynx. — The  pharyngeal  end  of   the  pri- 
mary respiratory  tract  is  surrounded  in  front  and  later- 
Kc,onstructions  of  developing    all7  bY  a  U-shaped  ridge,  known  as  the/«r™/a,  anterior 
bronchial  tree,   ^.fourth week;  B,     to  which  lies  the  paired  posterior  anlage  of  the  tongue. 

beginning  of  fifth  week ;  C,  close  of      r^t  •  •  r    .1  -j         r  j-  i 

fifth  week.   (His-Merkei.)  The  anterior  portion  of  this  ridge  forms  a  median  ele- 

vation from  which  is  formed  the  epiglottis  ;  the  later; 

portions  constitute  the  arytenoid  ridges  which  bound  the  laryngeal  aperture  at  the 
sides.  During  the  fourth  month  a  furrow  on  the  median  side  of  the  arytenoid  ridges 
marks  the  first  appearance  of  the  ventricle  of  the  larynx,  the  margins  of  the  groove 
later  becoming  the  vocal  cords.  About  the  eighth  week  the  cartilaginous  framework 
is  indicated  by  mesoblastic  condensations.  The  thyroid  cartilage  consists  for  a  time  of 
two  separate  lateral  mesoblastic  plates,  in  each  of  which  cartilage  is  formed  from  two 
centres.  These  are  regarded  as  representing  the  cartilages  of  the  fourth  and  fifth 
branchial  arches.  As  development  proceeds  the  cartilages  formed  at  these  centres 
fuse  and  extend  ventrally  until  they  unite  anteriorly  in  the  mid-line.  Chondrification 
is  completed  comparatively  late,  and  when  incomplete  or  faulty  may  result  in  the 
production  of  an  aperture, — the  thyroid  foramen.  The  anlages  of  the  cricoid  and 
arytenoid  cartilages  are  at  first  continuous,  but  later  become  differentiated  by  the 
appearance  of  a  centre  of  choiulrification  for  each  arytenoid  and  an  incomplete  ring, 
for  a  time  open  behind,  for  the  cricoid.  The  latter  thus  resembles  in  development 
a  trachea!  ring,  with  which  it  probably  morphologically  corresponds.  The  cartilages 


e. 

s   ! 


THE    PLEURA. 


1863 


of  Wrisberg  (cuneiform)   and  of  Santorini    (cornicula  laryngis)    are  formed   from 
small  portions  separated  from  the  epiglottis  and  the  arytenoids  respectively.      The 


Neural  canal 
Spinal  cord 


FIG.   1588. 


Spinal  ganglion 


X 


•  Vertebra 


Cardinal  vein; 


-Cardinal  vein 
-Aorta 


-(Esophagus 


Right  lutif 


*n?. 

Right  bronchus 

Dia 
Inferior  vena  cava 


3»~Pleural  cavity 


^r-*  "v  v? 
?f.v^|       V 

Liver 


Left  bronchus 


Portion  of  transverse  section  of  rabbit  embryo,  showing  developing  lungs.     X  30. 


FIG.  1589. 


Air-tube 


epiglottis  and  the  cricoid  possibly  represent  rudiments  of  the  cartilages  of  the  sixth 

and  seventh  branchial  arches. 

Changes  in  the  Relations  of 
the  Lungs  and  Pleurae  to  the 
Chest-Walls. — At  birth  the  thorax 
is  small,  relatively  very  narrow,  with 
the  lower  part  undeveloped  and  with 
more  horizontal  ribs.  The  costal  car- 
tilages are  relatively  long  to  the  ribs 
proper.  Nevertheless,  at  birth  and  in 
childhood  the  borders  of  the  lungs  have 
very  nearly  the  same  relations  to  the 
chest-walls  that  they  have  in  the  adult, 
excepting  in  front.  Here  they  do 
not  extend  so  far  forward,  and  conse- 
quently the  pericardium  is  at  first  less 
covered  by  the  left  lung.  The  course 
of  the  pleurae  is  much  less  certain. 
Tanja  found  much  variation  in  that  of 
the  lower  borders  of  the  pleurae,  the 
latter  crossing  all  the  costal  cartilages 
-._ ^  _,.^.  .,-_„,.,  ,.„  „„,*-.  m.  fourteen  times  in  twenty-four  bodies 

("nexpanded™ 
alveoli 


of  children  under  two  years  and  not 
a  single  time  in  the  adult.  In  eleven 
of  the  same  series  the  pleurae  did  not 
meet  behind  the  sternum,  and  in  nine 
the  left  pleura  did  not  reach  it.  He  found  neither  of  these  conditions  even  once 
in  the  adult.  According  to  Mehnert,  there  is  a  very  slight  progressive  sinking  of 


Branch  of r. 

pulmonary     *  :'  '*> .  •• 
artery  csf>^>'"' 


Bronchiole 


FT  -V,  '-— ^'-' 

Section  of  foetal  lung,  showing  compact  character  of  unin- 
flated  pulmonary  tissue.     X  200. 


i864  HUMAN    ANATOMY. 

the  lower  border  of  the  lung  during  the  period  preceding  old  age,  which  is  more 
rapid  than  the  senile  increase  of  the  declination  of  the  ribs. 

PRACTICAL   CONSIDERATIONS:    THE   LUNGS   AND    PLEURAE. 

The  Lungs  and  Pleurae. — Many  of  the  most  important  practical  questions 
arising  in  cases  of  injury  or  disease  of  the  lungs  and  pleurae  can  be  answered  only 
after  a  physical  examination,  the  value  of  which  will  depend  primarily  upon  com- 
plete knowledge  of  the  normal  phenomena  associated  with  respiration.  Such 
knowledge  must  be  based  upon  acquaintance  with  the  structural  conditions  that 
influence  the  sounds  caused  by  a  current  of  air  entering  and  leaving  the  normal  air 
passages  and  with  the  chief  modifications  caused  by  disease. 

Only  a  few  of  even  the  most  elementary  facts  bearing  upon  this  subject  can  here 
be  mentioned,  but  their  consideration  at  a  time  when  the  pulmonary  system  is  being 
studied  can  scarcely  fail  to  be  of  practical  value,  and  is  necessary  to  an  understanding 
of  those  symptoms  of  pulmonary  or  pleural  injury  or  disease  which  have  the  most 
obvious  anatomical  bearing. 

Anatomical  Basis  for  Varied  Character  of  Breath-Sounds. — The  normal  sounds 
of  respiration  vary  with  the  situation  of  the  air-passages  examined.  Their  loudness 
is  in  direct  proportion  to  their  nearness  to  the  larynx,  so  that  laryngeal,  trachea!, 
bronchial,  and  vesicular  breathing  sounds  are  here  mentioned  in  the  order  that  indi- 
cates progressively  increasing  softness. 

These  terms  acquire  pathological  significance  when  breathing  of  one  type  is 
heard  in  a  portion  of  the  chest  where  it  should  not  be  heard.  The  nearness  of  the 
larynx  to  the  surface  and  its  inclusion  of  air,  as  if  within  a  hollow  box  (West), 
make  laryngeal  sounds  loud  and  noisy  on  both  expiration  and  inspiration.  In  the 
trachea,  part  of  which  is  deeper,  and  a  portion  of  the  walls  of  which  is  of  soft 
muscular  and  fibrous  tissue,  both  these  sounds,  as  heard  over  the  suprasternal  notch, 
or  over  the  lower  cervical  or  upper  dorsal  vertebrae,  while  still  loud,  are  softer  and 
are  raised  in  tone.  Over  the  bronchi,  heard  best  between  the  scapulae  (page  1842), 
they  are  both  audible  and  are  harsh,  but  have  still  further  diminished  in  loudness. 
Over  the  pulmonary  tissue  inspiration  has  become  soft  and  blowing  and  expiration 
can  scarcely  be  heard.  The  reasons  for  these  differences  are  as  follows.  The  sounds 
of  breathing  are  produced  chiefly  at  or  about  the  glottis,  therefore  distance  from  the 
larynx  accounts  for  the  diminution  in  loudness.  The  decrease  in  the  diameter  of 
the  air-tubes  accounts  for  the  rise  in  pitch  of  the  respiratory  note.  The  entrance  of 
the  air  into  compartments  of  various  sizes  within  the  pulmonary  tissue  breaks  up  the 
air-column  which  carries  the  sound  and  distributes  the  vibrations,  so  that  the  sounds 
are  muffled  and  soft  (West). 

If  the  bronchial  tubes  or  tubules  are  obstructed,  as  from  hyperaemia  of  the 
mucosa,  or  the  presence  of  viscid  secretion,  the  exit  of  air  will  be  interfered  with, 
and  there  will  be  ' '  prolonged  expiration. ' ' 

,  In  a  broad  way,  it  may  be  said  that  in  cases  in  which  vesicular  breathing  is  dimin- 
ished or  absent  the  cause  should  be  sought  :  (i)  In  obstruction  (pseudo-membrane 
or  fibrinous  exudate).  (2)  In  compression  (aneurism,  glandular  swellings,  medias- 
tinal  tumors);  (3)  In  immobilization  of  the  chest-wall  on  the  affected  side  (fracture 
of  rib,  intercostal  neuralgia,  pleurisy  or  pleuritic  adhesions).  (4)  In  distention  of 
the  pleura  by  liquids  or  air  (pneumothorax,  empyema).  If  as  a  result  of  disease 
the  vesicular  structure  is  occupied  by  an  exudate  (as  in  pneumonia),  the  vibrations  art 
conveyed  more  directly  to  the  ear,  expiration  becomes  audible,  and,  as  consolidation 
increases,  the  sounds,  first  of  the  smaller  bronchioles  and  then  of  the  larger  bronchi, 
replace  the  normal  blowing  sound,  and  "bronchial  breathing"  is  established.  If  the 
cavity  of  the  pleura  is  distended  with  air  (  f»icuniotJioi-a\},  which  separates  the- lung- 
tissue  from  the  thoracic  wall  and  conducts  sound  vibrations  much  less  effectively 
than  do  solids,  the  breath-sounds  will  be  feeble  and  distant  or  absent.  If  the 
pleural  cavity  is  so  filled  with  either  air  or  fluid  (cmpyona  )  that  the  lung  is  collapsed 
or  compressed  against  the  spine,  the  breath-sounds  may  be  feeble  or  distant  or  entirely 
wanting  over  the  front  and  sides  of  the  chest,  but  bronchial  breathing  can  be  heard 
over  the  back.  In  exceptional  cases  of  pleural  effusion  such  breathing  is  also  heard 


PRACTICAL  CONSIDERATIONS  :  THE  LUNGS  AND  PLEUR/E.    1865 

over  the  sides  and  front,  and  it  has  been  suggested  that  this  is  due  to  contact  between 
a  bronchus  and  a  rib,  the  latter  conveying  the  breath-sounds  directly  to  the  c-ar. 

If  the  larynx  or  trachea  is  narrowed,  the  air  has  to  pass  through  a  constricted 
aperture,  must  do  so  at  a  greater  rate,  and  will  make  a  louder  noise, — stridor. 

Rales  are  caused  by  changes  in  the  mucous  and  epithelial  lining  and  contents 
of  the  air-passages.  Like  the  normal  breath-sounds,  they  are  louder  and  noisier  the 
nearer  they  are  to  the  larynx  or  the  larger  the  tubes  in  which  they  are  produced. 

Mucous  rales  are  moist,  are  thought  to  be  produced  by  the  bursting  of  air- 
bubbles  in  viscid  or  watery  mucus  occupying  the  larger  air-passages,  as  in  bronchitis, 
and  vary  in  character  (i.e.,  in  fineness  or  coarseness,  or  in  loudness)  in  accordance 
with  the  size  of  the  tube  that  they  occupy.  The  bubbling  of  air  through  the  ac- 
cumulating mucus  in  the  larynx,  trachea,  and  bronchi  of  a  moribund  person — the 
"  death-rattle" — is  an  example  of  the  larger  kind  of  mucous  rales. 

Crepitant  rales  are  dry  rales,  due,  it  is  thought,  to  the  gluing  together  of  the 
opposing  surfaces  of  a  number  of  air- vesicles  by  an  exudate,  the  entrance  .of  air  on 
inspiration  then  causing  a  fine  crackling  sound,  "like  that  which  is  heard  when  a 
small  bunch  of  hair  near  the  ear  is  rolled  backward  and  forward  between  the  tips  of 
the  finger  and  thumb"  (Owen).  If  a  similar  condition  affects  the  lumen  of  a  tube, 
i<-  may  produce  larger  rales,  still  dry,  known  as  rhonchi  (snoring)  or  sibili  (hissing  ). 
Other  factors  enter  into  the  production  of  rales,  but  the  chief  underlying  anatom- 
ical conditions  have  been  mentioned. 

Air  entering  a  cavity  ( pulmonary  vomic&,  bronchiectasis}  causes  a  sound  re- 
sembling that  produced  by  blowing  into  an  empty  bottle, — amphoric.  A  peculiar 
sound  heard  often  in  pneumothorax,  and  caused  by  the  air  from  the  fistulous  com- 
munication with  the  lung  entering  the  pleural  cavity  and  producing  a  bubbling 
sound  at  the  orifice,  is  described  as  metallic  tinkling.  It  is  also  thought  to  be  due  to 
the  dropping  of  liquid  into  an  accumulation  of  fluid  at  the  base  of  the  pneumo- 
thorax. 

Voice-sounds,  like  breath-sounds,  are  louder  over  the  laryngeal,  tracheal,  and 
bronchial  regions.  When  the  voice  seems  very  close  and  loud  to  the  ear  placed 
over  other  regions  ( pectoriloquy,  bronchophony),  it  indicates  increased  power  of 
conduction, — i.e.,  consolidation  of  lung-tissue. 

If  the  tremor  from  the  vibration  of  the  vocal  cords  in  speaking  (vocal  f rein  it  us  ) 
is  transmitted  with  increased  distinctness  to  the  hands  placed  on  the  surface  of  the 
thorax,,  it  has  the  same  significance.  If  it  is  absent,  it  usually  indicates  the  interpo- 
sition of  some  relatively  non-conducting  substance,  as  air  (  pneumothorax),  or  pus 
'  empvcmd},  or  blood  (hcemothorax^. 

Percussion- sounds  vary  with  the  region  and  the  condition  of  the  lungs  and 
pleurae.  Normally,  during  quiet  breathing,  the  resonance  is  increasingly  clear  from 
the  supraclavicular  region  downward  over  the  front  of  the  chest  to  about  the  fifth 
rib  on  the  right  side — where  the  pulmonary  tissue  begins  to  decrease  in  thickness  on 
account  of  the  presence  of  the  liver — and  to  the  sixth  rib  on  the  left  side.  It  is  less 
above  the  clavicle  and  over  it,  on  account  of  the  comparatively  small  amount  of  lung- 
tissue  in  the  apices  ;  and  over  the  upper  part  of  the  back,  on  account  of  the  interpo- 
sition of  the  scapulae  and  of  thick  muscular  masses.  It  becomes  diminished  in  the 
presence  of  moderate  effusion,  as  in  oedema  ;  dull  if  there  is  consolidation  of  lung- 
tissue  ;  and  is  absent  (flat)  if  there  is  either  plastic  exudate  or  fluid  effusion  in  the 
pleural  cavity.  In  pneumothorax,  or  over  a  cavity  in  the  pulmonary  tissue,  especially 
if  it  is  superficial,  the  percussion-note  is  fympanitie. 

Injuries.  —  Confusions  of  the  lung  may  occur  without  fracture  of  the  bones  of 
the  thorax  or  obvious  lesion  of  the  parietes.  They  are  thought  to  be  due  to 
suddenly  applied  elastic  compression  when — the  glottis  being  closed — the  lung  or 
the  lung  and  pleura  are  ruptured  as  one  may  burst  an  inflated  paper  bag  between  the 
hands. 

The  consequences  are  intcrlobnlar  emphysema,  the  air  having  escaped  from 
the  ruptured  air-cells  into  the  connective-tissue  spaces  of  the  lung  (  ride  infra ) ; 
general  emphysema,  the  air  reaching  the  subcutaneous  cellular  tissue  of  the  neck  and 
trunk  through  a  ruptured  pleura,  or,  the  pleura  being  unbroken,  passing  from  the 
root  of  the  lung  into  the  mediastinum  and  thence  to  the  base  of  the  neck ;  pneumo- 


i866  HUMAN   ANATOMY. 

thorax,  the  air  entering  the  pleural  cavity  ;  in  traumatic  interlobular  emphysema,  or 
pneumothorax,  the  chest  on  the  affected  side  will  be  hyper-resonant,  the  vesicular 
murmur  will  be  feeble  or  absent,  and  in  the  latter  there  may  be  amphoric  breathing 
and — if  there  is  a  coincident  effusion — metallic  tinkling  ;  haemoptysis,  not  an  invaria- 
ble symptom  in  either  these  injuries  or  lacerations  by  fractured  ribs,  probably  because 
they  are  usually  on  the  external  lung  surface  and  remote  from  the  larger  bronchi 
(Bennett) ;  hcemothorax,  indicated  by  percussion  dulness  gradually  extending  upward, 
by  weakness  or  absence  of  respiratory  murmur,  by  bronchial  breathing  over  the 
compressed  lung,  and  by  absence  of  vocal  fremitus. 

Penetrating  wounds  of  the  lung  will  have  many  of  these  signs  plus  the  escape 
of  blood  from  the  external  wound.  In  the  absence  of  haemoptysis,  the  possibility  of  a 
wound  of  the  costal  pleura  and  of  an  intercostal  or  internal  mammary  artery 
causing  haemothorax,  dyspnoea  (from  pressure),  and  hemorrhage,  apparently  in- 
fluenced by  respiration,  should  be  borne  in  mind.  Wounds  of  the  pleura  without 
involvement  of  the  lungs  are  rare,  the  visceral  pleura  being  closely  adherent  to  the 
lung  surface  and  the  two  pleural  layers  in  close  contact  with  each  other.  At  the  base 
of  the  pleura,  where  a  potential  cavity  (page  1859) — costo-phrcnic  sinus — exists 
between  the  costal  and  diaphragmatic  layers,  a  wound  could  penetrate  both  layers 
and  the  diaphragm  and  open  the  abdominal  cavity  and  involve  the  liver  or  spleen 
(page  1788)  without  implicating  the  lung,  which  even  in  forced  inspiration  does  not 
descend  to  the  bottom  of  this  sinus.  Wounds  of  the  pleura  are  apt  to  be  followed 
by  pneumothorax  and  by  collapse  of  the  lung,  which  is  partly  driven  back  towards 
its  root  and  the  vertebral  column  by  the  atmospheric  pressure  from  without,  and 
partly  drawn  there  by  its  own  elasticity  even  when  the  pressure  within  and  without 
is  equal.  In  operations  for  empyema  this  collapse  of  the  lung  may  take  place,  but 
is  infrequent  because  the  pulmonary  tissue  has  often  already  undergone  considerable 
compression,  and  because  the  atmospheric  pressure  is  resisted  by  preformed  pleural 
adhesions. 

General  emphysema  is  often  associated  with  wounds  of  the  lungs  and  pleura.  It 
may  be  due  to  (a)  escape  of  air  from  a  pneumothorax  into  the  subcutaneous  tissue 
during  respiratory  movements,  or  (b)  escape  of  air  direct  from  injured  lung-tissue 
when  pleural  adhesions  about  the  wound  prevent  the  formation  of  a  pneumothorax. 
Its  occasional  occurrence  in  laceration  of  the  lung  without  external  wound  and 
without  involvement  of  the  pleura  has  been  explained  (vide  supra}.  It  may  follow 
a  non-penetrating  wound  of  the  chest  if  the  opening  happens  to  be  valvular,  so  that 
the  air  drawn  in  during  respiratory  movements  cannot  make  its  exit  by  the  same 
channel. 

Pneumocele — hernia  of  the  lung — is  rare  as  a  result  of  thoracic  wounds  because 
the  elasticity  of  the  lung-tissue  and  atmospheric  pressure  tend  to  cause  collapse  and 
retraction  of  the  lung  rather  than  protrusion.  When  it  is  primary  it  therefore  follows 
(a)  a  limited  and  oblique  wound  through  which  air  cannot  freely  enter  the  pleural 
cavity,  although  the  egress  of  the  lung  under  the  pressure  of  muscular  effort  or  the 
strain  of  coughing  is  unopposed  ;  or  (£)  a  very  large  wound  when  the  lung  escapes 
at  the  moment  of  injury  (Bennett).  Treves  says  that  these  recent  herniae  are  most 
common  at  the  anterior  part  of  the  chest  where  the  lungs  are  most  movable,  and  that 
the  injuries  that  cause  them  are  often  associated  at  the  time  with  violent  respiratory 
efforts. 

Pneumocele  is  more  apt  to  follow  the  rare  wounds  that  divide  only  the  costal  pleura, 
as  a  wound  of  the  lung  itself  tends  to  the  production  of  a  pneumothorax — which 
would  lead  to  collapse  of  the  lung — and  instantly  lessens  the  pressure  of  air  con- 
tained in  the  lungs  and  trachea,  one  of  the  forces  favoring  protrusion. 

Diseases  of  the  pleurae  and  lungs  ran  here  be  very  briefly  summarized  only  with 
reference  to  the  anatomical  factors. 

/'//•/irisv  is  at  first  attended  by  a  "  friction-sound"  due  to  the  roughening  of  the 
opposed  surfaces  of  the  visceral  and  parietal  pleura'  by  librinmis  exudate.  Later  it 
may  be  lost  by  reason  of  (  a  }  the  temporary  disappearance  of  the  roughness,  i  />  j 
tlu  formation  of  adhesions  between  the  surfaces,  or  (r)  their  separation  by  effusion. 
It  is  lost  momentarily  when  the  patient  holds  his  breath,  which  will  serve  to  differ- 
entiate it  from  a  pericardia!  friction-sound.  As  the  costal  pleura,  the  intercostal 


PRACTICAL  CONSIDERATIONS  :  THE  LUNGS  AND  PLEURA.    1867 

muscles,  and  the  abdominal  muscles  are  all  supplied  by  the  lower  intercostal  nerves, 
the  respiratory  movements  on  the  affected  side  are  painful  and  are  therefore  greatly 
limited.  Accordingly  there  will  be  hurried,  shallow  breathing  with  a  weak  vesicular 
murmur  on  the  affected  side  and  exaggerated  respiratory  sounds  on  the  opposite 
side.  Pain  and  tenderness  in  the  epigastrium  may  result  from  implication  of  the 
trunks  of  the  lower  intercostal  nerves  when  the  pleurisy  is  near  the  base  of  the  chest. 
When  it  is  higher  the  pain  may  be  felt  in  the  axilla  and  down  the  inner  side  of  the 
arm  from  involvement  of  the  intercosto-humeral  nerve,  or  in  the  skin  over  the  seat 
of  disease  through  the  lateral  cutaneous  branches  of  the  upper  intercostals  (Hilton). 
In  diaphragmatic  pleurisy  the  pain  may  be  intensified  by  pressure  over  the  point  of 
insertion  of  the  diaphragm  into  the  tenth  rib  (Osier). 

Plcural  effusion  (hydrothora.v,  empyema),  in  addition  to  the  signs  already 
described  (vide  supra),  causes,  when  it  is  of  sufficient  amount,  additional  symptoms, 
as  bulging  of  the  side  of  the  chest  with  obliteration  of  the  intercostal  spaces,  disten- 
tion  of  the  net- work  of  superficial  veins  (from  pressure  on  the  vena  cava  or  greater 
azygos  vein),  and  displacement  of  other  viscera.  If  the  fluid  occupies  the  left 
pleura,  as  its  weight  depresses  the  diaphragm,  the  pericardium,  wrhich  is  attached  to 
the  central  tendon,  descends  also,  and  with  it  the  apex  of  the  heart.  At  the  same 
time  the  heart  is  pushed  towards  the  right  so  that  the  apex  beat  may  be  felt  in  the 
epigastrium  (Owen). 

An  empyema  may  point  and  discharge  itself  spontaneously,  in  which  case  it 
often  does  so  at  about  the  fifth  interspace  just  beneath  and  external  to  the  chondro- 
costal  junction  (Marshall ).  At  this  place  the  chest-wall  is  exceptionally  thin,  as  the 
region  is  internal  to  the  origin  of  the  serratus  magnus,  external  to  the  insertion  of 
the  rectus,  and  above  the  origin  of  the  external  oblique  (McLachlan). 

Evacuation  of  the  fluid  may  be  effected  by  paracentesis — in  pleurisy  with  serous 
effusion — through  the  sixth  or  seventh  intercostal  space  in  the  mid-axillary  line,  or 
through  the  eighth  or  ninth  space  just  anterior  to  the  angle  of  the  scapula.  The 
same  regions  are  selected  for  thoracotomy — incision  and  drainage — in  empyema.  The 
former  site  is  usually  preferred  for  anatomical  reasons  already  given  (page  170). 

Pneumonia  is  often  limited  to  one  lobe  of  a  lung,  usually  the  lower.  The  fis- 
sure between  the  two  lobes  of  the  narrower  left  lung  runs  from  the  third  rib  behind, 
or  from  about  the  third  dorsal  spinous  process  or  the  inner  end  of  the  spine  of  the 
scapula,  to  the  base  in  front.  The  fissure  between  the  two  lobes  of  the  right  lung 
begins  at  about  the  same  level  behind  and  extends  to  the  base  of  the  lung  anteriorly. 
Where  it  crosses  the  posterior  axillary  line  a  second  fissure  springs  from  it  which 
passes  horizontally  forward  to  the  fourth  chondro-costal  junction  making  the  middle 
lobe.  Both  lower  lobes  are  posterior  to  the  anterior  lobes,  and  on  both  sides  the 
fissures  run  from  the  level  of  the  inner  end  of  the  spine  of  the  scapula  behind  to  the 
base  in  front.  Therefore  the  dulness,  crepitant  rales,  bronchial  breathing,  and 
increased  vocal  fremitus  of  a  lobar  pneumonia  affecting  the  base  would  often  be  below 
that  line  posteriorly  and  would  be  less  marked  in  front  ;  while  the  flatness,  prolonged 
expiration,  and  other  physical  signs  of  a  tuberculous  infection  (which  affects  by 
preference  the  upper  lobe)  would  be  above  the  spine  of  the  scapula  posteriorly,  and 
lower  would  be  more  marked  anteriorly. 

The  relations  of  the  lungs  to  the  thoracic  walls  have  been  described  in  detail 
(page  1855). 

The  congestion  and  oedema  which  precede  the  so-called  ' '  hypostatic  pneumonia' ' 
are  very  apt  to  begin  in  the  thick  lower  and  posterior  portions  of  the  lower  lobes  in 
.  weak  or  aged  persons  kept  long  in  the  supine  position. 

Tuberculous  infection  of  the  lungs  is  found  oftenest  in  the  apices,  probably 
because  of  the  relatively  defective  expansion  in  that  region  \vhich  exists  in  all  persons, 
and  particularly  in  those  of  the  so-called  phthisical  type,  with  round  shoulders,  long 
necks  (page  143),  and  flat  chests  ;  possibly  also  because  of  the  greater  exposure  to 
changes  of  external  temperature  ;  and  perhaps  somewhat  owing  to  the  short  distance 
intervening  between  the  outside  atmosphere  and  the  ultimate  bronchioles  where 
tuberculous  pulmonary  disease  usually  has  its  inception. 

The  physical  signs  are  those  indicating  consolidation  followed  by  softening  or 
the  formation  of  a  cavity  (vide  supra}. 


1 868 


HUMAN    ANATOMY. 


Surface  Landmarks  of  Thorax. — The  most  important  of  the  bony  points 
have  already  been  described  in  connection  with  the  spine,  thorax,  clavicle,  and 
scapula.  The  relations  of  the  thoracic  viscera  to  the  surface  have  likewise  been  given 
(page  1855). 

Inspection  or  palpation  of  the  front  of  the  chest  will  show  (a)  the  oblique  eleva- 
tions of  the  ribs  and  the  intercostal  depressions  ;  (^)  the  curved  arch  of  the  costal 
cartilages  ;  (<:)  the  sternal  groove  ;  {d}  the  angulus  Ludovici  ;  (e)  the  infrasternal 
depression  ;  (_/")  the  lower  border  of  the  great  pectoral  muscle  ;  (£•)  the  dictations 
of  the  serratus  magnus  from  the  fifth  to  the  eighth  rib  ;  (//)  the  nipple  (pages  168, 
170,  171). 

The  infraclavicular  fossa,  the  coracoid  process,  and  the  pectoral  deltoid  groove 
have  been  described  in  connection  with  the  muscles  and  fascia-  of  the  shoulder 
579). 

FIG.  1590. 


Infraclavicufar  fossa 
Coracoid  process 


Suprasterna)  notch 

^Clavicle 
^Sternum 

'Acromion 


Groove  between  deltoid — £ — 
and  pectoralis  major    f 


Ensiform  cartilage 


Infrasternal 
—  depression 


Surface  !a 


Sis      ?. 
thnra.\. 


On  the  posterior  surface  of  the  thorax  the  most  useful  landmarks  that  may  l>e 
seen  or  felt  are  (#)  the  spine,  acromion,  vertebral  edge  and  inferior  angle  of  the 
scapula  (pages  255,  256)  ;  (£)  the  spines  of  the  dorsal  vertebrae  (page  148  )  ;  (<•}  tin 
median  spinal  or  dorso-lumbar  furrow,  the  groove  between  the  erector  spinae  masses 
overlaid  by  the  trapezius  above  and  by  the  latissimus  dorsi  below  ;  (d  )  the  depres- 
sion at  the  inner  end  of  the  scapular  spine  indicating  the  tendinous  insertion  of  the 
lower  fibres  of  the  trapezius,  the  level  of  the  third  intercostal  space,  and  a  portion  of 
the  right  bronchus  ;  (e)  a  slight  groove  passing  upward  anil  outward  over  the  erector 
spiiue  elevation  from  one  of  the  lowest  dorsal  spines  to  this  depression  and  marking 
the  lower  edge  of  the  trapezius  (Ouain). 

The  landmarks  of  the  ilio-costal  space  and  lumbo-sacral  region  are  sufficiently 
described  on  pages  148,  349. 


THE  URO-GENITAL  SYSTEM. 

THE  uro-genital  system  comprises  two  groups  of  organs,  the  urinary  and  the 
generative  ;  the  former  serves  for  the  elaboration  and  removal  of  the  chief  excretory 
fluid,  the  urine,  and  the  latter  provides  for  the  formation  and  liberation  of  the  prod- 
ucts of  the  sexual  glands.  The  primary  relations  between  these  sets  of  organs,  as 
seen  in  the  lowest  vertebrates,  are  so  intimate  that  the  excretory  duct  of  the  primitive 
kidney  may  also  transmit  the  sexual  cells,  both  groups  of  organs  being  inseparably 
united.  In  the  higher  vertebrates  the  primary  relations  are  suggested  by  only  tem- 
porary conditions  in  the  embryo,  since  with  the  development  of  a  definite  kidney 
differentiation  and  separation  take  place  until  the  urinary  and  generative  organs  con- 
stitute independent  apparatuses  except  at  their  terminal  segment,  where  they  are 
more  or  less  blended  in  the  external  organs  of  generation.  After  serving  for  a  time 
as  the  functionating  excretory  organ  of  the  foetus,  parts  of  the  Wolfnan  body  and  its 
duct  become  transformed  into  the  ducts  of  the  male  sexual  gland.  In  the  female 
analogous  canals,  represented  by  the  oviducts,  uterus,  and  vagina,  are  not  derived 
from  the  Wolfnan  duct,  but  from  an  additional  tube,  the  Miillerian  duct,  which,  how- 
ever, is  closely  related  to  the  primary  canal  of  the  fcetal  excretory  organ. 

THE  URINARY  ORGANS. 

These  include  the  kidneys,  the  glands  which  secrete  the  urine,  the  ureters,  the 
canals  which  receive  the  urine  and  convey  it  from  the  kidneys  to  the  bladder,  the 
receptacle  in  which  the  urine  is  temporarily  stored,  and  the  urethra,  the  passage 
through  which  the  urine  is  discharged. 

THE  KIDNEYS. 

The. kidneys  (renes)  are  two  flattened  ovoid  glands  of  peculiar  form,  described 
as  bean-shaped,  deeply  placed  within  the  abdominal  cavity  against  its  posterior  wall 
and  the  diaphragm,  one  on  either  side  of  the  lumbar  spine.  They  are  invested  in  a 
distinct,  although  thin,  smooth,  fibrous  capsule  (tunica  fibrosa)  and  lie  behind  the 
peritoneum,  surrounded  by  loose  areolar  tissue,  which  usually  contains  considerable 
fat  (tunica  adiposa).  This  fat  is  particularly  conspicuous  along  the  convex  lateral 
margin  and  about  the  lower  pole  of  the  kidney  and  is  least  abundant  around  the 
upper  end  and  over  the  anterior  surface.  The  fresh  adult  organ,  of  a  brownish-red 
color,  weighs  about  130  gm.  (4^  oz. )  in  the  male,  slightly  less  in  the  female,  and 
measures  about  11.5  cm.  (4^  in.  )  in  length,  6  cm.  (*%  in.)  in  width,  and  3.5  cm. 
(i  yz  in.  )  in  thickness.  The  left  kidney  is  usually  somewhat  longer,  narrower,  and 
thicker,  and  slightly  heavier  than  the  right.  Individual  variations,  especially  as  to 
length,  are  responsible  in  some  cases  for  organs  unusually  long  (15  cm.),  in  others 
for  those  relatively  short. 

Each  kidney  presents  two  surfaces,  a  convex  anterior  or  visceral,  when  the 
organ  is  in  place  directed  forward  and  outward,  and  a  posterior  or  parietal,  some- 
what flattened  and  looking  backward  and  inward  ;  two  rounded  ends,  or  poles,  of 
which  the  upper  is  usually  the  blunter  and  bulkier  ;  and  two  margins,  the  external, 
marking  the  convex  lateral  outline  of  the  organ,  and  the  straighter  internal.  Tin- 
latter  is  interrupted  by  a  slit-like  opening,  the  hilum  (  hilus  rcnalis),  bounded  by 
rounded  edges,  which  leads  into 'a  more  extended  but  narrow  space,  the  sinus  (sinus 
renalis),  enclosed  by  the  surrounding  renal  tissue.  The  capsule  is  continued  from 
the  exterior  of  the  kidney  through  the  hilum  into  the  sinus,  which  it  partly  lines. 
In  addition  to  the  blood-vessels,  lymphatics,  and  nerves  passing  to  and  from  the  kid- 
ney through  the  hilum,  the  sinus  contains  the  expanded  upper  end  of  the  renal  duct 

1*69 


1870 


HUMAN   ANATOMY. 


or  ureter,  which  also  emerges  at  the  hilum.  The  interspaces  between  these  structures 
are  filled  with  loose  areolar  tissue,  in  which  lie  accumulations  of  fat  continuous  with 
the  perirenal  tunica  adiposa. 

Position. — The  kidneys  lie  behind  the  peritoneum,  embedded  within  the  sub- 
peritoneal  tissue,  so  placed  against  the  side  of  the  vertebral  column  and  the  posterior 
abdominal  wall  that  they  occupy  an  oblique  plane,  their  anterior  surfaces  looking 
forward  and  outward.  The  long  axes  of  the  organs  are  not  parallel,  but  oblique  to 
the  spine,  in  consequence  of  which  disposition  the  upper  ends  of  the  two  organs  are 
closer  (8.5  cm.)  than  the  lower  extremities  (u  cm.),  the  planes  of  the  inner  margins 


Hepatic  veins 


FIG.   1591. 


Vas  deferens 
Spermatic  cord 


CuL-liac  axis 

Superior  mesenteric  artery 
x-^Left  suprarenal 
body 


Left  renal  vein 


ft  kidney 
— Left  renal  artery 


— Inferior  mcsen- 

teric  artery 
— Left  ureter 

[ yuadratus 

lumborum 

I Left  spermatic 

artery 

.Common  iliac 
artery 

Common  iliac 
vein 

Psoas  niagnus 


Lett  ureter, 
pelvic  portion 

Rectum  i  cut  ) 


-  Yns  (leleieli- 

.  Madder 


Dissection  of  abdomen,  showing  kidneys  in  position  and  course  and  relations  ol  uuteis. 

being  anterior  to  those  of  the  external.  The  greater  part  of  both  kidneys  lies  within 
the  epigastric  region,  but  their  outer  margins  reach  within  the  hypochondriac  areas 
and  their  lower  ends  ordinarily  encroach  to  a  limited  and  variable'  extent  upon  the 
umbilical  and  lumbar  regions.  The  intersection  of  the  plane  of  the  transverse  infra- 
costal line  and  that  of  the  vertical  Poupart  line  usually  passes  through  the  lower  pole 
of  tin-  kidnev,  falling,  as  a  rule,  somewhat  higher  in  the  right  than  in  the  left  organ. 
Approximately  the  kidneys  maybe  said  to  lie  opposite  the  last  thoracic  and  the 
upper  two  lumbar  vertebrae,  reaching  to  within  from  2.5-3.5  cm.  (i-il/>  in.  )  of  the 
highest  part  of  the  iliac  crest.  The  exact  level  of  the  kidneys,  however,  is  subject 


THE     KIDNEYS. 


1871 


to  ponsiderable  individual  variation,  as  well  as  usually  differing  on  the  two  sides  in 
the  same  subject.  The  right  organ  commonly  lies  somewhat  lower  than  the  left,  in 
consequence  chiefly  of  the  greater  permanent  volume  of  the  right  lobe  of  the  livrr. 
Not  infrequently  the  kidneys  occupy  the  same  level,  and  in  exceptional  cases  the 
ordinary  relations  may  be  reversed,  the  right  lying  a  trifle  higher  than  the  left. 

Addison  l  found  that  in  30  per  cent,  of  the  subjects  examined  by  him  the  right 
kidney  lay  as  high  or  higher  than  the  left.  According  to  Helm,2  in  women  the  kid- 
neys lie,  as  a  rule,  about  one-half  of  a  lumbar  vertebra  lower  than  in  men,  this  differ- 
ence depending  upon  the  smaller  size  of  the  vertebrae  and  the  greater  curvature  of 
the  lumbar  spine  in  the  female  subject. 

As  a  rule,  the  right  kidney  extends  from  the  upper  border  of  the  last  thoracic 
to  the  middle  of  the  third  lumbar  vertebra,  or  somewhat  below  the  lower  border  of 
the  third  lumbar  transverse  process.  While  always  obliquely  crossed  by  the  twelfth 
rib,  the  outer  margin  of  the  right  kidney  usually  falls  short  of  the  eleventh  rib. 


FIG.  1592. 


Stomach 


Pancrea 


(Castro-hepatic  omentum 

Superior  mesenteric  artery 


Hepatic  artery 


Portal  vein 


Left  kidney 

Perirenal  fat.    ^  — — _  '-'^Ri^^1'  .-          — ^«=«—       _ -=  \RiRht  kidney 

Cross-section  of  formalin-hardened  body  at  level  of  first  lumbar  vertebra. 

Since  the  left  kidney  usually  lies  from  1.5-2  cm.  higher  than  the  right,  its 
upper  pole  is  opposite  the  lower  half  of  the  eleventh  thoracic  vertebra,  its  lower  level 
being  opposite  the  lower  border  of  the  second  lumbar  vertebra  and  the  third  transverse 
process.  Its  outer  margin  may  reach,  or  be  crossed  by,  the  eleventh  rib  ;  the 
costal  relations  are,  however,  variable  and  influenced  by  the  obliquity  of  the  ribs, 
which  is  greater  when  the  ribs  are  well  developed  than  when  they  are  rudimentary. 
The  kidneys  in  young  children  in  general  lie  somewhat  lower  than  in  later  life. 

Fixation. — Although  possessed  of  mobility  to  a  limited  degree, — slight  depres- 
sion and  elevation  probably  normally  accompanying  respiratory  movements, — the 
kidneys  have  a  fairly  fixed  position.  The  maintenance  of  the  latter  has  been 
variously  ascribed  to  the  support  afforded  by  the  peritoneum,  the  perirenal  con- 
nective tissue  and  fat,  the  blood-vessels,  and  the  surrounding  organs,  all  of  which 
during  life  may  contribute  to  this  end.  Gerota,  however,3  has  shown  that,  apart 
from  the  blood-vessels  and,  especially  in  children,  the  suprarenal  bodies,  the  peri- 
toneum and  adjacent  organs  may  be  removed  without  materially  lessening  the  fixation 
of  the  kidneys,  the  latter  receiving  support  particularly  from  their  peculiar  and  inti- 
mate relations  with  the  subperitoneal  tissue.  This,  in  the  vicinity  of  the  kidney, 

1  Journal  of  Anatomy  and  Physiology,  vol.  xxxv.,  1901. 

2  Anatom.  Anzeiger,  Bd.  xi.,  1896. 

3  Archiv  f.  Anat.  und  Entwick.,  1895. 


IS;  2 


HUMAN    ANATOMY. 


assumes  the  character  of  a  distinct  fascia  (fascia  renalis),  which  at  the  outer  botder 
of  the  organ  splits  into  an  anterior  and  a  posterior  layer.  The  former  passes  in 
front  of  the  kidney,  renal  vessels,  and  ureter,  and,  crossing  the  great  prevertebral 
vascular  trunks,  joins  the  corresponding  layer  of  the  opposite  side.  Traced  upward, 
the  anterior  layer  covers  the  suprarenal  body,  above  this  organ  fusing  with  the  pos- 
terior layer  of  the  renal  fascia.  The  latter  passes  behind  the  kidney,  over  the  fascia 
covering  the  transversalis,  quadratus,  and  psoas,  as  far  as  the  inner  border  of  the  last 
muscle,  along  which  it  becomes  attached  to  the  spine.  The  posterior  layer  extends 
upward  behind  the  suprarenal  body,  which,  in  conjunction  with  the  anterior  layer, 
is  completely  invested  on  all  sides  except  below,  where  it  lies  against  the  kidney,  to 

Fro. 


Diaphragm  - 


"Diaphragm 

.ybt  suprarenal  body 
-•Liver 

Right  kidney 

iii!'  colon 
.is  muscle 


Posterior  aspect  of  kidneys  in  situ  in  formalin  subject;  portion  of  posterior  body. wall  bus  been  removed,  as 
bi'i-n  also  parts  of  pleural  sacs  and  diaphragm. 


the  support  of  which  organ  it  materially  contributes.  Although  everywhere  sepa- 
rated from  the  fibrous  tunic  of  the  kidney  by  the  intervening  layer  of  fat  (tunica 
adi/>osa},  the  renal  fascia  is  attached  to  the  renal  capsule  proper  by  bands  of  con 
nective  tissue,  which  are  especially  strong  at  the  lower  pole,  thus  directly  affording 
support  to  the  organ.  Behind,  the  posterior  layer  of  the  renal  fascia  is  likewise 
attached  to  the  transversalis  fascia  by  means  of  areolar  tissue,  between  the  connecting 
bands  of  which  a  variable  amount  of  fat  is  usually  present.  Above,  beyond  the 
suprarenal  body,  the  renal  fascia  fades  away  over  the  diaphragm  ;  below,  it  passes 
into  and  is  lost  within  the  fatty  subperitoneal  tissue  of  the  iliac  fossa. 

The  fixation  of  the  left  kidney  is  tinner  than  that  of  the  right,  greater  security 
being  gained  for  the  left  organ  in  consequence  of  its  more  extensive  relations  to  the 


THE   KIDNEYS. 


1873 


Diaphragm 


-  Liver 


XII  rib 


fusion  which  takes  place  during  the  development  (page  1704)  of  the  large  intestine 
between  the  original  parietal  peritoneum  and  that  covering  the  applied  surface  of  the 
primary  mesentery  of  the  descending  colon  ;  in  consequence,  the  left  kidney  is 
invested  anteriorly  with  a  subperitoneal  layer  of  exceptional  strength.  When,  for 
various  reasons,  the  tonicity  of  the  tissues  supporting  the  kidney  becomes  impaired 
and  these  structures  become  abnormally  lengthened,  the  organ  may  acquire  undue 
mobility  and  suffer  displacement. 

Relations. — The  position  of  the  kidneys  being  wholly  retroperitoneal,  the 
posterior  relations  of  both  organs  are  chiefly  muscular,  since  they  lie  closely 
applied  to  the  diaphragm,  psoas  magnus,  quadratus  lumborum,  and  the  posterior 
aponeurosis  of  the  transversalis,  the  parietal  fascia  and  perirenal  areolar  tissue  alone 
intervening.  The  inequalities  in  the  supporting  structures  produce  corresponding 
modelling  of  the  opposed  renal  surfaces,  which  is  clearly  distinguishable  on  organs 
hardened  in  situ.  In  specimens  hardened  in  formalin,  the  psoas  area  appears  as  a  nar- 
row, slightly  depressed  tract  along  the  inner  border  ;  an  adjoining  broader  band  marks 
the  area  for  the  quadratus  lumborum,  beyond  which  the  outer  part  of  the  posterior  sur- 
face rests  upon  the  transversalis  apo- 
neurosis. The  crescentic  diaphragmatic  FIG.  1594. 
area  crosses  the  upper  pole,  the  inner 
limb  of  the  crescent  marking  the  con- 
tact with  the  crus.  In  organs  hardened 
in  the  recumbent  posture,  conspicuous 
and  probably  exaggerated  indentations 
show  the  former  position  of  the  trans- 
verse processes  of  the  second  and  third 
lumbar  vertebrae.  An  oblique,  shallow 
furrow  crossing  the  kidney  from  the 
upper  pole  outward,  usually  locates  the 
course  of  the  twelfth  rib.  In  connec- 
tion with  the  posterior  relations  of  the 
kidneys,  it  is  important  to  recall  the 
inferior  limits  of  the  pleural  sacs  (page 
1859).  which,  where  they  cross  the 
twelfth  rib,  may  descend  as  low  as  the 
level  of  the  first  lumbar  transverse  pro- 
cess and  therefore  cover  the  upper  part 
of  the  kidneys. 

The  anterior  relations  of  the 
kidneys  differ  on  the  two  sides,  not 
only  as  to  the  viscera  concerned,  but 
also  in  the  manner  of  their  contact  and 
the  consequent  extent  of  the  renal  peri- 
toneal investment.  Primarily  the  entire 

visceral  surfaces  of  the  kidneys  are  covered  by  serous  membrane  ;  later  this  invest- 
.  ment  becomes  only  partial,  in  consequence  of  the  permanent  attachment  which  certain 
organs,  as  the  pancreas,  duodenum,  and  colon,  obtain.  When  these  viscera  undergo 
the  backward  displacement  incident  to  acquiring  their  final  location,  they  are  pressed 
against  the  abdominal  wall  and  the  kidneys,  to  which  they  become  attached  by 
areolar  tissue,  since  the  intervening  opposed  peritoneal  surfaces  lose  their  serous 
character.  Where  the  organs  touching  the  kidneys  remain  covered  with  peritoneum, 
the  renal  areas  of  contact  retain  the  original  serous  investment. 

The  right  kidney  is  in  relation  with  the  corresponding  suprarenal  body,  the  liver, 
the  duodenum,  the  hepatic  flexure  of  the  colon,  and,  to  a  limited  extent,  usually  the 
small  intestine.  The  right  suprarenal  body  covers  the  upper  pole  and  adjacent  part 
of  the  inner  border  of  the  kidney,  the  surface  of  contact  being  devoid  of  peritoneum, 
since  the  organs  are  closely  connected  by  areolar  tissue.  The  liver  covers  the  larger 
part  of  the  anterior  surface  and  outer  border  of  the  kidney,  which  models  the  hepatic 
tissue  as  the  conspicuous  renal  impression  seen  on  the  inferior  surface  of  the  organ. 
Both  the  liver  and  the  kidney  are  invested  by  serous  membrane,  and  are,  therefore, 

us 


Iliac  fascia 


Iliacus 
muscle 


Diagrammatic  longitudinal  section,  showing  relations  of 
supporting  tissue  to  right  kidney.     (Gerota.) 


i874 


HUMAN   ANATOMY. 


separated  by  an  extension  of  the  greater  sac  of  the  peritoneum.  The  second  part  of 
the  duodenum  overlies  the  hiluni  and  the  inner  renal  border,  the  non-peritoneal  area 
being  of  uncertain  extent  in  consequence  of  the  variations  in  the  position  of  this  part  of 
the  intestinal  tube.  Although  covering  usually  about  the  middle  two-fourths  of  the 
median  border,  the  duodenal  area  may  embrace  the  entire  inner  third  or  more  of  the 
anterior  surface  of  the  kidney,  extending  from  the  extreme  upper  to  the  lower  pole  ; 
or,  on  the  contrary,  the  duodenum  may  touch  the  kidney  only  near  its  lower  pole. 
The  hepatic  flexure  occupies  a  triangular  area,  external  to  the  adjoining  duodenal 
one  and  also  non-peritoneal,  which  includes  the  outer  and  lower  third,  more  or  less, 
of  the  anterior  surface  of  the  kidney.  The  extent  and  form  of  the  surfaces  of  con- 
tact between  the  kidney,  colon,  and  duodenum  are  very  variable  ;  when  large  they 
may  cover  the  entire  lower  half  of  the  kidney,  or  when  less  extensive  they  may 
leave  uncovered  the  lower  pole.  In  the  latter  case  coils  of  the  small  intestine  often 
occupy  this  area,  which  is  covered  with  peritoneum. 

The  left  kidney  is  in  relation  with  the  corresponding  suprarenal  body,  the 
spleen,  the  stomach,  the  pancreas,  the  splenic  flexure  of  the  colon,  and  the  small  in- 
testine. The  suprarenal  body  lies  upon  the  median  side  of  the  upper  pole,  attached 


FIG.  1595. 

Suprarenal  area  (non-peritoneal) 


Hepatic  area 
(peritoneal) 


Colic  area 
(non-peritoneal) 

Jejunal  area 
(peritoneal) 


Duodenal  area  (non-peritoneal) 

Right  renal  duct 


Suprarenal  area  (non-peritoneal) 


Gastric  area 
(peritoneal) 

Splenic  area 
(peritoneal) 


Pancreatic  area 
( non-peritonea  1 ) 


Colic  area 
(non-peritoneal) 

Jejunal  area 
i  peritoneal) 


Left  renal  duct  (ureter) 


Inferior  vena  cava 
Anterior  surface  of  kidneys  of  formalin-hardened  subject,  showing  visceral  areas,  blood-vessels,  and  renal  ducts. 

by  areolar  tissue  ;  its  area  is  therefore  non-serous.  The  upper  two-thirds  of  the 
outer  border  and  the  adjacent  part  of  the  anterior  surface  of  the  kidney  are  covered 
by  the  spleen,  the  peritoneum  intervening,  except  within  the  narrow  attachment  of 
the  layers  of  the  lieno-renal  ligament.  Below  the  splenic  area  the  kidney  is  covered 
to  a  variable  extent  by  the  splenic  flexure  of  the  colon,  this  non-peritoneal  area 
usually  including  the  outer  half  of  the  lower  pole.  The  pancreas  lies  in  front  of  the 
hilum  and  approximately  the  middle  third  of  the  kidney,  frequently  reaching  as  far 
as  the  outer  border.  Above  this  non-peritoneal  area,  between  the  latter  and  the 
suprarenal  and  splenic  surfaces,  lies  the  small  triangular  serous  area  which  the  stomach 
touches,  while  below  the  pancreatic  zone,  internal  to  that  for  the  splenic  flexure,  the 
kidney  presents  a  triangular  peritoneal  area  over  which  the  coils  of  the  jejunum  glide. 

From  the  foregoing  it  is  evident  that  each  kidney  rests  within  a  depression,  the 
"renal  fossa,"  formed  by  the  structures  with  which  it  comes  into  contact  above, 
behind,  at  the  sides,  and  below.  The  fossae  are  deeper  and  narrower  in  the  male 
than  in  the  female,  owing  chiefly  to  the  greater  development  of  the  muscles  against 
which  the  kidneys  lie. 

The  Renal  Sinus. — The  longitudinal,  slit-like  hilum,  occupying  somewhat  less 
than  the  middle  third  of  the  inner  border  of  the  kidney,  opens  into  a  more  extensive 
but  shallow  C-shaped  space,  the  renal  sinus,  which,  surrounded  by  the  kidney-tissue, 


THE   KIDNEYS. 


FIG.   1596. 


Area  still 
covered  by 
fibrous  cap- 
sule, exter- 
nal surface 
of  which  is 
roughened 
by  strands 
of  connec- 
tive tissue 


Renal 
artery 


takes  in  approximately  the  median  half  of  the  interior  of  the  organ.  The  greatest 
dimension  of  the  sinus  corresponds  with  the  long  axis  of  the  kidney,  the  shortest  with 
the  distance  between  the  anterior  and  posterior  walls.  The  space — most  extended 
vertically — is  compressed  from  before  backward,  while  its  greatest  depth  (2. 5-3. 5  cm.  ) 
is  just  above  the  upper  border  of  the  hilum.  The  sinus  is  occupied  in  large  measure 
by  the  dilated  upper  end  of  the  ureter,  the  renal  pelvis,  and  its  subdivisions,  the 
calyces;  the  remaining  space  accommodates  the  blood-vessels,  lymphatics,  and  nerves 
that  pass  through  the  hilum  and  the  intervening  cushion  of  areolar  and  adipose  tissue 
continuous  with  the  perirenal  fatty  capsule.  The  fibrous  capsule  of  the  kidney  covers 
the  rounded  lips  of  the  hilum  and  is  continued  into  the  sinus,  to  which  it  furnishes 
a  partial  lining. 

In  contrast  to  the  even  external  surface  of  the  kidney,  the  walls  of  the  sinus  are 
beset  with  conical  elevations,  the  renal  papill/z,  which  are  well  seen,  however,  only 
after  removal  of  the  contents  and  the  fibrous  lining  of  the  sinus.  The  papillae  mark 
the  apices  of  the  pyramidal  masses  of  kidney-tissue  of  which  the  organ  is  composed. 
The  individual  cones,  from  7  to  10  mm.  in 
height,  are  in  many  instances  somewhat  com- 
pressed, so  that  their  bases  are  elliptical  in 
section  instead  of  circular.  Adjacent  ones 
may  undergo  more  or  less  complete  fusion, 
the  resulting  compound  papillae  being  often 
grooved  and  irregular  in  form.  Usually  from 
eight  to  ten  papillae  are  present  in  each  kid- 
ney, but  their  number  varies  greatly,  as  few 
as  four  and  as  many  as  eighteen  having  been 
observed  (Henle).  The  walls  of  the  sinus 
between  the  bases  of  the  papillae  are  broken 
up  into  elevations  and  depressed  areas,  the 
latter  marking  the  localities  at  which  the 
blood-vessels  and  nerves  enter  and  leave  the 
renal  substance.  The  apex  of  each  papilla 
is  pierced  by  a  number  of  minute  openings, 
barely  recognizable  with  the  unaided  eye, 
which  mark  the  terminal  orifices  (foramina 
papillaria)  of  the  uriniferous  tubules  from 
which  the  urine  escapes  from  the  renal  tissue 
into  the  receptacles  formed  by  the  calyces 
which  surround  the  papillae  and  are  attached 
to  their  bases.  The  number  of  uriniferous  tu- 
bules opening  at  the  apex  of  a  single  papilla — 
the  field  in  which  the  pores  open  being  the 

area  cribrosa — varies  with  the  size  of  the  cone,  from  eighteen  to  twenty-four  being 
the  usual  complement  for  a  simple  papilla.  When  the  latter  is  compound  and  of 
large  size,  more  than  twice  as  many  orifices  may  be  present. 

Architecture  of  the  Kidney. — The  entire  organ — a  conspicuous  example  of 
a  compound  tubular  gland — is  made  up  of  a  number  of  divisions  which  in  the  mature 
condition  are  so  closely  blended  as  to  give  little  evidence  of  the  striking  lobulation 
marking  the  foetal  kidney.  The  external  surface  of  the  latter  (Fig.  1597)  is  broken 
up  by  furrows  into  a  number  of  irregular  polygonal  areas,  each  representing  the 
base  of  a  pyramidal  mass  of  renal  tissue,  the  kidney  lobe  or  rcnculus,  which,  sep- 
arated from  its  neighbors  by  an  envelope  of  connective  tissue,  includes  the  entire 
thickness  of  the  organ  between  its  exterior  and  the  sinus,  a  renal  papilla  being  the 
apex.  For  a  short  time  after  birth  the  lobulation  is  evident,  but  later  the  de- 
marcations gradually  disappear  from  the  surface,  which  becomes  smooth,  and  the 
interlobular  connective-tissue  septa  within  the  organ  disappear,  the  pyramids  alone 
indicating  the  original  lobulation. 


Anterior  surface  of  right  kidney  from  which 
fibrous  capsule  has  been  partly  removed ;  blood- 
vessels and  renal  duct  are  seen  entering  and  emerging 
through  hilum. 


Although  evidences  of  the  latter  occasionally  persist  in  the  adult  human  organ,  the  kidneys 
of  many  of  the  lower  animals  (reptiles,  birds,  ruminants,  cetaceans,  and  certain  carnivora)  retain 


1876 


HUMAN   ANATOMY. 


the  divisions  in  a  more  or  less  marked  degree,  the  renal  lobules  of  the  aquatic  mammals  being 
unusually  distinct.  In  some  mammals  (rodents,  insectivora)  the  entire  kidney  corresponds  to  a 
single  papilla,  while  in  others  (elephant,  horse)  no  distinct  papilla;  exist. 


Right  kidney  of  new- 
born child,  showing  tabula- 
tion of  surface. 


FIG.  1598. 


On  making  a  longitudinal  section  of  the  fresh  kidney,  from  its  convex  border 
through  the  sinus,  the  papillae  will  be  seen  to  form  the  free  apices  of  conical  masses, 
the  renal  pyramids,  the  bases  of  which  lie  embedded  within 
the  darker  surrounding  kidney-substance  composing  the  outer 
third  of  the  organ.  This  peripheral  zone,  which  appears  darker 
and  granular  in  contrast  to  the  lighter  and  striated  renal  pyra- 
mids, constitutes  the  cortex;  the  medulla  includes  the  conical 
areas  formed  by  the  pyramids  and  partially  occupies  the  inner 
two-thirds  of  the  thickness  of  the  organ.  The  cortex  contrib- 
utes the  bulk  of  the  kidney,  alone  forming  the  entire  surface, 
including  the  lips  of  the  hilum,  and  receiving  and  surrounding 
the  bases  of  the  pyramids.  The  cortical  tissue  further  pene- 
trates for  a  variable  distance  between  the  pyramids,  separating 
the  latter  and  in  places  gaining  the  sinus.  These  interpy- 
ramidal  extensions  are  the  renal  columns ,  or  columns  of  Berlin, 
and  consist  of  typical  cortical  substance.  Since  the  branches 
of  the  renal  blood-vessels  lie  within  the  interlobular  connective 
tissue  separating  the  primary  divisions  of  the  foetal  organ,  these  vessels  never  enter 
the  kidney  by  passing  into  the  papillae,  but  always  enter  at  the  side  of  these.  They 
therefore  sink  into  the  renal  substance  within  the  areas  occupied  by  the  renal  columns, 
the  surfaces  of  which  directed  towards  the  sinus  are  pitted  by  the  vascular  foramina. 
Within  the  sinus  the  blood-vessels  surround  the  calyces  with  coarse  net-works,  enter- 
ing and  emerging  from  the  renal  substance  through  the  orifices  encircling  the  papillae. 
On  close  inspection,  preferably  with  the  aid  of  a  hand-glass,  it  will  be  seen  that 
the  cortex,  including  that  within  the  renal  columns,  is  not  uniform,  but  is  subdivided 
by  narrow  striated  bands,  wedge-shaped 
in  outline  and  lighter  in  color,  into 
radially  disposed  darker  and  lighter 
areas.  The  latter,  consisting  of  groups 
of  parallel  tubules,  are  known  as  the 
medullary  rays  (pars  radiata),  since 
they  are  apparently  due  to  prolonga- 
tions of  the  medullary  tissue.  The 
darker  tracts  intervening  between  the 
medullary  rays  form  the  labyrinth  (pars 
convoluta),  and  appear  granular,  owing 
to  the  tortuous  character  of  the  com- 
ponent tubules.  The  labyrinth  is 
studded  with  bright  red  points  mark- 
ing the  position  of  the  vascular  tufts 
or  glomeruli,  which  are  never  present 
within  the  medullary  rays  or  the  renal 
pyramids,  although  found  within  the 
columns  of  Bertin.  « 

On  sectioning  minutely  injected 
organs,  it  will  be  observed  that  the 
larger  radially  coursing  interlobular  ar- 
teries, on  gaining  the  boundary  zone 
between  the  cortex  and  medulla,  break 
up  into  smaller  branches,  some  of  which 
pass  directly  towards  the  surface,  while  others  change  their  direction  and  assume  an 
arched  horizontal  course,  thus  producing  the  impression  of  "arcades"  at  the  baseot 
the  pyramids.  The  terminal  twigs — "  end-arteries,"  since  anastomoses  are  wanting 
— rim  generally  perpendicular  to  the  exterior  of  the  kidney  and  occupy  the  centre 
of  the  tracts  separating  tin-  im-dullary  rays.  The  latter,  therefore,  are  the  axes  of 


Cortex 


Interlobar 
blood- vessel 
Medulla 


oiigUudmal   section  of  right  kidney,  shoi 
pelvis  ami  its  divisions  to  renal  lUDStanC 


,  showing  relations  of 
v  and  to  sinus. 


THE   KIDNEYS. 


1877 


abvrinth 


minute  conical  masses  of  renal  substance,  the  cortical  lobules,  the  bases  of  which  lie 
at  the  surface  and  the  apices  within  the  pyramids  of  the  medulla.  From  the  fore- 
going it  is  evident  that  each  renal  pyramid  corresponds  to  a  group  of  cortical  lobules, 
the  tubules  of  which,  on  entering  the  medulla,  become  progressively  less  numerous 
but  larger,  in  consequence  of  repeated  juncture,  until,  as  the  wide  excretory  ducts, 
they  end  at  the  summit  of  the  papilla.  The  relations  of  the  pyramids  to  the  papillae 
are  less  simple  than  formerly  recognized,  since,  instead  of  each  of  the  latter  embracing 
but  one  of  the  former,  Maresch '  has  shown  that  a  single  papilla,  as  a  rule,  includes 
from  two  to  four  pyramids, 
which  are  blended  into  one 
conical  mass  culminating  in 
the  papillary  apex. 

Structure  of  the  Kid- 
ney. —  The  fundamental 
components  of  the  verte- 
brate excretory  organ,  both 
in  the  foetal  and  mature  con- 
dition, include  (i)  a  tuft  of 
arterial  vessels  derived  more 
or  less  directly  from  the 
aorta,  (2)  tubules  lined  with 
secretory  epithelium,  and 
(3)  a  duct  for  the  convey- 
ance of  the  excretory  pro- 
ducts. These  constituents 
are  represented  in  the  kid- 
ney of  man  and  the  higher 
animals  by  ( i )  the  glomeru- 
lus,  (2)  the  convoluted  uri- 
niferous  tubules,  and  (3)  the 
collecting  tubes,  pelvis,  and 
ureter.  Since,  in  a  general 
way,  to  the  epithelium  lining 
the  tubules  may  be  ascribed 
the  function  of  taking  from 
the  circulation  the  more  solid 
constituents  of  the  urine, 
and  to  the  glomerulus  the 
secretion  of  its  watery  parts, 
obviously  the  most  favora- 
ble arrangement  to  secure 
the  removal  of  the  excretory 
products  is  one  insuring 
flushing  of  the  entire  tubule 
with  the  fluid  secreted  by 
the  glomerulus.  Such  ar- 
rangement implies  the  loca- 
tion of  the  vascular  tuft  at  the  very  beginning  of  the  tubule, — a  disposition  which 
in  fact  is  found  in  the  kidneys  of  all  higher  animals.  The  number  of  the  glomeruli, 
therefore,  corresponds  with  that  of  the  uriniferous  tubules,  each  of  which  begins  in 
close  relation  with  the  vascular  tuft.  The  kidney-substance  consists  of  an  intricate 
but  definitely  arranged  complex  of  uriniferous  tubules,  supported  by  the  interstitial 
connective-tissue  stroma,  which  have  their  commencement  in  the  cortex  and  their 
termination  at  the  apices  of.  the  papillae,  their  intervening  course  being  marked  by 
many  and  conspicuous  variations  in  the  character,  size,  and  direction  of  the  tubules. 

The  uriniferous  tubule  begins  as  a  greatly  expanded  blind  extremity,  the 
capsule  (i),  which  surrounds  the  vascular  tuft  or  glomcrulus,  the  two  together  con- 
stituting the  Malpighian  body,  which  lies  within  the  labyrinth.  On  leaving  the  Mal- 

JAnatom.  Anzeiger,  Bd.  xii.,  1896. 


Proximal  con- 
voluted tubule 

Intermediate 

tubule  (distal 
convoluted) 

Intermediate 

tubule 

Efferent  vessel 
Neck 

Afferent  vessel 
Capsule 
Interlobular 
artery 


Descending 
limb 


-Ascending 
limb 


Loop  of  Henle 


Papillary  du 


Papilla 
Diagram  showing  course  of  uriniferous  tubule. 


1878 


HUMAN   ANATOMY. 


FIG.  1600. 

•Capsule 


Malpighian 
body  in 
labyrinth 


pighian  body  the  tubule  becomes  very  tortuous  and  arches  towards  the  free  surface 
as  the  proximal  convoluted  tubule  (2)  ;  this,  after  a  course  of  considerable  length, 

usually  leaves  the  labyrinth  and 
enters  the  medullary  ray,  which  it 
traverses,  somewhat  reduced  in 
diameter  and  slightly  winding  in 
course,  as  the  spiral  tubule  (3)  and 
passes  into  the  medulla.  Immedi- 
ately upon  gaining  the  latter,  the 
tubule  suffers  marked  decrease  in 
size,  penetrates  the  renal  pyramid 
for  a  variable  distance  towards  the 
papilla,  then  bends  sharply  upon 
itself  and  retraces  its  course  to  once 
more  enter  the  labyrinth.  Its  ex- 
cursion into  the  medulla  includes 
the  descending  limb  (4)  and  as- 
cending limb  (5)  of  the  loop  of 
Henle.  The  ascending  limb — the 
longer  and  wider  of  the  parallel 
limbs  of  the  loop — rises  within  the 
labyrinth  to  the  immediate  vicinity 
of  the  corresponding  Malpighian 
body,  the  neck  of  which  it  crosses, 
and  then,  after  arching  over  the  cor- 
puscle, gives  place  to  the  distal 
convoluted  or  intermediate  tubule 
(6),  a  segment  which,  marked  by 
increased  diameter  and  tortuosity, 
crosses  the  general  course  of  the 
convoluted  tubule  and  is  succeeded 
by  the  narrower  and  arching  con- 
necting tubule  (7).  The  latter 
enters  the  medullary  ray  and,  join- 
ing with  similar  canals,  forms  the 
straight  collecting  tubule  (8),  which, 
progressively  increasing  in  size  by 
junction  with  others,  traverses  the 
remaining  length  of  the  medullary 
ray  and  enters  the  renal  pyramid. 
Within  the  deeper  part  of  the  latter 
the  collecting  tubules  fuse  into  larger  and  larger  canals  until,  as  the  relatively  wide 
papillary  ducts  (9),  they  terminate  on  the  apex  of  the  papilla  at  the  orifices  (fe 
inina papillaria)  which  open  into  the  calyces. 

The  relations  between  the  various  segments  of  the  uriniferous  tubules  and 
subdivisions  of  the  kidney  are,  therefore,  as  follows  : 


Blood- 
vessels 


Section  of  cortex,  showing  relation  of  labyrinth 
and  medullary  rays.     X  50. 


CORTEX 


Labyrinth 


Medullary  ray 


MEDI  i  i  \ 


Malpighian  body, — capsule  and  glomerulus 

Proximal  convoluted  tubule 

Ascending  limb  of  Henle' s  loop 

Distal  convoluted  or  intermediate  tubule 

Connecting  tubule  (beginning  > 

Connecting  tubule  (termination) 

Spiral  tubule 

Collecting  tubule 

Descending  limb  and 

Ascending  limb  of  Henle' s  loop 

Collecting  tubule 

Papillary  ducts 


THE   KIDNEYS. 


1879 


FIG.   1601. 


Efferent 
vessel 


Injected  glomenilus,  showing  afferent  and  efferent  vessels  and 
continuation  into  intertubular  capillaries.     X  250. 


Although  as  a  matter  of  convenience  the  entire  canal,  from  its  commencement 
in  the  Malpighian  body  to  its  termination  on  the  papilla,  has  been  described  as  the 
uriniferous  tubule,  both  geneti- 
cally and  functionally  two  dis- 
tinct parts  must  be  recognized. 
These  are  the  unbranched  uri- 
nijerous  tubule  proper,  which 
includes  all  divisions  from  the 
Malpighian  body  to  the  termi- 
nation of  the  intermediate  tu- 
bule, and  the  duct-tube,  which, 
when  traced  from  the  papilla 
towards  the  cortex,  undergoes 
repeated  division  until  from  a 
single  stem  the  number  of  con- 
necting tubules  is  sufficient  to 
provide  each  uriniferous  tubule 
proper  with  its  own  excretory 
canal.  •^•W^-'"  -  .  ^fci  -'.  'i&m....*~^KZ : imenuhuiar 

capillaries 

I.  The  Malpighian  Body. — This 
structure,  spherical  in  form  and  from 
.OI2-.O20  mm.  in  diameter,  consists 
of  two  parts,  the  glomerulus  and  the 
capsule.  The  former  is  an  aggrega- 
ion  of  tortuous  capillary  blood-ves- 
sels into  which  break  up  the  lateral 
terminal  twigs  given  off  from  the 

arteries  as  these  pass  between  the  cortical  lobules  towards  the  free  surface  of  the  kidney.  The 
lateral  branches — very  short,  often  arched,  and  only  .oo2-.oo4  mm.  in  diameter — spring  at  vary- 
ing angles  from  all  sides  of  the  interlobular  arteriole  and  enter  the  Malpighian  body  as  the  vas 
afferent.  On  entering  the  glomerulus,  the  afferent  vessel  divides  into  from  four  to  six  twigs, 
each  of  which  breaks  up  into  capillaries.  These  may  anastomose  and  form  a  vascular  complex 
that  may  be  filled  from  any  branch  ;  not  infrequently,  however,  such  communication  does  not 

exist,  each  terminal  twig 
then  giving  rise  to  an  iso- 
lated capillary  territory, 
the  entire  glomerulus  con- 
sisting of  vascular  lobules, 
each  drained  by  its  own 
radicle.  Sooner  or  later 
all  the  channels  of  exit 
unite  to  form  the  single  vas 
efferent,  through  which 
the  blood  from  the  en- 
tire glomerulus  escapes. 
The  efferent  vessel  as  it 
emerges  from  the  Mal- 
pighian body  is  close  to 

«£t  .-A  ,"s,j. .—- -v.,...         the  vas  afferens,  both  usu- 
fs  •'  •         ;'      arteriole         „      .    .  .         ., 

ally  lying  on  the  side  op- 
posite to  that  occupied  by 
the  neck  of  the  capsule 
from  which  the  uriniferous 
tubule  is  continued.  In 
consequence  of  the  short 
course  and  manner  of  ori- 
gin of  the  twigs  from  the 
interlobular  arteries,  the 
glomeruli  are  disposed  in 
rows,  somewhat  like  berries  attached  to  a  straight  common  stalk. 

The  capsule  of  Bowman,  the  dilated  beginning  of  the  uriniferous  tubule,  almost  com- 
pletely invests  the  glomerulus  with  a  double  layer  derived  from  the  wall  of  the  tubule,  which 
seemingly  has  suffered  invagination  by  the  vascular  tuft.  Such  pushing  in,  however,  is  only 


FIG.   1602. 


Capsule 


Section  of  renal  cortex,  showing  details  of   Malpighian  body;   glomerulus  is 
surrounded  by  capsule  which  passes  into  obliquely  cut  neck.     X  200. 


i88o 


HUMAN   ANATOMY. 


FTG.  1603. 


Blood-vessel 


Convoluted  tubules,  cut  transversely  and  ob- 
liquely, showing  character  of  epithelial  lining. 
X  400. 


apparent,  since  the  close  relations  of  glomerulus  and  capsule  result  from  the  growth  of  the  latter 
around  the  vascular  tuft  and  not  from  invagination  of  the  dilated  tubule.     The  capsule  consists 

of  a  distinct  membrana  propria  and  a  lining  composed 
of  a  single  layer  of  flat,  plate-like  cells,  the  modified 
epithelium  of  the  uriniferous  tubule.  In  sections  pass- 
ing through  the  afferent  vessel  and  the  neck  the  lumen 
of  the  capsule  appears  crescentic  in  outline,  since  the 
space  between  its  outer  and  inner  walls  is  widest  at 
the  neck  and  reduced  to  a  mere  slit  where  the  two 
layers  are  continuous  around  the  narrow  stalk  tra- 
versed by  the  afferent  and  efferent  vessels.  The  inner 
or  "visceral"  layer  of  the  capsule,  the  thicker  of  the 
two,  is  firmly  attached  to  the  glomerulus  by  the  deli- 
cate intervening  connective  tissue,  the  entire  complex 
appearing  rich  in  nuclei  which  belong  to  the  epithe- 
lium of  the  capsule,  the  endothelium  of  the  capillaries, 
and  the  connective-tissue  cells. 

2.  The  Proximal  Convoluted  Tubule. — After  un- 
dergoing the  conspicuous  constriction  marking  the 
neck  of  the  capsule,  the  uriniferous  tubule  abruptly 
enlarges  into  the  convoluted  segment  which  forms  ap- 
proximately one-fifth  of  the  length  of  the  entire  canal 
and  has  a  diameter  of  from  .O4o-.o6o  mm.  In  com- 
mon with  other  parts  of  the  tubule,  its  wall  consists  of  a 
membrana  propria,  apparently  structureless,  but  com- 
posed of  a  delicate  reticulum  and  intervening  homoge- 
neous substance  and  a  single  layer  of  epithelial  cells. 
Although  the  histological  details  of  the  latter 
vary  in  different,  but  not  constant,  parts  of  the  convo- 
luted segment,  the  lining  cells  present  certain  charac- 
teristics, chief  among  which  is  the  differentiation  of 
the  cytoplasm  of  the  cells  into  a  broader  outer  and 
a  narrow  inner  z.one.  The  former  exhibits  coarse  radial  striations,  the  so-called  "rods,"  pro- 
duced by  rows  of  granules  within  the  vertically  disposed  threads  of  spongioplasm  (Rothstein) 
which  occupy  approximately  the  pe- 
ripheral half  of  the  cell  extending 
from  the  membrana  propria  towards 
the  inner  zone.  The  latter,  next  the 
lumen,  usually  appears  as  a  well- 
defined  narrow  border  which,  when 
successfully  preserved,  presents  a 
fine  vertical  striation  ("bristle  bor- 
der") that  depends  not  upon  rows 
of  granules,  as  do  the  rods  of  the  outer 
zone,  but  upon  the  disposition  of 
the  threads  of  the  spongioplasm.  In 
consequence  of  maceration  and  other 
post-mortem  changes,  the  inner  zone 
may  undergo  partial  disintegration 
and  break  up  into  short  hair-like  rods 
which  have  been  mistaken  for  cilia. 
Although  the  spherical  nuclei  (.005- 
.007  mm.)  of  the  epithelium  of  the 
convoluted  tubule  are  sharply  de- 
fined, the  demarcations  between  the 
individual  cells  are  obscure  and  often 
wanting,  the  tubule  being  lined  by  a 
seemingly  continuous  nucleated  layer 
or  syncytium.  The  lumen  is  not 
uniform  throughout  the  convoluted 
tubule,  in  sonic  places  bring ;  wide  and 
in  others  reduced  to  mere  clefts;  these  r.; I-VCMC! 

differences   depend    chiefly    upon    the      Portion  of  medullary  my,  showing  spiral  and  i-olUvtingtuhuli's.  X  4<»- 
varying  height  of  the  epithelial  lining. 

3.   The  Spiral  Tubule.— Following  the  tortuous  path  of  the  convoluted  tubule,  the  canal  is 
usually  continued  into  the  medullary  ray  by  a  segment  which,  while  comparatively  straight,  de- 


FIG.    i  604. 


ollecting 
tubule 


THE   KIDNEYS. 


1881 


scribes  a  wavy  or  spiral  course  in  its  descent  to  the  pyramid.  This,  the  spiral  tubule  of  Schachowa, 
liffersfrom  the  preceding  in  the  gradual  reduction  of  its  diameter  (.35-. 040  mm.)  and  in  the 
thickness  of  the  epithelial  lining,  the  cells  of  which,  although  ivtuining  the  general  character  of 
those  of  the  convoluted  tubule,  exhibit  a  distinct  demarcation  from  one  another  and  a  narrow 
homogeneous  inner  zone.  The  spiral  tubules  are  distinguishable  from  the  surrounding  collecting 
tubules  by  the  lighter  sharply  defined  cuboidal  lining  cells  of  the  latter.  Just  before  passing  into 
the  medulla  to  become  the  descending  limb  of  Henle's  loop,  the  spiral  tubule  diminishes  in  width 
and  in  consequence  ends  as  a  canal  of  conical  form. 

4.  The  Loop  of  Henle.— The  descending  /i»ib  of  this  U-like  segment  is  distinguished  not 
only  by  the  conspicuous  reduction  in  its  diameter  (.012-015  mm.),  being  the  narrowest  part  of 
the  entire  uriniferous  tubule,  but  also  by  the  altered  character  of  its  epithelium.  The  latter 
consists  of  low  elements,  so  thin  that  the  oval  nuclei  cause  distinct  elevations  in  the  cells  which 
project  beyond  the  general  level  of  the  epithelium.  Since  the  nuclei  usually  do  not  lie  exactly 


FIG.   1605. 


FIG.   1606. 


Henle's  loop 


Collecting  tubule 


Longitudinal  section  of  medulla  passing  through 
Henle's  loop.     X  400. 


Ascending  limb 


Longitudinal  section  of  medulla,  showing  parts 
of  limbs  of  Henle's  loop.    X  400. 

opposite  each  other,  the  projections  on 
one  wall  alternate  with  those  of  the 
other,  in  consequence  of  which  dispo- 
sition the  lumen  appears  wavy  and 
irregular,  although  not  much  reduced 
below  the  diameter  of  that  of  the  pre- 
ceding spiral  segment  and  generous  in 
proportion  to  the  entire  width  of  the 

tubule.      The  flattened  cells  consist  of  clear,  slightly  granular  cytoplasm,  in  which  is  embedded 
a  distinct  elliptical  nucleus  of  relatively  large  size. 

The  ascending  limb  differs  from  the  descending  in  its  increased  diameter  (.024-. 028  mm.), 
which  depends  upon  sudden  augmented  thickness  of  the  walls  and  not  upon  the  width  of  the 
lumen,  the  darker  and  striated  appearance  of  its  epithelium,  and  its  extension  from  the  medulla 
into  the  cortex.  The  outlines  of  the  individual  lining  cells  are  not  sharply  defined  in  well-pre- 
served organs,  although  the  readiness  with  which  these  elements  undergo  post-mortem  change 
often  results  in  their  artificial  separation.  The  cells  are  often  irregular  in  height,  the  lumen,  in 
consequence,  varying  and  in  places,  especially  within  the  cortex,  being  almost  obliterated.  The 
nuclei  often  occupy  a  clear  area,  and  are  separated  by  striations  of  unusual  length.  Although 
the  cells  exhibit  a  differentiation  into  an  outer  rodded  zone,  a  finely  striated  inner  border,  as  seen 
in  the  epithelium  of  the  convoluted  tubules,  is  wanting  ;  where  an  inner  zone  is  represented,  it 
assumes  a  variable  vesicular  rather  than  a  striated  character.  The  length  of  the  loop  of  Henle 
is  influenced  by  the  level  of  the  corresponding  Malpighian  body  within  the  cortex — the  nearer 
the  latter  lies  to  the  medulla  the  greater  the  descent  of  the  loop  towards  the  papilla,  and  rice 
rersa,  this  relation  probably  depending  upon  the  intimate  association  between  the  termination 
of  the  ascending  limb  and  the  Malpighian  body.  According  to  the  reconstructions  of  Huber,1 

1  Amer.  Journ.  of  Anatomy,  vol.  iv.,  Supplement,  1905. 


1 88  2 


HUMAN   ANATOMY. 


Vein 


on  gaining  the  Malpighian  corpuscle  the  ascending  limb  crosses  the  neck  in  close  proximity  to 
the  glomerulus,  with  which  it  is  connected  by  twigs  from  the  vas  efferens  (Hamburger1),  and 
then  arches  over  the  corpuscle  to  end  in  the  succeeding  connecting  tubule.  The  position  of 
the  sudden  transition  from  the  narrow  into  the  wider  tube  of  Henle's  loop  varies,  the  change 
exceptionally  occurring  after  the  turn  is  reached,  sometimes  within  the  loop  itself,  but  most  fre- 
quently within  the  descending  limb  a  short  distance  above  the  loop. 

5.  The  Distal  Convoluted  Tubule.— On  gaining  the  level  of  the  corresponding  Malpighian 
body,  the  ascending  limb  gradually  widens  into  the  distal  convoluted  or  intermediate  tubule,  a 
canal  approximating  the  diameter  (.o4o-.o45  mm.)  of  the  surrounding  convoluted  tubules,  but 
differing  from  the  latter  in  its  wider  lumen  and  in  the  character  of  its  epithelium.  This  consists 
of  well-defined  cuboidal  cells,  with  spherical  nuclei,  the  cytoplasm  of  which,  while  granular,  is 

comparatively  clear  and  devoid  of  stria- 

FIG.   1607.  tions.    The  moderately  tortuous  path  of 

the  intermediate  tubule  is  marked  by  a 
number  of  abrupt  changes  in  direction, 
but  in  general  lies  for  a  time  enclosed  by 
the  arch  described  by  the  corresponding 
convoluted  segment  (Schweiger-Seidel), 
which  it  finally  crosses  (Huber). 

6.  The  Connecting  Tubule. — This 
portion  of  the  tubule  (.023-. 025  mm.  in 
diameter)  resembles  the  preceding  seg- 
ment in  its  clear  epithelium,  the  lining 
cells,  however,  being  lower,  with  a  cor- 
responding increased   lumen.      After  a 
short  and  usually  arched  course,  the  con- 
necting tubule  enters  the  medullary  ray 
and,  uniting  with  similar  canals,  joins  in 
forming  the  collecting  tubule. 

7.  The    Collecting    Tubule.— This 
first  lies  within  the  medullary  ray,  where 
it  forms  the  beginning  of  the  system  of 
straight   duct-tubes   that   culminates   in 
the  canals  opening  upon    the    papilla, 
and  then  passes  into  the  renal  pyramid. 
During  their  course  through  the  medul- 
lary ray  the  collecting  tubules  repeatedly 
unite  to  produce  stems,  which,  while  in- 

"-'•'-    ft  G^MTOWfrflM  .TO  /  ft)  W'l        creasing  four-  or  fivefold  in  diameter,  are 
'OOP       :Hl®SiWlillWiy,f  1F«J        diminishing  in  number.    In  consequence 

of  this  fusion  within  the  pyramid,  the  col- 
lecting tubules  are  disposed  in  groups 
(Fig.  1609),  each  of  which  corresponds 
to  the  tubules  prolonged  from  a  single 
medullary  ray  and  is  surrounded  by  the 
limbs  of  the  loops  of  Henle.  On  enter- 
ing the  renal  pyramid,  the  groups  of  col- 
lecting tubules  at  first  are  separated  by 
the  intervening  bundles  of  straight  blood- 
vessels (t'tisa  recta-}  that  are  given  off 
from  the  larger  twigs  within  the  boun- 
dary /one  for  the  supply  of  the  medulla. 

After  passing  to  within  about  5  mm.  of  the  apex  of  the  papilla,  towards  which  they  converge, 
the  large  collecting  canals  undergo  repeated  junction,  increasing  in  diameter  but  rapidly  dimin- 
ishing in  number,  to  form  the  wide  papillary  ducts.  The  epithelium  lining  the  collecting  tubules 
— the  larger  as  well  as  the  smaller — consists  of  clear  cuboidal  or  low  columnar  cells,  sharply 
defined  from  one  another  and  provided  with  spherical  nuclei.  The  light-colored  cytoplasm 
and  distinct  demarcation  of  these  elements  render  the  collecting  tubules  conspicuous  and  their 
recognition  easy. 

«s.  The  Papillary  Ducts. — These,  the  final  segments  of  the  kidney  tubules,  number  from 
ten  to  eighteen  for  each  single  papilla,  at  the  apex  of  which  they  end.  Kach  is  formed  by  the 
junction  of  from  ten  to  thirty  of  the  larger  collecting  tubules  (.O5Q-.o6o  mm.)  and  attains  a 
diameter  of  from  .2-.3  mm.  The  lining  epithelium  is  composed  of  conspicuous,  clear  columnar 
cells,  about  .020  mm.  in  height  and  one-third  as  much  in  width,  which  rest  upon  a  distinct 

1  Archiv  f.  Anat.  u.  Entwick.,  Suppl.  Hd.,  1890. 


Collecting 
tubule 


Longitudinal  section  of  renal  medulla,  showing  Henle's 
loops  and  collecting  tubules.     X  45- 


THE    KIDNEYS. 


1883 


Blood-vessel 


YV>  m    ):< 

S     .       y\  C. 

I'ifc  Vq,.0'',..0  Descending 
A  *«(?^       F  1'i'b  of  loop 


membrana  propria  almost  as  far  as  the  termination  of  the  canal.     At  this  point  the  membrane 
fades  away  and  the  epithelium  of  the  duct  becomes  continuous  with  that  clothing  the  surface  of 
the  papilla  and  lining  the  pelvis  of 
the  kidney.  FIG-   1608. 

It  is  evident  that  the  num- 
ber of  Malpighian  bodies  and  uri- 
niferous tubules  proper  is  greatly 
in  excess  of  the  larj; 
tubes,  each  papillary 
senting  the  termination  of 
orate  system  of  dividing  canals 
far  as  the  connecting  tubules,  from 
which  point  the  true  uriniferous  tu- 
bules complete  their  tortuous  path 
without  further  subdivision. 

The  Supporting  Tissue. — 
The  interstitial  stroma  holding  in 
place  the  tubules  and  the  blood- 
vessels consists  of  a  net-work  of 
modified  connective  tissue,  or  re- 
ticulum,  whigh  has  been  shown 
by  Mall  to  withstand  pancreatic 
digestion  and  to  form  a  continu- 
ous framework  throughout  the 
kidney.  The  stroma  is  most  abun- 
dant along  the  paths  of  the  in- 
terlobular  and  the  larger  blood- 
vessels, from  the  adventitia  of 
which  delicate  trabeculae  extend 
in  all  directions  to  form  the  meshes 
lodging  the  tubules,  smaller  ves- 
sels, and  capillaries.  Within  the 
cortex  the  supporting  tissue  is  meagre,  being  best  developed  along  the  interlobular  vessels  and 
around  the  Malpighian  bodies.  According  to  Mall,  the  membrana  propria  of  the  tubules  is 
resolvable  into  delicate  net-works  of  reticulum  directly  continuous  with  the  surrounding  stroma, 
the  general  arrangement  of  which  corresponds  to  the  disposition  of  the  tubules.  Within  the 
medulla  the  interstitial  tissue  is  much  more  abundant  than  in  the  cortex,  its  amount  increasing 
towards  the  apex  of  the  papilla,  in  which  location  considerable  tracts  of  comparatively  coarse 
stroma-fibres  separate  the  papillary  ducts.  At  the  surfaces  of  the  divisions  of  the  renal  substance 


Ascending 
imbof  loop 


0> 


Section  of  medulla  across  renal  pyramid,  showing  large  collecting  tubules, 
limbs  of  Henle's  loops,  blood-vessels,  and  stroma.     X  13°- 


FlG.    1609. 


Section  across  upper  part  of  renal  pyr.-i- 
mid,  showing  groups  of  blood-vessels  sur- 
rounded by  uriniferous  tubules.  X  50. 


FIG.  1610. 

Space  for  blood-vessel 


Supporting  Stroma-tissue  of  kidney  after 
pancreatic  digestion;  spaces  lodged  tubules 
and  blood-vessels.  X  no. 


the  interstitial  tissue  is  continuous  with  the  investing  fibrous  capsule,  the  interlobar  septa,  or  the 
lining  of  the  pelvis,  as  the  case  may  be.  Not  only  the  blood-vessels,  but  likewise  the  nerve- 
trunks  and  the  lymphatics  are  provided  with  sheaths  of  the  renal  stroma. 


1 884 


HUMAN   ANATOMY. 


FIG.   1611. 

Two  calyces 


Blood-Vessels.— Arteries. — The  renal  arteries — usually  one  to  each  kidney, 
but  not  infrequently  two,  and  in  exceptional  cases  three  or  even  four — are  of  unequal 
length,  the  right  one  being  the  longer  in  consequence  of  the  parent  stem,  the  aorta, 
lying  to  the  left  of  the  mid-line.  Embedded  within  the  subperitoneal  tissue  and 
covered  by  the  renal  fascia  (page  1594),  they  pass  laterally,  accompanied  and  more 
or  less  masked  by  the  renal  veins,  to  the  hilum  of  the  kidney,  during  their  course 
giving  off  small  twigs  to  the  capsula  adiposa  as  well  as  to  the  suprarenal  bodies. 
Just  before  entering  the  kidney,  or  within  the  hilum,  the  renal  artery  divides  into  an 
anterior  (ventral)  and  a  posterior  (dorsal)  branch,  each  of  which  embraces  the  pel- 
vis and  divides  into  four  or  five  twigs  that  hug  their  respective  wall  of  the  sinus. 
Preparatory  to  entering  the  kidney,  each  twig  breaks  up  into  from  three  to  five 

smaller  divisions  which  enter  the 
renal  substance  through  the  vascu- 
lar foramina  surrounding  the  pa- 
pillae. On  entering,  they  pass 
along  the  sides  of  the  papillae,  their 
course  corresponding  in  position  to 
the  original  tracts  of  connective  tis- 
sue that  separate  the  primary  di- 
visions of  the  foetal  kidney  (page 
1876)  ;  they  are  therefore  appro- 
priately designated  intcrlobar  ar- 
teries. The  general  expansion  of 
the  branches  derived  from  the  an- 
terior and  posterior  arteries  is  par- 
allel to  the  corresponding  ventral 
and  dorsal  surfaces  of  the  kidney  : 
the  intervening  zone  along  the 
convex  border  of  the  organ  con- 
tains few,  if  any,  of  the  larger  ves- 
sels and,  in  consequence,  appears 
lighter  in  color,  constituting  the 
•white  line  of  Brodel.  The  vessels 
supplying  the  kidney  do  not  anas- 
tomose, each  such  ' '  end ' '  artery 
providing  for  a  particular  area  of 
renal  substance.  On  reaching  the 
level  of  the  bases  of  the  renal 
pyramids,  each  interlobar  artery 
breaks  up  into  a  tree-like  bundle 
of  twigs,  some  of  which  pursue  an 
arched  course  across  the  bases  of 
the  pyramids,  thereby  producing 
the  impression  of  a  series  of  arcades 

at  the  junction  of  the  medulla  and  cortex.     From  these  vessels  two  series  of  terminal 
branches  arise,  one  for  the  supply  of  the  cortex,  the  other  for  that  of  the  medulla. 

The  cortical  arterioles  pursue  a  course  generally  perpendicular  to  the  free-  surface,  towards 
which  they  run  between  the  cortical  lobules,  giving  off  short  lateral  twigs  that  end  as  the  vasa 
afferentia  in  the  glomeruli  of  the  Malpighian  bodies.  The  latter  are  arranged  in  columns  in 
correspondence  with  the  path  of  the  interlohular  cortical  arterioles.  Some  pf  these,  however, 
do  not  give  off  vasa  afferentia,  but  ascend  to  the  kidney  capsule,  for  the  supply  of  which  they 
provide  in  conjunction  with  the  direct  branches  from  the  renal  artery. 

After  traversing  the  capillary  complex,  the  blood  is  carried  from  the  glomerulus  by  the 
vas  efferens,  which,  smaller  than  the  vas  afferens,  on  its  exit  immediately  breaks  up  into  the 
Cortical  capillaries  that  form  net-works  enclosing  the  tubules  within  the  labyrinth,  and,  continuing, 
surround  those  within  the  medullary  ray,  in  the  latter  situation  the  meshes  being  relatively  longer 
and  more  open  and  containing  blood  that  has  already  supplied  the  proper  urinilerous  tulniles. 

The  int'<fn//tiry  (ir/rrio/rs,  derived  from  the  arching  terminal  branches  of  the  interlobar 
stems  at  tin-  bases  of  the  pyramids,  descend  within  the  latter  as  bundles  of  radially  disposed 


Inferior  division  of  pelvis 


Ureter 


Corrosion  preparation  of  injected  right  kidney, 
viewed  from  behind,  showing  relations  of  branches  of 
renal  artery  to  divisions  of  renal  pelvis. 


THE    KIDNEYS. 


1885 


straight  twigs  (arteriolce  recttz}  that  at  first  surround  the  groups  of  collecting  tubules  and  then 
break  up  to  take  part  in  forming  the  capillary  net-work  of  the  medulla.  From  these  meshes  the 
blood  is  collected  by  the  straight  venous  radicles  that  accompany  the  arterioles  and,  with  the 
latter,  constitute  the  vasce  rectcz,  owing  to  whose  presence  the  darker  striae  of  the  medulla  are  due. 
In  consequence  of  numerous  anastomoses  the  vascular  supply  of  the  medulla  is  less  independ- 
ent of  that  of  the  cortex,  than  was  formerly  supposed  (Huber). 

Veins. — The  veins  of  the  kidney  are  also  disposed  as  cortical  and  medullary 
branches  which  empty  into  larger  stems  (vence  arciformes)  that  cross  the  bases  of 
the  pyramids  as  a  series  of  communicating  venous  arcades. 

The  blood  within  the  cortical  capillaries  escapes  by  three  paths:  (i)  through  numerous 
small  veins  that  traverse  the  outer  third  of  the  cortex  towards  the  capsule,  beneath  which  they 
empty  into  larger  stems  running  parallel  to  the  free  surface  of  the  kidney.  From  three  to 
five  of  these  horizontal  ves- 
sels converge  towards  a  com-  FIG.  1612. 
mon  point  and  thereby  pro-  Capsule 
duce  a  star-like  figure  (vena 
stellata),  which  is  the  begin- 
ning of  the  interlobular  vein 
that,  in  company  with  the  cor- 
responding arteriole,  passes 
through  the  cortex  to  become 
tributary  to  the  venous  arcade 
at  the  base  of  the  pyramid  ; 
(2)  through  small  venous 
branches  that  empty  directly 
into  the  interlobular  veins  at 
various  levels ;  (3)  through 
the  deep  cortical  veins  that 
traverse  the  inner  third  of  the 
cortex  and  are  tributaries  of 
the  venae  arciformes.  The 
medulla  is  drained  by  the  ven- 
ul<z  rectcz,  straight  vessels 
that  begin  in  the  medullary 
capillary  net-work  and  empty 
into  the  arciforrri  veins.  The 
latter  terminate  in  the  larger 
interlobar  veins  that  accom- 
pany the  arteries  along  the 
sides  of  the  pyramids  and 
emerge  into  the  sinus  around 
the  papillae.  The  further 
course  of  the  relatively  large 
and  valveless  venous  trunks 
corresponds  with  that  of  the 
arteries  ;  the  veins  draining 
each  half  of  the  kidney  unite 
into  a  single  stem,  the  two 


Interlobar 
artery 

Medullary 
arterioles 


Capillary  net -work 


Papilla 
Diagram  showing  arrangement  of  blood-vessels  of  kidney.     (.After  Disse.) 


thus  derived  joining  to  form  the  renal  vein.  The  latter  usually  lies  anterior  to  the  renal  artery  in 
its  path  to  the  vena  cava,  the  left  vein  being  longer  than  the  right  in  consequence  of  the  position 
of  the  cava  on  the  right  of  the  spine. 

The  lymphatics  of  the  kidney  occur  as  a  superficial  and  a  deeper  net-work. 
According  to  the  investigations  of  Stahr1  and  of  Cune"o,2  the  superficial  lymphatics 
comprise  a  delicate  subcapsular  mesh-work  from  which  two  systems  of  collecting 
trunks  arise  ;  the  one  passes  into  the  kidney  to  join  the  deeper  lymphatics  within  the 
renal  substance,  the  other  pierces  the  capsule  to  unite  with  the  perirenal  lymphatics 
within  the  capsula  adiposa.  The  deep  lymphatics  arise  within  the  cortex  from  deli- 
cate interlobular  net-works,  the  general  path  of  the  more  definite  stems  being  that  of 
the  blood-vessels.  On  leaving  the  hilum,  the  larger  collecting  trunks — from  four  to 

1  Archiv  f.  Anat.  u.  Entwick.,  1900. 

2  Bull.  d.  Soc.  Anat.,  Fe\-.    1902. 


1 886 


HUMAN   ANATOMY. 


seven  in  number — follow  the  renal  artery  and  vein,  especially  the  latter,  which  they 
surround.  The  lymphatics  of  the  kidney  end  chiefly  in  the  nodes  lying  at  the  sides 
or  in  front  of  the  aorta  ;  small  lymph-nodes  frequently  occur  in  the  vicinity  of  the 
hilum. 

The  nerves  of  the  kidney  are  derived  from  the  renal  plexus  formed  by  contri- 
butions from  the  solar  and  aortic  plexuses  and  the  least  splanchnic  nerve.     The 

FIG.  1613. 


>—,<=~  Stellate  vein 


Glpmerulus  of 
Malpighian  body 


Interlobular  artery 


Interlobular  vein 


f/^f~  Capillary  net-work  in 
\ff    >•         labyrinth 


Capillary  net-work  in 
medullary  ray 


Large  blood-vessels  at 
junction  of  cortex  and 
medulla 


Longitudinal  section  of  injected  kidney  of  dog,  showing  general  arrangement 
of  blood-vessels  of  cortex  and  adjacent  medulla.    X  40. 

plexus  accompanies  the  renal  artery,  which  it  surrounds  with  its  mesh-work,  into  the 
sinus  ;  within  the  latter  is  formed  a  well-marked  perivascular  net-work  from  which  a 
number  of  twigs  are  given  off  to  supply  the  walls  of  the  pelvis  and  ureter,  while  the 
majority  accompany  the  vessels  into  the  kidney.  The  investigations  of  Ret/ins, 
Kolliker,  Disse,  Berkley,  and  especially  of  Smirnow,1  have  shown  that  all  the  renal 
blood-vessels  are  generously  provided  with  fibres  for  th'e  supply  of  the  muscular 

1  Anatom.  Anzeiger,  Bd.  xix.,  1901 


PRACTICAL  CONSIDERATIONS  :    THE    KIDNEYS.  1887 

tissue  of  their  walls.  In  continuation  the  nerve-fibres  pass  between  the  uriniferous 
tubules  and  form  plexuses  surrounding  the  membrana  propria.  Smirnow  traced 
the  ultimate  fibrilke  within  the  tubules,  their  free  endings  lying  between  the  epithelial 
cells.  The  vessels  and  tubules  of  the  medulla  are  provided  with  similar  but  less 
closely  disposed  nervous  filaments  which  are  destined  chiefly  for  the  muscular  tissue. 
According  to  the  last-named  investigator,  the  nerves  of  the  kidney  include  some 
sensory  and  both  medullated  and  non-medullated  fibres.  The  fibrous  capsule  also 
possesses  a  rich  nervous  supply. 

Variations. — More  or  less  conspicuous  furrows  are  frequently  seen  on  the  surface  of  the 
adult  kidney  ;  these  represent  a  persistence  of  the  lobulation  normally  present  in  the  foetus  and 
the  young  child. 

In  addition  to  variations  in  size,  a  marked  deficiency  on  one  side  being  usually  compensated 
by  a  large  organ  on  the  other,  the  kidneys  often  present  different  degrees  of  union  depending 
upon  abnormal  approximation  or  fusion  of  the  primary  renal  anlages.  The  connection  may 
consist  of  a  band,  chiefly  of  fibrous  tissue,  that  unites  otherwise  normal  organs  ;  or  it  may  be 
formed  by  an  isthmus  of  renal  tissue  that  extends  between  the  approximated  lower  poles  ;  or 
the  two  organs  may  form  one  continuous  U  "Shaped  mass  across  the  spine,  then  constituting  a 
"horseshoe"  kidney.  Extreme  displacement  and  fusion  may  produce  a  single  irregular  organ 
whose  primary  double  anlage  is  indicated  by  the  presence  of  two  renal  ducts  that  descend  on 
different  sides  of  the  pelvis  to  terminate  normally  in  the  bladder.  Absence  of  one  kidney 
occasionally  occurs,  the  organ  present  usually  being  correspondingly  enlarged.  Complete  absence 
of  both  kidneys  has  been  observed  as  a  rare  congenital  malformation. 

PRACTICAL  CONSIDERATIONS  :    THE  KIDNEYS. 

Congenital  abnormalities  of  the  kidneys  may  affect  (#)  their  shape,  size,  and 
number  ;  (£>)  their  position  ;  and  kidneys  that  are  abnormal  in  one  of  these  respects 
are  apt  to  be  so  in  others.  The  matter  is  of  practical  importance  in  relation  to  the 
diagnosis  of  intra-abdominal  swellings  and  to  the  many  operations  now  undertaken 
for  the  relief  of  various  renal  conditions. 

(a)  Anomalies  as  to  Shape,  Size,  or  Number. — One  kidney  may  be  congenitally 
absent  or  greatly  atrophied  ;  may  be  constricted  so  as  to  assume  an  hour-glass 
shape  ;  or  lobulated,  as  in  the  fcetal  condition  ;  or  the  two  kidneys  may  be  fused  so 
that  ( i )  their  inferior  portions  are  united  by  a  band  of  tissue — glandular  or  fibrous — 
that  crosses  the  vertebral  column,  usually  in  the  lumbar  region  ("horseshoe 
kidney")  ;  or  (2)  they  may  form  an  irregularly  bilobed  mass,  one  side  of  which  is 
much  larger  than  the  other,  or  become  one  single  ' '  disk-like' '  kidney  lying  in  the 
mid-line  on  the  lumbar  spine,  on  the  sacral  promontory,  or  in  the  hollow  of  the  sacrum 
(Rokitansky,  Morris). 

Of  these  conditions  the  rarest  is  the  true  congenital  absence,  or  extreme  atrophy 
of  a  kidney  ( i  in  2650)  ;  horseshoe  kidneys  are  more  than  twice  as  common  ( i  in 
1000)  ;  while  one-sided  renal  atrophy  associated  with  post-natal  disease  is  relatively 
frequent  (i  in  138)  (Morris). 

Both  kidneys  have  been  absent  in  many  still-born  children  and  acephalous 
monsters.  In  a  very  few  cases  a  supernumerary  kidney  has  been  found. 

Anomalies  affecting  the  blood-supply  to  the  kidney  occur  in  nearly  50  per  cent, 
of  cases.  The  renal  arteries  are  usually  increased  in  number,  or  divide  at  once — 
before  reaching  the  hilum — into  several  branches,  fcetal  conditions  in  the  human 
species  that  are  permanent  in  many  birds  and  reptiles.  Accessory  or  supernumerary 
veins  are  much  more  rarely  found. 

(&)  Anomalies  of  Position. — Congenital  displacement — apart  from  the  horseshoe 
kidney — usually  affects  one  kidney,  which  is  apt  to  be  found,  in  the  vicinity  of  the 
sacral  promontory  or  the  sacro-iliac  joint,  but  may  be  either  higher  or  lower,  and 
may,  by  its  malposition,  give  rise  to  serious  or  even  fatal  error  in  diagnosis  or  treat- 
ment. 

It  would  seem  proper  to  include  here  those  rare  temporary  displacements  that 
are  due  to  the  congenital  presence  of  a  mesonephron,  which — as  the  usual  support 
given  by  the  peritoneum  is  lacking,  and  as  the  contained  blood-vessels  are  in  such 
cases  of  abnormal  length — permits  mobility  of  the  kidney  beyond  the  physiological 
limits  (floating  kidney). 


1888  HUMAN   ANATOMY. 

Movable  Kidney. — The  extent  of  the  normal  kidney  movement — of  ascent  during 
expiration  or  while  lying  supine,  and  of  descent  during  inspiration  or  while  standing 
erect — does  not,  on  an  average,  much  exceed  an  inch  in  the  vertical  direction.  There 
may  also  be  a  slight  lateral  movement.  When  this  limit  is  distinctly  and  greatly 
overpassed  the  condition  known  as  ' '  movable  kidney' '  results.  The  normal  kidney- 
is  usually  not  palpable  below  the  costal  arch.  Occasionally  the  lower  end  of  the 
right  kidney  may  be  felt  there  just  external  to  the  rectus  muscle.  In  emaciation  the 
lower  ends  of  both  kidneys  may  be  palpable. 

Three  degrees  of  abnormal  mobility  have  been  arbitrarily  but  usefully  agreed 
upon  for  purposes  of  description  :  ( i )  The  lower  half  may  be  felt  by  bimanual  pal- 
pation— the  fingers  of  one  hand  being  pressed  into  the  ilio-costal  space  posteriorly, 
and  of  the  other,  into  the  subcostal  region  anteriorly — during  deep  inspiration. 
(2)  The  greater  part  of  the  kidney  or  the  whole  organ  may  be  felt  during  deep 
inspiration,  but  ascends  under  cover  of  the  ribs  and  liver  during  expiration.  (3)  The 
whole  kidney  descends  and  can  be  retained  between  or  below  the  examiner's  fingers 
during  the  respiratory  movements  (Morris). 

The  most  important  factors  in  holding  the  kidney  in  its  normal  position  in  the 
renal  fossa  (page  1874)  are  :  (a)  the  perirenal  fascia,  which  through  its  attachment  to 
the  transversalis  fascia  and  to  the  perinephric  fat,  in  conjunction  with  (<£)  the  peri- 
toneum, where  that  covering  exists,  prevents  any  undue  mobility;  (c~)  the  renal  vessels, 
which  must  correspond  in  length  to  the  radius  of  the  circle  of  movement  of  the  kidney 
and,  to  an  extent,  resist  elongation  ;  {d")  intra-abdominal  pressure,  which,  through 
the  upward  thrust  of  the  more  mobile  viscera,  adds  to  the  support  that  (e)  they  and 
their  attachments  give  to  the  viscera  in  the  upper  zone  of  the  abdomen  ;  (/")  the 
shape  of  the  renal  fossae,  which,  like  the  kidneys  themselves,  are  somewhat  narrower 
at  their  lower  extremities. 

Undue  mobility  of  the  kidney  is  thus  favored  by  (a)  congenital  absence  of  the 
peritoneal  support  (floating  kidney, — vide  supra)  ;  (^)  diminution  of  the  tension  of 
the  peritoneum  and  perirenal  fascia  from  absorption  of  perinephric  fat ;  (<:)  repeated 
jars  and  jolts,  as  from  jumping  or  falling,  or  from  coughing  or  straining,  that  tend 
to  elongate  the  renal  vessels  as  well  as  to  stretch  the  peritoneum  and  its  attachments 
and  thus  increase  both  the  retroperitoneal  space  in  which  the  kidney  moves  and  the 
radius  of  the  arc  of  its  movement  ;  (d  )  pregnancy,  the  removal  of  intra-abdominal 
tumors  or  of  accumulations  of  fluid,  or  other  conditions  that  produce  laxity  and 
weakness  of  the  abdominal  walls  ;  (^)  ptosis  of  other  viscera,  acting  either  by  their 
push  from  above  (liver,  spleen)  or  their  drag  from  below  (colon)  ;  or  (/")  general 
muscular  weakness,  acting  not  only  by  reason  of  the  associated  lack  of  tonicity  of 
the  abdominal  wall,  but  also  through  the  modification  in  shape  of  the  renal  fossae, 
the  depth  of  which  depends,  c&teris  paribus,  on  the  development  of  the  loin  muscles, 
and  especially  of  the  psoas  and  quadratus  lumborum. 

A  careful  study  of  the  body-form  in  its  relation  to  movable  kidney  seemed  to 
show  (Harris)  that  a  relative  diminution  in  the  capacity  of  the  middle  zone  or  area 
of  the  body-cavity  (containing  the  liver,  stomach,  spleen,  pancreas,  and  larger  por- 
tion of  each  kidney),  either  original  or  acquired  (as  from  tight  lacing),  acts  by  forcing 
the  liver  and  spleen  downward  upon  the  kidneys,  and  at  the  same  time  depriving 
them  of  the  support  afforded  by  the  narrowest  or  most  constricted  portion  of  the 
parietes  of  this  zone,  which  narrow  portion  is  then  above  the  centre  of  the  kidney 
instead  of  below  it,  as  it  should  be  normally. 

Consideration  of  the  above-mentioned  anatomical  factors  makes  clear  the  greater 
frequency  (80  per  cent.)  of  movable  kidney  in  women  than  in  men.  It  should  be 
added  that  in  women  the  renal  fossae  are  normally  shallower  and  less  narrowed  at  the 
lower  ends  than  in  men,  the  depth  and  the  narrowing  depending,  as  has  been  said, 
upon  muscular  development.  It  will  be  understood,  too,  why  among  the  women 
who  suffer  from  this  condition  is  found  a  so  considerable  proportion  who  are  thin  and 
round-shouldered,  with  long,  curved  spines  and  flattening  and  adduction  of  the  lower 
ribs,  or  who  have  had  several  children,  or  one  difficult  labor,  or  an  exhausting  illness 
attended  by  emaciation,  or  have  been  addicted  to  tight  lacing.  In  both  sexes  the 
history  of  a  violent  fall  or  of  a  chronic  cough  is  not  infrequent. 

Movable  kidney  is  thirteen  times  more  frequent  on  the  right  side  than  on  the 


PRACTICAL   CONSIDERATIONS  :    THE   KIDNEYS.  1889 

left,  because  of  the  following  conditions,  which  are  of  varying  relative  importance  in 
different  cases  :  (a)  the  left  perirenal  fascia  is  strengthened  by  some  fibrous  bands, 
remnants  of  the  fusion  of  the  descending  mesocolon  with  the  primitive  parietal  peri- 
toneum (Moullin),  the  left  kidney  being  thus  more  firmly  bound  to  the  descending 
colon  than  is  the  right  to  the  ascending  colon  ;  (6)  the  greater  size,  weight,  and 
density  of  the  liver  as  compared  with  the  spleen,  and  its  more  intimate  association 
with  respiratory  movements,  making  the  impact  of  the  former  on  the  upper  surface  of 
the  right  kidney  both  more  frequent  and  more  potent  than  the  similar  contact  of  the 
spleen  with  the  left  kidney  ;  (c)  the  greater  length  of  the  right  renal  artery,  which  has 
to  cross  the  mid-line  to  reach  the  kidney  ;  although  the  right  vein  is  similarly  shorter 
than  the  left  vein,  it  offers  less  resistance  to  elongation  than  does  the  left  renal  artery  ; 
(X)  the  right  kidney  is  usually  lower  than  the  left  kidney  (page  1871),  and  therefore 
more  easily  loses  the  support  of  the  parietes  at  the  region  where  that  support  is  most 
effective  (vide  supra}  ;  (<?)  the  connection  of  the  left  suprarenal  capsular  vein 
with  the  left  renal  vein  gives  some  fixation  to  the  left  kidney,  as  the  capsule  remains 
in  position  and  does  not  follow  the  kidney  in  its  abnormal  movements  (Morris,  Cru- 
veilhier)  ;  (/  )  the  right  renal  fossa  is  more  cylindrical — i.e. ,  less  narrowed  at  its 
lower  end — than  the  left,  especially  in  women,  owing  to  a  slight  torsion  of  the  lumbar 
spine  (Moullin),  or  perhaps  to  the  greater  width  and  development  of  the  right  side 
of  the  pelvis. 

From  an  anatomical  stand-point,  the  symptoms  caused  by  excessive  mobility  are  : 

1.  Those  due  to  traction  upon  and  irritation  of  the  nerves  ;  as,  for  example, 
pain,  felt  in  the  loins  and  often  referred  to  the  lower  abdomen  or  genitalia,  owing  to 
the  association  of  the  renal  plexus  with  the  spermatic  or  ovarian  plexus  ;  the  same 
association  gives  to  the  pain  produced  by  pressure  upon  a  movable  kidney  the  sick- 
ening quality  peculiar  to  testicular  nausea  (page  1951);   nausea  and  vomiting,  due  to 
a  similar  connection  with  the  solar  plexus  and  pneumogastrics  ;  neiir asthenia,  which 
may  be  either  a  result  of   movable  kidney — through  nerve  irritation — or  a  cause, 
when  it  has  produced  emaciation  and  muscular  weakness. 

2.  Those  due  to  traction  upon  the  gastro-intestinal  tract,  especially  upon  the 
duodenum  and  bile-ducts,  as  digestive  disturbance,  flatulence,  constipation,  and  even 
jaundice.     As  the  second  portion  of  the  duodenum   is   dragged  upon  through  its 
areolar-tissue  connection  with  the  right  kidney,  its  lack  of  mesentery  prevents  it  from 
moving  downward,  it  is  stretched  so  that  its  lumen  is  diminished,  and  interference 
with  the  digestive  current  and  secondary. dilatation  of  the  stomach  follow  (Bartels)  ; 
at  the  same  time  the  bile-ducts  are  elongated  and  narrowed  and  the  passage  of  bile 
through  them  is  interfered  with  (page  1731).      On  the  left  side  similar  disturbance  of 
digestion  may  follow  the  pull  of  the  kidney  on  the  stomach  and  colon. 

3.  Those  due  to  traction  upon  the  vessels,  resulting — as  the  compressible  vein  is 
more  readily  affected — in  congestion  of  the  kidney,  sometimes  so  marked  as  to  give 
rise  to  a  temporary  haematuria. 

4.  Those  due  to  traction  upon  or  angulation  or  twisting  of  the  ureter,  causing  an 
acute  hydronephrosis,  at  first  intermittent.      Tuffier  has  shown  that  the  bending  or 
kinking  of  the  ureter  when  a  kidney  is  displaced  occurs  in  more  than  50  per  cent, 
of  cases  at  a  point  a  few  centimetres  below  the  pelvis,  where  it  is  held  against  the 
abdominal  wall  by  strong  connective  tissue  and  cannot  follow  the    moving  kidney 
(Landau).      In  some  cases,  as  a  result  of  ureteral  stenosis  at  the  point  of  obstruc- 
tion, secondary  changes    occur  in  the   kidney  which   consist  essentially   in   (a)  an 
atrophy  of  the  renal  structure  most  directly  exposed  to  pressure  from  the  retained 
urine  (Virchow)  ;  and  (£)   interstitial  degeneration  resulting  from   interference  with 
nutrition,  due  to  the  facts  that  distention  of  the  pelvis  of  the  kidney  takes  the  direc- 
tion of  least  resistance,  which  is  forward,  and  that  the  pelvis  is  placed  behind  the 
vessels  where  they  enter  the  hilum,  so  that  as  it  distends  it  stretches,  flattens,  and 
obstructs  them  (Griffiths). 

As  Morris  has  pointed  out,  the  increased  resonance  and  diminished  resistance  in 
the  loin,  described  as  indicating  the  absence  of  the  kidney  from  its  normal  position,  are 
of  little  value  because  (a)  the  ilio-costal  space  in  some  positions  of  the  trunk  and 
thigh  is  somewhat  hollow  ;  (£)  the  thickness  of  the  loin  muscles  and  of  the  fat  makes 
the  percussion-note  dull  even  when  the  kidney  is  displaced  ;  and  (c)  in  its  normal 

119 


1890  HUMAN   ANATOMY. 

position  the  kidney  is  so  overlapped  by  the  lower  thoracic  wall  that  the  resonance 
and  resistance  of  the  loin  have  at  best  but  little  relation  to  it  (page  1873  ). 

Of  course,  obstruction  of  the  ureter  from  other  causes — as  valvular  folds  at  the 
ureteral  orifice,  thought  to  follow  a  congenital  exceptionally  oblique  insertion  of  the 
ureter  into  the  pelvis  (Virchow),  or  brought  about  by  distention  of  the  pelvis 
(Simon),  or  aggravated  by  swelling  of  the  pelvic  mucosa  (Kiister,  Cabot) — or  ob- 
structive disease  of  any  part  of  the  lower  urinary  tract  may  also  result  in  a  hydrone- 
phrosis  which,  if  infection  occurs, — as  it  often  does, — becomes  a  pyonephrosis.  Either 
a  purulent  collection  thus  formed  or  an  abscess  originating  in  the  renal  structure 
(pyogenic  or  tuberculous  infection)  may  find  its  way  into  the  fatty  and  connective 
tissue  of  the  loin, — perinephric  tissue, — or  suppuration  may  reach  that  region  from 
other  sources  or  may  occur  there  primarily. 

Perinephric  abscess  is  characterized  by  certain  symptoms  which  should  be  studied 
in  connection  with  the  anatomy  of  the  region,  as  (a)  pain,  radiating  to  the  lower  ab- 
domen, genitalia,  or  thigh, — i.e. ,  in  the  distribution  of  the  ilio-hypogastric,  ilio-ingui- 
nal,  anterior  crural,  obturator,  and  other  branches  of  the  lumbar  plexus  ;  (^)  flexion 
and  adduction  of  the  thigh,  from  irritation  of  the  motor  filaments  of  the  same  nerves, 
especially  if  the  abscess  is  about  the  lower  pole  of  the  kidney,  and  therefore  in  inti- 
mate relation  with  the  third  and  fourth  lumbar  nerves,  from  which  the  supply  of  the 
flexors  and  adductors  is  chiefly  derived  ;  (c~)  bending  of  the  body  towards  the 
affected  side,  towards  which  the  concavity  of  a  lateral  lumbar  curve  in  the  spine  is 
directed, — a  symptom  which,  like  b,  may  be  due  either  to  muscular  spasm  or  to  an 
instinctive  effort  to  increase  the  loin  space;  (</)  intestinal  disturbance  from  the 
proximity  of  the  abscess  to  the  colon,  into  which  it  may  open.  Such  abscess  may 
also  penetrate  the  lumbar  aponeurosis  and  the  quadratus  lumborum  muscle  and  ap- 
pear in  the  loin  at  the  outer  border  of  the  erector  spinae  between  the  latissimus  dorsi 
and  external  oblique  ( the  lower  part  of  which  interval  is  Petit' s  triangle,  q.  v. ) ,  or  may 
descend  by  gravity  into  the  pelvis,  or  may — very  exceptionally — open  into  the  peri- 
toneal cavity. 

Abscess  of  the  kidney  which  penetrates  the  renal  capsule  to  reach  the  perirenal 
region  usually  does  so  at  a  non-peritoneal  area  of  the  kidney  surface,  but  does  not 
necessarily  reach  the  loin.  As  reference  to  the  relations  of  the  kidney  (page  1873) 
will  show,  the  pus  may  be  evacuated  directly  into  the  colon  or  duodenum,  or  more 
frequently — because  the  apposed  areas  are  covered  with  peritoneum  which  favors 
limiting  adhesions — into  the  stomach  or  liver,  or  through  the  diaphragm  into  the 
base  of  the  chest. 

Renal  calculus  produces  symptoms  which  are  analogous  to  those  described 
above  as  associated  with  suppurative  disease  in  or  about  the  kidney,  and  which — 
apart  from  haematuria  and  pyuria  and  the  physical  evidence  of  the  presence  of  a  stone, 
such  as  is  afforded  by  the  X-rays — depend  for  their  interpretation  upon  a  knowledge 
of  the  renal  reflexes, — i.e.,  of  the  association  of  the  small  and  lesser  splanchnics  and 
the  tenth  to  twelfth  dorsal  and  first  lumbar  spinal  segments  with  the  sensory  and 
motor  nerves  derived  from  the  same  segments.  These  symptoms  are,  in  part,  pain 
radiating  to  the  genitalia,  vesical  irritability,  nausea  and  vomiting,  rectal  tenesmus, 
and  retraction  of  the  testicle.  The  last-named  symptom  is  more  marked  in  children 
and  young  persons,  in  whom  the  gland  is  often  drawn  up  to  the  external  ring  or 
even  into  the  inguinal  canal.  After  puberty,  as  the  testis  increases  in  weight  and  the 
cremaster  grows  feebler  with  age,  the  retraction  becomes  less  obvious  (Lucas). 

It  has  been  suggested  that  occasionally  the  sudden  exacerbation  of  pain  occur- 
ring at  night  when  the  patient  is  at  rest  may  be  due  to  the  passage  of  flatus  along 
the  colon  that  presses  against  the  kidney  (Jacobson). 

The  aching  pain  beginning  at  the  lower  edge  of  the  last  rib,  in  the  angle  between 
it  and  the  spine,  and  extending  along  the  edge  of  the  rectus  muscle  below  the  level 
of  the  umbilicus,  is  probably  reflected  along  the  last  dorsal  nerve,  as  it  is  almost 
certainly  relieved  by  operations  in  which  that  nerve  is  divided,  but  the  stone  is  not 
found  (Lucas). 

nixtasc  of  the  kidney,  when  Hon-8Uppurative,  has  but  little  obvious  anatomical 
bearing.  It  may  be  noted,  however,  that  the  time-honored  practice  of  applying 
counter-irritants  and  heat  to  the  loin  in  renal  congestions  has  a  scientific  basis  in  the 


PRACTICAL   CONSIDERATIONS  :    THE   KIDNEYS.  1891 

free  anastomosis  between  the  lower  intercostal  and  upper  lumbar  arteries,  supplying 
the  parietes  of  the  loin,  and  some  terminal  branches  of  the  renal  artery.  This — a 
part  of  the  "  subperitoneal  arterial  plexus"  (Turner) — is  accompanied,  of  course, 
by  a  similar  venous  anastomosis.  Thus  the  application  of  cups  or  hot  fomentations 
or  counter-irritants  to  the  loin  may  act,  at  least  temporarily,  by  enlarging  superficial 
vessels  and  withdrawing  blood  from  a  congested  or  inflamed  kidney. 

In  somewhat  the  same  line  of  thought,  as  to  congestion,  attention  may  be  called 
to  the  facts  that  the  capsule  and  pelvis  of  the  kidney  are  the  sensitive  portions  ;  that 
renal  pain,  not  dependent  on  infection,  or  on  the  irritation  of  a  calculus,  or  on  dis- 
placement, usually  means  increased  tension  ;  that  great  relief  of  both  pain  and  con- 
gestion is  therefore  often  experienced  after  nephrotomies  that  are  merely  exploratory, 
although,  if  the  tension  is  due  to  accumulation  of  fluid  within  the  renal  pelvis,  grave 
renal  congestion  may  follow  its  evacuation  and  the  accompanying  sudden  relief  from 
habitual  pressure  just  as  it  follows  some  cases  of  catheterization  of  habitually  distended 
bladders  (  Belfield)  ;  and  that  occasional  cures  of  various  forms  of  acute  or  subacute 
nephritis,  or  of  "  albuminuria  associated  with  kidney  tension"  (Harrison),  have  been 
obtained  merely  by  splitting  the  kidney  capsule  with  or  without  puncture  of  the 
kidney  itself.  The  more  recent  attempt  (Israel)  to  apply  the  method  to  chronic 
nephritis  with  severe  or  dangerous  symptoms  (especially  colic  and  haematuria),  and 
the  still  more  recent  introduction  (Edebohls)  of  bilateral  "  decortication" — decapsula- 
tion— in  chronic  nephritis  without  such  symptoms,  have  not  at  this  time  demonstrated 
their  value.  They  are  of  much  interest,  however,  in  relation  to  the  important  sub- 
ject of  tension  of  the  kidney  and  of  the  effects  of  modification  of  its  vascular  supply. 
The  beneficial  results  of  relief  of  tension  in  swellings  of  the  testicle  (acute  orchids) 
or  of  the  eye  (acute  glaucoma)  are  pointed  out  as  illustrations  of  the  manner  in 
which  splitting  the  capsule  benefits  some  forms  of  nephritis  (Harrison,  Israel).  De- 
cortication is  supposed  to  act  by  removing  a  barrier — the  fibrous  capsule — to  the 
establishment  of  collateral  circulation,  promoting  a  free  supply  of  blood  to  the  kidney 
previously  impoverished  by  reason  of  the  inadequacy  of  its  vessels,  and  favoring  the 
absorption  of  excessive  interstitial  connective  tissue,  the  regeneration  of  renal  epi- 
thelium, and  the  removal  of  injurious  pressure  upon  the  uriniferous  tubules  (Edebohls). 
The  problems  presented  have  so  distinct  an  anatomical  bearing  that  their  mention 
here  does  not  seem  inappropriate. 

The  rich  blood-supply  of  the  kidney, — an  amount  of  blood  equal  in  weight  to 
that  of  the  organ  itself  flowing  through  it  each  minute  during  full  functional  activity 
(Tilden  Brown), — while  it  favors  congestive  conditions,  makes  total  embolic  necrosis 
— such  as  occurs  in  other  glands  confined  within  dense  capsules,  as  in  the  submaxillary 
salivary  gland  as  a  secondary  result  in  angina  Ludwigii  (page  553)  and  in  the  testi- 
cle in  some  cases  of  torsion  with  complete  venous  and  partial  arterial  obstruction 
(Gerster) — very  rare,  only  one  case  (Friedlander)  having  been  reported. 

Subparietal  injuries  to  the  kidney  are  common,  constituting  39  per  cent,  of 
visceral  lesions  resulting  from  contusions  of  the  abdomen  or  loin.  Rupture  of  the 
kidney  by  abdominal  or  lumbar  contusion  has  been  experimentally  shown  (Kiister) 
to  depend  upon  the  effect  of  a  force  (hydraulic)  acting  through  the  full  vessels  and 
the  pelvis  and  causing  the  kidney  to  burst,  usually  along  the  lines  radiating  from  the 
hilum  in  the  direction  of  the  tubules, — i.e.,  transverse  to  the  long  axis  of  the  kid- 
ney, towards  the  point  of  maximum  impact  of  the  lower  ribs,  the  opposing  resistance 
being  supplied  by  the  spine  (Morris).  There  is  reason  to  believe  that  the  direc- 
tion of  ruptures — radiating  from  the  hilum  to  the  periphery — is  influenced  by  the 
lines  of  least  resistance  indicating  the  original  absence  of  vascular  loops  and  of  their 
accompanying  connective  tissue  between  the  adjoining  lobules  of  which  the  fcetal 
kidney  is  composed. 

As  the  ribs  in  immediate  relation  to  the  kidney  are  the  eleventh  and  twelfth, 
which  are  rarely  fractured,  laceration  by  direct  impact  of  broken  ribs  is  relatively 
uncommon,  although  it  does  occur. 

Ruptures  may  much  more  rarely  be  produced  by  muscular  action  alone,  but  in 
such  cases  the  violent  muscular  effort  that  usually  adducts  the  ribs  and  forces  them 
against  the  kidney  and  towards  the  spine  is  almost  always  associated  with  forward 
or  lateral  bending  of  the  vertebral  column.  Forcible  anterior  flexion  of  the  spine,  as 


1892  HUMAN   ANATOMY. 

from  a  weight  falling  on  the  shoulders,  may  cause  compression  of  the  kidney  between 
the  lower  ribs  and  the  ilium,  and  is,  therefore,  not  infrequently  followed  by  haema- 
turia,  indicating  some  degree  of  rupture  of  kidney-substance. 

The  rupture  may  be  (a)  incomplete, — i.e.,  may  involve  the  parenchyma  alone, 
the  symptoms  in  these  relatively  rare  cases  being  those  of  excessive  renal  tension 
(  ride  supra},  the  constitutional  signs  of  hemorrhage  and  of  toxaemia  (usually  due  to 
urinary  extravasation  or  to  perinephric  cellulitis)  being  moderate  or  lacking  ;  (£) 
complete  internally, — into  the  pelvis  of  the  kidney, — a  more  common  condition,  in 
which  haematuria,  acute  hydronephrosis,  from  blocking  of  the  ureter  with  blood- 
clot,  and  vesical  irritability  are  prominent  symptoms,  and  the  constitutional  signs 
of  hemorrhage  and  toxaemia  are  more  marked  ;  (f)  complete  externally, — extending 
through  the  fibrous  capsule, — in  which,  in  addition  to  the  immediate  indications  of 
hemorrhage  and  the  later  symptoms  of  sepsis,  the  usually  free  urino-sanguineous 
effusion  into  the  loin  produces  marked  lumbar  swelling  and  tenderness  ;  or  (</)  com- 
plete,— running  from  the  pelvis  to  and  through  the  capsule, — in  which,  with  a  com- 
mingling of  the  above  symptoms,  there  is  often  profound  shock  which  may  terminate 
fatally. 

Rupture  of  the  kidney  extending  through  its  outer  surface  may  be  (e~)  transperi- 
toneal,  in  which  case  hemorrhage  is  apt  to  be  very  free,  as  there  is  no  surrounding 
pressure  to  resist  and  limit  the  extravasation,  and  fatal  peritonitis  will  almost  surely 
follow  unless  the  escaped  urine  is  normal,  acid,  and  sterile,  and  unless  both  it  and 
the  blood-clots  are  speedily  evacuated. 

When,  in  addition  to  the  laceration  of  the  kidney,  a  single  intraperitoneal  organ 
is  also  injured,  it  is  always  on  the  same  side  as  the  injured  kidney  (Watson).  The 
liver,  for  example,  or  the  ascending  colon,  may  be  involved  in  a  case  of  subparietal 
rupture  of  the  right  kidney,  but  never  the  spleen  or  the  descending  colon.  This  will 
readily  be  understood  from  a  consideration  of  the  frequency  with  which  the  cause  of 
rupture  is  a  forcible  forward  bending  of  the  vertebral  column,  the  kidney  being  caught 
in  the  angle  of  the  bend,  any  lateral  deviation  of  which  may  determine  the  side  on 
which  the  injury  occurs  and  the  involvement  of  liver  or  spleen  respectively. 

Transperitoneal  rupture  of  the  kidney  is  relatively  far  more  common  in  children 
than  in  adults.  Until  the  age  of  eight  or  ten  years  is  reached  the  kidney  lacks  its 
covering  of  perinephric  fat,  and  its  anterior  surface  lies  in  contact  with,  and  is  closely 
connected  to,  the  peritoneum.  A  rupture  involving  that  surface  is  therefore  practi- 
cally certain  to  open  the  peritoneal  cavity  and  is  likely  to  be  followed  by  excessive 
hemorrhage  and  septic  infection.  In  children  under  ten  years  of  age  85  per  cent, 
of  subparietal  ruptures  of  the  kidney  have  proved  fatal  (Maas). 

Wounds  of  the  kidney  must,  of  course,  involve  the  capsule  and  external  surface, 
so  that  hemorrhage  into  the  perinephric  tissues  is  an  almost  constant  symptom.  If 
the  wound  has  reached  the  calyces  or  the  pelvis,  urine  will  be  commingled  with  the 
blood.  Vesical  haematuria  may  be  prevented  by  the  presence  of  a  clot  in  the  ureter, 
or  by  the  actual  severance  of  that  tube.  If  large  vessels  have  been  opened,  the  blood, 
in  addition  to  reaching  the  bladder  or  the  perinephric  space  or  the  peritoneal  cavity, 
may  pass  upward  to  the  diaphragm,  downward  to  the  iliac  fossa,  or  along  the  spermatic 
vessels  to  the  external  abdominal  ring,  or  outside  of  the  ureter  to  the  perivesical  space, 
or  forward  between  the  two  layers  of  the  mesocolon.  In  a  reported  case  of  gunshot 
wound  in  which  the  missile  reached  the  kidney  from  above  downward,  injuring 
pleura  and  diaphragm  en  route,  the  concomitant  injury  to  the  lower  intercostal  nerves 
caused  rigidity  and  tenderness  of  the  anterior  abdominal  wall  and  gave  rise  to  the 
unfounded  suspicion  that  the  wound  was  transperitoneal. 

Anuria  due  to  reflex  effect  upon  the  normal  kidney  may  follow  a  rupture  or 
wound  or  even  calculous  irritation  of  the  other  kidney,  although,  as  a  rule,  calculous 
amiria  indicates  a  bilateral  lesion.  Both  kidneys  are,  of  course,  supplied  from  the 
same  segments — the  tenth,  eleventh,  and  twelfth  dorsal  and  first  lumbar — of  the 
spinal  cord.  Excessive  tension  from  compensatory  hyperaemia  has  been  thought  to 
explain  this  form  of  anuria,  and  the  theory  is  supported  by  the  facts  that  the  condi- 
tion sometimes  follows  a  nephrectomy,  the  remaining  kidney  being  normal,  and  that, 
whatever  its  cause,  it  is  often  relieved  by  nephrotomy  of  the  hitherto  sound  kidney. 
The  susceptibility  of  the  kidney  to  reflex  stimulation  or  inhibition  must  be  admitted, 


PRACTICAL   CONSIDERATIONS:    THE   KIDNEYS.  1893 

however,  as  cases  of  both  polyuria  and  threatened  suppression  have  followed  the 
gentle  and  partial  insertion  of  the  ureteral  catheter  (Tilden  Brown). 

Tumors  of  the  kidney  have,  as  a  class,  the  following  distinctive  anatomical 
characters,  which  have  been  well  summarized  by  Morris  : 

(a)  The  large  intestine  is  in  front  of  the  tumor.  Normally  the  right  kidney, 
unless  enlarged,  lies  a  little  way  from  the  lateral  wall  of  the  abdomen,  behind  and  to 
the  inner  side  of  the  ascending  colon  ;  not  in  close  contact  with  the  abdominal  wall 
and  outside  the  ascending  colon,  as  the  liver  does.  When  the  kidney  is  enlarged, 
the  ascending  colon  is  usually  placed  in  front  of  and  towards  the  inner  side  of  the 
tumor.  On  the  left  side  the  descending  colon  is  in  front  of,  and  inclines  towards  the 
outer  side  of,  the  kidney  below  ;  in  some  cases  coils  of  small  intestine  may  overlie  either 
right  or  left  tumor  if  the  enlargement  is  not  sufficient  to  bring  the  kidney  into  direct 
contact  with  the  front  abdominal  wall.  When  the  colon  is  empty  or  non-resonant, 
it  can  be  felt  as  a  roll  on  the  front  surface  of  the  tumor.  Bowel  is  not  thus  found  in 
front  of  splenic  tumors  and  very  rarely  in  front  of  a  tumor  of  the  liver. 

(^)  There  is  no  line  of  resonance  between  the  kidney  dulness  and  the  vertebral 
spine,  and  no  space  between  the  kidney  and  the  spinal  groove  into  which  the  fingers 
can  be  dipped  with  but  little  relative  resistance,  as  there  is  between  the  spleen  and 
the  spine. 

(c)  While  a  renal  tumor  fills  up  the  "hollow  of  the  back"  somewhat,  it  does 
not  often  protrude  or  project  backward.      Marked  posterior  projection  usually  indi- 
cates perinephric  swelling,  as  from  an  abscess  or  a  urino-sanguineous  effusion. 

(d)  A  kidney  tumor  can  sometimes  be  recognized  by  its  proneness  to  maintain 
an  outline  resembling  that  of  the  normal  kidney. 

(^)  A  kidney  swelling,  if  inflammatory  in  origin,  descends  less  in  inspiration 
than  does  a  splenic,  hepatic,  or  adrenal  swelling;  this  symptom  in  a  case  of  new 
growth  is  not  very  valuable,  as  the  renal  tumor  may  have  a  considerable  degree  of 
movement. 

(_/")  As  a  rule,  kidney  tumors  do  not  reach  the  mid-line,  do  not  invade  the 
bony  pelvis,  and  are  separated  from  the  hepatic  dulness  by  a  line  of  resonance.  If 
large  enough,  the  tumor  may  reach  the  anterior  abdominal  parietes  about  the  level 
of  the  umbilicus,  but  external  to  it. 

(£•)  In  large  renal  tumors  varicocele,  from  compression  or  distortion  and  dis- 
tention  of  the  spermatic  vein,  has  been  noticed  in  a  number  of  instances. 

Operations  upon  the  kidney  for  its  fixation  (nephrorrhaphy,  nephropexy),  for 
drainage  or  relief  of  tension  (nephrotomy),  for  the  extraction  of  a  calculus  (nephro- 
lithotomy),  or  for  the  establishment  of  collateral  circulation  (decortication),  are  almost 
invariably  done  through  the  loin. 

The  vertical  incision — on  a  line  about  an  inch  posterior  to  the  middle  of  the 
crest  of  the  ilium  and  running  from  that  level  to  the  twelfth  rib — does  not,  as  a  rule, 
give  sufficient  room,  divides  the  last  dorsal  and  the  lumbar  vessels  and  nerves,  and 
hence  jeopardizes  the  subsequent  integrity  of  the  ilio- costal  wall. 

The  oblique  incision  begins  about  a  half  inch  below  the  twelfth  rib  and  at  the 
outer  border  of  the  erector  spinae.  It  is  well  to  count  the  ribs  from  above  downward, 
as  when  the  twelfth  rib  is  rudimentary  it  may  not  project  beyond  the  edge  of  the 
erector  spinae  and  may  be  mistaken  for  the  transverse  process  of  the  first  lumbar 
vertebra.  In  such  circumstances  the  incision,  having  by  error  been  made  close  to 
the  edge  of  the  eleventh  rib,  has,  in  reported  cases,  opened  the  pleura. 

The  oblique  incision  is  extended  forward  for  three  or  four  inches  parallel  with 
the  twelfth  rib, — i.e.,  with  the  vessels  and  nerves  of  the  region.  The  skin  and  super- 
ficial fascia,  the  latissimus  dorsi,  and  the  external  and  internal  oblique  muscles  having 
been  divided  and  the  lumbar  aponeurosis  and  the  transversalis  fascia  severed,  a 
layer  of  fat  will  then  appear  or  will  bulge  into  the  incision  (perirenal  or  transversalis 
fat).  As  this  is  cut  through  or  separated  with  fingers  or  forceps,  a  layer  of  con- 
nective tissue  may  be  recognized — the  posterior  layer  of  the  perirenal  fascia — and 
then  a  second  layer  of  fat  (perinephric  fat,  capsula  adiposa),  which  is  sometimes  finer 
in  texture  and  more  distinctly  yellowish  (Morris),  and  which,  if  it  is  incised  or  torn 
through  and  drawn  into  the  wound,  will  present  a  funnel-shaped  opening  leading 
down  directly  to  the  kidney  (Gerota),  which  can  then  often  be  isolated  by  blunt 


1 894 


HUMAN   ANATOMY. 


dissection  with  the  finger,  and  either  stitched  in  place,  decapsulated,  or  opened,  in 
accordance  with  the  indications. 

It  may  be  noted  that  bleeding  from  the  separation  of  the  capsule  is  comparati\rely 
trifling;  and  that  if  the  kidney  itself  is  to  be  incised,  the  fact  that  its  blood-supply  is 
naturally  divisible  into  two  independent  segments — anterior  and  posterior — which 
are  completely  separated  by  the  renal  pelvis,  and  the  vessels  of  which  are  given  off 
from  the  main  trunk  of  the  renal  artery  (Hyrtl),  indicates,  as  the  line  of  safety,  the 
convex  posterior  or  outer  border.  When  the  pelvis  of  the  kidney  is  distended  with 
fluid,  a  white  line  on  that  border  (Brodel's  line)  is  said  to  indicate  the  relatively  avas- 
cular  area.  The  anterior  vascular  division  is  said  to  carry  three-fourths  of  the  arterial 
blood-supply  and  the  posterior  division  the  remaining  fourth  (Brodel),  so  that  in  the 
majority  of  cases  the  posterior  surface  of  the  kidney  would  furnish  the  lesser  quantity 
of  blood. 

For  removal  of  the  kidney  (nephrectomy)  the  oblique  incision  may  be  prolonged 
forward,  the  peritoneum  being  detached  and  pushed  in  that  direction  ;  or  a  vertical 
incision  running  downward  from  it  may  be  added  ;  or,  if  the  nephrectomy  is  to  be 
done  for  the  removal  of  an  exceptionally  large  tumor,  the  anterior  or  transperitoneal 
route  may  be  adopted  and  the  incision  made  in  either  the  linea  semilunaris  or  the 
linea  alba,  the  outer  layer  of  the  mesocolon  being  opened  to  gain  access  to  the  retro- 
peritoneal  space.  The  nerves  and  vessels,  as  they  enter  the  hilum  of  the  kidney,  the 
vein  lying  in  front,  constitute  the  ' '  pedicle. ' '  The  ureter  lies  more  posteriorly  and 
on  a  slightly  lower  plane.  The  irregularities  in  the  division^  distribution,  and  points 
of  entrance  of  the  renal  artery  should  be  remembered,  as  should  also — on  the  right 
side — the  proximity  of  the  vena  cava  during  the  separation  of  close  adhesions. 

In  all  the  lumbar  operations  upon  the  kidney  the  colon  may  present  in  the 
wound  after  the  transversalis  fascia  has  been  opened,  and  should  be  looked  for  and 
displaced  antero-externally  to  avoid  danger  of  wounding  it. 


THE   RENAL   DUCTS. 

The  duct  of  the  kidney — the  canal  which  receives  the  urine  as  it  escapes  from 
the  kidney  and  conveys  it  to  the  bladder — consists  of  a  short  dilated  and  sub- 
divided upper  segment,  the  renal  pelvis,  and  a  long,  narrow,  tubular  lower  segment, 

the  ureter.      Since  not  only 

FIG.  1614.  these  but  also  the  papillary 

ducts  of  the  kidney  are  de- 
veloped from  a  common  out- 
growth from  the  Wolffian 
duct,  the  renal  duct  stands 
in  most  intimate  relations 
with  the  renal  substance. 

The  pelvis  of  the 
kidney  (pelvis  rcnalis),  al- 
though beginning  and  lying 
chiefly  within  the  sinus,  ex- 
tends beyond  the  latter, 
passing  downward  to  be- 
come continuous  with  the 
ureter.  Its  widest  part,  just 
within  the  hilum,  presents  an 
unbroken  convex  postero- 
mesial  surface,  its  opposite 
side,  directed  towards  the 
renal  substance,  being  inter- 
rupted by  tin-  subdivisions 
of  the  pelvis.  These  include 
the  divisions  of  the  pelvis  into  an  nf>f)cr  and  a  lower  segment  (calyces  majores), 
extending  towards  the  respective  poles  of  the  kidney.  Each  of  these  segments 
receives  a  group  of  from  four  to  six  smaller  conical  passages,  the  calyces  or  infun- 


Depression  — 
on  calyx  re- 
ceiving   re- 
nal papilla 


Calyces 


Casts  obtained  by  corrosion,  showing  two  forms  of  renal  pelvis: 

A,  usual  tvpi-  ;    /.'.  \aiiation. 


THE    RENAL    DUCTS.  1895 

dibula  (calyces  minores),  that 'proceed  from  the  renal  substance,  where  they  surround 
the  papillae. 

The  latter  are  embraced  by  the  expanded  bases  of  the  conical  calyces,  the  walls 
of  which  are  intimately  blended  with  the  kidney-substance  around  the  sides  of  the 
free  part  of  the  papillae,  a  narrow  cleft  separating  the  latter  from  the  enclosing  calyx. 
The  epithelium  of  the  papillary  ducts  is  directly  continuous  with  that  lining  the 
calyx,  while  the  subepithelial  tissue  of  the  latter  blends  with  the  intertubular  renal 
stroma.  On  laying  open  the  calyx,  the  papilla  is  seen  as  a  conical  elevation  project- 
ing into  the  funnel-shaped  envelope  (Eig.  1598);  although  usually  enclosing  a  single 
papilla,  the  calyx  may  receive  two  or  even  more  such  projections. 

The  two  general  groups  of  calyces — an  upper  and  a  lower — open  into  the  two 
large  primary  subdivisions  {superior  and  inferior  pelvis")  that  join  to  produce  the 
main  compartment  of  the  pelvis.  The  lower  end  of  the  latter  emerges  through  the 
hilum  and  arches  downward  to  pass — about  midway  between  the  hilum  and  the 
inferior  pole  of  the  kidney — Insensibly  into  the  ureter;  exceptionally  this  junction 
is  marked  by  a  constriction  in  the  lumen  of  the  canal.  Although  surrounded  in  its 
upper  part  and  smaller  divisions  by  the  branches  of  the  renal  blood-vessels,  the  general 
position  of  the  pelvis  within  the  sinus  and  as  it  emerges  through  the  hilum  is  behind 
the  blood-vessels,  the  intervals  between  the  renal  duct  and  the  other  occupants  of 
the  sinus  being  filled  with  adipose  tissue.  On  the  right  side  the  lower  part  of  the 
pelvis  is  covered  in  front  by  the  second  part  of  the  duodenum  ;  on  the  left  by  the 
pancreas. 

The  Ureter. — Tfiis  part  of  the  renal  duct  is  a  flattened  tube  which  connects  the 
renal  pelvis  with  the  bladder.  It  lies  beneath  the  parietal  peritoneum,  embedded 
within  the  subserous  tissue  and  surrounded  by  fat,  and  descends  along  the  posterior 
abdominal  wall  to  the  pelvic  brim  ;  crossing  the  latter,  it  follows  the  lateral  wall  of 
the  pelvis,  curving  downward,  forward  and  finally  inward  along  the  pelvic  floor, 
to  reach  the  bladder.  The  general  direction  of  its  course  is  indicated  by  a  vertical 
line  on  the  surface  of  the  abdomen  drawn  from  the  junction  of  the  inner  and  middle 
thirds  of  Poupart's  ligament  (Tourneux).  The  average  length  of  the  undisturbed 
ureter  is  approximately  27  cm.  (10.5  in.),  the  left  duct  being  usually  about  one 
centimetre  longer  than  the  right  in  consequence  of  the  higher  position  of  the  corre- 
sponding kidney.  Apart  from  the  uncertainty  of  determining  just  where  the  pelvis 
ends  and  the  ureter  begins,  its  length  is  influenced  by  several  factors,  such  as  the 
level  of  the  kidneys  and  of  the  bladder,  the  descent  of  the  renal  pelvis,  body  height, 
and  sex,  so  that  considerable  variation  is  encountered  ;  the  excessive  figures  some- 
times given  are  probably  based  upon  measurements  of  the  ducts  after  removal  and 
abnormal  relaxation.'  The  diameter  of  the  ureter — from  4-5  mm. — is  not  uniform, 
since  at  certain  points,  corresponding  to  changes  in  the  direction  or  relations  of  the 
canal  (Solger),  constrictions  regularly  occur,  above  which  the  tube  exhibits  fusiform 
dilatations  or  spindles  (Schwalbe).  The  most  constant  narrowings  are  situated 
(i)  from  4-9  cm.  (1^-3^2  in.)  below  the  hilum,  at  which  point — the  upper  isthmus 
of  Schwalbe — the  diameter  of  the  canal  is  reduced  to  almost  3  mm.;  (2)  near  the 
pelvic  brim  as  the  duct  crosses  the  iliac  vessels  {lower  isthmus},  preceded  by  a  fusi- 
form enlargement  {chief  spindle")  ;  and  (3)  at  the  lower  end  of  the  ureter  as  the 
canal  penetrates  the  wall  of  the  bladder.  Since  its  course  and  relations  vary  in 
different  parts  of  its  path,  the  ureter  is  divided  for  description  into  an  abdominal  and 
a  pelvic  portion. 

The  abdominal  portion  (pars  abdominalis) — from  13-14 cm.  (about  5-5^  in.) 
in  length — begins  a  short  distance  below  the  hilum  and  descends  upon  the  anterior 
surface  of  the  psoas  magnus  muscle  and  its  fascia  towards  the  sacro-iliac  articulation, 
with  a  slight  inclination  towards  the  mid-line  (Fig.  1591).  The  distance  between  the 
two  ureters  at  their  upper  ends  is  about  9  cm.  (3^  in.)  and  at  the  pelvic  brim  about 
6  cm.  (2^/3  in.).  Just  before  reaching  the  latter  level  the  ureters  obliquely  cross 
the  common  iliac  vessels,  approximately  the  point  at  which  the  artery  divides  into  its 
external  and  internal  divisions,  or,  especially  on  the  right  side,  they  may  pass  over 
the  external  iliac  vessels  instead.  About  midway  in  their  course  to  the  pelvis  both 
ducts  are  crossed  in  front,  at  a  very  acute  angle,  by  the  spermatic  (or  ovarian)  ves- 
sels and  behind  and  obliquely  by  the  genito-crural  nerve.  The  right  ureter  passes 


1896 


HUMAN   ANATOMY. 


J2u-  Reflection 
-,-        of  calyx 
onto  renal 
papilla 


behind  the  descending  part  of  the  duodenum,  lies  to' the  right  of  the  inferior  vena 
cava,  which  it  approaches  and  even  touches  in  its  descent,  and  is  covered  by  the 
attachment  of  the  mesentery.  Above  the  left  ureter  may  be  covered  by  the  pancreas 
when  that  organ  is  unusually  broad,  and  below  it  is  crossed  by  the  attachment  of  the 
sigmoid  flexure. 

The  pelvic  portion  (pars  pelvina) — from  12-13  cm-  (5  m-)  m  length — lies 
against  the  lateral  wall  of  the  pelvis,  close  beneath  the  serous  membrane  embedded 
within  the  subperitoneal  tissue,  and  curves  downward  and  forward  to  about  the  level 
of  the  ischial  spine,  where  it  turns  inward  upon  the  visceral  layer  of  the  pelvic  fascia 
to  reach  the  dorsal  wall  of  the  bladder  (Fig.  1619).  In  its  descent  it  lies  in  front  of 
the  internal  iliac  artery  as  far  as  the  greater  sciatic  notch  (Merkel),  crosses  the  ob- 
literated hypogastric  artery  and  the  obturator  nerve  and  vessels  to  their  inner  side, 
and,  as  it  traverses  the  pelvic  floor,  is  surrounded  by  the  tributaries  from  the  vesical 
plexus  to  the  internal  iliac  vein  and  may  lie  upon  the  middle  and  inferior  vesical 

arteries.      The   ureter  is  crossed 

FIG.  1615.  on  its  inner  side  by  the  vas  defer- 

ens,  and  pierces  the  bladder-wall 
immediately  in  front,  or  under 
cover  of  the  anterior  part,  of  the 
seminal  vesicle  or  of  the  ampulla 
(  Fraenkel l ) .  The  space  between 
the  ureter  and  the  seminal  vesi- 
cle, which  when  the  bladder  is 
empty  may  be  considerable,  is 
filled  by  areolar  tissue  containing 
veins  and  fat.  The  relations  of 
the  ureter  to  the  bladder  are  pe- 
culiar, since,  in  addition  to  pene- 
trating the  latter  so  obliquely  that 
the  last  1 8  mm.  (|^  in- )  of  the 
renal  duct  are  embedded  within 
the  vesical  wall,  the  muscular  tis- 
sue of  the  latter  is  seemingly  pro- 
longed (page  1897)  over  the  ure- 
ter outside  the  bladder  for  some 
5  mm.  as  a  distinct  sheath  (Wal- 
deyer).  The  ureteral  orifices  on 
the  inner  surface  of  the  vesical 
wall  are  slit-like  and  valvular  in 
form  and,  in  the  contracted  condi- 
tion of  the  bladder,  about  2. 5  cm. 
apart,  thisdistance  being  increased 
twofold  or  even  more  when  that 
organ  becomes  distended. 

The  female  ureter  (Fig.  1622)  calls  for  special  description  on  account  of  the 
relations  of  its  pelvic  portion  to  the  generative  organs.  On  gaining  the  lateral  wall 
of  the  pelvis,  the  ureter  descends  in  close  proximity  to  the  unattached  border  of  the 
ovary  and  constitutes  the  postero-inferior  boundary  of  the  ovarian  fossa  (page  1986). 
On  the  pelvic  floor  the  ureter  enters  the  base  of  the  broad  ligament,  within  which 
duplicature  it  crosses  the  uterine  artery,  passes  between  the  veins  of  the  vesico- 
vaginal  plexus,  and  continues  downward  and  forward  in  the  vicinity  <>f  the  uterine 
cervix  to  the  vagina;  its  terminal  segment  lies  embedded  within  the  connective  tissue 
between  the  cervix  and  bladder,  close  to  the  anterior  vaginal  wall  for  a  distance  of 
from  1-1.5  cm->  where,  bending  somewhat  inward,  it  reaches  the  posterior  vesical 
wall,  which  it  pierces  obliquely  in  the  manner  above  described. 

Structure. — The  wall  of  all  parts  of  the  renal  duct  is   tin-  same  in  its  general 
construction  and  includes  three  layers,  (i)  the   mucous  membrane,  (2)  the  mus- 
cular tunic,  and  (3)  the  outer  fibrous  coat;  the  mucosa  and  the  muscular  layer  are 
1  Die  Samenblasen  der  Menschen,   Berlin,  1901. 


Renal 
blood- 
vessels 


Ureter 


Sagittal  section  through  sinus  of  child's  kidney,  showing  lower 
part  of  pelvis  and  commencement  of  ureter.     X  10. 


THE  RENAL    DUCTS. 


1897 


more  or  less  blended,  a  distinct  submucosa  being  wanting.  The  mucous  membrane 
is  clothed  with  "transitional"  epithelium  consisting  of  several  strata  of  cells,  the  su- 
perficial elements  being  plate-like  and  the  deepest  ones  irregularly  columnar.  The 
tunica  propria  constitutes  a  subepithelial  layer  of  fibre-elastic  tissue  which  blends  with 
the  subjacent  muscular  tunic.  Within  the  ureter  the  mucous  membrane  is  usually 
thrown  into  longitudinal  folds,  and  in  consequence  in  transverse  section  the  lumen 
of  the  canal  appears  stellate.  Neither  well-marked  papillae  nor  true  glands  are  pres- 
ent, although  in  places  the  subepithelial  tissue  invades  the  epithelium  and  subdivides 
the  latter  into  nest-like  groups  of  cells.  Occasional  aggregations  of  lymphoid  cells 
occur,  which  in  the  vicinity  of  the  calyces  sometimes  form  distinct  minute  lymph- 
nodules  within  the  mucosa  (Toldt).  On  the  papillae  the  epithelium  lining  the  renal 
duct  passes  uninterrupted  into  that  of  the  papillary  canals,  while  the  underlying  tunica 
propria  becomes  continuous  with  the  intertubular  renal  stroma.  The  muscular  tunic 
consists  of  bundles  of  the  involuntary  variety  disposed  as  a  thin  inner  longitudinal 
and  a  chief  external  circular  layer.  Within  the  renal  pelvis  and  its  larger  subdivisions 
both  layers  are  well  represented,  but  are  reduced  on  the  calyces  ;  at  the  junction  of 
the  latter  with  the  kidney  the  circular  muscle  increases  and  surrounds  the  papilla 
with  a  minute  sphincter-like  bundle  (Henle).  Except  in  the  upper  part  of  the  renal 


FIG.  1616. 


. 


Epithelium 


Mucous  coat,  thrown 
into  longitudinal  folds 


•&"~^  * -••  ;£>;  ; -\  .'-;<*»^' -'<£v 
';•.  ^i^y/*Mfi^&fc«:  CTJSs&im 


.Fibrous  coat 


Inner  longitudinal 
muscular  bundles 


Circular  muscular  bundles 


Transverse  section  of  ureter.    X  25. 


duct,  an  additional  imperfect  outer  longitudinal  layer  of  muscle  is  represented  by 
irregularly  scattered  bundles.  The  fibrous  coat,  or  tunica  adventitia,  composed  of 
bundles  of  fibrous  and  elastic  tissue,  invests  the  renal  duct  as  its  outer  tunic  and  con- 
nects it  with  the  surrounding  areolar  tissue.  At  the  kidney  the  outer  coat  of  the 
renal  duct  blends  with  the  tunica  fibrosa  that  invests  the  renal  substance  between  the 
calyces.  Beginning  several  centimetres  above  the  bladder,  the  adventitia  of  the 
ureter  is  strengthened  and  thickened  by  robust  longitudinal  bundles  of  involuntary 
muscle  that  follow  the  duct  to  its  vesical  orifice  and,  in  conjunction  with  the  fibrous 
tissue  in  which  they  are  embedded,  form  the  ureteral  sheath  (Waldeyer).  Accord- 
ing to  Disse,  this  muscle  belongs  to  the  wall  of  the  ureter  and  is  distinct  from  the 
musculature  of  the  bladder. 

Vessels. — The  arteries  supplying  the  different  segments  of  the  renal  duct  are 
derived  from  several  sources.  Those  distributed  to  the  pelvis  and  the  adjoining  part 
of  the  ureter  are  small  branches  from  the  renal  artery,  the  abdominal  portion  of  the 
canal  being  additionally  supplied  by  twigs  given  off  from  the  spermatic  (ovarian)  artery 
as  the  latter  crosses  the  duct  and  by  a  special  vessel  (a.  ureterica)  proceeding  from 
the  internal  or  common  iliac  artery  or  from  the  aorta  (Krause).  The  pelvic  portion 
receives  branches  from  the  middle  hemorrhoidal  or  the  inferior  vesical  arteries.  The 


1898  HUMAN   ANATOMY. 

vessels  from  these  several  sources  anastomose  and  produce  a  net-work  that  encloses 
the  canal  and  sends  twigs  that  break  up  into  capillaries  that  supply  the  coats  com- 
posing its  wall.  The  veins  begin  within  the  mucosa,  beneath  which  they  form  an  in- 
ternal plexus  that  communicates  with  a  wider-meshed  outer  plexus  within  the  fibrous 
coat,  from  which  tributaries  pass  to  the  internal  or  common  iliac  and  the  spermatic 
veins.  The  lymphatics  within  the  mucous  membrane  and  submucosa,  according  to 
Sakata,1  are  not  demonstrable  as  distinct  net-works,  but  as  such  are  seen  within  the 
muscular  tissue  and  on  the  surface.  The  lymph-trunks  from  the  middle  third  of  the 
ureter,  which  are  the  most  numerous,  pass  to  the  lumbar  nodes  ;  those  from  the  lower 
segment  are  tributary  to  the  internal  iliac  nodes  or  communicate  with  the  lymphatics 
of  the  bladder  ;  while  those  of  the  upper  part  either  empty  into  the  aortic  nodes  or 
join  the  renal  lymphatics. 

The  nerves  of  the  renal  duct,  derived  from  the  sympathetic  system,  accompany 
the  arteries  and  come  from  the  renal,  spermatic,  and  hypogastric  plexuses.  Within 
the  adventitia  they  form  a  plexus  containing  numerous  microscopic  ganglia,  the  largest 
of  which  are  at  the  upper  and  lower  ends  of  the  duct.  In  addition  to  the  fibres  sup- 
plying the  blood-vessels,  both  medullated  and  non-medullated  fibres  pass  to  the  mus- 
cular and  mucous  coats. 

Variations. — These  consist  most  often  in  more  or  less  complete  doubling  of  the  canal  on 
one  or  both  sides.  While  subdivision  of  the  pelvis  into  an  unusual  number  of  tubular  calyces 
is  rare,  its  cleavage  into  two  separate  compartments,  either  alone  or  in  correspondence  with 
doubling  of  the  ureter,  is  relatively  common.  The  division  may  be  so  complete  that  the  two 
resulting  ducts  open  into  the  bladder  by  separate  orifices.  The  termination  of  the  ureter  in 
the  seminal  vesicle — a  malformation  occasionally  encountered — depends  upon  the  close  embryo- 
logical  relations  (page  2039)  which  exist  between  the  two  structures.  While  congenital  absence 
of  the  kidney  is  not  necessarily  associated  with  entire  absence  of  the  ureter,  failure  of  the 
latter  to  develop  implies  incompleteness  or  absence  of  the  kidney,  since  a  part  of  the  duct- 
system  of  the  latter  is  derived  from  the  primitive  ureter  (page  1937). 

PRACTICAL   CONSIDERATIONS:    THE   URETERS. 

The  ureters  may  be  multiple  from  a  fused  kidney,  or  two  or  more  ureters  may 
spring  from  the  pelvis  of  a  single  kidney,  indicating  a  defect  in  the  development  of 
the  primary  fcetal  ureter.  The  separate  ureters  may  unite  at  any  point  between  the 
kidney  and  the  bladder  or  may  remain  distinct  throughout. 

Marked  obliquity  of  insertion  of  the  ureter  into  the  pelvis  (page  1896)  may 
leave  on  a  lower  level  than  the  ureteral  origin  a  pouch  of  the  pelvis — corresponding 
to  the  lowest  of  its  original  subdivisions — which,  when  it  fills  with  urine,  compresses 
the  upper  end  of  the  ureter,  narrows  its  lumen,  and  favors  the  production  of  hydro- 
nephrosis.  This  condition  may  also  occur  in  either  the  second  or  third  of  the  fol- 
lowing variations  in  the  upper  end  of  the  ureter  thus  described  by  Hyrtl  :  (a)  there 
is  no  pelvis,  but  the  ureter  divides  into  two  branches  without  dilatation  at  the  point 
of  division,  each  branch  having  a  calibre  a  little  larger  than  that  of  the  ureter  ;  (£) 
there  is  a  pelvis, — that  is,  a  funnel-shaped  dilatation  at  the  point  of  division  ;  the 
upper  portion  is  the  smaller,  and  terminates  in  three  short  calyces  ;  the  lower  and 
more  voluminous  portion  terminates  in  four  or  five  calyces  ;  (V)  there  is  only  half  a 
pelvis, — that  is,  the  lower  branch  divides  and  is  funnel-shaped,  forming  a  narrow 
pelvis,  which  terminates  in  one,  two,  or  three  short  calyces;  while  the  upper  is  not 
dilated,  and  extends  to  the  upper  portion  of  the  kidney  as  a  continuation  of  the 
ureter  (Fenger). 

The  lower  end  of  the  ureter  may  in  the  male,  as  a  rare  anomaly,  open  within 
the  boundaries  of  the  sphincter. vesicse,  or  into  the  prostatic  urethra,  or  into  the 
seminal  vesicle,  ejaculatory  duct,  or  vas  deferens. 

As  the  opening  is  never  anterior  to  the  compressor  urethrae,  incontinence  of 
urine  does  not  result,  but  interference  with  its  free  exit  causes  ureteral  dilatation  and 
hydronephrosis. 

In  the  female  the  ureter  may  open  into  the  urethra,  vagina,  or  vestibule. 
There  may  be  incontinence  of  urine,  or  again  such  obstruction  as  to  'cause  uretero- 
renal  dilatation. 

1  Archiv  f.  Anat.  u.  Kntwick.,  1903. 


PRACTICAL    CONSIDERATIONS  :    THE   URETERS.  .1899 

These  anomalies  are  readily  understood  by  reference  to  the  embryology  of  the 
ureter  (page  1937). 

Ureteral  calculus  is  most  often  arrested  (<z)  at  a  point  from  4-6.5  cm.  (i^j— 
2^  in.)  from  the  renal  pelvis  ;  (£)  at  the  point  where  the  ureter  crosses  the  iliac 
artery;  (c)  at  the  junction  of  the  pelvic  and  vesical  portions;  (X)  at  its  vesical 
orifice.  At  these  places  normal  narrowings  are  found  in  the  majority  of  subjects. 
The  symptoms  of  calculus  impacted  in  the  ureter  are  difficult  of  distinction  from  those 
of  stone  occupying  or  engaging  in  the  pelvis  of  the  kidney,  but  it  may  be  said  that 
if,  after  the  usual  phenomena  of  renal  colic,  vesical  symptoms  are  marked  and  per- 
sistent, and  especially  if  they  are  associated  with  slight  haematuria  and  no  calculus 
is  detected  in  the  bladder,  the  existence  of  stone  in  the  ureter  should  be  strongly 
suspected.  The  bladder-symptoms — irritability,  frequent  urination,  tenesmus — will 
be  more  marked  the  nearer  the  situation  of  the  stone  to  the  lower  end  of  the  ureter. 
The  relations  of  the  nerve-supply  of  the  ureter  with  that  of  the  bladder  and  the  geni- 
talia  and  with  the  great  intra-abdominal  plexuses  sufficiently  explain  the  chief  sub- 
jective symptoms  of  calculus. 

Complete  and  sudden  blocking  of  the  ureter  by  a  calculus  often  produces  an 
acute  hyclronephrosis,  the  symptoms  of  which  may  overshadow  those  directly  referri- 
ble  to  the  region  of  impaction.  The  muscular  walls  of  the  ureter  are  capable  of 
strong  contraction,  and,  indeed,  the  painful  "colicky"  symptoms  attending  the 
passage  of  a  stone  along  the  ureter  would  better  be  described  as  ' '  ureteral' '  rather 
than  ' '  renal. ' ' 

At  present  the  diagnosis  of  ureteral  stone  and  its  localization  are  to  be  made  with 
much  certainty  by  the  X-rays. 

In  an  effort  to  find  tenderness  which,  in  the  presence  of  the  above  symptoms, 
might  locate  a  stone,  or  might  determine  the  region  of  rupture  or  other  ureteral 
injury,  or  might  confirm  a  diagnosis  of  ureteritis  or  of  tuberculous  infiltration  (as  a 
result  of  ascending  or  descending  infection),  it  should  be  noted  that  the  beginning 
of  the  ureter,  the  lower  extremity  of  the  kidney,  and  the  level  of  origin  of  the 
spermatic  or  ovarian  artery  are  all  approximately  defined  byTourneur's  point,  which 
is  situated  at  the  intersection  of  a  transverse  line  between  the  tips  of  the  twelfth  ribs, 
with  a  vertical  line  drawn  upward  from  the  junction  of  the  inner  and  middle  thirds  of 
Poupart's  ligament  ;  the  course  of  the  abdominal  portion  of  the  ureter  corresponds 
to  the  same  vertical  line.  Tourneur  considers  its  direction  vertical  from  the  border 
of  the  kidney  down  to  the  pelvic  brim,  over  which  it  passes  4^  cm.  (2  in.)  from 
the  median  line.  The  exact  location  of  this  point  is  the  intersection  of  a  horizontal 
line  drawn  between  the  anterior  superior  iliac  spines  and  a  vertical  line  passing 
through  the  pubic  spine.  Morris  thinks  that  this  point  would  usually  be  too  low 
and  too  far  inward,  and  that  the  junction  of  the  upper  and  middle  thirds  of  the 
line  for  the  iliac  arteries  would  better  indicate  the  point  of  crossing  of  the  ureter 
over  the  artery.  At  this  point,  under  favorable  circumstances,  a  dilated  or  tender 
ureter  may  be  felt  by  gentle,  steady  pressure  backward  upon  the  abdominal  wall  until 
the  resistant  brim  of  the  pelvis  is  reached.  The  vesical  portion  of  the  ureter  can  be 
palpated  in  man  through  the  rectum.  Guyon  has  called  attention  to  the  exquisite 
sensitiveness  of  this  portion  of  the  ureter  upon  rectal  exploration  in  cases  of  stone, 
even  when  the  calculus  is  located  high  up.  In  woman  vaginal  examination  permits 
the  palpation  of  the  ureter  to  an  extent  of  two  or  even  three  inches,  as  it  runs  beneath 
the  broad  ligament  in  close  relation  to  the  antero-lateral  wall  of  the  vagina  (Cabot, 
Fenger). 

Morris  gives  the  following  directions  for  palpating  the  lower  extremity  of  the 
ureter  : 

(a)  Vaginal  Palpation. — The  part  of  the  ureter  which  is  capable  of  being  felt 
through  the  vaginal  wall  is  about  three  inches  or  a  little  less,  or,  roughly  speaking, 
about  a  quarter  of  the  whole  length  of  the  duct.  It  is  that  part  which  extends  from 
the  vesical  orifice  of  the  ureter  backward,  outward,  and  upward  to  the  base  of  the 
broad  ligament  and  towards  the  lateral  wall  of  the  true  pelvis. 

It  is  in  the  superior  third  of  the  anterior  and  lateral  wall  of  the  vagina  that  the 
examination  must  be  made,  and  it  is  at  the  part  between  the  level  of  the  internal 
orifice  of  the  urethra  and  the  anterior  fornix,  where  the  tissues  are  very  lax,  that  the 


HUMAN   ANATOMY. 

ureter  will  be  most  readily  felt.  The  examination  should  be  made  very  gently,  and 
the  ringer  should  be  passed  comparatively  lightly  over,  not  pressed  firmly  against, 
the  vaginal  surface.  The  ureter  courses  about  midway  between  the  cervix  uteri  and 
the  wall  of  the  pelvis,  and  by  hard  pressure  the  ureter  is  displaced  before  the  finger 
in  a  direction  towards  the  pelvic  wall.  The  uterine  artery  or  the  muscular  fibres  of 
the  obturator  internus  or  levator  ani  (Sanger)  should  not  be  mistaken  for  the  ureter. 

(£)  Rectal  Palpation. — The  lower  extremity  of  the  ureter,  when  occupied  by  a 
foreign  body  or  in  a  state  of  disease,  can  be  felt  through  the  rectum  in  the  male,  but 
less  readily  than  through  the  vagina  in  the  female.  A  calculus  impacted  in  the  lower 
end  of  the  ureter  has  been  located  and  removed  through  the  rectum.  It  is  through 
the  antero-lateral  wall  of  the  bowel  and  a  little  higher  than  the  level  of  the  base  of  the 
vesicula  seminalis  that  we  feel  for  the  ureter.  The  pulp  of  the  finger  should  be 
directed  towards  the  back  of  the  bladder  and  pushed  as  far  as  possible  beyond  the 
upper  edge  of  the  prostate  ;  afterwards  the  finger-pulp  should  be  turned  towards  the 
lateral  wall  of  the  pelvis,  and  whilst  still  pushed  as  far  as  possible,  it  should  traverse 
the  wall  of  the  fectum  forward  and  backward.  The  examination  is  difficult,  and  if 
the  prostate  is  much  enlarged  the  detection  of  the  ureter  is  impossible.  The  normal 
ureter  is  not  likely  to  be  distinguished,  even  if  the  perineum  be  thin  and  the  prostate 
normal. 

(c)  Vesical palpation — through  the  dilated  urethra  of  the  female — may  disclose 
dilatation,  oedema,  prolapse,  or  infiltration,  inflammatory  or  tuberculous,  of  the 
vesical  end  or  orifice  of  the  ureter,  or  may  reveal  the  presence  of  an  impacted 
calculus. 

Wounds  or  siibparietal  injuries  of  the  ureter,  unassociated  with  other  intra- 
abdominal  lesions,  are  rarer  than  similar  injuries  of  the  kidney,  decrease  in  frequency 
from  above  downward,  and,  on  account  of  the  bony  protection  afforded  it,  are  very 
uncommon  in  the  pelvic  portion  of  the  ureter. 

The  upper  portion  may  be  crushed  against  the  transverse  process  of  the  first 
lumbar  vertebra  (Turner),  or  so  stretched  as  to  tear  or  sever  it  (Fenger). 

Unless  the  escape  of  urine  from  an  external  wound  occurs,  the  symptoms  are 
merely  those  of  ureteral  irritation,  usually  with  slight  transient  haematuria  and  the 
evidence  of  slow  urinary  extravasation  superadded. 

After  extraperitoneal  rupture  or  wound  the  swelling  due  to  extravasated  urine 
and  subsequent  cellulitis  might  be  recognized  in  the  loin  or  detected  by  rectal  or 
vaginal  examination  in  the  pelvis.  Longitudinal  wounds  gape  less  (and  therefore 
heal  more  readily)  than  transverse  wounds,  on  account  of  the  longitudinal  disposition 
of  the  thicker  internal  layer  of  muscular  fibres. 

Tumors  of  the  ureters  are  almost  unknown  as  primary  conditions,  but  consider- 
ation of  the  relations  of  the  ureter  (page  1895)  will  show  that  it  may  be  pressed  upon 
by  growths  or  involved  in  inflammatory  processes  originating  in  the  caecum  or  in  the 
ascending  or  descending  colon.  Its  pelvic  portion  is  more  exposed  to  pressure  than 
is  the  abdominal  on  account  of  the  counter-resistance  of  the  pelvic  walls,  and  here  it 
may  be  compressed  by  fecal  masses  in  the  sigmoid  or  rectum,  by  iliac  aneurism,  or 
by  growths  of  the  uterus,  ovary,  or  Fallopian  tube,  or  may  become  involved  in  dis- 
ease of  the  appendix  when  it  occupies  a  pelvic  position,  or  of  the  bladder  or  seminal 
vesicles. 

The  tough,  resistant  character  of  the  walls  of  the  tube,  the  laxity  of  the  con- 
nective tissue  in  which  it  lies,  the  layer  of  loose  fat  that,  in  part  of  its  course, 
surrounds  and  protects  it  in  well-nourished  individuals  (Luschka),  and  its  rich  vas- 
cular supply  (from  the  renal,  spermatic  or  ovarian,  and  vesical  arteries)  enable  it  to 
resist  or  avoid  injury  or  to  undergo  speedy  repair.  It  is  thus  possible  to  separate  it 
extensively  from  surrounding  structures  during  operations  with  little  or  no  risk  of 
necrosis. 

The  oblique  course  of  the  ureter  through  the  vesical  wall  subjects  it  to  pressure 
when  the  bladder  contracts,  or  when  it  becomes  rigid  from  arterio-sclerotic  disease. 
Frequency  of  urination  alone  has  been  thought  competent — by  the  constantly  recur- 
ring obstruction  to  the  entrance  of  urine  into  the  bladder — to  produce  ureteral  dila- 
tation and  hydronephrosis.  As  its  obliquity  leaves  it  on  the  inner  aspect  covered  by 
mucous  membrane  only,  and  as  the  outer  aspect  is  covered  by  the  muscular  layer  of 


THE    BLADDER.  1901 

the  bladder-wall,  it  can  be  understood  that  incision  of  the  mucosa  over  the  intra- 
parietal  part  of  the  ureter,  for  the  purpose  of  extracting  a  calculus,  involves  little 
risk  of  pelvic  cellulitis  from  extravasation  of  urine.  It  cannot  be  said  that  there  is 
no  risk,  as  in  one  case  a  peritoneal  fistula  and  death  resulted  (Thornton). 

Operations  upon  the  ureter  are  frequent  for  the  extraction  of  a  calculus  (uretero- 
lithotomy);  or  the  extirpation  (ureterectomy)  of  an  infected  ureter  (tuberculous  or 
pyogenic)  either  at  the  same  time  with  its  kidney  (nephro-ureterectomy)  or  at  a  later 
period;  or  for  the  closure  of  wounds  or  fistulae,  or  the  relief  of  stricture,  or  the 
implantation  of  the  distal  end  of  the  ureter — after  removal  of  a  diseased,  injured,  or 
obliterated  portion — into  the  bladder,  rectum,  or  elsewhere. 

The  anatomical  factors  relating  to  these  operations  cannot  here  be  described, 
but  it  may  be  said  generally  that  whenever  it  is  possible  the  extraperitoneal  route  is 
selected  to  lessen  the  danger  of  peritonitis,  and  that  the  oblique  lumbar  incision 
employed  to  reach  the  kidney  (page  1893)  will,  if  prolonged  downward  and  forward 
parallel  to  Poupart's  ligament  and  to  the  outer  edge  of  the  rectus,  give  access  to 
the  whole  abdominal  ureter  and  to  the  upper  part  of  its  pelvic  portion.  Cabot  has 
shown  that  the  ureter  is  bound  to  the  external — or  under — surface  of  the  peritoneum 
by  fibrous  bands,  and  that  when  that  membrane  is  stripped  up  from  the  posterior 
abdominal  wall  the  ureter  accompanies  it.  He  found  that  the  relation  of  the  ureter 
to  that  part  of  the  peritoneum  which  becomes  adherent  to  the  spine  is,  within  a  slight 
range  of  variation,  fairly  constant,  the  ureter  lying  just  outside  the  line  of  adhesion. 
Hence,  if  the  surgeon  has  stripped  up  the  peritoneum  and  has  come  down  to  that 
point  where  it  refuses  to  separate  readily  from  the  spinal  column,  he  will  find  the 
ureter  upon  the  stripped-up  peritoneum  at  a  short  distance  outside  of  this  point. 
On  the  left  side  the  distance  from  the  adherent  point  to  the  ureter  is  from  one-half 
an  inch  to  an  inch,  while  on  the  right  side  it  is  somewhat  greater,  owing  to  the 
ureter  being  displaced  to  the  outside  by  the  interposition  of  the  vena  cava  between 
it  and  the  spine.  It  should  be  remembered  that  the  peritoneum  adherent  to  the 
abdominal  portion  of  the  ureter  is  very  thin  and  may  be  torn  in  an  attempt  to 
separate  it. 

After  the  ureter  dips  down-  into  the  true  pelvis  it  is  less  easily  located  because 
it  has  no  fixed  relation  to  a  bony  landmark.  Cabot  has  suggested,  that  osteoplastic 
resection  of  the  sacrum  would  give  access  to  this  lower  pelvic  portion  of  the  ureter. 
In  women  it  can  often  be  reached  through  the  vagina.  The  ureter  is,  of  course, 
accessible  transperitoneally  through  its  whole  route. 

THE   BLADDER. 

The  bladder  (vesica  urinaria) — the  reservoir  in  which  the  urine  is  received  from 
the  renal  ducts  and  retained  until  discharged  through  the  urethra — is  a  muscular  sac, 
lined  with  mucous  membrane,  situated  in  the  anterior  part  of  the  pelvic  cavity  imme- 
diately behind  the  symphysis  pubis.  Its  form  and  size,  and  likewise  to  a  considerable 
extent  its  relations,  vary  with  the  degree  of  distention,  so  that  in  describing  the 
organ  the  condition  of  expansion  must  be  taken  into  account.  When  containing  little 
fluid  and  hardened  in  situ,  the  general  shape  of  the  bladder  is  pyriform,  presenting  a 
free,  slightly  convex  superior  surface,  covered  with  peritoneum  and  projecting  into 
the  pelvic  cavity,  and  a  distinctly  convex  non-peritoneal  inferior  surface,  attached 
by  areolar  tissue  to  the  pubic  symphysis  and  the  pelvic  floor  upon  which  it  rests. 
The  urethra,  surrounded  by  the  prostate,  emerges  from  the  most  dependent  portion 
of  the  lower  surface,  behind  which  point  the  latter  ascends  to  join  the  upper  surface 
along  the  indistinct  posterior  border.  The  part  of  the  bladder  between  the  urethra 
and  the  posterior  border  constitutes  \hefundus  or  base  (fundus  vesicae),  which  in  the 
male  is  in  relation  with  the  seminal  ducts  and  vesicles  and  the  recto-vesical  pouch 
and  is  directed  towards  the  rectum,  and  in  the  female  is  attached  to  the  anterior 
vaginal  wall.  In  the  empty  organ  the  superior  and  inferior  surfaces  blend  along  the 
sides  in  the  convex  lateral  borders  ;  anteriorly  these  meet  at  the  apex  or  summit  (vertex 
vesicae),  from  which  a  median  fibrous  band  (ligamentum  urabilicale  medium)  that  rep- 
resents the  urachiis — the  obliterated  segment  of  the  intra-embryonic  part  of  the  allan- 
tois — extends  to  the  umbilicus  along  the  abdominal  wall.  The  body  (corpus  vesicae) 


1902 


HUMAN   ANATOMY. 


includes  the  uncertain  part  of  the  bladder  between  the  apex  and  the  fundus.  The 
term  neck  is  sometimes  applied  to  the  region  -immediately  surrounding  the  urethral 
orifice,  although  a  distinct  neck  in  the  usual  sense  does  not  exist.  The  intersections 

of  the  lateral  and  posterior  bor- 

FIG.  1617.  clers    mark    approximately    the 

points  at  which  the  ureters  enter 
the  vesical  wall.  As  pointed  out 
by  Dixon,1  the  attachments  of 
the  ureters  correspond  to  the  lat- 
eral angles  of  the  trigonal  figure 
that  the  empty  bladder  resembles 
when  viewed  from  above,  the 
apex  being  the  anterior  angle. 


Apex,  from  which  passes  the 
rachus 


Ampulla 

Seminal  vesicle 

Urinary  bladder,  slightly  distended  and  hardened  in  situ, 
from  formalin  subject ;  viewed  from  above. 


FIG.  1618. 


The  cavity  of  the  strongly  con- 
tracted bladder,  as  seen  in  sagittal 
sections  of  organs  hardened  in  situ, 
is  little  more  than  a  cleft  bounded 
above  and  below  by  the  thick  vesi- 
cal walls  and  below  continuous  with 
the  urethra  ;  in  the  vicinity  of  the 
ureteral  orifices,  however,  the  lumen 
broadens  into  the  lateral  recesses 
which  are  never  entirely  effaced 
(Luschka).  The  modifications  of  the 

lumen  sometimes  seen,  more  frequently  in  women  and  especially  in  organs  not  hardened  in  situ, 
in  which  the  superior  surface  is  more  or  less  sunken  and  in  consequence  the  vesical  cavity  is 
crescentic  or  V-shaped  in  mesial  section,  are  to  be  regarded  as  the  result  of  post-mortem  change 
and  not  as  representing  conditions  existing  during  life,  since  normal  contractions  of  the  muscular 
vesical  sac  are  little  calculated  to  produce  such  forms.  The  empty  bladder  measures  in  length 
from  5-6  cm.  (2-2)^  in.),  in  breadth  from  4-5  cm.  (1^-2  in.),  and  in  thickness  from  2-2.5  cm. 
(#-i  in.)  (Waldeyer). 

In  the  distended  bladder  the  demarcation  between  the  surfaces  above  described  is  gradually 
effaced  until,  in  extreme  expansion,  the  organ  assumes  a  general  ovoid  form  in  which  the  supe- 
rior and  inferior  surfaces  and  the  fundus  are  uninterruptedly  continuous  and  all  indication  of 
the  borders  is  completely  obliterated.  Such  extreme  changes,  however,  accompany  only  exces- 
sive and  unusual  distention,  the  alterations  taking  place  under  normal  conditions,  with  a  prob- 
able maximum  capacity  of  from  250-300 
cc.  (7^-9  fl.  oz.),  being  much  less  radical. 
When  the  bladder  begins  to  fill,  the  region 
first  to  be  affected  is  the  posterior  and  lower 
lateral  portions  of  the  organ,  expansion  oc- 
curring more  rapidly  in  the  transverse  than 
in  the  longitudinal  axis  (Uelbet),  which  for 
a  time  retains  a  generally  horizontal  direc- 
tion. With  increasing  distention  the  blad- 
der invades  the  paravesical  fossae  at  its  sides, 
behind  is  pressed  against  the  seminal  vesi- 
cles, which  in  the  empty  condition  of  the 
bladder  extend  laterally  as  transverse  wings 
and  touch  the  vesical  wall  only  with  their 
inner  ends,  and  encroaches  upon  the  recto- 
vesical  pouch  and  the  rectum.  The  con- 
dition of  the  latter  also  influences  the  direc- 
tion of  the  vesical  expansion,  since  the  filled 
rectum  decreases  the  available  space  behind 
and  forces  the  bladder  upward  and  forward. 
Not  until  the  distention  has  progressed  to  a 
considerable  degree  does  the  antero-inferior 
segment  lengthen  and  undergo  upward  displacement  and  the  apex  rise  much  above  the  pubic 
symphysis  ;  and  only  after  the  distention  greatly  exceeds  physiological  limits  and  becomes  very 
excessive  does  the  bladder  altogether  lose  its  pyriform  contour  and  become  symmetrically  ovoid. 
The  highest  point  of  the  greatly  enlarged  organ  no  longer  corresponds  with  the  attachment  of 

1  Anatom.  Anzeiger,  Bd.  xv.,  1899. 


Left  ureter 


Vasa  deferentia 

Superior  surface 
i 

Apex 


Cut  edge  of 
peritoneum 

Prostate  — ^r1-  Latero-inferior 

gland,  pos-          ;     /     .  ^j^^  surface 

terior   sur- 
face 

•^•^^ 

1'iosUiU-  gland,  lateral  surface 

Preceding  preparation  viewed  from  side,  showing  relations 
of  bladder,  associated  ducts,  and  prostate. 


THE    BLADDER. 


1903 


the  urachus,  but  lies  farther  above  and  behind,  since  the  antero-inferior  wall  always  remains 
shorter  than  the  postero-superior.  The  condition  of  the  rectum  and  the  pressure  exerted  by 
the  abdominal  viscera  influence  in  no  slight  degree  the  form  and  position  of  the  distended 
bladder,  since,  when  these  factors  are  both  unfavorable  to  unhampered  expansion,  the  inferior 
surface  and  fundus  are  depressed  to  a  greater  degree  than  when  the  bowel  is  empty  and  the 
superior  surface  is  little  impressed  by  the  overlying  organs,  the  entire  bladder  assuming  a  more 
vertical  position  and  the  ovoid  form  being  modified  (Merkel).  Under  pathological  conditions 
the  bladder  may  suffer  such  enormous  expansion  that  it  reaches  as  high  as  or  even  above  the 
umbilicus  and  occupies  a  large  part  of  the  abdominal  cavity.  Owing  to  its  intimate  attachment, 
the  part  of  the  inferior  surface  united  to  the  prostate  and  the  pelvic  floor  undergoes  least  change 
both  as  to  form  and  relations. 

FIG.   1619. 


External  iliac 
artery 

External  iliac 

vein 
Deep  epigastric 

artery 
Spermatic  vessels 

Internal  abdominal 
ring 


Obliterated, 
hypogastric  artery 

Urachus 


Suspensory 
ligament  of  peni: 

Internal  urethral  orifice — 

Fatty  tissue 
containing  veins 


Pectinate  septum — I 


Spongy  urethr; 


Navicular  fossa 


Internal  iliac 
vessels 


Ureter,  pelvic 
portion 


Vas  deferens 


Ureter,  entering 
bladder 


Seminal  vesicle 
Rectum 

Ejaculatory  duct 

Prostatic  urethra 
and  utricle 

Prostate 


Membranous  urethra 
Bulb  of  cavernous  body 

Bulbous  urethra 


Scrotum 
Dissection  of  sagittally  cut  pelvis,  showing  relations  of  organs  after  fixation  by  formalin  injection. 

The  capacity  of  the  bladder  during  life  so  obviously  depends  upon  individual 
peculiarities  and  habit  that  it  is  impossible  to  more  than  indicate  approximately  the 
quantity  of  fluid  that  ordinarily  induces  a  desire  for  the  evacuation  of  the  vesical 
contents.  This  quantity — the  physiological  capacity  of  the  bladder — may  perhaps  be 
said  to  vary  from  175-250  cc.  (6-9  fl.  oz. ),  700  cc.  (24  fl.  oz. )  representing  the 
maximum  for  the  normal  organ  (Disse).  Under  pathological  conditions,  as  in 
paralysis  of  the  vesical  wall,  the  bladder  may  contain  from  3-4  litres  without  rupture. 
As  a  means  of  determining  its  capacity  during  life,  estimates  based  upon  artificial 
distention  of  the  bladder  after  death  are  worthless,  since  the  maximum  resistance 


1904 


HUMAN   ANATOMY. 


FIG.  1620. 


without  rupture  of  the  dead  vesical  wall  is  much  less  than  that  of  the  living  organ. 
The  bladder  in  the  female  has  a  smaller  capacity  than  in  the  male. 

The  interior  of  the  bladder  varies  in  appearance  according  to  the  condition 
of  the  mucous  membrane.  The  latter  is  loosely  attached  to  the  muscular  tunic 
by  submucous  areolar  tissue,  and  hence  in  the  contracted  state  of  the  organ  is  thrown 
into  conspicuous,  mostly  longitudinal  plications  ;  when  the  bladder  is  filled  these 
folds  are  effaced  and  the  inner  surface  appears  smooth.  With  excessive  distention, 
the  interlacing  bundles  of  the  muscular  wall  may  be  stretched  so  far  apart  that  the 
submucous  tissue  and  the  mucosa  may  occupy  the  interstices  so  formed,  an  irregular 
pitting  or  pouching  of  the  mucous  lining  resulting.  A  triangular  area,  the  trigonum 
vesiccs,  included  between  the  urethral  orifice  in  front  and  theureteral  openings  behind, 
is  distinguished  by  its  smoothness  under  all  degrees  of  contraction,  even  in  the 
empty  bladder  being  only  indistinctly  wrinkled.  Over  the  trigone  (Fig.  1620) 
the  submucosa  is  absent  and  the  mucous  membrane  rests  directly  upon  a  compact 
muscular  stratum  in  which  the  closely  placed  transverse  bundles  of  the  vesical  wall  are 
reinforced  by  radiating  fibres  continued  from  the  ureteral  sheath  (page  1897).  The 
slightly  curved  posterior  border  or  base  of  the  trigonum  is  marked  by  a  band-like 
elevation,  the/>/zra  uretericce,  or  iorus  uretericus  of  Waldeyer,  that  unites  the  open- 
ings of  the  renal  ducts.  This  ridge,  best  marked  at  its  outer  ends,  is  less  evident 
and  often  interrupted  near  the  mid-line,  and  is  subject  to  much  individual  variation. 

Its  production  depends  upon  the  eleva- 
tion of  the  mucosa  and  muscular  tissue 
in  consequence  of  the  oblique  path  of 
the  ureters  through  the  vesical  wall. 
The  margins  of  the  trigonum — lateral 
as  well  as  posterior — are  raised  and  its 
central  area  is  somewhat  depressed 
towards  the  urethral  opening .  The  lat- 
ter (orificium  urethrae  interntim)  occu- 
pies the  apex  of  the  trigonum,  and  is 
usually  not  circular,  but  crescentic, 
owing  to  the  projection  of  its  posterior 
border  as  a  small  median  elevation,  the 
vesical  crest  (uvula  vesicae),  that  ex- 
tends from  the  apical  end  of  the  trigone 
into  the  urethra  to  become  continuous 
with  the  urethral  crest  in  the  prostatic 
part  of  the  canal.  The  vesical  crest 
consists  of  a  thickening  of  the  mucous  membrane  enclosing  bundles  of  muscular 
tissue.  When  hypertrophied,  as  it  not  infrequently  is  in  aged  subjects,  this  fold 
may  form  a  valvular  mass  that  occludes  the  urethral  orifice.  The  anterior  wall  of 
the  latter  is  commonly  marked  by  low  converging  folds  continuous  with  the  longi- 
tudinal plications  of  the  urethral  mucous  membrane. 

The  ureteral  orifices  are  usually  slit-like  in  form  (4-5  mm.  long),  obliquely  trans- 
verse in  direction,  but  may  be  oval,  round,  or  punctiform  (Disse).  The  lateral  bor- 
der of  the  opening  is  guarded  by  a  valve-like  projection  (valvula  ureteris)  that  forms 
part  of  the  nodular  elevation  that  is  produced  by  the  wall  of  the  ureter.  The  median 
margin  of  the  opening  is  embedded  in  the  interureteral  plica.  The  urethral  and  the 
two  ureteral  openings  mark  the  angles  of  an  approximately  equilateral  triangle,  the 
sides  of  which,  in  the  contracted  condition  of  the  bladder,  measure  from  2-2.5  cm.; 
when  the  organ  is  expanded,  this  distance  increases  to  from  3. 5-5  cm.  or  even  more. 
The  urethral  orifice  lies  from  1.75—2.2  cm.  in  front  of  the  base  of  the  trigone  when  the 
latter  is  contracted.  Immediately  behind  the  vesical  'triangle  the  posterior  bladder- 
wall  presents  a  slight  depression,  the  rctrotrigonal  fossa  or  fovea  retroureterica 
(Waldeyer),  that  corresponds  to  the  "bas-fond"  of  the  French  writers.  When 
abnormally  enlarged  and  pouch-like,  as  it  often  is  in  advanced  life  when  associated 
with  an  enlarged  prostate,  this  fossa  becomes  of  practical  importance  (page  1981). 

Peritoneal  Relations. — The  superior  surface  of  the  empty  or  but  slightly 
filled  bladder  is  completely  covered  by  peritoneum  as  far  as  the  lateral  and  posterior 


Interior  of  lower  segment  of  partly  distended  and  hardened 
bladder,  viewed  from  above  and  behind. 


THE   BLADDER.  1905 

borders.  On  each  side  the  serous  covering  passes  from  the  organ  to  line  the  para- 
vesical  fossa,  the  sickle-shaped  depression  that  separates  the  contracted  bladder  from 
the  adjacent  pelvic  wall.  In  front  these  side  folds,  the  lateral  false  ligaments,  meet 
at  the  vesical  apex,  where  they  cover  the  fibrous  band  of  the  urachus  and  are  reflected 
onto  the  anterior  abdominal  wall  as  the  anterior  false  ligament  (ligamcntura  umbiliculc 
medium).  An  uncertain  fold,  the  plica  I'esicalis  transi'crsa,  often  crosses  the  other- 
wise smooth  upper  surface  of  the  bladder.  This  peritoneal  ridge,  sometimes  repre- 
sented by  two  or  more  low  wrinkles,  extends  laterally  to  be  lost  either  on  the  pelvic 
wall  or,  passing  over  the  pelvic  brim,  towards  the  internal  abdominal  ring.  Dixon  ' 
found  the  fold  well  represented  in  the  male  foetus,  and  inclines  to  the  view  that  its 
production  is  connected  with  a  drag  on  the  peritoneum  incident  to  the  formation  of 
the  inguinal  pouches.  Behind  the  peritoneum  passes  from  the  posterior  border  of 
the  empty  bladder  over  the  upper  end  of  the  seminal  vesicles  and  the  vasa  deferentia, 
to  form  a  horizontal  crescentic  shelf-like  fold  (plica  recto vesicalis)  from  1-1.5  cm- 
wide,  that  extends  from  the  bladder  backward,  embracing  the  rectum  and  ending  at 
the  sacrum  on  either  side  of  the  gut  (Fig.  1619). 

Since  this  duplicature  includes  parts  of  the  seminal  ducts  and  vesicles,  Dixon  and  Birming- 
ham 3  have  suggested  for  its  lateral  and  backward  extensions,  which  contain  bundles  of  invol- 
untary muscle  (tn.  rectovesicalis)  attached  to  the  sacrum  and  rectum,  the  appropriate  name, 
sacro-genital folds,  and  pointed  out  their  correspondence  to  the  utero-sacral  folds  in  the  female 
(page  2007).  The  median  part  of  the  shelf-like  plica,  conspicuous  behind  the  empty  bladder, 
but  more  or  less  obliterated  on  the  distended  organ,  overhangs  the  lowest  part  of  the  peritoneal 
recess,  the  recto-vesical  fossa,  that  intervenes  between  the  rectum  and  the  seminal  vesicles  and 
ampullae  of  the  vasa  deferentia,  and  towards  which  the  fundus  of  the  bladder  is  directed.  In 
recognition  of  these  relations,  the  anterior  wall  of  this  recess  being  in  direct  relation  with  the 
seminal  tracts,  the  authors  last  mentioned  propose  to  call  this  depression  the  recto-genital  fossa, 
— a  term  alike  applicable  to  both  sexes,  since  the  relations  of  the  rectum  to  the  uterus  in  the 
pouch  of  Douglas  in  the  female  are  similar.  All  other  parts  of  the  bladder,  including  the 
postero-inferior  (fundus)  and  the  antero-inferior  surfaces,  are  entirely  devoid  of  peritoneal 
covering.  In  the  female  the  serous  membrane  passes  from  the  posterior  border  of  the  bladder 
onto  the  anterior  uterine  wall,  the  shallow  utero-vesical fossa  intervening.  Occasionally  a  corre- 
sponding depression  exists  in  the  male  as  a  slight  indentation  between  the  posterior  vesical  wall 
and  the  seminal  vesicles  (Dixon). 

With  the  changes  of  form  and  position  which  the  bladder  undergoes  when  it  becomes  dis- 
tended are  associated  alterations  in  its  peritoneal  relations.  These  include  the  gradual  obliter- 
ation of  the  upper  part  of  the  recto-vesical  fossa,  along  with  the  shelf-like  fold,  and  the  elevation 
of  the  line  of  peritoneal  reflection  at  the  sides,  so  that  the  lateral  false  ligaments  no  longer  reach 
the  pelvic  floor,  but  pass  from  the  lateral  wall  of  the  pelvis  directly  to  the  superior  surface  of  the 
bladder,  from  which  the  plica  transversa  has  disappeared.  Anteriorly  the  relations  of  the  serous 
covering  are  also  affected,  since  with  the  rise  of  the  bladder  above  the  level  of  the  symphysis 
the  peritoneum  is  carried  upward  and  a  suprapubic  non-peritoneal  area  becomes  progressively 
more  extensive  until,  in  extreme  distention,  a  space  measuring  vertically  from  8-9  cm.,  or  about 
2,l/i  in.,  may  be  uncovered. 

Fixation. — The  attachments  of  an  organ  so  subject  to  considerable  alterations 
in  size  and  form  as  is  the  bladder  must  obviously  provide  for  such  changes  as  well 
as  the  maintenance  of  a  more  or  less  definite  position.  The  ' '  ligaments ' '  of  the 
bladder  are  conventionally  described  as  tnie  andjfa&e,  under  the  latter  being  included 
the  peritoneal  folds  (above  described)  that  pass  from  the  organ  to  the  adjacent  ab- 
dominal and  pelvic  walls.  The  sacro-genital  folds  were  formerly  sometimes  called 
the  posterior  false  ligaments.  From  the  manifest  instability  of  the  relations  and 
attachments  of  the  peritoneum  incident  to  distention  and  contraction,  it  is  evident  that 
such  peritoneal  folds  can  contribute  little  to  the  definite  support  or  fixation  of  the 
bladder  ;  hence  those  parts  of  the  organ  possessing  a  serous  covering  are  movable. 
The  inferior  surface,  on  the  contrary,  is  comparatively  fixed  on  account  of  its  close 
relations  to  the  pelvic  floor  (and  in  the  male  to  the  prostate)  and  the  presence  of 
fascial  bands  or  true  ligaments.  The  latter  are  derived  from  the  pelvic  fascia,  which 
in  the  vicinity  of  the  bladder  presents  a  stout,  glistening,  band-like  thickening  (arcus 
tendineus)  that  on  each  side  stretches  from  the  posterior  surface  of  the  symphysis,  a 

1  Journal  of  Anatomy  and  Physiology,  vol.  xxxiv.,  1900. 

2  Journal  of  Anatomy  and  Physiology,  vol.  xxxvi.,  1902. 


1906 


HUMAN   ANATOMY. 


short  distance  above  its  lower  border,  backward  to  the  ischial  spine  (page  1899). 
On  either  side  of  the  mid-line  the  anterior  ends  of  these  tendinous  arches  pass  as 
strong  fascial  bands,  the  pubo-prostatic  ligaments,  from  the  symphysis  to  the  prostate, 
blending  with  its  capsule,  and  thence  continue  to  the  inferior  surface  of  the  bladder, 
where  they  are  lost  in  the  outer  fibrous  coat  of  the  vesical  wall.  In  the  female  these 
fascial  bands  pass  directly  to  the  bladder  as  the  anterior  true  ligaments.  After  leaving 
the  symphysis,  the  tendinous  arches  send  expansions — the  lateral  true  ligaments — to 
the  side  of  the  bladder,  which  materially  assist  in  fixing  the  organ. 

The  cleft  left  between  the  medial  borders  of  the  two  levator  ani  muscles  is  occupied  in  the 
male  by  the  rectum  and  prostate  and  in  the  female  by  the  rectum,  vagina,  and  urethra,  over 
some  of  which  organs  (rectum,  vagina,  and  prostate)  the  pelvic  fascia  covering  the  upper  sur- 
face of  the  levator  ani  muscles  (fascia  diaphragma  pelvis  superior)  sends  more  or  less  extensive 
investments  and  thus  binds  them  to  the  pelvic  floor. 

Additional  support  is  afforded  by  more  or  less  definite  processes  of  muscular  tissue  pro- 
longed from  the  bladder  to  adjacent  structures  ;  those  passing  within  the  arcus  tendineus  to  be 
attached  on  either  side  to  the  back  of  the  symphysis  constitute  the  pubo-vvsical  musc/es,  while 
others,  the  recto-vesical  muscles,  extend  backward  to  blend  with  the  rectal  wall. 


FIG.  1621. 


Symphysis  pubis 


Pubo-vesical  space,  cleaned  out 


Arcus  tendineus  _  _ 
fasciae  pelvis 

White  line, 
(arcus  tendineus  in. 
levatoris  ani) 


Pubo-vesical  ligament 

Arcus  tendineus 
^Levator  ani  muscle 
^Obturator  canal 

White  line 


Bladder,  partly  distended 

Anterior  part  of  pelvis  of  female,  viewed  from  above  and  behind,  showing  relations  of  bladder 
to  pelvic  fascia ;  bladder  has  been  partly  distended  and  pulled  backward. 


Hetween  the  lateral  pubo-prostatic  ligaments,  the  symphysis,  and  the  bladder  lies  a  deep 
recess  (fovea  pubovesicalis),  traversed  by  the  dorsal  vein  of  the  penis  and  filled  with  fatty  areolar 
tissue,  the  floor  of  which  is  formed  by  the  fusion  of  the  pelvic  fascia  with  the  transverse  ligament 
of  the  perineum.  Above  the  level  of  the  pubo-prostatic  ligaments  lies  the  preresical  space,  or 
space  of  Retzius,  which  is  bounded  in  front  by  the  anterior  wall  of  the  pelvis  below  and  the 
transversalis  fascia  above,  and  behind  by  a  thin  membranous  condensation  of  areolar  tissue,  the 
fascia  umbilico-vesicalis  (Karabeuf),  that  passes  from  the  pelvic  floor  over  the  prostate  and 
bladder  to  the  abdominal  wall,  to  fuse  with  the  transversalis  fascia  at  a  variable  distance  In-low 
the  umbilicus.  Laterally  the  boundaries  of  this  space,  filled  with  areolar  tissue  loaded  with  fat, 
are  uncertain,  since  when  distended,  as  when  the  seat  of  an  abscess,  it  may  embrace  the  sides  of 
the  bladder  below  and  extend  above  as  far  as  the  obliterated  hypogastric  arteries.  Under  usual 
conditions,  however,  the  space  may  be  regarded  as  confined  chiefly  between  the  antero-inferior 
surface  of  the  bladder  and  the  adjacent  anterior  pelvic  wall. 

Relations. — When  empty,  or  containing  only  a  small  quantity  of  fluid,  the 
bladder  possesses  two  general  surfaces,  a  superior  and  an  inferior.  The  anterior  two- 
thirds  of  the  the  latter  rests  upon  the  prostate  and  the  pelvic  floor,  and,  according  to 
Dixon,1  when  hardened  ///  situ  presents  a  rounded  median  ridge  which,  together  with 
the  ureters,  outlines  two  forward,  upward,  and  outward  sloping  infero-lateral  areas. 
These  rest  upon  the  pelvic  floor  and  the  posterior  surface  of  the  pubis,  separated 
1  Journal  of  Anatomy  and  Physiology,  vol.  xxxiv.,  1900. 


THE   BLADDER. 


1907 


from  the  latter  by  the  retropubic  pad  of  fat  from  .5-1  cm.  thick.  The  fundus — the 
posterior  part  of  the  inferior  surface  included  between  the  urethral  opening  and  the 
posterior  border — is  in  contact  with  the  median  ends  of  the  seminal  vesicles  and  of 
the  ampullae  of  the  seminal  ducts,  by  which  structures  and  their  musculo-adipose 
bed  the  bladder  is  separated  from  the  anterior  wall  of  the  recto- vesical  fossa. 

The  internal  orifice  of  the  urethra  lies  immediately  above  the  prostate,  usually 
from  1.2-2.5  cm.  (X~i  m- )  above  the  plane  passing  through  the  lower  border  of  the 
symphysis  and  the  lower  end  of  the  sacrum  ;  the  distance  from  the  upper  border  of 
the  symphysis  to  the  orifice  measures  from  5-6  cm.  (2-2^  in.)  ;  in  the  horizontal 
plane  it  lies  from  2. 5-3  cm.  behind  the  symphysis,  its  nearest  point  on  the  latter 
being  about  2  cm.  (Disse).  These  measurements  are  influenced  by  changes  in  the 
position  of  the  inferior  surface,  being  shortest  when  the  empty  bladder  is  pushed 
upward. 

FIG.  1622. 


Ureter 

Suspensory 
ligament  of  ovary 

Fallopian  tube — ll_ 


Round  ligament 
Ovary 

Obliterated 
hypogastric  artery 

Uterus 


Symphysis  pubis 


External  ureth 
orifice  in  vestibi 


1 

,'  Vi 

_Utero-sacral  fold 

—  Rectum 

.  External  os  uteri 

Bottom  of  recto- 
uterine  pouch 


.Vagina 


Perinea]  body 
Sagittal  section  of  female  pelvis  of  formalin  subject. 

Laterally  the  paravesical  fossa"  intervene  between  the  empty  bladder  and  the 
sides  of  the  pelvis.  In  the  contracted  condition  the  superior  surface  usually  lies 
below  the  plane  of  the  pelvic  inlet,  the  entire  bladder  being  within  the  anterior  third 
of  the  pelvis  and  close  to  the  pelvic  floor.  This  tipper  surface,  covered  with  peri- 
toneum, is  in  contact  with  coils  of  small  intestine  which,  when  the  rectum  is  empty, 
may  occupy  a  part  of  the  recto-vesical  fossa. 

In  the  distended  bladder  the  relations  of  the  inferior  surface  suffer  little  change  on  account 
of  the  intimate  attachments  of  the  vesical  wall  to  the  prostate  and  to  the  fixation  to  the  pubis 
afforded  by  the  pubo-prostatic  (pubo-vesical)  ligaments  and  enclosed  muscle.  The  postero- 
inferior  surface,  expanding  backward  and  outward,  comes  into  more  extensive  and  closer  rela- 


igo8 


HUMAN   ANATOMY. 


Uterus 


•Uiachus 


Bladder 


Symphysis  pubis 
Urethra 


tions  with  the  seminal  vesicles  and  ducts.  The  condition  of  the  rectum  markedly  influences  the 
degree  to  which  the  distending  bladder  rises  above  the  symphysis,  since,  when  the  bowel  is  empty, 
and  hence  more  intrapelvic  space  is  available,  the  bladder  gains  a  lower  suprapubic  level  than 
when  its  ascent  is  favored  by  a  distended  rectum.  With  the  elevation  of  the  vesical  apex  above 
the  level  of  the  symphysis,  the  bladder  acquires  a  temporary  relation  with  the  anterior  abdominal 
w:all  in  front,  and  its  sides,  in  case  of  marked  distention,  may  come  nearly  or  actually  into  con- 
tact with  the  vasa  deferentia,  the  obliterated  hypogastric  arteries,  and  the  obturator  vessels  and 
nerves,  as  these  structures  lie  along  the  pelvic  wall  embedded  within  the  fat-laden  subperitoneal 
tissue. 

The  bladder  in  the  female  lies  lower  within  the  pelvis  than  in  the  male,  chiefly  in  conse- 
quence of  the  absence  of  the  prostate,  and  when  empty  never  quite  reaches  the  level  of  the  upper 
border  of  the  symphysis.  When  distended,  therefore,  it  less  often  rises  into  the  abdomen, 
since  the  capacity  of  the  normal  organ  in  the  female  is  somewhat  less  than  in  the  male.  The 
fundus,  or  postero-inferior  surface,  is  firmly  united  by  connective  tissue  with  the  anterior  vaginal 
wall  and  sometimes  the  lower  part  of  the  uterus.  Where  reflected  from  the  anterior  surface  of 
the  uterus  onto  the  bladder,  the  peritoneum  lines  the  shallow  utero-vesical  fossa  and  then  con- 
tinues over  the  superior  vesical  surface.  Upon  the  latter  rests  the  body  of  the  uterus,  rising  or 
falling  with  the  expansion  or  contraction  of  the  bladder-wall,  but  normally  remaining  in  contact, 

— a  relation  predisposing  to  the  production 

FIG.   1 623.  of  the  concave  or  sunken  condition  of  the  su- 

Rectum  perior  surface  not  infrequently  seen  in  frozen 

sections  of  the  female  pelvis. 

The  infantile  bladder  differs  both  in  form 
and  position  from  the  adult  organ.  Since 
the  greater  part  of  the  bladder  represents  a 
persistent  and  dilated  portion  of  the  intra- 
embryonic  segment  of  the  allantois,  its  fcetal 
form  is  essentially  tubular.  In  the  new-born 
child  (Fig.  1623),  in  both  sexes  alike,  the 
bladder  is  spindle-shaped  and  extends  from 
about  midway  between  the  umbilicus  and 
the  symphysis  to  the  level  of  the  pelvic  brim, 
its  anterior  surface  being  in  contact  with  the 
abdominal  wall.  Only  the  lower  pole  of  the 
infantile  bladder,  corresponding  to  the  ure- 
thral  orifice,  lies  slightly  below  the  upper 
border  of  the  symphysis,  the  body  lying 
entirely  within  the  abdomen,  lateral  and 
posterior  surfaces  being  undifferentiated. 
Leaving  the  anterior  abdominal  wall,  the 
peritoneum  completely  invests  the  posterior 
surface  of  the  bladder,  as  well  as  the  semi- 
nal vesicles  and  the  ampullae  of  the  seminal 
ducts,  before  passing  onto  the  rectum.  The 

bottom  of  the  recto-vesical  fossa  lies  often  below  the  level  of  the  urethral  orifice,  which  does  not 
come  into  relation  with  the  pelvic  floor.  In  the  new-born  female  child  the  uterus  is  situated  rela- 
tively high  and  comes  into  contact  with  the  bladder,  while  the  vagina  does  not,  only  touching 
the  urethra.  The  reflection  of  the  peritoneum  to  form  the  utero-vesical  fossa  varies  in  position, 
and  when  high,  as  it  often  is,  may  leave  a  part  of  the  young  bladder  unprovided  with  a  serous 
covering.  Coincident  with  the  descent  of  the  bladder,  associated  with  the  growth  and  expansion 
of  the  pelvis,  its  posterior  wall  increases  more  rapidly  than  the  anterior,  this  inequality  resulting 
in  the  production  of  a  fundus  that  gradually  approaches  the  pelvic  floor.  According  to  Disse,1 
the  descent  of  the  young  bladder  is  rapid  during  the  first  three  years,  slower  from  the  fourth 
to  the  ninth  year,  between  which  and  puberty  little  change  occurs.  Succeeding  this  period  of 
rest  the  bladder  renews  its  descent,  and  by  the  twenty-first  year  has  gained  its  definite  position 
on  the  pelvic  floor.  Before  the  third  year  the  empty  bladder  always  remains  above  the  symphy- 
sis ;  by  the  ninth  year  it  has  sunken  below  that  level,  but  when  distended  the  apex  rises  within 
the  abdomen.  During  descent  the  non-peritoneal  area  on  the  posterior  surface  progressively 
increases,  the  serous  investment  in  general  extending  farther  downward  in  the  male  than  in  the 
female  child.  Persistence  of  infantile  relations  often  ace.  units  f<  >r  variations  observed  in  the  adult. 

Structure. — The  bladder  consists  essentially  of  a  muscular  sac  lined  with  mucous 
membrane  and  covered  on  its  upper  surface  with  peritoneum,  a  layer  of  connective  tis- 
sue loosely  uniting  the  mucous  and  muscular  coats.  From  within  outward,  four  coats 

1  Anatomische  Hefte,  Hd.  i.,  1892. 


— Vagina 


Sagittal  section  through  pelvis  of  new-horn  female  child, 

hardened  in  formalin,  showing  infantile  form 

and  suprapubic  position  of  bladder. 


THE    BLADDER. 


1909 


FIG.  1624. 


Epithelium 


Mucous  mem- 
brane, thrown 
into  folds 


are  distinguishable, — the  mucous,  the  submucous,  the  muscular,  and  the  incomplete 
serous. 

The  mucous  coat  varies  in  thickness  with  both  location  and  the  degree  of  con- 
traction. Over  the  vesical  trigone,  where  always  comparatively  smooth,  it  is  thin, 
measuring  only  about  .  i  mm. ;  where  strongly  wrinkled  by  contraction,  it  may  attain 
a  thickness  of  over  2  mm.  The  mucosa  resembles  closely  that  of  the  renal  duct, 
consisting , of  a  fibro-elastic  tunica  propria  covered  with  transitional  epithelium.  The 
latter  includes  several  strata  of  cells,  the  deepest  of  which  are  columnar,  the  middle 
irregularly  polygonal  or  club-shaped,  and  the  inner  plate-like,  their  deeper  surface 
fitting  over  and  between  the  underlying  elements.  Although  glands  may  be  con- 
sidered as  absent,  tubular  depressions  are  occasionally  found  in  the  vicinity  of  the 
trigone  which  are  regarded  by  some  (Kalischer,  Brunn)  as  true  glands.  Waldeyer 
has  suggested  that  these  structures  may  be  interpreted  as  representing  in  a  sense 
urethral  glands  displaced  during  the  development  of  the  vesical  trigone. 

The  submucous  coat,  loose  and  elastic,  permits  free  gliding  of  the  mucous  over 
the  muscular  tunic  when  readjustment  becomes  necessary  during  contraction.  Com- 
posed of  bundles  of  fibrous  tissue  interwoven  with  elastic  fibres,  it  supports  the 
blood-vessels  and  nerve-plexuses,  and  contains  numerous  bundles  of  involuntary 
muscle.  It  is  not 
sharply  defined 
from  the  adjoin- 
ing coats,  but 
blends  with  the 
stroma  of  the  mu- 
cosa on  the  one 
side  and  extends 
between  the 
tracts  of  the  mus- 
cular coat  on  the 
other.  Beneath 
the  trigonum  a 
distinct  submu- 
cous layer  is 
wanting  or  re- 
placed by  a  sheet 
of  muscular  tis- 
sue. 

The  muscu- 
lar coat,  thicker 
than  the  mucosa 
and  compara- 
tively robust,  va- 
ries according  to 

the  condition  of  the  bladder,  being  thin  during  distention  and  very  thick  in  strong 
contraction,  when  it  may  measure  as  much  as  1.5  cm.  The  bundles  of  involuntary 
muscle  are  arranged  in  two  fairly  distinct  chief  layers, — a  thin  outer  longitudinal  and 
a  thick  inner  circular.  Inside  the  latter,  and  virtually  within  the  submucosa,  lies  an 
incomplete  additional  layer.  The  longitudinal  bundles,  best  developed  on  the  upper 
and  lower  surfaces,  do  not  constitute  a  continuous  sheet,  but  interlace,  leaving  inter- 
fascicular  intervals  which  are  occupied  by  connective  tissue.  In  the  vicinity  of  the 
prostate  extensions  of  the  outer  layer  are  attached  to  the  anterior  pelvic  wall  as  the 
pubo-vesical  muscles  ;  others  pass  backward  to  blend  with  the  intestinal  wall  as  the 
recto-vesical  muscles,  while  from  the  apex  bundles  are  prolonged  into  the  urachus. 
The  circular  layer,  although  more  robust  and  uniform  than  the  outer,  is  weak  and 
imperfect  over  the  trigonal  region,  and  in  both  sexes  is  well  developed  only  after 
attaining  the  level  of  the  internal  ureteral  orifices  (Disse).  Towards  the  apex  of  the 
bladder  the  bundles  of  the  circular  layer  assume  an  oblique  and  less  regular  dispo- 
sition. The  innermost  layer — that  within  the  submucosa — is  represented  by  isolated 
and  indefinite  muscular  bundles  that  are  blended  with  the  connective  tissue.  Over 


Obliquely  cut 
longitudinal 
bundles 


Section  of  wall  of  bladder,  under  very  low  magnification, 
showing  general  disposition  of  coats.    X  12. 


HUMAN   ANATOMY. 

the  vesical  trigone,  however,  this  layer  becomes  condensed  and  forms  a  compact 
transverse  muscular  sheet  that  is  closely  united  to  the  overlying  mucous  membrane 
and,  in  conjunction  with  the  muscular  tissue  of  the  urethra,  surrounds  the  beginning 
of  that  canal  with  a  constrictor-like  tract,  the  internal  vesical  sphincter. 

The  outer  fibrous  coat  of  the  vesical  wall  is  strongest  over  the  inferior  surface, 
where  it  receives  reflections  from  the  pelvic  fascia;  towards  the  apex  and  beneath  the 
peritoneum  it  is  less  definite  and  often  intermingled  with  adipose  tissue.  Over  the 
postero-inferior  surface  in  the  male  it  is  fused  with  the  fibrous  tissue  surrounding  the 
seminal  vesicles  and  ducts,  and  in  the  female  is  blended  with  the  anterior  vaginal  wall. 

Vessels. — The  arteries  supplying  the  bladder  are  chiefly  the  superior  and 
inferior  vesical,  from  the  anterior  division  of  the  internal  iliac  ;  these  are  reinforced 
by  branches  from  the  middle  hemorrhoidal,  as  well  as  by  small  twigs  from  the  internal 
pudic  and  the  obturator  arteries.  The  superior  vesical  supplies  the  upper  segment 
of  the  bladder  and  sends  small  branches  along  the  urachus.  The  inferior  vesical 
divides  into  two  or  more  branches  which  are  distributed  to  the  infero-lateral  and 
postero-inferior  surfaces.  In  addition  to  twigs  to  the  region  of  the  trigone,  others 
pass  to  the  prostate,  seminal  vesicles,  and  ducts.  On  gaining  the  bladder,  the  vesical 
branches  anastomose .  and  enclose  that  organ  in  an  arterial  net-work  from  which 
twigs  enter  the  muscular  coat  and  break  up  into  capillaries  for  its  supply.  Others 
penetrate  the  muscular  tunic  and  within  the  submucosa  form  a  net-work  from  which 
arterioles  pass  inward  for  the  supply  of  the  mucous  membrane. 

The  veins  do  not  accompany  the  arteries,  but  form  a  submucous  plexus  that 
drains  the  mucous  membrane  and  empties  into  a  muscular  plexus  which,  in  turn,  is 
received  by  an  external  subperitoneal  plexus.  From  the  latter  the  blood  from  the 
entire  organ  passes  into  the  large  prostatico-vesical  plexus  at  the  sides  of  the  bladder 
and  thence  into  the  tributaries  of  the  internal  iliac  veins.  With  the  exception  of  the 
smaller  ones  on  the  inferior  surface,  all  the  vesical  veins  possess  valves  (Fenwick). 

The  lymphatics  of  the  bladder  begin  as  a  close-meshed  net-work  within  the  mus- 
cular coat,  according  to  Gerota,1  being  absent  within  the  mucous  membrane.  Out- 
side the  muscular  coat  they  form  a  wide-meshed  subperitoneal  plexus,  those  from  the 
apex  and  body  coursing  downward  and  laterally  and  those  from  the  fundus  upward. 
Leaving  the  sides  of  the  bladder,  the  efferent  channels,  chiefly  in  company  with  the 
arteries,  pass  to  the  internal  iliac  lymph-nodes  and  to  those  situated  at  the  bifurca- 
tion of  the  aorta.  Along  the  path  of  the  lymphatics  on  the  antero-inferior  surface  of 
the  bladder  Gerota  describes  one  or  two  very  small  nodes  as  usually  present. 

The  nerves  of  the  bladder  include  both  sympathetic  and  spinal  fibres.  The 
former,  distributed  chiefly  to  the  muscular  tissue,  are  from  the  vesical  plexuses,  which, 
as  subordinate  divisions  of  the  pelvic  plexuses,  lie  at  the  sides  of  the  bladder. 
The  sympathetic  fibres  accompany  the  arteries  and  are  joined  by  the  vesical  branches 
from  the  sacral  plexus  derived  from  the  third  and  fourth,  possibly  also  the  second, 
sacral  spinal  nerves.  The  principal  trunks  reach  the  bladder  in  the  vicinity  of  the 
ureters,  the  trigonal  region  receiving  the  most  generous  nerve-supply  and  the  apical 
segment  the  fewest  fibres.  Within  the  outer  fibrous  coat  the  larger  nerves  divide 
into  smaller  branches  that  are  connected  with  ganglia,  especially  in  the  neighborhood 
of  the  ureters,  from  which  twigs  enter  the  muscular  tunic  and  break  up  into  smaller 
ones  bearing  terminal  microscopic  ganglia  before  ending  in  the  muscle.  Other 
branches  penetrate  the  submucosa,  where  they  form  plexiform  enlargements  contain- 
ing numerous  minute  ganglia,  from  which  fine  twigs  proceed  to  the  mucosa  to  end, 
according  to  Retzius,  between  the  epithelial  cells.  In  general  the  sensibility  of  the 
normal  bladder  is  comparatively  slight,  the  trigonal  region,  especially  at  the  ureteral 
openings,  being  its  most  sensitive  area. 

PRACTICAL   CONSIDERATIONS:    THE   BLADDER. 

Absence  of  the  bladder  is  a  very  rare  abnormality,  but  in  more  than  one  case 
has  proved  to  be  consistent  with  prolonged  life,  the  dilated  ureters — opening  into  the 
urethra — having  acted  as  reservoirs  for  the  urine  and  the  muscle-fibres  at  their  con- 
stricted orifices  having  taken  on  sphincteric  action  and  prevented  urinary  incon- 

1  Anatom.  Anzeiger,  Bd.  xii.,  1896. 


PRACTICAL   CONSIDERATIONS:    THE   BLADDER.  1911 

tinence.  In  other  less  fortunate  cases  in  which  the  ureteral  openings  were  on  the 
surface  of  the  body,  implantation  of  the  ureters  into  the  intestinal  tract  (page  1901) 
has  been  done  with  varying  degrees  of  success. 

Extroversion  (exstrophy)  of  the  bladder,  the  most  frequent  congenital  ab- 
normality of  this  organ,  is  associated  with  failure  of  the  ventral  plates  forming  the 
abdominal  wall  to  unite  in  the  mid-line.  In  this  condition,  which  occurs  in  males  in 
from  80  to  90  per  cent,  of  cases,  the  symphysis  pubis  and  the  anterior  wall  of  the 
bladder  frequently  are  also  lacking,  and  the  posterior  vesical  wall — protruded  by 
intra-abdominal  pressure — forms  a  rounded  prominence,  deep  red  in  color,  from 
chronic  congestion.  The  ureteral  orifices  are  often  plainly  visible.  Cryptorchism, 
bifid  scrotum,  inguinal  hernia,  and  epispadias  are  frequently  present.  Although  the 
opinions  regarding  the  causes  and  factors  leading  to  these  malformations  are  various 
and  conflicting,  it  is  certain  that  these  defects  depend  upon  faulty  development  at  a 
very  early  period  of  foetal  life,  probably  in  connection  with  abnormalities  of  the 
allantois  and  of  the  cloacal  region  of  the  embryo,  and  that  the  suggested  explana- 
tions on  a  mechanical  basis,  as  over-distention  of  the  allantois  or  unusual  shortness  or 
location  of  the  umbilical  cord,  are  entirely  inadequate  to  account  for  malformations 
which  often  so  profoundly  affect  the  entire  lower  segment  of  the  anterior  body-wall 
and  the  associated  organs. 

Occasionally  a  vesico- abdominal  fissure  occurs  without  extroversion,  when  the 
posterior  wall  of  the  bladder  will  be  concave  instead  of  convex  and  partially  covered 
by  the  imperfect  abdominal  wall. 

The  posterior  wall  of  the  bladder  and  the  anterior  wall  of  the  rectum  or  vagina 
may  be  defective  at  birth,  resulting  in  a  congenital  vesico-rectal  or  vesico-vaginal 
fistula. 

The  foetal  communication  between  the  extra-  and  intra-abdominal  portions  of 
the  allantoic  sac  may  remain  pervious,  so  that  the  urachus,  instead  of  becoming  a 
fibrous  cord  extending  from  the  umbilicus  to  the  summit  of  the  bladder,  is  patent 
and  constitutes  a  channel  by  means  of  which  urine  is  discharged  at  the  navel. 

Cystocele. — A  portion  of  the  bladder  may  be  found  either  alone  or  together 
with  intestine  or  omentum  in  the  sac  of  an  inguinal  or  femoral  hernia,  or  more 
rarely  it  may  be  part  of  an  obturator  or  perineal  or  ventral  hernia. 

The  ordinary  causes  of  abdominal  hernia  (page  1759)  favor  the  production  of 
this  condition.  In  their  presence,  and  especially  if  there  is  also  present  an  intestinal 
hernia  of  long  standing,  a  thinned  and  dilated  bladder  may  readily  be  drawn  by 
gravity  into  one  of  the  hernial  orifices  by  the  connection  of  its  extraperitoneal 
portion  with  the  subperitoneal  fat  with  which  it  is  in  close  contact.  The  bladder 
"  diverticulum,"  thus  formed,  is  a  result,  not  a  cause  of  the  hernia,  and  in  75  per 
cent,  of  cases  includes  only  the  extraperitoneal  bladder-wall.  As  vesical  dilatation 
and  atony  are  usually  the  result  of  obstructive  disease, — most  common  in  elderly 
males, — and  as  abdominal  hernia  is  frequent  during  late  middle  life  (page  1762),  it 
will  be  understood  why  75  per  cent,  of  cases  of  hernia  of  the  bladder  occur  in  men 
(irrespective  of  cases  of  vaginal  cystocele)  and  more  than  50  per  cent,  in  persons 
over  fifty  years  of  age.  In  old  herniae  there  has,  of  course,  been  an  opportunity 
for  the  stretching  and  elongation  of  the  bladder-wall  essential  for  the  production  of 
the  cystocele. 

The  laxity  of  the  attachments  of  the  bladder  to  surrounding  structures  necessi- 
tated by  its  changes  in  size  or  capacity  favors  the  production  of  hernia. 

Effects  of  Distention.  —The  cavity  of  the  normal  empty  bladder,  which  is  strongly 
contracted  during  life,  presents  little  more  than  a  narrow,  cleft-like  lumen,  with  a 
gentle  upward  curve,  continuous  with  that  of  the  urethra.  As  it  distends  the 
pyriform  bladder  becomes  oval  in  shape,  its  summit  rises  from  the  pelvis  above  the 
symphysis  pubis,  its  anterior  wall  becomes  applied  to  the  inner  surface  of  the  ab- 
dominal wall  in  the  hypogastric  region,  and  the  whole  organ  assumes  an  ovoid  shape 
or,  in  extreme  distention,  one  nearly  spherical.  Its  normal  capacity  in  the  adult  is 
about  one  pint,  but  the  looseness  of  the  submucosa  over  the  greater  part  of  its  sur- 
face, the  reticular  arrangement  of  its  muscle-fibres,  and  the  yielding  nature  of  the 
structures  by  which  it  is  surrounded  when  it  has  risen  from  the  pelvis  permit  of 
its  enormous  distention,  especially  as  a  result  of  slowly  increasing  obstructive  dis- 


i9i 2  HUMAN   ANATOMY. 

ease.      Its  summit  may  then  pass  above  the  level  of  the  umbilicus  and  it  may  fill 
almost  the  whole  abdomen. 

Retention  of  urine — inability  to  empty  the  bladder — may  be  due  (a)  to  obstruc- 
tion at  the  neck  of  the  bladder,  the  prostate,  or  the  urethra,  as  from  clots  in  bleeding 
from  the  kidneys,  ureters,  or  the  bladder  itself,  prostatic  hypertrophy,  stricture,  or 
rupture  of  the  urethra  ;  (<5)  to  affections  of  the  bladder  muscles,  as  paresis  or 
paralysis  of  the  detrusors  in  cerebral  or  spinal  injury  or  disease,  or  reflex  spasm  of  the 
sphincter  after  operations  on  the  anus  or  rectum  ;  or  incoordination,  as  in  hysteria, 
or  neurasthenia,  or  shock. 

The  distended  bladder  forms  a  rounded  fluctuating  tumor  in  the  hypogastric 
region,  which,  as  the  intestines  are  pushed  up  with  the  fold  of  peritoneum  back  of 
the  urachus  (plica  vesico-umbilicalis),  is  always  dull  on  percussion.  If  the  disten- 
tion  is  acute,  the  pressure  on  the  sensory  nerves  of  the  bladder  gives  rise  to  dis- 
tressing pain.  If  it  takes  place  slowly,  or  if  it  follows  cerebral  or  spinal  injury,  it 
may  be  quite  painless. 

After  a  time,  in  cases  of  great  distention,  the  sphincter  vesicae  and  compressor 
urethrae  yield  to  the  pressure  and  the  urine  overflows  the  bladder  more  or  less  con- 
tinuously,— incontinence  of  retention, — a  condition  which  should  always  be  suspected 
to  exist  in  aged  male  patients  who  have  either  very  frequent  urination  or  constant  uri- 
nary dribbling.  Great  paresis  or  actual  paralysis  of  the  detrusors  may  result  from 
distention,  so  that  the  power  to  empty  the  bladder  is  temporarily  or  permanently  lost 
even  after  all  obstruction  has  been  removed. 

During  marked  distention  certain  changes  take  place  in  its  relations  that  are  of 
much  practical  importance.  The  neck  of  the  bladder  is  so  firmly  fixed  in  position  by 
the  base  of  the  prostate,  with  its  dense  capsule  continuous  with  the  deep  layer  of  the 
triangular  ligament  (page  1977),  by  the  anterior  true  ligaments  of  the  bladder  itself, 
and  by  its  close  attachment  to  the  rectum  or  to  the  uterus  and  vagina,  that  it  does  not 
participate  in  the  upward  movement  of  the  summit  and  body,  but  if  the  rectum  is 
not  distended,  rather  sinks  slightly  in  the  pelvis.  The  looseness  of  the  fatty  con- 
nective tissue  occupying  the  space  of  Retzius  (page  1906)  and  separating  the  antero- 
lateral  walls  of  the  bladder  below  the  peritoneal  reflection  from  the  pubes  and  the 
obturator  internus  and  levator  ani  muscles  permits  the  elevation,  during  distention,  of 
all  the  remainder  of  the  bladder. 

The  anterior  peritoneal  fold,  which,  with  the  bladder  undistended,  reaches  to  the 
symphysis  pubis,  is  so  raised  that  if  the  summit  of  the  bladder  is  half-way  between 
the  pubes  and  the  umbilicus,  there  will  be  from  5-6.5  cm.  (2-2^4  in.)  of  the  non- 
peritoneal  portion  of  the  anterior  bladder-wall  in  close  apposition  with  a  similar  area 
of  the  inner  surface  of  the  abdominal  wall.  In  a  male  child  five  years  of  age  the 
space  between  the  upper  edge  of  the  symphysis  pubis  and  the  reflection  of  the  peri- 
toneum will  be  one  inch  when  the  bladder  contains  three  ounces  of  liquid.  The  close 
attachment  of  the  peritoneum  to  the  summit  of  the  bladder  and  its  very  loose  attach- 
ment to  the  parietes  (necessitated  by  the  changes  in  size  and  position  of  the  bladder) 
permit  this  upward  displacement. 

Coincident  distention  of  the  rectum  by  a  rubber  bag  limits  the  backward  and 
downward  extension  of  the  distended  bladder,  adds  slightly  to  its  elevation  in  the 
abdomen,  keeps  it  in  close  contact  with  the  abdominal  parietes,  and  increases  the 
distance  between  the  recto-vesical  fold  and  the  anus  from  two  and  a  half  inches  to 
three  and  a  half  inches.  The  use  of  the  rectal  bag  has  practical  disadvantages  which 
have  led  to  its  abandonment  in  most  cases.  The  Trendelenburg  position  elevates 
the  partly  distended  bladder  and  carries  upward  the  peritoneal  folds  by  gravity. 
Various  operations  (vide  infra}  are  so  planned  as  to  take  advantage  of  this  uncover- 
ing of  the  bladder-wall,  which  permits  access  to  that  viscus  and  to  its  cavity  without 
danger  of  peritoneal  infection. 

Prevesical  inflammation  may  follow  infection  through  an  operation  or  other 
wound,  involving  tin-  prevesical  space  of  Retzius,  or  may  be  caused  by  extravasa- 
tion of  urine  into  that  space  ;  and  as  the  connective  tissue  occupying  it  is  continuous 
superiorly  with  the  abdominal  and  inferiorly  with  the  pelvic  extraperitoneal  tissue,  a 
cellulitis  beginning  there  may  be  widespread,  or  may  result  fatally.  Some  of  the 
relations  of  this  space  are  indicated  in  the  fact  that  such  infection  has  been  known  to 


PRACTICAL   CONSIDERATIONS  :    THE   BLADDER.  1913 

follow  chronic  cystitis,  uterine  or  periuterine  inflammation,  post-partum  suppuration 
of  the  symphysis  pubis,  and  purulent  thrombosis  of  the  umbilical  vein  in  a  new-born 
infant  (Thorndike). 

Collections  of  pus  have  opened  from  here  spontaneously  through  the  anterior 
abdominal  wall,  into  the  rectum,  the  bladder,  or  the  urethra,  and  into  the  peritoneal 
cavity. 

Rupture  of  the  bladder  rarely  follows  distention  alone,  but  is  not  uncommon  as 
a  result  of  trauma  expended  upon  the  pelvis  or  lower  abdomen  when  the  bladder  is  dis- 
tended. The  cases  in  which  rupture  follows  over-distention  from  obstructive  disease, 
without  the  intervention  of  force,  are  usually  prostatic  in  origin,  as  in  retention  from 
stricture  the  urethra  ordinarily  ulcerates  behind  the  constriction  and  periurethral 
extravasation  of  urine  relieves  the  tension. 

The  liability  to  traumatic  rupture  is  directly  proportionate  to  the  degree  of  dis- 
tention and  consequent  elevation  of  the  viscus,  and  if  that  condition  exists  in  a  blad- 
der the  subject  of  chronic  dilatation  and  atrophy,  or  in  one  rendered  unnaturally 
immobile  by  pericystitis  or  pelvic  cellulitis,  the  force  required  to  produce  rupture  is 
much  lessened.  Occasionally  in  the  presence  of  fracture  of  the  pelvis  it  is  difficult  to 
decide  whether  a  given  lesion  of  the  bladder  is  a  rupture  or  a  wound  from  a  fragment 
of  bone. 

Eighty-five  per  cent,  of  ruptures  are  intraperitoneal,  because,  (a)  in  distention 
the  peritoneal  becomes  the  most  tense  of  the  coats  of  the  bladder-wall  ;  (£)  it  is  the 
least  elastic  ;  (c)  it  covers  that  portion  of  the  bladder  which,  as  it  rises  into  the 
abdomen,  first  loses  the  protection  afforded  by  the  pelvis,  and  is  less  reinforced  by 
pressure  from  surrounding  tissues  ;  {d )  the  bladder- walls  are  thinnest  over  that 
area  ;  (<?)  the  region  is  exposed  to  counter-pressure  against  the  promontory  of  the 
sacrum.  These  conditions  also  explain  the  usual  situation  of  intraperitoneal  ruptures 
in  the  upper  and  posterior  bladder-wall. 

Extraperitoneal  rupture  is  apt  to  be  in  the  anterior  wall, — i.e. ,  that  portion  most 
immediately  in  contact  with  the  pelvic  bones,  which  in  these  cases  are  often  found 
to  be  fractured. 

Pathological  (spontaneous)  rupture  is  usually  in  the  extraperitoneal  portion  of 
the  bladder,  because  there  the  influence  of  gravity  is  most  potent  in  aiding  in  the 
production  of  the  protrusion  of  the  thinned  mucosa  between  the  often  hypertrophied 
bands  of  muscular  fibres.  The  early  stage  of  tljis  condition — in  which  the  muscle 
hypertrophy  is  the  prominent  change — constitutes  the  so-called  fasciculated  bladder ; 
later,  when  the  pouching  has  become  marked,  it  is  known  as  sacculated  bladder. 

In  children  rupture  of  the  bladder  is  rare  in  spite  of  its  thinness  and  of  the  fact 
that  in  them  it  is  an  abdominal  rather  than  a  pelvic  organ,  because  (a)  the  chief 
causes  of  distention  are  absent  ;  (<$)  the  greater  sensibility  of  the  bladder  renders  its 
evacuation  more  frequent  or  less  likely  to  be  neglected  ;  in  the  adult  incontinence  of 
urine  generally  means  distention,  in  the  child  irritation  (Owen);  (c)  owing  to  the 
undeveloped  condition  of  the  prostate  the  bladder  is  more  movable. 

Wounds  of  the  bladder  may  occur  from  within, — during  instrumentation, — or  the 
bladder  may  be  reached  by  weapons,  missiles,  or  vulnerating  bodies  of  any  sort, 
through  the  suprapubic  region,  the  rectum,  the  perineum,  the  obturator  or  the 
sciatic  foramen.  They  often  result  from  the  direct  laceration  of  the  bladder-wall  by 
a  bony  fragment  in  fracture  of  the  pelvis.  Like  ruptures,  they  may  or  may  not  in- 
volve the  peritoneum. 

The  symptoms  of  rupture  or.  wound  will  obviously  vary  with  the  situation  of  the 
lesion.  The  most  important  are  due  to  the  escape  of  urine  from  the  bladder  either 
into  the  space  of  Retzius  or  into  the  peritoneal  cavity.  The  determination  of  the 
general  character  of  the  injury — made  in  part  by  catheterization,  which,  in  the 
presence  of  inability  to  urinate,  yet  fails  to  draw  more  than  a  little  bloody  urine,  and 
does  not  withdraw  all  of  a  measured  quantity  of  injected  fluid — should  be  followed 
by  instant  operation,  whether  the  lesion  is  extra-  or  intraperitoneal  in  its  situation. 

Occasionally,  after  a  small  stab  or  pistol  wound,  the  loose  mucosa  may  act  as  a 
plug,  and,  aided  by  the  muscular  contraction  of  the  bladder-wall,  will  for  a  time 
prevent  extravasation,  and  then  the  above-mentioned  signs  may  be  absent  or  may 
appear  later,  when  ulcerative  or  necrotic  processes  have  opened  the  way  for  the 


I9H  HUMAN    ANATOMY. 

escape  of  urine.  A  similar,  but  usually  permanent  closure  of  the  wound — by  mus- 
cular contraction,  or  by  a  valvular  action  from  the  change  in  the  relation  of  the  coats 
of  the  vesical  wall  after  tension  has  been  relieved — takes  place  when  the  bladder  has 
been  tapped  above  the  pubes  {suprapubic puncture}. 

Cystitis,  in  so  far  as  it  has  an  anatomical  bearing,  should  be  studied  with  regard 
to  the  possible  sources  of  the  essential  infection  and  of  the  almost  equally  essential 
predisposing  condition  of  congestion.  No  explanation  is  required  of  the  influence 
of  (a)  frequent  micturition,  however  caused  ;  (b)  trauma  ;  (e)  vesical  distention  ; 
(V )  acid  urine  ;  (<?)  calculi  or  tumors  ;  (_/)  cold  and  wet  ;  (£•)  prolonged  sexual 
excitement  ;  (/*)  cardiac  weakness,  in  bringing  about  a  congestion  of  the  vesical 
and  vesico-prostatic  plexuses.  The  sudden  removal  of  pressure  when  an  habitually 
distended  bladder  is  emptied  may  be  followed  by  congestion  so  excessive  as  to  cause 
haematuria. 

Infection  may  occur  by  spreading  from  the  urethra  or  prostate,  by  instrumenta- 
tion, by  descent  from  the  kidneys,  by  extension  from  any  pericystic  focus  of  suppu- 
ration, or  by  direct  passage  of  the  microbic  cause  from  the  rectum.  The  great 
venous  plexus  at  the  base  of  the  bladder,  emptying  into  the  valveless  internal  iliac 
veins,  is  engorged  whenever  pressure  is  made  upon  the  latter,  as  by  fecal  masses  in  the 
sigmoid  flexure  or  rectum.  Constipation  is  thus  both  a  predisposing  and — through 
the  migration  of  microbes  to  the  contiguous  bladder — an  exciting  cause  of  cystitis. 

The  mucosa  of  the  bladder,  supplied  by  the  hypogastric  plexus,  is  not  very 
sensitive  normally,  except  in  the  region  of  the  trigonum.  There  it  is  tightly  con- 
nected with  the  muscular  layer,  and  the  loose,  elastic,  submucous  connective  tissue 
found  in  the  remainder  of  the  bladder  is  absent.  The  difference  is  shown  by  the 
smooth  surface  of  the  trigonum  as  contrasted  with  the  rugae  of  the  lax  mucosa  seen 
over  the  rest  of  the  interior  of  the  empty  bladder.  The  laxity  in  the  superior  por- 
tions of  the  bladder  is  determined  by  the  necessity  for  great  changes  in  its  size.  At 
the  trigonum  a  similar  looseness  of  the  mucosa  would  encourage  its  prolapse,  and 
might  result  in  frequent  obstruction  of  the  ureteral  and  vesical  outlets.  This  close 
adhesion  of  mucous  and  muscular  layers  prevents  free  swelling  when  inflammation 
occurs,  and,  in  conjunction  with  the  particularly  generous  vascular  and  nerve-supply 
to  the  trigonum  and  neck  of  the  bladder,  explains  the  pain  and  sensitiveness  of  that 
region  in  cystitis.  In  a  marked  case  the  whole  bladder  may  become  sensitive,  so 
that  hypogastric  pressure  is  painful* 

Frequent  micturition,  as  a  result  of  cystitis  or  of  other  conditions  in  which  vesical 
irritation  is  present,  is  due  to  stimulus  of  the  sensory  nerves  supplied  by  the  third 
and  fourth  sacral  nerves  from  the  second,  third,  and  fourth  sacral  segments  of  the 
cord.  The  motor  impulse  reaches  the  bladder  from  the  eleventh  and  twelfth  dorsal 
and  first  lumbar  segments  through  the  hypogastric  and  pelvic  plexuses. 

The  skin  of  the  scrotum  and  of  the  penis  and  the  urethral  mucous  membrane 
are  supplied  with  sensation  from  the  same  spinal  segments  as  is  the  bladder,  and 
therefore  the  referred  pains  in  vesical  irritation  or  inflammation  are  often  felt  in  those 
regions  in  the  distribution  of  the  perineal  branches  of  the  pudic  and  inferior  gluteal 
nerves.  As  the  inferior  hemorrhoidal  nerve — supplying  the  skin  over  the  external 
sphincter  ani  and  about  the  anus — is  often  derived  from  the  sacral  plexus,  itching  or 
tickling  in  that  region  or  painful  spasm  of  the  anal  sphincter  may  be  caused  by 
vesical  irritation. 

Other  referred  pains  in  vesical  disease  are  to  the-lumbo-sacral  region,  through 
the  communication  between  the  second,  third,  and  fourth  sacral  nerves  and  the  hypo- 
gastric  plexus  ;  to  the  kidney,  by  the  junction  in  the  spermatic  plexus  of  filaments 
from  the  vesical  and  renal  plexuses  ;  and  to  the  lower  limb,  occasionally  to  the  foot 
(pododynia),  through  the  sacral  nerves  which  enter  into  the  sacral  plexus  and  the 
lumbo-sacral  cord,  giving  off  the  great  sciatic  nerve,  and  also  into  the  pelvic 
plexuses. 

The  important  muscular  element  in  the  vesical,  as  in  the  ureteral,  walls  gives 
the  "colicky"  character  to  the  symptoms  of  irritation  and,  in  the  case  of  the  in- 
flamed bladder,  causes  the  violent  tenesmus  accompanying  the  discharge  of  the  last 
drops  of  urine,  when  the  muscles  in  the  vicinity  of  the  sensitive  trigonum  contract 
spasmodically. 


PRACTICAL   CONSIDERATIONS  :    MALE    PERINEUM. 


1915 


The  same  symptoms — frequent  micturition,  referred  pains,  tenesmus — are  caused 
by  a  vesical  calculus  and  have  the  same  anatomical  basis.  They  are  most  marked 
if  the  stone  is  small,  rough,  and  movable,  so  that  in  the  erect  position  it  falls  upon 
the  trigonal  surface.  Such  a  stone  may  roll  or  be  forced  by  the  stream  of  urine 
into  the  vesical  outlet  and  produce  sudden  interruption  of  micturition.  This 
symptom  is  seen  most  often  in  young  male  children,  in  whom  the  relatively  vertical 
position  of  the  bladder,  the  marked  tenesmus  caused  by  the  presence  of  the  stone, 
and  the  small  size  of  the  vesical  orifice  favor  its  production.  The  tenesmus  in 
children  is  often  so  excessive  as  to  result  in  prolapse  of  the  rectum,  which  is  affected 
by  and  participates  in  the  straining  expulsive  efforts. 

In  a  sacculated  bladder  a  very  large  stone  may  lie  in  a  pouch  with  but  little  of 
its  surface  presenting  towards  the  bladder-cavity  (encysted  stone)  and  give  rise  to 
almost  no  subjective  symptoms. 

Perineal  lithotomy  is  much  less  frequently  done  than  formerly,  on  account  of  the 
application  of  Bigelow's  operation  of  litholapaxy  to  the  great  majority  of  calculi,  and 
of  the  revival  of  suprapubic  lithotomy  and  its  use  in  a  considerable  proportion  of  the 
remainder.  A  description  of  the  parts  involved  in  this  operation  serves,  however, 
as  Treves  has  said,  to  give  a  proper  conception  of  their  important  anatomical  re- 
lationships. 

The  Male  Perineum. — This  region — a  fissure  when  the  thighs  are  approxi- 
mated— becomes  an  ample  lozenge-shaped  space  when  the  legs  and  thighs  are  flexed 

FIG.  1625. 


Tuber  ischii  — 


Tuber  ischii 


Anus 


-  Subcutaneous 
fibres  of  sphinc- 
ter ani  externus 


-  Tip  of  coccyx 


Dissection  of  perineum;  skin  has  been  removed,  leaving-  superficial  fascia  undisturbed. 
Sound  has  been  passed  through  urethra  into  bladder  and  scrotum  drawn  forward. 

and  the  latter  are  strongly  abducted, — the  lithotomy  position.  It  corresponds  to 
the  outlet  of  the  pelvis.  On  the  surface  it  is  bounded  roughly  by  the  scrotum 
anteriorly,  the  buttocks  posteriorly,  and  the  upper  limits  of  the  inner  aspects  of  the 
thighs  laterally.  More  deeply  the  boundaries  are  the  symphysis  pubis  and  subpubic 
ligament  anteriorly,  the  coccyx  posteriorly,  and  the  greater  sacro-sciatic  ligaments,  the 


1916 


HUMAN   ANATOMY. 


ischial  tuberosities and  rami,  and  the  pubic  rami  laterally  (Fig.  1627).  It  is  divided 
into  two  lateral  symmetrical  halves  by  a  dense  cutaneous  ridge,  the  raphe,  across 
which,  as  it  represents  the  junction  of  the  two  fcetal  halves  of  the  perineum,  no  blood- 
vessels pass  from  one  side  to  the  other ;  and  into  two  unsymmetrical  antero-posterior 
triangular  portions  by  an  imaginary  transverse  line  drawn  between  the  anterior 
borders  of  the  ischial  tuberosities  and  running  in  front  of  the  anus.  The  posterior 
of  these  two  divisions — the  portion  of  the  outlet  of  the  pelvis  which  contains  the 
rectum  and  anus — is  the  rectal  triangle  (anal  perineum).  Its  practical  relations  have 
been  sufficiently  dealt  with  in  the  article  on  the  rectum  and  anus  (page  1693). 

The  anterior  division,  the  iiro-genital  triangle  (urethral  perineum),  has  for  its 
deep  boundaries  :  posteriorly  the  deep  layer  of  the  superficial  fascia  (fascia  of  Colles) 
as  it  passes  behind  the  transverse  perineal  muscles  to  become  continuous  with  the 
inferior  layer  of  the  triangular  ligament  (page  563);  laterally  the  rami  of  the  pubes 


FIG.  1626, 


Internal  per- 
ineal  nerve 

Inferior- 
pudendal 
nerve 


Int.  pudic  artery  - 

Pudic  nerve  - 

Anal  fascia 

Inferior  hemor-f- 

rhoidal  arteryU 

Inferior  hemor-f  - 

rhoidal  nervesl . 


-Position  of 
urethra 

-Colles's  fascia 


.Sphincter  ani 

externus 
.Tuber  ischii 


-Tip  of  coccyx 


Dissection  of  perineum,  showing  superficial  and  hemorrhoiclal  branches  of  internal  pudic 
artery  and  of  pudic  nerves  on  right  side ;  Colles's  fascia  exposed  on  left. 

and  ischia  ;  anteriorly  the  pubic  arch.  Over  the  uro-genital  triangle  the  superfici 
fascia  is  separable  into  two  distinct  layers,  the  superficial  and  the  deep.  The  super- 
ficial layer  contains  a  considerable  amount  of  fat,  and  is  continuous  with  the  corre- 
sponding layer  over  the  thighs  and  buttocks  and  with  the  masses  of  fatty  tissue  that 
fill  the  ischio-rectal  fossEe.  The  deep  layer,  or  fascia  of  Colles,  is  membranous  and 
free  from  fat,  and  is  not  only  applied  closely  to  the  lower  edges  of  the  transverse 
perineal  muscles  and  attached  to  the  base  of  the  inferior  layer  of  the  triangular  liga- 
ment, but  is  also  attached  to  the  external  margin  of  the  rami  of  the  pubis  and  ischium. 
Anteriorly  it  is  continuous  with  the  deep  layer  of  superficial  fascia  of  the  scrotum 
(dartos),  penis,  and  spermatic  cords,  and  with  the  fascia  of  Scarpa  (page  515) 
on  the  front  of  the  abdomen.  When  it  is  divided,  a  definite  space,  the  superficial 
perineal  interspace,  is  opened,  which  is  bounded  below  by  Colles's  fascia,  above  by 
the  inferior  layer  of  the  triangular  ligament,  laterally  by  the  attachments  of  the  fascia 


PRACTICAL   CONSIDERATIONS  :    MALE    PERINEUM. 


1917 


and  the  ligament  to  the  pubo-ischiatic  rami,  and  behind  by  the  union  of  the  fascia 
with  the  base  of  the  ligament. 

This  space  or  pouch  contains  the  bulb  and  the  crura  of  the  penis  and  the 
muscles  covering  them,  the  superficial  transverse  perineal  muscles,  the  superficial 
perineal  nerves  and  vessels,  and  the  long  pudendal  nerves  ;  in  its  anterior  part  the 
internal  pudic  artery  divides  into  its  terminal  branches,  the  dorsal  artery  of  the  penis 
and  the  artery  to  the  corpus  cavernosum.  It  is  very  important  in  its  relations  to 
wounds  and  ruptures  of  the  urethra  (q.v.'). 

In  the  uro-genital  triangle,  half-way  between  the  centre  of  the  anus  and  the 
perineo-scrotal  junction,  is  the  so-called  "perineal  centre,"  where  the  bulbo-caver- 
nosus,  the  sphincter  ani,  and  the  superficial  transverse  perineal  muscles  meet,  and 
which  corresponds  to  the  middle  of  the  posterior  edge  of  the  fibrous  shelf  formed 
by  the  union  of  the  two  layers  of  the  triangular  ligament.  These  structures  are 
exposed  when  Colics' s  fascia  is  turned  back,  and  on  either  side  a  triangular  space  is 

FIG.  1627. 


Bulbo-cavernosus  muscle 


Ischio-cavernosus  muscle 
Crus  penis 

Colles's  fascia,  reflected 

Triangular  lig.,  inf.  layer 

Ischio-cavernosus,  stump 

Transver.  perinei  muscle 

Tuber  ischii 

Sphincter  ani  externus 

Levator  ani 

Pudic  nerve 

Internal  pudic  artery 

Greater  sacro-sciatic  lig. 

Gluteus  maximus 


— Colles's  fascia,  reflected 
— Ischio-cavernosus  muscle 

Internal  perineal  nerve 

External  perineal  nerve 

— -Superficial  perineal  artery 


Anal  fascia 

Greater  sacro-sciatic  lig. 

Inf.  hemorrhoidal  nerve 

Inf.  hemorrhoidal  artery 

Branch  of  fourth  sacral 


.Branch  of  fourth  sacral 
nerve 


•  Dissection  of  perineum ;  Colles's  fascia  has  been  cut  and  reflected  to  expose  crura  and  bulb  of 
penis  covered  by  muscles  ;  on  right  side  ischio-rectal  fossa  is  partly  cleaned  out. 

seen,  the  floor  of  which  is  constituted  by  the  inferior  layer  of  the  triangular  ligament. 
At  the  lateral,  median,  and  posterior  sides  of  the  triangle  lie  the  bulbo-cavernosus, 
ischio-cavernosus,  and  superficial  transverse  perineal  muscles  respectively  (Fig.  1627). 
When  the  inferior  layer  of  the  triangular  ligament  is  divided,  the  space  (deep 
perineal  interspace}  between  that  and  the  superior  layer  (as  this  portion  of  the  parie- 
tal layer  of  the  pelvic  fascia  is  called)  is  opened  and  is  found  to  be  broader  in- 
feriorly  and  behind,  the  two  layers  fusing  anteriorly  with  a  dense  band  (ligamentum 
transversum  pelvis}  stretching  from  one  pubic  bone  to  the  other,  and  leaving  only 
sufficient  space  above  it,  beneath  the  subpubic  ligament,  to  permit  the  passage  of 
the  dorsal  vein  of  the  penis.  The  space  between  the  two  layers  (Fig.  1629)  is 
occupied  by  (a)  the  compressor  urethrse  muscle  ;  (<5)  the  membranous  urethra, 
about  half  an  inch  in  length;  (r)  Cowper's  glands  (glandules  bidbo-urethrales}; 
(rf)  the  beginning  of  the  artery  of  the  bulb  ;  (<?)  the  continuation  of  the  internal 
pudic  artery,  which,  while  between  the  two  layers  of  the  triangular  ligament  and 


HUMAN   ANATOMY. 


before  piercing  the  superficial  layer,  gives  off  the  artery  to  the  bulb.  This  latter 
artery  may  come  off  from  the  accessory  pudic  when  that  vessel  is  present  (page  818), 
and  will  then  be  more  anterior,  and  less  exposed  to  division  in  lithotomy,  than 
usual  ;  or  it  may  come  off  from  the  internal  pudic  before  the  latter  has  penetrated 
the  superficial  layer  of  the  triangular  ligament,  and  will  then  be  behind  its  usual 
position  and  more  likely  to  be  wounded.  When  the  superior  or  deep  layer  of  the 
triangular  ligament  is  opened,  the  prostate — partly  covered  by  the  median  fibres  of 
the  levator  ani — and  the  neck  of  the  bladder  are  exposed  (Fig.  1631).  this  deep  layer 
being  continuous  with  the  prostatic  sheath. 

It  will  be  seen  that  in  reaching  this  point  by  dissection  there  will  have  been 
exposed  certain  alternating  layers  of  fascial  and  muscular  structures  (Cunning- 
ham) as  follows  :  (a)  superficial  fascia  (superficial  and  deep  layers)  ;  (6~)  super- 
ficial perineal  muscles  ;  (<:)  inferior  or  superficial  layer  of  the  triangular  ligament 


FIG.  1628. 


Greater  sacro- 

sciatic  ligament 

Coccyx- 
Cluteus  maximus^ 


Ischio-cavernosus  muscle, 
turned  aside 


Crus  penis 

Dorsal  artery  of  penis,  artery  of 
corpus  cavernosum  to  the  right 
Bulb  of  penis 

Superfi  :ial  perineal  artery 

—    Superficial  perineal  nerves 

Tuber  ischii 

—Dorsal  nerve  of  penis 

Perineal  division  of 

_    pudic  nerve 
"Internal  pudic  artery 
Inf.  hemorrhoidal  nerve 

-  Inferior  hemorrhoidal 

artery 


Dissection  of  perineum,  showing  inferior  layer  of  triangular  ligament 
and  inner  wall  of  ischio-rectal  fossa  partially  exposed. 

(fascia  trigoni  urogenitalis  inferior);   (d)  compressor  urethrae  muscle;  (e*)  superi 
or  deep   layer  of  the  triangular  ligament  (fascia   trigoni  urogenitalis   superior  (_/) 
levator  ani  muscle  ;  (  g}  prostatic  fascia  (sheath). 

Landmarks. — With  the  patient  in  the  lithotomy  position:  (i)  The  pubis, 
coccyx,  tuberosities,  ischio-pubic  rami,  and  greater  sacro-sciatic  ligaments  may  be 
felt.  (2)  The  transverse  diameter,  between  the  tuberosities,  is  9  cm.  (3^2  in.)  ; 
the  antero-posterior  diameter,  from  the  coccyx  to  the  pubis,  is  also  9  cm.  (3^  in.) 
on  the  skeleton,  10  cm.  (4  in.)  as  measured  on  the  living  person.  (3)  The  centre 
of  the  anus  is  about  4  cm.  (i}4  in. )  from  the  tip  of  the  coccyx,  and  is  on  a  line  drawn 
between  the  tips  of  the  ischial  tuberosities.  (4)  The  perineal  centre  is  approxi- 
mately 4  cm.  (1^2  in.)  in  front  of  the  anus.  (5)  The  bulb  (and  its  artery)  are  just 
anterior  to  this  ;  its  position  may  be  indicated  by  a  slight  median  surface  elevation  ; 
the  artery  passes  inward  between  the  layers  of  the  triangular  ligament  about  a  half 


PRACTICAL    CONSIDERATIONS  :    MALE    PERINEUM. 


1919 


inch  above  the  base  of  the  latter, — i.e. ,  about  one  and  a  half  inches  from  the  anus. 
(6)  Measured  in  the  mid-line  from  the  symphysis  to  the  centre  of  its  base,  the  tri- 
angular ligament  extends  backward  about  one  and  a  half  inches.  (7)  The  mem- 
branous urethra,  lying  between  the  two  layers  of  the  triangular  ligament,  is  a  little 
below  the  middle  of  this  line, — i.e.,  a  little  less  than  an  inch  below  the  symphysis  and 
from  one-half  to  three-quarters  of  an  inch  above  the  anus.  It  measures  from  one- 
half  to  three-quarters  of  an  inch  in  length.  (8)  The  dorsal  vein  passes  above  the 
triangular  ligament  a  little  less  than  a  half  inch  below  the  lower  margin  of  the  sym- 
physis ;  the  pudic  artery  and  nerve  pierce  the  superficial  layer  of  the  triangular  liga- 
ment a  little  lower.  (9)  The  distance  from  the  surface  of  the  perineum  to  the  pelvic 
floor  is  about  one  inch  near  the  symphysis  and  from  two  to  three  inches  posteriorly 
and  laterally.  (10)  The  vesical  orifice  is  on  a  horizontal  antero-posterior  line  drawn 
through  a  point  a  little  below  the  middle  of  the  symphysis,  is  about  an  inch  to  an 
inch  and  a  quarter  behind  it,  and  is  from  two  and  a  half  to  three  inches  above  the 

FIG.  1629. 


Corpus  spongiosum, —    - 
cut 

Urethra-      • 
Colles's  fascia-  -  - 

Crus  penis 

Portion  of  bulb 

Cowper's  gland — 

Posterior  edge  of-     • 
triangular  ligament 

Tuber  ischii 

Internal  pudic  artery— 


-  Crus  penis 

-Dorsal  artery  of  penis 
-Ischio-cavernosus  muscle 
-Artery  of  corpus  cavernosum 
-Dorsal  nerve  of  penis 
-Compressor  urethra  muscle 
-Artery  of  bulb 
-Deep  transverse  perineal 
muscle 

-  Dorsal  nerve  of  penis 
'Internal  pudic  artery 

— .Sphincter  ani 

Perineal  division  of 
pudic  nerve 

—  Levatorani 

Greater  sacro-sciatic 

ligament 


Coccyx 


Dissection  of  perineum,  in  which  inferior  layer  of  triangular  ligament  and  corpus  spongiosum  have  been  par- 
tially removed,  exposing  urethra  covered  by  compressor  urethrse  muscle  and  Cowper's  gland. 

perineal  surface.  ( 1 1 )  The  prostate  is  about  three-quarters  of  an  inch  below  the 
symphysis.  (12)  The  pudic  artery,  as  it  lies  in  Alcock's  canal,  is  about  one  and  a 
half  inches  above  the  lower  margin  of  the  ischial  tuberosity. 

These  measurements  are,  of  course,  approximate,  and  vary  with  the  size  of  the 
pelvis  and  its  outlet  and  the  amount  of  subcutaneous  fat,  which,  in  the  lithotomy 
position,  may  much  increase  the  normal  antero-posterior  convexity  of  the  perineal 
surface. 

Lateral  Lithotomy.— It  will  now  be  understood  that  in  opening  the  bladder 
through  one  side  of  the  perineum  the  incision  must  not  extend  too  far  forward,-  as  it 
might  ^involve  the  artery  of  the  bulb,  which  lies  a  little  anterior  to  the  "perineal 
centre"  (Fig.  1629)  ;  or  too  much  externally,  as  the  pudic  might  be  wounded  where 
it  lies  on  the  ramus  of  the  ischium  ;  or  too  far  posteriorly,'  as,  after  dividing  the 
layer  of  the  superficial  perineal  fascia  covering  the  rectal  triangle,  and  thus  opening  up 
the  ischio-rectal  space,  it  might  open  the  rectum  itself.  In  the  deeper  parts  of  the 
wound  it  will  be  seen  that  if  it  is  too  extensive,  or  carried  too  far  upward,  it  might 
pass  completely  through  the  left  lobe  of  the  prostate  and  divide  the  visceral  layer  of 


1 920 


lit  MAN    ANATOMY. 


the  pelvic  fascia  (which  is  reflected  from  the  gland  near  its  upper  end),  favoring  the 
development  of  pelvic  cellulitis  from  urinary  infiltration  (page  1933)  ;  or  it  might 
divide  the  neck  of  the  bladder  and  open  up  the  recto-vesical  fossa  with  the  same 
results  ;  or,  if  the  prostatic  incision  were  too  extensive  and  too  vertical,  it  might 
wound  the  ejaculatory  ducts  or  seminal  vesicles.  The  incision — which  is  made  after 
a  grooved  staff  has  been  introduced  into  the  bladder,  and  while  it  is  held  in  place  by 
an  assistant — accordingly  begins  at  a  point  a  little  to  the  left  of  the  raphe  and  a  little 
posterior  to  the  perineal  centre — i.e.,  about  one  to  one  and  a  quarter  inches  in  front 
of  the  anus — and,  opening  the  left  ischio-rectal  fossa,  ends  at  the  junction  of  the 
outer  and  middle  thirds  of  a  line  drawn  between  the  posterior  margin  of  the  anus 
and  the  ischial  tuberosity.  This  incision  should  be  deepest  near  its  upper  end — not 
far,  at  its  upper  and  deepest  portion,  from  the  apex  of  the  "  perineal  triangle" — and 
should  become  shallower  as  it  passes  into  the  ischio-rectal  space.  It  divides  skin, 

FIG.  1630. 


Adductor  brevis  - 


Greater  sacro- 
sciatic  ligament 

Coccygeus 

Glutens 
maxitmis,  cut 


Corpus  ca  vernosum , 

cut 
Urethra 

Subpubic  ligament 
Prostate 

-Tuber  ischii 

( Ibturator 
intern  us 

;iter  sacro- 
sciatic  ligament 

-     -Gluteus 

maximus 

-  Coccyx 


Deep  dissection  of  perineum,  in  which  root  of  penis  has  been  removed,  showing  urethra 
emerging  from  prostate,  which  is  partly  exposed  between  levatores  am. 

both  layers  of  superficial  fascia,  the  superficial  transverse  perineal  muscle,  artery,  and 
nerve,  the  lower  edge  of  the  superficial  layer  of  the  triangular  ligament,  and,  as  it 
crosses  the  ischio-rectal  fossa,  the  inferior  hemorrhoidal  vessels  and  nerves. 

The  left  forefinger  of  the  operator  now  guides  the  knife  into  the  groove  of  the 
staff,  and  the  incision  is  deepened  with  the  knife-blade  inclined  laterally  and  pushed 
onward  into  the  bladder,  dividing  the  compressor  urethrae  muscle,  the  membranous 
urethra,  the  superior  layer  of  the  triangular  ligament,  a  few  median  fibres  of  the  leva- 
tor  ani,  the  prostatic  urethra,  and  a  portion  of  the  left  lobe  of  the  prostate. 

The  neck  of  the  bladder  should  be  dilated  with  the  finger  rather  than  incised, 
and  will,  without  serious  laceration,  permit  the  extraction  of  a  stone  of  the  diameter 
of  an  inch  to  an  tnrh  and  a  quarter. 

In  children  the  following  facts  should  be  borne  in  mind  :  (a)  the  relative  nar- 
rowness of  the  pelvis,  limiting  the  operative  space  ;  (£)  the  undeveloped  condition 


PRACTICAL   CONSIDERATIONS  :    MALE    PERINEUM. 


1921 


of  the  prostate,  necessitating  the  division  of  more  of  the  vesical  neck  and  increasing 
the  risk  of  opening  up  the  pelvic  fascia  ;  O)  the  greater  mobility  of  the  bladder 
(the  neck  of  which  in  the  adult  is  largely  fixed  by  its  connection  with  the  base  of 
the  prostate),  so  that  it  has  been  pushed  before  the  finger  and  torn  from  the  urethra  ; 
(d  )  the  situation  of  the  bladder  above  rather  than  in  the  pelvis,  the  neck,  therefore, 
being  relatively  higher  than  in  the  adult  ;  (<?)  the  looseness  and  delicacy  of  the 
recto-vesical  fascia,  permitting  the  easy  separation  of  the  bladder  and  rectum  and 
forming  a  cavity  which  the  finger  may  mistake  for  that  of  the  bladder  ;  (f )  the 
relatively  low  level  of  the  recto-vesical  fold  of  peritoneum,  exposing  it  to  injury  if  the 
wound  is  unduly  prolonged  upward. 

Median  lithotomy  involves  the  division,  through  the  median  raphe  of  the  peri- 
neum, of  the  skin,  superficial  fascia,  sphincter  ani  and  portions  of  the  other  struc- 

FIG.  1631. 


Corpus  spongiosum,  cut 


Adductor  bre 
Corpus  cavernosum  — — 


Adductor  magnus  —  - 
Ramus  ischii 


Biceps  and 
semitendinosus 


-Cut  edge  of  visceral  layer 

of  pelvic  fascia 
-Cut  edge  of  levator  ani 
-Cut  edge  of  pelvic  fascia 

-Seminal  vesicle,  vas 
deferens  to  inner  side 

-Greater  sacro-sciatic 
ligament 


.  Rectum,  turned  back 


Deep  dissection  of  perineum,  in  vyhich  pelvic  floor  has  been  partly  removed,  exposing  bladder, 
seminal  vesicles,  spermatic  ducts,  and  prostate;   rectum  has  been  turned  back. 

tures  entering  into  the  "  perineal  centre,"  the  lower  portion  of  the  superficial  layer 
of  the  triangular  ligament,  the  compressor  urethrae  muscle,  the  membranous  urethra, 
and  the  apex  of  the  prostate.  The  bladder  is  entered  by  dilating  with  the  finger  the 
prostatic  urethra  and  vesical  neck.  The  advantages  claimed  for  it  are  :  (a)  dimin- 
ished hemorrhage  on  account  of  the  relatively  slight  vascularity  of  the  mid-line  ;  (£) 
lessened  risk  of  opening  the  pelvic  fascia  ;  (c~}  lessened  risk  of  wounding  the  ejacu- 
latory  ducts  or  seminal  vesicles.  The  disadvantages  are  :  (a]  the  narrow  space 
between  the  rectum  and  the  deep  urethra,  exposing  the  bulb  and  its  artery  to 
danger  anteriorly  and  the  rectum  posteriorly  ;  (b}  the  lack  of  space  for  the  extrac- 
tion of  even  moderately  large  calculi  ;  (c}  the  increased  risk  of  pushing  the  bladder 
before  the  finger  and  tearing  it  from  the  urethra.  All  these  objections  are  much 
greater  in  the  case  of  children. 

Suprapubic  lithotomy  is  done  by  means  of  an  incision  in  the  mid-line,  imme- 
diately above  the  symphysis,   dividing   skin,   superficial  fascia,   transversalis  fascia 


1922  HUMAN   ANATOMY. 

(there  is  no  distinct  linea  alba  at  this  point),  and  prevesical  fatty  connective  tissue 
in  the  space  of  Retzius.  Sometimes  this  fat  can  be  gently  pushed  or  sponged 
upward  and  carries  the  peritoneum  with  it.  The  method  of  securing  a  non-peritoneal 
area  of  bladder  and  abdominal  wall  for  this  operation  (as  for  others  involving  a 
suprapubic  cystotomy)  has  been  sufficiently  described. 

'The  female  bladder  is  less  capacious  than  the  male  bladder.  Its  longest  diame- 
ter is  transverse,  as  posteriorly  the  pelvic  space  is  occupied  by  the  uterus  and 
vagina,  and  as  the  female  pelvis  is  relatively  wider  than  that  of  the  male. 

The  lesser  depth  of  the  pubic  symphysis  in  the  female  and  the  absence  of  the 
prostate  result  in  a  relatively  lower  vesical  outlet  and  a  short,  direct,  distensible 
urethra,  the,  dilatability  of  which  (also  on  account  of  the  absence  of,  the  prostate) 
extends  to  and  includes  the  vesical  neck. 

As  these  conditions  favor  easy  and  full  evacuation  of  the  bladder,  cystitis  and 
stone  are  comparatively  uncommon  ;  and  as  they  facilitate  intravesical  exploration 
or  operation  per  urethram,  cystotomy  in  the  female  is  rarely  called  for.  Foreign 
bodies  introduced  by  the  urethra  are  relatively  common  in  the  female  bladder. 

The  utero-vesical  pouch  of  peritoneum  does  not  descend  so  low  as  the  recto- 
vesical  pouch  in  the  male.  Below  it  the  close  relations  between  the  bladder  and  the 
cervix  uteri  and  the  upper  half  of  the  vagina  lead  to  the  involvement  of  the  bladder 
in  many  of  the  diseases  originating  in  these  structures.  The  latter  relation  permits 
of  the  recognition  by  vaginal  touch  of  calculi  impacted  in  the  lower  ends  of  the 
ureters,  the  orifices  of  which  are  about  opposite  the  middle  of  the  vagina. 

THE   URETHRA. 

The  urethra — the  canal  conveying  the  urine  from  the  bladder  to  the  exterior  of 
the  body — differs  in  the  two  sexes,  since  in  the  male,  in  addition  to  its  primary  com- 
mon function  of  conducting  the  urine,  it  serves  for  the  escape  of  the  secretions  of  the 
testicles,  seminal  vesicles,  prostate,  Cowper's  glands,  and  urethral  glands.  It  is  of 
interest  to  note  that  in  the  lowest  mammals,  the  monotremes,  in  which  the  urethra  and 
intestine  open  into  a  common  space,  the  cloaca,  the  seminal  duct  is  prolonged  to  the 
end  of  the  penis  as  a  separate  canal.  Embryologically  the  male  urethra  consists  of 
two  parts,  a  posterior  segment — homologous  with  the  canal  in  the  female — beginning 
at  the  bladder  and  ending  at  the  openings  of  the  ejaculatory  ducts,  and  an  anterior 
segment  including  the  remainder  of  the  canal.  With  regard  to  the  regions  of  the 
body  in  which  they  lie,  the  urethra  may  be  considered  as  being  composed  of  a  pel- 
vic, a  perineal,  and  a  penile  portion.  It  is  more  usual,  however,  to  describe  the 
male  urethra  as  consisting  of  the  prostatic,  membranous,  and  spongy  portions, — a 
division  based  upon  more  or  less  definite  anatomical  relations  of  structures  through 
which  it  passes. 

The  prostatic  portion  .(pars  prostatica),  from  2-3  cm.  (^-i^  in.)  in  length, 
descends  with  a  slight  curve,  but  almost  vertically,  from  the  internal  urethral  orifice 
of  the  urethra  to  the  superior  layer  of  the  triangular  ligament.  Beyond  the  vesical 
wall,  which  embraces  its  commencement  (pars  intramuralis  of  Waldeyer),  it  is  en- 
tirely surrounded  by  the  prostate,  which  it  pierces  from  base  to  apex  (Fig.  1619). 
Notwithstanding,  this  part  of  the  urethra  admits  of  considerable  dilatation,  although 
ordinarily  its  lumen  is  more  or  less  obliterated  by  the  apposition  of  the  anterior  and 
posterior  walls.  At  the  two  ends  of  this  division  the  lumen  is  narrower  than  in  the 
intervening  part,  although  this  spindle-form  dilatation  is  reduced  by  the  encroach- 
ment of  a  fusiform  elevation,  the  urethral  crest  (crista  urethralis)  or  verutnontanttm\ 
that  extends  along  the  dorsal  wall  from  the  ridge  (uvula}  on  the  vesical  trigone  above 
to  the  membranous  urethra  below,  into  the  folds  of  which  it  fades,  usually  by  diverging 
ridges  (frenula  cristae  urethralis).  On  transverse  section  (Fig.  1681),  the  lumen  of 
this  part  of  the  urethra  appears  crescentic  in  outline  in  consequence  of  the  projection 
of  the  crest.  The  most  prominent  and  expanded  part  of  the  latter  (colliculus  scnii- 
nalis)  is  occupied  by  the  slit-like  opening  of  the  prostatic  utricle  (utriculus  prostnticus) 
or  sinus  pocularis,  a  tubular  diverticulum,  usually  from  6—8  mm.  in  length,  but  some- 
times much  longer,  that  leads  upward  and  backward  into  the  substance  of  the  pros- 
tate and  represents  the  fused  lower  ends  of  the  Miillerian  ducts  of  the  embryo  ;  the 


THE   URETHRA. 


1923 


FIG.  1632. 


sinus  is,  therefore,  regarded  as  the  morphological  equivalent  of  the  vagina  and  uterus. 
On  the  lateral  lips  of  this  recess  lie  the  small  orifices  of  the  ejaculatory  ducts,  while 
those  of  the  prostatic  tubules  open  into  the  groove-like  depressions  on  either  side  of 
the  urethral  crest.  The  internal  urethral  orifice  lies  approximately  on  a  horizontal 
plane  passing  through  the  middle  of  the  symphysis,  about  2.5  cm.  (i  in.)  behind 
the  latter  and  an  equal  distance  from  its  lower  border. 

The  membranous  portion  (pars  membranacea)  curves  downward  and  forward 
from  the  apex  of  the  prostate  to  the  bulb  of  the  corpus  spongiosum,  which  it  enters 
somewhat  (about  i  cm.  )  in  advance  of  its  posterior  extremity.  In  its  course  the 
membranous  urethra  pierces  both  layers  of  the  triangular  ligament  and  is  surrounded 
by  the  fibres  of  the  compressor  urethrae  muscle  ;  behind  it,  on  either  side  of  the 
mid-line,  lie  the  glands  of  Cowper.  This  part  of  the  canal  measures  only  about  i  cm. 
in  length,  and  is  the  shortest,  narrowest,  and  least  distensible  of  the  segments. 
When  empty,  its  mucous  membrane  is  thrown  into  longitudinal  folds,  and  on  cross- 
section  its  lumen  is  stellate.  In 
consequence  of  its  curved  course, 
the  anterior  wall  is  shorter  than  the 
posterior,  which  marks  the  most 
dependent  point  of  the  subpubic 
curve  that  lies  about  18  mm.  (^ 
in. )  below  and  behind  the  lower 
border  and  in  the  plane  of  the  sym- 
physis. Since  almost  the  entire 
membranous  portion  lies  between 
the  layers  of  the  triangular  liga- 
ment, its  mobility  is  much  less  Vesical  trigone 
than  that  of  the  other  parts  of  the 
urethra.  The  short  terminal  part 
of  the  membranous  urethra  that 
lies  below  the  triangular  ligament 
and  above  and  in  front  of  the  bulb 
as  it  enters  the  corpus  spongiosum 
(pars  praetrigonalis)  is,  however, 
not  only  wider  and  thin-walled, 
but  much  more  movable, — charac- 
teristics that  increase  the  difficulty 
of  guiding  instruments  into  the 
narrow  and  fixed  intratrigonal  seg- 
ment beyond. 

The  spongy  portion  (pars 
cavernosa)  includes  the  remainder 
of  the  canal  and  terminates  at 
the  external  urethral  orifice.  Its 
length  varies  with  the  size  and 

condition  of  the  penis,  but  averages  about  14  cm.  (5^  in.).  In  the  flaccid  condi- 
tion of  the  penis  it  presents  a  double  curve  (Fig.  1619),  the  fixed  proximal  part  of 
which  continues  the  subpubic  curve  forward  and  slightly  upward  through  the  peri- 
neum to  a  point  corresponding  approximately  with  the  attachment  of  the  suspensory 
ligament  to  the  dorsum  of  the  penis,  while  the  freely  movable  distal  part,  or  prepubic 
curve,  follows  the  pendent  penis.  Throughout  its  course  this  part  of  the  urethra  is 
surrounded  by  the  corpus  spongiosum,  at  first  embedded  near  its  upper  border,  then 
about  in  the  middle,  and  at  the  termination  near  its  lower  margin  covered  by  the 
thick  cap  of  spongy  substance  forming  the  glans.  The  lumen  of  the  spongy  portion 
is  variable  both  in  size  and  form  ;  at  its  two  ends,  where  surrounded  by  the  bulb  and 
the  glans,  it  presents  fusiform  dilatations,  the  intermediate  part  being  of  more  uniform 
calibre.  The  first  of  these  dilatations  (fossa  bulbi)  occupies  the  bulb  of  the  corpus 
spongiosum  for  about  2  cm.,  beginning  about  half  that  distance  in  front  of  its  posterior 
extremity.  Abruptly  narrowing  behind,  towards  the  pars  membranacea,  in  front  the 
fossa  gradually  diminishes  into  the  ordinary  lumen  of  the  canal.  The  ducts  of  Cow- 


Ejaculatory  duct 
Prostatic  ducts 


Membranous  urethra 


Spongy  urethra 


Bladder  wall,  cut 


Urethral  crest 

Prostatic  utricle 
Prostate,  cut 


Cowper's  gland 


Opening  of  duct  of 

Cowper's  gland 

Corpus 

cavernosum,  cut 
and  turned  out 


Part  of  bladder  and  male  urethra,  exposed  by  opening  and 
turning-  aside  anterior  wall,  showing  posterior  surface  of  prostatic, 
membranous,  and  beginning  of  spongy  portions  of  urethra. 


1924  HUMAN   ANATOMY. 

per's  glands  open  by  slit-like  orifices  on  the  posterior  wall  or  floor  of  this  part  of  the 
urethra.  The  terminal  dilatation,  the  navicular  fossa  (fossa  navicularis  urethrae), 
occurs  at  the  extreme  distal  end  of  the  canal  within  the  glans  and  opens  onto  the 
surface  by  a  vertical  slit-like  aperture,  the  external  urethral  orifice  (orificium  urethrae 
externum)  or  meatus,  the  most  contracted  and  least  distensible  part  of  the  entire  pas- 
sage. Since  the  lateral  walls  of  the  navicular  fossa  are  in  apposition  except  during 
the  passage  of  fluid,  its  lumen  appears  as  a  vertical  slit  on  cross-section  (Fig.  1674)  ; 
beyond  the  fossa,  however,  the  anterior  and  posterior  walls  come  into  contact,  and 
hence  the  lumen  is  here  represented  by  a  transverse  cleft  (Fig.  1674,  C~),  which  in  the 
region  of  the  bulb  is  replaced  by  one  of  irregularly  stellate  outline. 

The  female  urethra — about  3.5  cm.  (i^  in. )  in  length — is  much  shorter  than 
the  canal  in  the  male  and  embryologically  corresponds  to  the  portion  of  the  latter  that 
lies  between  the  internal  urethral  orifice  and  the  openings  of  the  ejaculatory  ducts. 
Except  at  its  beginning,  the  canal  is  firmly  united  behind  with  the  anterior  vaginal 
wall,  the  downward  and  forward  curve  of  which  it  closely  follows  until  near  its  termi- 
nation, where  it  turns  more  sharply  forward  (Fig.  1622).  In  consequence,  the  lower 
part  of  the  urethro-vaginal  septum  is  somewhat  thicker  below  than  above.  With  the 
exception  of  a  slight  spindle-form  dilatation  about  the  middle  of  its  course,  the  lumen 
of  the  female  urethra  is  fairly  uniform,  with  a  diameter  of  about  7.5  mm.  during 
physiological  distention  ;  except  during  the  passage  of  fluid,  however,  its  walls  are  in 
contact  and  the  mucous  membrane  is  thrown  into  slight  longitudinal  folds.  One  of 
these  on  the  upper  half  of  the  posterior  wall,  known  as  the  urethral  crest,  is  more 
conspicuous,  ineffaceable,  and  continuous  with  the  apex  of  the  vesical  trigone  ;  it  cor- 
responds, therefore,  with  the  similar  ridge  in  the  male  urethra.  The  position  of  its 
termination  below,  on  the  roof  of  the  vestibule,  is  marked  by  a  low,  corrugated,  coni- 
cal elevation  or  papilla  which  surrounds  the  external  urethral  orifice  and  lies  from 
1. 5-2  cm.  below  the  subpubic  border.  The  urethral  orifice,  usually  a  small  sagittal 
slit  about  5  mm.  in  length,  is  subject  to  much  variation  in  size  and  shape,  being  at 
times  triangular,  crescentic,  cruciate,  or  stellate  in  form.  On  the  papilla,  on  either 
side  of  the  mid-line  and  close  to  the  posterior  margin  of  the. urethral  orifice,  lie  the 
minute  openings  of  the  paraurethral  ducts,  or  tubes  of  Skene,  from  1-2  cm.  long, 
which  are  the  excretory  passages  of  small  groups  of  tubular  glands  situated  without 
the  wall  of  the  urethra.  These  ducts,  regarded  as  the  homologues  of  the  prostatic 
ducts  that  open  into  the  grooves  at  the  sides  of  the  urethral  crest,  sometimes  open 
directly  onto  the  posterior  urethral  wall  just  within  the  orificium  externum. 

Structure. —  The  Jlfale  Urethra. — The  wall  of  this  canal  consists  of  a  mucous 
membrane  containing  a  rich  renous  plexus  and  supplemented  in  the  prostatic  and 
membranous  portions  by  considerable  tracts  of  muscular  tissue.  The  mucous  mem- 
brane, which  possesses  an  unusual  amount  of  fine  elastic  fibres,  is  clothed  with  an 
epithelium  that  varies  in  different  parts  of  the  canal.  Throughout  the  upper  two- 
thirds  of  the  prostatic  portion  it  resembles  that  of  the  bladder,  belonging  to  the 
transitional  variety  ;  on  approaching  the  pars  membranacea  the  epithelium  becomes 
columnar  in  type,  usually  being  simple,  bt|t  in  places  suggesting  a  stratified  arrange- 
ment on  account  of  the  presence  of  small  reserve  cells '  between  the  outer  ends  of  the 
chief  epithelial  elements.  This  variety  is  continued  through  the  cavernous  portion  as 
far  as  the  navicular  fossa,  where  the  epithelium  becomes  stratified  squamous  in  type, 
and  at  the  external  orifice  is  directly  continuous  with  the  epidermis  covering  the  glans. 
The  deeper  parts  of  the  mucosa  contain  a  rich  venous  plexus,  and  in  places,  notably 
in  the  urethral  crest,  assume  the  character  of  erectile  tissue.  The  constriction  of  the 
external  orifice  is  due  to  a  ring  of  fibro-elastic  tissue  prolonged  from  the  envelope 
and  septa  of  the  cavernous  tissue  of  the  glans. 

The  muscular  tissue  associated  with  the  male  urethra  includes  intrinsic  and  ex- 
trinsic fibres,  the  former  being  involuntary  in  character  and  directly  incorporated 
with  the  wall  of  the  canal  and  the  latter  being  accessory  bands  of  striped  muscle  de- 
rived from  structures  surrounding  the  duct.  The  intrinsic  musculature  consists  of  an 
inner  longitudinal  and  an  outer  circular  layer,  of  which  the  former  is  thinner  but 
more  widely  distributed,  extending  from  the  internal  urethral  orifice  (where  it  is  con- 
tinuous with  the  superficial  layer  of  the  muscle  of  the  vesical' trigone)  as  far  forward  as 

1  Herzog  :  Archiv  f.  mikro.  Anat.  u.  Kntuirk.,  B<1.  Ixiii.,  1904. 


THE   URETHRA. 


FIG 


1633- 

, Surface  epithelium 


the  orifices  of  the  ducts  of  Cowper's  glands.  The  circular  fibres,  outside  the  longitudi- 
nal, are  best  developed  at  the  internal  orifice,  where  they  form  a  layer  three  or  four 
times  as  thick  as  the  longitudinal,  which  they  accompany  as  a  distinct,  although  di- 
minishing, stratum  as  far 
forward  as  the  termination 
of  the  membranous  ure- 
thra, disappearing  first  on 
the  lower  and  last  on  the 
upper  wall  of  the  fossa 
bulbi.  Beyond  the  pos- 
terior third  of  the  pars 
spongiosum  the  intrinsic 
muscle  is  wanting,  the 
muscular  tissue  surround- 
ing the  remaining  parts 
belonging  to  the  erectile 
tissue  of  the  corpus  spon- 
giosum (Zuckerkandl). 

The  internal  vesical 
sphincter  encircling  the 
commencement  of  the  ure- 


Section  of  mucous  membrane  of  prostatic  urethra,  showing 
gland-like  crypts  in  mucosa.     X  45- 


thra  is  derived  from   the 
deeper  layer  of  the  mus- 
cular sheet  of  the  trigone  ; 
the  muscle  of  the  adjacent  vesical  wall  does  not  directly  take  part  in  its  production 
(Kalischer). 

At  the  apex  of  the  prostate  the  urethra  is  encircled  by  bundles  of  striped  muscle 
known  as  the  external  vesical  sphincter.  Higher  up  these  bundles  lie  entirely  in 
front  of  the  urethra  in  close  relation  with  the  lower  border  of  the  involuntary  sphincter, 
in  front  of  which  they  extend.  Below,  the  external  sphincter  is  continuous  with  the 
compressor  urethrae  muscle,  as  an  upward  prolongation  of  which  it  may  be  regarded 
(Holl).  As  it  passes  between  the  two  layers  of  the  triangular  ligament,  the  mem- 
branous portion  of  the 

FIG.  1634.  urethra    is    enclosed    by 

stout  annular  bundles  of 
the  compressor  urethrae 
muscle,  which  when  stim- 
ulated to  contraction,  as 
by  the  presence  of  an  in- 
strument in  the  canal, 
may  tightly  embrace  the 
urethra  and  embarrass 
the  passage  of  the  cathe- 
ter. These  fibres  are 
continued  forward  for 
some  distance  beyond  the 
lower  layer  of  the  trian- 
gular ligament. 

Since  they  affect  the 
canal,  although  not  in 
intimate  relation  with  its 
wall,  the  fibres  of  the 
bulbo-cavernosus  muscle 
may  also  be  included  in 
the  extrinsic  urethral 
musculature. 


Surface  epithelium 


£r-  Crypt 


Blood-vessels 
in  mucosa 


Venous  spaces 
of  cavernous 
tissue 


Section  of  wall  of  urethra  in  spongy  portion,  showing  crypts 
in  mucosa  and  numerous  venous  spaces.     X  35. 


The  urethral glands \ 

or  glands  of  Littre,  embrace  two  groups— those  within  the  mucous  membrane  and 
those  within  the  submucous  tissue— the  ducts  of  which  are  seen  with  a  magnifying- 


1926 


HUMAN   ANATOMY. 


Surface 
epithelium 

Crypts 


glass  as  minute  openings  on  the  mucous  membrane.  The  former,  the  intramucous 
glands,  are  simple  in  structure,  consisting  usually  of  a  single  alveolus,  less  frequently 
of  two  or  three,  from  .070-.  loomm.  in  diameter.  They  are  lined  with  cylindrical 
epithelium  and  occur  in  all  parts  of  the  urethra,  being  most  numerous  in  the  spongy 
portion  (Herzog).  The  submucous  glands,  although  small,  are  larger  than  those 
limited  to  the  mucosa,  but  are  less  widely  distributed,  being  absent  in  the  distal  half 
of  the  pars  membranacea  and  the  proximal  third  of  the  spongy  portion.  They  are 
most  abundant  and  best  developed  on  the  upper  wall  of  the  spongy  portion,  anterior 
to  the  openings  of  the  ducts  of  Cowper's  glands  (Herzog).  Their  ducts  often  extend 
several  millimetres  obliquely  backward,  more  or  less  parallel  to  the  urethra,  and  divide 
into  two  or  more  slightly  expanded  terminal  tubules  which  are  lined  with  cylindrical 
epithelium.  Where  surrounded  by  the  corpus  spongiosum,  the  submucous  glands  lie 
embedded  within  the  fibrous  tissue  of  the  albuginea  ;  in  the  pars  membranacea  the 
glands  are  surrounded  by  the  bundles  of  the  compressor  urethrae  muscle. 

In  addition  to  the  foregoing  true,  although  small  glands,  the  urethral  mucous 
membrane  is  beset,  along  its  upper  wall  and  near  the  mid-line,  with  small  diverticula 
(lacunae  urethrales)  which  are  little  more  than  tubular  depressions  within  the  lining  of 
the  canal  and  cannot  be  regarded  as  glands,  although  they  often  receive  the  ducts  of 

submucous    glands    that 

FIG.  1635.  open  into  them.     One  of 

exceptional  size  (from  4— 
12  mm.  in  length)  is  com- 
monly found  on  the  roof 
of  the  navicular  fossa,  its 
orifice  being  guarded  by 
a  fold  of  mucous  mem- 
brane (valvula  fossae  na- 
vicularis). 

The  Female  Urethra. 
- — As  in  the  male,  the  wall 
of  this  canal  consists  es- 
sentially of  a  mucous 
membrane  supplemented 
by  an  outer  muscular  tu- 
nic. The  mucous  mem- 
brane, thrown  into  longi- 
tudinal folds  when  the 
canal  is  closed,  is  composed  of  a  tunica  propria,  rich  in  elastic  fibres,  covered  with 
stratified  squamous  epithelium  that  above  resembles  the  vesical  type  and  below  that 
of  the  vestibule.  In  the  female  the  urethral  glands  are  represented  by  small  groups 
of  tubular  alveoli  that  open  by  minute  orifices  on  the  mucous  surface  and  correspond 
to  Lit-tre"' s  glands  in  the  male.  They  are  most  plentiful  in  the  upper  part  of  the  ure- 
thra, and  often,  especially  in  aged  subjects,  contain  concretions  resembling  those 
found  in  the  prostatic  tubules  (Luschka).  The  mucosa  is  also  beset  with  small  pit- 
like  depressions,  similar  in  character  to  the  lacunae  in  the  male,  into  which  the  ducts 
of  the  glands  frequently  open. 

The  muscular  tissue  of  the  female  urethra  comprises  intrinsic  unstriped  fibres 
forming  part  of  the  wall  and  extrinsic  striated  tissue  outside  of  the  canal.  The 
former  are  represented  by  an  inner  layer  of  longitudinally  disposed  fibres  and  an 
outer  one  of  circular  bundles,  the  two  being  separated  by  an  intervening  stratum  of 
areolar  tissue  on  which  a  rich  venous  plexus  confers  the  character  of  erectile  tissue. 
At  the  internal  orifice  the  circular  fibres,  in  conjunction  with  those  from  the  trigone, 
form  the  internal  vesical  sphincter.  Between  the  layers  of  the  triangular  ligament  the 
canal  is  surrounded  by  bundles  of  the  compressor  urethne,  fibres  of  which  arc  pro- 
longed into  the  anterior  vaginal  wall.  The  lower  end  of  the  urethra  is  embraced  by 
the  anterior  fibres  of  the  sphincter  vaginae  muscle  (Lesshaft). 

Vessels. — The  arteries  supplying  the  urethra  are  from  several  sources,  since 
those  distributed  to  the  canal  are  usually  branches  derived  from  the  vessels  passing 
to  the  surrounding  organs.  The  pars  prostatica  receives  twigs  from  the  middle  hem- 


Longitudinal 

muscle 


Circular 
muscle 


Longitudinal  section  of  wall  of  female  urethra. 


X5°- 


PRACTICAL   CONSIDERATIONS  :    MALE   URETHRA.           1927 

orrhoidal  and  the  inferior  vesical  ;  the  membranous  portion  from  the  inferior  hem- 
orrhoidal  and  the  superhcial  perineal  ;  and  the  spongy  portion  from  the  bulbar, 
cavernous,  and  dorsal  arteries  from  the  internal  pudic.  In  the  female  the  urethra  is 
supplied  by  branches  from  the  inferior  vesical,  the  uterine,  and  the  internal  pudic  for 
the  upper,  middle,  and  lower  thirds  respectively. 

The  veins,  which  form  a  rich  plexus  beneath  the  mucous  membrane,  in  the 
proximal  part  are  tributary  to  the  vesical  and  prostatic  veins,  and  in  the  spongy  por- 
tion to  the  dorsal  vein  of  the  penis  and  the  internal  pudic  veins.  In  the  female  the 
veins  empty  into  the  vesico-vaginal  and  pudendal  plexus.  Below  they  communicate 
with  the  venous  spaces  of  the  clitoris  and  the  bulbus  vestibuli  (Waldeyer). 

The  numerous  lymphatics  within  the  mucous  membrane  form  a  proximal  and  a 
distal  set.  The  former  pass  backward  to  join  the  lymphatics  of  the  vesical  trigone, 
the  latter  course  forward  and  unite  with  those  of  the  glans.  The  lymph-tracts  from 
the  spongy  and  membranous  portions  of  the  urethra  communicate  with  the  internal 
or  pubic  group  of  inguinal  lymph-nodes  ;  those  from  the  prostatic  portion  are  affer- 
ents  to  the  internal  iliac  nodes.  In  the  female  the  lymphatics  from  the  upper  part  of 
the  canal  pass  to  the  internal  iliac  nodes  ;  below  they  empty  into  the  lymph-vessels 
of  the  labia  minora  and  communicate  with  the  inguinal  nodes. 

The  nerves  are  from  the  pudic,  which  conveys  sensory  fibres  to  the  mucous 
membrane  and  motor  fibres  to  the  striped  muscle,  and  from  the  hypogastric  plexus 
of  the  sympathetic  by  way  of  the  prostatic  and  cavernous  plexuses. 

PRACTICAL   CONSIDERATIONS  :    THE   MALE   URETHRA. 

• 

Congenital  abnormalities  of  the  urethra  are  not  common.  Absence  of  the  urethra 
usually  causes  death  of  the  foetus  before  birth,  as  urine  is  secreted  and  enters  the 
bladder  during  intra-uterine  life,  the  vesical  distention  then  causing  pressure  upon 
the  umbilical  arteries  and  embarrassment  of  the  fcetal  circulation.  Atresia  of  the 
urethra  may  be  found  at  birth  at  any  point  in  the  canal,  but  if  posterior  to  the  meatus 
is  apt  to  result  in  death  of  the  foetus.  Occasionally  it  affects  only  the  meatus,  the 
mucous  membrane  of  the  glans  presenting  no  orifice,  but  either  yielding  spontane- 
ously to  the  child's  efforts  to  urinate  or  being  readily  penetrated  by  a  probe. 

Contraction  of  the  meatus  so  that  it  will  admit  only  the  finest  probe  is  a  not 
uncommon  congenital  condition,  is  often  associated  with  phimosis,  and  may  cause  a 
sufficient  degree  of  urinary  obstruction  and  of  reflex  irritation  of  the  susceptible 
nerve-centres  of  an  infant  to  require  meatotomy  (q.  v. ). 

Hypospadias. — This  is  a  congenital  deficiency  in  the  lower  wall  of  the  urethra 
which  may  terminate  at  the  perineo-scrotal  junction  or  at  any  point  anterior  to  it. 
The  varieties  of  hypospadias  are  described  in  accordance  with  the  degree  of  arrest 
of  development  (page  2040)  which  has  occurred.  If  this  has  been  extreme,  the 
anterior  orifice  of  the  urethra  may  even  lie  in  the  perineum,  the  two  halves  of  the 
scrotum  remaining  ununited,  and  often  consisting  of  two  separate  pouches,  which  are 
empty  when  the  testicles  have  failed  to  descend,  and  which,  therefore,  resemble 
strongly  the  external  genitalia  of  the  female.  In  these  cases  the  penis  is  atrophied 
and  is  closely  applied  to  the  fissure  in  the  scrotum.  In  the  pcno-scrotal  variety  the 
opening  is  at  the  junction  of  the  anterior  fold  of  the  scrotum  with  the  inferior  surface 
of  the  penis,  and  the  latter  is  apt  to  be  somewhat  better  developed,  although  still 
strongly  curved  downward,  owing  to  its  being  much  shorter  on  its  inferior  than  on 
its  upper  surface.  In  the  penile  variety  of  hypospadias  the  urethral  opening  may 
be  at  any  point  on  the  lower  surface  of  the  penis  between  the  peno-scrotal  junction 
and  the  corona  glandis.  In  the  so-called  balanic  hypospadias  the  opening  of  the 
urethra  is  situated  on  the  under  surface  of  the  glans  ;  the  frenum  is  absent.  There 
is  often  a  little  groove  at  the  anterior  extremity  of  the  glans  which  resembles  the 
normal  meatus,  but  which  usually  ends  posteriorly  in  a  blind  pouch.  When  the 
urethral  orifice  is  situated  far  back,  the  patient  is  usually  sterile,  although  not  neces- 
sarily impotent  if  the  organ  is  well  developed.  Often,  however,  it  is  so  rudimentary 
or  so  markedly  curved  upon  itself  that  intercourse  is  impossible.  The  forms  of  hy- 
pospadias involving  the  glans  are  of  no  physiological  importance  and  require  no 
treatment. 


1928  HUMAN    ANATOMY. 

Epispadias  is  an  absence  of  the  upper  wall  of  the  urethra,  is  much  rarer  than 
hypospadias,  and  is  often  associated  with  exstrophy  of  the  bladder  (page  1911).  It 
may  be  extensive,  in  which  case  the  opening  of  the  urethra  is  close  to  the  pubes,  or 
there  may  be  congenital  absence  of  the  pubic  symphysis. 

In  relation  to  its  injuries  and  diseases  and  to  its  use  as  the  route  by  which  instru- 
ments are  introduced  into  the  bladder,  the  urethra  may  be  divided  into  various  por- 
tions, as  (a)  anterior  and  posterior  ;  (b)  fixed  and  movable  ;  (c)  curved  and  straight ; 
(a)  narrow  and  wide;  (e)  dilatable  and  non-dilatable;  (/)  erectile  and  muscular ; 
(g)  penile,  perincal,  and  prostatic. 

(a)  The  anterior  urethra  includes  all  the  spongy  portion  and  the  posterior  or 
deep  urethra  all  the  prostatic  portion.  They  are  separated,  especially  as  regards 
infectious  processes,  by  the  intervening  membranous  urethra, — that  portion  lying 
between  the  two  layers  of  the  triangular  ligament  and  surrounded  by  the  compressor 
urethrse  muscle.  The  contraction  of  that  muscle,  acting  on  the  narrowed  urethra 
of  this  region,  constitutes  a  natural  barrier  to  the  backward  progress  of  infection, 
and  is  doubtless  aided  in  this  by  the  resistance  to  tumefaction  offered  by  the  un- 
yielding inferior  layer  of  the  triangular  ligament  (the  arbitrary  boundary  of  the 
"anterior"  urethra  posteriorly),  and  possibly,  in  the  ordinary  position  of  the  male 
organ,  by  gravity,  as  the  movable  prepubic  downward  curve  of  the  urethra  (vide 
infra}  begins  only  a  little  anterior  to  that  point.  The  division  is  a  practical  one, 
and  in  its  relation  to  the  most  common  urethral  infection  (gonorrhoea)  affects  both 
prognosis  and  treatment  (page  1931). 

(£)  The  fixed  portion  of  the  urethra  includes  the  prostatic  and  the  membranous 
•portions  and  a  little — from  one  to  one  and  a  half  inches — of  the  posterior  part  of 
the  spongy  portion.  It  may  be  said  to  extend  from  the  neck  of  the  bladder  to  the 
posterior  margin  of  the  suspensory  ligament  of  the  penis,  about  two  and  a  half  inches 
anterior  to  the  inferior  layer  of  the  triangular  ligament.  Of  this  relatively  fixed  portion 
the  membranous  urethra  is  the  only  part  that  has  practically  no  mobility.  The  pros- 
tatic portion  may  be  moved  slightly  within  the  limits  allowed  by  the  pubo-prostatic 
ligaments  and  by  the  connection  of  its  capsule  with  the  superior  layer  of  the  triangular 
ligament  in  front  and  the  recto-vesical  fascia  and  rectum  beneath  and  above.  The 
posterior  part  of  the  spongy  urethra,  the  "bulbous"  portion,  has  even  more  motion 
both  laterally  and  inferiorly,  as  its  movement  in  those  directions  is  not  opposed  by 
any  strong  membranous  or  ligamentous  structure.  Of  course,  anterior  to  the  suspen- 
sory ligament  the  spongy  urethra  moves  with  the  corresponding  portion  of  the  penis. 

This  division,  like  the  one  following,  is  of  great  practical  importance  in  urethral 
or  vesical  instrumentation. 

(c}  The  terms  curved  and  straight,  as  applied  to  the  urethra,  are  purely  rela- 
tive. With  the  penis  flaccid  and  pendent  there  is  almost  no  straight  portion,  and  the 
urethra  presents  a  reversed,  irregular,  S-shaped  curve,  the  upper  segment  of  which 
begins  a  little  anterior  to  the  vesical  orifice  and  is  nearly  vertical,  with  its  concavity 
forward  in  the  erect  position  of  the  subject,  while  the  lower  and  longer  segment  is 
less  vertical,  is  convex  anteriorly,  and  ends  at  the  meatus.  The  whole  urethra  may 
be  divided,  as  to  its  curves,  into  (i)  a  comparatively  fixed  snbpnbic  curve,  including 
most  of  the  prostatic  urethra,  all  of  the  membranous  urethra,  and  that  portion  of  the 
spongy  urethra  posterior  to  the  suspensory  ligament  ;  and  (2)  a  prepubic  curve, 
including  the  remainder.  The  former,  or  fixed,  curve  is,  for  convenience,  described 
as  that  part  of  a  circle  of  three  and  one-quarter  inches  diameter  which  is  subtended  by 
a  cord  two  and  three-quarters  inches  long.  Practically  it  varies  greatly  from  this  stand- 
ard. It  maybe  flattened  out  by  downward  pressure  (the  patient  being  supine)  with 
a  finger  on  each  side  of  the  root  of  the  penis,  thus  elongating  somewhat  the  slightly 
elastic  suspensory  ligament  and  depressing  the  anterior  limb  of  the  curve  ;  it  can 
temporarily  be  obliterated,  as  in  passing  through  it  a  straight  instrument  or  the 
straight  shaft  of  an  instrument  with  a  terminal  curve.  The  two  ends  of  the  curve 
are  approximately  on  the  level  of  a  line  drawn  through  the  under  surface  of  the 
symphysis  at  right  angles  to  its  vertical  axis.  The  summit  of  the.  curve — the  lowest 
point  with  the  subject  erect — is  on  a  line  prolonging  the  vertical  axis  of  the  sym- 
physis, and  is  at  the  centre  of  the  membranous  urethra  and  about  an  inch  behind 
and  below  the  subpubic  ligament. 


PRACTICAL   CONSIDERATIONS  :    MALE   URETHRA.  1929 

The  prepubic  curve  can  be  straightened  by  erecting  or  raising  up  the  penis  as 
is  done  during  the  use  of  urethral  instruments,  most  of  which,  especially  sounds  and 
catheters,  are  made  so  as  to  correspond  in  their  curves  to  the  theoretical  fixed  curve 
above  described.  The  catheters  employed  in  certain  conditions,  especially  prostatic 
hypertrophy,  are  elongated  and  given  a  larger  curve  to  correspond  with  the  elonga- 
tion of  the  prostatic  urethra  and  the  greater  curve  given  it  by  the  elevation  of  the 
vesical  neck  (page  1981). 

(d)  As  the  urethra,  when  not  distended  by  the  passage  of  urine,  semen,  or 
instruments,  is  a  mere  valvular  slit,  the  walls  lying  in  contact,  it  has  to  be  studied  as 
to  width  or  narrowness  by  various  methods  of  dilatation  during  life  and  of  injection 
upon  the  cadaver.  The  result  of  such  studies  demonstrates  that  the  narrow  and 
wider  portions  of  the  urethra  alternate  as  follows  :  the  external  meatus  (the  nar- 
rowest), the  fossa  navicularis,  the  spongy  urethra,  the  bulbous  portion,  the  mem- 
branous urethra,  the  prostatic  urethra,  the  vesical  orifice. 

(<?)  As  to  its  dilatability ', — i.e.,  its  susceptibility  to  distention  by  instruments, — 
the  meatus  is  the  least  distensible,  and  then,  in  order,  follow  the  membranous, 
spongy,  bulbous,  and  prostatic  portions,  the  latter  being  the  most  distensible. 

A  definite  ratio  (nine  to  four)  has  been  thought  to  exist  (Otis)  between  the  cir- 
cumference of  the  flaccid  penis  and  that  of  the  distended  urethra.  A  certain  propor- 
tionate relationship  in  size  between  the  calibre  of  the  urethra  and  the  circumference  of 
the  penis  does  undoubtedly  exist,  but  neither  is  it  so  definite  nor  is  the  urethral  cali- 
bre so  large  as  the  above  figures  would  indicate. 

(f)  At  the  point  at  which  the  prostatic  urethra  enters  the  bladder  it  is  sur- 
rounded by  the  internal  vesical  sphincter,  a  muscle  made  up  of  unstriped  fibres  ;  anteriqr 
to  this  a  double  layer  of  unstriped  muscular  fibres  and  the  glandular  structure  of  the 
prostate  surround  the  urethra.      At  the  apex  of  the  prostate  lies  the  external  vesical 
sphincter,  made  up  chiefly  of  voluntary  muscular  fibres. 

The  discharge  of  urine  from  the  bladder  is  prevented  by  the  tonic  contraction  of 
the  muscular  apparatus  of  the  membranous  and  prostatic  urethra.  As  the  bladder 
becomes  distended,  the  internal  vesical  sphincter  yields  and  the  urine  enters  the  pos- 
terior part  of  the  prostatic  urethra,  causing  a  desire  to  urinate,  which  is  resisted  by  the 
action  of  the  voluntary  fibres  of  the  external  vesical  sphincter  and  the  compressor 
urethrae.  On  passing  a  catheter  when  the  bladder  is  full,  the  urethra  seems  about  an 
inch  shorter  than  it  does  immediately  after  micturition  ;  this  is  owing  to  the  participa- 
tion of  the  posterior  portion  of  the  prostatic  urethra  in  the  retentive  function  of  the 
bladder. 

The  compressor  urethrae  muscle  is  readily  excited  to  reflex  spasm.  Ordinarily, 
on  the  passage  of  instruments,  a  moderate  degree  of  resistance  can  be  detected,  due 
to  the  contraction  of  this  muscle.  In  irritable  conditions  of  the  mucous  membrane 
there  may  be  excited  a  spasm  so  violent  that  it  will  be  impossible  to  introduce  a  soft 
instrument.  Such  spasm  may  also  be  excited  by  irritation  of  the  prostatic  urethra 
either  from  distention  of  the  bladder  or  from  any  other  cause.  Thus  it  is  often  found 
extremely  difficult  to  evacuate  the  bladder  when  the  desire  to  urinate  has  been  re- 
sisted for  many  hours,  and  acute  inflammation  of  the  posterior  urethra  not  infrequently 
requires  the  use  of  catheters  to  overcome  the  tight  muscular  contraction  of  the  com- 
pressor urethrae  which  prevents  micturition.  Not  only  the  introduction  of  sounds,  but 
even  the  injection  of  bland  liquids  will  cause  contraction  of  the  compressor  urethrae 
muscle,  and  hence  prevent  such  injection  from  reaching  the  membranous  or  the  pros- 
tatic urethra.  Any  inflammation  in  these  portions  of  the  urethra  will  also  cause  the 
tonic  contraction  of  the  sphincter  muscles  to  be  accentuated.  Hence  inflammatory 
discharge  from  the  membranous  or  the  prostatic  urethra  will  tend  to  flow,  not  for- 
ward, but  into  the  bladder,  and  injections  intended  to  reach  the  deep  urethra  will,  if 
driven  in  at  the  meatus,  extend  no  farther  back  than  the  inferior  layer  of  the  trian- 
gular ligament. 

There  seem,  then,  to  be  good  grounds,  both  from  a  physiological  and  from  a 
clinical  stand-point,  for  dividing  the  urethra  into  an  anterior  erectile  part  and  a  pos- 
terior muscular  part. 

(g)  The  penile  urethra  terminates  at  the  anterior  margin  of  the  suspensory  liga- 
ment ;  the  perineal  urethra  includes  the  bulbous  (with  the  so-called  pretrigonal  or 


1930  HUMAN   ANATOMY. 

prediaphragmatic  portion)  and  membranous  urethrae  ;  the prostatic  urethra,  of  course, 
extends  thence  to  the  bladder.  All  of  these  terms  are  in  constant  use,  and  a  consid- 
eration of  the  urethra  from  the  stand-points  suggested  by  its  subdivisions  as  above 
described  cannot  fail  to  be  useful  in  relation  to  its  injuries  and  diseases. 

Subcutaneous  rupture  of  the  urethra  is  rarely  seen  in  its  penile  portion.  In  the 
great  majority  of  cases  (92  per  cent.)  it  affects  the  perineal  portion  (80  per  cent,  from 
falls  astride,  12  per  cent,  from  perineal  blows),  and  in  the  majority  of  these  the  bul- 
bous urethra  suffers  most  severely.  The  mechanism  of  rupture  varies  with  the  size 
and  shape  of  the  vulnerating  body,  but  the  urethra  is  usually  crushed  against  either 
the  transverse  ligament  or  subpubic  arch,  the  anterior  face  of  the  pubis  (which  is 
placed  at  an  angle  of  only  30  degrees  with  the  horizon),  or  the  ischiatic  or  pubic 
rami.  In  cases  of  fracture  of  the  pelvis  or  temporary  or  permanent  disjunction  of  the 
pubic  symphysis,  the  membranous  urethra  may  be  lacerated  by  the  fragments  or  may 
be  torn  partly  or  completely  across  by  the  drag  upon  it  of  the  triangular  ligament. 

The  rupture  may  be  complete  or  incomplete,  the  former  being  more  common  in 
the  membranous  urethra  on  account  of  (a)  its  fixity  ;  (£)  the  density  of  the  triangular 
ligament ;  (c)  its  proximity  to  the  pubes  and  ischium  ;  (</)  the  relative  thinness  of  its 
walls  ;  and  (e}  the  absence  of  the  protection  afforded  by  erectile  tissue,  which  is 
present  in  only  a  scanty  layer.  The  symptoms  are  hemorrhage  from  the  meatus  or 
into  the  bladder,  or  both  ;  difficult  or  painful  urination,  or  retention  of  urine  ;  swelling 
usually  in  the  perineum  or  at  the  perineo-scrotal  junction  ;  and  later  extravasation  of 
urine,  which  will  be  guided  in  certain  definite  directions  in  accordance  with  the  locality 
of  the  rupture  (vide  infra). 

Urethritis,  almost  always  due  to  gonococcus  infection,  but  sometimes  caused  by 
the  ordinary  pyogenic  organisms  aided  by  congestion  from  trauma  (catheter  urethritis), 
may  from  the  anatomical  stand-point  best  be  divided  into  anterior  and  posterior. 

Anterior  urethritis  affects  that  portion  of  the  urethra  in  front  of  the  compressor 
urethrae  muscle  ;  the  following  characteristic  symptoms  and  complications  are  due  to 
its  situation  :  (a)  free  discharge  from  the  meatus  ;  (^)  ardor  urines,  due  partly  to 
the  mechanical  disturbance  of  the  flow  of  the  stream  of  urine  (converting  the  urethral 
slit  into  a  suitable  channel  and  separating  the  apposed  walls),  but  chiefly  to  the  con- 
tact of  the  acid  and  saline  urine  with  the  inflamed  mucosa  ;  (c)  frequent  and  painful 
erection,  due  (i)  to  irritation  of  the  lumbar  centre,  causing  increased  blood-supply 
through  the  dorsal  arteries  and  the  arteries  to  the  bulb  and  corpora  cavernosa  ;  (2) 
to  the  compression  of  the  dorsal  vein  of  the  penis  by  clonic  contraction  of  the  com- 
pressor urethrae  and  bulbo-cavernosus  muscles,  and  to  the  compression  of  the  penis 
itself  against  the  pubic  arch  by  similar  contraction  of  the  ischio-cavernosus  also 
obstructing  the  return  current  ;  (3)  to  the  loss  of  elasticity  by  the  congested,  infil- 
trated mucous  membrane  and  submucous  connective  tissue,  which  are  not  able  to 
stretch  as  they  normally  do  when  the  cavernous  bodies  become  engorged  with  blood  ; 
(d)  chordee,  a  curvation  of  the  penis  due  to  the  fact  that  the  inflammation  extends  to  the 
submucous  connective  tissue,  and  thence  to  the  trabeculae  of  the  erectile  tissue  of  the 
spongy  body.  The  exudation  of  lymph  consequent  upon  this  fills  up  the  intratra- 
becular  spaces,  which  by  engorgement  furnish  the  ordinary  mechanical  element 
of  normal  erection.  When  the  organ  becomes  erect  the  corpora  cavernosa  are  fully 
engorged  with  venous  blood.  The  infiltrated  portion  of  the  corpus  spongiosum,  how- 
ever, remains  rigid  and  undilatable,  the  blood  being  unable  to  find  its  way  into  the 
partially  obliterated  spaces.  If  the  inflammation  extends  to  the  corpora  cavernosa, 
erections  will  be  equally  painful  ;  but  in  this  case  the  curve  will  be  upward.  If  only 
one  cavernous  body  is  involved,  the  curve,  of  course,  will  be  towards  the  affected 
side  ;  (e*)  follicular  m  peri-urethral  abscess,  due  to  involvement  of  the  urethral  folli- 
cles and  to  occlusion  of  their  mouths  by  swelling  of  the  mucosa,  preventing  drainage 
into  the  urethra  ;  (f)  lymphangitis  and  bubo,  usually  associated  with  retention  of 
discharge  and  inflammation  between  the  prepuce  and  glans,  the  infection  extending 
by  the  superficial  lymphatics  and  reaching  one  of  the  superficial  nocli-s  lying  just  below 
Poupart's  ligament,  embedded  in  the  subcutaneous  cellular  tissue'  and  above  tin-  fascia 
lata.  The  lymphatics  more  directly  connected  with  the  urethra  itself  belong  to  the 
deeper  set,  and  run  beneath  the  pubic  arch  to  join  the  deep  pelvic  lymphatics  and  to 
terminate  in  the  lumbar  nodes. 


PRACTICAL   CONSIDERATIONS:    MALE   URETHRA.  1931 

A  rare  complication  ( Cowperitis}  may  result  from  infection  of  the  bulbo- 
urethral  glands  through  their  ducts  which  empty  into  the  bulbous  urethra.  The 
first  symptom  usually  developed  is  pain  in  the  perineum,  much  increased  by  press- 
ure, and  rendering  sitting  or  walking  markedly  painful.  The  inflammatory  swell- 
ing of  the  glands  is  resisted  by  the  two  layers  of  the  triangular  ligament  between 
which  they  are  situated  and  by  the  deep  perineal  fascia,  and  this  resistance,  associ- 
ated with  the  determination  of  blood  to  the  part  by  gravitation,  imparts,  as  in  other 
inflammations  where  the  same  conditions  exist,  a  throbbing  element  to  the  pain 
which  renders  it  peculiarly  distressing. 

Posterior  Urethritis. — Although  it  is  true  that  the  compressor  urethrse  muscle 
constitutes  a  sphincter  which,  by  its  tonic  contraction,  keeps  the  membranous  part 
of  the  canal  constantly  closed  against  injections  forced  through  the  meatus,  the 
gonococcus,  as  it  passes  backward  in  the  deeper  layers  of  the  epithelium,  is  not 
arrested  by  this  muscle,  but  with  few  exceptions  invades  the  posterior  urethra,  from 
which  region  it  can  readily  extend  to  the  prostatic  ducts,  the  seminal  vesicles,  the 
vas  and  epididymis,  and,  much  more  exceptionally,  to  Cowper's  glands  and  to  the 
bladder. 

To  some  or  all  of  the  above  symptoms  may  then  be  added  :  (a}  frequent  and 
urgent  urination,  as  the  normal  slight^  desire  to  urinate,  felt  when  the  bladder  is 
moderately  distended,  the  internal  vesical  sphincter  dilates,  and  the  urine  comes  in 
contact  with  the  prostatic  urethra,  is  transformed  into  an  uncontrollable  desire  when 
the  prostatic  mucosa  is  inflamed  and  hypersensitive  ;  (<£)  tenesmus  from  spasm  of 
the  internal  sphincter  transmitted  to  the  detrusors  and  due  to  the  same  excitation 
in  the  neighborhood  of  the  vesical  neck  ;  (V)  cystitis  (page  1914)  may  follow  direct 
extension  of  the  infection  by  way  of  the  mucosa  ;  (</)  prostatitis  (page  1980)  from 
its  spread  along  the  prostatic  ducts  or  into  the  prostatic  follicles  ;  (e)  epididymitis 
(page  1952);  or  (_/)  vesiculitis  (page  1960),  from  its  following  the  vas  deferens  or 
the  seminal  ducts. 

Chronic  iirethritis  is  apt  to  follow  an  acute  attack  because  :  (a)  the  canal  affords 
periodical  passage  to  a  secretion,  the  urine,  which  is  liable,  by  reason  of  changes  in 
its  constitution,  to  become  an  actual  irritant;  (3)  it  is  exposed,  at  times  of  erection, 
to  intense  congestion  of  all  its  vessels,  and  the  converse  is  also  true,  a  congested  or 
irritated  spot  along  the  urethra  predisposing  to  erection  ;  (<:)  gravitation,  the  propor- 
tionately excessive  supply  of  blood  to  the  region,  and  the  absence  of  extravascular 
resistance  due  to  the  loose  character  of  the  spongy  tissue,  all  favor  the  persistence 
of  any  congestion  left  after  a  first  attack  of  urethritis  ;  (d)  the  condition  of  approxi- 
mation of  mucous  surfaces,  as  of  the  urethral  walls  during  the  intervals  of  micturition, 
is  here,  as  elsewhere,  unfavorable  to  the  disappearance  of  granular  or  injected  areas 
or  other  traces  of  inflammation.  The  tendency  of  the  gonococcus  to  establish  itself 
in  the  deeper  layers  of  the  mucous  lining,  and  to  multiply  there  where  it  is  compara- 
tively inaccessible,  is  another  cause  of  the  frequent  occurrence  of  the  chronic  forms 
of  urethral  inflammation. 

Stricture  of  the  urethra  is  an  important  and  frequent  sequel  of  urethritis.  It 
consists  essentially  in  a  contracting  peri-urethral  deposit  of  fibrous  tissue  due  to  the 
organization  of  the  exudate  deposited  in  the  submucosa  during  the  existence  of  a 
urethritis.  The  situation  of  stricture  varies,  but  there  can  be  no  doubt  that  the  great 
majority  are  to  be  found  in  the  bulbo-membranous  region,  which  includes  a  space 
from  about  one  inch  in  front  of  the  anterior  layer  of  the  triangular  ligament  to  the 
prostato-membranous  junction.  The  next  most  frequent  seat  is  in  the  first  two  inches 
of  the  urethra.  The  frequency  of  strictures  in  these  regions  is  due  to  the  fact  that 
they  are  exceptionally  vascular  and  that  chronic  urethritis  is  especially  apt  to  become 
localized  at  those  points.  The  especial  abundance  of  follicles  in  the  bulbous  urethra 
favors  urine  leakage  and  submucous  exudate  there.  Gravitation  in  both  regions 
favors  chronic  congestion  and  may  possibly  of  itself  explain  the  clinical  facts  as  to 
frequency.  The  smallest  number  are  found  in  the  middle  of  the  spongy  urethra. 
These  remarks  apply  to  the  form  of  stricture  produced  by  urethritis.  Traumatic 
stricture  usually  affects  the  membranous  urethra.  Stricture  of  the  prostatic  urethra 
is  practically  unknown,  probably  because  in  that  region  the  submucous  connective 
tissue  is  relatively  scanty,  the  urethra  is  lined  with  vesical  or  transitional  instead  of 


1932  HUMAN   ANATOMY. 

columnar  epithelium  and  is  supported  on  all  sides  by  the  firm  glandular  structure, 
thus  offering  greater  resistance  to  and  limiting  the  outward  passage  of  inflammatory 
exudate  or  of  urine. 

The  subjective  symptoms  of  stricture  are  due  to  the  interference  of  the  coarctation 
with  the  normal  passage  of  urine  through  the  urethral  canal  and  to  the  physical 
changes  in  the  urethra,  and  the  resulting  irritation  and  inflammation. 

The  urethra  behind  a  stricture  becomes  dilated  and  thinned,  the  walls  atrophy,  it 
is  deeply  congested,  the  increasing  pressure  produces  pouching  or  dilatation,  the 
retained  urine,  decomposing,  sets  up  a  superficial  inflammation,  the  mucosa  is  denuded 
of  its  epithelial  layer,  urine  escapes  into  the  spongy  tissue,  and  abscess  or  serious 
extravasation  may  follow. 

During  this  process  (which  may  not  pass  through  all  these  stages)  the  most 
important  symptoms  having  a  definite  anatomical  basis  are  as  follows  : 

(a)  Frequency  of  urination  :  this  arises  first  from  the  change  in  relation  between 
the  expulsive  force  required  of  the  bladder  and  the  accustomed  demands  upon  it  ;  then 
from  extension  of  inflammation  backward  by  continuity  until  the  vesical  neck  is 
involved  ;  often  from  the  production  of  a  genuine  cystitis  ;  later  from  atony  with 
retention. 

(6)  Dribbling  after  urination  depends  ^upon  the  retention  behind  the  stricture 
of  some  drops  of  urine,  which  escape  by  gravity  after  the  act  of  micturition  is  com- 
plete. It  is  not  infrequently  a  very  early  symptom,  dependent  on  irregular  action  of 
the  circular  muscle-fibres  of  the  urethra.  The  dribbling,  which  is  called  the  ' '  incon- 
tinence of  retention," — the  overflow  from  a  distended  bladder, — is  a  very  late  symp- 
tom, following  retention  and  usually  associated  with  a  high  degree  of  atony.  The 
incontinence  of  stricture  is  to  be  diagnosticated  from  the  incontinence  of  prostatic 
hypertrophy  by  the  fact  that  it  is  at  first  worse  in  the  daytime,  and  only  becomes 
nocturnal  later.  The  reverse  is  the  case  in  prostatic  incontinence.  The  mechanism 
of  incontinence  of  urethral  origin  is  simple.  The  dilatation  of  the  urethra  behind  the 
stricture  having  extended  to  the  neck  of  the  bladder,  the  urinary  reservoir  becomes 
in  shape  a  funnel,  the  bladder  representing  the  base,  the  neck  situated  at  the  point  of 
stricture.  The  patient  being  in  the  erect  position,  the  weight  of  the  column  of  urine 
comes  directly  on  the  stricture,  which  permits  it  to  filter  through  drop  by  drop.  In 
dorsal  decubitus,  on  the  other  hand,  the  bladder  fills  up  and  retains  its  contents  until 
the  changes  in  it  and  in  the  urethra  are  very  far  advanced.  In  the  prostatic  patient 
it  is  possible  that  the  physiological  congestion  of  the  lumbar  cord  produced  by  the 
recumbent  posture  makes  urination  more  frequent  at  night  and  during  the  early 
morning  hours.  It  lessens  as  the  day  goes  on,  and  it  is  only  later  when  the  bladder 
becomes  confirmed  in  irritability  that  diurnal  frequency  follows. 

(c)  Retention  of  urine  may  occur  early  and  suddenly  from  an  acute  increase  of 
the  congestion  of  the  mucous  membrane  of  the  strictured  region,  or  it  may  be  a  late 
symptom  and  dependent  on  the  great  obstruction  offered  by  the  stricture. 

Ardor  urinze,  change  in  the  character  of  the  stream,  diminution  of  expulsive 
power,  vesical  tenesmus,  and  urethral  discharge  may  occur,  but  are  not  constant,  and 
require  no  explanation  from  an  anatomical  stand-point. 

(af)  Extravasation  of  urine  is  one  of  the  most  serious  of  the  late  results  of 
stricture.  The  localizing  symptoms — those  which  indicate  the  point  at  which  the 
urethra  has  given  way — depend  upon  the  course  taken  by  the  urine.  In  all  that  part 
from  the  meatus  to  the  scrotal  curve,  extravasation  is  accompanied  by  a  swelling  of 
the  penis,  greatest  in  the  immediate  neighborhood  of  the  point  of  escape.  In  the 
region  included  between  the  attachment  of  the  scrotum  and  the  posterior  part  of  the 
bulb  the  course  of  extravasated  urine  is  governed  by  the  attachments  of  the  deep 
layer  of  the  superficial  fascia,  or  the  fascia  of  Colles.  Extravasation  <>f  urim-  occurring 
through  a  solution  of  continuity  in  this  region  of  the  urethra  will  first  follow  the  space 
enclosed  by  this  fascia  in  front  and  below  and  by  the  inferior  layer  of  the  triangular 
ligament  posteriorly,  and  as  it  cannot  reach  the  ischio-rectal  space  on  account  of  the 
attachment  of  the  fascia  to  the  base  of  the  ligament,  and  cannot  reach  the  thighs  on 
account  of  the  attachment  of  tin-  fascia  to  the  ischio-pubic  line,  it  is  directed  into  the 
scrotal  tissues,  and  thence  up  between  the  pubic  spine  and  symphysis  until  it  reaches 
the  abdomen. 


PRACTICAL   CONSIDERATIONS  :    MALE   URETHRA.           1933 

When  it  escapes  from  the  membranous  urethra,  extravasated  urine  is  confined 
to  the  region  included  between  the  layers  of  the  triangular  ligament,  and  only  gains 
access  to  the  other  parts  after  suppuration  and  sloughing  have  given  it  an  outlet,  the 
consecutive  symptoms  then  depending  upon  the  portion  of  the  aponeurotic  wall  which 
first  gave  way.  If  the  opening  is  situated  behind  the  superior  layer  of  the  triangular 
ligament, — i.e.,  in  the  prostatic  urethra, — the  urine  may  either  follow  the  course  of 
the  rectum,  making  its  appearance  in  the  anal  perineum,  or,  as  it  is  separated  from 
the  pelvis  only  by  the  thin  pelvic  fascia,  it  may  make  its  way  through  the  latter  near 
the  pubo-prostatic  ligament,  and  may  spread  rapidly  through  the  subperitoneal  con- 
nective tissue. 

(e)  The  bladder,  ureteral,  and  kidney  changes  are  similar  to  those  that  follow 
obstruction  from  any  other  cause,  and  cystitis,  sacculated  bladder,  ureteral  dilatation, 
and  pyonephritis  are  not  uncommonly  terminal  conditions  in  cases  of  stricture. 

Catheterism  is  one  of  the  most  important  of  the  minor  operations  of  surgery. 
For  its  proper  performance,  even  in  the  normal  urethra,  an  acquaintance  with  the 
differences  in  direction,  mobility,  dilatability,  and  contractility  of  that  canal  is  essen- 
tial (vide  supra},  as  is  familiarity  with  its  relations  to  such  structures  and  organs  as 
the  triangular  ligament,  the  prostate,  and  the  rectum  (q.v.}.  The  following  points 
are  worthy  of  mention  here  in  their  relation  to  the  anatomy  of  the  urethra,  (a) 
The  penis  is  gently  stretched,  the  dorsum  facing  the  abdominal  wall  to  avoid  folds  or 
twists  in  the  mobile  anterior  urethra,  (b)  In  persons  with  protuberant  bellies  the 
shaft  of  the  catheter  is  at  first  kept  parallel  with  the  line  of  the  groin  ;  if  this  is  not 
done,  the  point  of  the  instrument  may  be  made  to  catch  in  the  upper  wall,  at  the  tri- 
angular ligament,  owing  to  the  elevation  of  the  handle  necessitated  by  the  protrusion 
of  the  abdomen  ;  the  handle  should,  in  any  event,  be  kept  low  until  the  tip  of  the 
instrument  is  about  to  enter  the  membranous  urethra,  (c)  The  penis  is  drawn  up 
with  the  left  hand  while  the  instrument  is  gradually  pushed  onward,  the  handle  being 
finally  swept  around  to  the  median  line,  the  shaft  being  kept  parallel  to  the  anterior 
plane  of  the  body  and  nearly  touching  the  integument.  The  instrument  is  now  . 
pressed  downward  towards  the  feet,  while  the  left  hand  still  steadies  the  penis  and 
makes  slight  upward  traction.  After  four  or  five  inches  of  the  shaft  have  disappeared 
within  the  urethra,  it  will  be  found  that  the  downward  motion  of  the  instrument  is 
arrested,  (d)  The  fingers  of  the  left  hand  are  then  shifted  to  the  perineum  and  used 
as  a  fulcrum,  while  the  handle  is  lifted  from  its  close  relation  with  the  anterior  abdomi- 
nal wall  and  swept  gently  over  in  the  median  line,  describing  the  arc  of  a  circle,  (e) 
After  the  shaft  has  reached  and  passed  the  perpendicular,  the  handle  should  be  taken 
in  the  left  hand  and  the  index  and  middle  fingers  of  the  right  hand  should  be  placed 
one  on  either  side  of  the  root  of  the  penis,  making  downward  pressure  (to  straighten 
the  anterior  limb  of  the  subpubic  curve,  vide  supra},  while  the  left  hand,  depressing 
the  handle,  carries  the  point  of  the  instrument  through  the  membranous  and  prostatic 
urethra  into  the  bladder.  The  entrance  into  that  organ  will  be  recognized  by  the  free 
motion  that  can  be  given  the  tip  of  the  instrument  when  the  handle  is  rotated,  and  by 
the  latter  remaining  exactly  in  the  median  line  and  pointing  away  from  the  pubes 
when  the  hold  upon  it  is  relaxed. 

In  urethral  instrumentation  it  should  never  be  forgotten  that  the  elasticity  or 
extensibility  of  the  urethra  resides  for  the  most  part  in  the  spongy  portion,  as  is  clearly 
demonstrated  by  erection,  and  this  elasticity  belongs  in  the  greatest  degree  to  the 
inferior  wall,  which  permits  of  easy  distention  or  elongation,  and  changes  its  dimen- 
sions and  form  with  notable  facility  ;  while  the  superior  wall  yields  with  much  more 
reluctance,  and  offers  a  certain  resistance  to  all  agents  tending  to  depress  or  elongate 
it.  This  difference  increases  with  age,  and  obtains  especially  in  senile  urethra. 

The  extensibility  of  the  inferior  wall  is  brought  into  play  even  by  a  moderate 
force,  and  the  surgeon  cannot  count  on  its  resistance.  It  glides  before  an  instrument, 
and  cannot  serve  to  guide  it  ;  it  cannot  be  incised  with  any  accuracy  or  precision  ;  it 
lacerates  or  ruptures  when  surprised  by  distention  ;  and  it  yields  rapidly  and  easily 
to  mechanical  pressure  testing  its  extensibility.  It  should  be  noted,  too,  that  this 
elongation  of  the  canal  is  chiefly  at  the  expense  of  the  anterior  urethra.  Again,  the 
spongy  portion  does  not  yield  equally  in  all  its  parts,  since  it  has  been  shown  that  of 
the  different  regions  the  perineo-bulbar  is  the  most  distensible.  The  inferior  wall  of 


1934 


HTM  AN   ANATOMY. 


the  urethra  can  then  be  considered  as  normally  longer  than  the  superior  surface.  The 
term  "surgical  wall,"  proposed  for  the  upper  wall  by  Guyon,  would  seem  to  be 
merited,  because  it  offers  the  shortest  route  to  the  bladder,  is  the  most  regular  and 
constant  as  to  form  and  direction,  presents  the  smoothest  and  firmest  surface,  is  the 
less  capable  of  gliding  before  an  instrument  or  being  modified  by  mechanical  pressure, 
offers  the  greatest  resistance  to  rupture  and  penetration,  is  less  intimately  connected 
with  important  structures,  and  is  the  less  vascular  of  the  two  walls.  As  to  the  calibre 
and  distensibility  of  the  urethra,  enough  has  already  been  said  ;  but  it  should  not  be 
forgotten  that  there  are  three  relatively  constricted  parts,  the  internal  or  vesical  mea- 
tus,  the  external  meatus,  and  the  membranous  regions  ;  and  three  dilatations,  the 
fossa  navicularis,  the  bulbar  cul-de-sac,  and  the  prostatic  depression,  the  last  two  dila- 
tations presenting  numerous  individual  variations  ;  and  in  this  connection  it  is  impor- 
tant to  remark  that  all  three  of  these  dilatations  are  excavated  at  the  expense  of  the 
inferior  wall  of  the  canal.  The  urethral  curve  only  remaining  regular  in  the  superior 
wall,  it  results  that  the  more  pronounced  the  curve  the  more  accentuated  are  the  bul- 
bar and  prostatic  depressions  ;  and  as  a  certain  degree  of  lengthening  of  the  urethra 
always  corresponds  to  the  greatest  curve, — since  these  are  both  produced  by  bulbar 
and  prostatic  augmentation  of  volume, — one  can  reasonably  conclude  that  urethrae  of 
the  greatest  curves  present  at  the  same  time  the  greatest  length.  With  a  knowledge 
of  these  facts,  the  instrumental  exploration  of  the  urethra  becomes  a  matter  of  much 
accuracy  and  precision  (Morrow). 

The  anatomy  of  the  various  forms  of  urethrotomy  and  other  operations  on  the 
urethra  is  sufficiently  dealt  with  in  the  foregoing  and  in  the  practical  considerations 
relative  to  the  bladder,  male  perineum,  and  prostate  (q.v.}. 


DEVELOPMENT   OF   THE   URINARY   ORGANS. 

The  development  of  the  essential  parts  of  the  urinary  tract — the  kidney  and  its 
duct — is  so  intimately  related  with  the  foetal  excretory  organ,  the  Wolffian  body,  that 
a  brief  account  of  the  latter  and  of  the  principles  underlying  its  genesis  is  a  necessary 
introduction  to  the  intelligent  consideration  of  the  subject  here  to  be  presented.  The 
excretory  apparatus  of  amniotic  vertebrates,  even  in  the  highest  mammals  and  man, 
includes  three  structures  which,  although  as  functionating  organs  existing  in  no 
single  animal,  stand  in  genealogical  sequence.  These  are  the  pronephros,  the  meso- 
nephros  or  Wolffian  body,  and  the  metancphros  or  definitive  kidney. 

The  Pronephros. — The  first  of  these,  the  pronephros,  sometimes  called  the  "  head-kidney" 
on  account  of  its  anterior  position  in  its  primary  condition,  in  all  higher  forms  is  at  best  a  rudi- 
mentary and  functionless  organ  ;  nevertheless,  it  is  of  extreme  interest  as  indicating  the  funcla- 


FIG.   1636. 
Neural  tube        Somite 


FIG.   1637. 

Neural  tube 

Somite 


Intermediate  mass 
Ectoblast 
Parietal  mesoblast 


Body-cavity 
Visceral  mesoblast 
ntoblast 

Part  of  transverse  section  of  c.irlv  rabbit  em- 
bryo, showing  primary  division  of  mesoblast  into 
somite,  internu'diati-  mass,  and  parietal  and  vis- 
ceral layers.  X  100. 


Anlage  of  nephric  duct 
Parietal  mesoblast 


Body-cavity 

Visceral  mesoblast 
Remains  of  inU-itm'iliaU-  mass 

Section  of  slightly  older  embryo,  show- 
ing differentiation  of  duct-anlagc  and  mass  in 
which  tubules  develop.  X  100. 


mental  plan  upon  which,  in  a  modified  form,  the  later  Wolffian  body  is  developed.  Although,  so 
far  as  known  existing  as  a  permanent  organ  alone  in  the  hag  fishes  (  MyxiiwkeY  as  a  temporary 
structure  the  pronephros  attains  considerable  development  in  many  fishes  and  amphibians;  in 
the  higher  animals,  even  as  an  embryonal  organ,  it  remains  very  rudimentary  and  transient. 
When  adequately  represented,  the  pronephros  consists  of  a  more  or  less  extensive  series  of 


DEVELOPMENT   OF   THE   URINARY   ORGANS. 


1935 


slightly  transverse  tubules  within  the  postero-lateral  body-wall  that  internally  communicate 
with  the  body-cavity  or  ccelom,  the  openings  being  known  as  nephrostomata,  and  externally 
join  a  common  canal,  the  pronephric  duct,  which  extends  caudally  and  empties  into  the  dilated 
terminal  segment  of  the  intestinal  tube,  the  cloaca.  In  relation  with  the  inner  end  of  each 
tubule,  but  projecting  freely  into  the  body-cavity,  lies  a  group  of  convoluted  blood-vessels,  the 
glomerulus,  supplied  by  branches  of  the  aorta.  These  three  parts  of  the  primitive  excretory 


FIG.   1638. 


tegument 


Semitic  ca 

Malpighian  body  of  m 
Mesonephr 


Mesonephric  d 


Pron 


Parietal  peritoneum 
Body-ca 


ity  of  somite  continuous  with  ccelom 
otochord 


phric  tubule 

Pronephric  duct 
Mesoblast  of  body-wall 


cavity  (coelom) 
omerulus  of  pronephros 


Suprarenal  body/         Gut-tube 


Aorta 
Visceral  peritoneum 


Diagram  showing  fundamental  relations  of  pronephros  (on  right  side)  and  of  mesonephros 
or  Wolffian  body  (on  left  side  of  figure).     (Wiedersheim.) 


FIG.  1639. 


organ  provide  for  the  essential  requirements  of  the  most  elaborate  urinary  apparatus, — the  pro- 
duction of  the  watery  constituents,  the  excretion  of  the  waste  products,  and  the  conveyance  of  the 
excretion  so  elaborated.  The  pronephros  is  fundamentally  a  segmental  organ,  the  tubules  being 
so  arranged  that  each  corresponds  to  a  single  body-segment  or  metamere,  although  by  no  means 
every  such  division  contains  a  tubule.  It  may  be  assumed  that  the  tubules  of  the  pronephros 
represent  the  segmental  ducts  which  in  ancestral  forms  extended  from  the  body-cavity  directly 
onto  the  external  surface  of  the  body  and  thus  carried  off  the  fluids  accumulated  within  the 
coelom.  In  consequence  of  the  closure  of  this  direct  communication  with  the  exterior,  which 
may  be  accepted  as  having  occurred  during  the  evolution  of  a  more  elaborate  excretory  system, 
the  necessity  for  a  new  path  of  exit  is  met  by  the  formation  of  the  common  pronephric  duct  into 
which  the  tubules  open,  and  which,  by  its  prolongation  to  and  termination  in  the  end-gut,  insures 
the  escape  of  the  excretions. 

The  development  of  the  pronephros  is  closely  associated  with  the  mesoblastic  somites.  A 
transverse  section  of  an  early  mammalian  embryo  (Fig.  1636)  shows  theparaxial  mesoblast,  be- 
tween the  neural  canal  and  the  cleavage  of  the  lateral 
mesoblast  into  the  somatic  and  visceral  plates,  to  comprise 
two  parts,  the  mesial  forming  the  somite  and  the  lateral  or 
intermediate  cell-mass.  It  may  be  assumed  that  in  the 
higher  types  the  solid  somite  and  the  intermediate  cell- 
mass  have  arisen  by  fusion  of  the  primarily  distinct  dorsal 
and  ventral  mesoblastic  plates  (Fig.  1638).  The  inter- 
mediate cell-mass  soon  separates  into  a  small  duct-anlage, 
situated  dorsally  and  in  close  relation  with  the  ectoblast, 
and  a  larger  ventral  tract  comprising  the  remainder  of  the 
intermediate  cell-mass.  Within  this  ventral  area  the  tu- 
bules shortly  appear,  and  later  the  glomeruli.  Although 
reaching  a  comparatively  high  development  in  certain  fishes 
and  amphibians  (especially  in  Ichthyophis  described  by  Se- 
mon),  in  mammals  the  pronephros  consists  of  a  few  tubules 
connected  with  the  duct,  and  even  as  an  organ  of  embryonic 
life  never  attains  more  than  a  feeble  and  transient  exist- 
ence. In  the  human  embryo  of  3  mm.  length,  studied  by 
Janosik,  it  was  represented  by  two  rudimentary  tubules  that 
extended  from  the  mesothelial  lining  of  the  body-cavity 
towards  the  pronephric  duct,  with  which  one  of  the  tubules 
still  communicated.  The  pronephros  of  the  amniotic  ver- 
tebrates, therefore,  must  be  regarded  as  a  rudimentary 
inherited  organ  which  appears  in  response  to  transmitted 
ancestral  tendencies. 

The    Mesonephros    or  Wolffian  Body. — This   organ 

may  conveniently  be  regarded  as  comprising  a  later  generation  of  excretory  tubules  opening  into 
a  common  canal,  the  Wolffian  duct,  which  is  usually  looked  upon  as  the  continuation  and  mor- 
phological persistence  of  the  pronephric  duct.  In  their  development  these  tubules  and  duct  bear 
a  similar  relation  to  the  intermediate  cell-mass  as  do  those  of  the  pronephros,  only  the  body- 
segments  involved  lie  farther  tail  ward  and  the  strict  segmental  arrangement  of  the  tubules  is  lost 
owing  to  their  multiplication  and,  as  in  mammals,  precocious  development.  In  contrast  to  the 


Body-cavity 


Longitudinal  section  of  young  embryo, 
showing  early  stage  of  Wolffian  body ;  tu- 
bules are  joining  duct.  X  50. 


1936 


HUMAN   ANATOMY. 


FIG.    1640. 


rudimentary  character  of  the  pronephros,  the  Wolffian  body  not  only  serves  for  a  time  as  the 
chief  excretory  organ  of  the  embryo,  but  in  many  lower  vertebrates  continues  to  functionate 
during  life.  The  anlage  of  the  Wolffian  duct  first  appears  as  bud- like  outgrowths  from  the  dor- 
sal side  of  the  intermediate  cell-mass  ;  these  fuse  into  a  strand  which,  separating  from  the  cell- 
mass,  lies  as  a  solid  cord  beneath 
the  ectoblast.  The  latter  takes  no 
part  in  the  formation  of  the  duct, 
which  is  entirely  of  mesoblastic 
origin,  the  appearances  leading  to 
the  assumption  by  certain  authori- 
ties of  its  derivation  from  the  outer 
germ-layer  depending  upon  the 
temporary  apposition  or  attach- 
ment that  the  duct  effects  in  con- 
sequence, probably,  of  its  inher- 
ited inclination,  since  in  ancestral 
forms  the  tubules  opened  on  the 
free  ectoblastic  surface.  At  first 
solid,  the  Wolffian  duct  later  pos- 
sesses a  lumen  which  gradually 
follows  the  tailward  growth  of  the 
strand  until,  finally,  it  opens  into 
Wolffian  duct 

Mesothelium 

Wolffian  tubule  Developing  capsule 


"Aortic 
branch  to 
glomerulus 


Part  of  transverse  section  of  embryo,  showing  commencing  develop- 
ment of  Malpighian  corpuscle  in  Wolffian  body.     X  150. 


Capsule  of  Malpighian 
body 


the  dilated  end-gut  or  cloaca. 

In  mammals  the  Wolffian 
tubules  are  developed  within  the 
ventral  division  of  the  intermedi- 
ate cell-mass  as  solid  cords  that 
later  acquire  a  lumen  and  an  at- 

tachment to  the  Wolffian  duct.     Although  in  the  lower  vertebrates  (fishes,  amphibians)  retain- 

ing a  communication  with  the  coelom  by  means  of  a  nephrostome,  in  mammals  this  connection 

is  lost  and  the*  expanded  inner  end  of  each  tubule  comes  in  close  relation  with  the  convoluted 

vascular  tuft,  the  glomerulus,  which  now,  however,  no  longer  projects  freely  into  the  body- 

cavity.     As  in  the  kidney,  the  glomerulus  is  supplied  by  an  afferent  twig  from  a  branch  of  the 

aorta,  and  is  drained  by  an  efferent  vessel  that  breaks  up  into  a  capillary  net-work  surrounding 

the   convoluted  tubule  and  eventually 

becomes  tributary  to  the  cardinal  vein.  FIG.   1641. 

The  first  appearance  of  the  Wolffian 

body  in  the  human  embryo  occurs  very 

early  (2.4  mm.  length)  and  at  a  time 

when  the  remains  of  the  pronephros  are 

still  present.      The  duct  precedes  the 

tubules  and  opens  into  the  cloaca  in  em- 

bryos of  4.2  mm.  length  (Keibel),  the 

tubules,  which  develop  independently, 

establishing    communication    with    the 

duct  shortly  before.     The  development 

of  the  glomeruli  is  relatively  tardy,  since 

these  bodies  are    not  found    until   the 

human  embryo  has  attained  a   length 

of  about  7  mm.      Their  formation  and 

growth  continue  during   the  first  and 

second  months  until  the  embryo  meas- 

ures 22  mm,  in  length,  when  their  great- 

est perfection  is  reached  (Nagel). 

When  fully  developed,  about  the 

end  of  the  second  month,  the  Wolffian 

body  appears   as  an    elongated   organ 

(Fig.  1720  }  which  extends  along  almost 

the  entire  length  of  the  posterior  wall 

of  the  body-cavity,  on  either  side  of  the 

mid-line,  from  behind  the  lung-anlage  to 

the  lower  end  of  the  gut-tube.     About 

the  eighth  week,  the  Wolffian  body  en- 

ters upon  its  stage  of  regression  which, 

continuing  during  the  third  and  fourth 

months  of  foetal  life,  results  in  the  grad- 

ual atrophy  of  the  organ  and  its  replace- 

ment   as    the    functionating    excretory 

gland  by  the  kidney  which  meanwhile 

lias  been  formed.    This  atrophy  invokes 


Wolffian  duct 

Transverse  section  of  fully  developed  Wolffian  body, 
showing  also  indifferent  sexual  gland.     X  80. 


first  the  glomeruli  of  the  anterior  portion  of  the  organ,  which,  together  with  many  of  the  tubules, 
completely  degenerate,  the  retrogressive  process  extending  tailward  and  gradually  involving  the 
middle  and  posterior  segments.  Although  the  glomeruli  suffer  destruction,  some  of  the  tubules 
and  the  Wolffian  duct  for  a  time  remain  and  contribute  in  varying  degree,  according  to  the  sex 


DEVELOPMENT   OF   THE   URINARY   ORGANS. 


1937 


pIQ 


Primary  collecting 
tubules  opening 
into  subdivisions 
of  pelvis 

Renal  pelvis 


Stroma 


Malpighian  body 


Malpighian 
corpuscle  of 

atrophic 
Wolffian 
-body 


Longitudinal  section  through  developinc 
tion  of  atrophic  Wolffian  body  is  seen  1 


kidney ;  por- 
elow.    X  35- 


of  the  foetus,  to  the  formation  of  certain  structures  and  parts  of  the  excretory  canals  of  the 

sexual  glands.     In  the  male  the  Wolffian  duct  and  tubules  persist  chiefly  as  the  vas  deferens  and 

the  epididymis  ;  in  the  female,  in  whom  the 

atrophy  is  more  complete,  these  remains  are 

represented  principally  by  the  epoophoron  and 

Gartner's  duct.      In  both  sexes  certain  ad- 

ditional  rudimentary   organs  —  the  paradidy- 

mis  in  the  male  and  the  paroophoron  in  the 

female  —  are  derived  from  the  tubules  of  the 

sexual  segment  of  the  Wolffian  body.    A  more 

detailed  account  of  these  transformations  is 

given  in  connection  with  the  development  of 

the  reproductive  organs  (page  2037  and  Fig. 

1719). 

The  Metanephrosor  Kidney.  — 
The  development  of  the  definitive  kidney 
in  mammals  begins  as  a  pouch-like  out- 
growth from  the  posterior  wall  of  the 
Wolffian  duct,  a  short  distance  above  its 
termination  into  the  cloaca.  In  man  the 
renal  diverticulum  makes  its  appearance 
during  the  fourth  week,  at  which  time 
the  embryo  measures  from  6-7  mm.  in 
length.  At  first  short  and  wide,  the  stalk 
of  the  pyriform  sac  soon  becomes  tubu- 
lar, growing  upward  and  backward  into 
the  mesoblast  of  the  posterior  body-wall. 
This  stalk  rapidly  elongates,  and  termi- 
nates above  in  a  blind  club-shaped  ex- 
tremity which  after  a  time  lies  behind  the 
upper  atrophic  segment  of  the  Wolffian 
body.  The  tubular  duct  becomes  the 

ureter  and  its  dilated  end-segment  the  renal  pelvis.     The  latter  is  surrounded  by  a 
sharply  defined  oval  area  of  compact  mesoblast  that  is  intimately  concerned  in  the 

production  of  the  convo- 
FIG.  1643.  luted    kidney-tubules  (of 

Ampullary  terminations  of  _**?-  __  which    as    yet    no   trace  is 

s  ^^.^^ri^ss^SSSg^^s&^^SSBSEs^        present),    and    hence    is 

termed  therenal  'blastema. 
From  the  ventral  and 
dorsal  walls  of  the  primi- 
tive pelvis,  which  is  com- 
pressed from  before  back- 
ward, a  number  of  hollow 
sprouts  grow  into  the 
surrounding  mesoblastic 
stroma.  Each  is  a  short 
cylinder  that  terminates 
in  a  slight  dilatation.  At 
first  few,  these  sprouts  in- 
crease rapidly  in  number 
as  well  as  in  length,  and 
by  repeated  dichotomous 
division  give  rise  to  a  sys- 
tem of  branching  canals 
that  later  are  represented 
by  the  straight  collecting 
tubules  of  the  kidney. 
Concerning  the  ori- 

gin of  the  remaining  portions  of  the  uriniferous  tubules  two  opposed  views  obtain. 

According  to  the  one,  all  parts  of  these  canals  develop  as  direct  continuations  of  the 


Developing  v 

Malpighian 

bodies 


„    . 

Primary 
collecting 
tube 


Large  col- 
lecting duct 


Section  of  developing  kidney,  showing  formation  of  urinifer- 
ous tubules  and  collecting  canals.     X  100. 


1938 


HUMAN    ANATOMY. 


Right 
umbilical  artery 


Gut-tube 


outgrowths  from  the  primitive  renal  pelvis  ;  according  to  the  other,  the  convoluted 
tubules  (from  their  beginning  in  the  capsule  to  their  termination  in  the  collecting 
tubules  within  the  medullary  ray)  arise  independently  within  the  renal  blastema, 
and,  secondarily,  unite  with  the  duct-system  from  the  pelvis  to  complete  the  canals. 
The  careful  studies  and  reconstructions  of  Huber l  leave  little  doubt  as  to  the  cor- 
rectness of  the  latter  view,  which, 

FIG.  1644.  moreover,  accords  with  the  prin- 

ciple observed  in  the  develop- 
ment of  the  pronephros  and  the 
Wolffian  body,  in  which  the  tu- 
bules and  the  duct  join  subse- 
quent to  an  independent  forma- 
tion. The  attenuated  proximal 
end  of  the  convoluted  tubule — for 
a  short  time  solid  and  in  close  rela- 
tion with  the  anlage  of  the  glom- 
erulus — soon  becomes  a  sickle-like 
process  which  gradually  incom- 
pletely surrounds  the  vascular  tuft 
and  later  expands  into  the  charac- 
teristic capsule.  With  the  con- 
tinued growth  of  the  tubules  their 
tortuosity  becomes  more  marked, 
the  loop  of  Henle  early  becoming 
a  conspicuous  feature  of  their  course.  By  the  third  month  the  formation  and  group- 
ing of  the  tubules  have  progressed  to  such  extent  that  the  surface  of  the  young 
kidney  exhibits  the  outlines  of  the  individual  lobes  composing  the  organ.  This  lobu- 
lation  is  retained  until  some  months  after  birth.  In  addition  to  the  convoluted  tubules, 
the  vascular  and  supporting  tissues  are  derived  from  the  renal  blastema,  the  con- 
densed peripheral  part  of  which  becomes  the  fibrous  capsule  of  the  kidney.  As  the 
latter  assumes  the  r61e  of  active  excretory  organ,  the  Wolffian  body  undergoes  atrophy, 
with  the  exception  of  such  parts  as  are  concerned  in  the  development  of  the  sexual 
ducts. 

The  Bladder  and  the   Urethra. — The  details  of   the  development  of   the 
bladder  and  urethra  in  mammals  and  man  have  been  materially  advanced  by  the 


Notochord 


End-gut 
Tail-bud 

Reconstruction  of  caudal  portion  of  human  embryo  of  seven- 
teen days  (3  mm.  greatest  length),  showing  cloaca  connected 
with  gut  and  allantoic  duct.  X  48.  (Drawnfrom  Keibel  model.) 


AHantoic  duct 


Fio.  1645 

Gut-tube 


FIG.  1646. 


Gut-tube 


Allantoic  duct 


Cloacal  membrane 


Reconstruction  of  cloacal  region  of  human 
embryo  of  twenty-six  days  (6.5  mm.  length)  ; 
Wolffian  duct  opens  into  ventral  segment  of 
cloaca.  X  75-  (Drawn  from  Keibel  model. ) 


Cloacal  membrane 


Preceding  model  viewed  from  li.uht  M<|<-.  ^l 
ing  beginning  division  of  clo:u\i  into  vi-ntral  (uro- 
xenitul)  and  dorsal  (intestinal)  segment  by  longi- 
tudinal septal  fold.  (Drawn  from  Keibel  model.) 


investigations  of  Keibel,  Retterer,  and  Nagel,  upon  whose  conclusions  the  following 

account  is  based.       A  sagittal  section  through  the  caudal  pole  of  an  early  human 

embryo  of   6.5  mm.,  about  the  beginning  of  the  fourth  week  (Fig.  1645),  exhibits 

'American  Journal  of  Anatomy,  vol.  iv.,  Supplement,  1905. 


DEVELOPMENT   OF   THE   URINARY    ORGANS. 


1939 


FIG.   1647. 


Aorta 


Allantoic 
duct 


the  end-segment  of  the  gut  dilated  into  an  elongated  chamber,  the  cloaca,  from  the 
upper  end  of  which  the  allantois  passes  forward  and  on  the  sides  of  which  open  the 
Wolffian  ducts.  The  ventral  wall  of  this  space  is  thin,  and  consists  of  the  opposed 
outer  and  inner  germ-layers  alone,  no  mesoblast  intervening.  This  ecto-entoblastic 
septum  is  the  cloacal  mem- 
brane. During  the  fourth  week 
the  subdivision  of  the  cloaca 
into  a  ventral  and  a  dorsal 
compartment  begins  by  the  for- 
mation of  a  frontal  fold  that  Belly-stall^ 
projects  downward  from  the 
angle  between  the  gut  and  the 
allantois.  Subsequently  this 
partition  is  supplemented  by 
two  lateral  folds  that  appear  on 
the  side  walls  of  the  cloaca  and 
are  continuous  above  with  the 
frontal  fold  (Fig.  1646).  By 
the  union  of  these  three  plicae, 
above  and  from  the  sides,  a 
septum  is  formed  that  gradu- 
ally grows  caudally  and  sub- 
divides the  cloaca  into  a  ventral 
allantoic  and  a  dorsal  intestinal  chamber.  This  partition,  however,  for  a  time  is  incom- 
plete below,  communication  between  the  two  spaces  being  thus  maintained. 

During  these  changes  the  short  canals  common  to  the  Wolffian  ducts  and  the 
primitive  ureters  are  drawn  into  the  ventral  chamber,  the  four  tubes  thereafter  open- 
ing independently,  but  in  close  proximity,  on  the  posterior  wall  of  the  ventral  cloaco- 
allantoic  space.  This  undergoes  further  differentiation  into  an  upper  (vesical)  and  a 
lower  (genital)  segment,  the  latter  gradually  narrowing  into  a  tubular  space,  closed 
below  by  the  fore  part  of  the  cloacal  membrane,  which  becomes  the  uro-genital 
sinus  and,  after  rupture  of  the  membranous  floor,  communicates  with  the  exterior. 
For  a  time  the  orifices  of  the  Wolffian  ducts  and  the  ureters  are  closely  grouped, 

those  of  the  former,  how- 
1648. 


Tail  

\  \  Notochord 

duct     Renal  pelvis 

Reconstruction  of  cloacal  region  of  human  embryo  of  thirty-three 
days  (11.5  mm.  length);  cloaca  now  incompletely  separated  into  uro- 
genital  and  intestinal  segments.  X  25.  (Drawn  from  Keibel  model.) 


FIG. 


Notochord 


Wolffian  duct 


Reconstruction  of  cloacal  region  of  human  embryo  of  thirty-seven  days 
(14  mm.  length);  ureter  now  opens  independently  into  uro-genital  sinus, 
which  above  contributes  lower  segment  of  bladder  and  below  is  now  almost 
separated  from  gut-tube.  X  17.  (Drawn  from  Keibel  model.') 


ever,  lying  nearer  the 
mid-line  and  slightly 
higher  than  the  more 
widely  separated  ureteral 
openings. 

During  the  second 
month  an  important 
modification  of  these 
relations  occurs,  associ- 
ated with  elongation  and 
expansion  of  the  upper 
part  of  the  vesical  seg- 
ment, by  which  the  ure- 
ters are  drawn  upward 
and  the  Wolffian  ducts 
downward.  The  inter- 
vening tract  corresponds 
to  the  lower  segment  of 
a  spindle-shaped  sac  that 
extends  upward  and  is 


continued  towards  the 
umbilicus  by  the  allantois.  The  upper  part  of  this  sac,  which  is  the  dilated  allantois, 
forms  the  body  and  summit  of  the  bladder  and  the  urachus  ;  the  lower  part,  into 
which  the  ureters  open  (Fig.  1649)  and  which  is  derived  from  both  allantois  and 
cloaca,  differentiates  into  the  vesical  trigone  and  the  urethra  as  far  as  the  openings  of 


1940 


HUMAN   ANATOMY. 


the  ejaculatory  ducts, — the  permanent  representatives  of  the  Wolffian  ducts.  In  the 
female  the  tract  produces  the  entire  urethra,  since  the  orifice  of  the  sexual  canals 
opens  into  the  uro-genital  sinus.  The  bladder,  therefore,  is  composite  in  origin,  its 


Broad  ligament 


FIG.  1649. 


,Ovary 


Bladder 


Symphysi; 


Clitoris 

Glans 
Epithelial  knob. 


Uro-genital  sinus 


Rectum 


L  Spinal  cord 


Notochord 


Ureter 
Miillerian  ducts 


Wolffian  duct 


Reconstruction  of  human  embryo  of  nine  weeks  (25  mm.  length) ;  ureter  has  migrated  to 
bladder,  leaving  Wolffian  and  Miillerian  ducts  attached  to  uro-genital  sinus,  which  is  com- 
pletely separated  from  intestine.  X  10.  (Drawn  from  Keibel  model.) 

upper  part  being  from  the  allantois  alone,  while  in  the  formation  of  the  trigonal  region 
both  allantois  and  cloaca  take  part.  The  remaining  portions  of  the  urethra  in  the 
male  are  formed  by  the  extension  of  the  uro-genital  sinus  along  the  under  surface  of 
the  corpora  cavernosa  of  the  developing  penis  (page  2044). 


THE   TESTES. 


1941 


THE  MALE  REPRODUCTIVE  ORGANS. 

THIS  group  comprises  the  sexual  glands  (the  testes),  the  ducts  (vasa  deferentia) 
and  their  appendages  (the  seminal  vesicles'),  the  copulative  organ  (the  penis),  and 
certain  accessory  glands  (the  prostate  and  Cowper1  s  glands).  Although  at  first 
situated  within  the  abdominal  cavity,  the  testes  migrate  through  the  inguinal  canal 
into  the  scrotum,  which  sac  they  usually  gain  shortly  before  birth.  In  their  descent 
they  are  accompanied  by  blood-vessels,  lymphatics,  nerves  and  their  ducts,  which 
structures,  with  the  supporting  and  investing  tissue,  constitute  the  spermatic  cord  that 
extends  from  the  internal  abdominal  ring  through  the  abdominal  wall  to  the  scrotum. 


THE   TESTES. 

As  often  employed,  the  term  "  testicle"  includes  two  essentially  different  parts, 
the  testis— the  true  sexual  gland — and  the  epididymis,  the  highly  convoluted  begin- 
ning of  the  spermatic  duct. 

The  testes,  or  testicles  proper,  the  glands  producing  the  seminal  elements,  are  two 
slightly  compressed  ellipsoidal  bodies  so  suspended  within  the  scrotum — the  left  lower 

FIG.  1650. 


Lower  end  of  spermatic  cord,  with 

strands  of  cremaster  muscle' 


Tunica  vaginalis 
communis,  cut 


Tunica  vaginalis 
cut 


Epididymis. 


Globus 
minor 

Reflection  of 
tunica  vaginalis 
covering  scrotal 
ligament 


Tunica  vaginalis  communis 


Tunica  vaginalis 

Globus  major  of 

epididymis 
Appendix  epididymidis 


Appendix  testis 


Sac  of  tunica 
vaginalis 

Right  testis 


Serous  sa 


Reflection  of  serous  covering 


A,  antero-lateral  view  of  right  testicle  after  enveloping  membranes  have  been  cut  and 
turned  aside ;  £,  antero-median  view  of  same. 

than  the  right — that  their  long  axes  are  not  vertical,  but  directed  somewhat  forward 
and  outward.  Each  testis  measures  from  4-4.5  cm.  (i^-i^  in.)  in  length,  about 
2.5  cm.  in  breadth,  and  2  cm.  in  thickness,  and  presents  a  lateral  and  a  medial  sur- 
face, separated  by  an  anterior  and  a  posterior  border,  and  an  upper  and  a  lower  pole. 
The  lateral  surface  looks  outward  and  backward,  and  the  flatter  medial  one  inward 
and  forward.  Both  surfaces,  as  well  as  the  anterior  border,  are  completely  covered 
with  serous  membrane  (the  visceral  layer  of  the  tunica  vaginalis)  and  are,  therefore, 
smooth.  The  rounded  anterior  border  is  free  and  most  convex,  the  much  less  arched 
posterior  border,  covered  by  the  epididymis  and  attached  to  the  spermatic  cord,  being 
devoid  of  serous  membrane  and  corresponding  to  the  hilum.  In  consequence  of  the 
obliquity  of  the  long  axis  of  the  organ,  the  upper  pole,  capped  by  the  head  of  the 
epididymis,  lies  farther  outward  and  forward  than  the  more  pointed  lower  one,  which 
is  related  to  the  tail  of  the  epididymis  and  attached  to  the  scrotal  ligament  (page 


1942 


HUMAN   ANATOMY. 


2042).     The  testis  is  of  a  whitish  color,  and,  although  readily  yielding,  imparts  a 
characteristic  impression  of  resilience  when  compressed  between  the  fingers. 

Architecture  of  the  Testis. — The  framework  of  the  testicle  proper  consists 
of  a  stout  capsule,  the  tunica  albuginea,  a  dense  fibre-elastic  envelope  from  .4-.  6  mm. 
in  thickness,  that  gives  form  to  the  organ  and  protects  the  subjacent  soft  glandular 
tissue.  Along  the  posterior  border  of  the  testis  the  capsule  is  greatly  thickened 
and  projects  forward  as  the  mediastinum  testis  or  corpus  Highnwri,  a  wedge-shaped 
body  (from  2.5-3  cm-  m  length),  from  which  radiate  a  number  of  membranous  septa 
that  pass  to  the  inner  surface  of  the  tunica  albuginea.  In  this  manner  the  space 
within  the  capsule  is  subdivided  into  pyramidal  compartments,  the  bases  of  which  lie 
at  the  periphery  and  the  apices  at  the  mediastinum.  These  spaces  contain  from  150 
to  200  pyriform  masses  of  glandular  tissue,  more  or  less  completely  separated  from 
one  another,  that  correspond  to  lobules  (lobuli  testis).  Each  of  the  latter  is  made  up 
of  from  one  to  three  greatly  convoluted  seminiferous  tubules,  held  together  by  delicate 
vascular  intertubular  connective  tissue. 

The  seminiferous  tubules — from  .15-.  25  mm.  in  diameter  and  from  25-70  cm. 
(10—28  in.)  in  length — begin  as  blind  canals,  which  are  moderately  branched  and 

very  tortuous  ( tubuli  contorti)  throughout  their 
course  until  they  converge  at  the  apex  of  the 
lobule,  where  they  pass  over,  either  directly 
or  after  junction  with  another  canal,  into  the 
narrow,  straight  tubules  (tubuli  recti}  that 
enter  the  mediastinum  and  unite  into  a  close 
net-work,  the  rete  testis.  The  latter  extends 
almost  the  entire  length  of  the  mediastinum, 
and  consists  of  a  system  of  irregular  inter- 
communicating channels,  the  cuboid  epithelial 
lining  of  which  rests  directly  upon  the  en- 
sheathing  fibrous  tissue  of  the  mediastinum. 
With  these  passages  the  canals  of  the  testicle 
proper  end,  the  immediate  continuation  of  the 
spermatic  tract  being  formed  by  from  fifteen 
to  twenty  tubules,  the  ductuli  efferentes,  that 
pierce  the  tunica  albuginea  along  the  posterior 
border  and  near  the  upper  pole  of  the  testis 
and,  forming  the  coni  vasculosi,  connect  the 
sexual  gland  with  the  tube  of  the  epididymis. 
Structure. — In  contrast  to  the  dense 
fibre-elastic  tissue  that  composes  the  frame- 
work of  the  testis, — the  capsule,  mediastinum,  and  interlobular  septa, — the  con- 
nective tissue  occupying  the  spaces  between  the  seminiferous  tubules  is  loose  in 
texture  and  arrangement,  consisting  of  delicate  bundles  of  white  fibrous  tissue  in 
which  elastic  fibres  are  few  or  absent.  In  addition  to  the  plate-like  cells,  leucocytes, 
and  eosinophiles  that  occur  in  varying  numbers  within  the  meshes  of  this  tissue  in 
conjunction  with  blood-vessels  and  nerves,  groups  or  cord-like  masses  of  peculiar 
polygonal  elements,  the  interstitial  cells,  also  occupy  the  intertubular  stroma,  especi- 
ally in  the  vicinity  of  the  mediastinum.  These  cells  (Fig.  1654),  from  .01 5-. 020 
mm.  in  diameter,  possess  relatively  small  round  or  oval  eccentrically  placed  nuclei 
and  a  finely  granular  protoplasm  that  usually  contains  numerous  brownish  droplets, 
pigment  particles,  and,  sometimes,  crystalloid  bodies  in  the  form  of  minute  needles 
or  rods.  In  some  animals,  notably  in  the  hog,  the  deeply  colored  interstitial  cells 
form  conspicuous  tracts  that  impart  a  dark  tint  to  the  testicle  in  section.  Their 
significance  is  obscure,  but  they  are  probably  modified  connective-tissue  elements 
derived  from  the  mesoblast  of  the  germinal  ridge  (Allen,  Whitehead). 

The  wall  of  the  convoluted  seminiferous  tubules  consists  of  a  delicate  tunica 
propria,  composed  of  an  inner  elastic  lamella  strengthened  externally  by  circularly 
disposed  fibres,  within  which  are  several  layers  of  epithelial  cells.  The  latter  vary 
not  only  before  and  after  the  attainment  of  sexual  maturity,  but  subsequently  with 
functional  activity  or  rest  ;  in  man,  however,  the  variations  depending  upon  these 


FIG.  1651. 

Globus  major  of  epididymis 
— Vas  deferens 

Coni 

vasculosi 

Ductus 

epididymidis 

Ductuli 

efferentes 

Tubuli  recti 

Rete  testis  in 

mediastinum 

Tubuli 

contorti 

Vas  aberrans 

Ductus 
epididymidis 
Globus  minor 


Septum        Tunica  albuginea 


Diagram  showing  relations  of  secretory 
tubules  and  system  of  ducts. 


THE   TESTES. 


1943 


causes  are  much  less  marked  than  in  animals,  in  which  sexual  activity  is  limited  to 
definite  periods.  Seen  in  sections  of  the  mature  human  testicle  (Fig.  1656),  the  epi- 
thelium lining  the  seminiferous  tubules  includes  two  chief  kinds  of  cells,  the  support- 
ing and  the  spermatogenetic.  The  former — the  cells  of  Sertoli — take  no  active  part 
in  the  production  of  the  spermatozoa,  but  serve  chiefly  as  temporary  supports  for  the 
more  essential  elements  during  certain  stages  of  spermatogenesis.  They  are  elongated 
elements  of  irregularly  pyramidal  form  that  rest  by  expanded  bases  upon  the  mem- 
brana  propria,  and  project  towards  the  lumen  of  the  tubule  between  the  layers  of  the 


FIG.  1652. 


Epididym 


Convolutions  of  duct  of  epididymis  in  globus  major 


t%r^*t\ ^S*//**^*        -<?°  Q^ppkos*  -a  o^O^Q    .r*<^*1v^ 

^$8?%  »sdls^L^2BRlSs.  v, 

v;i»a  o/lOJSi^.  ^ 


Joni  vasculpsi 
(convolutions  of 


Digital  fos 
Serous  surface  of  testis 


"  •        - 

••• 


Sections  of  duct  of 
epididymis 


Blood-vessels 


Rete  testis  in  mediastinum 


Interlobular  septum 
Tunica  albuginea 


— r — Lobules  of  gland-tissue 


Convolutions  of  duct  of 
epididymis  in  globus  minor 


Sagittal  section  of  testicle  of  child,  showing  general  arrangement  of  framework  and 
gland-tissue  and  of  canals  connecting  epididymis  with  testis.     X  10. 

surrounding  spermatogenetic  cells.  The  large  oval  nuclei  of  the  Sertoli  cells  are  con- 
spicuously meagre  in  chromatin,  and  lie  towards  the  middle  of  the  cell  at  some  distance 
from  its  base.  The  outer  part  of  the  protoplasm  contains  fat-droplets,  the  inner  zone 
being  granular  or  often  longitudinally  striated.  Where  the  tubuli  contorti  pass  into 
the  straight  tubules  the  supporting  cells  become  reduced  in  height  and  form  a  layer 
of  simple  columnar  cells  continuous  with  the  low  cuboidal  epithelium  lining  the  rete 
testis. 

The  spermatogenetic  cells  include  three  forms  that  stand  in  the  relation  of  suc- 
ceeding generations  to  one  another,  those  representing  the  oldest  lying  nearest  the 


1944 


HUMAN   ANATOMY. 


membrana  propria,  and  the  youngest,  from  which  the  spermatic  filaments  are  directly 
derived,  next  the  lumen  of  the  tubule.  The  first  generation,  the  spermatogones,  lie 
at  the  periphery  between  the  cells  of  Sertoli,  and,  although  small  round  elements, 

FIG.  1653. 


Seminiferous  tubule, 
cut  obliquely 


Tunica  albuginea 


Seminiferous  tubule, 
cut  transversely 


Group  of  interstitial  cells 


Tunica  vaginalis 


Portion  of  cross-section  of  testis,  showing  dense  fibrous  envelope 
and  adjacent  seminiferous  tubules.     X  30. 

possess  nuclei  exceedingly  rich  in  chromatin.  The  division  of  these  cells  results  in 
two  cells,  of  which  one  retains  the  position  of  the  parent  cell,  which  it  replaces  as  a 
new  spermatogone  destined  for  a  succeeding  division,  while  the  other  passes  inward, 
enlarges,  and  becomes  a  mother  cell  or  primary  spermatocyte  of  the  second  genera- 
tion. This  element,  conspicuous  by  reason  of  its  size  and  large  nucleus,  undergoes 
mitotic  division  and  gives  rise  to  daughter  cells  or  secondary  spermatocytes.  The 
latter  almost  immediately  divide  and  produce  smaller  cells,  the  spermatids,  by  the 
transformation  of  which  the  spermatic  filaments  are  directly  produced.  It  is  impor- 
tant to  note  that  the  spermatids 
contain  only  one-half  of  the  num- 
ber of  chromosomes  normal  for 
the  ordinary  (somatic)  cells,  a 
like  reduction  (page  18)  occur- 
ring in  the  matured  ovum. 

Spermatogenesis.  --The 
cytological  cycle  resulting  in  the 
production  of  the  spermatozoa 
from  the  epithelial  cells  lining  the 
seminiferous  tubules  comprises 
four  principal  stages:  (i)  divi- 
sion of  the  spermatogones  into 
spermatocytes ;  (2)  division  of 
the  latter  into  spermatids  ;  (3) 
transformation  of  spermatids  into 

^ 

Group  of  interstitial  cells  lying  wfthin  intertubular  stroma. 


FIG.  1654. 


-  Blood-vessel 


^•Epithelial 
cells  of 
tubule 

•  Interstitial 
cells 


Intertubular 
connective 
tissue 


propria 
of  tubule 


X  300. 


•Tunica 

spermatozoa  ;  (4)  completed  dif- 
ferentiation and  liberation  of  sper- 
matozoa. The  changes  incident 
to  the  first  and  second  of  these 

stages  have  been  outlined  ;  a  brief  account  of  the  subsequent  changes  may  here  be 
added.  The  spermatids,  at  first  small  cells  with  round  nuclei,  elongate,  their  nuclei 
coincidently  becoming  oval  and  smaller,  but  rich  in  chromatin,  and  shifting  to  the 


THE   TESTES. 


1945 


end  of  the  cell  most  removed 
from  the  lumen.    The  modified 
spermatids  now  become  closely 
related  with  a  Sertoli  cell,  with 
the  protoplasm  of  which  they 
fuse.       The    structure    thus 
formed,  known  as  the  sperma- 
toblast,  consists  of  an  irregular 
nucleated    conical    protoplas- 
mic   mass   (Fig.    1657,     27), 
with  the  inner  end  of  which  the 
radiating  clusters  of  partially 
fused  spermatids  are  blended. 
The   succeeding  changes    in- 
clude the  transformation  of  the 
elongated  nucleus  of  the  sper- 
matid  into  the  head  and  of  its 
centrosome   into  the  middle- 
piece  of  the  spermatic  filament, 
while  from  the  protoplasm  of 
the  spermatid,  possibly  in  con- 
junction with  that  of  the  sper- 
matoblast,   the  flagellate  tail- 
filament  is  derived.      As  the 
spermatozoa     become     more 
and  more  differentiated,  they 
appear  as  fan-shaped  groups 
in  which  the  heads  are  always 
buried    within  the   spermato- 
blast  and  the  tails  directed  to- 
wards the  lumen  of  the  canal. 
After  separation,  which  subse- 
quently takes  place,  the  liber- 
ated spermatozoa  occupy  the 
centre  of  the  tubule  as  masses 
which  often  occlude  its  lumen 
and  in  which  the  seminal  fila- 
ments are  disposed  in  peculiar 
whorl-like  groups.   Their  com- 
plete development,   however, 
is  deferred    until    they  reach 
the  tube  of    the  epididymis, 
during   the    passage    through 
which    highly    tortuous    path 
they  attain  maturity  and  lose 
the   protoplasmic    remains  of 
the  spermatids  that  usually  for 
a  time  adhere  to  the  middle- 
piece.     The   spermatogenetic 
process  does  not  involve  uni- 
formly all  parts  of  the  seminif- 
erous tubule,  but  is  manifested 
with    wave -like    periodicity  ; 
consequently    sections    taken 
through  the  same  tubule  a  few 
millimetres  apart  exhibit  dif- 
ferent stages  of  the  cycle,  al- 
though the  cells  are  never  all 
of  one  phase. 


FIG.   1655. 


Dilated  duct 


Connecting 
canal 


--Epithelium 


-  Blood-vessel 


Part  of  mediastinum,  showing  irregular  channels  of  rete  testis.    X  75. 

FIG.  1656. 


Tunica  propria 


Secondary  spermatocyte 


Spermatids 


Spermatids  being 
transformed  into  spermatozoa 


Secondary  spermatocyte 
Spermatozoa 


^ 

Sertoli  cell 
Resting  spermatogo'ne 

Dividing  spermatogone  (primary  spermatocyte} 
Portion  of  seminiferous  tubule,  cut  transversely,  showing  lining 
cells  in  various  stages  of  spermatogenesis.     X  350. 


1946 


HUMAN   ANATOMY. 


The  spermatic  filaments  or  spermatozoa,  the  essential  male  reproductive 
elements,  are,  like  the  ova,  direct  derivations  of  t  epithelial  cells  that  are  descendants 


FIG.  1657. 


Diagram  illustrating  phases  of  one  complete  cycle  of  spermatogenesis.  Sequence  of  figures  shows  in 
detail  growth  (1-6)  and  division  (7-8)  of  spermatogone ;  growth  and  division  of  primary  spermatocyte  (9-19) 
into  secondary  spermatocytes;  division  of  fatter  (20-21)  into  spermatids  (22-24);  fusion  of  these  with  Sertoli  cell 
to  form  spermatoblast  (25-26);  differentiation  (27-31)  and  final  liberation  (32)  of  spermatozoa.  (After  Ebner.) 


FIG.  1658. 


of  the  primary  indifferent  sexual  elements.     Unlike  the  ova,  however,  which  are  rela- 
tively large  and  often  absolutely  huge,  and,  apart  from  size  and  minor  distinctions, 

fairly  similar  in  all  vertebrates,  the  sper- 
matic filaments  present  great  diversity 
in  form  and  detail  and  represent  a  high 
degree  of  specialization.  The  human 
spermatic  filament  is  small,  and  consists 
of  an  ovoid  head,  a1  cylindrical  middle- 
piece  of  uncertain  extent,  and  a  greatly 
attenuated  and  prolonged  tail, — the 
propelling  organ  of  the  flagellated  cell. 
The  mature  element  measures  about 
.050  mm.  in  its  entire  length,  of  which 
only  about  .005  mm.  is  contributed  by 
the  head,  probably  about  the  same  by 
the  middle-piece,  and  from  .040-. 045 
mm.  by  the  tail.  The  head,  somewhat 
flattened  in  front  and  hence  pyriform 
in  profile,  although  rich  in  chromatin, 
appears  homogeneous,  since  the  chro- 
inatin  is  uniformly  distributed  and  not 
arranged  as  threads  or  mesh -works. 
The  structural  basis  of  the  remaining  parts  of  the  spermatic  element  is  a  drlirate 
axial  Jihr,  that  extends  from  the  head  to  the  tip  ol  the  tail  (,^'ig.  12)  and  is  in- 


Human  spermatic  filaments  seen  from  the  broad  sur- 
fai-f.  CM  <-pt   ii,  whirh  is  in  profile.     X  800. 


THE   EPIDIDYMIS. 


1947 


vested  by  a  delicate  envelope,  with  the  exception  of  the  last  .005-.  006  mm.  that  con- 
tinues uncovered  as  the  attenuated  end-piece.  In  front  a  minute  spherical  thicken- 
ing, the  end-knob,  marks  the  termination  of  the  axial  fibre,  where  it  joins,  but  does 
not  penetrate,  the  head,  and  probably  represents  the  centrosome  of  the  spermatid. 
Within  the  middle-piece  the  envelope  surrounding  the  axial  fibre,  after  the  action 
of  certain  stains,  exhibits  markings  that  suggest  the  presence  of  a  spirally  arranged 
filament  of  great  delicacy. 

THE   EPIDIDYMIS. 

The  epididymis,  the  greatly  convoluted  beginning  of  the  seminal  duct,  is  a 
crescentic  body,  triangular  in  section,  that  covers  the  entire  posterior  border  and  the 
adjacent  part  of  the  outer  surface  of  the  testis.  Its  enlarged  upper  end  or  globus 
major  (caput  epididymidis)  covers  the  superior  pole  of  the  sexual  gland  and  is  attached 
to  the  latter  not  only  by  connective  tissue  and  serous  membrane  (as  is  the  globus 
minor), but  by  the  efferent  ducts  that  establish  communication  between  the  testis  and 
its  excretory  canal.  The  succeeding  part,  the  body,  gradually  tapers  as  it  descends  to 
the  lower  pole,  at  which  point  the  epididymis  presents  a  second  and  less  conspicuous 
enlargement,  the  glo bus  minor  (cauda  epididymidis),  that  bends  backward  to  become 
the  vas  deferens.  The  latter  passes 

upward  along  the  median  side  of  FlG-  l659- 

the  posterior  border  of  the  epidid- 
ymis to  ascend  in  the  spermatic 
cord.  Where  attached  to  sur- 
rounding structures,  as  at  its  two 
ends  where  in  contact  with  the  tes- 
ticle and  along  its  posterior  border 
where  blended  with  the  spermatic 
cord,  the  epididymis  is  devoid  of 
serous  covering  ;  in  other  places 
it  is  completely  invested  by  the 
tunica  vaginalis,  a  deep  recess,  the 
digital  fossa  (sinus  epididymidis) 
intervening  between  the  body  of 
the  epididymis  and  the  adjacent 
surface  of  the  testis.  The  bulk  of 
the  globus  major  depends  upon 
the  aggregation  of  from  twelve  to 
fifteen  conical  masses  (lobuli  epi- 
didymidis) formed  by  the  efferent 
ducts  and  their  tortuosities,  the 
coni  vasculosi,  that  pass  from  the 
upper  end  of  the  testis  and  connect 
the  rete  testis  with  the  canal  of 
the  epididymis. 

The  latter  (ductus  epididymi- 
dis), beginning  in  the  globus  major,  receives  the  efferent  ducts  and  becomes  greatly 
convoluted,  the  extraordinary  windings  of  the  single  tube  contributing  the  chief  bulk 
of  the  body  and  the  tail  of  the  epididymis.  When  unravelled,  the  canal  measures 
from  5-5.5  m.  (18-20  ft. )  in  length,  its  remarkable  convolutions  sufficing  to  pack 
away  this  long  duct  within  the  small  volume  of  the  epididymis. 

Structure. — The  conical  lobules  of  the  globus  major  are  enclosed  by  a  fibrous 
envelope  resembling  but  less  robust  than  the  tunica  albuginea  testis,  within  which  the 
convolutions  of  a  single  tubule  are  held  together  by  delicate  vascular  connective  tissue. 
The  transition  of  the  channels  of  the  rete  testis  into  the  efferent  ducts  is  marked  by 
an  abrupt  change  in  the  character  of  the  lining  epithelium,  the  low  cuboidal  cells  of 
the  former  giving  place  to  irregularly  ciliated  columnar  elements  within  the  latter. 
The  tubules — from  .  2-.  5  mm.  in  diameter — present  an  irregular  lumen,  owing  to  the 
inconstant  thickness  and  pitted  surface  of  their  epithelium.  Just  before  terminating 


Efferent  ducts 

iRete  testis 


Globui 
minor 


Pyramidal  lobules  of  gland-tissue  (seminiferous  tubules) 


Dissection  of   testicle  after  tubules  have  been  filled  with  quick- 
silver ;  testis  has  been  separated  into  the  component  lobules. 


1948 


HUMAN   ANATOMY. 


Fibrous  envelope 


Canal  of 
epididymis 


in  the  canal  of  the  epididymis,  the  tubules  become  narrowed  and  surrounded  by  a 

thin  layer  of  circularly  disposed  involuntary  muscle.      The  canal  of  the  epididymis 

from  .4-.  5  mm.  in  diameter — is  lined  throughout  by  a  double  layer  of  tall  and 
slender  columnar  cells,  the  free  ends  of  which  bear  groups  of  cilia  of  exceptional 
length  that  adhere  and  form  pointed  tufts  surmounting  the  cells.  A  noteworthy 
feature  of  the  wall  of  the  canal  is  the  layer  of  involuntary  muscle,  from  .01 5-.  030  mm. 
in  thickness,  that  encircles  the  membrana  propria  and,  especially  in  the  globus  minor, 

almost  entirely  replaces  the  stroma 

FIG.  1660.  Of  tne  mucous  membrane.      Exter- 

nally the  muscle  fades  into  the  con- 
nective tissue  holding  together  the 
convolutions  of  the  canal. 

Vessels  of  the  Testis  and 
Epididymis. — The  arteries  sup- 
plying these  organs  are  the  sper- 
matic and  the  deferential,  the  former 
being  distributed  especially  to  the 
testis  and  the  latter  to  the  epi- 
didymis. An  additional  source  is 
provided  by  anastomoses  with  the 
cremasteric  artery.  The  spermatic 
artery  (a.  testicularis) — a  slender 
branch  from  the  abdominal  aorta 
arising  a  short  distance  below  the 
renal — is  distinguished  by  its  long 
course  necessitated  by  the  migra- 
tion of  the  sexual  gland  from  the 
lumbar  region  into  the  scrotum. 
On  reaching  the  posterior  surface  of 
the  testicle,  it  divides  into  three  or 
four  branches  that  enter  the  medi- 
astinum and  break  up  into  super- 
ficial and  deep  twigs,  which  follow 
the  tunica  albuginea  and  the  septa 
respectively  and  form  the  rich  ca- 
pillary net-works  surrounding  the 
seminiferous  tubules.  One  or  more 
branches  pass  to  the  head  of  the 
epididymis  and  anastomose  with  the 
artery  of  the  vas.  The  latter  (a.  deferentialis),  from  the  inferior  or  superior  vesical, 
accompanies  the  spermatic  duct  and  supplies  chiefly  the  body  and  tail  of  the  epididy- 
mis, by  its  connections  with  the  spermatic  artery  establishing  an  anastomosis  that 
may  become  of  importance  in  maintaining  the  nutrition  of  the  testicle. 

The  veins,  superficial  and  deep,  emerge  from  the  testis  and,  joining  with  those 
from  the  globus  major,  form  several  stems  of  considerable  size  that  ascend  within  the 
spermatic  cord  in  front  of  the  vas  deferens,  while  those  from  the  body  and  tail  of 
the  epididymis  unite  into  a  smaller  posterior  group  that  accompany  the  canal 
(page  1960). 

The  lymphatics  of  the  testicle,  beginning  in  the  walls  of  the  tubules  and  the  sur- 
rounding connective  tissue,  follow  in  general  the  course  of  the  veins  as  a  superficial 
and  a  deep  set,  and  emerge  as  a  half-dozen  or  more  relatively  large  trunks  to  which 
the  lymphatics  of  the  epididymis  are  tributary.  Within  the  spermatic  cord  they  ac- 
company the  groups  of  veins,  and  finally  empty  into  the  lumbar  lymph-nodes. 

The  nerves  of  the  testis  and  epididymis,  chiefly  sympathetic  fibres  destined 
for  the  walls  of  the  blood-vessels,  accompany  the  latter  as  the  spermatic  and  the 
deferential  plexiises  that  surround  the  corresponding  arteries.  Medullated  fibres, 
probably  conveying  sensory  impressions,  occur  among  the  more  usual  pale  ones. 
The  relations  between  the  terminations  of  the  nerves  and  the  tubules  are  uncertain, 
Letzerich  and  Sclavunos  describing  intercellular  filaments  within  the  canals  in  addition 


deferens 
Section  across  lower  part  of  epididymis.    X  15. 


THE   APPENDAGES   OF   THE  TESTICLE. 


1949 


FIG.   1661. 


Epididymis 


Appendix  testis 


to  the  well-established  end-plexuses  on  the  external  surface  of  their  membrana  pro- 
pria.     The  existence  of  intratubal  nerves,  however,  needs  further  evidence. 

THE  APPENDAGES  OF  THE  TESTICLE. 

Under  this  heading  are  included  several  vestigial  structures 'that  remain  fora 
variable  period,  some  throughout  life,  as  more  or  less  conspicuous  bodies  attached  to 
the  testis  or  to  the  epididymis.  They  claim  attention  not  only  on  account  of  their 
interesting  morphological  relations,  but  also  since  they  may  become  the  seat  of 
cystic  and  other  pathological  changes.  The  most  important  are  (i)  the  appendix 
testis,  (2)  the  appendix  epididymidis,  (3)  the  paradidymis,  and  (4)  the  vasa  aber- 
rantia. 

The  appendix  testis,  often  called  the  unstalked  or  sessile  hydatid,  is  a  small 
but  fairly  constant  body  (being  present  in  over  90  per  cent,  according  to  Toidt) 
from  5-10  mm.  in  length  and  less  than  half  as  much  in  breadth,  fixed  to  the  upper 
pole  of  the  testis  close  to  or  slightly  overlaid  by  the  globus  major  (Fig.  1650).  The 
term  ' '  hydatid' '  is  inappropriate,  since  the  body  is  solid  and  not  vesicular  and  its 
form  is  irregular.  Its  free  end  often 
presents  a  shallow,  funnel-like  de- 
pression surrounded  by  a  dentated 
margin,  the  whole  suggesting  the 
fimbriated  end  of  the  oviduct  in  minia- 
ture, a  resemblance  supported  by  the 
embryological  significance  of  the  ap- 
pendage as  the  remains  of  the  cranial 
end  of  the  Miillerian  duct  (page 
2038)  overgrown  and  enclosed  by 
connective  tissue.  In  structure  the 
appendage  consists  of  a  vascular  con- 
nective-tissue stroma  in  which  lies 
embedded  a  minute  canal,  of  variable 
size  and  extent,  lined  with  columnar 
epithelium.  Usually  the  canal  ends 
blindly,  but  in  exceptional  cases  it 
may  open  on  the  free  surface. 

Inconspicuous  additional  appen- 
dages of  the  rete  testis  have  been 


described  by  Roth  and   by  Poirier,  Testis 

which    consist  of   blind  tubules  that 

extend  from  the  testicle  into  the  lower 

end  of  the  globus  major,  either  lying 

buried  within   the  latter  behind  the 

testis  or  projecting  as  small  elevations  on  the  free  surface.      They  probably  represent 

the  remains  of  Wolffian  tubules  that  failed  to  retain  their  connection  with  the  canal  of 

the  epididymis  (Wolffian  duct). 

The  appendix  epididymidis,  or  stalked  hydatid,  much  less  constant  than  the 
sessile  one  (27  per  cent,  according  to  Toldt),  appears  as  a  small  pyriform  body  (from 
3-4  mm.  in  length)  attached  to  the  upper  pole  of  the  globus  major  (Fig.  1650). 
This  appendage  is  variable  in  form,  size,  and  number  (since  two  or  more  may  be 
present),  and  corresponds  with  the  pedunculated  hydatid  in  the  female,  both  bodies 
probably  being  derived  from  anlages  of  the  tubules  of  the  Wolffian  body,  although 
their  origin  is  still  a  subject  of  discussion  and  by  some  referred  to  the  Miillerian 
duct. 

According  to  Toldt,  an  additional  minute  body  {lower  paradidymis},  consisting 
of  a  single  convoluted  tubule,  is  sometimes  found,  even  in  aged  subjects,  behind  the 
head  of  the  epididymis,  but  in  front  of  the  veins.  It  may  be  isolated,  connected  with 
the  canal  of  the  epididymis,  with  the  rete  testis,  or  with  both,  these  variable  relations 
being  explained  by  its  probable  nature  as  an  efferent  duct  that  has  become  com- 
pletely or  partly  disconnected.  This  tube  is  frequently  the  seat  of  cysts  which, 


Sagittal  section  of  appendix  testis.    X  25. 


1950  HUMAN   ANATOMY. 

when  the  canal  retains  its  connection  with  the  epididymis  or  testis,  may  contain 
spermatozoa. 

The  paradidymis,  or  organ  of  Giraldes,  consists  of  an  irregular  group  of  blind 
tubules  (from  5-6  mm.  in  extent)  that  lie  within  the  lower  end  of  the  spermatic  cord, 
above  but  close  to  the  globus  major  and  always  in  front  of  the  venous  plexus.  This 
organ  (iipper  paradidymis  of  Toldt)  is  regarded  as  representing  a  partial  per- 
sistence of  the  rudimentary  tubules  of  the  Wolffian  body  (page  1936)  and  is,  there- 
fore, the  homologue  of  the  paroophoron.  It  is  essentially  a  foetal  structure,  usually 
entirely  disappearing  after  the  first  few  years  of  childhood.  The  tubules  (from  .  i-.  2 
mm.  in  diameter  and  lined  with  ciliated  epithelium)  rarely  give  rise  to  cysts. 

The  vasa  aberrantia  (ductuli  abcrrantes)  include  tubular  appendages — usually 
two,  but  sometimes  only  one — that  extend  for  a  variable  distance  within  the  epididymis 
and  end  blindly.  The  upper  and  shorter  one  is  attached  to  the  rete  testis  and  pur- 
sues a  downward  course  within  the  epididymis.  The  lower  and  larger  one,  often 
30  cm.  (12  in. )  or  more  in  length,  passes  upward  from  the,  lower  part  of  the  canal 
of  the  epididymis  and  consists  of  one  or  more  convoluted  tubes  of  considerable  size. 
Both  are  to  be  regarded  as  probably  originating  from  the  Wolrfian  tubules. 

PRACTICAL   CONSIDERATIONS:    THE  TESTICLES. 

Monorchism — the  absence  of  one  testicle  (not  to  be  confounded  with  cryptor- 
chism,  vide  infra) — has  been  shown  at  autopsies  to  occur  occasionally.  It  is 
attended  by  no  symptoms. 

Anarchism — the  absence  of  both  testicles — may  be  inferred  when  the  scrotum 
is  also  absent  or  incompletely  developed,  and  there  is  a  rudimentary  condition  of 
the  external  genitalia  ;  impotence,  sterility,  and  the  physical  and  mental  attributes 
of  eunuchism  appear  later. 

Arrest  of  descent  of  one  or  both  testicles  (page  2040)  may  occur  at  any  point 
between  the  lower  border  of  the  kidney  and  the  bottom  of  the  scrotum.  The  chief 
forms  are  :  (a)  Abdominal  Retention  (cryptorchism,  unilateral  or  bilateral)  :  the 
testicle  may  be  applied  to  the  posterior  abdominal  wall  in  close  relation  to  the  lower, 
outer  border  of  the  kidney  ;  it  may  be  provided  with  a  long  mesorchium,  allowing 
it  to  move  freely  in  the  abdominal  cavity,  or  it  may  lie  in  the  iliac  fossa  close  to  the 
internal  ring  ;  (b~)  Inguinal  Retention :  the  testicle  may  be  arrested  at  the  internal 
ring,  in  the  inguinal  canal,  or  at  the  external  ring.  It  is  usually  extremely  mobile 
until  subject  to  repeated  attacks  of  inflammation  and  fixed  by  adhesion,  (f )  Cruro- 
Scrotal  Retention :  the  testicle  may  pass  through  the  external  abdominal  ring,  but 
fail  to  descend  completely,  lying  in  close  relation  to  the  ring  or  at  a  varying  distance 
below  it.  Of  these,  inguinal  retention  is  the  most  common.  Adhesions  from  prenatal 
peritonitis  in  a,  small  size  of  the  external  ring  in  b,  and  undue  shortness  of  the  cord 
or  of  one  of  its  constituents  in  c  have  been  thought  to  explain  some  of  these  cases. 

Aberrant  descent  (ectopy),  in  which  the  testicle  leaves  its  normal  route,  may 
occur  in  one  of  several  forms,  (a)  I n  pcno-pubic  ectopy  the  testicle  is  found  beneath 
the  skin  of  the  abdomen  above  the  root  of  the  penis.  (6')  In  perineal  ectopy  the 
testicle  is  felt  as  a  freely  movable,  ovoid  tumor,  sensitive  to  pressure,  lying  on  one 
side  of  the  central  raphe,  and  placed  in  front  of  the  anus  ;  the  cord  can  often  be 
traced  from  the  tumor  to  the  external  abdominal  ring.  The  overlying  skin  some- 
times exhibits  rugae,  and  the  corresponding  side  of  the  scrotum  is  often  atrophied. 
(c)  Femoral  ectopy  appears  as  a  movable  tumor  exhibiting  the  physical  character- 
istics of  the  testicle  and  the  peculiar  sensitiveness.  Its  position  is  that  of  complete 
femoral  hernia  or  of  the  inflammatory  swellings  which  so  commonly  affect  the  glands 
overlying  the  saphenous  opening. 

Of  these,  perineal  ectopy  is  the  usual  form.  Irregular  development  of  the 
gubernaculum  may  explain  a  and  c,  as  certain  of  the  fibres  of  the  genito-inguinal 
ligament  run  to  the  pubic,  lower  inguinal,  and  inguino-femoral  regions,  and  their 
over-development  might  draw  the  testicle  in  front  of  the  pubes  or  into  the  femoral 
canal.  Exceptional  attachments  (which  have  been  shown  to  exist)  of  the  gubcr- 
narnlum  below  to  the  tuber  ischii  or  sphincter  ani  may  account  for  at  least  sonic  of 
tin-  cases  included  in  b. 


PRACTICAL   CONSIDERATIONS  :    THE   TESTICLES.  1951 

In  its  bearing  on  the  development  and  course  of  hernia  and  inflammation  the 
relation  of  misplaced  testicle  to  the  peritoneal  pouch,  which  accompanies  it,  is  of 
great  importance.  This  pouch  may  remain  open,  communicating  freely  with  the  gen- 
eral peritoneal  cavity,  thus  enhancing  the  probability  of  the  formation  of  hernia  or  of 
the  extension  of  inflammation  ;  it  may  be  closed  above  but  open  below  the  testicle, 
favoring  the  development  of  hydrocele  ;  it  may  be  obliterated.  Exceptionally,  espe- 
cially when  the  testicle  is  retained  but  the  vas  has  partly  or  completely  descended, 
the  funicular  process  of  the  peritoneum  may  extend  as  an  open  pouch  to  the  bottom 
of  the  scrotum,  thus  allowing  a  hernia  to  pass  far  beyond  the  position  of  the  retained 
testis. 

Occasionally  the  testicle  is  found  in  the  front  of  the  scrotum  (the  epididymis 
anterior  and  the  vas  deferens  in  front  of  the  other  constituents  of  the  cord),  as  if  it 
had  made  a  semi-revolution  on  its  vertical  axis  {inversion  of  the  testicle).  The  pos- 
sibility of  the  existence  of  this  anomaly  emphasizes  the  propriety  of  determining  by 
palpation  and  by  the  test  of  translucency  the  position  of  the  testicle  before  tapping 
for  hydrocele  ;  or,  if  these  fail,  of  evacuating  the  fluid  by  incision  instead  of  with  a 
trocar. 

Torsion  (axial  rotation)  of  the  testicle,  including  the  spermatic  cord, — also  on 
its  longitudinal  axis, — is  an  accident  which  usually  affects  imperfectly  descended  tes- 
ticles, but  is  not  confined  to  them.  The  cause  is  probably  a  congenital  malformation, 
since,  as  Owen  has  pointed  out,  a  testis  properly  placed  in  the  scrotum  and  possessed 
of  a  normal  mesorchium  cannot  be  twisted.  The  twist  may  be  in  either  direction, — 
to  the  right  or  to  the  left, — and  in  accordance  with  its  extent  and  the  degree  of  con- 
striction to  which  the  vessels  are  subject  the  symptoms  are  slight  or  severe.  In  slight 
cases  the  epididymis  alone  becomes  infiltrated.  In  severe  cases  the  entire  gland  with 
the  epididymis  becomes  gangrenous. 

Orchitis — as  .distinguished  from  epididymo-orchitis — is  rare  as  a  result  of  either 
trauma  or  infection,  owing  to  the  firm  support  the  gland  receives  from  the  tunica  albu- 
ginea  and  to  the  free  movement  of  the  testicle,  not  only  within  its  serous  tunic,  but 
also  within  the  scrotum,  and,  on  the  other  hand,  to  the  fact  that  septic  organisms 
gaining  access  to  the  ejaculatory  duct,  or  brought  to  the  gland  in  the  general  circula- 
tion, are  in  either  case  arrested  and  given  the  opportunity  to  multiply  in  the  neigh- 
borhood of  the  epididymis. 

The  intimate  investment  of  the  testicle  by  the  tunica  vaginalis,  which  is  complete 
except  at  the  point  of  entry  and  emergence  of  the  vessels  at  its  posterior  border,  but 
which  leaves  the  whole  hinder  aspect  of  the  epididymis  without  a  serous  covering, 
determines  the  frequency  with  which  serous  effusion  (acute  hydrocele)  occurs  in 
contusions  or  inflammations  of  the  testicle  proper  as  compared  with  those  of  the 
epididymis. 

The  similar  close  investment  of  the  former  by  the  tunica  albuginea  accounts  for 
the  relatively  greater  pain  and  slower  swelling  in  orchids.  It  also  brings  about,  when 
by  ulceration  a  communication  with  the  cutaneous  surface  has  been  established,  the 
slow  protrusion  of  the  swollen  and  infected  testicular  substance,  known  as  hernia  or 
fungus  testis,  analogous  to  hernia  or  fungus  cerebri,  the  physical  conditions — enclo- 
sure of  peculiarly  soft  and  yielding  tissue  within  a  dense  and  resisting  membrane — 
being  similar  in  the  two  instances.  The  sickening  pain  following  contusion  of  the  tes- 
ticle, or  often  associated  with  orchitis,  is  due  to  pressure  upon  or  irritation  of  testicu- 
lar nerves  which,  by  way  of  the  spermatic  plexus,  communicate  with  the  aortic  and 
solar  sympathetic  plexuses.  A  similar  communication  with  the  renal  plexus  explains 
the  testicular  pain  and  retraction  accompanying  the  passage  of  a  renal  calculus.  The 
primary  development  of  the  testicle  in  the  vicinity  of  the  tenth  dorsal  vertebra  has 
determined  its  chief  innervation  from  the  tenth  dorsal  segment  of  the  cord  (Head) 
and  thus  its  relation  to  the  posterior  divisions  of  the  lower  dorsal  and  the  lumbar 
nerves  which  causes  the  "  backache"  so  commonly  felt  in  orchitis,  in  the  presence  of 
a  solid  tumor  of  the  testicle,  or  after  injecting  the  sac  of  a  hydrocele.  The  epididy- 
mis derives  its  nerve-supply  chiefly  from  the  pelvic  plexus,  which  also  supplies  the 
vas  deferens  and  the  seminal  vesicles.  As  it  communicates  with  the  spermatic  plexus, 
the  same  symptoms  may  be  associated  with  an  epididymitis  ;  but  as  swelling  is  less 
resisted  and  pressure  is  therefore  less,  and  as  the  communication  with  the  great 


1952  HUMAN    ANATOMY. 

abdominal  plexuses  is  more  indirect,  ' '  testicular  nausea' '   is  less  pronounced  and  is 
often  absent. 

Epididymo-orchitis  is  usually  of  infectious  origin,  the  gonococcus  and  the  bacillus 
tuberculosis  being  the  micro-organisms  most  often  found,  although  the  inflammation 
may  occur  in  the  course  of  any  infectious  disease,  as  scarlatina,  mumps,  or  typhoid 
fever. 

The  direct  channel  offered  by  the  vas  deferens  explains  the  localization  of  the 
gonorrhceal  infection  (page  1954);  the  division  of  the  spermatic  artery  at  the  epiclid- 
ymis,  and  the  fact  that  the  arteries  of  the  epididymis  are  smaller  and  more  tortuous 
than  those  of  the  vas  or  of  the  testicle,  and  the  consequent  slowing  up  of  the  blood- 
current  (favoring  bacterial  growth),  may  account  for  the  preference  shown  the  epidid- 
ymis by  the  general  infections.  Syphilis  more  often  affects  the  testicle  itself  because 
syphilitic  orchids  is  usually  a  late  manifestation  ;  the  disease  at  this  stage  shows  its 
customary  predilection  for  fibrous  and  connective-tissue  structures,  and,  beginning,  as 
it  often  does,  as  a  cellular  infiltration  of  the  tunica  albuginea,  it  follows  the  trabeculae 
into  the  interior  of  the  gland.  When  syphilis  affects  the  testicle  during  the  second- 
ary stage,  it  behaves  like  other  infections  and  is,  at  least  at  first,  localized  in  the 
epididymis. 

A  certain  number  of  cases  of  epididymo-orchitis  follow  strain,  there  having 
been  no  known  infectious  cause  and  no  direct  trauma.  They  have  the  usual  symp- 
toms,— apt  to  be  slight  at  first, — and  occur  with  much  greater  frequency  on  the  left 
than  on  the  right  side.  Two  of  various  theories  as  to  their  production  are  inter- 
esting from  the  anatomical  stand-point.  (a)  Violent  contraction  of  the  cremaster 
muscle,  which,  by  suddenly  jerking  the  testicle  against  the  pillars  of  the  external 
ring,  causes  bruising  of  the  gland-tissue  and  the  epididymis.  The  cremaster  is  cer- 
tainly capable  of  vigorous  contraction.  Thus  it  is  not  rarely  observed  that  direct 
trauma -of  the  testicle  is  followed  by  marked  retraction  of  the  organ,  so  that  it  may 
be  drawn  into  the  inguinal  canal  or  even  into  the  abdominal  cavity.  Even  in  severe 
pain,  such  as  that  which  accompanies  renal  colic,  the  testicles  are  frequently  found 
in  close  apposition  to  the  external  ring,  while  any  one  can  observe  the  contraction 
of  the  cremaster  by  noticing  the  motion  of  one  or  both  testicles  during  the  passage 
of  a  catheter.  Certain  cases  of  chorea  of  the  testicle  are  at  times  observed  when 
this  organ  is  moved  by  the  cremaster  with  considerable  rapidity  and  violence. 
(£)  Rupture  of  some  of  the  veins  of  the  spermatic  pie x^^s,  which  are  peculiarly  under 
the  influence  of  intra-abdominal  pressure,  are  provided  with  but  few  and  imperfect 
valves,  are  feebly  supported  by  the  surrounding  tissues,  and  hence  are  especially 
subject  to  disease.  Thus  varicosity  of  these  veins  is  one  of  the  most  common  sur- 
gical affections,  and  the  effect  of  the  contraction  of  the  abdominal  parietes  and  the 
diaphragm  upon  the  dilated  veins  is  so  marked  that  succussion  on  coughing  or 
straining  in  any  way  is  sufficiently  distinct  to  simulate  that  of  an  omental  hernia. 
Given,  then,  a  sudden  and  violent  increase  of  pressure  in  these  vessels,  it  is  perfectly 
possible  to  conceive  that  rupture  may  occur,  even  although  they  are  healthy  ;  this  is, 
of  course,  more  probable  if  they  are  weakened  and  dilated.  Such  a  rupture  would 
naturally  take  place  in  the  cord,  in  the  epididymis,  or  even  in  the  substance  of  the 
testicle.  And,  if  the  theory  of  venous  rupture  from  pressure  is  correct,  we  should 
expect  the  left  testicle  to  be  more  frequently  involved  (as  the  veins  of  this  side  are 
more  frequently  varicose),  and  the  pain  to  be  slight  at  first  and  gradually  increase  as 
more  blood  was  effused  and  inflammatory  symptoms  developed. 

It  is  not  improbable  that  both  of  these  factors  are  concerned  in  the  production 
of  this  form  of  epididymo-orchitis. 

The  various  tumors  of  the  testicle  have  no  especial  anatomical  significance  except 
as  to  the  routes  by  which  they  involve  the  nearest  lymph-nodes  (vide  infra'}. 

Castration,  unless  modified  by  extensive  malignant  disease,  is  usually  done  by 
means  of  an  incision  which  may  be  placed  over  or  just  beneath  the  external  abdomi- 
nal ring  or  even  lower,  and  extends  through  the  scrotal  tissues,  but  not  into  tin.- 
tunica  vaginalis.  The  gland  with  its  coverings  may,  if  normal,  easily  be  shelled  out 
and  the  cord  isolated,  transfixed,  lignted,  and  divided.  If  the  vascular  constituents 
of  the  cord  are  ligated  separately,  three  arteries — the  cremasteric,  the  spermatic,  and 
the  deferential — must  be  tied.  The  deferential  artery  is  found  close  to  the  vas,  and 


THE   SPERMATIC    DUCTS.  1953 

with  it  are  a  few  veins  ;  the  cremasteric  lies  to  the  outer  side  of  the  cord,  near  its 
surface  ;•  the  spermatic  is  in  front  of  the  cord,  surrounded  by  the  anterior  group  of 
veins,  and  can  scarcely  be  distinguished  from  them.  Each  artery  should  have  a 
separate  ligature,  but  the  two  sets  of  veins  may  be  tied  en  masse  ;  the  divided  cord 
should  be  secured  with  artery  forceps  until  the  end  of  the  operation. 

When  the  cord  is  extensively  involved,  the  incision  should  be  extended  up  along 
Poupart's  ligament.  It  is  deepened  to  the  peritoneum,  which  is  stripped  up,  allowing 
access  to  the  lymph-nodes  of  the  pelvis.  When  the  lymphatic  involvement  extends 
upward  beyond  reach,  it  may  be  attacked  through  a  transperitoneal  opening.  The 
nodes  into  which  the  lymph-vessels  of  the  cord  pass  completely  surround  the  aorta. 
There  is,  moreover,  one  lying  upon  the  external  iliac  artery  which  probably  will  be 
involved. 

Hydrocele — an  effusion  into  the  tunica  vaginalis — may  begin  in  the  acute  form 
(vide  supra},  may  result  from  disease  of  the  cord,  the  epididymis,  or — more  par- 
ticularly— the  testis,  or  may  appear  to  be  "  idiopathic," — i.e. ,  with  no  discoverable 
preceding  pathological  condition  of  the  scrotal  contents.  In  the  majority  of  such 
cases  it  is  thought  (Jacobson)  that  the  effusion  of  fluid  commences  passively  and 
without  any  irritation  or  inflammation  to  begin  with,  the  causes  predisposing  to  its 
production  being  the  pendent  position,  the  less  vigorous  condition  of  the  cremaster 
and  dartos,  feebler  cardiac  circulation,  deficiency  of  tone  in  the  scrotal  blood-vessels 
and  lymphatics,  together  with,  perhaps,  a  tendency  to  venous  congestion  from 
hepatic  and  renal  degeneration.  All  these  conditions,  which  combine  to  bring  about 
a  passive  effusion,  are  naturally  most  active  in.  middle  life,  this  being  the  age  when 
the  ordinary  hydrocele  of  the  tunica  vaginalis  is  most  frequently  met  with.  After  a 
while,  as  the  fluid  increases  in  bulk,  it  becomes,  from  exposure  to  friction,  etc., 
liable  to  irritation  and  to  inflammatory  changes,  which  show  themselves  in  both  the 
fluid  and  the  tunica  vaginalis  itself. 

The  anatomical  relations  of  the  effusion  to  the  testicle  and  epididymis,  the  char- 
acteristic slow  increase  in  size  of  the  affected  side  of  the  scrotum,  the  effacement  of 
the  rugae,  the  drag  upon  the  cord,  and  the  referred  pains  sometimes  caused  by  it 
have  been  sufficiently  explained  (vide  supra}. 

Congenital  hydrocele  depends  for  its  existence  upon  the  maintenance  of  a  com- 
munication between  the  tunica  vaginalis  and  the  abdominal  cavity.  The  funicular 
portion  of  the  tunic  does  not  become  obliterated.  The  fluid  may  come  from  the 
general  abdominal  cavity  or  may  be  exuded  from  the  vaginal  tunic.  It  may  develop 
in  early  infancy  or  not  until  later  in  life. 

Infantile  hydrocele  is  an  effusion  into  a  sac  formed  by  more  or  less  of  the  unob- 
literated  funicular  portion  of  the  vaginal  tunic.  This  sac  is  closed  from  the  peritoneal 
cavity  above  and  communicates  with  the  tunica  vaginalis  testis  below. 

Bilocular  hydrocele  is  a  comparatively  rare  form  of  infantile  hydrocele.  The 
funicular  portion  of  the  tunica  vaginalis  is  commonly  obliterated  at  the  internal  ring. 
Below  this  the  whole  tunica  vaginalis  may  be  patulous,  or  it  may  be  closed  just  above 
the  position  of  the  testis.  As  the  fluid  accumulates,  sacculation  develops,  the  tumor 
extending  either  backward  and  downward  into  the  pelvis  or  more  commonly  upward 
and  inward  between  the  abdominal  muscles  and  the  peritoneum. 

Encysted  hydrocele  of  the  cord,  or  funicular  hydrocele,  consists  of  an  accumula- 
tion of  fluid  within  an  unobliterated  portion  of  the  funicular  portion  of  the  tunica 
vaginalis.  This  accumulation  is  closed  from  the  peritoneal  cavity  above  and  from  the 
tunica  vaginalis  testis  below.  •  The  hydrocele  may  be  unilocular,  bilocular,  or  multi- 
locular,  in  the  latter  case  forming  a  series  of  small  cysts  along  the  course  of  the  cord. 
These  cysts  may  be  placed  in  the  inguinal  canal,  and  are  more  common  on  the  right 
side.  They  are  usually  observed  in  children,  and  may  be  complicated  by  hernia. 

THE  SPERMATIC  DUCTS. 

The  spermatic  ducts  are  two  tortuous  canals,  one  on  either  side,  that  connect  the 
epididymi  with  the  urethra  and  thus  provide  channels  for  the  escape  of  the  products 
of  the  sexual  glands.  Each  duct  is  divisible  into  the  vas  deferens  and  its  ampulla 
and  the  ejaculatory  duct ;  at  the  upper  end  of  the  latter  the  spermatic  duct  is  connected 

123 


1954 


HUMAN   ANATOMY. 


with  the  seminal  vesicle,  a  saccular  organ  representing  an  outgrowth  from  the  main 
canal. 

The  Vas  Deferens. — This  tube  (ductus  deferens)  extends  from  the  epididymis 
to  the  ejaculatory  duct  and  includes  almost  the  entire  length  of  the  spermatic  duct, 
with  a  diameter  of  from  2-3  mm.  Beginning  at  tne  globus  minor  as  the  direct  con- 
tinuation of  the  convoluted  canal  of  the  epididymis,  the  vas  deferens  is  at  first  also  very 
tortuous,  and  by  its  windings  forms  a  tapering  mass  (pars  testicularis)  about  2.5  cm. 
in  length.  From  the  latter  the  seminal  duct  is  prolonged  upward  along  the  inner 
side  of  the  epididymis  and  behind  the  testis,  becoming  progressively  less  wavy  and 


External  iliac 
artery 

External  iliac 
vein 

Deep  epigastric 

artery 
Spermatic  vessels 

Internal  abdominal 
ring 


Obliterated  — 
hypogastric  artery 

Urachus 


Suspensory 
ligament  of  penis  — 

Internal  urethral  orifice — 

Fatty  tissue 
containing  veins 


Pectinate  septum — 


Spongy  urethra 


Navicular  fossa 


Internal  iiiac 
vessels 


'Ureter,  pelvic 
portion 


— Vas  deferens 


reter,  entering 
bladder 


Seminal  vesicle 
Rectum 

Ejaculatory  duct 

Prostatic  urethra 
and  utricle 

Prostate 


Membranous  urethra 
Bulb  of  cavernous  body 

Bulbous  urethra 


Scrotum 
Dissection  of  sagittally  cut  pelvis,  showing  relations  of  organs  after  fixation  by  formalin  injection. 

• 

of  larger  and  more  uniform  size  (3  mm.)  as  it  enters  the  spermatic  cord.  Although 
the  apparent  entire  length  of  the  canal  is  about  30  cm.  (12  in.),  its  actual  extent  is 
some  45  cm.  (18  in.)  on  account  of  the  tortuosity  of  its  first  part. 

Within  the  spermatic  cord  (pars  funicularis),  accompanied  by  the  deferential 
artery  and  the  posterior  plexus  of  veins  (Fig.  1682),  tin-  vas  occupies  a  position 
behind  the  other  constituents  of  the  cord,  and  may  be  recogni/ed  by  the  hard,  conl- 
likc  feel  imparted  by  its  thick  fibro-inuscular  wall.  The  duct  ascends  almost  verti- 
cally to  the  pubic  spine,  and  on  gaining  tin-  abdominal  wall  passes  through  the  external 
abdominal  ring,  traverses  the  inguinal  canal,  and  completes  its  passage  of  the  body- 


THE   SPERMATIC   DUCTS. 


1955 


wall  by  going  through  the  internal  abdominal  ring.  After  emerging  from  the  latter 
it  parts  company  with  the  spermatic  vessels,  hooks  over  the  external  and  posterior 
surface  of  the  deep  epigastric  artery,  crosses  obliquely  the  external  iliac  vessels  and 
the  pelvic  brim,  and  enters  the  true  pelvis.  From  its  entrance  at  the  internal  ring 
the  vas  lies  within  the  subserous  tissue  immediately  beneath  the  peritoneum,  through 
which  it  may  usually  be  traced. 

During  its  further  course  (pars  pelvina)  the  duct  at  first  lies  along  the  lateral 
pelvic  wall,  directed  backward  and  slightly  upward  towards  the  ischial  spine,  crossing 
to  their  inner  or  median  side  the  obliterated  hypogastric  artery,  the  obturator  nerve 
and  vessels,  the  vesical  vessels,  and  the  ureter.  After  passing  in  front  and  to  the 
inner  side  of  the  ureter,  the  duct  turns  sharply  downward  and  inward  and  traverses 
the  subperitoneal  tissue  covering  the  pelvic  rloor  to  reach  the  vicinity  of  the  seminal 
vesicle  in  the  space  between  the  posterior  surface  of  the  bladder  and  the  rectum. 

Where  in  relation  with  the  seminal  vesicle,  the  vas  deferens  presents  a  somewhat 
flattened  spindle-form  enlargement,  known  as  the  ampulla  (ampulla  ductus  deferen- 
tis),  from  3-4  cm.  in  length  and  from  7-10  mm.  in  its  greatest  width,  that  passes  in 
front  and  then  along 

the  median  side  of  the  FlG-  I(563- 

seminal  vesicle  in  its 
descent  to  the  pros- 
tate gland.  The  con- 
tour of  the  ampulla  is 
uneven  and  humpy, 
especially  after  re- 
moval of  the  invest-  iJi 
ing  fibrous  tissue,  due  .. 
to  the  sacculations 
and  tortuosity  of  the  ,\ 
canal  (Fig.  1666)  and 
the  short  diverticula 
that  pass  off  from  the 
main  duct  at  various 
angles,  thus  antici- 
patingin  simplerform 
the  arrangement  seen 
in  the  seminal  vesicle. 
Just  before  reach- 
ing the  latter  the  vas 
usually  describes  a 

curve  directed  backward  and  outward  (Fig.  1469)  and  occupies  the  crescentic  recto- 
vesical  (sacro-genital)  peritoneal  fold.  At  the  lower  end  of  the  ampulla  the  vas  loses 
its  sacculations  and  again  becomes  a  narrow  tube  which,  joining  with  the  passage 
from  the  seminal  vesicle,  is  continued  as  the  ejaculatory  duct  that  traverses  the  sub- 
stance of  the  prostate  gland  and  terminates  in  the  urethra  at  the  side  of  the  pros- 
tatic  utricle.  The  ampullae  of  the  two  sides  converge  as  they  descend,  so  that  their 
lower  ends  are  almost  in  contact  where  the  spermatic  duct  receives  the  seminal  vesi- 
cles. The  intimacy  of  the  relation  between  the  vasa  deferentia  and  the  bladder 
varies  with  the  condition  of  the  latter  organ.  With  the  increased  volume  incident  to 
its  distention,  the  posterior  surface  of  the  bladder  is  pressed  against  the  spermatic 
ducts;  on  the  other  hand,  when  the  bladder  is  empty,  only  the  lower  parts  of  these 
structures  are  in  close  relation  with  the  vesical  wall. 

The  ejaculatory  duct  (ductus  ejaculatorius),  the  terminal  segment  of  the 
spermatic  canal  and  apparently  formed  by  the  union  of  the  duct  of  the  corresponding 
seminal  vesicle  and  the  vas  deferens,  is  really  the  morphological  continuation  of  the 
latter,  from  which  the  seminal  vesicle  is  developed  as  a  secondary  outgrowth.  Be- 
ginning with  a  diameter  of  froni  1.5-2  mm.,  the  ejaculatory  duct  enters  the  posterior 
surface  of  the  prostate  (Fig.  1680),  defining  the  lower  limit  of  the  middle  lobe,  and 
after  a  course  from  18-20  mm.  (about  ^  in.)  in  length,  ends  in  the  urethra  by  a 
minute  elliptical  opening  situated  on  the  crest  at  the  side  of  the  orifice  of  the  prostatic 


Circular  muscle 


• 

Cross-section  of  ampulla  of  spermatic  duct.     X  18. 


Longitudinal 

muscle 


I956 


HUMAN   ANATOMY. 


FIG.  1664. 


Fibrous  coat 


utricle  (Fig.  1632).  In  rare  cases  the  ducts  of  the  two  sides  may  join  before  reach- 
ing the  urethra  and  communicate  with  the  latter  by  a  common  aperture,  or  they  may 
open  independently  into  the  prostatic  utricle.  In  the  descent  of  the  duct  the  lumen 
of  its  upper  and  middle  thirds  is  modified  by  a  series  of  four  or  five  diverticula  of  de- 
creasing size  (Felix;.  At  such  levels  the  usual  oblique  oval  outline  of  the  canal  is 
amplified  by  the  irregular  dilatations. 

Structure  of  the  Spermatic  Duct. — The  vas  deferens  is  distinguished  by  the 
conspicuous  thickness  of  its  wall  (from  1-1.5  mm- )  tnat  encloses  a  relatively  narrow 
lumen  (.5-. 7  mm.)  and  confers  upon  the  canal  its  characteristic  hard,  cord-like  feel. 
The  wall  consists  of  three  coats,  the  mucous,  muscular,  and  fibrous  (Fig.  1664).  The 

mucous  coat  is  clothed  with 
epithelium  which  in  the  vi- 
cinity of  the  testicle  and  for 
an  uncertain  distance  beyond 
resembles  that  lining  the  duct 
of  the  epididymis,  consist- 
ing of  an  imperfect  double 
layer  of  tall,  columnar  cili- 
ated cells.  Throughout  the 
greater  part  of  the  duct,  how- 
ever, the  cells  are  lower  and 
without  cilia  and  contain 
numerous  particles  of  pig- 
ment. The  tunica  propria 
possesses  a  dense  felt-work 
of  elastic  fibres  intermingled 
with  bundles  of  fibrous  tissue. 
The  robust  muscular  coat 
(from  .8—1.2  mm.  in  thick- 
ness) constitutes  approxi- 
mately four-fifths  of  the  en- 
tire wall,  and  consists  of  pale 
fibres  arranged  as  an  outer 
longitudinal,  a  middle  circu- 
lar, and  an  inner  longitudinal 
layer,  the  latter  being  less 
well  developed  than  the  outer  and  middle  strata.  The  external  fibrous  coat  that 
invests  the  muscular  tunic  is  thin  and  serves  to  connect  the  spermatic  duct  with  the 
surrounding  structures. 

In  its  general  structure  the  ampulla  corresponds  with  the  vas  deferens,  the  walls 
of  this  part  of  the  duct,  however,  possessing  a  much  thinner  muscular  coat,  in  which 
the  inner  longitudinal  layer  is  wanting,  and  a  mucosa  modelled  by  numerous  ridges 
and  depressions  (Fig.  1663)  and  covered  with  a  single  layer  of  low,  columnar,  non- 
ciliated  epithelial  cells. 

The  cjaculatory  duct  likewise  possesses  a  structure  essentially  the  same  as  in 
other  parts  of  the  spermatic  canal.  Its  walls,  however  are  thinner  than  those  of  the 
ampulla,  this  reduction  being  due  to  the  diminished  thickness  and  incompleteness  of 
the  muscular  coat,  which  on  nearing  the  urethra  becomes  attenuated  and  mingled  with 
fibrous  tissue.  In  some  places  the  epithelium  of  the  duct  consists  of  a  single  and  in 
others  of  a  double  layer  of  columnar  cells  until  within  a  short  distance  from  the  termi- 
nation of  the  canal,  where  it  assumes  the  transitional  character  of  the  epithelium 
lining  the  prostatic  urethra. 

THE  SEMINAL  VESICLES. 

The  seminal  vesicles  (  vesiculac  seminales  >  arc  two  sacculated  appendages  of  the 
vasa  deferentia  that  lie  behind  the  bladder  and  in  front  of  the  rectum.  Flattened  from 
before  backward,  their  gnu-nil  shape  is  pyriform,  with  the-  larger  ends,  or  bases, 
directed  upward  and  outward,  the  !<>n-  axes  converging  towards  the  mid-line  as  the 


Cross-section  of  vas  deferens.     X  20. 


THE   SEMINAL   VESICLES. 


1957 


Bladder,  longi- 
tudinal muscle 
exposed 

Vas  deferens 


— Ureter 

Ampulla 
Seminal  vesicle ' 
Ejaculatory  duct 


Membranous  urethra 


Cowper's  glands 


Dissection  showing  seminal  ducts  and  vesicles,  prostate 
and  Cowper's  glands ;  viewed  from  behind. 


organs  taper,  often  abruptly,  at  their  lower  ends  to  join  the  spermatic  ducts.  Usually 
from  4-5  cm.  in  length,  sometimes  much  longer  and  relatively  slender  and  at  others 
short  and  broad,  the  seminal  vesicles  vary  greatly  in  size  and  in  the  detail  of  arrange- 
ment of  their  component  parts  and  not  infrequently  are  markedly  asymmetrical,  the 
right  one  being  often,  but  not  in- 
variably, the  larger.  FIG.  1665. 

Divested  of  the  nbro-muscular 
tissue  that  invests  the  organ  as  its 
capsule  and  blends  its  divisions  into 
a  tuberculated  common  mass,  each 
vesicle  may  be  resolved  into  a  chief 
duct  and  diverticula.  The  former 
— from  10-12  cm.  (4-5  in.)  in 
length — ends  blindly  after  a  more 
or  less  tortuous  course,  its  terminal 
part  often  describing  a  sharp  hook- 
like  returning  curve  (Fig.  1667). 
From  the  main  canal  an  uncertain 
number  (from  four  to  eight  or 
more *)  of  blind  tubular  diverticula 
branch  at  varying  angles  and  in 
different  directions  and  by  their 
tortuosities  add  to  the  complexity 
of  outline.  The  lumen  of  the  chief 
duct,  as  seen  in  section,  is  irregu- 
lar, constrictions  and  dilatations 
following  one  another  with  little 
regularity.  The  opening  of  the 
duct  into  the  lateral  wall  of  the  vas 

deferens  is  large  in  comparison  with  the  terminal  lumen  of  the  ejaculatory  duct,  thus 
favoring  the  entrance  of  the  secretions  temporarily  stored  within  the  ampulla  into  the 
sacculated  vesicle.  The  latter  contains  a  fluid  of  light  brownish  color  in  which  sper- 
matozoa are  nearly  always  found  during  the  period  of  sexual  activity. 

Relations. — The  seminal  vesicles,  together  with  the  ampullae,  lie  embedded 
within  a  dense  fibro-muscular  layer,  so  that  their  position  remains  relatively  fixed, 
especially  below,  and  to  a  certain  degree  independent  of  the  changes  in  volume  of  the 

bladder  and  the  rectum,  neither 

FIG.  1666.  of   which    they    directly  touch. 

Although  when  distended  these 
organs  are  in  close  relation  with 
the  seminal  vesicles,  when  empty 
the  bases  of  the  latter  lie  laterally 
and  at  some  distance  from  both 
the  vesical  and  rectal  wall,  sur- 
rounded by  numerous  veins  that 
continue  the  prostatic  and  vesi- 
cal plexuses.  The  lower  half 
of  the  seminal  vesicles  and  the 
ampullae  lie  behind  the  fundus 
of  the  bladder,  their  axes  ap- 
proximately corresponding  with 
the  sides  of  the  vesical  trigone 
and  embracing  the  retroureteric 
fossa,  which  part  of  the  bladder- 
wall,  when  distended,  may  pro- 
ject between  and  even  displace  laterally  the  seminal  ducts  and  vesicles.  In  passing 
from  the  slightly  expanded  bladder  onto  the  rectum,  the  peritoneum  covers  the 
upper  fourth  of  the  seminal  vesicles  and  the  adjoining  part  of  the  ampullae.  The 

1  Pallin  :  Archiv  f.  Anat.  u.  Entwick.,  1901. 


Ejaculatory  ducts 


Cast  ot  ampullae  and  seminal  vesicles,  showing  wind- 
ings and  sacculations  of  lumen.     (Pallin.) 


1958 


HUMAN   ANATOMY. 


FIG.  1667. 


extent  of  this  investment,  however,  varies  with  the  depth  of  the  recto-vesical  pouch, 

which  in  turn  depends  upon  the  degree  of  distention  of  the  bounding  organs,  the 

bladder  and  the  rectum. 

Structure. — In  their  general  make-up  the  seminal  vesicles  closely  resemble  the 

ampulke,  possessing  a  robust  muscular  wall  composed  of  an  inner  circular  and  an 

outer  longitudinal  layer  of  involun- 
tary muscle.  The  mucous  mem- 
brane is  conspicuously  modelled 
by  numerous  ridges  and  pits,  so 
that  the  free  surface  appears 
honey-combed  (Fig.  1668).  The 
epithelial  covering  consists  of  a 
single  or  imperfect  double  layer 
of  low  columnar  cells,  many  of 
which  present  changes  indicating 
secretory  activity.  Although  true 
glands  are  wanting  within  the 
seminal  vesicles,  the  minute  di- 
verticula  within  the  epithelium 

Diagram  showing  course  of  main  canal  in  preceding  preparation:       Containing  goblet-Cells  may  be  re- 
a,  ampulla  ;  c,  seminal  vesicle;  d,  ejaculatory  duct.     (Palhn.)  garded  as  Concerned  in  producing 

the   peculiar   fluid   found    within 

these  sacs,  which  is  of  importance  probably  not  only  in  diluting  the  secretion  of  the 
testicle  and  supplying  a  medium  favorable  for  the  motility  of  the  spermatic  fila- 
ments, but  also  in  completing  the  volume  of  fluid  necessary  for  efficient  ejaculation 
(Waldeyer). 

Vessels  of  the  Seminal  Ducts  and  Vesicles. — The  arteries  supplying  the 
spermatic  duct  are  derived  chiefly  from  the  deferential,  a  vessel  of  small  size  but  long 
course  that  arises  either  directly 
from  the  internal  iliac  or  from  its 
vesical  branches.  On  reaching  the 
duct,  just  above  the  ampulla,  the 
artery  divides  into  a  smaller  de- 
scending and  a  larger  ascending 
division.  The  former,  in  conjunc- 
tion with  accessory  twigs  from  trie 
middle  hemorrhoidal  and  the  in- 
ferior vesical  arteries,  generously 
provides  for  the  ampulla,  and  the 
latter  accompanies  and  supplies  the 
vas  deferens  throughout  its  long 
course,  finally,  in  the  vicinity  of  the 
testicle,  anastomosing  with  branches 
from  the  spermatic, — a  communica- 
tion of  importance  for  collateral  cir- 
culation. The  twigs  passing  to  the 
spermatic  duct  enter  its  wall  and 
break  up  into  capillary  net-works 
within  the  muscular  and  mucous 
layers.  The  rich  arterial  supply  for 
the  seminal  vesicle  includes  anterior 
and  upper  and  lower  branches,  con- 
tributed by  the  deferential,  the  in- 

*..'.«  .  j  Cross-section  of  seminal  vesicle,  showing 

fe'nor  vesical,  and  the  superior  ana  modelling  <>t  aracouturfece.    x  16. 

middle  hemorrhoidal  arteries.     The 

minute  distribution  is  effected  by  capillary  net-works  to  the  muscular  and  mucous 

coats. 

The  veins  that  follow  the  spermatic  duct  as  the  deferential  plexus,   and   within 
the  spermatic  cord  communicate  with  the  pampiniform  plexus,  increase  in  size  and 


FIG.   1668. 


Lumen 


Pits  of  mu- 
cous coat 


Partition  separating  adjacent  diverticula 


Epithelium 


PRACTICAL  CONSIDERATIONS  :    SEMINAL  VESICLES.         1959 

number  as  they  approach  the  bladder  and  seminal  vesicle  ;  in  the  vicinity  of  the  latter 
they  communicate  with  the  seminal  plexus  and  empty  with  the  trunks  of  the  posterior 
bladder-wall  into  the  vesico-prostatic  plexus.  The  posterior  and  lateral  surfaces  of 
the  seminal  vesicle  are  covered  with  a  net- work  of  large  veins  (plexus  venosus  semi- 
nalis)  that  become  tributary  to  the  vesico-prostatic  plexus. 

The  lymphatics  of  the  seminal  ducts  and  vesicles  are  numerous  and  arranged  as 
deeper  and  superficial  sets  which  form  afferent  trunks  that  pass  to  the  internal  iliac 
lymph-nodes.  Those 

from  the  lower  part  FIG.   1669. 

of  the  seminal  vesi- 
cles join  the  vesical 
lymphatics. 

The  nerves  sup- 
plying the  spermatic 
duct  are  derived 
from  the  hypogastric 
plexus  of  the  sympa- 
thetic and  consist 
chiefly  of  pale  fibres 
destined  for  the  in- 
voluntary muscle, 
some  medullated 
fibres,  however,  be- 
ing present.  They 
accompany  the 
greater  part  of  the 
duct  as  the  deferen- 
tial plexus  and  have 
been  traced  into  the 
muscular  tissue  and 
the  mucosa.  Within 

the  former  they  form  the  dense  plexus  myospermaticus  described  by  Sclavunos,1  and 
are  fairly  plentiful  within  the  mucous  coat  (Timofeew2).  The  nerves  distributed  to 
the  seminal  vesicles  are  very  numerous  and  are  derived  in  part  directly  from  the 
hypogastric  plexus  (Fraenkel3),  or  through  prolongations  of  the  latter  as  secondary 
plexuses  that  follow  the  vesical  and  middle  hemorrhoidal  arteries. 


Fibrous  Coat 


Portion  of  wall  of  seminal  vesicle  in  longitudinal  section, 
showing  pitting  of  mucous  coat.     X  45- 


PRACTICAL   CONSIDERATIONS:    THE   SEMINAL   VESICLES. 

The  seminal  vesicles  are  rarely  injured.  The  two  forms  of  infection  that  are 
most  common  are  the  gonorrhceal  and  the  tuberculous,  although  vesiculitis  may  be 
due  to  the  ordinary  staphylococci  or  to  the  colon  bacillus.  The  channels  of  infection 
are  comparable  to  those  which  convey  disease  to  the  epididymis;  the  ejaculatory 
ducts  are  continuous  with  the  vas  deferens  and  the  vesicular  duct,  and  the  inferior 
vesical  and  middle  hemorrhoidal  arteries  replace  the  spermatic  artery.  The  tuber- 
culous disease  is,  however,  usually  secondary  to  similar  infection  of  the  prostate  or 
of  the  epididymis. 

The  anatomical  relations  of  the  vesicles  to  (a)  the  vesical  trigonum,  (3)  the 
prostate  and  prostatic  urethra,  and  (r)  the  rectum  sufficiently  explain  the  usual 
symptoms  of  acute  vesiculitis  :  (#)  frequent,  painful,  straining  urination,  hypogastric 
pain  ;  (^)  priapism,  painful  emissions  of  blood-stained  semen,  occasionally  epididy- 
mitis  as  a  complication  ;  (<:)  painful  defecation,  rectal  tenesmus,  perineal  and  anal 
pain. 

Rectal  exploration  (page  1692)  will  usually  establish  the  diagnosis,  as  it  will  in 
tuberculous  vesiculitis,  in  which  condition,  as  in  other  forms — acute  and  chronic — 
of  vesiculitis,  there  are  apt  to  be  pains  referred  to  the  loins,  the  hypogastrium,  the 

1  Anatom.  Anzeiger,  Bd.  ix.,  1894. 

2  Anatom.  Anzeiger,  Bd.  ix.,  1894. 

3  Zeitsch.  f.  Morph.  u.  Anthrop.,  Bd.  v.,  1903. 


1960  HUMAN   ANATOMY. 

anus  and  perineum,  the  hip-joint  and  sacro-iliac  articulation  of  the  affected  side  and 
the  other  side  of  the  thigh,  due  to  the  association  of  the  vesical,  prostate,  and  pelvic 
plexuses  with  the  lumbar  and  sacral  nerves  and  their  plexuses. 

Vesiculitis  may  be  a  very  serious  condition,  as  it  may  result  in  abscess  with  per- 
foration into  the  bladder  within  the  limits  of  the  peritoneal  covering,  or  directly  into 
the  peritoneal  cavity  by  way  of  the  recto-vesical  cul-de-sac.  Cases  of  both  these  acci- 
dents have  been  reported.  Pyaemia  has  also  been  known  to  follow  a  septic  phlebitis 
of  the  adjacent  venous  plexuses;  pelvic  cellulitis  with  diffuse  suppuration  has  resulted  ; 
and  various  troublesome  abscesses  burrowing  between  the  bladder  and  rectum,  and 
leaving  fistulous  tracts  very  slow  to  heal,  have  had  their  origin  in  suppurative  vesicu- 
litis.  The  chronic  form  may  be  associated  with  persistent  vesical  irritability,  with  some 
pain  on  emission  of  semen,  with  sexual  excitability  accompanied  by  premature  ejacu- 
lation, and  with  persistent  urethral  discharge  often  mistaken  for  an  ordinary  gleet. 

In  chronic  cases  "  massage"  through  the  rectum  has  been  advised  and  practised 
with  some  benefit  in  comparatively  rare  cases.  The  contents  of  the  vesicles  can 
sometimes  be  pressed  through  the  ejaculatory  ducts  into  the  prostatic  urethra  and  so 
evacuated.  A  similar  expression  of  the  normal  secretion  of  the  vesicles  by  fecal 
masses  at  stool  is  a  fertile  source  of  sexual  hypochondriasis  in  young  male  neuras- 
thenics, who,  in  consequence,  imagine  that  they  are  afflicted  with  "  spermatorrhoea. " 

THE  SPERMATIC  CORD. 

In  consequence  of  its  migration  from  the  abdominal  cavity  into  the  scrotal  sac, 
the  testicle  is  followed  by  its  duct,  vessels,  and  nerves  through  the  abdominal  wall 
into  the  scrotum.  These  structures,  held  together  by  connective  tissue  and  invested 
by  certain  coverings  acquired  in  their  descent,  form  a  cylindrical  mass,  known  as  the 
spermatic  cord  (funiculus  -spermaticus),  that  extends  from  the  internal  abdominal  ring 
obliquely  along  the  inguinal  canal,  emerging  at  the  external  ring,  and  thence  descends 
vertically,  beneath  the  integument,  into  the  scrotum  to  end  at  the  posterior  border  of 
the  testicle.  Most  constant  within  the  inguinal  canal,  where  its  diameter  is  about 
1 5  mm.  ( ^i  in. ) ,  the  thickness  and  length  of  the  spermatic  cord  vary  with  the  con- 
traction of  the  cremasteric  muscular  fibres  that 
FIG.  1670.  control  the  position  of  the  testicle. 

Posterior  veins  The  constituents  of  the  spermatic  cord 

vas  deferens  are  numerous  and  fall  under  four  groups. 

I.   The  vas  deferens  with  its  accompanying 
deferential  artery  and  plexuses  of  veins,  lym- 
phatics, and  nerves.      The  vas,  surrounded  by 
pampini-      jj-s  artery  and  a  venous  plexus,    occupies  the 

plexus  ,      .  .  .    . 

posterior  part  of  the  spermatic  cord,  and  is 
ic  artery  readily  distinguished  as  a  hard,  round  cord, 
inaiis  from  2-3  mm.  in  diameter,  by  virtue  of  its 
L,a  unusually  firm  walls. 

_     .  .  .„  2.   The  spermatic  artery,  zn/is,  Ivmphatics, 

Section  across  left  spermatic  cord  hardened   in  11-  •    i 

formalin,  showing  position  of  vas  deferens.        and  nerves  belonging  to    the  testicle    proper. 

In  contrast  to  the  artery,  the  veins  are  particu- 
larly large  and  numerous  and  form  the  conspicuous  pampiniform  plexus  which  con- 
tributes in  no  small  measure  to  the  bulk  of  the  cord. 

3.  The  coverings  with  their  blood-vessels  and  nerves.  The  coverings  proper  of 
the  spermatic  cord,  contributed  by  the  layers  of  the  abdominal  wall,  correspond  to 
those  of  the  testicle,  with  the  exception  of  the  serous  coat,  which  is  wanting  after 
closure  of  the  processus  vaginalis.  From  within  outward  they  are  :  (a)  the  infundib- 
uliform  fascia  (tunica  vaginalis  communis),  a  distinct  layer  continued  from  the  trans- 
versalis  fascia  ;  (b)  the  cremasteric  fascia,  consisting  of  the  muscular  fibres  prolonged 
from  the  internal  oblique  and  transversalis,  blended  together  by  connective  tissue. 
The  muscular  fibres  descend  as  loops  along  the  spermatic  cord,  especially  on  the 
posterior  surface  as  far  as  the  testicle,  over  the  coverings  of  which  they  spread  out  in 
festoons  and  net-works  ;  and  (c~}  the  intercolitwnar  fascia,  a  delicate  sheet  derived 
from  the  aponeurosis  of  the  external  oblique  at  the  margin  of  the  external  abdominal 


WpVeins  of 
ll  \     form  pi 


THE   SCROTUM.  1961 

ring,  is  most  distinct  above,  becoming  thinner  as  it  descends,  until  over  the  testicle  it 
loses  its  identity  as  a  distinct  investment. 

The  coverings  of  the  spermatic  cord  receive  their  blood-supply  from  chiefly  the 
cremasteric  branch  of  the  deep  epigastric  artery  ;  additional  cremasteric  twigs  from 
the  spermatic  artery  are  distributed  to  the  upper  part  of  the  cord,  anastomosing  with 
those  from  the  first-named  source.  The  nerves  include  the  genital  branch  of  the 
genito-crural  and  usually  a  twig  along  the  front  of  the  cord  from  the  terminal  branch 
of  the  ilio-inguinal. 

4.  The  rudimentary  structures,  the  remains  of  the  processus  vaginalis,  the  para- 
didymis,  and  sometimes  the  vas  aberrans.  After  closure  of  the  communication  between 
the  serous  pouch  and  the  peritoneal  cavity,  the  processus  vaginalis  is  represented  by 
a  delicate  fibrous  band  (ligamentum  vaginale)  that  maybe  traced,  under  favorable  con- 
ditions, from  the  internal  abdominal  ring  above  through  the  spermatic  cord  as  far  as 
the  upper  margin  of  the  tunica  vaginalis  below.  The  paradidymis  (page  1950)  lies 
within  the  lower  end  of  the  spermatic  cord,  immediately  above  the  epididymis,  or 
behind  its  upper  pole,  and  in  front  of  the  venous  plexus.  Occasionally,  when  unusu- 
ally developed,  the  vas  aberrans  (page  1950)  may  also  extend  into  the  lower  end  of 
the  spermatic  cord. 

In  addition  to  the  foregoing  coverings  proper,  the  spermatic  cord  is  enveloped 
by  the  skin,  the  superficial  and  the  deep  layer  of  the  superficial  fascia.  The  deep 
layer  of  the  latter  is  important,  being  continuous  above  with  the  fascia  on  the  abdomen 
and  below,  after  investing  the  testicle,  with  Colics' s  fascia  in  the  perineum. 

PRACTICAL   CONSIDERATIONS  :    THE   SPERMATIC   CORD. 

The  most  frequent  pathological  condition  associated  with  the  cord  (and  not  else- 
where described)  is  varicocele,  an  enlargement — with  dilatation  and  lengthening — of 
the  veins  of  the  cord,  occurring  most  frequently  in  young  unmarried  adults  (fifteenth 
to  twenty-fifth  year)  and  on  the  left  side  (90  per  cent,  of  cases). 

The  veins  composing  the  spermatic  plexus  can  be  ranged  in  three  groups,  the 
most  anterior  of  which  has  in  its  midst  the  spermatic  artery,  the  middle  the  vas  def- 
erens,  and  the  posterior  is  composed  of  those  veins  which  pass  upward  from  the  tail 
of  the  epididymis.  The  anterior  group  is  the  one  first  affected,  or,  if  the  dilatation 
affects  all  the  veins,  is  most  extensively  involved. 

It  is  thought  that  varicocele  often  depends  upon  a  congenital  predisposition, 
but  many  anatomical  reasons  have  been  given  to  account  (a)  for  its  occurrence,  and 
(£)  for  its  greater  frequency  on  the  left  side,  (a)  i.  The  relative  length  and  the 
vertical  course  of  the  veins.  2.  The  lax  tissue  surrounding  them,  so  that  (as  with 
the  long  saphenous  vein)  they  derive  little  support  and  their  blood-current  receives 
no  aid  from  the  presence  or  contraction  of  surrounding  muscles.  3.  Their  large  size 
as  compared  with  the  corresponding  artery,  so  that  the  vis  a  tergo  must  be  reduced  to 
a  minimum  (Treves).  4.  Their  tortuosity,  frequent  anastomosis,  and  few  and  imper- 
fect valves.  5.  The  pressure  exerted  upon  them  as  they  pass  through  the  inguinal 
canal,  not  altogether  unlike  that  experienced  by  the  hemorrhoidal  veins  in  their  passage 
through  the  walls  of  the  rectum.  (£)  i.  The  veins  in  the  left  cord  are  much  larger 
than  those  in  the  right.  2.  The  left  testicle  hangs  lower  than  the  right,  so  that  the 
column  of  blood  in  the  left  veins  is  longer.  3.  The  left  spermatic  vein  empties  into 
the  left  renal  vein  at  a  right  angle,  whereas  the  right  spermatic  vein  empties  into  the 
vena  cava  at  an  acute  angle.  4.  The  left  spermatic  vein  running  behind  the  sigmoid 
flexure  of  the  colon  is  constantly  subjected  to  pressure  from  accumulation  of  faeces  in 
the  bowel. 

In  the  operation  for  varicocele  by  excision  of  the  pampiniform  plexus  the  sper- 
matic artery  is  often  included,  but  gangrene  of  the  testicle  does  not  follow  because 
of  the  escape  of  the  deferential  artery  and  of  its  free  anastomosis  with  the  spermatic 
and  scrotal  vessels. 

THE  SCROTUM. 

The  scrotum,  the  more  or  less  pendulous  sac  of  integument  that  contains  the 
testicles  and  the  associated  structures  and  the  lower  part  of  the  spermatic  cords,  is 
attached  to  the  under  surface  of  the  penis  in  front  and  to  the  perineum  behind.  Flat- 


1962 


HUMAN   ANATOMY. 


tened  in  front  above,  where  attached  to  the  penis  and  receiving  the  spermatic  cords, 
its  general  form  is  pear-shaped  and  somewhat  asymmetrical,  since  the  left  of  the  two 
oval  swellings  produced  by  the  enclosed  testicles  and  separated  by  a  shallow  longi- 
tudinal furrow  is  lower  than  the  right  owing  to  the  position  of  the  corresponding 
sexual  gland.  The  scrotum  varies,  however,  in  form  and  appearance,  even  in  the 
same  individual,  with  the  condition  of  the  subcutaneous  muscular  tissue.  When  the 
latter  is  contracted,  as  after  the  influence  of  cold,  the  scrotum  is  drawn  up  and  com- 
pact and  its  surface  corrugated  by  numerous  transversely  curved  folds  ;  when  relaxed, 
it  becomes  smooth,  flaccid,  and  pendulous. 

Indications  of  its  formation  from  two  distinct  parts  are  seen  externally  in  the 
longitudinal  raphe,  which  marks  the  line  of  fusion  of  the  original  halves  and  extends 
longitudinally  from  the  urethral  surface  of  the  penis  over  the  scrotum  onto  the  peri- 

FIG.  1671. 


Aponeurpsis  of 
external  oblique 


External  abdominal 
ring 

Suspensory  ligament 
of  penis 

Stump  of  penis 

Skin 

Septum  of  scrotum 


Loops  of  cremaster 
muscle 


Dartos 
Skin 


T-Skin 

Supcrf.  fascia,  superf.  layer 

Deep  layer 

Aponeurosis  of 
external  oblique 

Internal  oblique 


Infundibuliform 
fascia 

Aponeurosis  of 
external  oblique,  cut 
and  reflected 


—  Spermatic  cord 


Intercolumnar  fascia, 
reflected 


Dissection  of  spermatic  cord  and  scrotum. 

rieum.  Owing  to  the  greater  dependence  of  the  left  half  of  the  sac,  the  raphe  does 
not  occupy  a  strictly  median  position,  but  is  deflected  towards  the  left.  Internally 
evidence  of  the  union  of  the  scrotal  halves  is  found  in  the  sagittal  partition  {septum 
scroll}  that  is  continued  inward  from  the  raphe  and  effectually  divides  the  scrotum 
into  a  right  and  a  left  pouch.  This  septum,  consisting  of  fibrous  tissue  rich  in  elastic 
fibres  and  the  prolongations  of  tlte  dartos  muscle,  is  attached  above  to  the  root  of  the 
penis  and  the  perineum,  blending  with  the  sheath  of  the  bulbo-cavernosus  muscle. 

Since  the  labio-scrotal  folds,  which  produce  the  scrotum  or  its  homologue,  the 
labia  majora,  according  to  sex,  are  developed  (page  2041)  independently  of  the  cov- 
erings of  the  spermatic  cord  and  the  testicle  derived  from  the  musculo-fascial  walls  of 
the  abdomen,  the  scrotum  contributes  additional  envelopes  for  the  enclosed  structures. 
These  envelopes  are  the  skin,  which  is  here  thin,  delicate,  and  very  elastic,  unusually 
dark,  and  beset  with  scattered  crisp  hairs  and  numerous  sweat  and  sebaceous  glands  ; 


THE   SCROTUM.  1963 

and  the  tunica  dartos,  a  layer  of  modified  subcutaneous  tissue — the  superficial  fascia — 
distinguished  by  the  presence  of  numerous  longitudinally  disposed  bundles  of  invol- 
untary muscle-fibres  and  much  elastic  tissue  and  by  the  entire  absence  of  fat. 

The  muscular  tissue  {dartos  muscle},  where  best  developed,  as  in  the  anterior 
and  lateral  walls  of  the  scrotum,  is  sufficient  in  quantity  to  be  recognized  as  a  dis- 
tinct layer,  but  so  closely  attached  to  the  integument  as  to  form  practically  a  part  of 
it.  At  the  raphe,  while  some  fibres  follow  the  skin  and  remain  superficial,  the  majority 
enter  the  septum,  being  especially  well  developed  in  the  lower  part,  and  at  the  attached 
upper  border  pass  over  into  the  dartos  of  the  penis  and  the  perineum.  The  numerous 
bundles  of  elastic  tissue  within  the  tunica  dartos  in  the  upper  and  anterior  part  of  the 
scrotum  become  condensed  into  robust  bands  which  efficiently  aid  in  supporting  the 
scrotal  sac,  since  they  are  continued  laterally  at  the  sides  of  the  penis  and  over  the 
spermatic  cords  into  the  superficial  fascia  of  the  abdomen,  and  in  the  mid-line  blend 
with  the  suspensory  ligament  of  the  penis.  Those  on  the  posterior  surface  are 
attached  over  the  pubic  and  ischial  rami. 

Enumerated  from  without  inward,  the  layers  interposed  between  the  surface  of 
the  scrotum  and  the  serous  cavity  surrounding  the  testis  are  :  (i)  the  skin,  (2)  the 
modified  superficial  fascia  or  tunica  dartos,  (3)  the  intercolumnar  fascia,  (4)  the  cre- 
masteric fascia,  (5)  the  infundibuliform  fascia,  and  (6)  the  tunica  vaginalis.  Of 
these  the  first  two  alone,  strictly  considered,  are  contributed  by  the  scrotum,  the 
remaining  layers  being  derived  from  the  deeper  structures  of  the  abdominal  wall  and 
associated  with  the  descent  of  the  testicle.  The  connection  between  the  tunica  dartos 
and  the  underlying  intercolumnar  fascia  is  by  no  means  firm,  being  effected  by  a  loose 
layer  of  areolar  tissue,  devoid  of  fat,  that  permits  a  ready  separation,  particularly  in 
front,  between  the  external  scrotal  envelope  and  the  coverings  proper  of  the  testis. 
Beneath  the  posterior  surface  of  the  scrotum  the  connection  is  firmer  (Disse).  This 
separation,  however,  is  arrested  at  the  lower  part  of  the  scrotum,  owing  to  the  presence 
of  the  scrotal  ligament  (Fig.  1723),  a  mass  of  fibrous  tissue  that  anchors  the  lower 
end  of  the  tunica  vaginalis  and  the  testicle  to  the  external  envelopes. 

With  the  exception  of  the  serous  coat,  the  tunica  vaginalis,  these  coverings  have 
been  considered  in  connection  with  the  spermatic  cord  (page  1960)  ;  it  remains,  there- 
fore, to  describe  more  fully  the  serous  coat  to  which  incidental  reference  has  been  made 
(page  1941)  in  its  relations  to  the  testis  and  the  epididymis. 

The  production  of  an  isolated,  closed  serous  sac  within  each  half  of  the  scrotum 
results  from  partial  obliteration  of  the  serous  pouch,  the  processus  vaginalis,  that 
during  fcetal  life  extends  from  the  general  peritoneal  cavity  into  the  scrotum  in  an- 
ticipation of  the  descent  of  the  sexual  gland. 

The  tunica  vaginalis  (tunica  vaginalis  propria  testis),  in  correspondence  with 
other  serous  membranes,  consists  of  a  parietal  and  a  visceral  portion,  the  latter  pro- 
viding an  extensive  but  incomplete  investment  for  the  testis  and  the  epididymis  and 
the  former  lining  the  serous  cavity  into  which  these  organs,  thus  covered,  project. 
With  the  exception  of  small  spaces  caused  by  the  elevation  of  the  epididymis,  espe- 
cially of  the  globus  major,  these  two  layers  are  practically  in  contact  and  separated 
by  only  a  capillary  cleft.  Whatever  space  exists  is  filled  by  a  clear  straw-colored 
serous  fluid. 

In  addition  to  walling  the  cavity,  the  parietal  layer  invests  the  spermatic  cord  for 
about  12  mm.  above  the  testicle  and  the  blood-vessels  behind,  and  then  is  continued 
into  the  visceral  layer  along  the  line  of  reflection  that  passes  over  the  back  of  the 
testis  to  its  lower  pole  on  the  one  side  and  along  the  posterior  surface  of  the  epi- 
didymis on  the  other,  thus  leaving  an  intervening  uncovered  strip  as  a  passage-way 
for  the  duct,  vessels,  and  nerves. 

From  the  line  of  reflection  the  thin  visceral  layer  completely  invests  the  testis 
and  the  epididymis,  adhering  intimately  with  the  tunica  albuginea,  and  dipping 
deeply  between  these  organs  to  form  the  digital  fossa  (sinus  epididymidis).  This 
pocket  (Fig.  1650),  the  entrance  to  which  is  narrowed  by  two  transverse  folds  (liga- 
menta  epididymidis  superior  et  inferior),  may  be  so  deep  that  the  serous  membrane  at 
its  bottom  is  in  contact  with  that  reflected  from  the  median  side  of  the  testicle.  Nu- 
merous bundles  of  involuntary  muscle — -the  in.  cremaster  internus  of  Henle — radiate 
from  the  scrotal  ligament  at  the  lower  part  of  the  scrotum  to  spread  out  between  the 


1964 


HUMAN    ANATOMY. 


parietal  layer  of  the  tunica  vaginalis  and  the  infundibuliform  fascia,  extending  upward 
into  the  spermatic  cord. 

Vessels. — The  arteries  supplying  the  scrotum, — as  distinguished  from  those  des- 
tined for  the  spermatic  cord  and  the  sexual  gland  and  associated  structures, — although 
of  small  size,  are  derived  from  different  sources.  Those  distributed  to  the  front  and 
sides  are  the  anterior  scrotal  branches  from  the  deep  external  pudics,  supplemented 
above  by  twigs  from  the  superficial  external  pudics.  The  back  of  the  scrotum  and  the 
septum  are  supplied  by  the  posterior  scrotal  arteries,  superficial  branches  from  the 
internal  pudics.  Free  communication  exists  not  only  between  the  vessels  of  the  two 
sides  across  the  mid-line,  but  also  between  the  anterior  and  posterior  branches  at  the 
sides.  The  scrotal  arteries  anastomose  with  twigs  from  the  obturator  and  internal 
circumflex,  as  well  as  with  those  from  the  cremasteric  artery. 

The  veins,  numerous  and  plexiform  in  arrangement,  form  trunks  that  follow  the 
general  course  of  the  chief  arteries,  becoming  tributary  to  the  external  saphenous  or 
the  femoral  and  the  internal  pudic  veins.  They  anastomose  freely  with  the  adjoining 
venous  paths  of  the  penis,  perineum,  and  pubic  region. 

FIG.  1672. 


Veins 


^^^  -Vas  deferens 
^n>\  •••<'*'   \    _^-js**Spermatic  veins 

^V'^v   •- 

**?> — X- — Spermatic  arteries 

Saw  \ 


Blood-vessels 


Sac  of  tunica  vaginalis 
Tunica  vagina 


Mediastinum  teslis 
•Visceral  tunica  vaginalis 

Parietal  tunica  vaginalis 


Lobules  of  left  testis 


lis 


Cremasteric  fascia 

Skin  and  dartos  Septum  of  scrotum 

Obliquely  cut  vas  deferens 
Section  across  formalin-hardened  scrotum,  showing  lower  end  of  spermatic  cords  and  testes  in  section. 

The  lymphatics  of  the  scrotum  are  very,  numerous  and  form  a  superior  and  an 
inferior  group  of  vessels,  all  of  which  lead  to  the  median  group  of  superficial  inguinal 
lymph-nodes.  Frequent  communications  occur  with  those  of  the  penis  and  perineum, 
but  only  sparingly  with  the  deep  lymph-tracts  within  the  spermatic  cords. 

The  nerves  supplying  the  scrotum  are  derived  from  both  the  lumbar  and  sacral 
plexuses.  Those  from  the  former  source  are  distributed  to  the  front  and  sides  of  the 
scrotum  and  include  cutaneous  twigs  from  the  genital  branch  of  the  genito-crural 
nerve,  usually  reinforced  by  twigs  from  the  ilio-inguinal  that  end  in  the  integument  in 
the  vicinity  of  the  root  of  the  scrotum.  Those  from  the  sacral  plexus  supply  the 
posterior  surface  of  the  scrotum  and  are  from  the  perineal  or  inferior  pudenda! 
branches  of  the  small  sciatic  nerves  and  the  anterior  or  external  superficial  perineal 
branches  of  the  pudic  nerves.  Sympathetic  fibres  accompany  the  cutaneous  nerves 
for  the  dartos  muscle. 

PRACTICAL   CONSIDERATIONS:    THE   SCROTUM. 

The  scrotum,  from  a  practical  stand-point,  may  be  studied  as  if  composed  of 
two  layers,  an  external,  made  up  of  the  skin  and  dartos,  and  an  internal,  consisting 
of  the  three  coverings — fascial,  muscular,  and  aponeurotic — derived  from  the  abdomi- 
nal wall,  the  infundibuliform,  cremasteric,  and  intercolumnar. 

As  the  testes  are  safer  from  injury  in  a  loose  pouch,  in  which  they  can  readily 
glide  away  from  threatened  trauma,  the  scrotum  is  redundant  (more  so  on  the  left 


THE    PENIS.  1965 

side  on  account  of  the  greater  length  of  the  left  spermatic  cord)  and  lax.  Advantage 
of  these  facts  is  taken  in  certain  operative  procedures,  as  in  making  the  flaps  in  Roux's 
operation  for  vesical  exstrophy,  or  excising  a  portion  of  the  scrotum  (to  secure  firmer 
support  for  the  vascular  structures  of  the  cord)  in  varicocele. 

The  redundancy,  thinness,  and  elasticity  of  the  skin  and  the  laxity  of  the  fatless 
areolar  tissue  connecting  the  internal  and  external  layers  combine  to  favor  :  («)  marked 
discoloration  and  great  extravasation  of  blood  in  cases  of  hemorrhage  from  the  vessels 
between  the  two  layers  ;  hence  in  orchitis  leeches  are  applied,  not  over  the  scrotum, 
but  in  the  line  of  the  cord  in  the  groin  ;  (£)  extreme  distention,  as  in  large  scrotal 
herniae,  in  hydrocele,  in  bulky  testicular  tumors;  (c)  extensive  oedema  in  general 
anasarca,  as  a  result  of  pelvic  venous  thrombosis,  or  accompanying  an  infectious  cellu- 
litis  or  an  extravasation  of  urine,  which,  when  it  proceeds  from  a  solution  of  contin- 
uity anterior  to  the  triangular  ligament,  is  directed  by  Colics' s  fascia  into  this  cellular 
space  between  the  two  layers.  The  thinness  of  the  scrotal  skin,  increased  when  it 
is  distended,  makes  it,  in  spite  of  its  vascularity,  very  susceptible  to  gangrene  from 
pressure,  as  in  ; '  strapping' '  an  inflamed  testicle,  or  from  underlying  cellulitis. 

The  longitudinal  contractile  fibres  of  the  dartos  draw  the  redundant  skin  into 
transverse  rugse  which,  by  retaining  extraneous  dirt  and  the  secretions  of  the  sweat- 
glands  and  sebaceous  follicles,  become  often  the  starting-point  of  eczema,  of  mucous 
patches,  or  even  (as  in  "  chimney-sweep's  cancer"  )  of  epithelioma.  The  contractil- 
ity of  the  dartos  is  marked  in  young  and  robust  persons,  and  is  increased  by  cold,  by 
sexual  excitement,  and  by  light  friction.  It  is  lessened  in  old  age,  by  debility,  or  by 
continued  warmth  and  moisture,  the  scrotum,  in  the  presence  of  those  conditions, 
becoming  smooth,  elongated,  and  pendulous.  It  is  useful  in  aiding  the  scrotum  to 
regain  its  normal  size  after  distention,  as  following  the  tapping  of  a  hydrocele  or  the 
removal  of  a  tumor.  On  the  other  hand,  the  dartos  tends  to  invert  the  edges  of  a 
scrotal  wound  (as  the  platysma  does  those  of  a  wound  of  the  neck),  and  warm  appli- 
cations may  therefore  be  useful  before  a  scrotal  incision  is  sutured. 

The  muscular  (cremasteric)  element  of  the  inner  layer  gives  it  contractility,  and 
the  intimate  connection  between  it,  the  deeper  (infundibuliform)  plane  of  fascia,  and 
the  parietal  layer  of  the  tunica  vaginalis  enables  it  to  elevate  the  -testicle  with  its 
coverings  when  it  is  excited  to  contraction.  This  may  be  done  {cremasteric  reflex} 
by  drawing  the  finger-nail  over  the  skin  of  the  thigh  a  little  below  Poupart'  s  liga- 
ment, the  sensory  impression  being  conveyed  from  the  skin  through  the  crural  branch, 
and  to  the  cremaster  through  the  genital  branch,  of  the  genito-crural  nerve. 

The  infundibuliform  (internal  spermatic)  fascia,  by  its  close  relation  to  the  pos- 
tero-inferior  portion  of  the  testicle,  on  the  one  hand,  and  to  the  external  scrotal  layer, 
on  the  other,  assists  the  scrotal  ligament  (page  2042)  in  preventing  the  testicle  from 
being  floated  up  when  the  space  between  the  two  layers  of  the  tunica  vaginalis  is 
filled  with  fluid  (hydrocele,  haematocele),  and  holds  it  in  the  lower  back  part  of  the 
scrotum. 

In  exploratory  puncture,  or  in  the  tapping  of  hydrocele,  the  spot  selected  is 
therefore  on  the  anterior  surface  of  the  upper  two-thirds  of  the  scrotum,  care  being 
taken  to  avoid  the  large  superficial  veins. 

THE  PENIS. 

The  penis,  the  organ  of  copulation  of  the  male,  consists  of  three  cylinders  of 
erectile  tissue — the  paired  corpora  cavernosa  and  the  single  corpus  spongiosum — 
united  with  one  another  and  invested  by  coverings  of  fascia  and  skin.  Since  the 
upper  or  proximal  portion  of  the  penis  (pars  perinealis)  is  buried  beneath  the  integu- 
ment and  fascia  of  the  perineum  and  the  scrotum,  only  the  free  pendulous  distal 
portion  of  the  organ  is  visible  in  the  undissected  subject. 

When  exposed  throughout  its  entire  extent,  the  penis  presents  a  cylindrical  shaft 
or  body  (corpus  penis),  which  begins  above  in  a  three-pronged  root  (radix  penis) 
attached  to  the  pubic  arch  and  the  triangular  ligament  and  terminates  below  in  a 
blunted  conical  end,  the  glans penis.  The  anterior  or  upper  surface  (dorsum  penis) 
is  somewhat  flattened  and  formed  by  the  corpora  cavernosa.  The  posterior,  under, 
or  urethral  surface  (facies  urethralis)  corresponds  to  the  corpus  spongiosum,  traversed 


1966 


HUMAN   ANATOMY. 


FIG.  1673. 


Glaus 


corpus 


by  the  urethra,  and  is  marked  by  a  median  raphe,  which  is  continuous  with  that  of 
the  scrotum  and,  as  the  latter,  indicates  the  line  of  fusion  of  the  original  components 
of  the  spongy  body. 

The  conical  glans,  which  forms  the  distal  end  of  the  organ,  is  limited  along  its 
oblique  base  by  a  prominent  rounded  border,  the  corona  glandis,  that  runs  downward 
and  forward  from  the  dorsum  towards  the  under  surface  and  marks  a  groove  (sulcus 
retroglandularis)  that  separates  the  glans  from  the  body  of  the  penis.  The  constricted 
zone  immediately  behind  the  glans  constitutes  the  neck  (collum  penis).  In  conse- 
quence of  the  obliquity  of  the  corona,  the 
dorsal  expansion  of  the  glans  measures 
about  twice  the  length  of  its  under  sur- 
face. 

The  skin  covering  the  pendulous 
portion  of  the  penis — very  thin,  delicate, 
and  elastic,  and  possessing  only  fine 
hair  (lanugo)  except  in  the  immediate 
vicinity  of  the  pubes — is  loosely  attached 
over  the  body  of  the  organ  by  subcu- 
taneous tissue,  devoid  of  fat,  that  permits 
of  ready  movement  of  the  integument. 
Along  the  under  surface  of  the  organ 
bundles  of  involuntary  muscle  closely 
adhere  to  the  integument  and  constitute 
a  stratum,  the  tunica  darlos  penis,  that 
resembles  the  similar  layer  of  the  scro- 
tum. Just  behind  the  corona  the  skin 
forms  a  free  duplicature,  the  prepuce  or 
foreskin  (praeputium  penis),  that  covers 
the  glans  to  a  variable  extent  ( in  children 
and  in  some  adults  completely)  and  is 
firmly  attached  by  its  inner  layer  to 
the  neck  of  the  penis  along  a  line  about 
3  mm.  above  the  corona.  From  this 
point  the  skin  is  prolonged  over  the 
glans,  to  which  it  is  intimately  applied, 
as  far  as  the  meatus,  where  the  integu- 
ment becomes  continuous  with  the  ure- 
thral  mucous  membrane.  The  lines  of 
reflection  of  the  prepuce  on  the  two  sides 
converge  and  finally  meet  along  the 
under  surface  of  the  glans  in  a  sharp 
median  fold,  \\\efrcnum  (frenulum  prae* 
putii),  that  extends  as  far  as  the  pos- 
terior border  of  the  slit-like  urethral 
opening.  On  either  side  of  this  fold  a 
shallow  recess  (fossa  frenuli)  extends  the 
preputial  sac.  The  skin  lining  the  latter 
and  covering  the  glans  is  modified  so 
that  it  somewhat  resembles  a  mucous  membrane,  as  which  it  is  often  inaccurately 
described.  While  entirely  devoid  of  hairs,  small  sebaceous  glands  are  sparingly 
distributed  over  the  glans,  corona,  and  inner  layer  of  the  prepuce.  These,  formerly 
supposed  to  be  of  large  size  and  named  the  glands  of  Tyson  (  ^landnlae  praeputiaU-s  , 
secrete  unctuous  material  which,  mixed  with  discarded  epithelial  cells,  may  collect 
in  the  groove  behind  the  corona  as  a  cheesy  substance,  the  snicgnia. 

The  corpora  cavernosa  (corpora  cavernosa  penis)  are  two  cylinders  of  erectile 
tissue,  when  relaxed  about  15  cm.  (6  in.)  in  length,  that  form  the  chief  bulk  of  the 
body  of  the  penis.  Each  is  enclosed  within  a  dense  fibro-elastir  envelope,  or  tunica 
albuginca,  which  internally  is  continuous  with  the  trabecnla-  between  the  blood- 
spaces.  Beginning  above  at  the  root  of  the  penis  as  the  diverging  pointed  and  then 


of  triangular         >>-**• 
ligament 
Attachment  of  bulb,  cut 

Dissection  of  penis,  showing  three  component  cylin- 
ders of  erectile  tissue  ;  distal  end  of  corpus  spongiosum, 
with  glans,  has  been  freed  and  turned  aside;  attachment 
of  urethral  bulb  has  been  cut  and  bulb  drawn  aside. 


THE   PENIS. 


1967 


somewhat  expanded  crura  attached  to  the  inner  border  of  the  pubic  arch,  the  cavern- 
ous bodies  are  at  first  separated  by  an  interval  occupied  by  the  bulb  of  the  corpus 

FIG.  1674. 


D 


ddv  sdv      sk 


da  ddv    sdv 


FIG.  1675. 


Cross-sections  of  formalin-hardened  penis  at  different  levels.  A,  through  glans,  near  tip;  B,  about 
middle  of  glans ;  C,  through  corona;  D,  body,  distal  part;  E,  body,  proximal  part,  cc,  corpus  caver- 
nosum ;  cs,  corpus  spongiosum  ;  da,  dorsal  artery  ;  ddv,  deep  dorsal  vein  ;  r,  fibrous  envelope  ;  eg,  erectile 
tissue  of  glans  ;  f,  frenum  ;  ft,  fibrous  tissue ;  s,  fibrous  septum  ;  sdv,  superficial  dorsal  vein  ;  sf,  super- 
ficial fascia;  s&,  skin;  ta,  tunica  albuginea  ;  u,  urethra. 

spongiosum.  Farther  forward,  in  the  vicinity  of  the  penile  angle,  the  corpora  caver- 
nosa  press  against  each  other  with  their  median  surfaces,  the  opposed  flattened  cap- 
sules blending  to  form  a  median  partition  (septum  penis).  Lower  the  latter  becomes 
imperfect  and  replaced  by  a  series  of  vertical  bands,  and  hence  is  often  designated  the 
pectiniform  septum,  the  intervening 
slit-like  apertures  permitting  commu- 
nication between  the  blood-spaces  of 
the  two  cavernous  bodies,  as  well  as 
the  passage  of  anastomotic  branches 
of  their  arteries.  In  certain  mammals, 
especially  the  carnivora  and  some 
marsupials,  a  bone  (os  penis)  is  de- 
veloped within  the  fibrous  septum. 
On  approaching  the  corona,  the  cor- 
pora cavernosa  again  become  discrete 
and  rapidly  taper  to  blunt-pointed 
ends  that  are  separated  externally  by  a 
slight  furrow  and  capped  by  the  over- 
lying glans.  The  dorsal  and  under 
surfaces  common  to  the  closely  ap- 
plied cavernous  bodies  are  marked  by 
longitudinal  grooves  ;  that  along  the 
former  surface  lodges  the  dorsal  ves- 
sels of  the  penis,  while  the  under  fur- 
row is  filled  by  the  spongy  body. 

The  corpus  spongiosum  (cor- 
pus cavernosum  urethrae),  the  third  and 
much  smaller,  although  longer  (about 
17  cm.  or  6^  in.),  cylinder  of  erectile  tissue,  occupies  the  groove  along  the  under 
surface  of  the  cavernous  bodies.      The  two  ends  of  this  cylinder  are  enlarged,   the 


Dorsal  v 
now  doubl 


Pubic  bo 


Cms 

Deep  artery  in 

corpus  cavernosum 

Urethra 

Ischio-cavernosus 
muscle 

Bulb 


Bulbo-cavernos 
muscle 
Colles's  fascia- 


Frontal  section  through  pubic  arch  and  root  of  penis. 


1968 


HUMAN   ANATOMY. 


upper  expanding  into  a  pyriform  mass  of  erectile  tissue,  the  urethral  bulb  (bulbus 
urethrae),  and  the  lower  broadening  into  a  conical  cap  of  erectile  tissue  that  covers  the 
ends  of  the  corpora  cavernosa  and  contributes  the  bulk  of  the  glans.  With  the 
exception  of  the  bulb,  the  major  part  of  which  lies  behind  the  canal,  the  corpus  spon- 
giosum  is  traversed  by  the  urethra,  the  cavernous  tissue  completely  surrounding  the 
urinary  tube.  The  bulb,  attached  by  its  upper  surface  to  the  inferior  layer  of  the 
triangular  ligament  and  covered  below  by  the  bulbo-cavernosus  muscle,  presents  a 
slight  median  furrow  (sulcus  bulbi)  that  suggests  a  division  into  the  so-called  hemi- 
spheres. Internally  an  imperfect  median  septum  bulbi  partially  subdivides  the  erectile 
tissue  below  and  behind. 

The  glans  penis  consists  almost  entirely  of  erectile  tissue  (corpus  cavernosum 
glandis)  directly  continuous  with  that  of  the  spongy  body.  Its  upper  surface  is 
hollowed  out  to  receive  the  pointed  extremities  of  the  corpora  cavernosa,  so  that  a 
section  across  the  upper  part  of  the  glans  shows  the  erectile  tissue  of  the  cavernous 
bodies  surrounded  by  an  overhanging  crescent  of  the  cavernous  tissue  of  the  glans 
(Fig.  1674,  C).  Along  the  frenum  the  fibrous  envelope  of  the  glans  is  prolonged 
inward  towards  the  urethra  as  a  fibro-elastic  band  (ligamentum  medianum  glandis) 
which,  in  conjunction  with  a  similar  band  connecting  the  ends  of  the  cavernous  bodies 
with  the  upper  urethral  wall,  forms  a  median  partition,  the  septum  glandis,  that  in- 
completely divides  the  erectile 
FIG.  1676. 

Erectile  tissue  of  corpus 
Tunica  albuginea     cavernosum  broken  up 
/      by  pectiniforrn  septum 


Prepuce- 


Erectile  tissue 
of  glans 

Anterior 
extremity  of 
corpus  cav- 
ernosum 
External 
urethral 
orifice 
Navicular  fossa 


Frenum          Erectile  Urethra 

tissue  of  corpus  spongiosum 

Mesial  longitudinal  section  of  end  of  penis. 


tissue  of  the  glans  and  sur- 
rounds the  terminal  part  of  the 
urethra. 

The  penile  portion  of  the 
urethra  is  described  with  the 
other  parts  of  the  urinary  tract 
in  the  male  (page  1923). 

Beneath  the  skin  and  sub- 
cutaneous tissue  the  cylinders 
of  erectile  tissue,  enclosed  and 
united  by  their  albuginea,  are 
enveloped  by  the  superficial 
fascia  (Fig.  1674,  E}.  The 
latter,  directly  continuous  with 
that  of  the  perineum  (Colles1 
fascia)  behind  and  of  the  ab- 
domen (Scarpa's  fascia)  above,  invests  the  penis  as  far  as  the  neck,  where  it  becomes 
blended  with  the  prepuce.  This  fibro-elastic  sheath  is  often  called  the  fascia  penis. 

In  addition  to  the  attachment  of  the  crura  of  the  corpora  cavernosa  to  the  peri- 
osteum of  the  pubic  arch  and  of  the  bulb  of  the  spongy  body  to  the  triangular  liga- 
ment, the  penis  is  supported  by  fibrous  bands,  that  extend  from  the  abdominal  wall 
and  pubes  to  the  dorsum  penis.  This  triangular  sheet,  the  suspensory  ligament,  in- 
cludes a  superficial  and  a  deeper  portion.  The  former  (ligamentum  fundiforme  penis) 
begins  at  the  linea  alba,  from  4-5  cm.  ( I  ^-2  in. )  above  the  symphysis,  and  consists 
of  elastic  bundles  prolonged  from  the  deep  layer  of  the  superficial  fascia  downward  to 
the  dorsum  of  the  penis  (Fig.  1671)  at  the  so-called  angle,  where  it  divides  into  two 
arms  that  embrace  the  penis  and,  after  uniting  on  the  urethral  surface,  are  continued 
into  the  septum  scroti.  The  deeper  portion  (ligamentum  suspensorium  penis)  contains 
compact  fibrous  bands  that  pass  from  the  symphysis  to  the  corpora  cavernosa,  just  in 
advance  of  their  separation  into  the  diverging  crura,  to  blend  with  the  dense  albuginea. 
Structure. — Each  of  the  component  cylinders  of  erectile  tissue  is  enclosed  in  a. 
robust  sheath,  the  tunica  albuginea,  composed  of  dense  white  fibrous  tissue,  inter- 
mingled with  relatively  few  elastic  fibres  and  no  muscle.  The  sheath  surrounding  the 
corpora  cavernosa,  which  in  places  attains  a  thickness  of  2  mm.  and  is  much  stronger 
than  that  enclosing  the  spongy  body,  is  imperfect  along  the  opposed  median  surfaces 
of  the  two  cylinders,  where  it  forms  the  pectiniforrn  septum. 

From  the  inner  surface  of  the  tunica  albuginea  septa  and  trabeculae  are  given  off 
which  constitute  the  framework  supporting  tin-  vessels  and  nerves  and  enclosing  the 
characteristic  blood-spaces  of  the  erectile  tissue.  Numerous  bundles  of  involuntary 


THE    PENIS. 


1969 


muscle,  circularly,  longitudinally,  and  obliquely  disposed,  occupy  the  connective-tissue 
trabeculse  and  plates  separating  the  venous  lacunae,  around  which  they  form  imperfect 
layers  of  contractile  tissue.  The  trabecular  muscle  is  most  developed  within  the  cav- 
ernous and  spongy  bodies  and  least  so  within  the  glans. 

The  arteries  conveying  blood  to  the  cylinders  of  erectile  tissue  are  of  two  kinds, 
— those  nourishing  the  tissues  themselves  (vasa  nutritia)  and  those  carrying  blood  to 
the  venous  lacunae.  The  latter  are  connected  with  the  arteries  either  directly  by 
minute  channels  or  through  intervening  capillaries.  Within  the  trabeculse  of  the 
deeper  parts  of  the  erectile  masses  the  deep  arteries  of  the  penis  give  off  short,  tortuous 
branches  {arteries  helicince},  about  2  mm.  in  length,  that  project  into  the  blood-spaces 
with  which  they  directly  communicate  by  minute  openings  at  their  ends.  Notwith- 
standing their  exceptional  development  in  man,  the  fact  that  the  helicine  arteries  are 
wanting  in  many  mammals  shows  that  they  are  not  essential,  although  advantageous, 
for  erection.  The  arteries  of  the  erectile  tissue  are  distinguished  by  the  unusual  thick- 
ness of  the  circular  muscle  within  their  walls.  In  places  the  intima  likewise  exhibits 
excessive  thickness.  Since  the  increase  is  not  uniform  but  local,  it  leads  to  the  pro- 
duction of  cushion- 
like  elevations  that  FlG-  I(577- 
encroach  upon  and 
even  temporarily  oc- 
clude the  lumen  of  the 
arteries. 

The  blood-spaces 
or  lacuncz  that  occupy 
the  interstices  between 
the  trabeculse  are  to 
be  regarded  as  venous 
net- works  which  com- 
municate with  the  ar- 
teries, on  the 


Deep  dorsal  vein 


Subcutaneous 
tissue 


Skin 


Tunica  albuginea 


Septum 


one 


fascia 


Urethra 


Corpus 
spongiosum 


Transverse  section  of  penis  of  child.    X  10. 


hand,  and  with  the 
radicles  forming  the 
veins,  on  the  other. 
Their  form  and  size  Superficial! 
evidently  depend 
upon  the  degree  of 
distention,  when  con- 
taining little  blood  the 
spaces  being  often 
mere  slits  or  irregu- 
larly stellate  clefts, 
while  when  filled  they 
become  more  cylin- 
drical in  form.  In  a  general  way  three  districts  may  be  distinguished  :  («)  a  narrow 
outer  peripheral  zone  of  almost  capillary  spaces,  for  the  most  part  narrow  and  trian- 
gular in  outline  ;  (^)  an  inner  peripheral  zone  of  larger  spaces  of  uncertain  form  and 
from  .  15-.  20  mm.  in  diameter  ;  and  (c}  a  central  zone  of  still  more  extensive  spaces, 
which  in  places  attain  a  diameter  of  one  or  more  millimetres  and  are  enclosed  by  rela- 
tively thin  intervening  lamellae  and  trabeculae.  Since  their  expansion  is  usually 
greater  in  one  direction,  the  general  form  of  the  larger  and  deeper  lacunae  is  often  ap- 
proximately cylindrical.  Within  the  corpus  spongiosum  in  the  immediate  vicinity  of 
the  urethra  the  blood-spaces  are  somewhat  concentrically  disposed  owing  to  the  feeble 
development  of  the  radial  lamellae  (Eberth).  The  spongy  body  is  further  distin- 
guished by  the  robustness  of  its  trabeculae  and  the  consequent  reduction  in  the  size  of 
the  blood-spaces.  Beyond  the  single  layer  of  endothelial  plates,  the  lacunae  do  not 
possess  a  distinct  wall  other  than  the  fibro-muscular  tissue  of  the  surrounding  trabeculae. 
The  deep  veins  draining  the  cylinders  of  erectile  tissue  do  not  directly  open  into 
the  blood-spaces,  but  are  formed  by  tributaries  of  various  size  that  begin  as  apertures 
in  the  walls  of  the  lacunae,  of  which  they  are  in  fact  extensions.  The  tributaries  of  the 

124 


HUMAN   ANATOMY. 


more  superficially  situated  venous  trunks,  as  the  dorsal  vein,  arise  chiefly  from  the 
venous  net-works  of  the  peripheral  zone.  The  veins  possess  an  unusually  well- 
developed  muscular  coat,  and  in  places  exhibit  local  cushion-like  thickenings  of  their 
intima  similar  to  but  less  marked  than  those  seen  in  the  arteries. 

Vessels. — The  arteries  of  the  penis  constitute  a  superficial  and  a  deep  set,  the 
former  supplying  the  integument  and  associated  envelopes,  while  the  latter  convey 
blood  to  the  masses  of  erectile  tissue.  The  superficial  arteries  include  twigs  from 
the  external  pudic  branches  of  the  femorals  to  the  lateral  and  under  surface  of  the 
penis,  from  the  dorsal  arteries  to  the  anterior  surface  and  the  prepuce,  and  from  the 
superficial  perineals  by  small  vessels  to  the  posterior  part  of  the  urethral  surface. 
The  deep  arteries — all  branches  from  the  internal  pudics — supply  the  three  cylinders 
of  erectile  tissue,  including  the  glans.  The  corpus  spongiosum  receives  the  arteries 
of  the  bulb,  their  continuations  (sometimes  described  as  the  urethral  arteries)  accom- 
panying the  urinary  canal  as  far  as  the  glans,  where  they  anastomose  with  the  terminal 
branches  of  the  dorsal  arteries.  The  last-named  vessels  also  send  small  twigs  around 
the  corpora  cavernosa  to  the  spongy  body.  The  corpora  cavernosa  are  supplied 
chiefly  by  the  deep  arteries  of  the  penis,  supplemented  by  twigs  from  the  dorsal 

arteries  that  pierce  the  albu- 

FIG.  1678.  ginea.     Entering  the  cavern- 

Central  blood-spaces       Inner  peripheral  spaces      Outer  peripheral  spaces      OUS   bodies  about  where   the 

crura  unite,  the  deep  arteries 
of  the  penis  traverse  the  cyl- 
inders somewhat  eccentri- 
cally, to.  the  median  side  of 
their  axes.  Communication 
between  the  vessels  of  the 
two  bodies  is  established  by 
anastomotic  twigs  that  pass 
through  the  apertures  in  the 
median  septum,  as  wrell  as 
by  the  terminal  loop.  The 
dorsal  arteries,  the  longest 
branches  of  the  internal 
pudics,  pass  along  the  dor- 
sum  between  the  fascia  and 
the  albuginea,  in  company 
with  the  dorsal  nerves  and 
vein,  and,  in  addition  to  the 
twigs  distributed  to  the  cov- 
erings, the  cavernous  bodies, 
and  the  corpus  spongiosum, 
supply  the  erectile  tissue  of 
the  glans.  The  anastomoses 
between  the  various  vessels 
supplying  the  penis  are  very  free,  not  only  between  the  corresponding  and  other 
branches  of  the  two  sides,  but  also  between  those  of  the  superficial  and  deep  sets. 

The  veins  of  the  penis,  like  the  arteries,  constitute  a  superficial  and  a  deep 
group  which  freely  communicate  and  carry  off  the  blood  from  the  envelopes  and  from 
the  erectile  tissue  respectively.  The  superficial  veins  for  the  most  part  are  tributary 
to  a  subcutaneous  trunk  (v.  dorsalis  penis  superficialis)  that  passes  upward  along  the 
dorsum  beneath  the  skin  to  the  pubes  and  terminates  either  by  dividing  into  branches 
that  empty  into  the  internal  saphenous  or  the  femoral  veins  on  either  side  or  by 
joining  the  deep  dorsal  vein  ;  both  modes  of  ending,  however,  may  exist.  A  number 
of  vessels  from  the  integument  covering  the  posterior  part  of  the  urethral  surface  are 
collected  by  the  anterior  scrotal  veins. 

The  deep  veins,  which  begin  by  tributaries  from  the  erectile  tissue  that  they 
drain,  to  a  large  extent  discharge  their  contents  into  the  deep  dorsal  vein  (  v.  dorsalis 
penis  profunda )  that  lies  beneath  the  fascia  and  occupies  the  groove  on  the  dorsum 
as  far  as  the  suspensory  ligament,  between  the  superficial  and  deep  parts  of  which  it 


Trabeculae 


V 

Bundles  of  muscle 


Dense  fibrous  tissue  of 
tunica  albuginea 


Transverse  section  through  periphery  of  corpus  cavernosum.     X  50. 


THE  PENIS.  1971 

passes.  Continuing  between  the  subpubic  and  transverse  ligaments  and  piercing  the 
fascia,  it  gains  the  pelvis  and  ends,  after  dividing  into  two  trunks,  in  the  prostatic 
plexus.  Beginning  above  the  corona  by  the  union  of  two  stems  that  collect  branches 
from  the  glans  and  the  prepuce,  the  deep  dorsal  vein,  as  it  courses  upward,  receives 
tributaries  from  all  three  cylinders  of  erectile  tissue.  Those  from  the  corpora  caver- 
nosa  either  pierce  the  albuginea  as  short  branches  that  pass  directly  into  the  dorsal 
vein,  or  emerge  from  their  under  surface  along  the  urethral  groove  and  wind  around 
the  body  of  the  penis  to  reach  the  collecting  trunk  on  the  dorsum,  the  anterior  of 
these  circumflex  veins  taking  up  tributaries  from  the  under  surface  of  the  glans. 
Within  the  posterior  part  of  the  cavernous  bodies  are  formed  the  deep  veins  of  the 
penis,  which  emerge  where  the  crura  diverge  and,  after  establishing  communications 
with  the  prostatic  plexus,  become  important  tributaries  of  the  internal  pudic  veins 
that  accompany  the  corresponding  arteries.  The  corpus  spongiosum  is  drained  by 
anterior  branches  that  convey  the  blood  to  the  dorsal  vein  by  joining  the  circumflex 
or  other  veins  from  the  corpora  cavernosa,  and  by  posterior  stems  (vv.  urethrales)  that 
pass  upward  and  backward  and  empty  partly  into  the  prostatic  plexus  and  partly  into 
the  internal  pudic  veins,  the  veins  from  the  urethral  bulb  having  a  similar  destination. 
Numerous  anastomoses  between  the  cutaneous  veins  and  those  from  the  erectile  tissue 
establish  free  communication  between  the  superficial  and  deep  vessels. 

The  lymphatics  are  numerous  and  disposed  as  superficial  and  deep  vessels.  The 
former  are  tributary  chiefly  to  a  superficial  dorsal  stem  that  accompanies  the  cor- 
responding vein  and  begins  by  the  confluence  of  plexiform  lymphatics  within  the 
integument  of  the  prepuce  and  frenum.  During  its  course  the  dorsal  trunk  receives 
lymphatics  from  the  adjacent  territory  as  well  as  others  from  the  under  surface  that 
gain  the  dorsum  by  following  the  circumflex  veins  around  the  body  of  the  penis. 
At  the  pubes  the  superficial  dorsal  lymph-trunk  passes  either  to  the  right  or  left,  or, 
when  double,  as  it  occasionally  is,  to  both  or  even  opposite  sides,  and  joins  the 
median  group  of  superficial  inguinal  lymph-nodes.  Direct  comrriunications  with  the 
deep  subinguinal  nodes  sometimes  exist  (Kiittner).  The  deeper  lymphatics  are 
particularly  numerous  in  the  periphery  of  the  glans,  around  the  meatus  communi- 
cating with  the  urethral  and  preputial  plexuses.  Trunks  are  formed  which  occupy 
the  retroglandular  sulcus  and  unite  into  a  deep  dorsal  lymph-stem,  sometimes  double, 
that  accompanies  the  corresponding  vein  beneath  the  fascia  and  terminates,  when 
single,  in  the  median  inguinal  nodes  of  the  left  side  (Marchant). 

The  nerves  of  the  penis  include  both  spinal  and  sympathetic  fibres,  the  former 
from  the  ilio-inguinal  and  the  pudic  nerves,  and  the  latter  from  the  hypogastric 
plexus.  The  integument  around  the  root  of  the  penis  is  supplied  by  the  cutaneous 
branches  of  the  ilio-inguinal  and  the  inferior  pudendal  nerves,  while  that  of  the  body 
and  the  prepuce  is  provided  with  the  cutaneous  branches  of  the  dorsal  nerves.  The 
cylinders  of  cavernous  tissue  also  receive  twigs  from  the  pudic  nerves,  the  bulbar 
branches  of  which  pass  to  the  bulbus  urethrae  and  in  addition  supply  the  mucous 
membrane  of  the  urethra.  Each  corpus  cavernosum  receives  a  deep  branch  from  the 
dorsal  nerve  which  is  given  off  as  the  latter  lies  between  the  layers  of  the  triangular 
ligament.  The  sympathetic  fibres  destined  for  the  blood-vessels  and  muscle  of  the 
erectile  tissue  are  continued  from  the  hypogastric  plexus  through  the  prostatic  plexus 
to  the  plexus  cavernosus,  where,  joining  the  dorsal  nerves  of  the  penis,  twigs  (nervi 
cavernosi  penis  minores)  are  sent  to  the  posterior  part  and  the  crura  of  the  corpora 
cavernosa,  while  others  (nervi  cavernosi  penis  majores)  are  distributed  to  the  lower 
portions  of  the  erectile  masses,  some  fibres  terminating  within  the  spongy  body. 
Close  net-works  of  non-medullated  fibres  have  been  traced  within  the  bundles  of  invol- 
untary muscle  of  the  blood-vessels  and  trabeculae  of  the  erectile  tissue.  Certain 
cerebro-spinal  fibres  (nervi  erigentes)  supposed  to  be  especially  concerned  in  erection 
are  conveyed,  in  company  with  the  sympathetic  fibres,  along  the  paths  of  the  cavernous 
plexus. 

In  addition  to  a  generous  supply  of  the  more  usual  nerve-terminations,  the  skin 
of  the  glans  and  the  prepuce  is  provided  with  special  nerve-endings, — the  tactile 
bodies  and  the  genital  corpuscles  of  Krause  (page  1017)  lying  within  the  papillae  and 
the  Pacinian  corpuscles  within  the  subcutaneous  stratum.  The  paths  of  the  sensory 
impressions  lie  within  the  dorsal  nerves. 


1972  HUMAN   ANATOMY. 

Variations. — Apart  from  the  unimportant  individual  differences  due  to  age,  growth,  and 
sexual  activity,  the  variations  of  the  penis  are  for  the  most  part  referable  to  imperfect  develop- 
ment and  are  recognized  as  malformations  rather  than  as  anatomical  deviations.  The  explana- 
tion of  many  of  these  conditions  is  supplied  by  the  developmental  history  of  the  structures 
involved  (page  2044) . 

PRACTICAL  CONSIDERATIONS  :    THE    PENIS. 

The  size  of  the  penis  bears  less  constant  relation  to  general  physical  develop- 
ment than  does  any  other  organ  of  the  body.  The  normal  average  size  of  the  flaccid 
penis  of  the  adult  is  about  three  inches  in  circumference  and  from  three  and  a  half  to 
four  inches  in  length,  measured  from  the  suspensory  ligament.  When  erect,  this 
length  increases  to  about  six  and  a  half  inches  and  the  circumference  to  three  and  a 
half  or  more. 

Absence  of  the  penis  may  occur,  but  is  rare  unassociated  with  other  anomalies. 
Apparent  absence  (concealed  penis)  may  be  due  to  the  subcutaneous  situation  of  an 
atrophic  or  undeveloped  organ  which  may  be  palpated  through  the  skin  and  revealed 
by  an  incision. 

Micropenis  (infantile  penis)  is  not  uncommon,  and  varies  in  degree  from  a  mere 
failure  to  attain  quite  the  average  size  (annoying  chiefly  to  sexual  neurasthenics)  to  a 
retention  throughout  life  of  the  dimensions  and  development  normal  in  early  childhood 
or  infancy.  Occasionally  in  such  cases,  after  puberty  and  following  physiological 
activity  of  the  organ,  rapid  growth  takes  place  and  conditions  approximating  normal- 
ity may  result. 

Megalopenis. — As  has  already  been  observed,  the  size  of  the  organ  bears  no 
constant  relation  to  the  size  or  strength  of  the  individual.  In  congenital  imbeciles  it 
is  often  of  unusual  size,  and  in  dwarfs  and  hunchbacks  it  is  not  uncommonly  devel- 
oped, not  only  out  of  proportion  to  the  other  parts  of  the  organism,  but  beyond  even 
the  average  for  individuals  of  normal  growth.  Hypertrophy  of  the  penis  is  at  times 
an  inconvenience,  and  may  even  be  a  source  of  danger,  since  an  excessive  develop- 
ment predisposes  to  abrasions  and  fissures  through  which  inoculation  with  venereal 
diseases  may  occur. 

Double  penis  has  been  .recorded  in  a  few  instances,  in  at  least  two  of  which  each 
organ  was  functionally  perfect. 

The  skin  of  the  penis  is  thin  and  delicate  (to  maintain  the  sensitiveness  of  the 
organ),  and  is  lax  and  elastic  (to  permit  of  its  changes  in  size).  On  account  of  these 
qualities  abrasions  are  not  unusual,  and  through  them  syphilitic  infection  frequently 
takes  place. 

The  loose,  plentiful  layer  of  subcutaneous  connective  tissue  permits  of  enormous 
cedematous  swelling  as  a  result  of  ordinary  staphylococcic  or  streptococcic  (pyogenic 
or  erysipelatous)  infection;  its  abundance  in  conjunction  with  the  elasticity  of  the  skin, 
accounts  for  the  disappearance  of  the  penis  in  cases  of  very  large  scrotal  hernia,  in 
hydroceles  of  similar  size,  and  in  elephantiasis  scroti. 

Anterior  to  the  corona  the  skin  is  modified  and  resembles  a  mucous  mem- 
brane, at  the  meatus  becoming  continuous  with  the  mucosa  of  the  urethra.  The  line 
of  demarcation  between  the  ordinary  and  modified  cutaneous  surfaces  is  not,  however, 
so  distinct  as  on  the  lips  or  the  nostrils,  the  passage  of  one  surface  into  the  other  more 
closely  resembling  that  which  takes  place  at  the  margin  of  the  anus.  On  the  proxi- 
mal face  of  the  corona  the  subcutaneous  tissue  is  still  abundant.  Over  the  glans  it 
practically  disappears  and  the  modified  integument  closely  embraces  the  erectile  tissue 
of  the  expanded  anterior  extremity  of  the  corpus  spongiosum. 

Chancres  anterior  to  the  corona  (except  at  the  frenum)  are  apt  to  exhibit  the 
variety  of  induration  known  as  "laminated"  or  "parchment-like,"  corresponding  to 
a  sclerosis  limited  to  the  papillary  layer  of  the  derma  and  to  the  vascular  net-work  of 
the  papillae.  At  the  frenum,  corona,  or  cervix,  where  the  cellular  tissue  is  abundant, 
"  nodular"  induration — a  sclerosis  of  the  whole  thickness  of  the  derma,  of  thesubder- 
moid  areolar  tissue,  and  of  the  associated  vascular  net-work,  which  is  much  larger 
than  the  superficial  or  papillary  supply — is  apt  to  occur,  and  is,  as  the  name  indicates, 
deeper,  thicker,  and  harder.  On  the  skin  of  the  penis  chancres  are  apt  to  be  exten: 
sive  in  area,  but  are  limited  in  depth  by  the  firm,  resistant  fascia  penis. 


PRACTICAL   CONSIDERATIONS:    THE   PENIS. 

At  birth  the  prepuce  is  normally  adherent  to  the  glans,  its  moderate  retraction 
barely  exposing  the  meatus.  Continued  retraction  everts  the  lips  of  the  meatus  and 
then  separates  the  epithelial  adhesions  between  glans  and  prepuce,  ultimately  exposing 
a  congested  surface  and  causing  punctate  hemorrhages. 

This  separation  should  normally  take  place  during  infancy  or  early  childhood,, 
either  spontaneously  as  a  result  of  erections  and  of  the  growth  of  the  organ  or  because 
of  gradual  mechanical  retraction  by  nurse  or  mother.  When  it  fails  to  do  this,  the 
condition  of  phimosis — inability  to  retract  the  prepuce — follows,  and  is  due  partly  to  the 
persistent  adhesions  and  partly  to  a  frequently  associated  narrowing  of  the  preputial 
orifice. 

Both  these  factors  may  be  the  result  of  disease,  and  acquired  phimosis  may  occur 
at  any  time  of  life  and  follow  any  form  of  inflammation  of  the  skin  covering  the  glans 
(Jbalanitis*) ,  of  the  inner  surface  and  cellular  tissue  of  the  prepuce  ( posthitis'} ,  or  of 
both  (balano-posthitis) ,  the  last  named  being  the  most  common.  Following  phimosis 
there  may  be,  (a)  as  a  result  of  retention  of  secretion  and  of  urine  in  the  subpreputial 
space,  balanitic  or  herpetic  ulceration,  or  the  development  of  papillomata  (venereal 
warts)  ;  (£)  as  a  result  of  obstruction  to  the  flow  of  urine  and  the  consequent  strain- 
ing, vesical  irritability,  dilatation  of  the  bladder,  ureters,  and  kidneys,  hemorrhoids, 
and  hernia  (62  per  cent,  of  cases  of  congenital  phimosis)  (Kempe,  quoted  by  Jacob- 
son)  ;  (c)  as  a  result  of  nerve  irritation  (the  region  having  an  unusually  rich  nerve- 
supply),  spastic  palsies,  reflex  joint  pains  and  muscular  spasm  (simulated  coxalgia), 
or  even  general  convulsions. 

These  complications  -are  most  apt  to  occur  in  infants  and  very  young  children, 
and  their  frequency  has  been  exaggerated. 

As  a  result  of  phimosis,  even  when  the  preputial  orifice  is  ample,  there  may  be 
a  contracted  or  ' '  pin-point' '  meatus,  which  may  give  rise  to  the  same  train  of  symp- 
toms and  will  require  to  be  divided  (meatoiomy)  by  a  linear  incision  directed  towards 
the  frenum,  and  kept  open  during  the  process  of  healing. 

Circumcision,  whether  done  for  phimosis  or  to  meet  other  indications,  requires 
for  its  successful  performance  attention  to  the  following  anatomical  points  :  (a)  the 
laxity  of  the  skin,  permitting  it  easily  to  be  drawn  so  far  in  front  of  the  glans  that 
when  it  is  severed  at  that  point  so  much  may  be  removed  that  the  remainder  retracts 
quite  to  the  root  of  the  organ,  which  is  left  denuded  ;  (£)  the  close  attachment  of  the 
inner  or  mucous  layer  of  the  prepuce  to  the  corona,  so  that  the  length  of  the  portion 
of  that  layer  that  is  allowed  to  remain  will  determine  the  distance  of  the  operative 
scar  (at  the  muco-cutaneous  junction)  from  the  meatus  ;  if  this  stump  is  not  exces- 
sive, it  will  thus  effectually  prevent  the  mortifying  but  not  infrequent  accident  of  re- 
formation of  a  phimosis  after  a  circumcision  ;  (c)  the  loose,  abundant  cellular  tissue 
and  rich  vascular  supply  in  the  frenal  region,  which,  together  with  the  dependent 
position  of  the  part,  may  determine  an  excess  of  exudate  that  will  result  in  an  objec- 
tionable fibrous  mass  in  that  region  if  full  haemostasis  is  not  secured  or  if  any  redun- 
dant tissue  is  left  there. 

When  a  relatively  small  preputial  orifice  is  drawn  behind  the  corona  it  causes 
marked  constriction  at  that  point,  especially  if  it  is  not  only  small  but  also  inelastic  as 
a  result  of  chronic  inflammation.  If  the  constriction  remains  unrelieved,  paraphimo- 
sis  results  ;  the  glans  becomes  distinctly  enlarged,  increasing  the  constriction,  purplish 
in  color,  and  glossy.  It  is  often  partially  concealed  by  a  thick  collar  of  shiny,  cedem- 
atous  skin,  behind  which  there  is  a  deep,  excoriated  sulcus,  and  back  of  this  sulcus 
there  is  usually  a  second  cedematous  band  less  marked  than  the  one  lying  immediately 
behind  the  coronary  sulcus.  The  penis  seems  to  have  a  distinct  upward  kink  or  bend 
just  behind  the  glans.  This  appearance  is  due  to  the  deep  notch  caused  by  the 
margin  of  the  retroverted  orifice  of  the  prepuce  and  to  the  oedematous  swelling 
which  is  particularly  marked  about  the  position  of  the  frenum.  In  some  cases,  where 
the  tense,  inelastic  edge  of  the  orifice  exerts  a  more  than  usual  amount  of  constriction, 
circulation  is  markedly  interfered  with,  and  ulceration  and  even  sloughing  involving 
both  the  foreskin  and  the  head  of  the  penis  may  take  place.  This  complication  would 
undoubtedly  be  more  frequent  were  it  not  for  the  rich  blood-supply  to  the  glans 
and  the  anastomosis  between  its  vessels  and  those  of  the  corpora  cavernosa.  The 
ulceration  usually  involves  the  foreskin  only. 


1974  HUMAN   ANATOMY. 

When  the  swelling  consequent  upon  paraphimosis  is  well  developed  there  is  en- 
countered first  a  furrow,  the  coronary  sulcus,  which  is  normally  found  behind  the 
corona  ;  in  these  cases  it  appears  deeper  because  it  is  intensified  by  the  cedematous 
swelling.  Covering  this  furrow,  and  even  overlapping  the  glans  somewhat,  is  the 
portion  of  the  prepuce  which  is  normally  in  contact  with  the  posterior  face  and  border 
of  the  corona.  Behind  this  swollen  fold  is  found  a  second  deep,  often  ulcerated  fur- 
row indicating  the  position  of  the  preputial  muco-cutaneous  margin ;  this  is  the  actual 
seat  of  constriction,  and  behind  it  is  placed  yet  another  ridge  of  swollen  integument. 

The  fascia  penis  (page  1968)  gives  the  organ  some  of  its  most  important  physical 
characteristics.  The  tensile  strength  of  the  penis,  because  of  its  tough  fibrous  invest- 
ments, is  sufficient  to  bear  the  entire  weight  of  the  body.  That  portion  of  this  fibrous 
investment  which  covers  the  blunt  extremities  of  the  two  cavernous  bodies  where  they 
are  capped  by  the  glans,  delays,  and  sometimes  prevents,  the  backward  extension  of 
inflammatory  or  infiltrating  processes,  particularly  cancerous  infiltration,  which  pri- 
marily involve  the  glans.  This  fibrous  sheath,  being  a  continuation  of  the  deep  layer  of 
the  superficial  fascia,  also  limits  the  forward  extension  of  urinary  and  purulent  infiltra- 
tions beneath  this  fascia,  such  infiltrations  leaving  the  glans  uninvolved.  The  free 
blood-supply  to  the  penis  and  its  rich  innervation  insure  rapid  healing  in  case  of 
wounds,  and  justify  conservative  treatment  even  although  the  organ  has  been  nearly 
severed  or  extensively  crushed. 

Contusion  of  the  penis  is  often  followed — owing  to  the  laxity  of  the  skin — by 
such  rapid  and  pronounced  ecchymosis  and  oedema  as  to  simulate  gangrene. 

When  the  vessels  of  the  cavernous  bodies  are  involved  there  is  free  subcutaneous 
bleeding,  giving  rise  to  a  circumscribed  fluctuating  tumor,  most  prominent  during 
erection.  This  tumor  is  somewhat  slow  in  forming,  and  occasionally  suppurates. 
Under  conservative  treatment  it  usually  disappears.  When  injury  has  not  only  occa- 
sioned extensive  extravasation  of  blood,  but  has  lacerated  the  urethral  canal,  the 
inflammatory  phenomena  observed  after  rupture  of  the  urethra  quickly  develop. 
Moreover,  there  is  immediately  bleeding  from  the  meatus,  which  should  lead  to 
prompt  diagnosis  and  appropriate  treatment. 

Wounds,  if  involving  the  erectile  tissue,  bleed  freely,  and,  if  transverse  and  ex- 
tensive, may  be  followed  by  loss  of  erectile  power  in  the  region  anterior  to  the  wound. 
Fracture,  in  a  literal  sense,  is  possible  only  when  the  organ  has  undergone  calcifica- 
tion or  ossification  (vide  infra],  but  the  term  is  applied  to  injuries  that  result  when, 
during  vigorous  erection,  the  penis  is  subjected  to  a  sudden  twist  or  bend.  The 
resulting  condition  is  not  unlike  that  caused  by  contusion,  but  the  subcutaneous 
effusion  is  apt  to  be  lacking.  The  chief  lesion  is  usually  in  the  corpora  cavernosa,  or 
in  one  of  them,  and  is  apt,  as  a  result  of  obliteration  of  erectile  spaces,  to  leave  a 
flail-like  organ,  erection  anterior  to  the  break  being  impossible. 

Chronic  induration  (ossification,  calcification,  chronic  inflammation)  of  the  sheath 
and  erectile  tissue,  especially  of  the  corpora  cavernosa,  is  marked  by  the  formation 
of  fibrous,  calcareous,  or  bony  thickenings  or  plates,  which  form  usually  in  middle- 
aged  or  elderly  men  of  gouty  diathesis.  They  cause  but  little  pain,  are  easily  recog- 
nized by  palpation,  and  are  accompanied  by  bending  of  the  penis  to  the  affected  side 
during  erection,  which  is  incomplete  in  the  region  anterior  to  the  induration.  The 
condition  is  unknown  before  forty  or  forty-five,  and  is  probably  analogous  to  the 
thickening  and  toughening  of  the  palmar  fascia,  which  goes  by  the  name  of  Dupuy- 
tren's  contraction,  and  which  we  recognize  as  partly  due  to  gout  and  partly  to  some 
constant  irritation.  Thus  they  may  be  met  with  in  both,  the  penis  and  the  hands  of 
the  same  gouty  person  (Jacobson).  It  has  been  suggested  (Metchnikoff)  that  in 
their  osseous  form  they  represent  reversions  to  the  condition  existing  in  many  mam- 
mals and  even  in  the  anthropoid  apes,  in  whom  an  os  pen  is  is  present. 

Lymphangitis  may  follow  peripheral  inflammation  of  any  type,  but  is  usually  of 
venereal  origin. 

The  diagnosis  between  lymphangitis  and  phlebitis  of  the  dorsal  vein  is  based 
upon  the  much  smaller  size  of  the  lymphatic  vessels  as  compared  with  the  vein  ;  upon 
the  fact  that  the  former  vessels  do  not  pass  upward  in  the  middle  line,  but  are  directed 
.into  the  groins  ;  and  finally  upon  the  ability  to  lift  the  indurated  vessel  up  from 
the  deeper  parts,  this  not  being  possible  in  the  case  of  the  vein,  since  it  is  placed  in  a 


THE    PROSTATE   GLAND.  1975 

furrow  between  the  two  cavernous  bodies.  Phlebitis  occasions  much  more  marked 
cedema. 

Epithelioma  of  the  penis  is  not  uncommon.  It  usually  follows  prolonged  subpre- 
putial  irritation.  It  involves  ultimately  both  the  inguinal  and  the  deep  pelvic  nodes. 

Amputation  of  the  entire  penis  may  be  required  for  the  relief  of  malignant  dis- 
ease. The  following  description  (Treves)  should  be  studied  in  connection  with  the 
anatomy  of  the  penis  and  of  the  urethra.  The  patient  is  placed  in  the  lithotomy  posi- 
tion, and  the  skin  of  the  scrotum  is  incised  along  the  whole  length  of  the  raphe.  With 
the  finger  and  the  handle  of  the  scalpel  the  halves  of  the  scrotum  are  separated  down 
to  the  corpus  spongiosum.  A  full-sized  metal  catheter  is  passed  as  far  as  the  trian- 
gular ligament,  and  a  knife  is  inserted  transversely  between  the  corpora  cavernosa  and 
the  corpus  spongiosum.  The  catheter  is  withdrawn,  the  urethra  is  cut  across,  and 
its  deep  end  is  detached  from  the  penis  back  to  the  triangular  ligament.  An  incision 
is  made  around  the  root  of  the  penis  continuous  with  that  in  the  median  line.  The 
suspensory  ligament  is  divided  and  the  penis  is  separated,  except  at  the  attachment 
to  the  crus.  The  knife  is  then  laid  aside,  and  with  a  stout  periosteal  elevator  or  rugine 
each  crus  is  detached  from  the  pubic  arch.  The  two  arteries  of  the  corpora  cavernosa 
and  the  two  dorsal  arteries  require  ligature.  The  urethra  and  corpus  spongiosum  are 
split  up  for  about  half  an  inch,  and  the  edges  of  the  cut  are  stitched  to  the  back  part 
of  the  incision  in  the  scrotum.  The  scrotal  incision  is  closed  by  sutures,  and  if  drain- 
age is  used,  the  tube  is  so  placed  in  the  deep  part  of  the  wound  that  its  end  can  be 
brought  out  in  front  and  behind.  No  catheter  is  retained  in  the  urethra. 

THE    PROSTATE   GLAND. 

Although  developed  as  an  appendage  of  the  urinary  tract,  and  not  directly  as 
part  of  the  sexual  apparatus,  the  prostate  is  functionally  so  closely  related  to  the  gen- 
erative organs  that  it  may  appropriately  be  regarded  as  one  of  the  accessory  glands,  the 
others  being  the  glands  of  Cowper. 

The  prostate  is  complex  in  both  its  make-up  and  relations,  being  partly  glandu- 
lar and  partly  muscular  and  traversed  by  the  urethra  and  the  ejaculatory  ducts.  In 
general  form  it  resembles  an  inverted 

Spanish  chestnut,   having   the  base  FIG.  1679. 

applied  to  the  under  surface  of  the 
bladder  and  the  small  end,  or  apex, 
directed  downward.  Additional  an-  ^^— -Slight  groove  produced 

,  i  j  .  r  f  HBk          by  symphysis 

tenor,  lateral,  and  posterior  surfaces 

are    recognized.        Grayish    red    in  ^-inferior  surface 

color  and  of  firm  consistence,  the 
adult  prostate  varies  considerably 
within  physiological  limits  in  size 
and  weight.  The  former  includes  a 
length,  from  apex  to  base,  of  from 
2. 5-3. 5  cm.  ( i  to  i  y%  in.  ) ,  a  breadth 
or  transverse  diameter  of  from  3. 5- 
4.5  cm.  (i-Hi— 1^4  m-)>  and  a  thick- 
ness of  from  2-2.5  cm-  (I-"1  m-)- 
Its  average  weight  is  about  22  gm. 
(24  oz. ).  Marked  increase  in  size  ^  surface 

and     weight    is     Common     in     elderly  Slightly  distended  bladder,  hardened  in  situ,  show- 

i  •  ing  prostate,  seminal  vesicles,  and  semitial  ducts  ;  viewed 

SUDjeCtS.  from  below  and  behind. 

The   oblique    upper  surface  or 

base  (basis  prostatae,  facics  vesicalis)  is  applied  to  the  under  surface  of  the  bladder, 
with  which  it  is  inseparably  blended  by  muscular  tissue  surrounding  the  urethral  ori- 
fice, and  is  pierced  by  the  urethra  usually  slightly  in  advance  of  the  middle.  The 
base  is  outlined  by  free  rounded  borders,  so  that  its  limits  are  separated  from  the 
vesical  wall  by  a  groove.  The  posterior  surface  (fades  posterior),  directed  backward 
and  towards  the  rectum,  is  defined  laterally  by  prominent  rounded  borders  that 
extend  from  the  base  to  the  apex  and  enclose  a  flattened  cordiform  or  triangular  area 


1976 


HUMAN   ANATOMY. 


Seminal 
vesicle 


Ampulla 


Prostate,  middle  lobe 

Ejaculatory  duct 


Inferior  wall 
of  bladder 

Internal  urethral       V 
orifice  \ 

Urethral  crest^ 


Prostatic  urethra 


Portion  of  sagittal  section  showing  prostate  and  related  structures. 


that  often  presents  a  shallow  concavity.     The  junction  of  the  upper  and  posterior 
surfaces  is  marked  by  a  transverse,  crescentic  slit  (incisura  prostatae)  into  which  sink 
the  ejaculatory  ducts  in  their  course  to  the  urethra.     The  imperfectly  denned  wedge- 
shaped    mass    bounded    by 

FIG.   1 680.  the  urethra  in  front,  the  ejac- 

ulatory ducts  at  the  sides 
and  behind,  constitutes  the 
so-called  middle  lobe  (lobus 
medius),  the  base  of  which 
lies  beneath  the  vesical  tri- 
gone.  The  prominent  por- 
tions of  the  prostate  lying 
external  to  the  ejaculatory 
ducts  are  known  as  the  lat- 
eral lobes,  which,  however, 
superficially  are  not  dis- 
tinctly marked  off.  The 
prominent  convex  lateral 
surfaces,  directed  outward, 
downward,  and  forward,  and 
behind  limited  by  rounded 
borders,  in  front  pass  insen- 
sibly into  the  narrow  con- 
vex anterior  surface  (fades 
anterior)  that  is  approximately  vertical  and  faces  the  symphysis. 

The  urethra  traverses  the  prostate  with  a  vertically  placed  curve,  the  concavity 
looking  forward,  that  above  begins  slightly  in  advance  of  the  middle  of  the  base,  and 
below  ends  on  the  anterior  surface  just  in  front  and  above  the  apex.  The  posterior 
wall  of  the  prostatic  urethra  is  marked  by  a  longitudinal  median  ridge,  the  urethral 
crest,  on  the  most  expanded  and  elevated  part  of  which  (colliculus  seminalis)  are  situ- 
ated the  openings  of  the/rar- 

talic  utricle  (utriculus  prostati-  FIG.  1681. 

cus)  and  of  the  ejaculatory 
ducts  (page  1955).  In  the 
grooves  or  recesses  on  either 
side  of  the  crest,  open  the  mi- 
nute orifices  of  the  prostatic  tu- 
bules, some  twenty  in  number, 
that  discharge  the  products  of 
the  glandular  tissue. 

Owing  to  the  continuity 
of  the  muscular  tissue  with 
the  surrounding  structures  in 
front,  above,  and  below,  the 
outlines  of  the  prostate  in 
places  lack  definition.  Except 
over  its  base,  apex,  and  lower 
anterior  surface,  the  prostate 
is  enclosed  by  a  fibrous  envel- 
ope or  capsule,  the  extension 
of  the  visceral  layer  of  the  pel- 
vic fascia  in  conjunction  with 
the  investment  of  the  bladder 
and  the  seminal  vesicles.  The 
capsule  is  best  developed  on 

the  posterior  surface,  where  it  separates  the  prostate  from  the  rectum  and  constitutes 
a  part  of  the  recto-vesical  fascia  in  its  restricted  sense. 

Relations. — Lodged  between  the  bladder  and  the  pelvic  floor,  the  prostate  is 
in  relation  with  a  number  of  important  structures.  Above,  its  base  is  intimately 


Folds  of 
mucous  membrane 


Urethral  mucous 


tory  ducts 

Section  across  prostatic  urethra  above  entrance  of  ejacula- 
tory ducts,  showing  crescentic  form  of  urethral  lumen  pro- 
duced by  encroachment  of  urethral  crest.  X  10. 


THE    PROSTATE   GLAND. 


1977 


Terminal  duct  opening  into  alveol 


Involuntary  muscle, 


attached  to  the  lower  surface  of  the  bladder,  lying  beneath  the  vesical  trigone. 
Below,  its  apex  rests  upon  the  superior  layer  of  the  triangular  ligament,  surrounded 
by  fibres  of  the  compressor  urethras  muscle  that  constitute  the  external  vesical 
sphincter  (page  1925).  In  front,  the  rounded  anterior  surface  is  directed  towards 
the  pubic  symphysis,  from  which  it  is  separated  by  an  intervening  wedge-shaped 
space  occupied  by  loose  areolar  tissue  containing  part  of  the  prostatic  plexus  of  veins 
and  fat.  The  pubo-prostatic  ligaments  (the  continuations  of  the  arcus  tendineus  of 
the  two  sides)  stretch  between  the  symphysis  and  the  prostate  and  contain  muscular 
tissue  prolonged  from  the  latter  and  the  bladder.  At  the  sides,  the  prostate  is  embraced 
by  the  levator  ani  muscles,  the  prostatic  venous  plexuses,  embedded  within  the 
reflections  of  the  pelvic  fascia  that  here  constitute  the  capsule  of  the  gland,  inter- 
vening. Behind,  the  prostate  is  in  relation  with  the  ampullae  of  the  vasa  deferentia 
and  the  seminal  vesicles  above  and  with  the  lower  part  of  the  rectum  below,  separated 
from  the  latter  by  the  dense  capsule  and  the  overlying  layer  of  areolar  tissue.  The 
position  of  the  prostate  is  not  constant,  since  it  is  affected  by  movements  of  the  vesi- 
cal wall,  with  which  the  prostate  is  intimately  united,  incident  to  marked  distention 
and  contraction  of 
the  bladder.  On  the 
other  hand,  the  at- 
tachments of  the 
prostate  to  the  trian- 
gular ligament  and 
pelvic  fascia  indi- 
rectly confer  upon 
the  lower  segment  of 
the  bladder  its  most 
efficient  means  of 
fixation.  The  pros- 
tate is  further  influ- 
enced by  changes  in 
the  anterior  wall  of 
the  rectum,  under- 
going compression 
and  displacement 
forward  when  the 
bowel  is  distended. 

Structure. — 
The  prostate  is  a 
gland  of  the  tubo- 
alveolar  type  and  is 
made  up  of  three 

chief  components, — the  connective-tissue  framework,  involuntary  muscle,  and  the  glan- 
dular tissue.  Of  these  the  latter  constitutes  usually  a  little  more  than  one-half  of  the 
entire  organ,  and  the  connective  tissue  and  muscle  each  somewhat  less  than  one-quarter. 

The  connective-tissue  framework  consists  of  an  external  investing  fibro-elastic  en- 
velope, the  capsule  proper,  and  a  median  septum,  which  encloses  and  blends  with  the 
walls  of  the  urethra.  Between  these  denser  lamellae  numerous  partitions  radiate  and 
subdivide  the  organ  into  from  thirty  to  forty  pyramidal  lobules  occupied  by  the  glandu- 
lar tissue.  The  involuntary  muscle,  embedded  within  the  capsule  and  ramifications 
of  the  connective-tissue  framework,  surrounds  the  gland-substance  as  a  superficial 
layer  from  which  a  median  septum,  about  2  mm.  in  width,  extends  ventro-dorsally, 
enclosing  the  urethra  in  an  annular  thickening.  In  consequence,  the  interior  of  the 
prostate  is  occupied  by  a  dense  fibro-muscular  nucleus,  in  which  the  glandular  tissue 
is  represented  by  only  the  narrow  prostatic  ducts  passing  towards  the  urethra.  The 
muscle  is  not  limited,  however,  to  the  foregoing  positions,  but  extends  also  between 
the  ultimate  divisions  of  the  gland-tissue,  the  interalveolar  septa  in  places  consisting 
largely  of  the  variously  disposed  muscle-bundles. 

The  glandidar  tissue  consists  of  twenty  or  more  distinct  tube-systems,  each 
drained  by  an  independent  duct  that  opens  into  the  urethra  in  the  groove  on  either  side 


Alveoli 


Blood-vessel 


Portion  of  cross-section  of  prostate  gland.    X  75. 


1978 


HUMAN   ANATOMY. 


Muscle  cell 


Small  concretion 


of  the  colliculus.  Beginning  at  their  narrow  orifices,  these  excretory  tubules  (ductuli 
prostatici )  pass  outward  into  the  lobules,  and  after  a  course  of  about  I  cm.  divide  into 
tubules  that  repeatedly  branch  and  expand  into  the  terminal  alveoli.  Throughout  the 
greater  part  of  their  course  the  wavy  ducts  are  beset  with  saccular  and  tubular  diver- 
ticula,  simple  or  compound,  that  give  the  canal  an  irregular  lumen  and  constitute  what 
have  been  termed  the  duct  alveoli  as  distinguished  from  the  terminal  alveoli.  The 
latter  form  a  series  of  irregularly  branched  tubular  and  saccular  spaces  lined  with  a 
single  or  imperfect  double  layer  of  columnar  epithelial  cells, — the  secreting  elements  of 
the  gland.  In  places  the  alveoli  intercommunicate  and  form  net-works  of  spaces  of 
variable  lumen.  The  epithelium  in  the  ducts  and  their  diverticula  corresponds  with 
that  lining  the  more  deeply  situated  alveoli,  the  change  into  the  transitional  variety 
of  the  prostatic  urethra  not  taking  place  until  very  near  the  termination  of  the  ducts. 
Peculiar  concretions  ( ' '  amyloid  bodies' '  or  "  prostatic  calculi' '  )  are  almost  con- 
stantly present  within  some  of  the  tubules  of  the  adult  organ,  especially  in  advanced 
life.  These  bodies  (Fig.  1683),  round  or  oval  in  outline  and  very  variable  in  size 
(from  .2-1  mm.  and  more  in  diameter),  usually  exhibit  a  faint  concentric  striation 

and  a  light  brownish  color. 

FIG.  1683.  Their  nature  is  uncertain, 

but  they  probably  consist  of 
a  colloid  substance  giving 
the  reactions  of  albumen. 

The  secretion  of  the 
prostate  gland  (sticcus 
prostaticus)  is  milky  in  ap- 
pearance, thin  in  consist- 
ence, slightly  alkaline  in 
reaction,  and  possesses  a 
characteristic  odor  (Fiar- 
bringer).  It  is  discharged 
into  the  urethra  and  min- 
gled with  the  fluid  enter- 
ing by  the  seminal  ducts 
during  ejaculation,  and 
probably  serves  an  impor- 
tant purpose  in  facilitating 
and  perhaps  stimulating 
the  motility  of  the  sper- 
matozoa. The  "sperm 
crystals"  formed  in  semen 

after  standing,  and  attributed  to  the  products  of  the  prostate,  are  not  found  in  the 
secretion  of  the  living  subject  (although  frequently  present  in  the  gland  after  death  ) 
until  after  the  addition  of  ammonium  sulphate  (Furbringer). 

Vessels. — The  arteries  supplying  the  prostate  are  small  branches  from  the 
inferior  vesical  and  middle  hemorrhoidal.  They  enter  the  periphery  of  the  gland  at 
various  points,  particularly  in  company  with  the  ejaculatory  ducts,  and  break  up  into 
capillary  net-works  that  surround  the  alveoli.  The  veins  are  exceedingly  numer- 
ous, forming  close  mesh-works  within  the  glandular  tissue  and  around  the  ducts. 
They  leave  the  organ  on  either  side  and  unite  into  a  plexus  within  the  capsule,  which, 
receiving  the  deep  dorsal  veins  of  the  penis  and  communicating  with  trunks  from  the 
bladder,  seminal  vesicles,  and  rectum,  is. continued  as  the  prostatico-vesical  plexus, 
tributary  to  the  internal  iliac  veins.  The  lymphatics  are  numerous  and  form  a  net- 
work on  the  lower  and  posterior  surface  of  the  organ  from  which  on  either  side  pass 
two  trunks,  a  superior  and  a  lateral.  The  upper  and  smaller  trunks  are  afferent  to 
the  obturator  lymph-nodes  of  the  pelvic  wall,  and  the  lateral  and  larger  terminate  in 
the  internal  iliac  nodes  (Sappey). 

The  nerves  of  the  prostate  are  chiefly  sympathetic  fibres  derived  from  the 
hypogastric  plexus,  numerous  minute  ganglia  being  included  along  their  course. 
Peripherally  situated  Pacinian  corpuscles  are  said  to  be  connected  with  the  sensory 
fibres  (Griffiths). 


Epithelium 
ing  alveoli 


Intcralveolar 
tissue 


vessel 


'Portion  of  section  of  prostate  gland,  showing  details  of  alveolf     X  270. 


PRACTICAL   CONSIDERATIONS  :    PROSTATE  GLAND. 

Development. — At  about  the  third  month  of  foetal  life  the  wall  of  the  primitive 
urethra  undergoes  thickening,  leading  to  the  production  of  an  annular  mass  of  meso- 
blastic  tissue  that  surrounds  the  lower  ends  of  the  Wolffian  and  Mullerian  ducts 
(later  the  ejaculatory  ducts  and  the  prostatic  utricle  respectively)  and  subsequently 
becomes  differentiated  largely  into  unstriped  muscle.  Into  this  penetrate  solid' epi- 
thelial outgrowths,  from  the  lining  of  the  urethra,  which  expand  into  branched  cylinders 
that  give  rise  to  the  prostatic  glandular  tissue.  These  outgrowths  are  arranged  in 
three  groups  (Pallin),  a  ventral,  an  upper  and  a  lower  dorsal.  The  ventral  group 
gives  rise  to  the  glandular  tissue  in  front  of  the  urethra,  which  at  first  is  relatively 
abundant,  but  soon  suffers  reduction,  and  in  the  adult  organ  is  often  almost  wanting. 
The  dorsal  groups  produce  the  important  glands  of  the  median  and  lateral  lobes. 
For  a  time  the  latter  are  arranged  as  two  separate  lobes,  but  afterward  become 
consolidated  by  the  capsule  and  broken  up  by  the  invasion  of  the  nbro-muscular 
septa. 

At  birth  the  prostate  measures  about  12  mm.  in  its  transverse  dimension  and 
remains  small  until  puberty,  when  it  begins  to  rapidly  enlarge,  acquiring  its  full  pro- 
portions with  the  establishment  of  sexual  activity.  With  the  approach  of  old  age, 
the  prostate  usually  undergoes  increase  in  size, — an  augmentation  often  resulting  in 
pathological  conditions. 

Variations. — Apart  from  abnormalities  in  size,  the  prostate  is  subject  to  few  variations. 
Among  the  latter  have  been  persistence  of  the  original  independence  of  the  lateral  lobes,  ab- 
sence of  the  middle  and  the  presence  of  a  fourth  lobe.  Variations  in  the  relations  and  mode 
of  ending  of  the  ejaculatory  ducts  (fusion  into  a  single  canal  or  termination  in  the  prostatic  utricle 
or  by  a  special  canal  below  the  crest)  or  in  the  prostatic  utricle  (absence,  enlarged  size,  or  un- 
usual opening)  are  properly  referred  to  deviations  in  the  development  of  the  generative  tract. 

PRACTICAL   CONSIDERATIONS  :    THE    PROSTATE   GLAND. 

The  prostate  gland  is  a  portion  of  the  male  generative  system.  The  prostatic 
utricle,  or  sinus  pocularis,  is  the  homologue  of  the  sinus  genitalis  in  the  female, — the 
uterine  and  vaginal  cavities, — since  it  represents  the  persistent  part  of  the  fused  Mul- 
lerian ducts  (page  2039).  Alhough  the  prostate  and  the  uterus  cannot  be  regarded 
as  homologous  organs,  they  are  similar  in  structure,  and  would  be  strikingly  alike 
if  the  tubular  glands  found  in  the  inner  walls  of  the  uterus  were  prolonged  into  its 
muscular  substance. 

During  infancy  and  childhood  the  prostate  is  still  immature  ;  at  puberty  it  enlarges 
coincidently  with  the  enlargement  of  the  testicles.  In  eunuchs  and  after  castration  in 
man  and  other  animals  it  is  atrophied.  The  seminal  vesicles  are  in  close  relation  to 
it  and  the  ejaculatory  ducts  penetrate  it  (page  1955).  Its  size  and  perfection  of  struc- 
ture in  animals  rise  and  fall  with  the  breeding  season  (Hunter,  Owen,  Griffiths). 
These  facts  sufficiently  demonstrate  the  essential  relation  of  the  prostate  to  the  gen- 
erative system.  It,  however,  affords  passage  to  the  prostatic  urethra,  its  unstriped 
muscle-fibres  are  continuous  with  the  vesical  muscle  at  the  trigonum  and  with  the 
circular  fibres  of  the  bladder,  and  both  the  anatomical  and  subjective  effects  of  the 
more  common  pathological  changes  in  the  prostate  are  observed  in  relation  to  the 
urinary  system,  with  which,  therefore,  it  is  most  intimately  associated. 

Injuries  of  the  prostate  are  rare  on  account  of  its  protected  position,  and  usually 
involve  also  the  rectum  or  the  bladder.  Hemorrhage  from  the  prostato-vesical 
plexus  may  be  dangerous  in  amount  ;  and  if  a  wound  extend  upward  into  the  neck 
of  the  bladder,  that  organ  may  become  distended  with  blood  and  form  a  tense,  globu- 
lar hypogastric  tumor.  Infiltration  of  urine  following  a  prostatic  wound  may,  in 
accordance  with  the  situation  of  the  latter,  reach  the  hypogastrium  from  the  pre- 
vesical  space,  the  ischio-rectal  region  or  the  perineum  from  coincident  division  of 
the  fascia  of  Colles,  or  the  recto-vesical  space  and  the  pelvis  from  similar  division  of 
the  recto-vesical  fascia. 

Disease  of  the  prostate,  if  infectious,  is  usually  gonorrhoeal  in  origin.  It  is  often 
due  to  the  use  of  unclean  urethral  or  vesical  instruments.  It  tends  to  suppuration 
on  account  of  the  very  imperfect  drainage  of  the  products  of  inflammation  from  the 
numerous  follicles. 


1980  HUMAN   ANATOMY. 

Prostatitis  is  attended  by  (a)  much  swelling,  owing  to  the  vascularity  and 
spongy  structure  of  the  gland.  As  the  forward  enlargement  of  the  prostate  is  pre- 
vented by  the  resistance  of  the  dense  pubo-prostatic  ligaments,  the  subpubic  liga- 
ment, and  the  firm  superior  layer  of  the  triangular  ligament,  the  swelling  is  greatest 
in  tne  posterior  two-thirds  of  the  gland.  Its  downward  extension  is  evidenced  by 
(6)  a  sense  of  weight  and  uneasiness  in  the  perineum  and  (c)  rectal  irritation  and 
tenesmus.  Its  upward  and  backward  spread  is  shown  by  (d  )  interference  with  mic- 
turition, due  to  compression  of  the  prostatic  urethra  and  elevation  of  the  vesical  out- 
let. The  symptoms  of  (V)  painful  and  frequent  micturition  and  (_/)  vesical  tenesmus 
are  due  in  part  to  the  mechanical  obstruction,  but  chiefly  to  the  extension  of  the 
inflammation  to  the  trigonal  region  and  to  the  obstruction  by  pressure  of  the  pros- 
tatic venous  plexus  into  which  the  vesical  plexus  empties,  causing  intense  conges- 
tion of  the  vesical  mucosa.  The  unyielding  character  of  the  prostatic  sheath  produces 
(£•)  the  heavy,  throbbing  pain  felt  in  the  infrapubic,  perineal,  and  rectal  regions,  and 
results  in  such  tension  that  (//)  referred  pains  are  very  common,  and,  on  account  of 
the  derivation  of  the  nerve-supply  of  the  prostate  from  the  lower  three  dorsal  and 
upper  three  sacral  segments,  are  apt  to  be  widely  distributed,  as,  e.g. ,  pain  over  the 
tip  of  the  last  rib  (tenth  dorsal  nerve),  over  the  posterior  iliac  spine  (eleventh  dorsal 
nerve),  or  even  in  the  soles  of  the  feet  (third  sacral  nerve)  (Treves);  reflex  irrita- 
tion of  the  inferior  hemorrhoidal  nerve  may  cause  intense  pruritus  ani, — sometimes 
a  very  annoying  symptom. 

Prostatic  abscess  usually  takes  the  direction  of  least  resistance  and  opens  into- 
the  urethra.  Its  progress  towards  the  pelvis  is  resisted  by  the  dense  investment 
contributed  by  the  pelvic  fascia;  towards  the  perineum,  by  the  superior  layer  of  the 
triangular  ligament.  It  sometimes  points  towards  the  rectum,  from  which  it  is  sepa- 
rated by  a  thinner  and  less  resistant  layer  of  the  pelvic  fascia,  and  may  then  open 
directly  into  the  rectum,  or  be  guided  by  it  to  the  perineum. 

Hypertrophy  of  the  prostate  to  some  degree  occurs  in  about  one-third  of  all 
males  who  have  passed  middle  life,  and  in  about  one-tenth  of  all  males  over  fifty-five 
the  enlargement  becomes  of  pathological  importance.  Its  cause  is  unknown. 
Various  theories  having  a  more  or  less  direct  bearing  upon  its  anatomical  and  physio- 
logical characteristics  have  been  advanced  to  explain  its  occurrence,  but  none  has 
been  demonstrated.  It  has  been  attributed  to  (a)  the  general  arterio-sclerosis  of  old 
age  (Guyon);  (£)  a  primary  change  in  the  bladder  necessitating  a  compensatory 
hypertrophy  of  the  prostate  (Harrison);  (<:)  a  growth  analogous  to  uterine  fibro- 
myoma  (Thompson) ;  (d)  the  persistence,  in  an  adjunct  sexual  organ,  of  physiological 
activity  intended  for  the  control  and  determination  of  the  masculine  characteristics 
after  the  need  for  such  activity  had  disappeared  (White);  (e)  an  attempt  to  com- 
pensate quantitatively  for  a  qualitative  deterioration  in  the  prostatic  secretion,  whose 
function  (Fiirbringer)  is  to  facilitate  the  mobility  and  vitality  of  the  spermatozoa 
(Rovsing);  and,  recently,  (/")  infection  (most  often  by  the  gonococcus),  aggravating 
a  senile  degenerative  process  (Crandon). 

The  enlargement  may  affect  chiefly  any  of  the  separate  components  of  the  pros- 
tate, and  may  thus  be  adenomatous,  myomatous,  or  fibrous  in  its  character,  although 
usually  the  glandular  element  predominates.  It  may  involve  particularly  the  lateral 
lobes,  or  may  affect  almost  exclusively  the  so-called  median  portion  placed  at  the 
lower  posterior  part  of  the  gland,  between  the  ejaculatory  ducts.  This  portion  is 
directly  beneath  the  vesical  neck. 

The  degree  of  hypertrophy  is  extremely  variable,  the  prostate  being  increased 
from  its  normal  weight  of  between  four  and  six  drachms  to  a  weight  of  many  ounces, 
and,  of  course,  correspondingly  increased  in  size. 

It  is  not  possible  here  to  do  more  than  call  attention  to  these  varieties  of  hyper- 
trophy, but  its  usual  and  general  effects  may  be  considered  with  reference  to  their 
anatomical  causation. 

i.  The  direction  of  greatest  resistance  to  enlargement  is  forward  (ride  supra} 
and  next  downward  (towards  the  rectum).  Hence  the  growth  usually  takes  place 
in  an  upward  and  backward  direction,  although  the  resistance  offered  by  the  recto- 
vesical  layer  of  fascia  does  not  prevent  marked  extension  in  that  direction  in  many 
cases.  As  a  direct  result  of  this  enlargement  there  follow  :  (a)  compression,  flatten- 


PRACTICAL   CONSIDERATIONS  :    PROSTATE  GLAND.         1981 

ing,  and  elongation  of  the  prostatic  urethra,  or  lateral  deviation  of  that  canal  (if  one 
lobe  greatly  exceeds  the  other  in  size);  (6)  elevation  of  the  vesical  neck  and  outlet, 
which  are  carried  up  by  reason  of  their  intimate  connection  with  the  prostate, 
especially  with  its  median  lobe,  the  base  of  the  bladder  remaining  relatively  un- 
affected ;  (<r)  the  formation  in  this  manner  of  a  pouch  or  pocket  (post-prostatic  pouch) 
in  the  bladder  at  a  lower  level  than  the  vesical  outlet. 

The  indirect  results  of  these  conditions  are  the  changes  in  the  bladder  occasioned 
by  (a)  the  mechanical  obstruction  which  the  enlarged  prostate  offers  to  the  ready 
and  complete  evacuation  of  its  contents,  (b)  the  circulatory  disturbance  incident  to 
pressure  on  the  prostatic  veins  into  which  the  blood  from  the  vesical  veins  passes, 
and  (c)  septic  infection. 

As  a  result  of  the  narrowing  or  deflection  of  the  urethra,  the  elevation  of  the 
vesical  outlet,  and  the  formation  of  the  post-prostatic  pouch,  the  bladder  is  not 
entirely  emptied  at  each  act  of  micturition,  a  certain  amount  of  residual  urine  remain- 
ing behind.  This  may  gradually  increase  as  the  obstruction  becomes  more  marked, 
ultimately  causing  dilatation  of  the  bladder,  with  atony  consequent  on  partial  de- 
generation of  its  muscular  walls,  or,  in  consequence  of  the  more  vigorous  bladder 
contraction  required  to  empty  the  bladder,  the  trabeculae  may  become  enormously 
hypertrophied,  the  inner  layers  forming  pronounced  ridges.  These  by  their  con- 
traction exert  a  powerful  pressure  upon  the  vesical  contents,  which,  escaping  very 
slowly,  transmit  the  pressure  in  all  directions  and  occasion  bulgings  or  sacculations 
in  such  weak  parts  of  the  bladder-walls  as  are  not  supported  by  muscular  bands  or 
by  strong  investing  fasciae.  The  hypertrophy  and  sacculation  are  further  encouraged 
by  the  vesical  irritability  incident  to  venous  congestion  at  the  neck  of  the  bladder, 
which,  as  the  prostatic  veins  become  more  obstructed,  keeps  up  a  condition  of  passive 
hyperaemia  and  erethism  more  potent  than  residual  urine  alone  to  occasion  the  fre- 
quently recurring  desire  to  urinate  and  the  muscular  spasm  of  the  sphincter  at  the 
beginning  of  the  act,  which  calls  for  such  strong  and  repeated  efforts  on  the  part  of 
the  detrusor  muscles. 

Septic  infection  of  a  healthy  mucous  membrane  by  the  pyogenic  microbes  caus- 
ing acute  or  chronic  cystitis  is  not  possible,  even  although  such  bacteria  are  present 
in  the  urine;  when,  however,  the  vesical  mucous  membrane  is  congested  in  conse- 
quence of  obstruction  to  venous  relurn,  and  of  distention  of  the  viscus  and  frequently 
recurring  contractions  of  the  detrusor  muscles,  it  offers  but  slight  resistance  to  the 
microbic  invasion.  The  pyogenic  microbes  are  generally  carried  to  the  bladder  by 
dirty  instruments,  or,  if  these  are  rendered  sterile,  through  failure  to  cleanse  the 
anterior  urethra  before  the  instrument  is  introduced  into  the  bladder.  Often  cystitis 
develops  independently  of  the  use  of  instruments,  probably  as  a  result  of  infection 
conveyed  by  way  of  the  urethral  mucous  membrane. 

2.  The  siibjective  symptoms  brought  about  by  these  conditions  may  be  briefly 
summarized  and  will  be  readily  understood  by  reference  to  the  foregoing  and  to  the 
article  on  the  bladder,  (a)  Freq^tent  urination,  due  partly  to  the  inability  completely 
to  empty  the  bladder,  but  chiefly  to  the  venous  congestion  about  the  trigonum.  (£) 
Difficulty  in  starting  iirination,  due  to  muscular  spasm  of  the  external  vesical  sphinc- 
ter, which,  excited  by  reflexes  from  the  hyperaesthetic  prostatic  urethra 'and  neck  of 
the  bladder,  is  not  fully  under  the  control  of  the  will.  A  temporary  reflex  inhibition 
of  the  detrusor  muscles  may  also  delay  the  act  of  urination,  (c)  Feeble  urination, 
due  to  the  weakness,  atony,  or  paresis  of  the  overstretched  detrusors.  (d)  Inter- 
rupted urination,  due  usually  to  spasmodic  contraction  of  the  external  vesical  sphinc- 
ter and  compressor  urethras  muscles,  reflexly  excited  by  urethro-cystitis  ;  occasionally 
the  result  of  intermittent  contraction  of  the  detrusors,  often  (as  in  many  cases  of 
cardiac  palpitation)  a  sign  of  beginning  muscular  atony.  The  physiology  of  micturi- 
tion requires  continuous  contraction  of  the  detrusor  muscles  and  relaxation  of  the 
sphincter  for  a  brief  interval  only.  When  there  is  sufficient  obstruction  to  triple  or 
quadruple  the  time  normally  required  fully  to  empty  the  bladder,  the  detrusor  mus- 
cles, exhausted  by  their  effort,  may  relax,  whereupon  the  sphincter  muscles,  relieved 
of  the  vis  a  tergo,  promptly  contract.  After  some  seconds  or  minutes  the  detrusors 
recover  sufficiently  to  make  further  efforts  at  evacuation.  (<?)  Incontinence  of  urine, 
which  may  always  be  taken  as  a  symptftm  of  retention  with  overflow,  the  intravesical 


1982  HUMAN   ANATOMY. 

tension  of  the  overfull  bladder  being  sufficient  to  overcome  the  resistance  offered  by 
the  tonic  contraction  of  the  sphincter  muscle  plus  that  due  to  the  prostatic  enlarge- 
ment. (_/")  Complete  retention  of  urine,  due  either  to  an  aggravation  of  the  chronic 
congestion  of  the  urethro-vesical  mucosa  or  to  the  completion  of  an  atrophic  process 
which  has  finally  destroyed  all  power  of  contraction  in  the  bladder,  (g)  Referred 
pains,  similar  to  those  noted  as  occurring  in  acute  prostatic  swelling  (vide  supra), 
(h}  Constitutional  disturbance,  due  to  septicaemia  or  uraemia,  or  both. 

Operations. — Prostatotomy. — Incision  or  puncture  of  the  prostate  for  the  evac- 
uation of  an  abscess  may  be  made  through  the  rectum  or  by  a  median  perineal 
incision.  The  same  name  is  applied  to  an  operation  which  consists  in  opening  the 
urethra  at  the  apex  of  the  prostate  by  a  median  perineal  incision,  and  dividing  the 
obstructing  portion  of  the  gland  by  means  of  a  probe-pointed  bistoury,  cutting  from 
within  outward.  The  channel  may  be  further  enlarged  by  divulsion  with  the  finger. 
The  anatomy  and  relations  of  the  parts  involved  have  already  been  described  (page 
1921). 

Of  the  various  operative  procedures  to  which  the  prostate  is  subjected,  prostatec- 
tomy is,  however,  by  far  the  most  important.  Under  this  name  operations  have  been 
described  which  consist  of  the  removal  of  the  enlarged  median  lobe,  or  of  portions  of 
one  or  both  lateral  lobes,  or  of  the  whole  prostate,  by  either  perineal  or  suprapubic 
routes. 

In  suprapubic  prostatectomy  the  prostate  is  approached  by  means  of  a  supra- 
pubic  cystotomy  (page  1921).  The  mucous  membrane  over  the  most  prominent 
portion  of  the  intravesical  protuberance  is  scratched  through  and,  as  a  rule,  the 
growths  or  the  prostate  removed  by  enucleation  with  the  finger. 

The  possibility  of  total  removal  of  the  prostate,  and  especially  of  such  removal 
without  coincident  injury  or  removal  of  the  prostatic  urethra  and  ejaculatory  ducts, 
has  been  vigorously  discussed.  It  has  been  complicated  by  confusion  as  to  the  struc- 
tures described  as  the  ' '  capsule' '  and  as  the  ' '  sheath. ' ' 

The  views  of  Freyer  appear  at  present  to  explain  most  satisfactorily  the  actual 
anatomical  conditions  found  at  operation,  and  are  thus  summarized  by  him  :  The 
prostate  is  in  reality  composed  of  twin  organs,  which  in  some  of  the  lower  animals 
remain  distinct  and  separate  throughout  life,  as  the^  exist  in  the  human  male  during 
the  first  four  months  of  fcetal  existence.  After  that  period,  in  the  human  foetus,  they 
approach  each  other,  and  their  inner  aspects  become  agglutinated,  except  along  the 
course  of  the  urethra, -which  they  envelop  in  their  embrace.  These  two  glandular 
organs,  which  constitute  the  lateral  lobes  of  the  prostate,  although  welded  together, 
as  it  were,  to  form  one  mass,  remain,  so  far  as  their  secreting  substance  and  functions 
are  concerned,  practically  as  distinct  as  the  testes,  their  respective  gland  ducts  open- 
ing into  the  urethra  in  the  depression  on  either  side  of  the  urethral  crest.  Each  of 
these  two  glandular  bodies,  or  prostates,  is  enveloped  by  a  thin,  strong,  fibrous 
capsule  ;  and  it  is  these  capsules — less  those  portions  of  them  that  dip  inward,  cover- 
ing the  opposing  aspects  of  the  glandular  bodies  or  lobes,  and  thus'  disappear  from 
view,  being  embedded  in  the  substance  of  the  prostatic  mass — that  constitute  the 
true  capsule  of  the  prostate  regarded  as  a  whole.  This  capsule  extends  over  the  entire 
organ  except  along  the  upper  and  lower  commissures,  or  bridges  of  tissue,  that  unite 
the  lateral  lobes  above  and  below  the  urethra,  thus  filling  in  the  gaps  between  them. 
This  true  capsule  is  intimately  connected  with  the  prostatic  mass  and  incapable  of 
being  removed  from  it  save  by  dissection. 

The  urethra,  accompanied  by  its  surrounding  structures, — viz.,  its  longitudinal 
and  circular  coats  of  muscles  continued  forward  from  the  bladder,  its  vessels  and 
nerves, — passes  forward  and  upward  between  the  inner  aspects  of  the  two  glands  or 
lobes  and  is  embraced  by  them.  The  ejaculatory  ducts  enter  the  prostatic  mass  close 
together,  in  an  interlobular  depression  at  the  lower  part  of  its  posterior  aspect,  each 
coursing  along  the  inner  surface  of  the  corresponding  lobe.  They  do  not  penetrate 
the  capsules  of  the  lobes,  but  pass  forward  in  the  interlobular  tissue,  to  open  into  the 
urethra. 

The  prostate,  thus  constituted  and  enveloped  by  its  true  capsule,  is  further 
encased  in  a  second  capsule  or  sheath,  formed  by  the  visceral  division  of  the  pelvic 
fascia,  numerous  connecting  bands  passing,  h*owever,  between  the  two  (Thompson). 


PRACTICAL   CONSIDERATIONS  :    PROSTATE  GLAND.         1983 

Between  these  two  capsules,  or  rather  mainly  embedded  in  the  outer  one,  lies  the 
prostatic  plexus  of  veins,  most  marked  in  front  and  on  the  sides  of  the  prostate.  The 
larger  arteries  also  lie  between  the  true  capsule  and  the  sheath,  numerous  small 
branches  passing  from  them  through  the  true  capsule  for  the  supply  of  the  prostatic 
substance. 

Freyer  illustrates  his  view  by  imagining  the  edible  portion  of  an  orange  composed 
of  two  segments  only,  instead  of  several,  with  the  septum  between  them  placed 
vertically,  and  says  that  the  thin,  strong,  fibrous  tissue  which  covers  the  segments  of 
the  orange,  and  which  is  intimately  connected  with  the  pulp,  would  then  represent 
the  true  capsule  of  the  prostate,  the  two  segments  or  halves  of  the  orange  being  rep- 
resented by  the  two  lobes  of  the  prostate.  Further,  the  rind  of  the  orange  would 
represent  the  outer  capsule  or  prostatic  sheath,  contributed  by  the  pelvic  fascia.  In 
the  method  of  suprapubic  prostatectomy  now  known  by  his  name,  it  is  the  true  cap- 
sule as  above  described  that  is  removed,  the  sheath  being  left  behind,  thus  pre- 
venting infiltration  of  urine  into  the  cellular  tissues  of  the  pelvis. 

In  most  cases  of  hypertrophy  of  the  prostate  the  overgrowth  is  adenomatous  in 
character,  numerous  encapsuled  adenomatous  tumors  being  found  embedded  within 
the  substance  of  the  lobes  and  frequently  protruding  on  their  surfaces.  They  some- 
times assume  the  form  of  polypoid  outgrowths,  which,  however,  are  invariably  en- 
closed within  the  true  capsule,  which  is  pushed  before  them. 

As  the  lobes  enlarge  they  bulge  out  and  have  a  tendency,  each  enclosed  within 
its  own  capsule,  to  become  more  defined  and  isolated,  thus  recalling  their  separate 
existence  in  early  foetal  life.  They  become  more  loosely  attached  along  their  com- 
missures (particularly  the  upper  one),  which  in  the  normal  prostate  unite  them 
above  and  below  the  urethra.  And  in  the  course  of  this  change  the  urethra,  with 
its  accompanying  structures,  is  loosened  from  its  close  attachment  to  the  inner  sur- 
faces of  the  lobes,  thus  facilitating  its  being  detached  and  left  behind  uninjured  in 
the  removal  of  the  prostate. 

In  the  earlier  stages  of  the  adenomatous  overgrowth  the  enlargement  is  proba- 
bly entirely  extravesical.  Its  expansion  in  this  position  is,  however,  limited  by  the 
pubic  arch  above,  the  triangular  ligament  in  front,  and  the  sacrum  below.  As  the 
enlargement  progresses,  it  advances  in  the  direction  of  least  resistance, — namely,  into 
the  bladder.  The  sheath,  which  at  the  posterior  aspect  of  the  prostate  is  least  de- 
fined, becomes  gradually  thinner  as  the  enlargement  in  this  direction  progresses,  till 
eventually  the  prostate  has  burst  through  it,  and  is  then  merely  covered  by  the  mucous 
membrane  of  the  bladder  (Freyer). 

It  has  been  asserted  that  what  has  here  been  called  "  capsule"  is  in  the  normal 
prostate  really  only  a  thin  outer  non-glandular  portion — cortex — containing  both 
muscular  and  fibrous  tissue  (Shattock),  and  that  the  envelope  formed  from  the  pros- 
tate by  the  expansion  of  adenomata  represents  more  than  the  ' '  cortex' '  and  contains 
glandular  tissue  derived  from  the  stretched  and  compressed  outer  portion  of  the 
prostate  (Wallace). 

However  this  question  may  ultimately  be  settled,  the  anatomical  views  set  forth 
above  explain  the  separability  of  the  mass  of  the  prostate  from  (a')  the  prostatic 
plexus  of  veins  (avoiding  hemorrhage),  (£)  the  under  surface  of  the  recto-vesical 
fascia  (avoiding  urinary  infiltration),  and  (<r)  the  prostatic  urethra  and  ejaculatory 
ducts  (minimizing  interference  with  micturition  and  with  potency),  which  separa- 
bility has  been  shown  to  be  at  least  occasionally  possible  during  operation. 

Perinea!  prostatectomy  is  done,  with  the  patient  in  the  lithotomy  position,  by 
means  of  a  semilunar  incision  in  front  of  the  anus  carried  down  through  the  successive 
structures  of  the  urethral  perineum  until  the  sheath  of  the  prostate  is  reached.  After 
division  of  the  sheath  on  either  side  in  a  direction  parallel  with  the  medial  fibres  of 
the  levator  ani,  the  prostate  in  its  capsule — or  portions  of  it— may  be  enucleated  with 
the  finger.  The  gland  may  be  made  more  accessible  by  downward  pressure  through 
the  space  of  Retzius  (by  means  of  a  suprapubic  incision)  or  through  the  bladder 
itself  (after  a  preliminary  suprapubic  cystotomy).  It  may  be  reached  by  a  lateral 
incision  half  encircling  the  anus.  It  should  be  remembered  that  it  is  separated  from 
the  ischio-rectal  fossa  only  by  the  levator  ani  muscle,  with  the  visceral  layer  of  the 
pelvic  fascia  on  its  upper  and  the  anal  fascia  on  its  lower  surface. 


1984  HUMAN   ANATOMY. 

THE   GLANDS    OF   COWPER. 

Cowper's  glands  (glandulae  bulbourethrales)  are  two  small  ovoid  bodies  situated 
along  the  under  surface  of  the  membranous  portion  of  the  urethra  (Fig.  1632),  one 
on  either  side  of  and  close  to  the  mid-line.  In  general  form  and  size  (from  5-8  mm. 
in  diameter)  they  resemble  a  pea,  although  their  contour  is  irregular  and  somewhat 
knobbed.  Their  color  is  reddish  yellow  and  their  consistence  firm.  They  lie  within 
the  deep  perineal  interspace  between  the  two  layers  of  the  triangular  ligament  em- 
bedded within  the  fibres  of  the  compressor  urethrae  muscle. 

The  ducts  of  the  glands — about  1.5  mm.  in  diameter  and  from  3—4  cm.  in 
length — run  forward  and  medially,  at  first  between  the  bulbus  spongiosum  and  the 
membranous  urethra,  then  within  the  bulb  itself,  and,  finally,  for  about  2  cm.  be- 
neath the  urethral  mucous  membrane  to  open  by  small  slit-like  orifices  on  the  lower 
wall  of  the  bulbus  urethrae  near  the  mid-line.  The  position  of  these  inconspicuous 
openings  is  sometimes  masked  by  a  fold  of  mucous  membrane  or  a  slight  de- 
pression. Quite  frequently  the  two  ducts  unite  and  open  by  a  common  orifice. 

Structure. — These  glands  are  mucous  tubo-alveolar  in  type,  their  terminal 
divisions  ending,  after  more  or  less  branching,  in  irregularly  sacculated  compart- 
ments. In  places  the  latter  communicate  by  means  of  a  reticulum  of  connecting 
canals  (Braus).  The  alveoli  are  lined  with  low  columnar  or  pyriform  epithelial 
cells,  among  which  mucus-secreting  cells  are  plentiful.  The  cuboidal  epithelium 
that  clothes  the  smaller  ducts  and  the  dilatations  connected  with  them  gives  place  to 
clear  columnar  cells  within  the  larger  excretory  canals.  The  divisions  of  the  gland 
are  united  by  interlobular  connective  tissue  and  invested  in  a  general  fibrous  en- 
velope in  which  a  considerable  quantity  of  unstriped  muscle  occurs.  The  secretion 
of  Cowper's  glands,  clear  and  viscid  and  of  alkaline  reaction,  is  probably  of  service 
in  maintaining  favorable  conditions  for  the  spermatozoa  by  neutralizing  acidity  of 
the  urethral  canal  due  to  passage  of  urine  (Eberth).  In  addition  to  their  recognized 
homology  with  the  glands  of  Bartholin  in  the  female,  the  observed  histological 
changes  incident  to  sexual  excitation  warrant  the  grouping  of  these  glands  as  acces- 
sory sexual  organs. 

Vessels. — The  arteries  supplying  Cowper's  glands  are  twigs  given  off  from 
the  arteries  of  the  bulb  as  they  course  between  the  two  layers  of  the  triangular  liga- 
ment. The  veins  are  tributary  to  those  returning  the  blood  from  the  bulbus  spongi- 
osum which  empty  into  the  internal  pudic.  The  lymphatics  are  afferents  to  the 
internal  iliac  lymph-nodes. 

The  nerves  are  derived  from  the  pudic. 

Development. — The  bulbo-urethral  glands  appear  about  the  end  of  the  third 
month  of  foetal  life  as  solid  outgrowths  from  the  entoblastic  lining  of  the  uro- 
genital  sinus.  With  the  elongation  of  the  latter  incident  to  the  formation  of  the 
male  urethra  and  the  penis  (page  2044),  the  glands  assume  a  lower  position  and 
their  ducts  are  correspondingly  lengthened.  During  the  first  ten  or  twelve  years  the 
glands  undergo  only  small  increase  in  volume,  but  between  the  sixteenth  and 
eighteenth  years  they  attain  their  full  size.  In  aged  subjects  they  atrophy  and  are 
frequently  so  small  that  their  recognition  is  difficult. 

Variations. — In  addition  to  abnormalities  in  size,  the  two  glands  may  be  fused  into  a  single 
mass,  or  one  or  both  may  be  wanting.  Sometimes  their  absence  is  only  apparent,  since  the 
organs  may  be  represented  by  rudimentary  glands  embedded  entirely  within  the  substance  of 
the  corpus  spongiosum. 


THE   OVARIES.  1985 


THE  FEMALE  REPRODUCTIVE  ORGANS. 

The  reproductive  organs  of  the  female  comprise  two  groups — the  internal,  situ- 
ated for  the  most  part  within  the  pelvis  and  above  the  pelvic  floor,  and  the  external, 
embraced  by  the  subpubic  arch  and  below  the  triangular  ligament  and  supported  by 
attachments  to  the  surrounding  bones,  fascia,  and  integument.  The  internal  organs 
are  the  sexual  glands,  the  ovaries,  which  produce  the  ova,  the  oviducts  or  Fallopian 
tubes,  the  canals  conveying  the  sexual  cells,  the  uterus,  and  the  vagina,  the  passage 
which,  beginning  within  the  pelvis,  embraces  the  lower  end  of  the  uterus  above, 
pierces  the  pelvic  floor,  and  ends  below  within  the  external  genital  cleft.  The  Fallo- 
pian tubes,  uterus,  and  vagina  represent  the  excretory  canals  of  the  sexual  glands 
which  in  the  embryo,  as  the  Mullerian  ducts,  for  a  time  are  separate.  After  fusion 
of  their  lower  segments  has  taken  place,  the  unpaired  tube  thus  formed  becomes  the 
vagina  and  the  uterus,  the  latter  being  specialized  for  the  reception  and  retention  of 
the  fertilized  ovum  during  gestation. 

The  external  organs,  often  termed  collectively  the  vulva  (pudendum  muliebre), 
include  the  clitoris,  the  labia,  and  the  enclosed  vestibule  and  vaginal  orifice  and  the 
glands  of  Bartholin.  In  a  general  way  these  parts  represent  structures  homologous 
with  the  penis  and  scrotum,  but  in  a  less  advanced  and  specialized  stage  of  develop- 
ment. 

THE   OVARIES. 

The  ovary  (ovarium),  one  on  either  side  of  the  body,  is  the  sexual  gland  proper, 
within  and  from  which  are  developed  and  liberated  the  mature  maternal  sexual  cells, 
the  ova.  It  is  a  solid  body,  resembling  in  form  a  large  almond,  and  in  the  adult 
lies  against  or  near  to  the  lateral  pelvic  wall  invested  by  peritoneum  continued  from 
the  posterior  surface  of  the  broad  ligament  of  the  uterus.  Even  when  mature,  the 
organ  presents  considerable  individual  variations  in  size,  its  average  dimensions  being 
36  mm.  (1^2  in.)  in  length,  18  mm.  (^  in. )  in  breadth,  and  12  mm.  (^  in.)  in  thick- 
ness. Variations  in  size  include  a  length  of  from  2.5—5  cm-  (I—2  m-)>  a  width  of 
from  1.5-3  cm-  (y%-iy%  in.),  and  a  thickness  of  from  .6-1.5  cm-  (/^-^8  in.), 
according  to  German  authorities.  The  right  ovary  is  frequently  somewhat  larger 
than  the  left.  The  adult  organ  weighs  about  7  grm.  (^  oz. ).  After  the  cessation 
of  menstruation,  about  the  forty-fifth  year,  the  ovary  decreases  in  size  and  weight,  in 
old  women  being  reduced  to  one-half  or  less  of  its  normal  proportions. 

The  ovary  presents  two  surfaces — a.  median  (fades  medialis),  directed  inward, 
and  a  lateral  (facics  lateralis),  looking  outward  and  in  more  or  less  close  relation 
with  the  pelvic  wall  ;  two  margins  connecting  the  surfaces — an  anterior  (margo  meso- 
varicus),  which  is  thin,  straight,  and  attached  to  the  posterior  surface  of  the  broad 
ligament  by  a  short  peritoneal  fold  or  mesovarium,  and  a  posterior  (margo  libra), 
which  is  thicker,  rounded,  convex,  and  unattached  ;  and  two  poles — an  upper  (ex- 
tremitas  tubaria),  rounded,  embraced  by  the  oviduct  and  attached  to  the  suspensory 
ligament  of  the  ovary  and  usually  to  the  fimbriated  extremity  of  the  Fallopian  tube, 
and  a  lower  (extremitas  uterina),  pointed  and  attached  to  the  uterus  by  a  fibro- 
muscular  band,  the  utero-ovarian  ligament.  The  portion  of  the  attached  anterior 
border  through  which  the  vessels  and  nerves  enter  and  emerge  is  known  as  the 
hi  I um  (hilus  ovarii).  The  surfaces  of  the  mature  ovary  are  not  even,  as  in  early 
life,  but  modelled  by  rounded  elevations  of  uncertain  number  and  size  and  by  irregu- 
lar pits  and  scars.  The  elevations  are  produced  by  the  underlying  Graafian  follicles 
in  different  stages  of  growth,  while  the  irregular  scar-like  areas  indicate  the  position 
of  corpora  lutea  of  varying  age  and  development.  Just  behind  the  attachment  of 
the  mesovarium  and  parallel  to  the  hilum,  the  surfaces  of  the  fresh  ovary  are  crossed 
by  a  narrow  stripe  of  lighter  color,  straight  or  curved  and  often  slightly  raised.  This 
band,  the  white  line  of  Farre,  marks  the  transition  of  the  usual  peritoneal  endothe- 
lium  into  the  cylindrical  germinal  epithelium  that  covers  the  exterior  of  the  organ 
and  appears  dull  and  lacking  in  the  lustre  characteristic  of  serous  surfaces. 

125 


HUMAN   ANATOMY. 


Position  and  Fixation. — Although  subject  to  deviations  due  to  the  influence 
of  other  organs,  especially  the  pull  of  the  uterus,  and  of  pregnancy,  the  long  axis  of 
the  normally  placed  ovary,  in  the  erect  posture,  is  approximately  vertical  (Fig.  1684). 
The  margin  attached  to  the  broad  ligament  of  the  uterus  is  directed  forward  and 
slightly  outward  'and  the  free  convex  border  backward  and  inward.  The  outer  sur- 
face usually  lies  in  contact  with  the  peritoneum  covering  the  lateral  pelvic  wall  within 
a  more  or  less  well-marked  depression,  the  ovarian  fossa  (fossa  ovarica).  This  recess, 
triangular  in  its  general  outline  and  variable  in  depth,  is  included  within  the  angle 
formed  by  the  diverging  peritoneal  folds  covering  the  external  and  internal  iliac  vessels. 
In  favorable  subjects,  in  which  the  amount  of  subperitoneal  fat  is  small  and  the  em- 
bedded structures,  therefore,  not  masked,  the  ureter  and  the  uterine  artery  will  be 
seen  forming  the  immediate  boundary  of  the  ovarian  fossa  behind,  while  above  and 
in  front  extends  the  remains  of  the  obliterated  hypogastric  artery.  Below,  where  its 

FIG.  1684. 


Internal  iliac  artery 

Fimbriated  end  of  Fallopian 
tube,  pulled  forward 


Suspensory 

ligament  of  ovary 

External  iliac — 
vessels 

Round  ligament- 
Deep  epigastric 
artery 
Mesosalpinx 

Obliterated 

hypogastric  artery 

Fallopian  tube 


Bladder 
Symphysis  pubis 


^Peritoneum,  cut  edge 


L'reter 


.  Right  ovary, 
median  surface 


—Ligament  of  ovary 


Utero-sacral 
ligament 

Rectum 
Recto-uterine  pouch 


\Uterus,  pulled  to  the  left 


Right  lateral  wall  of  pelvis,  showing  ovary  in  position  ;  Fallopian 
tube  has  been  pulled  forward  and  uterus  to  the  left. 


boundary  is  indistinct  and  uncertain,  it  fades  into  the  pelvic  floor,  often  without 
demarcation.  The  floor  of  the  fossa  is  obliquely  crossed  by  the  obturator  vessels 
and  nerve.  Within  this  depression  the  ovary  lies,  hidden  to  a  considerable  extent 
beneath  the  oviduct,  which  arches  over  the  upper  pole  and  largely  covers  the  median 
surface  with  its  expanded  fimbriated  end.  The  upper  or  tubal  pole  reaches  almost 
to  the  level  of  the  external  iliac  vein  and  the  pelvic  brim,  and  is  overhung  by  the 
inner  edge  of  the  psoas  muscle.  The  lower  pole  rests  upon  the  upper  (posterior)  sur- 
face of  the  broad  ligament  and  nearly  touches  the  pelvic  floor — about  2  cm.  above 
and  in  front  of  the  upper  border  of  the  pyriformis  muscle  and  the  trunk  of  the  greater 
sciatic  nerve  (Rieffel). 

The  vertical  position  of  the  ovary  is  maintained  by  the  suspensory  ligament 
(ligamcntuin  suspensorium),  also  called  infundibulo-pdvic  ligament,  which  is  a  trian- 
gular band  of  fibre-muscular  tissue,  attached  to  the  upper  tubal  pole  of  the  ovary  and 
invested  by  a  peritoneal  fold  continued  from  the  upper  and  outer  corner  of  the  broad 


THE   OVARIES. 


1987 


Surface  -- 
epithelium 


ligament.  It  passes  outward  across  the  external  iliac  vessels  in  front  of  the  sacro-iliac 
articulation  and  is  lost  in  the  fascia  covering  the  psoas  muscle.  Embedded  within 
the  enclosed  fibro-muscular  tissue  lie  the  ovarian  vessels  and  nerves,  which  thus  gain 
the  broad  ligament  in  their  passage  to  the  ovary. 

The  anterior  margin  of  the  ovary  is  attached  to  the  posterior  surface  of  the 
broad  ligament  by  a  short  but  broad  band — the  mesovarium — covered  on  both  sides 
by  peritoneum,  that  conveys  the  ovarian  vessels  proper  and  the  nerves  to  the  hilum 
through  which  they  enter  and  emerge  from  the  organ.  The  somewhat  pointed  lower 
end  of  the  ovary  is  connected  with  the  posterior  border  of  the  uterus,  between  the 
oviduct  and  the  round  ligament,  by  a  cord-like  band,  the  utero-ovarian  ligament  or 
ligament  of  the  ovary  (ligamentuin  ovarii  proprium).  This  band,  from  3-4  mm. 
thick,  lies  within  the  posterior  layer  of  the  broad  ligament  beneath  the  peritoneum, 
through  which  it  is  seen  as  a  distinct  cord. 

Since  the  uterus  and  its  broad  ligament  are  subject  to  continual  changes  of  posi- 
tion, the  attachment  of  the  ovary  to  these  structures  often  produces  deviations  from 
its  typical  location.  These  in- 
fluences affect  particularly  the  FlG-  l68s> 
lower  pole,  the  upper  enjoying 
greater  fixation  from  the  support 
afforded  by  the  suspensory  liga- 
ment. Asymmetry  in  the  po- 
sition of  the  two  ovaries  is  usual, 
as  the  fundus  of  the  uterus  seldom 
lies  strictly  in  the  mid-line,  and 
hence  the  lower  pole  of  the  ovary 
of  the  opposite  side  is  dragged 
medially.  The  long  axis  of  the 
ovary,  under  such  conditions,  is 
oblique  on  the  side  opposite  to 
that  towards  which  the  uterus  is 
deflected.  Conversely,  relaxa- 
tion of  the  ligaments  occurs  on 
the  side  towards  which  the  uterus 
tends  and  thus  favors  the  reten- 
tion of  the  vertical  position  of  the 
ovary.  Notwithstanding  the  lati- 
tude of  movement  possible,  the 
position  of  the  normal  ovary  is 
fairly  constant,  the  close  relation 
of  the  oviduct  to  the  median 
surface,  aided  by  the  pressure 
exerted  by  other  organs  within 
the  pelvis,  materially  assisting 
in  retaining  the  ovary  within  its 
fossa.  The  stretching  and  subsequent  relaxation  of  the  suspensory  ligament  incident 
to  pregnancy  are  predisposing  causes  of  displacement  of  the  ovary  due  to  insufficient 
fixation. 

Structure. — The  ovary  consists  of  two  principal  parts,  the  cortex  (zona 
parenchymatosa) — a  narrow  superficial  zone,  from  2-3  mm.  thick,  that  forms  the 
entire  periphery  of  the  organ  beyond  the  white  line  ;  and  the  medulla  (zona  vascu- 
losa,)  that  embraces  the  deeper  and  more  central  remaining  portion  of  the  gland. 
The  cortex  alone  contains  the  characteristic  Graafian  follicles  and  the  ova,  while  the 
medulla  is  distinguished  by  the  number  and  size  of  the  blood-vessels,  especially 
the  veins. 

The  cortex,  as  seen  in  vertical  sections  of  the  functionally  active  organ,  con- 
sists chiefly  of  the  compact  ovarian  stroma  that  is  composed  of  peculiar  spindle- 
shaped  connective  tissue-cells,  from  .01 5-.  030  mm.  in  length  and  about  one-fifth  as 
much  in  width,  and  fibrillar  intercellular  substance.  The  stroma-cells,  which  some- 
what resemble  the  elements  of  involuntary  muscle  in  appearance,  are  arranged  in 


Ovarian  • 
stroma 


Immature  . 

primary  ( 

follicle 


Follicle 
beginning ;,; 
to  grow 

Stratum 
granulosum 

Ovum  \ 
Theca- 


Section  of  cortex  of  ovary  of  young  woman,  showing  primary 
and  growing  follicles  within  ovarian  stroma.     X  190. 


1988 


HUMAN   ANATOMY. 


Blood-vessel 


Connective-  jj 
tissue  stroma 


bundles  that  extend  in  all  directions  (chiefly,  however,  obliquely  vertical  to  the 
surface)  and  are  seen  cut  in  different  planes.  Immediately  beneath  the  germinal 
epithelium  covering  the  surface,  the  stroma-elements  are  disposed  with  greater  reg- 
ularity and  form  a  compact  superficial  stratum,  the  tunica  albuginea.  Embedded 
within  the  stroma  lie  the  most  characteristic  components  of  the  cortex,  the  egg-sacs 
or  Graafian  follicles.  These  are  seen  in  different  stages  of  development,  but  for  the 
most  part  are  small,  inconspicuous,  and  immature,  in  the  human  ovary  being  much 
fewer  and  less  prominent  than  in  many  other  mammals.  Corresponding  with  their 
stages  of  development  the  egg-sacs  may  be  divided  into  primary,  growing,  and  ma- 
turing follicles.  In  general,  the  youngest  lie  nearest  the  surface,  the  more  advanced 

deeper  and  towards  the 

FIG.   1686.  medulla,  while  those  ap- 

proaching maturity  ap- 
pear as  huge  vesicles 
that  occupy  not  only 
the  entire  thickness  of 
the  cortex,  but  often 
produce  marked  eleva- 
tion of  the  free  surface. 
The  medulla,  the 
vascular  zone  of  the 
ovary,  consists  of  loosely 
disposed  bundles  of 
fibre-elastic  tissue  sup- 
porting the  blood-ves- 
sels, lymphatics,  and 
nerves.  In  the  mature 
organ,  with  the  excep- 
tion of  the  encroaching 
ripening  Graafian  folli- 
cles, egg-sacs  are  not 
found  within  the  me- 
dulla. The  larger  ves- 
sels are  accompanied  by 
bundles  of  involuntary 
muscle  prolonged  from 
the  utero-ovarian  ligament  through  the  mesovarium  and  the  hilum  into  the  medulla. 
The  veins  are  particularly  large  and  appear  in  sections  as  huge  blood-spaces  of  irregu- 
lar outline  in  consequence  of  their  tortuosity  and  plexiform  arrangement. 

Follicles  and  Ova. — The  immature  primary  follicles  (folliculi  oophori  primarii)  are  micro- 
scopic in  size  (from  .04-. 06  mm.  in  diameter)  and  vary  greatly  in  number,  in  the  ovaries  of 
young  adults  forming  an  incomplete  and  scattered  single  or,  at  most,  double  layer.  Each 
follicle  consists  of  the  centrally  situated  young  egg  (ovulum)  surrounded  by  a  single  layer  of 
flattened  epithelium  or  mantle  cells  (Fig.  1685).  Immediately  outside  the  latter  lies  the  stroma, 
in  the  interstices  of  which  the  young  egg-sacs  are  lodged.  The  primary  ova  are  approximately 
spherical  and  measure  from  .O35-.045  mm.  in  diameter  in  ordinary  sections,  but  a  third  more  in 
the  fresh  unshnmken  condition  (Nagel).  They  possess  a  finely  granular  cytoplasm,  a  centrally 
placed  spherical  nucleus,  about  .016  mm.  in  diameter,  and  a  nucleolus.  The  primary  ova  may 
remain  for  years,  sometimes  from  early  infancy  to  advanced  age,  practically  unchanged,  until 
they  undergo  either  atrophy,  as  do  most  of  them,  or  further  growth  leading,  under  favorable 
conditions,  to  the  development  of  the  mature  sexual  cell.  Of  the  thousands  of  primary  eggs 
contained  in  the  ovaries  just  before  puberty,  only  comparatively  few  attain  perfection.  Sooner 
or  later,  but  at  some  uncertain  time,  the  primary  follicles  enclosing  ova  destined  for  complete 
development  enter  upon  a  period  of  active  growth,  the  earliest  indication  of  which  is  the  con- 
version of  the  flat  mantle  cells  of  the  egg-sac  into  a  single  layer  of  cuboid  epithelium. 

In  addition  to  increasing  sixe,  the  growing  follicles  are  distinguished  by  rapid  prolifera- 
tion of  the  cuboid  epithelium,  which  results  in  the  production  of  a  stratified  follicular  epithe- 
lium that  surrounds  the  ovum.  Outside  these  polygonal  elements  the  stroma  becomes  con- 
densed into  a  connective-tissue  envelope  or  theca  (thcca  folliculi).  Increasing  in  thickness,  the 
latter  is  subsequently  differentiated  into  two  layers,  an  outer  (tunica  externa),  consisting  of 


Section  of  medulla  of  ovary,  showing  numerous  blood- 
vessels and  fibro-muscular  stroma.     X  75- 


•  i 


THE   OVARIES.  1989 

centrically  disposed  connective-tissue  fibres,  and  an  inner  (tunica  interna),  composed  of  round 
and  spindle  cells,  and  provided  with  numerous  capillaries.  After  the  follicular  epithelium  has 
been  formed,  the  ovum  itself  begins  to  grow,  the  expansion  proceeding  uniformly  and  affecting 
all  parts  of  the  cell,  including  nucleus  and  nucleolus.  It  attains  its  maximum  diameter  com- 
paratively early  and  long  before  the  follicle  has  reached  full  growth.  Through  the  agency  of 
the  follicular  epithelium,  the  egg  becomes  invested  with  a  protecting  envelope,  the  zona 
pellucida,  after  which  little  or  no  further  increase  in  the  size  of  the  ovum  takes  place  (Nagel). 

At  first  solid,  the  growing  follicle  is  converted  into  a  vesicle  containing  fluid  by  the 
vacuolation  and  breaking  down  of  cells  within  the  middle  layers  of  the  follicular  epithelium,  the 
resulting  clefts  fusing  into  a  common  space.  The  intra-epithelial  cavity  so  formed  contains 
accumulating  fluid,  the  liquor folliculi,.i\ia.t  is  supplied  by  the  continued  proliferation,  vacuolation, 
and  destruction  of  the  follicle  cells  and  by  the  transudation  from  the  surrounding  blood-vessels. 
This  fluid  increases  in  amount  to  such  an  extent  that  it  soon  occupies  the  greater  part  of  the 
expanding  egg-sac,  now  entering  upon  its  final  stage  of  growth. 

The  maturing  follicles  (folliculi  oophori  vesiculosi)  occupy  the  deeper  parts  of  the  cortex 
and  reach  to  the  medulla.  With  their  expansion  and  consequent  requirement  of  space,  the 
vesicles  seemingly  rise,  appropriating  more  and  more  of  the  cortex,  until  the  entire  thickness  of 
the  latter,  and  sometimes  a  part  of  the  medulla  in  addition,  is  occupied  by  the  ripe  follicle, 
which  just  before  its  final  rupture  attains  a  diameter  of  from  1-2  cm.  or  more,  and  appears  on  the 

FIG.  1687. 

Surface  epitheliunv — ^-VX^-FF^^S*- 


Primary  follicles  ~^r  ,.: 

' 

. 
Theca  of  follicle rr-; 

: 
.' .  , 

ir" 

Stratum  — 
granulosum    ,.N>,  •  <\  ,  V 


Zona  pellucida          .  /"  " 


Cavity  filled  by  liquor  folliculi 
Section  of  ovary,  showing  partially  developed  Graafian  follicle.     X  100. 

free  surface  of  the  ovary  as  a  tense  rounded  elevation.     After  liberation  of  the  ovum,  the  folli- 
cle is  converted  into  the  conspicuous  corpus  luteum  (page  1990). 

Seen  in  section,  the  wall  of  the  ripe  follicle,  now  known  as  the  Graafian  follicle,  consists 
of  a  well-developed  capsule  or  fheca  (from  .I4-.20  mm.  in  thickness),  of  which  the  outer  layer 
is  a  lamellated  fibrous  membrane,  and  the  inner  tunic  is  composed  of  looser  connective  tissue 
containing  numerous  peculiar  large  cells  which,  as  maturity  approaches,  exhibit  granularity  and 
a  faint  yellowish  color.  Next  the  inner  layer  of  the  capsule  lies  a  delicate  membrana  propria, 
against  the  inner  surface  of  which  is  applied  the  stratum  granulosum,  composed  of  the  outer 
layers  of  the  follicular  epithelium  that  bound  externally  the  fluid-space  of  the  vesicle.  At  one 
point,  always  opposite  the  place  where  the  follicle  ruptures  (stigma),  the  stratum  granulosum  is 
prolonged  into  a  pedunculated  spherical  mass  of  epithelial  cells  that  projects  into  the  cavity 
occupied  by  the  liquor  folliculi.  This  mass  (cumulus  oophorus)  contains  the  egg  and  on  section 
appears  as  a  ring  ( discus  proligerus )  that  encircles  the  zona  pellucida  and  the  enclosed  ovum 
and  consists  of  two  or  three  layers  of  epithelial  cells.  Those  next  the  zona  are  elongated,  with 
their  ends  directed  towards  the  ovum  pointed  and  prolonged  into  delicate  processes  that  are 
attached  to  or  penetrate  within  the  zona  pellucida.  The  latter,  from  .ooy-.on  mm.  in  thickness, 
is  the  product  of  the  surrounding  follicular  cells  and  does  not  form  a  part  of  the  ovum  proper. 
The  radial  striations  which  the  envelope  sometimes  exhibits  (hence  the  name,  zona  radiata, 
under  which  it  is  often  described)  are  probably  due  to  the  processes  of  the  epithelial  cells  and 
not  to  the  existence  of  minute  canals  (micropyfes)  seen  in  the  eggs  of  many  lower  animals. 


1990 


HUMAN   ANATOMY. 


FIG.  1688. 


The  human  ovum  when  about  to  be  liberated  from  the  Graafian  follicle  pos- 
sesses a  diameter  of  from  .16-.  20  mm.  Its  cytoplasm,  or  rite/his,  exhibits  differ- 
entiation into  a  peripheral  protoplasmic  and  a  central  dciitoplasmic  zone.  According 
to  Nagel,  within  the  former  are  to  be  distinguished  a  narrow  slight  superficial 

marginal  layer,  apparently 
homogeneous  and  free  from 
yolk-particles,  and  a  finely 
granular  zone  containing  mi- 
nute and  scattered  deutoplas- 
mic  granules.  The  dark  or 
central  deutoplasmic  zone  is 
conspicuous  on  account  of 
the  irregular  refraction  of  the 
enclosed  yolk-particles  that 
represent  the  important  nutri- 
tive materials  for  the  embryo 
contained  in  the  eggs  of  birds 
and  reptiles,  but  which  in  the 
mammalian  ovum,  especially 
in  that  of  man,  have  been  for 
the  most  part  lost  during  the 
evolution  of  the  higher  types. 
Beyond  a  slight  condensation 
of  the  surface,  the  presence 
of  a  distinct  cell-wall,  or  zv- 
ttiline  membrane,  in  the  mam- 
malian ovum  is  doubtful.  In 
the  fresh  condition  the  egg- 

Cytoplasm    is    usually    closely 

~~i:~.j  +      *u^  '      11       -j 

applied  to  the  ZOna  pellucida 

(Ebner),  the  narrow  inter- 
vening cleft  that  is  sometimes  seen  being  the  perivitelline  space.  Embedded  within  the 
deutoplasmic  zone,  and  always  eccentrically  placed,  lies  the  spherical  germinal  reside, 
as  the  egg-nucleus  is  termed.  The  vesicle  measures  from  .030-.  045  mm.  in  diameter, 
is  bounded  by  a  sharply  defined  double-contoured  nuclear  membrane,  and  contains 
the  germinal  spot  or  nucleolus  (from  .004-.  008  mm.)  and  the  nuclear  reticulum. 

Corpus  Luteum.  —  The  causes  leading  to  the  final  rupture  of  the  Graafian 
follicle  are  still  uncertainly  known,  although  in  the  light  of  later  researches  the  older 
view,  attributing  the  bursting  of  the  ripe  vesicle  to  mechan- 
ical overdistention  induced  by  accumulation  of  the  liquor 
folliculi,  is  inadequate.  According  to  Nagel,  when  the 
follicle  approaches  maturity  the  inner  layer  of  the  theca 
becomes  the  seat  of  great  activity.  The  blood-vessels  in- 
crease in  size  and  number  and  the  cells  undergo  not  only 
rapid  proliferation,  but  extraordinary  growth,  the  enlarged 
elements  becoming  filled  with  a  peculiar  yellowish  sub- 
stance and  transformed  into  lutein  cells. 

In  consequence  of  this  activity,  the  formerly  smooth 
theca  becomes  thickened  and  wavy  and  projects  into  the 
cavity  of  the  follicle  as  vascular  papillae  and  ridges.  The 
encroachment  thus  effected  gradually  forces  the  contents 
of  the  vesicle  towards  the  surface  and  that  part  of  the  dis- 
tended follicular  wall  possessing  least  vitality  and  resist- 
ance, until,  finally,  rupture  takes  place.  Coincidently  with 
the  proliferation  of  the  lutein  cells,  the  follicular  epithelium 

undergoes  fatty  change  which  results  in  the  breaking  down  of  the  cumulus  and  the 
setting  free  of  the  ovum,  encircled  with  the  cells  of  the  discus  proligerus,  into  the 
cavity  of  the  ogg-sac.  When  rupture  of  the  follicle  occurs,  the  expulsion  of  the 
egg  and  the  epithelial  cells  immediately  surrounding  it  is  followed  by  hemorrhage 


Almost  mature  human  ovum  taken  from  fresh  ovary.  Ovum,  with 
germinal  vesicle  and  spot,  is  encircled  by  clear  zona  pel'lucida,  which  is 
surrounded  by  cells  of  the  follicular  epithelium.  X  300.  (Waldeyer.) 


FIG.  1689. 


Ligament 


Ovary  has  boon  laid  opi'ti  by 
longitudinal  incision,  exposing 
follicli-s  ami  coi;>us  luteum. 


THE   OVARIES. 


1991 


Central 
connective  tissue 


into  the  cavity  of  the  former  egg-sac,  which  now  becomes  converted  into  a  corpus 
luteum. 

The  latter,  long  known  as  the  corpus  luteum  verum  when  associated  with  preg- 
nancy, grows  to  huge  dimensions  and  forms  a  conspicuous  oval  mass  that  may 
approach  3  cm.  in  length  and  occupy  a  considerable  part  of  the  entire  cortex. 
When  impregnation  does  not  take  place,  the  yellow  body  (now  called  the  corpus 
luteum  spurium)  is  smaller,  seldom  exceeding  1.5-2  cm.  in  diameter.  The  classic 
distinction  of  "true"  and  "false,"  apart  from  difference  of  size,  has  no  anatomical 
basis,  since  both  forms  possess  identical  structure.  The  assumption  that  the  presence 
of  a  large  corpus  luteum  is  positive  proof  of  the  existence  of  pregnancy,  must  be 
accepted  with  caution,  since  yellow  bodies  of  unusual  size  are  sometimes  observed  in 
ovaries  of  virgins. 

Shortly  after  the  rupture  of  the  follicle  and  the  replacement  of  its  contents  by 
blood,  the  opening  in  the  wall  of  the  egg-sac  is  closed.  The  rapid  proliferation  and 
growth  of  the  lutein  cells  pro- 
duces an  irregularly  plicated  FIG.  1690. 
wall  of  increasing  thickness 
that  encloses  the  remains  of  the 
degenerating  follicular  epithe- 
lium (granulosa)  and  invades 
the  hemorrhagic  mass.  The 
latter  is  gradually  absorbed 
until,  finally,  the  encroaching 
projections  of  lutein  cells  and 
connective  tissue  meet  and  the 
cavity  of  the  follicle  obliter- 
ated, its  former  position  being 
subsequently  indicated  by  a 
central  core  of  connective  tis- 
sue. The  cells  of  the  stratum 
granulosum,  the  original  epi- 
thelial lining  of  the  egg-sac, 
entirely  disappear  and  take  no 
direct  part  in  the  formation 
of  the  corpus  luteum,  their 
function  during  the  develop- 
ment of  the  Graafian  follicle 
having  been  to  contribute  the 
liquor  folliculi  (Schottlaender). 
Along  with  the  proliferating 
masses  of  lutein  cells,  strands 
of  connective  tissue  are  car- 
ried inward  from  the  theca, 
whereby,  after  a  time,  the  yel- 
low body  becomes  broken  up  by  numerous  radially  disposed  vascular  septa  and  their 
prolongations.  With  the  production  of  a  solid  corpus  luteum  and  the  absorption  of 
the  blood  (evidences  of  which  latter  for  a  long  time  remain  as  hematoidin  crystals), 
the  active  role  of  the  lutein  cells  is  finished.  These  elements  now  lose  their  distinc- 
tive yellow  pigment  (luteiii),  undergo  fatty  metamorphosis,  and  finally  entirely  dis- 
appear. With  the  subsequent  shrinking  and  decrease  in  the  vascularity  of  the  corpus 
luteum,  the  connective  tissue,  which  now  constitutes  the  entire  mass  (corpus  fibro- 
sum),  undergoes  hyaline  change,  becoming  clear  and  non-fibrillar.  In  consequence 
the  aging  corpus  luteum  loses  its  former  appearance  and  is  transformed  into  an  irreg- 
ular body,  light  in  color  and  sinuous  in  outline,  sometimes  known  as  the  corpus 
albicans  (Fig.  1691).  This  gradually  suffers  absorption,  but  remains  for  a  consider- 
able time,  especially  when  associated  with  pregnancy,  as  a  conspicuous  light  corru- 
gated area  within  the  cortex,  the  last  traces  of  its  scar-like  tissue  finally  disappearing 
in  the  ovarian  stroma.  The  greatly  increased  vascularity,  within  the  wall  of  the  ripe 
Graafian  follicle  and  later  around  the  corpus  luteum,  subsides  as  the  yellow  body 


Lutein  cells 


Proliferating 
*     cells  of  inner 
layer  of  theca 


fcijr-  Outer  layer 
*"    of  theca 


^~~ —  Blood-vessels 


Section  of  human  corpus  luteum.     X  7°. 


1992 


HUMAN    ANATOMY. 


undergoes  regression,  until  all  the  new  vessels  concerned  in  its  nutrition  have  disap- 
peared and  the  circulation  of  that  particular  part  of  the  ovary  is  permanently  reduced. 

The  function  usually  ascribed  to  the  corpus  luteum  is  that  of  filling  the  empty  follicles  and 
thus  restoring  the  equilibrium  of  circulation  and  tension.  Clark  l  regards  the  corpus  luteum  as 
a  preserver  of  the  circulation,  since,  when  performing  its  functions  most  perfectly  (during  the 
earlier  years  of  menstrual  life),  it  effects  the  elimination  of  the  effete  follicle  and  the  superfluous 
blood-  vessels  without  leaving  dense  and  disturbing  scars.  Later  in  life,  however,  when  the 
ovarian  stroma  becomes  denser,  the  corpora  lutea  are  less  efficient  and  are  incompletely  absorbed, 
their  remains  impairing  the  circulation  until,  finally,  the  follicles  are  no  longer  matured  and 
ovulation  ceases. 

The  origin  of  the  lutein  cells  has  long  been  a  subject  of  discussion,  and  even  at  present 
two  opposed  views  share  the  support  of  eminent  anatomists.  According  to  the  older  theory, 
advanced  by  Baer,  these  cells  are  modified  connective-tissue  elements,  derived  from  the  pro- 


FIG.  1691. 


Blood-vessels 


Mesosalpinx 


Corpus  luteum 


Mesovarium 


Corpora  lutea 


Remains  of  corpora  lutea 


Sections  of  Fallopian  tube 


Cross-section  through  ovary,  oviduct,  and  part  ot  broad  ligament.     X  6. 

liberation  of  the  cells  of  the  inner  layer  of  the  theca  folliculi.  The  other  view,  formulated  by 
Bischoff,  regards  the  lutein  cells  as  modified  follicular  epithelium.  In  the  foregoing  sketch  of 
the  corpus  luteum,  the  lutein  cells  are  ascribed  to  the  theca,  a  conclusion  based  upon  the  con- 
vincing observations  of  Nagel,  Rabl,  and  Clark,  and  confirmed  by  the  writer's  own  studies. 
Sobotta,  on  the  other  hand,  is  most  positive  in  his  support  of  the  follicular  origin  of  the  lutein 
cells,  based  upon  an  exhaustive  investigation  on  the  ovaries  of  the  mouse  and  rabbit.  The 
difficulty  of  obtaining  human  corpora  lutea  in  the  earliest  stages  places  the  conclusions  as  to  man 
not  beyond  challenge. 

Vessels. — The  arteries  supplying  the  ovary  are  four  or  five  branches  that  arise 
from  the  anastomosis  of  the  ovarian  artery  with  the  ovarian  branch  of  the  uterine. 
The  trunks  (aa.  ovaricce  proprice}  given  off  from  this  anastomotic  arch  pass  to  the 
ovary  between  the  layers  of  the  mesovarium  and,  entering  through  the  hilum  as 
closely  grouped  tortuous  vessels,  reach  the  medulla.  According  to  Clark,2  whose 
description  is  here  followed  (Fig.  1692),  immediately  after  gaining  the  medulla  each 
stem  divides  into  two  branches,  the  medullary  or  parallel  arteries,  that  proceed  in  a 
direct  course. towards  the  opposite  free  margin  of  the  organ,  lying  just  beneath  the 
cortex*  to  which  they  distribute  cortical  branches  at  regular  intervals.  In  their  course 
to  the  periphery  the  cortical  branches,  losing  the  characteristic  corkscrew-like  1  \\ist- 
iu^s  of  the  parent  stems,  supply  hundreds  of  follicidar  hcigs  to  the  egg-sacs,  each 
of  the  latter  being  provided  with  a  rich  vascular  net-work  anastomosing  with  two  or 
more  follicular  branches — an  arrangement  of  ^ivat  importance  in  assuring  an  adequate 
blood-supply  for  the  growth  of  the  follicle  (Clark).  At  the  periphery,  the  cortical 
arterioles  pass  into  the  veins  through  an  intervening  capillary  net-work. 

1  Archiv  f.  Anat.  u.  Physioloi;.,  Anat.  Abth.,  1898. 
1  Welch  Anniversary  Contributions,  1900. 


THE   OVARIES. 


1993 


FIG.  1692. 


Superficial 
anastomoses 


Follicular 
anastomoses 
Follicular 
branches 


The  veins  follow  the  general  arrangement  of  the  arteries  within  the  cortex  and 
medulla  ;  the  pairs  of  parallel  veins,  however,  do  not  unite  into  single  stems,  but 
emerge  from  the  hilum  as  independent  tortuous  trunks.  Within  the  mesovarium  they 
are  interwoven  with  the  bundles  of  involuntary  muscle,  and  when  distended  present 
a  conspicuous  venous  complex  (bulb us  ovarii).  The  veins  proceeding  from  the 
ovary  (vv.  ovaricce proprite)  become  tributary  to  both  the  uterine  and  the  ovarian 
(pampiniform)  plexus. 

The  lymphatics  begin  in  the  cortex  as  net-works  within  the  thecse  surrounding 
the  Graafian  follicles  and  as  lymphatic  clefts  within  the  ovarian  stroma.  From  these 
radicles  the  larger  and  irregular  channels  enter  the  medulla,  where  they  form  con- 
verging stems  that  follow  the  blood-vessels  and  leave  the  hilum  of  the  ovary  usu- 
ally as  nine  larger  trunks  (Polano)  that  pass  upward  along  the  free  border  of  the 
suspensory  ligament  and  empty  into  the  lumbar  lymph-nodes  surrounding  the  aorta. 
Occasionally,  but  by  no  means  constantly,  the 
ovarian  lymphatics  communicate  with  those 
from  the  fundus  of  the  uterus  and  the  oviduct. 

The  nerves  supplying  the  ovary  are  de- 
rived from  the  sympathetic  plexus  surrounding 
the  ovarian  artery  (plexus  arteriae  ovaricse), 
which,  in  turn,  is  formed  by  contributions  from 
the  renal  and  aortic  plexuses  and  corresponds 
to  the  spermatic  plexus  in  the  male.  The 
small  nerve-trunks,  composed  for  the  most 
part  of  non-medullated  fibres,  accompany  the 
arteries  through  the  hilum  into  the  ovary, 
where  they  are  distributed  chiefly  to  the  walls 
of  the  blood-vessels,  around  the  larger  of  which 
terminal  plexuses  are  formed.  From  the  fairly 
close  plexus  within  the  cortex,  additional  mi- 
nute twigs  pass  to  the  periphery,  to  end  in 
close  relation  with  the  surface  (germinal)  epi- 
thelium, and  others  to  the  follicles.  The  ulti- 
mate relation  between  the  latter  and  the  sur- 
rounding net-works  is  uncertain,  but  it  is  probable  that  the  nerve-fibrillae  end  in  the 
walls  of  the  follicular  blood-vessels  and  do  not  penetrate  beyond  the  inner  tunic  of 
the  theca,  the  terminations  within  the  follicular  epithelium  described  by  some  ob- 
servers needing  confirmation.  Sensory  fibres  are  probably  contained  within  the 
cortical  branches.  The  claimed  existence  of  minute,  true,  sympathetic  ganglia  within 
the  medulla,  has  not  been  established. 

Development. — The  primary  development  proceeds  from  the  indifferent 
germinal  ridge  which  is  early  formed  on  the  median  surface  of  the  Wolffian  body 
(page  2038).  Whether,  as  usually  accepted,  the  ova  in  common  with  the  follicular 
epithelium  are  directly  derived  from  the  modified  mesothelium  (germinal  epithelium) 
covering  the  sexual  ridge,  or  are  the  descendants  of  germ-cells  early  set  apart  from 
the  somatic  cells  for  the  special  role  of  reproduction,  remains  to  be  decided,  al- 
though evidence  in  support  of  this  latter  hypothesis — the  continuity  of  the  germ- 
cells — is  accumulating  from  observations  on  the  lower  animals,  in  which  the  origin  of 
the  primordial  sex-cells  is  less  obscured. 

In  human  embryos  of  12  mm.  in  length,  among  the  cells  of  the  germinal  ridge, 
certain  elements  are  already  distinguished  by  their  exceptional  size  and  large,  clear 
nuclei.  These  are  the  primary  sexual  cells,  the  primordial  ova  (Fig.  1717),  usually 
regarded  as  originating  from  the  transformation  of  the  germinal  epithelium.  At 
first  the  latter  and  the  subjacent  stroma  of  the  Wolffian  body  are  well  differentiated 
from  each  other.  This  demarcation  is  soon  lost  in  consequence  of  the  active  inter- 
growth  which  takes  place  between  the  proliferating  germinal  epithelium  and  the  in- 
growing vascular  connective  tissue  of  the  Wolfrian  body — the  two  chief  factors  in 
the  histogenesis  of  the  ovary. 

As  the  mass  of  epithelial  elements  increases,  it  becomes  broken  up  by  the  con- 
nective-tissue strands  into  large  tracts,  composed  of  the  primary  ova  surrounded  by 


Arteria  propria 


Ovarian  artery 


Diagram  illustrating  arranj 
vessels  of  ovary. 


Ovarian 
veins 


ement  of  blood- 
Clark.) 


1994 


HUMAN   ANATOMY. 


FIG.  1693. 

Germinal  epithelium 


Primordial  ovum 


Ova 


multitudes  of  the  smaller  and  less  specialized  cells  of  the  germinal  epithelium.  The 
larger  tracts  are  subdivided  into  smaller  spherical  cell-aggregations  (the  egg-balls 
of  Waldeyer)  by  the  continued  intergrovvth  and  mutual  invasion  of  the  tissues,  and 
the  "  egg-balls,"  in  turn,  are  broken  up  by  the  same  process  until  the  final  division 
results  in  the  isolation  of  the  ultimate  groups,  the  primary  follicles,  that  include  the 
primary  ova  surrounded  by  a  single  layer  of  flattened  germinal  epithelium.  In 
places  the  larger  compartments  are  cylindrical  and  attached  to  the  germinal  epithe- 
lium, appearing  as  solid  outgrowths  connected  with  the  surface  ;  to  them  Prliiger 
gave  the  name  "egg-tubes"  and  attributed  an  aggressive  invasion.  Since  the  con- 
nective tissue  of  the  Wolffian  stroma  first  invades  the  deeper  stratum  of  the  germinal 

epithelium,  this  region,  the  fu- 
ture medulla  of  the  ovary,  is 
subdivided  into  the  ultimate 
groups  of  cells,  the  primary  fol- 
licles, earlier  than  the  more  su- 
perficial and  younger  layers, 
this  genetic  relation  being  seen 
in  the  fully  developed  ovary,  in 
which  the  youngest  and  least 
mature  follicles  always  occupy 
the  peripheral  zone.  The  most 
superficial  stratum  of  the  ger- 
minal ridge  remains  as  the  ger- 
minal epithelium  that  covers 
the  exterior  of  the  ovary  and 
replaces  the  usual  peritoneal 
mesothelium  plates. 

The  details  of  the  trans- 
formation of  the  primary  folli- 
cles, consisting  of  the  ovum  and 
the  investing  single  layer  of 
mantel-cells,  into  the  ripening 
Graafian  follicles  have  been  de- 
scribed (page  1988).  Of  the 
thousands  of  primary  follicles 
within  the  young  ovary  (esti- 
mated by  Waldeyer  at  over 
100,000  in  the  two  ovaries  of 
the  new-born*  child)  very  few  reach  maturity,and  by  advanced  life  nearly  all  have 
disappeared.  This  reduction  begins  during  intrauterine  life  and  first  affects  the  fol- 
licles situated  within  the  deeper  parts  of  the  ovary  destined  to  become  the  medulla, 
from  which  the  ova  are  later  entirely  absent.  The  remains  of  these  earl}-  follicles 
probably  account  for  certain  of  the  minute  epithelial  bodies  occasionally  seen  in  the 
medulla  of  young  adults. 


Section  of  developing  ovary  from  human  embryo, 
wing  intergrowth  between 
stroma  tissue  derived  from  We 


showing  intergrowth  between  germinal  epithelium  a'nd 
"Yolfnanbody. 


Numbers  of  follicles  within  the  cortex  also  are  continually  undergoing;  destruction.  This 
affects  especially  the  primary  follicles  while  they  lie  naked  wjthin  the  stroma,  and  are  unpro- 
vided with  a  theca,  the  ovum  undergoing  hyaline  degeneration  and,  along  with  the  mantel- 
cells,  finally  entirely  disappearing  within  the  ovarian  stroma.  Beginning  in  the  young  ovary 
long  before  puberty,  as  well  as  throughout  the  period  of  sexual  maturity,  certain  egg-sacs  are 
continually  transformed,  more  or  less  fully,  into  (iraafian  follicles  that  develop  to  a  certain 
stage  and  an-  then  arrested,  after  which  they  enter  upon  regression,  degenerate,  and  finally  may 
completely  disappear.  This  process,  known  as  atn-sia  of  the  follicles,  is  probably  closely 
related  to  alterations  in  their  blood-supply  ((.Mark). 

With  possibly  few  exceptions,  the  formation  of  new  follicles  ceases  during  the  first  few 
years  after  birth,  the  supply  developed  early  in  life  being  in  such  lavish  excess  of  all  possible 
needs  that  ample  provision  is  made  against  dearth  of  reproductive  cells.  Infrequently 
follicles  are  encountered  in  which  two  or  more  ova  an-  (in-sent.  This  condition  results  from 
the  inclusion  of  more  than  a  single  primary  egg  when  the  follicle  was  formed,  and  not  from 
•division  of  an  ovum  already  enclosed,  since  after  the  mantel-cells  surround  the  ovum  it  is 


PRACTICAL   CONSIDERATIONS:    THE   OVARY.  1995 

doubtful  whether  the  latter  ever  undergo  division.  In  certain  cases  it  is  also  possible  that  the 
delicate  partition  separating  two  closely  applied  follicles  may  disappear,  the  ova  thence 
occupying  the  common  sac  ( Ebner. ) 

The  changes  in  form  and  position  which  the  ovary  undergoes  during  life  are 
conspicuous.  In  the  new-born  child  the  organ  is  relatively  long  (from  12-18  mm.) 
and  narrow  (from  4-5  mm.),  triangular  on  cross  section,  and  lies  entirely  above  the 
brim  of  the  pelvis,  with  its  long  axis  transversely  placed  and  its  inner  pole  close  to 
the  fundus  uteri.  During  the  first  two  years,  owing  to  the  increasing  capacity  of  the 
pelvis  and  interabdominal  pressure  and  its  attachments  to  the  uterus,  it  gradually 
sinks  into  the  pelvic  cavity,  during  this  descent  the  direction  of  its  long  axis  becoming 
more  vertical.  At  birth  the  surface  of  the  ovary  is  marked  with  furrows  and  folds, 
inequalities  that  disappear  as  the  organ  expands  in  consequence  of  the  rapid  increase 
in  its  stroma-tissue  during  the  first  year  or  two.  Later  the  growth  of  the  young 
ovary  is  gradual  and  slow,  until  the  advent  of  sexual  maturity,  from  the  twelfth  to 
the  fifteenth  year,  when  the  organ  undergoes  sudden  increase  and  acquires  its  definite 
form  and  size.  Further  enlargement,  however,  usually  takes  place  in  women  who 
bear  children,  until  towards  the  fortieth  year.  The  repeated  development  and  rupture 
of  the  Graafian  follicles  and  the  formation  of  the  corpora  lutea  produce  irregularity 
of  the  surface,  which  becomes  knobbed  and  scarred  and  contrasts  strongly  with  the 
smooth  organ  of  childhood.  After  the  cessation  of  menstruation,  about  the  forty- 
fifth  year,  gradual  decrease  (involution)  of  the  ovary  follows,  until  the  organ  may  be 
reduced  to  a  dense  fibrous  body  of  less  than  half  of  the  original  size. 

Variations. — Abnormalities  in  the  sexual  glands  of  the  female  are,  for  the  most  part, 
referrible  to  developmental  deviations.  Incompleteness  or  modification  of  its  descent  affect 
the  position  of  the  organ,  so  that  it  may  retain  its  original  suprapelvic  position  and  lie  above  or 
upon  the  psoas  magnus  muscle  ;  or  it  may  follow  the  pull  of  the  round  ligament  (the  homologue 
of  the  genito-inguinal  ligament  of  the  male,  page  2006)  and  pass  partly  or  entirely  through  the 
inguinal  canal  into  the  labium  majus.  Variations  of  position  in  the  adult  are  commonly  asso- 
ciated with  diseased  conditions  of  the  peritoneum  and  adjacent  organs  and  are  therefore  patho- 
logical. The  adult  ovary  may  present  marked  deviations  from  its  typical  form,  sometimes 
being  unusually  long,  spheroidal,  flattened,  triangular,  crescentic,  or  irregular. 

Supernumerary  ovaries,  varying  in  size  from  a  hempseed  to  a  small  hazelnut,  are  not  in- 
frequent, occurring  in  from  over  2  (Beigel)  to  4  (Rieffel)  per  cent.  Their  usual  situation  is 
along  the  white  line  marking  the  transition  of  the  peritoneum  into  the  germinal  epithelium. 
•Isolation  of  a  portion  of  the  ovarian  anlage,  often  probably  by  a  peritoneal  band  (Nagel),  is 
responsible  for  these  bodies,  which  consist  of  normal  follicle-bearing  ovarian  tissue. 

PRACTICAL   CONSIDERATIONS  :    THE   OVARY. 

Since  the  ovaries  project  below  the  Fallopian  tubes  from  the  posterior  surface  of 
the  broad  ligaments,  in  seeking  for  them  in  abdominal  operations  the  hand  should  be 
passed  outward  from  the  posterior  surface  of  the  uterus  along  the  broad  ligament,  on 
each  side. 

In  its  usual  position  the  long  axis  of  the  ovary  is  approximately  vertical,  its 
external  surface  lying  against  the  pelvic  wall  close  to  the  obturator  vessels  and  nerve. 
The  ureter  and  uterine  artery  lie  behind  and  below  it. 

Prolapse  of  the  ovary  occurs  most  frequently  as  the  result  of  subinvolution  after 
labor.  If  involution  is  in  any  way  arrested  or  rendered  incomplete,  the  conditions 
favorable  for  prolapse  of  the  ovary  will  be  present, — increased  weight  of  the  ovary 
and  relaxation  and  lengthening  of  its  attachments. 

The  left  ovary  is  more  frequently  prolapsed  than  the  right,  because  it  normally 
becomes  more  enlarged  during  pregnancy,  and  therefore  suffers  more  from  subinvolu- 
tion, and  because  the  arrangement  of  the  veins  on  the  left  side  is  such  that  venous 
congestion  is  very  liable  to  occur  (Penrose).  An  analogous  anatomical  condition 
exists  to  that  which,  in  the  male,  favors  left-sided  varicocele,  the  left  ovarian  vein 
emptying  into  the  renal  vein  at  a  right  angle,  while  the  right  ovarian  vein  empties 
into  the  vena  cava  at  an  acute  angle  (page  1961). 

In  complete  prolapse  the  organ  lies  in  Douglas's  pouch  between  the  rectum  and 
the  posterior  vaginal  wall.  There  is  apt  to  be  pain  on  walking,  because  the  ovary  is 
then  compressed  between  the  cervix  and  the  sacrum,  and  on  coitus  or  defecation, 


1996 


HUMAN   ANATOMY. 


because  of  direct  trauma.      The  pain  is  often  nauseating  and  may  be  felt  in  the  breast 
on  the  same  side. 

In  spite  of  its  small  size  the  ovary  gives  origin  to  a  great  variety  of  tumors  and 
cysts  which  may  grow  to  enormous  proportions,  filling  and  distending  the  abdomen. 
As  they  grow  they  at  first  crowd  the  uterus  and  other  pelvic  structures  towards  the 
opposite  side  ;  later  they  ascend  into  the  abdomen,  drawing  the  attached  structures 
upward  with  them  in  their  pedicles.  The  pedicle  is  the  base  of  attachment,  and 
consists  of  the  same  anatomical  structures  as  those  by  which  the  ovary  is  normally 
attached.  The  relations  of  the  structures  making  up  the  pedicle  to  one  another  will 
vary  greatly  according  to  the  manner  in  which  the  tumor  grows.  This  relationship 
should  be  studied  carefully  to  establish  a  correct  diagnosis  as  to  the  origin  of  the 
tumor.  The  anatomical  structures  involved  in  the  pedicle  are  the  mesovarium^ 
mesosalpinx,  Fallopian  tube,  and  broad  ligament. 

THE   FALLOPIAN   TUBES. 

The  Fallopian  tube  (tuba  uterinae)  or  oviduct  is  in  principle  the  excretory  canal 
of  the  sexual  gland,  the  ovary,  since  it  conveys  the  ova  liberated  from  the  Graafian 
follicles  to  the  uterus, "into  which  it  opens.  The  relation  between  the  ovary  and  its 
duct,  however,  is  exceptional  in  that  these  organs  are  not  continuous,  but  only  in  ap- 
position, the  ova  liberated  from  the  ovary  finding  their  way  into  the  expanded  end  of 

FIG.  16)4. 


Sigmoid  artery 


Internal  iliac 
vessels 

External  iliac — 
vessels 
Ureter — 

Suspensory 
ligament     • 
of  ovary 
Right  ovary 


Fimbrias  of 
oviduct 
Ligament  - 
of  ovary 
Oviduct 


Round  -•' 
ligament 


Bladder 

Pelvic  organs  of  young  woman,  viewed  from  above  and  in  front;  hardened  hi  situ  and  undisturbed 
Kimbriated  extremity  of  right  oviduct  lay  in  position  shown  and  not  in  relation  with  o\xry. 

the  oviduct.  This  canal,  one  on  each  side  of  the  body,  lies  within  the  free  margin  of 
the  upper  division  of  the  broad  ligament,  known  as  the  mesosalpinx,  and  extends 
from  the  uterus  medially  to  the  ovary  laterally,  in  relation  to  the  inner  surface  of 
which  it  ends  after  numerous  windings. 

The  entire  length  of  the  tube  is  about  11.5  cm.  (4^  in.),  although  variations 
from  6-20  cm.  (2^-7^  in.)  have  been  observed.  Emerging  from  the  lateral  angle 
of  the  fundus  uteri,  in  the  immediate  vicinity  and  just  above  the  uterine  attachments 
of  the  utero-ovarian  and  round  ligaments,  the  first  part  of  the1  tube  is  narrow  and 


THE   FALLOPIAN   TUBES.  1997 

^comparatively  straight  and  constitutes  the  isthmus  (isthmus  tubae  uterinae),  about  .35 
cm.  ( 1 2/6  in.  )  in  length  and  from  3-4  mm.  in  diameter.  Throughout  the  succeeding 
8  cm.  (3^  in.)  of  the  tube,  known  as  the  ampulla  (ampulla  tubae  uterinae),  the 
diameter  gradually  increases  (from  6-8  mm.)  until  the  canal  suddenly  expands  into 
the  terminal  trumpet-shaped  infundibulum.  The  margins  of  the  latter  are  prolonged 
and  slit  up  into  long,  irregular  processes,  \hzjimbri(e,  from  10-15  mm.  in  length,  the 
resulting  Jimbriatcd  extremity  of  the  tube  resembling,  when  examined  in  fluid,  an  ex- 
panded sea-anemone  (Nagel).  One  of  the  fimbriae  (timbria  ovarica)  is  usually  longer 
than  the  others,  attached  to  the  free  border  of  the  mesosalpinx  and  stretches  towards 
the  ovary,  the  tubal  pole  of  which  it  often,  but  by  no  means  always,  reaches.  The 
lumen  of  the  oviduct  varies  greatly  at  different  points.  Beginning  at  the  lateral  angle 
of  the  uterine  cavity  as  a  minute,  inconspicuous  opening  (ostium  uterinum  tubae), 
-commonly  obscured  by  mucus  and  about  i  mm.  in  diameter,  the  canal  traverses  the 
uterine  wall  (pars  uterina)  and  gains  in  size  and  longitudinal  folds,  so  that  on  cross- 
section  the  isthmus  presents  a  stellate  lumen.  Within  the  ampulla  the  plications  of 
the  mucous  membrane  become  progressively  more  marked,  appearing  in  transverse 
sections  as  a  complex  figure  of  primary  and  secondary  folds  (Fig.  1695)  that  greatly 
encroach  upon  the  calibre  of  the  tube.  The  folds  are  continued  into  the  infundibulum 
and  onto  the  inner  side  of  the  fimbriae.  The  outer  or  ovarian  end  of  the  oviduct 
opens  directly  into  the  peritoneal  cavity  by  a  small  aperture  (ostium  abdominale 
tubae),  2  mm.  or  less  in  diameter,  that  lies  at  the  bottom  of  the  infundibulum  and  is 
produced  by  local  contraction  of  the  muscular  tissue  of  the  wall  of  the  tube,  a  special 
sphincter,  however,  not  being  demonstrable.  The  mucous  lining  of  the  oviduct  is 
continued  from  the  infundibulum  onto  the  fimbriae,  the  line  of  transition  into  the  peri- 
toneum following  the  bases  and  outer  sides  of  the  fringes.  The  exceptional  relation 
of  the  tubal  lining  to  the  serous  membrane,  this  being  the  only  place  in  the  body 
where  a  mucous  tract  opening  onto  the  exterior  communicates  with  a  closed  serous 
sac,  is  referrible  to  the  similar  original  relation  of  the  embryonal  Miillerian  duct  from 
which  the  Fallopian  tube  is  directly  derived  (page  2038). 

Course  and  Relations. — Since  each  Fallopian  tube  occupies  the  free  border  of 
the  broad  ligament,  changes  in  the  position  of  the  uterus  affect  the  course  of  the 
oviduct.  From  the  upper  angle  of  the  uterus  the  tube  may,  therefore,  first  pass  out- 
ward towards  the  ovary  in  a  strictly  transverse  direction,  or  describe  a  gentle  forward 
or  backward  curve,  depending  upon  the  position  of  the  fundus  uteri,  this  part  of  the 
tube,  however,  never  being  tortuous.  On  gaining  the  uterine  or  lower  pole  of  the 
ovary,  it  there  bends  upward  and  winds  obliquely,  from  below  upward  and  backward, 
across  the  median  surface  of  the  ovary,  close  to  the  anterior  border  and  tubal  pole,  to 
the  convex  posterior  margin,  where  the  tube  bends  sharply  downward,  its  fimbriated 
end  being  in  relation  with  the  lower  and  back  part  of  the  median  surface.  When  in 
its  usual  position,  the  ovary  is,  thus,  partly  covered  not  only  by  the  tortuous  oviduct 
itself,  but  also  necessarily  by  the  mesosalpinx  in  which  the  tube  lies,  so  that  when 
viewed  from  above  the  ovary  is  often  entirely  hidden  by  the  Fallopian  tube  and  the 
attached  portion  of  the  broad  ligament.  In  consequence  of  this  arrangement,  the 
ovary  is  partly  surrounded  by  a  hood  of  serous-membrane  and  lies  within  a  pocket, 
known  as  the  bursa  ovarii,  which  may  facilitate  the  entrance  of  the  liberated  ova  into 
the  Fallopian  tube.  In  its  course  from  the  uterus  to  the  ovary  the  oviduct  lies  in 
front  of  and  generally  parallel  with  the  utero-ovarian  ligament  and  is  overlaid  by  the 
coils  of  the  small  intestine.  As  the  tube  ascends  and  arches  over  the  ovary,  the 
intestinal  coils  cover  its  medial  surface,  the  sigmoid  colon  also  occasionally  being  in 
relation  on  the  left  side.  In  formalin-hardened  subjects,  with  otherwise  normal  pel- 
vic contents,  we  have  so  often  found  the  termination  of  the  Fallopian  tube  lying  away 
from  the  ovary,  that  Merkel's  suggestion,  that  the  assumed  constant  close  relation 
between  the  fimbriated  extremity  and  the  ovary  may  sometimes,  at  least  temporarily, 
be  wanting  during  life,  seems  well  founded. 

Structure. — The  wall  proper  of  the  Fallopian  tube,  consisting  of  the  mucous 
and  muscular  coats,  lies  embedded  within  the  loose  connective  tissue  of  the  broad 
ligament  (tunica  adventitia)  surrounded  by  the  peritoneum,  which  completely  invests 
the  tube  with  the  exception  of  the  narrow  interval  through  which  the  tubal  vessels 
-and  nerves  pass.  The  wall  is  thickest  and  firmest  in  the  isthmus,  less  so  in  the 


1998 


HUMAN   ANATOMY. 


FIG.   1695. 


Mucosa- 


Epithelium  —r^f^r'T 

:'M 

•-'-  :'      •  .'.-• 


Lumen 


ampulla,  and  thinnest  and  most  relaxed  in  the  infundibulum  and  fimbriae.  The 
mucous  membrane  is  thrown  into  longitudinal  folds,  which  increase  from  5—15  low 
ridges  in  the  commencement  of  the  isthmus  to  double  the  number  in  the  ampulla, 
where  they  attain  a  much  greater  height  as  well  as  complexity  of  arrangement,  the 
main  folds  being  supplemented  by  secondary  and  tertiary  ones,  so  that  in  transverse 
section  the  lumen  appears  almost  occluded  by  branching  villus-like  projections.  The 
surface  of  the  mucosa  is  covered  with  a  single  layer  of  columnar  epithelium  (from 
.015—  .020  mm.  in  height)  provided  with  cilia  that  produce  a  current  directed  from 
the  infundibulum  towards  the  uterus,  and  thus,  while  facilitating  the  progress  of  the 
ova  along  the  tube,  retard  the  ascent  of  the  spermatozoa.  The  elaborate  plications 
and  recesses  within  the  outer  part  of  the  ampulla  favor  the  temporary  retention  of  the 
sexual  cells  and  thereby  promote  the  chance  of  their  meeting,  fertilization  usually 
taking  place  within  this  part  of  the  tube.  The  vascular  connective-tissue  stroma  of 

the  folds,  which  in  the 
chief  plications  may 
reach  a  thickness  of  .  2 
mm.  ,  within  the  acces- 
sory folds  is  reduced 
to  a  narrow  interepi- 
thelial  layer  in  places 
measuring  less  than  the 
height  of  the  covering- 
cells.  The  tunica  pro- 

I)r'a  °^  ^ie  mucosa  is 
directly  continuous 
with  the  intermuscular 
connective  tissue,  and, 
with  the  exception  of  a 
few  bundles  prolonged 
into  the  deepest  part 
of  the  mucous  mem- 
brane, does  not  contain 
muscular  tissue. 

The  muscular  coat, 
most  robust  towards 
the  uterus  and  thinnest 
at  the  infundibulum 
(therefore  the  reverse 
of  the  arrangement  of 
the  mucosa),  includes 
an  inner  circular  and  an  outer  longitudinal  layer  of  involuntary  muscle.  At  the 
isthmus,  where  the  firmness  of  the  tubal  wall  depends  chiefly  upon  the  muscular  coat, 
the  circular  layer  is  the  thicker  (from  .5-1  mm.)  and  the  longitudinal  one  repre- 
sented by  an  incomplete  stratum  of  muscle-bundles.  Towards  the  infundibulum,  on 
the  contrary,  the  longitudinal  layer  is  better  developed,  the  circular-muscle  being- 
reduced  to  .2  mm.  or  less  in  thickness.  The  surrounding  fibrous  tissue,  sometimes 
regarded  as  a  distinct  coat  of  the  tube  (tunica  advent  ilia),  and  the  outer  serous  in- 
vestment are  only  the  usual  connective  tissue  and  peritoneal  constituents  of  the  broad 
ligament,  and,  therefore,  call  for  no  further  description  in  connection  with  the  oviduct. 
As  evidenced  in  pathological  conditions,  and  especially  in  tubal  pregnancy,  the  wall 
of  the  oviduct  is  capable  of  distention  to  a  remarkable  degree. 

Vessels.  —  The  arteries  supplying  the  oviduct  are  derived  from  the  tubal 
branches  of  the  uterine  and  ovarian  vessels.  The  branch  from  the  uterine  artery 
(rn>nus  tubarius  a.  nterinai)  passes  in  front  of  the  utero-ovarian  ligament  to  the 
median  end  of  the  oviduct,  along  the  under  side  of  which  it  courses  outward  until  it 
meets  the  tubal  branch  from  the  ovarian  artery.  The  latter  (rain  us  tu  bar  ins  a. 
ovariccz}  passes  within  the  mesosalpinx,  in  front  of  the  ovarian  timbria,  towards  the 
outer  part  of  the  ampulla,  distributing  branches  to  the  fimbriated  extremity,  and 
mesially  joins  the  tubal  branch  from  the  uterine.  From  the  anastomotic  branch  so 


Fold  cut- 


Circular- 
muscle 


Cross-section  of  oviduct  near  outer  end  of  ampulla.     X  35 


PRACTICAL   CONSIDERATIONS  :     FALLOPIAN   TUBES.         1999 

formed  numerous  twigs  are  given  off  to  the  wall  of  the  Fallopian  tube  and  to  the 
mesosalpinx.  Those  distributed  to  the  oviduct  gain  the  canal  along  its  nonperitoneal 
tract  between  the  peritoneal  reflection  and,  piercing  the  wall,  break  up  into  capillary 
net-works  within  the  muscular  and  mucous  coats.  The  veins,  which  begin  within  the 
walls  of  the  tube,  especially  between  the  muscular  layers,  and  as  a  subserous  net-work, 
follow  the  arteries  and  become  tributary  to  both  the  uterine  and  ovarian  trunks. 

The  lymphatics,  after  emerging  from  the  wall  of  the  tube,  form  three  or  four 
stems  that  accompany  the  blood-vessels  and  pass  in  front  of  the  attached  border  of 
the  ovary.  For  the  most  part  they  follow  the  ovarian  lymphatics  through  the  sus- 
pensory ligament  to  become  finally  tributary  to  the  lumbar  lymph-nodes  surrounding 
the  aorta.  It  is  probable  that  some  of  the  lymphatics  of  the  tube  communicate  with 
those  of  the  fundus  uteri  (Poirier,  Bruhns). 

The  nerves  supplying  the  Fallopian  tube,  numerous  and  chiefly  sympathetic 
fibres,  follow  the  arteries  and,  therefore,  reach  the  oviduct  from  both  the  ovarian  and 
the  uterine  plexus.  Within  the  subserous  tissue  they  form  a  pcritubal  plexus  from 
which  twigs  penetrate  the  wall  of  the  canal  and  are  distributed  principally  to  the 
muscular  tissue,  some  filaments  taking  part  in  the  production  of  a  subepithelial  plexus 
within  the  mucous  membrane  (Jacques). 

Development  and  Changes. — The  early  development  of  the  oviducts  is 
directly  associated  with  that  of  the  embryonal  Miillerian  ducts  (page  2038),  the 
unfused  portions  of  which  the  tubes  represent.  The  margin  of  the  abdominal  open- 
ing (the  persistent  original  evagination  from  the  primary  body-cavity  or  ccelom)  is 
at  first  cushion-like,  but  soon  exhibits  indentations  which,  by  the  fifth  foetal  month, 
devek>p  into  distinct  fimbriae.  At  birth,  while  smaller,  the  latter  possess  their  charac- 
teristic appearance  and  are  lined  by  ciliated  columnar  epithelium  that  covers  the 
plications  of  the  tube.  The  upper  (outer)  segment  of  the  oviduct  participates  in  the 
migration  incident  to  the  descent  of  the  ovary,  lying  for  a  time  within  the  abdomen 
above  the  pelvic  brim.  In  contrast  to  the  ovary,  the  tube  early  acquires  its  definite 
form,  in  the  new-born  child  presenting  its  chief  characteristics,  although  it  is  more 
twisted  than  later  and  the  fimbriae  are  still  small  ;  the  plication  of  the  mucosa,  how- 
ever, is  almost  fully  developed.  During  childhood,  beginning  at  the  uterine  end,  the 
tube  becomes  less  tortuous  and  the  fimbriated  extremity  assumes  its  definite  propor- 
tions. In  advanced  age,  the  oviduct  suffers  atrophy,  losing  its  former  tortuosity,  the 
infundibulum  becoming  flaccid  and  the  fimbriae  shrivelled.  Owing  to  the  atrophy  of 
the  muscle  its  wall  becomes  thinner  ;  the  ciliated  columnar  epithelium  is  replaced  by 
cuboidal  cells,  the  lumen  narrows  and  in  places  may  disappear  in  consequence  of 
the  adhesion  of  the  mucous  folds. 

Variations. — Apart  from  anomalous  situation  depending  upon  malposition  of  the  uterus  and 
ovary,  in  which  the  tube  of  necessity  shares,  the  variations  of  the  oviduct  usually  depend  upon 
developmental  faults  traceable  to  imperfect  or  aberrant  formation  of  the  Miillerian  ducts. 
Retention  of  the  foetal  tortuosity,  stunted  development  or  entire  absence  may  affect  one  or  both 
tubes.  Complete  doubling  of  the  oviducts  may  occur  in  association  with  supernumerary  ovaries. 
Occasionally  partial  duplication  of  the  tube  is  observed,  consisting  of  a  short  canal  ending  in  a 
diminutive  fimbriated  extremity  in  the  vicinity  of  the  infundibulum.  Such  accessory  tubes  are 
to  be  referred  probably  to  a  repetition  of  the  invagination  that  normally  produces  the  infundi- 
bulum (Nagel).  Quite  frequently  the  oviduct  is  beset  with  from  one  to  three  fringed  accessory 
openings  that  may  lie  close  to  the  fimbriated  end,  or  at  a  distance  from  the  latter  along  the  tube. 
The  explanation  of  these  apertures  is  uncertain,  although  it  seems  most  probable  that  they  result 
from  aberrant  development  of  the  Miillerian  duct,  rather  than  as  secondary  perforations  of  the 
tube  and  prolapse  of  its  mucosa,  as  held  by  Nagel  and  others. 

PRACTICAL   CONSIDERATIONS  :    THE   FALLOPIAN   TUBES. 

The  function  of  the  Fallopian  tube  is  to  transmit  the  ovum  from  the  ovary  to 
the  uterus,  the  ciliated  epithelium  of  the  tube  favoring  movement  in  that  direction. 
An  impregnated  ovum  may  adhere  to  the  wall  of  the  tube,  giving  rise  to  an  ectopic 
gestation  (tubal  pregnancy).  Such  pregnancy  may  occur  in  the  ampulla, — the  most 
usual  place, — in  the  infundibulum  (tubo-ovarian  pregnancy),  or  in  the  intra-mural 
portion  of  the  tube, — i.e.,  that  part  traversing  the  wall  of  the  uterus. 


2000  HUMAN    ANATOMY. 

The  chief  causes  of  tubal  pregnancy  are  pathological  or  abnormal  conditions  of 
the  tube.  The  more  important  of  these  are:  (a)  congenital,  such  as  exaggerated  con- 
volutions, diverticula,  and  atresias  ;  (b)  sagging  and  attachments  by  adhesions  dis- 
torting the  tube  ;  (c)  pressure  from  surrounding  structures  ;  (d  )  thickening  of  the 
tubal  walls,  interfering  with  peristalsis  ;  and  (e)  destruction  of  the  cilia  or  narrowing 
of  the  tube  following  salpingitis.  Complete  occlusion  of  the  tubes  of  both  sides 
would  result  in  sterility. 

The  great  danger  of  ectopic  gestation  is  that  of  hemorrhage  following  rupture 
of  the  tube  by  the  growing  fcetus.  This  will  occur  some  time  prior  to  the  fourth 
month,  and  may  be  intraperitoneal, — i.e.,  directly  into  the  peritoneal  cavity;  or 
extraperitoneal, — i.e.,  downward,  cleaving  the  layers  of  the  broad  ligament,  and 
finally  rupturing  the  tube  within  the  layers  of  the  ligament  ;  or,  in  case  the  pregnancy 
is  "interstitial,"  the  rupture  may  be  intrauterine.  The  intraperitoneal  rupture 
usually  takes  place  before  the  seventh  week  ;  the  extraperitoneal  usually  from  the 
seventh  to  the  twelfth  week.  If  the  fcetus  should  survive  the  primary  rupture  in  the 
extraperitoneal  variety,  secondary  rupture  into  the  general  peritoneal  cavity  may 
occur  later,  and  the  ovum  may  go  on  to  full  term  within  the  abdominal  cavity. 

The  Fallopian  tube  offers  a  passageway  in  the  opposite  direction  for  the  entrance 
of  infections,  especially  gonorrhceal,  from  the  vagina  and  uterus  into  the  peritoneal 
cavity.  When  inflammation  involves  the  tube,  it  is  followed  soon  by  a  closure  of 
the  fimbriated  extremity,  the  fimbriae  adhering  to  each  other,  to  the  ovary,  or  to 
some  adjacent  peritoneal  surface.  Later  the  uterine  end  of  the  tube  also  closes,  and 
the  pus  which  results  from  the  infection  now  accumulates  within  the  tube  {Pyo- 
salpinx^) and  may  greatly  distend  it.  If  the  infection  is  gonorrhceal,  such  a  pus-tube 
without  rupture  is  frequently  unaccompanied  by  acute  symptoms.  Slight  ruptures 
with  leakage  into  the  peritoneal  cavity  followed  by  sharp  attacks  of  localized  pelvic 
peritonitis  often  occur.  A  large  rupture  may  give  rise  to  a  diffuse  septic  peritonitis, 
although  the  danger  of  this  result  in  a  case  of  chronic  pyosalpinx,  even  if  of  enormous 
size,  is  far  less  than  after  acute  gangrene  of  the  appendix  with  escape  of  a  relatively 
minute  portion  of  its  contents.  In  the  former  case  a  certain  degree  of  immunity  has 
probably  been  established  during  the  slow  formation  of  the  pyosalpinx  (Binnie)  ;  and 
moreover,  in  many  such  cases  (61  per  cent.,  Penrose)  the  contained  pus  has  become 
sterile. 

When  the  inflammation  is  of  a  mild  grade  the  accumulation  may  be  of  a  serous 
character  (hydrosalpinx),  and  may  become  so  large  as  to  reach  half-way  to  the 
umbilicus.  If  hemorrhage  occurs  into  the  tube  it  is  called  an  htzmatosalpinx. 

The  proximity  of  the  right  Fallopian  tube  to  the  appendix  should  be  recalled,  as 
salpingitis  on  that  side  has  not  infrequently  been  mistaken  for  appendicitis,  and  vice 
versa.  The  right  ovary  is  often  connected  with  the  meso-appendix  by  a  fold  of  peri- 
toneum,— the  appendiculo-ovarian  ligament  ;  and  it  is  stated  that  the  fact  that  this 
fold  often  contains  a  small  artery  which  gives  an  additional  blood-supply  to  the  ap- 
pendix helps  to  account  for  the  relative  infrequency  of  appendicitis  in  females. 

RUDIMENTARY  ORGANS  REPRESENTING  FCETAL  REMAINS. 

The  development  of  the  reproductive  organs  (page  2042)  emphasizes  the  fact 
that  whereas,  in  the  male,  the  Wolffian  body  and  its  duct  play  a  very  important  r6le 
in  the  production  of  the  excretory  canals  for  the  sexual  gland,  and  .the  Miillerian  duct 
remains  rudimentary;  in  the  female,  the  converse  is  true,  the  Miillerian  ducts  forming 
the  excretory  canals — the  tubes,  the  uterus,  and  the  vagina — while  the  Wolffian 
structures  are  secondary  in  importance  and  give  rise  to  only  rudimentary  and  func- 
tionless  organs,  situated  chiefly  in  the  vicinity  of  the  ovary  and  Fallopian  tube  between 
the  layers  of  the  broad  ligament.  These  fcetal  remains  include  the  epoophoron, 
Gartner  s  duct,  the  paroophoron,  and  the  vesicular  appendages,  which  may  be  appro- 
priately described  in  this  place. 

The  Epoophoron. — This  rudimentary  organ,  parovariuni  or  organ  of 
Rosenmuller,  lies  between  the  layers  of  the  broad  ligament  (mesosalpinx  )  in  front 
of  the  ovarian  vessels,  in  the  area  bounded  by  the  ampulla  of  the  oviduct,  the 
ovarian  fimbria  and  the  tubal  pole  of  the  ovary.  It  is  quite  flat,  triangular,  or 


RUDIMENTARY  ORGANS. 


2001 


trapezoidal  in  outline,  and  measures  from  2-2.5  cnl-  m  length  and  about  1.75  cm. 
in  width.  It  consists  of  from  8-20  narrow  wavy  canals,  which,  beginning  with 
closed  and  slightly  expanded  ends,  diverge  from  the  vicinity  of  the  hilum  of  the 
ovary  and  join,  almost  at  right  angles,  a  common  chief  duct  that  lies  close  and  parallel 
to  the  oviduct  and  bears  to  the  smaller  tubules  the  relation  of  the  back  of.  a  comb  to 
its  teeth.  The  transverse  tubules  (ductuli  transversi),  the  remains  of  the  sexual 
tubules  of  the  Wolffian  body,  may  extend  as  far  as  the  hilum,  or,  as  in  the  young 
child,  even  penetrate  into  the  medulla  of  the  ovary  and  be  continuous  with  the  rudi- 
mentary medullary  tubes  therein  found,  since  the  latter,  as  well  as  the  transverse 
tubules  themselves,  are  vestiges  of  the  same  embryonic  structures.  The  common 
longitudinal  canal  (ductus  epoophori  longitudinalis),  closed  at  both  ends,  is  a  persistent 
portion  of  the  Wolffian  duct.  From  its  embryological  relations  it  is  evident  that  the 
epoophoron  is  homologous  with  the  epididymis  (the  transverse  tubules  corresponding 
to  the  ductuli  efferentes  and  the  coni  vasculosi,  and  the  longitudinal  duct  to  the 
canal  of  the  epididymis),  since  both  are  direct  derivations  from  the  Wolffian  tubules 
and  duct.  In  the  erect  posture,  when  in  its  normal  position  within  the  mesosalpinx, 
the  longitudinal  duct  is  approximately  vertical  and  lies  parallel  with  the  Fallopian 


FIG.  1696. 


Ligament 

Epoophoron    Oviduct    °f  ovary 
Ostium  <  I        f 

abtlominale         \  I     / 


Cavity  of 
uterus 


Ligament 
of  ovary 


Oviduct 
laid  open 


Hydatid  of 
Morgagni 


Left  ovary      |     V, 
•--^ 

Round  ligament 

Broad  ligament 


Epoophoron 
r  I  Infundibulum 


Fimbriae 
Fimbria  ovarica 
'Round  ligament 

Right  ovary 


^Vagina 


Broad  ligaments,  viewed  from  behind,  have  been  stretched  out  and  pinned,  the  posterior 
wall  of  uterus  and  vagina  removed  and  right  oviduct  laid  open.  Ovaries  do  not  occupy  their 
normal  position,  their  long  axes  here  being  horizontal  instead  of  approximately  vertical. 

tube,  while  the  transverse  tubules  are  horizontally  disposed.  The  chief  duct  may  be 
interrupted  and  connected  with  the  secondary  tubules  in  groups,  or,  on  the  other 
hand,  it  may  be  prolonged  as  Gartner's  duct  (page  2043)  far  beyond  its  usual  length. 
In  the  child,  the  transverse  tubules,  from  .3-.  4  mm.  in  diameter,  usually  possess  a 
lumen  throughout  their  entire  length,  but  later  in  life  the  minute  canals  may  undergo 
partial  or  complete  occlusion  and  may  be  the  seat  of  cystic  dilatations.  The  walls  of 
the  tubules  and  duct  consist  of  a  fibrous  coat,  which  sometimes  contains  bundles 
of  involuptary  muscle,  lined  by  a  single  layer  of  epithelial  cells  that  vary  in  form  from 
low  cuboid  to  columnar,  and  in  places,  or  occasionally  in  the  adult  and  frequently  in 
the  child,  bear  cilia.  The  epoophoron  is  most  satisfactorily  demonstrated  by  holding 
the  stretched  mesosalpinx  against  the  light  ;  it  is  more  conspicuous  in  the  broad  liga- 
ment of  the  young  child  on  account  of  its  development  and  the  greater  transparency 
of  the  overlying  tissues.  In  common  with  the  sexual  organs,  the  epoophoron  increases 
during  the  years  leading  to  sexual  maturity  and  atrophies  in  advanced  age.  During 
pregnancy  it  is  said  to  be  unusually  vascular  (Merkel). 

Gartner's  duct  results  from  the  more  or  less  extensive  persistence  of  portions 
of  the  Wolffian  duct  that  usually  disappear  by  the  end  of  fcetal  life,  and  is,  therefore, 
a  continuation,  direct  or  interrupted,  of  the  longitudinal  canal  of  the  epoophoron. 
Although  by  no  means  constant  and  often  represented  by  only  a  short  atrophic 

126 


2oo2  HUMAN   ANATOMY. 

segment,  the  duct  is  present  in  about  twenty  per  cent.  (Merkel)  of  adult  subjects,  in 
children  being  relatively  better  developed.  When  complete,  as  it  exceptionally  is, 
the  duct  continues  from  the  epoophoron  along  the  Fallopian  tube  to  the  fundus  of 
the  uterus,  then  descends  within  the  lateral  border  of  the  uterus,  between  the  vessels, 
and  sooner  or  later  (usually  in  the  lower  part  of  the  body)  enters  the  uterine  muscle. 
As  it  traverses  the  cervix,  the  duct  becomes  more  and  more  medially  placed  until,  in 
the  supravaginal  segment,  it  approaches  the  mucosa.  The  duct  then  assumes  a  more 
lateral  course,  and  in  the  vagina  descends  within  the  muscular  coat,  at  first  along  the 
side  and  lower  more  on  the  anterior  wall,  to  end  blindly  in  the  vicinity  of  the  hymen 
(R.  Meyer).  Such  complete  persistence  is,  however,  very  unusual,  Gartner's  duct 
being  most  frequently  represented  in  the  lower  part  of  the  body  and  the  upper  part 
of  the  cervix,  less  often  in  the  cervical  segment  alone  (Maudach).  The  canal  is  lined 
by  a  single  layer  of  columnar  epithelium  and  beset  with  lateral  diverticula,  uncertain 
in  number  and  form,  which  in  the  lower  part  of  the  duct  are  often  short-branched 
tubules  that  resemble  glands.  Accumulations  of  secretion  within  the  tubules  or  the 
duct  may  lead  to  the  production  of  cysts. 

The  Paroophoron. — Under  this  name  Waldeyer  described  an  inconspicuous 
rudimentary  organ,  distinct  at  birth,  but  usually  disappearing,  and  only  exceptionally 
retained  after  the  second  year,  that  lies  between  the  layers  of  the  mesosalpinx  medially 
to  the  epoophoron  and,  therefore,  nearer  the  uterus.  It  consists  of  a  small,  flat, 
irregularly  round  group  of  blind  canals,  which  represent  the  remains  of  Wolffian 
tubules.  The  accuracy  of  Waldeyer' s  assumption  that  this  organ  is  homologous  with 
the  paradidymis  (page  1950)  has  been  challenged  by  later  investigators  (Aschoff, 
R.  Meyer),  who  have  discovered  similar  groups  of  rudimentary  tubules  within  the 
lateral  part  of  the  mesosalpinx  near  the  division  of  the  ovarian  artery,  in  a  position 
corresponding  to  that  of  the  paradidymis.  It  is  to  this  group,  therefore,  that  the 
term,  paroophoron,  may  be  applied  with  greater  propriety,  although  there  can  be 
little  doubt  that  both  sets  of  tubules  are  deviations  from  those  of  the  Wolffian  body. 
The  tubules  are  blind,  lined  with  columnar  epithelium,  and  in  places  resemble  the 
tortuous  canals  of  the  Wolffian  body.  Apart  from  their  interesting  morphological 
relations,  they  may  become  of  importance  as  the  seat  of  cysts. 

Vesicular  Appendages. — Under  this  heading  are  included  the  little  vesicles  or 
hydatids  (appendices  vesiculosi)  attached  to  the  broad  ligament  by  longer  or  shorter 
pedicles.  These  structures  present  two  general  groups,  the  first  including  the  con- 
spicuous long-stalked  hydatids  of  Morgagni,  and  the  second  the  smaller  vesicles,  vary- 
ing in  form  and  size,  connected  by  short  stems.  The  hydatid  of  Morgagni,  present 
on  one  or  both  sides  in  fifty  per  cent,  or  over  of  all  female  subjects,  is  a  spherical  or 
pyriform  thin-walled  sac,  that  contains  a  clear  fluid,  and  usually  measures  from  4-8 
mm.  in  diameter,  but  sometimes  much  more,  and  is  attached  by  a  slender  stalk 
(from  1.5-4  cm-  in  length)  to  the  anterior  surface  of  the  broad  ligament.  Traced 
towards  the  latter,  the  stalk  crosses  the  ovarian  or  other  fimbriae  without  being 
attached  and  sinks  into  the  mesosalpinx  about  i  cm.  from  its  free  border,  from  which 
point  it  may  be  followed  through  the  broad  ligament  to  the  upper  end  of  the  main  or 
longitudinal  duct  of  the  epoophoron,  as  the  continuation  of  which  it  may  be  identified 
(Watson).  In  structure  the  hydatid  consists  of  a  fibrous  coat,  lined  by  a  layer  of 
columnar  epithelium  and  covered  externally  with  a  delicate  prolongation  of  the  peri- 
toneum. The  smaller  vesicles,  present  in  about  twenty  per  cent.  (Rossa),  often  num- 
ber two  or  three  on  each  side,  and  are  attached  to  the  anterior  surface  of  the  mesosal- 
pinx, usually  over  the  epoophoron.  They  are  found  at  birth  and  even  in  the  foetus, 
as  well  as  later  in  life,  in  advanced  age  undergoing  atrophy  The  origin  and  mor- 
phological significance  of  the  vesicular  appendages  have  occasioned  much  discussion, 
but  it  may  be  accepted  as  established  that  the  chief  hydatid  of  Morgagni  is  derived 
from  the  upper  end  of  the  Wolffian  (pronephric)  duct,  and  is,  therefore,  the  equivalent 
of  the  stalked  appendage  of  the  epididymis  (page  1949).  The  smaller  vesicles  prob- 
ably owe  their  origin  to  the  distention  and  elongation  of  the  transverse  canals  of  the 
epoophoron  (Rossa),  and,  hence,  are  derivatives  of  the  Wolffian  tubules. 


THE    UTERUS. 


2003 


FIG.  1697. 


Internal 


Peritoneum 
(perimetrium) 

Cavity  of 
body 


Posterior 
fornix 


External  os 


THE  UTERUS. 

The  uterus,  or  womb,  is  a  hollow  muscular  organ,  receiving  the  Fallopian  tubes 
above  and  opening  into  the  upper  part  of  the  vagina  below,  in  which  the  fertilized 
ovum  is  retained  and  undergoes  development,  and  from  which  the  resulting  foetus 
is  expelled  at  the  completion  of  pregnancy.  Its  lower  segment  is  embedded  within 
the  pelvic  floor  between  the  bladder  and  the  rectum,  while  its  upper  and  larger  end 
is  free  and  movable  and  rests  upon  the  superior  surface  of  the  bladder  (Fig.  1700). 
Before  undergoing  the  profound  changes  incident  to  pregnancy,  the  uterus,  pear- 
shaped  in  its  general  form,  measures  about  7  cm.  (2^  in.)  in  length,  of  which  the 
lower  2.5  cm.  (i  in.)  constitutes  the  cylindrical  neck  or  cervix  (cervix  uteri),  and  the 
remainder  the  body  (corpus  uteri).  Its  greatest  breadth  is  about  4  cm.  (iys  in.)  and 
its  thickness  about  2.5  cm.  (i  in.).  In  women  who  have  borne  children,  the  uterus 
seldom  quite  returns  to  its  virgin  size,  but  shows  a  permanent  increase  of  about  i  cm. 
in  its  various  dimensions,  except  in  the  cervix,  which  is  relatively  shorter  than  before. 
The  convex  upper  extremity  of  the  organ,  above 
the  level  of  the  entrance  of  the  Fallopian  tubes, 
is  known  as  the  fundus  (fundus  uteri),  which  in 
front  and  behind  passes  into  the  anterior  and 
posterior  surfaces  and  at  the  sides  into  the  lat- 
eral borders  (margo  late  rales).  Of  the  two  sur- 
faces, the  anterior  (facies  vesicalis)  is  the  more 
flattened  and  less  convex  and  only  partially  cov- 
ered with  peritoneum,  while  the  more  rounded 
and  projecting  posterior  surface  (facies  intesti- 
nalis)  is  completely  invested  with  serous  mem- 
brane. The  lower  end  of  the  cylindrical  cervix, 
flattened  somewhat  from  before  backward  and 
slightly  tapering  downward,  is  divided  by  the 
attachment  of  the  surrounding  vaginal  wall, 
which  it  seemingly  pierces,  into  a  free  lower  seg- 
ment (portio  vaginalis),  that  projects  into  the 
vault  of  the  vagina,  and  an  upper  one  above  the 
ring  of  attachment  (portio  supra  vaginalis).  Be- 
low, the  vaginal  segment  of  the  cervix  termi- 
nates in  thick,  rounded,  and  .prominent  lips  that 
bound  a  sunken  opening,  the  external  os  (ori- 
ficiura  externura  uteri)  that  marks  the  lower  limit 
of  the  cervical  canal  and  is  directed  towards  the 
posterior  vaginal  wall.  Owing  to  the  horizontal  position  of  the  cervix,  the  thicker 
anterior  lip  (labium  anterius  cervicis)  is  shorter  and  somewhat  lower  than  the  over- 
hanging posterior  lip  (labium  posterius  cervicis). 

The  weight  of  the  virgin  uterus  varies  between  forty  and  fifty  grammes  (i/^- 
i^  oz. ),  that  of  the  organ  after  pregnancy  being  about  twenty  grammes  (.7  oz. ) 
more. 

The  cavity  of  the  uterus  is  small  in  comparison  with  the  size  of  the  organ  and 
the  thickness  of  its  walls,  and  differs  in  form  according  to  the  plane  of  section.  In 
sagittal  section,  it  is  little  more  than  a  narrow  cleft  separating  the  opposed  anterior 
and  posterior  walls,  and  measures  about  6  cm.  (2^4  in.),  of  which  2.5  cm.  (i  in.) 
belongs  to  the  cervix.  In  frontal  section,  the  cavity  of  the  body  is  triangular  in  out- 
line (Fig.  1698),  the  apex  being  below,  where  the  upper  end  of  the  cavity  of  the  cer- 
vix passes  into  that  of  the  body,  and  the  base  above,  between  the  tubal  orifices  which 
mark  the  lateral  angles.  The  sides  of  the  triangle  are  not  straight  but  convex,  owing 
to  the  inward  curve  of  the  thick  projecting  uterine  walls.  The  greatest  transverse 
width  of  the  cavity  of  the  body,  just  below  the  tubal  openings,  is  about  2.5  cm. 

The  canal  of  the  cervix  (canalis  cervicis  uteri),  as  the  lower  segment  of  the  uterine 
cavity  is  called,  is  fusiform  in  longitudinal  sections,  being  widest  midway  between  the 
external  os  below  and  the  somewhat  smaller  and  more  circular  internal  os  (orificium 
internum  uteri)  above,  where  the  contracted  lumen  of  the  virgin  uterus  expands  into 


t 'torus  laid  open  by  sagittal  section,  showing 
cavity  and  relations  of  labia  to  vagina. 


2004 


HUMAN    ANATOMY. 


FlG.    i6g8. 


Oviduct 


Internal 


the  cavity  of  the  body.  In  cross-section  the  canal  appears  as  a  markedly  compressed 
oval.  The  position  of  the  internal  os  corresponds  with  the  slight  external  constriction 
(isthmus  uteri)  that  uncertainly  marks  the  neck  from  the  body  of  the  uterus.  In 
contrast  to  the  smooth  mucous  surface  of  the  body,  that  of  the  anterior  and  posterior 
walls  of  the  cervical  canal  is  marked  by  conspicuous  ridges  (plicae  palmatae) — the 
arbor  vita  uteriruz  of  the  older  writers — consisting  of  a  chief  median  longitudinal  fold 
from  which  numerous  secondary  rugae  divert  upward  and  outward  on  each  wall. 

Attachments  and  Peritoneal  Relations. — In  addition  to  the  Fallopian  tubes 
that  embryologically  are  direct  continuations  of  the  component  Miillerian  ducts  by 
the  fusion  of  which  the  uterus  is  formed,  the  uterus  is  connected  with  the  ovaries, 
the  abdominal  wall,  the  lateral  and  posterior  walls  and  the  floor  of  the  pelvis,  the 
vagina,  the  bladder,  and  the  rectum  by  fibre-elastic  tissue,  muscular  bands,  and  peri- 
toneal folds.  Most  of  these  attach- 
ments, or  so-called  ligaments,  however, 
have  little  influence  in  supporting  the 
uterus,  but,  owing  to  the  intimate  con- 
nection of  the  cervix  with  the  vagina, 
and  thus  with  the  pelvic  floor,  and  with 
the  sacrum  by  fibre-muscular  bands, 
the  lower  segment  enjoys  a  relatively 
fixed  position  ;  the  body,  on  the  con- 
trary, being  freely  movable. 

The  Broad  Ligament. — With  the 
exception  of  a  narrow  strip  along  the 
sides  between  the  layers  of  the  broad 
ligaments,  the  body  of  the  uterus  is 
completely  invested  by  peritoneum. 
The  cervix,  on  the  contrary,  possesses 
a  serous  covering  only  behind  and  at 
the  sides  above  the  attachment  of  the 
vagina.  From  each  lateral  border  of 
the  uterus  this  serous  investment  is 
reflected  to  the  pelvic  wall  and  floor 
as  a  conspicuous  transverse  duplicature 
of  peritoneum,  the  broad  ligament  ( lig- 
;i men tu in  latum),  that  passes  across  the  pelvis  and  encloses  between  its  layers  the  round 
and  ovarian  ligaments,  the  Fallopian  tube,  the  epoophoron  and  the  paroophoron, 
together  with  the  associated  vessels  and  nerves.  Although  enclosed  by  a  peritoneal 
duplicature  continued  from  its  posterior  surface,  the  ovary  is  attached  to,  rather  than 
lies  within,  the  broad  ligament.  When  detached  from  the  pelvic  wall  and  floor  and 
spread  out  (Fig.  1699),  the  broad  ligament  is  wing-like  in  form  and  has  four  borders, 
of  which  the  median  or  uterine  is  vertical,  the  upper  or  tubal  is  horizontal,  longest, 
and  free,  the  lateral  short  and  approximately  vertical  to  correspond  with  the  plane 
of  the  pelvic  wall,  and  the  lower  sloping  downward  and  inward  in  agreement  with  the 
direction  of  the  pelvic  floor.  Within  the  body,  the  plane  of  the  median  portion  of 
the  fold  depends  upon  the  position  of  the  uterus,  in  the  erect  posture  usually  extend- 
ing more  or  less  horizontally,  so  that  the  posterior  surface  presents  upward  and 
backward,  and  the  anterior  downward  and  forward  ;  when  the  uterus  assumes  an 
upright  position,  the  fold  likewise  becomes  erect.  On  nearing  its  lateral  attachment, 
the  upper  border  of  broad  ligament  becomes  not  only  more  vertical,  but  also  parallel 
with  the  pelvic  wall  in  consequence  of  the  support  afforded  by  the  suspensory  liga- 
ment of  the  ovary.  From  their  attachment  to  the  pelvic  walls  and  floor  the  two 
serous  layers  of  the  broad  ligament  pass  in  opposite  directions  and  are  continuous 
with  the  general  peritoneal  lining  of  the  pelvis.  Along  the  pelvic  floor  their 
divergence  leaves  a  non-peritoneal  interval  through  which  the  vessels  and  nerves 
and  the  ureter  gain  the  side  of  the  uterus. 

The  free  border  of  the  broad  ligament  is  occupied  by  the  Fallopian  tube,  the 
course  of  which  it  follows  as  far  as  the  outer  end  of  the  infundibulum,  and  thence 
passes  to  the  pelvic  wall  to  become  continuous  with  the  suspensory  ligament  of  the 


"^External  os 


•Vagina 


Uterus  laid  open  by  frontal  section,  showing 
form  of  cavity  "of  body  and  cervix. 


THE   UTERUS. 


2005 


ovary.  As  the  tube  crosses  the  medial  surface  of  the  latter  organ  the  broad  liga- 
ment is  drawn  over  it,  so  that  the  ovary  lies  partly  within  a  peritoneal  pocket,  the 
bursa  ovarii.  The  anterior  border  of  the  ovary  is  attached  to  the  posterior  surface 
of  the  broad  ligament  by  a  short  fold,  the  mcsovarium,  that  encloses  the  hilum  and 
is  continued  into  the  modified  serous  investment  that  covers  the  sexual  gland.  The 
utero-ovarian  ligament  and  the  attached  border  of  the  ovary  unequally  divide  the 
broad  ligament  into  an  upper  narrow  triangular  portion,  the  mesosalpinx,  that 
encloses  the  tube,  and  a  lower  broad  part,  the  mcsometrium,  that  passes  medially  to 
the  sides  of  the  uterus  and  becomes  continuous  with  the  perimetrium,  as  the  serous 
investment  of  that  organ  is  termed.  Within  the  mesosalpinx  the  connective  tissue 
filling  the  interval  between  the  two  serous  layers  of  the  broad  ligament  is  very  scanty, 
but  within  the  mesometrium  this  tissue  increases  to  a  considerable  stratum  and  con- 
tains numerous  strands  of  smooth  muscle  prolonged  from  the  uterus.  Surrounding 
the  uterus,  it  is  known  as  the  parametrium,  and  along  the  attached  borders  of  the 
ligament  laterally,  and  below,  becomes  continuous  with  the  general  subserous  layer 
of  the  pelvis. 

The  Round  Ligament. — In  addition  to  the  Fallopian  tube  and  the  ligament  of 
the  ovary,  already  described  (page  1987),   a  third  band,  the  round  ligament   (liga- 

FIG.   1699. 


Fallopian  tube,  ampulla     Ligament  of  ovary 


Abdominal  opening 
of  Fallopian  tube 


Epoophoron 


Mesosalpinx       |  Fallopian  tube 


Hydatid  of  Morgag 

Ovarian  fimbr 


Round  ligament 


Mesometriutn 


Anterior  wall  of  Douglas's  pouch/     I" 


Vagina 

Uterus  and  appendages  seen  from  behind  ;  broad  ligament  and 
oviduct  have  been  stretched  out  to  show  mesosalpinx. 


mentum  teres),  passes  on  each  side  from  the  upper  lateral  angle  of  the  uterus.  This 
structure,  a  flattened  cord  from  12-14  cm.  (4^-5^  in.)  long  and  about  .5  cm. 
thick,  springs  from  the  side  of  the  uterus,  in  front  and  below  the  entrance  of  the 
oviduct,  and  extends  (Fig.  1684)  between  the  layers  of  the  broad  ligament  horizon- 
tally outward  to  the  lateral  pelvic  wall,  which  it  reaches  near  the  floor.  Thence  it 
continues  its  course  beneath  the  peritoneum  forward  and  slightly  upward,  crosses  the 
obliterated  hypogastric  artery,  the  pelvic  brim,  and  the  external  iliac  vessels,  and, 
hooking  around  the  outer  side  of  the  deep  epigastric  artery,  gains  the  internal  ab- 
dominal ring.  Passing  through  the  latter  and  traversing  the  entire  length  of  the 
inguinal  canal,  the  round  ligament  emerges  from  the  external  abdominal  ring  and 
ends  by  breaking  up  into  a  number  of  diverging  fibrous  bands  that  become  mostly 
lost  in  the  subcutaneous  tissue  of  the  labium  majus,  while  a  few  find  attachment  to 
the  pubic  spine.  In  its  median  third  the  round  ligament  contains  robust  bundles  of 
involuntary  muscle  prolonged  from  the  superficial  layers  of  the  uterus,  but  beyond 
the  muscular  tissue  disappears,  and  in  its  lower  part  the  band  consists  entirely  of  fibro- 
elastic  tissue.  During  its  passage  through  the  inguinal  canal,  the  ligamentum  teres 
is  accompanied,  along  its  upper  border,  by  small,  short  bundles  of  striped  muscle 


2006 


HUMAN    ANATOMY. 


derived  from  the  internal  oblique  and  transversalis,  which  represent  a  feebly  developed 
cremaster  muscle.  After  gaining  the  pelvic  wall,  the  round  ligament  pursues  a  course 
very  similar  to  that  of  the  vas  deferens  ;  morphologically,  it  corresponds  to  the 
genito-inguinal  ligament  (page  2040).  In  the  foetus  the  round  ligament  is  preceded 
by  a  small  peritoneal  diverticulum  representing  the  larger  processus  vaginalis  peri- 
tonaei  in  the  male  ;  usually  this  disappears,  but  may  persist  as  a  distinct  serous  pouch, 
the  canal  of  Nuck,  that  accompanies  the  round  ligament  for  a  short  distance  within 
the  inguinal  canal.  In  exceptional  cases  it  may  extend  throughout  the  entire  length 
of  the  canal  into  the  labium  majus. 

The  peritoneal  relations  of  the  two  surfaces  of  the  uterus  (Fig.  1700)  are  dif- 
ferent, the  anterior  surface  being  covered  with  serous  membrane  only  as  far  as  the 

FIG.  1700. 


Ureter 


Suspensory 
ligament  of  ovary 

Fallopian  tube 


Round  ligament 
Ovary 

Obliterated 
hypogastric  artery 

Uterus 


Symphysis  pubis 


Urethra 


External  urethral 
orifice  in  vestibule 


s  uteri 


Bottom  of  recto- 
uterine  pouch 


.Vagina 


Perinea!  body 

Sagittal  section  of  pelvis  of  female. 

junction  of  the  body  and  cervix,  from  which  line  the  peritoneum  passes  on  to  the 
bladder  as  the  utero-vesical  fold  and  lines  the  shallow  utero-vesical  pouch  (excavatio 
vesicouterina).  Below  the  reflection  of  the  peritoneum  and  as  far  as  its  attachment  to 
the  vagina,  the  anterior  surface  of  the  cervix  is  connected  by  areolar  tissue  with  the 
adjacent  posterior  wall  of  the  bladder.  As  far  as  the  attachment  of  the  vaginal  wall, 
the  posterior  surface  of  the  uterus  is  covered  with  peritoneum,  which  then  continues 
downward  for  about  2.5  cm.  over  the  upper  part  of  the  back  wall  of  the  vagina  before 
being  reflected  onto  the  rectum  as  the  vagi  no-rectal  fold.  The  latter  forms  the  bot- 
tom of  the  deep  serous  pouch  of  Douglas  (excavatio  rectouterina)  that  lies  between  the 
uterus  in  front  and  the  rectum  behind.  The  lateral  boundaries  of  the  opening  into 
this  pouch  are  formed  by  the  two  crescentic  utero-rectal  folds  (plicae  rectouterina  )  that 
curve  from  the  hind  surface  of  the  cervix  backward  to  the  posterior  pelvic  wall  at  the 


THE   UTERUS.  2007 

sides  of  the  rectum.  Between  the  layers  of  these  folds  robust  bundles  of  fibrous  and 
smooth  muscular  tissue  extend  from  the  uterus  to  be  inserted  partly  in  the  rectum, 
there  constituting  the  utero-rectal  muscle,  and  partly  into  the  front  of  the  sacrum  as 
the  utero-sacral  ligament.  The  latter  structure  contributes  efficient  aid  in  supporting 
the  cervical  segment  of  the  uterus,  which  is  thus  enabled  to  maintain  its  position 
independently,  to  a  certain  degree,  of  that  of  the  body. 

Position  and  Relations. — The  attachment  of  the  cervix  to  the  vaginal  walls  and 
utero-sacral  ligaments  give  to  the  lower  uterine  segment  a  more  definite  position  than 
that  enjoyed  by  the  body,  which,  being  little  restrained  by  its  lateral  attachments,  is 
especially  affected  by  the  condition  of  the  bladder  and  rectum.  When  these  organs 
are  but  slightly  distended,  the  uterus  normally,  in  the  erect  posture,  lies  tilted  for- 
ward (anteverted),  with  the  body  resting  upon  the  upper  vesical  surface.  Since, 
under  these  conditions,  the  cervix  is  comparatively  fixed  and  directed  backward  and 
the  body  more  or  less  bent  forward  (antiflexed),  the  uterine  axis  exhibits  a  marked 
flexure  at  the  beginning  of  the  cervical  segment.  This  angle  varies  continually  with 
the  position  of  the  fundus,  which,  receiving  little  support  from  its  peritoneal  and 
other  attachments,  is  influenced  by  the  changing  condition  of  the  bladder.  When 
the  latter  is  contracted  and  the  uterus  strongly  anteflexed,  the  angle  is  more  pro- 
nounced than  when  the  upper  vesical  wall,  and  consequently  the  fundus,  lies  higher. 
With  increasing  distention  of  the  bladder  the  angle  gradually  disappears  and  the 
uterine  axis  becomes  straight  ;  in  excessive  vesical  expansion,  associated  with  an 
empty  rectum,  the  entire  uterus  may  be  tilted  backward  (retro verted),  its  axis  then 
corresponding  with  that  of  the  vagina.  When  both  bladder  and  rectum  are  dis- 
tended, the  entire  uterus  may  be  pushed  up  above  the  level  of  the  symphysis. 
Usually  the  fundus  does  not  lie  strictly  in  the  mid-line  but  to  one  side,  probably 
more  frequently  to  the  left  (Waldeyer,  Merkel).  This  deflection  may  also  affect 
the  axis  of  the  ovary  of  the  opposite  side,  which,  in  consequence  of  the  pull  thus 
exerted,  then  lies  more  obliquely  than  on  the  side  on  which  the  utero-ovarian  liga- 
ment is  relaxed.  The  anterior  surface  of  the  uterus  following  the  changes  of  the 
upper  vesical  wall  upon  which  it  lies,  the  utero-vesical  fossa  very  seldom  contains  in- 
testinal coils,  which,  on  the  contrary,  frequently  occupy  the  pouch  of  Douglas. 
The  posterior  (upper)  surface  of  the  uterus  is  overlaid  by  coils  of  the  small  intestine, 
and  may  also  be  in  contact  with  the  pelvic  and  sigmoid  colon.  Anteriorly,  below 
the  reflection  of  the  utero-vesical  fold,  the  lower  segment  of  the  uterus  is  connected 
with  the  posterior  bladder-wall  by  loose  connective  tissue  ;  posteriorly,  it  is  sepa- 
rated from  the  rectum  by  the  intervening  peritoneal  pouch  of  Douglas  ;  laterally,  it  is 
crossed  by  the  ureters,  which,  opposite  the  middle  of  the  cervix,  lie  about  2  cm.  from 
the  uterine  wall.  In  the  erect  position,  the  level  of  the  external  os  corresponds  ap- 
proximately with  that  of  the  upper  margin  of  the  symphysis,  and  in  the  antero- 
posterior  axis  lies  slightly  behind  a  frontal  plane  passing  through  the  ischial  spines 
{Waldeyer). 

Structure. — The  uterine  walls,  thickest  in  the  fundus  and  posterior  wall  of  the 
body,  where  they  measure  from  1-1.5  cm-'  and  somewhat  thinner  (from  8-9  mm.) 
at  the  entrance  of  the  tubes  and  in  the  cervix,  comprise  three  coats,  the  mucous, 
muscular,  and  serous.  The  mucous  coat,  or  endometrium,  of  a  light  reddish  color, 
soft,  and  friable,  and  from  .5-1  mm.  thick,  consists  of  a  connective-tissue  stroma, 
loose  in  texture  but  rich  in  cells  and  resembling  the  tunica  propria  of  the  intestinal 
mucous,  and  the  surface  epithelium.  The  latter  is  a  single  layer  of  columnar  cells, 
about  .028  mm.  high,  that  in  their  typical  condition  possess  cilia  by  which  a  down- 
ward current  is  established  towards  the  external  os.  It  is  probable,  however,  that 
the  cilia  are  neither  always  present,  nor  uniformly  distributed,  since  they  are  lost 
during  the  disturbances  incident  to  menstruation,  and  are  often  present  only  in 
patches  (Gage).  The  uterine  glands  are  simple  tubular,  or  slightly  bifurcated, 
wavy  invaginations  of  the  mucosa,  said  to  be  lined  with  a  single  layer  of  ciliated  col- 
umnar cells  resembling  those  covering  the  interior  of  the  uterus.  They  are  dis- 
tributed at  fairly  regular  intervals  and  extend  the  entire  thickness  of  the  mucosa, 
their  tortuous,  blind  extremities  in  many  cases  being  lodged  between  the  adjacent 
muscular  bundles,  since  a  distinct  submucosa  is  wanting.  In  the  vicinity  of  the  orifices 
of  the  Fallopian  tubes,  the  uterine  mucosa  becomes  thinner,  the  epithelium  lower, 


2OO8 


HUMAN   ANATOMY. 


Gland 
opening  on 
mucoussur- 
face. 


Gland 


and  the  glands  shorter  and  fewer,  until  they  finally  disappear,  glands  being  absent 
in  the  tubal  mucous  membrane. 

The  cervical  mucosa  differs  from  that  lining  the  body  in  being  somewhat  denser, 
owing  to  the  greater  amount  of  fibrous  tissue  within  its  stroma,  and  in  possessing  a 
taller  epithelium,  a  single  layer  of  columnar  cells  from  .040-.  060  mm.  in  height, 
and  larger  mucous  glands.  The  latter  (glandulae  cervicales  uteri),  from  1-1.5  mm! 
long  and  .5  mm.  wide,  are  branched  and  often  reach  with  their  blind  ends  between 
the  muscle  bundles.  The  mucus  secreted  by  these  glands  is  peculiar,  being  clear 
and  exceeding  tenacious,  and  sometimes  is  seen  as  a  plug  protruding  from  the 
external  os.  Not  infrequently  the  orifices  of  the  cervical  glands  become  blocked, 

which    condition    results    in 

FIG.    1701.  the  production  of  retention 

cysts  that  appear  as  minute 
vesicles  between  the  folds  of 
the  plicae  palmatae.  These 
bodies  were  formerly  de- 
scribed as  the  ovules  of  Na- 
both  (ovula  Nabothi).  The 
transition  of  the  cylindrical 
epithelium  of  the  cervical 
canal  into  the  squamous  cells 
covering  the  vaginal  portion 
of  the  uterus  takes  place  ab- 
ruptly at  the  inner  border  of 
the  external  os.  At  the  inner 
os,  where  the  cervical  mu- 
cosa passes  into  that  lining 
the  body,  the  change  is  so 
gradual  and  inconspicuous 
that  no  sharp  demarcation 
exists. 

The  muscular  coat,  or 
myometrium,  although  com- 
posed of  bundles  of  involun- 
tary muscle  arranged  with 
little  individual  regularity, 
may  be  resolved  into  a  robust 
inner  layer,  in  which  the 
bundles  possess  a  general 
circular  disposition,  and  a 
thin,  imperfect  outer  /aver  in 
which  their  course  is  for  the 
most  part  longitudinal.  The 
longitudinal  muscle  bundles 


Muscle  bun- 
dles invad- 
ing mucosa 


—  Blood-vessel 


Section  of  endometrium,  showing  uterine  glands 
cut  in  various  planes.     X  40. 


of  the  feeble  outer  layer,  which  is  present  only  over  the  fundus  and  body,  are  con- 
tinued beyond  the  uterus  onto  the  tubes  and  into  the  broad,  round,  ovarian  and 
utero-sacral  ligaments.  The  thick  inner  layer,  the  chief  component  of  the  myome- 
trium, is  distinguished  by  the  number  and  size  of  the  blood-vessels  that  traverse  the 
intermuscular  connective  tissue  and,  hence,  is  known  as  the  stratum  vascnlarc  (  Kreit- 
zer).  The  bundles  of  this  layer  are  confined  to  the  uterus,  except  below,  where 
they  become  continuous  with  the  muscle  of  the  vaginal  walls.  At  the  three  angles 
of  the  body,  corresponding  to  the  two  tubal  orifices  and  the  internal  os,  the  dispo- 
sition of  the  bundles  surrounding  these  openings  suggests  the  existence  of  distinct 
sphincters.  In  other  places  the  innermost  bundles  are  less  regularly  disposed  and 
are  oblique  or  even  longitudinal.  Within  the  cervix  the  outer  longitudinal  layer  is 
unrepresented,  the  musculature  of  this  segment  consisting  chiefly  of  circular  and 
oblique  bundles,  intermingled  with  a  considerable  amount  of  dense  fibrous  and  elastic- 
tissue  that  confer  upon  the  cervix  greater  resistance  and  hardness.  The  component 
fibre-cells  of  the  uterine  muscle  vary  in  form,  being  in  some  places  short  and  broad 


THE   UTERUS. 


2009 


and  in  others  long  and  spindle  form.  During  pregnancy  their  usual  length  (from 
.04o-.o6o  mm.)  may  increase  tenfold. 

The  serous  coat,  or  peri  met  rium^  continuous  laterally  with  the  peritoneal  invest- 
ment of  the  broad  ligament,  is  so  closely  adherent  to  the  uterine  muscle  over  the 
fundus  and  adjacent  parts  of  the  anterior  and  posterior  surfaces  that  it  is  removed 
with  difficulty.  Lower,  the  presence  of  the  intervening  loose  connective  tissue  ( para- 
mdrinm}  renders  the  attachment  less  intimate. 

Vessels. — The  arteries  supplying  the  uterus  are  the  two  uterine,  each  a  branch 
of  the  internal  iliac  that  accompanies  the  ureter  along  the  pelvic  wall,  behind  and 
below  the  ovarian  fossa,  to  the  attached  border  of  the  broad  ligament  beneath  which 
it  passes  in  its  course  to  the  uterus.  On  gaining  a  point  about  2  cm.  from  the 
cervix  and  on  a  level  with  the  internal  os  (Merkel),  the  uterine  artery  bends  medially 
and  crosses  the  ureter  obliquely  and  in  front.  It  then  traverses  dense  connective 
tissue,  and  on  approaching  the  lateral  wall  of  the  cervix  bends  sharply  upward  to 
course  between  the  layers  of  the  broad  ligament  along  the  lateral  borders  of  the 
uterus,  as  far  as  the  lateral  angle.  Immediately  below  the  ovarian  ligament  the 

FIG.  1702. 

Anterior  surface 

—  Longitudinal  muscle 

Blood-vessels 


• ,  ., 

ligament  en-        *  (t.  Jim1,      / /'    5  '/ 

"  " 


Mucosa  (endometrium)  /    '^'  V':  •''  jJS      >        -  ft    -i 

gp:  m 

'•••^  ••>. 


Longitudinal  muscle     -  -     £^L±^,~. ._' -:c^> 


—  Peritoneum  (perimetrium) 


Posterior  surface 
Transverse  section  of  uterus  through  body.     X  2. 


uterine  artery  divides  into  its  terminal  branches  distributed  to  the  fundus,  Fallo- 
pian tube,  and  ovary.  In  addition  to  a  small  branch  to  the  ureter,  just  before 
bending  upward  it  gives  off  the  vaginal  artery  that  passes  downward  and  assists 
in  supplying  the  cervix  and  the  vagina.  As  it  ascends  along  the  sides  of  the 
uterus,  from  5-10  mm.  removed  and  surrounded  by  a  dense  plexus  of  veins,  the 
very  tortuous  uterine  artery  sends  numerous  but  variable  branches  to  the  cervix  and 
body,  as  well  as  to  the  broad  ligament,  those  distributed  to  the  posterior  surface 
being  somewhat  larger  than  those  to  the  anterior  (Robinson).  The  terminal  branch 
passing  to  the  fundus  (ramus  fundi)  is  especially  strong  and  freely  anastomoses  with 
the  corresponding  vessel  from  the  opposite  artery,  thus  insuring  exceptional  vascu- 
larity  to  that  part  of  the  uterus  in  which  the  placenta  is  usually  attached  ( Charpy). 
Twigs  also  accompany  the  ovarian  and  round  ligaments.  After  the  establishment  of 
the  junction  between  the  ovarian  artery  and  its  ovarian  branch,  the  uterine  artery 
plays  am  important  part  in  maintaining  the  nutrition  of  the  ovary.  On  gaining  the 
muscular  coat  the  larger  branches  divide  into  vessels  that  penetrate  the  outer  layer 
of  the  myometrium  and  within  the  inner  muscular  layer  break  up  into  numerous 
minute  twigs  that  confer  upon  this  stratum  its  highly  vascular  character.  Within 


20io  HUMAN   ANATOMY. 

the  mucosa  the  capillaries  surround  the  glands  and  form  a  superficial  net-work  beneath 
the  epithelium. 

The  veins,  already  of  considerable  size  within  the  inner  muscular  layer,  emerge 
from  the  myometrium  and  form  a  dense  plexus  of  thin-walled  vessels  that  surround 
the  uterine  artery  at  the  sides  of  the  uterus  between  the  layers  of  the  broad  ligament. 
The  veins  are  arranged  as  an  upper,  middle,  and  lower  group.  The  first  of  these 
includes  the  veins  from  the  fundus  and  upper  part  of  the  body,  which  become  tribu- 
tary to  trunks  that  join  the  ovarian  veins  and  leave  the  pelvis  by  way  of  the  sus- 
pensory ligament.  The  middle  group  comprises  the  venous  radicles  from  the  lower 
half  of  the  body  and  upper  part  of  the  cervix  that  unite  into  one  or  two  main  stems 
that  accompany  the  uterine  artery.  The  lower  group  is  formed  by  the  veins  from 
the  most  dependent  part  of  the  uterus,  the  anterior  vaginal  wall,  and  the  posterior 
surface  of  the  bladder.  These  unite  into  robust  ascending  stems  that  become  tribu- 
tary to  the  trunks  following  the  uterine  artery.  •  The  middle  and  lower  groups  freely 
anastomose  with  the  vesical  plexus  and  also  communicate  with  the  hemorrhoidal 
plexus. 

The  lymphatics,  within  the  mucosa  not  demonstrable  as  definite  vessels  but  only 
as  uncertain  clefts,  constitute  an  intermuscular  net-work  of  which  the  larger  trunks 
follow  the  blood-vessels  and  establish  communication  between  the  cervical  lymphatics 
and  those  of  the  body.  On  emerging  from  the  myometrium  a  superficial  (subserous) 
plexus  is  formed,  especially  over  the  posterior  surface  in  the  vicinity  of  the  lateral 
angles  ;  large  trunks  also  accompany  the  blood-vessels  along  the  sides  of  the  uterus. 
The  lymphatics  from  the  cervix,  usually  two  or  three  stems,  pass  to  the  lymph-nodes 
occupying  the  angle  between  the  external  and  internal  iliac  arteries.  According  to 
Bruhns,1  those  from  the  remaining  parts  of  the  uterus  follow  different  paths  :  one 
set,  from  the  body,  goes  likewise  to  the  iliac  nodes  ;  another,  from  the  fundus, 
courses  towards  the  ovary,  and  in  company  with  the  trunks  from  the  latter  organ 
follows  the  ovarian  artery  to  terminate  in  the  lumbar  nodes.  A  third  set,  also  from 
the  fundus,  eventually  gains  the  lumbar  glands  after  joining  the  lymphatics  of  the 
Fallopian  tube,  while  a  fourth  group  diverges  from  the  fundus  along  the  round  liga- 
ment to  become  afferents  of  the  inguinal  lymph-nodes.  In  addition  to  free  anasto- 
mosis among  themselves,  the  uterine  lymphatics  communicate  with  those  of  the 
vagina,  rectum,  ovaries,  Fallopian  tubes,  and  broad  ligament. 

The  nerves  of  the  uterus,  being  chiefly  destined  for  the  involuntary  muscle, 
are  numerous  and  of  large  size  to  correspond  with  the  highly  developed  myome- 
trium. They  are  derived  not  only  from  the  sympathetic  system  from  the  utero- 
vaginal  subdivision  of  the  pelvic  plexus  (the  continuation  from  the  hypogastric),  but 
also  directly  from  the  second,  third,  and  fourth  sacral  spinal  nerves.  According  to 
the  classic  description  of  Frankenhiiuser,  the  utero- vaginal  plexus  divides  into  two 
parts,  the  smaller  of  which  is  distributed  to  the  posterior  and  lateral  parts  of  the 
uterus,  while  the  larger  includes  a  chain  of  minute  ganglia  along  the  cervix  and 
vaginal  vault.  One  of  these,  the  cervical  ganglion,  is  especially  large,  and  lies  behind 
the  upper  part  of  the  vagina,  receiving,  in  addition  to  the  sympathetic,  spinal  fibres 
from  the  sacral  nerves  and  giving  off  twigs  to  the  uterus.  These  latter  pass  to  the 
uterine  walls  between  the  layers  of  the  broad  ligament,  particularly  at  the  sides  in 
company  with  the  blood-vessels,  and  penetrate  the  myometrium,  to  the  fibre-cells  of 
which  the  nerve-filaments  are  chiefly  distributed  ;  others  pass  into  the  mucosa  to  end 
beneath  the  epithelium. 

Development  and  Changes. — In  consequence  of  the  medial  rotation  of  the 
ventral  border  of  the  Wolffian  body,  the  relations  of  the  Mullerian  to  the  Wolffian 
duct  change.  Instead  of  lying  laterally  to  the  Wolffian  duct,  as  it  does  above,  the 
Mullerian  duct  gains  the  inner  side  of  that  tube  as  they  pass  into  the  urogenital  fold 
(page  2038)  which  prolongs  the  lower  end  of  the  Wolffian  body  into  a  median 
strand  known  as  the  genital  cord.  Within  the  latter,  formed  by  the  fusion  of  the 
plicae  urogenitales,  the  two  Mullerian  ducts  lie  next  the  mid-line,  side  by  side  and  in 
contact  with  the  Wolffian  duct  on  either  hand.  Beginning  about  the  eighth  \v«  k. 
the  opposed  smtares  become  united,  the  intervening  septum  disappears  and  the  two 
Mullerian  ducts  are  converted  into  a  single  tube  from  which  the  uterus  is  derived. 

1  Archiv  f.  Anat.  u.  1'hys.,  1898. 


THE   UTERUS.  2011 

For  a  time  this  tube  ends  blindly  and  is  continued  to  the  urogenital  sinus,  with  which 
it  unites,  as  a  solid  cylinder  of  larger  cells  ;  this  lumenless  segment  of  the  fused 
Mullerian  ducts  represents  the  anlage  of  the  vagina.  The  extent  to  which  the 
Miillerian  ducts  undergo  fusion  is  early  indicated  by  a  sharp  inward  bend  of  these 
tubes  just  below  the  lower  and  medial  ends  of  the  Wolffian  bodies,  the  flexure  on 
each  side  corresponding  to  the  attachment  of  fibres  that  pass  to  the  anterior  abdom- 
inal wall  and  later  from  the  round  ligament.  The  portions  of  the  Mullerian  ducts 
above  this  point  remain  separate  and  ununited  and  become  the  oviducts,  those  below 
undergo  fusion  and  produce  the  uterus  and  vagina. 

After  the  vaginal  portion  of  the  united  Mullerian  ducts  acquires  a  lumen  (by 
the  end  of  the  fourth  month),  the  uterine  and  vaginal  segments  of  the  tube  are  dif- 
ferentiated by  the  tall  cylindrical  and  the  larger  cuboidal  epithelial  cells  that  line 
the  two  portions  respectively.  The  transition  zone,  which  becomes  progressively 
more  marked,  corresponds  to  the  position  where  later  the  cylindrical  uterine  epithe- 
lium changes  into  the  squamous  vaginal  cells  at  the  inner  margin  of  the  external  os. 
Soon  the  distinction  between  the  uterine  and  vaginal  portions  of  the  genital  canal  is 
additionally  emphasized  by  the  forward  curve  of  the  former  and  the  straighter 
downward  course  of  the  latter.  The  more  definite  division  of  the  uterus  from  the 
vagina  is  effected  by  the  appearance  of  crescentic  thickenings  of  the  anterior  and 
posterior  walls  of  the  canal  which  mark  the  beginnings  of  the  corresponding  lips  of 
the  cervix.  Distinction  between  the  body  and  cervix  is  early  suggested  by  the 
uterine  epithelium,  the  cells  lining  the  lower  portion  being  taller,  more  cylindrical 
and  numerous  than  those  of  the  body.  The  connective  and  muscular  tissue  of  the 
uterine  wall  are  differentiated  from  the  condensed  mesoderm  that  surrounds  the 
epithelial  tube.  Distinct  muscle  is  not  distinguishable  before  the  fifth  month,  about 
which  time  the  cervical  glands  also  make  their  appearance  (Nagel),  thus  anticipa- 
ting by  some  weeks  the  development  of  the  glands  in  the  corpus  uteri. 

At  birth  the  uterus  measures  about  3  cm.  in  length,  of  which  the  cervix  con- 
tributes more  than  half,  and  is  thicker  and  denser  than  the  thin-walled  and  flaccid 
body.  The  characteristic  arched  form  of  the  fundus  is  lacking  and  the  lateral 
angles  are  prolonged  into  the  tubes,  often  recalling  a  bicornate  condition.  The 
portio  vaginalis  is  inconspicuous  and  projects  to  only  a  slight  degree,  although  the 
plicae  palmatae  are  well  developed  and  not  limited,  as  they  later  are,  to  the  cervical 
canal,  but  extend  throughout  the  uterine  cavity.  Since  at  this  time  the  internal  os  is 
still  immature,  the  division  of  the  uterine  cavity  into  an  upper  and  a  lower  segment 
is  only  suggested.  The  general  position  of  the  uterus  is  higher  than  later,  it, 
together  with  the  bladder,  lying  above  the  level  of  the  pelvic  brim,  with  the  fundus 
opposite  about  the  fifth  lumbar  vertebra  (Merkel).  With  the  increasing  capacity  of 
the  pelvis,  the  uterus  sinks,  so  that  by  the  end  of  the  sixth  year  the  external  os  is 
little  higher  than  in  the  adult  (Symington).  Apart  from  the  gradual  development 
of  the  glands  and  the  disappearance  of  the  folds  of  the  mucosa  within  the  body, 
during  childhood  the  uterus  grows  slowly  until  near  puberty,  when  the  body 
thickens,  lengthens,  and  acquires  the  arched  contours  of  its  mature  form.  In  its 
relatively  long  cervix  and  slightly  prominent  fundus,  the  uterus  of  the  virgin  retails 
the  characteristics  of  early  childhood.  The  repeated  changes  incident  to  the  men- 
strual cycle,  produce  gradual  thickening  of  the  uterine  walls  and  enlargement  of  the 
lumen,  so  that,  even  independently  of  pregnancy,  the  uterus  increases  somewhat  in 
size  and  weight  during  the  years  of  sexual  activity. 

After  the  cessation  of  menstruation,  between  the  forty-fifth  and  fiftieth  years, 
the  uterus  suffers  gradual  atrophy  (involution).  This  first  affects  the  cervix,  which 
becomes  smaller  and  more  slender,  the  entire  organ  in  consequence  assuming  a 
more  pronounced  pyriform  outline.  The  general  reduction  in  the  size  and  prom- 
inence of  the  vaginal  portion  is  accompanied  by  atrophy  of  the  plicae  palmatae  of  the 
cervical  canal.  The  walls  of  the  body  are  also  involved  and  become  thinner  and 
less  resistant  with  atrophy  of  the  muscular  tissue  and  decreased  vascularity,  and 
hence  paler  color,  of  the  mucosa.  For  a  time  the  uterine  cavity  is  enlarged,  but, 
later,  sharing  in  the  general  atrophy  and  not  inconsiderable  diminution  in  size  of  the 
organ,  the  lumen  likewise  undergoes  reduction  and,  in  some  cases,  suffers  obliteration 
in  the  vicinity  of  the  internal  os. 


2012  HUMAN   ANATOMY. 

Changes  during  Menstruation  and  Pregnancy. — Although  liberation  of  a  mature  ovum 
may  occur  at  any  time,  such  independence  is  exceptional,  and  in  the  vast  majority  of  cases 
o\  ulution  and  menstruation  are  synchronous  processes,  the  uterine  changes  occurring  regularly, 
every  twenty-eight  days,  only  when  the  ovaries  are  functionally  active.  In  anticipation  of  the 
possible  reception  of  a  fertilixed  ovum,  the  uterine  mucous,  membrane  becomes  swollen,  exces- 
sively vascular  and  hypertrophied,  with  conspicuous  enlargement  of  the  subepithelial  blood- 
vessels and  the  glands.  The  resulting  thickened  and  modified  mucosa,  now  from  3-6  mm. 
in  thickness,  offers  a  soft  velvety  surface  favorable  for  the  implantation  of  the  embryo-sac. 
Should  this  purpose  be  realixed,  the  hypertrophy  proceeds,  and  the  lining  of  the  uterus  is  con- 
verted into  the  deciduu?  and  takes  an  important  part  in  the  formation  of  the  placenta  and  at- 
tached membranes  (page  44).  If,  on  the  contrary,  fertilization  does  not  occur,  the  proliferative 
processes  are  arrested  and  the  hypertrophied  mucosa  (now  called  the  dccidua  nicnstrualis} 
enters  upon  regression.  Incidental  to  the  latter  are  subepithelial  extravasation  and  rupture  and 
partial  destruction  of  the  epithelium,  followed  by  the  characteristic  discharge  of  blood.  While 
usually  the  destruction  of  the  mucosa  is  limited  to  the  epithelium,  it  is  probable  that  at  times 
the  superficial  layer  of  the  subjacent  tissue  is  involved. 

During  pregnancy  the  most  conspicuous  changes  are  occasioned  by  the  growth  necessary 
to  accommodate  the  rapidly  augmenting  volume  of  the  uterine  contents,  by  the  provision  of  an 
adequate  source  of  nutrition  and  protection  for  the  fcetus,  and  by  the  development  of  an  efficient 
contractile  apparatus  for  the  expulsion  of  the  same.  From  an  organ  ordinarily  weighing  about 
45  grams  (\y2  oz.),  measuring  7  cm.  in  length  and  possessing  a  capacity  of  from  3-5  cc.,  by  the 
close  of  pregnancy  the  uterus  has  expanded  into  a  rounded  or  oval  sac  about  36  cm.  (14  in. )  in 
its  greatest  length,  from  900-1000  grm.  (about  2  Ibs. )  in  weight  and  with  a  capacity  of  5000  cc. 
(169  fl.  oz. )  or  more.  This  enormous  increase  depends  especially  upon  the  hypertrophy  of  the 
muscular  coat  of  the  organ,  which  during  the  first  half  of  pregnancy  becomes  greatly  thickened, 
but  later  thinner  and  membranous  owing  to  stretching.  The  increase  in  this  coat  results  from 
both  the  growth  of  the  previously  existing  muscle-cells  and,  during  the  first  half  of  pregnancy, 
the  development  of  new  muscle  elements.  The  individual  cells  may  increase  tenfold  in  length 
and  measure  between  -4-.5  mm.  Although  the  cervix  actually  almost  doubles  in  size,  its  growth 
is  overshadowed  by  that  of  the  body,  since  it  remains  relatively  passive.  During  the  first  five 
months,  the  mucous  membrane  of  the  body  of  the  uterus  also  becomes  greatly  hypertrophied, 
in  places  attaining  a  thickness  from  7-10  mm.  The  glands  and  blood-vessels,  particularly  the 
arteries,  enlarge  and,  within  the  specialized  area,  are  concerned  in  the  formation  of  the  placenta 
(page  48).  The  cervical  mucosa  takes  no  direct  part  in  the  formation  of  the  deciduae,  although 
it  thickens  and  is  the  seat  of  enlarged  glands  that  secrete  the  plug  of  mucus  that  for  a  time 
occludes  the  mouth  of  the  uterus. 

After  the  termination  of  pregnancy,  the  uterus  enters  upon  a  period  of  involution  and 
repair,  the  excessive  muscular  tissue  undergoing  degeneration  and  absorption  and  the  lacerated 
mucosa  regeneration,  the  latter  process  being  completed  in  from  five  to  six  weeks  (Minot).  In 
sympathy  with  the  growth  of  the  myometrium,  the  round  ligaments  enlarge  and  also  show  marked 
augmentation  of  their  muscular  tissue.  The  peritoneal  relations  are  disturbed  by  the  excessive 
bulk  of  the  uterus,  so  that  at  the  sides  the  layers  of  the  broad  ligament  become  separated. 

Variations. — The  chief  anomalous  conditions  of  the  uterus  depend  upon  defective  devel- 
opment or  imperfect  fusion  of  the  Mullerian  ducts  by  the  union  of  which  the  normal  organ  is 
formed.  Arrested  development  of  the  lower  part  of  these  fcetal  canals  accounts  for  entire  ab- 
sence of  the  uterus  and  vagina.  Depending  upon  the  extent  to  which  failure  of  fusion  occurs, 
all  degrees  of  doubling  are  produced.  In  the  most  pronounced  cases,  in  which  the  Mullerian 
ducts  remain  separate  throughout  their  entire  length,  two  completely  distinct  uteri  and  vagina' 
may  result,  each  pair  being  capable  of  performing  the  functions  of  the  normal  organs.  On  the 
other  hand,  slight  indentation  of  the  fundus  may  be  the  only  evidence  of  imperfect  union.  Be- 
tween these  extremes  all  gradations  occur  ;  the  "body  may  be  completely  cleft  ( uterus  informs), 
with  or  without  divided  cervix  ;  or  the  duplicity  may  be  partial  and  limited  to  branching  of  the 
fundus  ;  or  the  faulty  fusion  may  be  manifested  by  only  a  partition,  more  or  less  complete,  that 
divides  the  uterine  cavity  into  two  compartments  (it ferns  S<-/>/HS),  although  the  external  form  of 
the  organ  is  almost  or  quite  normal.  When,  in  conjunction  with  any  of  the  foregoing  variations, 
one  of  the  component  Miillerian  ducts  fails  to  keep  pace  in  its  growth,  all  decrees  of  asymmet- 
rical development  may  result,  from  complete  suppression  of  one  of  the  tubes  in  a  bicornate  uterus 
to  merely  unilateral  diminution  of  the  fundus.  Subsequent  arrest  of  what  to  a  certain  stage  was 
a  normal  development  may  result  in  permanent  retention  of  the  fcetal  or  infantile  type  of  uterus. 

PRACTICAL  CONSIDERATIONS  :    UTERUS  AND  ITS  ATTACHMENTS. 

In  the  female  the  pelvis  is  subdivided  into  two  compartments  by  a  fold  of  peri- 
toneum reflected  from  the  floor  and  sides  of  the  cavity.  This  fold  passes  from  one 
side  to  the  other  and  includes  between  its  layers  in  the  median  line  the  uterus.  On 
each  side  of  the  uterus  it  is  known  as  the  broad  ligament,  and  encloses  the  uterine 


PRACTICAL   CONSIDERATIONS:    THE   UTERUS.  2013 

appendages,  their  blood-vessels,  together  with  their  nerves  and  their  enveloping 
connective  tissue.  This  transverse  fold  of  peritoneum  is  analogous  to  the  mesentery 
of  the  small  intestine,  serving  the  same  purpose  for  the  uterus  and  its  appendages — 
i.e.,  to  hold  them  in  position  and  to  transmit  their  blood-vessels  and  nerves. 

The  posterior  compartment  of  the  pelvis,  the  recto- uterine,  is  the  larger  and 
deeper  of  the  t\vo.  The  lower  portion  of  it,  included  between  the  two  recto-uterine 
folds  of  the  peritoneum,  is  the  pouch  of  Douglas,  or  recto-vaginal  pouch,  because  it 
lies  between  the  rectum  and  the  upper  fourth  of  the  vagina,  from  which  it  is  separated 
only  by  subperitoneal  connective  tissue.  The  rectum,  bulging  forward  the  posterior 
wall,  and  the  ovaries,  hanging  from  the  anterior  wall,  tend  to  fill  this  compartment, 
the  remaining  space  being  occupied  by  small  intestine  and  a  portion  of  the  sigmoid 
flexure. 

Abnormally  it  may  be  encroached  upon  by  a  retroposed  uterus,  which  tends  to 
drag  downward  and  backward  its  appendages,  the  tubes  and  ovaries,  towards 
Douglas's  pouch,  where  they  may  be  palpated  by  the  finger  through  the  vagina. 
Because  of  the  greater  depth  of  the  posterior  compartment  and  because  of  the  fact 
that  abscess  and  other  pelvic  operative  conditions  are  usually  situated  in  it,  it  must 
almost  always  be  drained,  if  drainage  is  necessary  after  operation  in  this  region. 

The  anterior  or  vesico- uterine  compartment  of  the  pelvis  extends  below  only 
to  the  isthmus  of  the  uterus.  The  remaining  supravaginal  portion  of  the  cervix 
is  in  close  relation  to  the  bladder,  but  the  loose  intervening  layer  of  subperitoneal 
tissue  permits  a  ready  separation  of  the  two  in  the  operation  for  the  removal  of 
the  uterus  (hysterectomy).  Since  the  body  of  the  uterus  inclines  forward,  nor- 
mally, touching  the  bladder,  the  space  in  this  compartment  is  slight.  It  excep- 
tionally contains  a  few  coils  of  small  intestine,  and  may  lodge  also  a  part  of  the 
sigmoid  flexure. 

A  tumor  or  pregnant  uterus  filling  the  pelvis  may  press  upon  the  iliac  veins, 
producing  cedema  and  varicose  veins  of  the  lower  extremities,  of  the  vulva,  and  of 
the  rectum  (hemorrhoids)  ;  upon  the  lumbar  and  sacral  nerves,  causing  cramps, 
neuralgia,  or  paralysis  ;  upon  the  bladder,  with  resulting  vesical  irritability  and  pain  ; 
upon  the  rectum,  inducing  constipation  and  hemorrhoids  ;  upon  the  ureters,  giving 
rise  to  hydronephrosis  ;  or  upon  the  renal  veins  and  kidney,  producing  albuminuria 
and  possibly  uraemia. 

The  uterus  is  held  in  position  between  the  bladder  and  the  rectum  by  its  liga- 
ments, and  is  kept  from  dropping  to  a  lower  level  (prolapse)  mainly  by  the  support 
received  from  atmospheric  pressure  acting  through  the  floor  of  the  pelvis.  The  broad 
or  lateral  ligaments  attach  it  and  its  appendages — the  Fallopian  tubes  and  ovaries 
— to  the  sides  of  the  pelvis.  The  round  ligaments  act  chiefly  in  tending  to  prevent 
retro-displacements.  The  musculo-fibrous  utero-sacral  ligaments  and  the  anterior  and 
posterior  reflections  of  peritoneum  materially  steady  the  cervix,  which  is  also  fixed  by 
its  attachments  to  the  bladder  and  vagina.  Moreover,  the  intra-abdominal  pressure 
applied  through  the  intestinal  convolutions  that  are  normally  in  contact  with  its 
posterior  surface  aids  in  holding  it  in  position.  The  body  of  the  uterus  is  more 
freely  movable  than  the  cervix,  and  in  spite  of  its  supports  the  uterus,  as  a  whole,  is 
one  of  the  most  mobile  of  the  viscera.  The  cervix,  for  example,  may  easily  be  made, 
through  traction  by  means  of  a  tenaculum,  to  present  at  the  orifice  of  the  vagina,  in 
such  operations  as  amputation  of  the  cervix,  repair  of  lacerations,  or  dilatation  and 
curettement.  On  account  of  its  mobility,  its  intrapelvic  situation,  and  the  elastic 
support  received  from  the  bladder,  and  indirectly  from  the  levator  ani  muscles,  the 
uterus  is  very  rarely  injured  by  blows  on  the  abdomen.  If  upon  examination  it  is 
found  to  be  fixed,  or  not  easily  movable,  some  abnormal  cause  should  be  sought  for, 
such  as  pelvic  inflammations  or  tumors. 

The  essential  conditions  in  the  production  of  a  prolapsed  uterus  obtain  when  the 
uterus  is  the  seat  of  subinvolution  from  any  cause,  especially  a  puerperal  infection, 
and  the  pelvic  floor  is  relaxed  or  torn.  The  stretching  of  the  pelvic  ligaments  has 
then  not  been  fully  overcome  by  later  contraction,  and  the  atmospheric  support 
(dependent  upon  a  tightly  closed  vaginal  outlet)  is  lacking  because  of  the  weak- 
ened perineal  floor.  As  the  uterus  reaches  a  lower  level  its  ligaments  become  truly 
' '  suspensory' '  and  resist  its  further  downward  progress  as  soon  as  their  uterine  attach- 


2014  HUMAN   ANATOMY. 

ments  are  below  their  pelvic  attachments.  Normally  their  insertions  and  origins  lie 
approximately  in  the  same  horizontal  plane  when  the  woman  is  erect  (Penrose). 

The  integrity  of  the  levator  ani  muscle,  ensuring  a  well-closed  vaginal  outlet,  is 
the  most  important  factor  in  supporting  the  uterus  within  the  pelvis.  It  keeps  the 
outlet  forward  under  the  pubic  arch  out  of  the  line  of  abdominal  pressure,  gives  it  the 
form  of  a  narrow  slit,  preventing  the  protrusion  of  the  pelvic  viscera,  and  directs  the 
axis  of  the  vaginal  canal  forward  instead  of  directly  downward,  so  that  the  intra- 
abdominal  pressure  strikes  the  pelvic  floor  at  a  right  angle  ;  and  by  aiding  in  main- 
taining the  vagina  in  its  normal  condition  of  a  closed  slit  with  its  walls  in  contact,  it 
prevents  disturbance  of  the  forces  which  hold  the  uterus  in  place.  If  a  laceration  of 
the  perineum  converts  the  vagina  into  an  open  air-containing  tube,  the  equilibrium  of 
these  forces  is  destroyed  and  prolapse  often  follows.  In  severe  cases  of  prolapse  the 
ureters  are  so  stretched  that,  at  their  vesical  ends,  their  lumen  is  narrowed  and 
ureteral  dilatation  or  hydronephrosis  may  result. 

Anterior  and  posterior  flexions  of  the  uterus  occur  at  the  isthmus,  which  is  the 
weakest  point  and  is  the  junction  of  the  larger  and  more  movable  portion — the  body 
— with  the  smaller  and  more  fixed  portion — the  cervix. 

On  account  of  the  normal  anteflexion  of  the  uterus,  it  is  not  always  easy  to 
decide  in  a  given  case  whether  the  degree  of  anteflexion  is  normal  or  abnormal. 
When  it  is  abnormal  the  most  important  symptom  is  dysmenorrhcea,  from  obstruc- 
tion of  the  canal  by  the  flexion  ;  if  irritability  of  the  bladder  occurs,  it  is  probably 
reflex  in  its  origin. 

Anything  which  weakens  the  support  of  the  uterus,  or  increases  its  weight, 
tends  not  only  to  cause  prolapse,  but  also  to  the  production  of  retroflexion  or  retro- 
version  of  the  uterus,  the  first  degree  of  prolapse  being  associated  with  some  retro- 
displacement.  The  uterus  then  loses  its  normal  anteversion,  and  the  intra-abdominal 
pressure  is  brought  to  bear  on  its  anterior  surface,  especially  if  the  patient  is  either 
confined  too  long  in  the  supine  position  after  labor,  with  the  abdomen  too  tightly 
bandaged,  or  if  she  leaves  her  bed  too  soon  or  undertakes  any  physical  work. 

The  uterus  is  larger  and  heavier  than  normal,  as  a  result  of  imperfect  involution  ; 
the  uterine  ligaments  are  lax  ;  the  vagina  and  the  vaginal  orifice  are  relaxed,  and 
the  support  of  the  pelvic  floor  is  consequently  deficient  ;  the  abdominal  walls  are 
flabby  and  the  retentive  power  of  the  abdomen  is  diminished.  These  are  also  the 
causes  that  favor  prolapse  of  the  uterus  ;  in  fact,  a  slight  degree  of  uterine  prolapse 
usually  accompanies  such  cases  of  retrodisplacement.  A  certain  amount  of  retro- 
version  must  always  exist  before  the  uterus  can  pass  along  the  vagina.  It  must  turn 
backward,  so  that  its  axis  becomes  parallel  to  the  axis  of  the  vagina  (Penrose). 

In  the  purely  retroverted  positions  the  uterus  revolves  on  the  isthmus  as  on  a 
pivot,  so  that  as  the  fundus  goes  in  one  direction  the  cervix  passes  in  the  other. 
Therefore,  as  the  cervix  is  turned  forward  against  the  base  of  the  bladder,  the  fundus 
presses  backward  on  the  rectum,  often  producing  reflex  symptoms. 

The  uterus  may  be  found  inclined  to  one  side — more  usually  the  fundus  to  the 
left,  and  the  cervix,  on  account  of  the  presence  of  the  sigmoid  and  rectum  on  the  left 
side,  to  the  right.  Unless  extreme,  such  inclination  is  not  to  be  regarded  as  patho- 
logical. 

Between  the  layers  of  the  broad  ligaments  is  a  quantity  of  loose  adipose  cellu- 
lar tissue,  the  parametrium,  separating  the  contained  structures — those  of  the  most 
importance  being  the  tubes  and  ovaries  with  their  vessels  and  nerves — from  one 
another  and  from  the  serous  membrane.  This  cellular  connective  tissue  is  continuous 
with  the  surrounding  subperitoneal  areolar  tissue  of  the  pelvis,  and  is  especially 
abundant  near  the  base  of  the  broad  ligaments. 

In  f>chic  cell  id  itis  there  is  infection  of  this  loose  cellular  tissue,  usually  through 
the  lymphatics  and  often  puerperal  in  origin.  It  may  follow  other  septic  intrapdvic 
conditions,  especially  salpingitis,  but  a  simple  cellulitis  unaccompanied  by  tubal 
inflammation  is  in  the  vast  majority  of  cases  due  to  infection  through  the  uterus  from 
a  septic  endometritis.  Because  of  the  laxity  of  the  tissue  it  may  spread  rapidly  and 
extensively  in  virulent  cases.  It  may  extend  backward  along  the  utero-sacral  liga- 
ments, then  upward  along  the  retroperitoneal  tissue,  as  far  as  the  kidneys.  It  may 
pass  forward  and  upward  to  the  groin,  where,  should  an  abscess  form,  it  may  be 


PRACTICAL   CONSIDERATIONS:    THE   UTERUS.  2015 

opened.      It  may  also  burrow  into  the  vagina  or  rectum.      Suppuration  takes  place, 
however,  in  only  a  small  percentage  of  cases. 

The  condition  is  usually  recognized  by  the  rapid  swelling  and  induration  at  the 
sides  of  or  behind  the  uterus,  and  in  closer  relation  to  it  than  is  the  swelling  of  a  pyo- 
salpinx  or  of  an  ovarian  abscess.  Pelvic  collections  of  pus  of  this  nature  may  be 
evacuated  through  the  vagina  by  an  incision  made  close  to  the  cervix, — to  avoid  the 
ureters  and  the  uterine  arteries  ;  but  it  should  be  remembered  that  this  procedure 
does  not  remove  the  focus  of  primary  infection,  such  as  a  diseased  Fallopian  tube. 

Blood  collections  (haematoceles)  or  tumors  (intraligamentous)  may  also  occur 
between  the  layers  of  the  broad  ligaments. 

The  narrow  lower  border  of  each  ligam  ^nt  lies  on  the  floor  of  the  pelvis,  but  is 
separated  from  it  by  a  thick  layer  of  subperitoneal  tissue,  in  which  the  uterine  artery 
with  its  veins  passes  nearly  transversely  inward  from  the  internal  iliac  artery  at  the 
side  of  the  pelvis  to  the  cervix  at  about  the  level  of  the  vault  of  the  vagina. 

The  ureter,  on  its  way  from  behind  forward  to  the  bladder,  passes  through  this 
loose  cellular  tissue  just  below  the  base  of  the  broad  ligament.  It  lies  close  under 
the  uterine  artery  from  one-half  to  one  inch  from  the  side  of  the  cervix.  It  is  within 
this  short  distance  that  the  uterine  vessels  are  tied,  either  from  within  the  abdomen 
or  from  the  vagina,  according  to  the  method  of  operation,  in  the  removal  of  the 
uterus  (hysterectomy).  The  inclusion  of  the  ureter  within  the  ligature  is  one  of  the 
greatest  dangers  in  this  operation.  This  accident  is  more  likely  to  occur  if  the 
artery  is  crowded  closer  to  the  ureter  of  one  side,  by  a  tumor  or  other  mass,  in  the 
opposite  side  of  the  pelvis.  The  ureter  is  also  in  danger,  as  it  lies  along  the  side  and 
floor  of  the  posterior  compartment  of  the  pelvis.  It  may  there  be  injured  in  the 
removal  of  adherent  masses,  such  as  inflamed  tubes  and  ovaries,  or  of  retroperitoneal 
tumors  or  cysts.  Calculi  in  the  vesical  ends  of  the  ureters  may  be  removed  through 
the  vaginal  wall  (page  2020). 

The  free  upper  border  of  the  broad  ligament  between  the  fimbriated  extremity 
of  the  tube  and  ovary  and  the  side  of  the  pelvis — the  suspensory  ligament  of  the 
ovary  or  the  infundibulo-pelvic  ligament — is  of  practical  importance  because,  in 
addition  to  supporting  the  ovary,  it  contains  the  ovarian  vessels  where  they  are  usu- 
ally tied  in  the  operations  for  the  removal  of  the  uterus  or  its  appendages.  Kelly 
calls  attention  to  a  space  immediately  below  the  vessels  in  this  region,  where  the  two 
layers  of  the  peritoneum,  forming  the  broad  ligament,  come  close  together.  By  pass- 
ing a  ligature  through  this  membranous  interval  and  tying  over  the  top  of  the  broad 
ligament,  all  the  ovarian  veins  and  the  artery  are  included.  If  the  uterine  vessels 
also  are  tied  by  a  separate  ligature,  at  the  cornu  of  the  uterus,  there  should  be  no 
danger  of  hemorrhage  in  a  salpingo-oophorectomy ;  or,  if  the  uterine  vessels  are 
secured  at  the  sides  of  the  cervix,  in  the  floor  of  the  pelvis,  and  the  ovarian  vessels 
are  ligated,  as  above,  on  both  sides  of  the  pelvis,  the  hemorrhage  will  be  controlled 
for  a  hysterectomy. 

The  round  ligaments,  passing  outward  and  forward  from  the  sides  of  the 
uterus  through  the  internal  ring  and  inguinal  canals  to  the  labia  majora,  tend  by  their 
direction  to  maintain  the  uterus  in  its  normal  anteflexed  position.  When  retrodis- 
placements  of  the  uterus  do  occur  these  ligaments  become  stretched  and  lengthened. 
They  have  frequently  been  shortened  by  operation  to  correct  such  displacements. 
This  may  be  done  by  the  extra-abdominal  method  in  the  inguinal  canal  (Alexander's 
operation),  or  within  the  abdomen  (Palmer  Dudley  operation),  the  latter  method  per- 
mitting a  more  accurate  estimate  of  the  special  peculiarities  or  difficulties  of  a  given 
case. 

Occasionally  in  the  adult — always  in  the  foetus  and  in  20  per  cent,  of  cases  in 
children  (Zuckerkandl,  quoted  by  Woolsey) — a  patulous  process  of  peritoneum,  the 
canal  of  Nuck,  accompanies  the  round  ligament,  lying  above  and  in  front  of  it  for 
a  variable  distance  through  the  inguinal  canal.  If  is  analogous  to  the  vaginal  process 
of  peritoneum  which  descends  with  the  testicle,  and,  like  it,  predisposes  to  congenital 
inguinal  hernia  (page  1767)  and  to  hydrocele  (page  1953).  Should  its  lumen  become 
constricted  at  some  point,  the  portion  beyond  the  obstruction  may  secrete  fluid  and 
give  rise  to  the  so-called  "cyst  of  the  canal  of  Nuck,"  which  is  analogous  to  an 
encysted  hydrocele  of  the  cord  in  the  male  (page  1953). 


2Ol6 


HUMAN   ANATOMY. 


FIG.  1 703. 


THE   VAGINA. 

The  vagina  is  a  flattened  muscular  tube,  lined  with  mucous  membrane  and  about 
7.5  cm.  (3  in. )  long,  that  extends  from  the  genital  cleft  enclosed  by  the  labia  minora 
below  to  the  uterus  above,  to  the  lower  segment  of  which  it  is  attached  a  short  dis- 
tance above  the  external  os.  From  this  relation  and  the  direction,  downward  and 
backward,  of  the  portio  vaginalis,  the  vagina  is  seemingly  pierced  obliquely  by  the 
uterus,  whose  external  os  looks  towards  the  posterior  vaginal  wall.  In  the  erect 
posture  the  long  axis  of  the  vagina  is  approximately  straight,  directed  from  below 
upward  and  backward,  and  corresponds  in  general  with  the  lower  part  of  the  pelvic 
axis.  With  the  horizontal  plane  it  forms  an  angle  of  about  70°,  and  with  the  axis 
of  the  cervix  one  that  is  usually  somewhat  more  than  a  right  angle. 

The  arched  upper  blind  end  of  the  vagina,  known  as  the  vault  (fornix  vaginae), 
is  largely  occupied  by  the  obliquely  placed  portio  vaginalis  and  thereby  reduced  to 
an  annular  groove  that  surrounds  the  neck  of  the  uterus.  This  groove  is  deepest 

behind,  where  it  constitutes  the  posterior  fornix,  a 
narrow  pouch  from  i .  5-2  cm.  in  length  lying  between 
the  cervix  and  the  adjacent  vaginal  wall.  The  recess 
in  front  of  the  cervix,  the  anterior  fornix ,  is  shallow 
and  only  slightly  marked.  In  consequence,  the  length 
of  the  posterior  wall  of  the  vagina,  measured  from  the 
summit  of  the  posterior  fornix  to  the  vaginal  orifice,  is 
from  8.5-9  cm.  (3^4-3^  in.),  that  of  the  anterior 
wall  being  about  7  cm.  (2^  in.),  or  from  1.5-2  cm. 
shorter. 

The  opening  at  the  lower  end  of  the  vagina  (ori- 
ticiuin  vaginae)  is  contracted,  and  in  the  virgin  is  still 
further  narrowed  by  a  duplicature  of  mucous  mem- 
brane, the  hymen,  of  variable  form  but  usually  cre- 
scentic  in  outline,  that  stretches  from  the  posterior 
wall  forward  and  occludes  more  or  less  the  vaginal 
entrance.  After  rupture  the  hymen  is  for  a  time 
represented  by  a  series  of  irregular  or  fimbriated  pro- 
jections that  become  the  carunculcc  hymenales.  These 
surround  the  opening  of  the  vagina  and  undergo  re- 
duction and  partial  effacement  after  childbirth.  The 
anterior  and  posterior  walls  of  the  main  and  widest 
part  of  the  canal  (corpus  vaginae)  are  modelled  by 
median  elevations  (columnae  rugarum),  from  which 
numerous  oblique  folds  diverge  laterally.  These 
markings,  most  pronounced  in  the  lower  half  of  the 
vagina,  are  particularly  conspicuous  on  the  front  wall. 
Here  the  anterior  column  is  beset  with  close  V-like 
ridges  and  ends  below  in  a  crest-like  elevation — the 
carina  urethralis — that  lies  behind  the  urethral  orifice. 

Relations. — With  the  exception  of  the  triangular  area,  from  1.5-2  cm.  long, 
over  the  uppermost  part  of  the  posterior  wall,  where  the  bottom  of  the  recto-uterine 
pouch  reaches  the  canal,  the  vagina  is  devoid  of  peritoneum,  being  attached  to  the 
surrounding  organs  by  areolar  tissue.  In  front  its  upper  fourth  is  in  relation  with  a 
small  part  of  the  fundus  and  the  trigone  of  the  bladder,  being  attached  to  the  vesical 
wall  by  loose  connective  tissue.  Embedded  within  the  latter  and  surrounded  by  veins, 
course  the  converging  ureters,  which  reach  the  anterior  vaginal  wall  at  about  the 
level  of  the  lower  end  of  the  cervix.  Below  the  bladder,  the  anterior  wall  of  the 
vagina  and  the  urethra  are  intimately  connected  by  the  intervening  dense  fibrous 
tissue-  (  septum  urethrovnginalis  ),  with  which  the  vaginal  wall  blends  without  sharp 
demarcation.  In  consequence  of  the  forward  curve  of  the  urethra  this  partition 
broadens  below. 

Behind,  the  chief  relation  is  with  the  rectum,  which  is  separated  from  the  upper- 
most part  of  the  vagina,  for  a  short  distance  (from  1.5-2  cm.),  by  the  pouch  <4 


Vagina  of  virgin,  posterior  wall 
has  been  removed  exposing  rugous 
condition  of  anti-riot  wall. 


THE   VAGINA. 


2017 


Douglas.  Below  the  latter,  as  far  as  the  levator  ani  muscles,  the  vagina  and  bowel 
are  connected  by  the  dense  recto-vaginal  septum,  strengthened  by  the  intervening 
prolongation  of  the  pelvic  fascia.  Further  down,  where  the  rectum  bends  backward, 
the  partition  broadens  into  a  wedge-shaped  mass,  the  perineal  body,  which  on 
sagittal  section  appears  as  a  triangle  with  the  base  below  in  the  perineum  (Fig.  1700). 
At  the  sides  the  vagina  is  embraced  by,  although  unattached  to,  the  median  (pubo- 
rectal)  portion  of  the  levator  ani  muscles,  which,  in  conjunction  with  the  pelvic  fascia, 
afford  efficient  support.  Below  the  pelvic  floor,  the  vagina  gains  additional  fixation 
in  passing  through  the  triangular  ligament  with  which  it  is  intimately  attached.  In 
relation  with  the  lower  end  of  the  vagina  lie  the  bulbus  vestibuli  and  Bartholin's 
glands.  The  triangular  interval,  on  each  side,  between  the  levator  ani  and  the  pelvic 
fascia  and  the  lateral  surface  of  the  vagina,  is  occupied  by  the  veins  of  the  vesico- 


FIG.  i  704. 


Pubo-vesical  ligament^ 


Pelvic  fascia  covering 
levator  ani 


Obturator  membrane.^ 

Visceral  exten- 
sion of  pelvic 
fascia 

Obturator  fascia 

Fat  removed  ex 

posing  pelvic  floor 

Visceral  reflec- 
tion of  pelvic 
fascia 

Obturatoi- 
internus 
Levator  an'i-  - 

Ischium,  cur 


Anal  fascia-" 


--Symphysis  pubis 
,  Pubic  bone,  cut 

Prevesical  space, 
cleaned  out 


_— Portion  of  wall 
of  bladder 


Urethra 


Vesico-vaginal 
venous  plexus 


-Rectum 


Ischio-rectal  fossa 


Anterior  portion  of  horrzontal  section  through  pelvis,  of  temale,  passing  just  below  bladder ; 
visceral  reflections  of  pelvic  fascia  are  seen  extending  to  bladder,  vagina,  and  rectum. 


vaginal  plexus  that  above  surrounds  the  ureter  and  the  vaginal  branches  of  the 
uterine  artery. 

Structure. — The  vaginal  walls,  from  2-3  mm.  thick,  include  a  mucous  and  a 
muscular  coat,  supplemented  externally  by  an  indefinite  fibrous  tunic.  The  mucous 
coat  consists  of  a  tunica  propria,  exceptionally  rich  in  elastic  fibres  and  veins,  the 
inner  surface  of  which  is  beset  with  numerous  conical  papillae  that  encroach  upon  the 
overlying  epithelium,  but  do  not  model  the  free  surface.  The  epithelium,  from 
o.  15-0. 20  mm.  thick,  is  stratified  squamous  in  type  and  possesses  a  superficial  stratum 
of  plate-like  cells  (.020-. 030  mm.  in  diameter)  that  resemble  the  epidermal  ele- 
ments of  the  skin  and  are  constantly  undergoing  maceration  and  abrasion.  Although 
normally  moistened  by  a  thin  mucous  secretion  of  acid  reaction,  the  vagina  is  devoid 
of  true  glands  and  probably  derives  its  lubricating  fluid  for  the  most  part  from  the 
uterine  glands,  the  alkaline  secretion  becoming  modified.  Small  nodules  of  lymphoid 
tissue  are  scattered  within  the  mucosa,  especially  in  the  upper  part  of  the  canal. 
The  duplicature  of  the  mucous  membrane  forming  the  hymen  corresponds  in  structure 
with  that  lining  other  parts  of  the  canal.  The  muscular  coat,  which  directly  sup- 
ports the  mucosa  without  the  intervention  of  a  submucous  tunic,  consists  of  bundles 
of  involuntary  muscle  that  are  arranged,  although  not  with  precision,  as  an  inner 
circular  and  an  outer  longitudinal  layer.  The  latter  is  best  developed  over  the 

127 


201 8 


HUMAN   ANATOMY. 


Tuni 
propria 


anterior  vaginal  wall,  from  which  bundles  of  muscular  tissue  are  continued  into  the 
urethro-vagmal  septum;  behind,  bundles  pass  into  the  recto-vaginal  partition.  Above, 
the  vaginal  muscle  is  directly  continuous  with  that  of  the  uterus  and  below  penetrates 
the  perineal  body.  Within,  the  conspicuous  columnae  rugarum,  the  muscular  coat, 
as  well  as  the  mucous,  is  thickened,  the  elevations  acquiring  the  character  of  erectile 

FlG   J.Q,.  tissue  owing  to  the  great  num- 

ber of  veins  intermingled  with 
the  irregularly  disposed  mus- 
cle bundles.  After  piercing 
the  superior  layer  of  the  tri- 
angular ligament  and  in  the 
vicinity  of  the  orifice,  the  vagi- 
nal walls  receive  strands  of 
striated  fibres  derived  from 
the  middle  part  of  the  com- 
pressor urethrae  (m.  urethro- 
vaginalis)  and  the  bulbo-cav- 
ernosus  muscles.' 

Vessels. — The  arteries 
supplying  the  vagina,  all  de- 
rived from  the  internal  iliac, 
reach  the  organ  by  various 
routes.  The  upper  part  of 
the  vagina  is  supplied  by  twigs 
continued  from  the  cervical 
branch  of  the  uterine  arteries, 
that  descend  along  the  sides 
of  the  canal  and  communicate 
with  the  branches  from  the 
middle  hemorrhoidal  and  vagi- 
nal (vesico-vaginal),  that  are 
distributed  to  the  middle  and 
lower  portions  of  the  vagina  respectively.  Those  from  the  vaginal,  of  the  two  sides, 
form  encircling  anastomoses  from  which  an  unpaired  vessel  (a.  azygos  vagina)  fre- 
quently is  given  off  on  the  posterior,  and  sometimes  anterior,  wall.  Additional 
branches  pass  to  the  lower  part  of  the  vagina  from  the  arteries  to  the  bulbus  vestibuli 
from  the  internal  pudics.  Free  anastomosis  exists  between  the  vessels  derived  from 
these  various  sources.  The  veins,  numerous  and  large,  after  emerging  from  the  mus- 
cular tunic  unite  on  each  side  to  form  the  rich  vaginal  plexus  that  extends  along  the 
sides  of  the  genital  canal  and  communicates  with  the  vesical  and  uterine  plexuses. 
It  receives  tributaries  from  the  external  generative  organs  and  is  drained  by  a  trunk, 
the  vaginal  vein,  that  passes  from  its  upper  part  to  the  internal  iliac  vein. 

The  lymphatics  within  the  mucous  membrane  form  a  close  net-work  that  commu- 
nicates with  the  lymph-vessels  of  the  muscular  coat.  The  collecting  trunks  pass 
from  the  upper  and  middle  thirds  of  the  vagina,  in  company  with  those  from  the 
cervix  uteri,  chiefly  to  the  lymph-nodes  along  the  internal  iliac  artery.  Additional 
stems  from  the  posterior  vaginal  wall  encircle  the  bowel  and  terminate  either  in  the 
rectal  or  the  lumbar  nodes  (Bruhns).  The  lymphatics  from  the  vicinity  of  the  vagi- 
nal orifice  pass  chiefly  to  the  upper  median  group  of  inguinal  nodes  ;  some,  however, 
join  the  lymph-paths  from  the  upper  segments. 

The  nerves  are  derived  from  the  hypogastric  sympathetic  plexus,  through  the 
pelvic,  and  from  the  second,  third,  and  fourth  sacral  nerves.  The  immediate  source 
of  the  sympathetic  fibres  is  the  cervical  ganglion,  at  the  side  of  the  neck  of  the  uterus, 
from  which,  in  association  with  the  sacral  branches,  twigs  pass  to  form,  on  each  side, 
the  vaginal  plexus  that  embraces  the  vagina  and  provides  filaments  chiefly  for  the 
involuntary  muscle  of  its  walls  and  blood-vessels.  The  sensory  fibres  supplying  the 
mucous  membrane  of  the  upper  part  of  the  vagina  are  meagre,  since,  under  normal 
conditions,  this  part  of  the  canal  possesses  sensibility  in  only  very  moderate  degree. 
Towards  the  orifice  the  vagina  receives  fibres  from  the  pudic  nerves  which  endow 


Section  of  wall  of  vagina.     X  80. 


PRACTICAL   CONSIDERATIONS  :    THE   VAGINA.  2019 

the  mucous  membrane  of  the  lower  third  with  greater  sensibility  and  send  motor  fila- 
ments to  the  striated  muscle  surrounding  the  entrance.  Sensory  nerve-endings  of 
different  kinds  have  been  described  within  the  mucosa. 

Development. — The  vagina  is  formed  by  the  downward  extension  and  fusion 
of  the  Miillerian  ducts.  After  union  of  the  latter  with  the  posterior  wall  of  the  uro- 
genital  sinus  and  the  appearance  of  a  lumen,  which  at  first  is  wanting,  the  genital 
canal  opens  into  the  sinus  by  an  aperture,  later  the  orificium  vaginae,  that  lies  between 
and  closely  united  with  the  Wolffian  ducts.  The  latter  subsequently  atrophy  and 
disappear,  but  may,  in  exceptional  cases,  persist  to  a  greater  or  less  extent  as  Gart- 
ner's ducts.  The  entrance  of  the  immature  vagina  is  early  guarded  by  an  annular 
fold  that  becomes  the  hymen  and  owes  its  differentiation  to  a  pouching  of  the  vaginal 
wall  behind  a  zone  of  thickened  epithelium  (Nagel).  For  a  time,  usually  until  about 
the  seventh  month  of  fcetal  life,  the  orifice  of  the  vagina  is  occluded  by  epithelium. 
The  proliferation  and  thickening  of  the  vaginal  lining,  which  begin  below,  gradually 
extend  upward  and  result  in  the  production  of  conspicuous  rugae,  which,  during  the 
last  months  of  pregnancy,  cover  not  only  the  entire  surface  of  the  vagina,  but  also 
that  of  the  cervix,  which  even  at  birth  is  slightly  corrugated.  In  consequence  of  the 
increasing  irregularity  and  thickening  of  the  mucosa,  the  vaginal  walls,  which  for  a 
time  are  adherent,  become  separated  and  the  lumen  of  the  canal  is  definitely  estab- 
lished, remains  of  the  desquamated  epithelium  being  often  visible  in  the  new-born 
child.  Distinct  muscular  tissue  within  the  vaginal  wall  is  not  distinguishable  before 
the  fifth  month. 

At  birth,  the  vagina  is  relatively  long  (Fig.  1623)  and  its  wall  is  comparatively 
thick,  with  conspicuous  rugae  extending  as  far  as  the  vault.  During  the  early  years 
of  childhood  the  vagina  remains  small  and  vertical,  but  after  the  tenth  year  grows 
rapidly,  the  increased  width  causing  reduction  in  the  rugae,  which  from  now  on  are 
feebly  marked  in  the  upper  part  of  the  canal.  After  undergoing  the  stretching  inci- 
dent to  labor,  the  rugae  and  columns  are  much  less  conspicuous,  and  after  repeated 
distention  may  suffer  almost  complete  effacement.  The  vagina  shares  in  the  general 
involution  of  the  sexual  organs,  and  in  advanced  years  loses  much  of  its  former  elas- 
ticity and  undergoes  atrophy. 

Variations. — The  most  important  variations  depend  upon  defective  development  and  im- 
perfect fusion  of  the  component  Miillerian  ducts,  and  are,  therefore,  often  associated  with 
anomalies  of  the  uterus.  When  these  tubes  fail  to  reach  the  urogenital  sinus,  the  vagina  ends 
blindly  above  the  vestibule  ;  or  when  their  lower  segments  are  stunted,  the  vagina  (and  often 
uterus)  may  be  entirely  wanting.  Duplication,  more  or  less  complete,  follows  persistence  of 
separate  or  imperfectly  fused  Miillerian  ducts.  The  doubling  may  not  extend  throughout  the 
length  of  the  vagina,  but  may  be  represented  by  an  imperfect  and  partial  septum,  isolated  bands, 
or  a  twin  hymen.  Unequal  development  of  the  Miillerian  ducts  accounts  for  the  marked  asym- 
metry occasionally  observed,  notably  in  double  vaginae,  where  one  canal  may  be  very  rudi- 
mentary or  end  blindly.  The  hymen  presents  great  variety  in  the  details  of  its  opening,  which 
may  be  crescentic,  circular,  stellate,  linear,  double,  or  multiple  (hymen  cribriformis] .  It  may 
be  a  mere  pin-hole  or  entirely  wanting  (imperf orate),  in  which  case  retention  of  menstrual  dis- 
charges occurs. 

PRACTICAL   CONSIDERATIONS  :    THE   VAGINA. 

Congenital  malformations  of  the  vagina,  such  as  absence  of  the  vagina,  rudi- 
mentary vagina,  or  vaginal  septa,  are  usually  associated  with  corresponding  errors 
in  development  of  the  uterus.  While  other  malformations  due  to  faulty  union  of  the 
Miillerian  ducts  occur,  the  more  common  is  a  uterus  bicornis,  or  a  double  uterus  and 
vagina.  They  are  not  incompatible  with  pregnancy,  labor  and  the  puerperium  often 
passing  without  unusual  incident  ;  indeed,  this  condition  is  usually  recognized  by 
accident,  since  no  external  evidence  is  seen.  Conception  may  occur  on  one  or  both 
sides  simultaneously.  A  vaginal  septum  which  interfered  with  the  progress  of  the 
head  should  be  divided.  From  imperfect  development  of  one  side  of  a  bicornate 
uterus,  pregnancy  may  lead  to  great  danger  of  rupture  of  the  weak  uterine  wall,  or 
to  a  failure  to  expel  the  child. 

While  varying  within  normal  limits  with  the  distention  of  the  bladder,  when  the 
latter  is  empty  the  axis  of  the  fundus  of  the  uterus  lies  at  about  a  right  angle  with 
the  vagina.  The  inner  or  uterine  end  of  the  broad  ligament  is,  except  at  its  base, 


2020  HUMAN   ANATOMY. 

more  nearly  horizontal  than  vertical  in  direction.  As  a  result  of  this  position  of  the 
uterus,  it  will  be  seen  that  the  lower  surface  of  the  cervix  presents  against  the  pos- 
terior vaginal  wall,  and  that,  therefore,  this  wall  of  the  vagina  must  be  longer  than 
the  anterior.  The  posterior  wall  is  usually  about  three  and  a  half  inches  long  ;  and 
the  anterior  about  two  and  a  half  to  three  inches.  The  length  of  the  ordinary  ringer 
is  about  three  inches  ;  it  can,  therefore,  reach  the  anterior  fornix  of  the  vagina  and 
anterior  lip  of  the  cervix.  To  explore  the  posterior  fornix  of  the  vagina  considerable 
pressure  is  required.  To  palpate  structures  in  Douglas's  cul-de-sac  the  bimanual 
method  of  examination  will  be  necessary,  and  a  relaxed  abdominal  wall,  to  obtain 
which  a  general  anaesthetic  may  exceptionally  be  required.  An  empty  bladder  facili- 
tates a  bimanual  examination.  In  the  knee-chest  posture  the  vagina  becomes  dis- 
tended with  air,  permitting  a  more  thorough  visual  examination  of  its  walls.  The 
rectum  posteriorly,  and  the  base  of  the  bladder  and  the  urethra  anteriorly,  are  within 
reach  of  the  finger  in  the  vagina.  Calculi,  either  in  the  lower  ends  of  the  ureters 
(vide  supra)  or  in  the  bladder,  can  be  removed  through  the  anterior  vaginal  wall 
(page  2015). 

The  intravaginal  portion  of  the  cervix  uteri  can,  with  little  or  no  pain,  be  grasped 
by  a  tenaculum  and  drawn  down  towards  the  vaginal  orifice  so  that  local  applications 
can  be  made.  It  is  so  insensitive  that  such  applications,  even  when  strong  and  irri- 
tating, do  not  necessitate  the  use  of  an  anaesthetic.  Since  it  is  the  part  of  the  cervix 
most  exposed  to  traumatism  and  infection,  it  is  the  most  frequent  seat  of  pathological 
lesions,  such  as  the  so-called  "erosions."  Persistent — i.e. ,  unhealed — lacerations 
are  often  sources  of  irritation,  of  reflex  pains,  and  of  some  forms  of  dysmenorrhcea. 
Much  of  the  pelvic  pain,  associated  with  them,  is  probably  due  to  pelvic  lymphangitis 
or  lymphadenitis  (Penrose).  These  lacerations  seem  to  invite  the  development  of 
cancer.  Primary  involvement  of  the  body  of  the  uterus  is  comparatively  rare,  the 
great  majority  of  cancers  of  the  uterus  beginning  in  the  cervix.  As  a  result  of  the 
relations  and  contiguity  of  the  cervix  to  surrounding  important  structures,  such  as  the 
bladder,  ureters,  and  rectum,  the  prognosis  of  cancer  of  the  cervix  is  less  favorable 
than  that  of  the  body  of  the  uterus,  where  infiltration  of  neighboring  structures  does 
not  occur  so  early.  As  a  rule,  dissemination  by  lymphatic  channels  from  carcinoma 
of  the  cervix,  affects  first  the  sacral  or  the  iliac  glands;  carcinoma  of  the  body  of  the 
uterus  is  more  likely  to  involve  the  lumbar  glands  surrounding  the  common  iliacs, 
the  aorta,  and  the  vena  cava.  Pressure  on  the  last-named  vessel  may  result  in 
cedematous  swelling  of  the  lower  extremities  or  in  ascites. 

An  hypertrophied  cervix  shows  as  an  increased  projection  into  the  vagina  and  a 
deepening  of  the  vaginal  fornices.  This  condition  may  be  a  cause  of  sterility. 

The  vagina  is  most  roomy  in  its  upper  portion,  and  is  narrowest  at  its  lower 
end,  where  it  passes  through  the  triangular  ligament  and  is  surrounded  by  the  con- 
strictor vaginae  muscle.  This  favors  the  retention  of  blood-clots  within  the  vagina 
during  the  menstrual  period  and  after  labor.  Spasmodic  contraction  of  this  muscle 
(vaginismus)  is  described  as  being  sometimes  strong  enough  to  prevent  coitus  and 
to  call  for  surgical  treatment,  though  such  cases,  if  they  exist  at  all,  are  due  to  reflex 
irritation,  such  as  from  urethral  caruncle.  The  dilatation  of  the  vagina  seems  to  be 
limited  only  by  the  pelvic  wall.  In  nullipara  the  rugosity  of  its  mucous  membrane- 
necessitated  by  its  great  changes  in  diameter — is  marked.  The  transverse  folds 
favor  retention  of  secretions  and  of  discharges  resulting  from  infection  and  render 
sterilization  of  the  vagina  difficult.  Vaginitis  may  be  followed  by  endometritis,  as 
the  uterine  and  vaginal  mucosae  are  directly  continuous. 

The  hymen  rarely  may  have  no  opening,  when  it  will  require  incision  to  relieve 
the  obstructed  first  menstrual  flow.  The  exact  importance  to  be  attached  to  the 
presence  or  absence  of  the  hymen  in  medical  jurisprudence  is  still  undetermined. 
While  it  is  usually  broken  at  the  first  coitus,  it  may  remain  intact  until  the  first 
parturition.  Therefore  its  presence  does  not  prove  virginity.  Its  original  perfora- 
tion may  have  been  large  enough  to  leave  little  or  no  evidence  of  the  membrane, 
so  that  its  absence  does  not  prove  that  coitus  has  taken  place. 

Fistula1  between  the  bladder  and  vagina  (vesico- vaginal),  between  the  urethra 
and  vagina  (urethro- vaginal),  between  tin-  rectum  and  vagina  (recto-vaginal),  and 
between  the  cervical  canal  and  the  bladder  (utero-vesical),  may  occur. 


THE   LABIA   AND   THE   VESTIBULE.  2021 

Recto-vcsical  fistula  in  a  woman  has  followed  ischio-rectal  abscess,  after  the  dis- 
charge of  which  the  patient  passed  gas  and  faecal  matter  through  the  urethra  (Noble). 

Vesuo-vaginal  fistulae  are  usually  due  to  sloughing  consequent  upon  the  impac- 
tion  of  the  head  in  a  difficult  labor  ;  they  are  not  due,  as  erroneously  believed,  to  the 
use  of  forceps,  but  to  too  long  delay  in  using  them  (Emmet). 

Urethro-vaginal  fistulae  following  labor  are  rare.  More  frequently  the  com- 
munication between  the  vagina  and  the  upper  part  of  the  urethra  is  part  of  a  larger 
opening  into  the  bladder.  It  is  in  reality  a  vesico-urethro-vaginal  fistula. 

Vesico-uterine  fistulae  are  usually  due  to  a  tear  extending  forward  through  the 
anterior  vaginal  fornix  into  the  bladder,  and  upward  along  the  cervical  canal.  The 
lower  part  of  the  tear  heals,  leaving  an  opening  between  the  bladder  and  cervical 
canal,  the  urine  dribbling  outward  from  the  bladder  into  the  cervical  canal  and  thence 
into  the  vagina.  If  the  lower  part  of  the  tear  does  not  heal,  we  then  have  a  vesico- 
utcro-vaginal  fistula. 

Recto-vaginal  fistulae  are  found  usually  at  the  upper  or  lower  end  of  the  vagina. 
At  the  upper  end  they  are  most  frequently  due  to  extension  of  an  epithelioma  of  the 
cervix  into  the  rectum,  and  in  the  lower  end  to  incomplete  closure  of  a  torn  perineum 
extending  into  the  rectum.  They  are  very  rarely  due  to  labor  itself. 

THE    FEMALE    EXTERNAL    GENITAL   ORGANS. 

The  external  generative  organs  of  the  female  include  those  parts  of  the  repro- 
ductive apparatus  that  lie  below  the  triangular  ligament  and  in  front  of  and  below  the 
pubic  arch.  They  are  the  labia  majora,  with  the  mons  pubis  above  and  the  urogen- 
ital  cleft  between  them,  the  labia  minora  or  nymphcz,  and  the  enclosed  vestibule,  the 
clitoris  and  the  bulbus  vestibuli,  together  with  the  glands  of  Bartholin  ;  within  the 
vestibule  are  the  orifices  of  the  urethra  and  of  the  vagina.  Of  these  structures,  col- 
lectively termed  \he  pudendum  (pudendum  muliebre),  or  vulva,  in  the  upright  posture 
usually  little  more  than  the  mons  pubis  and  the  labia  majora  are  visible,  although 
exceptionally  the  labia  minora  and  the  clitoris  may  be  seen  within  the  genital  fissure. 

THE  LABIA  AND  THE  VESTIBULE. 

The  labia  major  (labia  majora  pudendi)  are  two  prominent  rounded  cutaneous 
folds,  the  homologue  of  the  scrotum,  about  7.5  cm.  (3  in.)  long  and  2.5  cm.  thick, 
that  extend  backward  from  the  mons  pubis  and  enclose  between  their  medial  surfaces 
the  urogenital  cleft  (rima  pudendi).  Above,  their  inner  margins  are  continuous  (com- 
missura  labiorum  anterior)  over  the  ridge  formed  by  the  body  of  the  clitoris  ;  behind, 
where  their  tapering  ends  blend  with  the  perineum,  they  are  connected  by  a  trans- 
verse fold  (commissura  labiorum  posterior),  often  only  slightly  marked  and  sometimes 
wanting,  that  crosses  the  mid-line  in  advance  of  the  anus.  Their  outer  surface  is 
covered  with  thick,  dark-hued  integument  and  beset  with  hairs,  in  varying  profusion, 
that  encroach  for  a  limited  zone  on  the  inner  surface  of  the  labia  and  may  extend  as 
far  as  the  anus.  The  medial  surface,  on  which  the  hairs  are  few  and  minute,  is 
clothed  with  skin  of  much  more  delicate  texture,  that  at  the  bottom  of  the  nympho- 
labial  furrow  passes  onto  the  outer  surface  of  the  nymphae.  In  addition  to  the  skin, 
each  labium  consists  of  a  layer  of  subcutaneous  fat,  between  which  and  the  integu- 
ment in  the  posterior  half,  a  thin  stratum  of  involuntary  muscle  (tunica  darto- 
labialis)  is  continued  forward  from  the  dartos  of  the  perineum  and  represents  the 
similar  but  better  developed  sheet  in  the  scrotum.  The  centre  of  the  labium  is  occu- 
pied by  a  fairly  well  defined  mass  of  fat  (corpus  adiposum)  that  is  connected  with  the 
adipose  tissue  within  the  inguinal  canal  continuous  with  the  subperitoneal  tissue  and 
is,  therefore,  of  different  derivation  than  that  of  the  subcutaneous  fat,  from  which  it 
is  separated  by  a  delicate  fascia.  Into  the  latter  are  inserted  some  of  the  fibres  of 
the  round  ligament  of  the  uterus  that  ends  within  the  labium  majus.  Sweat  and 
sebaceous  glands  are  numerous  within  the  integument  of  the  labia. 

The  mons  pubis  or  Veneris,  as  the  triangular  rounded  eminence  above  the 
genital  cleft  is  called,  consists  of  a  cushion  of  fat,  enclosed  by  dense  skin  and  thickly 
covered  with  hair.  The  subcutaneous  fatty  layer,  usually  from  2—3  cm.  thick,  but 


2022 


HUMAN   ANATOMY. 


sometimes  as  much  as  8  cm.  or  more,  is  supported  by  connective-tissue  septa  that 
pass  from  the  underlying  periosteum  to  the  skin,  whereby  the  tension  of  the  latter  is 
maintained. 

The  labia  minora,  or  nymphae  (labia  minora  pudendi),  are  two  thin  folds  of 
delicate  skin  that,  for  the  most  part,  lie  concealed  between  the  larger  labia,  unless 
the  latter  are  separated,  and  enclose  the  vestibule.  Their  length  is  from  2.5-3.5  cm-. 
their  width  about  half  as  much,  and  their  thickness  from  3-5  mm.  Near  its  anterior 
end,  each  labium  divides  into  a  lateral  and  a  medial  limb  ;  the  lateral  divisions  of  the 
two  sides  unite  above  the  free  end  of  the  clitoris,  which  they  enclose  with  a  hood,  the 
preputium  clitoridis,  while  the  medial  limbs  join  at  an  acute  angle  on  the  under  side 
of  the  clitoris  to  form  \\sfrenum  (frenulum  clitoridis).  Behind,  the  nymphae  grad- 
ually fade  away  by  joining  the  inner  surface  of  the  labia  majora.  In  the  virgin,  and 
when  well  developed,  the  medial  border  of  the  posterior  ends  of  the  nymphse  are  usu- 
ally connected  by  a  slight 

FIG    1706  transverse    crescentic    fold, 

the  frenum  or  fourchette 
(frenulum  labiorum  pudendi) 
that  marks  the  posterior 
boundary  of  the  shallow 
navicular  fossa  (Fig.  1706). 
Both  surfacesof  the  nymphae 
are  covered  with  delicate 
skin,  which,  on  account  of 
the  protection  afforded  by 
the  greater  labia  and  con- 
stant contact  with  the  vagi- 
nal secretions,  remains  moist 
and  soft  and  assumes  the 
color  and  appearance  of  a 
mucous  membrane.  The 
entire  absence  of  mucous 
glands  and  the  presence  of 
numerous  sebaceous  folli- 
cles, on  the  inner  as  well 
as  on  the  outer  surface,  to- 
gether with  the  develop- 
ment of  the  nymphae  from 
the  margin  of  the  cloacal 
fossa,  establish  their  cuta- 
neous character.  The  skin 
covering  the  nymphae  ex- 
ternally is  continuous  with 
that  of  the  labia  majora  at 
the  bottom  of  theinterlabial 

furrow  ;  internally  the  line  of  transition  into  the  mucous  membrane  lining  the  vesti- 
bule follows  the  medial  attachment  of  the  folds  which  overlie  the  vestibular  bulb.  In 
addition  to  the  two  cutaneous  layers,  the  nymphae  consist  of  an  intermediate  stratum 
of  loose  connective  tissue,  rich  in  blood-vessels,  and  containing  many  bundles  of  in- 
voluntary muscles  that  possess  the  character  of  erectile  tissue.  Hairs  and  fat  are 
entirely  wanting  in  the  labia  minora,  but  sebaceous  and  sweat  glands  are  present,  the 
latter  small  and  scattered  but  most  plentiful  in  the  anterior  part  and  in  the  prepuce 
(Webster). 

The  vestibule  (vestibuluiii  vaginae)  is  the  elliptical  space  enclosed  between  the 
labia  minora,  extending  from  the  clitoris  in  front  to  the  crescentic  frenum  behind. 
When  the  nympha-  arc  separated,  the  vestibule  resembles  an  almond  in  outline,  being 
pointed  in  front  and  broader  behind.  In  the  roof  (as  usually  examined  the  floor)  of 
this  space  are  seen  the;  urethral  and  vaginal  orifices  and  the  minute  openings  of  the 
paraurethral  ducts  and  of  the  canals  of  Bartholin's  glands.  The-  urdliral  orifice  occu- 
pies a  more  or  less  conspicuous  corrugated  elevation  (  papilla  urethral  is  )  that  lies  about 


Posterior 
commissure 


External  genital  organs  of  virgin  ;  lahia  have  been  separated  to  expose 
vestibule  and  vaginal  orifice. 


THE    LABIA   AND   THE   VESTIBULE. 


2023 


2  cm.  behind  the  clitoris  and  breaks  the  smooth  mucous  surface  of  the  vestibular  roof. 
The  opening'  of  the  urethra  is  very  variable  in  form,  being  crescentic,  stellate,  crucial 
or  linear,  a  sagittal  cleft  of  about  5  mm.  being  the  most  usual  type.  Close  to  the 
urethral  orifice,  at  the  sides  or  somewhat  behind,  lie  the  minute  depressions  marking 
the  openings  of  the  paraurethral  ducts  (page  1706).  In  young  subjects,  a  pair  of 
fine  sagittal  folds  can  often  be  traced  over  the  roof  of  the  vestibule  from  the  urethral 
papilla  to  the  frenum  of  the  clitoris. 

The  area  between  the  orifice  of  the  urethra  and  that  of  the  vagina  is  subject  to 
considerable  individual  variation  in  size  and  detail  owing  to  differences  in  the  extent 
to  which  the  lower  end  of  the  anterior  vaginal  column  (carina  urethralis)  encroaches 
upon  the  vestibule.  After  rupture  of  the  hymen  has  occurred,  the  vaginal  entrance 
is  surrounded  by  a  series  of  irregular  fimbriated  projections  that  form  the  caruncula 
hymenales  which,  after  labor,  become  reduced  to  inconspicuous  nodules.  Included 
between  the  posterior  margin  of  the  hymen  and  the  backwardly  directed  arching  fold 
of  the  fourchette  is  the  fossa  navicularis,  a  shallow,  crescentic,  pocket-like  depres- 


FIG.  1707. 


Labium  majus 


n-- 
Central  fat-body 


Labium  minus 


—   Inner  surface 


Sebaceous  glands  on  external^ 
cutaneous  surfaces 


Interlabial  groove 


Section  across  the  labia  of  very  young  child.    X  18. 

sion.    This  recess  is  best  marked  in  the  virgin,  when  the  nymphee  are  well  developed, 
and  is  usually  effaced  after  child-bearing. 

Vessels. — The  arteries  supplying  the  labia  majora  are  chiefly  the  anterior  and 
posterior  labial  branches  from  the  external  and  internal  pudics  respectively.  A 
small  twig  from  the  superficial  external  pudic  is  distributed  in  the  vicinity  of  the 
anterior  commissure  ;  several  others  from  the  deep  external  pudic  end  in  the  anterior 
half  of  the  labium,  while  the  posterior  half  is  supplied  by  the  posterior  labial  twigs 
from  the  superficial  perineal  branch  from  the  internal  pudic  artery.  Additional 
small  twigs  from  the  anterior  terminal  branch  of  the  obturator  artery  are  distributed 
to  the  outer  surface  of  the  labia.  The  nymphse  also  receive  their  blood  from  the 
anterior  and  posterior  labial  arteries  through  small  branches  that  enter  the  front  and 
hind  parts  of  the  folds  and  assist  in  nourishing  the  mucous  membrane  lining  the  roof 
of  the  vestibule.  The  arteries  from  these  various  sources  freely  anastomose  with  one 
another  as  well  as  with  adjacent  vessels.  While  the  veins  of  the  labia  majora  in 
general  follow  the  corresponding  arteries,  they  communicate  with  neighboring 
systems,  particularly  with  the  inferior  hemorrhoidal  and  the  pelvic  plexuses.  The 
veins  of  the  nymphae,  unusually  numerous  and  large,  present  a  plexiform  arrangement, 
whereby  the  labia  acquire  the  character  of  erectile  structures.  The  collecting  stems 


2024 


HUMAN   ANATOMY. 


join  those  of  the  labia  majora,  as  well  as  communicate  with  the  veins  of  the  clitoris 
and  bulb.  The  lymphatics  of  the  labia  are  very  numerous,  notably  in  the  more 
superficial  parts  of  the  folds,  a  half  dozen  or  more  trunks  passing  to  the  upper  and 
medial  group  of  inguinal  lymph-nodes.  The  lymphatics  from  the  nymphae,  also 
very  numerous,  join  the  afferents  from  the  labia  majora  and  end  in  the  same  inguinal 
nodes.  Communications  sometimes  exist  with  the  nodes  of  the  opposite  sides 
(Bruhns). 

The  nerves  supplying  the  anterior  half  of  the  labia  majora  are  derived  from 
the  ilio-inguinal  and  the  genital  branch  of  the  genito-crural,  while  the  posterior  part 
of  the  labia  receive  filaments  from  the  perinea!  branches  of  the  pudic  and  the  small 
sciatic  trunks.  The  nymphae  are  highly  sensitive  and  receive  branches  from  the 
superficial  perineal  nerves  upon  which  special  sensory  endings  are  found  within  the 
subepithelial  tissue. 

THE   CLITORIS. 

The  clitoris,  the  homologue  of  the  penis,  repeats  in  reduced  size  and  modified 
form  the  chief  components  of  the  organ  of  the  male.  Morphologically  considered,  it 
consists  of  two  corpora  cavernosa,  united  in  front  into  the  body  and  separated  behind 
into  the  crura  attached  to  the  pubic  arch,  and  the  imperfectly  developed  and  cleft 
corpus  spongiosum — known  as  the  bulbus  vestibuli  and  usually  described  as  an  inde- 
pendent organ. 

The  clitoris  lies  so  buried  within  the  subcutaneous  tissue  and  beneath  the  labia 
that  only  its  small  conical  anterior  end,  called  the  glans  clitoridis,  and  the  low  verti- 

FIG.  1708. 


•Suspensory  ligament 
of  clitoris 


orpus  clitoridis 
lans  clitoridis 


Pars  intermedia 
Urethral  orifice 

Bulbus  vestibuli — 
Vaginal  orifice 


Inferior  layer  of  - 
triangular  ligament 


•Crus  clitoridis  curved 
by  ischio-cavernosus 
muscle 


Cut  edge 

Compressor  bulbi 
Transversus  perinei 


Dissection  of  urogenital  triangle  of  female,  showing  clitoris  and  bulbus  vestibuli. 

cal  ridge  of  integument  over  the  body  (torus  clitoridis)  appear  when  the  labia  are 
separated.  The  glans,  about  5  mm.  in  diameter,  is  partly  concealed  by  an  annular 
duplicature  of  skin,  the  prcputium  clitoridis,  that  is  free  in  front  and  at  the  sides,  but 
behind  is  attached  by  a  median  fold,  the  frcniim,  continuous  with  the  nymphae. 
When  exposed  after  removal  of  the  labia  and  skin,  the  clitoris  (using  the  term  in  the 
more  restricted  and  conventional  sense)  is  seen  to  consist  of  the  small  unpaired  body 
(corpus  clitoridis),  from  2  to  2.5  cm.  long,  composed  of  the  fused  corpora  earcrnosa, 
and  the  diverging  and  much  larger  crura,  from  3.5-4  cm.  in  length,  that  are  attached 
to  the  sides  of  the  subpubic  arch,  as  are  the  corresponding  parts  of  the  penis.  The 
crura  clitoridis  are,  however,  relatively  flat  and  blunt.  The  dependent  body  forms 
a  sharp  bend  with  the  diverging  crura,  bring  fixed  to  the  lower  part  of  the  symphy- 
sis  pubis  by  a  diminutive  suspensory  ligament.  Owing  to  its  attachments  to  the  in- 


THE   CLITORIS.  2025 

tegument  and  nymphae,  the  position  of  the  body  and  its  angle  undergo  but  slight 
change  even  in  the  turgescent  condition  of  the  organ.  In  their  general  structure 
the  corpora  cavernosa  clitoridis,  apart  from  their  reduced  size  and  feebler  develop- 
ment, correspond  with  those  of  the  penis,  including  cylinders  of  erectile  tissue  en- 
closed by  a  tunica  albuginea  and  separated  where  blended  by  a  septum.  The  glans, 
however,  is  composed  chiefly  of  fibrous  tissue  and  contains  little  true  cavernous 
structure  ;  it  is,  of  course,  not  perforated  by  the  urethra. 

The  Bulbus  Vestibuli. — The  vestibular  bulb  consists  of  two  converging 
elongated  masses  of  cavernous  tissue,  completely  separated  except  in  front,  where 
they  are  connected  by  a  narrow  isthmus,  the  pars  intermedia.  They  embrace  the 
lower  end  of  the  vagina  and  the  urethra,  and  anteriorly  meet  the  under  surface  of  the 
cavernous  bodies  of  the  clitoris.  The  organ,  as  above  noted,  represents  the  bulbar 
and  adjoining  parts  of  the  corpus  spongiosum,  of  which  the  component  parts  have 
remained  ununited  in  consequence  of  the  persistence  of  the  urogenital  cleft,  each 
half  corresponding  to  a  semibulb  of  the  united  structure  in  the  male.  Each  bulb, 
regarding  the  organ  as  paired,  is  a  wedge-shaped  body,  narrow  in  front  and  broad 
and  rounded  behind,  that  measures  from  3-4  cm.  in  length,  where  broadest  from 
1-1.5  cm.  in  width,  and  less  than  i  cm.  in  thickness.  Above,  it  rests  against  the 
inferior  layer  of  the  triangular  ligament,  its  lower  margin,  somewhat  medially  di- 
rected, being  covered  by  the  base  of  the  labium  majus  and  the  nympha.  Behind, 
the  medial  surface  is  closely  related  to  the  lateral  wall  of  the  vaginal  entrance,  and 
when  well  developed  may  extend  backward  as  far  as  the  posterior  wall  of  the  vagina. 
In  front,  the  bulb  passes  at  the  side  of  the  urethra  and  joins  the  under  surface  of  the 
clitoris.  Laterally  and  below,  it  is  covered  by  the  fibres  of  the  bulbo-cavernosus  mus- 
cle. The  rounded  hind  end  meets  or  covers  the  gland  of  Bartholin.  The  two  bodies 
together  form  a  compressed  crescentic  or  horseshoe-shaped  complex  of  venous  spaces, 
enclosed  by  a  thin  tunica  albuginea,  that  resembles  the  cavernous  tissue  of  the  corpus 
spongiosum,  although  less  definite  in  structure. 

Vessels. — The  arteries  supplying  the  clitoris  and  vestibular  bulb  correspond 
with  those  distributed  to  the  homologous  parts  of  the  penis,  but  are  of  smaller  size. 
As  in  the  male,  the  first  branch  to  the  cavernous  tissue  is  the  artery  of  the  bulb 
(a.  bulbi  vestibuli),  which  enters  that  body  near  its  posterior  end  as  a  short  and 
comparatively  strong  vessel  and  joins  with  additional  twigs  to  the  bulb  from  the  deep 
artery  of  the  clitoris  (a.  profunda  clitoridis),  a  branch  corresponding  to  the  urethral 
artery  passing  to  the  pars  intermedia.  Each  cavernous  body  receives  the  deep  branch 
that  enters  the  crus  and,  sending  a  minute  twig  backward,  traverses  the  cylinder  of 
erectile  tissue  towards  the  glans,  communicating  with  its  fellow  of  the  opposite  side 
as  well  as  with  the  dorsal  artery  (a.  dorsalis  clitoridis).  The  latter,  the  terminal  part 
of  the  internal  pudic  and  smallest  of  the  vessels  supplying  the  clitoris,  pursues  a 
course  identical  with  that  of  the  corresponding  vessel  of  the  penis,  but  is  minute  in 
consequence  of  the  reduced  dimensions  of  the  parts  supplied. 

The  veins  follow  the  general  arrangement  observed  in  the  penis,  the  blood  being 
carried  off  chiefly  by  the  dorsal  vein  and  the  venous  channels  that  more  closely 
accompany  the  arteries.  The  most  important  modification  is  the  presence  of  the 
plexus  intermedius  (Kobelt),  a  venous  complex  that  lies  between  the  under  surface 
of  the  corpora  cavernosa,  just  as  they  begin  to  diverge  into  the  crura,  and  the  united 
anterior  ends  of  the  halves  of  the  bulbus  vestibuli.  This  plexus  not  only  establishes 
connections  between  the  blood-spaces  of  the  corpora  cavernosa  and  the  bulbus 
vestibuli,  but  also  receives  tributaries  from  the  prepuce  and  frenum  of  the  clitoris,  the 
nymphae,  and  the  adjacent  parts  of  the  vestibule.  In  addition  to  the  stems  that  join 
the  internal  pudic  veins,  the  cavernous  spaces  of  the  bulb  communicate  with  the 
urethral,  vaginal,  and  hemorrhoidal  plexuses.  In  consequence  of  the  connections 
between  the  plexus  intermedius  and  the  dorsal  vein  of  the  clitoris,  the  latter  vessel 
is  relatively  of  large  size. 

The  lymphatics  for  the  most  part  are  afferents  of  the  superficial  inguinal  lymph- 
nodes;  communications  exist,  however,  with  the  deeper  intrapelvic  paths  and  nodes. 

The  nerves  of  the  clitoris  are  derived  and  distributed  in  correspondence  with 
the  plan  observed  in  the  penis.  They  are,  therefore,  extensively  from  the  sympa- 
thetic system  for  the  walls  of  the  blood-spaces  and  from  the  pudic  nerves.  The 


2026  HUMAN   ANATOMY. 

dorsal  nerve  is  relatively  large  and  supplies  the  integument  of  the  glans  and  prepuce 
with  fibres  connected  with  special  sensory  end-organs. 

THE  GLANDS  OF   BARTHOLIN. 

The  glands  of  Bartholin  (glandulae  vestibulares  majores),  the  homologues  of 
Cowper's  glands  in  the  male,  are  a  pair  of  small  organs,  situated  one  on  either  side 
of  the  vaginal  orifice,  behind  the  bulbus  vestibuli  and  about  the  middle  of  the  base 
of  the  labium  majus.  The  organ  measures  from  1-1.5  cm-  m  length  and  somewhat 
less  than  i  cm.  in  width,  and  is  covered  on  its  anterolateral  aspect  by  the  bulbo- 
cavernosus  muscle  and,  often,  also  by  the  end  of  the  bulbus  vestibuli.  Its  superior 
surface  lies  against  the  inferior  layer  of  the  triangular  ligament,  and  its  medial  about 

1  cm.  external  to  the  vestibule,  from  which  it  is  separated  by  dense  fibrous  tissue. 
From  the  anteromedial  border  of  the  gland  emerges  the  duct,  a  narrow  tube,  about 

2  mm.  in  diameter  and  from  1.5—2  cm.  long,  that  passes  obliquely  inward  and  for- 
ward, beneath  the  base  of  the  nympha,  to  open  in  the  groove  between  the  latter  and 
the  hymen  about  opposite  the  posterior  third  of  the  lateral  boundary  of  the  vagi- 
nal orifice.     The  minute 

FIG.  1709.         Dorsalnerve  opening  of  the  duct,  from 

Corpus  clitoridis  Dorsal  artery      /  Artery  of  bulb  .  5-.  6  mm.  Wide,  IS  often 

Glans  ciitoridis   X.  /          /Crusof        at  the  bottom  of  a  small 

j^tf^^^^^^aMMMtf^^_     /  /    clitoris  <  •**.!_ 

>*•    \  j^^ttg^T'T'l  pulled         depression    in    the    mu- 

upward       cous   membrane   of    the 

/  7\  vestibule. 

/'          \  *n    structure    the 

gland  corresponds  to  the 

Crus  of     -  mucous      tubo  -  alveolar 

Jjr/i  1  ^.Portion  of     type,  the  small  compo- 

Right  lobe  —  /      •  1    u    1  u 

of  bulbus  M  /     A  *C\  nent    lobules,    however, 

being  separated  by  con- 

-Tube.r          siderable  tracts  of  fibro- 

ischii         muscular  tissue.   Theter- 

hgament  t  minal  compartments  are 

lined  with  columnar  epi- 
thelium containing  many 
rf  goblet  cells.   The  lobular 

Glands  of  Bartholin  •  .\ 

ducts  unite  to  torm  the 

Dissection  of  uroeenital  triangle  of  female;  left  lobe  of  cincr1i=>      ^vrr^rr^rv     rani! 

vestibular  bulb  has  been  removed. 

which  is  beset  with  mi- 
nute mucous  follicles.  The  main  duct,  which  sometimes  exhibits  ampullary  enlarge- 
ments, is  clothed  with  columnar  epithelium  until  near  its  termination,  where  its  lining 
becomes  stratified  squamous  in  character,  to  correspond  with  that  of  the  vestibule. 
The  secretion  of  the  gland  is  whitish  in  color  and  viscid. 

Vessels. — The  arteries  supplying  the  gland  are  usually  twigs  given  off  from  the 
bulbar  branch  of  the  internal  pudic.  The  veins  are  tributary  chiefly  to  the  internal 
pudic,  but  also  communicate  with  the  trunks  of  the  vestibular  bulb  and  of  the  vagina. 
The  lymphatics  join  those  of  the  vagina  and  rectum  that  are  afferents  of  the  internal 
iliac  nodes.  Tt  is  probable  that,  to'a  limited  extent,  communication  also  exists  with 
the  paths  ending  in  the  superficial  inguinal  nodes. 

The  nerves  are  very  numerous,  and  include  sympathetic  fibres  and  twigs  from 
the  pudic. 

Development. — The  glands  of  Bartholin  first  appear  in  embryos  from  4-5  cm. 
Ion-,  as  solid  epithelial  outgrowths  from  the  lateral  walls  of  the  urogenital  sinus.  At 
first  simple  cylinder,  they  later  become  branched,  acquire  a  lumen  and,  in  embryos 
of  from  12-15  cm.  in  length,  begin  to  exhibit  alveoli  lined  with  mucus  secreting  fells 
i  V.  Miiller).  Although  fully  developed  at  birth,  the  glands  remain  small  until  lu-ar 
puberty,  when  they  enlarge,  acquiring  their  greatest  si/e  during  the  years  of  sexual 
activity.  After  the  cessation  of  menstruation  they  gradually  diminish,  and  are 
atrophic  in  the  aged  subject. 


THE    MAMMARY   GLANDS.  2027 

Variations.— The  glands  of  the  two  sides  often  vary  in  size  and  may  be  asymmetrically 
placed.  The  ducts  may  be  doubled  and  the  lobules  so  separated  that  the  usual  gland-mass  is 
replaced  by  isolated  divisions.  The  glands  are  sometimes  seemingly  wanting  on  one  or 
both  sides. 

PRACTICAL   CONSIDERATIONS  :    THE   EXTERNAL   GENITALS. 

Owing  to  the  protected  position  of  the  vulva  it  is  rarely  wounded  except  from 
tears  in  childbirth.  When  lesions  from  external  violence  do  occur,  they  are  usually 
the  result  of  falls  astride  hard  objects,  of  kicks,  of  blows,  or  of  wounds  inflicted  by 
horned  cattle.  Because  of  the  laxity  of  the  tissues  and  the  free  blood-supply  in  the 
labia  majora  large  haematomata  may  collect,  especially  if  the  bulbus  vestibuli  is 
opened.  Again,  because  of  the  free  blood-supply  and  loose  tissue  in  this  region, 
plastic  operations  are  commonly  very  successful.  The  hemorrhage  is  free,  but  ordi- 
narily stops  spontaneously  unless  the  erectile  tissue  of  the  clitoris  or  its  continuations 
backward,  the  bulbus  vestibuli,  is 'wounded. 

The  lymphatics  and  veins  of  the  vulva  pass  to  the  groin,  thus  explaining  the  en- 
largement of  the  vulva  in  lymphatic  obstructions  in  the  inguinal  nodes,  such  as 
elephantiasis,  and  in  venous  stasis  in  the  same  region,  as  in  milk  leg.  The  clitoris 
is  especially  involved  in  elephantiasis,  either  alone  or  as  part  of  a  general  enlarge- 
ment. The  absorbents  of  the  vagina  pass  to  the  pelvis.  About  the  orifice  of  the 
vagina  is  a  zone  in  which  the  two  sets  intercommunicate. 

Cysts  of  the  vulva  are  commonly  due  to  retention  of  secretion  within  the  glands 
of  Bartholin.  They  occupy  the  posterior  third  on  each  side  of  the  vaginal  orifice,  and 
project  more  from  the  mucous  than  from  the  cutaneous  surface.  These  glands  are 
often  the  seat  of  abscess,  almost,  if  not  always,  the  result  of  gonorrheal  infection.  The 
female  urethra,  running  downward  and  forward — so  that  it  is  nearest  to  the  vaginal 
wall  in  its  upper  portion — is  much  shorter,  much  less  curved,  relatively  much  wider, 
and — as  it  is  not  surrounded  at  any  point  by  structures  of  such  density — much  more 
dilatable  than  the  male  urethra.  In  consequence  of  its  shortness,  its  width,  the  direc- 
tion of  its  course,  and  the  limitation  of  its  function  to  serving  as  a  passage  for  urine, 
it  is,  as  compared  with  the  male  urethra,  infected  less  frequently,  and  its  inflammation 
is  associated  with  less  severe  symptoms,  yields  more  readily  to  treatment,  and  gives 
rise  to  fewer  complications  and  sequelae, — stricture,  for  example,  being  very  rare. 

As  a  result  of  its  dilatability  it  may  be  used  as  a  channel  for  digital  exploration 
of  the  bladder,  or  for  the  extraction  of  vesical  calculi  or  pedunculated  tumors,  if 
small,  or  of  foreign  bodies.  The  dilatation  should  be  accomplished  very  slowly — 
under  an  anaesthetic — and  is  then  rarely  followed  by  persistent  paralysis.  The  imper- 
fect development  of  the  triangular  (subpubic)  ligament  in  the  female  and  of  the 
muscular  wall  of  the  urethra — the  emptying  of  the  canal  being  so  facilitated  by  its 
direction,  width,  and  shortness — explains  the  relative  ease  and  safety  of  extreme 
dilatation. 

A  small  red  vascular  tumor,  called  a  urethra!  caruncle,  is  sometimes  found  pro- 
truding, usually  from  the  posterior  wall  of  the  female  urethra.  It  is  extremely  sensi- 
tive, giving  rise  to  much  pain  on  pressure,  movement,  or  urination. 

The  vaginal  process  of  peritoneum  accompanying  the  round  ligament,  already 
spoken  of,  may  reach  as  far  as  the  labium  majus,  and  may  give  rise  to  a  congenital 
hernia  or  hydrocele  in  that  part.  Owing  commonly  to  the  presence  of  vaginal  dis- 
charge, the  vulvar  region  is  frequently  the  seat  of  venereal  warts.  Because  of  the 
warmth,  moisture,  and  friction  to  which  syphilitic  papules  are  exposed  in  these  parts, 
condylomata  and  mucous  patches  are  common  and  well  marked.  One  of  the  most 
frequent  seats  of  chancre  in  women  is  about  the  fourchette  and  anus,  because  the 
infected  discharges  of  the  vagina  tend  to  run  over  and  lodge  on  these  structures. 

THE  MAMMARY  GLANDS. 

Although  morphologically  considered  they  are  modified  cutaneous  glands  and 
developed  in  both  sexes,  the  functional  importance  of  the  mammary  glands  (mammae) 
in  the  female  entitle  them  to  be  reckoned  as  organs  accessory  to  the  reproductive 
apparatus.  Each  mamma,  or  breast,  consists  of  a  group  of  twenty  or  more  individual 


2028 


HUMAN   ANATOMY. 


and  separate  glands,  opening  by  independent  ducts,  that  collectively  constitute  the 
true  secreting  organ  (corpus  mammae),  as  distinguished  from  the  enveloping  layer  of 
fat  and  areolar  tissue. 

As  seen  in  the  young,  well-developed  subject,  before  the  occurrence  of  preg- 
nancy, the  mammae  form  two  hemispherical  projections  that  lie  upon  the  thoracic 
wall,  one  on  either  side  of  the  sternum,  extending  from  the  outer  margin  of  the  latter 
to  the  axillary  border  and  from  the  level  of  the  second  to  that  of  the  sixth  rib.  The 
outline  of  the  organ  is  not  quite  circular  but  elliptical,  the  horizontal  diameter,  from 
10-12  cm.  (4-4^4  in.),  being  about  one  centimetre  more  than  the  vertical.  The 
height  of  the  projection  measures  about  5. 5  cm.  The  rounded  contour  of  the  breast 
depends  chiefly  upon  the  fat  that  forms  a  complete  envelope  for  the  glandular  tissue, 

FIG.  1710 


Areol 


Lobule  of  gland-tissue 


Excretory  duct 


Nipple 


\ 
Ampulla 

Lactiferous  duct 
Lilt  mamma  drawn  from  living  subject ;  ducts  and  glandular  tissue  have  been  drawn  from  dissection. 


except  beneath  the  nipple  and,  in  places,  on  the  deep  muscular  surface.  In  the  young 
subject,  in  whom  the  gland  has  never  enlarged  in  consequence  of  pregnancy,  the  secre- 
tory tissue  is  relatively  small  in  amount  and  masked  by  the  fat  that  penetrates  between 
the  lobules.  The  approximate  summit  of  each  breast,  when  firm  and  non-pendulous 
as  in  young  women,  is  marked  by  the  conical  or  wart-like  nipple  (papilla  mammai- 
which  lies  opposite -the  lower  border  of  the  fourth  rib  and  is  pierced  by  the  excretory 
canals,  or  lactiferous  ducts,  from  the  lobes.  The  nipple,  about  I  cm.  high,  and 
marked  by  numerous  shallow  furrows,  is  surrounded  by  the  arcola,  a  cutaneous  /one 
about  4.5  cm.  in  diameter  that  is  modelled  by  minute  low  elevations  produced  by  the 
small  subcutaneous  areolar  ^  land .^,  Vt  glands  of  Montgomery ,  which  represent  isolated 
accessory  portions  of  secretory  tissue.  Although  varying  with  the  complexion,  the 


THE   MAMMARY    GLANDS. 


2029 


Suspensory  band 


Pectoral  muscle 


pigmentation  of  the  integument  covering  the  nipple  and  areola  is  very  slight,  and 
hence  the  color  of  these  parts  is  usually  a  rosy  pink.  After  the  earlier  months  of 
pregnancy  the  color  of  the  nipple  and  areola  changes  to  brown,  in  varying  shades  of 
intensity,  which  tint  thereafter  never  entirely  disappears,  but  becomes  temporarily 
augmented  with  each  pregnancy. 

The  mammary  gland  lies  within  the  superficial  fascia  of  the  thorax,  which  not 
only  forms  a  general  investment  for  the  or- 
gan, but  also  sends  into  it  septa  that  mate-  FIG.  1711. 
rially  aid  in  supporting  the  fat  and  glandular 
tissue.  Local  peripheral  thickenings  of  the 
fascia  occur  above  and  below  and  assume  the 
character  of  suspensory  bands,  those  above 
being  known  as  the  ligaments  of  Cooper. 
Although  for  the  most  part  separated  from 
the  underlying  muscle  by  a  layer  of  fascia  that 
permits  of  shifting  of  the  mamma,  its  deepest 
lobules  may  occupy  recesses  between  the  fas- 
ciculi of  the  pectoralis  major. 

Structure. — The  corpus  mam  nice  con- 
sists of  from  15-20  or  more  flattened  pyrami- 
dal lobes  (lobi  mammae),  each  of  which  is  a 
distinct  gland  measuring  from  1.5-2  cm.  The 
lobes  are  radially  disposed,  the  groups  of  al- 
veoli or  lobules  lying  towards  the  periphery 
and  the  excretory  ducts  converging  towards 
the  nipple,  upon  which  they  open.  When 
enlarged,  as  during  lactation,  the  lobes  pro- 
duce irregularities  in  the  outline  and  on  the 
surface  of  the  gland-mass  that  may  be  felt 
through  the  covering  of  adipose  tissue.  Each 
lobe  is  subdivided  by  connective  tissue  into 
several  lobules  (lobuli  mammae),  which  in  turn 
are  made  up  of  the  ultimate  divisions  of  the 
secreting  tissue  or  alveoli.  The  latter  are 
sacular  compartments,  the  walls  of  which  con- 
sist of  a  well-defined  membrana  propria,  or 
basement  membrane,  lined,  in  the  resting  con- 
dition, by  a  double  layer  of  cells.  Those 
next  the  membrana  propria  are  probably  to 
be  regarded  as  muscular  in  nature  (Lacroix, 
Benda),  thus  emphasizing  the  resemblance 
between  the  mammary  and  sweat  glands. 

The  inner  cells,  the  secretory  elements,  are  cuboid  or  low  columnar,  from  .005- 
.007  mm.  high,  and  present  the  usual  appearances  of  glandular  epithelium. 

Ditring  lactation  the  alveoli  become  greatly  enlarged  and  distended  and  the 
intervening  connective  tissue  correspondingly  reduced,  so  that  the  alveoli  are  pressed 
closely  together,  the  general  appearance  of  the  tissue  often  recalling  that  of  the 
lung.  Under  such  conditions  the  secreting  cells  vary  with  the  distention  of  the 
alveoli,  being  low  in  large  compartments  and  higher  in  those  less  expanded.  The 
protoplasm  of  the  cells  actively  engaged  in  the  production  of  milk  contain  minute 
oil  droplets  that  occupy  chiefly  the  inner  zone.  As  these  increase  in  size,  they  press 
the  nucleus  towards  the  basement  membrane  and  project  into  the  alveolus,  being 
separated  from  the  lumen  by  only  a  thin  protoplasmic  stratum.  Finally,  the  latter 
ruptures,  and  the  oil  droplets  escape  into  the  albuminous  fluid  that  is  additionally 
secreted  by  the  glands  and  occupy  the  alveolus.  After  liberation  of  the  oil  droplets, 
the  epithelial  cell  is  much  reduced  in  height,  but  after  a  time  again  becomes  the 
seat  of  renewed  accumulation  of  fat  and  the  production  of  milk-globules.  Destruc- 
tion of  the  fat-liberating  cells,  therefore,  does  not  take  place. 

The  excretory  ducts  begin   as  the   minute   canals  into  which  the  alveoli  open. 


Gland- 
tissue 


Fascial  envelope 


Sagittal  section  of  mamma  of  young  woman  who  had 
never  borne  children  ;  hardened  in  formalin. 


2030 


HUMAN   ANATOMY. 


•      ._- 


-Excretory  duct 


' 


Section  of  mammary  gland  before  lactation.     X  170. 


At  first  they  are  small  and  much  like  the  terminal  compartments  of  the  gland  and 
lined  with  a  thin  stratum  of  longitudinally  disposed  involuntary  muscle,  upon  which 
rests  a  single  layer  of  cuboid  epithelial  cells.      The  latter  give  place  to  cells  of  col- 
umnar type  within  the  lactiferous 

FIG.  1712.  ducts   that   are   formed    by    the 

junction  of  the  smaller  canals. 
On  approaching  the  base  of  the 
nipple,  beneath  the  areola,  each 
milk-duct  presents  a  spindle-form 
enlargement  or  ampulla  ( sinus 
lactifcrus),  from  10-12  mm.  long 
and  about  half  as  wide,  that 
serves  as  a  temporary  reservoir 
for  the  secretion  of  the  gland. 
Beyond  the  ampulla  the  duct 
narrows  to  a  calibre  of  little  over 
2  mm. ,  passes  into  the  nipple, 
and  ends,  after  traversing  the  lat- 
ter parallel  with  the  other  ducts, 
in  a  minute  orifice  from  .  5-.  7 
mm.  in  diameter,  at  the  summit 
of  the  papilla.  On  gaining  the 
last-named  point,  the  lining  epi- 
thelium of  the  duct  assumes  the 
stratified  squamous  type  of  the 
adjacent  epidermis.  Embedded 
within  the  delicate  but  more  or 
less  pigmented  skin  that  covers  their  exterior,  the  areola  and  nipple  contain  well- 
marked  bundles  of  involuntary  muscle,  by  the  contraction  of  which  the  nipple  becomes 
erect  and  prominent,  as  after  the  application  of  mechanical  stimulus.  Within  the 
areola  this  contractile  tissue  forms  a  layer,  in  places  almost  2  mm.  thick,  that  encircles 
the  base  of  the  nipple  and  is  continued  into  its  substance  as  a  net-work  of  bundles, 
between  which  the  lactiferous  ducts  pass.  Deeper  longitudinal  strands  of  unstriped 
muscle  occupy  the  axial  portions  of  the  nipple. 

Over  both  areola  and  nipple  the  skin  is  provided  with  large  sebaceous  glands,  the 
secretion  of  which  is  increased 

during  lactation   and   designed  FIG.  1713. 

for  protection  while  nursing. 
Sweat-glands  are  absent  over 
the  nipple,  but  large  and  modi- 
fied in  the  vicinity  of  the  periph- 
ery of  the  areola.  The  surface  of 
the  latter  is  modelled,  especially 
towards  the  close  of  pregnancy, 
by  low  rounded  elevations  that 
indicate  the  positions  of  the  sub- 
cutaneous areolar  or  Montgom- 
ery* s  glands.  The  latter  are 
rudimentary  accessory  masses  of 
glandular  tissue,  from  1-4  mm. 
in  diameter,  that  correspond  in 
their  general  structure  with  that 
of  the  mammary  glands.  Their 
ducts  open  by  minute  orifices 
on  tin-  surface  of  tin-  areola. 

Milk. — The    fully    estab- 
lished secretion  of  the  mammary  gland  (lac  femininuin)  is  an  emulsion,  the  fatty  milk- 
globules  being  suspended   in    a   clear,    colorless,    and    watery   plasma,    the   variations 
in  tint — from  bluish  to  yellowish-white — depending  upon  the  amount  of  fat. 


Section  of  mammary  gland  during:  lactation,  showing  distended 
alveoli  liiifd  with  fat-bearing  cells.    X  '7"- 


The 


THE   MAMMARY   GLANDS.  -  2031 

composition  of  human  milk  includes  over  86  per  cent,  of  water,  about  3  of  albuminous 
substances,  5.3  of  fat,  5  of  sugar,  and  less  than  i  per  cent,  of  salts.  The  chief  mor- 
phological constituents  of  milk  are  the  milk-globules  (fat  droplets  liberated  from  the 
alveolar  cells),  that  vary  in  size  from  the  most  minute  spherules  to  those  having  a 
diameter  of  from  .003—  .005  mm.  and,  exceptionally,  even  twice  as  much.  Their 
average  number  per  cubic  millimetre  is  something  over  one  million  (Bouchut). 
Whether  the  milk-globules  are  enclosed  within  extremely  thin  envelopes  of  casein  is 
still  uncertain.  Whether  the  fat  is  actually  produced  within  the  cells,  or  is  to  be 
regarded  as  only  in  transit,  and,  likewise,  whether  the  milk  leaves  the  cells  already 
emulsified,  are  also  questions  undecided. 

During  the  last  weeks  of  pregnancy  and  for  two  or  three  days  after  its  termina- 
tion, the  breasts  contain  a  clear  watery  secretion,  known  as  colostrum,  that  differs 
from  milk  in  containing  relatively  little  fat  and  numerous  conspicuous  bodies  —  the 
colostrum  corpuscles  —  of  uncertain  form  and  size.  These  bodies  are  usually  spherical, 
but  may  be  irregular  in  outline,  and  measure  from  .oi2-.oi8  mm.,  although  they 
may  attain  a  diameter  of  more  than  .040  mm.  Their  protoplasm  is  markedly  granu- 
lar and  often  of  a  yellowish  or  reddish-yellow  tint.  The  colostrum  corpuscles  are 
modified  alveolar  epithelial  cells  that  have  been  cast  off  during  the  initial  changes  and 

FIG.   1714.  FIG.  1715. 


"~  ot) 

0 

Jft 

L-' 

c 

0 

O 

O  r   r 

O 

or 

\ 

0 

Human  milk.     X  500.  Colostrum,  showing  corpuscles 

and  oil-drops.     X  500. 

expansion  of  the  alveoli  preparatory  to  the  establishment  of  lactation.  They  again 
appear  after  this  function  has  ended,  and  may  continue  to  be  expressed  from  the  gland 
for  months  or,  in  exceptional  cases,  for  even  years. 

Vessels. — The  arteries  supplying  the  mamma  are  principally  the  second,  third, 
and  fourth  anterior  perforating  branches  of  the  internal  mammary.  These  vessels,  in 
addition  to  their  distribution  to  the  skin  and  more  superficial  parts  of  the  breast,  send 
deeper  twigs  to  the  glandular  tissue,  which  eventually  break  up  into  capillary  net-works 
enclosing  the  alveoli.  The  lower  and  lateral  portion  of  the  organ  receives  an  addi- 
tional supply  from  the  external  mammary  branches  from  the  long  thoracic  artery  from 
the  axillary.  During  lactation  these  vessels  are  markedly  increased  in  size.  The 
veins  follow  chiefly  the  arteries,  emptying  into  the  internal  mammary  and  the  long 
thoracic.  The  cutaneous  veins,  which  during  lactation  are  enlarged  and  show  through 
the  delicate  skin  as  a  net-work  of  blue  lines,  in  part  join  those  accompanying  the  arteries 
and  in  part  form  vessels  that  take  an  independent  course  over  the  clavicle  to 
become  tributary  to  the  external  jugular  vein.  Within  the  areola  the  cutaneous 
veins  form  a  plexus  that  more  or  less  completely  encircles  the  nipple  and  receives 
its  blood. 

The  lymphatics  of  the  mamma  are  exceptionally  numerous  and  important.  The 
deeper  ones  surround  the  groups  of  alveoli  as  channels  that  lie  within  the  interlobular 
connective  tissue  and  pass  towards  the  surface,  where  they  join  the  rich  subareolar 
plexus.  The  latter  also  receives  the  collecting  stems  from  the  close  cutaneous  net- 
works that  drain  the  integument  covering  the  nipple  and  areola.  With  the  exception 


2032  HUMAN   ANATOMY. 

of  a  few  trunks  that  follow  the  perforating  arteries  and  become  afferents  of  the  lymph- 
nodes  lying  along  the  internal  mammary  artery,  all  the  lymphatics  of  the  breast  join 
to  form  two  or  three  large  trunks  that  pass  from  the  lower  and  lateral  border  of  the 
organ  through  the  subcutaneous  tissue  towards  the  axilla  to  empty,  sometimes  united 
into  a  single  stem,  into  the  lymph-node  that  lies  upon  the  serratus  magnus  over  the 
third  rib. 

The  nerves  supplying  the  glandular  tissue  are  from  the  fourth,  fifth,  and  sixth 
intercostals,  the  accompanying  sympathetic  fibres  passing  by  way  of  the  rami  com- 
municantes  from  the  thoracic  portion  of  the  gangliated  cord.  Their  ultimate  distri- 
bution may  be  traced  to  the  plexuses  upon  the  basement  membrane  surrounding  the 
alveoli  and,  according  to  Arnstein,  even  between  the  secretory  cells.  The  cutaneous 
nerves  are  derived  from  both  the  supraclavicular  branches  of  the  cervical  plexus  and 
the  anterior  and  lateral  cutaneous  branches  of  the  second  to  the  fifth  intercostals. 

Development. — The  arrangement  of  the  several  pairs  of  mammary  glands 
possessed  by  a  majority  of  the  lower  animals  in  two  longitudinal  rows  is  foreshadowed 
in  the  earliest  stage  of  the  development  of  these  organs,  so  characteristic  of  the  highest 
class  of  vertebrates  (mammalia).  A  linear  thickening  of  the  ectoblast,  known  as  the 
milk-ridge,  appears  as  a  low  elevation  that  extends  obliquely  from  the  base  of  the 
fore  to  the  inguinal  region.  Along  this  ridge  a  series  of  enlargements,  later  sepa- 
rated by  absorption  of  the  intervening  portions  of  the  ridge,  indicates  the  anlage  for 
a  corresponding  number  of  mammae.  The  occurrence  of  a  definite  milk-ridge  in 
the  human  embryo  is  uncertain,  although  its  presence  has  been  observed  (Kallius), 
and  the  position  of  supernumerary  mammae  suggests  its  influence. 

In  man  a  knob-like  thickening  of  the  ectoblast  appears  during  the  second  month 
of  foetal  life.  This  thickening  sinks  into  the  underlying  mesoblastic  tissue,  which 
undergoes  proliferation  and  condensation  and  forms  an  investment  for  the  growing 
epithelial  mass.  From  this  envelope  the  fibrous  and  muscular  tissue  of  the  areola 
and  nipple  are  derived,  while  the  subjacent  mesoblast  produces  the  connective-tissue 
stroma.  The  ectoblastic  ingrowth  represents  a  sunken  area  of  integument  that  in 
principle  corresponds  to  the  marsupial  pouch  of  the  lowest  mammals  (monotrctncs}. 
Solid  epithelial  sprouts  grow  out  from  the  sides  of  the  conical  or  flask-shaped 
epidermal  plug  and  are  the  first  anlages  of  the  true  mammary  gland,  later  becoming 
the  excretory  ducts.  Subsequently  the  central  part  of  the  ectoblastic  ingrowth 
undergoes  degeneration  and  destruction,  and  what  at  first  was  an  elevation  now 
becomes  a  depression  of  the  surface.  From  the  middle  of  this  depressed  area  there 
appears,  shortly  before  or  immediately  succeeding  (Basch)  birth,  an  elevation  that 
later  becomes  the  nipple.  Meanwhile,  the  epithelial  duct-outgrowths  penetrate  the 
surrounding  condensed  mesoblastic  stroma,  increase  in  length,  subdivide,  and  acquire 
a  lumen  at  their  expanded  distal  ends,  thus  giving  rise  to  the  system  of  ducts  and 
the  lobules  of  immature  gland-tissue.  With  the  further  development  of  the  latter, 
the  surrounding  mesoblastic  stroma  is  broken  up  into  the  interlobular  septa  and 
fibrous  framework  of  the  corpus  mammae. 

At  birth  the  gland  is  represented  by  the  lactiferous  ducts  with  their  ampullae,  the 
smaller  ducts,  and  the  immature  alveoli.  Quite  commonly  the  mammary  glands  in 
both  sexes  are  the  seat  of  temporary  activity  during  the  first  few  days  after  birth,  the 
breasts  yielding  a  secretion  resembling  colostrum,  popularly  known  as  "witch-milk." 

The  mammae  remain  rudimentary  during  childhood  until  the  approach  of  sexual 
maturity,  when  they  increase  in  size  and  rotundity  in  consequence  chiefly  of  the 
deposition  of  fat.  The  full  development  of  the  true  gland  is  deferred  until  the  occur- 
rence of  pregnancy,  when  active  proliferation  and  increase  in  the  gland-tissue  take 
place  in  preparation  for  its  functional  activity  as  a  milk-producing  organ.  After  lacta- 
tion has  ended,  the  mammre  undergo  regression  or  involution,  the  glandular  tissue  being 
reduced  in  amount  and  returning  to  a  condition  resembling  that  existing  before 
pregnancy.  With  the  recurrence  of  the  latter,  the  gland  again  enters  upon  a  period 
of  renewed  growth  and  preparation,  to  be  followed  in  time  by  return  to  the  resting 
condition,  in  which  the  amount  of  glandular  tissue  is  inconspicuous.  After  cessation 
of  menstruation  the  mammary  gland  gradually  decreases  in  size,  and  in  advanced 
years  the  corpus  mammae  may  be  reduced  to  a  fibrous  disc  in  which  gland-tissue  is 
almost  entirely  wanting. 


PRACTICAL   CONSIDERATIONS  :    MAMMARY    GLANDS.        2033 

Variations. — The  mammae  are  frequently  asymmetrically  developed,  the  left  being  often 
larger  than  the  right.  While  very  rarely  one  or  both  may  be  wanting,  with  or  without  associated 
absence  of  the  nipple,  increase  in  their  number  is  of  relatively  common  occurrence.  The  super- 
numerary mammae  vary  greatly  in  the  extent  to  which  they  are  developed,  sometimes  being 
represented  by  well-formed  accessory  glands  (polymastia)  that  may  become  functionating  organs, 
but  more  often,  particularly  in  the  male  subject,  by  only  rudimentary  nipples  (polythelia),  or 
even  by  pigmented  areas  suggesting  areolae.  In  women  polythelia  is  usually  associated  with 
greater  or  less  development  of  glandular  tissue.  Although  the  astonishing  frequency  (14  per 
cent. )  of  polythelia  in  men,  as  announced  by  Bardeleben,1  is  to  be  reconciled  only  by  accepting 
many  doubtful  pigment  spots  as  of  significance,  the  occurrence  of  rudimentary  supernumerary 
nipples  in  males  is  undoubtedly  more  common  than  formerly  recognized.  Exceptionally  above 
and  to  the  outer  side,  the  usual  position  of  the  accessory  mammas  is  below  and  somewhat 
medial  to  the  normal  glands,  and  in  general  corresponds  to  the  mammary  line  of  the  lower 
animals,  The  number  of  the  accessory  glands  varies,  as  many  as  three  pairs  in  one  case,  and 
five  milk-secreting  organs  in  another,  having  been  observed.  They  are  often  asymmetrically 
placed  and  not  uniformly  developed.  Comparative  studies  of  the  mammae  in  the  lower  animals 
and  the  disposition  of  the  supernumerary  organs  in  the  human  subject,  suggest  the  probability 
that  man's  remote  ancestors  normally  possessed  a  greater  number  than  two,2  the  occasional 
occurrence  of  the  anomalous  mammae  indicating  a  reversion  to  the  primary  condition.  In  addi- 
tion to  the  supernumerary  mammae  in  positions  anticipated  by  the  milk-ridges,  rudimentary 
organs  sometimes  occupy  very  unusual  situations,  among  which  have  been  the  back,  shoulder, 
thigh,  and  labium  majus.  Erratic  mammae  are  also  met  with  among  the  lower  animals. 

PRACTICAL   CONSIDERATIONS:    THE   MAMMARY   GLANDS. 

The  skin  covering  the  bfeast  is  thin  and  movable,  with  plainly  visible  cutaneous 
veins  which  enlarge  during  lactation,  or  in  cases  of  mammary  hypertrophy,  or  when 
obstruction  due  to  abscess  or  new  growth  exists  in  the  breast  or  in  the  post-mam- 
mary region.  The  frequent  occurrence  of  asymmetry  in  size,  the  left  breast  being 
larger,  is  said  (Williams)  probably  to  be  due  to  the  fact  that  most  mothers,  being 
right-handed,  suckle  chiefly  with  the  left  breast,  which  is  also  said  to  be  on  an  aver- 
age heavier,  more  intimately  associated  with  the  pelvic  sexual  organs,  more  prone 
to  hypertrophy,  and  more  likely  to  be  the  seat  of  carcinoma  or  other  neoplasms. 
The  greater  part  of  the  breast  lies  upon  the  sheath  of  the  pectoralis  major  muscle, 
on  which  it  is  freely  movable,  the  intervening  cellular  tissue  being  extremely  lax. 
About  one-third  of  the  gland,  however,  extends  beyond  and  below  the  axillary 
border  of  the  pectoralis  major,  and  is  in  relation  in  the  axilla  with  the  serratus  mag- 
nus  and,  when  large,  with  the  origins  of  the  rectus  and  the  external  oblique.  While 
the  normal  breast  moves  freely  over  the  pectoral  muscle,  it  also  moves  slightly  with 
it  when  the  muscle  is  contracted.  Hence  in  inflammation  of  the  breast,  or  after 
operation  upon  it  or  for  its  removal,  the  muscle  should  be  kept  at  rest  by  binding 
the  arm  to  the  side.  In  testing  for  pathological  adhesion  of  the  breast  to  the  pec- 
toral sheath,  it  is  well  to  move  the  breast  in  the  direction  of  the  fibres  of  the  pecto- 
ralis major.  If  it  is  moved  transversely  to  them,  it  may  carry  the  relaxed  muscle 
with  it  and  no  diminution  of  mobility  will  be  noticeable. 

In  examining  for  growths  of  the  breast,  the  normal  lobes,  especially  if  at  all 
enlarged,  may  be  felt  through  the  adipose  envelope  and  may  be  mistaken  for  tumors. 
To  avoid  this,  the  gland  should  be  palpated  with  the  flat  hand,  which  should  gently 
compress  it  against  the  chest  wall.  In  this  manner  very  small  cysts  or  neoplasms 
may  be  recognized,  as  they  become  more  resistant  and  more  prominent  than  the 
normal  gland  tissue.  The  two  breasts  should  be  thus  examined  at  the  same  time, 
so  that  any  difference  in  their  size,  consistence,  or  sensitiveness  may  be  detected. 

The  nipple  in  men  and  in  young  virgins  is  found  over  the  fourth  intercostal 
space,  or  over  the  fifth  rib,  about  three-quarters  of  an  inch  external  to  the  costo- 
ch'ondral  junction.  In  older  women  its  position  is  not  constant,  and,  of  course,  it 
varies  with  the  degree  of  the  enlargement,  laxness,  and  pendency  that  follow  preg- 
nancy and  that  are  common  in  women  of  tropical  lands  and  in  negresses  and  women 
of  other  of  the  lower  races. 

The  development  of  the  nipple  may  be  arrested  at  the  stage  when  the  central 
part  of  the  ectoblastic  ingrowth  has  undergone  degeneration  and  when  a  depression 

1  Anatom.  Anzeiger,  Bd.  vii.,  1892. 

2  An  interesting  review  of  the  subject  is  given  by  Bonnet  in  Ergebrisse  d.  Anat.  n.  Entwick., 
Bd.  ii.,  1892. 

128 


2034  HUMAN   ANATOMY. 

exists  towards  the  bottom  of  which  the  ducts  of  the  mamma  converge.  In  such 
cases  the  depression  persists  ;  in  others  the  areola  is  present,  but  the  nipple  absent. 
In  both,  while  lactation  may  be  normal,  the  suckling  of  children  is  impossible.  The 
nipple  may  be  absent  or  defective  as  a  result  of  trauma  or  of  disease — wounds,  burns, 
ulcers,  abscesses — during  infancy. 

The  normal  nipples  of  virgins  or  nulliparae  may  be  almost  on  a  level  with  the 
areola,  while  those  of  multipart  are  often  greatly  elongated  from  the  traction 
upon  them.  Temporary  elongation  or  erection  of  the  nipple  may  be  caused  by 
reflex  stimulation  of  the  unstriped  muscular  tissue  of  the  skin  of  the  nipple  and 
areola. 

Infection  of  the  nipple  is  common,  because,  on  the  one  hand,  of  the  many  folds 
of  its  delicate  cutaneous  covering,  containing  a  number  of  sebaceous  glands  and 
closely  connected  to  the  underlying  structures  ;  and,  on  the  other,  of  its  frequent 
exposure  during  suckling  to  irritation  from  unhealthy  discharges  from  the  child's 
mouth,  leading  to  epidermic  maceration  and  to  painful  erosions,  fissures,  and  ulcers. 

Atrophy  of  the  mammary  glandular  elements  is  of  normal  occurrence  after  the 
menopause,  the  fibrous  and  fatty  structure  being  also  affected  in  many  instances  of 
noticeable  withering  of  the  breasts.  In  early  life  this  condition  may  result  from 
disease,  or  from  removal  of  the  ovaries,  and  become  a  true  deformity. 

Hypertrophy  of  the  breast  consists  in  an  overgrowth  of  both  the  glandular  and 
the  fibrous  elements,  the  latter  predominating,  and  occurs  usually  between  14  and 
30  years  of  age — the  period  of  greatest  sexual  activity.  Amenorrhcea  and  pregnancy 
are  frequently  associated  with  it. 

Infection  of  the  breast  is  usually  carried  through  either  the  lymphatics  or  the 
milk  ducts,  most  commonly  during  the  early  period  of  lactation  ;  more  rarely  it 
appears  during  the  other  notable  periods  of  mammary  physiological  excitement — 
i.e. ,  in  the  newly  born — the  "witch-milk"  period  (vide  supra) — and  at  puberty. 
In  the  nursing  woman  the  presence  of  fissures  or  abrasions  of  the  nipple  predisposes 
to  lymphatic  infection.  Lack  of  cleanliness,  with  fermentation  or  decomposition  of 
milk  and  of  cutaneous  secretions  in  the  folds  or  crevices  of  the  nipple,  favors  infec- 
tion in  the  ampullae  of  the  ducts. 

If  the  superficial  lymphatics  are  the  channels  of  infection,  suppuration  in  the 
cellulo-fatty  tissue  superficial  to  the  breast  may  result  (supramammary  abscess) 
and,  owing  to  the  lack  of  tension,  pointing  will  occur  early,  the  course  of  the  case 
will  be  rapid,  and  the  constitutional  symptoms  relatively  slight.  If  the  deeper  lym- 
phatics or  milk  ducts  convey  the  infection,  suppuration  occurs  within  the  lobules 
(intramammary  abscess)  and  spreads  slowly  from  one  to  another  through  the  inter- 
lobular  connective  tissue.  As  the  pus  is  surrounded  by  the  unyielding  breast  tissue 
and  confined  by  the  capsule  of  subcutaneous  fascia  and  its  septa,  pain,  tenderness, 
fever,  and  other  constitutional  symptoms  are  marked  and  the  progress  of  the  disease 
is  slow.  Occasionally,  by  extension  from  an  intramammary  focus,  the  connective 
tissue  lying  between  the  breast  and  the  pectoral  sheath  is  involved  (retro,  infra,  or 
submammary  abscess),  but  suppuration  in  this  region  is  more  apt  to  be  consecutive 
to  caries  of  a  rib  (usually  tuberculous).  The  constitutional  symptoms  are  less 
marked.  The  whole  breast  is  pushed  forward  and  made  more  prominent.  Point- 
ing— by  reason  of  the  effect  of  gravity — is  apt  to  occur  somewhere  at  the  circum- 
ference of  the  breast,  usually  towards  the  inframaxillary  region.  Sometimes  these 
abscesses  ulcerate  directly  through  the  breast  tissue  to  the  subcutaneous  area,  making 
two  cavities,  one  infra,  the  other  supramammary,  connected  by  a  narrow  channel, 
a  form  of  Velpeau's  "abces  de  bouton  en  chemise."  As  the  breast  is  thinnest 
along  a  line  drawn  from  the  sterno-clavicular  joint  to  the  nipple,  it  is  in  that  region 
that  such  perforation  of  the  gland  usually  occurs.  As  the  breast — glandular  and 
other  structures,  including  the  skin  covering  it — is  supplied  chiefly  by  the  lateral  cuta- 
neous branches  of  the  second  to  sixth  intercostal  nerves,  pain  in  inflammatory  or  sup- 
purative  affections,  or  in  the  case  of  new  growth,  may  be  felt  down  the  arm  ( intercosto- 
humeral)  ;  over  the  shoulder-blade  (posterior  branches  of  the  thoracic  nerves)  ; 
down  the  side  or  along  the  posterior  parietes  of  the  thorax  (intercostals)  ;  or  up  the 
neck  (supraclavicular  from  the  cervical  plexus  anastomosing  with  the  second  inter- 
costal). Incisions  for  the  evacuation  of  pus  should  be  made  on  lines  radiating  out- 


PRACTICAL   CONSIDERATIONS  :    MAMMARY    GLANDS.        2035 

ward  from  the  nipple  so  that  the  larger  lactiferous  ducts  converging  to  that  point 
may  not  be  wounded. 

Carcinoma  of  the  breast  is  ,the  most  important  of  the  diseases  affecting  that 
gland,  about  85  per  cent,  of  the  neoplasms  involving  the  female  mamma  being  can- 
cerous. About  99  per  cent,  of  all  neoplasms  of  the  breast  occur  in  the  female,  only 
i  per  cent,  in  the  male,  "  illustrating  the  law — of  which  many  other  instances  might 
be  cited — that  functionless,  obsolete  structures  have  but  little  tendency  to  take  on 
the  neoplastic  process"  (Williams).  It  begins  most  often  in  the  cuboid  (glandular) 
epithelium  of  the  alveoli — acinous  cancer  ;  but  not  uncommonly  in  the  columnar 
epithelium  of  the  ducts — duct  cancer.  In  either  case  it  is  usually  at  first  a  dense 
nodule  of  small  size,  growing  by  infiltration  of  the  neighboring  tissues.  In  tracing 
the  methods  of  extension  and  dissemination  from  the  original  nodule  in  the  gland 
substance,  the  various  structural  relationships  must  be  borne  in  mind.  The  ana- 
tomical routes  along  which  such  a  growth  may  spread,  and  the  chief  symptoms 
thereby  produced,  are  as  follows  : 

1.  By  way  of  the  lymphatic  vessels  that  empty  into  the  lymph  nodes  (pectoral 
or  anterior)  overlying  the  digitation  of  the  serratus  magnus  arising  from  the  third 
rib.      This  is  the  most  frequent  form  of  lymphatic  dissemination,  because  (a)  these 
vessels  include  the  great  majority  of  the  mammary  lymphatics  ;   (£)  the  nodes  .first 
involved  in  cancer  are  those  into  which  is  emptied  the  lymph  from  the  part  of  the 
gland  affected  by  the  primary  growth  ;  and  (<:)  cancer  originates  most  frequently  in 
the   upper  and  outer  quadrant  of  the   breast,   possibly  because  that  area  is  most 
exposed  to   minor  traumatism  ;    or  possibly   because    the   alveoli    are  much   more 
numerous  in  the  peripheral  than  the  central  part  of  the  gland,  the  majority  of  mam- 
mary neoplasms  arising  in  the  seats  of  the  greatest  development  of  postembryonal 
activity  where  cells  still  capable  of  growth  and  development  most  abound  (Williams) 
— i.e. ,  in  the  vicinity  of  the  alveoli.      Williams  calls  attention  to  the  fact  that  the 
' '  axillary  tail' '  of  the  mamma  lies  close  to  the  pectoral  nodes  and  might  be  mistaken 
for  the  enlarged  gland.      By  placing  the  flat  of  the  hand  or  the  palmar  surfaces  of 
the  fingers  against  the  inner  (thoracic)  wall  of  the  axilla  and  moving  the  superficial 
structures  to  and  fro,  enlargement  of  the  pectoral  nodes  may  easily  be  detected. 

2.  From  these  pectoral  nodes  situated  along  the  anterior  border  of  the  axilla, 
carcinoma  may  invade  (#)  the  central  nodes,  receiving  the  lymph  from  the  upper 
extremity,  and  lying  on  the  inner  side  of  the  axillary  vein,  on  either  the  superfi- 
cial or  deep  aspect  of  the  axillary  fascia,  embedded  in  a  quantity  of  fat,  and  half- 
way between  the  anterior  and  posterior  folds  of  the  axilla.      The  inner  portion  of  the 
axillary  tuft  of  hair  overlies  this  group  of  glands.      The  axillary  fascia  at  this  place 
may  present  an  opening  very  similar  to  the  saphenous  opening  of  the  thigh  (Poirier, 
Leaf)  and  the  nodes  may  occupy  this.      These  nodes  may  be  palpable,  but  if  only 
slightly  enlarged  cannot  readily  be  felt  in  stout  persons.      If  no  axillary  opening  is 
present  and  the  nodes  lie  on  the  superficial  aspect  of  the  fascia,  they  can  best  be  felt 
by  pressing  them  against  the  unyielding  fascia,  with  the  arm  in  the  abducted  posi- 
tion ;  if,  on  the  other  hand,  an  opening  is  present,  the  arm  should  be  adducted  so 
as  to  relax  the  fascia,  when  the  nodes  may  be  recognized  by  pressing  them  against 
the  thoracic  wall.      For  these  reasons,  in  examining  for  enlarged  axillary  nodes,  the 
arm  should  always  be  placed  in  both  these  positions  (Leaf).      As  this  set  of  nodes  is 
traversed  by  the  intercosto-humeral   nerve,  carcinoma  involving  them  often  causes 
pain  down  the  inner  and  posterior  aspect  of  the  arm.      As  they  receive  the  lymph 
vessels  of  the  upper  limb,  the  structures  in  the  deltoid  region  and  down  the  arm  may 
become  infiltrated.      Or  the  disease  may  invade  (<5)  the  deep  axillary  nodes,  lying 
along  the  inner  and  anterior  aspect  of  the  axillary  vessels,  and  communicating  with 
both  the  pectoral  and  the  lower  deep  cervical  nodes;  extensive  implication  of  this  group 
results  in  oedema  and  swelling  of  the  upper  limb,  compression  of  the  axillary  vein,  and 
in  widely  distributed  pain  in  the  regions  supplied  by  the  brachial  plexus;  (f)«  the  infra- 
clavicular  (cephalic)  nodes,  lying  just  below  the  clavicle,  between  the  deltoid  and  pec- 
toralis  major  muscles  and,  like  the  deep  axillary  nodes,  communicating  below  with 
the  pectoral  nodes,  and  above  with  the  supraclavicular  or  inferior  cervical  nodes,  the 
disease  often  reaching  these  latter  ;   (d")  the  subscapular  nodes,  lying  along  the  sub- 
scapular  vessels  and  receiving  lymph  from  the  scapular  region,  and  often,  when  the 


2036  HUMAN   ANATOMY. 

central  group  of  nodes  lies  on  the  deep  surface  of  the  axillary  fascia,  forming  one 
large  group  with  it.  Involvement  of  these  nodes  with  their  afferent  lymph  vessels 
probably  accounts  for  the  extensive  infiltration  o,f  the  structures  over  the  upper 
lateral  and  posterior  aspects  of  the  thoracic  parietes  occasionally  seen  in  advanced 
cases. 

3.  The  nodes  at  the  summit  of  the  axilla  may  be  involved  through  lymph  vessels 
passing  above  the  pectoralis  minor  and  through  Mohrenheim's  fossa  without  entering 
the  pectoral  nodes. 

4.  The   anterior  mediastinal   glands  may  be  invaded — especially   if  the  inner 
segment  of  the  breast  is  affected — by  way  of  the  lymph  vessels  following  the  per- 
forating arteries  and  emptying  into  the  nodes  along  the  internal  mammary  artery. 
In  this  manner,  as  well  as  by  direct  extension  through  the  inframammary  tissue,  the 
pectoral  fascia  and  muscles,  and  the  chest  wall,  the  pleura  and  lung  may  become 
involved.     Other  symptoms  due  to  mediastinal  growth  have  been  described  in  rela- 
tion to  that  region  (page  1833). 

5.  The   free  communication   in  the  subareolar  plexus  between  the  glandular 
lymphatics,  deep  and  superficial,  (paramammary)  and  the  subcutaneous  and  thoracic 
lymphatics,   together  with    the   connection    established   between   the   periglandular 
tissue  below  and  the  skin  above  by  the  ligaments  of  Cooper  (suspensory  ligaments), 
explains  the  frequency  with  which  mammary  carcinoma  extends   to  the  overlying 
skin.     As  a  result  of  its  infiltration  the  latter  becomes  dense,  inelastic,   brawny, 
dusky,  and  adherent.      It  cannot  be  picked  up  between  the  thumb  and  finger  in  a 
fold;  and  often  quite  early  and  before  it  has  become  adherent,  and  as  a  result  of  con- 
traction of  the  growth  pulling  on  the  fibrous  bands  uniting  it  to  the  deeper  parts,  it 
is  drawn  into  a  number  of  little  depressions  or  dimples  like  those  on  the  skin  of  an 
orange.      When  such  infiltration  is  diffuse  and  spreads  largely  through  the  subcu- 
taneous net-work  of  lymph  vessels,  the  condition  known  as  cancer  en  cuirasse  is  pro- 
duced.     In  the  later  stages  ulceration,  infection,  hemorrhage,  and  foul  discharge  are 
frequent  results  of  the  cutaneous  involvement. 

6.  If  the  growth  is  central  it  may  extend  to  the  lactiferous  ducts  or  to  the  peri- 
acinous  tissue  continuous  with  that  surrounding  the  ducts,  and  through  its  own  or 
their  cicatricial  contraction  it  may  depress  or  retract  the  nipple  or  pull  it  so  that  it 
deviates  from  its  normal  direction.     This  is  not  so  valuable  a  symptom  as  the  dim- 
pling of  the  skin  above  described,  as  it  may  be  caused  by  injury  or  by  chronic  disease, 
such  as  abscess,  tubercle,  or  mastitis.     Moreover,  it  may  not  be  present  if  the  growth 
is  peripheral. 

7.  The  carcinoma  may  extend  through  the  lymph  communications  between  the 
gland  and  the  underlying  connective  tissue  and  pectoral  fascia  and  muscle,  so  as  to 
become  fixed  to  or  incorporated  with  those  structures,  the  breast  losing  much  of  its 
mobility,  especially  in  a  direction  parallel  with  the  pectoralis  major  fibres.      It  may 
thence  continue  through  the  thoracic  wall  and  invade  the  pleural  or  mediastinal  cavity 
directly. 

8.  Through  the  intercommunication  of  the  lymph  system  of  the  two  breasts 
through  the  subcutaneous  thoracic  lymphatics,  cancer  of  one  breast  may  extend  to  the 
other  (Moore),  or  to  the  glands  of  the  opposite  axilla  (Volkmann,  Stiles),  or  to  the 
glands  of  both  axillae  (Scarpa,  Cooper  ;  quoted  by  Williams).  , 

9.  General  dissemination  of  the  cancerous  disease  may  also  take  place  through 
detached   cells  or  particles  (emboli)  from  the  primary  growth  entering  the  blood 
stream.     The  liver  is  the  organ  most  frequently  affected  by  metastasis  in  cases  of 
breast  cancer.     The  bones,  the  lungs,  and  the  pleurae  come  next,  but  almost  no 
organ  or  structure  of  the  body  is  exempt. 

In  removal  of  the  breast  the  following  anatomical  points  should  be  borne  in  mind  : 
(a)  The  intimate  connection  between  the  skin  and  the  gland  itself  by  means  of  lymph- 
and  blood-vessels,  by  the  suspensory  ligaments,  and  by  glandular  processes  accom- 
panying or  contained  within  these  ligaments  (Stiles),  shows  the  necessity  for  free 
sacrifice  of  the  skin  overlying  the  breast. 

(  h  )  The  irregular  shape  of  the  breast,  which  has  two  extensions  that  frequently 
reach  into  the  axilla,  and  one  that  reaches  to  or  overlaps  the  border  of  the  sternum, 
and  not  uncommonly  similar  processes  that  spring  from  other  parts  of  the  surface  of 


DEVELOPMENT   OF   THE   REPRODUCTIVE    ORGANS.         2037 

the  gland  and  radiate  in  the  paramammury  fatty  tissue  (Williams)  emphasizes  the 
need  for  incisions  that  shall  permit  the  removal  of  all  such  portions  of  possibly  dis- 
eased glandular  tissue. 

O)  The  usual  defect  in  the  retroglandular  fatty  envelope,  bringing  the  glandu- 
lar lobules  into  intimate  relation  with  the  pectoral  fascia  and  muscle  (Heidenhain), 
facilitates  extension  of  the  disease  in  that  direction  and  indicates  the  free  removal  of 
the  pectoralis  major  in  most  cases. 

(d}  The  lymphatic  distribution  (vide  supra}  supplies  the  same  indication  as  to 
removal  of  the  greater  pectoral  and — to  a  lesser  degree — as  to  the  lesser  pectoral  also. 
It,  of  course,  points  unmistakably  to  the  need  for  thorough  cleaning  out  of  the  axilla. 
In  doing  this  it  is  well  to  remove  the  chain  of  lymphatic  nodes — pectoral,  central, 
deep,  subscapular,  etc. — in  one  piece,  not  only  because  it  minimizes  the  risk  of 
infection  of  healthy  structures  during  the  operation  (Cheyne),  but  because  if  the 
clavi-pectoral  fascia  (suspensory  ligament  of  the  axilla)  and  the  axillary  fascia, 
together  with  the  greater  part  of  the  pectoralis  minor  muscle  (on  account  of  the 
continuity  of  its  sheath  with  the  clavi-pectoral  fascia),  are  removed  in  one  piece,  the 
groups  of  nodes  enumerated  above  and  embedded  in  them  will  be  removed  also 
(Leaf).  To  this  there  are  three  exceptions:  ( i )  a  node  of  the  subscapular  group 
sometimes  projects  backward  and  is  found  between  the  teres  minor  and  infraspinatus 
muscles  ;  (2)  some  nodes  of  the  infraclavicular  group  may  lie  to  the  outer  side  of 
the  axillary  vein,  and  when  this  is  so,  as  the  suspensory  ligament  is  stripped  off  the 
inner  side  these  glands  would  remain  behind  ;  (3)  the  cephalic  node  would  not  be 
reached  during  the  removal  in  one  piece  of  the  ligament  and  axillary  fascia  with  their 
contained  groups  of  nodes.  Of  course  all  these  nodes  should  be  sought  for  and 
removed  separately  (Leaf). 

(e)  The  most  important  blood-vessel  in  danger  during  the  operation  is  the 
axillary  vein  (page  888),  made  somewhat  more  prominent — together  with  the  artery 
and  the  brachial  plexus — when  the  arm  is  raised  and  the  head  of  the  humerus  is  made 
to  project  into  the  axilla.  These  structures  normally  lie  on  the  outer  wall  of  the 
axilla,  but  may  be  so  embedded  in  a  mass  of  cancerous  tissue  as  to  be  difficult  of 
recognition.  On  the  posterior  aspect  of  the  axilla  the  subscapular  vessels  and  (in 
close  proximity  to  the  subscapular  nodes)  the  long  subscapular  nerve  supplying  the 
latissimus  dorsi  muscle  should  be  avoided.  The  inner  (thoracic)  wall  of  the  axilla 
is  the  region  in  which  the  dissection  may  be  conducted  with  the  greatest  freedom, 
the  posterior  thoracic  nerve  running  almost  vertically  downward  in  close  contact  with 
the  outer  surface  of  the  serratus  magnus  muscle  to  which  it  is  distributed.  The 
arteries  met  with  or  divided  in  the  course  of  the  operation  are  ( i )  the  pectoral 
branches  of  the  acromial  thoracic  ;  (2)  the  alar  thoracic  ;  (3)  the  long  thoracic 
(external  mammary)  running  along  the  lower  border  of  the  pectoralis  minor  muscle  ; 
(4)  lateral  branches  from  the  second,  third,  and  fourth  intercostal  arteries  ;  and  (5) 
anterior  perforating  branches  of  the  internal  mammary  artery,  emerging  at  the  second, 
third,  and  fourth  intercostal  spaces.  The  vessels  in  the  last  two  groups  are  normally 
small,  but  by  enlarging  during  the  growth  of  a  carcinoma  and  by  retracting  after 
division  to  beneath  the  surface  of  the  chest- wall,  they  are  sometimes  slightly  trouble- 
some during  operation. 

DEVELOPMENT   OF   THE    REPRODUCTIVE   ORGANS. 

The  development  of  the  internal  organs  of  reproduction  includes  two  distinct 
but  closely  related  processes,  the  one  leading  to  the  formation  of  the  sexual  glands, 
the  testes  or  ovaries,  and  the  other  to  the  provision  of  the  canals  for  the  conveyance 
and  temporary  storage  of  the  products  of  these  glands.  Provision  of  the  excretory 
canals  is  accomplished  by  the  secondary  changes  and  further  growth  of  parts  of  the 
Wolffian  tubules  and  ducts  in  conjunction  with  two  additional  canals — the  Miillerian 
ducts. 

References  to  the  preceding  account  of  the  Wolffian  body  (page  1935)  will  recall 
the  constitution  of  the  latter  as  including  a  series  of  transverse  tubules  opening  into 
a  common  longitudinal  duct,  and,  further,  that  the  Wolffian  tubules  comprise  an 
anterior  sexual  and  a  posterior  excretory  group. 


2038 


HUMAN   ANATOMY. 


During  the  development  of  the  Wolffian  body,  or  mesonephros,  a  second  tube, 
the  Miillerian  duct,  is  formed  within  a  linear  thickening,  the  genital  ridge,  that 
appears  upon  the  ventro-lateral  surface  of  the  Wolffian  body.  Near  the  cephalic  end 
of  the  latter,  an  evagination  of  the  lining  of  the  body-cavity  into  the  genital  ridge 

occurs,  by  the  contin- 

FIG.  1716.  ued  proliferation  and 

'Aorta  downward  growth  of 

the  cells  of  which  the 
evagination  is  con- 
verted into  a  tube — 
the  Miillerian  duct. 
This  tube  communi- 
cates directly  with  the 
body-cavity  by  means 
of  its  trumpet-shaped 
cephalic  extremity, 
extends  parallel  with 
and  closely  related  to 
the  Wolffian  duct 
and,  later,  below 
reaches  the  urogeni- 
tal  sinus.  The  con- 


Mesothelium 


Ipighian  body 


1  Anlage  of  sexual  glands 

Portion  of  cross-section  of  early  human  embryo,  showing  first  appear- 
ance of  sexual  glands  within  germinal  ridges.     X  60. 


verging  lower  seg- 
ments of  the  two  Wolffian  and  the  two  Miillerian  ducts  are  embedded  within  a  median 
mesoblastic  band,  the  genital  cord,  that  represents  the  continuation  of  the  fused  geni- 
tal ridges  of  the  two  sides.  Within  the  genital  cord  the  Miillerian  ducts  lie  in  the 
middle,  closely  applied  to  each  other,  with  one  Wolffian  duct  on  each  side  (Fig.  1649). 

The  development  of  'the  sexual  glands  begins  about  the  time  that  the  Miillerian 
ducts  are  forming,  as  a  linear  thickening  of  the  mesothelium  and  underlying  meso- 
blastic stroma,  situated,  however,  on  the  median  surface  of  the  Wolffian  body  (Fig. 
1716).  Over  this  raised  area,  the  germinal  ridge,  the  character  of  the  primary  peri- 
toneum changes,  its  cells  becoming  taller  and  undergoing  proliferation.  Very  early 
among  the  increasing  elements  appear  specialized  cells  distinguished  by  their  large 
size,  clear  protoplasm,  and  conspicuous  nucleus.  These  are  \he  primary  germ-cells, 
which  later  become  the  primordial  ova  or  sperm-cells,  according  to  sex.  For  a  time 
this  cannot  be  determined,  since  in  this  indifferent  stage  of  the  sexual  gland  special- 
ization has  not  yet  progressed  sufficiently  to  make  differentiation  possible.  The  dis- 
tinctive features  of 

both  sexes,  there-  FIG.  1717. 

fore,  are  acquired 
by  farther  devel- 
opment of  a  neutral 
sex-type  in  which 
the  indifferent  sex- 
ual glands,  the 
Wolffian  tubules, 
the  Wolffian  and 
the  Miillerian  ducts 
are  the  chief  com- 
ponents. Whether 
determination  of 
sex  is  dependent 
upon  nutrition, 
and,  therefore, 
more  or  less  acci- 
dental, or  is  established  early  and  antedates  the  appearance  of  indifferent  organs, 
is  a  question  still  undecided. 

Differentiation  of  the  Male  Type. — The  development  of  the  testis  from  the 
indifferent  sexual  gland  includes  the  invasion  of  the  proliferated  mesothelial  cells  of 


Primary  germ-cells 


Proliferating 
Wolffian  stroma 


Cross-sue  tii  in  df  germinal   ridjji-  of   young  human  embryo,  showing 
early  dinVrrntiution  <>t  pimi.uv  mTin-cells.     X  500. 


DEVELOPMENT   OF   THE    REPRODUCTIVE   ORGANS. 


2039 


Globus  major 


FlG.    1718. 


the  germinal  ridge  by  the  underlying  mesoblastic  stroma,  whereby  the  epithelial 
muss  becomes  broken  up  into  cylinders  and  cords  that  extend  into  the  subjacent 
stroma.  The  cell-cords  are  composed  of  two  kinds  of  elements,  the  numerous  chief 
epithelial  cells  and  the  larger  sperm-cells,  the  direct  descendants  of  the  indiffer- 
ent primary  germ-cells,  which  they  embrace.  About  the  fifth  week  a  layer  of 
mesoderm  insinuates  itself  between  the  superficial  and  deeper  portions  of  the  epi- 
thelial mass,  thereby  separating  a  peripheral  zone.  This  ingrowth  results  in  the 
formation  of  a  robust  fibrous  envelope,  the  tunica  albuginea,  around  the  entire  testis, 
while  the  separated  mesothelial  layer  differentiates  into  the  serous  covering.  The 
cell-cords  become  subdivided  by  the  ingrowth  of  the  mesoblastic  stroma  into  smaller 
spherical  masses,  which  subsequently  are  converted  into  the  seminiferous  tubules, 
while  from  the  stroma  are  supplied  the  interlobular  septa  and  the  intralobular  support- 
ing tissue.  About  the  sixth  week  additional  cell-cords  grow  into  the  young  testis 
from  the  adjacent  Wolfifian  tubules.  These 
ingrowths  invade  the  attached  border  of 
the  testicle  and  become  the  medullary 
cords,  which  are  so  disposed  that  each 
comes  into  relation  with  one  of  the  spheri- 
cal epithelial  cell-masses.  Although  both 
the  latter  and  the  medullary  cords  are 
solid,  the  later  relation  of  the  secreting 
tubules  of  the  gland  to  the  excretory 
channels  is  thus  foreshadowed,  since  from 
the  ingrowths  from  the  Wolffian  tubules 
are  derived  the  straight  tubules  and  those 
of  the  rete  testes.  The  farther  differen- 
tiation of  the  seminiferous  canals,  which, 
as  well  as  the  medullary  cords,  are  with- 
out lumen  until  near  puberty,  proceeds 
from  the  growth  and  branching  of  the  cell- 
masses,  the  cells  of  which  become  the  epi- 
thelium of  the  tubules.  The  latter  are 
enclosed  by  an  investment  of  condensed 
mesoblastic  stroma  continuous  with  the 
supporting  tissue  and  framework  of  the 
gland.  At  the  approach  of  sexual  ma- 
turity the  primary  sperm-cells  within  the 
tubules  proliferate  and  become  the  sperma- 
togonia,  while  from  other  epithelial  ele- 
ments are  derived  the  Sertoli  cells.  The 
roles  played  by  these  elements  in  the  pro- 
duction of  the  spermatozoa  are  described 
under  Spermatogenesis  (page  1945). 

Coincidently  with  the  growth  of  the 

testis  the  Wolfifian  body  atrophies,  with  the  exception  of  some  of  its  tubules  and  duct, 
which  increase  and,  in  conjunction  with  the  medullary  cords  also  derived  from  the 
mesonephros,  establish  the  elaborate  excretory  passages  of  the  sexual  gland.  From 
the  Wolfifian  tubules  are  developed  the  coni  vasculosi  and  the  cluctuli  efferentes,  while 
the  Wolfifian  duct  gives  rise  to  the  tube  of  the  epididymis,  the  vas  deferens,  and,  as 
a  secondary  outgrowth,  the  seminal  vesicle.  The  caudal  group  of  mesonephric  tubules 
are  represented  in  both  sexes  by  rudimentary  structures,  which  in  the  male  are  the 
paradidymis  and  the  vasa  aberrantia.  The  appendix  of  the  epididymis,  or  stalked 
hydatid,  probably  also  owes  its  origin  to  the  Wolfifian  duct. 

Although,  as  is  evident  from  the  foregoing,  the  Wolffian  tubules  and  duct  are 
largely  concerned  in  the  development  of  the  generative  tract  in  the  male,  the  Mul- 
lerian  duct  is  not  without  representation,  since  its  two  extremities  persist.  The 
upper  (after  migration  lower)  end  remains  as  the  appendix  of  the  testis,  and  the 
lower,  fused  with  its  fellow,  is  seen  as  the  prostatic  utricle,  which,  therefore,  is  the 
homologue  of  the  vagina  and,  possibly,  the  uterus.  In  exceptional  cases,  where  it 


Longitudinal  section  of  developing  testicle.     X  20. 


2040 


HUMAN   ANATOMY. 


persists,  the  intervening  portion  of  the  Miillerian  duct  is  represented  by  Rathke's 
duct.  Since  the  prostate  gland  arises  as  an  outgrowth  from  the  urogenital  sinus 
(page  1979),  it  has  no  genetic  relation  with  the  seminal  ducts. 

Descent  of  the  Testes. — The  development  of  the  sexual  glands,  in  both 
sexes,  is  attended  with  conspicuous  migration  from  their  original  position  on  either 
side  of  the  upper  two  lumbar  vertebrae,  opposite  the  lower  pole  of  the  kidney.  In 
the  case  of  the  testis,  this  migration  is  so  extensive  that  by  birth  the  organ  usually  has 
passed  through  the  abdominal  wall  and  entered  the  scrotum,  having  completed 
its  so-called  descent. 

Certain  peritoneal  folds  (mesenteries)  and  fibre-muscular  bands  (ligaments)  merit 
brief  description,  since  they  are  more  or  less  concerned  in  the  migration  of  the  sexual 
glands.  The  Wolffian  body  is  enclosed  and  attached  to  the  posterior  body-wall 
by  a  fold  (mesonephridium),  of  which  the  upper  elongated  end  is  continued  to  the 

FIG.   1719. 


AE 


AT 


rVGM 


WT 


WT 


RD 


Ur  CG  Pr 


EC, 


Diagrams  illustrating  differentiation  of  two  sexes  from  indifferent  type.  A,  Indifferent :  G,  sexual  gland;  WD, 
Wolffian  duct;  WT.  WT,  groups  of  Wolffian  tubules;  MD,  Miillerian  duct;  RD.  renal  diverticultim  ;  C,  cloaca; 
G,  gut;  A,  allantois.  B,  Male:  T,  testicle;  VE,  vasa  efferentia  ;  GM.  globus  major;  VD,  vas  deferens  ;  Pa,  para- 
didymis  ;  VA.  vas  aberrans  ;  SV,  seminal  vesicle  ;  AT,  appendix  testis  •  AE,  appendix  epididymidis  ;  B,  bladder  ;  PU, 
prostatic  utricle;  Pr,  prostate;  Ur,  urethra;  CG,  Cowper's  gland;  CC,  corpus  cavernosum  ;  R.  rectum;  RD,  renal 
duct ;  K,  kidney.  C,  Female  :  O,  ovary  ;  Ov,  oviduct ;  F,  fimbria  ;  U,  uterus ;  V,  vagina  ;  DEp,  duct  of  epoophorpn  ; 
TEp.  tubules  of  epoophpron  ;  Po,  paroophoron  ;  HM,  hydatid  of  Morgagni ;  GD  Gartner's  duct;  BG,  Bartholin's 
gland;  C,  clitoris;  K,  kidney;  R,  rectum.  (Modified from  Wiedershetni.) 

diaphragm  (plica  phrenico-mcsonephricd)  and  the  lower  to  the  abdominal  wall  in 
the  inguinal  region  (plica  inguino-mesoncphrica).  The  early  sexual  gland  is  also 
provided  with  a  mesentery  (mesorchium  or  mesovariurri),  that  above  and  below  is 
continuous  with  folds  that  pass  from  the  upper  and  lower  poles  of  the  gland  to  the 
mesentery  of  the  mesonephros.  Within  the  inferior  plica,  of  the  two  much  the  better 
marked,  lies  a  fibro-musciilar  strand  (the  ligament  of  the  testis  or  orarv},  that  below 
is  attached  at  first  to  both  the  Wolffian  and  Mullerian  ducts.  Later,  owing  to  the 
atrophy  of  the  one  or  the  other  of  these  ducts,  according  to  sex,  the  ligament  of  the 
testes  remains  connected  with  the  Wolffian  duct  and  the  ligament  of  the  ovary  with 
the  Mullerian  duct. 

A  second  band  of  muscular  tissue  appears  within  the  lower  part  of  the  inguino- 
mesonephric  fold,  and  has  its  upper  attachment  also  to  the  Wolffian  and  Mullerian 
ducts  at  a  point  about  where  they  receive  the  insertion  of  the  ligament  of  the  testes  or 
ovary.  The  lower  end  of  the  band  blends  with  the  subperitoneal  tissue  of  the  anterior 
abdominal  wall  in  the  vicinity  of  the  future  abdominal  ring.  This  band,  the  gcnito- 


1720. 


Wolffian 
duct 


DEVELOPMENT   OF   THE    REPRODUCTIVE   ORGANS.          2041 

inguinal  ligament,  corresponds  with  the  gubernaculum  testis  in  the  male  and  with  the 
round  ligament  of  the  uterus  in  the  female.  In  the  former  it  is  not  directly  attached 
to  the  testis,  but  only  through  its  ligament,  the  point  of  attachment  later  corre- 
sponding to  the  origin 

of    the     vas    deferens  FIG. 

from  the  epididymis. 

The  testicle  begins 
its  descent  during  the 
second  foetal  month, 
coincidently  with  com- 
mencing atrophy  of  the 
Wolffian  body,  and, 
under  the  influence  and 
guidance  of  the  genito- 
inguinal  ligament,  by 
the  end  of  the  third 
month  reaches  the  an- 
terior abdominal  wall 
in  the  vicinity  of  the 
later  internal  abdomi- 
nal ring.  This  position 
it  retains  until  the  close 
of  the  sixth  month, 
when  it  enters  upon  its 
final  descent. 

Meanwhile,  the 
musculo-fascia  layers 
of  the  abdominal  wall  undergo  evagination,  resulting  in  the  production  of  a  shallow 
pouch,  the  inguinal  bursa,  into  which  a  sac  of  peritoneum,  the  processus  vaginalis, 
extends,  together  with  the  closely  associated  genito-inguinal  ligament.  The  inguinal 
bursa,  in  turn,  sinks  into  the  shallow  scrotal  pouch  that  has  independently  devel- 
oped as  an  integumentary  fold.  The  wall  of  the  bursa  contains  the  constituents  that 
later  differentiate  into  the  coverings  proper  of  the  spermatic  cord  and  testicle — the 
intercolumnar,  cremasteric,  and  infundibuliform  fasciae.  Its  muscular  fibres,  pro- 
longed from  the  internal  oblique  and  transversalis  layer,  correspond  with  the  cre- 
master,  and  surround  the  genito-inguinal  ligament. 

Owing  to  the  thickening  of  the  lower  end  of  the  latter,  a  slight  elevation  appears 
on  the  floor  of  the  bursa,  which  thus  seemingly  becomes  pushed  up  towards  the 
testis  to  form  the  rudiment  of  what  in  some  animals  becomes  a  well-marked  projec- 
tion, the  conns  ingualis,  but  in  man  always  remains  insignificant.  In  consequence 
of  these  changes,  during  the  fourth  month  the  testis  is  displaced  upward  and  its 

descent    temporarily    inter- 
FIG.  1721. 

.  Epididymis 
Testis 


Plica  phrenic 
mesonephrica 


Sexual  gland 


Wolffian  bodvk- 


Mesentery  of 
gland 

Wolffian  duct 


Genito-inguinal 
ligament 

Plica  inguino- 
mesonephrica 


Ligament  of  gland 


Umbilical  arterie: 


Gut 


Allantoic  duct 


Umbilical  vein 


Wolffian  bodies  and  sexual  glands  of  human  embryo  of  about  six  weeks 
(17  mm.  long).     X  15.     (Modified from  Kollmann.) 


fascia 


s  deferens 

Deep  epig-asti 


Rectus  muscle 


rupted. 

About  the  beginning  of 
the  seventh  month,  the  final 
descent  of  the  testicle  is  in- 
augurated with  deepening 
of  the  bursa  and  downward 
extension  of  the  peritoneal 
pouch,  accompanied  by  the 
now  thickened  and  short- 
ened genito-inguinal  liga- 
ment. Although  shorten- 
ing of  the  latter,  together 
with  the  pull  exerted  by  the 

cremasteric  fibres,  plays  an  active  role  in  drawing  the  testicle  through  the  abdominal 
wall  and  into  the  scrotum,  these  factors  are  undoubtedly  supplemented  by  forces  result- 
ing from  the  growth  and  expansion  of  the  pelvis  and  inguinal  regions. 

The  processus  vaginalis  reaches  the  bottom  of  the  scrotal  sac  in  advance  of  the 


Peritoneal  cavity 

Int.  obi.  and  transver.  muse 
Aponeurosis  of  external  oblique 
Periton 

Genito-inguinal  ligai 

Transversal 

Cremastei 

Intercolumn? 

Integumentary  scrotal  pouch 


5cessus  vaginalis 
•:)       Attachment  of  ligament  to 
Mr  thickened    floor  of   inguinal 

Diagram  showing  early  stage  in  descent  of  testicle.     (After  Waldeyer.} 


2042 


HUMAN   ANATOMY. 


Peritoneum 

,Vasd 


rens 
p  epigastric  vessels 


testicle,  which,  drawn  from  its  mesentery  (mesorchium),  descends  outside  and  behind 
the  peritoneal  pouch  that  later  constitutes  its  partial  serous  investment,  the  tunica 
vaginalis.      After  the  descent  is  completed,  usually  shortly  before  birth,   but  some- 
times   not    until   afterward,  the  tubular 

FIG.  1722.  upper    segment    of   the    peritoneal    sac 

closes  normally  during  the  early  months 
of  childhood.  This  closure  takes  place 
first  in  the  vicinity  of  the  internal  ab- 
dominal ring  and  in  the  middle  of  the 
tube,  passing  upward  towards  the  ring 
and  downward  to  within  a  short  distance 
of  the  sexual  gland.  The  occluded 
portion  of  the  vaginal  process  is  later 
represented  by  a  small  fibrous  band  (lig- 
amentum  vaginale)  that  extends  from  the 
internal  abdominal  ring  above,  through 
the  inguinal  canal  and  for  a  variable  dis- 
tance down  the  spermatic  cord,  some- 
times, although  not  commonly,  as  far  as 
the  tunica  vaginalis.  When  the  pro- 


processus  vag 
Perito 


Interco 

fasc 

Skin  and  d 


Diagram  showing  relations  of  descended  testicle  to 
processus  vaginalis,  which  still  freely  communicates  with 
peritoneal  sac  of  abdomen.  (After  Waldeyer.) 


cessus  vaginalis  fails  to  close,  as  it  oc- 
casionally does  in  man  and  always  in 
certain  animals,  as  the  rat,  in  which  de- 
scent and  retraction  of  the  testis  periodically  occur,  the  serous  sac  surrounding  the  tes- 
ticle communicates  throughout  life  with  the  peritoneal  cavity,  a  condition  favorable  to 
the  production  of  hernia.  With  the  obliteration  of  the  lumen  of  the  processus  vaginalis, 
an  inguinal  canal,  in  the  sense  of  a  distinct  tube,  disappears,  the  spermatic  duct  and 
associated  vessels  and  nerves,  that  necessarily  share  in  the  migration  of  the  sexual  gland 
into  the  scrotum,  passing  between  the  muscular  and  fascial  layers  of  the  abdominal  wall 
embedded  in  connective  tissue.  The  remains  of  the  shrunken  genito-inguinal  liga- 
ment, or  gubernaculum,  are  represented  by  a  fibro-muscular  band,  the  scrotal  liga- 
ment, that  connects  the  lower  end  of  the  epididymis  to  the  scrotal  wall  (Fig.  1687). 
Descent  of  the  testicle  may  be  imperfectly  accomplished,  so  that  the  gland,  failing 
to  reach  the  bottom  of  the  scrotal  sac,  may  be  arrested  within  the  inguinal  canal  or 
spermatic  cord,  or  permanently  retained  within  the  abdomen,  a  condition  known  as 
cryptorchism,  usually  leading  to  atrophy  of  the  gland.  Associated  with  faulty  descent 
may  be  anomalous  situation,,  the  testis 
lying  beneath  the  integument  near  the 
external  abdominal  ring,  in  the  thigh,  or 
in  the  perineum.  After  descent  the  axis 
of  the  testicle  may  be  abnormally  di- 
rected, the  gland  assuming  a  transverse, 
rotated,  or  even  inverted  position. 

Differentiation  of  the  Female 
Type. — Development  of  female  internal 
reproductive  organs  proceeds  along  the 
same  lines  as  in  the  male,  the  ovary  being 
differentiated  from  the  indifferent  sexual 
gland  and  the  genital  canals  from  the 
Mullerian  and  Wolffian  ducts. 

Differentiation  of  the  ovary  has  been 
described  in  connection  with  that  organ 
(page  1993).  That  of  the  Fallopian 
tubes,  uterus,  and  vagina  results  from 
further  growth,  fusion,  and  modification 
of  the  Mullerian  ducts.  Lower  segments 
of  the  latter,  below  the  attachment  of  the  ligament  of  the  ovary  (page  2040),  undergo 
fusion  and  form  the  uterus  and  vagina.  Their  upper  segments  remain  unfused  and  be- 
come Fallopian  tubes.  Details  of  these  changes  are  given  under  the  respective  organs. 


FIG.  1723- 

Peritoneum 

Vas  deferens 

Deep  epigastric  vesse 


Closed  portion  of 
processus  vaginalis 


Cremaster 

Infundibuliform  f  is.  i,i 
Sac  of  tunica  vaginalis 

Visceral  layer 
Parietal  layer 


Skin  and  dartos 


Diagram  showing  relation 
brane  after  upper  part  of  pro 
(After  Waldry,->  ) 


--tir].-  to  serous  mem- 
vat>inalis  has  closed. 


Suprarenal 
body 


DEVELOPMENT   OF    THE    REPRODUCTIVE   ORGANS.          2043 

In  the  female  the  Wolffian  tubules  and  duct  play  a  subordinate  role,  remaining 
to  form  rudimentary  organs,  the  epoophoron  (page  2000),  the  paroophoron  (page 
2002),  and,  when  the  Wolffian  duct  persists,  the  duct  of  Gartner  (page  2001).  The 
broad  ligament  is  formed  by  the  enlargement  of  the  primary  peritoneal  fold  containing 
the  Miillerian  and  Wolffian  ducts. 

Descent  of  the  Ovary. — The  primary  position  of  the  ovary,  at  the  side  of 
the  upper  two  lumbar  vertebrae,  corresponds  with  that  of  the  testis,  the  sexual 
gland,  as  in  the  male,  undergoing  migration  in  order  to  gain  its  permanent  loca- 
tion. In  the  case  of  the  ovary,  however,  this  migration  is  much  more  limited, 
notwithstanding  the  provision  of  the  same  equipment  for  descent  as  in  the  male,  in- 
cluding the  genito-inguinal  ligament,  inguinal  bursa,  peritoneal  evagination,  and  even 
cremaster  muscle.  The  gland 

fails  to  reach  the  internal  FIG.  1724. 

abdominal  ring  and  remains 
until  birth  at  the  brim  of  the 
pelvis  in  consequence  of  the 
large  size  of  the  uterus  in 
relation  to  the  small  pelvis. 
When  the  growth  and  expan- 
sion of  the  latter  have  pro- 
vided additional  capacity,  as 
the  uterus  sinks  to  its  definite 
position,  the  ovaries,  attached 
by  their  ligaments  and  ovi- 
ducts, follow  into  the  pelvis. 

The  genito-inguinal  liga- 
ment becomes  the  round 
ligament  of  the  uterus,  the 
lower  end  of  which  is  attached 
to  the  subcutaneous  tissue  of 
the  labium  majus  at  the  exter- 
nal abdominal  ring.  These 
relations  are  foreshadowed  by 
the  close  association  of  the 
lower  end  of  the  fcetal  liga- 
ment to  the  bottom  of  the 
inguinal  bursa  and  the  wall  of 
the  processus  vaginalis.  The 
lumen  of  the  latter  usually 
disappears,  but  in  exceptional 

rww  mav  r,f-r«i'Qt  a*  rh<-  ranal  Sexual  organs  of  female  foetus  of  third  month,  showing  ovaries 

Cabeb  may  perblbl  ab  trie  canal  still  undescended  and  bicornate  uterus.     X  2. 

of  Nuck  (page  2015).     Asso- 
ciated with  this  condition,  occasionally  the  ovary  more  closely  imitates  the  descent 
of  the  testicle  by  passing  into  or  even  through  the  inguinal  canal. 

DEVELOPMENT  OF  THE  EXTERNAL  ORGANS. 

The  external  genital  organs  develop  from  an  indifferent  type  and,  until  the 
beginning  of  the  third  month,  do  not  exhibit  the  distinguishing  characteristics  of 
either  sex.  While  the  differentiation  of  the  sexual  glands  occurs  early,  in  embryos 
of  22  mm.  length,  not  until  about  the  ninth  week,  in  embryos  of  31  mm.,  is  sex 
determinable  by  inspection  of  the  internal  organs.  The  earliest  trustworthy  external 
indication  of  sex  is  the  downward  curve  of  the  growing  genital  tubercle,  later  the 
clitoris,  that  takes  place  at  this  time  in  the  female  (Herzog). 

About  the  fifth  week,  before  the  rupture  of  the  cloacal  membrane,  the  tissue 
bordering  the  external  cloacal  fossa  in  front  grows  forward  into  a  rounded  projection, 
the  genital  tubercle.  The  latter  rapidly  increases  in  size  and  differentiates  into  a  distal 
knob-like  end  and  a  bulbous  ventral  expansion  at  its  base  which  becomes  divided 
by  a  groove  that  extends  along  the  under  surface  of  the  genital  tubercle.  The  lips 
of  this  groove  elongate  into  the  genital  folds  that  lie  on  either  side  of  the  opening  into 


Hypogas- 
tnc  artery 


2044 


HUMAN   ANATOMY. 


FIG.  1725. 


Cloacal  membrane 


Surface  markings  of  cloacal  region  of  human  embryo 
of  seventeen  days  (Fig.  1644).  X  12.  (Keibel.) 


FIG.  1726. 


the  urogenital  sinus  that  appears  when  the  cloacal  membrane  ruptures.  Somewhat 
later,  about  the  ninth  week,  a  pair  of  thick  crescentic  swellings,  the  outer  genital,  or 
labio-scrotal  folds,  make  their  appearance  on  either  side  of  the  genital  tubercle. 

In  the  female,  in  which  the  original  relations  are  largely  retained,  the  genital 
tubercle  grows  slowly  and  is  converted  into  the  glans  and  body  of  the  clitoris,  while 
the  inner  genital  folds  become  the  nymphae  and  the  outer  ones  the  labia  majora. 
The  urogenital  sinus  remains  as  the  vestibule  and  its  opening  as  the  vulvar  cleft. 
The  wedge  of  tissue  between  the  posterior  margin  of  the  latter  and  the  anus  becomes 
the  perineal  body. 

A  description  of  the  development  of  the  glands  of  Bartholin  is  given  in  connec- 
tion with  the  consideration  of  these  organs  (page  2026). 

In  the  male  the  modifications  lead- 
ing to  the  fully  differentiated  external 
organs  are  more  pronounced  in  conse- 
quence of  the  formation  of  the  urethra. 

The  genital  tubercle  rapidly  increases 
in  size,  becomes  somewhat  conical  and 
differentiated  into  the  glans  and  shaft  of 
the  penis.  The  parts  of  the  outer  genital 
folds  behind  the  penis  soon  become  en- 
larged, rounded,  approach  each  other, 
and,  finally,  unite  along  a  line  afterward 
indicated  by  the  median  raphe,  so  that  in 
embryos  of  45  mm.  length  the  scrotum  is 
already  well  defined.  According  to  Her- 
zog,1  the  development  of  the  urethra  pro- 
ceeds from  an  epithelial  ridge  that  appears 
on  the  cloacal  membrane  and  extends  for- 
ward along  the  under  surface  of  the  geni- 
tal tubercle  towards  its  distal  end.  This 
ridge  sinks  into  the  mesoblastic  tissue  of 
the  elongating  genital  tubercle  as  a  nar- 
row longitudinal  strand  (urethral  septum), 
and  later  becomes  partially  divided  by  a 
superficial  furrow,  the  urethral  groove,  the 
lips  of  which  correspond  to  the  inner  geni- 
tal folds.  In  consequence  of  the  cleavage 
of  the  posterior  third  of  the  epithelial 
ridge,  the  cloacal  membrane  is  ruptured 
and  communication  established  with  the 
urogenital  sinus  by  means  of  a  small  canal 
that  opens  into  the  urethral  groove.  As 
the  latter  grows  farther  forward  towards 
the  glans,  approximation  and  fusion  of 
its  edges  occur  behind,  whereby  the  groove 
is  gradually  converted  into  the  urethral 
canal.  In  this  manner  the  distal  opening 

of  the  urethra  is  carried  forward  until  its  definite  position  on  the  glans  is  reached. 
Arrested  development  or  fusion  of  the  edges  of  the  urethral  groove  results  in  defec- 
tive closure  of  the  canal,  a  condition  known  as  hypospadias  (page  1927). 

The  formation  of  the  prepuce  begins  as  a  thickening  and  ingrowth  of  the  surface 
epithelium  at  the  bottom  of  an  annular  groove  that  separates  the  glans  from  the 
body  of  the  penis.  From  this  thickening  the  epithelium  grows  backward,  invading 
the  young  connective  tissue  as  a  narrow  wedge-shaped  mass  that  encircles  the  glans, 
except  below,  where  it  is  incomplete  and  the  frenum  later  appears.  In  this  manner 
an  annular  fold,  the  prepuce,  is  defined  around  the  base  of  the  glans  that  later,  just 
before  or  shortly  after  birth,  becomes  free  by  the  partial  solution  of  the  intervening 
solid  epithelial  stratum  and  its  conversion  into  the  preputial  sac. 
1  Archiv  f.  mikros.  Anatom.,  Bd.  Ixiii.,  1904. 


Genital  tubercle 
Cloacal  membrane 
Lower  limb 

Caudal  process 


External  genitals  of  human  embryo  of  about  twenty- 
seven  days.     (Kollmann.) 


FIG.  1727. 


Glans 
enital  folds 

Labio-scrotal 
folds 

Opening  of 
urogenital  sinus 

Anal  groove 

'  Coccygeal  eminence 
Indifferent  stage  of  external  genitals  of  human  embryo 
of  thirty-three  days  (Fig.  1647).     X  8.     (Keibel.) 


DEVELOPMENT   OF   THE   REPRODUCTIVE   ORGANS. 


2045 


The  developmental  relations  of  the  various  parts  of  the  urogenital  system  to  the 
embryonal  structures,  as  well  as  their  morphological  relations  to  one  another  in  the 
two  sexes,  are  shown  in  the  diagrams  (Fig.  1995)  and  accompanying  table  : 


MALE. 


FIG.  1728. 


FEMALE. 


Glans 


Urethral  groove — . 

Scrotal  fold 

Anal  groove 

Coccygeal 

eminence 


.Glans  clitoridis 

.abium  majus 
Nympha 
Urogenital  sinus 

nus 
Coccygeal  eminence 


Seven  and  a  half  weeks.     (Herzog.) 


Glans 
Urethral  groove  closing 


Nine  weeks.    (Keibel.) 


Glans  clitoridis 
'Nymphae 
Labium  majus 

Vaginal  orifice 


Eleven  weeks.     (Kollmann.) 


Epithelial  knob 

Urethral  groove 
closed 


Glans  clitoridis 


Prepuce 
Urethra 
Nympha 
.Vaginal  orifice 

Anus 


Fifteen  weeks.     (Herzog.) 


Sixteen  weeks.     (Kollmann.) 


Development  of  external  generative  organs. 


Male 

Testis 

Coni  vasculosi  and  ductulieffer- 

entes 

Paradidymis 
Duct  of  epididymis 
Vas  aberrans 
Seminal  vesicle 
Appendix  of  epididymis 
Appendix  of  testis 

Prostatic  utricle 

Ureter 

Pelvis  and    collecting  tubules 

of  kidney 
Bladder 

Prostatic  urethra 

Prostate  gland 

Cowper's  gland 

Penis 

Lips  of  urethral  groove 

Scrotum 


Indifferent  Type 
Sexual  gland 

Wolffian  tubules 
(sexual  groiip) 

Wolffian  duct 


(upper  end] 
Miillerian  duct 


Renal  outgrowth 
from  Wolffian  duct 

Lower  segment  of  allantois 

and  part  of  cloaca 

Urogenital  sinus 

(outgrowths  from  wall] 

Genital  tubercle 

Genital  folds 
Labio-scrotal  folds 


Female 
Ovary 
Short  tubules  of  epoophoron 

Paroophoron 

Main  tube  of  epoophoron 

Gartner's  duct,  when  persisting 

Hydatid  of  Morgagni 

Oviduct 

Uterus 

Vagina 

Ureter 

Pelvis  and  collecting  tubules  of 

kidney 
Bladder 

Urethra  and  vestibule 
Paraurethral  tubes 
Bartholin's  gland 
Clitoris 
Labia  minora 
Labia  majora 


2046 


HUMAN   ANATOMY. 


THE   FEMALE    PERINEUM. 

The  structures  closing  the  pelvic  outlet  in  the  female  correspond  with  those 
found  in  the  male,  modified,  however,  by  the  presence  of  the  urogenital  cleft  and  the 
small  size  of  the  clitoris. 

Owing  to  the  greater  divergence  of  the  bony  boundaries  of  the  subpubic  angle 
and  the  increased  distance  between  the  ischial  tuberosities,  the  width  of  the  lozenge- 
shaped  perineal  space  (when  the  limbs  are  separated)  is  somewhat  greater  in  the 
female.  As  in  the"  male  (page  1916),  the  perineal  region  is  divisible  into  a  posterior 
rectal  and  an  anterior  urogenital  triangle  by  an  imaginary  transverse  line  drawn 
between  the  anterior  borders  of  the  ischial  tuberosities.  Distinction  must  be  made 
between  the  term  "perineum,"  as  above  used,  to  indicate  the  entire  region,  and 
when  applied  in  a  restricted  sense  to  the  bridge  separating  the  anal  and  vulvar  orifices. 
Reference  to  sagittal  sections  (Fig.  1700)  shows  that  this  superficial  bridge  forms  the 

FIG.  1729. 


Cut  edge  of  super- 
ficial layer  of  su-  — 
perficial  fascia 

Prepuce  of  clitoris  - 
Glans  clitoridis — 


Labia  minora{ 
Labia  majora 

Superficial  fascia 


/        Superficial  layer 

of  superficial 

II        fascia  reflected 


—  Colles's  fascia 


•  Vulvar  fissure 


-Posterior 
commissure 


Cut  edge  of  skin 
Anus 


Superficial  dissection  of  female  perineum  ;  on  right  side  skin  only  has  been  removed ; 
on  left,  superficial  layer   of  superficial  fascia  has  been  reflected. 


lower  part  of  a  triangular  fibre-muscular  mass,  fat  perineal  body,  that  divides  the 
vagina  from  the  rectum  and  anal  canal  and  contains  the  perineal  centre  with  the  con- 
verging fibres  of  the  external  sphincter,  transverse  perineal,  and  bulbo-cavernosus 
(sphincter  vaginae)  muscles. 

Apart  from  its  somewhat  greater  breadth  and  more  generous  layer  of  fat,  the 
rectal  triangle  presents  no  special  features  and  contains  the  same  structures  as  in  the 
male.  The  superficial  fascia,  prolonged  from  the  thighs  and  buttocks  and  usually 
laden  with  fat,  closes  in  the  ischio-rectal  fossae  and  is  directly  continuous  with  the 
fatty  areolar  tissue  filling  these  spaces.  The  internal  pudic  vessels  and  pudic  nerve 
occupy  the  fascial  (Alcock's)  canal  on  the  outer  wall  of  the  ischio-rectal  fossa  and 
give  off  the  inferior  hemorrhoidal  branches  distributed  to  the  skin  and  muscles  sur- 
rounding the  anal  canal. 

Over  the  urogenital  triangle  the  superficial  fascia  is  divisible  into  two  distinct 
layers,  a  superficial  and  a  deep.  The  former,  loaded  with  fat,  is  continuous  above 
and  at  the  sides  with  the  corresponding  stratum  on  the  abdomen  and  the  thighs,  and 
behind  with  the  superficial  fascia  covering  the  rectal  triangle.  The  deep  layer,  or 
Colles's  fascia,  is  devoid  of  fat  and  membranous  in  character.  Behind,  where  it  turns 


he 


THE   FEMALE   PERINEUM. 


2047 


over  the  transverse  perineal  muscles,  it  blends  with  the  posterior  border  of  the  tri- 
angular ligament  along  the  perineal  shelf  ;  laterally,  it  is  attached  to  the  ischial  and 
pubic  rami  ;  and  in  front  it  is  prolonged  over  the  labia  majora  to  become  continuous 
with  the  corresponding  fascia  (Scarpa's)  over  the  abdomen. 

FIG.  1730. 


Glaus  clitoridis- 

Superficial- 
fascia 

Labia  minora- 
Vulvar  fissure- 

Labia  majora- 

Colles's  fascia- 
Edge  of  cut  skin- 


Anus 


-Inferior 

pudenda]  nerve 
-Fascia  lata 
of  thigh 

Inferior 

-pudenda!  nerve 
-Tuber  ischii 

Cutaneous  In 


ofinte 


lUndexte 


nal  perineal  nerves 
-From  internal 

perineal  nerve 
"Inf.  hemorrhoidal  art. 
-Inf.  hemorrhofdal 


.From  fourth 
sacral  nerve 


Coccyx — 


Superficial  layer  of  superficial  fascia  has  been  removed  from  urogenital  triangle  ;   Colles's  fascia  and  cutaneous 

nerves  and  vessels  exposed. 


Pubic  ramus  - 


FIG.  1731. 


Dorsal  artery  of  clitoris      Dorsal  nerve  of  clitoris 
Dorsal  vein  of  clitoris  K  /     /  Dorsal  artery  of  clitoris 


Glans  clitoridis 


Crus  clitoridis 


Cms  clitoridis  — 


Triangular 
ligament,  in- 
ferior layer 


"Labium 
majus, 
denuded 


Tuber  ischii 


Glands  of  Bartholin 


Dissection  exposing  bulbus  vestibuli,  Bartholin's  glands  and  inferior  layer  of  triangular  ligament  after  removal 
of  overlying  structures  ;  left  crus  clitoridis  displaced. 

The  fascia  of  Colles  forms  the  lower  boundary  of  the  superficial  perineal  inter- 
space, a  triangular  pocket  limited  above  by  the  inferior  layer  of  the  triangular  liga- 
ment and  behind  by  the  fusion  of  the  latter  with  Colles's  fascia.  In  addition  to  the 
superficial  perineal  vessels  and  nerves,  the  long  pudendal  nerves,  the  transverse  peri- 


2048 


HUMAN   ANATOMY. 


neal  muscles,  and  the  glands  of  Bartholin,  this  space  contains  the  crura  of  the  clitoris, 
the  vestibular  bulb  and    their  associated   muscles  (ischio-  and  bulbo-cavernosus). 


¥IG.    1732. 

Dorsal  vein  Left  dorsal 

artery  of  clitoris 


bnjiaai  vein 
of  clitoris 


Colles's  fascia  - 

reflected 

Pars  intermedia - 
Ischio- 
cavernosus" 
Bulbus  vestibuli 
Bulbo- 
cavernosus 
Triangular  liga-~ 
ment,  inf.  layer 
Transversus~ 
perinei 


Superficial  fascia- 


External - 
sphincter 


Glans  clitoridis 

Ischio- 
cavernosus 
Superficial 
perineal  artery 

Inf.  pudendal  nerve 
Ant.  perineal  artery 
Post,  perineal  nerve 

-Trans,  perineal  art. 
Inf.  hemorrhoidal 

-artery 
int.  hemorrhoidal 

-Anal  fascia 


-Coccyx 


Deep  layer  of  superficial  fascia  (Colles's  fascia)  removed,  exposing  structures  within  superficial  interspace. 


Crus  clitoridis- 

Triangular 
ligament,  deep 
layer 


Tuber  ischii— 


External 
sphincter 


FIG.   1733. 

Glans  clitoridis 


Dorsal  artery  of  clitoris 
Dorsal  vein  of  clitoris 


f  Dorsal  artery  of  clitoris 
Artery  of  corpus  cavernosus 


Dorsal  nerve  of  clitoris 


•Internal  pudic 
artery 


..Triangular 

ligament 

— — —  —Artery  of  bulb 


Internal 
-pudic  artery 


-Perineal  division 
of  pudic  nerve 

-Inf.  hemorrhoidal  art 
-Pudic  nerve 
-Levator  ani 

From  fourth 
sacral  nerve 

Creator  sacro- 
seiatii-  ligament 
"Glutens 

maximus,  cut 


Glutens  maximus 


Coccyx 


Inferior  hemorrhoidal  nerve         Coccygeus 


Deeper  dissection  of  perineum  ;  inferior  layer  of  triangular  ligament  has  been  removed,  exposing  deep  perineal 
Interspace;    isrhio-tvctal   fossa   partially  >  li-ani'cl   out. 

Owing  to  the  diminutive  size  of  the  crura  clitoridis,  the  ischio-cavernosus  muscles  are 
correspondingly  small,  but  otherwise  agree  with  those  in  the  male. 


THE   FEMALE   PERINEUM. 


2049 


The  presence  of  the  urogenital  cleft  prevents  the  fusion  not  only  of  the  vestibular 
hemibulbs  (the  homologues  of  the  halves  of  the  corpus  spongiosum),  but  also  of  the 
bulbo-cavernosus  muscles,  which,  therefore,  are  present  in  the  female  as  separate 
bands  that  encircle  the  vestibule. 

The  bulbo-cavernosus  muscle,  often  called  the  sphincter  vagince,  arises  from  the 
perineal  centre,  blending  with  the  fibres  of  the  external  sphincter  and  the  transverse 
perineal  muscles,  and  divides  into  a  median  and  a  lateral  portion  as  it  passes  forward. 
The  lateral  and  more  superficial  strand  encircles  the  vagina,  crosses  the  crus  to  gain 
the  dorsum  clitoridis,  and  ends,  with  the  tendon  of  the  opposite  muscle,  by  blending 
with  the  fibrous  sheath  of  the  clitoris.  The  median  and  deeper  portion  of  the  muscle 
(the  compressor  bulbi  of  Holl  )  partly  covers  the  gland  of  Bartholin  and  the  vestibular 
bulb,  and  in  front  unites  with  the  corresponding  strand  of  the  opposite  side  in  a 


Glans  of  clitoris 


" 


Gluteus 
maximus 
Coccygeus 


Vulvar  fissure 
White  line  of  pel- 
vic fascia  slightly 
displaced    toward 
midline 
Tuber  ischii 


-Levator  ani 

Anus 


-  Coccygeus 


Greater 
sacro-sciatic 
ligament 

Gluteus 
maximus  (cut) 


Coccyx 


Deep  dissection  of  perineum,  exposing  muscles  of  pelvic  floor. 

delicate  tendinous  expansion  that  passes  beneath  the  body  of  the  clitoris  and  is  attached 
to  the  crura. 

Between  the  inferior  and  superior  layers  of  the  triangular  ligament  is  included 
the  deep  perineal  interspace.  In  addition  to  the  continuations  of  the  internal  pudic 
vessels  and  pudic  nerves,  this  interfascial  space  is  occupied  by  a  thin  and  imperfect 
muscular  sheet  that  corresponds  with  the  compressor  urethrae.  The  posterior  part 
of  this  sheet  is  differentiated,  with  variable  distinctness,  into  the  deep  transverse 
perineal  muscles  which,  arising  from  the  ischial  tuberosities,  pass  behind  the  vagina 
to  the  perineal  centre.  The  remaining  part  of  the  sheet,  collectively  much  less 
developed  than  the  sphincter-like  compressor  urethrae  in  the  male,  is  continued 
forward  from  the  perineal  centre  as  a  thin  stratum  that  closely  encircles  the  vagina, 
and  in  front  either  surrounds  the  urethra  or  passes  in  front  of  the  urethra  in  the 
interval  between  the  latter  and  the  transverse  ligament  (Kalischer).  In  recognition 
of  its  relations  to  both  the  vaginal  and  urethral  canals,  this  muscular  sheet  has  been 
appropriately  called  the  urogenital  sphincter. 

129 


INDEX. 


Abdomen,  examination  of,  anatomical  rela- 
tions, 536 

fascia,  superficial  of,  515 
landmarks  and  topography  of,  53 1 
lymphatics  of,  972 
lymph-nodes  of,  974 
muscles  of,  515 
pract.  consid.,  526 
ventral  aponeurosis  of,  521 
Abdominal  cavity,  1615 

region,  epigastric,  1615 
hypochondriac,  1615 
hypogastric,  1615 
iliac,  1615 
lumbar,  1615 
umbilical,  1615 
hernia,  1759 

incisions,  anatomy  of,  535 
ring,  external,  524 

internal,  524 
walls,  lymphatics  of,  976 

posterior  surface  of,  525 
Acervulus,  1125 
Acetabulum,  of  ischium,  336 
Acromio-clavicular  articulation,  262 

pract.  consid.,  264 
Adamantoblasts,  1561 
Adipose  tissue,  79 

chemical  composition  of,  83 
After-birth,  55 
Agger  nasi,  193 
Air-cells,  ethmoidal,  1424 

pract.  consid.,  1429 
Air-sacs  of  lung,  1850 
Air-spaces,  accessory,  1421 

pract.  consid.,  1426 
Ala  cinerea,  1097 
Albinism,  1461 
Alcock's  canal,  817 
Alimentary  canal,  1538 

tract,  development  of,  1694 
Allantois,  32 

arteries  of,  33 
human,  35 
stalk  of,  33 
veins  of,  33 
Alveoli  of  lung,  1850 
Ameloblasts,  1561 
Amitosis,  14 
Amnion,  30 
false,  31 
folds  of,  30 
human,  35 

cavity  of,  35 
fluid  of,  41 
liquor  of,  31 
suture  of,  31 
Amniota,  30 
Amphiarthrosis,  107 
Anal  canal,  1673 
Analogue,  4 
Anamnia,  30 
Anaphases  of  mitosis,  13 
Anastomoses,  of  ophthalmic  veins,  880' 


Anatomy,  i 

Ankle,  landmarks  of,  672 

muscles  and  fasciae  of,  pract.  consid.,  666 
Ankle-joint,  438 

movements  of,  440 
pract.  consid.,  450 
Annuli  fibrosi,  of  heart,  698 
Annulus  ovalis,  695 
tympanicus,  1493 
of  Vieussens,  695 
Anorchism,  1950 
Anthropology  of  skull,  228 
Anthropotomy,  i 
Antihelix,  1484 
Antitragus,  1484 
Antrum,  227 

of  Highmore,  1422 

pract.  consid.,  1428 
pylori,  1618 
of  superior  maxilla,  201 
Anus,  1673 

formation  of,  1695 
muscles  and  fascias  of,  1675 
pract.  consid.,  1689 
Aorta,  abdominal,  794 

branches  of,  pract.  consid.,  806 
plan  of  branches,  796 
pract.  consid.,  796 
dorsal,  721 
pulmonary,  722 
segmental  arteries  of,  847 
systemic,  723 
thoracic,  791 
valves  of,  700 
ventral,  721 
Aortic  arch,  723 

pract.  consid.,  726 
variations  of,  724 
bodies,  1812 
bows,  847 
septum,  707 
Aponeurosis,  468 

abdominal,  ventral,  521 
epicranial,  482 
(fascia)  plantar,  659 
palmar,  606 

Appendages,vesicular,of  broad  ligament,  2 002 
Appendices  epiploicae,  1660 
Appendix  epididymidis,  1949 
testis,  1949 
vermiform,  1664 

blood-vessels  of,  1667 
development  and  growth  of,  1668 
lymphatics  of,  1667 
mesentery  of,  1665 
nerves  of,  1668 
orifice  of,  1662 
peritoneal  relations  of,  1665 
pract.  consid.,  1681 
Aquaeductus  cochleae,  1514 
Aqueduct  of  Fallopius,  1496 

sylvian,  1108 
Aqueous  humor,  1476 

chamber,  anterior  of,  1476 
2051 


2052 


INDEX. 


Aqueous  humor,  chamber,  posterior  of,  147 

pract.  consid.,  1476 
Arachnoid,  of  brain,  1203 

of  spinal  cord,  1022 
Arantius,  nodules  of,  700 
Archenteron,  25 
Arches,  visceral,  59 

fifth  or  third  branchial,  61 
first  or  mandibular,  60 
fourth  or  second  branchial,  61 
second  or  hyoid,  60 
third  or  first  branchial,  61 
Arcuate  nerve-fibres,  1071 
Area  acustica,  1097 
embryonic,  23 
parolfactory,  1153 
pellucida,  25 
Areola,  2028 
Arm,  lymphatics,  deep,  of,  965 

superficial,  of,  963 

muscles  and  fascia  of,  pract.  consid.,  589 
Arnold's  ganglion,  1246 
Arrectores  pilorum,  1394 
Arterial  system,  general  plan  of,  720 
Artery  or  arteries,  719 

aberrant,  of  brachial,  775 
allantoic,  33 
alveolar,  741 

of  internal  maxillary,  741 
aorta,  systemic,  723 
anastomoses  around  the  elbow,  778 
anastomotica  magna,  of  brachial,  778 

of  femoral,  831 
angular,  738 

of  facial,  738 

articular,  of  popliteal,  833 
auditory,  internal,  759 
auricular,  anterior,  of  temporal,  745 
deep,  740 

of  internal  maxillary,  740 
of  occipital,  744 
posterior,  744 
axillary,  767 

pract.  consid.,  769 
azygos,  of  vaginal,  812 
basilar,  758 
brachial,  773 

pract.  consid.,  776 
brachialis  superficjalis,  775 
bronchial,  792 
buccal,  741* 

of  internal  maxillary,  741 
to  bulb  (bulbi  urethrae),  817 
calcaneal,  external,  838 
internal,  839 
of  external  plantar,  840 
calcarine,  760 
carotid,  common,  730 

pract.  consid.,  731 
external,  733 

pract.  consid.,  733 
internal,  746 

pract.  consid.,  747 
system,  anastomoses  of,  753 
carpal,  of  anterior  radial,  788 
of  anterior  ulnar,  782 
arch,  posterior,  789 
of  posterior  radial,  788 
of  posterior  ulnar,  782 
reta,  anterior,  791 
centralis  retinae,  749 
cerebellar,  inferior,  anterior,  759 
posterior,  759 


Artery  or  arteries,  cerebellar,  superior,  759 
cerebral,  anterior,  753 

middle,  752 

posterior,  760 
cervical,  ascending,  of  inferior  thyroid, 

766 
of  transverse  cervical,  767 

deep,  764 

superficial,  766 

transverse,  767 
choroid,  anterior,  752 
ciliary,  749 

anterior,  749 

posterior,  749 
circle  of  Willis,  760 
circumflex,  anterior,  773 

external,  of  deep  femoral,  828 

internal,  of  deep  femoral,  828 

posterior,  773 

circumpatellar  anastomosis,  834 
coccygeal,  of  sciatic,  815 
cceliac  axis,  797 
colic,  left,  803 

right,  802 

comes  nervi  ischiadici,  815 
communicating,  anterior,  753 

of  peroneal,  838 

posterior,  751 

of  posterior  tibial,  839 
coronary,  inferior,  738 
of  facial,  738 

left,  728 

right,  728 

superior,  738 

of  facial,  738 

of  corpus  cavernosum,  817 
cremasteric,  of  deep  epigastric,  820 

of  spermatic,  805 
crico-thyroid,  734 

of  superior  thyroid,  734 
cystic,  of  hepatic,  799 
dental,  anterior,  of  internal  maxillary, 

74i 

inferior,  740 
development  of,  846 

of  lower  limb,  848 

of  upper  limb,  848 
digital,  collateral,  of  ulnar,  784 

of  ulnar,  784 
dorsal,  of  foot,  845 

of  penis  (clitoris),  817 
dorsalis  hallucis,  846 

indicis,  789 

pedis,  845 

pollicis,  789 
epigastric,  deep,  820 

superficial,  826 

superior,  763 
ethmoidal,  749 

anterior,  750 

posterior,  749 
facial,  737 

anastomoses  of,  738 

glandular  branches  of,  737 

pract.  consid.,  738 

transverse,  745 
femoral,  821 

anastomoses  of,  831 

deep,  828 

development  of,  823 

pract.  consid.,  824 
fibular,  superior,  of  anterior  tibial,  844 
frontal,  of  ascending  middle  cerebral,  7  53 


INDEX. 


2053 


Artery  or  arteries,  frontal,  of  inferior  middle 

cerebral,  753 
internal,  anterior,  753 
middle,  753 
posterior,  753 
of  ophthalmic,  750 
Gasserian,  of  middle  meningeal,  740 
gastric,  798 

short,  of  splenic,  800 
gastro-duodenal,  799 
gastro-epiploic,  left,  80 1 

right,  799 

glandular,  of  facial,  737 
gluteal,  8n 

pract.  consid.,  814 
hemorrhoidal,  inferior,  817 
middle,  813 
superior,  803 
hepatic,  799 
hyaloidea,  1474 
hypogastric  axis,  808 
obliterated,  808 
ileo-colic,  802 
iliac,  circumflex,  deep,  821 

superficial,  826 
common,  807 

pract.  consid.,  807 
external,  818 

anastomoses  of,  821 
pract.  consid.,  819 
of  ilio-lumbar,  810 
internal,  808 

anastomoses  of,  818 
pract.  consid.,  810 
ilio-lumbar,  810 

infrahyoid,  of  superior  thyroid,  734 
infraorbital,  741 

of  internal  maxillary,  741 
innominate,  729 

pract.  consid.,  729 

intercostal,   of  anterior  internal  mam- 
mary, 763 
aortic,  792 

of  internal  mammary,  765 
superior,  764 

internal  mammary,  pract.  consid.,   764 
interosseous,  anterior,  781 
common,  781 
dorsal,  846 
posterior,  782 

intestinal,  of  superior  mesenteric,  802 
labial,  inferior,  738 

of  facial,  738 
of  internal  maxillary,  741 
lachrymal,  749 
laryngeal,  inferior,  766 

superior,  of  superior  thyroid,  734 
lateral  cutaneous,  of  aortic  intercostals, 

793 

lenticulo-striate,  of  middle  cerebral,  752 
lingual,  735 

anastomoses  of,  736 

dorsal,  736 

pract.  consid.,  736 
lumbar,  805 

of  ilio-lumbar,  810 
malleolar,  external,  844 

internal,  of  anterior  tibial,  844 

of  posterior  tibial,  839 
mammary,  of  aortic  intercostals,  793 

internal,  763 

lateral  internal,  764 
masseteric,  740 


Artery  or  arteries,  masseteric,  of  facial,  738 

of  internal  maxillary,  740 
mastoid,  of  occipital,  744 
maxillary,  internal,  739 

anastomoses  of,  742 
development  of,  742 
median,  781 
mediastinal,  of  internal  mammary,  763 

of  thoracic  aorta,  792 
meningeal,  anterior,  748 

of  ascending  pharyngeal,  743 

middle,  740 

of  internal  maxillary,  740 

posterior,  of  occipital,  744 
of  vertebral,  758 

small,  740 
mesenteric,  inferior,  802 

superior,  80 1 
metacarpal,  dorsal,  789 
metatarsal,  of  foot,  845 
middle,  colic,  802 
musculo-phrenic,  763 
nasal,  lateral,  738 

of  facial,  738 

of  ophthalmic,  750 

naso-palatine,  of  internal  maxillary,  742 
nutrient,  of  brachial,  774 

of  peroneal,  838 

of  posterior  tibial,  838 

of  ulnar,   781 
obturator,  813 

from  deep  epigastric,  814 
occipital,  743 

pract.  consid.,  744 
cesophageal,  of  gastric,  798 

of  thoracic  aorta,  792 
omphalomesenteric,  32 
ophthalmic,  748 

anastomoses  of,  750 
orbital,  of  middle  meningeal,  740 

of  temporal,  745 
ovarian,  805 

of  uterine,  813 
palatine,  ascending,  737 
of  facial,  737 

descending,  741 

of  internal  maxillary,  741 
palmar  arch,  deep,  785 
superficial,  784 

deep,  782 

interosseous,  790 
palpebral,  of  internal  maxillary,  741 

of  ophthalmic,  750 
pancreatic,  of  splenic,  800 
pancreatico-duodenal,  inferior,  802 

superior,  799 

parietal,  of  middle  cerebral,  753 
parieto-occipital,  760 

temporal,  753 
parotid,  of  temporal,  745 
perforating,  of  anterior  internal  mam- 
mary, 763 

of  deep  femoral,  828 

posterior,  of  external  plantar,  840 

of  radial,  791 
perineal,  superficial,  817 

transverse,  817 
peroneal,  anterior,  838 

posterior,  838 

of  posterior  tibial,  838 
petrosal,  of  middle  meningeal,  740 
pharyngeal,  ascending,  743 

of  ascending  pharyngeal,  743 


2054 


INDEX. 


Artery  or  arteries,  phrenic,  inferior,  804 

superior,  763 
plantar  arch,  840 

digital,  840 

external,  840 

internal,  839 

interosseous,  840 
popliteal,  831 

pract.  consid.,  832 
posterior  choroidal,  760 
princeps  cervicis,  744 

hallucis,  841 

pollicis,  789 
profunda,  inferior,  777 

superior,  777 
prostatic,  812 
pterygoid,  740 

of  internal  maxillary,  740 
pterygo-palatine,  742 

of  internal  maxillary,  742 
pubic,  of  deep  epigastric,  820 

of  obturator,  813 
pudic,  external,  deep,  828 
superficial,  826 

internal,  815 

accessory,  818 
pulmonary,  722 

valves  of,  700 
pyloric,  of  hepatic,  799 
radial,  785 

development  of,  786 

pract.  consid.,  786 

recurrent,  787 
radialis  indicis,  790 

superficialis,  775 
ranine,  736 
recurrent,  of  palm,  791  »> 

of  posterior  interosseous,  782 
renal,  804 
sacral,  lateral,  810 

middle,  806 
scapular,  dorsal,  773 

posterior,  767 
sciatic,  815 
septal,  of  nose,  738 
sigmoid,  803 
spermatic,  805 
spheno-palatine,  742 

of  internal  maxillary,  742 
spinal,  anterior,  of  vertebral,  759 

posterior,  of  vertebral,  758 
splenic,  800 

sterno-mastoid,  of  external  carotid,  743 
of  occipital,  744 
of  superior  thyroid,  734 
striate,  external,  of  middle  cerebral,  752 

internal,  of  middle  cerebral,  752 
structure  of,  675 
stylo-mastoid,  745 
subclavian,  753 

pract.  consid.,  756 
subcostal,  792 
sublingual,  736 
submental,  737 

of  facial,  737 
subscapular,  772 
suprahyoid,  736 
supraorbital,  749 
suprarenal,  804 

inferior,  804 
suprascapular,  767 
tarsal,  external,  845 

internal,  845 


Artery    or   arteries,    temporal,    anterior,    of 

vertebral,  760 
deep,  740 

of  internal  maxillary,  740 
middle,  745 

posterior,  of  vertebral,  760 
superficial,  745 

pract.  consid.,  745 
thoracic,  acromial,  771 
alar,  772 
long,  772 
superior,  771 
thyroid  axis,  765 

pract.  consid.,  766 
inferior,  766 
superior,  734 

pract.  consid.,  735 
tibial,  anterior,  842 

anastomoses  of,  844 
pract.  consid.,  842 
posterior,  834 

anastomoses  of,  841 
development  of,  836 
pract.  consid.,  836 
recurrent,  anterior,  844 

posterior,  844 
tonsillar,  737 

of  facial,  737 
tubal,  of  ovarian,  805 

of  uterine,  813 

tympanic,  of  internal  carotid,  748 
of  internal  maxillary,  740 
of  middle  meningeal,  740 
ulnar,  778 

accessory,  776 
development  of,  779 
pract.  consid.,  780 
recurrent,  anterior,  781 

posterior,  781 
umbilical,  54 
ureteral,  of  ovarian,  805 
of  renal,  804 
of  spermatic,  805 
of  uterine,  813 
urethral,  817 
uterine,  812 
vaginal,  812 
vertebral,  758 

pract.  consid.,  761 
vesical,  inferior,  811 
middle,  81 1 
of  obturator,  813 
superior,  81 1 
vesiculo-deferential,  812 
Vidian,  742 
vitelline    32 
volar,  superficial,  788 
Arthrodia,  113 
Articulation  or  articulations,  acromio-clavic- 

ular,  pract.  consid.,  264 
carpo-metacarpal,  325 

movements  of,  326 
costo- vertebral,  160 
of  ethmoid,  194 
of  foot,  440 
of  frontal  bone,  197 
of  inferior  turbinate  bone,  208 
of  lachrymal  bone,  207 
of  malar  bone,  210 
metacarpo-phalangeal,  327 

movements  of,  328 
of  nasal  bone,  209 
of  occipital  bone,  atlas,  and  axis,  135 


INDEX. 


2055 


Articulation  or  articulations,  of  palate  bone, 
205 

of  parietal  bone,  199 

sacro-iliac,  338 

scapulo-clavicular,  262 

of  sphenoid  bone,  190 

sterno-clavicular,  261 
pract.  consid.,  263 

of  superior  maxilla,  202 

of  temporal  bone,  184 

temporo-mandibular,  214 
development  of,  215 
movements  of,  215 

thoracic  anterior,  158 

of  thorax,  157 

of  thumb,  326 

tibio-fibular,  inferior,  396 
superior,  396 

of  vertebral  column,  132 

of  vomer,  206 
Arytenoid  cartilages,  1816 
Asterion,  228 
Astragalus,  423 

development  of,  425 
Astrocytes,  1003 
Atlas,  1 20 

development  of,  131 

variations  of,  120 
Atria  of  lung,  1850 
Auditory  canal,  external,  1487 

blood-vessels  of,  1489 
nerves  of,  1490 
pract.  consid.,  1491 
internal,  1514 

ossicles,  1496 

path,  1258 

Auerbach,  plexus  of,  1643 
Auricle  or  auricles,  1484 

antihelix  of,  1484 

antitragus  of,  1484 

blood-vessels  of,  1486 

cartilage  of,  1485 

concha  of,  1484 

of  heart,  693 

helix  of,  1484 

ligaments  of,  1486 

lobule  of,  1484 

muscles  of,  1486 

nerves  of,  1487 

pract.  consid.,  1490 

structure  of,  1485 

tragus  of,  1484 
Auricular  canal,  705 
Axilla,  574 

muscles  and  fascia  of,  pract.  consid.,  579 
Axis,  121 

development  of,  131 
Axis-cylinder,  1001 
Axones,  of  neurones,  997 
Azygos  system  of  veins,  893 

Bartholin,  glands  of,  2026 

Basion,  228 

Bell,  external  respiratory  nerVe  of,  1295 

Bertin,  bones  of,  191 

columns  of,  1876 
Bicuspid  teeth,  1545 
Bile-capillaries,  1715 
Bile-duct,  common,  1720 
opening  of,  1720 
pract.  consid.,  1731 

interlobular,  1717 

lymphatics  of,  981 


Biliary  apparatus,  1718 
Bladder,  lymphatics  of,  985 
urinary,  1901 

capacity  of,  1903 
development  of,  1938 
in  female,  1908 
fixation  of,  1905 
infantile,  1908 
interior  of,  1904 
nerves  of,  1910 
peritoneal  relations  of,  1904 
pract.  consid.,  1910 
relations  of,  1906 
structure  of,  1908 
trigone  of,  1904 
vessels  of,  1910 
Blastoderm,  22 
bilaminar,  23 
trilaminar,  23 
Blastodermic  layers,  22 

derivatives  of,  24 
vesicle,  stage  of,  56 
Blastomeres,  21 
Blastopore,  25 
Blastula,  25 
Blood,  680 

Blood-cells,  colored,  68 1     , 
colorless,  684 
development  of,  687 
Blood-crystals,  68 1 

lakes  of  dural  sinuses,  852 
plaques,  685 

Blood-vascular  system,  673 
Blood-vessels  of  auricle,  1486 
of  bone,  93 
of  brain,  1206 
capillary,  678 
of  cartilage,  81 
development  of,  686 
of  duodenum,  1649 
of  Eustachian  tube,  1504 
of  external  auditory  canal,  1489 
of  eyelids,  1445 
of  glands,  1535 
of  hair-follicles,  1394 
of  kidney,  1884 
of  liver,  1709 
lobular,  of  liver,  1713 
of  lung,  1853 

of  membranous  labyrinth,  1522 
of  nasal  fossa,  1425 
of  non-striated  muscle,  456 
of  nose,  1407 
of  pericardium,  716 
of  pleura,  1860 
of  small  intestine,  1642 
of  rectum,  1679 
of  retina,  1467 
of  skin,    1387 
of  spinal  cord,  1047 
of  stomach,  1627 
of  striated  muscle,  464 
structure  of,  673 
of  sweat  glands,  1400 
vasa  vasorum,  674 
Body-cavity,  differentiation  of,  1700 
Body-form,  general  development  of,  56 
Body-stalk,  37 
Bone  or  bones,  84 
age  of,  1 06 
astragalus,  423 
of  Bertin,  191 
blood-vessels  of,  93 


2056 


INDEX. 


Bone  or  bones,  calcaneum,  419 
canaliculi  of,  86 
cancellated,  85 
carpus,  309 
cells  of,  89 

chemical  composition  of,  84 
clavicle,  257 
compact,  86 

development  of,  100 
cranium,  172 
cuboid,  422 
cuneiform,  310 

external,  428 

internal,  426 

middle,  427 
development  of,  94 

endochondral,  94 
intramembranous,  98 
diaphysis  of,  104 
elasticity  of,  105 
ethmoid,  191 
femur,  352 
fibula,  390 
frontal,  194 

general  considerations  of,  104 
growth  of,  1 01 
Haversian  canals  of,  88 

system  of,  86 
humerus,  265 
hyoid,  216 
ilium,  332 

inferior  turbinate,  208 
innominate,  332 
intramembranous,  101 
ischium,  336 
lachrymal,  207 
lacunae  of,  86 

lamellae  of,  circumferential,  86 
Haversian,  86 
interstitial,  86 
lymphatics  of,  93 
malar,  209 
maxilla,  inferior,  211 

superior,  199 
mechanics  of,  105 
metacarpal,  314 
metatarsal,  428 
nasal,  209 
nerves  of,  94 
number  of,  107 
occipital,  172 
os  magnum,  312 
palate,  204 
parietal,  197 
parts  of,  1 06 
patella,  398 
periosteum  of,  89 
phalanges  of  foot,  432 

of  hand,  317 

physical  properties  of,  85 
pisiform,  311 
pubes,  334 
radius,  287 

relation  of  to  figure,  107 
ribs,  149 
scaphoid,  309 

of  foot,  425 
scapula,  248 
semilunar,  310 
sesamoid,  104 
sex  of,  1 06 
shapes  of,  104 
Sharpey's  fibres  of,  87 


Bone  or  bones,  of  shoulder-girdle,  248 

skull,  172 

sphenoid,  186 

sphenoidal,  turbinate,  191 

sternum,  155 

structure  of,  85 

subperiosteal,  98 

tarsal,  419 

temporal,  176 

of  thorax,  149 

tibia,  382 

trapezium,  311 

trapezoid,  311 

ulna,  281 

unciform,  312 

variations  of,  107 

Volkmann's  canals  of,  89 

vomer,  205 
Bone-marrow,  90 

cells  of,  92 

eosinophiles,  92 

giant  cells  of,  92 

nucleated  red  cells  of,  92 
erythroblasts,  92 
normoblasts,  92 

primary,  95 

red,  90 

yellow,  93 
Bowman,  glands  of,  1415 

membrane  of,  1451 
Brachium,  inferior,  1107 

internal  structure  of,  uio 

superior,  1107 
Brain,  1055 

blood-vessels  of,  1206 

general  development  of,  1058 

lymphatics  of,  948 

measurements  of,  1195 

membranes  of,  1197 

pract.  consid.,  1207 

pract.  consid.,  1207 

weight  of,  1196 
Brain-sand  (acervulus),  1125 
Brain-stem,  1056 
Brain-vesicles,  primary,  1059 

secondary,  1061 

Branchial  arches,  derivatives  of,  847 
Bregma,  228 
Bronchial  tree,  1847 

variations  of,  1849 
Bronchus  or  bronchi,  1838 

distribution  of,  1849 

eparterial,  1848 

homologies  of,  1848 

hyparterial,  1848 

pract.  consid.,  1840 

terminal,  1850 
Bruch,  membrane  of,  1456 
Brunner,  glands  of,  1639 
Buccal  fat-pad,  489 
Bulb,  1063 

of  internal  jugular  vein,  86r 

olfactory,  1151 

urethral,  "1968 

Bulbo-tecto-thalamic  strands,  1116 
Bulbus  vestibuli,  2025 
Bulla,  of  ethmoid,  194 
Burns,  space  of,  543 
Bursa  or  bursse,  in 

iliopectineal,  623 

ischiatic,  of  gluteus  maximus,  630 

of  knee-joint,  406 

of  m.  pyriformis,  561 


INDEX. 


2057 


Bursa  or  bursse,  subdeltoid,  578 

subscapular,  578 

troc-hanteric,   of  gluteus   maximus,    630 
Buttocks,  landmarks  of,  669 

muscles  and  fasciae  of,  pract.  consid.,  641 

Cascum,  1660 

blood-vessels  of,  1667 

development  and  growth  of,  1668 

interior  of,  1661 

lymphatics  of,  1667 

nerves  of,  1668 

peritoneal  relations  of,  1665 

position  of,  1662 

pract.  consid.,  1680 

structure  of,  1663 
Calamus  scriptorius,  1096 
Calcaneum,  419 

development  of,  422 

structure  of,  421 

variations  of,  421 
Camper's  fascia,  515 
Canal  or  canals,  alimentary,  1538 

anal,  1673 

auditory,  external,  1487 

auricular  of  heart,  705 

carotid,  184 

central,  of  spinal  cord,  1030 

of  Cloquet,  1474 

facial,  184 

femoral,  625 

Haversian,  of  bone,  88 

Hunter's,  628 

hyaloid,  1474 

incisive,  1413 

inguinal,  523 

neural,  26 

neurenteric,  25 

of  Nuck,  2006 

palatine,  anterior,  201 
posterior,  204 

reuniens,  1515 

of  Scarpa,  201 

of  Schlemm,  1452 

semicircular  membranous,  1515 
osseous,  1512 
structure  of,  1516 

of  Stenson,  201 

of  Stilling,  1474 

Vidian,  189 

Volkmann's,  of  bone,  89 
Canaliculi,  of  bone,  86 

lachrymal,  1478 
Canine  teeth,  1544 
Canthi  of  eye,  1442 
Capitellum  of  humerus,  268 
Capsule,  external,  1172 

internal,  1173 

of  Tenon,  504 
Caput  medusas,  534 
Cardiac  muscle,  462 
Cardinal  system  of  veins,  854 
Carina  tracheae,  1837 

urethralis,  2016 
Carotid  body,  1809 

chromamne  cells  of,  1810 
sheath,  543 

Carpo-metacarpal  articulations,  325 
Carpus,  309 

development  of,  313 

pract.  consid.,  319 

variations  of,  313 
Cartilage  or  cartilages,  80 


Cartilage  or  cartilages,  articular,  81 

arytenoid,  1816 

of  auricle,  1485 

blood-vessels  of,  8 

capsule  of,  80 

chemical  composition  of,  83 

costal,  1 53 

cricoid,  1813 

cuneiform  of  Wrisberg,  1817 

development  of,  82 

elastic,  81 

fibrous,  82 

hyaline,  80 

lacunas  of,  80 

lateral,  of  nose,  1405 

matrix  of,  80 

of  nasal  septum,  1405 

of  nose,  1404 

perichondrium  of,  81 

of  Santorini,  1817 

thyroid,  1814 

triangular,  of  nasal  septum,  224 

vomerine,  1406 
Cartilage-cells,  80 
Carunculas  hymenales,  2016 

salivares,  1581 
Caruncle,  lachrymal,  1443 
Cauda  equina  of  spinal  cord,  1025 
Cavity,  abdominal,  1615 

nasal,  223 

pneumatic  accessory,  226 

segmentation,  22 

synovial,  of  foot,  447 

tympanic,  1492 

of  tympanum,  183 
Cell  or  cells,  animal,  6 

of  bone,  89 

of  connective  tissues,  73 

decidual,  47 

gustatory,  1435 

mastoid,  1 504 

of  Rauber,  23 

spermatogenetic,  1943 

tactile,  of  Merkel,  1016 
Cell-division,  10 

direct,  14 

indirect,  1 1 

reduction  division,  18 
Cell-mass,  inner,  23 

intermediate,  29 
Cementoblasts,  1563 
Cementum,  1552 

formation  of,  1563 
Centrosome,  9 
Cephalic  flexure,  1061 
Cerebellar  peduncle,  fibre-tracts  of,  1093 
inferior,  1067 

inferior,  fibre-tracts  of,  1093 
middle,  fibre-tracts  of,  1094 
superior,  fibre-tracts  of,  1094 
Cerebellum,  1082 

architecture  of,  1088 

cortex  of,  1090 

histogenesis  of,  1105 

development  of,  1103 

flocculus  of,  1085 

hemispheres  of,  1082 

lobus  cacuminis  of,  1085 
centralis  of,  1084 
clivi  of,  1085 
cultninis  of,  1084 
lingulas  of,  1084 
noduli  of,  1085 


2058 


INDEX. 


Cerebellum,  lobus  pyramidis  of,  1086 
tuberis  of,  1087 
uvulae  of,  1086 

medullary  substance  of,  1093 

nuclei,  internal  of,  1088 

nucleus,  dentate  of,  1088 

emboliformis  (embolus)  of,  1089 
fastigii  of,  1089 
globosus  of,  1089 

Purkinje  cells  of,  1090 

tonsil  (amygdala)  of,  1086 

worm  of,  1082 
Cerebral  commissures,  development  of,  1194 

convolutions  (gyri),  1135 

fissures  (sulci),  1135 

hemispheres,  1133 

architecture  of,  1155 
longitudinal  fissure  of,  1133 

lobes,  1135 

localization,  1210 

peduncles,  1107 
Cerebro-spinal  fluid,  1023 
Cerumen,  1489 
Cervical  flexure,  1062 
Cheeks,  1538 

lymphatics  of,  951 

pract.  consid.,  1594 
Choanae,  1413 

(bony),  224 

primitive,  1429 
Chorda  dorsalis,  27 
Chordae  tendineae,  of  heart,  697 
Choriocapillaris,  1456 
Chorion,  32 

allantoic,  33 

canalized  fibrin  of,  49 

epithelium  of,  49 

frondosum,  38 

human,  41 

laeve,  38 

primitive,  31 

syncytium  of,  49 

villi  of,  49 
Choroid,  1455 

development  of,  1482 

plexus  of  fourth  ventricle,  noo 
of  third  ventricle,  1131 

pract.  consid.,  1459 

structure  of,  1456 

Chromaffine  cells  of  carotid  body,  1810 
Chromatin,  9 
Cilia,  70 
Ciliary  body,  1457 

ganglion,  1236 

muscle,  1458 

processes,  1457 

ring,  1457 

Circulation,  general  plan  of,  719 
Cisterna  magna,  1203 
Claustrum,  1172 
Clava,  1066 
Clavicle,  257 

development  of,  258 

fracture  of,  259 

landmarks  of,  260 

pract.  consid.,  258 

sexual  differences,  258 

surface  anatomy  of,  258 
Clinoid  process,  anterior,  189 

processes,  middle,  186 

posterior,  186 
Clitoris,  2024 

glans  of,  2024 


Clitoris,  nerves  of,  2025 
prepuce  of,  2024 
vessels  of,  2025 
Cloaca,  1696 
Cloquet,  canal  of,  1474 

lymph-nodes  of,  992 
Coccygeal  body,  1810 
Coccyx,  127 

development  of,  131 
Cochlea,  membranous,  1517 
nerves  of,  1521 
organ  of  Corti  of,  1519 
Reissner's  membrane  of,  1517 
structure  of,  1518 
osseous,  1513 

Cceliac  plexus,  lymphatic,  973 
Ccelom,  28 

pericardial,  1700 
pleural,  1700 

Cohnheim's  fields  of  striated  muscle-fibre,  461 
Collagen,  83 
Colles,  fascia  of,  562 
ligament  of,  523 
Colliculi  inferiores,  1107 

superiores,  1107 
Colliculus,    inferior,    internal    structure    of, 

mo 

superior,  internal  structure  of,   mo 
Colon,  1668 

ascending,  1668 
blood-vessels  of,  1672 
descending,  1669 
flexure,  hepatic  of,  1668 

splenic  of,  1668 
lymphatics  of,  1672 
nerves  of,  1672 
peritoneal  relations  of,  1670 
pract.  consid.,  1685 
relations  of,  1668 
transverse,  1668 
Colostrum,  2031 

corpuscles,  2031 
Columnae  carneae,  of  heart,  697 
Column,  spinal,  114 
Columns,  anterior,  of  spinal  cord,  1027 
lateral,  of  spinal  cord,  1027 
of  Morgagni,  1674 
posterior,  of  spinal  cord,  1027 
Commissura  habenulae,  1124 
hippocampi,  1158 
hypothalamica,  1128 
Commissure,  anterior,  1185 
of  Meynert,  1115 
middle,  1 1 19 
posterior,  1125 
Concha,  1484 
Condylarthrosis,  113 
Conjunctiva,  1441 
bulbar,  1445 
palpebral,  1445 
pract.  consid.,  1447 

Connective    substances,    chemical    composi- 
tion of,  83 
tissues,  73 

cells  of,  73 
fixed,  74 
typical,  74 
wandering,  74 
chemical  composition  of,  83 
granule-cells  of,  74 
ground-substance  of,  75 
intercellular    constituents  of,  74 
pigment -cells  of,  74 


INDEX. 


2059 


Construction,  general  plan  of,  r 
Conus  medullaris,  of  spinal  cord,  1021 
Convolutions  (gyri)  cerebral,  1135 
Cooper,  ligaments  of,  2029 
Cord,  spermatic,  1960 
Corium,  1383 
Cornea,  1450 

nerves  of,  1452 
pract.  consid.,  1453 
structure  of,  1451 
Corniculae  laryngis,  1817 
Cornua  sphenoidalia,  191 
Corona  radiata,  1186 
Coronoid  process,  of  ulna,  281 
Corpora  cavernosa  of  penis,  1966 
mammillaria  (albicantia),  1128 
quadrigemina,  1106 
Corpus  albicans,  1991 
callosum,  1155 
fibrosum,  1991 
Highmori,  1942 
luteum,  1990 

spurium,  1991 
verum,  1991 

spongiosum,  of  penis,  1967 
striatum,  1169 

connections  of,  1172 
development  of,  1193 
structure  of,  1171 
subthalamicum,  1128 
trapezoides,  1079 
Corpuscles,  corneal,  1452 
genital,  1017 
of  Grandry,  1016 
of  Hassall,  1799 
of  Herbst,  1019 
of  Meissner,  1017 
of  Ruffini,  1017 
Vater-Pacinian,  1018 
Cortex  of  cerebellum,  1090 

cerebral,  histogenesis  of,  1192 
local  variations  in,  1180 
nerve-cells  of,  1176 
nerve-fibres  of,  1179 
structure  of,  1175 
Corti,  ganglion  of,  1257 
membrane,  1521 
organ  of,  1519 
Costal  cartilage,  153 
Cotyledons  of  placenta,  50 
Cowper,  glands  of,  1984 
Cranial  capacity,  230 
nerves,  1219 

abducent  (6th),  1249 
auditory  (8th),  1256 
development  of,  1376 
facial  (7th),  1250 
glosso-pharyngeal  (gth),  1260 
hypoglossal  (i2th),  1275 
oculomotor  (3rd),  1225 
olfactory  (ist),  1220 
optic  (2nd),  1223 
pract.  consid.,  1220 
spinal-accessory  (nth),  1274 
trigeminal  (sth),  1230 
trochlear  (4th),  1228 
vagus  (loth),  1265 
Cranio-cerebral  topography,  1214 
Cranium,  172 

architecture  of,  220 
exterior  of,  218 
fossa,  anterior,  220 
middle  of,  220 


Cranium,  fossa,  posterior  of,  220 
fractures  of,  238 
interior  of,  220 

muscles  and  fascia1,   pract.  consid.,  489 
pract.  consid.,  235 
vault  of,  220 
Cretinism,  1794 
Cricoid  cartilage,  1813 
Crista  galli,  of  ethmoid,  191 
Crura  of  penis,  1967 
Crusta,  1115 
Cuboid  bone,  422 

development  of,  423 
Cumulus  oophorus,  1989 
Cuneate  tubercle,  1067 
Cuneiform  bone,  310 
external,  428 
internal,  426 
middle,  427 
Cuticle,  1385 
Cuvier,  ducts  of,  854 
Cystic  duct,  1720 

pract.  consid.,  1731 
Cytoplasm,  structure  of,  7 

Dacryon,  228 

Darwin,  tubercle  of,  1484 

Decidua,  44 

capsularis,  46 

cells  of,  47 

placentalis,  48 

reflexa,  45 

serotina,  48 

vera,  46 
Decussation  of  pyramids,  1064 

sensory,  1070 
Deiters,  cells  of,  1521 

nucleus,  1076 

Demours,  membrane  of,  1452 
Dendrites,  of  neurones,  997 
Dental  formula,  1542 

papilla,  1558 
Dentine,  1550 

formation  of,  1559 
Dentition,  first  and  second,  1564 
Derma,  1383 

Descemet's  membrane,  1452 
Deutoplasm,  i  5 
Development  of  alimentary  tract,  1694 

of  atlas,  131 

of  auditory  nerves,  1525 

of  axis,  131 

of  bone,  94 

of  carpus,  313 

of  cartilage,  82 

of  cerebellum,  1103 

of  clavicle,  258 

of  coccyx,  131 

of  cranial  nerves,  1376 

of  ear,  1523 

early,  15 

of  elastic  tissue,  77 

of  ethmoid  bone,  194 

of  external  ear,  1526 

of  external  genital  organs,  2043 

of  eye,  1480 

of  face,  62 

of  Fallopian  tube,  1999 

of  femur,  359 

of  fibrous  tissue,  76 

of  fibula,  393 

of  frontal  bone,  197 

of  ganglia,  1012 


2060 


INDEX. 


Development,  general,  of  brain,  1058 
of  general  body-form,  56 
of  glands,  1537 
of  hairs,  1401 
of  heart,  705 
of  humerus,  269 
of  hyoid  bone,  216 
of  inferior  turbinate  bone,  208 
of  innominate  bone,  337 
of  internal  ear,  1523 
of  lachrymal  bone,  207 
of  liver,  1723 
of  lungs,  1 86 1 
of  lymphatic  vessels,  939 
of  lymph-nodes,  940 
of  malar  bone,  210 
of  mammary  glands,  2032 
of  maxilla,  inferior,  213 
of  maxilla,  superior,  202 
of  medulla  oblongata,  1101 
of  mesencephalon,  1117 
of  middle  ear,  1525 
of  muscle,  non-striated,  457 
of  muscle,  striated,  465 
of  nails,  1403 
of  nasal  bone,  209 
of  nerves,  1375 
of  nervous  tissues,  1009 
of  nose,  1429 
of  occipital  bone,  175 
of  oral  cavity,  62 
glands,  1589 
of  ovary,  1993 
of  palate  bone,  205 
of  pancreas,  1737 
of  parietal  bone,  199 
of  patella,  400 
of  pelvis,  344 
of  peripheral  nerves,  ion 
of  peritoneum,  1702 
of  pharynx,  1603 
of  pituitary  body,  1808 
of  pons  Varolii,  1103 
of  prostate  gland,  1979 
of  radius,  293 

of  reproductive  organs,  2037 
of  respiratory  tract,  1861 
of  ribs,  1 53 
of  sacrum,  129 
of  scapula,  253 
of  skin,  1400 
of  sphenoid  bone,  190 
of  spinal  cord,  1049 
of  spleen,  1787 
of  sternum,  157 
of  suprarenal  bodies,  1 804 
of  sweat  glands,  1404 
of  sympathetic  system,  1013 
of  teeth,  1556 
of  temporal  bone,  184 
of  thymus  body,  1800 
of  thyroid  body,  1793 
of  tibia,  387 
of  ulna,  285 
of  urethra,  1938 
of  urinary  bladder,  1938 

organs,  1934 
of  uterus,  2010 
of  vagina,  2019 
of  veins,  926 
of  vertebrae,  128 
of  vomer,  206 
Diaphragm,  556 


Diaphragm,  lymphatics  of,  970 

of  pelvis,  1676 
Diaphragma  sellae,  1200 
Diaphysis,  of  bone,  104 
Diarthrosis,  107 
Diencephalon ,  1 1 1 8 

development  of,  1193 
Diverticulum  of  Meckel,  44 
Dorsum  sellag,  186 
Douglas,  fold  of,  522 

pouch  of,  1743 
Duct  or  ducts,  cochlear,  1517 

of  Cuvier,  854 

cystic,  1720 

ejaculatory,  1955 

Gartner's,  2001 

hepatic,  1718 

lactiferous,  2028 

nasal  (naso-lachrymal)  1479 

pancreatic,  1736 

.papillary,  of  kidney,  1882 

paraurethral,  1924 

parotid,  1583 

renal,  1894 

spermatic,  1953 

sublingual,  1585 

submaxillary,  1584 

thoracic,  941 

thyro-glossal,  1793 

vitelline,  32 

vitello-intestinal,  human,  37 

Wolffian,  1935 
Ductus  arteriosus,  723 

endolymphaticus,  1514 

venosus,  fissure  of,  on  liver,  1707 
Duodenal  glands,  1639 
Duodeno-hepatic  ligament,  1644 
Duodeno-jejunal  flexure,  1645 

fossae,  1647 
Duodenum,  1644 

blood-vessels  of,  1649 

interior  of,  1648 

lymphatics  of,  1649 

nerves  of,  1649 

papilla  of,  1720 

peritoneal  relations  of,  1646 

variations  of,  1649 
Dupuytren's  contraction,  616 
Dura  mater  of  brain,  1198 

of  spinal  cord,  1022 

Ear,  1483 

development  of,  1523 
external,  1484 

development  of,  1526 
internal,  1510 

development  of,  1523 

membranous  labyrinth  of,  1514 

osseous  labyrinth  of ,  1 5 1 1 

perilymph  of,  1514 
lymphatics  of,  950 
middle,  1492 

antrum  of,  1 508 

development  of,  1525 

Eustachian  tube,  1501 

mastoid  cells,  1 504 

sigmoid  sinus,  1 509 

suprameatal  triangle,  1510 

suprameatic  spine,  1 508 

tympanum  of,  1492 
Ear-point,  1484 
liar-wax,  1489 
Ectoblast,  23 


INDEX. 


2061 


Egg-nucleus,  16 
Elastic  tissue,  76 

development  of,  77 
Elastin,  83 
Elbow-joint,  301 

landmarks  of,  308 

movements  of,  303 

pract.  consid.,  305 

Embryo,  stage  of,  56 

Eminentia  hypoglossi,  1098 

teres,  1097- 
Enamel,  1548 

formation  of,  1561 
Enamel-cells,  1561 
Enamel-cuticle,  1550 
Enamel-organ,  1 560 
Enarthrosis,  113 
Encephalon,  1055 
End-bulbs  of  Krause,  1016 
End-knobs   of    free   sensory   nerve-endings, 

1015 

Endocardium,  702 

Endolymph  of  membranous  labyrinth,  1514 
Endometrium,  2007 
Endomysium,  458 
Endoneurium,   1006 
Endothelium,  71 
Enophthalmos,  1439 
Ensiform  cartilage  of  sternum,  156 
Entoblast,  23 
Entoskeleton,  84 
Ependymal  cells,  1004 
Epicardium,  702 
Epidermis,  1385 
Epididymis,  1947 

appendix  of,  1949 
canal  of,  1948 
digital  fossa  of,  1947 
globus  major  of,  1947 

minor  of,  1947 
nerves  of,  1948 
structure  of,  1947 
vasa  abberrantia  of,  1950 
vessels  of,  1948 
Epiglottis,  1816 

ligaments  of,  1817 
movements  of,  1817 
Epimysium,  458 
Epineurium,  1006 
Epiphysis,,  1124 

ossification  of,  98 
Epispadias,  1928 
Epithalamus,  1123 
Epithelium  of  chorion,  49 
columnar,  69 
glandular,  70 
'  modified,  70 
pigmented,  70 
specialized,  70 
squamous,  68 

stratified,  68 
transitional,  69 
Epitrichium,  1401 
Eponychium,  1403 
Epoophoron,  2000 
Erythroblasts,  92 
Erythrocytes,  68 1 

development  of,  687 
Ethmoid  bone,  191 

articulations  of,  194 
bulla  of,  194 
cells  of,  192 
development  of,  194 


Ethmoid  turbinate  bone,  middle  of,  193 

superior  of,  193 
uncinate  process  of,  193 
Eustachian  tube,  1501 

blood-vessels  of,  1 504 
cartilaginous  portion,  1502 
mucous    membrane  of,  1 503 
muscles  of,  1503 
osseous  portion,  1502 
pract.  consid.,  1507 
valve,  694 
Exocoelom,  32 
Exophthalmos,  1439 
Exoskeleton,  84 
Extremity,  lower,  332 

landmarks  of,  669 
lymphatics  of,  991 
upper,  landmarks  of,  618 

lymphatics  of,  961 
Eye,  1436 

development  of,  1480 
lymphatics  of,  949 
plica  semilunaris  of,  1443 
pupil  of,  1459 
Eyeball,  1448 

aqueous  humor  of,  1476 
chamber  anterior  of,  1476 

posterior  of,  1476 
choroid  of,  1455 
ciliary  body  of,  1457 

processes  of,  1457 
cornea  of,  1450 
fovea  centralis  of,  1466 
iris  of,  1459 

lens,  crystalline  of,  1471 
macula  lutea  of,  1466 
movements  of,  505 
optic  nerve  of,  1469 
ora  serrata  of,  1467 
pract.  consid.,  1449 
retina  of,  1462 
sclera  of,  1449 
vascular  tunic  of,  1454 
vitreous  body  of,  1473 
Eye-lashes,  1442 
Eyelids,  1441 

blood-vessels  of,  1445 
development  of,  1483 
lymphatics  of,  1445 
nerves  of,  1446 
pract.  consid.,  1446 
structure  of,  1443 

Face,  222 

architecture  of,  228 
development  of,  62 
landmarks  of,  246 

muscles  and  fasciae,  pract.  consid.,  492 
pract.  consid.,  242 
Falciform  ligament,  1745 
Fallopian  tube,  1996 

changes  in,  1999 

course  of,  1997 

development  of,  1999 

fimbriae  of,  1997 

infundibulum  of,  1997 

isthmus  of,  1997 

lymphatics  of,  988 

nerves  of,  1999 

pract.  consid.,  1999 

relations  of,  1997 
Fallopian  tube,  structure  of,  1997 

vessels  of,  1998 


2062 


INDEX. 


Fallopius,  aqueduct  of,  181 
Falx  cerebelli,  1200 

cerebri,  1199 
Fascia  or  fasciae,  470 

anal,  1678 

of  ankle,  pract.  consid.,  666 

antibrachial,  592 

of  anus,  1675 

of  arm,  pract.  consid.,  589 

of  axilla  and  shoulder,  pract.  consid.,  579 

axillary,  574 

bicipital  (semilunar),  586  . 

brachial,  585 

bucco-pharyngeal,  488 

of  buttocks,  pract.  consid.,  641 

of  Colles,  562 

of  cranium,  pract.  consid.,  489 

cribriform,  635 

crural,  647 

deep,  470 

of  back,  508 
cervical,  542 
of  hand,  606 

dentata,  1166 

of  face,  pract.  consid.,  492 

of  foot,  pract.  consid.,  666 

of  hip  and  thigh,  pract.  consid.,  642 

iliac,  624 

infundibuliform,  524 

intercolumnar  (external  spermatic),  524 

of  knee,  pract.  consid.,  645 

lata,  633 

of  leg,  pract.  consid.,  665 

obturator,  559 

of  orbit,  504 

palmar,  606 

palpebral,  1438 

parotido-masseteric,  474 

pectoral,  568 

pelvic,  558 

perineal,  superficial,  562 

plantar,  659 

prevertebral,  543 

rectal,  1678 

recto- vesical,  1678 

of  rectum,  1675 

of  scalp,  pract.  consid.,  489 

superficial,  470 

of  abdomen,  515 

temporal,  475 

transversalis,  520 
Fasciculus,  auriculo- ventricular  of  heart,  701 

posterior  longitudinal,  1 1 1 6 

retroflexus,  1124 

solitarius,  1074 
Fat,  orbital,  1437 
Fat-cells,  79 
Fauces,  isthmus  of,  1 569 

pillars  of,  1569 
Femoral  canal,  625 

ring,  625 
Femur,  352 

development  of,  359 

landmarks  of,  366 

pract.  consid.,  361 

structure  of,  357 

surface  anatomy,  360 

variations,  sexual  and  individual,  359 
Fertilization,  18 
Fibres,  intercolumnar,  524 
Fi1>rin,  canalized,  of  chorion,  49 
Fibro-cartilage,  82 
Fibrous  tissue,  74 


Fibrous  tissue,  development  of,  76 
Fibula,  390 

development  of,  393 
landmarks  of,  396 
pract.  consid,,  393 
Fillet,  decussation  of,  1070 

median,  1115 
Fimbria,  1159 

hippocampi,  1165 
Fissure,  calcarine,  1146 

calloso-marginal,  1139 
central,  of  cerebrum,  1137 
collateral,  1139 
ethmoidal,  1411 
of  Glaser,  178 
palpebral,  1441 
parieto-occipital,  1138 
portal,  of  liver,  1708 
pterygo-maxillary,  204 
of  Rolando,  1137 
sphenoidal,  188 
(sulci)  cerebral,  1135 
of  Sylvius,  1136 
Fistula,  cervical,  61 
Flexure,  cephalic,  58 

cervical,  of  embryo,  59 
dorsal,  of  embryo,  59 
sacral,  of  embryo,  59 
Flocculus,  1085 
Foetus,  membranes  of,  30 
stage  of,  63 

eighth  month,  66 

week,  64 
fifth  month,  66 

week,  63 

fourth  month,  65 
ninth  month,  66 
seventh  month,  66 

week,  64 
sixth  month,  66 

week,  63 
third  month,  65 
Follicles,  Graafian,  1988 
Fontana,  spaces  of,  1452 
Fontanelles,  231 
Foot,  articulations  of,  440 
as  whole,  447 
bones  of,  419 

landmarks  of,  437 
pract.  consid.,  436 
joints  of,  landmarks  of,  453 
landmarks  of,  672 
muscles  of,  659 

and  fasciae  of,   pract.  consid.,   666- 
surface  anatomy,  449 
synovial  cavities  of,  447 
Foramen  or  foramina,  caecum,  1574 
ethmoidal,  anterior,  192 

posterior,  192 
jugular,  220 
of  Luschka,  1 100 
of  Majendie,  noo 
mastoid,  180 
of  Monroe,  1131 
optic,  189 
ovale,  1 88 

of  heart,  695 
pterygo-spinosum,  190 
rotundum,  187 
sacro-sciatic,  great,  341 

lesser,  341 
sphenoidal,  187 
spheno-palatine,  204 


INDEX. 


2063 


Foramen  or  foramina,  spinosum,  188 

stylo-mastoid,  182 

thyroid  (obturator),  337 

of  vena  cava,  of  diaphragm,  557 

of  Vesalius,  188 

of  Winslow,  1746 
Forceps  anterior,  of  corpus  callosum,  1157 

posterior,  of  corpus  callosum,  1158 
Forearm,  281 

as  whole,  299 

intrinsic  movements  of,  299 

motion  of  on  humerus,  303 

pract.  consid.,  603 
Fore-brain,  1059 
Formatio  reticularis,  1076 

reticularis  alba,  1076 

grisea,  1074 
Fornix,  1158 

pillars  of,  anterior,  1 1 59 

posterior,  1159 
Fossa  or  fossae, 

duodeno-jejunal,  1647 

glenoid,  178 

hyaloidea,  1473 

ileo-caecal,  1666 

infraspinoue,  250 

inguinal,  inner,  526 
lateral,  1743 
median,  1742 
outer,  526 

interpeduncular,  1107 

intersigmoid,  1671 

ischio-rectal,  1678 

jugular,  182 

nasal,  1409 

navicular  of  urethra,  1924 

ovalis,  695 

ovarian,  1986 

pararectal,  1744 

paravesical,  1744 

pericaecal,  1666 

pineal,  1106 

pituitary,  186 

retro-colic,  1667 

of  Rosenmiiller,  1 598 

spheno-maxillary,  227 

subscapular,  249 

supraspinous,  250 

supratonsillar,  1600 

supra vesical,  526 

Sylvii,  1137 

temporal,  218 

zygomatic,  227 
Fourchette,  2022 
Fourth  ventricle,  1096 

choroid  plexus  of,  noo 
floor  of,  1096 
roof  of,  1099 
Fovea  centralis,  1466 

vagi,  1098 

Frenulum  of  Giacomini,  1166 
Frenum  of  prepuce,  1966 

of  tongue,  1573 
Frontal  bone,  194 

articulations  of,  197 
development  of,  197 

lobe,  1139 

sinus,  1423,  226  (bony) 
Fundamental  embryological  processes,  26 
Funiculus  cuneatus,  1066 

gracilis,  1066 

of  Rolando,  1067 
Furrows,  visceral,  59 


Furrows,  visceral,  external,  61 
external,  first,  61 
inner,  61 
inner,  fourth,  62 
inner,  second,  62 
inner,  third,  62 

Galen,  vein  of,  856 
Gall-bladder,  1719 

cystic  duct  of,  1720 

fossa  of,  1708 

lymphatics  of,  981 

nerves  of,  1720 

pract.  consid.,  1729 

vessels  of,  1719 
Ganglion  or  ganglia,  1007 

basal,  1 1 69 

cervical  inferior  (sympathetic),  1362 
middle  (sympathetic),  1362 
superior  (sympathetic),  1359 

ciliary,  1236 

coccygeal  (impar),  sympathetic,  1367 

development  of,  1012 

Gasserian,  1232 

geniculate,  1252 

habenulae,  1123 

interpeduncular,  1124 

jugular,  of  glosso-pharyngeal,  1263 
of  vagus,  1267 

lenticular,  1236 

mesenteric,  inferior,  1373 
superior,  1372 

nodose  of  vagus,  1268 

ophthalmic,  1236 

otic,  1246 

petrous,  of  glosso-pharyngeal,  1264 

semilunar,  sympathetic,  1369 

spheno-palatine,  1240 

spinal,  1279 

spiral,  1257 

spirale  of  cochlea,  1522 

splanchnic,  great,  sympathetic,  1365 

submaxillary,  1247 

sympathetic,  1009 

of  sympathetic  system,  1356 

vestibular,  1259 
Ganglion-crest,  1012 
Gartner's  duct,  2001 
Gasserian  ganglion,  1232 
Gastric  glands,  1623 
Gastro-pulmonary  system,  1527 
Gastrula,  25 
Gelatin,  83 
Geniculate  bodies,  lateral,  1107 

median,  1107 

(internal)  internal  structure  of,  mo 

ganglion,  1252 
Genital  cord,  2038 

folds,  2043 

organs,  external,  development  of,  2043 
female,  2021 

pract.  consid.,  2027 

ridge,  2038 

tubercle,  2043 

Genu  of  corpus  callosum,  1155 
Germinal  spot,  16 
Gestation,  ectopic,  1999 
Giacomini,  frenulum  of,  1166 
Gianuzzi,  crescents  of,  1 534 
Gimbernat,  ligament  of,  523 
Ginglymus,  113 
Giraldes,  organ  of,  1950 
Glabella,  228 


2064 


INDEX. 


Gladiolus  of  sternum,  155 
Gland  or  glands,  1531 

alveolar  (saccular)  compound,  1535 
(saccular)  simple,  1535 

anal,  1674 

areolar,  2028 

of  Bartholin,  2026 

blood-vessels  of,  1535 

of  Bowman,  1415 

of  Brunner,  1639 

cardiac  of  stomach,  1624 

ceruminous,  1489 

ciliary,  1400 

circumanal,  1400 

of  Cowper,  1984 

cutaneous,  1397 

development  of,  1537 

gastric,  1623 

of  Henle,  1445 

of  intestines,  1637 

of  Krause,  1445 

lachrymal,  1477 
ducts  of,  1477 

of  Lieberkuhn,  1637 

lymphatics  of,  1536 

mammary,  2027 

Meibomian  (tarsal),  1444 

of  Moll,  1444 

of  Montgomery,  2028 

mucous,  1534 

nerves  of,  1536 

parotid,  1582 

prostate,  1975 

pyloric,  1624 

salivary,  1582 

sebaceous,  1397 

serous,  1534 

sexual,  development  of,  2038 

sublingual,  1585 

submaxillary,  1 583 

sweat,  1398 

blood-vessels  of,  1400 
development  of,  1404 
duct  of,  1399 
nerves  of,  1400 
structure  of,  1399 

of  tongue,  1575 

tubo-alveolar,  1532 

tubular,  compound,  1532 
simple,  1532 

of  Tyson,  1966 

unicellular,  1531 

of  Zeiss,  1444 
Glans  of  clitoris,  2024- 

penis,  1968 
Glaser,  fissure  of,  178 
Glisson's  capsule  of  liver,  1708 
Globus  pallidus,  1170 
Goblet-cells,  70 

Golgi-Mazzoni  corpuscles,  1019 
Gonion,  228 
Graafian  follicles,  1988 
Grandry,  corpuscles  of,  1016 
Growth,  6 

of  bone,  101 

Gudden,  inferior  commissure  of,  mo 
Gums,  1567 

lymphatics  of,  951 

pract.  consid.,  1590 
Gustatory  cells,  1435 
Gyrus  or  gyri,  callosal  (fornicatus),  1150 
(convolutions)  cerebral,  1135 
dentate,  1166 


Gyrus  or  gyri,  development  of,  "i  190 
hippocampal,  1151 

Hair-cells  (auditory)  inner,  1520 

outer,  1520 
Hair-follicle,  1392 

blood-vessels  of,  1394 
nerves  of,  1394 
Hairs,  1389 

arrangement  of,  1391 
development  of,  1401 
growth  of,  1402 
structure  of,  1391 
whorls  of,  1391 
Hair-shaft,  1391 

Hamular  process  of  inner  pterygoid  plate,  189 
Hamulus  of  bony  cochlea,  1514 
Hand,  309 

deep  fascia  of,  606 
landmarks  of,  320 
lymphatics  of,  964 
muscles  of,  606 
pract.  consid.,  613 
surface  anatomy  of,  328 
Harelip,  1589 
Haversian  canals  of  bone,  88 

system  of  bone,  86 

Hassall,  corpuscles  of,  1799 

Head,  movements  of,  142 

Heart,  annuli  fibrosi  of,  698 

annulus  ovalis,  695 

of  Vieussens,  695 
architecture  of  walls,  700 
auricles  of,  693 
blood-vessels  of,  703 
canal  auricular  of,  705 
chambers  of,  693 
chordae  tendineae  of,  697 
columns?  carnese  of,  697 
development  of,  705 
endocardium  of,  702 
epicardium  of,  702 
fasciculus  auriculo-ventricular,  701 
foramen  ovale  of,  695 
fossa  ovalis  of,  695 
general  description  of,  689 
His's  bundle,  701 
lymphatics,  703 
muscle  of,  462 
muscles,  pectinate  of,  695 
nerve-endings  in,  1015 
nerves  of,  704 
position  of,  692 
practical  considerations,  710 
relations  of,  693 
septum,  aortic,  707 

auricular  of,  694 

intermedium,  706 

interventricular  of,  696 

primum,  706 

secundum,  708 

spurium,  707 
Thebesian  veins  of,  694 
tubercle  of  Lower,  695 
valves,  Eustachian,  '><)( 

auriculo-ventricular,  699 

mitral,  699 

position  of,  692 

structure  of,  703 

Thebesian,  695 

tricuspid,  699 
vein,  oblique  of,  695 
ventricles  of,  696 


INDEX. 


206  s 


Heidenhain,  demilunes  of,  1534 

Helicotrema,  1514 

Helix,  1484 

Hemispheres,  association  fibres  of,  1182 

of  cerebellum,  1082 

cerebral,  1133 

commissural  fibres  of,  1184 

lobes  of,  1139 

projection  fibres  of,  1186 

white  centre  of,  1182 
Henle,  glands  of,  1445 

loop  of,  1 88 1 
Hensen,  node  of,  25 
Herbst,  corpuscles  of,  1019 
Hernia,  abdominal,  1759 

diaphragmatic,  1778 

femoral,  1773 

funicular,  1768 

infantile,  1767 

inguinal,  1763 
direct,  1770 
indirect,  1766 

internal    (intra-abdominal    retroperito- 
neal),  1779 

interparietal,  1768 

labial,  1769 

lumbar,  1777" 

obturator,  1777 

perineal,  1778 

sciatic,  1778 

scrotal,  1769 

umbilical,  1775 

acquired,  1776 
congenital,  1775 

ventral,  1776 
Hesselbach,  ligament  of,  525 

triangle  of,  526 
Hiatus,  aortic,  of  diaphragm,  557 

Fallopii,  181 

oesophageal,  of  diaphragm,  557 

semilunaris,  of  nasal  cavity,  194 

of  nose,  1411 

Highmore,  antrum  of,  1422 
Hind-brain,  1061 
Hip,  landmarks  of,  669 

muscles  and  fasciae  of,  pract.  consid.,  642 
Hip-joint,  367 

movements  of,  373 

pract.  consid.,  374 

synovial  membrane  of,  372 
Hippocampus,  1165 
His's  bundle,  of  heart,  701 
Histogenesis  of  neuroglia,  1010 

of  neurones,  ion 
Homologue,  4 
Horner,  muscle  of,  484 
Howship,  lacunae  of,  97 
Humerus,  265 

development  of,  269 

pract.  consid.,  270 

sexual  differences,  269 

structure  of,  269 

surface  anatomy,  270 
Humor,  aqueous,  1476 
Hunter's  canal,  628 
Hyaloid  canal,  1474 
Hyaloplasm,  8 
Hydatid  of  Morgagni,  2002 
Hydramnion,  42 
Hymen,  2016 
Hyoid  bone,  216 

development  of,  216 
Hyomandibular  cleft,  61 


Hypogastric  lymphatic  plexus,  984 
Hypophysis,  1806 
Hypospadias,  1927 
Hypothalamus,  1127 
Hypothenar  eminence,  607 

Ileo-caecal  fossae,  1666 

valve,  1 66 1 

Ilio-femoral  ligament,  369 
liio-pectineal  line,  334 
Ilio-tibial  band,  634 
Ilium,  332 
Implantation,  35 
Impregnation,  18 
Incisor  teeth,  1543 
Incus,  1497 

Inferior  caval  system  of  veins,  898 
Infundibulum,  1129 

of  nasal  cavity,  194 
of  nose,  1411 
Inguinal  canal,  523 

lymphatic  plexus,  991 
Inion,  228 
Innominate  bone,  332 

development  of,  337 
structure  of,  337 
Insula,  1149 
Intersigmoid  fossa,  1671 
Intervertebral  disks,  132 
Intestine    or   intestines,    development    and 

growth  of,  1671 
glands  of,  1637 
large,  1657 

appendices  epiploicae,  1660 
blood-vessels  of,  1660 
glands  of  Lieberkuhn  of,  1657 
lymphatics  of,  1660 
lymphatic  tissue  of,  1658 
nerves  of,  1660 
pract.  consid.,  1680 
structure  of,  1657 
taenia  coli  of,  1660 
lymph-nodules  of,  1640 
small,  1633 

blood-vessels  of,  1642 
glands  of  Lieberkuhn  of,  1637 
lymphatics  of,  1643 
nerves  of,  1643 
Peyer's  patches  of,  1640 
pract.  consid.,  1652 
structure  of,  1634 
valvulae  conniventes  of,  1636 
villi  of,  1635 
solitary  nodules  of,  1640 
Involuntary  muscle,  1015 
Iris,  1459 

pract.  consid.,  1461 
structure  of,  1460 
Irritability,  6 
Ischio-rectal  fossa,  1678 
Ischium,  336 
Islands  of  Langerhans,  1735 

of  Reil,  1 149 
Isthmus  of  fauces,  1569 
rhombencephali,  1061 

Jacobson's  nerve,  1264 

organ,  1417 

development  of,  1432 
Jejuno-ileum,  1649 

blood-vessels  of,  1652 

lymphatics  of,  1652 

mesentery  of,  1650 


130 


2O66 


INDEX. 


Jejuno-ileum,  nerves  of,  1652 

topography  of,  1650 
Joint  or  joints,  of  ankle,  438 

calcaneo-astragaloid,  posterior,  445 

calcaneo-cuboid,  446 

calcaneo-scapho-astragaloid,       anterior, 

445 

capsule  of,  no 
of  carpus,   metacarpus  and   phalanges, 

pract.  consid.,  330 
costo-central,  160 
costo-sternal,  160 

motions  in,  166 
costo-transverse,  160 
costo- vertebral,  motions  in,  165 
crico-arytenoid,  1816 
crico-thyroid,  1815 
elbow,  301 
fixed,  107 

general  considerations,  107 
half,  1 08 
of  hip,  367 
interchondral,  160 
intersternal,  159 

motions  in,  165 
of  knee,  400 

limitation  of  motion,  112 
metatarso-phalangeal,  447 
modes  of  fixation,  112 
of  pelvis,  337 

of  pelvis,  pract.  consid,  350 
raaio-ulnar,  297 

inferior,  pract.  consid.,  308 
saddle,  113 

scapho-cubo-cuneiform,  446 
of  shoulder,  274 
synovial  membrane  of,  no 
tarso-metatarsal,  446 
of   tarsus,    metatarsus    and    phalanges, 

pract.  consid.,  45 
true,  1 08 

motion  in,  112 

structure  of,  109 

varieties  of,  113 
vessels  and  nerves  of,  in 
Jugular  ganglion,  of  glosso-pharyngeal,  1263 

of  vagus,  1267 
plexus,  lymphatics,  956 

Karyokinesis,  1 1 

Karyosomes,  9 

Kidney  or  kidneys,  1869 

architecture  of,  1875 

blood-vessels  of,  1884 

capsule  of,  1869 

cortex  of,  1876 

development  of,  1937 

ducts  of,  1894 

fixation  of,  1871 

glomeruli  of,  1876 

hilum  of,  1869 

labyrinth  of,  1876 

lobule  of,  1875 

loop  of  Henle  of,  1881 

lymphatics  of,  1885 

Malpighian  body  of,  1879 

medulla  of,  1876 

medullary  rays  of,  1876 

movable,  1888 

nerves  of,  1886 

papillae  of,  1875 

papillary  ducts  of,  1882 

pelvis  of,  1894 


Kidney  or  kidneys,  position  of,  1870 

pract.  consid.,  1887 

pyramids  of,  1876 

relations  of,  1873 

sinus  of,  1874 

structure  of,  1877 

supporting  tissue  of,  1883 

surfaces  of,  1869 

tubule,  collecting  of,  1882 
connecting  of,  1882 
distal  convoluted  of,  1882 
proximal  convoluted  of,  1880 
spiral  of,  1880 
uriniferous  of,  1877 
Knee,  landmarks  of,  671 

muscles  and  fasciae  of,  pract.  consid.,  645 
Knee-joint,  400 

bursas  of,  406 

capsule  of,  400 

landmarks  of,  416 

movements  of,  408 

pract.  consid.,  409 

semilunar  cartilage  of,  402 

synovial  membrane  of,  405 
Krause,  end-bulbs  of,  1016 

glands  of,  1445 
Kupffer,  cells  of,  1717 

Labia  major,  2021 
minora,  2022 
nerves  of,  2024 
vessels  of,  2023 
Labyrinth,  membranous,  1514 

blood-vessels  of,  1522 

canalis  reuniens  of,  1515 

cochlea  of,  1517 

ductus  endolymphaticus  of,  1514 

endolymph  of,  1514 

maculae  acustica;  of,  1516 

saccule  of,  1515 

semicircular  canals  of,  1515 

utricle  of,  1514 
osseous,  1511 

cochlea  of,  1513 

semicircular  canals  of,  1512 

vestibule  of,  1511 
Lachrymal  apparatus,  1477 

pract.  consid.,  1479 
bone,  207 

articulations  of,  207 

development  of,  207 
canaliculi,  1478 
caruncle,  1443 
gland,  1477 
lake,  1443 
papillae,  1478 
puncta,  1478 
sac,  1478 
Lactation,  2029 
Lacteals,  1643 
Lacunae,  of  bone,  86 
of  cartilage,  80 
of  Howship,  97 
Lambda,  228 

Lamina  cinerea  (terminalis),  1130 
fusca,  1450 
suprachoroidea,  1456 
Landmarks,  of  abdomen,  531 
of  ankle  and  foot,  672 
of  bones  of  foot,  437 
of  buttocks  and  hip,  669 
of  clavicle,  260 
of  elbow-joint,  308 


INDEX. 


2067 


Landmarks,  of  face,  246 

of  femur,  366 

of  fibula,  396 

of  hand,  320 

of  joints  of  foot,  453 

of  knee,  671 

of  knee-joint,  416 

of  leg,  671 

of  lower  extremity,  669 

of  male  perineum,  1918 

of  neck,  554 

of  pelvis,  349 

of  radius,  296 

of  scapula,  255 

of  shoulder-joint,  280 

of  skull,  240 

of  spine,  146 

of  surface  of  thorax,  1868 

of  thigh,  670 

of  thorax,  170 

of  tibia,  390 

of  ulna,  287 

of  upper  extremity,  618 

of  wrist-joint,  330 
Langerhans,  islands  of,  1735 
Lanugo,  66 

Laryngo-pharynx,  1598 
Larynx,  1813 

age  changes  of,  1828 

arytenoid  cartilages  of,  1816 

corniculag  laryngis,  1817 

cricoid  cartilage  of,  1813 

cuneiform  cartilages  of,  1817 

development  of,  1862 

elastic  sheath  of,  1817 

epiglottis,  1816 

form  of,  1818 

lymphatics  of,  958 

mucous  membrane  of,  1823 

muscles  of,  1824 

nerves  of,  1827 

ossification  of,  1818 

position  and  relations  of,  1828 

pract.  consid.,  1828 

region,  glottic  of,  1820 
infraglottic  of,  1823 
supraglottic  of,  1818 

sexual  differences  of,  1828 

thyroid  cartilage  of,  1814 

ventricle  (sinus)  of,  1822 

vessels  of,  1826 

vocal  cords,  false  of,  1820 

true  of,  1820 
ligaments  of,  1818 

Leg,  bones  of,  as  one  apparatus,  397 
surface  anatomy,  397 

framework  of,  382 

landmarks  of,  671 

lymphatics,  deep  of,  994 
superficial  of,  993 

muscles  and  fasciae  of,  pract.  consid.,  665 
Lens,  crystalline,  1471 

development  of,  1481 
pract.  consid.,  1473 
suspensory  apparatus  of,  1475 
Leptorhines,  1404 
Leucocytes,  684 

development  of,  688 

varieties  of,  685 
Lieberkuhn,  glands  of,  1637 
Lieno-phrenic  fold,  1785 
Ligament  or  ligaments,  112 

alar,  of  knee-joint,  405 


Ligament  or  ligaments,  anterior  annular,  of 
ankle,  647 

of  wrist,  325,  607 
posterior,  of  wrist,  325 

annular,  of  wrist,  607 
arcuate,  external,  557 

internal,  557 

atlanto-axial,  anterior,  137 
atlan to-axial,  posterior,  137 
of  auricle,  1486 
broad,  of  uterus,  2004 
broad,  vesicular  appendages  of,  2002 
check,  of  orbit,  1438 
of  Colles,  523 
common  anterior  and  posterior,  of  spine, 

J33 

coraco-acromial,  256 
coraco-clavicular,  262 

conoid  part,  262 

trapezoid  part,  262 
coronary,  of  liver,  1721 
costo-clavicular  or  rhomboid,  262 
cotyloid,  of  hip-joint,  367 
crucial,  of  knee-joint,  404 
cruciform,  of  axis,  136 
deltoid  (lat.  int.)  of  ankle-joint,  439 
denticulate,  of  spinal  cord,  1023 
duodeno-hepatic,  1644 
dorsal,  of  foot,  442 
of  epiglottis,  1817 
external  check,  of  eyeball,  505 
falciform,  1745 

of  liver,  1721 
gastro-phrenic,  1747 
of  Gimbernat,  523 
of  Hesselbach,  525 
ilio-femoral,  369 
ilio-lumbar,  339 
interclavicular,  262 
interosseous,  of  foot,  441 
interspinous,  134 
intertransverse,  135 
ischio-femoral,  370 

of  laminae  and  processes  of  vertebrae,  133 
lieno-renal,  1747 
of  liver,  1721 
nuchae,  134 
occipito-atlantal,  accessory,  137 

anterior,  137 

posterior,  137 
occipito-axial,  137 
odontoid,  or  check,  136 
orbicular,  of  radius,  297 
of  ovary,  1987 
palpebral,  1441 

internal,  484 
patellae,  400 
pectinate  of  iris,  1452 
of  pelvis,  337 
of  pericardium,  716 
plantar,  444 
of  Poupart,  523 
pterygo-mandibular,  488 
radio-ulnar,  297 
round,  of  hip-joint,  370 

of  liver,  1721 

of  uterus,  2005 
sacro-iliac,  posterior,  338 
sacro-sciatic,  339 

great  or  posterior,  339 

lesser  or  anterior,  341 
of  scapula,  256 
of  shoulder-joint,  274 


2068 


INDEX. 


Ligament  or  ligaments,  spino-glenoid,  257 

stylo-mandibular,  475 

subflava,  133 

suprascapular  or  transverse,  256 

supraspinous,  133 

suspensory,  of  lens,  1475 
of  orbit,  1438 
of  ovary,  1986 

thyro-arytenoid,  inferior,  1818 
superior,  1817 

thyro-hyoid,  1815 

transverse,  of  atlas,  136 

triangular,  of  liver,  1721 
of  perineum,  563 

of  vertebral  bodies,  132 

of  Winslow,  of  knee-joint,  401 

of  wrist  and  metacarpus,  320 
Limb,  lower,  muscles  of,  623 
Limbic  lobe,  1150 
Linea  alba,  522 

semilunaris,  of  abdomen,  532 

transverse,  of  abdomen,  532 
Linin,  9 
Lips,  1538 

lymphatics  of,  951 

muscles  of,  1 540 

nerves  of,  1542 

pract.  consid.,  1590 

vessels  of,  1542 
Liquor  amnii,  31 

pericardii,  714 
Littre,  glands  of,  1925 
Liver,  1705 

bile-capillaries  of,  1715 

biliary  apparatus,  1718 

blood-vessels  of,  1709 

borders  of,  1707 

caudate  lobe  of,  1709 

cells  of  Kupffer,  1717 

common  bile-duct,  1720 

cystic  duct  of,  1720 

development  and  growth  of,  1723 

fissure  of  ductus  venosus  of,  1707 

fossa  for  gall-bladder  of,  1708 

gall-bladder  of,  1719 

Glisson's  capsule  of,  1708 

hepatic  artery  of,  1711 
ducts  of,  1718 
veins  of,  1710 

impression,  oesophageal  of,  1708 
renal  of,  1 709 

intralobular  connective  tissue  of,  1717 
bile-ducts  of,  1717 
veins  of,  1710 

ligaments  of,  1721 
coronary,  1721 
falciform,  1721 
round,  1721 
triangular,  1721 

lobes  of,  1706 

lobular  blood-vessels  of,  1713 

lobules  of,  1712 

lymphatics  of,  1711 

nerves  of,  1711 

non-peritoneal  area  of,  1707 

peritoneal  relations  of,  1721 

portal  (transverse)  fissure  of,  1708 
vein  of,  1709 

position  of,  1722 

pract.  consid.,  1726 

quadrate  lobe  of,  1 709 

size  of,  1706 

Spigelian  lobe  of,  1707 


Liver,  structure  of,  1712 

sublobular  veins  of,  1710 

surfaces  of,  1707 

tuber  omentale  of,  1709 

umbilical  fissure  of,  1708 
notch  of,  1707 

weight  of,  1706 
Liver-cells,  1714 
Lobe  or  lobes,  cerebral,  1135 

frontal,  1139 

of  hemispheres,  1139 

limbic,  1150 

occipital,  1145 

olfactory,  1151 

parietal,  1 143 

temporal,  1147 
Lobule  of  auricle,  1484 
Loin,  pract.  consid.,  530 
Lordosis,  144 

Lumbar  plexus,  lymphatic,  973 
Lumbo-sacral  cord,  1331 
Lung  or  lungs,  1843 

air-sacs  of,  1850 

alveoli  of,  1850 

atria  of,  1850 

blood-vessels  of,  1853 

borders  of,  1843 

development  of,  1861 

external  appearance  of,  1846 

fissures  of,  1845 

ligament  broad  of,  1858 

lobes  of,  1845 

lobule  of,  1849 

nerves  of,  1855 

physical  characteristics  of,  1846 

pract.  consid.,  1864 

relations  to  chest-walls,  changes  in,  1863 
to  thoracic  walls,  1855 

roots  of,  1838 

dimensions  of,  1840 
nerves  of,  1839 
relations  of,  1840 

structure  of,  1851 

surfaces  of,  1843 

vessels  of,  1839 
Lunula,  of  nail,  1395 
Luschka,  foramina  of,  1 1  oo 

gland  of,  1 8 10 
Lutein  cells,  1990 
Luys,  nucleus  of,  1128 
Lymphatic  or  lymphatics,  of  abdomen,  972 

of  abdominal  walls,  976 

of  arm,  deep,  965 
superficial,  963 

of  bile-duct,  981 

of  bladder,  985 

of  bone,  93 

of  brain,  948 

of  brain  and  meninges,  948 

broncho-mediastinal  trunk,  968 

capillaries,  933 

of  cervical  skin  and  muscles,  958 

of  cheeks,  951 

of  diaphragm,  970 

duct,  right,  945 

of  ear,  950 

of  eye  and  orbit,  949 

of  eyelids,  1445 

of  Fallopian  tubes,  988 

of  gall-bladder,  981 

of  glands,  1536 

of  gums,  951 

of  hand,  <jf>  t 


INDEX. 


2069 


Lymphatic  or  lymphatics,  of  the  head,  945 

of  heart,  970 
hemolymph  nodes,  936 
intercostal,  969 
of  intestine,  large,  978 

small,  977 
jugular  trunk,  958 
of  kidney,  982 
lacteals,  931 
of  larynx,  958 
of  leg,  deep,  994 

superficial,  993 
of  lips,  951 
of  liver,  980 
of  lower  extremity,  991 
mammary  gland,  968    • 
of  meninges,  948 
of  muscle,  non-striated,  456 
of  nasal  fossa,  1426 

region,  951 
nodes,  935 
of  nose,  1407 
of  oesophagus,  971 
of  palate,  954 
of  pancreas,  979 
of  pelvis,  983 
of  pericardium,  716 
of  perineum,  987 
of  pharynx,  954 
of  prostate  gland,  985 
of  rectum,  1680 

of    reproductive    organs,    external,    fe- 
male, 987 

external,  male,  986 

internal,  female,  988 

internal,  male,  987 
of  retina,  1468 
of  scalp,  948 
of  seminal  vesicles,  988 
of  skin,  1388 
of  small  intestine,  1643 
of  spleen,  982 
of  stomach,  976 
of  striated  muscle,  464 
subclavian  trunk,  963 
of  suprarenal  body,  983 
system,  931 
of  teeth,  951 
of  testis,  987 
thoracic  duct,  941 

pract.  consid.,  944 
of  thorax,  966 

cutaneous,  968 
of  thyroid  gland,  959 
of  tongue,  952 
of  tonsils,  954 
of  trachea,  958 
of  upper  extremity,  961 
of  ureter,  982 
of  urethra,  986 
of  uterus,  989 
of  vagina,  989 
of  vas  deferens,  988 
vessels,  development  of,  939 
Lymph-corpuscles,  931 

Lymph-nodes,  of  abdomen,  pract.  consid.,  990 
abdominal,  visceral,  974 
ano-rectal,  976 
anterior  auricular,  946 
appendicular,  975 
of  arm,  pract.  consid.,  965 
of  axilla,  pract.  consid.,  965 
axillary,  961 


Lymph-nodes,  brachial,  deep,  961 
superficial,  961 

bronchial,  967 

buccinator,  947 

cervical,  deep,  inferior,  958 
superior,  957 

of  Cloquet,  992 

coeliac,  973 

delto-pectoral,  961 

development  of,  940 

epigastric,  972 

epitrochlear,  961 

facial,  947 

gastric,  974 

of  head,  pract.  consid.,  955 

hepatic,  975 

hypogastric,  984 

iliac,  circumflex,  972 
internal,  984 

inguinal,  991 

intercostal,  966 

of  intestine,  1640 

jugular  plexus,  956 

of  leg,  pract.  consid.,  994 

lingual,  947 

mammary,  internal,  966 

mandibular,  947 

mastoid,  945 

maxillary,  947 

mediastinal,  anterior,  967 
posterior,  967 

mesenteric,  975 

mesocolic,  976 

of  neck,  956 

pract.  consid.,  959 

occipital,  945 

pancreatico-splenic,  975 

parotid,  946 

pectoral,  962 

of  pelvis,  pract.  consid.,  990 

popliteal,  992 

posterior  auricular,  945 

retro-pharyngeal,  948 

of  Rosenmuller,  992 

sternal,  966 

structure  of,  937 

submaxillary,  946 

submental,  946 

subscapular,  962 

superficial  cervical,  956 

thorax,  pract.  consid.,  971 

tibial,  anterior,  993 

tracheal  nodes,  967 

umbilical,  972 
Lymph-nodules,  936 
Lymphocytes,  931 

varieties  of,  685 
Lymphoid  structures  of  pharynx,  1599 

tissue,  structure  of,  936 
Lymph-spaces,  931 
Lymph -vessels,  934 
Lyra,  1158 

Macula  lutea,  1466 

Maculae  acusticae,  1516 

Majendie,  foramen  of,  noo 

Maxilla,  inferior,  211 

development  of,  213 
structure  of,  213 
superior,  199 
antrum  of,  201 
articulations  of,  202 
development  of,  202 


2070 


INDEX. 


Maxillary  sinus,  1422 
Malar  bone,  209 

articulations  of,  210 
development  of,  210,  2032 
Malleus,  1497 

Malphighian  bodies  of  spleen,  1784 
Mammary  glands,  2027 

development  of,  2032 
lymphatics,  968 
nerves  of,  2032 
pract.  consid.,  2033 
structure  of,  2029 
variations  of,  2033 
vessels  of,  2031 
Manubrium  of  sternum,  155 
Marrow,  of  bone,  90 
Mast-cells  of  connective  tissue,  74 
Mastoid  cells,  1 504 

pract.  consid.,  1508 
process,  pract.  consid.,  1508 
subdivision,  of  petro-mastoid  bone,  179 
Maturation  of  ovum,  16 
Meatus,  auditory,  internal,  181 
inferior,  of  nose,  1412 
middle,  of  nose,  1411 
superior,  of  nose,  1411 
Meckel,  diverticulum  of,  44 
Mediastinum,  anterior,  1833 
middle,  1833 
posterior,  1833 
pract.  consid.,  1833 
superior,  1833 
Medulla  oblongata,  1063 

central  gray  matter  of,   1073 
development  of,  nor 
internal  structure  of,  1068 
Medullary  folds,  26 
groove,  26 
sheath,  1001 
velum,  inferior,  1099 

superior,  1099 
Medullated  fibres,  1003 
Megakaryocytes,  689 
Meibomian  (tarsal)  glands,  1444 
Meissner,  corpuscles  of,  1017 

Slexus  of,  1643 
rane  or  membranes,  Bowman's, 

I451 

of  Bruch,  1456 
cloacal,  1939 
costo-coracoid,  568 
cri  co-thyroid,  1815 
of  Demours,  1452 
Descemet's,  1452 
fenest rated,  77 
fcetal,  30 

human,  35 

chief  peculiarities  of,  39 
hyaloid,  1474 

interosseous,  of  tibia  and  fibula,  396 
mucous,  1528 
obturator,  341 
pharyngeal,  1694 
pleuro-pericardial,  1700 
pleuro-peritoneal,  1700 
of  Ruysch,  1456 
of  spinal  cord,  1022 
synovial,  of  joint,  no 
tectoria,  1521 
thyro-hyoid,  1815 
of  tympanum,  1494 
vitelline,  15 
vitrea,  1456 


Meninges  of  brain,  pract.  consid.,  1208 

lymphatics  of,  948 
Menstruation,  2012 
Merkel,  tactile  cells  of,  1016 
Mesencephalon,  1105 

development  of,  1117 

internal  structure  of,  1109 
Mesenteries,  1741 
Mesenterium  commune,  1697 
Mesentery,  anterior,  1744 

of  appendix,  1665 

of  jejuno-ileum,  1650 

permanent,  1752 

posterior,  part  ist,  1746 
part  2nd,  1751 
part  3rd,  1753 

primitive,  1697 
Meso-appendix,  1665 
Mesoblast,  23 

lateral  plates  of,  29 

paraxial,  29 

parietal  layer,  29 

visceral  layer,  29 
Mesogastrium,  1697 
Mesognathism,  229 
Mesometrium,  2005 
Mesonephros,  1935 
Mesorarium,  2040 
Mesorchium,  2040 
Mesorhines,  1404 
Mesosalpinx,  1996 
Mesotendons,  471 
Mesothelium,  71 
Mesovarium,  1987 
Metabolism,  6 
Metacarpal  bones,  314 

development  of,  317 
peculiarities  of,  315 

Metacarpo-phalangeal  articulations,  327 
Metacarpus,  pract.  consid.,  319 
Metanephros  (kidney),  1937 
Metaphase  of  mitosis,  12 
Metaplasm,  8 
Metatarsal  bones,  428 

development  of,  432 
Metathalamus,  1126 
Meynert,  commissure  of,  1115 
Mid-brain,  1061 
Milk,  2030 
Milk-ridge,  2032 
Mitosis,  ii 

anaphases  of,  13 

metaphase  of,  12 

prophases  of,  12 

telophases  of,  13 
Molar  teeth,  1 546 
Moll,  glands  of,  1444 
Monorchism,  1950 
Monroe,  foramen  of ,  1131 
Mons  pubis,  2021 

veneris,  2021 

Montgomery,  glands  of,  2028 
Morgagni,  columns  of,  1674 

hydatid  of,  2002 

sinus  of,  497 

valves  of,  1674 
Morula,  22 
Mouth,  1538 

floor  of,  pract.  consid.,  1593 

formation  of,  1694 

pract.  consid.,  1589 

roof  of.  228 

pract.  consid.,  1592 


INDEX. 


2071 


Mouth,  vestibule  of,  1538 

Mucoid,  83 

Mucous  membranes,  1528 

structure  of,  1528 
Mullerian  duct,  2038 
Muscle  or  muscles,  abdominal,  515 
abductor  hallucis,  66 1 

minimi  digiti,  608 

minimi,  of  foot,  662 

pollicis,  608 
adductor  brevis,  626 

hallucis,  662 

longus,  626 

magnus,  628 

pollicis,  610 
anconeus,  589 

of  ankle,  pract.  consid.,  666 
antibrachial,  591 

post-axial,  598 

pre-axial,  592 
of  anus,  1675 
appendicular,  566 
of  arm,  pract.  consid.,  589 
arytenoid,  1826 
of  auricle,  1486 
auricularis  anterior,  483 

posterior,  483 

superior,  483 
axial,  502 
of    axilla  and  shoulder,  pract.  consid. 

579 

azygos  uvulae,  496 
biceps,  586 

femoris,  636 
brachial,  585 

post-axial,  588 

pre-axial,  586 
brachialis  anticus,  586 
brachio-radialis,  598 
branchiomeric,  474 
buccinator,  488 
bulbo-cavernosus,  565 
of  buttocks,  pract.  consid.,  641 
cardiac,  462 
cervical,  542 
chondro-glossus,  1578 
ciliary,  1458 
coccygeus,  561,  1676 
compound  pinnate,  469 
compressor  urethrae,  565 
constrictor  inferior  of  pharynx,  1606 

middle  of  pharynx,  1605 

pharyngis  inferior,  499 
medius,  498 
superior,  497 

superior  of  pharynx,  1604 
coraco-brachialis,  575 
of  cranium,  pract.  consid.,  489 
cremaster,  519 
crico-arytenoid  lateral,  1825 

posterior,  1825 
crico-thyroid,  1824 
crural,  647 

post-axial,  655 

pre-axial,  648 
crureus,  640 
dartos,  1963 
deltoideus,  578 
depressor  anguli  pris,  487 

labii  inferioris,  485 
diaphragma,  5.56 
digastricus,  477 
dilator  pupillae,  1460 


Muscle  or  muscles,  dorsal,  of  trunk,  507 
of  Eustachian  tube,  1503 
extensor  brevis  digitorum,  665 
pollicis,  602 

carpi  radialis  brevior,  598 
longior,  598 
ulnaris,  60 1 

communis  digitorum,  599 

indicis,  603 

longus  digitorum,  655 

longus  hallucis,  656 
pollicis,  603 

minimi  digiti,  600 

ossis  metacarpi  pollicis,  602 
of  face,  pract.  consid.,  492 
facial,  479 
femoral,  633 

post-axial,  638 

pre-axial,  636 
flexor  accessorius,  654 

brevis  digitorum,  of  foot,  660 
hallucis,  660 
minimi  digiti,  609 

digiti  of  foot,  664 
pollicis,  608 

carpi  radialis,  593 

radialis  brevis,  597 
ulnaris,  594 

longus  digitorum,  651 
hallucis,  651 
pollicis,  596 

profundus  digitorum,  595 

sublimis  digitorum,  595 
of  foot,  659 

post-axial,  665 

pract.  consid.,  666 

pre-axial,  659 
gastrocnemius,  649 
gemelli,  630 
genio-glossus,  1578 
genio-hyoid,  1578 
genio-hyoideus,  545 
gluteus  maximus,  630 

medius,  631 

minimus,  633 
gracilis,  626 
of  hand,  606 

pre-axial,  607 

of  hip  and  thigh,  pract.  consid.,  642 
hypoglossal,  506 
hyo-glossus,  1578 
hyoidean,  480 

variations  of,  480 
iliacus,  624 
ilio-costalis,  508 
infraspinatus,  576 
intercostales  externi,  538 

interni,  539 

interossei  dorsales  of  foot,  664 
of  hand,  613 

plantares,  663 

volares,  612 
interspinales,  513 
intertransversales,  513 

anteriores,  547 

laterales,  521 
intratympanic,  1499 
involuntary,  arrectores  pilorum,  1394 

nerve-endings  of,  1015 
ischio-cavernosus,  564 
of  knee,  pract.  consid.,  645 
of  larynx,  1824 
latissimus  dorsi,  574 


2072 


INDEX. 


Muscle  or   muscles,  of   leg,    pract.    consid., 

665 

levator  anguli  oris,  487 
scapulae,  571 

ani,  560,  1675 

labii  superioris,  487 

labii  superioris  alaeque  nasi,  485 

menti  (superbus),  485 

palati,  496,  1571 

palpebrae  superioris,  502 
levatores  costarum,  540 
lingualis,  1579 
of  lips,  1540 
longissimus,  510 
longus  colli,  548 
of  lower  limb,  623 
lumbricales,  of  hand,  610 

of  foot,  662 
masseter,  474 
of  mastication,  474 

variations  of,  477 
metameric,  502 
multifidus,  512 
mylo-hyoideus,  477 
nasalis,  486 
non-striated,  blood-vessels  of,  456 

development  of,  457 

(involuntary),  454 

lymphatics  of,  456 

nerves  of,  456 

structure  of,  455 
obliquus  capitis  inferior,  514 
superior,  514 

externus,  517 

inferior,  504 

internus,  517 

superior,  504 
obturator  externus,  629 

internus,  629 
occipito-frontalis,  482 
omo-hyoideus,  544 
opponens  minimi  digiti,  608 

pollicis,  608 
orbicularis  oris,  486 

palpebrarum,  484 
orbital,  502 

of  palate  and  pharynx,  495 
palato-glossus,  497,  1579 
palato-pharyngeus,  497,  1571 
palmaris  brevis,  607 

longus,  593 

pectinate,  of  heart,  695 
pectineus,  625 
pectoralis  major,  569 

minor,  570 
pelvic,  559 
perineal,  562 
peroneus  brevis,  658 

longus,  657 

tertius,  656 
of  pharynx,  1604 
pinnate,  469 
plantaris,  649 
platysma,  481 
popliteus,  655 
pronator  quadratus,  597 

radii  teres,  592 
psoas  magnus,  623 

parvus  (minor),  624 
pterygoideus  externus,  476 

internus,  476 
pyloric  sphincter,  1626 
pyramidalis,  517 


Muscle  or  muscles,  pyriformis,  561 
quadratus  femoris,  629 

lumborum,  521 
quadriceps  femoris,  639 
of  rectum,  1675 
rectus  abdominis,  516 

capitis  anticus  major,  549 

capitis  anticus  minor,  550 
lateralis,  547 
posticus  major,  513 
posticus  minor,  514 

externus,  503 

femoris,  639 

inferior,  503 

internus,  503 

superior,  503 
rhomboideus  major,  572 

minor,  572 
risorius,  487 
rotatores,  of  back,  513 
sacro-spinalis,  508 
salpingo-pharyngeus,  1606 
sartorius,  638 
scalene,  variations  of,  547 
scalenus  anticus,  546 

medius,  546 

posticus,  547 

of  scalp,  pract.  consid.,  489 
semimembranosus,  438 
semi-pinnate,  469 
semispinalis,  511 
semitendinosus,  638 
serratus  magnus,  571 

posticus  inferior,  541 

posticus  superior,  541 
of  soft  palate,  1570 
soleus,  649 

sphincter  ani,  external,  1676 
externus,  563 
internal,  1677 

pupillae,  1460 

vesical,  external,  1925 

internal,  1925 
spinalis,  511 
splenius,  510 
stapedius,  480,  1499 
sternalis,  570 

sterno-cleido-mastoideus,  499 
sterno-hyoideus,  543 
sterno-thyroideus,  545 
striated,  attachments  of,  468 

blood-vessels  of,  464 

bursse  of,  471 

classification  of,  471 

development  of,  465 

form  of,  469 

general  considerations  of,  468 

lymphatics  of,  464 

nerves  of,  464 

nerve-supply,  general,  473 

structure,  general  of,  458 

variations,  461 

(voluntary),  457 
stylo-glossus,  1579 
stylo-hyoideus,  480 
stylo-pharyngeus,  495,  1606 
subclavius,  570 
subcostal,  539 
subcrureus,  640 
submental,  477 
subscapularis,  578 
supinator,  60 1 
supraspinatus,  575 


INDEX. 


2073 


Muscle  or  muscles,  temporalis,  475 
tensor  fasciae  latas,  631 
palati,  479,  I57° 
tympani,  479,  1499 
teres  major,  577 
minor,  576 
thoracic,  538 
thyro-arytenoid,  1825 
thyro-hyoideus,  545 
tibialis  anticus,  655 

posticus,  654 
of  tongue,  1577 
trachealis,  1835 
transversalis,  519 
transverso-costal  tract,  508 
transverso-spinal  tract,  511 
transversus  perinei  profundus,  565 

superficialis,  564 
of  tongue,  1579 
trapezius,  500 
triangularis  sterni,  540 
triceps,  588 
trigeminal,  474 
palatal,  479 
tympanic,  479 
of  trunk,  507 
of  upper  limb,  568 
vago-accessory,  495 
vastus  externus,  640 

internus,  640 
ventral,  of  trunk,  515 
voluntary,  motor  nerve-endings  of,  1014 
zygomaticus  major,  485 

minor,  485 

Muscle-fibre,  structure  of,  459 
Muscular  system,  454 

tissue,  general,  454 
Myelin,  1001 

Myelocytes,  of  bone-marrow,  92 
Myeloplaxes,  of  bone-marrow,  92 
Myometrium,  2008 
Myotome,  30 
Myxcedema,  1794 

Naboth,  ovules  of,  2008 
Nail,  structure  of,  1395 
Nail-bed,  1396 
Nail-plate,  1395 
Nails,  1394 

development  of,  1403 
Naress  anterior,  1404 

posterior,  1413 
Nasal  bone,  209 

articulations  of,  209 
development  of,  209 
cavities,  pract.  consid.,  1417 
cavity,  223 

hiatus  semilunaris  of,  194 
infundibulum  of,  194 
meatus  inferior  of,  225 
middle  of,  225 
superior  of,  225 
chamber,  224 
fossa,  blood-vessels  of,  1425 

floor  of,  1413 
lymphatics  of,  1426 
nerves  of,  1426 
roof  of,  1412 
fossae,  1409 
index,  1404 

mucous  membrane,  1413 
(naso-lachrymal)  duct,  1479 
septum,  223,  1410 


Xasal    septum,    triangular   cartilage   of, 

224 

Nasion,  228 

Nasmyth,  membrane  of,  1550 
Naso-pharynx,  1  598 
Naso-optic  groove,  62 
Navel,  37 

Neck,  landmarks  of,  554 
pract.  consid.,  550 
triangles  of,  547 
Nephrotome,  30 
Nerve    or    nerves,    abdominal,    of   vagus, 

1272 
abducent,  1249 

development  of,  1379 
aortic  (sympathetic),  1364 
auditory,  1256 

development  of,  1379 
of  auricle,  1487 
auricular,  great,  1286 

posterior,  of  facial,  1254 
of  vagus,  1268 

auriculo-temporal,  of   mandibular,  1244 
of  bone,  94 

buccal,  of  mandibular,  f  243 
calcanean,  internal,  1344 
cervical,  anterior  divisions  of,   1285 
cardiac  inferior,  of  vagus,  1270 

superior,  of  vagus,  1270 
first,  posterior  division  of,  1281 
posterior  divisions  of,  1281 
second,  posterior  division  of,  1281 
superficial,  1287 

third,  posterior  division  of,  1281 
cervico-facial,  of  facial,  1254 
chorda  tympani,  of  facial,  1253 
ciliary,  long,  of  nasal,  1234 
circumflex,  1307 

pract.  consid.,  1308 
of  clitoris,  2025 

coccygeal,  posterior  division  of,   1284 
of  cochlea,  membranous,  1521 
cochlear,  of  auditory,  1256 
of  cornea,  1452 
cranial,  1219 

crural,  anterior  (femoral),  1327 
cutaneous  internal,   of  anterior  crural, 

1328 

middle,  of  anterior  crural,  1327 
perforating,    of    pudendal    plexus, 

1347 
dental,  inferior,  of  mandibular,  1245 

superior      anterior,     of    maxillary, 
1239 

middle,  of  maxillary,  1239 
posterior,  of  maxillary,  1238 
descendens  hypoglossi,  1277 
development  of,  1375 
digastric,  of  facial,  1254 
digital  of  median,  1301 
dorsal  of  clitoris,  1351 

of  penis,  1351 
of  epididymis,  1948 
of  external  auditory  canal,  1490 
external  cutaneous,  of  lumbar  plexus, 


of  eyelids,  1446 

facial,  1250,  1251 

development  of,  1378 
genu  of,  1251 
pract.  consid.,  1255 

of  Fallopian  tube,  1999 

frontal,  1234 


INDEX. 


Nerve  or  nerves,  ganglionic,  of  nasal, 

1234 

genito-crural,  1322 
of  glands,  1536 
glosso-pharyngeal,  1260 

development  of,  1379 
gluteal,  inferior,  1333 

superior,  1333 
of  hair-follicles,  1394 
of  heart,  704 

hemorrhoidal,  inferior,  1350 
hypoglossal,  1275 

development  of,  1380 

pract.  consid.,  1277 
ilio-hypogastric,  1320 
ilio-inguinal,  1321 
infratrochlear,  1235 
intercosto-humeral,  1317 
intermedius   of   Wrisberg,   of  facial, 

1250 
internal  cutaneous,  1303 

cutaneous  lesser,  1303 
interosseous  anterior  of  median,  1300 
of  kidney,  1886 
of  labia,  2024 

labial,  superior,  of  maxillary,  1240 
lachrymal,  1233 

laryngeal,   external,   of  superior  laryn- 
geal, 1270 

inferior  (recurrent)  of  vagus,  1270 

internal,  of  superior  laryngeal,  1270 

superior,  of  vagus,  1270 
of  larynx,  1827 
lingual,  of  glosso-pharyngeal,  1264 

of  hypoglossal,  1277 

of  mandibular,  1244 
of  lips,  1542 
of  liver,  1711 

lumbar,  posterior  divisions  of,   1282 
of  lungs,  1855 
of  mammary  glands,  2032 
mandibular,  (maxillary  inferior),  1242 
masseteric,  of  mandibular,  1242 
maxillary  (superior),  1237 
median,  1298 

branches  of,  1300 

pract.  consid.,  1301 
meningeal,  of  hypoglossal,  1277 

of  vagus,  1268 

mental,  of  inferior  dental,  1246 
of  muscle,  non-striated,  456 
muscular  of  glosso-pharyngeal,  1264 
musculo-cutaneous,  of  arm,  1298 

of  leg,  1338 
musculo-spiral,  1308 

branches  of,  1309 

pract.  consid.,  1314 
mylo-hyoid,  of  inferior  dental,  1245 
nasal,  1234,  1235 

anterior,  1235 

external,  1235 

fossa,  1426 

internal  (septal),  1235 

lateral,  of  maxillary,  1240 

septum,  1410 

suj>erior  posterior,  of  spheno-pala- 

tine  ganglion,  1241 

naso-palatine,   of  spheno-palatine  gan- 
glion, 1241 
of  nose,  1407 
obturator,  1324 

accessory,  1326 
occipital,  small,  1286 


Nerve  or  nerves,  oculomotor,  1225 

development  of,  1377 
cesophageal,  of  vagus,  1272 
of  oesophagus,  1613 
olfactory,  1220 

development  of,  1376 

pract.  consid.,  1222 
ophthalmic,  1233 
optic,  1223 

development  of,  1482 

pract.  consid.,  1470 

orbital,  of  spheno-palatine  ganglion,  1241 
of  ovary,  1993 
of  palate,  1573 
palatine,    of   spheno-palatine    ganglion, 

1241 

palmar  cutaneous  of  median,  1301 
palpebral,  inferior,  of  maxillary,  1240 
of  pancreas,  1737 
of  parotid  gland,  1583 
of  penis,  1971 
pericardial  of  vagus,  1272 
of  pericardium,  716 
perineal,  1350 

peripheral,  development  of,  ion 
peroneal,  communicating,    of    external 

popliteal,  1335 
petrosal,  deep,  small,  1264 

superficial,    external,    of    facial, 


great,  of  facial,  1252 
small,  1264 

pharyngeal  of  glosso-pharyngeal, 
1264 

of  vagus,  1269 
of  pharynx,  1606 
phrenic,  1290 
plantar  external,  1345 

internal,  1344 
of  pleurae,  1861 
popliteal,  external  (peroneal),  1335 

internal  (tibial),  1339 
posterior  interosseous,  1311 
of  prostate  gland,  1978 
pterygoid,  external,  of  mandibular, 
1243 

internal,  of  mandibular,  1242 
pterygo-palatine     (pharyngeal),     of 

spheno-palatine  ganglion,  1242 
pudic,  1349 
pulmonary,  anterior,  of  vagus,  1272 

posterior,  of  vagus,  1272 

(sympathetic),  1364 
radial,  1313 
of  rectum,  1680 
recurrent,  of  mandibular,  1242 

of  maxillary,  1237 
respiratory,  external  of  Bell,  1295 
sacral,  posterior  divisions  of,  1282 
sacro-coccygeal,  1352 

posterior,  1283 

saphenous,  internal    (long),  of  anteriof 
crural,  1329 

short  (external),  1342 
scapular,  posterior,  1295 
sciatic,  great,  1335 

small,  1348 
of  scrotum,  1964 
of  skin,  1389 
of  small  intestine,  1643 
somatic,  1218 
of  spermatic  ducts,  1959 
spheno-palatine,  of  maxillary,  1237 


INDEX. 


2075 


Nerve  or  nerves,  spinal,  1278 
spinal-accessory,  1274 

.  pract.  consid.,  1275 
splanchnic,  (sympathetic),  1364 
of  spleen,  1787 
stapedial,  of  facial,  1253 
of  stomach,  1628 
of  striated  muscle,  464 
stylo-hyoid,  of  facial,  1254 
of  sublingual  gland,  1585 
of  submaxillary  gland,  1585 
subscapular,  1306 
supraorbital,  1234 
of  suprarenal  bodies,  1803 
suprascapular,  1295 
supratrochlear,  1234 
sural,  of  external  popliteal,  1335 
of  sweat  glands,  1400 
of  taste-buds,  1435 
temporal,  deep,  of  mandibular,  1243 

superficial,     of     auriculo-temporal, 

1244 

temporo-facial,  of  facial,  1254 
temporo-malar    (orbital),   of  maxillary, 

1238 

of  testis,  1948 
thoracic,  1314 

anterior,  external,  1297 
internal,  1303 

branches  of,  1317 

cardiac,  of  vagus,  1272 

first,  1315 

lower,  1315 

posterior  divisions  of,  1282 

posterior  (long),  1295 
pract.  consid.,  1296 

pract.  consid.,  1318 

second,  1317 

third,  1317 

twelfth  (subcostal)  1317 

upper,  1315 
of  thyroid  body,  1793 
of  thymus  body,  1800 
thyro-hyoid,  of  hypoglossal,  1277 
tibial,  anterior,  1336 

communicating,  1342 

posterior,  1342 

recurrent,  1335 
of  tongue,  i 580 

tonsillar  of  glosso-pharyngeal,  1264 
of  trachea,  1836 
trigeminal,  1230 

development  of,  1378 

divisions  of,  1232 

pract.  consid.,  1248 
trochlear,  1228 

development  of,  1377  t 

tympanic,  of  glosso-pharyngeal,  1264 
to  tympanic  plexus,  of  facial,  1252 
ulnar,  1303 

branches  of,  1305 

pract.  consid.,  1306 
of  ureter,  1898 
of  urethra,  1927 
of  urinary  bladder,  1910 
of  uterus,  2010 
of  vagina,  2018 
vagus,  1265 

and  spinal  accessory,  development 
of,  1380 

ganglia  of,  1267 

pract.  consid.,  1272 
vestibular,  of  auditory,  1256 


Xerve  or  nerves,  visceral,  1218 
Nerve-cells,  998 
bipolar,  999 
multipolar,  1000 
unipolar,  999 
Nerve-endings,  motor,  1014 

of  cardiac  muscle,  1015 
of  involuntary  muscle,  1015 
of  voluntary  muscle,  1014 
sensory,  1015 

encapsulated,  1016 
free,  1015 

genital  corpuscles,  1017 
Golgi-Mazzoni  corpuscles,  1019 
Krause's  end-bulbs,  1016 
Meissner's  corpuscles,  1017 
Merkel's  tactile  cells,  1016 
neuromuscular  endings,  1019 
neurotendinous  endings,  1020 
Rumni's  corpuscles,  1017 
Vater-Pacinian  corpuscles,  1018 
Xerve-fibres,  1000 
arcuate,  1071 
axis-cylinder  of,  1001 
cerebello-olivary,  1072 
cerebello-thalamic,  1114 
cortico-bulbar,  1115 
cortico-pontine,  1115 
cortico-spinal,  1115 
medullary  sheath  of,  1001 
medullated,  1003 
neurilemma  of,  1001 
nonmedullated,  1003 
rubro-thalamic,  1114 
of  sympathetic  system,  1356 
Nerve-terminations,  1014 
Nerve-trunks,  1006 

endoneurium  of,  1006 
epineurium  of,  1006 
funiculi  of,  1006 
perineurium  of,  1006 
Nervous  system,  996 
central,  1021 
peripheral,  1218 
sympathetic,  1353 

development  of,  1013 
tissues,  997 

development  of,  1009 
Neurilemma,  1001 
Neuroblasts,  1010 
Neuro-epithelium,  70 
Neuroglia,  1003 

ependymal  layer  of,  1004 
glia-fibres  of,  1004 
of  gray  matter,  of  spinal  cord,  1035 
histogenesis  of,  1010 
spider  cells  of,  1004 
Neurokeratin,  1001 
Neuromuscular  endings,  1019 
Neurone  or  neurones,  996 
axones  of,  997 
dendrites  of,  997 
histogenesis  of,  ion 
nerve-cells  of,  998 
Neurotendinous  endings,  1020 
Nipple,  2028 

Nodose,  ganglion  of  vagus,  1268 
Nodules  of  Arantius,  700 
Nonmedullated  fibres,  1003 
Nor'moblasts,  92 
Nose,  1404 

blood-vessels  of,  1407 
cartilages  of,  1404 


2076 


INDEX. 


Nose,  development  of,  1429 

hiatus  semilunaris  of,  1411 

inferior  meatus  of,  1412 

infundibulum  of,  1411 

lateral  cartilages  of,  1405 

lymphatics  of,  1407 

middle  meatus  of,  1411 

nerves  of,  1407 

olfactory  region  of,  1413 

pract.  consid.,  1407 

respiratory  region  of,  1415 

superior  meatus  of,  1411 

vestibule  of,  1409 
Nostrils,  1404 
Notochord,  27 
Nuck,  canal  of,  2006 
Nuclein,  9 
Nucleolus,  9 
Nucleus  or  nuclei,  abducent,  1249 

acoustic,  1257 

ambiguus,  1074 

amygdaloid,  1172 

arcuate,  1076 

caudate,  1 169 

cuneate,  1069 

facial,  1251 

dentate,  of  cerebellum,  1088 

emboliformis   (embolus)   of  cerebellum, 
1089 

facial,  1251 

fastigii,  of  cerebellum,  1089 

globosus,  of  cerebellum,  1089 

gracile,  1069 

internal,  of  cerebellum,  1088 

of  lateral  fillet,  1258 

lenticular,  1 1 69 

mammillaris,  1129 

olivary,  1071 

olivary,  superior,  1257 

red,  1114 

structure  of,  8 

trapezoideus,  1257 

vago-glosso-pharyngeal,  1073 

vestibular,  of  reception,  1259 
Nuhn,  glands  of,  1577 
Nutrition,  accessory  organs  of,  1781 
Nymphas,  2022 

Obelion,  228 
Obex,  1096 
Occipital  bone,  172 

development  ot,  175 

lobe,  1145 

protuberance,  external,  174 

internal,  175 
Odontoblasts,  1558 
(Esophagus,  1609 

course  and  relations  of,  1609 

lymphatics  of,  971 

nerves  of,  1613 

pract.  consid.,  1613 

structure  of,  1611 

vessels  of,  1612 
Olecranon,  of  ulna,  281 
Olfactory  bulb,  1151 

cells,  1414 

hairs,  1415 

lobe,  1151 

pits,  62 

region  of  nose,  1413 

striae,  1153 

tract,  1 152 

trigone,  1153 


Olivary  eminence,  1066 

nuclei,  1071 

accessory,  1072 

nucleus,  inferior,  1072 
Omental  sac,  1703 
Omentum,  duodeno-hepatic,  1746 

gastro-colic,  1747 

gastro-hepatic  (lesser),  1745 

gastro-splenic,  1747 

greater,  1747 

greater,  structure  of,  1749 
Oocyte,  primary,  17 

secondary,  17 
OSplasm,  15 
Opercula  insulae,  1137 
Ophryon,  228 
Opisthion,  228 
Optic  commissure,  1130 

recess,  1132 

thalami,  1118 

tracts,  1130 
Ora  serrata,  1467 
Oral  cavity,  development  of,  62 

glands,  development  of,  1589 
Orbit,  222 

axes  of,  222 

dimensions  of,  222 

fasciae  of,  504 

lymphatics  of,  949 

pract.  consid.,  1438 

Organ   or    organs,    accessory,    of    nutrition,. 
1781 

of  Corti,  1519 

genital,  external  female,  2021 

Jacobson's,  1417 

reproductive  female,  1985 
male,  1941 

of  respiration,  1813 

of  sense,  1381 

of  taste,  1433 

urinary,  1869 
Oro-pharynx,  1598 
Orthognathism,  229 
Os  intermetatarseum,  432 

magnum,  312 
Osseous  tissue,  84 
Ossicles  auditory,  1496 

articulations  of,  1498 
incus,  1497 
malleus,  1497 
movements  of,  1500 
stapes,  1498 

of  ear,  development  of,  1525. 
Ossification,  centres  of,  94 

of  epiphyses,  98 
Osteoblasts,  95 
Ost;um  maxillare,  1422 
Otic  ganglion,  1246 
Ova  or  ovum,  15 

centrolecithal,  22 

fertilization  of,  18 

holoblastic,  22 

homolecithal,  21 

human,  1990 

maturation  of,  16 

meroblastic,  22 

primordial,  1993 

segmentation  of,  21 

stage  of,  56 

telolecithal,  22 

x.ona  pellucida  of,  1989. 
Ovary  or  ovaries,  1985 

cortex  of,  1987 


INDEX. 


2077 


Ovary  or  ovaries,  descent  of,  2043 

development  of,  1993 

fixation  of,  1986 

Graafian  follicles  of,  1988 

hilum  of,  1985 

ligament  of,  1987 

medulla  of,  1988 

nerves  of,  1993 

position  of,  1986 

pract.  consid.,  1995 

surfaces  of,  1985 

suspensory  ligament  of,  1986 

structure  of,  1987 

vessels  of,  1992 
Oviduct,  1996 

Pacchionian  bodies,  1205 

depressions,  198 
Palate,  1567 

bone,  204 

articulations  of,  205 
development  of,  205 

hard,  1567 

lymphatics  of,  954 

nerves  of,  1573 

pract.  consid.,  1592 

soft,  1568 

muscles  of,  1570 

vessels  of,  1572 

Pallium,  development  of,  1189 
Palmar  aponeurosis,  606 

fascia,  606 
Pancreas,  1732 

body  of,  1733 

development  of,  1737 

ducts  of,  1736 

head  of,  1732 

interalveolar  cell-areas  of,  1735 

islands  of  Langerhans  of,  1735 

lymphatics  of,  979 

nerves  of,  1737 

pract   consid.,  1738 

relations  to  peritoneum  of,  1736 

structure  of,  1734 

vessels  of,  1736 
Panniculus  adiposus,  1384 
Papilla  or  papilla?,  circumvallate,  1575 

dental,  1558 

of  duodenum,  1720 

filiform,  1575 

fungi  form,  1575 

lachrymal,  1478 

renal,  1875 
Paradidymis,  1950 
Parametrium,  2005 
Parathyroid  bodies,  1795 

structure  of,  1795 
Parietal  bone,  197 

articulations  of,  199 
development  of,  199 

impressions,  199 

lobe,  1143 
Paroophoron,  2002 
Parotid  duct,  1 583 

gland,  1582 

nerves  of,  1 583 
relations  of,  1582 
structure  of,  i  586 
vessels  of,  1 583 
Parovarium,  2000 
Patella,  398 

development  of,  400 

movements  of,  409 


Patella,  pract.  consid.,  416 
Peduncle,  cerebellar,  inferior,  1067 

cerebral,  1107 
Pelvic  girdle,  332 
Pelvis,  332 

development  of,  344 

diameters  of,  342 

diaphragm  of,   559 

index  of,  343 

joints  of,  337 

pract.  consid.,  350 

of  kidney,  1894 

landmarks  of,  349 

ligaments  of,  337 

lymphatics  of,  983 

position  of,  342 

pract.  consid.,  345 

sexual  differences,  343 

surface  anatomy  of,  345 

white  line  of,  559 

as  a  whole,  341 
Penis,  1965 

corpora  cavernosa  of,  1966 

corpus  spongiosum  of,  1967 

crura  of,  1967 

glans  of,  1968 

nerves  of,  1971 

pract.  consid.,  1972 

prepuce  of,  1966 

structure  of,  1968 

vessels  of,  1970 
Pericaecal  fossae,  1666 
Pericardium,  714 

blood-vessels  of,  716 

ligaments  of,  716 

lymphatics  of,  716 

nerves  of,  716 

pract.  consid.,  716 
Perichondrium,  81 
Pericranium,  489 
Perilymph  of  internal  ear,  1514 
Perimetrium,  2009 
Perimysium,  458 
Perineal  body,  2046 
Perineum,  female,  2046 

lymphatics  of,  987 

male,  1915 

landmarks  of,  1918 

triangular  ligament  of,  563 
Perineurium,  1006 
Periosteum,  89 

alveolar,  1553 
Peritoneum,  1740 

cavity,  lesser  of,  1749 

development  of,  1702 

parietal,  anterior,  1742 
folds  of,  1742 
fossae  of,  1742 

pract.  consid.,  1754 
Peri  vascular  lymph-spaces,  931 
Pes  anserinus,  1252 

hippocampi,  1165 
Petit,  triangle  of,  574 
Petro-mastoid  portion  of  temporal  bone, 

179 

Petrous    ganglion,     of    glosso-pharyngeal, 
1264 

subdivision,    of    petro-mastoid    bone, 

181 

Peyer's  patches,  1641 
Phalanges  of  foot,  432 

development  of,  432 

of  hand,  317 


2078 


INDEX. 


Phalanges  of  hand,  development  of,  318 
peculiarities,  318 
pract.  consid.,  320 
variations  of,  319 
Pharyngeal  pouches,  1695 
Pharynx,  1596 

development  of,  1603 

growth  of,  1603 

laryngo-,  1598 

lymphatics  of,  954 

lymphoid  structures  of,  1599 

muscles  of,  1604 

naso-,  1598 

nerves  of,  1606 

oro-,  1598 

pract.  consid.,  1606 

primitive,    1694 

relations  of,  1601 

sinus  pyriformis  of,  1598 

vessels  of,  1606 
Philtrum  of  lips,  1 540 
Pia  mater,  of  brain,  1202 

of  spinal  cord,  1022 
Pigment-cells  of  connective  tissue,  74 
Pillars  of  fauces,  1569 
Pineal  body,  1124 
Pinna,  1484 
Pisiform  bone,  311 

Pituitary  body,  anterior  lobe  of,  1806 
development  of,  1808 
(hypophysis),  1129 
Placenta,  49 

basal  plate  of,  51 

cotyledons  of,  50 

discoidal,  34 

foetal  portion,  50 

giant  cells  of,  51 

intervillous  spaces  of,  51 

marginal  sinus  of,  53 

maternal  portion,  51 

multiple,  34 

septa  of,  51 

vitelline,  32 

zonular,  33 
Placentalia,  34 
Plane,  frontal,  3 

sagittal,  3 

transverse,  3 

Plasma-cells  of  connective  tissue,  74 
Plasm  osome,  9 
Plates,  tarsal,  1444 
Platyrhines,  1404 
Pleura  or  pleurae,  1858 

blood-vessels  of,  1860 

nerves  of,  1861 

outlines  of,  1859 

pract.  consid.,  1864 

relations  to  chest-walls,  changes  in,  1863 
of  to  surface,  1859 

structure  of,  1860 
Plexus  or  plexuses,  aortic,  1373 

of  Auerbach,  1643 

brachial,  1292 

branches,  infraclavicular  of,  1297 

supraclavicular  of,  1295 
constitution  and  plan  of,  1293 
pract.  consid.,  1294 

cardiac,  1367 

carotid  (sympathetic),  1360 

cavernous,  of  penis,  1374 
(sympathetic),  1361 

cervical,  1285 

branches  of,  1285 


Plexus  or   plexuses,   cervical,    branches, 

communicating  of,  1289 
deep,  of,  1289 
descending  of,  1288 
muscular  of,  1289 
superficial  of,  1286 
supraacromial  of,  1289 
supraclavicular  of,  1288 
suprasternal  of,  1288 
pract.  consid.,  1292 
coccygeal,  1352 
cceliac,  1370 

lymphatic,  973 
gastric,  1370 
hemorrhoidal,  1374 
hepatic,  1370 
hypogastnc,  1373 

lymphatic,  984 
iliac,  lymphatic,  983 
inguinal,  lymphatic,  991 
lumbar,  1319 

constitution  and  plan  of,   1319 
lymphatic,  973 
muscular  branches  of,  1320 
of  Meissner,  1643 
mesenteric  inferior,  1373 

superior,  1372 
cesophageal,  1272 
ovarian,  1371 
pampiniform,  1960 
parotid,  1252 
pelvic,  1374 
phrenic,  1371 
pract.  consid.,  1330 
prostatic,  1374 
pudendal,  1345 

branches,  muscular  of,  1346 

visceral  of,  1346 
pulmonary,  anterior,  1272 

posterior,  1272 
renal,  1371 
sacral,  1331 

branches,  articular  of,  1334 
collateral  of,  1332 
muscular  of,  1333 
terminal  of,  1334 
lymphatic,  984 
posterior,  1282 
pract.  consid.,  1352 
solar,  1368 
spermatic,  1371 
splenic,  1370 
suprarenal,  1371 
of  sympathetic  nerves,  1367 
tympanic,  1264 
utero-vaginal,  1374 
vesical,  1374 
Plica  fimbriata,  1573 

semilunaris,  of  eye,  1443 
sublingualis,  1573 
Polar  body,  first,  16 
second,  16 
Pons  Varolii,  1077 

development  of,  1103 
internal  structure  of,  1078 
Pontine  flexure,  1062 

nucleus,  1078 

Portal  system  of  veins,  919 
Postaxial,  4 

Pouch  of  Douglas,  1743 
pharyngeal,  61 
recto-uterine  '1743 
recto-vesical,  1743 


INDEX. 


2079 


Poupart,  ligament  of,  523 
Preaxial,  4 
Pregnancy,  2012 
Prepuce  of  penis,  1966 
Primitive  streak,  24 

significance  of,  25 
Process  or  processes,  ciliary,  1457 
fronto-nasal,  62 
mandibular,  62 
maxillary,  62 
nasal,  mesial,  62 

lateral,  62 

styloid,  of  petrous  bone,  183 
uncinate  of  ethmoid,  193 
Processus  cochleariformis,  182 

vaginalis,  2041 
Proctodaeum,  1695 
Prognathism,  229 
Pronephros,  1934 
Pronucleus,  female,  16 

male,  20 

Prophases  of  mitosis,  12 
Prosencephalon,  1059 
Prostate  gland,  1975 

development  of,  1979 

lymphatics  of,  985 

nerves  of,  1978 

pract.  consid.,  1979 

relations  of,  1976 

structure  of,  1977 

vessels  of,  1978 
Proteins,  8 
Protoplasm,  7 
Protovertebrae,  29 
Psalterium,  1158 
Pseudostomata,  72 
Pterion,  228 
Pterygoid  plate,  inner,  189 

outer,  189 

processes  of  sphenoid  bone,  189 
Pubes,  334 

Pulmonary  system  of  veins,  852 
Pulp  of  teeth,  1554 
Pulvinar,  1119 
Puncta,  lachrymal,  1478 
Pupil,  1459 

Purkinje  cells  of  cerebellum,  1090 
Putamen,  1170 
Pyramid,  1065 

Pyramidal  tract,  in  medulla,  1075 
Pyramids,  decussation  of,  1064 

renal,  1876 
Pyrenin,  9 

Radius,  287 

development  of,  293 

landmarks  of,  296 

pract.  consid..  293 

structure  of,  292 

surface  anatomy,  300 
Kami  communicantes  of  sympathetic  system, 

1356 

Ranvier,  nodes  of,  1001 
Rauber,  cells  of,  23 
Recto-uterine  pouch,  1743 
Recto-vesical  pouch,  1743 
Rectum,  1672 

blood-vessels  of,  1679 

growth  of,  1680 

lymphatics  of,  1680 

muscles  and  fascia?  of,  1675 

nerves  of,  1680 

peritoneal  relations  of,  1679 


Rectum,  pract.  consid.,  1689 

structure  of,  1674 

valves  of,  1674 
Reduction  division,  18 
Reil,  island  of,  1149 

limiting  sulcus  of,  1139 
Reissner's  fibre,  1030 

membrane,  of  cochlea,  1517 
Remak,  fibres  of,  1003 
Reproduction,  6 
Reproductive   organs,    development    of, 

2037 
external,     female,     lymphatics 

of,   987 

male,  lymphatics  of,  986 
female,  1985 
internal,  female,  lymphatics  of, 

male,  lymphatics  of,  987 
male,  1941 

Respiration,  organs  of,  1813 
Respiratory  region  of  nose,  1415 

tract,  development  of,  1861 
Restiform  body,  1067 
Rete  Malpighi,  1386 
Reticular  tissue,  75 
Reticulin,  83 
Retina,  1462 

blood-vessels  of,  1467 

development  of,  1482 

layers  of,  1463 

lymphatics  of,  1468 

pars  optica  of,  1462 

pract.  consid.,  1468 

structure  of,  1463 
Retro-colic  fossa,  1667 
Retzius,  prevesical  space  of,  525 

space  of,  1906 
Rhinencephalon,  1151 

development  of,  1193 
Rhombencephalon,  derivatives  of,  1063 
Ribs,  149 

asternal,  150 

development  of,  153 

exceptional,  152 

floating,  150 

pract.  consid.,  169 

sternal,  150 

variations  of,  1 53 
Right  lymphatic  duct,  945 
Rima  glottidis,  1820 
Ring,  abdominal,  external,  524 
internal,  524 

femoral,  1773 
Riolan,  muscle  of,  484 
Rivini's  ducts,  1585 
Rivinus,  notch  of,  1493 
Rolando,  fissure  of,  1137 

funiculus  of,  1067 
Rosenmiiller,  fossa  of,  1598 

lymph-nodes  of,  992 

organ  of,  2000 
Rostrum,  of  corpus  callosum,  1156 

of  sphenoid  bone,  187 
Ruffini,  corpuscles  of,  1017 
Ruysch,  membrane  of,  1456 

Sac,  conjunctival,  1443 

lachrymal,  1478 

vitelline,  32 
Saccule,  1515 

structure  of,  1516 
Sacral  lymphatic  plexus,  984 
Sacro-ihac  articulation,  338 


2080 


INDEX. 


Sacro-sciatic  ligaments,  339 
Sacrum,  124 

development  of,  129 

sexual  differences  of,  127 

variations  of,  127 
Salivary  glands,  1582 

structure  of,  1585 
Santorini,  cartilages  of,  1817 

duct  of,  1736 
Saphenous  opening,  635 
Sarcolemma,  459 

Sarcous  (muscular)  substance,  459 
Scala  tympani,  1514 

vestibuli,  1514 
Scalp,  lymphatics  of,  948 

muscles  and  fasciae,  pract.  consid.,  489 
Scaphoid,  309 

bone  of  foot,  425 

development  of,  426 
Scapula,  248 

development  of,  253 

landmarks  of,  255 

ligaments  of,  256 

pract.  consid.,  253 

sexual  differences,  252 

structure  of,  253 

Scapulo-clavicular  articulation,  262 
Scarpa,  canals  of,  201 

fascia  of,  515 

ganglion  of,  1259 

triangle  of,  639 
Schlemm,  canal  of,  1452 
Schwann,  sheath  of,  1001 
Sclera,  1449 

development  of,  1482 

pract.  consid.,  1453 

structure  of,  1450 
Sclerotome,  30 
Scoliosis,  144 
Scrotum,  1961 

dartos  muscle  of,  1963 

nerves  of,  1964 

pract.  consid.,  1964 

raphe  of,  1962 

tunica  vaginalis  of,  1963 

vessels  of,  1964 
Segmentation,  21 

complete,  22 

equal,  22 

partial,  22 
Sella  turcica,  186 
Semilunar  bone,  310 

cartilages  of  knee-joint,  402 

valves,  700 
Seminal  vesicles,  1956 

lymphatics  of,  988 
pract.  consid.,  1959 
relations  of,  1957 
structure  of,  1958 
vessels  of,  1958 
Seminiferous  tubules,  1942 
Sense,  organs  of,  1381 
Septum  or  septa,  aortic,  707 

auricular,  694 

crurale  (femorale),  625 

intermedium,  706 

intermuscular,  470 

interventricular,  696 

lucidum,  i  i  50 

median,  posterior,  of  spinal  cord,  1027 

nasal,  1410 

cartilage  of,  1405 

plaivntal,  51 


Septum  or  septa,  primum,  706 
secundum,  708 
spurium,  707 
transversum,  1701 
Serosa,  31 

Sertoli,  cells  of,  1943 
Sesamoid  bones,  104 
of  foot,  432 
of  hand,  318 

Sharpey's  fibres  of  bone,  87 
Shoulder,    muscles    and    fascia 

consid.,  579 
Shoulder-girdle,  248 

surface  anatomy  of,  263 
Shoulder-joint,  274 
bursae  of,  277 
dislocation  of,  582 
landmarks  of,  280 
ligaments  of,  274 
movements  of,  277 
pract.  consid.,  278 
Shrapnell's  membrane,  1494 
Sigmoid  cavity,  greater,  of  ulna, 

lesser,  of  ulna,  281 
flexure,  1669 

peritoneal  relations  of, 
pract.  consid.,  1685 
Sinus  or  sinuses,  basilar,  874 

pract.  consid.,  874 
cavernous,  872 

pract.  consid.,  873 
circular,  872 
confluence  of,  868 
of  dura  mater,  867 
frontal,    1423;  226  (bony) 
development  of,  1432 
pract.  consid.,  1427 
intercavernous,  872 
lactiferus,  2030 
lateral,  867 

pract.  consid.,  869 
longitudinal,  inferior,  871 
superior,  870 

pract.  consid.,  870 
marginal,  872 

of  placenta,  53 
maxillary,  1422;  20  (bony) 
development  of,  1431 
pract.  consid.,  1428 
of  Morgagni,  497 
occipital,  872 
palatal,  1425 
petrosal,  inferior,  874 

superior,  874 
pocularis,  1922 
praecervicalis,  61 
pyriformis  of  pharynx,  1 598 
renal,  1874 
Reunions,  707 
sphenoidal,  1425 

development  of,  1432 
pract.  consid.,  1428 
spheno-parietal,  874 
straight,  872 
uro-genital,  1939 
of  Valsalva,  700 
venosus,  705 
Skeleton,  103 

appendicular,  104 
axial,  103 

Skene,  tubes  of,  1924 
Skin,  blood-vessels  of,  1387 
development  of,  1400 


of,     pract 


281 
1671 


INDEX. 


2081 


Skin,  end-bulbs  of  Krause,  1389 
end-organs  of  Ruffini,  1389 
genital  corpuscles,  1389 
Golgi-mazzoni  corpuscles,  1389 
lymphatics  of,  1388 
Meissner's  corpuscles,  1389 
nerves  of,  1389 
pigmentation  of,  1387 
stratum  corneum  of,  1387 

germinativum  of,  1385 

granulosum  of,  1386 

lucidum  of,  1386 
structure  of,  1382 
Vater-Pacinian  corpuscles,  1389 
Skull,  172 

alveolar  point  of,  228 
anthropology  of,  228 
asymmetry,  230 
auricular  point  of,  228 
capacity  of,  230 
changes  in  old  age,  233 
chordal  portion,  28 
dimensions  of,  229 
fontanelles  of,  231 
glenoid  point  of,  228 
growth  and  age  of,  230 
index,  cephalic  of,  229 

facial  of,  229 

of  height  of,  229 

nasal  of,  229 

orbital  of,  229 

palatal  of,  229 
landmarks  of,  240 
malar  point  of,  228 
mental  point  of,  228 
occipital  point  of,  228 
pract.  consid.,  235 
prechordal  portion,  28 
sexual  differences,  234 
shape  of,  229 
subnasal  point  of,  229 
surface  anatomy,  234 
weight  of,  233 
as  whole,  216 
Smegma,  1966 

Solitary  nodules  of  Intestine,  1640 
Somatopleura,  29 
Somites,  29 

Space  or  spaces,  of  Burns,  543 
of  Fontana,  1452 
perforated,  anterior,  1153 

posterior,  1107 

quadrangular,  of  m.  teres  major,  578 
of  Retzius,  1906 

subarachnoid,  of  spinal  cord,  1022 
subdural,  of  spinal  cord,  1022 
sublingual,  1581 
of  Tenon,  1437 

triangular,  of  m.  teres  major,   578 
Spermatic  cord,  1960 

constituents  of,  1960 

pampiniform  plexus  of,  1960 

pract.  consid.,  1961 
ducts,  1953 

nerves  of,  1959 

structure  of,  1956 

vessels  of,  1958 
filaments,  1946 
Spermatids,  1944 
Spermatocytes,  primary,  1944 

secondary,  1944 
Spermatogenesis,  1944 
Spermatogones,  1944 


Spermatozoa,  1946 
Spermatozoon,  16 
Sperm-nucleus,  20 
Spheno-ethmoidal  recess,  1411 
Sphenoid  bone,  186 

articulations  of,  190 
development  of,  190 
great  wings  of,  187 
lesser  wings  of,  188 
pterygoid  processes  of,  189 
Sphenoidal  sinus,  1425 
Spheno-palatine  ganglion,  1240 
Spigelius,  lobe  of,  1707 
Spinal  column,  114 
Spinal  cord,  1021 

anterior  horn,  nerve-cells  of,    1030 
arachnoid  of,  1022 
blood-vessels  of,  1047 
cauda  equina  of,  1025 
central  canal  of,  1030 
columns  of,  1027 
anterior,  1027 
lateral,  1027 
posterior,  1027 
commissure,  gray  of,  1028 

white,  anterior  of,  1028 
conus  medullaris,  1021 
denticulate  ligaments  of,  1023 
development  of,  1049 
dura  mater  of,  1022 
enlargement,  cervical,  of,  1026 

lumbar  of,  1026 

fibre-tracts  of  white  matter,  1038 
fissure,  median  anterior  of,  1027 
form  of,  1026 
gray  matter  of,  1028 

nerve-fibres  of,  1036 
neuroglia  of,  1035 
ground-bundle,  anterior,  1046 

lateral,  1045 
horn,  anterior  of,  1029 
lateral  of,  1029 
posterior  of,  1029 
membranes  of,  1022 
microscopical  structure  of,    1030 
nerve-cells,  grouping  of,  1032 
pia  mater  of,  1022 
posterior  horn,  nerve-cells  of,  1033 
pract.  consid.,  1051 
root-line,  ventral  of,  1027 
segments  of,  1024 
septum,  median  posterior  of,  1027 
substantia   gelatinosa    Rolandi    of, 

1029 

sulcus  postero-lateral  of,  1027 
tract,   anterior  pyramidal  (direct), 
1046 

of  Burdach,  1039 

direct  cerebellar,  1044 

of  Goll,  1039 

of  Gower,  1044 

lateral     (crossed     pyramidal), 


t  T 

of  Lissauer,  1042 

white  matter  of,  1036 
ganglia,  1279 
nerves,  1278 

constitution  of,  1278 

divisions,  primary,  anterior,  of,  1284 
posterior,  of,  1279 

number  of,  1279 

size  of,  1279 

typical,  1284 


13* 


2082 


INDEX. 


Spinal  nerves,  ventral  (motor)  roots  of,  1279 
Spine,  114 

articulations  of,  132 
aspect,  anterior  of,  138 
lateral  of,  138 
posterior  of,  138 
curves  of,  138 

dimensions  and  proportions  of,  141 
landmarks  of,  146 
lateral  curvature  of,  144 
ligaments  of,  132 
movements  of,  142 
practical  considerations,  143 
sprains  of,  144 
as  whole,  138 
Splanchnopleura,  29 
Splanchnoskeleton,  84 
Spleen,  1781 

development  and  growth  of,  1787 
lymphatics  of,  982 
movable,  1788 
nerves  of,  1787 

nodules   (Malphighian  bodies)   of,    1784 
peritoneal  relations  of,  1785 
pract.  consid.,  1787 
pulp  of,  1783  * 

structure  of,  1783 
surface  anatomy  of,  1787 
basal,  1782 
gastric,  1782 
phrenic,  1781 
renal,  1782 

suspensory  ligament  of,  1786 
vessels  of,  1786 
Spleens,  accessory,  1787 
Splenium,  of  corpus  callosum,  1156 
Spongioblasts    i  o  i  o 
Spongioplasm,  8 
Sprains,  of  spine,  144 
Squamous  portion  of  temporal  bone,  177 
Stapes,  1498 
Stenson,  canals  of,  201 

duct,  1583 
Stephanion,  229 
Sterno-clavicular  articulation,  261 

pract.  consid.,  263 
Sternum,  155 

development  of,  157 
pract.  consid.,  168 
sexual  differences  of  156 
variations  of,  1 56 
Stigmata,  72 
Stilling,  canal  of,  1474 
Stomach,  1617 

blood-vessels  of,  1627 
curvature  greater  of,  1617 
curvature  lesser  of,  1617 
fund  us  of,  1618 
glands  of,  1623 
growth  of,  1629 
lymphatics  of,  976,  1628 
nerves  of,  1628 
peritoneal  relations  of,  1619 
position  and  relations  of,  1619 
pract.  consid.,  1629 
pylorus,  1618 
shape  of,  1618 
structure  of,  1621 
variations  of,  1629 
weight  and  dimensions  of,  1619 
Stomata,  72 
Stomodaeum,  1694 
Strabismus,  1440 


Stratum  zonale,  of  thalamus,  1123 
Stria  medullaris,  1119 
Striae,  acoustic,  1096 
Structure,  elements  of,  5 
Styloid  process  of  ulna,  285 
Sublingual  ducts,  1585 
gland,  1585 

nerves  of,  1585 
structure  of,  1587 
vessels  of,  1585 
space,  1581 

Submaxillary  duct,  1584 
ganglion,  1247 
gland,  1583 

nerves  of,  1585 
structure  of,  1587 
vessels  of,  1585 
Subpatellar  fat,  405 
Subperiosteal  bone,  98 
Sub-peritoneal  tissue,  1742 
Substantia  nigra,  1109 
Sulci,  development  of,  1190 
fissures,  cerebral,  1135 
Sulcus  hypothalamicus,  1119 
Suprarenal  bodies,  1801 
accessory,  1805 
development  of,  1804 
growth  of,  1804 
nerves  of,  1803 
pract.  consid.,  1806 
relations  of,  1801 
structure  of,  1802 
vessels  of,  1803 
body,  lymphatics  of,  983 
Suture  or  sutures,  107 
amniotic,  3 1 
coronal,  216 
cranial,  216 

closure  of,  233 
lambdoidal,  217 
sagittal,  216 
Sylvian  aqueduct,  1108 
gray  matter,  1109 
Sylvius,  fissure  of,  1136 
Sympathetic  nerves,  plexuses  of,  1367 
Sympathetic  system,  1353 
aortic  nerves,  1364 
association  cords  of,  1357 
constitution  of,  1355 
ganglia  of,  1356 
gangliated  cord  of,  1355 
gangliated     cord,     cervico-cephalic 
portion,  1358 

lumbar  portion,  1366 
sacral  portion,  1367 
thoracic  portion,  1364 
nerve -fibres  0^-1356 
plexus,  aortic,  1372 
cardiac,  1367 
carotid,  1360 
cavernous,  1361 
cavernous,  of  penis,  1374 
coeliac,  1370 
gastric,  1370 
hemorrhoidal,  1374 
hepatic,  1370 
hypogastnc,  1374 
mesenteric,  inferior,  1373 

superior,  1372 
ovarian,  1372 
ivlvic,  1374 
phrenic,  1371 
prostatic,  1374 


INDEX. 


2083 


Sympathetic  system,  plexus,  renal,  1371 
solar,  1368 
spermatic,  1372 
splenic,  1370 
suprarenal,  1371 
utero-vaginal,  1374 
vesical,  1374 
plexuses  of,  1356 
pract.  consid.,  1375 
pulmonary  nerves,  1364 
rami  communicantes  of,  1356 
splanchnic  afferent  fibres  of,  1357 
efferent  fibres  of,  1357 
nerves,  1364 
Symphysis,  108 
pubis,  339 
Synarthrosis,  107 
Synchondrosis,  108 
Syncytium  of  chorion,  49 
Syndesmosis,  108 
System,  gastro-pulmonary,  1527 
muscular,  454 
nervous,  996 
uro-genital,  1869 

Tasnia  coli,  1660 

semicircularis,  1162 

thalami,  1119 
Tapetum,  1157 
Tarsal  bones,  419 

plates,  1444 
Tarsus,  419 
Taste,  organ  of,  1433 
Taste-buds,  1433 

development  of,  1436 

nerves  of,  1435 

structure  of,  1434 
Teeth,  1542 

alveolar  periosteum,  1553 

bicuspids  (premolars),  1545 

canines,  1544 
milk,  1545 

cementum  of,  1552 

crown  of,  1542 

dentine  of,  1550 

development  of,  1556 

enamel  of,  1548 

fang  of,  1542 

homologies  of,  1566 

implantation  and  relations  of,  1554 

incisors,  1543 
milk,  1544 

lymphatics  of,  951 

milk,  eruption  of,  1564 
(temporary),  1542 

molars,  1546 

milk,  1547  • 

neck  of,  1542 

permanent,  1542 

development  of,  1564 
eruption  of,  1565 
relations  of,  1554 

pract.  consid.,  1591 

pulp  of,  1554 

pulp-cavity  of,  1542 

temporary,  relations  of,  1556 

variations  of,  1566 
Tegmen  tympani,  1496 
Tegmentum,  1112 
Tela  chorioidea,  1097 

subcutanea,  1384 
Telencephalon,  1132 
Telophases  of  mitosis,  13 


Temporal  bone,  176 

articulations  of,  184 
cavities  and  passages,  183 
development  of,  184 
portion,  petro-mastoid,  179 
squamous,  177 
tympanic,  179 
lobe,  1147 

Temporo-mandibular  articulation,  214 
Tendo  oculi,  484 
Tendon,  77,  468 

conjoined,  518 
Tendon-cells,  78 
Tendon-sheaths,  470 
Tenon,  capsule  of,  504 

space  of,  1437 
Tentorium  cerebelli,  1199 
Terms,  descriptive,  3 
Testis  or  testes,  1941 

appendages  of,  1949 
architecture  of,  1942 
descent  of,  2040 
lymphatics  of,  987 
mediastinum  of,  1942 
nerves  of,  1948 
pract.  consid.,  1950 
structure  of,  1942 
tubules  seminiferous  of,  1942 
tunica  albuginea  of,  1942 
vessels  of,  1948 
Thalamic  radiation,  1122 
Thalamus,  1 1 1 8 

connections  of,  1121 
structure  of,  1120 
Thebesian  valve,  695 

veins,  694 

Theca  folliculi,  of  hair,  1392 
Thenar  eminence,  607 
Thigh,  landmarks  of,  670 

muscles  and    fasciae  of,   pract.   consid. 

642 
Third  ventricle,  1131 

choroid  plexus  of,  1131 
Thorax,  149 

articulations  of,  157 
in  infancy  and  childhood,  164 
landmarks  of,  170 
lymphatics  of,  966 
movements  of,  165 
pract.  consid.,  167 
sexual  differences,  164 
subdivisions  of,  1832 
surface  anatomy,  166 

landmarks  of,  1868 
as  whole,  162 

Thumb,  articulation  of,  326 
Thymus  body,  1796 

changes  of,  1797 
development  of,  1800 
nerves  of,  1800 
shape  and  relations  of,   1796 
structure  of,  1798 
vessels  of,  1 799 
weight  of,  1797 

Thyroid  bodies,  accessory,  1793 
Thyroid  body,  1789 

development  of,  1793 
nerves  of,  1793 
pract.  consid.,  1794 
shape  and  relations  of,  1789 
structure  of,  1791 
vessels  of,  1792 
cartilage,  1814 


2084 


INDEX. 


Thyroid    cartilage,   development    of, 

1815 
growth  of,  1815 

gland,  lymphatics  of,  959 
Tibia,  382 

development  of,  387 

landmarks  of,  390 

pract.  consid.,  387 

structure  of,  387 

variations  of,  383 
Tibio-fibular  articulation,  inferior,  396 

superior,  396 
Tissue  or  tissues,  adipose,  79 

connective,  73 

elastic,  76 

elementary,  67 

epithelial,  67 

fibrous,  74 

muscular,  general,  454 

nervous,  997 

osseous,  84 

reticular,  75 
Tongue,  1573 

foramen  caecum  of,  1574 

frenum  of,  1573 

glands  of,  1575 

growth  and  changes  of,  1580 

lymphatics  of,  952 

muscles  of,  1577 

nerves  of,  1580 

papillae,  circumvallate  of,  1575 
filiform  of,  1575 
fungiform  of,  1575 

pract.  consid.,  1594 

vessels  of,  1 580 

Tonsil  or  tonsils  (amygdala),  of  cerebellum, 
1086 

faucial,  1600 

faucial,  relations  of,  1602 

lingual,  1575 

lymphatics  of,  954 

pharyngeal,  1601 

pract.  consid.,  1608 

tubal,  1503 
Tooth-sac,  1562 
Tooth-structure,  1 548 
Topography,  of  abdomen,  531 

cranio-cerebral,  1214 
Trachea,  1834 

bifurcation  of,  1837 

carina  of,  1837 

growth  of,  1837 

lymphatics  of,  958 

nerves  of,  1836 

pract.  consid.,  1840 

relations  of,  1836 

structure  of,  1835 

vessels  of,  1836 

Tract   or  tracts,    (fibre)    rubro-spinal, 
1114 

habenulo-peduncular,  1124 

mammillo-thalamic,  1121 

of  mesial  fillet,  1076 

olfactory,  1152 

thalamocipetal,  lower,  1122 
Tragus,  1484 
Trapezium,  311 
Trapezoid  bone,  311 
Treitz,  muscle  of,  558 
Triangle  of  Hesselbach,  526 

rectal,  1916 

uro-genital,  1916 
Triangles  of  neck,  547 


Trigone  of  bladder,  urinary,  1904 
Trigonum  acustici,  1097 

habenulae,  1 1  23 

hypoglossi,  1097 

lemnisci,  1108 

urogenitale,  563 

vagi,  1097 
Trochanter,  greater,  of  femur,  352 

lesser,  of  femur,  353 
Trochlea  of  humerus,  268 

of  orbit,  504 
Trochoides,  113 
Trophoblast,  46 

Truncus    bronchomediastinalis,     lymphatic, 
968 

subclavius,  lymphatic,  963 
Tube,  Eustachian,  1501 
Tuber  cinereum,  1129 
Tubercle  of  Lower,  695 
Tuberculum  acusticum,  1097 

olfactorium,  1153 
Tubes,  Fallopian,  1996 
Tunica  vaginalis  of  scrotum,  1963 
Turbinate  bone,  inferior,  208 

articulations  of,  208 
development  of,  208 
middle,  of  ethmoid,  193 
superior,  of  ethmoid,  193 
Tympanic  portion  of  temporal  bone,  179 
Tympanum,  1492 

attic  of,  1 500 

cavity  of,  183 

contents  of,  1496 

membrane  of,  1494 

pract.  consid.,  1505 

mucous  membrane  of,  1 500 

oval  window  of,  1495 

pract.  consid.,  1504 

promonotory  of,  1405 

pyramid  of,  1496 

round  window  of,  1495 

secondary  membrane  of,  1495 

tegmen  of,  1496 
Tyson,  glands  of,  1966 

Ulna,  281 

development  of,  285 
landmarks  of,  287 
pract.  consid.,  285 
structure  of,  285 
surface  anatomy,  300 
Umbilical  cord,  53 

allantoic  duct  of,  54 
amniotic  sheath  of,  54 
blood-vessels  of,  54 
furcate  insertion  of,  55 
jelly  of  Wharton  of,  54 
marginal  insertion  of,  55 
velamentous  insertion  of,  55, 
fissure  of  liver,  1708 
hernia,  1775 
notch  of  liver,  1707 
vesicle,  42 
Umbilicus,  37 
Unciform  bone,  312 
Uncus,  1154 

Upper  limb,  muscles  of,  568 
Urachus,  525 
Ureter  or  ureters,  1895 
female,  1896 
lymphatics  of,  982 
nerves  of,  1898 
pract.  consid.,  1898 


INDEX. 


2085 


Ureter  or  ureters,  structure  of,  1896 

vessels  of,  1897 
Urethra,  1922 

crest  of,  1922 
development  of,  1938 
female,  1924 

structure  of,  1926 
fossa,  navicular  of,  1924 
glands  of,  1925 
lymphatics  of,  986 
male,  pract.  consid.,  1927 

structure  of,  1924 
meatus  of,  1924 
nerves  of,  1927 
orifice  of,  external,  1924 

internal,  1904 

portion,  membranous  of,  1923 
prostatic  of,  1922 
spongy  of,  1923 
vessels  of,  1926 
Urethral  bulb,  1968 

crest,  1922 
Urinary  organs,  1869 

development  of,  1934 
Uriniferous  tubule,  1877 
Urogenital  cleft,  2021 
sphincter,  2049 
system,  1869 
Utero-sacral  folds,  1743 
Utero-vesical  pouch,  1943 
Uterus,  2003 

attachments  of,  2004 

body  of,  2003 

broad  ligament  of,  2004 

cavity  of,  2003 

cervical  canal  of,  2003 

cervix  of,  2003 

changes  of  menstruation,  2012 

of  pregnancy,  2012 
development  of,  2010 
fundus  of,  2003 
glands  of,  2007 
lymphatics  of,  989 
nerves  of,  2010 
os,  external  of,  2003 
peritoneal  relations  of,  2004 
position  of,  2007 
pract.  consid.,  2012 
relations  of,  2007 
round  ligament  of,  2005 
structure  of,  2007 
variations  of,  2012 
vessels  of,  2009 
Utricle,  1514 

prostatic,  1922 
structure  of,  1516 
Uveal  tract,  1454 
Uvula,  1569 

Vagina,  2016 

development  of,  2019 

fornix,  anterior  of,  2016 
posterior  of,  2016 

lymphatics  of,  989 

nerves  of,  2018 

pract.  consid.,  2019 

relations  of,  2016 

structure  of,  2017 

variations  of,  2019 
Vagina,  vessels  of,  2018 

vestibule  of,  2022 

Vaginal    process  of    inner  pterygoid   plate, 
189 


Vallecula,  1083 
Valsalva,  sinus  of,  700 
Valve  or  valves,  aortic,  700 

uuriculo-ventricular,  of  heart,  699 
Eustachian,  694 
ileo-cascal,  1661 
mitral,  699 
of  Morgagni,  1674 
pulmonary,  700 
of  pulmonary  artery,  700 
rectal,  1674 
semilunar,  700 
Thebesian,  695 
tricuspid,  699 
Valvulae  conniventes,  1636 
Vasa  aberrantia  of  epididymis,  1950 
Vas  deferens,  1954 

ampulla  of,  1955 

lymphatics  of,  988 
Vasa  vasorum,  674 
Vater,  ampulla  of,  1721 
Vater-Pacinian  corpuscles,  1018 
Vein  or  veins,  allantoic,  33 

circulation,  929 
angular,  of  facial,  864 
auditory,  internal,  869 
auricular,  anterior,  882 

posterior,  883 
axillary,  887 

pract.  consid.,  888 
azygos,  893 

arch,  893 

development  of,  928 

major,  893 

minor,  895 

superior,  895 

pract.  consid.,  895 

system,  893 
basilar,  877 
basilic,  890 

median,  891 
basi vertebral,  897 
brachial,  886 
brachio-cephalic,  858 
bronchial,  893 
of  bulb,  907 
cardiac,  854 

anterior,  856 

great,  855 

middle,  856 

posterior,  856 

small,  856 

valves  of,  856 
cardinal,  926 

posterior,  854 

superior,  854 

system  of,  854 
centralis  retinas,  879 
cephalic,  890 

accessory,  890 

median,  891 
cerebellar,  inferior,  879 

superior,  878 

median,  878 
cerebral,  877 

great,  877 

inferior,  877 

posterior,  869 

internal,  877 

middle,  877 

pract.  consid.,  878 

superior,  877 
cervical,  ascending,  of  vertebral,  860 


2o86 


INDEX. 


Vein  or  veins,  cervical,  deep,  859 

middle,  884 
chordae  Willissi,  870 
choroid,  877 
ciliary,  anterior,  879 

posterior,  879 
circulation,  foetal,  929 
circumflex,  iliac,  deep,  910 
superficial,  917 

of  leg,  914 
classification  of,  852 
clitoris,  909 
colic,  middle,  921 

right,  921 

condyloid,  anterior,  874 
confluence  of  the  sinuses,  868 
coronary,  of  facial,  865 

inferior,  of  facial,  865 

left,  855 

right,  856 

of  corpus  callosum,  anterior,  878 
posterior,  877 

cavernosum,  907 

striatum,  877 
costo-axillary,  896 

crico-thyroid,  of  superior  thyroid,   867 
cystic,  923 
deep  dorsal  of  penis  (clitoris),  909 

of  forearm,  886 

of  hand,  886 
dental,  inferior,  883 

superior,  883 
development  of,  926 
diploic,  874 

anterior,  875 

occipital,  875 

pract.  consid.,  875 

temporal,  anterior,  875 

posterior,  875 
dorsal,  of  foot,  910 

interosseous,  886 
ductus  Arantii,  929 

arteriosus,  930 

Botalli,  930 

venosus,  929 
emissaries  of  foramen  lacerum  medium, 

876 
emissary,  875 

condyloid,  anterior,  876 
posterior,  876 

of  foramen  ovale,  876 
of  Vesalius,  876 

mastoid,  876 

occipital,  876 

parietal,  876 

pract.  consid.,  876 
epigastric,  deep,  909 

superficial,  917 

superior,  of  internal  mammary,  860 
ethmoidal,  870 
facial,  864 

common,  864 

deep,  865 

pract.  consid.,  864 

transverse,  882 
femoral,  deep,  914 

pract.  consid.,  918 
foetal  circulation,  929 
of  foot,  deep,  910 

stijH-rlicial,  914 

foramen  lacvrum  medium,  876 
fnmtal,  of  facial,  865 
of  Galen,  856 


Vein  or  veins,  gastric,  923 

short,  921 
gastro-epiploic,  left,  921 

right,  921 
gluteal,  905 
hemiazygos,  895 

accessory,  895 
hemorrhoidal,  inferior,  907 

middle,  908 

plexus,  908 

superior,  922 
hepatic,  902 

pract.  consid.,  904 
hepatica  communis,  900 
ileo-colic,  921 
iliac,  common,  905 

pract.  consid.,  917 

external,  909 

pract.  consid.,  918 

internal,  905 

pract.  consid.,  918 
ilio-lumbar,  906 
inferior  cava,  pract.  consid.,  900 

caval  system,  898 
innominate,  858 

development  of,  859 

pract.  consid.,  859 
intercapitular  of  hand,  889 
intercostal,  896 

anterior,  of  internal  mammary,  860 

superior,  896 

accessory  left,  896 
intervertebral,  898 
jugular,  anterior,  884 

external,  880 

posterior,  884 
pract.  consid.,  88 1 

internal,  861 

bulbs  of,  86 1 
prac.  consid.,  863 
labial,  inferior,  of  facial,  865 

superior,  865 

lacunae  of  dural  sinuses,  852 
laryngeal,  inferior,  86 1 

superior,   of   superior  thyroid,    867 
of  leg,  deep,  911 

pract.  consid.,  918 
of  limbs,  development  of,  929 
lingual,  deep,  of  facial,  867 

of  facial,  867 
lumbar,  901 

ascending,  901 
mammary,  external,  888 

internal,  860 
marginal,  right,  856 
marginalis  sinistra,  855 
of  Marshall,  856 
masseteric,  of  facial,  866 
mastoid  emissary,  869 
maxillary,  internal,  882 

internal,  anterior,  of  facial,  865 
median,  890 

deep,  886 

mediastinal,  anterior,  86 1 
medulli-spinal,  898 
meningeal,  middle,  883 
mesenteric,  inferior,  922 

superior,  921 
metacarpal,  dorsal,  889 
nasal,  lateral,  of  facial,  865 
oblique,  of  heart,  605 

of  left  auricle,  856 
obturator,  907 


INDEX. 


2087 


Vein  or  veins,  occipital,  859 

ophthalmic,  anastomoses  of,  880 

inferior,  879 

pract.  consid.,  880 

superior,  879 
ovarian,  903 
palatine,  ascending,  of  facial,  866 

inferior,  of  facial,  866 
palmar  arches,  886 
superficial,   890 
palpebral,  of  facial,  865 
pampiniform  plexus,  903 
pancreatic,  921 
pancreatico- duodenal,  921 
parotid,  anterior,  of  facial,  866 

posterior,  882 
parumbilical,  923 

perforating,  of  internal  mammary,  860 
pericardial,  86 1 
perineal,  superficial,  907 
peroneal,  911 
pharyngeal,  863         % 

plexus,  864 
phrenic,  inferior,  901 

superior,  86 1 
plantar,  910 

external,  910 
plexus,  alveolar,  882 

external,  spinal,  897 

hemorrhoidal,  venous,  908 

internal,  spinal,  897 

pterygoid,  882 

sacral,  905 

of  Santorini,  909 

venosus  mammillag,  888 
popliteal,  911 

pract.  consid.,  918 
portal,  919 

accessory,  923 

collateral  circulation  of,  923 

development  of,  928 

of  liver,  1709 

system,  919 

pract.  consid.,  925 
pterygoid,  plexus,  882 
pudendal  plexus,  909 
pudic,  external,  916 

internal,  907 
pulmonary,  852 

anastomoses  of,  853 

development  of,  929 
pyloric,  923 
radial,  886 

superficial,  891 

accessory,  891 
renal,  902 

pract.  consid.,  904 
sacral,  anterior,  plexus,  905 

lateral,  906 

middle,  905 
saphenous,  accessory,  916 

long,  916 

short,  915 
sciatic,  906 

of  septum  lucidum,  877 
sigmoid,  922 
sinus,  basilar,  874 

pract.  consid.,  874 

cavernous,  872 

pract.  consid.,  873 

circular,  872 

coronary,  854 

of  dura  mater,  867 


Veins  or  veins,  sinus,  dural,  blood-lakes  of, 

852 
structure  of,  851 

intercavernous,  872 

lateral,  867 

pract.  consid.,  869 

longitudinal,  inferior,  871 
superior,  870 

pract.  consid.,  870 

marginal,  872 

occipital,  872 

petrosal,  inferior,  874 
superior,  874 

sphe no-parietal,  874 

straight,  872 
small,  of  Galen,  877 

intestine,  921 
spermatic,  903 

pract.  consid.,  904 
spheno-palatine,  882 
spinal,  897 

cord,  898 

pract.  consid.,  898 
splenic,  921 
sterno-mastoid,    of   superior   thyroid, 

867 

structure  of,  677 
subclavian,  884 

pract.  consid.,  885 
subcostal,  896 
sublingual,  867 
submental,  of  facial,  866 
superficial  of  hand,  889 
superior  caval  system,  857 
supraorbital,  of  facial,  865 
suprarenal,  middle,  903 

inferior,  902 
suprascapular,  884 
Sylvian,  deep,  878 
temporal,  deep,  883 

middle,  882 

superficial,  882 
temporo-maxillary,  882 
testicular,  903 
Thebesian,  694 
thoracic,  acromial,  890 

long,  887 

thoraco-epigastric,  888 
thymic,  86 1 
thyroid,  inferior,  860 

pract.  consid.,  86 1 

middle,  867 

plexus,  860 

superior,  867 
tibial,  anterior,  911 

posterior,  911 
torcular  Herophili,  868 
tympanic,  of  temporal,  882 
ulnar,  886 

superficial,  890 
umbilical,  54 
of  upper  extremity,  886 

pract.  consid.,  891 
ureteric,  of  renal,  902 

of  spermatic,  903 
uterine,  908 

plexus,  908 

utero-vaginal  plexus,  908 
vaginal,  908 

plexus,  908 
valves  of,  850,  851 
vena  cava  inferior,  899 

development  of,  927 


2088 


INDEX. 


Vein  or  veins,  vena  cava  superior,  857 
development  of,  927 
pract.  consid.,  858 
cephalica  pollicis,  889 
salvatella,  889 
supraumbilicalis,  923 
thyreoidea  ima,  861 

venae  comites,  851 
vorticosae,  879 

vertebral,  860 

vesical,  908 

vesico-prostatic  plexus,  909 

vesico-vaginal  plexus,  909 

vitelline  circulation,  929 
Velum  interpositum,  1162 
Ventricle  or  ventricles,  fifth,  1160 

fourth,  1096 

of  heart,  696 

lateral,  1160 

anterior  horn  of,  1 1 60 

body  of,  1161 

choroid  plexus  of,  1162 

inferior   (descending)    horn   of, 

1 164 
posterior  horn  of,  1 1 68 

(sinus)  of  larynx,  1822 

third,  1131 

Vermiform  appendix,  1664 
Vernix  caseosa,  66 
Vertebra  or  vertebras,  114 

articular  surfaces  of,  1 1 6 

body  of,  115 

cervical,  116 

development  of,  128 

dimensions  of,  122 

gradual  regional  changes  of,  122 

laminae  of,  115 

lumbar,  117 

mammillary  processes  of,  1 1 8 

peculiar,  119 

pedicles  of,  115 

presacral,  128 

prominens,  121 

spinal  foramen  of,  115 

spinous  process  of,  115 

structure  of,  128 

thoracic,  115 

transverse  processes  of,  115 

variations  of,  131 
Verumontanum,  1922 
Vesalius,  foramen  of,  188 
Vesicle,  germinal,  15 

umbilical,  42 
Vesicles,  seminal,  1956 
Vessels  of  clitoris,  2025 

of  epididymis,  1948 

<>i"  Fallopian  tube,  1998 

of  gall-bladder,  1719 

of  labia,  2023 

of  larynx,  1826 

of  lips,  1542 

of  mammary  glands,  2031 

of  oesophagus,  1612 

of  ovary,  1992 

of  palate,  1572 

of  pancreas,  1736 

of  parotid  gland,  1 583 

of  penis,  1970 

of  pharynx,  1606 

of  prostate  gland,  1978 

of  roots  of  lungs,  1839 

of  scrotum,  1964 


Vessels  of  seminal  vesicles,  1958 

of  spermatic  ducts,  1958 

of  spleen,  1786 

of  sublingual  gland,  1585 

of  submaxillary  gland,  1585 

of  suprarenal  bodies,  1803 

of  testis,  1948 

of  thymus  body,  1799 

of  thyroid  body,  1792 

of  tongue,  1 580 

of  trachea,  1836 

of  ureter,  1897 

of  urethra,  1926 

of  urinary  bladder,  1910 

of  uterus,  2009 

of  vagina,  2018 
Vestibule  of  mouth,'  1538 

of  nose,  1409 

of  osseous  labyrinth,  1511 

of  vagina,  2022 
Vicq  d'Azyr,  bundle  of,  1121 
Vidian  canal,  189 
Villi  of  chorion,  49 

of  intestine,  1635 

lacteals  of,  1636 
Vincula  tendinum,  471 
Vital  manifestations,  6 
Vitelline  arteries,  32 

duct,  32 

membrane,  1 5 

sac,  32 

Vitello-intestinal  duct,  37 
Vitellus,  15 
Vitreous  body,  1473 

development  of,  1483 
pract.  consid.,  1474 
Vocal  cords,  false,  1820 

true,  1820 

Volkmann's  canals,  of  bone,  89 
Volvulus,  1687 
Vomer,  205 

articulations  of,  206 

development  of,  206 

Wharton  duct  of,  1 584 

jelly  of,  54 

Winslow,  foramen  of,  1746 
Wirsung,  duct  of,  1736 
Wisdom-tooth,  1546 
Wolffian  body,  1935 

duct,  1935 
Womb,  2003 

Worm  of  cerebellum,  1082 
Wrist,  anterior  annular  ligament,  607 

movements  of,  326 

pract.  consid.,  613 

surface  anatomy  of,  328 
Wrist-joint,  landmarks  of,  330 

pract.  consid.,  329 

Xiphoid  process  of  sternum,  156 
Yolk-stalk,  37 

Zeiss,  glands  of,  1444 
Zinn,  annulus  of,  503 

zonula  of,  1475 
Zona  pellucida,  1 5 

radiata,  15 
Zonula  of  Zinn,  1475 
Zuckerkandl,  bodies  of,  1812 
Zygomatic  process  of  temporal  bone,  178 


This  book  is  due  on  last  date  given  below.     A  fine  of 
5c  will  be  charged  for  each  day  the  book  is  kept  overtime. 


Date  Due 


> 

1-4 

DAY 

DEC 

17  1963 

p 

. 

; 

Mi 

•  3  s 

-•  \  '* 

JUL  1 

2  1994 

618477 


3   1378  00618  4777 


. 


University 


